Correlation between Roll-Off Phenomena and Carrier Injections for OLEDs

In organic light-emitting diodes (OLEDs), the roll-off phenomenon was observed in the EL efficiency - current density characteristics. Although the EL efficiency in the inverted OLED with HAT-CN was 1.5-2 times higher than that in the inverted OLED with MoOx, the former maximum EL efficiency was observed in the higher current density. On the other hand, the EL efficiency in the inverted OLEDs decreased rapidly after the maximum as compared with the conventional OLED. The roll-off was thought to depend on carrier injections.