Organic photovoltaic (OPV) cells have the potential to make a significant contribution to the increasing energy needs of the future. In this book, 15 chapters written by selected experts explore the required characteristics of components present in an OPV device, such as transparent electrodes, electron- and hole-conducting layers, as well as electron donor and acceptor materials. Design, preparation, and evaluation of these materials targeting highest performance are discussed. This includes contributions on modeling down to the molecular level to device-level electrical and optical testing and modeling, as well as layer morphology control and characterization. The integration of the different components in device architectures suitable for mass production is described. Finally, the technical feasibility and economic viability of large-scale manufacturing using fast inexpensive roll-to-roll deposition technologies is assessed.
Preface xvii
Part I: Materials and Device Architectures
1 Solution-Processed Donors 3 (68)
Beate Burkhart
Barry C. Thompson
1.1 Introduction 3 (7)
1.2 Design Principles for Bandgap and 10 (5)
Energy-Level Control of Donor Materials
1.3 State-of-the-Art Polymer and Small 15 (34)
Molecule Donors for Organic Solar Cells
1.3.1 Homopolymers 15 (2)
1.3.2 Perfectly Alternating 17 (1)
Donor/Acceptor Copolymers
1.3.2.1 BTD-based donor/acceptor 19 (1)
copolymers
1.3.2.2 TPD-based donor/acceptor 27 (1)
copolymers
1.3.2.3 Diketopyrrolopyrrole-and 28 (1)
isoindigo-based donor/acceptor
copolymers
1.3.2.4 Quinoxaline-based 33 (1)
donor/acceptor copolymers
1.3.2.5 Quinoidal acceptors: TT, TP, 34 (5)
and ITN
1.3.3 Random and Semirandom 39 (6)
Donor/Acceptor Copolymers
1.3.4 Small Molecule Donors 45 (4)
1.4 Conclusion and Outlook 49 (22)
2 Small-Molecule and Vapor-Deposited Organic 71 (56)
Photovoltaics
Richard R. Lunt
Russell J. Holmes
2.1 Introduction 71 (4)
2.2 Photovoltaic Characteristics 75 (6)
2.2.1 Thermodynamics and Open-Circuit 77 (4)
Voltage
2.3 Excitons 81 (4)
2.3.1 Spin and Intersystem Crossing 82 (2)
2.3.2 Singlet Fission 84 (1)
2.3.3 Implication of Oxygen Ground State 85 (1)
2.4 Energy Transfer and Exciton Migration 85 (10)
2.4.1 Exciton Diffusion and Crystalline 92 (1)
Order
2.4.2 Exciton Diffusion and 92 (2)
Photophysical Relaxation
2.4.3 Exciton Diffusion and Long-Range 94 (1)
Energy Transfer
2.5 Vapor Deposition Methods 95 (6)
2.5.1 Vacuum Thermal Evaporation 95 (2)
2.5.2 Organic Vapor-Phase Deposition 97 (2)
2.5.3 Crystalline Morphology of Vapor 99 (2)
Deposition
2.6 Advances in Device Architecture 101 (15)
2.6.1 Engineering Planar Heterojunction 101 (3)
OPVs
2.6.2 Improving Active Layer Properties 104 (2)
with Structural Templating
2.6.3 Engineered Nanostructure for 106 (8)
Enhanced Dissociation唯ulk
Heterojunction OPVs
2.6.4 Vapor Deposition Routes to 114 (2)
Induced Bulk-Heterojunction Formation
2.7 Conclusions 116 (11)
3 Acceptor Materials for Solution-Processed 127 (54)
Solar Cells
Youjun He
3.1 Introduction 128 (3)
3.2 Fullerene Acceptor Materials 131 (27)
3.2.1 The History of Fullerene Acceptor 133 (1)
Materials
3.2.1.1 PCBM and PCBM-like derivatives 135 (1)
3.2.1.2 PCBM multi-adducts and 143 (1)
PCBM-like multi-adducts
3.2.1.3 Non-PCBM-like mono-adducts 145 (1)
3.2.1.4 Non-PCBM-like bis- and 150 (1)
multi-adducts
3.2.1.5 Fullerene acceptor materials 154 (3)
for low bandgap polymer solar cells
3.2.2 Conclusions Regarding Fullerenic 157 (1)
Acceptor Materials for High-Performance
Solar Cells
3.3 Inorganic Semiconductor Acceptor 158 (9)
Materials
3.3.1 CdSe, CdTe, CdS and Related 160 (3)
Materials
3.3.2 ZnO and ZnS 163 (2)
3.3.3 TiO2 165 (1)
3.3.4 Future Prospects for Inorganic 166 (1)
Nanoparticle Acceptor Materials
3.4 Summary 167 (14)
4 Interfacial Layers 181 (38)
Riccardo Po
Chiara Carbonera
Andrea Bernardi
Nadia Camaioni
4.1 Introduction 181 (1)
4.2 Charge Collection at Electrode 182 (1)
Interfaces
4.3 Roles of Interfacial Layers 183 (6)
4.3.1 Electrical Effects 185 (2)
4.3.2 Optical Effects 187 (1)
4.3.3 Mechanical Effects 188 (1)
4.3.4 Barrier Effects 188 (1)
4.4 Classes of Materials Used as 189 (18)
Interfacial Layers
4.4.1 Polymeric Compounds 189 (1)
4.4.1.1 PEDOT 189 (1)
4.4.1.2 Polymerized triphenylamines and 192 (1)
carbazoles
4.4.1.3 Conjugated cationic polymers 193 (1)
4.4.1.4 Miscellaneous polymers 194 (2)
4.4.2 Low-Molecular-Weight Organic 196 (1)
Compounds
4.4.2.1 Fullerene derivatives and 196 (1)
carbonaceous materials
4.4.2.2 Organic salts and metal 197 (1)
complexes
4.4.2.3 Miscellaneous 198 (2)
4.4.3 Inorganic Compounds 200 (1)
4.4.3.1 Metal oxides 200 (1)
4.4.3.2 Miscellaneous 204 (1)
4.4.4 Hybrid Buffer Layers 205 (1)
4.4.4.1 Metal oxides + organic compounds 205 (1)
4.4.4.2 Other multilayer buffers made 206 (1)
by miscellaneous materials
4.4.4.3 Composite materials 207 (1)
4.5 Deposition Methods 207 (3)
4.5.1 Wet Deposition 208 (1)
4.5.2 Vacuum Deposition 209 (1)
4.6 Outlook 210 (9)
5 Electrodes in Organic Photovoltaic Cells 219 (58)
Seunghyup Yoo
Jung-Yong Lee
Hoyeon Kim
Jaemin Lee
5.1 Introduction 219 (1)
5.2 Electrodes in OPVs: Their Role and 220 (13)
Importance
5.2.1 Overview 220 (2)
5.2.2 Effect of Sheet Resistance of 222 (1)
Electrodes
5.2.2.1 Effect on the performance of 222 (1)
individual cells
5.2.2.2 Considerations for modules 224 (2)
5.2.3 Optical Role of Electrodes in 226 (3)
Organic Solar Cells: Effect on the
Photocurrent Generation
5.2.4 Choosing the Right Transparent 229 (1)
Electrode
5.2.4.1 Correlation between optical and 229 (1)
electrical properties: figure of merit
for transparent conductors
5.2.4.2 Other considerations 230 (3)
5.3 Examples of Electrodes in OPVs 233 (29)
5.3.1 Transparent Conductive Oxides 233 (1)
5.3.1.1 Overview 233 (1)
5.3.1.2 TCOs in OPVs 234 (1)
5.3.1.3 Pending issues 235 (2)
5.3.2 Conducting Polymers 237 (1)
5.3.2.1 Overview: working principles 237 (1)
and potential advantages
5.3.2.2 Conducting polymers used in OPVs 240 (5)
5.3.3 Thin Metallic Films 245 (1)
5.3.3.1 Overview 245 (1)
5.3.3.2 Practical considerations: 246 (1)
morphological effect
5.3.3.3 Multilayer transparent 249 (2)
electrodes based on
dielectric-metal-dielectric structure
5.3.4 Nanowire Network 251 (1)
5.3.4.1 Overview 251 (1)
5.3.4.2 Fabrication of AgNWs 253 (1)
5.3.4.3 Example of nanowire network 254 (4)
used in OPVs
5.3.5 Carbon-Based Nanomaterials: CNTs 258 (1)
and Graphene
5.3.5.1 Overview 258 (1)
5.3.5.2 Carbon nanotubes for 258 (1)
transparent electrodes in OPVs
5.3.5.3 Graphene for transparent 259 (3)
electrodes in OPVs
5.4 Summary and Outlook 262 (15)
6 Tandem and Multijunction Organic Solar Cells 277 (40)
Jan Gilot
Ren? A.J. Janssen
6.1 Introduction on Tandem Cells 278 (2)
6.2 History and Current Status of Tandem 280 (4)
Solar Cells
6.2.1 History of Tandem Solar Cells 280 (3)
6.2.2 High-Efficiency Tandem Solar Cells 283 (1)
6.3 Intermediate Layers 284 (8)
6.3.1 Materials 285 (1)
6.3.2 Aligning of Energy Levels of ET 286 (3)
and HT Layers in the Intermediate Layer
6.3.3 The Use of PEDOT as HT layer in 289 (1)
Solution-Processed Tandem Solar Cells
6.3.4 Triple- and Multiple-Junction 290 (2)
Solar Cells Leading to High
Open-Circuit Voltages
6.4 Optimization 292 (7)
6.4.1 Optimization of 294 (4)
Solution-Processed Tandem Cells
6.4.2 Optimization of Evaporated Tandem 298 (1)
Solar Cells
6.5 Characterization of Organic Tandem 299 (4)
Solar Cells
6.5.1 Determination of Power Conversion 300 (1)
Efficiency
6.5.2 Determination of External Quantum 301 (2)
Efficiency
6.6 Alternative Constructions of Tandem 303 (2)
Solar Cells
6.6.1 Tandem Cells Connected in Parallel 303 (1)
6.6.2 Stacked, Folded and Laminated 304 (1)
Discrete Cells
6.6.3 Combination of Inorganic and 305 (1)
Organic Subcells
6.7 Conclusion 305 (12)
Part II: Characterization, Modeling, and
Fundamental Insights
7 Bulk Heterojunction Morphology Control and 317 (50)
Characterization
Tao Wang
David G. Lidzey
7.1 Introduction 318 (2)
7.2 Organization of Polymers and 320 (4)
Fullerenes at the Molecular Level
7.3 Organization of Polymers and 324 (5)
Fullerenes during Solvent Casting
7.4 Miscibility of the Polymer and 329 (4)
Fullerene
7.5 Phase Separation and Domain Size 333 (4)
7.6 Impact of Solvent Additives on 337 (2)
Morphology
7.7 Post-Deposition Processes and 339 (11)
Techniques
7.7.1 Impact of Thermal Annealing on 339 (1)
Nanoscale Morphology and Optoelectronic
Properties
7.7.1.1 Two contrasting effects on 339 (1)
structural order and device performance
7.7.1.2 Time-resolved morphology 341 (4)
characterization during thermal
annealing
7.7.2 Impact of Solvent Annealing on 345 (4)
Nanoscale Morphology and Optoelectronic
Properties
7.7.3 Comparison between Thermal and 349 (1)
Solvent Annealing
7.8 Vertical Component Distribution 350 (5)
7.9 A Brief Summary of Characterization 355 (2)
Techniques
7.10 Conclusions 357 (10)
8 Optical Modeling and Light Management in 367 (62)
Organic Photovoltaic Devices
Olle Ingan舖
Zheng Tang
Jonas Bergqvist
Kristofer Tvingstedt
8.1 Introduction 367 (2)
8.2 Optical Modeling of Materials 369 (4)
8.3 Optical Modeling of Devices 373 (24)
8.3.1 The Transfer Matrix Method 374 (11)
8.3.2 Optical Electrical Field 385 (1)
Distribution from Simulations
8.3.2.1 Light Redistribution in 386 (1)
Standard and Nonstandard Geometries
8.3.2.2 Quantum Efficiencies of Charge 386 (1)
Generation
8.3.2.3 Spatial Distribution of Power 391 (2)
Dissipation
8.3.3 Integrated Power Dissipation for 393 (1)
Polychromatic Illumination
8.3.4 Coherence and Incoherence Mixed 394 (1)
8.3.4.1 Anisotropy in Multilayers 397 (1)
8.4 Light Management in OPVs 397 (5)
8.4.1 One Transparent Electrode and One 398 (1)
Reflective
8.4.1.1 Optical Spacers 398 (1)
8.4.2 Transparent Devices 399 (2)
8.4.3 Optical Cavities 401 (1)
8.5 Out of Planarity祐tructured OPVs 402 (8)
8.5.1 Microstructured Interfaces in OPV 402 (2)
8.5.2 Nano- and Microstructured 404 (2)
Interfaces in OPV
8.5.3 Plasmonics 406 (1)
8.5.3.1 Plasmons at Planar 407 (1)
Metal/Dielectric Interfaces
8.5.3.2 Plasmons at Nanoparticle 408 (2)
Metal/Dielectric Interfaces
8.6 The Solar Day and the Solar Year 410 (2)
8.7 Optical Imaging of Processing of 412 (1)
Polymer Photovoltaic Modules
8.8 Summary 413 (16)
9 Spectroscopy of Charge-Carrier 429 (68)
Dynamics友rom Generation to Collection
Sarah R. Cowan
Natalie Banerji
9.1 Introduction 430 (3)
9.2 Controversy and Uncertainty Regarding 433 (8)
the Physical Concepts in a BHJ Solar Cell
9.3 Overview of Spectroscopic and 441 (12)
Electrical Methods for Probing Internal
Processes
9.3.1 Absorption/Transmission 441 (4)
Spectroscopy
9.3.2 Photoluminescence 445 (1)
9.3.3 Transient and Photoinduced 446 (1)
Absorption Spectroscopy
9.3.4 Transient Microwave Conductivity 447 (1)
9.3.5 Photoelectron Spectroscopies 448 (2)
9.3.6 Transient 450 (1)
Photocurrent/Photovoltage Measurements
9.3.7 Internal/External Quantum 451 (2)
Efficiency Measurement
9.4 Case Study: Photoexcitation and 453 (6)
Charge Separation
9.5 Case Study: Role of the Charge 459 (10)
Transfer State in Charge Dissociation and
Recombination
9.6 Case Study: Role of the Internal 469 (5)
Field in Charge Collection
9.7 Case Study: Bias- and Charge 474 (8)
Density-Dependent Charge-Carrier
Recombination
9.8 Case Study: Role of the Contacts in 482 (1)
Charge Collection
9.9 Summary 483 (14)
10 Modeling OPV Performance柚orphology, 497 (40)
Transport and Recombination
Chris Groves
10.1 Introduction to Modeling and Charge 497 (4)
Transport in Organic Materials
10.1.1 Charge Transport幽opping and 498 (2)
Disorder
10.1.2 Charge Transport友unctional 500 (1)
Dependencies
10.2 Methods and Applications 501 (14)
10.2.1 Kinetic Monte Carlo 501 (1)
10.2.1.1 Monte Carlo method and rate 502 (1)
equations
10.2.1.2 Electrostatic interactions and 504 (1)
energetic disorder
10.2.1.3 Injection 504 (1)
10.2.1.4 Queuing 505 (1)
10.2.1.5 Morphology 506 (1)
10.2.1.6 Calculating Coulomb 508 (1)
interactions
10.2.2 Drift-Diffusion 508 (1)
10.2.2.1 Current continuity and 509 (1)
recombination
10.2.2.2 Drift, diffusion and the 512 (1)
Einstein relation
10.2.2.3 Electrostatics and boundary 513 (1)
conditions
10.2.2.4 Solution of equations 514 (1)
10.2.3 Master Equation 514 (1)
10.3 Charge Transport 515 (3)
10.4 Recombination 518 (5)
10.4.1 Geminate Recombination 518 (3)
10.4.2 Non-geminate Recombination 521 (2)
10.5 Charge Injection and Extraction 523 (2)
10.6 Devices 525 (1)
10.7 Summary and Outlook 526 (11)
11 Modeling the Electronic and Optical 537 (54)
Processes in Organic Solar Cells: Density
Functional Theory and Beyond
Jean-Luc Br馘as
Veaceslav Coropceanu
Curtis Doiron
Yao-Tsung Fu
Thomas K?rzd?rfer
Laxman Pandey
Chad Risko
John Sears
Bing Yang
Yuan ping Yi
Cairong Zhang
11.1 Introduction 538 (2)
11.2 Density Functional Theory 540 (17)
Description of the Lowest Excited States
in Small-Gap Polymers and D/A Complexes
11.2.1 Recent Advances in DFT 541 (5)
Methodologies
11.2.2 Nature of the Lowest Excitations 546 (5)
in Small-Gap Polymers
11.2.3 Donor/Acceptor Charge-Transfer 551 (6)
Excitations
11.3 Exciton-Dissociation and 557 (11)
Charge-Recombination Processes at
Donor/Acceptor Interfaces
11.3.1 Evaluation of the Electronic 558 (2)
Couplings and Electron-Transfer Rates
11.3.2 The Pentacene-C60 Complex 560 (4)
11.3.3 Oligothiophene/Fullerene and 564 (4)
Oligothiophene/Perylenediimide Complexes
11.4 Molecular Dynamics Description of 568 (5)
the Pentacene-C60 Interface
11.5 Synopsis 573 (18)
Part III: Technology, Lifetime, and Production
12 Flexible Substrates and Barriers 591 (48)
Yulia Galagan
12.1 Substrates 592 (17)
12.1.1 Metal Foil Substrates 592 (1)
12.1.2 Flexible Plastic Substrates 593 (3)
12.1.3 Glass Substrates 596 (1)
12.1.4 Substrate Properties 596 (1)
12.1.4.1 Electrical properties 598 (1)
12.1.4.2 Surface quality 603 (1)
12.1.4.3 Surface energy of the 604 (1)
substrates
12.1.4.4 Dimensional stability 604 (1)
12.1.4.5 Optical properties 606 (1)
12.1.4.6 Stability under UV exposure 608 (1)
12.1.4.7 Solvent resistance 608 (1)
12.1.4.8 Impact of environmental 609 (1)
conditions
12.2 Encapsulation and Barriers 609 (30)
12.2.1 Requirements for the Barrier 612 (1)
12.2.2 Single-Layer Barrier 613 (2)
12.2.3 Multilayer Barrier Coatings 615 (3)
12.2.4 Mechanical Properties of 618 (2)
Organic/Inorganic Barrier Films
12.2.5 Solution-Processable Barriers 620 (1)
12.2.6 Methods of Applying Barriers 621 (2)
12.2.7 Side Leakage 623 (2)
12.2.8 Conclusions 625 (14)
13 Large-Area Processing of Organic 639 (24)
Photovoltaics
Roar R. S?ndergaard
Markus H?sel
Frederik C. Krebs
13.1 Introduction 639 (2)
13.2 Established Noncontact Coating 641 (3)
Techniques
13.2.1 Knife Coating 641 (2)
13.2.2 Slot-Die Coating 643 (1)
13.3 Printing Techniques 644 (5)
13.3.1 Screen Printing 644 (2)
13.3.2 Flexoprinting 646 (2)
13.3.3 Gravure Printing 648 (1)
13.4 "Printing" and Coating through 649 (3)
Droplets and Brushes
13.4.1 Inkjet Printing 650 (1)
13.4.2 Spray Coating 651 (1)
13.4.3 Brush Painting 652 (1)
13.5 Lamination 652 (1)
13.5.1 Cold Lamination 652 (1)
13.5.2 Hot Lamination 653 (1)
13.5.3 UV-Lamination 653 (1)
13.6 Device Testing 653 (1)
13.7 Demonstrations of Device Integration 654 (2)
13.8 Summary and Outlook 656 (7)
14 Module Design, Fabrication, and 663 (50)
Characterization
Roland R?sch
Harald Hoppe
14.1 Motivation 664 (3)
14.2 Architecture of Polymer Solar Cells 667 (2)
14.3 Material Properties 669 (3)
14.3.1 Photoactive Materials 669 (1)
14.3.2 Charge Carrier 670 (2)
Transport/Blocking Layers
14.3.3 Electrodes 672 (1)
14.4 Monolithic Polymer Solar Modules 672 (2)
14.5 Efficient Module Design 674 (7)
14.6 Characterization Methods 681 (10)
14.6.1 Current-Voltage Characterization 681 (4)
14.6.2 Imaging Methods 685 (6)
14.7 Roll-to-Roll Processing裕echnology 691 (7)
and Challenges
14.8 Lifetime Measurements of Polymer 698 (4)
Solar Modules
14.9 Summary and Outlook 702 (11)
15 Stability of Organic Photovoltaic Cells: 713
Failure Mechanisms and Operational Stability
Eszter Voroshazi
15.1 Introduction 714 (1)
15.2 Failure Mechanisms in Photovoltaic 715 (28)
Cells
15.2.1 Degradation Mechanisms of the 716 (1)
Photoactive Layer
15.2.1.1 Degradation mechanisms in 716 (1)
polymer: fullerene blends
15.2.1.2 Physical degradation of the 716 (1)
polymer: fullerene blend morphology
15.2.1.3 Chemical degradation of the 720 (1)
polymer: fullerene blend
15.2.1.4 Degradation mechanisms of 726 (4)
small-molecule: fullerene blends
15.2.2 Degradation Mechanisms of the 730 (1)
Buffer Layers
15.2.2.1 Degradation mechanisms of hole 730 (1)
transport layers
15.2.2.2 Degradation mechanisms of the 734 (3)
electron transport layers
15.2.3 Degradation Mechanisms Linked to 737 (1)
the Electrodes
15.2.3.1 Degradation mechanisms of 737 (1)
indium tin oxide
15.2.3.2 Degradation mechanisms of 739 (3)
metal electrodes
15.2.4 Summary 742 (1)
15.3 Current Device Stability of OPVs 743 (13)
15.3.1 Current Standards and Protocols 744 (4)
for Lifetime Evaluation
15.3.2 State-of-the-Art Operational 748 (8)
Stability of OPVs
15.4 Conclusions and Outlook 756
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