Soft-sputtered p-type amorphous TeO₂ as a hole-selective interlayer enabling bias-free solar water splitting over Mo:BiVO₄ photoanodes

Efficient hole-selective interfaces are crucial for mitigating interfacial charge recombination and oxygen evolution reaction (OER) losses in BiVO₄-based photoanodes for bias-free solar water splitting. Here, we report an oxygen fraction–engineered p-type amorphous TeO₂ hole transport layer deposited by isolated plasma soft deposition and integrated into FTO/SnO₂/Mo:BiVO₄/TeO₂/CoFeO_x photoanodes. By optimizing the Ar/O₂ flow ratio during room-temperature IPSD process, ultrathin (∼10 nm) amorphous TeO₂ films exhibiting stable p-type conductivity and high optical transparency of 99.05% were obtained. Ultraviolet photoelectron spectroscopy reveals defect-induced band alignment that provides hole blocking at the SnO₂/Mo:BiVO₄ interface and electron blocking at the Mo:BiVO₄/TeO₂ interface, enabling efficient hole extraction toward the CoFeO_x OER catalyst. As a result, the optimized photoanode delivers a photocurrent density of 5.3 mA cm−2 at 1.23 V_RHE with an onset potential of 0.29 V_RHE and an applied bias photon-to-current efficiency of 2.2%. Bias-free tandem operation with a Cu₂O-based photocathode achieves a solar-to-hydrogen efficiency of water splitting systems.