Comparative studies on the inorganic and organic p-type dopants in organic light-emitting diodes with enhanced hole injection

Comparative studies on inorganic and organic electron acceptors used as p-dopants in N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB) in organic light-emitting diodes (OLEDs) are carried out. It demonstrates that 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) doped hole-injecting layer is superior to molybdenum trioxide (MoO3) doped one in device efficiency and stability. Combining with absorption spectral measurement, the effectiveness of a p-doped NPB in OLEDs does not solely rely on the generation of charge-transfer complexes in the doped NPB. The detailed difference between MoO3 and HAT-CN as p-dopants in NPB is further investigated by evaluating the hole injection efficiency, hole barrier height, and surface morphology of the doped films.