Pursuing the tribovoltaic effect for direct-current triboelectric nanogenerators

The shortage of fossil energy and global climate change have driven humankind to find a new type of renewable, accessible, and clean energy. The triboelectric nanogenerator (TENG) is a new energy technology relying on the coupling of triboelectrification and electrostatic induction. To alleviate the issues of low current density and requirements for complex management circuits, direct-current triboelectric nanogenerators (DC-TENGs) based on the tribovoltaic effect have emerged, exhibiting DC output signals with higher current density and simpler structure design. In this review, the development progress and microscopic mechanisms of DC-TENGs based on the tribovoltaic effect are elaborately summarized for the first time, which is of great significance for designing high-performance DC-TENGs and advancing energy-harvesting technology. The reported DC-TENGs are scientifically classified and the corresponding working mechanisms are explained in detail. The output performances of different types of devices are systematically compared from the aspects of current density, peak power density, open-circuit voltage, short-circuit current, peak power output, and internal resistance. Furthermore, this review delivers a constructive discussion on how to improve the output performance from three perspectives, namely, materials and structures, external parameters, and multiple energy harvesting strategies. Finally, the potential application fields and development prospects of DC-TENGs are discussed. It is expected that the diversified DC-TENGs will bring about revolutionary development in high-efficiency energy harvesting and broaden the applications in intelligent IoTs. We summarise for the first time the development and microscopic mechanisms of DC-TENGs based on the tribovoltaic effect, which is of great significance for designing high-performance devices and advancing future energy-harvesting technology.