Enhancing high-temperature energy density of dielectric composites by tailoring molecular semiconductors

Abstract

To overcome the challenge where the exponential increase in leakage current of aromatic dielectric polymers under high-temperature and high-electric-field conditions leads to a mutual constraint between capacitive performance and thermal stability, in this study, diketopyrrolopyrrole derivatives (DPP-X, X = Cl, Ph, and O) with different electron-donating groups were doped into the PEI matrix. Based on the differences in the electron-donating ability of these electron-donating groups, the depth of charge carrier (electron and hole) traps in the PEI-DPP-X (X = Cl, Ph, and O) composite materials, as well as the strength of hydrogen bonding and electrostatic interactions between DPP-X (X = Cl, Ph, and O) and the PEI matrix, can be optimized—ultimately achieving an improvement in their high-temperature capacitive energy storage performance. As a result, DPP-O, with the strongest electron-donating ability, constructs deeper hole traps. At 200 °C, compared with pure PEI, the leakage current of PEI-DPP-O (0.2 wt%) is reduced by 3.37 times. Meanwhile, due to the strong electron-donating groups of DPP-O, it forms a more robust physical crosslinking network with the PEI matrix through hydrogen bonding and electrostatic interactions, enhancing the mechanical strength and breakdown strength (E_b). This synergistic regulation mechanism achieves the joint enhancement of electrical insulation and heat resistance of composites, enabling PEI-DPP-O-0.2 wt% composites to achieve excellent energy storage densities of 5.64 J cm⁻³ and 3.98 J cm⁻³ at 150 °C and 200 °C (η = 90%), respectively, outperforming lots of reported dielectric composites. In addition, the excellent cycling stability, the ability to prepare large-area high-quality uniform thin films, and the ultra-low filler loading characteristics further confirm the potential application of dielectric composites through molecular structure level regulation under extreme conditions.