Currently, the highest efficiency of CIGS solar cells with conventional CdS buffer layers is obtained at Eg = 1.15 eV, and theoretically the highest performance is expected at Eg = 1.4–1.5 eV. However, at Eg ≥ 1.3 eV, the CdS/CIGS interface has a cliff-type conduction band offset, which results in large carrier recombination and low open circuit voltage. In this study, we applied Zn1−xSnxO as a wide-gap buffer layer to improve the open-circuit voltage and conversion efficiency of wide-gap CIGS thin-film solar cells.
