Deposition of bismuth sulfide and aluminum doped bismuth sulfide thin films for photovoltaic applications

Binary bismuth sulfide (Bi₂S₃) and ternary aluminum-doped bismuth sulfide (Al@Bi₂S₃) thin films were prepared by the chemical bath deposition method for photovoltaic applications. The newly designed materials synthesized at room temperature were thoroughly analyzed by several characterization techniques i.e., X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, optical absorption, thickness measurement, and Hall effect techniques. Correlation between structural, morphological, optical, electrical, and transport properties was evaluated. The parent material i.e., Bi₂S₃ is reported to have an orthorhombic phase, while doped derivatives revealed the amorphous phase. Optical band gaps in the range of 1.6–1.3 eV and absorption coefficients were found in the range of 10⁴ to 10⁶ cm⁻¹. The thickness of the films changed with the change in the composition of the solution matrix and the films were well adhered, compact, and crack free. Hall measurements show that the dominant carriers in all studied compounds were electrons and that the carrier density for ternary films is almost two orders of magnitude greater than binary Bi₂S₃. The disorderliness in these newly designed materials is traced through the estimation of the change in the Urbach energy.