Active solid-state devices (e.g. – transistors – solid-state diode – Organic semiconductor material
Reexamination Certificate
1999-06-25
2001-07-17
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Organic semiconductor material
C257S040000, C257S079000, C257S094000, C313S503000, C313S504000, C313S506000, C428S690000
Reexamination Certificate
active
06262433
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
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 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. Another problem is that the deterioration of an organic thin film is much severer than that of an LED or LD.
An electroluminescent (EL) device emits light under the influence of an 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 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.
SUMMARY OF THE INVENTION
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 high efficiency and an increased service life, and can be fabricated at low cost.
The above object is achieved by the embodiments defined below.
(1) An organic EL device which comprises:
a hole injecting electrode, an electron injecting electrode and an organic layer interleaved between these electrodes and including at least a light emitting layer,
a high-resistance inorganic electron transporting layer interleaved between said light emitting layer and said electron injecting electrode,
said high-resistance inorganic electron transporting layer being capable of blocking holes and having a conduction path for carrying electrons, and
an organic electron injecting layer interleaved between said high-resistance inorganic electron transporting layer and said electron injecting electrode.
(2) The organic EL device according to (1), wherein said high-resistance inorganic electron transporting layer comprises as a first component at least one oxide having a work function of 4 eV or lower and selected from the group consisting of oxides of an alkali metal element, an alkaline earth metal element, and a lanthanide element, and as a second component at least one metal selected from the group consisting of metals having a work function of 3 to 5 eV.
(3) The organic EL device according to (1), wherein said second component is at least one metal selected from the group consisting of Zn, Sn, V, Ru, Sm, and In.
(4) The organic EL device according to (1), wherein said alkali metal element is at least one element selected from the group consisting of Li, Na, K, Rb, Cs, and Fr, said alkaline earth metal element is at least one element selected from the group consisting of Mg, Ca, and Sr, and said lanthanide element comprises at least one element selected from the group consisting of La, and Ce.
(5) The organic EL device according to (1), wherein said high-resistance inorganic electron transporting layer has a resistivity of 1 to 1×10
11
&OHgr;·cm.
(6) The organic EL device according to (1), wherein said high-resistance inorganic electron transporting layer contains said second component in an amount of 0.2 to 40 mol % relative to all components thereof.
(7) The organic EL device according to (1), wherein said high-resistance inorganic electron transporting layer has a thickness of 0.2 to 30 nm.
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Arai Michio
Kobori Isamu
Mitsuhashi Etsuo
Chaudhuri Olik
Louie Wai-Sing
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
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