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

Abstract

Copper tin sulfide (Cu 2 SnS 3 ) 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 Cu 2 SnS 3 (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 Cu 2 SnS 3 and the secondary phases, Sn 2 Sn 3 and Snrich CTS phase Cu 2 Sn 3 S 7 . Films obtained on annealing stack S-II resulted in monoclinic CTS phase with minor Cu 2 Sn 3 S 7 , tetragonal/cubic CTS phases. The direct optical band gap of monoclinic CTS phase is found to be 0.82 eV.

Effect of the stacking order, annealing temperature and atmosphere on crystal phase and optical properties of Cu2SnS3

“…This synthesis route is regarded as an optimal solution to avoid the formation of CTS and ZnS as secondary phases during the growth of CZTS 21 . On the other hand, CTS is a p-type semiconductor with a high absorption coefficient and a suitable band gap (0.9–1.40 eV) that can be used as an absorber layer in TFSC 22 – 24 . The tuning of the band gap is possible due to the polymorphic nature of the CTS material 25 , which crystallizes in three structures: cubic (E g = 0.96 eV), monoclinic (E g = 0.94 eV), and tetragonal (E g = 1.35 eV) 26 – 28 .…”