An organic electroluminescent device (hereinafter referred to as organic EL device) in the simplest structure is generally constituted of a pair of counter electrodes between which a light-emitting layer is sandwiched. The organic EL device functions by utilizing the following phenomenon; upon application of an electric field between the electrodes, electrons are injected from the cathode and holes are injected from the anode and they recombine in the light-emitting layer with emission of light.
In recent years, organic thin films have been utilized in the development of organic EL devices. In particular, in order to enhance the luminous efficiency, the kind of electrodes has been optimized for the purpose of improving the efficiency of injecting carriers from the electrodes and a device has been developed in which a hole-transporting layer composed of an aromatic diamine and a light-emitting layer composed of 8-hydroxyquinoline aluminum complex (Alq3) are disposed between the electrodes. This device has brought about a marked improvement in the luminous efficiency over the conventional devices utilizing single crystals of anthracene and the like and thereafter the developmental works of organic EL devices have been directed toward commercial applications to high-performance flat panels featuring self-luminescence and high-speed response.