Bismuth Silver Oxysulfide for Photoconversion Applications: Structural and Optoelectronic Properties

Single-phase bismuth silver oxysulfide (BiAgOS) was prepared by a hydrothermal method. Its structural, morphological, and optoelectronic properties were investigated and compared with those of bismuth copper oxysulfide (BiCuOS). Rietveld refinement of the powder X-ray diffraction measurements revealed that the BiAgOS and BiCuOS crystals have the same structure as ZrSiCuAs, tetragonal space group P4/nmm. X-ray photoelectron spectroscopy analyses confirmed that BiAgOS has a high purity, in contrast with BiCuOS, which tends to have Cu vacancies. The Ag has a monovalent oxidation state, whereas Cu is present in the +1 and +2 oxidation states in the BiCuOS system. Combined with experimental measurements, density functional theory calculations employing the range-separated hybrid HSE06 exchange-correlation functional with spin–orbit coupling quantitatively elucidated photophysical properties such as absorption coefficients, effective masses, and dielectric constants. BiCuOS and BiAgOS were found to have indirect bandgaps of 1.1 and 1.5 eV, respectively. Both possess high dielectric constants and low electron and hole effective masses. Therefore, these materials are expected to have strong exciton dissociation capabilities and excellent carrier diffusion properties. This study reveals that BiAgOS is a promising candidate for photoconversion applications.