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.