Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-06-25
2001-11-27
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C313S502000, C313S503000, C313S504000, C252S301160, C257S103000
Reexamination Certificate
active
06322910
ABSTRACT:
BACKGROUND OF THE INVENTION
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.
PRIOR 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 Alq3 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. Another 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 semiconductor 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 difficult to obtain an organic EL device superior to prior art organic ELs in terms of emission performance and basic device reliability.
One object of the invention is to provide an organic EL device which possesses the merits of both an organic material and an inorganic material, has an extended life, an improved light emission efficiency and a low driving voltage, and is fabricated at low cost.
SUMMARY OF THE INVENTION
The above object is achieved by the inventions defined below as (1) to (9).
(1) An organic electroluminescent device comprising a substrate, a hole injecting electrode and an electron injecting electrode formed on said substrate, and at least an organic layer located between said electrodes, said organic layer taking part in light emitting function, wherein:
between said electron injecting electrode and said organic layer there is an inorganic insulating electron injecting layer comprising as a main component an oxide having an electron affinity of up to 3 eV, with a stabilizing component added thereto.
(2) The organic electroluminescent device according to (1), wherein said inorganic electron injecting layer comprises as said stabilizing component germanium oxide or GeO
2
and/or silicon oxide or SiO
2
.
(3) The organic electroluminescent device according to (1) or (2), wherein the germanium oxide or GeO
2
and/or silicon oxide or SiO
2
acting as said stabilizing component are contained in an amount, as calculated on GeO
2
and/or SiO
2
bases, of up to 50 mol % relative to said main component.
(4) The organic electroluminescent device according to any one of (1) to (3), wherein said inorganic insulating electron injecting layer comprises as said main component one or two or more of lithium oxide or Li
2
O
3
, sodium oxide or Na
2
O, potassium oxide or K
2
O, rubidium oxide or Rb
2
O, cesium oxide or Cs
2
O, calcium oxide or CaO, strontium oxide or SrO, barium oxide or BaO, yttrium oxide or Y
2
O
3
, hafnium oxide or HfO
2
, terbium oxide or Tb
2
O
3
, and thorium oxide or ThO
2
.
(5) The organic electroluminescent device according to any one of (1) to (4), which comprises, in order from a substrate, at least an electron injecting electrode, an inorganic insulating electron injecting layer, a light emitting layer and a hole injecting layer laminated together thereon.
(6) The organic electroluminescent device according to any one of (1) to (5), wherein said inorganic electron injecting layer has a structure where oxygen is present in a larger amount on an organic layer side and oxygen is present in a smaller amount on an electron injecting electrode side.
(7) The organic electroluminescent device according to (6), which comprises, in order from a substrate, at least a hole injecting electrode, an organic layer, an inorganic electron injecting layer and an electron injecting electrode laminated together thereon.
(8) A method of fabricating an organic electro-luminescent device by forming between an electron injecting electrode and an organic layer an inorganic electron injecting layer comprising as a main component an oxide having an electron affinity of up to 3 eV with a stabilizing component added thereto, wherein:
one portion of said inorganic electron injecting layer corresponding to ⅕ to ⅘ of a total thickness thereof is formed with no oxygen added thereto, and another portion is formed with about 1 to 99% Of O
2
added thereto.
(9) The organic electroluminescent device fabrication method according to (8), wherein an organic electro-luminescent device as recited in (6) or (7) is obtained.
REFERENCES:
patent: 5952779 (1999-09-01), Arai et al.
patent: 5969474 (1999-10-01), Arai
patent: 5981092 (1999-11-01), Arai et al.
patent: 5990605 (1999-11-01), Yoshikawa et al.
patent: 6166488 (2000-12-01), Arai
patent: 6198219 (2001-03-01), Arai et al.
patent: 2-139893 (1990-05-01), None
patent: 5-3080 (1993-01-01), None
Arai Michio
Kobori Isamu
Mitsuhashi Etsuo
Garrett Dawn
Kelly Cynthia H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
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