High efficiency and low operating voltage yellow phosphorescent organic light-emitting diodes with a simple doping-free structure.

Yellow phosphorescent organic light-emitting diodes (PhOLEDs) with high efficiency and a low operating voltage were reported through using a simple doping-free structure. The structure of the PhOLEDs was ITO/C 60 /MoO 3 /mCP/PO-01-TB/PO-T2T/Liq/Al. The np-type C 60 /MoO 3 heterojunction acted as hole injection layer, and the ultrathin PO-01-TB layer (0.1 nm) was inserted at the interface between mCP and PO-T2T to serve as yellow phosphorescent emitter. Detailed investigation suggested that the complete energy transfer occurred from the mCP/PO-T2T interfacial exciplex to yellow PO-01-TB. Furthermore, the np-type C 60 /MoO 3 heterojunction could supply more free charge carriers, giving rise to further enhanced PhOLED efficiency. By adjusting the thickness of the C 60 /MoO 3 heterojunction, a yellow PhOLED with a power efficiency of 71.6 lm W -1 was demonstrated with an extremely low operating voltage of 3.79 V at 1000 cd m -2 .