Influence of thickness and annealing temperature on properties of solution processed bismuth sulfide thin films.

Non-toxic, stable, and earth abundant bismuth is an ideal alternative to poisonous lead in environmentally friendly perovskite solar cell devices. Bi₂S₃ thin film is a metal chalcogenide, which presents substantial promise because of its optical and electronic properties. In contrast to expensive methods, there are few studies in the literature on n-Bi₂S₃ thin films prepared using low-cost sol–gel method. Detailed studies on the preparation of Bi₂S₃ thin film structures by easy, non-toxic and low-cost sol–gel methods have not yet been reported. Therefore, in this study, Bi₂S₃ thin films were prepared by sol–gel spin coating method. The effects of the thickness and annealing temperature of the films on the film properties are elaborated through crystallinity, morphological and optoelectronic characterizations. The study indicated that both the thickness and the annealing temperature have a great influence on the properties of the films. Thickness-dependent analysis revealed that the films prepared at 650 nm thickness exhibited the best properties; orthorhombic phase polycrystalline structure and n-type conductivity. The room temperature electrical resistivity is in the order of 10⁵ Ω cm. Champion film with optimum crystallinity was achieved by annealing at 350 °C, while the best optoelectronic properties acquired by annealing at 400 °C. The direct optical band gap and crystallite size were 1.5 eV and 18.4 nm, respectively. Additionally, the high-absorption coefficient was in the order of 10⁵ cm⁻¹ state that the suitability of the material for optoelectronic applications. [ABSTRACT FROM AUTHOR]