Synthetic Variation and Structural Trends in Layered Two-Dimensional Alkylammonium Lead Halide Perovskites

03 April 2019, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

We report the cooling-induced crystallization of layered two-dimensional lead halide perovskites with controllable inorganic quantum-well thickness (n = 1, 2, 3, 4), organic spacer chain length (butyl-, pentyl-, hexylammonium), A-site cation (methylammonium, formamidinium), and halide anion (iodide, bromide). We report crystal structures for the iodide family as a function of these compositional parameters, and across their temperature dependent phase transitions. In general, lower symmetry crystal structures, increasing extents of organic-spacer interdigitation, and increasing organic-spacer corrugation tilts are observed at low temperature. In addition, greater structural distortions are seen in lead halide octahedra closest to the organic spacer layer, and larger-structures exhibit periodic variation in Pb-I bond lengths. We also provide detailed guidance regarding the combination of synthetic parameters needed to achieve phase-pure crystals of each composition, and discuss difficulties encountered when trying to synthesize particular members of the 2D perovskite family containing formamidinium or cesium as the A-site cation. These results provide a foundation for understanding structural trends in 2D lead halide perovskites and the effect these trends have on their thermal, electrical, and optical properties.

Keywords

perovskite
crystal structure
crystallization
phase transition

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