Growth of Cu2SnS3 thin films by a two-stage process: structural, microstructural and optical properties

Copper tin sulfide (Cu2SnS3) thin films were grown by a two-stage process of sequential deposition of precursor layers CuS and SnS by chemical bath deposition technique followed by annealing in sulfur atmosphere. Two stacks of SnS–CuS thin films were prepared in which SnS thickness alone was varied keeping CuS film thickness fixed in an attempt to optimize SnS layer thickness to obtain Cu2SnS3 (CTS). The annealed films were characterized by studying their structural, microstructural and optical properties. X-ray diffraction analysis of the films obtained by annealing stack S-I revealed that they are multi-phase containing Cu2SnS3 and the secondary phases, Sn2Sn3 and Sn-rich CTS phase Cu2Sn3S7. Films obtained on annealing stack S-II resulted in monoclinic CTS phase with minor Cu2Sn3S7, tetragonal/cubic CTS phases. The direct optical band gap of monoclinic CTS phase is found to be 0.82 eV.