Hybrid Perovskite Solar Cells

Hiroyuki Fujiwara is Professor in the Department of Electrical, Electronic and Computer Engineering, Gifu University, Japan. Hiroyuki Fujiwara received his Ph.D. degree from Tokyo Institute of Technology. He was a research associate at Pennsylvania State University during 1996-1998. In 1998, he joined the Electrotechnical Laboratory at the Ministry of International Trade and Industry, Japan. During 2007-2008, he was a team leader of Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST) in Japan. Professor Fujiwara has authored and edited six books and has published more than 130 scientific articles. His book on spectroscopic ellipsometry, published by Wiley, has become the most cited book on the topic.

1 Introduction 1
Hiroyuki Fujiwara
1.1 Hybrid Perovskite Solar Cells 1
1.2 Unique Natures of Hybrid Perovskites 4
1.2.1 Notable Characteristics of Hybrid Perovskites 5
1.2.2 Fundamental Properties of MAPbI3 8
1.2.3 Why Hybrid Perovskite Solar Cells Show High Efficiency? 11
1.3 Advantages of Hybrid Perovskite Solar Cells 12
1.3.1 Band Gap Tunability 12
1.3.2 High V oc 13
1.3.3 Low Temperature Coefficient 16
1.4 Challenges for Hybrid Perovskites 16
1.4.1 Requirement of Improved Stability 17
1.4.2 Large-Area Solar Cells 19
1.4.3 Toxicity of Pb and Sn Compounds 20
1.5 Overview of this Book 22 Acknowledgment 23 References 23

2 Overview of Hybrid Perovskite Solar Cells 29
Tsutomu Miyasaka and Ajay K. Jena
2.1 Introduction 29
2.2 Historical Backgrounds of Halide Perovskite Photovoltaics 32
2.3 Semiconductor Properties of Organo Lead Halide Perovskites 34
2.4 Working Principle of Perovskite Photovoltaics 37
2.5 Compositional Design of the Halide Perovskite Absorbers 40
2.6 Strategy for Stabilizing Perovskite Solar Cells 41
2.7 All Inorganic and Lead-Free Perovskites 48
2.8 Development of High-Efficiency Tandem Solar Cells 52
2.9 Conclusion and Perspectives 54
References 55

Part I Characteristics of Hybrid Perovskites 65

3 Crystal Structures 67
Mitsutoshi Nishiwaki, Tatsuya Narikuri, and Hiroyuki Fujiwara
3.1 What Is Hybrid Perovskite? 67
3.2 Structures of Hybrid Perovskite Crystals 68
3.2.1 Crystal Structure of MAPbI3 68
3.2.2 Lattice Parameters of Hybrid Perovskites 71
3.2.3 Secondary Phase Materials 75
3.3 Tolerance Factor 77
3.3.1 Tolerance Factor of Hybrid Perovskites 79
3.3.2 Tolerance Factor of Mixed-Cation Perovskites 82
3.4 Phase Change by Temperature 84
3.5 Refined Structures of Hybrid Perovskites 86
3.5.1 Orientation of Center Cations 86
3.5.2 Relaxation of Center Cations 88 Acknowledgment 89 References 89

4 Optical Properties 91
Hiroyuki Fujiwara, Yukinori Nishigaki, Akio Matsushita, and Taisuke Matsui
4.1 Introduction 91
4.2 Light Absorption in MAPbI3 93
4.2.1 Visible/UV Region 96
4.2.2 IR Region 98
4.2.3 THz Region 99
4.3 Band Gap of Hybrid Perovskites 101
4.3.1 Band Gap Analysis of MAPbI3 101
4.3.2 Band Gap of Basic Perovskites 103
4.3.3 Band Gap Variation in Perovskite Alloys 105
4.4 True Absorption Coefficient of MAPbI3 106
4.4.1 Principles of Optical Measurements 107
4.4.2 Interpretation of a Variation 108
4.5 Universal Rules for Hybrid Perovskite Optical Properties 111
4.5.1 Variation with Center Cation 111
4.5.2 Variation with Halide Anion 112
4.6 Subgap Absorption Characteristics 114
4.7 Temperature Effect on Absorption Properties 116
4.8 Excitonic Properties of Hybrid Perovskites 117
References 119

5 Physical Properties Determined by Density Functional Theory 123
Hiroyuki Fujiwara, Mitsutoshi Nishiwaki, and Yukinori Nishigaki
5.1 Introduction 123
5.2 What Is DFT? 124
5.2.1 Basic Principles 124
5.2.2 Assumptions and Limitations 126
5.3 Crystal Structures Determined by DFT 128
5.3.1 Hybrid Perovskite Structures 128
5.3.2 Organic-Center Cations 131
5.4 Band Structures 132
5.4.1 Band Structures of Hybrid Perovskites 132
5.4.2 Direct-Indirect Issue of Hybrid Perovskite 134
5.4.3 Density of States 139
5.4.4 Effective Mass 140
5.5 Band Gap 141
5.5.1 What Determines Band Gap? 142
5.5.2 Effect of Center Cation 143
5.5.3 Effect of Halide Anion 143
5.6 Defect Physics 144 Acknowledgment 147 References 147

6 Carrier Transport Properties 151
Hiroyuki Fujiwara and Yoshitsune Kato
6.1 Introduction 151
6.2 Carrier Properties of Hybrid Perovskites 153
6.2.1 Self-Doping in Hybrid Perovskites 153
6.2.2 Effect of Carrier Concentration on Mobility 155
6.3 Carrier Mobility of MAPbI3 155
6.3.1 Variation of Mobility with Characterization Method 156
6.3.2 Temperature Dependence 159
6.3.3 Effect of Effective Mass 160
6.3.4 What Determines Maximum Mobility of MAPbI3? 161
6.4 Diffusion Length 164
6.5 Carrier Transport in Various Hybrid Perovskites 166
References 168

7 Ferroelectric Properties 173
Tobias Leonhard, Holger Röhm, Alexander D. Schulz, and Alexander Colsmann
7.1 On the Importance of Ferroelectricity in Hybrid Perovskite Solar Cells 173
7.2 Ferroelectricity 174
7.2.1 Crystallographic Considerations 174
7.2.2 Ferroelectricity in Thin Films 178
7.2.3 Crystallography of MAPbI3 Thin Films 178
7.3 Probing Ferroelectricity on the Microscale 179
7.3.1 Atomic Force Microscopy 179
7.3.2 Piezoresponse Force Microscopy 180
7.3.3 Characterization of MAPbI3 Thin Films with sf-PFM 183
7.3.4 Correlative Domain Characterization 188
7.3.4.1 Transmission Electron Microscopy 188
7.3.4.2 X-ray Diffraction 189
7.3.4.3 Electron Backscatter Diffraction 189
7.3.4.4 Kelvin Probe Force Microscopy 191
7.3.5 Polarization Orientation 191
7.3.6 Ferroelastic Effects in MAPbI3 Thin Films 193
7.4 Ferroelectric Poling of MAPbI3 195
7.4.1 AC Poling of MAPbI3 196
7.4.2 Creeping Poling and Switching Events on the Microscopic Scale 197
7.4.3 Macroscopic Effects of Poling 200
7.5 Impact of Ferroelectricity on the Performance of Solar Cells 201
7.5.1 Pitfalls During Sample Measurements 201
7.5.2 Charge Carrier Dynamics in Solar Cells 203
References 203

8 Photoluminescence Properties 207
Yasuhiro Yamada and Yoshihiko Kanemitsu
8.1 Introduction 207
8.2 Overview of Luminescent Properties 208
8.3 Room-Temperature PL Spectra of a Hybrid Perovskite Thin Film 209
8.4 Time-Resolved PL of a Hybrid Perovskite 213
8.5 PL Quantum Efficiency 218
8.6 Temperature-Dependent PL 220
8.7 Material and Device Characterization by PL Spectroscopy 222
8.7.1 Degradation and Healing of Hybrid Perovskites 222
8.7.2 Charge Transfer Mechanism in Perovskite Solar Cell 223
8.8 Conclusion 224 Acknowledgment 225 References 225

9 Role of Grain Boundaries 229
Jae Sung Yun
9.1 Introduction 229
9.2 Role of Grain Boundaries in Device Performance 230
9.2.1 Potential Barrier at GBs and Charge Transport 231
9.2.2 Engineering of GB Properties 234
9.3 Ion Migration Through Grain Boundaries 241
9.3.1 Enhanced Ion Transport at Grain Boundaries 241
References 250

10 Roles of Center Cations 253
Biwas Subedi, Juan Zuo, Marie Solange Tumusange, Maxwell M. Junda, Kiran
10.1 Ghimire, and Nikolas J. Podraza
Introduction 253
10.2 Cubic Perovskite Phase Tolerance Factor 256
10.3 Thin Film Stability 258
10.4 Optoelectronic Property Variations 263
10.5 Solar Cell Performance 268
References 271

Part II Hybrid Perovskite Solar Cells 275
11 Operational Principles of Hybrid Perovskite Solar Cells 277
Hiroyuki Fujiwara, Yoshitsune Kato, Yuji Kadoya, Yukinori Nishigaki, Tomoya Kobayashi, Akio Matsushita, and Taisuke Matsui
11.1 Introduction 277
11.2 Operation of Hybrid Perovskite Solar Cells 278
11.2.1 Operational Principle and Basic Structures 278
11.2.2 Band Alignment 281
11.3 Band Diagram of Hybrid Perovskite Solar Cells 283
11.3.1 Device Simulation 283
11.3.2 Experimental Observation 285
11.4 Refined Analyses of Hybrid Perovskite Solar Cells 287
11.4.1 Carrier Generation and Loss 287
11.4.2 Power Loss Mechanism 291
11.4.3 e-ARC Software 295
11.5 What Determines V oc? 295
11.5.1 Effect of Interface 297
11.5.2 Effect of Passivation 300
11.5.3 Effect of Grain Boundary 303
References 305

12 Efficiency Limits of Single and Tandem Solar Cells 309
Hiroyuki Fujiwara, Yoshitsune Kato, Masayuki Kozawa, Akira Terakawa, and Taisuke Matsui
12.1 Introduction 309
12.2 What Is the SQ Limit? 310
12.2.1 Physical Model 311
12.2.2 Blackbody Radiation 313
12.2.3 SQ Limit 315
12.3 Maximum Efficiencies of Perovskite Single Cells 319
12.3.1 Concept of Thin-Film Limit 319
12.3.2 EQE Calculation Method 321
12.3.3 Maximum Efficiencies of Single Solar Cells 323
12.3.4 Performance-Limiting Factors of Hybrid Perovskite Devices 325
12.4 Maximum Efficiency of Tandem Cells 327
12.4.1 Optical Model and Assumptions 328
12.4.2 Calculation of Tandem-Cell EQE Spectra 329
12.4.3 Maximum Efficiencies of Tandem Devices 331
12.4.4 Realistic Maximum Efficiency of Tandem Cell 334
12.5 Free Software for Efficiency Limit Calculation 335
References 336

13 Multi-cation Hybrid Perovskite Solar Cells 339
Jacob N. Vagott and Juan-Pablo Correa-Baena
13.1 Introduction 339
13.2 Types of A-Site Multi-cation Hybrid Perovskite Solar Cells 341
13.2.1 Pb-Based Multi-cation Hybrid Perovskite Solar Cells 341
13.2.2 Sn-Based Multi-cation Hybrid Perovskite Solar Cells 344
13.3 Cation Selection in Mixed-Cation Hybrid Perovskite Solar Cells 345
13.3.1 Organic A-Cations 345
13.3.2 Inorganic A-Cations 347
13.4 Fabrication of Mixed-Cation Hybrid Perovskite Solar Cells 349
13.4.1 Traditional Fabrication Approach 349
13.4.2 Emerging Fabrication Technologies 350
13.5 Charge Transport Materials 353
13.6 Surface Passivation 357
13.7 Mixed B-Cation Hybrid Organic?Inorganic Perovskite Solar Cells 361
13.8 Basic Characterization of Mixed-Cation Hybrid Perovskite Solar Cells 362
References 365

14 Tin Halide Perovskite Solar Cells 373
Gaurav Kapil and Shuzi Hayase
14.1 Introduction 373
14.1.1 Device Structure and Operating Principle 374
14.1.2 Crystal Structure 375
14.2 Tin Perovskite Solar Cells 376
14.2.1 Intrinsic Properties 377
14.2.2 Carrier Lifetime and Diffusion Length 378
14.3 The Status of Sn Perovskite Solar Cells 379
14.3.1 Different Type of Sn Perovskite Solar Cells 380
14.3.1.1 CsSnI3 380
14.3.1.2 MASnI3 383
14.3.1.3 FASnI3 384
14.3.1.4 FAxMA1-xSnI3 385
14.3.1.5 2D/3D FASnI3 387
14.3.1.6 Sn-Ge mixed PSCs 387
14.3.2 Strategies to Improve the Efficiency 389
14.3.2.1 Film Fabrication Methods 389
14.3.2.2 Use of Reducing Agents 389
14.3.2.3 Doping Effect of Large Organic Cations 390
14.3.2.4 Device Engineering and Lattice Relaxation 391
14.4 Sn-Pb Perovskite Solar Cells 393
14.4.1 Anomalous Bandgap of SnPb (The Bowing Effect) 396
14.4.2 Physical Properties 398
14.4.2.1 Intrinsic Carrier Concentration 398
14.4.2.2 Carrier Lifetime and Diffusion Length 399
14.5 The Status of Sn-Pb Perovskite Solar Cells 399
14.5.1 Different Types of Sn-Pb Perovskite Solar Cells 401
14.5.1.1 First Kind of Sn-Pb PSC absorber: MASnxPb1-xI3 401
14.5.1.2 Multi Cation Sn-Pb Perovskites: (FA, MA, Cs) (Sn, Pb) (I, Br, Cl)3 401
14.5.2 Strategies to Improve the Efficiency 403
14.5.2.1 Use of Additives 403
14.5.2.2 Device Engineering 404
14.6 Conclusion and Outlook 406
References 406

15 Stability of Hybrid Perovskite Solar Cells 411
Seigo Ito
15.1 Introduction: Trigger of the Degradation 411
15.2 Crystal Quality for Stable Perovskite Solar Cells 413
15.3 Water-Stable and MA-Free Perovskites 415
15.4 Defects and Grain-Surface Ion Migration, and Passivation (Including 2-D Crystal) 417
15.5 Degradation at Interface with Metal Oxides 420
15.6 Porous Carbon Electrode to Be Very Stable Multiporous-Layered- Electrode Perovskite Solar Cells (MPLE-PSC) 420
15.7 Damp Heat Tests 421
15.8 Conclusion 422
References 425

16 Hysteresis in J-V Characteristics 429
Wolfgang Tress
16.1 Introduction and Definitions: What Do We Mean by Hysteresis? 429
16.2 The JV Curve of a Solar Cell: What Does It Tell? 431
16.3 Characteristics of Hysteresis: What Does It Depend on? 437
16.4 Mechanistic and Microscopic Origin of Hysteresis: What Changes Slowly? 442
16.5 Issues with Hysteresis: How to Tune/Avoid/Suppress? 453
16.6 Conclusion and Open Questions 453
References 454

17 Perovskite-Based Tandem Solar Cells 463
Klaus Jäger and Steve Albrecht
17.1 Introduction 463
17.2 Architectures of Tandem Solar Cells 465
17.2.1 Monolithic Two-Terminal Solar Cells 466
17.2.2 Four-Terminal Tandem Solar Cells 467
17.2.3 Other Concepts 468
17.2.4 Bifacial Solar Cells 469
17.3 Efficiency Limits of Multi-Junction Solar Cells 469
17.3.1 Efficiency Limit for Four-Terminal Tandem Solar Cells 470
17.3.2 Efficiency Limit for Two-Terminal Tandem Solar Cells 472
17.3.3 Efficiency Limit for Cells with More Junctions 474
17.4 Perovskites as Tandem Solar Cell Materials 474
17.5 Experimental Results on Perovskite-Based Tandem Solar Cells 477
17.5.1 Perovskite/Silicon Tandem Solar Cells 482
17.5.2 Perovskite-Chalcogenide Tandem Solar Cells 489
17.6 Energy Yield Calculations 493
17.6.1 Illumination Model 494
17.6.2 Optical Model 494
17.6.3 Electrical Model 496
17.6.4 Temperature Model 498
17.6.5 Energy Yield Calculation 498
17.7 Conclusions and Outlook 499 Acknowledgments 500 References 500

18 All Perovskite Tandem Solar Cells 509
Zhaoning Song and Yanfa Yan
18.1 Introduction 509
18.2 Working Principles of Tandem Solar Cells 511
18.2.1 Why to Use Tandem Solar Cells 511
18.2.2 Tandem Device Architectures 513
18.2.3 PCE of Tandem Solar Cells 514
18.3 Wide-Bandgap Perovskite Solar Cells 516
18.3.1 Wide-Bandgap Mixed I-Br Perovskites 516
18.3.2 Current State of Wide-Bandgap Perovskite Solar Cells 518
18.3.3 Critical Issues of Wide-Bandgap Perovskite Cells 519
18.4 Low-Bandgap Perovskite Solar Cells 520
18.4.1 Low-Bandgap Mixed Sn-Pb Perovskites 520
18.4.2 Current State of Low-Bandgap Perovskite Solar Cells 524
18.4.3 Critical Issues of Low-Bandgap Perovskite Cells 525
18.5 All-Perovskite Tandem Solar Cells 527
18.5.1 4-T All-Perovskite Tandem Solar Cells 527
18.5.2 2-T All-Perovskite Tandem Solar Cells 528
18.5.3 Limitations and Challenges of All-Perovskite Tandem Solar Cells 533
18.6 Conclusion and Outlooks 534 Acknowledgments 535 References 535

A Optical Constants of Hybrid Perovskite Materials 541
Yukinori Nishigaki, Akio Matsushita, Alvaro Tejada, Taisuke Matsui, and
Hiroyuki Fujiwara
References 562

B Numerical Values of Shockley-Queisser Limit 563
Yoshitsune Kato and Hiroyuki Fujiwara

Index 567