Deep blue phosphorescent organic light-emitting diodes with excellent external quantum efficiency

Park, Jungeun; Oh, Hongseok; Oh, Sihyun; Kim, Jin-Ho; Park, Hyun Jin; Kim, Oh Young; Lee, Jun Yeob; Kang, Youngjin

doi:10.1016/j.orgel.2013.09.017

Cited by 26 publications

(6 citation statements)

References 18 publications

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“…In the past two decades, bipyridine-based organometallic complexes, particularly those of C^N chelating 2,3′-bipyridine, have been of great interest owing to their applications as triplet emitters in phosphorescent organic light-emitting diodes (PHOLEDs). − In particular, bipyridine-based Ir(III) complexes have shown high photoluminescent quantum efficiency (PLQY) and excellent organic light-emitting diode (OLED) performance. − Both homoleptic and heteroleptic Ir(III) complexes substituted at the 2′ and 6′-positions of C-coordinating pyridine rings have been employed as dopant materials in OLED devices. − Moreover, color tuning from blue to orange can be achieved by incorporating different substituents on cyclometalated C^N ligands. − A blue phosphorescent iridium(III) complex bearing difluorine-substituted bipyridine (dfpypy) exhibits diverse intermolecular interactions caused by the pyridine and fluorine moieties (i.e., C–H···N, C–H···F, and face-to-face type π–π interactions), which led to unique supramolecular networks in the crystal packing . The unique crystal packing of Ir(III) molecules, originating from strong intermolecular interactions between the main bipyridine ligands of two adjacent molecules, is the main reason that high thermal stability, high PLQY, and excellent OLED performance is achieved. , Although there are many reports on the photophysical properties and OLED characteristics of bipyridine-based Ir(III) complexes with high triplet energy, those of bipyridine-based Pt(II) complexes are scarce …”

Section: Introductionmentioning

confidence: 99%

Cyclometalated Platinum(II) β-Diketonate Complexes as Single Dopants for High-Efficiency White OLEDs: The Relationship between Intermolecular Interactions in the Solid State and Electroluminescent Efficiency

Kang

Zaen

Park

et al. 2020

Crystal Growth & Design

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Three cyclometalated platinum(II) β-diketonate complexes were developed to investigate the relationship between intermolecular interactions in the solid state according to the position of a bulky trimethylsilyl (TMS) substituent and organic light-emitting diode performance. A variety of intermolecular interactions was observed (i.e., Pt(II)···π, Pt···Pt, and π–π interactions) that were dependent on the presence or absence of TMS and its position on the 2′,6′-difluoro-2,3′-bipyridine ligand. Hirshfeld analysis was performed for the quantitative analysis of intermolecular interactions, indicating that the incorporation of TMS at the 4- or 5-position of the ligand results in strong intermolecular interactions between the Pt(II) complexes. All three complexes show blue to sky blue emissions with high photoluminescent quantum efficiency of ∼0.6–0.8. A relatively remarkable decrease in the highest occupied molecular orbital energy was observed compared to the increase in the lowest unoccupied molecular orbital energy, which is attributed to the stronger electronegativity of difluorinated-bipyridine than phenylpyridine. All complexes effectively formed excimers under low doping concentration, which made it possible to prepare single-doped white organic light-emitting diodes (WOLEDs). WOLEDs were successfully fabricated using the three different Pt(II) complexes as single dopant materials, resulting in over 10% external quantum efficiency. Moreover, the Pt(II) complex substituted with TMS at the 5-position was used as a single dopant at 3 wt % in a nonoptimized WOLED, exhibiting an external quantum efficiency of 12.3%, white emission with Commission Internationale de L’Eclairage (1931) coordinates (x, y) of (0.40, 0.42), and good color rendering index (80), providing one of the highest performance results among single-doped WOLEDs.

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Section: Introductionmentioning

confidence: 99%

Cyclometalated Platinum(II) β-Diketonate Complexes as Single Dopants for High-Efficiency White OLEDs: The Relationship between Intermolecular Interactions in the Solid State and Electroluminescent Efficiency

Kang

Zaen

Park

et al. 2020

Crystal Growth & Design

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“…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 . Moreover, bipyridine‐based blue phosphorescent iridium complexes have shown high PLQY and EQE when used in PHOLEDs . This is especially true for those blue iridium complexes possessing bulky and electron‐donating substituents, such as the trimethylsilyl (TMS) unit at the 4‐position of N ‐coordinating pyridine ring, which is recently known to have a high EQE (>30%) in comparison with those of their nonsubstituted counterparts .…”

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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“…The typical structure of a multi-layered device is indium tin oxide (ITO, 50 nm)/poly(3,4-ethylenedioxy nm), as shown inFigure 5a, and is based on previous work [10]. Devices with Ir(III) compound doping levels from 3 wt% to 10 wt% were fabricated, with the best device performance resulting froma concentration of 5 wt% for 2.…”

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Deep-blue phosphorescent iridium(III) dyes based on fluorine-functionalized bis(2,3′-bipyridyl) ligand for efficient organic light-emitting diodes

Lee

Park

et al. 2015

Dyes and Pigments

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Deep blue phosphorescent organic light-emitting diodes with excellent external quantum efficiency

Cited by 26 publications

References 18 publications

Cyclometalated Platinum(II) β-Diketonate Complexes as Single Dopants for High-Efficiency White OLEDs: The Relationship between Intermolecular Interactions in the Solid State and Electroluminescent Efficiency

Cyclometalated Platinum(II) β-Diketonate Complexes as Single Dopants for High-Efficiency White OLEDs: The Relationship between Intermolecular Interactions in the Solid State and Electroluminescent Efficiency

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

Deep-blue phosphorescent iridium(III) dyes based on fluorine-functionalized bis(2,3′-bipyridyl) ligand for efficient organic light-emitting diodes

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