A New Molecular Design Based on Thermally Activated Delayed Fluorescence for Highly Efficient Organic Light Emitting Diodes

Rajamalli, Pachaiyappan; Senthilkumar, N.; Gandeepan, Parthasarathy; Huang, Pei-Yun; Huang, Min‐Jie; Ren-Wu, Chen-Zheng; Yang, Chi-Yu; Chiu, Ming-Jui; Chu, Li‐Kang; Lin, Huey-Wen

doi:10.1021/jacs.5b10950

Cited by 364 publications

(232 citation statements)

References 48 publications

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“…12,13 Metal-free, thermally activated delayed fluorescence (TADF) materials are considered to be third-generation emitters for OLEDs. [14][15][16][17][18] The basic requirement for efficient TADF is that the highest occupied and lowest unnocupied molecular orbital (HOMO and LUMO, respectively) are spacially separated to achieve a small energy gap between the lowest lying singlet and triplet states. In this way, both triplet and singlet excitons are utilized via thermal up-conversion of the lowest excited triplets (T 1 ) to singlets (S 1 ) together with fluorescence from the S 1 state, leading to a potential IQE of up to 100%.…”

Section: Introductionmentioning

confidence: 99%

Pendant Homopolymer and Copolymers as Solution-Processable Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes

Ren

Nobuyasu²,

Dias³

et al. 2016

Macromolecules

145

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. This study reports a series of polymers with an insulating backbone and varying ratios of 2-(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide as a pendant TADF unit. Steady-state and time-resolved fluorescence spectroscopic data confirm the efficient TADF properties of the polymers. Styrene, as a co-monomer, is shown to be a good dispersing unit for the TADF groups, by greatly supressing the internal conversion and triplet-triplet annihilation.Increasing the styrene content within the copolymers results in relatively high triplet energy, small energy splitting between the singlet and triplet states (E ST ) and a strong contribution from delayed fluorescence to the overall emission. Green emitting OLED devices employing these polymers as spin-coated emitting layers give high performance, which is dramatically enhanced in the copolymers compared to the homopolymer. Within the series, Copo1 with a regiorandom ratio of 37% TADF units : 63% styrene units displays the best performance with a maximum external quantum efficiency (EQE) of 20.1% and EQE at 100 cd m -2 of 5.3%.2

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Section: Introductionmentioning

confidence: 99%

Pendant Homopolymer and Copolymers as Solution-Processable Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes

Ren

Nobuyasu²,

Dias³

et al. 2016

Macromolecules

145

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“…[5][6][7][8][9][10][11][12] Generally, a small singlet-triplet energy splitting (ΔE ST ), which can be realized by spatially separating the overlap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distribution, is required to ensure effective RISC process; [13][14][15][16] meanwhile a certain degree of frontier molecular orbital (FMO) overlap is also necessary to guarantee intrinsically high photoluminescence quantum yield (PLQY). [17][18][19][20] However, the intrinsic tradeoff between these two requirements has to be carefully managed towards designing ideal TADF emitters. [21,22] Numerous attempts to achieve this compromise have revealed that the feasible design strategy is to introduce pre-twisted charge-transfer configuration in donoracceptor (D-A) systems with or without aryl linkage.…”

Section: Introductionmentioning

confidence: 99%

“…[13,18,23] Therefore, the suitable selection of electron D, A units and their linking tactics are of vital importance to achieve excellent TADF emitters with near-zero ΔE ST and high PLQY. [6,7,14,20,24] Although promising results have been achieved on TADF emitters with the state-of-art external quantum efficiencies (η ext s) close to those of phosphorescent OLEDs, the further improvement in the device efficiency and stability is still in demand, and the insight into the relationship between the TADF molecular structures and properties is to be deepened. [10,[24][25][26][27][28] Phenanthroline derivatives have been widely used as efficient electron-transporting materials, [29,30] good host materials, [31,32] and ligand of phosphorescent emitters [33][34][35][36][37][38] in OLEDs, in virtue of their efficient electron transporting properties, good thermal stability, rigid planar structure, and easy structure modification.…”

Section: Introductionmentioning

confidence: 99%

Tailoring Optoelectronic Properties of Phenanthroline‐Based Thermally Activated Delayed Fluorescence Emitters through Isomer Engineering

Zhang

Zhan

et al. 2016

Advanced Optical Materials

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Three isomeric phenanthroline compounds, namely o-PXZP, m-PXZP, and p-PXZP, are constructed by incorporating electron-donor phenoxazine unit into ortho-, meta-, or para-positions of a rigid electron-acceptor phenanthroline core. This approach functionalizes these compounds to exhibit thermally activated delayed fluorescence (TADF) characteristics with microsecondscale photoluminescence (PL) lifetimes. Their thermal, electrochemical properties, emissive characteristics, and energy levels can be finely tailored through isomer engineering. The meta-and para-linking compounds (m-PXZP and p-PXZP) possess higher decomposition temperatures, deeper lowest unoccupied molecular orbital levels, higher PL quantum efficiencies, smaller singlet-triplet energy splitting, and reduced DF lifetimes relative to their ortho-disposition isomer (o-PXZP). Consequently, a green fluorescence organic light-emitting diode (OLED) based on m-PXZP achieves a maximum external quantum efficiency of 18.9%, and has a slow efficiency roll-off of 28% at the luminance of 1000 cd m −2 . Notably, m-PXZP-based device exhibits a nearly 100% utilization efficiency of electro-generated singlet and triplet excitons. These results demonstrate for the first time that phenanthroline derivatives can be employed as TADF emitters for high-efficiency OLEDs. The isomer engineering for TADF emitters provides a simple method to extend structure diversity of TADF emitters, and moreover it provides a flexible method to optimize optoelectronic properties and thereby manipulate electroluminescence performance.

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“…[8][9][10][11][12][13][14][15][16][17][18][19][20] The use of pure organic TADF emitters allows almost 100% internal electroluminescence (EL) quantum efficiency by harvesting the triplet excitons (T 1 ) to the emissive singlet excited states (S 1 ) via reverse intersystem crossing (RISC). [8][9][10][11][12][13][14][15][16][17][18][19][20] The use of pure organic TADF emitters allows almost 100% internal electroluminescence (EL) quantum efficiency by harvesting the triplet excitons (T 1 ) to the emissive singlet excited states (S 1 ) via reverse intersystem crossing (RISC).…”

mentioning

confidence: 99%

High‐Performance Nondoped Blue Delayed Fluorescence Organic Light‐Emitting Diodes Featuring Low Driving Voltage and High Brightness

Zou

Xie

et al. 2019

Advanced Science

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TADF) materials without using heavy metals have gained great attention as the third-generation organic light-emitting diode (OLED) emitters. [8][9][10][11][12][13][14][15][16][17][18][19][20] The use of pure organic TADF emitters allows almost 100% internal electroluminescence (EL) quantum efficiency by harvesting the triplet excitons (T 1 ) to the emissive singlet excited states (S 1 ) via reverse intersystem crossing (RISC). To date, high external quantum efficiency (EQE) exceeding 20% has been achieved for blue, green, and red TADF emitters in OLEDs. [8][9][10][11][12][13][14][15][16][17][18][19][20] However, achieving high-performance deep blue TADF OLEDs is still challenging, since most of them suffer from poor color purity, low brightness, severe EL efficiency roll-off, as well as short operational stability. [21][22][23][24][25] It remains an urgent demand to develop new blue TADF emitters that can simultaneously achieve high efficiency, high brightness, low driving voltage, long operational lifetime, and low Commission Internationale de l'Eclairage (CIE) y coordinate (CIEy) for various applications.Several strategies have been proposed to realize highly efficient blue TADF emitters. Generally, the TADF molecules are designed with a donor-acceptor-type rigid and symmetrical molecular configuration, exhibiting high optical bandgap (E g ), small S 1 -T 1 energy splitting (ΔE ST ), and high photoluminescence quantum yield (PLQY). [26][27][28] For narrowband emission, Thermally activated delayed fluorescence (TADF) provides great potential for the realization of efficient and stable organic light-emitting diodes (OLEDs). However, it is still challenging for blue TADF emitters to simultaneously achieve high efficiency, high brightness, and low Commission Internationale de l'Eclairage (CIE) y coordinate (CIEy) value. Here, the design and synthesis of two new benzonitrile-based TADF emitters (namely 2,6-di(9H-carbazol-9-yl)-3,5-bis(3,6-diphenyl-9H-carbazol-9-yl)benzonitrile (2PhCz2CzBn) and 2,6-di(9H-carbazol-9-yl)-3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)benzonitrile (2tCz2CzBn)) with a symmetrical and rigid heterodonor configuration are reported. The TADF OLEDs doped with both the emitters can achieve a high external quantum efficiency (EQE) over 20% and narrowband blue emission of 464 nm with a CIEy < 0.2. Moreover, the incorporation of a terminal tert-butyl group can weaken the intermolecular π-π stacking in the nondoped TADF emitter, and thus significantly suppress self-aggregation-caused emission quenching for enhanced delayed fluorescence. A peak EQE of 21.6% is realized in the 2tCz2CzBn-based nondoped device with an extremely low turn-on voltage of 2.7 V, high color stability, a high brightness over 20 000 cd m −2 , a narrow fullwidth at half-maximum of 70 nm, and CIE color coordinates of (0.167, 0.248).

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A New Molecular Design Based on Thermally Activated Delayed Fluorescence for Highly Efficient Organic Light Emitting Diodes

Cited by 364 publications

References 48 publications

Pendant Homopolymer and Copolymers as Solution-Processable Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes

Pendant Homopolymer and Copolymers as Solution-Processable Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes

Tailoring Optoelectronic Properties of Phenanthroline‐Based Thermally Activated Delayed Fluorescence Emitters through Isomer Engineering

High‐Performance Nondoped Blue Delayed Fluorescence Organic Light‐Emitting Diodes Featuring Low Driving Voltage and High Brightness

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