Active solid-state devices (e.g. – transistors – solid-state diode – Organic semiconductor material
Reexamination Certificate
1999-06-25
2001-06-26
Mintel, William (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Organic semiconductor material
C257S094000, C257S096000, C257S103000, C313S503000, C313S504000, C313S506000, C438S046000, C438S047000
Reexamination Certificate
active
06252246
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Art Field
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 in applied electric field.
2. Background Art
An organic EL device is now under development and investigation so that it can be used for display purposes, because it can be formed over a large area. In general, an organic EL device is basically built up of 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. 2 and 3
.
In
FIG. 2
, 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. 3
, 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 more severe than that of an LED or LD.
An electroluminescent (EL) device emits light under the influence of an applied electric field. The action of a semiconductor layer forming such an EL manifests itself through radiative combination of electron-hole pairs injected from a pair of electrodes into the semiconductor. One example of this is a light emitting diode based on a GaP semiconductor or other similar group III-V semiconductor. Although these devices are utilized effectively and in wide fields, yet application thereof to large-area displays is not only difficult but also uneconomical because their size is very minute. Some replacements applicable to large-area displays are known in the art. Of such inorganic semiconductors, ZnS is the most useful. However, one non-negligible practical problem with this system is that it is poor in reliability. In one mechanism to which ZnS relates, a kind of carrier is accelerated through the semiconductor in a strong electric field. This is believed to cause local excitation of the semiconductor, which decays upon radiative emission.
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 under consideration. Such consideration has been reviewed 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.
SUMMARY OF THE INVENTION
One object of the invention is to provide a high-efficiency, long-life yet low-cost organic EL device which possesses the merits of both an organic material and an inorganic material.
The above object is achieved by the embodiments defined below.
(1) An organic EL device which comprises:
a hole injecting electrode and an electron injecting electrode between which an organic layer having at least a light emitting layer is provided,
an inorganic insulating electron transporting layer provided between said light emitting layer and said electron injecting layer,
a hole injecting and transporting layer provided between said light emitting layer and said hole injecting electrode, and
an organic electron injecting layer provided between said inorganic insulating electron transporting layer and said electron injecting layer.
(2) The organic EL device according to (1), wherein said inorganic insulating electron transporting layer contains as a main component one or two or more oxides selected from strontium oxide, magnesium oxide, calcium oxide, lithium oxide, rubidium oxide, potassium oxide, sodium oxide, and cesium oxide.
(3) The organic EL device according to (1), wherein said inorganic insulating electron transporting layer contains said main component in an amount of 80 to 99 mol % and a stabilizer in an amount of 1 to 20 mol %, each per all components thereof.
(4) The organic EL device according to (1), wherein said inorganic insulating electron transporting layer has a thickness of 0.1 to 2 nm.
(5) The organic EL device according to (1), wherein said hole injecting and transporting layer is defined by a high-resistance inorganic hole injecting and transporting layer capable of blocking electrons and having a conduction path for carrying holes.
(6) The organic EL device according to (5), wherein said high-resistance inorganic hole injecting and transporting layer has a resistivity of 1 to 1×10
11
&OHgr;·cm.
(7) The organic EL device according to (5), wherein said high-resistance inorganic hole injecting and transporting layer contains at least one of a metal and/or an oxide, carbide, nitride, silicide and boride of said metal.
(8) The organic EL device according to (5), wherein said high-resistance inorganic hole injecting and transporting layer contains as a main component an oxide of silicon and/or germanium as represented by (Si
1−x
Ge
x
)O
y
where 0≦x≦1 and 1.7≦y≦2.2, and further contains at least one of a metal having a work function of at least 4.5 eV and/or an oxide, carbide, nitride, silicide and boride of said metal.
(9) The organic EL device according to (8), wherein said metal is at least one selected from Au, Cu, Fe, Ni, Ru, Sn, Cr, Ir, Nb, Pt, W, Mo, Ta, Pd, and Co.
(10) The organic EL device according to (8), which contains said metal and/or said oxide, carbide, nitride, silicide and boride of said metal in an amount of 0.2 to 40 mol %.
(11) The organic EL device according to (5), wherein said high-resistance inorganic hole injecting and transporting layer has a thickness of 0.2 to 100 nm.
(12) The organic EL device according to (1), wherein said hole injecting and transporting layer is defined by an inorganic insulating hole injecting and transporting
Arai Michio
Kobori Isamu
Mitsuhashi Etsuo
Mintel William
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
LandOfFree
Organic electroluminescent device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Organic electroluminescent device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Organic electroluminescent device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2532335