In-Plane Ferroelectric p/n Superstructure Photoelectrode for Bias-Free Solar-Fuel Conversion.

Multijunction photoelectrodes, which generate active photocarriers with sufficient energy to drive unassisted solar-fuel conversion, represent a promising avenue for sustainable energy applications. However, achieving controllable p/n-type doping and high-quality growth remains a challenge for most emerging metal oxide semiconductors. In this study, we demonstrate the creation of in-plane ferroelectric p/n homojunction superstructures in BiFeO3 (BFO) films, enabling bias-free photoelectrochemical (PEC) reactions. By leveraging in situ oxygen vacancy (VO) engineering, we enabled reversible switching between p- and n-type conductivity in BFO, thereby constructing p/n superstructures with densely packed depletion regions. Consequently, the superstructure achieves a dramatic improvement in carrier collection efficiency, as evidenced by an increased H2O2 production (8.6 times higher than that of p-BFO and 16.7 times higher than that of n-BFO). Furthermore, selective catalyst deposition on the p- and n-regions facilitates bias-free water splitting. The approach is readily adaptable to other ferroelectric materials, where VO-mediated conductivity modulation is feasible.