observed for devices with a thick rather than a thin BCP layer,
but we surmise that it is probably due to the different
morphological packing of BCP molecules in the solid film. It is
quite common that the thin film morphology is thickness-
dependent, such as the a- and b-form stacking of copper
Acknowledgements
We thank the financial support from the National Science
Council and Academia Sinica. Professor Yu-Tai Tao is
acknowledged for his instruction in the fabrication and
measurement of OLEDs.
2
0
21
phthalocyanine (CuPc) on the substrate. There are reports
about the insufficient stability of the hole-blocking BCP that
can be related to our observations here. A better hole-blocking
material, probably with a higher conductivity and wider band
gap but less tendency for aggregation, should further improve
the performance of the device.
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Fig. 4 illustrates that the EL of the non-doped red OLEDs with
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3
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We have demonstrated that NPAMLMe can be synthesized
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8
Synthetic route B adopting the same tricks, i.e. high concentration
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3
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1
1
9
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3
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In this study, we have found that the hole-blocking layer, BCP
in this case, is crucial to the performance of non-doped, red
OLEDs. BCP helps to free the red EL from the green emission
of Alq under high driving voltages as well as enhancing the
3
efficiency and brightness at low current density. The insightful
information obtained through the systemetic study reported
here is valuable in understanding the non-doped, host-emitting,
red OLEDs.
1
2 9 8
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 2 9 3 – 1 2 9 8