various scattered and irregular energy sources in the natural environment. [10] Although this type of energy is small, it is distributed extremely widely. If utilized reasonably, it will certainly make a significant contribution to human energy strategy.Coupled with contact electrification and electrostatic induction, Prof. Wang's group first invented the triboelectric nanogenerator (TENG) in 2012. [11] Presently, as the mainstream technology for energy harvesting, TENG has shown great application prospects in the fields of micro-nano energy, self-powered system, and blue energy due to its environmental friendliness, high efficiency, and accessibility. [12][13][14][15] After decades of research, the theory and output of TENG based on solid-solid interface has been deeply explored and improved. [16][17][18] However, in addition to the mechanical energy-electricity conversion between the solidsolid interface, the triboelectricity at solid-liquid interface can also be seen everywhere in the environment, such as in the falling raindrops. [19] Recently, the mechanism of solid-liquid electrification has been explored, and theories such as the electric-double-layer model and Wang's hybrid layer model have also been proposed to expand its applications. [20,21] However, these works of research are mainly concentrated on the solid-liquid electrificationThe working principle of the triboelectric nanogenerator (TENG), contact electrification and electrostatic induction, has been used to harvest raindrop energy in recent years. However, the existing research is mainly concentrated on solid-liquid electrification, and adopts traditional electrostatic induction (TEI) for output. As a result, the efficiency of droplet electricity generators (DEGs) is severely constrained. Therefore, previous studies deem that the DEG output is limited by interfacial effects. This study reveals that this view is inappropriate and, in reality, the output strategy is the key bottleneck restricting the DEG performance. Here, a switch effect based on an electricdouble-layer capacitor (EDLC) is introduced, and an equivalent circuit model is established to understand its working mechanism. Without pre-charging, a single droplet can generate high voltage over 100 V and the output is directly improved by two-orders of magnitude compared with TEI, which is precisely utilizing the interfacial effect. This work provides insightful perspective and lays solid foundation for DEG applications in large scale.
