Bismuth(III) Sulfide Films by Chemical Bath Deposition Method Using L-Cysteine as a Novel Sulfur Source

Thin films of bismuth(III) sulfide (Bi2S3) on fluorine doped tin oxide (FTO) coated glass slides were successfully formed by the chemical bath deposition (CBD) method. In this work, a new sulfur precursor L-cysteine was used instead of the typical sulfur precursors, such as urea, thiosulfate, or thioacetamide, used for the formation of the Bi2S3 films by the CBD method. The synthesized Bi2S3 thin film on the FTO substrate was subjected to characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and UV–Visible spectroscopy analysis. An X-ray diffraction analysis showed that, initially, Bi2S3 films of an amorphous structure with elemental sulfur impurities were formed on the FTO surface. During the annealing of the samples, amorphous Bi2S3 was transformed into its crystalline phase with an average crystallite size of about 22.06 nm. The EDS studies confirmed that some of the sulfur that was not part of the Bi2S3 was removed from the films during annealing. The influence of the morphology of Bi2S3 films on their optical properties was confirmed by studies in the UV-visible range.