JP2002334792A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescent element capable of making an organic electroluminescent display see-through and increasing the size thereof at low cost. SOLUTION: This organic electroluminescent element has a transparent substrate 1, a transparent positive electrode 2, a luminescent layer (organic layer) 3 and a transparent negative electrode 4. The positive electrode 2 and the negative electrode 4 each comprise a thin metal film and a thin metal oxide film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device (hereinafter abbreviated as "organic EL device").

[0002]

2. Description of the Related Art Organic electroluminescent displays, which are promising in the future from the viewpoints of self-emission, wide viewing angle, thinness and light weight, and reproducibility of moving images, can be used by sticking them to windows or the like, or sticking them to walls or the like. It is expected to be used as a large area poster type display.

[0003] By the way, an organic EL element used for such an organic electroluminescent display is
In general, an anode electrode is formed on a transparent substrate, an organic layer including a light emitting layer is formed on the surface of the anode electrode, and a cathode electrode is formed on the surface. In order to extract light emission, a transparent and conductive indium tin oxide (ITO) film is usually used as the anode electrode.
Further, as the cathode electrode, a metal alloy electrode made of a metal having a low energy level, for example, magnesium, lithium, aluminum, silver, or the like is used because of ease of electron injection. Further, Japanese Patent Application Laid-Open No. Hei 5-41286 proposes an organic EL device in which aluminum is added to zinc oxide as a cathode electrode so that the cathode electrode is transparent and light can be extracted from the cathode electrode side.

[0004]

However, in order to increase the area of the organic electroluminescence display, it is necessary to reduce the resistance of both the anode electrode and the cathode electrode of the organic EL element (5 Ω / □ or less). Yes,
If the anode electrode is formed only of ITO, the thickness must be increased in order to reduce the resistance, so that there is a problem that the cost is extremely high. That is, by increasing the film thickness,
This is because an increase in the amount of indium, which is a rare metal, an increase in film formation processing time and an increase in pattern formation (etching) time occur. Further, the above-mentioned thickening has a problem that the surface unevenness is increased, and the light emitting function of the organic EL element is reduced (the dark spot is generated) due to the electric field concentration at the edge. On the other hand, when the transparent cathode electrode is formed by adding aluminum to zinc oxide as described above in order to realize see-through, as in the case of the anode electrode formed only of ITO, the thickness is increased to reduce the resistance. However, there is a disadvantage that the cost is high. Therefore, at present, an organic EL device capable of realizing a see-through and a large area of an organic electroluminescent display at a low cost has not yet been obtained.

The present invention has been made in view of such circumstances, and has as its object to provide an organic EL device capable of realizing a see-through and large-area organic electroluminescence display at low cost.

[0006]

In order to achieve the above object, an organic EL device according to the present invention is an organic EL device having a transparent substrate, an anode electrode, an organic material layer, and a cathode electrode. The cathode electrode is a transparent electrode formed by laminating a metal thin film and a high refractive index thin film.

That is, the present inventor has conducted intensive studies to solve the above-mentioned problems. As a result, when both the anode electrode and the cathode electrode are formed by laminating a metal thin film and a high-refractive-index thin film, the thickness of both electrodes is reduced, so that the transparency is excellent, and light can be extracted from both surfaces. In addition, the inventors have found that even if the thickness of both electrodes is reduced, the resistance of the electrodes can be reduced and the cost can be suppressed, and the present invention has been achieved.

[0008]

Next, an embodiment of the present invention will be described.

In the organic EL device of the present invention, for example, as shown in FIG. 1, a transparent anode electrode 2 is formed on a transparent substrate 1, a light emitting layer 3 is formed on the surface, and a transparent cathode electrode is further formed on the surface. 4 are formed.

The transparent substrate 1 is not particularly limited as long as it has excellent transparency, and examples thereof include a glass substrate.

The thickness of the transparent substrate 1 is usually 0.00
It is 3 to 10 mm, preferably 0.025 to 5 mm.

The transparent anode electrode 2 formed on the transparent substrate 1 is a transparent electrode formed by laminating a metal thin film and a high refractive index thin film, and has a visible light transmittance of 30% or more. Examples of the laminated structure of the metal thin film and the high refractive index thin film include a two-layer structure of a metal thin film and a high refractive index thin film, and a three-layer structure of a metal thin film sandwiched by a high refractive index thin film (high refractive index thin film). Index thin film / metal thin film / high refractive index thin film).

The total thickness of the transparent anode electrode 2 (metal thin film +
The thickness of the high refractive index thin film is usually 5 to 500 nm, preferably 10 to 400 nm.

The above-mentioned high refractive index thin film is a thin film formed by lamination for the purpose of reducing the reflection on the surface of the metal thin film. When the refractive index is 1.8 or more at a light wavelength of 633 nm, the metal thin film is formed. This is preferable because the effect of reducing the reflection on the surface works effectively.

As the material for the high refractive index thin film,
Is, for example, titanium oxide (TiO 2)_Two) 、 Zirconium oxide
(ZrO_Two), Indium oxide (In)_TwoO_Three), Oxidation
Indium tin (ITO), aluminum oxide (Al_TwoO
_Three), Tantalum oxide (Ta_TwoO _Five), Tin oxide (Sn
O_Two), Zinc oxide (ZnO), magnesium oxide (Mg
O) and other metal oxides, silicon nitride (Si_ThreeN_Four) 、 Ni
Boron nitride (BN), aluminum nitride (AlN), nitride nitride
ROM (CrN), tantalum nitride (TaN), titanium nitride
Metal nitride such as (TiN) and zirconium nitride (ZrN)
Materials, zinc sulfide (ZnS), cadmium sulfide (CdS), etc.
Metal sulfide, silicon oxynitride (SiO_xN _y)
Metal carbonization such as metal oxynitride and silicon carbide (SiC)
Things are given.

The thickness of the high-refractive-index thin film is appropriately set in accordance with the refractive index, but is usually from 5 to 350 nm, preferably from 10 to 200 nm.

As the material for the metal thin film, a metal having low light absorption in the visible light region and low electric resistance is preferable, and examples thereof include silver, gold, copper, platinum, palladium, aluminum and alloys thereof. . Among these, silver alloys are preferably used in consideration of low resistance, high transparency, durability, energy level, and the like.

The thickness of the metal thin film is 1 to 50 nm, preferably 5 to 30 nm, in consideration of transparency and electric resistance.

The material for the light-emitting layer 3 formed on the transparent anode electrode 2 is not particularly limited, and examples thereof include fluorescent brighteners such as benzothiazole, benzimidazole and benzoxazole, and styrylbenzene-based compounds. , 12
-Phthaloperinone, 1,4-diphenyl-1,3-butadiene, 1,1,4,4-tetraphenyl-1,3-butadiene, naphthalimide derivative, perylene derivative, oxadiazole derivative, aldazine derivative, pyrazirine derivative, Cyclopentadiene derivatives, pyrrolopyrrole derivatives, styrylamine derivatives, coumarin compounds, International Publication WO90 / 13148 and Appl. Phys. Lett., Vol.
58, 18, P1982 (1991), a polymer compound, an aromatic dimethylidin compound, and a compound represented by the following general formula (1)
And organic light-emitting materials such as compounds represented by These may be used alone or in combination of two or more.

[0020]

(R-Q) ₂ -Al-OL (1) wherein R is sterically hindering the binding of more than two substituted 8-quinolylate ligands to the aluminum atom. 8-quinolinolate ring substituent, Q is a substituted quinolinolate ligand, L is a C6-C24 hydrocarbon group containing a phenyl moiety, and OL is a phenolate ligand, respectively. . ]

The thickness of the light emitting layer 3 is usually 5 to 200.
nm, preferably 10 to 100 nm.

The transparent cathode electrode 4 formed on the light emitting layer 3 is a transparent electrode formed by laminating a metal thin film and a high refractive index thin film, like the transparent anode electrode 2, and has a visible light transmittance of 30. % Is set. The transparent cathode electrode 4 has a multilayer structure including a metal thin film and a high-refractive-index thin film, and has a two-layer structure of a metal thin film and a high-refractive-index thin film, and a three-layer structure in which the metal thin film is sandwiched by the high-refractive-index thin films. (High refractive index thin film / metal thin film / high refractive index thin film) is preferable. When a metal thin film and a high refractive index thin film are formed on the light emitting layer 3 to form the transparent cathode electrode 4 having a two-layer structure, the transparency,
From the viewpoint of light emission, it is preferable that a metal thin film is formed on the light emitting layer 3 and a high refractive index thin film is formed on the surface thereof.

The material for the metal thin film, the material for the high refractive index thin film, and the thickness of these thin films (including the total thickness of the transparent cathode electrode 4) in the transparent cathode electrode 4 are the same as those of the transparent anode electrode 2.

Here, in the organic EL device of the present invention, it is necessary to improve the hole injection property of the transparent anode electrode 2 and the electron injection property of the transparent cathode electrode 4 in order to improve the luminous efficiency. For this purpose, among the thin films constituting the transparent anode electrode 2, the thin film adjacent to the light emitting layer 3 (the organic material layer adjacent layer)
Is preferably set to 4 eV or more, and the work function of the organic material layer adjacent layer in the transparent cathode electrode 4 is set to less than 4 eV.

The material for forming the organic material adjacent layer in the transparent anode electrode 2 is ITO, In ₂ O ₃ , Sn.
O ₂ , ZnO, ZrO ₂ , TiO ₂ , antimony oxide,
Examples of the material include carbon, aluminum, copper, silver, gold, platinum, and a mixed material containing these materials for the high refractive index thin film.

As the material for forming the organic layer adjacent layer in the transparent cathode electrode 4, an alloy containing magnesium, calcium, manganese, lithium, cesium, etc., and a mixed material containing the above materials for the high refractive index thin film are used. A thin film.

The organic EL device of the present invention can be manufactured, for example, as follows. That is, first, the above-mentioned material for a high-refractive-index thin film is deposited on the surface of the transparent substrate 1 using a magnetron-sputtering deposition apparatus to form a high-refractive-index thin film. A metal is vapor-deposited using a vapor deposition device to form a metal thin film, and a material for a high refractive index thin film (a material for an organic material layer adjacent layer in the transparent anode electrode 2) is formed on the surface of the metal thin film using a magnetron sputter vapor deposition device. The transparent anode electrode 2 having a three-layer structure including a high refractive index thin film, a metal thin film, and a high refractive index thin film is formed by vapor deposition to form a high refractive index thin film. Next, the light emitting layer 3 is formed on the surface of the organic metal oxide thin film of the transparent anode electrode 2 by vacuum evaporation or the like. Subsequently, a material for a high-refractive-index thin film (material for a layer adjacent to the organic material layer in the transparent cathode electrode 4) is deposited on the surface of the light-emitting layer 3 using a magnetron sputter deposition apparatus to form a high-refractive-index thin film. A metal is deposited on the surface of the high-refractive-index thin film using a magnetron sputter deposition apparatus to form a metal thin film, and a material for a high-refractive-index thin film is deposited on the surface of the metal thin film using a magnetron sputter deposition apparatus to achieve high refraction. A transparent cathode electrode 4 having a three-layer structure including a high refractive index thin film, a metal thin film, and a high refractive index thin film is formed by forming a high refractive index thin film. Thus, an organic EL device can be obtained (see FIG. 1).

In the organic EL device of the present invention, the high refractive index thin film and the metal thin film are formed by, for example, vacuum evaporation, ion plating, plating, or the like in addition to the magnetron sputter deposition as described above. Can also do.

Further, in the organic EL device of the present invention, the organic material layer provided between the transparent anode electrode 2 and the transparent cathode electrode 4 is limited to a single-layer structure of only the light emitting layer 3 as shown in FIG. For example, a two-layer structure of a hole injection layer and a light-emitting layer, a two-layer structure of a light-emitting layer and an electron injection layer, and a three-layer structure of a hole injection layer, a light-emitting layer, and an electron injection layer. can give.

The material for the hole injection layer is not particularly limited. For example, triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, Amino-substituted chalcone derivative, oxazole derivative, styryl anthracene derivative, fluorenone derivative, hydrazone derivative, stilbene derivative, silazane derivative, polysilane,
Aniline copolymers, conductive polymer oligomers (preferably thiophene oligomers), porphyrin compounds, aromatic tertiary amine compounds, styrylamine compounds, aromatic dimethylidin compounds that can also be used as organic light emitting materials, p-type Inorganic semiconductors such as -Si and p-type -SiC. These may be used alone or in combination of two or more.

The thickness of the hole injection layer is usually 1 to 10
0 nm, preferably 10 to 50 nm.

The material for the electron injecting layer is not particularly limited. Examples thereof include nitro-substituted fluorenone derivatives, anthraquinodimethane derivatives, diphenylquinone derivatives, thiopyrandioxide derivatives, and heterocyclic tetracarboxylic acids such as naphthalene perylene. Acid anhydride, carbodiimide, fluorenylidenemethane derivative, anthrone derivative, oxadiazole derivative, JP-A-59-19439
Patent Document 3 discloses a series of electron-transporting compounds disclosed as materials for a light-emitting layer, a thiazole derivative in which an oxygen atom of an oxadiazole ring is substituted with a sulfur atom, and a quinoxaline having a quinoxaline ring known as an electron-withdrawing group. Derivatives, metal complexes of 8-quinolinol derivatives, metal-free or metal phthalocyanines or those whose terminals are substituted with alkyl groups, sulfone groups, etc., distyrylpyrazine derivatives, inorganics such as n-type Si and n-type SiC Semiconductors and the like. These may be used alone or in combination of two or more.

The thickness of the electron injection layer is usually from 1 to 10
0 nm, preferably 10 to 50 nm.

In the organic EL device of the present invention, the order of lamination and formation on the transparent substrate 1 may be reversed from that shown in FIG. That is, the transparent cathode electrode 4 may be formed on the transparent substrate 1, the light emitting layer 3 may be formed on the surface thereof, and the transparent anode electrode 2 may be formed on the surface.

Next, examples will be described together with comparative examples.

[0036]

Example 1 A transparent glass (10 mm × 20 mm, thickness 0.5 mm) was prepared, and ZnO was deposited on the surface thereof using a magnetron sputter deposition apparatus to form a high refractive index thin film [thickness 50 nm, refractive index 2.3 ( 633n wavelength of light at the time of measurement
m)] was formed. Next, silver was deposited on the surface of the high refractive index thin film using a magnetron sputter deposition apparatus to form a metal thin film (thickness: 20 nm). Further, ZnO was deposited on the surface of the metal thin film using a magnetron sputter deposition apparatus to form a high refractive index thin film [thickness: 10 nm, refractive index: 2.3 (wavelength of light at the time of measurement: 633 nm), work function: 4.
5 eV]. In this way, a transparent anode electrode having a three-layer structure composed of a high refractive index thin film, a metal thin film, and a high refractive index thin film was formed on the surface of the transparent glass. Next, an aluminum quinolium complex (Alq ₃ ) was formed on the surface of the transparent anode electrode.
Is deposited using a vacuum deposition machine, and a light-emitting layer (thickness: 50 nm)
Was formed. Then, on the surface of the light emitting layer, a magnesium-silver alloy (the ratio of the number of atoms of magnesium is 90 atm%) is deposited using a magnetron sputter deposition apparatus to form a metal thin film (thickness: 20 nm, work function: 3.2 eV). After that, ZnO was vapor-deposited on the surface using a magnetron sputtering vapor deposition apparatus to form a high refractive index thin film [thickness 50 nm, refractive index 2.3 (wavelength of light at the time of measurement: 633 nm)]. A transparent cathode electrode having a two-layer structure with a thin film was formed. In this way, an organic EL device was formed by laminating the transparent glass, the transparent anode electrode, the light emitting layer, and the transparent cathode electrode in this order.

[0037]

Example 2 A transparent glass (10 mm × 20 mm, thickness 0.5 mm) was prepared, and ZnO was deposited on the surface thereof using a magnetron sputter deposition apparatus to form a high refractive index thin film [thickness 50 nm, refractive index 2.3 ( 633n wavelength of light at the time of measurement
m)] was formed. Next, on the surface of the high refractive index thin film, a magnesium-silver-based alloy (magnesium atom ratio was 90 at.
%), and a metal thin film (thickness: 20 nm, work function: 3).
2 eV). Thus, a transparent cathode electrode having a two-layer structure of a high refractive index thin film and a metal thin film was formed on the transparent glass surface. Next, an aluminum quinolium complex (Alq ₃ ) was vapor-deposited on the surface of the transparent anode electrode using a vacuum vapor deposition machine to form a light-emitting layer (thickness: 50 nm). Then, ZnO was deposited on the surface of the light emitting layer using a magnetron sputter deposition apparatus to form a high refractive index thin film [thickness 10 n
m, a refractive index of 2.3 (wavelength of light at the time of measurement: 633 nm), and a work function of 4.5 eV], and then a metal thin film (thickness: 20 nm) is deposited on the surface by using a magnetron sputter deposition apparatus. A high refractive index thin film [thickness: 50 nm, refractive index: 2.3 (wavelength of light at the time of measurement: 633 nm)] is formed on the surface of the metal thin film using a magnetron sputter deposition apparatus. Thus, a transparent anode electrode having a three-layer structure including a high refractive index thin film, a metal thin film, and a high refractive index thin film was formed. In this way, an organic EL device was formed by laminating the transparent glass, the transparent cathode electrode, the light emitting layer, and the transparent anode electrode in this order.

[0038]

Example 3 A transparent glass (10 mm × 20 mm, thickness 0.5 mm) was prepared, and TiN was vapor-deposited on the surface thereof using a magnetron sputter vapor deposition apparatus to form a high refractive index thin film [thickness 50 nm, refractive index 2.8 ( 633n wavelength of light at the time of measurement
m)] was formed. Next, silver was deposited on the surface of the high refractive index thin film using a magnetron sputter deposition apparatus to form a metal thin film (thickness: 20 nm). Further, TiN is deposited on the surface of the metal thin film using a magnetron sputter deposition apparatus to form a high-refractive-index thin film [thickness: 10 nm, refractive index: 2.8 (wavelength of light at the time of measurement: 633 nm), work function: 4.
8 eV]. In this way, a transparent anode electrode having a three-layer structure composed of a high refractive index thin film, a metal thin film, and a high refractive index thin film was formed on the surface of the transparent glass. Next, an aluminum quinolium complex (Alq ₃ ) was formed on the surface of the transparent anode electrode.
Is deposited using a vacuum deposition machine, and a light-emitting layer (thickness: 50 nm)
Was formed. Then, on the surface of the light emitting layer, a magnesium-silver alloy (the ratio of the number of atoms of magnesium is 90 atm%) is deposited using a magnetron sputter deposition apparatus to form a metal thin film (thickness: 20 nm, work function: 3.2 eV). Then, TiN is deposited on the surface using a magnetron sputter deposition apparatus to form a high-refractive-index thin film (thickness: 50 nm, refractive index: 2.8 (wavelength of light at the time of measurement: 633 nm)). A transparent cathode electrode having a two-layer structure with a thin film was formed. In this way, an organic EL device was formed by laminating the transparent glass, the transparent anode electrode, the light emitting layer, and the transparent cathode electrode in this order.

[0039]

Example 4 A transparent glass (10 mm × 20 mm, thickness 0.5 mm) was prepared, and ZnS was vapor-deposited on the surface thereof using a magnetron sputter vapor deposition apparatus to form a high refractive index thin film [thickness 50 nm, refractive index 2.3 ( 633n wavelength of light at the time of measurement
m)] was formed. Next, on the surface of the high refractive index thin film, a magnesium-silver-based alloy (magnesium atom ratio was 90 at.
%), and a metal thin film (thickness: 20 nm, work function: 3).
2 eV). Thus, a transparent cathode electrode having a two-layer structure of a high refractive index thin film and a metal thin film was formed on the transparent glass surface. Next, an aluminum quinolium complex (Alq ₃ ) was vapor-deposited on the surface of the transparent anode electrode using a vacuum vapor deposition machine to form a light-emitting layer (thickness: 50 nm). Then, ZnS was deposited on the surface of the light emitting layer using a magnetron sputter deposition apparatus to form a high refractive index thin film [thickness 10 n
m, a refractive index of 2.3 (wavelength of light at the time of measurement: 633 nm), and a work function of 4.2 eV], and then a metal thin film (thickness: 20 nm) was deposited on the surface by using a magnetron sputter deposition apparatus. On the surface of the metal thin film, ZnS is deposited using a magnetron sputter deposition apparatus to form a high-refractive-index thin film [thickness: 50 nm, refractive index: 2.3 (wavelength of light at the time of measurement: 633 nm)]. Thus, a transparent anode electrode having a three-layer structure including a high refractive index thin film, a metal thin film, and a high refractive index thin film was formed. In this way, an organic EL device was formed by laminating the transparent glass, the transparent cathode electrode, the light emitting layer, and the transparent anode electrode in this order.

[0040]

[Comparative Example] Transparent glass (10 mm x 20 mm, thickness of 0.1 mm).
5 mm), and ITO was deposited on this surface using a magnetron sputter deposition apparatus to form an ITO film (thickness: 400 mm).
nm), and this was used as a transparent anode electrode. Next,
Aluminum quinolium complex (Al
q ₃ ) was deposited using a vacuum deposition machine to form a light-emitting layer (thickness: 50).
nm). Aluminum-
A lithium-based alloy was deposited using a vacuum deposition machine to form a cathode electrode (thickness: 50 nm). In this way, an organic EL device was formed by laminating the transparent glass, the transparent anode electrode, the light emitting layer, and the cathode electrode in this order.

Using the thus obtained organic EL devices of Examples and Comparative Examples, the visible light transmittance, luminous efficiency and electrode cost (anode electrode cost + cathode electrode cost) of the entire organic EL device were determined. Comparative evaluation was performed. The results are shown in Table 1 below.

[0042]

[Table 1]

From the results shown in Table 1 above, all of the products of Examples have a very high visible light transmittance of the whole organic EL device (about 20% of the visible light transmittance of a commercially available heat ray reflective glass) and are see-through. It can be seen that light emission from both sides can be confirmed, and that the electrode cost can be reduced as compared with the comparative example.

On the other hand, in the comparative example, since the cathode electrode is formed using an aluminum-lithium alloy, a thick film has to be formed in order to obtain a surface resistance that can be used as an electrode. It can be seen that the visible light transmittance is 0% because the film is opaque.

[0045]

As described above, the organic EL device of the present invention is an organic EL device having a transparent substrate, an anode electrode, an organic layer and a cathode electrode, wherein the anode electrode and the cathode electrode are made of a metal thin film. It consists of a high refractive index thin film. As described above, since the anode electrode and the cathode electrode are formed using the metal thin film and the high-refractive-index thin film, the thickness of both electrodes is small, the transparency is excellent, and light can be extracted from both surfaces. In addition, since the resistance of the electrodes can be reduced even when the thickness of both electrodes is reduced, the see-through and large area of the organic electroluminescent display can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of the organic EL device of the present invention.

[Brief description of reference numerals]

 Reference Signs List 1 transparent substrate 2 transparent anode electrode 3 light emitting layer 4 transparent cathode electrode

Claims (5)

[Claims] 1. An organic electroluminescent device having a transparent substrate, an anode electrode, an organic material layer, and a cathode electrode, wherein the anode electrode and the cathode electrode are formed by laminating a metal thin film and a high refractive index thin film. An organic electroluminescent device, characterized in that: 2. The organic electroluminescence device according to claim 1, wherein the refractive index of the high refractive index thin film in each of the anode electrode and the cathode electrode is 1.8 or more at a light wavelength of 633 nm. 3. The organic electroluminescent device according to claim 1, wherein the work function of the organic material layer adjacent layer in the anode electrode is 4 eV or more, and the work function of the organic material layer adjacent layer in the cathode electrode is less than 4 eV. 4. The metal thin film in the anode electrode and the cathode electrode contains at least one selected from the group consisting of silver, gold, copper, platinum, palladium and aluminum. The organic electroluminescence device according to claim 1. 5. The organic electroluminescence device according to claim 1, wherein the visible light transmittance of the anode electrode and the cathode electrode is 30% or more.