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

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 [InBr₆^3-] or tetrahedral [InBr₄^-] anions in solution or a combination of both, depending on the loading ratios of MABr and InBr₃ reactants. Understanding the solution chemistry of this system and recognizing the optical fingerprints of these polyanions allow for targeted crystallization of two novel compounds: MAInBr₄ featuring tetrahedral [InBr₄^-] anions and MA₂InBr₅ containing both octahedral [InBr₆^3-] and tetrahedral [InBr₄^-] anions. Further increase of the MABr content leads to the formation of previously reported MA₄InBr₇, containing only octahedral [InBr₆^3-] 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.

Stabilized photoemission from organic molecules in zero-dimensional hybrid Zn and Cd halides

This work explores the utilization of a photoactive organic cation for the preparation of R2MCl4 (M = Zn, Cd; R = (E)-4-styrylpyridinium, C13H12N+).

(NH4)2AgX3 (X = Br, I): 1D Silver Halides with Broadband White Light Emission and Improved Stability

Recently, ternary copper(I) halides have emerged as alternatives to lead halide perovskites for light emission applications. Despite their high-efficiency photoluminescence (PL) properties, most copper(I) halides are blue emitters with unusually poor tunability of their PL properties. Here, we report the impact of substitution of copper with silver in the high-efficiency blue-emitting Cu(I) halides through hydrothermal synthesis and characterization of (NH₄)₂AgX₃ (X = Br, I). (NH₄)₂AgX₃ are found to exhibit contrasting light emission properties compared to the blue-emitting Cu(I) analogues. Thus, (NH₄)₂AgBr₃ and (NH₄)₂AgI₃ exhibit broadband whitish light emission at room temperature with PL maxima at 394 and 534 nm and full width at half-maximum values of 142 and 114 nm, respectively. Based on our combined experimental and computational results, the broadband emission in (NH₄)₂AgX₃ is attributed to the presence of high-stability self-trapped excitons and defect-bound excitons. (NH₄)₂AgBr₃ and (NH₄)₂AgI₃ both have significantly improved air and moisture stability as compared to the related copper(I) halides, which are prone to degradation via oxidation. Our results suggest that silver halides should be considered alongside their copper analogues for high-efficiency light emission applications.