Enhanced-performance droplet-triboelectric nanogenerators with composite polymer films and electrowetting-assisted charge injection

Droplet-Triboelectric nanogenerators (droplet-TENGs) are a promising renewable energy resource. Enhancing the dielectric surface properties is a primary requirement to increase the output performance of TENG device. In this study, droplet-TENGs are fabricated on indium tin oxide glass substrates with either (1) a pure amorphous fluoropolymer (AF) dielectric film; (2) a composite AF film doped with silk powder (AF/Silk); or (3) a composite AF film doped with polytetrafluoroethylene (PTFE) particles (AF/PTFE_p). The energy-harvesting performance of the three devices is examined experimentally with and without the application of electrowetting-assisted charge injection (EWCI). For the AF and AF/Silk devices, the output current increases by approximately 12 times following the application of EWCI. Furthermore, the composite AF/Silk device also improves the current stability. The AF/PTFE_p TENG increases the output current by approximately 5 times compared to that produced by the TENG with a pure dielectric layer. Moreover, the performance improvement increases to around 25 times following the application of EWCI. For all three devices, the output current increases with a reducing dielectric layer thickness. The output current also increases with an increasing concentration of the droplet solution. Overall, the results presented in this study provide a useful general understanding of the mechanisms underlying the operation of droplet-triboelectric nanogenerators. This research explores, for the first time, the effect of EWCI on composite material used for droplet-TENG and suggests possible strategies for enhancing the performance of such devices through an appropriate design of the dielectric layer and operating conditions.