Above 20% External Quantum Efficiency in Thermally Activated Delayed Fluorescence Device Using Furodipyridine-Type Host Materials

Im, Yirang; Lee, Jun Yeob

doi:10.1021/cm403358h

Cited by 96 publications

(68 citation statements)

References 22 publications

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“…In contrast, in 2014, Yirang Im and Jun Yeob Lee fabricated an OLED with external quantum efficiency above 20%. 1,2 This massive improvement results directly from many years of investigation into methods to overcome the limitation imposed by spin statistics in the charge recombination mechanism, i.e. the fact that three times more triplet excitons than singlet excitons are generated in OLEDs, when the injected charge carriers recombine to give excitons.…”

Section: Introductionmentioning

confidence: 99%

Engineering the singlet–triplet energy splitting in a TADF molecule

et al. 2016

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The key to engineering an efficient TADF emitter is to achieve a small energy splitting between a pair of molecular singlet and triplet states. This work makes important contributions towards achieving this goal. By studying the new TADF emitter 2,7-bis(phenoxazin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DPO-TXO2) and the donor and acceptor units separately, the available radiative and non-radiative pathways of DPO-TXO2 have been identified. The energy splitting between singlet and triplet states was clearly identified in four different environments, in solutions and solid state. The results show that DPO-TXO2 is a promising TADF emitter, having ∆EST = 0.01 eV in zeonex matrix. We further show how the environment plays a key role in the fine tuning of the energy levels of the 1 CT state with respect to the donor 3 LED triplet state, which can then be used to control the ∆EST energy value. We elucidate the TADF mechanism dynamics when the 1 CT state is located below the 3 LE triplet state which it spin orbit couples to, and we also discuss the OLED device performance with this new emitter, which shows maximum external quantum efficiency (E.Q.E) of 13.5% at 166 cd/m 2 .

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Section: Introductionmentioning

confidence: 99%

Engineering the singlet–triplet energy splitting in a TADF molecule

et al. 2016

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“…Thermally activated delayed fluorescence (TADF) has recently become one of the favorite methods to overcome the 25% limitation on the internal quantum efficiency of organic light-emitting diodes (OLEDs) due to spin statistics [1,2]. The ratio (1 : 3) between singlet and triplet excited states created from charge recombination in OLEDs imposes that only 25% of the charge recombination events will give origin to emissive singlet states, the rest is wasted by other non-radiative processes [3].…”

Section: Introductionmentioning

confidence: 99%

Kinetics of thermal-assisted delayed fluorescence in blue organic emitters with large singlet–triplet energy gap

Dias

2015

Phil. Trans. R. Soc. A.

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The kinetics of thermally activated delayed fluorescence (TADF) is investigated in dilute solutions of organic materials with application in blue lightemitting diodes (OLEDs). A method to accurately determine the energy barrier ( E a ) and the rate of reverse intersystem crossing (k Risc ) in TADF emitters is developed, and applied to investigate the tripletharvesting mechanism in blue-emitting materials with large singlet-triplet energy gap ( E ST ). In these materials, triplet-triplet annihilation (TTA) is the dominant mechanism for triplet harvesting; however, above a threshold temperature TADF is able to compete with TTA and give enhanced delayed fluorescence. Evidence is obtained for the interplay between the TTA and the TADF mechanisms in these materials. IntroductionThermally activated delayed fluorescence (TADF) has recently become one of the favorite methods to overcome the 25% limitation on the internal quantum efficiency of organic light-emitting diodes (OLEDs) due to spin statistics [1,2]. The ratio (1 : 3) between singlet and triplet excited states created from charge recombination in OLEDs imposes that only 25% of the charge recombination events will give origin to emissive singlet states, the rest is wasted by other non-radiative processes [3]. This imposes a serious limitation for the application of organic materials in displays and lighting devices [4]. Different methods have been used when trying to overcome this limitation, including the use of organic phosphors containing Ir(III), Pt(II) or other heavy metals, which can convert dark triplet states into emissive 2015 The Author(s) Published by the Royal Society. All rights reserved. species with 100% efficiency due to the enhanced intersystem crossing via the heavy atom effect. These emitting complexes have to be dispersed in charge-transporting host materials with relatively higher energy triplet levels to avoid emission quenching. Finding appropriate host materials for emitters in the blue region is difficult. Also, the performance of blue-emitting phosphors is affected by substantial degradation, thus obtaining stable, long lifetime and deep blue-emitting phosphors has been difficult. Owing to these reasons, deep blue phosphorescent OLEDs with long operation lifetime have not yet been demonstrated [5]. Moreover, heavy metals are not abundant elements in nature, which will cause unnecessary stress on the fabrication costs of these devices.Using triplet-triplet annihilation (TTA) to up-convert non-emissive triplet states to emissive singlet states has also been attempted. In this case, the yield of singlet emissive states is highly dependent on the relative energy order of the excited singlet and triplet energy levels in the molecule, and the maximum total singlet yield is limited to 62.5%. OLEDs with TTA contribution as large as 40% have been demonstrated but the relative merit of this approach is still unsatisfactory [6,7].The TADF mechanism uses the thermal energy to assist reverse intersystem crossing and promote the up-conversion of lowe...

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“…5), one can find a plethora of nitrogen-containing heterocycles, 63,64 as well as various benzonitriles. [47][48][49]56,57,59,65,66 A third acceptor-class is sulfones, 31,54,58,60,67,68 which seems to be particularly useful to realize deep-blue TADF emission.…”

Section: Molecular Design Principlesmentioning

confidence: 99%

“…3). 5,[47][48][49] In summary, TADF is an alternate concept, which can help to realize efficient OLEDs with maximum efficiency. It competes with phosphorescence, the commercial state-of-the-art solution for efficient OLEDs.…”

mentioning

confidence: 99%

Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays

Volz

2016

J. Photon. Energy

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Daniel Volz, "Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays," J. Photon. Energy 6(2), 020901 (), doi: 10.1117/1.JPE.6.020901. Abstract. Thermally activated delayed fluorescence (TADF) is an emerging hot topic. Even though this photophysical mechanism itself has been described more than 50 years ago and optoelectronic devices with organic matter have been studied, improved, and even commercialized for decades now, the realization of the potential of TADF organic light-emitting diodes (OLEDs) happened only recently. TADF has been proven to be an attractive and very efficient alternative for phosphorescent materials, such as dopants in OLEDs, light-emitting electrochemical cells as well as potent emitters for chemiluminescence. In this review, the TADF concept is introduced in terms that are also understandable for nonchemists. The basic concepts behind this mechanism as well as state-of-the-art examples are discussed. In addition, the future economic impact, especially for the lighting and display market, is addressed here. We conclude that TADF materials are especially helpful to realize efficient, durable deep blue and white displays.

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Above 20% External Quantum Efficiency in Thermally Activated Delayed Fluorescence Device Using Furodipyridine-Type Host Materials

Cited by 96 publications

References 22 publications

Engineering the singlet–triplet energy splitting in a TADF molecule

Engineering the singlet–triplet energy splitting in a TADF molecule

Kinetics of thermal-assisted delayed fluorescence in blue organic emitters with large singlet–triplet energy gap

Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays

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