Hole-transporting-layer-free high-efficiency fluorescent blue organic light-emitting diodes

Abstract

High-efficiency fluorescent blue organic light-emitting diodes were fabricated using hole-injection and carrier-confining effective device architecture without a hole-transporting layer. The diodes consist of 1250 Å indium tin oxide/ 300 Å blue-emissive layer/ 400 Å electron-transporting layer/ 10 Å lithium fluoride/ 1500 Å aluminum. A high efficiency of 6.0% (12.5 lmW) at 100 cd m2 with a pan-blue emission of (0.19, 0.31) when trans-1,2-bis-(6- (N,N -di-p-tolylamino)naphthalene-2-yl) ethene was used in the emissive layer, or 3.9% (6.7 lmW) with a blue emission of (0.15, 0.20) when 2- (N,N -diphenylamino)-6-[4- (N,N -diphenylamino)-styryl] naphthalene was used. Besides having a thinner device structure, the marked improvement in efficiency is attributable mainly to the relatively low hole-injection barrier. © 2007 American Institute of Physics.