UV-A-Irradiated P(VDF-TrFE-CFE) as a High-Efficiency Refrigerant for Solid-State Cooling

Thin P(VDF-TrFE-CFE) films have become an essential active material in the manufacturing of solid-state refrigeration systems. Films prepared by solvent casting fall short of the performance needs of today's cooling devices due to their low electrocaloric (EC) response, 1.5 °C at 50 V/μm, and to their high dielectric losses. Here, we present a straightforward method for enhancing the EC effect and minimizing dielectric losses in P(VDF-TrFE-CFE) through low-energy UV-A irradiation. This approach offers a potential path for postimprovement in the functional properties of EC materials. The material, after irradiation, shows new functional groups, thicker crystalline lamellae, and a denser structure. Direct measurements of the adiabatic temperature change have shown an increase in the EC response from 1.76 to 2.88 °C at 60 V/μm, accompanied by a reduction of the losses, two key improvements for potential applications. X-ray diffraction under an electric field reveals an adiabatic temperature change related to the electric field-induced appearance of the so-called defective ferroelectric phase jointly with the ferroelectric (FE) one. After irradiation, the FE phase appears at a lower field, indicating that UV-induced modifications favor the polar phase. This work shows an easy-to-implement road toward property enhancement of EC P(VDF-TrFE-CFE) films for cooling applications.