Interface engineering based on self-assembled monolayers(SAMs) represents a critical strategy to unleash the full photoelectrical potential of perovskite solar cells by passivating interfacial defects and enhancing charge extraction. Herein, two methoxy-substituted carbazole-based SAMs (MeO-2PACz and MeO-4PACz) were systematically investigated to reveal their effects on interfacial energy level modulation, defect passivation, perovskite crystallization and device performance. Density functional theory calculations demonstrate that MeO4PACz possesses a larger molecular dipole moment of 1.47 D than MeO2PACz (1.24 D), enabling more efficient modulation of interfacial energy level alignment. Furthermore, MeO-4PACz exhibits superior defect passivation capability relative to MeO-2PACz, contributing to prolonged carrier lifetime,reduced trap-filled limit voltage and decreased defect state density.Ultimately, the perovskite solar cells based on MeO-4PACz achieves a champion power conversion efficiency of 24.98%, accompanied by an open-circuit voltage of 1.161 V and a fill factor of 83.85%, while its operational stability is markedly enhanced compared with the MeO-2PACz-based device. This study establishes a clear structure-performance relationship for carbazole-based SAMs, providing a reasonable paradigm for the molecular design of high-efficiency perovskite solar cells.