Performance improvement of flexible CZTSSe thin film solar cell by adding a Ge buffer layer

Abstract Flexible CZTSSe thin film solar cells were prepared on Ti foil substrate. With adding a Ge buffer layer between the Ti foil substrate and the Mo back contact, CZTSSe thin film showed a better crystallization and less secondary phases. It was confirmed that Ge diffused into CZTSSe layer and had a promoting effect on Sn +4 state formation and stress release. The flexible CZTSSe solar cell with Ge buffer layer showed a conversion efficiency of 2.00%, which presented a 200% enhancement comparing to the solar cell without Ge buffer layer.