where A is the pre-exponential factor. Fig. shows the linear fit between ln(v) and 1/T for systems with different water contents (ρ). Water molecules act as catalysts, and increasing their concentration enhances the interfacial ion diffusion coefficient, promotes effective collisions, and subsequently elevates the pre-exponential factor A in the Arrhenius equation. . Fig. shows ∆E tran as a function of ρ at 710 K. The results indicate that ∆E tran decreases as ρ increases. Compared to the zero-water system in which ∆E tran is 1.63 eV, ∆E tran decreases to 1.34 eV when ρ reaches 2.17 nm -2 . In general, our calculated energy barriers of transitions in CsPbI 3 are consistent with experimental observations that the water molecules accelerate the B↔Y transitions in perovskite materials by decreasing the transition barriers. However, it is challenging to accurately measure the relationship between the transition barrier and the water content in high-temperature experiments 8,14 . Unlike our simulations, experiments control the environmental humidity rather than the exact number of water molecules at the CsPbI 3 B/Y interface, which varies significantly with temperature .