New Route for Fabrication of High-Quality Zn(S,O) Buffer Layer at High Deposition Temperature on Cu(In,Ga)Se$_2$ Solar Cells

Employing Cd-free buffer layer for Cu(In,Ga)Se2 (CIGS) solar cells is very important for improving the device power conversion efficiency and for solving the environmental issues of Cd for mass production. Zn(S,O) buffer layer as one of the most promising alternatives to CdS have shown higher short-circuit current density JSC but much lower open-circuit voltage V
_OC
due to the improper energy alignment with CIGS. In this study, we developed a novel chemical bath deposition process that effectively removes the stationary bubbles and enables the growth of high-quality Zn(S,O) thin film at high temperatures. Devices with Zn(S,O) buffer layer grown at 95 °C have shown V
_OC
comparable to that of devices with CdS buffer layer. Systematic characterization results suggest that our method leads to Zn(S,O) buffer layers with larger oxygen concentration and thus better band alignment with CIGS layer, which well explains the improved V
_OC
and power conversion efficiency.