Exciton management by co-doping of blue triplet emitter as a lifetime improving method of blue thermally activated delayed fluorescent devices

Co-doping of a blue phosphorescent emitter in a thermally activated delayed fluorescent (TADF) emitter based emitting layer was developed as an approach to extend the lifetime of blue TADF devices by managing excitons and polarons in the emitting layer. The blue phosphorescent emitter was doped at a very low doping concentration below 1 wt% to suppress triplet-triplet and triplet-polaron quenching effect in the TADF emitting layer. The doping of the blue phosphorescent emitter led to great extension of the lifetime of the TADF devices by hole trapping effect of the blue triplet emitter which widened exciton formation zone in the TADF emitting layer. More than twice extension of the operational lifetime of the device was demonstrated by the co-doping approach irrespective of the doping concentration of the TADF emitter in the emitting layer.