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.
Role of lattice distortion and A site cation in the phase transitions of methylammonium lead halide perovskites
