Full-space potential gradient driven charge migration inside BiFeO₃ Photocathode

Abstract

Solar–fuel conversion depends on effective collection of photocarriers in the photoelectrode. In practice, however, considerable photocarriers are lost in the bulk through recombination due to the absence of a driving force. To overcome this, herein, a full-space electric field is induced in BiFeO₃ photocathodes by building a gradient homojunction through Fermi level engineering. As expected, the BiFeO₃ photocathodes with forward electric field show significantly enhanced performance: a state-of-the-art photocurrent of −1.02 mA·cm⁻² at 0.5 V vs RHE and H₂O₂ production of 380 mmol·(L·m²)⁻¹ within 50 min. First-principles calculations and experimental analysis suggest that the Bi vacancies as shallow acceptors can significantly modulate the Fermi level of BiFeO₃. The resulting internal electric field serves as an additional driving force to promote charge collection. This work provides an approach to induce a full-space electric field in semiconductor films through gradient defects modulation, which can be broadly applied to other optoelectronic systems.