Full-Space Potential Gradient Driven Charge Migration inside BiFeO₃ Photocathode

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.