Utilizing triazine/pyrimidine acceptor and carbazole-triphenylamine donor based bipolar novel host materials for highly luminescent green phosphorescent OLEDs with lower efficiency roll-off

In this work, two novel bipolar host materials were designed, synthesized and applied in green phosphorescent based OLEDs. Both the host materials, 4-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)-9H-carbazol-9-yl)-N,N-diphenylaniline (TRZ 1) and 4-(2-(4,6-diphenylpyrimidin-2-yl)-9H-carbazol-9-yl)-N,N-diphenylaniline (PYR 1) exhibited high thermal stability, with decomposition temperatures of 425 °C and 400 °C, respectively. The triplet energy of PYR 1 (2.63 eV) was higher than that of TRZ 1 (2.44 eV), and facilitated suitable energy transfer to the green dopant. The PYR 1 based green device demonstrated an excellent maximum current efficiency of 48.7 cd/A and external quantum efficiency of 16.4%. Interestingly, the green device with PYR 1 showed an outstanding brightness of 95,870 cd/m2, which is three times greater than that of the reference CBP based device (31,370 cd/m2). The bipolar host PYR 1 is a promising material for high luminescent and low efficiency roll off applications, especially for green PhOLEDs.