Printed 2D WS2-based flexible triboelectric nanogenerator for self-powered force and UV sensing applications

The efficient scavenging of mechanical energy from the environment has become an eco-friendly and sustainable strategy to explore greener and cleaner energy resources. The triboelectric nanogenerator (TENG) is an attractive candidate for the efficient conversion of mechanical energy prevailing in nature into useful electrical energy. Further, the flexible and sustainable nature of TENG device makes it a potential candidate for real world applications in diverse fields such as self-powered sensors in wearable electronics, motion monitoring for rehabilitation, artificial-skin for robots, structural health and environment monitoring applications etc. Herein, we fabricated a printed, flexible 2D WS₂ based TENG for the efficient harvesting of mechanical energy prevalent around us. Few layered WS₂ was developed by liquid phase exfoliation process. The TEM analysis demonstrates the formation of single crystalline, WS₂ sheets with an interplanar spacing of 0.62 nm. A flexible TENG was fabricated using screen-printed WS₂ film and polymethyl methacrylate as the counter layer with an active contact area of 4 cm². On comparison, an output voltage of 520 V, short circuit current density (J_SC) of 68 mA/m² was obtained for few layered WS₂ based TENG against its bulk counterpart which could produce only an open circuit voltage (V_oc) of 70 V and J_SC of 10 mA/m². Under resistive load testing, the exfoliated WS₂ based TENG device delivered a peak power density of ∼ 0.6 W/m² at 80 MΩ load while the bulk WS₂ based TENG could produce only ∼ 0.093 W/m² at 60 MΩ. Further, the TENG was demonstrated harvesting biomechanical energy from human motions such as finger tapping and elbow bending. In addition, a highly sensitive force sensor was fabricated that showed an impressive sensitivity of 2.87 V/N at lower force range < 1 N and 0.69 V/N at higher force range (1 N < F < 5 N) respectively. The performance of few layered WS₂ nanosheet TENG was also demonstrated under the illumination of UV light of wavelengths 254 nm, 365 nm and 410 nm, which resulted in drastic change in the output, enabling self-powered UV sensing application. These results indicate a facile way to effectively scavenge mechanical energyas well as a novel approach towards self −powered sensors.