Giant recoverable energy storage density for lead-free SrTiO ₃ -based dielectric films coated by the amorphous Al ₂ O ₃ insulating layers

SrTiO₃ paraelectric materials, characterized by their linear polarization behavior, low polarization loss, and lead-free composition, are promising candidates for environmentally friendly energy storage dielectrics. However, their energy storage capabilities are limited by low breakdown field strength and polarization intensity. This work proposes a design strategy involving an insulator-paraelectric heterojunction multilayers by incorporating the amorphous Al₂O₃ (AO) insulating layers into SrTi_0.99Mn_0.01O₃(STM) thin films. By adjusting the number and spatial placement of the Al₂O₃insulating layers, the effect mechanisms of Al₂O₃ layers on the microstructure and energy storage performance of STM films have been revealed. The results demonstrate that the AO/STM/AO top-bottom configuration exploits the synergistic effects of electrode interface barriers and the built-in electric field (<em>E</em>_in) within the heterojunction to create a full-path charge transport barrier. This arrangement significantly enhances breakdown strength and reduces conduction losses. The optimized composite film exhibits a breakdown field strength of 6467 kV/cm and a giant recoverable energy storage density of 73.33 J/cm³, with an energy storage efficiency of 80.17%, outperforming existing SrTiO₃-based energy storage materials. Furthermore, the composite film demonstrates excellent stability across a wide temperature range (20-250 °C), a broad frequency band (0.2-10 kHz), and high-frequency switch cycles (10⁷ cycles).