Roll-off characteristics of electroluminescence efficiency of organic blue electrophosphorescence diodes

We studied the relaxation of electroluminescence roll-off characteristics by changing the dopant concentration and thickness of the emitting layer in organic blue electrophosphorescence diodes composed of 2,6-dicarbozolo-1.5-pyridine host doped with iridium(III)-bis[(4,6-di-fluorophenyl)-pyridinato-NC(2)]picolinate. Analyzing the roll-off characteristics using the theoretical models of triplet-triplet annihilation and triplet-polaron annihilation (TPA). We found that the roll-off characteristics of these devices were determined primarily by TPA.