Confinement Effects in Low-Dimensional Lead Iodide Perovskite Hybrids

We use a layered solution crystal growth technique to synthesize high-quality single crystals of phenylalkylammonium lead iodide organic/inorganic hybrid compounds. Single-crystal X-ray diffraction reveals low-dimensional structures consisting of inorganic sheets separated by bilayers of the organic cations. The shortest alkyls yield two-dimensional structures consisting of inorganic sheets of corner-sharing PbI6-octahedra. However, the longer alkyls induce both corner- and face-sharing of the PbI6-octahedra, and form new compounds. Density functional theory calculations including spin-orbit coupling show quantum confinement in two dimensions for the shorter alkyls, and in one dimension for the longer alkyls, respectively. The face-sharing PbI6-octahedra create a confinement leading to effectively one-dimensional behavior. These confinement effects are responsible for the observed peak shifts in photoluminescence for the different phenylalkylammonium lead iodide hybrids. Our results show how the connectivity of the octahedra leads to confinement effects that directly tune the optical band gap.