Comprehensive physical and chemical properties of sulfurized Bi2S3 films prepared by CBD process

Bismuth sulfide (Bi₂S₃) is one of the novel semiconductors that has gained significant interest in recent years for the development of solar photovoltaics. The present work reports a comprehensive analysis of the physical and chemical properties of chemical bath deposited (CBD) Bi₂S₃ films upon sulfurization in relation to sulfurization temperature. The as-grown Bi₂S₃ films were subjected to sulfurization at temperatures ranging from 250 °C to 400 °C for a duration of one hour. X-ray diffraction patterns indicated the (130) plane as the predominant orientation for all sulfurized layers, which exhibited the orthorhombic crystal structure. Films prepared at 350 °C showed large crystallites with minimum lattice strain and dislocation density. Raman spectra exhibited three major peaks that correspond to the A_g and B_1g vibrational modes of Bi₂S₃ with a space group of Pbnm. The films exhibited a rough surface morphology that increased with increasing sulfurization temperature. Energy dispersive spectroscopy study confirmed the nearly stoichiometric composition of Bi and S, whereas the X-ray photoelectron spectroscopy analyses revealed the presence of Bi³⁺ and S²⁻ oxidation states. With increasing sulfurization temperature, the optical band gap values decreased from 1.66 eV to 1.37 eV, which closely aligns with optimal absorber layer requirements. Hall effect measurements revealed p-type conductivity, with the lowest resistivity value 0.24 Ω.cm at T_s = 350 °C. The Bi₂S₃ films sulfurized at 350 °C exhibited good structural, morphological, optical, and electrical properties that are highly suitable for absorber layers in thin-film solar cells in a cost-effective manner.