title: New Benzimidazole-Based Bipolar Hosts: Highly Efficient Phosphorescent and Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes Employing the Same Device Structure.
abstract: The rapid development of the thermally activated delayed fluorescence (TADF) emitters makes it necessary to produce new versatile host materials for both phosphorescent and TADF emitters. Three new bipolar host materials, 9,9'-(2'-(1H-benzimidazol-1-yl)-[1,1'-biphenyl]-3,5-diyl)bis(9H-carbazole) (o-mCPBI), 9,9'-(3'-(1H-benzimidazol-1-yl)-[1,1'-biphenyl]-3,5-diyl)bis(9H-carbazole) (m-mCPBI), and 9,9'-(4'-(1H-benzimidazol-1-yl)-[1,1'-biphenyl]-3,5-diyl)bis(9H-carbazole) (p-mCPBI), are designed and synthesized by integrating mCP with benzimidazole moiety via the ortho-, meta-, and para-positions of N-phenyl. The influence of different linking modes on the thermal, photophysical, electrochemical, and charge transport properties of the compounds is studied. By employing the same device structure except the emitting layer, the device performances of the blue, green, yellow, red, white phosphorescent and blue, green TADF organic light-emitting diodes (OLEDs) based on the three hosts are investigated. Among these three hosts, o-mCPBI exhibits the best device performance with external quantum efficiencies of over 20% for phosphorescent OLEDs and enhanced efficiencies for TADF devices. All these devices show relatively low efficiency roll-offs at high brightness. The versatility of the benzimidazole-based bipolar host o-mCPBI, such as an extremely high triplet energy level, suitable molecular orbital energy levels, improved thermal and charge transport properties, and excellent device performances for various colors, makes it a universal host material for highly efficient both phosphorescent and TADF OLEDs.
authors.affiliation: School of Materials Science and Engineering, Shaanxi Normal University , Xi'an 710062, P. R. China.
authors.forename: Yali
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: School of Materials Science and Engineering, Shaanxi Normal University , Xi'an 710062, P. R. China.
authors.forename: Chao
authors.initials: C
authors.lastname: Wu
authors.affiliation: School of Materials Science and Engineering, Shaanxi Normal University , Xi'an 710062, P. R. China.
authors.forename: Panlong
authors.initials: P
authors.lastname: Qiu
authors.affiliation: College of Chemistry and Chemical Engineering, Qufu Normal University , Qufu 273165, P. R. China.
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Li
authors.affiliation: School of Materials Science and Engineering, Shaanxi Normal University , Xi'an 710062, P. R. China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, University of Chinese Academy of Sciences , Changchun 130022, P. R. China.
authors.forename: Jiangshan
authors.initials: J
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, University of Chinese Academy of Sciences , Changchun 130022, P. R. China.
authors.forename: Dongge
authors.initials: D
authors.lastname: Ma
keywords: benzimidazole; bipolar host; organic light-emitting diode; phosphorescence; thermally activated delayed fluorescence