Low-Dimensional Hybrid Indium/Antimony Halide Perovskites: Supramolecular Assembly and Electronic Properties

The phenomenon of quantum confinement in hybrid low-dimensional lead-free perovskite derivatives continues to hinder the development of these materials for electron carrier devices such as next-generation solar cells. Spatial separation of metal–halide octahedra within crystal structures yields materials with greater moisture and photodegradation resistance, but at the expense of desired photophysical properties such as small band gaps. We report the synthesis and characterization of an unexplored isomorphic series of perovskite derivatives consisting of isolated dimeric metal–halide M 2 X 10 4– (M = In, Sb; X = Cl, Br) anions charge-balanced with halopyridinium cations. Assembly of these species results in a supramolecular network via extensive noncovalent interactions and may be described as a pseudo-zero-dimensional arrangement. Despite the low dimensionality, these materials display semiconductive optical band-gap energies owing to the appearance of an intermediate band due to hybridization of metal–halide atomic and molecular orbitals. Low-temperature luminescence measurements provide evidence of electron delocalization where photoexcited metal/halide electrons are captured by organic cations via energetically accessible π* molecular orbitals, separating electron/hole pairs. Natural bonding orbital (NBO) calculations reveal that metal hybridization is more pronounced in compounds containing Sb 3+ and can be influenced by noncovalent interactions between anionic and cationic building units.