Optoelectronic Analysis of Bismuth Sulfide and Copper-Doped Bismuth Sulfide Thin Films

Bismuth sulfide (Bi₂S₃), which has an optimal bandgap range and high absorption coefficient, is an attractive candidate for photovoltaic applications. Undoped and Cu-doped Bi₂S₃ thin films with different Cu content have been deposited by the solution growth technique. Bismuth nitrate and thioacetamide were used as bismuth and sulfur precursors, while ethylene diamine tetra-acetic acid was used as the complexing agent. The results show that all the deposited thin films are appreciated absorbers in the UV–Vis region. Results from the spectrophotometer showed that values of refractive index (n) ranged between 1.4 and 1.8 with an extinction coefficient (k) of 0.12–0.42. PL analysis showed a strong characteristic peak of Bi₂S₃ at 555 nm while the intensity gradually reduces with increasing Cu²⁺ content. Parental intrinsic defects of orthorhombic Bi₂S₃ make it an n-type charge carrier which incorporates Cu²⁺ in the orthorhombic crystal phase. The crystal lattice also prefers to act as a donor by increasing the number of electron carriers in Bi₂S₃ thin films.