1 Photoinduced Charge Transfer in Bulk Heterojunction
Composites
Christoph J. Brabec, Vladimir Dyakonov ....................... 1
1.1 Conjugated Polymer-Fullerene Blend: A Highly Efficient
System for Photoinduced Charge Generation ............... 2
1.2 Molecular Semiconductor Picture of Conjugated Polymers .. 4
1.2.1 Molecular Structure .............................. 4
1.2.2 Optical and Electronic Properties ................ 6
1.2.3 Characterisation of Excited States ............... 7
1.2.4 Photoinduced Electron Transfer in Pure
Conjugated Polymers and Molecules ............... 10
1.2.5 Photoinduced Electron Transfer in Donor-
Acceptor Systems ................................ 15
1.3 Detection of Charges in Conjugated Polymers ............ 16
1.3.1 Pump-Probe Spectroscopy ......................... 16
1.3.2 Application of Pump-Probe Spectroscopy in the
ms Range to Conjugated Polymer/Fullerene
Blends .......................................... 19
1.4 Kinetics of Photoinduced Charge Generation in
Conjugated Polymer/Fullerene Blends .................... 21
1.5 Light-Induced Electron-Spin Resonance Detection of
the Charge Transfer Process ............................ 26
1.6 Oligo-Phenylene Vinylene: A Model System for Donor-
Acceptor Interactions .................................. 29
1.7 Conclusion ............................................. 51
References .................................................. 51
2 Optical and Spectroscopic Properties of Conjugated
Polymers Davide Comoretto, Guglielmo Lanzani ................ 57
2.1 Material and Optical Properties ......................... 58
2.1.1 Optical Constants and Electronic Structure ...... 61
2.1.2 Determination of n by Spectroscopic Methods ..... 62
2.1.3 Anisotropy ...................................... 65
2.1.4 Examples ........................................ 67
2.2 Spectroscopic Properties of Excited States ............. 71
2.2.1 Basic Notions of Pump-Probe Spectroscopy ........ 72
2.2.2 Interpretation of Pump-Probe Experiments ........ 73
2.2.3 Isolated Molecules .............................. 75
2.2.4 Condensed Phase ................................. 77
2.3 Conclusion ............................................. 80
2.4 Appendix: Derivation of (2.17) ......................... 80
2.5 Appendix: Overview of Decay Kinetics ................... 82
References .................................................. 84
3 Transport Properties of Conjugated Polymers
Reghu Menon ................................................. 91
3.1 Disorder and Localization .............................. 92
3.2 Conduction in Conjugated Systems ....................... 95
3.3 Metal-Insulator Transition ............................. 99
3.4 Hopping Transport ..................................... 105
3.5 Magnetoresistance ..................................... 108
3.6 Thermopower ........................................... 11З
3.7 Conclusion ............................................ 115
References ................................................. 116
4 Quantum Solar Energy Conversion and Application to
Organic Solar Cells
Gottfried H. Bauer, Peter Würfel ........................... 118
4.1 Solar Radiation ....................................... 118
4.2 Solar Cells and General Quantum Converters ............ 120
4.2.1 Two-Level Systems .............................. 121
4.2.2 Fermi Distribution ............................. 122
4.2.3 Quasi-Fermi Distribution ....................... 122
4.2.4 Transition Rates and Optical Properties ........ 123
4.2.5 Current-Voltage Characteristic ................. 125
4.3 Semiconductor Solar Cells as Two-Band Systems ......... 127
4.3.1 Fermi Distribution ............................. 128
4.3.2 Doping ......................................... 129
4.3.3 Quasi-Fermi Distributions ...................... 130
4.3.4 Interaction of Light with Matter ............... 131
4.3.5 Generation of Electron-Hole Pairs .............. 135
4.3.6 Recombination .................................. 136
4.4 Radiative Limit for Solar Cell Efficiencies ........... 138
4.4.1 Current-Voltage Characteristic .................. 139
4.5 Charge Separation in Solar Cells ...................... 141
4.5.1 Charge Transport ............................... 143
4.5.2 Transport Equations for Semiconductor Solar
Cells .......................................... 147
4.5.3 Charge Transport in Low Mobility Materials ..... 148
4.5.4 Carrier Mobilities in Organic Semiconductors ... 150
4.5.5 Equivalent Circuits for Solar Cells ............ 151
4.6 Conclusions for Solar Cell Requirements ................ 153
4.6.1 Special Geometrical Design ..................... 153
4.6.2 Particular Optical Design/Multispectral
Conversion ..................................... 155
References ................................................. 156
5 Semiconductor Aspects of Organic Bulk Heterojunction
Solar Cells
Christoph J. Brabec ........................................ 159
5.1 Device Architectures .................................. 160
5.1.1 Single-Layer Diodes ............................ 160
5.1.2 Heterojunction Diodes .......................... 162
5.1.3 Bulk Heterojunction Solar Cells ................ 163
5.2 Device Aspects and Transport Properties ............... 169
5.2.1 Transport Properties of Diodes ................. 169
5.2.2 Metal/Conjugated Polymer Contacts .............. 177
5.2.3 Simulation and Modelling ....................... 183
5.3 Performance Analysis of Bulk Heterojunction Solar
Cells ................................................. 185
5.3.1 Precise Calibration of Solar Cells ............. 186
5.3.2 Production: Device Geometry .................... 188
5.3.3 Short-Circuit Current .......................... 190
5.3.4 Open-Circuit Voltage Voc ....................... 205
5.3.5 Fill Factor FF ................................. 214
5.3.6 Spectral Response .............................. 221
5.3.7 Temperature Behavior of Bulk Heterojunction
Solar Cells .................................... 229
5.3.8 Stability of Polymeric Semiconductors and
Devices: A Molecular View ...................... 236
5.3.9 Processing of Polymeric Semiconductors:
Blending with Conventional Polymers ............ 240
5.4 Conclusion ............................................ 242
References ................................................. 243
6 Organic Photodiodes: Prom Diodes to Blends
Olle Inganäs, Lucimara Stolz Roman ......................... 249
6.1 Thin Film Organic Photodiodes ......................... 250
6.2 Optical Mode Structure in Thin Film Organic
Structures. Optimization of Bilayer Geometries ........ 251
6.3 Internal and External Quantum Efficiencies of
Organic Photodiodes ................................... 263
6.4 Electrical Transport in Photodiodes ................... 264
6.5 Nanostructure in Polymer/Molecule and Polymer/
Polymer Blends ........................................ 265
6.6 Conclusion ............................................ 270
References ................................................. 271
7 Dye-Sensitized Solar Cells
Jan Kroon, Andreas Hinsch .................................. 273
7.1 Operating Principles and Cell Structure of the
nc-DSC ................................................ 275
7.2 Manufacture of a Standard Glass/Glass nc-DSC .......... 277
7.3 Module Designs ........................................ 278
7.3.1 Series Connection of Glass/Glass Devices:
Z- and W-Type Interconnection .................. 279
7.3.2 Series Connection: Three-Layer or Monolithic
Module ......................................... 280
7.4 Sealing Aspects ....................................... 280
7.5 Technological Development and the State of the Art .... 281
7.6 Large Scale Batch Processing of Mini-Modules .......... 283
7.7 Long Term Stability ................................... 285
7.7.1 Stability Tests on Indoor Dye PV Modules ....... 285
7.7.2 Long Term Stability Tests on High Power
nc-DSC ......................................... 286
7.8 Outlook ............................................... 288
References ................................................. 289
Index ......................................................... 291
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