From negligible to giant electrocaloric effect of poly(vinylidene fluoride)

Poly(vinylidene fluoride) (PVDF), the most widely used ferroelectric polymer, typically exhibits a negligible electrocaloric effect (ECE) due to its symmetrical molecular configuration and bulky ferroelectric domains. PVDF-based ferroelectric terpolymers with giant ECE are expensive and have a narrow temperature window (T_w). Here, we report that PVDF films prepared by solid-phase pressure forming (PVDF-SPF) show a giant ECE of up to 12.8 K at 25 °C and a wide T_w of 60 °C. PVDF films underwent significant plastic deformation and extensive crystal fragmentation, forming loose and tiny β crystal grains under 30 MPa solid-phase pressure. The giant ECE primarily originates from orientation entropy changes of molecular chains associated with the reversible transition between loose and compact β crystals, as well as switching entropy changes of polar dipoles in tiny grains. Given the availability of PVDF, this work opens a route for the development of scalable solid-state cooling techniques.