Tribovoltaic effect: Fundamental working mechanism and emerging applications

The triboelectric nanogenerator (TENG) is currently a promising technology operated by coupling mechanisms between contact electrification and electrostatic induction for efficiently converting mechanical energy into electricity. Broad applications have been demonstrated practically. However, the electrical signal produced from the TENG has a pulsed alternating current output, which needs to be rectified by the circuit from alternating current to direct current (DC) appropriately for powering/storing small electronic systems. This limits utilization by the drawbacks of conversion efficiency, size, and portability. The development of a DC TENG is thus essential. This novel physical phenomenon (DC TENG) emerged just recently, mainly based on Schottky, p-n and liquid-semiconductor junctions, and a multilayered structure junction (i.e. metal/semiconductor-insulator-semiconductor), called the tribovoltaic nanogenerator (TVNG). Pair sliding from two triboelectric materials with different electronic band energies serves as continuous DC with a unique mechanism. The excited carriers (corresponding with the generated outputs) can be enhanced from the tribovoltaic effect through theoretical design, and the concept can be hybridized with other technologies. This provides the potential of in-depth study and practical demonstrations for advanced harvesting and sensing. This review comprehensively presents the origins of triboelectric and tribovoltaic effects, related to fundamental and dynamic TVNG mechanisms in various material systems, and recent progress of the TVNG in designs and applications. Moreover, the challenge and outlook are discussed lastly for the future direction of TVNG development.