The low dielectric constant, limited breakdown strength, and large polarization hysteresis and conduction loss constrain discharged energy density and efficiency of polymer-based dielectric capacitors at elevated temperatures. To address these challenges, the [0.8(Na_0.2Bi_0.2Ba_0.2Sr_0.20Ca_0.2)TiO₃-0.2NaNbO₃]@Al₂O₃ high-entropy ferroelectric nanoparticles/polyetherimide-AlN/polyetherimide-triptycene bilayer nanocomposites are designed. The bilayer nanocomposites capitalize on advantages of high-entropy ferroelectric fillers, which contribute to the high dielectric constant and minimal hysteresis at high temperatures. Additionally, they also benefit from high thermal conductivity of AlN, enhanced rigidity and charge carrier traps in polyetherimide-triptycene, and suppressed carrier transport at the bilayer film interfaces. Consequently, the bilayer nanocomposites exhibit significantly improved dielectric constant and breakdown strength, and marked reduction in conduction loss at elevated temperatures. Remarkably, a record-high discharged energy density of 12.35 J cm⁻³ is achieved in the optimized bilayer nanocomposites at 150 °C, accompanied by a large efficiency of 90.25% under an electric field of 6341 kV cm⁻¹.

Pyroelectric energy harvesting has received increasing attention due to its ability to convert low-grade waste heat into electricity. However, the low output energy density driven by low-grade temperature limits its practical applications. Here, we show a high-performance hybrid BNT-BZT-xGaN thermal energy harvesting system with environmentally friendly lead-free BNT-BZT pyroelectric matrix and high thermal conductivity GaN as dopant. The theoretical analysis of BNT-BZT and BNT-BZT-xGaN with x = 0.1 wt% suggests that the introduction of GaN facilitates the resonance vibration between Ga and Ti, O atoms, which not only contributes to the enhancement of the lattice heat conduction, but also improves the vibration of TiO₆ octahedra, resulting in simultaneous improvement of thermal conductivity and pyroelectric coefficient. Therefore, a thermoelectric coupling enhanced energy harvesting density of 80 μJ cm⁻³ has been achieved in BNT-BZT-xGaN ceramics with x = 0.1 wt% driven by a temperature variation of 2 ^oC, at the optical load resistance of 600 MΩ.

PI–AgNbO₃ NPs/P(VDF-HFP) bilayer nanocomposites possess slim D–E loops, large E_b, and high D_max, thus displaying simultaneously a large U_e of 13.77 J cm⁻³ and high η of 86.87%.

We demonstrate 0–3 type heterogeneous NBT–NN–ST/HfO₂ composites to achieve high E_b and P_max. Some HfO₂ are concentrated in grain boundaries to suppress local electric branches’ development for enhancing E_b while others diffuse into lattice to improve bonds’ polarity for maintaining high P_max.