New World-Record Efficiency for Pure-Sulfide Cu(In,Ga)S2 Thin-Film Solar Cell With Cd-Free Buffer Layer via KCN-Free Process

World-record conversion efficiency of 15.5%, which is a number independently certified by an external accredited laboratory, was achieved on a pure-sulfide Cu(In,Ga)S
₂
(CIGS) thin-film solar cell fabricated by metal sputtering and H
₂
S gas sulfurization. This is the highest conversion efficiency reported for pure-sulfide CIGS thin-film solar cells. We exceeded the limit of 15% efficiency thanks to the buffer layer optimization. The buffer layer consists of Cd-free materials, and the absorber was fabricated via a KCN-free process.