Photo‐Induced Dipole Engineering for Enhanced Dielectric Polarization in High‐Temperature Capacitive Energy Storage Polymers

Cross‐linked polymer dielectrics have emerged as promising materials for high‐temperature electrostatic capacitors due to their exceptional thermal stability and high breakdown strength. However, their cross‐linked molecular chains restrict dipole orientational polarization, resulting in a lower dielectric constant compared to linear polymers. Consequently, cross‐linked polymers require significantly higher applied electric fields to achieve energy storage densities comparable to their linear counterparts. This not only increases the risk of electrical breakdown but also accelerates insulation degradation. To address this challenge, this study proposes a photo‐induced dipole engineering strategy that leverages coumarin cross‐linking to simultaneously introduce polar oxygen groups and high‐dipole‐moment cyclobutane dimers. This approach simultaneously enhances the dielectric constant (from 3.85 to 4.64) and the high‐temperature breakdown strength (from 525 to 712 MV m −1 ), leading to a substantial improvement in high‐temperature capacitive performance. Consequently, the cross‐linked polymer delivers excellent discharged energy densities of 7.4 J cm −3 at 150 °C and 3.9 J cm −3 at 200 °C, while maintaining a high charge–discharge efficiency >90%. Remarkably, the cross‐linked polymer exhibits an outstanding cycling stability under high‐power operation, coupled with excellent self‐cleaning capability against electrical breakdown. These results underscore the potential of coumarin photo‐cross‐linking in developing next‐generation high‐performance polymer dielectrics.