Highly Efficient Nondoped OLEDs with Negligible Efficiency Roll-Off Fabricated from Aggregation-Induced Delayed Fluorescence Luminogens (original) (raw)
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CCS Chemistry, 2021
Severe efficiency instability is still a huge challenge for most organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) molecules, frustrating their industrial application. To address this issue, herein we report two robust luminogens, 3,6-bis(9,9-dimethylacridin-10-yl)-xanthen-9-one (BDMAC-XT) and 3,6-bis(9,9-diphenylacridin-10)-yl)-xanthen-9-one (BDPAC-XT), comprised of electron-accepting 3,6-dibromoxanthen-9-one and electron-donating 9,9-dimethyl-9,10-dihydroacridine and 9,9-diphenyl-9,10-dihydroacridine. BDMAC-XT and BDPAC-XT show interesting aggregationenhanced delayed fluorescence characteristics with excellent photoluminescence quantum yields of 96% and 94% in neat films. Nondoped OLEDs based on BDMAC-XT emit intense green light with high external quantum yields (η ext ; 21%) and hardly any efficiency roll-off (∼0%) at 1000 cd m −2. High-performance sky-blue nondoped OLEDs are achieved using BDPAC-XT as emitter, providing impressive η ext values (21%). Both luminogens can also function efficiently as dopants in doped OLEDs, furnishing excellent η ext values (27%) and very small efficiency roll-offs down to 3.7% at 1000 cd m −2. Moreover, they can perform as excellent hosts for orange and red phosphorescent OLEDs, leading to η ext values of up to 26% and 20%, respectively. These results demonstrate that they are promising versatile functional materials for high-efficiency nondoped and doped OLEDs with superb efficiency stability.
Aggregation‐Induced Delayed Fluorescence Luminogens for Efficient Organic Light‐Emitting Diodes
Chemistry – An Asian Journal, 2018
A fast reverse intersystem crossing (RISC) is of high importance for delayed fluorescence emitters in terms of increasing exciton utilization and suppressing efficiency roll-off. Herein, new robust luminogens comprised of carbonyl, phenoxazine and chlorine-substituted carbazole derivatives are synthesized and characterized. They own distinct aggregationinduced delayed fluorescence (AIDF) feature, and exhibit high photoluminescence efficiencies and short delayed fluorescence lifetimes in neat films. The RISC is conspicuously accelerated owing to their tiny singlet-triplet energy splitting and greatly enhanced spin-orbit coupling by heavy atom effect in neat films. They can function efficiently as light-emitting layers in nondoped OLEDs, providing excellent maximum electroluminescence (EL) efficiencies of 20.4-21.7%, and can also perform outstandingly in doped OLEDs in a wide doping concentration range (5-90 wt%), affording impressive EL efficiencies of up to 100.1 cd A-1 , 104.8 lm W-1 and 29.1%, with small efficiency roll-off. These findings demonstrate the AIDF luminogens with fast RISC are promising candidates to fulfill various demands of production and application of OLEDs. ASSOCIATED CONTENT Supporting Information General information, synthesis and characterization, OLED fabrication and characterization, TGA and DSC curves, cyclic voltammograms, molecular packing in crystals, PL spectra in THF/water mixtures, transient PL decay spectra, fluorescence and phosphorescence spectra in neat films, photophysical data, character curves and key values of doped OLEDs of 9-CCP-BP-PXZ and 3,9-CCP-BP-PXZ, and NMR spectra.
Angewandte Chemie (International ed. in English), 2018
Nondoped organic light-emitting diodes (OLEDs) possess merits of higher stability and easier fabrication than doped devices. However, luminescent materials with high exciton utilization are generally unsuitable for nondoped OLEDs because of severe emission quenching and exciton annihilation in neat films. Herein, we wish to report a novel molecular design of integrating aggregation-induced delayed fluorescence (AIDF) moiety within host materials to explore efficient luminogens for nondoped OLEDs. By grafting 4-(phenoxazin-10-yl)benzoyl to common host materials, we develop a series of new luminescent materials with prominent AIDF property. Their neat films fluoresce strongly and can fully harvest both singlet and triplet excitons with suppressed exciton annihilation. Nondoped OLEDs of these AIDF luminogens exhibit excellent luminance (~100000 cd m-2), outstanding external quantum efficiencies (22.1-22.6%), negligible efficiency roll-off and improved operational stability. To the best...
Advanced Functional Materials, 2020
Increasing exciton utilization and reducing exciton annihilation are crucial to achieve high performance of organic light-emitting diodes (OLEDs), which greatly depend on molecular engineering of emitters and hosts. A novel luminogen (SBF-BP-DMAC) is synthesized and characterized. Its crystal and electronic structures, thermal stability, electrochemical behavior, carrier transport, photoluminescence, and electroluminescence are investigated. SBF-BP-DMAC exhibits enhanced photoluminescence and promotes delayed fluorescence in solid state and bipolar carrier transport ability, and thus holds multifunctionality of emitter and host for OLEDs. Using SBF-BP-DMAC as an emitter, the nondoped OLEDs exhibit maximum electroluminescence (EL) efficiencies of 67.2 cd A −1 , 65.9 lm W −1 , and 20.1%, and the doped OLEDs provide maximum EL efficiencies of 79.1 cd A −1 , 70.7 lm W −1 , and 24.5%. A representative orange phosphor, Ir(tptpy) 2 acac, is doped into SBF-BP-DMAC for OLED fabrication, giving rise to superior EL efficiencies of 88.0 cd A −1 , 108.0 lm W −1 , and 26.8% for orange phosphorescent OLEDs, and forwardviewing EL efficiencies of 69.3 cd A −1 , 45.8 lm W −1 , and 21.0% for two-color hybrid warm-white OLEDs. All of these OLEDs can retain high EL efficiencies at high luminance, with very small efficiency roll-offs. The outstanding EL performance demonstrates the great potentials of SBF-BP-DMAC in practical display and lighting devices. luminous efficiencies and efficient exciton utilization approaching 100%. [2] However, commercial phosphors depend on rare metal elements such as iridium and platinum, and thus are usually expensive. What is more, high doping concentrations (5-20 wt%) of phosphors were recently reported to optimize the device performance, leading to a high manufacturing cost. [3] As promising alternatives, Adachi and co-workers developed purely organic luminescent materials with thermally activated delayed fluorescence (TADF), which can fully utilize the electrogenerated excitons in OLEDs and thus afford excellent external quantum efficiencies (ƞ ext) of >20% via reverse intersystem crossing (RISC) process based on small singlet-triplet energy gaps (ΔE ST ≤ 0.3 eV) of the molecules. [4] However, on account of the long triplet lifetimes, most phosphors and TADF emitters suffer from negative nonradiative processes in OLEDs, such as aggregation and concentration caused quenching, [5] triplet-triplet annihilation (TTA), [6] singlet-triplet annihilation (STA), [7] and so on, [8] which greatly limits their practical applications. To address the issue, robust luminogens that can alleviate emission quenching and exciton annihilation are extremely desired. According to the previous works, reducing the intermolecular interactions (e.g., π-π interactions) has been evidenced to be an effective strategy to develop efficient luminescent materials with high photoluminescence quantum yields (Φ F s) in neat films and prominent delayed fluorescence. [9] By this way, the emitters are usually insensitive to concentrations, which means they can be utilized in nondoped OLEDs as well as doped OLEDs with various doping concentrations. [10] For example, in order to suppress intermolecular annihilations, the bulky 3,6-di-tert-butyl-9H-carbazol-9-yl (tCz) group was introduced in t2tCz2CzBn, a TADF emitter. Nondoped and doped blue OLEDs were fabricated based on t2tCz2CzBn, affording high ƞ ext values of 21.6% and 23.8%, respectively. [11] Similarly, the tCz group was used to block intermolecular electron exchanges in another blue TADF emitter, DPAc-DtCzBN, displaying ƞ ext values of 20.0% and 23.1% for nondoped and doped OLEDs, respectively. [12] However, the efficiency roll-offs in these systems were serious, probably due to the imbalanced charges in the OLEDs.
Activated Delayed-Fluorescence Organic Light-Emitting Diodes
2016
DOI: 10.1002/adma.201504490 still lower than those of vacuum deposited multilayer TADFOLEDs. Furthermore, use of these PEDOT:PSS/PVK multilayer can make mass production of solution-processed TADF-OLEDs diffi cult due to the complex fabrication process. [ 4–6 ] Thus, the solution processed TADF devices should be further simplifi ed without a hole transport layer (HTL) and the effi ciency of the simplifi ed devices should be boosted up to the level of vacuumdeposited multilayer TADF-OLEDs. The effi ciency of simplifi ed TADF devices without HTL can be limited possibly due to the severe exciton quenching at the PEDOT:PSS/EML interface [ 7 ] and at the aggregation of TADF materials, which have long exciton lifetime (≥1 μs), in the EML due to poor solubility. [ 3,8 ] Therefore, we have to overcome luminescence quenching at the conducting hole injection layer (HIL)/EML interface and in the aggregated EML in simplifi ed TADF-OLEDs. Furthermore, making 4CzIPN with deep-lying highest occupie...
Nature Communications, 2020
Aromatic organic deep-blue emitters that exhibit thermally activated delayed fluorescence (TADF) can harvest all excitons in electrically generated singlets and triplets as light emission. However, blue TADF emitters generally have long exciton lifetimes, leading to severe efficiency decrease, i.e., rolloff, at high current density and luminance by exciton annihilations in organic light-emitting diodes (OLEDs). Here, we report a deep-blue TADF emitter employing simple molecular design, in which an activation energy as well as spin–orbit coupling between excited states with different spin multiplicities, were simultaneously controlled. An extremely fast exciton lifetime of 750 ns was realized in a donor–acceptor-type molecular structure without heavy metal elements. An OLED utilizing this TADF emitter displayed deep-blue electroluminescence (EL) with CIE chromaticity coordinates of (0.14, 0.18) and a high maximum EL quantum efficiency of 20.7%. Further, the high maximum efficiency we...
Beilstein Journal of Organic Chemistry, 2018
The design of highly emissive and stable blue emitters for organic light emitting diodes (OLEDs) is still a challenge, justifying the intense research activity of the scientific community in this field. Recently, a great deal of interest has been devoted to the elaboration of emitters exhibiting a thermally activated delayed fluorescence (TADF). By a specific molecular design consisting into a minimal overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) due to a spatial separation of the electron-donating and the electron-releasing parts, luminescent materials exhibiting small S1–T1 energy splitting could be obtained, enabling to thermally upconvert the electrons from the triplet to the singlet excited states by reverse intersystem crossing (RISC). By harvesting both singlet and triplet excitons for light emission, OLEDs competing and sometimes overcoming the performance of phosphorescence-based OLEDs could be fabricated, j...