Organic electroluminescence (OEL) is the phenomenon of electrically-driven emission of light from organic materials; including both fluorescent and phosphorescent organic solids. The organic light-emitting device (OLED), which exploits OEL emission from organic semiconducting thin films (with thicknesses of less than a few hundred nanometers), sandwiched between electrodes, has attracted keen interest in its application to flat-panel displays, due to its high luminous efficiency, low driving voltage, tunable colors as well as a convenient device-structure design and low fabrication costs when compared with every other known display device.