JP2015095284A - Organic el element, and image display device and lighting system including the organic el element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an organic EL element improved in light extraction efficiency by effectively extracting waveguide mode light and SPP mode light and achieving light emission with high diffusion properties; and an image display device and a lighting system including the organic EL element.SOLUTION: An organic EL element includes a scattering layer, a first electrode, an organic layer including a light emitting layer, a second electrode, a low refractive index layer and a metal layer, in the order. The second electrode comprises a translucent conductive material. The low refractive index layer has a lower refractive index than the organic layer. The scattering layer comprises a medium and a scattering part existing in the medium and having a refractive index different from that of the medium, while the refractive index nof the medium and the refractive index nof the scattering part satisfy n-n>0.5 or n-n>0.25.

Description

 The present invention relates to an organic EL element, and an image display device and an illumination device including the organic EL element.

Organic EL elements have features such as a wide viewing angle, high-speed response, clear self-luminous display, etc., and they are thin, lightweight, and have low power consumption. It is expected as a pillar of
Organic EL elements are classified into a bottom emission type in which light is extracted from the support substrate side and a top emission type in which light is extracted from the opposite side of the support substrate, depending on the direction in which the light generated in the organic light emitting layer is extracted. .

For example, in a bottom emission type organic EL device including a transparent electrode, an organic layer including a light emitting layer, and a metal electrode in this order on a transparent substrate, light incident on the transparent substrate out of the light emitted from the light emitting layer is The light passes through the transparent substrate and is taken out of the device. Of the light emitted from the light emitting layer, a small incident angle that is less than the critical angle at the interface between a transparent substrate (for example, glass (typical refractive index: 1.52)) and air (refractive index: 1.0). Light incident at (the angle formed by the incident light and the normal of the incident interface) is refracted at the interface and extracted outside the device. In this specification, these lights are called external mode lights.
On the other hand, of the light emitted from the light emitting layer, the light incident on the interface between the transparent substrate and air at an incident angle larger than the critical angle is totally reflected at the interface and is not taken out of the device, and finally Can be absorbed by the material. In this specification, this light is referred to as substrate mode light, and the loss due to this is referred to as substrate loss.
Further, of the light emitted from the light emitting layer, a critical angle is formed at the interface between the transparent electrode made of a transparent conductive oxide (for example, indium tin oxide (ITO (typical refractive index: 1.8)) and the transparent substrate. Light incident at a large incident angle is also totally reflected at the interface and is not taken out of the device, but can be finally absorbed by the material.In this specification, this light is referred to as waveguide mode light, This loss is called waveguide loss.
In addition, the light emitted from the light emitting layer is incident on the metal electrode and combined with the free electrons of the metal electrode, and the light captured on the surface of the metal electrode as surface plasmon polariton (SPP) is also outside the device. And can be finally absorbed into the material. In this specification, this light is referred to as SPP mode light, and the loss due to this is referred to as plasmon loss.

The light extraction efficiency of the organic EL element (ratio of the light extracted outside the element with respect to the light emitted from the light emitting layer) is generally limited to about 20% (for example, Patent Document 1). That is, about 80% of the light emitted from the light emitting layer is lost, and it is a big problem to reduce these losses and improve the light extraction efficiency.
Here, the extraction of the substrate mode light can be dealt with by providing a light diffusion sheet or the like on the transparent substrate (for example, Patent Document 2), but the reduction and extraction of the waveguide mode light and the SPP mode light, particularly the SPP mode light. It can be said that research has just begun on the reduction and removal of odors.

Since guided mode light is generated when total reflection occurs when light enters a low refractive index material from a high refractive index material, total reflection is less likely to occur in order to reduce guided mode light. There are known measures for reducing guided mode light by reducing the proportion of light that causes reflection.
Patent Document 3 discloses a configuration in which a high refractive index layer having a higher refractive index than that of an organic light emitting layer or a transparent electrode is inserted in the vicinity of the organic light emitting layer. Patent Document 2 discloses a configuration in which the refractive index of the organic light emitting layer and the transparent electrode is equivalently lowered by dispersing fine particles having a lower refractive index than the organic light emitting layer and the transparent electrode in the organic light emitting layer and the transparent electrode. It is disclosed.

Patent Documents 4 and 5 disclose a configuration in which a cavity is provided in a transparent electrode layer and a dielectric layer that are sequentially formed on a substrate.
Light incident on the side surface of the cavity (interface extending perpendicular to the substrate) is refracted toward the substrate at this interface. The light refracted to the substrate side can reduce the proportion of light that causes total reflection at the interface between the transparent electrode and the substrate and between the substrate and the air.

  On the other hand, as a method for extracting SPP mode light captured on the surface of the metal electrode, a configuration in which a periodic uneven structure is formed on the surface of the metal electrode is known (Patent Documents 6 to 9).

JP 2008-210717A JP 2011-243625 A JP 2011-233288 A Japanese translation of PCT publication No. 2003-522371 JP 2011-82192 A JP 2006-313667 A JP 2009-158478 A Special Table 2005-535121 Japanese Patent Laid-Open No. 2004-31350

A. Otto, Z. Physik 216, 398 (1968)

  However, even if the SPP mode light is extracted from the metal surface, if the light is captured as guided mode light, it is not extracted outside the device, and the light extraction efficiency is not improved.

  Furthermore, since the SPP mode light is extracted at a predetermined angle, even if the SPP mode light is extracted, the luminance only in a certain direction becomes high, and it is difficult to realize light emission with high diffusibility.

  The present invention has been made in view of the above circumstances, and an organic EL element that effectively extracts SPP mode light and waveguide mode light, improves light extraction efficiency, and realizes light emission with high diffusibility, and the organic EL element. It is an object of the present invention to provide an image display device and an illumination device provided.

The present inventors first assume a two-step light extraction mechanism in which SPP mode light is extracted as propagating light into an organic layer, and then the propagating light is extracted out of the device without being guided mode light. Thus, an effective structure for improving the light extraction efficiency has been intensively studied from a number of structures.
Since it is difficult to directly measure the light extraction efficiency, the investigation was mainly based on simulation.

  The organic EL device of the present invention has a structure in which an organic layer including a light emitting layer is sandwiched between a first electrode and a second electrode. Here, the above-described two-step light extraction mechanism generates the SPP mode light and the second electrode side structure of the Otto type arrangement (Non-Patent Document 1) that extracts the generated SPP mode light as the propagation light, and its propagation. It consists of the first electrode side structure that takes out light without using guided mode light and realizes light emission with high diffusibility.

  By simulation, the present inventors have made a second electrode side structure with an Otto-type arrangement and a first electrode side having a scattering layer that scatters guided mode light to the substrate side (opposite side of the substrate in the top emission type). It was found that by combining the structure with the second electrode-side structure and the first electrode-side structure, a remarkable effect that could not be predicted from the effect of improving the light extraction efficiency of each of the second electrode-side structure and the first electrode-side structure was found.

ここで、ｋ_０は前記発光層で発光する光の最大ピーク波長における真空中の光の波数である。
（５）前記散乱部のサイズが発光光の前記媒質中における実効波長の半分以上であることを特徴とする（１）〜（４）のいずれか一項に記載の有機ＥＬ素子。
（６）上記散乱部１個当たりの散乱断面積の平均値と、単位発光面積あたりの上記散乱部の個数の積が０．０５〜２であることを特徴とする（１）〜（５）のいずれか一項に記載の有機ＥＬ素子。
（７）前記低屈折率層の厚さが２０ｎｍ〜３００ｎｍであることを特徴とする（１）〜（６）のいずれか一項に記載の有機ＥＬ素子。
（８）前記低屈折率層の屈折率はさらに、前記第２電極の屈折率よりも低いことを特徴とする（１）〜（７）のいずれか一項に記載の有機ＥＬ素子。
（９）前記第２電極の屈折率はさらに、前記有機層の屈折率よりも低いことを特徴とする（８）に記載の有機ＥＬ素子。
（１０）前記低屈折率層は、前記第２電極及び前記有機層のうちの少なくとも一方よりも屈折率が０．２以上小さい材料からなることを特徴とする（１）〜（９）のいずれか一項に記載の有機ＥＬ素子。
（１１）（１）〜（１０）のいずれか一項に記載の有機ＥＬ素子を備えたことを特徴とする画像表示装置。
（１２）（１）〜（１０）のいずれか一項に記載の有機ＥＬ素子を備えたことを特徴とする照明装置。 In order to solve the above-mentioned problems, the present invention having the outline adopts the following configuration.
(1) An organic EL element comprising a scattering layer, a first electrode, an organic layer including a light emitting layer, a second electrode, a low refractive index layer and a metal layer in this order, wherein the second electrode is a light-transmitting conductive material. The low refractive index layer is made of a material, and the refractive index of the low refractive index layer is lower than the refractive index of the organic layer.The scattering layer is composed of a medium and a scattering portion that exists in the medium and has a different refractive index. the organic EL element in which the refractive index _{n p} of the scattering portion and the refractive index _{n m,} characterized in that satisfy n _p -n m> 0.5 or _n m _-n p> 0.25.
(2) The organic EL element according to (1), wherein an absolute value of an average refractive index of the scattering layer and a refractive index difference of the organic layer is 0.2 or less.
(3) The organic EL device according to (1) or (2), wherein an intermediate layer is provided between the scattering layer and the first electrode.
(4) the intermediate layer has a layer portion in the portion in contact with the first electrode, the refractive index n _o of the organic layer and the refractive index n _m1 of the layer portion satisfies the n _m1 ≧ n _o, or, the refractive index n _m1, the refractive index n _o and an organic EL element according to any one of the thickness t of the layered portion is characterized by satisfying the following equation (1) to (3).

Here, k ₀ is the wave number of light in vacuum at the maximum peak wavelength of light emitted from the light emitting layer.
(5) The organic EL element according to any one of (1) to (4), wherein the size of the scattering portion is at least half the effective wavelength of the emitted light in the medium.
(6) The product of the average value of the scattering cross section per scattering portion and the number of scattering portions per unit light emitting area is 0.05 to 2, (1) to (5) Organic electroluminescent element as described in any one of these.
(7) The organic EL element according to any one of (1) to (6), wherein the low refractive index layer has a thickness of 20 nm to 300 nm.
(8) The organic EL element according to any one of (1) to (7), wherein a refractive index of the low refractive index layer is further lower than a refractive index of the second electrode.
(9) The organic EL element according to (8), wherein the refractive index of the second electrode is further lower than the refractive index of the organic layer.
(10) The low refractive index layer is made of a material having a refractive index smaller by 0.2 or more than at least one of the second electrode and the organic layer. Any one of (1) to (9) An organic EL device according to claim 1.
(11) An image display device comprising the organic EL element according to any one of (1) to (10).
(12) An illumination device comprising the organic EL element according to any one of (1) to (10).

  According to the present invention, an organic EL element that effectively extracts SPP mode light and waveguide mode light to improve light extraction efficiency and emits light with high diffusibility, and an image display device and an illumination device including the organic EL element are provided. Can be provided.

It is a cross-sectional schematic diagram for demonstrating an example of the organic EL element which concerns on embodiment of this invention. It is the figure which showed the shape of the scattering layer typically, (a) is what the particle-like scattering part disperse | distributed in the medium, (b) shows the random-shaped scattering part in the medium. (C) shows the case where random irregularities are formed at the interface between the medium and the scattering portion. In the organic EL element 10 which concerns on the 1st Embodiment of this invention, it is a cross-sectional schematic diagram in the case of having the intermediate | middle layer 8 between the scattering layer 7 and the anode 2. FIG. In the organic EL element 10 which concerns on the 1st Embodiment of this invention, propagation of light is shown by the arrow, and it is the schematic diagram shown typically in order to demonstrate the principle of the refractive effect of an organic EL element intelligibly. It is a cross-sectional schematic diagram for demonstrating an example of the image display apparatus provided with the organic EL element of this invention. It is a cross-sectional schematic diagram for demonstrating an example of the illuminating device provided with the organic EL element of this invention. In an organic EL element having a standard structure having an anode, an organic layer, and a cathode (metal) on a substrate, an energy dissipation calculation was performed to develop the intensity of light emitted from the organic layer with a wave number in the surface direction of the organic EL element. Results are shown. It is the figure which showed the dependence by the film thickness of a low-refractive-index layer of energy dissipation calculation in Otto type | mold arrangement | positioning, the refractive index of a low-refractive-index layer shall be 1.38, (a) makes a reflective layer Al, ( b) is a diagram showing the results when Ag is used as the reflective layer. It is a cross-sectional schematic diagram of the organic EL element of Otto type | mold arrangement | positioning for demonstrating the change of the peak in FIG. (A) is a case where the film thickness of a low refractive index layer is 0 nm. (B) is a case where SPP mode light and waveguide mode light coexist as the film thickness of the low refractive index layer increases. (C) is a case where the film thickness of the low refractive index layer is sufficiently thick so that the evanescent wave does not reach the metal layer and is not captured as SPP mode light. In the result of energy dissipation calculation in FIG. 8, it is the figure which showed the change of the peak width (half value width) with respect to the film thickness of a low refractive index layer. In the Otto-type organic EL element, (a) is a graph of Expression (8) when the reflective layer is Al and (b) is Ag as the reflective layer. It is sectional drawing which shows the model structure of the organic EL element of embodiment of this invention used by simulation. The results of calculating the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method when the thickness of the scattering layer 7 and the refractive index of the scattering portion 7p and the medium 7m of the scattering layer 7 are changed are shown. FIG. In Example 2, the graph which listed the relationship between the examined scattering part 7p and the medium 7m is shown. (A) shows the result of calculating the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method when the refractive index of the medium 7m is fixed at 1.45 and the refractive index of the scattering portion 7p is changed. (B) shows the figure which showed the change of the light extraction efficiency for every wavelength of emitted light by making the refractive index of the scattering part 7p into a horizontal axis. (A) shows the result of calculating the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method when the refractive index of the scattering portion 7p is fixed at 2.30 and the refractive index of the medium 7m is changed. (B) shows the figure which showed the change of the light extraction efficiency for every wavelength of emitted light by making the refractive index of the medium 7m into a horizontal axis. (A) shows the result of calculating the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method when the refractive index of the medium 7m is fixed at 1.90 and the refractive index of the scattering portion 7p is changed. (B) shows the figure which showed the change of the light extraction efficiency for every wavelength of emitted light by making the refractive index of the scattering part 7p into a horizontal axis. (A) shows the result of calculating the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method when the refractive index of the scattering portion 7p is fixed at 1.45 and the refractive index of the medium 7m is changed. (B) shows the figure which showed the change of the light extraction efficiency for every wavelength of emitted light by making the refractive index of the medium 7m into a horizontal axis. It is a figure which shows the result of having calculated | required the light extraction efficiency of the organic EL element 10 by the computer simulation using the FDTD method at the time of changing the number of the scattering parts 7p of the scattering layer 7. FIG. It is a figure which shows the result of having calculated | required the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method at the time of fixing the number of the scattering parts 7p of the scattering layer 7, and changing the size. It is a figure which shows the result of having calculated | required the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method at the time of fixing the space filling rate of the scattering part 7p of the scattering layer 7, and changing the size. It is a figure which shows the result of having calculated | required the light extraction efficiency of the organic EL element 10 by the computer simulation using the FDTD method when it has the intermediate | middle layer 8 and the film thickness of the intermediate | middle layer 8 was changed.

Hereinafter, the structure of an organic EL element to which the present invention is applied, an image display apparatus and an illumination apparatus including the organic EL element will be described with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. . In addition, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately changed and implemented without changing the gist thereof.
In the present invention, one of the first electrode and the second electrode is an anode and the other is a cathode. In the following description, a configuration in which the first electrode is an anode and the second electrode is a cathode will be described as an example.
Moreover, the organic EL element of this invention may be provided with the layer which is not described below in the range which does not impair the effect of this invention. Furthermore, the so-called top emission type or bottom emission type may be applied to the organic EL element of the present invention. Hereinafter, a bottom emission type configuration will be described as an example.

(Organic EL device (first embodiment))
FIG. 1 is a schematic cross-sectional view for explaining an example of the organic EL element according to the first embodiment of the present invention.
The organic EL element 10 according to the first embodiment of the present invention includes a scattering layer 7, an anode (first electrode) 2, an organic layer 3 including a light emitting layer, a cathode (second) on one surface of a substrate 1. Electrode) 4, an organic EL element having a low refractive index layer 5 and a metal layer 6 in this order (downward in the figure), wherein the cathode 4 is a transparent conductive layer made of a translucent conductive material. The refractive index of the low refractive index layer 5 is lower than the refractive index of the organic layer 3. Here, the scattering layer 7 includes a medium 7m and a scattering portion 7p. The refractive index _{n p} of the refractive index _{n m} and scattering portion 7p of the medium 7m _meets a relation of n _p -n m> 0.5 or _n m _-n p <0.25.
The refractive index of the low refractive index layer 5 is preferably lower than the refractive index of the cathode 4.
The refractive index of the cathode 4 is preferably lower than the refractive index of the organic layer 3.
When comparing the refractive index of the structure on the cathode side, the refractive index of the organic layer means the average refractive index of all the layers including the light emitting layer made of the organic EL material.
In addition, the structure shown with a continuous line in FIG. 1 is a bottom emission type. In FIG. 1, reference numeral 1a indicated by a broken line indicates the arrangement of the substrate 1a in the case of the top emission type in order to easily explain the configuration of the present invention. In this case, the substrate 1 does not need to be provided, and the substance in which the scattering layer 7 is adjacent to the surface opposite to the anode 2 may be air, for example. The substrate arrangement in the case of the top emission type is the same in the other embodiments.

  In the laminated structure of the metal layer / low refractive index layer / organic layer, which is a structure on the cathode side common to the organic EL element of the present invention, in order for these to be Otto type arrangement, the refractive index of the low refractive index layer is organic. It must be lower than the refractive index of the layer. With such a refractive index configuration, SPP mode light generated at the metal layer / low refractive index interface can be extracted into the organic layer. More preferably, the refractive index of the cathode is higher than the refractive index of the low refractive index layer. When the refractive index of the cathode is higher than the refractive index of the low refractive index layer, the structure of the metal layer / low refractive index layer / cathode is also an Otto type arrangement. Can be led into a layer or scattering layer. Furthermore, the refractive index of the cathode is preferably lower than the refractive index of the organic layer. SPP mode light can be extracted into the organic layer more efficiently by evanescent waves due to total reflection at the cathode / organic layer interface.

The organic EL element 10 according to the present invention includes a bottom emission type (when the substrate 1 is on the opposite side of the organic layer 3 when viewed from the anode 2) and a top emission type (when viewed from the metal layer 6 on the side opposite to the low refractive index layer 5). It can be applied to any of the organic EL elements in the case where the substrate 1a is present.
When applied to the bottom emission type, the substrate 1 is a light-transmitting substrate and usually needs to be transparent to visible light. Here, “transparent to visible light” means that it is only necessary to transmit visible light having a wavelength emitted from the light emitting layer, and it is not necessary to be transparent over the entire visible light region. A smooth substrate having a transmittance in visible light of 400 to 700 nm of 50% or more is preferable. Further, the transmittance is more preferably 70% or more.
Specific examples of the material constituting the substrate 1 include glass and polymer. Examples of the glass include soda lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz. Examples of the polymer include polycarbonate, polymethyl methacrylate (PMMA), polyethylene terephthalate, polyethylene naphthalate, polyether sulfide, and polysulfone.
Even when the emitted light is not visible light, it is necessary to be transparent at least in the emission wavelength region as in the case of visible light. The transmittance is preferably 50% or more and more preferably 70% or more with respect to the wavelength at which light emission has the maximum intensity.
In order to apply to the top emission type, an opaque material can be used in addition to the same as described above. Specifically, for example, Cu, Ag, Au, Pt, W, Ti, Ta, Nb, Al alone, an alloy containing these elements, or a metal material such as stainless steel, Si, SiC, AlN, GaN, Nonmetallic materials such as GaAs and sapphire, and other substrate materials usually used in top emission type organic EL elements can be used. In addition, in order to release heat generated due to light emission of the element, it is preferable to use a material having high thermal conductivity for the substrate.

  The thickness of the substrate 1 is not particularly limited depending on the required mechanical strength, but is preferably 0.01 mm to 10 mm, more preferably 0.05 mm to 2 mm.

The anode 2 is an electrode for applying a voltage between the anode 4 and injecting holes into the organic layer 3 from the anode 2, and is made of a metal, an alloy, a conductive compound, or a mixture thereof having a high work function. It is preferable to use a material, and it is preferable to use a material having a work function of 4 eV or more and 6 eV or less so that the difference from the HOMO (Highest Occupied Molecular Orbital) level of the organic layer 3 in contact with the anode 2 does not become excessive. The material of the anode 2 is not particularly limited as long as it is a translucent and conductive material. For example, transparent inorganic oxidation such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide, and zinc oxide is possible. , PEDOT: PSS, conductive polymer such as polyaniline and conductive polymer doped with any acceptor, conductive light transmissive material such as carbon nanotube, thin film metal, metal nanowire formed in thin film, these Can be mentioned. Here, the anode 2 can be formed on the substrate 1 by, for example, a sputtering method, a vacuum deposition method, a coating method, or the like.
Although the thickness of the anode 2 is not specifically limited, For example, it is 10-2000 nm, Preferably it is 50-1000 nm. When the thickness is less than 10 nm, the sheet resistance of the anode 2 increases. When the thickness is more than 2000 nm, the flatness of the organic layer 3 cannot be maintained, and the transmittance of the anode decreases.

The organic layer 3 may include a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, and the like in addition to a light emitting layer made of an organic EL material. As a material of the light emitting layer, any material known as a material for an organic EL element can be used.
The hole injection layer is a layer that assists hole injection from the anode 2 to the organic layer 3, and its ionization energy is usually as low as 5.5 eV or less. Such a hole injection layer is preferably a material that injects holes into the organic layer 3 with a lower electric field strength. However, the material to be formed is not particularly limited as long as it can perform the above functions, and is well known. Any one can be selected and used. The hole transport layer is a layer that transports holes to the light emitting region and has a high hole mobility. The material to be formed as such a hole transport layer is not particularly limited as long as it can perform the above function, and any material can be selected and used from known materials.
The electron injection layer is a layer that assists electron injection from the cathode 4 to the organic layer 3. As such an electron injection layer, a material that injects electrons into the organic layer 3 with a lower electric field strength is preferable. However, the material to be formed is not particularly limited as long as it can perform the above-described function. Any one can be selected and used. The electron transport layer is a layer that transports electrons to the light emitting region and has a high electron mobility. The material for forming such an electron transport layer is not particularly limited as long as it can perform the above function, and any material can be selected and used from known materials.

The organic layer 3 may be formed by a dry process such as an evaporation method or a transfer method, or may be formed by a wet process such as a spin coating method, a spray coating method, a die coating method, or a gravure printing method.
Although the thickness of the organic layer 3 is not specifically limited, For example, it is 50-2000 nm, Preferably it is 100-1000 nm. If it is thinner than 50 nm, extinction other than SPP coupling occurs, such as a decrease in internal quantum efficiency due to punch-through current and lossy surface wave mode coupling due to metal layer 6, and if it is thicker than 2000 nm, it is driven The voltage rises.

The cathode 4 is an electrode for injecting electrons into the light emitting layer, and it is preferable to use a material made of a metal, an alloy, a conductive compound, or a mixture thereof having a small work function. It is preferable to use a work function of 1.9 eV or more and 5 eV or less so that the difference from the LUMO (Lowest Unoccupied Molecular Orbital) level does not become excessive.
As a material of the cathode 4, it is necessary to use a light-transmitting conductive material in order to form a cathode side structure having an Otto type arrangement. Therefore, the same anode material as described above can be used.
Although the thickness of the cathode 4 is not specifically limited, For example, it is 30 nm-1 micrometer, Preferably it is 50-500 nm. When the thickness is less than 30 nm, the sheet resistance increases and the driving voltage increases. When the thickness is greater than 1 μm, damage due to heat and radiation during film formation and mechanical damage due to film stress accumulate in the electrode and the organic layer. .

The low refractive index layer 5 is provided on the surface of the cathode 4 opposite to the organic layer 3 and is made of a material having a refractive index lower than that of the organic layer 3. The low refractive index layer 5 is preferably made of a material having a refractive index lower than that of the translucent conductive material constituting the cathode 4.
When the light emitted from the light emitting layer propagates to the cathode 4 side and reaches the interface between the cathode 4 and the low refractive index layer 5, total reflection occurs when the light is incident at an angle greater than the critical angle.

The material of the low refractive index layer 5 is not particularly limited as long as it is a material having a refractive index lower than that of the organic layer 3. For example, when the average refractive index of all the layers of the organic layer 3 is 1.72. SOG satisfying this refractive index, metal fluoride such as magnesium fluoride (MgF ₂ (typical refractive index 1.38)), polytetrafluoroethylene (PTFE (typical refractive index 1.35)), etc. Organic fluorine compounds, silicon dioxide (SiO ₂ (typical refractive index 1.45)), various low-melting-point glasses, and porous materials. Further, the low refractive index layer 5 is composed of a layer including an air layer, and may have a refractive index lower than that of the translucent conductive material constituting the cathode 4.

  The low refractive index layer 5 is preferably made of a material having a refractive index smaller by 0.2 or more than at least one of the cathode 4 and the organic layer 3. This corresponds to a high refractive index medium in which the cathode 4 and the organic layer 3 are in an Otto type arrangement, and if the refractive index difference between the low refractive index medium and the high refractive index medium is 0.2 or more in the Otto type arrangement, the SPP mode light Because the in-plane component of the wave number of becomes small, the dispersion curve of the propagation light in the high refractive index medium and the SPP mode light intersect, and the SPP mode light is extracted to the cathode 4 or the organic layer 3 more efficiently. It is.

  The thickness of the low refractive index layer 5 is preferably 20 nm to 300 nm. If the thickness is less than 20 nm, the film thickness of the low refractive index layer 5 is too thin, so that the metal layer 6 and the organic layer 3 come close to increase the wave number of the SPP mode light, and the dispersion curve intersects with the dispersion curve of the propagation light. As a result, the SPP mode light is hardly extracted into the organic layer. If it is thicker than 300 nm, the film thickness of the low refractive index layer 5 is too thick, so that the SPP mode electromagnetic field does not reach the metal layer 6 and SPP mode light is not easily extracted into the organic layer. Furthermore, the thickness of the low refractive index layer 5 is more preferably 200 nm or less.

The metal layer 6 is provided on the opposite side of the cathode 4 from the organic layer 3 via a low refractive index layer 5.
As the material for the metal film 6, any material or alloy of any metal can be used as long as it reflects the light emitted from the light emitting layer to the anode 2 side. A material whose real part has a negative value with a large absolute value is preferable. Examples of such materials include simple substances such as Au, Ag, Cu, Zn, Al, Mg, alkali metals and alkaline earth metals, alloys of Au and Ag, alloys of Ag and Cu, and alloys such as brass. It is done. Further, the metal layer 6 may have a laminated structure of two or more layers.
Although the thickness of the metal layer 6 is not specifically limited, For example, it is 20-2000 nm, Preferably it is 50-500 nm. If it is thinner than 20 nm, the reflectance is lowered and the front luminance is lowered. If it is thicker than 2000 nm, damage due to heat and radiation during film formation and mechanical damage due to film stress accumulate in the electrode and the organic layer.

  The scattering layer 7 is not particularly limited as long as it includes the medium 7m and the scattering portion 7p, and has random interfaces having different refractive indexes. For example, the scattering layer 7 may be configured as shown in FIG. FIG. 2A shows a case where the particle-like scattering portion 7p is dispersed in the medium 7m. For example, a case where particles such as silica are dispersed in the resin can be mentioned. FIG. 2B shows a case where a randomly shaped scattering portion 7p is formed in a medium 7m. For example, a material that becomes polycrystalline at the time of curing is used and its crystal grain boundary is used. . FIG. 2C shows a case where random irregularities are formed at the interface between the medium 7m and the scattering part 7p. For example, an irregularity is formed using a self-assembled film, or the medium 7m and the scattering part are etched. The thing which roughened the interface of 7p etc. are mentioned.

The refractive index _{n p} of the refractive index _{n m} and scattering portion 7p of the medium 7m _meets a n _p -n m> 0.5 or _n m _-n p> 0.25 relations. If the refractive index difference between the medium 7m and the scattering portion 7p is small, the light cannot be sufficiently scattered at the interface between the medium 7m and the scattering portion 7p, and the SPP mode light and emitted light re-radiated into the organic layer are not emitted. The light is totally reflected on the substrate 1 and the outer surface, and light cannot be extracted efficiently. When the refractive index of the scattering portion 7p is larger than the refractive index of the medium 7m, the refractive index difference needs to be larger than 0.5, and when the refractive index of the scattering portion 7p is smaller than the refractive index of the medium 7m, The difference in refractive index needs to be larger than 0.25. When the refractive index of the scattering portion 7p is smaller than the refractive index of the medium 7m, the light can be efficiently extracted with a small refractive index difference, as will be described later, the occupation ratio of the scattering layer 7 becomes moderately high. This is because the light in the organic layer can be scattered while being guided into the scattering layer 7, so that the propagation direction of the light refracted or reflected at the interface between the medium 7m and the scattering portion 7p can be changed efficiently. On the other hand, when the refractive index of the scattering portion 7p is larger than the refractive index of the medium 7m, the light in the organic layer 3 becomes difficult to be guided to the scattering layer 7, so that a higher refractive index is required to improve the light extraction efficiency. A differential scattering layer is required.

The material of the medium 7m and the scattering portion 7p is not particularly limited as long as the difference in refractive index satisfies the above relationship. For example, the following known materials can be appropriately combined.
Silicon oxide such as SOG (typical refractive index: 1.1 to 2.0), silica (SiO ₂ ), magnesium oxide (MgO) (typical refractive index: 1.74), zinc oxide ( ZnO) (typical refractive index: 2.02) and other oxides, magnesium fluoride (MgF ₂ ) (typical refractive index: 1.38) and other metal halides, aluminum nitride (AlN ) And other nitrides, oxynitrides such as aluminum oxynitride (AlON) and silicon oxynitride, and polytetrafluoroethylene (PTFE (typical refractive index: 1.35)). Fluorine resin, polymethyl methacrylate (PMMA (typical refractive index: 1.49)), polyethylene naphthalate (PEN (typical refractive index: 1.77)), melamine resin, etc. It can be used by selecting from a high molecular compound resin. In addition, a porous material, a mixture thereof, or a material in which fine particles of an inorganic material are dispersed in a transparent medium can be used.

  In addition, the absolute value of the difference between the average refractive index of the scattering layer 7 and the refractive index of the organic layer 3 is preferably 0.2 or less. Here, the average refractive index of the scattering layer 7 is a value obtained by dividing the wave number of light propagating straight in the scattering layer 7 without being scattered by the wave number in vacuum. The average refractive index varies depending on the refractive index of the scattering portion 7p and the medium 7m and the respective volume fractions, as well as the distribution shape of the scattering portion 7p in the scattering layer 7, but the scattering portion 7p in the scattering layer 7 is spatial. In this case, as the average refractive index, the relative dielectric constant of the medium 7m and the scattering portion 7p is weighted and averaged by the volume fraction, and the square root of the average value can be used. When the average refractive index of the scattering layer 7 is smaller than the refractive index of the organic layer 3 and the difference is larger than 0.2, the light propagating in the organic layer is organic layer 3 / anode 2 or anode 2 / scattering layer 7. It becomes easy to totally reflect at the interface, and light cannot be efficiently guided into the scattering layer 7. On the other hand, when the average refractive index of the scattering layer 7 is larger than the refractive index of the organic layer 3 and the difference is larger than 0.2, the light propagating in the scattering layer 7 is less likely to be totally reflected at the interface. Total reflection is likely to occur at the scattering layer 7 / substrate 1 interface, and light is easily trapped in the scattering layer 7. The light confined in the scattering layer 7 is scattered by the scattering portion 7m, and can be extracted if the scattered light enters the interface of the scattering layer 7 / substrate 1 at a critical angle or less. That is, even after total reflection at the interface between the scattering layer 7 and the substrate 1, it can be taken out of the substrate sometime by repeating scattering. However, since light is attenuated each time scattering is repeated, light cannot be extracted efficiently.

  Also, as shown in FIG. 3, it is preferable to have an intermediate layer 8 between the scattering layer 7 and the anode 2 for the purpose of flattening the surface of the anode 2 on the scattering layer 7 side. Since the scattering layer 7 includes the medium 7m and the scattering portion 7p, it is difficult to make the interface between the scattering layer 7 and the anode 2 flat. If the interface between the scattering layer 7 and the anode 2 is not flat, the organic layer 3, the cathode 4, the low refractive index layer 5, and the metal layer 6 formed thereon are not flat. Therefore, it is difficult to produce the organic EL element uniformly over the entire surface, and it is impossible to obtain light emission with high diffusibility. Further, when external stress is applied, it is possible to suppress the scattering portion 7p from damaging the element portion (the anode 2 to the cathode 4). For this purpose, the intermediate layer is formed so as to have a layered portion at a portion in contact with the anode 2 (first electrode).

The refractive index of the intermediate layer 8 is more preferably equal to or higher than the refractive index of the medium 7m in the scattering layer 7. If the refractive index of the intermediate layer 8 is equal to or higher than the refractive index of the medium 7m of the scattering layer 7, unnecessary reflection at the interface can be suppressed.
The intermediate layer 8 may be formed integrally with the medium 7m. When the intermediate layer 8 is formed integrally with the medium 7m, the film thickness of the intermediate layer 8 is the flat region sandwiched between the anode 2 and the portion of the scattering portion 7p that is closest to the anode 2 side. It means the maximum film thickness.

ただし、ｋ_０は前記有機層で発光する光のピーク波長における真空中の光の波数である。中間層８の屈折率ｎ_ｍ１が有機層３の屈折率ｎ_ｏより小さいと、有機層３側から臨界角以上の角度で中間層８に入射した光Ａ１は全反射（矢印Ａ１ｒ）する。本来、この全反射による光を素子外部に取り出すことはできないが、式（１）を満たす場合には、全反射により発生したエバネッセント波（矢印Ａ２）が、散乱部７ｐに届き、散乱によって取り出される（矢印Ａ３）。 Also, if the refractive index n _m1 of the intermediate layer 8 is the refractive index n _o or more organic layers 3, otherwise, the thickness t of the intermediate layer 8 preferably satisfies the formula (1).

Here, k ₀ is the wave number of light in vacuum at the peak wavelength of light emitted from the organic layer. Refractive index and n _o is smaller than the refractive index n _m1 is an organic layer 3 of the intermediate layer 8, light A1 which is incident on the intermediate layer 8 at an angle greater than the critical angle from the organic layer 3 side is totally reflected (arrow A1r). Originally, the light due to total reflection cannot be extracted outside the element. However, when the expression (1) is satisfied, the evanescent wave (arrow A2) generated by total reflection reaches the scattering portion 7p and is extracted by scattering. (Arrow A3).

Equation (1) can be derived as follows. If the propagation angle of light in the organic layer is close to 90 degrees, the wave number k _z in a direction perpendicular to the element plane of the evanescent wave leaking into the intermediate layer 8 can be represented by the following formula (2).

となる。 The evanescent wave is generated at the interface between the anode 2 and the intermediate layer 8 where the evanescent wave is generated, and the intensity propagates through the intermediate layer 8 while being attenuated exponentially. That is, the amplitude of the evanescent wave at the position where the distance from the generation point is t is approximately

It becomes.

When the amplitude at the anode 2 / intermediate layer 8 interface is normalized to 1, a sufficient amount of evanescent wave can be used when the amplitude of the evanescent wave at the position propagated in the thickness direction of the intermediate layer is 0.4 or less. Cannot be done (for details, see the section (Removal of SPP in Otto type arrangement) described later). In other words, if the film thickness of the intermediate layer is set to satisfy Equation (1), the evanescent wave reaches the scattering layer, and light can be extracted by scattering. This can also be confirmed from Example 4 described later.
In the case the intermediate layer 8 comprises both a higher layer and lower layer of refractive index than the refractive index n _o of the organic layer, the film thickness of the lower, respectively the refractive index and t and n _m1 layers formula (1) and It is desirable to satisfy the refractive index.

The size D of the scattering portion 7p is preferably at least half of the effective wavelength of the emitted light (maximum peak wavelength) in the medium 7m. Here, when the scattering portion 7p is in the form of particles as shown in FIG. 2A, D is the average diameter of the particles (the diameter of a sphere having the same volume as the particles), and is in a polycrystalline form as shown in FIG. In this case, D is the average diameter of crystal grains, and in the case of a layered shape having an uneven interface as shown in FIG. The reason why D is greater than or equal to the effective wavelength in the medium 7m (the value obtained by dividing the vacuum wavelength by the refractive index of the medium) is that the size of the scattering portion 7p is less than or equal to half the effective wavelength of the emitted light in the medium 7m. This is because light is hardly scattered. In general, the scattering phenomenon in the region below the wavelength of light is represented by Rayleigh scattering, and the scattering cross section is proportional to the sixth power of the size of the scattering portion 7p. That is, when the size of the scattering portion 7p is reduced, the scattering cross section is rapidly reduced and light is not easily scattered.
On the other hand, if the size of the scattering portion 7p is at least half the effective wavelength of the emitted light, light can be sufficiently scattered between the scattering portion 7p and the medium 7m. In a region where the size of the scattering portion 7p is more than half of the effective wavelength of the emitted light, the scattering cross section is proportional to the square of the size of the scattering portion 7p because it is close to the scattering of classical particles by geometric approximation. That is, the influence of the size of the scattering portion 7p is reduced.

  Furthermore, as will be described later, it is preferable that the occupation ratio, which is the product of the scattering cross section per scattering portion 7p and the number of scattering portions 7p per unit light emitting area of the element, is in the range of 0.05 to 2. . Here, the number of the scattering parts 7p is the total number of the scattering parts 7p whose size D is half or more of the effective wavelength in the medium 7m. When the occupation ratio is larger than 2, the light incident on the scattering layer 7 from the organic layer 3 side is strongly scattered by the scattering portion 7p, so that the light does not easily pass through the scattering layer 7 and the light extraction efficiency decreases.

これに対して、比誘電率ε_２の誘電体中を伝播する通常の伝播光の分散関係（角振動数ｗ、波数ベクトルｋ）は、次式（５）によって与えられる。

表面プラズモンポラリトン（ＳＰＰ）の分散曲線は通常の伝播光の分散直線と交差しない。そのため、通常の伝播光では平坦な金属表面にＳＰＰを励起することはできない。また、平坦な金属表面に存在するＳＰＰから直接伝播光を取り出すこともできない。 (Otto type arrangement)
The effect of the second electrode side structure by the Otto type arrangement of the organic EL element of the present invention will be described below. The following is a principle explanation based on the calculation formula, and therefore, the first electrode and the second electrode are not associated with either the anode or the cathode, respectively, and are described as the first electrode and the second electrode.
When the angular frequency of surface plasmon polariton (SPP) generated on a flat metal surface is ω, and the in-plane direction component of the wave number is k _sp , this dispersion relation (relation between angular frequency and wave number) is It is determined by the real part ε ₁ of the relative permittivity of the metal and the relative permittivity ε ₂ of the dielectric that contacts the metal surface, and is approximately given by the following equation (4) (c is the speed of light in vacuum) .

On the other hand, the dispersion relationship (angular frequency w, wave vector k) of normal propagating light propagating through a dielectric having a relative dielectric constant ε ₂ is given by the following equation (5).

The dispersion curve of surface plasmon polariton (SPP) does not intersect the normal dispersion light dispersion line. For this reason, normal propagating light cannot excite SPP on a flat metal surface. Further, it is not possible to directly extract propagating light from the SPP present on the flat metal surface.

従って、ε₃が十分大きければ、入射角δを変えることにより、ＳＰＰの分散曲線と全反射によるエバネッセント波（以降、単に「エバネッセント波」という場合も、全て全反射によって生じたものをさすものとする）の分散直線に交点を持たせることが可能となる。すなわち、エバネッセント波を用いれば、有機層３中の伝播光から平坦な金属層６の表面にＳＰＰを励起することができ、また、逆の過程として平坦な金属層６の表面に存在するＳＰＰからエバネッセント波を介して有機層３中へ伝播光として取り出すことが可能となる。ＳＰＰを取り出す場合は、式（６）中のδは、ＳＰＰの放射角度ということになる。
言い換えると、Otto型配置を用いると、ＳＰＰの分散曲線とエバネッセント波の分散直線とが交差するようになる。これは、所定の角度で有機層３中を伝播する光だけが、エバネッセント波と共鳴することによりＳＰＰとエネルギーをやり取りできる状態となることを意味する。そして、ＳＰＰを、エバネッセント波を介して所定の角度で放射される伝播光として取り出すことが可能となる。 On the other hand, the Otto type arrangement, that is, the structure of metal / low refractive index medium / high refractive medium, and in the organic EL device of the present invention, the metal layer 6 (real part ε ₁ of relative dielectric constant) Consider the case of using a laminated structure of / low refractive index layer 5 (relative permittivity ε ₂ ) / organic layer (relative permittivity ε ₃ ). When the refractive index of the organic layer 3 is higher than the refractive index of the low refractive index layer 5, the light incident from the organic layer 3 side to the low refractive index layer 5 side at an incident angle larger than the critical angle is incident on the organic layer 3 and the cathode 4. Total reflection occurs at the interface or the interface between the cathode 4 and the low refractive index layer 5. At this time, an evanescent wave that is non-propagating light is generated on the low refractive index layer 5 side of the interface, and the electromagnetic field intensity attenuates exponentially as the distance from the total reflection interface increases (incident light is totally reflected at the interface). The electromagnetic field oozes out of the interface). The dispersion curve of this evanescent wave is given by the following equation (6). Here, δ is an incident angle of incident light from the organic layer 3 to the medium on the low refractive index layer 5 side.

Therefore, if ε ₃ is sufficiently large, by changing the incident angle δ, the dispersion curve of the SPP and the evanescent wave due to total reflection (hereinafter also referred to simply as “evanescent wave” refers to all generated by total reflection). It is possible to give an intersection to the dispersion straight line. That is, if evanescent waves are used, SPP can be excited from the propagating light in the organic layer 3 to the surface of the flat metal layer 6, and as a reverse process, from the SPP existing on the surface of the flat metal layer 6. It becomes possible to extract the propagating light into the organic layer 3 through the evanescent wave. When taking out the SPP, δ in the equation (6) is the radiation angle of the SPP.
In other words, when the Otto type arrangement is used, the dispersion curve of the SPP and the dispersion line of the evanescent wave intersect each other. This means that only the light propagating through the organic layer 3 at a predetermined angle is in a state where energy can be exchanged with the SPP by resonating with the evanescent wave. And it becomes possible to take out SPP as propagation light radiated | emitted at a predetermined angle via an evanescent wave.

However, the excitation / extraction of the SPP mode light via the evanescent wave occurs when the low refractive index layer 5 is sufficiently thin. This is because if the low refractive index layer 5 is too thick, the evanescent wave oozes out from the organic layer 3 does not reach the metal layer 6, and the evanescent wave and the SPP mode light cannot exchange energy. If the rate layer 5 is too thin, the metal layer 6 and the organic layer 3 or the cathode 4 approach each other, the wave number of the SPP mode light becomes larger than the equation (4), and the dispersion curve becomes any of the dispersion curve (6) of the evanescent wave. This is because the angle δ also does not intersect.
As described above, the light extracted from the SPP is emitted at a predetermined angle corresponding to the intersection of the dispersion curve of the SPP and the dispersion line of the evanescent wave.

(Scattering by scattering layer)
Next, the effect of scattering by the scattering layer of the organic EL element of this embodiment will be described below. FIG. 4 is a schematic diagram schematically showing the propagation of light with an arrow, in order to easily understand the principle of the refraction effect of the organic EL element.
The organic EL element 10 of the present invention has a scattering layer 7 composed of a scattering portion 7p and a medium 7m.

As shown in FIG. 4, in the organic EL element 10 of the first embodiment of the present invention, a part of the light emitted at the point A of the light emitting point included in the organic layer 3 passes through the dipole field around the light emitting point. Direct energy transfer to (arrow A1), SPP (arrow A2) mode. Such energy transfer to the SPP mode is widely known to occur when a light emitting molecule and a metal layer are close to each other in a general organic EL element.
The excited SPP mode light is radiated to the cathode 4 at a predetermined angle (arrow A4) through resonance with the evanescent wave (arrow A3), and can be extracted to the organic layer 3 as propagating light.
Here, since the light emitted from the point A of the organic layer 3 travels in all directions, there is naturally light emitted as propagating light into the organic layer without transferring energy to the SPP, but the arrows A1 to A4 and the arrow B1 schematically shows typical light propagation having the effects of the present invention in order to explain the effects of the present invention.
Although refraction occurs at interfaces having different refractive indexes, refraction at interfaces that are not particularly necessary for explaining the effects of the present invention is not shown.

The light extracted from the cathode side structure (cathode 4, low refractive index layer 5, metal layer 6) to the point B of the organic layer 3 propagates as shown by arrow B1 and is extracted to the substrate 1.
That is, the light B <b> 1 traveling from the point B through the organic layer 3 or the like reaches the scattering layer 7 and is then scattered in various directions by the scattering layer 7. Here, after being scattered, the light incident on the interface between the medium 7 m and the substrate 1 at an angle larger than the critical angle is totally reflected and returned to the inside of the scattering layer 7. Since it is scattered again and the propagation angle changes, it can be taken out to the substrate 1 side. As described above, one propagation process of the SPP mode light extracted up to the point B is schematically shown, but is extracted from various positions on the surface of the metal layer 6. That is, as shown in FIG. 4, SPP mode light is extracted also at, for example, point C other than point B of the organic layer 3. In addition, since the SPP mode light propagates in an arbitrary direction on the surface of the metal layer 6, there is a path through which the SPP is extracted at point D of the organic layer 3 after traveling as indicated by arrows A ′ 1 to A ′ 4. sell. The light extracted up to these points C and D is scattered in various directions by the scattering layer 7 in the same manner as the arrow B1, and is extracted to the substrate 1 side.
Therefore, the organic EL element 10 can diffuse the SPP mode light in various directions, and can obtain light emission with high diffusibility.

(Image display device)
Next, an image display apparatus provided with the above organic EL element will be described. Since the image display apparatus provided with the organic EL elements 10 and 20 is not different depending on the organic EL element, the following description will be given on behalf of the organic EL element 10 as a representative.
FIG. 5 is a diagram illustrating an example of an image display device including the organic EL element.
The image display device 100 shown in FIG. 5 is a so-called passive matrix type image display device. In addition to the organic EL element 10, the anode wiring 104, the anode auxiliary wiring 106, the cathode wiring 108, the insulating film 110, and the cathode partition 112 are used. , A sealing plate 116 and a sealing material 118.

  In the present embodiment, a plurality of anode wirings 104 are formed on the substrate 1 of the organic EL element 10. The anode wirings 104 are arranged in parallel at a constant interval. The anode wiring 104 is made of a transparent conductive film, and for example, ITO can be used. The thickness of the anode wiring 104 can be set to 100 nm to 150 nm, for example. An anode auxiliary wiring 106 is formed on the end of each anode wiring 104. The anode auxiliary wiring 106 is electrically connected to the anode wiring 104. With this configuration, the anode auxiliary wiring 106 functions as a terminal for connecting to the external wiring on the end portion side of the substrate 1, and the drive circuit (not shown) provided outside via the anode auxiliary wiring 106. A current can be supplied to the anode wiring 104. The anode auxiliary wiring 106 is formed of, for example, a metal film having a thickness of 500 nm to 600 nm.

  A plurality of cathode wirings 108 are provided on the organic EL element 10. The plurality of cathode wirings 108 are arranged so as to be parallel to each other and orthogonal to the anode wiring 104. For the cathode wiring 108, Al or an Al alloy can be used. The thickness of the cathode wiring 108 is, for example, 100 nm to 150 nm. Further, similarly to the anode auxiliary wiring 106 for the anode wiring 104, a cathode auxiliary wiring (not shown) is provided at the end of the cathode wiring 108 and is electrically connected to the cathode wiring 108. Therefore, a current can flow between the cathode wiring 108 and the cathode auxiliary wiring.

  Further, an insulating film 110 is formed on the substrate 1 so as to cover the anode wiring 104. A rectangular opening 120 is provided in the insulating film 110 so as to expose a part of the anode wiring 104. The plurality of openings 120 are arranged in a matrix on the anode wiring 104. In the opening 120, the organic EL element 10 is provided between the anode wiring 104 and the cathode wiring 108. That is, each opening 120 becomes a pixel. Accordingly, a display area is formed corresponding to the opening 120. Here, the thickness of the insulating film 110 can be, for example, 200 nm to 1000 nm, and the size of the opening 120 can be, for example, 100 μm × 100 μm.

  The organic EL element 10 is located between the anode wiring 104 and the cathode wiring 108 in the opening 120. In this case, the anode 2 of the organic EL element 10 is in contact with the anode wiring 104 and the cathode 4 is in contact with the cathode wiring 108. The thickness of the organic EL element 10 can be set to 150 nm to 200 nm, for example.

  On the insulating film 110, a plurality of cathode partition walls 112 are formed along a direction perpendicular to the anode wiring 104. The cathode partition 112 plays a role for spatially separating the plurality of cathode wirings 108 so that the wirings of the cathode wirings 108 do not conduct with each other. Accordingly, the cathode wiring 108 is disposed between the adjacent cathode partition walls 112. As the size of the cathode partition 112, for example, the one having a height of 2 μm to 3 μm and a width of 10 μm can be used.

  In addition, the substrate 1 is bonded to each other through a sealing plate 116 and a sealing material 118. Thereby, the space in which the organic EL element 10 is provided can be sealed, and the organic EL element 10 can be prevented from being deteriorated by moisture in the air. As the sealing plate 116, for example, a glass substrate having a thickness of 0.7 mm to 1.1 mm can be used. The sealing plate 116 may not be transparent when light is extracted from the substrate 1 side as in the case of a bottom emission type element. On the other hand, when light is extracted from the sealing plate 116 side as in the case of the top emission type, the sealing plate 116 needs to be transparent to at least a part of the emission wavelength region.

  In the image display apparatus 100 having such a structure, a current can be supplied to the organic EL element 10 through a positive electrode auxiliary wiring 106 and a negative electrode auxiliary wiring (not shown) by a driving device (not shown) to cause the light emitting layer to emit light. Then, light can be emitted from the substrate 1 through the substrate 1. An image can be displayed on the image display device 100 by controlling the light emission and non-light emission of the organic EL element 10 corresponding to the above-described pixel by the control device.

(Lighting device)
Next, a lighting device using the organic EL element will be described. Since the image display apparatus provided with the organic EL elements 10 and 20 is not different depending on the organic EL element, the following description will be given on behalf of the organic EL element 10 as a representative.
FIG. 6 is a diagram illustrating an example of a lighting device including the organic EL element 10 described above.
The lighting device 200 shown in FIG. 6 includes the organic EL element 10 described above and a terminal 202 that is installed adjacent to the substrate 1 (see FIG. 1) of the organic EL element 10 and connected to the anode 2 (see FIG. 1). The terminal 203 is connected to the cathode 4 (see FIG. 1), and the lighting circuit 201 is connected to the terminal 202 and the terminal 203 to drive the organic EL element 10.

  The lighting circuit 201 has a DC power source (not shown) and a control circuit (not shown) inside, and supplies a current by applying a voltage between the anode layer 2 and the cathode 4 of the organic EL element 10 through the terminal 202 and the terminal 203. To do. Then, the organic EL element 10 is driven, the light emitting layer emits light, the light is emitted through the substrate 1, and used as illumination light. The light emitting layer may be made of a light emitting material that emits white light, and each of the organic EL elements 10 using light emitting materials that emit green light (G), blue light (B), and red light (R). A plurality of them may be provided so that the combined light is white.

(Manufacturing method of organic EL element)
The scattering part 7 is produced on the substrate 1. In the case of a structure in which particles are dispersed as shown in FIG. 2A, the method for producing can be produced by applying a resin or the like in which particles are dispersed and further curing the resin or the like. In addition, when a crystal grain boundary as shown in FIG. 2B is used, a polycrystalline substance is formed. As a substance constituting a polycrystal, it is generally known that most ceramics form crystal grain boundaries, and aluminum oxide, titanium oxide, yttrium oxide, and the like can be used. Finally, in the case where the medium 7m and the scattering portion 7p form random irregularities as shown in FIG. 2C, for example, after the medium 7m is formed, the surface is roughened by etching, and further on the roughened surface. It can be produced by forming the scattering portion 7p. In addition, it can also be produced using a self-assembled film such as a block copolymer.

  Further, the anode 2, the organic layer 3, the cathode 4, the low refractive index layer 5, and the metal layer 6 can be laminated in this order on the formed scattering layer 7 to form the organic EL element 10. The anode 2 can be formed using a dry film formation method such as a vacuum evaporation method typified by a resistance heating evaporation method or an electron beam evaporation method, a sputtering method, an ion plating method, or a CVD method. In addition, when a wet film forming method such as a coating film forming method can be adopted, for example, a film is formed using a spin coating method, a dip coating method, an ink jet method, a printing method, a spray method, a dispenser method, or the like. can do. By performing the surface treatment of the anode 2 after forming the anode 2, the performance of the overcoated layer (adhesion with the anode 2, surface smoothness, reduction of hole injection barrier, etc.) can be improved. . The surface treatment includes high-frequency plasma treatment, sputtering treatment, corona discharge treatment, UV ozone irradiation treatment, ultraviolet irradiation treatment, oxygen plasma treatment, and the like.

  Furthermore, the same effect as the surface treatment can be expected by forming an anode buffer layer (not shown) instead of or in addition to the surface treatment of the surface treatment of the anode 2. When the anode buffer layer is applied by a wet process, spin coating, casting, micro gravure coating, gravure coating, bar coating, roll coating, wire bar coating, dip coating The film can be formed using a coating method such as a spray method, a spray coating method, a screen printing method, a flexographic printing method, an offset printing method, or an inkjet printing method.

  In the case where the anode buffer layer is formed by a dry process, the anode buffer layer can be formed by using a plasma treatment or the like exemplified in Japanese Patent Application Laid-Open No. 2006-303412. In addition, a method of forming a film of a single metal, a metal oxide, a metal nitride, or the like can be given. Specific film forming methods include an electron beam evaporation method, a sputtering method, a chemical reaction method, a coating method, and a vacuum evaporation method. The method etc. can be used.

A conventionally known method can be used to form the organic layer 3 and is not particularly limited. For example, a method such as a vacuum deposition method, a spin coating method, a casting method, or an LB method can be used.
Here, in the case where the surface of the anode 2 serving as a base on which the organic layer 3 is formed is uneven, a polishing process, an etching process, or the like for flattening may be appropriately performed.

  The cathode 4 can be formed by the same method as the anode 2 and is not particularly limited. For example, a resistance heating vapor deposition method, an electron beam vapor deposition method, a sputtering method, an ion plating method, a CVD method, or the like is used. Can do.

  Although the formation method of the low refractive index layer 5 is not specifically limited, For example, resistance heating vapor deposition method, electron beam vapor deposition method, sputtering method, ion plating method, CVD method etc. can be used.

  Although the formation method of the metal layer 6 is not specifically limited, For example, a vapor deposition method and sputtering can be used.

  The organic EL element 10 can be manufactured by the above process. Moreover, after these series of processes, it is preferable to use the organic EL element 10 stably for a long period of time and to attach a protective layer and a protective cover (not shown) for protecting the organic EL element 10 from the outside. As the protective layer, polymer compounds, metal oxides, metal fluorides, metal borides, silicon compounds such as silicon nitride and silicon oxide, and the like can be used. And these laminated bodies can also be used. Further, as the protective cover, a glass plate, a plastic plate whose surface has been subjected to low water permeability treatment, a metal, or the like can be used. The protective cover is preferably bonded to the substrate 1 with a thermosetting resin, a photocurable resin, frit glass or the like and sealed. In this case, it is preferable to use a spacer because a predetermined space can be maintained and the organic EL element 10 can be prevented from being damaged. If an inert gas such as nitrogen, argon, or helium or an inert liquid such as perfluorocarbon is sealed in this space, the oxidation of the metal layer 6 can be easily prevented. In particular, when helium is used, heat conduction is high, and thus heat generated from the organic EL element 10 when voltage is applied can be effectively transmitted to the protective cover, which is preferable. Furthermore, by installing a desiccant such as barium oxide and a deoxidizing material in this space, it becomes easy to suppress the moisture adsorbed in the series of manufacturing steps from damaging the organic EL element 10.

(SPP extraction in Otto type arrangement)
The film thickness of the low refractive index layer capable of taking out the SPP captured on the surface of the metal layer by the organic EL element Otto type arrangement in the present invention will be examined.

FIG. 7 shows the result of energy dissipation calculation for the organic EL element 20 having the standard structure, in which the intensity of light emitted from the organic layer is developed with the wave number component in the organic EL element surface direction. The horizontal axis represents the wave number of the light emitted from the organic layer, the organic EL element surface direction component divided by the vacuum wave number k ₀ , that is, the effective refractive index, and the vertical axis represents the light intensity of the wave number, that is, the development. The coefficient is shown. The calculation was performed separately for the TM polarization component and the TE polarization component. This calculation shows the result of an organic EL element having a standard structure in which an anode 12, an organic layer 13, and a cathode 14 (metal) each having a flat layer are stacked on a substrate 11 (glass). In this case, the peak area on the highest wavenumber side of the TM polarized light with respect to the total integrated area of the TM / TE polarized light component represents the intensity ratio of the SPP mode light, but most of the light emitted from the organic layer 13 is the SPP mode light. As you can see it is captured. In the organic EL element shown in FIG. 7, the film thicknesses of the anode 12 and the organic layer 13 are 150 nm and 100 nm, respectively.

On the other hand, in the organic EL element 30 (see FIG. 9) having the Otto type arrangement, the dependence of the intensity of the light emitted from the organic layer (TM polarization component) by the energy dissipation calculation on the film thickness of the low refractive index layer 25 is shown. The figure shown is shown in FIG. The substrate 21, the anode 22, and the organic layer 23 of the organic EL element 30, which is an example of an organic EL element having an Otto type arrangement, have the same configuration as the element 20 of FIG. 7, but are a transparent conductive material on the organic layer 23. A cathode 24 (50 nm) made of ITO is formed, and further, a low refractive index layer 25 and a metal layer 26 are sequentially formed thereon.
The refractive index of the low refractive index layer 25 is 1.38, FIG. 8A shows the case where the metal layer 26 is Al, and FIG. 8B shows the case where the metal layer 26 is Ag. The film thickness (nm) of the low refractive index layer 25 is shown.

  8 (a) and 8 (b), it can be seen that as the film thickness of the low refractive index layer 25 is increased, the peak wave number is decreased and the peak width is decreased. Further, it can be confirmed that as the film thickness increases, the peak wave number shifts slightly and the peak width approaches a constant value. Note that the decrease in the peak wave number indicates that the film thickness of the low refractive index layer 25 in contact with the metal layer 26 is large, and the wave number of the SPP becomes small due to the influence of the refractive index of the low refractive index layer 25. In addition, the narrowing of the peak width indicates that the light captured as the SPP is extracted into the organic layer and the attenuation when the light is guided in the plane is small. This will be described next.

The peak change will be described below with reference to FIGS. 9A, 9B, and 9C.
In FIG. 9A, the light is completely trapped on the surface of the metal layer 26 as SPP mode light. This represents the time when the film thickness of the low refractive index layer 25 is 0 nm, the laminated structure on the organic layer 23 to metal layer 26 side does not form an Otto type arrangement, and the SPP mode light is transmitted between the metal layer 26 and the cathode 24. The peak width is large because it rapidly attenuates while propagating in the in-plane direction.
Next, as the film thickness of the low refractive index layer 25 is increased, as shown in FIG. 9B, the SPP mode light and the waveguide mode light are mixed due to the Otto type arrangement. This means that the extracted SPP mode light becomes guided mode light and is recaptured as SPP mode light again by the metal layer 26 by interface reflection. In this case, since the light is less likely to attenuate than the SPP mode light of FIG. 9A, the peak width becomes gradually narrower.
Finally, when the film thickness of the low refractive index layer 25 becomes sufficiently large, it becomes as shown in FIG. In this case, although the Otto type arrangement is used, the evanescent wave at the light emission point does not reach the metal layer 26 and is not captured as SPP mode light. In this case, the emitted light is captured as guided mode light. That is, when the film thickness of the low refractive index layer 25 exceeds a certain thickness, the trapped light is only guided mode light, so that the ease of attenuation does not change and the peak width also does not change.

FIG. 10 is a diagram showing a change in peak width (half width) with respect to the film thickness of the low refractive index layer 25. When the metal layer 26 is Al, the film thickness of the low refractive index layer 25 is 200 nm or more. It can be seen that the change in the peak width becomes smaller and the emitted light is not easily captured by the SPP. It can also be seen that when the metal layer 26 is Ag, the change in peak width is small when the film thickness of the low refractive index layer 25 is 150 nm or more, and it is difficult to be captured as SPP mode light.
That is, it can be seen that the film thickness of the low refractive index layer 25 trapped as SPP mode light is at least 300 nm or less, and the trapping effect becomes remarkable at 200 nm or less. In this study, the case where the refractive index of the low refractive index layer 25 is n = 1.38 is calculated, but the refractive index is not limited to 1.38, and the metal layer 26 is also made of Ag and Al. It is not limited.

Further, in the Otto type arrangement, the surface plasmon polariton (SPP) trapped on the surface of the metal layer 26 can be taken out by an evanescent wave generated by light totally reflected at the interface between the cathode 24 and the low refractive index layer 25. That is, the wave number of the evanescent wave, it is necessary to have a wave number k _'sp and the intersection of the SPP that is generated on the surface of the metal layer 26.

The real part of the relative permittivity of the metal layer 26 is ε ₁ , the relative permittivity of the low refractive index layer 25 is ε ₂ , and the wave number of light in the vacuum at the peak wavelength of light emitted from the light emitting layer (angular frequency / vacuum). If the speed of light in the middle is k ₀ , the real part of the wave number k ′ _sp of the SPP generated on the surface of the metal layer 26 is the same as the expression of k _{sp in the} above equation (4).

On the other hand, the vertical component of the wave number in the low refractive index layer 25 of the surface plasmon polariton (SPP) generated on the surface of the reflective layer 26 can be expressed by the following equation (7).

となる。
つまり、式（８）が十分大きければ、金属層２６の表面に生成されるＳＰＰの電磁場が陰極や有機層に滲み出し、陰極２４と低屈折率層２５の界面での全反射により生じたエバネッセント波とカップリングして、取り出すことができる。
図１１（ａ）は金属層２６をＡｌ、（ｂ）は金属層２６をＡｇとした場合の式（８）をグラフ化した図である。 When the magnitude (strength) of the electromagnetic field of the SPP generated on the surface of the metal layer 26 is normalized with the value on the surface of the metal layer 26 set to 1, bleeding occurs while exponentially decaying in a direction perpendicular to the metal layer 26. The strength of the SPP that reaches the interface of the low refractive index layer 25 / cathode 24 is approximately when the thickness of the low refractive index layer 55 is h ₂ and the reflection at each interface can be ignored.

It becomes.
That is, if the equation (8) is sufficiently large, the electromagnetic field of the SPP generated on the surface of the metal layer 26 oozes out to the cathode and the organic layer, and evanescent generated by total reflection at the interface between the cathode 24 and the low refractive index layer 25. Coupling with the wave can be taken out.
FIG. 11A is a graph showing the equation (8) when the metal layer 26 is Al, and FIG. 11B is a graph when the metal layer 26 is Ag.

  Comparing this result with FIGS. 8A and 8B, in the formula (8), the strength of the SPP generated on the surface of the metal layer 26 at the interface of the low refractive index layer 25 / cathode 24 is When the intensity at the surface of the metal layer 26 is normalized as 1, the peak width is the thickness of the low refractive index layer 25 at which the SPP intensity is 0.4 or less at the position propagated in the thickness direction of the low refractive index layer 25. Is saturated to a constant value. That is, when the formula (8) is 0.4 or less, it can be said that the strength of the SPP that oozes out to the interface between the low refractive index layer 25 and the cathode 24 is reduced, and the light extraction effect by the Otto type arrangement is reduced. In other words, it can be understood that the light extraction effect by the Otto type arrangement can be sufficiently obtained when the thickness of the low refractive index layer 25 is 0.4 or more in the formula (8). In this study, the case where the refractive index of the low refractive index layer 25 is n = 1.38 is calculated, but the refractive index is not limited to 1.38, and the metal layer 26 is also made of Ag and Al. It is not limited. If the condition that the intensity of SPP at the interface between the low refractive index layer 25 and the cathode 24 expressed by the equation (8) is larger than a certain value (for example, 0.4) is satisfied, the SPP mode light is converted into the organic layer 23 by Otto arrangement. As long as this condition is satisfied, the refractive index of the low refractive index layer 25 and the material of the metal layer 26 are not limited.

  Examples of the organic EL device of the present invention will be described below.

In the present invention, the effect on the light extraction efficiency of the organic EL element of each embodiment was confirmed by simulation. First, the finite difference time domain method (FDTD method) used for the simulation will be described.
The FDTD method is an analysis method that temporally differentiates Maxwell's equation describing the time change of the electromagnetic field and tracks the time change of the electromagnetic field at each point in the space. In order to calculate the light extraction efficiency of the organic EL element by the FDTD method, the light emission in the light emitting layer is regarded as the radiation from the minute dipole, and the intensity of the radiation is counted. More specifically, the frequency dependence is calculated using the ratio of the light extracted to the substrate with respect to the total radiation intensity of the dipole as the light extraction efficiency. Hereinafter, the calculation result of the light extraction efficiency is shown in a graph. Λ on the horizontal axis represents the frequency of the dipole as a wavelength in vacuum (hereinafter, this λ may be simply referred to as wavelength), and η on the vertical axis represents the light extraction efficiency. The same applies to the following drawings.
In order to simulate a light emission phenomenon close to reality, the calculation was performed with a dipole as a light emission source being random (dipole moment is random in all directions).

FIG. 12 is a cross-sectional view showing a model structure of the organic EL element 10 used in the simulation. The substrate 1 is made of glass, and a refractive index of 1.52 is used. Assuming that the anode 2 and the cathode 4 are made of ITO, the refractive index is 1.82 + 0.009i at 550 nm, and other wavelengths are extrapolated by the Lorentz model. Further, 1.72 was used as the refractive index of the organic layer 3. The low refractive index layer 5 is made of magnesium fluoride (MgF), and the refractive index is 1.38. Further, assuming that the metal layer 6 is made of aluminum (Al), the refractive index is 0.649 + 4.32i at 550 nm, and other wavelengths are extrapolated by the Drude model.
The anode 2, the organic layer 3, the cathode 4, the low refractive index layer 5, and the metal layer 6 were 150 nm, 210 nm, 50 nm, 100 nm, and 100 nm, respectively.
The position of the light emission source was a point (star mark in the figure) that was 132.5 nm away from the cathode 4 in the organic layer 3.
The scattering portion 7p of the scattering layer 7 is a cube having a side of 200 nm unless otherwise specified. Furthermore, each scattering part is randomly arranged three-dimensionally in the scattering layer 7 so as not to overlap each other (the same applies to all the following examples).
Moreover, about all the following examples, all the planar shapes (shape of a light emission area | region) of the board | substrate 1-the metal layer 6 are squares with a side of 9600 nm.

Example 1
FIG. 13 shows the result of calculating the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method when the film thickness of the scattering layer 7 and the refractive index configuration of the scattering layer 7 are changed. Regarding the configuration of the refractive index of the scattering layer 7, when the refractive index of the medium 7m is 1.45 and the refractive index of the scattering portion 7p is 2.30 (denoted as highly bent particles in FIG. 13), Each of the cases where the refractive index is 1.90 and the refractive index of the scattering portion 7p is 1.45 (described as low-refractive particles in FIG. 13) was examined. Further, in each case, the film thickness of the scattering portion was calculated for two types of 500 nm and 1000 nm. In any case, the space filling rate in the scattering layer 7 of the scattering portion 7p was set to 26%. Further, the total number N of the scattering portions 7p in the scattering layer 7 at this time is 1500 and 3000, respectively, when the thickness of the scattering portion 7 is 500 nm and 1000 nm.
Further, for comparison, there is a structure that does not have the second electrode side structure of the Otto type arrangement and does not have the scattering layer 7 (hereinafter referred to as “standard structure”) and only the Otto type arrangement that does not have only the scattering layer 7. The structure (hereinafter referred to as “solid structure”) was calculated. In FIG. 13, the horizontal axis λ is the wavelength of the emitted light in vacuum, and the vertical axis η is the light extraction efficiency up to the substrate (relative value of the light intensity extracted up to the substrate with respect to the total light emission intensity). The same).
From FIG. 13, it can be seen that the organic EL element 10 in which the scattering portion 7 is introduced has improved light extraction efficiency compared to the standard structure or the solid structure. Also, in the case of highly bent particles, the light extraction efficiency is improved when the film thickness is thin, whereas in the case of low bent particles, the light extraction efficiency is improved when the film thickness is large. I understand. As will be described later in Example 3, the highly bent particles have a larger scattering cross-sectional area per scattering portion 7p. Therefore, if the film thickness is too thick, light is less likely to pass through the scattering layer 7 and the organic layer. This is probably because the light in 3 cannot be extracted sufficiently.

(Example 2)
In Example 1, it was confirmed that the difference in refractive index between the scattering portion 7p of the scattering layer 7 and the medium 7m affects the light extraction. Therefore, the light extraction efficiency was obtained by computer simulation using the FDTD method while changing each refractive index. FIG. 14 shows the range of combinations of the refractive indexes of the studied scattering portion 7p and medium 7m.
FIG. 15A shows the light extraction efficiency of the organic EL element 10 when the refractive index of the medium 7m is fixed at 1.45 and the refractive index of the scattering portion 7p is changed as shown in FIG. The result calculated | required by computer simulation using the FDTD method is shown. The refractive index of the scattering portion 7p was calculated in each case of 1.60, 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, 2.30. In addition, the film thickness of the scattering layer 7 and the total number N of the scattering portions 7p in the scattering layer 7 are the same as in the case where the film thickness of the scattering layer in Example 1 is 1000 nm.
From FIG. 15A, the light extraction efficiency is improved as the refractive index difference between the scattering portion 7p and the medium 7m increases (that is, the refractive index of the scattering portion 7p increases). It can be seen that when the refractive index is 2.00 or more, although the light extraction efficiency is lower than that of the solid structure at a part of the short wavelength side, the light extraction efficiency is generally improved as compared with the solid structure. That is, the light extraction efficiency is improved when the refractive index difference between the scattering portion 7p and the medium 7m is larger than 0.5.
FIG. 15B is a diagram showing the light extraction efficiency for each wavelength of the emitted light, with the refractive index of the scattering portion 7p as the horizontal axis. For comparison, the light extraction efficiency for each wavelength in the case of the solid structure is indicated by a dotted line. It can be seen that the longer the light, the more efficiently the light can be extracted even when the difference in refractive index between the scattering portion 7p and the medium 7m is small. As will be described later in Example 3, for a short wavelength light, the scattering cross section per one scattering portion 7p is larger than that for a long wavelength, and light is emitted from the organic layer to the outside. This is thought to be because it becomes impossible to take out.

FIG. 16A shows the light extraction efficiency of the organic EL element 10 when the refractive index of the scattering portion 7p is fixed at 2.30 and the refractive index of the medium 7m is changed as shown in FIG. The result calculated | required by computer simulation using the FDTD method is shown. The refractive index of the medium 7m was calculated in each case of 1.45, 1.60, 1.70, 1.80, 1.90, 2.00, 2.10, and 2.20. In addition, the film thickness of the scattering layer 7 and the total number N of the scattering portions 7p in the scattering layer 7 are the same as in the case where the film thickness of the scattering layer in Example 1 is 1000 nm.
As shown in FIG. 16A, the light extraction efficiency is improved as the refractive index difference between the scattering portion 7p and the medium 7m increases (that is, the refractive index of the medium 7m decreases), and in particular, the refractive index of the medium 7m. However, at 1.80 or less, it can be seen that the light extraction efficiency is improved from the solid structure in most visible light wavelength regions. That is, the light extraction efficiency is improved when the refractive index difference between the scattering portion 7p and the medium 7m is 0.5 or more.
FIG. 16B is a diagram showing the light extraction efficiency for each wavelength of the emitted light, with the refractive index of the medium 7m as the horizontal axis. For comparison, the light extraction efficiency for each wavelength in the case of the solid structure is indicated by a dotted line. It can be seen that the light extraction efficiency of the light of any wavelength is improved as compared with the solid structure when the refractive index difference between the scattering portion 7p and the medium 7m is 0.5 or more.

FIG. 17A shows the light extraction efficiency of the organic EL element 10 when the refractive index of the medium 7m is fixed at 1.90 and the refractive index of the scattering portion 7p is changed as shown in FIG. The result calculated | required by computer simulation using the FDTD method is shown. The refractive index of the scattering part 7p was calculated for each case of 1.20, 1.30, 1.45, 1.60, 1.70, 1.80. In addition, the film thickness of the scattering layer 7 and the total number N of the scattering portions 7p in the scattering layer 7 are the same as in the case where the film thickness of the scattering layer in Example 1 is 1000 nm.
As shown in FIG. 17A, the light extraction efficiency is improved as the refractive index difference between the scattering portion 7p and the medium 7m increases (that is, the refractive index of the scattering portion 7p decreases). It can be seen that when the rate is 1.60 or less, the light extraction efficiency is improved over the solid structure in most visible light wavelength regions. That is, the light extraction efficiency is improved when the refractive index difference between the scattering portion 7p and the medium 7m is 0.3 or more.
FIG. 17B is a diagram showing the light extraction efficiency for each wavelength of the emitted light, with the refractive index of the medium 7m as the horizontal axis. For comparison, the light extraction efficiency for each wavelength in the case of the solid structure is indicated by a dotted line. As a result, it can be seen that the light extraction efficiency is improved when the refractive index difference is larger than 0.25.

FIG. 18A shows the light extraction efficiency of the organic EL element 10 when the refractive index of the scattering portion 7p is fixed at 1.45 and the refractive index of the medium 7m is changed as shown in FIG. The result calculated | required by computer simulation using the FDTD method is shown. The refractive index of the medium 7m was calculated for each case of 1.60, 1.70, 1.80, 1.90, 2.00, 2.10. In addition, the film thickness of the scattering layer 7 and the total number N of the scattering portions 7p in the scattering layer 7 are the same as in the case where the film thickness of the scattering layer in Example 1 is 1000 nm.
From FIG. 18A, the light extraction efficiency is improved when the refractive index of the medium 7m is 1.90 to 2.00 (the refractive index difference between the scattering portion 7p and the medium 7m is 0.45 to 0.5). In particular, when the refractive index of the medium 7m is 1.70 or more, although the light extraction efficiency is lower than that of the solid structure in a part of the short wavelength side, the light extraction efficiency is improved as a whole than the solid structure. I understand that That is, the light extraction efficiency is improved when the refractive index difference between the scattering portion 7p and the medium 7m is 0.25 or more.
FIG. 18B is a diagram showing the light extraction efficiency for each wavelength of the emitted light, with the refractive index of the medium 7m as the horizontal axis. For comparison, the light extraction efficiency for each wavelength in the case of the solid structure is indicated by a dotted line. It can be seen that the light extraction efficiency of the light of any wavelength is improved as compared with the solid structure when the refractive index difference between the scattering portion 7p and the medium 7m is 0.25 or more.

  As described above, when the refractive index of the scattering portion 7p is larger than the refractive index of the medium 7m, the light extraction efficiency can be improved when the refractive index difference is larger than 0.5, and the refractive index of the scattering portion 7p is increased. When the refractive index is smaller than that of the medium 7m, the light extraction efficiency can be improved when the refractive index difference is larger than 0.25. When the refractive index of the scattering portion 7p is small, the effect of sufficiently improving the light extraction efficiency is obtained even if the refractive index difference is small. This is because the refractive index of the scattering portion 7p is smaller than the refractive index of the medium 7m. This is probably because all the light incident on the scattering portion 7p from the medium 7m at a critical angle or more is totally reflected, and the effect of total reflection is added in addition to the normal scattering effect.

(Example 3)
FIG. 19 shows the result of calculating the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method when the total number N of the scattering portions 7p of the scattering layer 7 is changed. Regarding the configuration of the refractive index of the scattering layer 7, the refractive index of the medium 7m is 1 when the refractive index of the medium 7m is 1.90 and the refractive index of the scattering portion 7p is 1.45 (FIG. 19A). .45 and the case where the refractive index of the scattering portion 7p is 2.30 (FIG. 19B) was examined. The number density of the scattering portions 7p in the scattering layer 7 is constant, and the number of the scattering portions 7p is decreased by reducing the thickness of the scattering layer. Calculation was performed for each of the cases where the total number N of the scattering portions 7p in the scattering layer 7 was 500, 1000, 1500, 2000, 2500, and 3000. The arrangement of the medium 7m and the scattering portion 7p when N is 3000 is the same as that in Example 1 where the scattering layer thickness is 1000 nm. In addition, as in Example 1, the standard structure and the solid structure were also compared. In addition, according to the above-mentioned definition, the average diameter D of the scattering portion 7p in this embodiment is 248 nm.
First, in FIG. 19A, it can be seen that the light extraction efficiency improves as the total number N of the scattering portions 7p increases. This is presumably because the total reflection on the outer surface of the substrate 1 can be suppressed because the scattering increases as the number of scattering portions 7p increases.
On the other hand, in FIG. 19B, the extraction efficiency is most improved when the total number N of the scattering portions 7p is 1000. When the total number N of the scattering portions 7p is 1000 or more, the scattering portion 7p is visible in any visible light wavelength region. It can be seen that the light extraction efficiency decreases almost monotonically as the number increases. In the short wavelength region with a wavelength of 500 nm or less, when the total number N of the scattering portions 7p is 3000, the extraction efficiency is lowered with respect to the solid structure. These results show that, under the refractive index conditions used in this computer simulation, the scattering layer 7 using high refractive index particles for the scattering portion 7p is compared to the scattering layer 7 using low refractive index particles for the scattering portion 7p. Therefore, it is considered that the light passing through the scattering layer 7 is difficult to transmit from the organic layer 3 to the substrate 1 when the number of the scattering portions 7p is too large.

ここで、Ｄは誘電体球の直径、ｎ_ｐは誘電体球の屈折率、ｎ_ｍは誘電体球の周囲の媒質の屈折率、λは光の波長である。式（９）はｎ_ｍとｎ_ｐの差がそれほど大きくない場合に使用することができる。ただし、散乱断面積σを計算する手法はこの限りではなく、例えば、誘電体球のより厳密な散乱断面積を求めるための式としてＭｅｅ散乱の式を用いることができるし、さらに、球形に限らないより一般的な形状の散乱部７ｐに対しては離散双極子近似等による数値計算を用いることも可能である。
図１９（ａ）の計算で用いた散乱層７について、波長λ＝５５０ｎｍにおける散乱部７ｐ（粒子）1個当たりの散乱断面積を求めるために、上記（９）式に散乱部７ｐの条件（ｎ_ｐ＝１．４５、ｎ_ｍ＝１．９０、Ｄ＝２４８ｎｍ）を代入すると、散乱部７ｐ（粒子）１個当たりの散乱断面積σは１．１×１０^４ｎｍ^２となる。これより、散乱体７ｐの総数Ｎ＝３０００（Ｎ_Ｓ＝３．２６×１０^−５／ｎｍ^２）の場合の占有率Ｎ_Ｓσは０．３５となる。尚、シミュレーションモデルの散乱部７ｐは1辺が２００ｎｍの立方体であるが、ここでは式（９）に適用するために、同じ体積の球（直径が２４８ｎｍ）として扱った。同様にして、図１９（ｂ）の計算で用いた散乱層７（ｎ_ｐ＝２．３０、ｎ_ｍ＝１．４５、Ｄ＝２４８ｎｍ、Ｎ＝３０００）について、波長λ＝５５０ｎｍでの散乱断面積σおよび占有率Ｎ_Ｓσを求めると、それぞれ５．７×１０^４ｎｍ^２、１．８６となる。これから、散乱部７ｐの数が同じでも、図１９（ｂ）の散乱層７は（ａ）の散乱層７よりも光が透過しにくいことがわかる。 In order to confirm this, as parameters representing the degree of scattering in the scattering layer 7, the scattering cross section σ per scattering portion 7 p (particle) and the number of scattering portions 7 p (particle) per light emitting area of the element (area) The product N _S σ (hereinafter referred to as the occupation ratio) of the particle density N _S was adopted. When the number of the scattering portions 7p is small, the occupation ratio is equal to the scattering probability of the light perpendicularly incident on the scattering layer 7, and thus the occupation ratio is a guideline for estimating the difficulty of transmitting the light of the scattering layer 7.
The specific calculation of the scattering cross section σ was performed by the van de Hulst approximation (formula (9)) that gives the scattering cross section of the dielectric sphere shown below.

Here, D is the diameter of the dielectric spheres, n _p is the refractive index of the dielectric spheres, n _m is the refractive index of the medium surrounding the dielectric spheres, lambda is the wavelength of light. Equation (9) can be used when the difference between _nm and _np is not very large. However, the method for calculating the scattering cross section σ is not limited to this, and, for example, the Mee scattering formula can be used as a formula for obtaining a stricter scattering cross section of the dielectric sphere, and the method is not limited to a spherical shape. It is also possible to use numerical calculation by discrete dipole approximation or the like for the scattering portion 7p having a more general shape.
For the scattering layer 7 used in the calculation of FIG. 19 (a), in order to obtain the scattering cross section per scattering portion 7p (particle) at the wavelength λ = 550 nm, the condition of the scattering portion 7p ( Substituting n _p = 1.45, n _m = 1.90, D = 248 nm), the scattering cross section σ per scattering portion 7p (particle) is 1.1 × 10 ⁴ nm ² . Accordingly, the occupancy N _S σ when the total number N of the scatterers 7p is N = 3000 (N _S = 3.26 × 10 ⁻⁵ / nm ² ) is 0.35. In addition, although the scattering part 7p of the simulation model is a cube having one side of 200 nm, it is treated as a sphere having the same volume (diameter is 248 nm) here in order to apply to the equation (9). Similarly, with respect to the scattering layer 7 (n _p = 2.30, n _m = 1.45, D = 248 nm, N = 3000) used in the calculation of FIG. 19B, the scattering interruption at the wavelength λ = 550 nm. When the area σ and the occupation ratio N _S σ are obtained, they are 5.7 × 10 ⁴ nm ² and 1.86, respectively. From this, it can be seen that the scattering layer 7 in FIG. 19B is less likely to transmit light than the scattering layer 7 in FIG.

Also, in FIG. 19B, when N = 3000, the reason why the light extraction efficiency at a short wavelength is slightly lower than the solid structure (element having only the Otto arrangement) is This can be explained by the fact that the scattering cross section σ increases in the short wavelength region. Actually, in the case of N = 3000 in FIG. 19B, the scattering cross section σ and the occupancy N _S σ at λ = 500 nm, which is the wavelength at which the solid structure and the light extraction efficiency match, are calculated by the equation (9). 6.7 × 10 ⁴ nm ² and 2.2, respectively. That is, when the occupancy N _S sigma exceeds 2, the scattering layer 7 light to become more difficult to transmit the light extraction efficiency decreases.

On the other hand, in FIG. 19A, when N = 500, the reason why the light extraction efficiency is reduced to almost the same level as that of the solid structure in the vicinity of λ = 650 nm is that the scattering interruption in this wavelength region is obtained from the equation (9). This can be explained by the fact that the area σ becomes smaller. Actually, in the case of N = 500 in FIG. 19B, the scattering cross section σ and the occupancy N _S σ at λ = 650 nm, which is a wavelength at which the light extraction efficiency substantially coincides with the solid structure, are calculated by Expression (9). Then, it becomes 7.6 × 10 ³ nm ² and 0.04, respectively. That is, when the occupation ratio N _S σ is smaller than 0.05, the scattering layer 7 becomes difficult to scatter light, so that the light extraction efficiency is lowered.
From the above, it is preferable that the occupation ratio N _S σ in the scattering layer 7 is in the range of 0.05 to 2 in that the effect of improving the light extraction efficiency can be obtained by the scattering layer.

In order to determine the actual scattering cross section sigma and occupancy of the scattering layer 7 in the organic EL element N _S sigma, the number N _{S (area} particle density of the scattering portion 7p diameter and per unit light emission area of the scattering portion 7p However, this can be obtained by observing with a TEM (transmission electron microscope) a thin film sample of a cross section of the device produced by FIB (focused ion beam) processing. That is, the diameters of the plurality of scattering portions 7p observed with the TEM are measured (in the case of an ellipse and an ellipse, the average of the long axis length and the short axis length is taken), and the average value is used to obtain the equation (9) Calculate the mean value of the scattering cross section. Here, the wavelength λ is the maximum emission peak wavelength. The number N _S of the scattering portion 7p per unit light emission area can be obtained as follows. First, the thickness of the thin film sample subjected to FIB processing is measured in advance (thickness b [nm]). The thin film sample is observed with a TEM, and the film thickness of the scattering layer 7 is measured (referred to as film thickness d [nm]). Subsequently, an in-plane range for counting the scattering portion 7p in the thin film sample is determined (area A [nm ² ]), and the scattering portion 7p in the in-plane range (half the effective wavelength in a medium having a light emission wavelength). Count the above (m). The number N _S [nm ⁻² ] of the scattering portions 7p per unit light emitting area can be obtained by the following equation (10).

Example 4
FIG. 20 shows the result of calculating the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method when the number density of the scattering portions 7p in the scattering layer 7 is fixed and the size is changed. . The film thickness of the scattering layer 7 was 1000 nm, and the total number N of the scattering portions 7p was fixed at 3000. The light extraction efficiency was determined when the scattering portions 7p were all cubic, and the length of one side was 0 nm (that is, no scattering portion 7p), 100 nm, 125 nm, 150 nm, 175 nm, and 200 nm. Note that, for any size of the scattering portion 7p, the arrangement of the scattering portions 7p (the coordinate position of the center of each scattering portion 7p in the scattering layer 7) is the same as that of the scattering layer film thickness of Example 1 of 1000 nm. .
Regarding the configuration of the refractive index of the scattering layer 7, the refractive index of the medium 7m is set to 1.90 when the refractive index of the medium 7m is 1.90 and the refractive index of the scattering portion 7p is 1.45 (FIG. 20A). Each of the cases with 1.45 and the refractive index of the scattering portion 7p of 2.30 (FIG. 20B) was examined.
From FIG. 20A, it can be seen that when the size of the scattering portion 7p is 175 nm or less, the extraction efficiency is lower than in the case of the solid structure. It can be seen from FIG. 20B that when the size of the scattering portion 7p is 150 nm or less, the extraction efficiency is lower than in the case of the solid structure.

FIG. 21 shows the result of calculating the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method when the space filling rate of the scattering portion 7p in the scattering layer 7 is fixed and the size is changed. Show. The space filling factor means the volume ratio of the scattering portion 7p in the scattering layer 7. The light extraction efficiency was determined when the scattering portions 7p were all cubic and the length of one side was 100 nm, 125 nm, 150 nm, 200 nm, and 250 nm, respectively. Note that the scattering portions 7p in the scattering layer 7 are three-dimensionally dispersed and arranged so as not to overlap each other.
Regarding the configuration of the refractive index of the scattering layer 7, the refractive index of the medium 7m is 1 when the refractive index of the medium 7m is 1.90 and the refractive index of the scattering portion 7p is 1.45 (FIG. 21A). .45, and the case where the refractive index of the scattering portion 7p is 2.30 (FIG. 21B) was examined.
In addition, the space filling factor of the scattering part 7p in the scattering layer 7 was fixed to 26%, and the film thickness of the scattering layer 7 was 1000 nm.
When the space filling factor is fixed, it can be seen that the extraction efficiency decreases as the size decreases although it is gentler than the case where the number density of the scattering portions 7p in FIG. 20 is constant (FIG. 24 (a), (B)).

From these results, it can be seen that when the size of the scattering portion 7p is less than or equal to half the effective wavelength of the emitted light, light cannot be extracted effectively. This is because if the size of the scattering portion 7p is less than or equal to half the effective wavelength of the emitted light, the light is difficult to be scattered. In general, the scattering phenomenon in the region below the wavelength of light is represented by Rayleigh scattering, and the scattering cross section is proportional to the sixth power of the size of the scattering portion 7p. Therefore, when the size of the scattering portion 7p is reduced, the scattering cross section is rapidly reduced and light is not easily scattered.
On the other hand, if the size of the scattering portion 7p is at least half the effective wavelength of the emitted light, light can be sufficiently scattered between the scattering portion 7p and the medium 7m. In a region where the size of the scattering portion 7p is more than half of the effective wavelength of the emitted light, the scattering cross section is proportional to the square of the size of the scattering portion 7p because it is close to the scattering of classical particles by geometric approximation. That is, the influence of the size of the scattering portion 7p is reduced.

(Example 5)
FIG. 22 shows the result of calculating the light extraction efficiency of the organic EL element 10 by computer simulation using the FDTD method when the intermediate layer 8 is provided and the thickness of the intermediate layer 8 is changed. The refractive indexes of the medium 7p, the scattering portion 7p, and the intermediate layer 8 were 1.45, 2.30, and 1.45, respectively. The thickness of the intermediate layer 8 was calculated for each case of 0 nm (that is, the configuration of FIG. 12 without the intermediate layer 8), 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, and 300 nm. In addition, the film thickness of the scattering layer 7 and the total number N of the scattering portions 7p in the scattering layer 7 are the same as in the case where the film thickness of the scattering layer in Example 1 is 1000 nm. Further, as in Example 1, the results of the standard structure and the solid structure are also shown as a comparison.
From FIG. 22, when the film thickness of the intermediate layer 8 is increased, light cannot be extracted efficiently, and when the film thickness is 100 nm or more, the extraction efficiency is comparable or lower than that of the solid structure. I understand that. This is because the intermediate layer 8 has a lower refractive index than the organic layer 7, and light that is incident on the side 8 from the organic layer 3 at an incident angle that is greater than the critical angle is totally reflected. In particular, if the thickness of the intermediate layer 8 is too thick, the evanescent wave that has spilled to the intermediate layer 8 side due to total reflection does not reach the scattering layer 7, so that the light confined in the organic layer 3 without being scattered increases. , Light extraction efficiency decreases. Therefore, even when the intermediate layer 8 is used to flatten the surface of the anode 2 on the scattering layer 7 side, it is necessary that the thickness of the intermediate layer 8 is not too thick.
Specifically, the amount of change in the amplitude of the evanescent wave in the case where the thickness of the intermediate layer 8 is 100 nm at a wavelength of 600 nm is approximately 0.4 when calculated from Equation (3), and the amplitude of the evanescent wave reaches the scattering layer 7 until it reaches It turns out that it has fallen greatly. Even when the refractive indices of the organic layer 3 and the intermediate layer 8 are other than those used in the present embodiment, it is considered that the light trapped in the organic layer 3 is increased and the extraction efficiency is lowered when the amplitude change amount is the same or less. It is done.

10, 20, 30 Organic EL elements 1, 11, 21 Substrate 2, 12, 22 Anode 3, 13, 23 Organic layer 4, 14, 24 Cathode 5, 25 Low refractive index layer 6, 26 Metal layer 7 Scattering layer 7m Medium 7p scattering unit 100 image display device 104 anode wiring 106 anode auxiliary wiring 108 cathode wiring 110 insulating film 112 cathode partition wall 116 sealing plate 118 sealant 120 opening 200 lighting device 201 lighting circuit 202 terminal 203 terminal

Claims (12)

An organic EL device comprising a scattering layer, a first electrode, an organic layer including a light emitting layer, a second electrode, a low refractive index layer and a metal layer in this order,
The second electrode is made of a translucent conductive material,
The refractive index of the low refractive index layer is lower than the refractive index of the organic layer,
The scattering layer is composed of a medium and a scattering part existing in the medium and having a different refractive index,
The organic EL element in which the refractive index _{n p} of the scattering portion and the refractive index _{n m} of the _medium, characterized by satisfying the n _p -n m> 0.5 or _n m _-n p> 0.25.   2. The organic EL element according to claim 1, wherein an absolute value of an average refractive index of the scattering layer and a difference in refractive index of the organic layer is 0.2 or less.   The organic EL device according to claim 1, further comprising an intermediate layer between the scattering layer and the first electrode. The intermediate layer has a layered portion in a portion in contact with the first electrode,
Refractive index _{n o} of the organic layer and the refractive index _{n m1} of the layer portion _satisfies the _{n m1} ≧ _{n o,} or the refractive index _{n m1,} the refractive index _{n o} and the layered portion of the thickness t is less The organic EL element according to claim 1, wherein the organic EL element is satisfied.

Here, k ₀ is the wave number of light in vacuum at the maximum peak wavelength of light emitted from the light emitting layer.   5. The organic EL element according to claim 1, wherein a size of the scattering portion is at least half of an effective wavelength of emitted light in the medium.   6. The product of the average value of the scattering cross-sectional area per scattering portion and the number of the scattering portions per unit light emitting area is 0.05 to 2. 6. The organic EL element as described in.   The organic EL element according to claim 1, wherein the low refractive index layer has a thickness of 20 nm to 300 nm.   The organic EL element according to claim 1, wherein a refractive index of the low refractive index layer is further lower than a refractive index of the second electrode.   The organic EL element according to claim 8, wherein the refractive index of the second electrode is further lower than the refractive index of the organic layer.   The said low refractive index layer consists of a material whose refractive index is 0.2 or less smaller than at least one of the said 2nd electrode and the said organic layer, It is any one of Claims 1-9 characterized by the above-mentioned. Organic EL element.   An image display device comprising the organic EL element according to claim 1.   An illuminating device comprising the organic EL element according to claim 1.

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