Interface Modification of Quantum Dots Altering Electrical Characteristics of PP-Composites for HVDC Cable Insulation

Abstract

Polypropylene (PP) insulation for HVDC cables faces critical challenges under combined high-temperature and high-field conditions, including elevated conductivity and electric field distortion. To elucidate the role of interfacial structure engineering in governing carrier confinement mechanisms, three PP composites were developed, incorporating bare CdSe quantum dots (QDs), silane-modified CdSe@KH570 QDs and CdSe@ZnS core–shell QDs, each at 0.10 wt% loading. At 90°C, PP/CdSe@ZnS achieves a characteristic breakdown strength of 284.9 kV/mm with 44.8% enhancement and exhibits an 87.5% reduction in conductivity, significantly outperforming other modifications. Thermally stimulated depolarisation current measurements reveal that core–shell quantum dots introduce deep trap levels at 1.06 eV compared to 1.02 eV for bare CdSe composites. Interfacial potential barrier and carrier probability distribution analysis demonstrate that the inorganic ZnS shell creates high-barrier double confinement for both electrons and holes with spatial separation that minimises recombination. In contrast, the valence band energy of the organic KH570 coating closely matches that of CdSe, resulting in hole wavefunction extension into the organic layer and substantial electron–hole overlap that increases recombination probability. These findings demonstrate that interfacial engineering through inorganic core–shell architectures provides optimal carrier confinement for next-generation HVDC cable insulation operating under demanding electrothermal conditions.