Photon Management in Solar Cells

Written by renowned experts in the field of photon management in solar cells, this one-stop reference gives an introduction to the physics of light management in solar cells, and discusses the different concepts and methods of applying photon management. The authors cover the physics, principles, concepts, technologies, and methods used, explaining how to increase the efficiency of solar cells by splitting or modifying the solar spectrum before they absorb the sunlight. In so doing, they present novel concepts and materials allowing for the cheaper, more flexible manufacture of solar cells and systems. For educational purposes, the authors have split the reasons for photon management into spatial and spectral light management. Bridging the gap between the photonics and the photovoltaics communities, this is an invaluable reference for materials scientists, physicists in industry, experimental physicists, lecturers in physics, Ph.D. students in physics and material sciences, engineers in power technology, applied and surface physicists.

Table of Contents:
Preface XIII List of Contributors XV 1 Current Concepts for Optical Path Enhancement in Solar Cells 1 Alexander N. Sprafke and Ralf B. Wehrspohn 1.1 Introduction 1 1.2 Planar Antireflection Coatings 2 1.3 Optical Path Enhancement in the Ray Optical Limit 4 1.4 Scattering Structures for Optical Path Enhancement 5 1.5 Resonant Structures for Optical Path Enhancement 7 1.6 Ultra-Light Trapping 10 1.7 Energy-Selective Structures as Intermediate Reflectors for Optical Path Enhancement in Tandem Solar Cells 13 1.8 Comparison of the Concepts 16 1.9 Conclusion 17 References 17 2 The Principle of Detailed Balance and the Opto-Electronic Properties of Solar Cells 21 Uwe Rau and Thomas Kirchartz 2.1 Introduction 21 2.2 Opto-Electronic Reciprocity 21 2.2.1 The Principle of Detailed Balance 21 2.2.2 The Shockley–Queisser Limit 22 2.2.3 Derivation of the Reciprocity Theorem 24 2.3 Connection to Other Reciprocity Theorems 29 2.3.1 Emitter and Collector Currents in Transistors 29 2.3.2 Tellegens’s NetworkTheorem 30 2.3.3 Differential Reciprocity Relations byWong and Green 31 2.3.4 Würfel’s Generalization of Kirchhoff’s Law 33 2.3.5 Reciprocity Relation for LED Quantum Efficiency 33 2.3.6 Shockley–Queisser Revisited 34 2.3.7 Influence of Light Trapping 35 2.4 Applications of the Opto-Electronic Reciprocity Theorem 37 2.4.1 Experimental Verifications 37 2.4.2 Spectrally Resolved Luminescence Analysis 39 2.4.3 Luminescence Imaging 40 2.5 Limitations to the Opto-Electronic Reciprocity Theorem 43 2.6 Conclusions 44 References 44 3 Rear Side Diffractive Gratings for Silicon Wafer Solar Cells 49 Marius Peters, Hubert Hauser, Benedikt Bläsi, Matthias Kroll, Christian Helgert, Stephan Fahr, SamuelWiesendanger, Carston Rockstuhl, Thomas Kirchartz, Uwe Rau, AlexanderMellor, Lorenz Steidl, and Rudolf Zentel 3.1 Introduction 49 3.1.1 Gratings for Solar Cells – Basic Idea and Challenges 49 3.1.2 A Short Literature Review 50 3.2 Principle of Light Trapping with Gratings 52 3.3 Fundamental Limits of Light Trapping with Gratings 56 3.4 Simulation of Gratings in Solar Cells 58 3.4.1 Optical Simulation Using RCWA/FMM 58 3.4.2 Optical Simulation Using the Matrix Method 61 3.4.3 Electro-Optically Coupled Simulation Using RCWA and Sentaurus Device 65 3.5 Realization 67 3.5.1 Electron-Beam Lithography 68 3.5.2 Self-Organizing Photonic Crystals 72 3.5.3 Fabrication of Rear Side Gratings via Interference Lithography and Nanoimprint Lithography 75 3.6 Topographical Characterization 78 3.6.1 Atomic Force Microscopy 78 3.6.2 Scanning Electron Microscopy 80 3.6.3 Focused Ion Beam Milling 81 3.7 Summary 84 References 84 4 Randomly Textured Surfaces 91 Carsten Rockstuhl, Stephan Fahr, Falk Lederer, Karsten Bittkau, Thomas Beckers, Markus Ermes, and Reinhard Carius 4.1 Introduction 91 4.2 Methodology 93 4.2.1 Structure of a Referential Solar Cell and Description of Available Substrates 94 4.2.2 Rigorous Methods 96 4.2.3 Scalar Methods 97 4.2.4 Properties of Interest 98 4.2.5 Near-Field Scanning Optical Microscopy 99 4.3 Properties of an Isolated Interface 100 4.3.1 Near-Field Properties 100 4.3.2 Far-Field Properties 102 4.4 Single-Junction Solar Cell 104 4.4.1 Absorption Enhancement 104 4.4.2 Design of Optimized Randomly Textured Interfaces 106 4.5 Intermediate Layer in Tandem Solar Cells 110 4.6 Conclusions 112 Acknowledgments 113 References 113 5 Black Silicon Photovoltaics 117 Kevin Füchsel, Matthias Kroll, Martin Otto, Martin Steglich, Astrid Bingel, Thomas Käsebier, Ralf B.Wehrspohn, Ernst-Bernhard Kley, Thomas Pertsch, and Andreas Tünnermann 5.1 Introduction 117 5.1.1 Fabrication Methods 117 5.1.2 Reactive Ion Etching 119 5.1.3 Laser Processing 122 5.1.4 Chemical and Electrochemical Etching 124 5.2 Optical Properties and Light Trapping Possibilities 126 5.2.1 Overview 126 5.2.2 ICP-RIE Black Silicon 128 5.2.3 Influence of Dielectric Coatings 130 5.2.4 Influence of the SubstrateThickness and Limiting Efficiency 132 5.3 Surface Passivation of Black Silicon 135 5.3.1 Requirements for Black Silicon Passivation 136 5.3.2 Possible Passivation Schemes 136 5.3.3 Passivation of Black Silicon Surfaces 139 5.3.3.1 Surface Damage and Sample Cleaning 139 5.3.3.2 Effective Passivation of ICP-RIE Black Silicon 140 5.4 Black Silicon Solar Cells 142 References 144 6 Concentrator Optics for Photovoltaic Systems 153 Andreas Gombert, Juan C.Mi˜nano, Pablo Benitez, and Thorsten Hornung 6.1 Fundamentals of Solar Concentration 153 6.1.1 Introduction 153 6.1.2 Concentration and Acceptance Angle 153 6.1.3 Optical Efficiency 157 6.1.4 Effect of Spatial and Spectral Non-uniformities on the Cell Illumination 158 6.2 Optical Designs 159 6.2.1 Classical Imaging Concentrators 160 6.2.2 Nonimaging Secondary Optics 161 6.2.3 Advanced Concentrator Designs 162 6.2.4 Freeform SMS Concentrators 163 6.2.5 Multifold Köhler Concentrators 164 6.2.6 Comparison 166 6.3 Silicone on Glass Fresnel Lenses 169 6.3.1 Physical Influence of Lens Temperature 170 6.3.2 Influence of Lens Temperature on Efficiency 172 6.4 Considerations on Concentrators in HCPV Systems 175 6.4.1 General Requirements on CPV Concentrator Optics 175 6.4.2 Design Considerations 176 6.4.3 Experiences with Concentrator Designs 178 6.5 Conclusions 179 References 179 7 Light-Trapping in Solar Cells by Directionally Selective Filters 183 Carolin Ulbrich, Marius Peters, Stephan Fahr, Johannes Üpping, Thomas Kirchartz, Carsten Rockstuhl, Jan Christoph Goldschmidt, Andreas Gerber, Falk Lederer, RalfWehrspohn, Benedikt Bläsi, and Uwe Rau 7.1 Introduction 183 7.2 Theory 185 7.2.1 Radiative Efficiency Limit 185 7.2.2 Ultra-Light-Trapping 187 7.2.2.1 Universal Light-Trapping Limit for Completely Randomized Light 187 7.2.3 Annual Yield for Directionally Selective Solar Absorbers 190 7.3 Filter Systems 192 7.3.1 1D Layer Stack Rugate Filters 192 7.3.2 3D Photonic Crystal Opal Structures 193 7.4 Experimental Realization 197 7.4.1 Bragg Filter Covering a Hydrogenated Amorphous Silicon Solar Cell 197 7.4.2 Bragg Filter Covering a Germanium Solar Cell 201 7.5 Summary and Outlook 202 References 203 8 Linear Optics of Plasmonic Concepts to Enhance Solar Cell Performance 209 Gero von Plessen, Deepu Kumar, Florian Hallermann, Dmitry N. Chigrin, and Alexander N. Sprafke 8.1 Introduction 209 8.2 Metal Nanoparticles 210 8.2.1 Optical Excitations in Metal Nanoparticles 210 8.2.2 Control of Optical Properties 212 8.2.2.1 Resonance Energies of Particle Plasmons 213 8.2.2.2 Linewidths of Particle-Plasmon Resonances 215 8.2.2.3 Peak Heights of Particle-Plasmon Resonances 216 8.2.2.4 Scattering Quantum Efficiencies 216 8.2.2.5 Light-Scattering Patterns 217 8.2.2.6 Near-Field Effects 217 8.2.2.7 Combinations of Effects 218 8.3 Surface-Plasmon Polaritons 218 8.4 Front-Side Plasmonic Nanostructures 219 8.5 Rear-Side Plasmonic Nanostructures 221 8.6 Further Concepts 222 8.7 Summary 226 Acknowledgments 226 References 227 9 Up-conversion Materials for Enhanced Efficiency of Solar Cells 231 Jan Christoph Goldschmidt, Stefan Fischer, Heiko Steinkemper, Barbara Herter, SebastianWolf, Florian Hallermann, Gero von Plessen, Jacqueline Anne Johnson, Bernd Ahrens, Paul-TiberiuMiclea, and Stefan Schweizer 9.1 Introduction 231 9.2 Up-Conversion in Er3+-Doped ZBLAN Glasses 232 9.2.1 Samples 232 9.2.2 Optical Absorption 233 9.2.3 Up-Conversion 234 9.3 Up-Conversion in Er3+-Doped β-NaYF4 237 9.3.1 Device Measurements 239 9.4 Simulating Up-Conversion with a Rate Equation Model 240 9.5 Increasing Up-Conversion Efficiencies 242 9.5.1 The Up-Converter Material 242 9.5.1.1 Phonon Energy 242 9.5.1.2 Doping Concentration 243 9.5.2 The Environment around the Up-Converter 245 9.5.2.1 Plasmon Enhanced Up-Conversion 245 9.5.2.2 Modeling Dielectric Nanostructures 246 9.5.3 Spectral Concentration 248 9.6 Conclusion 251 Acknowledgments 252 References 252 10 Down-Conversion in Rare-Earth Doped Glasses and Glass Ceramics 255 Stefan Schweizer, Christian Paßlick, Franziska Steudel, Bernd Ahrens, Paul-TiberiuMiclea, Jacqueline Anne Johnson, Katharina Baumgartner, and Reinhard Carius 10.1 Introduction 255 10.2 Physical Background 257 10.2.1 Rare-Earth Ions 257 10.2.2 Glass Systems 258 10.2.2.1 Phonons 259 10.2.2.2 ZBLAN Glasses 259 10.2.2.3 Borate Glasses 260 10.3 Down-Conversion in ZBLAN Glasses and Glass Ceramics 260 10.3.1 Samples 261 10.3.2 Glass-Ceramic Cover Glasses for High Efficiency Solar Cells 261 10.3.2.1 Absorption 262 10.3.2.2 Short-Circuit Current 264 10.3.2.3 Internal Conversion Efficiency 265 10.3.2.4 Quantum Efficiency Increase 266 10.3.3 Influence of Multivalent Europium-Doping 267 10.3.3.1 X-Ray Absorption near Edge Structure 268 10.3.3.2 X-Ray Diffraction 270 10.3.3.3 Photoluminescence 272 10.3.4 Conclusion 274 10.4 Down-Conversion in Sm-Doped Borate Glasses for High-Efficiency CdTe Solar Cells 275 10.4.1 Samples 275 10.4.2 External Quantum Efficiency of CdTe Solar Cells 276 10.4.3 Optical Absorption and Fluorescence Emission 276 10.4.4 Efficiency Increase 277 10.4.5 Conclusion 279 10.5 Summary 280 Acknowledgment 281 References 281 11 Fluorescent Concentrators for Photovoltaic Applications 283 Jan Christoph Goldschmidt, Liv Prönneke, Andreas Büchtemann, Johannes Gutmann, Lorenz Steidl, Marcel Dyrba, Marie-Christin Wiegand, Bernd Ahrens, ArminWedel, Stefan Schweizer, Benedikt Bläsi, Rudolf Zentel, and Uwe Rau 11.1 Introduction 283 11.2 The Theoretical Description of Fluorescent Concentrators 285 11.2.1 Detailed Balance Considerations 285 11.2.2 Photonic Structures to Increase Fluorescent Collector Efficiency 286 11.2.3 Possible System Configurations – Side-Mounted and Bottom-Mounted Solar Cells 287 11.2.3.1 Thermodynamic Efficiency Limits of Fluorescent Concentrators 290 11.2.3.2 Non-perfect Photonic Structure 292 11.2.3.3 Luminescent Materials in Photonic Structures 293 11.3 Materials for Fluorescent Concentrators 296 11.3.1 Systems Based on Organic Matrix Materials 296 11.3.1.1 The Matrix Material 296 11.3.1.2 The Luminescent Species 299 11.3.2 Completely Inorganic Systems Based on Rare Earths 304 11.4 Experimentally Realized Fluorescent Concentrator Systems 307 11.4.1 Systems with Side-Mounted Solar Cells 307 11.4.2 Systems with Bottom-Mounted Monocrystalline Silicon Solar Module 308 11.4.3 Increasing Efficiency with Photonic Structures 310 11.4.3.1 Systems with Side-Mounted III–V Solar Cell 310 11.4.3.2 Systems with Bottom-Mounted Amorphous Silicon Solar Cell 312 11.5 Conclusion 314 Acknowledgments 314 References 315 12 Light Management in Solar Modules 323 Gerhard Seifert, Isolde Schwedler, Jens Schneider, and Ralf B.Wehrspohn 12.1 Introduction 323 12.2 Fundamentals of Light Management in Solar Modules 324 12.2.1 Basic Physical Concepts of Light Management in Solar Modules 324 12.2.1.1 Optical Losses due to Reflection and Absorption 324 12.2.1.2 Optical Description of Textured Interfaces or Surfaces 326 12.2.1.3 Spectral Effects and Solar Concentration 329 12.2.1.4 Effects of Incidence Angle Variation and Diffuse Light 331 12.2.2 Assessment of the Optical Performance of Solar Modules 331 12.2.2.1 Experimental Techniques 331 12.2.2.2 Simulation Approaches and Studies 333 12.3 Technological Solutions for Minimized Optical Losses in Solar Modules 334 12.3.1 Minimization of Optical Losses in Front Glass Sheets 334 12.3.2 Anti-reflection (AR) Technologies for PV Module Front Surface 336 12.3.2.1 Nano-scale Technologies for Anti-reflective Treatment of PV Front Glass 336 12.3.2.2 Micro-scale Structures for Light-Trapping on PV Front Glasses 338 12.3.3 Material Selection and Optimization for Encapsulation Film 338 12.3.4 Minimization of Losses due to Metallization and Contact Tabs 340 12.3.5 Optical Optimization of Cell Front and Back Interface 342 12.3.6 Redirection of Light from Cell Interspaces 343 12.4 Outlook 343 References 344 Index 347

About the Author :
Ralf B. Wehrspohn studied physics at the University of Oldenburg, Germany, and received his PhD degree from the Ecole Polytechnique in Paris in 1997. Until 1999 he worked on thin-fi lm transistors for AMLCDs at Philips Research. From 1999 until 2003 he led the Porous Materials/Photonic Crystals group at the Max Planck Institute of Microstructure Physics in Halle, after which he held a chair at the Physics department of the University of Paderborn for three years. Since 2006, he has been the director of the Fraunhofer-Institute for Mechanics of Materials and a Professor of Physics at the Martin-Luther-University Halle-Wittenberg. Professor Wehrspohn was awarded the Maier-Leibnitz Prize of the German Science Foundation in 2003. Uwe Rau studied physics at the University of Tübingen, Germany, and at the University Claude Bernard, Lyon, France. He obtained his PhD 1991 from the Physical Institute of the University Tübingen. From 1991-1993 he worked at the Max Planck Institute for Solid-State Research. He was scientifi c group leader from 1993-2007 at the University Bayreuth and at the University Stuttgart. Since 2007 he is full professor at RWTH Aachen (Faculty Electrical Engineering and Information Technology, Chair of Photovoltaics). Simultaneously he is director of the Institute of Energy and Climate Research IEK5-Photovoltaics at Forschungszentrum Jülich). Andreas Gombert studied photo engineering and optics in Cologne, Germany, and Strasbourg, France, and received his PhD from the University Louis Pasteur, Strasbourg. His professional career started in 1986 at the Fraunhofer Institute for Physical Measurement Techniques in the fi eld of integrated optics. From 1991 to 2008, he worked at the Fraunhofer Institute for Solar Energy Systems where headed the department Materials Research and Applied Optics. Since 2008 he is Vice President System Platform and R&D and since 2014 also Managing Director of Soitec Solar GmbH, Freiburg, Germany, a division of the Soitec Group. He lectures at Technical Faculty of the University of Freiburg, Germany where he also habilitated.

Review :
"The book is clearly written, with a lot of excellent illustrations. At the end of each chapter there are substantial references, which are very important for a book of this type." (Optics and Photonics 2016)