Strain-Gradient-Mediated Coupling of Flexo-Photovoltaic and Ferro-Photovoltaic in BiFeO₃ Thin Films

The synergistic interplay between flexo-photovoltaic and ferro-photovoltaic effects presents a promising route to surpass the efficiency limits of traditional solar cells. While these effects individually leverage strain-gradient-induced symmetry breaking and ferroelectric polarization fields to regulate carrier transport, their cooperative mechanisms for enhancing photovoltaic output remain unexplored. Here, we investigate the photovoltaic devices based on BiFeO₃ thin films, revealing that the dynamic modulation of photocurrent can be achieved by aligning the direction of strain gradients with the ferroelectric polarization, resulting in a maximum enhancement of photocurrent by up to 33%. The synergistic effect between the flexoelectric field induced by lattice symmetry breaking through strain gradients and the ferroelectric field is the underlying mechanism for optimizing the efficiency of photogenerated charge separation and transport. These findings provide critical insights into the design of high-efficiency photovoltaic devices through the strategic coupling of symmetry-breaking mechanisms.