Monomeric-to-pentameric aggregation of molecular Cs4PbBr6 halide perovskite: a first-principles investigation

Abstract

The zero-dimensional halide perovskite, including the molecular state of the halide perovskite represented by A4BX6, has received much attention for their optoelectronic applications. In this manuscript, we employ first-principles calculations to systematically investigate the aggregation of the molecular Cs4PbBr6 halide perovskite. The monomeric, dimeric, trimeric, tetrameric and pentameric forms of Cs4PbBr6 are constructed. The structures of the aggregates are stabilized via the halogen bonds and the sharing of the A-site cations, and the charge transfer features from the halogen to the cesium species are observed upon the light excitation. Monotonic electronic band gap reductions and systematic red-shifts in the UV–vis absorption spectra are observed as the aggregation shifts to the higher degree. The detailed structural and electronic properties of the aggregates are further examined via the calculation of the Fukui function, electrostatic potential and frontier orbital energy levels. The present study facilitates the fundamental understanding of the higher-degree aggregates of the molecular halide perovskites and their structure-properties relationships for the optoelectronic applications such as the solar cells and photodetectors where the band gaps and the light-absorbing properties are essential.