On the origin of enhanced power output in ferroelectric polymer-based triboelectric nanogenerators: Role of dipole charge versus piezoelectric charge

Abstract

While ferroelectric polymer-based triboelectric nanogenerators (FE-TENGs) have been regarded as one of the most efficient mechanical energy harvesting devices, their fundamental mechanism is still debated. Here, we propose a dipole charge-shifted work function as the main origin of enhanced performance rather than a piezoelectric charge-increased electrostatic induction. P(VDF-TrFE) FE polymers were contacted with and separated from an ITO metal electrode and another P(VDF-TrFE) FE polymer under the variation of poling voltage, pressure, and temperature. The power outputs of the ITO-P(VDF-TrFE) and P(VDF-TrFE)-P(VDF-TrFE) FE-TENGs increased with poling voltage and pressure, but decreased with temperature; these behaviors are consistent with that of dipole charge rather than piezoelectric charge. Surface-sensitive spectroscopy and microscopy investigations suggested that electrons should be transferred, depending on the dipole direction, in the ITO-P(VDF-TrFE), whereas electrons and material should be transferred, depending on Young's modulus, in the P (VDF-TrFE)-P(VDF-TrFE). The dipole- and piezoelectric charge-induced electric field plays a crucial role in the overlapped electron cloud model for the triboelectrification of FE-TENGs.