POSTER TEMPLATE BY: Spectroscopic Studies of Charge and Energy Transfer Processes in...
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POSTER TEMPLATE BY: www.PosterPresentations.com Spectroscopic Studies of Charge and Energy Transfer Processes in Self-Organizing Heterogeneous Photovoltaic Materials Michael Kelley, Volodimyr Duzhko, Kenneth Singer Department of Physics. Case Western Reserve University, Cleveland, Ohio, 44106 Photovoltaic Cells Requirements to self- assembled structures for efficient exciton photo- excitation and interfacial dissociation: • Long fibers length (1 µm) to maximize light absorption • Distance to p-n junction less than exciton diffusion length ( 10 nm) • Homeotropic alignment (perpendicular to electrodes) Blended Spectra Traditional photovoltaic cells consist of a junction of doped P-type (positively charged) and N-type (negatively charged) inorganic semiconducting crystals, mostly silicon. The surplus charge on each plate generates an electric field drawing charges toward the junction. Photons strike electrons at the junction, exciting them. And generating free electrons in the semiconducting band and holes. These electrons and holes then pass through the junction in opposite directions and are carried through the plates to electrodes, generating electric current through a load. Organic Photovoltaics Absorbance and Photoluminescence Spectroscopy S 0 S 1 S 2 T 1 Processes: S 2 S 1 – internal conversion (<ps) S 1 S 0 – radiative decay (5 ns) S 1 S 0 – internal conversion (?) S 1 T 1 – Inter System Crossing (?) T 1 S o – internal conversion (100 s) HOMO LUMO HOMO LUMO E=hc/λ At the p-n junction, upon exciton dissociation, the free electron is transferred from the lowest unoccupied molecular orbital (LUMO) of the donor material to the LUMO of the acceptor material. If excitons efficiently dissociate between molecules of different species, the evidence appears in the absorbance and photoluminescence spectra. When the individual absorbance and photoluminescence spectra of the two species are summed together, and that sum is compared the spectra of the samples blended together, if the two spectra demonstrate distinct differences, charge in the ground state (absorption spectra) or in the first excited state (photoluminescence spectra) is being transferred. Acknowledgements I would like to extend my thanks to my research mentor, Dr. Volodimyr Duzhko, for his guidance throughout the summer, and to Dr. Kenneth D. Singer, the primary investigator of the laboratory. I would also like to extend my thanks to SOURCE, the Case Alumni Association, and to the Dominion foundation for the generous funding and for the opportunity to participate in this project. References N.S. Lewis, G. Crabtree, A.J. Nozik, and M.R. Wasielewski. Basic Research Needs for Solar Energy Utilization: Report of the Basic Energy Sciences Workshop on Solar Energy Utilization. United States Department of Energy: Office of Basic Energy Sciences, OSTI ID: 899136, 2005 Tang, C.W. Two-layer Organic Photovoltaic Cell. Applied Physics Letters. 48: 183-185 (1986). Hoppe, H.; Sariciftci, N. Organic Solar Cells: An Overview. J. Mater. Res. 19(7): 1924-1945 (2004). Duzhko, V.; Aqad, E.; Imam, M.R.; Peterca, M.; Percec, V.; Singer, K.D. Long-Range Electron Transport in a Self-Organizing N-Type Organic Material. Applied Physics Letters 92:113312 (3 pages) (2008). Kasha, M.; Rawls, H.R.; Ashraf El-Bayoumi, M. The Donor-Acceptor Molecular Electronic Transitions Kasha’s Theory* Conclusions Spectra of Each Species and Blend Sample Nanostructures Desirable Interaction Undesirable Interaction UV-vis-NIR Spectroscopy Photoluminescence Spectroscopy UV-vis-NIR absorption spectroscopy and photoluminescence spectroscopy are two versatile and non-destructive methods of probing the electronic configuration of a material and can be used to determine how charge carriers behave in different materials Absorption spectroscopy analyzes the structure of a material’s electronic energy levels by measuring the intensity of light emitted by deexcited electrons in a material compared to the wavelength of the light transmitted to excite the material. Photoluminescence spectroscopy measures the intensity of light emitted by a material over a spectrum of wavelengths after being excited by a monochromatic light source. The absence or presence of photoluminescence features can determine whether excited electrons transfer between molecules different materials or not. *M. Kasha et al. Pure Appl. Chem. 2, 371 (1965). According to Kasha’s molecular exciton theory, the energy stored in a dimer depends on arrangement of molecules and can be described as the potential interaction energy between electric dipole moments of two molecules. This energy can vary between the extremes of the maximum where the molecules’ transition moment vectors are parallel (H-type aggregate) and the minimum where the transition moment vectors are in line (J-type aggregate). Spectroscopy of energy levels of a given nanostructure versus those of single molecules in solution reveals information on molecular orientation in the nanostructure. Below are simulated graphs of the interaction energies between molecules of the two sample materials versus their relative orientations. 3 5 3 u u u v Mr Mr MM r r J-type Dipole Energy Equation and Monomer- Dimer Energy Diagrams for Extreme Orientations H-type λ ex = 525 nm Bulk Heterojunction Acceptor material Donor material Acceptor material Acceptor material Original Silicon Architecture “1-D” Architecture 2,3,9,10,16,17,23,24- Octakis(octyloxy)-29H,31H- phthalocyanine (Phthalocyanine derivative, H 2 PC) Electron Donor N,N′-bis(1-hexylheptyl)- perylene-3,4:9,10-bis- (dicarboximide) (Perylene Diimide derivative, PBI) Electron Acceptor N H N N N N NH N N OC 8 H 17 OC 8 H 17 H 17 C 8 O OC 8 H 17 H 17 C 8 O H 17 C 8 O OC 8 H 17 H 17 C 8 O O O O O C 13 H 27 H 27 C 13 This research was concerned with the correlated measurements of the structural and charge transfer properties in self-assembled nanofibers and donor- acceptor architectures of phthalocyanine (p-type) and perylene-dicarboximide (n-type) derivatives using UV-vis-NIR optical absorption and photo- emission spectroscopy. 400 500 600 700 800 -50000 0 50000 100000 150000 200000 250000 E xtin ctio n C oefficient(L*m ol -1 *cm -1 ) W a ve le n g th (n m ) H2PC+PTCBI 1 *1 0 -3 M PTC BI-C 6,7 in ch lo ro fo rm 1 *1 0 -3 M H 2PC -O C 8 in ch lo ro fo rm B le n d e d S olution C om p a riso n A bsorbance M e a su re m e n ts o f H 2PC -O C 8/PTC BI-C 6,7 B le n d in C hloroform Measurement of Molecular Orientation in Aggregates In order to gain information about the specific orientations of the molecules of the nanostructures of each species, temperature-dependent absorbance spectrum and photoluminescence spectrum measurements of the two species were taken. Shifts or new features in the spectra of the nanostructures and single molecule samples can reveal the characteristic formation patterns of the nanostructures. Measurements were performed while varying the concentration of the material in the sample, the temperature of the sample, and the type of solvent. 400 500 600 700 800 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 A bsorbance (arb.units) W a ve le ng th (n m ) 2 4.7 D egrees 30 D egrees 35 D egrees 40 D egrees 45 D egrees 50 D egrees 55 D egrees 60 D egrees 65 D egrees 70 D egrees 75 D egrees 80 D egrees 85 D egrees 90 D egrees 95 D egrees T em p e ra tu re D ependence ofP T C B IF ibers in C hlorobenzene 400 500 600 700 800 -0.1 0 -0.0 5 0 .00 0 .05 0 .10 0 .15 0 .20 0 .25 0 .30 0 .35 0 .40 0 .45 0 .50 0 .55 0 .60 0 .65 0 .70 0 .75 A bsorbance (arb.units) W a ve le n g th (n m ) 2 6 .1 D egrees 3 0 .5 D egrees 3 5 .3 D egrees 4 0 .3 D egrees 4 5 .3 D egrees 5 0 .3 D egrees 5 5 .3 D egrees 6 0 .3 5 D egrees Tem p e ra tu re D e p e n d e n ce o f P TC B IFibers in C holro form 400 500 600 700 800 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 A bsorbance (arb.units) W a ve len gth (nm ) 26.4 D egrees 30 D egrees 35 D egrees 40 D egrees 45 D egrees 50 D egrees 55 D egrees 60 D egrees 65 D egrees 70 D egrees 75 D egrees 80 D egrees 85 D egrees 90 D egrees 95 D egrees 100 D egrees 105 D egrees Tem p e ra tu re D ependence ofP T C B IF ib e rs in T olu en e Chlorobenzen e Chloroform Tolue ne -20000 0 20000 40000 60000 80000 100000 400 500 600 700 0 20000 40000 60000 80000 100000 E xtin ctio n C o e fficie n t (L *m ol -1 *c m -1 ) 1*10 -6 M 1*10 -5 M 1*10 -4 M 1.74*10 -3 M 2.2*10 -2 M A bsorbance S pectra ofV ario us C oncentrations ofH 2PC -O C 8 in C hloroform A bsorbance S pectra ofV arious C oncentrations ofP TC B I-C 6 ,7 in C hloroform W a ve le n gth (n m ) 5*10^-7 M 5*10^-6 M 5*10^-5 M 1*10^-3 M 5*10^-3 M 1.7*10^-2 M The manufacturing costs of today’s silicon-based photovoltaic cells are very high, rendering the large- scale production of solar panels prohibitively expensive. A potential solution for this problem is the development of photovoltaic cells from cost-effective organic semiconductors. However, the bilayer p-n junction, typical device architecture for inorganic photovoltaic cells, is inefficient due to the small diffusion length of excitons (bound electron and hole pairs) in organic materials. A solution to this problem is to make a nanostructured one-dimensional donor-acceptor device architecture. When light excites the electrons in such blends, excitons are created. At the junctions between the p-type and n-type materials, these excitons dissociate into free electrons and holes, with the electrons traveling through the n-type material and the holes traveling through the p-type material to the electrodes. The geometry of nanostructures needs to be optimized to improve charge generation and transportation. Self-assembly of discotic molecules was used to fabricate two types of nanofibers with electron (n-type) and hole (p-type) conductivities, and to embed the nanofibers into one-dimensional donor-acceptor blends. Concentration –Dependent Measurements of H2PC-OC 8 and PTCBI-C 13 in Chloroform Temperature-Dependent Measurements of PTCBI-C 13 in Various Solvents Interaction Energies vs. Orientation α θ The data reveal that upon cooling and high concentrations , the spectra of indvidual peaks gives way to plateaus of blended features and the appearance of additional features confirms the transition from single molecules in a solution to the formation of stacked nanostructures of particular orientations. The absence of additional features in the blended absorbance spectrum of single molecules compared to the spectrum of the sum confirms the absence of ground-state charge transfer. The quenching of the blended photoluminescence spectrum compared to the spectrum of the sum confirms excited-state charge transfer. 500 550 600 650 700 750 800 0 100000 200000 300000 400000 500000 600000 700000 800000 900000 P hotolum in e sce n ce (a rb . u n its) W ave le n g th (n m ) H2PC B lend PBIPL Sum P hotolum inescence S pectra ofS eparate S pecies and B lend
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Transcript of POSTER TEMPLATE BY: Spectroscopic Studies of Charge and Energy Transfer Processes in...
POSTER TEMPLATE BY:
www.PosterPresentations.com
Spectroscopic Studies of Charge and Energy Transfer Processes in Self-Organizing Heterogeneous Photovoltaic Materials
Michael Kelley, Volodimyr Duzhko, Kenneth SingerDepartment of Physics.
Case Western Reserve University, Cleveland, Ohio, 44106
Photovoltaic Cells
Requirements to self-assembled structures for efficient exciton photo-excitation and interfacial dissociation:
• Long fibers length (1 µm) to maximize light absorption
• Distance to p-n junction less than exciton diffusion
length ( 10 nm)• Homeotropic alignment (perpendicular to
electrodes)
Blended SpectraTraditional photovoltaic cells consist of a junction of doped P-type (positively charged) and N-type (negatively charged) inorganic semiconducting crystals, mostly silicon. The surplus charge on each plate generates an electric field drawing charges toward the junction. Photons strike electrons at the junction, exciting them. And generating free electrons in the semiconducting band and holes. These electrons and holes then pass through the junction in opposite directions and are carried through the plates to electrodes, generating electric current through a load.
Organic Photovoltaics
Absorbance and Photoluminescence Spectroscopy
S0
S1
S2
T1
Processes:S2 S1 – internal conversion (<ps) S1 S0 – radiative decay (5 ns)S1 S0 – internal conversion (?)S1 T1 – Inter System Crossing (?)T1 So – internal conversion (100 s)
HOMO
LUMO
HOMO
LUMO
E=hc/λAt the p-n junction, upon exciton dissociation, the free electron is transferred from the lowest unoccupied molecular orbital (LUMO) of the donor material to the LUMO of the acceptor material.
If excitons efficiently dissociate between molecules of different species, the evidence appears in the absorbance and photoluminescence spectra. When the individual absorbance and photoluminescence spectra of the two species are summed together, and that sum is compared the spectra of the samples blended together, if the two spectra demonstrate distinct differences, charge in the ground state (absorption spectra) or in the first excited state (photoluminescence spectra) is being transferred.
AcknowledgementsI would like to extend my thanks to my research mentor, Dr. Volodimyr Duzhko, for his guidance throughout the summer, and to Dr. Kenneth D. Singer, the primary investigator of the laboratory. I would also like to extend my thanks to SOURCE, the Case Alumni Association, and to the Dominion foundation for the generous funding and for the opportunity to participate in this project.
ReferencesN.S. Lewis, G. Crabtree, A.J. Nozik, and M.R. Wasielewski. Basic Research Needs for Solar Energy Utilization: Report of the Basic Energy Sciences Workshop on Solar Energy Utilization. United States Department of Energy: Office of Basic Energy Sciences, OSTI ID: 899136, 2005
Tang, C.W. Two-layer Organic Photovoltaic Cell. Applied Physics Letters. 48: 183-185 (1986).
Hoppe, H.; Sariciftci, N. Organic Solar Cells: An Overview. J. Mater. Res. 19(7): 1924-1945 (2004).
Duzhko, V.; Aqad, E.; Imam, M.R.; Peterca, M.; Percec, V.; Singer, K.D. Long-Range Electron Transport in a Self-Organizing N-Type Organic Material. Applied Physics Letters 92:113312 (3 pages) (2008).
Kasha, M.; Rawls, H.R.; Ashraf El-Bayoumi, M. The Exction Model in Molecular Spectroscopy. Pure Applied Chemistry 11(3-4): 371-392 (1965).
Donor-Acceptor Molecular Electronic Transitions
Kasha’s Theory*
Conclusions
Spectra of Each Species and Blend
Sample Nanostructures
Desirable Interaction Undesirable InteractionUV-vis-NIR Spectroscopy Photoluminescence Spectroscopy
UV-vis-NIR absorption spectroscopy and photoluminescence spectroscopy are two versatile and non-destructive methods of probing the electronic configuration of a material and can be used to determine how charge carriers behave in different materials Absorption spectroscopy analyzes the structure of a material’s electronic energy levels by measuring the intensity of light emitted by deexcited electrons in a material compared to the wavelength of the light transmitted to excite the material. Photoluminescence spectroscopy measures the intensity of light emitted by a material over a spectrum of wavelengths after being excited by a monochromatic light source. The absence or presence of photoluminescence features can determine whether excited electrons transfer between molecules different materials or not.
*M. Kasha et al. Pure Appl. Chem. 2, 371 (1965).
According to Kasha’s molecular exciton theory, the energy stored in a dimer depends on arrangement of molecules and can be described as the potential interaction energy between electric dipole moments of two molecules. This energy can vary between the extremes of the maximum where the molecules’ transition moment vectors are parallel (H-type aggregate) and the minimum where the transition moment vectors are in line (J-type aggregate). Spectroscopy of energy levels of a given nanostructure versus those of single molecules in solution reveals information on molecular orientation in the nanostructure. Below are simulated graphs of the interaction energies between molecules of the two sample materials versus their relative orientations.
3 5
3 u uu vM r M rM M
r r
�������������������������������������������������������� J-type
Dipole Energy Equation and Monomer-Dimer Energy Diagrams for Extreme Orientations
H-type
λ ex= 525 nm
Bulk Heterojunction
Acceptor materialDonor
material
Acceptor material
Acceptor material
Original Silicon Architecture
“1-D” Architecture
2,3,9,10,16,17,23,24-Octakis(octyloxy)-29H,31H-phthalocyanine (Phthalocyanine derivative, H2PC)
Electron Donor
N,N′-bis(1-hexylheptyl)-perylene-3,4:9,10-bis-(dicarboximide) (Perylene Diimide
derivative, PBI)Electron Acceptor
NH
N
NN
N
NH
NN
OC8H17
OC8H17
H17C8O OC8H17
H17C8O
H17C8O
OC8H17H17C8O
O
O
O
O
C13H27H27C13
This research was concerned with the correlated measurements of the structural and charge transfer properties in self-assembled nanofibers and donor-acceptor architectures of phthalocyanine (p-type) and perylene-dicarboximide (n-type) derivatives using UV-vis-NIR optical absorption and photo-emission spectroscopy.
400 500 600 700 800-50000
0
50000
100000
150000
200000
250000
Ext
inct
ion
Co
effi
cie
nt (
L*m
ol-1
*cm
-1)
Wavelength (nm)
H2PC+PTCBI
1*10-3 M PTCBI-C6,7
in chloroform
1*10-3 M H2PC-OC8 in chloroform
Blended Solution
Comparison Absorbance Measurements of H2PC-OC8/PTCBI-C6,7
Blend in Chloroform
Measurement of Molecular Orientation in Aggregates
In order to gain information about the specific orientations of the molecules of the nanostructures of each species, temperature-dependent absorbance spectrum and photoluminescence spectrum measurements of the two species were taken. Shifts or new features in the spectra of the nanostructures and single molecule samples can reveal the characteristic formation patterns of the nanostructures. Measurements were performed while varying the concentration of the material in the sample, the temperature of the sample, and the type of solvent.
400 500 600 700 800-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Abs
orba
nce
(arb
. uni
ts)
Wavelength (nm)
24.7 Degrees 30 Degrees 35 Degrees 40 Degrees 45 Degrees 50 Degrees 55 Degrees 60 Degrees 65 Degrees 70 Degrees 75 Degrees 80 Degrees 85 Degrees 90 Degrees 95 Degrees
Temperature Dependence of PTCBI Fibers inChlorobenzene
400 500 600 700 800-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
Abs
orba
nce
(arb
. uni
ts)
Wavelength (nm)
26.1 Degrees 30.5 Degrees 35.3 Degrees 40.3 Degrees 45.3 Degrees 50.3 Degrees 55.3 Degrees 60.35 Degrees
Temperature Dependence of PTCBI Fibersin Cholroform
400 500 600 700 800
-0.10-0.050.000.050.100.150.200.250.300.350.400.450.500.550.600.650.700.750.800.85
Abs
orba
nce
(arb
. uni
ts)
Wavelength (nm)
26.4 Degrees 30 Degrees 35 Degrees 40 Degrees 45 Degrees 50 Degrees 55 Degrees 60 Degrees 65 Degrees 70 Degrees 75 Degrees 80 Degrees 85 Degrees 90 Degrees 95 Degrees 100 Degrees 105 Degrees
Temperature Dependence of PTCBI Fibers in Toluene
Chlorobenzene Chloroform Toluene
-20000
0
20000
40000
60000
80000
100000
400 500 600 700
0
20000
40000
60000
80000
100000
Extin
ctio
n C
oe
ffic
ien
t (L
*mo
l-1*c
m-1) 1*10-6 M
1*10-5 M
1*10-4 M
1.74*10-3 M
2.2*10-2 M
Absorbance Spectra of Various Concentrations of H2PC-OC8 in Chloroform
Absorbance Spectra of Various Concentrations of PTCBI-C6,7
in Chloroform
Wavelength (nm)
5*10^-7 M 5*10^-6 M 5*10^-5 M 1*10^-3 M 5*10^-3 M 1.7*10^-2 M
The manufacturing costs of today’s silicon-based photovoltaic cells are very high, rendering the large-scale production of solar panels prohibitively expensive. A potential solution for this problem is the development of photovoltaic cells from cost-effective organic semiconductors. However, the bilayer p-n junction, typical device architecture for inorganic photovoltaic cells, is inefficient due to the small diffusion length of excitons (bound electron and hole pairs) in organic materials. A solution to this problem is to make a nanostructured one-dimensional donor-acceptor device architecture. When light excites the electrons in such blends, excitons are created. At the junctions between the p-type and n-type materials, these excitons dissociate into free electrons and holes, with the electrons traveling through the n-type material and the holes traveling through the p-type material to the electrodes. The geometry of nanostructures needs to be optimized to improve charge generation and transportation. Self-assembly of discotic molecules was used to fabricate two types of nanofibers with electron (n-type) and hole (p-type) conductivities, and to embed the nanofibers into one-dimensional donor-acceptor blends.
Concentration –Dependent Measurements of H2PC-OC8 and PTCBI-C13 in Chloroform
Temperature-Dependent Measurements of PTCBI-C13 in Various Solvents
Interaction Energies vs. Orientation
α
θ
The data reveal that upon cooling and high concentrations , the spectra of indvidual peaks gives way to plateaus of blended features and the appearance of additional features confirms the transition from single molecules in a solution to the formation of stacked nanostructures of particular orientations. The absence of additional features in the blended absorbance spectrum of single molecules compared to the spectrum of the sum confirms the absence of ground-state charge transfer. The quenching of the blended photoluminescence spectrum compared to the spectrum of the sum confirms excited-state charge transfer.
500 550 600 650 700 750 800
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
Pho
tolu
min
esce
nce
(arb
. uni
ts)
Wavelength (nm)
H2PC Blend PBI PL Sum
Photoluminescence Spectra of Separate Species and Blend
