Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
2001-05-01
2003-09-30
Reichard, Dean A. (Department: 2831)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
C445S023000, C445S025000, C445S022000, C445S026000, C313S503000, C313S504000, C313S506000
Reexamination Certificate
active
06626722
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for selecting a combination of a host material and a light-emitting material to be used for a light-emitting layer of an organic light-emitting device, and an organic light-emitting device using the combination of the host material and the light-emitting material selected by the method.
Organic light-emitting devices generally comprise a light-emitting layer of a light-emitting material disposed between an electron-injecting electrode (negative electrode) and a hole-injecting electrode (positive electrode). Electrons and holes are injected into the light-emitting layer and recombined therein to produce excitons, and the excitons are deactivated so that the light-emitting material emits fluorescence and/or phosphorescence. C. W. Tang, et al. have demonstrated in 1987 that an organic light-emitting device where a positive electrode, an organic hole-transporting layer, a light-emitting layer, an organic electron-transporting layer and a metal negative electrode are laminated on a glass substrate can be driven by a lowered applying voltage. Since then, organic light-emitting devices have been considered to be useful as a novel displaying device for flat panel displays, etc., and much attention has been paid thereto. However, the organic light-emitting devices are inferior in light-emitting efficiency to inorganic LED devices and fluorescent tubes, thereby being far from practicable. Most of the conventional organic light-emitting devices are such that utilizes fluorescence provided by singlet excitons in the organic light-emitting material. According to simple mechanism in quantum chemistry, ratio of the singlet excitons providing fluorescence to triplet excitons providing phosphorescence is ⅓ in an excitation state. Therefore, the organic light-emitting devices utilizing the fluorescence can practically apply only 25% of the excitons, thereby inevitably being poor in the light-emitting efficiency.
M. A. Baldo, et al. have disclosed that an organic light-emitting device comprising a light-emitting layer composed of 100 weight % of 4,4′-N,N′-dicarbazole biphenyl (CBP) and 6 weight % of tris(2-phenylpyridine) iridium complex (Ir(ppy)
3
) exhibits a high external quantum efficiency of 7.5% (M. A. Baldo, et al., Appl. Phys. Lett., Vol. 75, Page 4 (1999)). It has been supposed that this organic light-emitting device utilizes phosphorescence provided by the triplet excitons in Ir(ppy)
3
. After this disclosure, some proposals have been made to an organic light-emitting device excellent in the light-emitting efficiency, for example, Tsutsui, et al. have obtained 13.7% of the external quantum efficiency (T. Tsutsui, et al., Jpn. J. Appl. Phys., Vol. 38, Page L1502 (1999)). However, the organic light-emitting devices are required to have further improved light-emitting efficiency and luminance to be put into practical use.
To improve the light-emitting efficiency and the luminance of the organic light-emitting device, structure or materials thereof should be improved. Known as an organic light-emitting device having an improved structure is such as disclosed by above-mentioned T. Tsutsui, et al., etc. On the other hand, the materials for the organic light-emitting device have not been improved, the materials superior to the combination of the host material CBP and the light-emitting material Ir(ppy)
3
having not been known. This is because long period of time is necessitated to evaluate the materials. Since light-emitting mechanism of the organic light-emitting device, in particular, such that utilizes triplet excitons, has not yet been sufficiently solved, the materials must be evaluated after practically producing the device. The production of the device requires a plurality of processes including vacuum deposition, so that a plurality of the devices cannot be produced at the same time in the same apparatus. Therefore, selecting a preferred combination of a host material and a light-emitting material have needed remarkably long period of time, and it has been highly desired to develop a method for easily selecting or screening the preferred combination.
OBJECT AND SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for easily selecting a preferred combination of a host material and a light-emitting material to be used for a light-emitting layer of an organic light-emitting device, and to provide an organic light-emitting device containing the combination selected by the method to exhibit a high light-emitting efficiency.
As a result of intense research in view of the above object, the inventor has found that a preferred combination of a host material and a light-emitting material can be easily selected by evaluating light-emitting properties of a mixture film containing a light-emitting material and a host material without production of organic light-emitting devices using different materials from each other. The present invention has been accomplished by the finding.
Thus, a method of the present invention for selecting a combination of a host material and a light-emitting material to be used for a light-emitting layer of an organic light-emitting device comprises the steps of: (a) disposing a mixture film containing a host material and a light-emitting material on a substrate; and (b) evaluating the mixture film with respect to light-emitting properties while irradiating a light that is absorbed by the host material to the mixture film.
In the method of the present invention, on the mixture film side surface of the substrate is preferably provided an inert polymer layer. The inert polymer layer is preferably made of poly(methylmethacrylate) (PMMA). Further, the mixture film is preferably disposed by applying a solution containing the host material and the light-emitting material to the substrate, and by drying the applied solution. Weight ratio of the light-emitting material is preferably 1 to 10 weight % to the host material in the mixture film.
An organic light-emitting device of the present invention comprises a pair of electrodes and a light-emitting layer disposed therebetween, the light-emitting layer containing a combination of a host material and a light-emitting material selected by the above-mentioned method of the present invention. In the organic light-emitting device of the present invention, the light-emitting layer is particularly preferably such that is disposed by a vacuum deposition method, and weight ratio of the light-emitting material is preferably 1 to 10 weight % to the host material in the combination. Absorbance to the light that is absorbed by the host material of the light-emitting material is preferably ⅕ or less to that of the host material.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[1] Method for Selecting Combination of Host Material and Light-Emitting Material
A method of the present invention is for selecting a combination of a host material and a light-emitting material to be used for a light-emitting layer of an organic light-emitting device. The method comprises the steps of: (a) disposing a mixture film containing a host material and a light-emitting material on a substrate; and (b) evaluating the mixture film with respect to light-emitting properties while irradiating a light that is absorbed by the host material to the mixture film. The method can be utilized for production of an organic light-emitting device excellent in light-emitting efficiency. Incidentally, the terms “host material” and “light-emitting material” as used herein may mean candidate materials for the host material and the light-emitting material to be used for the light-emitting layer of the organic light-emitting device, respectively.
By the method of the present invention, a combination of a host material and a light-emitting material such that the organic light-emitting device using the combination exhibits easy energy transfer and high light-emitting efficiency can be easily selected from host materials such as carbazole compounds
Mishima Masayuki
Takematsu Masakazu
Fuji Photo Film Co. , Ltd.
Ha Nguyen
Reichard Dean A.
Sughrue & Mion, PLLC
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