Solar Cell Materials - Developing Technologies

List of Contributors xiii Series Preface xv Preface xvii Acknowledgements xix Abbreviations xxi 1 Introduction 1 Gavin Conibeer and Arthur Willoughby 1.1 Introduction 1 1.2 The Sun 1 1.3 Book Outline 3 References 4 2 Fundamental Physical Limits to Photovoltaic Conversion 5 J.F. Guillemoles 2.1 Introduction 5 2.2 Thermodynamic Limits 8 2.2.1 The Sun is the Limit 9 2.2.2 Classical Thermodynamics Analysis of Solar Energy Conversion 10 2.3 Limitations of Classical Devices 12 2.3.1 Detailed Balance and Main Assumptions 13 2.3.2 p-n Junction 14 2.3.3 The Two-Level System Model 17 2.3.4 Multijunctions 19 2.4 Fundamental Limits of some High-Efficiency Concepts 23 2.4.1 Beyond Unity Quantum Efficiency 24 2.4.2 Beyond Isothermal Conversion: Hot-Carrier Solar Cells (HCSC) 29 2.4.3 Beyond the Single Process/ Photon: Photon Conversion 32 2.5 Conclusion 33 References 33 3 Physical Characterisation of Photovoltaic Materials 37 Daniel Bellet and Edith Bellet-Amalric 3.1 Introduction 37 3.2 Correspondence between Photovoltaic Materials Characterisation Needs and Physical Techniques 37 3.3 X-Ray Techniques 38 3.3.1 X-Ray Diffraction (XRD) 39 3.3.2 Grazing-Incidence X-Ray Diffraction (GIXRD) 42 3.3.3 X-Ray Reflectivity (XRR) 44 3.3.4 Other X-Ray Techniques 46 3.4 Electron Microscopy Methods 47 3.4.1 Electron Specimen Interactions and Scanning Electron Microscopy (SEM) 50 3.4.2 Electron Backscattering Diffraction (EBSD) 51 3.4.3 Transmission Electron Microscopy (TEM) 53 3.4.4 Electron Energy Loss Spectroscopy (EELS) 54 3.5 Spectroscopy Methods 55 3.5.1 X-Ray Photoelectron Spectroscopy (XPS) 55 3.5.2 Secondary Ion Mass Spectrometry (SIMS) 57 3.5.3 Rutherford Backscattering Spectrometry (RBS) 58 3.5.4 Raman Spectroscopy 58 3.5.5 UV-VIS-NIR Spectroscopy 60 3.6 Concluding Remarks and Perspectives 61 Acknowledgements 62 References 62 4 Developments in Crystalline Silicon Solar Cells 67 Martin A. Green 4.1 Introduction 67 4.2 Present Market Overview 68 4.3 Silicon Wafers 69 4.3.1 Standard Process 69 4.3.2 Multicrystalline Silicon Ingots 72 4.3.3 Ribbon Silicon 73 4.4 Cell Processing 75 4.4.1 Screen-Printed Cells 75 4.4.2 Buried-Contact and Laser Doped, Selective-Emitter Solar Cells 78 4.4.3 HIT Cell 79 4.4.4 Rear-Contact Cell 80 4.4.5 PERL Solar Cell 81 4.5 Conclusion 84 Acknowledgement 84 References 84 5 Amorphous and Microcrystalline Silicon Solar Cells 87 R.E.I. Schropp 5.1 Introduction 87 5.2 Deposition Methods 89 5.2.1 Modifications of Direct PECVD Techniques 90 5.2.2 Remote PECVD Techniques 91 5.2.3 Inline HWCVD Deposition 93 5.3 Material Properties 93 5.3.1 Protocrystalline Silicon 94 5.3.2 Microcrystalline or Nanocrystalline Silicon 95 5.4 Single-Junction Cell 98 5.4.1 Amorphous (Protocrystalline) Silicon Cells 100 5.4.2 Microcrystalline (c-Si:H) Silicon Cells 101 5.4.3 Higher Deposition Rate 103 5.5 Multijunction Cells 104 5.6 Modules and Production 105 5.6 Acknowledgments 108 References 108 6 III-V Solar Cells 115 N.J. Ekins-Daukes 6.1 Introduction 115 6.2 Homo- and Heterojunction III-V Solar Cells 117 6.2.1 GaAs Solar Cells 119 6.2.2 InP Solar Cells 122 6.2.3 InGaAsP 123 6.2.4 GaN 123 6.3 Multijunction Solar Cells 124 6.3.1 Monolithic Multijunction Solar Cells 125 6.3.2 Mechanically Stacked Multijunction Solar Cells 131 6.4 Applications 133 6.4.1 III-V Space Photovoltaic Systems 133 6.4.2 III-V Concentrator Photovoltaic Systems 134 6.5 Conclusion 136 References 136 7 Chalcogenide Thin-Film Solar Cells 147 M. Paire, S. Delbos, J. Vidal, N. Naghavi, and J.F. Guillemoles 7.1 Introduction 147 7.2 CIGS 150 7.2.1 Device Fabrication 150 7.2.2 Material Properties 164 7.2.3 Device Properties 173 7.2.4 Outlook 183 7.3 Kesterites 187 7.3.1 Advantages of CZTS 187 7.3.2 Crystallographic and Optoelectronic Properties 189 7.3.3 Synthesis Strategies 192 Acknowledgements 198 References 198 8 Printed Organic Solar Cells 217 Claudia Hoth, Andrea Seemann, Roland Steim, Tayebeh Ameri, Hamed Azimi, and Christoph J. Brabec 8.1 Introduction 217 8.2 Materials and Morphology 218 8.2.1 Organic Semiconductors 219 8.2.2 Control of Morphology in oBHJ Solar Cells 224 8.2.3 Monitoring Morphology 233 8.2.4 Numerical Simulations of Morphology 235 8.2.5 Alternative Approaches to Control the Morphology 235 8.3 Interfaces in Organic Photovoltaics 237 8.3.1 Origin of Voc 237 8.3.2 Determination of Polarity-Inverted and Noninverted Structure 238 8.3.3 Optical Spacer 239 8.3.4 Protection Layer between the Electrode and the Polymer 240 8.3.5 Selective Contact 240 8.3.6 Interface Material Review for OPV Cells 240 8.4 Tandem Technology 243 8.4.1 Theoretical Considerations 243 8.4.2 Review of Experimental Results 248 8.4.3 Design Rules for Donors in Bulk-Heterojunction Tandem Solar Cells 255 8.5 Electrode Requirements for Organic Solar Cells 257 8.5.1 Materials for Transparent Electrodes 258 8.5.2 Materials for Nontransparent Electrodes 263 8.6 Production of Organic Solar Cells 265 8.7 Summary and Outlook 273 References 273 9 Third-Generation Solar Cells 283 Gavin Conibeer 9.1 Introduction 283 9.2 Multiple-Energy-Level Approaches 285 9.2.1 Tandem Cells 285 9.2.2 Multiple-Exciton Generation (MEG) 291 9.2.3 Intermediate-Band Solar Cells (IBSC) 293 9.3 Modification of the Solar Spectrum 294 9.3.1 Downconversion, QE > 1 294 9.3.2 Upconversion of Below-Bandgap Photons 297 9.4 Thermal Approaches 302 9.4.1 Thermophotovoltaics (TPV) 303 9.4.2 Thermophotonics 303 9.4.3 Hot-Carrier Cells 303 9.5 Other Approaches 308 9.5.1 Nonreciprocal Devices 308 9.5.2 Quantum Antennae Light as a Wave 308 9.6 Conclusions 309 Acknowledgements 309 References 310 Concluding Remarks 315 Gavin Conibeer and Arthur Willoughby Index 319