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Effect of intermolecular interaction on excited-state properties of thermally activated delayed fluorescence molecules in solid phase: A QM/MM study
摘要： Recently, thermally activated delayed fluorescence (TADF) molecules have attracted great attention since nearly 100% exciton usage efficiency was obtained in TADF molecules. Most TADF molecules used in organic light-emitting diodes are in aggregation state, so it is necessary to make out the intermolecular interaction on their photophysical properties. In this work, the excited-state properties of the molecule AI-Cz in solid phase are theoretically studied by the combined quantum mechanics and molecular mechanics (QM/MM) method. Our results show that geometry changes between the ground state (S0) and the first singlet excited state (S1) are limited due to the intermolecular π-π and CH-π interactions. The energy gap between S1 and the first triplet excited state is broadened and the transition properties of excited states are changed. Moreover, the Huang-Rhys factors and the reorganization energy between S0 and S1 are decreased in solid phase, because the vibration modes and rotations are hindered by intermolecular interaction. The non-radiative rate has a large decrease in solid phase which improves the light-emitting performance of the molecule. Our calculation provides a reasonable explanation for experimental measurements and highlights the effect of intermolecular interaction on excited-states properties of TADF molecules.
关键词： Hybridized local and charge transfer state,Thermally activated delayed fluorescence,Intermolecular interactions,QM/MM method
更新于2025-09-23 15:21:01
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Carbazole/Benzimidazole-Based Bipolar Molecules as the Hosts for Phosphorescent and Thermally Activated Delayed Fluorescence Emitters for Efficient OLEDs
摘要： A series of carbazole/benzimidazole-based molecules, namely, o-CbzBiz, m-CbzBiz, and p-CbzBiz, were readily synthesized in three steps by integrating carbazole with benzimidazole via the ortho-, meta-, and para-positions of phenyl linked to N-phenyl carbazole. These bipolar molecules exhibited a maximum UV absorption band ranging from 310 to 327 nm and a maximum emission band ranging from 380 to 400 nm. Density functional theory calculations showed that the twist angles between the donor and acceptor moieties of these molecules were from 54.9 to 67.1°. Such a twisted structure hampered the π-electron conjugation within the molecule and resulted in high-lying LUMO levels and triplet energies, which make them suitable to be applied as host materials in OLED devices. Our results showed that a maximum external quantum efficiency (EQE) of OLED reached 21.8% when p-CbzBiz was applied as the host of a green phosphorescent emitter, i.e., Ir(ppy)2(acac). In addition, a maximum EQE of OLED reached 16.7% when o-CbzBiz with the host of a green TADF emitter, i.e., 4CzIPN. Moreover, these devices exhibited lower efficiency roll-off than the CBP-hosted device using the same emitters, which demonstrated the bipolar charge carrier property of carbazole/benzimidazole-based molecules.
关键词： thermally activated delayed fluorescence,bipolar molecules,phosphorescent,carbazole,OLEDs,benzimidazole
更新于2025-09-23 15:21:01
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Purine-based thermally activated delayed fluorescence emitters for efficient organic light-emitting diodes
摘要： Organic fluorescent materials possessing thermally activated delayed fluorescence (TADF) characteristics have attracted tremendous attention. Herein, two TADF emitters (1PXZP and 2PXZP) based on a novel biological base acceptor of 9-methylpurine and commonly used donor of phenoxazine (PXZ) have been successfully synthesized and characterized. Both target compounds possess nearly orthogonal configurations to reduce singlet-triplet splitting energy (ΔEST) for remarkable TADF character. The two emitters show good photoluminescence quantum yields (PLQYs), and thus the organic light-emitting diodes employing 1PXZP and 2PXZP as emitters display good performance with maximum external quantum efficiencies of 10.6% and 13.8%, respectively. The efficiencies of 1PXZP based device show nearly no roll-off at 100 cd m-2 luminance due to the short delayed lifetime (τd) of 3.2 μs. This work manifests that the biological base is a promising acceptor for designing TADF materials.
关键词： Thermally activated delayed fluorescence,organic light-emitting diode,aggregation-induced emission,purine
更新于2025-09-23 15:21:01
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Synergetic interface and morphology modification to achieve highly efficient solution-processed sky-blue organic light-emitting diodes
摘要： Solution-processed organic light-emitting diodes (OLEDs), especially blue OLEDs, generally suffer from the low efficiency. Herein, we report an efficient approach to achieve high efficiency by synergetic interface and morphology modification with a polymer, Poly(9-vinylcarbazole) (PVK). Sky-blue thermally activated delayed fluorescent (TADF) material, 10-(4-(4,6-diphenyl-1,3,5- triazin-2-yl)phenyl)-10H- spiro[acridine-9,9-fluorene] (SpiroAC-TRZ), is used as the emitter. The incorporation of PVK thin layer at the hole injection layer/emission layer (EML) interface and a small amount of PVK inner the EML modify the carrier behaviors at the interface and improve the EML morphology. As a result, balanced carrier distribution and reduced carrier recombination are realized at the interface and inner the EML. Through these strategies, the maximum external quantum efficiency and current efficiency of the optimal OLED achieve 25.1% and 53.5 cd/A. To the best of our knowledge, the efficiencies are the highest values ever achieved by the solution-processed sky-blue TADF OLEDs.
关键词： Blue organic light-emitting diodes,Thermally activated delayed fluorescence,High efficiency,All-solution process,Film morphology
更新于2025-09-23 15:21:01
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Flexible diphenylsulfone versus rigid dibenzothiophene-dioxide as acceptor moieties in donor-acceptor-donor TADF emitters for highly efficient OLEDs
摘要： Flexible versus rigid molecular structures of donor-acceptor-donor type compounds are investigated with respect to efficiency of thermally activated delayed fluorescence (TADF) by theoretical and experimental approaches. Three highly efficient TADF emitters based on flexible diphenylsulfone and rigid dibenzothiophene dioxide as acceptor units and di-tert-butyldimethyldihydroacridine as donor moiety were designed and synthesized. Despite they showed similar singlet-triplet splitting (0.01-0.02 eV) and high photoluminescence quantum yields in appropriate hosts, maximum external quantum efficiencies as different as 24.1 and 15.9/19.4% were obtained for organic light emitting devices based on these emitters with, respectively, flexible and rigid molecular structures. The high efficiency of the light-emitting compounds with the flexible molecular structure could be traced to the bi-configurational nature of the lowest singlet and triplet states resulting in higher spin-orbit coupling than for molecules with rigid structures. All derivatives showed bipolar charge transport character. High device efficiency with electron mobility of 3×10-5 cm2V-1s-1 and hole mobility of 1.3×10-4 cm2V-1s-1 at the electric field of 5×105 Vcm-1 was recorded for the layer of para-disubstituted diphenylsulfone with flexible molecular structure. This TADF emitter showed an excellent performance in the organic light emitting device, exhibiting a maximum current efficiency, power efficiency, and external quantum efficiency of 61.1 cdA-1, 64.0 lmW-1, and 24.1%, respectively.
关键词： Thermally activated delayed fluorescence,diphenylsulfone,di-tert-butyldimethyldihydroacridine,bipolar charge transport,dibenzothiophene dioxide
更新于2025-09-23 15:21:01
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Organic Upconversion Display with an over 100% Photon-to-photon Upconversion Efficiency and a Simple Pixelless Device Structure
摘要： Comparing to traditional near infrared (NIR) imaging devices, NIR-to-visible upconversion display which integrated a NIR photodetector with a visible light-emitting diode have merits of simple device structure, low cost, high resolution, and a simple pixelless structure. However, photon-to-photon upconversion efficiencies of these devices are typically much lower than unity. Here we report an all-organic NIR-to-visible upconversion display with a photon-to-photon upconversion efficiency higher than 100% by integrating a photomultiplying organic NIR photodetector with a high-efficiency thermally activated delayed fluorescent organic light-emitting-diode. To the best of our knowledge, this is the first report showing a photon-to-photon upconversion efficiency over 100% without using a built-in transistor for current amplification.
关键词： organic photodetector,NIR-to-visible upconversion,photon-to-photon efficiency,thermally activated delayed fluorescence,organic light-emitting diode
更新于2025-09-23 15:21:01
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Efficient Aggregation-Induced Delayed Fluorescence Luminogens for Solution-Processed OLEDs With Small Efficiency Roll-Off
摘要： Purely organic small molecules with thermally-activated delayed fluorescence have a high potential for application in organic light-emitting diodes (OLEDs), but overcoming severe efficiency roll-off at high voltages still remains challenging. In this work, we design and synthesize two new emitters consisting of electron-withdrawing benzoyl and electron-donating phenoxazine and 9,9-dihexylfluorene. Their electronic structures, thermal stability, electrochemical behaviors, photoluminescence property, and electroluminescence performance are thoroughly investigated. These new emitters show weak fluorescence in dilute solution, but they can emit strongly with prominent delayed fluorescence in the aggregated state, indicating the aggregation-induced delayed fluorescence (AIDF) character. The solution-processed OLEDs based on the two emitters show high external quantum efficiency of 14.69%, and the vacuum-deposited OLEDs can also provide comparable external quantum efficiency of 14.86%. Significantly, roll-offs of the external quantum efficiencies are very small (down to 0.2% at 1,000 cd m?2) for these devices, demonstrating the evidently advanced efficiency stability. These results prove that the purely organic emitters with AIDF properties can be promising to fabricate high-performance solution-processed OLEDs.
关键词： thermally activated delayed fluorescence,aggregation-induced fluorescence,efficiency roll-off,delayed fluorescence,organic light-emitting diodes,electroluminescence
更新于2025-09-23 15:19:57
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High External Quantum Efficiency in Fluorescent OLED by Cascade Singlet Harvesting Mechanism
摘要： The cascade singlet harvesting (CSH) organic light-emitting diodes (OLEDs) are devised to resolve the low quantum efficiency issue of fluorescent OLEDs by efficient singlet exciton harvesting of the fluorescent emitters. The CSH mechanism is realized by doping a fluorescent emitter in the singlet exciton harvesting matrix consisted of high energy exciplex and low energy exciplex. The high energy exciplex serves as the main component of the emitting layer and the low energy exciplex is a medium harvesting the singlet excitons of the fluorescent emitter. Both exciplexes are thermally activated delayed fluorescence type exciplexes to effectively harvest singlet excitons by reverse intersystem crossing process. The singlet excitons of the low energy exciplex are harvested by the high energy exciplex through F?rster energy transfer and then the singlet excitons of the fluorescent emitter are harvested by the low energy exciplex through the second F?rster energy transfer process. The CSH mechanism maximizes the singlet exciton formation in the fluorescent emitter, which significantly enhances the external quantum efficiency (EQE) of the fluorescent OLEDs. The optimization of the emitting layer structure provides high EQE of 19.9% in the fluorescent OLEDs compared with 10.4% of a conventional singlet harvesting fluorescent OLED.
关键词： energy transfer,external quantum efficiency,fluorescent OLEDs,thermally activated delayed fluorescence,cascade singlet harvesting,exciplex
更新于2025-09-23 15:19:57
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Tert-butyl Substituted Hetero-donor TADF compounds for Efficient Solution-Processed Non-doped Blue OLEDs
摘要： For the development of solution-processed organic light-emitting diodes (OLEDs), it is highly desirable and challenging for releazing solution-processable non-doped thermally activated delayed fluorescence (TADF) emitters due to their high efficiency and excellent compatibility to the wet methods. Herein, two pairs of blue TADF isomers are designed and synthesized with a hetero-donor configuration for the realization of high photoluminescent quantum yield. The incorporation of two tert-butyl groups in the molecules can effectively increase the molecular solubility and reduce the aggregation-caused self-quenching of excitons in neat films by inhibiting the intramolecular vibrational relaxation and the intermolecular π-π stacking. Solution-processed non-doped OLEDs are achieved with these blue TADF emitters, exhibiting the record-high external quantum efficiencies (EQE) of 25.8%. Furthermore, all-TADF white OLED with an EQE of 27.3% is also achieved by employing a single emitting layer with the blue TADF emitter as a host for an orange-red TADF dopant.
关键词： non-doped OLED,blue fluoresecent materials,Organic light-emitting diodes,solution process,thermally activated delayed fluorescence
更新于2025-09-23 15:19:57
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Rotation-restricted thermally activated delayed fluorescence compounds for efficient solution-processed OLEDs with EQEs of up to 24.3% and small roll-off
摘要： Two triphenylamine or 4,4’-di(tert-butyl)triphenylamine groups are introduced at 1,8-positions of 3,6-di(tert-butyl)-9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)carbazole to yield two emitters containing a cofacial donor-acceptor-donor chromophore, which exhibit strong TADF characteristic dominated by through-space charge-transfer. The solution-processed OLEDs achieve the maximum external quantum efficiencies of up to 17.4% and 24.3% with small efficiency roll-off rate.
关键词： Thermally Activated Delayed Fluorescence,solution-processed,efficiency roll-off,OLEDs
更新于2025-09-23 15:19:57