Interface-Engineered Core–Shell Quantum Dots Enable Carrier Confinement in Polymer Nanodielectrics for High-Voltage Direct Current Applications

Reliable polymer dielectrics are critical for high-voltage direct current (HVDC) power transmission, but their performance is fundamentally limited by detrimental charge carrier migration, particularly under the extreme electric fields and elevated temperatures encountered in service. This study addresses these challenges by engineering novel polymer nanodielectrics based on polyethylene (PE) modified with CdSe@ZnS core-shell quantum dots (QDs). Nanocomposites are fabricated via a solvent-assisted blending method, with homogeneous QD dispersion confirmed through microstructural analyses. The optimized 0.10 wt % QD-modified PE achieves a 59.2% reduction in DC conductivity at 30 °C and 70.2% reduction at 90 °C, alongside a 25.1% improvement in breakdown strength at 90 °C. Thermally stimulated depolarization current (TSDC) spectra reveal that core-shell QDs introduce deep trap energy levels at 1.007-1.036 eV (ZnS shell) and 1.060-1.075 eV (CdSe core), which dominate charge absorption under high fields. First-principles calculations uncover interfacial energy barriers of 0.69 eV (electron) and 0.47 eV (hole) at the CdSe/ZnS interface and of 5.31 eV (electron) and 0.95 eV (hole) at the ZnS/PE interface. These potential wells effectively localize carriers through dual mechanisms: deep trapping at the high-barrier ZnS/PE interface and quantum confinement within the CdSe core. The high energy barriers effectively inhibit carrier escape from the QD-based traps, while the discrete and isolated energy levels of well-dispersed QDs prevent detrimental inter-QD tunneling pathways. However, at excessive QD concentrations (>0.15 wt %), reduced interparticle distance leads to significant overlapping, diminishing the confinement efficacy through barrier weakening and enhanced tunneling, resulting in increased conductivity and reduced breakdown strength. This work establishes core-shell QDs as a transformative tool for engineering polymer nanodielectrics to enable next-generation HVDC insulation materials capable of withstanding extreme operational stress.