Revealing stability origin of Dion-Jacobson 2D perovskites with different-rigidity organic cations

Dion-Jacobson (DJ) phase 2D perovskites have received wide atten-tion due to their higher stability compared with 3D ones. However, some of the reported DJ 2D perovskites are not really robust, lead-ing to a controversy over their stability. This necessitates clarifica-tion of the ambiguous stability mechanism. We herein elucidate that the stability of DJ 2D perovskites is determined by the rigidity of organic cations, which can induce co-adaptation of organic diammonium cations and inorganic [PbI6]4- octahedra to stabilize the 2D structure. By comparing three DJ 2D perovskites containing high-, medium-, and low-rigidity cations, we find that the medium -ri-gidity cation-based one presents higher structural stability. The finding is attributed to the appropriate cation rigidity, which en-ables organic diammoniums and inorganic octahedra to regulate their geometries to accommodate each other. This work explains the stability mechanism of DJ 2D perovskites and provides guidance for constructing highly stable candidates by adjusting the rigidity of organic cations.