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 M2X104– (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 Sb3+ and can be influenced by noncovalent
interactions between anionic and cationic building units.