The dual role of molecular semiconductors in insulation performance of polymer composites: A trade-off between carrier trapping and excitation

Dielectric polymers for high-temperature and high-voltage applications face significant challenges in maintaining excellent electrical insulation properties. Incorporating n-type molecular semiconductors from the field of organic solar cells into polymer composites presents a promising approach to enhancing dielectric performance. However, a systematic understanding and rational design principle for employing these structurally complex molecular semiconductors in insulation enhancement are still lacking. In this study, statistical analysis of existing molecular semiconductors reveals a competitive relationship between electron affinity and bandgap, which respectively govern carrier trapping and excitation dynamics. A trade-off between these two electronic parameters is therefore essential for optimizing dielectric performance. Specifically, a wider bandgap promotes higher trap density, while a larger electron affinity deepens trap energy levels, both contributing to suppressed charge transport. Through both computational simulations and experimental measurements, we demonstrate that the deep-level traps introduced by these molecular semiconductors outweigh the negative effects of carrier excitation and injection. By incorporating just 0.05 wt % of high electron affinity molecular semiconductors, the DC breakdown strength of the composite achieved 237.72 kV mm⁻¹ at 120 °C, significantly outperforming pristine EP (153.83 kV mm⁻¹). These findings provide a novel perspective on the design of advanced dielectric polymers, emphasizing the strategic incorporation of high electron affinity molecular semiconductors over wide-bandgap semiconductors for high-performance electrical insulation.