Highly efficient sky blue electroluminescence from ligand-activated copper iodide clusters: Overcoming the limitations of cluster light-emitting diodes

Abstract

Organic light-emitting diodes using cluster emitters have recently emerged as a flexible optoelectronic platform to extend their biological and optical applications. However, their inefficient cluster-centered excited states and deficient electrical properties limit device performance. Here, we introduce donor groups in organic ligands to form ligand-activated clusters, enabling the fabrication of the first cluster-based sky blue–emitting device with a record 30- and 8-fold increased luminance and external quantum efficiency up to ~7000 nits and ~8%, respectively. We show that the electron-donating effect of donor groups can enhance ligand-centered transitions and thoroughly eliminate cluster-centered excited states by delocalizing the molecular transition orbitals from the cluster unit to the ligand, leading to 13-fold increased photoluminescence quantum yield. In turn, the excellent rigidity and photostability of the cluster unit improve the color purity and efficiency stability of the devices. These results will motivate the further development of high-performance optoelectronic clusters by ligand engineering.

Self‐Assembly and Aggregation‐Induced Emission in Aqueous Media of Responsive Luminescent Copper(I) Coordination Polymer Nanoparticles

“…The lack of evident redshift indicates values of ΔE(S‐T) that are even smaller than those determined for compounds 3 and 4 . This mechanism is in agreement with recent studies of Xu on TADF mechanism in other Cu 4 I 4 clusters [26] . The scheme in Figure 3e summarizes the proposed transitions.…”

“…However, when L is a conjugated ligand, contributions from MLCT states are observed. Such behavior is beneficial since the photoluminescent quantum yield (PLQY) can be enhanced, as recently shown, [26] by the activation of MLCT emission along with effective suppression of the 3 CC state, which displays high non‐radiative relaxation rates. In addition, for Cu(I) complexes coordinated to specific ligands, the presence of TADF is a well‐known strategy to increase the emission efficiency of this kind of luminophores [1,26,27] …”

Eco-friendly, solution-processable and efficient low-energy lighting phosphors: copper halide based hybrid semiconductors Cu4X6(L)2(X = Br, I) composed of covalent, ionic and coordinate bonds

“…Confirmed by the room temperature solid state photoluminescence (PL) experiments, emission profile of all four compounds demonstrates single band feature with a full width at half maximum (FWHM) around 150 nm, characteristic of a dominating (M+X)LCT process. 10,18,40,41 Optical absorption spectra for compounds 1-4 were recorded at room temperature and converted to the Kubelka-Munk function (Fig. 3e).…”

Crystalline Metal‐Organic Materials with Thermally Activated Delayed Fluorescence

“…Similar copper iodide clusters compared with [DBFDP] 2 Cu 4 I 4 reported in 2017 were prepared with two DArDBFDP ligands chelating a Cu 4 I 4 cluster. [115] However, the new [DBFDP] 2 Cu 4 I 4 geometry involved the Cu•••Cu and Cu•••P distances and ligandmetal interactions were remarkably disturbed by DArDBFDP ligands. Consequently, the metal-ligand interactions were weakened and excited-state characteristics were simultaneously changed, in other words, the formation of 3 CC radiation charge transfer was dramatically suppressed and the ILCT effect was facilitated, leading to a remarkably enhanced photoluminescence characteristic.…”