Understanding phase evolution in CuSbS₂ absorbers via rapid sulfurization of Cu/Sb/Cu stacks

Copper-antimony-sulfide (CuSbS₂) is a promising absorber for use in thin-film solar cells. In this study, we report the fabrication of CuSbS₂ films by sulfurizing sequentially evaporated Cu/Sb/Cu stacks at 450 °C for 5 min and investigate the influence of Cu thickness (Cu-poor, Cu-correct, and Cu-rich) on the phase evolution. The film prepared with a Cu-poor composition exhibited the formation of phase-pure CuSbS₂ with several micron-sized grains uniformly grown on the surface, a bandgap energy of 1.55 eV, an electrical resistivity of 16.8 Ω cm, and a carrier concentration of 7.27 × 10¹⁷ cm⁻³. The CuSbS₂ film fabricated with the stoichiometric and Cu-rich composition contained a minor Cu₁₂Sb₄S₁₃ and Cu₃SbS₄ secondary phases with increased grain size, decreased bandgap (1.55–1.51 eV), electrical resistivity (8.63–5.59 Ω cm), and increased carrier concentration (1.63–2.28 × 10¹⁸ cm⁻³ cm⁻³). This investigation reveals that a slightly Cu-poor composition is required for the growth of phase-pure CuSbS₂ films suitable for thin-film solar cells.