JP2001319777A - Organic electroluminescence element and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescence element in which injection efficiency of hole is enhanced by making a work function of positive electrode large and in which a low voltage of element driving voltage is made possible. SOLUTION: This is concerning the organic electroluminescence element which is formed by being equipped with an organic luminous layer 3 between a positive electrode 6 and a negative electrode 1. In this material, the work function becomes larger by the acid treatment not less than 0.5 eV than that before the treatment as for the positive electrode 6.

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 used for various displays, display devices, backlights for liquid crystals, and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art An electroluminescent element is a light emitting device utilizing the electroluminescence of a solid phosphor substance. At present, an inorganic electroluminescent element using an inorganic material as a light emitter has been put to practical use, and the back light of a liquid crystal display has been developed. Some applications are being developed for lights and flat panel displays. However, an inorganic electroluminescence element requires a voltage of 100 to emit light.
V or higher, and it is difficult to emit blue light.
It is difficult to achieve full color by primary colors.

On the other hand, research on electroluminescent devices using organic materials has been attracting attention for a long time, and various studies have been made. However, since the luminous efficiency is very poor, full-scale practical research has not been achieved. . However, 198
In 7 years, Kodak C.I. W. Tang et al. Proposed an organic electroluminescence having a function-separated stacked structure in which an organic material was divided into two layers, a hole transport layer and a light-emitting layer. In this case, despite the low voltage of 10 V or less,
It was found that a high emission luminance of 1000 cd / m ² or more was obtained. Since then, organic electroluminescence devices have begun to attract attention, and active research has been conducted.

[0004] As a result of such research and development, organic electroluminescent devices can emit high-intensity surface light of about 100 to 100000 cd / m ² at a low voltage of about 10 V, and select the type of fluorescent substance. As a result, light emission from blue to red became possible.

However, when considering application development as a full-color display and a light emitting element for illumination, it is necessary to lower the element driving voltage to further increase the efficiency. In order to realize such a low device drive voltage, it is necessary to increase the efficiency of injecting holes from the anode and electrons from the cathode into the light emitting layer. As a method of increasing the hole injection efficiency from the anode, there is a method of increasing the work function of the anode and reducing the energy barrier with the hole transport layer.

Here, in the case of ITO (indium-tin oxide) which is generally used as an anode material, when it is washed with a commonly used organic solvent or the like, 4.7 to 4.7% is used.
The work function is about 4.8 eV. This is considered to be due to contamination such as residual carbon due to an organic solvent or the like remaining on the surface of the anode. For this reason, after the cleaning step, processing such as UV-O ₃ cleaning or oxygen plasma processing may be performed.

On the other hand, as a method of increasing the work function of the anode, a method of treating the surface of the anode with an acid is disclosed in Japanese Patent Laid-Open No. 4-1479.
No. 5, JP-A-9-120890.

In JP-A-4-14795, the surface of the anode is treated with an acid and then washed and dried with an organic solvent so that the work function of the anode is 0.1% lower than that of the anode material before the acid treatment. About 0.3 eV,
By increasing the work function of the anode in this way, the drive voltage of the element is reduced.

In Japanese Patent Application Laid-Open No. Hei 9-120890, the surface of the anode is polished, then treated with an acid, and then washed and dried with an organic solvent, thereby flattening the anode surface and thinning the outermost surface. Holes are formed to reduce the driving voltage of the element and improve the life.

[0010]

However, in those disclosed in JP-A-4-14795 and JP-A-9-120890, after the anode is treated with an acid, the anode is washed with an organic solvent or the like. Therefore, a residual carbon content due to an organic solvent or the like remains on the surface of the anode, and the effect of increasing the work function is insufficient.

In addition, when the organic electroluminescent element is driven continuously, there is a problem that the luminance decreases and the resistance of the element further increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has an effect that the work function of the anode is increased to increase the hole injection efficiency, the device driving voltage can be reduced, and the life during continuous driving is further improved. It is an object of the present invention to provide an organic electroluminescent device capable of improving stability of characteristics and chromaticity and suppressing an increase in resistance as much as possible, and a method for manufacturing the same.

[0013]

According to a first aspect of the present invention, there is provided an organic electroluminescent device comprising an organic light emitting layer provided between an anode and a cathode. The function is characterized in that the function is 0.5 eV or more larger than before the processing.

According to a second aspect of the present invention, there is provided an organic electroluminescent element having an organic light emitting layer between an anode and a cathode, wherein the anode is subjected to an acid treatment and retains its acid. An organic light-emitting layer and a cathode are laminated on the anode in a state where the anode has been treated.
It is characterized in that it is larger.

The invention of claim 3 is characterized in that, in claim 1 or 2, the acid used for the acid treatment is an inorganic protonic acid.

[0016] In a fourth aspect of the present invention, in the first or second aspect, the acid used for the acid treatment is an organic acid.

The invention of claim 5 is the invention according to claim 1 or 2, wherein the acid used for the acid treatment is a high molecular weight organic acid,
It is characterized in that a high molecular organic acid is held in a film on the surface of the anode.

According to a sixth aspect of the present invention, in the fifth aspect, the film thickness of the high molecular weight organic acid is 1 to 100 °.

The invention of claim 7 is characterized in that, in the above-mentioned claims 1 to 6, the pH of the acid used for the acid treatment is 6 or less.

An eighth aspect of the present invention is characterized in that in any one of the first to seventh aspects, the surface of the anode is treated with a silane coupling agent.

According to a ninth aspect of the present invention, there is provided a method of manufacturing an organic electroluminescent device, comprising: laminating an organic light emitting layer on an anode; and laminating a cathode on the organic light emitting layer. When an organic light emitting element is laminated and formed, the anode is subjected to an acid treatment, and then the organic light emitting layer is formed while holding the acid on the surface of the anode.

A tenth aspect of the present invention is characterized in that, in the ninth aspect, the anode is subjected to a plasma treatment before the acid treatment.

The invention of claim 11 is the invention of claim 9 or 1
0, the organic light emitting layer is formed within one week after the acid treatment of the anode.

[0024]

Embodiments of the present invention will be described below.

As shown in FIG. 1, the organic electroluminescent device according to the present invention comprises an anode 6, a hole transport layer 4, an organic light emitting layer 3, an electron transport layer 2, and a cathode 1, which are laminated in this order on a substrate 7. It is formed in the provided structure. When a positive voltage is applied to the anode 6 and a negative voltage is applied to the cathode 1, electrons injected into the organic light emitting layer 3 via the electron transport layer 2 and electrons injected into the organic light emitting layer 3 via the hole transport layer 4. The holes are recombined in the organic light emitting layer 3 to emit light.

Here, in the present invention, after the surface of the anode 6 is treated with an acid, the acid layer 5 is held on the surface of the anode 6 without performing washing with water or a solvent after the acid treatment. In this state, the hole transport layer 4, the organic light-emitting layer 3, the electron transport layer 2, and the cathode 1 are stacked on the anode 6 to provide an organic electroluminescent device. As described above, since the surface of the anode 6 is not washed after the acid treatment, dirt such as residual carbon due to an organic solvent or the like can be minimized, and the electric double layer is not damaged. The function can be made larger than the anode material, and the hole injection efficiency from the anode 6 can be increased,
This makes it possible to reduce the element drive voltage.

In order to increase the work function of the anode 6 by the acid treatment as described above, in the present invention, it is necessary that the work function of the surface of the anode 6 is larger than the work function before the treatment by 0.5 eV or more. is there. If the work function of the anode 6 is not increased by 0.5 eV or more, the effect of increasing the hole injection efficiency by increasing the work function of the anode 6 becomes insufficient, and the purpose of lowering the element drive voltage is not sufficient. Can not be achieved. Since the work function of the anode 6 is preferably as large as possible, the upper limit for increasing the work function is not particularly set. However, there is a limit in increasing the work function of the anode 6 by acid treatment. Is about 1.3 eV.

In the acid treatment of the anode 6 as described above, a common inorganic proton acid or organic acid can be used as the acid. Examples of the inorganic protonic acid include, but are not limited to, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, hydroiodic acid, hydrofluoric acid, hydrobromic acid, and a mixture thereof. . In addition, as the organic acid, acetic acid, oxalic acid, benzoic acid, formic acid, citric acid, succinic acid, a mixture thereof, or the like can be used, but the organic acid is not limited thereto.

Examples of the method of treating the anode 6 with an acid include a method of immersing the anode 6 in the above-mentioned acid solution for a predetermined time and a method of exposing the anode 6 to the vapor of the acid solution for a predetermined time. . The pH of the acid for treating the anode 6 is desirably 6 or less. If the pH exceeds 6, the effect of increasing the work function of the anode 6 cannot be sufficiently expected. The lower limit of the pH is not particularly set, but the lower limit is preferably about pH 0.01. The acid treatment time varies depending on the pH of the acid and the temperature of the acid, but is usually in the range of 1 second to 1 hour, and may be appropriately selected within this range. Furthermore, it is preferable that the hole transport layer 4, the organic light emitting layer 3, and the like be laminated on the anode 6 within one week after the acid treatment of the anode 6.
If the anode 6 is left after being acid-treated, the surface of the anode 6 is gradually contaminated. Therefore, it is preferable to provide the hole transport layer 4, the organic light-emitting layer 3, and the like as soon as possible after the anode 6 is acid-treated. After one week, the effect of the acid treatment of the anode 6 may not be sufficiently obtained.

In the present invention, a high molecular organic acid can be used as another acid. Since the high molecular weight organic acid can form a film on the surface of the anode 6, the anode 6
Is easily fixed to the surface of the anode 6, and stable characteristics can be obtained with respect to increasing the work function of the anode 6 by the acid treatment. As the high molecular weight organic acid, an ion dissociable polymer exhibiting acidity can be used. Specifically, sulfonic acid compounds such as polystyrene sulfonic acid and polyvinyl sulfonic acid, polyacrylic acid, polymethacrylic acid, polymethacrylic acid, and polymers containing these units can be used, but are not limited thereto. is not.

By coating these high molecular organic acids on the anode 6 in a state of being dissolved in water or an organic solvent,
As shown in FIG. 2, a thin film 5b of a high molecular organic acid can be formed on the surface of the anode 6. Here, the thickness of the high molecular organic acid thin film 5b is desirably 1 ° or more and 100 ° or less. If the film thickness exceeds 100 °, there is a possibility that a problem may occur in that the thin film 5b of the high molecular weight organic acid acts as an insulating layer, making it difficult for current to flow through the device. On the other hand, if the film thickness is less than 1 °, the desired effect of the present invention by treating with an acid cannot be sufficiently obtained.

Preferably, the surface of the anode 6 is further treated with a silane coupling agent. Then, the hole transport layer 4 is further treated on the silane coupling agent.
By forming an organic layer such as the organic light emitting layer 3 and the like, the adhesion between the organic layer and the anode 6 can be increased, and the effect of the acid treatment of the anode 6 can be further enhanced. . Here, as the silane coupling agent, those generally used having an epoxy group, a mercapto group, or an amino group as a reactive group can be used. Specifically, 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, N-2- (aminoethyl) 3-aminopropyltrimethoxysilane, N-2- (Aminoethyl)
3-Aminopropylmethyldimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, and the like can be used, but are not particularly limited thereto. This silane coupling agent treatment can be performed simultaneously with the acid treatment by applying a mixture of an acid and the silane coupling agent to the surface of the anode 6.

Further, by subjecting the surface of the anode 6 to oxygen plasma treatment prior to the acid treatment of the anode 6, the effect of the acid treatment can be more effectively brought out. this is,
The surface of the anode 6 is hydrophilized by the oxygen plasma treatment, and the affinity of the acid treatment is increased when the surface of the anode 6 is subjected to an aqueous acid treatment using an aqueous acid solution or the like, so that the acid is more strongly applied to the surface of the anode 6. This is because it is fixed.

Next, the organic layers and electrodes constituting the organic electroluminescence device of the present invention will be described.
However, the organic electroluminescence device of the present invention
It is characterized in that an acid treatment is performed to use the anode 6 in a state where the acid is held. Regarding the configuration of the organic layer formed on the anode 6, the conventional method has been used for producing an organic electroluminescent element. Known ones used can be appropriately used, and it is needless to say that the present invention is not limited to the following ones.

First, the anode 6 is an electrode for injecting holes into the element as described above. It is possible to use an electrode material made of a metal, an alloy, an electrically conductive compound having a large work function, or a mixture thereof. Preferably, a material having a work function of 4 eV or more is used. Such an anode 6
Specifically, as a material of the metal, metal such as gold, CuI, IT
Conductive transparent materials such as O (indium-tin oxide: indium tin oxide), SnO ₂ , and ZnO can be given. The anode 6 can be manufactured by forming these electrode materials into a thin film on a surface of a substrate 7 formed of a transparent material such as glass or transparent resin by a method such as a vacuum evaporation method or a sputtering method. Things. When the light emitted from the organic light emitting layer 3 is transmitted through the anode 6 and irradiated to the outside, the light transmittance of the anode 6 is set to 70%.
% Is preferable. Further, the sheet resistance of the anode 6 is preferably several hundred Ω / □ or less, particularly preferably 100 Ω / □ or less. Here, the thickness of the anode 6 varies depending on the material in order to control the characteristics of the anode 6 such as light transmittance and sheet resistance as described above.
It is good to set it to 500 nm or less, preferably in the range of 10 to 200 nm.

On the other hand, for the cathode 1, which is an electrode for injecting electrons into the organic light emitting layer 3, it is preferable to use an electrode material composed of a metal, an alloy, an electrically conductive compound and a mixture thereof having a small work function. The work function is preferably 5 eV or less. Such electrode materials for the cathode 1 include sodium, sodium-potassium alloy,
Lithium, magnesium, aluminum, magnesium - silver mixture, a magnesium - indium mixture, an aluminum - lithium alloy, Al / Al ₂ O ₃ mixture, Al /
LiF mixtures and the like can be mentioned. This cathode 1
Can be manufactured by forming these electrode materials into a thin film by a method such as a vacuum evaporation method or a sputtering method. When light emitted from the organic light-emitting layer 3 is transmitted through the cathode 1 and irradiated to the outside, the light transmittance of the cathode 1 is preferably set to 10% or more. In this case, the thickness of the cathode 1 varies depending on the material in order to control the characteristics such as the light transmittance of the cathode 1 as described above, but it is usually 500 nm or less, preferably 100 to 200 nm. .

The light emitting material or doping material usable for the organic light emitting layer 3 includes anthracene, naphthalene, pyrene, tetracene, coronene, perylene, phthaloperylene, naphthaloperylene, diphenylbutadiene, tetraphenylbutadiene, coumarin, oxadiazole, bisbenzo. Xazoline, bisstyryl, cyclopentadiene, quinoline metal complex, tris (8-hydroxyquinolinato) aluminum complex, tris (4-methyl-8-quinolinato) aluminum complex, tris (5-phenyl-8-quinolinato) aluminum complex, Aminoquinoline metal complex, benzoquinoline metal complex, tri- (p-terphenyl-4-yl) amine, 1
-Aryl-2,5-di (2-thienyl) pyrrole derivative, pyran, quinacridone, rubrene, distilbenzene derivative, distilarylene derivative, various fluorescent dyes, and the like, but are not limited thereto. The light emitting material selected from these compounds is 80 to 9
It is also preferable to include 9.9 parts by weight and 0.1 to 20 parts by weight of the doping material. The thickness of the organic light emitting layer 3 is equal to 0.
The thickness is 5 to 500 nm, more preferably 0.5 to 200 nm.

The hole transporting material constituting the hole transporting layer 4 has the ability to transport holes, has the effect of injecting holes from the anode 6, and has excellent hole transporting properties with respect to the organic light emitting layer 3 or the light emitting material. Compounds that have an injection effect, prevent the transfer of electrons to the hole transport layer 4, and have excellent thin film forming ability can be given. Specifically, phthalocyanine derivatives, naphthalocyanine derivatives, porphyrin derivatives, N, N'-bis (3-methylphenyl)-(1,1'-biphenyl) -4,4'-diamine (TPD) and 4,4 ' -Bis [N- (naphthyl) -N-
Aromatic diamine compounds such as phenyl-amino] biphenyl (α-NPD), oxazole, oxadiazole,
Triazole, imidazole, imidazolone, stilbene derivative, pyrazoline derivative, tetrahydroimidazole, polyarylalkane, butadiene, 4,4 ′,
4 "-tris (N- (3-methylphenyl) N-phenylamino) triphenylamine (m-MTDATA),
And polymer materials such as polyvinylcarbazole, polysilane, and conductive polymers such as polyethylenedioxidethiophene (PEDOT), but are not limited thereto.

The electron transporting material constituting the electron transporting layer 2 has the ability to transport electrons, has the effect of injecting electrons from the cathode 1, and has an excellent electron transporting property with respect to the organic light emitting layer 3 or the light emitting material. Compounds that have an injection effect, further prevent holes from moving to the electron transport layer 2, and have excellent thin film forming ability can be given. Specifically, fluorene, bathophenanthroline, bathocuproine, anthraquinodimethane, diphenoquinone, oxazole, oxadiazole, triazole, imidazole, anthraquinodimethane and the like and compounds thereof, a metal complex compound or a nitrogen-containing five-membered ring derivative. is there. Specifically, as the metal complex compound, tris (8-hydroxyquinolinato) aluminum, tri (2-methyl-8-hydroxyquinolinato) aluminum, tris (8-hydroxyquinolinato) gallium, bis ( 10-hydroxybenzo [h] quinolinato) beryllium, bis (10-hydroxybenzo [h] quinolinato) zinc, bis (2-methyl-8-quinolinato) (o-cresolate) gallium, bis (2-methyl-8-quinolinate) ) (1-Naphtholate) aluminum and the like, but are not limited thereto. As the nitrogen-containing five-membered ring derivative, an oxazole, thiazole, oxadiazole, thiadiazole or triazole derivative is preferable. Specifically, 2,5-bis (1-phenyl) -1,3,4-oxazole, 2,5-bis (1-phenyl) -1,3,3
4-thiazole, 2,5-bis (1-phenyl) -1,
3,4-oxadiazole, 2- (4′-tert-butylphenyl) -5- (4 ″ -biphenyl) 1,3,4
-Oxadiazole, 2,5-bis (1-naphthyl)-
1,3,4-oxadiazole, 1,4-bis [2-
(5-phenylthiadiazolyl)] benzene, 2,5-
Bis (1-naphthyl) -1,3,4-triazole, 3
-(4-biphenylyl) -4-phenyl-5- (4-
(t-butylphenyl) -1,2,4-triazole and the like, but are not limited thereto. Further, a polymer material used for a polymer organic electroluminescence device can also be used. For example, polyparaphenylene and its derivatives, fluorene and its derivatives, and the like.

[0040]

Next, the present invention will be described specifically with reference to examples.

(Example 1) An ITO (indium-tin oxide) was sputtered on a glass substrate 7 having a thickness of 0.7 mm to form an anode 6 having a sheet resistance of 7Ω / □.
An O glass substrate (manufactured by Sanyo Vacuum Corporation) was used. And first,
This was ultrasonically washed with acetone, pure water, and isopropyl alcohol for 15 minutes each, and then dried.

Next, the ITO glass substrate was exposed to a vapor of a nitric acid aqueous solution (pH <1, concentration: 60 to 61% by mass) at room temperature for 10 minutes to acid-treat the surface of the anode 6. Here, the work function of the surface of the anode 6 made of ITO before the acid treatment was 4.80 eV. By performing the acid treatment, the work function of the anode 6 became 5.70 eV, and the work function was increased by 0.90 eV. The work function is measured as
Ultraviolet photoelectron analyzer ("AC-1" manufactured by Riken Keiki Co., Ltd.)
This was performed using

Next, one minute after the acid treatment, the ITO glass substrate was set in a vacuum evaporation apparatus without washing, and the substrate was set to 133.322 × 10 ⁻⁶ Pa (1 × 10 ⁻⁶ To
rr) under vacuum conditions, 4,4'-bis [N- (naphthyl) -N-phenyl-amino] biphenyl (α-NP
D) (manufactured by Dojindo Laboratories Inc.) was deposited at a deposition rate of 1 to 2 Å / s to form a hole transport layer 4 having a thickness of 400 Å.

Next, a tris (8-hydroxyquinolinato) aluminum complex (“Al” manufactured by Dojin Chemical Laboratory Co., Ltd.)
q3 ”) at a deposition rate of 1-2 ° / s and a thickness of 40
An organic light emitting layer 3 and an electron transport layer 2 of 0 ° were formed.

Thereafter, LiF is first deposited at a thickness of 5 ° at a deposition rate of 0.5 to 1.0 °, and then Al is deposited at a rate of 10 ° / s.
The cathode 1 was formed by vapor deposition at a vapor deposition rate of 1500 °.

Next, the ITO glass substrate on which these layers were formed was placed in a glove box in a dry nitrogen atmosphere having a dew point of -76 ° C. or less, and was transported without being exposed to the atmosphere. On the other hand, barium oxide powder as a water-absorbing agent is put in a bag having air permeability to produce a water-absorbing material 10, and this water-absorbing material 10 is attached to a glass sealing plate 11 with an adhesive. A sealant 12 made of an ultraviolet curable resin is previously applied to the outer peripheral portion of the sealing member 11, and the sealing plate 1 is attached to the ITO glass substrate 7 on which the above layers 1 to 6 are formed in a glove box.
3 were bonded together with a sealant 12, and the sealant 12 was cured by UV irradiation to obtain an organic electroluminescence device as shown in FIG.

(Example 2) An aqueous solution of hydrochloric acid having a pH of 3 was used as an acid, and an ITO glass substrate was immersed in the aqueous solution of hydrochloric acid for 3 minutes at room temperature and dried, so that the surface of the anode 6 was acid-treated. did. By performing the acid treatment in this manner, the work function of the anode 6 became 5.65 eV, and the work function was increased by 0.85 eV. Otherwise in the same manner as in Example 1, an organic electroluminescence device was obtained.

Example 3 An aqueous acetic acid solution (pH = 4) was used as the acid for the acid treatment,
The surface of the anode 6 was acid-treated by exposing the TO glass substrate at room temperature for 10 minutes. By performing the acid treatment in this way, the work function of the anode 6 became 5.60 eV, and the work function was increased by 0.80 eV. Otherwise in the same manner as in Example 1, an organic electroluminescence device was obtained.

Example 4 Polystyrenesulfonic acid (M
(W = 100000) was dissolved in a mixed solution of 10 g of water and 7.9 g of methanol to obtain a polymer organic acid solution (pH = 2). This solution was dropped on the anode 6 of the ITO glass substrate, and the spin coater was used at 2000 rpm and 1 rpm.
The polymer organic acid film 5b was formed to a thickness of 50 ° by spin coating under the conditions of minutes. By performing the acid treatment in this manner, the work function of the anode 6 is 5.68 eV.
And the work function increased by 0.88 eV. Otherwise in the same manner as in Example 1, an organic electroluminescence device was obtained.

Example 5 An ITO glass substrate was placed for 1 minute.
Oxygen plasma treatment was performed. After the oxygen plasma treatment, an acid treatment was performed in the same manner as in Example 1. By performing the acid treatment in this manner, the work function of the anode 6 becomes 5.7.
4 eV, and the work function increased by 0.94 eV.
Otherwise in the same manner as in Example 1, an organic electroluminescence device was obtained.

Example 6 1 g of nitric acid (pH <1) and 3-g
1 g of aminopropyltriethoxysilane ("A1100" manufactured by Nippon Unicar) was mixed. Add IT
After dipping the O glass substrate for 10 seconds, the surface of the anode 6 was subjected to an acid treatment and a coupling agent treatment by performing a drying treatment. By performing the acid treatment in this manner, the work function of the anode 6 became 5.69 eV, and the work function was increased by 0.89 eV. Otherwise in the same manner as in Example 1, an organic electroluminescence device was obtained.

(Example 7) The anode 6 was produced in the same manner as in Example 1.
Was acid treated. By performing the acid treatment in this manner, the work function of the anode 6 became 5.72 eV, and the work function was increased by 0.92 eV. One minute after the acid treatment as described above, PEDOT (manufactured by Bayer Corporation) was placed on the anode 6 of the ITO glass substrate for 2500 minutes without washing.
The hole transport layer 4 was formed as a conductive polymer buffer layer having a thickness of 400 ° by spin coating under the conditions of rpm and 1 minute, and dried at 150 ° C. for 15 minutes in a nitrogen atmosphere. Thereafter, the organic light-emitting layer 3 and the electron transport layer 2 and the cathode 1 were formed in the same manner as in Example 1 to obtain an organic electroluminescence device.

Example 8 An organic electroluminescent device was obtained in the same manner as in Example 1, except that the organic light emitting layer was formed as follows. That is, the α-NPD was deposited on an ITO glass substrate at a deposition rate of 1 to 2 ° / s to form a hole transport layer 4 having a thickness of 300 °. Then, as a yellow light emitting layer, a layer obtained by doping rubrene (manufactured by Across Corporation) at 1% by mass to α-NPD with a thickness of 100 ° is laminated, and then as a blue light emitting layer, a distyrylbiphenyl derivative (DPVBi: manufactured by Idemitsu Kosan) DSA derivative having a carbazolyl group at the terminal (BCzVBi: manufactured by Idemitsu Kosan)
Was doped at a thickness of 500 °. Thereafter, as an electron transport layer, bathophenanthroline (manufactured by Dojindo Laboratories Inc.) and Cs were mixed at a molar ratio of 1: 1 to 2
The cathode 1 was deposited by co-evaporation at a thickness of 00 °, followed by deposition of Al at a thickness of 1500 ° at a deposition rate of 10 ° / s.
Was formed.

Comparative Example 1 An organic electroluminescent device was obtained in the same manner as in Example 1, except that the ITO glass substrate was not subjected to the acid treatment.

(Comparative Example 2)
After acid treatment of the glass substrate, the substrate was ultrasonically washed with pure water, acetone and isopropyl alcohol for 15 minutes each, and dried. Even if the acid treatment is performed, the work function of the anode 6 becomes 4.95 eV and the work function is increased only by 0.15 eV by performing the cleaning. Otherwise in the same manner as in Example 1, an organic electroluminescence device was obtained.

(Comparative Example 3) ITO in the same manner as in Example 1
After acid treatment of the glass substrate, it was left at room temperature for 10 days.
Even if the acid treatment is performed, the work function of the anode 6 becomes 5.05 V and the work function is increased only by 0.25 eV after being left for 10 days. Otherwise in the same manner as in Example 1, an organic electroluminescence device was obtained.

Comparative Example 4 An organic electroluminescent device was obtained in the same manner as in Example 7, except that the ITO glass substrate was not subjected to the acid treatment.

Comparative Example 5 An organic electroluminescent device was obtained in the same manner as in Example 8, except that the ITO glass substrate was not subjected to the acid treatment.

The above Examples 1 to 8 and Comparative Examples 1 to
The organic electroluminescent device produced in Comparative Example 5 was connected to a power supply (KEYTHLEY236 model), and the luminance of the device was measured with a luminance meter (“LS-110” manufactured by Minolta). Further, a voltage at which the luminance became 1 cd / m ² was measured as a light emission starting voltage, and a 6 V current density was measured. Further, a life test was performed by continuously driving the fabricated device at a constant current of 10 mA / cm ² , a half life until the luminance was reduced to half, and a change in driving voltage after the half life was measured. Table 1 shows the results and the work function.

[0060]

[Table 1]

As shown in Table 1, in each of the examples, the work function of the anode was increased by 0.5 eV or more by the acid treatment, and the light emission starting voltage and the luminance were lower than those of the comparative examples. , The half-life is long, and the increase in resistance is small.

For the white light emitting devices of Example 8 and Comparative Example 5, the chromaticity coordinates at 100 cd / m ² before and after the life test were measured with a “multi-channel analyzer PMA-10” manufactured by Hamamatsu Photonics. The results are shown in Table 2.

[0063]

[Table 2]

As can be seen from Table 2, it is confirmed that Example 8 has higher chromaticity stability than Comparative Example 5.

[0065]

As described above, the organic electroluminescent device according to the first aspect of the present invention is an organic electroluminescent device formed by providing an organic light emitting layer between an anode and a cathode. Since the function is 0.5 eV or more larger than that before the processing, the efficiency of hole injection from the anode can be increased, and the device drive voltage can be reduced. It is possible to improve the life characteristics and the chromaticity stability at the time and suppress the increase in resistance as much as possible.

The organic electroluminescent device according to claim 2 of the present invention is an organic electroluminescent device formed by providing an organic light emitting layer between an anode and a cathode. Since the organic light-emitting layer and the cathode are stacked on the held anode, the efficiency of hole injection from the anode can be increased, and the device drive voltage can be reduced. It is possible to improve the life characteristics and chromaticity stability during continuous driving and to suppress the increase in resistance as much as possible.

The invention according to claim 3 is characterized in that the acid used for the acid treatment is an inorganic protonic acid, so that the effect of increasing the work function of the anode can be effectively obtained by the acid treatment. .

Further, the invention of claim 4 is characterized in that the acid used in the acid treatment is an organic acid, so that the effect of increasing the work function of the anode can be effectively obtained by the acid treatment.

The invention of claim 5 is characterized in that the acid used for the acid treatment is a high molecular organic acid, and the high molecular organic acid is held in a film on the surface of the anode. Acid is easy to form and fix a film on the surface of the anode, and can stably obtain the effect of increasing the work function of the anode by the acid treatment.

Further, the invention of claim 6 is characterized in that the film thickness of the high molecular organic acid is 1 ° to 100 °, so that the effect of increasing the work function of the anode by the high molecular organic acid can be effectively obtained. You can do it.

The invention of claim 7 is characterized in that the acid used for the acid treatment has a pH of 6 or less, so that the effect of increasing the work function of the anode by the acid treatment can be effectively obtained. is there.

The invention of claim 8 is characterized in that the surface of the anode is treated with a silane coupling agent, so that the silane coupling agent improves the adhesion between the anode and an organic layer such as an organic light emitting layer. The acid treatment can effectively increase the work function of the anode by the acid treatment.

According to a ninth aspect of the present invention, in the method of manufacturing an organic electroluminescent device, when the organic light emitting device is laminated on the anode, the anode is subjected to an acid treatment, and then the organic light emitting device is kept on the surface of the anode while holding the acid. Since the light emitting layer is formed, the work function of the anode can be increased by 0.5 eV or more without the problem of contamination such as residual carbon due to cleaning, and the efficiency of hole injection from the anode can be significantly improved. It is possible to reduce the element drive voltage, and it is also possible to improve the life characteristics and chromaticity stability at the time of continuous driving and suppress the increase in resistance as much as possible. Things.

Further, the invention according to claim 10 is that, before the acid treatment,
Since the anode is subjected to plasma treatment, the surface of the anode is made hydrophilic by oxygen plasma treatment to increase the affinity of the acid treatment, and the acid can be firmly immobilized on the anode surface,
The effect of increasing the work function of the anode by the acid treatment can be effectively obtained.

According to the eleventh aspect of the present invention, since the organic light emitting layer is formed within one week after the acid treatment of the anode, the effect of increasing the work function of the anode by the acid treatment can be effectively obtained. Can be done.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an example of an embodiment of the present invention.

FIG. 2 is a schematic diagram of another example of the embodiment of the present invention.

FIG. 3 is a sectional view of still another example of the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cathode 2 Electron transport layer 3 Organic light emitting layer 4 Hole transport layer 5 Acid treatment layer 5b High molecular organic acid thin film 6 Anode 7 Substrate

Continued on the front page (72) Inventor Junji Kido 9-4-3, Mamikita, Koryo-cho, Kitakatsuragi-gun, Nara Prefecture (72) Inventor Yukihiro Kondo 1048 Odakadoma, Kazuma, Osaka Prefecture Matsushita Electric Works, Ltd. (72) Invention Person Yasuhisa Kishigami 1048 Kadoma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Works, Ltd. (reference) 3K007 AB02 AB04 AB06 AB11 AB18 BB01 BB04 CA01 CB01 CB03 CC00 DA01 DB03 EB00 FA01

Claims (11)

[Claims] 1. An organic electroluminescent device formed by providing an organic light emitting layer between an anode and a cathode,
The work function of the anode is 0.5e lower than that before treatment by acid treatment.
An organic electroluminescence device characterized in that it is larger than V. 2. An organic electroluminescent device formed by providing an organic light emitting layer between an anode and a cathode,
An organic electroluminescent device, wherein an anode is subjected to an acid treatment and an organic light emitting layer and a cathode are laminated on the anode holding the acid. 3. The organic electroluminescent device according to claim 1, wherein the acid used for the acid treatment is an inorganic protonic acid. 4. The organic electroluminescent device according to claim 1, wherein the acid used for the acid treatment is an organic acid. 5. The organic electroluminescence according to claim 1, wherein the acid used for the acid treatment is a polymer organic acid, and the polymer organic acid is held in a film on the surface of the anode. element. 6. The organic electroluminescent device according to claim 5, wherein the thickness of the high molecular weight organic acid is 1 ° to 100 °. 7. The organic electroluminescent device according to claim 1, wherein the acid used for the acid treatment has a pH of 6 or less. 8. The organic electroluminescence device according to claim 1, wherein the surface of the anode is treated with a silane coupling agent. 9. A method for manufacturing an organic electroluminescent device by laminating an organic light emitting layer on an anode and laminating a cathode on the organic light emitting layer, the method comprising: A method for producing an organic electroluminescent device, comprising forming an organic light-emitting layer while holding an acid on the surface of an anode after the treatment. 10. The method of claim 9, wherein the anode is subjected to a plasma treatment before the acid treatment. 11. The method for producing an organic electroluminescent device according to claim 9, wherein the organic light emitting layer is formed within one week after acid treatment of the anode.