Characteristics of organic light-emitting diode modified with mixed layer of chelate complex and metal

Organic light-emitting diodes (OLED) were successfully fabricated using the thin polymeric film by dispersing a hole transport material into a soluble polyimide and the molecular film of a chelate complex. In order to improve the injection of electrons into the emissive layer as well as the interfacial adhesion, we have attempted the mixing of the chelate complex and metal between the emissive layer and the cathodic electrode. The structural investigations of the mixed layer between the chelate complex and metal electrode were carried out using x-ray photoemission spectroscopy (XPS) and atomic force microscopy (AFM). Especially, ultraviolet photoemission spectroscopy (UPS) was applied to verify the electronic structure of the mixed layer. The charge injection of the device having the mixed layer was initialized at the applied voltage of 4.19 V, and the brightness was about 10³ cd/m² at 7 V. The dramatic enhancement in the oscillator strength was observed from the electroluminescent spectra measured with the applied voltage.