Chalcogenide Photovoltaics

386 Pages·2008·2.718 MB·English

by  Scheer R.

S Roland Scheer, Hans-Werner Schock
c
T h
his fi rst comprehensive description of the most important material e
properties and device aspects closes the gap between general books on e
r
solar cells and journal articles on chalcogenide-based photovoltaics.
· Chalcogenide
Written by two very renowned authors with years of practical experi- S
ence in the fi eld, the book covers II-VI and I-III-VI2 materials as well as c
h
energy conversion at heterojunctions. It also discusses the latest semi-
o
conductor heterojunction models and presents modern analysis con- c
cepts. Thin fi lm technology is explained with an emphasis on current k Photovoltaics
and future techniques for mass production, and the book closes with a
compendium of failure analysis in photovoltaic thin fi lm modules.
With its overview of the semiconductor physics and technology need-
ed, this practical book is ideal for students, researchers, and manufac-
turers, as well as for the growing number of engineers and researchers
working in companies and institutes on chalcogenide photovoltaics.
Physics, Technologies, and Thin Film Devices
Roland Scheer received his diploma degree in electronic engineering from the University of
Applied Sciences Berlin, Germany. He joined AEG Konstanz, Germany, in 1983 as electronic
engineer. In parallel, he studied physics at the University of Konstanz and at the Technical
University of Berlin where he received his physics diploma in 1990. In 1994, he fi nished his
C
doctoral thesis in physics and joined the Helmholtz-Centre (former Hahn-Meitner Institute)
in Berlin. His R&D activities are focused on thin fi lm solar cells where he invented a new solar h
a
cell based on CuInS2. In 2002, Roland Scheer was visiting scientist at the Advanced Institute l
for Science and Technology (AIST) in Tsukuba, Japan. He was lecturer at the University of c
o
Potsdam until in 2010 he became full professor holding the endowed chair for photovoltaics
g
at the Martin-Luther-University in Halle-Wittenberg.
e
n
i
Hans-Werner Schock became head of the Institute of Technology at the Helmholtz Zentrum d
Berlin für Materialien und Energie (former Hahn-Meitner Institute) in the division “Solar e

Energy Research” in late 2004. He received his diploma in electrical engineering in 1974 P
and obtained his PhD in electrical engineering from Stuttgart University, Germany, in 1986. h
Starting in the early 70s, he has taken the development of chalcogenide solar cells from basic o
investigations to the transfer to a pilot fabrication plant. From 1986 to 2003 he coordinated t
o
the research on chalcopyrite based solar cells in the framework of the European photovoltaic
v
program. From 1982 to 2004 he was head of the compound semiconductor thin fi lm group of
o
the Institute of Physical Electronics at the University of Stuttgart. He is author or co-author
l
of more than 300 contributions in books, scientifi c journals and published conference proceed- t
a
ings. For his achievements in the development of chalcopyrite based solar cells he received the
i
prestigious “Becquerel Prize” in 2010. c
s
www.wiley-vch.de

RolandScheerandHans-WernerSchock
ChalcogenidePhotovoltaics
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978-3-527-40857-3
Roland Scheer and Hans-Werner Schock
Chalcogenide Photovoltaics
Physics, Technologies, and Thin Film Devices
Prof.Dr.RolandScheer AllbookspublishedbyWiley-VCHare
Martin-LutherUniversita¨tHalle-Wittenberg carefullyproduced.Nevertheless,authors,
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Photovoltaik includingthisbook,tobefreeoferrors.
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06120Halle(Saale) statements,data,illustrations,procedural
Germany detailsorotheritemsmayinadvertentlybe
inaccurate.
Prof.Dr.Hans-WernerSchock
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V
Contents
Preface XI
SymbolsandAcronyms XIII
1 Introduction 1
1.1 HistoryofCu(In,Ga)(S,Se) SolarCells 1
2
1.1.1 MilestonesofCu(In,Ga)(S,Se) Development 3
2
1.2 HistoryofCdTeSolarCells 5
1.2.1 MilestonesofCdTeDevelopment 6
1.3 ProspectsofChalcogenidePhotovoltaics 7
2 ThinFilmHeterostructures 9
2.1 EnergiesandPotentials 9
2.2 ChargeDensitiesandFluxes 11
2.3 EnergyBandDiagrams 13
2.3.1 RulesandConventions 13
2.3.2 Absorber/Window 17
2.3.3 Absorber/Buffer/Window 20
2.3.4 InterfaceStates 24
2.3.5 InterfaceDipoles 29
2.3.6 DeepBulkStates 29
2.3.7 BandgapGradients 32
2.4 DiodeCurrents 36
2.4.1 SuperpositionPrincipleandShiftingApproximation 36
2.4.2 RegionsofRecombination 37
2.4.3 RadiativeRecombination 40
2.4.4 AugerRecombination 43
2.4.5 DefectRelatedRecombination 44
2.4.5.1 SCRRecombination 50
2.4.5.2 QNRRecombination 60
2.4.5.3 BackSurfaceRecombination 62
2.4.5.4 InterfaceRecombination 63
2.4.6 ParallelProcesses 73
2.4.6.1 SCRandQNRRecombination 73
ChalcogenidePhotovoltaics:Physics,Technologies,andThinFilmDevices.
RolandScheerandHans-WernerSchock
Copyright2011WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
ISBN:978-3-527-31459-1
VI Contents
2.4.6.2 SCRandIFRecombination 75
2.4.7 BarriersforDiodeCurrent 76
2.4.8 BiasDependence 78
2.4.9 Non-Homogeneities 79
2.5 LightGeneratedCurrents 80
2.5.1 GenerationCurrents 81
2.5.2 GenerationFunction 84
2.5.3 PhotoCurrent 86
2.5.4 CollectionFunction 87
2.5.4.1 AbsorberQuasiNeutralRegion 87
2.5.4.2 QNRwithGradedBandgap 90
2.5.4.3 QNRwithBackSurfaceField 91
2.5.4.4 AbsorberSpaceChargeRegion 92
2.5.4.5 BufferLayer 94
2.5.4.6 SimulatingtheCollectionFunction 95
2.5.5 QuantumEfficiencyandChargeCollectionEfficiency 96
2.5.6 BarriersforPhotoCurrent 97
2.5.7 VoltageDependenceofPhotoCurrent 99
2.5.7.1 WidthofSCR 99
2.5.7.2 InterfaceRecombination 100
2.5.7.3 PhotoCurrentBarriers 100
2.6 DeviceAnalysisandParameters 101
2.6.1 EquivalentCircuits 101
2.6.1.1 DCEquivalentCircuit 101
2.6.1.2 ACEquivalentCircuit 103
2.6.1.3 ModuleEquivalentCircuit 105
2.6.2 Current–VoltageAnalysis 107
2.6.2.1 ExternalCollectionEfficiency 107
2.6.2.2 DiodeParameters 108
2.6.2.3 OpenCircuitVoltage 112
2.6.2.4 FillFactor 116
2.6.3 Capacitance–VoltageAnalysis 119
2.6.4 AdmittanceSpectroscopy 122
3 DesignRulesforHeterostructureSolarCellsandModules 129
3.1 AbsorberBandgap 129
3.2 BandAlignment 131
3.3 EmitterDopingandDopingRatio 137
3.4 FermiLevelPinning 140
3.5 AbsorberDoping 142
3.6 AbsorberThickness 147
3.7 GrainBoundaries 150
3.8 BackContactBarrier 156
3.9 BufferThickness 159
3.10 FrontSurfaceGradient 162
Contents VII
3.11 BackSurfaceGradients 165
3.12 MonolithicSeriesInterconnection 171
4 ThinFilmMaterialProperties 175
4.1 AII-BVIAbsorbers 175
4.1.1 Physico-ChemicalProperties 175
4.1.2 LatticeDynamics 179
4.1.3 ElectronicProperties 180
4.1.3.1 PracticalDopingLimits 180
4.1.3.2 DefectSpectroscopy 182
4.1.3.3 MinorityCarrierLifetime 182
4.1.4 OpticalProperties 185
4.1.4.1 CdTe 185
4.1.4.2 MultinaryPhases 187
4.1.5 SurfaceProperties 188
4.1.6 PropertiesofGrainBoundaries 189
4.2 AI-BIII-CVIAbsorbers 192
2
4.2.1 Physico-ChemicalProperties 193
4.2.1.1 TernaryPhaseDiagrams 193
4.2.1.2 MultinaryPhases 198
4.2.1.3 DiffusionCoefficients 200
4.2.2 LatticeDynamics 201
4.2.3 ElectronicProperties 203
4.2.3.1 SinglePointDefects 204
4.2.3.2 DefectComplexes 209
4.2.3.3 DefectSpectroscopy 210
4.2.3.4 PracticalDopingLimits 214
4.2.3.5 CarrierMobility 215
4.2.3.6 MinorityCarrierLifetime 216
4.2.4 OpticalProperties 216
4.2.4.1 TernarySemiconductors 217
4.2.4.2 MultinarySemiconductors 218
4.2.5 SurfaceProperties 220
4.2.5.1 SurfaceComposition 220
4.2.5.2 SurfaceElectronics 222
4.2.6 PropertiesofGrainBoundaries 224
4.3 BufferLayers 226
4.4 WindowLayers 226
4.4.1 LowResistanceWindows 226
4.4.2 HighResistanceWindows 230
4.5 Interfaces 230
5 ThinFilmTechnology 235
5.1 CdTeCellsandModules 235
5.1.1 Substrates 235
VIII Contents
5.1.2 WindowLayersforCdTeCells 236
5.1.3 BufferLayersforCdTeCells 237
5.1.4 CdTeAbsorberLayer 240
5.1.5 ActivationbyChlorineTreatment 243
5.1.6 InfluenceofOxygen 245
5.1.7 InfluenceofCopper 246
5.1.8 BackContact 249
5.1.8.1 SurfaceModification 249
5.1.8.2 PrimaryandSecondaryContacts 250
5.1.9 ModuleFabricationandLifeCycleAnalysis 251
5.2 Cu(In,Ga)(S,Se) CellsandModules 252
2
5.2.1 Substrates 253
5.2.2 BackContacts 253
5.2.3 Cu(In,Ga)(S,Se) AbsorberLayers 255
2
5.2.3.1 Co-evaporation 257
5.2.3.2 DepositionReaction 260
5.2.3.3 Sputtering 262
5.2.3.4 Epitaxy,ChemicalVaporDeposition,andVaporTransport
Processes 262
5.2.4 InfluenceofSodium 262
5.2.5 InfluenceofGallium 265
5.2.6 InfluenceofSulfur 265
5.2.7 InfluenceofOxygen 266
5.2.8 BufferLayersofCIGS 268
5.2.8.1 ChemicalBathDepositedCdS 268
5.2.8.2 AlternativeBufferLayers 270
5.2.9 WindowLayersofCIGS 272
5.2.10 ModuleFabrication 273
6 PhotovoltaicPropertiesofStandardDevices 277
6.1 CdTeDeviceProperties 277
6.1.1 SolarCellParameters 277
6.1.2 DiodeCurrents 277
6.1.3 CollectionFunctions 279
6.1.4 DeviceAnomalies 280
6.1.5 TransientEffectsandMetastability 281
6.1.6 DeviceModel 282
6.1.7 Stability 285
6.2 AI-BIII-CVIDeviceProperties 286
2
6.2.1 SolarCellParameters 286
6.2.2 DiodeCurrents 288
6.2.3 CollectionFunction 290
6.2.4 TransientEffectsandMetastability 292
6.2.4.1 RelaxedState 292
6.2.4.2 ModelsforRelaxedState 293