Multi-Resonant Indolo[3,2,1- jk]carbazole-Based Host for Blue Phosphorescent Organic Light-Emitting Diodes

In organic light-emitting diodes, positive and negative charge carriers mostly migrate at different rates. This could result in excitons formed in the EML often migrating to the vicinity of the hole transport layer and the electron transport layer. To address this, it is important to design high-quality multi-resonance hosts that can balance the migration rate of carriers. Here, we report two newly developed multi-resonance hosts, m-ICzPBI and o-ICzPBI. The hosts contain an indolo[3,2,1-jk]carbazole (ICz) motif, which functionalized as either a donor or an acceptor unit. The hosts exhibit extremely high molecular rigidity and thermal stability. Devices A and B were constructed using FIrpic as a phosphorescent emitter with m-ICzPBI or o-ICzPBI as a host. Device A achieved high maximum values of EQE, PE and CE of 13.4%, 24.8 lm W^-1 and 31.6 cd A^-1, respectively, and low efficiency roll-off at 5000 cd m^-2 of 8.6%, 10.6 lm W^-1 and 20.3 cd A^-1, respectively.