Dielectric films with ultra-high energy storage density and efficiency are urgently needed due to the energy crisis. Here, we construct novel ferroelectric/dead-layer/superparaelectric (FE/DL/SPE) double-heterojunction capacitors, utilizing interface and dead-layer engineering to achieve outstanding energy storage performance. Bi0.9Sm0.1Fe0.9Co0.05Zn0.05O3 (BSFCZ) with large polarization, Ba0.985Na0.015Ti0.95Ni0.05O3 (BNTN) with low hysteresis and high breakdown strength (Eb), and artificial Al0.9Ga0.1O3 (AGO) with wide band-gap were chosen as the FE, SPE, and DL phases, respectively. Interface engineering enables the BSFCZ/AGO/BNTN films to maintain a high polarization of 55 μC cm−2, while the linear dielectric AGO and SPE BNTN substantially suppresses the remnant polarization. This can be clarified by the evolution of domains in the BSFCZ layer: nanodomains are scaled down to polar clusters, reducing polarization hysteresis while maintaining relatively high polarization. Simultaneously, two opposing intrinsic electric fields are formed to offset a portion of the external electric field, and the low dielectric constant AGO layer bears a significant part of the applied electric field due to electromagnetic boundary conditions. Consequently, the Eb is significantly increased from 4.4 MV cm−1 of BSFCZ/BNTN to 5.5 MV cm−1 of BSFCZ/AGO/BNTN, resulting in a giant recoverable energy density of 132 J cm−3 and a high efficiency of 84 % in BSFCZ/AGO/BNTN films. Moreover, the BSFCZ/AGO/BNTN films excel in temperature stability (RT∼200 °C), fatigue resistance (up to 107 cycles), and frequency stability (200 Hz to 20 kHz), alongside an exceptionally rapid discharge rate of 2.6 μs. This innovative approach suggests new possibilities for producing environmentally friendly, large-area, high-performance dielectric capacitors.
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