Investigation of the Solution Chemistry of Hybrid Organic–Inorganic Indium Halides for New Material Discovery

Abstract

Recently, metal halide perovskites (MHPs) have emerged as a new class of materials for optical and electronic applications such as solar cells and ionizing radiation detectors. Although the solution-processability of MHPs is among their greatest advantages, the solution chemistries of most metal halide systems and their relationship with the observed structural and chemical diversity are poorly understood. In this work, we study the solution chemistry of a model indium halide system, methylammonium (MA)−In−Br, using a combination of the UV−vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS) measurements, small-angle X-ray scattering (SAXS), and density functional theory (DFT) calculations. Our results show that indium could form either octahedral [InBr 6 3− ] or tetrahedral [InBr 4 − ] anions in solution or a combination of both, depending on the loading ratios of MABr and InBr 3 reactants. Understanding the solution chemistry of this system and recognizing the optical fingerprints of these polyanions allow for targeted crystallization of two novel compounds: MAInBr 4 featuring tetrahedral [InBr 4 − ] anions and MA 2 InBr 5 containing both octahedral [InBr 6 3− ] and tetrahedral [InBr 4 − ] anions. Further increase of the MABr content leads to the formation of previously reported MA 4 InBr 7 , containing only octahedral [InBr 63− ] anions separated by Br − anions. Our results suggest that understanding the solution chemistry of multinary metal halide systems could be a valuable tool for discovering functional materials for practical applications.

Crystal growth, structural and electronic characterizations of zero-dimensional metal halide (TEP)InBr4 single crystals for X-ray detection

“…Polyhedral distortions in metal halides are most typically attributed to electronic effects such as the presence of stereoactive ns 2 lone pair electrons, which does not apply in the case of In 3+ with [Kr] 4d 10 5s 0 electronic configuration. The observed bond lengths in [InBr 4 ] − are similar to that of the other indium bromides containing tetrahedral In 3+ 24,25 and are close to the sum of Shannon ionic radii for tetrahedral In 3+ and Br − ions, which is 2.58 Å. 25 Although (TEP)InBr 4 nominally has a 0D crystal structure, the separation between neighboring [InBr 4 ] − tetrahedra is small, the inter-tetrahedra Br–Br distances are 3.893 Å and 4.133 Å along the c - and b -axes, respectively (see Fig.…”

Ultrabright Light Emission Properties of All-Inorganic and Hybrid Organic–Inorganic Copper(I) Halides

“…To this end, our group is currently conducting spectroscopic studies aimed at recognizing the optical fingerprints of different metal halide polyanions during the growth phase of crystals in the solution medium. 80 Additional concomitant studies are needed to explore new synthesis routes, build synthesis− crystal structure−optical property maps, and ultimately, to develop Cu(I) halide materials design methodologies.…”

“…Therefore, while the wealth and variety of structures displayed by Cu­(I) halides provides an exciting playground for synthetic materials chemists, more systematic studies are required to achieve predictive synthesis of Cu­(I) halides for fundamental studies. To this end, our group is currently conducting spectroscopic studies aimed at recognizing the optical fingerprints of different metal halide polyanions during the growth phase of crystals in the solution medium . Additional concomitant studies are needed to explore new synthesis routes, build synthesis–crystal structure–optical property maps, and ultimately, to develop Cu­(I) halide materials design methodologies. Mechanistic studies of light emission in hybrid and alkali Cu­(I) halides: All-inorganic and hybrid organic–inorganic Cu­(I) halide families reviewed in this perspective have all been reported as STE-based emitters.…”

High quantum yield of In‐based halide perovskites for white light emission and flexible x‐ray scintillators

“…Out of all the potential elements, In 3+ with a six‐coordinated metal ion is a promising candidate for the substitution of Pb 2+ . Due to the relatively small atomic size of In 3+ , In‐based metal halide perovskites are inclined to form a low‐dimensional structure 31–34 . In addition, the inorganic component will be separated due to the steric effect of the organic cation, which can generate zero‐dimensional (0D) metal halides.…”

“…Due to the relatively small atomic size of In 3+ , In-based metal halide perovskites are inclined to form a low-dimensional structure. [31][32][33][34] In addition, the inorganic component will be separated due to the steric effect of the organic cation, which can generate zero-dimensional (0D) metal halides. In 0D In-based halides, the free excitons are easily converted to a strongly localized excited state due to the small energy barrier, providing beneficial factors to create self-trapped excitons (STEs).…”