Guanidinium-Formamidinium Lead Iodide: A Layered Perovskite-Related Compound with Red Luminescence at Room Temperature

Two-dimensional hybrid organic–inorganic lead halides perovskite-type compounds have attracted immense scientific interest due to their remarkable optoelectronic properties and tailorable crystal structures. In this work, we present a new layered hybrid lead halide, namely [CH­(NH₂)₂]­[C­(NH₂)₃]­PbI₄, wherein puckered lead-iodide layers are separated by two small and stable organic cations: formamidinium, CH­(NH₂)₂⁺, and guanidinium, C­(NH₂)₃⁺. This perovskite is thermally stable up to 255 °C, exhibits room-temperature photoluminescence in the red region with a quantum yield of 3.5%, and is photoconductive. This study highlights a vast structural diversity that exists in the compositional space typically used in perovskite photovoltaics