Structural Manipulation of the Oriented Amorphous Fraction to Improve the Piezoelectricity of Poly(vinylidene fluoride- <i>co</i> -trifluoroethylene) by Thermal Annealing

Piezoelectric polymers like poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymers are ideal for flexible electronics but suffer from low piezoelectric coefficients (|d33| < 30 pC/N). While intrinsic structural regulation offers enhancement potential, uncertainty persists regarding the primary piezoelectric contributor (crystal/amorphous/interface). We recently identified the oriented amorphous fraction (OAF) at crystalline–amorphous interfaces as critical for high piezoelectricity. However, the OAF induction requires extreme processing (>600 MV/m poling), presenting a great challenge for further manipulating the OAF structure. Here, we demonstrate for the first time thermal annealing as an effective OAF control strategy in stretched P(VDF-TrFE) 55/45 mol % films. When annealed at 130 °C, OAF content reaches 0.37, which contributes to a breakthrough d33 of −54 pC/N, far surpassing the −17 pC/N of commercial PVDF piezoelectric films and most PVDF-based polymers (|d33| < 30 pC/N). This exceptional d33 enhancement originates from the increased concentration of mechanically reorientable dipoles and the elevated polarization enabled by increased OAF content. This work presents a novel strategy for improving piezoelectric polymers by manipulating the structure of OAF through thermal annealing.