Microscopic Mechanisms, Morphology, and Defect Formation in the Thermally Activated Crystallization of Methylammonium Lead Iodide

In
this study, we unravel the atomistic mechanisms that govern
the crystallization process of methylammonium lead iodide through
the application of microsecond time scale molecular dynamics simulations.The
findings indicate that methylammonium iodide (MAI) and lead iodide
(PbI2) precursors exhibit a propensity to aggregate into
a disordered film, which ultimately undergoes a thermally activated
disorder-to-order transformation to achieve crystallization. Notably,
the crystal evolution during the annealing process reveals morphological
characteristics consistent with the Straski–Krastanov growth
mode. The temperature dependence of the crystal growth rate demonstrates
an activation energy of 0.37 eV, which may be ascribed to the energy
required to dissociate defective Pb–I bonds and facilitate
Pb diffusion. Finally, the mechanisms underlying the spontaneous generation
of lead vacancies are examined, suggesting a kinetic origin for such
optically active defects. In principle, the latter suggests the potential
for reducing their concentration through optimization of the growth
parameters.