Effect of composition on high efficiency CZTSSe devices fabricated using co-sputtering of compound targets

Recent work on Cu₂ZnSn(S,Se)₄ (CZTSSe) has shown that it is an excellent candidate for use in thin film solar cells due to its earth abundant, inexpensive, non-toxic constituents and optimal material properties. However, the composition window for growth of CZTSSe capable of high efficiency is still unknown. The focus of this work is to use sputter deposition to synthesize this material as a thin film and determine a composition window for growth of high efficiency CZTSSe devices. CZTSSe thin films of various compositions were grown using co-sputtering of compound targets followed by an anneal at high temperature. Efficiency of devices was mapped as function of copper, zinc, tin, selenium and sulfur content in the films. Extraneous phases that are relatively benign (ZnS, SnS2) and those that are detrimental (Cu2S) to device performance were identified using x-ray diffraction. The range of efficiencies mapped in this work was 0-8% and the best efficiency achieved using this fabrication process was 9.3%.