JP2001076874A - Organic el display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an organic EL display device in a simple process, and to prevent generation of a leak current by forming a light emitting layer by a printing method, forming a cushioning layer of an organic material by a vapor deposition method, and setting the film thickness not more than a specific value. SOLUTION: An anode electrode 2, a light emitting layer 3, a cushioning layer 5 and a cathode electrode 6 are provided in order on a base board 1. The light emitting layer 3 is formed by a printing method. The cushioning layer 5 includes an organic material having hole implantation/transport performance and/or electron implantation/transport performance, and is formed by a vapor deposition method, and the film thickness is set not more than 40 nm. A patterned insulating layer 4 is formed around the light emitting layer 3. Thus, the cushioning layer 5 is arranged between the light emitting layer 3 and the cathode electrode 6 to prevent generation of a leak current caused by clearance formed between a pinhole of the light emitting layer 3 and the insulating layer 4. The lower limit of the film thickness of the cushioning layer 5 is preferably set to about 10 nm to fill up this pinhole and the clearance.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic EL display device using an organic material and having a display function by electroluminescence (EL).

2. Description of the Related Art In recent years, organic EL devices have been actively studied. In this method, a hole transporting material such as triphenyldiamine (TPD) is deposited on a hole injecting electrode to form a thin film, and a fluorescent substance such as an aluminum quinolinol complex (Alq3) is laminated thereon as a light emitting layer.
It is an element that has a basic structure in which a metal electrode (electron injection electrode) with a small work function is formed, and is attracting attention because a very high luminance of several hundreds to tens of thousands of cd / m ² can be obtained at a voltage of about 10 V. .

[0003] Such a high-luminance and high-efficiency organic EL device has hitherto been obtained mainly by thinning a low-molecular organic material into a thin film by a vacuum evaporation method. However, in recent years, polymer organic EL devices, which are made by thinning a polymer organic material by spin coating or the like, have made remarkable progress, being cheap and easy to fabricate, and creating flexible devices. It is drawing attention because it is possible.

By the way, patterning of elements is indispensable for producing a device, especially a full-color device. Several proposals have been made so far as a patterning method for a polymer organic EL element.

For example, Japanese Patent Application Laid-Open No. Hei 6-13184 discloses an example in which a photosensitive material is imparted to a polymer organic EL material and optically patterned, and a photosensitive resin is doped with an organic EL material and patterned. As an example,
Japanese Patent Application Laid-Open Nos. 0-699981 and 10-289785 disclose an example in which a polymer precursor is mixed with a photoacid to generate an acid by electromagnetic radiation, and the precursor is polymerized to be patterned. 10-3
No. 26675 is known.

However, in order to use such a method, it is necessary to introduce a material necessary for patterning or a substituent in addition to a material functioning as an organic EL, which not only deteriorates the characteristics of the organic EL device but also decreases the characteristics. This also affects the material design. Further, in the case of using a photosensitive resin, the element is greatly deteriorated by the etchant.

[0005] In addition, as an example of performing physical patterning by dry etching using a metal protective film, Appl. Phys. Lett.
69, 3117 (1996), pp. 3117 to 3119, but the process is long and the advantages of low cost of the polymer organic EL cannot be utilized. Another example of patterning by gravure printing is disclosed in Japanese Unexamined Patent Publication No. 3-26995, and an example of patterning by an ink jet method is disclosed in
JP-A-12377, JP-A-10-153967, and EPO880303A1.

[0006] However, each of these methods has a problem of flatness of the film,
There has been a problem that a leak easily occurs due to the generation of a pinhole due to the disorder of the edge portion.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an organic EL display device which can be produced at a low cost by a simple process and which does not cause a current leak or the like.

[0008]

The above object is achieved by the following constitution. (1) A substrate, and at least a positive electrode, a light emitting layer, a buffer layer, and a negative electrode are sequentially provided on the substrate, the light emitting layer is formed by a printing method, and the buffer layer is formed by an evaporation method from an organic material. And an organic EL display device having a thickness of 40 nm or less. (2) The organic EL display device, wherein the buffer layer contains an organic material having a hole injection / transport property and / or an electron injection / transport property. (3) The organic EL display device according to (1) or (2), wherein the buffer layer has a thickness of 40 nm or less. (4) The organic EL display device according to any one of (1) to (3), wherein the buffer layer is a metal doping layer and has a thickness of 1 to 200 nm. (5) The organic EL display device according to any one of (1) to (4), wherein the light emitting layer is formed by an inkjet method. (6) The organic EL display device according to any one of (1) to (5), wherein the light emitting layer is formed by a gravure printing method.

[0009]

DETAILED DESCRIPTION OF THE INVENTION As shown in FIG. 1, for example, an organic EL display device of the present invention comprises a substrate 1 and at least a positive electrode 2, a light emitting layer 3, a buffer layer 5, and a negative electrode 6 on the substrate 1. The light emitting layer 3 is formed by a printing method, the buffer layer 5 contains an organic material having a hole injecting and transporting property and / or an electron injecting and transporting property, and is formed by a vapor deposition method, The thickness is set to 40 nm or less.
In FIG. 1, a patterned insulating layer 4 is formed around the light emitting layer 1. Further, a so-called reverse lamination structure in which the substrate / negative electrode / light emitting layer / buffer layer / positive electrode are laminated may be used. These stacked configurations may be appropriately set in accordance with the direction in which light is emitted, the configuration of the device, and the like.

As described above, by providing the buffer layer formed by the vapor deposition method between the light emitting layer formed by the printing method and the negative electrode, the buffer layer is formed between the pin hole of the light emitting layer and the insulating layer. It is possible to prevent the occurrence of a leak current caused by a gap or the like.

That is, the light emitting layer formed by the printing method is different from the thin film layer formed by the vapor deposition method in that a gap is easily generated between a pinhole due to uneven coating or a passivation layer such as an insulating layer.

Specifically, as shown in FIG. 2, a gap 11 is formed between an insulating layer 4 for forming a pixel and the light emitting layer 3 printed on the opening of the insulating layer 4. May be done. This is because, particularly when printing is performed by the ink jet method, the ejected ink spreads in a conical shape and scatters, so that the shape of the printed light emitting layer tends to have a circular shape or a rounded shape. For this reason, even if an attempt is made to form a square pixel, the light emitting layer material may not be applied well to the corner.

[0013] Due to such coating unevenness, unpainted portion peculiar to the printing method, and the like, a gap is formed between the light emitting layer and the pinhole or the insulating layer. When a negative electrode material is formed by vapor deposition from above the pinholes and gaps, fine material particles enter the pinholes and gaps and reach the positive electrode formed below the light emitting layer to form a cathode. The electrode and the positive electrode are short-circuited, which causes a leak current.

Therefore, a leak current can be prevented by forming a buffer layer by a vapor deposition method before forming the negative electrode to close the pinholes and gaps, and then forming the negative electrode thereon.

[0015] The buffer layer is formed of an organic material. The organic material forming the buffer layer is preferably an electron injecting material in order to ensure electron injecting properties and hole blocking properties. In addition, a material used for the light emitting layer may be used in order to secure an affinity with the light emitting layer. in this case,
When a plurality of organic materials are used for the light-emitting layer, it is preferable to use at least one or two or more of them.
In the case where the buffer layer is formed of the material used for the light emitting layer, when a hole injecting and transporting material is used for the light emitting layer, a hole injecting and transporting material may be used for the buffer layer.

As the compound capable of injecting and transporting electrons, it is preferable to use a quinoline derivative, furthermore a metal complex having 8-quinolinol or its derivative as a ligand, particularly tris (8-quinolinolato) aluminum (Alq3). It is also preferable to use the above-mentioned phenylanthracene derivatives and tetraarylethene derivatives.

As the compound capable of injecting and transporting holes, an amine derivative having strong fluorescence, for example, a triphenyldiamine derivative which is the above-described hole transporting material, a styrylamine derivative, or an amine derivative having an aromatic condensed ring is used. Is preferred.

The thickness of the buffer layer is 40 nm or less. It is preferably at most 30 nm, more preferably at most 20 nm. As a lower limit, it is sufficient that a film thickness sufficient to fill a pinhole or a gap can be ensured, and is usually about 10 nm. When the thickness of the buffer layer is larger than the above thickness, the buffer layer may function as a light-emitting layer, emit light in a portion other than the light-emitting layer separately painted, shift a designed light emission center, or design a light emission color. It emits light different from that of.

The buffer layer of the present invention can be a metal doping layer as described below. By using a metal doping layer, it is not necessary to use a metal having a low work function as a cathode constituent material.

That is, in the organic EL device, the process of injecting electrons from the cathode into the organic compound layer, which is basically an insulator, is reduction of the organic compound on the cathode surface, that is, formation of a radical anion state (Phys. Rev. Lett., 14, 229 (196
Five)). This is the lowest empty level (LUMO) of organic compounds
Electron injection. Therefore, an organic compound having a lower LUMO level is easier to inject electrons from the cathode. In the device of the present invention, a metal oxide or a metal salt having an effect of lowering the LUMO of the organic compound is doped in the organic compound layer in contact with the cathode in advance, so that an energy barrier upon electron injection from the cathode electrode is formed. Can be reduced. The metal doping layer 5 is an organic compound layer doped with a dopant material such as a metal oxide or a metal salt. Since the metal-doped organic compound has a low LUMO level as described above, the barrier against electron injection from the cathode is small, and the driving voltage can be reduced as compared with a conventional organic EL device. Moreover, a metal such as stable Al generally used as a wiring material can be used for the cathode.

The dopant is an alkali metal such as Li, an alkaline earth metal such as Mg, or a transition metal containing a rare earth metal, which can change the electron energy level of an organic compound serving as a host and lower the LUMO level. There is no particular limitation as long as it is a metal oxide or a metal salt of, but in the case of a metal oxide, Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, Cs ₂ O, M
For metal salts such as gO and CaO, LiF, NaF, K
F, RbF, CsF, MgF ₂ , CaF ₂ , SrF ₂ ,
BaF ₂ , LiCl, NaCl, KCl, RbCl, C
sCl, MgCl ₂ , CaCl ₂ , SrCl ₂ , BaC
l ₂ or the like can be suitably used.

The dopant concentration of the metal doping layer is not particularly limited, but is preferably 0.1 to 99% by weight. If it is less than 0.1% by weight, the concentration of the dopant is too low and the effect of doping is small.
Since the concentration of the dopant in the film is too high and the concentration of the organic compound into which electrons are to be injected near the cathode is too low, the effect of doping is reduced. The thickness of the metal doping layer is not particularly limited, but may be 1 nm to 200 nm, particularly 10 nm.
~ 100 nm is preferred. If the angle is less than 10 °, the thickness of the metal doping layer is too small, a uniform film cannot be obtained, and the amount of organic molecules having a lowered LUMO level to which electrons are to be injected is too small. On the other hand, if it exceeds 2000 °, the thickness of the entire organic layer is too large, and on the contrary, the driving voltage is increased, which is not preferable. If the thickness is in the above range, even if the thickness of the metal doping layer is thicker than a normal buffer layer, an increase in voltage and the like hardly occur.

The buffer layer is formed by a vapor deposition method. By forming the buffer layer by the vapor deposition method, the organic material particles enter or cover the inside of the pinholes and gaps, thereby preventing generation of a leak current. The evaporation method is not particularly limited, and any evaporation method may be used as long as the buffer layer can be formed within the above-mentioned thickness range. Note that in the case where the above-described doping layer is formed, a co-evaporation method may be used.

The conditions for vacuum deposition are not particularly limited.
The degree of vacuum is 0 ^-4 Pa or less, and the deposition rate is 0.01 to 1 nm /
It is preferable to set it to about sec.

The light emitting layer of the present invention is formed by a printing method. By using a printing method, a light emitting layer can be easily formed, which is particularly advantageous when an organic EL display device is sulfuric acid. Also, in particular, full-color displays,
In the case of separately applying a plurality of emission colors, various patterns can be formed by a simple process without using a mask or the like by using a printing method.

The printing method for forming the light emitting layer is not particularly limited, and various printing methods can be used. Among them, an ink jet method, a gravure printing method, a screen printing method and the like are preferable, and an ink jet method and a gravure printing method are particularly preferable. In addition, the gravure printing method is sometimes excellent for reasons such as tact and cost.

When the light emitting layer is formed by gravure printing, a method described in the above-mentioned Japanese Patent Application Laid-Open No. 3-26995 can be used. Further, when the light emitting layer is formed by an ink jet method, the method described in JP-A-10-12
377, JP-A-10-153967, EP
The method described in O880303A1 or the like can be used.

The light emitting layer comprises at least one kind or two or more kinds of organic compound thin films involved in the light emitting function, or a laminated film thereof.

The light emitting layer has a function of injecting holes (holes) and electrons, a function of transporting them, and a function of generating excitons by recombination of holes and electrons. By using a relatively electronically neutral compound for the light emitting layer, electrons and holes can be easily injected and transported in a well-balanced manner.

In the ink jet printing technology,
Conventionally, water-based, alcohol-based, and glycol-based inks have been mainly used. The reason is that the ink does not attack the ink flow path and the ink head material. Further, since organic solvent-based inks are harmful to the human body, many inkjet printers using water-based inks have been developed.

Therefore, in order to make an organic EL material into an ink and perform ink-jet patterning, the material is water-soluble or soluble in an organic solvent such as alcohol, tetrahydrofuran (THF), chloroform, xylene, chlorobenzene and a glycol-based solvent. It is more desirable.

As a material particularly suitable for the light emitting layer, polyfluorene can be mentioned. The polyfluorene is preferably a polyfluorene copolymer, and more preferably a polyfluorene-anthracene copolymer having the following structure.

[0033]

Embedded image

In the above formula, n: m representing the polymerization ratio is:
Preferably from 40:60 to 90:10, more preferably 5
0:50 to 85:15. The molecular weight of the copolymer is usually about 80,000 in weight average molecular weight and about 130 to 145 ° C. in glass transition temperature Tg.

Such a copolymer can be synthesized, for example, according to the following scheme. That is, 2,
7-dibromo-9,9-di-n-hexylfluorene (DHF) and 9,10-
Dibromoanthracene is polymerized with zero-valent nickel. At this time, 2-Br bonded to the terminal of the polymer
Add omofiuorene. In the following scheme, NiCOD = bis (1,5-cyclooctadiene) nickel (0),
COD = cyclooctadiene.

[0036]

Embedded image

Such a copolymer can be used by dissolving it in a usual organic solvent. For example, tetrahydrofuran (THF), chloroform, xylene, chlorobenzene, and the like.

The copolymer of the present invention may have the following structure.

[0039]

Embedded image

As another preferred host substance, a water-soluble conjugated polymer (Conjugated Polymer) can be mentioned. The conjugated polymer is dissolved in water as a salt, and polymerized by heating after film formation to form a light emitting layer. The cyanated conjugated polymer emits red light. These are materials having sufficient durability as a light emitting layer. The conjugated polymer is preferably poly (p-phenylenevinylene). Also, preferably, the polymer film has a uniform thickness in the range of approximately 10 nm to 5 μm, and the conjugated polymer has a semiconductor band gap in the range of 1 eV to 3.5 eV. Further, it is desirable that the ratio of the conjugated polymer in the electroluminescent region of the polymer film is such that charge transfer in the conjugated polymer present in the film can be ensured.

Other fluorescent substances that can be used in the light emitting layer include, for example, JP-A-63-2646.
No. 92, for example, at least one selected from compounds such as quinacridone, rubrene, styryl dyes and the like. Further, quinoline derivatives such as metal complex dyes having 8-quinolinol or a derivative thereof as a ligand, such as tris (8-quinolinolato) aluminum, tetraphenylbutadiene, anthracene, perylene, coronene, and 12-phthaloperinone derivatives. Further, phenylanthracene derivatives described in JP-A-8-12600 (Japanese Patent Application No. 6-110569), tetraarylethene derivatives described in JP-A-8-12969 (Japanese Patent Application No. 6-114456), and the like are described. Can be used.

Further, it is preferable to use in combination with a host substance capable of emitting light by itself, and it is preferable to use it as a dopant. In such a case, the content of the compound in the light emitting layer is preferably 0.01 to 10% by volume, and more preferably 0.1 to 5% by volume. In the case of rubrene, the content is preferably about 0.01 to 20% by volume. When used in combination with a host substance, the emission wavelength characteristics of the host substance can be changed, light emission shifted to a longer wavelength becomes possible, and the luminous efficiency and stability of the device are improved.

The host substance is preferably a quinolinolato complex, and more preferably an aluminum complex having 8-quinolinol or a derivative thereof as a ligand. Such an aluminum complex is disclosed in JP-A-63-26469.
No. 2, JP-A-3-255190, JP-A-5-7073
3, JP-A-5-258859, JP-A-6-2158
No. 74 and the like.

Specifically, first, tris (8-quinolinolato) aluminum, bis (8-quinolinolato) magnesium, bis (benzo {f} -8-quinolinolato) zinc, bis (2-methyl-8-quinolinolato) aluminum Oxide, tris (8-quinolinolato) indium,
Tris (5-methyl-8-quinolinolato) aluminum, 8-quinolinolatolithium, tris (5-chloro-
8-quinolinolato) gallium, bis (5-chloro-8-
Quinolinolato) calcium, 5,7-dichloro-8-quinolinolatoaluminum, tris (5,7-dibromo-
8-hydroxyquinolinolato) aluminum and poly [zinc (II) -bis (8-hydroxy-5-quinolinyl) methane].

In addition to 8-quinolinol or a derivative thereof, an aluminum complex having another ligand may be used, such as bis (2-methyl-
8-quinolinolato) (phenolato) aluminum (III)
, Bis (2-methyl-8-quinolinolato) (ortho-
Cresolato) aluminum (III), bis (2-methyl-
8-quinolinolato) (meth-cresolate) aluminum
(III), bis (2-methyl-8-quinolinolato) (para-cresolato) aluminum (III), bis (2-methyl-8-quinolinolato) (ortho-phenylphenolate)
Aluminum (III), bis (2-methyl-8-quinolinolato) (meth-phenylphenolato) aluminum (II
I), bis (2-methyl-8-quinolinolato) (para-
Phenylphenolato) aluminum (III), bis (2-
Methyl-8-quinolinolato) (2,3-dimethylphenolato) aluminum (III), bis (2-methyl-8-quinolinolato) (2,6-dimethylphenolato) aluminum (III), bis (2-methyl- 8-quinolinolato)
(3,4-dimethylphenolato) aluminum (III),
Bis (2-methyl-8-quinolinolato) (3,5-dimethylphenolato) aluminum (III), bis (2-methyl-8-quinolinolato) (3,5-di-tert-butylphenolato) aluminum (III) ), Bis (2-methyl-8)
-Quinolinolato) (2,6-diphenylphenolato) aluminum (III), bis (2-methyl-8-quinolinolato) (2,4,6-triphenylphenolato) aluminum (III), bis (2-methyl- 8-quinolinolato)
(2,3,6-trimethylphenolato) aluminum (I
II), bis (2-methyl-8-quinolinolato) (2,
3,5,6-tetramethylphenolato) aluminum (I
II), bis (2-methyl-8-quinolinolato) (1-naphthrat) aluminum (III), bis (2-methyl-8
-Quinolinolato) (2-naphthrat) aluminum (II
I), bis (2,4-dimethyl-8-quinolinolato)
(Ortho-phenylphenolato) aluminum (III),
Bis (2,4-dimethyl-8-quinolinolato) (para-
Phenylphenolato) aluminum (III), bis (2,
4-dimethyl-8-quinolinolato) (meta-phenylphenolato) aluminum (III), bis (2,4-dimethyl-8-quinolinolato) (3,5-dimethylphenolato) aluminum (III), bis (2 4-dimethyl-8
-Quinolinolato) (3,5-di-tert-butylphenolato) aluminum (III), bis (2-methyl-4-ethyl-8-quinolinolato) (para-cresolato) aluminum (III), bis (2-methyl) -4-methoxy-8-quinolinolato) (para-phenylphenolato) aluminum (III), bis (2-methyl-5-cyano-8-quinolinolato) (ortho-cresolato) aluminum (III),
Bis (2-methyl-6-trifluoromethyl-8-quinolinolato) (2-naphthrat) aluminum (III);

In addition, bis (2-methyl-8-quinolinolato) aluminum (III) -μ-oxo-bis (2-
Methyl-8-quinolinolato) aluminum (III), bis (2,4-dimethyl-8-quinolinolato) aluminum
(III) -μ-oxo-bis (2,4-dimethyl-8-quinolinolato) aluminum (III), bis (4-ethyl-
2-methyl-8-quinolinolato) aluminum (III)-
μ-oxo-bis (4-ethyl-2-methyl-8-quinolinolato) aluminum (III), bis (2-methyl-4
-Methoxyquinolinolato) aluminum (III) -μ-oxo-bis (2-methyl-4-methoxyquinolinolato)
Aluminum (III), bis (5-cyano-2-methyl-
8-quinolinolato) aluminum (III) -μ-oxo-
Bis (5-cyano-2-methyl-8-quinolinolato) aluminum (III), bis (2-methyl-5-trifluoromethyl-8-quinolinolato) aluminum (III) -μ
-Oxo-bis (2-methyl-5-trifluoromethyl-8-quinolinolato) aluminum (III) and the like.

Other host materials are disclosed in
Phenylanthracene derivative described in JP-A-12600 (Japanese Patent Application No. 6-110569) and JP-A-8-1296
No. 9 (Japanese Patent Application No. 6-114456) is also preferable.

The light emitting layer may also serve as an electron injection / transport layer. In such a case, it is preferable to use tris (8-quinolinolato) aluminum or the like.

The light emitting layer is preferably a mixed layer of at least one kind of hole injecting and transporting compound and at least one kind of electron injecting and transporting compound, if necessary.
Further, it is preferable that a dopant is contained in the mixed layer. The content of the compound in such a mixed layer is preferably 0.01 to 20 wt%, more preferably 0.1 to 15 wt%.

In the mixed layer, a carrier hopping conduction path is formed, so that each carrier moves in a material having a favorable polarity and injection of a carrier having the opposite polarity is unlikely to occur, so that the organic compound is less likely to be damaged. This has the advantage that the element life is extended. Further, by including the above-described dopant in such a mixed layer, the emission wavelength characteristics of the mixed layer itself can be changed, the emission wavelength can be shifted to a longer wavelength, and the emission intensity is increased, The stability of the device can be improved.

The hole injecting and transporting compound and the electron injecting and transporting compound used in the mixed layer may be selected from the above-described hole injecting and transporting compounds and electron injecting and transporting compounds, respectively.

The thickness of the light emitting layer is not particularly limited, and varies depending on the forming method.
It is preferable that the thickness be in the range of 10 to 300 nm.

The negative electrode (electron injection electrode) does not need to be particularly limited because it does not need to have a low work function and an electron injection property when combined with the following high resistance inorganic electron injection layer. Ordinary metals can be used. Among them, Al, Ag, In, T in terms of conductivity and ease of handling.
One, two or more metal elements selected from i, Cu, Au, Mo, W, Pt, Pd and Ni, particularly Al and Ag are preferable.

The thickness of the negative electrode thin film may be a certain thickness or more that can provide electrons to the high-resistance inorganic electron injecting and transporting layer, and may be 50 nm or more, preferably 100 nm or more. Although the upper limit is not particularly limited, the film thickness may be generally about 50 to 500 nm.

The following may be used as the electron injection electrode, if necessary. For example, K, Li, Na, M
g, La, Ce, Ca, Sr, Ba, Sn, Zn, Zr
Or a two-component or three-component alloy system containing them for improving stability, for example, Ag.Mg.
(Ag: 0.1 to 50 at%), Al.Li (Li: 0.
01 to 14 at%), In.Mg (Mg: 50 to 80 at%)
%), Al.Ca (Ca: 0.01 to 20 at%), and the like.

The thickness of the electron injecting electrode thin film may be a certain thickness or more for sufficiently injecting electrons.
The thickness is preferably 0.5 nm or more, particularly 1 nm or more.
The upper limit is not particularly limited.
It may be about 500 nm. On the electron injection electrode,
Further, an auxiliary electrode (protection electrode) may be provided.

The thickness of the auxiliary electrode may be a certain thickness or more, preferably 50 nm or more, more preferably 100 nm or more, in order to secure electron injection efficiency and prevent entry of moisture, oxygen or an organic solvent. A range from 100 to 500 nm is preferred. If the auxiliary electrode layer is too thin, the effect cannot be obtained, and the step coverage of the auxiliary electrode layer is reduced, and the connection with the terminal electrode is not sufficient. On the other hand, if the auxiliary electrode layer is too thick, the stress of the auxiliary electrode layer increases, which causes adverse effects such as an increase in the growth rate of dark spots.

As the auxiliary electrode, an optimum material may be selected and used depending on the material of the electron injection electrode to be combined. For example, if importance is placed on ensuring electron injection efficiency, a low-resistance metal such as Al may be used, and if importance is placed on sealing properties, a metal compound such as TiN may be used.

The total thickness of the electron injection electrode and the auxiliary electrode is not particularly limited, but is usually 50 to 500 nm.
It should be about the degree.

The hole injecting electrode material is preferably a material capable of efficiently injecting holes into a high-resistance inorganic hole injecting and transporting layer or an organic hole injecting and transporting layer, and has a work function of 4.5 eV to 5.5 eV. Is preferred. Specifically, tin-doped indium oxide (ITO), zinc-doped indium oxide (IZO), indium oxide (In
₂ O ₃ ), tin oxide (SnO ₂ ) and zinc oxide (Zn
O) having a main composition of either of them is preferable. These oxides may deviate somewhat from their stoichiometric composition. The mixing ratio of SnO ₂ to In ₂ O ₃ is 1 to 20.
wt%, more preferably 5 to 12 wt%. Also, IZO
The mixing ratio of ZnO to In ₂ O ₃ is usually 12
About 32% by weight.

The hole injection electrode may contain silicon oxide (SiO ₂ ) in order to adjust the work function.
The content of silicon oxide (SiO ₂ ) is preferably about 0.5 to 10% by mol ratio of SiO _{2 to} ITO. S
The inclusion of iO ₂ increases the work function of ITO.

The electrode on the light extraction side has an emission wavelength band,
The light transmittance is usually 400 to 700 nm, particularly preferably 50% or more, more preferably 80% or more, and particularly preferably 90% or more for each emitted light. If the transmittance is too low, the light emission itself from the light emitting layer is attenuated, and it becomes difficult to obtain the luminance required for the light emitting element.

The thickness of the electrode is 50 to 500 nm, especially 50 to 500 nm.
The range of -300 nm is preferred. The upper limit is not particularly limited. However, if the thickness is too large, there is a fear that the transmittance is reduced or the layer is peeled off. If the thickness is too small, a sufficient effect cannot be obtained, and there is a problem in film strength at the time of production and the like.

Further, in order to prevent deterioration of the organic layers and electrodes of the device, it is preferable to seal the device with a sealing plate or the like. The sealing plate adheres and seals the sealing plate using an adhesive resin layer in order to prevent moisture from entering. The sealing gas is A
An inert gas such as r, He, and N ₂ is preferable. Further, the moisture content of the sealing gas is preferably 100 ppm or less, more preferably 10 ppm or less, and particularly preferably 1 ppm or less. Although there is no particular lower limit for the water content, it is usually about 0.1 ppm.

The material of the sealing plate is preferably a flat plate, and may be a transparent or translucent material such as glass, quartz, resin, etc., and glass is particularly preferred. As such a glass material, an alkali glass is preferable from the viewpoint of cost, and in addition, a glass composition such as soda lime glass, lead alkali glass, borosilicate glass, aluminosilicate glass, and silica glass is also preferable. In particular, soda glass, a glass material without surface treatment can be used at low cost,
preferable. As the sealing plate, other than a glass plate, a metal plate, a plastic plate, or the like can be used.

The height of the sealing plate may be adjusted to a desired height by using a spacer. Examples of the material of the spacer include resin beads, silica beads, glass beads, and glass fibers, and glass beads are particularly preferable. The spacer is usually a granular material having a uniform particle size, but the shape is not particularly limited, and may be various shapes as long as it does not hinder the function as the spacer. As the size, the diameter in terms of a circle is 1 to 20 μm, more preferably 1 to 10 μm, and especially 2 to 20 μm.
8 μm is preferred. Those having such a diameter have a grain length of 10
It is preferably about 0 μm or less, and the lower limit is not particularly limited, but is usually about the same as or larger than the diameter.

When a recess is formed in the sealing plate,
Spacers may or may not be used. The preferred size when used is within the above range,
Particularly, the range of 2 to 8 μm is preferable.

The spacer may be mixed in the sealing adhesive in advance, or may be mixed at the time of bonding. The content of the spacer in the sealing adhesive is preferably 0.01
-30 wt%, more preferably 0.1-5 wt%.

The adhesive is not particularly limited as long as it can maintain stable adhesive strength and has good airtightness, but it is preferable to use a cationic curing type ultraviolet curing epoxy resin adhesive. .

In the present invention, the substrate on which the organic EL structure is formed is an amorphous substrate such as glass or quartz, or a crystalline substrate such as Si, GaAs, ZnSe, or Z.
Examples thereof include nS, GaP, and InP, and a substrate in which a crystalline, amorphous, or metal buffer layer is formed on these crystalline substrates can also be used. As the metal substrate, Mo, Al, Pt, Ir, Au, Pd, or the like can be used, and a glass substrate is preferably used. When the substrate is on the light extraction side, it is preferable that the substrate has the same light transmittance as the above-mentioned electrodes.

Further, a large number of the elements of the present invention may be arranged on a plane. By changing the emission color of each element arranged on a plane, a color display can be obtained.

The emission color may be controlled by using a color filter film, a color conversion film containing a fluorescent substance, or a dielectric reflection film on the substrate.

As the color filter film, a color filter used in a liquid crystal display or the like may be used.
The characteristics of the color filter may be adjusted in accordance with the light emitted from the organic EL element to optimize the extraction efficiency and the color purity.

When a color filter capable of cutting off short-wavelength external light that is absorbed by the EL element material or the fluorescent conversion layer is used, the light resistance of the element and the contrast of display are improved.

An optical thin film such as a dielectric multilayer film may be used instead of the color filter.

The fluorescent conversion filter film absorbs EL light and emits light from the phosphor in the fluorescent conversion film to convert the color of the emitted light. It is formed from a fluorescent material and a light absorbing material.

As the fluorescent material, basically, a material having a high fluorescence quantum yield may be used, and it is desirable that the fluorescent material has strong absorption in the EL emission wavelength region. In practice, laser dyes and the like are suitable, and rhodamine compounds, perylene compounds, cyanine compounds, phthalocyanine compounds (including subphthalocyanines, etc.) naphthalimide compounds, condensed ring hydrocarbon compounds, condensed heterocyclic compounds A styryl compound, a coumarin compound or the like may be used.

As the binder, a material that does not quench the fluorescence may be basically selected, and a binder that can be finely patterned by photolithography, printing, or the like is preferable. In the case where the hole injection electrode is formed on the substrate in contact with the hole injection electrode, a material which is not damaged when the hole injection electrode (ITO, IZO) is formed is preferable.

The light absorbing material is used when the light absorption of the fluorescent material is insufficient, but may be omitted when unnecessary. As the light absorbing material, a material that does not quench the fluorescence of the fluorescent material may be selected.

The organic EL device of the present invention is generally used as a DC-driven or pulse-driven EL device, but it can also be driven by an AC device. The applied voltage is usually 2 to 30
V.

The elements of the present invention may be stacked in multiple layers in the film thickness direction. With such an element structure, it is also possible to adjust the color tone of the emitted light and to make it multi-colored.

The organic EL device of the present invention can be applied to various optical applications such as an optical pickup used for memory read / write, a relay device in an optical communication transmission line, a photocoupler, etc., in addition to a display application. Can be used for devices.

[0083]

<Example 1> A 7059 substrate (trade name, manufactured by Corning Incorporated) as a glass substrate was scrub-cleaned using a neutral detergent.

On this substrate, a film thickness of 85 was formed by RF magnetron sputtering using an ITO oxide target.
An ITO hole injection electrode layer having a thickness of nm was formed. After patterning, a 100 × 100 μm ITO pixel was formed, and an edge cover was formed using polyimide to prepare a test substrate.

The substrate on which the ITO and the edge cover were formed was subjected to ultrasonic cleaning in the order of a neutral detergent, acetone, and ethanol, followed by UV / O ₃ cleaning, and used for the experiment.

A fluorene / anthracene copolymer was dissolved in a xylene solution as a light emitting layer, and a film having a thickness of 50 nm was formed using an ink jet printer. After vacuum drying, it is fixed to the substrate holder of the vapor deposition device, and the inside of the tank is 1 × 10 ⁻⁴ Pa
The pressure was reduced to the following, and tris (8-quinolinolato) aluminum (Alq3) was deposited as a buffer layer at a deposition rate of 0.2 nm / sec.
Was deposited to a thickness of 40 nm.

Next, while maintaining the reduced pressure, AlLi (L
i: 7 at%) to a thickness of 1 nm, followed by Al
Evaporation was performed to a thickness of 0 nm to form a negative electrode for an electron injection electrode and an auxiliary electrode.

Finally, glass sealing was performed to obtain an organic EL display device.

The obtained organic EL device was placed in air for 10 hours.
It was driven at a constant current density of mA / cm ² .

As a result, blue light emission of the fluorene copolymer was observed from the sample of the present invention. In addition, light emission with a high luminance of 4000 cd / m ² when a voltage of 15 V was applied was confirmed. Even when the applied voltage was increased to 25 V, no destruction phenomenon of the element was observed.

<Example 2> Organic E was prepared in the same manner as in Example 1 except that a gravure printing method was used for patterning the light emitting layer.
An L display was obtained. When the obtained sample was driven in the same manner as in Example 1, the luminance when 15 V was applied was 3600.
Light emission with a high luminance of cd / m ² was confirmed, and even when the applied voltage was increased to 25 V, no destructive phenomenon of the device was observed.

Example 3 In the same manner as in Example 1, a fluorene copolymer was formed into a film, and then LiF was formed to a thickness of 40 nm at a deposition rate of 1 nm / sec so as to be 2 wt% with respect to Alq3. Next, Al was deposited to a thickness of 200 nm to form a negative electrode. Otherwise, an organic EL display device was obtained in the same manner as in Example 1.

When the obtained sample was driven in the same manner as in Example 1, the luminance when 13 V was applied was 4000 cd / m ^2.
And high-luminance light emission was confirmed. No destructive phenomenon of the element was observed even when the applied voltage was increased to 25V.

Example 4 A 7059 substrate (trade name, manufactured by Corning Incorporated) as a glass substrate was scrub-cleaned with a neutral detergent.

Al was used as a negative electrode on this glass substrate.
AlLi (Li: 7 at%) was deposited to a thickness of 1 nm to a thickness of 00 nm.

Next, a fluorene / anthracene copolymer was dissolved in a xylene solution as a light emitting layer, and a film was formed to a thickness of 50 nm using an ink jet printer. After vacuum drying, fix it to the substrate holder of the vapor deposition device,
The pressure was reduced to 10 ⁻⁴ Pa or less, and TPD as a buffer layer was deposited to a thickness of 40 nm at a deposition rate of 0.2 nm / sec.

While maintaining the reduced pressure, an 85 nm-thick ITO hole injection electrode layer was formed by an RF magnetron sputtering method using an ITO oxide target.

When the obtained sample was driven in the same manner as in Example 1, the luminance when 18 V was applied was 3200 cd / m ^2.
And high-luminance light emission was confirmed. No destructive phenomenon of the element was observed even when the applied voltage was increased to 25V.

<Comparative Example> In Example 1, after forming the fluorene copolymer, a comparative sample was formed in which the negative electrode was formed and the buffer layer was not formed.

When each of the obtained comparative samples was driven in the same manner as in Example 1, light emission was possible. However, due to the problem of leakage due to pinholes in the printed film and disturbance of the edge portion, the leakage was reduced from around 11V. As a result, a decrease in luminance was observed, and heat generation increased at 17 V, causing dielectric breakdown from the leaked portion.

[0101]

As described above, according to the present invention, it is possible to realize an organic EL display device which can be produced in a simple process at a low cost and which does not cause a current leak or the like.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a basic configuration of an organic EL display device of the present invention.

FIG. 2 is a plan view illustrating a state in which a light emitting layer is formed by a printing method in a region to be a pixel to be patterned.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Positive electrode 3 Light emitting layer 4 Insulating layer 5 Buffer layer 6 Negative electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K007 AB05 AB18 BB06 CA00 CA01 CA02 CA04 CB01 DA00 DB03 EB00 FA01

Claims (6)

[Claims] 1. A substrate, and at least a positive electrode, a light emitting layer, a buffer layer, and a negative electrode are sequentially formed on the substrate, the light emitting layer is formed by a printing method, and the buffer layer is formed from an organic material by an evaporation method. And an organic EL display device having a thickness of 40 nm or less. 2. The method according to claim 1, wherein the buffer layer has a hole injecting / transporting property and / or
Alternatively, an organic EL display device containing an organic material capable of injecting and transporting electrons. 3. The organic EL display according to claim 1, wherein the thickness of the buffer layer is 40 nm or less. 4. The organic EL display according to claim 1, wherein said buffer layer is a metal doping layer and has a thickness of 1 to 200 nm. 5. The organic EL display according to claim 1, wherein the light emitting layer is formed by an ink-jet method. 6. The organic EL display device according to claim 1, wherein the light emitting layer is formed by a gravure printing method.