Tunable phase junctions in Bi2O3–BiVO4 thin films via reactive magnetron Co-sputtering for efficient carrier separation and enhanced photoelectrochemical performance

Engineering efficient photoelectrodes requires precise control over the structure, interfaces, and optoelectronic properties of thin semiconductor films. Here, reactive magnetron co-sputtering (RMS), combined with post-deposition annealing, was used to achieve in situ formation of Bi 2 O 3 –BiVO 4 thin films with tunable phase composition and p–n heterojunctions. Unlike conventional wet-chemical methods, this approach allows direct control of Bi/V ratios during deposition, while annealing governs phase evolution on the substrate. By adjusting the Bi/V target power ratio and annealing temperature, Bi 2 O 3 –dominant, pure BiVO 4 , and mixed-phase Bi 2 O 3 –BiVO 4 heterojunction films were synthesized, as confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. High-temperature grazing incidence X-ray diffraction revealed phase transitions, with Bi 2 O 3 stable at lower temperatures and BiVO 4 forming above ∼400 °C. Photoelectrochemical characterization showed that Bi 2 O 3 –BiVO 4 heterojunction films outperform single-phase films, owing to enhanced charge separation driven by internal electric fields at the p–n interface. The optimized BO/BVO–1 film exhibited photocurrent densities 2.5–9 times higher than pure BiVO 4 , depending on applied bias. Electrochemical impedance spectroscopy indicated reduced charge transfer resistance and suppressed recombination in the heterojunction samples. These findings demonstrate that RMS combined with annealing provides a scalable route for phase engineering and heterojunction design in thin-film photoelectrodes. • Bi 2 O 3 –BiVO 4 heterojunction films deposited via reactive magnetron co-sputtering • Phase junctions tuned by Bi/V sputtering power ratio and annealing temperature • Optimized film shows 2.5–9× higher photocurrent than BiVO 4 (1.23–1.63 V vs RHE) • EIS confirms reduced charge-transfer resistance in heterojunction films • Formation of p–n heterojunctions improve interfacial charge separation efficiency