Unveiling the Anomalous Photovoltaic Effect of Ferroelectric Domain Walls in BiFe O3 Thin Films

The presence of ferroelectric domain walls (DWs) can generate an above-band-gap photovoltage of a ferroelectric photovoltaic device, which is the anomalous photovoltaic (APV) effect, and its mechanism is still under debate. Here, the effective electric field and the local bulk photovoltaic (BPV) component at 71° DWs are reported by quantitatively analyzing the light polarization angle-dependent photovoltaic effect of nonperiodic DWs and periodic stripe DWs in BiFeO3 films. The photovoltaic measurement under white light illumination directly reveals a significantly enhanced electric field at stripe DWs in comparison with the domains. The BPV effect at stripe DWs is about 25 times as large as that of the domains. Furthermore, the defect states at the DWs may recombine the photogenerated carriers and drastically weaken the electric field of the DWs, whereas they negligibly mitigate the BPV effect. This work offers a deeper insight into the mechanism of the APV effect at ferroelectric DWs.