Effect of sulfur doping on the photocatalytic performance of sputtered BiVO₄ thin films

BiVO4 thin films doped with various concentrations of sulfur were fabricated using RF sputtering followed by post-deposition sulfurization. The incorporation of sulfur in the samples was calculated to be approximately 8-11 at% from the S2s peak in their X-ray photoelectron spectra. The optical bandgap of sulfur-doped BiVO4 was generally smaller than that of the undoped sample. BiVO4 films doped with similar to 8 at% sulfur showed the highest photoelectrochemical performance compared to the undoped sample. Almost similar minority-carrier lifetimes in undoped and low sulfur-doped BiVO4, measured by time resolve photoluminescence, suggest that the crystal qualities in terms of the recombination properties are roughly the same for both cases. Thus, although further investigation may be necessary, the improved photocurrent in 8 at% sulfur-doped BiVO4 in our study can roughly be attributed to the decrease in the bandgap, which facilitates more photoexcited carriers to contribute to the photoelectrochemical reaction. A further increase in sulfur doping above 10 at% distorted the BiVO4 local crystal structure, inducing defects, thus resulting in a lower photocurrent.