Multifunctional ZnS:Cu-based epoxy composites with PEDOT:PSS interfaces for breakdown reinforcement and defect visualization

PEDOT:PSS-treated ZnS:Cu@Al 2 O 3 fillers were designed for epoxy composites. • Interfacial energy-level regulation introduces deep traps and suppresses charge migration. • The optimized composite shows 7.35 % higher breakdown strength than pristine epoxy. • The composite enables real-time electroluminescent visualization of micro-defects. • Thermal conductivity and tensile strength are improved by 74.87 % and 19.81 %, respectively. Epoxy resins (EP) are widely used in electrical insulation and power electronic packaging, but defects such as bubbles and micropores can induce local electric field distortion and partial discharge, accelerating degradation and failure. Precise detection of micro-defects is therefore important for insulation reliability. In this work, PEDOT:PSS surface-treated ZnS:Cu@Al 2 O 3 (ZA) fillers (ZA-P x ) were incorporated into EP to develop self-diagnostic composites (EP/ZA-P x ). The ZnS:Cu core provides electroluminescent response for defect visualization. However, direct incorporation of electroluminescent fillers may promote charge transport and weaken dielectric reliability. To mitigate this issue, the Al 2 O 3 shell and PEDOT:PSS-regulated interface were introduced to create deep charge traps, suppress carrier migration, and enhance breakdown strength. Consequently, the EP/ZA-P x exhibit green electroluminescence under localized electric fields, enabling real-time micro-defect visualization. More importantly, the optimized EP/ZA-P0.01 shows a 7.35 % increase in breakdown strength over pristine EP, together with 19.81 % improvements in tensile strength, respectively. Experiments reveal deeper traps and suppressed carrier migration after PEDOT:PSS treatment, while DFT provides qualitative support for the trapping behavior. The EP/ZA-P x also detect scratches, internal/surface high-permittivity defects, and bubbles. This work provides a promising route for integrating defect visualization and insulation enhancement in electrical equipment and power electronic devices.