Tuning electro-thermo-mechanical coupling in electroactive nanocomposites for self-oscillating solid-state heat pumps

Solid-state cooling based on the electrocaloric effect (ECE) offers low power consumption and zero greenhouse gas emissions. Among various designs of electrocaloric cooling devices, the flexible self-oscillating EC heat pumps, enabled by synergistic ECE and electrostriction in polymeric ferroelectrics, provide compact solutions. However, the development of such pumps has been hindered by the limited availability of polymeric ferroelectric materials that simultaneously exhibit strong ECE and electrostriction. Here, we present an industrially applicable strategy by incorporating amino-functionalized carbon dots (N-CDs) into a P(VDF-TrFE-CFE) terpolymer (TP). This approach yields a peak ECE of 75.2 J kg−1 K−1 at 1 wt% loading, while the transverse strain is maximized at 2.0% for the 2 wt% loading. Using multiple X-ray and infrared characterizations, we reveal that the N/CDs-fluoropolymer interface could markedly enhance the electric field-induced conformational transition. We evaluated the performance trade-off between ECE and electrostriction for self-oscillating EC devices, identifying the 2 wt% N-CDs/TP as the optimal material. Furthermore, a fabricated thin-film EC heat pump achieves a 4.2 K temperature span under 70 MV m−1 in an open environment, doubling the performance of the pristine terpolymer. Our findings underscore that synergistic optimization is crucial for advancing the performance of self-oscillating electrocaloric cooling devices.