Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2000-01-31
2002-09-24
Kim, Robert H. (Department: 2882)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S503000, C313S502000, C313S506000, C428S690000, C428S917000
Reexamination Certificate
active
06456003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an organic electroluminescent device and a panel for use in a plane light source and display device.
2. Description of the Related Art
Electroluminescent devices (hereinafter simply referred to as “EL devices”) are favorably useful for a plane display device of self-light-emission type. Among those, unlike inorganic EL devices, organic EL devices are not required to drive with AC at a high voltage. In addition, they can be easily multi-colored due to the variety of organic compounds. Thus, their applications to a full-color display and so forth are expected and greatly studied to develop a structure with a high brightness at a low voltage.
The inorganic EL device causes light emissions of electric field exciting type. On the other hand, the organic EL device operates by injecting holes from the anode (positive electrode) and electrons from the cathode (negative electrode), and causes light emissions of carrier injection type. Positive and negative carriers injected from both electrodes respectively travel toward their opposite electrodes to generate excitons from their recombination. The light emissions of the organic EL device are ones emitted when the excitons are relieved.
A high-purity single crystalline anthracene has been used to study the organic EL device. Anthracene has low brightness and light emission efficiency values while it requires a high voltage application, and is poor in stability.
C. W. Tang et al of Eastman Kodak Co. reported in 1987 that they could achieve a stable light emission with a high brightness at a low voltage with a two-layered laminate structure of organic thin films. Their device had an organic layer, consisting of a two-layered laminate structure with a light emission layer and a hole transportation layer, which was sandwiched between a pair of electrodes and exhibited an unprecedented excellent property of 1,000 cd/cm
2
at an applied voltage of 10 V (Tang et al,
Appl. Phys. Lett.,
51, 913 (1987)). Since then, the research and development of organic EL devices was sharply activated.
An electron transportation layer may recently be formed between the cathode and the light emission layer in addition to the light emission and hole transportation layers. A hole injection layer may also be formed between the hole transportation layer and the anode. Some light emission materials such as tris-(8-hydroxyquinolinol)aluminum (hereinafter referred to as Alq) represented by the following structural formula (1) may also serve as electron transportation materials.
On the other hand, there are materials that serve as hole transportation and light emission materials. The light emission materials include the above-mentioned aluminum complex and distyrylarylene derivative {structural formula (2)}. The hole transportation materials include: diamine compounds such as N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (hereinafter referred to as TPD) {structural formula (3)}; and N,N′-diphenyl-N,N′-bis(&agr;-naphthyl)-1,1′-biphenyl-4,4′-diamine(hereinafter referred to as &agr;-NPD) {structural formula (4)}, and poly(vinylcarbazole).
The electron transportation materials other than Alq include 3-(4-biphenylyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4,-triazole (hereinafter referred to as TAZ) {structural formula (5)}.
The hole injection materials include 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (hereinafter referred to as m-MTDATA); and phthalocyanines such as copper phthalocyanine.
Materials that form various organic layers are not limited to the above-mentioned materials, and various organic compounds have been developed for the purpose of achieving high brightness and high efficiency. After a long period of continuous driving, however, such phenomena are observed that a dark spot without a light emission ability is generated and grown even in the organic compound of high brightness and efficiency and a drive voltage must be elevated.
There are possible reasons for the above-mentioned phenomena: the organic materials are thermally degraded; and the electrode and organic layer have a low adhesive property therebetween. Materials useful for the electrode in the organic EL device include metal oxides such as ITO (indium-tin oxide), metals such as gold, silver, magnesium, lithium and aluminum, and their alloys. Other electrically conductive polymers and various semiconductor materials may also serve as the electrode in the organic EL device.
An extremely thin film typically with a thickness of 10-100 nm is used for each organic layer that composes the organic EL device. Therefore, in order to achieve a dense film structure without pinholes, such a material is preferred, which has a high glass transition point (Tg) and excellent amorphous property. A high Tg material for use in the film can increase the thermal stability of the film and improve the durability and thermal resistance of the film for a long period of driving. However, the adhesion of the film to the electrode is not directly correlated with its Tg.
The electrodes for use in the organic EL device mainly use the above-described metal oxides or metals that are typically hydrophilic. On the other hand, the organic materials that are in contact with the electrodes in order to exchange and transport carriers are hydrophobic. Therefore, the interface between the electrode/organic layer can not have a sufficient adhesion property.
As described above, the organic EL device is quite disadvantageous in that the brightness would be lowered due to the generation and growth of dark spots and the power consumption would be increased due to a drive voltage increase after continuous driving.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of such disadvantages and has an object to provide an organic EL device and a panel with its improved adhesion property between an electrode and an organic layer. The device can also be prevented from decreasing its brightness due to the generation and growth of dark spots and from increasing its power consumption due to the elevation of a drive voltage. The present invention also provides a process of manufacturing the device and panel.
The inventors experimented and studied a lot to find out the structure of an organic EL device that can suppress the generation and growth of dark spots and simultaneously have a less amount of elevation of the drive voltage. As a result, the inventors found an approach to eliminate the above-mentioned disadvantages and finally reached to the present invention. The approach is to introduce an interaction caused between an organic compound having a sulfur-atom-containing substituent in a specific structure and the surface of a specific material into an interface between electrode/organic layers in an organic EL device.
The specific material includes metal oxides such as ITO (tin-doped indium oxide), ATO (antimony-doped tin oxide), FTO (fluorine-doped tin oxide), AZO (aluminum-doped zinc oxide), and metal oxides such as tin dioxide and zinc oxide. It also includes metals selected from the group consisting of copper and noble metals (gold, silver, platinum group (platinum, ruthenium, rhodium, palladium, osmium and iridium)), their alloys, and semiconductor compounds.
The semiconductor compounds include a p-type semiconductor compound for use in a hole injection (transportation) electrode and an n-type semiconductor compound for use in an electron injection (transportation) electrode. The p-type semiconductor compound includes a material mainly consisting of either compound of metal chalcogenide, metal halide and metal carbide. In further detail, the p-type semiconductor compound includes a material mainly consisting of either compound of nickel oxide, copper oxide, lead oxide, rare earth oxide, copper iodide and lead sulfide.
The compound having a sulfur-atom-containing substituent in a specific structure includes
Mori Kenji
Sakaguchi Yoshikazu
Foley & Lardner
Kim Robert H.
NEC Corporation
Yun Juric
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