Study of interface properties of electrodes for the Alq3 base OLEDs

We have studied the carrier transport properties of amorphous organic material tris (8-hydroxyquinoline) aluminum (Alq(3)) for Al, LiF/Al, NaCl/Al, KBr/Al cathodes and ITO and ITO/HTL anodes at room temperature. The investigation was made by the current - voltage, luminescence - current characteristic measurements. The current density increases by several orders for LiF/Al and NaCl/Al cathodes over that of Al at a given bias voltages The electron injection processes at the metal/organic contact dominate the current - voltage characteristics. The carrier injection seems to be limited by the charge hopping of interfacial molecular sites. We have also developed a process method for the preparation of anodic indium-tin-oxide (ITO) surface for high efficient organic light emitting diodes (OLEDs). X-ray photoelectron spectroscopy (XPS) was used to measure atomic concentration of each element In, Sn, O and C on treated ITO surface. Scanning electron microscopy and atomic force microscopy were used to scan the surface profiles of ITO. The OLED performance considerably improved by the ITO surface treatments as well as by ITO/HTL anode due to the reduction of holes injection barrier between ITO and Alq3 interface.