Bipolar host materials comprising carbazole, pyridine and triazole moieties for efficient and stable phosphorescent OLEDs

Achieving an excellent device performance with slow roll-off efficiency is still a crucial requirement for phosphorescent OLEDs in displays and white lighting applications. Three bipolar host materials comprised of carbazole, pyridine and triazole units, namely o-CzTPy, p-CzTPy, and 3-CzTPy were synthesized and developed. They are designed by selecting the pyridine and triazole groups together as an electron-transporting unit, and varying the different linking modes of the functional groups to optimize performance. These materials possessed high triplet energies (2.66 eV-2.69 eV), and good bipolar charge transporting abilities. FIrpic and Ir(ppy)3 based blue and green PhOLEDs incorporating these bipolar hosts show low turn-on voltage, high efficiencies and slow efficiency roll-off. Among them, a maximum efficiency of 22.25% (41.98 cd A-1) was achieved for o-CzTPy based blue device. More importantly, the o-CzTPy based green device achieved the desirable high efficiency of 29.08% (96.98 cd A-1), which is among the highest values for PhOLEDs with dopant Ir(ppy)3 ever reported in public scientific literatures. These excellent results demonstrated that these bipolar hosts possess high practical value for application in commercial PhOLEDs.

Automated summary

By designing bipolar host materials with high triplet energies and bipolar charge transporting abilities, high efficiencies and slow efficiency roll-off were achieved in blue and green PhOLEDs, demonstrating high practical value for commercial applications.