Multiple defects are likely to be produced during perovskite film preparation and exposure to a high humidity environment, which would negatively affect charge transport mechanisms and finally degrade the performance of perovskite solar cells (PSCs). In this work, we introduced a surface hydrophobic modifier, 1-dodecanethiol (DDT), to repair defects and enhance the moisture resistance of perovskite films. Through a series of tests, we found that defect repair by the thiol group in DDT can reduce trap density, inhibit non-radiative recombination and improve charge carrier transportation and extraction performance. In addition, benefiting from the excellent hydrophobicity of the dodecyl alkyl chain in DDT, both device efficiency and stability are significantly improved. Consequently, the device post-treated with DDT delivered a champion power conversion efficiency (PCE) of 20.89%, accompanied by outstanding long-range stability that exceeded 90% of its initial PCE after 1000 hours at a relatively high humidity of 80 ± 5% and without any encapsulation.