Electrocaloric refrigeration is one of the most promising, environmentally-friendly technology to replace current cooling platforms-if a notable electrocaloric effect (ECE) is realized around room temperature where the highest need is. Here, we report a straightforward , onepot chemical modification of P(VDF-ter-TrFE-ter-CTFE) through the controlled introduction of small fractions of double bonds within the backbone that, very uniquely, decreases the lamellar crystalline thickness while, simultaneously, enlarging the crystalline coherence along the a-b plane. This increases the polarizability and polarization without affecting the degree of crystallinity or amending the crystal unit cell-undesirable effects observed with other approaches. Specifically, the permittivity increases by >35%, from 52 to 71 at 1 kHz, and ECE improves by >60% at moderate electric fields. At 40 C, an adiabatic temperature change >2 K is realized at 60 MVꞏm-1 (>5.5 K at 192 MVꞏm-1), compared to 1.3 K for pristine P(VDFter-TrFE-ter-CTFE), highlighting the promise of our simple, versatile approach that allows direct film deposition without requiring any post-treatment such as mechanical stretching or high-temperature annealing for achieving the desired performance. Enhanced Electrocaloric Response of Vinylidene Fluoride-based Polymers via One-Step Molecular Engineering

Active thermal control will be a major challenge of the twenty-first century, which has emphasized the need for the development of energy-efficient refrigeration techniques such as electrocaloric (EC) cooling. Highly polar semi-crystalline VDF-based polymers are promising organic EC materials, however, their cooling performance, which is highly structurallydependent, needs further improvement to become competitive. Here, we report a simple method to increase the crystalline coherence of P(VDF-ter-TrFE-ter-CFE) ter-polymer in the plane including the polar direction. This is achieved by blending P(VDF-ter-TrFE-ter-CFE) with minute amounts of P(VDF-co-TrFE) co-polymer with similar VDF/TrFE unit content. This similarity allows for a cocrystallization of the co-polymer chains in the terpolymer crystalline lamellae, preferentially extending the lateral coherence without lamellar thickening, as validated with a wide range of structural characterisation. This results in a significant dielectric and electrocaloric enhancement, with a remarkable electrocaloric effect, ΔTEC = 5.2 K, confirmed by direct measurements for a moderate electric field of 90 MV•m -1 in a blend with 1 wt% of co-polymer.