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Issue 4, 2013
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A CBP derivative as bipolar host for performance enhancement in phosphorescent organic light-emitting diodes

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Abstract

N,N′-Dicarbazolyl-4,4′-biphenyl (CBP) is one of the most successful uni-polar host materials for phosphorescent organic light-emitting diodes (PhOLEDs). We report the synthesis and properties of one novel CBP derivative, CBP-CN, with two cyano groups (CN) at the 3-site of carbazole rings. The strong electron-withdrawing CN group was introduced with the expectation to promote electron-injecting/-transporting abilities and to achieve bipolar features for CBP-CN. In comparison with the parent CBP, CBP-CN possesses lowered HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) levels and dramatically increased Tg (glass transition temperature, 162 °C), but unaltered HOMO–LUMO band gap and triplet energy (2.69 eV). Green and red PhOLEDs were fabricated with CBP-CN as hosts for traditional iridium phosphors. The maximum luminance efficiency (ηL) of 80.61 cd A−1 (23.13%) was achieved for the green PhOLED, and 10.67 cd A−1 (15.54%) for the red one, which represent efficiency increases of 25–33% compared with those of the best devices with CBP host and are even among the best data for phosphorescent OLEDs reported so far. The theoretical calculation and the carrier-only devices investigation confirmed that the electron-injecting/-transporting character and the bipolar nature of CBP-CN should be responsible for the performance enhancements.

Graphical abstract: A CBP derivative as bipolar host for performance enhancement in phosphorescent organic light-emitting diodes

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Publication details

The article was received on 29 Sep 2012, accepted on 07 Nov 2012 and first published on 07 Nov 2012


Article type: Paper
DOI: 10.1039/C2TC00305H
J. Mater. Chem. C, 2013,1, 757-764

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    A CBP derivative as bipolar host for performance enhancement in phosphorescent organic light-emitting diodes

    T. Zhang, Y. Liang, J. Cheng and J. Li, J. Mater. Chem. C, 2013, 1, 757
    DOI: 10.1039/C2TC00305H

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