Flexible Lead‐Free Perovskite Oxide Multilayer Film Capacitor Based on (Na0.8K0.2)0.5Bi0.5TiO3/Ba0.5Sr0.5(Ti0.97Mn0.03)O3 for High‐Performance Dielectric Energy Storage

Abstract Flexible thin film dielectric capacitors with high energy storage density and a fast charging–discharging rate have attracted increasing attention as the development of microelectronics progresses toward flexibility and miniaturization. In this work, an all‐inorganic thin film dielectric capacitor with a multilayer structure based on (Na 0.8 K 0.2 ) 0.5 Bi 0.5 TiO 3 and Ba 0.5 Sr 0.5 (Ti 0.97 Mn 0.03 )O 3 is designed and synthesized on a mica substrate. By optimizing the periodic number ( N ), concomitantly enhanced breakdown strength and large polarization difference are achieved in the film with N = 6, which contributes to the large energy density ( W rec ) of 91 J cm −3 , high efficiency (η) of 68%, and fast discharging rate of 47.6 µs. The obtained energy density is the highest value up to now in flexible dielectric capacitors, including lead‐free and lead‐based inorganic films as well as organic dielectric films. Moreover, no obvious deterioration of the energy storage performance is observed in the wide ranges of working temperature (−50–200 °C), operating frequency (500 Hz to 30 kHz), and fatigue cycles (1–10 8 ). Besides, the W rec and η are ultra‐stable under various bending radii ( R = 12–2 mm) and even after 10 4 bending cycles at R = 4 mm, demonstrating an outstanding mechanical bending endurance. This excellent performance will allow the capacitor thrive in flexible microenergy storage systems.