Fabrication of Cu2SnS3 thin film solar cells by sulphurization of sequentially sputtered Sn/CuSn metallic stacked precursors

Abstract

In this present work, we report a novel fabrication technique of ternary Cu2SnS3 (CTS) thin films by sulphurization of sequentially sputtered Sn/CuSn (elemental/alloy) stacked metallic precursors. The focal aim of our investigation is on the impact of metallic precursors’ Cu/Sn ratio on the overall material properties of CTS films, which in turn, influence the photovoltaic device performance. All CTSs exhibited polycrystalline films with a mixture monoclinic CTS and orthorhombic SnS compound, p-type conductivity, and optical band gap in the range of 0.84–0.90 eV. Metallic precursor with Cu/Sn ratio of 1.09 produced optimum CTS film with post-sulphurization Cu/Sn ratio of 1.98 and highest conversion efficiency of 0.71%, respectively, despite exhibiting pronounced formation of SnS secondary phase. The correlation between XRD, Raman, and SEM-EDX outcomes revealed that CTS films from metallic precursors with Cu/Sn ratio higher than 1.09 undergo severe microstructural degradation due to Sn-loss through decomposition of volatile SnS phase and consequently, resulted in poorer absorber layer quality and lower device performance. Finally, several efficiency impeding factors are discussed and practical propostions to overcome them are presented. © 2018 Elsevier Ltd