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Journal of Materials Chemistry C
Page 4 of 5
DOI: 10.1039/C7TC03937A
COMMUNICATION
Journal Name
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efficiency and its gentle efficiency roll-off is among the best
ever reported for green devices without any out-coupling
technology.28-30
Under the same conditions, the reference device based on
12 wt.% Ir(ppy)3 doped into CBP gives an inferior EQE of 24.9%
despite the different CIE coordinates (Figure S9 and Table S4).
Therefore, the obtained over 30% EQE for (pfupy)2Ir(acac) is
without our expectation. The EQE can be well described by the
following equation:31
12. Y. Miyata, T. Nishinaga and K. Komatsu, J. Org. Chem., 2005,
70, 1147.
EQE = γ × ηr × ηPL × ηout = γ × ηPL × ηout (1)
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Funct. Mater., 2013, 23, 47.
where γ is the ratio of the recombined carriers to the
injected carriers; ηr is the efficiency of radiative exciton
production; ηPL is the PL quantum efficiency and ηout is the light
out-coupling constant. Assuming that both γ and ηr are close to
1 as well as the determined ηPL of 0.80, ηout is estimated to be
at least 0.38 according to the equation (1), much higher than
the theoretical value.32 Consistent with the literatures,33-35 the
favorable horizontal orientation of (pfupy)2Ir(acac) in CBP may
tentatively contribute to the high ηout and thus over 30% EQE
when free of any out-coupling technology. Further
experiments should be performed to verify this hypothesis,
but they are now beyond the aim of this work.
18. L. Huo, T. Liu, B. Fan, Z. Zhao, X. Sun, D. Wei, M. Yu, Y. Liu and
Y. Sun, Adv. Mater., 2015, 27, 6969.
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J. Phys. Chem. A, 2000, 104, 6907.
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In summary, we have newly designed and synthesized a
furo[3,2-c]pyridine based Ir complex (pfupy)2Ir(acac) by
changing sulfur with oxygen in the C^N ligand. Such a small
variation of the molecular structure brings about the elevated
LUMO level and unaffected HOMO level, thus resulting in a
blue-shifted emission. The corresponding device of
(pfupy)2Ir(acac) realizes
a state-of-art EQE of 30.5% at
maximum and 25.6% even at 5000 cd/m2. In view of the
achieved promising device efficiency associated with the
gentle roll-off at high luminance, we believe that this work will
shed light on the development of furan-based functional
materials used for OLEDs in the future.
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Acknowledgements
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This work was supported by the National Key Research and
Development Program of China (No. 2016YFB0400701) and
the National Natural Science Foundation of China (No.
51573183, 91333205, 21174144 and 51322308).
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4 | J. Name., 2012, 00, 1-3
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