▁with ▁catal yz ing ▁o xygen ▁absor ption . ▁O xygen ▁pass iv ates ▁Se ▁vac an cies ▁that ▁act ▁as ▁compens ating ▁don ors ▁and ▁recom bin ation ▁cent ers . ▁ <0x09> ▁Al loy ing ▁C IS ▁( C u In Se 2 ) ▁with ▁CG S ▁( C u G a Se 2 ) ▁increases ▁the ▁band g ap . ▁To ▁reach ▁the ▁ideal ▁band g ap ▁for ▁a ▁single ▁j unction ▁solar ▁cell , ▁ 1 . 5 ▁e V , ▁a ▁Ga /( In + G a ) ▁ratio ▁of ▁roughly ▁ 0 . 7 ▁is ▁optimal . ▁However , ▁at ▁r ati os ▁above ▁~ 0 . 3 , ▁device ▁performance ▁dro ps ▁off . ▁Indust ry ▁currently ▁targets ▁the ▁ 0 . 3 ▁Ga /( In + G a ) ▁ratio , ▁resulting ▁in ▁band g aps ▁between ▁ 1 . 1 ▁and ▁ 1 . 2 ▁e V . ▁The ▁decre asing ▁performance ▁has ▁been ▁post ulated ▁to ▁be ▁a ▁result ▁of ▁CG S ▁not ▁forming ▁the ▁O DC , ▁which ▁is ▁necessary ▁for ▁a ▁good ▁interface ▁with ▁C d S . ▁ ▁The ▁highest ▁efficiency ▁devices ▁show ▁substantial ▁text uring , ▁or ▁preferred ▁cry stal log raph ic ▁orientation . ▁A ▁( 2 0 4 ) ▁surface ▁orientation ▁is ▁observed ▁in ▁the ▁best ▁quality ▁devices . ▁A ▁smooth ▁absor ber ▁surface ▁is ▁preferred ▁to ▁maxim ize ▁the ▁ratio ▁of ▁the ▁ill umin ated ▁area ▁to ▁the ▁area ▁of ▁the ▁interface . ▁The ▁area ▁of