Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 8, Issue 34, Pages 22382-22391Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.6b05355
Keywords
phosphorescent organic light-emitting diodes (PhOLEDs); bipolar host materials; 3-(1H-pyrazol-1-yl)pyridine; white; simple structure
Funding
- National Natural Science Foundation of China [21274016, 21374013, 21421005]
- Fundamental Research Funds for the Central Universities [DUT15YQ101, DUT16ZD221]
- Program for Changjiang Scholars and Innovative Research Team in University [IRT-13R06]
- Program for DUT Innovative Research Team [DUT2016TB12]
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3-(1H-Pyrazol-1-yl)pyridine is used as electron-transporting unit to construct bipolar host materials o-CzPyPz, m-CzPyPz, and p-CzPyPz for application in phosphorescent organic light-emitting diodes (PhOLEDs). By varying the ortho-, meta-, or para-linking mode between the n-type 3-(1H-pyrazol-1-yl)pyridine and the p-type carbazole on phenylene bridge, the optoelectronic parameters are tuned to large extent. The highly twisted o-CzPyPz has high triplet energy of 2.95 eV, while the isomer p-CzPyPz with more coplanar conformation has smaller triplet energy of 2.67 eV. The m-CzPyPz-hosted blue PhOLED exhibits a peak current efficiency of 49.1 cd A(-1) (corresponding to an external quantum efficiency of 24.5%) and low-efficiency roll-off, while the p-CzPyPz-hosted green PhOLEDs turns on at 2.8 V and exhibits high efficiencies of 91.8 cd A(-1) (96.1 lm W-1 and 27.3%). Furthermore, two-emitting-layer white OLEDs are fabricated with m-CzPyPz or p-CzPyPz as common hosts for both blue and orange phosphors, which realize high efficiencies of 57.8 cd A(-1) (45.4 lm W-1 and 23.6%) and 60.7 cd A(-1) (38.1 lm W-1 and 23.1%). The optimization of host structure for good matching of host and dopant and finally for the ideal performance is discussed.
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