Coupling oxygen vacancy gradient distribution and flexoelectric effects for enhanced photovoltaic performance in bismuth ferrite films

Although the anomalous ferroelectric photovoltaic effect of bismuth ferrite (BiFeO₃) has recently drawn widespread attention, very low photocurrent density and poor power conversion efficiency severely hinder its practical application as a photovoltaic device. A novel photovoltaic architecture was herein designed and constructed to achieve enhanced photovoltaic performance in (Sm and Ni) gradient-doped BiFeO₃ multilayers. The experimental results and analysis show that the gradient distribution of oxygen vacancies greatly enhances the photovoltaic performance of the gradient-doped BiFeO₃ multilayer. In particular, its photocurrent density (J_sc) of 80 μA cm⁻² and open-circuit voltage (V_oc) of 0.49 V are much higher than those of pure BiFeO₃ films reported in previous literature. Meanwhile, a possible underlying mechanism was finally proposed to demonstrate the enhanced photovoltaic property, that is, the oxygen vacancy gradient distribution coupled with the flexoelectric effect greatly enhances the separation of photogenerated carriers, thereby ultimately enhancing the photovoltaic output of the above photovoltaic architecture.