▁ 5 0 0   ° C . ▁Films ▁formed ▁at ▁lower ▁temper atures ▁from ▁element al ▁Se ▁were ▁Se ▁def ic ient , ▁but ▁had ▁multiple ▁phases ▁including ▁metal ▁s elen ides ▁and ▁various ▁allo ys . ▁Use ▁of ▁H 2 Se ▁provides ▁the ▁best ▁compos itional ▁uniform ity ▁and ▁the ▁largest ▁gra in ▁sizes . ▁However , ▁H 2 Se ▁is ▁highly ▁to xic ▁and ▁is ▁class ified ▁as ▁an ▁environmental ▁ha z ard . ▁ ▁S put ter ing ▁of ▁met all ic ▁layers ▁followed ▁by ▁s elen ization ▁▁ ▁In ▁this ▁method ▁a ▁metal ▁film ▁of ▁Cu , ▁In ▁and ▁Ga ▁is ▁s put tered ▁at ▁or ▁near ▁room ▁temperature ▁and ▁react ed ▁in ▁a ▁Se ▁atmosphere ▁at ▁high ▁temperature . ▁This ▁process ▁has ▁higher ▁through put ▁than ▁co ev ap oration ▁and ▁compos itional ▁uniform ity ▁can ▁be ▁more ▁easily ▁achieved . ▁ ▁S put ter ing ▁a ▁stack ed ▁mult il ayer ▁of ▁metal ▁– ▁for ▁example ▁a ▁Cu / In / G a / C u / In / G a ... ▁structure ▁– ▁produces ▁a ▁sm o other ▁surface ▁and ▁better ▁cry st all inity ▁in ▁the ▁absor ber ▁compared ▁to ▁a ▁simple ▁bil ayer ▁( C u - G a ▁al loy / In ) ▁or ▁tr il ayer ▁( C u / In / G a ) ▁s put ter ing . ▁These ▁attributes ▁result ▁in ▁higher ▁efficiency ▁devices , ▁but ▁forming ▁the ▁mult il ayer ▁is ▁a ▁more ▁complicated ▁de position ▁process