Collective Molecular Mechanisms in the CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Dissolution by Liquid Water.
basic_science · Level V
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- Also identified by DOI 10.1021/acsnano.7b04116.
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Abstract
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 PbI<sub>2</sub> 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/H<sub>2</sub>O and wetting energy of 0.23 N/m. The water vapor absorption is energetically favored (0.29 eV/H<sub>2</sub>O), and the infiltrated molecules can migrate within the crystal with a diffusion coefficient D = 1.7 × 10<sup>-8</sup> cm<sup>2</sup>/s and activation energy of 0.28 eV.