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 motifs 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, and 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, and 2D metal halides. In addition, heterovalent doping of aziridinium lead halides with bismuth allowed us 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 metal halides 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 among the crystal structure, dimensionality, octahedral connectivity, and halogen type with key optical properties. The 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. The optical band gaps of Sb and Bi aziridinium metal halides were determined to range from 2.61 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 the dopant dimensionality and the ability to support a 3D framework. DFT calculations were performed in order to study the band structures of (AzrH)₃Bi₂X₉ and (AzrH)₃Sb₂X₉, and the partial density of states was used to establish which orbitals are located in the vicinity of the 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.