Highly stable photovoltaic effects in A²⁺-Zr⁴⁺ (A = Ca, Sr, Ba) co-doped BiFeO₃ films with self-polarization

The self-polarization of ferroelectric thin films plays a crucial role in simplifying the fabrication process of ferroelectric photovoltaic (FE-PV) devices, however, achieving stable self-polarization of thin films remains a challenge. Here, we demonstrate that FE-PV effects are obtained in both BiFeO₃ and A²⁺-Zr⁴⁺ (A = Ca, Sr, Ba) co-doped BiFeO₃ films, the as-fabricated films without artificial polarization, because self-polarizations exist in the films. Significantly, large FE-PV effects and high-temperature stability are simultaneously achieved. Self-polarization is enhanced by the rhombohedral to monoclinic phase transition, resulting in a large photovoltaic effect in the Bi_0.97Ba_0.03Fe_0.97Zr_0.03O₃ film under 450 nm illumination, and the photocurrent density (J_SC) and open circuit voltage (V_OC) are 0.65 mA cm⁻² and 0.39 V, respectively. The J_SC and V_OC of Bi_0.97Ba_0.03Fe_0.97Zr_0.03O₃ are 94.9% and 90.1% after 373 K heat treatment, respectively. This work provides a simple method for improving the FE-PV performance and temperature stability in ferroelectric films with self-polarization.