Plasma-Tailored Intrinsic Defect Engineering for BiFeO ₃ 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 BiFeO 3 (BFO)-based homojunction was fabricated by precisely regulating oxygen vacancy (V O ) concentration via O 2 /Ar plasma treatment. The optimized BFO photocathode achieves a photocurrent density of ∼0.68 mA/cm 2 at 0.2 V vs RHE, nearly double that of pristine BFO (∼0.36 mA/cm 2 ), along with a high H 2 O 2 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 O 2 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.