Diarylboron‐Based Asymmetric Red‐Emitting Ir(III) Complex for Solution‐Processed Phosphorescent Organic Light‐Emitting Diode with External Quantum Efficiency above 28%

Abstract

Organic light‐emitting diodes (OLEDs) are one of the most promising technologies for future displays and lighting. Compared with the blue and green OLEDs that have achieved very high efficiencies by using phosphorescent Ir(III) complexes, the red OLEDs still show relatively low efficiencies because of the lack of high‐performance red‐emitting Ir(III) complexes. Here, three highly efficient asymmetric red‐emitting Ir(III) complexes with two different cyclometalating ligands made by incorporating only one electron‐deficient triarylboron group into the nitrogen heterocyclic ring are reported. These complexes show enhanced photoluminescence quantum yields up to 0.96 and improved electron transporting capacity. In addition, the asymmetric structure can help to improve the solubility of Ir(III) complexes, which is crucial for fabricating OLEDs using the solution method. The photoluminescent and oxidation–reduction properties of these Ir(III) complexes are investigated both experimentally and theoretically. Most importantly, a solution‐processed red OLED achieves extremely high external quantum efficiency, current efficiency, and power efficiency with values of 28.5%, 54.4 cd A−1, and 50.1 lm W−1, respectively, with very low efficiency roll‐off. Additionally, the related device has a significantly extended operating lifetime compared with the reference device. These results demonstrate that the asymmetric diarylboron‐based Ir(III) complexes have great potential for fabricating high‐performance red OLEDs.

The damaging effects of the acidity in PEDOT:PSS on semiconductor device performance and solutions based on non-acidic alternatives

“…This material is popular due to its high conductivity and transparency, the ability to reduce surface roughness when coating ITO and its suitability for orthogonal processing. Indeed, it can be considered the default hole transport material (HTM) for solution-processed organic semiconductor devices and has been applied successfully in some benchmark OPV [1][2][3][4] (including the current record PCE device) 5 and OLED devices [6][7][8] over the last 10 years. However, there are disadvantages in using PEDOT:PSS, which include acidity, hygroscopicity, anisotropic charge injection 9 and batch-to-batch variation in electrical and physical properties.…”

Novel Emission Color‐Tuning Strategies in Heteroleptic Phosphorescent Ir(III) and Pt(II) Complexes

“…[58] Complexes 69-71 possess a ppy-type ligand bearing electron-accepting B(Mes) 2 group and their emissive T 1 excited states also exhibit LLCT and MLCT characters ( Figure 22). [60] Complexes 69-71 exhibit a bathochromic effect in their emission wavelengths relative to their corresponding symmetric complexes 1, 13 and 42 (Figures 1, 3, 8, 22 and 23). [38,51] Introduction of the electron-accepting R D 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 B(Mes) 2 group in complexes 69-71 can stabilize the MLCT states and significantly reduce the LUMO levels.…”

“…On the basis of these considerations aforementioned, our group has successively developed new ppy-type Ir(III) complexes 62-75 with the aim of not only tuning phosphorescence emission color but also achieving high EL performance (Figures 18,20,22,24 and 26). [56][57][58]60,61] By judicious combination of two ppy-type ligands with different electrochemical properties into one asymmetric heteroleptic structure, the broad range of color tuning from yellow-green (complex 67, l = 544 nm) to red (complex 71, l = 623 nm) is achieved (Figures 20 and 22). In addition, a fine modulation of the emission wavelength among these complexes can be observed (Figures 18, 20, 22, 24 and 26).…”

“…Hence, the red-emitting OLED using complex 70 as emitter shows a low turn-on voltage of 3.4 V, and external quantum efficiency (EQE) of 28.5 %, current efficiency (CE) of 54.4 cd A À1 , and power efficiency (PE) of 50.1 lm W À1 . [60] Complexes 72 and 73 possess two electron-withdrawing/ accepting groups (SO 2 Ph and B(Mes) 2 groups) bonded to the two ppy ligand, respectively ( Figure 24). [57] Based on our previous report, SO 2 Ph and B(Mes) 2 moieties can host electrons in the MLCT transition process and give more stable MLCT states, thus leading to a red-shift effect in the emission wavelengths of the resulting complexes.…”

Efficient Aggregation-Induced Delayed Fluorescence Luminogens for Solution-Processed OLEDs With Small Efficiency Roll-Off

“…In opposition, small molecules have the advantages of clearly defined structures, easy purification, and better photoluminescence (PL) performance. So, in addition to conventional fluorescent and phosphorescent small molecules (Zhao et al, 2007(Zhao et al, , 2009Yang et al, 2018), developing solution-processable small molecules with delayed fluorescence is of high significance. However, the currently reported solution-processable TADF molecules also suffer from severe efficiency roll-off at high voltages (Wu et al, 2009;Suzuki et al, 2015;Zhong et al, 2020).…”