Effect of Ramped Oxygen Flow During Magnetron Sputtering on the Structural, Optical, and Photoelectrochemical Properties of WO _3‐x Thin Films

ABSTRACT The growing need for sustainable energy sources to replace fossil fuels has led to the exploration of green hydrogen production. Photoelectrochemical (PEC) water splitting, utilizing photoanodes composed of semiconductors such as WO 3 , presents a promising solution. In this work, WO 3‐x thin films were deposited by DC reactive magnetron sputtering, and the effect of oxygen flow ramping during deposition on the films' structural, optical, and photoelectrochemical properties was investigated. The films exhibited the monoclinic γ‐WO 3 phase, with changes in their structural properties observed through X‐ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). Transmittance measurements confirmed that films grown under low oxygen flow were visually opaque and dark. In contrast, those grown under intermediate to high oxygen flow rates exhibited significantly higher transparency, consistent with lower oxygen‐vacancy concentrations. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) revealed enhanced charge transfer and photoactivity in samples with intermediate oxygen flow rates. The results suggest that oxygen vacancy engineering, combined with precise control of deposition conditions, significantly enhances the photoelectrochemical performance of WO 3‐x films. The study also highlights the importance of post‐deposition annealing conditions for optimizing the material's photoelectrochemical response.