Highly Efficient Phosphorescent Organic Light-Emitting Diodes Using Benzo[4,5]imidazo[2,1:2,3]imidazo[4,5,1-jk]carbazole as a Rigid and Effective Electron Acceptor in Bipolar Host

A novel bipolar host architecture was investigated toimprove theexternal quantum efficiency (EQE) of green phosphorescent organiclight-emitting diodes (PhOLEDs). The host was developed by incorporatingcarbazole as a hole-transport unit and fused rigid benzo[4 & PRIME;,5 & PRIME;]imidazo[2 & PRIME;,1 & PRIME;:2,3]imidazo[4,5, 1-jk]carbazole (BzICz) as a new electrontransport unit. The primary goal of the BzICz-based hostdesign was to achieve a high triplet energy and bipolar charge transportcharacteristics. The green PhOLEDs fabricated using the new BzICz and carbazole-based host demonstrated a high EQE of26.6% due to their high triplet energy and good bipolar charge transportingcharacteristics.