Collective Molecular Mechanisms in the CH₃NH₃PbI₃ Dissolution by Liquid Water

The origin of the dissolution of methylammonium lead trihalide (MAPI) crystals in liquid water is clarified by finite-temperature molecular dynamics by developing a MYP-based force field (MYP1) for water-MAPI systems. A thermally activated process is found with an energy barrier of 0.36 eV consisting of a layer-by-layer degradation with generation of inorganic PbI₂ films and solvation of MA and I ions. We rationalize the effect of water on MAPI by identifying a transition from a reversible absorption and diffusion in the presence of vapor to the irreversible destruction of the crystal lattice in liquid due to a cooperative action of water molecules. A strong water-MAPI interaction is found with a binding energy of 0.41 eV/H₂O and wetting energy of 0.23 N/m. The water vapor absorption is energetically favored (0.29 eV/H₂O), and the infiltrated molecules can migrate within the crystal with a diffusion coefficient D = 1.7 × 10^-8 cm²/s and activation energy of 0.28 eV.