Technische Universität München
Morphology of bulk heterojunction systems
for polymer-based photovoltaics
Matthias A. Ruderer, S.M. Prams, M. Rawolle, G. Kaune,
W. Wang, Q. Zhong, E. Metwalli, P. Müller-Buschbaum
Technische Universität München, Physik-Department E13,
Lehrstuhl für Funktionelle Materialien, James-Franck-Str.1, 85747 Garching
J. Perlich, S.V. Roth1
1HASYLAB at DESY, Notkestr. 85, 22603 Hamburg
1st Colloquium of the Munich Scholl of Engineering
Technische Universität München
18.07.2011 Matthias A. Ruderer 2
Conventional photovoltaics
• energy-consuming production
• high vacuum treatment needed
• mechanically inflexible
• expensive encapsulation
solarpaneltips.org
First Solar Inc.
Technische Universität München
Efficiencies
8.3 %
in 2010
2008 Solar Technologies Market Report, Jan 2010
spacetoday.org
solarpaneltips.org
konarka.com
18.07.2011 Matthias A. Ruderer 3
Technische Universität München
Polymer-based technology
konarka.com
konarka.com
konarka.com
konarka.com
solopower.com
18.07.2011 Matthias A. Ruderer 4
Technische Universität München
transparent conducting
electrode
metal electrode
Organic solar cell
blocking layers
optical spacers ii) high exciton binding energy (~ 1 eV)
charge carrier separation at interfaces
G. Yu et al., J. Appl. Phys., 78, 4510 (1995)
organic materials
short exciton diffusion length (~ 10 nm)
performance strongly depending on
morphology
i) high absorption coefficient
18.07.2011 Matthias A. Ruderer 5
Technische Universität München
Morphologies
interfacial area ~ free charge carrier creation
efficiency
K. M. Coakley et al. Chem. Mater.,16, 4533 (2004).
M. A. Ruderer et al. Soft Matter, 7, 5482 (2011).
bulk heterojunction
18.07.2011 Matthias A. Ruderer 6
self assembly process
chemical structure
solvent
blending ratio
post production
treatments
Technische Universität München
Solvent dependent morphologies
M. A. Ruderer et al. Adv. Funct. Mater. (2011), in press.
1. high interfacial area
2. high conductivity
influence of
blending ratio
polymer
crystallinity
0.0 0.2 0.4 0.6
U (V)
-8
-6
-4
-2
0I
(mA
/cm
2)
400 600 800
(nm)
0.000
0.005
0.010
0.015
(n
m-1)
550 600 650 700 750 800 850 900
(nm)
0
5
10
15
20
25
PL
(a.u
.)a)
b)
c)
AM1.5G
AM1.5D
18.07.2011 Matthias A. Ruderer 7
electronic characteristics
Poster: Shuai Guo
Technische Universität München
morphology of bulk heterojunctions
P3HT MEH-PPV
M.A. Ruderer et al. ChemPhysChem, 10, 664 (2009).
poly(3-hexylthiophene-2,5-diyl)
Mw = 16 kg/mol
poly[(1-methoxy)-4-(2-
ethylhexyloxy)-p-phenylenevinylene]
Mw = 2600 kg/mol
18.07.2011 Matthias A. Ruderer 8
blending
ratio
Technische Universität München
Blending ratio
blending ratio independent absorption
no preferred blending ratio
thin films via spin coating
dissolve polymer in chloroform with
different blending ratios
homogeneous polymer films
with constant thickness
substrates:
acidic cleaned glass
slides
18.07.2011 Matthias A. Ruderer 9
absorption
Technische Universität München
Blending ratio
lateral inner film structure
121
1
NNC
Flory-Huggins theory: accessible with
scattering techniques
(GISAXS)
10 nm – 2 µm
good estimation of minimal structure
size with Flory-Huggins theory
18.07.2011 Matthias A. Ruderer 10
M.A. Ruderer et al. ChemPhysChem, 10, 664 (2009).
Technische Universität München
crystallinity in bulk heterojunctions
P3OT
M.A. Ruderer et al. J. Phys. Chem. B, 114, 15451 (2010).
poly(3-octylthiophene-2,5-diyl)
Mw = 34 kg/mol b
ind
ing
en
erg
y [
eV
]
CN-PPV
poly(2,5-di(hexyloxy)
cyanoterephthalyliden)
Mw 29 kg/mol
18.07.2011 Matthias A. Ruderer 11
Technische Universität München
Crystallinity
18.07.2011 Matthias A. Ruderer 12
molecular arrangement/crystalline structure
accessible with scattering techniques (GIWAXS)
resolution 2 Å – 5 nm
as-spun
annealed
(140 oC)
P3OT
increased crystallinity
higher charge carrier mobility
similar results for CN-PPV
conjugation planes
a
b a
b
Technische Universität München Bulk Heterojunction Film
P3OT:CN-PPV as-spun
annealed
(140 oC)
blending retards crystallization low performance
no signal from
CN-PPV
P3OT
18.07.2011 Matthias A. Ruderer 13
M.A. Ruderer et al. J. Phys. Chem. B, 114, 15451 (2010).
Technische Universität München
Summary
a) organic solar cells preparation
self assembly process
b) minimal structure size at critical blending ratio
predicted by theory
c) retardation of crystallization due to blending
low photovoltaic performance
Internal morphology is crucial for photovoltaic performance!
Funding:
Bavarian State Ministry of Science, Research and Art
International Graduate School “Material Science of Complex Interfaces“
18.07.2011 Matthias A. Ruderer 14
Thank
you!
Technische Universität München
18.07.2011 Matthias A. Ruderer 15
Technische Universität München
3/21/2011 Matthias A. Ruderer 16
Grazing incidence wide/small angle scattering
resolution: 10 nm – 2 µm
resolution: 0.2 nm – 5 nm
Top Related