Flexoelectric-induced photovoltaic effects and tunable photocurrents in flexible LaFeO3 epitaxial heterostructures

By engineering strain gradients in dielectrics, the flexoelectric effect can be created, which yields interesting physical properties via electromechanical coupling. Here, we report flexoelectric-induced photovoltaic effects in centrosymmetric LaFeO3 thin-film heterostructures grown on flexible mica substrates, in which partial relaxation of lattice-mismatch strain against LaAlO3 stretching layers results in giant strain gradients and pronounced electrical polarizations. The flexoelectric polarization modulates band alignment and leads to significant photovoltaic effects with a short-circuit current density of ∼0.4 mA/cm2 and an open circuit voltage of ∼ -0.45 V in Pt/LaFeO3/LaNiO3 devices. In addition, by concavely/convexly bending the mica substrate, mechanical strain gradients give rise to bi-directionally tunable photocurrents, in which continuously change of short-circuit current density with a magnitude of ∼100% and good reproducibility in repetitive bending operations are observed in the Pt/LaFeO3/LaNiO3 devices. The present work demonstrates an approach to design self-powered photoelectric devices with an electromechanical degree of freedom based on the flexoelectric effect in flexible thin-film heterostructures.