Hierarchical Wrinkling on Elastomer with Plasma-Polymer Fluorocarbon Thin Film for High-Performance and Transparent Triboelectric Nanogenerator

Triboelectric nanogenerators (TENGs) have recently received extensive attention as a new technology of energy harvesting to serve the increasing demand of energy in the internet of things (IoT) era. Polytetrafluoroethylene (PTFE) is a representative triboelectrification material because of F atom makes it the most attractive to electrons. In addition, properties of PTFE, which are chemical resistance, thermal resistance, low coefficient of friction or good lubricity, and biocompatibility also provide a variety of applications in TENG device. However, PTFE has limited applications in various devices the low flexibility due to its thickness, difficulty in adhering to a substrate due to its low surface energy, and low transparency due to haze. In this study, a plasma polymer fluorocarbon (PPFC) thin film is suggested as a high-performance triboelectrification material for TENG. The PPFC thin film fabricated by sputtering using a carbon nanotubes (CNT)-PTFE composite target exhibits properties similar to those of PTFE, such as hydrophobicity, high surface charge potential and chemical resistance. Additionally, the PPFC thin film shows ultrathin thickness and transparency. Not only that, when a PPFC thin film is coated on a stretchable and biocompatible styrene-ethylene-butylene-styrene (SEBS) substrate, wrinkles are simultaneously generated on the surface, which increases the surface contact area and hydrophobicity. The surface contact area is regarded as a crucial factor that influences TENG performance by increasing surface charge density upon electrification event. We fabricated a PPFC coated hierarchical wrinkled architecture (HWA) TENG with dual-wavelength wrinkles though additional plasma surface treatment. HWA-TENG shows a high output performance of 200V and 30 μA due to the combination of increased surface area effect of HWA and high surface charge potential characteristics of PPFC thin film. It has been demonstrated that HWA-TENG can be successfully applied to a transparent triboelectric rain drops energy harvester and a conformal artificial triboelectric skin. HWA-TENG, which has eco-friendly, simple fabrication process and high output performance, is expected to be applied to various devices such as conformal human body sensors.