Key factor of Device Lifetime in Exciplex Host Based Blue Phosphorescent Organic Light Emitting Diodes

In this study, we investigated the key factor of device lifetime in blue phosphorescent organic light emitting diodes (PhOLEDs) by managing hosts and dopants in the emitting layer. We manufactured four phosphorescent devices using the exciplex type mixed host and single bipolar host doped with either Pt type and Ir type phosphors. The mixed host was better than single host in the Pt emitter doped device, while it was similar to the single host in the Ir emitter doped device. Investigation of the light-emission mechanism of the PhOLEDs revealed that the mixed host is essential in the device showing strong hole trapping behavior. The strong p-type host in the mixed host relieves the hole trapping by the Pt phosphor, resulting in less polaron formation and polaron accumulation. As a result, the mixed host reduces triplet-polaron annihilation and extends the device lifetime of the Pt emitter doped PhOLEDs.