Performance Enhancement of Organic Light–Emitting Diodes Using Electron–Injection Materials of Metal Carbonates

Performance of organic light-emitting diodes was investigated depending on the electron-injection materials of metal carbonates (Li₂CO₃ and Cs₂CO₃ ); and number of layers. In order to improve the device efficiency, two types of devices were manufactured by using the hole-injection material (Teflon-amorphous fluoropolymer -AF) and electron-injection materials; one is a two-layer reference device ( ITO/Teflon-AF/Alq₃/Al ) and the other is a three-layer device (ITO/Teflon-AF/Alq₃/metal carbonate/Al). From the results of the efficiency for the devices with hole-injection layer and electron-injection layer, it was found that the electron-injection layer affects the electrical properties of the device more than the hole-injection layer. The external-quantum efficiency for the three-layer device with Li₂CO₃ and Cs₂CO₃ layer is improved by approximately six and eight times, respectively, compared with that of the two-layer reference device. It is thought that a use of electron-injection layer increases recombination rate of charge carriers by the active injection of electrons and the blocking of holes.