A pentacene-doped hole injection layer for organic light-emitting diodes

Pentacene-doped N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) film as the hole injection layer (HIL) in tris(8-hydroxyquinoline) aluminium (Alq(3))-based organic light-emitting devices (OLEDs) was studied. It was found experimentally that the introduction of the pentacene-doped NPB hole injection layer results in higher brightness and electroluminescent (EL) efficiency of the devices. A maximum luminance of 21000 cd m(-2) was achieved, and the maximum current efficiency and luminous efficiency reached was 5.1 cd A(-1) and 3.6 lm W-1, respectively, enhanced by a factor of over 1.3 with respect to the devices without the doped hole injection layer. The significant improvement is attributed to control of the injected holes, leading to more balanced electrons and holes within the recombination zone.