Surface charge density regulation has been used for diverse range of applications. As a newly emerged high-efficiency energy converter, triboelectric nanogenerator (TENG) is sensitive to the surface charge density, making triboelectric polymers with high charge density crucial for expanding the range of TENG applications. Direct charge injection is an efficient strategy to boost output performance of TENG. However, it traditionally requires a high voltage (about 10   kV) and an injection period over minutes. The fast (<1   second) and low-voltage (< 3   kV) electron-injection process in this study for a contact-separate nanogenerator yields an output charge density of 252 μC·m-2, which is twice as large as that of the pristine device. The provided strategy can be applied to various polymers, providing opportunities for investigations in multi-science fields, not just limited to TENGs.