Carrier transfer and luminescence characteristics of concentration-dependent phosphorescent Ir(ppy)3 doped CBP film

• Superior hole-transporting capacity of Ir(ppy)3:CBP film.
• High efficiency and low roll-off phosphorescent OLEDs with 10wt% Ir(ppy)3 doped CBP being EML.
• Bathochromic-shift PL and EL emission due to concentration quenching effect.
• A reduced fluorescent lifetime of excitons at high doping concentration.

The carrier transfer and luminescence characteristic of concentration-dependent tris(2-phenylpyridine) iridium (Ir(ppy)3) doped in 4,4′-bis(carbazol-9-yl)-biphenyl (CBP) film of 40 nm have been investigated. Based on the charge-only devices with different concentration of Ir(ppy)3:CBP, we have found that an increasing dopant concentration can facilitate hole transfer, whereas suppress electrons transfer reversely. The ratio of Ir(ppy)3 in CBP plays a significant role in energy transfer process. Results have shown that excess Ir(ppy)3 possessed a shortened fluorescence lifetime, indicating a concentration quenching effect in Ir(ppy)3:CBP film. The performance of the device decreased rapidly with increasing of doping concentration of Ir(ppy)3 in CBP. A high efficiency of 65.2 cd/A with low efficiency roll-off phosphorescent OLED was achieved, in which 10 wt% Ir(ppy)3 in CBP was light-emitting layer.