Carbazole-endcapped Spiro[fluorene-9,9'-xanthene] for Heavily-doped and High Performance OLEDs
doping ratio of <10 wt%,[33] owning to the excessively
long lifetime as well as serious aggregation-assisted
quenching effect arising from strong intermolecular in-
teractions at high doping levels. However, in this work,
device I with a doping ratio of 10% achieves a lumi-
nance of 10220 cd•m−2 at 7 V, while devices II and III
with higher mixed concentration of 20% and 30% ob-
tained higher maximum luminance of 10330 cd•m−2 and
12110 cd•m−2 at 7 V (Figure 3c), respectively. The per-
formance of device IV declined to 3700 cd•m−2 at 7 V
with the doping concentration increasing to 50%, which
probably results from concentration quenching and trip-
let-triplet annihilation of guest at high mixed ratio. In
addition, the maximum current efficiencies (CEs) of
20.0 cd•A−1, 17.3 cd•A−1, and 21.1 cd•A−1 for devices
I-III (Table S1), respectively, which are also depend-
ent on the concentration increasing from 10% to 30%.
Furthermofore, the maximum power and external quan-
tum efficiencies are 17.9 lm•W−1, 15.4 lm•W−1, 18.8
lm•W−1, and 8.9%, 7.4% and 9.1% for devices I-III
(Table S1), respectively, which are also independent on
the variation of dopant concentration. It is noteworthy
that the performance of devices I-III shows slight
variation as doping concentration increases from 10% to
30%, which indicates the three blue PhOLEDs are con-
centration-insensitive using bulky steric hindrace of
SFX-Cz as host. Moreover, the Commission Interna-
tionale deL’Eclairage (CIE) color coordinates of devices
I-III are almost the same as each other at about (0.34,
0.15). In addition, Figure S4 shows the EL spectra of
devices I-IV under the driving voltage ranging from 4
V to 7 V, which shows the EL spectra are independent
of the voltage. This result also illustrates the figure of
EL spectra is concentration-insensitive of the guest. All
of these aforementioned events demonstrate bulky steric
hindrace of host SFX-Cz could disperse blue emtter
FIrpic in a wide doping range with stable EL spectra
and performance, which proves the bulky steric hin-
drance effect of SFX-Cz is helpful to improve device
repeatability and simplify the fabrication process to re-
alize production of PhOLED in large scale. It is notice-
able that the doping concentration of devices II and III
with high performance are 20% and 30%, which are
extremely higher than most of concentration-sensitive
phosphor as guest in PhOLEDs.
50%, respectively. The performance of heavily-doped
PhOLEDs exhibit no abvious change and is independent
of dopant concentration varying from 10% to 30%
without increasing fabrication complexity, which is ap-
pealing to highly reproducible and inexpensive fabrica-
tion technics of high performance WOLEDs. It is ex-
pectable that spiro[fluorene-9,9'-xanthene] derivatives
based PhOLEDs with higher performance and lower
cost would be achieved by optimizing the host structure
and fabrication process.
Acknowledgements
For the financial support, we thank National Natural
Scince Foundation of China (No. 61405170) and Stu-
dents Sustentation Fund of Xinyang Normal University
(No. 2014-DXS-136).
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Conclusions
In conclusion,
a novel spirocyclic compound
SFX-Cz has been designed and synthesized via Friedel-
Crafts and Ullmann reaction containing carbazole and
spiro[fluorene-9,9'-xanthene] units with bulky steric
hindrance used as host for the application in PhOLEDs.
A series of blue PhOLEDs using FIrpic as emitter with
doping concentration varying from 10% to 50% have
been fabricated successfully. The SFX-Cz based de-
vices show the maximum EQEs of 8.9%, 7.4%, 9.1%,
and 4.7% with the doping ratios of 10%, 20%, 30% and
[20] Huang, B.; Tang, J.; Jiang, W.; Yang, W.; Ban, X. X.; Sun, Y. M.
Chin. J. Org. Chem. 2013, 33, 1395.
Chin. J. Chem. 2015, 33, 955—960
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