Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-06-24
2001-07-24
Yamnitzky, Marie (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S704000, C428S009000, C313S504000, C313S506000
Reexamination Certificate
active
06265088
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an organic electroluminescent device (organic EL device) wherein an organic layer having a luminescent region is provided between an anode and a cathode.
BACKGROUND OF THE INVENTION
Lightweight, high-efficiency flat panel displays have been extensively studied and developed, for example, for picture display of computers and television sets.
Since Cathode ray tubes (CRT) are high in luminance and exhibit good color reproducibility, they are most widely employed for display at present. Nevertheless, the problems are involved in that the tubes are bulky, heavy and high in power consumption.
For lightweight and high efficiency flat panel displays, there have been put on the market liquid crystal displays such as an active matrix drive type. However, liquid crystal displays have the problems that their angle of field is narrow, they do not rely on spontaneous light and thus, need great power consumption for back light when placed in a dark environment, and they do not have a sufficient response to high-speed video signals of high fineness which have been expected as being in use in future. Especially, it is difficult to produce a liquid crystal display with a large picture size, with the attendant problem of its high fabrication costs.
As a substitute therefor, a display of the type using a light-emitting diode may be possible, but such a display is also high in fabrication costs, coupled with another problem that it is difficult to form a matrix structure of light-emitting diodes on one substrate. Thus, when considered as a candidate for a low-cost display used in place of Cathode ray tubes, this type of display has a great problem to solve before putting to practical use.
As a flat panel display which has the possibility of solving these problems, attention has been recently paid to organic electroluminescent devices (organic EL devices) using organic luminescent materials. More particularly, when using organic compounds as a luminescent material, it has been expected to realize a flat panel display, which makes use of spontaneous light, has a high response speed and has no dependence on an angle of field.
The organic electroluminescent device is arranged that an organic thin film which contains a luminescent material capable of emitting light through charge of an electric current and is formed between an optically transparent anode and a metallic cathode. In the research report published in Applied Physics Letters, Vol. 51, No. 12, pp. 913 to 915 (1987), C. W. Tang and S. A. VanSlyke set forth a device structure (an organic EL device having a single hetero structure), which has a double-layered structure including, as organic thin films, a thin film composed of a hole transport material and a thin film composed of an electron transport material and wherein luminescence occurs by re-combination of holes and electrons injected from the respective electrodes into the organic films.
In this device structure, either of the hole transport material or the electron transport material serves also as a luminescent material. Luminescence takes place in a wavelength band corresponding to the energy gap between the ground state and the energized state of the luminescent material. When using such a double-layered structure, a drive voltage can be remarkably reduced, along with an improved luminescent efficiency.
Thereafter, there has been developed a three-layered structure (organic EL device having a double hetero structure) of a hole transport material, a luminescent material and an electron transport material as set out in the research report of C. Adachi, S. Tokita, T. Tsutsui and S. Saito, published in Japanese Journal of Applied Physics, Vol. 27, No. 2, pp. L269 to L271 (1988) Moreover, a device structure comprising a luminescent material present in an electron transport material has been developed as set out in the research report of C. W. Tang, S. A. VanSlyke and C. H. Chen published in Journal of Applied Physics, Vol. 65, No. 9, pp. 3610 to 3616 (1989). Through these researches, evidence has been given to the possibility of luminescence of high luminance at low voltage, thus leading to recent, very extensive studies and developments.
Organic compounds used as a luminescent material are considered to be advantageous in that because of their diversity in kind, a luminescent color can be arbitrarily changed theoretically by changing their molecular structure. Accordingly, it may be easier on comparison with thin film EL devices using inorganic materials to provide, via proper molecular design, three colors of R (red), G (green) and B (blue) having good color purities necessary for full color displays.
However, organic electroluminescent devices still have problems to solve. More particularly, a difficult is involved in the development of a stable red luminescent device with high luminance. In an instance of red luminescence attained by doping DCM[4-dicyanomethylene-6-(p-dimethylaminostyryl)-2-methyl-4H-pyran] in tris(8-quinolinol)aluminum (hereinafter abbreviated as Alq
3
) for use as a currently reported electron transport material, this material is not satisfactory as a display material with respect to both maximum luminance and reliability.
BSB-BCN, which was reported by T. Tsutsui and D. U. Kim in the meeting of Inorganic and Organic Electroluminescence (at Berlin, 1996), is able to realize a luminance as high as 1000 cd/m
2
or over, but is not always perfect with respect to the chromaticity for use as a red color for full color display.
Therefore, there is a need for a red luminescent device which is high in luminance, stable and high in color purity.
In Japanese Laid-open Patent No. Hei 7-188649 (Japanese Patent No. Hei 6-148798), it has been proposed to use a specific type of distyryl compound as an organic electroluminescent material. However, the intended luminescent color is blue, not for red.
As a result, there is a need for an organic electroluminescent device, which ensures high luminance and stable red luminescence.
SUMMARY OF THE INVENTION
Intensive studies have been made in order to solve the above problem, and as a result, it has been found that when using a specific type of distyryl compound as a luminescent material, there can be provided a highly reliable red luminescent device which is very useful for realizing a stable full color display of high luminance, thus reached completion of the invention.
More particularly, the invention relates to an organic electroluminescent device of the type which comprises an organic layer which has a luminescent region and is provided between an anode and a cathode and which contains, as an essential component, an organic material capable of generating luminescence by charge of an electric current, characterized in that the organic layer contains, as an organic luminescent material, at least one distyryl compound represented by the following general formula (1) or the following general formula (3).
general formula (1):
provided that, in the above general formula (1), R
1
, R
2
, R
3
and R
4
are, respectively, groups which may be the same or different and represent a phenyl group or an aryl group of the following general formula (2),
general formula (2):
and provided that, in the above general formula (2), R
11
, R
12
, R
13
, R
14
and R
15
are, respectively, groups which may be the same or different and represent a hydrogen atom, or at least one of them is a saturated or unsaturated alkoxyl group or an alkyl group preferably a methyl group or a tertiary butyl group, and R
5
, R
6
, R
7
, R
8
, R
9
and R
10
may be the same or different and, respectively, represent a hydrogen atom, a cyano group, a nitro group or a halogen atom (including F, Cl, Br or I).
The use, as a luminescent material, of a distyryl compound represented in the above general formula (1) and/or (3) enables one not only to obtain stable red luminescence of high luminance, but also to provide a device which has electrically, thermally or chemically good stability. The distyryl compounds of the gener
Mari Ichimura
Shinichiro Tamura
Tadashi Ishibashi
Sonnenschein Nath & Rosenthal
Sony Corporation
Xu Ling
Yamnitzky Marie
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