200 °C‐Stable Dielectric Polymer Enabled by Molecular‐Scale Carrier Trapping: Synergy of Steric Hindrance and Deep Energy Level Engineering

Abstract High‐temperature capacitive energy storage requires dielectric materials to maintain low conduction losses and high discharged energy density under extreme thermal conditions, a critical challenge that drives innovation in advanced dielectric polymers. Herein, amino‐functionalized polyhedral oligomeric silsesquioxane (NH 2 ‐POSS) moieties are covalently grafted onto polyamide‐ether‐imide (PAEI) backbone terminal groups. The NH 2 ‐POSS expands intermolecular spacing from 6.94 to 8.11 Å to sterically hinder interchain charge transport. Molecular engineering of the PAEI backbone through DABA and BPADA forms restricts intra‐chain charge conduction by ‐CH 3 ‐CH‐CH 3 ‐ groups. Concurrently, a local state energy level shift (0.14 eV) and carrier deep trap capture (1.21 eV) achieve multidimensional suppression of carrier migration. The modified film exhibits ultralow conductivity (3.29 × 10 −12 S cm −1 at 200 °C) and high energy storage densities of 7.43 J cm −3 (150 °C) and 6.54 J cm −3 (200 °C) with η > 90%. Multiscale simulations, including density functional theory (DFT) calculations of trap depth distributions, molecular dynamics (MD) analyses quantifying chain spacing and fractional free volume (FFV) increase, and finite element modeling of field‐dependent conduction pathways, collectively validate the suppression mechanisms. This molecular topology engineering paradigm, synergizing steric confinement and electronic structure tailoring, establishes a generalized framework for extreme‐condition dielectric design.