JP6199059B2 - Organic electroluminescence device and method for manufacturing the same - Google Patents

Description

  The present invention relates to a method for producing a multilayer organic electroluminescence device including a low molecular weight organic material layer having a molecular weight of 2,000 or less using an electrospray (ES) method, and a multilayer organic electroluminescence device produced by the production method About.

  An organic electroluminescence (hereinafter sometimes abbreviated as “organic EL”) element is injected into an organic thin film from both electrodes by providing electrodes on both surfaces of a thin film made of an organic material and applying a voltage between the electrodes. Current-driven light-emitting elements that use light emission due to recombination of charge (electrons and holes), and are thin and light-weight displays and lighting because of high light emission brightness at low voltage and high visibility due to self-light emission Application research is actively promoted.

  Currently, organic thin film formation methods mainly used for organic EL device fabrication include a dry process typified by vacuum deposition and a wet process typified by spin coating. The dry process is a film formation process that uses relatively low molecular weight organic materials. The film thickness can be easily controlled, and can be applied separately using a mask with an appropriate opening. A laminated structure of organic materials with different properties. It is easy to create. Of these, the “multi-layer technology” that allows easy creation of a laminated structure is particularly important, and this technology particularly improves the light emission efficiency and element life of organic EL, making it a practical device for many applications. It has made a leap forward until it is adopted. However, since this technology requires a vacuum device, the initial introduction and maintenance cost of the device is expensive, and it is difficult to use a large substrate, which restricts improvement of productivity, that is, improvement of manufacturing cost. It is said that there is.

  On the other hand, the wet process is suitable for mass production because it can be applied to polymer materials with excellent physical stability such as film formability and heat resistance, and the equipment is simple and does not require a special atmosphere such as vacuum. It is said to be suitable for energy-saving and low-cost product manufacturing. However, in order to achieve higher efficiency and longer life, it is important to produce a laminated structure made of materials having different properties as described above. However, in the wet process, the upper layer coating solvent is used for the lower layer. The organic material is eluted or the lower layer is peeled off by permeation. In order to suppress these phenomena, additives such as cross-linking curing agents are sometimes used. However, these additives are known to hinder the light emitting function, and a high-performance multilayer without impairing the device function. It is extremely difficult to realize the structure.

  On the other hand, a plurality of proposals have been made to use the ES method for manufacturing an organic semiconductor thin film element such as an organic EL because a pattern can be easily created. The ES method is a method in which a solution in which a functional material is dissolved is sprayed on a substrate while applying a high voltage between a conductive substrate and a nozzle that discharges the solution. In this method, the charged solution is repelled and dispersed into fine nano-order level droplets to form fine nano-order level droplets, and the solvent evaporates as the surface area increases rapidly. Since only a solute (functional material) in the solution adheres to the substrate in a substantially dry state to form a uniform layer, it is useful for laminating a plurality of layers.

Patent Document 1 describes that the coating liquid used in the ES method contains a solvent having a vapor pressure of 500 Pa or less at room temperature. Patent Document 2 describes that charge application and ejection are performed stepwise on the ES raw material liquid. Furthermore, Patent Document 3 describes an invention relating to a device having a charge transport function, particularly an electrophotographic photosensitive member.
Non-Patent Documents 1 and 2 describe production of an organic EL element using a polymer organic EL material.

Patent Document 4 discloses a method for producing an organic EL device using a low molecular weight organic material similar to that of the present invention, but the surface of a substrate such as an electrode or an inorganic material has a hydrophilic surface. In addition, it is difficult to directly form a thin film of a low molecular weight organic material by the ES method, and information on the necessity of surface modification is not disclosed. Also, no information is disclosed regarding the properties of solvents that can be suitably used in the ES method. In Non-Patent Document 3, the dielectric constant (εm) of the mixed solvent is indicated by the sum of the dielectric constants (ε ₁ , ε ₂ ) and volume fractions (φ ₁ , φ ₂ ) of the mixed solvents. It is shown.

JP 2007-305507 A JP 2009-43561 A JP 2009-251386 A WO2011-001613

R. Saf et al., Nature Materials, vol. 3, p323 (2004) J. Ju, Y. Yamagata and T.K. Higuchi, Adv. Mater., Vol. 21, p 4343 (2009) A. Joyban et al., International Journal of Pharmaceuticals, vol. 269, p353 (2004)

  An object of the present invention is to produce a multilayer organic EL light emitting device having a low molecular weight organic material layer having a molecular weight of 2,000 or less by the ES method.

  The ES method is characterized by the fact that the solute dissolved in the solvent is almost dry when it reaches the substrate (landing), but at the same time, there is no buffering action of the solvent or the like. It is considered that the material and the properties of the substrate surface are more strongly influenced by the process.

  That is, N, N′-bis (naphthalen-1-yl) is formed on the surface of a hydrophilic electrode such as ITO (indium-tin alloy) whose surface is cleaned by a cleaning method generally used in organic EL device fabrication. -N, N′-bis (phenyl) -benzidine (α-NPD) and N, N′-bis (3-methylphenyl) -N, N′-bis (phenyl) -benzidine (TPD) The low-molecular-weight organic EL material having a strong property has the property that the sprayed fine particles do not become a thin film but form a network-like aggregated structure, and when spraying continues, an insulating thick film is formed.

  In the ES method, the charged droplets repel and disperse with each other, so that the surface area increases rapidly, and along with this, the solvent is volatilized and a fine solute is deposited. For this reason, the coating solution is easily charged, that is, a highly polar solvent such as water, acetic acid, formic acid and other organic acids, methanol, ethanol, isopropanol and other alcohols, acetonitrile, dimethylformamide (DMF), dimethylsulfo. A highly polar aprotic solvent such as xoxide (DMSO) or a mixture thereof is employed.

  On the other hand, low molecular weight organic semiconductor materials that form amorphous thin films by vapor deposition under high temperature vacuum cause high boiling points and high melting points due to intermolecular interactions such as hydrogen bonding, and decomposition phenomena due to decarbonation and dehydration. Most low-polar molecules do not have high-polar functional groups such as carboxylic acid groups (COOH groups) or alcohol groups (OH groups) in the molecular structure as the starting point. Polar solvents such as toluene and xylene are used.

  That is, when a thin film made of an organic EL material is to be formed using the ES method, it is necessary to prepare a solution having both sprayability and material solubility. However, the knowledge about film formation using the conventional ES method is based on the assumption of the use of high molecular weight materials, and the quantitative index to determine what kind of solvent is suitable for low molecular weight materials is not exist.

  As a result of intensive studies by the present inventors in view of such a situation, when forming an organic semiconductor thin film on an electrode surface having a hydrophilic surface using the ES method, the hydrophilic electrode surface is made hydrophobic with a surface modifier. There are two conflicting requirements: control, necessities to ensure sprayability (= high polarity solvent, hydrophilicity), and requirements to ensure solubility (= low polarity solvent, hydrophobicity) By designing the coating liquid using the dielectric constant of the solvent as an index to find a solvent system that can satisfy both, the inventors have found the conditions for forming a highly smooth thin film with suppressed aggregation, and have completed the present invention. .

  The present invention relates to a method for producing an organic electroluminescence device having a plurality of organic material layers between an anode and a cathode, wherein the surface of the electrode having a hydrophilic surface with a water contact angle of less than 70 degrees is formed by a surface modifier. After adjusting the contact angle of water to 70 degrees or more and less than 100 degrees, the film is formed by electrospray using a solution in which a charge transport material having a molecular weight of 2,000 or less is dissolved in a solvent in contact with this electrode. It is a manufacturing method of an organic electroluminescent element.

  In the method for manufacturing the organic electroluminescence element, the solvent for dissolving the charge transport material is preferably a solvent having a dielectric constant of 5.5 to 18.0.

In the method for producing an organic electroluminescence device, the surface modifier is a self-assembled monomolecule capable of adjusting an electrode surface having a hydrophilic surface with a water contact angle of less than 70 degrees to a water contact angle of 70 degrees to less than 110 degrees. A film (SAM) forming material is used. Hexamethyldisilazane (HMDS) or n-octylphosphonic acid (OPA) is preferred .

  According to the present invention, a high-performance multilayer organic EL device including a low molecular weight organic material layer using an electrospray method can be provided.

It is a schematic diagram for demonstrating the structure of ES apparatus. It is an atomic force microscope image of a surface when an organic semiconductor material solution is sprayed directly onto ITO having a hydrophilic surface by the ES method. It is an image figure of the surface movement of the particle | grains which reached | attained the board | substrate by ES method, aggregation, and solidification. It is the microscope picture of the surface which carried out ES spraying of the solution on the electrode which performed different surface treatment. It is a polarizing microscope photograph of the surface which carried out ES spraying of the solution on the electrode which performed different surface treatment.

Hereinafter, the present invention will be described in detail.
As described above, the ES method is characterized in that the solute (substrate) dissolved in the solvent is almost dry when the substrate lands, but at the same time, there is no buffering action of the solvent or the like. It is considered that the material and the properties of the substrate surface are more strongly influenced during the growth process.

  That is, on a so-called hydrophilic surface such as an ITO (indium-tin alloy) electrode whose surface is cleaned by a cleaning method generally used in the production of organic EL elements, etc., it has a strong hydrophobic property represented by α-NPD and TPD. In the low molecular weight organic semiconductor material, sprayed fine particles do not become a thin film but aggregate to form a network-like aggregated structure, and when spraying is continued, an insulating thick film is formed.

  FIG. 2 shows an atomic force microscope (AFM) image of a film obtained by spraying an α-NPD or TPD solution on the ITO surface by the ES method. In FIG. 2, (1) shows an α-NPD film, and (2) shows a TPD film. It can be seen that both are in a state of agglomerating in a network.

The ES spray conditions at the time of sample preparation are as follows.
Solution concentration: 0.05% by weight
Solvent composition (volume ratio): dichloromethane / DMF = 4/1 (ε = 14.9)
Applied voltage: 10 kV
Glass capillary tip diameter: 10 μm
Spray distance (distance from nozzle to substrate): 50 mm
Discharge time: 600 seconds

  The network-like aggregated state as shown in FIG. 2 indicates that when a low-polarity / hydrophobic low molecular weight organic semiconductor material lands on a highly polar and hydrophilic substrate, the particles are immobilized. It is thought that it does not become a thin film but moves and aggregates and solidifies on the surface.

FIG. 3 shows an image of aggregation and solidification from surface movement. The upper diagram in FIG. 3 shows an ideal film formation state, and the lower diagram shows an actual film formation state.
On the other hand, such a phenomenon has not been observed in a high molecular weight material excellent in film formability, and an ideal film can be formed, which is considered to be a phenomenon peculiar to a low molecular material.

  In the present invention, in order to suppress such agglomeration phenomenon and form a stable thin film, attention was paid to control of the properties (wetting properties) of the base.

  As described above, on the ITO having a hydrophilic surface, the sprayed TPD is in a network-like aggregated state, but when the surface is controlled to an appropriate hydrophobicity by the surface modifier, the TPD does not aggregate and the surface smoothness A thin film is formed. Here, the surface modifier as referred to in the present invention refers to those that reduce the hydrophilicity of the surface or improve the hydrophobicity. The thickness of the surface modifier layer is preferably about 1 nm to 1 nm so as not to affect the device performance as much as possible.

As the surface modifier, a self-assembled monolayer (SAM) forming material is preferably exemplified. Here, SAM is an abbreviation for Self-Assembles Monolayer and is a general term for monomolecular films formed by self-assembly and self-assembly on a solid surface in the process of chemical adsorption of organic molecules.
Organic sulfur molecules on the surface of the gold electrode are particularly famous as materials exhibiting such properties, but the hydrophilic electrode as in the present invention, that is, the oxide surface has carboxylic acid, phosphonic acid, phosphate ester, organic It is said that silane molecules and the like easily form SAM.

Table 1 shows the contact angles between various surface modifiers and their water and the film quality.
FIG. 4 (1) shows a photomicrograph of TPD directly sprayed on ITO with ES.
Further, (2) in FIG. 4 shows a photomicrograph of the state in which HMDS is adsorbed on ITO and then TSP is sprayed with ES, and (1) in FIG. (3) in FIG. 4 shows a micrograph of the state in which OPA is adsorbed on ITO and then TPD is sprayed with ES, and (2) in FIG. 5 shows a polarization micrograph thereof. (4) in FIG. 4 shows a photomicrograph of the state in which FOPA (fluorinated octylphosphonic acid ) is adsorbed on ITO and then TPD is sprayed with ES, and (3) in FIG. 5 shows a polarizing photomicrograph thereof.

The samples shown in Table 1 and FIGS. 4 and 5 show a state in which TPD is sprayed by the ES method after each surface modification treatment is performed on the cleaned ITO substrate. The spraying conditions of the ES method at this time are as follows.
TPD solution concentration: 0.07% by weight
Solvent composition (volume ratio): dichloromethane / DMF = 4/1
Applied voltage: 10 kV
Glass capillary tip diameter: 10 μm
Spray distance: 50mm
Discharge time: 600 seconds

The contact angle measurement conditions after each surface modification treatment on the cleaned ITO substrate are as follows.
Equipment used: DM-301, manufactured by Kyowa Interface Chemical Co., Ltd.
Solvent used: Water Measurement droplet volume: 1 μL
Measurement temperature: 25 ° C

  The gas phase adsorption method here refers to a method in which a modifier (in this experiment, HMDS, OPA, FOPA) stock solution is placed in a small container such as a petri dish and the substrate before modification is partitioned into a large container. The properties of the substrate surface are improved by heat treatment. That is, the substrate is taken out after being heated in a container at 110 ° C. for 5 minutes to sufficiently adsorb the modifier vapor onto the substrate surface, and dried on a 110 ° C. hot plate for 5 minutes.

  As shown in FIGS. 4A and 4B, the surface smoothness in Table 1 indicates that the scattered light was not observed in the polarization image in the microscopic observation, and is shown in FIG. 4C. As described above, the case where scattered light was observed in the polarization image in the microscopic observation was taken as x.

  As described above, when an organic EL material thin film layer is formed by spraying on an electrode having high hydrophilicity by the ES method, it is necessary to treat the surface to an appropriate hydrophobic surface with a surface modifier. The coating method may be a dry process such as sublimation vapor deposition or a wet process such as spin coating, printing, or adsorption as long as it is other than the ES method, but the contact angle of the surface is 70 degrees or more. , Preferably 75 degrees or more, less than 110 degrees, preferably less than 105 degrees. Examples of coating methods other than the ES method include the methods described in CMC Publishing, “Latest technology of printable organic electronics”, 2008. Specifically, a dry process such as a sublimation vapor deposition method, a spin coating method, and the like. And wet processes such as an inkjet method, a nozzle printing method, a gravure printing method, and a slit coating method.

  Preferred surface modifiers include low molecular weight organic materials that can impart moderate hydrophobicity, so-called self-assembled monolayer materials. More preferably, silylating agents such as hexamethyldisilazane (HMDS), trimethylsilyl chloride, N, N′-bis (trimethylsilyl) urea, octylphosphonic acid (OPA), tetradecylphosphonic acid (TDPA), hexadecyl Phosphonic acids such as phosphonic acid (HDPA) can be used.

  At least one organic layer (an organic material layer including a charge transport material) is provided by an ES method in contact with an electrode having a surface contact angle of 70 degrees or more. When there are a plurality of organic layers, the first layer in contact with the electrode is the modified layer, the second layer in contact with the modified layer is the organic layer (2), and the third layer in contact with the organic layer (2) is the organic layer. In the same manner, it is preferable to form the organic layer (n) up to the nth layer. Here, if the contact angle of the organic layers (2) to (n-1) is 70 degrees or more and 110 degrees or less, the next organic layer formed thereon is also preferably formed by the ES method. When an organic layer having a contact angle of 70 degrees or more and 110 degrees or less cannot be obtained, the surface can be modified by vapor deposition or adsorption similarly to the modification of the electrode surface.

Table 2 shows boiling points of various solvents, solubility of TPD and α-NPD which are typical organic semiconductor materials (charge transport materials), sprayability by ES method, and dielectric constant.
From this, regarding the sprayability, the lower limit of the dielectric constant of the solvent is in the range of THF (7.5) and chloroform (4.8), and regarding the solubility of TPD, the upper limit of the dielectric constant of the solvent is MEK ( 15.5) and IPA (18). In addition, it is preferable that the boiling point of the solvent used by ES method is 150 degrees C or less which can volatilize rapidly.

In Table 2, the solubility was evaluated as “◯” when dissolved at 1.0 mg / ml or more, and “×” when less than 1.0 mg / ml. As for the sprayability, a case where a fine and uniform conical mist-like spread (state as shown in FIG. 1) was generated by charging was indicated by ◯, and a case where droplets were dropped without being charged was indicated by ×.
The solubility and dielectric constant were measured at room temperature (25 ° C.). Moreover, the film formation by the ES method was also performed at room temperature (25 ° C.).

Furthermore, it is known that the dielectric constant (εm) of the mixed solvent is expressed as the sum of the dielectric constants (ε ₁ , ε ₂ ) and the volume fractions (φ ₁ , φ ₂ ) of the mixed solvents. Therefore, this was compared with the sprayability in the electrospray apparatus.
εm = ε ₁ φ ₁ + ε ₂ φ ₂ (A)

Table 3 shows toluene (ε = 2.4), dioxane (ε = 2.2), chloroform (ε = 4.8) as low dielectric constant (= low polarity) solvents, and high polarity (= high dielectric constant) solvents. As DMF (ε = 38) isopropyl alcohol (IPA, ε = 18), methyl ethyl ketone (MEK, ε = 15.5), and mixed at different volume ratios (1/5, 1/10, 1/20) The dielectric constant (calculated value) derived from the above formula (A) and sprayability are summarized.
In Table 3, the evaluation of sprayability is the same as in Table 2.

The spraying conditions for electrospray are as follows.
Discharge rate: 1 ml / hour Applied voltage: 8-12 kV
Glass capillary tip diameter: 10 μm
Spray distance: 50mm

  From these results, the lower limit of the dielectric constant that can be sprayed is within the range of 5.5 (dioxane / DMF = 10/1) and 5.4 (dioxane / IPA = 5/1, chloroform / IPA = 20/1). It can be seen that

  The solvent used in the present invention may be a single solvent or a mixed solvent, but dissolves a low molecular weight organic material as a charge transport material used to form an organic layer. It is selected from the inside. Since low molecular weight organic materials generally tend to dissolve in nonpolar solvents, a mixed solvent of a nonpolar solvent and a polar solvent is preferred. Many low-molecular-weight organic materials as charge transport materials can be sprayed well if the dielectric constant is in the above range, and therefore a solvent having a dielectric constant in this range is preferable.

  The charge transport material used for forming the organic semiconductor thin film layer by the ES method in the present invention is a low molecular weight organic material, and as such a material, a known organic EL material, that is, tris (8-hydroxy-quinolinato) is used. ) Aluminum (Alq3, molecular weight 459.4), 2-tertiarybutyl-9,10-di (naphth-2-yl) anthracene (TBADN, molecular weight 486.6), 1,4-bis (4- (9H- Fluorescent organic compounds such as carbazol-9-yl) styryl) benzene (BCzSB, molecular weight 612.76), 4,4′-bis (carbazol-9-yl) biphenyl (CBP, molecular weight 484.59), tris ( Phosphorescent organic compounds such as 2-phenylpyridine) iridium (III) (Ir (PPy3, molecular weight 696.86), TP D (molecular weight 516.7), α-NPD (molecular weight 588.7), 2,2 ′, 2 ′ ′-(1,3,5-benztolyl) -tris (1-phenyl-1-H-benzimidazole) ) (TPBi, molecular weight 654.76) and many other examples such as charge transporting organic materials.

  Furthermore, 2,2 ′, 7,7′-tetrakis [N-naphthalenyl (phenyl) -amino] -9,9′-spirofluorene (Spiro-2NPB, molecular weight 1185.5) and N, N′-bis (naphthalene) -2-yl) -N, N′-bis (phenyl) -tris (9,9′-dimethylfluorenylene) (BNP3FL, molecular weight 1013.3) and other materials having a molecular weight region exceeding 1000 can also be used. .

  Examples of the organic layer that can be formed using such a charge transport material include, but are not limited to, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer. These layers may be formed from a mixture of two or more kinds of low molecular weight organic materials, or may be formed from two or more organic layers.

  If the charge transport material is dissolved in the solvent at a concentration of about 0.01% by weight or more, it can be used in the present invention. However, in consideration of the film forming speed, the concentration is about 0.05 to 0.5% by weight. Is appropriate. On the other hand, a high concentration range of 0.5% by weight or more can be used if the material dissolves, but the range up to less than 1% by weight is suitable when considering the clogging at the tip of the microcapillary and the crystallinity of the material. It is believed that there is.

  As a substrate used for manufacturing the organic EL element, a glass substrate, a plastic film, or a sheet can be used. As the plastic, for example, polyethylene terephthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate and the like can be used. In addition, these films include a metal oxide such as silicon oxide that exhibits water vapor barrier properties and oxygen barrier properties, metal nitrides such as silicon nitride, polyvinylidene chloride, polyvinylene chloride, saponified ethylene-vinyl acetate copolymer. Layers are provided as needed.

  An anode is provided on the translucent substrate, and the material thereof is a transparent electrode such as ITO (indium tin composite oxide), IZO (indium zinc composite oxide), tin oxide, indium oxide, aluminum oxide composite oxide, etc. Material can be used.

  For electrospray devices, devices that used wire-like voltage application electrodes made of glass capillaries and platinum materials were used before, but now commercially available devices (eg Nanofiber spinning device SD series manufactured by MEC) Etc.) can also be used.

  A metal or glass capillary such as stainless steel having a tip diameter of about 1 μ to 1 mm can be used at the tip of the spray nozzle. However, a glass capillary of about 1 μ to 50 μm is used for forming a nano-level thin film as in the present invention. Is preferred.

  The distance between the conductive substrate and the tip of the spray nozzle is about 30 mm to 100 mm, and the sample solution is discharged as a spray frame by applying a voltage of about 1 kV to 30 kV therebetween.

  In order to prevent disproportionation due to spraying, the voltage application unit can be moved in the lateral direction or sprayed while rotating the conductive substrate.

  In the present invention, the surface of the electrode on the substrate, preferably the anode, is previously controlled to be hydrophobic using a surface treatment agent, and the organic layer in contact with the surface is formed by the ES method. In the case of a multilayered organic layer, it is preferable to form at least one layer other than the organic layer in contact with the electrode by the ES method. After forming the organic layer, a cathode layer is formed to form an organic EL element.

  As the cathode material, those according to the characteristics of the organic layer can be used. Examples thereof include simple metals such as lithium, magnesium, calcium and aluminum, and alloys of these with stable metals such as gold and silver. In addition, conductive oxides such as indium, zinc, and tin can also be used. As a method for forming the cathode layer, a vacuum deposition method using a mask, sputtering, or the like is used.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples.

Example 1
A glass substrate on which an anode made of ITO having a film thickness of 100 nm is formed is subjected to ultrasonic cleaning in each solvent of neutral detergent water (Cica Clean LX-2), pure water, and an organic solvent (acetone, isopropanol), and then UV / Ozone cleaning was performed. HMDS, which is a surface modifier, is treated on this ITO by a gas phase adsorption method (a substrate and a HMDS stock solution are placed in a petri dish and heated at 110 ° C. for 5 minutes), and dried on a hot plate at 110 ° C. for 5 minutes. did. Thereby, the ITO surface was adjusted to be hydrophobic, and the contact angle of water on the surface (electrode surface) of the obtained substrate was 90 °. The contact angle of water on the substrate surface before the surface modification is 15 °.
Next, an organic layer is formed using the ES apparatus shown in FIG.

  In FIG. 1, 1 is a syringe for storing solution, 2 is a sample solution, 3 is a spray frame, 4 is a conductive layer (ITO), 5 is a glass substrate, 6 is a voltage application unit, 7 is a power supply for spraying, and 8 is for grounding. Copper tape, 9 is an aluminum foil, and 10 is a main body table.

  A glass substrate 5 in which the ITO electrode 4 on which the thin film layer of the first TPD, which is a coating layer, is formed is electrically connected to the aluminum foil 9 by the copper tape 8 is placed on the sample table 10 of the ES apparatus.

  On the other hand, TPD is dissolved in a mixed solvent (volume ratio 4: 1, dielectric constant (calculated value) 14.9) of dichloromethane (boiling point 40 ° C.) which is a low polarity solvent and dimethylformamide (boiling point 153 ° C.) which is a high polarity solvent. The TPD thin film layer was formed by spraying the coating liquid (0.08 wt%) on the glass substrate 5 with an ITO electrode surface-treated with the HMDS by the ES method. The spraying conditions at this time were a substrate-nozzle tip distance of 50 mm, rotation at a speed of 15 rpm, an applied voltage of 10 kV, and a spraying time of 600 seconds. The thin film layer of the formed TPD was 34 nm, and was a smooth thin film in which scattered light was not observed in the microscope polarization image.

Next, Alq3 was laminated to a thickness of 50 nm by a vapor deposition method under a vacuum degree of 5.0 × 10 ⁻⁴ Pa. Thereafter, magnesium-silver and silver were formed as electrodes to a thickness of 100 nm and 10 nm, respectively, by vapor deposition to produce an organic EL device.

While connecting an external power source to the obtained organic EL element and applying a DC voltage, the characteristics were evaluated at 300 K using a C9920-02 type absolute quantum yield measuring apparatus manufactured by Hamamatsu Photonics Co., Ltd. As a result, light emission of 520 nm derived from Alq3 was confirmed, and the external light emission efficiency at that time was 1.0% at a current density of 1.0 mA / cm ² .

Example 2
A TPD thin film was formed in the same manner as in Example 1 except that OPA was used as a surface modifier instead of HMDS. The film thickness was 39 nm, and smooth light in which no scattered light was observed in the microscope polarization image. It was a thin film. Furthermore, as a result of producing an organic EL element and evaluating the characteristics at 300 K in the same manner as in Example 1, 520 nm emission derived from Alq3 was confirmed, and the external luminous efficiency at that time was 1.0 mA / cm ² . The density was 1.0%. In addition, the contact angle of water on the substrate surface after the surface modification is 94 °.

Comparative Example 1
An organic EL device was produced in the same manner as in Example 1 except that a surface modifier such as HMDS was not used. Although an attempt was made to evaluate the device characteristics of this device at 300K, the fabricated device was short-circuited and the light emission characteristics could not be measured.

Comparative Example 2
When a TPD thin film was formed in the same manner as in Example 1 except that FOPA was used as a surface modifier instead of HMDS, a thin film having a smooth surface was obtained by observing scattered light in a microscope polarization image. There wasn't. Further, an organic EL element was produced in the same manner as in Example 1, and an attempt was made to evaluate the element characteristics of this element at 300K. However, the produced element was short-circuited and the light emission characteristics could not be measured. The contact angle of water on the substrate surface after the surface modification is 113 °.

1 solution storage syringe, 2 sample solution, 3 spray frame,
4 conductive layer (ITO), 5 glass substrate, 6 voltage application unit,
7 Power supply for spray, 8 Copper tape for grounding,
9 Aluminum foil, 10 Main body table

Claims (4)

A manufacturing method of an organic electroluminescent device having an anode and a plurality of organic material layers between the cathode, an electrode having a hydrophilic surface contact angle of less than 70 degrees of water is the self-assembled monolayer-forming material The film is formed by electrospray using a solution in which a charge transport material having a molecular weight of 2,000 or less is dissolved in a solvent after being adjusted to 70 degrees or more and less than 110 degrees with a surface modifier. A method for producing an organic electroluminescent element.   The method for producing an organic electroluminescent element according to claim 1, wherein the solvent for dissolving the charge transport material has a dielectric constant of 5.5 to 18.0. The surface modifier that is a self-assembled monolayer forming material is hexamethyldisilazane, trimethylsilyl chloride, N, N′-bis (trimethylsilyl) urea, octylphosphonic acid, tetradecylphosphonic acid, or hexadecylphosphine The method for producing an organic electroluminescent element according to claim 1, wherein the organic electroluminescent element is phonic acid. The method for producing an organic electroluminescent element according to claim 1 or 2, wherein the surface modifier, which is a self-assembled monolayer forming material, is hexamethyldisilazane or octylphosphonic acid.