Organic light-emitting diodes using potassium chloride as efficiency and stability enhancers

A multilayer organic light-emitting diode (OLED) has been fabricated with a thin (1 nm) potassium chloride (KCl) layer inserted inside an electron transport layer (ETL), tris (8-hydroxyquinoline) aluminum (Alq(3)). The structure of device was ITO/NPB/Alq(3)/KCl/Alq(3)/Al. The KCl layer was inserted inside 60 nm Alq(3) at 10, 20 and 30 rim positions away from the Alq(3)/Al interface. The device shows the optical power and electroluminescence (EL) efficiency enhancements. The highest optical power density of devices with KCl at different positions is more than twice as high as that of the device without KCl. The EL efficiency is enhanced by more than 50% by inserting the thin KCl insulating layer. The mechanism of KCl EL efficiency enhancer is that the thin KCl layer induces carrier trap sites and gives better recombination in the device. After air-exposure 42 h, the efficiency of the devices with KCl is enhanced but not for the device without KCl. The insertion of KCI inside Alq3 may improve the stability of OLED. (C) 2009 Elsevier B.V. All rights reserved.