Principles of Solar Cells, LEDs and Diodes

Introduction xi Acknowledgements xv 1 Semiconductor Physics 1 1.1 Introduction 2 1.2 The Band Theory of Solids 2 1.3 The Kronig Penney Model 3 1.4 The Bragg Model 8 1.5 Effective Mass 8 1.6 Number of States in a Band 10 1.7 Band Filling 12 1.8 Fermi Energy and Holes 14 1.9 Carrier Concentration 15 1.10 Semiconductor Materials 25 1.11 Semiconductor Band Diagrams 26 1.12 Direct Gap and Indirect Gap Semiconductors 29 1.13 Extrinsic Semiconductors 35 1.14 Carrier Transport in Semiconductors 40 1.15 Equilibrium and Non-Equilibrium Dynamics 43 1.16 Carrier Diffusion and the Einstein Relation 45 1.17 Quasi-Fermi Energies 48 1.18 The Diffusion Equation 50 1.19 Traps and Carrier Lifetimes 53 1.20 Alloy Semiconductors 56 1.21 Summary 59 Suggestions for Further Reading 61 Problems 63 2 The PN Junction Diode 69 2.1 Introduction 70 2.2 Diode Current 72 2.3 Contact Potential 75 2.4 The Depletion Approximation 78 2.5 The Diode Equation 85 2.6 Reverse Breakdown and the Zener Diode 97 2.7 Tunnel Diodes 100 2.8 Generation/Recombination Currents 101 2.9 Ohmic Contacts, Schottky Barriers and Schottky Diodes 104 2.10 Heterojunctions 113 2.11 Alternating Current (AC) and Transient Behaviour 115 2.12 Summary 117 Suggestions for Further Reading 118 Problems 119 3 Photon Emission and Absorption 123 3.1 Introduction to Luminescence and Absorption 124 3.2 Physics of Light Emission 125 3.3 Simple Harmonic Radiator 128 3.4 Quantum Description 129 3.5 The Exciton 132 3.6 Two-Electron Atoms 135 3.7 Molecular Excitons 141 3.8 Band-to-Band Transitions 144 3.9 Photometric Units 148 3.10 Summary 152 Suggestions for Further Reading 153 Problems 155 4 The Solar Cell 159 4.1 Introduction 160 4.2 Light Absorption 162 4.3 Solar Radiation 164 4.4 Solar Cell Design and Analysis 164 4.5 Thin Solar Cells 172 4.6 Solar Cell Generation as a Function of Depth 176 4.7 Solar Cell Efficiency 179 4.8 Silicon Solar Cell Technology: Wafer Preparation 184 4.9 Silicon Solar Cell Technology: Solar Cell Finishing 187 4.10 Silicon Solar Cell Technology: Advanced Production Methods 191 4.11 Thin Film Solar Cells: Amorphous Silicon 192 4.12 Telluride/Selenide/Sulphide Thin-Film Solar Cells 199 4.13 High-Efficiency Multijunction Solar Cells 200 4.14 Concentrating Solar Systems 203 4.15 Summary 204 Suggestions for Further Reading 205 Problems 207 5 Light Emitting Diodes 215 5.1 Introduction 216 5.2 LED Operation and Device Structures 217 5.3 Emission Spectrum 220 5.4 Non-Radiative Recombination 221 5.5 Optical Outcoupling 223 5.6 GaAs LEDs 225 5.7 GaAs1 xPx LEDs 226 5.8 Double Heterojunction AlxGa1 xAs LEDs 228 5.9 AlGaInP LEDs 234 5.10 Ga1 xInxN LEDs 236 5.11 LED Structures for Enhanced Outcoupling and Power Output 244 5.12 Summary 247 Suggestions for Further Reading 248 Problems 249 6 Organic Semiconductors, OLEDs and Solar Cells 253 6.1 Introduction to Organic Electronics 254 6.2 Conjugated Systems 255 6.3 Polymer OLEDs 260 6.4 Small-Molecule OLEDs 266 6.5 Anode Materials 270 6.6 Cathode Materials 270 6.7 Hole Injection Layer 271 6.8 Electron Injection Layer 272 6.9 Hole Transport Layer 272 6.10 Electron Transport Layer 275 6.11 Light Emitting Material Processes 276 6.12 Host Materials 278 6.13 Fluorescent Dopants 279 6.14 Phosphorescent Dopants 283 6.15 Organic Solar Cells 283 6.16 Organic Solar Cell Materials 289 6.17 Summary 292 Suggestions for Further Reading 294 Problems 295 Appendix 1: Physical Constants 301 Appendix 2: Properties of Semiconductor Materials 303 Appendix 3: The Boltzmann Distribution Function 305 Index 309