2区-Voltage dependent photocurrent collection in CdTe CdS solar cells.pdf

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1、PROGRESSINPHOTOVOLTAICS:RESEARCHANDAPPLICATIONSProg.Photovolt:Res.Appl.2007;15:587–602Publishedonline8May2007inWileyInterScience(www.interscience.wiley.com)DOI:10.1002/pip.767ResearchVoltageDependentPhotocurrentCollectioninCdTe/CdSSolarCells,yStevenHegedus*,Dar

2、shiniDesaiandChrisThompsonInstituteofEnergyConversion,UniversityofDelaware,Newark,DE19716,USAThevoltagedependenceofthephotocurrentJL(V)ofCdTe/CdSsolarcellshasbeencharacterizedbyseparatingtheforwardcurrentfromthephotocurrentatseveralilluminationintensities.JL(V)

3、reducesthefillfactor(FF)oftypicalcellsby10–15points,theopencircuitvoltage(VOC)by20–50mV,andtheefficiencyby2–4points.EliminatingtheeffectofJL(V)establishessuperpositionbetweenlightanddarkJ(V)curvesforsomecells.Twomodelsforvoltagedependentcollectiongivereasonablefit

4、stothedata:(1)asinglecarrierHechtmodeldevelopedfordriftcollectioninp-i-nS9solarcellsinwhichfittingyieldsaparameterconsistentwithlifetimesof10sasmeasuredbyothers;or(2)thestandarddepletionregionandbulkdiffusionlengthmodelfitsalmostaswell.ThesimpleHecht-likedriftcol

5、lectionmodelforphoto-currentgivesverygoodagreementtoJ(V)curvesmeasuredunderAM1
5lightonCdTe/CdSsolarcellswithFFfrom53%to70%,CdTethicknessfrom1
8to7
0mm,ininitialandstressedstates.AcceleratedthermalandbiasstressingincreasesJL(V)lossesasdoesinsufficientCu.Thismeth

6、odprovidesanewmetricfortrackingdeviceperformance,characterizestransportinthehighfielddepletionregion,andquantifiesasignificantFFlossinCdTesolarcells.Copyright#2007JohnWiley&Sons,Ltd.keywords:CdTesolarcells;currentcollectionReceived12January2007;Revised22March2007I

7、NTRODUCTIONfficientsolarcellperformancerequiresminimizingtheforwardrecombinationcurrentJF(V)andmaximizingthelightgeneratedcurrentJL.ThelatterprocessrequiresmaximizingboththeopticalEgenerationintheabsorberlayerandthecollectionofthephotogeneratedcarriers.Collectio

8、nlossescanbeespeciallysignificantinsomethin-filmsolarcellsduetotheirhighabsorptionandshortdiffusionlengths.Generationinthehighfieldjunctionregionleadstoarelativelygreaterrelian