Improved Efficiency and Stability of Blue Phosphorescent Organic Light Emitting Diodes by Enhanced Orientation of Homoleptic Cyclometalated Ir(III) Complexes

Abstract

Novel homoleptic cyclometalated Ir(III) complexes are designed to improve their emission dipole orientations in the emitting layer of blue phosphorescent organic light emitting devices. Biphenyl group is introduced into the imidazole of cyclometalated Ir(III) complexes to simultaneously achieve enhanced efficiency and operation lifetime, resulting in one of the best device performances of single‐stacked organic light emitting diodes with 91% emission dipole orientation, 26.3% maximum external quantum efficiency (maximally calculated as 41%), and 169 h lifetime at 1000 cd m−2 (LT80), color coordinate (0.17, 0.30). To elucidate the physical origin of this significant improvements, the orientational and positional distributions of the homoleptic dopants are analyzed with consideration on intermolecular interactions through atomistic modeling of the emitting layer. With the findings, the phosphorescent dopants could be designed in the future to achieve enhanced performance.

Near-infrared emitting iridium complexes: Molecular design, photophysical properties, and related applications

“…In some cases, the alkoxy groups are more detrimental to the PLQY than the alkyl groups, probably because the nπ∗ state brought by the oxygen atom would quench the emissive excited state, as in complex 44 ( You et al., 2020b ). Similar side effect appeared in complexes with ethoxy acyl group, as in complexes 24 and 41 ( Kim et al., 2018a , 2020a , 2020b ).

Figure 7 Representative NIR-emitting Ir(III) complexes with flexible chains linked directly on the core of ligands

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“…Notably, for fac -Ir(ppy) 3 -type complexes, the can also be improved, which has been reported in blue-emitting facial homoleptic Ir(III) complexes ( Kim et al., 2020b ). An electron-withdrawing CN group was introduced to the phenyl ring on the C part, which made the TDMs shift toward the Ir-C bond and nearly perpendicular to the C 3 -axis and thus enhanced EDO.…”

Rational Design of Ir(III) Phosphors to Strategically Manage Charge Recombination for High-Performance White Organic Light-Emitting Diodes

“…Cyclometalated Ir­(III) complexes are increasingly considered to be ideal phosphors for organic light-emitting diodes (OLEDs) because of their intense phosphorescence emission, good stability, relatively short lifetime, and versatile tuning of the photophysical properties. Ir­(III) complexes possess the capability of capturing all singlet and triplet excitons for emission induced by a strengthened spin–orbital couple effect induced by heavy atoms. − Importantly, the photoelectric characteristic of Ir­(III) complexes and corresponding device performance can be conveniently tuned by the systematic regulation of organic ligands including their structural framework and electronic nature. − In addition, functional substituents and their positions at the ligand also play a crucial role in the emitting properties. − Therefore, various Ir­(III) phosphors have been successfully designed and constructed based on the platform with desired performance.…”

Fine Emission Tuning from Near-Ultraviolet to Saturated Blue with Rationally Designed Carbene-Based [3 + 2 + 1] Iridium(III) Complexes

“…The high versatility of synthesizing iridium­(III) complexes enables different coordination modes of cyclometallating ligands onto the metal center, which include the extensively reported [2 + 2 + 2] with bidentate and [3 + 3] with tridentate ligands. While there are numerous types of C^N, C^C, C^N^N, and C^C^C ligands bearing different moieties having C or N as the coordination atom, 2-phenylpyridine-, N -pyrazolyl-, and N-heterocyclic carbene (NHC)-based ligands are of particular interest to broaden the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the complex to achieve a nice blue emission. ,− Notably, Thompson et al first reported NHC ligand-containing iridium­(III) complexes Ir­(pmi) 3 (pmi = 1-phenyl-3-methylimidazolin-2-ylidene- C , C 2′ ) and Ir­(pmb) 3 (pmb = 1-phenyl-3-methylbenzimidazolin-2-ylidene- C , C 2′ ) in the [2 + 2 + 2] coordination mode. Both the fac - and mer -Ir­(C^C) 3 complexes showed saturated violet-blue-emission peaking at ∼394 nm in both solution and doped p -bis­(triphenylsilyl)­benzene thin films. , On the other hand, bis-tridentate iridium­(III) complexes incorporated with monoanionic di-imidazolylidene (C^CH^C) and dianionic chromophoric chelates (CH^NH^N) − have been reported recently.…”