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

Takuya Ohmi, Wataru Taniguchi, Bhawna, Tomoya Fukui, Yuki Haruta, Takayuki Nakanishi, Takanori Fukushima, Makhsud I. Saidaminov, Masaki Azuma, Takafumi Yamamoto*

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.

J. Am. Chem. Soc. 2026, in press.