High‐Efficiency Fluorescent Organic Light‐Emitting Devices Using Sensitizing Hosts with a Small Singlet–Triplet Exchange Energy

Zhang, Dongdong; Li, Chen; Li, Yilang; Li, Haoyuan; Zhang, Deqiang; Qiu, Yong

doi:10.1002/adma.201401476

Cited by 514 publications

(364 citation statements)

References 42 publications

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“…The device with 20% 2CzPN produces a maximum forward viewing power efficiency of 50.2 lm W 21 (Figure 3d). Because illumination sources are typically characterized by their total emitted power, our WOLED exhibits a total EQE max of 33.3% and a total PE max of 85.3 lm W 21 (measured using an integrating sphere), which roll off to 22.7% and 34.0 lm W 21 at a high brightness of 1000 cd m 22 . To the best of our knowledge, these values are among the best results reported thus far for hybrid white devices (see Table 1) and are even comparable to the values of all phosphor white devices.…”

Section: Resultsmentioning

confidence: 99%

Highly efficient hybrid warm white organic light-emitting diodes using a blue thermally activated delayed fluorescence emitter: exploiting the external heavy-atom effect

et al. 2015

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To attain high efficiencies in hybrid white organic light-emitting diodes (WOLEDs), mutual quenching of the fluorophors and phosphors should be minimized. Efforts have been devoted to reducing the triplet quenching of phosphors; however, the quenching of fluorophors by the external heavy-atom effect (EHA) introduced by the phosphors is often ignored. Here, we observed that conventional fluorophors and fluorophors with thermally activated delayed fluorescence (TADF) behave differently in the presence of EHA perturbers. The efficiencies of the conventional fluorophors suffer greatly from the EHA, whereas the TADF fluorophors exhibit negligible changes, which makes TADF materials ideal fluorophors for hybrid devices. WOLEDs using a blue TADF fluorophor and an orange phosphor achieve a maximum forward viewing external quantum efficiency of 19.6% and a maximum forward viewing power efficiency of 50.2 lm W 21 , among the best values for hybrid WOLEDs. This report is the first time that the EHA effect has been considered in hybrid WOLEDs and that a general strategy toward highly efficient hybrid WOLEDs with simple structures is proposed. Keywords: external heavy-atom effect; hybrid white OLEDs; thermally activated delayed fluorescence INTRODUCTION Recent conceptual advancements have led to many exciting approaches to white organic light-emitting diodes (WOLEDs). 1-4 For practical use, high efficiency and long lifetime are the most critical parameters. Blue phosphors can obtain high luminous efficiency but suffer from short lifetime, while blue fluorophors are exactly the opposite. 5,6 Efforts have been devoted to resolve the tradeoff between the high efficiency and long lifetime by combining the advantages of phosphors and fluorophors, that is, by fabricating hybrid WOLEDs with blue fluorophors and green/red or orange phosphors. [6][7][8][9] To attain high efficiencies in hybrid WOLEDs, mutual quenching of the fluorophors and phosphors should be minimized. It has been long realized that the quenching of the green and red phosphorescence by the low triplet energy fluorophors is one of the main losses of excitation energy in these devices. 6 Therefore, a 'triplet harvesting' strategy by doping a blue fluorophor and red/green phosphors in separated regions of high-triplet-energy host materials has been proposed 1,10 and is further improved by incorporating blue fluorophors with high triplet energy (T 1 ) to prevent the undesirable 'back energy transfer' from the phosphors to the blue fluorophors. 2,7,8 However, the heavy metal in the phosphors introduce an external heavy-atom effect (EHA) in the emissive layer (EML) and may lead to

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Section: Resultsmentioning

confidence: 99%

Highly efficient hybrid warm white organic light-emitting diodes using a blue thermally activated delayed fluorescence emitter: exploiting the external heavy-atom effect

et al. 2015

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“…Generally, efficient reverse intersystem crossing (RISC) process and high fluorescence quantum yield ( Φ F ) are two essential requirements for efficient TADF emitters 1, 5. For the former one, an extremely small singlet‐triplet energy split (Δ E ST ) between lowest singlet excited state (S 1 ) and lowest triplet excited state (T 1 ) is highly desired to up‐convert triplet excitons to singlet excitons through thermal excitation 4, 6, 7, 8, 9, 10.…”

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confidence: 99%

Red Organic Light‐Emitting Diode with External Quantum Efficiency beyond 20% Based on a Novel Thermally Activated Delayed Fluorescence Emitter

et al. 2018

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A novel thermally activated delayed fluorescence (TADF) emitter 12,15‐di(10H‐phenoxazin‐10‐yl)dibenzo[a,c]dipyrido[3,2‐h:2′,3′‐j]phenazine (DPXZ‐BPPZ) is developed for a highly efficient red organic light‐emitting diode (OLED). With rigid and planar constituent groups and evident steric hindrance between electron‐donor (D) and electron‐acceptor (A) segments, DPXZ‐BPPZ realizes extremely high rigidity to suppress the internal conversion process. Meanwhile, the highly twisted structure between D and A segments will also lead to an extremely small singlet–triplet energy split to DPXZ‐BPPZ. Therefore, DPXZ‐BPPZ successfully realizes an efficient fluorescent radiation transition and reverse intersystem crossing process, and possesses an extremely high photoluminescence quantum efficiency of 97.1 ± 1.1% under oxygen‐free conditions. The OLED based on DPXZ‐BPPZ shows red emission with a peak at 612 nm and a Commission Internationale de L'Eclairage (CIE) coordinate of (0.60, 0.40), and it achieves high maximum forward‐viewing efficiencies of 20.1 ± 0.2% (external quantum efficiency), 30.2 ± 0.6 cd A−1 (current efficiency), and 30.9 ± 1.3 lm W−1 (power efficiency). The prepared OLED has the best performance among the reported red TADF OLEDs. These results prove that DPXZ‐BPPZ is an ideal candidate for red TADF emitters, and the designing approach is valuable for highly efficient red TADF emitters.

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“…On one hand, PHOLEDs are much more expensive than *Corresponding author (email: duanl@mail.tsinghua.edu.cn) fluorescent OLEDs due to the high cost of phosphors containing rare metals, such as iridium [17,18] and platinum [19] and the high dopant concentration of phosphors (5 wt%-20 wt%) required to achieve optimum device performance [20][21][22][23]; on the other hand, the efficiencies of PHOLEDs tend to decrease with the brightness increasing, which is called efficiency roll-off [24]. Efforts have been paid to solve these problems, such as replacing the high-cost phosphorescent emitters to pure organic ones [25][26][27][28][29][30][31][32], or decreasing the excitons' lifetime and broadening the recombination zone to reduce molecular aggregation [24,[33][34][35], however, the performance of these devices are not satisfactory enough.…”

Section: Introductionmentioning

confidence: 97%

Red phosphorescent organic light-emitting diodes based on a novel host material with thermally activated delayed fluorescent properties

Zhang

et al. 2016

Sci. China Chem.

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High cost of phosphors and significant efficiency roll-off at high brightness are the two main factors that limit the wide application of phosphorescent organic light-emitting diodes (PHOLEDs). Efforts have been paid to find ways to reduce the phosphors' concentration and efficiency roll-off of PHOLEDs.In this work, we reported red emission PHOLEDs with low dopant concentration and low efficiency roll-off based on a novel host material 2,4-biscyanophenyl-6-(12-phenylindole[2,3-a]carbazole-11-yl)-1,3,5-triazine (BCPICT), with thermally activated delayed fluorescent (TADF) properties. The device with 1.0% dopant concentration displayed a maximum external quantum efficiency of 10.7%. When the dopant concentration was increased to 2.0%, the device displayed a maximum external quantum efficiency of 10.5% and a low efficiency roll-off of 5.7% at 1000 cd/m 2 . phosphorescent organic light-emitting diodes, red emission, efficiency roll-off, thermally activated delayed fluorescence Citation:Li Y, Zhang D, Zhang Y, Cai M, Duan L. Red phosphorescent organic light-emitting diodes based on a novel host material with thermally activated delayed fluorescent properties.

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High‐Efficiency Fluorescent Organic Light‐Emitting Devices Using Sensitizing Hosts with a Small Singlet–Triplet Exchange Energy

Cited by 514 publications

References 42 publications

Highly efficient hybrid warm white organic light-emitting diodes using a blue thermally activated delayed fluorescence emitter: exploiting the external heavy-atom effect

Highly efficient hybrid warm white organic light-emitting diodes using a blue thermally activated delayed fluorescence emitter: exploiting the external heavy-atom effect

Red Organic Light‐Emitting Diode with External Quantum Efficiency beyond 20% Based on a Novel Thermally Activated Delayed Fluorescence Emitter

Red phosphorescent organic light-emitting diodes based on a novel host material with thermally activated delayed fluorescent properties

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