Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-02-01
2001-10-16
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C257S096000, C257S103000, C313S502000, C313S503000, C313S509000
Reexamination Certificate
active
06303239
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Art
The present invention relates generally to an organic EL (electroluminescent) device, and more specifically to an inorganic/organic junction structure used for a device comprising an organic compound thin film which emits light at an applied electric field.
2. Background Art
In general, an organic EL device is basically built up of an ITO or other transparent electrode formed on a glass substrate, an organic amine base hole transporting layer laminated on the transparent electrode, an organic light emitting layer formed of a material having electronic conductivity and giving out strong light emission, for instance, an Alq
3
material, and an electrode provided on the organic light emitting layer and formed of a material having a low work function, for instance, an MgAg material.
As reported so far in the art, the device has a structure wherein one or plural organic compound layers are interleaved between a hole injecting electrode and an electron injecting electrode. The organic compound layer has a double- or triple-layer structure.
Examples of the double-layer structure are a structure wherein a hole transporting layer and a light emitting layer are formed between the hole injecting electrode and the electron injecting electrode, and a structure wherein a light emitting layer and an electron transporting layer are formed between the hole injecting electrode and the electron injecting electrode. In an exemplary triple-layer structure, a hole transporting layer, a light emitting layer and an electron transporting layer are provided between the hole injecting electrode and the electron injecting electrode. A single-layer structure wherein a single layer has all functions, too, is reported in conjunction with a polymer or mixture system.
Typical structures of the organic EL device are shown in
FIGS. 3 and 4
.
In
FIG. 3
, a hole transporting layer
14
and a light emitting layer
15
, each made of an organic compound, are formed between a hole injecting electrode
12
provided on a substrate
11
and an electron injecting electrode
13
. In this case, the light emitting layer
15
also functions as an electron transporting layer.
In
FIG. 4
, a hole transporting layer
14
, a light emitting layer
15
and an electron transporting layer
16
, each made of an organic compound, are formed between a hole injecting electrode
12
provided on a substrate
11
and an electron injecting electrode
13
.
A problem common to these organic EL devices is reliability. In principle, an organic EL device comprises a hole injecting electrode and an electron injecting electrode and requires an organic layer for efficient injection and transportation of holes and electrons from between these electrodes. However, these materials are sensitive to damages during device fabrication, and offer a problem in conjunction with an affinity for electrodes. For the electron injecting electrode for the injection of electrons, it is required to use a metal having a low work function. For this reason, there is no choice but to use MgAg, AlLi, etc. for materials. However, these materials are susceptible to oxidation and lack stability, and so are a grave factor responsible for a reduction in the service life of the organic EL device and a reliability problem. A further problem is that the deterioration of an organic thin film is much severer than that of an LED or LD.
Most organic materials are relatively expensive. Otherwise stated, there is a great merit in providing low-cost organic EL device products by substituting a partial constitution film with an inexpensive inorganic material.
Furthermore, the development of a device having higher light emission efficiency, lower driving voltage and lesser power consumption than ever before is strongly desired.
To provide a solution to such problems, methods of taking advantage of merits of both an organic material and an inorganic material have been envisaged. That is, an organic/inorganic semiconductor junction structure wherein an organic hole transporting layer is substituted by an inorganic p-type semiconductor has been contemplated. Such contemplation has been investigated in Japanese Patent No. 2636341, and JP-A's 2-139893, 2-207488 and 6-119973. However, it is still impossible to obtain an organic EL device superior to prior art organic ELs in terms of emission performance and basic device reliability.
SUMMARY OF THE INVENTION
An object of the invention is to achieve an organic EL device which has an ever-longer service life, weather resistance, high stability and high efficiency, and is inexpensive as well.
The above object is achieved by the inventions defined below.
(1) An organic EL device comprising a substrate, a pair of a hole injecting electrode and a cathode formed on said substrate, and an organic layer located between these electrodes and taking part in at least a light emission function, wherein:
between said organic layer and said cathode there is provided an inorganic insulating electron injecting and transporting layer comprising:
a first component comprising at least one oxide selected from the group consisting of lithium oxide, rubidium oxide, potassium oxide, sodium oxide and cesium oxide,
a second component comprising at least one oxide selected from the group consisting of strontium oxide, magnesium oxide and calcium oxide, and
a third component comprising silicon oxide and/or germanium oxide.
(2) The organic EL device according to (1), wherein said cathode is formed of one or two or more metal elements selected from the group consisting of Al, Ag, In, Ti, Cu, Au, Mo, W, Pt, Pd, and Ni.
(3) The organic EL device according to (1), wherein in said inorganic insulating electron injecting and transporting layer, the ratio of each constituent with respect to all components is:
5 to 95 mol % for said first component,
5 to 95 mol % for said second component, and
5 to 95 mol % for said third component.
(4) The organic EL device according to (1), wherein said inorganic insulating electron injecting and transporting layer has a thickness of 0.1 to 2 nm.
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Arai Michio
Kobori Isamu
Mitsuhashi Etsuo
Garrett Dawn L.
Hess Bruce H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
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