Fabricatinghighlyefficient Cu(In,Ga)Se2 solar cellsatlow glass-substratetemperaturebyactivegalliumgradingcontrol

WehavesystematicallyinvestigatedthegalliumgradinginCu(In,Ga)Se2 (CIGS) solarcellsgrownonglass at lowsubstratetemperaturebyanumberoftechniquesincludingX-raydiffraction,scanningelectron microscopy,energyX-raydispersivespectrometry,andphotoluminescencespectroscopy.Theresults revealthattheperformanceoftheCIGSsolarcellsdepositedatlowsubstratetemperaturestrongly depends onthegalliumgradingandthemicro-structuresofthethin films. Bymodifyingthe conventionalthree-stageco-evaporationprocessfromelementalsources,inparticularinthe first and third stageforCIGSgrowthtoreduceGagrading,ithasbeenshownthatfabricationofCIGSsolarcells at lowsubstratetemperaturewithefficiency comparabletothatathightemperatureisachievable. Tooptimizethedeviceefficiency,thegalliumgradinginthe(InGa)2Se3 precursor growninthe first stage and theGacontentinthethirdstagearerequiredtobecarefullydesignedtomatchtheemployed substratetemperature.