Understanding moisture stability and degradation mechanisms of 2D hybrid perovskites: insights from ab initio molecular dynamics simulations†

2D hybrid perovskites have been in focus as better alternatives to their 3D counterparts to solve long-term stability issues. In this regard, investigation of their stability and possible degradation mechanism in the presence of moisture is of utmost necessity. A detailed analysis with the help of ab initio molecular dynamics simulations has been carried out to understand their interaction with water interfaces for the first time. Various possible terminations of Ruddlesden–Popper (RP) and Dion–Jacobson (DJ) phases of 2D hybrid perovskites have been considered. We monitor the various possible interactions in the perovskite/water interface model to reveal the robustness of various terminations. PbI₂ terminated structures are found to interact mainly through Pb–O interactions, and the DJ phase is found to be more robust. I₂ formation is found to be the possible degradation route for I terminated phases. The importance of the bulky hydrophobic organic cation layer is highlighted, whose unique arrangement plays an essential role in resisting water infiltration and dissolution of surface components in the case of organic cation terminated phases. Interestingly, the organic cation layer is found to be robust in 2D hybrid perovskites compared to reported 3D perovskites. Our study signifies the opportunity to tune the cation layer, thereby maintaining moisture stability without compromising the optoelectronic properties of 2D hybrid perovskites, thus contributing to the fundamental understanding of 2D hybrid perovskites at water interfaces.