Silver Substitutional Doping to Enhance the Photoelectrochemical Properties of BiFeO ₃ Photocathodes via Promoting Photon Absorption and Bulk Carrier Transport

Perovskite‐type BiFeO 3 (BFO) has been considered as a promising candidate for photoelectrochemical cells due to its suitable band alignment, robust ferroelectric behavior, and good chemical stability. However, the photoelectrochemical performance of BFO is limited by poor photon utilization and severe charge carrier losses. In this work, the Bi 3+ sites of p‐type BFO thin films are substitutionally doped by Ag + to improve their photon absorption and bulk carrier transport, thereby enhancing photoelectrochemical responses. The results show that Ag doping reduces the bandgap of BFO photocathodes, broadening spectral absorption. Furthermore, Ag doping regulates the growth of BFO grains to form the films composed of single‐layer grains, which effectively reduces bulk charge recombination associated with grain boundaries. Also, the bulk charge transport is further improved by the increase in majority carrier density induced by Ag doping. As a result, the photocurrent density of 6% Ag‐doped BFO photocathodes reaches −0.88 mA·cm −2 at 0.5 V vs RHE in O 2 ‐saturated electrolytes, which is more than 5 times higher than that of pristine BFO photocathodes. This study lays a solid foundation for facilitating efficient solar fuel generation based on BFO photocathodes.