8.1% efficient Cu2Zn(Sn,Ge)(S,Se)4 solar cell based on a single-target sputtering method

In this paper, we prepared Cu2Zn(Sn,Ge)(S,Se)4 (CZTGSSe) films based on a single-target sputtering method. This method involves the sputtering of precursor film from a compound target and a following selenization process with Se and GeSe2. The properties of the CZTGSSe film was compared with the CZTSSe film which was prepared using the same process but without using GeSe2 during the selenization. We find the usage of GeSe2 can incorporate Ge element into the selenized films and modify its composition. The crystallization process in the films is influenced and a uniform morphology can be achieved by using GeSe2. The GeSe2 may also influence the defect formation and electrical properties of the selenized films. By using GeSe2 during the selenization process, the efficiency of the solar cell can be improved from 4.2% for CZTSSe to 8.1% for CZTGSSe.