Organic electroluminescent device

#This application is a national stage application (under 35 U.S.C. §371) of PCT/EP2011/001870, filed Apr. 13, 2011, which claims benefit of German Application No. 10 2010 020 044.1, filed May 11, 2010. Both are incorporated by reference herein in their entirety.

#The present invention relates to white-emitting organic electroluminescent devices having two emitting layers which comprise an emitting layer comprising a phosphorescent dopant and an emitting layer comprising a fluorescent dopant.

#The structure of organic electroluminescent devices (OLEDs) in which organic semiconductors are employed as functional materials is described, for example, in U.S. Pat. Nos. 4,539,507, 5,151,629, EP 0676461 and WO 98/27136. A development in the area of organic electroluminescent devices are white-emitting OLEDs. These can be employed either for monochrome-white displays or, with coloured filters, for full-colour displays. They are furthermore suitable for lighting applications. White-emitting organic electroluminescent devices based on low-molecular-weight compounds generally have at least two emission layers. Electroluminescent devices having precisely two emission layers are used, in particular, for passive-matrix applications, where frequently in accordance with the prior art only fluorescent emitters are used for this purpose. The electroluminescent devices mostly have at least three emission layers, which exhibit blue, green and orange or red emission. Either fluorescent or phosphorescent emitters are used in the emission layers, where the phosphorescent emitters exhibit significant advantages owing to the higher achievable efficiency. The general structure of a white-emitting OLED of this type having at least one phosphorescent layer is described, for example, in WO 2005/011013. Owing to the higher achievable efficiency, a white-emitting OLED which comprises only phosphorescent emitter layers would be desirable. However, since blue-phosphorescent emitters generally do not meet current requirements, in particular with respect to the operating lifetime, hybrid OLEDs, i.e. a fluorescent blue emitter layer combined with phosphorescent orange or red and green emitter layers (in the case of three-colour white) or a fluorescent blue emitter layer combined with a phosphorescent yellow to orange emitter layer (in the case of two-colour white), are used in accordance with the prior art in most applications.

#Production and Characterisation of Organic Electroluminescent Devices in Accordance with the Invention

#Electroluminescent devices according to the invention can be produced as described, for example, in WO 2005/003253. The structures of the materials used are depicted below for clarity.

#These as yet unoptimised OLEDs are characterised by standard methods; for this purpose, the electroluminescence spectra and colour coordinates (in accordance with CIE 1931), the efficiency (measured in cd/A) as a function of the luminance, the operating voltage, calculated from current-voltage-luminous density characteristic lines (IUL characteristic lines), and the lifetime are determined. The results obtained are summarised in Table 1.