Highly efficient Cu(Ga,In)(S,Se)2 thin film solar cells with zinc-compound buffer layers

Abstract Chemical bath deposited Zn-compound buffer layers have been applied as an alternative to the CdS buffer layer in the development of Cu(In,Ga)(S,Se)2 (CIGSSe) thin film solar cells. We used CIGSSe absorbers developed by Shell Solar for large-scale production. When ZnO is sputtered directly on such absorbers, very poor performances are obtained. In contrast, when the CIGSSe films are treated in electrolyte containing Zn-ions before sputtering, device efficiency of 12% is achieved. Including a sulfur or selenium source, we have developed a process to fabricate Cd-free CIGSSe devices with over 14% efficiency, certified at NREL. The structure and composition of the CBD-ZnSe on CIGSSe surface were investigated. The growth mechanism of chemical bath deposited ZnSe and ZnS on CIGSSe are discussed.