On the mechanism and optimization of triboelectric nanogenerators.

The mechanism for a triboelectric nanogenerator (TENG) with contacting materials being different conductors is essentially the same as that of a Kelvin probe. The difference between the two is that the former is designed for harvesting mechanical energy while the latter is used for measuring contact potential differences. The formalism developed for the conductor-conductor TENG can be equivalently applied to conductor-dielectric and dielectric-dielectric TENGs under appropriate approximations. The phenomenological parameter of tribo-charge surface density used in the previous model can also be accounted for in the current formalism. The dependence of average output power on load resistance and motion speed is analyzed, and the optimal output power and corresponding resistance are calculated for different motions. The formula that relates output power to charge and displacement is given, and based on this formula different ways to improve output power and load resistance matching have been conceived.