Enhanced Bulk Photovoltaic Effect of Single‐Domain Freestanding BiFeO3 Membranes

Abstract The bulk photovoltaic effect (BPVE), which uniquely exists in non‐centrosymmetric materials, has been received extensive attention recently due to its potential to overcome the theoretical Shockley‐Queisser limit in traditional p–n junction solar cells. Here, freestanding single‐domain BiFeO3 membranes are exfoliated from miscut SrTiO3 substrates by dissolving Sr3Al2O6 sacrificial layers, and transferred on SiO2/Si substrates. This study finds that the freestanding BiFeO3 membranes maintain the single‐domain structure and exhibits the significantly enhanced bulk photovoltaic response (≈200% enhancement), compared to the strained BiFeO3 films. The comprehensive atomic imaging analyses manifest that the freestanding BiFeO3 membrane demonstrates the bigger noncentral ion (Fe) displacement, which results in the larger in‐plane ferroelectric polarization and substantial increase in the BPVE photocurrent. This work not only provides an effective approach to enhance the BPVE of ferroelectric oxide films, but also can potentially promote the exploration of BPVE of oxide membranes integrated with silicon‐based or 2D electronics.