Acetamidinium-Methylammonium-Based Layered Hybrid Halide Perovskite [CH3C(NH2)2][CH3NH3]PbI4: Synthesis, Structure, and Optical Properties

In this article we prepared a novel layered hybrid halide perovskite (Ac,MA)PbI4 containing acetamidinium (Ac+) and methylammonium (MA+) cations in form of single crystals and thin films. This compound exhibits a rare for (100)‑oriented perovskites crystal structure with an alternating cations in the interlayer space (ACI) where rotating distortions of adjacent inorganic layers results in alternating cuboctahedral voids of different sizes: the larger ones are occupied by Ac+ and the smaller ones by MA+. The crystal structure is also characterized by an unusually short distance (4.23 Å) between axial iodine atoms of adjacent layers, which is less than the sum of corresponding Van der Waals radii. In addition, we proposed an easy route for the preparation of single-phase smooth and homogenous (Ac,MA)PbI4 thin films and studied their optical properties by means of absorption spectroscopy and photoluminescence spectroscopy. The material has an optical bandgap about 2.22 eV which is significantly smaller than typical (100)‑oriented layered iodide perovskites and demonstrates a relatively large Stokes shift of photoluminescence with a maximum at 590 nm (2.10 eV).