Reactive sputtering of Cu2ZnSnS4 thin films — Target effects on the deposition process stability

Cu2ZnSnS4 (CZTS) is a promising material for thin film solar cells which contains only abundant elements. This work focuses on the stability of elemental composition of films deposited by reactive sputtering of CuSn alloy targets in H2S. Long equilibration times of several hours were observed. The main reason is the formation of a thick Cu2S layer on the target surface. Especially in areas with low erosion rate, the Cu2S thickness reaches up to 700 μm and is accompanied by a preferential loss of Sn from the target. Based on the results, it is suggested that the formation of Cu2S may be limited either by more uniform erosion of the target surface or by reduction of the H2S partial pressure.