Compositional Asymmetry-Driven Charge Reorientation Leading to Photocurrent Polarity Reversal in BiFeO 3 via the Photoelectrochemical Photocurrent Switching Effect

Abstract The photoelectrochemical photocurrent switching (PEPS) effect, in which the direction of photocurrent reverses under an applied potential, offers a direct way to understand how interfacial energetics influence charge transport. In most materials, the potential at which this polarity change occurs is essentially fixed, and methods to tune it in a controlled manner remain scarce. Being able to adjust this critical switching potential through simple and predictable parameters is important for advancing efficient photoelectrochemical devices. In this work, we show that BiFeO3 nanoparticulate films exhibit a clearly tunable switching potential, achieved by systematically varying the Bi:Fe stoichiometry. Changes in composition modify the oxygen-vacancy concentration and reshape the electronic energy landscape, which directly influence the band alignment and charge-transfer behavior at the semiconductor–electrolyte interface. This approach focuses on tailoring interfacial energetics through intrinsic material design rather than altering the overall device configuration. Electronic-structure analysis confirms that compositional asymmetry governs defect chemistry and the resulting shift in switching potential. These findings establish stoichiometry as a powerful and accessible control parameter for directing PEPS behavior and provide a versatile strategy for designing oxide photoelectrodes with customizable and predictable photoelectrochemical responses.