Polymer Dielectrics Exhibiting Anomalously Improved Dielectric Constant and Simultaneously Achieved High Energy Density and Efficiency Enabled by CdSe/Cd1–xZnxS Quantum Dots

Flexible dielectric polymer and nanocomposites have attracted intensive attention owing to their high electrical breakdown strength, high power density and excellent cycle reliability which are highly demanded for electrostatic energy-storing system and devices. However, to achieve concurrently high discharged energy density (Ue) and efficiency (η) without impairing polymer-endowed mechanical and processing advantages remians a great challenge. In this work, a strategy of doping diminutive CdSe/Cd1–xZnxS quantum dots (QDs) with a dual-ligand structure into polymer is demonstrated, by which high Ue and η together with largely enhanced mechanical properties are obtained simultaneously. Contrary to conventional sense, a high dielectric constant (K, 17.8 at 1 kHz) is obtained by adding less than 1 volume percent of QDs into polymer while both the polymer and QDs are intrinsically low-K materials (<10 and 6~9, respectively). Meanwhile, the slight filling ratio of QDs causes no damage but large improvement to mechanical strength and tenacity of the polymer. The energy loss from carrier conduction is greatly suppressed owing to the confinement effect offered by the dual-ligand structure. Thus, a high η (~90% and 78.3% at 300 and 531.6 MV m–1, respectively) and high Ue (21.4 J cm–3) which is 1792% times of the commercially available dielectric capacitor, biaxially oriented polypropylene (1.2 J cm−3 at 640 MV m−1) are achieved. This strategy opens up a new avenue for high-performance polymer dielectrics and related applications.