Aziridinium cation as a versatile template for hybrid organic-inorganic perovskites of all dimensionalities

Abstract

Hybrid perovskites form a large group of novel functional materials with diverse structural motives based on metal-halide polyhedra. Here we report on a series of hybrid perovskite-like materials of the general formula (AzrH)₃M₂X₉ (M = Sb, Bi; X = Cl, Br, I), the structure of which is templated with the exclusive aziridinium cation (AzrH)⁺. Notably, single crystal X-ray experiments show that representatives of the reported series exhibit variable crystal structures with different dimensionalities: 0D, 1D, 2D metal halides were obtained. In addition, heterovalent doping of aziridinium lead halides by bismuth allowed to obtain mixed-metal 3D perovskites as well. (AzrH)₃M₂I₉ metal halides form 0D structures in which discrete bi-octahedra are surrounded by aziridinium cations. (AzrH)3M2Br9 form 2D layers separated by (AzrH)+ cations. (AzrH)3Bi2Cl9 is isotypical with bromides, while (AzrH)₃Sb₂Cl₉ forms 1D polymeric bi-chains. For the obtained set of all dimensionality perovskites we aimed to establish the correlation between crystal structure, dimensionality, octahedral connectivity, and halogen type with key optical properties. Optical absorbance of (AzrH)₃M₂X₉ metal halides features strong excitonic peaks centered at 330–499 nm with binding energies of 0.06 – 0.61 eV. Optical band gaps of Sb and Bi aziridinium metal halides were determined to range from 2.91 to 4.09 eV. The lowest obtained band gap for mixed-metal 3D perovskites was found to be 1.49 eV. In addition, doping experiments show a correlation between dopant dimensionality and ability to support a 3D framework. DFT calculations were performed in order to study band structures of (AzrH)₃Bi₂X₉ and (AzrH)₃Sb₂X₉, the partial density of states was used to establish which orbitals are located in the vicinity of Fermi level. This in-depth analysis highlights the transformative potential of (AzrH)₃M₂X₉ perovskites for the next-generation optoelectronic devices and their versatility towards both research and practical applications.