JP2008204792A - Organic electroluminescence device and method for manufacturing the same - Google Patents

Abstract

An organic EL device capable of suppressing the increase in thickness of a hole transport layer at an edge where an insulating layer and a pixel electrode are in contact with each other and eliminating unevenness of light emission and lowering in luminance and displaying with good uniformity. A production method and an organic EL device produced thereby are provided.
An organic light emitting medium layer comprising a pixel electrode, an insulating layer defining a light emitting region on the pixel electrode, and at least two layers of a hole transporting layer and an organic light emitting layer stacked on the light emitting region. And a method for producing an organic electroluminescence element comprising a counter electrode 6, wherein a hole transport ink in which a hole transport material is dissolved or dispersed in a solvent is formed in a light emitting region from a convex portion of a relief plate by a relief printing method. A step of forming the hole transport layer 4 by printing on the pixel electrode 2 between the insulating layers 3 is provided, and at this time, a time for the hole transport ink to be semi-dried on the relief printing is provided.
[Selection] Figure 1

Description

  The present invention relates to an organic EL element used for an organic electroluminescence (EL) display panel and the like and a manufacturing method thereof, and more particularly to an organic EL element in which an organic light emitting medium layer is formed by a printing method and a manufacturing method thereof.

  An organic EL element is one in which an organic light emitting layer made of an organic light emitting material is formed between two opposing electrodes, and light is emitted by passing a current through the organic light emitting layer. The film thickness is important, and it is necessary to form a thin film of about 100 nm. Furthermore, in order to make this a display panel, it is necessary to pattern it with high definition.

  The organic light emitting material for forming the organic light emitting layer includes a low molecular material and a high molecular material. Generally, a low molecular material is formed into a thin film by a vacuum deposition method or the like, and is patterned using a fine pattern mask at this time. This method has a problem that the larger the substrate is, the less patterning accuracy is obtained. In addition, since the film is formed in a vacuum, there is a problem that the throughput is poor.

Therefore, recently, a method in which a polymer material is dissolved in a solvent to form a coating solution and a thin film is formed by a wet coating method has been tried. When the organic light emitting medium layer is formed by a wet coating method using a coating liquid of a polymer material, a two-layer structure in which a hole transport layer and an organic light emitting layer are laminated from the anode side is general. At this time, the organic light emitting layer is formed by dissolving or stably dispersing organic light emitting materials having respective emission colors of red (R), green (G), and blue (B) in a solvent in order to form a color panel. It is necessary to paint with organic luminescent ink. An offset printing method has been proposed as a coloring method. (For example, refer to Patent Document 1).
As another method for forming a fine pattern, a relief printing method has been proposed. For example, Patent Document 2 discloses a technique for forming a semiconductor circuit pattern on a substrate.
Japanese Patent Laid-Open No. 2001-93668 JP 2002-217248 A

  In the organic EL display panel having the organic EL element having the above-described configuration, the hole transport layer is generally not patterned but the entire surface of the portion related to image formation is generally applied, so-called solid coating, and the spin coating method is generally used. And a coating method such as a die coating method. This is because the film thickness of the hole transport layer is generally a thin film of 100 nm or less, and the current flowing in the thickness direction is overwhelmingly easier to flow than the current flowing in the lateral direction of the layer, so if the electrode is patterned, This is because it was said that there is very little leakage of current outside the pixel.

  The present inventors patterned a pixel electrode as an anode on a glass substrate, patterned an insulating layer between the pixel electrodes, and applied a hole transport layer to the entire surface of the organic EL element by a slit coating method. In the passive matrix type organic EL device in which the organic light emitting layer is patterned and the cathode layer is patterned, the hole transport layer applied over the entire surface is thickened at the edge where the insulating layer and the pixel electrode are in contact with each other, It was confirmed that the light emission luminance was lower at the pixel edge than at the pixel center due to the difficulty in flowing.

  The present invention has been made to solve the above-described problems, and suppresses the hole transport layer from becoming thicker at the edge where the insulating layer and the pixel electrode are in contact with each other, thereby eliminating light emission unevenness and luminance reduction. An object of the present invention is to provide an organic EL device manufacturing method capable of performing display with good uniformity and an organic EL device manufactured thereby.

In order to achieve the above-mentioned object, the invention according to claim 1 includes a pixel electrode, an insulating layer defining a light emitting region on the pixel electrode, and a layer stacked on the light emitting region and at least a hole transport layer and an organic light emitting layer. A method for producing an organic electroluminescence device comprising an organic light emitting medium layer including two medium layers and a counter electrode facing the pixel electrode through the organic light emitting medium layer,
In the light emitting region, a hole transporting layer in which a hole transporting material is dissolved or dispersed in a solvent is printed on a pixel electrode between a convex portion of the relief printing and the insulating layer by a relief printing method. An organic electroluminescence device comprising: a step of forming, wherein at that time, a time for the semi-drying of the hole transport ink on the relief printing plate is provided, thereby increasing the concentration and viscosity of the hole transport ink. It is a manufacturing method.

  The invention according to claim 2 has a solid concentration of 0.5 to 4.0% by weight, a viscosity of 10 to 30 mPa · s, and a vapor pressure under the conditions of relative humidity 40 to 50% and temperature 23 to 26 ° C. The method for producing an organic electroluminescent element according to claim 1, wherein the semi-drying time is 5 to 60 seconds when printing a hole transport ink of 0.1 to 20 kPa.

  Invention of Claim 3 is a manufacturing method of the organic electroluminescent element of Claim 1 whose solid content concentration of the hole transport ink after the said semi-drying is 5 to 30 weight%.

  Invention of Claim 4 is a manufacturing method of the organic electroluminescent element of Claim 1 whose viscosity of the hole transport ink after the said semi-drying is 30-100 mPa * S.

  According to a fifth aspect of the present invention, there is provided an organic device including a pixel electrode, an insulating layer defining a light emitting region on the pixel electrode, and at least two layers of a hole transport layer and an organic light emitting medium layer stacked on the light emitting region. Organic electroluminescence comprising a light emitting medium layer and a counter electrode facing the pixel electrode through the organic light emitting medium layer, and causing the organic light emitting medium layer to emit light by passing a current from both electrodes to the organic light emitting medium layer It is an organic electroluminescent element characterized by using the manufacturing method in any one of Claims 1-4 in an element.

  According to the organic EL element and the manufacturing method thereof of the present invention, the hole transport ink is semi-dried on the relief printing by the relief printing method, thereby suppressing the flow of the ink immediately after printing on the pixel electrode and wetting the insulating layer. The rise can be suppressed. The effect of being able to obtain an organic EL element excellent in uniformity without light emission unevenness and luminance reduction because the formation of a flat hole transport layer is possible by suppressing the increase in thickness at the edge where the insulating layer and the pixel electrode are in contact with each other. There is.

Hereinafter, an example in which the embodiment of the present invention is applied to a passive matrix type organic EL display panel will be described. There are a passive matrix type and an active matrix type as a driving method of the organic EL element, but the organic EL element of the present invention can be applied to both a passive matrix type organic EL element and an active matrix type organic EL element. .
The passive matrix method is a method in which stripe-shaped electrodes are opposed to each other so as to be orthogonal to each other, and light is emitted at the intersection, whereas the active matrix method uses a so-called thin film transistor (TFT) substrate in which a transistor is formed for each pixel. Thus, the light is emitted independently for each pixel.
FIG. 1 is a sectional view showing the structure of an organic EL display panel according to an embodiment of the present invention.
The organic EL element in this organic EL display panel is formed on a substrate. When this organic EL display panel is an organic EL element of the pottom emission type that extracts light from the substrate side, it is necessary to use a transparent substrate, but the top emission method that extracts light from the opposite side of the substrate In this case, the substrate does not need to have translucency.
As the substrate 1, a glass substrate or a plastic film or sheet can be used. If a plastic film is used, a polymer EL element can be produced by winding, and a display panel can be provided at a low cost. In addition, as the plastic in that case, for example, polyethylene terephthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, or the like can be used. In addition, these films have a barrier layer made of a metal oxide such as silicon oxide that exhibits water vapor barrier property and oxygen barrier property, oxynitride such as silicon nitride, polyvinylidene chloride, polyvinyl chloride, saponified ethylene-vinyl acetate copolymer. Is provided as necessary.

A pixel electrode 2 patterned as an anode is provided on the substrate 1. As the material of the pixel electrode 2, transparent electrode materials such as ITO (indium tin composite oxide), IZO (indium zinc composite oxide), tin oxide, zinc oxide, indium oxide, and aluminum oxide composite oxide can be used. ITO is preferred because of its low resistance, solvent resistance, transparency, and the like. ITO is formed on the substrate by sputtering and patterned by photolithography to form line-shaped pixel electrodes 2.
Then, after the line-shaped pixel electrode 2 is formed, an insulating layer 3 is formed by a photolithography method using a photosensitive material between adjacent pixel electrodes. The insulating layer 3 defines a light emitting region on the pixel electrode 2.

  The insulating layer 3 in the present embodiment desirably has a thickness in the range of 0.5 μm to 5.0 μm. In addition, by providing an insulating layer between adjacent pixel electrodes, the spread of the hole transport ink printed on each pixel electrode is suppressed, and leaks due to the presence of the hole transport layer on the insulating layer when a display is made. Generation of current can be prevented. If the insulating layer is too low, ink spreading cannot be prevented and a hole transport layer is formed on the insulating layer.

  For example, in an organic EL display panel of a passive matrix type, when an insulating layer is provided between pixel electrodes, a cathode layer is formed with the insulating layers orthogonal to each other. When the cathode layer is formed so as to straddle the insulating layer in this way, if the insulating layer is too high, the cathode layer is disconnected, resulting in a display defect. When the height of the insulating layer exceeds 5.0 μm, disconnection of the cathode tends to occur.

  The photosensitive material for forming the insulating layer may be either a positive resist or a negative resist, and may be a commercially available one, but it must have insulating properties. Note that if the partition does not have sufficient insulation, a current flows to the adjacent pixel electrode through the partition and a display defect occurs. Specific examples thereof include polyimide, acrylic resin, novolac resin, and fluorene, but are not limited thereto. Further, for the purpose of improving the display quality of the organic EL element, a light shielding material may be included in the photosensitive material.

  The photosensitive resin for forming the insulating layer 3 is applied using a coating method such as a spin coater, bar coater, roll coater, die coater, gravure coater, and patterned by a photolithography method. Alternatively, the insulating layer may be formed using a gravure offset printing method, a reverse printing method, a flexographic printing method, or the like without using a photosensitive resin.

After forming the insulating layer 3 as described above, the hole transport layer 4 is then formed. Examples of the hole transport material forming the hole transport layer 4 include polyaniline derivatives, polythiophene derivatives, polyvinylcarbazole (PVK) derivatives, poly (3,4-ethylenedioxythiophene) (PEDOT), and the like. These materials are dissolved or dispersed in a solvent to form a hole transport material ink, which is formed using the relief printing method according to the present embodiment. The volume resistivity of the formed hole transport layer is preferably 1 × 10 ⁶ Ω · cm or less from the viewpoint of light emission efficiency.

  Examples of the solvent for dissolving or dispersing the hole transport material include toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, polyethylene glycol, glycerin, and ethyl acetate. , Butyl acetate, isopropyl acetate, methyl cellosolve, ethyl cellosolve, methyl cellosolve, ethyl cellosolve, butyl cellosolve, ethyl lactate, ethylene glycol diethyl ether, 1-propanol, methoxypropanol, ethoxypropanol, water, etc. Etc. Moreover, surfactant, antioxidant, a viscosity modifier, a ultraviolet absorber, etc. may be added as needed.

FIG. 2 shows an outline of a relief printing apparatus when pattern printing is performed on a substrate to be printed on which a pixel electrode and an insulating layer are formed using a hole transport ink made of a hole transport material.
As shown in the figure, the apparatus includes an ink tank 10, an ink chamber 12, an anilox roll 14, and a plate cylinder 18 on which a plate 16 provided with a relief plate is mounted. The ink tank 10 contains hole transport ink diluted with a solvent, and the hole transport ink is fed into the ink chamber 12 from the ink tank 10. The anilox roll 14 is rotatably supported with respect to the ink supply part of the ink chamber 12.

As the anilox roll 14 rotates, the ink layer 14a of the hole transport ink supplied to the anilox roll surface is formed with a uniform film thickness. This ink layer is transferred to the convex portion of the plate 16 mounted on the plate cylinder 18 that is driven to rotate in the vicinity of the anilox roll.
On the flat table 20, the substrate to be printed 24 on which the pixel electrode and the insulating layer are formed is transported to a printing position by the convex portion of the plate 16 by a transport unit (not shown). Then, the ink on the convex portion of the plate 16 is subjected to the predetermined semi-drying of the present invention, then printed on the printing substrate 24, and if necessary, a hole is formed on the printing substrate through a drying process. A transport layer is formed.

  In this example, the photosensitive resin relief plate used for the relief plate was a water development type. The photosensitive resin plate includes a solvent development type in which the developer used when developing the exposed resin plate is an organic solvent and a water development type in which the developer is water. In general, solvent development type is resistant to water-based ink, and water development type tends to be resistant to organic solvent-based ink. Any resin relief can be used.

  Further, it is preferable that the difference in depth between the convex portion and the concave portion of the relief printing, that is, the portion where the ink is not transferred is 40 μm or more. If the difference between the convex part and the concave part is smaller than this, depending on the printing conditions, not only the convex part but also the concave part comes into contact with the substrate, and ink is transferred to the extra part, causing problems such as leakage. Because.

  Next, the hardness of the resin relief printing plate is preferably 45 to 90 degrees (Shore A) and 18 to 75 degrees (Shore D). This is because if the hardness is less than 45 degrees (Shore A), the margin for the printing pressure is narrow and the image line is twisted or crushed, making it very difficult to form a uniform pattern. Further, when the angle is greater than 75 degrees (Shore D), the printing pressure appropriate for pattern formation becomes too high, and the substrate and the insulating layer are overloaded, and there is a risk of cracking, distortion, and scratches. .

  Moreover, it is preferable that the viscosity of hole transport ink is 10-30 mPa * s on the conditions of relative humidity 40-50% and temperature 23-26 degreeC. In the relief printing method used in the present embodiment, the ink is first transferred from the anilox to the relief plate. However, at a viscosity exceeding 30 mPa · s, the ink is transferred from the anilox to the relief plate, and then on the relief plate. Insufficient ink leveling causes unevenness.

  Moreover, it is preferable that it is 0.5 to 4.0 weight% as solid content concentration of hole transport ink on the said relative humidity and temperature conditions. This is because the hole transport ink used in the present embodiment is not stable when the concentration exceeds 4.0% by weight, and causes ink aggregation and hole transport layer unevenness.

  Further, the vapor pressure of the hole transport ink is preferably 0.1 to 20 kPa under the above relative humidity and temperature conditions. In the relief printing method used in this embodiment, the ink is first transferred from the anilox to the relief plate, but after the ink is transferred from the anilox to the relief plate at a vapor pressure of more than 20 kPa, the ink is transferred onto the relief plate. This is because the drying of the toner is too fast, causing transfer defects and causing unevenness.

  Moreover, it is preferable that the density | concentration of the hole transport ink after semi-drying is 5 to 30 weight%, and a viscosity is 30-100 mPa * s. When the viscosity is less than 30 mP · s, wetting to the insulating layer cannot be suppressed, and the film is thickened at the edge where the insulating layer and the pixel electrode are in contact with each other, resulting in light emission unevenness and luminance reduction.

  Next, after the formation of the hole transport layer 4 as described above, the organic light emitting layer 5 is formed. The organic light emitting layer is a layer that emits light by passing an electric current, and the organic light emitting material forming the organic light emitting layer is, for example, a coumarin type, a perylene type, a pyran type, an anthrone type, a porphyrene type, a quinacridone type, N, N ′. -Dialkyl substituted quinacridone-based, naphthalimide-based, N, N'-diaryl-substituted pyrrolopyrrole-based, iridium complex-based luminescent dyes dispersed in polymers such as polystyrene, polymethyl methacrylate, polyvinyl carbazole, Examples thereof include polyarylene-based, polyarylene vinylene-based, and polyfluorene-based polymer materials.

  These organic light emitting materials are dissolved or stably dispersed in a solvent to form an organic light emitting ink. Examples of the solvent for dissolving or dispersing the organic light-emitting material include toluene, xylene, acetone, anisole, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, or a mixed solvent thereof. Among these, aromatic organic solvents such as toluene, xylene, and anisole are preferable from the viewpoint of solubility of the organic light emitting material. Moreover, surfactant, antioxidant, a viscosity modifier, a ultraviolet absorber, etc. may be added to organic luminescent ink as needed.

  As a method for forming the organic light emitting layer 5, when using a letterpress printing method, a resin letterpress suitable for an organic light emitting ink can be used, and a water developing type photosensitive resin letterpress is particularly preferable.

  The printing method for printing the organic light emitting ink can be performed in the same manner as the hole transport layer printing.

  Next, after forming the organic light emitting layer 5 as described above, the counter electrode 6 is formed in a line pattern orthogonal to the line pattern of the pixel electrode. As the material of the counter electrode 6, a material according to the light emission characteristics of the organic light emitting layer can be used. For example, a simple metal such as lithium, magnesium, calcium, ytterbium, or aluminum or a stable metal such as gold or silver can be used. And alloys thereof. Alternatively, a conductive oxide such as indium, zinc, or tin can be used. As a method of forming the counter electrode, a method of forming by a vacuum deposition method using a mask can be given.

  Note that the organic EL element of the present embodiment has a structure in which a hole transport layer and an organic light emitting medium layer are stacked from the anode layer side between a pixel electrode as an anode and a counter electrode as a cathode. Between the cathode layers, in addition to the hole transport layer and the organic light emitting medium layer, a layered structure in which layers such as a hole block layer, an electron transport layer, and an electron injection layer are selected as necessary can be employed. The method of the present invention can also be used when forming these layers.

  Finally, in order to protect these organic EL elements from external oxygen and moisture, the organic EL display panel can be obtained by hermetically sealing with a glass cap 7 and an adhesive 8. In the case where the substrate has flexibility, sealing may be performed using a sealing agent and a flexible film.

  EXAMPLES Hereinafter, although an Example and a comparative example further demonstrate this invention, this invention is not restrict | limited to the following example.

Example 1
First, an ITO (indium-tin oxide) thin film is formed on a 300 mm square glass substrate by sputtering, and the ITO film is patterned by photolithography and etching with an acid solution to obtain a 5 inch diagonal size. Pixel electrodes were formed so that two displays could be taken. The line pattern of the pixel electrode per display surface was a pattern in which 1950 lines were formed with a line width of 40 μm and a space of 20 μm.

  Next, an insulating layer was formed as follows. First, an acrylic photoresist material was spin-coated on the entire surface of a glass substrate on which pixel electrodes were formed. The spin coating condition was rotated at 150 rpm for 5 seconds, and then rotated at 500 rpm for 20 seconds to make a single coating, and the height of the insulating layer was 1.5 μm. An insulating layer having a line pattern between pixel electrodes was formed on the photoresist material applied to the entire surface by photolithography.

Next, it was prepared by using PEDOT solution Vitron CH-8000 as a hole transport ink, and the viscosity of the ink was 15 mPa · s, vapor under conditions of solid content concentration of ink 1.5%, relative humidity 45%, temperature 25 ° C. An ink having a pressure of 1.1 kPa was prepared. The ink received from the anilox roll was dried for 15 seconds on the plate under conditions of 45% relative humidity and a temperature of 25 ° C. using ink and plate. A transport layer was formed.
The solid content concentration of the hole transport ink after semi-drying was 7.5% by weight and the viscosity was 45 mPa.s. s.
A 180 line / inch anilox roll was used for printing, and after printing, drying was performed in the atmosphere at 200 ° C. for 30 minutes to form a hole transport layer. The film thickness at this time was 50 nm. And the patterning state was confirmed with respect to the formed positive hole transport layer.

  Next, organic light-emitting ink in which polyphenylene vinylene derivative, an organic light-emitting material, is dissolved in toluene to a concentration of 1% is used, and organic light emission is performed in line with the line pattern directly above the pixel electrode sandwiched between insulating layers. The layer was printed by letterpress printing. At this time, an anilox roll of 150 lines / inch and a photosensitive resin plate of water development type were used. As a result, the film thickness of the organic light emitting layer after printing and drying was 80 nm.

A cathode layer made of Ca and Al was formed thereon by mask vapor deposition using a resistance heating vapor deposition method in a line pattern orthogonal to the pixel electrode line pattern. Finally, in order to protect these organic EL elements from external oxygen and moisture, they were hermetically sealed using a glass cap and an adhesive to produce an organic EL display panel.
In the periphery of the display part of the organic EL display panel obtained in this way, there are an extraction electrode on the anode side connected to each pixel electrode and an extraction electrode on the cathode side, which are obtained by connecting them to a power source. The lighting display of the obtained organic EL display panel was confirmed, and the light emission state was checked.

Example 2
The same procedure as in Example 1 was performed except that the viscosity of the hole transport ink was 150 mPa · s.

Example 3
The same as Example 1 except that the vapor pressure of the hole transport ink was 0.05 kPa.

Example 4
Example 1 was repeated except that the semi-drying time was 2 seconds.

Comparative Example 1
It carried out like Example 1 except not providing a half-dry time.

  The evaluation results of the line pattern shape of the hole transport layer in Examples 1 to 4 and Comparative Example 1 as described above and the evaluation results of the display state of the produced organic EL display are shown in Table 1 below.

[Table 1]

  As can be seen from the results in Table 1, it can be seen that better results are obtained in the examples of the present invention than in the comparative examples.

  The organic EL device of the present invention is useful for an organic EL display panel because it can perform display with good uniformity without causing unevenness of light emission and lowering of luminance.

It is sectional drawing which shows the structure of the organic EL element in the organic EL panel by embodiment of this invention. It is a figure which shows the outline | summary of the relief printing apparatus in embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Pixel electrode, 3 ... Insulating layer, 4 ... Hole transport layer, 5 ... Organic light emitting layer, 6 ... Counter electrode, 7 ... Glass cap, 8 ... Adhesive, DESCRIPTION OF SYMBOLS 10 ... Ink tank, 12 ... Ink chamber, 14 ... Anilox roll, 14a ... Ink layer, 16 ... Plate, 18 ... Plate cylinder, 20 ... Flat bed, 24 ... Printed substrate.

Claims (5)

A pixel electrode; an insulating layer defining a light emitting region on the pixel electrode; an organic light emitting medium layer including at least two layers of a hole transport layer and an organic light emitting medium layer stacked on the light emitting region; and the organic light emitting medium A method for producing an organic electroluminescent element comprising a counter electrode facing the pixel electrode through a layer,
In the light emitting region, a hole transporting layer in which a hole transporting material is dissolved or dispersed in a solvent is printed on a pixel electrode between a convex portion of the relief printing and the insulating layer by a relief printing method. An organic electroluminescence device comprising: a step of forming, wherein at that time, a time for the semi-drying of the hole transport ink on the relief printing plate is provided, thereby increasing the concentration and viscosity of the hole transport ink. Production method.   Holes having a solid content concentration of 0.5 to 4.0% by weight, a viscosity of 10 to 30 mPa · s, and a vapor pressure of 0.1 to 20 kPa under conditions of a relative humidity of 40 to 50% and a temperature of 23 to 26 ° C. The method for producing an organic electroluminescence device according to claim 1, wherein when printing the transport ink, the semi-drying time is 5 to 60 seconds.   The method for producing an organic electroluminescent element according to claim 1, wherein the solid content concentration of the hole transport ink after the semi-drying is 5 to 30% by weight.   The method for producing an organic electroluminescent element according to claim 1, wherein the viscosity of the hole transport ink after the semi-drying is 30 to 100 mPa · S.   A pixel electrode; an insulating layer defining a light emitting region on the pixel electrode; an organic light emitting medium layer including at least two layers of a hole transport layer and an organic light emitting medium layer stacked on the light emitting region; and the organic light emitting medium An organic electroluminescent device comprising: a counter electrode facing the pixel electrode through a layer, wherein the organic light emitting medium layer emits light by passing a current from both electrodes to the organic light emitting medium layer. An organic electroluminescence element formed by using the manufacturing method according to any one of the above.

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