Flexible High‐Temperature Polymer Dielectrics Induced by Ultraviolet Radiation for High Efficient Energy Storage

Abstract Polymer‐based dielectrics with fast electrostatic energy storage and release, are crucial for advanced electronics and power systems. However, the deterioration of insulation performance and charge–discharge efficiency of polymer dielectrics at elevated temperatures and high electric fields hinder the applications of capacitors in harsh environments. Herein, a facile and scalable approach is reported to fabricating flexible high‐temperature polymer dielectrics for high‐efficiency energy storage by ultraviolet irradiation. The resultant dielectric films exhibit an augment of 493% in energy density and exceeding 800% in discharge efficiency at 200 °C (3.2 J cm⁻³ and over 90% discharge efficiency at 480 M V⁻¹m for irradiated polyetherimide (PEI), 0.54 J cm^−3, and below 10% discharge efficiency at 400 MV m⁻¹ for pristine PEI) and excellent cycle performance. The injected space charge is found to be the dominant contributor to energy loss during the charge–discharge process. Free radicals introduced by ultraviolet irradiation can act as deep traps to capture injected charge and suppress space charge migration. This work clarifies the contribution of space charge to energy loss and demonstrates the effectiveness of ultraviolet irradiation in improving the capacitive performance of high‐temperature polymer dielectrics. These findings provide a novel paradigm for the rational design of high‐temperature polymer dielectrics for high‐efficiency energy storage.