Sulfide Chalcopyrite Solar Cells––Are They the Same as Selenides with a Wider Bandgap?

Abstract

Sulfide chalcopyrite solar cells are receiving renewed interest since they have reached a certified efficiency above 15%. Due to their wider bandgap, they are interesting candidates for top cells in tandem applications. They share many properties with the much deeper studied selenide chalcopyrites, but also some important differences. While the structure of shallow and deep defects appears very similar, the phase diagram is different with a much smaller existence range of Cu-poor CuInS2. The problematic character of the surface of material grown under Cu excess is present in both sulfides and selenides. Both materials show increased tail states when grown Cu-poor. To achieve sufficient bulk quality of sulfide absorbers, higher growth temperatures and a higher supply of sodium appear to be necessary.