Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-02-22
2002-08-20
Yamnitzky, Marie (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S704000, C428S917000, C313S504000, C313S506000
Reexamination Certificate
active
06436558
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an organic electroluminescence element which is used as a luminescent element and the like for use in various display units, light sources or back lights of display units, and optical communication devices.
BACKGROUND OF THE INVENTION
An electroluminescence element is a luminescent device making use of electroluminescence of a solid fluorescent material. Inorganic electroluminescence elements using inorganic materials as an illuminant have been now put to practical use, and the application to a back light of a liquid display and a flat display is devised in some parts, but as the voltage necessary for the luminescence of an inorganic electroluminescence element is high such as 100 V or more and, moreover, blue luminescence is difficult, realization of full colors by three primary colors of RGB is difficult.
On the other hand, studies concerning electroluminescence elements using organic materials have so far attracted public attention and various examinations have been done but did not develop into full-scale practical studies because the luminous efficacy was extremely bad. However, an organic electroluminescence element having a function-separating type laminate structure in which an organic material is divided into two layers of a hole-transporting layer and a luminescent layer was suggested by C. W. Tang, et al. of Eastman Kodak Co. in 1987, by which it became apparent that high luminant brightness of 1,000 cd/m
2
or more can be obtained even by low voltage of 10 V or less (see C. W. Tang and S. A. Vanslyke,
Appl. Phys. Lett
., 51, 913 (1987)). On and after that time, organic electroluminescence elements have abruptly attracted public attention and similar organic electroluminescence elements having function-separating type laminate structure are eagerly studied even now.
A conventionally used organic electroluminescence element is explained below with referring to the figure. The figure is a constitution drawing of an organic electroluminescence element which has so far been used. In the figure, symbol 1 is a substrate, 2 the anode, 3 a hole-transporting layer, 4 a luminescent layer, and 5 the cathode. As shown in the figure, a conventional organic electroluminescence element comprises transparent or translucent substrate 1 comprising, e.g., glass, anode 2 comprising a transparent electrically conductive film such as ITO, etc., having provided on substrate 1 by a sputtering method or vapor deposition with resistance heating, etc., hole-transporting layer 3 comprising, e.g., N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine (hereinafter referred to as “TPD”) having provided on anode 2 by vapor deposition with resistance heating, etc., luminescent layer 4 comprising 8-hydroxyquinoline aluminum (hereinafter referred to as “Alq”) having provided on hole-transporting layer 3 by vapor deposition with resistance heating, etc., and cathode 5 comprising a metal film having a film thickness of from 100 nm to 300 nm having provided on luminescent layer 4 by vapor deposition with resistance heating, etc.
When a direct current electric pressure or a direct current electric current is applied to the organic electroluminescence element having the above-described constitution with making anode 2 a positive electrode and cathode 5 a negative electrode, holes are injected into luminescent layer 4 from anode 2 via hole-transporting layer 3, and electrons are injected into luminescent layer 4 from cathode 5. Recombination of holes and electrons are generated in luminescent layer 4, and a luminescence phenomenon is caused when the exciton which is formed with the recombination transfers from an excitation state to a ground state. When Alq is used in the above constitution, green luminescence can be obtained. It is also possible theoretically to obtain arbitrary luminescent colors by modifying molecular structures of organic compounds. Accordingly, an organic electroluminescence element can cope with the realization of full colors and it is promising as a display element in the future, with the advantage of low voltage driving. Further, the organic compound layer in the above constitution comprises the laminate structure of a hole-transporting layer for transporting holes and a luminescent layer, but other constitutions can be selected by selecting constitutional materials, such as the constitution of a luminescent layer alone, the three-layer structure comprising a hole-transporting layer, a luminescent layer, and an electron-transporting layer, or the constitution of a mixed layer comprising a luminescent layer and a hole-transporting layer, or a luminescent layer and an electron-transporting layer.
Further, a method is available which comprises doping an organic compound having high fluorescent quantum yield in a part of a luminescent layer as a dopant, and taking out luminescence from the dopant (a host-guest system). In this case, it is necessary that the transfer of exciton attended on the luminescence of the host material by itself should be conducted smoothly for the smooth transfer of the exciton to the dopant. Accordingly, it is necessary that conditions should be selected to be satisfied such that overlapping of the luminescent spectrum of the host material and the excitation wavelength of the dopant is large and the dopant is liable to be subjected to oxidation reduction as compared with the host material. Moreover, there is a case in which luminescence is caused without energy transfer of the luminescent spectrum from the host material by the element constitution taking an energy barrier into consideration. In such a case, as a material to be used as the host material, characteristics of efficiently injecting and transporting holes or electrons to the dopant are selected. Therefore, luminescence can be taken out by mixing the dopant in a hole-transporting layer and an electron-transporting layer which do not have a luminescent region. Highly efficient element can be provided by the realization of full colors of from blue to red by virtue of the luminescence by the dopant and by taking out strong luminescence of the dopant. In general, materials to be used as a dopant show strong quenching due to concentration and do not show distinct fluorescence in a solid state but show strong luminescence in a diluted solution in many cases, therefore, the use amount is preferably in a concentration of several mol % or less. Accordingly, the thinner the thickness of the film, the less is required the film forming property of the material, which is also advantageous in that the material can be selected from among the broader range.
As described above, arbitrary luminescent colors can be obtained by modifying molecular structures of the organic luminescent material to be used in a luminescent layer of an organic electroluminescence element. Further, various high efficient luminescence elements by adopting function-separating type laminate structure using a hole-transporting layer or by a host-guest system have been proposed. However, all of these are lacking in practicably satisfactory brightness characteristics and durability as characteristics of an electroluminescence element. In view of the above-described problems, the present invention aims at providing an organic electroluminescence element having high luminescent efficacy and high stability.
SUMMARY OF THE INVENTION
The present inventors have eagerly investigated for solving the above problems. As a result, we found that the above object of the present invention could be attained by using a certain organic compound. The present invention has been done based on the knowledge.
That is, the present invention provides:
(1) An organic electroluminescence element comprising a substrate having provided thereon an anode for injecting holes, a cathode for injecting electrons, and at least one organic compound layer therebetween, wherein the organic compound layer contains at least one compound represented by formula (I), and at least one compound rep
Gyoutoku Akira
Hara Shintaro
Iwanaga Hideaki
Komatsu Takahiro
Sato Tadahisa
Fuji Photo Film Co. , Ltd.
Yamnitzky Marie
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