inent ▁manufact ur ers ▁of ▁C IG S ▁phot ov olta ics ▁were ▁the ▁now - bank rupt ▁companies ▁N anos olar ▁and ▁Sol y nd ra . ▁Current ▁market ▁leader ▁is ▁the ▁Japanese ▁company ▁Sol ar ▁Front ier , ▁with ▁Global ▁Sol ar ▁and ▁G SH K ▁Sol ar ▁also ▁producing ▁solar ▁modules ▁free ▁of ▁any ▁heavy ▁met als ▁such ▁as ▁cad m ium ▁and / or ▁lead . ▁ ▁Properties ▁▁ ▁C IG S ▁is ▁a ▁I - III - VI 2 ▁comp ound ▁sem icon duct or ▁material ▁composed ▁of ▁co pper , ▁ind ium , ▁gal li um , ▁and ▁selenium . ▁The ▁material ▁is ▁a ▁solid ▁solution ▁of ▁co pper ▁ind ium ▁s elen ide ▁( o ften ▁abbre vi ated ▁" C IS ") ▁and ▁co pper ▁gal li um ▁s elen ide , ▁with ▁a ▁chemical ▁formula ▁of ▁Cu In x G a ( 1 - x ) Se 2 , ▁where ▁the ▁value ▁of ▁x ▁can ▁vary ▁from ▁ 1 ▁( p ure ▁co pper ▁ind ium ▁s elen ide ) ▁to ▁ 0 ▁( p ure ▁co pper ▁gal li um ▁s elen ide ). ▁It ▁is ▁a ▁t etra hed r ally ▁bond ed ▁sem icon duct or , ▁with ▁the ▁ch al copy rite ▁cry stal ▁structure . ▁The ▁band g ap ▁var ies ▁continu ously ▁with ▁x ▁from ▁about ▁ 1 . 0 ▁e V ▁( for ▁co pper ▁ind ium ▁s elen ide ) ▁to ▁about ▁ 1 . 7