Stretching, Tapping, or Compressing–What Role Does Triboelectricity Play in the Signal Output from Piezoelectric Nanogenerators?

Piezoelectric energy generation is relevant for developing advanced electronics. However, the poor understanding of the influence of triboelectricity as an alternate charge generation mechanism has, in many cases, resulted in the reporting of exaggerated piezoelectric outputs. Herein, the signal output is systematically investigated from a range of organic piezoelectric materials (poled polyvinylidene fluoride (PVDF)), moderately piezoelectric (heat-treated PVDF), and non-piezoelectric (non-poled PVDF), polytetrafluoroelthylene (Teflon) and nylon) under tapping and compression (33 direction) and stretching (31 direction) in both encapsulated and non-encapsulated forms. This findings reveal that regardless of their piezoelectric properties, all tested materials exhibit substantial voltage outputs (4.2–4.6 V) during tapping, primarily attributed to the triboelectric effect at the contact interface. The triboelectric contribution to the signal is reduced by 99% in compression mode for non-piezoelectric materials and the piezoelectric signal is the primary contributor in the stretching mode with a high signal output of 7.71 V N⁻¹ for poled PVDF and a negligible signal (0.01–0.12 V N⁻¹) for non-piezoelectric materials. Moreover, elastomeric encapsulation is demonstrated to markedly increase triboelectric signals in tapping mode. These results have important implications for the future design of piezoelectric-triboelectric devices and the accurate interpretation of the data obtained from such devices.