Photovoltaic and Photoelectrochemical Solar Energy Conversion

431 Pages·1981·14.7 MB·English

by  Peter T. Landsberg (auth.), F. Cardon, W. P. Gomes, W. Dekeyser (eds.)

Photovoltaic and
Photoelectrochemical
Solar Energy Conversion
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Volume 69 - Photovoltaic and Photoelectrochemical Solar Energy Conversion
edited by F. Cardon, W. P. Gomes, and W. Dekeyser
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Photovoltaic and
Photoelectrochemical
Solar Energy Conversion
Edited by
F. Cardon
w.
P. Gomes
and
w.
Dekeyser
Laboratory /or Crystallography and the Study 0/ Solids
and
Laboratory /or Physical Chemistry
State University 0/ Gent
Gent, Belgium
PLENUM PRESS • NEW YORK AND LONDON
Published in co operation with NATO Scientific Affairs Division
Library of Congress Cataloging in Publication Data
NATO Advanced Study Institute on Photovoltaic and Photoelectrochemical Solar
Energy Conversion (1980: Ghent, Belgium)
Photovoltaic and photoelectrochemical solar energy conversion.
(NATO advanced study institutes series. Series B, Physics; v. 69)
"Proceedings of a NATO Advanced Study Institute on Photovoltaic and
Photoelectrochemical Solar Energy Conversion held August 25 - September 5, 1980,
at Gent, Belgium."-T. p. verso.
"Published in cooperation with NATO Scientific Affairs Division."
Includes bibliographies and indexes.
1. Solar cells-Congresses. 2. Photovoltaic power generation-Congresses. I.
Cardon, Felix. II. Gomes, Walter. III. Dekeyser, W. (Willy) IV. North Atlantic Treaty
Organization. Division of Scientific Affairs. V. Title. VI. Series.
TK2960.N38 1980 621.31 '244 81-10666
AACR2
ISBN 978-1-4615-9235-8 ISBN 978-1-4615-9233-4 (eBook)
DOl 10.1007/978-1-4615-9233-4
Proceedings of a NATO Advanced Study Institute on Photovoltaic and Photoelectro
chemical Solar Energy Conversion held August 25-September 5, 1980, at Gent, Belgium
© 1981 Plenum Press, New York
Softcover reprint of the hardcover 1 st edition 1981
A Division of Plenum Publishing Corporation
233 Spring Street, New York, N.Y. 10013
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted,
in any form or by any means, electronic, mechanical, photocopying, microfilming,
recording, or otherwise, without written permission from the publisher
PREFACE
In recent years there has been an increasing interest in
syscems which enable the conversion of solar energy into electri
calor chemical energy. Many types of systems have been proposed
and studied experimenta11y, the fundamentals of which extend from
solid state physics to photo- and electrochemistry. For most
of the systems considered excitation of an electron by absorption
of a photon is fo1lowed by charge separation at an interface. It
follows that the different fields involved (photovo1taics, photo
electrochemistry, photogalvanics, etc.) have several essential
aspects in common.
It was the main purpose with the NATO Advanced Study Insti
tute held at Gent, Belgium, from August 25 to September 5, 1980,
to bring together research workers specializing in one of these
fields in order to enab1e them not only to extend their knowledge
into their own field but also to promote the interdisciplinary
exchange of ideas. The scope of the A.S.I. has been 1imited to
systems which have not or have hardly reached the stage of prac
tica1 development. As a consequence, no lectures on economica1
aspects of solar energy conversion have been included.
The topics covered in this volume are the fundamentals of
recombination in solar ce1ls (P. Landsberg), theoretical and
experimental aspects of heterojunctions and semiconductor/metal
Schottky barriers (J.J. Loferski, W.H. Bloss and W.G. Townsend),
photoelectrochemica1 ce11s (H. Gerischer and A.J. Nozik), photo-
v
vi PREFACE
ga1vanic ce11s (W.J. Albery) and fina11y, surfactant assemb1ies
(M. Grätzel).
The editors are gratefu1 to the 1ecturers of this Institute
for providing extended 1ecture notes. In most cases this invo1-
ved a considerab1e writing task in order to cover the subject in
a comprehensive way.
The support of the NATO Science Committee is gratefu11y
acknow1edged. Our gratitude also goes to the authors and editors
of books and periodica1s who granted permission to reproduce
figures, diagrams, or other material.
Fina11y we also wish to thank Plenum Press for providing the
necessary support for the pub1ication of these Proceedings.
F. CARDON
W.P. GOMES
W. DEKEYSER
Gent, December 1980
CONTENTS
Recombination in Solar Cells Theoretical Aspects
Peter T. Landsberg
1. Introduction
2. Conventions Usually Made for p-n Junctions and
Solar Cells 2
3. Three Laws of Photovoltaics 2
4. Maximum Power, Recombination and the Ideality Factor 11
5. Junction Currents as Recombination Currents 14
6. Steady-State Recombination Rates at a Given Plane X 17
7. Junction Model and Space-Dependences 21
8. Transition Region Recombination Current Density 27
9. The Bulk-Regions Recombination Current Density 33
10. Summery of p-n Junction Current Densities from
Sections 8 and 9 37
11. Configuration and Electrostatics of the Schottky
Barrier Solar Cell 39
12. The Place of Recombination Effects in (p-type)
Schottky Barrier Solar Cells 44
13. Recombination Currents and Voltage Drops in (p-type)
Schottky Barrier Solar Cells 48
14. Conclusion 54
A Few Hore General Topics
(I) Thermodynamic Efficiency 55
(11) Simple Theory to See that an Optimum Energy Gap Exists 57
(111) Is Dollars per Peak Watt a Good Unit ? 57
(IV) Energy Unit for Global Use 58
(V) When will Solar Conversion be Economically Viable ? 61
Appendix 62
References 63
vii
viii CONTENTS
Schottky Barrier Solar Cells
W.G. Townsend 67
I. Introduction 67
2. The Schottky Barrier Cell Principle 68
2.J. Principle of SBSC Operation 70
2.2. Current Transport Mechanism in Schottky Barriers 72
2.3. Effect of the MIS Potential Distribution upon the
Diode Quality Factor n 78
2.4. The MIS SBSC under Illumination 79
2.5. The Minority Carrier MIS SB Cell 82
3. Solar Cell Parameters and Design Considerations 87
3,1. Metal-Semiconductor Barrier Height 87
3.2, Diode Quality Factor n 88
3.3. Interfacial Oxide Thickness 89
3.4. Transmission Properties of the Metal 91
3.5. Spectral Response 92
3.6. Substrate Resistivity 94
3.7. Substrate Thickness 94
3.8. Series Resistance 95
4. Results and Discussion of Typical Silicon MIS Cells 97
4.1. Open Circuit Voltage 97
4.2. Short Circuit Current Density 98
4.3. Fill Factor 101
4.4. Efficiency 102
4.5. The Min MIS Cell 103
4.6. The MIS Inversion Layer Cell 106
4.7. Stability of MIS Solar Cells 107
4.8. The Future for MIS Cells - Cheaper Substrates? 112
Acknowledgement 113
References 113
CdS-Cu S Thin Film Solar Ce11s 117
x
W.H. Bloss and H.-W. Schock
]. Introduction 117
2. CdS Thin Film Technology 119
2.1. Vacuum Vapor Deposition of CdS Films 119
2.2. Sputtering 122
2.3. Spray Deposition 122
2.4. Sintering 123
3. Cu S Thin Film Technology 124
3.t. Dipping Process (Wet Process) 124
3.2. Evaporation of CuCI 125
3.3. Evaporation of Cu S 125
3.4. Sputtering of CuxS 126
x
4. Properties of the GdS Layer 127
4.1. Crystallography and Grain Size of CdS Films 127
4.2. Optical Properties of the GdS Films 129
4.3. Luminescence 130
4.4. Electrical Properties of CdS Films 131
5. Properties of Cu S Films 131
5.1. Stoichiomet~y 131
5.2. Coulometric Titration 132
5.3. Optical Properties 133
5.4. Electrical Properties 135
6. Properties of the Heterojunction 135
6.1. Structure of the Heterojunction 135
6.2. Surface Effects of the Cu S Film 139
6.3. Capacitance Measurements x 140
6.4. Diffusion Length in Cu Sand CdS 143
x
6.5. Spectral Response 146
6.6. Band Diagram 147
7. Technology of CdS-Cu S Photovoltaic Generators 147
7.1. Cell Structuresx 148
7.2. Fabrication Process of CdS-Cu S Cells 149
8. Performance Characteristics of Sol~r Gells and
Generators 152
References 154
Conversion of Solar Energy Using Tandem Photovoltaic Cells
Made from Multi-Element Semiconductors 157
Joseph J. Loferski
I. Introduction 157
11. Increasing Efficiency by Recourse to Tandem
PV Gell Systems 158
111. Design of an Optimized Solar Cell Structure for
Tandem Ce11 Systems 166
IV. Selection of Semiconductors for Tandem Solar Cell
Systems 170
V. Optimized Design of Direct Gap Photovo1taic Cells 175
VI. Monolothic and Split Spectrum Tandem Gell Systems 182
VII. Synthesis and Properties of Ternary Alloy Ghalcopyrite
Semiconductors 185
VIII. Thin Films of CuInSe2 and Solar Cells Made from Them 192
IX. Summary and Gonclusions 196
References 197
x CONTENTS
The Principles of Photoelectrochemical Energy Conversion 199
Heinz Gerischer
I. Sunlight Conversion into Chemical Energy 199
Photoredox Reactions 201
Redox Energies and the Scales of Redox Potentials 203
Photosynthesis as an Example 206
Artificial Systems for Energy Conversion 209
References to Lecture for Further Reading 213
11. Fundamentals of Semiconductor Electrochemistry 214
The Space Charge Layer 214
Kinetics of Electron Transfer Reactions 220
References 230
111. The Semiconductor Electrolyte Contact under Illumi-
nation and Photodecomposition Reactions 231
Distribution of Electrons and Holes under Illumi
nation 231
Photodecomposition of Semiconductors 239
References 245
IV, Photoelectrochemical Cells and their Problems 246
Regenerative Cells 246
Storage Cells 252
Energy Conversion Efficiency 258
References 261
Photoelectrochemical Devices for Solar Energy Conversion 263
A.J. Nozik
Introduction 263
General Discussion of Photoelectrochemical Devices 265
Semiconductor Electrolyte Junctions - Conventional
Picture 265
Photo-Induced Charge Transfer Reactions 268
Semiconductor Electrode Stability 268
Electrochemical Photovoltaic Cells 271
Photoelectrosynthetic Cells 273
Photoelectrolysis Cells 273
Photocatalytic Cells 278
General Considerations 280
Effects and lmportance of Surface States 280
Unpinned Band Edges 283
Hot Carriers 289
Surface Modification 297
Electrochemical Photovoltaic Cells 299
Reduced Surface and Grain Boundary Recombination 299
Non-aqueous Electrolytes 301