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Interfacial properties between passivation molecules and perovskite surface determine passivation effects on the performance and stability of perovskite solar cells. [Display omitted] • Passivation effect is related to binding strength and probability. • Strong polarity of 2-MP enhances charge separation and adsorption capacity. • 2-MP passivation improves carrier transfer capability. • 2-MP passivation leads to large bandgap. • AIMD simulations reveal water blocking effects of 2-MP, Py, and PTT. Chemical passivation implemented by Lewis base has been demonstrated as an effective method to overcome the water vulnerability of perovskite solar cells (PSCs) along with better performance. Comprehensive understanding of the surface passivation effects is crucial to future improve the PSCs efficiency and stability. Herein, we utilized first-principles to simulate the structure and electronic properties of the passivated perovskite, and carried out ab initio molecular dynamics (AIMD) to understand the effectiveness of the experimental passivation molecules, 2-MP , Py , and PTT , on the classical perovskite (Zhu et al., 2019). Calculations show that introducing both -SH and the N atom of 2-MP enhances the electric dipole moment, the binding strength, the adsorption probability and the carrier transfer rate compared to these of Py and PTT. Moreover, the efficient separation of electrons and holes at the interface and the large bandgap can be achieved by the 2-MP treatment, which is beneficial to improve the photovoltaic performance. AIMD simulations indicate that the interactions of N⋯Pb, S⋯Pb, and H⋯I between 2-MP and the MAPbI 3 surface lead to a stronger passivation effect than that of Py and PTT , which is in agreement with the experimental observations. Our results are expected to provide new ideas for developing more distinguished passivation molecules to endow the PSCs stability against water. [ABSTRACT FROM AUTHOR]