太阳能电池研究现状Word文档格式.docx
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太阳能电池研究现状Word文档格式.docx
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INTRODUCTION
TheJapanAerospaceExplorationAgency(JAXA),theformerNationalSpaceDevelopmentAgencyofJapan(NASDA),hadconcentratedsolelyonthedevelopmentofsiliconspacesolarcellsuntiltheyear2000.Withtheneedforhigher-efficiencysolarcellsinspace,JAXAbegandevelopingIII–Vmulti-junction(MJ)spacesolarcellsin2001.Twotypesofhigh-efficiencytriple-junction(3J)solarcellshavebeendeveloped.ThesecellsarefabricatedusingepitaxialwafersgrownbycompaniesintheUnitedStatesandhaveanaverageefficiencyof28%orhigheratthebeginning-of-life(BOL).
Forthenewlydeveloped3Jcellstobeusedforspacemissions,however,itwasalsonecessarytocollectradiationtoleranceorend-of-life(EOL)data.Accordingly,irradiationtestshavebeenconductedtostudyradiationdegradationbehaviorofthe3JcellsusingvarioustypesofacceleratorsintheJapanAtomicEnergyResearchInstitute(JAERI)atTakasakiaspartofJAXA–JAERIcollaborationactivities.Anumberofbasicstudiesoncomponentsub-cellsina3JcellhavecontinuedtofurtherimproveMJcellperformance.OnesuchstudyattemptstoclarifythedependencyofradiationdegradationtrendsofIII–Vsingle-junctionsolarcellsontheirstructureorenvironmentalconditionstounderstandthedegradationmechanismsofMJcells.AflightdemonstrationexperimentofanInGaP/GaAssolarcellandgroundirradiationtestswerecompletedinanotherstudy.Theresultswillbeappliedtodevelopasolarcelldevicesimulator,whichshouldenablepredictionsofEOLperformanceofanyMJcellstructure.
Acopperindiumgalliumdiselenide(CuInGaSe2(CIGS))thin-filmsolrcellisapromisingcandidateforfuturethin-filmspacesolarcellssincethecellsnotonlyhavethepotentialtoachievehigherconversionefficienciesthanotherthin-filmsolarcells,butalsoshowpossesssuperradiaiontolerance.Inaddition,theCIGSthin-filmsolarcellshavesuperiorproperties,suchaslowcostandlightweight,becausethecellscanbeformedonpolyimideormetalfoilsubstrates.AflightdemonstrationexperimentoftheCIGSsolarcellswasper-formed,andgroundirradiationtestswereconductedtoinvestigatethemechanismsofthesuperionradiationtolerance.
ThispaperdescribesR&
DactivitiesinJapanonspacesolarcells.Theresultsoftheactivitiesaredescribed.
III–VMULTIJUNCTIONSOLARCELL
Triple-junctioncelldevelopment
Triple-junctioncellshavebeendevelopedundercontractswithSharpCorporation.ThesecellsaremadeofepitaxialwafersproducedintheUS;
however,anewanti-reflectioncoatinghasbeendesigned.Figure1depictsthetypicalcurrent–voltage(I–V)characteristicunderAM0,1sunsimulatedlightillumination.Anaverageefficiencyexceeding27%hasbeenachieved.Thequantumefficiency(QE)ofthetopcellisdesignedtoberelativelylowinordertoimproveEOLcurrentoutput.
Radiationresponseofatriple-junctioncell
Thenewlydeveloped3Jcellsweresubjectedtoprotonirradiationtestswithprotonaccelerationenergyvaryingfrom30keVto10MeV.Figure2illustratestypicaldegradationtrendsof:
(a)open-circuitvoltageVoc;
(b)short-circuitcurrentIsc;
and(c)maximumpowerPmaxasafunctionofprotonenergyselectedintheexperiment.Relativedamagecoefficients(RDCs)aredefinedataremainingfactorof80%forPmaxand90%forVocandIscfromthedegradationcurvesobtained,andtheRDCisindicatedinFigure3.TheRDCofVocexhibitsthreeenergymaximaaround30keV,250keVand2MeV.Whenprotonsareacceleratedwiththeseenergies,theprotonrangesagreewiththedepthsofp–njunctionsofthethreesub-cellsaccordingtotheTRIMcalculation.BecauseVocofa3Jcellisthesumofgeneratedvoltagesfromconstituentthreesub-cells,Vocisdirectlyinfluencedbydamagetoeachsub-cell.Therefore,Vocdegradationofa3Jcellstronglydependsonboththecellstructureandtherangeoftheirradiatedprotonswherethedensityofinduceddefectsisconsideredtobemaximized.
Tobetterunderstand3Jcelldegradation,thedegradationtrendswerereplottedasafunctionofthedisplace-mentdamagedoseDd.Thismethodologyisalsousefulfordegradationpredictioninanactualspaceenviron-ment.Figure4presentstheresults.ForVoc(Figure4a),thedegradationisfoundtosplitdistinctlyintotwocurves.Theuppercurveconsistsofdataofenergylessthan100keVandtheloweronerefersto150keVorhigher.AccordingtotheTRIMcalculation,theuppercurverepresentsdegradationofonlytheInGaPtopcell,andtheloweroneinvolvestheInGaPtopandtheGaAsmiddlecelldegradation.SincethecontributionoftheGebottomcellVoctothe3JVocissmall,thethirdcurvecannotbeobserved.InthecaseofIsc(Figure4b),alldatafitonasinglecurve,exceptafewanomalouspointscorrespondingtoseveredegradationintheDd
rangeof1–2*1011MeV/g.TheseDdvaluesareconsistentwithaprotonirradiationof150–380keVatafluxrangeof1012cm-2.Asaresult,forPmax(Figure4c),thedegradationtrendisexpressedwithtwocurvesandafewanomalouspoints.
Figure2.Degradationof:
(a)Voc;
(b)Isc;
(c)Pmaxofa3Jcellasafunctionofprotonfluxforvariousprotonenergies
TheQEofthe3JcellwereinvestigatedtoestimateIscofeachsub-cellafterirradiation.Figure5exhibitstypicalchangeinQEofthetopandmiddlecellina3Jcellduetoprotonirradiation.TheQEdataoftheGebottomcellareomittedbecausethecurrentoutputofthebottomcelldoesnotaffectthatofa3Jcell(Figure6).NumericalconvolutionoftheAM0solarspectrumwiththeQEdataprovidestherelativeIscforthespecificsub-cell.Figure6illustratesIscdegradationoftheInGaP,GaAsandGesub-cellsasfunctionsofprotonenergyandflux.Forcomparison,measuredIscvaluesofthe3Jcellarealsoplottedinthefigure.Whenprotonfluenceislessthan1011cm-2,theInGaPtopcellisconsideredtolimittheIscofthe3Jcellovertheentireenergyregion.
Afterirradiationwithenergiesbetween150and380keVatafluenceof1012cm-2,however,Isc
oftheGaAsmiddlecellissignificantlydecreased,andtheGaAscellbecomesthecurrent-limitingcell.Thismeansthatthecurrent-limitingcellchangesduetospecificprotonirradiationconditions.ThisisalsowhytheanomalousdegradationpointswereobservedinFigure4(b).Inaddition,sincetheestablishedempiricalequationusedtodescribeadegradationcurveisbasedonsingle-junctioncells,itcannotaccuratelyexpresstheIscdegradationcharacteristicsofa3Jcellthatinvolvesthecurrent-limitingcellchangephenomenainhigher-fluenceregions.
Spacedemonstrationofadual-junctioncell
Theperformanceofa3JcellisalmosttotallygovernedbythatoftheInGaPtopcellandtheGaAsmiddlecellbecausethecontributionoftheGebottomcellissmall.TheradiationresponseofanInGaP/GaAsdual-junction(2J)solarcell(BOLefficiency¼
245%underAM0,1sun)wasdemonstratedbyMissionDemonstration-testSatelliteNo.1(MDS-1)‘Tsubasa’,whichflewinageostationarytransferorbit(GTO).The2Jcellisoriginallydesignedforterrestrialuse,therefore,theInGaPtopcellisrelativelythickerthanthesamecellsforspaceapplications.Threecellswereconnectedinparalleltoadjustthecurrentoutputtothemeasurementrange.Apairofthree-cellsetswasprepared,and500-or100-mm-thickradiation-shieldingcoverglasseswereattachedtoeachofthesets.Themissiondurationwasapproximately600daysafterlaunch.TheGTOcutsacrosstheinnerandouterVanAllenBeltssothattheMDS-1wasexposedtoamuchmoresevereradiationenvironmentthanincasesofalow-Earthorbit(LEO)orageostationaryorbit(GEO).
TheI–Vcharacteristicsofthe2Jcellweresuccessfullycollectedfromthebeginningtotheendofthemission,andthecurrentandvoltagevalueswerecorrectedforvoltageshiftcausedbythemeasurementcircuit,temperature,angletotheSun,andsolarirradiance(distancebetweentheSunandtheEarth).Figure7presentstheremainingfactorsofIsc,VocandPmaxagainstthemissionelapsedtime(MET)indaysafterlaunchobtainedfortheentiremissionduration.InthecaseofPmax,afittingI–Vcurvewascalculatedfirst,andthenthePmaxvaluewasobtained.ThefirstdataataMETof2daysafterlaunchwereusedastheinitialvalues.Thechangeindegradationrateappearingfromthetrendswasconfirmedtocomefromthechangeintheradiationfluxinorbitduetosolarflaresaccordingtothedatafromtheradiationdosemonitorsinstalledonthesatellite.Althoughthe2Jcellwasdesignedforterrestrialuse,thecellshavesufficientlyhighremainingfactorsforspaceuse;
theremainingfactorattheendofmissiondurationwas76%forIsc,88%forVocand64%forPmax.Priortothelaunch,groundirradiationtestswereconductedatJAERI,Takasakionthe2JcellaswellasitsInGaPtopandGaAsbottomcellswith1MeV-electronsand10MeV-protons.Theresultsaredescribedelsewhere.Anequivalent1MeVelectronfluxwasestimatedforthemissionenvironmentusingthegroundtestresults.ThefluencescorrespondingtotheremainingfactorsattheendofthemissionofIscare1.1*1015cm-2;
Voc7.0*1015cm-2;
andPmax1.3*1015cm-2.TheequivalentfluenceofVocisaboutoneorderofmagnitudegreaterthanthatofIscandPmax.Anequivalent10MeVprotonfluencewasestimatedinthesameway,andthefluencewas1.2*1013cm-2forIsc,7.0*1012cm-2forVocand5*1012cm-2forPmax.Inthiscase,thefluenceagreerelativelywell,presumablyduetotheproton-richradiationenvironmentinorbit.TableIsummarizestheresults.
F
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