Atomistic Mechanism of the Nucleation of Methylammonium Lead Iodide Perovskite from Solution

TL;DR

This study uses metadynamics simulations to reveal the atomistic nucleation mechanism of methylammonium lead iodide perovskite from solution, highlighting the stages from amorphous clusters to crystal formation.

Contribution

It provides the first detailed atomistic insight into perovskite nucleation from solution, emphasizing the role of methylammonium ions in crystal transformation.

Findings

Nucleation involves amorphous clusters evolving into PbI₂-like structures.

Methylammonium ions diffuse into PbI₂-like aggregates, triggering perovskite formation.

The process occurs in multiple stages with distinct structural transformations.

Abstract

In the ongoing intense quest to increase the photoconversion efficiencies of lead halide perovskites, it has become evident that optimizing the morphology of the material is essential to achieve high peformance. Despite the fact that nucleation plays a key role in controlling the crystal morphology, very little is known about the nucleation and crystal growth processes. Here, we perform metadynamics simulations of nucleation of methylammonium lead triiodide (MAPI) in order to unravel the atomistic details of perovskite crystallization from a $\gamma$-butyrolactone solution. The metadynamics trajectories show that the nucleation process takes place in several stages. Initially, dense amorphous clusters mainly consisting of lead and iodide appear from the homogeneous solution. These clusters evolve into lead iodide (PbI$_{2}$) like structures. Subsequently, methylammonium (MA$^{+}$) ions diffuse into this PbI$_{2}$-like aggregates triggering the transformation into a perovskite crystal through a solid-solid transformation. Demonstrating the crucial role of the monovalent cations in crystallization, our simulations provide key insights into the evolution of the perovskite microstructure which is essential to make high-quality perovskite based solar cells and optoelectronics.