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4th Hybrid and Organic Photovoltaics

Conference

HOPV12

Uppsala - Sweden

6th to 9thMay 2012

© SEFIN 2012 www.nanoge.org

http://www.nanoge.org/

SUPPORT

The 4th International Conference on Hybrid and Organic Photovoltaics (HOPV12)

organized in the beautiful and historical city of Uppsala, Sweden, from 6 to 9 May 2012

will provide a great opportunity for scientists and engineers around the world for

discussions of the latest developments in hybrid and organic photovoltaics.

Solar energy has the largest potential to satisfy the future global need for

renewable energy sources. The main topics of this conference are the development,

function and modelling of materials and devices for hybrid and organic solar cells,

including dye-sensitized solar cells, polymer / fullerene solar cells, small molecule

organic solar cells, and other 'excitonic' solar cell technologies, including hybrid organic

/ inorganic and nanostructured devices. These solar cell technologies are showing

rapid advances both in academia and, increasingly, in commercial development.

Chair of the HOPV12 Conference Prof. Anders Hagfeldt Uppsala University, Sweden

4th

Hybrid and Organic Photovoltaic Conference -Uppsala 2012 5

4th International Conference on Hybrid and Organic Photovoltaics (HOPV12), Uppsala, Sweden

Scientific Committee

Anders Hagfeldt (Chair of the HOPV12 Conference)

Uppsala University, Sweden

Mats Andersson Chalmers University of Technology, Sweden

Gerrit Boschloo Uppsala University, Sweden

Olle Inganäs Linköping University, Sweden

Erik Johansson Uppsala University, Sweden

Lars Kloo KTH, The Royal Institute of Technology, Sweden

Ellen Moons Karlstad University, Sweden

Hakan Rensmo Uppsala University, Sweden

4th International Conference on Hybrid and Organic Photovoltaics (HOPV12), Uppsala, Sweden

Keynote Speakers

Michael Grätzel Ecolé Polytechnique Fédérale de Lausanne, Switzerland

Rene Janssen Eindhoven University of Technology, NL

Jao van de Lagemaat National Renewable Energy Laboratory, US

Invited Speakers

Petra Cameron The University of Bath, GB

Filippo De Angelis CNR-ISTM, IT

James Durrant Imperial College London, GB

Elena Galoppini Rutgers University Chemistry Department, US

Joseph Hupp Northwestern University, US

Ryuzi Katoh Nihon university, JP

Karl Leo TU Dresden, DE

Jean Manca Universiteit Hasselt / IMEC, BE

Jenny Nelson Imperial College London, GB

Brian O´Regan Imperial College London, GB

Licheng Sun Royal Institute of Technology (KTH), SE

Satoshi Uchida RCAST, The University of Tokyo, JP

4th


INDEX

INVITED CONTRIBUTIONS

A1 Michael Graetzel “Nanostructured systems for the generation of electricity from sunlight”

16

A2 Karl Leo “Small Molecule Organic Solar Cells: Status and Recent Developments”

17

A3 Brian O'Regan “Fast times and too bright lights. Understanding the Kinetics and Mechanics of Liquid Junction and Solid State Dye Sensitized Solar Cells”

18

A4 Elena Galoppini “Star-Shaped Ruthenium Polypyridyl Complexes: Binding Control on Metal Oxide Surfaces”

19

A5 Ryuzi Katoh, Akihiro Furube “Charge generation and recombination in dye-sensitized nano-structured TiO2 films”

20

A6 Jao van de Lagemaat “Exciton/plasmon interactions: a new paradigm in solar photoconversion”

21

A7 Satoshi Uchida, Bruno Ieiri Ito, Takaya Kubo, Hiroshi Segawa “High Performance Dye-Sensitized Solar Cells with Nano-clay Electrolyte”

22

A8 Jenny Nelson, Mark Faist, Thomas Kirchartz, Sheridan Few, James Kirkpatrick “Understanding heterojunction solar cells through studies of the charge transfer state”

23

A9 Joseph Hupp “Designed Photoelectrode Interfaces and Architectures for Dye-Sensitized Solar Cells”

24

A10 Sabine Bertho, Bert Conings, Fortunato Piersimoni, Donato Spoltore, Jan D’Haen, Laurence Lutsen, Bruno Van Mele, Guy Van Assche, Dirk Vanderzande, Jean Manca

“Lifetime of bulk heterojunction solar cells: the next challenge”

25

A11 René Janssen “Efficient tandem polymer solar cells in normal and inverted device configurations”

26

A12 Thomas Risbridger, Kathryn Wills, Petra Cameron “Aqueous electrolytes in dye sensitized solar cells”

27

A13 Licheng Sun, Haining Tian, Lars Kloo, Xichuan Yang “Efficient DSCs Based on Organic Dyes and Iodine-Free Redox Couples”

28

A14 James R. Durrant “Influence of film microstructure and crystallinity upon the function of organic bulk heterojunction solar cells”

29

A15 Filippo De Angelis “Modeling Materials and Processes in Dye-Sensitized Solar Cells from First Principles”

30

ORAL CONTRIBUTIONS

B1 Torben Daeneke, Udo Bach, Leone Spiccia “Dye Regeneration by Single Electron Redox Couples”

31

B2 Sandra Feldt, Peter Lohse, Hanna Ellis, Gerrit Boschloo, Anders Hagfeldt “Dye Regeneration Kinetics in Solar Cells using Cobalt Polypyridine Redox Couples”

32

B3 Shogo Mori, Takurou Murakami, Takayuki Uchiyama, Nagatoshi Koumura, Kohjiro Hara, Kazumichi Obuchi, Naruhiko Masaki, Mutsumi Kimura “Combined effect of the structures of sensitizers and cobalt complex redox couples on the electron lifetime in dye-sensitized solar cells”

34

B4 Hongxia Wang “How does the nanostructure of TiO2 material affect the electron trapping/detrapping process in dye-sensitized solar cells?”

35

B5 Giorgio Divitini, Ole Stenzel, Fabio Di Fonzo, Carlo S. Casari, Valeria Russo, Andrea Li Bassi, Volker Schmidt, Caterina Ducati “3D quantitative characterisation of a TiO2-based photoanode”

36

B6 Maria Fravventura, Dimitrios Deligiannis, Juleon Schins, Laurens Siebbeles, Tom Savenije “Time-resolved real and imaginary photoconductance studies on nanocrystalline and polycrystalline TiO2”

38

B7 Harm van Eersel, René Janssen, Martijn Kemerink “Mechanism for efficient photoinduced charge separation at disordered organic heterointerfaces”

39

B8 Fortunato Piersimoni, Koen Vandewal, Sylvain Chambon, Kristofer Tvingstedt, Olle Inganäs, Peter Adriaensens, Jean Manca “‘Charge Transfer Complexes’ and ‘Exciplexes’ in polymer:polymer solar cells”

40

B9 Giulia Grancini, Daniele Fazzi, Margherita Maiuri, Hans Egelhaaf, Annamaria Petrozza, Daniele Brida, Giulio Cerullo, Guglielmo Lanzani “Ultrafast Hot Charge Transfer in Low Band-Gap Polymer Blend for Photovoltaics”

41

B10 Ying Woan Soon, Safa Shoaee, Iain McCulloch, James R Durrant “On the correlation between crystallinity and photophysics for donor polymers of interest for organic photovoltaic devices”

43

B11 Donato Spoltore, Wibren D. Oosterbaan, Samira Khelifi, John Clifford, Aurelien Viterisi, Emilio 44

4th


Palomares, Marc Burgelman, Laurence Lutsen, Dirk Vanderzande, Jean Manca “Effect of crystallinity in P3HT:PCBM solar cells on bandgap trap states and apparent recombination order”

B12 Aurora Rizzo, Anna Loiudice, Giuseppe Gigli “Improved Performance of Diffused-Bilayer Polymer Solar Cells by Solution p-Type Doping”

46

B13 Curtis Berlinguette “High-Performance Thiocyanate-Free Ruthenium DSSC Dyes”

48

B14 Simona Fantacci , Maria Grazia Lobello, Filippo De Angelis “DFT/TDDFT computational investigation of Ru(II) and Os(II) panchromatic dye sensitizers”

49

B15 Nina Chadwick, Lesley Yellowlees, Neil Robertson “Tuning the HOMO of ruthenium dyes for dye-sensitised solar cells”

51

B16 Gerda Fuhrmann, David Danner, Ameneh Bamedi, Markus Obermaier, Lars-Peter Scheller, Gabriele Nelles “Squarylium Dyes and Semi-squarylium Dyes: Molecular Engineering and Their Application in Multiple-dyes Systems”

52

B17 Valerie Vaissier, Davide Moia, Piers Barnes, James Kirkpatrick, Jenny Nelson “Modelling of lateral hole diffusion on dye-sensitized electrodes”

53

B18 Seunghyup Yoo, Hoyeon Kim, Sooyeon Lim, Dong-Geon Han, Soohyun Lee, Koeng Su Lim “Toward commercialization of organic photovoltaic (OPV) cells: ITO-free approach for low cost cells and maskless fabrication of high-density modules”

54

B19 Marco Bernardi, Priyank Kumar, Nicola Ferralis, Maurizia Palummo, Shenqiang Ren, Jeffrey C. Grossman “All-Carbon Photovoltaics”

56

B20 Ellen Moons, Ana Sofia Anselmo, Andrzej Dzwilewski, Krister Svensson, Jan van Stam

“Vertical Phase Separation in Polymer:Fullerene Films For Photovoltaics 57

B21 R. K. M. (Ricardo) Bouwer, G. A. H. (Gert-Jan) Wetzelaer, P. W. M. (Paul) Blom, J. C. (Kees) Hummelen “Fullerene bisadducts for organic photovoltaics”

58

B22 Andreas Opitz, Andreas Wilke, Norbert Koch, Mark Gruber, Ulrich Hörmann, Michael Kraus, Julia Wagner, Wolfgang Brütting “Bipolar organic semiconductors: application in thin film tran¬sistors and photovoltaic cells”

60

B23 Emma Artuso, Nadia Barbero, Carlo Bignozzi, Rita Boaretto, Luca Bonandini, Thomas M. Brown, Eva Busatto, Stefano Carli, Daniele Colonna, Gabriele De Angelis, Aldo Di Carlo, Fabrizio Giordano, Alessandro Guglielmotti, Andrea Guidobaldi, Alessando Lanuti, Angelo Lembo, Simone Mastroianni, Valentina Mirruzzo, Stefano Penna, Eleonora Petrolati, Andrea Reale, Riccardo Riccitelli, Giuseppe Soscia, Luigi Vesce, Guido Viscardi “Industrialization efforts toward Dye Solar Cells for Building Integrated Applications”

61

B24 Yuhei Ogomi, Terumi Nishimura, Jun Usagawa, Takeshi Kogo, Shyam Pandey, Shuzi Hayase “Transparent conductive oxide-less (TCO-less) dye-sensitized solar cells with back contact structure”

63

B25 Peter J. Holliman, Arthur Connell, Matthew L. Davies, Moneer Mohsen, Kareem Al-Salihi, Norasikin Ludin “Controlling ultra-fast multiple sensitization in dye sensitized solar cells”

65

B26 Adriano Sacco, Andrea Lamberti, Giorgia Musso, Diego Pugliese, Irene Berardone, Nadia Shahzad, Rossana Gazia, Angelica Chiodoni, Stefano Bianco, Claudia Barolo, Marzia Quaglio, Elena Tresso, Giuseppe Caputo, Candido Fabrizio Pirri “An efficient dye-sensitized solar cell based on a microfluidic cell architecture and a small hemi-squaraine organic dye”

67

B27 Lioz Etgar, Wei Zhang, Stefanie Gabriel, Stephen G. Hickey, Md K. Nazeeruddin, Alexander Eychmüllerand, Bin Liu, Michael Grätzel “Highly Efficient TiO2 Nanosheets /PbS Quantum Dots Heterojunction solar cells”

68

B28 Edward Crossland, Henry Snaith “Charge Transport in a Novel Mesoporous TiO2 Semiconductor”

69

B29 Jan C. Brauer, Arianna Marchioro, Jacques-E. Moser “Dynamics of Charge-Transfer Interfacial Excitons at Dye-Sensitized Donor/ Acceptor Hybrid Heterojunction”

70

B30 Ana Flavia Nogueira, Jilian Nei de Freitas, Lasantha Korala, Luke Reynolds, Saif Haque, Stephanie Brock “Hybrid photovoltaic devices based on chalcogenide aerogels”

72

B31 Katja Willinger, Christoph Hunger, Mukundan Thelakkat “Cosensitization and multichromophore light harvesting in hybrid devices”

73

B32 Anna Loiudice, Aurora Rizzo, Gianluca Latini, Giuseppe Gigli “Graded Vertical Phase Separation of Donor/Acceptor Species for Polymer Solar Cells”

74

B33 George Margulis, Bo Gyu Lim, Brian Hardin, Johann Feckl, Shaik Zakeerudin, Thomas Bein, Michael Grätzel, Alan Sellinger, Michael McGehee “Enhanced Light Harvesting in Dye-Sensitized Solar Cells Using Highly Soluble Energy Relay Dyes”

76

4th


B34 Hong Lin, Heping Shen, Yizhu Liu, Dan Oron “A New Quantum dot/Inorganic layer/Dye molecule Sandwich-structure for Electrochemical Solar Cells with Improved Photovoltaic Performance and High Photostability”

78

B35 Adèle Renaud, Benoit Chavillon, Loic Le Pleux, Laurent Cario, Yann Pellegrin, Errol Blart, Mohammed Boujtita, Thierry Pauporté, Stéphane Jobic, Fabrice Odobel “Is CuGaO2 a potential substitute for NiO in p-type dye solar cells (p-DSSCs)?”

80

B36 Kenrick Anderson, Emily Border, Timothy Jones, Clint Woodward, Gregory Wilson, Christopher Fell “The Application and Physical Properties of DCDHF dyes in Organic Photovoltaics”

81

B37 Jonas Sandby Lissau, Marie-Pierre Santoni, James M. Gardner, Sascha Ott, Ana Morandeira “Photon Upconversion on Dye-Sensitized Nanostructured ZrO2 Films”

82

B38 Udo Bach, Torben Daeneke, Dongchuan Fu, Andrew Nattestad “New Concepts for Dye-Sensitized Solar Cells”

84

B39 Zaifei Ma, Ergang Wang, Markus Jarvid, Patrik Henriksson, Olle Inganäs, Fengling Zhang, Mats Andersson “Synthesis and characterization of benzodithiophene–isoindigo polymers for solar cells”

85

B40 Antonio Guerrero, Juan Bisquert, Germà Garcia-Belmonte Recombination in Organic Bulk Heterojunction Solar Cells: A Study of Interfacial Charge Transfer “Kinetics with Fullerene Affinity”

86

B41 Gianpaolo Susanna, Luigi Salamandra, Thomas Brown, Andrea Reale, Francesca Brunettia,

Aldo Di Carlo Spray-coating technique for the realization of Polymer Solar-Cells

87

B42 D. H. K Murthy, Min Gao, Martien Vermeulen, Laurens Siebbeles, Tom Savenije Mechanism of Mobile Charge Carrier Generation in Blends of Conjugated Polymers and Fullerenes: “Significance of Charge Delocalization and Excess Free Energy”

88

B43 Musubu Ichikawa, Yusuke Imamura “Using excitation transfer and plasmon enhanced excitation transfer for organic thin-film solar cell”

89

B44 Lilian Ellis-Gibbings, Viktor Johansson, Rick B Walsh, Lars Kloo, Jamie S Quinton, Gunther G Andersson “Formation of N719 Dye Multilayers on Dye Sensitized Solar Cell Photoelectrode Surfaces”

90

B45 Andreas Bartelt, Robert Schütz, Joachim Schaff, Ivo Kastl, Christian Strothkämper, Rainer Eichberger, Gabrielle Nelles, Gerda Fuhrmann “Efficient Electron Injection from Organic Sensitizer Dyes Containing an Acyloin-Type Anchor Group”

91

B46 Gustavo de Miguel, Maria jose Marchena, Marcin Ziolek, Shyam Pandey, Shuzi Hayase, Abderrazzak Douhal “FEMTO- to Milisecond Dynamics of Selected Squaraines Embedded in TIO2 Nanoparticles Thin Films and Solar Cells”

92

B47 Shuai Ma, Federica Cappelluti, Giovanni Ghione, Adriano Sacco, Diego Pugliese, Andrea Lamberti, Elena Tresso “Consistent physics-based modeling of DC and small-signal behavior of dye-sensitized solar cells under different illumination conditions”

93

B48 Viktoria Gusak, Leo-Philipp Heiniger, Michael Graetzel, Christoph Langhammer, Bengt Kasemo “Time-resolved Indirect Nanoplasmonic Sensing spectroscopy of dye molecule interactions with dense and mesoporous TiO2 films”

95

B49 Saif Haque, Simon Dowland, Luke Reynolds, Neha Bansal, Andrew Maclachlan, Thierry Lutz, Flannan O'Mahony “Hybrid inorganic nanocrystal – polymer solar cells: new device concepts and improved fundamental understanding of device function”

96

B50 Julian Burschka, Amalie Dualeh, Florian Kessler, Etienne Baranoff, Ngoc-Lê Cevey-Ha, Chenyi Yi, Mohammad K. Nazeeruddin, Michael Grätzel “Co(III) complexes as p-type dopants for organic semiconductors and their application in Solid-State Dye-Sensitized Solar Cells”

97

B51 Bert Conings, Linny Baeten, Hans-Gerd Boyen, Donato Spoltore, Marlies K. Van Bael, Jean V. Manca “Impedimetric probing of recombination kinetics in ZnO nanorod array/poly (3-hexylthiophene) solar cells”

98

B52 Rebecka Schölin, Martin H. Karlsson, Susanna K. Eriksson, Johan Oscarsson, Hans Siegbahn, Erik M. J. Johansson, Håkan Rensmo “Energy Level Alignment in Hole Transporting Molecular Layers studied with Hard X-ray Photoelectron Spectroscopy”

99

POSTER CONTRIBUTIONS

C1 Mindaugas Juozapaviciusa, Brian C. O’Regana, Marius Kaucikasb, Jasper J. van Thorb “Picosecond electron injection in optimised dye-sensitised solar cells with visible-pump mid-infrared-probe transient absorption spectroscopy”

100

C2 Abd Rashid Mohd Yusoff, Hyeong Pil Kim, Jin Jang 101

4th


“Organic Photovoltaic Cells based on Trilayer Graphene Oxide

C3 Mi-Hee Junga, Moo-Jung Chu “Fabrication of Ag Nanoparticles Embedded TiO2 Nanotubes using Electrospun Nanofibers for Plasmonic

Enhanced Solar Cells”

102

C4 Andreas Bauer, Tina Wahl, Jonas Hanisch, Erik Ahlswede “Highly efficient semitransparent organic solar cells with sputtered ZnO:Al cathodes: Influence of light

management at the transparent electrode”

103

C5 Florian Auras, Vivian Carolina Farías Rivera, Ilina Kondofersky, Thomas Bein “Oriented nanowire arrays with high aspect ratios for solid-state dye-sensitized solar cells”

104

C6 Emad Al-Imarah, Peter J. Derrick, Shane G. Telfer, Ashton Partridge “Donor-Acceptor Substituted Aza-BODIPYs for Molecular Bulk Heterojunction Solar Cells: Synthesis and Optical Properties”

105

C7 Noel Duffy, Jacek Jasieniak, Brandon MacDonald, Anthony Chesman, Scott Watkins “Inorganic Solution Processed Nanoparticle Solar Cells”

106

C8 Irene Gonzalez-Valls, Juan A. Reparaz, Frank Guell, Markus R. Wagner, Gordon Callsen, Belen Ballesteros, Axel Hoffmann, Monica Lira-Cantu “Modification of surface defects in vertically-aligned ZnO nanostructures to improve power conversion

efficiency of dye sensitized solar cells”

107

C9 Thomas Pfadler, Lukas Schmidt-Mende, Ricky Dunbar “Plamonics in nanostructured organic solar cells”

109

C10 Michiel Petrus, Ricardo Bouwer, René Kist, Neil Greenham, Theo Dingeman “All-aromatic Triphenylamine-based Poly(azomethine)s as Hole Transport Materials for Polymer

Photovoltaics”

110

C11 Manuel Reinhard, Johannes Kuhn, Christoph Simon, Alexander Colsmann, Uli Lemmer “Copper indium gallium diselenide hybrid solar cells comprising solution-deposited window and organic buffer layers”

111

C12 Holger Borchert, Nikolay Radychev, Rany Miranti, Dorothea Scheunemann, Marta Kruszynska, Christopher Krause, Florian Witt, Irina Lokteva, Joanna Kolny-Olesiak, Jürgen Parisi “Hybrid solar cells based on CuInS2 nanocrystals and their comparison to the polymer/CdSe system”

112

C13 Nikolaos Balis, Theodoros Makris, Vassilios Dracopoulos, Panagiotis Lianos “Organic conductive polymers as alternative electrocatalysts for Dye-sensitized solar cells”

114

C14 Eva M Barea, Roberto Trevisan, Iván Mora Seró, Pablo P. Boix “Advances in the Application of Graphene-Titania paste to enhance DSC performance”

115

C15 Meinan Liu, Cheng Yan “Fabrication of titanium oxide and its photovoltaic study”

116

C16 Nikolaos Balis, Theodoros Makris, Vassilios Dracopoulos, Panagiotis Lianos “Organic conductive polymers as alternative electrocatalysts for Dye-sensitized solar cells”

117

C17 Thomas Kolbusch “Production Technologies for Large Area Printed Flexible Electronics”

118

C18 Vennesa Williams, Nak Cheon Jeong, Chaiya Prasittichai, Michael Pellin, Joseph Hupp “Fast Transporting ZnO-TiO2 Coaxial Photoanodes for Dye-Sensitized Solar Cells Based on ALD-Modified

SiO2 Aerogel Frameworks”

119

C19 Thomas Kirchartz, Jenny Nelson “The effect of the spatial and energetic carrier distribution on the charge carrier lifetime in bulk heterojunction solar cells”

120

C20 Mariachiara Pastore, Filippo De Angelis “Modelling of Energy and Hole Transfer in Co-sensitized Dye-Sensitized TiO2: Electronic structure, optical properties and FRET”

121

C21 Andrea Guidobaldi, Fabrizio Giordano, Eleonora Petrolati, Luigi Vesce, Simone Mastroianni, Riccardo Riccitelli, Andrea Reale, Thomas M. Brown, Aldo Di Carlo “Design and Realization of High Performance Z-TYPE Dye Solar Cell Modules”

123

C22 Satish Patil, Gitish Dutta, Richard Friend, Doo-Hyan Ko “Diketopyrrolopyrrole: P3HT blend Thin Films for All-Polymer Solar Cells”

125

C23 Mahmoud Zendehdel, Gerrit Boschloo, Anders Hagfeldt, Mohammad Hossein Habibi “Fabrication and characterization of thin film Titania as a blocking under layer in organic dye sensitized

solar cells with cobalt and ferrocene mediators base by sol-gel method”

126

C24 Adriano Sacco, Andrea Lamberti, Diego Pugliese, Nadia Shahzad, Rossana Gazia, Angelica Chiodoni, Stefano Bianco, Marzia Quaglio, Elena Tresso, Candido Fabrizio Pirri “Microfluidic housing system for innovative dye-sensitized solar cell architecture”

129

C25 Ross Hatton, Helena Stec “Optically-thin gold electrodes on flexible polyester substrates for organic photovoltaics”

131

C26 Anna Loiudice, Aurora Rizzo, Luisa De Marco, Davide Cozzoli, Giuseppe Gigli 132

4th


“Organic Photovoltaic Devices with Colloidal TiO2 Nanorods as Key Functional Components”

C27 Karl Börjesson, Kasper Moth-Poulsen, Dusan Coso, Nikolai Vinokurov, Arun Majumdar, Peter Vollhardt, Rachel Segalman “Ruthenium Fulvalene Compounds for Solar Thermal Energy Storage and Conversion”

134

C28 Thitikorn Boonkoom, Saif Haque, John de Mello “The Effect of Thermal Annealing on Charge and Photocurrent Generation in Hybrid P3HT-InP Quantum Dot Solar Cells”

135

C29 Bruce Philip, Trystan Watson, David Worsley, Gavin Reynolds “Identification of suitable metallic substrate /electrolyte combinations for Dye-sensitised Solar Cells”

136

C30 Kati Miettunen, Tapio Saukkonen, Xiaoe Li, ChunHung Law, Piers Barnes, Brian O'Regan “Performance of metal based dye solar cells with cobalt electrolyte”

138

C31 Alessandra Operamolla, Aurora Rizzo, Omar Hassan Omar, Anna Loiudice, Alessia Lasorsa, Giuseppe Gigli, Francesco Babudri, Gianluca M. Farinola “Improvement of P3HT:PCBM bulk-heterojunction solar cells efficiency by addition of conjugated

aryleneethynylene tetrathiol”

139

C32 Matthew Davies, Trystan Watson, Peter Holliman, Arthur Connell, David Worsley “Monitoring ultra-fast multi-sensitization of dye sensitized solar cells using a rapid, continuous in situ

process”

140

C33 Oliver Hutter, Ross Hatton “Transparent, air-stable copper electrodes for electron-extraction in organic photovoltaics”

142

C34 Ulrich Hörmann, Julia Wagner, Mark Gruber, Andreas Opitz, Wolfgang Brütting “Approaching the ultimate open circuit voltage in thiophene based single junction solar cells by applying

diindenoperylene as acceptor”

143

C35 David Worsley, Cecile Charbonneau, Matthew Carnie, Trystan Watson “Electron transport in ultrafast sintered TiO2 thin films; application to the manufacture of dye-sensitized solar cells”

144

C36 Fabrizio Giordano, Andrea Guidobaldi, Eleonora Petrolati, Thomas M. Brown, Andrea Reale, Aldo Di Carlo “Series Interconnections for Dye Solar Cell Modules: Stability and Materials”

145

C37 Simone Guarnera, Annamaria Petrozza, Stefano Perissinotto, Antonio Bonucci, Guglielmo Lanzani “Stable Dye-Sensitized Solar Cells Based on Nanosized Zeolites Dispersion in the TiO2 Layer”

147

C38 Roberto Giannuzzi, Michele Manca, Giuseppe Gigli “A new electrical model for the analysis of partially shaded dye solar cell modules”

148

C39 Kerttu Aitola, Maryam Borghei, Antti Kaskela, Albert Nasibulin, Esko Kauppinen, Peter Lund, Virginia Ruiz, Janne Halme “Carbon nanomaterials as flexible dye solar cell counter electrodes”

150

C40 Rubén D. Costa, Xinjiao Wang, Philipp Grönninger, Sebastian Feihl, Fabian Werner, Karsten Meyer, Dirk M. Guldi “Damning Evidence of the Beneficial Effect of Liquid Crystalline Phases in Solid-State Dye-Sensitized Solar Cells”

151

C41 Roberto Giannuzzi, Michele Manca, Giuseppe Gigli “A new electrical model for the analysis of partially shaded dye solar cell modules”

152

C42 Francisco Fabregat-Santiago, Sonia R. Raga “Effect of temperature on the performance of dye solar cells”

154

C43 Luiz Carlos P. Almeida, Valtencir Zucolotto, Neil J. Coville, Ana F. Nogueira “Electrostatic layer-by-layer films based on conjugated polyelectrolytes: an alternative approach towards solar energy conversion”

156

C44 Luisa De Marco, Michele Manca, Roberto Giannuzzi, Rita Agosta, Davide Cozzoli, Giuseppe Gigli “Engineered multilayer photoelectrodes for dye solar cells based on shape-tailored TiO2 nanocrystals”

158

C45 Allison Brown, Lindsey Jamula, James McCusker “Excited-State Dynamics of Iron (II)-based Charge-Transfer Chromophores”

160

C46 Varun Sivaram “Fast charge transport in Solid State Dye Sensitized Cells Using Metal Oxide Nanowires”

161

C47 Hauke Harms, Nicolas Tétreault, Viktoria Gusak, Kislon Voitschovsky, Shaik Zakeeruddina, Francesco Stellacci, Bengt Kasemo, Michael Grätzel “In-situ Investigation of Dye Adsorption on TiO2 Films Using a Quartz Crystal Microbalance with

Dissipation Technique”

162

C48 Andrzej Dzwilewski, Ana Sofia Anselmo, Krister Svensson, Ellen Moons “Light induced effects in PCBM:P3HT blend films”

164

C49 Monica Lira-Cantu, Gerardo Teran-Escobar, David M. Tanenbaumb, Eszter Voroshazid, Martin Hermenau, Kion Norrman, Matthew T. Lloyd, Yulia Galagan, Birger Zimmermann,

165

4th


Markus Hösel, Henrik F. Dam, Mikkel Jogersen, Suren Gevorgyan, Lauren Lutsen, Dirk 1Vanderzande, Uli Würfel, Ronn Andriessen, Roland Rösch, Harald Hoppe, Agnès Rivaton, Gülşah Y. Uzunoğlul, David Germack, Brigitta Andearsen, Morten V. Madsen, Eva Bundgaard, Frederik C. Krebs “On the stability of a variety of organic photovoltaic devices by IPCE and in-situ IPCE analyses - The ISOS-3 inter-laboratory collaboration”

C50 Bayram Kilic, Didem Omay, Ergin Kosa, Huseyin Kizil, Levent Trabzon “Noval Solar Cell Based on Biopolymer”

167

C51 Renaud Demadrille, Zaireen Yahya, Evan Spadafora, Benjamin Grevin, Mathieu Linares, Patrice Rannou, Adam Pron, Remi Debettignies, Jean-Pierre Travers “Oligomers and alternating copolymers designed for bulk heterojunction solar cells: synthesis, opto-

electronic properties and device performances”

168

C52 Shuyan Shao, Fengling Zhang “PEO modified ZnO enhances the performance of hybrid solar cells”

170

C53 James M Gardner, Jonas Petersson, Julien Warnan, Yann Pellegrin, Errol Blart, Fabrice Odobel, Leif Hammarström “The Photochemistry and Photovoltaic Performance of a New Class of Pan-Chromatic, Donor-Acceptor Sensitizers in p-Type Dye-Sensitized Solar Cells”

171

C54 Desiree Gentilini, Alessio Gagliardi, Aldo Di Carlo “Theoretical investigation on drift current in Dye Solar Cell and comparison with experimental data”

172

C55 Mutsumi Kimura, Hirotaka Nomoto, Naruhiko Masaki, Shogo Mori “Development of High-performance Zinc Phalocyanine Sensitizers for Dye-sensitized Solar Cells”

173

C56 Giuseppe Calogero, Jun-Ho Yum, Alessandro Sinopoli, Gaetano Di Marco, Michael Grätzel, Mohammad Khaja Nazeeruddin “Natural Dye sensitized solar cells based on Anthocyanins and betalains”

174

C57 Jacqueline Cole “Materials Discovery of Dyes for Dye-Sensitized Solar Cells: Prediction, Validation and Rationalisation”

175

C58 Elizabeth Gibson, Jean-François Lefebvre, Christopher Wood “Dye-sensitized Photocathodes for Tandem Dye-Sensitized Solar Cells”

176

C59 Karel Žídek, Kaibo Zheng, Carlito S. Ponseca Jr., Maria E. Messing, L. Reine Wallenberg, Pavel Chábera, Mohamed Abdellah, Villy Sundström, Tõnu Pullerits “Ultrafast electron transfer in CdSe quantum-dot-sensitized ZnO nanowires: time-resolved absorption and terahertz study”

177

C60 Rachel Howden, Miles Barr, Karen Gleason “Design and Construction of Novel Photovoltaic Devices via Oxidative Chemical Vapor Deposition (oCVD)”

179

C61 Servane Haller, Jean Rousset, Daniel Lincot “Electrodeposition and characterization of zinc oxide nanostructures for anode in Dye-Sensitized Solar

Cells”

180

C62 Marisa Arunchaiya, Voranuch Somsongkul, Atchana Wongchaisuwat, Attera Worayingyong “Improved stability of unsealed quasi-solid-state dye-sensitized solar cell based on carbon materials with LaCoO3 additive as counter electrode”

181

C63 Ergang Wang, Zaifei Ma, Patrik Henriksson, Olle Inganäs, Fengling Zhang, Mats Andersson “Design and synthesis of isoindigo-based low band gap polymers for polymer solar cells”

182

C64 Jonas Bergqvist, Hans Arwin, Olle Inganäs “In situ reflectance imaging of organic thin film formation from solution”

183

C65 Abdulrahman Alwarthan, Ahmad Aqel “Incorporation of Carbon Nanotubes into Organic Polymer Monolithic Columns for Capillary

Chromatography”

185

C66 Leslie W. Pineda, Karina Torres Castro, Andrea Soto Navarro, Darío Chinchilla, Catalina Murillo Cruz, Kattia Rosales Ovares, Cindy Torres Quirós, Carlos Meza, Mavis L. Montero “Harnessing biodiversity potential in the quest of pigment molecules for dye-sensitized solar cells: From

plant extracts to microorganism metabolites”

186

C67 André L. A. Parussulo, Bernardo A. Iglesias , Koiti Araki, Henrique E. Toma “Sevenfold Enhancement on Porphyrin Dye Efficiency by Coordination of Ruthenium Polypyridine Complexes”

187

C68 Andrew Pearson, Paul Hopkinson, Tao Wang, Athene Donald, David Lidzey “Correlating Phase Transitions with Thermal Annealing Temperatures for P3HT:PCBM Organic Photovoltaic Devices”

189

C69 Andrew Pearson, Stuart Boden, Darren Bagnall, David Lidzey, Cornelia Rodenburg “Imaging the Bulk Nanoscale Morphology of Polymer:Fullerene Blend Thin-films Using Helium Ion

Microscopy”

190

C70 Jesús Baldenebro-López, José Castorena-González, Norma Flores-Holguín, Jorge Almaral Sánchez, Daniel Glossman Mitnik

191

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“DFT Study of Triphenylamine-Based Dyes for their Use as Sensitizers in Molecular Photovoltaics”

C71 Yeru Liu, James Jennings, Qing Wang “Impedance study of dye-sensitized solar cells employing cobalt bipyridyl redox mediators”

192

C72 Iuliia Shcherbakova, Marina Simeunovic, Simone Hochleitner, Toby Meyer, Frederic Ostwald, Thomas Geiger “Novel NIR Sensitizers for Dye Sensitized Solar Cells”

193

C73 Muhammad Imran Asghar, Niko Humalamäki, Liisa Antila, Sampo Kaukonen, Janne Halme, Peter Lund, Jouko Korppi-Tommola “Finger prints of dye solar cell’s components using Fourier Transform Infrared spectroscopy”

195

C74 Chian Haw Yong, L. N. S. A. Thummalakunta, Ananthanarayanan Krishnamoorthy, Joachim Luther ““Pseudo bi-layer” Organic Solar Cells”

196

C75 Chang Su Kim, Ji-Hoon Seo, Jae-Wook Kang “Organic solar cells using simply grown graphene transparent electrode”

198

C76 Dong Chan Lim, Kwang-Dae Kim, Jae-Hong Lim, Kyu Hwan Lee, JooYul Lee “Spontaneous formation of ZnO nanoripples and surface modification for high efficient OPV”

199

C77 Erik M. J. Johansson, Lei Yang, Erik Gabrielsson, Peter W. Lohse, Gerrit Boschloo, Licheng Sun, Anders Hagfeldt “Efficient dye regeneration in thick solid state dye-sensitized solar cells”

200

C78 Erica DeMarco, Hanning Chen, Stacey Standridge, George Schatz, Michael Pellin, Joseph Hupp “Enhancing Light Absorption through Localized Surface Plasmon Resonance: Fundamental Studies in DSSCs”

201

C79 Katja Gräf, Mukundan Thelakkat “Tailor-made synthesis of BODIPY dyes as panchromatic sensitizers”

202

C80 Carlos Ramos, Juan Rodriguez, Luis Sanchez, Mikhail Gorlov, Lars Kloo, Walter Estrada, Maria Quintana “Dye-sensitized solar cells based on ZnO nanorod photoanodes: influence of the band gap”

204

C81 Donghoon Song, Woohyung Cho, Mi Jin Choi, Yong Soo Kang “Efficiency Enhancement by A Fairly Stable I-/(SeCN)2 Redox Mediator in Dye-Sensitized Solar Cells”

205

C82 Giuseppe Calogero, Alessandro Sinopoli, Ilaria Citro, Gaetano Di Marco, Vesselin Petrov, Ana M. Dinizb, A. Jorge Parolab, Fernando Pin “Flavylium salts as novel photosensitizers for dye-sensitized solar cells”

206

C83 Ranjith K, Arun Rao, Praveen Ramamurthy “Novel ketone containing alternating copolymer for organic solar cells”

207

C84 Taewoo Jeon, Bernard Geffroy, Denis Tondelier, Linwei Yu, Pascale Jegou, Bruno Jousselme, Serge Palacin, Pere Roca i Cabarrocas, Yvan Bonnassieux “Acid treatments on silicon nanowires for efficient hybrid solar cells”

208

C85 Ricardo Bouwer, Jan-Carlos Kuhlmann, Paul de Bruyn, Paul Blom, Kees Hummelen “Compatibilizing donor and acceptor in polymer:fullerene bulk heterojunction solar cells”

210

C86 Woohyung Cho, Donghoon Song, Yong Bum Pyun, Tea Yon Kim, Yong Gun Lee, Yong Soo Kang “Efficient Binary Organic Redox Mediators in Dye-Sensitized Solar Cells Based on Carbon Black Counter

Electrode”

212

C87 M.M. Rashad, A.E. Shalan, Youhai Yu, Monica Cantu, M.S.A. Abdel-Mottaleb “A Facile Low temperature synthesis of TiO2 nanorods for high efficiency dye sensitized solar cells”

213

C88 Omer Gullu, Enise Ozerden, Serif Ruzgar, Sezai Asubay, Osman Pakma, Tahsin Kilicoglu, Abdulmecit Turut “Characterization of Au/n-InP Photovoltaic Structure with Organic Thin Film”

214

C89 Robert Schuetz, Andreas Bartelt, Joachim Schaff, Ivo Kastl, Christian Strothkaemper, Rainer Eichberger, Gabriele Nelles, Gerda Fuhrmann “Influences of the Chemical Environment on the Electron Injection Efficiency of a New Class of Semi-Squarylium Dyes”

215

C90 Alex Sangiorgi, Riccardo Bendoni, Nicola Sangiorgi, Barbara Ballarin, Alessandra Sanson “Optimized TiO2 blocking layers for dye-sensitized solar cells (DSSC)”

217

C91 Camilla Lindqvist, Patrik Henriksson, Renee Kroon, Ergang Wang, Mats R. Andersson “Photo-Oxidative Stability of Conjugated Polymers for Organic Solar Cells”

218

C92 Thitinun Karpkird, Pattraporn Saiwattanasuk, Supa Hannongbua, Licheng Sun “Photo-Induce Electron Transfer of Ruthenium Complexes with One and Two Linked Viologens Trapped CB[7] in Organic Solution”

219

C93 Andréia de Morais, Flávio Santos Freitas, Helton Pereira Nogueira, Ana Flávia Nogueira “Preparation and characterization of nanocomposites based on TiO2/graphene and their application on inverted solar cells”

220

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C94 Negar Ashari Astani, Basile F. E. Curchod, Ivano Tavernelli, Ursula Roethlisberger “Computational study of porphyrin sensitizers for solar cells: molecular design and binding mechanisms”

222

C95 Johannes Brendel, Mukundan Thelakkat “Functional amphiphilic blockcopolymers for hybrid donor-acceptor composites”

223

C96 Christina Pang, John de Mello “Silver Nanowire Electrodes for Organic Solar Cells”

224

C97 Daniel Grasseschi, André Luis Parussulo, Robson Raphael Guimaraes, Koiti Araki, Henrique E. Toma “Spectroscopic Study of Gold Nanoparticles functionalized with Ru-Triazine dye for application in

Plasmonic-Enhanced Dye Sensitized Solar Cells”

225

C98 Jae-Wook Kang, Do-Geun Kim, Jong-Kuk Kim, Chang Su Kim “Flexible transparent electrode with printed metal grids”

227

C99 Meysam Pazoki, Gerrit Boschloo, Anders Hagfeldt, Nima Taghavinia “Mesoporous TiO2 microbead electrodes in cobalt-electrolyte based dye-sensitized solar cells”

228

C100 Haining Tian, Bo Xu, Licheng Sun “P-type Dye-Sensitized Solar Cells Based on Porphyrin and Fullerene Derivatives”

229

C101 Mihai Mihaila, Cristian Diaconu, Octavian Buiu, Bogdan Serban, Viorel Avramescu “Search for Dye Sensitized Solar Cell High Efficiency Organic Cromophore Loci”

230

C102 Mukhamed Keshtov, Vitaliy Kochurov, Levent Toppare, Dmitriy Godovsky, Alexei Khokhlov “Synthesis and Characterization of Benzo*1,2-b:3,4-b’+dithiophene-based Low Band gap Copolymers Containing Electron –Withdrawing Thienopyrazine and thieno[3,4-c]thiadiazole Derivatives for Photovoltaic Application”

234

C103 Gabriella Di Carlo, Daniela Caschera, Marco Brucale, Alessio Mezzi, Giuseppe Calogero, Gaetano Di Marco, Giuseppina Padeletti, Gabriel Maria Ingo “The influence of titania morphology on dye loading for dye-sensitized solar cells”

236

C104 Armantas Melianas, Zheng Tang, Olle Inganäs “Charge Carrier Mobility and Recombination in TQ1:*70+PCBM Solar Cells Studied by TOF and CELIV Techniques”

237

C105 Andreas Bartelt, Christian Strothkämper, Rainer Eichberger “Charge separation dynamics in photovoltaic ZnPc:C60 blend films”

239

C106 Jesse Ondersma, Thomas Hamann “Determination of Conduction Band Minimum in TiO2 Via Temperature Dependent Spectroelectrochemistry”

240

C107 Mónica B. Della Pirriera, Pau Bosch Jimenez, Laurent Auboy, David Gutierrez Tauste, José M. García, Jose L. Bautista, Manus Kennedy, Hind Ahmed, J. Doran, Joaquim Puigdollers, Cristobal Voz, Sergi Galindo “DSSC with Large Stokes Shift layer as UV blocking layer”

241

C108 Phuong Tuyet Nguyen, Poul Erik Hansen, Torben Lund “The effect of 4-tert-butylpyridine and Li+ on the thermal degradation of TiO2 – bound ruthenium dye N719”

242

C109 Kamila Zarebska, Magdalena Skompska “Electrochemical deposition of ZnO nanorods for application in light harvesting solar cells”

243

C110 Flavio S. Freitas, Agnaldo S. Gonçalves, Andréia de Morais, João E. Benedetti, Luiz C. P. Almeida, Ana F. Nogueira

“Low cost counter electrodes for dye-sensitized solar cells based on graphene-like MoS2”

244

C111 Zuzanna Glebicka, Magdalena Skompska

“Synthesis and characterization of semiconductor nanoparticles for application in solid state solar cells” 246

C112 Matthew Carnie, Trystan Watson, David Worsley “Triiodide Loss and Subsequent Regeneration in UVA Exposed Dye-Sensitized Solar Cells”

248

C113 Daniel Staff, Alison Walker “A monte carlo study of increased charge mobility in molecular hole transporters due to coulomb traps”

250

C114 Markus Pfau, Rubén Costa, Dirk Guldi, Tim Clark “A theoretical study on Zn-porphyrins as potential dyes on ZnO-based dye-sensitized solar cells”

251

C115 Eva Unger, Burkhard Zietz “Effect of Aggregation on the Internal Quantum Efficiency of Squaraine Sensitizers”

252

C116 Johan Oscarsson, Rebecka Schölin, Susanna K Eriksson, Kristofer Fredin, Erik M. J. Johansson, Håkan Rensmo “Atomic level characterization of D35/TiO2 interfaces - co-sensitization and thermal degradation”

253

C117 Askhat Jumabekov, Mihaela Nedelcu, Laurence Peter, Hiroaki Sai, Ulrich Wiesner, Thomas Bein

“Block Copolymer Templated TiO2 Films in Extremely Thin Absorber Solar Cells”

254

C118 Elham Ghadiri, Jacques-E Moser

“Charge carrier dynamics in dye sensitized solar cells by diffuse reflectance spectroscopy” 255

C119 Madsakorn Towannang, Samuk Pimanpang, Anongnad Thiangkaew, Phikun Rutphonsan, Wasan Maiaugree, Vittaya Amornkitbamrung

256

4th


“Chemically deposited polypyrrole-nanoparticle counter electrode for inorganic I-/I3- and organic T-/T2 dye-sensitized solar cells”

C120 Dimitar Valtakari, Roger Bollström, Mikko Tuominen, Hannu Teisala, Mikko Aromaa, Martti Toivakka, Jurkka Kuusipalo, Jyrki M. Mäkelä, Jun Uozumi, Jarkko J. Saarinen

“Conductive surfaces on coated papers by flexographical printing”

257

C121 Timo Peltola, Alison Walker

“Decoupling Recombination Order and Electron Statistics in Dye Solar Cell Nonideality Measurements” 259

C122 Amani Chams, Anders Hagfeldt, Leif Hägmann, Erik Johansson, Mohamed Jouini, Lars Kloo, Christian Perruchot, Yang Shen, Alan Snedden, Nick Vlachopoulos, Lei Yang “Efficient solid state dye sensitised solar cell based on PEDOT conducting polymer and organic dye”

260

C123 Magdalena Marszalek, Aswani Yella, Hoi Nok Tsao, Leo-Philipp Heiniger, Shaik M. Zakeeruddin, Michael Grätzel “Gradient TiO2 films employed to reduce the photocurrent losses in high performing DSCs with ionic-liquid-based electrolyte”

261

C124 Satvasheel Powar, Qiang Wu, Amaresh Mishra, Leone Spiccia, Udo Bach “Improved photocurrents for p-type dye-sensitized solar cells using nano-structured nickel(II) oxide microballs”

262

C125 Alessandra Operamolla, Silvia Colella, Roberta Musio, Omar Hassan Omar, Mazzeo Marco, Giuseppe Gigli, Pynalisa Cosma, Angela Agostiano, Gianluca M. Farinola, Francesco Babudri, Marinella Striccoli “Low band-gap poly(arylenethienylene)s with benzothiadiazole units: Synthesis, characterization and application in polymer solar cells”

263

C126 Aswani Yella, Magdalena Marszalek, Micheal Graetzel “Influence of the alkyl chains on the cobalt (II/III) redox-mediated dye sensitized solar cells”

264

C127 Arianna Marchioro, Amalie Dualeh, Michael Grätzel, Jacques-Edouard Moser

“Investigation of TiCl4 treatment on carrier dynamics in solid-state dye-sensitized solar cells studied by time-resolved spectroscopy”

265

C128 Carsten Dosche, Ushula Mengesha Tefashe, Wiebke Schulte, Kazuteru Nonomura, Nikolaos Vlachopoulos, Anders Hagfeldt, Gunther Wittstock

“Kinetics at the illuminated dye/TiO2-electrolyte interface investigated by SECM”

266

C129 Kristofer Fredin, Rebecka Schölin, Johan Oscarsson, Erik Johansson, Håkan Rensmo

“Measurements on Solid State Dye-Sensitized Solar Cells Utilizing Transparent Counter Electrodes” 267

C130 Iwona A. Rutkowska, Pawel J. Kulesza

“Mixed-Valent Cyanometallate as Inorganic Redox Mediator for Dye-Sensitized Solar Cell” 268

C131 Alison Walkera, Laurence Peter

“Modelling charge transport in TiO2 film and electrolyte in a dye-sensitized solar cell” 269

C132 Dmitri Godovsky, Natalia Golubko, Yulianna Roginskaya, Anastasia Ozimova, Dmitri Paraschuk

“New polylinkers for low temperature annealed titania layes of dye synthesized solar cells”

270

C133 Katarzyna Grzejszczyk, Anders Hagfeldt, Leif Häggman, Erik Johansson, Pawel Kulesza, Magdalena Skunik, Nick Vlachopoulos, Lei Yang “Photocapacitors based on solid state dye solar cells and metal oxide charge-storage materials”

271

C134 Ida Josefsson, Michael Odelius “Quantum chemical calculations of transient L-edge X-ray spectra of Transition Metal complexes”

273

C135 César A. Henriques, Sara M. Pinto, Hugh D. Burrows, Mariette M. Pereira, Mário J. F: Calvete, Carlos Serpa “Self-Assembling a Water-Soluble Polythiophene derivate with Cationic Porphyrins for Application in Organic Solar Cells”

274

C136 Tiago A. Matias, André Luís A. Parussulo, Sérgio H. Toma, Koiti Araki, Henrique E. Toma

“Synthesis and Properties of an Asymmetric Binuclear Ruthenium Polypyridine Dye” 276

C137 Amalie Dualeh, Thomas Moehl, Mohammad K. Nazeeruddin, Michael Grätzel “Temperature dependence of transport-properties of spiro-MeOTAD as a hole-conductor in solid-state dye-sensitized solar cells”

278

C138 Kenrick Anderson, Emily Border, Timothy Jones, Clint Woodward, Gregory Wilson, Christopher Fell “The Application and Physical Properties of DCDHF dyes in Organic Photovoltaics”

279

C139 Ida Josefsson, Susanna K. Eriksson, Niklas Ottosson, Gunnar Öhrwall, Anders Hagfeldt, Håkan Rensmo, Olle Björneholm, Michael Odelius “The electronic structure of I3- in aqueous solution”

280

C140 Gang Wang, Ka Kan Wong, Yip Hang Ng, Yu Hang Leung, Aleksandra B. Djurisic, Wai Kin Chan “The influence on annealing condition for ZnO nanoparticle based Dye Sensitized Solar Cells”

281

C141 Johannes T. Margraf, Vito Sgobba, Tim Clark, Dirk M. Guldi “A Joint Experimental and Theoretical Approach for Probing Interfaces in Quantum Dot Sensitized Solar Cells”

282

C142 Fabian Lodermeyer, Rubén D. Costa, Jenny Malig, Norbert Jux and Dirk M. Guldi “Benzoporphyrins as novel light-harvesting dyes for dye-sensitized solar cells (DSSCs)”

283

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C143 Maria Brites, Érica Torres, Sara Sequeira, Paulo Mendes, Killian Lobato “Coumarin Dyes with Triple Bonds as pi-Spacer Units for Dye Sensitized Solar Cells”

285

C144 Liisa Antila, Mikko Heikkilä, Ville Mäkinen, Viivi Aumanen, Marianna Kemell, Pasi Myllyperkiö, Karoliina Honkala, Hannu Häkkinen, Markku Leskelä, Jouko Korppi-Tommola “Effect of atomic layer deposited metal oxide barriers on interfacial electron transfer in dye-sensitized solar cells”

286

C145 Tânia Frade, Killian Lobato, Anabela Gomes “Electrodeposited ZnO Nanorods for Dye-Solar Cells”

287

C146 Norma Minar, Thomas Bein “Filling the pores: In-Situ Polymerization of MEH PPV into Porous Titania”

289

C147 Ana Sofia Anselmo, Andrzej Dzwilewski, Ergang Wang, Mats R. Andersson, Jan van Stam, Krister Svensson, Ellen Moons

“Molecular orientation and composition at the surface of APFO3:PCBM blend films”

290

C148 Robson Raphael Guimarães, André Luis Araújo Parussulo, Henrique Eisi Toma, Koiti Araki “New Efficient and Tunable Ruthenium Photosensitizer for Dye Sensitized Solar Cells”

291

C149 Sebastian Feihl, Rubén D. Costa, Stephan Pflocka, Cordula Schmidt, Susanne Backes, Jörg Schönamsgruber, Andreas Hirsch, Dirk M. Guldi “Nickel Oxide Nanostructured Electrodes for Perylenediimide-Based Dye-Sensitized Solar Cells”

293

C150 Lei Yan, Xiaohui Wang, Xingzhu Wang, Xun Chen

“A platinum-based poly(aryleneethynylene) containing thiazolothiazole group with high hole mobility for organic photovoltaic and field-effect transistor applications”

294

C151 Jelissa De Jonghe, Jacques-Edouard Moser, Gaetan Wicht, Roland Hany, Frank Nueusch “Photoinduced Processes in Small Molecule/Fullerene Bilayers”

296

C152 Alesja Ivanova, Thomas Bein “Synthesis and Characterization of Biotemplated Titania Porous Films”

297

C153 Maurizio Furlani, T.M.W.J. Bandara, Bengt-Erik Mellander, Tommy Svensson, W.J.M.J.S.R. Jayasundara, Vito Di Noto, Christopher Frisk “Tetrahexylammonium Iodide containing Gel Polymer Electrolytes for Dye Sensitized Solar Cells and CdS QD Sensitized Solar Cells”

298

C154 Erik Gabrielsson, Hanna Ellis, Haining Tian, Sandra Feldt, Gerrit Boschloo, Anders Hagfeldt, Licheng Sun “The Effect of the Auxiliary Donor Substituents on the D35 DYE”

299

C155 Lorenzo Franco, Antonio Toffoletti, Marco Ruzzi, Luciano Montanari, Lucia Bonoldi, Claudio Carati, Riccardo Po

“Which information EPR spectroscopy can provide on polymer/fullerene photovoltaic materials?”

300

C156 Lei Yan, Juhua Ou, Xingzhu Wang, Chengxi Li “Novel Platinum-Containing Metallopolyynes as Polymer Semiconductors for Thin-Film Transistors and Bulk Heterojunction Solar Cells”

302

C157 Pavel Chabera, Tobias Harlang, Sophie Canton, Villy Sundström “Ultrafast electron transfer of a Ru-Co photocatalysis model system”

303

C158 Michele Tonezzer, Enrico Menin, Sara Carturan, Gianluigi Maggioni, Monica della Pirriera, David Gutierrez - Tauste, Stefano Conci, Alberto Quaranta

“Novel hybrid and flexible photovoltaic devices”

305

C159 Michele Tonezzer, Enrico Menin, Sara Carturan, Gianluigi Maggioni, Monica della Pirriera, David Gutierrez - Tauste, Stefano Conci, Alberto Quaranta

“Improving solar cell efficiency with rare earth –based luminescent thin films”

307

C160 Michele Manca, Francesco Todisco, Roberto Giannuzzi, Alessandro Cannavale, Raffaella Buonsanti, Luisa De Marco, Delia Milliron, Giuseppe Gigli “Dynamical modulation of the optical transmittance in multifunctional dye-sensitized photelectrochemical devices based on the implementation of indium-tin oxide plasmonic resonators”

308

C161 Francesco Malara, Michele Manca, Christof Hübner, Elpida Piperopoulos, Giuseppe Gigli “Engineered carbon-nanotube-based composite plates as highly efficient free-standing counter electrodes for dye solar cells”

310

C162 Ahmed El-Zohry, Burkhard Zietz “Aggregation and Isomerisation in the Solar Cell Dye D149”

312

C163 Poul Erik Hansen, Phuong Tuyet Nguyen, Jacob Krake, Jens Spanget-Larsen, Torben Lund “Dye-sensitized Solar Cells and Complexes between Pyridines and Iodines. A NMR, IR and DFT study”

313

C164 Andrea Lamberti, Adriano Sacco, Stefano Bianco, Diana Hidalgo, Diego Manfredi, Rossana Gazia, Marzia Quaglio, Angelica Chiodoni, Elena Tresso, Candido Fabrizio Pirri “High electron lifetime in transparent TiO2 nanotubes-based photoanode for front-illuminated dye-sensitized solar cell”

314

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© SEFIN 2012

A1 - Nanostructured systems for the generation of electricity from sunlight

Michael Graetzel Laboratory of Photonics and Interfaces, Ecole Polytechnique Fédérale de Lausanne, Station 6,LPI EPFL, CH-1015, Lausanne, Switzerland

The performance of solar energy conversion devices employing mesoscopic photoelectrodes depends critically on their nanostructure [1,2] This is evident for the dye sensitized solar cell (DSC) where charge percolation through the TiO2 to the transparent conductive (TCO) electrodes takes milliseconds. Slow charge extraction increases chances of electron-hole recombination at the mesoporous TiO2 - electrolyte interface, and limits DSCs to be used with only a few electrolytes that offer low recombination rates. These limitations can be overcome with advanced nanostructuring techniques, the design of new sensitizers and new electrolytes. Here we describe our latest efforts to improve the photon harvesting and the charge carrier collection transport in these mesoscopic solar energy conversion systems. For the last tow decades, only triodide/iodide based redox electrolytes have attained PCEs over 10%. However recently a particularly exciting advance has been made by combining Co(II/III) complexes with organic donor –acceptor dyes [3]. Poprhyrien based donor acceptor systems have now attained already PECs of 12.3 % [4] and the recent achievement of strikingly high open circuit voltages close to 1.1. V [5] forebodes well for realizing DSC with new record performance in the near future. References [1]Grätzel, M. "Photoelectrochemical Cells", Nature 2001, 414, 338-344 [2] Grätzel, M. "Recent advances is mesoscopic solar cells" Acc. Chem. Res. 2009. 42, 1781-1798. [3] Feldt S. M.; Gibson E. A.; Gabrielsson, E. ; Sun L.; Boschloo, G.; Hagfeldt, A. Design of Organic Dyes and Cobalt Polypyridine Redox Mediators for High-Efficiency Dye-Sensitized Solar Cells J. Am. Chem. Soc. 2010, 132, 16714-16724. [4] Yella A.; Lee H.-W.; Tsao H. N.; Yi C.;Kumar Chandiran A., Nazeeruddin Md. K.. W-G Diau W- G I E, Yeh, C.-Y. Zakeeruddin S. M.; Grätzel M. Porphyrin-sensitized solar cells with cobalt (II/III)-based redox electrolyte exceed 12 percent efficiency. Science 2011, 334, 629 - 634. [5] Yum J-H, Baranoff,E ; Kessler F; Moehl T; Shahzada A; Bessho T, Machioro M; Ghadin E; Moser J-E; Yi C; Nazeeruddin Md-K; Grätzel M. A cobalt complex redox shuttle for dye sensitized solar cells with high open circuit potential, Nature Comm 2012, DOE 10.1038/ncomm1635.

4th


© SEFIN 2012

A2 - Small Molecule Organic Solar Cells: Status and Recent Developments

Karl Leo

a, Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany b, Fraunhofer IPMS, 01009 Dresden, Germany

Organic solar cells have recently mad much progress in terms of efficiency and lifetime and have reached the 10% efficiency mark. However, they will need further significant improvements to achieve broad application, in particular for the challenging power applications where inorganic PV technologies are well established. Organic solar cells have been realized by both polymer and oligomer (small-molecule) organic semiconductors, with the polymer technology being initially investigated far broader. In this talk, I will give an overview over the key features of small-molecule organic solar cells deposited by vacuum processes. Using this technology, one can easily deposit multilayer structures which allow to fine tune the optical and electrical properties. I will discuss recent experiments which relate the molecular structure of absorber materials with the layer morphology and the cell properties. Furthermore, highly efficient tandem structures with optimized electrical and optical properties will be discussed. Finally, I will address the question of low-cost manufacturability of small-molecule materials. Here, we have introduced vacuum roll-to-roll processing as an efficient deposition method for multilayer organic solar cells.

4th


© SEFIN 2012

A3 - Fast times and too bright lights. Understanding the Kinetics and Mechanics of Liquid Junction and Solid State Dye Sensitized Solar Cells.

Brian O'Regan

Imperial College London, Department of Chemistry, London, GB

We have measured femtosecond to nanosecond transient absorption (TA) of dye sensitized TiO2 in standard electrolytes. The TA has been measured with average pulse intensities from under one sun to over 10 suns. We have probed in the infrared, observing both the electrons in the TiO2 and the time evolution of molecular vibrations from the excited and oxidized states of the dye. The results shed light on the current debate about the time scale of electron transfer from excited dyes to TiO2 in optimized dye sensitized cells. New methods of fabricating solid state DSSCs will also be discussed. We present comparisons of charge generation, transport, and recombination using the hole conductors CuSCN and SpiroOMeTAD. We also discuss several complimentary ways of estimating collection efficiencies in both standard DSSCs and solid state cells. Lastly, we will briefly review our progress on measuring iodine binding coefficients to common DSSC dyes, measuring the effects of dye layers on recombination, and transport and recombination in water based electrolytes.

4th


© SEFIN 2012

A4 - Star-Shaped Ruthenium Polypyridyl Complexes: Binding Control on Metal Oxide Surfaces

Elena Galoppini Rutgers University Chemistry Department, 73 Warren Street, Newark, New Jersey, 0, US

Control of charge transfer between dye-linker-anchor sensitizers to metal oxide (MO) semiconductor interfaces is important for renewable energy projects involving nanostructured semiconductors. However, it is difficult to control effectively the positioning of a molecule on a MO surface, a prerequisite to engineer and study this complex interface. Uncertainty over the binding mode and orientation, and the heterogeneity of the nanostructured metal oxide films can prevail over the molecular design. A series of novel homoleptic Ru(II) star complexes were synthesized as part of a new surface engineering strategy. In the nano-sized, highly symmetrical star-shaped complexes, the Ru(II) center is coordinated to three identical bipyridine ligands carrying conjugated oligophenylenethynylene rigid linker units with or without solubilizing alkoxy chains, and terminating with carboxylic anchor groups. The chromophoric Ru(bpy) core cannot come in close contact to the semiconductor surface. We will describe the synthesis, properties in solution and bound. Synthetic modifications, computational studies and binding studies to enhance injection yield are in progress and will be presented in the poster.We will also describe other new surface engineering concepts involving host-guest chemistry that are being developed in our group. References [1] Y. Zhang, E. Galoppini, P. G. Johansson, G. J. Meyer, Pure Appl. Chem., 2011, 83, 861–868. [2] P. G. Johansson, Y. Zhang, M. Abrahamsson, G. J. Meyer, E. Galoppini, Chem. Commun., 2011, in press DOI: 10.1039/c1cc11210d

4th


© SEFIN 2012

A5 - Charge generation and recombination in dye-sensitized nano-structured TiO2

films

Ryuzi Katoha, Akihiro Furubeb

a, Nihon university, Koriyama,, Fukushima, 963, JP b, AIST, Tsukuba, Ibaraki 305-8565, JP

Physical chemistry of photo-energy conversion reaction systems is very important issue leading to feature solar energy conversion devices. In this context, we have so far studied primary reaction processesin dye-sensitized solar cells and organic solar cells using time-resolved laser spectroscopy. Novel techniques are required and we have developed highly sensitive transient absorption spectrometer with wide-wavelength detection range (400-2500 nm). Since electron injection process is a key process torealizehigh performance in DSSC, we have systematically studied electron injection process in dye-sensitized nano-structured semiconductor films[1]. We estimated the absolute valueof electron injection efficiency from excited dyes to nano-structured semiconductor films in various sensitizer dyesand semiconductors. We also examined the effect of excitation wavelength, excitation density, solvents and ions. Finally, we found that almost unity injection efficiency can be realized in such films under particular conditions. We are studying transient absorption in wide-time range to identify the limiting factor of electron injection efficiency. Recombination between an injected electron and a parent cation is also important issue to optimize solar cell performance. It has been reported that the recombination is very slow process in 10-3 sec compared with the electron injection time (<10-12 sec), indicating that such long lived charge separated state is key factor to realize high performance of solar cells. In order to clarify the origin of the slow charge recombination, we recently measured temperature dependence of the rate of the recombination [2]. References [1]Katoh, R.; Furube, F. "Efficiency of Electron Injection in Dye-sensitized Semiconductor Films" Key Engineering Materials, 451, 79-95(2010). [2] Katoh, R.; Furube, F. "Tunneling-Type Charge Recombination in Nanocrystalline TiO2 Films at Low Temperature" J. Phys. Chem. Lett. 2, 1888-1891 (2011).

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A6 - Exciton/plasmon interactions: a new paradigm in solar photoconversion

Jao van de Lagemaat a, National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado, 80401, US b, Renewable and Sustainable Energy Institute, University of Colorado at Boulder, Boulder, Colorado, US

The efficiency of excitonic photoconversion devices such as organic, organic/inorganic hybrids as well as full quantum dot devices, while rapidly increasing, remains lower than its ultimate limit because of low carrier mobilities as well as insufficient light absorption in the thin layers used in such devices because of otherwise excessive recombination. Advances will have to be made in the fundamental understanding of the photophysics and carrier dynamics of the organic semiconductors used in these systems as well as strategies devised to more effectively capture solar light in the thin layer structures. This presentation discusses basic research into the exciton and charge carrier dynamics that is aimed at precipitating deeper insight into the necessary approaches to gain control over these fundamental processes and consequently increase the device efficiencies.

Figure 1

I will focus on the use of plasmonics to both increase optical absorption as well as to drive excitonic processes in organics and quantum dots.For example, the inclusion of metal nanoparticles in organic solar cell structures will be shown to effectively increase the optical absorption of active layers. Also, such structures enhance the photoluminescence of the organic semiconductors, giving a method that can be used to estimate fundamental parameters such as the exciton diffusion length. Finally, I will discuss how to use plasmon/exciton hybrid states to drive third-generation energy conversion processes such as singlet fission, photon pooling and multiple exciton generation. Such concepts, when used in solar photoconversion structures can potentially push the efficiency into much higher regions, even breaking the Shockley-Queisser limit.

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A7 - High Performance Dye-Sensitized Solar Cells with Nano-clay Electrolyte

Satoshi Uchida, Bruno Ieiri Ito, Takaya Kubo, Hiroshi Segawa

RCAST, The University of Tokyo, 4-6-1, Komaba, Meguro, Tokyo, 153, JP The dye-sensitized solar cells (DSCs) introduced by Grätzel in 1991 have received great attention over the past decade because of their potential for high energy conversion efficiency and low production cost. However, the presence of liquid electrolytes in such modules may result in some practical limitations of sealing and long-term stability due to the leakage of the liquid electrolyte. Toward the further improvement of durability of DSCs, the quasi-solid state electrolytes have been examined. It is well known that the conventional solidification methods have problems such as low ionic conductivity and poor electrolyte/electrode interface contact. In this point of view, here in this study, the artificial nano-clay powder was newly examined as a gelator of electrolyte of DSCs. The size of clay has two main distributions with 1.4 nm and 20 nm in diameter which are confirmed by STEM observation. The gelation point was quantitatively determined by using Rheometer with air bearing drives. The gel state maintained with more than 5wt% nano-clay powder in the acetonitrile based solvent. From photovoltaic measurement, the photo-electro conversion efficiency showed over 10% with clay electrolyte that is almost the same value of normal liquid type DSCs. The resulting cell performances are as follows. Liquid electrolyte; Jsc=19.46 Voc=0.77 FF=0.68 Eff=10.19. Clay electrolyte; Jsc=18.21 Voc=0.81 FF=0.69 Eff=10.18. Compared with the conventional solidification methods, the quasi-solid state DSSC using clay mineral showed significant better performance due to the high ionic conductivity and enough electrolyte/electrode interface contact. Further chemical and physical properties of these clay electrolyte were also discussed in related with surface impedance analysis.

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A8 - Understanding heterojunction solar cells through studies of the charge transfer state

Jenny Nelsona, Mark Faista, Thomas Kirchartza, Sheridan Fewa, James Kirkpatrickb

a, Imperial College London, Department of Physics, Blackett Laboratory, Prince, London, 0, UK b, University of Oxford, Parks Road, Oxford OX1 3LB,UK, UK

Efficient current and voltage generation in organic and hybrid heterojunction devices depends upon the driving forces for charge separation at the heterojunction and on the energies of the states involved. In this work we use electroluminescence spectroscopy to probe the energy of charge transfer (CT) states relative to the energies of excited states in the donor and acceptor components and, together with device measurements, to study the relationship between the CT state energy in and photocurrent generation efficiency. Through study of a wide range of polymer:fullerene combinations we show that CT state emission is positively correlated to photocurrent generation and that charge separation is switched off when the CT state energy approaches the energy of the lowest singlet excited state of the donor or acceptor. The experimental results are rationalised through theoretical calculations of the CT states. We extend the studies to other types of heterojunction and, finally, use our results to discuss the factors that limit current and voltage generation in heterojunction solar cells.

References [1] Faist MA, Kirchartz T, Gong W, et al, Competition between the Charge Transfer State and the Singlet States of Donor or Acceptor Limiting the Efficiency in Polymer:Fullerene Solar Cells., J Am Chem Soc, 2012, Vol:134, Pages:685-692

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A9 - Designed Photoelectrode Interfaces and Architectures for Dye-Sensitized Solar Cells

Joseph Hupp a, Northwestern University, Dept. of Chemistry, 2145 Sheridan Road, Evanston, IL 60208, US b, Argonne National Laboratory, Materials Science Division, 9800 South Cass Ave., Argonne, IL, 60439, US

This presentation will describe recent work from Northwestern on the design, fabrication, and utilization of photoelectrode interfaces and architectures designed to enable us to boost charge-collection lengths, employ conceptually new redox shuttles, facilitate dual-chromophore device sensitization, and/or inhibit interception of electrons without also inhibiting photochemical charge injection. Also to be described are the results of fundamental investigations of interfacial electron tunneling, especially as they relate to optimizing interfaces for DSC-based solar energy conversion. Much of the work relies upon nontraditional techniques for electrode fabrication such as atomic layer deposition.

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A10 - Lifetime of bulk heterojunction solar cells: the next challenge

Sabine Berthoa, Bert Coningsa, Fortunato Piersimonia, Donato Spoltorea, Jan D’Haena, Laurence Lutsenb, Bruno Van Melec, Guy Van Asschec, Dirk Vanderzandea,b, Jean Mancaa,b

a, Institute for Materials for Research, Hasselt University, Wetenschapspark 1, 3590 Diepenbeek, Belgium. b, IMEC vzw, associated lab IMOMEC (Diepenbeek), Belgium c, Department of Physical Chemistry and Polymer Science, Faculty of Engineering Sciences, Vrije Universiteit Brussels, Belgium.

With the first commercial organic photovoltaic (OPV) applications on the market (e.g. the solar bag of Neuber) and efficiencies approaching 10%, increasing the lifetime of the devices becomes the next crucial challenge for OPV. Several degradation mechanisms can occur in organic BHJ solar cells. Polymers exhibit a low resistance towards oxygen in combination with UV/Vis light or high temperatures, which results in a degradation of the solar cells. This talk provides an overview of the thermal instability of organic BHJ solar cells. The effect of thermal annealing on both the short circuit current and the open circuit voltage of the devices is discussed and a link is made with changes in the active layer morphology during the ageing process. An accelerated ageing system is used to study in-situ the degradation kinetics of BHJ solar cells at various temperatures in order to obtain an accelerated ageing model to predict lifetime. Complementary, the effect of temperature on morphology and photovoltaic properties is investigated with Transmission Electron Microscopy (TEM), in-situ Fourier Transform Photocurrent Spectroscopy (FTPS) and thermal analysis. Various solutions are proposed towards next generation BHJ solar cells with an increased intrinsic thermal stability.

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A11 - Efficient tandem polymer solar cells in normal and inverted device configurations

René Janssen

Eindhoven University of Technology, PO Box 513, Eindhoven, 5600, NL

In a tandem solar cell the photon energy can be better preserved. Hence, these devices form a promising and viable strategy to further increase the power conversion efficiency of polymer solar cells, eventually beyond the limits of single junction cells. Recent advances in this area will be discussed. Based on a new efficient low band gap polymer and an efficient wide band gap material, and a ZnO/PEDOT:PSS recombination layer, fully solution processed tandem polymer solar cells with a power conversion efficiency of 7% have been achieved in a normal polarity configuration. The tandem cell performs 20% better than the corresponding single junction solar cells, showing the relevance of the tandem configurations for polymer solar cells. We further demonstrate a solution processed PEDOT:PSS/ZnO recombination layer to make efficient tandem solar cells with inverted polarity. The inverted tandem cell reaches a power conversion efficiency of 5.8%, again 20% higher than that of the corresponding single junction inverted cells. The power conversion efficiencies of 7.0% for the normal tandem and of 5.8% for the inverted tandem are among the highest reported for this type of solar cells to date. Further advances in efficiency can be expected when polymer materials for more efficient single junction layers become available and when the resistive losses in the recombination contact can be further reduced.

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A12 - Aqueous electrolytes in dye sensitized solar cells

Thomas Risbridger, Kathryn Wills, Petra Cameron

The University of Bath, 1 South, Department of Chemistry, University of Ba, Bath, GB

Water was frequently used as an electrolyte in early dye sensitized solar cells (DSCs) but was abandoned in favour of organic solvents that gave much higher cell efficiencies. Since then many reports have considered the presence of even trace water in the electrolyte to be detrimental to cell performance and to reduce cell stability. Recently however, O’Regan et al published work suggesting that cells properly optimized to work with aqueous solvents can give reasonable efficiencies1, and other groups have also shown benefits to using water2,3. The highest published efficiencies for cells made using an100% aqueous electrolyte have increased slightly over the values obtained before 1991, with 2.4% being the best recorded1a. In our work we are using a range of characterisation techniques to cast light on the differences between cells with aqueous and organic electrolytes. In this presentation the processes that limit cell efficiency when an aqueous electrolyte is used will be discussed. Solar conversion efficiencies of up to 3.5% have been achieved and infrared transmission measurements show that the trapped electron density in an aqueous DSC behaves very differently to that in a conventional DSC. References [1](a) Law, C. H.; Pathirana, S. C.; Li, X. O.; Anderson, A. Y.; Barnes, P. R. F.; Listorti, A.; Ghaddar, T. H.; O'Regan, B. C. Adv Mater 2010, 22, 4505(b) Jung, Y. S.; Yoo, B.; Lim, M. K.; Lee, S. Y.; Kim, K. J. Electrochim Acta 2009, 54, 6286. [2] (a) Zou, J. J.; Pan, L.; Zhang, X. W.; Wang, L. J Am Chem Soc 2011, 133, 10000(b) Miyasaka, T.; Murakami, T. N.; Saito, H.; Uegusa, S.; Kawashima, N. Chem Lett 2003, 32, 1154. [3] Halin, M.; Johyansson, E.M.J.; Scholin; R.; Siegbahn, H.; Rensmo, H.; J Phys Chem C 2011, 115, 11996.

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A13 - Efficient DSCs Based on Organic Dyes and Iodine-Free Redox Couples

Licheng Suna, Haining Tiana, Lars Klooa, Xichuan Yangb

a, Department of Chemistry, School of Chemical Science and Engineering, KTH Royal Institute of Technology, Teknikringen 30, Stockholm, 10044, SE b, State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT), 116024 Dalian, China,

One of the most attractive ways to solve our climate problems and to meet the increasing demanding for global sustainable energy systems is the highly efficient and low cost solar cells. During this conference, development of organic dyes for dye sensitized solar cells (DSCs) based on nanostructured TiO2 will be presented. We have adopted different strategies to design the organic dyes with donor units, linkers and acceptors. Particular attention has been paid to avoid the application of cyanoacidic acid as the acceptor/anchoring unit, and alternative anchoring groups are developed. To replace iodide/tri-iodide, recent development of iodine free redox couples based electrolytes, such as sulfide/polysulfide based electrolytes will be discussed. By using these iodine free electrolytes, DSCs based on organic dyes has been fabricated with high efficiencies. References [1] A. Hagfeldt, G. Boschloo,L. Sun, L. Kloo, H. Pettersson: Chem. Rev.2010, 110, 6595-6663. [2] H. Tian, X. Jiang, Z. Yu, L. Kloo, A. Hagfeldt, L. Sun:Angew. Chem. Int. Ed.2010, 49, 7328-7331. [3] S. Feldt, E. Gibson, E. Gabrielsson, L. Sun, G. Boschloo, A. Hagfeldt: J. Am. Chem. Soc.2010, 132, 16714-16724. [4] L. Li, X. Yang, J. Gao, H. Tian, J. Zhao, A. Hagfeldt, L. Sun, J. Am. Chem. Soc. 2011, 133, 8458-8460. [5] H. Tian, Z. Yu, A. Hagfeldt, L. Kloo, L. Sun, J. Am. Chem. Soc. 2011, 133, 9413-9422. [6] H. Tian, E. Gabrielsson, Z. Yu, A. Hagfeldt, L. Kloo, L. Sun, Chem. Commun.2011, 47, 10124-10126. [7] H. Tian, L. Sun, J. Mater. Chem. 2011, 21, 10592-10601.

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A14 - Influence of film microstructure and crystallinity upon the function of organic bulk heterojunction solar cells

James R. Durrant

Centre for Plastic Electronics, Department of Chemistry, Imperial College London, U.K

In this talk, I will report some of our studies addressing the impact of film microstructure and crystallinity upon the processes of exciton diffusion, charge separation and charge recombination in organic bulk heterojunction solar cells. I will particularly focus upon the importance of amorphous versus crystalline domains and domain purity and size in determining the dynamics and yields of these processes. My talk will address the diffusion and dissociation of both polymer and fullerene excitons, polymer to fullerene energy transfer, electron and hole transfer, the role of film microstructure in influencing non-geminate recombination and thereby cell voltage and the importance of polymer and PCBM crystallization in modulating the ionization potential and electron affinities of these materials, thereby stabilizing spatial separation of the photogenerated charge carriers.

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A15 - Modeling Materials and Processes in Dye-Sensitized Solar Cells from First Principles

Filippo De Angelis

ISTM-CNR Perugia, Via Elce di Sotto 8, Perugia, I-06123, Italy

We present state-of-the art computer simulations on the fundamental constituents of Dye-sensitized solar cells (DSCs) and their interactions at the respective molecular/solid/liquid interfaces. Predictive dye design and modeling of realistic semiconductor (TiO2, ZnO) nanostructures enables us to investigate the structural, electronic and optical properties of dyes adsorbed onto semiconductor surfaces by means of DFT and TDDFT calculations. Thus, the alignment of ground and excited state energy levels for the interacting DSC constituents is presented and discussed in relation to experimental photovoltaic performances. Modeling of the combined dye / semiconductor / electrolyte heterointerfaces is then achieved by performing ab initio molecular dynamics simulations of semiconductor-adsorbed dyes in the solution / electrolyte environment. In particular, we present the case of Ru(II)-dyes on TiO2 and their interaction with a Cobalt-based electrolyte.

Figure 1 Interaction between a TiO2-adsorbed N719 dye and Co(bpy)3. Molecular orbitals involved in the regeneration / recombination processes are also shown.

The nature and localization of the electronic states at the dye/semiconductor/electrolyte interface is discussed in relation to the device efficiency parameters. The mechanistic details of dye regeneration and the recombination pathways with the oxidized dye and with TiO2-injected electrons are finally presented.

References [1] M. Pastore, F. De Angelis ACS Nano 2010, 4, 556. [2] F. De Angelis, S. Fantacci, R. Gebauer J. Phys. Chem. Lett. 2011, 2, 813. [3] F. De Angelis, S. Fantacci, E. Mosconi, M. K. Nazeeruddin, M. Grätzel J. Phys. Chem. C 2011, 115, 8825. [4] S. A. Sapp, C. M. Elliott, C. Contado, S. Caramori, C. A. Bignozzi J. Am. Chem. Soc. 2002, 124, 11215. [5] Nusbaumer, H.; S. M. Zakeeruddin, J.-E. Moser, M. Grätzel Chem. Eur. J. 2003, 9, 3756. [6] Y. Liu, J. R. Jennings, Y. Huang, Q. Wang, S. M. Zakeeruddin, M. Grätzel J. Phys. Chem. C 2011, 115, 18847.

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B1 - Dye Regeneration by Single Electron Redox Couples

Torben Daeneke, Udo Bach, Leone Spiccia

Monash University, Calyton, 3800, AU

Dye regeneration is a crucial step in the charge generation cycle of dye sensitized solar cells as the reaction has to be rapid to minimize recombination between the oxidized dye and the injected electrons. The driving force for dye regeneration arising from the potential difference between the redox mediator and the oxidized dye however needs to be kept minimal in order to ensure efficient use of the solar spectrum and high open circuit potentials. As a result the ideal redox couple should be matched to the sensitizing dye, providing just the right amount of driving force to ensure fast dye regeneration. To date however, little data is available on the driving force dependency of the dye regeneration reaction. Previous studies are limited to a small selection of redox couples or dyes, never exceeding six data points. In this study we utilized a group of 10 ferrocene derivatives covering a redox potential range of over 800 mV. The regeneration of six structurally analog ethylcarbazole dyes featuring different oxidation potentials was studied by nanosecond transient absorption spectroscopy, leading to overall 60 different conditions. This is allowing us for the first time to extract reliable relations on how the dye regeneration reaction kinetics are dependant on the provided driving force. We found that the regeneration rapidly accelerates with increasing driving force showing Marcus-normal behavior in the regime of small driving forces until it reaches a threshold potential. Above the threshold potential the reaction enters diffusion control. Structural modifications of the dye as well as the redox mediator had surprisingly little influence on the overall regeneration reaction. All in all, the rate controlling parameter was found to be the provided driving force. In conclusion our observations provide certain selection rules which are applicable in general to all single electron redox couples including cobalt and copper polypyridyl redox shuttles as well as ferrocenes.

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B2 - Dye Regeneration Kinetics in Solar Cells using Cobalt Polypyridine Redox Couples

Sandra Feldt, Peter Lohse, Hanna Ellis, Gerrit Boschloo, Anders Hagfeldt

Department of Chemistry - Ångström Laboratory, Box 523, Uppsala, 751 20, SE

Recently, there has been significant progress in dye-sensitized solar cell (DSC) research on alternative redox mediators to the conventional iodide/triiodide (I-/I3

-) couple. The major drawback of I-/I3

- is the large driving force needed for dye regeneration, which limits the voltage output and thus the power conversion efficiency of the DSC. Cobalt polypyridine redox couples with more positive redox potential can replace I-/I3

-, when used in combination with sensitizers that have suitable steric properties to prevent fast recombination processes.1, 2The Nernst potential of cobalt complexes can be tuned over a large range by changing the coordination sphere. A record efficiency of 12.3% has been reported for a cobalt-based DSC.3

Figure 1 Regeneration of the triphenylamine-based organic dye, D35, by cobalt tris(2,2´- bipyridine).

The recombination and regeneration kinetics in D35-sensitized TiO2 electrodes was investigated for a series of different cobalt redox couples.4 Open circuit potentials of more than 1 V were obtained by using cobalt phenanthroline complexes. The photocurrent of the devices decreased, however, with increasing Nernst potential of the redox couples, because of slower regeneration of the oxidized dye and faster recombination of photoinjected electrons with Co(III) species. Here we will present new results of photovoltaic performance and regeneration kinetics of cobalt-based DSCs for a new series of structurally modified triphenylamine dyes, as well as for co-sensitized DSCs. The Marcus theory is applied to explain the observed electron transfer kinetics. References [1] Feldt, S.M.; Gibson, E. A.; Gabrielsson, E.; Sun, L.; Boschloo, G.; Hagfeldt, A. "Design of Organic Dyes and Cobalt Polypyridine Redox Mediators for High-Efficiency Dye-Sensitized Solar Cells". J. Am. Chem. Soc. 132, 16714-16724 (2010). [2] Tsao, H. N.; Yi, C.; Moehl, T.; Yum, J.-H.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Grätzel, M. "Cyclopentadithiophene Bridged Donor–Acceptor Dyes Achieve High Power Conversion Efficiencies in Dye-Sensitized Solar Cells Based on the tris-Cobalt Bipyridine Redox Couple". ChemSusChem. 4. 591-594 (2011). [3] Aswani , Y.; Lee, H.-W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E. W.-G.; Yeh, C.-Y.; Zakeeruddin, S. M.; Grätzel, M. "Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency" Science. 334, 629-634 (2011).

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[4] Feldt, S. M.; Wang, G.; Boschloo G.; Hagfeldt, A. "Effects of Driving Forces for Recombination and Regeneration on the Photovoltaic Performance of Dye-Sensitized Solar Cells using Cobalt Polypyridine Redox Couples". J. Phys. Chem. C. 115, 21500-21507 (2011).

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B3 - Combined effect of the structures of sensitizers and cobalt complex redox couples on the electron lifetime in dye-sensitized solar cells

Shogo Moria, Takurou Murakamib, Takayuki Uchiyamaa, Nagatoshi Koumurab, Kohjiro Harab, Kazumichi Obuchia, Naruhiko Masakia, Mutsumi Kimuraa

a, Shinshu University, 3-15-1 Tokida , Ueda, 386-8567, JP b, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, JP

Recently cobalt redox couples have been paid large attention for dye-sensitized solar cells (DSCs). This is due to their tuning capability of redox potential. Since the open circuit voltage of DSCs is determined by the difference between the Fermi level of the TiO2 electrode and the redox potential of the electrolyte, more positive redox potential would provide higher open circuit voltage. On the other hand, utilizing such redox couple often results in faster recombination rate because of the higher free energy difference. Therefore, employing such redox couple usually require bulky sensitizers, where the dye layer’s steric hindrance to the approach of the cobalt complex to the surface of the TiO2 retards the probability of the interfacial charge transfer. The degree of the hindrance depends on the size of the both sensitizers and cobalt redox couple (1). On the other hand, this is not always the case. For the case of DSCs using iodine/triiodide redox couples, the difference in the electron lifetime with different sensitizers was explained with electrostatic force and dispersion force between the dye molecules and redox couple (2). In this work, we examined the effect of the structure of the cobalt complex and how the effect depends on the structure of the dyes. In order to do that, we prepared DSCs with various cobalt redox couples and dyes whose structures were systematically altered, and measured the electron lifetime References [1]Ohta, et al, Electrochem. Commun. 13 (2011) 778 [2]Miyashita et al, JACS 130 (2008) 17874

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B4 - How does the nanostructure of TiO2 material affect the electron trapping/detrapping process in dye-sensitized solar cells?

Hongxia Wang

Queensland University of Technology, 2 George Street, Brisbane, 4001, AU

One of the key components of a dye-sensitized solar cell (DSC) is the thin titanium dioxide (TiO2) film, which plays the role of anchoring the dye molecules and transporting the photo-generated electrons before they are collected by the external circuit. Conventional DSCs employ mesoporous TiO2 film consisting of nanoparticles (particle size: 20-30 nm) which are randomly connected together. Previous research has reported that the electron transport in the nano-particulates based network is 2-3 orders of magnitude lower than that of the bulk TiO2 material.[1] This unsatisfying electron transport property has direct impact on the performance of a DSC by influencing the electron collection efficiency. Thus nanostructures with orderly electron transport pathways such as nanowires and nanotubes have been proposed to replace the randomly connected nanoparticulates to overcome the issue of low electron transport in the TiO2 film. However, the photovoltaic performance of the DSCs with these 1-D order materials is generally lower than that of the nanoparticulates counterpart. This work aims to answer the following two questions: 1) Whether one-dimensional nanostructure is superior to the randomly connected nanoparticulates in terms of electron transport in the TiO2 film for DSCs? 2) How strong is the electron transport property dependent of the morphology of a material? Inorder to answer these questions, TiO2 materials with various morphologies including vertical grown 1-D nanorods on FTO substrate[2] and hierarchical structured spheres with 100% [001] facet exposed have been synthesized and characterized comprehensively in terms of the kinetics of electron transport and back reactions in the corresponding DSCs. The results indicated that the effective electron diffusion coefficient is actually not sensitive to the structure and shape of TiO2 material as assumed. However, the effective electron lifetime is strongly dependent on the morphology of TiO2 material. References [1] L.M. Peter. " J. Phys. Chem. C,"Characterization and modeling of dye-sensitized solar cells", 111, 6601-6612 (2007) [2] M. N. Liu, H.X. Wang, C. Yan, G. Will, J. Bell. "One-step synthesis of titanium oxide with trilayer structure for dye-sensitized solar cells", Appl. Phys. Lett., 98, 133113 (2011)

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B5 - 3D quantitative characterisation of a TiO2-based photoanode

Giorgio Divitinia, Ole Stenzelb, Fabio Di Fonzoc, Carlo S. Casaric, Valeria Russod, Andrea Li Bassic, Volker Schmidtb, Caterina Ducatia

a, Department of Materials Science & Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, GB b, Institute of Stochastics, Ulm University, 89069, Ulm, DE c, CNST - Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, via Pascoli 70/3, I-20133 Milano, IT d, Department of Energy and NEMAS – Center for NanoEngineered MAterials and Surfaces, Politecnico di Milano, via Ponzio 34/3, I-20133 Milano, IT

Studying the micro- and nano-structure of the photoanode is vital in designing and manufacturing efficient dye-sensitised and hybrid solar cells. Transmission electron microscopy (TEM) is a good candidate for investigating such length scales, but the limitation of conventional TEM to extract only bi-dimensional information hinders our ability to have a full understanding of the three-dimensional structure and properties, particularly when the structure being analysed has a complex morphology. We instead apply advanced TEM techniques to characterise a photoanode prototype, combining high resolution crystallographic studies with three-dimensional information obtained from dark field electron tomography. In this work we present the study of a TiO2-based photoanode where the titania layer has been produced via pulsed laser deposition. The photoanode TiO2 layer is composed by small (10-20 nm) crystalline particles assembled in columnar aggregates, which constitute a forest-like film with high porosity (1). Such a hierarchical structure combines a large surface area with good electrical transport properties, leading to promising performance. We employed a dual beam FIB (FEI Helios Nanolab) to prepare a cross-section of a polymer heterojunction solar cell based on said photoanode and acquired a tilt series in a FEI Tecnai F20 (200 kV acceleration voltage).

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Figure 1 Reconstruction of a sample extracted from a TiO2 photoanode, obtained with electron tomography.

The characterisation provided information on surfaces and interfaces of the nanocrystalline titania, as well as a view of the fine scale cell architecture after the infiltration of the polymer hole transporter. The TiO2 network reconstructed through electron tomography is studied using descriptive statistical analysis, extracting quantitative information on electron percolation. We quantify the influence of the hierarchical structure on the paths electrons can take and compare the results with other geometries. We also identify and quantify the parts of the structure that are poorly connected to the electrode and can lead to losses in light conversion efficiency.

References [1] Sauvage, F.; Di Fonzo, F.; Li Bassi, A.; Casari, C. S.; Russo, V.; Divitini, G.; Ducati, C.; Bottani, C. E.; Comte, P. and Graetzel, M. "Hierarchical TiO2 Photoanode for Dye-Sensitized Solar Cells". Nano Lett. 10 (7), 2562 (2010)

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B6 - Time-resolved real and imaginary photoconductance studies on nanocrystalline and polycrystalline TiO2 Maria Fravventura, Dimitrios Deligiannis, Juleon Schins, Laurens Siebbeles, Tom Savenije

Delft University of Technology, Julianalaan 136, Delft, 2628, NL

Anatase nanocrystalline (NC) TiO2 is one of the most versatile inorganic wide band-gap semiconductors, utilized for a variety of applications including solar cells and catalysis. Since the performance of these devices depends strongly on the charge transport properties through the TiO2 matrix, more quantitative information on e.g. electron trap densities, and intra- and inter-particle charge motion is required. Despite extensive investigations, these properties are only partially known for NC TiO2. The time dependent microwave conductance at ca 9 GHz on pulsed UV illumination was recorded using a microwave cavity. Analysis of the transients yields the real and imaginary components of the conductance. Unexpectedly, these two components decay with comparable time profiles, showing that they are determined by one transient species. The same is true for polycrystalline TiO2, although the decay profiles are much slower. Using the Drude-Smith model the same scattering momentum time (τ) of 3.2x10-13 s and effective electron mass of ca 8 Me were found for NC and polycrystalline TiO2. This means that in the two materials the mobile electrons experience scattering events at comparable time intervals. Hence the presence of grain boundaries and nanoparticle surfaces within the NC TiO2 does not affect τ and the electron mobility. The yield for mobile charge carriers, however, is two orders of magnitude smaller in the NC material due to the presence of electron traps. This type of measurements makes a quantitative analysis of the trap concentration in NC TiO2 feasible. Also determination of the number of mobile electrons injected from an excited dye into the NC TiO2 is within reach, of interest for characterizing dye sensitized solar cells.

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B7 - Mechanism for efficient photoinduced charge separation at disordered organic heterointerfaces

Harm van Eersel, René Janssen, Martijn Kemerink

Eindhoven University of Technology, PO Box 513, Eindhoven, 5600, NL

Despite the poor screening of the Coulomb potential in organic semiconductors, excitons can dissociate efficiently into free charges at a donor-acceptor heterojunction. We present a kinetic Monte Carlo model that quantitatively explains this high efficiency as a two-step process (see figure). Driven by the band offset between donor and acceptor, one of the charge carriers first hops across the interface, forming a charge transfer (CT) complex. Since the electron and hole forming the CT complex have typically not relaxed within the disorder-broadened density of states (DOS, indicated by the shaded vertical bars), their remaining binding energy can be overcome by further relaxation in the DOS. As this process is driven by the internal energy of the non-relaxed system the dissociation yield therefore only shows a moderate thermal activation and a weak dependence on electric field. The model predicts dissociation yields in excess of 90% for a prototypical heterojunction. Field, temperature, and band offset dependencies are investigated and found to be in full agreement with earlier experiments. Whereas the investigated heterojunctions show substantial energy losses associated with the dissociation process, our results suggest that with proper materials design it is possible to reach high dissociation yields at low (~0.1-0.2 eV) energy loss.

Figure 1 Two-step exciton dissociation mechanism in a disordered density of states. For simplicity only the electron motion is shown.

Unlike previous Monte Carlo works, the parameters describing the charge carrier hopping were extracted from independent measurements. For this, space-charge limited current-voltage characteristics of electron- and hole-only diodes were fitted using a drift-diffusion model with parameterized expressions for the field- and density-dependent electron and hole mobility. The extracted parameters were used as input in the Monte Carlo model which therefore only contained independently determined parameters. Even under the conditions in which, irrespective of electric field, the vast majority of excitons dissociates into free charges, we find that the (small) fraction of polaron pairs that do recombine is strongly field dependent. Hence, the field dependence of the polaron pair recombination yield is not a relevant measure for the exciton dissociation yield.

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B8 - ‘Charge Transfer Complexes’ and ‘Exciplexes’ in polymer:polymer solar cells

Fortunato Piersimonia, Koen Vandewalb, Sylvain Chambonc, Kristofer Tvingstedtd, Olle Inganäsd, Peter Adriaensensa, Jean Mancaa

a, IMO-IMOMEC, Wetenschapspark 1, Diepenbeek, 3590, Belgium b, Stanford University, Stanford, CA 94305, USA c, Laboratory of Integration from Materials to Systems (IMS) - University of Bordeaux, UMR CNRS 5218, 16 Av. Pey Berland, 33607 PESSAC Cedex, France d, Linköping University, SE-581 83 LINKÖPING, Sweden

Charge Transfer Complexes (CTC’s), electronic states formed at the interface between donor and acceptor materials, play a crucial role as intermediate electronic stepping stones in polymer:fullerene bulk heterojunction solar cells. While CTC’s are intensively studied in polymer:fullerene systems [1-5], this contribution aims to discuss in more detail the effect of CTC’s in polymer:polymer solar cells and to elucidate the terminology ‘CTC’s’ versus ‘exciplexes’. In polymer:polymer bulk heterojunction solar cells, absorption and emission from interfacial donor:acceptor electronic states (termed ‘CTC’s’ and/or ‘exciplexes’) has already been observed [6-7], while the photocurrent generated by direct excitation of the Charge Transfer ground state has so far not been the subject of study. In order to address this latter, Fourier Transform Photocurrent Spectroscopy (FTPS) is used. FTPS is an ultrasensitive technique able to measure the External Quantum Efficiency over up to 9 order of magnitude, [8] hence capable of detecting the weak photocurrent produced from the direct excitation of the CTC ground state into the fully charge transferred (CT) state. Field dependent FTPS measurements and current-voltage characterization with sub- and above gap illumination show that CT states in the polymer:polymer system MDMO-PPV:PCNEPV [9] dissociate equally efficient and with the same field dependence as above gap excitations. Further, the energetic position of the observed CT absorption and emission bands for annealed and unannealed photovoltaic devices correlates well with their open-circuit voltage. References [1] Benson-Smith, J. J.;Goris, L.; Vandewal, K.; Haenen, K .; Manca, JV.; Vanderzande, D.; Bradley, D.D.C.; Nelson, J.; "Formation of a Ground-State Charge-Transfer Complex in Polyfluorene/[6, 6]-Phenyl-C61 Butyric Acid Methyl Ester (PCBM) Blend Films and Its Role in the Function of Polymer/PCBM Solar Cells." Adv. Funct. Mater. 17, 451-457 (2007) [2] Veldman D.; Meskers, S. C. J; Janssen. R. A. J; “The Energy of Charge-Transfer States in Electron Donor-Acceptor Blends: Insight into the Energy Losses in Organic Solar Cells.” Adv. Funct. Mater. 19 , 1939-1948 (2009) [3] Vandewal, K.; Tvingstedt, K.; Gadisa, A.; Inganäs, O.; Manca, J.V.; “On the origin of the open-circuit voltage of polymer–fullerene solar cells.” Nat. Mater. 8, 904-909 (2009) [4] Deibel, C.; Strobel, T.; Dyakonov, V.; “Role of the charge transfer state in organic donor–acceptor solar cells.” Adv. Mat. 22, 4097-4111 (2010) [5] Clarke, T. M.; Durrant, J. R.; “Charge photogeneration in organic solar cells.” Chem. Rev. 110, 6736–6767 (2010) [6] Offermans, T.; van Hal, P.A.; Meskers, S.C.J; Koetse, M.M.; Janssen, R.A.J; “Exciplex dynamics in a blend of π-conjugated polymers with electron donating and accepting properties: MDMO-PPV and PCNEPV.” Phys. Rev. B 72 045213 (2005) [7] Panda, P.; Veldman, D.; Sweelssen, J.; Sweelssen J.; Bastiaansen, J. J. A. M.; Langeveld-Voss, B. M. W.; Meskers, S. C. J; “Charge Transfer Absorption for π-Conjugated Polymers and Oligomers Mixed with Electron Acceptors.” J. Phys. Chem. B 111, 5076–5081 (2007) [8] Vandewal, K.; Goris, L.; Haeldermans, I.; Nesládek, M.; Haenen, K.; Wagner, P.; Manca, J. V.; “Fourier-Transform Photocurrent Spectroscopy for a fast and highly sensitive spectral characterization of organic and hybrid solar cells.” Thin Solid Films 516, 7135-7138 (2008) [9] Veenstra, S. C.; Verhees, W. J. H.; Kroon, J. M.; Koetse, M. M.; Sweelssen, J.; Bastiaansen, J. J. A. M.; Schoo, H. F. M.; Yang, X.; Alexeev, A.; Loos, J.; Schubert, U. S.; Wienk, M. M.; “Photovoltaic properties of a conjugated polymer blend of MDMO-PPV and PCNEPV.” Chem. Mater. 16, 2503-2508 (2004)

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B9 - Ultrafast Hot Charge Transfer in Low Band-Gap Polymer Blend for Photovoltaics Giulia Grancinia, Daniele Fazzia, Margherita Maiurib, Hans Egelhaafc, Annamaria Petrozzaa, Daniele Bridab, Giulio Cerullob, Guglielmo Lanzania

a, Center for Nano Science and Technology (CNST) - IIT@PoliMi , Via Pascoli 70/3 20133 Milan - Italy , IT b, Politecnico di Milano, P.zza L. da Vinci 32 20133 Milan- Italy, IT c, Konarka Technologies GmbH, Landgrabenstrasse 94, 90443 Nürnberg, Germany, DE

Harnessing some of the excess energy of hot charges generated by above-gap photon excitation is an effective strategy to boost the power conversion efficiency in standard solar cells. In inorganic system this could be done either by slowing down the electron-phonon interactions and collecting the hot carriers or by exploiting the extra energy to generate more carriers (impact ionization) [1]. In organic polymer-based system a similar limit is applied: upon high energy excitation, the excess energy is usually dissipated via internal energy conversion, a process that competes with charge generation on the same time scale (few tens of fs). In this work, by combining ultrafast pump-probe spectroscopy (sub 15-fs time resolution) with high level quantum chemical calculations, we demonstrate that ultrafast hot dissociation occurs upon high energy excitation in a low band gap polymer:fullerene (PCPDTBT:PCBM) blend, used for highly efficient organic photovoltaics [2]. We investigate both the pristine polymer and the blend by tuning the photon excitation to be resonant to the first excited (S1) and higher singlet states (Sn). The pristine polymer shows for all the excitation a broad positive signal due to stimulated emission (SE) (S1→S0) in the near IR spectral region (red line in Figure 1a). In presence of the electron acceptor the SE signal is totally quenched and a negative signal is formed within few tens of fs, signature of photoinduced absorption band of interfacial charge transfer (CT) states (CT1→CTn). By exciting the blend with higher photon energies we found that the Sn→CTn transfer rate is higher with respect to S1→CT1. We demonstrate that hot dissociation, via high photon energy excitation, occurs effectively at PCPDTB:PCBM interface, with a rate of kct=30 fs-1. Quantum chemical calculations provide the interfacial CTs energies, DOS and electronic couplings, validating the experimental findings, and demonstrating that hot CT states are more delocalized, thus having a larger probability for dissociation. The higher charge generation yield is also supported by measuring the external quantum efficiency in a PCPDTBT:PCBM prototypical device.

Figure 1 (a) Pump-probe time traces at 930 nm probe wavelength for pristine PCPDTBT (red line) and blend PCPDTBT:PCBM (black line) upon photoexcitation at 510 nm. (b) Sketch of the energy level scheme when pumping Sn in both pristine and blend systems: in the pure polymer (left panel) energy relaxation occurs by internal conversion to the S1 state (kSn-S1~(140 fs)-1), from which SE is probed at later times; in the blend (right panel) an ultrafast hot injection to an interfacial CT* state prevails (k1~(30 fs)-1), leading to weakly bound CT pairs that can more easily split into charge separate states (CSS).

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The spectrum reveals a higher yield of charge separation in the spectral region corresponding to photon energy above the band-gap, thus suggesting that charges generated via hot CT mechanism contribute to the photovoltaic action. From our results we infer that hot dissociation mechanism can be an efficient route to be explored for optimizing the efficiency of low-band gap polymer-based organic solar cells.

References [1]Nelson, J.; "The Physics of Solar Cells". Imperial College Press (2003) [2] Mühlbacher, D.; Scharber, M.; Morana, M.; Zhu, Z.; Waller, D.; Gaudiana, R.; Brabec, C. J. "High Photovoltaic Performance of a Low-Bandgap Polymer". Adv. Mater. 18, 2884–2889 (2006).

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B10 - On the correlation between crystallinity and photophysics for donor polymers of interest for organic photovoltaic devices

Ying Woan Soon, Safa Shoaee, Iain McCulloch, James R Durrant

Imperial College London, Chemistry department, South Kensington campus, London, SW7 2AZ, GB

Crystalline materials have been widely reported to give good charge carrier mobilities which can enhance charge transport.(1-2) Hence, in the field of OPV and OLED, highly crystalline materials have been considered as favourable for obtaining efficient devices. However, the fluorescence quenching associated with the process of ‘concentration quenching’ has been observed to be more efficient in crystalline materials.(3-4) This fluorescence quenching process is thought to be related to faster internal conversion, leading to a potential loss of device efficiency. In this study, photophysical properties of a range of conjugated donor-acceptor polymers with varying crystallinity are investigated using techniques including wide angled x-ray diffraction, single photon counting, and transient absorption spectroscopy (TAS). The more crystalline polymers are found to have shorter singlet and triplet lifetimes compared to the more amorphous polymers. This is consistent with the lack of triplet observation upon photoexcitation of the more crystalline polymers while high triplet yields are usually found in the amorphous polymers using microsecond TAS. Although amorphous polymers typically have lower charge mobilities than the more crystalline polymers, the longer singlet and triplet lifetimes of the amorphous polymers can potentially aid charge separation. Therefore, both the highly crystalline and amorphous polymers have different attributes that can compromise on the performance of OPV devices. Furthermore, the yield of polaron photogeneration in neat polymer films is found to be maximum in the semi-crystalline polymers. Recent high performing polymers in the literature such as poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) and poly[N-9”-hepta-decanyl-2,7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-benzothiadiazole)] (PCDTBT) are found to be semi-crystalline in our context. This finding can have direct implication on the future design of conjugated polymers for use in organic solar cells. References [1] Ma, W.; Yang, C.; Gong, X.; Lee, K.; Heeger, A.J. "Thermally Stable, Efficient Polymer Solar Cells with Nanoscale Control of the Interpenetrating Network Morphology".Adv.Funct.Mater.15, 1617-1622 (2005) [2] Mihailetchi, V.D.; Xie, H.X.; De Boer, B.; Koster, L.J.A.; Blom, P.W.M. "Charge transport and photocurrent generation in poly (3-hexylthiophene): Methanofullerene bulk-heterojunction solar cells".Adv. Funct. Mater. 16, 699-708 (2006) [3] Huignard, A.; Gacoin, T.; Boilot, J-P. "Synthesis and Luminescence Properties of Colloidal YVO4:Eu Phosphors".Chem. Mater.12,1090-1094 (2000) [4]Huang, H.; Xu, G.Q.; Chin, W.S.; Gan, L.M.; Chew, C.H."Synthesis and characterisation of Eu:Y2O3 nanoparticles". Nanotechnology 13, 318-323 (2002)

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B11 - Effect of crystallinity in P3HT:PCBM solar cells on bandgap trap states and apparent recombination order

Donato Spoltorea, Wibren D. Oosterbaana, Samira Khelifib, John Cliffordc, Aurelien Viterisic, Emilio Palomaresc, Marc Burgelmanb, Laurence Lutsena, Dirk Vanderzandea, Jean Mancaa

a, Institute for Materials Research (IMO-IMOMEC), Universiteit Hasselt, Wetenschapspark 1, Diepenbeek 3590, Belgium b, Department of Electronics and Information Systems (ELIS), University of Gent, Sint-Pietersnieuwstraat 41, Gent 9000, Belgium c, Institute of Chemical Research of Catalonia (ICIQ), Avda. Països Catalans 16, Tarragona 43007, Spain d, Institut Català de Recerca I Estudis Avançats (ICREA), Avda. Lluís Companys 23, Barcelona 80810, Spain

In this work we investigate how varying the polymer crystalline fraction in nanofiber-P3HT:PCBM solar cells influences bandgap trap states and apparent recombination order. The recombination of charge carriers in polymer-fullerene solar cells is generally considered to be a second order non-geminate process.1,2 It depends on the concentration of free electrons and free holes in the device through a recombination constant, which is proportional to the mobility. In the last few years recombination orders higher than two were found in P3HT:PCBM solar cells.3-5

The most accepted explanation for this phenomenon stems from a multiple trapping model6,7 which considers the recombination as a second order process with a recombination constant depending on the concentration of charge carriers. This is due to the dependence of mobility on the charge-carrier density caused by the presence of a tail of trapped states inside the gap:8 the higher the number of traps the slower the mobility and the higher the apparent recombination order. In this work we varied, by temperature control of the nanofibers-P3HT casting dispersion,9,10 the mass fraction of highly crystalline nanofibrillar P3HT to the total P3HT content in P3HT:PCBM solar cells. We show a clear correlation between the fraction of crystalline P3HT nanofibers, the apparent recombination order (measured with a transient photovoltage technique)5,11 and the amount of traps in the bandgap (measured with an admittance spectroscopy technique).12

References [1] Langevin, P. "Recombinaison et Mobilités des Ions dans les Gaz." Ann. Chim. Phys. 28, 433–530 (1903). [2] Pope, M.; Swenberg, C. E. "Electronic processes in organic crystals and polymers", Oxford University Press, USA, (1999). [3] Juška, G.; Genevičius, K.; Nekrasas, N.; Sliaužys, G.; Dennler, G. "Trimolecular recombination in polythiophene: fullerene bulk heterojunction solar cells". Appl. Phys. Lett. 93, 143303 (2008). [4] Deibel, C.; Baumann, A.; Dyakonov, V. "Polaron recombination in pristine and annealed bulk heterojunction solar cells". Appl. Phys. Lett. 93, 163303 (2008). [5] Shuttle, C. G.; O’Regan, B.; Ballantyne, A. M.; Nelson, J.; Bradley, D. D. C.; De Mello, J.; Durrant, J. R. "Experimental determination of the rate law for charge carrier decay in a polythiophene: Fullerene solar cell". Appl. Phys. Lett. 92, 093311 (2008). [6] Nelson, J. "Diffusion-limited recombination in polymer-fullerene blends and its influence on photocurrent collection". Phys. Rev. B 67, 155209 (2003). [7] Shuttle, C. G.; O’Regan, B.; Ballantyne, A. M.; Nelson, J.; Bradley, D.; Durrant, J. R. "Bimolecular recombination losses in polythiophene: Fullerene solar cells". Phys. Rev. B 78, 113201 (2008). [8] Shuttle, C. G.; Hamilton, R.; Nelson, J.; O'Regan, B. C.; Durrant, J. R. "Measurement of Charge-Density Dependence of Carrier Mobility in an Organic Semiconductor Blend". Adv. Funct. Mater. 20, 698–702 (2010). [9] Bertho, S.; Oosterbaan, W. D.; Vrindts, V.; D’Haen, J.; Cleij, T. J.; Lutsen, L.; Manca, J.; Vanderzande, D. "Controlling the morphology of nanofiber-P3HT:PCBM blends for organic bulk heterojunction solar cells". Organic Electronics 10, 1248–1251 (2009). [10] Bertho, S.; Oosterbaan, W. D.; Vrindts, V.; Bolsée, J.-C.; Piersimoni, F.; Spoltore, D.; D’Haen, J.; Lutsen, L.; Vanderzande, D.; Manca, J. V. "Poly (3-alkylthiophene) Nanofibers for Photovoltaic Energy Conversion". Adv. Mater. Res. 324, 32–37 (2011). [11] O'Regan, B. C.; Scully, S.; Mayer, A. C.; Palomares, E.; Durrant, J. "The Effect of Al 2O 3Barrier Layers in TiO 2/Dye/CuSCN Photovoltaic Cells Explored by Recombination and DOS Characterization Using Transient Photovoltage Measurements". J. Phys. Chem. B 109, 4616–4623 (2005). [12] Khelifi, S.; Decock, K.; Lauwaert, J.; Vrielinck, H.; Spoltore, D.; Piersimoni, F.; Manca, J.; Belghachi, A.; Burgelman, M. "Investigation of defects by admittance spectroscopy measurements in poly (3-

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hexylthiophene):(6,6)-phenyl C61-butyric acid methyl ester organic solar cells degraded under air exposure". J. Appl. Phys. 110, 094509 (2011).

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B12 - Improved Performance of Diffused-Bilayer Polymer Solar Cells by Solution p-Type Doping

Aurora Rizzoa, Anna Loiudiceb, Giuseppe Giglic

a, NNL-CNR-Istituto di Nanoscienze, via per Arnesano Km5, Lecce, 73100, IT b, Center for Biomolecular Nanotechnologies @UNILE Istituto Italiano di Tecnologia, via Barsanti, 73010 Arnesano (LE), IT c, Dipartimento di Ingegneria dell’Innovazione, Università del Salento, via per Arnesano, 73100 Lecce, IT

The control of the p- and n-type doping with well-defined levels of impurity represent one of the main strategies for the development of efficient both inorganic and organic optoelectronic devices. [1,2] The addition of impurities with appropriate electronic properties can lead to a shift of the Fermi level toward the transport states and to a reduction of the Ohmic losses.[3] Motivated by the successful p-type doping in small molecule based devices,[4] we report, for the first time, improved power conversion efficiency (PCE) by p-type doping of the donor species in polymer solar cells. So far the implementation of doping technology in the conventional bulk heterojunction (BHJ) devices was limited because the p-dopant, directly blended in the active layer, acts as an electron trap and leads to a lowering of the photovoltaic performances. For this reason, to efficiently exploit the doping effect we propose analternative device fabrication strategy, which consists in a sequential coating of the donor (i. e., P3HT) and acceptor (i. e., [6,6]-phenyl-C61-butyric acid methyl ester, PCBM) species from orthogonal solvents and results in a diffused bilayer (DB) device structure. The doping of P3HT withthe strong electron acceptor, tetrafluoro-tetracyanoquinodimethane(F4-TCNQ), occurs via solution based co-blending prior the deposition. We demonstrate that a light doping, 0.2%, 0.5% and 1% (w/w dopant-polymer percentage), of the P3HT in DB devices leads to a considerable improvement in the PCE. In particular at 0.5% doping, the FF significantly increase from 63% to 68% and the JSC also increase from 8.96 mA/cm2 to 9.89 mA/cm2. (See Figure) Most notably overall the PCE is improved from 3.45% to 4.02%. Moreover by means of VOC-light intensity dependence measurements,[5] we verify that this device configuration is particularly advantageous, compared to the standard BHJ, because it avoids the direct contact of the strong electron acceptor F4-TCNQ with the PCBM, minimizing the effect of trapping.

Figure 1 Current density of the DB versus applied bias at 0% and 0.5% dopant percentage under illumination. The inset shows a sketch of the DB device stack.

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Our results demonstrate that efficient p-doped polymer solar cell can be realized by simply doping the donor layer in solution; such doping both improves the transport properties of the polymer and leads to ~17% enhancement of the PCE efficiency compared to the device made from pristine P3HT. This method can be applied to various polymer materials and can open novel routes towards highly efficient, multi-stacked solution processable devices.

References [1] Sze, S. M.; Ng,K. K. "Physics of Semiconductor Devices" (Ed. 3rd ), John Wiley & Sons, Inc.: Hoboken, NJ, (2007). [2] M. Riede; Mueller, T.; Tress, W.; Schueppel, R.; Leo K. "Small-molecule solar cells—status and perspectives" Nanotechnology 19, 424001 (2008) [3] Blochwitz, J.; Fritz, T.; Pfeiffer, M; Leo, K.; Alloway, D. M.; Lee, P. A.; Amstrong, N. R. "Interface electronic structure of organic semiconductors with controlled doping levels", Org. Elec. 2, 97 (2001) [4] Yim, K.-H.; Whiting,G. L.; Murphy, C. E.; Halls,J. J. M.; Burroughes, J. H.; Friend, R. H.; Kim, J. S. "Controlling electrical properties of conjugated polymers via a solution-based p-type doping", Adv. Mater. 20, 3319, (2008) [5] Mandoc, M. M.; Kooistra, F. B.; Hummelen, J. C.; de Boer, B.; Blom, P. W. M. "Effect of traps on the performance of bulk heterojunction organic solar cells", Appl. Phys. Lett. 91, 263501 (2007).

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B13 - High-Performance Thiocyanate-Free Ruthenium DSSC Dyes

Curtis Berlinguette

University of Calgary, 2500 University Drive NW, Calgary, CA Centre for Advanced Solar Materials, 2500 University Drive NW, Calgary, CA

High power output in dye-sensitized solar cells (DSSCs) had, until only very recently, been achieved by sensitizing TiO2 with dyes related to [Ru(dcbpy)2(NCS)2] (1; dcbpy = dicarboxy-2,2`-bipyridine). Departing from this line of inquiry, our program has focused on the development of cyclometalated Ru(II) complexes of type [RuII(N^N)2(C^N)]z and [RuII(N^N^N)2(N^C^N)]z to accomplish the requisite light-absorption and charge-separation events.1-4 This class of molecules offers a distinct advantage over 1 for DSSC applications because the replacement of the NCS- ligands with aromatic ligands presents the opportunity to manipulate both the ground- and excited-state energy levels.2 Moreover, these complexes are devoid of NCS- ligands - a potential source of degradation in the DSSC - that are common to 1 and other commercially relevant dyes. This presentation will outline our specific strategies for tuning the absorption profiles of these complexes and optimizing their regeneration by electrolytes in pursuit of robust, high-performance DSSC dyes. References [1] Bomben, P. G.; Robson, K. C. D.; Sedach, P.; Berlinguette, C. P. “On the Viability of Cyclometalated Ru(II) Complexes for Light-Harvesting Applications” Inorg. Chem. 48, 9631-9643 (2009). [2] Bomben, P. G.; Koivisto, B. D.; Berlinguette, C. P. “Cyclometalated Ru(II) Complexes of Type *RuII(N^N)2(C^N)+z: Physicochemical Response to Substituents Installed on the Anionic Ligand” Inorg. Chem. 49, 4960-4971 (2010) [3] Robson, K. C. D.; Sporinova, B.; Koivisto, B. D.; Baumgartner, T.; Yella, A.; Nazeeruddin, M. K.; Grӓtzel, M.; Berlinguette, C. P. “Design and Development of Functionalized Cyclometalated Ruthenium Chromophores for Light-Harvesting Applications” Inorg. Chem. 50 (12), 5494-5508 (2011) [4]Bomben, P. G.; Gordon, T. J.; Schott, E.; Berlinguette, C. P. “A Trisheteroleptic Sensitizer that Enables High Power Output in the Dye-Sensitized Solar Cell” Angew. Chem., Int. Ed. 50, 10682-10685 (2011).

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B14 - DFT/TDDFT computational investigation of Ru(II) and Os(II) panchromatic dye sensitizers

Simona Fantacci , Maria Grazia Lobello, Filippo De Angelis

Istituto CNR di Scienze e Tecnologie Molecolari (CNR-ISTM), via Elce di Sotto n. 8, Perugia, 6123, IT

A new and bright interest has been addressed towards the Ru(II) panchromatic dyes as sensitizers in Dye-sensitized Solar Cells (DSCs). These dyes show a broad absorption of light ranging the entire visible region up to near-IR and the idea is to exploit the extended light harvesting for enhancing the DSC efficiency. Black Dye, [Ru(H3tcterpy)(NCS)3]

- (tcterpy=4,4’,4”-tricarboxy-2,2’:6’,2”-terpyridine), despite to be one of the first panchromatic dyes employed in DSC,1,2 is still widely investigated, since only a deepened comprehension of its acid-base chemistry, its photophysics and photochemistry allow to design new panchromatic dyes with specific target functionalities. Here the results obtained in an extensive Density Functional Theory (DFT) and Time Dependent DFT study on Black Dye (BD) and analogous panchromatic dyes are presented. BD and its possible deprotonated formshave been investigated with the aim to understand and rationalize their acid-base, electrochemical and optical properties and finally to define a relationship between these properties and the dye-sensitized solar cell (DSC) working efficiency parameters.

Figure 1 Comparison between the theoretical and experimental absorption spectrum. Optimized geometry of BD@TiO2.

The pKa associated to the stepwise deprotonation of the dye carboxylic groups have been calculated, assigning the deprotonation order. The ground and excited state oxidation potentials have been evaluated and compared to the available experimental data. The influence of deprotonation on the absorption and emission processes has been analyzed and the spectral changes as a function of the pH have been assigned. The adsorption geometry of the BD with extended TiO2 models is presented, along with a detailed analysis of the excited states energy and localization at the dye/semiconductor interface. Calculations with inclusion of the spin-orbit coupling have been performed on BD and on the analogous Os-dye. Our results suggest a minor role of singlet-triplet excitation in the light-

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harvesting of the Ru-system, while a substantial absorption at the read-end of the spectrum in the Os-dye is due to spin-forbidden transitions. New design rules for panchromatic Ru dyes are finally presented. References [1] Nazeeruddin, M. K.; Pèchy, P.; Renouard, T.; Zakeeruddin, S. M.; Humphry-Baker, R.; Comte, P.; Liska, P.; Cevey, L.; Costa, E.; Shklover, V.; Spiccia, L.; Deacon, G. B.; Bignozzi, C. A.; Grätzel, M. "Engineering of Efficient Panchromatic Sensitizers for Nanocrystalline TiO2-Based Solar Cells". J. Am. Chem. Soc. 123, 1613-1624 (2001). [2] Bauer, C.; Boschloo, G.; Mukhtar, E.; Hagfeldt, A. "Interfacial Electron-Transfer Dynamics in Ru(tcterpy)(NCS)3-Sensitized TiO2 Nanocrystalline Solar Cells". J. Phys. Chem. B 106, 12693-12704 (2002).

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B15 - Tuning the HOMO of ruthenium dyes for dye-sensitised solar cells

Nina Chadwick, Lesley Yellowlees, Neil Robertson

University of Edinburgh, School of Chemistry, West Mains Road., Edinburgh, GB

Much of the recent focus in the development of new ruthenium dyes has been on tuning the ancillary bipyridyl ligand of Z907 type dyes to enhance the light absorption properties of the dye1. However, limited understanding of the mechanisms of dye regeneration and electron recombination within the solar cell has hampered efforts to increase cell efficiencies. It has been shown that electron recombination can be significantly reduced and the VOC increased by changing from two sulfur atoms to two oxygen atoms within a dye molecule2. This was reasoned to be due to weaker interactions between the dye molecule and iodine, which can promote electron recombination at the surface of TiO2. To explore this effect, we have developed a novel synthetic procedure to overcome the acid sensitivity of the -NCO ligand and synthesise dyes of the type K4[Ru(dcbpy)2(NCX)2] (where X = O, S, Se).

Figure 1 The UV/vis spectra of K4[Ru(dcbpy)2(NCX)2] in methanol where X = O, S, Se.

This series has shown that the type of group 16 atom has a surprising effect on the electrochemical and spectroscopic properties of the dye (Fig. 1). Our results have therefore allowed us to clarify the nature of the Ru-NCX bond and show the significant effects of the -

NCX ligand on the electronic properties of the dye and consequently on the cell performance.

References [1] Abbotto, A.; Manfredi, N. "Electron-rich heteroaromatic conjugated polypyridine ruthenium sensitizers for dye-sensitised solar cells". Dalton Trans. 40, 12421-12438 (2011). [2] O'Regan, B.; Walley, K.; Juozapavicius, M.; Anderson, A.; Matar F.; Ghaddar T.; Zakeeruddin, S.; Klein, C.; Durrant, J. "Structure/function relationships in dyes for solar energy conversion: A two atom change in dye structure and the mechanism for its effect on cell voltage". J. Am. Chem. Soc. 131, 3541-3548 (2009)

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B16 - Squarylium Dyes and Semi-squarylium Dyes: Molecular Engineering and Their Application in Multiple-dyes Systems

Gerda Fuhrmann, David Danner, Ameneh Bamedi, Markus Obermaier, Lars-Peter Scheller, Gabriele Nelles

Sony Deutschland, Hedelfingerstr. 61, Stuttgart, 70327, DE

Metal-free organic dyes have become a focus of intensive research in view of their potential applications as sensitizers in dye-sensitized solar cell (DSSC). Compared to the conventional ruthenium based dyes, organic dyes exhibit much higher extinction coefficients. This allows the use of thinner TiO2 films due to the more efficient light harvesting; consequently non-volatile or solid-state electrolytes can be used without showing limited charge transport through the nanoporous layer. Another main advantage of these materials is that by rational structure design their physical and photophysical properties such as light absorbance, energy levels, electron density distribution, but also their adsorption, assembly and interaction on the semiconductor surface can be manipulated.

Figure 1

Here we present our recent progress in the design and synthesis of two classes of organic sensitizer dyes. Firstly, new and highly efficient squarylium dyes with a broad and extended photoactivity into red region up to 800 nm (see Figure 1), following, newly developed semi-squarylium dyes with acyloin-type anchoring groups will be shown (see Figure 2). Then we report our investigations towards the successful combination of these materials in multiple-dyes systems for the improvement of photovoltaic efficiency. Finally, we will discuss our studies to clarify the interactions of dyes and co-adsorbents, and their effect at the dye-semiconductor interface.

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B17 - Modelling of lateral hole diffusion on dye-sensitized electrodes.

Valerie Vaissiera, Davide Moiaa, Piers Barnesa, James Kirkpatrickb, Jenny Nelsona

a, Imperial College London, South Kensigton campus, Exhibition Road, London, 0, GB b, Oxford University, Oxford, GB

In Dye Sensitized Solar Cells (DSSC), photocurrent generation results from electron injection into a nanocrystalline oxide electrode from a photo-oxidized dye molecule adsorbed on to the oxide surface while the dye is normally regenerated by a Hole Transporting Medium (HTM) (1). In an alternative mechanism, the dye may be regenerated through the lateral transport of holes between dye molecules on the oxide surface. Such lateral transport may have application in solid state devices by providing an additional pathway for the holes to reach the solid HTM, especially when the HTM is in poor contact with the dye molecules (2). Although there is experimental evidence (3) for this ‘hole hopping’ mechanism in some systems, it is not yet understood in detail. In this work we introduce a multi-scale method to model hole diffusion dynamics within a monolayer of dye molecules. We treat the intermolecular charge transfer step as a non-adiabatic hopping process and calculate the hopping rate as a function of the electronic coupling (J) and the reorganization energy (lambda). First we use quantum chemical methods to study the influence of the intermolecular distance, nature of ligands and relative orientation of a selection of Ruthenium based dye molecules on J. Next, we propose a numerical method to calculate the inner and outer sphere reorganization energy, and show that the nature of the solvent dominates lambda. Finally we estimate the hole diffusion coefficient from the charge transfer dynamics and compare results with experimental data for different dye structures. The initial results appear consistent with experimental data. Our method should provide a deeper insight on how to control the lateral hole transport between dye molecules and may assist in the design of higher performance devices. References [1] O'Regan, B.;Gratzel, M. "A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films" Nature 353,737-740 (1991) [2] Melas-Kyriazi, J. Ding, IK. Marchioro, A. and al "The Effect of Hole Transport Material Pore Filling on Photovoltaic Performance in Solid-State Dye-Sensitized Solar Cells" Adv. Energy Mater. 1,407-414 (2011) [3] Wang, Q. Shaik, M, Zakeeruddin and al "Molecular Wiring of Nanocrystals : NCS-Enhanced Cross Surface Charge Transfer in Self Assembled Ru-Complex Monolayer on Mesoscopic Oxide Films". JACS 128, 4446-4452 (2006)

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B18 - Toward commercialization of organic photovoltaic (OPV) cells: ITO-free approach for low cost cells and maskless fabrication of high-density modules

Seunghyup Yoo, Hoyeon Kim, Sooyeon Lim, Dong-Geon Han, Soohyun Lee, Koeng Su Lim

Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong-dong, Daejeon, 305, KR

Organic photovoltaic (OPV) cells have recently made great strides toward the “10% - efficiency” target, which has been regarded as an important milestone to achieve for commercialization. While the importance of improving efficiency cannot be overemphasized, the strategies for harnessing these technologies for practical applications should carefully balance many different aspects such as reliability, differentiating features, cost competitiveness, and module fabrication with efficient usage of substrate area. This work tries to address some of those issues in two different case studies: (i) development of ITO-free low-cost OPV cells and their applications to highly flexible solar cells; and (ii) maskless fabrication of high-density integrated OPV modules. The first part of the talk will describe our study on OPV cells in which ITO electrodes, which are known to be responsible for the largest portion in the cost structure of OPV cells, are replaced with thin Cu layers that can be prepared at a fraction of cost to that of ITO. The thin Cu layers are sandwiched between high-index, wide-gap dielectric/ semiconducting layers to allow the combination of layers to function effectively as anodes and to promote the optical enhancement in the efficiency of OPV cells made thereof. Upon optimization considering the overall thin-film optical structure and resonance effect (1), Cu-based ITO-free OPV cells exhibit as large as 85% of that of ITO-based conventional cells [Fig. 1(a)]. It is also shown that the proposed structure perform significantly better than conventional cells in terms of mechanical flexibility.

Figure 1 (a) J-V characteristics of the proposed ITO-free organic solar cells (dash and dash-dot lines) in comparison to that of ITO-based control cells (solid line). Inset: a photograph of Cu-based transparent electrode. (b) SEM image of a printed high-contact-angle structure ("separator") used for fabrication of high-density OPV modules using oblique deposition. Inset: a photograph of the proposed OPV module.

The second part of the talk will describe our recent efforts to develop maskless techniques to fabricate high-density OPV modules using angled deposition. A series of linear structures with a high contact angle or low contact angle are realized in a controlled yet straight-forward manner using nozzle-jet printing of UV curable resin. With the help of oblique deposition (2), the high-contact-angle structures function as a "separator" that defines respective deposition areas for organic and metal layers while ensuring proper interconnections for series-connected OPV modules [Fig. 1(b)]. Likewise, the low-contact-angle structures are used for edge passivation to suppress the leakage current. With the proposed method, small-molecular OPV

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modules are fabricated with the active-to-inactive area ratio as large as 91% for the unit cell width of 6 mm.

References [1] Han, S.; Lim, S.; Kim, H.; Cho,H.; Yoo, S.¡°Versatile multilayer transparent electrodes for ITO-free and flexible organic solar cells,¡± IEEE J. Sel. Topics in Quant. Elect. 16 (6) 1656-1664 (2010). [2] Lim, K. S. et al. |Integrated thin-film solar cells and method of manufacturing thereof and processing method of transparent electrode for integrated thin-film solar cells and structure thereof, and transparent substrate having processed transparent electrode," US Patent 7,927,497 B2 (2011).

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B19 - All-Carbon Photovoltaics

Marco Bernardia, Priyank Kumara, Nicola Ferralisa, Maurizia Palummoc, Shenqiang Renb, Jeffrey C. Grossmana

a, Dept. of Materials Science, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge MA, 02139, USA b, Dept. of Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence KS, 66045, USA c, Dept. of Physics, University of Roma Tor Vergata, Via della Ricerca Scientifica 1, Rome, 00100, Italy

We present an alternative scheme for nanostructured solar cells, where carbon nanomaterials are the only constituents of a bulk-heterojunction active layer and fulfill the role of absorbers, donors and acceptors, in the absence of conductive polymers. We employed ab-initio simulations to calculate the band alignment for interfaces between carbon nanotubes, fullerene derivative PCBM and reduced graphene oxide, showing the presence of Type-II and Schottky heterojunctions useful for charge separation in the active layer. We prepared all-carbon solar cells with optimized proportions of these three components that achieved AM1.5 efficiencies up to 1.5%, with fill factors up to 70% and increased thermal stability and lifetime compared to polymer based devices. In addition, we show our recent results on understanding and tuning the optoelectronic properties of hybridized Carbon-Boron Nitride sheets (see Ref. 1). We show how their interfaces with carbon nanomaterials such as PCBM fullerene and carbon nanotubes can provide novel design opportunities for excitonic photovoltaic devices. Taken together, our results show the potential of all-carbon solar cells as an alternative to polymer based ones: the key combination of high carrier mobility, visible and IR absorption and stability under illumination makes them highly appealing for next-generation flexible photovoltaics.

References [1] C. Li et al., Nature Mater. 9, 430-435 (2011).

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B20 - Vertical Phase Separation in Polymer:Fullerene Films For Photovoltaics

Ellen Moons*a, Ana Sofia Anselmoa, Andrzej Dzwilewskia, Krister Svenssona, Jan van Stamb

a, Department of Physics and Electrical Engineering, Karlstad University, Universitetsgatan 2, Karlstad, 651 88, Sweden b, Department of Chemistry and Biomedical Sciences, Karlstad University, Universitetsgatan 2, Karlstad, 651 88, Sweden

Morphology control has been one major key to the recent improvements in energy conversion efficiency of polymer-based photovoltaic devices. Such devices consist of solution-cast thin films of electron donor and electron acceptor molecules mixed with one another, a so-called bulk heterojunction. This molecular distribution has a strong effect on the charge generation processes in the solar cell, such as the separation of excitons into mobile charges at the donor/acceptor interface and the transport of these mobile charges to the electrodes. When a thin film is prepared by spincoating a blend of a conjugated polymer and the fullerene-based acceptor material, PCBM, demixing determines the nanostructure in the film, which is influenced by the polymer-fullerene-solvent interactions, the molecules’ tendency to self-organise, and the kinetics of the film formation. During spincoating, characterized by rapid solvent evaporation, the kinetics of crystallization and of liquid-liquid phase separation compete. The formation of lamellar phases and vertical concentration gradients has been reported for several blend systems, among which P3HT:PCBM and APFO3:PCBM.[1-4] Characterization of the composition and molecular orientation at these interfaces is a major challenge, because very few techniques exhibit both the chemical contrast and the lateral or depth resolution required to unveil the nanostructure of these bulk heterojunctions. We have used a combination of Atomic Force Microscopy (AFM), dynamic Secondary Ion Mass Spectrometry (d-SIMS), and Near-Edge Absorption Fine Structure (NEXAFS) spectroscopy to probe the surface and bulk composition of polymer:fullerene blends. Differences in composition between surface, sub-surface, and bulk are observed and form strong evidence for vertical phase separation. Moreover, the dependence of the NEXAFS resonance peaks on the angle of incidence of the X-rays yields information about molecular orientation at the air interface. Reference [1] Björström, C. M.; Bernasik, A.; Rysz, J.; Budkowski, A.; Nilsson, S.; Svensson, M.; Andersson, M. R.; Magnusson, K. O.; Moons, E. J. Phys.: Condens. Matter "Multilayer Formation in Spin-Coated Films of Low-Bandgap Polyfluorene:Fullerene Blends" 17, L529 (2005). [2] Germack, D.S.; Chan, C. K.; Hamadani, B. H.; Richter, L. J.; Fischer, D. A.; Gundlach, D. J.; DeLongchamp, D. M. Appl. Phys. Lett. "Substrate-Dependent Interface Composition and Charge Transport in Films for Organic Photovoltaics" 94, 233303 (2009). [3] Xue, B.; Vaughan, B.; Poh, C.-H.; Burke, K. B.; Thomsen, L.; Stapleton, A.; Zhou, X.; Bryant, G. W.; Belcher, W.; Dastoor, P. C. "Vertical Stratification and Interfacial Structure in P3HT:PCBM Organic Solar Cells" J. Phys. Chem. C 114 15797-15805 (2010). [4] Anselmo, A. S.; Lindgren, L.; Rysz, J.; Bernasik, A.; Budkowski, A.; Andersson, M. R.; Svensson, K.; van Stam, J.; Moons, E."Tuning the Vertical Phase Separation in Polyfluorene:Fullerene Blend Films by Polymer Functionalization" Chem. Mater. 23, 2295-2302 (2011).

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B21 - Fullerene bisadducts for organic photovoltaics

R. K. M. (Ricardo) Bouwer*a, G. A. H. (Gert-Jan) Wetzelaerb, P. W. M. (Paul) Blomb, J. C. (Kees) Hummelenb

a, Delft University of Technology, Kluyverweg 1, Delft, 2629 HS, NL b, University of Groningen, Nijenborgh 4, Groningen, 9747 AG, NL c, Dutch Polymer Institute, P.O. Box 902, Eindhoven, 5600 AX, NL

Fullerene bisadducts are attracting increased attention as acceptor materials in organic bulk heterojunction solar cells. Power conversion efficiencies of up to 4.5% have been demonstrated for bis-PCBM as acceptor in combination with P3HT.[1] ICBA in combination with the same donor material resulted in efficiencies as high as 6.5%, outperforming even the best known acceptors to date.[2] It is quite remarkable for bisadducts to perform this well, as they consist of complex mixtures of many isomers, the properties of which depending strongly on their substitution pattern. Devices based on bisadducts exhibit higher open-circuit voltages (Voc) as compared to their parent monoadducts. The short-circuit current (Jsc), however, is generally lower. A possible explanation for this decrease in Jsc lies in the isomeric nature of these bisadducts; It is expected that the isomeric nature affects the properties of the bulk and especially the ability to crystallize, which is important in the formation of a bicontinuous interpenetrating network of fullerene and polymer. In addition, this low crystallinity might lower the charge transport characteristics as compared to a single isomer. For P3HT-based devices it is likely that the polymer predominantly determines the morphology of the active layer. This explains why bisadducts show better performance compared to their monoadduct parents as an acceptor material in bulk heterojunctions with P3HT but that this effect is harder to obtain with other, less-crystalline polymers.

Figure 1 Structures of bis-PCBM, P3HT and ICBA.

In order to gain an understanding of the isomeric makeup, bis-PCBM was chosen as a model compound. The isomeric composition was investigated through molecular modeling of the individual bisadducts and the reactivity of the parent monoadduct PCBM. Attempts to isolate single isomers using a combination of column chromatography and preparative HPLC techniques were undertaken. The resulting isomers, or isomer subfractions, were analyzed and their electronic properties were examined. Preliminary results in bulk heterojunction solar cells will be presented. Due to the time consuming nature of chromatographic techniques we explored synthetic methods to reduce the number of isomers of bis-PCBM. For the formation of isomerically pure bisadducts two methods are widely used in fullerene chemistry; directed synthesis and tether-directed synthesis. We have compared the performances of three different isomeric subpopulations of bis-PCBM isomers in organic solar cells obtained via tether-directed

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synthesis using alkyl spacers of increasing length.[3,4] The results of this study will be presented as well. References [1] Lenes, M; Wetzelaer, G. A. H.; Kooistra, F. B.; Veenstra, S. C.; Hummelen, J. C.; Blom, P. W. M."Fullerene Bisadducts for Enhanced Open-Circuit Voltages and Efficiencies in Polymer Solar Cells". Adv. Mater. 20, 2116-2119 (2008). [2] Zhao, G.; He, Y.; Li, Y. "6.5% Efficiency of Polymer Solar Cells Based on poly(3-hexylthiophene) and Indene-C60 Bisadduct by Device Optimization". Adv. Mater. 22, 4355-4358 (2010). [3] Bouwer, R. K. M.; Hummelen, J. C. "The Use of Tethered Addends to Decrease the Number of Isomers of Bisadduct Analogues of PCBM". Chem. Eur. J. 16, 11250-11253 (2010). [4] a. Bouwer, R. K. M.; Wetzelaer, G. A. H.; Blom, P. W. M.; Hummelen, J. C. "Influence of the Isomeric Composition of the Acceptor on the Performance of Organic Bulk Heterojunction P3HT:bis-PCBM Solar Cells". submitted for publication; b. Bouwer, R. K. M. "Fullerene bisadducts for organic photovoltaics" Zernike PhD thesis series 2012-04, ISBN 978-90-367-5304-6 (electronic version).

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B22 - Bipolar organic semiconductors: application in thin film tran¬sistors and photovoltaic cells

Andreas Opitza, Andreas Wilkea, Norbert Kocha, Mark Gruberb, Ulrich Hörmannb, Michael Krausb, Julia Wagnerb, Wolfgang Brüttingb

a, Humbold-Universität zu Berlin, Institut für Physik, Humboldt-Universität zu Berlin, DE b, Universität Augsburg, Institut für Physik, Universität Augsburg, DE

Organic semiconductors used in thin-film devices have traditionally been reported as either electron or hole transporting materials. For this contribution the transport of electrons and holes in molecular semiconductors is analysed in organic field-effect transistors [1]. Additionally the ability of molecular semiconductors to act as donor or acceptor material in organic photovoltaic cells was investigated [2,3]. Furthermore the device behaviour is compared to the energy levels of the semiconductors measured by ultraviolet photoelectron spectroscopy [2]. Our findings show that the classical distinction between hole and electron conducting organic semiconductors is mostly related to two reasons. The first one is the suppression of electron transport due to electron traps at oxide surfaces as normally used in thin film transistors. Secondly, hole injection from standard electrode materials is impossibly into the deep lying HOMO level of electron-conducting materials. By adjusting the energy levels for injection at the contacts the transport behaviour in transistors with a passivated insulator/semiconductor interface can be tuned to be electron-only, hole-only or bipolar [1]. The application of an organic material in organic solar cells as donor or acceptor depends on the energy level alignment at the organic/organic interface with the appropriate counterpart [2,3]. With our findings we show that the same molecular semiconductors (e.g. diindenoperylene) can be used as active material in light-emitting transistors and as donor or acceptor material in solar cells. References [1] Horlet, M.; Kraus, M.; Brütting, W.; Opitz, A.; "Diindenoperylene as ambipolar semiconductor: influence of electrode materials and mobility asymmetry in organic field-effect transistors". Appl. Phys. Lett. 98, 233304 (2011). [2] Wagner, J.; Gruber, M.; Hinderhofer, A.; Wilke, A.; Bröker, B.; Frisch, J.; Amsalem, P.; Vollmer, A.; Opitz, A.; Koch, N.; Schreiber, F.; Brütting, W.; "High fill factor and open circuit voltage in organic photovoltaic cells with diindenoperylene as donor material". Adv. Funct. Mater. 20, 4295–4303 (2010). [3] Hörmann, U.; Wagner, J.; Gruber, M.; Opitz, A.; Brütting, W.; "Approaching the ultimate open circuit voltage in thiophene based single junction solar cells by applying diindenoperylene as accept". phys. stat. sol. RRL 5, 241–243 (2011).

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B23 - Industrialization efforts toward Dye Solar Cells for Building Integrated Applications

Emma Artuso, Nadia Barbero, Carlo Bignozzi, Rita Boaretto, Luca Bonandini, Thomas M. Brown, Eva Busatto, Stefano Carli, Daniele Colonna, Gabriele De Angelis, Aldo Di Carlo, Fabrizio Giordano, Alessandro Guglielmotti, Andrea Guidobaldi, Alessando Lanuti, Angelo Lembo, Simone Mastroianni, Valentina Mirruzzo, Stefano Penna, Eleonora Petrolati, Andrea Reale, Riccardo Riccitelli, Giuseppe Soscia, Luigi Vesce, Guido Viscardi DYEPOWER Consortium, Viale Castro Pretorio, 122 - 00185 - Rome (Italy), IT

The strong request for renewable energy sources has recently boosted the interest in photovoltaic devices. New technologies are now available to improve the photovoltaic conversion efficiencies and/or to reduce system costs. Among all the organic and hybrid organic-inorganic solar cell technologies, dye solar cells (DSCs) have demonstrated the highest conversion efficiencies and a mature research and development plan. Compared to traditional photovoltaics, DSCs have several advantages, such as improved performances at low light intensities and diffuse light, colour tunabilty, and transparency, which make DSC very appealing for building-integrated photovoltaics (BIPV). Based on this consideration, the Dyepower consortium which includes a leading company for glass façades, Permasteelisa and an energy company, ERG Renew, has been established to pursue industrialization of DSC technologies for BIPV applications and in particular for the development of a pilot line for the production of photovoltaic glass façades. The optimization of DSC for glass façade requirements is very challenging. Color uniformity, color stability, color tuning and cell transparency are parameters as important as cell efficiency and stability. In this work we will present the effort made by Dyepower researchers to optimize these parameters considering, at the same time, the industrial process for glass panel fabrication.

Figure 1 a) 15cm x 21cm DSC modules with two different dyes, b) 0.45 m2 DSC panel, c) Outdoor performance of a DSC panel

In particular we will show:

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Co-sensitization as an effective way to account for cell transparency and efficiency both of which are required in façade applications;

Effective sealing technologies developed for both parallel and Z connected modules, which ensure stability of the module and good enough color uniformity over the entire module at the same time;

Large area modules (> 300 cm2) with 6% efficiency on active area and 20% transparency with Z interconnection technology

Stability of the module and the panels in both outdoor conditions and under indoor accelerated stress tests.

Cobalt based electrolytes as effective alternatives used to alleviate sealing issues Efficient automation of DSC panel manufacturing

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B24 - Transparent conductive oxide-less (TCO-less) dye-sensitized solar cells with back contact structure

Yuhei Ogomi, Terumi Nishimura, Jun Usagawa, Takeshi Kogo, Shyam Pandey, Shuzi Hayase

Kyushu Institute of Technology , 204 Hibikino Wakamatsu-ku, Kitakyushu - Fukuoka, 808, JP

Efficiency of dye-sensitized solar cells (DSC) reached 10.9 % which is almost the same as that of amorphous Si solar cells. Fabrication of large modules and their durability are now extensively being researched. DSC single cells can be prepared relatively easy by coating-based processes. However, in the case of modules with parallel connection structures, current collectors covered by protection layers have to be fabricated on the transparent conductive oxide layers because of the low conductivity of TCO layers. The fabrication of the protected collectors is not easy and these collectors spoil appearance of DSCs. We now report some structures on TCO-less DSCs with back-contact structures (BC-TCO-less DSC) including previous reports(1-4). The BC-TCO-less DSC consists of glass (or plastics)/titania layer stained by dyes/porous metal structure/gel electrolyte layer/Pt thin layers on a Ti foil. Porous metal layers were fabricated by porous Ti layers or protected metal wires or protected metal sheets. These structures were actually prepared and these photovoltaic performances were measured. From these results, advantages and disadvantages of each TCO-less structure are discussed from the view point of large module preparation. In addition, the relationship between cell structure and solar cell performance is discussed and directions toward high efficiency BC-TCO-less DSC are reported. A gap between two electrodes (cathode and anode) should be minimized and back contact porous metal layers with thin thickness and high conductivity were needed. A flexible BS-TCO-less DSC with 6.1 % efficiency is reported. Recently, electrolytes consisting of Co complexes are being attracted interest. Co redox systems may have some advantages over iodine/iodide redox electrolytes in terms of metal corrosion. DC-TCO-less DSC consisting of Co redoxes (iodine/iodide free BC-TCO-less DSCs) was fabricated. The efficiency increased from 0.25% to 3.2% after the metal surface was protected.

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Figure 1 Structures of TCO-less back contact DSCs and iodine/iodide free TCO-less DSC

It was concluded that the surface protection of metal electrode was indispensable for the DSCs with Co redox from the view point of high efficiency. In conclusion, it was proved that BC-TCO-less structures have potential for DSC modules without surface current collectors. In addition, we showed that BC-TCO-less DSCs with Co redoxes (iodine/iodide free) worked as solar cells. References [1] J. M. Kroon. et al Prog. Photovolt: Res. Appl. 15, 1 (2007) [2] N. Fuke, A. Fukui, Y. Chiba, R. Komiya, R. Yamanaka, and L. Han, Jpn. J. Appl. Phys., Vol. 46, No. 18, pp. L420-L422 (2007) [3] Y. Kashiwa, Y. Yoshida, and S. Hayase, Appl. Phys. Lett., 92, 033308 (2008) [4] Y. Yoshida, S. S. Pandey, K. Uzaki, S. Hayase, Appl. Phys. Lett., 94, 093301 (2009)

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B25 - Controlling ultra-fast multiple sensitization in dye sensitized solar cells

Peter J. Holliman, Arthur Connell, Matthew L. Davies, Moneer Mohsen, Kareem Al-Salihi, Norasikin Ludin

School of Chemistry, Bangor University, Bangor, LL57 2UW, UK

Since the major breakthrough in dye-sensitized solar cells (DSC) in 1991 when O’Regan and Grätzel reported sensitizing nano-particulate TiO2 films with the Ru-bipy dye (N3) achieving η = 7.3%,1 DSC efficiency has reached > 11%.2 Although there have been efforts to industrialize DSC manufacture, large scale DSC production has not yet been realized. One of the slowest manufacturing procedures is the dyeing step which takes many hours. However, in 2010, we reported an ultra-fast (co-)sensitization procedure to dye TiO2 films with N719, SQ1 or a combination of these dyes in 5 minutes.3 This paper will report our recent successes in further developing and controlling ultra-fast co-sensitization for DSC both for other dye combinations and also for more multiple dyeing. In this context, successful multiple dyeing for DSC requires bespoke dyes which allow co-sensitization to take place in a competitive sorption environment. Co-sensitization dyes must also possess energy levels which prevent any interference during device operation. Such dyes must also absorb different wavelengths of light which coordinate well together to enable broad energy harvesting across the solar spectrum. Thus, this paper will report the development of new dyes which are tailored to increase DSC light harvesting by co-sensitization. The paper will also discuss the ultra-fast dyeing of combinations of selected dyes (successful and otherwise) and link these data to the influences of dye uptake and dye energy levels. Importantly, these approaches offer great potential to be transferable into large-scale DSC manufacture.

Figure 1 (a) AM1.5 solar spectrum (source NREL) showing theoretical light harvesting from multiple dyes, (b) dyes and devices, (c) new dye and (d) EQE showing successful co-sensitization

We gratefully acknowledge WAG and ERDF Low Carbon Research Institute (LCRI) convergence funding for MD and AC through the Solar Photovoltaic Academic Research Consortium (SPARC–Cymru), and EPSRC and TSB support for MD through the SPECIFIC Innovation and Knowledge centre, Iraqi Govt support for MM and KJA, and Malaysian Govt support for NL.

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References [1] O’Regan B.; Grätzel M. "A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films". Nature, 353, 737-740 (1991). [2] Cao Y.; Bai Y.; Yu Q.; Cheng Y.; Liu S.; Shi D.; Gao F.; Wang P. "Dye-Sensitized Solar Cells with a High Absorptivity Ruthenium Sensitizer Featuring a 2-(Hexylthio)thiophene Conjugated Bipyridine". J. Phys. Chem. C 113, 6290-6297, (2009). [3] Holliman P.J.; Davies M.L.; Connell A.; Vaca Velasco B.; Watson T.M. "Ultra-fast sensitisation and co-sensitisation for dye-sensitised solar cells". Chem. Comm., 46, 7256-7258 (2010).

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B26 - An efficient dye-sensitized solar cell based on a microfluidic cell architecture and a small hemi-squaraine organic dye

Adriano Saccoa, Andrea Lambertia, Giorgia Mussoc, Diego Pugliesea, Irene Berardonea, Nadia Shahzada, Rossana Gaziab, Angelica Chiodonib, Stefano Biancob, Claudia Barolod, Marzia Quagliob, Elena Tressoa, Giuseppe Caputoc, Candido Fabrizio Pirria

a, Applied Science and Technology Department, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, 10129, IT b, Center for Space Human Robotics @PoliTo, Istituto Italiano di Tecnologia, Corso Trento 21, Torino, 10129, IT c, Cyanine Technologies S.p.A, Via Quarello, 11/A, Torino, 10135, IT d, Dipartimento di Chimica, Università degli Studi di Torino, Via Pietro Giuria 7, Torino, 10125, IT

We report on the synthesis and the photophysical/electrochemical characterization of one of the smallest and most compact dye molecules ever used as sensitizer in a dye-sensitized solar cell with obtained conversion efficiencies well above 3%. This novel molecule, a hemi-squaraine based organic dye (CT1) has been synthesized, fully characterized and used to sensitize titanium dioxide-based dye sensitized solar cells (DSSCs). The squarate moiety acts as anchoring linker on the titania surface. The dye has a molecular weight of 319 uma, a maximum absorption wavelength at 348 nm, a maximum emission wavelength at 465 nm and a molar extinction coefficient of 13234 Lmol-1cm-1. CT1 sensitized DSSCs were fabricated using a cell based on a customized microfluidic architecture, constituted by a PDMS membrane reversibly sealed between the two transparent electrodes with a PMMA clamping [1]. The loading, aggregation and degradation of the dye were analyzed by means of UV-Vis absorption and fluorescence emission spectroscopy. The dependence of the microfluidic cell efficiency on dye incubation time, dye aggregation and TiO2 thickness was studied by I-V electrical characterization, electrochemical impedance spectroscopy (EIS) and incident photon-to-electron conversion efficiency (IPCE) measurements. A short-circuit current density of 7.89 mAcm−2, an open-circuit voltage of 0.64 V and a fill factor of 0.70 were obtained under standard AM 1.5G irradiation (1000 Wm−2), with an overall solar-to-electricity conversion efficiency of 3.54%. These results suggest that the small organic dye CT1 is highly promising as sensitizer in DSSC fabrication and the use of squarate as linking group could be efficiently further exploited for organic dye-based DSSCs.

References [1] Lamberti, A.; Sacco, A.; Bianco, S.; Giuri, E.; Quaglio, M.; Chiodoni, A.; Tresso, E. “Microfluidic sealing and housing system for innovative dye sensitized solar cell architecture” Microelectron. Eng. 88, 2308-2310 (2011).

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B27 - Highly Efficient TiO2 Nanosheets /PbS Quantum Dots Heterojunction solar cells

Lioz Etgara, Wei Zhang b, Stefanie Gabrielc, Stephen G. Hickeyc, Md K. Nazeeruddina, Alexander Eychmüllerandc, Bin Liub, Michael Grätzela

a, Department of Sciences and Chemical Engineering , EPFL SB ISIC LPI CH B2 475 Station 6 , Lausanne, 1015, Switzerland b, Department of Chemical and Biomolecular Engineering , National university of Singapore , Singapore c, Department of Physical Chemistry/Electrochemistry, , Dresden,TU , Germany

Semiconductor quantum dots (QDs) currently attracted widespread attention for photovoltaic devices due to the possibility of controlling their optoelectronic properties. Here we report on a high efficiency solid state PbS QDs/TiO2 heterojunction solar cell. The heterojunction solar cells were produced using layer-by-layer deposition of PbS QDs on a 400nm thick of anatase TiO2 nanosheets film. The TiO2 nanosheets are known for their slightly higher conduction band and their higher surface energy compared to normal anatase TiO2 nanoparticles (NPs).

Figure 1 (A) The architecture of the PbS(QD)/nanosheets TiO2 heterojunction photovoltaic device, the light is incident through the glass. (B) Cross sectional HR-SEM of the photovoltaic device.

As a result their surface is more reactive than anatase TiO2 NPs. To complete the electrical circuit of the solar cell an Au film was evaporated as a back contact on top of the PbS QDs. Importantly, the PbS QDs act here as photosensitizers and at the same time as hole conductors. The PbS QDs/TiO2 heterojunction solar cell produces a short circuit photocurrent (Jsc) of 20.5 mA/cm2, an open circuit photovoltage (Voc) of 0.545 V and a fill factor (FF) of 0.38, corresponding to a light to electric power conversion efficiency (η) of 4.7% under AM1.5 illumination. This is the first report of using anatase TiO2nanosheets in a QDs solar cell, while reaching one of the highest efficiencies reported in literature.

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B28 - Charge Transport in a Novel Mesoporous TiO2 Semiconductor

Edward Crossland, Henry Snaith

University of Oxford, Clarendon Laboratory, Parks rd, Oxford, GB

Mesoporous inorganic semiconducting layers lie at the heart of many promising hybrid photovoltaic device concepts. The mesoscale pore size and morphology of the inorganic phase are critical for achieving a high specific surface semiconductor heterojunction for efficient charge generation. Transport of charge within the inorganic phase, on the other hand, is limited by a high density of electronic defect states that depend on atomic scale order – i.e. crystal domain size. Using the classic route of thermally sintering of pre-formed nanocrystals, the increase in exposed surface achieved by decreasing particle size is necessarily accompanied by an increase in the number and frequency of inter-particle grain boundaries. Macromolecular self-assembly of structure-directing agents and porous templates are routes to pattern mesoporous ceramics that decouple atomic from mesoscale order and offer the possibility of extending crystallinity far beyond the characteristic pore dimension. This goal of this concept is to produce materials combining rapid charge transport with high exposed surface and to disentangle how surface states vs. grain boundaries influence charge transport. We present the synthesis and characterisation of an exciting new class of mesoporous TiO2 semiconductor and use transient photocurrent and photovoltage decay to probe charge transport properties in model solid-state and liquid electrolyte DSC devices.

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B29 - Dynamics of Charge-Transfer Interfacial Excitons at Dye-Sensitized Donor/ Acceptor Hybrid Heterojunction

Jan C. Brauer, Arianna Marchioro,Jacques-E. Moser

Photochemical Dynamics Group, Ecole Polytechnique Fédérale de Lausanne, EPFL SB ISIC GR-MO, Station 6, CH-1015 Lausanne, Switzerland

A combination of ultrafast laser transient absorption and optical pump-THz probe (OPTP) spectroscopies was applied to scrutinize the details of interfacial photoinduced charge separation in the dye-sensitization of wide bandgap oxides. When a suitable dye-sensitizer (S), such as RuII(H2dcbpy)(dnbpy)(NCS)2 (Z907), is adsorbed onto the surface of nanocrystalline TiO2, optical absorbance of the dye cation (S+) is readily observed upon photo-excitation of the sensitizer and fully develops within < 20 fs. Provided all dye molecules are strongly achored on the surface and no dye aggregates are formed, kinetics of the fs electron injection into the conduction band of the solid appears to be independent of the medium (solvent, electrolyte, solid hole conductor material, ...). The charge injection process was monitored in identical samples by OPTP spectroscopy with sub-ps time resolution. In the presence of various electrolytes, a multiphasic behaviour was observed, where ~ 25 % of the total number of injected electrons contributed immediately to the THz conduction, while the mobility of the remaining charges increased slowly with a half-process time of ~ 100 ps. In a pure solvent, the slower kinetic part was missing, yielding a 4-fold abatement of the final conduction of photo-injected electrons. These results lead to the conclusion that Coulomb attraction between injected electrons and positive charges left on dye molecules must give rise to charge-transfer (CT) interfacial excitons. Such bound electron-hole pairs formed across the interface prevent a majority of injected charges to contribute to the THz conduction. In the presence of an electrolyte, however, the mobility of conduction-band electrons in TiO2 nanoparticles increases markedly when anions are adsorbed onto the surface, screening the Coulomb interaction and decreasing the exciton binding energy.

Figure 1 Formation and dissociation of a charge transfer interfacial exciton at the organic donor (D) | dye-sensitizer (S) | metal oxide acceptor (A) heterojunction.

The system above involves the simplest type of CT interfacial exciton, namely, a free electron in the semiconductor interacting with a localized hole in the sensitizer cation. This picture is further complicated when the hole is injected into an organic donor material (D). Similar to the effect of the electrolyte, filling the pores of a nanostructured TiO2 film with the organic hole-conducting material spiro-OMeTAD gave rise to an additional slow component in

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the measured transient THz conductivity signal, whose kinetics was correlated with the hole injection dynamics into the donor material. The effect of various ions and additives adsorbed at the hybrid interface on the free carriers generation dynamics was studied. Results are rationalized, taking into account delocalization and spatial correlation of charges, as well as electron-nuclear coupling leading to self-trapped excitons.

References [1] Němec, H.; Kužel, P.; Sundström, V. J. Photochem. Photobiol. A: Chem. 215, 123-139 (2010). [2] Brauer, J. C.; Teuscher, J.; Punzi, A.; Moser, J.-E. "Transient photoconductivity of dye-sensitized titanium dioxide nanocrystalline films probed by optical pump-THz probe spectroscopy" in Ultrafast Phenomena XVII; Chergui, M. et al. (Eds.), Oxford University Press, New York (2011); pp. 358-360. [3] Brauer, J. C.; Marchioro, A.; Moser, J.-E., manuscript in preparation.

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B30 - Hybrid photovoltaic devices based on chalcogenide aerogels

Ana Flavia Nogueiraa, Jilian Nei de Freitasa, Lasantha Koralac, Luke Reynoldsb, Saif Haqueb, Stephanie Brockc

a, Chemistry Institute, University of Campinas, Instituto de Quimica, Campinas, 13083970, BR b, Dept. Chemistry, Imperial College, South Kensington, London SW7 2AZ, UK c, Dept. Chemistry, Wayne State University, Detroit MI, 48202, USA

Organic solar cells based on conjugated polymers are among the most promising devices for cheap solar energy conversion. The “classical” device consists of a bulk-heterojunction of a polymer-fullerene network, using poly(3-hexylthiophene) (P3HT) and the soluble fullerene derivative, PCBM. The introduction of small alkyl thiol molecules, optimization of solvent conditions, novel copolymers and PC71BM are responsible for significant improvements in the efficiency of these devices, reaching more than 7 %. Bottlenecks still persist: morphology control, the mismatch with the solar spectrum and stability. Inorganic nanoparticles have been used as sensitizers and/or electron acceptor materials in polymer solar cells and devices with efficiencies of ~ 3 % have been reported by using CdSe tetrapods [1]. The use of inorganic nanoparticles as a third component in polymer/fullerene devices is another promising approach. The investigation of devices assembled with PFT (a polymer based on fluorene and thiophene units) and PCBM showed an increase in device efficiency after incorporation of CdSe nanoparticles, related to an enhancement of light absorption and a morphology effect induced by the presence of the nanoparticles [2]. However, transport between inorganic nanoparticles is still a problem in such photovoltaic devices. An elegant way to improve electron hopping from dot to dot is to “connect” the quantum dots together to form an electrically integrated network. Chalcogenide sol-gel methods enable assembly of II-VI and IV-VI quantum dots into mesoporous colloidal networks with inorganic particle interfaces that do not present the barriers to electrical transport, yet remain quantum-confined [3]. In this talk, we explore the use of CdSe and CdSe@ZnS aerogels in P3HT-based solar cells. Photoelectrochemistry and transient absorption spectroscopy were employed to compare the performance of aerogels to the performance of regular quantum dots. The contributions of morphology and native transport characteristics of the CdSe and CdSe@ZnS framework on the charge generation and device performance will be discussed. References [1] S. Dayal, N. Kopidakis, D. C. Olson, D. S. Ginley, G. Rumbles, Nano Lett. 10, 239, 2010. [2] J. N. de Freitas, I. R. Grova, L. A. Akcelrud, E. Arici, N. S. Sariciftci, A. F. Nogueira, J. Mater. Chem. 20, 4845, 2010. [3] I. R. Pala, I. U. Arachchige, D. G. Georgiev, S. L. Brock, Angew. Chem. Int. Ed. 2010, 49, 3661.

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B31 - Cosensitization and multichromophore light harvesting in hybrid devices

Katja Willinger, Christoph Hunger, Mukundan Thelakkat

Applied Functional Polymers, University of Bayreuth, Universitystr-30, Bayreuth, 95440, DE

We present innovative concepts of multichromophore light harvesting in hybrid blend devices [1] and highly efficient cosensitization of organic dyes in solid-state dye-sensitized solar cells. The synthesis and charcterization of some novel organic dyes belonging to the class of BODIPY, triphenyldiamine [2] and squaraines [3] and the UV-vis absorption properties under various conditions of chemisorption are described. The structure-property relationship in a series of BODIPY dyes carrying suitable anchor groups and donor-antenna groups will be explained. Further, the application of individual dyes in devices are described.

Figure 1 Scheme of preparation of dye-coated nanocrystals and device structure of multichromophore sensitized hybrid blend solar cell

Two types of devices sensitized using a combination of dyes will be presented. In the first case of multichromophore light harvesting, the principle of hybrid blend was used to demonstrate the potential of this concept, which is suitable for room temperature fabrication of large area devices. In the second type, cosensitized solid-state dye sensitized devices are described. Both concepts have high potentials in improving light harvesting in solid-state devices. Especially the hybrid blend concept can be adapted to tandem hybrid cells and for extending the absorption by using a combination of any number of dyes. The achievemnents, perspectives and limitations will be discussed in the contribution

References [1] Bandara,J.; Gräf, K.;Thelakkat,M."Multichromophore light harvesting in hybrid solar cells" Phys. Chem. Chem. Phys.13, 12906–12911 (2011). [2] Erten-Ela,S.; Brendel,J.; Thelakkat,M. "Solid-state dye-sensitized solar cells fabricated with nanoporous TiO2 and TPD dyes: Analysis of penetration behavior and I-V characteristics,Chemical physics letters, 510, 93-98, (2011). [3] Kolemen,S.; Cakmak,Y.; Erten-Ela, S.; Altay, Y.; Brendel,J.; Thelakkat,M.; Akkaya, E. "Solid-State Dye-Sensitized Solar Cells Using Red and Near-IR Absorbing Bodipy Sensitizers" Org. Lett., 12, 3812-3815 (2010)

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B32 - Graded Vertical Phase Separation of Donor/Acceptor Species for Polymer Solar Cells

Anna Loiudicea, Aurora Rizzob, Gianluca Latinia, Giuseppe Giglic

a, IIT, Italian Institute of Technology , VIA BARSANATI, 1, Lecce, 73010, IT b, NNL CNR, Via per Arnesano km 5, Lecce, 73100, IT c, Universita` del Salento, Via per Arnesano, Lecce, 73100, IT

The donor/acceptor inter-mixing in bulk heterojunction (BHJ) solar cells is a critical parameter, often leading to irreproducible performance of the finished device.[1] An alternative solution-processed device fabrication strategy towards a better control of the micro/nano-structured morphology consists in a sequential coating of the donor (e.g., poly-(3-hexylthiophene), P3HT) and acceptor (e.g., [6,6]-phenyl-C61-butyric acid methyl ester, PCBM) from orthogonal solvents.[2] We demonstrate that, in spite of the solvent orthogonality, this technique does not lead to a well-defined bilayer with a sharp interface, but it rather results in a graded vertical phase-separated junction, resulting from the diffusion of the PCBM in the P3HT bottom layer. We are able to control the diffusion of PCBM, which occurs preferentially in the amorphous P3HT domains, by easily varying the ratio between crystalline/amorphous domains in the P3HT. Such a ratio can be simply modified by changing the solvent for P3HT. We show that the donor-acceptor diffused bilayer (DB) junction is an intermediate structure which combines both advantages of the well-defined bilayer and conventional BHJ configurations. Indeed, the DB device geometry ensures the good reproducibility and charge percolation, like the well-defined bilayer, while preserving the interpenetration of the donor and acceptor species, resulting in an efficient charge separation, characteristic of the BHJ.

Figure 1 Current Density–Voltage characteristics under illumination (a) for the devices made with as-cast DB, annealed DB and BHJ structure; schematic representation of (b) the as-cast DB and (d) annealed DB.

Overall the annealed DB device geometry can be assimilated to a graded BHJ with an improved reproducibility and mean power conversion efficiency (PCE) of 3.45%, higher than that of the standard BHJ devices of 3.07%. Accordingly, the DB device exhibits improved open circuit voltage, fill factor, series and shunt resistances, that are a direct consequence of the vertically phase separation, which ensures better transport properties. Moreover we find that our as-cast DB (non annealed) device has the highest efficiency (2.58%) achieved in solution processed as-cast solar cells to date, which is important in the frame of low temperature processing conditions for plastic electronic production.To correlate the device performances

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with the micro/nano-structure of P3HT and to further deepen our understanding on the DB device, we report a systematic characterisation, which comprises cross-section scanning electronic microscopy images and transient photoluminescence measurements.

References [1]Riede, M.K.; Sylvester-Hvid, K.O.; Glatthaar, M.; Keegan, N.; Ziegler, T.; Zimmermann, B.; Niggemann, M.; Liehr, A.; Willeke, G.; Gombert, A. “High throughput testing platform for organic solar cells”. Prog. Photovolt: Res. Appl. 2008, (2008). [2]Lee, K.H.; Schwenn, P.E.; Smith, A.R.G.; Cavaye, H.; Shaw, P.E.; James, M.; Krueger, K.B.; Gentle, I.R.; Meredith, P.; Burn, P.L. ”Morphology of all-solution-processed "bilayer" organic solar cells”. Adv. Mater. 23, (2011).

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B33- Enhanced Light Harvesting in Dye-Sensitized Solar Cells Using Highly Soluble

Energy Relay Dyes

George Margulisa, Bo Gyu Limb, Brian Hardinb, Johann Feckld, Shaik Zakeerudinc, Thomas Beind, Michael Grätzelc, Alan Sellingerb, Michael McGeheeb a, Applied Physics, Stanford University, Stanford, Ca, 94305, US b, Materials Science and Engineering, Stanford University, Stanford, Ca. 94305, US c, Laboratory of Photonics and Interfaces, Ecole Polytechnique de Lausanne, Lausanne, Switzerland d, Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU), Munich, Germany

Energy Relay Dyes (ERDs) have been utilized in dye sensitized solar cells (DSCs) to enhance light harvesting through complementary absorption with subsequent long-range Förster resonance energy transfer to a sensitizing dye(1). This new paradigm allows for a relaxation DSC of design principles: the ERD is given the task of light absorption, while efficient charge injection and recombination reduction is left to the sensitizing dye. However, the efficiency of ERD DSCs is limited by insufficient absorption by the ERD. To significantly improve performance, either the solubility and/or extinction coefficient of the ERD must be improved significantly(2). We present a new electrolyte and highly soluble ERDs which allow for near 100% absorption at peak wavelength even in 3 micron-thick DSCs.

Figure 1 Normalized EQE of 3 micron DSC sensitized with TT1 using no ERD (blue) and BL302 ERD (green)

These highly soluble energy relay dyes allow for a greater than 50% enhancement in the short circuit photocurrent of the DSC, greatly improving performance. In addition, we measure and quantify the effects of concentration quenching and electrolyte quenching, mechanisms which lower the energy transfer efficiency of ERDs to sensitizing dyes. We are able to achieve 80% energy transfer efficiency in 3 micron thick DSCs with near unity absorption by the energy relay dye, showing the potential for the use of energy relay dyes for highly efficient light harvesting.

References [1]Hardin, B.E.; Hoke, E.T.; Armstrong P.B.; Yum J.-H.; Comte, P.; Torres, T.; Fréchet, J.M; Nazeeruddin, M.K.; Grätzel, M. McGehee, M.D. “Increasing Light Harvesting in Dye-Sensitized Solar Cells With Energy Relay Dyes”. Nat. Phot. 3, 406-411 (2009).

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[2]Hardin, B.E.; Yum J.H.; Hoke, E.T.; Jun Y.C.; Péchy, P.;Torres, T.; Brongersma, M.L.; Nazeeruddin, M.K.; Grätzel, M. McGehee, M.D. “High Excitation Transfer Efficiency from Energy Relay Dyes in Dye-Sensitized Solar Cells” Nano Let., 10 3077-3083 (2010).

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B34 - A New Quantum dot/Inorganic layer/Dye molecule Sandwich-structure for Electrochemical Solar Cells with Improved Photovoltaic Performance and High Photostability

Hong Lina, Heping Shena, Yizhu Liua, Dan Oronb a, Department of Material Science and Engineering, Tsinghua University, Department of Material Science and Engineering, Tsinghua University, Beijing 100084, China b, Department of Physics of Complex Systems, Weizmann Institute of Science, Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel

A highly efficient quantum dot/inorganic layer/dye molecule sandwich-structure was designed and applied in electrochemical solar cells with improved photovoltaic performance and high photostability. The key component TiO2/CdS/ZnS/N719 hybrid photoanode with ZnS insertion between the two types of sensitizers was demonstrated to not only efficiently extend the light absorption, but also dramatically suppress CdS corrosion and charge recombination from either TiO2 or CdS quantum dots (QDs) to electrolyte redox species. Notably, charge separation between two sensitizers, especially the hole transfer from CdS’s valence band to N719’s HOMO as CdS regeneration, was efficient due to the type-II alignment between CdS QD and N719 molecule according to Raman and PL measurements. Even in the presence of ZnS deposition between two sensitizers, the strong photoinduced charge transfer was not hindered. This was also confirmed by the excellent photovoltaic performance of the solar cell employing this TiO2/CdS/ZnS/N719 hybrid film, yielding a photocurrent density of 11.04 mA cm-2, an open-circuit voltage of 713 mV, a fill factor of 0.559, and an impressive overall energy conversion efficiency of 4.4%. The photostability of both CdS sensitized and CdS-N719 co-sensitized solar cells by using the I-/I3

- based electrolyte was evaluated by measuring the short circuit current density as a function of time using periodic illumination intervals.

Figure 1 The energetic diagram of the bi-sensitizer nanoporous electrode (TiO2/CdS/ZnS/N719). Undesired direct recombination channels from the TiO2 and the CdS QDs to the electrolyte, which are strongly suppressed by the ZnS, are indicated by dashed lines.

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It was found that the synergistic stabilizing effect of both the organic and inorganic passivation layers helped to achieve long-term cell stability in the presence of a corrosive electrolyte, which potentially points at the use of combined inorganic-organic system. Cobalt complexes were then exploited to further enhance the cell stability. Such a strategy serves as a promising alternative to the conventional configuration of QD-sensitized solar cells and opens up a new way of fabricating highly efficient nanocrystalline hybrid solar cells.

References [1]Shalom, M.; Albero, J.; Tachan, Z.; Ferrero, E.M.; Zaban, A.; Palomares, E."Quantum Dot-Dye Bilayer-Sensitized Solar Cells: Breaking the Limits Imposeed by the Low Absorbance of Dye Monolayers". J. Phys. Chem. Lett. 1, 1134–1138(2010). [2]Buhbut, S.; Itzhakov, S.; Tauber, E.; Shalom, M.; Hod, I.; Geiger, T.; Garini, Y.; Oron, D.; Zaban, A. "Built-in Quantum Dot Antennas in Dye-Sensitized Solar Cells". ACS Nano 4, 1293-1298(2010). [3]Mora-Seró, I.; Likodimos, V.; Giménez, S.; Martínez-Ferrero, E.; Albero, J.; Palomares, E.; Kontos, A. G.; Falaras, P.; Bisquert, J. "Fast Regeneration of CdSe Quantum Dots by Ru Dye in Sensitized TiO2 Electrodes".J. Phys. Chem. C 114, 6755-6761(2010). [4]Yang, S. M.; Huang, C. H.; Zhai, J.; Wang, Z. S.; Jiang, L. "High Photostability and Quantum Yield of Nanoporous TiO2 Thin Film Electrodes Co-sensitized with Capped Sulfides". J. Mater. Chem. 12, 1459-1464 (2002). [5]Shalom, M.; Dor, S.; Ruhle, S.; Grinis, L.; Zaban, A. "Core/CdS Quantum Dot/Shell Mesoporous Solar Cells with Improved Stability and Efficiency Using an Amorphous TiO2 Coating". J. Phys. Chem. C 113, 3895-3898(2009).

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B35 - Is CuGaO2 a potential substitute for NiO in p-type dye solar cells (p-DSSCs)?

Adèle Renauda, Benoit Chavillonb, Loic Le Pleuxc, Laurent Carioh, Yann Pellegrind, Errol Blarte, Mohammed Boujtitaf, Thierry Pauportég, Stéphane Jobici, Fabrice Odobelj a, Institut des Matériaux Jean Rouxel, 2 rue de la Houssiènière - BP32229, 44322, Nantes cedex 3, FR b, CEISAM, 2 rue de la Houssiènière - BP92208, 44322, Nantes cedex 3, FR c, Chimie Paristech, 11, rue Pierre et Marie Curie, 75231 PARIS Cedex , FR

Dye sensitized solar cells based on the sensitization of n-type semi-conductors may become competitive in the near future with classic photovoltaic cells made of silicon.1 One way currently explored to increase the performances of DSSCs is to develop tandem cells, namely cells combining a photoanode using a n-type semiconductor (n-SC) and a photocathode using a p-type semiconductor (p-SC).2 However despite numerous efforts, the efficiency of p-type DSSCs3 is still low compared to n-type DSSCs which prevents the fabrication of efficient tandem cells. To date, the most investigated p-type metal oxide used for DSSCs is NiO.3 Nevertheless, this semi-conductor may not represent the optimal choice because the valence band edge potential is too close to the oxydo-reduction potential of the iodide/triiodure redox mediator, limiting thereby the maximum photopotential delivered by these cells. Thus, the replacement of NiO appears to be a crucial point to enhance the photovoltaic performances. In this context, we are currently investigating new p-type materials for DSSC applications. We have first focused our researches on CuGaO2 since the literature reports that this delafossite compound has a lower valence band and a higher conductivity than NiO.4 The CuGaO2 nanoparticles were synthesized for the first time using a hydrothermal method assisted by ethylene glycol.5 The p-type character of these nanoparticles was checked by photo-electrochemistry measurements, while electrochemical impedance spectroscopy has demonstrated that its flat band potential is deeper than that of NiO. All these results confirm that CuGaO2 is a promising substitute of NiO. The CuGaO2 nanoparticles were therefore used to build up a dye solar cell. This presentation will focus on the characterizations and the performances of this first CuGaO2 based dye solar cell. References [1]Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H. "Dye-Sensitized Solar Cells". Chem. Rev. 110, 6595-6663 (2010). [2]He, J.J.; Lindstrom, H.; Hagfeldt, A.; Lindquist, S.E. "Dye-sensitized nanostructured tandem cell-first demonstrated cell with a dye-sensitized photocathode". Sol. Energy Mater. Sol. Cells 62, 265 (2000). [3]Odobel, F.; Lepleux, L.; Pellegrin, Y.; Blart, E. "New photovoltaic devices based on the sensitization of p-type semiconductors:challenges and opportunities". Acc. Chem. Res. 43, 1063 (2010). [4]Benko, F.A.; Koffyberg, F.P. "Opto-electronic properties of CuAlO2". J. Phys. Chem. Solids 45, 57-59 (1984). [5]Srinivasan, R.; Chavillon, B.; Doussier-Brochard, C.; Cario, L.; Paris, M.; Gautron, E.; Deniard, P.; Odobel, F.; Jobic, S. "Tuning the size and color of the p-Type wide band gap Delafossite CuGaO2 with an Ethylene glycol assisted Hydrothermal synthesis". J. Mater. Chem. 18, 5647 (2008).

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B36 - The Application and Physical Properties of DCDHF dyes in Organic Photovoltaics

Kenrick Andersona, Emily Borderb, Timothy Jonesa, Clint Woodwardb, Gregory Wilsona, Christopher Fella

a, CSIRO Energy Technology, Mayfield West, NSW 2304, AU b, CSIRO Energy Technology, Clayton South, Vic., 3169, AU

Solution processed deposition of organic solar cells (OSCs) make them attractive for large scale/volume production. Typically a blend of poly (3- hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) are used yet a competitive approach utilising small molecular light absorption chromophores can afford well-defined molecular structures, ease of purification and enhanced batch-to-batch reproducibility. Early trials with triphenylamine-based donor-acceptor (D–A) materials achieved power conversion efficiencies of approx. 2.2%. Recently, L-Y. Lin et al. described a donor–acceptor–acceptor (D–A–A) donor molecule, coded DTDCT, exhibiting λmax= 663 nm and a large εof 42 × 103 M–1 cm–1 achieving a record-high power conversion efficiency (PCE) of 5.81% for bulk heterojunction (BHJ) devices. [1] Comparatively, the use of novel donor–p-spacer–acceptor (D–pi–A) chromophores, based on the dicyanomethylenedihydrofuran (DCDHF) acceptor functional group, where the acidic anchor is de-coupled from the acceptor fragment have been reported for OSCs based on the dye-sensitised solar cell (DSC) architecture. Y. Hao et al. have reported a series of (D–p–A) structures based on the DCDHF acceptor, with lateral, de-coupled, anchoring groups exhibiting promising light harvesting (HY103, ε = 66 × 103 M–1 cm–1λmax= 610 nm, PCE of 2.45%) and charge collection extending into the NIR. [2] Clearly there are synergies between the complementary architectures of the DSC and that of BHJ organic photovoltaics (OPV). These small molecular chromophores are compact, readily synthesised in high yield, have high extinction coefficients (>60 × 103 M–1 cm–1) and exploit through space pi→ pi* electron transfer from the oxidised DCDHF moiety to the titania surface – not unlike the intermolecular electron transfer observed for BHJ solar cells. The molecular configuration in D–pi–A dyes readily facilities further de-coupling of light absorption and electron transfer giving the ability to ‘tune’ molecular fragments – a vital optimisation step in design of component materials for BHJ devices. Here we present a study on promising derivatives of the DCDHF moiety. These chromophores possess ε in the range 50–100 × 103 M–1 cm–1 extending into the NIR. For this study, DCDHF derivatives were blended with PCBM and fabricated using a BHJ architecture yielding reasonable device performance. Preliminary device optimization was performed and the two chromophores compared and contrast for device/optical properties, correlated to TD-DFT calculations and the most promising of these devices was demonstrated in a 10cm × 10cm mini-module. References [1] L-Y. Lin, Y-H Chen, Z-Yu Huang, H-W. Lin, S-H. Chou, F. Lin, C-W. Chen, Y-H. Liu, and K-T. Wong, J. Am. Chem. Soc., 2011, 133 (40), 15822 [2] Y. Hao, X. Yang, J. Cong, H. Tian, A. Hagfeldt, L. Sun, Chem. Comm. (2009) 4031.

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B37 - Photon Upconversion on Dye-Sensitized Nanostructured ZrO2 Films

Jonas Sandby Lissaua, Marie-Pierre Santonia, James M. Gardnera, Sascha Otta, Ana Morandeiraa a, Department of Chemistry, Ångström Laboratories, Uppsala University, Box 523, Uppsala, 75120, SE b, Department of Chemistry - Division of Applied Physical Chemistry, KTH Royal Institute of Technology, Stockholm, 10044, SE

Photon upconversion is the generation of a high-energy photon by two or more low-energy photons. One viable route to this phenomenon is the photophysical process known as photon upconversion through triplet-triplet annihilation (UC-STTA)[1] (see Scheme 1). In photovoltaics photon upconversion can provide a way to harvest photons with energies lower than the bandgap, thereby increasing electric currents without sacrificing the voltage. The renewed interest in UC-STTA stems from the fact, that the process occurs under low-intensity, noncoherent light [2], which allows for potential applications in photovoltaics. In particular the UC-STTA mechanism is well-suited for implementation in dye-sensitized solar cells (DSSCs), where it improves the theoretical maximum efficiency of these devices from ~30% to more than 40% [3].

Figure 1

By using nanostructured ZrO2 films as a model of the semiconductors used in DSSCs, we have shown by simple steady-state emission detection that UC-STTA is possible on a sensitized mesoporous metal oxide using low-intensity (5 mW/cm2), noncoherent light [4]. For this proof-of-principle experiment, we used platinum(II) octaethylporphyrin (PtOEP) as the triplet sensitizer and 9,10-diphenylanthracene (DPA) as the singlet emitter (see Scheme 2). A non-linear (quadratic or higher) dependence of the upconverted signal on the incident excitation light intensity was seen, which further supports the TTA-based mechanism. Time-resolved emission measurements showed a fast rise of the upconverted signal, which indicates that triplet energy migration most likely occurs through a "static" Dexter mechanism. While the described simple system provided a proof-of-principle, unfavorable orientation of the emitter dyes on the surface, porphyrin dimer formation, as well as the presence of oxygen, all contributed to a great limitation on the efficiency of the UC-STTA process. To address these issues a new emitter dye has been synthesized, methyl 4-(10-p-tolylanthracen-9-yl)benzoate (MTAB), which contains a group for chemical anchoring onto the metal oxide surface. By using this new compound we have managed to address all three aforementioned problems and thereby greatly increase the efficiency of the photon upconversion.

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References [1] Singh-Rachford, T. N.; Castellano, F. N. "Photon Upconversion Based on Sensitized Triplet-Triplet Annihilation". Coord. Chem. Rev. 254, 2560–2573 (2010). [2] Baluschev, S.; Yakutkin, V.; Miteva, T.; Avlasevich, Y.; Chernov, S.; Aleshchenkov, S.; Nelles, G.; Cheprakov, A.; Yasuda, A.; Müllen, K.; Wegner, G. "Blue-Green Up-Conversion: Noncoherent Excitation by NIR Light". Angew. Chem., Int. Ed. 46, 7693–7696 (2007). [3] Ekins-Daukes, N. J.; Schmidt, T. W. "A Molecular Approach to the Intermediate Band Solar Cell: The Symmetric Case". Appl. Phys. Lett. 93, 063507 (2008). [4] Lissau, J. S.; Gardner, J. M., Morandeira, A. "Photon Upconversion on Dye-Sensitized Nanostructured ZrO2 Films". J. Phys. Chem. C 115, 23226-23232 (2011).

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B38 - New Concepts for Dye-Sensitized Solar Cells

Udo Bacha, Torben Daenekeb, Dongchuan Fua, Andrew Nattestada a, Monash University, Department of Materials Engineering, Clayton, 3800, AU b, Monash University, School of Chemistry, AU

Dye-sensitized solar cells (DSCs) are viable low-cost alternatives to conventional silicon solar cells. A number of novel concepts are currently being developed that promise to improve the manufacturability and efficiency of these devices. Tandem and back-contact solar cell concepts have successfully been applied in the field of conventional solid-state semiconductor solar cells to realize devices with improved performance.

Figure 1 Schematic diagram of a back-contact dye-sensitized solar cell.

Here we report on the successful implementation of these concepts in DSCs and discuss the potential benefits and challenges associated with these technologies. Finally we will report on DSCs employing novel non-corrosive electrolytes that yield efficiencies of up to 7.9% under simulated sunlight.

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B39 - Synthesis and characterization of benzodithiophene–isoindigo polymers for solar cells

Zaifei Maa, Ergang Wangb, Markus Jarvidb, Patrik Henrikssonb, Olle Inganäsa, Fengling Zhanga, Mats Anderssonb a, Department of Physics, Chemistry and Biology (IFM), Linköping university, Linköping university, Linköping, 58183, Sweden b, Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, Göteborg, 41296, Sweden

Three new alternating polymers with the electron-deficient isoindigo group as the acceptor unit and benzo[1,2-b:4,5-b0]dithiophene (BDT) or BDT flanked by thiophenes (or octylthiophenes) as the donor unit were designed and synthesized. All the polymers have good thermal stability, solubility and broad absorption spectra. Their photophysical, electrochemical and photovoltaic (PV) properties were investigated. To understand their different PV performance in the resulting polymer solar cells (PSCs), the morphology of their blends with fullerene derivatives was investigated by atomic force microscopy, and the molecular geometries as well as the molecular frontier orbitals were simulated by density functional theory calculations (Gaussian 09). The polymer PBDT-TIT, with BDT flanked by thiophenes as the donor unit and isoindigo as the acceptor unit, exhibits quite planar backbones and its blend with fullerene derivatives shows optimal morphology. As a result, the PSCs based on PBDT-TIT with a conventional device configuration of ITO/PEDOT:PSS/PBDT-TIT:PC61BM/LiF/Al showed a power conversion efficiency of 4.22%, with a short-circuit current density of 7.87 mA/cm2, an open- circuit voltage of 0.79 V and a fill factor of 0.68 under the AM 1.5G illumination with an intensity of 100 mW/cm2 from a solar simulator.

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B40 - Recombination in Organic Bulk Heterojunction Solar Cells: A Study of Interfacial Charge Transfer Kinetics with Fullerene Affinity

Antonio Guerrero, Juan Bisquert, Germà Garcia-Belmonte Universidad Jaume I, Avda. Sos Baynat, s/n Universidad Jaume I , Castellón, 12071, ES

One of the current strategies to improve power conversion efficiencies (PCE) of solution-processed organic solar cells is looking at increasing the open circuit potential (Voc). By increasing the energy offset between the donor highest occupied molecular orbital (HOMO) and acceptor lowest unoccupied molecular orbital (LUMO) this can be achieved. Thus, one of the followed approach is to replace [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) as acceptor molecules by different fullerene derivatives with a lower electron affinity.1 In this work a detailed analysis of the charge carrier recombination mechanism will be presented for a series of three different fullerene derivatives. 2,3The impedance technique allows extracting parameters related to energetics as well as recombination kinetics simultaneously. By using active layers of P3HT blended with fullerene acceptors of different electron affinity, we demonstrate that the recombination coefficient is only slightly dependent on the fullerene LUMO energy. Chemical capacitance values indicate that the distribution of excess carriers within bandgap density-of states is very similar for all three. Moreover the energy location of recombining carriers within the DOS has also a minor influence on the recombination coefficient value. It is proposed that charge transfer events accounting for the recombination process take place in the vicinity of the maximum rate in the framework of the Marcus theory, with large reorganization energy values. References [1] He, Y.; Chen, H.-Y.; Hou, J.; Li, Y., "Indene-C60 Bisadduct: a New Acceptor for High-Performance Polymer Solar Cells". J. Am. Chem. Soc., 132, 1377-1382 (2010). [2] Bisquert, J.; Garcia-Belmonte, G., "On Voltage, Photovoltage, and Photocurrent in Bulk Heterojunction Organic Solar Cells". J. Phys. Chem. Let., 2, (15), 1950-1964 (2011). [3] Boix, P. P.; Guerrero, A.; Marchesi, L. F.; Garcia-Belmonte, G.; Bisquert, J., C"urrent-Voltage Characteristics of Bulk Heterojunction Organic Solar Cells: Connection Between Light and Dark Curves". Adv. Energy Mat. 1, (6), 1073-1078 (2011).

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B41 - Spray-coating technique for the realization of Polymer Solar-Cells

Gianpaolo Susannaa, Luigi Salamandraa, Thomas Browna, Andrea Realea, Francesca Brunettia, Aldo Di Carloa a, University of Rome Tor Vergata, viale del politecnico 1,Rome,00133, IT b, CHOSE, Via Giacomo Peroni 400/402 Roma 00131, IT

Organic solar cells have gained within the last years a growing interest within the research community. Among all organic solar cells, small molecule and polymer based technology are very promising. In particular, polymer bulk-heterojunction based technology has shown wide margins of improvement in terms of energy conversion efficiency, reaching values above 8% (certified by NREL), and uncertified 9%, actually doubling the performance in the last two years [1-4]. Despite the low efficiency, when compared with the conventional inorganic solar cells, the potential of a Roll-to-Roll (R2R) process and the low-cost large-area definition on flexible substrates, make the BHJ-SCs technology an interesting and economic solution for the production of energy. The solar cell is built up in a multilayer structure in which the deposition of the layers can be performed with different techniques like for example casting, spin-coating, screen and ink-jet printing [5]. Recently conventional spray-coating was introduced as a large area deposition method for the layers of organic solar cells (OSCs) [6]. In this context, we present polymer solar cells that use as active layer P3HT:PCBM, in which we replaced the standard spin-coating deposition of the active layer and of the hole transporting layer (PEDOT:PSS) with the spray-coating technique, reaching power conversion efficiency in the rage of 4%. In these cells a fine tuning of the realization parameters such as the solvent used, the substrate temperature, the film thickness, time of spray, distance between sample and airbrush, substrate temperature has been performed. Furthermore different cells architectures will be presented as function of the required characteristics of the substrate and of the electrode deposition. These results point out the spray-coating as a powerful printing technique to be embedded in a R2R process for the realization of flexible organic photovoltaic devices. References [1] C.J. Brabec et al. Organic Photovoltaics: Materials, Device Physics, and Manufacturing Technologies, Wiley-VCH, Weinheim (2008). [2] Konarka Power Plastic (www.konarka.com) [3] Solarmer (www.solarmer.com) [4] J.Nelson, Materials Today, 14 (2011), pp. 462-470 [5] F.C. Krebs et al. Sol. Energy Mater. Sol. Cells 93 (2009), pp. 1968–1977. [6] G.Susanna et al. Sol. Energy Mater.Sol Cells, 93 (2011), pp. 1775-1778.

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B42 - Mechanism of Mobile Charge Carrier Generation in Blends of Conjugated Polymers and Fullerenes: Significance of Charge Delocalization and Excess Free Energy

D. H. K Murthya, Min Gaoa, Martien Vermeulena, Laurens Siebbelesa, Tom Savenijea a, Optoelectronic Materials Section, Department of Ch, Julianalaan 136, Delft, 2628, NL b, Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, NL

Efficient photoinduced generation of charge carriers in blends of soluble conjugated polymers and fullerene derivatives is promising for the development of low-cost bulk-heterojunction solar cells. Despite the fact that these cells with efficiencies over 8% have been realised, the mechanism involved in the photogeneration of mobile charge carriers is still unclear. The microwave photoconductance measurements are performed to investigate the importance of the excess free energy involved in the exciton dissociation process for blends of poly(3-hexyl-thiophene) (P3HT) with monoPCBM and bisPCBM. To this end, the effect of the excitation wavelength (visible to NIR) and of the temperature (88 K to 300 K) on the yield of charge carriers is examined. NIR excitation corresponds to the transition of an electron from the HOMO of the P3HT directly to the LUMO of the fullerene derivative forming the charge transfer band (CT). For P3HT:PCBM, the yield of charge carriers was identical on both visible and NIR excitation, even at 88 K temperature. This observation indicates that the excess energy does not affect the yield of charges for P3HT:PCBM even at 88 K. From these results it is inferred that the binding energy between the electron and hole in a CT state is smaller than thermal energy at 88 K that is in large contrast to previously reported values of 0.3 eV. This is ascribed to efficient charge delocalization, which increases the mean distance between the electron and hole at the interface. For P3HT:bisPCBM, the yield of charges decreases by a factor of three on changing the wavelength from the vis to the NIR. Note that the CT state in P3HT:bisPCBM is energetically matches with the triplet level of the P3HT, owing to its smaller electron affinity as compared to monoPCBM. Therefore, a CT state can recombine to triplet level of P3HT resulting in a reduction of the yield on NIR excitation. However, as the yields for P3HT:PCBM and P3HT:bisPCBM are equall on visible excitation, we conclude that for the latter blend formation of mobile charge carrier occurs primarily via the thermally non-relaxed, hot CT state. These observations indicate that the excess energy involved in the exciton dissociation process is indeed important to avoid recombination of the CT states to the triplet level of the polymer in order to achieve higher yields of charge carrier generation.

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B43- Using excitation transfer and plasmon enhanced excitation transfer for organic thin-film solar cell

Musubu Ichikawaa, Yusuke Imamuraa a, Shinshu Univ., 3-15-1 Tokida, Ueda, 386, JP b, Presto-JST, 4-8-1 Honcho, Kawaguchi 332-0012, JP

In general, organic materials show intense absorption because of their large oscillator strength. Thus, organic materials are very suitable as active materials of photovoltaics. This is because strong absorption leads to reducing the thickness of the active layer. On the other hand, organic materials generally exhibit rather narrower optical absorption bands compared with inorganic semiconducting material which have large electronic band dispersion due to strong electronic coupling. Cells composed of a thin organic semiconductor material layer can only absorb a part of the whole solar spectrum. This leads to making them colorful but brings a limitation of power conversion efficiency. Utilizing several organic semiconductors with different optical absorption is an idea for resolving this limitation. However, if several materials were just mixed for forming a thin-film, this could not work well. This is because a material with the smallest bandgap, in other words, the longest absorption wavelength, among them works as an excitation energy trap. This trap disturbs exciton diffusions, a key process of organic photovoltaics.

Figure 1 Schematic illustration of the concept for improving organic solar cells.

On the other hand, we have demonstrated an organic photovoltaic system based on two or more p-type organic semiconductors. (1) This cell is schematically composed as shown in Fig. 1. In the figure, three different p-type organic semiconductor layers and an n-type layer are laminated, and the bandgaps of the p-type materials sequentially become small toward the n-type layer. This structure enables one-direction excitation energy transferring toward the p3/n junction from the p1 side. The talk will deal about experimental proofs of this organic photovoltaic system, quantum yields of interlayer excitation transfer, and enhancements of interlayer excitation transfer based on plasmon. Furthermore, measurements exciton diffusion length by using the device structure also will be discussed. (2)

References [1]Ichikawa, M.; Suto, E.; Jeon, H.-G.; Taniguchi Y. "Sensitization of Organic Photovoltaic Cells Based on Interlayer Excitation Energy Transfer". Org. Electron. 11, 700-704 (2010). [2]Ichikawa, M. "Measurement of Exciton Diffusion Lengths of Phthalocyanine Derivatives based on Interlayer Excitation Transfer". Org. Electron., (submitted)

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B44 - Formation of N719 Dye Multilayers on Dye Sensitized Solar Cell Photoelectrode Surfaces

Lilian Ellis-Gibbingsa, Viktor Johanssonb, Rick B Walshc, Lars Kloob, Jamie S Quintona, Gunther G Anderssona a, Flinders Centre for NanoScale Science and Technology, Flinders University, GPO Box 2100, Adelaide, 5001, Australia b, Applied Physical Chemistry, KTH Royal Institute of Technology, S-10044 Stockholm, Sweden c, Department of Applied Mathematics, Research School of Physics and Engineering, The Australian National University, Canberra ACT 0200, Australia

The structure of the dye layer adsorbed on the titania substrate in a dye-sensitized solar cell is of fundamental importance for the function of the cell, since it strongly influences the injection of photoelectrons from the excited dye molecules into the titania substrate. The adsorption isotherms of the N719 ruthenium-based dye were both determined with a direct method using the depth profiling technique Neutral Impact Collision Ion Scattering Spectroscopy (NICISS) and with the standard indirect solution depletion method. It is found that the dye layer adsorbed on the titania surface is laterally inhomogeneous in thickness and growth already from low coverage levels involving a combination of monolayers and multilayers. It is also found that the amount of N719 adsorbed on the substrate depends on the titania structure. The present results show that dye molecules in dye-sensitized solar cells are not, as presumed, necessarily adsorbed as self-assembled monolayer on the substrate.

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B45 - Efficient Electron Injection from Organic Sensitizer Dyes Containing an Acyloin-Type Anchor Group

Andreas Bartelt*a, Robert Schütza, Joachim Schaffa, Ivo Kastla, Christian Strothkämpera, Rainer Eichbergera, Gabrielle Nellesb, Gerda Fuhrmannb

a, Helmholtz Center Berlin for Materials and Energy, Hahn-Meitner-Platz 1, Berlin, 14109, DE b, SONY Deutschland GmbH, Hedelfinger Straße 61, DE

In a dye-sensitized solar cell the interaction between the dye and the semiconductor surface is a determining factor for the overall efficiency of the photovoltaic device. The dye has to be stably attached to the semiconductor surface, and the electron injection from the excited dye into the conduction band of the oxide must be efficient. This dye-oxide interaction is mediated by an anchor group. Most sensitizer dyes reported today contain carboxylic acid anchor groups. Recently, a new highly efficient acyloin-type anchor group and a new class of metal-free sensitizer dyes comprising this new anchor group were reported. DSSCs fabricated with these so-called Semi-squarylium dyes show remarkable performances particularly with regard to incident photon-to-current efficiencies. Here we report on the injection properties of these Semi-squarylium dyes.

Figure 1

We will show ultrafast electron injection processes of ~100 fs upon photo-excitation,indicating a very good electronic coupling between the dye and TiO2due to the direct participation of the anchor group in the conjugated p-system of the chromophore. The high performance of the new acyloin-type anchor group is demonstrated by comparison with an indoline dye (D131) of similar optical characteristics, which has a conventional carboxylic acid anchor. Furthermore, the electron injection effect of various donors systematically attached to the main core of the dye molecules will be presented. A comparison of fs-transient absorption and optical-pump terahertz-probe spectroscopy results provides insights into the ultrafast injection processes from both the molecular dye and the semiconductor side.The different injection dynamics will be connected to results obtained from photoelectron spectroscopy and DFT calculations of electron density distributions within the molecules.

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B46- FEMTO- to Milisecond Dynamics of Selected Squaraines Embedded in TIO2 Nanoparticles Thin Films and Solar Cells

Gustavo de Miguela, Maria jose Marchenaa, Marcin Zioleka, Shyam Pandeyb, Shuzi Hayaseb, Abderrazzak Douhala a, university of Castilla La Mancha, Departamento de Quimica Fisica, Facultad del Medio, Toledo, 45071, ES b, Kyushu Institute of Technology, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu, Kitakyushu, Japan, JP

Photodynamic of three types of squaraines (SQs) [1,2] molecules deposited onto quartz substrates and embedded in TiO2nanoparticle thin films [3] have been studied by means of steady-state and time-resolved absorption techniques with the aim of a better understanding of their excited state properties. In pure SQs thin films, the formation of two species at the excited state, monomer and H- or J-aggregates was proved. Non-exponential fit of the experimental time profiles together with the power-dependence of the transient absorption signal makes us to propose a singlet-singlet annihilation process to account for the rapid deactivation of the aggregate excited state. In SQs embedded in TiO2nanoparticles thin films, we only detected the formation of H-aggregates and monomer species. However, co-adsorption of the chenodeoxycholic acid (CDCA) additive eliminates considerably the aggregation. Femtosecond transient absorption measurements revealed competition between the charge injection and the annihilation process in the samples without the CDCA, which reduces the efficiency of the system. However, in the samples with CDCA, charge injection is quantitative.

Figure 1 Femtosecond transient absorption (left) and nanosecond flash photolysis (right) decays of the three SQs in TiO2 thin films with the CDCA additive, representing the charge injection and recombination, respectively.

On the other hand, rate constant for charge recombination turned out to be one order of magnitude higher for the samples with CDCA, which leads to slower recombination in the samples exhibiting the aggregates. We will also discuss the fs to ms electron injection and recombination processes using the real cells of the used SQs, and give a full picture on the effect of aggregates on their working electron channels.

Acknowledgements: This work was supported by the MICINN through project MAT2008-01609 and PLE-2009-0015. G. M. thanks the Ministerio de Ciencia e Innovación for a “Juan de la Cierva” postdoctoral fellowship.

References [1] L. Beverina, P. Salice, Eur. J. Org. Chem. 2010, 1207. [2] G. de Miguel, M. Marchena, M. Zitnan, S. S. Pandey, S. Hayase and A. Douhal, Phys. Chem. Chem. Phys., 2012, 14, 1796. [3] G. de Miguel et al. J. Phys Chem. C, submitted for publication.

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B47- Consistent physics-based modeling of DC and small-signal behavior of dye-sensitized solar cells under different illumination conditions

Shuai Maa, Federica Cappellutia, Giovanni Ghionea, Adriano Saccob, Diego Puglieseb, Andrea Lambertib, Elena Tressoc a, Department of Electronics and Telecommunications, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, 10129, IT b, Center for Space Human Robotics @PoliTo, Istituto Italiano di Tecnologia, Corso Trento 21, Torino, 10129, IT c, Applied Science and Technology Department, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, 10129, IT

The development of physics-based tools able to consistently predict the cell behavior under different operating conditions is a key issue toward the technological development of dye-sensitized solar cells (DSSCs), since it may provide deeper understanding of the many physical mechanisms involved in the cell operation and their interplay [1-3]. In this contribution we investigate through experiments and device-level numerical simulations, the static and dynamic small-signal behavior of DSSCs with different architectures and under different illumination conditions. The adopted model exploits a mixed-mode approach where electron transport through the nanoporous dyed TiO2 film is described by a diffusion transport model, including non-uniform optical generation [1-2], electron trapping mechanisms [4] and recombination with iodine species in the electrolyte and/or oxidized dye molecules [3], while electrical loss induced by contacts, electrolyte, and series parasitic paths are modeled by compact equivalent circuit elements. The cells analyzed in this study were fabricated following a standard procedure, with a layer of dye sensitized TiO2 nanoparticles as photoanode, a counter electrode constituted by a FTO-covered glass coated with a thermally evaporated Pt thin layer, I3-/I- redox electrolyte, and a thermoplastic polymer as sealing material. The devices were characterized through I-V measurements under AM1.5G solar simulator, Electrochemical Impedance Spectra (EIS) under AM1.5G illumination and in dark condition (bias voltages from 0 to 0.8 V, frequency range 10-1 – 105 Hz), and Incident Photon-to-electron Conversion Efficiency (IPCE) spectra acquired in DC mode using a 150W Xenon halogen lamp and a dual grating Czerny Turner monochromator.

Figure 1 Comparison between measured and simulated performance. Left: IPCE for photoelectrode-side (PE) and counter-electrode-side (CE) illumination; Center: I-V under AM1.5G sun simulator; Right: Small-signal impedance of the TiO2 film under AM1.5G sun simulator for PE illumination at bias voltage from 0.55 to 0.8 V with 0.05 V step (parasitic series resistance, electrolyte and counter electrode contribution have been de-embedded).

The model is applied to analyze the impact of different technological parameters (TiO2 layer thickness, used dye, cell total thickness) on the cell operation. As an example, Fig. 1 shows a comparison between experiments and simulations of a cell with 7 um thick TiO2 film and N719 dye. All the reported simulations (I-V, IPCE, and EIS) exploit the same set of physical parameters, and predict the overall cell behavior consistently and with good accuracy, under both directions of illumination. The cell shows a comparatively low IPCE with respect to the photovoltaic performance. This has been attributed to low collection efficiency under weak

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incoming light, as also suggested by the significant dependence of the IPCE spectra on the illumination direction. Among the key features of the model exploited is the presence of nonlinear recombination [3]. In the full paper we will provide a preliminary discussion on the correlation of such a model with the DSSC physics. References [1] S. Wenger, M. Schmid, G. Rothenberg, A. Gentsch, M. Graetzel, J.O. Schumacher, "Coupled Optical and Electronic Modeling of dye-sensitized solar cells for steady-state parameter extraction", J. Phys. Chem. C, 115, 10218-10229 (2011). [2] J. Halme, G. Boschloo, A. Hagfeldt, P. Lund, "Spectral Characteristics of light harvesting electron injection, and steady-state charge collection in pressed TiO2 dye solar cells", J. Phys. Chem. C, 112, 5623-5637 (2008). [3] P. R. F. Barnes, A. Y. Anderson, J. D. Durrant, B. C. O'Reagan, "Simulation and measurement of complete dye sensitised solar cells: including the influence of trapping, electrolyte, oxidised dyes and light intensity on steady state and transient device behaviour", Phys. Chem. Chem. Phys, 13, 5798-5816 (2011). [4] J. Bisquert, "Doubling Exponent Models for the Analysis of Porous Film Electrodes by Impedance. Relaxation of TiO2 Nanoporous in Aqueous Solution",J. Phys. Chem. B, 104, 2287-2298 (2000).

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B48 - Time-resolved Indirect Nanoplasmonic Sensing spectroscopy of dye molecule interactions with dense and mesoporous TiO2 films

Viktoria Gusaka, Leo-Philipp Heinigerb, Michael Graetzelb, Christoph Langhammera, Bengt Kasemoa a, Department of Applied Physics, Chalmers University of Technology, , SE-412 96 Göteborg b, Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, Station 6, CH-1015 Lausanne, CH

The properties of the adsorbed monolayer of dye molecules on the mesoporous TiO2 photoelectrode are crucial to the dye-sensitized solar cell (DSC) function and efficiency. The important characteristics include the density of molecules in the monolayer, their stability toward desorption, and also time and kinetics of the monolayer formation. In this work we use a novel Hidden Interface – Indirect Nanoplasmonic Spectroscopy (HI-INPS) technique to study dye diffusion and adsorption kinetics locally within mesoporous TiO2 films of the kind used in DSCs. The HI-INPS technique employs the phenomenon of localized surface plasmon resonance in metal nanoparticles. The spectral position of the resonance is sensitive to minute changes in the dielectric function of the very close (typically extending up to about 50 nm) environment around the plasmonic nanoparticle. By placing such particles (gold in this work) at the mesoporous TiO2 film – support interface, we demonstrate a local sensitivity of the plasmon resonance to dye molecule adsorption and desorption inside a 10 μm thick TiO2 film, at the internal hidden interface.1 We showed that it takes 15-50 minutes to fully impregnate the mesoporous TiO2 film with dye molecules, the impregnation time being dependent on the film thickness and pore/particle size. The HI-INPS technique provides a new type of information, which is valuable for optimizing the dye monolayer formation in the DSC research.1 In a more general context, the HI-INPS approach can provide new insights into diffusion/adsorption kinetics in a broad range of other (meso-)porous systems. Using standard INPS,2 we were furthermore able to analyze the dye adsorption/desorption kinetics of a dye monolayer on thin (<70 nm) dense TiO2 films. Langmuir-like monolayer formation kinetics with saturation on a time scale of the order of 100 s, i.e., much shorter than for the mesoporous samples, were found.1 For dense films the adsorption-desorption kinetics, saturation times and adsorbed dye amounts can be studied in detail with minimized influence of transport effects. The INPS approach is generic and can easily be extended to other surface-adsorbate systems. References [1] Gusak, V,; Heiniger, L.-P.; Graetzel, M.; Langhammer C.; Kasemo, B. "Time-resolved Indirect Nanoplasmonic Sensing spectroscopy of dye molecule interactions with dense and mesoporous TiO2 films" Submitted. 2. [2] Langhammer, C.; Larsson, E. M.; Kasemo, B.; Zoric, I. "Indirect Nanoplasmonic Sensing: ultrasensitive experimental platform for nanomaterials science and optical nanocalorimetry" Nano Letters 10, 3529–3538 (2010).

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B49 - Hybrid inorganic nanocrystal – polymer solar cells: new device concepts and improved fundamental understanding of device function

Saif Haque, Simon Dowland, Luke Reynolds, Neha Bansal, Andrew Maclachlan, Thierry Lutz, Flannan O'Mahony Centre for Plastic Electronics and Department of Chemistry, Imperial College London, South Kensington, London, GB

Hybrid solar cells that comprise both organic and inorganic semiconductor materials are emerging as a promising power generation technology. This primarily stems from the attractive possibility to design devices that take advantage of the versatility and processability of organic materials and the superior electronic properties of inorganic semiconductors. The design of efficient hybrid inorganic- organic solar cells critically depends on the ability to control the charge photogeneration efficiency at the donor-acceptor heterojunction. In this talk I will report some of our recent work aimed at better understanding of the mechanisms of charge photogeneration in inorganic-organic heterojunction solar cells. In particular we will consider the influence of key parameters such as interfacial energetics and thin film nanomorphology on the charge photogeneration yields and lifetimes. These studies will be complimented by device fabrication and characterization. A key aim of this work is to develop quantitative structure-function relationships that can be used to guide the design of hybrid heterojunctions for high performance solar cells. In this talk I will also report some of our recent work addressing the development of new nanofabrication approaches for hybrid polymer – nanocrystal solar cells. Here we will focus on a promising approach based on the in-situ growth of inorganic nanoparticle networks directly in polymer films.

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B50 - Co(III) complexes as p-type dopants for organic semiconductors and their application in Solid-State Dye-Sensitized Solar Cells

Julian Burschka, Amalie Dualeh, Florian Kessler, Etienne Baranoff, Ngoc-Lê Cevey-Ha, Chenyi Yi, Mohammad K. Nazeeruddin, Michael Grätzel Ecole Polytechnique Fédérale de Lausanne, Station 6, Lausanne, 1015, CH

During the last two decades, the Dye-sensitzed Solar Cell (DSC) has emerged as one of the most promising alternatives to cost-intensive Silicon-based photovoltaic devices. However, one of the major drawbacks of the DSC technology is the use of a liquid electrolyte that requires meticulous encapsulation and leads to poor long-term stability. This issue demands the development of an all solid-state Dye-sensitized solar cell (ssDSC), where the liquid electrolyte is replaced by a solid hole-transporting material (HTM) such as the commonly employed 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene (spiro-MeOTAD). Several advantageous properties make spiro-MeOTAD a suitable candidate for ssDSCs, although it is well known that the electrical conductivity of the pristine material is too low to achieve high performance.

Figure 1

In this context we report on the use of Co(III) complexes – in particular tris(2-(1H-pyrazol-1-yl)pyridine)cobalt(III) – to carefully control the charge transport properties of spiro-MeOTAD in ssDSCs via p-type doping. We show that the proposed compounds fulfill the necessary requirements for this application and investigate the influence of the doping ratio on photovoltaic performance. In this manner, we give evidence that the controlled one-electron oxidation of spiro-MeOTAD using molecular p-dopants is capable of competing with generally employed photo-doping, the latter clearly being a process that is not easy to control. By combining p-doped spiro-MeOTAD with a recently developed high-molar extinction coefficient organic D-pi-A sensitizer, we finally reached a new record power conversion efficiency of 7.2% measured under standard solar conditions (AM1.5G, 100 mW cm-2). (1) References [1] Burschka, J.; Dualeh, A.; Kessler, F.; Baranoff, E.; Cevey-Ha, N.-L.; Yi, C.; Nazeeruddin, M. K.; Grätzel, M. "Tris(2-(1H-pyrazol-1-yl)pyridine)cobalt(III) as p-Type Dopant for Organic Semiconductors and Its Application in Highly Efficient Solid-State Dye-Sensitized Solar Cells". J. Am. Chem. Soc. 133, 18042–18045 (2011).

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B51- Impedimetric probing of recombination kinetics in ZnO nanorod array/poly(3-hexylthiophene) solar cells

Bert Coningsa, Linny Baetenb, Hans-Gerd Boyena, Donato Spoltorea, Marlies K. Van Baelb, Jean V. Mancaa a, Hasselt University - Institute for Materials Research, Materials Physics, Wetenschapspark 1, Diepenbeek, 3590, BE b, Hasselt University - Institute for Materials Research, Inorganic and Physical Chemistry, Agoralaan Building D, Diepenbeek, 3590, BE

It is well established that for organic solar cells, non-geminate recombination is the main loss mechanism that limits their open-circuit voltage.1,2 For hybrid (metal oxide/polymer) solar cells, however, recombination related studies are still scarce, and there is no certainty to what extent the loss mechanisms of this type of devices coincide with the fully organic case. To optimize also hybrid solar cells in a systematic fashion, likewise the understanding of recombination dynamics in these devices should be better. In this work, we use impedance spectroscopy under varying light intensity to show that the recombination kinetics of hybrid solar cells based on ZnO nanorod arrays and poly(3-hexylthiophene) (P3HT) behave very similarly to the widely investigated fully organic P3HT:PCBM devices. We demonstrate the compatibility of our hybrid solar cells with a model, able to predict the open-circuit voltage, which was recently developed for organic solar cells (see Figure).1

Figure 1 Comparison of measured and calculated open-circuit voltages for a selection of cells.

Additionally, we show how the morphology of solely the nanorod array or the P3HT has a signature impact on charge carrier densities and lifetimes.

References [1] Credgington, D.; Hamilton, R.; Atienzar, P.; Nelson, J.; Durrant, J. R. "Non-Geminate Recombination as the Primary Determinant of Open-Circuit Voltage in Polythiophene:Fullerene Blend Solar Cells: an Analysis of the Influence of Device Processing Conditions". Adv. Funct. Mater. 21, 2744-2753 (2010). [2] Cowan, S. R.; Roy, A.; Heeger, A. "Recombination in Polymer-Fullerene Bulk Heterojunction Solar Sells". J. Phys. Rev. B 82, 245207 (2010)

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B52- Energy Level Alignment in Hole Transporting Molecular Layers studied with Hard X-ray Photoelectron Spectroscopy

Rebecka Schölina, Martin H. Karlssonb, Susanna K. Erikssonb, Johan Oscarssona, Hans Siegbahna, Erik M. J. Johanssonb, Håkan Rensmoa a, Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden b, Department of Physical and Analytical Chemistry, Uppsala University, Box 259, SE-751 05 Uppsala, Sweden

Dye-sensitized solar cells, and their solid state equivalent, are nowadays a large research field. For the solid state devices that uses a hole conducting molecule, or polymer, instead of a liquid electrolyte, there are though still some work before they can compete in efficiency with the liquid analogues. Important for the photocurrent and photovoltage in the solar cell is the relation between the energy levels in the different materials. Oxide material, dye molecule and/or hole conductor can be changed in order to manipulate the energy alignment. Other ways are by using different additives, dopants or small dipole molecules, to name a few. This study shows how direct measurements of the energy levels and their alignment can be performed using X-ray photoelectron spectroscopy (XPS). In focus of the study is hole conducting molecules, such as spiro-OMeTAD and P3HT and how changes of the position of the energy levels in these materials can be achieved with additives or dipole molecules. By measuring photoelectron spectroscopy using X-rays with high energy, so called hard X-rays (the technique is called HArd X-ray PhotoElectron Spectroscopy, HAXPES), it is possible to study buried interfaces in a nondestructive way. HAXPES is also convenient for measurements where one would like to minimize direct spectroscopic effects from surface structures which otherwise could be a reason for energy level shifts seen in normal XPS. Measurements have been performed at the synchrotrons BESSY II in Berlin (Germany) and MAXlab in Lund (Sweden). The convenience of using hard X-rays was shown in a study of P3HT/dipole molecule/ TiO2 interfaces where direct measurements of the energy levels in the interfaces were achieved (1). Measurements of spiro-OMeTAD with and without the additive Li-TFSI showed that the Li-salt shifts the Fermi level towards the HOMO in spiro-OMeTAD. The effect of adding Li-TFSI is hence the same as p-doping of the molecule. This could be confirmed with absorbance measurements where a contribution from oxidized spiro-OMeTAD could be observed. By varying the photon energy of the X-rays, it could also be concluded that there is a concentration gradient of Li-TFSI in the spiro-OMeTAD film, with a larger amount of salt closer to the surface of the molecular film. In the solid state dye-sensitized solar cells, this means that the spiro-OMeTAD is oxidized in the presence of Li-TFSI, and that the concentration of Li-salt is as highest at the interface between the hole transport material and the counter electrode. References [1] Johansson, E. M. J.; Schölin, R.; Siegbahn, H.; Hagfeldt, A.; and Rensmo, H. "Energy level alignment in TiO2/dipole-molecule/P3HT interfaces". Chemical Physics Letters 515, 146-150 (2011).

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C1 - Picosecond electron injection in optimised dye-sensitised solar cells with visible-pump mid-infrared-probe transient absorption spectroscopy Mindaugas Juozapaviciusa, Brian C. O’Regana, Marius Kaucikasb, Jasper J. van Thorb

a, Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom b, Division of Molecular Biosciences, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom

Femtosecond transient absorption spectroscopy of samples closely resembling complete

dye-sensitised solar cells is reported. A visible-pump infrared-probe system is utilized with a 1.5 ns delay line. In the presence of an inert acetonitrile solvent, a freshly prepared mesoporous TiO2 film with a highly acidic N3 dye exhibits femto to several picosecond injection dynamics. When the acetonitrile is replaced with an electrolyte optimized for highest power conversion efficiency, the injection dynamics become significantly slower, with ~50% of the injection occuring on the ~500 ps timescale. The same slower kinetics are observed on samples in both redox active and inactive electrolytes, with films dyed with a less acidic N719 solution. Similar results are reported for an organic dye D149. Low laser light intensities were used in these experiments, with a photon flux similar in magnitude to what the solar cell would see at one sun illumination to obtain practical conditions.

If the frequently used high intensity pump pulses are used for excitation, ultrafast kinetics can be observed on all samples.To further reduce possible charging effects, the samples were spatially translated to guarantee that no spot on the cell is hit by more than 2 laser pulses every 5 minutes. At low pump pulse intensities, injection kinetics are found to be invariant in a range of light intensities and spatial translation speeds.

These results support the assertion that injection is quite sensitive to conduction band edge shifts and high power conversion efficiency devices will have injection occuring on hundreds of picoseconds. These kinetics were observed to be just fast enough to compete efficiently with the dye luminescence lifetime.

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C2 - Organic Photovoltaic Cells based on Trilayer Graphene Oxide

Abd Rashid Mohd Yusoff, Hyeong Pil Kim, Jin Jang Kyung Hee University, Dongdaemoon-ku, Seoul, 130, KR

In this contribution, we report the solution-processed trilayer graphene served as an anode interfacial layer in organic photovoltaic cells (OPVs). The OPVs employing indium zinc oxide (IZO), indium zinc oxide/graphene oxide (IZO/GO), and graphene oxide/indium zinc oxide (GO/IZO) exhibited the conversion efficiency of 3.4, 3.5 and 3.9%, respectively. When operated at room temperature, no obvious degradation was observed from the OPVs with the GO layer after continuously illuminating the devices for 5 h. Though, a significant degradation was observed from the OPVs without the GO hole transport layer (HTL) after illuminating the devices for only 1 h. All these results demonstrate that the GO HTL plays an important role in the enhancement of OPV’s performance with conventional device architecture.

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C3 - Fabrication of Ag Nanoparticles Embedded TiO2 Nanotubes using Electrospun Nanofibers for Plasmonic Enhanced Solar Cells

Mi-Hee Junga, Moo-Jung Chub a, Thin Film Solar Cell Technology Research Team, Advanced Solar Technology Research Department, Convergence Components and Materials Research Laboratory, Electronics and Telecommunications Research Institute, 138 Gajeongno, Yuseong-gu, , Daejeon , 305-700, KR b, Package Research Team, Advanced Solar Technology Research Department, Convergence Components and Materials Research Laboratory, Electronics and Telecommunications Research Institute, 138 Gajeongno, Yuseong-gu, , Daejeon , 305-700, KR

Electrospun polyethylene oxide(PEO) fibers and an Ag nanoparticles(NPs) composite were used as a soft template for coating TiO2 via an atomic layer deposition technique. While the as-deposited TiO2 layers onto PEO and Ag NPsfibers were completely amorphous with atomic layer deposition, the TiO2 layers were properly converted into Ag NPsembedded polycrystalline TiO2 nanotubes (NTs) after calcination. We demonstrate that the Ag NPsembedded TiO2 NTs are corrosion resistant in the electrolyte and have no apparent detrimental electronic consequences in the solar cells in terms of charge recombination. Through both electronic and spectroscopic analyses, we demonstrate enhanced photocurrent generation and solar cell performance as a result of the intense electromagnetic field of the dye from the surface plasmon effect due to the metal Ag NPs.

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C4 - Highly efficient semitransparent organic solar cells with sputtered ZnO:Al cathodes: Influence of light management at the transparent electrode

Andreas Bauer, Tina Wahl, Jonas Hanisch, Erik Ahlswede Centre for Solar Energy and Hydrogen Research Bade, Industriestr. 6, Stuttgart, 70565, DE

Research in organic photovoltaics (OPV) has become a fast emerging field over the last years due to its potential for cheap and fast mass production while also being lightweight and flexible. These properties make OPV suitable not only for mobile applications but also for building integrated applications. Semitransparent organic solar cells can expand the range of application even to energy-harvesting windows. Furthermore, tandem solar cells also require semitransparent solar cells which allow the transmitted light to generate current in the second cell. For these purposes semitransparent electrodes are needed and have to be deposited on top of an organic layer. A cheap and suitable material comprising high transmittance as well as high conductivity is aluminum doped ZnO (ZAO). However, sputtering is required for deposition of ZAO and will damage the underlying organic layer leading to low power conversion efficiencies. For that reason, a sol-gel processed TiOx electron transport layer (8 nm) was coated on top of a thin (70 nm) organic PCDTBT:PC71BM (poly[[9-(1-octylnonyl)-9h-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]: [6,6]-phenyl-C71-butyric acid methyl esters) absorber layer to protect it from sputter damage during the subsequent sputtering of a thin aluminum interlayer (ALI) and the ZAO cathode.

Figure 1 (a) Impact on the reflectance exclusively by the ALI/ZAO cathode at different ALI thicknesses. (b) Transmitted spectrum of semitransparent solar cells altered according to the upper image, using either thick (130 nm) or thin (70 nm) absorber layers.

We show that the light management inside the active layer and hence the solar cell efficiency can be engineered by adjusting the reflectivity of the transparent electrode. By increasing the ALI thickness, the solar cell’s short circuit current increases because a higher fraction of light is reflected at the back contact, leading to higher power conversion efficiencies of up to 4.0 % (average) for the thickest ALIs but low transmittance above 700 nm wavelength. Furthermore, the absorption could be improved in devices with thicker (130 nm) absorber layers. In these thicker devices, the ALI thickness was of minor importance regarding the power conversion efficiency which remained at 3.9 % (average) similar to the power conversion efficiency of 70 nm absorber layer devices utilizing thick ALIs. Since the thick absorber device’s performance does not depend on the ALI thickness, the usage of thin ALIs allows moreover a high transmittance above 700 nm wavelength.

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C5 - Oriented nanowire arrays with high aspect ratios for solid-state dye-sensitized solar cells

Florian Aurasa, Vivian Carolina Farías Riverab, Ilina Kondoferskya, Thomas Beina a, Department of Chemistry & Center for Nanoscience, Ludwig-Maximilians-University Munich, Butenandtstr. 11, Munich, 81377, Germany b, Current Adress: Center for Space Human Robotics, Istituto Italiano di Tecnologia, Corso Trento 21, Turin, 10129, Italy

Ordered arrays of zinc oxide nanowires have attracted much attention as substitutes for particle-based TiO2 photoanodes in dye-sensitized solar cells (DSCs). While ZnO-nanowire-based DSCs that use an I2/I3

- electrolyte have reached photovoltaic conversion efficiencies of several percent,(1,2) the efficiency of solid-state DSCs remains below 1 %.(3) One of the reasons for this is the incomplete light absorption due to much lower surface area of short nanowire arrays, which limits the maximum achievable photocurrent.

Figure 1 a) 1.4 µm thick high aspect ratio nanowire array; b) nanowire array grown on a pre-formed blocking layer.

Our research focuses on the synthesis of dense, vertically oriented nanowire arrays with a high aspect ratio for maximum surface area. We developed a synthesis protocol for the rapid growth of nanowires while completely suppressing the formation of precipitates in solution. Nanowire arrays grown by this method can reach aspect ratios of above 40 at a nanowire length of only 2 µm (Figure 1). Control of the composition and pH of the growth solution enables us to tune the nanowire shape, density and dimensions. We achieved the synthesis of dense and oriented blocking layers of defined thickness through an intermediate step before nanowire growth. The absence of any adhering precipitate makes our nanowire arrays ideal candidates for photoanodes in efficient solid-state DSCs and extremely thin absorber cells. References [1] Law, M.; Greene, L. E.; Johnson, J. C.; Saykally, R.; Yang, P. "Nanowire dye-sensitized solar cells". Nature Mater. 4, 455-459 (2005). [2] Xu, C.; Shin, P.; Cao, L.; Gao, D. "Preferential Growth of Long ZnO Nanowire Array and Its Application in Dye-Sensitized Solar Cells". J. Phys. Chem. C 114, 125-129 (2010). [3] Plank, N. O. V.; Howard, I.; Rao, A.; Wilson, M. W. B.; Ducati, C.; Mane, R. S.; Bendall, J. S.; Louca, R. R. M.; Greenham, N. C.; Miura, H.; Friend, R. H.; Snaith, H. J.; Welland, M. E. "Efficient ZnO Nanowire Solid-State Dye-Sensitized Solar Cells Using Organic Dyes and Core-shell Nanostructures". J. Phys. Chem. C 113, 18515-18522 (2009).

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C6 - Donor-Acceptor Substituted Aza-BODIPYs for Molecular Bulk Heterojunction Solar Cells: Synthesis and Optical Properties

Emad Al-Imaraha, Peter J. Derrick a, Shane G. Telfera, Ashton Partridgeb a, MacDiarmid Institute for Advanced Materials and Nanotechnology, Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand b, Chemical and Materials Engineering, The University of Auckland, Auckland, New Zealand

The use of small molecules for bulk heterojunction (BHJ) solar cells is attractive comparing with their polymer counterparts. Their advantages include well defined molecular structure and molecular weight, as well as showing great prospect in large-scale and low-cost organic solar cell commercialization applications.[1] Boron-chelated tetraarylazadipyrromethenes (Aza-BODIPYs) are promising materials for photovoltaic applications because of their excellent spectral properties such as high extinction coefficients in the visible region (70000-80000 M-1 cm-1) and large fluorescence quantum yields.[2]

Figure 1 Terthiophene substituted Aza-BODIPY dyes

New terthiophene substituted Aza-BODIPY dyes have been synthesized under standard conditions. Their optical properties have been characterized by UV–VIS absorption and fluorescence spectroscopies. These dyes showed an absorption in the NIR region with high molar extinction coefficients. Terthiophene substituted Aza-BODIPY exhibit emission spectral maxima at around 734 nm. Intermolecular charge transfer from 2 to PCBM has been confirmed by a fluorescence quenching study. Future direction of this work will be synthesizing a range of other donor-acceptor Aza-BODIPYs and implementing them in bulk heterojunction solar cells.

References *1+ Haijun Fan, Huixia Shang, Yongfang Li, and Xiaowei Zhan.”Efficiency enhancement in small molecule bulk heterojunction organic solar cells via additive”. Applied Physics Letters 97, 133302 (2010). *2+ Tasior, M.; O'Shea, D. F. “BF2-Chelated Tetraarylazadipyrromethenes as NIR Fluorochromes” Bioconjugate Chem. 21, 1130–1133 (2010).

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C7 - Inorganic Solution Processed Nanoparticle Solar Cells

Noel Duffy, Jacek Jasieniak, Brandon MacDonald, Anthony Chesman, Scott Watkins CSIRO, Bayview Ave, Clayton, 3169, AU

Inorganic semiconductors are ideal for long lifetime and efficient solar cells due to their thermal and photo stability, are spectrally broad absorbers and do not have sealing issues associated with rival approaches. One major disadvantage of bulk inorganic semiconductors is their difficultly in processability compared to solution soluble materials. Recently we described the use of 1-10 nm CdTe inks to fabricate efficient, solution processed solar cells.1 These devices use significantly less material (< 500 nm film thickness) than conventional inorganic semiconductor devices, typically 3000nm. Moreover they are also amenable to deposition on flexible substrates.

Figure 1 (a) CZTS nanoparticles (~12 nm diameter, the smallest circle containing the triangular nanocrystals), (b) i-V response to chopped light (1s on, 1s off) for a variety of thin film CZTS nanoparticles immobilised on ITO coated glass.

We are currently focusing on utilizing alternative inorganic materials, based on CIGS and CZTS nanopartilce inks, and printed device architectures. Characterisation of these thin films by techniques such as photoelectron spectroscopy in air (PESA) will be presented along with the photoelectrochemisty and device performance of the normal and inverted architectures. Photoelectrochemistry has proven to be valuable in investigating the effect of morphology and electronic properties of the solution deposited and annealed nanoparticles.

References [1] Jacek Jasieniak, Brandon I. MacDonald, Scott E. Watkins, Paul Mulvaney. Nano Lett., 2011, 2856

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C8- Modification of surface defects in vertically-aligned ZnO nanostructures to improve power conversion efficiency of dye sensitized solar cells

Irene Gonzalez-Vallsa, Juan A. Reparazb, Frank Guellc, Markus R. Wagnerd, Gordon Callsend, Belen Ballesterosa, Axel Hoffmannd, Monica Lira-Cantua a, Nanoscience and Nanotechnology Research Center (CIN2), ETSE, Campus UAB, Bellaterra, Barcelona, 8193, ES b, Institut de Ciència de Materials de Barcelona (CSIC), Esfera UAB, Bellaterra (Barcelona), E-08193, ES c, M-2E. IN2UB, Department d'Electrònica, Universitat de Barcelona, C/Marti i Franques 1. Barcelona E- 08028, ES d, Institut fur Festkorperphysik, Technische Universitat Berlin, Hardendergstr. 36, 10623 Berlín, GE

The application of vertically-aligned ZnO nanoforms (e.g. nanorods, nanowires, nanotips) in Dye sensitized solar cells has evolved slowly in the past years due to the low power conversion efficiencies (PCE) obtained. The causes behind the low PCE have been attributed to the low surface area of the ZnO NRs (which results in low dye loading capacity), the chemical instability of the ZnO in acidic media, or the high amount of surface defects (which translates in high recombination and low photovoltaic performance). All these issues have limited the efficiency of DSCs applying ZnO NRs to no more than 2.5% with electrode thickness ranging between 10 µm - 40 µm. Different strategies have been implemented in order to overcome these limitations. For example, the synthesis of branched nanorods (nanoforest, nanotrees) have been applied in order to increase surface area, the application of neutral organic Dyes to reduce ZnO solubility and stability problems, or the application of different nanoforms, e.g. core-shell nanostructures, where a thin layer of an inorganic semiconductor shapes an outer protective layer against corrosion. All these strategies have improved the final photovoltaic performance of the ZnO-based DSCs though the addition of extra synthesis steps or external aids, but have not uncovered a solution towards the fundamental problems that attain the ZnO intrinsic properties. In this work, we have modified the chemical bath deposition method applied for the synthesis of vertically-aligned NRs at low temperature.

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Figure 1 Vertically-aligned ZnO nanorods synthesized by the chemical bath deposition method at low temperature and by a modification of the same (new method). Application in Dye sensitized solar cells.

We have introduced two factors: pressure and temperature. We will demonstrate that this slight modification of the synthesis method results in vertically-aligned ZnO nanorods with higher volumetric storage properties, which translates into higher dye loading capacity and higher power conversion efficiencies when applied in DSCs. Our results show that, for the same growth time and applying the new synthesis methodology, the resulting vertically-aligned ZnO NRs are 1/5 of the original length with 60% enhancement in power conversion efficiency. The latter is attributed to the modification of the growth mechanism which results in highly homogeneous and thin NRs, and high packing density electrodes. Analyses by photoluminescence (PL) and time-resolved photoluminescence (TRPL), reveals a decrease on the surface defects of the ZnO Nanorods obtained by the modified synthesis technique. The improved efficiency has also been observed when the ZnO NRs are applied in organic solar cells with efficiencies around 2.5% for 3 µm electrode thickness.

References [1] Gonzalez-Valls, I. and Lira-Cantu, M. Vertically-aligned ZnO nanostructures for Excitonic solar cells: a review. Energy Environ. Sci., 2 (2009), 19. [2] Gonzalez-Valls, I.; Yu Y,; Ballesteros, B.; Oro, J.; Lira-Cantu, M. Synthesis conditions, light intensity and temperature effect on the performance of ZnO nanorods-based Dye sensitized solar cells. J. Power Sources. 196 (15), (2011) 6609-6621 [3] Gonzalez-Valls, I. and M. Lira-Cantu, M. Energy Environ. Sci., 3 (2010), 789.

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C9 - Plamonics in nanostructured organic solar cells

Thomas Pfadlera, Lukas Schmidt-Mendea, Ricky Dunbarb a, Faculty of Physics - Hybrid Nanostructures, Amalienstr. 54, Sommerfeldkeller, Munich, 80799, DE b, Department of Physics, Universitätsstrasse 10, Constance, 78457, DE

Organic solar cells have the potential to become an important low-cost alternative to conventional solar cells. However, before this can happen, the energy harvesting potential of organic solar cells must become more comparable with that of the pervading technology. This research is based upon the construction of organic solar cells that demonstrate highly favourable light-plasmonic coupling at a nanostructured silver electrode. These nanostructured silver electrodes are prepared via nanoimprint lithography (NIL) and optimised to improve the light harvesting of organic thin-film solar cells. Simplified absorption samples are prepared and the influence of nanostructuring on spectral reflectance is examined in detail. Absorption enhancements up to 40% are found. The influence of a nanostructured backelectrode on solar cell performance is characterized in terms of IV-and EQE-measurements. Our recent results on the organic solar cells with this nanostructured backelectrode are presented.

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C10 - All-aromatic Triphenylamine-based Poly(azomethine)s as Hole Transport Materials for Polymer Photovoltaics

Michiel Petrusa, Ricardo Bouwera, René Kistc, Neil Greenhamc, Theo Dingemansa a, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, Delft, 2629 HS, NL b, Dutch Polymer Institute (DPI), ), P.O. Box 902, 5600 AX Eindhoven, NL c, Opto-electronics Group, University of Cambridge, Opto-electronics Group, Cavendish Laboratory, J.J. Thomson Avenue, UK

In the last years a wide range of low band gap hole-transporting polymers have been published, which are mostly synthesized via Suzuki and Wittig type of reactions. These chemistries, however, require stringent reaction conditions, i.e. one needs to exclude moisture and oxygen, and expensive metal catalysts and monomers are required. In our previous work we demonstrated that a series of hole-transporting triphenylamine-based poly(azomethine)s could be synthesized via well-known polycondensation chemistry using cheap and readily available starting materials. 4,4’-Diaminotriphenylamine (TPA) was polymerized in a simple one-step process with 2,5-thiophenedicarboxaldehyde (25Th) with water being the only side product. A photovoltaic device based on a TPA-25Th/PCBM blend (1:3) showed an external quantum efficiency (EQE) of 21% at 500 nm. Under simulated sunlight, the device gives an open-circuit voltage of 0.41 V, a short-circuit current of 1.23 mA.cm-2 and a fillfactor of 0.24, resulting in a power conversion efficiency (PCE) of 0.12%. [1] In order to improve the performance we have prepared a new series of TPA-based poly(azomethine)s. By functionalizing the TPA moiety we are able to tune the band gap of the polymer. Introducing an electron donating methoxy group will push more electron density towards the polymer backbone, resulting in a smaller band gap, while an electron withdrawing cyano group increases the band gap of the polymer. By end-capping the polymers with triphenylamine, as shown below, and varying the polymer chain length, i.e. Mn= 1000, 5000 and 9000 g.mol-1 we want to elucidate the charge transport characteristics as function of molecular chain length.

Fig.1. Structure of the poly(azomethine)s and the TPA-based fullerenes.

To improve the compatibility between the electron acceptor and the polyazomethine hole-transport polymertwo new TPA-based fullerene derivatives were synthesized. In order to investigate the performance of the polymer and the combination with the new fullerenes, a series of bulk heterojunction photovoltaic cells was prepared and their optoelectronic properties were investigated.

References [1] Hindson, J.C.; Ulgut, B; Friend, R.H.; Greenham, N.C.; Norder, B.; Kotlewski, A.; Dingemans, T.J. "All-Aromatic Liquid Crystal Triphenylamine-based Poly(azomethine)s as Hole Transport Materials for Opto-electronic Applications" J. Mater. Chem., 20, 937-944 (2010)

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C11 - Copper indium gallium diselenide hybrid solar cells comprising solution-deposited window and organic buffer layers

Manuel Reinhard, Johannes Kuhn, Christoph Simon, Alexander Colsmann, Uli Lemmer Karlsruhe Institute of Technology, Light Technology Institute, Engesserstr. 13, Karlsruhe, 76131, DE

Thin-film chalcopyrite solar cells based on copper indium gallium diselenide (CIGS) exhibit record power conversion efficiencies of more than 20%. In order to compete with the predominant silicon based devices it is key to further reduce the cost per watt and hence explore new device and fabrication concepts for cheaper production processes. In this study, we present solution-processable, non-toxic and potentially printable organic semiconductors as a replacement for the commonly used cadmium sulfide (CdS) buffer layer. In particular, organic semiconductors with LUMO energies above 3eV allow for the fabrication of efficient hybrid solar cells. By performing bias dependent impedance spectroscopy we can show that these organic semiconductors reduce the recombination at the CIGS interface and enhance the minority carrier lifetimes as compared to buffer-free devices. Furthermore, we find a relation between the open circuit voltage (VOC) of the devices and the position of the N2 defect level within the absorber bulk as identified by temperature-dependent admittance spectroscopy. The higher the VOC of the photovoltaic device the further this defect level approaches the valence band of CIGS indicating a reduced Shockley-Read-Hall recombination rate. We further replace the commonly used transparent zinc oxide top electrode with a solution-processable highly conductive mesh electrode comprising commercially available silver nanowires. These electrodes exhibit a transmittance of more than 80% in the visible range and sheet resistances of less than 20Ω/, hence allowing for the fabrication of 5% efficient solar cells.

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C12 - Hybrid solar cells based on CuInS2 nanocrystals and their comparison to the polymer/CdSe system

Holger Borcherta, Nikolay Radycheva, Rany Mirantia, Dorothea Scheunemanna, Marta Kruszynskaa, Christopher Krausea, Florian Witta, Irina Loktevab, Joanna Kolny-Olesiaka, Jürgen Parisia a, University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, Oldenburg, 26129, DE b, University Erlangen-Nürnberg, Martensstr. 7, Erlangen, 91058, DE

By using organic ligands that bind to the surface of inorganic nanoparticles, colloidal chemistry enables the preparation of semiconductor nanocrystals with precisely controllable structural and optical properties, such as the particle size and shape as well as the optical band gap. Therefore, important material properties can be adjusted to the demands of an application, for example as electron acceptor in bulk heterojunction (BHJ) solar cells. The controllable material properties render semiconductor nanocrystals promising candidates to replace the widely-used fullerene derivate PCBM in organic solar cells. However, the efficiency of hybrid polymer/nanoparticle solar cells still lacks behind that of polymer/fullerene cells. Today, the highest efficiencies are achieved in hybrid devices with CdSe nanocrystals as the inorganic component. For a long time, pyridine was chosen as a standard capping ligand, and the efficiency of hybrid solar cells with quasi-spherical CdSe quantum dots was limited to approximately 1%. Recently, an increase to about 2% was achieved by using short chain alkylamines instead of pyridine as ligands. Within the present work, we studied the physical reasons for this increase and found the ligands to play a crucial role with respect to charge carrier trap states that are present in the bulk heterojunction [1]. Although the results reveal the ligand shell to play a key role for the performance and allow deducing strategies for further optimization, a general drawback of CdSe-based solar cells will always remain the high toxicity of the material. An alternative may be CuInS2 nanocrystals which can also be prepared in high quality by colloidal chemistry (see Figure).

Figure 1 TEM image of colloidal CuInS2 nanocrystals

However, much less attention was devoted to polymer/CuInS2 BHJ solar cells in the past. In the present work, we prepared colloidal CuInS2 nanocrystals [2], elaborated procedures for ligand exchange with small molecules such as pyridine or short alkanethiols and investigated the applicability of these nanocrystals in solar cells. Different device concepts were tested by combining CuInS2 nanocrystals with conductive polymer, PCBM or ZnO nanocrystals. Apart from the standard electrical characterization of solar cells, experiments on elementary

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processes are presented as well. For example, cyclic voltammetry was used to determine the energy levels of the nanocrystals, and light-induced electron spin resonance as well as photoinduced absorption spectroscopy [3] was used to study charge separation and recombination processes. Results are compared to the more established CdSe-based solar cells. Although the CuInS2-based systems have inferior performance so far, conclusions for their further improvement can be drawn.

References [1] Radychev, N.; Lokteva, I.; Witt, F.; Kolny-Olesiak, J.; Borchert, H.; Parisi, J. "Physical Origin of the Impact of Different Nanocrystal Surface Modifications on the Performance of CdSe/P3HT Hybrid Solar Cells". J. Phys. Chem. C 115, 14111-14122 (2011). [2] Kruszynska, M.; Borchert, H.; Parisi, J.; Kolny-Olesiak, J. "Synthesis and Shape Control of CuInS2 Nanoparticles". J. Am. Chem. Soc. 132, 15976- 15986 (2010). [3] Kruszynska, M.; Knipper, M.; Kolny-Olesiak, J.; Borchert, H.; Parisi, J. "Charge transfer in blends of P3HT and colloidally prepared CuInS2 nanocrystals". Thin Solid Films 519, 7374-7377 (2011).

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C13 - Organic conductive polymers as alternative electrocatalysts for Dye-sensitized solar cells

Nikolaos Balisa, Theodoros Makrisa, Vassilios Dracopoulosb, Panagiotis Lianosb a, University of Patras, Engineering Science Dept., Patras, 26500, GR b, FORTH/ICE-HT, Stadiou Str.Platani, 26504 Patras, GR

Nanoparticulate platinum is the uncontestable electrocatalyst employed with Dye-sensitized Solar Cells (DSSC). Due to the scarcity and the cost of this noble metal, a large effort has been devoted to the search of alternative materials to functionalize the transfer of electrons from the cathode electrode to the electrolyte. Conductive polymers, deposited in the form of nanostructured thin films offer this possibility. Reported works claim to have made organic electrocatalysts sometimes being even more effective than Pt itself [1-2]. In reality, the matter of both structural and electrochemical stability remains an open question when it comes to the materials usually employed to make a DSSC. In the present work, this matter is critically examined by taking into account literature data and our own experience [3,4] in an effort to settle the question to its proper dimensions. References [1] Winther-Jensen, B.; MacFarlane, D.R., “New generation, metal-free electrocatalysts for fuel cells, solar cells and water splitting”. Energy Environ. Sci. 4, 2790-2798(2011) [2] Trevisan, R.; Doebbelin, M.; Boix, P.P.; Barea, E.M.; Tena-Zaera, R.; Mora-Sero, I,; Bisquert, J., “PEDOT Nanotube Arrays as High Performing Counter Electrodes for Dye Sensitized Solar Cells. Study of the Interactions Among Electrolytes and Counter Electrodes”. Advanced Energy Materials 1,781-784(2011) [3] Balis, N.; Makris, Th.; Dracopoulos, V.; Stergiopoulos, Th.; Lianos, P. “Quasi-Solid-State Dye-sensitized Solar Cells made with poly(3,4-ethylenedioxythiophene) (PEDOT)-functionalized counter electrodes”. J.Power Sources, 203, 302-307(2012) [4] Makris, Th.; Dracopoulos, V.; Stergiopoulos, Th.; Lianos, P. “A quasi solid-state dye-sensitized solar cell made of polypyrrole counter electrodes” Electrochimica Acta 56, 2004-2008(2011)

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C14 - Advances in the Application of Graphene-Titania paste to enhance DSC performance

Eva M Barea, Roberto Trevisan, Iván Mora Seró, Pablo P. Boix Universitat Jaume I, Av. Vicent Sos Baynat s/n, Castello, 12071, ES

In the process of DSC fabrication there are several points to be optimized, like new materials for counterelectrodes,1 new redox media that can get higher open circuit potential2 and new semiconductors materials, different from titania, or mixtures of materials, like for example those involving the use of graphene.3,4

Different kinds of counterelectrodes have been studied for DSCs: platinum, graphite, activated carbon, carbon black, single-wall carbon nanotubes, PEDOT, polypyrrole, and polyaniline.5 In general, the best performances were obtained for platinized electrodes. But PEDOT is especially interesting due to its high stability, electrical conductivity and catalytic capability.6 Related with the use of graphene in the working electrode there are several papers using nanoribbons, nanotubes, layers and nanoparticles3 that increase the DSC efficiency conversion, but the mechanism and the role that nanoparticles of grapheme plays in it, is still unknown. It is clear that the use of new material is focuses to improve the performance of the devices but at the same time new studies are required to understand the new mechanism involved in the operation of the device and find the reasons why is possible to improve the efficiency of the dye solar cells. Based on large experience on DSC characterization by Impedance Spectroscopy (IS), we provide detailed understanding of the factors determining the cell performance and explain why using ordered one-dimensional PEDOT like counterelectrode and Graphene-Titania in the working electrode is possible increase the efficiency of the DSC. References [1] Trevisan, R.; Döbbelin, M.; Boix, P. P.; Barea, E. M.; Tena-Zaera, T.; Mora-Seró, I.; Bisquert, J., Adv. Energy Mater. 2011, 1, 781–784. [2] Mingfei, X.; Difei, Z.; Ning, C.; Jingyuan, L.; Renzhi, L.; Peng, W., Energy & Environmental Science 2011, DOI: 10.1039/c1ee02432a. [3] Yang, N.; Zhai, J.; Wang, D.; Chen, Y.; Jiang, L., ACS Nano 2010, 4 (2), 887–89. [4] Song, J.; Yin, Z.; Yang, Z.; Amaladass, P.; Wu, S.; Ye, J.; Zhao, Y.; Deng, W.-Q.; Zhang, H.; Liu, X.-W. Chemistry – A European Journal 17, (39), 10832-10837. [5] T. N. Murakami , M. Grätzel , Inorg. Chim. Acta 2008 , 361 , 572 [6] H. Tian , Z. Yu , A. Hagfeldt , L. Kloo , L. Sun , J. Am. Chem. Soc. 2011 , DOI: 10.1021/ja2030933 .

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C15- Fabrication of titanium oxide and its photovoltaic study

Meinan Liu, Cheng Yan Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, 2 George Street GPO Box 2434, Brisbane, 4001, AU

Titanium oxide (TiO2) is one of the most important semiconductors because of its unique electrical, chemical and optical properties and also because it has been widely used in a variety of fields of solar cells, photocatalysis, gas sensors and batteries. As theoretically and experimentally studied, the properties and the performance of TiO2 strongly depend on its crystal phases, surface area, crystallinity and morphologies. Therefore, the fabrication of TiO2 with different structures like tubes, rods, spheres, flowers and assembled architectures attracts much attention. In this work, several synthesis methods have been developed to fabricate TiO2 with controllable morphologies. TiO2 powders with different morphologies were individually assembled in to solar cells and the morphology effect on the performance has been studied.

Figure 1 SEM images of the as-obtained TiO2 powders with different morphologies.

Typical morphology results are shown in Fig. 1. Complicated spherical architectures assembled by cubes or rods can be achieved by a simple fluorine or chlorine ions assisted hydrothermal method. As shown in Fig. 1a, the spheres obtained from fluorine ion assisted hydrothermal system are constructed by numerous cubes and the size of spheres is around 2 mm. The edge length of the cube is around 500 nm. The spheres prepared from chlorine ions assisted hydrothermal system are shown in Fig. 1b, which are assembled by rods. The diameter of spheres is around 3mm. One-dimensional nanotubes and nanorods were fabricated by the electrochemical anodization method and the hydrothermal method, respectively. It can be observed that the diameter of the nanotubes is around 200 nm and the length can be controlled between 5-20 mm through tuning the reaction time. In contrast, the diameter of nanorods is smaller, about 80 nm and also the length of nanorods is shorter, around 500 nm. These TiO2 crystallites with of complicated sphere, nanotube and nanorod structure have a significant impact on the performance of solar cell. References [1] O'Regan, B.; Gratzel, M. "A Low-Cost, High-Efficiency Solar Cell Based on Dye-Sensitized Colloidal TiO2 Films". Nature 353, 737-740 (1991). [2] Wang, H.; Li, H.; Xue, B.; Wang, Z.; Meng, Q.; Chen, L. "Solid-State Composite Electrolyte LiI/3-Hydroxypropionitrile/SiO2 for Dye-Sensitized Solar Cells". J. Am. Chem. Soc. 127, 6394-6401 (2005). (3)Hochbaum, A.I.; Yang, P. "Semiconductor Nanowires for Energy Conversion". Chem. Rev. 110, 527-546 (2010).

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C16 - Organic conductive polymers as alternative electrocatalysts for Dye-sensitized solar cells

Nikolaos Balisa, Theodoros Makrisa, Vassilios Dracopoulosb, Panagiotis Lianosb a, University of Patras, Engineering Science Dept., Patras, 26500, GR b, FORTH/ICE-HT, Stadiou Str.Platani, 26504 Patras, GR

Nanoparticulate platinum is the uncontestable electrocatalyst employed with Dye-sensitized Solar Cells (DSSC). Due to the scarcity and the cost of this noble metal, a large effort has been devoted to the search of alternative materials to functionalize the transfer of electrons from the cathode electrode to the electrolyte. Conductive polymers, deposited in the form of nanostructured thin films offer this possibility. Reported works claim to have made organic electrocatalysts sometimes being even more effective than Pt itself [1-2]. In reality, the matter of both structural and electrochemical stability remains an open question when it comes to the materials usually employed to make a DSSC. In the present work, this matter is critically examined by taking into account literature data and our own experience [3,4] in an effort to settle the question to its proper dimensions. References [1] Winther-Jensen, B.; MacFarlane, D.R., “New generation, metal-free electrocatalysts for fuel cells, solar cells and water splitting”. Energy Environ. Sci. 4, 2790-2798(2011) [2] Trevisan, R.; Doebbelin, M.; Boix, P.P.; Barea, E.M.; Tena-Zaera, R.; Mora-Sero, I,; Bisquert, J., “PEDOT Nanotube Arrays as High Performing Counter Electrodes for Dye Sensitized Solar Cells. Study of the Interactions Among Electrolytes and Counter Electrodes”. Advanced Energy Materials 1,781-784(2011) [3] Balis, N.; Makris, Th.; Dracopoulos, V.; Stergiopoulos, Th.; Lianos, P. “Quasi-Solid-State Dye-sensitized Solar Cells made with poly(3,4-ethylenedioxythiophene) (PEDOT)-functionalized counter electrodes”. J.Power Sources, 203, 302-307(2012) [4] Makris, Th.; Dracopoulos, V.; Stergiopoulos, Th.; Lianos, P. “A quasi solid-state dye-sensitized solar cell made of polypyrrole counter electrodes” Electrochimica Acta 56, 2004-2008(2011)

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C17 - Production Technologies for Large Area Printed Flexible Electronics

Thomas Kolbusch Coatema Coating Machinery GmbH, Roseller Str. 4, Dormagen, 41539, DE

The lecture gives an introduction to the variety of devices out of the area of large area printed electronics and polymer solar cells and the technology challenges implemented in these developments. Then these influencing parameters are explained for the different coating and printing processes and systems used for flexible electronic systems and organic photovoltaic. This part gives a complete overview on the existing printing and coating methods used today. He also gives an outlook on the development of different technologies and the possibility for scaling-up of processes during the next years. Equipment in clean room conditions is described and specific Roll to Roll solutions in inert atmosphere are explained to the audience. At the end, he gives a case study of a European FP7 project called FACESS in which a printed thin film battery is powering an autonomous sensor. The printed battery itself is powered by a printed polymer solar cell. Therefore a demonstrator will be shown.

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C18 - Fast Transporting ZnO-TiO2 Coaxial Photoanodes for Dye-Sensitized Solar Cells Based on ALD-Modified SiO2 Aerogel Frameworks

Vennesa Williamsa, Nak Cheon Jeonga, Chaiya Prasittichaia, Michael Pellina, Joseph Huppa a, Depatment of Chemistry and Argon-Northwestern Solar Energy Research Center (ANSER), Northwestern University, 2145 N Sheridan Rd, Evanston, 60208, USA b, Materials Science Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA c, Chemical Science and Engineering Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA

A doubly co-axial photoanode architecture based on templated SiO2 aerogels was fabricated on transparent conducting oxides for use in dye-sensitized solar cells (DSSCs). These templates were coated with ZnO via atomic layer deposition (ALD) to yield an electronically interconnected, low density, high surface area, semiconductor framework. Addition of a thin conformal layer of a second metal oxide (alumina, zirconia, or titania) via ALD was found to suppress the dissolution of ZnO that otherwise occurs when it is soaked in alcohol solutions containing acidic dyes used for sensitization or in acetonitrile solutions containing a pyridine derivative and the iodide/tri-iodide (I-/I-

3) redox shuttle. Electron transport in SiO2-ZnO-TiO2 photoelectrodes was found to be nearly two orders of magnitude faster than in SiO2-TiO2 structures, implying that the interior ZnO sheath serves as the primary electron conduit. In contrast, rates of electron interception by the oxidized form of the redox shuttle were observed to decrease when a TiO2 shell was added to SiO2-ZnO, with the decreases becoming more significant as the thickness of the titania shell increases.

Figure 1 A doubly co-axial photoanode architecture (ZnO-TiO2) based on templated SiO2 aerogels for use in DSSCs to effectively improve photocurrents, photovoltages and electron lifetimes

These effects lead to improvements in efficiency for DSSCs that utilize I-/I-3, but much larger

improvements for DSSCs utilizing ferrocene/ferrocenium, a notoriously fast redox shuttle. For the former, overall energy conversion efficiencies maximize at 5.2%. From a variety of experiments, the primary factor limiting aerogel-based DSSC performance is light loss due to scattering. Nevertheless, variants of the doubly coaxial structure may prove useful in devising DSSCs that can achieve excellent energy conversion efficiencies even with fast redox shuttles.

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C19 - The effect of the spatial and energetic carrier distribution on the charge carrier lifetime in bulk heterojunction solar cells

Thomas Kirchartz, Jenny Nelson Imperial College London, Department of Physics, South Kensington Campus, London, 0, GB

Charge extraction and transient photovoltage measurements have been extensively used to study non-geminate recombination in polymer:fullerene solar cells.1-3 In particular, it has been shown that a combination of both enables a successful reconstruction and explanation of the recombination current of different polythiophene:fullerene devices.4 However, what is missing so far is a detailed theoretical study on the relation between the spatial and energetic distribution of carriers on the results obtained from charge extraction and transient photovoltage measurements. We show that the voltage and carrier concentration dependence of the lifetime can be derived from the diode ideality factor and the voltage dependence of the carrier concentration. To study the effect of the density of states as a function of energy on the results, we employ a drift-diffusion solver using a Shockley-Read-Hall model for recombination via continuous distributions of localized states. In case of sufficiently thick (> 150nm) and undoped solar cells, the ideality factor and the voltage dependence of the carrier concentration reflect the shape of the density of states with deeper states leading to higher ideality factors.5,6 When reducing the thickness, the ideality factor will still reflect the dominant recombination mechanism, while the voltage dependence of the carrier concentration will now be affected by the spatial distribution and the energetic distribution of charge carriers. This leads to a slow increase of carrier concentration with voltage and therefore to very high apparent reaction orders as seen in experiment. Unintentional doping of the active layer can have a similar effect depending on the device thickness. For low thicknesses and low doping concentrations, the space-charge region would be bigger than the active layer thickness and the effect of the doping is negligible. For higher active layer thicknesses, doping can alter the spatial distribution of electron and hole concentrations such that again a rather slow increase of carrier concentrations with voltage is observed, which then causes high apparent reaction orders that do not reflect the physical recombination mechanism anymore. This study will be applicable and relevant to bulk heterojunction solar cells made from organic or inorganic materials with thicknesses in the range of a few hundred nanometers or less. References [1] Shuttle, C. G.; O'Regan, B.; Ballantyne, A. M.; Nelson, J.; Bradley, D. D. C.; de Mello, J.; Durrant, J. R. "Experimental determination of the rate law for charge carrier decay in a polythiophene: Fullerene solar cell". Appl. Phys. Lett. 92, 093311 (2008). [2] Maurano, A.; Hamilton, R.; Shuttle, C. G.; Ballantyne, A. M.; Nelson, J.; O'Regan, B.; Zhang, W. M.; McCulloch, I.; Azimi, H.; Morana, M.; Brabec, C. J.; Durrant, J. R. "Recombination Dynamics as a Key Determinant of Open Circuit Voltage in Organic Bulk Heterojunction Solar Cells: A Comparison of Four Different Donor Polymers." Adv Mater 22, 4987-4992 (2010) [3] Credgington, D.; Hamilton, R.; Atienzar, P.; Nelson, J.; Durrant, J.R. "Non-Geminate Recombination as the Primary Determinant of Open-Circuit Voltage in Polythiophene:Fullerene Blend Solar Cells: an Analysis of the Influence of Device Processing Conditions". Adv Funct Mater 21, 2744 - 2753 (2011). [4] Shuttle, C. G.; Hamilton, R.; O'Regan, B.; Nelson, J.; Durrant, J. R. "Charge-density-based analysis of the current–voltage response of polythiophene/fullerene photovoltaic devices". P Natl Acad Sci USA 107, 16448 (2010). [5] van Berkel, C.; Powell, M. J. Franklin, A. R., French, I. D., "Quality factor in a‐Si:H nip and pin diodes". J. Appl. Phys. 73, 5264-5268 (1993) (6) Kirchartz, T.; Pieters, B. E.; Kirkpatrick, J.; Rau, U.; Nelson, J. "Recombination via tail states in polythiophene: fullerene solar cells." Phys. Rev. B 83, 115209 (2011).

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C20 - Modelling of Energy and Hole Transfer in Co-sensitized Dye-Sensitized TiO2: Electronic structure, optical properties and FRET

Mariachiara Pastore, Filippo De Angelis ISTM-CNR, Via Elce di sotto, 8, Perugia, 6123, IT

Dye-sensitized solar cells (DSSCs)1 are attracting a wide-spread interest as low-cost alternatives to conventional photovoltaics. A possible way to increase the power conversion efficiency in DSSCs is to enhance the light harvesting in the near–infrared portion of the solar spectrum by co-sensitization of TiO2 with organic dyes having high NIR absorption; this strategy was recently investigated by Hardin et al.2 employing a zinc naphthalocyanine-based dye (AS02) and the Ru(II) C106 dye The main drawback of co-sensitization is the usually low Voc due to higher recombination rates of NIR dyes.3 Higher Voc can be obtained by insulating the NIR dye from the oxide surface thus using it as an energy rely dye (ERD), able to absorb energy and undergo Forster resonant energy transfer (FRET) to the sensitizing-dye (SD). To enhance the FRET efficiency and reduce the voltage losses, a careful tuning of the optical and structural properties of the NIR-ERD is required: it should have intense absorption and high photoluminescence quantum efficiency, its emission spectrum should largely overlap the absorption spectrum of SD, its HOMO should be lower than the redox mediator potential to have fast regeneration and finally, it should intimately mix and interact with the SD. Motivated by the work of Hardin et al.2 and by the great interest in the design of new NIR-ERDs having the proper electronic and structural properties, we carried out a computational investigation of (AS02+C106) co-sensitized TiO2 models based upon DFT, Time-Dependent (TD) DFT and ab initio MP2 calculations.

Figure 1 Model of AS02 and C106 co-adsorption on a grid of Ti atoms representing the TiO2 anatase (101) surface.

On the basis of our experience in the computational prediction of the optical properties of organic4 and inorganic5 sensitizers and in the modeling of dye/TiO2 heterointerfaces6-7 we calculated the electronic absorption and emission spectra of the dyes in solution and grafted to the titania surface, determined the preferred adsorption geometry of the AS02 and C106 dyes onto the semiconductor surface and the relative energy level alignments with respect to the semiconductor CB. Employing a larger TiO2 model, we modeled the coadsorption of AS02 and C106 dyes, evaluating at MP2 level of theory the relative stability of various co-adsorption patterns and then the associated optical response. Owing to our high-level computational methodology, we are able to provide new insights into the energy transfer mechanisms in co-sensitized solar cells, suggesting guidelines to design new ERDs with extended NIR absorption and the proper energy level alignment to suppress hole transfer processes.

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References [1] O'Regan, B.; Grätzel, M. “A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films.” Nature. 353, 737-740 (1991). [2] Hardin, B. E.; Sellinger, A.; Mohel, T.; Humphry-Baker, R.; Moser, J.-E.; Wang, P.; Zakeeruddin, S. M.; Grätzel, M.; McGehee, M. D. “Energy and Hole Transfer between Dyes Attached to Titania in Cosensitized Dye-Sensitized Solar Cells” J. Am. Chem. Soc. 133, 10662-10667 (2011) [3] Miyashita, M.; Sunahara, K.; Nishikawa, T.; Uemura, Y.; Koumura, N.; Hara, K.; Mori, A.; Abe, T.; Suzuki, E.; Mori, S. “Interfacial Electron-Transfer Kinetics in Metal-Free Organic Dye-Sensitized Solar Cells: Combined Effects of Molecular Structure of Dyes and Electrolytes” J. Am. Chem. Soc. 130, 17874–17881 (2008). [4] Pastore, M.; Mosconi, E.; De Angelis, F.; Grätzel, M. “A Computational Investigation of Organic Dyes for Dye-Sensitized Solar Cells: Benchmark, Strategies, and Open Issues” J. Phys. Chem. C 114, 7205-7212 (2010). [5] Nazeeruddin, M. K; De Angelis, F,; Fantacci, S.; Selloni, A.; Viscardi, G.; Liska, P.; Ito, S.; Takeru, B.; Grätzel, M. “Combined Experimental and DFT-TDDFT Computational Study of Photoelectrochemical Cell Ruthenium Sensitizers” J. Am. Chem. Soc. 127, 16835-16847 (2005). [6] Pastore, M.; De Angelis, F. “Computational Modeling of Stark Effects in Organic Dye-Sensitized TiO2 Heterointerfaces” J. Phys. Chem. Lett. 2, 1261-1267 (2011) [7] Pastore, M.; De Angelis, F. “Computational Modelling of TiO2 Surfaces Sensitized by Organic Dyes with Different Anchoring Groups: Adsorption Modes, Electronic Structure and Implication for Electron Injection/Recombination” Phys. Chem. Chem. Phys. 14, 920-928 (2011)

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C21–Design and Realization of High Performance Z-TYPE Dye Solar Cell Modules

Andrea Guidobaldia, Fabrizio Giordanoa, Eleonora Petrolatib, Luigi Vesceb, Simone Mastroiannia, Riccardo Riccitellib, Andrea Realea, Thomas M. Browna, Aldo Di Carloa a, CHOSE - Centre for Hybrid and Organic Solar Energy, University of Rome “Tor Vergata”, Electronic Engineering Department, Via del Politecnico 1, Rome, 00133, IT b, DYEPOWER Consortium, Viale Castro Pretorio 122, Rome, 00185, IT

Dye Solar Cells (DSCs) are a promising low cost PV technology[1]. The choice of cell geometry and interconnection strategy is a crucial issue to design high performance devices[2-4]. Efficiency losses due to substrate resistances and reduction of active area due to electrical contacts and device sealing are crucial aspects to consider in module design[3-4]. We realized a simple and powerful DSC model in PSPICE in order to design different schemes for large area DSCs. The most widespread interconnection schemes, Z, W and Parallel[5], were considered and validated by the comparison with experimental data. Optimized layouts were designed for differing device performance and Jsc considering the effect of resistance losses and active/total area ratios. We investigated the role of vertical contacts inside the Z-type module, how they contribute to limit the performance and the percentage of the total area occupied by the active area,and how this affects the proper design of the cells in a module. Using the Z scheme, Sastrawan et al. achieved a conversion efficiency of 3.1% on active area on (30x30)cm2 modules[6-7]. Jun et al. have shown 100cm2 modules with conversion efficiency on active area (47.5cm2) of 6.3%, reaching 6.6% when using a scattering layer or a back reflector. The efficiency on total area was almost half of that active area efficiency[8].

Figure 1 IV curves of the Z-module with 13 cells and 42 cm2 of total area with a Transparent-Opaque multilayer TiO2 with (circles) and without (squares) a diffusive backreflector on the counter-electrode

We have carried out an optimization of the materials, processes and the layout using PSPICE simulations of Z-type modules. We realized Z modules with thirteen TiO2 cells of area (5x50)mm2 on a substrate area of 56cm2, sensitized with commercial N719-dye and using a electrolyte for high performance. The inactive interdistance between cells was 2mm occupied in the middle by a ~0.5mm wide vertical interconnection, made by silver based screen-printable commercial paste, along the length of the cell. In order to improve light harvesting, different TiO2 combinations of transparent (20nm diameter particles) and opaque (20nm and

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300nm particles) layers were tested, in addition to the effect of TiCl4 treatments[9], and compared these to a reference device with a transparent double layer with no TiCl4 treatment. Modules reached a conversion efficiency(using a back reflector) of 6.9% on the aperture area (defined as the area inside the four corners of the outermost cells of the module) and 9.4 % on active area. Moreover all the materials used to produce these high performance DSC modules were commercial available thus also demonstrating the maturity of such technology. References [1] B. O’Regan, M. Grätzel ”A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films”, Nature vol. 353, 737 (1991). [2] S. Deb, B. Ghosh,”Series resistance and optimum grid design for a thin film solar cell of rectangular shape”, Solar Cells vol. 13, 145–162 (1984). [3] Y. Huang, S. Dai, S. Chen, C. Zhang, Y. Sui, S. Xiao, L. Hu ” Theoretical modeling of the series resistance effect on dye-sensitized solar cell performance”, Applied Physics Letters vol. 95, 243503 (2009). [4] F. Giordano, E. Petrolati, T.M. Brown, A. Reale, A. Di Carlo “Series-Connection Designs for Dye Solar Cell Modules”, IEEE Transactions On Electron Devices vol. 58 n°8, 2759-2764 (2011). [5]G. E. Tulloch “Light and energy - Dye solar cells for the 21st century”, Journal of Photochemistry and Photobiology A: Chemistry vol. 164, 209–219 (2004). [6] R. Sastrawan, J. Beier, U. Belledin, S. Hemming, A. Hinsch, R. Kern, C. Vetter, F.M. Petrat, A.Prodi-Schwab, P. Lechnerf, W. Hoffmann “A glass frit-sealed dye solar cell module with integrated series connections”, Solar Energy Materials & Solar Cells vol. 90, 1680–1691 (2006). [7] R. Sastrawan, J. Beier, U. Belledin, S. Hemming, A. Hinsch, R. Kern, C. Vetter, F.M. Petrat, A.Prodi-Schwab, P. Lechnerf, W. Hoffmann “New Interdigital Design for Large Area Dye Solar Modules Using a Lead-free Glass Frit Sealing”, Progress In Photovoltaics: Research and Applications vol. 14, 607–709 (2006). [8] Yongseok Jun, Jung-Ho Son, Dongwook Sohn, Man Gu Kang “A module of a TiO2 nanocrystalline dye-sensitezed solar cell with effective dimesions”, Journal of Photochemistry and Photobiology A: Chemistry Vol. 200, 314–317 (2008). [9] L. Vesce, R. Riccitelli, G. Soscia, T. M. Brown, A. Di Carlo, A. Reale “Optimization of nanostructured titania photoanodes for dye-sensitized solar cells: study and experimentation of TiCl4 treatment”, Journal of Non-Crystalline Solids vol. 356, 1958-1961 (2010).

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C22- Diketopyrrolopyrrole:P3HT blend Thin Films for All-Polymer Solar Cells

Satish Patila, Gitish Duttaa, Richard Friendb, Doo-Hyan Kob a, Indian Institute of Science, SSCU, Indian Institute of Science, Bangalore, 560012, IN b, Cavendish Labratory, University of Cambridge, UK

Diketopyrrolopyrrole (DPP) based polymers have recently emerged as a new class of ambipolar materials.1 In this study, we have synthesized DPP based conjugated polymers with various combination of donor and acceptor segments. By gradually changing the acceptor strength we fine tune the energy levels of polymers suitable for all-polymer solar cell application. We have utilized these polymers for fabricating all-polymer solar cells in combination with P3HT. The blend of P3HT:DPP thin films was systematically investigated for the photovoltaic properties by using various percentage of donor/acceptor combinations.

Figure 1 Shows the optical absorption spectra of one such polymer (PIDT-TDPP) blended with P3HT in 1: 1 weight ratio and it nicely covers entire solar spectra.

This work reports the progress towards the synthesis of new DPP-based conjugated polymers and the physical properties that governs the OPV performance of these materials in nonfullerene bulk heterojunction devices.

References [1] Yuning Li.; Samarendra P. S.; Sonar P. "A High Mobility P-Type DPP-Thieno[3,2- b ]thiophene Copolymer for Organic Thin-Film Transistors". Adv. Mater. 22, 4862–4866 (2010)

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C23 - Fabrication and characterization of thin film Titania as a blocking under layer in organic dye sensitized solar cells with cobalt and ferrocene mediators base by sol-gel method

Mahmoud Zendehdela, Gerrit Boschloob, Anders Hagfeldtb, Mohammad Hossein Habibia a, Isfahan university, P.O.Box 117 Chemistry Department University of I, Isfahan, 81745, IR b, Uppsala University, Department of Physical and Analytical Chemistry, Box 259, 5105, Uppsala, Sweden

SUMMARY

The properties of thin blocking under layer of titania prepared with sol-gel process used to improve the performance of organic dye sensitized nanocrystalline solar cells with cobalt and ferrocene based mediators in two different solvents have been studied. TiO2 blocking layers prepared on fluorine-doped tin oxide coated glass by dip-coating have been characterized by current-voltage (I-V) measurement, IPCE, SEM, Cyclic Voltammetry, Chronoamperometry and Impedance spectroscopy. The results showed that the ability of the blocking layer to prevent the back reaction of electrons with cobalt complex and ferrocene in the electrolyte was excellent with good improvements in open-circuit photovoltage (Voc) and fill factor of the cell (FF). We have designed the new method for assembling of working electrode with minimum misspend of energy and we prepared a DSC with good advantage when faster redox couples such as ferrocene/ferrocenium are employed with using titania blocking layer to limit the rapid interfacial recombination of photoinjected electrons with the oxidized half of the redox couple. INTRODUCTION

Dye-sensitized solar cells (DSCs) have received great interest as cost-effective alternatives to silicon-based photovoltaic devices. Identification of the factors limiting the performance of (DSCs)1 is a key objective of current research, as attempts are made to increase the AM 1.5 solar power efficiency of these cells beyond 12.3 %.2 In the DSC, light is absorbed by a dye molecule, which is anchored to a mesoporous wide band gap semiconductor, normally TiO2. In the case of these solid-state cells, it has been demonstrated that the fluorine-doped tin oxide (FTO) substrates must be covered by a thin blocking layer of titania3 in order to prevent efficiency loss due to electron transfer to mediator as a unlike recombination process. Blocking layers are necessary for DSCs that utilize one electron redox systems such as cobalt complexes4 or for cells using solid organic hole-conducting media.5 Recently some research have been studied by using a compact blocking layer of oxide deposited on the anode by spray pyrolysis6 but there are some problems like expending high energy, not simple controlling on diameter of layers and producing of big particle size of titania that lead to decrease the connectivity to mesoporous nanocrystalline layer. We have tried to use simple and effective method like sol-gel for assembeling of working electrode dye-sensitized solar cells.7 EXPERIMENTAL RESULTS

Titanium isopropoxide and isopropyl alcohol (i-PrOH) were mixed and stirred at room temperature for 1 h. EAcAc was added to the solution as a chelating agent, and the solution was stirred for 3 h. Water diluted with i-PrOH was then carefully added to the solution for hydrolysis with addition of HNO3 to reach the pH of solution to 3 and this solution was used for coating. Fluorine-doped tin oxide (FTO) glass substrates (Pilkington, TEC15) were cleaned in an ultrasonic bath overnight using (in order) detergent, water, and ethanol. The conducting glass substrates coated in a dipping–withdrawing manner (withdrawing speed: 0.1 mm/s) (one layers) with titanium sol and preheated in 105 °C for 10 min. Mesoporous TiO2 films were prepared with an area of 0.25 cm2 by screen printing colloidal TiO2 paste (Dyesol DSL 30 NRD-T) and preheating at 120 °C then another time screen printing of scattering TiO2 paste (PST-

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400C) and sintering. Sample (A) has prepared by thin film blocking under layer that fabricated with sol-gel method. Also sample (B) has prepared by TiCl4 treatment as a common blocking under layer and sample (C) was without under layer and prepared as a blank sample. The working electrodes were immersed in a dye bath containing 0.2 mM D35 in ethanol and left 1 hr in 50 °C. The solar cells were assembled, using a 30 µm thick thermoplastic Surlyn frame, with a platinized counter electrode, which was prepared by depositing 10 µL cm-2, 4.8 mM H2PtCl6 solution in ethanol to the glass substrate followed by heating in air at 400 °C for 30 min.

Figure 1 Current density versus applied potential curves. (a), (c) and (e) are under dark but (b), (d) and (f) are under AM1.5G illumination for DSC sensitized with D35. (a) and (b) are in 3-methoxy proponitrile with cobalt mediator, (c) and (d) are in acetonitrile with cobalt mediator and (e) and (f) are in acetonitrile with ferrocene mediator. () for solar cells with sol-gel treatment blocking layer, () for solar cells with TiCl4 treatment blocking layer and () for solar cells without under layer.

An electrolyte solution was then introduced through two holes predrilled in the counter electrode, and the cell was sealed with thermoplastic Surlyn covers and a glass coverslip. Unless otherwise noted, the electrolyte1 consisted of 0.22 M [Co(bpy)3](PF6)2, 0.033 M [Co(pby)3](PF6)3, 0.1 M LiClO4, and 0.2 M 4-tert-butylpyridine (TBP) in 3-methoxy proponitrile as same as for acetonitrile and electrolyte 2 consisted of 0.22 M ferrocene, 0.033 M ferrocenium and same previous amont of LiClO4 and TBP. The current-voltage curves for this series of DSCs are shown in Figure 1. In result from the I-V curves we can see very good dark effect for (A) sample in 3-methoxy proponitrile solvent and partial good dark effect in

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acetonitrile solvent, Fig 1a and 1c respectively. We have observed a good improvement in Voc and fill factor (FF) in sample (A) in compare with other samples that show less recombination of electron to oxidized dye or cobalt mediator with good nanocrystalline interaction between mesoporous layer and titania blocking thin film because of same particle size and same anathase crystalline phases. This lead to faster electron injection from mesoporous layer to under layer and FTO.

References [1] B. O'Regan, M. Grätzel. Nature, 353, 737 (1991). [2]A. Yella, H.-W. Lee, H.N. Tsao, C. Yi, A.K. Chandiran, Md.K. Nazeeruddin, E.W.G. Diau, C.-Y. Yeh, S.M. Zakeeruddin, M. Grätzel. Science, 334, 629 (2011). [3] J. Kruger, R. Plass, L. Cevey, M. Piccirelli, M. Grätzel, U. Bach. Appl. Phys. Lett., 79, 2085 (2001). [4] P.J. Cameron, L.M. Peter, S.M. Zakeeruddin, M. Grätzel. Coord. Chem. Rev., 248, 1447 (2004). [5] J. Kruger, R. Plass, M. Grätzel, P.J. Cameron, L.M. Peter. J. Phys. Chem. B, 107, 7536 (2003). [6] P.J. Cameron, L.M. Peter. J. Phys. Chem. B, 107, 14394 (2003). [7] M.H. Habibi, M. Zendehdel. Current Nanoscience, 6, 642 (2010).

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C24 - Microfluidic housing system for innovative dye-sensitized solar cell architecture

Adriano Sacco*a, Andrea Lambertia, Diego Pugliesea, Nadia Shahzada, Rossana Gaziab, Angelica Chiodonib, Stefano Biancob, Marzia Quagliob, Elena Tressoa, Candido Fabrizio Pirria

a, Applied Science and Technology Department, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, 10129, IT b, Center for Space Human Robotics @PoliTo, Istituto Italiano di Tecnologia, Corso Trento 21, Torino, 10129, IT

Microfluidics is a versatile technology implemented in several application fields,from chemical synthesis and biological analysis to optics and information technology, withmany advantages. We have proposed [1] a new microfluidic-based design for dye sensitized solar cells (DSSCs) which effectively confines the liquid electrolyte in the final device, preventing failure due to electrolyte leakage or solvent evaporation. Microfluidics allows a controlled reagent delivery, since dye or electrolyte can be introduced and removed in the already sealed architecture, avoiding waste and eluding the possible electrode deterioration thanks to a faster assembly process.We have designed and fabricated more than 200 small laboratory DSSCs based on a microfluidic structure, interfaced with a housing system consisting of mechanical clamping, inlet/outlet ports and interconnections to external fluids handling devices. Our modular device enables to substitute one or more components, guarantees the reproducibility of the assembly parameters and allows the direct analysis of each components of the device itself thanks to the reversible sealing system.

Figure 1 Scheme of the microfluidic dye-sensitized solar cell

We have investigated the electrical response of the microfluidic DSSC to an external voltage of variable frequency, under light and dark conditions, at different bias voltages ranging from 0 V to 0.8 V and for two different thicknesses of the cells [2]. In addition, using the microfluidic DSSC architecture, we were able to test different materials: photoanodes based on nanostructured metal oxides (like TiO2 nanotubes or coral-shaped ZnO) and new kind of dyes (like hemi-squaraines).

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Finally, we have performed a study on the photoanode and counter electrode degradation over time thanks to the easy assembling and disassembling of the cell architecture. We will present and discuss the main results obtained on the photoanodes and counter-electrodes from UV-visible-NIR absorption spectroscopy and FESEM morphological analysis, and the results obtained on the cells from I-V and electrochemical impedance spectroscopy (EIS) characterization. References [1] Lamberti, A.; Sacco, A.; Bianco, S.; Giuri, E.; Quaglio, M.; Chiodoni, A.; Tresso, E. “Microfluidic sealing and housing system for innovative dye sensitized solar cell architecture” Microelectron. Eng. 88, 2308-2310 (2011). [2] Sacco, A.; Lamberti, A.; Quaglio, M.; Bianco, S.; Tresso, E.; Alexe-Ionescu, A.-L.; Pirri, C. F. "Electric characterization and modeling of microfluidic-based dye sensitized solar cell" Int. J. Photoenergy, in press (2012).

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C25 - Optically-thin gold electrodes on flexible polyester substrates for organic photovoltaics

Ross Hatton, Helena Stec University of Warwick, Library Road, Coventry, CV4 7AL, GB

We report an innovative scalable protocol for the preparation of nano-thickness (5.6 – 8.4 nm), ultra-smooth Au electrodes on the technologically important transparent flexible substrates polyethylene naphthalate (PEN) and polyethylene terephthalate (PET). The key step in the preparation of these films is derivatization of the plastic surface with a molecular nanolayer prior to metal deposition. Crucially the nanolayer is deposit from the vapour phase under low vacuum, avoiding complexity resulting from the use of solvents and rendering it scalable. The resulting films are highly electrically conductive, highly transparent and remarkably robust towards ultra-sonication in common solvents.

Figure 1

Furthermore, brief thermal annealing dramatically alters the film microstructure such that the electrode surface reverts almost entirely to the (111) crystal face. We show that the performance of 1.0 cm2 organic photovoltaic devices supported on these electrodes is comparable to that achieved on commercially available indium-tin oxide coated PET substrates, whilst only the former are resistant to repeated bending through a small radius of curvature. Vacuum deposition of the window electrode opens the door to the fabrication of entire molecular photovoltaics under the same vacuum, greatly increasing the economic viability of this class of organic photovoltaic.

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C26 - Organic Photovoltaic Devices with Colloidal TiO2 Nanorods as Key Functional Components

Anna Loiudice*a, Aurora Rizzob, Luisa De Marcoa, Davide Cozzolic, Giuseppe Giglic

a, IIT, Italian Institute of Technology , VIA BARSANATI, 1, Lecce, 73010, IT b, NNL CNR istituto nanoscienze, Via per Arnesano km 5, Lecce, 73100, IT c, Universita` del Salento, Via per Arnesano km 5, Lecce, 73100, IT

We report on a novel approach to integrate colloidal anatase TiO2 nanorods as key functional components into polymer organic photovoltaic (OPV) devices by means of mild, all-solution-based processing techniques. Recently, solution-processed of nonstoichimetric titanium oxide (TiOX) has been exploited as an optical spacer, oxygen barrier and electron-transporting/hole-blocking layer in the fabrication of conventional and inverted organic solar cell geometries.[1,2] The preparation of such material involves the sol-gel reaction of metal alkoxide precursors and thermal annealing at 100°C in ambient atmosphere to generate amorphous TiOX. This thermal treatment in the presence of oxygen results in the degradation of OPV active materials; therefore, a simple coating process of TiO2 without the requirement of the additional annealing step in air is deemed necessary.[3] In addition, due to their amorphous nature, most of the reported TiOX layers exhibit relatively low carrier mobility compared with their crystalline counterparts.[4]

Figure 1 Schematic representation of the UV- treatment in film (a) and in solution (b) with the layered structure for the inverted and conventional devices respectively.

In this frame, we have explored a novel strategy that enables straightforward utilization of crystalline colloidal anatase TiO2 NRs into both inverted and conventional solar cell geometries with improved performances. The successful integration of colloidal nanoparticles in organic solar cells relies on the ability to remove the long chain insulating ligands, which indeed severely reduces the charge transport. To this aim we have exploited the concomitant mechanisms of UV-light-driven photocatalytic removal of adsorbed capping ligands and hydrophylicization of TiO2 surfaces in both solid-state and liquid-phase conditions. The inverted devices show a power conversion efficiency of 2.3% that is ca. three times improvement over their corresponding cell counterpart incorporating untreated TiO2,

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demonstrating the excellent electron-collecting property of the UV-irradiated TiO2 films. The integration of UV-treated TiO2 solutions in conventional devices results in doubled power conversion efficiency for the thinner active layer and in maximum power conversion efficiency of 2.8% for 110 nm thick device. In addition, we have demonstrated, with the support of device characterizations and optical simulations that the TiO2 nanocrystal buffer layer acts both as electron-transporting/hole-blocking material and optical spacer. Refenereces *1+Kim, J.Y.; Lee, K.; Coates, N.E.; Moses, D.; Nguyen, T.Q.; Dante, M.; Heeger, A.J. “Efficient Tandem Polymer Solar Cells Fabricated by All-Solution Processing”. Science 317, (2007). *2+Chen, L.-M.; Hong, Z.; Li, G.; Yang, Y. “Recent Progress in Polymer Solar Cells: Manipulation of Polymer:Fullerene Morphology and the Formation of Efficient Inverted Polymer Solar Cells”. Adv. Mater. 21, (2009). *3+Park, M.H.; Li, J.H.; Kumar, A.; Li, G.; Yang, Y. “Doping of the Metal Oxide Nanostructure and its influence in Organic Electronics”. Adv. Funct. Mater. 19, (2009). *4+Park, J.H.; Lee, T.W.; Chi, D.; Wang, D.H.; Park, O.O. “Roles of Interlayers in Efficient Organic Photovoltaic Devices”. Macromol. Rapid Commun. 31, (2010).

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C27 - Ruthenium Fulvalene Compounds for Solar Thermal Energy Storage and Conversion

Karl Börjessona, Kasper Moth-Poulsena, Dusan Cosob, Nikolai Vinokurovc, Arun Majumdarb, Peter Vollhardtc, Rachel Segalmanc a, Chalmers Tekniska Högskola/kemi/polymerteknik, Kemivägen 10, Göteborg, 41296, SE b, Mechanical Engineering, UC Berkeley, Berkeley, CA, United States c, College of Chemistry, UC Berkeley, Berkeley, CA, United States

In a future society with limited access to fossil fuels, technologies for efficient on demand delivery of renewable energy are highly desirable. In this regard, methods that allow for solar energy storage and on demand solar driven power generation are particularly relevant since the sun is the most abundant energy source.1Recently, some attention has been directed toward an organometallic fulvalene diruthenium couple which has shown great potential for energy storage capabilities and photoconversion in solution.2-4Here, we report on a derivative of this organometallic molecule that can store solar energy in the form of chemical bonds and release the stored energy in the form of heat in a reversible manner when stimulated thermally or catalytically.

Figure 1 Conceptual illustration of a solarthermal energy storage system. The energy storage material is energetically excited by flow through a high surface area solar collector. From there it either can be temporarily stored or directly pumped to a solid state catalysis device where the stored heat is extracted by heat exchange.

Demonstration of the practical function of this material in a device is achieved by near complete conversion of highly concentrated solutions of the molecule in a continuous flow micro fluidic reactor by the means of light generated by a solar simulator. Our DSC measurements indicate that this novel organometalic compound can store 109 kJ/mol and with a solubility of more than 0.4 M in toluene could then potentially provide an adiabatic temperature rise of up to 30 oC.

References [1] Acc. Chem. Res. 42, 1859-1860 (2009). 2. J. Am. Chem. Soc. 119, 6757-6773 (1997). 3. Synthesis, 3373-3379, (2005). 4. Angew. Chem. Int. Ed. 49, 1-5, (2010).

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C28 - The Effect of Thermal Annealing on Charge and Photocurrent Generation in Hybrid P3HT-InP Quantum Dot Solar Cells

Thitikorn Boonkoom a, Saif Haqueb, John de Melloc a, Imperial College London, 134, Chemistry, South Kensington Campus, GB b, Imperial College London, 164b, Chemistry, South Kensington Campus, GB c, Imperial College London, 440, Chemistry, South Kensington Campus, GB

Polymer-quantum dot hybrid solar cells have attracted significant research interest due to the possibility of cost effective production by solution processing. Power conversion efficiencies exceeding 3% have been reported in polymer-CdSe solar cells. However, studies using lower toxicity semiconductor nanoparticles have been limited to date. In this work, we consider the use of InP nanocrystals as the electron accepting and transporting species. The use of such materials offers the prospect of improved light harvesting due to a low band gap (1.35 eV) and good charge carrier collection due to the high electron mobility of InP. In this work we first report the synthesis and functionalization of InP quantum dots. We then investigate the potential of such InP dots as electron acceptors in hybrid solar cells. We present a study involving optical, morphological, and device characterization. More specifically, UV-Vis and photoluminescence spectroscopy were performed to characterize the optical properties of the composite poly(3-hexylthiophene) (P3HT)-InP material. We found quenching of P3HT emission when InP quantum dots are blended into the P3HT matrix. More importantly, we used transient absorption spectroscopy (TAS) to determine the influence of InP quantum dot weight ratio and thermal annealing on charge generation yield in the blend. Transmission electron microscopy (TEM) was used to investigate the morphology of the P3HT-InP films. Photovoltaic devices of structure ITO/PEDOT:PSS/P3HT:InP/Ca/Al were fabricated and tested under simulated AM1.5 conditions. The effect of thermal annealing on device performance was also monitored to determine the correlation between charge generation yield and the device photocurrent.

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C29 - Identification of suitable metallic substrate /electrolyte combinations for Dye-sensitised Solar Cells

Bruce Philip, Trystan Watson, David Worsley, Gavin Reynolds Specific, Swansea university, College of engineering, Baglan Bay Innovation and knowledge Centre, Central avenue, Baglan energy park, baglan, Port Talbot, Swansea, SA12 7AX, GB

Dye-sensitised Solar Cells (DSC) are attracting significant interest from a number of prominent sheet metal manufacturers who are keen to incorporate building integrated PV to capitalise on the enormous areas of steel cladding erected on walls and roofs of industrial buildings every year. With the introduction of new and more efficient electrolytes the problem of corrosion is of major concern for the longevity of metal based DSC [1,2]. This work investigates the corrosion of metals exposed to an iodide / triiodide (I- / I3

-) electrolyte and demonstrates novel techniques that provide a rapid screening mechanism for identification of suitable metals or alloys for use as stable DSC substrates. The anodic dissolution of a metal is coupled with cathodic reduction of triiodide (I3

-) to colourless iodide ions (I-) in solution. This colour shift has been exploited using two optical techniques, analysis of red, green and blue (RGB) values of time laps photographic images and changes in the absorption spectra using UV-vis reflectance spectroscopy, to provide a quick and simple means of quantifying corrosion rates for a range of metallic substrates. In addition, the Scanning Vibrating Electrode Technique (SVET), commonly used to determine the location and intensity of anodic and cathodic activity on the surface of corroding samples immersed in aqueous electrolyte solutions, has been adapted to allow measurements in non-aqueous I- / I3

- electrolytes.

Figure 1 False colour, profile map illustrating SVET image of 4.5mm x 4.5mm hot dip galvanised steel substrate after 12 hours exposure to I- / I3- electrolyte. The red areas denote anodic activity, the blue areas cathodic activity and the white areas electrochemical neutrality.

Analysis of a 25mm electrolyte layer encapsulated between a glass slide and a range of metals showed good correlation of results using the photographic and UV-vis techniques. Zinc, a commonly used metallic coating in the steel industry, reacted rapidly with the complete and irreversible loss of I3

- in a number of minutes. Conversely, titanium remained impervious to the aggressive electrolyte for months. The SVET experiments give greater clarity to the distribution and intensity of corrosion events on the substrate surface allowing the results to be plotted as a series of false colour maps, an example of which is illustrated in figure 1. The results obtained further reinforce the order of corrosion activity demonstrated using the optical techniques.

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This work emphasises the need for careful consideration and screening of potential metallic substrate / electrolyte combinations for DSC applications and the techniques described provide an accurate means of evaluating protection methodologies to enable suitable materials selection for product durability.

References [1] Minna Toivola, Fredrik Ahlskog and Peter Lund. “Industrial sheet metals for nanocrystalline dye-sensitized solar cell structures”. Solar Energy Materials and Solar Cells, 90, 2881 – 2893, (2006). [2] Aswani Yella, Hsuan-Wei Lee, Hoi Nok Tsao, Chenyi Yi, Aravind Kumar Chandiran, Md.Khaja Nazeeruddin, Eric Wei-Guang Diau, Chen-Yu Yeh, Shaik M Zakeeruddin and Michael Grätzel. “Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency”. Science, 334, 629, (2011).

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C30 - Performance of metal based dye solar cells with cobalt electrolyte

Kati Miettunena, Tapio Saukkonenb, Xiaoe Lic, ChunHung Lawc, Piers Barnesc, Brian O'Reganc a, Aalto University, P.O.B. 15100, Aalto, 00076, FI b, Aalto University, P.O.B. 14200, Aalto, 00076, FI c, Imperial College London, South Kensington Campus, SW7 2AZ, UK

To enable roll-to-roll mass production dye solar cell (DSC), the transfer of the technology on flexible substrates such as plastic and metal foils is required. The use of metallic substrate has many advantages such as very high conductivity, endurance of high temperature treatments, non-permeability and it can give significant cost savings, for instance Al foil is 1000-times cheaper compared to traditional conductive glass used in DSCs [1]. The major challenge with metallic electrodes is their tendency to corrode in the conventional iodine containing electrolyte and because of that even stainless steel needs additional protective coating [2,3]. To facilitate the use of cheap metals as substrates without the additional cost increasing coatings, the electrolyte needs to be changed to a less aggressive one. Using cobalt complexes instead of iodine has attracted a lot of attention after it was found that the key to high efficiencies is the good matching of the dye with the electrolyte [4]. Here a selection of metals is tested as counter electrode substrates for DSCs filled with cobalt electrolyte: Al, Cu, Ni, Zn, stainless steels (StS) 304 and 312, as well as Ti and glass as a reference. Besides initial performance also the stability of the devices was investigated under light soaking under ~1 Sun at 40 °C. The counter electrodes based on Ni, StS 304, StS 312 and Ti gave similar photovoltaic performance and stability as the glass based cells in the 500 h long stability test. Here a DSC with a StS 304 was recorded to give 1.9 % efficiency. In contrast, Cu based cells showed visible signs of degradation moments after the cell assembly and they also had very low performance in the initial measurements. Further investigations made with SEM showed clear marks of corrosion in the case of Cu. Al and Zn electrodes had also very low performance in the initial measurements; namely the fill factor of the cells was very low (~25 %). This indicated serious problems in the charge transfer at the counter electrode and it seems likely that the oxide layers of these two metals are causing them. Thus in the case of very cheap metals such as aluminum the primary challenge is not the stability but the initial performance. References [1] Hashmi, G.; Miettunen, K.; Peltola, T.; Halme, J.; Asghar, I.; Aitola, K.; Toivola, M.; Lund, P. "Review of materials and manufacturing options for large area flexible dye solar cells". Renew. Sust. Energy. Rev., 15, 3717-3732 (2011). [2] Miettunen, K.; Asghar, I.; Ruan, X.; Halme, J.; Saukkonen, T.; Lund, P. "Stabilization of metal counter electrodes for dye solar cells" J. Electroanal. Chem. 653, 93-99 (2011). [3]Miettunen, K.; Ruan, X.; Saukkonen, T.; Halme, J.; Toivola, M.; Lund, P. "Stability of Dye Solar Cells with Photoelectrode on Metal Substrates", J. Electrochem. Soc. 152, B814-B819 (2010). [4] Feldt, S. M.; Gibson, E. A.; Gabrielsson, E.; Sun, L.; Boschloo, G.; Hagfeldt, A. "Design of Organic Dyes and Cobalt Polypyridine Redox Mediators for High-Efficiency Dye-Sensitized Solar Cells" J. Am. Chem. Soc. 192, 16714-16724 (2010).

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C31 - Improvement of P3HT:PCBM bulk-heterojunction solar cells efficiency by addition of conjugated aryleneethynylene tetrathiol

Alessandra Operamollaa, Aurora Rizzod, Omar Hassan Omarc, Anna Loiudiceb, Alessia Lasorsaa, Giuseppe Giglib, Francesco Babudria, Gianluca M. Farinolaa a, UNIVERSITA' DEGLI STUDI DI BARI , Via Orabona 4, BARI, Italy, IT b, Università del Salento, via Arnesano, I-73100 Lecce, Italy , IT c, Istituto di Chimica dei Composti Organometallici CNR-ICCOM , Via Orabona 4, BARI, Italy, IT d, NNL CNR-Istituto Nanoscienze, c/o Distretto Tecnologico,via per Arnesano km.5, 73100 Lecce, Italy , IT

The improvement of polymer solar cells performances by modification of the blend nanoscale morphology has a crucial role in the development of efficient organic solar panels (1). Alkyl thiols have been widely investigated as processing additives in bulk heterojunction (BHJ) polymer solar cells for the substitution of post-production treatment with low energy consuming alternative processes (2). However, if the commonly adopted alkyl thiols have the main role to modify the solubility of the donor:acceptor couple in the host solvent, there is no knowledge about the effect of the introduction in the blend of conjugated structures with pending alkylthiol groups to be used as third components in the active layer of polymer solar cells.

Figure 1 Structure of compounds 1

We recently synthesized a family of polyvalent thiols having a chelating geometry and an extended conjugation like compounds 1 (Figure 1) (3). Their study in all organic or hybrid nanostructures is still unexplored. Their UV-vis properties make them suitable materials for investigation in photovoltaics, in combination with polymer blends or hybrid organic-inorganic systems. Building on this ground, in this communication we present the synthesis of compounds 1 and we demonstrate the photovoltaic response of one of these compounds employed as third component in P3HT:PCBM solar cells. We demonstrate the ability of the conjugated S-acetyl tetrathiol 1 in nanomorphology modification which, in combination to its contribution in the charge generation processes operating in the device, benefits the short circuit current and the overall performances, causing a significant increase in efficiency from 2 to 2.5%. References [1] Peet, J.; Senatore, M. L.; Heeger, A. J.; Bazan, G. C. “The Role of Processing in the Fabrication and Optimization of Plastic Solar Cells”, Adv. Mater., 21, 1521–1527 (2009); [2] Pivrikas, A.; Neugebauer, H.; Sariciftci, N. S. “Influence of processing additives to nano-morphology and efficiency of bulk-heterojunction solar cells: A comparative review”, Solar Energy 85,1226–1237, (2011); [3] Hassan Omar, O; Babudri, F. Farinola, G. M.; Naso, F.; Operamolla, A. “Synthesis of S-Acetyl Oligo-p-aryleneethynylene Tetrathiols”, Eur. J. Org. Chem. 529-537, (2011).

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C32- Monitoring ultra-fast multi-sensitization of dye sensitized solar cells using a rapid, continuous in situ process

Matthew Daviesa, Trystan Watsonb, Peter Hollimana, Arthur Connella, David Worsleyb a, The School of Chemistry, Bangor University, Bangor, Gwynedd, LL57 2UW, GB b, SPECIFIC, College of Engineering, Swansea University, Baglan Bay Innovation Centre, Central Avenue, Baglan Energy Park, Baglan, Port Talbot, SA12 7AZ , GB

For dye sensitized solar cells (DSC) to achieve commercial success, two key issues must be addressed; firstly, time consuming laboratory-scale DSC manufacture needs to be replaced with rapid, continuous commercial-scale processing and, secondly, device efficiencies must increase to compete with Si and thin film PV. One key DSC manufacturing step is dye sorption to the photo-anode surface which typically takes up to 24 h. The dye sorption needs speeding up significantly to hasten device development and facilitate the commercial manufacture of these devices to realise the promise of DSC as a low cost and scalable PV technology. Recently significant developments have been made in the field of ultra-fast sensitisation of DSC (<5min) giving 6.0% for the Ru dye N719, 3.7% for the IR absorbing squaraine SQ1 and 7.9% for co-sensitization using N719 and SQ1.1

Figure 1 (a) Percentage dye uptake for; (i) multi-sensitized device (black) with a <5 min saturation time, (ii) squaraine dye SQ1 with a co-adsorbent (light blue) and (iii) SQ1 with no co-adsorbent (dark blue). (b) Degradation of SQ1 with co-adsorbent (no degradation without).

Related research has developed accurate, in situ measurements of passive dye uptake in DSC photo-electrodes using digital image capture (DIC) followed by image analysis.2 This paper will describe further developments of these procedures to quantify dye uptake in real time using the ultra-fast dyeing method for both single dye and multi-dye systems. It has been found that mixing different dyes and co-adsorbents can have a significant effect of the saturation time and stability of dye systems. The effect of a co-adsorbent, chenodeoxycholic acid (CDCA), on the stability of and saturation time of dye systems, has also been investigated. We will also report a multi-dye system that saturates a TiO2 photo-electrode in sub-5 minutes at room temperature yielding higher efficiencies than those achieved with the individual dyes dyed at temperature (50 °C). This paper will also describe some of the advantages of ultra-fast multi-sensitization coupled with real time digital image capture; particularly it’s simplicity and wide applicability. Thus, in theory, any single dye, or multiple dyes, can be studied by this method. The method of rapid and controlled multi-dye sensitization could have a significant impact for DSC

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manufacture; producing very highly efficient cells in a short amount of time via a simple and easy method. References [1] P.J. Holliman, M.L. Davies, A. Connell, B. Vaca Velasco, T.M. Watson. "Ultra-fast sensitisation and co-sensitisation for dye-sensitised solar cells". Chem. Comm., 46, 7256-7258 (2010). [2] T.M. Watson, P.J. Holliman and D. Worsley. "Rapid, continuous in situ monitoring of dye sensitisation in dye-sensitized solar cells" J. Mater. Chem., 21, 4321-4325 (2011).

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C33 - Transparent, air-stable copper electrodes for electron-extraction in organic photovoltaics

Oliver Hutter, Ross Hatton Univeristy of Warwick, University of Warwick, Coventry, 0, GB

Optically thin metal films are receiving growing attention as an economically viable alternative to conducting oxide electrodes. Whilst copper is particularly attractive for this application, owing to its high electrical conductivity and relatively low cost, its susceptibility to oxidation is a serious drawback.

Figure 1

We report the fabrication and properties of optically thin nano-structured copper electrodes that are resistant to oxidation in air and ozone treatment. These chemically well-defined window electrodes are employed as the electron-extracting electrode in efficient bulk heterojunction organic photovoltaics, removing the requirement for a low work function metal electrode. The science that underpins the operation of these electrodes is discussed with reference to measurements of the interfacial energetics.

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C34 - Approaching the ultimate open circuit voltage in thiophene based single junction solar cells by applying diindenoperylene as acceptor

Ulrich Hörmanna, Julia Wagnera, Mark Grubera, Andreas Opitzb, Wolfgang Brüttinga a, Institut für Physik, Universität Augsburg, Universitätsstr. 1, Augsburg, 86135, DE b, Institut für Physik, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 6, Berlin, 12489, DE

The efficiency of a photovoltaic cell is directly proportional to its open circuit voltage. This in turn is eventually set by the intermolecular gap, i.e. the energy of the donor-acceptor charge-transfer state in organic solar cells. In this contribution we introduce diindenoperylene (DIP) as a new molecular acceptor and compare it to C60 in planar heterojunction cells. Being able to deliberately change the morphology of the molecular films by varying the substrate temperature during the growth process, we demonstrate that the Voc not only scales with the intermolecular gap but also strongly depends on the morphology of the organic films.

Figure 1 An open circuit voltage of almost 1.4 V is reached in planar heterojunction cells of heat treated 6T and DIP.

We show that planar heterojunctions of thiophene derivatives and DIP yield extraordinarily high open circuit voltages of approximately 1.2 V for poly(3-hexylthiophene) and almost 1.4 V for heat treated α-sexithiophene [1]. Those values are close to the maximum Voc attainable for these material systems.

References [1] Hörmann, U.; Wagner, J.; Gruber, M.; Opitz, A.; Brütting, W. “Approaching the ultimate open circuit voltage in thiophene based single junction solar cells by applying diindenoperylene as acceptor”, phys. stat. sol. RRL 5, 241–243 (2011).

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C35 - Electron transport in ultrafast sintered TiO2 thin films; application to the manufacture of dye-sensitized solar cells

David Worsley, Cecile Charbonneau, Matthew Carnie, Trystan Watson SPECIFIC, Swansea University, Baglan Bay Innovation and Knowledge Centre, Baglan, SA12 7AX , UK

As the industrialisation of dye-sensitized solar cells proceeds, manufacturing techniques that address process bottlenecks are being developed to facilitate cost effective roll to roll fabrication. Prior to the implementation of any new manufacturing techniques it is essential that the effects of the process on the material properties, and the resulting photovoltaic characteristics, are known. Sintering of TiO2, which typically can take up to 30 minutes in a conventional oven, is one such process bottleneck. Recently, near infra red (NIR) radiative heat treatment has reduced the sintering time of TiO2 on a flexible metal foil to 12 seconds leading to potentially increased manufacturing throughput (1.). A peak metal temperature of over 500 °C can be achieved within seconds and it is this principle that can be applied inline to deliver high intensity heating to a TiO2 paste. Here we present a detailed study on ultrafast sintered TiO2 films (continuous NIR heating, 12 seconds) and compare their properties to conventionally sintered films (static convection, 1800 seconds).

Figure 1 Transport resistances of typical cells made with NIR and conventionally sintered films.

Our data shows that progressive increases in NIR lamp power cause an increasing improvement in fill factor and a decreasing trend in TiO2 transport resistance which is indicative of improving TiO2 particle interconnectivity (figure 1). It appears that NIR sintered films not only match conventionally sintered films in terms of efficiency and transport resistance but in some cases can have lower transport resistances suggesting improved particle interconnectivity in films sintered using NIR radiation. This trend only occurs to a certain point as TiO2 films sintered using the highest NIR lamp powers show a drop off in performance. Further information is derived from XRD analyses which have identified morphological changes (anatase-to-rutile phase transition and particle size) of the TiO2 film that occur during longer heating processes as opposed to novel fast heating methods.

References [1] Watson, T.; Mabbett, I.;Wang, H.; Peter, L.; Worsley, D. "Ultrafast near infra red sintering of TiO2 layers on metal substrates for dye-sensitized solar cells" Progress in Photovoltaics: Research and Applications 19 482-486 (2011).

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C36 - Series Interconnections for Dye Solar Cell Modules: Stability and Materials

Fabrizio Giordanoa, Andrea Guidobaldia, Eleonora Petrolatib, Thomas M. Browna, Andrea Realea, Aldo Di Carloa a, CHOSE- Centre for Hybrid and Organic Solar Energy, University of Rome “Tor Vergata”, Electronic Engineering Department, Via Giacomo Peroni 400, Rome, 131, IT b, DYEPOWER, Viale Castro Pretorio, 122 - 00185 - Rome, IT

Dye Solar Cells (DSCs) represent now the most mature technology of the new generation Photovoltaics. Series connection can be realized in “W” or “Z” configurations. Such schemes were optimized in our previous works(1,2) by accounting for losses due to up-scaling processes and large area design such as the resistance of series interconnections, transparent conducting oxides TCO, the ratio between active and total areas of the module. Here we will consider DSC modules fabricated using the Z and W interconnection schemes(Fig 1 a and b) and their behaviour in temperature and during ageing tests.W moduels that were geometrically balanced at standard illumination conditions (AM1.5G) and at fixed temperature (22 deg)show remarkable instability in temperature (Fig 1 c). An explanation to this phenomenon as well as possible solutions will be given here.

Figure 1 Z connection scheme (a) and W connection scheme (b); “W” module I-V characteristics at different Temperatures(c);I-V characteristics of a dye solar cell illuminated from the Front (squares) and back (circles) at 30

•C (black) and 60•C (red)(d).The same loss in current density was observed for both front and back illuminated cells when temperature was increased from 30 ·C to 60 ·C(Fig 1 d). Indeed no differences were observed (over the same range of temperatures) for cells with different cell width.An efficient way to seal modules properly by thermoplastic is presented.Moreover the use of different materials such as electrolytes and organic dyes was evaluated over these two schemes, in comparison with the standard ones ( I-/I-

3, N719).

In conclusion we present a quantitative comparison of the performance provided by these two different types of optimized modules (Z and W), to evince technological necessities, advantages and disadvantages of both configurations.

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References [1] F.Giordano; E.Petrolati; Thomas M. Brown;Andrea Reale; Aldo Di Carlo, “Series-Connection Design for Dye Solar Cell Modules” IEEE Transactions on Electron Devices Aug. 2011 Vol:58 Issue:8 pp: 2759 - 2764 [2] F.Giordano; E.Petrolati;Simone Mastroianni; Thomas M. Brown;Andrea Reale; Aldo Di Carlo, “W and Z Dye solar cell modules ”- HOPV 2009

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C37 - Stable Dye-Sensitized Solar Cells Based on Nanosized Zeolites Dispersion in the TiO2 Layer

Simone Guarneraa, Annamaria Petrozzab, Stefano Perissinottob, Antonio Bonuccic, Guglielmo Lanzanib a, Politecnico di Milano, piazza Leonardo da Vinci 32, Milano, 20133, IT b, Center for Nano Science and Technology @Polimi Istituto Italiano di Tecnologia, via Pascoli 70/3, Milano, 20133, IT c, SAES Getters S.p.A., viale Italia 77, Lainate (MI), 20020 , IT

Dye-sensitized solar cells (DSSCs) are a promising technology for a variety of applications and long term stability is an essential feature to wide commercialization [1]. In particular, water infiltration inside the cell has been found as one of the main cause of efficiency degradation [2]. Permeation can be reduced by barrier layers, but most of the time, good quality barriers increase the cost and/or the weight of the device. To address this problem we propose, as an alternative solution, the use of integrated getter [3]. We have dispersed inside the mesoporous TiO2 layer, LTA-Na zeolites (300nm nanoparticles), a well known class of moisture getters that are able to absorb moisture; in this way water molecules that can get through the sealant and infiltrate inside the cell are neutralized. These particles are already introduced in the first fabrication steps and they are activated during the sintering process of TiO2 porous substrates. Therefore they can protect the cell already during the fabrication process when they are not shielded from the external world by any kind of barrier. The optical properties of this innovative structure have been first investigated. We found that these particles are efficient light scattering centers, therefore, though the dye loading in presence of the nanozeolites is lower, these substrates present a gain in terms of light absorption. Then, these unconventional substrates have been tested as photoanodes in working DSSCs. Performances are almost unchanged in presence of nanozeolites while aging tests show a clear and encouraging improvement of the devices stability. References [1] Asghar, M. I.; Miettunen, K.; Halme, J.; Vahermaa, P.; Toivola, M.; Aitola, K.; Lund, P. "Review of stability for advanced dye solar cells". Energy Environ. Sci. 3, 418–426 (2010). [2] Agrell, H. G.; Lindgren, J.; Hagfeldt, A. "Degradation mechanisms in a dye-sensitized solar cell studied by UV–VIS and IR spectroscopy". Solar Energy 75, 169–180 (2003). [3] Bonucci, A.; Macchi, R.; Giannantonio, R. Patent No WO2011076492

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C38 - A new electrical model for the analysis of partially shaded dye solar cell modules

Roberto Giannuzzi, Michele Manca, Giuseppe Gigli Italian Institute of Technology, via Barsanti 1 , Arnesano (LECCE), 73010, IT

Partial shading is a commonly encountered mismatch problem in a photovoltaic system. In the drawing near perspective of their massive building integration, dye solar cell (DSC) modules may realistically receive different levels of irradiance, a situation similar to partial shading. In these conditions, the electrical characteristics of the DSC module change significantly. To date only few studies about the effect of the partial shadowing on the photovoltaic characteristics of DSC module have been reported. In such reports the electrical behavior of the cell in forward bias is described by means of a model based on the continuity equation (or more specifically by means of the diode equation) whereas the Butler–Vollmer model is generally used to describe the cell in reverse bias conditions. 1-2 Starting from these remarks, we have been focused on the elaboration of a more accurate analytical model capable to adequately describe the I-V characteristics of a DSC module even when it is operating upon partial shadowing conditions. In particular we intended to modify the one diode equation equivalent circuit model of a photovoltaic cell by properly introducing a second diode in order to conveniently take into account the cell’s electrical behavior even in reverse bias conditions. Such a two-diode model has been thus implemented to examine the photovoltaic behavior of a DSC module constituted by four series elements in the case in which one (or more) of them resulted partially or totally shadowed.3

Figure 1 left) I-V characteristics of a 4-cells module with 0, 2 and 3 fully shadowed cells . right )Equivalent electrical circuit based on the two-diodes model

In this work the experimental I-V characteristics measured under systematically different illumination conditions have been investigated and compared with the corresponding simulated plots as obtained through the implementation of the above referred two-diodes based equivalent circuit. A perfect matching between the experimentally measured I-V characteristics and the simulation results, as obtained through the implementation of the two-diodes-based model, has been revealed. It has to be also highlighted that our approach has recourse to a significantly less number of physical and chemical parameters with respect to the previously proposed models, that makes it definitively more reliable and effective.

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References [1] Sastrawan R, Renz J, Prahl C, Beier J, Hinsch A, Kern R. “Interconnecting dye solar cells in modules—I–V characteristics under reverse bias”. Journal of Photochemistry and Photobiology A: Chemistry 2006; 178 : 33-40. [2] Chen S, Weng J, Huang Y, Zhang C, Hu L, Kong F, Wang L, Dai S. “Numerical model analysis of the shaded dye-sensitized solar cell module”. J. Phys. D: Appl. Phys. 2010; 43 : 305102. 3.Giannuzzi R. , Manca M. and Gigli G. “A new electrical model for the analysis of partially shaded dye solar cell modules” Prog. Photov. Res. Appl. , accepted.

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C39 - Carbon nanomaterials as flexible dye solar cell counter electrodes

Kerttu Aitolaa, Maryam Borgheia, Antti Kaskelaa, Albert Nasibulina, Esko Kauppinena, Peter Lunda, Virginia Ruizb, Janne Halmea a, Aalto University School of Science, P.O.Box 15100, Aalto, 00076, Finland b, CIDETEK-IK4 - Centre for Electrochemical Technologies, Paseo Miramón 196, E-20009 Donostia-San Sebastián, Spain

The dye solar cell (DSC) can be manufactured cost-effectively in the industrial scale by roll-to-roll deposition techniques, but for those the active materials and substrates have to be flexible. We tested several carbon nanomaterials and their composites as DSC counter electrodes (CE) and compared them in terms of their flexibility, conductivity, catalytic performance, thickness and transparency (1,2). The tested materials were thin, semitransparent single-walled carbon nanotube (SWCNT) random network film on plain plastic (polyethylene terephthalate, PET), vertically aligned multi-walled carbon nanotube (MWCNT) “forest” film on quartz and Inconel steel, carbon nanoparticle composite film on indium tin oxide-PET (ITO-PET) and SWCNT-conductive polymer composite film on plain PET substrate. The catalytic performance of the pristine SWCNT and MWCNT films was only modest toward the triiodide reduction reaction of the DSC CE. The SWCNT film had to be relatively thick (10 % transparent) to obtain sufficient conductivity, and in the MWCNT film the lateral conductivity had to be ensured with a metal layer. The carbon nanoparticle composite had to be very thick to obtain sufficient catalytic performance, nevertheless an additional conductive layer was needed. The SWCNT film was however the most flexible of the studied films, it offered the best potential for (semi)transparency and it could be deposited with an easy press-transfer method. Therefore it was investigated whether its catalytic performance could be improved, and conductive poly(3,4-ethylenedioxythiophene) (PEDOT) was electrochemically deposited on a 10 % transparent SWCNT film (2). The resulting PEDOT-SWCNT film outperformed sputtered platinum on ITO-PET as catalyst, as well as electrochemically deposited PEDOT on ITO-PET. It was observed that the reason for the superior catalytic performance was the fact that the porous SWCNT film provided a high-surface area platform for the PEDOT nucleation and growth, thus maximizing the composite catalyst film interfacial area. It was concluded that the SWCNT network film is an interesting potentially cheap and flexible alternative material for the DSC CE, but for the iodide/triiodide redox couple its catalytic performance has to be improved with e.g. PEDOT polymer. References [1] Aitola, K.; Halme, J.; Halonen, N.; Kaskela, A.; Toivola, M.; Nasibulin, A.G.; Kordás, K.; Tóth, G.; Kauppinen, E.I.; Lund, P.D. "Comparison of dye solar cell counter electrodes based on different carbon nanostructures". Thin Solid Films, 519, 8125-8134 (2011). [2] Aitola, K.; Borghei, M.; Kaskela, A.; Kemppainen, E.; Nasibulin, A.G.; Kauppinen, E.I.; Lund, P.D.; Ruiz, V.; Halme, J. "Flexible metal-free counter electrode for dye solar cells based on conductive polymer and carbon nanotubes". Submitted.

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C40 - Damning Evidence of the Beneficial Effect of Liquid Crystalline Phases in Solid-State Dye-Sensitized Solar Cells

Rubén D. Costaa, Xinjiao Wangb, Philipp Grönningera, Sebastian Feihla, Fabian Wernera, Karsten Meyerb, Dirk M. Guldia a, Friedrich-Alexander-Universität Erlangen-Nürnberg, Department of Chemistry and Pharmacy& Interdisciplinary Center for Molecular Materials (ICMM) , Egerlandstrasse 3,, Erlangen, 91058, DE b, Friedrich-Alexander-Universität Erlangen-Nürnberg, Department of Chemistry and Pharmacy, Inorganic Chemistry, Egerlandstrasse 3,, Erlangen, 91058, DE

Nowadays, one of the most promising solar energy conversion devices are Dye-Sensitized Solar Cells (DSSCs) owing to their high efficiencies and their cheap and low-energy production.[1] However, their short lifetime is a clear bottleneck that happens when they are commercialized. The main reason is the use of solvent electrolytes to regenerate the dye. These fail to be stable as a function of time due to solvent leakage and evaporation processes, especially, under outdoor temperature conditions (50 -80 ºC).[2] Hence, the long term objective is to develop solid-state DSSCs (ssDSSCs) with high performances at the above mentioned conditions.[2,3] En route towards ssDSSCs novel ionic liquids (ILs), that is, double alkyl-substituted imidazolium iodine derivatives, were synthesized and integrated into ssDSSCs as a single-component electrolyte. In contrast to standard solvent-based DSSCs, our devices reveal better performances under outdoor temperature conditions. A likely rationale for this finding is the fact that the selected ionic liquids are at the given temperature regime in a liquid crystalline phase, in which the ionic conductivity and diffusion are optimum, and the leakage and evaporation processes, typically observed in standard DSSCs, are completely eliminated. Indeed, our most valuable result is the unambiguous confirmation of the beneficial effect of liquid crystalline phases in ssDSSCs owing to the relationship between maximum slope in efficiency changes, which reaches a high value of 2.5 % between 50 – 80 ºC, and the thermal behavior of the studied ionic liquids. References [1] M. Pagliaro, et al. Flexible Solar Cells. Wiley-VCH, 2008. [2] a) Asghar, M. I. et al. Energy & Enviromental Science 3, 418, (2010). b) Li, D. et al. Energy Environ. Sci. 2, 283 (2009). [3] a) Zhao, Y et al . Chem. Mater., 20, 6022 (2008). b) Wang, H. et al. Adv. Mater. 24, 121(2012)

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C41 - A new electrical model for the analysis of partially shaded dye solar cell modules

Roberto Giannuzzi, Michele Manca, Giuseppe Gigli Italian Institute of Technology, via Barsanti 1 , Arnesano (LECCE), 73010, IT

Partial shading is a commonly encountered mismatch problem in a photovoltaic system. In the drawing near perspective of their massive building integration, dye solar cell (DSC) modules may realistically receive different levels of irradiance, a situation similar to partial shading. In these conditions, the electrical characteristics of the DSC module change significantly. To date only few studies about the effect of the partial shadowing on the photovoltaic characteristics of DSC module have been reported. In such reports the electrical behavior of the cell in forward bias is described by means of a model based on the continuity equation (or more specifically by means of the diode equation) whereas the Butler–Vollmer model is generally used to describe the cell in reverse bias conditions. 1-2

Figure 1 left) I-V characteristics of a 4-cells module with 0, 2 and 3 fully shadowed cells . right )Equivalent electrical circuit based on the two-diodes model

Starting from these remarks, we have been focused on the elaboration of a more accurate analytical model capable to adequately describe the I-V characteristics of a DSC module even when it is operating upon partial shadowing conditions. In particular we intended to modify the one diode equation equivalent circuit model of a photovoltaic cell by properly introducing a second diode in order to conveniently take into account the cell’s electrical behavior even in reverse bias conditions. Such a two-diode model has been thus implemented to examine the photovoltaic behavior of a DSC module constituted by four series elements in the case in which one (or more) of them resulted partially or totally shadowed.3 In this work the experimental I-V characteristics measured under systematically different illumination conditions have been investigated and compared with the corresponding simulated plots as obtained through the implementation of the above referred two-diodes based equivalent circuit. A perfect matching between the experimentally measured I-V characteristics and the simulation results, as obtained through the implementation of the two-diodes-based model, has been revealed. It has to be also highlighted that our approach has recourse to a significantly less number of physical and chemical parameters with respect to the previously proposed models, that makes it definitively more reliable and effective.

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References [1] Sastrawan R, Renz J, Prahl C, Beier J, Hinsch A, Kern R. “Interconnecting dye solar cells in modules—I–V characteristics under reverse bias”. Journal of Photochemistry and Photobiology A: Chemistry 2006; 178 : 33-40. [2] Chen S, Weng J, Huang Y, Zhang C, Hu L, Kong F, Wang L, Dai S. “Numerical model analysis of the shaded dye-sensitized solar cell module”. J. Phys. D: Appl. Phys. 2010; 43 : 305102. 3.Giannuzzi R. , Manca M. and Gigli G. “A new electrical model for the analysis of partially shaded dye solar cell modules” Prog. Photov. Res. Appl. , accepted

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C42 - Effect of temperature on the performance of dye solar cells

Francisco Fabregat-Santiago, Sonia R. Raga Universitat Jaume I, Avda. V. Sos Baynat s/n, Castell, 12003, ES

The energy conversion efficiency of Dye solar cells rises with temperature with a maximum at around 30-40ºC decreasing at higher temperatures. This behaviour diverges from the typical decrease, at a constant rate, in the performance of standard solar cell technologies such crystalline silicon and cadmium telluride with rising temperatures. (1) In this work, the origin of this characteristic behaviour is explained. Data show that under illumination the recombination kinetics remains the same in the range of temperatures between -7 and 40 ºC and very similar to the one obtained in the dark at 40ºC. A further increase of temperature to 50ºC produces an increase in the recombination kinetics, again similar both in the dark and under illumination.

Figure 1 Comparison of energy conversion efficiencies for different photovoltaic technologies and temperatures. Black squares represent the efficiency obtained from J-V curves in Figure 3 normalized to match the published data of a 9.3% efficient DSC module (red void circles). Yellow square represents the estimation obtained for the record 9.9% efficient module taking into consideration the extra energy collected by DSCs in real outdoor conditions. pc-Si experimental (green triangles) stands for data from a commercial polycrystalline silicon solar module and CdTe estimated (orange dash line) is the simulation of a 11% module with temperature coefficient -0.25 % K-1. The dotted line marks NOCT temperature, where performance comparison approaches real operation conditions.

These results suggest that the illumination produces a rise in the temperature of the active layer to temperatures around 40ºC. As a consequence, the efficiency of the cell, which in this situation is dominated by recombination, remains virtually constant, with only small differences in the fill factor associated to changes in the series resistance. The increase of recombination at 50ºC yields to a lower photopotential and consequently lower device performance. (2) Finally, we discuss on the comparison of conversion efficiencies among different technologies. Simple calculations show that at the normal operating temperatures, the gap among DSC and other standard technologies is much smaller than generally acknowledged. (3), (4)

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References [1] Nozawa, T. "Organic Solar Cells Now Produced in Volume" Nikkei Electronics Asia 2008, July, http://techon.nikkeibp.co.jp/article/HONSHI/20080625/153868/ [2] Fabregat-Santiago, F.; Garcia-Belmonte, G.; Mora-Sero, I.; Bisquert, "Characterization of nanostructured hybrid and organic solar cells by impedance spectroscopy" Phys. Chem. Chem. Phys. 2011, 13, 9083 [3] Green, M. A.; Emery, K.; Hishikawa, Y.; Warta, W. "Solar cell efficiency tables (version 37)," Prog. Photov.: Res. Appl. 2011, 19, 84. [4] Toyoda, T.; Sano, T.; Nakajima, J.; Doi, S.; Fukumotoa, S.; Ito, A.; Tohyamaa, T.; Yoshida, M.; Kanagawa, T.; Motohiro, T.; Shiga, T.; Higuchi, K.; Tanaka, H.; Takeda, Y.; Fukano, T.; Katoh, N.; Takeichi, A.; Takechi, K.; Shiozawa, M. “Outdoor performance of large scale DSC modules” J. Photochem. Photobiol. A: Chem. 2004, 164, 203.

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C43 - Electrostatic layer-by-layer films based on conjugated polyelectrolytes: an alternative approach towards solar energy conversion

Luiz Carlos P. Almeidaa, Valtencir Zucolottob, Neil J. Covillec, Ana F. Nogueiraa a, Chemistry Institute, University of Campinas (UNICAMP), Campinas SP, P.O. Box 6154, Zip Code 13083970, Brazil b, Physics Institute of São Carlos, University of São Paulo, São Carlos SP, Brazil c, DST/NRF Centre of Excellence in Strong Materials and Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg, South Africa

Different techniques have been employed to fabricate organic photovoltaic devices, including spin-coating, thermal evaporation and chemical vapor deposition. These techniques, however, exhibit drawbacks such as high temperature requirement and the high amount of toxic materials often employed such as organic solvents. As an alternative for thin film fabrication, electrostatic self-assembly layer-by-layer (LBL) technique has attracted much attention because it is a simple and versatile method to prepare multilayer thin films1. Moreover, because water is part of the LbL fabrication process, films made from conjugated polyelectrolytes are less sensitive to moisture and may show improved stability under atmospheric conditions. In this presentation, we will discuss the application of LBL technique to fabricate multilayer thin films based on poly(p-phenylenevinylene) (PPV) and polythyophene (PTEBS) derivatives, carboxylic-functionalized single-walled carbon nanotubes (SWNT-COOH) and water-soluble fulleropirrolidine (C60

+).

Figure 1 AFM images of (a) [(PPV/DBS)100:(PEI/SWCNTs-COOH)8] and (b) (PTEBS/C60+) LbL films deposited onto ITO/glass substrates (scanned area of 5.0 × 5.0 µm2). (c) Current-voltage characteristics of ITO/(PTEBS/C60+)40 electrode in aqueous solution (0.5 mol L-1, Na2SO4) under AM 1.5 illumination.

First, we investigated a bilayer architecture consisting of a block of (PPV/DBS)100 (electron-donating layer) assembled onto ITO electrodes, followed by an electron-accepting block comprising (PEI/SWCNTs-COOH)n bilayers (where n=3, 5 and 8), resulting in a final [(PPV/DBS)100:(PEI/SWCNTs-COOH)n] architecture2. In the sequence, we studied multilayer films consisting of alternating layers of PTEBS and C60

+ fullerene. These films, represented as (PTEBS/C60

+)m, were prepared with up to 40 bilayers. Multilayer adsorption and film growth of both types of films were investigated upon collecting the electronic spectrum after deposition of each bilayer and morphological aspects of the films were obtained by epifluorescence and AFM microscopies (Figure 1). Steady-state PL spectroscopy and photoelectrochemical experiments confirm charge transfer from PPV to SWCNT and from PTEBS to C60

+ through photocurrent generation obtained from chronoamperometric measurements and I×V curves under illumination.

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References [1] Decher, G. "Fuzzy nanoassemblies: toward layered polymeric multicomposites". Science 277, 1232-1237 (1997). [2] Almeida, L.C.P.; Zucolotto, V.; Domingues, R.A.; Atvars,T.D.Z; Nogueira, A.F."Photoelectrochemical, photophysical and morphological studies of electrostatic layer-by-layer thin films based on poly(p-phenylenevinylene) and single-walled carbon nanotubes" Photochem. Photobiol. Sci. 10, 1766-1772 (2011).

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C44 - Engineered multilayer photoelectrodes for dye solar cells based on shape-tailored TiO2 nanocrystals

Luisa De Marcoa, Michele Mancaa, Roberto Giannuzzia, Rita Agostaa, Davide Cozzolib, Giuseppe Giglia a, CBN - I.I.T. Italian Institute of Technology , via Barsanti, Lecce, 73010, IT b, NNL - Nanoscience Institute of CNR, Via Arnesano 16 – 73100 Lecce , IT

The ability to fabricate photoanodes in which structural and morphological features of the TiO2 building blocks provide tailored nanotextures with an high degree of functionalities still represents a crucial issue towards boosting the ultimate light-to-electricity conversion efficiency a of dye solar cell. With this aim we recently developed a novel, facile and cost-effective method for preparing high-quality mesoporous films made by different breeds of shape-controlled anatase TiO2 nanorods, which have been conveniently synthesized by means of simple one-step solvothermal routes.[1] The original shape and dimensions of individual nanocrystals were preserved in the final photoelectrodes thanks to the protective action of native organic capping layer at their surface, which prevented coalescence phenomena during the sintering stage. [2] From the analysis of the most relevant electrochemical parameters an intrinsic correlation between the photovoltaic performances and the structure of the nanocrystal building blocks in the photoelectrodes has been deduced and explained on the basis of relative contributions of the electron transport and light-harvesting properties.[3] It has been ascertained that DSSCs based on high aspect-ratio linear nanorods allow for a remarkable improvement in the charge-collection efficiency due to minimization of detrimental charge-recombination processes at the photoelectrode/electrolyte interface. On the other side, DSSCs fabricated from branched nanocrystals with a peculiar bundle-like configuration are characterized by a drastic reduction of undesired charge-trapping phenomena.

Figure 1 SEM images showing the morphology of the multi-layered photoelectrodes prepared from shape-tailored anatase TiO2 nanocrystals along with the corresponding sketch. Photovoltaic performance of multilayered and reference DSSCs (active area: 0.16 cm2, thickness: 16 ìm, aperture mask: 0.25 cm2, average of six devices measurement).

These findings have been useful exploited in the design and fabrication of photoelectrodes with properly engineered properties. We thus defined an optimized photoelectrode

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architecture which embodies three TiO2 layers with different, complementary, peculiarities: a bottom layer, made by small nanorods which assure tremendous specific surface area and exceptional transparency in the dye’s absorption spectrum; a middle layer made by high aspect-ratio nanorods which guarentee a superior electron transport and good dye loading capability; a third upper layer made of relatively bigger hyperbranched nanocrystals which offer adequate light scattering capacity and favorable interfacial charge-transfer characteristics. Such a balanced combination of high specific surface area, efficient electron transport and pronounced light-scattering turned into significant improvement in the dye solar cell’s performances with respect to the case of a conventional nanoparticles-based photoelectrode. An as high power conversion efficiency as 9.5% was eventually achieved by means of our best multilayer configuration[4].

References [1] De Marco, L.; Manca, M.; Giannuzzi, R.; Malara, F.; Melcarne, G.; Ciccarella, G.; Zama, I.; Cingolani, R.; Gigli, G. “Novel Preparation Method of TiO2 Nanorod-Based Photoelectrodes for Dye-Sensitized Solar Cells with Improved Light-Harvesting Efficiency”. J. Phys. Chem. C, 114, 4228-4236 (2010). [2] Buonsanti, R.; Carlino, E.; Giannini, C.; Altamura, D.; De Marco, L.; Giannuzzi, R.; Manca, M.; Gigli, G.; Cozzoli, P. D. “Hyperbranched Anatase TiO2 Nanocrystals: Nonaqueous Synthesis, Growth Mechanism and Exploitation in Dye-Sensitized Solar Cells”. J. Am. Chem. Soc., 133 (47), 19216–19239 (2011). [3] De Marco, L.; Manca, M.; Buonsanti, R.; Giannuzzi, R.; Malara, F.; Pareo, P.; Martiradonna, L.; Giancaspro, N. M.; Cozzoli, P. D.; Gigli, G. “High-quality Photoelectrodes Based on Shape-Tailored TiO2 Nanocrystals for Dye-Sensitized Solar Cells”. J. Mater. Chem., 21, 13371-13379 (2011). [4] De Marco, L.; Manca, M.; Cozzoli, P. D.; Gigli, G.; paper in preparation

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C45 - Excited-State Dynamics of Iron(II)-based Charge-Transfer Chromophores

Allison Browna, Lindsey Jamulab, James McCuskerb a, Department of Chemistry-Ångström Laboratory, Uppsala University, P.O. Box 523, Uppsala, 75120, SE b, Department of Chemistry, Michigan State University, 485 Chemistry, East Lansing, MI, 48823, USA

Dye-sensitized solar cells (DSCs) continue to be an important area of research in the quest for next-generation energy conversion devices. Since Grätzel’s 1991 report on the topic,1 ruthenium-based sensitizers have played a central role as chromophores in DSC technology. Despite initial improvements in overall efficiency - and notwithstanding possible future breakthroughs - such devices have an important practical limitation due to the low natural abundance of ruthenium. Finding a replacement for ruthenium-based chromophores based on earth-abundant materials constitutes the underpinning of our research efforts in the development of new classes of sensitizers for DSCs. Motivated by a 107-fold higher natural abundance, isoelectronic valence configuration, and an initial report suggesting photocurrent production in a (non-optimized) DSC, we are focusing on charge-transfer complexes of Fe(II) as a first step toward scalable dye sensitized solar cells.2

Figure 1 Variable temperature kinetic data for a series of substituted iron(II)terpyridyl complexes. Thermodynamic values were determined by fitting to the Arrhenius equation.

Initial work from our group intimated that a very short (< 100 fs) charge transfer-state lifetime was responsible (at least in part) for the 102-fold lower cell efficiency observed by Ferrere and Gregg. A series of iron(II) based terpyridyl complexes have been synthesized and spectroscopically characterized in an effort to determine the reaction coordinate associated with charge transfer state deactivation with the goal of designing new chromophores with longer MLCT lifetimes. Time-resolved absoprtion spectroscopy revealed a correlation among the structures of these compounds, the activation parameters for ground state recovery, and the MLCT lifetimes. Possible origins of these correlations will be discussed, along with more recent data on a new class of Fe(II) polypyridyl chromophores that appear to hold considerable promise as sensitizers for semiconductor-based DSCs. References [1] ORegan, B.; Grätzel, M. "A LOW-COST, HIGH-EFFICIENCY SOLAR-CELL BASED ON DYE-SENSITIZED COLLOIDAL TIO2 FILMS". Nature 353, 737-740 (1991). [2] Ferrere, S.; Gregg, B. A. "Photosensitization of TiO2 by [Fe-II(2,2 '-bipyridine-4,4 '-dicarboxylic acid)(2)(CN)(2)]: Band selective electron injection from ultra-short-lived excited states". Journal of the American Chemical Society 120, 843-844 (1998).

http://www.nanoge.org/HOPV12/abstract_fig2/out3.html#sdfootnote1sym

http://www.nanoge.org/HOPV12/abstract_fig2/out3.html#sdfootnote2sym

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C46 - Fast charge transport in Solid State Dye Sensitized Cells Using Metal Oxide Nanowires

Varun Sivaram Oxford Physics, St John's College, St Giles St, Oxford, 0, GB

Recent progress in synthesizing and incorporating nanowires into solid state dye sensitized solar cells (SDSC) will be presented. SnO2, TiO2, and ZnO nanowires are compared with respect to structural characteristics (aspect ratio, length uniformity, crystallinity) and device performance, with efficiencies reaching 0.9%. All nanowires are synthesized through a low cost hydrothermal route; challenges and solutions to tuning the morphologies via growth temperature, time, and precursor concentration will be illustrated. Transient photovoltage and photocurrent methods measure over an order of magnitude increase in electron transport rate in nanowire solar cells compared with nanostructured semiconductor counterparts, and the resulting charge collection efficiencies for nanowire solar cells remain close to unity through a wide range of charge densities.

Author: Varun Sivaram Supervisor: Dr. Henry Snaith

Figure 1 ZnO, SnO2, and TiO2 nanowires (left to right). Credit to Jonathan Downing, Imperial College, for growth of ZnO nanowires.

The resulting losses due to comparatively slow hole diffusion in the solid-state hole transporter are probed through photoinduced charge-conductivity modulation spectroscopy, and the conductivity results will be explained using a 2D numerical simulation of a nanowire SDSC.

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C47 - In-situ Investigation of Dye Adsorption on TiO2 Films Using a Quartz Crystal Microbalance with Dissipation Technique

Hauke Harmsa, Nicolas Tétreaulta, Viktoria Gusakb, Kislon Voitschovskyc, Shaik Zakeeruddina, Francesco Stellaccic, Bengt Kasemob, Michael Grätzela

a, Laboratory of Photonics and Interfaces, EPFL, CH F1 494 (Bâtiment CH) Station 6, Lausanne, 1015, Switzerland b, Chemical Physics Group, Department of Applied Physics, Chalmers University of Technology, 412 96 Göteborg, Sweden

c, Supramolecular Nanomaterials and Interfaces Laboratory, MXG 031 (Bâtiment MXG) Station 12, CH-1015 Lausanne, Switzerland

Recently, dye-sensitized solar cells have achieved a record power conversion efficiency of 13.1% (0.5 sun) and 12.3% (1.0 sun) using a Co(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with donor −π-bridge – acceptor (D-π-A) zinc porphyrin dye as sensitizer (YD2-o-C8) and Y123 as cosensitizer.(1,2) We are going through a transition in the field due to recent development of new high extinction porphyrin and organic D-π-A sensitizers that are rapidly supplanting the panchromatic Ru(II) polypyridylsensitizers. In addition, Bazzan et al. have shown an increases of 15% in Jsc and 8% in Voc leading to an overall 23% increase in device performance using acetonitrile:t-butanol/H2O adsorption/desorption cycles.(3) The improvements in photocurrent and photovoltage are assumed to be due to better packing of dye molecules on the TiO2 surface, but only indirect absorption measurements in solution or on thin transparent photoanodes could be carried out. Yet we know alarmingly little about the dynamics of dye adsorption, self-assembly of the monolayer, and formation of multilayers or aggregates. In addition, several reports have pointed out the role of molecular coadsorbates like DINHOP and Cheno that positively affect interfacial recombination and reduce aggregation.

Figure 1 Frequency shift over time, showing two subsequent exposures to Z907 dye solution (55 µM in t-butanol:acetonitrile). The plain solvent mixture without the dye is used as a baseline and for rinsing. Here, the frequency shift corresponds directly to mass uptake.

Herein, we demonstrate for the first time the use of a quartz crystal microbalance with dissipation technique (QCM-D) to study dynamically and quantitatively dye sensitization of TiO2.

(4) To exemplify the concept, we have quantitatively studied dye loading for Z907, a well-studied panchromatic Ru(II) polypyridylsensitizer and Y123, a state-of-the-art high-extinction coefficient D-π-A dye on flat TiO2 films. We find footprints of 1.33 nm2 and 0.9 nm2 per

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molecule, respectively. Measurements at varying concentration and in different solvents have already yielded significant insights into the competitive adsorption between solvent and dye as well as the mechanism and kinetics of self-assembled dye monolayer formation. Furthermore, we present the first quantitative study of cosensitization with Y123 and Cheno and determine their molar ratio when coadsorbed on the surface. Finally, we demonstrate first measurements of loading of a mesoporous TiO2 film directly attached to a QCM-D sensor, which will be important for sensing applications as well as for DSCs. Beyond QCM-D measurements on the ensemble, we will present first studies using liquid-phase AFM on the adsorbed dye monolayer, thus obtaining complementary microscopic information that may in the end lead to understanding of the adsorption mechanism on the molecular scale.

References [1] Yella, A.; Lee, H. W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E. W. G.; Yeh, C. Y.; Zakeeruddin, S. M.; Grätzel, M. "Porphyrin-Sensitized Solar Cells with Cobalt (II/III)−Based Redox Electrolyte Exceed 12 Percent Efficiency" Science, 334, 629–634 (2011). [2] Feldt, S.; Gibson, E.; Gabrielsson, E.; Sun L.; Boschloo, G., Anders H. "Design of Organic Dyes and Cobalt Polypyridine Redox Mediators for High-Efficiency Dye-Sensitized Solar Cells" JACS 132, 16714-16724 (2010). [3] Bazzan, G.; Deneault, J. R.; Kang, T.-S.; Taylor, B. E.; Durstock, M. F. "Nanoparticle/Dye Interface Optimization in Dye-Sensitized Solar Cells" Adv. Funct. Mater., n/a–n/a, (2011). [4] Rodahl, M.; Hook, F.; Krozer, A.; Brzezinski, P.; Kasemo, B. "Quartz crystal microbalance setup for frequency and Q-factor measurements in gaseous and liquid environments" Review of Scientific Instruments 66, 3924–3930 (1995).

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C48 - Light induced effects in PCBM:P3HT blend films

Andrzej Dzwilewski, Ana Sofia Anselmo, Krister Svensson, Ellen Moons

Karlstad University, Universitetsgatan 2, Karlstad, 65188, SE

Blends of poly(3-hexylthiophene) (P3HT), and phenyl-C61-butyric acid methyl ester (PCBM) are model systems for studies of active material for organic bulk hetero-junction solar cells. Recently we have observed light induced changes in transport properties in the active materials based on P3HT:PCBM blends measured in field-effect transistors [1]. The Fullerene component of the blends isknown to form dimers under exposure to visible laser light [2]. Additionally light exposure of PCBM:P3HT blends affects the morphology of the blend films, increasing the degree of already present polymer enrichment at the free surface. Polymer enrichment has also been seen in non illuminated films of similar systems [3,4,5]. Light induced morphology changes are of great interest for understandingthe long-term performance of organic solar cells as they may affect their lifetime. Here we present the results of a systematic Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy study on thin films of P3HT and PCBM (both in pure form and in blends of the two) under different conditions: as cast films, films illuminated in air and films illuminated under UHV conditions. We have observed clear changes in the NEXAFS spectra of PCBM and PCBM:P3HT blends, while pure P3HT was not affected by visible laser-light exposure. Our data suggest that oxygen plays an important role in photo-dimerization of PCBM as films illuminated in UHV were much less affected by light, than films illuminated in air. Observed changes in NEXAFS spectra suggest a reorganization of the molecules caused by light illumination for PCBM, both in pure form and in blends. Light induced changes in film morphology are of key importance for understanding light induced degradation effects in organic solar cells. References [1] A. Dzwilewski, P. Matyba, L. Edman J. Phys. Chem. B 2010, 114, 135 [2] A. Dzwilewski, T. Wågberg, L. Edman J. Am. Chem. Soc. 2009, 131, 4006 [3] B. Xue, B. Vaughan, C.-H. Poh, K. B. Burke, L. Thomsen, A. Stapleton, X. Zhou, G.W. Bryant, W. Belcher, P. C. Dastoor J. Phys. Chem. 2010, 114, 1 [4] A. S. Anselmo, L. Lindgren, J. Rysz, A. Bernasik, A. Budkowski, M. R. Andersson, K. Svensson, J. van Stam, E. Moons Chem. Mater. 2011, 23, 2295 [5] Germack, D. S.; Chan, C. K.; Hamadani, B. H.; Richter, L. J.; Fischer, D. A.; Gundlach, D. J.; DeLongchamp, D. M. Appl. Phys. Lett. 2009, 94, 233303.

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C49 - On the stability of a variety of organic photovoltaic devices by IPCE and in-situ IPCE analyses - The ISOS-3 inter-laboratory collaboration.

Monica Lira-Cantu*a, Gerardo Teran-Escobara, David M. Tanenbaumbb, Eszter Voroshazidd, Martin Hermenaue, Kion Norrmanb, Matthew T. Lloydf, Yulia Galagang, Birger Zimmermannh, Markus Höselb, Henrik F. Damb, Mikkel Jogersenb, Suren Gevorgyanb, Lauren Lutseni, Dirk Vanderzandej, Uli Würfelh, Ronn Andriesseng, Roland Röschk, Harald Hoppek, Agnès Rivatonn, Gülşah Y. Uzunoğlull, David Germackm, Brigitta Andearsenb, Morten V. Madsenb, Eva Bundgaardb, Frederik C. Krebsb

a, Centre d’Investigacio´ en Nanocie`ncia i Nanotecnologia (CIN2, CSIC), Laboratory of Nanostructured Materials for Photovoltaic Energy, ETSE, Campus UAB, Bellaterra, Barcelona, 08193, ES b, Department of Energy Conversion and Storage, Technical University of Denmark, Frederiksborgvej 399, DK-4000, Roskilde, DK c, Department of Physics and Astronomy, Pomona College, , Claremont, CA, 91711, , USA d, IMEC, Kapeldreef 75, 3000 Leuven, Belgium and Katholieke Universiteit Leuven, , ESAT, Kasteelpark Arenberg 10, 3000, Leuven, , Belgium e, IAPP (Institut fuer Angewandte Photophysik), , TU Dresden, 01062, Dresden, , Germany f, National Renewable Energy Laboratory, , Golden, CO, 80401, , USA g, Holst Centre, , High Tech Campus 31, 5656 AE Eindhoven, , The Netherlands h, Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstrasse 2, D-79110, Freiburg, , Germany i, IMEC, IMOMEC associated laboratory, Campus University of Hasselt, Wetenscharpspark 1, B-3590, Diepenbeek, , Belgium j, Hasselt University, Campus, Agoralaan 1, Building D, WET/OBPC, B-3590 Diepenbeek, , Belgium k, Institute of Physics, Ilmenau University of Technology, Weimarer Str. 32, 98693, Ilmenau, , Germany l, TÜBITAK National Metrology Institute (UME), Photonic and Electronic Sensors Laboratory, P.O. Box 54, 41470, Gebze, Kocaeli,TURKEY m, Condensed Matter Physics, Brookhaven National Lab, Building 510B Upton, NY, 11973, USA n, Clermont Universite´, Universite´ Blaise Pascal, Laboratorie de Photochemie, Mole´culaire et Macromoléculaire (LPMM), BP10448 Clermont-Ferrand, France and CNRS, UMR6505, LPMM, F-63177, Aubiere, FRANCE

Organic photovoltaics (OPVs) have reached a mature stage with power conversion efficiencies around 8-10%. Next-generation OPVs requires the development of large-area OPVs with longer lifetimes and high stability. In order to improve OPV stability it is important to understand the different degradation mechanisms taking place in the device. Many characterization techniques have been applied up to date with this purpose. This work is part of a research collaboration established at the Third International Summit on Organic Photovoltaic Stability (ISOS-3) [1-3]. Seven distinct state-of-the-art organic photovoltaic (OPVs) devices were prepared by leading research laboratories (NREL, IMEC, HOLST, ISE, DTU Energy Conversion (former RISØ-DTU) and IAPP). The devices were aged at different degradation conditions at DTU: accelerated full sun simulation, low level indoor fluorescent lighting and dark storage. The first publication related to this work deals with the overall degradation behaviour of the devices by reporting on the changes observed on power conversion efficiency with aging time [1]. The second report deals with the analysis of the degradation of the solar cells by the combination of different imaging characterization techniques such as laser beam induced current (LBIC), dark lock-in thermography (DLIT), electroluminescence (ELI) and photoluminescence (PLI) imaging [2].

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Figure 1 An IMEC sample with the configuration: ITO/ZnO/P3HT:PCBM/MoO3/Ag under full-sun stability test. a) IPCE analysis, and b) IV-Curves at different aging time.

We present in this work, the application of the Incident Photon-to-electron Conversion Efficiency (IPCE) and the in-situ IPCE techniques as tools to analyze the different degradation paths observed on the OPV devices [3]. An IPCE spectrum of a solar cell can be considered as the fingerprint of the device since almost each solar cell material can be identified by the corresponding peak at a given wavelength. The changes observed on any of the IPCE peaks, indicate the solar cell materials that are more susceptible to degradation at the given testing condition. This technique presents several advantages since it is a non-destructive methodology and a basic analytical technique found at almost any photovoltaic laboratory. The aging results presented in this work are divided depending on the type of encapsulation of the devices under analysis: encapsulated devices in glass (IAPP, HOLST and ISE devices), semi-encapsulated devices in plastic (RISØ-P and RISØ-S) and un-encapsulated devices (IMEC and NREL). The obtained results give insight on the intrinsic stability of the devices with two ITO-free alternatives (HOLST and ISE), two different P3HT polymers (RISØ-P and RISØ-S solar cells) and the stability under ambient air depending on two different hole extraction layers like PEDOT and MoO3

(NREL and IMEC). Figure 1 shows an example of the observed results for an IMEC sample. References [1] Tanenbaum, D.M. ; Hermenau, M.; Voroshazi, E.; Lloyd, M.T.; Galagan, Y.; Zimmermann, B.; Hösel, M.; Dam, H.F.; Jørgensen, M.; Gevorgyan, S.A.; Kudret, S.; Maes, W.; Lutsen, L.; Vanderzande, D.; Würfel, U.; Andriessen, R.; Rösch, R.; Hoppe, H.; Teran-Escobar, G.; Lira-Cantu, M.; Rivaton, A.; Uzunoğlu, G.Y.; Germack, D.; Andreasen, B.; Madsen, M.V.; Norrman, K.; Krebs, F.C. “The ISOS-3 inter-laboratory collaboration focused on the stability of a variety of organic photovoltaic devices”. RSC Adv. 2, 882-893 (2012). [2] Rösch, R.; Tanenbaum, D.M.; Jørgensen, M.; Seeland, M.; Bärenklau, M.; Hermenau, M.; Voroshazi, E.; Lloyd, M.T.; Galagan, Y.; Zimmermann, B.; Hösel, M.; Dam, H.F.; Gevorgyan, S.A.; Kudret, S.; Maes, W.; Lutsen, L.; Vanderzande, D.; Würfel, U.; Andriessen, R.; Teran-Escobar, G.; Lira-Cantu, M.; Rivaton, A.; Uzunoğlu, G.Y.; Germack, D.; Andreasen, B.; Madsen, M.V.; Norrman, K.; Hoppe, H.; Krebs, F.C. “The ISOS-3 inter-laboratory collaboration- Investigation of the degradation mechanism of a variety of organic photovoltaic devices by combination of imaging techniques”. Energ.y & Env. Sci. In press, (2012). [3] Lira-Cantu, M.; Teran-Escobar, G.; Tanenbaum, T.M.; Voroshazi, E.; Hermenau, M.; Norrman, K.; Lloyd, M.T.; Galagan, Y.: Zimmermann, B.; Dam H.F.; Jørgensen, M.; Gevorgyan, S.; Lutsen, L.; Vanderzande, D.; Würfel, U.; Andriessen, R.; Rösch, R.; Hoppe, H.; Rivaton, A.; Uzunoğlu, G.Y.; Germack, D.; Andreasen, B.; Madsen, M.V.; Bundgaard, E.; Krebs, F.C. “On the stability of a variety of organic photovoltaic devices by IPCE and in-situ IPCE analyses - The ISOS-3 inter-laboratory collaboration”. Submitted (2012).

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C50 - Noval Solar Cell Based on Biopolymer

Bayram Kilica, Didem Omaya, Ergin Kosab, Huseyin Kizilc, Levent Trabzonb

a, Yalova University, Department of Energy System Engineering, Sehit Omer Faydalý street, No:254, Yalova, TR b, Istanbul Technical University, Mechanical Engineering Department, Inonu street, No: 65 Gumussuyu/ Istanbul, 34437, TR c, Istanbul Technical University, Metallurgy and Materials Science Engineering Department, ITU Ayazaga Kampusu, Maslak/Istanbul, 34469, TR

We have grown solar cells by ZnO nanowire, nanorod and nanoflower semiconductors on chitosan based biopolymer for investigation solar cell efficiency of nano-biopolymers. A possible model of 1-D and 3-D architectures self-assembled with biopolymer assistance is presented using minimum energy considerations. We characterized the nano-structures by Scanning electron microscopy, X-ray diffraction, Fourier Transform Infrared Spectroscopy, and Energy Dispersive X-ray analyses. We found that novel 1-D and 3-D architectures are built from high-purity ZnO nanostructures with chitosan based biopolymer structure. The highest solar conversion efficiency of 4% and IPCE of 35% was obtained using ZnO nanoflowers/N719 dye/I-

/I-3electrolyte. The corresponsding solar conversion efficiency and IPCE values were 2.5% and

25% for ZnO nanowires and 1.59% and 18% for the nanorods structures, respectively.

Keywords: Dye Sensitized Solar Cell,ZnO, Biopolymer, Nanowires, Nanorods, Nanoflower

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C51 - Oligomers and alternating copolymers designed for bulk heterojunction solar cells: synthesis, opto-electronic properties and device performances.

Renaud Demadrillea, Zaireen Yahyaa, Evan Spadaforaa, Benjamin Grevina, Mathieu Linaresb, Patrice Rannoua, Adam Prona, Remi Debettigniesc, Jean-Pierre Traversa

a, CEA-INAC-SPRAM, 17 rue des Martyrs , Grenoble, 38054, FR b, Department of Computational Physics, IFM, Linkoping University, S-58183, Linkoping, Sweden, SE c, INES-CEA-RDI-DTS, Laboratoire Cellules Solaires, Le Bourget du Lac, Technolac Chambery, F-73370, France, FR

Nanostructured bulk heterojunctions (BHJ) solar cells, which consist of pi-conjugated oligomers or polymers as electron donors and fullerenes as electron acceptors, are very promising in view of their relatively high power conversion efficiency. The inherent advantages of organic materials such as their light weight and low cost, and the possibility of fabricating large active area devices facilitated by their solution processability, have stimulated intensive research in this field during the last decade. Up to now, BHJ solar cells employing pi-conjugated oligomers or polymers have demonstrated power conversion efficiencies of ca. 6.7% and 8.3% respectively [1-2]. However, further improvement in the device performance could be expected, by developping new materials better matching the solar spectrum and more efficiently converting the sunlight to electricity. In the first part of this communication, we will discuss the design rules and the synthesis of new solution processable oligomers suitable for the use as active components in molecular BHJ solar cells. Their design is based on the combination of tailor-made oligothiophene segments as peripheral electron-donor subunits and indacenodithiophenone, benzothiadiazole or fluorenone as central electron-withdrawing units [3]. The use of this strategy which results in a significant extension of the absorption spectral range, affords the possibility to finely tune the energy levels position and the value of their band gap. We will discuss basic supramolecular chemistry concepts enabling the preparation of molecular nanowires [4-5] and the fabrication of nanostructured composites using these oligomers.

Figure 1 Chemical structures of fluorenone-based oligomer and polymer studied in this work.

In the second part, we will demonstrate that some of these oligomers can also be considered as smart building blocks to achieve the synthesis of copolymers showing perfectly controlled structures, well-suited for solar cells applications. In the final part, optoelectronic properties of the materials will be described in details and their electrical performances in devices will be discussed [6]. Promising reliminary results demonstrate high open circuit voltages (of ca. 0.8-0.9V) and power conversion efficiencies up to 2.2% for tested devices with an active area of 0.28 cm².

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References [1]Sun Y., Welch G. C., Leong W. L., Takacs C. J., Bazan G. C., Heeger A. J., “Solution-processed small-molecule solar cells with 6.7% efficiency” Nature Mater. 11, 44 (2012) [2] http://www.konarka.com [3] Lincker F., Delbosc N., Bailly S., De Bettignies R., Billon M., Pron A., Demadrille R., “Fluorenone-Based Molecules for Bulk-Heterojunction Solar Cells: Synthesis, Characterization, and Photovoltaic Properties” Adv. Funct. Mater., 18, 3444 (2008). [4] Grevin B., Demadrille R., Linares M., Lazzaroni R., Leclère P., “Probing the local conformation within pi-conjugated one-dimensional supramolecular stacks using Frequency Modulation Atomic Force Microscopy”, Adv. Mater., 4124,(2009) [5] Spadafora E. J., Linares M., Yahya W. Z. N., Lincker F., Demadrille R., Grevin B., “Local contact potential difference of molecular self-assemblies investigated by Kelvin probe force microscopy”. Appl. Phys. Lett.,(99), 233102, (2011) [6] Lincker, F., Heinrich, B., De Bettignies, R., Rannou, P., Pécaut, J., Grévin, B., Pron, A., Donnio, B., Demadrille, R. “Fluorenone core donor–acceptor–donor p-conjugated molecules end-capped with dendritic oligo(thiophene)s: synthesis, liquid crystalline behaviour, and photovoltaic applications” J. Mater. Chem., 21 (14), 5238, (2011)

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C52 - PEO modified ZnO enhances the performance of hybrid solar cells

Shuyan Shao, Fengling Zhang

Linköping university, IFM, Linköping university, , Linköping, SE

ZnO nanoparticles (NPs) modified with poly(ethylene oxide) (PEO) were used as either electron acceptors in the active layer or an buffer layer between ITO and active layers in inverted hybrid solar cells (HSCs). It is observed that all photovoltaic parameters (short-circuit current density (Jsc), open-circuit voltage (Voc) and fill factor (FF)) of inverted HSCs are increased, which result in an overall efficiency increased from 3% to 4.7% by adding PEO modified ZnO buffer layer between active layer and ITO via thermal annealing. In addition, the performance of normal HSCs composed of a polymer and ZnO nano-particles as electron acceptors is also improved by modifying ZnO nano-particles with PEO. The enhanced PCE from 0.75% to 1% due to increase Jsc from 1.9 mA/cm2 to 2.4 mA/cm2 and FF from 0.47 to 0.50. Mobility measurement indicates that the enhanced Jsc and FF is attributed to transportation property improvement by ZnO nano-particles modified with PEO. To understand the mechanism of improvement in devices with thermal annealing or/and modified with PEO, the morphology, optical and electrical properties of the active layers were investigated with Atomic Force Microscopy (AFM), Absorption, Charge Extraction with Linearly Increasing Voltage (CELIV), Ultraviolet Photoelectron Spectroscopy (UPS), Photoluminescence, Electroluminescence and Dynamic Light Scattering (DLS).

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C53 - The Photochemistry and Photovoltaic Performance of a New Class of Pan-Chromatic, Donor-Acceptor Sensitizers in p-Type Dye-Sensitized Solar Cells

James M Gardnera, Jonas Peterssona, Julien Warnanb, Yann Pellegrinb, Errol Blartb, Fabrice Odobelb, Leif Hammarströma

a, Dept. of Chemistry - Ångström, Uppsala University, Regementsvägen 1, Uppsala, 75237, SE b, Faculté des Sciences et des Techniques de Nantes, 2 rue de la Houssinière, Nantes, 44322, FR c, Div. of Appl. Phys. Chem.; Dept. of Chemistry, KTH, Teknikringen 30, Stockholm, 10044, SE

Efforts to utilize greater fractions of the solar spectrum have resulted in the design of a series of three p-type sensitizers based on Squaraine. The incorporation of additional sub-units generated sensitizers with broad absorbances throughout the NIR and visible, and in addition produced electron donating and accepting groups that promoted electron transfer and reduced interfacial charge recombination. The electron and energy transfer dynamics for these three novel sensitizers were studied by fs- to ms- transient absorption spectroscopy on mesoporous nickel oxide (NiO) thin films. The three sensitizers (NDI-PMI-Sq, PMI-Sq, and Sq) were as well utilized in complete dye-sensitized solar cells and a correlation was established between the charge-transfer dynamics and the performance in p-type dye-sensitized solar cells (DSCs). Both PMI-Sq and NDI-PMI-Sq contained multiple light absorbing sub-units. The efficiency of charge injection from each sub-unit was probed by selective excitation of each sub-unit. From this, an excitation wavelength dependence on charge injection and intramolecular electronic coupling was established. For all three of the sensitizers, the electron transfer events were mapped from the initial light absorption, to intramolecular charge-transfer, to charge-injection into NiO, and finally to interfacial charge recombination.

Figure 1 Light absorption by three novel p-type sensitizers (NDI-PMI-Sq, PMI-Sq, and Sq) results in intramolecular charge-transfer, hole injection, and gradual interfacial recombination. The molecular design leads to long-lived charge separation and a broad absorbance in the visible and NIR, which translates into dramatic increases in solar cell performance.

The highest performing sensitizer was NDI-PMI-Sq, for which an exceptionally long interfacial charge-separation was maintained (~350 μs). The time scale of charge separation resulted in efficiencies for solar cells that were more than an order of magnitude larger than for Sq or PMI-Sq when matched with a cobalt trisbipyridine redox couple. The implications for the design of future pan-chromatic sensitizers will also be discussed.

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C54 - Theoretical investigation on drift current in Dye Solar Cell and comparison with experimental data.

Desiree Gentilini, Alessio Gagliardi, Aldo Di Carlo

University of Rome Tor Vergata, Via del Politecnico 1, Rome, 133, IT

In the last years many theoretical investigations have attempt to explain the interplay and interconnections among the physical processes governing the functioning of Dye Solar Cell device, but some aspect on the energy conversion, particularly on the charge transport are not completely unrevealed. Here a numerical simulation of the complete cell is presented, where ionic and electronic transport , electron trapping and electrostatic potential are treated on equal footing.The core of the model is constituted by steady state drift diffusion equations for each carrier coupled with continuity and Poisson equations, implemented in the framework of TiberCAD simulation tool [1]. The Poisson equation for the electrostatic potential is often neglected by many models in literature because it is generally accepted that the long range electric field are sufficiently screened by the electrolyte with solar intensity up to one sun [2]. Here we quantify the impact of this assumption both on a theoretical point of view and by means of a systematical comparison with real cells [3]. The model allows to evaluate electric field intensity and profile at different working points inside the cell. We show that there is a non negligible effects in terms of ionic drift current and charge density profiles when a real exponential distribution of localized energy states under the conduction band edge (Real Traps Model) is considered. (see Fig. 1.)

Figure 1 Charge density profiles calculated for a typical cell with 10 µm active layer thickness. The conduction band (black continuous line) and the trapped(dashed black line) electron density are reported.

Non negligible effects on the repartition of the current in drift and diffusion components are revealed. Moreover we will show the variation of the electric field at the photoanode/TCO interface when a non ideal contact is considered. References [1] «www.tibercad.org,» [Online]. [2] J. van de Langemaat e A. J. Frank, The Journal of Physical Chemistry, vol. 105, p. 11194, 2001. [3] D. Gentilini, A. Gagliardi, M. Auf der Maur, L. Vesce, D. D'Ercole, T. M. Brown, A. Reale e A. Di Carlo, «Correlation between Cell Performance and Physical Transport Parameters in Dye Solar Cells,» The Journal of Physical Chemistry C, vol. 116, p. 1151–1157, 2012.

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C55 - Development of High-performance Zinc Phalocyanine Sensitizers for Dye-

sensitized Solar Cells

Mutsumi Kimura, Hirotaka Nomoto, Naruhiko Masaki, Shogo Mori Shinshu University, Tokida 3-15-1, Ueda, 386, JP

Since the development of dye-sensitized solar cells (DSSCs) with high power conversion efficiency, DSSCs have been regarded as one of the most promising candidates among alternative photovoltaic devices. After extensive optimization of the porous TiO2 layer, redox electrolytes, dyes, and device structures, conversion efficiencies above 11 % have been achieved with red-colored polypyridylruthenium complex sensitizers. However, these dyes harvest photons with wavelength mostly below 650 nm. In order to improve further the performance of DSSCs, harvesting the photons in the red and near IR spectral regions is essential. Metallophthalocyanines (MPcs) possess strong absorption bands in the near IR region. Therefore, they have a good potential as red/near-IR absorbing sensitizers. However, their strong tendency to aggregate and the lack of directionality in the excited state lead to DSSCs incorporating MPcs to have low conversion efficiencies. Therefore, further enhancement in the conversion efficiency is needed to explore the molecular designs for MPcs. In this prenentation, we report on the syntheses and photovoltaic properties of a series of unsymmetrical ZnPcs PcS6 and PcS15 having bulky substituents. The synthesized ZnPcs adsorbed onto TiO2 exhibited a sharp Q band, indicating that the molecular aggregation among ZnPcs were completely diminished by the introduction of bulky substituents. Three-dimensional enlargement of the molecular structure is an effective way to reduce intermolecular interactions, the resultingenergy conversion efficiency of DSSCs with PcS15 was 5.3 % under one-sun conditions.1,2

References [1] Mori, S.; Nagata, M.; Nakahata, Y.; Yasuta, K.; Goto, R.; Kimura, M, Taya, M. "Enhancement of Incident Photo-to-Current Conversion Efficiency for Phthalocyanine-Sensitized Solar Cells by 3D Molecular Structuralization", J. Am. Chem. Soc., 132, 4054-4055 (2010). [2]Kimura, M.; Nomoto, H.; Masaki, N.; Mori, S., Angew. Chem. Int. Ed., 2012, in press

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C56 - Natural Dye sensitized solar cells based on Anthocyanins and betalains.

Giuseppe Calogeroa, Jun-Ho Yumb, Alessandro Sinopolia, Gaetano Di Marcoa, Michael Grätzelb, Mohammad Khaja Nazeeruddinb

a, CNR-IPCF, viale F. Stagno D'Alcontres 37, MESSINA, 0, IT b, Laboratory of Photonics and Interfaces, EPFL SB ISIC LPI, CH-1015 Lausanne, Switzerland

Since the widespread use of highly purified silicon for solar cells is impracticable due to their expensive and complex manufacturing process, dye-sensitized solar cells (DSSC), are one of the most promising devices for large scale solar energy conversion due to their low production cost and low environmental impact. One key component of the DSSC is the sensitizer. In view of the search for new metal-free organic dyes, the natural ones offer low cost, abundance, non-toxicity and limited pollution. We present DSSC using natural pigments extracted with low cost and simply procedures and methods. The dyes extracted from grape, mulberry, blackberry, red Sicilian orange, wild Sicilian prickly pear, eggplant and radicchio have shown a monochromatic incident photon to current efficiency (IPCE) ranging from 40 % to 69 %.

Figure 1 Current-voltage characteristics curves of DSSCs sensitized with red mulberry natural pigments (black line), red Sicilian orange concentrated juice (blu line), blackberry (green line) and Sicilian prickly pear (red line). The photoanode, characterized by multilayer TiO2 structures, is 13.3 ƒÝm thick. The counter-electrode is Pt/FTO optically transparent. Power intensity of 100 mW/cm2 (AM 1.5) as simulated solar source, is used.

In this Fig. 1 are reported short circuit photocurrent densities (Jsc) up to 8.8 mA / cm2, and open circuit voltage (Voc) ranging from 316 to 419 mV, obtained from these natural dyes under 100 mW/cm2 (AM 1.5) simulated sunlight. The best solar conversion efficiency of 2.06 % was achieved with wild Sicilian prickly pear fruits juice. [1]

References [1] Calogero, G.; Yum, J.-H.;, Sinopoli A.; Di Marco G.; Grätzel, M.; Nazeeruddin, Md K.;"Anthocyanins and betalains as light-harvesting pigments for dye-sensitized solar cells". Solar Energy (2012) DOI:10.1016/j.solener.2012.02.018

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C57 - Materials Discovery of Dyes for Dye-Sensitized Solar Cells: Prediction, Validation and Rationalisation

Jacqueline Colea,b

a, Cavendish Laboratory, University of Cambridge, Cavendish Laboratory, J J Thomson Av, Cambridge, CB3 0HE, GB b, Department of Chemistry, University of New Brunswick, P. O. Box 4400, Fredericton, E3B 5A3, Canada

This paper illustrates a range of methods that are being employed in order to systematically discover new classes of dyes for dye-sensitized solar-cell (DSC) applications. The importance of engaging in the full 'life-cycle' of materials prediction, experimental validation and DSC performance rationalisation, in order to afford success in this materials discovery program, is illustrated by several case studies. Large-scale data-mining methods which are able to predict new chemical dyes are presented together with results from subsequent DSC performance testing. Such experimental validation is complemented with quantitative structure-property relationship (QSPR) methods that have a dual function:- to help to rationalise the experimental results and to provide new design rules that are then fed back into the materials prediction aspect of this work. The 'life-cycle' of the materials discovery process then repeats via this feedback-loop creating a continuous 'design-to-device' operational program. An overview of the prediction methods includes a demonstration of how large-scale quantum-chemical calculations can reveal new classes of dyes [1,2]. The benefit of mining the data from these results in concert with a database of optical spectra is discussed. The importance of complementary calculations that match the band-gap of electrolyte to dye are described as well as considerations of other selection criteria. A few case studies that show the DSC performance tests of new dyes generated from these predictions are presented. QSPR methods are then presented which employ a priori knowledge from successful classes of dyes in order to generate new design rules that, in turn, afford more superior classes of dyes. Several applications of QSPR are illustrated whereby new design rules for DSC dyes are realised from associated empirical models [3] and statistical correlation [4]. The paper concludes with an outlook on future developments in materials discovery in the context of this field of research. References [1] Cole, J. M "Systematic prediction of dyes for dye-sensitized solar cells: data-mining via molecular charge-transfer algorithms". Complex Systems, 20, 141-149 (2012). [2] Cole, J. M. "Large-scale chemical data-mining predicts high-performance dyes for dye-sensitized solar cells", J. Am. Chem. Soc. (in preparation). [3] Liu, X.; Cole, J. M.; Waddell, P. G.; Lin, T. C.; Radia, J. Zeidler, A. "Molecular origins of optoelectronic properties in coumarin dyes: toward designer solar cell and laser applications", J. Phys. Chem. A 116, 727-737 (2012). [4] Low, K. S.; Cole, J. M.; Zhou, X.; Yufa, N. "Rationalising the molecular origins of Ru and Fe-based dyes for dye-sensitized solar cells", Acta Crystallographica B (submitted).

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C58 - Dye-sensitized Photocathodes for Tandem Dye-Sensitized Solar Cells

Elizabeth Gibson, Jean-François Lefebvre, Christopher Wood

The University of Nottingham, The University of Nottingham, Nottingham, GB

One way of improving the efficiency of dye-sensitized solar cells is to use two photoelectrodes in a tandem device (see Figure 1), one harvesting the high energy photons, and the other harvesting the low energy photons, thus enabling the possibility to increase the photovoltage, whilst maximizing light harvesting across the solar spectrum. Despite their promise, a tandem cell with a higher efficiency than the state-of-the-art “Grätzel” cell has not yet been achieved. This is because the performances of photocathodes are significantly lower than TiO2-based anodes, and the p-type concept has been largely unexplored since the first device was prepared in 1999.

Figure 1 Schematic illustration of a tandem dye-sensitized solar cell incorporating a NiO cathode.

The small potential difference between the valence band of the NiO, p-type semiconductor, and the redox potential of the electrolyte and the faster charge-recombination reactions compared to the TiO2 system limits the efficiency. To increase the efficiency we are tackling 3 key components of the device: the semiconductor morphology to improve the stability and porosity; the redox couples to improve the photovoltage and dark-current; the dye molecules to improve the light harvesting across the spectrum. In parallel we are investigating the charge-transfer processes to determine the mechanism and limitations to efficiency. Highlights from these recent efforts to improve the device efficiency and our understanding of the device will be presented.

References [1] Li, L. et al. Adv. Mater., 2010, 15, 1759-1762. [2] E. A. Gibson et al., Angew. Chem. Int. Ed. 2009, 48, 4402 –4405. [3] Le Pleux, L. et al. Energy Environ. Sci. 2011. [4] Gibson, E. A. et al. J. Phys. Chem. C, 2011. [5] Boschloo, G. et al. J. Phys. Chem. Lett., 2011, 2, 3016–302.

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C59 - Ultrafast electron transfer in CdSe quantum-dot-sensitized ZnO nanowires: time-resolved absorption and terahertz study

Karel Žídeka, Kaibo Zhenga, Carlito S. Ponseca Jr.a, Maria E. Messingb, L. Reine Wallenbergc, Pavel Cháberaa, Mohamed Abdellaha, Villy Sundströma, Tõnu Pulleritsa

a, Department of Chemical Physics, Lund University, Box 124, 22100, Lund, Swedenartment of Chemical Physics, Lund University, Box 124, 22100, Lund, Sweden, SE b, Solid State Physics, Lund University, Box 118, 22100, Lund, Sweden, SE c, Center for Analysis and Synthesis/nCHREM, Lund University, Box 124, 22100 Lund, Sweden, SE

Quantum dot (QD) sensitized solar cells (SCs) count among the most promising concept of the photovoltaics.1-7 Compared to the analogous dye-sensitization, the QDs feature number of interesting properties, such as tunable absorption spectrum or multiple exciton generation.6 However, the resulting conversion efficiencies obtained so far by QDs-sensitization (up to 5.1 %) are far behind expected values (15-20 %) and offer a big room for improvement.5,7 The conversion efficiency is determined to a big extent by an electron transfer from QD to metal oxide (MO) – this process is responsible for charge separation in the system. Despite importance of the transfer, many of its properties (even the exact process timescale) are still not known. Moreover, the transfer presence is often proven only indirectly.1-4 We have carried out a series of spectroscopic studies of the QD-MO system by employing a combination of transient absorption (TA) and time-resolved terahertz (THz) measurements (both with sub-picosecond time resolution). The two experiments provide us complementary information about electrons in QDs (TA measurements) as well as MO (THz measurements). For our study we have chosen a typical system of CdSe QDs on ZnO nanowires. The measurements unambiguously and directly reveal an ultrafast electron transfer in our samples, which takes place already on picosecond timescale (typical transfer times 3-12 ps for QD sizes 2.5-3.1 nm). According to our results the ultrafast channel is dominant in our system. In agreement with previous reports, the obtained ultrafast electron transfer can be described on the basis of Marcus theory.2

Figure 1 Simultaneous decay of transient absorption signal (log scale, black squares, exc. wavelength = 470 nm, probe wavelength = 536 nm) and rise in terahertz signal (log scale, red line, exc. wavelength = 529 nm), which reflect the electron dissaperance from QD and transfer to ZnO.

Furthermore, the unique combination of TA and THz measurements allows us to follow even the processes after the primary electron injection. Our measurements indicate that

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electrons are in fact injected into a charge-transfer state near ZnO surface and the transport into the ZnO volume follows with a typical timescale of 60-120 ps. Our results have important implications on many aspects of QD-sensitized SCs. The ultrafast electron transfer is important for the multiple-exciton generation – the fast charge separation is able to effectively block here the unwanted Auger recombination. Secondly, possible creation of charge transfer state can have consequences on the real SC performance, because only the electrons in the ZnO volume can be used for energy harvesting. References [1] Pernik,D. R.; Tvrdy, K.; Radich, J.; Kamat, P. V. “Tracking the Adsorption and Electron Injection Rates of CdSe Quantum Dots on TiO2: Linked Versus Direct Attachment”. J. Phys. Chem. C 115, 13511-13519 (2011). [2] Tvrdy, K.; Frantsuzov, P. A.; Kamat, P. V. "Photoinduced electron transfer from semiconductor quantum dots to metal oxide nanoparticles". Proc. Natl. Acad. Sci. U. S. A. 108, 29-34 (2011). [3] Robel, I.; Subramanian, V.; Kuno, M.; Kamat, P. V. "Quantum dot solar cells. harvesting light energy with CdSe nanocrystals molecularly linked to mesoscopic TiO2 films". J. Am. Chem. Soc. 128, 2385-93 (2006). [4] Tisdale, W. A.; Zhu, X.-Y. "Surface chemistry special feature: Artificial atoms on semiconductor surfaces". Proc. Natl. Acad. Sci. U. S. A. 108, 965-70 (2011). [5] Shalom, M.; Dor, S.; Ruhle, S.; Grinis, L. "Core/CdS quantum dot/shell mesoporous solar cells with improved stability and efficiency using an amorphous TiO2 coating". J. Phys. Chem. C 2, 3895-3898 (2009). [6] Sambur, J. B.; Novet, T.; Parkinson, B. A. "Multiple Exciton Collection in a Sensitized Photovoltaic System". Science 330, 63-66 (2010). [7] Pattantyus-Abraham, A. G.; Kramer, I. J.; Barkhouse, A. R.; Wang, X.; Konstantatos, G.; Debnath, R.; Levina, L.; Raabe, I.; Nazeeruddin, M. K.; Grätzel, M.; Sargent, E. H. "Depleted-heterojunction colloidal quantum dot solar cells". ACS Nano 4, 3374-80 (2010).

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C60 - Design and Construction of Novel Photovoltaic Devices via Oxidative Chemical Vapor Deposition (oCVD)

Rachel Howden, Miles Barr, Karen Gleason

Chemical Engineering, MIT, 77 Massachusetts Ave. 66-409, Cambridge, 2139, US

The conductive polymer poly(3,4-ethylenedioxythiophene), (PEDOT), deposited via oxidative chemical vapor deposition (oCVD) has been investigated for use in organic electronic devices. The oCVD process as well as the application of oCVD PEDOT in photovoltaic devices is described. The oCVD process of forming the polymer film allows compatibility with a wide range of substrates, including those that are flexible or fragile, and provides a relatively low-energy means of depositing film layers that may not be possible through solution or other processing (due to solvent incompatibility or high processing temperatures). Films deposited using varying oCVD process parameters (temperature, pressure, monomer flow, and oxidant exposure) were characterized based on their physical and electrical properties. The process parameters were optimized to create repeatable films with conductivities greater than 1000 S/cm on silicon, glass, and various paper and plastic substrates, with thicknesses ranging from 10-200 nm. The oCVD PEDOT has been demonstrated as a replacement for solution-processed PEDOT:PSS as a hole transporting layer as well as for the transparent electrode material (typically ITO) in typical organic photovoltaic structures. ITO-free, fully dry processed devices were fabricated using small molecule active layers. Top-illuminated photovoltaic cells were created using direct deposition of PEDOT top electrodes, yielding efficiencies of up to 2.8% (75% that of the conventional architecture with ITO). The top-illuminated architectures also allowed for devices to be fabricated on opaque substrates, such as paper, with over 2.0% power conversion efficiency, the highest to date on such fiber-based substrates. The solvent-free, conformal oCVD technique gives a unique compatibility between the conductive polymer and the other photovoltaic device layers that will allow for constructing novel device architectures.

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C61 - Electrodeposition and characterization of zinc oxide nanostructures for anode in Dye-Sensitized Solar Cells

Servane Haller, Jean Rousset, Daniel Lincot

IRDEP, 6 quai Watier, Chatou, 78401, FR

Main requirements for Dye-Sensitized Solar Cells (DSSC) anode are the achievement of a high surface area, in order to optimize the light absorption, and good transport properties, in order to avoid losses in the semiconductor material.In this respect, ZnO nanostructures are suitable for integration in DSSC [1]. The possibility to deposit ZnO under mild conditions enables the preparation of crystalline porous layers, in which electron transport is promoted. Deposition process of ZnO nanostructures, as well as the properties of the resulting layer, have been widely discussed in order to determine the most adapted structure for integration as anode in DSSC. Among a large variety of nanostructures, co-electrodeposition of ZnO and Eosin-Y leads to a nanoporous layer with pore size in the range of 10 nm. These dimensions are consistent with surface area in the range of those reached by TiO2 porous layers. Efficiency close to 6% could therefore be obtained with this specific structure, that is among the highest recorded for ZnO-based DSSC. We further explored the electrodeposition of the nanoporous structure by replacing the classical deposition substrate – Fluorine Tin Oxide – by sputtered Aluminium-doped ZnO. The morphology of the deposition is strongly modified by the deposition substrate, which could be explained by an epitaxial growth. A strongly organized structure with vertical pores is observed and the adhesion of the layer on the substrate is enhanced [2]. In order to characterize precisely the nanostructure, Electrochemical Impedance Spectroscopy (EIS) has been performed on the ZnO nanoporous material before and after annealing. Measuring the capacity in the potential range where the semiconductor is in accumulation, the Helmoltz capacity can be determined. The developed surface of porous layer is measured by comparing the Helmoltz capacity with one of a flat ZnO deposited by Atomic Layer Deposition (ALD) on a silicon buffer [3]. After application of a voltage bias, the evolution of the depletion in the nanoporous structure can be studied. A model is proposed for this phenomenon in respect with the morphology of nanoporous layer extracted from the previous experiment. Optoelectronic of the material is discussed depending on the treatment conditions. Solar cells prepared with this material could reach up to 4.5% efficiency with classical components (D149 as a dye and Iodine-based electrolyte) [2]. This study brings a better understanding on the behaviour of nanostructured ZnO regarding key properties for integration as anode in DSSC. References [1]Lincot, D."Solution growth of functional zinc oxide films and nanostructures". MRS Bulletin 35,778-789 (2010). [2]Haller, S.; Rousset, J.;Renou, G.; Lincot, D. "Electrodeposition of nanoporous ZnO on Al-doped ZnO leading to a highly organized structure for integration in Dye Sensitized Solar Cells". EPJ Photovoltaics 2, 20401 (2011). [3] Dupuy, L.; Haller, S.; Rousset, J.; Donsanti, F.; Guillemoles, J-F.; Lincot, D.; Decker, F. "Impedance measurements of nanoporosity in electrodeposited ZnO films for DSSC" Electrochem. Com. 12, 697-699 (2010).

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C62 - Improved stability of unsealed quasi-solid-state dye-sensitized solar cell based on carbon materials with LaCoO3 additive as counter electrode

Marisa Arunchaiyaa, Voranuch Somsongkula, Atchana Wongchaisuwata, Attera Worayingyonga

a, Department of Chemistry, Faculty of Science, Kasetsart University, 50 Ngam Wong Wan Rd, Ladyaow, Chatuchak, Bangkok, 10900, TH b, Center of Advanced Studies in Tropical Natural Resources, National Research University-Kasetsart University, Kasetsart University, 50 Ngam Wong Wan Rd, Ladyaow, Chatuchak, Bangkok, 10900, TH

Carbon materials are good candidates to substitute platinum noble metal as a counter electrode in a dye-sensitized solar cell (DSSC) device due to their low cost, low resistance, high surface area and electrical conductance. In this work, quasi-solid-state DSSCs based on N719 dye-sensitizer, composite poly(ethylene oxide) electrolyte and two different carbon materials (carbon black and carbon nanopowder) incorporated with LaCoO3 as counter electrodes were fabricated and the current-voltage characteristics of DSSCs on storage under atmospheric condition were examined. It was observed from cyclic voltammograms that the composite carbon black-LaCoO3 and carbon nanopowder-LaCoO3 counter electrodes showed increased cathodic current compared with those ofthe carbon materials without LaCoO3 additive. These were consistent with increased surface roughness of the composite materials as depicted from scanning electron microscopy (SEM) and atomic force microscopy (AFM). The performance of quasi-solid-state DSSC based on carbon black-LaCoO3 showed superior energy conversion efficiency (4.40%) over the device based on the carbon nanopowder-LaCoO3

(3.43%) and was compatible to that achieved from platinum counter electrode (4.44%). Furthermore, the unsealed DSSC fabricated withcarbon black-LaCoO3 counter electrode displayed better long-term stability than those fabricated withcarbon nanopowder-LaCoO3 or platinum counter electrode. References [1] Grätzel, M. “Solar energy conversion by dye-sensitized photovoltaic cells”. Inorg. Chem. 44, 6841-6851 (2005). [2] Hu, H.; Chen, B.-L.; Bu, C.-H.; Tai, Q.-D.; Guo, F.; Xu, S.; Xu, J.-H.; Zhao, X.-Z. “Stability study of carbon-based counter electrodes in dye-sensitized solar cells”. Electrochim. Acta 56, 8463-8466 (2011). [3] Somsongkul, V.; Wongchaisuwat, A.; Worayingyong, A.; Arunchaiya, M. “Carbon black-LaCoO3 composite material as counter electrode for quasi-solid-state dye-sensitized solar cell”. Mater. Sci. Forum 663-665, 451-454 (2011). [4] Worayingyong, A.; Kangvansura, P.; Kityakarn, S. “Schiff base complex sol–gel method for LaCoO3 perovskite preparation with high-adsorbed oxygen”. Collids Surf. A 320, 123-129 (2008).

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C63 - Design and synthesis of isoindigo-based low band gap polymers for polymer solar cells

Ergang Wanga, Zaifei Mab, Patrik Henrikssona, Olle Inganäsb, Fengling Zhangb, Mats Anderssona

a, Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden b, Biomolecular and Organic Electronics, IFM, Linköping University, Linköping, SE-581 83, Sweden

Polymer solar cells (PSCs) are promising sustainable solar energy converters, which are attracting more and more attention because of their unique advantages of low cost, light weight, and potential use in flexible devices.To further improve the efficiencies of PSCs for practical applications, it is necessary to develop new conjugated polymers with several merits including low band gap, appropriate HOMO and LUMO positions, high mobility, decent solubility. A facial method to design polymers withthese merits is to combine electron-rich (donor) and electron-deficient (acceptor) groups as repeating units, forming internal donor-acceptor (D-A) structures.

Figure 1 Simultaneous decay of transient absorption signal (log scale, black squares, exc. wavelength = 470 nm, probe wavelength = 536 nm) and rise in terahertz signal (log scale, red line, exc. wavelength = 529 nm), which reflect the electron dissaperance from QD and transfer to ZnO.

Isoindigo is a symmetrical molecule consisting of two indolin-2-one units, which contribute towards its strong electron-withdrawing character.1 On the basis of the D-A structures, we take isoindigo groups as acceptor and carbazole, thiophene, bithiophene and benzo[1,2-b:4,5-b']dithiophene as donor units, respectively, and then developed a series of D-A types polymers.1-3 Their photophysical, electrochemical and PV properties were investigated. The best performance was achieved by solar cells based on P3TI:PC71BM with an efficiency of 6.3%, an open-circuit voltage of 0.70V, a short-circuit current density of 13.1 mA cm−2 and a decent fill factor of 0.69 under illumination of AM 1.5G simulated solar light (100 mW cm–2).3 Further optimization is ongoing. The preliminary PV performance demonstrated the high promise of the easily accessible isoindigo groups as electron-deficient units in designing D-A polymers for efficient PSCs.

References [1] Wang, E. G.; Ma, Z. F.; Zhang, Z.; Henriksson, P.; Inganas, O.; Zhang, F. L.; Andersson, M. R. "An isoindigo-based low band gap polymer for efficient polymer solar cells with high photo-voltage". Chem. Commun. 2011, 47, 4908. [2] Ma, Z.; Wang, E.; Jarvid, M. E.; Henriksson, P.; Inganas, O.; Zhang, F.; Andersson, M. R. "Enhance performance of organic solar cells based on an isoindigo-based copolymer by balancing absorption and miscibility of electron acceptor". J. Mater. Chem. 2012, 22, 2306. [3] Wang, E. G.; Ma, Z.; Zhang, Z.; Vandewal, K.; Henriksson, P.; Inganäs, O.; Zhang, F.; Andersson, M. R. "An Easily Accessible Isoindigo–Based Polymer for High–Performance Polymer Solar Cells". J. Am. Chem. Soc. 2011, 133, 14244.

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C64 - In situ reflectance imaging of organic thin film formation from solution

Jonas Bergqvista, Hans Arwinb, Olle Inganäsa

a, 1Biomolecular and Organic Electronics, IFM, and Center of Organic Electronics, Linköpings Universitet, Linköping, 581 83, SE b, Laboratory of Applied Optics, IFM, Linköpings Universitet, Linköping, 581 83, SE

The rapid progress of organic photovoltaic devices during the last decade, with power conversion efficiencies now exceeding 8%, has brought the technology close to an industrial breakthrough. For polymer solar cells, roll to roll printing is desired to gain the production advantage. The formation of the photoactive material from solutions needs to be controlled and optimized. Therefore a suitable method to monitor the deposition process is needed as deviations of drying times1 and drying rates2 during the coating process have proven to generate morphology variations causing variations in photocurrent generation. Here we demonstrate how reflectance imaging can be used to monitor the drying process, both for spin coating and blade coating deposition. A blue LED is used as light source to generate specular reflections imaged by a CMOS camera. The thinning of the wet film can then be observed by thin film interference, and can be recorded for each pixel. This enables an estimation of the evaporation rate for each pixel mapped over the substrate. For spin coating the evaporation rate is shown to increase with the distance from the rotation center, whereas the air flow is the determining parameter during blade coating.

Figure 1 Snapshot during the spin coating process of a polymer:PCBM blend dissolved in orthodichlorbenzene on a 1.5x2 cm silicon substrate. The shifting light intensities are due to thin film interference.

By mapping the times when interference ceases, lateral variations in drying time are visualized. Furthermore the quenching of polymer photoluminescence during the drying process can be visualized, thus creating a possibility to estimate morphological variations. Moreover lateral thickness variations of the dry film can be visualized by scanning ellipsometry. After depositing a top electrode photocurrent images can be generated by a laser scanning method. This allows for a direct comparison of drying conditions and photocurrent generation. The possibility to monitor the thin film formation as well as lateral variations in thickness in-situ by a non-invasive method, is an important step for future large scale applications where stable high performing generating morphologies have to be formed over large areas.

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References [1]Schmidt-Hansberg, B.; Sanyal, M.; Klein, M.F.G.; Pfaff, M.; Schnabel, N.; Jaiser, S.; Vorobiev, A.; Müller, E.; Colsmann, A.; Scharfer, P.; Gerthsen, D.; Lemmer, U.; Barrena, E.; and Schabel, W., ACS Nano 5, 8579-8590 (2011) [2] Hou, L.; Wang, E.; Bergqvist, J.; Andersson, V.B.; Wang, Z.; Müller, C.; Campoy-Quiles, M.; Andersson, M.R.; Zhang, F.; Inganäs, O., Adv. Func. Mat. 21, 3169–3175 (2011)

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C65 – Incorporation of Carbon Nanotubes into Organic Polymer Monolithic Columns for Capillary Chromatography

Abdulrahman Alwarthana, Ahmad Aqelb

a, King Saud University, Chemistry Department, Science College , Riyadh, 11456, SA b, King Abdullah Institute for Nanotechnology, College of Science, SA

This work describes fabrication of polymer monolithic materials to be used as stationary phases in capillary liquid chromatography. Multi-wall carbon nanotubes (MWCNT) were incorporated into an organic polymer monolith containing benzyl methacrylate (BMA) and ethylene dimethacrylate (EDMA). The porogenic solvents were selected to maintain a uniform polymer matrix in the capillary column. Several columns have been synthesized in the confines of 320 µm i.d. and 150 mm length fused-silica capillaries by single step in-situ copolymerization reaction. The porous and hydrodynamic properties; i.e. porosities, permeabilities and mechanical stabilities of the prepared monolithic columns were thoroughly investigated. Also, their morphology were characterized by using different techniques, such as the optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra and thermogravimetric analysis (TGA). The columns were then chromatographically evaluated; efficiency and performance towards different sets of analytes were obtained and compared, mixtures of ketonic and phenolic compounds were successfully separated and evaluated.

.

Figure 1 References [1] Y. Xu, Q. Cao, F. Svec, JMJ. Frechet, Anal Chem 82 (2010) 3352. [2] A. Duan, S. Xie, L. Yuan, Anal Bioanal Chem 399 (2011) 143.

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C66 - Harnessing biodiversity potential in the quest of pigment molecules for dye-sensitized solar cells: From plant extracts to microorganism metabolites

Leslie W. Pinedaa, Karina Torres Castroa, Andrea Soto Navarroa, Darío Chinchillab, Catalina Murillo Cruzc, Kattia Rosales Ovaresc, Cindy Torres Quirósa, Carlos Mezad, Mavis L. Monteroa

a, Centro de Investigación en Electroquímica y Energía Química (CELEQ), Ciudad de la Investigación, Apartado 11501 2060, Universidad de Costa Rica, San José, Costa Rica b, Escuela de Química, Universidad de Costa Rica, Apartado 2060, San José, Costa Rica c, Unidad de Bioprospección del Instituto Nacional de Biodiversidad (INBio), Apartado 22-3100, Santo Domingo de Heredia, Costa Rica d, Laboratorio de Sistemas Electrónicos para la Sostenibilidad (SESLab), Instituto Tecnológico de Costa Rica, Cartago, Costa Rica

The current and growing energy consumption projections in the medium- and long-term suggest the contribution of various renewable energy sources. A viable option for Costa Rica and other tropical countries is the use of solar energy using solar cells featuring high efficiencies and competitive costs.1 Indeed, a model that portrait these concepts are sensitized solar cells based on photosynthesis bioinspired principles.2 Relevant components in the operation of such photovoltaic devices are molecules that function as light-capturing.3 Hence, the extraction and evaluation of novel sensitizing molecules stemming from plant extracts and microorganism metabolites might be the venue for new sources of chemical compounds that could lead to an enhancement in the efficiency of such devices.4,5 Herein we report on the assembly and physical measurements of dye-sensitized solar cells containing natural plant dyes extracted from Justicia colorífera, Solanum mamosum, and Tradescantia zebryna, and exhibiting energy conversion efficiencies of 1.2%. Furthermore, the national bioprospecting information of a collection consisting of ca. 8.000 fungal strains is also being screened for fungal pigment production that can be used as sensitizing molecules. Interestingly, several fungal pigment colorations are obtained during its cultivation process. References [1] Torres, K.; Arrieta, J. P.; Torres, C. Q.; Montero, M. L.; Pineda, L. W. Revista Energía, 2011, 60, 69.

[2] Grätzel, M. Nature 2001, 414, 338344.

[3] O´Reagan, B.; Grätzel, M. Nature 1991, 353, 737740. [4] Velmurugan, P.; Kamala-Kanan, S.; Balachandar, V.; Lakshmanaperumalsamy, P.; Chae, J.; Oh, B. Carbohydrate

Polymers 2010,. 79: 262268. [5] Ito,S.; Saitou, T.; Imahori, H.; Uehara, H.; Hasegawa, N. Energy & Environmental Science 2011, 3, 905-909.

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C67 - Sevenfold Enhancement on Porphyrin Dye Efficiency by Coordination of Ruthenium Polypyridine Complexes

André L. A. Parussulo, Bernardo A. Iglesias , Koiti Araki, Henrique E. Toma

Universidade de São Paulo- Institute of Chemistry, José Alvares Maciel 787, São Paulo, 5539080, BR

Since Grätzel’s seminal paper in 19911, research on dye sensitized solar cells (DSSCs) increased explosively all over the world. Several classes of molecules have been synthesized and tested since then. Many efforts have been focused on innovative strategies to improve the efficiency of photosensitizer using the supramolecular approach.2 In fact, porphyrins and ruthenium (II) polypyridyne complexes have been successfully employed as building-blocks of supermolecules showing photoelectrochemical properties. Energy transfer and photoinjection from the ruthenium polypyridine and porphyrin moiety were observed in the photoaction spectra of DSSCs prepared with those dyes, but no significant effect was observed on hprobably because they lack TiO2 binding sites.3 Accordingly, here we designed a new supramolecular porphyrin dye encompassing a meso-4-carboxyphenyl binding site as well as three [Ru(dmbpy)2Cl]+ complexes (dmbpy=4,4’-dimethyl-2,2’-bipyridine) coordinated to the meso-(4-pyridyl) positions as antennae (Figure). This supermolecule was characterized by elemental analyses, NMR spectroscopy, mass spectroscopy and cyclic voltammetry. The I-V curves consistently reflected the superior efficiency of the new supramolecular porphyrin dye in comparison with the parent free-base 5-(4-carboxyphenyl)-10,15,20-tri(4-pyridyl)porphyrin (MCTPyP) and its respective zinc(II) complex (Zn-MCTPyP). In fact, the short-circuit photocurrents measured for the parent porphyrin dyes were 0.5 and 0.8 mA cm-2, while the cells prepared with MCTPyPRu3 and Zn-MCTPyPRu3 showed much higher performance of 3.1 and 4.6 mA cm-2 respectively. Since the optical density of the cells were similar for the cells prepared with the conventional and ruthenated porphyrins, a sevenfold enhancement on η(from 0.11 to 0.77 and 0.17 to 1.2 %, respectively) was achieved as a consequence of coordination of [Ru(dmbpy)2Cl]+ complexes to the parent MCTPyP and Zn-MCTPyP porphyrin dyes.

Figure 1 A) Scheme showing the supramolecular Zn-MCTPyPRu3 dye anchored on TiO2 surface. Electron injection takes place after direct excitation of the zinc(II) porphyrin moiety or energy transfer (ET) from the peripheral ruthenium complexes. B) Energy diagram showing the photo-induced processes at the TiO2/dye interface.

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The analysis of the photoaction spectra allowed us to evaluate the contribution of the peripheral ruthenium complexes to the quantum efficiency of the supramolecular dyes. The photoaction of Zn-MCTPyPRu3 exhibited broadened Soret and Q bands at 430, 563 and 609 nm, as well as the MLCT band characteristic ruthenium(II) polypyridines at 505 nm. As expected, this band is absent from the parent MCTPyP and Zn-MCTPyP porphyrin dye photoaction. In conclusion, more than enhancing the light harvesting in the visible spectrum, the peripheral ruthenium complexes promoted a sevenfold enhancement of the energy conversion efficiency (as compared with the parent species) by playing several key roles (inhibiting aggregation, transferring energy to and accepting the hole generated in the porphyrin after electron injection), revealing important new insights for the design of more efficient supramolecular porphyrin dyes. References [1] Oregan, B. and Gratzel, M. "A low-cost high-efficiency solar-cell based on dye-sensitized colloidal TiO2 films". Nature 353, 737-740 (1991). [2] Warnan, J.; Pellegrin, Y.; Blart, E.; and Odobel, F. "Supramolecular light harvesting antennas to enhance absorption cross-section in dye-sensitized solar cells". Chem. Comm. 48, 675-677 (2012). [3] Nogueira, A. F.; Furtado, L. F. O.; Formiga, A. L. B.; Nakamura, M.; Araki, K.; Toma, H. E. "Sensitization of TiO2 by supramolecules containing zinc porphyrins and ruthenium-polypyridyl complexes". Inorg. Chem. 43, 396-398 (2004).

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C68 - Correlating Phase Transitions with Thermal Annealing Temperatures for P3HT:PCBM Organic Photovoltaic Devices

Andrew Pearsona, Paul Hopkinsonb, Tao Wanga, Athene Donaldb, David Lidzeya

a, Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield, S3 7RH, GB b, Department of Physics, University of Cambridge, JJ Thompson Avenue, Cambridge, CB3 0HE, GB

We have studied a range of organic photovoltaic devices (OPVs) based on a thin-film blend of P3HT and PCBM, and show that by comparing device studies with a characterisation of the thermal transitions of the blend, we can provide a mechanistic description of the minimumtemperature required to improve device efficiency (1). For as-cast P3HT:PCBM blend thin-films we evidence two glass transition temperatures corresponding to the existence of two compositionally different amorphous states.

Figure 1 Power conversion efficiencies (PCEs) (%) of P3HT:PCBM blend OPVs as a function of both active layer composition and annealing temperature.

We demonstrate that an improvement in device efficiency only occurs once the film has been heated above the upper apparent glass transition temperature of the blend. If annealing is performed above the optimum temperature, excessive phase-separation and a partial reduction in film optical density leads to a general decrease in device efficiency. Both of these characteristic temperatures are dependent upon the composition of the blend. The temperature-dependent competition between such processes therefore opens a ‘window’ within which device efficiency can be optimised and provides an opportunity to design effective annealing protocols for future polymer:fullerene blend OPVs.

References [1] Pearson, A. J.; Hopkinson, P. E.; Wang, T.; Staniec, P. A.; Jones, R. A. L.; Donald, A. M.; Lidzey. D. G., Rationalising Phase Transitions with Thermal Annealing Temperatures for P3HT:PCBM Organic Photovoltaic Devices. Macromolecules 2012 45(3), 1499-1508

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C69 - Imaging the Bulk Nanoscale Morphology of Polymer:Fullerene Blend Thin-films Using Helium Ion Microscopy

Andrew Pearson*a, Stuart Bodenb, Darren Bagnallb, David Lidzeya, Cornelia Rodenburgc

a, Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield, S3 7RH, GB b, Electronics and Computer Science, University of Southampton, Highfield, Southampton, SO17 1BJ, GB c, Engineering Materials, University of Sheffield, Mappin Street, Sheffield, S1 3JD , GB

The development of Organic Photovoltaics (OPVs) has seen the use of a wide range of complimentary techniques for materials characterisation. Here we report and evaluate the use of helium ion microscopy (HeIM) for imaging the nanoscale structure in samples applicable for OPVs (1). For a poly(3-hexylthiophene)/[6,6]-phenyl C61-butric acid methyl ester (P3HT/PCBM) blend thin-film subject to a thermal anneal at 140°C, we identify a network structure that is not apparent at the film surface, with slightly elongated PCBM nanodomains.

Figure 1 HeIM image of a P3HT/PCBM (60:40 wt%) blend thin-film after thermal annealing at 140°C

The absence of similar features in blend thin-films subject to different annealing treatments, or correlation between secondary electron yield and variations in surface topography suggest the HeIM is capable at imaging spatial variations in chemical structure with nanometer resolution. The calculated lateral spatial periodicity of the film (20±4nm) is consistent with other studies of this system, demonstrating HeIM as a promising technique for the characterization of organic semiconductor thin-films.

References [1] Pearson, A. J.; Boden, S. A.; Bagnall, D. M.; Lidzey, D. G.; Rodenburg, C., Imaging the Bulk Nanoscale Morphology of Organic Solar Cell Blends Using Helium Ion Microscopy. Nano Letters 2011, 11 (10), 4275-4281.

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C70 - DFT Study of Triphenylamine-Based Dyes for their Use as Sensitizers in Molecular Photovoltaics

Jesús Baldenebro-Lópeza, José Castorena-Gonzálezb, Norma Flores-Holguína, Jorge Almaral Sánchezb, Daniel Glossman-Mitnika

a, CIMAV, SC, Miguel de Cervantes 120, Chihuahua, 31109, MX b, Universidad Autónoma de Sinaloa, Prol. Ángel Flores y Fuente de Poseidón, S.N., 81223, Los Mochis, Sinaloa, MX

In this work we have studied three dyes which are proposed for potential photovoltaic applications and they were called Dye7, Dye7-2t and Dye7-3t.

Figure 1 Sensitizers diagrams studied in this research (Dye7, Dye7-2t and Dye7-3t)

The Density Functional Theory (DFT) has been utilized, using the M05-2X hybrid meta-GGA functional and the 6-31+G(d,p) basis set. This level of calculation has been used to find the optimized molecular structure and to predict the main molecular vibrations, the absorption and emission spectra, the molecular orbitals energies, dipole moment, isotropic polarizability and the chemical reactivity parameters that arise from Conceptual DFT. Also, the pka values were calculated with the semi-empirical PM6 method.

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C71 - Impedance study of dye-sensitized solar cells employing cobalt bipyridyl redox mediators

Yeru Liu, James Jennings, Qing Wang

National University of Singapore, Blk EA #03-09, 9 Engineering Drive 1, Singapore, 117576, SG

Dye-sensitized solar cells employing cobalt (II/III)-based redox mediators have recently shown comparable performance to cells using conventional iodide/triiodide based redox electrolytes.1 This is partly due to the more positive standard potential of cobalt (II/III) compared to I-/I3

-. However, fast recombination in cobalt (II/III) system can limit the obtainable open circuit voltage and fill factor, which are major factors that limit the overall performance of cobalt (II/III)-based devices. We will present our recent study of charge transfer and transport in dye-sensitized solar cells employing cobalt bipyridyl redox mediators. To test standard model of charge transport and shed light on recombination mechanism, we have utilized impedance spectroscopy at different temperatures. We find that the standard multiple trapping model cannot fully explain our results. Specifically, the variation of transport and recombination resistances with cell voltage are highly non-ideal, and the “chemical” capacitance of the photoelectrode has a different temperature dependence to that in I-/I3

-electrolyte systems.2,3 These phenomena are consistent with the band edge unpinning during operation, which is expected to influence the charge recombination kinetics. References [1] Yella, A et al. ¡°Porphyrin-Sensitized Solar Cells with Cobalt (II/III)-Based Redox Electrolyte Exceed 12 Percent Efficiency¡±. Science 334, 629-634 (2011). [2] Wang, Q et al. ¡°Characteristics of High Efficiency Dye-Sensitized Solar Cells¡±. J. Phys. Chem. B 110, 25210-25221 (2006). [3] O¡¯Regan, B. C. and Durrant, J. R. ¡°Calculation of Activation Energies for Transport and Recombination in Mesoporous TiO2/Dye/Electrolyte Films-Taking into Account Surface Charge Shifts with Temperature¡±. J. Phys. Chem. B 110, 8544-8547 (2006)

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C72 - Novel NIR Sensitizers for Dye Sensitized Solar Cells

Iuliia Shcherbakovaa, Marina Simeunovica, Simone Hochleitnera, Toby Meyerb, Frederic Ostwaldb, Thomas Geigera

a, Empa, Überlandstrasse 129, Dübendorf, 8600, CH b, Solaronics SA, Rue de l'Ouriette 129, Aubonne VD, CH

Dye-sensitized solar cells (DSC) are important low-cost alternatives to conventional solid-state photovoltaic devices.(1) The charge transfer sensitizers commonly applied in this type of solar cell are ruthenium polypyridyl complexes that show a major absorption in the visible spectrum. The spectral match of the sensitizer absorption to the solar radiation is the crucial factor for efficient energy conversion. In this regard, development of the sensitizing dyes converting photons to electrons in the near IR region is essential for increasing short circuit current (Jsc). Thus, we focus on the preparation of new unsymmetrical squaraine and heptamethine dyes, their optical, electrochemical and photovoltaic properties. These metal-free dyes are well-known for their intense absorption in the visible and far red to NIR domain of the solar spectrum and high molecular extinction coefficients (up to 300000 dm3mol-1cm-

1).(2,3) A number of unsymmetrical squaraine and heptamethine dyes with different heterocyclic moieties were synthesized using a building block technique. Introduction of a new quinoline anchor group in the squaraine and heptamethine dye structures shifts bathochromic the absorption peak to over 700 nm. Especially, UV-vis investigations of the unsymmetrical dyes impressively demonstrate the great spectral diversity above 700 nm. Exemplarily, the UV-vis spectra of the dyes in solution and the spectrum of the Sun's solar radiation (AM1.5) are shown in Fig. 1.

Figure 1 UV-vis spectra of the novel NIR sensitizing dyes in chloroform and the spectrum of the Sun's solar radiation (AM1.5).

Finally, the unsymmetrical heptamethine and squaraine dyes were tested in laboratory dye sensitized spot cells (glas/FTO/TiO2/dye/iodid-triiodid(acetonitril)/Pt/FTO/glas) with an active area of 0.72 cm2. Optimized dye sensitized solar cell showed a short circuit current density (Jsc) of 3.47 mAcm-2, an open circuit voltage (Voc) of 495 mV and a fill factor (ff) of 0.76 leading to an overall conversion efficiency η of 1.31% in case of the heptamethine dye (Hepta12) and a short circuit current density (Jsc) of 7.54 mAcm-2, an open circuit voltage (Voc) of 520 mV and a fill factor (ff) of 0.71 leading to an overall conversion efficiency η of 2.78% for the squaraine dye (SQQ3) obtained under 1000 Wm-2 illumination intensity. Remarkably, dye sensitized solar

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cells with heptamethin dyes, which absorb light in the NIR, almost appear in light yellow, the colour of the electrolyte.

References [1] O’Regan, B.; Graetzel, M. “A Low-Cost, High-Efficiency Solar-Cell Based on Dye-Sensitized Colloidal TiO2 Films”. Nature 353, 737–740 (1993). [2] Geiger, T.; Kuster, S.; Yum, J.-H.; Moon, S.-J.; Nazeeruddin, M. K.; Graetzel, M.; Nueesch, F. “Molecular Design of Unsymmetrical Squaraine Dyes for High Efficiency Conversion of Low Energy Photons into Electrons Using TiO2 Nanocrystalline Films”. Adv. Funct. Mater. 19, 2720-2727 (2009). [3] Kazumasa F.; Hiroyoshi M.; Atsuhiko H; Nagisa T.; Noriko M.;Yukako S.; Akihiko N.; Tsukasa Y.; Yasuhiro K.; Masaki M. “Synthesis of a Novel Heptamethine–Cyanine Dye for Use in Near-Infrared Active Dye-Sensitized Solar Cells with Porous Zinc Oxide Prepared at Low Temperature”. Energy Environ. Sci. 4, 2186-2192 (2011).

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C73 - Finger prints of dye solar cell’s components using Fourier Transform Infrared spectroscopy

Muhammad Imran Asghara, Niko Humalamäkib, Liisa Antilab, Sampo Kaukonena, Janne Halmea, Peter Lunda, Jouko Korppi-Tommolab

a, Department of Applied Physics, Aalto University, P.O. Box 15100, FIN-00076 Aalto, Finland, FI b, Department of Chemistry, University of Jyväskylä, Nanoscience center (NSC), P.O. Box 35, FI-40014 Jyväskylä, Finland, FI

Long term stability of dye solar cells (DSCs) is a prerequisite for their commercialization. The flexible DSCs based on plastics or metals have additional challenges with regards to the degradation. Several degradation mechanisms have been reported [1,2]. To improve the stability of DSCs it is essential to understand the degradation reactions using techniques giving information about chemical structural changes [1,2]. In this work, using Fourier transform Infrared (FTIR) spectroscopy a database library of dye solar cell components is presented. It covers five different dyes N3, N719, Z907, Osmium dye and thiocyanate free Ruthenium dye and different electrolyte additives i.e. Iodine (I2), Lithium iodide (LiI), 4-tert-butylpyridine 4-TBP, Guanidinium thiocyanate (GuSCN), 1-propyl-3-methylimidazolium iodide (PMII), 1-Methyl-benzimidazole (NMBI) in 3-methoxypropionitrile and acetonitrile as solvents. The measurements were done in a specially designed cell arrangement through Calcium Fluoride window. The focus of the work is to understand the chemical behavior of the molecules in the electrolyte and the photoelectrode. This DSC library will act as reference point to examine the chemical changes occurred during the degradation of DSCs. The results are a step forward towards the understanding the chemical interactions of different DSCs components and their effect on the lifetime of the DSCs.

Key words:Degradation, Dye, Electrolyte, Infrared, Solar

References [1] Asghar, M.I., Miettunen, K., Halme, J., Vahermaa, P., Toivola, M., Aitola, K., and Lund, P., Review of stability for advanced dye solar cells, Energy & Environmental Science 3, pp. 418-426 (2010). [2] Miettunen, K., Asghar, M.I., Mastroianni, S., Halme, J., Barnes,P.R. F., Rikkinen, E., Regan, B. C., and Peter Lund, P., Effect of molecular filtering and electrolyte composition on the spatial variation in performance of dye solar cells, Journal of Electroanalytical Chemistry 664, pp. 63-72 (2012).

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C74 - “Pseudo bi-layer” Organic Solar Cells

Chian Haw Yong, L. N. S. A. Thummalakunta, Ananthanarayanan Krishnamoorthy, Joachim Luther

Solar Energy Research Institute of Singapore (SERIS), National University of Singapore, 7 Engineering Drive 1, Block E3A, #06-01, SINGAPORE, 117574, SG

The state of the art solution processed organic photovoltaic (OPV) cells are based on the bulk heterojunction (BHJ) architecture, consisting of an active layer, in which the donor and the acceptor material are dissolved in a common solvent. In this poster presentation we showed an efficient solution-processed pseudo bi-layer organic solar cell with standard donor material poly (3-hexyl thiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) or indene-C60 bisadduct (ICBA) as acceptor. These pseudo bi-layer organic solar cells were fabricated by sequential processing of donor and acceptor components using orthogonal solvent followed by subsequent thermal annealing [1, 2]. The optimized pseudo bi-layer organic solar cells showed efficiency values of 4.1% and 5.9% under AM 1.5G irradiation (1000W/m2) respectively for P3HT:PCBM and P3HT:ICBA.The obtained high efficiency is attributed to an enhanced nanomorphology that arises from the inter-diffusion between fullerene nanoparticles and pre-organised polymer (P3HT) and also due to the subsequent crystallisation of the fullerene nanoparticles induced by thermal annealing. These processes facilitate efficient charge generation and extraction. Time of flight – secondary ion mass spectroscopy(TOF-SIMS) depth profiling and X-ray Photoelectron Spectroscopy(XPS) were carried out for different thermal annealing treatments of these pseudo bi-layer devices, which reveals full inter-diffusion between fullerene and polymer P3HT. Photo-CELIV (Charge extraction by linearly increasing voltage) studies elucidates that the thermal annealing imparts crystallinity to the fullerene phase which results in the improvement of charge carrier mobility.

Figure 1 Schematic of device structure before and after thermal annealing.

The thermal annealing induced crystallinity effect is more pronounced in ICBA as compared to PCBM. These results demonstrated that the above mentioned sequential deposition process can yield higher efficiency values than a comparable conventional bulk heterojunction organic solar cell. These pseudo bi-layer organic solar cells have certain advantages over their BHJ counterparts like control over processing conditions, thermal stability and minimal usage of active components. The reasons for the relatively high performance of these solar cells will be presented in detail.

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References [1] A. L. Ayzner, C. J. Tassone, S. H. Tolbert, and B. J. Schwartz "Reappraising the Need for Bulk Heterojunctions in Polymer-Fullerene Photovoltaics: The Role of Carrier Transport in All-Solution-Processed P3HT/PCBM Bilayer Solar Cells." J. Phys. Chem. C, 113, 20050 (2009). [2] M. D. Heinemann, K. Ananthanarayanan, LNSA Thummalakunta, C. H. Yong, J. Luther, Formation and characterisation of solution processed pseudo-bilayer organic solar cells, Green - The International Journal of Sustainable EnergyConversion and Storage. 1 (2011) 291- 298.

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C75 - Organic solar cells using simply grown graphene transparent electrode

Chang Su Kim, Ji-Hoon Seo, Jae-Wook Kang

Korea Institute of Materials Science, Changwon Daero 797, Changwon, 641, KR

We report a simple method for growing wafer-scale graphene films using PCBM (phenyl-C61-butyric acid methyl ester), a fullerene derivative, as a solid carbon source. PCBM films spin-coated on nickel catalyst were easily converted to graphene films having a thickness of a few layers by thermal annealing without any reactive gas. This method of converting PCBM to graphene is safe, unlike the chemical vapor deposition (CVD) method that uses explosive precursor gases. PCBM-derived graphene films were also transferred through a simple process to plastic substrates with a supporting layer for use in organic solar cells.

Figure 1 Schematic illustration of the method for growing graphene films.

The power conversion efficiency (PCE) of bulk heterojunction organic solar cells prepared on the PCBM-derived graphene electrode was 0.98%. This study indicates that PCBM-derived graphene films can serve as an inexpensive, flexible alternative to indium tin oxide (ITO) films, and therefore, they can improve the economic viability and flexibility of organic solar cells.

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C76 - Spontaneous formation of ZnO nanoripples and surface modification for high efficient OPV

Dong Chan Lim, Kwang-Dae Kim, Jae-Hong Lim, Kyu Hwan Lee, JooYul Lee

Korea Institute of Materials Science, 66 Sangnam-dong, Changwon, 641-010 Korea, Changwon, 641, KR

A simple method for spontaneous formation of nanoripples on ZnO thin films was developed, and these nanostructured ZnO films were used as hole-blocking layer in inverted organic solar cells. Moreover, the size (height) of nanoripples on ZnO surface could be controlled in the range of several tens of nanometers. Among various ZnO films, surface structures with ~70 nm-high nanoripples resulted in the best photovoltaic performance of the organic solar cell. In addition, ZnO and TiO2 ultra-thin films were deposited on 3-D ZnO surfaces using atomic layer deposition. Ultrathin ZnO and/or TiO2 layers with a mean thickness of less than 5 nm could enhance photovoltaic performance of the inverted organic solar cell; in particular, short-circuit current (Jsc) and power conversion efficiency (PCE) was increased by deposition of TiO2 layers. A higher thickness of additional oxide thin film resulted in reduced photovoltaic performance. Evidence is provided that recombination of electrons and holes on the surface of ZnO can be quenched by ultra-thin layer. And also, this additional process turned out to increase stability of the IOPV significantly. References [1] Spontaneous formation of nanoripples on the surface of ZnO thin films as hole-blocking layer of inverted organic solar cells, Dong Chan Lim, Won Hyun Shim, Kwang-Dae Kim, Hyun Ook Seo, Jae-Hong Lim, Yongsoo Jeong, Young Dok Kim, Kyu Hwan Lee, Solar Energy Materials & Solar Cells, 95, 2011, 3036-3040 [2] Ultrathin TiO2 Films on ZnO Electron-Collecting Layers of Inverted Organic Solar cell" Author(s): Seo, Hyun Ook; Park, Sun-Young; Shim, Won Hyun; Lee, Kyu-Hwan; Jo, Mi Young; Kim, Joo Hyun; Lee, Eunsongyi; Kim, Dong-Wook; Kim, Young Dok; Lim, Dong Chan, Journal of Physical Chemistry C, 115, 21517-21520 , 2011

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C77 - Efficient dye regeneration in thick solid state dye-sensitized solar cells

Erik M. J. Johanssona, Lei Yanga, Erik Gabrielssonb, Peter W. Lohsea, Gerrit Boschlooa, Licheng Sunb, Anders Hagfeldta

a, Uppsala Universitet, Department of Chemistry-Ångström, SE-751 05 Uppsala, Sweden b, KTH Royal Institute of Technology, Department of Chemistry, SE-10044 Stockholm, Sweden

An efficient transfer of holes from the oxidized dye to the counter electrode is a crucial step for the performance of a dye-sensitized solar cell (DSC). In solid state DSCs this step is performed by hole-conductor material. We show that a small hole-conductor molecule has in contrast to larger polymers the capability to regenerate dye molecules in the pores of the dye-sensitized TiO2 nanoparticle electrode efficiently also for thick (>5µm) electrodes. However, the performance of the solar cells with the small hole-conductor molecules is poor due to a less efficient charge transfer to the back contact. Polymer hole-conductors, which may have a good hole conductivity, also have a high molecular weight, which makes these polymers difficult to infiltrate into the smallest pores of the electrode. Adding conducting polymers to the small molecule hole-conductor enables better transport of the charges to the contact and reduces recombination, and therefore increases the photocurrent. This new device construction with a small molecule efficiently regenerating the dye molecules, and a polymer conducting the holes to the contact is a promising pathway for solid state dye-sensitized solar cells.

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C78 - Enhancing Light Absorption through Localized Surface Plasmon Resonance: Fundamental Studies in DSSCs

Erica DeMarco, Hanning Chen, Stacey Standridge, George Schatz, Michael Pellin, Joseph Hupp

Northwestern University, 2145 Sheridan Rd. Evanston, IL 60208, US

Incorporation of metallic nanostructures into the photoelectrode of a dye-sensitized solar cell (DSSC) leads to amplification of light absorption of the dye sensitizer through localized surface plasmon resonance. This presentation will show that dye absorption enhancement, and thus photocurrent enhancement, is achievable for a broad range of dye sensitizers using colloidal silver nanoparticles as plasmonic optical elements of the photoanode. Use of different metal oxide films grown by atomic layer deposition (ALD) is employed to investigate the influence of dielectric environment on photocurrent enhancement in dye cells containing colloidal silver nanoparticles. Mie-based computational methods are used to model these experimental systems and predict photoanode conditions that yield maximum dye absorption enhancement. This includes examining the effects of the extent of silver oxidation on dye enhancement. Plasmon-enhanced light absorption in a multi-component Ag/Ag2O/TiO2/N3 DSSC core-shell nanostructure is studied using a hybrid quantum mechanics/classical electrodynamics (QM/ED) methodology.

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C79 - Tailor-made synthesis of BODIPY dyes as panchromatic sensitizers

Katja Gräf, Mukundan Thelakkat

University of Bayreuth, Universitätsstr. 30, Bayreuth, 95440, DE

We present the synthesis and properties of four new BODIPY sensitizers for the application in solid-state dye-sensitized solar cells. Meso-phenyl BODIPYs with and without TPA-donor-antenna groups (m-P-BODIPY and m-P-TPA-BODIPY) are compared to newly developed meso-ethynylphenyl BODIPYs (m-EP-BODIPY and m-EP-TPA-BODIPY). It is known, that the phenyl group of meso-phenyl BODIPYs is oriented orthogonal relative to the BODIPY core. This disturbs the electronic communication between both parts. From porphyrin chemistry it is further know that an ethynyl bridge allows efficient electronic interaction between two chromophores. Therefore, we introduced a meso-ethynylphenyl bridge between the BODIPY core and the anchoring moiety with the goal to improve the electron flow from the BODIPY/donor-antenna unit to the anchoring group. Additionally, we introduced donor-antenna groups to meso-phenyl and meso-ethynylphenyl BODIPYs to reach a panchromatic behaviour. The meso-phenyl derivatives were synthesised starting from an aromatic aldehyde, and the corresponding meso-ethynylphenyl BODIPYs were synthesised starting from an aliphatic aldehyde in comparable yields. An essential part of the synthesis is the Knoevenagel-type condensation for the covalent attachment of donor-antenna groups to the BODIPY framework. We proved that this condensation follows an organocatalytic mechanism forming a vinylic trans connection. The final products were fully characterised regarding their configuration, optical and electrochemical properties by NMR, UV-vis absorption measurements and cyclic voltammetry experiments. The Influence of the meso-ethynyl bridge and the TPA-donor antenna group on the properties was investigated.

Figure 1 Structures of the meso-phenyl BODIPYs (m-P-BODIPY and m-P-TPA-BODIPY) and the corresponding meso-ethynylphenyl BODIPYs (m-EP-BODIPY and m-EP-TPA-BODIPY).

By comparing the absorption of m-P-BODIPY and m-EP-BODIPY it could be proved that the ethynyl bridge is able to improve the electronic connection between the BODIPY core and the

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anchoring group. Furthermore, the donor substituted BODIPYs show an excellent panchromatic behaviour. The absorption edge was found at 825 nm and 1031 nm for m-P-TPA-BODIPY and m-EP-TPA-BODIPY, respectively. The extinction coefficients ε are higher than 1*104 M-1cm-1 over the whole visible up to the NIR region. All compounds were found to be stable against repeated oxidations and rereductions. It was observed that the LUMO level is strongly influenced by the meso-substituent and the HOMO level is determined by the donor group. Finally, all BODIPY compounds were used as sensitizers in solid-state dye-sensitized solar cells.

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C80 - Dye-sensitized solar cells based on ZnO nanorod photoanodes: influence of the band gap

Carlos Ramosa, Juan Rodrigueza, Luis Sancheza, Mikhail Gorlovb, Lars Kloob, Walter Estradaa, Maria Quintanaa

a, Universidad Nacional de Ingenieria, Monte Caoba 1125. Surco, LIma, 0, Peru b, Royal Institute of Technology, Teknikringen 30.SE 100 44, Sweden

The effect of ZnO photoanode morphology and microstructure on the performance of Dye sensitized solar cells (DSSCs) is reported. Different structures of dye-loaded ZnO films have been fabricated. A significant variation in device efficiency with ZnO nanorod arrays as photoanodes has been achieved by varying the seeds microtructure. Although the overall power conversion efficiency increases from 0.2% to 0.4%, the IPCE is high. The higher device efficiency in DSSCs with nanorod photoanodes is originated from both large surface area provided by nanorod and efficient charge transport provided by the nanorod arrays.

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C81 - Efficiency Enhancement by A Fairly Stable I-/(SeCN)2 Redox Mediator in Dye-Sensitized Solar Cells

Donghoon Songa, Woohyung Chob, Mi Jin Choib, Yong Soo Kangb

a, Department of Chemical Engineering, Hanyang University, Seoul, 133-791, KR b, WCU program Department of Energy Engineering, Hanyang University, Seoul, 133-791, KR

An I−/(SeCN)2 redox mediator was newly developed exhibiting favorable properties related to visible light absorption, ionic conductivity, and redox potential than I−/I3

− for dye-sensitized solar cells (DSCs). It was then successfully demonstrated that the new redox mediator enhanced the energy conversion efficiency for DSCs, proposing a new potential for an alternative redox mediator.

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C82 - Flavylium salts as novel photosensitizers for dye-sensitized solar cells

Giuseppe Calogero*a, Alessandro Sinopolia, Ilaria Citroa, Gaetano Di Marcoa, Vesselin Petrovb, Ana M. Dinizb, A. Jorge Parolab, Fernando Pinab

a, CNR-IPCF, viale F. Stagno D'Alcontres 37, MESSINA I- 98158, IT b, REQUIMTE Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal

Seven flavylium salt dyes were employed for the first time as novel sensitizers for dye-sensitized solar cells (DSSCs). Photophysical and photoelectrochemical measurements showed that these flavylium dyes are very promising for DSSC applications (1). Among the investigated compounds, the best performance has been obtained by a DSSC based on the novel 7-(N,N-Diethylamino) - 3’,4’-dihydroxyflavylium salt. Our results suggests that the substitution of a hydroxylic group with an diethylamine unit (NC2H5) into the position 7 of ring A of flavylium framework expanded the p-conjugation in the dye and thus resulted in a high absorption in the visible region and is advantageous for effective electron injection from the dye into the conduction band of TiO2. In addition, the amine group, owing to its strong electron-donor ability, might play an important role in electron injection in addition to a red shift in the absorption region. This work open new possibility to develop new class of sensitizers synthetic analogues of natural anthocyanidins. References [1] Pina , F.; Melo,M. J.; Laia,C. A.T.; Jorge Parola,A.; Lima J. C. "Chemistry and applications of flavylium compounds: a handful of colours". Chem. Soc. Rev. 41, 869(2011).

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C83 - Novel ketone containing alternating copolymer for organic solar cells

Ranjith K, Arun Rao, Praveen Ramamurthy

Indian Institute of Science, Bangalore, India, Deparartment of Materials Engineering, IISc, Bangalore, 560012, IN

Alternating copolymer poly7, 9-di (thiophen-2-yl)-8H-cyclopenta[a]acenaphthylen-8-one-co-9-hexyl-9H-carbazole was synthesized by palladium (0) catalyzed Stille coupling reaction of tributyl stannane and dibromo derivative of the respective monomers. Structural, thermal, electrochemical and optical characterizations of the synthesized copolymer were carried out.

Figure 1 Structure of poly7, 9-di (thiophen-2-yl)-8H-cyclopenta[a]acenaphthylen-8-one-co-9-hexyl-9H-carbazole

This solution processable copolymer shows an excellent thermal stability. UV-Visible spectroscopy shows that the synthesized copolymer has a broad absorption range from 300-900 nm. Cyclic voltammetric technique was used for the electrochemical characterization of the synthesized copolymer. Photovoltaic devices were fabricated from the blend of copolymer and phenyl-C61- butyric acid methyl ester as the active material.

References [1]Ranjith, K.; Swathi, SK.; Kumar, P.; Praveen, CR. “Dithienylcyclopentadienone derivative-co-benzothiadiazole: An alternating copolymer for organic photovoltaics”. Sol. Energy Mater. Sol. Cells. 98, 448–454 (2012).

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C84 - Acid treatments on silicon nanowires for efficient hybrid solar cells

Taewoo Jeona, Bernard Geffroya, Denis Tondeliera, Linwei Yua, Pascale Jegoub, Bruno Jousselmeb, Serge Palacinb, Pere Roca i Cabarrocasa, Yvan Bonnassieuxa

a, LPICM, Ecole Polytechnique, LPICM, Ecole polytechnique, Route de Saclay, Palaiseau, 91128, FR b, DSM/IRAMIS/SPCSI/LCSI, CEA, CEA saclay, 91191, GiF Sur Yvette, FR

Silicon nanowires (SiNWs) are considered as a promising material for next generation solar cells. In recent researches, SiNWs are applied to hybrid solar cells based on their combination with organic materials. Most studies are focused on etched SiNWs from bulk silicon wafer. On the other hand, there are a few works based on bottom-up grown SiNWs. Bottom-up approaches generally have the advantages of cost effectiveness and simpler process. Here, we employed SiNWs grown by plasma enhanced chemical vapor deposition (PECVD) to fabricate hybrid solar cells. For growing SiNWs by PECVD, a metal catalyst is necessary to initiate SiNWs growth from the precursor gas. However, this metal catalyst remains on top of the SiNWs which may cause deleterious problems such as large leakage current and defects resulting in poor photovoltaic performance. In addition, native oxide on SiNWs’ surface may further decrease the photovoltaic performance.

Figure 1 Current-Voltage characteristics of hybrid solar cells according to surface treatments.

In this study, we propose a simple method to eliminate the remaining metal catalyst and native oxide by dipping the SiNWs in hydrochloric (HCl) and hydrofluoric (HF) acids for higher efficiency hybrid solar cells. We fabricated hybrid solar cells based on SiNWs and organic materials consisting of spin-coated layers of Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and poly(3-hexylthiophene) (P3HT) : phenyl C61 butyric acid methyl ester (PCBM) (1:1, 2 wt% in 1,2-dichlorobenzene) blend. XPS results clearly reveal that a certain amount of catalyst is effectively removed by the acid treatment. Current-Voltage characteristics of hybrid solar cells are shown in Fig.1. HCl improves the open-circuit voltage

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and the short-circuit current while HF increases strongly the short-circuit current and the fill factor. Therefore, a power conversion efficiency of about 1.5% is obtained after acid treatments although it was about 0.35 % without treatments. A detailed analysis was carried out to explain the reasons of improvement of efficiency and open-circuit voltage by investigating transmittance changes and light intensity dependence measurements upon acid treatments. Especially, light dependent open-circuit voltage shows reduced trap-assisted recombination. In addition, native oxide removal also considerably contributes to further efficiency improvement by decreasing the series resistance.

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C85 - Compatibilizing donor and acceptor in polymer:fullerene bulk heterojunction solar cells

Ricardo Bouwera, Jan-Carlos Kuhlmannc, Paul de Bruynb, Paul Blomc, Kees Hummelenc

a, Delft University of Technology, Kluyverweg 1, Delft 2629 HS, NL b, Dutch Polymer Institute, P.O. Box 902, Eindhoven, 5600 AX , NL c, University of Groningen, Nijenborgh 4, Groningen, 9742 AG, NL

Among the building blocks for p-type conjugated copolymers for organic solar cells, the fluorene group is widely used for its high charge carrier mobility, good processability, stability, and high absorption coefficients. Efficiencies well over 4% were reached with fluorene-based copolymers like PF10TBT (Figure 1, left) in combination with PCBM. Even though high efficiencies can be reached with some polymers based on fluorene there are still many of these polymers known, which result in lower than expected efficiencies based on their bandgap alone. For most of these polymers it was concluded that the morphology of the active layer often limits the performance of these materials.The morphology of the active layer is crucial for efficient bulk heterojunction organic solar cells. The nanophase segregated morphology initially formed in polymer fullerene blends is a kinetically trapped, non-equilibrium state that is formed during spin-casting and subsequent evaporation of the solvent at temperatures below that of the glass transition (Tg) of the polymers. However the immiscibility of both donor and acceptor and their tendency to crystallize can drive larger scale phase segregation and can cause discontinuity of the bicontinuous network. Several possibilities to tune the extent of phase separation have been demonstrated: depositing from various solvents having different boiling temperatures and/or polarities; chancing the regio regulartity of the polymer; and varying the subsequent annealing conditions of the cast films. Other methods include the addition of additives to the casting solvent, locking the morphology by subsequent reaction of crosslinkable groups after casting, or by the use of compatibilizers; Borrowed from established methods of blending chemically incompatible polymers, compatibilizers have been introduced in organic solar cells as an attempt to improve the morphology of the active layer. These materials, also known as interfacial agents, generally reside at the interfaces of the mixed materials to minimize unfavorable enthalpic contacts

Figure 1 Left; A fluorene based copolymer (R = C10H21 ,PF10TBT). Right; A compatibilized fluorene-containing PCBM analogue.

Herein we will present the synthesis and characterization of fluorene-containing PCBM analogues (Figure 1, right) as compatibilizing agents for fluorene-bearing small bandgap polymers. Their performance as acceptor material in bulk heterojunction solar cells in combination with PF10TBT is tested both as a substitute for PCBM and as an additive in cells comprising PCBM as the acceptor in order to improve the morphology of the active layer.[1,2]

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References [1] Kuhlmann, J. C.; de Bruyn, P.; Bouwer, R. K. M.; Blom, P. W. M.; Hummelen, J. C. "Improving the compatibility of fullerene acceptors with fluorene-containing donor-polymers in organic photovoltaic devices". Chem. Commun., 46, 7232- ,(2010). [2] Bouwer, R. K. M. “Fullerene Bisadducts for Organic Photovoltaics”, PhD thesis, Chapter 5, pp 145-178, (2012).

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C86 - Efficient Binary Organic Redox Mediators in Dye-Sensitized Solar Cells Based on Carbon Black Counter Electrode

Woohyung Choa, Donghoon Songb, Yong Bum Pyuna, Tea Yon Kima, Yong Gun Leea, Yong Soo Kanga

a, WCU program Department of Energy Engineering and Center for Next Generation Dye-sensitized Solar Cells, Hanyang University, FTC 1013, Hanyang Univ. Haengdang-dong, Seongdong-, Seoul, 133, KR b, Departments of Chemical Engineering, Hanyang University, FTC 1013, Hanyang Univ. Haengdang-dong, Seongdong-, Seoul, 133, KR

We present binary redox mediators combining new thiolate/disulfide redox couples for tuning the electron lifetime and diffusion coefficient. Carbon black (CB) counter electrode was introduced and showed better photovoltaic performance and improved stability in dye-sensitized solar cells (DSCs).

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C87 - A Facile Low temperature synthesis of TiO2 nanorods for high efficiency dye sensitized solar cells

M.M. Rashada, A.E. Shalana, Youhai Yub, Monica Cantub, M.S.A. Abdel-Mottalebc

a, Central Metallurgical Research and Development Institute (CMRDI) , P. O. Box : 87 Helwan - Egypt , Cairo, 431, EG b, Centre de Investigacio en Nanociencia I Nanotecnologia (Cin2, CSIC), ETSE, Campus UAB, Edifici Q, 2nd Floor, Bellaterra (Barcelona), E-08193, Spain, E-08193, Spain, Spain c, Nano-Photochemistry and Solar chemistry Lab, Department of Chemistry, Faculty of Science, Ain Shams University, 11566 Abbassia, Cairo, Egypt, 11566 Abbassia, Cairo, Egypt, Cairo, Egypt

A facile low temperature synthesis of TiO2 nanorods for high efficiency dye sensitized solar cells A. E. Shalan1,2, M. M. Rashad 1* , Youhai Yu2, Mónica Lira-Cantú2, and M. S.A. Abdel-Mottaleb3 1Central Metallurgical Research & Development Institute (CMRDI), Electronic and Magnetic Materials Division, Advanced Materials Department, P.O.Box 87 Helwan, Cairo, Egypt 2 Centre de Investigacio en Nanociencia I Nanotecnologia (Cin2, CSIC), ETSE, Campus UAB, Edifici Q, 2ndFloor, Bellaterra (Barcelona), E-08193, Spain 3 Nano-Photochemistry and Solar chemistry Lab, Department of Chemistry, Faculty of Science, Ain Shams University, 11566 Abbassia, Cairo, Egypt *Tel: 202-25010640-43, Fax: 202-25010639 *E-mail: [email protected] Abstract A low-temperature hydrothermal process is developed to synthesize titania nanorods with controlled size for dye-sensitized solar cells (DSSCs). The TiO2 nanorods are characterized using XRD, SEM, TEM/HRTEM, UV-vis Spectroscopy, FTIR and BET specific surface area (SBET) as well as pore-size distribution by BJH. The results indicate that the bulk traps and the surface states within the TiO2 nanorods films enhance the efficiency of DSSCs. The size of the formed titania nanorods was 6.7 nm width and 22 nm length, the specific surface area SBET was 77.14 m2g-1. However, the band gap energy of the obtained titania nanorods was 3.2 eV. A nearly quantitative absorbed photon-to-electrical current conversion achieved upon excitation at wave length of 550 nm and the power efficiency is enhanced from 5.6% for commercial TiO2 nanoparticles Degussa (P25) cells to 7.2% for TiO2 nanorods cells under AM1.5 illumination (100 mWcm-2). The TiO2 cells performance is enhanced due to their high surface area and hierarchically mesoporous structures compared with the "Degussa (P25)".

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C88 – Characterization of Au/n-InP Photovoltaic Structure with Organic Thin Film

Omer Gullua, Enise Ozerdena, Serif Ruzgara, Sezai Asubayb, Osman Pakmaa, Tahsin Kilicoglua, Abdulmecit Turutc

a, Batman University, Batman University, Science and Art Faculty, Physics Dept., Batman, 72060, TR b, Dicle University, Dicle University, Science Faculty, Physics Department, 21000, Diyarbakir, TR c, Ataturk University, Ataturk University, Science Faculty, Physics Department, 25240, Erzurum, TR

During the last 20 years organic semiconductors have attracted considerable attention due to their interesting physical properties followed by various technological applications in the area of electronics and optoelectronics. One of the main advantages is the fact that they can be produced in large quantities by simple techniques[1]. Besides, ithas been carried out the fabrications and electrical/optical characterizations of photovoltaics using organic semiconductors. Organic semiconductors show many unusual electrical, optical and magnetic properties, which could be used for the fabrication of molecular electronic devices[2].These materials also offer low cost and processing ease and can attain new roles not realized by conventional solar cells[3-6].Among the organic materials, Rhodamine-101 (Rh-101) is considered to be a good candidate for organic semiconductor device fabrication such as Schottky device and solar cell, because it offers a possibility of low-cost and large-area devices. The Rh-101 is a xanthene-type molecule and has a fluorescence quantum yield in ethanol close to unity, being independent of temperature. It appears as green solid[7,8]. Rh-101 organic material has been considered as one of the most stable organic semiconductors for various electronic and optoelectronic applications and has not been used for the modification of n-InP diodes. In this study, we present that Rh-101 organic molecules can control the electrical characteristics of conventional Au/n-InP metal–semiconductor contacts. An Au/n-InP Schottky junction with Rh-101 interlayer has been formed by using a simple cast process. A potential barrier height as high as 0.88 eV has been achieved for Au/Rh-101/n-InP Schottky diodes, which have good current–voltage (I–V) characteristics. This good performance was attributed to the effect of formation of interfacial organic thin layer between Au and n-InP. By using capacitance-voltage (C-V) measurement of the Au/Rh-101/n-InP Schottky diode the diffusion potential and the barrier height have been calculated as 0.78 V and 0.88 eV, respectively. By using the I–V measurement of the diode under illumination, short circuit current and open circuit voltage have been extracted as 1.70 μA and 240 mV, respectively. References [1] Stallinga, P., Gomes, H.L., Murgia, M., Müllen, K., 2002. Interface state mapping in a Schottky barrier of the organic semiconductor terrylene. Organic Electronics 3, 43–51. [2] R.K. Gupta, R.A. Singh, J. Polym. Res. 11 (2004) 269. [3] P. Lizon, Dye sensitized organic semiconductor photovoltaics with resonance energy transfer, Master Thesis, University of Toronto, Toronto, 2004. [4] F. Yakuphanoglu, Sol. Energy Mater. Sol. Cells 91 (13) (2007) 1182. [5] M.M. El-Nahass, K.F. Abd-El-Rahman, A.A.M. Farag, A.A.A. Darwish, Org. Electron. 6 (2005) 129. [6] M.M. El-Nahass, H.M. Zeyada, K.F. Abd-El-Rahman, A.A.A. Darwish, Sol. Energy Mater. Sol. Cells 91 (2007) 1120. [7] T. Karstens and K. Kobs, J. Phys. Chem. 84 (1980) 1871. [8] M. Cakar, N. Yildirim, S. Karatas, C. Temirci, A. Turut, J. Appl Phys. 100 (2006) 074505.

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C89 - Influences of the Chemical Environment on the Electron Injection Efficiency of a New Class of Semi-Squarylium Dyes

Robert Schuetza, Andreas Bartelta, Joachim Schaffa, Ivo Kastla, Christian Strothkaempera, Rainer Eichbergera, Gabriele Nellesb, Gerda Fuhrmannb

a, Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, DE b, SONY Deutschland GmbH, Hedelfinger Straße 61, 70327 Stuttgart, DE

Dye sensitized solar cells (DSSCs) operate by injecting electrons from the excited state of a light-harvesting dye into the continuum of conduction band states of a wide bandgap semiconductor.The dye / semiconductor interaction is mediated by the dye anchor group, which plays a crucial role in the DSSC performance. The use of co-adsorbents,so-called additives and different solvents used for sensitization can have an impact on the overall photovoltaic performance. Even though the exact operation mode of these components is poorly understood due to its inherent complexity, it is known that this complex interplay of processes can be easily disturbed by the variation of just one component, leading to lower efficiencies. While pure organic dyes easily achieve higher absorption coefficients and feature a more efficient electron injection in comparison to metal-organic dyes, their light harvesting efficiency is limited by a narrow spectral electronic transition. A beneficially broad ground state absorption in the VIS region can be achieved by co-sensitization with several dyes, creating an even more complex situation in the device.

Figure 1

In this systematic study we are scanning the influences of co-adsorbents, additives, solvents and co-sensitizers on the spectral properties, the electronic level alignment and the charge carrier dynamics of a new class of semi-squarylium dyes bound to the surface of nano porous TiO2 films with an acyloin-type anchor group. We employ photoelectron spectroscopy (PES) as

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well as stationary and time resolved optical spectroscopy, covering the fs to ms regime. This study is done for a series of these dyes with different spectral and more or less distinct donor-acceptor properties. The measurements are performed in different environments with respect to the applied methods, ranging from UHV to typical conditions in a working DSSC. The results from PES measurements are connected to the observed charge carrier dynamics in different chemical environments. The high performance of this new pure organic dye class is demonstrated by comparison with a commercially available indoline dye (D131) of similar spectral characteristics, which has a common carboxylic acid anchor.

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C90 - Optimized TiO2 blocking layers for dye-sensitized solar cells (DSSC)

Alex Sangiorgia, Riccardo Bendonib, Nicola Sangiorgia, Barbara Ballarinc, Alessandra Sansona

a, CNR - Institute for Science and Technology for Cer, Via Granarolo 64, Faenza, 48018, IT b, University of Bologna, Viale Risorgimento 4, Bologna, 40136, IT c, Laboratory of Electroanalytical Chemistry, Department of Inorganic and Physical Chemistry, University of Bologna, Viale Risorgimento 4, Bologna, 40136, IT

In recent years much attention has been paid to dye-sensitized solar cells[1] due to their low cost and wide applicability. The modest efficiencies achieved by these devices are caused by several phenomena including electronic losses due to parasitic electronic reactions (back transfer reaction)[2]. Each of the single element of the cell has therefore to be carefully engineered in order to increase the overall performances of the device. One of the most common ways to reduce the electronic losses is to introduce a compact layer of conductive material (blocking layer) between the transparent conductive substrate and the sensitized semiconductor film[3]. Aim of this work was to asses the correlation between the most common deposition processes and the spectrophotometric, morphological and electrochemical properties of the blocking layers produced. The blocking layer of TiO2 was prepared on FTO glass using two of the most common colloidal deposition processes: dip and spin coating. The results obtained with the conventional dip coating[4] (immersion of a conductive substrate FTO in an aqueous solution of TiCl4 50 mM at 70 °C for 30 minutes) were compared with the ones coming from spin coating of two different solutions (aqueous and alcoholic). The two solutions were characterized in terms of viscosity, surface tension and contact angle. On the basis of these analysis, the spin coating parameters (speed of rotation and the duration of the deposition) were optimized in order to obtain a uniform single layer observed through optical and scanning electron microscopy.The samples prepared either by dip and spin coating were heat-treated at 450 °C for 30 minutes. The presence of TiO2 in the anatase crystalline phase required for the blocking layer was assessed through XRD analysis. The influence of more cycle of deposition (2,4,6) was also evaluated. The TiO2 films obtained were characterized by spectrophotometric (UV-vis), morphological (SEM and AFM) and electrochemical analysis (voltammetry sweep linear and cyclic, electrochemical impedance spectroscopy EIS). These analysis allows to identify the best process and deposition parameters necessary to obtain an efficient blocking layer. The ethanol system allowed the production of the most thick (120 nm), homogeneous, continuous and dense film among the all conditions and the two processes tested. Moreover, the EIS analysis shown that the TiO2 blocking layer made by alcoholic solution promotes a decrease of the dark current and therefore an improvement of the cell efficiency as expected. References [1] O’Regan, B.; Grätzel, M. “A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films”. Nature 353, 737-740 (1991). [2]Gregg, B.A.; Pichot, F.; Ferrere, S.; Fields, C.L. “Interfacial recombination processes in Dye-Sensitized Solar Cells and methods to passivate the interfaces”. J. Phys. Chem. B 105, 1422-1429 (2001). [3] Vesce, L.; Riccitelli, R.; Soscia, G.; Brown, T.M.; Di Carlo, A.; Reale, A.”Optimization of nanostructured titania photoanodes for dye-sensitized solar cells: Study and experimentation of TiCl4 treatment”. Journal of Non-Crystalline Solids 356, 1958-1961 (2010). [4] Shi, J.; Liang, J.; Peng; S.; Xu, W.; Pei, J.; Chen, J. “Synthesis, characterization and electrochemical properties of a compact titanium dioxide layer”. Solid State Sciences 11, 433–438 (2009).

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C91 - Photo-Oxidative Stability of Conjugated Polymers for Organic Solar Cells Camilla Lindqvist, Patrik Henriksson, Renee Kroon, Ergang Wang, Mats R. Andersson

Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology , Kemigården 4, Gothenburg, 41258, SE

To meet the increasing energy demand and the fact that we would not be able to use as much fossil fuels in the future as we do today, the research for new and more sustainable energy sources are important. One alternative is solar cells and a lot of research is done within the area. Today the most efficient solar cells are silicon based but a promising alternative to those solar cells is organic solar cells that include polymers as the light harvesting material. Polymer based solar cells can offer a lower production cost but also a more flexible material and a light weight product. Two of the challenges with polymer based solar cells are that to increase the efficiency and the lifetime of these solar cells. In this study the photo-oxidative stability were compared for several of the conjugated polymers that have been synthesized at the department. To do this the samples were illuminated by a solar simulator under accelerated conditions. After different times the samples were removed from the light and the UV-vis spectra of the samples were measured (see Figure 1) and from those the decrease in the amount of absorbed photons were calculated.

Figure 1 Example of how the UV-vis spectra change with time for a conjugated polymer.

The goal is to use this study to compare the photo-oxidative stability of the different polymers and connect it to the difference in chemical structure.

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C92 - Photo-Induce Electron Transfer of Ruthenium Complexes with One and Two Linked Viologens Trapped CB[7] in Organic Solution

Thitinun Karpkirda, Pattraporn Saiwattanasuka, Supa Hannongbuaa, Licheng Sunb

a, Department of Chemistry, Faculty of Science, Kasetsart University, 50 Phahonyothin Rd. Chatuchak , Bangkok, 10900, Thailand b, School of Chemical Science and Engineering, Department of Chemistry, Royal Institute of Technology (KTH), Teknikringen 30, Stockholm, 10044 , Sweden

The supramolecular of Ruthenium complexes, Ru(bpy)3-viologen-Ru(bpy)3, with one and two viologen units, containing the CB[7] host (1 and 2) were synthesized and isolated in this work. The binding behavior of CB[7] to the guest Ruthenium complexes was investigated by using 1H-NMR showed that the CB[7] preferable bind to the hydrocarbon linker in acetonitrile solution. The photophysical properties of the rotaxane 1 and 2 were also studied in acetonitrile solution resulting that the emission of Ru(bpy)3 unit could be increase in the presence of CB[7].

Figure 1

The photo-induce viologen radical formation could be monitored by UV-Vis spectrometry showed that the viologen radical could be formed and the longer live time of viologen radical could be longer by CB[7] host in non-aqueous solution. The viologen radical formation is more stabilized by the second viologen unit probably due to the intramolecular viologen radical dimer formed. These results demonstrate potentially new applications.

References [1] Monhaphol, T. K.; Andersson, S.; Sun, L., "Isolated supramolecular Ru(bpy)3-Viologen- Ru(bpy)3 complexes with trapped CB[7,8] and photoinduced electron transfer study in non aqueous solution" Chem. Eur. J. 17, 11604-11612 (2011). [2] Andersson, S.; Zou, D.; Zhang, R.; Sun, S.; Sun, L. "Light driven formation of a supramolecular system with three CB[8]s locked between redox-active Ru(bpy)3 complexes" Org. Biomol. Chem. 7, 3605-3609 (2009).

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C93 - Preparation and characterization of nanocomposites based on TiO2/graphene and their application on inverted solar cells

Andréia de Moraisa, Flávio Santos Freitasa, Helton Pereira Nogueirab, Ana Flávia Nogueiraa

a, Laboratório de Nanotecnologia e Energia Solar (LNES), Chemical Institute, Universidade Estadual de Campinas, Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas - SP, 13084-87, Brazil b, Grupo de Pesquisa em Polímeros (GPol), Chemical Institute, Universidade Estadual de Campinas, Cidade Universitária Zeferino Vaz - Barão Geraldo, Campinas - SP, 13084-87, Brazil

The application of graphene in photovoltaic devices has received considerable attention due to its differential properties. However, many parameters of these devices must be improved, for example, the electron transport that occurs by diffusion through the oxide semiconductor film. The use of graphene incorporated into the oxide semiconductor film is an alternative to enhance the electron transport, since this material has excellent conductive properties [1]. In this work we present the synthesis of nanocomposites based on graphene and TiO2 nanoparticles and their application on inverted solar cells. The graphene oxide samples were obtained by the Hummers method [2]. Then, the reduced graphene oxide (rGO) was obtained by the method of ultraviolet irradiation-assisted photocatalytic reduction [3]. The TiO2-rGO nanocomposites were characterized by X-ray diffraction and Raman spectroscopy. The FEG-SEM images showed that the rGO sheets were decorated with TiO2 nanoparticles unevenly, but enough to prevent agglomeration. In general, the inverted solar cells were mounted with the following configuration: Au / PEDOT-PSS / poly (3-hexiltiofeno) (P3HT) / TiO2-rGO / blocking layer de TiO2 / conductive glass (FTO).

Figure 1 FEG-SEM images obtained for TiO2–rGO nanocomposite.

These solar cells were characterized using the current-potential curves (I-V) under polychromatic light irradiation at intensity of 41 mW cm-2. The TiO2 electrode containing 0.07

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wt.% of rGO provided the following electrical parameters: Jsc of 0.08 mA cm-2, Voc of 0.26 V, and a conversion efficiency of 0.013 %. Compared with inverted solar cells based on the TiO2 porous films, the TiO2-rGO devices exhibited an increase in Jsc attributed to the improved interconnectivity between TiO2 nanoparticles and graphene. In this case, the carbonaceous material introduced an alternative electrical conduction pathway which facilitates rapid electron transport in the photoelectrode.

We acknowledge support from CAPES, CNPq and FAPESP.

References [1] Singh, V., Joung, D., Zhai, L., Das, S., Khondaker, S. I., Seal, S. "Graphene based materials: Past, present and future". Progress in Materials Science. 56, 1178-1271 (2011. [2] Yang, N. L., Zhai, J., Wang, D., Chen, Y. S., Jiang, L. "Two-Dimensional Graphene Bridges Enhanced Photoinduced Charge Transport in Dye-Sensitized Solar Cells". ACS Nano. 4, 887-894 (2010). [3] Kovtyukhova, N. I., Ollivier, P. J., Martin, B. R., Mallouk, T. E., Chizhik, S. A., Buzaneva, E. V., Gorchinskiy, A. D. "Layer-by-layer assembly of ultrathin composite films from micron-sized graphite oxide sheets and polycations". Chemistry of Materials. 11, 771-778 (1999). [4]Ng, Y. H., Lightcap, I. V., Goodwin, K., Matsumura, M., Kamat, P. V. "To What Extent Do Graphene Scaffolds Improve the Photovoltaic and Photocatalytic Response of TiO2 Nanostructured Films?" Journal of Physical Chemistry Letters. 1, 2222-2227 (2010).

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C94 - Computational study of porphyrin sensitizers for solar cells: molecular design and binding mechanisms

Negar Ashari Astani, Basile F. E. Curchod, Ivano Tavernelli, Ursula Roethlisberger

EPFL, EPFL SB ISIC LCBC BCH 4118 (Bâtiment de chimie UN, Lausanne, 1004, CH

An extensive computational study on porphyrin-based dyes including the design of dyes with optimal optical properties and the study of their chemisorption on the TiO2 substrate has been performed. These bioinspired porphyrin-based dyes have very similar key characteristics of the electron transfer processes as the best performing more conventional Ru-based sensitizers[1]. Furthermore, they exhibit strong Soret and long-wave length Q-band absorption spectra. In this work, we systematically explored substitutions at the four meso and eight β positions available for functionalization, to tune the UV-visible absorption spectra of these promising dyes. Time dependent density functional theory (TDDFT) calculations were carried out to determine the vertical absorption spectra. Results of these calculations revealed several new dyes with better absorption in the red. The additional practical problem of insufficiently strong anchoring of the dyes on the TiO2 substrate was also addressed.

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C95 - Functional amphiphilic blockcopolymers for hybrid donor-acceptor composites

Johannes Brendel, Mukundan Thelakkat

University of Bayreuth, Universitätsstraße 30, Bayreuth, 95440, DE Blockcopolymers feature unique properties for organizing in ordered structures on length scales of several tenths of nanometers due to microphase separation. This special attribute enables the formation of ideal donor and acceptor domains for photovoltaic devices in the size of the exciton diffusion length. Therefore we designed different amphiphilic blockcopolymers, carrying a hole conductor segment and a block which coordinates inorganic semiconductor nanoparticles as electron acceptors. Utilizing controlled radical polymerization and “click” chemistry techniques, defined amphiphilic blockcopolymers were synthesized. The first type consists of triphenylamine side chain hole conductor polymer and a hydrophilic polystyrene sulfonate block. The sysnthesis of these blockcopolymers, poly(bis(4-methoxyphenyl)-4’-vinylphenylamine)-block-poly(tetrabutylammonium styrene sulfonate)(PDMTPA-b-PTbaSS) was optimized with respect to initiation efficiency and control of molecular weight and polydispersity. Special attention had to be paid on the polymerization of the hole conductor block. The high reactivity of the triphenylamine monomer caused side reaction resulting in the loss of the active chain end. Therefore we altered the synthesis conditions to reduce the amount of dead chain ends and, in consequence, gained narrowly distributed chain ends. The second type comprises of tetraphenylbenzidine as hole conductor block maintaining polystyrene sulfonate as hydrophilic block. In this class, poly(N,N’-bis(4-methoxyphenyl)-N-phenyl-N’-4-triazolylphenyl-(1,1‘-biphenyl)-4,4‘-diamine)-block-poly(triethylammonium styrene sulfonate (PTPD-b-PTeaSS) the composition and molecular weight was varied. All the polymers were characterized SEC, NMR and DSC. These blockcopolymers create narrow distributed micelles in aqueous solution exhibiting domain sizes suitable for photovoltaic applications.

Figure 1 Scheme of the self-assembly process combining functional amphiphilic blockcopolymers with inorganic semiconductor nanoparticles.

The strong anionic sulfonate groups offer high loading capacities for various cationic nanoparticles while maintaining the solubility. First results of incorporation of CdSe into these self-assembling blockcopolymers indicate preferential loading of inorganic nanoparticles in the micellar shell. Additionally these blockcopolymers form well-defined microstructures in thin films. During annealing processes vertical cylindrical domains are created independent of the blockcopolymer composition. The advantages of possible high loading capacity and ideal alignment combined with the processability from aqueous dispersions promises a novel alternative for preparation of solar cells with controlled domain sizes in the desired length scale and orientation. The design, synthesis and characterization of these novel amphiphilic semiconductor blockcopolymers suitable for solar cell applications will be presented.

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C96 - Silver Nanowire Electrodes for Organic Solar Cells

Christina Pang, John de Mello

Imperial College London, Exhibition Road , London, SW7 2AZ, GB

Highly conducting transparent electrodes form an important part of any organic solar cell and may be a limiting factor in terms of cost, flexibility or performance of the device. Indium tin oxide (ITO) has been the most commonly used transparent electrode for organic solar cells but it cracks upon bending and is relatively expensive, which limits its viability in flexible devices or commercial applications. It is therefore imperative to identify alternative electrode materials which are inexpensive, solution processable and suitable for roll-to-roll processing. We have investigated solution processed silver nanowires (AgNWs) as a possible alternative to ITO. Silver nanowires of high aspect ratio form sparse continuous networks when deposited in thin films, allowing them to form robust highly conductive electrodes with high transparency and low cost due to the high void content. A typical spin coated silver nanowire film displays sheet resistance of 15 ohm/sq at 93% transmittance, which is comparable to device-grade ITO (17 ohm/sq at 97% transmittance), as seen in Figure 1(a).

Figure 1 a) Transmittance versus sheet resistance characteristics for a silver nanowire film b) current density versus voltage characteristics for inverted devices on AgNW and ITO

Inverted solar cells on glass substrates were fabricated on ITO (17 ohm/sq) or AgNWs (15 ohm/sq) by spin coating a layer of ZnO sol gel, followed by P3HT:PCBM, PEDOT:PSS and 100 nm of evaporated Ag. Current density versus voltage characteristics are shown in Figure 1(b), with a PCE of 3.3% obtained for the ITO device and 2.5% for the AgNW device. Current work is focused on reducing the high leakage current from the AgNW devices (not shown) so as to improve device performance. Preliminary results obtained thus far show silver nanowires to be a promising material for replacing ITO.

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C97 - Spectroscopic Study of Gold Nanoparticles functionalized with Ru-Triazine dye for application in Plasmonic-Enhanced Dye Sensitized Solar Cells

Daniel Grasseschi, André Luis Parussulo, Robson Raphael Guimaraes, Koiti Araki, Henrique E. Toma

University of São Paulo, Av. Professor Lineu Prestes , 748, São Paulo, 5508, BR

The development of new sensitizers1and nanotechnological approaches for improving the efficiency of Dye Sensitized Solar Cells (DSSC) has been pursued in this work. In this context, we are exploring the use of plasmonic gold nanoparticles in association with ruthenium complexes, as recently introduced in DSSC.2 Accordingly, we focused on the synthesis, and spectroscopic investigation of the complex [Ru(dcbH2)2(TMTH2)] ruthenium(II), where dcbH2 and TMT = bis 2-2´-bipyridine-4,4´dicarboxylic acid and 1,3,4-triazine-tris(thiolate), respectively, aiming its association with gold nanoparticles (Figure 1) and anchoring to the TiO2 interface. As can be seen in Fig. 1, the charge of complex can change from +2 to -4 because of the multiple acid-base groups interacting with the negatively charged gold surface. The pKa´s found by electronic spectroscopy were 2.9, assigned to the deprotonation of dcbH3, and 4.9 and 11.8, assigned to the successive deprotonation of the TMTH2 species.

Figure 1 Representation of the interaction of AuNp with Ru(dcbH2)2TMT and TiO2.(a) Eletronic and SERS Spectra of AuNp-Ru(dcbH2)2TMT. (b) SEM image of TiO2+Ru(dcbH2)2TMT+ AuNp film in FTO

Raman spectroscopy was employed to study the interaction between AuNp4and the complex as a function o pH, using the laser lines of 785 nm (in resonance with the plasmonic coupling band of the AuNp) and 532 nm (in resonance with the MLCT band of the complex and also with plasmon band of the AuNp). At pH 4 the interaction between the gold nanoparticles and the complex can be readily detected by the Raman spectra (Figure 1.b), either at 532 or 785 nm. The rising of the ring deformation mode of TMT at 700 cm-1 using the

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laser in 785 nm and the higher intensity of the spectrum utilizing the laser in 532 nm suggest the presence of the Raman Resonant and Chemical mechanism of SERS5. In order to prevent the hydrolysis of the ester formed between the carboxylate group and the TiO2 film, the gold nanoparticles functionalized with [Ru(dcbH2)2(TMTH2)] was precipitated and dispersed in ethanol. A TiO2 film, made with P25, was submerged in the ethanolic solution of AuNp-[Ru(dcb)2(TMTH2)] overnight and washed with ethanol. This film showed a high coverage of the TiO2 surface with the functionalized AuNp, as can be seen by Scanning Electron Microscopy, Figure 1.c , providing a promising strategy to be explored in DSSC.

References [1]Nogueira, A. F.; Furtado, L. F. O.; Formiga, A. L. B.; Nakamura, M.; Araki, K.; Toma, H. E., Sensitization of TiO2 by supramolecules containing zinc prophyrins and ruthenium polypiriyl complexes. Inorg Chem 2004 43 [2] (2)Qi, J.; Dang, X.; Hammond, P. T.; Belcher, A. M., Highly Efficient Plasmon-Enhanced Dye-Sensitized Solar Cells through Metal@Oxide Core–Shell Nanostructure. Acs Nano 2011, 5 (9), 7108-7116. [3] Nazeeruddin, M. K.; Zakeeruddin, S. M.; Humphry-Baker, R.; Jirousek, M.; Liska, P.; Vlachopoulos, N.; Shklover, V.; Fischer, C.-H.; Grätzel, M., Acid-Base equilibria of (2,2'-Bipyridyl-4,4'-dicarboxylic acid)ruthenium(II) complexes and the effect of protonation on charge-transfer sensitization of nanocrystalline titania. Inorg. Chem. 1999, 38 (26), 6298-6305. [4] Turkevich, J.; Stevenson, P. C.; Hillier, J., A study of the nucleation and growth processes in the synthesis of colloidal gold. Discussions of the Faraday Society 1951, 11, 55-75. [5]Lombardi, J. R.; Birke, R. L., A Unified View of Surface-Enhanced Raman Scattering. Accounts Chem Res 2009, 42 (6), 734-742.

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C98 - Flexible transparent electrode with printed metal grids

Jae-Wook Kang, Do-Geun Kim, Jong-Kuk Kim, Chang Su Kim

Korea Institute of Materials Science (KIMS), 66 sangnamdong, Changwon, Gyeongnam, 641-831, Korea

Recently, organic solar cells (OSCs) have enormously advanced for last two decades. Flexible transparent conductive electrode (TCE) is one of the most important elements of flexible organic devices and it must have high flexibility and transmittance with low sheet resistance. Crystalline indium-tin-oxide (c-ITO) is the most widely used material for TCE. In spite of many advantages of c-ITO, large-area device performance is much lower than small devices because lower conductivity of c-ITO causes electrical power loss of devices.

Figure 1 Flexible transparent electrode with printed metal grids and ITO electrode (200cm x 200cm)

Moreover c-ITO cannot apply in flexible electronics because of its brittle property. Recently, various TCEs are developed such as indium-zinc-oxide (IZO), carbon nanotube, graphene, metal nanowire, and conducting polymer. But there still remains the trade-off among flexibility, sheet resistance and transparency. In this research, we propose novel concept of TECs which consists of metal electrodes embedded in a plastic substrate by printing process and ultra-thin amorphous ITO deposited by sputtering. We successfully demonstrated extremely flexible OSCs that continue to operate without degradation while being folded into a radius of <500 μm.

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C99 - Mesoporous TiO2 microbead electrodes in cobalt-electrolyte based dye-sensitized solar cells

Meysam Pazokia, Gerrit Boschloob, Anders Hagfeldtb, Nima Taghaviniaa

a, Department of Physics,sharif university of technology, Azadi street, Tehran, 11155, IRan b, Department of Physical Chemistry, Uppsala University, Uppsala, Sweden

Mesoporous TiO2 microbeads were synthesized by a combination of sol-gel and hydrothermal processes, and applied as photoanodes in dye-sensitized solar cells (DSCs). Microbeads were used in two different manners: as a pure microbead layer and on top of a transparent mesoporous TiO2 layer as a scattering layer. After sensitization with D35 and in combination with a cobalt trisbipyridine electrolyte, efficiencies of 3.7 % were obtained for a 5 micron microbeads layer and 5.9 % for 5 micron DSL 18NR-T + 5 micron microbeads double-layer.

Figure 1 Mesoporous Micro-Bead photoanode for Cobalt electrolyte based dye sensitized solar cell

The fabricated DSCs were characterized by square wave small perturbation, electrochemical impedance spectroscopy and absorption/transmission techniques. Microbead electrodes show very rapid electron transport, but similar electron lifetimes as standard mesoporous films. They possess very good light scattering properties.

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C100 - P-type Dye-Sensitized Solar Cells Based on Porphyrin and Fullerene Derivatives

Haining Tiana, Bo Xua, Licheng Suna

a, Royal Institute Of Technology, Teknikringen 30,Royal Institute of Technology(KTH), Stockholm, 10044, SE b, Dalian Unicersity of Technology, 116024, Dalian, China, CN

Due to the potential application in tandem DSCs with n-type DSCs as well as in the artificial photosynthesis system, the p-type dye-sensitized solar cells (DSCs) 1-3 have attracted more interest from scientists. In order to improve the photovoltaic properties of p-type DSCs, the judicious design of the photosensitizer including extension of the conjugated system should be designed to make the electron acceptor unit far away from the p-type semiconductor surface, thus displaying longer charge separation state lifetime. Inspired by the features of supramolecular interaction between porphyrin and C60 and the fast charge transfer process from porphyrin to C60 derivatives, we adopted C60 derivatives, to carry out the formation of the supramolecular photosensitizer with porphyrin dyes on NiO surface.

Figure 1 The structures of ZnTCPP and C60PPy

The photovoltaic properties of DSC based on the supramolecualr dye are significantly improved as compared with that based the pure porphyrin dye. Subsequently, we synthesized some dyes based on porphyrin and C60 via the covalent band. These dyes also performed better photovoltaic properties than the pure porphyrin dyes.

References [1] O'Regan, B.; Greatzel, M. Nature 1991, 353, 737; [2] P. Qin, H. Zhu, T. Edvinsson, G. Boschloo, A. Hagfeldt and L. Sun, J. Am. Chem. Soc, 2008, 130, 17629. [3] A. Nattestad, A. J. Mozer, M. K. R. Fischer, Y. B. Cheng, A. Mishra, P. Bauerle and U. Bach, Nat. Mater., 2010, 9, 31.

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C101 - Search for Dye Sensitized Solar Cell High Efficiency Organic Cromophore Loci

Mihai Mihaila, Cristian Diaconu, Octavian Buiu, Bogdan Serban, Viorel Avramescu

Honeywell Romania, ACS Sensors and Wireless Laboratory – Bucharest, Floreasca str. 161B, Sector 1, 014459, Bucharest, Romania, RO

In this work, we investigate how the efficiency of the organic dye-based DSSCs distributes into the plane having the absolute electronegativity (χ) [1] and the global hardness (η) [2] of the cromophore as coordinates. To this purpose, experimental HOMO/LUMO values of 133 organic cromophores were collected from literature [3]-[38] and their χ[1] and η[2] were calculated assuming the validity of the Koopman’s theorem *39+. Fig. 1 shows the distribution of the efficiency (y) in the (χ,η) plane. For χ<4.2eV (coincident with the TiO2 conduction band edge), only (harder) cromophores with η>1.083eV were found. These molecules cannot easily attract electrons from the TiO2 conduction band and, consequently, the dominant recombination mechanism in these cells could be the electron interception by electrolyte. As Fig. 1 shows, neither harder (high η) nor softer (low η) cromophores are very efficient. On the hardness scale, except for three cromophores, the locus of the most efficient (y>6.75%) ones is defined by 1.1eV<η<1.26eV. Similarly, neither stronger nor less electrophilic cromophores feature high efficiency. On the χ scale, with three exceptions, the most efficient cromophores are located in the 4.2eV<χ<4.45eV range. Therefore, the majority of the efficient cromophores features (close to) intermediate χ and η values. This indicates that most of the efficient cromophores realize a balance between the capability to transfer and to accept electrons.<h </h

Figure 1 Projection of the yield (y, cell efficiency) onto the cromophores’ (χ, η) plane. The locus of the most efficient cromophores is defined by 1.1eV<η<1.26eV (horizontal discontinuous lines) and 4.2eV<χ<4.45eV. (vertical discontinuous lines). The yield color code is shown in the key box on the right. The red square stands for the YD2-o-C8 "champion" Zn-based porphyrin dye [41].

To undestand the exceptions, the cells efficiency was further projected onto the free-energy driving forces (−ΔG1, −ΔGe) plane. The driving forces at the cromophore/TiO2 (−ΔG1) and cromophore/electrolyte (−ΔGe) interfaces were calculated assuming that the position of the

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TiO2 conduction band edge and the redox potential of iodide/iodine couple are at 4.2eV and 4.9eV, respectively. 18 of 21 cromophores with y>6.75% are located in the region −ΔG1>0.9eV (middle of the scale), suggesting that most of the efficient cromophore-TiO2 interfaces are in the Marcus [40] inverted region. Similarly, 16 of 21 cromophores have −ΔGe>0.58eV (middle of the scale), suggesting an inverted Marcus region for the hole transfer, too. Although three of the exceptions are more electrophilic than the other two, all have reorganization energies for hole transfer smaller than −ΔGe<0.58eV, indicating a faster hole transfer for these molecules. For the more acidic cromophores, this condition is necessary to avoid recombination, while for the cromophores with a lower electronegativity, besides avoiding recombination, this condition is strongly required to assure a good absorption. These results can be useful for cromophores design. References [1] Mulliken, Robert S. “A New Electroaffinity Scale; Together with Data on Valence States and on Valence Ionization Potentials and Electron Affinities”. J. Chem. Phys. 2, 782-793 (1934). [2] Parr, Robert G. and Pearson, Ralph G. “Absolute Hardness: Companion Parameter to Absolute Electronegativity”. J. Am. Chem. Soc. 105, 7512-7516 (1983). [3]Edvinsson, Tomas; Li, Chen; Pschirer, Neil; Schoneboom, Jan; Eickemeyer, Felix; Sens, Ruddiger; Boschloo, Gerrit; Herrmann, Andreas; Mu1llen, Klaus and Anders Hagfeldt ”Intramolecular Charge-Transfer Tuning of Perylenes: Spectroscopic Features and Performance in Dye-Sensitized Solar Cells”. J. Phys. Chem. C 111, 15137-15140 (2007). [4] Numata, Youhei; Ashraful, Islam; Shirai, Yasuhiro and Han, Liyuan “Preparation of donor–acceptor type organic dyes bearing various electron-withdrawing groups for dye-sensitized solar cell application”. Chem. Commun.10, DOI: 10.1039/c1cc11130b (2011). [5]Hwang, Suyoung; Lee, Jung Ho; Park, Chanmoo; Lee, Hoinglae; Kim, Chaekyu; Park, Chiyoung; Lee, Mi-Hyeon; Lee, Wanin; Park, Jihee; Kim, Kyungkon; Park, Nam-Gyu and Kim, Chulhee ”A highly efficient organic sensitizer for dye-sensitized solar cells”. Chem. Commun. 4887-4889 (2007) [6]Wu, Tzi-Yi; Tsao, Ming-Hsiu; Chen, Fu-Lin; Su, Shyh-Gang; Chang, Cheng-Wen; Wang, Hong-Paul; Lin, Yuan-Chung; Ou-Yang, Wen-Chung and Sun, I-Wen ”Synthesis and Characterization of Organic Dyes Containing Various Donors and Acceptors”. Int. J. Mol. Sci. 11, 329-353 (2010). [7]Liu, Wei-Hsin; Wu, I-Che; Lai, Chin-Hung; Lai, Cheng-Hsuan; Chou, Pi-Tai; Li, Yi-Tsung; Chen, Chao-Ling; Hsu, Yu-Yen and Chi, Yun “Simple organic molecules bearing a 3,4-ethylenedioxythiophene linker for efficient dye-sensitized solar cells”. Chem. Commun. 5152-5154 (2008). [8] Kim, Sanghoon; Lee, Jae Kwan; Kang, Sang Ook; Ko, Jaejung; Yum, J.-H.; Fantacci, Simona; De Angelis, Filippo; Di Censo, D.; Nazeeruddin, Md. K. and Gratzel, Michael ”Molecular Engineering of Organic Sensitizers for Solar Cell Applications”. J. Am. Chem. Soc. 128, 16701-16707 (2006). [9] Gang Li; Ke-Jian Jiang; Ying-Feng Li; Shao-Lu Li and Lian-Ming Yang “Efficient Structural Modification of Triphenylamine-Based Organic Dyes for Dye-Sensitized Solar Cells”. J. Phys. Chem. C 112, 11591-11599 (2008). [10] Zhou, Gang; Pschirer, Neil; Schöneboom, Jan C.; Eickemeyer, Felix; Baumgarten, Martin and Müllen, Klaus ”Ladder-Type Pentaphenylene Dyes for Dye-Sensitized Solar Cells“. Chem. Mater. 20, 1808-1815 (2008). [11] Bolag, Altan; Nishida, Jun-ichi; Hara, Kohjiro and Yamashita, Yoshiro “Dye-sensitized Solar Cells Based on Novel Diphenylpyran Derivatives”. Chem. Lett. 40, 510-5011 (2011). [12] Tian, Haining; Yang, Xichuan; Chen, Ruikui; Pan, Yuzhen; Li, Lin; Hagfeldt, Anders and Sun, Licheng “Phenothiazine derivatives for efficient organic dye-sensitized solar Cells”. Chem. Commun. 3741-3743 (2007). [13] Justin Thomas, K. R.; Hsu,Ying-Chan; Lin, Jiann T.; Lee, Kun-Mu; Ho, Kuo-Chuan; Lai, Chin-Hung; Cheng, Yi-Ming and Chou, Pi-Tai “2,3-Disubstituted Thiophene-Based Organic Dyes for Solar Cells”. Chem. Mater. 20, 1830–1840, (2008). [14] Hagberg, Daniel P.; Yum, Jun-Ho; Lee, HyoJoong; De Angelis, Filippo; Marinado, Tannia; Karlsson, Karl Martin; Humphry-Baker, Robin; Sun, Licheng; Hagfeldt, Anders; Grätzel, Michael and Nazeeruddin, Md. K. “Molecular Engineering of Organic Sensitizers for Dye-Sensitized Solar Cell Applications”. J. Am. Chem. Soc. 130, 6259- 6266 (2008). [15] Wang, Zhong-Sheng; Koumura, Nagatoshi; Cui, Yan; Takahashi, Masabumi; Sekiguchi, Hiroki; Mori, Atsunori; Kubo, Toshitaka; Furube, Akihiro and Hara, Kohjiro “Hexylthiophene-Functionalized Carbazole Dyes for Efficient Molecular Photovoltaics: Tuning of Solar-Cell Performance by Structural Modification”. Chem. Mater. 20, 3993 - 4003 (2008). [16] Liu, DaXi; Bin, Zhao; Shen, Ping; Huang, Hui; Liu, LiMing; Tan, Song Ting “Molecular design of organic dyes based on vinylene hexylthiophene bridge for dye-sensitized solar cells”. Sci. China Ser B-Chem 52, 1198-1209 (2009). [17] Li, Shao-Lu; Jiang, Ke-Jian; Shao, Ke-Feng and Yang, Lian-Ming “Novel organic dyes for efficient dye-sensitized solar cells”. Chem. Commun. 2792-2794 (2006).

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[18] Hara, Kohjiro; Wang, Zhong-Sheng; Sato, Tadatake; Furube, Akihiro; Katoh, Ryuzi; Sugihara, Hideki; Dan-oh, Yasufumi; Kasada, Chiaki; Shinpo, Akira and Suga, Sadaharu “Oligothiophene-Containing Coumarin Dyes for Efficient Dye-Sensitized Solar Cells”. J. Phys. Chem B 109, 15476-15482 (2005). [19] Hara, Kohjiro; Kurashige, Mitsuhiko; Ito, Shunichiro; Shinpo, Akira; Suga, Sadaharu; Sayama, Kazuhiro and Arakawa, Hironori “Novel polyene dyes for highly efficient dye-sensitized solar cells”. Chem. Commun. 252-253 (2003). [20] Wang, Zhong-Sheng; Cui, Yan; Hara, Kohjiro; Dan-oh, Yasufumi; Kasada, Chiaki; Shinpo, Akira “A High-Light-Harvesting-Efficiency Coumarin Dye for Stable Dye-Sensitized Solar Cells”. Adv. Mater. 19, 1138-1141(2007). [21] Wang, Zhong-Sheng; Cui, Yan; Dan-oh, Yasufumi; Kasada, Chiaki; Shinpo, Akira and Hara, Kohjiro “Thiophene-Functionalized Coumarin Dye for Efficient Dye-Sensitized Solar Cells: Electron Lifetime Improved by Coadsorption of Deoxycholic Acid”. J. Phys. Chem. C 111, 7224 -7230 (2007). [22] Choi, Hyunbong; Baik, Chul; Kang, Sang Ook; Ko, Jaejung; Kang, Moon-Sung; Nazeeruddin, Md. K. and Gratzel, Michael “Highly Efficient and Thermally Stable Organic Sensitizers for Solvent-Free Dye-Sensitized Solar Cells”. Angew. Chem. Ing. Ed. 47, 327 (2008). [23] Hara, Kohjiro; Kurashige, Mitsuhiko; Dan-oh, Yasufumi; Kasada, Chiaki; Shinpo, Akira; Suga, Sadaharu; Sayama, Kazuhiro and Arakawa, Hironori “Design of new coumarin dyes having thiophene moieties for highly efficient organic-dye-sensitized solar cells”. New J. Chem 27, 783 - 785 (2003). [24] Hara, Kohjiro; Sayama, Kazuhiro; Ohga, Yasuyo; Shinpo, Akira; Suga, Sadaharu and Arakawa Hironori “A coumarin-derivative dye sensitized nanocrystalline TiO2 solar cell having a high solar-energy conversion efficiency up to 5.6%”. Chem. Commun. 569 - 570 (2001). [25] Kohjiro Hara; Tadatake Sato; Ryuzi Katoh; Akihiro Furube; Yasuyo Ohga; Akira Shinpo; Sadaharu Suga; Kazuhiro Sayama; Hideki Sugihara and Hironori Arakawa “Molecular Design of Coumarin Dyes for Efficient Dye-Sensitized Solar Cells”. J. Phys. Chem B 107, 597-606 (2003). [26] Chen, Ruikui; Yang, Xichuan; Tian, Haining; Wang, Xiuna; Hagfeldt, Anders and Sun, Licheng “Effect of Tetrahydroquinoline Dyes Structure on the Performance of Organic Dye-Sensitized Solar Cells’. Chem. Mater 19, 4007- 4015 (2007). [27] Paek, Sanghyun; Choi, Hyunbong; Choi, Hyeju; Lee, Chi-Woo; Kang, Moon-sung; Song, Kihyung; Nazeeruddin, Mohammad K. and Ko, Jaejung “Molecular Engineering of Efficient Organic Sensitizers Incorporating a Binary π-Conjugated Linker Unit for Dye-Sensitized Solar Cells”. J. Phys. Chem. C 114, 14646 -14653 (2010). [28] Chow, Tahsin J.; Chang, Yuan-Chieh “Dye Compound and Dye-Sensitized Soalr Cell”. US Patent, US2010/0076205A1, March 25 (2010). [29] Velusami, Marappan; Thomas, Koilpitchai R. Justin, Lin; Jiann T’suen; Ho, Kuo-Chuan, Ho; Hsu, Ying-Chan “Organic Dye Used in Dye-Sensitized Soalr Cell”. US Patent, US 2011/0077408 A1, March 31 (2011). [30] Kim, Sanghoon; Kim, Duckhyun; Choi, Hyunbong; Kang, Moon-Sung; Song, Kihyung; Kang, Sang Ook and Ko, Jaejung “Enhanced photovoltaic performance and long-term stability of quasi-solid-state dye-sensitized solar cells via molecular engineering”. Chem. Commun. 4951-4953 (2008). [31] Ko, Sangwon; Choi, Hyunbong; Kang, Moon-Sung; Hwang, Hyonseok; Ji, Heesun; Kim, Jinho; Ko, Jaejung and Kang, Youngjin “Silole-spaced triarylamine derivatives as highly efficient organic sensitizers in dye-sensitized solar cells (DSSCs)”. J. Mater. Chem. 20, 2391-2399 (2010). [32] Miyazaki, Eigo; Okanishi, Takashi; Suzuki, Yuki; Ishine, Nozomi; Mori, Hiroki; Takimiya, Kazuo and Harima, Yutaka “Simple Oligothiophene-Based Dyes for Dye-Sensitized Solar Cells (DSSCs): Anchoring Group Effects on Molecular Properties and Solar Cell Performance”. Bull. Chem. Soc. Jpn. 84, 459-465 (2011). [33] Kira, Aiko; Shibano, Yuki; Kang, Soonchul; Hayashi, Hironobu; Umeyama, Tomokazu; Matano, Yoshihiro and Imahori, Hiroshi “Oligothiophene Bearing 1-Hydroxy-1-oxodithieno[2,3-b:3’,2’-d]phosphole as a Novel Anchoring Group for Dye-sensitized Solar Cells”. Chem. Lett. 39, 448-450 (2010). [34] Qu, Sanyin; Wu, Wenjun; Hua, Jianli; Kong, Cong; Long, Yitao and Tian, He “New Diketopyrrolopyrrole (DPP) Dyes for Efficient Dye-Sensitized Solar Cells”. J. Phys. Chem. C 114, 1343-1349 (2010) [35] Lin, Li-Yen; Tsai, Chih-Hung; Wong, Ken-Tsung; Huang, Tsung-Wei; Hsieh, Lun; Liu, Su-Hao; Lin, Hao-Wu; Wu, Chung-Chih; Chou, Shu-Hua; Chen, Shinn-Horng and Tsai, An-I “Organic Dyes Containing Coplanar Diphenyl-Substituted Dithienosilole Core for Efficient Dye-Sensitized Solar Cells ”. J. Org. Chem. 75, 4778-4785 (2010). [36] Caballero, Ruben ; Barea, Eva M.; Fabregat-Santiago, Francisco; de la Cruz, Pilar; Marquez, Lourdes; Langa, Fernando and Bisquert, Juan ”Injection and Recombination in Dye-Sensitized Solar Cells with a Broadband Absorbance Metal-Free Sensitizer Based on Oligothienylvinylene”. J. Phys. Chem. 112, 18623-18627 (2008). [37] Liang, Mao; Xu, Wei; Cai, Fengshi; Chen, Peiquan; Peng, Bo; Chen, Jun and Li, Zhengming “New Triphenylamine-Based Organic Dyes for Efficient Dye-Sensitized Solar Cells”. J. Phys. Chem. C 111, 4465-4472 (2007). [38] Zhang, Guangliang; Bala, Hari; Cheng, Yueming; Shi, Dong; Lv, Xueju; Yu, Qingjiang and Wang, Peng “High efficiency and stable dye-sensitized solar cells with an organic chromophore featuring a binary p-conjugated spacer”. Chem. Commun. 2198-2200 (2009). [39] Koopmans, T., ”Über die Zuordnung von Wellenfunktionen und Eigenwerten zu den Einzelnen Elektronen Eines Atoms“. Physica 1, 104-113 (1934). [40] Marcus, R. A. ”On the Theory of Oxidation-Reduction Reactions Involving Electron Transfer”. J. Chem. Phys. 24, 966-978 (1956).

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[41] Yella, Aswani; Lee, Hsuan-Wei; Tsao, Hoi Nok; Yi, Chenyi; Chandiran, Aravind Kumar; Nazeeruddin, Md. Khaja; Diau, Eric Wei-Guang; Yeh, Chen-Yu; Shaik M. Zakeeruddin; Michael Grätzel “Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency”. Science 334, 629-634 (2011).

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C102 - Synthesis and Characterization of Benzo[1,2-b:3,4-b’]dithiophene-based Low Band gap Copolymers Containing Electron –Withdrawing Thienopyrazine and thieno[3,4-c]thiadiazole Derivatives for Photovoltaic Application

Mukhamed Keshtova, Vitaliy Kochurova, Levent Toppareb, Dmitriy Godovskya, Alexei Khokhlova

a, INEOS RAS , Vavilova,28, Moscow, 119991, RU b, Department of Chemistry, Middle East Technical University, 06800, Ankara, TUR

Conjugated polymer-based solar cells that convert solar light directly into electricity have been extensively investigated in the past decades. The efficiency of such devices depends primarily by the ability of the active material to absorb light with subsequent exciton formation (high molar absorption in the red region of the visible spectrum), the generation of free charge carriers and their capture by the electrodes (charge mobility). Apart from specific device configuration, the prime factors that determine a solar cell behavior are the polymer structure and morphology. Establishing the correlation of these parameters with the photophysical and photovoltaic properties is the key for the design of high performance solar cells [1,2]. Two new donor/acceptor conjugated copolymers containing a benzo[1,2-b:3,4-b’+dithiophene donor unit and the acceptor unit ofthienopyrazine or thieno[3,4-c]thiadiazole U-1 and U-2 were synthesized by Suzuki coupling reaction [3].

Figure 1 Polymers U-1 and U-2.The thermal, optical, and electrochemical properties were investigated. U-1, U-2 exhibit good thermal stability with 10% weight loss temperatures of 340-350°C. U-1, U-2 in films exhibit absorption maximum of 450, 700 and 450, 750 nm with optical band gap 1.33 eV and 1.44 eV respectively. The HOMO energy levels are -5.01 eV and -5.02 eV for U-1 and U-2 respectively. Bulk heterojunction solar cell devices based on these copolymers as donor and PC60BM as acceptor in a weight ratio of 1:3 displayed open–circuit voltages of 0.62-0.67 V, a short–circuit current of 0.80-1.45 mA/cm

2 and achieved power conversion efficiency of

0.13-0.29% under the illumination of AM 1.5, 100 mW/cm2.

Acknowledgments.The work was carried out with financial support of the Russian Academy of Sciences (grants of programs: ОKH-3 ”Development and study of macromolecules and macromolecular structures of new generation”, ОKH-6 “Synthesis and properties of supramolecular structures”, ОKH-2 “Development of new metallic, ceramic, glass-, polymeric and compositional materials” and Presidium RAS Program P-7 “Multifunctional materials for molecular electronics”).

References [1] Facchetti, A. "Conjugated Polymers for Organic Electronics and Photovoltaic Cell Applications". Chem. Mater. 23, 733-758 (2011); [2]He, F.; Yu, L. "How Far Can Polymer Solar Cells Go? In Need of a Synergistic Approach". J. Phys. Chem. Lett. 2, 3102-3113 (2011);

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[3]Lin, H.-Ch.; Sung, H.-H.; Tsai, Ch.-M.; Li, K.-Ch. "Synthesis and characterization of alternating fluorene-based copolymers containing diaryl- and non-substituted bithiophene units". Polymer 46, 9810–9820 (2005).

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C103 - The influence of titania morphology on dye loading for dye-sensitized solar cells

Gabriella Di Carloa, Daniela Cascheraa, Marco Brucalea, Alessio Mezzia, Giuseppe Calogerob, Gaetano Di Marcob, Giuseppina Padelettia, Gabriel Maria Ingoa

a, ISMN-CNR, Via Salaria km 29300, Monterotondo Stazione (Rome), 00015, Italy b, IPCF-CNR, Viale F. Stagno D’Alcontres 37, Messina, 98158, Italy

Dye-sensitized solar cells (DSSCs) are receiving increasing interest as a viable technology for the conversion of sunlight into electricity [1]. In the DSSCs the dye, typically a ruthenium bipyridyl complex, is absorbed on a titania substrate and extends the spectral sensitivity of the photoelectrode. These devices are very promising systems for many different solar power applications due to their low cost and lightweight [2]. The performance of the dye-titania photoanode are directly related to the processes that occur at the dye/titania interface, since the photoinduced electron transfer from the excited state of the dye to the conduction band of the titania is responsible for the production of the photocurrent. At present, in order to improve the efficiency of the photoanode, the attention has been mainly focused on the chemical modification of the dye [3], whereas only a few studies have been addressed on the improvement of titania film properties. In the present study, N719 dye over titania films with significantly different morphology has been investigated. In particular, titania films with a flat surface have been obtained using a sol-gel procedure (TiSG). The roughness and the porosity of titania have been increased using a soft template which allows producing a porous structure with a long range order (TiMS). Finally, the morphology of the obtained samples has been compared with a reference titania film, prepared with commercial titania using the well-known doctor-blade technique (TiDB). The morphological properties of titania films and the N719 dye loading have been investigated by atomic force microscopy and UV-vis spectroscopy, respectively. Moreover, X-ray photoelectron spectroscopy (XPS) measurements have been performed to characterize the chemical interaction between dye and titania. Our findings suggest that the mesoporous structure improves the dye loading and that the morphological properties of titania film play a key role. However, sol-gel and mesoporous titania films were deposited by spin-coating and this procedure leads to coatings with a thickness which is significantly lower than doctor-blade technique. In order to improve the performance of the DSSCs, one of the main challenge is to increase the dispersion and the loading of dye over titania. To this purpose, the development of high surface area mesoporous titania films with a higher thickness is worthy of future investigations. References [1] Graetzel, M. "Solar energy conversion by dye sensitized photovoltaic cells". Inorg. Chem. 44, 6841–6851 (2005). [2] Gonçalves, L.M.; Bermudez, V.Z.; Ribeiro, H.A.; Mendes, A.M. "Dye-sensitized solar cells: A safe bet for the future". Energy Environ. Sci. 1, 655-667 (2008). [3] Nazeeruddin, Md.K.; Klein, C.; Liska, P.; Gratzel, M. " Synthesis of novel ruthenium sensitizers and their application in dye-sensitized solar cells". Coord. Chem. Rev. 249, 1460–1467 (2005).

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C104 - Charge Carrier Mobility and Recombination in TQ1:[70]PCBM Solar Cells Studied by TOF and CELIV Techniques

Armantas Melianasa, Zheng Tangb, Olle Inganäsb

a, Department of Solid State Electronics, Vilnius University, Saulėtekio 9, Vilnius, 10222, LT b, Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology, IFM, Linköping University, Linköping, SE-581 83, Sweden

Charge carrier mobility µ and recombination in semitransparent solar cells based on blends of TQ1:PC71BM(1) were investigated using TOF (Time of flight) and CELIV (Charge extraction by linearly increasing voltage) transient techniques. Semitransparent solar cells allow studying the photocurrent transient response of the device under illumination either from the cathode or the anode side. Moreover, to clarify charge carrier mobility µ and recombination properties the optical excitation pattern can be manipulated by varying the active layer thickness d. Hence, results obtained for a solar cell with an active layer thickness of d = 80 nm are compared to one with d = 450 nm, which are in good agreement.

Figure 1 Photo CELIV transient dependence on light pulse delay time. Arrow indicates increasing light pulse delay time. Sample thickness is 450 nm.

The faster charge carrier mobility µ estimated by photo CELIV(2) is of the order of 10-4 cm2/Vs. Both in TOF and photo CELIV experiments reduced bimolecular recombination as compared to the Langevin type β/βL<< 1 is observed (Figure 1). By using the methodology outlined in literature(3) and fit of the data, bimolecular recombination coefficient β values were estimated, which are comparable to the ones reported for RRP3HT:PCBM based solar cells(4).

References [1] Wang, E.; Hou, L.; Wang, Z.; Hellström, S.; Zhang, F.; Inganäs, O.; Andersson, M. R. "An Easily Synthesized Blue Polymer for High-Performance Polymer Solar Cells". Adv. Mater. 22, 5240-5244 (2010). [2] Nekrašas, N.; Genevičius, K.; Viliūnas, M.; Juška, G. "Features of current transients of photo generated charge carriers, extracted by linearly increased voltage". J. Chem. Phys. In press (2012). [3] Pivrikas, A.; Juška, G.; Mozer, A. J.; Scharber, M.; Arlauskas, K.; Sariciftci, N. S.; Stubb, H.; Österbacka, R. "Bimolecular Recombination Coefficient as a Sensitive Testing Parameter for Low-Mobility Solar-Cell Materials". Phys. Rev. Lett. 94, 176806 (2005).

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[4] Juška, G.; Šliaužys, G.; Genevičius, K.; Arlauskas, K.; Pivrikas, A.; Scharber, M.; Dennler, G.; Sariciftci, N. S.; Österbacka, R. "Charge-carrier transport and recombination in thin insulating films studied via extraction of injected plasma". Phys. Rev. B 74 115314 (2006).

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C105 - Charge separation dynamics in photovoltaic ZnPc:C60 blend films

Andreas Bartelt, Christian Strothkämper, Rainer Eichberger

a, Helmholtz Center Berlin for Materials and Energy, Hahn-Meitner-Platz 1, Berlin, 14109, DE

The morphologies of ZnPc:C60 blend films used as organic solar cell material composites can be optimized by controlling the growth temperature during deposition, inducing phase segregation and crystallinity. Here, the influence of growth temperature induced structural changes on the generation of free charges in ZnPc:C60 blend films is investigated with optical-pump terahertz-probe spectroscopy (1). After excitation, photo-generated ZnPc-excitons are split at the interface with C60. Taking advantage of the excess energy, some free charges are generated within 1 ps, while others stay Coulombically attracted in form of an interfacial charge transfer (CT) state. An improved time-dependent photoconductivity is observed for inproved C60 crystallinity and domain size in the film. While for amorphous blends the interfacial charge-transfer state hampers the generation of free charges, growing crystalline C60 nanodomains help reaching the charge-separated state. In this case, a sequential charge separation process is observed, which entails both vibrationally hot and relaxed charge transfer states, on time scales between <100 fs and ~100 ps. High local mobilities of minimal µ~0.3 cm2/Vs are found, which increase with improved domain growth. The increase of photoconductivity with film growth temperature correlates with formerly observed solar cell photocurrent improvements. References [1] Bartelt, A. F.; Strothkämper, C.; Schindler, W.; Fostiropoulos, K.; Eichberger, R. “Morphology effects on charge generation and recombination dynamics at ZnPc:C60 bulk hetero-junctions using time-resolved terahertz spectroscopy”, Appl. Phys. Lett. 99, 143304 (2011)

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C106 - Determination of Conduction Band Minimum in TiO2 Via Temperature Dependent Spectroelectrochemistry

Jesse Ondersma, Thomas Hamann

a, Michigan State University, Chemistry Building, Michigan State University, 578 S Shaw Lane Room 409, East Lansing, 48824, US

Transparent mesoporous anatase TiO2 electrodes (6-μm thick) were prepared by sintering 10 nm colloidal particles on conductive fluorine doped tin oxide substrates. The absorption of near-infrared wavelengths by these thin film semiconducting electrodes was measured while varying both bias potential and temperature. The energy of the conduction band minimum, Ecb, was determined for mesoporous transparent TiO2 in contact with electrolyte solutions using the effective mass of an electron and the measured absorbance at 950 nm at varying temperature and potential. The method applied herein does not require a priori knowledge of the extinction coefficient of free or trapped electrons in the semiconducting film, an important advantage over previous spectroelectrochemistry methods. Additionally, the absorbance measurements presented are absent from potential scan rate dependence which are present even at slow scan rates. Temperature dependent spectroelectrochemistry can be used to determine Ecb for mesoporous films under near working conditions as it changes with solvent and potential determining ions. Since accurate determination of Ecb for mesoporous wide band gap semiconductors is a critical step in determining heterogeneous electron transfer processes for energy conversion systems, knowledge of Ecb must prelude design of components for systems such as dye-sensitized solar cells.

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C107 - DSSC with Large Stokes Shift layer as UV blocking layer.

Mónica B. Della Pirrieraa, Pau Bosch Jimeneza, Laurent Auboya, David Gutierrez Taustea, José M. Garcíaa, Jose L. Bautistaa, Manus Kennedyb, Hind Ahmedb, J. Doranb, Joaquim Puigdollersc, Cristobal Vozc, Sergi Galindoc

a, Acondicionamiento Tarrasense, carrer de la Innovacio 2, Terrasa, 08225, Spain b, Dublin Energy Lab,Focas Institute, Dublin Institute of Technology, Dublin 8, Irland c, Micro and Nanotechnologies Group of the Polytechnic University of Catalonia, Campus Nord, Edifici C4, C/ Jordi Girona, 1-3, 08034 Barcelona, Spain

The solar spectrum received at the Earth surface covers a wide range of wavelengths from 290 nm to 3790. However, there is an important spectral mismatch between the solar spectrum and the absorption properties of present PV materials. This work is developed within the EPHOCELL project wich main goal is to enhance the PV conversion efficiency through two simultaneous mechanisms: down shifting and up conversion. The Down-Shifting involves an antenna molecule that transfers the absorbed energy (UV photons, non-absorbable by the PV cell) to the central metal emitter, which emits a photon in the absorption band of the cell. Large Stokes Shift systems, developed within EPHOCELL, are used for DS process. On the other hand, PV cells require UV protection especially the solar cell with organic component like DSSC and OPV, to prevent the degradation by a number of different processes including photolysis and photocatalysis. Usually this UV blocking layer consists of a high transparent (in visible range) polymer sheet with additives for UV absorption [[1], [2]] In this work, we present a transparent LSS-DS polymeric film which is designed as luminiscent solar concentrator and also can work like a UV-Blocking layer for DSSC. References [1]Kuang D., Klein C. , Zhang Z., Ito S., Moser J.E., Zakeeruddin S. M., Grätzel M. ,"Stable, High-Efficiency Ionic-Liquid-Based Mesoscopic Dye-Sensitized Solar Cells" Small 3, No. 12, p.2094 – 2102 (2007). [2]Shi D., Pootrakulchote N. , Li R., Guo J. , Wang Y., Zakeeruddin M., Grätzel M., Wang P., J.Phys. Chem. C, Vol. 112, No. 44, p.17046–17050 (2008)

http://www.nanoge.org/HOPV12/abstract_submission.php#_ftn1

http://www.nanoge.org/HOPV12/abstract_submission.php#_ftn2

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C108 - The effect of 4-tert-butylpyridine and Li+ on the thermal degradation of TiO2 – bound ruthenium dye N719

Phuong Tuyet Nguyen, Poul Erik Hansen, Torben Lund

a, Roskilde University, Universitetsvej 1, 18.2, Roskilde, 0, DK

Thermal stability experiments were performed at 100 ºC of the Dye-sensitized solar cell ruthenium dye N719. The experiments were performed as simple test-tube experiments carried out with colloidal solutions of N719-loaded TiO2 particles. The dye degradation was followed by the use of HPLC-coupled electrospray mass spectrometry spectroscopy. The longest half life of N719 of 84 hours at 100oC was obtained in 3-methoxypropionitrile based electrolytes containing 0.5 M 4-TBP, no Li+ ions and 0.25 M I3

-. If 4-TBP was removed from the solution the degradation rate of N719 increased up to 3-15 times depending on the I3

- concentration. If Li+ ions were added to the electrolyte the degradation increased by a factor of 4-16 times and the thermal degradation product mixture became more complex. A hypothesis was suggested that an adsorbed layer of 4-TBP on the TiO2 protects the N719 dye against solvent substitution and oxidation processes. A complextation constant of Li+ ions with 4-TBP equal to 9 M-1 was obtained by 13C-NMR. The Li+ complexation with 4-TBP was suggested to destroy the adsorbed protection layer of 4-TBP on the TiO2 surface. It was concluded that addition of 4-TBP or other N-additives to the DSC electrolyte is important to enhance the dye life time at elevated temperatures. Addition of Li+ to the electrolyte, however, should be avoided if the wish is to construct DSCs with high thermal stability.

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C109 - Electrochemical deposition of ZnO nanorods for application in light harvesting solar cells

Kamila Zarebska, Magdalena Skompska

Laboratory of Electrochemistry, Faculty of Chemistry, University of Warsaw, Pasteura 1, Warsaw, 02093, PL

The use of fossil fuels (oil, coal, gas) has led to adverse impacts on environment. It is necessary to make us independent on conventional energy sources - one of way is the sun energy. For many decades the solar cell industry has been dominated by inorganic solid state devices, mainly based on silicon. Manufacturing of this type large area devices is very expensive. One of possible alternatives are semiconductor-sensitized solar cells (SSSC), consisting of metal oxide (MeO) deposited on the light transparent conducting oxide (in this case indium tin oxide - ITO). MeO nanostructures are covered with semiconductor quantum dots (CdS, PbS) and layer of hole acceptor (conducting polymer). The MeO is a wide bandgap semiconductor, playing the role of an electron transporting material and support for organic or inorganic sensitizer. It should provide a large surface area for deposition of the light absorber and high electron mobility. These requirements are well fulfilled by mesoporous and nanotubular TiO2, which is the most-widely used material in the typical SSSC. A ZnO has been emerged as promising alternative due to its high electron mobility (10-100 times higher than that in TiO2) which may result in the decrease of the charge carriers recombination. Other advantage of this compound is easy way of its synthesis.

Figure 1 SEM image of ZnO nanorods deposited from solution containing Zn(NO3)2 and NH3 at 80oC at potential -0,9V for 2,5h on ITO surface seeded from Zn(NO3)2.

In this work the ZnO nanorods were prepared on ITO substrate by potentiostatic method. The growth was performed from the solution containing Zn(NO3)2 and NH3 at 80oC. Before deposition the ITO surface was seeded in zinc nitrate or zinc acetate solution by potentiostatic method. The main aim of these studies was to examine the influence of seeding layer and applied potential on morphology of ZnO nanostructures and determine the mechanism of seeding and growing processes. The samples were examined by SEM, X-ray diffraction and electrochemical methods and compared with the results obtained by means of hydrothermal method.

Acknowledgment:This work was partially supported by Polish Ministry of Science and Higher Education (grant NN 204117039).

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C110 - Low cost counter electrodes for dye-sensitized solar cells based on graphene-like MoS2 Flavio S. Freitas, Agnaldo S. Gonçalves, Andréia de Morais, João E. Benedetti, Luiz C. P. Almeida, Ana F. Nogueira

University of Campinas - UNICAMP, Cidade Universitária Zeferino Vaz, Campinas, 13083, Brazil

Molybdenum carbide, nitride, and oxide have demonstrated good catalytic properties in dye-sensitized solar cells (DSSC). Similarly, their sulfides are expected to have the same function due to their high catalytic activity, thermal and chemical stability as reported recently for MoS2 bulk material. Rao and co-workers have reported that typical layered transition metal sulfides have an analogous structure to graphite, which are composed of three atomic layers. These characteristics provide a good combination for applications as counter electrodes for DSSC, where graphene-like MoS2 provides a high interfacial area for triiodide reduction as alternative to high cost platinum counter electrodes. The graphene-like MoS2 was obtained as described elsewhere and applied directly using a doctor blading technique on the conducting glass without any thermal treatment. This is an advantage compared to platinum and decreases significantly the process cost. The layered structure can be viewed in FEG-SEM and TEM images, as showed in the inset of Fig.1. Cyclic voltammetry for iodide/triiodide redox pair demonstrated resolved peaks for anodic and cathodic reactions, indicating a good activity and a catalytic mechanism for the tri-iodide reduction. The linearity of the peak current densities vs. the square root of the scan rate, indicates that mass transport is controlled by diffusion. The application in DSSC presented a promising effect to substitute high cost counter electrodes, reaching to 2.5% in efficiency, as showed in Fig. 1.

Figure 1 J-V curves measured under illumination of 100 mW cm-2 (AM1.5). Geometrical cell area of 0.16 cm2. In the inset FEG-SEM and HR-TEM images of as-prepared MoS2.

The graphene-like MoS2 provided CE for DSCs with 86% of the performance compared to analogue devices based on Pt CEs. Poor FF values for MoS2 in this work might be associated to a relatively high series resistance of the corresponding DSCs, probably due to the electrical conductivity of the CE layers. FF can be enhanced by preparing composite CE layers with the

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addition of carbon-based materials, such as carbon black, carbon nanotubes, among others, in order to increase the electrical conductivity of the CE layer. In summary, we demonstrated the possibility to use graphene-like MoS2 as CE layers for DSCs at low temperature with considerable electrocatalytical activity towards the regeneration of the iodide/tri-iodide redox couple.

References [1] Wu, Mingxing, Wang, Y., Lin, X., Yu, N., Wang, L., Wang, L., Hagfeldt, A., Ma T. "Economical and effective sulfide catalysts for dye-sensitized solar cells as counter electrodes” Phys. Chem. Chem. Phys. DOI: 10.1039/c1cp22819f Matte, H. S. S. R., Gomathi, A., Manna, A. K., Late D. J., Datta, R., Pati, S. K., Rao, C. N. R. “MoS2 and WS2 Analogues of Graphene” Angew. Chem. Int. Ed., 49, 4059-4062 (2010). [2] Chang K., Chen W., Ma, L., Li, H., Li, H. , Huang, F., Xu, Z., Zhang, Q., Lee, J.-Y. "Graphene-like MoS2/amorphous carbon composites with high capacity and excellent stability as anode materials for lithium ion batteries" J. Mater. Chem., 21, 6251-6257 (2011).

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C111 - Synthesis and characterization of semiconductor nanoparticles for application in solid state solar cells

Zuzanna Glebicka, Magdalena Skompska

a, Laboratory of Electrochemistry, Faculty of Chemistry, University of Warsaw , Pasteura 1, Warsaw, 02093, PL

As third generation solar cells are considered as promising renewable energy sources, a lot of attention is focused on improving their efficiency and stability. These cells consist of metal oxide (ZnO, TiO2) nanostructures decorated with light harvesting material (most often a dye). Recently, solid state semiconductor-sensitized solar cells have been regarded as interesting alternative for dye-sensitized solar cells. For this application, CdS and CdSe quantum dots were obtained in this work by reversed micelle method (synthesis carried out in water-in-oil microemulsion). This procedure not only requires the use of surfactant but also allows the functionalization of nanoparticles by selected ligand which may act as a linker between metal oxide and nanoparticle. Depending on the kind and structure of the ligand used, its presence may facilitate the formation of hybrid material but on the other hand, it can also block the charge transfer across the interface. From this point of view, it is reasonable to use a short-chained ligand with specified charge (such as 2-mercaptoethane sulfonate) which may facilitate an electrophoretic deposition of nanoparticles on TiO2 or ZnO substrates. Thus, the key point of synthesis is absolute removal of basic emulsifier (in this case AOT - sodium dioctyl sulfosuccinate) from the nanoparticle surface to leave only the molecules of selected ligand. In this work two different methods of washing it out were applied to verify their effectiveness. The mechanism of purification nanoparticles from the surfactant and its further functionalization was carefully examined by infrared spectroscopy.

Figure 1 HRTEM image and SAED pattern of CdSe nanoparticles

Apart from that, the reversed micelle method allows also full control of the size, shape and crystallographic structure of obtained nanoparticles. The factors affecting these properties are: W parameter (water to surfactant molar ratio), the reactants molar ratio, kind of solvent used as dispersed phase, time and conditions of the reaction. All these parameters were changed during the subsequent syntheses so the obtained nanoparticles varied in size and properties. Characterization of nanoparticles was done by means of spectroscopic and microscopic methods: UV-Vis, FTIR spectroscopies, photoluminescence, X-ray diffraction and X-ray

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photoelectron spectroscopy. The size and shape of the obtained nanoparticles were determined by HRTEM.

Acknowledgements:This work was partially supported by Polish Ministry of Science and Higher Education (grant NN204117039).

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C112 - Triiodide Loss and Subsequent Regeneration in UVA Exposed Dye-Sensitized Solar Cells

Matthew Carnie, Trystan Watson, David Worsley

a, Swansea University, SPECIFIC - College of Engineering, Swansea University, Baglan Bay Innovation Centre, Baglan Energy Park, Port Talbot SA12 7AX, GB

The loss of triiodide from Dye-Sensitized Solar Cells (DSCs) undergoing long term stability testing is a cause of some concern. Explanations of this phenomena have been suggested as the sublimation of iodine or due to the reaction of iodine with impurities in the electrolyte [1]. We have recently reported [2] that one mechanism of triiodide removal in UVA exposed DSCs seems to be through photocatalytic oxidation of triiodide by direct band gap excitation of the TiO2 semiconductor. In this poster presentation we explore the mechanisms of triiodide removal in more detail. We show, using various spectroscopic techniques, that the electrolyte formulation used is extremely stable under UV exposure in the absence of TiO2 but suffers rapid triiodide loss in the presence of TiO2.

Figure 1 Average JSC of cells irradiated by UVA light over the exposure period shown and subjected to periodic regeneration treatment (after 500 hours initial exposure). This is compared to the JSC of cells that received that did not receive the regeneration treatment

Furthermore we explore an in-situ method of regenerating triiodide in UVA exposed test cells. By simple application of a reverse bias to UVA exposed test cells, photocurrents can be restored to near original levels in test cells where JSC had previously collapsed due to diffusion limitation caused by triiodide loss. We explore the long term consequences of periodic triiodide regeneration in operating DSC devices and show how this may impact upon the long term performance of DSC modules. Figure 1 shows the averaged photocurrent (JSC) of devices under constant UV illumination and subjected to periodic regeneration treatment after an initial 500 hours irradiation. The regeneration treatment consists of scanning cyclically from 0 V to + 1.4 V at a rate of 20 mV s-1, similarly to a cyclic voltammetry experiment. It appears that the periodic cell regeneration cannot prevent the reduction of JSC which is typical in DSCs exposed to UV irradiation. Nonetheless, although the recovery process does not permanently reverse the effects of UV exposure, it can be seen how cells subjected to periodic regeneration might maintain a higher average maximum photocurrent over their lifetime compared to those that do not receive the treatment.

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References [1] M.I Asghar, K. Miettunen, J. Halme, P. Vahermaa, M. Toivola, K .Aitola and P. Lund, "Review of stability for advanced dye solar cells", Energy & Environmental Science 2010 3(4) 418-426 [2] M. Carnie, D. Bryant, T. Watson and D. Worsley, "Photocatalytic Oxidation of Triiodide in UVA-Exposed Dye-Sensitized Solar Cells", International Journal of Photoenergy 2012

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C113 - A monte carlo study of increased charge mobility in molecular hole transporters due to coulomb traps

Daniel Staff, Alison Walker

University of Bath, University of Bath, Bath, BA2 7AY, GB

In the construction of Solid State Dye Sensitized Solar Cells, the addition of redox inactive ionic dopants such as Li-TFSI salt to molecular hole transporters increases the hole mobility1. Consequently these cells gain efficiency as holes move away from the interface between the mesoporous TiO2 film acting as electron acceptor and the hole transporter more rapidly and are extracted more readily, reducing recombination. To understand the mechanisms behind the increased hole mobility, we have developed a Monte Carlo model of charge hoping. The hopping sites are potential wells around the anion sites caused by an attractive electrostatic potential. We observe a similar order of magnitude increase in mobility with dopant concentration of a form like that of a insulating/conducting phase transition when the concentration of anions exceeds some critical value. The transition is typified by a change from nearest neighbor site to site hopping and long waiting times in isolated traps to hoping directly between traps with short waiting times in each trap. References [1] Snaith, H.; Grätzel, M. "Enhanced charge mobility in a molecular hole transporter via addition of redox inactive ionic dopant: Implication to dye-sensitized solar cells". Appl. Phys. Lett. 89, 262114 (2006).

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C114 - A theoretical study on Zn-porphyrins as potential dyes on ZnO-based dye-

sensitized solar cells

Markus Pfaua, Rubén Costaa, Dirk Guldia, Tim Clarkb

a, University of Erlangen, Egerlandstrasse 3, Erlangen, 91058, DE b, University of Erlangen, CCC, Nägelsbachstrasse 25, 91052 Erlangen, DE

Dye-Sensitized Solar Cells (DSSCs) are a promising source for solar energy conversing devices. As a matter of fact, a device with 13 % efficiency was recently reported using a porphyrin with a push-pull character.[1] This device was based on TiO2 photoanode electrodes. However, ZnO is evolving as an interesting alternative for TiO2, due to higher electron transport efficiency limiting the recombination current in the individual dyes.[2] Even so efficiencies as high as 7.5 % were recently reported for ZnO based DSSCs with a N719 dye,[3] up to today no in depth investigation has been performed on porphyrin based ZnO devices. Thus, the goal of this study is to show that different linkers binding archetypal Zn-based porphyrins exert substantial effects on the processes of the device, mainly the electron injection. To this end, we have performed theoretical assays based on semi-empirical and DFT methods to model ZnO in combination with the respective porphyrins. Notable, the different porphyrins give rise to a remarkable impact on the conduction and valance bands of ZnO. In addition, molecular dynamics show the individual energetic stabilities and spatial orientations for each type of porphyrin. This information was used to simulate the electron injection processes and, subsequently, to evaluate the prospect of the different linkers as integrated component in ZnO-based DSSCs. Indeed, our forefront research is currently focusing on the most promising linkers in the synthesis of porphyrins and in DSSC tests. References [1] Yella, A.; Lee, H.-W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, Md.K.; Diau, E. W.-G.; Yeh, C.-Y.; Zakeeruddin, S. M.; Grätzel, M. "Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency". Science 334, 629-634 (2011). [2] Marczak, R.; Werner, F.; Ahmad, R.; Lobaz, V.; Guldi, D. M.; Peukert, W. "Detailed investigations of ZnO photoelectrodes preparation for dye sensitized solar cells". Langmuir The Acs Journal Of Surfaces And Colloids 27, 3920-3929 (2011). [3] Memarian, N.; Concina, I.; Braga, A.; Rozati, S. M.; Vomiero, A.; Sberveglieri, G. "Hierarchically Assembled ZnO Nanocrystallites for High-Efficiency Dye-Sensitized Solar Cells". Angew. Chem. Int. Ed., 50, 12321–12325 (2011).

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C115 - Effect of Aggregation on the Internal Quantum Efficiency of Squaraine Sensitizers

Eva Unger, Burkhard Zietz

Dept. of Chemistry - Ångström, Uppsala University, Lägerhyddsvägen 1, Uppsala, 752, SE Squaraines are promising pure-organic dyes with very high absorption coefficients for use in dye-sensitised solar cells. Upon adsorption to mesoporous TiO2, partial formation of H-aggregates occurs. These show a characteristic absorption band and exhibit a lower internal quantum efficiency for solar energy conversion in dye sensitized solar cells compared to squaraine monomers. We have investigated the aggregation behaviour of the squaraine dye SQ02 on mesoporous ZrO2 and compared to a monomer/aggregates system in solution (water in the presence of cyclodextrins). Similar absorption spectra of aggregates in solution and on ZrO2 indicate the same kind of aggregation, with dimers dominating. Dimerisation leads to strongly reduced excited state lifetimes in solution and on the surface, giving rise to a lower internal quantum efficiency in solar cells.

Figure 1 Absorption Spectra of SQ02 in Solution and on ZrO2 Films

Interestingly, the results show that the aggregation not only quenches fluorescence of the molecules making up the aggregates, but also of surrounding monomers via energy transfer. The conclusions from this study stress the importance of avoiding aggregation and motivate the design of dyes with reduced aggregation.

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C116 - Atomic level characterization of D35/TiO2 interfaces - co-sensitization and thermal degradation

Johan Oscarssona, Rebecka Schölina, Susanna K Erikssonb, Kristofer Fredinc, Erik M. J. Johanssonb, Håkan Rensmoa

a, Department of Physics and Astronomy, Uppsala University, Box 516, Uppsala, SE-751 20, Sweden b, Department of Chemistry, Ångström, Uppsala University, Box 259, Uppsala, SE-751 05, Sweden c, Department of Applied Physical Chemistry, Royal Institute of Technology, Teknikringen 30, Stockholm, SE-100 44, Sweden

To understand the performance of a dye in a dye‐sensitized solar cell (DSC) the properties of the surface molecular- and electronic structures are very important. Photoelectron spectroscopy (PES) gives information about binding geometry and energy levels in the dye molecules versus TiO2. The surface sensitivity of the method being in the order of 20 Å makes photoelectron spectroscopy a suitable tool for studies on the dye/semiconductor interface at an atomic level. Here we present results from studies on the sensitizer D35 regarding co-sensitization with a Ruthenium based dye (RD) as well as effects of thermal treatment on the molecular level. Co‐sensitization is used to improve the light harvesting efficiency of the DSC by utilizing dyes with different absorption properties. The study of D35 co‐sensitized with RD is based on two different approaches for dying the porous TiO2 electrodes. In the first the electrodes are first sensitized with RD and thereafter with D35 whereas the second approach relates to simultaneous adsorption of RD and D35 in a solution comprising a 2:1 concentration ratio of the respective dyes. The two dyes are clearly distinguishable in the PES measurements and the results give information of the adsorption dynamics and how different mixing affect the surface structure. Because the DSC preparation scheme may contain steps involving heat treatment (1) it is important to obtain information about the thermal stability of the utilized dyes. Here we present results on D35/TiO2 interfaces (dye-sensitized electrodes) subjected to elevated temperatures in an ambient air atmosphere. The results indicate that the dye molecules transform into a single new compound at higher temperatures, which may affect the performance of the DSC. The results also indicate that D35 can adsorb to TiO2 in different ways. Already at lower temperatures the relative amounts of the two kinds of adsorption are affected. References [1] Fredin, K.; Johansson, E. M. J.; Hahlin, M.; Schölin, R.; Plogmaker, S.; Gabrielsson, E.; Sun, LC. and Rensmo, H. “Solid state dye‐sensitized solar cells prepared by infiltrating a molten hole conductor into a mesoporous film at a temperature below 150 degrees C”. Synthetic metals 161, 2280-‐2283 (2011).

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C117 - Block Copolymer Templated TiO2 Films in Extremely Thin Absorber Solar Cells

Askhat Jumabekova, Mihaela Nedelcua, Laurence Peterb, Hiroaki Saic, Ulrich Wiesnerc, Thomas Beina

a, Fakultät Chemie und Pharmazie, Ludwig-Maximilians-Universität München, München, 81377, Germany b, Department of Chemistry, University of Bath, Bath, BA2 7AY, UK c, Department of Materials Science and Engineering, Cornell University, Ithica, NY 14853, USA

Interest in ETA (extremely thin absorber layer) cells has increased steadily, but although performance values have improved progressively,1 they are still well below the values that would be interesting for industrial production.2,3 One of the main performance-limiting factors in ETA cells originates from the difficulty in finding suitable hole transporting materials (HTMs) that can provide complete pore filling and good charge transport. Key issues for further development of ETA cells include: 1) control of metal oxide structure in terms of pore size, surface area and crystallinity, 2) improvement of light harvesting, 3) improvement of HTM infiltration into the pores, 4) reduction of charge recombination and (5) enhancement of hole transport. Here we report the use of the structure-directing block-copolymer (BCP), poly(styrene-b-ethylene oxide) (PS-b-PEO), in preparation of porous TiO2 films for integration into ETA cells to enhance the porosity, crystallinity and structural regularity of the metal oxide layer. The porous TiO2 was obtained by mixing the BCP with a non-hydrolytic sol-gel, followed by annealing in air to remove the polymer and to transform the sol-gel into the pure crystalline anatase phase of TiO2. The porous TiO2 films obtained by this route were used in the fabrication of ETA solar cells in which a thin PbS absorber layer was deposited by the SILAR (successive ion layer adsorption and reaction) method, and the CuSCN HTM was infiltrated from solution phase by doctor blading. The performance of ETA cells based on these templated TiO2 films was compared with similar ETA cells made by sintering 25 nm sized P25 TiO2 nanoparticles. The comparison revealed that the use of BCP-templated porous TiO2 films improved the cell performance by a factor of 4 compared with the cells prepared using conventionally made porous TiO2 layers. The improvement of the device performance is attributed to higher BET surface area, enabling higher PbS uptake (better sensitization) and to the ordered pore structure, which results in better infiltration of the HTM. References [1] Dittrich, T; Belaidi, A; Ennaoui, A. "Concepts of inorganic solid-state nanostructured solar cells". Solar Energy Materials and Solar Cells, 95, 1527-1536 (2011). [2] Nezu, S; Larramona, G; Chone, C; Jacob, A; Delatouche, B; Pere, D; Moisan, C. "Light Soaking and Gas Effect on Nanocrystalline TiO2/Sb2S3/CuSCN Photovoltaic Cells following Extremely Thin Absorber Concept". The Journal of Physical Chemistry C, 114, 6854-6859 (2010). [3] Itzhaik, Y; Niitsoo, O; Page, M; Hodes, G. "Sb2S3-Sensitized Nanoporous TiO2 Solar Cells". The Journal of Physical Chemistry C, 113, 4254-4256 (2009).

http://www.nanoge.org/HOPV12/abstract_fig2/out3.html#_ENREF_1



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C118 - Charge carrier dynamics in dye sensitized solar cells by diffuse reflectance spectroscopy

Elham Ghadiri, Jacques-E Moser

EPFL, EPFL SB ISIC GR-MO CH G0 627 (Bâtiment CH) Stati, Lausanne, 1015, CH

Dye-sensitized solar cells (DSC) are a promising alternative to traditional inorganic semiconductor- based solar cells. Recently, their device performance has been increasing gradually, with a reported maximum efficiency of 12%. Pump-probe transient absorption spectroscopy is widely used to study the electron injection processes on model systems based on a transparent thin film, which is sensitized with dye [1]. Nanosecond flash photolysis technique also has been applied to study the electron back reaction and dye interception with electrolyte. However these techniques have been applied on dye sensitized transparent TiO2 mesoporous thin films as model systems. The high efficiency devices usually consistes of a scattering layer made of 400 nm TiO2 particles on top of a high surface area mesoporous transparent film, that makes the film optically opaque. Therefore current techniques cannot be applied to study the dynamic of reactions on the electrode itself and in the situation close to the situation of cell under operational conditions. Also other novel morphologies of TiO2, which show promising behaviour in cell performance, like nanowires and fibers [2,3], are not essentially transparent and cannot be studied by transient absorption pump probe in transmission mode. We have developed femtosecond diffuse reflectance spectroscopy technique to study the electron injection process on a DSC in the fashion applied in standard high efficiency devices. In these measurements the pump wavelength is set to the absorbance characteristic of the dye ground state and the probe wavelength corresponds to dye cation absorption. Two different dyes have been studied; first a well studied ruthenium based inorganic dye coded Z907 and a second D-π-A organic dye, coded Y123 which yielded a power conversion efficiency of over 10%. The results show an ultrafast electron injection in subpicosecond and a very fast decay of signal until some picoseconds and another decreasing component which happens in some hundered picoseconds. The later behaviour is not observed in the measurements of mesoporous transparent model system. Also the electron injection has been studied in the presence of Iodide and cobalt based electrolyte. References [1] B.Wenger, "Effect of electronic and nuclear factors on the dynamics of dye-to-semiconductor electron transfer", EPFL-3447, 170 (2006). [2] E. Ghadiri, N. Taghavinia, S. M. Zakeeruddin, M. Grätzel, J-E. Moser, "Enhanced electron collection efficiency in dye-sensitized solar cells based on nanostructured TiO2 hollow fibers", Nano Lett. 10, 1632-1638 (2010). [3] K. Shankar, J. Bandara, M. Paulose, H. Wietasch, O. K. Varghese, C. A. Grimes, "Highly Efficient Solar Cells using TiO2 Nanotube arrays Sensitized with a Donor-Antenna Dye", Nano Lett. 6, 1654-1659 (2008).

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C119 - Chemically deposited polypyrrole-nanoparticle counter electrode for inorganic I-/I3- and organic T-/T2 dye-sensitized solar cells

Madsakorn Towannanga, Samuk Pimanpanga, Anongnad Thiangkaewa, Phikun Rutphonsana, Wasan Maiaugreea, Vittaya Amornkitbamrunga

a, Department of Physics, Faculty of science, Khonkaen university, Khon Kean, 40002, TH b, Integrated Nanotechnology Research Center, Khon Kaen University, Khon Kean, 40002, TH c, Thaialnd Center of Excellence in Physics, CHE, Ministry of Education, Bangkok, 10400, TH

Pure polypyrrole (PPy) and composited PPy-nanoparticles (multiwall carbon nanotube, Ni or TiO2) films were coated on the conductive glass by chemical deposition method. They were used as the dye-sensitized solar cell counter electrodes. The performance of polymer based dye-sensitized solar cells (DSSCs) is ~6.22% and ~2.81% for the I-/I3

- and T-/T2 electrolytes, respectively. The efficiencies increase greatly after nanoparticle incorporations for both electrolytes. PPy-MWCNTs DSSCs delivers the highest efficiency; ~6.56% and ~3.05% for the I-

/I3- and T-/T2 electrolytes, respectively. The improvement of the energy conversion efficiency

after nanoparticle incorporation is attributed to the enlargement of the active surface area and the reduction of the charge-transfer resistance at the electrolyte/counter electrode interface.

References [1] B. O'Regan and M. Grätzel, “A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films”, Nature 353 (1991) [2] J. Wu, Q. Li, L. Fan, Z. Lan, P. Li, J. Lin, S. Hao, "High-performance polypyrrole nanoparticles counter electrode for dye-sensitized solar cells", J. Power Sources, 181, 172-176 (2008). [3] S. Peng, Y. Wu, P. Zhu, V. Thavasi, S.G. Mhaisalkar, S. Ramakrishna, "Facile fabrication of polypyrrole/functionalized multiwalled carbon nanotubes composite as counter electrodes in low-cost dye-sensitized solar cells", J. Photochem. and Photobio. A: Chem., 223 97-102(2011).

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C120 - Conductive surfaces on coated papers by flexographical printing

Dimitar Valtakaria, Roger Bollströma, Mikko Tuominenb, Hannu Teisalab, Mikko Aromaac, Martti Toivakkaa, Jurkka Kuusipalob, Jyrki M. Mäkeläc, Jun Uozumid, Jarkko J. Saarinena

a, Laboratory of Paper Coating and Converting, Åbo Akademi, Porthaninkatu 3-5, Turku, FI-20500, Finland b, Paper Converting and Packaging Technology, Tampere University of Technology, Tampere, Finland c, Aerosol Physics Laboratory, Institute of Physics, Tampere University of Technology, Tampere, Finland d, Faculty of Engineering, Hokkai-Gakuen University, Sapporo, Japan

Printed electronics and intelligence have been under a growing interest since the start of the 21stcentury. Conventionally such applications have been produced on plastic films and glass. However, paper based electronics (1) has been studied recently, and it has been shown that simple, all-printed transistors can be made on multilayer coated paper (2). Paper has many advantages over the plastic films: it is made of renewable materials and it is cheap with tailorable surface properties. Our study concentrates on using flexographical printing with conductive inks, PEDOT:PSS or silver, on various coated paper grades to form large area conductive surfaces. Such conductive surfaces are needed, for example, in electrochromic displays and in solar cells. We use two different natural fibre based substrates: a multilayer pigment coated grade and a nanoparticle coated paperboard in comparison to traditional plastic film. The paperboard surface is functionalized by TiO2nanoparticles using a liquid flame spray (LFS) coating process. In LFS process liquid precursor of titanium (IV) isopropoxide (TTIP) is fed into a high temperature and velocity flame in which the metal salt evaporates and nucleates to form nanoparticles of the metal oxide. These nanoparticles can be collected on a paperboard surface in on-line process flow and they cover the whole surface passing under the flame (3). It is known (4) that ultraviolet (UV) illumination can be used to change the wettability of TiO2surfaces, and similar photocatalytic wettability conversion has been observed on TiO2nanoparticle coated paperboard surfaces from superhydrophobic (water contact angle (CA) over 150°) to superhydrophilic (water CA less than 20°).

Figure 1 Microscopic images of the flexographical Ag prints with 9 ml/m2 and 100 lines/cm (magnification 100x).

Here we report the effects of coating structure and surface wettability on formation of conductive surfaces. Tunable wettability of TiO2nanoparticle coated substrates has an effect on printability with water-based inks such as PEDOT:PSS as ink setting is poorer on superhydrophobic surface that is also observed from measured optical densities of the printed layers. We also report significantly higher conductivities with Ag ink on multilayer coated paper than with PEDOT:PSS conductive polymer.

Acknowledgements: This work has been funded by the Academy of Finland (grant no 250 122 & 256 263). JJS wishes to thank the Japanese Society for the Promotion of Science (JSPS) for a research grant (L-11537).We also wish to acknowledge Imerys Minerals Ltd., UK,

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Paramelt B.V., NL, StoraEnso, FI, and Basf, DE for providing materials used in the multilayer coated paper.

References [1] Tobjörk, D.; Österbacka, R.; “Paper electronics”. Adv. Mater. 23, 1935–1961 (2011). [2] Bollström, R.; Määttänen, A.; Tobjörk, D.; Ihalainen, P.; Kaihovirta, N.; Österbacka, R.; Peltonen, J.; Toivakka, M.; “A multilayer coated fiber-based substrate suitable for printed functionality”. Org. Electron. 10, 1020–1023 (2009). [3] Mäkelä, J. M.; Aromaa, M.; Teisala, H.; Tuominen, M.; Stepien, M.; Saarinen, J. J.; Toivakka, M.; Kuusipalo, J.; “Nanoparticle deposition from liquid flame spray onto moving roll-to-roll paperboard material”. Aerosol Sci. Technol. 45, 817–827 (2011). [4] Caputo, G.; Nobile, C.; Kipp, T.; Blasi, L.; Grillo, V.; Carlino, E.; Manna, L.; Cingolani, R.; Cozzoli, P. D.; Athanassiou, A. “Reversible wettability changes in colloidal TiO2 nanorod thin-film coatings under selective UV laser irradiation” J. Phys. Chem. C 112, 701–714 (2008).

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C121 - Decoupling Recombination Order and Electron Statistics in Dye Solar Cell Nonideality Measurements

Timo Peltola, Alison Walker

Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, GB

It is well-known that in many dye-sensitized solar cells open circuit voltage increases more than is expected based on the ideal diode equation. At present, the exact mechanism of this nonideality is unclear though several theories have been advanced. In general, these theories can be divided into two categories: In the first, the effective recombination order is less than 1 (a possible physical origin being recombination from trap states) [1].

Figure 1 a) Open circuit voltage as a function of relative light intensity measured from LED driver input voltage. b) Natural logarithm of photoelectrode charge transfer resistance against open circuit voltage. c) Natural logarithm of photoelectrode charge transfer resistance (measured at open circuit) against natural logarithm of relative light intensity. Measured cell sensitized by N719 dye with I-/I3- redox couple in ACN. m is nonideality factor for electron statistics, ã is recombination order, kB Boltzmann constant, T absolute temperature, q electron charge and ϕ relative light intensity. Measurements are roughly consistent with ã = 0.98 and m = 1.50.

The second set of theories assumes that electron statistics do not conform to the simple picture of Boltzmann distribution with fixed conduction band and redox energy levels [2]. Here, we show how to decouple these two effects and measure their contributions to the overall nonideality factor using impedance data. Preliminary experimental results seem to indicate that nonideality is caused by electron statistics rather than nonlinear recombination.

References [1] Bisquert, J.; Fabregat-Santiago, F.; Mora-Sero, I; Garcia-Belmonte, G.; Gimenez, S. "Electron Lifetime in Dye-Sensitized Solar Cells: Theory and Interpretation of Measurements". J. Phys. Chem. C 113, 17278–17290 (2009) [2] Jennings, J. R.; Ghicov, A.; Peter, L. M.; Schmuki, P.; Walker, A. B. "Dye-Sensitized Solar Cells Based on Oriented TiO2 Nanotube Arrays: Transport, Trapping, and Transfer of Electrons". J. Am. Chem. Soc. 130, 13364–13372 (2008)

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C122 - Efficient solid state dye sensitised solar cell based on PEDOT conducting polymer and organic dye

Amani Chamsc, Anders Hagfeldta, Leif Hägmanna, Erik Johanssona, Mohamed Jouinic, Lars Kloob, Christian Perruchotc, Yang Shena, Alan Sneddenb, Nick Vlachopoulosa, Lei Yanga

a, Uppsala University, Blixtgatan 11, Uppsala, 75431, Sweden b, Royal Institute of Technology, Division of Inorganic Chemistry, S-10044 Stockholm, Sweden c, University Paris Diderot, Sorbonne Paris Cité, ITODYS, UMR 7086, F-75205 Paris 13, France

In recent years solid-state dye-sensitised solar cells (DSCs) have attracted a considerable interest (1). However, the variety based on conducting polymers has not been extensively studied as compared to that containing low-molecular weight hole conductors (e.g. Spiro-OMeTAD). In this study we described a type of DSC based on PEDOT generated by in-situ photoelectrochemical polymerization in a 3-electrode cell from bis-ethylenedioxythiophene (bis-EDOT) monomer in organic solvent. The potential is maintained at a constant value vs. a suitable reference electrode (2). The advantage of polymers generated this way as compared to pre-formed polymers or low-molecular weight hole conductors is the easy infiltration of bis-EDOT precursors into the mesopores of dye-coated titanium dioxide. After polymerisation, the modified electrode was treated with organic solution containing LiN(CF3SO2)2 and tert-butyl pyridine for optimisation both short-circuit current and open-circuit potential. The counter-electrode is a layer of vacuum-evaporated silver directly on the polymer surface. The sensitizer is an organic charge-transfer dye (D35) based on triphenylamine conjugated to a cyanoacrylic acid attachment group. Using this mediator-free hybrid organic/inorganic fully solid-state device, efficient photovoltaic operation has been demonstrated under simulated AM1.5 light with good linearity of photocurrent vs. light intensity and open-circuit cell photopotential exceeding 0.6V. The performance was stable over several days. Electrochemical, current-potential, photocurrent spectroscopy, and optoelectronic (toolbox) measurements will be presented and discussed. References [1] Yang, L.; Cappel, U. B.; Unger, E. L.; Karlsson, M.; Karlsson, K. M.; Gabrielsson, E.; Sun, L. C.; Boschloo, G.; Hagfeldt, A.; Johansson, E. M. J. "Comparing spiro-OMeTAD and P3HT hole conductors in efficient solid state dye-sensitized solar cells". Phys. Chem. Chem. Phys. 2012, 14, 779-789. [2] Manseki, K.; Jarernboon, W.; Youhai, Y.; Jiang, K. J.; Suzuki, K.; Masaki, N.; Kim, Y.; Xia, J. B.; Yanagida, S.: Solid-state dye-sensitized solar cells fabricated by coupling photoelectrochemically deposited poly(3,4-ethylenedioxythiophene) (PEDOT) with silver-paint on cathode". Chem. Comm. 47,3120-3122(2011).

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C123 - Gradient TiO2 films employed to reduce the photocurrent losses in high performing DSCs with ionic-liquid-based electrolyte

Magdalena Marszalek, Aswani Yella, Hoi Nok Tsao, Leo-Philipp Heiniger, Shaik M. Zakeeruddin, Michael Grätzel Laboratory for Photonics and Interfaces, Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne-1015, Switzerland, CH

Dye sensitized solar cells with ionic-liquid-based electrolytes are systems particularly interesting for the practical applications due to their processability and long-term stability. Nevertheless, their performance is still lower than traditional DSC employing electrolytes with volatile solvents such as acetonitrile. The state-of-art ionic liquid based electrolyte1 is over 50 times more viscous than acetonitrile. Its viscosity is a source of issues that are challenging the manufacture of the highly efficient solar cell. Often one can observe losses in photocurrent when the cell is exposed to the full sunlight conditions. In a broad view, these are signs of inefficient regeneration of the system. Whether they stem from the sluggish mass transport between the dye/electrolyte interface and counterelectrode, or hindered redox reactions at either electrode it is still under debate. It is generally believed that a Grotthus-type mechanism has a high probability to occur in such a viscous medium, enabling electron hopping between neighbouring iodides, thus improving the charge transport. Hereby we want to present a study on the engineering of TiO2 layers in order to make the sensitized surface more accessible for the electrolyte. TiO2 pastes of various porosities and consisting of nanoparticles differing in size were studied in order to minimize the losses of the photocurrent in regards to the values feasible to obtain under 0.1 Sun illumination. The study was done using highly efficient dyes2 in order to test the ability of the devices to support a large number of injected electrons. Preliminary screening of different pastes allowed us to fabricate a gradient films with carefully chosen pastes, where the losses in photocurrent were marginal and high performance of the device was maintained at 1 Sun, exceeding 8 % power conversion efficiency (8.7% at 0.1 Sun). References [1] Bai, Y. et al., "High-performance dye-sensitized solar cells based on solvent-free electrolytes produced from eutectic melts". Nature Materials 7, 626-630 (2008) [2] Yella A. et al., "Porphiryn-sensitized solar cells with cobalt (II/II)-based redox electrolyte exceed 12 % efficiency". Science 334, 629-634 (2011)

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C124 - Improved photocurrents for p-type dye-sensitized solar cells using nano-structured nickel(II) oxide microballs

Satvasheel Powara, Qiang Wub, Amaresh Mishrac, Leone Spicciaa, Udo Bachd

a, School of Chemistry, Monash University, Clayton, Victoria 3800, Australia b, Key Lab of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China c, Institute for Organic Chemistry II and Advanced Materials, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany d, Department of Materials Engineering, Clayton, Victoria 3800, Australia

Low cost dye-sensitized solar cells (DSC) have attracted attention as an alternative to conventional solar cells1, 2. In the conventional DSC configuration high-efficiency DSSC photoanodes (n-DSC) are used and the photocurrent results from dye-sensitized electron injection into n-type semiconductor such as TiO2. Dye-sensitized photocathodes (p-DSC) operate in an inverse mode I.e. the electrons flow in the reverse direction. Electron transfer takes place from the valence band of p-type semiconductor to the photo-excited dye3. These photocathodes can be sandwiched together with photoanodes to produce tandem devices. According to Kirchhoff’s law, this type of solar cell gives higher voltages however it is limited by the lower current output of the p-type semiconductor based electrode. The highest photocurrent density reported to date for p-DSCs (5.48 mA/cm2) under simulated sunlight (1,000 W/m2, AM1.5) is significantly lower than those typically reported for high efficiency n-DSCs (17.66 mA/cm2).Due to the mismatch in the photocurrents generated by the two electrodes the highest reported tandem solar cell efficiency with such a configuration is limited to 2.42%4. Here we report highly crystalline nanostructured nickel(II) oxide microballs (NiO-μBs) developed for their use in p-type dye-sensitized solar cells (p-DSC). Photocathodes based on nanostructured microballs achieved improved photocurrent (7.0 mA/cm2) under simulated sunlight (AM1.5; 1,000 W/m2) and incident photon to electron conversion efficiency of up to 74% compared to pDSC devices reported to date.4-11 The improved photocurrents can be explained based on their high specific surface area and favorable optical properties. References [1] B. O'Regan and M. Grätzel, Nature, 1991, 353, 737-740. [2] M. Grätzel, Nature, 2001, 414, 338-344. [3] J. J. He, H. Lindstrom, A. Hagfeldt and S. E. Lindquist, J. Phys. Chem. B, 1999, 103, 8940-8943. [4] A. Nattestad, A. J. Mozer, M. K. R. Fischer, Y. B. Cheng, A. Mishra, P. Bäuerle and U. Bach, Nat. Mater., 2010, 9, 31-35. [5] E. A. Gibson, A. L. Smeigh, L. Le Pleux, J. Fortage, G. Boschloo, E. Blart, Y. Pellegrin, F. Odobel, A. Hagfeldt and L. Hammarstrom, Angew. Chem. Int. Ed., 2009, 48, 4402-4405. [6] L. Li, E. A. Gibson, P. Qin, G. Boschloo, M. Gorlov, A. Hagfeldt and L. C. Sun, Adv. Mater., 2010, 22, 1759-1763. [7] F. Odobel, L. Le Pleux, Y. Pellegrin and E. Blart, Accounts Chem. Res., 2010, 43, 1063-1071. [8] P. Qin, M. Linder, T. Brinck, G. Boschloo, A. Hagfeldt and L. C. Sun, Adv. Mater., 2009, 21, 2993-2997. [9] J. F. Shi, G. Xu, L. Miao and X. Q. Xu, Acta Phys.-Chim. Sin., 2011, 27, 1287-1299. [10] X. L. Zhang, F. Z. Huang, A. Nattestad, K. Wang, D. C. Fu, A. Mishra, P. Bäuerle, U. Bach and Y. B. Cheng, Chem. Commun., 2011, 47, 4808-4810. [11] P. Qin, J. Wiberg, E. A. Gibson, M. Linder, L. Li, T. Brinck, A. Hagfeldt, B. Albinsson and L. C. Sun, J. Phys. Chem. C, 2010, 114, 4738-4748.






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C125 - Low band-gap poly(arylenethienylene)s with benzothiadiazole units: Synthesis, characterization and application in polymer solar cells

Alessandra Operamollaa, Silvia Colellac, Roberta Musioa, Omar Hassan Omard, Mazzeo Marcob, Giuseppe Giglic, Pynalisa Cosmaa, Angela Agostiano*a, Gianluca M. Farinola*a, Francesco Babudri*a, Marinella Striccolie

a, Università degli Studi di Bari , Via Orabona 4, BARI, I-70126, IT b, CNR Istituto di Nanoscienze, NNL-Nano, Via Arnesano 16, Lecce, I-73100, IT c, Università del Salento, Via per Monteroni, Lecce, I-73100, IT d, CNR Istituto di Chimica dei Composti Organometallici, CNR-ICCOM, Via Orabona 4, BARI, I-70126, IT e, CNR Istituto per i Processi Chimici e Fisici CNR-IPCF, Via Orabona 4, BARI, I-70126, IT

Our research group has a long lasting activity in the synthesis of polyconjugated materials by means of organometallic methodologies (1). Recently we became interested in a class of poly-p-arylenes, made-up by a combination of oligothiophene blocks and benzene units, that showed very good chemical and physical characteristics and were employed in the fabrication of sensors (2). In this communication, we report the synthesis of arylene-thiophenes polymers P1 and P2 by means of the versatile Suzuki-Miyaura cross-coupling reaction between pinacol boronates of thiophene derivatives and aryl iodides. Electronpoor heteroaromatic units, like the benzothiadiazole unit were inserted in the polyconjugated chain to confer to the repetitive unit the push-pull effect that shifts the band-gap in the low energy region of the visible spectrum for their application in bulk-heterojunction solar cells.

Figure 1 Structures of polymer P1 and P2

The polymers adopted for the fabrication of polymer solar cells in combination with the electron acceptor PCBM (3). Electrochemical properties of blends of P1 and TiO2 nanorods are also shortly presented.

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C126 - Influence of the alkyl chains on the cobalt (II/III) redox-mediated dye

sensitized solar cells

Aswani Yella, Magdalena Marszalek, Micheal Graetzel Laboratory of Photonics and Interfaces, Ecole Polytechnique Fédérale de Lausanne, Station 6, LPI EPFL, CH-1015, Lausanne , Switzerland.

Dye-sensitized solar cell (DSC) technology1 is under intense investigation owing to its efficient conversion of sunlight to electricity, while its key active materials and device processing remain cost-effective in comparison with those of conventional inorganic semiconductor photovoltaics. Recently we have shown that electrolytes that rely on the Co(II)/Co(III) redox mediators can produce highhvalues for organic dyes2 and zinc porphyrins3; however, a similar performance with Ruthenium-based dyes at full sun has not yet been demonstrated. Open-circuit photovoltage (VOC) for devices employing the Co(II)/Co(III) mediator in conjunction with the Ruthenium dyes is not higher than that for devices using the I3

-/I- mediator, despite the more positive redox potentials of the Cobalt based redox mediators. This indicates that with the ruthenium dyes the recombination is faster when using the cobalt based redox mediator either due to an increased recombination rate constant or due to a relatively low-lying conduction band edge, which increases electron concentration for any given cell voltage and thus increasing the recombination flux. Herein we studied the influence of the alkyl chain barriers on the ruthenium dyes when used in combination with the ruthenium dyes. As was shown previously for the I3

-/I- based electrolytes, additives can be used to optimize the electrolyte composition and to improve the solar-cell performance. Effects of the different additives such as the pyridines and the lithium salts were also studied to see the influence on the charge recombination. References [1] O’Regan, B.; Grätzel, M. Nature 1991, 353, 737– 740 [2] H. N. Tsao, C. Yi, T. Moehl, J.-H. Yum, S. M. Zakeeruddin, M. K. Nazeeruddin,M. Grätzel, ChemSusChem, 2011, 4, 591 [3] Yella, A.; Lee, H.-W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E. W.-G.; Yeh, C.-Y.; Zakeeruddin, S. M.; Grätzel, M. Science 2011, 334, 629– 634

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C127 - Investigation of TiCl4 treatment on carrier dynamics in solid-state dye-sensitized solar cells studied by time-resolved spectroscopy

Arianna Marchioroa, Amalie Dualehb, Michael Grätzelb, Jacques-Edouard Mosera

a, EPFL , EPFL SB ISIC LPI GR-MO, Lausanne, 1015, CH b, EPFL , EPFL SB ISIC LPI, Lausanne, 1015, CH

Solid-state Dye-Sensitized solar cells (ssDSCs) are a promising and challenging alternative to conventional liquid DSCs based on volatile and/or corrosive liquid electrolytes.(1) Although these systems, which use organic hole-transport materials (HTM) such as spiro-OMeTAD, are now reaching 7% PCE,(2) additional efforts need to be invested in order to reach the same efficiencies as their liquid equivalent. It has been observed that the cell efficiency, both for liquid and solid devices, is increased by an additional treatment by TiCl4, which modifies the metal-oxide semiconductor surface.(3) The actual effect of this fabrication step on the solid-state cell and the mechanism involved, however, are still unclear. Based on kinetic studies obtained by femtosecond and nanonsecond transient absorption spectroscopy, this surface treatment was shown to affect the dynamics of all charge carriers in the cell compared to non-treated films: electron injection into the TiO2 following light excitation, hole injection from the oxidized state of the dye into the hole transport material and charge recombination. Herein, we propose a model describing the interaction at the interface between TiO2, the dye-sensitizer and spiro-OMeTAD. Results also emphasize the importance of controlling the contact at the heterojunction between the HTM and the sensitized semiconductor. References [1] Bach, U.; Tachibana, Y.; Moser, J.-E.; Haque, S. A.; Durrant, J.R.; Grätzel, M.; Klug, D.R. "Charge Separation in Solid-State Dye-Sensitized Heterojunction Solar Cells". J. Am. Chem. Soc. 121, 7445-7446 (1999). [2] Burschka, J.; Dualeh, A.; Kessler, F.; Baranoff E.; Cevey-Ha, N.-L.; Yi, C.; Nazeeruddin, M.K. and Grätzel, M. "Tris(2-(1H-pyrazol-1-yl)pyridine)cobalt(III) as p-Type Dopant for Organic Semiconductors and Its Application in Highly Efficient Solid-State Dye-Sensitized Solar Cells" J. Am. Chem. Soc. 133, 18042-18045 (2011). [3] Sommeling, P. M.; O'Regan, B. C.; Haswell, R. R.; Smit,H. J. P.; Bakker, N. J.; Smits, J. J. T.; Kroon, J. M. and J. A. M. van Roosmalen "Influence of a TiCl4 Post-Treatment on Nanocrystalline TiO2 Films in Dye-Sensitized Solar Cells". J. Phys. Chem. B, 110. 19191-19197 (2006).

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C128 - Kinetics at the illuminated dye/TiO2-electrolyte interface investigated by SECM

Carsten Doschea, Ushula Mengesha Tefashea, Wiebke Schultea, Kazuteru Nonomurab, Nikolaos Vlachopoulosb, Anders Hagfeldtb, Gunther Wittstocka

a, University of Oldenburg, Carl-von-Ossietzky-St. 9-11, Oldenburg, 0, DE b, Uppsala University, S-75105 Uppsala, SE

A new approach for the characterization of dye-sensitized photoelectrochemical electrodes using scanning electrochemical microscopy (SECM) has been developed [1-4]. SECM feedback (FB), substrate generation-tip collection (SG-TC) and redox competition (RC) modes coupled with chronoamperometric measurements were used to investigate dye regeneration reaction on cis-di(thiocyanato)-bis(2,2’-bipyridyl-4,4”-dicarboxylate) ruthenium(II) (N719)-sensitized TiO2 photoelectrochemical electrodes [5]. Bimolecular heterogeneous electron transfer (ET) kinetics for the reduction of photo-oxidized N719 cation by iodide was studied by measuring SECM approach curves in FB mode for various electrolyte compositions and significant variation in effective heterogeneous first order rate constant keff was obtained. The effective dye regeneration rate constant kox was determined with the help of theoretical approximation model. The kox depends on the inherent kinetics of N719/TiO2 film, the local accessibility of adsorbed dye molecules for incident light and iodide ions, the external mass transport conditions at the vicinity of interface and the internal mass transport within the sensitized film. The internal mass transport is inturn influenced by the diffusional shielding of dye cations, redox species and electrons by the electrolyte adsorption. SG-TC and RC modes allowed investigation of localized dye regeneration reaction by monitoring the current transients at the SECM probe positioned at a known distance above the N719/TiO2 film while the incident light was switched on and off. Furthermore, SECM characterization of more efficient cobalt complex based electrolyte was reported. References [1] Y. Shen, K. Nonomura, D. Schlettwein, C. Zhao, G. Wittstock, Chemistry - A European Journal 2006, 12, 5832. [2] Y. Shen, U. M. Tefashe, K. Nonomura, T. Loewenstein, D. Schlettwein, G. Wittstock, Electrochimica Acta 2009, 55, 458. [3] U. M. Tefashe, T. Loewenstein, H. Miura, D. Schlettwein, G. Wittstock, Journal of Electroanalytical Chemistry 2010, 650, 24. [4] F. Zhang, V. Roznyatovskiy, F.-R. F. Fan, V. Lynch, J. L. Sessler, A. J. Bard, Journal of Physical Chemistry C 2011, 115, 2592. [5] U. Mengesha Tefashe, K. Nonomura, N. Vlachopoulos, A. Hagfeldt, G. Wittstock, Journal of Physical Chemistry C 2012, 116, 4316.

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C129 - Measurements on Solid State Dye-Sensitized Solar Cells Utilizing Transparent Counter Electrodes

Kristofer Fredina, Rebecka Schölinb, Johan Oscarssonb, Erik Johanssonc, Håkan Rensmob

a, Applied Physical Chemistry, Royal Institute of Technology, SE b, Physics and Astronomy, Uppsala University, SE c, Physical Chemistry, Uppsala University, SE

Solid state dye-sensitized solar cells comprising conducting glass substrates as counter electrodes were fabricated. The samples were based on the commercially available hole conductor 4-((diethyl-amino)benzaldehyde-1,1)-diphenyl-hydrazone mixed with bis(trifluoromethane)sulfonamide lithium salt and the dye 3-(5-4-(diphenylamino)styryl)thiophen-2-yl)-cyanoacrylic acid (D5). By using a melt process to infiltrate the hole conductor and seal the device in one step the interface between the hole conductor and the glass substrates were found to be mechanically strong so that no additional sealing was required. The high transparency of the glass substrates allowed for measurements with light incident both through the working- and counter electrode. Various measurements regarding the photon to electron conversion and the current response to modulation of the light intensity were conducted.

Figure 1 Incident photon to current conversion efficiency for a solid state dye-sensitized solar cell with a thickness of ~ 0.5 µm for light incident through the working- (solid line) and counter electrode (dotted line).

The absorbed photon to current conversion efficiency reached 75% however the values for power conversion at higher light intensities were modest. This was explained by a lower collection efficiency at higher light intensities.

References [1] K. Fredin et al. manuscript in preparation

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C130 - Mixed-Valent Cyanometallate as Inorganic Redox Mediator for Dye-Sensitized Solar Cell

Iwona A. Rutkowska, Pawel J. Kulesza

Department of Chemistry, University of Warsaw, Krakowskie Przedmiescie 26/28, 00-927 Warsaw, PL A polynuclear electronically/ionically (redox) conducting mixed-valent inorganic material such as nickel (II) hexacyanoferrate(II,III), NiHCF, was considered for potential application as a redox mediator (charge relay) in dye-sensitized solar cell (DSSC). The NiHCF redox reactions were found fast and reversible not only when the system was studied as thin film exposed to an aqueous supporting electrolyte but also as bulk material (pasted powder) in solid state, i.e., in the absence of contact with external liquid electrolyte phase. Usefulness of NiHCF material was diagnosed using conventional electroanalytical approaches, solid-state voltammetric methodology, as well as the dynamic electrochemical impedance spectroscopy technique that permitted monitoring of impedance spectra under potentiodynamic conditions. The material was utilized in a mixed-valent state, i.e., as a mixture of K4NiII[FeII(CN)6] and K3NiII[FeIII(CN)6] in which iron(II) and iron(III) sites were at the 1:1 ratio. Under such conditions, dynamics of electron-hopping between mixed-valent iron sites was maximized. Our DSSC utilized cis–dithiocyanoatobis(4,4′-dicarboxylic acid-2,2′-bipyridine) ruthenium(II) dye (N3) adsorbed onto TiO2 semiconductor and NiHCF as redox mediator. Although performance of our DSSC was not optimized in terms of the NiHCF film thickness and morphology, as well as lower photocurrents in comparison to those characteristic of the iodine/iodide based DSSC were obtained, our system yielded readily fairly high open-circuit photovoltages on the level of 800 mV. An important issue was that the formal potential of NiHCF was more positive relative to the potential of the iodide/triiodide couple while being still more negative than that equivalent to the ground state of the N3 dye. Thus, NiHCF mediator was able to regenerate the dye.

References [1] Rutkowska, I.A.; Andrearczyk, A.; Zoladek, S.; Goral, M.; Darowicki, K.; Kulesza, P.J. "Electrochemical characterization of Prussian blue type nickel hexacyanoferrate redox mediator for potential application as charge relay in dye-sensitized solar cells", J. Solid State Electrochem. 15, 2545-2552 (2011)

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C131 - Modelling charge transport in TiO2 film and electrolyte in a dye-sensitized solar cell

Alison Walkeraa, Laurence Peterb

a,University of Bath, Department of Physics, University of Bath, Bath BA2 7AY, UK b, University of Bath, Department of Chemestry, University of Bath, Bath BA2 7AY, UK

To date, most electrical transport studies in dye-sensitized solar cells, DSC, have focussed on electron transport in the TiO2 film. However, the performance of dye-sensitized cells (DSC) is also influenced by the rate of electron transfer at the counterelectrode and the rates at which reactants and products are transported to and from this electrode. I will present an extension of coupled electron-ion transport models [1],[2] to discuss the influence of the overpotential at the counterelectrode and diffusion limited currents arising from the need to conserve the number per unit area of iodide and tri-iodide ions.

References [1] Barnes,P.R.F; Anderson A.S.Y.; Durrant, J.R.;O'Regan, B.C. 'Simulation and measurement of complete dye sensitised solar cells' Phys Chem Chem Phys 13 5798 (2011) [2] Gagliardi, A; Mastroianni, D; Giordano, F; Reale, A; Brown, T.M.; Di Carlo, A. 'Multiscale Modeling of Dye Solar Cells and Comparison With Experimental Data' IEEE JSTQE, 16 1611 (2010)

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C132 - New polylinkers for low temperature annealed titania layes of dye synthesized solar cells

Dmitri Godovskya, Natalia Golubkoc, Yulianna Roginskayac, Anastasia Ozimovad, Dmitri Paraschukd

a, LG TCM, LG Electronics, Paveletskaya sq.2/3, Moscow, RU b, INEOS RAS, Vavilova st., 28, Moscow, RU c, Karpov Institute of Physical Chemistry, Vorontsovo Pole str.,10, Moscow, RU d, Moscow State University, Vorobievy Gory, 1, Moscow, RU

For the mass production of the dye type solar cells on flexible plastic substrates, like Polyethyleneterephtalate (PET) , the low temperature annealing (180-220oC) of titania is necessary, which would be compatible with plastics. Unfortunately standard procedure of titania preparation for DSSC requires 450oC and is not suitable for use with plastics, therefore special methods should be developed to allow lower temperature annealing ceramics to be prepared. The special polylinkers - binding agents, which are mixed with anatase titania were developed by us, which allow for making the dye type solar cells using low temperature annealing process (150-250oC). For the preparation of the precursor solutions titanium bytilate - Ti(OC4H9)4 and methylcellosolvate of titanium were used [1]. Layers were prepared using spin coating onto ITO-covered glass or plastic substrates.The preparation of layers consisted in temperature programmed annealing of titania layers, containing anatase nanoparticles (25 nm, Aldrich) and polylinker. The porous structure with channels, passing throughout the whole layer of titania is obtained as a result. Final layers thickness was around 10 microns. Afterwards, the standard procedure of dye type solar cell preparation was followed, using standard Ruthenium-type dyes N519 (Solaronix Co.), I-/I3- Iodolyte electrolyte (Solaronix Co.) and Platisol platinum pase (Solaronix Co.) . The best power conversion efficeincies, obtained on the non-optimized cells with the size 15 x 15 mm were in the range 1-1,5 % under AM 1,5 1 Sun conditions.

References [1] Russian patent application RU221645/20110807

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C133 - Photocapacitors based on solid state dye solar cells and metal oxide charge-storage materials

Katarzyna Grzejszczykb, Anders Hagfeldta, Leif Häggmana, Erik Johanssona, Pawel Kuleszab, Magdalena Skunikb, Nick Vlachopoulos*a, Lei Yanga

Diminishing reserves of fossil fuels as well as their high prices and their damaging effect on the environment force the intense development of alternative, environmentally friendly sources of energy. Therefore in recent years there is a growing interest in solar-energy conversion by photovoltaic cells which convert sunlight directly into electricity. However the intermittent nature of sunlight availability requires another device in conjunction with solar cell to storage of produced electricity. One important option is electrochemical storage by means of a secondary battery, where energy is stored inside the cell, or an electrolysis cell, where the products, usually hydrogen and oxygen, are externally stored [1]. Here we present a novel, interesting approach which is the direct storage of electric energy generated by light in high power, photo-rechargeable electrochemical supercapacitor (photocapacitor) integrated with a dye-sensitized solar cell (DSC) as one device. A three-electrode configuration whose concept was firstly proposed by Miyasaka [1] will be considered here, where bipolar electrode separates a solid-state solar cell and a supercapacitor element. An organic charge-transfer dye chemisorbed on a mesoporous TiO2 electrode is in contact with a poly(3-hexylthiophene) (P3HT) conducting polymer layer; the intermediate (bipolar) electrode is an evaporated Ag layer, which also serves as a support for one of the charge–storage layers.

Figure 1 Three-electrode photocapacitor.

The charge-storage supercapacitor layers on the intermediate electrode and the counterelectrode consist of ruthenium oxide separated by a proton-conducting polymer layer. Those materials are first examined in a symmetrical capacitor configuration by various electrochemical techniques. Then they are incorporated into a DSC-supercapacitor cell and exposed to AM1.5 simulated white light. Charging voltage, specific capacitance and energy

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storage efficiency for a complete photocharge-dark discharge cycle under constant current have been obtained.

References [1] Murakami, T.N.; Kawashima, N.;, Miyasaka, T. "A high-voltage dye-sensitized photocapacitor of a three-electrode system" Chem. Comm. 3346-3348, (2005)

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C134 - Quantum chemical calculations of transient L-edge X-ray spectra of Transition Metal complexes

Ida Josefsson, Michael Odelius

Fysikum, Stockholm University, FYSIKUM, Albanova, Stockholm University, 106 91 Stockholm, SE In many important applications, the active chromophores have transition metal centers, such as the metalloorganic complexes employed in artificial photo-synthesis or dye-sensitized solar-cells, for which L-edge X-ray spectroscopy contains valuable electronic information on the chemical bonding. In L-edge X-ray absorption (XA) and resonant inelastic X-ray scattering (RIXS) of transition metal compounds, core-excitations from the 2p levels into the d-levels, and the subsequent fluorescence decay back into the core-hole, can be monitored. Thereby, we can obtain a complete mapping of the electronic valance responsible for the chemical bonding and photo-chemistry. An ab initio approach to L-edge(2p -> 3d) X-ray spectroscopy is presented [1] and the quality is demonstrated by direct comparison to experimental data for a series of transition metal compounds, and discussed in relation to the electronic structure in both dye molecules and hole-conductors. The partial fluorescence yield XA spectrum can obtained as a sum over all fluorescence decay path-ways from the resonant inelastic X-ray scattering (RIXS) map. In the RIXS map, we can determine the relation between valence-excitations(Energy loss axis) and core-excitations(Excitation energy axis) and extract a detailed picture of the 3d valence electronic structure, including explicit information on the molecular orbitals.

Figure 1 Simulated Ni L-edge X-ray spectra of Ni2+(aq).The calculated X-ray absorption (XA) spectrum is evaluated against experimental data in 1 M NiCl2(aq) solution. The full resonant inelastic X-ray scattering map can be derived from the calculations.

Time-resolved XA and RIXS combined with a reliable theoretical analysis can by used to study changes in the local electronic structure at femto-second resolution in reaction sites in biochemical processes or in situ in working photovoltaic devices [2]. References *1+ I. Josefsson, K. Kunnus, S. Schreck, U. Wahlgren, F. de Groot, P. Wernet, and M. Odelius, “Ab initio L-edge x-ray spectra Multiconfigurational SCF calculations of L-edge x-ray spectra of Ni2+(aq),”. unpubl. (2012). [2] C. Bressler and M. Chergui, “Ultrafast X-ray Absorption Spectroscopy,”. Chem. Rev. 104, 1781 (2004).

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C135 - Self-Assembling a Water-Soluble Polythiophene derivate with Cationic Porphyrins for Application in Organic Solar Cells

César A. Henriques, Sara M. Pinto, Hugh D. Burrows, Mariette M. Pereira, Mário J. F: Calvete, Carlos Serpa

a, Chemistry Department, University of Coimbra, 3004-535 Coimbra , PT

Organic solar cells have potential application in flexible, light weight and large area energy-harvesting devices. Those devices have attracted much attention owing to their advantages of low-cost fabrication by solution processing and to open possibilities of chemical tailoring. Bulk heterojunction devices are fabricated by blending organic electron donor and acceptor materials in the same organic solvents.1 Most effort has been focused on developing new donor materials with low optical band gap, high hole mobility and sufficient solubility, which can lead to efficient solar cells. Polythiopheneconjugated polymers are the donor materials of choice for application in photovoltaic cells.2 Porphyrin macrocycles appear as good acceptor materials because they contain an extensively conjugated two-dimensionalp-systems which renders suitable light-harvesting, efficient electron transfer and the uptake or release of electrons, while showing minimal structural change.1

Figure 1

In this communication we present the fluorescence quenching and laser flash photolysis studies to probe the interaction between self-assembled water-soluble sodium poly[2-(3-thienyl)ethyloxy-4-butylsulfonate] and cationic porphyrins. We have studied the effect of the number of charges and presence of bulky lateral chains in the porphyrin template on the quenching interaction involving self-assembled oppositely charged materials. As the presence of surfactant modifies the polymer morphology in solution3 we also studied the effect of the presence of pentaethylene glycol monododecyl ether on the polymer excited state quenching processes by both porphyrins.

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References [1] Zhan H., Lamare S., Ng A., Kenny T., Guernon H.. Chan W.-K., Djurisic A. B., Harvey P. D., Wong W.-Y. ”Synthesis and Photovoltaic Properties of New Metalloporphyrin-Containing Polyplatinyne Polymers” Macromolecules 44, 5155-5167(2011). [2] Pinto S. M., Burrows H. D., Pereira M. M., Fonseca S. M., Dias F. B., Mallavia R., Tapia M. J. J. Phys. Chem. B 113, 16093-16100 (2009) [3] Laurenti M., Rubio-Retama J., Garcia-Blanco F., López-Cabarcos E. “Influence of the Surfactant Chain Length on the Fluorescence Properties of a Water-Soluble Conjugated Polymer” Langmuir 24, 13321-13327 (2008).

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C136 - Synthesis and Properties of an Asymmetric Binuclear Ruthenium Polypyridine Dye

Tiago A. Matias, André Luís A. Parussulo, Sérgio H. Toma, Koiti Araki, Henrique E. Toma

Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, S˜ao Paulo, CEP 05508-000, Brazil

Supramolecular approach has been used to design more efficient photosensitizers for Dye Sensitized Solar Cell (DSSC) with capable to harvest light by photoinduced charge separation, higher absorptivity in the visible/infrared range thanks to antenna effect and electron-transfer processes to enhance photoinduced charge separation, associated with slower charge recombination processes.1 Previously we described the symmetric binuclear complex Na6[[Ru(dcbpy)2Cl2(BPEB)] (dcbpy=2,2'-bipyridine-4,4'-dicarboxylate and BPEB=trans-1,4-bis[2-(4-pyridyl)ethenyl]benzene) which exhibited good photoelectrochemical properties.2 Here we focused on the asymmetric binuclear species [RuCl(dmbpy)2]-BPEB-[RuCl(dcbpyH2)2](PF6)2 (dmbpy=4,4’-dimetil-2,2’-bipyridine) containing a donor [RuCl(dmbpy)2] and acceptor [RuCl(dcbpyH2)2] moieties. BPEB is a π-conjugated bridging ligand allowing intramolecular electron-transfer or energy-transfer processes2 increasing solar-to-electrical energy conversion efficiency in dye sensitized solar cells, DSSCs. The [RuCl(dmbpy)2(BPEB)](PF6) and the binuclear species were successfully prepared using a similar procedure to literature.3 ESI-MS spectrum of the binuclear species showed a molecular ion peak in m/z=707.1 (Δm/z=0,5 Figure1A) and the daughter ion fragments [RuCl(dcbpyH2)2(BPE)]1+m/z=909.0, [RuCl(dmbpy)2(BPE)]1+m/z=789.2 and [RuCl(dmbpy)2]

1+m/z=505.0 as expected for the MS+ spectrum. The [RuCl(dmbpy)2(BPEB)] exhibited absorption bands at 295 and 355nm, ascribed to dmbpy and BPEB intraligand transitions (Figure1B),3 and metal-to-ligand charge transfer (MLCT) bands at 421 and 488nm.3 The binuclear species exhibited bands at 295, 316 and 355nm ascribed to intraligands transitions in the dmbpy, dcbpyH2 and BPEB, respectively, and the charge transfer bands at 419 and 499nm. These were broadened and intensified by the contributions of the MLCT bands of both, the [RuCl(dcbpyH2)2(BPEB)] and [RuCl(dmbpy)2(BPEB)] moieties. The [RuCl(dmbpy)2(BPEB)](PF6) showed two reversible ligand reduction processes at E1/2= -1.33 and -1.52V and the characteristic Ru(III/II) process at E1/2=0.80V.3 The binuclear complex exhibited two reversible Ru(III/II) processes at E1/2=0.84 and 1.28V respectively assigned to the [RuCl(dmbpy)2] and [RuCl(dcbpyH2)2] bridged by BPEB (Figure1D).

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Figure 1 ESI-MS spectrum of the binuclear species (A), the absorption spectra in dimethylformamide (B), the HOMO and LUMO orbitals (C) and CVs in 0.1 mol L-1 (n-Bu4N)ClO4 in DMF, using Pt-disk working and Ag/AgNO3(0.010M in acetonitrile) reference electrode (D).

Molecular modeling using ZINDO/S and Molecular Mechanics2 showed that visible bands were charge-transfer transitions centered on the [RuCl(dmbpy)2(BPEB)] and [RuCl(dcbpyH2)2(BPEB)] moieties. Also, the LUMO is centered on the dcbpy and BPEB π*-orbitals (Figure1C) which may allow RuII(dmbpy)2Cl-to-dcbpy(π*) charge-transfer transitions. A careful analysis of the spectrum showed that dmbpy complex has a slightly higher MLCT excited state than the dcbpy complex allowing energy transfer processes. In addition, the HOMO is localized on the [RuCl(dmbpy)2(BPEB)] complex, confirming the oxidation of the dmbpy complex at lower potentials than the dcbpy complex. Thus, the holes generated by electron injection from the [RuCl(dcbpyH2)2(BPEB)] moiety can be rapidly transferred to the [RuCl(dmbpy)2(BPEB)+ group (∆E=0.44V) which potential is suitable for fast hole transfer to the redox electrolyte, thus inhibiting electron-hole recombination processes.

References [1] Argazzi, R.; Murakami Iha, N. Y.; Zabri, H.; Odobel, F.; Bignozzi, C. A., "Design of molecular dyes for application in photoelectrochemical and electrochromic devices based on nanocrystalline metal oxide semiconductors". Coord. Chem. Rev. 248(13–14),1299-1316(2004). [2] Nogueira, A. F.; Toma, S. H.; Vidotti, M.; Formiga, A. L. B.; Cordoba de Torresi, S. I.; Toma, H. E., "A highly efficient redox chromophore for simultaneous application in a photoelectrochemical dye sensitized solar cell and electrochromic devices". N. J. Chem. 29(2),320-324(2005). [3] Toma, S. H.; Uemi, M.; Nikolaou, S.; Tomazela, D. M.; Eberlin, M. N.; Toma, H. E., "trans-1,4-Bis[(4-pyridyl)ethenyl+benzene(2,2‘-bipyridine)ruthenium(II) Complexes and Their Supramolecular Assemblies with β-Cyclodextrin". Inorg. Chem. 43(11),3521-3527(2004).

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C137 - Temperature dependence of transport-properties of spiro-MeOTAD as a hole-conductor in solid-state dye-sensitized solar cells

Amalie Dualeh, Thomas Moehl, Mohammad K. Nazeeruddin, Michael Grätzel Ecole Polytechnique Federale de Lausanne, Station 6, EPFL-SB-ISIC-LPI, Lausanne, 1015, CH In solid-state dye-sensitized solar cells the liquid electrolyte is replaced by a solid hole–transport material (HTM) to improve the processability and long-term stability of the devices. As such it is vital to gain a thorough understanding of the transport-properties of the chosen HTM to determine the resulting impact on the device performance. Electrical impedance spectroscopy (EIS) is a useful technique to investigate the internal electrical processes occurring at different conditions of steady-state in the dark of complete devices. In this work the internal transport and recombination parameters of ssDSCs using the HTM 2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)-9,9’-spirobifluorene (spiro-MeOTAD) were studied using EIS. Recent studies investigated the charge-transport properties of thin films of thermally evaporated spiro-MeOTAD [1,2]. Conversely, here we examined the properties in actual working configuration. To achieve this, ssDSC-like devices were fabricated using flat and nano-structured TiO2 and compared to devices using nano-structured ZrO2 to differentiate between the transport processes within the different elements in the ssDSC. The effect of chemical p-doping the HTM on the transport within the HTM was investigated and its temperature dependence was examined and analyzed using the Arrhe- nius equation. Using this approach the activation energy for the hole–hoping transport within the spiro-MeOTAD films was determined.

References [1] Rana, O.; Srivastava, R.; Grover, R.; Chauhan, G.; Bawa, S. S.; Zulfequar, M.; Husain, M.; Kamalasanan, M. N.; "Charge Transport Study of 2,2’,7,7’-Tetrakis( N, N-di-4-methoxyphenyl amino)-9,9’- spirobifluorene Using Impedance Spectroscopy". Jpn. J. Appl. Phys. 50, 061601 (2011). [2] Rana, O.; Srivastava, R.; Grover, R.; Zulfequar, M.; Hu- sain, M.; Kamalasanan, M. N.; "Charge transport studies in thermally evaporated 2,2,7,7-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9- spirobifluorene (spiro-MeOTAD) thin film". Syn. Metals 161, 828–832 (2011).

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C138 - The Application and Physical Properties of DCDHF dyes in Organic Photovoltaics

Kenrick Andersona, Emily Borderb, Timothy Jonesa, Clint Woodwardb, Gregory Wilsona, Christopher Fella

a, CSIRO Energy Technology, Mayfield West, NSW 2304, AU b, CSIRO Energy Technology, Clayton South, Vic., 3169, AU

Solution processed deposition of organic solar cells (OSCs) make them attractive for large scale/volume production. Typically a blend of poly (3- hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) are used yet a competitive approach utilising small molecular light absorption chromophores can afford well-defined molecular structures, ease of purification and enhanced batch-to-batch reproducibility. Early trials with triphenylamine-based donor-acceptor (D–A) materials achieved power conversion efficiencies of approx. 2.2%. Recently, L-Y. Lin et al. described a donor–acceptor–acceptor (D–A–A) donor molecule, coded DTDCT, exhibiting λmax= 663 nm and a large εof 42 × 103 M–1 cm–1 achieving a record-high power conversion efficiency (PCE) of 5.81% for bulk heterojunction (BHJ) devices. [1] Comparatively, the use of novel donor–p-spacer–acceptor (D–pi–A) chromophores, based on the dicyanomethylenedihydrofuran (DCDHF) acceptor functional group, where the acidic anchor is de-coupled from the acceptor fragment have been reported for OSCs based on the dye-sensitised solar cell (DSC) architecture. Y. Hao et al. have reported a series of (D–p–A) structures based on the DCDHF acceptor, with lateral, de-coupled, anchoring groups exhibiting promising light harvesting (HY103, ε = 66 × 103 M–1 cm–1λmax= 610 nm, PCE of 2.45%) and charge collection extending into the NIR. [2] Clearly there are synergies between the complementary architectures of the DSC and that of BHJ organic photovoltaics (OPV). These small molecular chromophores are compact, readily synthesised in high yield, have high extinction coefficients (>60 × 103 M–1 cm–1) and exploit through space pi→ pi* electron transfer from the oxidised DCDHF moiety to the titania surface – not unlike the intermolecular electron transfer observed for BHJ solar cells. The molecular configuration in D–pi–A dyes readily facilities further de-coupling of light absorption and electron transfer giving the ability to ‘tune’ molecular fragments – a vital optimisation step in design of component materials for BHJ devices. Here we present a study on promising derivatives of the DCDHF moiety. These chromophores possess ε in the range 50–100 × 103 M–1 cm–1 extending into the NIR. For this study, DCDHF derivatives were blended with PCBM and fabricated using a BHJ architecture yielding reasonable device performance. Preliminary device optimization was performed and the two chromophores compared and contrast for device/optical properties, correlated to TD-DFT calculations and the most promising of these devices was demonstrated in a 10cm × 10cm mini-module. References [1] L-Y. Lin, Y-H Chen, Z-Yu Huang, H-W. Lin, S-H. Chou, F. Lin, C-W. Chen, Y-H. Liu, and K-T. Wong, J. Am. Chem. Soc., 2011, 133 (40), 15822 [2] Y. Hao, X. Yang, J. Cong, H. Tian, A. Hagfeldt, L. Sun, Chem. Comm. (2009) 4031.

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C139 - The electronic structure of I3- in aqueous solution

Ida Josefssona, Susanna K. Erikssonb, Niklas Ottossonc, Gunnar Öhrwallc, Anders Hagfeldtb, Håkan Rensmoc, Olle Björneholmc, Michael Odeliusa

a, Fysikum, Stockholm University, Albanova, 106 91 Stockholm, SE b, Department of Chemistry, Ångström,, Box 530, 752 21 Uppsala, SE c, Department of Physics and Astronomy, Box 530, 752 21 Uppsala, SE The energy level matching in the photovoltaic cycle is crucial for the performance of the dye-sensitized solar cell (DSC). An efficient cell needs a hole conductor characterized by fast regeneration of the oxidized dye and slow recombination kinetics. The I-/I3- redox couple in an organic solvent is commonly used. However, it is desirable to find alternatives to organic electrolytes. A detailed knowledge of the molecular and electronic structure is important for our understanding of the processes in the DSC. With photoelectron spectroscopy (PES), element and site specific electronic structure information of the components in the complex system can be obtained. Theoretical calculations, such as molecular dynamics simulations of solvation structures and spectrum simulations, provide valuable information for interpretation of the experimental spectra (1).

Figure 1 Snapshot of I3-(aq) from ab initio MD simulation. The simulations shows large differences in the hydrogen-bonding network around the terminal iodine atoms, coupled to distortions in the I - I bond distances.

Here we present a study on I3-(aq), where experimental PE spectra together with ab initio

molecular dynamics simulations and high-level quantum chemical calculations indicate large fluctuations in the I - I distances (2). These couple to the hydrogen bond dynamics and lead to transient highly distorted configurations that can be described as partially dissociated into I- and I2 . References [1] Schiffmann, F.; VandeVondele, J; Hutter, J; Urakawa, A; Wirz, R; Baiker, A. "An atomistic picture of the regeneration process in dye sensitized solar cells". Proc. Natl. Acad. Sci. U. S. A., 107(11), 4830–4833 (2010) [2] Josefsson, I; Kaufmann-Eriksson, S; Ottosson, N; Öhrwall, G; Björneholm, O; Hagfeldt, A; Rensmo, H; Odelius, M "Ab initio molecular dynamics simulation of I3-(aq)", Unpub. (2012)

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C140 - The influence on annealing condition for ZnO nanoparticle based Dye Sensitized Solar Cells

Gang Wanga, Ka Kan Wonga, Yip Hang Nga, Yu Hang Leunga, Aleksandra B. Djurisica, Wai Kin Chanb

a, Department of Physics, The University of Hong Kong, Rm 314, Chong Yuet Ming Physics Building, The University of Hong Kong, Pokfulam Road, Hong Kong b, Department of Chemistry, The University of Hong Kong, Rm 403, Chong Yuet Ming Chemistry Building, The University of Hong Kong, Pokfulam Road, Hong Kong

Numerous metal oxide semiconductors such as titanium oxide (TiO2), zinc oxide (ZnO) and tin oxide (SnO2) have been studies extensively as a photoelectrode in dye sensitized solar cells (DSSCs). It is also known that TiO2 has exhibited the highest efficiency among the metal oxide semiconductors (1). ZnO has promising to be an alternative candidate because of similarity of bandgap and electronic properties of TiO2, although the efficiency is much lower than TiO2. Annealing conditions are known to affect the performance of both ZnO- and TiO2-based DSSCs (2, 3). Annealing also affects the nature defects in ZnO (4), and nature defects have been shown to affect the cell performance (5). Here we investigated the effect on ZnO DSSC performance under various annealing conditions by current-voltage measurement, photoluminescence measurement as well as electrochemical impedance spectroscopy (EIS). We found that the ZnO defect, EIS spectrum as well as cell performance are strongly affected by annealing condition at 400 oC, 600 oC and 800 oC. Detailed discussion of optical and electrochemical properties will be given. References [1] Chiba, Y.; Islam A.; Watanabe, Y.; Komiya, R.; Koide, N.; Han L. "Dye-Sensitized Solar Cells with Conversion Efficiency of 11.1%". Jpn. J. Appl. Phys. 45, L638-L640 (2006). [2] Lu, L.; Li, R.; Fan, K.; Peng, T. "Effects of annealing conditions on the photoelectrochemical properties of dye-sensitized solar cells made with ZnO nanoparticles". Sol. Energy 84, 844-853 (2010). [3] Zhao, D.; Peng, T. Y.; Lu, L. L.; Cai, P.; Jiang, P.; Bian, Z. Q. "Effect of Annealing Temperature on the Photoelectrochemical Properties of Dye-Sensitized Solar Cells Made with Mesoporous TiO2 Nanoparticles". J. Phys Chem. C., 112, 8486-8494 (2008). [4] Djurisic, A. B.; Leung, Y. H.; Tam, K. H.; Hsu, Y. F.; Ding, L.; Ge, W. K.; Zhong, Y. C.; Wong, K. S.; Chan, W. K.; Tam, H. L.; Cheah, K. W.; Kwok W. M.; Phillips, D. L. "Effect emissions in ZnO nanostructures". Nanotechnology 18, 095702 (2007). [5] Wong, K. K.; Ng, A.; Chen, X. Y.; Ng, Y. H.; Leung, Y. H.; Ho, K. H.; Djurisic, A. B.; Ng, A. M. C.; Chan, W. K.; Yu, L.; Phillips, D. L. "Effect of ZnO Nanoparticle Properties on Dye-Sensitized Solar Cell Performance". ACS Appl. Mater. Interfaces 4, 1254-1261 (2012).

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C141 - A Joint Experimental and Theoretical Approach for Probing Interfaces in Quantum Dot Sensitized Solar Cells

Johannes T. Margrafa, Vito Sgobbaa, Tim Clarkb, Dirk M. Guldia

a, Friedrich-Alexander-Universität Erlangen-Nürnberg, Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Egerlandstraße 3, 91058 Erlangen, DE b, Computer-Chemie-Centrum, Nägelsbachstraße 25, 91058 Erlangen, DE

Quantum dot sensitized solar cells (QDSSCs) are currently emerging as a promising candidate for a cheap and efficient third generation photovoltaic technology owing to their potentials with respect to tackling typical shortcomings of dye-sensitized solar cells (DSSCs) ranging from lifetimes to light-harvesting.[1] Nevertheless, their efficiencies are still below 5%. A likely rationale is that optimum cell architectures including linker, electrolyte, counter electrode, and cell assembly process, have not been found yet. In the current work, we have pursued of a joint experimental and theoretical study to shed light on the nature of the linker to govern the QDSSCs features. To this end, we compared QDSSCs, in which either cysteine (Cys) or mercaptopropionic acid (MPA) were employed as linkers. In accordance with recent results, we have found higher photocurrents for Cys based QDSSCs at comparable QD loadings.[2] This fact was further corroborated by using periodic DFT calculations of linkers adsorbed onto a TiO2 anatase (101) surface. Important is the zwitterionic adsorption geometry of Cys, which was found to be significantly more stable than a regular geometry, in which a TiO2 surface O-atom is protonated. In fact, the zwitterionic geometry results in a favorable dipole moment at the QD/TiO2 interface. Complementary IR-spectroscopic analyses confirm doubtlessly that the zwitterionic geometry is operative. Impelled by aforementioned results, we adsorbed Cys from aqueous solutions that were adjusted to a pH 6. The corresponding cells revealed efficiencies of 1.4%. Please compare this to the best previously published Cys-based QDSSC, which reached efficiencies of around 0.61%.[2] Our findings indicate that the selected conditions correlate with the isoelectric point of Cys and the point of zero charge of TiO2-anatase electrode. As a matter of fact, electrostatic repulsions between the two are minimized. Furthermore, using aqueous solutions rather than organic solvents allows employing higher Cys concentrations. As a consequence, an amelioration of the overall device performance due to higher QD loading was achieved. References [1] Yang, Z.; Chen, C.; Roy, P.; Chang, H. "Quantum dot-sensitized solar cells incorporating nanomaterials". Chem. Commun., 47, 9561-9571 (2011). [2] Guijarro, N.; Shen, Q.; Giménez, S.; Mora-Seró, I.; Bisquert, J.; Lana-Villarreal, T.; Toyoda, T.; Gómez, R. "Direct Correlation between Ultrafast Injection and Photoanode Performance in Quantum Dot Sensitized Solar Cells". J. Phys. Chem. C, 114, 22352–22360 (2010).

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C142 - Benzoporphyrins as novel light-harvesting dyes for dye-sensitized solar cells (DSSCs)

Fabian Lodermeyera, Rubén D. Costaa, Jenny Maligb, Norbert Juxb and Dirk M. Guldia

a, Friedrich-Alexander-Universität Erlangen-Nürnberg, Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Egerlandstrasse 3, 91058, Erlangen, Germany. b, Friedrich-Alexander-Universität Erlangen-Nürnberg, Department of Organic Chemistry II, Henkestraße 42, 91054 Erlangen, Germany.

Dye-Sensitized Solar Cells (DSSCs) represent one of the most promising solar energy conversion devices owing to their high efficiencies as well as their cheap and low-energy productions.[1] To this end, porphyrins evolved as encouraging chromophores due to their high extinction coefficients in the visible and the near-infrared regions of the solar spectrum.[2] As a matter of fact, recent DSSCs based on porphyrins have revealed efficiencies exceeding 13 %.[3] A platform of novel porphyrins, which has yet not been tested in DSSCs, are benzoporphyrins. Benzoporphyrins feature extended conjugated p-systems and, as consequence, their absorptions red-shift with respect to that known for porphyrins.[4] Hence, benzoporphyrins emerge as promising dyes in organic photovoltaics. Herein, we document the synthesis, photophysical, and electrochemical characteristics of four different benzoporphyrins – [Figure 1] – as well as their implementation into TiO2-based DSSCs. Particular emphasis has been paid on one of the most important bottlenecks when employing extended p-conjugated chromophores in DSSCs, that is, the formation of aggregates in solutions and in the solid state. Most importantly, aggregation has been shown to exert a detrimental effect on the device performance.[5]

Figure 1 Snapshot of I3-(aq) from ab initio MD simulation. The simulations shows large differences in the hydrogen-bonding network around the terminal iodine atoms, coupled to distortions in the I - I bond distances.

To optimize device efficiency, time-dependent adsorption assays with four different benzoporphyrins on TiO2-based DSSCs and with different TiO2 electrodes were performed. In the context of the latter, transparent TiO2-layer with and without a light scattering TiO2-layer was utilized. To this end, the optimum adsorption time at the different electrodes was established. In terms of device performance, the best values were obtained with a cisZn benzoporphyrin, a 16 h adsorption time, and a double-layer electrode. References [1] Pagliaro M.; et al. "Flexible Solar Cells". Wiley-VCH, (2008).

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[2] Torres T.; et al. "Lighting porphyrins and phthalocyanines for molecular photovoltaics". Chemical Communications. 46(38), 7090-7108 (2010). [3] Yella A.; et al. "Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency". Science, 334(6056), 629-634 (2011). [4] Jiang L.; et al. "Triphenylene-Fused Porphyrins". Organic Letters, 13(12), 3020-3023 (2011). [5] Luo L.; et al. "Effects of aggregation and electron injection on photovoltaic performance of porphyrin-based solar cells with oligo(phenylethynyl) links inside TiO2 and Al2O3 nanotube arrays". Physical Chemistry Chemical Physics, 12(5), 1064-1071 (2010).

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C143 - Coumarin Dyes with Triple Bonds as pi-Spacer Units for Dye Sensitized Solar Cells

Maria Britesa, Érica Torresa, Sara Sequeiraa, Paulo Mendesb, Killian Lobatoc

a, LNEG, Energy and Geology National Laboratory, LNEG Campus, Paço do Lumiar, 1649-038 Lisboa, Portugal, PT b, CQE/UE, Chemistry Center of the University of Évora, Rua Romão Ramalho, 59, 7000-671 Évora, Portugal, PT c, SESUL-FCUL, Centre for Sustainable Energy Systems of the University of Lisbon (SESUL) Lisboa, Portugal, PT

Among metal free organic dyes studied in dye-solar cells (DSC), coumarin derivatives are a promising sensitizer for TiO2 because of their good photoresponse in the visible region and good thermal stability under one sun soaking [1]. On the basis of concept of Donor-p-conjugation bridge-acceptor structure a series of coumarin dyes have been synthesized by inserting various numbers of thiophene or methine moieties as pbridge between coumarin as electron donor and cyano carboxylic acid as electron acceptor [2]. So far, influence of triple bond as pspacer unit in coumarin dyes has not been studied. Here we report our recent progress in the design and synthesis of coumarin dyes (C1-LEN and C2-LEN) with triple bond as linkers between the donor and acceptor units. Their absorption spectra and photovoltaic properties were investigated and, the electron distribution with different acceptors was performed using density functional theory (DFT) methods and time dependent DFT calculations. A complete optoelectronic characterization of obtained DSCs will be presented and discussed. References [1] Wang, Z.; Cui, Y.; Hara, K.; Dan-oh, Y.; Kasada, C.; Shinpo, A. “A High-Light-Harvesting-Efficiency Coumarin Dye for Stable Dye Sensitizer Solar Cells”, Adv. Mater., 19, 1138-1141 (2007). [2] Hara, K.; Miyamoto, K; .Abe, Y.; Yanagida, M. “Electron Transport in Coumarin Dye Sensitized Nanocrystalline TiO2 Electrodes”, J. Phys. Chem. B, 109, 23776-23778 (2005).

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C144 - Effect of atomic layer deposited metal oxide barriers on interfacial electron transfer in dye-sensitized solar cells.

Liisa Antilaa, Mikko Heikkiläb, Ville Mäkinena, Viivi Aumanena, Marianna Kemellb, Pasi Myllyperkiöa, Karoliina Honkalaa, Hannu Häkkinena, Markku Leskeläb, Jouko Korppi-Tommolaa

a, Nanosicence center, University of Jyväskylä, P.O. Box 35, Jyväskylä, 40014, FI b, Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki, 00014, FI

A recently used approach to improve the performance of dye-sensitized solar cells (DSSC’s) is to coat the photoactive semiconductor electrode with an ultrathin insulating metal oxide layer [1]. Optimally, such barrier layer would reduce the recombination reactions without hindering forward electron transfer too much. The search for a layer material meeting these requirements is underway. In this study, several thicknesses of AlOx, HfOx and TaOx layers were prepared by using atomic layer deposition (ALD). The effect of barrier layers on electron transfer at the dye-TiO2-electrolyte interface has been studied in a wide range of timescales. Ultrafast transient absorption spectroscopy was employed to monitor changes in forward electron injection in TiO2 films with barriers. The performance of AlOx containing DSSC’s was explored with electrochemical impedance spectroscopy (EIS) and current-voltage measurements. Density functional theory (DFT) calculations of the first cycle of AlOx ALD process were carried out to obtain information on layer morphology. At present, flash photolysis and time-correlated single photon counting measurements are used to study recombination in films with HfOx and TaOx layers in more detail. The results obtained for AlOx barriers have been used to develop a description of the underlying reasons for the observed deterioration of cell performance. It was found that already one ALD cycle of AlOx slowed down the electron injection [2]. DFT calculations [3,4] revealed atomic scale roughness and discontinuity of the layer deposited during the first cycle of AlOx ALD process. Calculations also indicate that the dye binds only to AlOxand is in average ~0.2 nm farther from the TiO2 surface than when binding to the bare TiO2 surface. This leads to weaker coupling between the dye and TiO2 and was considered as the main reason for the observed reduction in electron injection efficiency. EIS results indicated reduced recombination with the electrolyte oxidant [3]. However, the computational and experimental results suggest that injection was hindered relatively more than recombination – possibly due to the discontinuity of the AlOx barrier – leading to deterioration of the overall cell performance. References [1] Hagfeldt, A.; Boschloo, G.; Sung, L.; Kloo,L.; Pettersson, H. "Dye-Sensitized Solar Cells". Chem. Rev. 110, 6595 (2010). [2] Antila, L. J.; Heikkilä, M. J.; Aumanen, V.; Kemell, M.; Myllyperkiö, P.; Leskelä, M.; Korppi-Tommola, J. "Suppression of Forward Electron Injection from Ru(dcbpy)2(NCS)2 to Nanocrystalline TiO2 Film As a Result of an Interfacial Al2O3 Barrier Layer Prepared with Atomic Layer Deposition". J. Phys. Chem. Lett. 1, 535, (2010). [3] Antila, L. J.; Heikkilä, M. J.; Mäkinen, V.; Humalamäki, N.; Laitinen, M.; Linko, V.; Jalkanen, P.; Toppari, J.; Aumanen, V.; Kemell, M.; Myllyperkiö, P.; Honkala, K.; Häkkinen, H.; Leskelä, M.; Korppi-Tommola, J. "ALD Grown Aluminum Oxide Submonolayers in Dye-Sensitized Solar Cells: The Effect on Interfacial Electron Transfer and Performance". J. Phys. Chem. C 115, 16720-16729, (2011). [4] Mäkinen, V.; Honkala, K.; Häkkinen, H. "Atomic Layer Deposition of Aluminum Oxide on TiO2 and Its Impact on N3 Dye Adsorption from First Principles". J. Phys. Chem. C 115, 9250-9259, (2011).

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C145 - Electrodeposited ZnO Nanorods for Dye-Solar Cells

Tânia Fradeb, Killian Lobatoa, Anabela Gomesb

a, SESUL - Centre for Sustainable Energy Systems of the University of Lisbon, Faculdade de Ciências da Universidade de Lisboa, Edifício C8, Lisboa, 1749-016, Portugal b, CCMM - Centro de Ciências Moleculares e Materiais, Faculdade de Ciências da Universidade de Lisboa, Edifício C8, Lisboa, 1749-016, Portugal

The dye-solar cell (DSC) offers a fascinating paradigm with regards the generation of electricity directly from sunlight. There are a wide variety of architectures possible and one of the many components in a DSC that can be altered is the supporting structure onto which the dye is adsorbed. However there is fundamental prerequisite, that it have a high internal surface area. The use of suspensions of nanoparticles which are deposited onto TCOs and then sintered, tend to be more facile manner or preparing such structures. This is possible with a variety of semiconductors e.g. TiO2, ZnO, WO3, etc. However, the only simple manner in which an intimate contact can be obtained between the adsorbed dye-monolayer electron donor species to regenerate the oxidized dye, is via the use of liquid electrolytes. However, it is difficult to envisage a PV device for utility scale deployment that contains an encapsulated liquid. For this reason, the structure of the photoanode must be one that is amenable to the substitution of the liquid electrolyte for an organic or inorganic hole-transport-medium, providing the same intimate contact that is possible with an electrolyte. The simplest solution one can invisage is the use of highly orientated vertical nanostrucutures. This type of structure is easily attainable via the electrodeposition of ZnO and there are several reports describing the electrodeposition with conditions explored resulting in a variety of geometries e.g. rods, needle, tubes and porous layers[1–3]. This has the added bonus in that these structures can be obtained at relatively low temperatures, allowing the use of organic-TCO coated substrates that are lightweight and flexible. Here we will present a simple approach to produce high-density vertically aligned ZnO nanorod arrays on F-doped SnO2 (FTO) coated glass substrates, prepared at 70ºC from a neutral zinc nitrate solution[4]. Electrodeposition parameters, namely deposition time and bath composition were varied and the effects on film crystallinity, morphology and DSC device performance have been characterized.

Figure 1 SEM image of ZnO nanorod arrays on FTO substrates prepared by electrodeposition method. Inset: Diffractogram of ZnO nanorod arrays.

Film composition and morphology was characterized via XRD and FEG-SEM whilst DSC device charge transport and recombination properties were characterized via AM1.5 solar

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simulation, Incident photon to current conversion efficiency (IPCE), Intensity modulated photocurrent and photovoltage spectroscopy (IMPS/IMVS), Charge extraction, photovoltage decay transients and electrochemical impedance spectroscopy (EIS).

Acknowledgements:Funding provided by the FCT – project ref: PTDC/QUI-QUI/101497/2008

References [1] I. Gonzalez-Valls, Y. Yu, B. Ballesteros, J. Oro, and M. Lira-Cantu, “Synthesis conditions, light intensity and temperature effect on the performance of ZnO nanorods-based dye sensitized solar cells,” Journal of Power Sources, 196, 6609-6621 (2011). [2] S. Xu and Z. L. Wang, “One-dimensional ZnO nanostructures: Solution growth and functional properties,” Nano Research, 4, 11 (2011). *3+ N. Memarian, I. Concina, A. Braga, S. M. Rozati, A. Vomiero, and G. Sberveglieri, “Hierarchically Assembled ZnO Nanocrystallites for High-Efficiency Dye-Sensitized Solar Cells.,” Angewandte Chemie (International ed. in English), 12321-12325 (2011). *4+ T. Frade, A. Gomes, M. I. Pereira, and K. Lobato, “Electrodeposition of ZnO Nanorods for Dye Solar Cells,” in XIII Encontro Ibérico de Electroquímica (2011).

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C146 - Filling the pores: In-Situ Polymerization of MEH PPV into Porous Titania

Norma Minar, Thomas Bein

Ludwig-Maximilians-Universitaet munich, Butenandtstr. 13, Munich, 81377, DE

Organic photovoltaic materials are under intensive investigation for potential applications in low-cost, large-area solar cells. This research field gives cause for optimism to meet the global needs on clean and inexpensive energy sources.All-organic systems such as polymer/fullerene blends can suffer from poor photostability of the organic compounds and limited structural stability of the active layer through phase segregation. One promising alternative to all-organic cells is to use a nanostructured inorganic semiconductor as the electron-transport component. Crystalline titanium dioxide is an attractive material in this context on account of its low cost, high stability, ease of fabrication and the existing potential for controlling the morphology on the nanoscale. One of the greatest challenges for a hybrid heterojunction solar cell of this kind is to combine two materials that differ in many ways. On the one side a crystalline, rigid, inorganic metal oxide, on the other side a flexible, organic polymer. For the design of high performance photovoltaic devices, it is important to control the nature of the interface between the interpenetrating materials, while maintaining the desired properties of both electron and hole conductors. Infiltrating the long polymer chains into the narrow voids of a mesoporous TiO2 network is a difficult process. We have circumvented this by developing a way to grow the polymer chains inside the porous network, in order to cover the entire available titania surface with polymer. For this purpose, we functionalized the titania surface with a linker molecule to provide a starting point for the polymerization and to synthesize MEH-PPV inside the pores. With this approach we observed a significant increase in the filling efficiency of the polymer in the pores of the titania network, compared to conventional infiltration. SEM cross section images of the films confirm the high degree of filling of the titania pores compared to non-functionalized in situ polymerized or simply spin-coated samples. Preliminary experiments applying these in situ polymerized films in solar cell devices show power conversion efficiencies comparable to spin-coated controls. Although a significant improvement due to the higher fill-factor was not observed, this is certainly a promising first result. More in-depth characterization of these devices should help to understand and further improve the titania/polymer interface and hopefully lead to improved efficiencies.

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C147 - Molecular orientation and composition at the surface of APFO3:PCBM blend films

Ana Sofia Anselmoa, Andrzej Dzwilewskia, Ergang Wangb, Mats R. Anderssonb, Jan van Stamc, Krister Svenssona, Ellen Moonsa

a, Department of Physics and Electrical Engineering, Karlstad University, Karlstad, 65188, Sweden b, Department of Chemical and Biological Engineering, Chalmers University of Technology, Göteborg, 412 96, Sweden c, Department of Chemistry and Biomedical Sciences, Karlstad University, Karlstad, 65188, Sweden

Recent improvements in the performance of polymer-based photovoltaics have been closely linked to chemical design of the conjugated polymers used in such devices. Changes in the polymer chains affect the polymer’s electro-optical characteristics as well as its physical properties. Especially in bulk heterojunction configurations, where the polymer is blended with an acceptor material, the final nanostructure is determined to a great extent by the polymer’s tendency to self-organise. This nanostructure is of fundamental importance to device performance. In particular, the interfaces between the active layer and the electrodes are crucial to an adequate charge collection.[1] Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) probes unoccupied electronic states and the resulting spectra can be used to reveal the chemical composition and the molecular orientation of the surface region of the sample.[2] This technique has been successfully used in studies of surface composition and vertical phase separation in films of polymer:fullerene blends for photovoltaics [3-5], as well as in elucidating molecular orientation.[3,4] Here we present a variable-angle NEXAFS study of the surface organization in pure APFO-3 (poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3-benzo-thiadiazole)) films, and in blend films of this polymer with PCBM ([6,6]-phenyl-C61-butyric acid methyl ester). By using partial (PEY) and total (TEY) electron yield detection modes we were able to access information from different depths. Results show a preferential in-plane orientation of the polymer, i.e. the polymer’s conjugated plane is predominantly parallel to the surface. This orientation was found both in the pure films and in the blend films, although it is less pronounced in the latter. In the case of the pure polymer films, this preferential orientation was stronger at the subsurface than at the surface. The spectra taken at the magic angle (55°measured from the surface) were used to determine the surface compositional ratios of the blend films. We found polymer-enriched top surfaces and strong gradients in composition over the first few nanometers in all blend films. References [1] Chen, L.-M.; Xu, Z.; Hong, Z.; Yang, Y. "Interface investigation and engineering – achieving high performance polymer photovoltaic devices" J. Mater. Chem. 20, 2575-2598 (2010 [2] Watts, B.; Swaraj, S.; Nordlung, D.; Lüning, J.; Ade, H. "Calibrated NEXAFS spectra of common conjugated polymers" J. Chem. Phys. 134, 024702 (2011). [3] Germack, D.S.; Chan, C. K.; Hamadani, B. H.; Richter, L. J.; Fischer, D. A.; Gundlach, D. J.; DeLongchamp, D. M. Appl. Phys. Lett. "Substrate-Dependent Interface Composition and Charge Transport in Films for Organic Photovoltaics" 94, 233303 (2009). [4] Xue, B.; Vaughan, B.; Poh, C.-H.; Burke, K. B.; Thomsen, L.; Stapleton, A.; Zhou, X.; Bryant, G. W.; Belcher, W.; Dastoor, P. C. "Vertical Stratification and Interfacial Structure in P3HT:PCBM Organic Solar Cells" J. Phys. Chem. C 114 15797-15805 (2010). [5] Anselmo, A. S.; Lindgren, L.; Rysz, J.; Bernasik, A.; Budkowski, A.; Andersson, M. R.; Svensson, K.; van Stam, J.; Moons, E."Tuning the Vertical Phase Separation in Polyfluorene:Fullerene Blend Films by Polymer Functionalization" Chem. Mater. 23, 2295-2302 (2011).

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C148 - New Efficient and Tunable Ruthenium Photosensitizer for Dye Sensitized Solar Cells

Robson Raphael Guimarães, André Luis Araújo Parussulo, Henrique Eisi Toma, Koiti Araki Institute of Chemistry - University of São Paulo, Av. Prof. Lineu Prestes, BR

Dye sensitized solar cells (DSSCs)1 are one of the most interesting alternative renewable energy sources because delivers relatively high energy conversion efficiency and its simple fabrication. However, among all dyes tested for such purpose [Ru(dcbH2)2L2] complex derivatives, where dcbH2= 2,2’-bipyridine-4,4’-dicarboxilic acid and L are π-donor ligands show the highest performance. In fact, the derivatives where L = SCN– and different degrees of deprotonation were shown to be the best photosensitizers. Benzotriazol attracted our attention because is a strong donor ligand and exhibits an additional acid-base site that can be used to tune its properties and adequate the complex excited state energy2.

Figure 1 Absorbance spectrum of the [Ru(4,4'-dicarboxy-2,2'-piridine)2(benzotriazole)2](PF6) and two successive deprotonation products (a) and photoaction spectrum compared with the N719 dye (b).

Thus, we describe in this work the synthesis, characterization and photosensitizing properties of the [Ru(dcbH2)2(btzH)2] complex, where btz= benzotriazole, in DSSCs. Elemental analysis for C36H36F6O8N10PRu·4H2O, Exp. (Calc.): %C 41,88(41,39); %H 3,41(3,28); %N 12,46 (13,41). Only the molecular peak with the characteristic isotopomeric distribution was observed in the mass spectrum at m/z 827.1, consistent with the [Ru(dcbpyH)(dcbpyH2)(btzH)2]

+ species. Its UV-vis spectrum was sensitive to the solution pH, exhibiting three acid-base equilibria in aqueous solution whose pKa’s were determined to be 3.1, 6.4 and 12. The [Ru(dcbH2)2(btzH)2] species exhibits metal-to-ligand charge-transfer bands (MLCT bands) at 488 and 359 nm, in addition to a band at 309 nm with a shoulder at 297 nm assigned to 4,4’-dicarboxy-2,2’-bipyridine ligand p(pi)→p(pi)* transition.3 The deprotonation of the btzH ligands (pKa = 6.4 and 12.0) led to the batochromic shifts (Figure 1a) of the MLCT bands as a consequence of the enhanced π-donor properties and rise of the HOMO. The cyclic voltammograms of the complex in aqueous solution at pH 9.5 presented a reversible pair of waves at E1/2 = 0.8, assigned to the Ru(III/II) redox pair. The IPCE pattern of all cells showed a maximum around 500 nm and a shoulder at 600 nm, covering all the visible range from 400 to 650 nm. Interestingly the IPCE curves were only slightly lower than the results obtained with cells prepared with the N719 dye, suggesting that both have similar solar energy conversion efficiencies. However, it is important to remember at this point that the electron injection properties of the new ruthenium complex dye can be tuned by deprotonation, enhancing the electron injection kinetics and hole transfer properties, improving the solar light harvesting efficiency.

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References [1] O’Regan, B.; Gratzel, M. "A low-cost, high-efficiency solar cell based dye-sensitized". Nature 353, 737 (1991). [2] Toma, H. E.; Giesbrecht, E.; Rojas, R. L. E. "Espectroscopic and electrochemical studies on linkage isomerism in iron(II) complexes of benzotriazole", Canad. J. Chem. 61, 2520-2525. [3] Nazeeruddin, M. K.; Zakeeruddin, S. M.; Humphry-Baker, R.; Jirousek, M.; Liska, P.; Vlachopoulos, N.; Shklover, V.; Fischer, C.-H.; Gratzel, M. "Acid−Base Equilibria of (2,2‘-Bipyridyl-4,4‘-dicarboxylic acid)ruthenium(II) Complexes and the Effect of Protonation on Charge-Transfer Sensitization of Nanocrystalline Titania", Inorg. Chem. 38, 6298-6305 (1999).

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C149 - Nickel Oxide Nanostructured Electrodes for Perylenediimide-Based Dye-Sensitized Solar Cells

Sebastian Feihla, Rubén D. Costaa, Stephan Pflocka, Cordula Schmidtb, Susanne Backesb, Jörg Schönamsgruberb, Andreas Hirschb, Dirk M. Guldia

a, Department of Chemistry and Pharmacy, Chair of Physical Chemistry I, Friedrich-Alexander-University Erlangen-Nuremberg, Egerlandstrasse 3, Erlangen, 91058, DE b, Department of Chemistry and Pharmacy, Chair of Organic Chemistry II, Friedrich-Alexander-University Erlangen-Nuremberg, Henkestrasse 42, Erlangen, 91054, DE

In this work we have addressed the grand challenges associated with nickel oxide (NiO) electrodes as photocathodes in p-type dye-sensitized solar cells (p-DSSCs) and with perylenediimide (PDIs) as light harvester / electron acceptors.[1, 2] To this end, two approaches were pursued towards preparing NiO nanoparticle pastes suitable for fabricating mesoporous electrodes on conductive fluorine doped tin oxide (FTO) glass substrates. Firstly, commercially available NiO nanoparticles were dispersed in a mixture of ethanol and terpineol. Here, in order to obtain a mesoporous network two types of ethylcelluloses - EC 5 – 15 and 30 – 50 mPas - were added in a 1:1 weight ratio. After evaporating ethanol, the resulting pastes were spread on FTOs by doctor blading and tempered at different temperatures. Importantly, the influence of the calcination temperature was crucial in terms of developing efficient performing electrodes. Despite all of our efforts, the visual appearance of the resulting NiO electrodes points towards a strong heterogeneity. To circumvent this obstacle, a second approach en route towards homogenous electrodes was investigated. In that case, commercial NiO nanoparticles were mixed with a mixture of EC 5 – 15 and 30 – 50 mPas at 1:1 weight ratio and triacetin as plasticizer in ethanol. In this way, pastes containing 7 wt% of EC, 3 wt% triacetin, and different contents of NiO nanoparticles (i.e., 5 to 20 wt%) were prepared. Most importantly, the resulting electrodes showed a much improved FTO coverage, which is corroborated by scanning electron microscopy (SEM) images. In the next step, a symmetrically functionalized PDI bearing two dendrons with three carboxylate anchors each was utilized to sensitize the different NiO photoelectrodes. To interpret our results, a second, non-symmetrically functionalized PDI was used as a reference. In this particular case, one dendron is replaced by a dodeca-alkyl chain. In addition, key aspects such as the influence of chenodeoxylcholic acid (Ch-A) as a coadsorbent to prevent aggregation as well as the time dependence of the PDI uptake were keenly investigated. To conclude, devices featuring electrodes prepared with the second paste containing 10 wt% of NiO nanoparticles, baked at 400 oC, and soaked for 3 h showed the highest efficiencies for both types of PDI. The corresponding values of 0.015 and 0.016 % evolved for the symmetric and the non-symmetric PDI, respectively. References [1] Morandeira; A., et al. "Improved Photon-to-Current Conversion Efficiency with a Nanoporous p-Type NiO Electrode by the Use of a Sensitizer-Acceptor Dyad". J. Phys. Chem. C 112, 1721-1728 (2008 [2] Le Pleux, L.; et al. "Synthesis, photophysical and photovoltaic investigations of aceptor-functionalized perylene monoimide dyes for nickel oxide p-type dye-sensitized solar cells". Energy Environ. Sci. 4, 2075-2084 (2011).

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C150 - A platinum-based poly(aryleneethynylene) containing thiazolothiazole group with high hole mobility for organic photovoltaic and field-effect transistor applications

Lei Yan, Xiaohui Wang, Xingzhu Wang, Xun Chen

Xiangtan University, Key Laboratory of Low Dimensional Materials and Application Technology of Ministry of Education and College of Chemistry, Xiangtan University, Xiangtan,411105, CN

Harvesting energy directly from the sun is one of the most important methods to address the world energy need. Polymer solar cells (PSCs) have attracted a lot of attention in recent years due to their potential use for the new generation renewable energy sources.1 They have many advantages over the silicon-based devices such as low cost, light weight, flexibility, an easy printing of polymer on the substrate, and easy manufacture of the devices. Recently, some devices made with conjugated polymers have shown a power conversion efficiency (PCE) approaching ~8% when blended with fullerene derivatives (such as PC61BM and PC71BM).2

Despite considerable progress in this field, the PCE of PSCs must be further improved for commercialization. The decisive parameters that determine the efficiency of PSCs are the open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF). Voc is limited by the difference between the highest occupied molecular orbital (HOMO) of the donor and the lowest unoccupied molecular orbital (LUMO) of the acceptor.

Figure 1 Absorbance spectrum of the [Ru(4,4'-dicarboxy-2,2'-piridine)2(benzotriazole)2](PF6) and two successive deprotonation products (a) and photoaction spectrum compared with the N719 dye (b).

However, the Jsc and FF are directly limited by the charge carrier mobility. Higher charge carrier mobilities enable better carrier transport within an active layer without significant photocurrent loss due to the recombination of opposite charges. High charge carrier mobilities also lead to high fill factors. Thiazolothiazole has a rigid and coplanar fused ring, and thereby ensures highly extended π-electron system and strong π-stacking. As a result, conjugated small molecules and polymers based on electron-poor thiazolothiazole exhibited high charge carrier mobilities. We and others have recently demonstrated efficient solar cells based on polyplatinyne:PCBM bulk heterojunctions with high photovoltaic performance.3 Here, we report the application of a new soluble, solution-processable metallopolyyne of platinum(II) functionalized with electron-deficient thiazolothiazole spacer in bulk heterojunction solar cells and organic field-effect transistors (OFETs). The new copolymer semiconductor indeed exhibited an impressive field-effect carrier mobility of up to 2.0 x10–2 cm2 · V–1 · s–1, and bulk heterojunction solar cells made from P produced a power conversion efficiency of 2.16% under 100 mW cm–2 AM 1.5 G irradiation in ambient air.

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Acknowledgments: This work was supported by the National Nature Science Foundation of China (Nos. 20974091;50803051), Natural Science Foundation of Hunan Province of China (No.10JJ1002), the Foundation of the Hunan Provincial Education Department (10B107) and the Undergraduate Innovation Experiment Plan in the Ministry of Education (No.101053019).

References [1] (a)S. Gunes, H. Neugebauer, N. S. Sariciftci, Chem. Rev. 2007, 1071324. (b)Y.-J. Cheng, S.-H. Yang, C.-S. Hsu, Chem. Rev. 2009, 109, 5868. [2] (a) He, C. Zhong, X. Huang, W.-Y. Wong, H. Wu, L. Chen, L. S. Su, Y. Cao, Adv. Mater. 2011, 23, 4636. (b) R. F. Service, Science 2011, 332, 293. (c) http://www.konarka.com; (f) http://www.solarmer.com [3] (a) W.-Y. Wong, X.-Z. Wang, Z. He, A. B. Djurišiæ, C.-T. Yip, K.-Y. Cheung, H. Wang, C. S.-K. Mak, W.-K. Chan, Nat. Mater. 2007, 6, 521; (b)N. S. Baek, S. K. Hau, H.-L. Yip, O. Acton, K.-S. Chen, A. K.-Y. Jen, Chem. Mater. 2008, 20, 5734.

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C151 - Photoinduced Processes in Small Molecule/Fullerene Bilayers

Jelissa De Jonghe*a, Jacques-Edouard Mosera, Gaetan Wichtb, Roland Hanyb, Frank Nueuschb

a, EPFL, EPFL SB ISIC LPI CH G0 628 (B, Lausanne, 1015, CH b, EMPA, Überlandstrasse 129, 8600 Dübendorf, CH

In the large domain of organic photovoltaics, small soluble molecules are gaining more and more interest. Compared to polymers, small molecules offer a large panel of advantages like ease of synthesis, monodisperse behavior as well as high purity, which is responsible for higher charge carrier mobility.1 Small molecules such as cyanine dyes are potential candidates for electron donors in organic photovoltaics (OPV) due to their high extinction coefficient, which enables the use of ultrathin layers and therefore enhances charge separation at the donor/acceptor interface. Moreover, the solubility of cyanine dyes in various organic solvents renders them solution-processable and applicable for low-cost solar cells. For cyanine/fullerene organic solar cells, a bilayer architecture is preferred to bulk heterojunction (BHJ) in order to avoid defects due to morphology.2 Those molecules exhibit charge separated states living up to the microsecond time scale, and the mechanism of formation of those states is currently addressed. Of particular interest also is the effect of the counter anion on charge separation. The photoinduced processes occurring in pristine and bilayer thin films are investigated via femtosecond transient absorption and nanosecond flash photolysis in order to determine the first steps of charge separation. References [1] Hoppe, H; Sariciftci, N.S. "Organic solar cells: An overview". J Mater Res 19, 1924–1945 (2004). [2] Hany, R. et al. "Strategies to improve cyanine dye multilayer organic solar cells". Prog. Photovolt. Res. Appl.(2010)

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C152 - Synthesis and Characterization of Biotemplated Titania Porous Films

Alesja Ivanova, Thomas Bein

a, Department of Chemistry, Ludwig-Maximilians University Munich, Butenandtstr. 5-13, Munich, 81377, Germany

Mesoporous titania films attract significant attention due to their successful implementation in photovoltaic devices, in particular dye-sensitized solar cells (DSC). One of the key issues in the performance of DSCs is the nanoporous morphology of the TiO2. Usually the porous network is created from sintered nanocrystals or with sol-gel chemistry using templating agents such as amphiphilic polymers. However, the tunability of the porous structures obtained in this way is limited. Nanocellulose (NCC) consists of structural units of different dimensions in the mesoscopic range. The attractive features of NCC include its shape anisotropy, its surface charge and an ability to self-organize.In addition, this novel material is obtained from abundant, “green” celluloses, which makes NCC even more attractive in comparison with organic copolymers.

Figure 1 Synthesis approach to the biotemplated mesoporous TiO2 films

The synthesis procedure for the biotemplated titania starts by mixing an NCC suspension and the precursor solution (Figure 1). Subsequent film deposition promotes sol-gel and evaporation-induced self-assembly processes, leading to the formation of a solid composite film. Finally, the composite is heated to remove the templating NCC and to crystallize the titania matrix. The current study investigates the influence of the NCC amount added to the precursor solution on the morphology of the TiO2 structures. Films and powders are characterized by gas sorption, X-ray diffraction measurements and electron microscopy. The obtained data show the high potential of NCC for introducing tuneable porosity into titania films.

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C153 - Tetrahexylammonium Iodide containing Gel Polymer Electrolytes for Dye Sensitized Solar Cells and CdS QD Sensitized Solar Cells

Maurizio Furlania, T.M.W.J. Bandarab, Bengt-Erik Mellandera, Tommy Svenssonb, W.J.M.J.S.R. Jayasundarab, Vito Di Notod, Christopher FriskC

a, Chalmers University of Technology, Fysikgränd 3, Göteborg, 41276, SE b, Department of Physical Sciences, Rajarata University of Sri Lanka, , Sri Lanka c, Department of Physics, University of Gothenburg, SE d,Department of Chemical Sciences, University of Padova, Via Marzolo 1, I-35131 Padova, IT

Solar cells provide an alternative energy source which can harness energy from freely available solar radiation in an environmental friendly manner. Dye and quantum-dot sensitized solar cells are alternatives that need an electrolyte for the efficient operation of the cell. Solid and gel polymer electrolytes are in many ways more promising than liquid-type electrolytes due to their many advantages such as geometrical confinement, limited leakage and absence of evaporation. However, their conductivity needs to be enhanced in order to use them in practical device applications. For the quantum-dot type cells a broad spectrum of the solar light may be used by tuning the particles size. The synthesis, sizing and deposition of these nano sized particles on the anodic side of a photoelectrochemical cells are important issues for the development of these techniques. In this work, an iodide conducting gel polymer electrolyte was prepared using tetrahexylammonium iodide, poly(acrylonitrile), ethylene carbonate and propylene carbonate. The salt composition was varied to find the optimum conductivity. The sample containing 120% weight salt with respect to poly(acrylonitrile) showed the highest conductivity. This electrolyte showed a glass transition at -102.3 °C and an ambient temperature conductivity of 2.1×10-3 S cm−1 at 30 °C. In a second example a quantum dot CdS sensititized solar cell was prepared and characterized synthetizing cadmium sulphide nano-particles in suspension using water based or organic solutions, and depositing the suspension on a substrate by dipping and by staining.

References [1] Bandara, T.M.W.J.; Svensson, T; Dissanayake, M.A.K.L.; Furlani, M.; Jayasundara, W.J.M.J.S.R.; Mellander, B.-E.; "Tetrahexyammonium Iodide Containing Solid and Gel Polymer Electrolytes for Dye Sensitized Solar Cells", Energy Procedia 14, 1607-1612 (2012) (2nd International Conference on Advances in Energy Engineering ICAEE 2011) http://www.sciencedirect.com/science/article/pii/S1876610211045607

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C154 – The Effect of the Auxiliary Donor Substituents on the D35 DYE

Erik Gabrielssona, Hanna Ellisb, Haining Tiana, Sandra Feldtb, Gerrit Boschloob, Anders Hagfeldtb, Licheng Suna

a, Organic Chemistry, KTH Royal Institute of Technology, Teknikringen 30, Stockholm, 10044, SE b, Department of Physical and Analytical Chemistry, Uppsala University, Box 259, Uppsala, 751 05, SE

The D35 dye has been thoroughly studied in dye-sensitized solar cell applications1. In particular it has received attention for its good performance in combination with cobalt based electrolytes2. It has been thought that the reason for the good compatibility with a wide range of redox mediators is due to the efficient blocking of recombination by the butoxy substituents on its donor part. To test this hypothesis, two new dyes were synthesized: D45, with methoxy groups in place of D35’s butoxy groups and D49, where the butoxy groups in the ortho-positions have been removed.

Figure 1 Structures of the dyes

I-V measurements of iodine based DSSCs sensitized with the different dyes show decreasing open circuit voltages in the order D35 > D45 > D49, whereas the short circuit current shows the opposite trend when 3 µm thin films were used. Similar observations were also made when a cobalt-based electrolyte was employed. Using toolbox methods an increase in electron recombination could be seen.

Table 1. Photovoltaic parameters of the DSSCs with an iodine based electrolyte.

JSC(mA/cm2) VOC(V) FF Eff. (%)

D35 8.1 0.83 0.61 4.2

D45 8.9 0.80 0.62 4.4

D49 9.0 0.76 0.65 4.4

References [1] (a) Hagberg, D. P.; Jiang, X.; Gabrielsson, E.; Linder, M.; Marinado, T.; Brinck, T.; Hagfeldt, A.; Sun, L., Symmetric and unsymmetric donor functionalization. comparing structural and spectral benefits of chromophores for dye-sensitized solar cells. Journal of Materials Chemistry, 19, 7232-7238 (2009); (b) Jiang, X.; Marinado, T.; Gabrielsson, E.; Hagberg, D. P.; Sun, L.; Hagfeldt, A., Structural Modification of Organic Dyes for Efficient Coadsorbent-Free Dye-Sensitized Solar Cells. Journal of Physical Chemistry C, 114, 2799-2805 (2010). [2] Feldt, S. M.; Gibson, E. A.; Gabrielsson, E.; Sun, L.; Boschloo, G.; Hagfeldt, A., Design of Organic Dyes and Cobalt Polypyridine Redox Mediators for High-Efficiency Dye-Sensitized Solar Cells. Journal of the American Chemical Society, 132, 16714-16724 (2010).

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C155 - Which information EPR spectroscopy can provide on polymer/fullerene photovoltaic materials?

Lorenzo Francoa, Antonio Toffolettia, Marco Ruzzia, Luciano Montanarib, Lucia Bonoldib, Claudio Caratib, Riccardo Poc

a, Department of Chemical Sciences, University of Padova, via Marzolo, 1, Padova 35131, Italy b, Refining and Marketing Division, Research Centre, ENI SpA, via Maritano 26, San Donato Milanese 20097, Italy c, Research Center for non Conventional Energies Istituto Eni Donegani, ENI SpA, Via Fauser 4, Novara 28100 , Italy

The photophysical pathways in polymer/fullerene blends have been studied in great details in the last two decades using many different spectroscopic methods. Since the first pioneering studies, EPR spectroscopy was used to identify the presence of paramagnetic radical ions produced upon excitation with visible light after exciton dissociation. However, from the direct evidence of long-living charge separated states provided by Light-Induced EPR (LEPR) in polymer/fullerene blends, several new EPR spectroscopic studies have appeared in recent years, which address the polaron structure and dynamics [1,2], lifetimes and recombination kinetics of charge separated states [3,4], density of state for trapped polarons [5] and photophysical pathways following light absorption [6]. New and direct insights into the energy degradation pathways in the photoactive donor/acceptor blends can be obtained using Time Resolved EPR (TREPR) with sub-microseconds time resolution. The results usually complements and clarify the results obtained by optical spectroscopies (fluorescence quenching, transient absorption and others), in cases where extended spectral overlapping cannot uniquely identify the presence of polarons, triplet excitons, exciplexes or other paramagnetic species. In this work we examined a series of polymer/PCBM blends by means of LEPR and TREPR methods, The polymers investigated include polythiophenes (P3HT), MDMO-PPV, polyfluorenes (F8BT), polycarbazoles (PCDTBT) and other newly synthesized random copolymers [7]. We assessed the charge carriers photogeneration efficiencies by means of LEPR and identified the presence of triplet excited states of the polymers or PCBM and spin-selective charge recombination processes by means of TREPR. According to our spectroscopic results, we could classify the different blends into few classes correlated to the relative energies of the main excited state species, namely the charge separated states, the triplet states (PCBM or polymers) or the exciplex states. The experimental results have been compared to theoretical estimates of state energies obtained by quantum chemical calculations. Our results provide an hint to explain the trends of photovoltaic efficiencies in different blends but may also provide guidelines for the molecular design and synthesis of more efficient polymeric materials. References [1] Schultz, N.A.; Scharber, M.C.; Brabec, C.J.; Sariciftci, N. S. “Low-temperature recombination kinetics of photoexcited persistent charge carriers in conjugated polymer/fullerene composite films”. Phys. Rev B, 64, 245210 (2001) [2] Krinichnyi, V.I.; Roth, H.-K.; Sensfuss, S.; Schrodner, M.; Al-Ibrahim, M. “Dynamics of photoinduced radical pairs in poly(3-dodecylthiophene)/fullerene composite”. Physica E, 36, 98–101 (2007). [3] Marumoto, K.; Muramatsu, Y.; Kuroda, S. “Quadrimolecular recombination kinetics of photogenerated charge carriers in regioregular poly.3-alkylthiophene/fullerene composites”. Appl. Phys. Lett., 84, 1317-1319 (2004). [4] De Ceuster, J; Goovaerts, E.; Bouwen, A.; Dyakonov, V.; Hummelen, J.C. “A high-frequency light-induced electron spin resonance study of conjugated polymer/fullerene composites”, Synthetic Metals 121, 1529–1532 (2001). [5] Carati, C.; Bonoldi, L.; Po, R. “Density of trap states in organic photovoltaic materials from LESR studies of carrier recombination kinetics”. Phys. Rev. B, 84, 245205 (2011). [6] Camaioni, N.; Tinti, F.; Franco L.; Fabris, M.; Toffoletti, A.; Ruzzi, M.; Montanari, L.; Bonoldi, L.; Pellegrino, A.; Calabrese, A.; Po, R. “Effect of residual catalyst on solar cells made of a fluorene-thiophene-benzothiadiazole copolymer as electron-donor: A combined electrical and photophysical study”. Org. Electron. 13, 550–559 (2012).

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[7] Bonoldi, L.; Calabrese, A.; Pellegrino, A.; Perin, N.; Po, R.; Spera, S.; Tacca, A. “Optical and electronic properties of fluorene/thiophene/ benzothiadiazole pseudorandom copolymers for photovoltaic applications” J. Mater. Sci. 46, 3960–3968 (2011).

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C156 - Novel Platinum-Containing Metallopolyynes as Polymer Semiconductors for Thin-Film Transistors and Bulk Heterojunction Solar Cells

Lei Yan*, Juhua Ou, Xingzhu Wang, Chengxi Li Xiangtan University, Key Laboratory of Low Dimensional Materials and Application Technology of Ministry of Education and College of Chemistry, Xiangtan University, Xiangtan 411105., CN

Organic semiconducting polymers have attracted intense interest for a variety of applications such as, organic photovoltaic, organic light-emitting diodes, and organic thin-film transistors by virtue of a number of enablers, including good solution processability, which permits a low-cost fabrication process via printing, and robust mechanical properties for lightweight, producing compact, and flexible electronic devices. Metal-containing conjugated organic polymers represent an intriguing and promising class of materials, and platinum alkylnyls have been a popular candidate for inclusion into such a polymeric backbone. One of the most important potential applications of these materials are the solar cells and transistors. Unfortunately, Broad applications of organic polymer solar cells and OFETs are currently limited by the lower power conversion efficiency and lower hole mobilities as compare to that of inorganic semiconductors.

Figure 1 The chemical structures of Pt-containing metallopolyyne polymers

The novel platinum metallopolyyne is based on planar conjugated segments with internal D-A functions between electron-rich Pt-ethynyl groups to achieve a low-bandgap and high hole mobilities material. Here we report the synthesis and characterization of a series of new metalated conjugated polymers with fluorene which were modified at the C9-position (see Figure 1). The spectroscopic, thermal and photophysical properties, OPV and OTFT performance characteristics will be be presented.

Acknowledgments: This work was supported by the National Nature Science Foundation of China (Nos. 20974091;50803051), Natural Science Foundation of Hunan Province of China (No.10JJ1002), the Foundation of the Hunan Provincial Education Department (10B107) and the Undergraduate Innovation Experiment Plan in the Ministry of Education (No.101053019).

References [1] W. P. Wu, Y. Q. Liu, D. B. Zhu, Chem. Soc. Rev., 2010, 39, 1489. (b)J. Zaumseil, H.Sirringhaus, Chem. Rev. 2007,107, 1296. [2] (a) W.-Y. Wong, X.-Z. Wang, Z. He, A. B. Djurišiæ, C.-T. Yip, K.-Y. Cheung, H. Wang, C. S. K. Mak, W.-K. Chan, Nat. Mater. 2007, 6, 521. (b) W.-Y. Wong, X.-Z. Wang, Z. He, K.-K. Chan, A. B. Djurišiæ, K.-Y. Cheung, C.-T. Yip, A. M.-C. Ng, Y. Y. Xi, C. S. K. Mak, W.-K. Chan, J. Am. Chem. Soc. 2007, 129, 14372.

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C157 - Ultrafast electron transfer of a Ru-Co photocatalysis model system

Pavel Chaberaa, Tobias Harlanga, Sophie Cantonb, Villy Sundströma

a, Lund university, Chemical Physics, Vipeholmsvagen 32, Lund, 22466, SE b, Lund University, MAX-lab, Ole Römers väg 1, Lund, 22363,

Nowadays, photocatalytic molecules and materials are considered a viable route to artificial photosynthesis and production of solar fuel, as a solution to the impending energy crisis [Lewis 2006]. However to reach this goal, the physical-chemical processes underlying the catalytic properties need to be understood more in depth. As a first step, we have investigated the excited state and electron transfer properties of a photocatalysis model system – [Ru(bpy)2tpphzCo(bpy)2](PF6)5 (bpy = 2,2′-bipyridine, tpphz = tetrapyrido[3,2-a:2’,3’c:3’’,2’’,- h:2’’’,3’’’-j]phenazine). Excitation with visible light induces a metal-ligand charge transfer from the Ru atom, followed by electron transfer towards the Co atom, yielding a series of transient states with lifetimes of roughly ~1 ps, ~10 ps and ~5 ns, respectively. Similar results have been reported for related compounds, but it is disputed whether this is the fingerprint of a stepwise electron transfer process [Tschierlei 2009] or if the electron transfer is a direct single-step transition [Indelli 2007]. As the Co atom is spectroscopically dark, it is also difficult to prove whether the electron actually reaches the Co-center. Transient absorption measurements on molecules lacking the Co-atom can hopefully clarify this point.

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Figure 1 Molecular structure of Ru-Co complex (top) and transient absorption data - kinetics (centre) and transient spectra (bottom).

As a next step towards full characterization of the electron transfer and structural dynamics, we will apply time resolved X-ray spectroscopy and scattering, where it is possible to definitely detect the arrival of the electron on the Co-center and to follow the structural reconfiguration that is a consequence of the electron transfer. Particularly we propose to probe the local changes in electronic properties and structure around the Co atom that have been predicted by Density Functional Theory [Vargas 2006].

References [1] Lewis et al. PNAS 2006. 103(43), 15729-35.

[2] Tschierlei et al. Chemistry 2009. 7678-7688. [3] Indelli et al. Inorganic Chemistry 2007. 46(14), 5630-5641. [4] Vargas et al. J. Chem. Theory Comput., 2006. 2 (5), 1342–1359.

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C158 - Novel hybrid and flexible photovoltaic devices

Michele Tonezzera, Enrico Meninc, Sara Carturanc, Gianluigi Maggionic, Monica della Pirrierab, David Gutierrez - Tausteb, Stefano Concia, Alberto Quarantaa

a, Dipartimento di Ingegneria dei Materiali e delle Tecnologie Industriali - UNIVERSITA' DI TRENTO, VIA MESIANO 77, POVO (TN), 38049, IT b, LEITAT Technological Centre, C/ de la Innovació, 2, 08225 Terrassa (Barcelona, Spain) , ES c, Legnaro National Laboratories – INFN, dell’Università 2, Legnaro (PD), IT d, Dipartimento di Fisica, Università di Padova, via Marzolo 8, 35100 Padova, IT

Within “Next photovoltaic generation” devices, luminescent solar concentrators (LSC) represents an attractive technology. Solar light incident on LSC devices is absorbed by dyes, re-emitted into a guided mode in the slab, and finally collected by conventional PV cell mounted at the edge of the slab.

This approach allows two principal advantages:

a. reduce sensitively the cost of the system due to the low quantity of solar cells in the final system;

b. maximize the conversion efficiency of the different solar spectrum window by optimizing the matching between the dye emission and the solar cell absorption external quantum efficiency.

These photovoltaic devices show several advantages also in comparison with concentrating photovoltaic (CPV) ones. In particular they:

a. use also the diffuse component of solar radiation;

b. do not require solar tracking systems.

These advantages allow to develop photovoltaic systems characterized by a high versatility and architectural integrability. In this work we report recent results obtained within PHOTOFUTURE, an European Project focused on developing novel LSC devices, on the development of novel high flexible luminescent solar concentrators obtained by doping optically and mechanically stable silicone matrices with different perylene dyes. The produced flexible slabs were finally coupled with different typologies of solar cells.

In this work the following phases are reported and discussed:

a. production of novel hybrid and flexible LSC devices;

b. characterization of the physical and optical properties of the different LSCs slabs;

c. testing and comparison of the I-V performances of the different LSCs devices coupled with different photovoltaic cells.

References [1] C. L. Mulder, L. Theogarajan, M. Currie, J. K. Mapel, M. A. Baldo, M. Vaughn, P. Willard, B. D. Bruce, M. W. Moss, C. E. McLain, and J. P. Morseman, “Luminescent Solar Concentrators Employing Phycobilisomes,” Adv. Mater. 21(31), 3181–3185 (2009).

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[2] B. C. Rowan, L. R. Wilson, and B. S. Richards, “Advanced Material Concepts for Luminescent Solar Concentrators,” IEEE J. Sel. Top. Quantum Electron. 14(5), 1312–1322 (2008) [3] M. Tonezzer, G. Maggioni, S. Carturan, M. Buffa, A. Quaranta, D. Gutierrez, M. Della Perreira, L. Aubouy, 2011. PHOTOFUTURE Project: Novel Luminescent Solar Concentrators, INFN-LNL Report 234, 139-140.

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C159 -Improving solar cell efficiency with rare earth –based luminescent thin films

Michele Tonezzer*a, Enrico Meninc, Sara Carturanc, Gianluigi Maggionic, Monica della Pirrierab, David Gutierrez - Tausteb, Stefano Concia, Alberto Quarantaa

a, Dipartimento di Ingegneria dei Materiali e delle Tecnologie Industriali, UNIVERSITA' DI TRENTO, VIA MESIANO 77, POVO (TN), 38049, IT b, LEITAT Technological Centre, C/ de la Innovació, 2, 08225 Terrassa (Barcelona, Spain) , ES c, Legnaro National Laboratories – INFN, Viale dell’Università 2, Legnaro (PD), IT d, Dipartimento di Fisica, Università di Padova, via Marzolo 8, 35100 Padova, IT

Solar power is the most promising energetic source and one of the most promising technology for converting sun light to electrical power is the photovoltaic (PV) one: although substantial gains in solar cell technical performance have been achieved in the past fifty years, widespread adoption of photovoltaic systems remains limited by its low conversion efficiency and high cost per Watt of generated power (Є/WP). Today the prices of PV modules are not competitive with conventional energy source (i.e. petroleum, gas) and widespread deployment of PV technology still needs financial support schemes, such as investment subsidies or feed-in tariffs. To be competitive with electricity across large parts of the United States and Europe, system level prices need to drop below € 1/WP. To reach lower cost per installed capacity (€/W), several routes are being pursued and referred to as Next or Third Generation PV: a promising solution on this road is represented by the luminescent solar concentrators (LSC), photovoltaic devices in which the light is absorbed by dyes, re-emitted into a guided mode in the slab, and finally collected by a PV cell mounted at the edge of the slab. Several advantages make LSCs really attractive: in particular they do not require expensive solar tracking (reducing the installed costs) and convert, differently from the conventional concentrating systems, also the diffuse component of solar radiation (which constitutes a significant fraction in the north part of U.S. and central Europe). LSCs devices are designed such that the luminescence energy closely matches the solar cell absorption edge allowing to convert the solar spectrum components more profitably than the conventional solar cells. LSC devices can be utilized alone or coupled with pre-existing solar cells: in this work we focused our attention on the case of Eu(TTA)3Phen (TTA =thenoyltrifluoroacetonate, Phen = 1,10-phenanthroline) thin films coupled with conventional solar cells demonstrated the possibility to improve the conversion efficiency of the conventional solar cells. In particular in this work the following steps are detailed:

a. fabrication of LSC devices;

b. characterization of the physical and optical properties of the different LSCs slabs;

c. testing and comparison of the I-V performances of the different LSCs devices.

References *1+ A. A. Earp et al., “Optimisation of a three-colour luminescent solar concentrator daylighting system,” Sol. Energy Mater. Sol. Cells, vol. 84, no. 1–4, pp. 411–426, 2004. [2] M. Tonezzer, G. Maggioni, S. Carturan, M. Buffa, A. Quaranta, D. Gutierrez, M. Della Perreira, L. Aubouy, 2011. PHOTOFUTURE Project: Novel Luminescent Solar Concentrators, INFN-LNL Report 234, 139-140. [3] Wilson, L.R., Rowan, B.C., Robertson, N., Moudam, O., Jones, A.C., Richards, B.S., 2010. Characterization and reduction of reabsorption losses in luminescent solar concentrators. Appl. Opt. 49 (9), 1651–1661.

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C160 -Dynamical modulation of the optical transmittance in multifunctional dye-sensitized photelectrochemical devices based on the implementation of indium-tin oxide plasmonic resonators

Michele Manca*a, Francesco Todiscob, Roberto Giannuzzia, Alessandro Cannavalea, Raffaella Buonsantic, Luisa De Marcoa, Delia Millironc, Giuseppe Giglia

a, Italian Institute of Technology, via Barsanti 1 , Arnesano (LECCE), 73010, IT b, Dipartimento Interateneo di Fisica , Via Amendola 173 - 70125 BARI , IT c, The Molecular Foundry - Lawrence Berkeley National Laboratory , Berkeley (CA) 94720 , USA

A photovoltachromic cell 1 may potentially act as a complex artificial skin, by generating electric energy as a photovoltaic system but also ‘‘perceiving’’ even small variations in external radiation and controlling the energy fluxes by means of a smart variation of their optical transmittance. To this aim we recently developed a specifically designed bi-functional counterelectrode by depositing a C-shaped platinum frame which bounds a square region occupied by a tungsten oxide (WO3) film, onto a transparent conductive substrate.2 These two regions have been electrically separated to make possible distinct operations on one or both of the available circuits. This allowed to measure two different sets of parameters: those corresponding to the photovoltaic functionality (PV circuit) and those corresponding to the photoelectrochromic one (PEC circuit). Such an unconventional counterelectrode makes it possible to achieve a twofold outcome: a smart and fast-responsive control of the optical transmittance and a relatively high photovoltaic conversion efficiency. At the same time, in the recent literature transparent conductive oxide (TCO) nanocrystals (NCs) have been demonstrated to act as plasmonic electrochromic materials able to selectively modulate the infrared region.3 Unlike metals, plasmon resonance frequencies of doped semiconductors can be modified by changing the material’s composition, creating new opportunities for plasmonic manipulation of light. In fact, a well-defined localized surface plasmon resonance have recently been observed in the optical (infrared) spectra of highly doped semiconductor nanocrystals, especially transparent conducting oxides such as indium-tin oxide (ITO) 4

Figure 1 Schematic representation of the photovoltachromic cells realized for the present study. 1.Electric separation on the counterelectrode; 2. Platinum catalyzer; 3. Dynamically switchable electrode; 4. TCO; 5. Glass substrate; 6. Sealant; 7. Titanium dioxide and dye absorbed; Circuitry: Red: photovoltaic; Blue: Photoelectrochromic.

Starting from these remarks, we recently implemented the above referred TCO NCs a switchable plasmonic resonators in the photoelectrochromic (PE) half of a PVCC making them possible to generate an effective dynamic (and reversible) modulation of the optical adsorption.5 To do this we advantageously combined the optical switchability in the NIR region of a TCO-NCs-based mesoporous film with the photovoltaic functionality of dye-sensitized solar cell, thus defining a rout for the development of a novel class of photoelectrochromic

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devices. The TCO-NCs mesoporous layer acts hence as an electrochromic electrode: it comes to be powered by a dye-sensitized TiO2 film ( acting as photoelectrode ) in a such way that coloration and bleaching could be responsively driven by the incoming solar radiation. In this configuration the photovoltage produced by the dye sensitized electrode drives electrons into the IR-absorbers NCs through the external electrical circuit and compensates the cations of the electrolytes to diffuse towards the plasmonic electrode, which turns thus in the colored state.4

References *1+ J. Wu et al “Fast-Switching Photovoltachromic Cells with Tunable Transmittance”, ACS Nano, 2009, 8, 2297-2303 [2] Cannavale A. et al. “Highly efficient smart photovoltachromic devices with tailored electrolyte composition”, En. Env. Sci., 2011, 4 (7), 2567 - 2574 *3+ Buonsanti R. et al. “Tunable infrared absorption and visible transparency of colloidal aluminum-doped zinc oxide nanocrystals” Nano Lett. 2011, 11 (11), 4706-10 *4+ Garcia G. et al. “Dynamically Modulating the Surface Plasmon Resonance of Doped Semiconductor Nanocrystals” Nano Lett., 2011, 11 (10), 4415–4420 *5+ Manca M. et al. “Implementation of ITO-nanoparticles-based mesoporous electrodes as effective infra-red plasmonic resonators for novel dye-sensitized photoelectrochemical devices” in preparation

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C161 -Engineered carbon-nanotube-based composite plates as highly efficient free-standing counter electrodes for dye solar cells

Francesco Malarab, Michele Manca*a, Christof Hübnerc, Elpida Piperopoulosd, Giuseppe Giglia

a, Italian Institute of Technology, via Barsanti 1 , Arnesano (LECCE), 73010, IT b, National Nanotechnology Laboratory , Consiglio Nazionale delle Ricerche , Area di Lecce, Via Arnesano 16 , 73100 , LECCE, IT c, Fraunhofer-Institut für Chemische Technologie ICT, Joseph-von-Fraunhofer-Str. 7, 76327 Pfinztal, DE d, Dept. Industrial Chemistry and Materials Engineering Faculty of Engineering, University of Messina , Contrada Di Dio, 98166 Messina , IT

Dye-sensitized solar cells (DSSCs) are going to became the first commercially available third generation solar cell technology. Usually, Pt is used as the catalytic material and fluorine-doped tin oxide (FTO) glass as the substrate for a counter-electrode. Although Pt exhibits excellent catalytic activity for tri-iodide reduction and good electric conductivity, it is expensive and has the problem of reserves for large scale application. Higher economic impact is produced by TCO (ITO or FTO) glass substrate, mainly attributable to the cost for the oxide deposition under high vacuum condition that is required to prepare the conductive glass plates. Beside this, for the fabrication of flexible DSSCs, conductive substrates made by indium tin oxide (ITO)-coated polymeric plates (mainly PEN and PET) are generally used. But ITO’s rigid inorganic crystal structure develops hairline fractures upon bending, which are quite detrimental to the overall electrical performances. Consequently, developing a alternative counter-electrode able to replace both Pt and TCO glassand to guarantee high catalytic activity, flexibility, low electrical resistance and low production cost is still an attractive and worthwhile target. 1-5

Figure 1 SEM micropgraphs of our engineered free-standing counter electrode showing a film of vertically aligned CNTs that after being transferred on the top of the CNTs-based nanocomposite plate.

Starting from these remarks, we recently developed a general approach to realize CNTs/polypropylene nanocomposite plates that can be conveniently implemented to fabricate flexible and free-standing counter-electrode for dye solar cells. 6 Both morphological and electrochemical analysis revealed that the oxygen plasma treatment constitutes an easy and effective method to selectively remove the excess polymer of this nanocomposite, allowing CNTs to properly protrude from the polymeric matrix. In order to achieve a major control of the electro-catalytic activity of the nanocomposite, different series of plates were realized by tuning the carbon nanotubes concentration from 5 wt% to 20 wt%. The most meaningful electrochemical parameters of all the plasma treated surfaces were quantitatively analyzed by means of both electrochemical impedance spectroscopy and cyclic voltammetry

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measurements in order to elucidate how composition and topography impact on the ultimate performances of the counterelectrode plates. Recently this approach has been further extended by the implantation of a layer of vertical aligned multi-walled carbon nanotubes (VACNTs) on the top of the nanocomposite plate. VACNTs were first grown up onto an aluminium foil by PECVD and then transferred to the nanocomposite surface by hot embossing. The plate was finally used as counter electrode in a dye solar cell: it exhibited a 7.7% energy conversion efficiency, that is comparable with efficiency value (8.0%) measured for Pt-based cells. 7

References [1] Li, P.; Wu, J.; Lin, J.; Huang, M.; Huang, Y.; Li, Q., High-performance and low platinum loading Pt/Carbon black counter electrode for dye-sensitized solar cells. Solar Energy 2009, 83, (6), 845-849. [2] Chen, J.; Li, K.; Luo, Y.; Guo, X.; Li, D.; Deng, M.; Huang, S.; Meng, Q., A flexible carbon counter electrode for dye-sensitized solar cells. Carbon 2009, 47, (11), 2704-2708. [3] Huang, Z.; Liu, X.; Li, K.; Li, D.; Luo, Y.; Li, H.; Song, W.; Chen, L.; Meng, Q., Application of carbon materials as counter electrodes of dye-sensitized solar cells. Electrochemistry Communications 2007, 9, (4), 596-598. [4] Ramasamy, E.; Lee, W. J.; Lee, D. Y.; Song, J. S., Spray coated multi-wall carbon nanotube counter electrode for tri-iodide reduction in dye-sensitized solar cells. Electrochemistry Communications 2008, 10, (7), 1087-1089. [5] Lee, K. S.; Lee, W. J.; Park, N.-G.; Kim, S. O.; Park, J. H., Transferred vertically aligned N-doped carbon nanotube arrays: use in dye-sensitized solar cells as counter electrodes. Chemical Communications 47, (14), 4264-4266. [6] Malara F. et al., Flexible carbon nanotubes-based electrocatalytic plates as efficient monolithic counterelectrodes for DSSCs. ACS Appl. Mater. Interf. 2011, 3 (9), 3625–3632 [7] Malara F. et al., "Engineered carbon-based nanocomposite foil as highly efficient free-standing counter electrode for dye solar cells". submitted to En. Env. Sci.

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C162 - Aggregation and Isomerisation in the Solar Cell Dye D149

Ahmed El-Zohrya, Burkhard Zietz*a

Dept. of Chemistry - Ångström, Uppsala University, Box 523, Uppsala, 751, SE

D149, a metal-free indoline dye, has shown very high solar energy conversion efficiencies of 9 % and is one of the most promising sensitisers for dye-sensitised solar cells (DSSC). Effective electron injection from the excited state is a prerequisite for high efficiencies and is lowered by competing deactivation pathways. Previous investigations have shown surprisingly short-lived excited states for this dye, with maximum components of 100 - 720 ps in different solvents and less than 120 ps for surface-adsorbed D149.2 Using steady-state and time-resolved fluorescence, we have investigated the photochemical properties of D149 in non-polar and polar solvents, polymer matrices and adsorbed on ZrO2, partially including a co-adsorbent. Results show that lifetimes of 100-330 ps in solution are increased to more than 2 ns for D149 in polymer matrices and on ZrO2.

Figure 1 Chemical Structure of D149

This is attributed to blocked isomerisation due to steric constrains. Conversely, concentration dependent aggregation leads to a dramatic reduction in lifetimes that also can affect solar cell performance. Our results explain the unexpectedly short lifetimes observed previously and show that photochemical properties such as lifetimes determined in solution are not transferable to the working environment in solar cells. The mechanistic understanding obtained should help developing design strategies for further improvement of solar cell dyes.

References [1] Lohse, P. W.; Kuhnt, J.; Druzhinin, S. I.; Scholz, M.; Ekimova, M.; Oekermann, T.; Lenzer, T.; Oum, K. "Ultrafast photoinduced relaxation dynamics of the indoline dye D149 in organic solvents", Phys. Chem. Chem. Phys., 13, 19632 (2011). [2] Fakis, M.; Stathatos, E.; Tsigaridas, G.; Giannetas, V.; Persephonis, P. "Femtosecond Decay and Electron Transfer Dynamics of the Organic Sensitizer D149 and Photovoltaic Performance in Quasi-Solid-State Dye-Sensitized Solar Cells", J. Phys. Chem. C, 115, 13429 (2011).

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C163 -Dye-sensitized Solar Cells and Complexes between Pyridines and Iodines. A NMR, IR and DFT study.

Poul Erik Hansen*a, Phuong Tuyet Nguyena, Jacob Krakea, Jens Spanget-Larsena, Torben Lunda

Roskilde University, Universitetsvej 1, 18.2, Roskilde, 0, DK

Interactions between triiode (I3-) and 4-tert-butylpyridine (4TBP) as postulated in dye-

sensitized solar cells (DSC) are investigated by means of 13C NMR and IR spectroscopy supported by DFT calculations. The charge transfer (CT) complex 4-TBP.I2 and potential salts such as (4TBP)2I

+, I3- were synthesized and characterized by IR and 13C NMR spectroscopy.

However, mixing (butyl)4N+, I3

- and 4TBP at concentrations comparable to those of the DSC solar cell did not lead to any reaction. Neither CT complexes nor cationic species like (4TBP)2I

+ were observed, judging from the 13C NMR spectroscopic evidence. This questions the previously proposed formation of (4TBP)2I

+ in the DSC cells.

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C164 - High electron lifetime in transparent TiO2 nanotubes-based photoanode for front-illuminated dye-sensitized solar cell

Andrea Lambertia, Adriano Sacco*a, Stefano Biancoa, Diana Hidalgoa, Diego Manfredia, Rossana Gaziaa, Marzia Quaglioa, Angelica Chiodonia, Elena Tressob, Candido Fabrizio Pirria

a, Istituto Italiano di Tecnologia IIT@polito, C.so Trento 21, Turin (Italy) , 10129, IT b, Politecnico di Torino, C.so Duca degli Abruzzi 24, Turin (Italy) , 10129, IT

In the present work, the fabrication and characterization of non-curling, free-standing TiO2 nanotubes (nts) membranes and their integration in front-side illuminated dye-sensitized solar cells (DSCs) are reported. Vertically oriented TiO2 nt arrays were fabricated by a two steps anodic oxidation of titanium foil. A sacrificial layer based on a thin photoresist film, spin coated on the titanium foil prior to anodization, helped in obtaining open-end tubes. Free-standing nts membranes were easily separated by the metallic substrate without any crack, following a self-detaching procedure consisting in repeated rinsing in DI-water and ethanol. The membranes were then transferred and bonded on transparent FTO/glass substrates employing a layer of tape-casted commercial titania nanoparticles paste as well as a TiO2 sol as a binder before sintering at 500 C for 1 hour. Stoichiometry, crystalline phase, quality and morphology of the film were investigated, evidencing the formation of a highly ordered 1D nts arrays, with a pure anatase crystalline structure.

Figure 1

The as prepared photoanodes were treated with TiCl4 in order to increase the surface area and to reduce recombination at the electrolyte/FTO interface. TiO2 nts-based DSCs were fabricated using both a reversible microfluidic architecture [1] and a standard thermoplastic irreversible sealing. Dye loading on the metal-oxide surface was analyzed with UV-Vis spectroscopy, and the dependence of the cell efficiency on nts thickness and dye incubation time was studied by I-V electrical characterization, incident-photon-to-electron conversion efficiency and impedance spectroscopy measurements under AM 1.5 illumination. Compared to the standard nanoparticle-based DSCs, the TiO2 nts-based devices show an increase in electrons lifetime. Employing TiO2 sol instead of nanoparticles paste it is possible to reduce the thickness of the adhesion layer, obtaining a lower electron recombination at the nts/nps/FTO interfaces.

References [1] Lamberti, A.; Sacco, A.; Bianco, S.; Giuri, E.; Quaglio, M.; Chiodoni, A.; Tresso, E. "Microfluidic sealing and housing system for innovative dye-sensitized solar cell architecture" Microelectron. Eng. 88, 2308-2310 (2011).

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