Tuning the electronic band structure and optoelectrical characteristics of ALD-grown Zn(O,S) buffer layers for SnS solar cells

Conduction band offset (CBO) is an important aspect in the development of SnS-based solar cells. Studies on buffer layers are needed to obtain a CBO that matches the SnS absorber layer. Zn(O,S) is a promising cadmium sulfide replacement for a thin film solar cell buffer layer due to its non-toxicity and large band gap, and its film characteristics can be optimized by adjusting the oxygen and sulfur ratio. However, very few studies have been conducted on processed Zn(O,S) film’s electronic band structure, and the absence is more serious for the case of atomic layer deposition (ALD) method. In this study, we deposited Zn(O,S) films with various ZnO/ZnS cycle ratios using the ALD supercycle method and identified their film characteristics and electronic band structures. Results showed that the Zn(O,S) films had high concentrations of ZnS compared to the ZnS cycle fraction. Mixing the ZnO and ZnS cycles reduced the film’s crystallinity and affected the Zn(O,S) films characteristics. Further, the electronic band structures were identified using UV–vis and UPS analysis. The Zn(O,S) films using 14:1 and 19:1 ZnO/ZnS cycle ratios showed an ideal flat CBO with SnS absorber.