<p>The urgent demand for capacitive energy storage at elevated temperatures is limited by significant leakage currents in existing polymer dielectrics, which lead to excessive heat generation and increase the risk of thermal runaway. Here we demonstrate a strategy to mitigate conduction loss by modulating energetic disorder within the polymer matrix. Incorporation of high-polarity organic molecules into polyetherimide enhances dipole-dipole interactions, increasing energetic disorder and thereby decreasing charge carrier mobility. Experimental measurements and computational simulations reveal that disorder-induced energy fluctuations broaden the energy separation between transport states, effectively suppressing charge transport. The resulting composite delivers an energy density of 6.45 J cm⁻³ with a charge-discharge efficiency of 90% at 200 °C, and exhibits stable performance over 100,000 cycles under an applied field of 400 MV m⁻¹. The observed uniformity and quality of the all-organic composite films address the challenges of scalable manufacturing for dielectric films, offering a practical pathway for the development of high-temperature dielectric materials.</p>