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 degrees C to 400 degrees 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 degrees C showed large crystallites with minimum lattice strain and dislocation density. Raman spectra exhibited three major peaks that correspond to the Ag and B1g 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 Omega.cm at Ts = 350 degrees C. The Bi2S3 films sulfurized at 350 degrees 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.