High contrast ratio organic light-emitting devices based on CuPC as electron transport material

In this paper, a high-contrast-ratio organic light-emitting device (OLED) of high brightness is demonstrated. In this device, reflection from the cathode is reduced by inserting a copper-phthalocyanine (CuPC) layer between the emitting layer (EML) and the cathode called the Black Cathode(TM) technique. The absorption and the destructive interference effect caused by this layer lead to the decrease of the ambient light. With the same injection current density at 6 mA/cm(2), the contrast ratio of this device increases from 1.9 to 2.5 under 10001x illumination, when compared with a conventional device. Although the thickness of this device increases by 54.5%, its driving voltage is nearly the same as that of a conventional device. This result implies the high electron mobility in the inserted CuPC layer. (C) 2004 Elsevier B.V. All rights reserved.