JP2012204202A - Organic electroluminescent panel and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the narrowing of a light emitting region in an organic EL element, thereby improving characteristics of the organic EL element.SOLUTION: In an organic electroluminescent element, a pixel electrode 2, a counter electrode 7, an organic light emitting layer 5, and a barrier rib 3 which comprises a resin composition and partitions a light emitting region corresponding to the pixel electrode 2 are formed on at least a translucent substrate 1, and a current is flown from the pixel electrode 2 and the counter electrode 7 to the organic light emitting layer 5 to emit light. A side face of the barrier rib 3 is roughened to have a surface roughness of about 3 nm or more.

Description

  The present invention relates to an organic EL panel using an electroluminescence (hereinafter abbreviated as organic EL) phenomenon of an organic thin film and a method for manufacturing the organic EL panel.

  An organic EL element has a structure in which an organic light emitting layer exhibiting at least an electroluminescence phenomenon is sandwiched between an electrode as an anode and an electrode as a cathode, and when a voltage is applied between the electrodes, This is a self-luminous element in which the organic light emitting layer emits light by injecting holes and electrons into the light emitting layer and recombining the holes and electrons in the organic light emitting layer.

  Further, for the purpose of increasing luminous efficiency, a hole injection layer, a hole transport layer, an electron blocking layer, or a hole between the organic light emitting layer and the cathode is provided between the anode and the organic light emitting layer. A block layer, an electron transport layer, an electron injection layer, and the like are appropriately selected and provided.

  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 of forming a thin film by a wet coating method has been attempted in which a high molecular material or a low molecular material is dissolved in a solvent to form a coating liquid (hereinafter referred to as ink). The wet coating method for forming a thin film includes a spin coating method, a bar coating method, a slit coating method, a dip coating method, and the like. However, it is considered difficult to form a thin film by a printing method that is good at coating and patterning.

  As a method for printing this organic light-emitting ink, an offset printing method using an elastic rubber blanket (Patent Document 1), a relief printing method using an elastic rubber plate or resin plate (Patent Document 2), and an inkjet A method (Patent Document 3), a nozzle printing method, and the like have been proposed.

  When an organic material is deposited on a pixel region, a partition member that partitions the pixel region (hereinafter also referred to as a bank. In addition, a layer constituting the partition member is used to prevent the discharged ink from flowing out to the adjacent pixel region. A bank layer is provided, and ink is filled in the pixel region surrounded by the partition member.

  When the bank is compatible with the ink, the adhesion between the bank and the ink is good and the ink tends to spread along the surface of the bank. For this reason, when the bank is filled with ink, the ink is not repelled on the bank side surface (referred to as an inclined surface forming a wall in the width direction of the bank), but the ink wets the bank side surface and narrows the light emitting area. .

  On the other hand, when the bank shows incompatibility with the ink, the adhesion between the bank and the ink is poor, and the ink is difficult to spread along the surface of the bank. For this reason, even if the bank is filled with ink, the adhesion between the bank and the ink is poor, so the ink does not get wet on the side of the bank. However, when the ink is heated to evaporate the solvent, the volume of the ink decreases while the ink is repelled on the side of the bank. For this reason, after film formation, a thin film is formed thick at the center and thin at the periphery. If the thin film is not formed so that the central portion and the peripheral portion have a uniform thickness and the surface is flat, color unevenness occurs or the reliability decreases.

  When the bank is compatible with the ink, the viscosity of the ink is low, so that wetting increases and a thick film is formed on the side surface of the bank layer.

  When a thick organic film is formed on the bank side surface due to wetting, the light emitting region is narrowed and the light emission efficiency and life characteristics are degraded.

  As a method for improving the flatness in the pixel, a method (Patent Document 4) in which a partition wall is partially water-repellent is proposed.

  Moreover, although the method of (patent document 5) is proposed regarding the wetting up, it is a roughening of only an upper part, and the method of the area | region of the partition lower part which is not roughened by this method wets up. is there.

JP 2001-93668 A JP 2001-155858 A JP 2002-305077 A Japanese Patent No. 3328297 Japanese Patent Laid-Open No. 11-329741

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an organic electroluminescence panel in which characteristics are improved by widening a light emitting region of an organic EL element and a method for manufacturing the same.

  In the first aspect of the present invention, at least a substrate is formed with a pixel electrode, a counter electrode, a light emitting medium layer including an organic light emitting layer, and a partition made of a resin composition that partitions a light emitting region corresponding to the pixel electrode, An organic electroluminescence panel that emits light from the organic light emitting layer by flowing current from both electrodes to the organic layer, wherein the surface roughness of the side surface of the partition wall of the support substrate is about 3 nm or more. It is an organic electroluminescence panel.

  Invention of Claim 2 is an organic electroluminescent panel of Claim 1 or 2, Comprising: The contact angle of the said partition is 10 degrees or less with respect to xylene, The organic electroluminescent panel characterized by the above-mentioned. is there.

  Invention of Claim 3 is a manufacturing method which manufactures the organic electroluminescent panel of Claim 1 or 2, Comprising: The process of forming the partition which consists of a resin composition on a support substrate, The said partition upper surface, And a step of subjecting the exposed side surface to a roughening treatment. A method for producing an organic electroluminescence panel, comprising:

  Invention of Claim 4 is a manufacturing method of the organic electroluminescent panel of Claim 3, Comprising: The said roughening process is a plasma process by oxygen plasma irradiation, The organic electroluminescent panel characterized by the above-mentioned. It is a manufacturing method.

  Invention of Claim 5 is a manufacturing method which manufactures the organic electroluminescent panel of Claim 1 or 2, Comprising: The process of forming the partition which consists of a resin composition on a support substrate, The said partition upper surface, A method for producing an organic electroluminescence panel, comprising: a step of roughening an exposed side surface; and a step of forming a pixel by applying ink to a region surrounded by a partition wall by a nozzle printing method. It is.

  According to the present invention, it is possible to suppress the light emitting region of the organic EL element from being narrowed and to improve the characteristics of the organic EL element.

It is a schematic diagram of the organic EL display panel cross section in the organic EL device according to the embodiment of the present invention. It is a schematic diagram of the partition in the organic electroluminescent apparatus which concerns on embodiment of this invention. It is a schematic diagram of the cathode coupling type plasma generator in the organic EL device according to the embodiment of the present invention. It is a schematic diagram of the anode coupling type plasma generator in the organic EL device according to the embodiment of the present invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings, taking as an example the case of creating a passive matrix type organic EL display panel. However, the present invention is not limited to these. FIG. 1 is a schematic diagram of a cross section of an organic EL display panel in the organic EL device of the present invention, and FIG. 2 is a schematic diagram of a partition wall portion in FIG.

  The organic EL element in the organic EL display panel is formed on the translucent substrate 1. As the translucent 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. As the plastic, for example, polyethylene terephthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate and the like can be used. Further, these films are barrier layers made of metal oxides such as silicon oxide, which exhibit water vapor barrier properties and oxygen barrier properties, oxynitrides such as silicon nitride, polyvinylidene chloride, polyvinyl chloride, saponified ethylene-vinyl acetate copolymers. Is provided as necessary.

  A pixel electrode 2 patterned as an anode is provided on the translucent 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 translucent substrate 1 by a sputtering method and patterned by a photolithography method to form a line-shaped pixel electrode 2.

  After the line-shaped pixel electrode 2 is formed, the partition wall 3 is formed by photolithography using a photosensitive material between the adjacent pixel electrodes 2. More specifically, it includes at least a step of applying the photosensitive resin composition to the translucent substrate 1 and a step of forming a partition wall pattern by pattern exposure and development. The partition wall 3 is formed of a resin composition so as to partition a light emitting region corresponding to each pixel. For example, the partition wall 3 is preferably formed so as to cover an end portion of the pixel electrode 2.

  As the photosensitive material for forming the partition walls 3, a positive resist is used in the present invention. However, the present invention is not limited to this, and a negative resist or other resin may be patterned by dry etching or the like. From the viewpoint of productivity, a positive resist is preferable. Although the positive resist may be a commercially available one, it needs to have insulating properties. If the partition 3 does not have sufficient insulation, a current flows to the adjacent pixel electrode 2 through the partition 3 and display defects such as abnormal light emission and current leakage occur.

  Specific examples of the photosensitive material include polyimide, acrylic resin, novolac resin, and fluorene resin, but the present invention is 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 forming the partition walls 3 is applied using a known coating method such as a spin coater, bar coater, roll coater, die coater, or gravure coater. Next, in the step of pattern exposure and development to form a barrier rib pattern, a pattern of the barrier rib 3 portion can be formed by a conventionally known exposure and development method.

  As a pattern exposure method, proximity exposure, which is also used in color filters, is preferable from the viewpoint of productivity and cost, but the present invention is not limited to this. Here, in the case of proximity exposure, a photomask is used to pattern the partition 3, but this photomask needs to be designed so that the partition 3 has the desired shape. In many cases, the partition wall shape to be obtained can be obtained by manufacturing a photomask having a pattern that is almost the same pattern as the partition wall 3 and that corresponds to a positive or negative difference.

  When the partition 3 is formed of a positive resist, the photomask is designed so that a portion of the partition 3 is shielded from light. After patterning the barrier ribs by exposure and development, the patterned photoresist resin is cured by heating in a baking process to form barrier ribs 3. The firing temperature at this time is preferably 180 ° C. or higher. If the firing temperature is lower than this, sufficient resistance and stability cannot be obtained.

  In addition to the exposure and development methods described above, the partition walls 3 can be patterned by a printing method or the like. For example, in the case of the reverse offset printing method, the resin for forming the partition walls 3 is first formed on the blanket, and then the unnecessary portions of the pattern are removed by transferring them to the printing plate. Finally, the pattern of the partition walls 3 is formed by a method in which the pattern remaining on the blanket is aligned with the substrate to be printed and transferred. Further, after the patterning of the partition walls 3, a curing process is performed by baking. Also in this reverse offset printing method, examples of the resin component forming the partition wall 3 include polyimide, acrylic resin, novolak resin, and fluorene resin, but the present invention is not limited thereto. .

  The partition wall 3 in the present invention desirably has a thickness in the range of 0.5 μm to 5.0 μm. If the partition wall 3 is too thin, it may not be possible to prevent the occurrence of leakage current between adjacent pixels via the hole transport layer and the effect of preventing a short circuit.

  In the organic EL display panel, when the partition 3 is provided between the pixel electrodes 2, the cathode layer (counter electrode) is formed by crossing the partition 3 directly and across. When the cathode layer is formed so as to straddle the partition wall 3 in this way, if the partition wall 3 is too high, the cathode layer is disconnected, resulting in a display failure. If the height of the partition wall 3 exceeds 5.0 μm, it is not preferable because the cathode is easily disconnected even if the section of the partition wall 3 has a forward taper shape.

  After firing the partition walls, the surface of the partition walls 3 is roughened. The treatment includes plasma treatment and corona discharge, and plasma treatment is particularly preferred. Examples of the gas used for the plasma treatment include oxygen, nitrogen, argon, tetrafluoromethane, or a mixed gas thereof, and oxygen gas is preferable, but the present invention is not limited to this. The surface roughness Ra of the side wall of the partition wall is preferably Ra = 3 nm to 500 nm, more preferably Ra = 10 nm to 100 nm.

  When the roughness of the side wall of the partition becomes less than Ra = 3 nm, the ink wets the side of the partition and narrows the light emitting region. On the other hand, if Ra exceeds 500 nm, the partition wall 3 becomes thin, and there is a risk of leakage current between adjacent pixels via the hole transport layer, which is not preferable.

  3 and 4 are schematic views of a plasma generator that can be used in the plasma treatment step. In the figure, 11 is an upper electrode, 12 is a lower electrode, 13 is a substrate to be processed, and 14 is a high-frequency power source. The plasma generator generates a plasma by applying a high-frequency voltage between two electrodes of a parallel plate of an upper electrode 11 and a lower electrode 12.

  FIG. 3 is a schematic diagram of a cathode coupling type plasma generator, and FIG. 4 is a schematic diagram of an anode coupling type plasma generator. In either method, pressure, gas flow rate, discharge frequency, processing time, etc. Depending on the conditions, the surface roughness of the surface of the partition wall 3 can be set to a desired level.

  In the plasma generator shown in FIGS. 3 and 4, the cathode coupling method of FIG. 3 can shorten the processing time, which is advantageous for the processing step. Further, the anode pulling method of FIG. 4 is advantageous in that the translucent substrate 1 is not damaged more than necessary. Therefore, the plasma generator used in this step may be selected according to the material of the light-transmitting substrate 1 and the partition 3.

  As described above, after the partition wall 3 is formed, the hole transport layer 4 is formed. Examples of hole transport materials forming the hole transport layer 4 include metal phthalocyanines such as copper phthalocyanine and tetra (t-butyl) copper phthalocyanine, and metal-free phthalocyanines, quinacridone compounds, 1,1-bis (4-di -P-tolylaminophenyl) cyclohexane, N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine, N, N'-di ( 1-naphthyl) -N, N′-diphenyl-1,1′-biphenyl-4,4′-diamine and other aromatic amine low molecular hole injection transport materials, poly (para-phenylene vinylene), polyaniline, etc. It can be selected from polymer hole transport materials, polythiophene oligomer materials, and other known hole transport materials.

  As a method for forming the hole transport layer 4, known coating methods such as a nozzle printing method, a spin coating method, a slit coating method, an ink jet method, and a relief printing method can be used for the coating type material.

  After the formation of the hole transport layer 4, the organic light emitting layer 5 is formed. In this case, the contact angle of the partition wall 3 with respect to the organic light emitting layer 5 is about 10 degrees or less. The organic light emitting layer 5 is a layer that emits light by passing an electric current, and the organic light emitting material that forms the organic light emitting layer 5 may be any material that is generally used as an organic light emitting material. Known low fluorescence that can emit light from a singlet state such as pyran, anthrone, porphyrene, quinacridone, N, N'-dialkyl substituted quinacridone, naphthalimide, N, N'-diaryl substituted pyrrolopyrrole Examples include molecular materials and known phosphorescent low-molecular materials capable of emitting light from a rare earth metal complex triplet state.

  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. In addition, a surfactant, an antioxidant, a viscosity modifier, an ultraviolet absorber and the like may be added to the organic light emitting ink as necessary.

  The organic light emitting layer 5 can be formed by a nozzle printing method, a spin coating method, a slit coating method, an ink jet method, a relief printing method, an intaglio offset printing method, a relief printing reverse offset printing method, or the like.

  After the formation of the organic light emitting layer 5, the electron transport layer 6 is formed. The material for the electron transport layer 6 may be any material that is generally used as an electron transport material, and examples thereof include low molecular materials such as triazole, oxazole, oxadiazole, silole, and boron. Film formation by vacuum deposition is possible.

  After the formation of the electron transport layer 6, a counter electrode (cathode layer) 7 is formed. As the material of the counter electrode 7, a material according to the light emission characteristics of the organic light emitting layer 5 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 And alloys thereof. Alternatively, a conductive oxide such as indium, zinc, or tin can be used. Examples of the method for forming the counter electrode (cathode layer) 7 include a vacuum evaporation method using a mask.

  In the organic EL device of the present invention, the hole transport layer 4, the organic light emitting layer 5, and the electron transport layer 6 are laminated from the pixel electrode 2 side between the pixel electrode 2 serving as the anode and the counter electrode 7 serving as the cathode. However, a layered structure in which layers such as a hole blocking layer and an electron injection layer in addition to the hole transport layer 4 and the organic light emitting layer 5 are selected between the pixel electrode 2 and the counter electrode 7 as necessary can be adopted. Moreover, when forming these layers, the formation method similar to the positive hole transport layer 4, the organic light emitting layer 5, and a cathode layer can be used.

  Finally, in order to protect these organic EL constituents from external oxygen and moisture, a glass cap 8 and an adhesive 9 are hermetically sealed to obtain an organic EL display panel. Moreover, when the translucent board | substrate 1 has flexibility, you may seal using a sealing agent and a flexible film.

  Next, examples of the present invention will be described.

  A glass substrate having a diagonal size of 1.8 inches is used as the translucent substrate 1, and an ITO (indium-tin oxide) thin film is formed on the substrate 1 using a sputtering method. The pixel electrode 2 was formed by patterning the ITO film by etching. The line pattern of the pixel electrode 2 is a pattern in which about 270 lines are formed in a line of about 32 mm square with a line width of 90 μm and a space of 30 μm.

  Next, the partition 3 was formed as follows so as to have a line shape parallel to the pixel electrode 2. A positive photosensitive resist: LC100 made by AZ Electric Materials was spin coated on the entire surface of the substrate 1 on which the pixel electrode 2 was formed. The spin coating condition was rotated at 150 rpm for 5 seconds and then at 500 rpm for 20 seconds, so that the height of the partition wall 3 was 2.0 μm. The photosensitive material applied on the entire surface was exposed and developed by a photolithography method to cover the space between the pixel electrodes 2 and to form partition walls 3 having a lattice pattern to form pixels. Thereafter, the partition walls 3 were baked in an oven at 230 ° C. for 30 minutes.

  Then, using the parallel plate type plasma generator, the substrate 1 was subjected to plasma treatment under the following conditions.

Gas used: O ₂
Gas flow rate: 80sccm
Pressure: 8Pa
RF power: 150W
Processing time: 30 min
After performing the above plasma treatment, the surface roughness of the partition walls 3 was measured and found to be Ra = 3 nm.

Next, Vitron CH-8000: 40 ml, ultrapure water: 40 ml, 1-propanol: 20 ml (20% by volume) were mixed and prepared as a hole transport ink to obtain an ink. In addition, as a pretreatment, the substrate 1 before applying the hole transport ink was irradiated with ultraviolet rays for 3 minutes using an ultraviolet ray-ozone cleaning device (UV / O ₃ ) manufactured by Oak Seisakusho. The hole transport layer 4 was applied by a nozzle printing method. Then, the board | substrate 1 was put into the 30 degreeC vacuum drying furnace, and the vacuum drying was performed. The pressure at this time became 10 kPa in about 40 seconds, and after 5 minutes it became 0.5 kPa. Then, the pressure was returned to atmospheric pressure, and the reduced pressure drying process was completed. Thereafter, the substrate 1 is taken out, and the portion where the hole transport layer 4 on the electrode is unnecessary is wiped off, and then the hole transport layer 4 is baked in the atmosphere at 200 ° C. for 30 minutes to transport the hole. Layer 4 was formed. The film thickness of the hole transport layer 4 at this time was 50 nm. The applied state of the formed hole transport layer 4 was confirmed.

  Next, an organic light-emitting ink in which a polyphenylene vinylene derivative, which is an organic light-emitting material, is dissolved in toluene so as to have a concentration of 1% is used. The light emitting layer 5 was patterned by a nozzle printing method. At this time, the thickness of the dried organic light emitting layer 5 was 50 nm at the center of the pixel.

  On top of this, Alq3 (tris (8-quinolinolato) aluminum), which is an electron transport material, was formed by mask vapor deposition to a thickness of 30 nm by resistance heating vapor deposition.

  Finally, the counter electrode 7 made of LiF (lithium fluoride) and Al (aluminum) was formed by mask vapor deposition using a resistance heating vapor deposition method in a line pattern orthogonal to the line pattern of the pixel electrode 2. The line pattern of the counter electrode 7 was a line width of 90 μm and a space of 30 μm. At this time, after forming the LiF layer with a thickness of 0.5 nm, Al was formed with a thickness of 150 nm. Finally, in order to protect these organic EL constituents from external oxygen and moisture, they were hermetically sealed using a glass cap and an adhesive to produce an organic EL element.

  In the periphery of the display portion of the obtained organic EL display panel, there are an anode-side extraction electrode connected to each pixel electrode 2 and a cathode (counter electrode 7) -side extraction electrode, which are connected to a power source. Thus, lighting display confirmation of the obtained organic EL element was performed, and in particular, the light emission state in the pixel was confirmed. When the light emission state was observed, a state where almost the entire pixel was emitting light was observed. When the light emitting region was evaluated, it was 90% with respect to the pixel opening area.

(Comparative Example 1)
In Comparative Example 1, after the partition walls were formed, UV treatment was performed, and then each layer was formed. When the surface roughness of the partition 3 was measured, it was Ra = 0.3 nm.

  When the obtained organic EL display panel was observed for light emission, only about half of the pixels were emitting light. When the light emitting region was evaluated, it was 45% with respect to the pixel opening area.

DESCRIPTION OF SYMBOLS 1 ... Translucent substrate, 2 ... Pixel electrode, 3 ... Partition, 4 ... Hole transport layer, 5 ... Organic light emitting layer, 6 ... Electron transport layer, 7 ... Counter electrode, 8 ... Glass cap, 9 ... Adhesive, DESCRIPTION OF SYMBOLS 11 ... Upper electrode, 12 ... Lower electrode, 13 ... Substrate to be processed, 14 ... High frequency power supply

Claims (5)

  A pixel electrode, a counter electrode, a light emitting medium layer including an organic light emitting layer, and a partition made of a resin composition that partitions a light emitting region corresponding to the pixel electrode are formed on at least the substrate, and the organic material is formed from the pixel electrode and the counter electrode. An organic electroluminescence panel that emits light from the organic light emitting layer by passing a current through a medium layer, wherein the side surface roughness of the partition wall is about 3 nm or more.   2. The organic electroluminescence panel according to claim 1, wherein a contact angle of the partition wall is 10 degrees or less with respect to xylene.   A manufacturing method for manufacturing the organic electroluminescence panel according to claim 1, wherein a step of forming a partition made of a resin composition on a substrate and a roughening treatment are performed on the upper surface of the partition and the exposed side surface. And a process for producing an organic electroluminescence panel.   4. The method for manufacturing an organic electroluminescence panel according to claim 3, wherein the roughening treatment is a plasma treatment by oxygen plasma irradiation.   A manufacturing method for manufacturing the organic electroluminescence panel according to claim 1, wherein a step of forming a partition made of a resin composition on a substrate and a roughening treatment are performed on the upper surface of the partition and the exposed side surface. And a step of forming a pixel by applying ink to a region surrounded by a partition wall by a nozzle printing method.

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