We report the cooling-induced crystallization of layered two-dimensional
lead halide perovskites with controllable inorganic quantum-well thickness (<i>n</i> = 1, 2, 3, 4)<i>,</i> 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-<i>n </i>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.
Photophysics of 2D Organic–Inorganic Hybrid Lead Halide Perovskites: Progress, Debates, and Challenges
