than that of red and green devices because of lack of stable
host materials with a triplet energy high enough for the blue
TADF emitters. Although mCBP was used in this work, it is
not the best material for blue TADF dopant because of rather
low triplet energy. The lifetime of the blue TADF device can
be improved further by developing stable host materials with a
high triplet energy.
Acknowledgements
This research was supported by Basic Science Research Program through
the National Research Foundation of Korea (NRF) funded by the Ministry
of Education, Science, and Technology (2013R1A1A2007991) and
Ministry of Science, ICT, and future Planning (2013R1A2A2A01067447)
and development of red and blue OLEDs with external quantum efficiency
over 20% using delayed fluorescent materials funded by MOTIE.
In conclusion, two blue TADF emitters, DCzTrz and DDC-
zTrz, were synthesized as stable TADF emitters for high effi-
ciency and long lifetime. DDCzTrz was efficient as a blue
TADF emitter and could show high maximum quantum effi-
ciency of 18.9% and lifetime of 52 h up to 80% of initial lumi-
nance at 500 cd m−2, which was almost three times as long as
that of blue phosphorescent OLEDs. Therefore, the triazine-
and dicarbazolyphenyl-based TADF design can pave a way to
develop stable blue TADF emitters for long lifetime and high
efficiency.
Received: January 18, 2015
Revised: February 12, 2015
Published online:
[1] H. Uoyama, K. Goushi, K. Shizu, H. Nomura, C. Adachi, Nature
2012, 492, 234.
[2] J. W. Sun, J. H. Lee, C. K. Moon, K. H. Kim, H. S. Shin, J. J. Kim,
Adv. Mater. 2014, 26, 5684.
[3] Q. Zhang, B. Li, S. Huang, H. Nomura, H. Tanaka, C. Adachi, Nat.
Photon. 2014, 8, 326.
[4] A. Endo, K. Sato, K. Yoshimura, T. Kai, A. Kawada, H. Miyazaki,
C. Adachi, Appl. Phys. Lett. 2011, 98, 083302.
[5] G. Mehes, H. Nomura, Q. Zhang, T. Nakagawa, C. Adachi, Angew.
Chem. Int. Ed. 2012, 51, 11311.
[6] T. Nakagawa, S. Y. Ku, K. T. Wong, C. Adachi, Chem. Commun. 2012,
48, 9580.
[7] S. Y. Lee, T. Yasuda, H. Nomura, C. Adachi, Appl. Phys. Lett. 2012,
101, 093306.
[8] H. Tanaka, K. Shizu, H. Miyazaki, C. Adachi, Chem. Commun. 2012,
48, 11392.
[9] Q. Zhang, J. Li, K. Shizu, S. Huang, S. Hirata, H. Miyazaki,
C. Adachi, J. Am. Chem. Soc. 2012, 134, 14706.
[10] K. Sato, K. Shizu, K. Yoshimura, A. Kawada, H. Miyazaki, C. Adachi,
Phys. Rev. Lett. 2013, 110, 247401.
[11] J. Lee, K. Shizu, H. Tanaka, H. Nomura, T. Yasuda, C. Adachi,
J. Mater. Chem. C. 2013, 1, 4599.
[12] K. Nasu, T. Nakagawa , H. Nomura, C. J. Lin, C. H. Cheng,
M. R. Tseng, T. Yasuda, C. Adachi, Chem. Commun. 2013, 49, 10385.
[13] S. Y. Lee, T. Yasuda, Y. S. Yang, Q. Zhang, C. Adachi, Angew. Chem.
2014, 126, 6520.
Experimental Section
Synthesis: Synthetic methods of DCzTrz and DDCzTrz were added in
Supporting Information.
Device Fabrication: All devices reported in this work were fabricated
using a thermal evaporator with a vacuum pressure of 1.0 × 10−6
torr. Organic layers were grown on a 120-nm-thick indium tin oxide
substrate cleaned using deionized water and hot 2-propanol at an
order
of
poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)
(PEDOT:PSS, 60 nm), 4,4′-cyclohexylidenebis[N,N-bis(4-methylphenyl)
aniline] (10 nm), tis(4-carbazol-9-ylphenyl)amine (10 nm), 1,3-bis(N-
carbazolyl)benzene (10 nm), DPEPO:DCzTrz, or DPEPO:DDCzTrz,
diphenylphosphine oxide-4-(triphenylsilyl)phenyl (5 nm), 1,3,5-tris(N-
phenylbenzimidazole-2-yl)benzene (30 nm), LiF (1 nm), and Al (200 nm).
The device structure of the blue devices for lifetime measurement was
ITO (120 nm)/N,N′-diphenyl-N,N′-bis-[4-(phenyl-m-tolyl-amino)-phenyl]-
biphenyl-4,4′-diamine (60 nm)/N,N,N′N′-tetra[(1,1′-biphenyl)-4-yl]-
(1,1′-biphenyl)-4,4′-diamine (30 nm)/mCBP:Ir(dbi)3 or mCBP:DCzTrz
or mCBP:DDCzTrz (25 nm)/LG201 (35 nm)/LiF (1 nm)/Al (200 nm).
Encapsulation of the devices was finished inside glove box after device
fabrication.
Measurements: Electrical characteristics of the fabricated devices
were analyzed using Keithley 2400 source measurement unit
and light emission characteristics were measured using CS 2000
spectroradiometer. Lifetime analysis of the TADF devices was done at a
constant current mode at an initial luminance of 500 cd m−2.
[14] H. Wang, L. Xie, Q. Peng, L. Meng, Y. Wang, Y. Yi, P. Wang, Adv.
Mater. 2014, 26, 5198.
[15] H. Nakanotani, K. Masui, J. Nishide, T. Shibata, C. Adachi, Sci. Rep.
2013, 3, 2127
[16] Y. J. Cho, J. Y. Lee, Adv. Mater. 2014, 24, 4050.
[17] J. Zhuanga, W. Lib, W. Sub, Y. Liuc, Q. Shena, L. Liaoc, M. Zhou,
Org. Electron. 2013, 14, 2596.
[18] S. Schmidbauer, A. Hohenleutner, B. Konig, Adv. Mater. 2013, 25,
2114.
[19] Y. Zhang, J. Lee, S. R. Forrest, Nat. Commun. 2014, 5, 5008.
[20] H. Nak anotani, K. Masui, J. Nishide, T. Shibata, C. Adachi, Sci. Rep.
2013, 3, 2127.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
©
6
wileyonlinelibrary.com
2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Mater. 2015,
DOI: 10.1002/adma.201500267