阅读说明：本技术 顶发射有机el元件及用于制造顶发射有机el元件的方法 (Top-emitting organic EL element and method for manufacturing top-emitting organic EL element ) 是由 石仓淳理 越智法彦 柴田尚存 诸桥将之 佐佐木茂树 于 2018-11-16 设计创作，主要内容包括：一种顶发射有机EL元件,该顶发射有机EL元件在基板(1)上包括具有孔部(23)的绝缘层(3)、下电极(5)、发光层(6)、围绕下电极(5)和发光层(6)的堤(4)以及上透明电极(8)。该顶发射有机EL元件被配置成使得：堤(4)布置在绝缘层(3)上以便围绕孔部(23)；下电极(5)覆盖孔部(23)的内侧和绝缘层(3)的未布置堤(4)的上表面；以及下电极(5)的各个部分的厚度(L1,L2,L3)为100nm或更大。(A top-emission organic EL element includes, on a substrate (1), an insulating layer (3) having an aperture (23), a lower electrode (5), a light-emitting layer (6), a bank (4) surrounding the lower electrode (5) and the light-emitting layer (6), and an upper transparent electrode (8). The top-emitting organic EL element is configured such that: a bank (4) arranged on the insulating layer (3) so as to surround the hole section (23); the lower electrode (5) covers the inner side of the hole part (23) and the upper surface of the insulating layer (3) where the dike (4) is not arranged; and the thickness (L1, L2, L3) of each portion of the lower electrode (5) is 100nm or more.)

1. A top-emission organic EL element comprising:

an insulating layer including a hole portion;

a lower electrode;

a light emitting layer;

a bank surrounding the lower electrode and the light emitting layer; and

an upper transparent electrode is arranged on the substrate,

wherein the insulating layer, the lower electrode, the light emitting layer, the bank, and the upper transparent electrode are disposed over the substrate,

the bank is disposed on the insulating layer so as to surround the hole portion,

the lower electrode is configured to cover an inner side of the hole portion and an area of the upper surface of the insulating layer where the bank is not disposed, and

the thickness at the central region of the lower electrode is 150nm or more.

2. A top-emission organic EL element comprising:

a lower electrode;

a light emitting layer;

a bank surrounding the lower electrode and the light emitting layer; and

an upper transparent electrode is arranged on the substrate,

wherein the lower electrode, the light emitting layer, the bank, and the upper transparent electrode are disposed over the substrate,

the thickness of the lower electrode is decreased once in a region from a boundary portion with the bank to the central region and then increased.

3. A top-emission organic EL element comprising:

a lower electrode;

a light emitting layer;

a bank surrounding the lower electrode and the light emitting layer; and

an upper transparent electrode is arranged on the substrate,

wherein the lower electrode, the light emitting layer, the bank, and the upper transparent electrode are disposed over the substrate, an

The lower surface of the lower electrode is arranged to be closer to the substrate at a central region than at a boundary portion with the bank.

4. The top-emitting organic EL element according to claim 2 or 3,

wherein the insulating layer with the hole part is arranged above the substrate,

the bank is disposed on the insulating layer so as to surround the hole portion, an

The lower electrode covers the inner side of the hole portion and an area of the upper surface of the insulating layer where the bank is not disposed.

5. The top-emitting organic EL element according to any one of claims 1 to 4, wherein if a thickness of the lower electrode at a boundary with the bank is set to L3 and a thickness at the central region is set to L1, then L1/L3 is 0.75 or higher.

6. The top-emission organic EL element according to any one of claims 1 to 5, wherein the lower electrode is electrically connected to a transistor.

7. The top-emitting organic EL element according to claim 5, wherein the insulating layer is configured to cover the transistor.

8. The top-emitting organic EL element according to any one of claims 1 to 7, wherein an intermediate layer is provided between the lower electrode and the upper transparent electrode in addition to the light-emitting layer.

9. The top-emitting organic EL element according to claim 8, wherein the intermediate layer comprises a hole injection layer disposed between the light-emitting layer and the upper transparent electrode.

10. A top-emitting organic EL device comprising a plurality of top-emitting organic EL elements, each of which is the top-emitting organic EL element according to any one of claims 1 to 9, wherein upper transparent electrodes of the plurality of top-emitting organic EL elements are electrically connected to each other.

11. The top-emitting organic EL device of claim 10, wherein each of the plurality of top-emitting organic EL elements emits a different emission color.

12. A method of manufacturing a top-emission organic EL element, comprising:

a step of providing an insulating layer including a hole portion over a substrate;

a step of forming a bank surrounding the hole portion on the insulating layer;

a lower electrode material applying step of applying a solution containing a material of a lower electrode to a region above the substrate surrounded by the bank;

a light emitting material application step of applying a solution containing a material of the light emitting layer to a region above the substrate surrounded by the banks after the lower electrode material application step; and

an upper transparent electrode forming step of forming an upper transparent electrode after the light emitting material applying step.

13. The method of manufacturing a top-emission organic EL element according to claim 12, wherein the lower electrode material applying step is a step of applying a solution containing a material of the lower electrode to the hole portions and an upper surface of a region of the insulating layer where the bank is not arranged.

14. The method of manufacturing a top-emission organic EL element as claimed in claim 12, wherein the lower electrode material applying step forms the lower electrode, and a thickness of the lower electrode is decreased once and then increased in a region from a boundary portion of the lower electrode and the bank toward the central region.

15. The method of manufacturing a top-emission organic EL element according to any one of claims 12 to 14, wherein the lower electrode is formed such that an upper surface is bent upward toward a boundary portion with the bank, an area of the upper surface above the hole portion is set as a bottom, and a distance of the lower surface from the substrate is smaller at the bottom of the hole portion than at the boundary portion with the bank.

16. The method for manufacturing a top-emission organic EL element according to any one of claims 12 to 15, further comprising an intermediate layer material application step of applying a solution containing a material of an intermediate layer between the lower electrode material application step and the upper transparent electrode formation step.

17. The method of manufacturing a top-emission organic EL element as claimed in claim 16, wherein the intermediate layer material applying step includes a hole injection layer forming step performed after the light-emitting material applying step.

18. The method of manufacturing a top-emission organic EL element according to any one of claims 12 to 17, wherein the step of providing the insulating layer including the hole portion is a step of providing an insulating layer covering a driving transistor formed on the substrate.

Technical Field

The present invention relates to a top-emission organic EL element and a method for manufacturing the same. In particular, the present invention relates to a top emission organic EL element including a lower electrode capable of enhancing light extraction efficiency and a method of manufacturing the same.

Background

An organic EL element is an element in which a light-emitting layer is formed of a low-molecular organic compound or a high-molecular organic compound having an EL light-emitting capability, and is actively researched and developed because it has excellent characteristics as a display element such as a wide viewing angle and excellent impact resistance due to its spontaneous light-emitting property.

As a method for manufacturing an organic EL device, a vacuum deposition method, an ink jet method, a printing method, a dispensing method, and the like have been widely studied. First, coating techniques such as an inkjet method and a dispensing method are expected to be suitable for mass production because the system can be downsized and has superior material utilization efficiency as compared with that of a vacuum deposition method. In general, in order to manufacture an organic EL element, it is necessary to stack many layers such as an electrode, a light emitting layer, an intermediate layer, and the like, and it may be desirable to manufacture as many layers by a liquid phase coating technique in order to enhance mass productivity. For example, patent document 1 proposes a method of forming an electrode, a hole transport layer, and the like by coating in addition to a light emitting layer.

Although the organic EL element can be classified into a top emission type element in which light is extracted above the laminated film and a bottom emission type element in which light is extracted through the substrate, in the top emission type organic EL element, the lower electrode on the substrate side is required to have a high light reflectance in order to enhance light extraction efficiency.

In the case of manufacturing a lower electrode on the substrate side by a liquid phase coating technique, a region surrounded by banks (banks) is first formed on the substrate. Then, for example, a solution in which nanoparticles of copper and/or silver are dispersed is coated on the region surrounded by the bank using an inkjet method, and then, the coating is baked at high temperature.

CITATION LIST

Patent document

Patent document 1: japanese patent application laid-open No. H11-329741

Disclosure of Invention

Technical problem

Although the liquid level is flat or the central region thereof is raised immediately after the solution in which the nanoparticles of copper and/or silver are dispersed is coated in the region surrounded by the bank, a flow advancing from the central region toward the edge portion is generated during the process in which drying is performed. The nanoparticles in the solution move toward the edge portion along with the flow, so that the edge portion of the electrode film is raised while having highly dense nanoparticles, and the center region of the electrode film is thin while having a low packing density of nanoparticles. In addition, in addition to the influence of the flow during drying, the shape of the formed film or the packing density of the particles is also influenced by the contact angle of the ink in which the nanoparticles are dispersed to the surface of the bank. In the case where the surface of the bank has high affinity with the ink, the solution is easily attracted to the bank, and the flow advancing toward the edge portion is further enhanced. As a result, the central region of the membrane tends to have a low packing density of nanoparticles and a smaller thickness. Even if the film is subsequently baked, the film quality of the lower electrode reflects the condition during drying, and the central region will have a lower density and a smaller thickness than the peripheral portion.

In the top emission type element, if the density of the central region of the lower electrode on the substrate side is low and thin, the light reflection efficiency of this portion becomes low and the light extraction efficiency as a light emitting element deteriorates.

There is a need for a simple technique to manufacture a top-emission organic EL element having high light extraction efficiency while ensuring sufficient density and thickness of the lower electrode even in the vicinity of the central region of the region surrounded by the bank.

Solution to the problem

A first aspect of the present invention is a top-emission organic EL element including an insulating layer having an aperture portion, a lower electrode, a light-emitting layer, a bank surrounding the lower electrode and the light-emitting layer, and an upper transparent electrode, wherein the insulating layer, the lower electrode, the light-emitting layer, the bank, and the upper transparent electrode are disposed over a substrate. The bank is disposed on the insulating layer so as to surround the hole portion. The lower electrode is configured to cover an inner side of the hole portion and an area of the upper surface of the insulating layer where the bank is not arranged, and a thickness at a central area of the lower electrode is 150nm or more.

A second aspect of the present invention is a top-emission organic EL element including a lower electrode, a light-emitting layer, a bank surrounding the lower electrode and the light-emitting layer, and an upper transparent electrode, wherein the lower electrode, the light-emitting layer, the bank, and the upper transparent electrode are disposed over a substrate. The thickness of the lower electrode is decreased once in a region from a boundary with the bank toward the central region and then increased.

A third aspect of the present invention is a top-emission organic EL element including a lower electrode, a light-emitting layer, a bank surrounding the lower electrode and the light-emitting layer, and an upper transparent electrode, wherein the lower electrode, the light-emitting layer, the bank, and the upper transparent electrode are disposed over a substrate. The lower surface of the lower electrode is arranged to be closer to the substrate at a central region than at a boundary portion with the bank.

A fourth aspect of the present invention is a method of manufacturing a top-emission organic EL element including a step of providing an insulating layer including a hole portion over a substrate, a step of forming a bank surrounding the hole portion on the insulating layer, a lower electrode material application step of applying a solution containing a material of a lower electrode to a region over the substrate surrounded by the bank, a light-emitting material application step of applying a solution containing a material of a light-emitting layer to a region over the substrate surrounded by the bank after the lower electrode material application step, and an upper transparent electrode formation step of forming an upper transparent electrode after the light-emitting material application step.

Advantageous effects of the invention

According to the present invention, a top-emission organic EL element having high light extraction efficiency can be easily manufactured while ensuring sufficient density and thickness of a lower electrode even at the central region of the region surrounded by the bank.

Other features and advantages of the present invention will be disclosed by the following description with reference to the accompanying drawings. It is noted that in the drawings, the same or similar elements are denoted by the same reference numerals.

Drawings

Fig. 1A is a schematic sectional view showing the configuration of an organic EL element of the first embodiment.

Fig. 1B is a schematic sectional view showing the lower electrode of the first embodiment.

Fig. 2A is a perspective view of the entire organic EL device of the first embodiment.

Fig. 2B is an example of a pixel circuit that drives an organic EL element.

Fig. 3A is a schematic diagram showing the manufacturing steps of the organic EL element of the first embodiment.

Fig. 3B is a schematic diagram showing the manufacturing steps of the organic EL element of the first embodiment.

Fig. 3C is a schematic diagram showing the manufacturing steps of the organic EL element of the first embodiment.

Fig. 3D is a schematic diagram showing the manufacturing steps of the organic EL element of the first embodiment.

Fig. 3E is a schematic diagram showing the manufacturing steps of the organic EL element of the first embodiment.

Fig. 3F is a schematic diagram showing the manufacturing steps of the organic EL element of the first embodiment.

Fig. 3G is a schematic diagram showing the manufacturing steps of the organic EL element of the first embodiment.

Fig. 4A is a schematic diagram showing the manufacturing steps of the organic EL element of the first embodiment.

Fig. 4B is a schematic diagram showing the manufacturing steps of the organic EL element of the first embodiment.

Fig. 4C is a schematic diagram showing the manufacturing steps of the organic EL element of the first embodiment.

Fig. 4D is a schematic diagram showing the manufacturing steps of the organic EL element of the first embodiment.

Fig. 5A is a schematic sectional view showing the configuration of an organic EL element of the second embodiment.

Fig. 5B is a schematic sectional view showing the lower electrode of the second embodiment.

Fig. 6 is a schematic sectional view showing a lower electrode of a comparative example.

Detailed Description

First embodiment

Now, a top-emitting organic EL element, an organic EL device including a plurality of top-emitting organic EL elements, and a method of manufacturing the same according to a first embodiment of the present disclosure will be described with reference to the drawings.

Configuration of organic EL device

Fig. 2A is an overall perspective view showing a display device as an example of an organic EL device according to the present disclosure.

As shown in fig. 2A, a plurality of organic EL elements 100R, 100G, and 100B are arranged in a matrix form on a substrate 1. In the case of a display device, each organic EL element functions as a pixel. In the present disclosure, a pixel refers to a minimum unit capable of controlling a light emitting state.

The light emission state of each organic EL element is controlled by a pixel circuit provided corresponding to each organic EL element. An example of a pixel circuit is shown in fig. 2B. The pixel circuit includes a control line 11 for transmitting a control signal, a data line 12 for transmitting a data signal, a power supply line 17 through which a power supply voltage is supplied, two transistors 13 and 14, and a capacitor 16. A control signal entered through a not-shown terminal of the organic EL device is transmitted to the control line 11, and a data signal entered therethrough is transmitted to the data line 12. The transistor 13 is a switching transistor for holding a voltage corresponding to a data signal in the capacitor 16. The transistor 14 is a driving transistor electrically connected to the lower electrode 5 of the organic EL element, and it supplies a current corresponding to the voltage held in the capacitor 16 to the organic EL element 100.

If the first organic EL element 100R, the second organic EL element 100G, and the third organic EL element 100B emit light of different colors, respectively, multicolor display is enabled. In this case, for example, red, green, and blue or yellow, cyan, and white are preferable for the colors emitted by the first organic EL element, the second organic EL element, and the third organic EL element.

Arrangement of organic EL elements

Fig. 1A is a schematic sectional view showing the configuration of an organic EL element according to a preferred embodiment of the present invention.

In fig. 1A, reference numeral 100 denotes an organic EL element, 1 denotes a substrate, 2 denotes a first insulating layer, 3 denotes a second insulating layer, 4 denotes a bank, 5 denotes a lower electrode, 6 denotes a light-emitting layer, 7 denotes a hole injection layer, 8 denotes an upper transparent electrode and 23 denotes a hole portion formed on the second insulating layer 3.

In the case where the organic EL element 100 according to the present embodiment is used as a pixel of a display panel or an element of a surface light source (these will be collectively referred to as "pixel" in the following description), a plurality of organic EL elements 100 are arranged one-dimensionally or two-dimensionally. In this case, the banks 4 may be formed in a stripe or lattice pattern corresponding to the array such that the banks 4 serve as walls separating the pixels. In addition, in the case where there are a plurality of pixels, the upper transparent electrode 8 of each pixel may be used as a common electrode by electrically connecting the upper transparent electrodes 8 of the pixels and forming them as an integral film.

The organic EL element 100 is provided with a sealing structure, not shown, in order to protect the element from external factors such as moisture and impact. A sealing structure in which a material having low moisture permeability such as glass is bonded using an adhesive such as a UV curable resin and glass frit may be used. In addition, a sealing structure in which the organic EL element 100 is covered with an inorganic film having low moisture permeability such as SiN and SiO and a laminated film of a resin film and an inorganic film having low moisture permeability may also be used. Since the present embodiment employs a top emission structure, materials having high light transmittance such as glass and SiN are preferably used.

The substrate 1 is a substrate of the organic EL element 100, and is composed of an inorganic material such as glass or an organic material such as resin. The substrate 1 is generally a plate-like member, but its shape is not limited as long as it serves as a substrate, and it may be a deformable film, for example.

The first insulating layer 2 is an insulating layer provided on the substrate 1, and is generally used such as SiO₂And the like. Although fig. 1A shows the first insulating layer 2 as a single layer for convenience, the first insulating layer 2 may be formed by laminating a plurality of layers, or may be formed using a resin material such as an acrylic resin, and a polyimide resin may be used. The wiring layer or the thin film transistor may be provided between the substrate 1 and the first insulating layer, between a plurality of first insulating layers, or on the first insulating layer. The first insulating layer may be provided for various purposes, such as for electrically insulating the wiring layer and the thin film transistor, providing a flat base for an upper layer, and blocking components of the substrate 1 or moisture from penetrating into the upper layer.

The second insulating layer 3 is an insulating layer provided on the first insulating layer 2, and an organic insulating material such as an acrylic resin and a polyimide resin is generally used. The bank 4 is disposed over the second insulating layer 3, and the hole portion 23 is formed at a central region of a region surrounded by the bank 4 on the second insulating layer 3.

The bank 4 is a wall provided on the second insulating layer 3, and an insulating material is preferably used as a material of the bank, and particularly, a photosensitive epoxy resin containing a fluorine resin and a resin material such as an acrylic resin and a polyimide resin are preferably used. The bank 4 is a structure that electrically separates light emitting regions (i.e., pixels), and also functions as a partition that prevents mixing of materials between pixels while applying a liquid-phase material, as described later. Lyophobicity may be applied to the surface of the bank by performing fluorine plasma treatment or the like.

The lower electrode 5 is one of two poles of the organic EL element, and is formed by applying a solution in which nanoparticles of silver and/or copper are dispersed to a region surrounded by the bank, and then baking at a high temperature. The lower electrode 5 generally functions as an electron injection layer, and also functions as a mirror for enhancing light extraction efficiency by reflecting light advancing toward the substrate 1 among light emitted from the light emitting layer 6. The lower electrode 5 is connected to a driving circuit at a region not shown. Details of the lower electrode 5 will be described later.

The light-emitting layer 6 may be made of any material as long as it has EL light-emitting capability, and may include a fluorescent organic compound or a phosphorescent organic compound corresponding to a desired emission color. The light-emitting layer 6 may also include a plurality of materials such as a guest material and a host material. The light emitting material includes a high molecular material, a middle molecular material, or a low molecular material, and is not particularly limited as long as the light emitting material can be used as a coating type material. For example, a high molecular material such as polyfluorene, a copolymer of polyfluorene, and polystyrene, or a medium molecular material such as oligofluorene may be used. In addition, low-molecular materials such as condensed polycyclic compounds, for example, fluorenyl, phenylene, fluoranthenyl, and anthracenyl condensed polycyclic compounds, and iridium-containing metal complexes may be used.

The hole injection layer 7 is a layer for injecting holes into the light emitting layer 6, and any material may be used for the hole injection layer 7 as long as the material has a hole injection property, and PEDOT: PSS which is widely used for a coating type organic EL element may be used, but the material is not particularly limited to PEDOT: PSS.

The upper transparent electrode 8 is the other electrode of the organic EL element, and is composed of a conductive material having optical transparency such as a metal oxide. Generally, the upper transparent electrode 8 supplies holes and serves as a light extraction window. The upper transparent electrode 8 is connected to a drive circuit in a region not shown. The upper transparent electrode is formed by vacuum deposition such as sputtering or by coating.

Although the light-emitting layer 6 and the hole injection layer 7 are provided as functional layers between the upper transparent electrode 8 and the lower electrode 5 according to the present embodiment, the layer structure of the functional layers is not limited to this example. For example, the layer structure may be a single layer in which only the light-emitting layer is not provided with a hole injection layer, a three-layer structure of a hole injection layer/a hole transport layer/a light-emitting layer, a three-layer structure of a hole injection layer/a light-emitting layer/an electron transport layer, or a four-layer structure of a hole injection layer/a hole transport layer/a light-emitting layer/an electron transport layer. The functional layers may be oppositely laminated from the upper transparent electrode to the lower electrode. There are cases where layers other than the light-emitting layer within the functional layer are simply referred to as intermediate layers, and the step of forming these layers is referred to as an intermediate layer material application step. In a state where a voltage is applied to the functional layer from the upper transparent electrode and the lower electrode, holes are injected from the anode to the functional layer, and electrons are injected from the cathode to the functional layer, and light is irradiated when the holes and the electrons injected in this manner are recombined in the light emitting layer.

Next, the features of the lower electrode of the present embodiment will be described with reference to fig. 1B. For convenience, fig. 1B is a schematic cross-sectional view showing only a part of the organic EL element 100. The lower electrode 5 of the present embodiment has a cross-sectional shape in which a portion entering the hole portion 23 of the second insulating layer is set as a bottom. The lower electrode 5 covers the inside of the hole portion 23 and the upper surface of the second insulating layer 3 where the bank 4 is not disposed.

In a state where the thickness of the lower electrode 5 is set to L1 at the center region, L2 between the center region and the bank 4, and L3 at the boundary with the bank 4, L1> L2 and L3> L2 are achieved. That is, the thickness of the lower electrode 5 decreases once from the boundary with the bank 4 toward the central region, and then increases again.

In the case where the central region is set as the bottom, the upper surface of the lower electrode 5 is bent upward toward the boundary with the bank 4. The distance between the substrate 1 and the lower surface of the lower electrode 5 is smaller at the central region than at the boundary with the bank 4.

In addition, the thickness L1 at the central region of the lower electrode 5 is 0.75 or higher, and preferably 1.0 or higher, more preferably 1.2 or higher, with respect to the thickness L3 or L1/L3 at the boundary with the bank 4.

According to a typical example of the present embodiment, L1 is 150nm to 250nm, L2 is 100nm and L3 is 200nm, and the thickness at the central region of the lower electrode is 150nm or more, the thickness at each region of the lower electrode is 100nm or more, and there is almost no difference in the packing density of the metal material between the central region and the peripheral region of the lower electrode.

In the conventional lower electrode, the thickness at the central region tends to be small as compared with the thickness in the peripheral region or the vicinity of the bank, and the packing density of the metal material at the central region tends to deteriorate. In contrast, the lower electrode 5 of the present embodiment has a sufficient thickness at the central region with respect to the peripheral region, and the packing density of the metal material at the central region is ensured to be either equal to or greater than that of the peripheral region. Therefore, uniformity of light reflectance is enhanced within the pixel, and the effective value of light extraction efficiency of the organic EL element is increased. The bulk density of the above metal material can be obtained by observing a cross section of the lower electrode using an SEM image or an STM image and by measuring an area ratio of the metal to the voids contained therein. In addition, the light reflectance of the lower electrode can be obtained by perpendicularly inputting light having the same light emission wavelength as the light emitting layer to the electrode surface in a state where the functional layer and the upper transparent electrode are removed and measuring the reflected light.

Manufacturing method

Next, a manufacturing method of the organic EL element 100 according to the present embodiment will be described with reference to fig. 3A to 3G and fig. 4A to 4D.

First, the substrate 1 is prepared as shown in fig. 3A.

Next, as shown in fig. 3B, the first insulating layer 2 and the unpatterned insulating layer 20 are disposed on the substrate 1. For example, the first insulating layer is formed of an inorganic material, and the insulating layer 20 is formed of a photosensitive resin material.

Next, as shown in fig. 3C, UV light 22 is irradiated through the exposure mask 21 to expose for patterning the insulating layer 20.

Thereafter, as illustrated in fig. 3D, the second insulating layer 3 having the hole portion 23 at the central region is formed by developing the layer using a developer solution. The second insulating layer can be patterned without corroding the first insulating layer by appropriately selecting materials of the first insulating layer and the second insulating layer and a developer solution.

Next, as shown in fig. 3E, the insulating layer 24, which is not patterned, is formed of a photosensitive resin material.

Next, as shown in fig. 3F, UV light 26 is irradiated through the exposure mask 25 to expose for patterning the insulating layer 24.

Thereafter, as shown in fig. 3G, the banks 4 are formed by developing the layer using a developer solution. The bank may be patterned without corroding the first and second insulating layers by appropriately selecting materials of the first and second insulating layers and the bank and a developer solution. After patterning, UV ozone treatment or O may be performed₂Plasma treatment to remove residual material. A fluorine plasma treatment may be performed on the surface of the bank in order to impart lyophobicity.

Next, as shown in fig. 4A, a coating unit 30 is used to coat a solution 31 containing a material of the lower electrode in an area surrounded by the bank (lower electrode material applying step). Although an inkjet unit is preferably used as the coating unit 30, other liquid-phase coating units such as a dispenser may be used. A solution in which silver and/or copper nanoparticles are dispersed may be used as the solution 31. A solution 31 containing a material of the lower electrode is applied to cover the upper surfaces of the hole portions 23 and the regions of the second insulating layer 3 where the banks 4 are not disposed. According to the present embodiment, the nanoparticles injected into the hole portion are bound in the hole and are not easily attracted even if the flow of the solution toward the peripheral area occurs. After applying a plurality of solution droplets as necessary, drying and baking are performed at an appropriate temperature of 100 ℃ to 200 ℃ to form the lower electrode 5 as shown in fig. 4B.

Next, as shown in fig. 4C, a coating unit 32 is used to coat a solution 33 containing a material of the functional layer 34 in an area surrounded by the banks 4. In the case where a light-emitting layer, a hole injection layer, and the like are sequentially laminated as functional layers, solutions respectively containing materials of each layer are sequentially applied.

In order to form the light-emitting layer, a solution containing a fluorescent organic compound or a phosphorescent organic compound corresponding to a desired emission color is applied (light-emitting material application step). The light-emitting layer may also contain multiple materials such as guest materials and host materials. The light emitting material contained in the solution includes a high molecular material, a medium molecular material, or a low molecular material, and is not particularly limited as long as the light emitting material can be used as a coating-type material. For example, the light emitting material may be a high molecular material such as polyfluorene, a copolymer of polyfluorene, or polystyrene, or an intermediate molecular material of oligofluorene. In addition, the light emitting material may be a low molecular material such as, for example, a condensed polycyclic compound of fluorenyl group, phenylene group, fluoranthenyl group, and anthracenyl group compound, and a metal complex including iridium.

For example, in order to form a red light emitting layer, a red light emitting layer coating solution including a red phosphorescent-emitting iridium metal complex as a guest material and polyfluorene as a host material is used. In addition, in order to form a green light emitting layer, a green light emitting layer coating solution containing a condensed polycyclic compound of a fluoranthene group as a guest material and polyfluorene as a host material is used. In addition, in order to form a blue light emitting layer, a blue light emitting layer coating solution including a condensed polycyclic compound containing phenylene as a guest material and oligofluorene as a host material is used.

To form the hole injection layer, for example, PEDOT/PSS solution as a hole injection material is applied (hole injection layer forming step).

After the formation of the functional layers is completed in this manner, a transparent conductive film 35 is coated by a sputtering process to cover the functional layer 34 and the bank 4 to form an upper transparent electrode (upper transparent electrode forming step).

The organic EL element 100 as shown in fig. 1A is manufactured as described above.

According to the present embodiment, as a result of providing the hole portion on the second insulating layer, particles of the electrode material around the central region will not be easily attracted to the peripheral region when the organic EL element is manufactured. This arrangement makes it possible to sufficiently secure the density and thickness at the central region of the lower electrode and easily manufacture a top-emission organic EL element having high light extraction efficiency.

Second embodiment

Now, a top-emission organic EL element and a manufacturing method thereof according to a second embodiment of the present disclosure will be described below with reference to the drawings.

Structure of organic EL element

Fig. 5A is a schematic cross-sectional view showing the configuration of an organic EL element according to a second embodiment of the present disclosure, which can be used as a pixel section of a display panel or a light emitting section of an illumination light source.

In fig. 5A, reference numeral 400 denotes an organic EL element, 40 denotes a TFT, 41 denotes a substrate, 42 denotes an insulating layer, 43 denotes a hole portion formed on the insulating layer 42, 44 denotes a bank, 45 denotes a lower electrode, 46 denotes a light-emitting layer, 47 denotes a hole injection layer, and 48 denotes an upper transparent electrode. In addition, 49 denotes a connector electrode electrically connecting the TFT40 and the lower electrode 45.

In the case where the organic EL element 400 according to the present embodiment is used as a pixel of a display panel or an element of a surface light source (these will be collectively referred to as "pixel" in the following description), a plurality of organic EL elements 400 are arranged one-dimensionally or two-dimensionally. In this case, the banks 44 may be formed in a stripe or lattice pattern corresponding to the array such that the banks 44 serve as walls separating the pixels. In addition, the upper transparent electrode 48 of each pixel may be used as a common electrode by electrically connecting the upper transparent electrodes 48 of each pixel and forming them as an integrated film.

The organic EL element 400 is provided with a sealing structure, not shown, to protect the element from external factors such as moisture and impact. A sealing structure in which a material having low moisture permeability such as glass is bonded using an adhesive such as a UV curable resin and glass frit may be used. In addition, a sealing structure in which the organic EL element 400 is covered with an inorganic film having low moisture permeability such as SiN and SiO and a laminated film of a resin film and an inorganic film having low moisture permeability may also be used. Since the present embodiment employs a top emission structure, materials having high light transmittance such as glass and SiN are preferably used.

The substrate 41 is a substrate of the organic EL element 400, and is composed of an inorganic material such as glass or an organic material such as resin. The substrate 41 is generally a plate-like member, but its shape is not limited as long as it serves as a substrate, and it may be a deformable film, for example.

The TFT40 is a thin film transistor that applies a voltage to the lower electrode 45 to drive a pixel.

The insulating layer 42 is an insulating layer covering the TFT40 and a part of the connector electrode 49, and the upper surface thereof is planarized. A hole portion 43 is formed at a central region of the insulating layer 42, and a bank 44 is formed on the insulating layer 42 to surround the hole portion 43.

The lower electrode 45 is one of two poles of the organic EL element, and is formed by applying a solution in which nanoparticles of silver and/or copper are dispersed to a region surrounded by the bank, and then baking at a high temperature. The lower electrode 45 generally functions as an electron injection layer, and also functions as a mirror for enhancing light extraction efficiency by reflecting light advancing toward the substrate 41 among light emitted from the light emitting layer 46. The lower electrode 45 is connected to the connector electrode 49 at the bottom of the hole portion 43. Details of the lower electrode 45 will be described later.

The bank 44, the light emitting layer 46, the hole injection layer 47, and the upper transparent electrode 48 are similar to those of the first embodiment, and thus the description thereof is omitted. The description of the variation of the functional layers between the lower electrode and the upper transparent electrode is similar to that of the first embodiment, and thus they are omitted.

Next, the features of the lower electrode of the present embodiment will be described with reference to fig. 5B. For convenience, fig. 5B is a schematic cross-sectional view showing only a portion provided on the substrate of the organic EL element 400. The lower electrode 45 of the present embodiment has a cross-sectional shape in which a portion entering the hole portion 43 of the insulating layer 42 is set to be a bottom portion. The lower electrode 45 covers the inside of the hole portion 43 and the upper surface of the insulating layer 42 where the bank 44 is not disposed.

In a state where the thickness of the lower electrode 45 is set to L4 at the center region, L5 between the center region and the bank 44, and L6 at the boundary with the bank 44, L4> L5 and L6> L5 are realized. That is, the thickness of the lower electrode 45 decreases once from the boundary with the bank 44 toward the central region, and then increases again.

In the case where the central region is set as the bottom, the upper surface of the lower electrode 45 is bent upward toward the boundary with the bank 44. The distance between the substrate 41 and the lower surface of the lower electrode 45 is smaller at the central region than at the boundary with the bank 44.

In addition, the thickness L4 at the central region of the lower electrode 45 is 0.75 or higher, and preferably 1.0 or higher, more preferably 1.2 or higher, with respect to the thickness L6 or L4/L6 at the boundary with the bank 44.

According to a typical example of the present embodiment, L4 is 150nm to 250nm, L5 is 100nm and L6 is 200nm, and the thickness at the central region of the lower electrode is 150nm or more, the thickness at each region of the lower electrode is 100nm or more, and there is almost no difference in the packing density of the metal material between the central region and the peripheral region of the lower electrode.

In the conventional lower electrode, the thickness at the central region tends to be small as compared with the peripheral region or the vicinity of the bank, and the packing density of the metal material tends to deteriorate. In contrast, the lower electrode 45 of the present embodiment has a sufficient thickness at the central region with respect to the peripheral region, and the packing density of the metal material at the central region is ensured to be either equal to or greater than that of the peripheral region. Therefore, uniformity of light reflectance is enhanced within the pixel, and the effective value of light extraction efficiency of the organic EL element is increased. The bulk density of the above metal material can be obtained by observing a cross section of the lower electrode using an SEM image or an STM image and by measuring an area ratio of the metal to the voids contained therein. In addition, the light reflectance of the lower electrode can be obtained by perpendicularly inputting light having the same light emission wavelength as the light emitting layer to the electrode surface in a state where the functional layer and the upper transparent electrode are removed and measuring the reflected light.

Manufacturing method

The manufacturing method of the organic EL element 400 according to the present embodiment is different from that of the first embodiment in that the TFT40 serving as the driving transistor and the connector electrode 49 are provided on the substrate 41 in advance, and the insulating layer 42 having the hole portion 43 is formed so as to cover the surface. The method of manufacturing the insulating layer 42 of the present embodiment is substantially the same as the method of manufacturing the second insulating layer 3 according to the first embodiment. The manufacturing methods of the bank 44, the functional layer, and the upper transparent electrode are similar to those of the first embodiment, and thus the description thereof will be omitted.

According to the present embodiment, as a result of providing the holes on the insulating layer 42, particles of the electrode material around the central region are bound in the holes and are not easily attracted to the peripheral region during manufacturing. This arrangement enables sufficient density and thickness of the lower electrode at the central region to be achieved, and a top-emission organic EL element having high light extraction efficiency is easily manufactured.

First example

A specific example of the lower electrode of the first embodiment will be described. The size of the opening of the hole portion 23 of the second insulating layer 3 is set to 1/10 which is the size of the element area, and the depth of the hole portion is approximately the same as the thickness of the second insulating layer. Polysiloxane is used as the material of the second insulating layer 3. An ink-repellent treatment is performed on the side surface of the bank 4 so that it has a contact angle of 60 ° to 70 ° with respect to an ink in which silver nanoparticles are dispersed (NAG series manufactured by Daiken Chemical co., Ltd.) manufactured by gay research Chemical Ltd. An ink (NAG series, large research chemical limited) in which silver nanoparticles are dispersed, having undecane as a main solvent, an average particle diameter of 10nm, and a solid fraction of 50 wt%, is coated on the above substrate by an inkjet method to form the lower electrode 5. The first droplet of 1pl is filled in the hole portion 23 at the central region, and then nine droplets of 1pl are coated in the region surrounded by the bank, and then dried and baked.

The thickness of each portion of the lower electrode was 200nm at L1, 100nm at L2, and 200nm at L3. That is, the thickness at the central region of the lower electrode was 200nm, and the thickness at each portion was 100nm or more. In addition, the packing density of the electrode material at the central region and the peripheral region of the lower electrode were both 80% and equal to the entire material.

When the reflectance was measured by inputting a light beam having the same emission wavelength as the light-emitting layer perpendicularly to the electrode surface, the reflectance at the central region and the peripheral region of the example was 90% based on the reflectance of the flat surface of the entire material.

Second example

A specific example of the lower electrode according to the second embodiment will be described. As shown in fig. 4B, an insulating layer having a contact hole electrically connected to the TFT40 disposed therein is formed at a central region surrounded by the bank 44. An insulating layer is formed on the glass substrate on which the TFTs 40 and the connector electrodes 49 have been formed, and a hole portion 43 is formed at the central region by photolithography. The opening size of the hole portion 43 is 1/10 of the size of the element area, and the depth of the contact hole is 200nm, which is equal to the thickness of the insulating layer 42. An ink-repellent treatment is performed on the side surface of the bank 44 so that it has a contact angle of 60 ° to 70 ° with respect to an ink (NAG series, manufactured by gay chemical ltd) in which silver nanoparticles are dispersed. An ink (NAG series) in which silver nanoparticles are dispersed, having undecane as a main solvent, an average particle diameter of 10nm, and a solid fraction of 50 wt%, is coated on the above-described substrate by an inkjet method to fill the inside of the contact hole and thereby form the lower electrode 45. The first droplet of 1pl is filled in the hole portion 43 at the central region, and then nine droplets of 1pl are coated in the region surrounded by the bank, and then dried and baked.

The thickness of each portion of the lower electrode was 200nm at L4, 100nm at L5, and 200nm at L6. That is, the thickness at the central region of the lower electrode was 200nm, and the thickness at each portion was 100nm or more. In addition, the packing density of the electrode material at the central region and the peripheral region of the lower electrode were both 80% and equal to the entire material.

When the reflectance was measured by inputting a light beam having the same emission wavelength as the light-emitting layer perpendicularly to the electrode surface, the reflectance at the central region and the peripheral region of the example was 90% based on the reflectance of the flat surface of the entire material.

First comparative example

As shown in fig. 6, the lower electrode 55 is formed on an insulating layer having a flat upper surface and having no hole portion formed therein. The structure has a planarization layer 53 and a bank 54 provided on a glass substrate, and an ink-repellent treatment is performed on a side surface of the bank 54 so that it has a contact angle of 60 ° to 70 ° with respect to an ink in which silver nanoparticles are dispersed. For comparison with other examples, the present comparative example does not have a hole portion provided on the planarization layer 53 of the region surrounded by the bank 54. Similar to the first and second examples, the silver nanoparticle-dispersed ink (NAG series, large research chemical limited) having undecane as a main solvent, an average particle diameter of 10nm, and a solid fraction of 50 wt% was coated with a total of 10 droplets of 1pl, and then dried and baked to form the lower electrode 55.

The thickness of each portion of the lower electrode was 50nm at L7, 100nm at L8, and 400nm at L9. That is, the thickness at the central region of the lower electrode was 50nm, and the minimum thickness at each portion was 50 nm. In addition, the packing density of the electrode material at the peripheral region of the lower electrode was 80% of the entire material, while the packing density at the central region thereof was only 30%.

When the reflectance was measured by perpendicularly inputting a light beam having the same emission wavelength as the light-emitting layer to the electrode surface, the reflectance at the peripheral region of the comparative example was 90%, while the reflectance at the central region of the comparative example was only 50%, based on the reflectance of the flat surface of the entire material.

Results of examples and comparative examples

As described above, it can be seen that, in the lower electrodes of the first and second examples, the difference between the film thickness of the central region and the film thickness of the peripheral region is small, and the difference between the packing density of the central region and the packing density of the peripheral region is small, as compared with the comparative examples. Therefore, the lower electrodes of the first and second examples exhibit high reflectance not only at the peripheral region but also at the central region. When the functional layer and the upper transparent electrode were formed on the lower electrodes of the examples and comparative examples to form the organic EL element, it was confirmed that the elements of both examples achieved high luminance with less input power as compared with the elements of the comparative examples.

OTHER EMBODIMENTS

The embodiments of the present disclosure are not limited to the first embodiment and the second embodiment described above, and may be modified or combined as appropriate.

INDUSTRIAL APPLICABILITY

For example, the present disclosure can be desirably implemented in the field of top-emission organic EL elements used as display devices.

The present invention is not limited to the above-described embodiments, and may be changed and modified in various ways within the concept and scope of the present invention. Accordingly, the appended claims are included to disclose the scope of the invention.

List of reference numerals

1: substrate

2: a first insulating layer

3: a second insulating layer

4: dyke

5: lower electrode

6: luminescent layer

7: hole injection layer

8: upper transparent electrode

23: hole part

40：TFT

41: substrate

42: insulating layer

43: hole part

44: dyke

45: lower electrode

46: luminescent layer

47: hole injection layer

48: upper transparent electrode

100: organic EL element

400: organic EL element

L1: thickness of central region of lower electrode

L3: thickness of peripheral region of lower electrode

L4: thickness of central region of lower electrode

L6: thickness of peripheral region of lower electrode