Enhanced Triplet–Triplet Annihilation of Blue Fluorescent Organic Light-Emitting Diodes by Generating Excitons in Trapped Charge-Free Regions

Lim, Hyoungcheol; Cheon, Hyung Jin; Lee, Gyeong Seok; Kim, Mi-Kyung; Kim, Yun‐Hi; Kim, Jang‐Joo

doi:10.1021/acsami.9b15303

Cited by 25 publications

(24 citation statements)

References 33 publications

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“…Using TTA material as light-emitting host in OLEDs is an efficient approach to produce blue, green or red emissions when doped with different dopants. [28,[234][235][236] In this strategy, singlet and triplet excitons are formed directly in host materials where TTA takes place. Singlet excited states generated via TTA are transferred to the guest materials through Förster resonance energy transfer.…”

Section: Doped Layer Structurementioning

confidence: 99%

“…2021, 33, 2100704 displaying TTA character. [236,247] Lu and co-workers found a CT-featured naphthalimide derivative (CzPhONI) with a quite small exchange energy but a lower lying 3 ππ* state than the 3 CT state, which is capable of harvesting triplets through TTA. [248] Another naphthalimide compound (E)-2-(4-(tbutyl)phenyl)-6-(2-(6-(diphenylamino)naphthalen-2-yl)vinyl)-1H-benzo[de] isoquinoline-1,3(2H)-dione (NA-TNA, Figure 13b) with intramolecular CT character was exploited by the same group, by using diphenylamine, vinylnaphthalene and 1,8-naphthalimide as the electron donor (D), π-bridge and electron acceptor (A), respectively.…”

Section: Doped Layer Structurementioning

confidence: 99%

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Application of Triplet–Triplet Annihilation Upconversion in Organic Optoelectronic Devices: Advances and Perspectives

et al. 2021

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Figure 14. a) EL spectra (inset: photographs of working devices) and b) EQE versus current density (inset: current efficiency-current density curves) for DPA, pyrene, rubrene, and TIPS-pentacene doped poly(9-vinylcarbazole)-based OLEDs. c) Device energy level diagram and d) EQE versus current density curve (inset: current efficiency versus current density) for inverted rubrene-doped F8BT-based OLED device. Reproduced with permission. [83] Copyright 2017, Wiley-VCH.

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Section: Doped Layer Structurementioning

confidence: 99%

Section: Doped Layer Structurementioning

confidence: 99%

Application of Triplet–Triplet Annihilation Upconversion in Organic Optoelectronic Devices: Advances and Perspectives

et al. 2021

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“…Specifically for blue-emitting devices recent progress in both efficiency and stability has been achieved by employing TTA. [51,52] Regarding stability of OLEDs and PLEDs TTA can also play an important role. First, a higher efficiency due to TTA means for a given light-output a lower current, so less polarons, which reduces triplet-polaron interactions.…”

Section: Discussionmentioning

confidence: 99%

Role of Singlet and Triplet Excitons on the Electrical Stability of Polymer Light‐Emitting Diodes

Zee

Paulus

Png

et al. 2020

Adv Elect Materials

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In contrast, small-molecule organic LEDs exploiting triplet excitons using phosphorescent molecules (ph-OLEDs) or thermally activated delayed fluorescence (TADF) clearly outperform fluorescent PLEDs in terms of efficiency. The low efficiency is also detrimental for the operational stability of PLEDs, since higher currents are required to reach a required light-output, which accelerates degradation. However, to reach high efficiencies, both ph-OLEDs and TADF based OLEDs generally have complex device architectures comprising different injection, transport, emission, and blocking layers. Despite dissimilar architectures, the multilayer TADF and phosphorescent OLEDs as well as single-layer PLEDs all show typical degradation features of a voltage increase and a luminance decrease under continuous electrical operation. [4] For multilayer OLEDs the physical processes behind degradation are hard to elucidate due to the presence of many materials and interfaces. [5,6] The standard PLED device structure, being an emitting polymer layer sandwiched between two different work function electrodes, is more basic, making degradation processes more straightforward to analyze. In earlier work on degradation of poly(phenylene vinylene) (PPV) based LEDs the effects of molecular weight, molecular structure, and defects that arise during synthesis on lifetime have been discussed. [7] In particular halogen related defects in PPVs are pointed out to have a negative influence on the lifetime. With regard to physical degradation mechanisms, in 2001, Silvestre et al. [4] were the first to propose that "voltage increase" and "luminance decrease" during degradation shared a common origin, namely the formation of trap states. Furthermore, Pekkola et al. [8] studied the influence of triplet excitons on the electrical stability of conjugated polymers. A triplet sensitizer was introduced into a PPV-based LED and a negative influence of triplet excitons on the lifetime was reported. As a possible mechanism the energy transfer from a PPV triplet to an oxygen triplet state, creating the reactive singlet oxygen molecule, was suggested. [9,10] Singlet oxygen has the ability to attack the vinyl bonds of PPVs, providing a chemical pathway for degrading the material. [11] Degradation due to extrinsic effects, such as oxygen and water, is typically minimized by proper encapsulation of organic LEDs and by working in a controlled environment. [5−7,12] Also in ph-OLEDs the harmful influence of Stability under electrical stress is an important aspect for the function of organic light-emitting diodes (OLEDs). Degradation is currently one of the key topics in this field, concerning all types of OLEDs, including fluorescent-, phosphorescent-, and thermally activated delayed fluorescence-based OLEDs. For single-layer polymer light-emitting diodes (PLEDs) it has recently been found that degradation is the result of hole trap formation due to excitonpolaron interactions. However, whether singlet or triplet excitons are responsible for degradation is an open questi...

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“…However, there are some exceptions that the delayed fluorescence is determined in the case of a large ΔE ST in the exciplex, which might originate from triplet-triplet annihilation (TTA). [58][59][60][61][62] To clarify the different luminescent mechanisms of exciplex, i.e., either TADF or TTA, Monkman's group compared three combinations of exciplexes, i.e., m-MTDATA:TPBi, TPD:TPBi, and TPD:OXD-7. [63] After elucidating the photophysical data, it was concluded that the exciplex m-MTDATA:TPBi with a small gap between charge transfer singlet ( 1 CT) state and locally excited triplet ( 3 LE) state respectively for the constituting donor and acceptor could exhibit almost pure TADF features.…”

Section: Exciplex From the Mixture Of Donor And Acceptormentioning

confidence: 99%

Thermally Activated Delayed Fluorescence beyond Through‐Bond Charge Transfer for High‐Performance OLEDs

Xue

Xie

2021

Advanced Optical Materials

119

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Charge transfer plays an important role in ruling the exciton dynamics of organic emitters. Most likely, intermolecular/intramolecular charge transfers occur when a donor meets a matched acceptor, which shapes the radiative decays of excitons. The generation and utilization of excitons are vital for organic light‐emitting devices (OLEDs). Thermally activated delayed fluorescence (TADF) emitters, which harvest the triplets via reverse intersystem crossing and thus have attracted intensive attention in the last decade, are very promising to address the issue of cost‐effectiveness in the commercialized OLEDs. Conventionally, intramolecular charge transfer via through‐bond interaction is ubiquitous in the state‐of‐the‐art TADF materials. Alternatively, through‐space charge transfer via either intermolecular or intramolecular interaction is found to be unique and effective in modulating the luminescent properties, such as the emissive colors, exciton lifetimes, and quantum yields. The emerging approaches to evoke the TADF mechanisms beyond through‐bond charge transfer in a single molecule and the related applications of the emitters in OLEDs are highlighted here. The timely and fashionable molecular design and device engineering regarding through‐space charge transfer to the emitting layers in OLEDs are compared and discussed. Finally, a conclusion and the perspectives of the electroluminescence of novel through‐space systems are proposed.

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Enhanced Triplet–Triplet Annihilation of Blue Fluorescent Organic Light-Emitting Diodes by Generating Excitons in Trapped Charge-Free Regions

Cited by 25 publications

References 33 publications

Application of Triplet–Triplet Annihilation Upconversion in Organic Optoelectronic Devices: Advances and Perspectives

Application of Triplet–Triplet Annihilation Upconversion in Organic Optoelectronic Devices: Advances and Perspectives

Role of Singlet and Triplet Excitons on the Electrical Stability of Polymer Light‐Emitting Diodes

Thermally Activated Delayed Fluorescence beyond Through‐Bond Charge Transfer for High‐Performance OLEDs

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