An effective host material with thermally activated delayed fluorescence formed by confined conjugation for red phosphorescent organic light-emitting diodes

Liu, Xiang-Yang; Liang, Feng; Yuan, Yi; Cui, Lin‐Song; Jiang, Zuo‐Quan; Liao, Liang‐Sheng

doi:10.1039/c6cc02856j

Cited by 39 publications

(24 citation statements)

References 39 publications

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“…As observed in Figure 8, both hole and electronc urrents of the cohost-based single-carrier devices are improved;t he hole current improved more significantly,p robablyd ue to the existence of an electron-rich component in the cohost. Thus, the improved carrier transporting property,w hich is beneficial for enlargement of the carrier recombination zone, is believed to be ar eason for the much improved performance of the two OLEDs.T he triplet-exciton upconversion of the exciplex, which was demonstrated to be able to reducet he triplet-triplet and triplet-polaron annihilation in the emitting layer, [16] shoulda lso be an important reasonf or the performance improvement of these devices. So far,t he lifetime of the devices have not been investigated due to the limitation of related instrumentsi no ur laboratory.I tw as demonstrated that the unencapsulated OLEDs in this study were electrically stable during the measurementso fE Ld ata in air.O nthe other hand, the device lifetime is not only dependento nt he emitting layer,b ut also strongly governed by the hole and electron-transporting layers and other organic functional layers.…”

Section: Resultsmentioning

confidence: 99%

Achieving High‐Performance Pure‐Red Electrophosphorescent Iridium(III) Complexes Based on Optimizing Ancillary Ligands

Liang

Zhuang

et al. 2020

Chemistry A European J

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Two new iridium(III) complexes were synthesized by introducing two trifluoromethyl groups into an ancillary ligand to develop pure‐red emitters for organic light‐emitting diodes (OLEDs). The electron‐donating ability of the ancillary ligands is suppressed, owing to the electron‐withdrawing nature of trifluoromethyl groups, which can reduce the HOMO energy levels compared with those of compounds without trifluoromethyl groups. However, the introduction of trifluoromethyl groups into the ancillary ligand has little impact on the LUMO energy levels. Therefore, a well‐tuned, pure‐red, excited‐state energy was achieved by regulating the relative energy level between the HOMO and LUMO. OLEDs with these complexes as emitters showed high external quantum efficiencies (EQEs) of 26 % and realized high EQEs of about 25 % and fairly low driving voltages of 3.3–3.6 V for practical luminance of 1000 cd m−2, as well as excellent Commission Internationale de L'Eclairage (CIE) coordinates of (0.66, 0.33) and (0.67, 0.33); thus, this demonstrates the successful molecular design strategy by modifying the electron‐donating ability of ancillary ligand.

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Section: Resultsmentioning

confidence: 99%

Achieving High‐Performance Pure‐Red Electrophosphorescent Iridium(III) Complexes Based on Optimizing Ancillary Ligands

Liang

Zhuang

et al. 2020

Chemistry A European J

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“…Liu et al developed the TADF compound PrDPhAc (Δ E ST : 0.07 eV) and applied it as a host for red phosphors such as [ Ir(MDQ) 2 (acac)] ( Figure ). The OLED achieved an EQE of 25.8% with CIE coordinates of (0.61, 0.39), much higher than the 12.4% EQE reported when using CBP as host.…”

Section: Tadf Emitters Employed As Host Materialsmentioning

confidence: 99%

Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light‐Emitting Diodes

2017

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The earliest account of electroluminescence, the process of converting electrical energy into light, using organic materials can be traced back to 1963 when Pope et al. applied a direct current to an anthracene single crystal under a bias of 400 V using silver-paste electrodes. [3] Although anthracene fluorescence was observed, a driving voltage of 400 V is evidently not viable in practical applications. The seminal breakthrough in the development of OLEDs appeared in 1987 when Tang and Van Slyke reported a double-layered device using tris(8-hydroxyquinoline)aluminum (Alq 3 ) as the emitting and electron-transporting layer. [1] The green-emitting device showed an external quantum efficiency (EQE) of about 1% when driven at less than 10 V. This marked the dawn of OLED development and tremendous interest and effort from both academia and industry have followed subsequent to this pioneering work, resulting in the ultimate wide-scale commercialization of OLEDs, particularly for display applications.In order to make OLEDs commercially viable for lighting applications, where the cost per unit must be competitive with presently used technology, there are a number of challenges that must be overcome aside from reducing the production cost. The organic emitters should have high photoluminescence quantum yields (PLQYs), which directly impact the device efficiency. The energy levels of the frontier molecular orbitals (i.e., highest occupied and lowest unoccupied molecular oribitals (HOMOs and LUMOs)) of each of the layers in the device should be optimally relatively aligned in order to: i) minimize the barrier to charge injection, and ii) control the recombination region within the device, which greatly affects both the device efficiency and lifetime. [4] The organic materials must demonstrate sufficient thermal stability to be compatible with their vacuum deposition during device fabrication or produce thin films of suitable morphology when spin-coated during solution processing. Regardless of the fabrication method, the organic material must be morphologically stable during device operation when Joule heat is produced in the device. [5] Aside from the aforementioned challenges, another key issue to address is the management of hole and electron recombination within the device, each possessing their own spin. Unlike photoexcitation, in which mainly singlet excited states are produced in the organic emitters, exciton formation through charge (hole and electron) recombination in OLED devices results in 25% singlets and 75% triplets, according to The design of thermally activated delayed fluorescence (TADF) materials both as emitters and as hosts is an exploding area of research. The replacement of phosphorescent metal complexes with inexpensive organic compounds in electroluminescent (EL) devices that demonstrate comparable performance metrics is paradigm shifting, as these new materials offer the possibility of developing low-cost lighting and displays. Here, a comprehensive review of TADF materials is presented, with a...

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“…Recently, many bipolar hosts have been developed to improve the device efficiency and lifetime of red phOLEDs. Developed bipolar host is composed of a number of electron acceptors (quinazoline, quinoxaline, triazine, oxadiazole, and imidazole) [2][3][4][5] and electron donor (carbazole, diazacarbazole, diphenylacridine and phenothiazine) [6][7][8][9] and proved that a number of bipolar hosts can show higher than 20% EQE in red phOLEDs but still many bipolar hosts with high efficiency and long lifetime have not yet been reported. [10][11][12] Herein, two bipolar hosts, 7-(4-(4,6-diphenyl-1,3,5-triazin-2yl)phenyl)-7H-benzo[c]carbazole (BCTrz1) and 7-(3-(4,6diphenyl-1,3,5-triazin-2-yl)phenyl)-7H-benzo[c]carbazole (BCTrz2), are introduced as red hosts for Ir(mphmq) 2 (tmd) [Iridium(III)bis(4-methyl-2-(3,5-dimethylphenyl)quinolinato-N ,C2′) tetramethylheptadionate] phosphorescent emitter.…”

Section: Objective and Backgroundmentioning

confidence: 99%

P‐185: Highly Efficient and Long Lifetime Bipolar Host Material for Red Phosphorescent Organic Light‐Emitting Diodes Using Benzocarbazole and Diphenyltriazine Derivatives

Park

Lee

2019

Symp Digest of Tech Papers

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Red phosphorescent organic light-emitting diodes (phOLEDs) can achieve 100% internal quantum efficiency by harvesting both singlet and triplet excitons through spin orbit coupling. To improve the external quantum efficiency (EQE) and device lifetime, many molecular designs of bipolar hosts with appropriate energy band gap and triplet energy were studied in doping system phOLEDs. Two kinds of bipolar hosts were synthesized by combining benzocarbazole hole type donor and diphenyltriazine electron type acceptor to achieve relatively low triplet energy for red phOLEDs. Two hosts with the benzocarbazole and diphenyltriazine linked through para and meta positions of the phenyl unit proved a triplet energy of 2.52 eV and bipolar carrier transport properties. The band gap of the emitters between highest energy occupied molecular orbital (HOMO) and lowest energy occupied molecular orbital (LUMO) is 2.89 eV and 2.83 eV, while the EQE was 21.7% and 20.7% respectively, as a result of doping with red emitter. It was confirmed that life time was 30 times longer than that of general 4,4′-bis(n-carbazolyl)-1,1′biphenyl (CBP) host at 5000 cd/m 2 .

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An effective host material with thermally activated delayed fluorescence formed by confined conjugation for red phosphorescent organic light-emitting diodes

Cited by 39 publications

References 39 publications

Achieving High‐Performance Pure‐Red Electrophosphorescent Iridium(III) Complexes Based on Optimizing Ancillary Ligands

Achieving High‐Performance Pure‐Red Electrophosphorescent Iridium(III) Complexes Based on Optimizing Ancillary Ligands

Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light‐Emitting Diodes

P‐185: Highly Efficient and Long Lifetime Bipolar Host Material for Red Phosphorescent Organic Light‐Emitting Diodes Using Benzocarbazole and Diphenyltriazine Derivatives

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