Co-reporter:Jeong-A Seo, Yirang Im, Si Hyun Han, Chil Won Lee, and Jun Yeob Lee
ACS Applied Materials & Interfaces November 1, 2017 Volume 9(Issue 43) pp:37864-37864
Publication Date(Web):October 5, 2017
DOI:10.1021/acsami.7b09351
Unconventional blue thermally activated delayed fluorescent emitters having electron-donating type indolocarbazole as an acceptor were developed by attaching carbazolylcarbazole or acridine donors to the indolocarbazole acceptor. Three compounds were derived from the indolocarbazole acceptor. The indolocarbazole–acridine combined products showed efficient delayed fluorescent behavior and a high quantum efficiency of 19.5% with a color coordinate of (0.15, 0.16) when they were evaluated as thermally activated delayed fluorescent emitters in deep blue fluorescent devices. This is the first demonstration of the use of electron-donating carbazole-derived moieties as efficient acceptor units of blue thermally activated delayed fluorescent emitters.Keywords: acceptor; blue device; delayed fluorescence; indolocarbazole; quantum efficiency;
Co-reporter:Jin-Wook Lee, Yung Ji Choi, June-Mo Yang, Sujin Ham, Sang Kyu Jeon, Jun Yeob Lee, Young-Hyun Song, Eun Kyung Ji, Dae-Ho Yoon, Seongrok Seo, Hyunjung Shin, Gil Sang Han, Hyun Suk Jung, Dongho Kim, and Nam-Gyu Park
ACS Nano March 28, 2017 Volume 11(Issue 3) pp:3311-3311
Publication Date(Web):March 9, 2017
DOI:10.1021/acsnano.7b00608
Excellent color purity with a tunable band gap renders organic–inorganic halide perovskite highly capable of performing as light-emitting diodes (LEDs). Perovskite nanocrystals show a photoluminescence quantum yield exceeding 90%, which, however, decreases to lower than 20% upon formation of a thin film. The limited photoluminescence quantum yield of a perovskite thin film has been a formidable obstacle for development of highly efficient perovskite LEDs. Here, we report a method for highly luminescent MAPbBr3 (MA = CH3NH3) nanocrystals formed in situ in a thin film based on nonstoichiometric adduct and solvent-vacuum drying approaches. Excess MABr with respect to PbBr2 in precursor solution plays a critical role in inhibiting crystal growth of MAPbBr3, thereby forming nanocrystals and creating type I band alignment with core MAPbBr3 by embedding MAPbBr3 nanocrystals in the unreacted wider band gap MABr. A solvent-vacuum drying process was developed to preserve nanocrystals in the film, which realizes a fast photoluminescence lifetime of 3.9 ns along with negligible trapping processes. Based on a highly luminescent nanocrystalline MAPbBr3 thin film, a highly efficient green LED with a maximum external quantum efficiency of 8.21% and a current efficiency of 34.46 cd/A was demonstrated.Keywords: high efficiency; light-emitting diode; nanocrystal; perovskite; type I band alignment;
Co-reporter:Sung Yong Byeon, Ji Han Kim, and Jun Yeob Lee
ACS Applied Materials & Interfaces April 19, 2017 Volume 9(Issue 15) pp:13339-13339
Publication Date(Web):March 31, 2017
DOI:10.1021/acsami.6b15502
CN-modified host materials, 9-(2-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-carbazole-3-carbonitrile (o-CzCN) and 9-(3-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-carbazole-3-carbonitrile (m-CzCN), which can improve the external quantum efficiency and lifetime of both blue phosphorescent and thermally activated delayed fluorescent (TADF) emitters were developed. A molecular design approach to stabilize the molecular structure and reduce the energy gap produced two high triplet energy host materials of o-CzCN and m-CzCN compatible with the phosphorescent and TADF emitters. The new host materials lowered operation voltage, increased quantum efficiency, and elongated lifetime of both phosphorescent and TADF devices.Keywords: blue device; delayed fluorescence; efficiency; host; lifetime;
Co-reporter:Ji Han Kim, Minsik Eum, Tae Hyung Kim, Jun Yeob Lee
Dyes and Pigments 2017 Volume 136() pp:529-534
Publication Date(Web):January 2017
DOI:10.1016/j.dyepig.2016.09.013
•A pyrrolocarbazole as a new donor moiety of donor-acceptor type emitter.•Small singlet-triplet energy splitting by strong donor strength of pyrrolocarbazole.•Improved quantum efficiency and elongated lifetime by the pyrrolocarbazole based molecular design.A novel pyrrolocarbazole moiety was developed as a new donor moiety of thermally activated delayed fluorescent emitters. The new pyrrolocarbazole donor moiety possessed stronger donor strength than carbazole and better stability than acridine, which enhanced the quantum efficiency and lifetime of the thermally activated delayed fluorescent emitters. The pyrrolocarbazole donor, diphenyltriazine acceptor, and a phenyl linker merged emitter performed as a highly efficient delayed fluorescent emitter by providing high quantum efficiency of 17.7%.
Co-reporter:Chohyun Seo, Jeong Min Choi, Seong-Soo Hong, Jun Yeob Lee, SungYong Seo
Dyes and Pigments 2017 Volume 136() pp:145-149
Publication Date(Web):January 2017
DOI:10.1016/j.dyepig.2016.08.045
•Carbazole, phosphine oxide, and benzothiophene based high triplet energy host material.•High quantum efficiency in blue phosphorescent organic light-emitting diodes.•High triplet energy for blue devices.An organic compound having carbazole, benzothiophene, and phosphine oxide moieties, (5-(9H-carbazol-9-yl)benzo[b]thiophen-2-yl)diphenylphosphine oxide (CBTPO), was synthesized and employed as a blue host material to harvest triplet excitons from blue triplet emitters. The CBTPO material is a bipolar host material because it includes carbazole and diphenylphosphine oxide charge transport units with both a high triplet energy of 2.76 eV and a high quantum efficiency of 19.1% in blue phosphorescent device.
Co-reporter:Chan Seok Oh, Chang-Ki Moon, Jeong Min Choi, Jin-Suk Huh, Jang-Joo Kim, Jun Yeob Lee
Organic Electronics 2017 Volume 42() pp:337-342
Publication Date(Web):March 2017
DOI:10.1016/j.orgel.2016.12.058
•Horizontal dipole orientation of thermally activated delayed fluorescent emitters.•Para-orientation of extended donor structure for high horizontal dipole orientation.•High dipole orientation in the emitters with high aspect ratio.The relationship between the chemical structure and the dipole orientation of thermally activated delayed fluorescent (TADF) emitters was examined by synthesizing three TADF emitters with donor and acceptor moieties at ortho-, meta-, and para-positions of a phenyl linker. Two carbazolylcarbazole donor moieties and two CN acceptor moieties were attached to the phenyl linker. The degree of dipole orientation of the three TADF emitters was in the order of para- (0.84)>meta- (0.76)>ortho- (0.72) substitution, demonstrating that extended molecular geometry by para-substitution is a key parameter to induce the dipole orientation of the TADF emitters.
Co-reporter:Wook Song;Ha Lim Lee
Journal of Materials Chemistry C 2017 vol. 5(Issue 24) pp:5923-5929
Publication Date(Web):2017/06/22
DOI:10.1039/C7TC01552F
High triplet energy exciplex hosts for deep blue phosphorescent organic light-emitting diodes were developed by synthesizing a high triplet energy hole transport type host material designed for exciplex formation with a high triplet energy electron transport type host material derived from a diphenyltriazine. The highest occupied molecular orbital level of the hole transport type host materials was precisely controlled to manage the exciplex formation with the electron transport type host. Two exciplex hosts with high triplet energies of 2.94 and 2.95 eV were demonstrated using the synthesized hole transport type hosts and they were effective as the hosts of a deep blue triplet emitter.
Co-reporter:Wook Song;Taekyung Kim;Yoonkyoo Lee
Journal of Materials Chemistry C 2017 vol. 5(Issue 16) pp:3948-3954
Publication Date(Web):2017/04/20
DOI:10.1039/C7TC00556C
A stepwise energy level doping structure for improving the lifetime of organic light-emitting diodes was developed by doping two emitters with different energy levels in the same host material as separated emitting layers. A hole-trapping phosphorescent emitter was doped in the emitting layer close to the electron transport layer and an electron-trapping thermally activated delayed fluorescent emitter was doped in the emitting layer close to the hole transport layer to show stepwise energy levels between emitting materials in the same host. The stepwise energy level doping structure improved the lifetime of organic light-emitting diodes through suppressed triplet–triplet annihilation and triplet–polaron annihilation by emission zone control and carrier confinement. Moreover, a high quantum efficiency close to 20% was realized in both green and blue organic light-emitting diodes in addition to the improved lifetime. This is the first work reporting both high quantum efficiency close to 20% and elongated lifetime simultaneously.
Co-reporter:Sung Moo Kim;Ju Hui Yun;Si Hyun Han
Journal of Materials Chemistry C 2017 vol. 5(Issue 35) pp:9072-9079
Publication Date(Web):2017/09/14
DOI:10.1039/C7TC02973J
Stable host materials based on benzocarbazole and quinazoline were synthesized to establish a design strategy of bipolar hosts for elongated lifetime in orange phosphorescent organic light-emitting diodes (PHOLEDs). Three host materials with benzocarbazole and quinazoline connected directly or through a phenyl linker were compared in terms of the device lifetime of the orange PHOLEDs. The connection between benzocarbazole and quinazoline through a phenyl linker was an effective way of improving the lifetime of the red PHOLEDs by more than twice and the molecular orbital distribution of the hosts was well correlated with the lifetime of the PHOLEDs. In particular, the lifetime of the PHOLEDs was extended by more than 30 times compared to a conventional PHOLED with a common CBP host.
Co-reporter:Hee-Jun Park;Si Hyun Han
Journal of Materials Chemistry C 2017 vol. 5(Issue 46) pp:12143-12150
Publication Date(Web):2017/11/30
DOI:10.1039/C7TC03133E
New green thermally activated delayed fluorescence (TADF) materials built on a directly coupled dual emitting core based backbone structure were designed, synthesized, and applied as green dopants in TADF devices. An ortho-linkage between a carbazole or 3,6-di-tert-butylcarbazole donor and a triazine acceptor facilitated the TADF emission, and direct coupling of the two TADF emitting cores more than doubled the external quantum efficiency of the TADF devices. The TADF emitter based on the directly coupled dual emitting core design exhibited a green emission with a CIE coordinate of (0.23, 0.52) and a maximum external quantum efficiency of 20.8% compared with less than 10% efficiency of a conventional TADF emitter with the corresponding chemical structure.
Co-reporter:Chan Seok Oh;Si Hyun Han
Journal of Materials Chemistry C 2017 vol. 5(Issue 35) pp:9106-9114
Publication Date(Web):2017/09/14
DOI:10.1039/C7TC02859H
The molecular design method of thermally activated delayed fluorescent emitters for blue-shifted emission was developed by modifying a phenyl linker using a methoxy substituent. One methoxy or two methoxy groups were introduced into the phenyl linker connecting a diphenyltriazine acceptor and a dimethylacridine donor to manage the emission spectrum. Substitution of one methoxy group shifted the emission color to a short wavelength while preserving the external quantum efficiency of the pristine material without the methoxy substituent. A high external quantum efficiency of over 20% was obtained while blue-shifting the emission wavelength by 12 nm. However, the substitution of two methoxy groups decreased the quantum efficiency of the devices although the emission color was shifted to a short wavelength.
Co-reporter:Jeong Min Choi, Dong Ryun Lee, Jun Yeob Lee
Dyes and Pigments 2017 Volume 142(Volume 142) pp:
Publication Date(Web):1 July 2017
DOI:10.1016/j.dyepig.2017.03.034
•Hybrid white organic light-emitting diodes with an external quantum efficiency over 20%.•High efficiency non-doped blue fluorescent organic light-emitting diodes using a donor-acceptor type emitter.•High efficiency in cool white and warm white devices using a hybrid type device structure.Distorted donor-acceptor type blue fluorescent emitter, 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-1,8-dimethyl-9H-carbazole (DmCzTrz), was developed for use as a high efficiency and non-doped deep blue fluorescent emitter and a deep blue emitter in hybrid white organic light-emitting diodes. The novel distorted donor-acceptor based non-doped DmCzTrz blue fluorescent organic light-emitting diodes achieved high quantum efficiency of 6.8% with a deep blue color coordinate of (0.15,0.10). The DmCzTrz blue emitter was doped with green and red triplet emitters to develop the hybrid white organic light-emitting diodes, and high quantum efficiency of 19.4% in cool white device and 20.8% in warm white device were demonstrated.
Co-reporter:Yu Jin Kang, Jun Yeob Lee
Dyes and Pigments 2017 Volume 138(Volume 138) pp:
Publication Date(Web):1 March 2017
DOI:10.1016/j.dyepig.2016.11.036
•A t-butyl modification of a triazine based acceptor moiety to manage the light emission of blue emitters.•Deep blue emission color in delayed fluorescent organic light-emitting diodes by t-butyl substituent.•Stable emission spectrum according to the change of doping concentration.A t-butyl modification method of an acceptor moiety was developed as a molecular design approach of blue emitters to shift the emission color to deep blue region and to stabilize the emission color according to doping concentration. A phenyl unit of triphenyltriazine acceptor moiety of blue thermally activated delayed fluorescent emitter was modified with either one or two t-butyl units to study the effect of the t-butyl unit on the electroluminescence emission of the blue thermally activated delayed fluorescent emitters. It was found that two t-butyl units introduced in the phenyl unit of the triphenyltriazine shifted the emission color to deep blue emission while keeping the deep blue color over wide doping concentration range.
Co-reporter:Jeong Min Choi, Woochul Lee, Kong Kyeom Kim, Jun Yeob Lee
Organic Electronics 2017 Volume 45(Volume 45) pp:
Publication Date(Web):1 June 2017
DOI:10.1016/j.orgel.2017.03.003
•Co-doping of triplet emitter in the emitting layer as a hole trapping additive.•Broad recombination zone by hole trapping effect of a triplet emitter.•Lifetime extension due to reduced triplet-polaron annihilation by a hole trapping triplet emitter.Co-doping of a blue phosphorescent emitter in a thermally activated delayed fluorescent (TADF) emitter based emitting layer was developed as an approach to extend the lifetime of blue TADF devices by managing excitons and polarons in the emitting layer. The blue phosphorescent emitter was doped at a very low doping concentration below 1 wt% to suppress triplet-triplet and triplet-polaron quenching effect in the TADF emitting layer. The doping of the blue phosphorescent emitter led to great extension of the lifetime of the TADF devices by hole trapping effect of the blue triplet emitter which widened exciton formation zone in the TADF emitting layer. More than twice extension of the operational lifetime of the device was demonstrated by the co-doping approach irrespective of the doping concentration of the TADF emitter in the emitting layer.Download high-res image (193KB)Download full-size image
Co-reporter:Jeong Min Choi, Ji Han Kim, Yu Jin Kang, Jun Yeob Lee
Organic Electronics 2017 Volume 49(Volume 49) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.orgel.2017.07.004
•Hole transport type host derived from pyrrolocarbazole for exciplex host.•Lifetime improvement of green phosphorescent organic light-emitting diodes using exciplex host.•Exciplex host of a pyrrolocarbazole based hole type host and triazine based electron type host.Lifetime improvement of green phosphorescent organic light-emitting didoes (PHOLEDs) by an exciplex type host was studied by mixing a hole transport type host and an electron transport type host. A pyrrolocarbazole type material was developed as the hole transport type host and a triazine type material was the electron transport type host. The exciplex type mixed host showed much longer lifetime and improved efficiency compared with each host material constituting the exciplex type mixed host. Hole and electron stability of the exciplex host was proposed as the key factor for the long lifetime of the green phosphorescent device.Download high-res image (116KB)Download full-size image
Co-reporter:Wook Song, Jun Yeob Lee
Organic Electronics 2017 Volume 49(Volume 49) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.orgel.2017.06.057
•Lifetime extension of blue phosphorescent device by suppression of triplet-positive polaron annihilation.•Device structure with a blue triplet emitter doped in the hole transport layer.•Improved stability of the blue device under current aging and ultraviolet-visible aging.A lifetime extending device structure by suppressing positive polaron induced triplet exciton-polaron annihilation was developed for improved lifetime in blue phosphorescent organic light-emitting diodes. A blue triplet emitter doped hole transport layer was introduced to control the triplet exciton-polaron annihilation of blue phosphorescent emitters in the emitting layer, which extended the lifetime of the blue phosphorescent devices. Current and ultraviolet light/current aging tests of hole and electron only devices proved that the lifetime extending mechanism of the blue triplet emitter doped hole transport layer is suppression of triplet exciton-positive polaron annihilation.Download high-res image (132KB)Download full-size image
Co-reporter:Sung Yong Byeon;Si Hyun Han
Advanced Optical Materials 2017 Volume 5(Issue 20) pp:
Publication Date(Web):2017/10/01
DOI:10.1002/adom.201700387
AbstractNegative polaron stabilizing host materials for blue phosphorescence organic light-emitting diodes are synthesized by modifying carbazolylcarbazole with dibenzothiophene or 9-phenylcarbazole. The host materials show high triplet energy above 2.95 eV and work as hole transport type hosts. Operational lifetime analysis of the blue devices with the two hosts demonstrates that the dibenzothiophene modified carbazolylcarbazole host functions better than the 9-phenylcarbazole modified carbazolylcarbazole host. Improved negative polaron stability from bond dissociation energy calculation and single carrier aging test results is the main factor for the lifetime extension in the dibenzothiophene modified carbazolylcarbazole host based blue phosphorescent organic light-emitting diodes.
Co-reporter:Sung Moo Kim, Ju Hui Yun, Sung Yong Byeon, Sang Kyu Jeon, Jun Yeob Lee
Journal of Industrial and Engineering Chemistry 2017 Volume 51(Volume 51) pp:
Publication Date(Web):25 July 2017
DOI:10.1016/j.jiec.2017.03.016
Organic compounds prepared from 1- position activated 9-phenylcarbazole interconnected with diphenyltriazine functionalized carbazole were examined as bipolar host materials of phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes. Interconnection position of the 9-phenylcarbazole was 1- position, and that of diphenyltriazine functionalized carbazole was changed from 1- position to 4- position. Main influence of the interconnection position was current density of the device and 2- or 3- position interconnection increased current density of the devices. All host materials derived from the 1- position activated 9-phenylcarbazole performed well as the host of phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes.Download high-res image (99KB)Download full-size image
Co-reporter:Ji Han Kim, Si Hyun Han, Jun Yeob Lee
Synthetic Metals 2017 Volume 232(Volume 232) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.synthmet.2017.08.014
•Dibenzothiophene derived host materials with CN substituted carbazole moieties.•Low driving voltage, improved efficiency and extended lifetime in blue thermally activated delayed fluorescent organic light-emitting diodes.•Increased bond dissociation energy under negative polaron by introducing CN substituted carbazole moiety.In this work, dibenzothiophene type host materials modified with 9H-carbazole, 9H-carbazole-3-carbonitrile and 9-phenylcarbazole were synthesized for high quantum efficiency and elongated lifetime in blue thermally activated delayed fluorescent (TADF) organic light-emitting diodes. Three host materials having one or two CN modified carbazole units were prepared for strengthened chemical bond as well as improved electron transport properties. The host materials designed using the carbazole and CN modified carbazole units built on the dibenzothiophene core showed low driving voltage, high quantum efficiency and elongated lifetime at the same time without any sacrifice of device performances in the blue TADF devices.Download high-res image (121KB)Download full-size image
Co-reporter:Hyeong Min Kim, Jeong Min Choi, Jun Yeob Lee
Synthetic Metals 2017 Volume 227(Volume 227) pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.synthmet.2017.03.004
•Positional effect of donors and acceptors in the molecular design of thermally activated delayed fluorescent emitters.•Ortho, meta, and para substitution of donors and acceptors at the phenyl linker connecting the donors and acceptors.•High quantum efficiency in the meta substituted emitter and low quantum efficiency in the para substituted emitter.Positional effect of donors and acceptors in the thermally activated delayed fluorescent (TADF) emitters was examined using TADF emitters with two donors and two acceptors. The position of the donors and acceptors at the phenyl linker was regulated as ortho-, meta- and para- to study the positional effect of the donors and acceptors. The comparison of the three TADF emitters with the different substitution positions suggested that ortho- or meta- substitution of each donor or acceptor is a useful way of improving light-emitting performances of the TADF emitters. The TADF emitter with the two donors at meta- position achieved high quantum efficiency of 18.0% compared with 15.1% and 3.8% of other emitters. High photoluminescence quantum yield, high fluorescence rate constant, and high reverse intersystem crossing rate constant were the main factors for the high quantum efficiency of the meta- substituted emitter.Download high-res image (141KB)Download full-size image
Co-reporter:Wook Song, Jun Yeob Lee
Organic Electronics 2017 Volume 48(Volume 48) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.orgel.2017.06.024
•Design rule of exciplex host for long lifetime in phosphorescent organic light-emitting diodes.•Large highest occupied molecular orbital-lowest unoccupied molecular orbital offset for improved lifetime.•Hole and electron carrier stability of the exciplex host under device operation condition.Design strategy of exciplex hosts made up of a hole transport type host and an electron transport type host for extended lifetime was established by developing exciplex hosts with different energy level offsets. An examination of the lifetime of the exciplex mixed host devices clarified the design rule of the exciplex hosts for extended lifetime. It was revealed that the HOMO and LUMO level offset between the hole type host and electron type host was the lifetime determining factor in the exciplex host devices. Long lifetime was obtained in the exciplex host devices with large HOMO and LUMO level offset between the hole type host and electron type host.Download high-res image (248KB)Download full-size image
Co-reporter:Wook Song, Jun Yeob Lee
Organic Electronics 2017 Volume 51(Volume 51) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.orgel.2017.08.034
•Triplet exciton guiding mixed host for improved lifetime in phosphorescent organic light-emitting diodes.•Triplet exciton and polaron separation by managing energy levels and triplet energy of hosts.•Lifetime improvement by suppressed triplet exciton-polaron annihilation.A novel triplet exciton guiding mixed host managing triplet exciton-polaron annihilation by separating the triplet excitons and polarons in the different host was developed. A high triplet energy/narrow gap host and a low triplet energy/wide gap host were mixed to isolate the triplet excitons and polarons, which could improve the extrapolated lifetime of the phosphorescent organic light emitting diodes by more than twice. The triplet exciton-polaron annihilation reducing mechanism was confirmed by triplet energy transfer, single carrier device test and triplet exciton-polaron annihilation rate constant study of the singlet host and mixed host.Download high-res image (203KB)Download full-size image
Co-reporter:Ju Hui Yun, Jun Yeob Lee
Dyes and Pigments 2017 Volume 144(Volume 144) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.dyepig.2017.05.036
•Benzoisoquinoline-1,3-dione as an acceptor of red thermally activated delayed fluorescent emitters.•Combination of benzoisoquinoline-1,3-dione and dimethylacridine in the donor-acceptor type molecular design.•High quantum efficiency of 11.2% in red thermally activated delayed fluorescent devices.A strong electron deficient moiety, benzoisoquinoline-1,3-dione, was applied as an electron acceptor of donor-acceptor type thermally activated delayed fluorescent (TADF) emitters. The connection of the benzoisoquinoline-1,3-dione acceptor moiety with a dimethylacridine donor moiety prepared 6-(9,9-dimethylacridin-10(9H)-yl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione and 5-(9,9-dimethylacridin-10(9H)-yl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione as red TADF emitters by strong electron deficiency of the benzoisoquinoline-1,3-dione acceptor. Device optimization of the red TADF emitters based on the delayed fluorescent behaviour of the red TADF emitters could offer high quantum efficiency of 11.2% in the red TADF devices.
Co-reporter:Yong Joo Cho, Sang Kyu Jeon, Sang-Shin Lee, Eunsun Yu, and Jun Yeob Lee
Chemistry of Materials 2016 Volume 28(Issue 15) pp:5400
Publication Date(Web):July 26, 2016
DOI:10.1021/acs.chemmater.6b01484
Deep blue thermally activated delayed fluorescent (TADF) emitters with a narrow emission spectrum were developed by managing the molecular structure of the TADF emitters. The deep blue TADF emitters were designed to show large steric hindrance at the central core of the molecule and small singlet–triplet energy gap. The molecular engineering of the deep blue TADF emitters enabled the fabrication of the deep blue TADF device with a full width at half-maximum of only 48 nm and a quantum efficiency of 14.0%. The full width at half-maximum of the deep blue TADF device was similar to that of conventional fluorescent devices, while the quantum efficiency was more than tripled.
Co-reporter:Chan Seok Oh, Jun Yeob Lee, Chang Ho Noh and Sung Han Kim
Journal of Materials Chemistry A 2016 vol. 4(Issue 17) pp:3792-3797
Publication Date(Web):14 Oct 2015
DOI:10.1039/C5TC02595H
A molecular design strategy to facilitate electron injection and to reduce driving voltage was proposed to reach high power efficiency in blue phosphorescent organic light-emitting diodes (PHOLEDs) doped with a phenylimidazole ligand based triplet emitter. The host materials were designed to keep the hole transport properties and triplet energy of a parent molecule. One or two CN units were attached to 3- or 3,6-positions of carbazole of 3,3-di(9H-carbazol-9-yl)biphenyl (mCBP) to manage electron transport properties of the parent mCBP host. The CN unit donated electron accepting character to the mCBP host and increased electron current density in the device, which improved power efficiency of the blue PHOLEDs from 41.8 lm W−1 to 57.1 lm W−1.
Co-reporter:Mounggon Kim, Sang Kyu Jeon, Seok-Ho Hwang, Sang-shin Lee, Eunsun Yu and Jun Yeob Lee
Chemical Communications 2016 vol. 52(Issue 2) pp:339-342
Publication Date(Web):30 Oct 2015
DOI:10.1039/C5CC07999C
High efficiency and color tuning of thermally activated delayed fluorescent emitters were achieved at the same time by designing emitters with a twin emitter molecular design. The control of the interconnect position between two emitters could manage the emission spectrum of the thermally activated delayed fluorescent emitters without affecting the quantum efficiency.
Co-reporter:Dong Ryun Lee, Jeong Min Choi, Chil Won Lee, and Jun Yeob Lee
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 35) pp:23190
Publication Date(Web):August 16, 2016
DOI:10.1021/acsami.6b05877
Highly efficient thermally activated delayed fluorescent (TADF) emitters, 5-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (oBFCzTrz), 5-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (mBFCzTrz), and 5-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (pBFCzTrz), were synthesized to study the effects of ortho-, meta-, and para- linkages between donor and acceptor moieties. oBFCzTrz having ortho- linked donor and acceptor moieties showed smaller singlet–triplet energy gap, shorter excited state lifetime, and higher photoluminescence quantum yield than mBFCzTrz and pBFCzTrz which are interconnected by meta- and para- positions. The TADF device using oBFCzTrz as a blue emitter exhibited high external quantum efficiency over 20%, little efficiency roll-off, and long device lifetime.Keywords: charge transfer; delayed fluorescence; ortho- linkage; singlet energy; triplet energy
Co-reporter:Mounggon Kim, Jeong Min Choi and Jun Yeob Lee
Chemical Communications 2016 vol. 52(Issue 65) pp:10032-10035
Publication Date(Web):22 Jul 2016
DOI:10.1039/C6CC04516B
Blue thermally activated delayed fluorescent (TADF) emitters having 1-carbazolylcarbazole based donor moieties were developed to resolve the low quantum efficiency and large singlet–triplet energy splitting issues of the linker free TADF emitters. Investigation of the 1-carbazolylcarbazole derived donors as the donor units of two blue TADF emitters in comparison with 3-carbazolylcarbazole demonstrated that the 1-carbazolylcarbazole based donors increased the triplet energy, decreased the singlet–triplet energy gap, blue-shifted the emission color, and enhanced the quantum efficiency of the blue TADF devices.
Co-reporter:Chan Seok Oh;Jeong Min Choi
Advanced Optical Materials 2016 Volume 4( Issue 8) pp:1281-1287
Publication Date(Web):
DOI:10.1002/adom.201600131
A high triplet energy host material for improved efficiency and elongated lifetime is developed by modifying carbazole linked terphenyl with a CN substituent. The CN modification strengthens electron injection and transport of the host material, which reduces the driving voltage, improved quantum efficiency, and power efficiency of blue phosphorescent organic light-emitting diodes. Furthermore, the CN modification also extends the lifetime of the blue device due to the chemical bond stabilizing effect of the CN moiety in radical, anion, and cation states. Therefore, the molecular design modifying the backbone structure with CN is an efficient approach for high efficiency and long lifetime.
Co-reporter:Yong Joo Cho;Sang Kyu Jeon
Advanced Optical Materials 2016 Volume 4( Issue 5) pp:688-693
Publication Date(Web):
DOI:10.1002/adom.201500634
Co-reporter:Seung Gun Yoo, Wook Song, Jun Yeob Lee
Dyes and Pigments 2016 Volume 128() pp:201-208
Publication Date(Web):May 2016
DOI:10.1016/j.dyepig.2016.01.021
•Acridine derived strong donor moiety for thermally activated delayed fluorescent emitters.•Combination of acridine derived donor with diphenyltriazine acceptor.•Efficient delayed fluorescence in the acridine donor based delayed fluorescent emitters.Acridine and carbazole derived electron donors, 8,8-dimethyl-5-phenyl-8,13-dihydro-5H-indolo[2,3-c]acridine (4IA) and 13,13-dimethyl-11-phenyl-11,13-dihydro-5H-indole[2,3-b]acridine(3IA), were synthesized as strong donor moieties of thermally activated delayed fluorescent (TADF) emitters. The new donor moiety was included in the molecular structure of diphenyltriazine based TADF emitter to study the effect of geometrical structure of the donor on the photophysical and device characteristics of TADF emitters. The 4IA donor was better than the 3IA donor for small singlet-triplet energy splitting and TADF emission. TADF behavior was observed only in the 4IA based TADF emitter due to geometrical structure. A TADF emitter having the 4IA based donor moiety exhibited a blue color coordinate of (0.21, 0.31) and a quantum efficiency of 13.7%.
Co-reporter:Sung Moo Kim, Ji Han Kim, Sang Kyu Jeon, Jun Yeob Lee
Dyes and Pigments 2016 Volume 125() pp:274-281
Publication Date(Web):February 2016
DOI:10.1016/j.dyepig.2015.10.030
•Dibenzothiophene derived high triplet energy host materials for blue devices.•Engineering of substitution position of dibenzothiophene for long lifetime.•Long lifetime in the host material with a substituent at 3 position of benzothiophene.Stable host materials based on dibenzothiophene and 9-phenylcarbazole were synthesized to elongate the life span of blue phosphorescent organic light-emitting diodes (PHOLEDs). Three host materials with the 9-phenylcarbazole moiety directly linked with dibenzothiophene moiety via 1, 3, and 4- positions of 9-phenylcarbazole were compared in terms of lifetime and efficiency of the blue PHOLEDs. The connection between dibenzothiophene and 9-phenylcarbazole through 3- position of carbazole was an effective way of improving the lifetime of the blue PHOLEDs more than twice and the molecular structure was well correlated with the lifetime of the blue PHOLEDs.
Co-reporter:Sung Yong Byeon, Jeong Min Choi, Jun Yeob Lee
Dyes and Pigments 2016 Volume 134() pp:285-290
Publication Date(Web):November 2016
DOI:10.1016/j.dyepig.2016.07.021
•Carbazole and pyridoindole based host materials for blue phosphorescent organic light-emitting diodes.•Improved electron transport by heteroatomic pyridoindole moiety.•Triplet energy keeping function of diphenylether linking unit.A meta-linked diphenylether based host material, 9-(3-(3-(9H-carbazol-9-yl)phenoxy)phenyl)-9H-pyrido[2,3-b]indole (CzDPEPI), was investigated as an intramolecular charge transfer type host material to harvest triplet excitons of phenylimidazole type blue Ir triplet emitters. A host with two carbazole units was a reference material to confirm the role of the pyridoindole moiety. The CzDPEPI host behaved as a high triplet energy and driving voltage reducing host due to the pyridoindole moiety assisting electron injection and improved power efficiency of blue phosphorescent device.
Co-reporter:Yirang Im, Jun Yeob Lee
Dyes and Pigments 2016 Volume 128() pp:84-88
Publication Date(Web):May 2016
DOI:10.1016/j.dyepig.2016.01.018
•Host materials with a 4-position modified dibenzofuran as a core structure.•Pyridoindole modification of dibenzofuran for high temperature stability.•High efficiency in blue phosphorescent organic light-emitting diodes using dibenzofuran derived host materials.A molecular design modifying 4- position of dibenzofuran with a pyridoindole moiety for high temperature stability and high efficiency was examined as an approach to develop host materials for blue phosphorescent organic light-emitting diodes. The simple pyridoindole modification of 4- position of carbazole substituted dibenzofuran lead to high glass transition temperature above 130 °C in addition to high quantum efficiency in the blue phosphorescent device.
Co-reporter:Jeong-A Seo, Sang Kyu Jeon, Jun Yeob Lee
Organic Electronics 2016 Volume 34() pp:33-37
Publication Date(Web):July 2016
DOI:10.1016/j.orgel.2016.03.038
•Acridine derived host material as a strong hole transport type host material.•High quantum efficiency by hole and electron balance in the emitting layer.•Long lifetime by recombination zone management using the hole transport type acridine host.A host material having acridine as a hole transport moiety, 10-(3′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-3-yl)-9,9-dimethyl-9,10-dihydroacridine (CZBPAC), was explored as the host material of phenylimidazole type Ir triplet emitter to realize both high quantum efficiency and stable operational lifetime. The acridine containing CZBPAC was superior to carbazole based host material with the same backbone structure in that it can improve driving voltage, quantum efficiency and lifetime of the blue phosphorescent organic light-emitting diodes simultaneously.
Co-reporter:Yu Jin Kang, Jun Yeob Lee
Organic Electronics 2016 Volume 32() pp:109-114
Publication Date(Web):May 2016
DOI:10.1016/j.orgel.2016.02.025
•High triplet energy electron transport materials derived from diphenyltriazine electron transport moiety.•Dibenzothiophene and dibenzofuran derived exciton blocking materials for blue phosphorescent devices.•Thermally stable exciton blocking materials for stable lifetime of the blue phosphorescent organic light-emitting diodes.High triplet energy electron transport materials with dibenzothiophene and dibenzofuran cores modified with a diphenyltriazine unit were investigated as electron transport type exciton blocking materials for stable blue phosphorescent organic light-emitting diodes. The two exciton blocking materials showed high triplet energy above 2.80 eV and enhanced quantum efficiency of the blue phosphorescent devices by more than 40% while maintaining stability of the pristine blue devices without the high triplet energy exciton blocking layer.
Co-reporter:Hyunsu Cho, Jonghee Lee, Jeong-Ik Lee, Nam Sung Cho, Jung Hwan Park, Jun Yeob Lee, Youngjin Kang
Organic Electronics 2016 Volume 34() pp:91-96
Publication Date(Web):July 2016
DOI:10.1016/j.orgel.2016.04.026
•Three homoleptic iridium(III) compounds were proposed for blue phosphorescent OLEDs.•OLEDs with these blue emitters demonstrated highly efficient and stable characteristics.•The external quantum efficiency (EQE) of OLED devices was as high as 20.1%.•The device lifetime (LT50) is larger than 300 h at 1000 cd/m2.In order to obtain triplet emitters with high stability and efficiency, three homoleptic iridium(III) compounds — specifically, Ir(tpim)3 (1), Ir(mtpim)3 (2), and Ir(itpim)3 (3), where tpim = 1-([1,1′:3′,1″-terphenyl]-2′-yl)-2-(4-fluorophenyl)-1H-imidazole, mtpim = 2-(4-fluorophenyl)-1-(5′-methyl-[1,1′:3′,1″-terphenyl]-2′-yl)-1H-imidazole, and itpim = 2-(4-fluorophenyl)-1-(5′-isopropyl-[1,1′:3′,1″-terphenyl]-2′-yl)-1H-imidazole — were prepared by one-pot reaction of the corresponding phenylimidazole ligand with an Ir(I) complex as a starting material. Compounds 1–3 emit bright sky-blue phosphorescence with λmax = 459–463 nm and phosphorescent quantum efficiencies of 0.38–0.50. Multi-layer phosphorescent organic light-emitting diodes using compounds 1–3 as the triplet emitters and mCBP (3,3-di(9H-carbazol-9-yl)biphenyl) as the host have been fabricated. Compound 3 doped in the emissive layer demonstrate external quantum efficiency as high as 20.1% at 1000 cd/m2. In addition, the device based on compound 1 as an emitter shows a stable lifetime greater than 300 h at 1000 cd/m2, which is one of the best results concerning the device lifetime.High efficiency and long lifetime are achieved in the blue phosphorescent organic light-emitting diodes by developing terphenyl modified phenylimidazole type phosphorescent emitters.
Co-reporter:In Ho Lee, Wook Song, Jun Yeob Lee
Organic Electronics 2016 Volume 29() pp:22-26
Publication Date(Web):February 2016
DOI:10.1016/j.orgel.2015.11.019
•Aggregation induced emission based thermally activated delayed fluorescent emitters.•Asymmetric substitution of donor moieties for improved efficiency in the delayed fluorescent emitter.•High efficiency in non-doped thermally activated delayed fluorescent devices.Aggregation-induced emission (AIE) type thermally activated delayed fluorescent (TADF) emitters were developed by asymmetric substitution of donor moieties to a diphenylsulfone acceptor. The AIE properties of the TADF emitters increased the quantum efficiency of the non-doped TADF devices and asymmetric substitution was more effective than symmetric substitution to enhance the quantum efficiency of the non-doped devices.
Co-reporter:Wook Song, Woochul Lee, Kong Kyeom Kim, Jun Yeob Lee
Organic Electronics 2016 Volume 37() pp:252-256
Publication Date(Web):October 2016
DOI:10.1016/j.orgel.2016.07.002
•Lifetime increase in thermally activated delayed fluorescent devices with a unipolar host according to doping concentration.•Constant lifetime in thermally activated delayed fluorescent device with a bipolar host according to doping concentration.•Correlation of recombination zone broadening with lifetime of thermally activated delayed fluorescent devices.Origin of doping concentration dependence of lifetime of thermally activated delayed fluorescent (TADF) devices was examined using a TADF emitter doped in a hole transport type and a bipolar host material. Lifetime of the hole transport type host based TADF device was increased according to doping concentration of TADF emitter, while that of the bipolar host based TADF device was decreased according to doping concentration of TADF emitter. The doping concentration dependence of the lifetime could be correlated with recombination zone of the emitting layer. Broad recombination zone at high doping concentration in the hole transport type host and at low doping concentration in the bipolar host was proposed as the main contributor of the doping concentration dependence of the lifetime.
Co-reporter:Sang Kyu Jeon, Kyoung Soo Yook, Jun Yeob Lee
Organic Electronics 2016 Volume 38() pp:278-282
Publication Date(Web):November 2016
DOI:10.1016/j.orgel.2016.08.027
•Oxidative coupling of polyvinylcarbazole for crosslinked network formation.•Surface initiated oxidative coupling method to form crosslinked hole transport layer.•Improved efficiency and lifetime by crosslinked hole transport layer formed by surface initiated crosslinking method.A surface initiated oxidative coupling method was developed as a crosslinking approach of hole transport materials for solution processed organic light-emitting diodes. The surface initiated crosslinking method was better than bulk oxidative crosslinking method in terms of quantum efficiency and lifetime of the organic light-emitting diodes by suppressing exciton quenching by the hole transport layer. Doubled efficiency and quadrupled lifetime were obtained using the new crosslinking approach without any chemical modification of the hole transport material.
Co-reporter:Inho Lee, Jun Yeob Lee
Organic Electronics 2016 Volume 29() pp:160-164
Publication Date(Web):February 2016
DOI:10.1016/j.orgel.2015.12.001
•A deep blue thermally activated delayed fluorescent emitter with a y color coordinate below 0.15.•A high quantum efficiency close to 20% in deep blue thermally activated delayed fluorescent device.•Rigid acceptor moiety to narrow the emission spectrum of blue thermally activated delayed fluorescent emitter.A thermally activated delayed fluorescent (TADF) emitter, 2,7-bis(9,9-dimethylacridin-10(9H)-yl)-9,9-dimethyl-9H-thioxanthene 10,10-dioxide (DMTDAc), was developed as a deep blue TADF emitter using a rigid 9,9-dimethyl-9H-thioxanthene 10,10-dioxide (DMTD) acceptor and an acridine donor. The rigid DMTD acceptor narrowed emission spectrum of DMTDAc by interlocking two phenyl units of diphenylsulfone. A deep blue TADF device with an external quantum efficiency close to 20% with a deep blue color coordinate of (0.15,0.13) was provided using the DMTDAc TADF emitter.
Co-reporter:Kyoung Soo Yook, Sang Kyu Jeon, Jun Yeob Lee
Journal of Luminescence 2016 Volume 169(Part A) pp:266-269
Publication Date(Web):January 2016
DOI:10.1016/j.jlumin.2015.09.012
•Recombination zone of blue thermally activated delayed fluorescent devices.•Electron trapping by thermally activated delayed fluorescent emitter.•Recombination zone close to electron transport layer side.Recombination zone of blue thermally activated delayed fluorescent devices was identified by inserting a yellow sensitizer in the emitting layer made up of 1,3-bis(N-carbazolyl)benzene (mCP) and 4,6-di(9H-carbazol-9-yl)isophthalonitrile (DCzIPN) blue thermally activated delayed fluorescent emitter. Recombination of the mCP:DCzIPN emitting layer was mostly observed near electron transport layer at low doping concentration because of strong electron trapping effect by DCzIPN. Recombination zone of mCP:DczIPN emitting layer was broadened at high doping concentration by controlling electron density in the emitting layer.
Co-reporter:Inho Lee, Sang Kyu Jeon, Jun Yeob Lee
Synthetic Metals 2016 Volume 215() pp:121-126
Publication Date(Web):May 2016
DOI:10.1016/j.synthmet.2015.11.034
•Constant triplet energy in the bipolar host materials irrespective of an aromatic spacer.•Design strategy of high triplet energy bipolar host material with improved thermal properties.•High quantum efficiency and low driving voltage using bipolar type host materials.Triplet host materials with spatially separated donor and acceptor moieties were synthesized and the effect of the spatial separation of the donor and acceptor moieties via aromatic linkage on the photophysical properties of the host materials was elucidated. It was revealed that the aromatic linkage had weak influence on the absorption and triplet energy of the donor-acceptor type host materials with completely separated donor and acceptor moieties. Charge transport properties and device performances were found to be changed by the type of the aromatic linkage. Therefore, the spatially separated donor-acceptor design was proven to independently control photophysical properties and charge transport properties.
Co-reporter:Ju Hui Yun, Chil Won Lee, Kyoung Soo Yook, Jun Yeob Lee
Synthetic Metals 2016 Volume 217() pp:216-219
Publication Date(Web):July 2016
DOI:10.1016/j.synthmet.2016.03.020
•Highly soluble host material for blue fluorescent organic light-emitting diodes.•Alkyl free molecular design of anthracene host material for soluble devices.•Ortho linked aromatic structure for good solubility in organic solvents.An alkyl free anthracene based host material, 9-([1,1′:2′,1″-terphenyl]-2-yl)-10-phenylanthracene (AnTP), was developed as a soluble host material for solution processed blue fluorescent organic light-emitting diodes by increasing the solubility of anthracene type host material using a twisted aromatic substituent. The good solubility of AnTP even without any alkyl substituent allowed solution coating of AnTP based emitting layer and fabrication of solution processed blue fluorescent organic light-emitting diodes with a current efficiency of 3.7 cd/A.
Co-reporter:Mounggon Kim
The Journal of Physical Chemistry C 2016 Volume 120(Issue 5) pp:2485-2493
Publication Date(Web):January 28, 2016
DOI:10.1021/acs.jpcc.5b09114
Thermally activated delayed fluorescent (TADF) emitters having bicarbazole as a donor unit based on a twin emitting core design were developed by substituting the bicarbazole donor with a diphenyltriazine acceptor. Three bicarbazole derived delayed fluorescent emitters linked via 2,3′-, 3,3′-, and 3,4′-positions of carbazole were synthesized and investigated as blue dopants of the TADF devices. A twin emitting core based TADF emitter derived from a 3,3′-bicarbazole donor exhibited a high quantum efficiency of 25.0% in the greenish blue TADF device. A 3,3′-linkage induced red shift of the emission wavelength, a small singlet–triplet energy gap, and a high quantum efficiency were revealed.
Co-reporter:Kyoung Soo Yook
The Chemical Record 2016 Volume 16( Issue 1) pp:159-172
Publication Date(Web):
DOI:10.1002/tcr.201500221
Abstract
It is important to balance holes and electrons in the emitting layer of organic light-emitting diodes to maximize recombination efficiency and the accompanying external quantum efficiency. Therefore, the host materials of the emitting layer should transport both holes and electrons for the charge balance. From this perspective, bipolar hosts have been popular as the host materials of thermally activated delayed fluorescent devices and phosphorescent organic light-emitting diodes. In this review, we have summarized recent developments of bipolar hosts and suggested perspectives of host materials for organic light-emitting diodes.
Co-reporter:Jeong-A Seo; Myoung-Seon Gong;Wook Song; Jun Yeob Lee
Chemistry – An Asian Journal 2016 Volume 11( Issue 6) pp:868-873
Publication Date(Web):
DOI:10.1002/asia.201501365
Abstract
A new donor moiety, 7,7,13,13-tetramethyl-7,13-dihydro-5H-indeno[1,2-b]acridine (IAc), was developed to control the highest occupied molecular orbital (HOMO) dispersion of thermally activated delayed fluorescent (TADF) emitters. The IAc unit expanded the HOMO dispersion of the emitters and increased the quantum efficiency of the TADF devices up to 20.9 %.
Co-reporter:Mounggon Kim;Sang Kyu Jeon;Seok-Ho Hwang
Advanced Materials 2015 Volume 27( Issue 15) pp:2515-2520
Publication Date(Web):
DOI:10.1002/adma.201500267
Co-reporter:Wook Song;Inho Lee
Advanced Materials 2015 Volume 27( Issue 29) pp:4358-4363
Publication Date(Web):
DOI:10.1002/adma.201501019
Co-reporter:Dong Ryun Lee;Mounggon Kim;Sang Kyu Jeon;Seok-Ho Hwang;Chil Won Lee
Advanced Materials 2015 Volume 27( Issue 39) pp:5861-5867
Publication Date(Web):
DOI:10.1002/adma.201502053
Co-reporter:Yong Joo Cho;Byung Doo Chin;Sang Kyu Jeon
Advanced Functional Materials 2015 Volume 25( Issue 43) pp:6786-6792
Publication Date(Web):
DOI:10.1002/adfm.201502995
Highly efficient solution-processed blue thermally activated delayed fluorescent (TADF) devices are developed by designing soluble blue TADF emitters. The solubility and emission color could be managed by introducing F as an electron withdrawing unit instead of CN. Two soluble blue TADF emitters are synthesized and show a high external quantum efficiency of 20.0% with a color coordinate of (0.16,0.26), and it is the best quantum efficiency reported in solution-processed TADF devices. The device performances of the solution-processed blue TADF devices are comparable to those of vacuum-processed blue TADF devices.
Co-reporter:Yirang Im, Wook Song and Jun Yeob Lee
Journal of Materials Chemistry A 2015 vol. 3(Issue 31) pp:8061-8065
Publication Date(Web):13 Jul 2015
DOI:10.1039/C5TC01065A
Two dibenzothiophene derived compounds, 4-(3-(triphenylen-2-yl)phenyl)dibenzo[b,d]thiophene (DBTTP1) and 4-(5′-phenyl-[1,1′:3′,1′′-terphenyl]-3-yl)dibenzo[b,d]thiophene (DBTTP2), were prepared as the host materials for green thermally activated delayed fluorescent (TADF) emitters to investigate the effect of the molecular structure of the host materials on the efficiency and lifetime of the green TADF devices. The green TADF devices fabricated using the DBTTP1 host material exhibited a high quantum efficiency of above 20% and a lifetime longer than 250 h up to 80% of initial luminance at 1000 cd m−2. Comparing the two host materials, triphenylene modified DBTTP1 was better than terphenyl modified DBTTP2 in terms of the lifetime of the green TADF devices.
Co-reporter:In Ho Lee, Wook Song, Jun Yeob Lee and Seok-Ho Hwang
Journal of Materials Chemistry A 2015 vol. 3(Issue 34) pp:8834-8838
Publication Date(Web):04 Aug 2015
DOI:10.1039/C5TC01626F
High efficiency blue fluorescent organic light-emitting diodes (OLEDs) were developed by doping the conventional 2,5,8,11-tetra-tert-butylperylene (TBPe) blue fluorescent dopant in a mixed emitting layer of a wide bandgap host and a blue thermally activated delayed fluorescent emitter which played the role of a sensitizer in blue fluorescence emission. 10-(4-((4-(9H-Carbazol-9-yl)phenyl)sulfonyl)phenyl)-9,9-dimethyl-9,10-dihydroacridine (CzAcSF) was the blue thermally activated delayed fluorescent emitter of the emitting layer and bis[2-(diphenylphosphino)phenyl]ether oxide (DPEPO) was the host material of the emitting layer. Doping of TBPe at a doping concentration of 0.1% in an emitting layer of DPEPO:CzAcSF achieved a high quantum efficiency of 18.1% in the blue fluorescent OLEDs, which is the best quantum efficiency reported in blue fluorescent OLEDs.
Co-reporter:Jeong-A Seo, Sang Kyu Jeon, Myoung Seon Gong, Jun Yeob Lee, Chang Ho Noh and Sung Han Kim
Journal of Materials Chemistry A 2015 vol. 3(Issue 18) pp:4640-4645
Publication Date(Web):15 Apr 2015
DOI:10.1039/C5TC00640F
An acridine derived compound, 9,9-dimethyl-10-(9-phenyl-9H-carbazol-3-yl)-9,10-dihydroacridine (PCZAC), was newly designed as a hole transport type high triplet energy material for application as a hole transport type exciton blocking layer of blue phosphorescent organic light-emitting diodes. The PCZAC compound provided a high triplet energy of 2.99 eV and a high glass transition temperature of 101 °C for high efficiency and long lifetime. PCZAC showed an improved quantum efficiency and more than 8 time improvement of the lifetime of blue phosphorescent organic light-emitting diodes.
Co-reporter:Dong Ryun Lee, Seok-Ho Hwang, Sang Kyu Jeon, Chil Won Lee and Jun Yeob Lee
Chemical Communications 2015 vol. 51(Issue 38) pp:8105-8107
Publication Date(Web):14 Apr 2015
DOI:10.1039/C5CC01940K
Benzofurocarbazole and benzothienocarbazole were used as electron donors of thermally activated delayed fluorescence (TADF) emitters and the performances of the TADF devices were examined. The benzofurocarbazole and benzothienocarbazole donor moieties were better than carbazole as the electron donors of the TADF emitters.
Co-reporter:Dong Ryun Lee, Bo Seong Kim, Chil Won Lee, Yirang Im, Kyoung Soo Yook, Seok-Ho Hwang, and Jun Yeob Lee
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 18) pp:9625
Publication Date(Web):April 29, 2015
DOI:10.1021/acsami.5b01220
Highly efficient green thermally activated delayed fluorescent organic light-emitting diodes with an external quantum efficiency of 31.2% were investigated by using 3-(3-(carbazole-9-yl)phenyl) pyrido[3′,2′:4,5]furo[2,3-b]pyridine (3CzPFP) derived from carbazole and pyrido[3′,2′:4,5]furo[2,3-b]pyridine. The host material showed well-matched photoluminescence emission with absorption of the green dopant material, (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) and harvested all excitons of 4CzIPN. The 3CzPFP:4CzIPN film exhibited high photoluminescence quantum yield of 100%, and the green delayed fluorescence device employing the 3CzPFP host showed high maximum quantum efficiency of 31.2 ± 0.5% at 1% doping after optimization of the device structure.Keywords: bipolar host; delayed fluorescence; green fluorescent device; high quantum efficiency; high triplet energy;
Co-reporter:Sung Moo Kim, Sung Yong Byeon, Seok-Ho Hwang and Jun Yeob Lee
Chemical Communications 2015 vol. 51(Issue 53) pp:10672-10675
Publication Date(Web):05 Jun 2015
DOI:10.1039/C5CC02188J
A novel carbazole moiety with bromine at the 1-position of carbazole was synthesized and four carbazole compounds derived from the 1-position modified carbazole were developed as the host materials for phosphorescent organic light-emitting diodes. The 1-position modified carbazole was coupled with another carbazole to prepare bicarbazole intermediates, which were substituted with 4,6-diphenyltriazine to yield four bicarbazole derivatives modified with the electron deficient diphenyltriazine unit. The triplet host materials showed high quantum efficiency above 20% and low driving voltage below 5.0 V at 1000 cd m−2 in green phosphorescent organic light-emitting diodes.
Co-reporter:Ji Won Yang and Jun Yeob Lee
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 37) pp:24468-24474
Publication Date(Web):28 Aug 2015
DOI:10.1039/C5CP03469H
Bicarbazole derivatives, 9,9′-bis(dibenzo[b,d]thiophen-2-yl)-9H,9′H-3,3′-bicarbazole (BCzDBT), 9,9′-bis(dibenzo[b,d]furan-2-yl)-9H,9′H-3,3′-bicarbazole (BCzDBF), and 9,9′-di([1,1′-biphenyl]-3-yl)-9H,9′H-3,3′-bicarbazole (BCzBP), were designed and examined as the hole transport type host materials of the tris[1-(2,4-diisopropyldibenzo[b,d]furan-3-yl)-2-phenylimidazole] (Ir(dbi)3) blue triplet emitter. BCzDBT performed better than BCzDBF and BCzBP as the hosts of Ir(dbi)3 and could demonstrate 24.8% quantum efficiency and long lifetime in the blue phosphorescent devices. Strong hole carrying properties of the bicarbazole derivatives were proposed as the main factors for the high quantum efficiency of the BCzDBT devices, and thermal and chemical stability of BCzDBT were suggested as crucial factors for the long lifetime of the BCzDBT devices.
Co-reporter:Ji Han Kim, Seok-Ho Hwang, Wook Song, Jun Yeob Lee
Dyes and Pigments 2015 Volume 122() pp:103-108
Publication Date(Web):November 2015
DOI:10.1016/j.dyepig.2015.06.014
•Acridine and disbenzothiophene based high triplet energy host material.•Hole transport type host material for imidazole based blue phosphorescent emitter.•Improved lifetime and efficiency by combining dibenzothiophene and acrididine moieties in the host design.Acridine modified dibenzothiophene derivatives were synthesized as host materials of imidazole ligand based Ir emitters for blue phosphorescent devices. The shallow energy levels of the acridine based host materials by the strong electron donating acridine moiety were well matched with the energy levels of Ir blue triplet emitter derived from imidazole. Additionally, strong electron transporting character of the acridine moiety could increase hole density in the emitting layer and balance holes and electrons. The energy level matching between the host and dopant materials and increased hole density in the emitting layer provided a very high external quantum efficiency of 27.8% in the blue phosphorescent organic light-emitting diodes.
Co-reporter:Jaeyoung Hwang, Kyoung Soo Yook, Jun Yeob Lee, Yun-Hi Kim
Dyes and Pigments 2015 Volume 121() pp:73-78
Publication Date(Web):October 2015
DOI:10.1016/j.dyepig.2015.05.004
•Solution-processable orange-phosphorescent.•Organic light-emitting diodes.•Phenylpyridine derivative containing an imide group on an iridium (III) complex.•Color coordinate of (0.53, 0.47) with FWHM of 73 nm.•Maximum current efficiency of 16.3 cd A−1 with maximum quantum efficiency of 6.1%.We report the synthesis and characterization of an orange-emitting iridium(III) complex, based on a phenylpyridine iridium derivative, bis[2-isopropyl-5-(pyridin-2-yl)isoindoline-1,3-dione]iridium(III) 2,2,6,6-tetramethyl-3,5-heptanedione ([(impy)2Ir(tmd)]), for orange-phosphorescent organic light-emitting diodes. The phenylpyridine derivative contained an imide functional group as the main ligand and a bulky 2,2,6,6-tetramethyl-3,5-heptanedione (tmd) as an ancillary ligand. The (impy)2Ir(tmd) dopant, easily processed by spin-coating, provided a maximum quantum efficiency of 6.1% and maximum current efficiency of 16.3 cd A−1. The FWHM of the orange OLED was 73 nm, and the color coordinate was (0.53, 0.47).
Co-reporter:Yu Jin Kang, Sang Kyu Jeon, Jun Yeob Lee
Dyes and Pigments 2015 Volume 114() pp:278-282
Publication Date(Web):March 2015
DOI:10.1016/j.dyepig.2014.12.001
•Bidibenzofuran derived host material for phosphorescent organic light-emitting diodes.•High quantum efficiency above 20% in green phosphorescent organic light-emitting diodes.•Zig-zag type host design for bipolar charge transport properties.A zig-zag type carbazole modified bidibenzofuran compound, 2,2'-di(carbazol-9-yl)-4,4'-bidibenzo[b,d]furan, was synthesized as the host material for green phosphorescent organic light-emitting diodes by coupling two 9-(dibenzo[b,d]furan-2-yl)carbazole moieties via 4- position of dibenzofuran. The carbazole modified bidibenzofuran host showed a triplet energy of 2.75 eV and the highest occupied molecular orbital/the lowest unoccupied molecular orbital of −6.10 eV/−2.87 eV for hole and electron injection. The bidibenzofuran host was doped with green emitting tris(2-phenylpyridine) iridium and high quantum efficiency of 20.6% was achieved in the green phosphorescent organic light-emitting diodes.
Co-reporter:Jeong-A Seo, Myoung Seon Gong, Sang Kyu Jeon, Jun Yeob Lee, Chang Ho Noh, Sung Han Kim
Dyes and Pigments 2015 Volume 123() pp:254-256
Publication Date(Web):December 2015
DOI:10.1016/j.dyepig.2015.08.010
•Acridine compound as a hole transport and exciton blocking material of blue devices.•High efficiency by triplet exciton confinement in blue phosphorescent devices.•Stable lifetime using an acridine based triplet exciton blocking layer.An acridine derived compound, 1,3-bis(9,9-dimethylacridin-10(9H)-yl)benzene (mAP), was investigated as a high triplet energy hole transport material for improved efficiency and stable lifetime. The mAP hole transport material showed a high triplet energy of 3.04 eV and good hole transport properties by the acridine moiety. The introduction of mAP as the hole transport layer of blue phosphorescent organic light-emitting diodes doubled the quantum efficiency of the device while keeping the lifetime of the control device without the mAP hole transport layer.
Co-reporter:Mounggon Kim, Sang Kyu Jeon, Seok-Ho Hwang and Jun Yeob Lee
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 20) pp:13553-13558
Publication Date(Web):05 May 2015
DOI:10.1039/C5CP01676B
We synthesized 3-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-methylphenyl)-9-phenyl-9H-carbazole (TrzmPCz) as a new bipolar host material for blue phosphorescent organic light-emitting devices and investigated the electro-optical properties of the blue devices fabricated using the TrzmPCz host. We managed the triplet energy of the host by inserting a methyl substituent in the phenyl linkage between triazine and carbazole. The methyl substituent distorted the backbone structure of TrzmPCz and lead to high triplet energy of 2.79 eV. After optimization of the device structure, the TrzmPCz based organic light-emitting diodes achieved the maximum quantum efficiency of 16.4%, a current efficiency of 32 cd A−1, and a power efficiency of 21.5 lm W−1.
Co-reporter:Sang Kyu Jeon, Bodakuntla Thirupathaiah, Choongik Kim, Kwon Taek Lim, Jun Yeob Lee, SungYong Seo
Dyes and Pigments 2015 Volume 114() pp:146-150
Publication Date(Web):March 2015
DOI:10.1016/j.dyepig.2014.10.025
•Carbazole and phosphine oxide based high triplet energy host material.•High triplet energy for blue devices.•High quantum efficiency in blue phosphorescent organic light-emitting diodes.A novel bipolar compound with a thiophene modified 9-phenylcarbazole and phosphine oxide moieties, (5-(4-(9H-carbazol-9-yl)phenyl)thiophen-2-yl)diphenylphosphine oxide (CPTPO), was synthesized and characterized as a high triplet energy host material. Bipolar charge transport character and a high triplet energy of 2.72 eV of CPTPO allowed the development of blue phosphorescent organic light-emitting diodes with an external quantum efficiency of 18.4%.
Co-reporter:Mounggon Kim, Sang Kyu Jeon and Jun Yeob Lee
RSC Advances 2015 vol. 5(Issue 121) pp:100378-100383
Publication Date(Web):23 Nov 2015
DOI:10.1039/C5RA17469D
We developed and synthesized 9,9′-(1-phenyl-1H-pyrrole-2,5-diyl)bis(9H-carbazole) (PPyCz2) as a hole transport type high triplet energy host material for blue phosphorescent organic light emitting diodes. We approached the molecular design by inserting a pyrrole moiety to prevent extension of conjugation of molecule and achieved a high triplet energy of 2.99 eV in the PPyCz2 host. Furthermore, the PPyCz2 host showed a high external quantum efficiency of 14.8% in blue phosphorescent organic light emitting diodes.
Co-reporter:Kyoung Soo Yook, Jun Yeob Lee
Journal of Luminescence 2015 Volume 161() pp:271-274
Publication Date(Web):May 2015
DOI:10.1016/j.jlumin.2015.01.017
•High quantum efficiency in yellow phosphorescent organic light-emitting diodes.•Narrow bandgap host material with donor–acceptor structure for low driving voltage.•Low optimum doping concentration of 1% for high quantum efficiency and power efficiency.A narrow bandgap host material, 4,5-di(9H-carbazol-9-yl)phthalonitrile (2CzPN), was used as a bipolar host material to improve the device performances of yellow phosphorescent organic light-emitting diodes(PHOLEDs). The device performances of the yellow PHOLEDs were optimized at a low doping concentration of 1%. A low turn-on voltage of 3.0 V and high quantum efficiency of 19.3% were achieved using the 2CzPN host material and no efficiency roll-off of the device was observed up to 1000 cd/m2 compared with 25% of reference device.
Co-reporter:Wook Song, In Ho Lee, Seok-Ho Hwang, Jun Yeob Lee
Organic Electronics 2015 Volume 23() pp:138-143
Publication Date(Web):August 2015
DOI:10.1016/j.orgel.2015.04.016
•White devices with a blue delayed fluorescent emitter and yellow fluorescent emitter.•Singlet energy transfer from a blue emitter to yellow emitter.•High quantum efficiency above 15% in the fluorescent white organic light-emitting diodes.Fluorescent white organic light-emitting diodes having a blue thermally activated delayed fluorescent emitter and a yellow fluorescent emitter was developed by co-doping the blue and yellow emitters in a single emitting layer. The blue delayed fluorescent device showed high quantum efficiency of 22.6% at a very high doping concentration of 50% and the white devices exhibited a high quantum efficiency of 15.5% even though a fluorescent yellow emitter was doped in the blue thermally activated delayed fluorescent emitting layer. Minimized charge trapping and Dexter energy transfer by low yellow doping concentration of 0.05% as well as efficient Förster energy transfer could develop the high efficiency fluorescent white organic light-emitting diodes.
Co-reporter:Ji Won Yang, Jun Yeob Lee
Organic Electronics 2015 Volume 22() pp:74-80
Publication Date(Web):July 2015
DOI:10.1016/j.orgel.2015.03.030
•We synthesized bipolar host materials with high triplet energy of 2.89 eV.•The bipolar host materials exhibited distinguishingly high thermal properties.•A maximum quantum efficiency of 25.4% was achieved in the Ir(dbi)3 doped device.Carbazole compounds modified with a pyridoindole moiety were examined as thermally stable high triplet energy host materials for tris[1-(2,4-diisopropyldibenzo[b,d]furan-3-yl)-2-phenylimidazole] (Ir(dbi)3) based blue phosphorescent organic light-emitting diodes. A well-known carbazole compound, N,N′-dicarbazolyl-3,5-benzene, was substituted with one or two pyridoindole moieties to develop the thermally stable host materials for Ir(dbi)3 blue triplet emitters. Remarkably high glass transition temperature of 196 °C and thermal decomposition temperature of 486 °C in addition to high triplet energy of 2.89 eV were achieved by the pyridoindole modification. The pyridoindole modified carbazole compounds also delivered high quantum efficiency of 25.4% in the blue phosphorescent devices by doping Ir(dbi)3.
Co-reporter:In Ho Lee and Jun Yeob Lee
RSC Advances 2015 vol. 5(Issue 118) pp:97903-97909
Publication Date(Web):16 Nov 2015
DOI:10.1039/C5RA19722H
Donor–acceptor type high triplet energy host materials were derived from a phenothiazine dioxide based electron transport moiety and a carbazole based hole transport moiety. Three phenothiazine dioxide type materials, 10-(3,5-di(9H-carbazol-9-yl)phenyl)-10H-phenothiazine 5,5-dioxide (DCzPO), 10-(3′,5′-di(9H-carbazol-9-yl)-[1,1′-biphenyl]-3-yl)-10H-phenothiazine 5,5-dioxide (DCzmPPO), and 10-(3′,5′-di(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-yl)-10H-phenothiazine 5,5-dioxide (DCzpPPO), could transport both holes and electrons effectively and showed high triplet energy for use in blue phosphorescent organic light-emitting diodes. Device optimization of the DCzPO, DCzmPPO, and DCzpPPO host based blue devices could realize high EQE of 24.3%.
Co-reporter:Sang Kyu Jeon, Jun Yeob Lee
Organic Electronics 2015 Volume 27() pp:202-206
Publication Date(Web):December 2015
DOI:10.1016/j.orgel.2015.09.016
•Four times lifetime improvement using a high triplet energy exciton blocking layer.•Recombination zone management using an exciton blocking layer.•Suppressed recombination zone shift for long lifetime in blue organic light-emitting diodes.Lifetime of blue phosphorescent organic light-emitting diodes (OLEDs) was improved by suppressing a recombination zone shift using a high triplet energy exciton blocking layer. Host material of the emitting layer was inserted as the exciton blocking layer between a hole transport layer and an emitting layer, and the exciton blocking layer kept the recombination zone near hole transport layer side without significant emission zone change during lifetime test. The suppressed recombination zone shift improved the lifetime of the blue phosphorescent OLED by four times.
Co-reporter:Chan Seok Oh, Jun Yeob Lee
Organic Electronics 2015 Volume 24() pp:315-319
Publication Date(Web):September 2015
DOI:10.1016/j.orgel.2015.05.002
•Be based organometallic host material derived from imidazole based ligand.•High quantum efficiency of 25.9% in green phosphorescent organic light-emitting diodes.•High triplet energy of 2.73 eV and high glass transition temperature of 181 °C.A 2-(4,5-dimethyl-1-phenyl-imidazol-2-yl)phenol ligand based Be complex, beryllium 2-(4,5-dimethyl-1-phenyl-imidazol-2-yl)phenolate (BePhIm), was investigated as a thermally stable host material of green phosphorescent organic light-emitting diodes (PHOLEDs). BePhIm was developed as a host material to have high triplet energy, thermal stability and balanced charge density. The triple energy of BePhIm was 2.73 eV and the glass transition temperature was 181 °C. Maximum quantum efficiency of the BePhIm based green PHOLEDs was 25.9%, which is better than any other quantum efficiency reported in green PHOLED using Be complexes as the host material.
Co-reporter:Bo Seong Kim, Jun Yeob Lee
Organic Electronics 2015 Volume 21() pp:100-105
Publication Date(Web):June 2015
DOI:10.1016/j.orgel.2015.02.022
•High quantum efficiency in hybrid white organic light-emitting diodes with a thermally activated delayed fluorescent emitter.•Efficient energy transfer from a thermally activated delayed fluorescent emitter to phosphorescent emitter.•Stack structure optimization for improved quantum efficiency in hybrid white organic light-emitting diodes.Two different hybrid white organic light-emitting diodes (WOLEDs) with red/blue phosphorescent emitters and a green thermally activated delayed fluorescent (TADF) emitter were designed to develop high efficiency hybrid WOLEDs. One hybrid WOLED (type I) had a device structure with a hybrid emitting layer of green TADF and red phosphorescent emitters stacked on a blue phosphorescent emitting layer and the other hybrid WOLED (type II) had a device architecture with the green TADF emitting layer stacked on a red and blue phosphorescent emitting layer. Efficient energy transfer from the green TADF emitter to the red phosphorescent emitter was observed and balanced white emission could be obtained by optimizing the device structure of the hybrid WOLEDs. A quantum efficiency of 16.2% with a color coordinate of (0.45,0.47) and a quantum efficiency of 18.0% with a color coordinate of (0.37,0.47) were achieved in the type I and type II hybrid WOLEDs, respectively.
Co-reporter:Yirang Im, Jun Yeob Lee
Synthetic Metals 2015 Volume 209() pp:24-28
Publication Date(Web):November 2015
DOI:10.1016/j.synthmet.2015.06.014
•Better charge injection by δ-carboline than α-carboline.•Low driving voltage and high power efficiency by carbazole–carboline compound.•High triplet energy bipolar host material for blue phosphorescent organic light-emitting diodes.A δ-carboline derived compound, 5-(3′-(9-carbazolyl)-[1,1′-biphenyl]-3-yl)pyrido[3,2-b]indole, was synthesized as a high triplet energy bipolar host material for blue phosphorescent organic light-emitting didoes and it was compared with α-carboline derived host material with the same backbone structure. The δ-carboline derived host material showed better electron transport properties than the host with α-carboline due to better electron accepting properties. Therefore, the new host material reduced driving voltage and increased the power efficiency of blue phosphorescent organic light-emitting diodes compared to a standard host with α-carboline moiety. A high external quantum efficiency of 25.3% and a high power efficiency of 36.4 lm/W were achieved in the blue phosphorescent organic light-emitting diodes.
Co-reporter:Mounggon Kim, Sang Kyu Jeon, Seok-Ho Hwang, Jun Yeob Lee
Synthetic Metals 2015 Volume 209() pp:19-23
Publication Date(Web):November 2015
DOI:10.1016/j.synthmet.2015.06.020
•A bicarbazole derived host material with a benzonitrile substituent showed bipolar charge transport properties.•A high external quantum efficiency above 20% was obtained in green thermally activated delayed fluorescent device.•Para substitution of CN was better than metal substitution for high efficiency.A bicarbazole based donor–acceptor compound, 4,4′-([3,4′-bicarbazole]-9,9′-diyl)dibenzonitrile (4CN34BCz), was synthesized as a host material for thermally activated delayed fluorescent emitter and the device performances of the green devices with the synthesized host and (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) delayed fluorescent emitter were investigated. 4CN34BCz with CN unit at para-position could effectively assist delayed fluorescent emission of 4CzIPN and achieved a high external quantum efficiency of 20.8% compared to 13.8% of the similar host with CN unit at meta-position because the orientation of the CN functional group at para position of the benzonitrile was favourable for charge balance in the emitting layer.
Co-reporter:Chan Seok Oh
The Journal of Physical Chemistry C 2015 Volume 119(Issue 39) pp:22618-22624
Publication Date(Web):September 21, 2015
DOI:10.1021/acs.jpcc.5b05292
A design rule of the acceptor material of exciplexes was studied by synthesizing two acceptor materials with only acceptor moieties and with both a donor and an acceptor simultaneously. Molecular calculation and photophysical measurements of the exciplexes revealed that the donor–acceptor type acceptor materials promoted the exciplex formation by charge transfer character and increased the photoluminescence quantum yield of the exciplexes. The combination of a donor material and the donor–acceptor type acceptor material achieved a high quantum efficiency of 12.6% in the green exciplex devices.
Co-reporter:Yong Joo Cho;Sang Kyu Jeon; Byung Doo Chin;Dr. Eunsun Yu; Jun Yeob Lee
Angewandte Chemie 2015 Volume 127( Issue 17) pp:5290-5293
Publication Date(Web):
DOI:10.1002/ange.201412107
Abstract
Dual emitting cores for thermally activated delayed fluorescent (TADF) emitters were developed. Relative to the corresponding TADF emitter with a single emitting core the TADF emitter with a dual emitting core, 3,3′,5,5′-tetra(carbazol-9-yl)-[1,1′-biphenyl]-2,2′,6,6′-tetracarbonitrile, showed enhanced light absorption accompanied by a high photoluminescence quantum yield. The quantum and power efficiencies of the TADF devices were enhanced by the dual emitting cores.
Co-reporter:Yong Joo Cho;Sang Kyu Jeon; Byung Doo Chin;Dr. Eunsun Yu; Jun Yeob Lee
Angewandte Chemie International Edition 2015 Volume 54( Issue 17) pp:5201-5204
Publication Date(Web):
DOI:10.1002/anie.201412107
Abstract
Dual emitting cores for thermally activated delayed fluorescent (TADF) emitters were developed. Relative to the corresponding TADF emitter with a single emitting core the TADF emitter with a dual emitting core, 3,3′,5,5′-tetra(carbazol-9-yl)-[1,1′-biphenyl]-2,2′,6,6′-tetracarbonitrile, showed enhanced light absorption accompanied by a high photoluminescence quantum yield. The quantum and power efficiencies of the TADF devices were enhanced by the dual emitting cores.
Co-reporter:Wook Song, Taekyung Kim, Yoonkyoo Lee, Jun Yeob Lee
Organic Electronics (April 2017) Volume 43() pp:82-86
Publication Date(Web):April 2017
DOI:10.1016/j.orgel.2017.01.016
Co-reporter:Hyeong Min Kim, Jeong Min Choi, Jun Yeob Lee
Organic Electronics (April 2017) Volume 43() pp:
Publication Date(Web):1 April 2017
DOI:10.1016/j.orgel.2017.01.021
•High glass transition temperature of bicarbazole and dibenzothiophene derived host materials by 4- position modification.•Longer lifetime in the blue phosphorescent devices by bicarbazole derivatives with 4- position modified dibenzothiophene.•High efficiency in the blue phosphorescent devices by hole transport type bicarbazole derived host materials.Two bicarbazole type host materials, 9-(dibenzo [b,d]thiophen-4-yl)-9ʹ-phenyl-9H,9′H-3,3ʹ-bicarbazole (DBTBCz) and 9,9ʹ-bis(dibenzo [b,d]thiophen-4-yl)-9H,9′H-3,3ʹ-bicarbazole (DDBTBCz), were developed as lifetime enhancing host materials for blue phosphorescent organic light-emitting diodes (PhOLEDs). The DBTBCz and DDBTBCz host materials were prepared by substituting one or two dibenzothiophene units to a 3,3ʹ-bicarbazole backbone structure for the purpose of improving thermal stability and rigidity of the host materials for stable operational lifetime. Device characterization of the host materials revealed that the dibenzothiophene modification via 4- position is better than that via 2- position for improved lifetime of blue PhOLEDs.Download high-res image (140KB)Download full-size image
Co-reporter:Ji Han Kim, Jun Yeob Lee
Journal of Industrial and Engineering Chemistry (25 June 2017) Volume 50() pp:111-114
Publication Date(Web):25 June 2017
DOI:10.1016/j.jiec.2017.02.001
2,8-Bis(9,9-dimethylacridin-10(9H)-yl)dibenzo[b,d]thiophene 5,5-dioxide (AcDBTO) was developed as a dibenzothiophene-dioxide acceptor based emitter for use as a thermally activated delayed fluorescent emitter for color tunable organic light-emitting diodes. The dibenzothiophene-dioxide acceptor was modified with two strongly electron donating dimethylacridine donors, which enabled delayed fluorescence behavior in the AcDBTO emitter. The AcDBTO based device demonstrated quantum efficiency of 14.5% as a green delayed fluorescent device and wide emission wavelength from 502 nm to 525 nm with little change of the quantum efficiency.Download high-res image (120KB)Download full-size image
Co-reporter:Yong Joo Cho, Jun Yeob Lee
Journal of Industrial and Engineering Chemistry (25 January 2016) Volume 33() pp:366-368
Publication Date(Web):25 January 2016
DOI:10.1016/j.jiec.2015.10.021
Stamp transfer printing process has been found to increase the efficiency of poly(3-hexylthiophene)(P3HT):indene-C60 bisadduct (ICBA) organic solar cells. Here, we show that the stamp transfer printing of P3HT:ICBA active layer on poly-(3,4-ethylenedioxythiophene); polystyrenesulfonate enhances the power conversion efficiency of P3HT:ICBA device by about 21% compared with that of spin coated devices mainly due to transfer printing induced crystallization of P3HT.Download full-size image
Co-reporter:Si Hyun Han, Jeong Min Choi, Jun Yeob Lee
Journal of Industrial and Engineering Chemistry (25 February 2017) Volume 46() pp:49-53
Publication Date(Web):25 February 2017
DOI:10.1016/j.jiec.2016.10.014
A novel emitting layer structure of white organic light-emitting diodes (WOLED) was developed using exciplex-forming two blue emitters, 2,3,4,5,6-penta(9H-carbazol-9-yl)benzonitrile (5CzCN) and tris(2-(1-(2,4-diisopropyldibenzo[b,d]furan-3-yl)-1H-imidazol-2-yl)phenyl)iridium (Ir(dbi)3). The 5CzCN blue delayed fluorescence material and Ir(dbi)3 phosphorescent emitter partially formed a red exciplex in the mixed film. Combination of blue emission from the blue emitters and red emission from the exciplex provided white emission in the blue emitting 5CzCN and Ir(dbi)3 co-doped device. The WOLED fabricated using the blue emitting 5CzCN and Ir(dbi)3 emitters achieved high color rendering index of 90.8 at 100 cd/m2.Download high-res image (108KB)Download full-size image
Co-reporter:Sang Kyu Jeon, Jun Yeob Lee
Journal of Industrial and Engineering Chemistry (25 December 2015) Volume 32() pp:332-335
Publication Date(Web):25 December 2015
DOI:10.1016/j.jiec.2015.09.011
Recombination zone of phosphorescent organic light-emitting diodes during lifetime measurement was directly monitored using a red sensing layer inserted at different positions of blue phosphorescent emitting layer. The shift of recombination zone could be identified by the change of red intensity of the red sensing layer because the red intensity reflects the exciton density around the red sensing layer. Gradual shift of the recombination zone from hole transport layer side to electron transport layer side could be directly tracked according to driving time of the device.Download high-res image (81KB)Download full-size image
Co-reporter:Seung Geon Yoo, Sang Kyu Jeon, Seok-Ho Hwang, Jun Yeob Lee
Journal of Industrial and Engineering Chemistry (25 December 2015) Volume 32() pp:72-76
Publication Date(Web):25 December 2015
DOI:10.1016/j.jiec.2015.07.020
A strong hole transport type host material derived from bicarbazole and ditolylamine, 4,4′-(9H,9′H-[2,3′-bicarbazole]-9,9′-diyl)bis(N,N-di-p-tolylaniline) (BCTA), was synthesized as the host material of blue emitting tris[1-(2,4-diisopropyldibenzo[b,d]furan-3-yl)-2-phenylimidazole] (Ir(dbi)3) triplet emitter. The strong hole transport character of BCTA compensated hole trapping effect of Ir(dbi)3 and optimized charge balance in the emitting layer, delivering 17.8% external quantum efficiency in the blue phosphorescent organic light-emitting diodes.Download high-res image (97KB)Download full-size image
Co-reporter:Wook Song, Taekyung Kim, Yoonkyoo Lee and Jun Yeob Lee
Journal of Materials Chemistry A 2017 - vol. 5(Issue 16) pp:NaN3954-3954
Publication Date(Web):2017/03/22
DOI:10.1039/C7TC00556C
A stepwise energy level doping structure for improving the lifetime of organic light-emitting diodes was developed by doping two emitters with different energy levels in the same host material as separated emitting layers. A hole-trapping phosphorescent emitter was doped in the emitting layer close to the electron transport layer and an electron-trapping thermally activated delayed fluorescent emitter was doped in the emitting layer close to the hole transport layer to show stepwise energy levels between emitting materials in the same host. The stepwise energy level doping structure improved the lifetime of organic light-emitting diodes through suppressed triplet–triplet annihilation and triplet–polaron annihilation by emission zone control and carrier confinement. Moreover, a high quantum efficiency close to 20% was realized in both green and blue organic light-emitting diodes in addition to the improved lifetime. This is the first work reporting both high quantum efficiency close to 20% and elongated lifetime simultaneously.
Co-reporter:Ji Won Yang, Jeong Min Choi and Jun Yeob Lee
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 45) pp:NaN31336-31336
Publication Date(Web):2016/10/31
DOI:10.1039/C6CP06308J
Bis(phenylsulfone) was developed as a strong electron acceptor of thermally activated delayed fluorescent emitters. The connection of two electron withdrawing phenylsulfone moieties through meta-position of phenyl produced the bis(phenylsulfone) acceptor and the strong electron acceptor strength of bis(phenylsulfone) enabled preparation of sky-blue and green thermally activated delayed fluorescent emitters in combination with weak carbazole donors. The bis(phenylsulfone) acceptor and carbazole donor combined organic materials performed as thermally activated delayed fluorescent emitters with a high quantum efficiency of 18.3%.
Co-reporter:Wook Song, Ha Lim Lee and Jun Yeob Lee
Journal of Materials Chemistry A 2017 - vol. 5(Issue 24) pp:NaN5929-5929
Publication Date(Web):2017/05/15
DOI:10.1039/C7TC01552F
High triplet energy exciplex hosts for deep blue phosphorescent organic light-emitting diodes were developed by synthesizing a high triplet energy hole transport type host material designed for exciplex formation with a high triplet energy electron transport type host material derived from a diphenyltriazine. The highest occupied molecular orbital level of the hole transport type host materials was precisely controlled to manage the exciplex formation with the electron transport type host. Two exciplex hosts with high triplet energies of 2.94 and 2.95 eV were demonstrated using the synthesized hole transport type hosts and they were effective as the hosts of a deep blue triplet emitter.
Co-reporter:Sang Kyu Jeon, Chan Seok Oh, Mounggon Kim, Kyoung Soo Yook and Jun Yeob Lee
Journal of Materials Chemistry A 2016 - vol. 4(Issue 8) pp:NaN1612-1612
Publication Date(Web):2016/02/04
DOI:10.1039/C5TC04028K
A low triplet energy host material with thermally activated delayed fluorescence character was applied as the host material of a blue phosphorescent emitter and was compared with a high triplet energy host material. The low triplet energy host material had triplet energy lower than the triplet energy of the triplet emitter and singlet energy higher than the triplet energy of the triplet emitter. The low triplet energy host material performed as well as a high triplet energy host material in terms of quantum efficiency by recycling triplet excitons of the phosphorescent emitter via an up-conversion process, but performed better than high triplet energy host materials in terms of driving voltage. Therefore, the thermally activated delayed fluorescence type low triplet energy host material increased the power efficiency of the devices. An energy transfer process from the low triplet energy host to the triplet emitter through the conversion of triplet excitons into singlet excitons was proposed and confirmed as the mechanism of efficient light emission.
Co-reporter:Dong Ryun Lee, Seok-Ho Hwang, Sang Kyu Jeon, Chil Won Lee and Jun Yeob Lee
Chemical Communications 2015 - vol. 51(Issue 38) pp:NaN8107-8107
Publication Date(Web):2015/04/14
DOI:10.1039/C5CC01940K
Benzofurocarbazole and benzothienocarbazole were used as electron donors of thermally activated delayed fluorescence (TADF) emitters and the performances of the TADF devices were examined. The benzofurocarbazole and benzothienocarbazole donor moieties were better than carbazole as the electron donors of the TADF emitters.
Co-reporter:Yirang Im, Wook Song and Jun Yeob Lee
Journal of Materials Chemistry A 2015 - vol. 3(Issue 31) pp:NaN8065-8065
Publication Date(Web):2015/07/13
DOI:10.1039/C5TC01065A
Two dibenzothiophene derived compounds, 4-(3-(triphenylen-2-yl)phenyl)dibenzo[b,d]thiophene (DBTTP1) and 4-(5′-phenyl-[1,1′:3′,1′′-terphenyl]-3-yl)dibenzo[b,d]thiophene (DBTTP2), were prepared as the host materials for green thermally activated delayed fluorescent (TADF) emitters to investigate the effect of the molecular structure of the host materials on the efficiency and lifetime of the green TADF devices. The green TADF devices fabricated using the DBTTP1 host material exhibited a high quantum efficiency of above 20% and a lifetime longer than 250 h up to 80% of initial luminance at 1000 cd m−2. Comparing the two host materials, triphenylene modified DBTTP1 was better than terphenyl modified DBTTP2 in terms of the lifetime of the green TADF devices.
Co-reporter:Chan Seok Oh, Jun Yeob Lee, Chang Ho Noh and Sung Han Kim
Journal of Materials Chemistry A 2016 - vol. 4(Issue 17) pp:NaN3797-3797
Publication Date(Web):2015/10/14
DOI:10.1039/C5TC02595H
A molecular design strategy to facilitate electron injection and to reduce driving voltage was proposed to reach high power efficiency in blue phosphorescent organic light-emitting diodes (PHOLEDs) doped with a phenylimidazole ligand based triplet emitter. The host materials were designed to keep the hole transport properties and triplet energy of a parent molecule. One or two CN units were attached to 3- or 3,6-positions of carbazole of 3,3-di(9H-carbazol-9-yl)biphenyl (mCBP) to manage electron transport properties of the parent mCBP host. The CN unit donated electron accepting character to the mCBP host and increased electron current density in the device, which improved power efficiency of the blue PHOLEDs from 41.8 lm W−1 to 57.1 lm W−1.
Co-reporter:Jeong-A Seo, Sang Kyu Jeon, Myoung Seon Gong, Jun Yeob Lee, Chang Ho Noh and Sung Han Kim
Journal of Materials Chemistry A 2015 - vol. 3(Issue 18) pp:NaN4645-4645
Publication Date(Web):2015/04/15
DOI:10.1039/C5TC00640F
An acridine derived compound, 9,9-dimethyl-10-(9-phenyl-9H-carbazol-3-yl)-9,10-dihydroacridine (PCZAC), was newly designed as a hole transport type high triplet energy material for application as a hole transport type exciton blocking layer of blue phosphorescent organic light-emitting diodes. The PCZAC compound provided a high triplet energy of 2.99 eV and a high glass transition temperature of 101 °C for high efficiency and long lifetime. PCZAC showed an improved quantum efficiency and more than 8 time improvement of the lifetime of blue phosphorescent organic light-emitting diodes.
Co-reporter:In Ho Lee, Wook Song, Jun Yeob Lee and Seok-Ho Hwang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 34) pp:NaN8838-8838
Publication Date(Web):2015/08/04
DOI:10.1039/C5TC01626F
High efficiency blue fluorescent organic light-emitting diodes (OLEDs) were developed by doping the conventional 2,5,8,11-tetra-tert-butylperylene (TBPe) blue fluorescent dopant in a mixed emitting layer of a wide bandgap host and a blue thermally activated delayed fluorescent emitter which played the role of a sensitizer in blue fluorescence emission. 10-(4-((4-(9H-Carbazol-9-yl)phenyl)sulfonyl)phenyl)-9,9-dimethyl-9,10-dihydroacridine (CzAcSF) was the blue thermally activated delayed fluorescent emitter of the emitting layer and bis[2-(diphenylphosphino)phenyl]ether oxide (DPEPO) was the host material of the emitting layer. Doping of TBPe at a doping concentration of 0.1% in an emitting layer of DPEPO:CzAcSF achieved a high quantum efficiency of 18.1% in the blue fluorescent OLEDs, which is the best quantum efficiency reported in blue fluorescent OLEDs.
Co-reporter:Ji Won Yang and Jun Yeob Lee
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 37) pp:NaN24474-24474
Publication Date(Web):2015/08/28
DOI:10.1039/C5CP03469H
Bicarbazole derivatives, 9,9′-bis(dibenzo[b,d]thiophen-2-yl)-9H,9′H-3,3′-bicarbazole (BCzDBT), 9,9′-bis(dibenzo[b,d]furan-2-yl)-9H,9′H-3,3′-bicarbazole (BCzDBF), and 9,9′-di([1,1′-biphenyl]-3-yl)-9H,9′H-3,3′-bicarbazole (BCzBP), were designed and examined as the hole transport type host materials of the tris[1-(2,4-diisopropyldibenzo[b,d]furan-3-yl)-2-phenylimidazole] (Ir(dbi)3) blue triplet emitter. BCzDBT performed better than BCzDBF and BCzBP as the hosts of Ir(dbi)3 and could demonstrate 24.8% quantum efficiency and long lifetime in the blue phosphorescent devices. Strong hole carrying properties of the bicarbazole derivatives were proposed as the main factors for the high quantum efficiency of the BCzDBT devices, and thermal and chemical stability of BCzDBT were suggested as crucial factors for the long lifetime of the BCzDBT devices.
Co-reporter:Sung Moo Kim, Sung Yong Byeon, Seok-Ho Hwang and Jun Yeob Lee
Chemical Communications 2015 - vol. 51(Issue 53) pp:NaN10675-10675
Publication Date(Web):2015/06/05
DOI:10.1039/C5CC02188J
A novel carbazole moiety with bromine at the 1-position of carbazole was synthesized and four carbazole compounds derived from the 1-position modified carbazole were developed as the host materials for phosphorescent organic light-emitting diodes. The 1-position modified carbazole was coupled with another carbazole to prepare bicarbazole intermediates, which were substituted with 4,6-diphenyltriazine to yield four bicarbazole derivatives modified with the electron deficient diphenyltriazine unit. The triplet host materials showed high quantum efficiency above 20% and low driving voltage below 5.0 V at 1000 cd m−2 in green phosphorescent organic light-emitting diodes.
Co-reporter:Mounggon Kim, Sang Kyu Jeon, Seok-Ho Hwang, Sang-shin Lee, Eunsun Yu and Jun Yeob Lee
Chemical Communications 2016 - vol. 52(Issue 2) pp:NaN342-342
Publication Date(Web):2015/10/30
DOI:10.1039/C5CC07999C
High efficiency and color tuning of thermally activated delayed fluorescent emitters were achieved at the same time by designing emitters with a twin emitter molecular design. The control of the interconnect position between two emitters could manage the emission spectrum of the thermally activated delayed fluorescent emitters without affecting the quantum efficiency.
Co-reporter:Mounggon Kim, Jeong Min Choi and Jun Yeob Lee
Chemical Communications 2016 - vol. 52(Issue 65) pp:NaN10035-10035
Publication Date(Web):2016/07/22
DOI:10.1039/C6CC04516B
Blue thermally activated delayed fluorescent (TADF) emitters having 1-carbazolylcarbazole based donor moieties were developed to resolve the low quantum efficiency and large singlet–triplet energy splitting issues of the linker free TADF emitters. Investigation of the 1-carbazolylcarbazole derived donors as the donor units of two blue TADF emitters in comparison with 3-carbazolylcarbazole demonstrated that the 1-carbazolylcarbazole based donors increased the triplet energy, decreased the singlet–triplet energy gap, blue-shifted the emission color, and enhanced the quantum efficiency of the blue TADF devices.
Co-reporter:Mounggon Kim, Sang Kyu Jeon, Seok-Ho Hwang and Jun Yeob Lee
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 20) pp:NaN13558-13558
Publication Date(Web):2015/05/05
DOI:10.1039/C5CP01676B
We synthesized 3-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-methylphenyl)-9-phenyl-9H-carbazole (TrzmPCz) as a new bipolar host material for blue phosphorescent organic light-emitting devices and investigated the electro-optical properties of the blue devices fabricated using the TrzmPCz host. We managed the triplet energy of the host by inserting a methyl substituent in the phenyl linkage between triazine and carbazole. The methyl substituent distorted the backbone structure of TrzmPCz and lead to high triplet energy of 2.79 eV. After optimization of the device structure, the TrzmPCz based organic light-emitting diodes achieved the maximum quantum efficiency of 16.4%, a current efficiency of 32 cd A−1, and a power efficiency of 21.5 lm W−1.
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