Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-08-25
2003-09-09
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C210S767000, C313S502000, C313S506000, C427S066000
Reexamination Certificate
active
06617051
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an organic electroluminescent device (hereinafter this will be referred to as an organic EL device) . More precisely, the invention relates to an organic EL device having the advantages of applicability to lightweight, thin and low-voltage driving displays, good luminescent capacity attenuating little even in long-term driving operation, and good durability.
BACKGROUND ART
As being self-luminescent, organic electroluminescent, EL devices have high visibility. In addition, they have high impact resistance as being completely solid devices. Therefore, they are much used in various fields of thin-film display devices, back lights for liquid-crystal displays, flat light sources, etc.
Distributed electroluminescent devices are now in practical use. As they require alternating voltage of at least tens volts and 10 kHz or more, their driving circuits are complicated.
In the circumstances, organic EL devices capable of being driven at lowered voltage of 10 volts or so and capable of emitting high-luminance light are much studied these days. For example, thin-film organic EL devices having a multi-layered structure of transparent electrode/hole injection layer/emitting layer/back electrode are proposed in Appl. Phys. Lett., Vol. 51, pp. 913-915 (1987) by C. W. Tang and S.A. Van Slyke, and in Japanese Patent Laid-Open No. 264629/1988. These are so designed that the hole injection layer therein can efficiently inject holes into the emitting layer therein. The emitting layer in such organic EL devices may have a single-layered structure, which, however, could not enjoy well-balanced electron transportation and hole transportation. To solve the problem, the emitting layer is modified to have a multi-layered structure of improved performance.
However, the process of forming the multi-layered emitting layer is complicated and takes a lot of time. Another problem with it is that the multi-layered structure is against the recent tendency in the art which is toward reducing the thickness of layers constituting organic EL devices. On the other hand, down-sized, compact and portable information appliances are much desired these days, and they are required to be driven at low voltage. In the circumstances, various types of light-emitting materials and hole-transporting materials are tried for such lightweight, low-voltage driving appliances.
Further, the most important theme in practical studies of organic EL devices is to establish the technique of preventing the attenuation of the luminance of the devices in long-term driving and to provide practicable organic EL devices. In this respect, it is said that the purity of organic compounds to be used for producing constituent materials for organic EL devices has a great influence on the attenuation of the luminous efficiency and the luminance of the devices produced, for example, as in “Monthly Display, Sept. 15, 1995”, and “Applied Physics, Vol. 66, No. 2, pp. 114-115, 1997”. However, the influences of the structures and the properties of organic compounds to be used for producing organic EL devices on the properties of the devices produced are not as yet clarified, and no method has heretofore been established capable of quantitatively determining the influences in question.
In that situation, the object of the present invention is to provide an organic EL device having the advantages of applicability to lightweight, thin and low-voltage driving displays, good luminescent capacity attenuating little even in long-term driving operation, and good durability.
DISCLOSURE OF THE INVENTION
We, the present inventors have assiduously studied in order to attain the object as above, and, as a result, have found that the object can be attained by an organic EL device in which at least one organic compound layer comprises an organic compound material having an impurity concentration of smaller than 1000 ppm including 0 ppm. On the basis of this finding, we have completed the present invention.
Specifically, the invention is summarized as follows:
(1) An organic electroluminescent device that comprises organic compound layer(s) including at least one organic emitting layer sandwiched between a pair of electrodes, wherein at least one organic compound layer is formed from an organic compound material having an impurity concentration of lower than 1000 ppm.
(2) An organic electroluminescent device that comprises organic compound layer(s) including at least one organic emitting layer sandwiched between a pair of electrodes, wherein at least one organic compound layer is formed from an organic compound material having an impurity concentration of lower than 500 ppm and the impurity therein is a halogen-containing compound.
(3) The organic electroluminescent device of above (2), wherein the halogen-containing compound is a halogen compound.
(4) The organic electroluminescent device of any of above (1) to (3), wherein the organic compound layers are a hole injection layer, an organic emitting layer and an electron injection layer.
(5) The organic electroluminescent device of any of above (1) to (4), wherein at least one organic compound material to form the organic compound layer(s) is purified through sublimation.
(6) The organic electroluminescent device of any of above (1) to (4), wherein at least one organic compound material to form the organic compound layer(s) is purified through recrystallization or reprecipitation, or through recrystallization combined with reprecipitation.
(7) A method for selecting organic compound materials for organic electroluminescent devices, comprising determining, through high-performance liquid chromatography, the impurity content of each organic compound material to form organic compound layers for the devices, selecting those having an impurity content of smaller than 1000 ppm out of the materials analyzed, and using the thus-selected materials for forming the organic compound layers.
(8) A method for selecting organic compound materials for organic electroluminescent devices, comprising determining the impurity content of at least one organic compound material to form organic compound layers for the devices, selecting those having an impurity content of smaller than 1000 ppm out of the materials analyzed, and using the thus-selected materials for forming the organic compound layers.
(9) The method of above (7) or (8) for selecting organic compound materials for organic electroluminescent devices, wherein the impurity in the organic compound materials is a halogen-containing compound.
BEST MODES OF CARRYING OUT THE INVENTION
Modes of carrying out the invention are described hereinunder.
The invention is an organic EL device that comprises organic compound layer (s) including at least one organic emitting layer sandwiched between a pair of electrodes, wherein at least one organic compound layer is formed from an organic compound material having an impurity concentration of lower than 1000 ppm (by weight, but, as the case may be, by volume).
The organic EL device of the invention comprises organic compound layer(s) including at least one organic emitting layer sandwiched between a pair of electrodes. Its typical structures are mentioned below, but are not limitative.
<1> Anode/emitting layer/cathode
<2> Anode/hole injection layer/emitting layer/cathode
<3> Anode/emitting layer/electron injection layer/cathode
<4> Anode/hole injection layer/emitting layer/electron injection layer/cathode
<5> Anode/organic semiconductor layer/emitting layer/cathode
<6> Anode/organic semiconductor layer/electron barrier layer/emitting layer/cathode
<7> Anode/organic semiconductor layer/emitting layer/adhesion improving layer/cathode
<8> Anode/hole injection layer/hole transporting layer/emitting layer/electron injection layer/cathode
The organic EL device of the invention may have any of these layer structures, but preferably has the layer structure <8>. The organic compound layers referred to herein include the emitting layers and others sandwiche
Higashi Hisahiro
Hosokawa Chishio
Sakai Toshio
Garrett Dawn L.
Idemitsu Kosan Co. Ltd.
Kelly Cynthia H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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