类单晶(准单晶)技术性权威文献

Seed-assistedcastquasi-singlecrystallinesiliconforphotovoltaicapplication:TowardshighefficiencyandlowcostsiliconsolarcellsXinGu,XuegongYun,KuanxinGuo,LinChen,DongWang,DerenYangStateKeyLabofSiliconMaterialsandDepartmentofMaterialsScience&Engineering,ZhejiangUniversity,Hangzhou310027,PRChinaarticleinfoArticlehistory:Received22December2011Receivedinrevisedform15February2012Accepted17February2012Availableonline17March2012Keywords:Castquasi-singlecrystallinesiliconSolarcellSeed-assistedcrystalgrowthHighefficiencyLight-induceddegradationabstractWehavedemonstratedtheseed-assistedcastquasi-singlecrystalline(QSC)silicontechniquetoachievehighefficiencysolarcellswithlowcost.Comparedtomulticrystalline(mc)silicon,theQSCsiliconhasbettermaterialproperties,havinghigherminoritycarrierlifetimeandfewergrainboundariesanddislocations.Furthermore,the/100SorientedQSCsiliconcanachievealowersurfacereflectanceusingalkalinetexturing.Basedonthesetwofactors,theefficiencyoftheQSCsiliconsolarcellswiththeindustrialsizehasbeenimprovedbyupto1%absolutelyfromthemc-Sicounterparts.ComparedtotheCzochralski(CZ)siliconsolarcells,theQSCcellshaveslightlylowerefficiencybuthighproductivityandnegligiblelight-induceddegradation.TheseresultssuggestagreatpotentialoftheQSCsiliconappliedinphotovoltaicindustryasthenextgenerationsubstrate.TomaketheQSCsiliconmorecompetitiveinindustry,furthereffortsshouldbefocusedontherecyclingofseedcrystals,thecoverageofmono-regionandthecontrolofstructuraldefects.&2012ElsevierB.V.Allrightsreserved.1.IntroductionCrystallinesiliconwafers,boththesinglecrystallineandthemulti-crystalline(mc)siliconwafers,arethedominatingsubstratematerialsforsolarcellsincurrentphotovoltaic(PV)industry.However,thesetwokindsofmaterialsarenotthemostappropriateforthesolarcellfabrication.Ononehand,comparedtothemcsilicon,thesinglecrystallinesilicon,usuallytheB-dopedp-typeCzochralski(CZ)siliconwafers,resultsinhighersolarcellperfor-manceduetothelowdefectdensityandthewelltexturedsurfaceoflowreflectance.ButtheroundCZsiliconwafershavetobecutintopseudo-squareswithroundcornersforthesakeofsolarmodules,leadingtonotonlythelossofmaterialbutalsothecoveragelossofthefinalmodule.Whatisworse,theB-dopedp-typeCZsiliconsolarcellsareunavoidablysufferingfromtheseriouslight-induceddegradation(LID)ofefficiencyunderthesunlight[1],furtherdecreasingthecost-effectivenessofthismaterial.Ontheotherhand,thesquarecastmcsiliconismoreinexpensiveandhencemorecost-effectiveforsolarmodules.ButtheaverageefficiencyofmcsiliconsolarcellsisfarlowerthanthatofCZsiliconcellssincetheelectricalperformanceofmcsiliconsolarcellsisrestrainedbytheubiquitousstructuraldefectsinthemsuchasgrainboundariesandinparticularthehighdensityofdislocationsinsomegrainsandthemetallicimpurityprecipitateatthesestructuraldefectsites[2–7].Thesedefectscanactastherecombinationcenterforminoritycarriers,degradingthebulklifetimeofsiliconwafersandfurtherthesolarcellperformance.Anotherdisadvantageofmcsiliconwafershasbeenrecognizedasthehighsurfacereflectanceaftertexturing.Therandomorientationofgrainsmakesthealkalietchingfutile,andtheisochemicaletchingformcsiliconwafersisfarbehindthealkalietchinginreflectance,whichleadstotheopticallossesofsolarcells.Therefore,bothCZsiliconandmcsiliconhavetheirownprosandconsandthedecisiononthesubstratematerialsofsiliconsolarcellsdependsonthetradeoffbetweenthepoweroutputandthecost.Hereweintroducethecastsinglecrystallinesilicontechnique,whichisdesignedtoproducethesinglecrystallinematerialinheritingtheadvantagesofbothCZandmcsilicon.Thismaterialcanbeconsideredasanidealmaterialforsiliconsolarcells:square,singlecrystalline,oflowstructuraldefectdensityandwithlowfabricationcost.Duetotheindispensabilityofthecrucibleinthecastprocess,state-of-the-arttillnowisonlythecastquasi-singlecrystalline(QSC)siliconortheso-calledmono-likesilicon,quasi-monosilcion,etc.,thatis,thecastcrystalwithonelargedominatinggraininthecenterandsmallgrainssurrounded.Somerecentresultsupto17%efficiencywereachievedonQSCwafersusingseed-assisteddirectionalsolidifica-tion(SDS)process[8],providingapromisingfutureoftheapplicationofthecastQSCtechniqueinPVindustry.Thereafter,bysimplyemployingtheinexpensiveconventionalcasttechni-que,theindustrycanproducemorecost-effectiveQSCsiliconasthealternativesubstrateforthesolarcell.ContentslistsavailableatSciVerseScienceDirectjournalhomepage::10.1016/j.solmat.2012.02.024nCorrespondingauthor.Tel.:þ8657187953003;fax:þ8657187952322.E-mailaddress:[e-mail](X.Yu).SolarEnergyMaterials&SolarCells101(2012)95–101Inthiswork,wehavedemonstratedthewholeprospectanddetailedanalysisofcastQSCsiliconwiththeindustrialstandardsizeusingaSDSprocess.ItisfoundthattheQSCsiliconsolarcellsgenerallyhavebetterperformancethanthecastmcsiliconsolarcellsmainlybecauseoftheabsenceofgrainboundaries,thegreatreductionofdislocationsandthegoodqualityofsurfacetextur-ization.Ithasalsobeenfoundthatthelightinduceddegradation(LID)intheQS