Novel donor-acceptor-donor hosts for green and red phosphorescent OLEDs achieving high device efficiency and low efficiency roll-off

Achieving high device efficiency and low roll-off efficiency in a phosphorescent organic light-emitting devices (PhOLEDs) is still an important challenge. We designed and synthesized two donor-acceptor-donor (D-A-D) hosts with the suitable torsion angle between donor and acceptor, namely p-pTCz and m-pTCz, which were constructed by linking 1,2,4-trizole derivative and carbazole at the para- and meta-positions of N-9. The results show both m-pTCz and p-pTCz exhibit high thermostability, high triplet level and good bipolar transporting characteristics. It was found that the PhOLEDs incorporating host m-pTCz and emitter tris(2-phenylpyridinato) iridium (III) (Ir(ppy)(3)) achieved the desirable high efficiency with an external quantum efficiency (EQE) of 22.8% and still remain at 19.2% under a brightness of 10 000 cd/m(2). And red PhOLEDs based p-pTCz host and bis(1-phenylisoquinoline-C2, N)(acetylacetonato)iridium(III) (Ir(piq) 2 acac) emitter exhibited the maximum EQE of 17.5% and maintain at 14.1% under 10 000 cd/m(2). Here, the device efficiency and efficiency roll-off value for the optimized green and red PhOLEDs are comparable to the reported ones, suggesting that two hosts have huge potential applications.