title: Simple Bipolar Host Materials for High-Efficiency Blue, Green, and White Phosphorescence OLEDs.
abstract: 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.
authors: State Key Laboratory of Fine Chemicals, College of Chemical Engineering, Dalian University of Technology , 2 Linggong Road, Dalian 116024, China.
authors: Wei
authors: W
authors: Li
authors: State Key Laboratory of Fine Chemicals, College of Chemical Engineering, Dalian University of Technology , 2 Linggong Road, Dalian 116024, China.
authors: Jiuyan
authors: J
authors: Li
authors: State Key Laboratory of Fine Chemicals, College of Chemical Engineering, Dalian University of Technology , 2 Linggong Road, Dalian 116024, China.
authors: Di
authors: D
authors: Liu
authors: State Key Laboratory of Fine Chemicals, College of Chemical Engineering, Dalian University of Technology , 2 Linggong Road, Dalian 116024, China.
authors: Qian
authors: Q
authors: Jin
keywords: 3-(1H-pyrazol-1-yl)pyridine; bipolar host materials; phosphorescent organic light-emitting diodes (PhOLEDs); simple structure; white