Understanding the Ferroelectric Polymer–Metal Contact Electrification for Triboelectric Nanogenerator from Molecular and Electronic Structure

The contact electrification of ferroelectric polymer can be more complicated due to its ordered permanent molecular dipoles and dipole–dipole interactions. Herein, the polyvinylidene fluoride (PVDF)-Cu is taken as an example to investigate the mechanism of ferroelectric polymer-metal contact electrification via first-principles calculations. It is revealed that different from non-ferroelectric polymers, when ferroelectric polymers are in contact with metals, the charge transfer occurs not only at the interface but also inside the polymer due to the existence of polar phases. Specifically, the polar phases in the crystallization region can effectively enhance the charge transfer between the ferroelectric polymer and metal because the polar molecules in PVDF possess the stronger electrostatic potential, more delocalized lowest unoccupied molecular orbital, and additional dipole–dipole interactions compared with nonpolar molecules. In addition, the coupling mechanism of piezoelectricity and triboelectricity in ferroelectric polymer-metal contact electrification under compression is also investigated. It is demonstrated that the deformation increases the degree of noncoincidence between positive and negative charge centers in polar phases and causes charge transfer between the polar molecular chains of PVDF, thus producing the extra charge transfer between the ferroelectric polymer and metal. This study provides a theoretical basis for the material design of triboelectric nanogenerators based on ferroelectric polymers.