Excellent energy storage performance of Mn-doped SrTiO3-BiFeO3 thin films by microstructure modulation

Dielectric thin film capacitors are expected to be a promising candidate for high-performance energy storage devices due to their high power density, fast charge/discharge speed, and excellent stability. Nevertheless, it remains a challenging endeavor to develop dielectrics with excellent energy storage density comparable to that of commercial batteries. In this work, lead-free 0.8SrTiO3-0.2BiFeO3 (0.8STO-0.2BFO) thin films with coexisting amorphous and nanocrystalline structure were prepared by a sol-gel method. The heat-treatment temperature was adjusted to form polar-nano regions, thereby modulate the breakdown strength and dielectric polarization, and increase the energy storage density. The electric potential, electric field, and current density of the films with different amorphous/crystalline volume fractions were evaluated by the finite element simulation to further verify that the proper crystallization can result in the improved polarization performance and increased breakdown strength of the films, which are beneficial to the enhancement of energy storage performance. Through structural tailoring, the 0.8STO-0.2BFO film annealed at 550 °C demonstrates the optimal energy storage properties with a giant discharge energy storage density of 65 J/cm3 and high efficiency of 75% at room temperature. Simultaneously, a broad temperature stability (20–160 °C), superb operating frequency stability (20 Hz-2 kHz), and excellent fatigue endurance (6.3 ×105) are observed without appreciable degradation of the energy storage performance. The excellent energy storage performance indicates a widespread potential of 0.8STO-0.2BFO films in pulse power applications, such as consumer electronics, microelectronics, and medical devices.