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.

杂化低维无铅钙钛矿衍生物中的量子限域（quantum confinement）现象，始终制约着这类材料在下一代太阳能电池等载流子器件中的应用发展。晶体结构内金属-卤八面体（metal–halide octahedra）的空间分离，可赋予材料更优异的耐湿性与抗光降解性能，但却以牺牲小带隙等理想光物理性质为代价。本文报道了一类此前未被探索的钙钛矿衍生物同构系列的合成与表征：该系列由孤立的二聚体金属-卤化物M₂X₁₀⁴⁻（M=In、Sb；X=Cl、Br）阴离子与卤代吡啶鎓阳离子电荷平衡构成。这类物种通过大量非共价相互作用组装形成超分子网络，可被归类为准零维结构。尽管维度较低，但由于金属-卤化物原子轨道与分子轨道的杂化形成中间带，这类材料仍展现出半导体光学带隙特性。低温发光测试结果证实了电子离域现象：光激发产生的金属/卤化物电子可通过能量可及的π*分子轨道（π* molecular orbitals）被有机阳离子捕获，从而实现电子空穴对的分离。自然键轨道（Natural Bonding Orbital, NBO）计算结果表明，含三价锑离子（Sb³+）的化合物中金属杂化效应更为显著，且该效应可受阴阳结构单元间非共价相互作用的调控。