Growth and characterization of Cu2SnS3 (CTS), Cu2SnSe3 (CTSe), and Cu2Sn(S,Se)3 (CTSSe) thin films using dip-coated Cu–Sn precursor

Ternary compounds Cu₂SnS₃, Cu₂SnSe₃ and Cu₂Sn(S,Se)₃ thin films used in thin film solar cell applications were prepared at the first time by such a two-stage process that includes dip-coating of Cu–Sn precursors as distinct from vacuum-based fabrication methods followed by sulfurization/selenization of prepared precursors via rapid thermal processing at 550 °C. All prepared thin films revealed Cu-poor composition. X-ray diffraction and Raman spectra of the samples showed that Cu₂SnS₃ and Cu₂SnSe₃ thin films had a monoclinic structure as a dominant phase and additionally some secondary phases such as tetragonal Cu₂SnS₃ and orthorhombic Cu₃SnS₄. However, the tetragonal and orthorhombic phases had more impact on Cu₂Sn(SSe)₃ thin film. Compact, dense, and small grained surface morphologies were obtained for the Cu₂SnS₃ and Cu₂Sn(SSe)₃ thin films, while the surface morphology of the Cu₂SnSe₃ thin film had larger grained surface morphology. The Cu₂SnS₃ thin film demonstrated higher transmittance (~ 65%) and two different absorption edges that indicates formation of two band gap energy. Band gap values of Cu₂SnS₃, Cu₂Sn(SSe)₃ and Cu₂SnSe₃ thin films were found 0.97 eV (and 1.51 eV), 1.25 eV and 0.78 eV, respectively. The lowest resistivity (2.48 × 10⁻¹ Ω cm) and the highest carrier concentration (1.64 × 10¹⁹ cm⁻³) values were observed for Cu₂Sn(SSe)₃ thin film.