Substrate temperature dependent physical properties of SnS1−xSex thin films

Recently, researchers showed great interest on SnS1−xSex alloy films because of their tunable physical properties that are suitable as an absorber layer in thin film solar cells. In the present work, SnS1−xSex thin films were deposited by thermal co-evaporation of SnS and Se at different substrate temperatures ranging from 200 to 350 °C. The influence of substrate temperature (Ts) on composition, structure, surface morphology, topography and optical properties of as-deposited films was investigated using appropriate techniques and the results are reported in detail. The EDS analysis of SnS1−xSex films showed that Sn/(S + Se) ratio was changed from 0.84 to 1.16 with increase of substrate temperature. All the films were polycrystalline in nature, exhibiting (111) plane as preferred orientation with orthorhombic crystal structure. From W–H analysis, the crystallite size and lattice strain in the films were evaluated, where the crystallite size varied in the range, 9–22 nm with substrate temperature. The layers showed a change in the shape of grains with the rise of substrate temperature, where the grain size has increased with Ts. The topographical results indicated an indirect relation between surface roughness and average grain size with change in substrate temperature. The band gap energy values of the films was decreased with increase of Ts and varied in the range, 1.59–1.46 eV. In addition, the photoconductivity measurements revealed that the as-deposited SnS1−xSex films had bimolecular type recombination (γ ~ 0.5) of photo-generated charge carriers.