Recently, active research works have been made on organic EL devices. As a basic configuration, the organic EL device includes a hole injecting electrode, a thin film formed thereon by evaporating a hole transporting material such as triphenyldiamine (TPD), a light emitting layer deposited thereon of a fluorescent material such as an aluminum quinolinol complex (Alq3), and a metal electrode or electron injecting electrode formed thereon from a metal having a low work function such as magnesium. Such organic EL devices are attractive in that they can achieve a very high luminance ranging from several 100 to several 10,000 cd/m.sup.2 with a drive voltage of approximately 10 volts.
With respect to the material used as the hole injecting electrode of such organic EL devices, a material capable of injecting more holes into the light emitting layer or the hole injecting and transporting layer is believed effective. The hole injecting material is also required to be transparent and electroconductive because in many arrangements, emitted light exits from the substrate side.
Transparent electrodes known to this end include tin-doped indium oxide (ITO), zinc-doped indium oxide (IZO), ZnO, SnO.sub.2, and In.sub.2 O.sub.3. Of these, ITO electrodes are widely used as transparent electrodes in liquid crystal displays (LCD), dimmer glass and solar cells because they have both a visible light transmittance of 90% or higher and a sheet resistivity of 10 .OMEGA./or lower. ITO electrodes are considered promising as the hole injecting electrode in organic EL devices.
Organic EL devices tend to deteriorate with the lapse of time. It is a key task to prevent the EL devices from deteriorating. While various factors cause to deteriorate EL devices, the deterioration at a film interface, for example, between an electrode and an organic layer has a significant influence on the lifetime and light emission of EL devices. It is thus important to modify physical properties at the film interface. It is also necessary to prevent an abnormal light emitting phenomenon due to current leakage and a phenomenon of generating and propagating non-luminous regions known as dark spots.