The electrical and the optical properties of the organic light-emitting diodes (OLEDs) utilizing a tetraphenylnaphthacene (rubrene) trapping layer and an 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) barrier layer with a nanoscale thickness were investigated. While the operating voltage of the OLED with a rubrene trapping layer in the HTL significantly increased because of a decrease in the hole mobility of the HTL, that of the OLED with a rubrene trapping layer in the EML slightly decreased resulting from an increase of the trapped electrons and holes in a rubrene trapping layer. The electroluminescence peak corresponding to the emission zone in the EML of OLEDs with a rubrene trapping layer and a TPBI barrier layer shifts to the EML center due to the existence of trapping layer in the EML. (C) 2009 Elsevier B.V. All rights reserved.