Earth-Abundant Materials for Solar Cells

Professor Sadao Adachi, Division of Electronics and Informatics, Faculty of Science and Technology, Gunma University, Japan

This book focuses on inorganic semiconductors made of nontoxic and abundant materials...The introductory chapter defines, with sample calculations, parameters such as abundance values, spectral efficiency, effective cubic lattice constant (used in later chapters to correlate properties of these 27 semiconductors), the effective medium approximation, and interpolation schemes...This book is an authoritative source of information due to the in-depth discussions and adequate references, figures, tables, and appendices (MRS Bulletin-December 2016)

• Preface ixAbbreviations and Acronyms xi1 Introduction 11.1 Natural Abundance of Elements in the Earth’s Crust 11.1.1 Chemical Elements 11.1.2 Solar Cells and Earth-Abundant Materials 41.2 Solar Radiation Spectrum 51.3 Shockley–Queisser Efficiency Limit 61.4 Fundamental Properties of Photovoltaic Semiconductor Materials 81.5 Solar Cell Device Characteristics 111.6 Prediction of Physical Properties for Complex Material System 131.6.1 An Effective Medium Approximation 131.6.2 An Interpolation Scheme 15References 192 Structural Properties 212.1 Grimm–Sommerfeld Rule 212.2 Crystal Structure and Phase Stability 222.2.1 Crystal Structure 222.2.2 Theoretical Phase Stability 242.3 Lattice Constant and Related Parameters 252.3.1 Bulk Material 252.3.2 Nanocrystalline Material 522.4 Structural Phase Transition 58References 613 Thermal Properties 673.1 Phase Diagram 673.1.1 Cu2Zn–IV–VI4 Quaternary 673.1.2 Cu2Cd–IV–VI4 Quaternary 723.1.3 Cu2Hg–IV–VI4 Quaternary 753.1.4 Cu2–II–IV–VI4 Solid Solution 783.2 Melting Point 813.3 Specific Heat 863.4 Debye Temperature 883.5 Thermal Expansion Coefficient 893.6 Thermal Conductivity 923.6.1 Quaternary Material 923.6.2 Alloy Material 1013.7 Thermal Diffusivity 107References 1074 Elastic, Mechanical, and Lattice Dynamic Properties 1114.1 Elastic Constant 1114.1.1 General Remark 1114.1.2 Theoretical Value 1134.1.3 Young’s Modulus, Poisson’s Ratio, and Similar 1154.1.4 Sound Velocity 1184.2 Microhardness 1214.3 Lattice Dynamic Properties 1244.3.1 Phonon Dispersion Relation 1244.3.2 Raman Scattering: Tetragonal Lattice 1264.3.3 Raman Scattering: Orthorhombic Lattice 1334.3.4 Effect of Atomic Mass on Phonon Frequency 1364.3.5 Raman Scattering: Solid Solution 1374.3.6 Raman Scattering: Excitation Wavelength Dependence 1434.3.7 Far-IR Spectroscopy 1484.3.8 External Perturbation Effect 1504.3.9 Nanocrystalline Material 156 References 1665 Electronic Energy-Band Structure 1735.1 General Remark 1735.1.1 Energy-Band Structure 1735.1.2 Γ-Point Energy-Band Scheme 1805.1.3 Band-Gap Energy: External Perturbation and Doping Effects 1835.1.4 Effective Mass: External Perturbation and Doping Effects 1855.2 Lowest Indirect and Direct Band-Gap Energies 1855.2.1 Quaternary Material 1855.2.2 Solid Solution 2015.3 Higher-Lying Band-Gap Energy 2055.4 External Perturbation Effect on the Band-Gap Energy: Experimental Data 2055.5 Effective Mass 2115.5.1 Electron Effective Mass 2115.5.2 Hole Effective Mass 2175.6 Nanocrystalline Band-Gap Energy 2185.6.1 Quaternary Material 2185.6.2 Solid Solution 2225.7 Heterojunction Band Offset 2235.7.1 General Consideration 2235.7.2 Theoretical Value 2245.7.3 Experimental Value 2255.8 Electron Affinity 2335.9 Schottky Barrier Height 235References 2366 Optical Properties 2456.1 General Remark 2456.1.1 Dielectric Permittivity: Tensor Representation 2456.1.2 Optical Dispersion Relation 2466.1.3 Optical Spectrum: Classification into Several Regions 2506.2 The Reststrahlen Region 2536.2.1 Static and High-Frequency Dielectric Constants 2536.2.2 Reststrahlen Spectrum 2546.3 At or Near the Fundamental Absorption Edge 2576.3.1 Exciton Parameter 2576.3.2 Optical Absorption 2616.3.3 Refractive Index 2716.4 The Interband Transition Region 2766.4.1 Model Dielectric Function 2766.4.2 Optical Spectrum and MDF Analysis 2796.4.3 Optical Absorption Spectrum 2886.4.4 Optical Constant in the 0–10 000 eV Spectral Region 288References 2967 Carrier Transport Properties 3017.1 Electron Transport Properties 3017.2 Hole Hall Mobility 3037.2.1 General Remark 3037.2.2 Room-Temperature Value 3047.2.3 Temperature Dependence 3127.2.4 Effect of Stoichiometry, Alloying, and Foreign Atom Doping 3197.3 Electrical Resistivity 3277.3.1 Free-Hole Conduction 3277.3.2 Hopping Conduction 3327.3.3 Transport in Degenerate Band 3347.3.4 Insulator-to-Metal Transition 3357.4 Minority-Carrier Transport 3397.4.1 Minority-Electron Mobility 3397.4.2 Minority-Electron Lifetime and Diffusion Length 3427.5 Effect of Grain Boundary 3507.6 Proposal: Graded-Absorber Solar Cell Structure 3527.7 Proposal: Controlling Transport Properties of Bulk Material by Heat Treatment 353References 354Appendix A Summary: Physical Properties of CZTS and CZTSe 363Appendix B Summary: Physical Properties of c-CdS, w-CdS, and ZnO 369References 376Appendix C Optical Constants of Some Cu2–II–IV–VI4 Quaternary Semiconductors 379References 414Appendix D Optical Constants of c-CdS, w-CdS, and ZnO 415References 441Index 443