The search for suitable materials for solar water splitting is addressed with combinatorial material science methods. Thin film Fe-V-O materials libraries were synthesized using combinatorial reactive magnetron cosputtering and subsequent annealing in air. The design of the libraries comprises a combination of large compositional gradients (from Fe10V90O x to Fe79V21O x) and thickness gradients (from 140 to 425 nm). These material libraries were investigated by high-throughput characterization techniques in terms of composition, structure, optical, and photoelectrochemical properties to establish correlations between composition, thickness, crystallinity, microstructure, and photocurrent density. Results show the presence of the Fe2V4O13 phase from ∼11 to 42 at. % Fe (toward low-Fe region) and the FeVO4 phase from ∼37 to 79 at. % Fe (toward Fe-rich region). However, as a third phase, Fe2O3 is present throughout the compositional gradients (from low-Fe to Fe-rich region). Material compositions with increasing crystallinity of the FeVO4 phase show enhanced photocurrent densities (∼160 to 190 μA/cm2) throughout the thickness gradients whereas compositions with the Fe2V4O13 phase show comparatively low photocurrent densities (∼28 μA/cm2). The band gap energies of Fe-V-O films were inferred from Tauc plots. The highest photocurrent density of ∼190 μA/cm2 was obtained for films with ∼54 to 66 at. % Fe for the FeVO4 phase with ∼2.04 eV for the indirect and ∼2.80 eV for the direct band gap energies.
Keywords: Fe−V−O thin films; combinatorial synthesis; high-throughput characterization; solar water splitting; transmission electron microscopy.