Efficient blue organic light-emitting device based on N,N′-di(naphth-2-yl)-N,N′-diphenyl-benzidine with an exciton-confining structure

A blue organic light-emitting device with improved efficiency and excellent color purity is reported (Commission Internationale de'l Eclairage coordinates of x=0.1659 and y=0.0772 at 5 V), where N, N '-di(naphth-2-yl)-N, N '-diphenyl-benzidine (NPB), a traditional hole-transporting layer, was used as the emission layer. A significant increase in efficiency was achieved by confining the excitons within the NPB layer by two wide-band-gap hole-blocking layers sandwiching the NPB layer. This structure also increases the direct exciton formation at the NPB layer by promoting electrons to cross the NPB layer, responsible for further efficiency improvement. Optimized structure showed an external quantum efficiency of 1.38%, which accounts for a 25% increase compared to a standard device. (c) 2006 American Institute of Physics.