Photo/electro-stimulated Charge Transfer in Triboelectric Nanogenerator

Abstract

Widespread energy harvesting, generating self-sufficient power from the surrounding environment, such as wind, solar and geothermal, have attracted increasing attention in the past decade due to the energy crisis and global warming. Among them, many technological devices converting mechanical energy into other forms of energy or vice versa have been proposed and investigated because of an extended life time, no recharging procedures, and their scalability. Generally, mechanical energy converted into electricity, namely, by using electromagnetic, electrostatic, and piezoelectric effects. Most recently, a new type of power generating device, named as triboelectric nanogenerator (TENG) based on triboelectric effects coupled with electrostatic effects have been demonstrated as powerful means of harvesting mechanical energy from living environment. Part 1. A simple fabrication route for ion gel nanofibers in a triboelectric nanogenerator was demonstrated. Using an electrospinning technique, we could fabricate a large-area ion gel nanofiber mat. The triboelectric nanogenerator was demonstrated by employing an ion gel nanofiber and the device exhibited an output power of 0.37 mW and good stability under continuous operation. Part 2. Understanding the charge transfer mechanism between two surfaces during the physical contact is crucial in the development of triboelectrification-related commercialized products. Here, we report that light illumination can reverse the direction of the charge transfer and significantly increase tribo-charge density occurring at the oxide/polyimide interface. Under light illumination, the surface potential maps of TiOx layer on P3HT:PC61BM/PEDOT:PSS/ITO substrate showed the significant decrease of the work function by approximately 0.2 eV, positioned to be at lower than that of the polyimide and thus increasing the work function difference with the polyimide. The wavelength-dependent measurement of the output open-circuit voltages revealed that the photogenerated electrons from active layer via visible light were accumulated at the surface of TiOx, enhancing the output short-circuit current of the triboelectric nanogenerator by 5 times, supported by the gate voltage-dependent output performance of the nanogenerator with TiOx/SiO2/Si substrate connected to the back gate metal. These results should help design improved energy harvesting devices as well as self-powered selective wavelength photodetectors.