[1,2,4]Triazolo[1,5‑a]pyridine as Building Blocks for Universal Host Materials
for High-Performance Red, Green, Blue and White Phosphorescent Organic
Light-Emitting Devices
posted on 2018-01-25, 00:00authored byWenxuan Song, Lijiang Shi, Lei Gao, Peijun Hu, Haichuan Mu, Zhenyuan Xia, Jinhai Huang, Jianhua Su
The electron-accepting
[1,2,4]triazolo[1,5-a]pyridine (TP) moiety was introduced
to build bipolar host materials for the first time, and two host materials
based on this TP acceptor and carbazole donor, namely, 9,9′-(2-([1,2,4]triazolo[1,5-a]pyridin-2-yl)-1,3-phenylene)bis(9H-carbazole)
(o-CzTP) and 9,9′-(5-([1,2,4]triazolo[1,5-a]pyridin-2-yl)-1,3-phenylene)bis(9H-carbazole)
(m-CzTP), were designed and synthesized. These two
TP-based host materials possess a high triplet energy (>2.9 eV)
and appropriate highest occupied molecular orbital/lowest unoccupied
molecular orbital levels as well as the bipolar transporting feature,
which permits their applicability as universal host materials in multicolor
phosphorescent organic light-emitting devices (PhOLEDs). Blue, green,
and red PhOLEDs based on o-CzTP and m-CzTP with the same device configuration all show high efficiencies
and low efficiency roll-off. The devices hosted by o-CzTP exhibit maximum external quantum efficiencies (ηext) of 27.1, 25.0, and 15.8% for blue, green, and red light
emitting, respectively, which are comparable with the best electroluminescene
performance reported for FIrpic-based blue, Ir(ppy)3-based
green, and Ir(pq)2(acac)-based red PhOLEDs equipped with
a single-component host. The white PhOLEDs based on the o-CzTP host and three lumophors containing red, green, and blue emitting
layers were fabricated with the same device structure, which exhibit
a maximum current efficiency and ηc of 40.4 cd/A
and 17.8%, respectively, with the color rendering index value of 75.