An overlapped electron-cloud model for the contact electrification in piezo-assisted triboelectric nanogenerators via control of piezoelectric polarization

Abstract

Huge demand for portable electronics and wearable devices in the era of the Internet of Things (IoT) has driven the demand for sources of clean energy harvested from ambient environments. Here, all-organic piezo-assisted triboelectric nanogenerators (P-TENGs) were fabricated by subsequently pairing polarized poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) with polyvinyl alcohol (PVA), which is a tribopositive polymer, and silicone rubber, which is a tribonegative polymer. This work aims to investigate the effect of piezoelectric polarization in P(VDF-TrFE) on the contact electrification (CE) of P-TENGs. By tuning the direction of piezoelectric polarization in P(VDF-TrFE), the electrical outputs (open circuit voltage, short circuit current density, and short circuit charge density) of the P-TENGs can be enhanced by an average of 135%. These observations were explained using a modified overlapped electron cloud (OEC) model. It is proposed that the CE was affected by the shift in energy levels of electrons which is induced by the piezoelectric polarization of P(VDF-TrFE). A maximum power density of 450 μW cm⁻² was achieved by applying a constant force of 100 N on the P-TENG reverse-polarized P(VDF-TrFE) with silicone rubber. The experimental results in this work show a reliable method of electrical power enhancement in a P-TENG by tuning the piezoelectric polarization into a favored state. Moreover, the modified OEC helps to elucidate the enhancement effect of the polymer–polymer CE by providing a fundamental understanding of the effect of piezoelectric polarization on CE.