next generation photovoltaics

Series in Optics and Optoelectronics Next Generation Photovoltaics High efficiency through full spectrum utilization Edited by Antonio Mart ´ ı and Antonio Luque Istituto de Energia Solar—ETSIT, Universidad Polit ´ ecnica de Madrid, Spain Institute of Physics Publishing Bristol and Philadelphia Next Generation Photovoltaics High efficiency through full spectrum utilization Series in Optics and Optoelectronics Series Editors: RGWBrown, University of Nottingham, UK ERPike, Kings College, London, UK Other titles in the series Applications of Silicon–Germanium Heterostructure Devices C K Maiti and G A Armstrong Optical Fibre Devices J-P Goure and I Verrier Optical Applications of Liquid Crystals L Vicari (ed) Laser-Induced Damage of Optical Materials R M Wood Forthcoming titles in the series High Speed Photonic Devices NDagli(ed) Diode Lasers D Sands High Aperture Focussing of Electromagnetic Waves and Applications in Optical Microscopy C J R Sheppard and P Torok Other titles of interest Thin-Film Optical Filters (Third Edition) H Angus Macleod c  IOP Publishing Ltd 2004 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. Multiple copying is permitted in accordance with the terms of licences issued by the Copyright Licensing Agency under the terms of its agreement with Un iversities UK (UUK). British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. ISBN 0 7503 0905 9 Library of Congress Cataloging-in-Publication Data are available Commissioning Editor: Tom Spicer Production Editor: Simon Laurenson Production Control: Sarah Plenty Cover Design: Victoria Le Billon Marketing: Nicola Newey and Verity Cooke Published by Institute of Physics Publishing, wholly owned by The Institute of Physics, London Institute of Physics Publishing, Dirac House, Temple Back, Bristol BS1 6BE, UK US Office: Institute of Physics Publishing, The Public Ledger Building, Suite 929, 150 South Independence Mall West, Philadelphia, PA 19106, USA Typeset in L A T E X2 ε by Text 2 Text Limited, Torquay, Devon Printed in the UK by MPG Books Ltd, Bodmin, Cornwall Contents Preface xi 1 Non-conventional photovoltaic technology: a need to reach goals Antonio Luque and Antonio Mart ´ ı 1 1.1 Introduction 1 1.2 On the motivation for solar energy 2 1.3 Penetration goals for PV electricity 7 1.4 Will PV electricity reach costs sufficiently low to permit a wide penetration? 9 1.5 The need for a technological breakthrough 14 1.6 Conclusions 17 References 18 2 Trends in the development of solar photovoltaics Zh I Alferov and V D Rumyantsev 19 2.1 Introduction 19 2.2 Starting period 20 2.3 Simple structures and simple technologies 21 2.4 Nanostructures and ‘high technologies’ 23 2.5 Multi-junction solar cells 28 2.6 From the ‘sky’ to the Earth 34 2.7 Concentration of solar radiation 35 2.8 Concentrators in space 43 2.9 ‘Non-solar’ photovoltaics 44 2.10 Conclusions 47 References 48 3 Thermodynamics of solar energy converters Peter W ¨ urfel 50 3.1 Introduction 50 3.2 Equilibria 50 3.2.1 Temperature equilibrium 51 3.2.2 Thermochemical equilibrium 52 vi Contents 3.3 Converting chemical energy into electrical energy: the basic requirements for a solar cell 57 3.4 Concepts for solar cells with ultra high efficiencies 59 3.4.1 Thermophotovoltaic conversion 60 3.4.2 Hot carrier cell 60 3.4.3 Tandem cells 60 3.4.4 Intermediate level cells 61 3.4.5 Photon up- and down-conversion 61 3.5 Conclusions 62 References 63 4 Tandem cells for very high concentration AWBett 64 4.1 Introduction 64 4.2 Tandem solar cells 66 4.2.1 Mechanically stacked tandem cells 67 4.2.2 Monolithic tandem cells 72 4.2.3 Combined approach: mechanical stacking of monolithic cells 77 4.3 Testing and application of monolithic dual-junction concentrator cells 77 4.3.1 Characterization of monolithic concentrator solar cells 77 4.3.2 Fabrication and characterization of a test module 80 4.3.3 FLATCON module 82 4.3.4 Concentrator system development 83 4.4 Summary and perspective 85 Acknowledgments 87 References 88 5 Quantum wells in photovoltaic cells C Rohr, P Abbott, I M Ballard, D B Bushnell, J P Connolly, N J Ekins-Daukes and K W J Barnham 91 5.1 Introduction 91 5.2 Quantum well cells 91 5.3 Strain compensation 94 5.4 QWs in tandem cells 96 5.5 QWCs with light trapping 97 5.6 QWCs for thermophotovoltaics 99 5.7 Conclusions 102 References 103 6 The importance of the very high concentration in third-generation solar cells Carlos Algora 108 6.1 Introduction 108 Contents vii 6.2 Theory 109 6.2.1 How concentration works on solar cell performance 109 6.2.2 Series resistance 112 6.2.3 The effect of illuminating the cell with a wide-angle cone of light 115 6.2.4 Pending issues: modelling under real operation conditions 118 6.3 Present and future of concentrator third-generation solar cells 120 6.4 Economics 122 6.4.1 How concentration affects solar cell cost 122 6.4.2 Required concentration level 124 6.4.3 Cost analysis 126 6.5 Summary and conclusions 134 Note added in press 136 References 136 7 Intermediate-band solar cells AMart ´ ı, L Cuadra and A Luque 140 7.1 Introduction 140 7.2 Preliminary concepts and definitions 142 7.3 Intermediate-band solar cell: model 148 7.4 The quantum-dot intermediate-band solar cell 150 7.5 Considerations for the practical implementation of the QD-IBSC 155 7.6 Summary 160 Acknowledgments 162 References 162 8 Multi-interface novel devices: model with a continuous substructure ZTKuznicki 165 8.1 Introduction 165 8.2 Novelties in Si optoelectronics and photovoltaics 167 8.2.1 Enhanced absorbance 168 8.2.2 Enhanced conversion 168 8.3 Active substructure and active interfaces 169 8.4 Active substructure by ion implantation 170 8.4.1 Hetero-interface energy band offset 173 8.4.2 Built-in electric field 174 8.4.3 Built-in strain field 176 8.4.4 Defects 178 8.5 Model of multi-interface solar cells 178 8.5.1 Collection efficiency and internal quantum efficiency 181 8.5.2 Generation rate 181 8.5.3 Carrier collection limit 181 8.5.4 Surface reservoir 182 8.5.5 Collection zones 183 8.5.6 Impurity band doping profile 184 viii Contents 8.5.7 Uni- and bipolar electronic transport in a multi-interface emitter 184 8.5.8 Absorbance in presence of a dead zone 186 8.5.9 Self-consistent calculation 187 8.6 An experimental test device 189 8.6.1 Enhanced internal quantum efficiency 190 8.6.2 Sample without any carrier collection limit (CCL) 191 8.7 Concluding remarks and perspectives 192 Acknowledgments 193 References 194 9 Quantum dot solar cells AJNozik 196 9.1 Introduction 196 9.2 Relaxation dynamics of hot electrons 199 9.2.1 Quantum wells and superlattices 201 9.2.2 Relaxation dynamics of hot electrons in quantum dots 206 9.3 Quantum dot solar cell configuration 214 9.3.1 Photoelectrodes composed of quantum dot arrays 216 9.3.2 Quantum dot-sensitized nanocrystalline TiO 2 solar cells 216 9.3.3 Quantum dots dispersed in organic semiconductor polymer matrices 217 9.4 Conclusion 218 Acknowledgments 218 References 218 10 Progress in thermophotovoltaic converters Bernd Bitnar, Wilhelm Durisch, Fritz von Roth, G ¨ unther Palfinger, Hans Sigg, Detlev Gr ¨ utzmacher, Jens Gobrecht, Eva-Maria Meyer, Ulrich Vogt, Andreas Meyer and Adolf Heeb 223 10.1 Introduction 223 10.2 TPV based on III/V low-bandgap photocells 224 10.3 TPV in residential heating systems 225 10.4 Progress in TPV with silicon photocells 227 10.4.1 Design of the system and a description of the components 227 10.4.2 Small prototype and demonstration TPV system 228 10.4.3 Prototype heating furnace 230 10.4.4 Foam ceramic emitters 231 10.5 Design of a novel thin-film TPV system 235 10.5.1 TPV with nanostructured SiGe photocells 240 10.6 Conclusion 243 Acknowledgments 243 References 243 Contents ix 11 Solar cells for TPV converters V M Andreev 246 11.1 Introduction 246 11.2 Predicted efficiency of TPV cells 247 11.3 Germanium-based TPV cells 251 11.4 Silicon-based solar PV cells for TPV applications 254 11.5 GaSb TPV cells 256 11.6 TPV cells based on InAs- and GaSb-related materials 260 11.6.1 InGaAsSb/GaSb TPV cells 261 11.6.2 Sub-bandgap photon reflection in InGaAsSb/GaSb TPV cells 263 11.6.3 Tandem GaSb/InGaAsSb TPV cells 263 11.6.4 TPV cells based on low-bandgap InAsSbP/InAs 264 11.7 TPV cells based on InGaAs/InP heterostructures 266 11.8 Summary 268 Acknowledgments 269 References 269 12 Wafer-bonding and film transfer for advanced PV cells C Jaussaud, E Jalaguier and D Mencaraglia 274 12.1 Introduction 274 12.2 Wafer-bonding and transfer application to SOI structures 274 12.3 Other transfer processes 277 12.4 Application of film transfer to III–V structures and PV cells 279 12.4.1 HEMT InAlAs/InGaAs transistors on films transferred onto Si 280 12.4.2 Multi-junction photovoltaic cells with wafer bonding using metals 281 12.4.3 Germanium layer transfer for photovoltaic applications 281 12.5 Conclusion 283 References 283 13 Concentrator optics for the next-generation photovoltaics PBen ´ ıtez and J C Mi ˜ nano 285 13.1 Introduction 285 13.1.1 Desired characteristics of PV concentrators 286 13.1.2 Concentration and acceptance angle 287 13.1.3 Definitions of geometrical concentration and optical efficiency 288 13.1.4 The effective acceptance angle 290 13.1.5 Non-uniform irradiance on the solar cell: How critical is it? 296 13.1.6 The PV design challenge 305 13.1.7 Non-imaging optics: the best framework for concentrator design 309 x Contents 13.2 Concentrator optics overview 312 13.2.1 Classical concentrators 312 13.2.2 The SMS PV concentrators 314 13.3 Advanced research in non-imaging optics 319 13.4 Summary 320 Acknowledgments 321 Appendix: Uniform distribution as the optimum illumination 321 References 322 Appendix: Conclusions of the Third-generation PV workshop for high efficiency through full spectrum utilization 326 Index 328 [...]... be preserved and made accessible to third parties in book form The result is a book that covers a variety of concepts: the economics of photovoltaics, thermodynamics, multi-junction solar cells, thermophotovoltaics, the application of low dimensional structures to photovoltaics, optics and technology Time will tell whether many of these ideas and concepts meet expectations For the moment, they are... Press) [4] Luque A 2001 Photovoltaic markets and costs forecast based on a demand elasticity model Prog Photovoltaics: Res Appl 9 303–12 [5] Yamaguchi M and Luque A 1999 High efficiency and high concentration in photovoltaics IEEE Trans Electron Devices 46 2139–44 Chapter 2 Trends in the development of solar photovoltaics Zh I Alferov and V D Rumyantsev Ioffe Physico-Technical Institute, 26 Polytechnicheskaya,... concerns but because new nuclear power is uncompetitive Even with emission constraints, the liberalisation of gas and power markets means this is unlikely to change over the next two decades Further ahead, technology advances could make a new generation of nuclear supplies competitive Renewable energy resources are adequate to meet all potential energy needs, despite competing with food and leisure for land... focusing oil demand on this sector Technology improvements are likely to outpace rising depletion costs for at least the next decade, keeping new supplies below $20 per barrel The costs of bio-fuels and gas to liquids should both fall well below $20 per barrel of oil equivalent over the next two decades, constraining oil prices Gas resource uncertainty is significant Scarcity could occur as early as 2025,... Telecomunicaci´ n, Ciudad Universitaria s/n, 28040, o Madrid, Spain 1.1 Introduction This book is the result of a workshop celebrated in the splendid mountain residence of the Polytechnic University of Madrid next to the village of Cercedilla, near Madrid There, a group of specialists gathered under the initiative of the Energy R&D programme of the European Commission, to discuss the feasibility of new forms... photovoltaic (PV) conversion and Martin Green, the celebrated scientist, who, after having established records of efficiency for the now common silicon cell, hoisted the banner for the need for a ‘third generation of solar cells’ able to overcome the limitations of the present technological effort in PV Together they closed the workshop This chapter will present the opening lecture that presented the... conventional energy (direct quotations to Shell report reproduced here with permission from Shell International Limited, 2001) Thus, in summary, no global energy shortage is expected to appear in the next 50 years but for Shell: Demographics, urbanisation, incomes, market liberalisation and energy demand are all important factors in shaping the energy system but are not likely to be central to its... pleasant, might perhaps not be sufficiently dramatic globally but they will become so in the centuries to come if we do not immediately initiate a vigorous programme of climatic change mitigation Intergenerational solidarity requests us to start acting now 1.3 Penetration goals for PV electricity In this section we are going to present some results from the Renewable Intensive Global Energy Supply (RIGES)... supply in RIGES The number above the columns gives the carbon emission as CO2 in Mt of C (elaborated with data from appendix A in [3]) Figure 1.5 Electricity supply in RIGES The fuels used for electricity generation are included in figure 1.4 (elaborated with data in appendix A from [3]) In all the IPCC demand scenarios, not only the ‘Accelerated Policies’ one, much of the final use energy is provided in... further growth of wind and solar energy Since 2025 when the first wave of renewables began to stagnate, biotechnology, materials advances and sophisticated electric network controls have enabled a new generation of renewable technologies to emerge A range of commercial solutions emerge to store and utilize distributed solar energy By 2050 renewables reach a third of world primary energy and are supplying . to retreat). In summary, a climatic change has already been triggered by human activity. Nature has always possessed a fearsome might. We might rightly say that we are awakening her wrath. By. cost and storage capability. Other characteristics of the coming climate are, according to the IPCC’s official opinion in its TAR, Nearly all land areas very likely to warm more than the global average, with. over many areas. On the motivation for solar energy 5 Figure 1.1. Variations in the Earth’s surface temperature: years 1000 to 2100. From year 1000 to year 1860 variations in average surface temperature