Enhancement of Output Power and Durability of DLC-Based Sliding TENGs Modified with Self-Assembled Monolayers

A triboelectric nanogenerator (TENG) is an efficient technology that can harvest various forms of mechanical energy and convert it into electrical energy. However, high output efficiency and durability are necessary for the mass application of TENGs, and these characteristics strongly depend on the frictional properties of triboelectric materials, especially for sliding TENGs. Diamond-like carbon (DLC) films, which are effective triboelectric materials, have better durability and tribological properties than those of other conventional dielectric materials. In this study, molecular self-assembly technology was applied to functionalize the surface of DLC films as an ultrathin lubricating layer to increase the output of TENGs and simultaneously improve durability. Three self-assembled monolayers (SAMs) with different functional groups, perfluorodecyltrichlorosilane (FDTS), octadecyltrichlorosilane (OTS), and 3-aminopropyltriethoxysilane (APTES), were successfully formed on the DLC film surfaces. The performance of the sliding TENGs with SAM-modified DLC films as triboelectric pairs revealed interesting findings. The TENGs with hydrogenated DLC (H-DLC) modified with the OTS SAM and fluorinated DLC (F-DLC) modified with the FDTS SAM produced the highest outputs, with a peak short-circuit current of 15.1 μA at a power density of up to 69.5 mW/m2, which is four times that of the bare DLC film pair. Furthermore, the DLC films modified with SAMs exhibited outstanding stability and durability in humidity and during prolonged evaluation studies. This research is expected to advance a methodology for designing highly durable and efficient thin-film TENGs owing to the thin film characteristics of DLC films and SAMs.