Plasma-Tailored Intrinsic Defect Engineering for BiFeO₃ Homojunctions: A Non-element Intrusive Doping Strategy

Homojunction engineering presents a promising route to enhance charge separation and transfer in photoelectrochemical (PEC) systems, provided that challenges such as controllable doping are addressed. Herein, a non-element intrusive doping strategy is proposed to construct homojunctions within perovskite-type semiconductors through intrinsic defect gradient engineering. A BiFeO₃ (BFO)-based homojunction was fabricated by precisely regulating oxygen vacancy (V_O) concentration via O₂/Ar plasma treatment. The optimized BFO photocathode achieves a photocurrent density of ∼0.68 mA/cm² at 0.2 V vs RHE, nearly double that of pristine BFO (∼0.36 mA/cm²), along with a high H₂O₂ production rate of 462.1 mmol·L^-1·h^-1·m^-2 and long-term stability. X-ray spectroscopy and optical simulations reveal that the treatment with an O₂ plasma reduces the surface V_O concentration, reduces the Fermi level, and establishes a continuous internal electric field across the homojunction to enhance electron transfer. Density functional theory (DFT) calculations further clarify the thermodynamic stability and electronic structure modulation induced by V_O regulation. This work provides a strategy for designing efficient photoelectrodes via intrinsic defect engineering.