A Double-Gradient All-Organic Dielectric Polymer Film Achieving Superior Breakdown Strength and Energy Density

Ferroelectric polymers have drawn tremendous attention in film capacitors owing to their high permittivity and ease of processing. Nevertheless, the energy density of such materials is severely constrained due to inferior breakdown strength. To address this dilemma, a double-gradient multilayered all-organic dielectric composite film is proposed, fabricated via a simple layer-by-layer solution-casting process. The experimental results demonstrate that the composite film significantly suppresses the leakage current compared to the pristine films, resulting in remarkable enhancement of the insulation properties. The finite element simulation results further reveal that the optimized electric field distribution induced by the gradient structure and the carrier traps at the interfaces between the adjacent layers play a crucial role in impeding the propagation of the breakdown path. As a result, the developed dielectric film reaches an unexpected breakdown strength of 712 MV m^-1 along with a high energy density of 19.68 J cm^-3, surpassing the bench-mark biaxially oriented polypropylene as well as the existing ferroelectric-based composites reported in the recent works. The synergy of gradient and multilayered structure presented in this work offers a novel perspective and approach for the scalable fabrication of dielectric films with eminent capacitive performance.