Enhanced Bulk Photovoltaic Effect of Single-Domain Freestanding BiFeO₃ Membranes

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.