Formation of Cu2ZnSnS4 and Cu2ZnSnS4-CuInS2 Thin Films Investigated by In-Situ Energy Dispersive X-Ray Diffraction
AbstractChalcopyrite CuInS2 and the structurally related kesterite Cu2ZnSnS4 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, Cu2-xS, Sn2S3 and SnS as main binary phases during annealing. The Sn2S3-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 Cu2ZnSnS4 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 CuInS2-Cu2ZnSnS4.