As shown in Fig. , the hydrogen bonds are formed between the [N H 3 ] + group of BA cations and the iodides at the terminal Pb-I bonds and those at the edges of the cage in proximity to the BA. These hydrogen bonds frequently break and reform due to the rotational movement of the N-H bonds in [N H 3 ] + group. Notably, the lifetime of these hydrogen bonds significantly decreases during the phase transition, from 1093 ps at 50 K to just 52 ps at 150 K. To assess the influence of this hydrogen bonding on the phase transition, we performed an MD simulation where the rotational freedom of N-H bonds in the [N H 3 ] + group was deliberately restricted. This simulated a scenario of extremely stable hydrogen bonds, preventing any spin and conical rotation of the [N H 3 ] + group. With these constraints, the system exhibited no phase transition when heated from 125 K to 200 K (see Supplementary Movie 12).