The urgent need for efficient water energy harvesting has led to the development of triboelectric nanogenerators (TENGs). In this study, considering the droplet spreading dynamics and the capacitive effects in a droplet-driven TENG (DD-TENG) device, an inverse relationship between the width of the top electrode and the output voltage was derived for the first time through a circuit model and was experimentally verified. Additionally, key performance parameters were optimized, including the types and widths of top electrodes, dropping height, inclination angle of the device, and solution types. A nonmonotonic relationship between the inclination angle of the device and the output voltage was established. Under optimal conditions, the output voltage of the DD-TENG achieved a 1133% increase compared to that of the device without a top electrode. The power density reached 1265 mW·m–2, which is among the state-of-the-art DD-TENG devices. These findings provide valuable insights for the performance improvement of DD-TENGs.