Self-Poling Polyvinylidene Fluoride-Based Piezoelectric Energy Harvester Featuring Highly Oriented β-Phase Structured at Multiple Scales

Self-poling poly(vinylidene fluoride) (PVDF) featuring uniformly aligned dipoles can convert mechanical vibrations into electrical energy without post-poling treatment, which is a topic of intense interest in self-powered flexible electronics. However, the current strategies to align PVDF rich in beta-crystals have some limitations, such as complex processing, low productivity, and so on. Herein, a self-poling flexible PVDF generator structured with a highly oriented beta-phase was prepared via a normal melt processing pathway, by combining flow-induced crystallization with the stabilizing effect of dopamine-functionalized carbon nanotubes (P-CNTs) on the oriented molecules. In this case, the intense flow field exerted by microinjection facilitated the gauche-trans transition and uniform orientation, while with the help of strong interaction between O-H groups of P-CNTs and F-C groups of PVDF, P-CNTs recruited and immobilized the neighboring short chains onto the surface, suppressing the molecular relaxation. As a result, rich electroactive beta-phases with preferential alignment characteristics were cultivated in situ, resulting in intrinsic self-oriented dipoles. The extraordinary piezoelectric properties of the PVDF were fully utilized even without polarization treatment, and the open-circuit voltage density reached similar to 11 V/cm(2), with over 4-fold improvement as compared to that of the randomly oriented sample fabricated by conventional cast method. Finally, the potential application as a robust energy harvester was explored by converting irregular mechanical energy from finger movements into utilizable electric energy, lighting green light-emitting diodes. This multi-scale control from crystalline composition to morphology based on flow-induced crystallization is achieved by simple melt-processing and thus can be suitable for large-scale continuous fabrication of self-poling piezoelectric PVDF energy harvesting devices.