JP2017033908A - Organic EL element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic EL element, having high brightness, whose extraction efficiency of light generated at a light-emitting layer is improved by suppressing total internal reflection occurring inside an organic EL element (at times, at an interface between a transparent electrode and a transparent substrate).SOLUTION: The organic EL element includes a first electrode, an organic layer having a light-emitting layer, a second electrode, a high refractive index scattering layer and a transparent substrate in this order. The high refractive index scattering layer contains diamond fine particles.SELECTED DRAWING: Figure 1

Description

Detailed Description of the Invention

  The present invention relates to an organic EL element with improved light extraction efficiency and high luminance.

  Organic EL devices (organic electroluminescence devices) are self-luminous devices that excel in luminous efficiency, image quality, power consumption, etc., and are expected to be used in displays, lighting, etc. as light-emitting devices with excellent design (thinness). Has been. Organic EL displays have the advantages of display performance such as high visibility and no viewing angle dependency compared to conventional CRTs and LCDs, and also have the advantages of lightening and thinning the display. Yes. In addition to the advantages of lightening and thinning the organic EL lighting, there is a possibility of realizing lighting having a shape that could not be realized by using a flexible substrate.

  In general, the organic EL element emits light because the refractive index of each layer constituting the element including the light emitting layer is higher than that of air (for example, the refractive index of the organic layer such as the light emitting layer is 1.6 to 2.1). Light is easily totally reflected at the interface, its light extraction efficiency is less than 20%, and most of the light is lost.

  The optical loss in the organic EL element will be described with reference to FIG. As shown in FIG. 6, the organic EL element basically includes a first electrode 10 (back electrode), an organic layer 20 including a light-emitting layer and two to three layers, a second electrode 30 (transparent electrode), and a transparent electrode. For example, holes injected from the first electrode 10 and electrons injected from the second electrode 30 are recombined in the organic layer 20 to excite a fluorescent substance or the like. It emits light. Light emitted from the organic layer 20 is reflected directly or by the first electrode 10 formed of aluminum or the like, and is emitted from the transparent substrate 40. However, as shown in FIG. 6, the light Lb and the light Lc generated inside the organic layer 20 cause total reflection depending on the incident angle to the adjacent layer interface having a different refractive index, and are guided inside the display device. It can't be taken out. The ratio of the guided light is determined by the relative refractive index with the adjacent layer, and the structure of a general organic EL element: [air (n = 1.0) / transparent substrate (n = 1.5) / transparent electrode ( n = 2.0) / organic layer (n = 1.7) / back electrode], the ratio of light that is not emitted to the outside (air) but is guided inside the display device is 81%. That is, only 19% of the total light emission amount can be used effectively.

  In order to improve the light extraction efficiency, (1) the total reflection at the transparent substrate / air interface is prevented and the light (Lb in FIG. 6) guided through the “organic layer + transparent electrode + transparent substrate” is extracted (2 ) A measure to prevent total reflection at the transparent electrode / transparent substrate interface and to extract light (Lc in FIG. 6) guided through the “organic layer + transparent electrode” is essential.

  Regarding (1), a method has been proposed in which irregularities are formed on the surface of the transparent substrate to prevent total reflection at the transparent substrate / air interface (see Patent Document 1).

  Regarding (2), a method of processing the transparent electrode / transparent substrate interface and the light emitting layer / adjacent layer interface into a diffraction grating shape has been proposed (see Patent Document 2 and Patent Document 3). For example, in the method of forming a diffraction grating at the light emitting layer / adjacent layer interface, the adjacent layer is made of a conductive medium, and the depth of the unevenness of the diffraction grating is about 40% of the thickness of the light emitting layer. By making the pitch and depth have a specific relationship, guided light is extracted. Furthermore, a method for increasing the luminous efficiency by processing the interface between the stacked organic layers into irregularities has been proposed (see Patent Document 4). In this method, unevenness having a depth of about 20% with respect to the thickness of the light emitting layer and an inclination angle of about 30 ° is formed at the interface between the organic layers, and the luminous interface is increased by increasing the bonding interface between the organic layers. To increase. However, these methods are difficult to process and have problems such as being susceptible to dielectric breakdown when energized, and further development of a useful light extraction method is desired.

On the other hand, a method has been proposed in which a light scattering layer is disposed between a transparent electrode and a transparent substrate to improve image extraction efficiency and reduce image blur (Patent Document 5 and Patent Document 6). reference). For example, Patent Document 5 discloses a configuration in which a fine particle dispersion layer is disposed on an optical path from the time when light emitted from a light emitting layer is emitted from an organic material layer to the light-transmitting insulating layer. The layer describes that a large number of fine particles (TiO ₂ , ZrO ₂ or ZnO) having an average particle diameter of 100 to 350 nm are dispersed in a base material such as a photosensitive resin.

In Patent Document 6, a light scattering layer containing high refractive index particles (TiO ₂ , ZrO ₂ , ZnO, SnO _2, etc.) having a refractive index of 1.6 or more is provided between a transparent electrode and a transparent substrate. In the light scattering layer, metal oxide ultrafine particles (ZrO ₂ , TiO ₂ , Al ₂ O ₃ , In ₂ O ₃ , ZnO, SnO ₂ , Sb ₂ O ₃ are provided in the light scattering layer. , ITO, etc.) may be contained.

  However, the methods described in Patent Literature 5 and Patent Literature 6 use a material having a refractive index of 1.5 to 1.6 and a material less than 1.6 as the base material of the light scattering layer, respectively. The improvement effect on the total reflection at the interface with the light scattering layer is small, and further improvement in light extraction efficiency is desired.

US Pat. No. 4,774,435 Japanese Patent Laid-Open No. 11-283951 JP 2002-31554 A JP 2002-31567 A JP 2006-107744 A JP 2006-107744 A

JP 2009-259792 A

  Therefore, an object of the present invention is to suppress the total reflection that occurs inside the organic EL element (sometimes at the interface between the transparent electrode and the transparent substrate) and to improve the extraction efficiency of the light generated in the light emitting layer. It is to provide an EL element.

  As a result of earnest research in view of the above object, the present inventors have increased the apparent refractive index of the base material in the light scattering layer described in Patent Document 5, Patent Document 6, and the like, and have a higher refractive index. It has been found that by including light scattering particles, total reflection at the interface between the transparent electrode and the light scattering layer can be made as small as possible and a high light scattering effect can be obtained, so that the light extraction efficiency can be further improved. The present invention has been conceived.

  That is, the organic EL device of the present invention is an organic EL device having a first electrode, an organic layer having a light emitting layer, a second electrode, a high refractive index light scattering layer, and a transparent substrate in this order. The high refractive index light scattering layer is characterized by containing diamond fine particles.

  The high refractive index light scattering layer is composed of a binder and diamond fine particles A having a median diameter of 10 to 200 nm, and the content of the diamond fine particles A is 1 to 50 with respect to the total of the binder and the diamond fine particles A. It is preferable that it is mass%.

  It is preferable that the density of the diamond fine particles A in the high refractive index light scattering layer has a gradient in the stacking direction so as to increase from the transparent substrate side toward the second electrode side.

  The high refractive index light scattering layer is composed of a plurality of layers having different densities of the diamond fine particles A, and is arranged so that the density of the diamond fine particles A in the layer increases from the transparent substrate side toward the second electrode side. It is preferable.

  The high refractive index light scattering layer preferably has a refractive index between the refractive index of the second electrode and the refractive index of the transparent substrate.

  The high refractive index light scattering layer may further contain 1 to 70% by mass of diamond fine particles B having a median diameter of 0.2 to 50 μm with respect to the total of the binder and the diamond fine particles B.

  It is preferable to have a low refractive index light scattering layer for scattering visible light on the opposite side of the transparent substrate from the side facing the high refractive index light scattering layer.

  The low refractive index light scattering layer is composed of a binder and diamond fine particles B having a median diameter of 0.1 to 50 μm, and the content of the diamond fine particles B is 1 with respect to the total of the binder and the diamond fine particles B. It is preferable that it is -70 mass%.

  Since the organic EL element of the present invention has excellent light extraction efficiency and high luminance, it is suitable for a light source of a lighting device, a display device such as a personal computer and a mobile phone, an exposure device such as a printer head, and the like. In addition, since the organic EL element of the present invention uses diamond fine particles having excellent chromatic aberration as a light scatterer included in the diffusion layer, a display device with high image quality can be obtained.

It is sectional drawing which shows typically the layer structure of the organic EL element of 1st embodiment of this invention. It is sectional drawing which shows typically the high refractive index light-scattering layer of the organic EL element of 1st embodiment of this invention. It is a schematic diagram which shows the example of a core / shell type composite particle. It is sectional drawing which shows typically the layer structure of the organic EL element of 2nd embodiment of this invention. It is sectional drawing which shows typically the low refractive index light-scattering layer of the organic EL element of 2nd embodiment of this invention. It is a schematic diagram for demonstrating the light extraction efficiency of an organic EL element.

[1] Configuration of Organic EL Element <First Embodiment>
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a layer configuration of the organic EL element 1 of the first embodiment. The organic EL element 1 has a configuration in which at least a first electrode 10, an organic layer 20, a second electrode 30, a high refractive index light scattering layer 50, and a transparent substrate 40 are stacked in this order. The organic EL element shown in FIG. 1 is an example showing a bottom emission type layer structure, but the present invention can also be applied to a top emission type organic EL element. The same applies to other embodiments.

(1) Transparent substrate The transparent substrate 40 is a smooth plate-like member for supporting the first electrode 10, the organic layer 20, the second electrode 30, and the high refractive index light scattering layer 50. The organic EL element 1 shown in FIG. 1 is a so-called bottom emission type element, and the light extraction direction of the radiated light emitted from the organic layer 20 is on the transparent substrate 40 side. Therefore, a transparent member is used for the transparent substrate 40, and it is preferable that the light transmittance in the visible region (400 to 700 nm) is 50% or more. Specifically, a glass plate, a polymer plate, etc. are mentioned. Examples of the glass plate include soda lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz. Examples of the polymer plate include those made of polycarbonate resin, acrylic resin, polyethylene terephthalate resin, polyether sulfide resin, polysulfone resin, triazine resin and the like as raw materials. The transparent substrate 40 is not limited to a plate shape, and may be a film shape. Usually, the refractive index of the glass used as the transparent substrate 40 is 1.5. Among the polymers, a relatively low refractive index is about 1.4, and a relatively high refractive index is 1.65. As a material having a higher refractive index, it is about 2.0.

(2) First electrode The first electrode 10 is provided adjacent to the organic layer 20, and an electrode material is used. In the bottom emission type element, the first electrode 10 is preferably made of a material that reflects light. For example, the first electrode 10 made of a metal such as Al, Cu, Ag, or Au, an alloy, or the like. May be composed of one layer or a plurality of layers. Layers composed of a material that reflects light may be stacked, or a layer composed of a transparent conductive member and a layer composed of a material that reflects light may be stacked.

(3) Second Electrode The second electrode 30 is provided adjacent to the organic layer 20 between the organic layer 20 and the high refractive index light scattering layer 50. The second electrode 30 is disposed to face the first electrode 10 with the organic layer 20 interposed therebetween. As described above, in the present embodiment, the second electrode 30 is a transparent electrode in order to extract the emitted light emitted from the organic layer 20 from the transparent substrate 40 side to the outside of the element. In this case, it is preferable that the visible light transmittance of the second electrode 30 is greater than 10%. The sheet resistance of the second electrode 30 is preferably several hundred Ω / □ (ohm / square) or less. The thickness of the second electrode 30 depends on the material, but is preferably selected in the range of 10 nm to 1 μm, more preferably 10 to 200 nm. In the present embodiment, the second electrode 30 is an anode and the first electrode 10 is a cathode, but the second electrode 30 may be a cathode and the first electrode 10 may be an anode. An electrode material is used for the second electrode 30, and examples thereof include ITO (indium tin oxide), IZO (indium zinc oxide) (“IZO” is a registered trademark), ZnO (zinc oxide), and the like. A transparent electrode material is used. The refractive index of the transparent electrode material is about 1.7 to 2.2.

(4) Organic Layer The organic layer 20 is provided between the first electrode 10 and the second electrode 30. The organic layer 20 is composed of a single layer or a plurality of layers. At least one of the organic layers 20 is a light emitting layer. Therefore, the organic layer 20 may be composed of a single light emitting layer, or an organic EL such as a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, a hole barrier layer, or an electron barrier layer. You may have the layer employ | adopted with an element. The organic layer 20 may contain an inorganic compound. In the present embodiment, the organic layer 20 constitutes a planar light emitting region.

For the light emitting layer, a light emitting material such as Alq ₃ [tris (8-hydroxyquinolinato) aluminium] is used, and the light emitting layer has a structure showing monochromatic light such as red, green, blue, yellow, etc. The thing of the structure which shows white light emission, etc. are used. In forming a light emitting layer, a doping method is known in which a host material is doped with a light emitting material as a dopant material. In the light-emitting layer formed by the doping method, excitons are efficiently generated from the charge injected into the host material, and the exciton energy of the generated excitons is transferred to the dopant material to obtain highly efficient light emission from the dopant material. be able to. In one embodiment of the present invention, the light-emitting layer can be a fluorescent light-emitting layer that utilizes light emitted from singlet excitons or a phosphorescent light-emitting layer that utilizes light emitted from triplet excitons. In the organic layer 20 of the organic EL element 1, an arbitrary compound can be selected and used from materials used in the organic EL element other than the compounds exemplified above.

(5) High-refractive-index light scattering layer The high-refractive-index light scattering layer 50 is formed with the second electrode 30 in order to efficiently extract the radiated light emitted from the light-emitting layer of the organic layer 20 to the outside of the organic EL element 1. It arrange | positions between the transparent substrates 40. The high refractive index light scattering layer 50 preferably has a refractive index between the refractive index of the second electrode 30 and the refractive index of the transparent substrate 40, and further contains fine particles that scatter light in the visible range. As described above, the refractive index of the second electrode 30 is about 1.5 to 2.0, and the refractive index of the transparent substrate 40 is about 1.7 to 2.2. The rate is preferably about 1.5 to 2.2. The refractive index of the high refractive index light scattering layer 50 is set so that the reflection at the interface between the second electrode 30 and the high refractive index light scattering layer 50 and the interface between the high refractive index light scattering layer 50 and the transparent substrate 40 is as small as possible. Set.

  Thus, by providing the high refractive index light scattering layer 50 having a refractive index between the second electrode 30 and the transparent substrate 40 adjacent to the second electrode 30, the interface between the second electrode 30 and the transparent substrate 40. The refractive index difference at the interface between the second electrode 30 and the high refractive index light scattering layer 50 is smaller than the refractive index difference at, so that the critical angle of light emitted from the second electrode 30 becomes larger, and more Total reflection is less likely to occur. For this reason, the amount of light emitted from the second electrode 30 increases. Further, the light emitted from the second electrode 30 and incident on the high refractive index light scattering layer 50 is scattered by the fine particles present in the high refractive index light scattering layer 50, and efficiently passes from the high refractive index light scattering layer 50 to the transparent substrate 40. Enters and exits into the air.

  The high refractive index light scattering layer 50 is a layer containing diamond fine particles, and preferably comprises a binder 51 and diamond fine particles 52 as shown in FIG. As will be described later, the diamond fine particles 52 include diamond fine particles A (52a) having a median diameter of 10 to 200 nm and diamond fine particles B (52b) having a median diameter of 0.2 to 50 μm as necessary. Diamond fine particles A (52a) mainly have a function of increasing the refractive index of the binder, and diamond fine particles B (52b) mainly have a function of scattering light in the visible range.

(A) Diamond fine particles The diamond fine particles 52 preferably have excellent affinity with the binder and the solvent in forming the layer in order to disperse uniformly in the high refractive index light scattering layer 50. Those having a relatively large number of functional groups such as sulfonic acid groups and hydroxyl groups on the particle surface are preferred. If necessary, the surface of the diamond fine particles 52 may be modified with a functional group such as a hydrophobic group. Examples of the diamond fine particles 52 include those obtained by pulverizing natural diamond or artificial diamond, or nanodiamond obtained by an explosion method.

  As a material obtained by pulverizing natural diamond or artificial diamond, it is preferable to use a material pulverized to 80 to 100 nm by a mechanical method. The fine diamond particles obtained by pulverization are preferably used in a state where the surface thereof is modified with a functional group as necessary to enhance the affinity with a solvent or the like.

  The nanodiamond obtained by the explosion method has a core / shell structure in which the surface of nano-sized diamond fine particles is covered with graphite-based carbon, and is colored black because of the presence of graphite-based carbon. Although it is possible to use it as it is, it is possible to remove the graphite-based carbon on the particle surface by the oxidation treatment and increase the transparency. Diamond fine particles obtained by oxidation treatment have a very good affinity for hydrophilic binders and solvents due to the hydrophilic functional groups such as -COOH and -OH present on the surface of the remaining graphite carbon. In addition, it has good dispersibility in glass or a polymer having a hydrophilic group. Further, the surface can be modified with a group containing fluorine or silicon.

  The nanodiamond obtained by the oxidation treatment is a secondary particle having a median diameter of 30 to 250 nm (dynamic light scattering method) made of nano-sized diamond having a median diameter of about 2 to 10 nm. it can. However, particles having a median diameter of 30 to 250 nm have a small effect on scattering visible light because the particle size is too small. Therefore, when used as a light scatterer, a particle size that causes Mie scattering (median diameter of 0.1 to 0.1). 50 μm) is preferably used after being aggregated.

The diamond fine particles preferably have a specific gravity of 2.55 to 3.48 g / cm ³ . Since the specific gravity of diamond fine particles increases with the degree of purification of nanodiamond (removal rate of graphite-based carbon), the diamond content (the amount of graphite-based carbon present on the particle surface) in the particle can be obtained from the specific gravity. it can. For example, diamond content: 24% by volume in the case of specific gravity of 2.55 g / cm ^3, diamond content: if the specific gravity is 3.48 g / cm ³ is 98% by volume.

Even if the specific gravity of the diamond fine particles is less than 2.55 g / cm ³ , that is, when oxidation treatment is not performed, the surface has functional groups such as carboxyl groups, sulfonic acid groups, and hydroxyl groups. To increase the number of them. In addition, when excessive oxidation treatment is performed, the graphite-based carbon in the nanodiamond shell is almost removed, so that the functional groups such as carboxyl group, sulfonic acid group, and hydroxyl group are decreased, resulting in the solvent. Therefore, the specific gravity is preferably not more than 3.48 g / cm ³ . Moreover, even when the specific gravity exceeds 3.48 g / cm ³ , surface modification with a functional group having an effect of increasing the affinity with the binder or the solvent is performed as necessary, so that Dispersibility can be increased.

The specific gravity is more preferably 3.0 g / cm ³ (diamond 84% by volume) or more and 3.46 g / cm ³ (diamond 97% by volume) or more, and 3.38 g / cm ³ (diamond 90% by volume) or more. Most preferably, it is 3.45 g / cm ³ (diamond 96% by volume) or less. The volume percentage of diamond in the nanodiamond is a value calculated from the specific gravity of the nanodiamond using the specific gravity of diamond of 3.50 g / cm ³ and the specific gravity of graphite of 2.25 g / cm ³ .

(I) Diamond fine particles A
The high refractive index light scattering layer 50 preferably contains diamond fine particles having a median diameter of 10 to 200 nm. Diamond fine particles having such a median diameter (hereinafter referred to as diamond fine particles A (52a)) are mainly composed of particles having a size smaller than the wavelength range of visible light (400 to 700 nm), and thus scatter visible light. Although the effect is small, the high refractive index (refractive index 2.42) exhibits the effect of increasing the refractive index of the entire layer. The median diameter of the diamond fine particles A is a size that does not cause scattering by visible light (Mie scattering), that is, 200 nm or less, more preferably 100 nm or less, and most preferably 50 nm or less. Even if the diamond fine particles have a median diameter of 10 to 200 nm, particles having a relatively large size of 200 nm or more are included to some extent, so that the effect of scattering light in the visible range is small.

  The refractive index of the high-refractive-index light scattering layer 50 in which diamond fine particles are uniformly dispersed in the binder is an additive property between the diamond fine particles and the binder, so that a weighted average of the refractive index of diamond and the refractive index of the binder is achieved. Can be expressed as For example, when 20 parts by mass of diamond fine particles (refractive index 2.42) are dispersed in a binder having a refractive index of 1.60 (80 parts by mass), the refractive index of the high refractive index light scattering layer 50 is 1.76. In this way, by dispersing the diamond fine particles in the binder, the refractive index of the high refractive index light scattering layer 50 can be easily adjusted.

  That is, the content of the diamond fine particles A in the high refractive index light scattering layer 50 may be determined depending on what refractive index the high refractive index light scattering layer 50 is designed. It is preferably 1 to 50% by mass, more preferably 2 to 45% by mass, and most preferably 5 to 40% by mass with respect to the binder material that forms the film.

  The diamond fine particles A in the high refractive index light scattering layer may be distributed at a uniform density in the thickness direction of the layer, but the density of the diamond fine particles A from the transparent substrate side toward the second electrode side is It may be distributed with a gradient in the thickness direction of the layer so as to be higher. Thus, by providing the density gradient of the diamond fine particles A in the thickness direction, the refractive index gradually changes from the transparent substrate side toward the second electrode side, and the transparent substrate and the second electrode side change. Can be smoothly connected. At this time, in order to make the connection of the refractive index smoother, the refractive index of the high refractive index light scattering layer on the transparent substrate side (the surface in contact with the transparent substrate) is set to the same refractive index as that of the transparent substrate. It is preferable that the refractive index on the second electrode side (the surface in contact with the second electrode) of the refractive index light scattering layer is the same as that of the second electrode. The density gradient of the diamond fine particles A in the thickness direction of the high refractive index light scattering layer may be continuous or stepped.

(Ii) Diamond fine particles B
In addition to the diamond fine particles A, the high refractive index light scattering layer 50 has a median diameter of 0.2 to 50 μm (hereinafter referred to as diamond fine particles B (52b)) in order to further improve the diffusibility of visible light. It may contain. Since the diamond fine particle B has a median diameter equal to or larger than the wavelength of light in the visible range, it is a light scatterer that exhibits a high scattering effect on light in the visible range by Mie scattering. work. The diamond fine particle B may be a primary particle of diamond or an aggregate of diamond fine particles (for example, a shape in which nanoparticles having a median diameter of about 1 to 10 nm are aggregated). The median diameter of the diamond fine particles B is more preferably 0.2 to 30 μm, and most preferably 0.5 to 20 μm.

  As the light scatterer, a core / shell type composite particle 100 comprising a diamond fine particle core 101 and an organic polymer or silica shell 102 as shown in FIGS. 3A to 3C may be used. it can.

  The content of the diamond fine particles B (52b) is preferably 1 to 70% by mass with respect to the total of the binder 51 and the diamond fine particles B (52b) in the high refractive index light scattering layer 50. More preferably, it is -65 mass%, and it is more preferable that it is 3-60 mass%.

(B) Binder The binder 51 is not particularly limited, but is preferably a glass material or a polymer resin. Examples of the glass material constituting the binder include soda-lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz.

  As the polymer resin, those having excellent visible light permeability are preferable. Polyethylene terephthalate resin, polyethylene naphthalate resin, polyester resin, acrylic resin, acrylic urethane resin, polyester acrylate resin, polyurethane acrylate resin , Polyether sulfide resin, polysulfone resin, epoxy acrylate resin, urethane resin, epoxy resin, polycarbonate resin, cellulose resin, acetal resin, vinyl resin, polyethylene resin, polystyrene resin, polypropylene resin Resin, polyamide resin, polyimide resin, melamine resin, phenol resin, cycloolefin resin, triazine resin, silicone resin, fluorine resin, etc., thermoplastic resin, thermosetting resin It can be used an ionizing radiation-curable resin or the like.

<Second embodiment>
Next, a second embodiment of the present invention will be described based on the drawings. FIG. 4 is a cross-sectional view schematically showing the layer configuration of the organic EL element 2 of the second embodiment. The organic EL element 2 includes at least the first electrode 10, the organic layer 20, the second electrode 30, the high refractive index light scattering layer 50, the transparent substrate 40, and the low refractive index light scattering layer 60 in this order. It has a laminated structure. The organic EL element 2 of the second embodiment is the same as the organic EL element 1 of the first embodiment, except that the low refractive index light scattering layer 60 is provided on the surface of the transparent substrate 40 opposite to the high refractive index light scattering layer 50. Since the first electrode 10, the organic layer 20, the second electrode 30, and the high refractive index light scattering layer 50 are the same as those of the organic EL element 1 of the first embodiment, the low refractive index light scattering layer 60 is here. Only explained.

(1) Low Refractive Index Light Scattering Layer As shown in FIG. 4, the low refractive index light scattering layer 60 is provided on the surface opposite to the high refractive index light scattering layer 50 of the transparent substrate 40 and emits light in the visible range. Has the function of scattering. By scattering light in the visible range with the low refractive index light scattering layer 60, the emitted light emitted from the light emitting layer of the organic layer 20 can be efficiently extracted outside the organic EL element 2.

  As shown in FIG. 5, the low refractive index light scattering layer 60 is preferably a layer in which diamond fine particles 62 are dispersed in a binder 61. The diamond fine particles 62 have a median diameter of 0.1 to 50 μm. The diamond fine particles B are preferred. The content of the diamond fine particles B is preferably 1 to 70% by mass with respect to the total of the binder and the diamond fine particles B. The diamond fine particles B may be diamond fine particles having a median diameter of 0.1 to 50 μm, and the diamond fine particles B described in the high refractive index light scattering layer can be used. In one organic EL element, the diamond fine particles used in the high refractive index light scattering layer and the diamond fine particles used in the low refractive index light scattering layer may be the same or different.

  The binder 61 constituting the low refractive index light scattering layer 60 preferably has the same refractive index as that of the transparent substrate 40. Thus, by making the refractive indexes of the low-refractive-index light scattering layer 60 and the transparent substrate 40 the same level, reflection of the emitted light at the interface between the low-refractive-index light scattering layer 60 and the transparent substrate 40 can be prevented. it can. Therefore, radiated light emitted from the light emitting layer of the organic layer 20 efficiently enters the low refractive index light scattering layer 60 and is scattered by the low refractive index light scattering layer 60, thereby directing the outside (in the air). Extracted as less light. Therefore, the light extraction efficiency can be improved by the low refractive index light scattering layer 60, and the uniformity of the light extracted outside the device can be further improved. Since the refractive index of the transparent substrate 40 is about 1.7 to 2.2, the refractive index of the binder constituting the low refractive index light scattering layer 60 is preferably about 1.7 to 2.2.

[2] Manufacturing Method of Organic EL Element (1) Formation of High Refractive Index Light Scattering Layer The high refractive index light scattering layer 50 is applied to the surface of the transparent substrate 40 with a coating liquid containing diamond fine particles and a binder or a precursor thereof. The film can be formed on the surface of the transparent substrate 40 by a method of forming a film containing diamond fine particles and a binder in advance, or by attaching the film to the surface of the transparent substrate 40. Moreover, you may form the high refractive index light-scattering layer 50 combining the said coating method and the affixing method. When combining these methods, the film may be applied after applying the diamond fine particle dispersion, or the diamond fine particle dispersion may be applied after applying the film. If necessary, the coating solution may have a solvent and various additives.

  The binder precursor is a monomer for forming a binder constituting the high refractive index light scattering layer 50, or the hard coat agent described above. The coating liquid containing this precursor may contain a polymerization initiator, a solvent, a catalyst, a thickener, a surfactant, and the like.

  The coating method can be appropriately selected according to the purpose from methods such as a dip coating method, an ink jet method, a spin coating method, a spray coating method, and a flow coating method. Of these, the inkjet method and spin coating method, which are advantageous for forming a uniform layer, are preferred. At this time, a high refractive index light scattering layer in which the density of the diamond fine particles A is changed in the thickness direction can be formed by sequentially applying and laminating a plurality of coating liquids having different concentrations of the diamond fine particles A.

  In the case of forming the high refractive index light scattering layer 50 by the attaching method, for example, a method of forming a film containing diamond fine particles and a binder by extrusion molding and attaching them by dry lamination, thermal lamination, or the like can be mentioned. When the high refractive index light scattering layer 50 is attached to the transparent substrate 40 with an adhesive, it is preferable to use an adhesive having a refractive index equivalent to that of the high refractive index light scattering layer 50 or the transparent substrate 40. As the adhesive, for example, an acrylic or epoxy optical adhesive can be used. In addition, a high refractive index light scattering layer in which the density of the diamond fine particles A is changed in the thickness direction can be formed by preparing films having different densities of the diamond fine particles A and sequentially laminating them.

(2) Formation of Low Refractive Index Light Scattering Layer The low refractive index light scattering layer 60 is formed by applying a coating liquid containing diamond fine particles and a binder or a precursor thereof onto the surface of the transparent substrate 40, or in advance diamond fine particles and a binder. The film can be formed on the surface of the transparent substrate 40 by a method of attaching the film to the surface of the transparent substrate 40. Further, the low refractive index light scattering layer 60 may be formed by combining the coating method and the attaching method. When combining these methods, the film may be applied after applying the diamond fine particle dispersion, or the diamond fine particle dispersion may be applied after applying the film. If necessary, the coating solution may have a solvent and various additives. The low refractive index light scattering layer 60 is formed on the surface of the transparent substrate 40 opposite to the surface on which the high refractive index light scattering layer 50 is formed. The formation of the low refractive index light scattering layer 60 may be performed before the high refractive index light scattering layer 50 is formed or after the high refractive index light scattering layer 50 is formed. It may be after forming the scattering layer 50, the organic layer 20, and the electrodes 10 and 30. As the binder, those mentioned in the formation of the high refractive index light scattering layer 50 can be used.

(3) Formation of organic light emitting layer and electrode On the formed high refractive index light scattering layer 50, the second electrode 30, the organic layer 20, and the first electrode 10 are sequentially laminated. Formation of the first electrode 10 and the second electrode 30 can employ a forming method such as a vacuum deposition method or a sputtering method. The organic layer 20 is formed by a dry film formation method such as a vacuum deposition method, a sputtering method, a plasma method, an ion plating method, or a wet film formation method such as a spin coating method, a dipping method, a flow coating method, or an ink jet method. A forming method can be adopted.

<Modification of Embodiment>
It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

Example 1
(1) Production of diamond fine particles BD produced by detonating 0.65 kg of explosives containing TNT (trinitrotoluene) and RDX (cyclotrimethylenetrinitroamine) at a ratio of 60/40 in a 3 m ³ explosion chamber. After forming an atmosphere for storing the BD, a second explosion occurred under the same conditions to synthesize BD. After the explosion product expanded and reached thermal equilibrium, the gas mixture was allowed to flow out of the chamber for 35 seconds through a supersonic Laval nozzle having a 15 mm cross section. Due to the heat exchange with the chamber walls and the work done by the gas (adiabatic expansion and vaporization), the product cooling rate was 280 ° C./min. The specific gravity of the product (black powder, BD) captured by the cyclone was 2.55 g / cm ³ , and the median diameter (dynamic light scattering method) was 220 nm. This BD was calculated from specific gravity, and was estimated to be composed of 76% by volume of graphite-based carbon and 24% by volume of diamond.

  This BD was mixed with a 60% by mass nitric acid aqueous solution and subjected to an oxidative decomposition treatment under the conditions of 160 ° C., 14 atm and 20 minutes. Particles from which graphite was partially removed from BD were obtained by oxidative etching treatment. The particles were refluxed with ammonia at 210 ° C., 20 atm for 20 minutes, neutralized, then naturally settled, washed with 35 mass% nitric acid by decantation, and further washed with water three times by decantation. It was dehydrated by centrifugation and heat-dried at 120 ° C. to obtain diamond fine particle powder.

This diamond fine particle powder was further dispersed in water, and decantation was repeated to separate the diamond fine particle A having a relatively small particle size in the supernatant portion and the diamond fine particle B having a relatively large particle size in the precipitated portion. . The median diameter of the diamond fine particles A was 130 nm (dynamic light scattering method), and the median diameter of the diamond fine particles B was 1.2 μm (dynamic light scattering method). The specific gravity was 3.38 g / cm ³ for both. Calculated from the specific gravity, these diamond fine particles were estimated to be composed of 90% by volume of graphite-based carbon and 10% by volume of diamond.

(2) Preparation of organic EL element UV curable acrylate hard coating agent [manufactured by GE Toshiba Silicone Co., Ltd., trade name “UVHC1105” solid content concentration 100 wt%] 100 parts, UV curable silicone resin [manufactured by Chisso Corporation] A coating solution for a high refractive index light scattering layer comprising 0.4 parts of a trade name “Silaplane FM-7711” (molecular weight 1000)], 20 parts by mass of the produced diamond fine particles A and 100 parts of isopropyl alcohol was produced.

On the surface of a glass substrate [refractive index: 1.50 (wavelength = 550 nm)] of 25 mm × 25 mm × 0.7 mm thick (manufactured by Nippon Sheet Glass, NA35), the film thickness after curing this coating solution becomes 0.5 μm. After coating with a spin coater and drying at 80 ° C. for 2 minutes, a high refractive index light scattering layer was formed by irradiating ultraviolet rays at an irradiation dose of 1000 mJ / cm ² . The refractive index of this high refractive index light scattering layer was 1.73. The refractive index of the hard coat layer when it was prepared without adding the diamond fine particles A was 1.60.

  On the formed high refractive index light scattering layer, IZO is vapor-deposited to form a 110 nm thick IZO transparent electrode (second electrode: refractive index 2.0), and a hole injecting compound is formed on the IZO film. HI-1 is vapor-deposited to form a 5 nm-thick hole injection layer, and a hole-transporting compound HT-1 is vapor-deposited on the hole-injection layer to form a 120-nm-thick first hole transport layer. Then, a hole transporting compound HT-2 was deposited on the first hole transport layer to form a second hole transport layer having a film thickness of 85 nm.

  Further, on this second hole transport layer, Compound RH-1 as a host material and Compound RD-1 as a phosphorescent dopant material were co-evaporated to form a light emitting layer having a film thickness of 45 nm. The concentration of Compound RD-1 in this light emitting layer was 5% by mass. The maximum emission peak wavelength of Compound RD-1 was 602 nm.

  An electron transporting compound ET-1 is deposited on the light emitting layer to form a first electron transporting layer having a thickness of 5 nm, and an electron transporting compound ET-2 is deposited on the first electron transporting layer. A second electron transport layer having a thickness of 10 nm is formed, and an electron transport compound ET-3 is deposited on the second electron transport layer to form a third electron transport layer having a thickness of 5 nm. LiF is deposited on the transport layer at a deposition rate of 0.1 angstrom / min to form a 1 nm-thick LiF film as an electron-injecting electrode (cathode), and metal A1 is deposited on the LiF film. A metal cathode having a thickness of 80 nm was formed. Thus, the organic EL element of Example 1 was produced.

(3) Evaluation of luminance A voltage was applied to the obtained organic EL element so that the current density was 5 mA / cm ^2, and the front luminance was measured with a luminance meter (BM5A manufactured by Topcon Corporation).

Example 2
(1) Preparation of coating liquids A to C for a high refractive index light scattering layer UV curable acrylate hard coating agent [manufactured by GE Toshiba Silicone Co., Ltd., trade name “UVHC1105” solid content concentration 100% by weight] 100 parts, UV curable Type silicone resin [made by Chisso Corporation, trade name “Silaplane FM-7711” (molecular weight 1000)] 0.4 parts, the produced diamond fine particles A 3 parts by weight and isopropyl alcohol 100 parts by high refractive index light scattering Layer coating solution A was prepared.

  The coating liquids B and C for the high refractive index light scattering layer were the same except that the addition amount of the diamond fine particles A was changed to 20 parts by mass and 40 parts by mass, respectively, with respect to the coating liquid A for the high refractive index light scattering layer. Was made.

(2) Production of organic EL element For a high refractive index light scattering layer on the surface of a glass substrate [refractive index: 1.50 (wavelength = 550 nm)] of 25 mm × 25 mm × 0.7 mm thickness (manufactured by Nippon Sheet Glass, NA35) The coating solution A was applied with a spin coater so that the film thickness after curing was 0.17 μm, and dried at 80 ° C. for 2 minutes. After the coating liquid A for the high refractive index light scattering layer is applied and dried, the coating liquid B for the high refractive index light scattering layer is applied and dried in the same manner, and further on the coating liquid A for the high refractive index light scattering layer. After the coating liquid C was applied and dried, ultraviolet rays were irradiated at a dose of 1000 mJ / cm ² to form high refractive index light scattering layers A to C. The refractive indexes of the high refractive index light scattering layers A to C were 1.62, 1.73, and 1.83, respectively.

  On the formed high refractive index light scattering layers A to C, in the same manner as in Example 1, a transparent electrode (IZO film), a hole injection layer, a first hole transport layer, a second hole transport layer, light emission A layer, a first electron transport layer, a second electron transport layer, a third electron transport layer, an electron injecting electrode (LiF film) and a metal cathode (metal Al) were formed, and an organic EL device of Example 2 was produced. The luminance of the obtained organic EL element was measured in the same manner as in Example 1.

Example 3
The organic EL device of Example 3 was the same as Example 1 except that 5 parts by mass of the diamond fine particles B prepared in Example 1 were further added to the coating solution for the high refractive index light scattering layer used in Example 1. Was made. The luminance of the obtained organic EL element was measured in the same manner as in Example 1.

Example 4
100 parts UV curable acrylate hard coat [GE Toshiba Silicone Co., Ltd., trade name “UVHC1105” solid concentration 100 wt%], UV curable silicone resin [Chisso Co., Ltd., trade name “Silaplane FM- 7711 "(molecular weight 1000)] A coating solution for a low refractive index light scattering layer comprising 0.4 parts of diamond fine particles B produced in Example 1 and 100 parts of isopropyl alcohol was prepared.

For the high refractive index light scattering layer produced in Example 1 on one surface of a glass substrate [refractive index: 1.50 (wavelength = 550 nm)] of 25 mm × 25 mm × 0.7 mm thickness (manufactured by Nippon Sheet Glass, NA35) The coating solution is applied with a spin coater so that the film thickness after curing is 0.5 μm, dried at 80 ° C. for 2 minutes, and then applied to the other surface of the glass substrate for the low refractive index light scattering layer coating solution. Was applied with a spin coater so that the film thickness after curing was 0.2 μm, dried at 80 ° C. for 2 minutes, and then irradiated with ultraviolet rays at a dose of 1000 mJ / cm ² on both sides, and a high refractive index light scattering layer and A low refractive index light scattering layer was formed. The high refractive index light scattering layer had a refractive index of 1.73, and the low refractive index light scattering layer had a refractive index of 1.59.

  On the formed high refractive index light scattering layer, in the same manner as in Example 1, the transparent electrode (IZO film), the hole injection layer, the first hole transport layer, the second hole transport layer, the light emitting layer, the first layer A one electron transport layer, a second electron transport layer, a third electron transport layer, an electron injecting electrode (LiF film) and a metal cathode (metal Al) were formed, and an organic EL device of Example 4 was produced. The luminance of the obtained organic EL element was measured in the same manner as in Example 1.

Comparative Example 1
An organic EL device of Comparative Example 1 was produced in the same manner as in Example 1 except that the high refractive index light scattering layer was not provided. The luminance of the obtained organic EL element was measured in the same manner as in Example 1.

Comparative Example 2
The diamond fine particles A added to the high refractive index light scattering layer were replaced with titanium dioxide fine particles (ST-700, manufactured by Fuji Titanium Industry Co., Ltd., refractive index 2.4 or more, average particle size 1.0 μm) with equal weight. Except that, the organic EL element of Comparative Example 2 was produced in the same manner as Example 1. The luminance of the obtained organic EL element was measured in the same manner as in Example 1.

<Evaluation results>
Table 1 shows the luminance measurement results of Examples 1 to 4 and Comparative Examples 1 and 2. In addition, the measured value of the luminance was shown as a relative value with the value of Comparative Example 1 being 1.00.

  As is apparent from Table 1, the luminance is remarkably increased by providing the high refractive index light diffusion layer containing the diamond fine particles A, and the diffusion effect is further increased by containing the diamond fine particles B in the high refractive index light diffusion layer. The brightness increased. Further, the luminance was further increased by providing a low refractive index light scattering layer on the surface of the transparent substrate.

Claims (8)

An organic EL element having a first electrode, an organic layer having a light emitting layer, a second electrode, a high refractive index light scattering layer, and a transparent substrate in order,
The high-refractive-index light scattering layer contains diamond fine particles.   2. The organic EL device according to claim 1, wherein the high-refractive-index light scattering layer includes a binder and diamond fine particles A having a median diameter of 10 to 200 nm, and the content of the diamond fine particles A includes the binder and the diamond fine particles. 1 to 50% by mass relative to the total of A   3. The organic EL device according to claim 1, wherein the density of the diamond fine particles A in the high refractive index light scattering layer increases in the stacking direction so as to increase from the transparent substrate side toward the second electrode side. An organic EL element having a gradient.   3. The organic EL device according to claim 1, wherein the high refractive index light scattering layer is composed of a plurality of layers having different densities of the diamond fine particles A, and is in the layer from the transparent substrate side toward the second electrode side. An organic EL device, wherein the diamond fine particles A are arranged so as to have a high density.   5. The organic EL element according to claim 1, wherein the high refractive index light scattering layer has a refractive index between a refractive index of the second electrode and a refractive index of the transparent substrate. An organic EL element.   6. The organic EL element according to claim 1, wherein the high refractive index light scattering layer further comprises diamond fine particles B having a median diameter of 0.2 to 50 [mu] m in the total of the binder and the diamond fine particles B. On the other hand, the organic EL element characterized by containing 1-70 mass%.   The organic EL element according to claim 1, wherein the low refractive index light for scattering visible light on the opposite side of the transparent substrate from the side facing the high refractive index light scattering layer. An organic EL element having a scattering layer.   The organic EL device according to claim 7, wherein the low refractive index light scattering layer includes a binder and diamond fine particles B having a median diameter of 0.1 to 50 μm, and the content of the diamond fine particles B is the binder and the 1 to 70% by mass based on the total amount of diamond fine particles B

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