太阳能电池研究现状.docx

太阳能电池研究现状.docx

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太阳能电池研究现状

太阳能电池研究现状

ActivityandCurrentStatusofR&DonSpaceSolarCells

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（BOLefficiency¼245%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.

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