JP2007026684A - Organic electroluminescent display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL display device hardly restricted in equipment and material and having an organic electroluminescent layer constructed of layers respectively formed into required shapes by a method easily carried out in a short time. <P>SOLUTION: A mask 11 having an aperture part patterned equally to a pattern of a hole transport layer is arranged on a substrate 1 upper face, and from the upper face of the mask 11, a solution or a dispersion liquid of a material constituting the hole transport layer is sprayed and dried up for forming the hole transport layer. Only the mask is required as equipment, while a layer with uniform film thickness can be formed since film thickness can be controlled easily. Differently from a method removing an unnecessary part after forming a layer over the whole surface, no removal of an unnecessary part is required, and consequently, there is no possibility of short-circuit due to dust generated in the removal process. Therefore, formation can be carried out efficiently and stably without requiring any complicated process. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic electroluminescence display device (hereinafter referred to as an organic EL display device) in which organic thin film electroluminescence elements (hereinafter referred to as organic EL elements) utilizing the electroluminescence phenomenon of an organic thin film are arranged.

  The organic EL element applies a voltage to a conductive light emitter, recombines injected electrons and holes, and causes the light emitter to emit light during the recombination. Generally, this organic EL element is configured by providing an anode made of a transparent electrode such as ITO on a translucent substrate, and sequentially laminating a light emitting layer and a cathode on the anode.

  Thus, although both electrodes can be directly laminated on both sides of the phosphor layer, for the purpose of increasing the luminous efficiency, a hole injection layer or a hole transport layer is provided between the anode and the phosphor layer. In many cases, a single layer or both layers are provided, or an electron injection layer, an electron transport layer, or the like is provided between the cathode and the phosphor layer. The whole of these hole injection layers sandwiched between both electrodes is called an organic light emitting medium layer.

  The organic EL display device is a display device in which the organic EL element is used as a pixel, a large number of the pixels are arranged on a plane, and each pixel is controlled to display a screen. For example, the transparent electrode (anode) is provided in a stripe shape, while the cathode is provided in a stripe shape in a direction intersecting the transparent electrode, the organic light emitting medium layer is provided at a position corresponding to the intersection of both electrodes, Constitutes a pixel. Then, by selecting one of the striped transparent electrodes (anodes) and selecting one of the striped cathodes, a voltage is applied between the transparent electrode (anode) thus selected and the cathode. Then, the organic light emitting medium layer arranged at the pixel portion at the intersection is selectively emitted to display on the screen. In order to apply a voltage between the striped transparent electrode (anode) and the striped cathode, an anode-side extraction electrode and a cathode-side extraction electrode are respectively provided on the substrate in the peripheral portion outside the display screen. Is formed. In general, the organic EL display device is configured by covering a display screen and sealing it with a metal sealing can, and adhering and fixing it to the substrate at the periphery.

  Although it is possible to arrange the light emitting layers provided in the respective pixel portions to emit light having the same color, in this case, a single color display device is obtained. In the case of displaying a color screen, it is necessary to arrange light emitting layers that emit light in different colors at respective pixel portions in a pattern. Generally, they are red (R), green (G), and blue (B) corresponding to the three primary colors of light. Further, yellow (Y), cyan (C), and magenta (M) corresponding to the complementary colors may be used.

  In addition, the hole transport layer or the like does not need to be arranged in a pattern at each pixel part. However, if the hole transport layer exists in the outer periphery of the display screen, the cathode and the hole transport layer are in direct contact with each other to leak. A current flows, and the voltage applied to the pixel portion is reduced. In addition, if there is a hole transport layer at a location where the sealing can is bonded to the translucent substrate, sealing may be insufficient, and deterioration of the element may be promoted. In addition, when a large substrate is used as a substrate and an image display device is produced on this substrate by multi-cavity, a portion where no hole transport layer is present is disposed between the display screen and the display screen. It is necessary to expose the anode side extraction electrode and the cathode side extraction electrode. For these reasons, the hole transport layer also needs to be provided in a pattern that covers the display screen and does not exist in the outer peripheral portion.

As a method of providing the light emitting layer and the hole transport layer in a pattern, there are roughly two types of methods.

  The first method is a method in which each of the light emitting layer and the hole transport layer is selectively applied to necessary portions to form each patterned layer. For example, by using an inkjet method or a screen printing method, a light-emitting layer or a hole transport layer can be selectively formed at a necessary portion (see Patent Document 1). This method has a problem that a large-scale apparatus is required or the film formation time becomes long, and the film thickness is difficult to control. In addition, there are many restrictions such as a narrow selection range of ink suitable for each printing method.

  The second method is a method in which the light emitting layer and the hole transport layer are once formed on the entire surface of the substrate, and then each layer of unnecessary portions is removed (see Patent Document 2). Examples of the method for forming the entire surface of the substrate include spin coating, dipping, bar coating, and slit coating. Further, as a method for removing unnecessary portions, for example, there is a method in which a hole transport layer is removed by wiping by adding a solvent to a water-absorbing elastic body such as urethane foam.

  This method is complicated because it requires a step of removing unnecessary portions after film formation on the entire surface of the substrate, and the complexity increases as the substrate size increases. In particular, when the film is formed by a spin coating method, the film thickness becomes large at the peripheral edge portion, so that the removal of the layer at the peripheral edge portion is complicated.

Further, when the hole transport layer is removed by adding a solvent to the water-absorbing elastic body, the solvent may permeate the hole transport layer and may permeate and diffuse to the periphery of the removed portion. For this reason, there exists a problem which a hole transport layer swells and a film thickness changes, or a film thickness tends to become non-uniform | heterogenous from the difference in a drying rate. In addition, dust may be generated when unnecessary parts are removed, which may cause a short circuit.
JP 2003-257654 A JP2005-5020

  Therefore, the present invention has an object to provide an organic EL display device in which each layer constituting the organic light emitting medium layer is formed in a necessary shape by a method that can be easily and quickly performed with less restrictions on equipment and materials. And

That is, the invention described in claim 1 is formed by laminating a patterned transparent electrode, an organic light emitting medium layer arranged in a pixel part, and a counter electrode in this order on a translucent substrate. An organic electroluminescence display element that emits light from the organic light emitting medium layer by applying a voltage therebetween,
The organic light emitting medium layer is composed of a single layer of a light emitting layer that emits light when a voltage is applied, or a multilayer structure in which a light emitting auxiliary layer having a function of improving luminous efficiency in addition to the light emitting layer is laminated,
In the organic electroluminescence display device in which at least one of the layers constituting the organic light emitting medium layer is provided in a pattern,
The patterned layer is formed by disposing a mask having openings of the same pattern as this pattern on the upper surface of the substrate, spraying the solution or dispersion liquid from the upper surface of the mask, and drying. It is an organic electroluminescence display element.

According to invention of Claim 1, since each said layer which comprises an organic light emitting medium layer is formed by spraying and drying the solution or dispersion liquid, the control of the film thickness is easy and it is uniform film thickness Each layer can be formed.

  Further, since it is formed by spraying and drying through a mask having openings having the same pattern as the pattern, only the mask is necessary.

  In addition, since each of these layers is formed in a pattern, unlike the second method, it is not necessary to remove unnecessary portions, and there is no possibility of a short circuit due to dust generation in this removal step. For this reason, not only in the case of one-sided manufacturing of a single display device from a single substrate, but also in the case of multiple-sided manufacturing of a large number of display devices on a large substrate using a large substrate, a complicated process It is possible to form each layer constituting the organic light emitting medium layer efficiently and stably without going through.

  The invention described in claim 1 can be applied to the case where the light emitting layer is formed in a pixel pattern, but can be preferably applied to the case where the layer is formed in a pattern that is relatively larger than such a fine pattern. For this reason, the inventions according to claims 2 and 3 are limited to the light emission auxiliary layer or the like that covers the display screen and is provided in a pattern shape that does not exist in the outer peripheral portion.

That is, the invention according to claim 2 is based on the invention according to claim 1,
The patterned layer is a light emission auxiliary layer.

The invention according to claim 3 is based on the invention according to claim 1 or 2,
The light emission auxiliary layer is a layer having a hole transport function or a hole injection function.

Next, the invention according to claim 4 is based on the invention according to any one of claims 1 to 3.
The solution or dispersion is an aqueous solution or an aqueous dispersion.

  According to the present invention, each of the layers constituting the organic light emitting medium layer can be easily and in a short time with a uniform film thickness, with few restrictions on equipment and materials. In addition, there is an effect that it is possible to form each layer constituting the organic light emitting medium layer efficiently and stably without fear of a short circuit due to dust generation.

  The organic EL display device according to the present invention is formed by laminating a patterned transparent electrode, an organic light emitting medium layer arranged in a pixel part, and a counter electrode in this order on a translucent substrate, and is laminated in the pixel part. The transparent electrode, the organic light emitting medium layer, and the counter electrode constitute an organic EL element. And by applying a voltage between both electrodes for every pixel, the said organic EL element is light-emitted and it displays on a screen. In addition to this, it is usual that the extraction electrode is connected to the transparent electrode and the counter electrode, respectively.

  Next, for convenience of explanation, an organic EL display device will be described by taking an organic EL display device composed of a single organic EL element as an example. That is, FIG. 1 a is a cross-sectional explanatory view of an organic EL display device composed of a single organic EL element. This apparatus includes a translucent substrate 1, a transparent electrode (anode) 2, an organic light emitting medium layer 5 and a counter electrode (cathode) 6 which are sequentially laminated thereon, an anode extraction electrode (not shown), and a cathode extraction. It is comprised with the electrode 8, the whole is covered with the sealing can 9, and it adheres and fixes with the electrically insulating sealing resin.

The organic light emitting medium layer 5 can be composed of a single light emitting layer, but can also be composed of a light emission auxiliary layer that functions to increase the light emission efficiency. The light emission auxiliary layer can be provided between the light emitter layer and the anode, and can also be provided between the light emitter layer and the cathode. Examples of the light emission auxiliary layer provided between the light emitter layer and the anode include a hole transport layer, a hole injection layer, and an electron block layer that assist the movement of holes from the anode to the light emitter layer. Examples of the light emission auxiliary layer provided between the light emitter layer and the cathode include, for example, an electron transport layer, an electron injection layer, a hole block layer, and the like that assist the movement of electrons from the cathode to the light emitter layer.

  In the example shown in the figure, it is composed of two layers of a hole transport layer 3 and a light emitter layer 4 that are sequentially stacked on the transparent electrode (anode) 2. In addition, it can also be composed of two layers of a hole injection layer and a phosphor layer. In addition, an organic light-emitting medium layer having a three-layer structure in which a hole injection layer, a hole transport layer, and a light-emitting layer are sequentially stacked can be used. One layer may have a plurality of these functions. For example, the light-emitting layer may have a hole transport function.

  The film thickness of the organic light-emitting medium layer is 1000 nm or less, preferably 50 to 300 nm as a whole of the organic light-emitting medium layer, regardless of whether it is composed of a single phosphor layer or a multilayer structure.

  As the translucent substrate 1, a glass substrate or a plastic film or sheet can be used. If a plastic film is used, an organic EL element or a display device can be manufactured by winding, and can be provided at a low cost.

  The transparent electrode (anode) 2 can be formed by depositing a complex oxide of indium and tin (hereinafter referred to as ITO) by vacuum deposition or sputtering. Further, instead of ITO, a metal such as aluminum, gold, silver, or the like is used, and a semi-transparent thin film having a thickness of 100 nm or less formed by vacuum deposition or sputtering can be used. Further, an organic semiconductor such as polyaniline can be applied and used as the transparent electrode (anode) 2. In addition, after applying a precursor such as indium octylate or indium acetone on the substrate, it may be formed by a coating pyrolysis method in which an oxide is formed by thermal decomposition. Note that an anode extraction electrode and a cathode extraction electrode 8 (not shown) can be formed in the same process and with the same material.

  Next, the hole injection layer is a layer having a function of transporting holes from the anode, and the hole transport layer is a layer having a function of transporting holes to the light emitting layer. These layers may have both a hole transport function and a hole injection function, and are referred to by either or both names depending on the degree.

  As a material constituting such a hole injection layer or a hole transport layer, for example, copper phthalocyanine, 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′- An aromatic amine-based low molecular weight compound such as biphenyl-4,4′-diamine can be used. Alternatively, a high molecular weight material such as polyaniline, polythiophene, polyvinyl carbazole, a mixture of poly (3,4-ethylenedioxythiophene) and polystyrene sulfonic acid can be used. A polymer material is preferably used in that a layer can be formed by a wet method. These can be used in the form of a solution or dispersion using water or a solvent.

  The luminescent layer 4 recombines electrons and holes injected by applying a voltage between the electrodes 2 and 6, and emits light upon the recombination. The emitted light is radiated to the outside through the transparent electrode (anode) 2 and the translucent substrate 1.

Examples of the material for the light-emitting layer 4 include coumarin-based, perylene-based, pyran-based, anthrone-based, porphyrin-based, quinacridin-based, N, N′-dialkyl-substituted quinacdolin-based, naphthalimide-based, N, N′-diaryl-substituted pyrrolopyrrole. A material obtained by dissolving a luminescent dye such as a polyaniline in a polymer such as polystyrene, polymethyl methacrylate, polyvinyl carbazole or the like can be used. It is also possible to use a dendrimer material, a polymer light emitting material such as PPV, PAF, or polyparaphenylene. Preferably, the material is soluble in water or a solvent and can be made into a solution.

  The electron injection layer is a layer having a function of transporting electrons from the cathode, and the electron transport layer is a layer having a function of transporting electrons to the light emitting layer. These layers may have both an electron transport function and an electron injection function, and are referred to by either or both names depending on the degree. Examples of the material constituting such an electron injection layer or electron transport layer include nitro-substituted fluorenes such as 1,2,4-triazole derivatives (TAZ), diphenylxone derivatives, and the like.

  Next, as the counter electrode (cathode) 6, in order to facilitate electron injection, for example, a metal having a small WF (work function) such as AlLi, FLi, MgIn, Li, Na, Mg, Ca is used alone or as an alloy. Can be used. It is also possible to use a thin film of an alloy of these metals and a stable metal such as gold or silver. Moreover, it can also be set as the multilayer structure comprised by laminating | stacking two or more layers of these metal thin films or alloy thin films. Alternatively, a thin film of conductive oxide such as indium oxide, zinc oxide, or tin oxide can be used. Note that these thin films can be formed by a vacuum film formation method. As the vacuum film forming method, a vacuum deposition method or a sputtering method using resistance heating, EB heating, or the like can be used. The film thickness is not particularly limited, but is preferably 1 nm or more and 500 nm or less.

  Next, FIG. 1B is a cross-sectional explanatory diagram of an organic EL display device configured by arranging organic light emitting medium layers in pixel portions. FIG. 1c is a plan view showing a state in which many such organic EL display devices are formed on one large substrate.

  In the display device of FIG. 1b, as shown in FIG. 2, the transparent electrode (anode) 2 is patterned in a stripe shape, while the counter electrode (cathode) 6 intersects the transparent electrode (anode) 2 It is patterned in a stripe shape. Then, an intersection of the transparent electrode (anode) 2 and the counter electrode (cathode) 6 is used as a pixel part, and a voltage is applied to each pixel part to selectively emit light from the organic light emitting medium layer at the part, thus A screen display is performed with all of the light-emitting pixels and non-light-emitting pixels.

  The transparent electrode (anode) 2 can be formed into a stripe shape by patterning a thin film such as the above-mentioned ITO thin film by a method such as photoetching. The anode extraction electrode 7 and the cathode extraction electrode 8 can be patterned in the same process.

  The organic light-emitting medium layer 5 provided on the transparent electrode (anode) 2 is the same as the case of FIG. 1a with respect to both the layer structure and the material, but the material of the light-emitting body layer 4 is the pixel. It is desirable to use a luminescent material having a different emission color for each. In the illustrated example, a red light emitting layer 4R, a green light emitting layer 4G, and a blue light emitting layer 4B are arranged, and a full color screen can be displayed.

  In the display device shown in FIG. 1b, the hole transport layer 3 is provided in a pattern that covers the display screen and does not exist in the outer peripheral portion. FIG. 3 is a plan view showing a state in which such a hole transport layer is provided on the substrate 12 on which the transparent electrode (anode) 2, the anode extraction electrode 7 and the cathode extraction electrode 8 are provided.

  Such a hole transport layer can be provided by the method shown in FIG. FIGS. 4A to 4C are examples in the case of multi-cavity using a large substrate as the substrate 1 and manufacturing a large number of display devices on the large substrate.

  That is, first, a substrate 1 provided with a transparent electrode (anode) 2, an anode extraction electrode 7 and a cathode extraction electrode 8 is prepared (FIG. 4a). A mask 11 having openings having the same pattern as the hole transport layer pattern is arranged on the substrate 1 in alignment with the substrate 1.

  The alignment between the mask 11 and the substrate 1 can be performed by providing an alignment mark for alignment on the substrate 1 and providing an alignment mark on the other mask 11 and aligning both alignment marks. Further, when the mask 11 and the substrate 1 are placed on the stage, they can be aligned by aligning posts or pins provided on the stage.

  Next, an aqueous solution or an aqueous dispersion of the material of the hole transport layer is sprayed from the spray unit 13 disposed above the aligned mask 11 and dried (FIG. 4b). When spraying over a wide area, the spray head 13 may be moved in the X and Y directions, or the spray head may be arranged on the entire coating surface. The film thickness can be controlled by the discharge amount of the solution or the moving speed of the spray head. The film thickness of the hole transport layer is preferably 10 nm to 200 nm, more preferably 30 to 120 nm.

  Then, by removing the mask 11, it is possible to form a patterned hole transport layer that covers the display screen and does not exist in the outer peripheral portion (FIG. 4c).

  Next, each of the light emitter layers 4R, 4G, and 4B is provided in a pattern at the pixel portion.

  Each of these light emitter layers 4R, 4G, 4B can be provided in the same manner as the hole transport layer 3 described above. That is, by spraying an aqueous solution or dispersion of a luminescent material through a mask having an opening having the same pattern as the pattern of each of the illuminant layers 4R, 4G, and 4B and drying, each illuminant of the pattern Layers 4R, 4G, 4B can be formed.

  Each of the light emitting layers 4R, 4G, and 4B can be formed by a printing method such as a screen printing method or an ink jet method. In the case of forming by these printing methods, the light emitting material can be dissolved in an organic solvent, water, or a mixed solvent thereof to obtain an ink. As the organic solvent, toluene, xylene, anisole, mesitylene, tetralin, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methanol, ethanol, isopropyl alcohol, ethyl acetate, butyl acetate and the like can be used. In addition, surfactants, antioxidants, viscosity modifiers, ultraviolet absorbers and the like may be added to the ink.

  Next, the counter electrode (cathode) 6 is formed in the stripe shape by selectively forming a film on the opening of the vapor deposition mask using a vapor deposition mask when the metal or alloy thin film is vacuum-formed. While forming in a pattern, electrical connection with the cathode extraction electrode 8 can be aimed at. A metal or ceramic mask can be used as the vapor deposition mask.

  An insulating protective layer can be provided on the counter electrode (cathode) 6 with an inorganic material, resin, or the like.

Then, the entire display screen is covered with a sealing can 9 and bonded and fixed with an electrically insulating sealing resin 10 to manufacture the display device of FIG. 1b. As shown in FIG. 1c, when a large number of display devices are manufactured on a large substrate, it is possible to manufacture individual display devices by cutting the substrate before or after bonding and fixing the sealing can 9. It is.

[Example 1]
An ITO thin film was formed thereon using a glass substrate as a translucent substrate. Then, this ITO was etched into a stripe shape to form a transparent electrode (anode) and an anode extraction electrode. At this time, a cathode extraction electrode was also formed.

  Next, a mixture of poly (3,4-ethylenedioxythiophene) and polystyrene sulfonic acid is sprayed through a metal mask having openings of the same pattern as the pattern of the display screen as a material for the hole transport layer, and dried. Thus, a hole transport layer having a thickness of 70 nm was formed.

  Subsequently, the polymer light emitting material poly [2- (2′-ethylhexyloxy) -5-methoxy-1,4-phenylenevinylene] (MEV-PPV) is printed on each pixel portion by screen printing, and the film thickness is increased. A light emitting layer that emits light of each color of red R, green G, and blue B at 90 nm was formed. Next, Mg and Ag were vapor-deposited by a binary vapor deposition method, and a thin film made of these alloys was formed to a thickness of 200 nm to form a counter electrode (cathode). Next, the sealing can was bonded to obtain an organic EL image display device.

When the organic EL image display device thus fabricated was connected to an external circuit and 11 V was applied, all pixels emitted light with an average luminance of 50 cd / m ² . In addition, no leakage current or short circuit was observed.

[Comparative example]
Instead of spraying and drying the hole transport layer, spin-coating a mixture of poly (3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, and no need to use urethane foam and organic solvent An organic EL image display device was produced in the same manner as in Example 1 except that the portions were removed. As a result, a short circuit occurred in this organic EL element, and a non-light emitting portion was generated in the display.

FIG. 1A is a cross-sectional explanatory view of an organic EL display device including a single organic EL element.

  FIG. 1B is a cross-sectional explanatory view of an organic EL display device configured by arranging an organic light emitting medium layer in a pixel portion.

FIG. 1c is a plan view showing a state of multiple imposition.
Plane | planar explanatory drawing which shows the pattern of a transparent electrode (anode), an anode extraction electrode, and a cathode extraction electrode. Plane explanatory drawing which shows the pattern of a positive hole transport layer. 4A to 4C are explanatory views of a method for forming a hole transport layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Translucent board | substrate 2 Anode 3 Hole transport layer 4 Light emitting layer 5 Organic luminescent medium layer 6 Cathode 7 Anode taking out electrode 8 Cathode taking out electrode 9 Sealing can 10 Sealing resin 11 Mask 12 Spray

Claims (4)

On the translucent substrate, a patterned transparent electrode, an organic light emitting medium layer arranged in a pixel portion, and a counter electrode are laminated in this order, and the organic light emission is performed by applying a voltage between both electrodes for each pixel. An organic electroluminescence display element that emits light from a medium layer,
The organic light emitting medium layer is composed of a single layer of a light emitting layer that emits light when a voltage is applied, or a multilayer structure in which a light emitting auxiliary layer having a function of improving luminous efficiency in addition to the light emitting layer is laminated,
In the organic electroluminescence display device in which at least one of the layers constituting the organic light emitting medium layer is provided in a pattern,
The patterned layer is formed by disposing a mask having openings of the same pattern as this pattern on the upper surface of the substrate, spraying the solution or dispersion liquid from the upper surface of the mask, and drying. Organic electroluminescence display element.   The organic electroluminescence display element according to claim 1, wherein the patterned layer is a light emission auxiliary layer.   The organic electroluminescence display element according to claim 1, wherein the light emission auxiliary layer is a layer having a hole transport function or a hole injection function.   The organic electroluminescence display element according to claim 1, wherein the solution or dispersion is an aqueous solution or an aqueous dispersion.