On the mechanism of solvents catalyzed structural transformation in metal halide perovskites.

Metal halide perovskites show the capability of performing structural transformation, allowing the formation of functional heterostructures. Unfortunately, the elusive mechanism governing these transformations limits their technological application. Herein, we unravel the mechanism of 2D-3D structural transformation, and enlighten that is catalyzed by solvents. By combining a spatial-temporal cation interdiffusivity simulation with experimental findings, we validate that, protic solvents foster the dissociation degree of formadinium iodide (FAI) via dynamic hydrogen bond, then the stronger hydrogen bond of phenylethylamine (PEA) cation with selected solvents compared to dissociated FA cation facilitates 2D-3D transformation from (PEA) 2 PbI 4 to FAPbI 3 . We discover that, the energy barrier of PEA out-diffusion and the lateral transition barrier of inorganic slab are diminished. Importantly, for 2D films, the protic solvents catalyze grain centers (GCs) and grain boundaries (GBs) transforming into 3D phases and quasi-2D phases, respectively. While in the solvent-free case, GCs transform into 3D-2D heterostructures along the direction perpendicular to the substrate, most GBs evolve into 3D phases. Finally, memristor devices fabricated using the transformed films with/without solvent-catalysis uncover that, GBs composed of 3D phases are more prone to the vertical ion migration. This work elucidates the fundamental mechanism of structural transformation, allowing their use to fabricate complex heterostructures. This article is protected by copyright. All rights reserved.