Novel Positive Polaron Stabilizing n-Type Host for High Efficiency and Long Lifetime in Blue Phosphorescent Organic Light-Emitting Diodes

Four electron transport type hosts withstanding the positive polaron stress were synthesized using the benzo[4,5]thieno[3,2-d]pyrimidine core to develop high triplet energy hosts. Four benzo[4,5]thieno[3,2-d]pyrimidine-derived hosts, 4-(9H-carbazol-9-yl)-2-(3-(triphenylsilyl)phenyl)benzo[4,5]thieno[3,2-d]pyrimidine (CzBTPmSi), 2,4-di(9H-carbazol-9-yl)benzo[4,5]thieno[3,2-d]pyrimidine (2CzBTP), 2-(9H-carbazol-9-yl)-4-(3-(triphenylsilyl)phenyl)benzo[4,5]thieno[3,2-d]pyrimidine (mSiBTPCz), and 2,4-bis(3-(triphenylsilyl)phenyl)benzo[4,5]thieno[3,2-d]pyrimidine (2mSiBTP), were designed to have either the tetraphenylsilyl blocking group or the hole transport type carbazole group. The CzBTPmSi and mSiBTPCz were prepared to study the effect of substitution positions of tetraphenylsilyl and carbazole on the device performances, and the 2CzBTP and 2mSiBTP were synthesized as reference materials. In the device application, the four hosts were used as electron transport type hosts mixed with a hole transport type 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (mCBP) host in the mixed host. Among the four mixed hosts, the mCBP/CzBTPmSi mixed host showed an external quantum efficiency of 23.9% and a device lifetime over 4000 h at 100 cd m^-2 in the blue phosphorescent organic light-emitting diodes.