Structural Dynamics of Two-Dimensional Ruddlesden-Popper Perovskites: A Computational Study.

Recently two-dimensional (2D) hybrid organic-inorganic perovskites have attracted a lot of interest as more stable analogues of their three-dimensional counterparts for optoelectronic applications. However, a thorough understanding of the effect that this reduced dimensionality has on dynamical and structural behavior of individual parts of the perovskite is currently lacking. We have used molecular dynamics simulations to investigate the structure and dynamics of 2D Ruddlesden-Popper perovskite with the general formula BAMA Pb I, where BA is butylammonium, MA is methylammonium, and is the number of lead-iodide layers. We discuss the dynamic behavior of both the inorganic and the organic part and compare between the different 2D structures. We show that the rigidness of the inorganic layer markedly increases with the number of lead-iodide layers and that low-temperature structural phase changes accompanied by tilting of the octahedra occurs in some but not all structures. Furthermore, the dynamic behavior of the MA ion is significantly affected by the number of inorganic layers, involving changes both in the reorientation times and in the occurrence of specific preferred orientations.