Probing the Performance Limitations in Thin-Film FeVO₄ Photoanodes for Solar Water Splitting

FeVO₄ is a potentially promising n-type multimetal oxide semiconductor for photoelectrochemical water splitting based on its favorable optical band gap of ca. 2.06 eV that allows for the absorption of visible light up to around 600 nm. However, the presently demonstrated photocurrent values on FeVO₄ photoanodes are yet considerably low when comparing with α-Fe₂O₃, although FeVO₄ can absorb comparable wavelengths of sunlight as α-Fe₂O₃. Donor-type doping and constructing nanoporous film morphology have afforded desirable (but far from satisfactory) improvements in FeVO₄ photoanodes, whereas the fundamental properties, such as absorption coefficients and the nature of optical transition, and a quantitative analysis of the efficiency losses for FeVO₄ photoanodes remain elusive. In the present study, we conduct a thorough experimental analysis of structural, optical, charge transport, and surface catalysis properties of FeVO₄ thin films to investigate and clarify how and where the efficiency losses occur. Based on the results, the charge recombination pathways and light-harvesting loss in FeVO₄ thin-film photoanodes are identified and quantitatively determined. Our study will deepen the understanding on the photoelectrochemical behaviors of FeVO₄ photoanodes and will also shed light on the optimization routes to engineer this material to approach its theoretical maximum.