Highly Transparent and Adhesive Poly(vinylidene difluoride) Films for Self-Powered Piezoelectric Touch Sensors

With the rapid development of internet of things, self-powered touch sensors made of piezoelectric fluorinated polymers have attracted significant interest because they can constantly convert mechanical energy into electrical energy without external power supply. However, it is still challenging to fabricate fluorinated polymer films with good adhesion and high output performance with a large-scale and low-cost method while maintaining high transparency, which are extremely important for simultaneous optical detection and electromechanical transduction. In this work, we demonstrate that the incorporation of a molecular ferroelectric-dabcoHReO4 (DH) into poly(vinylidene difluoride) (PVDF) solution enables high-throughput and low-temperature processing of flexible and transparent piezoelectric films by scalable processing method. The effects of multiaxial DH are multiple. First, DH can trigger the phase transition of PVDF from α- to β-phase and realize the orderly orientation of PVDF, which guarantees higher piezoelectric performance without any additional electrical poling process. Second, the hydrophilic nature of DH can improve the adhesion properties of PVDF, which in turn improve the stability and durability of the devices. By optimizing the fabrication processes, the transmittance of the piezoelectric touch sensors based on PVDF films and Ag nanowires coated poly(ethylene terephthalate) electrodes can be higher than 94%. The piezoelectric voltage constant g33 of the transparent films can reach to 1.2 V·m·N−1, which is at least three times higher than the commercially available PVDF films obtained by stretching. These results indicate that the flexible piezoelectric sensors have potential applications in transparent electronic devices for mechanical sensing and energy harvesting.