The versatility of organic photovoltaics is already well known and this completely revised, updated, and enlarged edition of a classic provides an up-to-date overview of this hot topic. The proven structure of the successful first edition, divided into the three key aspects of successful device design: materials, device physics, and manufacturing technologies, has been retained. Important aspects such as printing technologies, substrates, and electrode systems are covered. The result is a balanced, comprehensive text on the fundamentals as well as the latest results in the area that will set R&D trends for years to come. With its combination of both academic and commercial technological views, this is an optimal source of information for scientists, engineers, and graduate students already actively working in this field, and looking for comprehensive summaries on specific topics.
List of Contributors XIII Part One Materials for Thin Film Organic Photovoltaics 1 1 Overview of Polymer and Copolymer Materials for Organic Photovoltaics 3 Solon P. Economopoulos, Grigorios Itskos, Panayiotis A. Koutentis, and Stelios A. Choulis
1.1 Introduction 3
1.2 Early Efforts 4
1.3 Toward Devices with 5% Efficiencies 5
1.4 Novel Thiophene-Containing Polymers 8
1.5 Fluorene-Containing Molecules 11
1.6 Carbazole-Based Copolymers 13
1.7 New Heterocyclic Polymers 15
1.8 Polymers Based on Other Types of Building Blocks 16
1.9 Conclusions 17 References 18 2 Thiophene-Based High-Performance Donor Polymers for Organic Solar Cells 27 Bob C. Schroeder, Raja Shahid Ashraf, and Iain McCulloch
2.1 Introduction 27
2.2 Bandgap Engineering 28
2.3 Charge Generation in Bulk Heterojunction Organic Solar Cells 29
2.4 Polyalkylthiophenes 31
2.4.1 Synthesis 31
2.4.2 Optical and Solid-State Properties 33
2.5 Polyalkylthiophene/PCBM Blends 35
2.6 Polythiophene Copolymers 37
2.7 Side Chain Functionalized P3AT Derivatives 38
2.8 Third-Generation Polythiophenes 39
2.9 Thiophene-Based Push Pull Copolymers 42
2.10 Benzo[1,2-b:4,5-b0]dithiophene-Based Polymers 44
2.11 Cyclopenta[2,1-b:3,4-b0]dithiophene-Based Polymers 46
2.12 Indacenodithiophene-Based Polymers 50
2.13 Conclusion and Outlook 54 References 55 3 Molecular Design of Conjugated Polymers for High-Efficiency Solar Cells 61 Liqiang Yang, Huaxing Zhou, Andrew C. Stuart, and Wei You
3.1 Introduction 61
3.2 Structural Features of Conjugated Polymers 63
3.3 D A Approach 64
3.3.1 Rational Design of Conjugated Backbones: Weak Donor Strong Acceptor Copolymer 64
3.3.1.1 Weak Donor Moieties to Improve VOC 67
3.3.1.2 Balancing VOC and JSC: Interplay of Bandgap and Energy Levels 71
3.3.1.3 From BT to 4DTBT: Why is a Soluble Acceptor Better? 72
3.3.1.4 Strong Acceptor Moieties to Increase JSC 73
3.3.2 Side Chains Are NOT Trivial 76
3.3.2.1 Chain Positions 76
3.3.2.2 Shape and Size 80
3.3.3 Substituents Do Matter: The Curious Case of Fluorine 83
3.4 Quinoid Approach 88
3.5 Summary and Outlook 91 References 91 4 Solution-Processed Molecular Bulk Heterojunction Solar Cells 95 Jianhua Liu, Bright Walker, and Thuc-Quyen Nguyen
4.1 Introduction 95
4.2 Monochromophoric Molecules 96
4.2.1 Conjugated Macrocycles and Polycycles 96
4.2.2 Acenes and Heteroacenes 98
4.2.3 Oligothiophenes 103
4.3 Multichromophoric Molecules 105
4.3.1 Colorant Chromophore-Containing Derivatives 107
4.3.1.1 Diketopyrrolopyrrole and Isoindigo Derivatives 107
4.3.1.2 Squaraine Derivatives 111
4.3.1.3 Merocyanine and Borondipyrromethene Derivatives 116
4.3.2 Oligothiophene Derivatives 117
4.3.3 Benzothiadiazole Analogue Derivatives 121
4.3.4 Triphenylamine Derivatives 126
4.4 Summary and Future Directions 129 References 133 5 Vacuum-Processed Donor Materials for Organic Photovoltaics 139 Amaresh Mishra and Peter B auerle
5.1 Introduction 139
5.1.1 Basic Characterization of Organic Solar Cells 140
5.2 Planar and Bulk Heterojunction Solar Cells 142
5.3 Summary and Future Prospects 166 Acknowledgments 167 References 168 6 Polymer Nanocrystal Hybrid Solar Cells 171 Michael Eck and Michael Krueger
6.1 Introduction 171
6.2 Semiconductor Nanocrystals 172
6.3 Working Principles and Device Structure 177
6.3.1 Donor and Acceptor Materials 181
6.4 Evolution of Polymer NC Hybrid Solar Cells 184
6.5 Recent Approaches for Overcoming Current Limitations 188
6.5.1 In Situ Synthesis of NCs in the Polymer Film 188
6.5.2 Nanostructured Polymer-Based Assemblies in Solution 189
6.5.3 Lower Bandgap NC Acceptors 191
6.6 Novel Concepts and Perspectives 192
6.6.1 Ternary NC Systems: Energy Level and Bandgap Tuning 192
6.6.2 NC Ligand Design 195
6.6.3 Functionalized Polymers 195
6.6.4 Inorganic Framework for Interdigitated D A Layers 196
6.6.4.1 Porous Alumina Template-Assisted Approach 197
6.6.4.2 Nanostructured Inorganic Semiconductors as Acceptor Material 198
6.6.5 Nanostructured Polymer 199
6.6.6 Carbon-Based Acceptors and Nanocomposites 199
6.6.7 Less Toxic NC Acceptor Materials 200
6.7 Summary and Outlook 200 Acknowledgments 201 References 201 7 Fullerene-Based Acceptor Materials 209 Alexander B. Sieval and Jan C. Hummelen
7.1 Introduction and Overview 209
7.2 Fullerenes as n-Type Semiconductors 211
7.2.1 Electron-Accepting and Transporting Properties 211
7.2.2 Other Electronic Properties 213
7.3 Fullerene Derivatives 214
7.3.1 [60]PCBM 215
7.3.2 [60]PCBM Analogues 219
7.3.3 Substituents on the Phenyl Moiety of PCBM 221
7.3.3.1 Alkoxy Groups 221
7.3.3.2 Fluorination 222
7.3.3.3 Deuterium Labeling 222
7.3.4 Other C60 Derivatives in OPVs 223
7.4 Derivatives of C70 and C84 226
7.4.1 Derivatives of C70 226
7.4.2 Derivatives of C84 229
7.5 Fullerene Bisadducts 230
7.6 Endohedral Compounds 233
7.7 Commercialization of Fullerene Derivatives 233 References 234 8 Polymeric Acceptor Semiconductors for Organic Solar Cells 239 Antonio Facchetti
8.1 Introduction 239
8.2 Basics Principles and Operation for Organic Solar Cells 241
8.3 Polymeric Acceptor Semiconductors 245
8.3.1 Cyanated Polyphenylenevinylenes 246
8.3.2 Perylene- and Naphthalenediimide-Based Polymers 257
8.3.3 Benzothiadiazole-Based and Other Electron-Poor Polymers 275
8.4 Conclusions and Perspective 293 References 296 9 Water/Alcohol-Soluble Conjugated Polymer-Based Interlayers for Polymer Solar Cells 301 Fei Huang, Chengmei Zhong, Hongbin Wu, and Yong Cao
9.1 Introduction 301
9.2 The Development of Water/Alcohol-Soluble Conjugated Polymers as Interlayer Materials 302
9.3 Interface Engineering for Polymer Solar Cells 305
9.3.1 Interface Modification for Metal Electrodes 306
9.3.2 Interface Modification for Metal Oxide Electrodes 308
9.3.3 Interface Modification for Graphene and Carbon Nanotube Electrodes 311
9.4 Discussion of the Working Mechanism 311
9.5 Summary 315 References 316 10 Metal Oxide Interlayers for Polymer Solar Cells 319 Kevin M. O Malley, Hin-Lap Yip, and Alex K.-Y. Jen
10.1 Introduction 319
10.2 Conventional Structure 320
10.2.1 Hole-Selective Layer: Replacing PEDOT:PSS 320
10.2.1.1 Nickel Oxide 322
10.2.1.2 Vanadium, Molybdenum, and Tungsten Oxides 324
10.2.2 Electron-Selective Layer 326
10.2.2.1 Titanium and Zinc Oxides 326
10.3 Inverted Structure 329
10.3.1 Electron-Selective Layer: Reducing the Effects of Cathode Oxidation 329
10.3.1.1 Titanium, Zinc, and Cesium Oxides 331
10.3.1.2 Modification via Molecular Self-Assembly 332
10.4 Tandem Structure 333
10.5 Additional Oxides (Cr2O3, CuOx, PbO) 338
10.6 Conclusions 339 References 339 Part Two Device Physics of Thin Film Organic Photovoltaics 343 11 Bimolecular and Trap-Assisted Recombination in Organic Bulk Heterojunction Solar Cells 345 Gert-Jan A.H. Wetzelaer, L. Jan Anton Koster, and Paul W.M. Blom
11.1 Introduction 345
11.2 Recombination at Open Circuit 348
11.3 Trap-Assisted Recombination at Open Circuit 351
11.4 Investigation of the Nature Recombination by Electroluminescence Measurements 353
11.5 Bimolecular Recombination Strength in Organic BHJ Solar Cells 358
11.6 Bimolecular Recombination Losses Under Short-Circuit Conditions 366
11.7 Effect of Bimolecular Recombination on Fill Factor and Efficiency 372
11.8 Conclusions 373 References 373 12 Organic Photovoltaic Morphology 377 Brian A. Collins, Felicia A. Bokel, and Dean M. DeLongchamp
12.1 Introduction 377
12.2 Order in Bulk Heterojunctions 378
12.2.1 Optical Measurements of Order 378
12.2.2 X-Ray Measurement of Crystallinity 381
12.3 Nanoscale Morphology in Bulk Heterojunctions 385
12.3.1 Electron Microscopy 385
12.3.2 Small-Angle Scattering Measurements 388
12.4 Phases in a Bulk Heterojunction 390
12.5 Structure of the Interface between Phases 392
12.5.1 Inferences from Bulk Measurements 395
12.5.2 Surface-Sensitive Measurements 395
12.5.3 Measuring Buried Bilayer Interfaces 396
12.5.4 Measuring Buried Bulk Interfaces 401
12.6 In Situ Measurements of Morphology Development 403
12.6.1 In Situ X-Ray Measurements 403
12.6.2 In Situ Microscopy 407
12.6.3 In Situ Optical and Vibrational Spectroscopies 408
12.6.4 In Operando Measurements 412
12.6.5 The Future of In Situ Measurement 413 References 413 13 Intercalation in Polymer:Fullerene Blends 421 Nichole Cates Miller, Eric T. Hoke, and Michael D. McGehee
13.1 Introduction 421
13.2 Methods for Detecting Molecular Mixing 423
13.2.1 X-Ray Diffraction 423
13.2.2 Photoluminescence Measurements 424
13.2.3 Diffusion Measurements 425
13.2.4 Transmission Electron Microscopy Techniques 427
13.2.5 Small-Angle Scattering Techniques 427
13.3 Factors Affecting Molecular Mixing 428
13.3.1 Fullerene Size 428
13.3.2 Side-Chain Attachment Distance 430
13.3.3 Side-Chain Linearity 430
13.3.4 Thermal Treatments 432
13.4 The Effect of Molecular Mixing on Electronic Properties and Solar Cells 433
13.4.1 Exciton Harvesting 434
13.4.2 Geminate Pair Separation, Charge Extraction, and Optimal Blend Ratio 436
13.4.3 Additional Device Implications 439
13.5 Conclusions 440 References 441 14 Organic Tandem Solar Cells 445 Konstantin Glaser, Andreas P utz, Jan Mescher, Daniel Bahro, and Alexander Colsmann
14.1 Introduction and Working Principle 445
14.2 Measurement Techniques 448
14.3 Efficient Intermediate Charge Carrier Recombination 450
14.4 Light Management 452
14.5 Choice of Materials 457
14.6 Parallel Tandem Architectures 458
14.7 New Tandem Solar Cell Concepts 459
14.8 Conclusions 460 Acknowledgments 460 References 461 15 Solid-State Dye-Sensitized Solar Cells 465 Jonas Weickert and Lukas Schmidt-Mende
15.1 Introduction 465
15.2 Working Principles of Solid-State Dye-Sensitized Solar Cells 467
15.2.1 Solar Cell Geometries 467
15.2.2 Light Absorption and Charge Separation 471
15.2.3 Charge Transport 475
15.3 Loss Mechanisms in Solid-State Dye-Sensitized Solar Cells 478
15.4 Solid-State Dye-Sensitized Solar Cells with Spiro-OMeTAD as Hole Conductor 483
15.5 Hybrid Solar Cells with Absorbing Hole Conductors 484
15.6 Ordered Nanostructures for Solid-State Dye-Sensitized Solar Cells 486
15.6.1 TiO2 Nanowires 487
15.6.2 TiO2 Nanotubes 488
15.7 Summary and Outlook 489 References 490 Part Three Technology for Thin Film Organic PV 495 16 Reel-to-Reel Processing of Highly Conductive Metal Oxides 497 Matthias Fahland
16.1 Introduction 497
16.2 Materials 499
16.3 Deposition Technology 501
16.4 Equipment 503
16.4.1 Vacuum System 504
16.4.2 Winding System 505
16.4.3 Inline Measurement System 506
16.5 Alternative Approaches 507 References 510 17 Flexible Substrate Requirements for Organic Photovoltaics 513 William A. MacDonald and Julian M. Mace
17.1 Introduction 513
17.2 Polyester Substrates 514
17.3 Properties of Base Substrates 516
17.3.1 Optical Properties 516
17.3.2 Thermal Properties 517
17.3.3 Solvent Resistance 520
17.3.4 Surface Quality 523
17.3.5 Mechanical Properties 524
17.3.6 Hydrolysis Resistance 526
17.3.7 UV Stability 527
17.3.8 Barrier 531
17.3.9 Conductive Coated Film 535
17.3.10 Adhesion 535
17.4 Concluding Remarks 536 Acknowledgments 537 References 537 18 Adhesives for Organic Photovoltaic Packaging 539 Markus Rojahn, Marion Schmidt, and Kilian Kreul
18.1 Introduction 539
18.2 Encapsulation Process for Organic Photovoltaics 540
18.2.1 Basic Process Information 540
18.2.2 Lamination Process Examples 542
18.2.2.1 Radiation-only Curing Process 542
18.2.2.2 Dual Curing Process 544
18.3 Chemistry Aspects of Barrier Adhesives 545
18.3.1 Radically Light Curing Adhesives 545
18.3.2 Cationically Curing Adhesives 549
18.4 Barrier Performance of OPV Adhesives 554
18.4.1 The Intrinsic Barrier Performance of OPV Barrier Adhesives 554
18.4.2 Adhesion of the OPV Barrier Adhesives to the Interfaces 556
18.5 Conclusions 558 References 558 19 Roll-to-Roll Processing of Polymer Solar Cells 561 Dechan Angmo, Markus H osel, and Frederik C. Krebs
19.1 Introduction 561
19.2 The Roll-to-Roll Process 562
19.3 Structure of Modules 564
19.4 Coating and Printing Techniques for PSC Materials 565
19.4.1 Slot Die Coating 565
19.4.1.1 Novel Slot Die Techniques for Use in PSCs 568
19.4.2 Gravure Printing 568
19.4.3 Knife-Over-Edge 572
19.4.4 Flexographic Printing 573
19.4.5 Screen Printing 574
19.4.6 Inkjet Printing 576
19.4.7 Offset Lithography 578
19.5 Roll-to-Roll Printing of Electrodes 579
19.6 R2R Encapsulation 580
19.7 Roll-to-Roll Characterization 581
19.8 Future and Outlook 582 References 584 20 Current and Future Directions in Organic Photovoltaics 587 Giovanni Nisato and Jens Hauch
20.1 Scientific and Technological Aspects 590
20.2 Commercial Applications 592
20.3 Challenges and Major Hurdles 595 Acknowledgments 597 References 597 Index 599