Significantly different mechanical properties and interfacial structures of Cu2ZnSn(S,Se)4 films prepared from metallic and sulfur-contained precursors

• Comparative studies of precursor’s influences on Cu2ZnSn(S, Se)4 film formation are carried out.
• Mechanical properties of Cu2ZnSn(S, Se)4 films are experimentally studied.
• Film adhesion is significantly improved by sulfur incorporation into precursor.
• Interfacial Mo(S,Se)2 layer and voids are highly suppressed by sulfur incorporation into precursor.

To fill in the gap of experimental studies on the adhesion and mechanical properties of Cu2ZnSn(S,Se)4 (CZTSSe) films, mechanical measurements such as nano-indentation and scratch were performed on CZTSSe films prepared from metallic and partially sulfurized precursors on Mo substrates. Surprisingly and interestingly, obviously better film adhesion and elastic modulus values close to the theoretical predictions were achieved in the sample prepared using sulfur contained precursors, in comparison with the samples prepared using metallic precursors. Detailed characterization and analysis reveal that this better performance is attributed to a significantly improved CZTSSe/Mo interface when sulfur contained precursors are used. Mechanisms of the impacts of sulfur incorporation on the adhesion and mechanical properties of CZTSSe films and the suppression of the growth of unwanted Mo(S,Se)2 are analyzed and discussed, for potentially benefiting device performance.