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Tze-Chien Sum is an Associate Professor at the Division of Physics and Applied Physics, School of Physical and Mathematical Sciences (SPMS), Nanyang Technological University (NTU), where he leads the Femtosecond Dynamics Laboratory. He received his Ph.D. in 2005 from the National University of Singapore (NUS). His research focuses on investigating light matter interactions, energy and charge transfer mechanisms, and probing carrier and quasi-particle dynamics in a broad range of emergent nanoscale and light harvesting systems.Dr Sum received a total of 11 teaching awards from NUS and NTU, including the coveted Nanyang Award for Excellence in Teaching in 2006 and the 2010 SPMS Teaching Excellence Honour Roll Award. He is also a recipient of several research awards, including the Institute of Physics Singapore 2014 World Scientific Medal and Prize for Outstanding Physics Research, the 2014 Nanyang Award for Research Excellence, and the 2018 Singapore National Research Foundation Investigatorship.

Nripan Mathews is an Assistant Professor at the School of Materials Science and Engineering and also at the Energy Research Institute@NTU (ERIAN), Nanyang Technological University. He has worked on multiple material systems and explored the optical and transport properties within them. The material systems include perovskites, metal oxides, organic thin films, 1D nanostructures and molecular crystals. The primary focus of his work has centred around the fabrication of novel and high-performance devices which exploit the unique property of each material set. He has focused on applying the novel materials in applications such as solar cells, light emitting diodes, thin film transistors, artificial synapses and photoelectrochemical systems. Winner of multiple teaching and research awards, he was identified by Times Higher Education as among the top researchers in perovskite solar cells.

Part I Basic Properties and EarlyWorks in Organic–Inorganic Perovskites 1

1.1 Structural, Optical, and Related Properties of Some Perovskites Based on Lead and Tin Halides: The Effects on Going from Bulk to Small Particles 3
George C. Papavassiliou, George A. Mousdis, and Ioannis Koutselas

1.1.1 Introduction 3

1.1.2 Materials Based on Saturated Organic Moiety 4

1.1.2.1 Bulk Perovskites (SC)MX₃ 4

1.1.2.2 Particulate Perovskites (SC)MX₃ 5

1.1.2.3 Bulk Perovskites of the Type (BC)₂MX₄ 8

1.1.2.4 Particulate Perovskites of the Type (BC)₂MX₄ 8

1.1.2.5 Bulk Perovskites of the Type (SC)_n−1(BC)₂M_nX_3n+1 10

1.1.2.6 Particulate Perovskites of the Type (SC)_n−1(BC)₂M_nX_3n+1 11

1.1.2.7 Some Common Features in the Properties of 3D and q-2D Systems 13

1.1.2.8 Low-Dimensional (LD) Perovskites 15

1.1.2.9 Related Properties 15

1.1.3 Perovskites Consisting of Non-saturated Organic Moiety BC 16

1.1.4 Other Perovskite Structures 18

References 18

1.2 Ab Initio and First Principles Studies of Halide Perovskites 25
Jacky Even and Claudine Katan

1.2.1 Introduction to Ab Initio and DFT Studies of All-inorganic, 3D and Layered Hybrid Organic Metal Halide Perovskites 25

1.2.2 Brillouin Zone Folding, Lattice Strain, and Topology of the Electronic Structure 28

1.2.3 Importance of Spin–Orbit Coupling (SOC) 33

1.2.4 Interplay of SOC and Loss of Inversion Symmetry: Rashba and Dresselhaus Effects 36

1.2.5 Collective Vibrations, Stochastic Cation Reorientations, and Molecular Dynamics 40

References 47

1.3 Excitonics in 2D Perovskites 55
Wee Kiang Chong, David Giovanni, and Tze-Chien Sum

1.3.1 Introduction to Two-dimensional Perovskites 55

1.3.2 Excitonic Properties and Optical Transitions in 2D-OIHPs 56

1.3.3 White Light Emission (WLE) from 2D-OIHPs 57

1.3.3.1 Energy Transfer Mechanism 59

1.3.3.2 Broadband Defect Emission 60

1.3.3.3 Self-trapped Excitons 61

1.3.3.4 Role of Organic Framework in Broadband 2D-OIHP Emitters 63

1.3.4 Strong Exciton–Photon Coupling in 2D-OIHPs 64

1.3.4.1 Jaynes–Cummings Model 64

1.3.4.2 Exciton–Photon Coupling in 2D Perovskites Thin Films: Optical Stark Effect 65

1.3.4.3 Exciton–Photon Coupling in 2D Perovskite Microcavities: Exciton–Polariton 66

1.3.5 Concluding Remarks 73

References 74

Part II Organic–Inorganic Perovskite Solar Cells 81

2.1 Working Principles of Perovskite Solar Cells 83
Pablo P. Boix, Sonia R. Raga, and NripanMathews

2.1.1 Introduction 83

2.1.2 Charge Generation 84

2.1.3 Charge Transport 86

2.1.4 Charge Recombination 89

2.1.5 Charge Extraction/Injection: Interfacial Effects 93

2.1.6 Ionic Mechanisms 95

2.1.7 Concluding Remarks 96

References 97

2.2 The Photophysics of Halide Perovskite Solar Cells 101

Mingjie Li, BoWu, and Tze-Chien Sum

2.2.1 Introduction to Photophysics Studies of Halide Perovskites 101

2.2.2 Optical Properties of CH₃NH₃PbI₃ Polycrystalline Thin Films 102

2.2.2.1 Electronic Band Structure and Optical Transitions 102

2.2.2.2 Exciton Binding Energies and Photoexcited Species: Excitons Versus Free Carriers 103

2.2.2.3 Carrier Diffusion Lengths, Carrier Mobilities, and Defects 104

2.2.2.4 Transient Spectral Features and Charge Dynamics 107

2.2.2.5 Photophysical Processes and Their Recombination Constants 108

2.2.2.6 Hot Carriers in Perovskites 111

2.2.2.7 Summary and Outlook 112

2.2.3 Energetics and Charge Dynamics at Perovskite Interfaces 112

2.2.3.1 Introduction 112

2.2.3.2 Energetics at the Perovskite/Charge Transport Layer Interfaces 112

2.2.3.3 Charge-Transfer Dynamics at the Perovskite/Charge-Transport Layer Interface 115

2.2.3.4 Summary and Outlook 117

2.2.4 Toward Perovskite Single-Crystal Photovoltaics 117

2.2.4.1 Absorption and Emission Properties 118

2.2.4.2 Surface Versus Bulk Optical Properties 120

2.2.4.3 Carrier Lifetimes, Diffusion Lengths, and Diffusion Coefficients 121

2.2.4.4 Transient Spectral Features and Excitation Dynamics 122

2.2.4.5 Recombination Constants in the Surface and Bulk Regions of Perovskite Single Crystals 126

2.2.5 Concluding Remarks 127

References 128

2.3 Charge-Selective Contact Materials for Perovskite Solar Cells (PSCs) 131
Peng Gao and Mohammad Khaja Nazeeruddin

2.3.1 Hole-Selective Electron-Blocking Materials (HTMs) 132

2.3.1.1 Organic HTMs 132

2.3.1.1.1 Molecular HTMs 132

2.3.1.1.2 Polymeric HTMs 135

2.3.1.1.3 Organometallic Complex HTMs 136

2.3.1.2 Inorganic Hole-Selective Electron-Blocking Materials 138

2.3.2 Electron-Selective Hole-Blocking Materials 139

2.3.2.1 Inorganic Electron-Selective Hole-Blocking Materials 140

2.3.2.1.1 TiO₂ 140

2.3.2.1.2 ZnO 144

2.3.2.1.3 SnO₂ 144

2.3.2.2 Organic Electron-Selective Hole-Blocking Materials 146

2.3.2.3 Composite ETMs 147

2.3.3 Conclusion 147

References 148

2.4 BeyondMethylammonium Lead Iodide Perovskite 155
Teck M. Koh, Biplab Ghosh, Padinhare C. Harikesh, Subodh Mhaisalkar, and Nripan Mathews

2.4.1 Introduction: Beyond CH3NH3PbI3 155

2.4.1.1 Multidimensional Perovskites 155

2.4.1.2 Multidimensional Perovskite Photovoltaics 157

2.4.2 Theoretical Calculations for Pb-Free Halide Perovskites 161

2.4.2.1 ASnX3 Perovskites: 3D Pb-Free Structures 161

2.4.2.2 A₂SnX₆ Perovskites: Metal-Deficient Structures 165

2.4.2.3 Germanium-Based Perovskites 166

2.4.2.4 Bismuth/Antimony-Based Perovskites 168

2.4.2.5 Double Perovskites: Hybrid Binary Metal Structures 170

2.4.3 Experimental Efforts in Pb-Free Perovskite Photovoltaics 170

2.4.3.1 Sn²⁺ and Ge²⁺ as Replacements for Pb²⁺ 172

2.4.3.2 A₂SnX₆ as a Stable Alternative to ASnX₃ 174

2.4.3.3 Cu2+: an Alternative Divalent Metal Cation 175

2.4.3.4 Bi³⁺ and Sb³⁺: Toward TrivalentMetal Cations 175

2.4.4 Concluding Remarks and Outlook 176

References 178

2.5 Halide Perovskite Tandem Solar Cells 183
Teodor K. Todorov, Oki Gunawan, and Supratik Guha

2.5.1 Introduction 183

2.5.2 Tandem Device Type and Performance Limitations 184

2.5.2.1 Single TCE/Two-Terminal (2-T) Monolithic Stack 184

2.5.2.2 Multi-TCE/Two-Terminal (2-T) Mechanical Stack 185

2.5.2.3 Multi-TCE/Three-Terminal (3-T) Mechanical Stack 185

2.5.2.4 Multi-TCE/Four-Terminal (4-T) Mechanical Stack 186

2.5.2.5 Multi-TCE/Four-Terminal (4-T) Spectrum Split 186

2.5.3 Perovskite Tandem Photovoltaic Device Research 188

2.5.4 Conclusion and Outlook 194

References 194

Part III Perovskite Light Emitting Devices 199

3.1 Perovskite Light-Emitting Devices – Fundamentals and Working Principles 201
Michele Sessolo,Maria-Grazia La-Placa, LauraMartínez-Sarti, and Henk J. Bolink

3.1.1 Excitons, Free Carriers, and Trap States in Hybrid Perovskite Thin Films 202

3.1.2 Hybrid Perovskite Light-Emitting Diodes 205

3.1.3 Hybrid Perovskite Nanostructures and Nanoparticles 209

3.1.3.1 Inorganic Cesium Lead Halide Quantum Dots 212

3.1.3.2 Quasi-2D Hybrid Lead Halide Perovskites 215

3.1.3.3 Final Considerations 218

References 218

3.2 Toward Electrically Driven Perovskite Lasers – Prospects and Obstacles 223
Songtao Chen and Arto Nurmikko

3.2.1 Introduction 223

3.2.2 Electrical Injection in Perovskite-Based Light-Emitting Diodes (LEDs) 225

3.2.3 Optical Gain in Thin-film Solid-state Perovskites 228

3.2.4 Integrating Optical Resonators and Perovskite Gain Media 234

3.2.5 TheWay Forward Toward Electrical Injection 239

3.2.6 Summary 241

References 242

Part IV Beyond Perovskite Photovoltaics 249

4.1 Novel Spin Physics in Organic–Inorganic Perovskites 251
Chuang Zhang, Dali Sun, and Zeev V. Vardeny

4.1.1 Introduction 251

4.1.2 Magnetic Field Effect (MFE) on Photocurrent (PC), Photoluminescence (PL), and Electroluminescence (EL) 252

4.1.2.1 Observation of MFE in the CH₃NH₃PbI_3−xCl_x Films and Devices 253

4.1.2.2 MFE in Hybrid Perovskites; Morphology Dependence 255

4.1.2.3 The “Universal” Plot and the Spin-mixing Process via Δg of Electrons and Holes 258

4.1.3 High Magnetic Field Optical Phenomena 260

4.1.3.1 Direct Measurement of Δg by Field-Induced Circularly Polarized Emission 260

4.1.3.2 Magneto-absorption Spectroscopy at UltrahighMagnetic Field 263

4.1.4 Spin-Polarized Carrier Dynamics 263

4.1.4.1 Direct Measurement of Spin-pair Lifetime by Picosecond Pump–Probe Spectroscopy 263

4.1.4.2 Determination of Spin Relaxation Time from Circular Pump–Probe Technique 265

4.1.5 Conclusion and Outlook 265

Acknowledgements 268

References 268

4.2 Perovskite Solar Cells for PhotoelectrochemicalWater Splitting and CO₂ Reduction 273
Gurudayal, Joel Ager, and NripanMathews

4.2.1 Introduction 273

4.2.1.1 Photoelectrochemical Generation of H2 275

4.2.1.2 PEC Electrode Materials 276

4.2.2 Tandem Configurations 277

4.2.2.1 Photoanode–Photocathode Strategy 278

4.2.2.2 PEC-PV Tandem System 282

4.2.2.3 Photovoltaic-Electrocatalyst (PV-EC) Structure 285

4.2.3 EC/PEC-PV Approach for CO₂ Reduction 287

4.2.4 Concluding Remarks and Outlook 288

References 290

Index 293