Molecular Engineering in Perovskite Solar Cells: A Computational Study on 2-Mercaptopyridine Derivatives as Surface Passivators against Water

Contemporary perovskite solar cells (PSCs) have drawn substantial interest due to their high photovoltaic efficiency. However, the instability of perovskite in a humid environment restricts the service time extension and limits the large-scale application of PSCs. Herein, a series of passivation molecules (PMs), 2-MEP, 2-MDEP, 2-MTEP, and 2-MQEP, featuring different lengths of alkyl chains have been designed based on 2-mercaptopyridine (2-MP) which greatly improve the stability of PSCs in the humid environment. First-principles calculations demonstrate that the designed molecules offer stronger adsorption on the perovskite surface compared with 2-MP. The charge density difference and Bader charge analysis show that the newly designed Lewis bases improve the charge transfer ability, leading to effective separation of carriers at PM@MAPbI₃ interfaces. Furthermore, molecular dynamics simulations verify that the steady Pb-N/S interactions in the MAPbI₃/PM/H₂O system effectively prevent H₂O from approaching the perovskite surface. This work not only provides a set of promising surface passivators (especially 2-MDEP), but also paves a way for the design of PMs that endow PSCs stability and make PSCs highly competitive in the photovoltaic market.