Surface structures and equilibrium shapes of layered 2D Ruddlesden-Popper perovskite crystals from density functional theory calculations

Abstract

The layered organic inorganic lead halide 2D Ruddlesden-Popper perovskite materials, namely, the perovskite crystal of given number of anionic perovskite layers intercalated by bulky or aliphatic organic spacer cations, have drawn increasing attentions in the optoelectronic applications because of their superior stability during operation subjected to ambient conditions relative to their 3D counterparts, as well as their tunable band gap energies by manipulating perovskite layer thickness. The impacts of crystal morphology on optical/electronic properties of nanocrystals and device performance have been a subject of intensive focus of investigation. In this work, we investigated the equilibrium shape of 2D perovskite crystals with different perovskite principle numbers (n = 1, n = 2, n = 3) from density functional theory (DFT) calculations. The surface energies of low-index planes (100), (001), (011) and (111) were computed, and the equilibrium crystal shapes were extracted using the Wulff constructions. The equilibrium crystal shapes from Wulff constructions are in good agreements with available experimental results. Therefore, the present study revealed the atomistic details of crystal facets of 2D perovskite materials, which cannot be extracted directly from experiments, thereby providing insights into the structural stability of 2D perovskite materials for potential applications in renewable energy or optoelectronic devices.