Dimensionality Reduction of Formamidinium-Rich Lead Iodide Perovskite-Derived Structures

Formamidinium lead iodide, FAPbI3 (FA+ = CH(NH2)2+), with a cubic perovskite structure is among the most studied organic–inorganic hybrid perovskites. Despite several reports only on thin films of FA-rich lead iodide perovskites, such as FA2PbI4, their structures remain unknown due to challenges in characterizing polycrystalline films. Here, we report two new phases of FA-rich lead iodide perovskite-derived structures, FA2PbI4 and FA3PbI5, in the bulk form. These materials feature two- and one-dimensional octahedral networks of perovskite, respectively, allowing for bandgap tuning among FA–Pb–I compositions. This study presents a novel approach to controlling the structural dimensionality of perovskites and their optical properties.