Our droplet-based electricity generator (DEG) is based on our recent work19 showing that the continuous impinging of water droplets on a fluorinated material induces a high charge density on its surface. Our DEG device (Fig. 1a) is fabricated using drop-casting of polytetrafluoroethylene (PTFE), deposited with a tiny piece of aluminium, onto a glass substrate coated with indium tin oxide (ITO). As shown in Fig. 1b and Extended Data Fig. 1, the as-fabricated device is optically transparent, smooth and slippery. We hypothesized that, with continuous droplet impinging, the PTFE a promising electret material with high charge storage capability and stability20,21—could serve as an idealreservoir for charge storage, while electrostatically inducing opposite charge of the same amount on the ITO for possible charge transfer to an aluminium electrode. We find that when a falling water droplet spreads on the PTFE surface, it bridges the originally disconnected components (the PTFE/ITO and aluminium electrode) into a closed-loop, electrical system.