Copper Zinc Tin Sulfide–Based Thin–Film Solar Cells

Kentaro Ito Department of Electrical and Electronic Engineering, Shinsu University, Japan

Preface ix


List of Contributors xi


Part I Introduction 1


1 An Overview of CZTS-Based Thin-Film Solar Cells 3
Kentaro Ito


1.1 Introduction 3


1.2 The Photovoltaic Effect 4


1.3 In Pursuit of an Optimal Semiconductor for Photovoltaics 22


1.4 Conclusions 36


Acknowledgements 37


References 37


2 Market Challenges for CZTS-Based Thin-Film Solar Cells 43
Arnulf Jäger-Waldau


2.1 Introduction 43


2.2 Compound Thin-Film Technologies and Manufacturing 45


2.3 Challenges for CZTS Solar Cells in the Market 49


2.4 Conclusion 51


References 51


Part II The Physics and Chemistry of Quaternary Chalcogenide Semiconductors 53


3 Crystallographic Aspects of Cu2ZnSnS4 (CZTS) 55
Susan Schorr


3.1 Introduction: What Defines a Crystal Structure? 55


3.2 The Crystal Structure of CZTS 57


3.3 Point Defects in CZTS and the Role of Stoichiometry 68


3.4 Differentiation between Intergrown Kesterite- and Stannite-Type Phases: A Simulational Approach 71


3.5 Summary 72


References 73


4 Electronic Structure and Optical Properties from First-Principles Modeling 75
Clas Persson, Rongzhen Chen, Hanyue Zhao, Mukesh Kumar and Dan Huang


4.1 Introduction 75


4.2 Computational Background 77


4.3 Crystal Structure 80


4.4 Electronic Structure 82


4.5 Optical Properties 97


4.6 Summary 101


Acknowledgements 102


References 102


5 Kesterites: Equilibria and Secondary Phase Identification 107
Dominik M. Berg and Phillip J. Dale


5.1 Introduction 107


5.2 Chemistry of the Kesterite Reaction 108


5.3 Phase Identification 116


Acknowledgements 128


References 128


6 Growth of CZTS Single Crystals 133
Akira Nagaoka and Kenji Yoshino


6.1 Introduction 133


6.2 Growth Process 134


6.3 Properties of CZTS Single Crystals 141


6.4 Conclusion 145


Acknowledgements 146


References 146


7 Physical Properties: Compiled Experimental Data 149
Sadao Adachi


7.1 Introduction 149


7.2 Structural Properties 150


7.3 Thermal Properties 152


7.4 Mechanical and Lattice Dynamic Properties 157


7.5 Electronic Energy-Band Structure 162


7.6 Optical Properties 169


7.7 Carrier Transport Properties 170


References 176


Part III Synthesis of Thin Films and Their Application to Solar Cells 181


8 Sulfurization of Physical Vapor-Deposited Precursor Layers 183
Hironori Katagiri


8.1 Introduction 183


8.2 First CZTS Thin-Film Solar Cells 184


8.3 ZnS as Zn-Source in Precursor 184


8.4 Influence of Absorber Thickness 187


8.5 New Sulfurization System 188


8.6 Influence of Morphology 189


8.7 Co-Sputtering System with Annealing Chamber 190


8.8 Active Composition 191


8.9 CZTS Compound Target 192


8.10 Conclusions 201


References 201


9 Reactive Sputtering of CZTS 203
Charlotte Platzer-Björkman, Tove Ericson, Jonathan Scragg and Tomas Kubart


9.1 Introduction 203


9.2 The Reactive Sputtering Process 205


9.3 Properties of Sputtered Precursors 206


9.4 Annealing of Sputtered Precursors 214


9.5 Device Performance 215


9.6 Summary 217


References 217


10 Coevaporation of CZTS Films and Solar Cells 221
Thomas Unold, Justus Just and Hans-Werner Schock


10.1 Introduction 221


10.2 Basic Principles 221


10.3 Process Variations 227


Acknowledgements 236


References 236


11 Synthesis of CZTSSe Thin Films from Nanocrystal Inks 239
Charles J. Hages and Rakesh Agrawal


11.1 Introduction 239


11.2 Nanocrystal Synthesis 241


11.3 Nanocrystal Characterization 249


11.4 Sintering 251


11.5 Conclusion 264


References 264


12 CZTS Thin Films Prepared by a Non-Vacuum Process 271
Kunihiko Tanaka


12.1 Introduction 271


12.2 Sol-Gel Sulfurization Method 272


12.3 Preparation of CZTS Thin Films by Sol-Gel Sulfurization Method 274


12.4 Chemical Composition Dependence 279


12.5 H2S Concentration Dependence 282


12.6 CZTS Solar Cell Prepared by Non-vacuum Processes 284


References 285


13 Growth of CZTS-Based Monograins and Their Application to Membrane Solar Cells 289
Enn Mellikov, Mare Altosaar, Marit Kauk-Kuusik, Kristi Timmo, Dieter Meissner, Maarja Grossberg, Jüri Krustok and Olga Volobujeva


13.1 Introduction 289


13.2 Monograin Powder Growths, Basics of the Process 291


13.3 Influence of Chemical Etching on the Surface Composition of Monograins 295


13.4 Thermal Treatment of CZTS-Based Monograins 298


13.5 Optoelectronic Properties of CZTS-Based Monograins and Polycrystals 300


13.6 Conclusion 306


References 306


Part IV Device Physics of Thin-Film Solar Cells 311


14 The Role of Grain Boundaries in CZTS-Based Thin-Film Solar Cells 313
Joel B. Li and Bruce M. Clemens


14.1 Introduction 313


14.2 CIGSe and CdTe Solar Cells 314


14.3 CZTS-Based Thin-Film Solar Cells 318


14.4 Conclusion 327


References 328


15 CZTS-Based Thin-Film Solar Cells Prepared via Coevaporation 335
Byungha Shin, Talia Gershon and Supratik Guha


15.1 Introduction 335


15.2 Preparation of CZTS and CZTSe Absorbers 337


15.3 Fundamental Properties of Coevaporated CZTS and CZTSe Absorbers 338


15.4 Device Characteristics of Full-Sulfide CZTS Thin-Film Solar Cells 348


15.5 Device Characteristics of Full-Selenide CZTSe Thin-Film Solar Cells 354


15.6 Summary 358


References 358


16 Loss Mechanisms in Kesterite Solar Cells 363
Alex Redinger and Susanne Siebentritt


16.1 Introduction 363


16.2 Current State-of-the-Art CZTS-Based Thin-Film Solar Cells 364


16.3 Dominant Recombination Path 366


16.4 Band-Gap Variations 372


16.5 Series Resistance and its Relation to Voc Losses 376


16.6 Conclusion 381


Acknowledgements 382


References 382


17 Device Characteristics of Hydrazine-Processed CZTSSe 387
Oki Gunawan, Tayfun Gokmen and David B. Mitzi


17.1 Introduction 387


17.2 Device Characteristics 389


17.3 Summary 406


Acknowledgements 407


References 408


Subject Index 413