High stability and low driving voltage green organic light emitting diode with molybdenum oxide as buffer layer

Green organic light emitting diodes (OLEDs) with copper phthalocyanine (CuPc), 4,4′,4″-tris[3-methylphenyl(phenyl)amino]triphenymine (m-MTDATA) and molybdenum oxide (MoOx) as buffer layers have been investigated. The MoOx based device shows superior performance with low driving voltage, high power efficiency and much longer lifetime than those with other buffer layers. At the luminance of 100 cd/m2, the driving voltage is 3.8 V, which is 0.5 V and 2.2 V lower than that of the devices using CuPc (Cell-CuPc) and m-MTDATA (Cell-m-MTDATA) as buffer layer, respectively. Its power efficiency is 13.6 Lm/W, which is 38% and 30% higher than that of Cell-CuPc and Cell-m-MTDATA, respectively. The projected half-life under the initial luminance of 100 cd/m2 is 42,400 h, which is more than 3.8 times longer than that of Cell-m-MTDATA and 24 times that of Cell-CuPc. The superior performance of Cell-MoOx is attributed to its high hole injection ability and the stable interface between MoOx and organic material. The work function of MoOx measured by contact potential difference method and the J–V curves of “hole-only” devices indicate that a small barrier between MoOx/N,N′-di(naphthalene-1-y1)-N,N′-dipheyl-benzidine (NPB) leads to a strong hole injection, resulting in the low driving voltage and the high stability.