[1,2,4]Triazolo[1,5-a]pyridine based host materials for high-performance red PhOLEDs with external quantum efficiencies over 23%

In this work, two host materials, 9-(4-(7-(9,9'-spirobi[fluoren] - 2-yl)-[1,2,4]triazolo[1,5-a]pyridin-2-yl)phenyl) - 9H-carbazole (CzTP Spl) and 9-(4-(6-(9,9'-spirobi[fluoren] - 2-yl)-[1, 2,4]triazolo[1, 5-a]pyridin-2-yl)phenyl) - 9H-carbazole (CzTPSp2) were designed and synthesized by utilizing carbazole as hole-transport units and [1,2,4]triazolo[1,5-a]pyridine (TP) as electron-transport units. These two compounds exhibit good thermal stability, appropriate frontier orbital energy levels, high triplet energy levels, and balanced carrier transport properties. Red phosphorescent organic light-emitting devices (PhOLEDs) based on these two hosts and bis(1-phenylquinoline) (acetylacetonate)iridium (III) (Ir(pq)(2)acac) exhibit satisfactory efficiencies with the maximum external quantum efficiency (eta(ext), (max)) of 23.0% and 22.1%. To our knowledge, among the red-emitting OLEDs based on Ir(pq)(2)acac, the eta(ext), (max) (23.0%) of our device is the highest reported so far. Meanwhile, efficiency roll-off in these devices are far less obvious, at the luminance of 1000 cd m(-2), the eta(ext) of devices R1 and R2 can reach to be 22.0% and 21.6% with the efficiency roll-off value of 4.3% and 2.2%.