JP2013127910A - Optical element, and light-emitting device and organic electroluminescent device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element, a light-emitting device, and an organic EL device, capable of improving light extraction efficiency.SOLUTION: The optical element comprises: a transparent substrate; a nanostructure which is formed in an island shape on the transparent substrate and contains metal; and a high refractive index layer which is formed on the transparent substrate so as to cover the nanostructure and has a refractive index higher than that of the transparent substrate. Accordingly, the purpose described above is achieved.

Description

  The present invention relates to an optical element, a light emitting element and an organic electroluminescence element using a diffraction grating.

For light-emitting elements such as organic electroluminescence elements, light-emitting diodes, and plasma displays, improvement of light extraction efficiency and the like has been studied in order to improve light-emitting efficiency.
Hereinafter, electroluminescence may be abbreviated as EL.

  As means for improving the light extraction efficiency, for example, Patent Document 1 and Patent Document 2 propose providing a diffraction grating. Examples of such a diffraction grating include those in which irregularities are directly formed on the surface of a glass substrate or a resin substrate.

However, the light extracted from the transparent substrate is only a part of the light generated from the light emitting element. For example, in an organic EL element, only about 20% of the light generated from the light emitting layer can be used. It is known.
Therefore, further improvement in light extraction efficiency is required.

JP 2004-335301 A JP 2011-159427 A

  The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide an optical element, a light emitting element, and an organic EL element capable of improving the light extraction efficiency.

  To achieve the above object, the present invention provides a transparent substrate, an island-like nanostructure formed on the transparent substrate, and a metal-containing nanostructure, and the nanostructure covered on the transparent substrate. And an optical element having a high refractive index layer having a higher refractive index than that of the transparent substrate.

  According to the present invention, since the nanostructure contains a metal, the reflectance at the interface between the nanostructure and the high refractive index layer can be increased, and a large diffraction effect can be obtained, greatly increasing the light extraction efficiency. It is possible to improve it.

  In the said invention, it is preferable that the island part which comprises the said nanostructure has a width in the range of 100 nm-1000 nm, and a thickness in the range of 100 nm-1000 nm. This is because the light extraction efficiency of visible light can be improved when the width and thickness of the island portion constituting the nanostructure are within the above range.

  In the present invention, the high refractive index layer is preferably a transparent electrode layer. Although it is known that light loss occurs due to the difference in refractive index at the interface between the transparent substrate and the transparent electrode layer, the light extraction efficiency can be improved by employing the configuration of the present invention.

The present invention also provides a light emitting element comprising the above-described optical element.
Since the light emitting element of the present invention includes the above-described optical element, it is possible to improve the light extraction efficiency with respect to light generated in the light emitting element and emitted from the transparent substrate side.

  Furthermore, the present invention includes the above-described optical element, an organic EL layer formed on the transparent electrode layer of the optical element and including a light emitting layer, and a counter electrode layer formed on the organic EL layer. An organic EL element is provided.

  Since the organic EL element of the present invention includes the above-described optical element, it is possible to improve the light extraction efficiency with respect to light generated in the light emitting layer and emitted from the transparent substrate side.

  In the present invention, by using a nanostructure containing a metal in the diffraction grating, it is possible to significantly improve the light extraction efficiency.

It is a schematic plan view which shows an example of the optical element of this invention. It is a schematic sectional drawing which shows an example of the optical element of this invention, and is the sectional view on the AA line of FIG. It is a schematic sectional drawing which shows the other example of the optical element of this invention, and is the sectional view on the AA line of FIG. It is a schematic plan view which shows another example of the optical element of this invention. It is a schematic sectional drawing which shows the other example of the optical element of this invention. It is a schematic sectional drawing which shows an example of the organic EL element of this invention.

  Hereinafter, the optical element of the present invention, and the light emitting element and organic EL element using the optical element will be described in detail.

A. Optical element The optical element of the present invention is formed in a transparent substrate, an island shape on the transparent substrate, a metal-containing nanostructure, and the transparent substrate so as to cover the nanostructure, And a high refractive index layer having a refractive index higher than that of the transparent substrate.

The optical element of the present invention will be described with reference to the drawings.
1 and 2 are a schematic plan view and a cross-sectional view showing an example of the optical element of the present invention, and FIG. 2 is a cross-sectional view taken along line AA of FIG. In FIG. 1, the high refractive index layer is omitted.
As illustrated in FIG. 1 and FIG. 2, the optical element 1 includes a transparent substrate 2 having island-shaped recesses on the surface, and island-shaped nanostructures 3 embedded in the recesses of the transparent substrate 2 and containing metal. And a high refractive index layer 4 formed on the transparent substrate 2 in which the nanostructure 3 is embedded and having a higher refractive index than that of the transparent substrate 2.

1 and 3 are a schematic plan view and a sectional view showing another example of the optical element of the present invention, and FIG. 3 is a sectional view taken along line AA of FIG. In FIG. 1, the high refractive index layer is omitted.
As illustrated in FIGS. 1 and 3, the optical element 1 includes a transparent substrate 2, a nanostructure 3 that is formed in an island shape on the transparent substrate 2, and contains a metal, and a nanostructure on the transparent substrate 2. 3 and a high refractive index layer 4 having a refractive index higher than that of the transparent substrate 2.

  In the optical element 1 shown in FIGS. 1 to 3, the nanostructure 3 is a structure in which island portions 3 a having widths w1 and w2 and thickness t of nanometer order are regularly arranged and function as a diffraction grating. Is. The widths w1 and w2 and the thickness t of the island portion 3a constituting the nanostructure 3 are adjusted according to the wavelength of the light L that passes through the optical element 1.

In the present invention, the island shape means that the island portions are regularly arranged with a space between each other.
The nanostructure is formed in an island shape, and is an island portion having a width and thickness of nanometer order and regularly arranged with a space between each other.
Each island part may be independent and may be connected by a connecting part. For example, in FIG. 1, the island portions 3a constituting the nanostructure 3 are independent, and in FIG. 4, the island portions 3a constituting the nanostructure 3 are connected to each other by the connecting portions 3c. Yes.
The dimensions such as the widths w1, w2, thickness t, distance d, period p, etc. of the island part 3a constituting the nanostructure 3 illustrated in FIGS. 1 to 3 should be adjusted according to the wavelength used by the optical element. Can do.

Further, the nanostructure formed on the transparent substrate means that the nanostructure is formed in contact with the transparent substrate, and the nanostructure is embedded in the concave portion of the transparent substrate, and The case where the nanostructure is laminated on the transparent substrate is included.
The high refractive index layer formed on the transparent substrate so as to cover the nanostructure means that the high refractive index layer is formed in contact with the transparent substrate and the nanostructure.

  In the present invention, since the nanostructure contains a metal, the reflectance at the interface between the nanostructure and the high refractive index layer can be increased, and a large diffraction effect can be obtained, greatly increasing the light extraction efficiency. It is possible to improve.

The reason why the light extraction efficiency is improved by the nanostructure containing metal is considered as follows.
In an optical element, it is known that reflection at this interface is one of the causes of light loss at the interface between a high refractive index layer such as a transparent electrode layer and a transparent substrate. The refractive index of the high refractive index layer n _1, the n ₂ refractive index of the transparent substrate, when the incident angle of light into the transparent substrate from the high refractive index layer and theta _1, total reflection occurs theta ₁ is Fresnel equations Θ ₁ = arcsin (θ ₂ / θ ₁ ) = θ ₁ ′
It becomes. Therefore, normally, light incident on the interface between the high refractive index layer and the transparent substrate at an incident angle of θ ₁ ′ or more is totally reflected and cannot be extracted. However, in the present invention, light in this range can be extracted by diffraction.
The diffraction condition is Bragg's equation nλ = 2dsinθ
Can be expressed as n is an integer, λ is the wavelength of light, d is the lattice spacing, and θ is the incident angle of light.
Based on this, by providing a diffraction grating having a grating interval d that diffracts light incident at an angle of θ ₁ ′ at this interface, light lost due to reflection can be guided into the transparent substrate.
The diffraction grating is configured, for example, by arranging media having different refractive indexes in a lattice shape. Since a high refractive index layer such as a transparent electrode layer and a transparent substrate are required to transmit light, conventionally, it has been studied to provide a transmission type diffraction grating using a transparent medium. However, in this case, there is a problem that it is difficult to obtain a large difference in the refractive index of the medium, that is, a sufficient reflectivity at the interface of the medium constituting the diffraction grating cannot be obtained, so that it is difficult to obtain the effect of diffraction.
On the other hand, in the present invention, the reflectance at the interface of the medium constituting the diffraction grating is obtained by using a metal for one of the media constituting the diffraction grating, that is, by making the nanostructure contain metal. And the effect of diffraction can be enhanced. Although there is a concern about a decrease in transmittance due to light shielding by metal, in the present invention, the decrease in transmittance can be minimized by setting the lattice spacing to the nano order.
Hereinafter, each structure in the optical element of this invention is demonstrated.

1. Nanostructure The nanostructure in the present invention is formed in an island shape on a transparent substrate, contains a metal, and functions as a diffraction grating.

  The nanostructure is made of metal. The metal constituting the nanostructure is not particularly limited as long as the island portion constituting the nanostructure can be formed with a predetermined width and thickness. For example, silver, copper, gold, aluminum, Indium, platinum, palladium, ruthenium, rhodium, iridium, titanium, zirconium, tin, iron, cobalt, nickel, vanadium, niobium, tantalum, chromium, molybdenum, and the like can be given. Among them, as will be described later, the method using a nanoparticle-containing coating solution containing metal nanoparticles can easily form a nanostructure and is advantageous in terms of the process. Is preferred. Specific examples include silver, copper, gold, indium, platinum, palladium, tin, iron, cobalt, nickel, and the like.

In the present invention, the dimensions such as the width, thickness, interval, and period of the island portions constituting the nanostructure can be adjusted according to the wavelength of the light transmitted through the optical element.
In a nano-order pattern, light may be absorbed depending on the size of the width, thickness, interval, period, and the like. Therefore, the size is set while avoiding conditions that absorb light. The conditions under which light absorption occurs vary depending on the type of metal and the wavelength of light, and thus are appropriately selected according to the material used and the emission wavelength of the light emitting device in which the optical element of the present invention is used. Specifically, the size such as width, thickness, interval, period, etc. can be derived by simulation using the FDTD method in which Maxwell's equations are directly expanded into differential equations in the space / time domain and sequentially calculated. Maxwell's equation is

Can be expressed as Here, E is an electric field, H is a magnetic field, μ ₀ is a vacuum magnetic permeability, and ε ₀ is a vacuum dielectric constant.

When adjusting the dimensions such as the width, thickness, interval, and period of the islands constituting the nanostructure, the wavelength of the light transmitted through the optical element may be a specific wavelength or a certain wavelength range.
In particular, when adjusting dimensions such as the width, thickness, interval, period, and the like of the island portions constituting the nanostructure, it is preferable to use the wavelength in the visible light region as the wavelength of the light transmitted through the optical element. This is because, generally, wavelengths in the visible light region are used for display devices, illumination devices, light sources, and the like. In addition, dimensions such as the width, thickness, interval, and period of the island portions constituting the nanostructure can be adjusted in accordance with the emission wavelength of the light emitting device in which the optical element of the present invention is used. In this case, the light extraction efficiency can be effectively improved.

The width of the island portion constituting the nanostructure is appropriately adjusted according to the wavelength of light transmitted through the optical element. Among these, the width of the island portion is preferably adjusted as appropriate according to the wavelength in the visible light region, and specifically, preferably in the range of 100 nm to 1000 nm, more preferably in the range of 200 nm to 800 nm. Of these, more preferably in the range of 300 nm to 700 nm. This is because if the width is within the above range, the light extraction efficiency of visible light can be effectively improved.
The width of the island part constituting the nanostructure is the distance from the end part to the end part of the island part.For example, when the cross-sectional shape of the island part is rectangular, the length of the side is round. In the case of an ellipse, is the major axis diameter and minor axis diameter. Specifically, as shown in FIG. 1, when the cross-sectional shape of the island portion 3a is rectangular, the widths w1 and w2 of the island portion 3a are the lengths of the sides of the rectangle. In this case, when the widths w1 and w2 of the island portions are different, that is, when the lengths of the rectangular sides are different, all the widths of the island portions are adjusted according to the wavelength of light transmitted through the optical element.

Moreover, the thickness of the island part which comprises a nanostructure is suitably adjusted according to the wavelength of the light which permeate | transmits an optical element. Among them, the thickness of the island part is preferably adjusted as appropriate according to the wavelength in the visible light region, specifically, preferably in the range of 100 nm to 1000 nm, more preferably in the range of 200 nm to 800 nm. Of these, more preferably in the range of 300 nm to 700 nm. This is because the light extraction efficiency of visible light can be effectively improved when the thickness is within the above range.
In addition, the thickness of the island part which comprises a nanostructure is the distance from the bottom part of an island part to a top part, for example, is the thickness shown by t in FIG.2 and FIG.3.

The interval between the island portions constituting the nanostructure is not particularly limited as long as the nanostructure can function as a diffraction grating, and is appropriately adjusted according to the wavelength of light transmitted through the optical element. Especially, it is preferable that the space | interval of an island part is suitably adjusted according to the wavelength of visible region, Specifically, it is preferable to exist in the range of 50 nm-900 nm, More preferably, it is the range of 100 nm-700 nm. Of these, more preferably in the range of 300 nm to 700 nm. This is because if the interval is within the above range, the light extraction efficiency of visible light can be effectively improved. Moreover, it is because formation of a nanostructure may become difficult when a space | interval is too narrow.
Note that the interval between the island portions constituting the nanostructure is a distance between adjacent island portions, for example, a distance indicated by d in FIG.

Moreover, the period of the island part which comprises a nanostructure will not be specifically limited if a nanostructure can function as a diffraction grating, It adjusts suitably according to the wavelength of the light which permeate | transmits an optical element. . Especially, it is preferable that the period of an island part is suitably adjusted according to the wavelength of visible light region, Specifically, it is preferable to exist in the range of 100 nm-1800 nm, More preferably, it is the range of 200 nm-1400 nm Of these, more preferably in the range of 600 nm to 1400 nm. This is because the light extraction efficiency of visible light can be effectively improved when the period is within the above range. Moreover, it is because formation of a nanostructure may become difficult when a period is too short.
In addition, the period of the island part which comprises a nanostructure is the distance from the center part of an adjacent island part to a center part, for example, is the distance shown by p in FIG.

The diffraction function of the nanostructure is considered to be related to the reflectance of the metal constituting the nanostructure. Therefore, in order to further improve the light extraction efficiency, it is preferable that the reflectance of the metal constituting the nanostructure is appropriately adjusted according to the wavelength of the light transmitted through the optical element. Especially, it is preferable that the reflectance of a metal is suitably adjusted according to the wavelength of visible region, specifically, it is preferable to exist in the range of 20% -100%, More preferably, it is 50%- It is in the range of 100%, more preferably in the range of 80% to 100%. This is because, if the reflectance of the metal is within the above range, the light extraction efficiency of visible light can be effectively improved.
In addition, a reflectance can be measured by the method shown by JIS-R-3106, for example.

In addition, the diffraction function of the nanostructure is considered to be related to the wavelength dispersion of the reflectance of the metal constituting the nanostructure. Therefore, in order to further improve the light extraction efficiency, it is preferable that the wavelength dispersion of the reflectance of the metal constituting the nanostructure is appropriately adjusted according to the wavelength of light transmitted through the optical element. Among them, the chromatic dispersion of the reflectance of the metal is preferably adjusted as appropriate according to the wavelength in the visible light region. Specifically, it is desirable that there is almost no chromatic dispersion in the visible light region. It is preferable to select so that the emission wavelength of the light emitting device in which the optical element is used is well reflected.
The wavelength dispersion of the reflectance can be measured by using, for example, an ultraviolet-visible light spectrophotometer UV-3600 manufactured by Shimadzu Corporation.

  Furthermore, the diffraction function of the nanostructure is considered to be related to the type of metal constituting the nanostructure. Therefore, in order to further improve the light extraction efficiency, it is preferable that the type of metal constituting the nanostructure is appropriately adjusted according to the wavelength of the light transmitted through the optical element. Especially, it is preferable that the kind of metal is suitably adjusted according to the wavelength of visible light region, for example, the light emission wavelength for which the optical element of the present invention is used.

  The shape of the cross section perpendicular to the thickness direction of the island part is not particularly limited as long as the nanostructure can function as a diffraction grating, and may be, for example, a rectangle, a circle, an ellipse, or the like.

  The shape of the cross section parallel to the thickness direction of the island portion is not particularly limited as long as the nanostructure can function as a diffraction grating, and may be, for example, a rectangle, a trapezoid, an inverted trapezoid, or the like.

Further, in the nanostructure, as illustrated in FIG. 4, adjacent island portions may be connected by a connecting portion 3 c. Since the nanostructure contains a metal and has low electric resistance, the nanostructure can function as an auxiliary electrode or the like when adjacent island portions are connected. In particular, when the high refractive index layer is a transparent electrode layer as will be described later, the conductivity can be improved.
The connecting portion may be formed as long as the connecting portions connect the adjacent island portions, and the adjacent island portions may be connected in any of the horizontal direction, the vertical direction, and the oblique direction.

  The nanostructure is only required to be formed on the transparent substrate, and the nanostructure 3 may be embedded in the concave portion of the transparent substrate 2 as illustrated in FIG. 2, and the nanostructure as illustrated in FIG. 3 may be laminated on the transparent substrate 2. Especially, it is preferable that the nanostructure is embedded in the concave portion of the transparent substrate. This is because the formation of the nanostructure becomes easy. Moreover, it is because the surface of the transparent substrate which has a recessed part on the surface can be planarized by a nanostructure, and the short circuit between the electrodes by the unevenness | corrugation of a nanostructure can be suppressed.

  The method of forming the nanostructure is not particularly limited as long as it is a method capable of forming the island part constituting the nanostructure with a predetermined width and thickness using a metal, and the type of the metal and the nanostructure The position is appropriately selected according to the formation position of the film. For example, the method of apply | coating the nanoparticle containing coating liquid containing a metal nanoparticle, a vapor deposition method, etc. are mentioned. In the case of the vapor deposition method, in the case where the nanostructure is embedded in the concave portion of the transparent substrate, for example, after depositing metal on the entire surface of the transparent substrate, polishing the metal film until the transparent substrate is exposed, etc. By removing, a nanostructure can be formed. In addition, when nanostructures are stacked on a transparent substrate, for example, after depositing metal on the surface of the transparent substrate, applying a resist, forming an etching mask by photolithography, and unnecessary by etching A nanostructure can be formed by removing the portion.

2. Transparent substrate The transparent substrate used in the present invention supports the nanostructure and the high refractive index layer.
The transparent substrate has optical transparency, and in the optical element of the present invention, light incident from the high refractive index layer side is extracted from the transparent substrate side.

  The transparent substrate may have a recess in which the nanostructure is embedded on the surface as illustrated in FIG. 2, or may not have the recess on the surface as illustrated in FIG. 3.

  In the case where the transparent substrate has the concave portion on the surface, it may be a single member as illustrated in FIG. 2, and the unevenness formed on the base portion 2a and the base portion 2a as illustrated in FIG. It may have the structure 2b. When the transparent substrate has a base portion and a concavo-convex structure, the concavo-convex structure can be formed by a simple method by appropriately selecting a material for forming the concavo-convex structure.

  When the transparent substrate has a concave portion on the surface, the width, depth, interval, and period of the concave portion correspond to the width, thickness, interval, and period of the island portion that constitutes the nanostructure. The width, depth, interval, and period of the recesses can be the same as the width, thickness, interval, and period of the island portion that constitutes the nanostructure, and thus description thereof is omitted here.

  The refractive index of a transparent substrate should just be lower than the refractive index of the below-mentioned high refractive index layer, and can be specifically set to about 1.4-1.6.

  Further, when the transparent substrate has a basal part and a concavo-convex structure, the refractive index of the basal part and the concavo-convex structure is preferably approximately the same. Specifically, the difference in refractive index between the base part and the concavo-convex structure is 0.1 or less. Preferably, it is 0.05 or less, more preferably 0.03 or less. This is because if the difference in refractive index between the base and the concavo-convex structure is large, light loss may occur at the interface between the base and the concavo-convex structure.

The transparent substrate is light transmissive. The light transmittance of the transparent substrate only needs to be transparent to the wavelength in the visible light region. Specifically, the light transmittance for the entire wavelength range in the visible light region is 80% or more. Of these, 85% or more, particularly 90% or more is preferable.
The light transmittance can be measured by, for example, an ultraviolet-visible light spectrophotometer UV-3600 manufactured by Shimadzu Corporation.

  Examples of the material for forming the transparent substrate include soda lime glass, alkali glass, lead alkali glass, borosilicate glass, aluminosilicate glass, silica glass and the like, fluorine resin, polyethylene, polypropylene, polyvinyl chloride, and polyfluoride. Vinyl, polystyrene, ABS resin, polyamide, polyacetal, polyester, polycarbonate, modified polyphenylene ether, polysulfone, polyarylate, polyetherimide, polyethersulfone, polyamideimide, polyimide, polyphenylene sulfide, liquid crystalline polyester, polyethylene terephthalate, polybutylene Terephthalate, polyethylene naphthalate, polymicroixylene dimethylene terephthalate, polyoxymethylene, polyethersulfone, Examples include resins such as ether ether ketone, polyacrylate, acrylonitrile-styrene resin, phenol resin, urea resin, melamine resin, unsaturated polyester resin, epoxy resin, polyurethane, silicone resin, amorphous polyolefin, and copolymers thereof. It is done.

  In particular, when the transparent substrate has a base portion and a concavo-convex structure, the material for forming the concavo-convex structure is preferably a resin. This is because the concavo-convex structure can be formed by a simple method.

  When the transparent substrate has a recess on the surface, the method for forming the recess is not particularly limited as long as it is a method capable of forming a recess having a predetermined width, thickness, interval, and period. It is appropriately selected depending on the like. Examples thereof include etching and photolithography.

  The thickness of the transparent substrate is appropriately selected depending on the material of the transparent substrate and the use of the optical element. Specifically, the thickness of the transparent substrate is about 0.005 mm to 5 mm.

3. High Refractive Index Layer The high refractive index layer in the present invention is formed on the transparent substrate so as to cover the nanostructure, and has a higher refractive index than the transparent substrate.

As the difference in refractive index between the transparent substrate and the high refractive index layer, it is sufficient that the refractive index of the high refractive index layer is higher than the refractive index of the transparent substrate. Specifically, it is preferably 0.05 or more, more preferably 0.1 or more, more preferably 0.2 or more. When the refractive index difference between the transparent substrate and the high refractive index layer is within the above range, the configuration of the present invention suppresses light loss at the interface between the transparent substrate and the high refractive index layer and improves the light extraction efficiency. It is because the effect to make it show enough.
In addition, when a transparent substrate has a base part and an uneven structure, the uneven structure of a transparent substrate and the refractive index difference of a high refractive index layer should just be the said range.

  The refractive index of the high refractive index layer may be higher than the refractive index of the transparent substrate, and specifically can be about 1.6 to 2.4.

The high refractive index layer is light transmissive. The light transmittance of the high refractive index layer only needs to be transparent to the wavelength in the visible light region. Specifically, the light transmittance for the entire wavelength range in the visible light region is 80% or more. It is preferable that it is 85% or more, especially 90% or more.
The light transmittance can be measured by, for example, an ultraviolet-visible light spectrophotometer UV-3600 manufactured by Shimadzu Corporation.

  The type of the high refractive index layer is not particularly limited as long as it satisfies the above refractive index and has optical transparency, and is appropriately selected according to the use of the optical element of the present invention. For example, as a material, a metal oxide layer, a metal nitride layer, a metal oxynitride layer, an organic polymer layer, or the like can be used for the high refractive index layer. Further, when exemplified by function, a transparent electrode layer or the like can be used for the high refractive index layer. Among them, the high refractive index layer is preferably a transparent electrode layer. Although it is known that light loss occurs due to the difference in refractive index at the interface between the transparent substrate and the transparent electrode layer, the light extraction efficiency can be improved by adopting the configuration of the present invention. is there.

  The material for forming the high refractive index layer is not particularly limited as long as it satisfies the above refractive index and has optical transparency, and may be appropriately selected according to the use of the optical element of the present invention. Yes, both inorganic and organic materials can be used. For example, when the high refractive index layer is a transparent electrode layer, a conductive material is used. Specifically, inorganic materials such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide, and indium oxide are used. Examples thereof include conductive polymers such as oxide, polythiophene, polyaniline, polyacetylene, polyalkylthiophene derivatives, and polysilane derivatives.

  The thickness of the high refractive index layer is appropriately selected depending on the type and material of the high refractive index layer and the use of the optical element. For example, when the high refractive index layer is a transparent electrode layer, the thickness of the high refractive index layer can be the thickness of a general transparent electrode.

The method for forming the high refractive index layer is appropriately selected according to the type and material of the high refractive index layer, and both dry processes such as vapor deposition and wet processes such as coating and printing are used. be able to.
In particular, when the high refractive index layer is a transparent electrode layer and the nanostructure 3 is laminated on the transparent substrate 2 as illustrated in FIG. In order to suppress the short circuit, it is preferable that the surface of the high refractive index layer is flattened. In particular, when the optical element of the present invention is applied to a light emitting element in which a thin organic layer is formed on a high refractive index layer, a short circuit between the electrodes due to the unevenness of the nanostructure is likely to occur. The surface of the refractive index layer is preferably flattened. For example, in the case of a dry process, the surface can be flattened by performing a flattening process such as polishing after the formation of the high refractive index layer. In the case of the wet process, although depending on the size of the nanostructure, a high refractive index layer having a flat surface can be obtained due to the leveling effect.

4). Applications The optical element of the present invention functions as a diffraction grating, and is used in, for example, organic EL elements, light-emitting diodes, plasma displays, solar cells such as organic thin-film solar cells and dye-sensitized solar cells, and liquid crystal display elements. be able to. Among these, the optical element of the present invention is preferably used for light-emitting elements such as organic EL elements, light-emitting diodes, and plasma displays. In particular, it is suitable for an organic EL element.

B. Light-Emitting Element The light-emitting element of the present invention has the above-described optical element.
Since the light-emitting element of the present invention has the above-described optical element, it is possible to improve the light extraction efficiency.
Hereinafter, each structure of the light emitting element of the present invention will be described.

1. Optical Element The high refractive index layer of the optical element used in the light emitting element of the present invention is preferably a transparent electrode layer. In light-emitting elements, it is known that light loss occurs due to the difference in refractive index at the interface between the transparent substrate and the transparent electrode layer. However, by adopting the configuration of the present invention, it is possible to improve the light extraction efficiency. is there.

  In the optical element, the width and thickness of the island portion constituting the nanostructure are adjusted in accordance with the wavelength of the light transmitted through the optical element, that is, the emission wavelength of the light emitting element. Furthermore, the distance between the island parts constituting the nanostructure, the period, the reflectance of the metal constituting the nanostructure, the wavelength dispersion of the reflectance, and the type are the wavelengths of light transmitted through the optical element, that is, the light emission of the light emitting element It is preferable to adjust according to the wavelength. In the case where the light emitting element has a monochromatic light emitting layer, the width, thickness, and the like of the island portion constituting the nanostructure are adjusted in accordance with the light emission wavelength of the light emitting layer. In addition, when a plurality of light emitting layers are arranged in the light emitting element, the width, thickness, and the like of the island portion constituting the nanostructure are adjusted according to the light emission wavelength of each light emitting layer. In this case, the width and thickness of the island portion constituting the nanostructure are adjusted according to the wavelength range including the emission wavelength of each light emitting layer, and the width and thickness of the island portion are the same throughout the nanostructure. The width, thickness, etc. of the island part constituting the nanostructure is adjusted according to the emission wavelength of each light emitting layer, and the width, thickness, interval, etc. of the island part constituting the nanostructure according to each light emitting layer, Any of the periods or the like may be different.

  The optical element has been described in detail in the above section “A. Optical element”, and a description thereof will be omitted here.

2. Light emitting element As a light emitting element of this invention, an organic EL element, a light emitting diode, a plasma display etc. are mentioned, for example.
The configuration of the light-emitting element of the present invention is appropriately selected according to the type of the light-emitting element, and can be a general configuration.

C. Organic EL Element The organic EL element of the present invention is formed on the above-described optical element, the transparent electrode layer of the optical element, an organic EL layer including a light emitting layer, and a counter electrode layer formed on the organic EL layer. It is characterized by having.

FIG. 6 is a schematic cross-sectional view showing an example of the organic EL element of the present invention.
An organic EL element 10 illustrated in FIG. 6 is formed on the optical element 1, the transparent electrode layer 11 of the optical element 1, an organic EL layer 12 including at least a light emitting layer, and a counter formed on the organic EL layer 12. And an electrode layer 13. The optical element 1 has a transparent substrate 2 having an island-shaped recess on the surface, an island-shaped nanostructure 3 containing metal embedded in the recess of the transparent substrate 2, and a nanostructure 3 embedded in the recess. The high refractive index layer 4 is formed on the transparent substrate 2 and has a higher refractive index than the transparent substrate 2. The high refractive index layer 4 is a transparent electrode layer 11. The nanostructure 3 is a structure in which island portions 3a having a width and thickness on the order of nanometers are regularly arranged, and functions as a diffraction grating. The width and thickness of the island portion 3 a constituting the nanostructure 3 are adjusted according to the wavelength of the light emission L from the light emitting layer constituting the organic EL layer 12.

Since the organic EL element of the present invention has the optical element described above, it is possible to improve the light extraction efficiency.
Hereinafter, each structure of the organic EL element of this invention is demonstrated.

1. Optical Element In the optical element used for the organic EL element of the present invention, the high refractive index layer is a transparent electrode layer. That is, the optical element is used as a substrate for an organic EL element.
The optical elements are described in detail in the above-mentioned sections “A. Optical elements” and “B. Light emitting elements 1. Optical elements”, and thus the description thereof is omitted here.

2. Organic EL Layer The organic EL layer in the present invention is formed on the transparent electrode layer of the optical element and includes at least a light emitting layer.
Examples of the layer constituting the organic EL layer include a hole injection layer, a hole transport layer, an electron injection layer, and an electron transport layer in addition to the light emitting layer.
Hereinafter, each structure in the organic EL layer will be described.

(1) Light-Emitting Layer The light-emitting layer used in the present invention may be a monochromatic light-emitting layer or a multi-colored light-emitting layer, and is appropriately selected according to the use of the organic EL device of the present invention. . In the case of a monochromatic light-emitting layer, it is easy to adjust the width, thickness, and the like of the island portion constituting the nanostructure in the optical element.

  The light emitting material used for the light emitting layer may be any material that emits fluorescence or phosphorescence, and examples thereof include dye materials, metal complex materials, and polymer materials.

  Examples of dye-based materials include cyclopentadiene derivatives, tetraphenylbutadiene derivatives, triphenylamine derivatives, oxadiazole derivatives, pyrazoloquinoline derivatives, distyrylbenzene derivatives, distyrylarylene derivatives, silole derivatives, thiophene ring compounds, pyridine Examples thereof include a ring compound, a perinone derivative, a perylene derivative, an oligothiophene derivative, a coumarin derivative, an oxadiazole dimer, and a pyrazoline dimer.

  Examples of the metal complex material include an aluminum quinolinol complex, a benzoquinolinol beryllium complex, a benzoxazole zinc complex, a benzothiazole zinc complex, an azomethyl zinc complex, a porphyrin zinc complex, a europium complex, or a central metal such as Al, Zn, Be, etc. Alternatively, a metal complex having a rare earth metal such as Tb, Eu, or Dy and having a oxadiazole, thiadiazole, phenylpyridine, phenylbenzimidazole, quinoline structure, or the like as a ligand can be given. Specifically, tris (8-quinolinolato) aluminum complex (Alq3) can be used.

  Examples of the polymer material include polyparaphenylene vinylene derivatives, polythiophene derivatives, polyparaphenylene derivatives, polysilane derivatives, polyacetylene derivatives, polyvinylcarbazole, polyfluorenone derivatives, polyfluorene derivatives, polyquinoxaline derivatives, polydialkylfluorene derivatives, and Examples thereof include copolymers thereof. Moreover, what polymerized said pigment-type material and metal complex-type material as a polymeric material can also be used.

  As the phosphorescent material, for example, an iridium complex, a platinum complex, or a metal complex having a heavy metal having a large spin-orbit interaction such as Ru, Rh, Pd, Os, Ir, Pt, or Au as a central metal is used. Can do. Specific examples include iridium complexes having platinum pyridine, thienyl pyridine and the like as ligands, platinum porphyrin derivatives, and the like.

  These luminescent materials may be used alone or in combination of two or more.

  Further, a dopant that emits fluorescence or phosphorescence may be added to the light emitting material for the purpose of improving the light emission efficiency and changing the light emission wavelength. Examples of such dopants include perylene derivatives, coumarin derivatives, rubrene derivatives, quinacridone derivatives, squalium derivatives, porphyrin derivatives, styryl dyes, tetracene derivatives, pyrazoline derivatives, decacyclene, phenoxazone, quinoxaline derivatives, carbazole derivatives, and fluorene derivatives. Can be mentioned.

  The thickness of the light emitting layer is not particularly limited as long as it can provide a function of emitting light by providing a recombination field of electrons and holes, and may be, for example, about 10 nm to 500 nm. it can.

  The method for forming the light emitting layer may be a wet process in which a light emitting layer forming coating solution in which the above light emitting material or the like is dissolved or dispersed in a solvent may be applied, or may be a dry process such as a vacuum deposition method. Good. Among these, a wet process is preferable from the viewpoint of efficiency and cost.

  Examples of the application method of the light emitting layer forming coating liquid include an inkjet method, a spin coating method, a casting method, a dipping method, a bar coating method, a blade coating method, a roll coating method, a spray coating method, a gravure printing method, and screen printing. Method, flexographic printing method, offset printing method and the like.

(2) Hole Injecting and Transporting Layer In the present invention, a hole injecting and transporting layer may be formed between the light emitting layer and the anode.
The hole injection transport layer may be a hole injection layer having a hole injection function, or a hole transport layer having a hole transport function, and the hole injection layer and the hole transport layer are laminated. And may have both a hole injection function and a hole transport function.

  The material used for the hole injecting and transporting layer is not particularly limited as long as it is a material that can stabilize injection and transportation of holes to the light emitting layer, and is exemplified in the light emitting material of the light emitting layer. In addition to compounds, phenylamine, starburst amine, phthalocyanine, vanadium oxide, molybdenum oxide, ruthenium oxide, aluminum oxide, titanium oxide and other oxides, amorphous carbon, polyaniline, polythiophene, polyphenylene vinylene and their derivatives The conductive polymer can be used. Specifically, bis (N- (1-naphthyl) -N-phenyl) benzidine (α-NPD), 4,4,4-tris (3-methylphenylphenylamino) triphenylamine (MTDATA), poly-3 , 4 ethylenedioxythiophene-polystyrene sulfonic acid (PEDOT-PSS), polyvinylcarbazole and the like.

  The thickness of the hole injecting and transporting layer is not particularly limited as long as the hole injecting function and the hole transporting function are sufficiently exhibited. Specifically, the thickness is in the range of 0.5 nm to 1000 nm, particularly 10 nm to It is preferable to be in the range of 500 nm.

  The formation method of the hole injection transport layer may be a wet process in which a coating liquid for forming a hole injection transport layer in which the above-described materials or the like are dissolved or dispersed in a solvent may be applied. It may be a process and is appropriately selected according to the type of material.

(3) Electron Injecting and Transporting Layer In the present invention, an electron injecting and transporting layer may be formed between the light emitting layer and the cathode.
The electron injection / transport layer may be an electron injection layer having an electron injection function, may be an electron transport layer having an electron transport function, or may be a laminate of an electron injection layer and an electron transport layer. It may have both an electron injection function and an electron transport function.

  The material used for the electron injection layer is not particularly limited as long as it can stabilize the injection of electrons into the light emitting layer. In addition to the compounds exemplified as the light emitting material for the light emitting layer, aluminum may be used. Alkali metals such as lithium alloys, strontium, calcium, lithium, cesium, lithium fluoride, magnesium fluoride, strontium fluoride, calcium fluoride, barium fluoride, cesium fluoride, magnesium oxide, strontium oxide, sodium polystyrene sulfonate, and Alkaline earth metal metals, alloys, compounds, organic complexes, and the like can be used.

  Alternatively, a metal doped layer in which an alkali metal or an alkaline earth metal is doped on an electron transporting organic material may be formed and used as an electron injection layer. Examples of the electron-transporting organic material include bathocuproine, bathophenanthroline, and phenanthroline derivatives. Examples of the metal to be doped include Li, Cs, Ba, and Sr.

  The material used for the electron transport layer is not particularly limited as long as it can transport electrons injected from the cathode to the light emitting layer. For example, bathocuproin, bathophenanthroline, phenanthroline derivative, triazole derivative Oxadiazole derivatives, tris (8-quinolinolato) aluminum complex (Alq3) derivatives, and the like.

  The thickness of the electron injection / transport layer is not particularly limited as long as the electron injection function and the electron transport function are sufficiently exhibited.

  The method for forming the electron injecting and transporting layer may be a wet process in which a coating liquid for forming an electron injecting and transporting layer in which the above-described materials or the like are dissolved or dispersed in a solvent may be applied, or by a dry process such as a vacuum evaporation method. There may be, and it chooses suitably according to the kind etc. of material.

3. Counter electrode layer The counter electrode layer in the present invention is formed on the organic EL layer.

  The counter electrode layer may or may not have light transparency. However, in the present invention, light is extracted from the transparent electrode layer side, and therefore it is normally assumed not to have light transparency. .

  The counter electrode layer may be either an anode or a cathode.

The anode preferably has a low resistance, and a metal material that is a conductive material is generally used, but an organic compound or an inorganic compound may be used.
For the anode, a conductive material having a large work function is preferably used so that holes can be easily injected. For example, metals such as Au, Ta, W, Pt, Ni, Pd, Cr, Cu, Mo, alkali metals, alkaline earth metals; oxides of these metals; Al alloys such as AlLi, AlCa, AlMg, MgAg, etc. Mg alloys, Ni alloys, Cr alloys, alkali metal alloys, alkaline earth metal alloys, etc .; inorganic oxides such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide, indium oxide; Examples thereof include conductive polymers such as metal-doped polythiophene, polyaniline, polyacetylene, polyalkylthiophene derivatives, and polysilane derivatives; α-Si, α-SiC; and the like. These conductive materials may be used alone or in combination of two or more. When two or more types are used, layers made of each material may be stacked.

The cathode preferably has a low resistance, and a metal material that is a conductive material is generally used, but an organic compound or an inorganic compound may be used.
For the cathode, it is preferable to use a conductive material having a low work function so that electrons can be easily injected. Examples thereof include magnesium alloys such as MgAg, aluminum alloys such as AlLi, AlCa, and AlMg, and alloys of alkali metals and alkaline earth metals such as Li, Cs, Ba, Sr, and Ca.

  As a method for forming the counter electrode layer, a general electrode forming method can be used. For example, a vacuum deposition method, a sputtering method, an EB deposition method, a PVD method such as an ion plating method, a CVD method, or the like can be given. be able to.

4). Use The organic EL element of this invention can be used as a display apparatus, an illuminating device, a light source, etc. Among these, a lighting device is preferable. An illumination device using an organic EL element emits light in a certain area, and the organic EL element of the present invention capable of improving the light extraction efficiency is preferably used.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be specifically described using examples and comparative examples.

[Example 1]
1. Production of Optical Element First, a structure in which a Cr layer having a thickness of 0.11 μm was formed on a synthetic quartz substrate having a thickness of 6.35 mm was prepared. Next, a photoresist layer was formed on the Cr layer, and a resist pattern was formed through predetermined pattern exposure and development. Next, a Cr layer is etched using the resist pattern, followed by dry etching of the quartz substrate, and the resist pattern is dissolved and removed. A concave portion in which square columnar concave portions having a width of 500 nm and a depth of 300 nm are arranged at a pitch of 1000 nm. The convex part corresponding to was formed. Thereafter, etching was performed with an acid to remove the Cr layer, and further a hydrofluoric acid treatment was performed to produce a mold for molding.

Next, a molding resin composition (refractive index: about 1.5) having the following composition is dropped on a glass substrate (refractive index: about 1.5), and an alkali-free glass having a thickness of 0.7 mm is subjected to anchor treatment. (Refractive index: about 1.5) was superposed such that the treated surface side was the mold side. Next, the molding resin composition between the substrate and the molding die was cured by irradiating with ultraviolet rays from the molding die side using a high pressure mercury lamp under the conditions of a wavelength of 365 nm and an irradiation amount of 170 mJ / cm ² . Thereafter, the molding die is peeled to form a diffraction grating pattern in which square columnar concave portions having a width of 500 nm and a depth of 300 nm are arranged at a pitch of 1000 nm, and have a base portion and an uneven structure as illustrated in FIG. A transparent substrate was obtained.

<Resin composition for molding>
・ Urethane acrylate (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., GOSELAC UV-7500B): 35 parts by weight ・ 1,6-hexanediol acrylate (manufactured by Nippon Shokubai Co., Ltd.): 35 parts by weight ・ Pentaerythritol triacrylate (Toagosei Co., Ltd.) (Manufactured by Co., Ltd.): 10 parts by weight • vinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd.): 15 parts by weight • 1-hydroxycyclohexyl phenyl ketone (manufactured by Ciba Specialty Chemicals Co., Ltd., Irgacure 184): 2 parts by weight Benzophenone (manufactured by Nacalai Tesque): 2 parts by weight Alcohol-modified silicone oil (GE Toshiba Silicone, TSF4570): 1 part by weight

  Next, an Ag nanoparticle-containing coating solution was applied onto the transparent substrate by a blade coating method and embedded in the concave portions of the diffraction grating pattern to form nanostructures having a width of 500 nm, a thickness of 300 nm, and a period of 1000 nm. In addition, the width | variety, thickness, and period of a nanostructure were determined by the simulation using the FDTD method according to the light emission wavelength of the below-mentioned organic EL element.

2. Production of Organic EL Element An ITO thin film (refractive index: about 1.7) was formed on the optical element by a sputtering method to form an anode having a thickness of 200 nm. Thereafter, in a vacuum of 1 × 10 ⁻⁴ Pa, bis (N- (1-naphthyl) -N-phenyl) benzidine (α-NPD) was formed on the anode by resistance heating vapor deposition, and the thickness: A 150 nm hole injection transport layer was formed. Subsequently, in a vacuum of 1 × 10 ⁻⁴ Pa, a film of tris (8-quinolinolato) aluminum complex (Alq3) was formed on the hole injecting and transporting layer by a resistance heating vapor deposition method, and a light emitting layer having a thickness of 60 nm A cum / electron transport layer was formed. Subsequently, in a vacuum of 1 × 10 ⁻⁴ Pa, LiF was deposited on the light emitting layer / electron transport layer by resistance heating vapor deposition to form an electron injection layer having a thickness of 2 nm. Subsequently, in a vacuum of 1 × 10 ⁻⁴ Pa, Al was formed on the electron injection layer by resistance heating vapor deposition to form a cathode having a thickness of 300 nm.

The substrate formed up to the cathode is sealed with an alkali-free glass in a glove box having a low oxygen concentration of 1.0 ppm or less and a low humidity of water vapor concentration of 0.1 ppm or less. An element was obtained.
The maximum light emission wavelength of this organic EL element was 520 nm.

[Comparative Example 1]
An organic EL element was produced in the same manner as in Example 1 except that a glass substrate was used instead of the optical element.

[Comparative Example 2]
An organic EL device was produced in the same manner as in Example 1 except that a hollow silica body (refractive index: 1.35) -containing coating solution was used instead of the Ag nanoparticle-containing coating solution.
The nanostructure was formed by applying a hollow silica body-containing coating solution on a transparent substrate by a spin coating method and embedding it in the concave portion of the diffraction grating pattern.

[Evaluation]
Front luminance was measured in a state where a voltage of about 4.5 V was applied to the organic EL elements of Example 1 and Comparative Examples 1 and 2 to emit light. Topcon luminance meter BM-9 was used to measure the front luminance. Table 1 shows the front luminance of the organic EL elements of Example 1 and Comparative Example 2 when the front luminance of the organic EL element having no diffraction grating of Comparative Example 1 is 1. In the organic EL element of Example 1, the diffraction effect was increased and the light extraction effect was improved as compared with the organic EL element of Comparative Example 2.

DESCRIPTION OF SYMBOLS 1 ... Optical element 2 ... Transparent substrate 3 ... Nanostructure 3a ... Island part 4 ... High refractive index layer 10 ... Organic EL element 11 ... Transparent electrode layer 12 ... Organic EL layer 13 ... Counter electrode layer L ... Light d ... Island part Interval p… Island portion period t… Island portion thickness w1, w2… Island portion width

Claims (5)

A transparent substrate;
A nanostructure formed in an island shape on the transparent substrate and containing a metal;
An optical element comprising: a high refractive index layer formed on the transparent substrate so as to cover the nanostructure and having a refractive index higher than that of the transparent substrate.   2. The optical element according to claim 1, wherein the island portion constituting the nanostructure has a width in a range of 100 nm to 1000 nm and a thickness in a range of 100 nm to 1000 nm.   The optical element according to claim 1, wherein the high refractive index layer is a transparent electrode layer.   A light emitting element comprising the optical element according to claim 1. An optical element according to claim 3;
An organic electroluminescence layer formed on the transparent electrode layer of the optical element and including a light emitting layer;
An organic electroluminescence element comprising: a counter electrode layer formed on the organic electroluminescence layer.

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