The power conversion efficiency and stability of perovskite solar cells are affected by multiple factors, including the properties of the perovskite layers, interfaces, and transport layers. In this study, we propose the use of two multifunctional amino acid molecules, 2-ACL and 3-ACL, as additives to passivate perovskite films. The amino and carboxyl groups of these molecules interact strongly with the perovskite, effectively passivating defects at grain boundaries. This reduces non-radiative recombination and extends the lifetime of charge carriers, resulting in a significant improvement in device power conversion efficiency. Furthermore, the additives inhibit the decomposition of the perovskite layer, stabilizing the interface structure and enhancing the stability of perovskite solar cells. Density functional theory calculations were used to investigate the passivation effect of the two amino acids on the perovskite. By doping a small amount of 2-ACL molecule, we achieved a power conversion efficiency of more than 22% for CsFA-based inverted perovskite solar cells, compared to the reference efficiency of 18.82%. Additionally, the operating stability of the device was significantly improved. This work provides a comprehensive understanding of the role of multifunctional additives in enhancing the performance and stability of perovskite solar cells.