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Stability and Degradation of Organic
and Polymer Solar Cells
i
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Stability and
Degradation of Organic
and Polymer Solar Cells
Editor
FREDERIK C. KREBS
Department of Energy Conversion and Storage,
Technical University of Denmark, Roskilde, Denmark
A John Wiley & Sons, Ltd., Publication
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Thiseditionfirstpublished2012
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LibraryofCongressCataloging-in-PublicationData
Stabilityanddegradationoforganicandpolymersolarcells/editor,FrederikC.Krebs.
p.cm.
Includesbibliographicalreferencesandindex.
ISBN978-1-119-95251-0(cloth)
1.Polymers–Deterioration. 2.Photovoltaiccells. 3.Organiccompounds–Biodegradation.
I.Krebs,FrederikC.
QD381.9.D47S732012
621.3815(cid:2)42–dc23 2011051140
AcataloguerecordforthisbookisavailablefromtheBritishLibrary.
PrintISBN:9781119952510
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Contents
Preface xi
Acknowledgements xiii
ListofContributors xv
1. TheDifferentPVTechnologiesandHowTheyDegrade 1
FrederikC.Krebs
1.1 ThePhotovoltaicEffectandtheOverview 1
1.2 ThePhotovoltaicTechnologies 2
1.3 IntrinsicVersusExtrinsicStability 3
1.3.1 IntrinsicStability 3
1.3.2 ExtrinsicStability 3
1.4 Degradation–TheCulprits,theWhat,theWhyandtheHow 3
1.5 SomeRepresentativeTechnologiesandHowTheyDegrade 4
1.5.1 Mono-andPolycrystallineSiliconSolarCells 5
1.5.2 Amorphous,Micro-andNanocrystallineSiliconSolarCells 6
1.5.3 CIS/CIGSSolarCells 8
1.5.4 CdS/CdTeSolarCells 9
1.5.5 Dye-SensitizedSolarCells(DSSC) 10
1.5.6 OrganicandPolymerSolarCells(OPV) 11
References 12
2. ChemicalandPhysicalProbesforStudyingDegradation 17
BirgittaAndreasenandKionNorrman
2.1 Introduction 17
2.2 PhysicalProbes 18
2.2.1 UV-visSpectroscopy 18
2.2.2 AtomicForceMicroscopy(AFM) 18
2.2.3 InterferenceMicroscopy 20
2.2.4 ScanningElectronMicroscopy(SEM) 21
2.2.5 FluorescenceMicroscopy 23
2.2.6 Light-BeamInduced-CurrentMicroscopy(LBIC) 24
2.2.7 ElectroluminescenceandPhotoluminescenceImaging
Microscopy(ELIandPLI) 25
2.2.8 X-rayReflectometry 26
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vi Contents
2.3 ChemicalProbes 27
2.3.1 InfraredSpectroscopy(IR) 27
2.3.2 Time-of-FlightSecondaryIonMassSpectrometry(TOF-SIMS) 28
2.3.3 X-rayPhotoelectronSpectroscopy(XPS) 32
2.4 SummaryandOutlook 35
References 36
3. ImagingTechniquesforStudyingOPVStabilityandDegradation 39
MarcoSeeland,RolandRo¨schandHaraldHoppe
3.1 IntroductiontoImagingTechniques 39
3.1.1 MicroscopyandOpticalScanning 39
3.1.2 LuminescenceImaging 40
3.1.3 Lock-InThermography 43
3.1.4 Light-BeamInducedCurrent 45
3.2 Reports 46
3.2.1 Background:DegradationofOLEDDevices 46
3.2.2 Light-BeamInducedCurrent 50
3.2.3 LuminescenceImaging 54
3.2.4 OpticalMicroscopy 57
3.2.5 DarkLock-InThermographyandLBIC 58
3.2.6 DarkLock-InThermographyandOpticalScanningforFailure
Analysis 62
3.3 Discussion:ComparisonofImagingTechniques 63
3.4 Summary 66
Acknowledgement 66
References 66
4. PhotochemicalStabilityofMaterialsforOPV 71
MatthieuManceau,Agne`sRivatonandJean-LucGardette
4.1 Introduction 71
4.2 Methods 72
4.2.1 AgingCondition 72
4.2.2 DegradationMonitoring 74
4.3 State-of-the-Art 82
4.3.1 Degradationoftheπ-ConjugatedPolymer 82
4.3.2 AcceptorMaterialAgingandBlendDegradation 99
References 102
5. DegradationofSmall-Molecule-BasedOPV 109
MartinHermenau,MoritzRiedeandKarlLeo
5.1 ComparisontoSmall-MoleculeOLEDs 110
5.1.1 NumberofPhotoexcitationsperMolecule 113
5.2 ComparisontoPolymerSolarCells 115
5.2.1 SensitivitytoAir 115
5.2.2 TemperatureStability 115
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Contents vii
5.3 Small-MoleculeOrganicMaterials 116
5.3.1 ActiveMaterials 116
5.3.2 Transport-andExciton-BlockingMaterials 119
5.4 DegradationConditions 125
5.4.1 OxygenandWater 125
5.4.2 UVRadiation 132
5.5 State-of-the-ArtinLifetimeStudies 134
5.6 SummaryandOutlook 138
References 139
6. DegradationofPolymer-BasedOPV 143
MikkelJørgensenandFrederikC.Krebs
6.1 FocusontheDegradationandStabilityofPolymer
SolarCells 143
6.2 AChartofDegradationandStabilityofPolymer
SolarCells 143
6.3 AShortAccountoftheOPVStability/Degradation
History 144
6.3.1 TheDivisionsofDegradationMechanisms 146
6.3.2 TheMethodologies 148
6.4 ModusOperandiforEvolvingOPV 148
6.5 TheRecentDevelopments 149
6.5.1 ThePhotocatalyticOxides 149
6.5.2 Interlayers 150
6.5.3 TheInvertedStructure 151
6.5.4 R2RProcessing 152
6.5.5 LaminationandEncapsulation 153
6.5.6 WaterProcessing 154
6.5.7 MechanicalDegradation–Delamination 155
6.6 InterlaboratoryStudiesandRoundRobins 156
6.7 OutsideStudies 157
6.8 HowFarCanOPVBeTakeninTermsofStability? 158
References 158
7. TestEquipmentforOPVStability 163
OlivierHaillant
7.1 Introduction 163
7.2 ReliabilityandDurabilityTestingofPVProducts 165
7.2.1 Reliability,aFunctionofDurability 165
7.2.2 EnvironmentalDurability 166
7.2.3 DurabilityandWeatheringTesting 167
7.3 LaboratoryWeatheringTesting 168
7.3.1 Acceleration 168
7.3.2 Relevance 169
7.3.3 Precision 170
7.3.4 IntroductiontoDeterminationofAccelerationFactors 170
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7.4 DurabilityTestingTechniques 172
7.4.1 OutdoorWeathering 172
7.4.2 LaboratoryWeathering 175
7.4.3 LaboratoryPhotoaging 180
7.4.4 Others 183
7.5 Conclusion 185
References 186
8. CharacterizationandReportingofOPVDeviceLifetime 193
SurenA.Gevorgyan
8.1 Introduction 193
8.2 PhotoelectricCharacterizationofOPVDevices 194
8.2.1 PhotoelectricCharacterizationTools 194
8.2.2 CharacterizationinControlledEnvironments 197
8.3 InterlaboratoryStudiesofOPVs 202
8.3.1 Introduction 202
8.3.2 InterlaboratoryStudiesofFlexibleLarge-AreaRoll-to-Roll
ProcessedPolymerSolarCellModules 203
8.3.3 InterlaboratoryStabilityStudiesofOPVs 204
8.4 LifetimeTestingandReporting:StandardizedApproach 213
8.4.1 Introduction 213
8.4.2 ProceduresforStandardLifetimeMeasurements 214
8.4.3 ReportingLifetime 235
8.5 Conclusions 238
ListofAbbreviations 238
References 238
9. ConcentratedLightforOrganicPhotovoltaics 243
ThomasTromholt
9.1 Introduction 243
9.2 Light-ConcentrationSetups 245
9.2.1 RefractiveSunlightConcentration 245
9.2.2 ReflectiveSunlightConcentration 246
9.2.3 ConcentratedSolarSimulation 249
9.3 ExperimentalWorkPerformedwithConcentratedLight 251
9.3.1 IPVResponsetoConcentratedSunlight 251
9.3.2 PolymerResponsetoConcentratedLight 253
9.3.3 OrganicSolarCellResponsetoConcentratedLight 257
9.4 PhysicalCharacterizationbyConcentratedSunlight 261
9.5 Conclusion 265
References 265
10. BarrierTechnologyandApplications 269
LarsMu¨ller-Meskamp,JohnFahlteichandFrederikC.Krebs
10.1 EncapsulationRequirements 269
10.1.1 TypesofEncapsulation 270
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Contents ix
10.1.2 Glass/GlassEncapsulation 271
10.1.3 LaminationofBarrierFilms 272
10.1.4 Thin-FilmEncapsulation 273
10.1.5 PerimeterSealing 273
10.2 Thin-FilmPermeationPhysics 274
10.2.1 Solid-StateDiffusionandDiffusioninPolymers 274
10.2.2 Fick’sFirstLawofDiffusion 275
10.2.3 Sorption 276
10.2.4 PermeationinThinFilms 277
10.2.5 ModelsforthePermeationBarrierCoatedPolymerFilms 278
10.2.6 TemperatureDependenceofPermeation 279
10.2.7 DependenceofWaterPermeationonLayerThickness 280
10.2.8 TimeDependenceofPermeation 282
10.2.9 PermeationinMultilayerBarriers 284
10.2.10 PinholesinMultilayerSystems 287
10.3 MeasurementofBarrierProperties 288
10.3.1 GravimetricCup 289
10.3.2 Carrier-Gas-BasedCoulometricBarrierMeasurement 289
10.3.3 MassSpectrometer 290
10.3.4 DirectPressureMeasurement 291
10.3.5 RadioactiveIsotopes 292
10.3.6 CalciumTest(OpticalorElectrical) 293
10.3.7 DeviceTesting 294
10.3.8 StandardsandTypicalMeasurementConditions 295
10.3.9 TestMethodOverview 295
10.4 BarrierTechnologies 295
10.4.1 Single-LayerTechnologies 297
10.4.2 MultilayerTechnologies 309
10.5 BarrierApplicationinOPV 315
10.5.1 Products 316
10.5.2 BarrierCostandManufacturability 318
10.6 Conclusion 321
References 322
11. SummaryandOutlook 331
FrederikC.Krebs
Index 333
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Preface
Photovoltaic cells or solar cells made out of organic materials have become the subject
ofintensestudybymanyresearchgroupsandasignificantindustrialactivityisemerging
withinseveralareasspanningfromsuppliersofmaterials,substratesandbarriers,through
inkdevelopmenttofullmanufactureandintegrationoforganicphotovoltaics(OPV).The
traditionalphotovoltaicindustryiswellestablishedandthephotovoltaicasausefulenergy-
producing unit has been around for nearly 60 years. The interest in OPV technology is
thatitpotentiallyprovidesanefficientsolutiontomanyofthestrugglesthatthetraditional
PV technologies have been fighting for decades. OPV also has its share of problems but
theyaredifferentandtheinterestemergesinthebeliefthatthesenewproblemsforanew
and different technology might be easier to tackle than the ones we have failed to tackle
efficiently for the traditional PV technologies. Traditional PV in the form of crystalline
PV was born as an environmentally and inherently stable technology and many of the
laterdevelopmentsneverknewdifferent.However,theyallsufferfromthesameproblem
of a massive energy input being required in their manufacture, and sometimes also from
scarcityoftheelementsemployedorsignificanttoxicityofthecomponentsthatconstitute
themorintheprocessesleadingtothem.OPVinitsintendedformdoesnotshareeither
oftheseproblemsandpotentiallyallowsforveryshortenergypaybacktimesastheyare
very thin, common elements can be employed and very little energy is required for their
manufacture.Theyalsohaveaweaknessandthatistheirinstabilityduringoperationand
sensitivity to some of the atmospheric components that are evidently present on earth.
The early OPVs were not very stable and had a duration of operation in air measured
in seconds or some minutes at most. Today, many thousands of hours is common place,
however,itisstilllaggingbehindthestabilitypresentedbyforinstancecrystallinesilicon.
This book is dedicated to a description of what this instability is, where it has its roots,
how it is measured and characterized, the physical means available to investigate it and
also how it can be countermeasured through removal or elimination of the source of the
problemorthroughdesignofthematerialsanddevice.Thisbookisdedicatedtothetopic
ofdegradationofOPVandshouldserveasasourceofreferenceforthestudent,theexpert,
theexperimentalist,theinterestedandthegeneralist.Iwishyouapleasantreadandhope
thatyouwillfindmostofthequestionsonthetopicansweredorfindapathtowardsfurther
development.
FrederikC.Krebs
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Acknowledgements
Duringthewritingofthisbooktheauthorshavebeensupportedbyseveralfunding
organisationsandwouldliketoexpressthanksto:
– TheDanishStrategicResearchCouncil(2104-07-0022)andEUDP(j.no.64009-0050).
– TheDresdnerInnovationszentrumEnergieeffizienz,fundedbytheEuropeanUnion,the
StateSaxonyandtheFraunhoferGesellschaftforfundingencapsulationresearchatIAPP
andIPMS.
– TheThuringianMinistryofCultureintheframeworkofFIPVII.
– TheEuropeanCommission,theGermanMinistryforEducationandResearch(BMBF),
Deutsche Forschungsgemeinschaft (DFG), Free State of Saxony, and further funding
agencies.K.LeothankstheDFGforthesupportviatheLeibnizPrize.
– Public-fundedresearchprojectssupportedbytheGermanFederalMinistryforEducation
andResearchunderreferencenumber13N8858and01RI0628andbytheSaxonyState
MinistryforEconomicAffairs,LaborandTransportunderreferencenumber3957/623
Several people have supported the authors and we would like to express sincere
gratitudeto:
– Toni Mu¨ller and Bert Ma¨nnig from Heliatek GmbH for supporting this work with data
andknowledge.Furthermore,wewanttothanktheFraunhoferIPMSandthecompanies
CreaphysGmbH,HeliatekGmbH,NovaledAG,andSim4TecGmbHforcontinuedgood
collaboration.Thisworkwouldnothavebeenpossiblewithoutthehelpofthetechnical
and scientific staff of the organic solar cell group at the IAPP, especially Sven Kunze,
CarstenWolf,TobiasGu¨nther,InesRabelodeMoraesandSebastianScholz.
– SylvioSchubert,HannesKlumbiesandClaudiaKeiblerfortheircontributionstoencap-
sulationatIAPPandIPMS,KarlLeo,OlafHildandChristianMayfortheirsupport.
– Colleagues from Fraunhofer FEP, especially, Nicolas Schiller, Steffen Straach, Steffen
Gu¨nther,MatthiasFahland,OlafZywitzkiandThomasModesfortheirworkonsingle
and multilayer barriers as well as for providing some of the figures being used for this
bookchapter,AllessandroPatellifromCIVEN,Italy,forallowingreproductionofSEM
imagesofthemultilayerbarrierpresentedbyCIVEN.
– MarkusHo¨selisthankedfortakingphotographsforthecoverarttothisbook.
xiii
