JP2000340367A - Organic electroluminescence device and method of manufacturing the same - Google Patents

Abstract

(57) [Abstract] (with correction) [PROBLEMS] To develop a more efficient and stable surface modification method of an anode substrate. Provided is an organic electroluminescence device capable of improving the performance of an organic electroluminescence device, particularly, a drive voltage, a drive life, and a storage life, and realizing practical drive stability and an operation voltage. SOLUTION: An organic electroluminescence element in which at least an anode 2 mainly composed of a metal oxide, an organic electroluminescence medium layer including at least a molecular vapor deposition film layer, and a cathode are sequentially laminated on a transparent substrate 1 is provided. The surface of the anode is modified with nitrogen oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence (hereinafter, also referred to as "organic EL") element used as various display devices such as a monochrome or color display for information equipment, a sign, and a television, and a method of manufacturing the same. About.

[0002]

2. Description of the Related Art In recent years, an organic electroluminescent element, which is a light emitting device including an organic material layer, has been attracting attention, and research has been conducted for use in displays and the like. 2. Description of the Related Art Organic light-emitting devices have attracted attention as all-solid-state spontaneous light-emitting devices, as high-visibility displays that take advantage of features such as high luminance, low voltage, and high luminescence response. Organic EL
The element generally has a first electrode on a substrate, an organic EL medium,
It has at least a structure in which a second electrode and a second electrode are laminated, and a direct current voltage is applied between the first electrode and the second electrode so that the organic E
A desired light emission is obtained by applying a direct current to the L medium.

[0003] Since the anode used in the organic EL element is required to have transparency and electric conductivity in the visible light region, the main materials are indium-tin oxide, indium zinc oxide, tin oxide and the like. Metal oxides. These anodes are used after being formed in a desired shape on a transparent substrate such as glass.

[0004] When forming a thin film comprising an organic EL medium, particularly a low-molecular vapor-deposited film on the surface of the anode, it is an important technique to control the lamination interface. A laminated low molecular weight organic light-emitting device having a typical structure of anode / hole injection / transport layer / electron injection / transport light emitting layer / cathode will be described as an example. For example, phthalocyanine compounds such as copper phthalocyanine, titanyloxyphthalocyanine and metal-free phthalocyanine, or aryldiamine compounds and aryltriamine compounds such as tetraphenylbenzidine and N, N′-dinaphthyl-N, N′-diphenylbenzidine. When the hole injection transport layer is formed on the anode,
The hole injecting property at the anode / hole injecting / transporting layer interface greatly affects the initial performance such as the light emission starting voltage and the light emission quantum efficiency. In addition, the adhesiveness of the hole injection transport layer near this interface composed of a thermally heterogeneous metal oxide and a small organic molecule,
It is easily presumed that the thermal stability such as the filling rate, the crystalline state or the amorphous state is related to the storage stability and the driving stability of the organic EL device.

Therefore, as a method for controlling such an interface in the element manufacturing process, a dry cleaning method for the anode surface is effective. Generally, as a dry cleaning method for a substrate surface after a photolithography process, ultraviolet cleaning or plasma processing is known, and is practically used in a semiconductor or liquid crystal display manufacturing process. An example in which these treatments are applied to cleaning of a substrate of an organic EL device is disclosed in, for example, Japanese Patent Application Laid-Open No.
8, JP-A-9-23275, JP-A-10-261
484 and JP-A-10-255972.

[0006] These effects of the prior art are as follows, for example, as disclosed in JP-A-10-261484, when ultraviolet cleaning is used as a method for cleaning the anode surface.
Ozone and singlet excited oxygen atoms generated by exciting oxygen in the processing gas by ultraviolet rays decompose and remove hydrocarbons such as resist residues attached to the anode surface and clean the anode surface, It is said that the ionization potential of the anode surface changes accordingly.

[0007]

By applying the above-mentioned prior art to an organic EL device, a reduction in operating voltage and suppression of a decrease in luminance due to driving have been realized, but in a wide range of organic EL devices. However, it is not enough for practical use, and further improvement in luminance stability and reduction in operating voltage and power consumption have been expected.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to develop a more efficient and stable method for modifying the surface of the anode substrate, thereby improving the performance of the organic EL element, particularly, the driving voltage, the driving life, and the like. And to improve the shelf life.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the above-mentioned object can be achieved by performing nitrogen oxide modification on the anode substrate. It was completed. That is, the organic electroluminescence element of the present invention is formed by sequentially laminating at least an anode mainly composed of a metal oxide, an organic electroluminescence medium layer including at least a molecular vapor deposition film layer, and a cathode on a transparent substrate. In the organic electroluminescence element, the surface of the anode is modified with nitrogen oxide.

It is preferable that the molecular vapor deposition film layer contains a phthalocyanine compound as a main component.

Further, the method of manufacturing an organic electroluminescence device according to the present invention is characterized in that a nitrogen oxide modification is applied to the surface of the anode, and then a molecular vapor deposition film layer is formed.

In the production method of the present invention, the nitrogen oxide is modified by irradiating ultraviolet rays in a mixed gas atmosphere of nitrogen and oxygen, or after irradiating ultraviolet rays in an oxygen gas atmosphere, Can be suitably applied by substituting with a nitrogen-containing gas atmosphere.

According to the present invention, a low-molecular organic vapor-deposited film is formed on the surface of a metal oxide-based anode modified with a nitrogen oxide, whereby an interface between the metal oxide and the low-molecular organic is formed. , It is possible to control the adhesion, the filling rate, the crystalline state or the amorphous state of the hole injection transport layer. Although the detailed mechanism is still unknown, a relatively strong intermolecular force between a nitrogen oxide such as NO ₂ modified by a chemical bond on a metal oxide and a small organic molecule formed thereon by vapor deposition. It is considered that a thin film having a high density and a high packing ratio is realized by the interaction as compared with the case where the organic low molecule is directly formed on the metal oxide.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. However, the configuration of the organic EL element described below does not limit the applicable range of the present invention. The organic EL device shown in FIG. 1 includes a substrate 1, a transparent anode 2 formed on the substrate, and holes as organic films formed on a transparent electrode formed of the substrate 1 and the anode 2. Injection layer 3, hole transport layer 4 formed on hole injection layer 3, light emitting layer 5 which is an organic film formed on hole transport layer 4, and light emitting layer 5 Cathode 6 deposited on
The organic light-emitting device is formed by sequentially laminating the respective layers and finally sealing with the sealing plate 7.

The substrate 1 is made of glass or a highly transparent polymer. The anode 2 is mainly composed of a metal oxide, and may be an indium-tin oxide film, an indium zinc oxide film, or the like.

In the present invention, after forming the anode 2 on the substrate 1, the surface of the anode 2 is modified with nitrogen oxide. As a result, the filling rate, adhesion, and thermal stability near the interface between the nitrogen oxide such as NO ₂ modified on the metal oxide as the anode and the small molecule formed by vapor deposition on the oxide are It has been found that the properties are improved. In particular,
When the molecular vapor-deposited film layer is a vapor-deposited film mainly containing a phthalocyanine compound such as a crystalline molecule often used in an organic EL device, for example, copper phthalocyanine, titanyloxyphthalocyanine, or metal-free phthalocyanine, 2 to 10
X-ray diffraction and AFM (Atomic Force Microscopy) significantly improve the crystal orientation at the initial stage of thin film formation.
Have been found.

Means for realizing the nitrogen oxide modification on the anode surface according to the present invention include, for example, a method using a reactive gas and ultraviolet irradiation, and a method using a reactive gas and heat. From the viewpoints of homogeneity and controllability of the treatment effect, a method using a reactive gas and ultraviolet irradiation is preferable.

The ultraviolet light source used in the present invention is not particularly limited, but a low-pressure mercury lamp is preferred from the viewpoint of stability, irradiation intensity and economy.

As a first specific example of the method using the reactive gas and the ultraviolet irradiation, an operation of irradiating an ultraviolet ray in a pure oxygen gas atmosphere and a subsequent operation of replacing the atmosphere gas with a nitrogen-containing gas are used. A method of subjecting the surface to nitrogen oxide modification can be used. The modification is performed by a reaction between the anode surface chemically activated by ozone or singlet excited oxygen generated by irradiating ultraviolet rays in an oxygen atmosphere and nitrogen molecules.

As a second specific example of the method using the reactive gas and ultraviolet irradiation, there is a method using at least an operation of irradiating the substrate on which the anode is formed with ultraviolet light in a mixed gas atmosphere of nitrogen and oxygen. As can be understood from the first example described above, it is necessary for oxygen gas to occupy a certain mixing ratio in order to activate the metal oxide surface. At the same time, it also has the effect of removing organic substances such as resist residues in the photolithography process attached to the anode surface. From the above viewpoint, the oxygen ratio in the mixed gas of nitrogen and oxygen is preferably 1 to
The concentration is 90% by volume, more preferably 5 to 20% by volume, which is equivalent to the concentration of the atmospheric component from the viewpoint of safety.

In the above first and second operations, the modification of the anode interface by the nitrogen oxide having physical adsorption or chemical bond is identified by high vacuum thermal desorption spectrometry (U.S. Pat.
HV-TDS), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), and X-ray photoelectron spectroscopy (XPS).

The substrate, which has been subjected to the nitrogen oxide modification step using ultraviolet irradiation as described above, is used as quickly as possible in the step of forming a low-molecular vapor deposition film while minimizing recontamination and adsorption of moisture by hydrocarbon compounds. It is preferable to introduce into a vapor deposition apparatus to be used. However, in a clean room environment of a general class of about 1000, the modification effect is maintained even after exposure to the environment for about several tens of minutes. No special operation such as load lock is required.

An important point in maintaining the above-mentioned modifying effect is that an oil pump such as a cryopump, a terpomolecular pump, a dry pump or the like is used as an exhaust system of a vacuum device or a vapor deposition device used for carrying out load lock. The point is to use a free one. When using an oil pump, the partial pressure of organic substances and moisture existing in a vacuum environment
This is because it is not preferable from the viewpoints of the continuation of the modification effect and the continuation of the clean substrate surface.

With the above considerations in mind, after the end of the nitrogen oxide modification step using, for example, ultraviolet irradiation,
When introduced directly into the vapor deposition apparatus using a turbomolecular pump and a dry pump as an exhaust pump via the atmosphere, the duration of the above-described modification effect for several hours to about 10 hours and the duration of the clean substrate surface are both increased. The realization has been confirmed analytically.

Examples of the material for the hole injection layer 3 include phthalocyanine compounds such as copper phthalocyanine, titanyloxyphthalocyanine and metal-free phthalocyanine, or tetraphenylbenzidine, N, N'-dinaphthyl-N, N'-diphenyl. Examples include aryldiamine-based compounds and aryltriamine-based compounds represented by the following general formulas (1) and (2), such as benzidine. (Wherein, A ^{1 to} A ⁴ each independently represent an aryl group which may have a substituent having 6 or more carbon atoms, and B represents at least one arylene group which may have a substituent having 6 or more carbon atoms. Represents.) (Wherein, A ^{5 to} A ¹⁰ each independently represent an aryl group which may have a substituent having 6 or more carbon atoms, and B represents at least one arylene group which may have a substituent having 6 or more carbon atoms. Represents.)

Examples of the material for the hole transport layer 4 include the compounds represented by the above general formulas (1) and (2) such as copper tetraphenylbenzidine and N, N'-dinaphthyl-N, N'-diphenylbenzidine. Aryldiamine-based compounds and aryltriamine-based compounds.

As a material used for the light emitting layer 5, tris (8-hydroxyquinoline) aluminum (so-called Alq
3) a single film or a mixed film in which a fluorescent dye is dispersed in Alq3;

As the cathode 6, aluminum alone, an alloy of aluminum with another low work function metal, an alloy of magnesium with another low work function metal, or the like is used.

For the sealing plate 7, a material such as glass or stainless steel, which has a very low transmittance of oxygen and moisture, is used.
In addition, it is preferable to use a sealing adhesive used for a liquid crystal display or the like at the joint between the substrate 1 and the sealing plate 7.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. In the following Examples 1 and 2, two samples were prepared, one was used for analysis and evaluation, and the other was used for device performance evaluation. Example 1 An indium zinc oxide (IDI) was used as a transparent conductive film as an anode on a glass transparent substrate (Corning 1737).
XO, manufactured by Idemitsu Kosan Co., Ltd.) was formed to a thickness of about 100 nm at room temperature by a sputtering method. Next, a positive photoresist (OFPR-800, manufactured by Tokyo Ohka Kogyo Co., Ltd.)
Was applied to a thickness of about 1 μm using a spin coater, prebaked in a hot air circulation oven, and exposed using a photomask having a pattern with a pitch of 4 mm and a line width of 2 mm on a display unit. . This is used as a developer (NMD-
3, developed by Tokyo Ohka Kogyo Co., Ltd.), and after etching using oxalic acid, the photoresist was peeled off to form a metal pattern.

The substrate with electrodes was carried into an ultraviolet irradiation device, and a surface modification treatment was performed. The atmosphere was an oxygen / nitrogen mixed gas (oxygen ratio = 20% by volume), and was performed at atmospheric pressure using a low-pressure mercury lamp as an ultraviolet lamp.

After performing the above-mentioned treatment, the substrate with electrodes was placed in the substrate loading chamber of the vapor deposition apparatus. Note that the film forming apparatus used in this example has a structure in which the substrate can move between the cleaning chamber and the film forming chamber via the center chamber. It is possible to continuously form the organic EL medium and the cathode without touching the substrate.

Immediately after loading into the substrate loading chamber, evacuation was started to reach a degree of vacuum of 5 × 10 ⁻⁵ Pa level. After performing the processing up to this point on two samples simultaneously, 1
The sheet is immediately vacuum transferred to the film forming chamber to start evaporation, and
The sheet was taken out and subjected to surface analysis.

The film is formed by the structure shown in FIG.
Equation (3) below, 100n of copper phthalocyanine (CuPc) represented by
m, the following formula (4) as the hole transport layer 4: N, N′-dinaphthyl-N, N′-diphenylbenzidine (α-NPD) represented by the following formula: 40 nm of tris (8-hydroxyquinoline) aluminum (Alq3) represented by the following formula and a trace amount of coumarin 6 added as a fluorescent dye, and 200 nm of an AlLi alloy (Li ratio = 0.5 atomic%) as a cathode 6, The film formation was performed by using a resistance heating evaporation method in separate film forming chambers.

Finally, the substrate is taken out of the vapor deposition apparatus and transferred to a sealing apparatus having a water concentration of 10 ppm or less.
A room-temperature curing adhesive was applied to the edge of the substrate, and a glass sealing plate as the sealing plate 7 was bonded to perform sealing.

Example 2 Evacuation was started immediately after charging into the substrate charging chamber, and 5 × 10
After reaching a degree of vacuum of ⁻⁵ Pa level, 5 × 10 ⁻⁵
The substrate was stored under vacuum for 96 hours while maintaining the degree of vacuum of ８8 × 10 ⁻⁶ Pa. After the above-described processes were simultaneously performed on the two samples, one was immediately vacuum-transferred to a film forming chamber to start vapor deposition, and the other was taken out and subjected to surface analysis. An element was manufactured in the same manner as in Example 1 except for the above changes.

For the analysis of the surface analysis samples prepared in Examples 1 and 2, high vacuum TDS, TOF-SIMS,
And XPS. As a result of the analysis, the hydrocarbon ratio on the substrate surface in Examples 1 and 2 was minute without significant difference, and NO
_In Example 2, only the ratios of ₂ and NO ₃ were the same as those of Example 1
/ 3).

From the results of this analysis, it can be seen that the long-term high-vacuum storage in the substrate loading chamber performed in Example 2 did not suffer from contamination by hydrocarbon compounds, and only reduced the amount of nitrogen oxide modification. It was confirmed that an anode substrate different from No. 1 was formed. In other words, this indicates that a control experiment was established in which the difference in device performance between Examples 1 and 2 was caused by the difference in the amount of nitrogen oxide modification.

Next, with respect to the evaluation of the device performance of Examples 1 and 2, the measurement method and the results will be described below. (1) Luminance-voltage characteristics: frequency 60 Hz, duty 1
The peak luminance was evaluated with a defective lamp during the period of / 100. The results are shown in FIG. 2 for the voltage-luminance characteristics. Note that the unit of luminance (arb.units) in the figure represents an arbitrary intensity. As can be seen from FIG. 2, in Example 1 in which the amount of nitrogen oxide modification was large, a remarkable improvement in voltage-luminance characteristics was observed as compared with Example 2. (2) Constant current drive life characteristics: current density 10 mA / cm ²
Under the accelerated condition, in a constant temperature and humidity room at a temperature of 20 ° C. and a humidity of 40%, the brightness was lit continuously, and the luminance half-lives were compared. still,
The initial luminance was about 1200 cd / m ² in both Examples 1 and 2. The results are shown in Table 1 below.

[0040]

[Table 1]

As shown in Table 1 above, in Example 1 in which the amount of nitrogen oxide modification was large, a remarkable improvement in the constant current drive life characteristic was observed as compared with Example 2.

From the above results, it is clear that the modification of the nitrogen oxide on the anode surface according to the present invention has a remarkable effect on improving the performance of the organic EL device, and that the higher the amount of modification, the better the effect can be obtained. Is clear.

[0043]

According to the present invention, by forming a molecular vapor-deposited film layer after performing nitrogen oxide modification on the anode surface,
Organic EL that can achieve practical drive stability and operating voltage
An element and a method for manufacturing the same can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of the structure of an organic EL device according to the present invention.

FIG. 2 is a graph showing voltage-luminance characteristics of Example 1 and Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Hole injection layer 4 Hole transport layer 5 Light emitting layer 6 Cathode 7 Sealing plate

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yotaro Shiraishi 1-1-1 Tanabe Shinda, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture F-term within Fuji Electric Co., Ltd. (reference) 3K007 AB00 AB14 AB15 BB01 CA01 CA05 CB01 DA00 DB03 FA01 FA03

Claims (5)

[Claims] 1. An organic electroluminescence device comprising: a transparent substrate, at least an anode mainly composed of a metal oxide, an organic electroluminescence medium layer including at least a molecular vapor-deposited film layer, and a cathode sequentially laminated. An organic electroluminescence device, wherein the surface of the anode is modified with nitrogen oxide. 2. The organic electroluminescence device according to claim 1, wherein the molecular vapor deposition film layer contains a phthalocyanine compound as a main component. 3. The method for manufacturing an organic electroluminescence device according to claim 1, wherein the molecular deposition film layer is formed after the nitrogen oxide modification is performed on the surface of the anode. A method for manufacturing a luminescence element. 4. The method for producing an organic electroluminescence device according to claim 3, wherein said nitrogen oxide modification is performed by irradiating ultraviolet rays in a mixed gas atmosphere of nitrogen and oxygen. 5. The method for producing an organic electroluminescence device according to claim 3, wherein the nitrogen oxide modification is performed by irradiating ultraviolet rays in an oxygen gas atmosphere and then replacing the oxygen gas atmosphere with a nitrogen-containing gas atmosphere. .