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.