Development, characterization, and modeling of CuGaSe2/Cu(In,Ga)Se2 thin-film tandem solar cells/:

2006·5.1 MB·English

by  Song, Jiyon

DEVELOPMENT,CHARACTERIZATION,ANDMODELINGOF
CuGaSe2/Cu(In,Ga)Se2THIN-FILMTANDEMSOLARCELLS
By
JIYONSONG
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
2006
Copyright2006
by
JiyonSong
ACKNOWLEDGMENTS
Iwouldliketoexpressmysinceregratitudetomysupervisorycommitteechair.Dr.
Sheng S. Li, for his guidance, support, and knowledge during the course ofthis
dissertation. IwouldalsoliketothankProfessorsGijsBosman,TimothyJ.Anderson,
andPaulHollowayforservingonmysupervisorycommittee.
I extend special thanksto Dr. Oscar D. Crisalle forhis helpful advice on my
research;Dr.LeonChen,forsupplyingCIGSsamplesanddepositingofZnOlayers;Dr.
RommelNoufi,forsupplyingCGSsamples;Dr.ValentinCraciun,forhishelponfilm
characterization;andDr.JianChen,forhishelponHallmeasurement.
IwouldliketoextendmysincereappreciationtoDr.SeokhyunYoonandWoo
KyoungKimfortheirhelponfilmcharacterization;andmycolleagues,DrsXuegeWang
andChia-HuaHuang,fortheirdiscussionsondevicecharacterizationandfabrication.
I alsothankAndreBaran, RyanKaczynski,RyanAcher, Wei Liu,ChrisPeek,
JihyunKim,YonghoChoi,JosephPark,ZivinPark,andDr.LeiL.Kerrfortheirhelp
andassistance. Icouldnothaveaccomplishedthisworkwithouttheircooperationand
help.
The author gratefully acknowledges the collaborations with the National
RenewableEnergyLaboratoryandEnergyPhotovoltaicsInc.thatprovidedtheCGSand
CIGSsamples. FundingthroughtheNRELhigh-performancephotovoltaicprogramis
gratefullyacknowledged.
iii
My deepest gratitude goes to my parents. I thankthem for encouraging and
supportingmeinloveandtrust. Ithankmysisterandbrotherforalwaysgivingtheirbest
tosupportme. Idedicatethisdissertationtothem.
IV
1
TABLEOFCONTENTS
page
ACKNOWLEDGMENTS Hi
LISTOFTABLES viii
LISTOFFIGURES ix
ABSTRACT xii
CHAPTER
1 INTRODUCTION I
2 FUNDAMENTALSOFCIS-BASEDTHIN-FILMTANDEMSOLARCELLS 7
2.1 OverviewofSolarCellTechnologies 7
2.1.1 Introduction 7
2.1.2 CrystallineSiliconSolarCells 8
2.1.3 ThinFilmSolarCells 9
2.2 FundamentalSolarCellParameters 12
2.3 TandemSolarCellTechnologies 13
2.4 CuGaSe2TopCell 15
2.5 AlternativeTopCells 17
2.5.1 CuInS2TopCell 17
2.5.2 CuGa(Sx,Se,.x)2TopCell 18
2.6 AlternativeBufferLayersforWideBand-gapCuGaSe2TopCell 18
2.6.1 Cdi_xZnxSBufferLayers 19
2.6.2 ZnSeBufferLayers 20
2.6.3 Zn(Se,OH)BufferLayers 2
3 DEVICEMODELINGANDSIMULATIONOFCIGSANDCGSSOLAR
CELLS 28
3.1 Introduction 28
3.2 AMPS-IDDeviceSimulationProgram 29
3.3 ModelingandSimulationofCIGSCells 30
3.3.1 CellStructureandMaterialParameters 30
3.3.2 TheEffectofCdSLayerThicknessontheCISCellPerformance 31
3.3.3 TheEffectofUniformAbsorberBand-gapontheCellPerformance 32
3.3.4 TheGradedBand-gapStructureofCIGSCells 32
v
3.3.5
ComparisonwithExperimentalDataforC1GSCells 33
3.4 ModelingandSimulationofCGSCells 36
33..44..21 CCeolmlpaStrriuscotunrewiatnhdEMxapteerriimaelntPaalraDmaettaerfsorCGSCells 3367
3.5 SummaryandConclusions 37
4 NUMERICALSIMULATIONOFMECHANICALLY-STACKEDCGS/CIGS
TANDEMSOLARCELLS 52
4.1 Introduction 52
4.2 Mechanically-StackedCGS/CIGSTandemCellStructure 53
4.3 SimulationMethod 54
4.4 TheEffectofCGSTopCellThicknessonthePerformanceofCIGSBottom
Cell 54
4.5 TheEffectofCGSAbsorberThicknessonthePerformanceofCGS/CIGS
TandemCell 55
4.6 SummaryandConclusions 57
5 DEVELOPMENT,GROWTH,ANDCHARACTERIZATIONOFCHEMICAL-
BATH-DEPOSITIONCDZNSBUFFERLAYERS 62
5.1 Introduction 62
5.2 DevelopmentandGrowthofCBD-CdZnSBufferLayers 63
5.2.1 ChemicalBathDepositionTechnique 63
5.2.2 ChemicalBathDepositionCondition 64
5.2.3 DefinitionoftheRelativeZincContentintheBufferFilmandinthe
CBDSolution 65
5.3 CharacterizationofCBD-CdZnSThinFilms 65
5.3.1 ThicknessofCdZnSFilms 65
5.3.2 StructuralAnalysis 66
5.3.3 AnalysisofSurfaceMorphology 67
5.3.4 OpticalAnalysis 68
5.3.5 ElectricalAnalysis 69
5.4 SummaryandConclusions 70
6 F7.A1BRICATIONANDMEASUREMENTSYSTEMSFORCIGSANDCGS
SOLARCELLS 82
6.1 Introduction 82
6.2 FabricationofCIGSandCGSSolarCells 82
6.3 TheCurrent-VoltageandSpectralResponseMeasurementSystems 83
6.3.1 Current-VoltageMeasurementSystem 83
6.3.2 SpectralResponseMeasurementSystem 84
7 CURRENT-VOLTAGEANDSPECTRALRESPONSE
CHARACTERIZATIONSOFCIGSSOLARCELLSWITHCDZNSBUFFER
LAYERS 90
Introduction 90
vi
88
7.2 TheEffectofCIGSAbsorberSurfaceTreatmentbyKCNontheCell
Performance 91
7.3 Current-VoltageandQuantumEfficiencyofCIGSCellswithCdZnSBuffer
Layers 92
7.3.1 TheEffectofBufferLayerThicknessontheCellPerformance 92
7.3.2 TheEffectofDifferentZnCompositionsofCdZnSBufferLayeron
theCellPerformance 92
7.4 SummaryandConclusions 95
8 CURRENT-VOLTAGEANDSPECTRALRESPONSE
CHARACTERIZATIONSOFCGSSOLARCELLSWITHCDZNSBUFFER
LAYERS 105
8.1 Introduction 105
8.2 SurfaceMorphologyofaCGSFilmandaCdZnSFilmonCGS 107
8.3 Current-VoltageCharacteristicsandQuantumEfficiencyofCGSCellswith
CdZnSBufferLayers 108
8.4 SummaryandConclusions Ill
9 SUMMARYANDFUTURESTUDIES 11
9.1 SummaryandConclusions 11
9.2 FutureStudies 119
LISTOFREFERENCES 123
BIOGRAPHICALSKETCH 130
vii
2- LISTOFTABLES
3-
Table Egge
2-1. TheperformanceparametersofthebestCIS-basedsolarcells 23
2. TheperformanceparametersofCIS-basedthin-filmtandemsolarcells 25
1. MaterialparametersofC1GSbottomcell 40
3-2. SimulatedperformanceparametersoftheCIGSsolarcellswithadoubleband-
gapgradingprofile 44
3-3. Theenergyband-gapprofileoftheCIGSabsorberlayerusedinsimulation 47
5-1. EstimatedenergybandgapsofCdZnSfilmsforvariousrelativeZncomposition
values(x) 80
7-
58--2. Mfeorasasu-rdeedpovsailtueedsCodfZelneSctrfiiclamlsroensiIstTaOncceoa(Rt)e,drgelsaissstivsiutbyst(rpa)t,easnadscaonfduunccttiiovnitoyf(tah)e
relativeZncompositonx 81
7-1. PerformanceofCdS/CIGScellswithandwithoutaKCNtreatmentoftheCIGS
absorberlayers 96
7-2. PerformanceofCdZnS/CIGScellswithandwithoutaKCNtreatmentofthe
CIGSabsorberlayers 98
7-3. PerformanceparametersofCdZnS/CIGScellsasafunctionofdifferent
depositiontimesforarelativezinccompositionx=0.3inthebufferlayer 100
4. PerformanceparametersofCdZnS/CIGScellsasafunctionoftherelativezinc
contentxofthebufferlayer 101
1. PterreaftomremnatnscoenotfhCedCSG/SCGaSbsaonrdbeCrdlZayneSr/sC(GASMIce,l5lsG,wi1t0h0amnWd/wcitmho2)utKCN 114
8-2. TheperformanceofCdS/CGSandCdZnS/CGScellswithKCNtreatmentson
theCGSabsorberlayers(AM1.5G,100mW/crn") 117
vm
LISTOFFIGURES
Figure
2-1. Csoolnadruccetlilonandvalencebanddiagramforap-nheterojunctionZnO/CdS/CIGS 22
2-2. Two-junctionmonolithically-cascadedandmechanically-stackedtandemsolar
cellstructures 24
2-3. Current-densityvoltage(J-V)characteristicsofasolarcellinthedarkand
illuminated,definingthefundamentalsolarcellperformanceparameters:light-
generatedcurrentdensity(JL),short-circuitcurrentdensity(Jsc),andopen-circuit
voltage(Voc). Fillfactor(FF)isdeterminedbythemaximumrectanglegivenby
JmandVm 26
2-4. BanddiagramswithincreasingGacontentoftheCuIni„xGaxSe2absorberlayer....27
3-1. Theschematicenergy-banddiagramofatypicalZnO/CdS/CIGSsolarcellunder
equilibriumcondition 39
3-2. Thephoto-J-VcurvesforthesimulatedCIScellswithdifferentthicknessofCdS
bufferlayerfor(a)30nm,(b)60nm,and(c)80nm 41
3-3. Sxi,mGualx)aStee2d(pEegr=for1.m1a0n,ce1.1p8a,raamnedte1r.s22oefVt)heceClulIsnwSietih(dEifgf=ere1n.t04uneiVf)oramndabCsu(olrnbie.r
band-gapprofiles;(a)Voc,(b)Jsc,(c)FF,and(d)efficiency 42
3-4. Theschematicenergy-banddiagramofaCIGScellwithadoubleband-gap
gradingprofileunderequilibriumcondition 43
3-5. Thephoto-J-Vcurvesforthesimulatedresults(solidanddashedlines)andthe
reportedexperimentaldata(solidcircles) 45
3-6. ThenormalizedQEforthesimulatedresults(solidline)andthereported
experimentaldata(solidcircles) 46
3-7. Thephoto-J-Vcurvesforthesimulatedresults(solidline)andthepublisheddata
(solidcircles) 48
3-8. Acomparisonoftheperformanceparametersforthesimulatedresults(circles)
andthepublisheddata(triangles) 49
3-9. Theschematicenergy-banddiagramforaCGScellunderequilibriumcondition..50
IX
f 1
3-
4-
10. Thephoto-J-Vcurveforthesimulatedresultsandthepublisheddata 5
1. Aschematicofafour-terminalmechanically-stackedCGS/CIGStandemcell
structure 58
44--2. PerformanceparametersofC1GSbottomcellunderworkingCGStopcellasa
functionofCGSabsorberthickness 59
5-
4-3. EfficienciesofCGS/CIGStandemcell,CGStopcell,andCIGSbottomcell
undertopcellasafunctionofCGStopcellabsorberthickness 60
4. Simulatedphoto-J-VcurvesofaCGStopcellandaCIGSbottomcellunderthe
CGStopcellforaCGS/CIGStandemcellwithanefficiencyof25.22% 61
1. Fziilncmctohimcpkonseistsioanssaxfu=nc0t,i0o.n3,ofanddep0o.s5itiontimeforCdZnSfilmswithrelative 72
5-2. FilmthicknessvariationasafunctionofrelativezinccompositionxforCdZnS
filmswithdepositiontimeof50minutes 73
5-3. PowderXRDpatternsofCdZnSfilmsdepositedonSLGwithrelativezinc
compositionx=0(filmthicknessd«200nm),x=0.3(d»100nm),andx=0.5
(d»150nm) 74
5-4. GrazingincidenceXRDpatternsofCdZnSfilms,depositedonMo,withrelative
zinccompositionsx=0,0.3,and0.5 75
5-
5-5. SEMmicrographsofthesurfaceofaCdi_xZnxSthinfilmwithrelativezinc
6- compositionx=0(CdS) 76
5-6. SEMmicrographsofthesurfaceofaCdi_xZnxSthinfilmwithrelativezinc
compositionx=0.3 76
5-7. SEMmicrographsofthesurfaceofaCdi_xZnxSthinfilmwithrelativezinc
compositionx=0.5 76
5-8. OpticaltransmittancespectraofCdZnSfilmswithrelativezinccompositionx=
0.3fordifferentfilmthickness 77
5-9. OpticaltransmittancespectraofCdZnSfilmswithrelativezinccompositionsx=
0(thicknessd»200nm)andx=0.3(d«100nm) 78
10. Plotsof(ahv versushvforCdZnSfilmswithrelativezinccompositionsx=0
(thicknessd*200nm),x=0.3(d»100nm),andx=0.5(d»l50nm) 79
1. SolarcellstructureusedtofabricateaZnO/CdZnS/CIGS(orCGS)cell 87
6-2. AcompletelyfinishedCIGScellwithNi/Altopcontact 88
6-3. Across-sectionalSEMimageoftheZnO/CdZnS/CIGS/Mo/SLGcell(10,000X)..89
x