Development of phase-pure CuSbS2 thin films by annealing thermally evaporated CuS/Sb2S3 stacking layer for solar cell applications

In this work, we report the preparation and study of phase-pure CuSbS2 thin films fabricated by a two-stage process; 1) the growth of CuS/Sb2S3/glass by stacking layers through a sequential evaporation of Sb2S3 and CuS powders, 2) the annealing treatment to the stack layer at different temperatures. Under optimized conditions for the adequate thicknesses of the CuS and Sb2S3 layers, three scenarios with dependence on the annealing temperature were obtained. i) Annealing conditions below 350 °C are insufficient for the complete formation of CuSbS2 because of its co-existence with Cu12Sb4S13 and unreacted Sb2S3. ii) 350 °C is identified as the suitable temperature for accomplishment phase-pure CuSbS2. iii) At 400 °C some percentage of CuSbS2 decomposed in Cu12Sb4S13. The quantification of phase content by Raman spectroscopy of CuSbS2 and Cu12Sb4S13 as a function of the annealing temperature is provided. In addition, differences in the compositional depth profile with the annealing condition were obtained, and chemical species such as Cu+ and Cu2+ for the Cu12Sb4S13 compound were distinguished by x-ray photoelectron spectroscopy analysis. It was found that photosensitivity of the CuSbS2 film is affected by the presence of Cu12Sb4S13 phase. Phase-pure CuSbS2 thin films had an optical band gap of 1.55 eV and absorption coefficient around 104 cm−1; the films showed p-type conductivity, electrical resistivity, carrier density and hole mobility of 37.6 Ω-cm, 4.9 × 1016 cm−3 and 4.0 cm2/V s, respectively, and the presence of a dominant level with activation energy of 0.32 eV. Finally, the electrical parameters of the fabricated CuSbS2 solar cell device are reported.