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.