1. Field of the Invention
The present invention relates to a light-emitting device using an organic compound, and more particularly, relates to an organic light-emitting device which emits light by applying an electric field to a thin film comprising the organic compound.
2. Related Background Art
An organic light-emitting device is a device which forms excitons of a fluorescent organic compound by interposing a thin film comprising the fluorescent compound between an anode and a cathode and injecting electrons and holes (positive holes) from the electrodes, and utilizes light emitted when the excitons return to a ground state.
In a study according to Eastman Kodak Corporation in 1987 (Appl. Phys. Lett. 51, 913 (1987)), it has been reported that a device having a function-separated two-layer structure, which uses ITO for an anode, an alloy of magnesium and silver for a cathode, an aluminum quinolinol complex for an electron-transporting material and a light-emitting material and a triphenylamine derivative for a hole-transporting material, emits light of about 1,000 cd/m2 at an applied voltage of about 10 V (U.S. Pat. Nos. 4,539,507, 4,720,432 and 4,885,211).
Further, emission of light from ultraviolet to infrared region can be performed by changing the kind of a fluorescent organic compound. In these days, research has been actively made on various compounds (U.S. Pat. Nos. 5,151,629, 5,409,783, 5,382,477, Japanese Patent Application Laid-Open Nos. H02-247278, H03-255190, H05-202356, H09-202878, and H09-227576).
In addition to organic light-emitting devices using such low-molecular materials as those described above, a group of the University of Cambridge has reported organic light-emitting devices using conjugate polymers (Nature, 347, 539 (1990)). This report has confirmed that light emission can be obtained by a single layer by forming polyphenylene vinylene (PPV) in a film shape by use of an application system. Related patents on the organic light-emitting device using the conjugate polymers include U.S. Pat. Nos. 5,247,190, 5,514,878, 5,672,678, and Japanese Patent Application Laid-Open Nos. H04-145192 and H05-247460.
As described above, recent progress of an organic light-emitting device is remarkable, and is characterized in that a highly responsive, thin, and lightweight light-emitting device that can be driven at a low applied voltage and provides a high luminance and a variety of emission wavelengths can be made, which suggests the applicability to a wide variety of uses.
However, there still remain a large number of problems in terms of durability such as a change over time due to long-term use and deterioration due to an atmospheric gas containing oxygen or to moisture. Furthermore, when application to a full-color display or the like is attempted, an optical output of a higher luminance or light emission of a higher conversion efficiency is still required at present, so that various proposals have been made hitherto.
As for an example of a material and an organic light-emitting device containing an anthracene ring, Japanese Patent Application Laid-Open No. H08-12600 discloses use of a phenyl anthracene derivative compound. The publication describes that such compound can form a good organic film because of its low crystallinity particularly when used for a blue-light-emitting material or an electron-injecting/transporting material, but the emission efficiency and durability life have not practically been sufficient.
Japanese Patent Application Laid-Open Nos. H09-157643 and H10-72579 disclose use of an aminoanthracene derivative and a diaminoanthracene derivative, respectively. The publications describe that those anthracene derivatives provide green light emission when used as a light-emitting material, but when used to make a device, the emission efficiency of the device has been low and the durability life of the device has not practically been sufficient.
Japanese Patent No. 3,008,897 discloses that a device using a particular bianthryl compound for a light-emitting material shows light emission of a high luminance, but has no description about its emission efficiency and durability life.
Japanese Patent Application Laid-Open No. H11-8068 discloses that a device using a particular anthracene compound containing an olefin moiety for a light-emitting material shows light emission of yellow to red color range, but the emission efficiency has not been practically sufficient.
Japanese Patent Application Laid-Open No. 2001-284050 discloses a device using a light-emitting medium layer containing an anthracene derivative of a particular structure, an electron-transporting compound and a fluorescent compound. The patent describes that a red-light-emitting device with improved reliability is obtained, but the emission efficiency is not practically sufficient and it is difficult to emit blue light because of its device structure.
Japanese Patent Application Laid-Open No. 2002-324678 discloses that an organic light-emitting device using a material which has a pyrene-substituted benzene ring has good emission characteristics and durability, but the external quantum efficiency of the device is low, and the patent has no specific description about the durability life.