Giant switchable ferroelectric photovoltage in double-perovskite epitaxial films through chemical negative strain.

Double-perovskite films have been extensively studied in multifunctional fields due to their modifiability. Here, a controlled process strategy to induce chemical strain and anomalous Poisson deformation is proposed for perovskite-based films. The chemical negative strain in the local-ordering BiSmFeO double-perovskite films can be regulated by oxygen engineering to cause the effectively tunable bandgap. We markedly increased the switchable open-circuit voltage to ~1.56 V from ~0.50 V for Pt/BiSmFeO/Nb-SrTiO devices, which is the highest in single-layer perovskite-based ferroelectric photovoltaic perpendicular devices under white light-emitting diode irradiation. The multifield composite action mechanism reveals the electrical cause of the large open-circuit voltage. The synergy of the optical fields and ferroelectric fields provides the possibility of multilevel storage. Structural characterizations indicate that the chemical strain offers a dual role of lattice distortion and vacancy migration. The strategy of controllable chemical strain facilitates further exploration of the application potential of ferroelectric materials for multifunctional electronic devices.