Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-09-27
2002-07-09
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C313S506000, C313S509000, C257S101000, C427S066000
Reexamination Certificate
active
06416888
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an organic electroluminescent device (hereinafter may be called “organic EL device”) and a method of manufacturing the organic EL device. More particularly, the present invention relates to an organic EL device suitably used for display apparatuses for home use or industrial use, light sources for printer heads, and the like, and to a method of manufacturing the organic EL devices.
DESCRIPTION OF THE BACKGROUND
Development of organic EL devices with an organic light-emitting layer inserted between electrodes of the devices have intensively been undertaken for the following reasons.
BACKGROUND OF THE INVENTION
(1) Handling and production of organic EL devices become easy because the organic EL devices are complete solid elements.
(2) Organic EL devices do not require the additional luminous apparatuses because these devices can emit the light themselves.
(3) Organic EL devices are suitable for use with display apparatuses due to excellent visibility.
(4) A full color display can be easily provided using the organic EL devices.
However, because the organic light-emitting layer is an organic substance, injecting electrons from a cathode layer is not easy. In addition, because the organic substance generally can transfer electrons and positive holes only with difficulty, the organic light-emitting layer tends to deteriorate easily and produce leakage current when used for a long period of time.
Japanese Patent Application Laid-open No. 8-288069 discloses an organic EL device provided with an insulating thin layer between an electrode and an organic light-emitting layer as a means for extending the life of the organic EL device. The organic EL device disclosed in this patent application has a configuration in which an insulating thin layer of aluminum nitride, tantalum nitride, or the like is provided between an anode layer and an organic light-emitting layer or between a cathode layer and an organic light-emitting layer.
U.S. Pat. No. 5,853,905 discloses an organic EL device provided with an insulating thin layer between an anode layer and a light-emitting layer or a cathode layer and a light-emitting layer. The U.S. Patent also discloses SiO
2
, MgO, and Al
2
O
3
as materials for forming the insulating thin layers.
With an objective of providing an organic EL device at low cost without using expensive materials such as 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (hereinafter may be abbreviated as “MTDATA”) and tetraaryldiamine derivatives, Japanese Patent Application Laid-open No. 9-260063 discloses an organic EL device having an inorganic material layer comprising NiO and at least one compound selected from the group consisting of In
2
O
3
, ZnO, SnO
2
, and compounds containing B, P, C, N, or O, or an inorganic material layer of Ni
1−x
O (0.05≦x≦0.5) between an electrode and an organic light-emitting layer.
With an objective of extending the life of organic EL devices by reducing the energy difference between the work function of an anode layer and the ionization energy of a positive hole transport layer, Japanese Patent No. 2824411 discloses an organic EL device having an anode layer made of a conductive metal oxide material exhibiting a work function greater than indium tin oxide (ITO) such as RuO
x
, MoO
3
, and V
2
O
5
, for example. This Japanese Patent proposes in the specification an anode layer having a two layer structure consisting of these conductive metal oxide materials and an ITO to improve the light transmittance.
However, the inorganic compounds such as aluminum nitride, tantalum nitride, SiO
2
, and the like used as an insulating thin layer in the organic EL devices disclosed in Japanese Patent Application Laid-open No. 8-288069 and U.S. Pat. No. 5,853,905 have a great ionization potential which results in an increased driving voltage. Specifically, because the inorganic thin layers consisting of these inorganic compounds are electric insulating layers having an excessively large ionization energy, positive holes are injected from the anode layer by a tunnel effect. Therefore, a high driving voltage is required between the electrodes of the organic EL device to obtain a desired luminous brightness.
The organic EL device disclosed in Japanese Patent Application Laid-open No. 9-260063 is characterized by the use of NiO as a major component, which unduly limits the types of materials usable as an inorganic material layer and exhibits only a low luminous efficiency.
The organic EL device disclosed in Japanese Patent No. 282411 has the problems of small positive hole mobility and insufficient durability in spite of the use of the metal oxide materials such as RuO
x
(1≦x≦2), MoO
3
, and V
2
O
5
.
In addition, the metal oxide materials such as RuO
x
(1≦x≦2), MoO
3
, and V
2
O
5
exhibit a large optical absorption coefficient of 27,000 cm
−1
or more, giving rise to remarkable coloration. Therefore, the light transmittance in the visible radiation range of the anode layer made of these metal oxide materials is very low, for example, about {fraction (1/9)} to ⅕ that of ITO, giving rise to problems such as a poor luminous efficiency and a small quantity of light which can be emitted.
In addition, even an anode layer with a two-layer structure consisting of lamination of a thin film of these metal oxide materials and ITO exhibits only a small light transmittance (about ½ that of ITO). Such an anode layer cannot be used in practice. Moreover, when an anode layer having such a two-layer structure is fabricated, the thickness of the ITO and a metal oxide film must be restricted within a prescribed range, resulting in a limitation in the manufacturing process.
SUMMARY OF THE INVENTION
The present inventors have conducted extensive studies to overcome the above problems and have found that, even in the case where an inorganic thin layer is provided in an organic EL device, an intermediate level for injection of electric charges can be formed in the inorganic thin layer by forming the inorganic thin layer from a combination of several specific inorganic compounds.
The inventors have further found that the combined use of specific inorganic compounds for forming the inorganic thin layer may produce an organic EL device with excellent transparency and durability, and superior luminous brightness at a low applied voltage (for example, less than DC 10V).
Accordingly, an object of the present invention is to provide an organic EL device having a specific inorganic thin layer and exhibiting excellent durability, a low driving voltage, and superior luminous brightness, as well as a method of efficiently manufacturing such an organic EL device.
Another object is to provide an organic EL device having an electrode layer made from a combination of specific inorganic compounds and exhibiting excellent durability, a low driving voltage, and superior luminous brightness, as well as a method of efficiently manufacturing such an organic EL device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(1) One embodiment of the present invention (first invention) which is an organic EL device having an anode layer, an organic light-emitting layer, and a cathode layer is characterized by having a first inorganic thin layer formed between the anode layer and the organic light-emitting layer or a second inorganic thin layer formed between the cathode layer and the organic light-emitting layer, or having both the first and the second inorganic thin layers, wherein when the first inorganic thin layer is formed between the anode layer and the organic light-emitting layer, the intermediate level of the first inorganic thin layer is set at a value smaller than the ionization potential of the organic light-emitting layer; when the second inorganic thin layer is formed between the cathode layer and the organic light-emitting layer, the intermediate level of the second inorganic thin layer is set at a value greater than the electron affinity of the organic light-emitti
Hosokawa Chishio
Kawamura Hisayuki
Nakamura Hiroaki
Garrett Dawn
Idemitsu Kosan Co. Ltd.
Kelly Cynthia H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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