Formation of Cu 2 ZnSnS 4 and Cu 2 ZnSnS 4 -CuInS 2 Thin Films Investigated by In-Situ Energy Dispersive X-Ray Diffraction

Chalcopyrite CuInS 2 and the structurally related kesterite Cu 2 ZnSnS 4 are known as photovoltaic absorber materials. In this study different precursor thin films of the quaternary Cu-Zn-Sn-S system (stacking: Mo/CuS/ZnS-SnS) and of the pentenary Cu-In-Zn-Sn-S system (stacking: Mo/CuIn/ZnS-SnS) were annealed in sulfur atmosphere. The predominant crystalline phases were detected by in-situ energy dispersive X-ray diffraction (EDXRD). Additionally the X-ray fluorescence signals of the film components were recorded to detect diffusion effects. For the quaternary system we found ZnS, CuS, Cu 2-x S, Sn 2 S 3 and SnS as main binary phases during annealing. The Sn 2 S 3 -SnS phase transition had a significant impact on the later formation of ternary/quaternary phases. A high diffusivity of copper can explain the little influence of the precursor stacking on the reaction path and may also be responsible for the poor adhesion of the films. For annealing temperatures above 450°C Cu 2 ZnSnS 4 can be identified clearly by XRD. The incorporation of indium in the system leads to new diffraction peaks which can be explained by the formation of solid solutions in the system CuInS 2 -Cu 2 ZnSnS 4 .