Journal
ADVANCED FUNCTIONAL MATERIALS
Volume 24, Issue 21, Pages 3268-3275Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201303785
Keywords
organic light-emitting devices; blue phosphorescence; pyridine-containing electron-transport materials; low operating voltage; efficiency roll-off
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Funding
- National Natural Science Foundation of China [51073057, 91233116]
- Ministry of Science and Technology [2011AA03A110]
- Ministry of Education [NCET-11-0159]
- Fundamental Research Funds for the Central Universities [2013ZG0007]
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A series of pyridine-containing electron-transport materials are developed as an electron-transport layer for the FIrpic-based blue phosphorescent organic light-emitting diodes. Their energy levels can be tuned by the introduction of pyridine rings in the framework and on the periphery of the molecules. Significantly reduced operating voltage is achieved without compromising external quantum efficiency by solely tuning the nitrogen atom orientations of those pyidine rings. Unprecedented low operating voltages of 2.61 and 3.03 V are realized at 1 and 100 cd m-2, giving ever highest power efficiency values of 65.8 and 59.7 lm W-1, respectively. In addition, the operating voltages at 100 cd m-2 can be further reduced to 2.70 V by using a host material with a small singlet-triplet exchange energy, and the threshold voltage for electroluminescence can even be 0.2-0.3 V lower than the theoretical minimum value of the photon energy divided by electron charge. Aside from the reduced operating voltage, a further reduced roll-off in efficiency is also achieved by the combination of an appropriate host material.
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