Effect of Sn-layer addition to precursors on characteristics of Cu2ZnSn(S,Se)4 thin-film solar cell absorber

• Kesterite formed from sputtered Mo/Zn/(Cu + Sn) precursor showed poor adhesion.
• Selenized Mo/Sn/Zn/(Cu + Sn) precursor suppressed Sn loss and enhanced adhesion.
• Precursors were selenized at 550 °C and sulfurized at 550–590 °C under H2S/He flow.

Sequential sputtering and simultaneous sputtering were employed to prepare the following two precursor structures for kesterite thin films as photovoltaic absorbers: glass/Mo/Zn/(Cu + Sn) and glass/Mo/Sn/Zn/(Cu + Sn). The precursor films were then coated with a layer of Se via evaporation. The precursors were selenized at 550 °C and sulfurized at 550–590 °C under H2S/He gas flow. Inserting a thin (10–20 nm) layer of Sn at the interface between the Mo back contact layer and the Zn/(Cu + Sn) metal precursor suppressed Sn loss (e.g., from 7–15% to 2% loss) and improved the adhesion of Cu2ZnSn(S,Se)4 to the Mo layer by reducing the formation of ZnSe secondary phase. The thin Sn film is believed to induce the diffusion of Se or S to the bottom of the precursor layer, which is evident in the increased total Se + S content of the resulting CZTSSe films.