A 9-fluorenyl substitution strategy for aromatic-imide-based TADF emitters towards efficient and stable sky blue OLEDs with nearly 30% external quantum efficiency

Feng, Quanyou; Zheng, Xiaojun; Wang, Hongjian; He, Zhiqun; Qian, Yue; Tan, Kesheng; Cao, Hong‐Tao; Xie, Linghai; Huang, Wei

doi:10.1039/d1ma00181g

Cited by 18 publications

(8 citation statements)

References 48 publications

(56 reference statements)

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“…Fluorene is utilized as a bridge to link between the hole-transporting and electron-transporting moieties 48 in the development of phosphorescent organic light-emitting diodes (PhOLEDs) as its longer conjugation not only helps to provide good charge transportation, but also helps the hole stabilization. 49 A very recent study 50 indicates that the 9-phenyl-9-fluorene groups are superior than the tert -butyl groups for increasing electroluminescence (EL) performance and operational life span of blue OLEDs.…”

Section: Introductionmentioning

confidence: 99%

Photodetachment band of the fluorenyl anion: a theoretical rationalization

Kumar

Karmakar

Sarkar

et al. 2023

Phys. Chem. Chem. Phys.

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Section: Introductionmentioning

confidence: 99%

Photodetachment band of the fluorenyl anion: a theoretical rationalization

Kumar

Karmakar

Sarkar

et al. 2023

Phys. Chem. Chem. Phys.

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“…热活化延迟荧光(thermally activated delayed fluorescence, TADF)分子因具有高效率、低成本等优势已成为构筑高性能有机发光二极管(organic light-emitting diodes, OLEDs)的重要选择 [1][2][3][4][5][6][7][8][9][10] . 在设计 TADF 方面, 具有分子内给-受体特性(donor-acceptor, D-A)的单分子型结构由于具有小的单线态(S 1 )-三线态(T 1 )能隙差(ΔE ST ) 而成为科研工作者研究的热点 [11][12][13][14] . 单分子型 TADF 材料在器件制备时往往以较低的分子掺杂浓度(质量分数一般低于 20%)形成发光层, 且浓度比例不易控制, 因此需要精致的器件制备工艺 [15][16][17][18] .…”

Section: 引言unclassified

Exciplex Emission and Property Investigation Based on Cyano-substituted 9-Phenylfluorene Derivative

Cao¹,

Hou²,

Cao³

et al. 2022

Acta Chimica Sinica

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Exciplex-thermally activated delayed fluorescence (exciplex-TADF) devices have displayed great application potential in developing organic light-emitting diodes (OLEDs) with simple-process and high-performance, because the doped ratio of electron donor and acceptor in exciplex device is easily controlled as well as repeated, and small singlet-triplet energy splitting (ΔEST) can be easily achieved for harvesting TADF. However, the current reported electron acceptors are still rare, which mainly focus on traditional electron-attracting structures, such as nitrogen-heterocycles, triarylboron, triazinearenes and diphenylphosphine oxides, etc. Therefore, it is highly desirable to construct new acceptor structures for improving exciplex device performance. In this work, we design and synthesize a novel cyano-substituted 9-phenylfluorene derivative (TCNDPFCz) as an electron acceptor to form exciplex emission through adopting 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) as an electron donor. Our experimental results show that the mixed system (TAPC:TCNDPFCz) exhibits bright exciplex emission at 535 nm and a favourable photoluminescence quantum yield (PLQY) of 54%. Subsequently, temperature-dependent transient fluorescence decay experiment is carried out, which indicates that the TAPC:TCNDPFCz film possesses TADF feature. It is suggested that the satisfactory PLQY value benefits from the exciplex-TADF of TAPC:TCNDPFCz. The low-temperature fluorescence and phosphorescence measurements are also performed and show that the TAPC:TCNDPFCz film displays smaller ΔEST value of 0.05 eV. It is obvious that such small ΔEST value promotes the reverse intersystem crossing from non-radiative triplet state to radiative singlet state of TAPC:TCNDPFCz, thus achieving TADF process. Additionally, electrochemical measurement shows that the TAPC:TCNDPFCz system displays large driving force of 0.41 eV in its exciplex-formation processes, which implies that the exciplex-emission (TAPC:TCNDPFCz) can be realized easily. More than that, it indicates that the acceptor TCNDPFCz possesses strong electron-accepting ability through tetracyano-substitution. An exciplex-OLED using TAPC:TCNDPFCz as the emitting layer is then fabricated, which exhibits a low turn-on voltage of 2.6 V with a maximum current efficiency of 27.2 cd•A -1 , power efficiency of 32.9 lm•W -1 and external quantum efficiency of 12.5%. Therefore, the favourable photoluminescence and electroluminescence efficiencies of TAPC:TCNDPFCz are related to the strong electron-acceptability of TCNDPFCz and large driving force in the exciplex emission process. Our work suggests the 9-phenylfluorene can be used as a molecular skeleton to design new electron acceptors for exciplex-TADF.

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“…The devices with 4TCzBN reached an EQE max of 16.2% at CIE coordinates of (0.16, 0.22) and had an LT50 of 48 h, which is an improvement over the device with 4CzBN (EQE max of 10.6% at similar color coordinates of (0.17, 0.20) and with an LT50 of 18 h), suggesting that the increased intermolecular separation was responsible for the reduced exciton-polaron annihilation, thus elongating device lifetime. Similarly, in another report even larger bulky substituents were shown to be more beneficial compared to tert -butyl groups . An emitter 4-DPFCzAIAd containing adamantyl substituents (Figure d) was used in the EML together with DPEPO as the host, producing a device with an impressive EQE max of 28.2% and sky-blue emission at (0.20, 0.36), together with an LT50 of 51 h. Despite this, the high efficiency roll-off (EQE 1000 of only 6.4%) still needs to be addressed.…”

mentioning

confidence: 91%

The Blue Problem: OLED Stability and Degradation Mechanisms

Tankelevičiūtė,

Samuel,

Zysman-Colman

2024

J. Phys. Chem. Lett.

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OLED technology has revolutionized the display industry and is promising for lighting. Despite its maturity, there remain outstanding device and materials challenges to address. Particularly, achieving stable and highly efficient blue OLEDs is still proving to be difficult; the vast array of degradation mechanisms at play, coupled with the precise balance of device parameters needed for blue high-performance OLEDs, creates a unique set of challenges in the quest for a suitably stable yet high-performance device. Here, we discuss recent progress in the understanding of device degradation pathways and provide an overview of possible strategies to increase device lifetimes without a significant efficiency trade-off. Only careful consideration of all variables that go into OLED development, from the choice of materials to a deep understanding of which degradation mechanisms need to be suppressed for the particular structure, can lead to a meaningful positive change toward commercializable blue devices.

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A 9-fluorenyl substitution strategy for aromatic-imide-based TADF emitters towards efficient and stable sky blue OLEDs with nearly 30% external quantum efficiency

Abstract: Highly efficient and stable blue organic lighting-emitting diodes (OLEDs) continue to be a challenge. Substitution strategy has been proven to be one of the most effective chemical approaches to improve...

Cited by 18 publications

References 48 publications

Photodetachment band of the fluorenyl anion: a theoretical rationalization

Photodetachment band of the fluorenyl anion: a theoretical rationalization

Exciplex Emission and Property Investigation Based on Cyano-substituted 9-Phenylfluorene Derivative

The Blue Problem: OLED Stability and Degradation Mechanisms

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