Polarization Alignment in Polycrystalline BiFeO₃ Photoelectrodes for Tunable Band Bending

Abstract

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.

Enhanced Generation of Reactive Oxygen Species via Piezoelectrics based on p–n Heterojunctions with Built-In Electric Field

“…Additionally, the upward shift of the CB minimum has two important effects on the catalytic properties. First, it makes the excited electrons more negative, facilitating their reaction with molecular O 2 to generate superoxide free ions. Second, it enhances the transfer of excited electrons to reactants, suppressing electron–hole recombination .…”

The Ferroelectric Effects of Rhombohedral and Tetragonal BiFeO3 in Photoelectrochemical Water Splitting

“…This indicates that R-BFO is more reactive toward PEC water splitting than the T-BFO. The spontaneous polarization of ferroelectric materials may induce surface band bending that determines the open circuit potential. , Under the same experimental conditions, the two BFO films with comparable residual polarization parameters should give similar open circuit potentials (Figures e and S4). The relaxation dynamics of the photogenerated charges were analyzed through the open circuit potential decay profiles upon illumination (Figure f).…”

“…In the ideal scenario of R-BFO, the charge transfer processes can be divided into two steps. First, the photogenerated charges in domains may be separated and transferred to the surface driven by the depolarization field dominated by the out-of-plane component of the ferroelectric polarization. , However, some photogenerated charges may be separated and accumulated at the domain walls driven by the electric field caused by the in-plane polarization component (Figure ). Whereafter, the photogenerated charges of the former move to the surface via charger transfer channels, that is the domain walls, under an external electric field (Figure ).…”