It is essential to stabilize and enhance the power output performance of piezoelectric nanogenerators (NGs) in order to use them as a sustainable power source for wireless sensors, microelectronics, and optoelectronic devices. Here, we report a facile route to stabilize and maximize the output performance of a zinc oxide (ZnO) nanorod (NR)-based NG in the presence of ultraviolet (UV) light by reducing the piezoelectric potential screening effect caused by the free electrons in the ZnO NRs via surface passivation. We experimentally and theoretically investigated the piezoelectric potential drop in the ZnO NR-based NG due to the piezoelectric potential screening effect. A simple thermal annealing treatment was applied to the pristine ZnO NRs in air atmosphere to stabilize the output performance of the NG even in the presence of UV light. The piezoelectric output voltage from the surface-passivated NG was approximately 25 times higher than that from the NG with no passivation under UV light illumination.