Structural and optical properties of Cu₂SnS₃ and Cu₃SnS₄ thin films by successive ionic layer adsorption and reaction

Thin films of Cu₂SnS₃ and Cu₃SnS₄ were obtained by sulfurizing (Cu, Sn)S structured precursors prepared by successive ionic layer absorption and reaction method. The results of energy dispersive spectroscopy (EDS) indicate that some loss in Sn with increasing sulfurization temperature. For the sulfurization temperatures of 380, 400 and 500 °C, tetragonal (I-42m) Cu₂SnS₃, cubic (F-43m) Cu₂SnS₃ and tetragonal (I-42m) Cu₃SnS₄ were formed, respectively. The combination of X-ray diffraction (XRD) results and Raman spectroscopy reveals that there are small Cu_2−x S phase existing in the CTS thin films (400 and 500 °C). Scanning electron microscopy was used to study the morphology of the layers. The ternary compounds present a high optical absorption coefficient (>10⁴ cm⁻¹). The band gap energy (E _g ) of the CTS thin films is estimated by reflection spectroscopy. The ternary compounds present a high optical absorption coefficient (>10⁴ cm⁻¹). The estimated band gap energy (E _g ) is 1.05 eV for tetragonal (I-42m) Cu₂SnS₃, 1.19 eV for cubic (F-43m) Cu₂SnS₃, and 1.22 eV for tetragonal (I-42m) Cu₃SnS₄.