Studies on optical properties of Bi₂S₃ thin films synthesized by two-stage growth process

The present investigation involved the preparation of bismuth sulfide (Bi₂S₃) thin films using a two-stage process. Bi₂S₃ films were prepared by chemical bath deposition followed by sulfurization at various temperatures ranging from 250 to 400 °C. Transmittance and reflectance studies were conducted to determine the optical characteristics of the films formed at various sulfurization temperatures. The sulfurized thin films exhibited an optical band gap varied from 1.37 to 1.66 eV as the sulfurized temperature increased. The optical constants, the extinction coefficient (k) and refractive index (n), were determined. The other parameters such as optical conductivity, dissipation factor, dielectric constant dispersion parameters, the energy loss functions like the surface energy loss function, volume energy loss function, the ratio of carrier concentration to effective mass, and the plasma frequency were also evaluated in order to determine whether the Bi₂S₃ layers were suitable for use in solar cells.