Query: Highly efficient organic light-emitting diodes from delayed fluorescence

Candidate papers:

abstract: The inherent flexibility afforded by molecular design has accelerated the development of a wide variety of organic semiconductors over the past two decades. In particular, great advances have been made in the development of materials for organic light emitting diodes (OLEDs) from early devices based on fluorescent molecules to those using phosphorescent molecules. In OLEDs, electrically injected charge carriers recombine to form singlet and triplet excitons in a 1:3 ratio; the use of phosphorescent metal organic complexes exploits the normally non radiative triplet excitons and so enhances the overall electroluminescence efficiency. Here we report a class of metal free organic electroluminescent molecules in which the energy gap between the singlet and triplet excited states is minimized by design, thereby promoting highly efficient spin up conversion from non radiative triplet states to radiative singlet states while maintaining high radiative decay rates, of more than 106 decays per second. In other words, these molecules harness both singlet and triplet excitons for light emission through fluorescence decay channels, leading to an intrinsic fluorescence efficiency in excess of 90 per cent and a very high external electroluminescence efficiency, of more than 19 per cent, which is comparable to that achieved in high efficiency phosphorescence based OLEDs.
author_names: Hiroki Uoyama

Kenichi Goushi

Katsuyuki Shizu

Hiroko Nomura

Chihaya Adachi
title: Highly efficient organic light emitting diodes from delayed fluorescence
venue: Nature
year: 2012

abstract: Abstract Organic Light Emitting Diodes (OLEDs) using the thermally activated delayed fluorescence (TADF) emitter (4s,6s) 2,4,5,6 tetra(9H carbazol 9 yl)isophthalonitrile (4CzIPN) are demonstrated using a novel ambipolar host 3,5 di(carbazol 9 yl) 1 phenylsulfonylbenzene (mCPSOB) When doped in a 5 wt. concentration, OLEDs with EL efficiency values of more than 81 cd/A for current efficacy and 26.5% for external quantum efficiency are reported. These devices exhibit a low turn on voltage of 3.2 V at 10 cd/m2, as well as reduced efficiency roll off at high current densities. To the best of our knowledge, these are among the highest ever reported efficiencies for TADF OLEDs, and are even comparable to the highest reported efficiencies for phosphorescent OLEDs.
author_names: Michael P Gaj

Canek Fuentes-Hernandez

Yadong Zhang

Seth R Marder

Bernard Kippelen
title: Highly efficient Organic Light Emitting Diodes from thermally activated delayed fluorescence using a sulfone carbazole host material
year: 2015

abstract: Abstract The development of high performance universal host materials for both blue electrophosphorescence and thermally activated delayed fluorescence (TADF) is one of the main challenges for organic light emitting diode (OLED) technology. In this work, based on four quaternary ambipolar hosts with insulated donor acceptor (D A) structures, the influence of the excited state characteristics for these hosts on their device performance was systematically investigated. It was showed that on the premise of the similar electrical properties and excited state energy levels for positive host dopant energy transfer (ET) the weak exciton capture ability, embodied as low exciton binding energy (Eb) for the hosts could facilitate the Dexter ET to the dopant through charge migration. Since the charge transfer featured excited states and small Eb of blue TADF emitters, in contrast to the blue phosphorescence (PH) counterparts, the influence of the host Eb on the device efficiencies of blue TADF dyes was dramatically enlarged, reflecting the higher sensitivity of the latter to host characteristics. In consequence, 9CzFDBFDPO with the smallest Eb endowed its blue TADF and PH devices with the state of the art performance, e.g. EQE beyond 20% and EQE roll off within 20% at 500 cd m 2. This work showed that based on the systematically optimized excited state characteristics, the ambipolar hosts can be competent in both high efficiency blue PH and TADF OLEDs, which is crucial for their commercial applications.
author_names: Zhen Zhang

Dongxue Ding

Ying Wei

Jinwei Zhang

Chunmiao Han

Hui Xu
title: Excited state engineering of universal ambipolar hosts for highly efficient blue phosphorescence and thermally activated delayed fluorescence organic light emitting diodes
year: 2020

abstract: Two benzoylpyridine carbazole based fluorescence materials DCBPy and DTCBPy, bearing two carbazolyl and 4 (t butyl)carbazolyl groups, respectively, at the meta and ortho carbons of the benzoyl ring, were synthesized. These molecules show very small DEST of 0.03 and 0.04 eV and transient PL characteristics indicating that they are thermally activated delayed fluorescence (TADF) materials. In addition, they show extremely different photoluminescent quantum yields in solution and in the solid state: in cyclohexane the value are 14 and 36% but in the thin films, the value increase to 88.0 and 91.4% respectively. The OLEDs using DCBPy and DTCBPy as dopants emit blue and green light with EQEs of 24.0 and 27.2% respectively, and with low efficiency roll off at practical brightness level. The crystal structure of DTCBPy reveals a substantial interaction between the ortho donor (carbazolyl) and acceptor (4 pyridylcarbonyl) unit. This interaction between donor and acceptor substituents likely play a key role to achieve very small DEST with high photoluminescence quantum yield.
author_names: Pachaiyappan Rajamalli

Natarajan Senthilkumar

Parthasarathy Gandeepan

Pei-Yun Huang

Min-Jie Huang

Chen-Zheng Ren-Wu

Chi-Yu Yang

Ming-Jui Chiu

Li-Kang Chu

Hao-Wu Lin

Chien-Hong Cheng
title: A New Molecular Design Based on Thermally Activated Delayed Fluorescence for Highly Efficient Organic Light Emitting Diodes.
venue: Journal of the American Chemical Society
year: 2016

abstract: Abstract In this work, we describe a new approach of improving the external quantum efficiency (EQE) of exciplex organic light emitting diodes (OLEDs) A new approach of dispersing the exciplex in the thermally activated delayed fluorescence (TADF) host was developed to increase the EQE of the exciplex OLEDs. The new emitting layer structure was made up of a mixture of TADF material and an n type material which can generate exciplex with the TADF material. The content of the n type material was maintained below 10 wt to have a morphology with the exciplex dispersed in the TADF matrix material. The emitting layer structure with the exciplex dispersed in the TADF host suppressed exciton quenching and improved the photoluminescence quantum yield of the exciplex. As a result, the exciplex OLEDs with the n type material content of 1 wt% showed high EQE of 15.3% compared with EQE of 10.8% of the conventional exciplex OLEDs with the n type material content of 50%
author_names: Sang Kyu Jeon

Jun Yeob Lee
title: Highly efficient exciplex organic light emitting diodes by exciplex dispersion in the thermally activated delayed fluorescence host
year: 2020

abstract: Aromatic imide based thermally activated delayed fluorescence (TADF) materials with a twisted donor acceptor donor skeleton were efficiently synthesized and exhibited excellent thermal stability and high photoluminescence quantum yields. The small DEST value <0.1 eV) along with the clear temperature dependent delayed component of their transient photoluminescence (PL) spectra demonstrated their excellent TADF properties. Moreover, the performance of organic light emitting diodes in which TADF materials AI Cz and AI TBCz were used as dopants were outstanding, with external quantum efficiencies up to 23.2 and 21.1 respectively.
author_names: Meng Li

Yanwei Liu

Ruihong Duan

Xiaofang Wei

Yuanping Yi

Chuan-Feng Chen
title: Aromatic Imide Based Thermally Activated Delayed Fluorescence Materials for Highly Efficient Organic Light Emitting Diodes.
venue: Angewandte Chemie
year: 2017

abstract: Two new blue TADF emitters, namely, 9' (2,12 di tert butyl 5,9 dioxa 13b boranaphtho[3,2,1 de]anthracen 7 yl) 9,9' diphenyl 9H,9'H,9''H 3,3':6',3' tercarbazole (3CzTB) and 9' (5,9 dioxa 13b boranaphtho[3,2,1 de]anthracen 7 yl) 6,6' dimethyl 9,9' diphenyl 9H,9'H,9''H 3,3':6',3' tercarbazole (M3CzB) for application in highly efficient organic light emitting diodes are reported. These emitters consist of tercarbazole as donor and rigid oxygen bridged boron as acceptor units. Despite having the same donor and acceptor segments, an alkyl modification on the periphery of the donor and acceptor units altered their physicochemical properties and the electrochemical stability of the emitters. Blue TADF light emitting devices fabricated with these emitters exhibited a maximum external quantum efficiency (EQE) and luminance of 30.7% 18 160 cd m 2 and 29.1% 11 690 cd m 2 for M3CzB and 3CzTB, respectively. The operational lifetime (LT50) of the stable blue TADF device fabricated with these emitters was 81 h and 60.5 h at 400 nits with the maximum EQE and CIE color coordinates of 14.4% (0.13, 0.19) and 7.6% (0.14, 0.10) for M3CzB and 3CzTB, respectively.
author_names: Durai Karthik

Dae Hyun Ahn

Jaemin Ryu

Hyuna Lee

Jee Hyun Maeng

Ju Young Lee

Jang Hyuk Kwon
title: Highly efficient blue thermally activated delayed fluorescence organic light emitting diodes based on tercarbazole donor and boron acceptor dyads
year: 2020

abstract: Luminescent materials with aggregation induced emission (AIE) properties exhibit high solid state emission, while thermally activated delayed fluorescence (TADF) materials can fully harvest singlet and triplet excitons to achieve efficient electroluminescence (EL) Herein, the amalgamation of AIE and TADF properties, termed aggregation induced emission and thermally activated delayed fluorescence (AIE TADF) is a promising strategy to design novel desirable luminescent materials. In this paper, a new tailor made material, DCPDAPM, is obtained based on carbazole as the skeleton, 9,9 dimethyl 9,10 dihydroacridine as the donor group and benzophenone as the acceptor group. Its structure is fully characterized by elemental analysis, NMR spectroscopy and mass spectrometry. Furthermore, its thermal stability, photophysical properties, and electrochemical properties are investigated systematically. The results show that this AIE TADF compound exhibits good thermal stability, electrochemical stability and AIE and TADF properties. Ultimately, using DCPDAPM and DCPDAPM doped into CBP as light emitting layers, a non doped OLED (device A) and doped OLEDs (device B, device C and device D) were fabricated and studied. Device A displays green light with a turn on voltage of 3.2 V, a maximum brightness of 123 371 cd m 2, a maximum current efficiency of 26.88 cd A 1, a maximum power efficiency of 15.63 lm W 1 and an external quantum efficiency of 8.15% Among the doped OLEDs (device B, device C and device D) device D shows the best EL performance with a turn on voltage of 3.6 V, a maximum brightness of 116 100 cd m 2, a maximum current efficiency of 61.83 cd A 1, a maximum power efficiency of 40.45 lm W 1 and an external quantum efficiency of 19.67% These results adequately demonstrate the practicability of combining AIE and TADF to explore new efficient emitters.
author_names: Yaodong Zhao

Weigao Wang

Chen Gui

Li Fang

Xinlei Zhang

Shujuan Wang

Shuming Chen

He-ping Shi

Ben Zhong Tang
title: Thermally activated delayed fluorescence material with aggregation induced emission properties for highly efficient organic light emitting diodes
year: 2018

abstract: Three highly efficient blue thermally activated delayed fluorescence (TADF) emitters, 2SPAc HPM, 2SPAc MPM and 2SPAc PPM, have been synthesised based on pyrimidine (PM) 2 methylpyrimidine (MPM) and 2 phenylpyrimidine (PPM) as the acceptor and 10H spiro[acridan 9,9' fluorene] (2SPAc) as the donor moiety. With their appropriate molecular design, these emitters successfully achieve small singlet triplet splitting energies for efficient reverse intersystem crossing, and exhibit high photoluminescence quantum yields. As a result, TADF OLEDs based on 2SPAc HPM, 2SPAc MPM and 2SPAc PPM emit blue light peaking at 479 489 nm and generate very high external quantum efficiencies of 25.56% 24.34% and 31.45% respectively. The 2SPAc PPM based TADF OLED is also one of the very few blue TADF emitters with an external quantum efficiency of more than 30% and it has the best OLED performance among the pyrimidine based TADF emitters.
author_names: Bowen Li

Zhi-yi Li

Taiping Hu

Yong Zhang

Ying Wang

Yuanping Yi

Feng-yun Guo

Liancheng Zhao
title: Highly efficient blue organic light emitting diodes from pyrimidine based thermally activated delayed fluorescence emitters
year: 2018

abstract: Abstract Three new emitters, namely 10,10' (quinoline 2,8 diyl)bis(10H phenoxazine) (Fene) 10,10' (quinoline 2,8 diyl)bis(10H phenothiazine) (Fens) and 10,10' (quinoline 2,8 diyl)bis(9,9 dimethyl 9,10 dihydroacridine) (Yad) featuring quinoline as a new electron acceptor have been designed and conveniently synthesized. These emitters possessed small singlet triplet splitting energy (DEst) and twisted structures, which not only endowed them show thermally activated delayed fluorescence (TADF) properties but also afforded a remarkable aggregation induced emission (AIE) feature. Moreover, they also showed aggregation induced delayed fluorescence (AIDF) property and good photoluminescence (PL) property, which are the ideal emitters for non doped organic light emitting diodes (OLEDs) Furthermore, high performance non doped OLEDs based on Fene, Fens and Yad were achieved, and excellent maximum external quantum efficiencies (EQEmax) of 14.9% 13.1% and 17.4% respectively, were obtained. It was also found that all devices exhibited relatively low turn on voltages ranging from 3.0 V to 3.2 V probably due to their twisted conformation and the AIDF properties. These results demonstrated the quinoline based emitters could have a promising application in non doped OLEDs.
author_names: Lianwei Zhang

Yin-Feng Wang

Mengting Li

Qingyu Gao

Chuan-Feng Chen
title: Quinoline based aggregation induced delayed fluorescence materials for highly efficient non doped organic light emitting diodes
year: 2020