Combinatorial Synthesis and High-Throughput Characterization of Fe-V-O Thin-Film Materials Libraries for Solar Water Splitting.

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 FeVO to FeVO ) 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 FeVO phase from ∼11 to 42 at. % Fe (toward low-Fe region) and the FeVO phase from ∼37 to 79 at. % Fe (toward Fe-rich region). However, as a third phase, FeO is present throughout the compositional gradients (from low-Fe to Fe-rich region). Material compositions with increasing crystallinity of the FeVO phase show enhanced photocurrent densities (∼160 to 190 μA/cm) throughout the thickness gradients whereas compositions with the FeVO phase show comparatively low photocurrent densities (∼28 μA/cm). The band gap energies of Fe-V-O films were inferred from Tauc plots. The highest photocurrent density of ∼190 μA/cm was obtained for films with ∼54 to 66 at. % Fe for the FeVO phase with ∼2.04 eV for the indirect and ∼2.80 eV for the direct band gap energies.