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Polymer‐based pyroelectric thin films are crucial functional materials at the core of flexible and lightweight electronic devices, such as wearable monitoring sensors, energy harvesters, and infrared detectors. Nevertheless, the pyroelectric properties of the polymer films, such as poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)), vanish when the surrounding temperature exceeds the ferroelectric‐to‐paraelectric transition temperature, and thus limits their pyroelectric performance to a low‐temperature range. Herein, to mitigate this issue by employing a new class of P(VDF‐TrFE) copolymer which has a low TrFE molar content is proposed. Fine‐tuning of the structure through thermal annealing in a vacuum environment significantly favors robust and highly polarized polymer films with a large area. Electric poling combined with an optimal annealing temperature (110–120 °C) gives highly ordered ferroelectric crystalline domains in the polymer films. Consequently, this remarkably broadens the temperature range (roughly up to 140 °C) for which the polymer film still presents high pyroelectric properties (pyroelectric coefficient 50 µC (m2K)−1). This study provides an alternative choice for pyroelectric polymer films with enhanced pyroelectricity in applications that require wider temperature ranges. [ABSTRACT FROM AUTHOR]

Relaxor ferroelectric polymers exhibit high k at their structural phase transition around room temperature. They are particularly attractive as gate dielectric in organic field effect transistor (OFET). Nevertheless, their applications are limited due to their low thermal stability. A polymer blend system with a high and thermally stable dielectric constant is demonstrated by mixing terpolymer poly(vinylidene fluoride‐trifluoroethylene‐chlorofluorethylene) P(VDF‐ter‐TrFE‐ter‐CFE) with copolymer poly(vinylidene fluoride‐trifluoroethylene) P(VDF‐co‐TrFE). PVDF‐based blends of various compositions are characterized by dielectric spectroscopy, differential scanning calorimetry (DSC), infrared spectroscopy, small and wide angle X‐ray scattering (SAXS and WAXS), and atomic force microscopy (AFM) in order to investigate the relationship between morphology and crystallization of the blend and their dielectric properties. An optimized blend of P(VDF‐ter‐TrFE‐ter‐CFE) [55/37/8] and P(VDF‐co‐TrFE) [46/54] at a ratio of 70/30 is found to exhibit a quasi‐constant dielectric constant of 40 ± 2 over a wide temperature range (20–80 °C). Furthermore, electrical characteristics of the PVDF‐blend‐based gate dielectric OFET show further thermal stability in comparison to OFET based on high‐k terpolymer P(VDF‐ter‐TrFE‐ter‐CFE) [55/37/8]. An improvement of their drain current stability by up to 60% is demonstrated at 60 °C. These findings enable broader applications of fluoropolymers in organic electronics. [ABSTRACT FROM AUTHOR]

Poly(vinylidene fluoride- co -trifluoroethylene) (P(VDF- co -TrFE)) copolymer and poly(vinylidene fluoride- ter -trifluoroethylene- ter -chlorotrifluoroethylene) P(VDF- ter -TrFE- ter -CTFE) terpolymer thin films are usually produced by solvent-casting followed by annealing to enhance their electroactive properties in electronic devices. In this study, we investigate the effect of a different thermal treatment, namely crystallization from the melt, on the crystalline structure and morphology of P(VDF- ter -TrFE- ter -CTFE) terpolymers with varying CTFE content (ranging from 0 to 8.3 mol %) using a combination of different in-situ techniques. First, in-situ Wide-Angle X-Ray Scattering (WAXS) shows the different crystal-crystal transitions during cooling for all the samples. For the terpolymers, two sharp Bragg peaks ((110) and (200) family of planes) of the low temperature crystalline phase can be detected. Their sharpness reflects a high lateral extension of the crystalline domains. Moreover, coupled morphological studies by in-situ Small-Angle X-Ray Scattering (SAXS) and Atomic Force Microscopy (AFM) show that the crystallization starts with the formation of very extended semi-crystalline domains with a sub-micrometric thickness that contributes to the SAXS signal. For significant amounts of CTFE, crystallization is spread out, leading to the appearance of increasingly finer lamellar stacks during cooling, filling the spaces left unoccupied during crystallization at higher temperatures. This contrasts with the very rapid crystallization observed in the polymer with 0 mol % of CTFE. Finally, the Curie transition is clearly visible in the AFM mechanical images, providing an original method for detecting the structural transitions occurring in these polymers. [Display omitted] • Structural/morphological study of the melt-crystallization of P(VDF-TrFE - CTFE). • Coupled in-situ WAXS, SAXS, and AFM analyses during cooling from the melt. • During crystallization, extended semi-crystalline domains (SCD) appear first. • The sub-micrometric thickness of the extended SCD induces a specific SAXS profile. • The Curie transition is surprisingly highlighted also in AFM mechanical images. [ABSTRACT FROM AUTHOR]

Depending on their CTFE content (from 0 to 10 mol %), poly(VDF- ter -TrFE- ter -CTFE), poly(vinylidene fluoride- ter -trifluoroethylene- ter -chlorotrifluoroethylene) copolymers, exhibit ferroelectric (FE) or relaxor ferroelectric (RFE) properties at room temperature. Solvent cast films of these terpolymers can crystallize in three orthorhombic phases: FE, DFE (Defective Ferroelectric) or RFE according to their amount of CTFE. The relative amount of each crystalline phase depends on the amount of CTFE and evolves after annealing. We study the dependence of the electric displacement−electric field (D−E) loop with the amount of CTFE and with annealing step. We observed a closely link between the remnant polarization, P R , and the fraction of (FE + DFE) crystalline phase. Macroscopic properties, studied using thermo-mechanical experiments (DSC and DMA) and dielectric spectroscopy, evolve continuously with the CTFE amount and are well correlated with the structural properties. Finally, a temperature versus mol% CTFE phase diagram is established and discussed in relation-ship with material properties. Image 1 • Influence of the CTFE content on the crystal phase structure: FE, DFE or RFE • Effect of annealing on the bipolar D-E loops and on the crystal phases • Close link between the residual polarization and the (FE + DFE) crystal amount • Phase diagram (T, mol% CTFE, crystal structure, macroscopic properties) [ABSTRACT FROM AUTHOR]