Efficient Phosphorescent Organic Light Emitting Diodes Using F4TCNQ as the Indium-Tin-Oxide Modification Layer
A phosphorescent organic light emitting diode by using tetrafluorotetracyanoquinodimethane (F4TCNQ) as the indium-tin-oxide modification layer and 4,4'-bis(carbazol-9-yl)biphenyl (CBP) as the hole transporting layer is reported. CBP doped with a green phosphorescent dopant, tris(2-(p-tolyl)pyridine) iridium(III) (Ir(mppy)3) is used as the emission layer in this device, and the maximum current efficiency of 31.3 cd/A is achieved. Furthermore, low efficiency roll-off of 10.4% is observed with device luminance increasing from 100 cd/m2 (29.7 cd/A) to 10000 cd/m2 (26.5 cd/A). It is demonstrated that a charge-generation area is formed at F4TCNQ/CBP interface, which will benefit hole injection into the hole transporting layer. Moreover, use of the CBP hole transporting layer will benefit the low efficiency roll-off by broadening triplet exciton formation, as well as by avoiding accumulation of unbalanced carrier at the hole transporting layer/emission layer interface.