Edited by Daniel Abou-Ras, Thomas Kirchartz, and Uwe Rau Advanced Characterization ...

564 Pages·2012·7.83 MB·English

Edited by
Daniel Abou-Ras,
Thomas Kirchartz,
and Uwe Rau
Advanced Characterization
Techniques for Thin Film
Solar Cells
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Edited by
Daniel Abou-Ras, Thomas Kirchartz, and Uwe Rau
Advanced Characterization Techniques for
Thin Film Solar Cells
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V
Contents
Preface XVII
List of Contributors XXI
Acknowledgments XXVII
Abbreviations XXXI
Partone Introduction 1
1 IntroductiontoThin-FilmPhotovoltaics 3
ThomasKirchartzandUweRau
1.1 Introduction 3
1.2 ThePhotovoltaicPrinciple 5
1.2.1 TheShockley–QueisserTheory 5
1.2.2 FromtheIdealSolarCelltoRealSolarCells 9
1.2.3 LightAbsorptionandLightTrapping 10
1.2.4 ChargeExtraction 12
1.2.5 NonradiativeRecombination 16
1.3 FunctionalLayersinThin-FilmSolarCells 18
1.4 ComparisonofVariousThin-FilmSolar-CellTypes 20
1.4.1 Cu(In,Ga)Se 20
2
1.4.1.1 BasicPropertiesandTechnology 20
1.4.1.2 Layer-StackingSequenceandBandDiagramofthe
Heterostructure 22
1.4.2 CdTe 23
1.4.2.1 BasicPropertiesandTechnology 23
1.4.2.2 Layer-StackingSequenceandBandDiagramofthe
Heterostructure 24
1.4.3 Thin-FilmSiliconSolarCells 25
1.4.3.1 HydrogenatedAmorphousSi(a-Si:H) 25
1.4.3.2 Metastabilityina-Si:H:TheStaebler–WronskiEffect 27
1.4.3.3 HydrogenatedMicrocrystallineSilicon(mc-Si:H) 27
VI Contents
1.4.3.4 MicromorphTandemSolarCells 27
1.5 Conclusions 28
References 28
PartTwo DeviceCharacterization 33
2 FundamentalElectricalCharacterizationofThin-FilmSolarCells 35
ThomasKirchartz,KainingDing,andUweRau
2.1 Introduction 35
2.2 Current/VoltageCurves 36
2.2.1 ShapeofCurrent/VoltageCurvesandtheirDescriptionwith
EquivalentCircuitModels 36
2.2.2 MeasurementofCurrent/VoltageCurves 41
2.2.3 DeterminationofIdealityFactorsandSeriesResistances 42
2.2.4 Temperature-DependentCurrent/VoltageMeasurements 44
2.3 QuantumEfficiencyMeasurements 47
2.3.1 Definition 47
2.3.2 MeasurementPrincipleandCalibration 49
2.3.3 QuantumEfficiencyMeasurementsofTandemSolarCells 51
2.3.4 DifferentialSpectralResponse(DSR)Measurements 52
2.3.5 InterpretationofQuantumEfficiencyMeasurementsinThin-Film
SiliconSolarCells 53
References 58
3 ElectroluminescenceAnalysisofSolarCellsandSolarModules 61
ThomasKirchartz,AnkeHelbig,BartE.Pieters,andUweRau
3.1 Introduction 61
3.2 Basics 62
3.3 SpectrallyResolvedElectroluminescence 65
3.4 SpatiallyResolvedElectroluminescenceofc-SiSolarCells 68
3.5 ElectroluminescenceImagingofCu(In,Ga)Se Thin-Film
2
Modules 71
3.6 ModelingofSpatiallyResolvedElectroluminescence 75
References 77
4 CapacitanceSpectroscopyofThin-FilmSolarCells 81
JenniferHeathandPawelZabierowski
4.1 Introduction 81
4.2 AdmittanceBasics 82
4.3 SampleRequirements 83
4.4 Instrumentation 84
4.5 Capacitance–VoltageProfilingandtheDepletionApproximation 85
4.6 AdmittanceResponseofDeepStates 86
4.7 TheInfluenceofDeepStatesonCVProfiles 90
4.8 DLTS 91
Contents VII
4.8.1 DLTSofThin-FilmPVDevices 94
4.9 AdmittanceSpectroscopy 95
4.10 DriveLevelCapacitanceProfiling 97
4.11 Photocapacitance 98
4.12 TheMeyer–NeldelRule 99
4.13 SpatialInhomogeneitiesandInterfaceStates 100
4.14 Metastability 102
References 102
PartThree MaterialsCharacterization 107
5 CharacterizingtheLight-TrappingPropertiesofTexturedSurfaces
withScanningNear-FieldOpticalMicroscopy 109
KarstenBittkau
5.1 Introduction 109
5.2 HowDoesaScanningNear-FieldOpticalMicroscopeWork? 110
5.3 LightScatteringintheWavePicture 112
5.4 TheRoleofEvanescentModesforLightTrapping 113
5.5 AnalysisofScanningNear-FieldOpticalMicroscopyImagesbyFast
FourierTransformation 116
5.6 HowtoExtractFar-FieldScatteringPropertiesbyScanningNear-Field
OpticalMicroscopy? 120
5.7 Conclusion 122
References 122
6 SpectroscopicEllipsometry 125
SylvainMarsillac,MichelleN.Sestak,JianLi,andRobertW.Collins
6.1 Introduction 125
6.2 Theory 127
6.2.1 PolarizedLight 127
6.2.2 ReflectionfromaSingleInterface 128
6.3 EllipsometryInstrumentation 129
6.3.1 RotatingAnalyzerSEforEx-SituApplications 130
6.3.2 RotatingCompensatorSEforReal-TimeApplications 131
6.4 DataAnalysis 133
6.4.1 ExactNumericalInversion 133
6.4.2 Least-SquaresRegression 134
6.4.3 VirtualInterfaceAnalysis 134
6.5 RTSEofThinFilmPhotovoltaics 134
6.5.1 ThinSi:H 135
6.5.2 CdTe 139
6.5.3 CuInSe 141
2
6.6 SummaryandFuture 145
6.7 DefinitionofVariables 145
References 146
VIII Contents
7 PhotoluminescenceAnalysisofThin-FilmSolarCells 151
ThomasUnoldandLeventGütay
7.1 Introduction 151
7.2 ExperimentalIssues 154
7.2.1 DesignoftheOpticalSystem 154
7.2.2 Calibration 156
7.2.3 Cryostat 156
7.3 BasicTransitions 157
7.3.1 Excitons 158
7.3.2 Free-BoundTransitions 159
7.3.3 Donor–AcceptorPairRecombination 160
7.3.4 PotentialFluctuations 162
7.3.5 Band–BandTransitions 163
7.4 CaseStudies 164
7.4.1 Low-TemperaturePhotoluminescenceAnalysis 164
7.4.2 Room-TemperatureMeasurements:EstimationofV from
oc
PLYield 168
7.4.3 SpatiallyResolvedPhotoluminescence:Absorber
Inhomogeneities 170
References 173
8 Steady-StatePhotocarrierGratingMethod 177
RudolfBrüggemann
8.1 Introduction 177
8.2 BasicAnalysisofSSPGandPhotocurrentResponse 178
8.2.1 OpticalModel 178
8.2.2 SemiconductorEquations 180
8.2.3 DiffusionLength:Ritter–Zeldov–WeiserAnalysis 181
8.2.3.1 EvaluationSchemes 183
8.2.4 MoreDetailedAnalyses 184
8.2.4.1 InfluenceoftheDarkConductivity 184
8.2.4.2 InfluenceofTraps 184
8.2.4.3 Minority-CarrierandMajority-CarrierMobility-Lifetime
Products 186
8.3 ExperimentalSetup 187
8.4 DataAnalysis 189
8.5 Results 192
8.5.1 HydrogenatedAmorphousSilicon 192
8.5.1.1 TemperatureandGenerationRateDependence 192
8.5.1.2 SurfaceRecombination 193
8.5.1.3 Electric-FieldInfluence 193
8.5.1.4 Fermi-LevelPosition 194
8.5.1.5 DefectsandLight-InducedDegradation 194
8.5.1.6 Thin-FilmCharacterizationandDepositionMethods 195
8.5.2 HydrogenatedAmorphousSiliconAlloys 196
Contents IX
8.5.3 HydrogenatedMicrocrystallineSilicon 196
8.5.4 HydrogenatedMicrocrystallineGermanium 197
8.5.5 OtherThin-FilmSemiconductors 197
8.6 Density-of-StatesDetermination 198
8.7 Summary 198
References 198
9 Time-of-FlightAnalysis 203
TorstenBronger
9.1 Introduction 203
9.2 FundamentalsofTOFMeasurements 204
9.2.1 AnomalousDispersion 205
9.2.2 BasicElectronicPropertiesofThin-FilmSemiconductors 207
9.3 ExperimentalDetails 208
9.3.1 AccompanyingMeasurements 210
9.3.1.1 Capacitance 210
9.3.1.2 Collection 212
9.3.1.3 Built-inField 212
9.3.2 CurrentDecay 212
9.3.3 ChargeTransient 215
9.3.4 PossibleProblems 217
9.3.4.1 DielectricRelaxation 217
9.3.5 InhomogeneousField 218
9.4 AnalysisofTOFResults 219
9.4.1 MultipleTrapping 219
9.4.1.1 OverviewoftheProcesses 219
9.4.1.2 EnergeticDistributionofCarriers 220
9.4.1.3 TimeDependenceofElectricalCurrent 223
9.4.2 SpatialChargeDistribution 223
9.4.2.1 TemperatureDependence 223
9.4.3 DensityofStates 225
9.4.3.1 WidthsofBandTails 225
9.4.3.2 ProbingofDeepStates 226
References 228
10 Electron-SpinResonance(ESR)inHydrogenatedAmorphous
Silicon(a-Si:H) 231
KlausLips,MatthiasFehr,andJanBehrends
10.1 Introduction 231
10.2 BasicsofESR 232
10.3 HowtoMeasureESR 235
10.3.1 ESRSetupandMeasurementProcedure 235
10.3.2 PulseESR 238
10.3.3 SamplePreparation 239
10.4 ThegTensorandHyperfineInteractioninDisorderedSolids 240
X Contents
10.4.1 ZeemanEnergyandgTensor 240
10.4.2 HyperfineInteraction 243
10.4.3 Line-BroadeningMechanisms 245
10.5 DiscussionofSelectedResults 248
10.5.1 ESRonUndopeda-Si:H 248
10.5.2 LESRonUndopeda-Si:H 252
10.5.3 ESRonDopeda-Si:H 253
10.5.4 Light-InducedDegradationina-Si:H 257
10.5.4.1 ExcessCharge-CarrierRecombinationandWeakSi–SiBond
Breaking 258
10.5.4.2 Si–HBondDissociationandHydrogenCollisionModel 260
10.5.4.3 TransformationofExistingNonparamagneticCharged
Dangling-BondDefects 260
10.6 AlternativeESRDetection 263
10.6.1 HistoryofEDMR 264
10.6.2 EDMRona-Si:HSolarCells 265
10.7 ConcludingRemarks 268
References 269
11 ScanningProbeMicroscopyonInorganicThinFilmsforSolarCells 275
SaschaSadewasserandIrisVisoly-Fisher
11.1 Introduction 275
11.2 ExperimentalBackground 276
11.2.1 AtomicForceMicroscopy 276
11.2.1.1 ContactMode 277
11.2.1.2 NoncontactMode 278
11.2.2 ConductiveAtomicForceMicroscopy 279
11.2.3 ScanningCapacitanceMicroscopy 280
11.2.4 KelvinProbeForceMicroscopy 282
11.2.5 ScanningTunnelingMicroscopy 284
11.2.6 IssuesofSamplePreparation 285
11.3 SelectedApplications 286
11.3.1 SurfaceHomogeneity 286
11.3.2 GrainBoundaries 288
11.3.3 Cross-SectionalStudies 291
11.4 Summary 294
References 294
12 ElectronMicroscopyonThinFilmsforSolarCells 299
DanielAbou-Ras,MelanieNichterwitz,ManuelJ.Romero,
andSebastianS.Schmidt
12.1 Introduction 299
12.2 ScanningElectronMicroscopy 299
12.2.1 ImagingTechniques 301
12.2.2 ElectronBackscatterDiffraction 302