Polarization Alignment in Polycrystalline BiFeO₃ Photoelectrodes for Tunable Band Bending

Polarization in a semiconductor can modulate the band bending via the depolarization electric field (E_dP), subsequently tuning the charge separation and transfer (CST) process in photoelectrodes. However, the random orientation of dipole moments in many polycrystalline semiconductor photoelectrodes leads to negligible polarization effect. How to effectively align the dipole moments in polycrystalline photoelectrodes into the same direction to maximize the polarization is still to be developed. Herein, we report that the dipole moments in a ferroelectric BiFeO₃ photoelectrode can be controlled under external poling, resulting in a tunable CST efficiency. A negative bias of -40 voltage (V) poling to the photoelectrode leads to an over 110% increase of the CST efficiency, while poling at +40 V, the CST efficiency is reduced to only 41% of the original value. Furthermore, a nearly linear relationship between the external poling voltage and surface potential is discovered. The findings here provide an effective method in tuning the band bending and charge transfer of the emerging ferroelectricity driven solar energy conversion.