A multilayer organic light-emitting diode (OLED) was fabricated with a thin rubidium chloride (RbCl) layer inserted inside an electron transport layer (ETL), tris (8-hydroxyquinoline) aluminum (Alq(3)). Here, we set d is the distance of the RbCl layer away from the Alq(3)/Al interface. The rubidium chloride layer was inserted inside 60 nm Alq(3) at d = 0.0, 2.5, 5.0, 7.5, 10, 20 and 30 nm positions. When the RbCl layer is positioned closer to the Al cathode, both the current density and EL efficiency are enhanced due to the enhanced electron injection. The devices show the electroluminescent (EL) efficiency improvement without an enhanced injection if the value of d is lager than 5.0 nm. The suggested mechanism of RbCl EL efficiency enhancer is carrier trap sites induced by the thin RbCl layer. The trapped charges alter the distribution of the field inside the OLED and, consequently, give better recombination in the device. (C) 2009 Published by Elsevier Ltd.