Speed Matters: Standardizing Mechanical Testing Conditions for Contact-Separation Triboelectric Nanogenerators.

Triboelectric nanogenerators (TENGs) are a key emerging technology for powering wearable, implantable, remote, and autonomous small-scale electronics. Despite extensive reports, there is often a lack of rigor in reporting the mechanical testing conditions used to measure electrical performance in TENGs. Herein, we systematically vary the separation speed in contact-separation TENGs between 12.5 and 700 mm s-1 (both experimentally and via simulations) and measure a corresponding increase in power density from 10-7 to 10-4 W (along with analogous increases in measured current and voltage)-without changing any other material property or parameter. The transferred charge density (on the external electrodes, as separate from the surface charge density) also increased from 0.3 to 10 nC cm-2, demonstrating (along with supporting computational simulation experiments) that large changes in measured output can arise from testing conditions rather than changes in material chemistry or device structure. These results demonstrate the importance of separation speed in contextualizing literature reports of TENG performance and highlight the need to dramatically improve data reporting for the field. To address this, we propose the need to report a standard and consistent set of testing parameters for contact separation. Adoption of these conditions will enable meaningful benchmarking of TENGs and allow the field to progress more effectively.