Blending Ionic and Coordinate Bonds in Hybrid Semiconductor Materials: A General Approach toward Robust and Solution-Processable Covalent/Coordinate Network Structures

Abstract

Inorganic semiconductor materials are best known for their superior physical properties, as well as their structural rigidity and stability. However, the poor solubility and solution-processability of these covalently bonded network structures has long been a serious drawback that limits their use in many important applications. Here, we present a unique and general approach to synthesize robust, solution-processable, and highly luminescent hybrid materials built on periodic and infinite inorganic modules. Structure analysis confirms that all compounds are composed of one-dimensional anionic chains of copper iodide (Cu m I m+2 2–) coordinated to cationic organic ligands via Cu–N bonds. The choice of ligands plays an important role in the coordination mode (μ1-MC or μ2-DC) and Cu–N bond strength. Greatly suppressed nonradiative decay is achieved for the μ2-DC structures. Record high quantum yields of 85% (λex = 360 nm) and 76% (λex = 450 nm) are obtained for an orange-emitting 1D-Cu4I6(L 6). Temperature dependent PL measurements suggest that both phosphorescence and thermally activated delayed fluorescence contribute to the emission of these 1D-AIO compounds, and that the extent of nonradiative decay of the μ2-DC structures is much less than that of the μ1-DC structures. More significantly, all compounds are remarkably soluble in polar aprotic solvents, distinctly different from previously reported CuI based hybrid materials made of charge-neutral Cu m X m (X = Cl, Br, I), which are totally insoluble in all common solvents. The greatly enhanced solubility is a result of incorporation of ionic bonds into extended covalent/coordinate network structures, making it possible to fabricate large scale thin films by solution processes.

All-in-one: a new approach toward robust and solution-processable copper halide hybrid semiconductors by integrating covalent, coordinate and ionic bonds in their structures

“… 61–63 In an analogous manner, all 1D-Cu m I m +2 (L) 2 compounds show enhanced solubility in DMSO than CuI and especially neutral CuI(L) compounds, which may be attributed to a similar complexation process. 30 1 H NMR spectroscopy was used to confirmed this hypothesis. 31 The spectra of the DMSO solutions of AIO compounds show characteristic peaks of the free ligands but with some shifts.…”

“…Most recently, by using benzotriazole derived cationic ligands with deliberately designed coordination modes and active sites, we have succeeded in expanding the dimensionality of the inorganic module from molecular clusters (0D) to infinite chains (1D) and achieving a series of 1D-AIO compounds with enhanced framework stability and photoluminescence quantum yield (PLQY). 30 Since each ligand has two N atoms that are available to bind with Cu, two different coordination modes are possible which results in four different Cu m I m +2 2− anionic chains. 1D-μ 1 -Cu 4 I 6 2− (type-1) and 1D-μ 1 -Cu 6 I 8 2− chains ( Fig.…”

“…The AIO approach may serve as a general and powerful tool for the design of solution processable hybrid materials containing covalent/coordinate bonds, including but not limited to copper halide based systems. 30 Despite that AIO-type compounds are coordinate networks and often contain infinite inorganic modules ( e.g. 1D Cu m I m +2 2− chains and 2D-Cu 8 I 10 layer), they demonstrate remarkably high solubility in DMSO and other polar aprotic solvents, comparable with those of common inorganic salts.…”

“… 74 Therefore, the bandgap of the AIO compounds, which share exactly the same 1D-μ 2 -Cu 4 I 6 2− backbone, can be tuned from 2.2 to 2.5 eV, following the same trends as the LUMO energies of free ligands calculated by density functional theory (DFT) and thus lead to emission range from 570 to 615 nm. 30 …”

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“…The stabilities of functional materials in solvents will determine their real applications. 15,38 In this work, alkylbis-(triphenyl)phosphoniums with different spacer lengths might affect their water stability. Most of the functional properties of this work were conducted in water; therefore, their stabilities in water were studied.…”