Triazine and Indancarbazole Based Bipolar Host Materials With Fluorene Bridge for Red Phosphorescent Oleds Have Excellent Device Performance.

Abstract

In this work, two novel types of bipolar phosphorescent host materials derived from triazine and indenocarbazole, which were 5-(7-(4,6-diphenyl-1,3,5-triazin-2-yl)-9,9-dimethyl-4b,8a-dihydro-9H-fluoren-2-yl)-7,7-dimethyl-5,7-dihydroindeno[2,1-b] carbazole (m-TFFCz) and 5-(7-(4,6-diphenyl-1,3,5-triazin-2-yl)-9,9-dimethyl-4b,8a-dihydro-9H-fluoren-2-yl)-5H-benzofuro[3,2-c]carbazole (m-TFBFCz). Both host materials exhibit remarkable thermal stability, for example, their higher glass transition temperatures (T_g) exceed 170 °C and higher decomposition temperatures (T_d) above 400 °C. The m-TFFCz and m-TFBFCz have high triplet energy (E_T) of 2.67 eV and 2.75 eV, and their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are completely separated. In addition, the red PhOLEDs based on two host materials of m-TFFCz and m-TFBFCz exhibit the maximum external quantum efficiency (EQE_max) of 20.31 % and 25.40 %, and the time it takes for a device to decay from its initial maximum brightness to 95 % of its original brightness (T₉₅) are 8.96 h and 102.63 h, respectively. Based on the results, synthesizing bipolar phosphorescent host materials using triazines is a viable design method for high-efficiency PhOLEDs with great thermal stability.