Numerous defects on the surface of halide perovskite films considerably limit the photovoltaic efficacy of perovskite solar cells (PSCs). Herein, multifunctional carbon quantum dots (CQDs) were introduced to modify the perovskite film surface. The CQDs contain multiple functional groups, including C=O and –NH₂, that interact effectively with the uncoordinated Pb²⁺ and organic cations on the perovskite film surface. This interaction enables defect passivation and energy-level alignment optimization, leading to an extension of the charge carrier lifetime and enhancement of carrier-selective transfer. As a result, the best CQD-modified PSCs, boasting an impressive fill factor of 84.5%, achieved a power conversion efficiency of 24.48%, surpassing the 22.31% of pristine devices. In addition, the unencapsulated PSCs exhibit excellent stability, retaining 83% of the initial efficiency after operating for over 1,000 h under simulated AM 1.5G illumination.