Hydrothermally deposited Sb2S3 thin films: Effect of annealing conditions on the optoelectronic properties, the selenization, and photoelectrochemical performance

Sb₂S₃ is a no-toxic and earth-abundant semiconductor with suitable bandgap (1.7–1.8 eV) for opto-electronic devices operating in the UV–Vis region. It has strong optical absorption, and being a low-dimensional material shows anisotropic properties. Its favorable optoelectronic characteristics and compatibility with low-cost and scalable fabrication methods make it a strong candidate for photovoltaic and other optoelectronic applications. In this work a detailed study of the opto-electronic properties of the material Sb₂S₃ in relation to the post-deposition thermal processing of the thin films is discussed. The studies include the effect of annealing temperature, annealing duration, ambient pressure, and the partial substitution of sulfur (S) with selenium (Se). The studies were mainly focused on crystallite/grain orientation, Raman modes, and photocurrent response of the films subjected to the different annealing conditions. Raman analyses based on a reported empirical approach in literature showed that the quasi-1D [Sb₄S₆]_n chains are vertical, with an inclination of ≈ 16 degrees to the normal to the substrate, which remained within a 3 % change after the different annealing processes. The temperature and pressure variation studies found that the responsivity is maximum when [Sb₄S₆]_n chains are more closely aligned to the vertical, indicating a better charge transport. The role of S and Se vapor in the annealing chamber was manifested in the photoresponsivity. The films annealed in S atmosphere showed higher responsivity (5.29 × 10⁴ A/W) compared to those annealed without S (1.79 × 10⁴ A/W). The photoelectrochemical cell FTO/Au/Sb₂(S_0.71Se_0.29)₃/CdS achieved 6.52 mA/cm² current at 0 vs E_RHE which was further increased to 10.66 mA/cm² at 0 vs E_RHE after surface modification with Pt, attaining a PEC efficiency of 1.5 % at 0.2 E_RHE.