A heat transfer system is disclosed in which, an electrocaloric material includes a copolymer of a monomer mixture including (i) vinylidene fluoride, (ii) an addition polymerization monomer selected from tetrafluoroethylene, trifluoroethylene, or a monomer smaller than trifluoroethylene, and (iii) a halogenated addition polymerization monomer different than (ii) that is larger than vinylidene fluoride. The electrocaloric material also includes an additive selected from a nucleating agent having a polar surface charge, electrocalorically active solid particles, or a combination thereof. Electrodes are disposed on opposite surfaces of the electrocaloric material, and an electric power source is configured to provide voltage to the electrodes. The system also includes a first thermal flow path between the electrocaloric material and a heat sink, and a second thermal flow path between the electrocaloric material and a heat source.