The role of molybdenum oxide as anode interfacial modification in the improvement of efficiency and stability in organic light-emitting diodes

It has been experimentally found that molybdenum oxide (MoO3) as the interfacial modification layer on indium-tin-oxide (ITO) in organic light-emitting diodes (OLEDs) significantly improves the efficiency and lifetime. In this paper, the role of MoO3 and MoO3 doped N,N '-di(naphthalene-1-yl)-N,N '-diphenyl-benzidine (NPB) as the interface modification layer on ITO in improvement of the efficiency and stability of OLEDs is investigated in detail by atomic force microscopy (AFM), polarized optical microscopy, transmission spectra, ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS). The studies on the energy level and the morphology of the films treated at different temperatures clearly show that the MoO3 and MoO3:NPB on ITO can reduce the hole injection barrier, improve the interfacial stability and suppress the crystallization of hole-transporting NPB, leading to a higher efficiency and longer lifetime of OLEDs. (c) 2008 Elsevier B.V. All rights reserved.