The effect of alkaline metal chlorides on the properties of organic light-emitting diodes

The multilayer organic light-emitting diodes (OLEDs) have been fabricated with a thin alkaline metal chloride layer inserted inside an electron transport layer (ETL), tris (8-hydroxyquinoline) aluminum (Alq3). The alkaline metal chloride layer was inserted inside 60 nm Alq3 at d=0, 10, 20 and 30 nm positions (d is the distance of the interlayer away from the Al cathode). The devices, with alkaline metal chlorides inserted at the Alq3/Al interface, showed electron injection and electroluminescence (EL) intensity improvements. When the alkaline metal chlorides were inserted inside the Alq3 layer at 10, 20 or 30 nm position apart from the Al cathode, both EL intensity and efficiency were enhanced for the devices with a thin potassium chloride (KCl) or rubidium chloride (RbCl) layer. On the contrary, the improvements were not observed for the OLEDs with a thin sodium chloride (NaCl) layer. A proposed insulator buffer layer model is employed to explain these characteristics of the devices.