Enhanced energy storage of BaBi4Ti4O15 thin films via non-stoichiometric Ti-excess design

High energy density and high efficiency have long been the pursuit in the development of dielectric capacitors. In this work, energy density and efficiency are synergistically improved by non-stoichiometric Ti-excess design in BaBi4Ti4O15 thin films. On the one hand, excessive Ti promotes grain refinement and the formation of an amorphous phase, significantly inhibits leakage current, and enhances the breakdown field strength. On the other hand, relatively high polarization can be maintained despite the introduction of an amorphous phase by excessive Ti. Ultimately, a high energy density of 135.8 J cm−3, a high efficiency of 90.7%, and a remarkable energy storage figure of merit of 1460 J cm−3 were achieved in BaBi4Ti4.2Mn0.05O15 thin film. The thin film exhibits excellent stability and reliability regarding frequency (0.8–50 kHz) and temperature (20–230 °C), as well as cycling (106) performances. These results demonstrate that Ti-excess designed BaBi4Ti4O15 lead-free thin films are promising candidates for high-performance dielectric capacitor applications.