Tuning Optoelectronic Properties and Photoelectrochemical Performance of \b{eta}-TaON via Vanadium Doping
The application of beta-TaON for solar-driven water splitting is hindered by limitations in phase purity, stoichiometry, crystallinity, visible-light absorption, carrier mobility, and high recombination rates. This study investigates the impact of vanadium doping (0-25 at.% V) on the structural, optoelectronic, and photoelectrochemical properties of beta-TaON using both experimental and density functional theory (DFT) approaches. Phase-pure beta-TaON is retained up to 10 at.% V, beyond which secondary phases (Ta2O5 and VN) form, indicating a threshold of ~10 at.% under the applied synthesis conditions. All samples exhibit a porous microstructure. Increasing vanadium content induces a redshift in the absorption edge, reducing the bandgap from 2.72 eV (undoped) to 2.38 eV at 25 at.% V for the main beta-TaON phase, in agreement with DFT results. X-ray photoelectron spectroscopy confirms substitutional incorporation of V5+ for Ta5+ in the beta-TaON lattice. DFT calculations reveal reduced electron effective mass, enhanced n-type conductivity, and favorable band edge shifts enabling spontaneous overall water splitting at <=10 at.% V. Photoelectrochemical measurements show improved photocurrent and more negative onset potentials for 5-10 at.% V, while higher V doping degrades performance due to phase segregation, which likely increases recombination and hinders interfacial charge transport. Vanadium doping (<=10 at.% V) is an effective strategy for tuning the electronic structure and enhancing the optical properties and photoelectrochemical performance of beta-TaON.