Blue organic light-emitting diodes: current status, challenges, and future outlook

Lee, Jiun-Haw; Chen, Chia‐Hsun; Lee, Pei-Hsi; Lin, Hung‐Yi; Leung, M.‐k.; Chiu, Tien‐Lung; Lin, Chi‐Feng

doi:10.1039/c9tc00204a

Cited by 474 publications

(366 citation statements)

References 134 publications

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“…Organic light‐emitting diodes (OLEDs) have penetrated the high‐end market of commercial electronic devices, thanks to their lightweight, panel flexibility, low power consumption, high brightness, and high contrast. [ 1–3 ] In purely organic emitters with a closed‐shell electronic structure, according to spin statistics, the recombination of the electrons and holes injected at their respective electrodes generally produces singlet and triplet excitons in a ratio of 1:3. Since the lowest triplet electronic state (T 1 ) is normally located below the lowest singlet state (S 1 ) in fluorescent emitters, only 25% of generated excitons can be harvested.…”

Section: Introductionmentioning

confidence: 99%

Radiative and Nonradiative Recombinations in Organic Radical Emitters: The Effect of Guest–Host Interactions

Abroshan

Coropceanu

Brédas

2020

Adv Funct Materials

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Radical‐carrying organic molecules have received significant attention to bypass the issue related to harvesting triplet excitons in current light‐emitting materials. While the computational efforts conducted so far have treated these radical emitters as isolated entities, in actual devices, they are embedded in a host matrix and subject to emitter–host interactions. Here, by combining molecular dynamics simulations and density functional theory calculations, the impact of the host matrix on the optoelectronic performance of radical emitters is evaluated, taking as a representative example the (4‐ncarbazolyl‐2,6‐dichlorophenyl)bis(2,4,6‐trichlorophenyl)‐methyl (TTM‐3NCz) radical emitter dispersed in a 4,4‐bis(carbazol‐9‐yl)biphenyl (CBP) host. A morphological analysis shows that steric effects around the radical centers, carried by the TTM electron‐poor moieties of the emitters, disfavor π–π interactions with the host molecules, which leads to random intermolecular orientations around the TTM moieties. The 3NCz electron‐rich moieties of the emitters, however, have much lesser spatial hindrance for intermolecular π–π stacking, which modulates the structural and electronic properties of the emitters in the host matrix. The influence of dynamic and static disorders on the radiative and nonradiative recombination processes is also investigated and it is found that the rates of nonradiative recombination are small, which opens the way to 100% internal quantum efficiency for the doublet‐based emission process.

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Section: Introductionmentioning

confidence: 99%

Radiative and Nonradiative Recombinations in Organic Radical Emitters: The Effect of Guest–Host Interactions

Abroshan

Coropceanu

Brédas

2020

Adv Funct Materials

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“…The theoretical limit of EQE in OLEDs is 25–30%; without any extra light extraction structures and under the presence of randomly oriented emitting dipoles . In comparison to the EQE of green to red phosphorescent iridium complexes reported in previous studies, blue phosphorescent iridium complexes with over 30% of EQE are still rare . For blue phosphorescent OLEDs, the use of 3,3‐di(9 H ‐carbazol‐9‐yl)biphenyl (mCBP) and diphenylphosphineoxide‐4‐(triphenylsilyl)phenyl (TSPO1), with large triplet energy as a mixed host, has been reported recently for increasing the EQE up to 31.9% .…”

Section: Introductionmentioning

confidence: 99%

Blue Phosphorescent Ir(III) Complexes Achieved with Over 30% External Quantum Efficiency

Zaen

Park

Lee

et al. 2019

Advanced Optical Materials

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electrochemical stability, easily tunable energy gaps, and high photoluminescence (PL) quantum efficiency. [8] Toward blue phosphorescent OLEDs (PHOLEDs), there has been significant recent research effort focused on the development of new blue phosphorescent complexes with horizontally oriented emitting dipoles in order to achieve high external quantum efficiency (EQE). The theoretical limit of EQE in OLEDs is 25-30%; without any extra light extraction structures and under the presence of randomly oriented emitting dipoles. [9] In comparison to the EQE of green to red phosphorescent iridium complexes reported in previous studies, [10][11][12][13][14][15][16] blue phosphorescent iridium complexes with over 30% of EQE are still rare. [17][18][19][20] For blue phosphorescent OLEDs, the use of 3,3-di(9H-carbazol-9-yl) biphenyl (mCBP) and diphenylphosphineoxide-4-(triphenylsilyl)phenyl (TSPO1), with large triplet energy as a mixed host, has been reported recently for increasing the EQE up to 31.9%. [21] Therefore, the employment of a suitable host in PHOLEDs is considered an important factor for increasing the EQE. In our earlier research, blue PHOLEDs with 22.5% of EQE were successfully developed using a bipolar host material (9-[3-(9H-carbazol-9-yl)phenyl]-9H-carbazol-3-yl) diphenylphosphine oxide, mCPPO1), and an exciton-blocking material (TSPO1) with high triplet energy. [22] The resulting high efficiency is thought to be attributed to the improvement of the charge balance in the emitting layer (EML), and effective triplet exciton confinement by the TSPO1 in the emitter. Device optimization is still needed, depending on the varied materials including a host or common layer materials combined with the development of phosphorescent triplet emitters. Both the device engineering for optimization and the development of a new host play a key role in the enhancement of EQE; yet the development of phosphorescent emitters with high PL quantum yield (PLQY) is still necessary because the two factors are directly proportional to each other. [23] Consequently, we have prioritized developing bipyridine-based iridium complexes for the creation of efficient blue phosphorescent materials over the past 10 years. [8,[24][25][26][27][28][29][30] Bipyridine ligand, especially 2,3′-bipyridine, possesses larger triplet energy (T 1 = 2.70-2.82 eV) than phenylpyridine (ppy), and also provides an appropriate C^N chelating coordination mode to the metal ion. [31] Moreover, bipyridine-based blue phosphorescent iridium complexes have shown high PLQY and EQE when used in PHOLEDs. [32] This

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“…Researchers are focused on the two promising applications of OLEDs: display devices and lighting panels . However, further development of OLEDs technology is facing enormous challenges, such as cost, emitter, light extraction, etc . On the one hand, in recent years, with the fast progress in performance, newly developed light‐emitting devices such as quantum dot light‐emitting diodes (QLEDs) have approached the state‐of‐the‐art OLEDs only in one decade.…”

Section: Introductionmentioning

confidence: 99%

Microcavity‐Enhanced Blue Organic Light‐Emitting Diode for High‐Quality Monochromatic Light Source with Nonquarterwave Structural Design

Lin

Liu

2020

Advanced Optical Materials

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Despite their rapid development, organic light‐emitting diodes (OLEDs) are limited to display and lighting applications, and exploiting the application and development of OLEDs has become one of the critical issues. In this study, a new type of distributed Bragg reflector (DBR) with low absorption spacer as a bottom mirror is developed through nonquarterwave structural design. Different factors affecting the electroluminescence (EL) properties of microcavity OLEDs (MOLEDs) are investigated by using the optical microcavities with different structures to regulate the EL properties of 4,4′‐bis[(N‐carbazole)styryl] biphenyl (BSB‐Cz). The optimized MOLEDs with quarterwave DBRs exhibited a maximum external quantum efficiency of 8.86 ± 0.06%, demonstrating an enhancement of 79% compared to a reference device. Under the premise of almost not changing the electrical injection of the functional layer materials in the cavity, the spectral full‐width at half maximum of MOLEDs with a nonquarterwave structural design is as narrow as 2 ± 0.05 nm. These improvements are not only suitable for small organic molecules or polymeric materials, but also for novel nanoluminescent materials, such as quantum dots, perovskites, etc. Overall, the current study suggests the general applicability of this novel concept to obtain high‐quality monochromatic light, irrespective of the type of materials used.

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Blue organic light-emitting diodes: current status, challenges, and future outlook

Abstract: Emission mechanisms for OLEDs and their characteristics.

Cited by 474 publications

References 134 publications

Radiative and Nonradiative Recombinations in Organic Radical Emitters: The Effect of Guest–Host Interactions

Radiative and Nonradiative Recombinations in Organic Radical Emitters: The Effect of Guest–Host Interactions

Blue Phosphorescent Ir(III) Complexes Achieved with Over 30% External Quantum Efficiency

Microcavity‐Enhanced Blue Organic Light‐Emitting Diode for High‐Quality Monochromatic Light Source with Nonquarterwave Structural Design

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