High‐Efficiency Deep‐Blue‐Emitting Organic Light‐Emitting Diodes Based on Iridium(III) Carbene Complexes

Abstract

chromaticity standards defined by the National Television System Committee (NTSC) and European Broadcasting Union (EBU) with Commission Internationale de l'Éclairage (CIE) coordinates of (0.14, 0.08) and (0.15, 0.06), respectively; 2) possess high photoluminescence quantum yields (Φ PL ) that translate into high external quantum efficiencies in the OLED, particularly at useful brightnesses (at least 100 cd m −2 for displays and 1000 cd m −2 for lighting); and 3) exhibit competitive device stabilities to fluorescent complexes. [1] Of the phosphorescent complexes studied, iridium(III) compounds have attracted the widest interest as emitters in electroluminescent devices due to their high Φ PL , short phosphorescence lifetimes (τ PL ) and facile color tunability based on the choice of ligands around the metal center. [2] Despite these properties, the design of highly efficient pure blue phosphorescent iridium complexes remains a challenging target to achieve. [3] In order to tune the emission to the blue, electronwithdrawing substituents are typically incorporated on the cyclometalating ligands of the iridium complexes. Three issues arise when employing this strategy. The first is that the electrochemical stability of fluoro substituents, the most popular electron-withdrawing substituent, such as in the widely studied FIrpic [iridium(III)bis(4,6-difluopyridinato-N,C 2′ )picolinate] sky blue emitter, [4] is poor, translating to greatly reduced device stability; [5] while the use of other more strongly electron-withdrawing substituents do not necessarily translate into blueremitting complexes, despite deepening the highest occupied molecular orbital (HOMO) of the compound. [6] The second is that as the energy of the emissive triplet state increases, nonradiative recombination via thermally accessible metal-centered excited states becomes increasingly problematic, leading to emitter degradation. [7] Finally, most iridium(III) complexes do not meet the deep blue chromaticity requirements, and instead possess CIE y ordinates greater than 0.1 as their triplet energies are not sufficiently high (at least 2.8 eV); [3b,8] those that do possess maximal external quantum efficiency (EQE max ) values < 10%. [9] Another strategy to tune the emission of charge-neutral iridium(III) complexes to the blue is to replace the coordinating pyridine rings that are typically employed with more sigma-donating heterocycles that serve to destabilize the lowest unoccupied molecular orbital (LUMO) of the complexes, such as imidazoles [10] and N-heterocyclic carbene (NHC) ligands. [9b,10b,11] High-efficiency pure blue phosphorescent organic light-emitting diodes (OLEDs) remain one of the grand challenges, principally because the emissive complexes employed either do not possess sufficiently high photoluminescence quantum yields or exhibit unsatisfactory Commission International de l'Éclairage (CIE) coordinates. Here two deep-blue-emitting homoleptic iridium(III) complexes are reported and OLEDs are demonstrated with CIE coordinates of ...

Deep-blue organic light-emitting diodes based on a doublet d–f transition cerium(III) complex with 100% exciton utilization efficiency

“…The champion performance includes a turn-on voltage of 3.6 V, a high maximum EQE of 14.0%, and a typical emission from Ce-1 with CIE coordinates of (0.146, 0.078). This result is comparable to the best reported deep-blue OLEDs with a platinum complex, an iridium complex or TADF as the emitter (Supplementary Table S5) [31][32][33] . To estimate the EUE of D2, we measured the horizontal dipole ratio of Ce-1 in TSPO1: CzSi (0.18:0.72 in weight ratio) as only 56.0% (Supplementary Fig.…”

Aggregation‐Induced Dual‐Phosphorescence from Organic Molecules for Nondoped Light‐Emitting Diodes

“…Recently, luminescent materials, especially aggregation‐induced emission luminogens (AIEgens), have been a hotspot due to their wide applications in biosensors, information storage, and organic light‐emitting diodes (OLEDs) . The main benefit of aggregation‐induced emission (AIE) is the manifestation and augmentation of radiative excited states for organic molecular systems .…”

External Quantum Efficiency Exceeding 24% with CIEy Value of 0.08 using a Novel Carbene‐Based Iridium Complex in Deep‐Blue Phosphorescent Organic Light‐Emitting Diodes

“…(Figure 1). [9][10][11][12][13][14][15][16] The Ir(III) complex, mer-tris(N-phenyl, N-benzyl-pyridoimidazol-2-yl)iridium(III) (mer-Ir1), was prepared by reacting the NHC ligand in the presence of silver carbonate, IrCl 3 •3H 2 O and sodium carbonate in degassed 2-ethoxyethanol solution under reflux, as shown in Figure 2a. The mixture of the facial (fac) and meridonial (mer) isomer was obtained and separated by repeated column chromatography.…”

“…Comparison of CIE coordinates (0.14 ≤ x ≥ 0.16, 0.12 ≤ y ≥ 0.04) vs EQE max (left) and L max (right) (see refs [9][10][11][12][13][14][15][16]…”