An OLED display is regarded as the next generation display as it has advantages such as self-luminescence, high contrast ratio, no viewing angle limitation, fast response time, etc. An OLED device comprises a cathode, an anode and organic layers, and the organic layers are composed of a hole transporting material, an electron transporting material and a light-emitting material. Carbazole derivatives have properties such as good planarity, high it bond conjugation, effective charge transfer, rigid structure that can increase the glass transition temperature of a material, etc., and are usually used as the materials for the hole transporting layer or the emitting layer of an OLED.
For example, CN 1978441 discloses a phenyl carbazole compound having excellent charge transfer ability can be used as the material for a hole injection layer, a hole transporting layer or an emitting layer. WO 2007/069607 discloses a carbazole compound that can be used in the host of a blue phosphorescent organic light-emitting diode. A film made by co-deposition of the material of said patent and FIrpic (iridium(III) bis(4,6-difluorophenylpyridinato)picolate) almost has a phosphor efficiency of 100%. JP 2006-69962 discloses a carbazole compound that can be used in the host of a green phosphorescent organic light-emitting diode device. TW 1297038 discloses a carbazole compound having a high glass transition temperature. In said patent, a carbazole material is used for the hole transporting layer and the emitting layer, TPBI (1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene) is used for the electron transporting layer, and the luminescence efficiency of its device is 2.5 lm/W at 5 V. EP 1972625 discloses a series of materials having carbazole and oxadiazole structures, and the structural features of such compounds are that the third and sixth positions of the carbazole are hydrogen atoms or aliphatic functional groups. Said patent indicates that its materials are adapted to be used as a host of the emitting layer, which is, however, not demonstrated with real experimental data. Angew. Chem. Int. Ed. 2008, 47, 8104 mentions a carbazole compound adapted to be used as a host of a green phosphorescent organic light-emitting diode, and the efficiency of its device is up to 20.2%.
In the aforementioned prior art, the carbazole derivatives are widely used in the hole transporting layer and the emitting layer, and it has not been disclosed that carbazole derivatives are used as the materials for the electron transporting layer. In view of this, the present invention provides novel carbazole derivatives that can be used as the material for the electron transporting layer, and can be used as the hole transporting layer, the electron transporting layer and the emitting layer simultaneously, which can effectively simplify the procedure for manufacture of the devices.