90003865

open access

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Rotation mechanism of methylammonium molecules in organometal halide perovskite in cubic phase: An ab initio molecular dynamics study

English (英語)

Journal of Chemical Physics

145(22)

224503-224503

AIP Publishing

2016-12-14

2018-01-01

Rotation of methylammonium (CH(3)NH(3) or MA) molecules is believed to govern the excellent transport properties of photocarriers in the MA lead iodide (MAPbI(3)) perovskite. Of particular interest is its cubic phase, which exists in industrially important films at room temperature. In order to investigate the rotational behaviors of the MA molecules, we have performed ab initio molecular dynamics simulations of cubic-MAPbI(3) at room temperature. There are two types of rotational motions of MA molecules in a crystalline PbI(3) cage: reorientation of a whole molecule and intramolecular rotation around the C-N bond within MA molecules. Using a cubic symmetry-assisted analysis (CSAA), we found that the prominent orientation of the C-N bond is the crystalline < 110 > directions, rather than the < 100 > and < 111 > directions. Rapid rotation around the C-N bond is also observed, which easily occurs when the rotational axis is parallel to the < 110 > directions according to the CSAA. To explain the atomistic mechanisms underlying these CSAA results, we have focused on the relation between H-I hydrogen bonds and the orientation of an MA molecule. Here, the hydrogen bonds were defined by population analysis, and it has been found that, while H atoms in the CH(3) group (HC) hardly interacts with I atoms, those in the NH(3) group (HN) form at least one hydrogen bond with I atoms and their interatomic distances are in a wide range, 2.2-3.7 angstrom. Based on these findings, we have given a possible explanation to why the < 110 > directions are preferred. Namely, the atomic arrangement and interatomic distance between MA and surrounding I atoms are most suitable for the formation of hydrogen bonds. In addition to films, these results are potentially applicable to the rotational behaviors in bulk MAPbI(3) as well, considering that the atomistic structure and time constants regarding the rotation of MA molecules statistically agree with bulk experiments.

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©2016 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Journal of Chemical Physics 145(22), 224503 and may be found at http://dx.doi.org/10.1063/1.4971791