JP7518685B2 - Self-luminous display panel and method for manufacturing self-luminous display panel - Google Patents

Description

The present disclosure relates to a self-luminous display panel in which an organic functional layer in a self-luminous element such as an organic EL element is manufactured by a wet process, and a method for manufacturing the self-luminous display panel.

In recent years, there has been active development of organic EL (Electroluminescence) display panels that utilize the light emitted by organic EL elements. An organic EL element comprises, above a substrate, a pixel electrode for each pixel, an organic functional layer including an organic light-emitting layer, and a counter electrode common to multiple organic EL elements, in that order, and emits light when holes and electrons supplied from the pixel electrode and the counter electrode are recombined in the organic light-emitting layer.

Traditionally, organic functional layers in organic EL display panels have often been formed by dry processes such as vacuum deposition, but with advances in coating technology, the technology of forming organic functional layers by coating methods (wet processes) has become more widespread in recent years.

In the case of an organic light-emitting layer, the coating method involves applying a solution of an organic light-emitting material dissolved or dispersed in a solvent (hereinafter simply referred to as "ink") to the pixel formation area using the nozzle of a printing device, and then drying to form an organic light-emitting layer. This method is advantageous in terms of cost, as it can reduce equipment costs even for large organic EL display panels and has a high material utilization rate.

JP 2013-214397 A JP 2009-300909 A JP 2012-109286 A

In a wet process for forming an organic functional layer by filling a pixel formation region on such a substrate with ink and drying it, when comparing a central region of a predetermined range including the center of the film formation area on the substrate with a peripheral region located outside the surface of the central region in the process of evaporating and drying the ink solvent, the peripheral region has a tendency to have a higher solvent evaporation rate than the central region due to a lower solvent vapor pressure. As a result, the organic functional layer of the pixel formed in the central region of the substrate and the organic functional layer of the pixel formed in the peripheral region of the substrate tend to have different film thicknesses. In this way, when the organic functional layer thickness differs between the pixels in the central region of the substrate and the pixels in the peripheral region of the substrate, the characteristics of each organic functional layer also differ from each other, which causes uneven brightness within the surface of the self-luminous display panel.

The present disclosure has been made in consideration of the above problems, and aims to provide a self-luminous display panel that can achieve uniformity in the film thickness of an organic functional layer in a central region of a predetermined range including the center of the surface of the self-luminous display panel, and in a peripheral region located outside the central region, and a method for manufacturing the self-luminous display panel.

A self-luminous display panel according to one aspect of the present disclosure is a self-luminous display panel in which a plurality of light-emitting elements are arranged in a plane, the light-emitting elements including a pair of opposing electrodes and a plurality of organic functional layers including a light-emitting layer arranged between the pair of electrodes, the plurality of organic functional layers including a first functional layer made of a coating film including a low molecular weight material as a functional material, and a second functional layer including an organic compound having a cross-linked structure as a base layer for the coating film, the second functional layer being characterized in that, when a predetermined range including a central part in the plane of the second functional layer is defined as a first region and a region located outside the plane of the first region is defined as a second region, the cross-linking rate of the organic compound in the second region is higher than the cross-linking rate of the organic compound in the first region.

According to the self-luminous display panel and the method for manufacturing the self-luminous display panel according to the above aspect, it is possible to make the film thickness of the organic functional layer uniform in a central region of a predetermined range including the center of the surface of the self-luminous display panel, and in a peripheral region located outside the central region. This improves the unevenness of the in-plane brightness of the self-luminous display panel.

1 is a block diagram showing an overall configuration of an organic EL display device according to an embodiment; 1 is a plan view of an organic EL display panel 10 according to an embodiment. 2 is a schematic plan view showing an enlarged portion of an image display surface of an organic EL display panel 10. FIG. 4 is a schematic cross-sectional view of the organic EL display element 2 taken along line AA in FIG. 3. FIG. 13 is a process diagram illustrating a process for evaluating the change in the remaining film rate after cleaning of the hole transport layer when the constituent material is changed. FIG. 13 is a diagram showing the measurement results of the film thickness of a hole transport layer before and after a cleaning step, and the film remaining rate after cleaning. FIG. 6A is a schematic diagram of the solvent washing (step S24) in FIG. 5 , and FIG. 6B is a schematic diagram of a method for evaluating a change in the film thickness distribution of the organic light-emitting layer when the amount of the organic compound of the hole transport layer dissolved into the organic light-emitting layer is changed. 6A to 6C are diagrams showing the results of measuring the film thickness distribution of the organic light-emitting layer when the amount of the organic compound of the hole transport layer dissolved into the organic light-emitting layer is changed. 6A and 6B are diagrams showing the results of measuring the film thickness distribution of an organic light-emitting layer when the material constituting the hole transport layer is changed. FIG. 1A is a schematic cross-sectional view illustrating a process for forming an organic light-emitting layer by a coating method when an organic compound having a relatively low cross-linking rate is used as a constituent material of a hole transport layer, and FIG. 1B is a schematic cross-sectional view illustrating a process for forming an organic light-emitting layer by a coating method when an organic compound having a relatively high cross-linking rate is used. 2A and 2B are diagrams showing configurations of coating films and underlayers in the central region and peripheral region of a film formation area of an organic EL display panel 10. 4 is a flowchart showing a manufacturing process of the organic EL display panel 10. 1A to 1D are partial cross-sectional views illustrating a manufacturing process of an organic EL display panel 10. 14(a) to 14(d) are partial cross-sectional views illustrating the manufacturing process following FIG. 13. 15A and 15B are partial cross-sectional views each showing a schematic diagram of a manufacturing process subsequent to that shown in FIG. 14. 16A to 16D are partial cross-sectional views each showing a schematic diagram of a manufacturing process following FIG. 15. 5A to 5C are schematic cross-sectional views for explaining a process of forming an organic light-emitting layer by a coating method.

<<How the present invention was developed>>
When forming an organic functional layer by a coating method, for example, in the film formation process of the light-emitting layer of an organic EL element in an organic EL display panel, in order to define pixels while avoiding the mixing of inks of different organic light-emitting materials, a partition (bank) is provided on a substrate, and if ink is applied in a coating area surrounded by the partition and dried as is, there is a problem that the part in contact with the side of the partition rises up and the center of the organic light-emitting layer becomes a film shape with a recessed shape. Furthermore, in the wet process, as described above, in the process of evaporating and drying the ink solvent, the solvent evaporation speed is higher in the central and peripheral parts of the film formation area because the peripheral part has a lower solvent vapor pressure than the central part, and the drying time of the peripheral part on the substrate tends to be shorter than the drying time of the central part. In this case, the proportion of the part rising up along the side of the partition (hereinafter referred to as the "rising part") in the organic functional layer of one pixel is larger in the central part on the substrate than in the peripheral part, and the central part on the substrate becomes a film shape with a larger recessed center than the peripheral part. As a result, it is difficult to form an organic light-emitting layer with an equivalent thickness within the partition between the central and peripheral parts of the substrate, which tends to reduce the uniformity of the thickness of the light-emitting layer and the uniformity of the light emission within the surface.

This phenomenon can occur not only when forming an organic light-emitting layer, but also when forming other functional layers, such as a hole injection layer, hole transport layer, electron transport layer, or electron injection layer, by coating.

The inventors therefore conducted extensive research to improve the uniformity of the film thickness of the light-emitting layer formed by the coating method, and discovered that convection occurs within the ink between the time it is applied to the substrate and the time it dries, and that this convection is a major hindrance to achieving a uniform film thickness.

Figure 17 is a diagram that shows a schematic diagram of the process of forming a light-emitting layer using a conventional coating method, with the planarization layer, pixel electrode, hole injection layer, etc. not shown.

As shown in the left column of Figure 17, when ink 170 for forming an organic light-emitting layer is dropped from a coating head 301 into an opening 14a on a substrate 11, an ink puddle 171 is formed that rises upward from the opening 14a, as shown in the figure.

As described above, the ink 170 is formed by dissolving an organic light-emitting material in a volatile solvent (organic solvent), and the solvent gradually evaporates from the surface of the ink. The degree of this evaporation is not uniform, and it is generally known that the edge part E (the outer periphery of the surface of the ink reservoir 171) close to the partition wall 14 of the ink reservoir surface evaporates faster than the central part C, which causes convection currents inside the ink reservoir 171.

In other words, the specific gravity of the organic light-emitting material and the solvent are not exactly the same, and depending on the type of combination, the specific gravity of the organic light-emitting material may be greater or less than that of the solvent. As mentioned above, the evaporation speed of the solvent differs from part to part, which causes partial differences in the specific gravity (density) of the ink, and the ink with a relatively high specific gravity tends to move downward under the influence of gravity. Furthermore, if there is a difference in the density of the ink, a force is generated that causes the particles to diffuse in an attempt to make this uniform. Furthermore, it induces Rayleigh convection caused by differences in temperature distribution and Marangoni convection caused by differences in surface tension, and as a result of these convection currents being combined in a complex manner, ink convection occurs as shown by the thick arrow in the center column of Figure 17.

As a result of this convection, the ink is pressed against the inner surface of the partition 14 and moves along said inner surface. Moreover, since the solvent evaporates faster on the outside of the ink reservoir 171 (i.e., the side closer to the inner surface of the partition 14) as described above, a larger amount of ink dries while adhering to the inner surface of the partition 14 (rising portion 17b) as shown in the right column of Figure 17, and it is believed that the light-emitting layer 17 is formed with a large depression in the center portion 17a.

The ink convection direction shown by the dashed arrow in the center of Figure 17 is merely one example, and depending on the combination of the organic light-emitting material and the solvent and other conditions, the ink convection direction may be opposite to that shown in the figure. In any case, as long as convection occurs within the applied ink, the amount of ink moving along the inner wall surface of the partition 14 increases, and the problem of uneven film thickness as shown in the right column of Figure 17 still occurs.

In other words, when ink is applied to the application area surrounded by the partition walls, the solvent evaporates from the surface of the ink, but because there are local differences in the evaporation rate, the density of the ink becomes uneven, causing convection within the applied ink, which in turn creates a force that presses the ink against the side of the partition wall. If drying continues in this state, more of the ink rises up and adheres to the side of the partition wall, and the amount of ink in the center decreases accordingly, forming a concave shape, which is thought to result in uneven film thickness of the organic light-emitting layer after drying.

Therefore, suppressing ink convection caused by local differences in the evaporation speed of the solvent is considered to be an important factor in achieving uniformity in the film thickness of the light-emitting layer. Increasing the viscosity of the ink is an effective way to suppress such ink convection, but increasing the viscosity of the ink makes the nozzles of the printing device more likely to become clogged, causing problems in the printing process.

Therefore, we conducted extensive research into the form of the organic functional layer that can increase the viscosity of the ink while eliminating problems such as nozzle clogging in the printing device, and arrived at the form disclosed herein.

<Overview of the embodiment of the present invention>
The self-luminous display panel of this embodiment is a self-luminous display panel in which a plurality of light-emitting elements are arranged in a surface form, and the light-emitting elements include a pair of opposing electrodes and a plurality of organic functional layers including a light-emitting layer arranged between the pair of electrodes, and the plurality of organic functional layers include a first functional layer consisting of a coating film containing a low molecular weight material as a functional material, and a second functional layer containing an organic compound having a cross-linked structure as a base layer for the coating film, and is characterized in that when a predetermined range including a central part within the plane of the second functional layer is defined as a first region, and a region located outside the plane of the first region is defined as a second region, the cross-linking rate of the organic compound in the second region is higher than the cross-linking rate of the organic compound in the first region.

This configuration makes it possible to make the film thickness of the organic functional layer uniform in a first region (central region) of a predetermined range including the center O of the surface of the self-luminous display panel, and in a second region (peripheral region) located outside the surface of the first region. This makes it possible to improve the unevenness of the in-plane brightness of the self-luminous display panel.

In another aspect, in any of the above aspects, the second functional layer may be configured such that the intramolecular crosslink density of the organic compound in the second region is higher than the intramolecular crosslink density of the organic compound in the first region.

In another aspect, in any of the above aspects, the first functional layer may be configured such that the amount of organic compound per unit area in the light-emitting element located above the second region of the second functional layer is less than the amount of organic compound per unit volume in the light-emitting element located above the first region.

This configuration makes it possible to make the film thickness of the organic functional layer uniform across the surface of the self-luminous display panel, thereby improving the brightness unevenness across the surface.

In another aspect, any of the above aspects may further include a planarization layer on which the light-emitting elements are mounted, and the planarization layer may be configured such that the thermal conductivity in the second region is higher than the thermal conductivity in the first region.

With this configuration, the second region can be baked at a higher baking temperature than the first region, and the cross-linking rate in the second region of the second functional layer can be made higher than the cross-linking rate in the first region.

In another aspect, in any of the above aspects, the planarization layer may be configured such that the layer thickness in the second region is thinner than the layer thickness in the first region.

This configuration allows the thermal conductivity in the second region to be higher than the thermal conductivity in the first region. In another aspect, any of the above aspects may further include a substrate on which the light-emitting elements are mounted, and a resin film may be attached to the substrate below the first region.

This configuration allows the thermal conductivity in the second region to be higher than the thermal conductivity in the first region.

In another aspect, in any of the above aspects, the second functional layer may be configured such that the molecular weight of the organic compound in the second region is higher than the molecular weight of the organic compound in the first region.

This configuration allows the second functional layer to have a higher cross-linking rate of the organic compound in the second region than the cross-linking rate of the organic compound in the first region.

In another aspect, in any of the above aspects, the second functional layer may be configured such that the molecular weight of the organic compound in at least the first region is higher than the molecular weight of the low molecular weight material in the first functional layer.

This configuration increases the amount of organic compound that dissolves into the ink of the upper layer, the first functional layer, from the first region of the second functional layer, thereby thickening the ink of the first functional layer and suppressing convection, thereby making it possible to flatten the film thickness distribution of the first functional layer.

In another aspect, in any of the above aspects, the second functional layer may be a coating film.

In another aspect, in any of the above aspects, the first functional layer may be a light-emitting layer, and the second functional layer may be a hole transport layer.

In another aspect, any of the above aspects may be configured to include a bank that separates the light-emitting elements.

The method for manufacturing a self-luminous display panel according to the present embodiment is a method for manufacturing a self-luminous display panel in which a plurality of light-emitting elements are arranged in a planar shape, and includes the steps of preparing a substrate, forming a plurality of pixel electrodes above the substrate, forming a first functional layer containing an organic compound having a cross-linked structure above the pixel electrodes, forming a coating film containing a low molecular weight material as a functional material on the upper surface of the first functional layer, and forming a counter electrode above the second functional layer. In the step of forming the first functional layer, when a predetermined range including a central portion within the plane of the first functional layer is defined as a first region, and a region located outside the plane of the first region is defined as a second region, the second functional layer is formed such that the cross-linking rate of the organic compound in the second region is higher than the cross-linking rate of the organic compound in the first region.

In another aspect, in any of the above aspects, in the step of forming the lower functional layer, the lower functional layer may be manufactured so that the intramolecular crosslink density of the organic compound in the second region is greater than the intramolecular crosslink density of the organic compound in the first region.

In another aspect, in any of the above aspects, in the step of forming the lower functional layer, the temperature distribution may be adjusted in firing the lower functional layer so that the temperature in the second region is higher than the temperature in the first region.

In another aspect, in any of the above aspects, in the step of forming the upper functional layer, the upper functional layer may be configured to be formed such that the amount of organic compound per unit area contained in the light-emitting element located above the first region of the second functional layer is less than the amount of organic compound per unit volume contained in the light-emitting element located above the second region.

This configuration makes it possible to manufacture a self-luminous display panel in which the thickness of the organic functional layer is uniform in a first region (central region) of a predetermined range including the center O of the surface of the self-luminous display panel, and in a second region (peripheral region) located outside the first region.

<Embodiment>
Hereinafter, an organic EL element, an organic EL display panel, and an organic EL display device according to an embodiment of the present disclosure will be described with reference to the drawings. Note that the drawings include schematic drawings, and the scale and aspect ratio of each component may differ from the actual ones.

<Overall Configuration of Organic EL Display Device 1>
1 is a block diagram showing the overall configuration of an organic EL display device 1. The organic EL display device 1 is used, for example, as a display unit of a television, a personal computer, a mobile terminal, or other electronic device.

The organic EL display device 1 includes an organic EL display panel 10 and a drive control unit 200 electrically connected thereto. In this embodiment, the organic EL display panel 10 is a top-emission display panel in which a plurality of organic EL elements (not shown) are arranged along an image display surface, and an image is displayed by combining the light emitted by each organic EL element. As an example, the organic EL display panel 10 employs an active matrix system.

The drive control unit 200 has a drive circuit 210 connected to the organic EL display panel 10, and a control circuit 220 connected to an external device such as a computer or a receiving device such as a TV tuner. The drive circuit 210 has a power supply circuit that supplies power to each organic EL element, a signal circuit that applies a voltage signal that controls the power supplied to each organic EL element, and a scanning circuit that switches the location to which the voltage signal is applied at regular intervals. The control circuit 220 controls the operation of the drive circuit 210 according to data including image information input from an external device or receiving device.

<Overall configuration of display panel 10>
FIG. 2 is a plan view of the display panel 10 according to the first embodiment. FIG. 3 is an enlarged view of the portion A in FIG. 1. The display panel 10 is an organic EL display panel utilizing the electroluminescence phenomenon of organic materials, and is configured by arranging a plurality of organic EL elements, for example, in a matrix on the upper surface of a planarization layer 12 disposed on a substrate 11. As shown in the figure, the display panel 10 is divided into a central region 10a (first region) corresponding to a predetermined range including the center O of the substrate 11 surface, and a peripheral region 10b (second region) located outside the central region 10a in the substrate 11 surface when viewed in plan. Here, the dimensions of the central region 10a in the substrate 11 in the X direction and the Y direction may be, for example, 50% or more and 90% or less of the dimensions of the display panel 10 in the X direction and the Y direction, respectively. Furthermore, in the substrate 11, the dimensions in the X and Y directions of the peripheral region 10b on one side in the XY direction with respect to the center line CL may be, for example, greater than 5% and less than 25% of the dimensions in the X and Y directions of the display panel 10, respectively.

(A) Planar Configuration Fig. 3 is a schematic plan view showing an enlarged view of part A of the image display surface of the organic EL display panel 10. In the organic EL display panel 10, as an example, sub-pixels 100R, 100G, and 100B that emit light in R (red), G (green), and B (blue) (hereinafter also simply referred to as R, G, and B) are arranged in a matrix. The sub-pixels 100R, 100G, and 100B are alternately arranged in the X direction, and a set of sub-pixels 100R, 100G, and 100B arranged in the X direction constitutes one pixel P. In the pixel P, full color can be expressed by combining the emission luminance of the sub-pixels 100R, 100G, and 100B that have been subjected to gradation control.

In the Y direction, subpixel column CR, subpixel column CG, and subpixel column CB are formed by arranging only subpixel 100R, subpixel 100G, and subpixel 100B, respectively. As a result, pixels P are arranged in a matrix along the X and Y directions in the organic EL display panel 10 as a whole, and an image is displayed on the image display surface by combining the colors of the pixels P arranged in this matrix.

Subpixels 100R, 100G, and 100B (sometimes collectively referred to as "subpixel 100") are provided with organic EL elements 2(R), 2(G), and 2(B) (see FIG. 4; sometimes collectively referred to as "organic EL element 2") that emit R, G, and B colors, respectively.

The organic EL display panel 10 according to this embodiment employs a so-called line bank system. That is, a plurality of partition walls (banks) 14 that separate the sub-pixel columns CR, CG, and CB into individual columns are arranged at intervals in the X direction, and in each of the sub-pixel columns CR, CG, and CB, the sub-pixels 100R, 100G, and 100B share an organic light-emitting layer.

However, in each of the subpixel columns CR, CG, and CB, a plurality of pixel restriction layers 141 that insulate the subpixels 100R, 100G, and 100B from each other are arranged at intervals in the Y direction, so that each of the subpixels 100R, 100G, and 100B can emit light independently.

(B) Cross-sectional configuration Fig. 4 is a schematic cross-sectional view taken along line A-A in Fig. 3. In the organic EL display panel 10, one pixel is made up of three sub-pixels that respectively emit R, G, and B light, and each sub-pixel is made up of an organic EL element 2(R), 2(G), or 2(B) that emits a corresponding color. Since the organic EL elements 2(R), 2(G), and 2(B) of each emitting color basically have almost the same configuration, they will be described as organic EL element 2 when no distinction is required.

As shown in FIG. 4, the organic EL element 2 is composed of a substrate 11, a planarization layer 12, a pixel electrode (anode) 13, a partition wall 14, a hole injection layer 15, a hole transport layer 16, an organic light-emitting layer 17, an electron transport layer 18, an electron injection layer 19, a counter electrode (cathode) 20, and a sealing layer 21. Of these, the hole injection layer 15, the hole transport layer 16, the organic light-emitting layer 17, the electron transport layer 18, and the electron injection layer 19 sandwiched between a pair of opposing pixel electrodes 13 and counter electrodes 20 constitute the functional layers of the light-emitting element 2.

The substrate 11, the planarization layer 12, the electron transport layer 18, the electron injection layer 19, the counter electrode 20, and the sealing layer 21 are not formed for each pixel, but are formed in common for the multiple organic EL elements 2 included in the organic EL display panel 10.

In this embodiment, the organic light-emitting layer 17 is the first functional layer or upper functional layer, and the hole transport layer 16 is the second functional layer or lower functional layer.

(substrate)
The substrate 11 includes a base material 111 made of an insulating material, and a TFT (Thin Film Transistor) layer 112. A driving circuit is formed for each subpixel in the TFT layer 112. The base material 111 may be, for example, a glass substrate, a quartz substrate, a silicon substrate, a metal substrate such as molybdenum sulfide, copper, zinc, aluminum, stainless steel, magnesium, iron, nickel, gold, or silver, a semiconductor substrate such as gallium arsenide, or a plastic substrate.

As the plastic material, either a thermoplastic resin or a thermosetting resin may be used. Examples include polyethylene, polypropylene, polyamide, polyimide (PI), polycarbonate, acrylic resin, polyethylene terephthalate (PET), polybutylene terephthalate, polyacetal, other fluorine-based resins, various thermoplastic elastomers such as styrene-based, polyolefin-based, polyvinyl chloride-based, polyurethane-based, fluorine rubber-based, and chlorinated polyethylene-based, epoxy resin, unsaturated polyester, silicone resin, polyurethane, etc., or copolymers, blends, polymer alloys, etc. that mainly contain these, and a laminate in which one or two or more of these are laminated can be used.

To manufacture a flexible organic EL display panel, it is desirable for the substrate to be made of a plastic material.

(Planarization Layer)
The planarization layer 12 is formed on the substrate 11. The planarization layer 12 is made of a resin material and serves to planarize steps on the upper surface of the TFT layer 112. Examples of the resin material include a positive-type photosensitive material. Examples of such photosensitive materials include acrylic resins, polyimide resins, siloxane resins, and phenol resins. Although not shown in the cross-sectional view of FIG. 4, the planarization layer 12 has contact holes formed for each subpixel.

(Pixel electrode)
The pixel electrode 13 includes a metal layer made of a light-reflective metal material, and is formed on the planarization layer 12. The pixel electrode 13 is provided for each sub-pixel, and is electrically connected to the TFT layer 112 through a contact hole (not shown). In the present embodiment, the pixel electrode 13 functions as an anode.

Specific examples of metal materials with light reflectivity include Ag (silver), Al (aluminum), aluminum alloys, Mo (molybdenum), APC (an alloy of silver, palladium, and copper), and ARA (an alloy of silver, rubidium, and gold). The pixel electrode 13 may be composed of a metal layer alone, or may have a laminated structure in which a layer of a metal oxide such as ITO (indium tin oxide) or IZO (indium zinc oxide) is laminated on top of the metal layer.

(Partition wall/pixel regulation layer)
The partitions 14 separate the pixel electrodes 13 arranged for each sub-pixel above the substrate 11 into columns in the X direction (see FIG. 3), and have a line bank shape extending in the Y direction between the sub-pixel columns CR, CG, and CB arranged in the X direction. An electrically insulating material is used for the partitions 14. Specific examples of the electrically insulating material include insulating organic materials (e.g., acrylic resins, polyimide resins, novolac resins, phenolic resins, etc.).

The partitions 14 function as structures to prevent the inks of each color applied from overflowing and mixing when the organic light-emitting layer 17 is formed by a coating method. When using a resin material, it is preferable that the material has photosensitivity from the viewpoint of processability. The partitions 14 are preferably resistant to organic solvents and heat. In addition, in order to prevent the ink from flowing out, it is preferable that the surface of the partitions 14 has a predetermined liquid repellency.

The pixel restriction layer 141 is made of an electrically insulating material, covers the ends of the pixel electrodes 13 adjacent in the Y direction (Figure 2) in each subpixel column, and separates the pixel electrodes 13 adjacent in the Y direction. It has the role of suppressing discontinuity of the organic light-emitting layer 17 in each subpixel column CR, CG, CB, and improving the electrical insulation between the pixel electrodes 13 and the counter electrode 20.

The film thickness of the pixel restriction layer 141 is set to be smaller than the thickness up to the top surface of the organic light-emitting layer 17 in an ink state, but larger than the thickness of the top surface of the organic light-emitting layer 17 after drying. As a result, the organic light-emitting layer 17 in each subpixel row CR, CG, CB is not partitioned by the pixel restriction layer 141, and the flow of ink is not impeded when forming the organic light-emitting layer 17. This makes it easy to make the thickness of the organic light-emitting layer 17 in each subpixel row uniform.

(Hole injection layer)
The hole injection layer 15 is provided on the pixel electrode 13 for the purpose of promoting the injection of holes from the pixel electrode 13 to the light emitting layer 17. Examples of the hole injection layer 15 include oxides of Ag (silver), Mo (molybdenum), Cr (chromium), V (vanadium), W (tungsten), Ni (nickel), Ir (iridium), etc., low molecular weight organic compounds such as copper phthalocyanine (CuPc), and polymer materials such as polyethylenedioxythiophene/polystyrenesulfonic acid (PEDOT/PSS).

(Hole transport layer (second functional layer, lower functional layer))
The hole transport layer 16 has a function of transporting holes injected from the hole injection layer 15 to the organic light emitting layer 17. The hole transport layer 16 also functions as a base layer for the organic light emitting layer 17 described later, and has a configuration including an organic compound having a crosslinked structure. Examples of the hole transport layer 16 include arylamine derivatives, fluorene derivatives, spiro derivatives, carbazole derivatives, pyridine derivatives, pyrazine derivatives, pyrimidine derivatives, triazine derivatives, quinoline derivatives, phenanthroline derivatives, phthalocyanine derivatives, porphyrin derivatives, silole derivatives, oligothiophene derivatives, condensed polycyclic aromatic derivatives, and metal complexes. The hole transport layer 16 may be a high molecular compound such as a polymer or a low molecular compound such as a monomer, and is formed by a wet process such as a coating method using an ink in which a high molecular compound and/or a low molecular compound is dissolved in a solvent.

The hole transport layer 16 is configured such that the cross-linking rate of the organic compound in the second region 16b (see FIG. 2) located on the peripheral region 10b in the substrate 11 surface is higher than the cross-linking rate of the organic compound in the first region 16a (see FIG. 2) located on the central region 10a in the substrate 11 surface. Specifically, the cross-linking rate of the hole transport layer 16 in the second region 16b may be, for example, about 100%, and the cross-linking rate of the first region 16a may be 98% or more and 99% or less. Such a hole transport layer 16 can be realized by configuring the organic compound in the second region 16b so that the intramolecular cross-linking density is higher than the intramolecular cross-linking density of the organic compound in the first region 16a. Such a hole transport layer 16 can be manufactured, for example, by using a material containing an organic compound with a molecular structure having a higher intramolecular crosslink density in the second region 16b of the hole transport layer 16 than in the first region 16a, or by adjusting the temperature distribution of the substrate 11 in the baking process so that the baking temperature for the second region 16b is higher than the baking temperature for the first region 16a. For example, the temperature distribution of the substrate may be adjusted by controlling the distribution of airflow in the chamber or by varying the heat insulating structure of the substrate 11 within the plane. In this case, the airflow in the chamber may be controlled by giving an in-plane temperature distribution to the hot plate on which the substrate 11 is placed during the baking process.

(Organic Light Emitting Layer (First Functional Layer, Upper Functional Layer))
The organic light-emitting layer 17 is formed in the opening 14a, and has a function of emitting light of each color R, G, and B by recombination of holes and electrons. When it is necessary to particularly specify the emitted light color, they are referred to as organic light-emitting layers 17(R), 17(G), and 17(B).

In this embodiment, the organic light-emitting layer 17 is configured to be a coating film formed by applying an ink containing an organic light-emitting material and a predetermined solvent to a base layer and then drying it to form a film. Examples of organic light-emitting materials used in the organic light-emitting layer 17 include oxinoid compounds, perylene compounds, coumarin compounds, azacoumarin compounds, oxazole compounds, oxadiazole compounds, perinone compounds, pyrrolopyrrole compounds, naphthalene compounds, anthracene compounds, fluorene compounds, fluoranthene compounds, tetracene compounds, pyrene compounds, coronene compounds, quinolone compounds and azaquinolone compounds, pyrazoline derivatives and pyrazolone derivatives, rhodamine compounds, chrysene compounds, phenanthrene compounds, cyclopentadiene compounds, stilbene compounds, diphenylquinone compounds, styryl compounds, butadiene compounds, and the like. Fluorescent substances such as metal complexes of 8-hydroxyquinoline compounds, dicyanomethylenepyran compounds, dicyanomethylenethiopyran compounds, fluorescein compounds, pyrylium compounds, thiapyrylium compounds, selenapyrylium compounds, telluropyrylium compounds, aromatic aldadiene compounds, oligophenylene compounds, thioxanthene compounds, anthracene compounds, cyanine compounds, acridine compounds, metal complexes of 8-hydroxyquinoline compounds, metal complexes of 2-bipyridine compounds, complexes of Schiff salts and Group III metals, metal complexes of oxine, and rare earth complexes, as well as phosphorescent substances such as phosphorescent metal complexes such as tris(2-phenylpyridine)iridium, can be used.

It may also be formed using a polymeric compound such as polyfluorene or its derivatives, polyphenylene or its derivatives, or polyarylamine or its derivatives, or a mixture of the above low molecular weight compounds and the above high molecular weight compounds.

The organic light-emitting layer 17 is configured such that the amount of organic compound per unit area in the organic EL element 2 located above the second region 16b of the hole transport layer 16 is less than the amount of organic compound per unit volume in the organic EL element 2 located in the layer above the first region 16a of the hole transport layer 16. Here, the term "organic compound" refers to the amount of organic compound in the organic light-emitting layer 17 when the organic compound having a cross-linked structure contained in the hole transport layer 16, which is the base layer, moves into the organic light-emitting layer 17 and is present therein.

The ink used to form the organic light-emitting layer 17, which is a coating film, will be described in detail later.

(Electron Transport Layer)
The electron transport layer 18 has a function of transporting electrons from the counter electrode 20 to the light emitting layer 17. The electron transport layer 18 may be made of an organic material having high electron transport properties, such as a π-electron low molecular weight organic material such as an oxadiazole derivative (OXD), a triazole derivative (TAZ), or a phenanthroline derivative (BCP, Bphen).

(Electron Injection Layer)
The electron injection layer 19 has a function of injecting electrons supplied from the counter electrode 20 into the light emitting layer 17. The electron injection layer 19 is formed, for example, by doping an organic material having high electron transportability with a metal selected from alkali metals and alkaline earth metals, such as lithium (Li), sodium (Na), potassium (K), calcium (Ca), or barium (Ba).

Examples of organic materials used in the electron injection layer 19 include π-electron low-molecular-weight organic materials such as oxadiazole derivatives (OXD), triazole derivatives (TAZ), and phenanthroline derivatives (BCP, Bphen).

(Counter electrode)
The counter electrode 20 is made of a light-transmitting conductive material and is formed on the electron injection layer 19. The counter electrode 20 functions as a cathode.

The counter electrode 20 may be made of a metal such as silver, a silver alloy, aluminum, or an aluminum alloy. In this case, since the counter electrode 20 needs to be translucent, the thickness is preferably 10 nm to 50 nm.

(Sealing layer)
The sealing layer 21 is provided to prevent organic layers such as the hole transport layer 16, the light emitting layer 17, the electron transport layer 18, and the electron injection layer 19 from being deteriorated due to exposure to external moisture or air.

The sealing layer 21 is formed using a light-transmitting material such as silicon nitride (SiN) or silicon oxynitride (SiON).

(others)
4, an anti-glare polarizing plate or an upper substrate may be attached via a transparent adhesive onto the sealing layer 21. Also, a color filter may be attached to correct the chromaticity of the light emitted by each organic EL element 2. This can further protect the hole transport layer 16, the organic light-emitting layer 17, the second functional layer 19, etc. from external moisture and air.

<Formation of organic functional layers by coating method>
In this embodiment, the functional layers of hole injection layer 15, hole transport layer 16, and organic light-emitting layer 17 are formed by a coating method in which an ink containing a functional material and a solvent is applied to a base layer and then dried to form a film. The formation of hole injection layer 15, hole transport layer 16, and organic light-emitting layer 17 by the coating method will be described below.

(Composition of ink for forming functional layer)
First, the ink used in the process of forming the hole transport layer 16 and the organic light emitting layer 17 by a coating method will be described.

[Solute]
The following solutes can be used in the ink used in the process of forming the organic light-emitting layer 17.

Solutes with functionality include polymeric materials and low molecular weight materials. Polymeric materials have a relatively high viscosity, but have drawbacks such as a molecular weight distribution and being difficult to purify and achieve high purity. Therefore, when used in organic EL elements, the color purity of the emitted color, luminous efficiency, brightness, etc. tend to be low.

In contrast, the display panel 10 may be configured to include an organic light-emitting layer 17 that uses a light-emitting material made of a low molecular weight material. An organic light-emitting layer that uses a light-emitting material made of a low molecular weight material can be manufactured more easily and with a shorter synthesis route than the polymer functional materials described above, and can be purified to a high purity by known techniques such as column chromatography and recrystallization. Therefore, when used in an organic EL element, it has the advantages of excellent luminous efficiency, high color purity, and a wide variety of colors.

Here, "low molecular weight" preferably means a molecular weight Mw (weight average molecular weight) of 3000 or less. The molecular weight Mw of an organic material can be measured using known low molecular weight GPC (gel permeation chromatography) or LC (liquid chromatography).

In addition, if the ink for forming the organic light-emitting layer 17 satisfies the condition that the ink viscosity at a solute concentration of 3 wt % is less than twice the viscosity of the solvent alone, the solute is not limited to the above-mentioned "low molecular weight" so a polymeric organic compound with a relatively low molecular weight may be used.

In addition, the ink used in the process of forming the hole transport layer 16 can contain, as a solute, the various derivatives mentioned above, condensed polycyclic aromatic derivatives, metal complexes, polymers and other high molecular weight compounds, and monomers and other low molecular weight compounds.

Similarly, the ink used in the process of forming the hole transport layer 15 can contain the above-mentioned various metal oxides, low molecular weight organic compounds, polymeric materials, etc. as solutes.

[Solvent]
The inks used in the processes of forming the hole injection layer 15, the hole transport layer 16, and the organic light emitting layer 17 may contain the following solvents.

When the solute is a polymeric material, the viscosity of the ink naturally increases as the solvent evaporates, suppressing convection and allowing the formation of a relatively uniform film thickness. In contrast, when the solute is a low-molecular-weight material, the solute itself has little thickening effect, and the viscosity of the ink tends to depend almost entirely on the viscosity of the solvent.

In the display panel 10, the ink solvent for the solute, which is made of a low molecular weight functional material, can be an aromatic solvent, a hydrocarbon solvent, a halogen solvent, an ester solvent, an ether solvent, an alcohol solvent, etc.

Aromatic solvents include benzene, toluene, xylene, mesitylene, ethylbenzene, linear or branched propylbenzene, butylbenzene, pentylbenzene, hexylbenzene, nonylbenzene, decylbenzene, undecylbenzene, dodecylbenzene, tetralin, cyclohexylbenzene, etc.

Examples of hydrocarbon solvents include linear, branched, saturated, and unsaturated hydrocarbon solvents with 6 or more carbon atoms, such as hexane, heptane, octane, nonane, decane, and undecane.

Halogen-based solvents include dichloromethane, dichloroethane, chloroform, carbon tetrachloride, tetrachloroethane, trichloroethane, chlorobenzene, dichlorobenzene, and chlorotoluene.

Ester solvents include ethyl acetate, butyl acetate, amyl acetate, octyl acetate, etc.

Examples of ether solvents include dibutyl ether, tetrahydrofuran, dioxane, anisole, and 3-phenoxytoluene.

An example of an alcohol-based solvent is isopropyl alcohol.

The above-mentioned solvents may be used alone or in combination of two or more.

<Verification experiment>
(Relationship between baking temperature and cross-linking rate of hole transport layer 16)
The remaining film ratio after cleaning of the hole transport layer 16 was measured when the baking temperature for forming the hole transport layer 16 was changed. FIG. 5 is a process diagram of a process for evaluating the change in the crosslinking rate of the hole transport layer when the baking temperature is changed. FIG. 7(a) is a schematic diagram of the solvent cleaning (step S24) in FIG. 5. As shown in FIG. 5, this evaluation method forms an ink using an organic compound for forming the hole transport layer (step S21), forms a film of the ink on a glass substrate by a spin coating method, and bakes the ink to form a hole transport layer (step S22), and measures the film thickness (step S23). Thereafter, the surface of the formed hole transport layer is washed with a solvent used in the ink for forming the organic light-emitting layer (step S24, FIG. 7(a)), and the film thickness after cleaning is measured (step S25), and the remaining film ratio after cleaning is evaluated.

Figure 6 shows the results of measuring the thickness of the hole transport layer before and after the cleaning process, and the remaining film rate after cleaning. In the evaluation, the baking was performed under two conditions: Condition A: 190°C for 60 minutes, and Condition B: 200°C for 60 minutes. Note that the baking was performed in a nitrogen atmosphere in both cases.

As shown in Figure 6, a 100% film remaining rate was obtained under baking conditions of 200°C for 60 minutes (condition B), whereas a 98-99% film remaining rate was obtained under baking conditions of 190°C for 60 minutes (condition A).

From this, it can be seen that under the baking condition of 200°C for 60 minutes, the organic compounds in the hole transport layer do not dissolve into the solvent of the ink for forming the organic light-emitting layer, whereas under the baking condition of 190°C for 60 minutes, the organic compounds in the hole transport layer dissolve into the solvent of the ink for forming the organic light-emitting layer. In other words, when the cross-linking rate is relatively low, the organic compounds for forming the hole transport layer dissolve into the solvent of the ink for forming the organic light-emitting layer.

(Relationship between the amount of organic compound dissolved from the hole transport layer into the organic light-emitting layer and the film thickness distribution of the organic light-emitting layer)
The thickness distribution of the organic light-emitting layer was measured by changing the amount of the organic compound of the hole transport layer dissolved into the organic light-emitting layer. FIG. 7(b) is a schematic diagram of a method for evaluating the change in the thickness distribution of the organic light-emitting layer when the amount of the organic compound of the hole transport layer dissolved into the organic light-emitting layer is changed. In this evaluation method, a predetermined amount of an organic compound for forming a hole transport layer is added to an ink for forming an organic light-emitting layer made of a low molecular weight organic compound (FIG. 7(b)), the ink is applied in an area surrounded by a bank by inkjet, dried, and the thickness distribution is measured. In addition, a hole transport layer formed under baking conditions of 200° C. and 60 minutes was used as the underlayer when applying the ink. By forming the film under conditions of 100% remaining film rate at 200° C. and 60 minutes, the influence of dissolution of the organic compound after application can be reduced.

Figures 8 (a) to (c) show the results of measuring the thickness distribution of the organic light-emitting layer when the amount of the organic compound for the hole transport layer added to the organic light-emitting layer is changed. (b) shows the results when 2 wt% of the organic compound for forming the hole transport layer is added to the ink for forming the organic light-emitting layer, (c) shows the results when 5 wt% is added, and (a) shows the results when no organic compound is added. The horizontal axis shows the distance in the width direction (short axis direction) of the partition wall in units of [μm]. In this example, the width of the partition wall is 60 [μm], and the center position in the width direction is set to "0", and the partition walls exist at positions -30 [μm] and +30 [μm] almost perpendicular to the horizontal axis. The vertical axis shows the height of the surface of the light-emitting layer from the coating surface of the lower layer, i.e., the film thickness, in units of [nm].

As shown in Figure 8, when no organic compound was added (a), a film thickness distribution with a nearly uniform film thickness was obtained, while when 2 wt% and 5 wt% of organic compound were added (b) and (c), respectively, the film thickness distribution of the organic light-emitting layer had a convex shape at the center of the subpixel. In other words, it can be seen that when the ink for forming the organic light-emitting layer contains an organic compound for forming the hole transport layer, the film thickness distribution of the formed organic light-emitting layer has a convex shape at the center of the subpixel.

(Relationship between the baking temperature of the hole transport layer 16 and the film thickness distribution of the organic light emitting layer)
The thickness distribution of the organic light-emitting layer was measured when the baking temperature for forming the hole transport layer 16 was changed. Figures 9(a) and (b) are diagrams showing the measurement results of the thickness distribution of the organic light-emitting layer when the baking temperature for the hole transport layer was changed, where (a) is the thickness distribution when the baking condition of 190°C for 60 minutes was used, in which the cross-linking rate of the hole transport layer is relatively low, and (b) is the thickness distribution when the baking condition of 200°C for 60 minutes was used, in which the cross-linking rate is relatively high. As shown in Figure 9, when the baking condition of 190°C for 60 minutes was used (a), the thickness distribution of the organic light-emitting layer was such that the central part of the subpixel had a convex shape, whereas when the baking condition of 200°C for 60 minutes was used (b), the thickness distribution was almost uniform.

Figure 10(a) is a schematic cross-sectional view for explaining the process of forming the organic light-emitting layer in the case of Figure 9(a), and (b) is a schematic cross-sectional view for explaining the process of forming the organic light-emitting layer in the case of Figure 9(b).

As shown in Figure 10 (a), when the baking conditions are 190°C for 60 minutes, the ink for the organic light-emitting layer thickens due to the organic compounds of the hole transport layer dissolved in the ink for the organic light-emitting layer, causing the ink to lose fluidity in the middle of the drying process. As a result, convection does not continue until the end of the drying process, and the film thickness distribution of the organic light-emitting layer tends to have a convex shape in the center of the subpixel.

In contrast, as shown in Figure 10(b), when the baking conditions are 200°C for 60 minutes, the organic compound of the hole transport layer dissolves in the ink for the organic light-emitting layer, and the ink for the organic light-emitting layer is less likely to thicken. Therefore, the ink does not lose its fluidity in the middle of the drying process, and convection continues until the end of the drying process. Depending on the conditions, the ink may rise up on the bank wall, and the film thickness distribution of the organic light-emitting layer may have a relatively concave shape in the center of the subpixel compared to Figure 10(a).

These results show that when the cross-linking rate of the organic compound for forming the hole transport layer is relatively low, the organic compound dissolves in the ink for the organic light-emitting layer, causing the ink to thicken, resulting in a tendency for the thickness distribution of the organic light-emitting layer to have a convex shape in the center of the subpixel. Also, when the cross-linking rate of the organic compound for forming the hole transport layer is relatively high, the organic compound is less likely to dissolve in the ink for the organic light-emitting layer, causing the ink to thicken, resulting in a tendency for the thickness distribution of the organic light-emitting layer to have a concave shape in the center of the subpixel.

<Relationship between the cross-linking rate of the hole transport layer 16 and the in-plane film thickness distribution of the organic light-emitting layer 17>
The relationship between the configuration of the hole transport layer 16 and the film thickness distribution of the organic light emitting layer 17 in the display panel 10 according to the present embodiment will be described below.

In the coating method for manufacturing the organic light-emitting layer 17, in which an ink in which an organic light-emitting material is dissolved or dispersed in a solvent is applied to the substrate surface and then dried to form a coating film, there is a problem that the exhaust speed becomes non-uniform within the surface of the substrate 11 due to the position and structure of the exhaust port of the chamber used for drying, resulting in variation in the film shape. Specifically, as described above, the solvent vapor pressure is lower in the peripheral region than in the central region, so the solvent evaporation rate is faster, and the organic functional layer 17 of the pixel formed in the central region of the substrate and the organic functional layer of the pixel formed in the peripheral region of the substrate tend to have different film thicknesses.

In contrast, the display panel 10 according to the present embodiment changes the cross-linking rate of the hole transport layer 16 between the central region and the peripheral region of the deposition area, thereby changing the amount of organic compound dissolved from the hole transport layer 16, which serves as the base layer, into the ink when the ink of the organic functional layer 17 is applied, thereby controlling the thickening behavior of the ink in the organic functional layer 17 within the plane and suppressing unevenness in the film shape due to differences in exhaust speed. The cross-linking rate of the hole transport layer 16 can be adjusted by changing the material composition and bake temperature for forming the hole transport layer 16, which serves as the base layer, between the central region and the peripheral region of the deposition area, and the cross-linking rate of the hole transport layer 16 can be made different between the central region and the peripheral region.

The crosslinking rate of the organic functional layer can be measured using the following known measurement methods. For example, the relaxation time of the organic compound in the organic functional layer can be measured and calculated using TD-NMR (Time Domain NMR). Alternatively, the ion intensity distribution caused by the underlayer at the depth of the light-emitting layer can be measured using TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry), and the amount of dissolution into the upper layer can be calculated from the intensity.

Figure 11 shows the configuration of the coating film and base layer in the central and peripheral regions of the film formation area of the organic EL display panel 10.

As shown in the upper row of Figure 11, in the peripheral region where the exhaust speed is fast and convection is difficult to occur, convection does not continue due to the thickening of the ink caused by drying, and there is little ink movement toward the bank wall surface, and conventionally, the organic light-emitting layer has a film thickness distribution that is convex in the center of the subpixel. In contrast, the display panel 10 adopts a configuration in which the cross-linking rate of the lower layer, for example, the hole transport layer 16, is increased. This reduces the amount of organic compound that dissolves from the hole transport layer 16 into the ink of the upper layer, for example, the organic functional layer 17, suppresses the thickening of the ink of the organic functional layer 17, maintains convection, promotes ink movement toward the bank wall surface, and flattens the film thickness distribution of the organic light-emitting layer 17.

Also, as shown in the lower part of Figure 11, in the central region where the exhaust speed is slow and convection is likely to occur, conventionally, convection continues and a rise of the ink is formed on the bank wall surface, resulting in a concave film thickness distribution in the central part of the subpixel of the organic light-emitting layer. In contrast, the display panel 10 adopts a configuration in which the cross-linking rate of the lower layer, for example, the hole transport layer 16, is reduced. This increases the amount of organic compound that dissolves from the hole transport layer 16 into the ink of the upper layer, for example, the organic functional layer 17, thereby thickening the ink of the organic functional layer 17 and suppressing convection, thereby flattening the film thickness distribution of the organic light-emitting layer 17.

As a result, the display panel 10 can suppress variations in the film thickness of the organic functional layer 17 within the panel surface, making it possible to obtain uniform light-emitting characteristics within the surface.

<Method of Manufacturing Organic EL Element>
A top-emission organic EL element using the functional layer forming ink according to one embodiment of the present disclosure, an organic EL display panel using the organic EL element, and a method for manufacturing the organic EL element will be described below with reference to Figures 12 to 16. Figure 12 is a flow chart showing the manufacturing process of the organic EL element 2, and Figures 13 to 16 are cross-sectional views that typically show the manufacturing process of the organic EL element 2. Note that the drawings include schematic views, and the scale and aspect ratio of each component may differ from the actual ones.

(Substrate preparation process)
13A, the substrate 11 is prepared by forming a TFT layer 112 on a base material 111 (step S1 in FIG. 12). The TFT layer 112 can be formed by a known TFT manufacturing method.

(Planarization layer formation process)
Next, as shown in FIG. 13B, a planarizing layer 12 is formed on the substrate 11 (Step S2 in FIG. 12).

Specifically, a resin material having a certain degree of fluidity is applied, for example, by a die coating method along the upper surface of the substrate 11 so as to fill in the irregularities on the substrate 11 caused by the TFT layer 112. As a result, the upper surface of the planarization layer 12 has a planar shape along the upper surface of the base material 111.

A contact hole (not shown) is formed in the planarization layer 12 at a location, for example, on the source electrode of the TFT element, by dry etching, and then a connection electrode layer is formed along the inner wall of the contact hole. The connection electrode layer can be formed, for example, by forming a metal film using a sputtering method, and then patterning the metal film using photolithography and wet etching.

(Pixel electrode formation process)
Next, as shown in Fig. 13(c), a pixel electrode material layer 130 is formed on the planarization layer 12. The pixel electrode material layer 130 can be formed by, for example, a vacuum deposition method, a sputtering method, etc. Then, as shown in Fig. 13(d), the pixel electrode material layer 130 is patterned by etching to form a plurality of pixel electrodes 13 partitioned for each sub-pixel (step S3 in Fig. 12).

(Partition wall and pixel regulation layer formation process)
Next, the partition wall 14 and the pixel regulating layer 141 are formed (Step S4 in FIG. 12).

In this embodiment, the pixel regulation layer 141 and the partition wall 14 are formed in separate processes.

[Pixel regulation layer formation]
First, in order to divide the pixel electrode row in the Y direction (FIG. 3) into sub-pixels, a pixel regulating layer 141 extending in the X direction is formed.

As shown in FIG. 14(a), a photosensitive resin material that will be the material of the pixel regulation layer 141 is uniformly applied onto the planarization layer 12 on which the pixel electrodes 13 are formed, to form a pixel regulation layer material layer 1410. The amount of resin material applied at this time is determined in advance so that the pixel regulation layer 141 will have the desired film thickness after drying.

Specific examples of coating methods that can be used include wet processes such as die coating, slit coating, and spin coating. After coating, it is preferable to remove unnecessary solvent by performing, for example, vacuum drying and low-temperature heating and drying (pre-baking) at about 60°C to 120°C, and to fix the pixel regulation layer material layer 1410 to the planarization layer 12.

Then, the pixel regulation layer material layer 1410 is patterned using photolithography. For example, if the pixel regulation layer material layer 1410 has positive photosensitivity, the portions to be left as the pixel regulation layer 141 are shielded from light, and the pixel regulation layer material layer 1410 is exposed to light through a photomask (not shown) through which the portions to be removed are transparent.

Next, development is performed to remove the exposed areas of the pixel regulation layer material layer 1410, thereby forming the pixel regulation layer 141. A specific development method is, for example, to immerse the entire substrate 11 in a developer such as an organic solvent or an alkaline solution that dissolves the exposed portions of the pixel regulation layer material layer 1410, and then wash the substrate 11 with a rinse liquid such as pure water.

Then, by baking (post-baking) at a predetermined temperature, a pixel regulation layer 141 extending in the X direction can be formed on the planarization layer 12 (Figure 14 (b)).

[Partition wall formation]
Next, the partition wall 14 extending in the Y direction is formed in the same manner as the pixel regulating layer 141 .

That is, a resin material for the partition is applied by die coating or the like onto the planarization layer 12 on which the pixel electrodes 13 and pixel regulation layer 141 are formed, to form the partition material layer 140 (FIG. 14(c)). The amount of resin material applied at this time is determined in advance so that the partition 14 will have the desired height after drying. Then, the partition 14 extending in the Y direction is patterned on the partition material layer 140 by photolithography, and the partition 14 is formed by baking at a predetermined temperature (FIG. 14(d)).

In the above, the material layers of the pixel regulation layer 141 and the partition wall 14 are formed by a wet process and then patterned, but it is also possible to form one or both of the material layers by a dry process and then pattern them by photolithography and etching.

(Hole injection layer/hole transport layer formation process)
Next, the hole injection layer 15 and the hole transport layer 16 are formed (Step S5 in FIG. 12).

First, the hole injection layer 15 is formed by dissolving or dispersing a low molecular weight material having the above-mentioned hole injection properties in a mixed solvent, ejecting the ink from the nozzle 3011 of the coating head 301 of the printing device to coat the inside of the opening 14a, and then volatilizing and removing the solvent and/or baking the ink.

The hole transport layer 16 is formed on the hole injection layer 15 by the same coating method as the hole injection layer 15, using an ink in which a low molecular weight material having the above-mentioned hole transport properties is dissolved or dispersed in a mixed solvent. The ink for forming the hole injection layer 15 and the hole transport layer 16 can be applied by a wet film formation method such as an inkjet method, various printing methods such as screen printing, a spin coating method, a dispenser method, etc.

Here, as described above, the hole transport layer 16 is configured such that the cross-linking rate of the organic compound in the second region 16b (see FIG. 2) located on the peripheral region 10b in the substrate 11 surface is higher than the cross-linking rate of the organic compound in the first region 16a (see FIG. 2) located on the central region 10a in the substrate 11 surface. Such a hole transport layer 16 can be manufactured by baking the first region 16a and the second region 16b of the hole transport layer 16 under different baking conditions. For example, in the baking process of the hole transport layer 16, the temperature distribution may be adjusted so that the baking temperature for the second region 16b is higher than the baking temperature for the first region 16a, thereby manufacturing the hole transport layer 16 so that the intramolecular cross-linking density of the organic compound in the second region 16b is higher than the intramolecular cross-linking density of the organic compound in the first region 16a. In this embodiment, the second region 16b of the hole transport layer 16 is baked in a nitrogen atmosphere at a baking temperature of about 200°C for about 60 minutes to form a layer region with a cross-linking rate of 100%, and the first region 16a is baked in a nitrogen atmosphere at a baking temperature of about 190°C for about 60 minutes to form a layer region with a cross-linking rate of 98%. However, it goes without saying that the above-mentioned baking temperature and baking time are merely examples and are not limited to the above conditions.

In addition, if the hole transport layer 16 to be formed satisfies the above cross-linking rate, the hole injection layer 15 and the hole transport layer 16 may be formed by a vapor phase growth method such as vacuum deposition, sputtering, ion beam deposition, or CVD.

Note that FIG. 14(a) shows a schematic cross-sectional view of the display panel 10 when the hole transport layer 16 is being formed after the hole injection layer 15 is formed.

(Organic light-emitting layer formation process)
Next, the organic light-emitting layer 17 is formed above the hole transport layer 16 (Step S6 in FIG. 12).

Specifically, as shown in FIG. 15(b), for example, an ink made by dissolving a low molecular weight organic light-emitting material, which is a constituent material of an organic light-emitting layer of an emission color corresponding to each opening 14a, in the above-mentioned mixed solvent is sequentially discharged from the nozzle 3011 of the coating head 301 of the printing device to coat the hole transport layer 16 in the opening 14a, and the substrate 11 after the ink coating is carried into a vacuum drying chamber and heated in a vacuum environment to evaporate the organic solvent in the ink to form the ink.

At this time, in the second region 16b (peripheral region) where the exhaust speed is fast and convection is unlikely to occur, a configuration with an increased cross-linking rate for the hole transport layer 16 is adopted, thereby reducing the amount of organic compound dissolved from the hole transport layer 16 into the ink of the organic functional layer 17, suppressing thickening of the ink of the organic functional layer 17, maintaining convection and promoting the movement of ink toward the bank wall surface, thereby flattening the film thickness distribution of the organic light-emitting layer 17.

In addition, in the first region 16a (central region) where the exhaust speed is slow and convection is likely to occur, conventionally, convection continues, but by adopting a configuration in which the cross-linking rate of the hole transport layer 16 is reduced, the amount of organic compound dissolved from the hole transport layer 16 into the ink of the organic functional layer 17 is increased, the ink of the organic functional layer 17 is thickened, and convection is suppressed, and the film thickness distribution of the organic light-emitting layer 17 is flattened. In this case, by using ink made of a light-emitting material made of a low-molecular material whose viscosity is less likely to increase compared to polymeric materials, it is possible to suppress the nozzle 3011 while ensuring the fluidity of the ink even after application and appropriately control the film thickness.

In addition, here too, the method of applying the ink for forming the organic light-emitting layer 17 can be a wet film-forming method such as an inkjet method, various printing methods such as screen printing, a spin coating method, a dispenser method, etc.

(Electron transport layer formation process)
Next, as shown in FIG. 16A, ink in which a low molecular weight electron transport material is dissolved in the above-mentioned mixed solvent is applied onto the organic light emitting material layer 170 and the partition walls 14 through the nozzles of a coating head 301 of a printing device. The ink is discharged from 3011 and applied onto the organic light-emitting layer 17 in the opening 14a, and the organic solvent in the ink is evaporated to form the electron transport layer 18 (Step S7 in FIG. 12).

(Electron injection layer formation process)
Subsequently, as shown in FIG. 16B, an electron injecting material is vacuum-deposited on the electron transport layer 18 to form the electron injecting layer 19 (Step S8 in FIG. 12).

(Counter electrode formation process)
Next, the counter electrode 20 is formed on the functional layer 19 (step S9 in FIG. 12).
In the counter electrode formation step, first, a film of silver, aluminum, or the like is formed on the functional layer 19 by sputtering or vacuum deposition (FIG. 16C).

(Sealing layer forming process)
16D, a sealing layer 21 is formed on the counter electrode 20 (step S10 in FIG. 12). The sealing layer 21 can be formed by depositing SiON, SiN, or the like by a sputtering method, a CVD method, or the like.

In this manner, the display panel 10 shown in FIG. 4 is manufactured. Note that the above manufacturing method is merely an example and can be modified as appropriate according to the purpose.

<Summary>
As described above, the self-luminous display panel 10 of this embodiment is a self-luminous display panel 10 in which a plurality of light-emitting elements are arranged in a surface form, and the light-emitting elements include a pair of opposing electrodes 13, 19 and a plurality of organic functional layers 15, 16, 17, 18 including a light-emitting layer 17 arranged between the pair of electrodes 13, 19. The plurality of organic functional layers 15, 16, 17, 18 include a first functional layer 17 consisting of a coating film containing a low molecular weight material as a functional material, and a second functional layer 16 containing an organic compound having a cross-linked structure as a base layer for the coating film. When a predetermined range including the center O of the surface of the second functional layer 16 is defined as a first region 16a and a region located outside the surface of the first region is defined as a second region 16b, the cross-linking rate of the organic compound in the second region 16b is higher than the cross-linking rate of the organic compound in the first region 16a.

This configuration makes it possible to make the thickness of the organic functional layer 17 uniform in the first region 10a (central region) of a predetermined range including the center O of the surface of the self-luminous display panel 10, and in the second region 10b (peripheral region) located outside the surface of the first region 10a. This makes it possible to improve the unevenness of the brightness of the surface of the self-luminous display panel 10.

In other words, in the peripheral region where the exhaust speed is fast and convection is unlikely to occur, the amount of organic compound that dissolves from the hole transport layer 16 into the ink of the upper organic functional layer 17 is reduced, suppressing thickening of the ink of the organic functional layer 17, maintaining convection and promoting ink movement toward the bank wall surface, thereby making it possible to flatten the film thickness distribution of the organic light-emitting layer 17.

In addition, in the central region where the exhaust speed is slow and convection is likely to occur, the amount of organic compound dissolved from the hole transport layer 16 into the ink of the upper organic functional layer 17 can be increased to thicken the ink of the organic functional layer 17 and suppress convection, thereby flattening the film thickness distribution of the organic light-emitting layer 17.

As a result, it is possible to suppress variations in the film thickness of the organic functional layer 17 within the panel surface, and to obtain uniform light-emitting characteristics within the surface.

<<Variations>>
Although the organic EL element 2 and the like according to the embodiments have been described above, the present invention is not limited to the above-described embodiments except for the essential characteristic components. For example, the present invention also includes forms obtained by applying various modifications to the embodiments that a person skilled in the art can conceive, and forms realized by arbitrarily combining the components and functions of the embodiments without departing from the spirit of the present invention. Below, modified examples of the organic EL element and the organic EL display panel will be described as examples of such forms.

(1) In the above embodiment, the hole transport layer 16 is configured such that the cross-linking rate of the organic compound in the second region 16b is higher than the cross-linking rate of the organic compound in the first region 16a by baking the second region 16b located on the peripheral region 10b in the substrate 11 at a higher baking temperature than the first region 16a located on the central region 10a in the substrate 11 of the hole transport layer 16. However, the baking conditions of the first region 16a and the second region 16b may be different depending on the configuration. For example, the thickness of the planarization layer 12 in the second region 16b may be thinner than the thickness of the planarization layer in the first region 10a, and the planarization layer 12 having a higher thermal conductivity in the second region 16b than the thermal conductivity in the first region 10a may be laid on the hole transport layer 16. Alternatively, a heat insulating film having a thickness of several hundred μm may be attached to the back surface of the first region 16a of the substrate 11 to enhance the heat insulating property of the first region 16a. With this configuration, the second region 16b can be baked at a higher baking temperature than the first region 16a of the hole transport layer 16, as in the embodiment, and the cross-linking rate of the second region 16b of the hole transport layer 16 can be made higher than the cross-linking rate of the first region 16a.

(2) In another embodiment, when a low molecular weight material is used for the upper organic light-emitting layer 17, the underlying layer may be configured to use a material and process that results in a film remaining rate of 99% or more for the hole transport layer 16.

As the material for the organic light-emitting layer 17 used in the coating method, a low-molecular-weight material can be selected from the viewpoint of high material performance and maintaining low viscosity even when the ink is highly concentrated. On the other hand, the material for the hole transport layer 16, which is the underlayer of the organic light-emitting layer 17, does not dissolve when the organic light-emitting layer 17 ink is applied, so a polymeric material that can be insolubilized by thermal crosslinking or the like is generally used. If the material for the hole transport layer 16 is not sufficiently insolubilized, a part of the material of the hole transport layer 16 that is not completely insolubilized may dissolve when the organic light-emitting layer 17 ink is applied. When the organic light-emitting layer 17 is made of a polymeric material, the dissolution of a small amount of the polymeric hole transport layer 16 material does not significantly change the ink properties. Therefore, when a polymeric material is used for the upper layer, even if the remaining film rate of the hole transport layer 16 is about 95%, the variation in the amount of dissolution does not cause non-uniformity within the surface.

However, when the organic light-emitting layer 17 is made of a low-molecular-weight material, there is an issue that even the incorporation of a minute amount of polymer hole transport layer 16 material can significantly change the thickening behavior of the ink. As a result, variations in the amount of incorporation lead to variations in the film shape, making it difficult to obtain uniform characteristics within the surface. Therefore, when using a low-molecular-weight material for the upper organic light-emitting layer 17, it is possible to eliminate variations in the film shape within the surface and obtain uniform characteristics by using materials and processes for the hole transport layer 16 as the underlayer that result in a remaining film rate of 99% or more.

(3) In the above embodiment, of the functional layers (hole injection layer 15, hole transport layer 16, organic light-emitting layer 17, electron transport layer 18, and electron injection layer 19) included in the light-emitting element 2, the organic light-emitting layer 17 is the first functional layer or upper functional layer, and the hole transport layer 16 is the second functional layer or lower functional layer. However, in the present disclosure, the first functional layer or upper functional layer may be a coating film, and another functional layer may be the first functional layer or upper functional layer, and the layer serving as the base thereof may be the second functional layer or lower functional layer.

(4) In another embodiment, a polymer ink may be applied to the undercoat layer before applying the low molecular weight ink, and the polymer ink may be dissolved in the low molecular weight ink that is applied later, thereby controlling the thickening behavior during drying.

In the process of forming a functional layer by coating and drying using a coating method, inks made of low molecular weight materials have an extremely low viscosity due to the solid content, and it is difficult to control the viscosity to increase during drying, which poses the problem of making it difficult to control the film shape.

In response to this, before applying ink made of low molecular weight material, an ink made of high molecular weight material is applied to the base layer, and then the ink is dissolved in the low molecular weight ink that is applied later. This controls the thickening behavior during drying. For example, when the ink is ejected from the inkjet device, the high molecular weight ink has not yet dissolved in the ink, so it can be ejected with low viscosity. After landing, the ink thickens during the drying process, so the shape of the printed film can be controlled without affecting the ejection properties of the ink. This makes it possible to achieve a printed film shape with good flatness.

(5) In another embodiment, a trace amount of a polymeric material having a structure that does not affect the characteristics of the light-emitting element may be added to an ink made of a low molecular weight material to control the ink thickening behavior during drying and control the film shape.

In response to this, by adding a small amount of polymeric material with a structure that does not affect the characteristics of the light-emitting element to the ink made of molecular material, the ink thickens during the drying process, making it possible to control the shape of the printed film without affecting the characteristics of the light-emitting element. This makes it possible to achieve a printed film shape with good flatness.

(6) In the above embodiment, a low molecular weight material was considered as the solute, but a polymeric material may be used as the solute as long as the initial ink viscosity satisfies the conditions for ejection. Since a polymeric solute spontaneously thickens due to the evaporation of the solvent, it is believed that by dissolving or dispersing the polymeric solute in the mixed solvent according to the embodiment of the present disclosure, an ink that thickens more quickly can be provided, and ink convection during the drying stage can be suppressed, thereby further improving the flatness of the functional layer.

(7) As for the functional layers formed by the coating method, as long as at least one of the hole injection layer, hole transport layer, and hole injection transport layer that facilitate the movement of holes from the anode, the electron injection layer, electron injection transport layer, and electron injection transport layer that facilitate the movement of electrons from the cathode (hereinafter, these are collectively referred to as "charge transfer facilitating layers"), and/or the organic light-emitting layer is formed by the coating method using an ink in which a functional material is dissolved or dispersed in a mixed solvent according to an embodiment of the present disclosure, the remaining functional layers may be formed by a dry process such as a vacuum deposition method.

By forming at least one of the functional layers, particularly the organic light-emitting layer, using the mixed solvent according to the present invention, it is possible to improve the flatness of the film formation and provide an organic EL element with excellent light-emitting efficiency and durability.

(8) In the above embodiment, the cathode is the counter electrode, and the organic EL element is a top emission type. However, for example, the anode may be the counter electrode, and the cathode may be the pixel electrode. Also, for example, the organic EL element may be a bottom emission type.

(9) In the above embodiment, the organic EL element 2 has an electron transport layer 18, an electron injection layer 19, a hole injection layer 15, and a hole transport layer 16, but is not limited to this. For example, the organic EL element may not have the electron transport layer 18, or the organic EL element may not have the hole transport layer 16. Also, for example, instead of the hole injection layer 15 and the hole transport layer 16, a single-layer hole injection transport layer may be provided.

(10) As long as it is possible to apply ink with high precision through a nozzle, the printing device is not limited to the above-described embodiment, and a dispenser-type application device that continuously ejects ink onto a substrate may also be used.

(11) In the above embodiment, a line bank type organic EL display panel in which partitions are formed in rows has been described. However, a pixel bank type organic EL display panel in which partitions are formed in a grid pattern and each sub-pixel is surrounded by a partition may also be used.

(12) In the above embodiment, an organic EL display panel using organic EL elements as self-luminous elements has been described. However, other display panels such as quantum dot display panels using quantum dot light emitting elements (QLEDs: Quantum dot Light Emitting Diodes) (see, for example, JP 2010-199067 A) can also be used with the present invention, since they are the same as organic EL display panels in that a light emitting layer and other functional layers are interposed between a pixel electrode and an opposing electrode, except for the structure and type of the light emitting layer.

<Additional Information>
Although the ink for forming a functional layer and the method for manufacturing a self-luminous element according to one aspect of the present disclosure have been described above based on the embodiment and the modified examples, the present invention is not limited to the above embodiment and the modified examples. The present invention also includes forms obtained by applying various modifications to the above embodiment and the modified examples that a person skilled in the art can think of, and forms realized by arbitrarily combining the components and functions in the embodiment and the modified examples within the scope of the present invention.

The present invention is suitable as an ink for forming a functional layer when forming a functional layer in a self-luminous element such as an organic EL element by a coating method.

2 organic EL element 11 substrate 12 planarization layer 13 pixel electrode 14 partition wall 14a opening 15 hole injection layer 16 hole transport layer (second functional layer, lower functional layer)
17 Organic light-emitting layer (first functional layer, upper functional layer)
18 Electron transport layer 19 Electron injection layer 20 Counter electrode 21 Sealing layer

Claims (15)

A self-luminous display panel having a plurality of light-emitting elements arranged in a plane,
The light-emitting element includes a pair of electrodes facing each other and a plurality of organic functional layers including a light-emitting layer disposed between the pair of electrodes,
The plurality of organic functional layers include a first functional layer made of a coating film containing a low molecular weight material as a functional material, and a second functional layer containing an organic compound having a crosslinked structure as a base layer for the coating film,
In the second functional layer, a predetermined range including a central portion in a plane is defined as a first region, and a region located outside the plane of the first region is defined as a second region.
A self-luminous display panel, wherein a cross-linking rate of the organic compound in the second region is higher than a cross-linking rate of the organic compound in the first region. The self-luminous display panel according to claim 1 , wherein in the second functional layer, a cross-link density within the molecules of the organic compound in the second region is higher than a cross-link density within the molecules of the organic compound in the first region. the first functional layer has an organic compound content per unit area in a light-emitting element located above the second region of the second functional layer that is less than an organic compound content per unit volume in a light-emitting element located above the first region;
The organic compound in the first functional layer is the organic compound having the crosslinked structure in the second functional layer dissolved in the first functional layer.
3. The self-luminous display panel according to claim 1. The light emitting device further includes a planarization layer on which a plurality of the light emitting elements are mounted,
4. The self-luminous display panel according to claim 1, wherein the planarizing layer has a higher thermal conductivity in the second region than in the first region. The self-luminous display panel according to claim 4 , wherein the planarizing layer has a thickness smaller in the second region than in the first region. Further, a substrate on which a plurality of the light emitting elements are mounted is provided,
The self-luminous display panel according to claim 4 , wherein a resin film is attached to the substrate below the first region. 7. The self-luminous display panel according to claim 1, wherein in the second functional layer, a molecular weight of the organic compound in the second region is higher than a molecular weight of the organic compound in the first region. A self-luminous display panel as described in any one of claims 1 to 7, wherein the molecular weight of the organic compound in at least the first region of the second functional layer is higher than the molecular weight of the low molecular weight material in the first functional layer. 9. The self-luminous display panel according to claim 1, wherein the second functional layer is a coating film. 10. The self-luminous display panel according to claim 1, wherein the first functional layer is a light-emitting layer, and the second functional layer is a hole transport layer. 11. The self-luminous display panel according to claim 1, further comprising a bank that partitions the plurality of light-emitting elements. A method for manufacturing a self-luminous display panel having a plurality of light-emitting elements arranged in a plane, comprising the steps of:
providing a substrate;
forming a plurality of pixel electrodes above the substrate;
forming a lower functional layer containing an organic compound having a cross-linked structure above the pixel electrode;
a step of applying an ink containing a low molecular weight material as a functional material on an upper surface of the lower functional layer, and then drying the ink to form an upper functional layer made of a coating film;
forming a counter electrode above the upper functional layer;
In the lower functional layer, a predetermined range including a central portion in a plane is defined as a first region, and a region located outside the plane of the first region is defined as a second region.
A method for manufacturing a self-luminous display panel, wherein in the step of forming the lower functional layer, the lower functional layer is formed so that a cross-linking rate of the organic compound in the second region is higher than a cross-linking rate of the organic compound in the first region. The method for manufacturing a self-luminous display panel described in claim 12, wherein in the process of forming the lower functional layer, the lower functional layer is manufactured so that the intramolecular crosslink density of the organic compound in the second region is greater than the intramolecular crosslink density of the organic compound in the first region. A method for manufacturing a self-luminous display panel as described in claim 12 or 13, wherein in the process of forming the lower functional layer, the temperature distribution is adjusted in firing the lower functional layer so that the temperature for the second region is higher than the temperature for the first region. In the step of forming the upper functional layer, the upper functional layer is formed such that an amount of an organic compound per unit area contained in a light-emitting element located above the second region of the lower functional layer is smaller than an amount of an organic compound per unit volume contained in a light-emitting element located above the first region ,
The organic compound in the upper functional layer is the organic compound having the crosslinked structure in the lower functional layer dissolved in the upper functional layer.
A method for manufacturing the self-luminous display panel according to any one of claims 12 to 14.

Images