Intermediate layer for enhanced triboelectric nanogenerator

Triboelectric nanogenerator (TENG) has shown great advances in converting low-frequency discrete mechanical energy into electricity and multifunctional real-time self-powered sensing systems. It has confirmed that the air breakdown effect is the main factor limiting the maximum effective power output of the TENG. Charges generated on the surface of TENGs diffuse into the atmosphere and internal triboelectric layer, resulting in charge loss and decrease of surface charge density. Breaking through the limitation of air breakdown and prolonging charge decay time are the two priorities for boosting TENG output. By embedding superior intermediate layer into TENG induced output enhancement provides an effective strategy to improve the output performance. Here, the working mechanisms of different materials belonging to the classifications of metals, inorganic non-metal materials, and organic polymers as the intermediate layer are reviewed elaborately. Moreover, the influences of structure parameters, such as thickness of dielectric layer, dielectric layer number, and ground connection design are discussed accordingly. Future challenges and optimizations for improvement of the intermediate layer are finally presented in the review.