To address the key issues of energy level misalignment, high defect density and inadequate stability at the NiO_x/perovskite interface in inverted perovskite solar cells, this work systematically investigates the triphenylamine-based self-assembled monolayer (SAM) ((2-(4-(bis(4-methoxyphenyl)amino)phenyl)-1-cyanovinyl)phosphonic acid, MPA-CPA), with the carbazole-based SAMs ((2-(3,6-dimethoxy-9H-carbazol-9-yl) ethyl) phosphonic acid, MeO-2PACz) and ((4-(3,6-dimethoxy-9H-carbazol-9-yl)butyl)phosphonic acid, MeO-4PACz) as references. This work spans molecular theoretical design, interfacial self-assembly behavior analysis, substrate surface characteristic regulation, interface defect passivation and carrier dynamics evolution, and device photovoltaic performance optimization. Density functional theory calculations reveal that MPA-CPA possesses a high dipole moment of 10.15 D and a propeller-like nonplanar configuration, enabling superior adsorption stability and assembly orderliness on the NiO_x surface. Atomic force microscopy, Kelvin probe force microscopy and water contact angle measurements show that after MPA-CPA modification, the NiO_x film surface roughness decreases to 6.2 nm, the average surface potential drops to 471 mV and the water contact angle is 67.3°, indicating improved energy level alignment with the valence band maximum of the perovskite. Through process optimization, the device with NiO_x film modified by MPA-CPA achieves a peak power conversion efficiency of 26.21%, significantly higher than that of the control devices. Moreover, unencapsulated devices retain 99.5% and 88.0% of their initial efficiencies after 168 h of storage in ambient air (30%~40% relative humidity) and at (65±5) ℃ under a nitrogen atmosphere, respectively. Collectively, this study establishes a robust “molecular structure-interface property-device performance” relationship, offering important experimental guidance for the design of interfacial materials toward highly efficient and stable perovskite solar cells.