Organic light-emitting devices with a hole-blocking layer inserted between the hole-injection layer and hole-transporting layer

A hole-blocking layer (HBL), 2,9-dimethyl-4, 7-diphenylphenanthroline (BCP), was incorporated between the hole-transporting layer (HTL) and hole-injection layer for a tris-(8-hydroxyqunoline) aluminum-based organic light-emitting device. Such a structure helps to reduce the hole-leakage to the cathode resulting in improved current efficiency. Optimum BCP thickness of around 3 nm was observed to produce a current efficiency of 3.25 cd/A, which corresponds to a 30% improvement compared to that of the standard device without BCP (2.5 cd/A). Low operating voltage was also achieved by minimizing the thickness of the HTL. Both operating voltage and efficiency can be tuned by varying the thickness of HTL and HBL, respectively. (c) 2006 American Institute of Physics.