JP6533435B2 - Organic EL element - Google Patents

Description

Detailed Description of the Invention

  The present invention relates to an organic EL device having improved luminance and high luminance.

  Organic EL elements (organic electroluminescent elements) are self-luminous elements, excellent in luminous efficiency, image quality, power consumption, etc. Furthermore, they are expected in applications such as displays and lighting as light emitting elements excellent in design (thin) It is done. Organic EL displays have the advantage of display performance such as high visibility and no viewing angle dependency compared to conventional CRTs and LCDs, and also have the advantage of being able to reduce the weight and thickness of the display. There is. In addition to the advantages of weight reduction and thinning, organic EL lighting has the possibility of realizing illumination of a shape that could not be realized so far by using a flexible substrate.

  Organic EL devices generally emit light because the refractive index of each layer including the light emitting layer is higher than that of air (for example, the refractive index of an organic layer such as a light emitting layer is 1.6 to 2.1). Light is likely to be totally reflected at the interface, its light extraction efficiency is less than 20%, and most of the light is lost.

  The light loss in the organic EL element will be described with reference to FIG. As shown in FIG. 6, the organic EL device is basically made up of a first electrode 10 (rear electrode), an organic layer 20 including a light emitting layer and composed of 2 to 3 layers, a second electrode 30 (transparent electrode) and a transparent For example, the holes injected from the first electrode 10 and the electrons injected from the second electrode 30 are recombined in the organic layer 20 to excite the fluorescent substance and the like. It emits light as a result. The light emitted from the organic layer 20 is reflected by the first electrode 10 formed directly or by aluminum or the like and 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 angle of incidence on the interface between adjacent layers having different refractive indexes, and are guided inside the display It can not be taken out outside. The ratio of the guided light is determined by the relative refractive index with the adjacent layer, and the configuration of a general organic EL element: [air (n = 1.0) / transparent substrate (n = 1.5) / transparent electrode ( In the case of n = 2.0) / organic layer (n = 1.7) / back electrode], the proportion of light which 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 effectively used.

  In order to improve the light extraction efficiency, it is possible to (1) prevent total reflection at the transparent substrate / air interface and take out light (Lb in FIG. 6) for guiding “organic layer + transparent electrode + transparent substrate”; 6.) It is essential to take measures to prevent total reflection at the transparent electrode / transparent substrate interface and take out light (Lc in FIG. 6) that guides the “organic layer + transparent electrode”.

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

  With regard to the above (2), there has been proposed a method of processing the transparent electrode / transparent substrate interface and the light emitting layer / adjacent layer interface into a diffraction grating (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. Guided light is extracted by making the pitch and the depth have a specific relationship. Furthermore, there is also proposed a method of processing the interface between the stacked organic layers into irregularities to increase the light emission efficiency (see Patent Document 4). In this method, asperities with a depth of about 20% to the film thickness of the light emitting layer and an inclination angle of the interface of about 30 ° are formed at the interface between the organic layers, and the bonding interface between the organic layers is enlarged. It is an increase. However, these methods are difficult to process and have a problem that dielectric breakdown is likely to occur at the time of current application, and further development of a useful light extraction method is desired.

On the other hand, methods have been proposed to reduce the blurring of the image while improving the light extraction efficiency by arranging the light scattering layer between the transparent electrode and the transparent substrate (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 the optical path from the light emitted from the light emitting layer to the organic layer and the light transmission 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.

Patent Document 6 provides 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 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 disclosed. And ITO etc.) may be contained.

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

U.S. Pat. No. 4,774,435 Japanese Patent Application Laid-Open No. 11-283751 Unexamined-Japanese-Patent No. 2002-313554 JP, 2002-313567, A JP, 2006-107744, A JP, 2006-107744, A

Unexamined-Japanese-Patent No. 2009-259792

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

  In the light scattering layers described in Patent Document 5 and Patent Document 6 etc., the inventors of the present invention made the apparent refractive index of the base material higher, and the refractive index is higher. By containing the light scattering particles, it is possible to reduce the total reflection at the interface between the transparent electrode and the light scattering layer as much as possible, and to obtain a high light scattering effect, thereby further improving the light extraction efficiency. The present invention was conceived.

  That is, the organic EL element of the present invention is 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 this order, The high refractive index light scattering layer is characterized by containing diamond fine particles.

  The high refractive index light scattering layer comprises 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%.

  The density of the diamond fine particles A in the high refractive index light scattering layer preferably 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 such 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 that

  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 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 light in the visible range on the side opposite to the side facing the high refractive index light scattering layer of the transparent substrate.

  The low refractive index light scattering layer comprises 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%.

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

It is sectional drawing which shows typically the laminated constitution 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 core / shell type composite particle. It is sectional drawing which shows typically the laminated constitution 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 based on the drawings. FIG. 1 is a cross-sectional view schematically showing the layer structure 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 laminated in this order. Although the organic EL element shown in FIG. 1 is an example showing the layer configuration of the bottom emission type, the present invention is also applicable to the organic EL element of the top emission type. The same applies to the 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 emitted light emitted from the organic layer 20 is on the transparent substrate 40 side. Therefore, it is preferable that a transparent member is used for the transparent substrate 40, and the transmittance of light in the visible range (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, glass containing barium and strontium, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, quartz and the like. Further, examples of the polymer plate include those made of polycarbonate resins, acrylic resins, polyethylene terephthalate resins, polyether sulfide resins, polysulfone resins, triazine resins and the like as raw materials. The transparent substrate 40 is not limited to a plate, and may be a film. Usually, the refractive index of glass used as the transparent substrate 40 is 1.5, and among polymers, one having a relatively low refractive index is around 1.4 and one having a relatively high refractive index is 1.65 It is about 2.0 as a material having a large refractive index.

(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 is made of a metal or alloy such as Al, Cu, Ag, or Au. May be composed of a single layer or multiple layers. Layers made of materials that reflect light may be laminated, or layers made of a transparent conductive member and layers made of a material that reflects light may be laminated.

(3) Second Electrode The second electrode 30 is provided between the organic layer 20 and the high refractive index light scattering layer 50 adjacent to the organic layer 20. 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 device. In this case, the transmittance of light in the visible range of the second electrode 30 is preferably greater than 10%. The sheet resistance of the second electrode 30 is preferably several hundred ohms / square (ohms / square) or less. The thickness of the second electrode 30 is preferably in the range of 10 nm to 1 μm, more preferably 10 to 200 nm, depending on the material. 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. For the second electrode 30, an electrode material is used, and for example, ITO (indium tin oxide), IZO (indium zinc oxide) ("IZO" is a registered trademark), ZnO (zinc oxide), etc. 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 one or more layers. At least one layer of the organic layer 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 blocking layer, an electron blocking layer, etc. It may have a layer employed in the device. The organic layer 20 may contain an inorganic compound. In the present embodiment, the organic layer 20 constitutes a planar light emitting region.

A light emitting material such as Alq ₃ [tris (8-hydroxyquinolinato) aluminum] is used for the light emitting layer, and a light emitting material having a configuration showing monochromatic light such as red, green, blue and yellow, and a light emitting color by a combination thereof, for example The thing of the structure which shows white luminescence etc. are used. In forming a light emitting layer, a doping method is known in which a light emitting material is doped as a dopant material to a host material. In the light emitting layer formed by the doping method, the 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 utilizing light emission by singlet excitons or a phosphorescent light emitting layer utilizing light emission by triplet excitons. In the organic layer 20 of the organic EL element 1, any compound can be selected and used from materials used in the organic EL element other than the above-described exemplified compounds.

(5) High Refractive Index Light Scattering Layer The high refractive index light scattering layer 50 includes the second electrode 30 and the second electrode 30 in order to efficiently extract emitted light emitted from the light emitting layer of the organic layer 20 to the outside of the organic EL element 1. It is disposed between the transparent substrate 40. Preferably, the high refractive index light scattering layer 50 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 for scattering light in the visible range. As described above, since 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 refractive index of the high refractive index light scattering layer 50 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 the 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 is obtained. Since the difference in refractive index at the interface between the second electrode 30 and the high refractive index light scattering layer 50 is smaller than the difference in refractive index at the point of .alpha., The critical angle of light when emitted from the second electrode 30 becomes larger. Total reflection is less likely to occur. Therefore, the amount of light emitted from the second electrode 30 is increased. Furthermore, 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 the high refractive index light scattering layer 50 efficiently to the transparent substrate 40. Light into the air and emit into the air.

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

(A) Diamond fine particle As the diamond fine particle 52, one having excellent affinity with a solvent and a solvent at the time of forming a layer to be dispersed uniformly in the high refractive index light scattering layer 50 is preferable, for example, carboxyl group, It is preferable that relatively many functional groups such as sulfonic acid groups and hydroxyl groups be present on the particle surface. In addition, the surface of the diamond fine particle 52 may be modified with a functional group such as a hydrophobic group and used as needed. Examples of the diamond particles 52 include natural diamonds and those obtained by crushing artificial diamonds, or nano diamonds obtained by a blasting method.

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

  The nanodiamond obtained by the bombardment method has a core / shell structure in which graphitic carbon covers the surface of nanosized diamond fine particles, and is colored black due to the presence of graphitic carbon. Although it is possible to use it as it is, it is possible to remove much of graphitic carbon on the particle surface by oxidation treatment to enhance transparency. The fine diamond particles obtained by the oxidation treatment have very good affinity to hydrophilic binders and solvents because of the hydrophilic functional groups such as -COOH and -OH which are present on the surface of the remaining graphitic carbon remaining in trace amounts. Good dispersibility in glass and polymers having a hydrophilic group. In addition, the surface can be used after modification with a group containing fluorine or silicon.

  The nanodiamonds obtained by the oxidation treatment are secondary particles having a median diameter of 30 to 250 nm (dynamic light scattering method) consisting of nanosized diamonds 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 too small particle diameter and therefore have a small effect of scattering visible light, so when used as a light scatterer, the particle diameter at which Mie scattering occurs (median diameter 0.1 to 0.1) It is preferable to use it by aggregating to 50 μm).

The fine diamond 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 (removing rate of graphitic carbon), it is necessary to determine the diamond content in the particles (the amount of graphitic carbon present on the particle surface) 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 though the specific gravity of the diamond fine particles is less than 2.55 g / cm ³ , that is, even when the oxidation treatment is not performed, the surface has a functional group such as a carboxyl group, a sulfonic acid group, or a hydroxyl group. The number of them can be increased by applying. In the case of excessive oxidation treatment, most of graphitic carbon in the shell portion of nanodiamond is removed, and conversely, functional groups such as carboxyl group, sulfonic acid group and hydroxyl group decrease, and as a result, the solvent It is preferable that the specific gravity does not exceed 3.48 g / cm ³ because the dispersibility in etc. may decrease. Moreover, even if the specific gravity exceeds 3.48 g / cm ³ , surface modification with a functional group having an effect of enhancing the affinity to the binder and the solvent is carried out to the binder and the solvent, if necessary. Dispersibility can be enhanced.

The specific gravity is more preferably 3.0 g / cm ³ (diamond 84 volume%) or more and 3.46 g / cm ³ (diamond 97 volume%) or less, and 3.38 g / cm ³ (diamond 90 volume%) or more Most preferably, it is 3.45 g / cm ³ (diamond 96 volume%) or less. The volume percentage of diamond in nanodiamond is a value calculated from the specific gravity of 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 (400 to 700 nm) of visible light 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 such a size that does not cause scattering with visible light (Mie scattering), that is, 200 nm or less, more preferably 100 nm or less, and most preferably 50 nm or less. Even in the case of fine diamond particles having a median diameter of 10 to 200 nm, particles having a relatively large size of 200 nm or more are also included to some extent, so the effect of scattering light in the visible range is small.

  The refractive index of the high refractive index light scattering layer 50 formed by uniformly dispersing the diamond fine particles in the binder is an additive property of the diamond fine particles and the binder, so the weighted average of the refractive index of the diamond and the refractive index of the binder Can be represented by For example, when 20 parts by mass of diamond fine particles (refractive index 2.42) is dispersed in a binder (80 parts by mass) having a refractive index of 1.60, the refractive index of the high refractive index light scattering layer 50 is It becomes 1.76. Thus, 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 according to what refractive index the high refractive index light scattering layer 50 is designed, but the high refractive index light scattering layer 50 The content 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 forming the.

  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 is from the transparent substrate side toward the second electrode side 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 changes so as to gradually increase from the transparent substrate side to the second electrode side, and the transparent substrate and the second electrode side And the refractive index between can be connected smoothly. 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 made the same refractive index as that of the transparent substrate. It is preferable to make the refractive index of the second electrode side (the surface in contact with the second electrode) of the index light scattering layer the same as the refractive index of the second electrode. The density gradient of the diamond fine particles A in the direction of the high refractive index light scattering layer thickness may be continuous or stepped.

(Ii) Diamond fine particles B
The high refractive index light scattering layer 50 is a diamond fine particle having a median diameter of 0.2 to 50 μm (hereinafter referred to as a diamond fine particle B (52 b)) in order to further enhance the diffusibility of visible light in addition to the diamond fine particle A. May be contained. The diamond fine particle B has a median diameter equal to or longer than the wavelength of light in the visible region, and thus, as a light scatterer that exhibits a high scattering effect on light in the visible region 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, one having 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.

  It is also possible to use a core / shell type composite particle 100 composed of a core 101 of diamond fine particles and a shell 102 of an organic polymer or silica as shown in FIGS. 3 (a) to 3 (c) as the light scatterer. 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 in the high refractive index light scattering layer 50 and the diamond fine particles B (52b), It is more preferable that 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 a glass material or a polymer resin is preferable. Examples of the glass material constituting the binder include soda lime glass, glass containing barium and strontium, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, quartz and the like.

  As the polymer resin, those excellent in visible light transmittance are preferable, and 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 Thermoplastic resins such as resin, polyamide resin, polyimide resin, melamine resin, phenol resin, cycloolefin resin, triazine resin, silicone resin, fluorine resin, etc., 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 structure of the organic EL element 2 of the second embodiment. The organic EL element 2 includes at least a first electrode 10, an organic layer 20, a second electrode 30, a high refractive index light scattering layer 50, a transparent substrate 40, and a low refractive index light scattering layer 60 in this order. It has a stacked structure. The organic EL element 2 of the second embodiment is the organic EL element 1 of the first embodiment in which 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 device 1 of the first embodiment, the low refractive index light scattering layer 60 is used here. Only explain.

(1) Low Refractive Index Light Scattering Layer 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 as shown in FIG. It has the function of scattering. By scattering the light in the visible region 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 to the outside of the organic EL element 2.

  The low refractive index light scattering layer 60 is preferably a layer in which diamond fine particles 62 are dispersed in a binder 61 as shown in FIG. 5, and as the diamond fine particles 62, particularly, the median diameter is 0.1 to 50 μm. The fine particles of diamond 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 fine diamond particles B may be fine diamond particles having a median diameter of 0.1 to 50 μm, and the fine diamond 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 a refractive index similar to 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 degree, it is possible to prevent the reflection of the emitted light at the interface between the low refractive index light scattering layer 60 and the transparent substrate 40. it can. Therefore, the emitted 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 to be directed to the outside (in air). It is 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 to the outside of the element 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 applies a coating liquid containing diamond fine particles and a binder or a precursor thereof to the surface of the transparent substrate 40 Alternatively, a film containing diamond fine particles and a binder may be prepared in advance, and the film may be formed on the surface of the transparent substrate 40 by affixing the film to the surface of the transparent substrate 40. The high refractive index light scattering layer 50 may be formed by combining the application method and the attachment method. When combining these methods, the film may be attached after the diamond particle dispersion liquid is applied, or the diamond particle dispersion liquid may be applied after the film is attached. The coating solution may have a solvent and various additives if necessary.

  The said binder precursor is a monomer for forming the binder which comprises the high refractive index light-scattering layer 50, or the above-mentioned hard-coat agent. The coating solution 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 from methods such as dip coating method, ink jet method, spin coating method, spray coating method, flow coating method and the like according to the purpose. Among them, the inkjet method and spin coating method which are advantageous for forming a uniform layer are preferable. At this time, a high refractive index light scattering layer can be formed in which the density of the diamond fine particles A is changed in the thickness direction by sequentially applying and laminating a plurality of coating solutions having different concentrations of the diamond fine particles A.

  In the case of forming the high refractive index light scattering layer 50 by a bonding method, for example, there is a method of forming a film containing diamond fine particles and a binder by extrusion molding, and bonding them by dry lamination, thermal lamination or the like. 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 film with different densities of the diamond fine particles A is produced, and by laminating them in order, it is possible to form a high refractive index light scattering layer in which the density of the diamond fine particles A changes in the thickness direction.

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

(3) Formation of Organic Light Emitting Layer and Electrode The second electrode 30, the organic layer 20, and the first electrode 10 are sequentially laminated on the high refractive index light scattering layer 50 formed. The formation method of a vacuum evaporation method, sputtering method, etc. can be employ | adopted for formation of the 1st electrode 10 and the 2nd electrode 30. FIG. The organic layer 20 may be formed by a dry film forming method such as vacuum evaporation, sputtering, plasma or ion plating, or a wet film forming method such as spin coating, dipping, flow coating, or ink jet method. A formation method can be adopted.

<Modification of Embodiment>
Note that the present invention is not limited to the above-described embodiment, and modifications, improvements, and the like as long as the object of the present invention can be achieved are included in the present invention.

  The present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

Example 1
(1) Preparation of diamond fine particles BD produced by explosively generating 0.65 kg of explosive containing TNT (trinitrotoluene) and RDX (cyclotrimethylene trinitroamine) in a ratio of 60/40 in a 3 m ³ explosion chamber After forming the atmosphere for storing, a second explosion occurred under the same conditions to synthesize BD. After the explosion products had expanded and reached thermal equilibrium, the gas mixture was drained from the chamber for 35 seconds through a supersonic Laval nozzle with a 15 mm cross section. The cooling rate of the product was 280 ° C./min due to the heat exchange with the chamber walls and the work done by the gas (adiabatic expansion and vaporization). The specific gravity of the product (black powder, BD) captured by a cyclone was 2.55 g / cm ³ , and the median diameter (dynamic light scattering method) was 220 nm. The BD was calculated from specific gravity and was estimated to consist of 76% by volume of graphitic carbon and 24% by volume of diamond.

  This BD was mixed with a 60 mass% nitric acid aqueous solution and oxidatively decomposed at 160 ° C., 14 atm for 20 minutes, and then oxidatively etched at 130 ° C., 13 atm, for 1 hour. The oxidative etching process yielded particles in which graphite was partially removed from BD. The particles were neutralized with ammonia at 210 ° C. and 20 atm for 20 minutes, neutralized, allowed to settle naturally, washed with 35 mass% nitric acid by decantation, and further washed with water three times by decantation, It was dewatered by centrifugation and dried by heating at 120 ° C. to obtain a powder of diamond fine particles.

The powder of this diamond fine particle was further dispersed in water and repeated decantation to separate it into a relatively small particle size diamond fine particle A in the supernatant portion and a relatively large particle size diamond fine particle B in the precipitate 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 gravities were both 3.38 g / cm ³ . Calculated from specific gravity, these diamond fine particles were estimated to be composed of 90% by volume of graphitic 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 "UVHC 1105" solid content concentration 100% by weight) 100 parts, UV curable silicone resin (manufactured by Chisso Corp.) A coating liquid for a high refractive index light scattering layer was prepared, which was made of 0.4 parts of trade name "Syraplane FM-7711" (molecular weight 1000), 20 parts by mass of the prepared diamond fine particles A, and 100 parts of isopropyl alcohol.

The film thickness after curing of this coating solution is 0.5 μm 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, NA 35) After coating with a spin coater and drying at 80 ° C. for 2 minutes, ultraviolet light was irradiated at an irradiation amount of 1000 mJ / cm ² to form a high refractive index light scattering layer. The refractive index of this high refractive index light scattering layer was 1.73. The refractive index of the hard coat layer was 1.60 when it was prepared without separately adding the diamond fine particles A.

  On the high refractive index light scattering layer thus formed, 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 this IZO film. HI-1 is vapor deposited to form a hole injection layer having a thickness of 5 nm, and a hole transporting compound HT-1 is vapor deposited on the hole injection layer to form a first hole transport layer having a thickness of 120 nm. Then, a hole transporting compound HT-2 was vapor-deposited on the first hole transporting layer to form a second hole transporting layer having a thickness of 85 nm.

  Furthermore, on this second hole transport layer, a light emitting layer with a film thickness of 45 nm was formed by co-evaporation of a compound RH-1 as a host material and a compound RD-1 as a phosphorescent dopant material. The concentration of compound RD-1 in the light emitting layer was 5% by mass. The maximum emission peak wavelength of the compound RD-1 was 602 nm.

  An electron transporting compound ET-1 is vapor 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 vapor deposited on the first electron transporting layer. A second electron transport layer having a thickness of 10 nm is formed, and a compound ET-3 having an electron transport property is vapor-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 Å / min to form a 1 nm thick LiF film as an electron injecting electrode (cathode), and metal Al is deposited on the LiF film to form a film An 80 nm thick metal cathode 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 by a luminance meter (BM5A manufactured by Topcon Corporation).

Example 2
(1) Preparation of Coating Liquids A to C for High Refractive Index Light Scattering Layer Ultraviolet-curable acrylate hard coat agent (manufactured by GE Toshiba Silicone Co., Ltd., trade name "UVHC 1105" solid content concentration 100% by weight) 100 parts, ultraviolet curing -Refractive-index light scattering consisting of 0.4 parts of a silicone resin (Tysso Co., Ltd., trade name “Silaplain FM-7711” (molecular weight 1000)), 3 parts by mass of the prepared diamond fine particles A, and 100 parts of isopropyl alcohol Coating solution A for layer was produced.

  Coating solutions B and C for high refractive index light scattering layers are the same except that the addition amount of diamond fine particles A is changed to 20 parts by mass and 40 parts by mass respectively with respect to the coating liquid A for high refractive index light scattering layers Was produced.

(2) Preparation 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 x 25 mm x 0.7 mm thickness (manufactured by Nippon Sheet Glass, NA 35) Coating solution A was applied by a spin coater such that the film thickness after curing was 0.17 μm, and dried at 80 ° C. for 2 minutes. After coating and drying the coating solution A for the high refractive index light scattering layer, the coating fluid B for the high refractive index light scattering layer is similarly coated and dried in the same manner, and further, for the high refractive index light scattering layer After coating liquid C was applied and dried, ultraviolet light was irradiated at an irradiation amount 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.

  A transparent electrode (IZO film), a hole injection layer, a first hole transport layer, a second hole transport layer, light emission on the formed high refractive index light scattering layers A to C in the same manner as in Example 1. 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 the 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 in the same manner as Example 1 except that 5 parts by mass of the fine diamond particle B prepared in Example 1 was further added to the coating solution for high refractive index light scattering layer used in Example 1. Was produced. The luminance of the obtained organic EL element was measured in the same manner as in Example 1.

Example 4
UV curable acrylate hard coat agent [GE Toshiba Silicone Co., Ltd., trade name "UVHC 1105" solid content concentration 100% by weight] 100 parts, UV curable silicone resin [Chisso Corp., trade name "Syraplane FM- 7711 ′ ′ (molecular weight: 1000)] A coating solution for a light scattering layer having a refractive index of 0.4 parts, 5 parts by mass of the fine particles of diamond B prepared in Example 1, and 100 parts of isopropyl alcohol was prepared.

For the high refractive index light scattering layer prepared 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, NA 35) The coating solution is applied by a spin coater so that the film thickness after curing becomes 0.5 μm, dried at 80 ° C. for 2 minutes, and then the coating solution for a low refractive index light scattering layer prepared on the other surface of the glass substrate Is coated with a spin coater so that the film thickness after curing becomes 0.2 μm, dried at 80 ° C. for 2 minutes, then irradiated with ultraviolet light at an irradiation amount of 1000 mJ / cm ² on both sides to form a high refractive index light scattering layer A low refractive index light scattering layer was formed. The refractive index of this high refractive index light scattering layer was 1.73, and the refractive index of the low refractive index light scattering layer was 1.59.

  A transparent electrode (IZO film), a hole injection layer, a first hole transport layer, a second hole transport layer, a light emitting layer, and a second light emitting layer are formed on the formed high refractive index light scattering layer in the same manner as in Example 1. One electron transport layer, second electron transport layer, third electron transport layer, electron injecting electrode (LiF film), and metal cathode (metal Al) were formed, and the 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 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
Diamond fine particles A added to the high refractive index light scattering layer were replaced by titanium dioxide fine particles (manufactured by Fuji Titanium Industry Co., Ltd., ST-700, refractive index 2.4 or more, average particle diameter 1.0 μm) by equal weight An organic EL device of Comparative Example 2 was produced in the same manner as Example 1 except for the above. The luminance of the obtained organic EL element was measured in the same manner as in Example 1.

<Evaluation result>
Table 1 shows the results of the luminance measurement of Examples 1 to 4 and Comparative Examples 1 and 2. In addition, the measured value of the brightness | luminance was shown by the relative value which made the value of the comparative example 1 1.00.

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

Claims (7)

An organic EL device comprising 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 provided adjacent to the second electrode and the transparent substrate, and the high refractive index light scattering layer comprises a binder and diamond fine particles A having a median diameter of 10 to 200 nm, and the diamond Content of the microparticles | fine-particles A is 1-50 mass% with respect to the sum total of the said binder and the said diamond microparticles | fine-particles A, The organic EL element characterized by the above-mentioned. 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 is graded in the stacking direction so as to increase from the transparent substrate side toward the second electrode side. An organic EL element characterized by having. 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 the high refractive index light scattering layer is in the layer from the transparent substrate side toward the second electrode side. An organic EL element characterized in that the density of the diamond fine particles A is increased. The organic EL device according to any one of claims 1 to 3 , wherein the high refractive index light scattering layer has a refractive index between the refractive index of the second electrode and the refractive index of the transparent substrate. An organic EL element characterized by The organic EL device according to any one of claims 1 to 3 , wherein the high refractive index light scattering layer further comprises diamond fine particles B having a median diameter of 0.2 to 50 μm, the binder and the diamond fine particles B. The organic EL element characterized by containing 1-70 mass% with respect to the sum total. The organic EL device according to any one of claims 1 to 5 , wherein low refraction is used to scatter light in the visible range on the opposite side of the transparent substrate to the side facing the high refractive index light scattering layer. An organic EL device having a rate light scattering layer. The organic EL device according to claim 6 , wherein the low refractive index light scattering layer comprises 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 above An organic EL device characterized in that it is 1 to 70% by mass with respect to the total with the diamond fine particles B.

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