Solar energy conversion THE SOLAR CELL

Solar Energy Conversion THE SOLAR CELL (SECOND EDITION) This Page Intentionally Left Blank Solar Energy Conversion HE SOLArl CELL (SECOND EDITION) Richard C Neville College of Engineering & Technology Northern Arizona University Flagstaff, AZ, U.S.A 1995 ELSEVIER Amsterdam - Lausanne - New York - Oxford - Shannon - Tokyo ELSEVIER SCIENCE B.V Sara Burgerhartstraat 25 P.O Box 211,1000 AE Amsterdam, The Netherlands ISBN: o 444 89818 © 1995 Elsevier Science B.V 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 written permission of the pubHsher, Elsevier Science B.V., Copyright & Permissions Department, P.O Box 521, 1000 AM Amsterdam, The Netherlands Special regulations for readers in the U.S.A - This publication has been registered with the Copyright Clearance Center Inc (CCC), Salem, Massachusetts Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the U.S.A All other copyright questions, including photocopying outside of the U.S.A., should be referred to the copyright owner, Elsevier Science B.V., unless otherwise specified No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein This book is printed on acid-free paper Printed in The Netherlands PREFACE That the human race faced an energy crisis became painfully obvious during the 1970s Since that time the blatant obviousness of the problem has waned, but the underiying technical and political problems have not disappeared Humanity continues to increase in number (the world population is, at present, in excess of five billion) and, despite major efforts towards improving the efficiency of energy consumption, the overall per capita use of energy continues to increase Projections conceming the human population and its energy requirements during the next century estimate populations in excess of seven billion and energy consumption per person in excess of 40,000 kilowatt hours per year (approximately twice the current rate) This increasing energy use must be viewed in the light of the finite availability of conventional energy sources When done so the energy crisis can be seen to be all too real for any long term comfort A frequently mentioned solution to the problem of increasing requirements for energy and dwindling energy sources is to tap the energy in sunlight The solar energy falling on the earth's surface each year is over 20,000 times the amount presently required by the human race, making for a seemingly inexhaustible supply For effective utilization of any energy source civilization requires an easily storable, easily transportable form of energy (after all, it is dark at night) This implies that the incoming solar energy should be transformed into electrical energy In tum this means that we need to utilize photovoltaic (solar cell) conversion of the energy in sunlight Photovoltaic effects were initially observed more than a century and a half ago In 1839 E Becquerel observed a photovoltage (a voltage depending on the character and intensity of the illuminating light) when sunlight was allowed to shine on one of two electrodes in an electrolytic solution The first scientific paper on photovoltage using solids was published in 1877 and concemed the semiconductor, selenium In 1954 research groups at RCA and Bell Telephone Laboratories demonstrated the practical conversion of solar radiation into electrical energy by a silicon pn junction solar cell, and shortly thereafter Chapin, Fuller and Pearson reported on a six percent efficient solar cell (Journal of Applied Physics, Vol 25, 1954, p 676) VI The modem solar cell is an electronic device, fabricated from semiconducting materials It converts a fraction of the energy contained in sunlight directly to electrical energy at a voltage and current level determined by the properties of the semiconductor, the solar cell design and construction techniques, and the incident light To gain an understanding of how solar cells work and to be in a position to design and construct energy conversion systems using solar cells requires a background covering such diverse areas as: the nature of solar radiation; semiconductor physics; quantum mechanics; the techniques of energy storage; optics; heat flow in solids; the nature of elemental, compound, single crystal, polycrystalline and amorphous semiconductors; the technology of semiconductor device fabrication; and the economics of energy flow It is not physically possible to cover, in depth, all of these areas in a single work In writing this volume, I have endeavored to create a survey text; a book that explores a number of critical background areas and then outlines the theory of operation of solar cells while considering their design and fabrication Solar cell performance is treated both in the general sense and for some specific examples These examples select semiconductor, junction type, optical orientation and fabrication technology and then highlight the problems encountered in solar cell design and illustrate, both in general and specific fashion, areas of promising future research and development References are provided to facilitate deeper investigations of the various topics of interest—from quantum mechanics to economics This is the second edition of this work on solar cells Historically, this book originated from a series of lectures on energy and solar cells given to engineering students at the University of Califomia at Santa Barbara These lectures culminated in the first edition of this work, in 1978 Since that time there has been much change in the fields of energy generation and consumption, solar energy and solar cells Additional lectures at UCSB and at Northem Arizona University, coupled with considerable research into aspects of photovoltaic and solar energy have modified the original work This, the second edition, is thus the result of more than 20 years of interest in solar energy and solar cells coupled with steady changes in these fields and our understanding of thesefields.Since it is virtually impossible to separate design and operating theory, engineering, economics and politics in considering the use of solar cells in addressing the energy problem facing humanity, the systems aspect is present throughout this volume vu The first chapter is a broad (and brief) survey of the elements which make up the "energy crisis" It is devoted to illustrating the limited nature of presently utilized energy sources and to a discussion of the various "non-conventional" energy sources proposed for the future: biological, wind, wave and solar It has, as its major purpose, three points to make: (1) that our conventional energy sources will be exhausted at some point in the not-too-distant future, (2) that solar energy is capable of supplying the energy requirements of humanity for the foreseeable future, and (3) that photovoltaic energy conversion is a major candidate for supplying mankind with its required energy; perhaps the prime candidate The second chapter considers the nature of sunlight, discusses the solar spectrum, the effects of latitude, the earth's rotation and axial tilt, and atmosphere and weather A brief discussion of optics is included as a background for those individuals interested in this aspect of energy conversion The third chapter surveys the nature of semiconductors Solar cells are theoretically constructed of various semiconductors and their performance is shown to depend upon the properties of these materials These properties are best understood within the framework of quantum mechanics and solid state physics Chapter DI discusses crystals, quantum mechanics and semiconductor physics with a view towards outlining the principal properties of semiconductors and the manner in which these properties vary with device processing technology, temperature of operation, and the characteristics of the illumination Because the physics of single crystal semiconductors is best understood (as contrasted with polycrystalline or amorphous structured semiconductors), the emphasis in this chapter is on solar cells constructed from single crystal semiconductors It is in this chapter that certain specific example semiconductor materials are first introduced Chapter IV treats the interaction of light semiconductors including absorption, reflection and transmission The generation of hole-electron pairs is treated both in the abstract and in detail using the example semiconducting materials introduced in Chapter HI The maximimi potential output power density and the optimum output current density for photovoltaic cells are displayed for solar cells fabricated from six sample single crystal semiconductors The fifth chapter is devoted to a general discussion of solar cell performance as a function of the junction employed The ciurent versus Vlll voltage characteristics of pn, heterojunctions, mos junctions and Schottky barrier solar cells are considered and a general expression for the output power density as delivered to an optimum external load is obtained From this expression, the maximum expectable output power density for solar cells, as a function of the energy gap of the semiconductor employed, is derived This is displayed as a function of the saturation current of the solar cell In Chapter VI the six example semiconductors are employed to provide specific values of estimated solar cell performance, based on various technologies of junction fabrication and upon the optical orientation of the solar cells The solar cell performance levels computed in this chapter, and in later chapters, are not meant as absolute predictions of maximum performance Rather, they are intended to provide indications of "typical" solar cell performance as structured by technology and materials limitations It is intended that they will suggest areas in need of research and development The seventh chapter considers the effects upon solar cell operation of changes in junction temperature and the use of concentrated sunlight The power density in natural sunlight is very low (approximately one kw/m^ at sea level) and hence any sizeable energy requirement implies a large area of solar cells By utilizing relatively inexpensive mirrors or lenses to concentrate sunlight upon expensive solar cells a significant reduction in cost can be effected This chapter examines the limits imposed on optical concentration levels by the solar cells and shows that improved solar cell performance is possible using the six example single crystal semiconductors Chapter Vin carries the materials of the preceding chapter a step further In addition to considering the electrical energy output for solar cells operating under concentrated sunlight, the thermal energy available from such a situation is considered Thus a complete systems approach to producing energy from photovoltaic cells is developed Later in this chapter various approaches to further improving overall energy output (both electrical and thermal) from photovoltaic systems are considered Most of these systems involve modifying the spectral characteristics of the light used to illuminate the solar cells The altered light is a better match for the semiconductors used in fabricating the solar cells and so overall efficiency is improved In the ninth chapter the solar cells are constructed using polycrystalline and amorphous semiconductors The operation of these IX devices depends strongly on the crystal interfaces and the properties of unsaturated chemical bonds As a result, the theory of operation of polycrystalline and amorphous material solar cells is not well understood Thus, this chapter is less theoretical and more empirical in nature than the previous chapters Numerous examples of polycrystalline and amorphous solar cell operations and materials are provided The final chapter, Chapter X, is devoted to a brief survey of such topics as economics, energy storage, and overall systems effects Potential problems and proposed solutions are noted and briefly discussed It is intended that the reader treat this chapter as a question mark whose main purpose is to provoke inquiry The energy "problem" has not gone away, and will not go away Without strenuous and continuing efforts on the part of humanity we will see a continuing series of "crises" Fortunately, the field of photovoltaic energy conversion is growing rapidly, both in scope and complexity Of necessity I have been forced to treat lightly many areas which deserve considerably more intense study To those readers whose specialty in research or development lies in these areas, my apologies I can but plead lack of space and time In closing I would like to thank my fellow faculty members and my students for many hours of stimulating discussion and my wife, Laura Lou for her encouragement, patience, support and proof reading In the final analysis, any errors are, of course, my responsibility Richard C Neville Flagstaff, Arizona 86011 U.S.A 29 March 1994 412 AlSb A a APPENDIX aa-Si a-SiC a-SiGe a-Si:H a-SiC:H a-SiGe:H a(hu) a( Y) Aluminum antimonide Angstromis The radius of light sensitive area of a standard configuration solar cell Denotes the amorphous form of a semiconductor Amorphous silicon Amorphous silicon carbide Amorphous silicon-germanium Amorphous silicon containing hydrogen Amorphous silicon carbide containing hydrogen Amorphous silicon-germanium containing hydrogen Absorption coefficient Factor accounting for atmospheric losses of solar power B P Percentage of input light power lost to reflection C Cadmium selenide CdSe Cadmium sulfide CdS Cadmium sulfide/copper sulfide CdS/Cu2S Cadmium telluride CdTe See CuInSe2 CIS Carbon dioxide CO2 Copper Cu Copper gallium diselenide CuGaSe2 CuGao25lno.75 ^ ^ Copper gallium indium diselenide CU2S Copper sulfide CuInSe2 Copper indium selenide c Speed of light cDenotes the crystal form of a semiconductor D D D Ds D„ Deuterium Generalized diffusion constant Generalized diffusion constant for minority carriers in the substrate of a solar cell Diffusion constant for electrons APPENDIX D^p Dp Dpj, d A AE^ AE^ A Eg E E E^ E^ Ej) Ep Eg Ep Epi, Et E^ ^ ^ € F F f 413 Diffusion constant for electrons in a p-type semiconductor Diffusion constant for holes Diffusion constant for holes in an n-type semiconductor "Front Layer" thickness in a solar cell Substrate contact thickness for a solar cell The "notch" in the conduction band lower edge in heterojunctions The discontinuity in the valence band upper edge in heterojunctions The difference in energy gap widths for the two semiconductors in a heterojunction Energy Acceptor electron energy level Conduction band lower edge Donor electron energy level Fermi energy level Energy gap of a semiconductor Energy of a phonon Energy of a photon Energy level of a trap Valence band upper edge Electric field Electric field in a substrate Permittivity (1)B^ C1)BO Focal length of a lens Fraction of light reflected from a lens, mirror or semiconductor siuface The ratio of the optically absorbing siirface area to the total surface of a solar cell Schottky barrier energy adjusted for image force lowering Barrier energy for Schottky or mos junctions G Gaj.^Al^s GaAs Gallium aluminum arsenide Gallium arsenide O 414 APPENDIX GaAs^Sbi.^ GaP Ge GL Gallium arsenide antimonide Gallium phosphide Gemianium Light driven charge carrier generation H H He Hf HgTe H2O h 3K "h X Hydrogen Helium Haffmium Mercury telluride Water Planck's constant The hamiltonian Planck's constant divided by 2K Electron affinity for a semiconductor I I II InP 1^ T]^ lis Current Load current for a solar cell Indium phosphide Solar power density (insolation) Camot cycle engine efficiency Solar cell maximum efficiency J J JD JQ JGS Jn Jp Jph Js Jsc JsH Jss JT Current density Solar cell normal current density Generation-recombination current density Saturation current density for generation-recombination Electron current density Hole current density Photocurrent density Saturation current density for a pn junction and the generalized saturation current density for solar cells Short circuit ciurent density for a solar cell Saturation current desnity for a heterojunction Saturation current density for Schottky or mos solar cells Tunneling current density APPENDIX K Ki K' k k L L Li L^ L^p Lp Lpjj Lg X X Xg M M M(T) m* m^^ m^ nVe |x I^LM |in |x^ |Lip |Xpn |Xs |isM 415 Tunneling constant Solar cell loss factor Extinction coefficient Boltzmann's constant Generalized charge carrier diffusion length Lithium Electron diffusion length Electron diffusion length in p-type semiconductors Hole diffusion length Hole diffusion length in n-type semiconductors Generalized minority carrier diffusion length in the substrate of a solar cell Wavelength of a photon q/kT in expressions for diode current and resistance Wavelength of a photon when it has an energy equivalent to the energy band gap of a semicondcutor Width of a metal contact ring for a standard configuration solar cell The ratio of the saturation current density at a temperature, T, to that at 300'K Generalized effective mass Effective mass for electrons in the conduction band Free electron mass Effective mass for holes in the valence band Generalized mobility Majority carrier mobility of the "Front Layer" Electron mobility The mobility of electrons in a p-type semiconductor The mobility of holes The mobility of holes in an n-type semiconductor The generalized mobility of minority carriers in the substrate regions of a solar cell The majority carrier mobility in the substrate of a solar cell 416 N N N^ APPENDIX n n' n^ \) The optical concentration level Net acceptor impurity concentration in a p-type semiconductor Conduction band effective density of states Net donor impurity concentration in a n-type semiconductor Impurity concentration in the "Front Layer" of a solar cell Substrate impurity concentration at the junction Surface concentration of traps Generalized impurity concentration in a solar cell substrate Volume concentration of traps Valence band effective density of states Index of refraction Ideality factor in expressions for diode current versus voltage Electron concentration per unit volume Generalized carrier concentration in space charge regions Intrinsic carrier concentration Frequency n The intensity of incident light N^ ND NL Ngj Nst Ns H N^ n n P PCVED Pd PE Plasma enhanced chemical vapor deposition Palladium Electrical power delivered by a second or third stage solar cell power system Pp The radiated photon power density for a black b o d y Pj Solar power delivered by a second or third stage solar cell power system The thermal power delivered by a second or third stage solar cell power system Platinum Pih Pt PaT Pif Pmax p Available thermal power in a second or third stage solar cell p o w e r system Probability of an electron interband transition M a x i m u m delivered solar power Hole concentration per unit volume APPENDIX pc Y T T' 417 T" Tj Denotes that a semicondcutor is in polycrystalline form Angle between the sun and the normal to the earth's surface Schrodinger wave function Average north-south angle, for a given day, between the sun and the zenith Angle between the sun and the detector/collector normal The intrinsic Fermi level Q Q q An amount of energy equal to 2.93 x 10^^ kilowatt-hours Magnitude of the charge on the electron R RL Ri Rj rj) p PT S Si SiC SiF4 SiGe SiH4 Si02 Spn Resistive load for a solar cell The resistive load for a solar cell which yields maximum power transfer The thermal resistance Series resistance of a solar cell Charge density Thermal resistivity a Silicon Silicon carbide Silicon tetrafluoride Silicon-germanium Silane Silicon dioxide, also quartz or sand Surface recombination velocity for holes on an n-type semiconductor Surface recombination velocity for electrons on a p-type semiconductor Conductivity T T T Ti T^ Tritium The absolute temperature Titanium The "cold" reservoir temperature in a heat engine Sj^p 418 Th Tj Tg ATs APPENDIX ©T The "hot" reservoir temperature in a heat engine The temperature of a solar cell junction The temperature of a heat sink The temperature difference between a solar cell junction and its heat sink The light transmitted into a semiconductor The light which passes through a semiconductor Lifetime Lifetime due to Auger recombination Lifetime due to radiative recombination Maximum lifetime Small signal electron lifetime Lifetime of electrons in p-type semiconductors Small signal hole lifetime Lifetime of holes in n-type semiconductors Generalized substrate minority carrier lifetime East-west angle between the sun and the earth surface normal Heat energy flow (in a solar cell) U U Recombination rate T' T" T T^ T^ T^ T^o Tnp Tpo Tpj, Is V V Vi VA Vg Vj) VD' VQC Vp V V Vth Voltage Load voltage in a solar cell system Extemally applied voltage Junction built-in voltage Effective voltage across a diode junction The voltage across a solar cell junction when there is maximum power transfer Open circuit voltage Photovoltage Velocity of a charge carrier T h e voltage at which the forward generation-recombination current equals the forward diffusion current Thermal velocity of a charge carrier APPENDIX W W^ Xi Xg Xg' Xgs Xj x^ Xp Y Y Z Zno 35Cdo 65O ZnSe ZnTe z C 419 Width of the space charge region The collection distance for hole-electron pairs in a semiconductor Generalized space charge region width in the substrate of a solar cell The maximum space charge region in the substrate of a solar cell Substrate space charge region width for an extemally shorted junction Empirical factor for current in a heterojunction Space charge width in the n-type region of a junction Space charge width in the p-type region of a junction The thickness of a vertical configuration solar cell in the direction of photon travel Zinc cadmium oxide Zinc selenide Zinc telluride Factor accounting for surface recombination in a solar cell Energy difference between the conduction band edge and the Fermi level 420 SUBJECT INDEX Absorption 67, 120, 132-137, 139, 142, 145, 214, 219, 344, 349, 352, 354 Absorption Coefficient see Absorption Absorptivity see Absorption Acceptors 86-91, 160 Acid Rain 9, 11 Aluminum Antimonide (AlSb) -junctions 206, 208-210, 222, 251, 252, 261, 263, 268 - properties 85, 90, 93, 103, 122, 130, 138-141, 198, 213, 214 - solar cells 139, 143, 144, 146150, 218, 219, 227-229, 231-250, 270, 277, 284, 286, 291, 295-297, 302, 372 AMO (air mass zero) 40, 42, 43, 123, 124, 127, 129, 138-140, 143, 146-149, 177, 180, 182, 184, 186, 188, 190, 191, 223, 231-235, 239241, 245-247, 257, 270, 273-285, 287-294, 298, 299, 303, 305, 306, 309, 311, 313 AMI (air mass one) 40, 42, 43, 123, 124, 127, 129, 138, 139, 141, 144, 146-148, 150, 177, 181, 183, 185, 187-189, 191, 201, 223, 231, 232, 236-238, 242-244, 248-250, 257, 264, 270, 295-297, 303, 307, 310, 312, 314, 368 Amorphous 72, 92, 131, 156, 198, 329, 346, 348-358, 364, 371, 373, 388 Antireflection 67, 121-123, 145-150, 204, 341, 354 Antisite 342 Atmosphere see Weather Auger Recombination see Recombination B Bandpass 317-320, 326 Base Lxjad Power see Power Plant Battery 382-384, 386 Biological Sources 2, 8, 19, 20, 22, 26, 7>A-see also Wood, Plants, Energy -sources Built-in Voltage 158, 163, 174, 205, 251 Cadmium Selenide (CdSe) -junctions 206, 208-210, 222, 251, 261, 263, 268 - properties 85, 90, 93-95, 103, 122, 127, 130, 138-141, 198, 213, 214 - solar cells 139, 143, 144, 146-150, 218, 219, 227-250, 270, 278, 285, 286, 292, 295-297, 302, 342, 347, 372 Cadmium Sulfide (CdS) - properties 127 - solar cells 342, 345, 347 Cadmium Sulfide/Copper Sulfide see Copper Sulfide/Cadmiimi Sulfide Cadmium Teluride (CdTe) -junctions 206, 208-210, 222, 251, 252, 261, 263, 268 - properties 85, 90, 94, 95, 103, 122, 127, 130, 138-141, 198, 213, 214, 389 421 INDEX - solar cells 139, 142-144, 146-150, 218, 219, 227-229, 231-250, 270, 276, 283, 290, 293-299, 305-307, 309-314, 319-321, 325, 327, 331, 332, 342, 347, 372 Camot 6, 24, 25, 32, 304, 310, 318 CIS see Copper Indium Selenide Coal 2, 8, 9see also Fossil Fuels Collector 46-52, 55, 56, 63 Collection Distance 171, 172, 211 Computer 386, 387 Concentration 36, 57, 68, 69, 257, 258, 374, 375-380, 389-^ee also Lenses, Mirrors and Optical Concentration Conduction Band see Energy Band Conductivity 71, 72, 91, 132, 352 Conductor 71 Configuration see Optical Orientation Converter 315-318, 320, 322-325 Cooling see Heat Sink Cooling Systems see Heat Sink Copper Indium Gallium Selenide (Cu(In,Ga)Se2) see Copper Indiimi Selenide Copper Indium Selenide (CuInSe2) 342, 344 Copper Indium Gallium Sulfide, Telluride, Sulfide (Cu(In,Ga)(S, Se, Te)2 see CuInSe2 Copper Sulfide (CusS) 342-344 Copper Sulfide/Cadmium Selenide (Cu2S/CdS) 157, 342-344-jee also Solar Cell Cost 27, 42, 57, 205, 253, 257, 305307, 340, 344, 364, 366-370, 372381 Crystal see Crystalline Crystalline 72, 73, 76, 77, 79, 81, 82, 90, 92, 93, 97, 131, 155, 198, 364, 371, 373, 388 Current see Current Density Current Density 71, 91, 96, 160-162see also Photocurrent Density Czochralski 371, 388 D Dams 2, S-see also Energy-sources "Dead Layer" 142-150, 201, 205, 214-216, 218, 219, 279 Defect Density 342 Dember Effect 156 Demographics 1, 4, 10, 12-16, 26, 29, 34, 35 Dendritic Web 388 Density of States 178 Depletion Layer Width see Space Charge Region Depletion Region see Space Charge Region Detector see Collector Dichroic Mirror 333, 363, 390 Diffusion 91, 94, 166, 209, 334, 340 Diffusion Constant \60-see also Electron, Hole Diffusion Length 160, llS-see also Electron, Hole Donor 86-91, 160 Ecology 1, 25, 32, 33, 42, 389 Economics see Cost Effective Mass 93, 94, Xdd-see also Electron, Hole Efficiency see Energy Electric Field 92, 108, 109, 111, 112, 114, 132, 155-157, 159, 162, 216, 217, 226, 258, 352 Electrolysis 386, 387 Electron Affinity 164, 174 Electron-Hole Pairs 97, 103, 114, 120, 125, 126, 128, 132, 139, 142, 155, 158-161, 164, 170, 177, 197, 201, 202, 207, 211, 214, 215, 217, 269, 271, 317 Electron Lifetime see Electron Electron Mobility see Electron Electron 82-87, 89, 93-95, 98, 101, 103, 105, 124, 133, 134, 159, 161, 422 211, 214 Energy - capital see Energy-sources - efficiency 5, 20, 25, 31-33, 35, 36, 130 - heat see Thermal - income see Energy-sources - reserves 9-14 - sources 1, 2, 7-14, 19, 26, 29, 34, 35, 253, 365 - storage 18, 20, 29-31, 364, 381, 386, 387, 390 - thermal 263, 264, 304-312, 336, 380-382 - transport 382 - uses (and consumption) 1, 3-7, 9, 10, 12-15, 26, 29, 34, 35 Energy Band 76, 82-84, 86, 87, 98, 110, 124, 125, 133-135, 155, 159, 169, 216 Energy Gap 83, 85, 87, 103, 125, 127, 130-134, 136, 145, 146, 155, 161, 162, 165, 169, 177, 179-191, 197, 198, 206, 207, 317, 349-351 Environment see Ecology Epitaxy 90, 91, 94, 212, 334, 340, 388 Extinction Coefficient see Absorption Food 1, 3, 20 Fossil Fuel 2, 7-10, 14, 65, 366see also Energy-sources Fresnel Lens see Lens "Front Layer" 164, 165, 199, 201, 202, 206, 212-214, 216, 218, 219, 221, 226-229, 251, 252, 259 Fuel Cell 382, 384 G Gallium Arsenide (GaAs) -junction 166,206,208-210, 222, 251, 252, 261, 263, 268 - properties 83, 85, 90, 92, 94, INDEX 95, 102, 103, 122, 127, 129, 130, 137-142, 198, 213, 214, 389 - solar cells 36, 139, 144, 146-150, 218, 219, 227-229, 231-250, 270, 275, 282, 289, 293-299, 305-307, 309-314, 319-321, 324, 326, 330, 332, 342, 347, 372 Gallium Arsenide Antimonide (GaAs^Sb.J 347 Gallium Arsenide Phosphide (GaAs,P,J 129 Gallium Arsenide/Aluminium Gallium Arsenide (GaAs/Al,Ga,.xAs) 157, 166, \99-see also Solar Cells GalUum Phosphide (GaP) 85, 90, 94, 103, 122, 129-131 Gas 2, 8, 9-see also Fossile Fuels Generation-Recombination see Recombination Geothermal 2, 8, \l-\4-see also Energy-sources Germanium (Ge) -junction 166 - properties 83, 85, 90, 95, 103, 122, 130, 131 Glass 66-68, 341, 357 Glow Discharge 352 Grain Boundary 339-342 Greenhouse Effect 7, 9, 11, 15, 20, 21 H Heat Energy see Energy, Heat, Solar Thermal Energy Heat Flow 264, 265, 327 Heat Sink 199, 201, 204, 265, 302, 303 Heterojunction see Junction Hole-Electron Pairs see Electron-Hole Pairs Hole 84-87, 89, 93, 95, 99, 101, 103, 105, 133, 134, 159-161, 211, 214 Hole Lifetime see Lifetime, Hole Hole Mobility see Hole Hydrogen (H) 385, 386 Hydrogen Selenide (HjSe) 345 INDEX Hydropower 2, 8, 14, 15, 25, 26, 365, 366-5'^^ also Dams, Energy -sources Tides I Index of Refraction 67, 68, 120, 130, 132 Indium Phosphide (InP) -junction 206, 208-210, 213, 222, 251, 252, 261, 263, 268 - properties 85, 90, 103, 122, 130, 138-141, 198, 214 -solar cells 139, 143, 144, 146-150, 218, 219, 227-229, 231-250, 270, 274, 281, 286, 288, 295-297, 302, 372 Indium Tin Oxide (TTO) see Tin Oxide Insolation see Solar Insolation Insulator 71 Intermediate Load Power see Power Plants Interstitial 342 Intrinsic Carrier Concentration 84, 87, 162, 260, 271 Inverted Configuration see Optical Orientation Inverted Solar Cell see Optical Orientation Ion Implantation 91, 92, 94, 209, 212, 340 Junction 108-115, 170-175 178, 197 - heterojunction 143, 156-158, 163166, 199-203, 205, 206, 210, 214, 219-222, 227-229, 231-253, 259, 261, 263, 270, 273-299, 305-314, 318, 319, 323-326, 347, 348, 389 -mos 168, 169, 201, 203, 206, 208, 221, 260, 389 - p n junction 109-115, 156-159, 161-163, 178, 199-203, 205, 206, 209, 210, 214, 219, 220, 222, 228250, 253, 259-261, 263, 270, 273- 423 292, 295-299, 307, 389 - Schottky 156-158, 167-169, 201, 203, 206, 208-210, 219-222, 225, 227-253, 259, 260, 262, 264 269, 270, 273-292, 295-297, 307, 308, 389 - tunneling 357, 358 Lattice 73-76, 90 Lattitude 49-54, 56, 368 Lead-Acid see Battery Lens 32, 33, 36, 57-60, 66, 67-69, 257, 301, 302, 373, 379, 390 Lifestyle 1, 2, 5, 6, 7, 16 Lifetime 97, 99, 101-103, 107, 139, 142, 155, 161, 165, 178, 188, 197, 201, 212, 213, 222, 355 Lithium-Sulfide see Battery Loss Factor 175, 176, 180-191, 197, 229, 230, 267, 294-299, 326, 327 Luminescent 335, 336 Luminescent Concentrator see Luminescent M Mercury Telluride (HgTe) 342 Methane 22 Mirrors 32, 36, 57, 58, 60-69, 257, 301, 302, 373, 379, 390 Mobility 92, 93, 197, lU-see also Electron, Hole Molecular Beam Epitaxy see Epitaxy Momenttmi 133-136 MOS or MOS Solar Cell see Junction, Solar Cell N Nattaral Gas see Fossil Fuels Nickel-Zinc see Battery Nuclear - fission 2, 8, 11, 12, 365, SSS-see also Energy-sources - fusion 2, 8, 16, Usee also Energy-sources 424 INDEX Ocean 22, 24, 25 Ocean Thermal Energy Conversion 25 Oil 2, 1-9-see also Fossil Fuels Oil Shale Open Circuit Voltage 170, 173-175 Optical Concentration 258, 201, 267, 269, 271, 272-285, 287-299, 302307, 375-380 Optical Orientation 199, 363 - inverted configuration 199, 204, 205, 207, 211, 215,218, 223, 225231, 238, 241, 245-251, 253, 267, 269, 270, 287-294, 297, 299, 305314, 323-327, 389 - standard configuration 199, 200202, 205, 207, 211, 214, 216, 219, 223-227, 229-238, 250, 253, 265, 270, 273-279, 293-297, 298, 305314, 389 -vertical configuration 199, 200, 202-205, 207, 214, 215, 218, 223232, 235, 239-244, 250, 253, 265, 267, 270, 280-285, 296, 298, 305314, 389 Oxide see Quartz Peak Load Power see Power Plants Petroleum see Oil Phonon 93, 102, 133, 135, 136 Photon 43, 44, 67, 108, 114, 115, 119-121, 124-128, 132, 133-135, 136, 139, 142, 145, 155, 158, 164, 177, 186, 188, 258, 301, 319, 353, 355, 357, 358 Photocurrent 120, 121, 128, 129, 146-150, 155, 165, 170-172, 175177, 186, 188-191, 202, 215, 217220, 223, 225, 232, 235, 238, 247, 269, 270, 321, 322, 352 Photocurrent Density see Photocurrent Photosynthesis 19, 20 Photovoltage 120, 155, 159 170, 175, 176, 187, 189-191, 205, 206, 229, 232, 233, 236, 239, 241, 242, 245, 248, 251, 267, 286, 293, 295299, 326, 327, 346 Photovoltaic Cell see Solar Cell Planck's Constant 78 Plants 2, 19, 20, 2\-see also Energy -sources Plasma Enhanced Chemical Vapor Depostion 388 Plastic 66-68 PN Junction see Junction Politics 1, 6-8 Polyciystalline 72, 73, 92, 131, 155, 157, 198, 339-348, 364, 371-373, 388 Population see Demographics Power Plants 365, 366, 369, 381, 386, 387 Power Ratio 368, 369 Production 371 Quartz 66, 68, 122, 168, 169 Quantum Mechanics 76, 78, 84, 127, 133, 134 R Recombination 97-102, 104-107, 126, 142,161, 162, 165,166, 171,172, 177, 178,188,215, 218,219, 258,269, 271, 301, 345 Recombination-Generation see Recombination Reflection 119-123, 308 ReHability 370, 381 Resistance 165, 171, 175, 197, 212, 216~jee also Solar Cell Resistance Resources see Ecology Ribbon Silicon 342, 371, 388 Richardson Constant 221 Saturation Current see Saturation Current Density INDEX Saturation Current Density 160-162, 165, 172-175, 177-188, 190, 191, 197, 201, 212, 220-223, 247, 259, 261-263, 268, 279, 319 Schrodinger 78-81 Schottky Barrier see Junction Schottky Junction see Junction Semiconductor 71, 72, 76, 84, 90, 101, \\9'-see also individual semiconductor listings Series Resistance see Resistance or Solar Cell Resistance Short Circuit Current see Short Circuit Current Density Short Circuit Current Density 170, 172, 173 Silane (SiH4) 349, 350 Silicon (Si) - amorphous 353-358, 374-379 -junction 206, 208-210, 222, 251, 252, 261, 263, 268 - properties 77, 83, 85, 90, 94, 95, 103, 122, 130, 134, 137-141, 198, 213, 214, 349-352, 389 - solar cells 36, 139, 142-144, 146150, 215, 219, 227-229, 231-250, 270, 273, 280, 287, 293-299, 305307, 309-314, 319-321, 323, 326, 329, 332, 334, 343, 346, 372, 374 Sihcon Carbide (SiC) 342, 349 - amorphous 353-356, 358 Silicon Dioxide (SiOj) 122, 342see also Quartz Sihcon Germanium (SiGe) 349, 356 Silicon Tetrafluoride (SiF4) 356 Silver Indium Sulfide (AgInS2) 342 Single Crystal see Crystalline Solar - solar constant 39 - solar insolation 49-51, 53, 54, 56, see also -solar cell energy -solar electric 19, see also -solar cell energy and solar cell -solar cell energy 2, 8, 17-19, 26, 28-35, 44, 45, 52, 140, 141, 313, 425 314"See also Energy-sources Solar Cell 34-36, 42, 43, 57, 72, 108, 114, 120, 130, 131, 146-150, 156158, 164, 167, 175, 188, 199-202, 207, 212-214, 227, 228, 233-250, 253, 257, 258, 264, 265, 269, 270, 293-299, 301-315, 317, 318, 321, 323-331, 335, 336, 340, 342-349, 353-358, 364, 367, 371, 384, 388, 389 Solar Cell Arrays see Solar Cell Solar Cell Delivered Power Density 128, 129, 138, 139, 143, 144, 146, 148-150, 175-177, 180-187, 189-191, 197, 201, 229, 231-238, 240, 243, 246, 249, 273292, 295-299, 326, 327, 329-332, 334-5"^^ also individual semiconductors Solar Cell Efficiency 155, 169, 176, 177, 190, 191, 235, 238, 241, 244, 247, 250, 258, 272-292, 295-299, 301, 305-307, 322-326, 371, 375-380 Solar Cell Resistance 171, 175, 176, 188, 197, 201, 222, 227-230, 232, 235, 238, 247, 252, 253, 269, 271, 319, 355 Solar Spectral Irradiance see Sun Solar Spectrum see Sun Solar Thermal Energy 257, 258, 264, 304, 309-312, 314 Space 42, 148 Space Charge Region 159, 161, 163, 165, 205, 206, 210, 211 Spectrum Splitting 333 Sputtering 352 Stacking 202, 204, 356, 385, 389, 390 Staebler-Wronski Effect 356, 369 Stage Two Solar Cell System see Solar Cells Stage Three Solar Cell System see Solar Cells Standard Configuration see Optical Orientation Substrate 204-207, 209, 210, 212, 213, 215-217, 221, 223, 226, 227, 229, 231250, 253, 273-278, 280-285, 287-292, 305-307, 309-314, 318, 323-326 426 INDEX Sun 39-41, 43, 197, 315, 316, 363, 364, 367 Sunlight see Sun Tandem Solar Cell 333, 334 Tar Sands Temperature 12, 19, 22, 24, 26, 32, 84, 85, 92-94, 107, 135, 136, 142, 179, 198, 199, 201, 227-229, 231-250, 253, 259, 262, 263, 267, 268, 273-299, 303-307, 309-314, 322-327, 329332, 356, 363 Thermal Efficiency 303, 328-332 Thermal Resistance 265, 266 Thermal Resistivitiy see Thermal Reistance Thermoelectric 32, 33 Thermophotovoltaic 315-319, 322327, 329-332, 363, 390 Thin-film see Polycrystalline Third Stage Solar Cell System see Stage Three Solar Cell System Tides 2, i-see also Energy-sources Tin Oxide (SnO) 354, 355, 357, 358 Tracking 48-56, 257, 301, 315, 374, 390 Transmission 119, 123, 385 Traps 97-99, 101, 102 Trees see Wood Tunneling 166, 168, 169-5ee also Junction U Utility see Power Plants V Vacancies 342 Valence Band see Energy Band Vertical Configuration see Optical Orientation W Waste Usee also Biological Wave Form 78-81 Wavelength 138, 139 Waves 19 Weather 5, 18, 39, 40, 44, 45, 54-56, 375-380, 382, 385 Web see Dendritic Web Wind 2, 8, 19, 23, 24, 365-^^^ also Energy-sources Wood 2, 8, 14, 15, 19, l\-see also Energy-sources Wronski-Staebler Effect see Staebler-Wronski Effect Zinc Cadmium Oxide (Zn^Cd^^O) 347 Zinc Oxide (ZnO) 345 Zinc Sulfide (ZnS) 127 Zinc Selenide (ZnSe) 166 Zinc Telluride (ZnTe) 342 [...]... solar energy derived The length of the casual chain between the nuclear fusion reaction occurring in the sun and our eventual use of some form of energy may very well vary, but all of these energy sources are dependent on the existence of the sun Each hour the earth receives 173 x 10^^ kwh of energy from the sun Over a year, this corresponds to 5,160 Q, a figure more than 12,000 times the current energy. .. that the sun is not always shining, due to weather (clouds) or to the earth's rotation Thus, solar energy conversion occurs, on an average, some 12 hours of each day Therefore, some method of energy storage must be employed to assure the availability of energy on a 24 hour basis In some of the following solar energy conversion/ collection schemes (such as in the growing of trees for use as firewood) the. .. collector/converters alone, the potential solar energy supply available for use by man is in the neighborhood of 1,100 Q This value is still over two thousand times the present energy requirements of the human race In discussing solar energy we do have the option of considering ground-based solar energy collection systems, as implied in the preceding paragraph, or some type of solar energy collection system... source, there are possibilities for geothermal energy; and it is these we study here An estimate for the total recoverable energy from geothermal sources is 56 Q with a 50 year life span for any given geothermal "field" [17] Taking the five scenarios considered earlier, the time to exhaustion of our geothermal resources, when used as the sole energy source, is provided in Table 1.7 Table 1.7 The time... C: THE SATURATION CURRENT IN PN JUNCTION SOLAR CELLS 407 APPENDIX D: SOME USEFUL PHYSICAL CONSTANTS 411 APPENDIX E: SYMBOLS 411 SUBJECT INDEX 420 CHAPTER I: ENERGY NEEDS -ENERGY SOURCES Introduction This work is concerned with the theory, design and operation of solar cells However, we need to first ask thefimdamentalquestion-why consider solar cells at all? The answer to this question involves energy. .. thousand years) to "cool down" In the event that mankind is smart enough to solve the puzzles inherent in nuclear fusion (both in the fusion process itself and in disposing of its waste products), there is sufficient deuterium in the oceans of this planet to completely satisfy the energy needs of the human race for several miUion years Solar Energy The remainder of the energy sources listed in Tables... Geysers, indicates that the heat flow into this geothermal field from within the earth is dropping [4, 16] Averaged over the surface of the earth, the heat flux of geothermal energy is very low (0.06 watts per square meter) and is at a relatively low temperature Thus, CHAPTER I: ENERGY NEEDS -ENERGY SOURCES 13 the field approach indicated above is favored Note that the majority of these fields are geologically... to be fusion, if they exist at all the nature and reality of this process are not certain 18 CHAPTER I: ENERGY NEEDS -ENERGY SOURCES is employed in evaporating water from the oceans, lakes and rivers The remainder, 2,490 Q, is available for such purposes as powering photosynthesis, warming the surface of the earth and providing energy for the human race Utilizing land-based solar energy collector/converters... will the capital energy sources last? and (2) How many people can the energy income sources support? To answer these questions we need to consider how much energy the human race uses Consumption In Table 1.2 the per capita rate of energy use in the United States is presented for selected years Table 1.2 Per capita energy use in the United States [1, 2, 3, 4] Year 1800 1850 1900 1925 1940 Per Capita energy. .. geothermal energy reserves with geothermal as the sole energy supply Scenario A B C D E Population (billions) 5 5 5 10 10 1,098 131 16.4 10.9 Time (years) 32.7 We have now covered the principal energy sources which the human race is currently using Note that they are all capital energy sources and that all of them adversely affect our environment (steam is not the only gas that escapes from a geothermal ... not only the direct current electrical energy provided by the solar cells, but the excess thermal energy present in the solar cells is commonly extracted from the system as usefiil energy With... ENERGY NEEDS -ENERGY SOURCES 35 is important to us at the moment, is that the solar cells are potentially more efficient than any of the other solar energy options considered in this chapter Solar. . .Solar Energy Conversion THE SOLAR CELL (SECOND EDITION) This Page Intentionally Left Blank Solar Energy Conversion HE SOLArl CELL (SECOND EDITION) Richard C Neville