JP2008016347A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element and display element of a dot matrix type with high light extraction efficiency. <P>SOLUTION: The organic electroluminescent element is provided with at least one or more organic light emitting layers having a light emitting region, a positive electrode for injecting a positive hole in the organic light emitting layer, and a negative electrode for injecting an electron formed on a substrate. A first base layer, a second base layer, and a third base layer are provided in this order from a substrate side on the substrate. When refractive indexes of the first base layer, second base layer, third base layer are respectively n1, n2, n3 in a wavelength of light emitted by the organic light emitting layer, n1<n2, and n2<n3, and fine particles having a refractive index different from the refractive index of the respective base layers in the wavelength of the light emitted by the organic light emitting layer are dispersed on the second base layer and third base layer. The display element is provided with such the organic electroluminescent element. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a dot matrix type organic electroluminescent element among organic electroluminescent elements that extracts light from an organic light emitting layer by injecting electrons and holes into an organic light emitting layer sandwiched between a cathode and an anode.

  An organic electroluminescence element is a light emitting element having a structure in which an organic light emitting layer is sandwiched between an anode and a cathode. When a voltage is applied, holes are injected from the anode and electrons are injected from the cathode. Is an element that takes out the energy generated as a result of recombination of the pair in the surface or inside of the organic light emitting layer as light. Organic electroluminescence devices using organic substances in the light emitting layer have been studied for a long time, but their practical application has not progressed due to the problem of light emission efficiency. In contrast, in 1987, C.I. W. Tang proposed an organic electroluminescence device with a laminated structure in which the organic layer is divided into a light emitting layer and a hole transport layer, and confirmed high-efficiency light emission at a low voltage (see Non-Patent Document 1, etc.) and thereafter. Researches on organic electroluminescence devices have been actively conducted. By adopting such a laminated structure, it is possible to prevent electrons and holes injected into the light emitting layer from flowing to the counter electrode, and the recombination efficiency in the light emitting layer is improved. Further, the efficiency of injecting electrons and holes into the light emitting layer can be increased. Therefore, at present, organic electroluminescence elements generally have a laminated structure, and the structure is a two-layer structure of a light emitting layer and a hole injection layer, a three-layer structure of an electron injection layer, a light emitting layer, and a hole injection layer, Devices having a structure such as a four-layer structure of an electron injection layer, a light emitting layer, a hole transport layer, and a hole injection layer have been proposed.

  However, it is known that in the organic electroluminescence device, the probability of singlet generation necessary for emitting fluorescence upon recombination in the light emitting layer is statistically 25%. Therefore, theoretically, only 1/4 of the injected electrons and holes can be extracted as light. On the other hand, an organic electroluminescence element using phosphorescence from an excited triplet has been proposed (see Non-Patent Document 2, etc.), and in recent years, materials that exhibit phosphorescence at room temperature have been actively studied.

  Nevertheless, the refractive index of the material used for the organic layer is relatively high, and light is emitted three-dimensionally and isotropically inside the organic light emitting layer, so light generated at an angle greater than the critical angle with respect to the substrate surface is Total reflection occurs and light below the critical angle is partially reflected at the interface and cannot be extracted outside. For this reason, if the refractive index of the light emitting layer is assumed to be 1.6, only about 20% of the generated light can be extracted to the outside, and if the refractive index of the light emitting layer is high, this numerical value further decreases.

  Various proposals have been made as methods for improving the light extraction efficiency. Among them, as a technique for improving the light extraction efficiency by a relatively easy technique, several techniques for changing the traveling direction of light at the substrate portion have been proposed. For example, Patent Document 1 and Patent Document 2 have proposed that a scattering layer is provided outside the substrate. Further, in Patent Document 3, the substrate itself has a scattering property. Furthermore, in Patent Document 4, a lens structure is provided on the substrate surface. However, these structures are effective means for light reaching the substrate and do not affect the extraction efficiency of light incident on the substrate from the light emitting layer. Furthermore, these means are effective when an organic electroluminescence element is used as a surface light source, but a dot matrix element having fine pixels is not an effective means in consideration of parallax.

  Further, Patent Document 5 proposes an organic electroluminescence element characterized in that a layer having a refractive index equal to or higher than that of the light emitting layer and having a scattering property is provided between the substrate and the light extraction surface. In this case, the light extraction efficiency to the substrate is improved, but there is a problem of the critical angle between the substrate and the outside world, so that the light extraction efficiency is improved for light exceeding the critical angle to the outside world while reaching the substrate. I can't let you. In this case, the light extraction efficiency can be improved by taking a structure such as scattering or diffraction on the inside or outside surface of the substrate, but in this case as well, pixels having different emission colors are formed on the substrate like the dot matrix display as described above. It will not be an effective means with the element.

  Thus, in order to improve the light extraction efficiency of the elements of the dot matrix display, it is necessary to provide an extraction structure inside the substrate. Patent documents 6, 7, etc. are mentioned as what has proposed such a structure. In these proposals, the light extraction efficiency from the substrate is improved by providing a layer having a low refractive index on the substrate and laminating a layer having a function of changing the traveling direction of light such as scattering. By providing the scattering structure inside the substrate in this manner, it is possible to eliminate parallax and prevent pixel blurring when used in a dot matrix display. At this time, it is preferable that the refractive index is low from the viewpoint of the critical angle of the low refractive index layer formed on the substrate, and the low refractive index layer used to achieve this purpose is aligned with fluoride resin and magnesium fluoride. Among these materials, porous silica (porous silica) is proposed. However, among these materials, it is shown that porous silica is suitable as a material for the low refractive index layer. The process of forming a low refractive index layer with porous silica is performed by applying a porous silica precursor solution mainly composed of tetraalkoxysilane or its oligomer on a substrate, and then forming a porous silica film by a condensation reaction by heating. At this time, it is possible to control the refractive index of the formed porous silica film by the composition of the porous silica precursor.

  On the other hand, an organic light emitting layer in an organic electroluminescence element has absorption in the ultraviolet region due to the size of the energy band gap necessary for light emission, and the refractive index in the visible light region is increased due to the absorption. Often used. For this reason, the refractive index of the organic layer at the wavelength of light generated by the organic electroluminescence element is usually about 1.7 to 1.9, which is higher than that of a material such as a substrate. Therefore, a layer for efficiently extracting light generated from a light-emitting layer having a high refractive index and changing the traveling direction of light by scattering or the like preferably has a high refractive index from the viewpoint of the critical angle. It is preferable that the refractive index is higher.

  Films with a high refractive index and suitable for this application include silicon nitride, oxynitride, oxides of metals such as aluminum, titanium, zirconium and niobium, nitride sputtering films, CVD films, vapor deposition films, etc. Is mentioned. However, when forming a film using a vapor phase method such as sputtering or CVD, it is difficult to contain particles for scattering inside the film. On the other hand, a solution of a metal alkoxide such as titanium or zirconium is applied to a substrate, and the metal alkoxide is hydrolyzed and condensed by heating and baking to form an amorphous oxide film such as titanium or zirconium. -If the gel method is used, a scattering film having a high refractive index can be easily prepared by dispersing scattering particles in a solution of a metal alkoxide as a raw material. The amorphous oxide film of a metal obtained by the sol-gel method has a refractive index lower than that of the same oxide film of the same metal formed by the gas phase method, but it is still 1.7. It is possible to obtain a refractive index of 1.9 from

When a metal amorphous oxide film is formed on a substrate by the sol-gel method, the composition at the time of coating is baked by desorption of alcohol from the metal alkoxide by hydrolysis or evaporation of the solvent by heating. The latter composition is reduced in weight and the film is shrunk compared to when applied. Therefore, a shrinkage stress acts during firing. On the other hand, as described above, the porous silica used in the low refractive index layer can control the refractive index of the porous silica film to be formed by the composition of the precursor, but in order to improve the light extraction efficiency, Lowering the refractive index of the porous silica film increases the proportion of voids in the film, thus reducing the mechanical strength of the film, and a metal amorphous material is formed on the film by a sol-gel method. When forming a porous oxide film, it becomes a factor that causes cracks in the porous silica layer due to the shrinkage stress during firing.
C. W. Tang, S.M. A. VanSlyke, Applied Physics Letters, 51, 913, 1987 M.M. A. Baldo et al. , Nature, 395, 151, 1998 JP 2003-109747 A JP 2002-75657 A JP 2001-356207 A JP-A-8-83688 JP 2004-296429 A JP 2004-303724 A JP 2004-319331 A

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a dot matrix type organic electroluminescence element and a display element having high light extraction efficiency.

  As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, this invention provides the organic electroluminescent element shown by following (1)-(13), and the display apparatus shown by following (14).

(1)
An organic electroluminescent device comprising at least one organic light emitting layer having a light emitting region on a substrate, an anode for injecting holes into the organic light emitting layer, and a cathode for injecting electrons. Includes a first ground layer, a second ground layer, and a third ground layer in this order from the substrate side, and the first ground layer, the second ground layer, and the third bottom layer at the wavelength of light emitted by the organic light emitting layer. Assuming that the refractive indexes of the base layer are n1, n2, and n3, respectively, n1 <n2 and n2 <n3, and the second base layer and the third base layer have wavelengths of light emitted by the organic light emitting layer. In the organic electroluminescence device, fine particles having a refractive index different from the refractive index of each underlying layer are dispersed.

(2)
The organic material according to (1) above, wherein a refractive index of the first underlayer at a wavelength of light emitted from the organic light emitting layer is smaller than a refractive index of the substrate and is 1.4 or less. Electroluminescence element.

(3)
The organic electroluminescent element according to (2) above, wherein the refractive index of the first underlayer at the wavelength of light emitted from the organic light emitting layer is 1.3 or less.

(4)
Said (1) thru | or (3) characterized by the said 1st base layer containing porous silica.
Organic electroluminescent element of any one of these.

(5)
The organic electroluminescent element according to any one of (1) to (4), wherein the second underlayer includes a resin.

(6)
The organic electro of any one of (1) to (5) above, wherein a refractive index of the third underlayer at a wavelength of light emitted from the organic light emitting layer is 1.7 or more. Luminescence element.

(7)
The organic electroluminescence device according to (6) above, wherein a refractive index of the third underlayer at a wavelength of light emitted from the organic light emitting layer is 1.8 or more.

(8)
A smoothing layer is further provided on the third base layer, and the refractive index of the smoothing layer at a wavelength of light emitted from the organic light emitting layer is 1.7 or more. The organic electroluminescence device according to any one of (7).

(9)
The organic electroluminescence device according to (8) above, wherein the smoothing layer has a refractive index of 1.8 or more at a wavelength of light emitted from the organic light emitting layer.

(10)
(8) or (9), further comprising a gas barrier layer on the smoothing layer, wherein a refractive index of the gas barrier layer at a wavelength of light emitted from the organic light emitting layer is 1.7 or more. The organic electroluminescent element of description.

(11)
The organic electroluminescence device according to (10) above, wherein a refractive index of the gas barrier layer at a wavelength of light emitted from the organic light emitting layer is 1.8 or more.

(12)
The organic electroluminescence device according to any one of (1) to (11), wherein the fine particles are made of a metal, a metal compound, a silicon compound, a resin, or a mixture thereof.

(13)
The organic electroluminescent device as described in (12) above, wherein the metal compound is an oxide or nitride of titanium, zirconium, aluminum and cerium.

(14)
The display apparatus provided with the organic electroluminescent element of any one of said (1) thru | or (13).

  According to the present invention, there is provided an organic electroluminescent device comprising one or more organic light emitting layers having a light emitting region, an anode for injecting holes into the organic light emitting layer, and a cathode for injecting electrons, On the substrate, the first underlayer, the second underlayer, and the third underlayer are formed in this order from the substrate side. The second underlayer and the third underlayer are provided with scattering properties, and the refractive index of each layer is as described above. By optimizing, it is possible to provide a dot matrix organic electroluminescence element having excellent light extraction efficiency and a display device using the same.

  Several embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same or similar components are denoted by the same reference numerals.

  FIG. 1 is a schematic cross-sectional view showing an organic electroluminescence element 100 according to the first embodiment of the present invention. The organic electroluminescent element 100 includes a first base layer 102, a second base layer 103, and a third base layer 104 in this order from the substrate side on a substrate 101, and further sandwiched by two electrodes 105 and 107 thereon. An organic light emitting layer 106 is disposed. Further, assuming that the refractive indexes of the first ground layer 102, the second ground layer 103, and the third ground layer 104 at the wavelength of light emitted from the organic light emitting layer 106 are n1, n2, and n3, respectively, n1 <n2 and n2 < In the second base layer 103 and the third base layer 104, fine particles having a refractive index different from the refractive index of each base layer are dispersed in the second base layer 103 and the third base layer 104. ing. The wavelength of the light emitted from the organic light emitting layer 106 is usually in the range of 420 nm to 750 nm as the peak wavelength.

  The light generated in the organic light emitting layer 106 passes through the electrode 105 (usually a transparent electrode) on the substrate side. In this case, the refractive index of the normally transparent electrode 105 is higher than the refractive index of the organic light emitting layer 106. There is no critical angle. Further, when light passes through the electrode 105 and enters the third underlayer 104, the light reaching the interface between the electrode 105 and the third underlayer 104 is refracted according to Snell's law, and is at an angle greater than the critical angle. Since the light reaching the interface causes total reflection, it cannot enter the third underlayer 104.

  In general, since the electrode 105 needs to be light transmissive, an ITO (indium tin oxide) film or an IZO (indium zinc oxide) film is used for the electrode, and its refractive index is 1.8 to It is about 2.0. As described above, the refractive index of the organic light emitting layer 106 is often 1.6 or 1.7 or more. Therefore, in order to increase the critical angle, the refractive index n3 of the third underlayer 104 is preferably large, and in particular, the critical angle can be eliminated by increasing the refractive index of the organic light emitting layer 106. Therefore, the refractive index n3 of the third underlayer 104 is preferably 1.7 or more, more preferably 1.8 or more, at the wavelength of light emitted from the organic light emitting layer 106. However, if it is too large, reflection at the interface between the third underlayer 104 and the electrode 105 becomes strong, which is not preferable. The refractive index n3 of the third underlayer 104 is usually 2.5 or less.

  Further, light is incident on the second underlayer 103 from the third underlayer 104. The third underlayer 104 has a refractive index different from the refractive index n3 of the third underlayer 104 at the wavelength of light generated from the organic light emitting layer 106. Since the fine particles having the ratio are dispersed, when the incident light enters the third underlayer 104, the fine particles contained in the layer cause scattering. On the other hand, the second underlayer 103 can be formed of a resin, for example. In order to emit light generated from the organic light emitting layer to the outside, it is necessary to use a resin that does not absorb at the wavelength of the light. In the case of a dot matrix display type element, the organic light emitting layer 106 is patterned with a plurality of pixels having different emission colors, usually the three primary colors of red, blue, and green. It is necessary to use a transparent resin that does not absorb light in all regions of light. Examples of such transparent resins include acrylic resins, epoxy resins, and polyimide resins. When these resins are used, the refractive index n2 is as low as about 1.45 to 1.6. Therefore, a critical angle exists when light enters the second underlayer 103 from the third underlayer 104. However, since light scatters in the third underlayer 104, the angle is greater than the critical angle. Light that enters the second underlayer 103 from the third underlayer 104, undergoes total reflection at the interface between the third underlayer 104 and the second underlayer 103, and returns to the third underlayer 104 is transmitted to the third underlayer 104. Light is scattered inside to change the traveling direction of the light, and is incident on the second underlayer 103 again at a different angle. For this reason, since the angle of light incident at an angle greater than the critical angle changes every time scattering occurs, the light can enter the second underlayer 103 as indicated by an arrow in FIG.

  The light that has passed through the second underlayer 103 further enters the first underlayer 102, and the second underlayer 103 has the refractive index n 2 of the second underlayer 103 at the wavelength of the light generated by the organic light emitting layer 106. Since fine particles having different refractive indexes are dispersed, when light enters the second underlayer 103, the light is scattered by the fine particles contained in the layer. On the other hand, when the first underlayer 102 is made of, for example, porous silica, the refractive index thereof is 1.4 or less, more preferably 1.3 or less, at the wavelength of light emitted from the organic light emitting layer 106. Therefore, a critical angle exists when light is incident on the first ground layer 102 from the second ground layer 103. However, since light is scattered in the second ground layer 103, the angle is greater than the critical angle. The light that has entered the first ground layer 102 from the second ground layer 103, has undergone total reflection at the interface between the second ground layer 103 and the first ground layer 102, and has returned to the second ground layer 103 is reflected by the second ground layer 103. Light is scattered inside to change the traveling direction of the light, and is incident on the first underlayer 102 again at a different angle. For this reason, since the angle of light incident at an angle greater than the critical angle changes every time scattering occurs, it becomes possible to enter the first underlayer 102 as shown by an arrow in FIG. In addition, the refractive index of a 1st base layer is 1.0 or more normally.

  Furthermore, the critical angle θc when the light that has passed through the first underlayer 102 passes through the substrate and finally exits to the air layer (external world) having a refractive index of 1.0 is sin θc = 1 / n (n is the refractive index of the substrate). However, when the incident angle is θ ′ when incident on the substrate from the first underlayer 102, the angle θ of the light entering the substrate follows Snell's law sin θ = sin θ ′ · (n1 / n). In order to cause refraction, the critical angle θ′c with respect to the air layer viewed from the first underlayer 102 is expressed as sin θ′c = 1 / n1, and the critical angle is determined by n1 regardless of the refractive index n of the substrate, By setting the refractive index n1 of the first underlayer 102 to 1.4 or less, the critical angle to the outside world can be increased to about 46 ° or more, and by setting n1 to 1.3 or less. The critical angle to the outside world can be increased to about 50 ° or more.

  As described above, the lower the refractive index n1 of the first underlayer 102, the larger the critical angle and the higher the light extraction efficiency. However, as described above, the porous silica has a lower refractive index. The mechanical strength decreases as the value increases.

  Therefore, when the third underlayer which is a scattering layer having a high refractive index is directly laminated on the porous silica film by the sol-gel method, the same light extraction effect as that of the present invention can be obtained, but the mechanical property of the porous silica film Since the mechanical strength is low, cracks are generated in the porous silica layer when a metal oxide amorphous film is baked on the porous silica layer by a sol-gel method. However, in the present invention, in the present embodiment, the second base layer 103 that is a resin film is formed directly on the first base layer 102 of porous silica. It is possible to suppress the occurrence of cracks in one underlayer 102. Further, when the third underlayer 104 is formed on the second underlayer 103 by the sol-gel method, stress due to shrinkage is similarly generated when the third underlayer 104 is fired. Since 103 relieves stress, it becomes possible to suppress the occurrence of cracks in the first underlayer 102.

  FIG. 4 is a schematic sectional view showing an organic electroluminescence element 400 according to the second embodiment of the present invention. The organic electroluminescent element 400 shown in FIG. 4 has the same structure as the organic electroluminescent element 100 shown in FIG. 1 except that a smoothing layer 401 is provided between the third base layer 104 and the electrode 105.

  As described above, the second underlayer 103 and the third underlayer 104 contain fine particles having a refractive index different from the refractive index of each underlayer. For this reason, the surface of the third underlayer 104 is uneven. When the organic light emitting layer 106 sandwiched between the two electrodes 105 and 107 is formed thereon, unevenness occurs in the organic light emitting layer 106 due to the unevenness of the underlying layer, and the two electrodes 105 and 107 are locally short-circuited. There is a possibility that a part will occur. Therefore, by forming the smoothing layer 401 between the third underlayer 104 and the electrode 105, the unevenness of the underlayer can be eliminated. However, the difference in refractive index between the smoothing layer 401 and the organic light emitting layer 106 causes a critical angle problem and a reflection problem as well as the refractive index difference between the base layer and the organic light emitting layer. Therefore, if the refractive index of the smoothing layer 401 is 1.7 or more, the light extraction efficiency can be increased for the same reason as described above. More preferably, when the refractive index of the organic light emitting layer is high, the smoothing layer If the refractive index of 401 is 1.8 or more, the light extraction efficiency can be further increased for the same reason as described above.

  FIG. 5 is a schematic cross-sectional view showing an organic electroluminescence element 500 according to the third embodiment of the present invention. The organic electroluminescent element 500 has the same structure as the organic electroluminescent element 400 shown in FIG. 4 except that a gas barrier layer 501 is further provided on the smoothing layer 401.

  When the second underlayer 103 is formed of a resin as described above, outgas from the resin may adversely affect the organic light emitting layer 106 and the electrodes 105 and 107. Therefore, it is preferable to form the gas barrier layer 501 between the smoothing layer 401 and the electrode 105. However, the difference in refractive index between the gas barrier layer 501 and the organic light emitting layer 106 causes a critical angle problem as well as the difference in refractive index between the base layer and the organic light emitting layer. Therefore, if the refractive index of the gas barrier layer 501 is set to 1.7 or more, the light extraction efficiency can be increased for the same reason as described above, and more preferably, the refractive index of the gas barrier layer 501 when the refractive index of the organic light emitting layer is high. If the value is 1.8 or more, the light extraction efficiency can be increased for the same reason as described above.

  The display device of the present invention uses the organic electroluminescence element with improved light extraction efficiency of the present invention, can reduce the power consumption of the display device, and reduce the current flowing through the organic electroluminescence element. Therefore, the lifetime of the element can be extended.

  As the substrate used for the organic electroluminescence of the present invention, a substrate having translucency in visible light is used. In terms of translucency, the transmittance of the substrate is preferably 80% or more, more preferably 85% or more, and still more preferably 90% or more. The refractive index is not particularly limited as long as it has a refractive index higher than that of the underlying layer, but in the case of a high refractive index substrate with a refractive index exceeding 1.8, external light on the substrate surface This is not preferable because the reflectance of the light becomes high and the reflection of external light becomes remarkable. Further, since the refractive index of the first underlayer is smaller than the refractive index of the substrate, the critical angle θ′c of the first underlayer with respect to the air layer is larger than the critical angle θc of the substrate with respect to the air layer. For this reason, compared with the case where there is no first underlayer, the light totally reflected at the interface between the substrate and the outside returns to the underlayer and scatters at the interface with each underlayer, changes the angle below the critical angle and changes the substrate again. The light that reaches the outside and enters the outside world decreases. Therefore, it is possible to suppress the occurrence of pixel blur due to multiple reflection and scattering through the thick substrate 101 as shown in FIG. Note that FIG. 6 shows that in the present invention, when the first underlayer 102 is not provided, the light that has undergone total reflection at the interface between the substrate 101 and the air returns to the second underlayer 103 to be scattered again, and changes the traveling direction from the light source. It is the figure which showed the case where it will be taken out outside in the distant position.

  Examples of such substrates include optical substrates such as BK7, BaK1, and F2, quartz glass, glass substrates such as alkali-free glass, borosilicate glass, and aluminosilicate glass used for liquid crystal displays, and acrylics such as PMMA. Examples thereof include resin substrates such as resins, polycarbonate resins, polyethersulfone resins, styrene resins such as polystyrene, polyolefin resins, epoxy resins, and polyester resins such as polyethylene terephthalate. In addition, the thickness of the substrate is usually 0.1 mm to 10 mm, but considering the mechanical strength and the weight of the substrate, a thickness of 0.3 to 5 mm, preferably 0.5 to 2 mm is used.

  In the present invention, porous silica having a refractive index of 1.4 or less, more preferably 1.3 or less can be used for the first underlayer. For the porous silica, a method such as a method for producing mesoporous silica such as MCM-41 announced by Mobile in the United States in 1992 can be used. (C. T. Kresge et al., Nature, 359, 710, 1992, etc.) In this method, a self-organizing surfactant or liquid crystal and a silicate solution serving as a silica source are prepared as a template. By adjusting the pH, a tissue structure such as micelles and lamellas is created, and a solution in which silicate is dispersed in a mesh shape is applied to the substrate in the gaps between the tissues. As a means for coating, known methods such as spin coating, dip coating, slit coating, die coating, roll coating, spray coating and the like can be used. After applying the above silica precursor solution onto the substrate by these coating methods, the substrate is dried and then fired at a temperature of 200 ° C. to 550 ° C. under normal pressure or reduced pressure to form a micelle or lamella as a mold. A porous silica thin film can be obtained by removing the organic substances forming the.

  In the present invention, a transparent resin that does not absorb light in the entire visible light region can be used for the second underlayer. Examples of such a transparent resin include an acrylic resin, an epoxy resin, and a polyimide resin. In addition, fine particles having a refractive index different from the refractive index of the second underlayer are dispersed in the second underlayer at the wavelength of light emitted from the organic light emitting layer. Compounds, silicon compounds and resins can be preferably used. As the metal compound, an oxide or nitride of titanium, zirconium, aluminum, or cerium is preferably used. These fine particles preferably have a particle size of 50 nm or more in consideration of light scattering properties, and preferably have a particle size of 5 μm or less from the viewpoint of the smoothness of the second underlayer. Moreover, since the scattering occurs if the refractive index of the dispersed particles is higher or lower than the refractive index of the resin of the second underlayer, if it is different, it can be used in the present invention. In order to increase the refractive index, the difference in refractive index between the second underlayer and the particles should be large. Examples of metal compounds that meet this purpose include titanium oxide (Ti02: refractive index 2.3 to 2.55), zirconium oxide (ZrO2: refractive index 2.0 to 2.1), cerium oxide (CeO2: refraction). The ratio is about 2.2), but is not limited thereto. In order to disperse these fine particles in the resin, various dispersing means such as a roll mill, a sand mill, an attritor, a ball mill, a kneader, a paint shaker, and an ultrasonic disperser can be used. Various dispersion aids can also be added to improve the dispersion of the fine particles and prevent reaggregation. In particular, when fine particles of an inorganic compound are dispersed in a resin, a silane coupling agent may be added to improve the affinity of the organic / inorganic material.

  Further, in the present invention, in order to impart stability and mechanical strength to the film of the second underlayer, the film may be cured by thermosetting by adding a thermosetting monomer to the dispersed resin composition for forming the underlayer. The film may be cured by photocuring by adding a photocurable monomer or a photopolymerization initiator to the dispersion resin composition for forming the underlayer.

  Furthermore, the dispersion resin composition for forming the second undercoat layer of the present invention uses various solvents to obtain viscosity suitable for various coating processes, stability of the composition, and smoothness of the coating film during coating. Can do. Examples of solvents include methanol, ethanol, toluene, cyclohexane, isophorone, cellosolve acetate, diethylene glycol dimethyl ether, ethylene glycol diethyl ether, xylene, ethylbenzene, methyl cellosolve, ethyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, Examples include, but are not limited to, isoamyl acetate, ethyl lactate, ethyl methyl ketone, cyclohexanone, acetone, propylene glycol diacetate, ethyl ethoxypropionate, butyl carbitol, carbitol acetate, and the like. Moreover, you may use these various solvents in mixture suitably, as needed. Moreover, you may add various additives in order to obtain the smoothness of the coating film at the time of application | coating. In addition, when the dispersed particles have a large particle size or high concentration, the coating film may not be sufficiently smooth. In this case, a transparent resin layer may be further formed as an overcoat layer. However, the refractive index of the transparent resin at this time must be substantially equal to the refractive index of the second underlayer. Therefore, when forming an overcoat layer, it is preferable to use a dispersion resin composition for forming a second underlayer from which dispersed particles are removed.

  The third underlayer formed on the second underlayer preferably has a refractive index n3 at a wavelength of light generated from the organic light emitting layer of 1.7 or more, more preferably 1.8 or more. As a material having a refractive index of 1.7 or more and a high refractive index suitable for thin film formation, there is an amorphous metal oxide thin film formed by a sol-gel method. The sol-gel method can obtain a thin film having a high refractive index by a simple coating method. It is suitably used in the present invention. In the present invention, a coating solution for forming a thin film by a sol-gel method using a metal alkoxide such as titanium alkoxide or zirconium alkoxide as a raw material of the inorganic material for forming the third underlayer, alcohols, water, etc. as a solvent is prepared. Then, fine particles having a refractive index different from the refractive index of the second underlayer at the wavelength of light emitted from the organic light emitting layer are dispersed in this coating solution. As the fine particles to be dispersed, metals, metal compounds, silicon compounds, and resins can be preferably used in the same manner as the fine particles to be dispersed in the second underlayer. The metal compound is preferably titanium, zirconium, aluminum, cerium oxide or nitride. Further, since the refractive index of the third underlayer is as high as 1.7 or more, even if silica fine particles (refractive index 1.46) are dispersed, a sufficient scattering effect can be obtained. These fine particles preferably have a particle size of 50 nm or more in consideration of light scattering properties as in the second underlayer, and have a particle size of 5 μm or less from the viewpoint of the smoothness of the second underlayer. The dispersed particles of the second underlayer and the third underlayer may be the same or different. The means for dispersing these fine particles in the coating solution and the means for coating on the substrate can be the same as the means used for forming the second underlayer. Next, a thin film can be obtained by baking the dispersion coating liquid applied on the substrate at an appropriate temperature. The baking temperature may be 100 ° C. to 400 ° C. However, if the baking is performed at a very high temperature, the underlying resin layer may be altered, and therefore the baking temperature is preferably 100 ° C. to 200 ° C.

  When the particle size of the dispersed particles of the third underlayer is large or the concentration is high, the smoothness of the coating film may not be sufficiently obtained. In this case, a smoothing layer may be further formed. As described above, a high refractive index is preferable for the same reason that a high refractive index of the third underlayer is preferable, and a refractive index at a wavelength of light generated in the organic light emitting layer is 1.7 or more, and more preferable. Use 1.8 or more. In this case, it is preferable to use a smoothing layer obtained by removing dispersed particles from the dispersion coating liquid for forming the third underlayer.

  Furthermore, when applying the 3rd foundation | substrate layer and smoothing layer of this invention, you may add various additives to a coating liquid in order to obtain the smoothness of a coating film. Various coating means such as spin coating, dip coating, slit coating, die coating, roll coating, spray coating, etc. are used as means for coating the substrate with the composition for forming the third underlayer or the composition for forming the smoothing layer. Can be mentioned.

  On the other hand, in the present invention, the moisture contained in the resin used for the second underlayer and the overcoat layer thereon leaks from the underlayer to the organic light emitting layer after a long time, and this moisture is absorbed into the organic layer and the cathode. Reacting with a metal may cause a reduction in device lifetime or dark spots. Therefore, in the present invention, it is preferable to provide a gas barrier layer on the element side of the smoothing layer. The material of the gas barrier layer preferably has a high refractive index for the same reason as that of the above-mentioned third underlayer having a high refractive index, and the refractive index is preferably 1.7 or higher, more preferably 1.8 or higher. Use one.

  In general, a barrier layer used in an organic electroluminescence element is a thin film such as silicon nitride, silicon oxynitride aluminum oxide or the like, and since the refractive index of these thin films is sufficiently higher than the refractive index of an organic substance, there is no problem. However, silica often used in the gas barrier layer is not preferable in the present invention because the refractive index is as low as about 1.5. The film thickness is preferably in the range of 0.1 to 10 μm, and more preferably 0.1 to 1 μm in view of film stress and transparency.

  The method for forming the barrier layer in the present invention is not particularly limited as long as it can be used for this application, but various sputtering methods such as DC sputtering, RF sputtering, magnetron sputtering, ECR sputtering, counter target sputtering, and ion beam sputtering, Examples thereof include ion plating and CVD.

  In addition, a transparent conductive film is used as an electrode for extracting light generated in the organic light emitting layer. As the transparent conductive film, metal oxides such as indium tin oxide (ITO), indium zinc oxide, and zinc oxide are usually used, and indium tin oxide is particularly preferable from the viewpoint of transparency and conductivity. The film thickness of the transparent electrode layer is 80 to 400 nm, preferably 100 to 200 nm, from the viewpoint of ensuring transparency and conductivity. As a method for forming the transparent conductive film, a known method such as a sputtering method or an ion plating method can be used. In the case of a dot matrix display, it is necessary to pattern the transparent conductive film according to the shape of the pixel and the wiring. In the present invention, a known method can be used as a method for patterning the transparent electrode. A typical method is patterning by photolithography. In this case, a photoresist is applied to the substrate on which the transparent conductive film is formed by a method such as spin coating, and pattern exposure is performed using a photomask corresponding to the electrode pattern. Further, the transparent electrode is patterned by a method such as sandblasting, dry etching, or wet etching using an acid such as aqua regia on the substrate on which the resist has been patterned by development. It is also preferable to perform oxygen plasma treatment or UV ozone treatment on the transparent conductive film patterned before forming the organic light emitting layer. In this case, organic contamination on the surface of the transparent conductive film is removed, and when the transparent electrode is indium tin oxide, the work function of indium tin oxide is increased by oxygen plasma treatment or UV ozone treatment. It has been known that the injection of silicon becomes easy and the performance of the device is improved. In addition, the shape of the edge portion of the electrode pattern may cause a short circuit after processing the transparent electrode. In this case, the insulating layer pattern may be formed so as to cover the edge portion of the electrode.

  In the present invention, the material used for the organic light emitting layer is not particularly limited, and both low molecular weight materials and high molecular weight materials are preferably used. When using a low molecular weight material for the light-emitting layer, use a shadow mask with holes or slits according to the dot matrix pattern on the substrate on which the electrodes have been patterned, The light emitting layer is vapor deposited several times. Further, a common hole injection layer or transport layer may be provided under the light emitting layer. A common electron injection layer or transport layer may be provided on the cathode side of the light emitting layer. These light emitting layer, transport layer, and injection layer may be a film made of a single material, or may be formed by co-evaporating a plurality of materials for doping. After forming the organic light-emitting layer, the cathode is formed by vapor deposition. In this case, it is common to deposit metal using a shadow mask with slits according to the shape of the electrode, but where the cathode is not formed beforehand The insulating layer film (separator) patterned according to the above is formed, and the end of the insulating layer pattern is formed in a reverse taper shape (eave shape), so that the cathode mask can be used without using the shadow mask. There is also known a method of separating a cathode layer on a separator and a cathode layer on an organic light emitting layer by depositing a metal depending on the shape of the end of the separator pattern.

  In addition, when a polymer material is used for the organic light emitting layer, the material for the injection layer or the transport layer is dissolved in a solvent when the common hole injection layer or the transport layer formed under the light emitting layer is formed. Alternatively, the dispersed solution is generally applied by various coating means such as spin coating, dip coating, slit coating, die coating, roll coating, spray coating, and the like, and dried. It is necessary to form a light emitting layer on the common layer thus formed by patterning according to the pixel pattern of the dot matrix. Examples of the patterning method used at this time include an inkjet method and a printing method. The printing method is a method of printing on a substrate an ink obtained by mixing a material of a polymer light emitting layer and a solvent. The printing method to be used is a known method such as gravure printing, screen printing, letterpress printing, planographic printing, and reversal printing. As a result, a pattern of the light emitting layer can be obtained. The ink jet method supplies the ink jet nozzle ejection part with ink that is a mixture of the polymer light emitting layer material and solvent, and the ink particles are ejected from the nozzle by the vibration and thermal energy of the piezo element, resulting in a pattern shape. Accordingly, the light emitting layer pattern is formed by causing droplets to deposit on the substrate. In the case of the ink jet method, as described in Japanese Patent Application Laid-Open No. 59-75205, there is a limit to the accuracy of the landing position of the ink ejected from the nozzle. Using a photolithographic method or the like, a pattern made of a liquid-repellent material called a bank is formed, and when the ink ejected from the nozzle deviates from the target pixel to be deposited, The ink repels in the bank of the part that has come off and has landed, and the ink is moved to the pixel part to form the pattern shape accurately. In addition, it is not necessary to unify all of the transport layer, injection layer, and light emitting layer that form the organic light emitting layer with a low molecular weight or high molecular weight material. A light emitting layer may be formed by vapor deposition using a system material, and a low molecule or a polymer may be used in combination.

  An element was produced based on the method for producing an organic electroluminescence element shown in the embodiment of the present invention below. However, the present invention is not limited to the conditions of this embodiment.

Example [Formation of First Underlayer and Second Underlayer]
After thoroughly cleaning the 0.7 mm thick glass substrate, ULVAC ISM-2 (porous silica containing hexamethyldisiloxane, hexamethyldisilazane, etc.) is used as the first undercoat layer-forming coating solution for the low refractive index layer. The coating liquid for forming) was applied by spin coating, and the substrate was dried, and then baked at 400 ° C. using an oven depressurized to 5 Pa to form a first underlayer. The film thickness of the first underlayer on the baked substrate was 350 nm. Next, titania fine particles with an average particle diameter of 150 nm are dispersed in a solution of transparent acrylic resin and dipentaerythritol hexaacrylate (polyfunctional acrylic monomer) as a curing agent dissolved in propylene glycol monomethyl ether acetate, and dispersed with an ultrasonic homogenizer. The second underlayer forming coating solution was prepared. This coating solution was applied onto the substrate by spin coating, dried and baked. The weight percent of titania particles contained in the second underlayer film was 30%. The average film thickness of the second underlayer was 500 nm.

[Formation of third underlayer]
A 3% ethanol solution of 2N hydrochloric acid is added dropwise to a 1% isopropanol solution of titanium tetraisopropoxide to prepare a sol solution, and silica fine particles having an average particle size of 110 nm are mixed with this, followed by thorough stirring and dispersion. I let you. This solution was applied onto the substrate by spin coating, and heated on a hot plate at 200 ° C. to form a third underlayer which was a high refractive index scattering layer in which silica fine particles were dispersed in amorphous titania. The film thickness was 170 nm. Further, the sol solution from which particles were removed was prepared, and spin coating and baking were similarly performed to obtain a smoothing layer having a high refractive index. The film thickness of the smoothing layer was 100 nm. Next, a 150 nm thick silicon monooxide (SiO) thin film was deposited on the substrate as a gas barrier layer.

[Formation of electrode and organic light emitting layer]
An indium tin oxide (ITO) film having a thickness of 150 nm was formed on the substrate by RF sputtering, and an anode was obtained by etching into a pixel shape. Further, after washing with detergent and ultrasonic, the electrode surface was cleaned by irradiating with UV light from a low-pressure UV lamp in an ozone atmosphere. Subsequently, this substrate was put into a vacuum vapor deposition machine, and each organic layer was vapor-deposited in the following order.

Hole injection layer: Copper phthalocyanine represented by the following formula 1 was formed to a thickness of 15 nm at a deposition rate of 0.2 nm / second.

Light emitting layer 1: α-NPD represented by the following formula 2 was formed to a thickness of 20 nm at a deposition rate of 0.2 nm / second. At that time, 1% by weight of rubrene represented by the following formula 3 was doped.

Light-emitting layer 2: Dinaphthyl anthracene represented by the following formula 4 was formed to a thickness of 30 nm at a deposition rate of 0.2 nm / second. At that time, 1% by weight of perylene represented by the following formula 5 was doped.

Electron injection layer: Alq3 represented by the following formula 6 was formed to a thickness of 30 nm at a deposition rate of 0.2 nm / second.

Next, lithium fluoride is formed to a thickness of 0.5 nm (deposition rate 0.01 nm / second) on the electron injection layer, and finally aluminum is evaporated to 150 nm (deposition rate 5 nm / second) according to the cathode pattern. And it sealed in the glove box and obtained the element. When the fabricated device was observed with a microscope, no cracks or peeling was observed. Further, when the device was energized and the quantum efficiency was measured, it was 2.69% when the current density was 100 A / m ² . Further, the current luminance efficiency in the front direction was 10.5 cd / A at the maximum.

Comparative Example A comparative device was prepared for comparison with the example. This element does not form the first to third underlayers, but directly forms ITO on the glass substrate under the same conditions as in the example, and the subsequent patterning and formation of the organic light emitting layer are also performed under the same conditions as in the example. It was created. When the quantum efficiency of the fabricated device was measured, it was 1.92% when the current density was 100 A / m ² . Further, the current luminance efficiency in the front direction was 6.5 cd / A at the maximum.

1 is a schematic cross-sectional view showing an organic electroluminescence element according to a first embodiment of the present invention. In the organic electroluminescence device shown in FIG. 1, the incident light is incident on the second underlayer 103 from the third underlayer 104 at an angle greater than the critical angle, and the reflected light returns to the third underlayer 104 to cause scattering inside the 104. The figure which shows a mode that the advancing direction of light is changed and enters into 103 again. In the organic electroluminescence element, light incident on the first underlayer 102 from the second underlayer 103 at an angle equal to or greater than the critical angle and reflected light returns to the second underlayer 103 and scatters in the inside 103 to advance the light. The figure which shows a mode that it changes a direction and injects into 102 again. The schematic sectional drawing which shows the organic electroluminescent element which concerns on a 2nd aspect. The schematic sectional drawing which shows the organic electroluminescent element which concerns on a 3rd aspect. In the organic electroluminescence element shown in FIG. 1, when the first underlayer 102 is not provided, the light that has undergone total reflection at the interface between the substrate 101 and the air returns to the second underlayer 103 to be scattered again, and changes the traveling direction from the light source. The figure which showed the case where it will be taken out outside in the distant position.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100, 400, 500 ... Organic electroluminescent element 101 ... Substrate 102 ... 1st foundation layer 103 ... 2nd foundation layer 104 ... 3rd foundation layer 105, 107 ... Electrode 106 ... Organic light emitting layer 401 ... Smoothing layer 501 ... Gas barrier layer

Claims (14)

  An organic electroluminescent device comprising at least one organic light emitting layer having a light emitting region on a substrate, an anode for injecting holes into the organic light emitting layer, and a cathode for injecting electrons. Includes a first ground layer, a second ground layer, and a third ground layer in this order from the substrate side, and the first ground layer, the second ground layer, and the third bottom layer at the wavelength of light emitted by the organic light emitting layer. Assuming that the refractive indexes of the base layer are n1, n2, and n3, respectively, n1 <n2 and n2 <n3, and the second base layer and the third base layer have wavelengths of light emitted by the organic light emitting layer. In the organic electroluminescence device, fine particles having a refractive index different from the refractive index of each underlying layer are dispersed.   The organic electro according to claim 1, wherein a refractive index of the first underlayer at a wavelength of light emitted from the organic light emitting layer is smaller than a refractive index of the substrate and is 1.4 or less. Luminescence element.   The organic electroluminescent device according to claim 2, wherein a refractive index of the first underlayer at a wavelength of light emitted from the organic light emitting layer is 1.3 or less.   The organic electroluminescence element according to claim 1, wherein the first underlayer includes porous silica.   The organic electroluminescence element according to claim 1, wherein the second underlayer includes a resin.   6. The organic electroluminescence device according to claim 1, wherein a refractive index of the third underlayer at a wavelength of light emitted from the organic light emitting layer is 1.7 or more.   The organic electroluminescence device according to claim 6, wherein a refractive index of the third underlayer at a wavelength of light emitted from the organic light emitting layer is 1.8 or more.   8. A smoothing layer is further provided on the third underlayer, and the refractive index of the smoothing layer at a wavelength of light emitted from the organic light emitting layer is 1.7 or more. Organic electroluminescent element of any one of these.   9. The organic electroluminescence device according to claim 8, wherein a refractive index of the smoothing layer at a wavelength of light emitted from the organic light emitting layer is 1.8 or more.   10. The gas barrier layer according to claim 8, further comprising a gas barrier layer on the smoothing layer, wherein a refractive index of the gas barrier layer at a wavelength of light emitted from the organic light emitting layer is 1.7 or more. Organic electroluminescence device.   The organic electroluminescence device according to claim 10, wherein a refractive index of the gas barrier layer at a wavelength of light emitted from the organic light emitting layer is 1.8 or more.   The organic electroluminescence device according to any one of claims 1 to 11, wherein the fine particles are made of a metal, a metal compound, a silicon compound, a resin, or a mixture thereof.   The organic electroluminescence device according to claim 12, wherein the metal compound is an oxide or nitride of titanium, zirconium, aluminum, and cerium.   The display apparatus provided with the organic electroluminescent element of any one of Claims 1 thru | or 13.

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