▁the ▁interface ▁increases ▁with ▁rough ness ▁while ▁ill umin ated ▁area ▁remains ▁constant , ▁decre asing ▁open ▁circuit ▁voltage ▁( V OC ). ▁Studies ▁have ▁also ▁linked ▁an ▁increase ▁in ▁defect ▁density ▁to ▁decre ased ▁V OC . ▁Re com bin ation ▁in ▁C IG S ▁has ▁been ▁suggested ▁to ▁be ▁domin ated ▁by ▁non - rad i ative ▁processes . ▁The oret ically , ▁recom bin ation ▁can ▁be ▁controlled ▁by ▁engineering ▁the ▁film , ▁and ▁is ▁extr insic ▁to ▁the ▁material . ▁ ▁Production ▁ ▁Film ▁production ▁▁ ▁The ▁most ▁common ▁vac u um - based ▁process ▁is ▁to ▁co - ev apor ate ▁or ▁co - s put ter ▁co pper , ▁gal li um , ▁and ▁ind ium ▁onto ▁a ▁substr ate ▁at ▁room ▁temperature , ▁then ▁an ne al ▁the ▁resulting ▁film ▁with ▁a ▁s elen ide ▁v apor . ▁An ▁alternative ▁process ▁is ▁to ▁co - ev apor ate ▁co pper , ▁gal li um , ▁ind ium ▁and ▁selenium ▁onto ▁a ▁he ated ▁substr ate . ▁ ▁A ▁non - v acu um - based ▁alternative ▁process ▁depos its ▁nan op articles ▁of ▁the ▁prec ursor ▁materials ▁on ▁the ▁substr ate ▁and ▁then ▁s inter s ▁them ▁in ▁situ . ▁Elect ro pl ating ▁is ▁another ▁low ▁cost ▁alternative ▁to ▁apply ▁the ▁C IG S ▁layer . ▁ ▁The ▁following ▁sections ▁outline ▁the ▁various ▁techniques ▁for ▁prec ursor ▁de position ▁processing , ▁including ▁s put ter ing ▁of ▁met all ic ▁layers ▁at ▁low ▁temper atures