JP7004613B2 - Organic electroluminescence element - Google Patents

Description

The present invention relates to an organic electroluminescence device (hereinafter, also referred to as "organic EL device").

It has been conventionally known that when metal particles are miniaturized to nano size, they exhibit functions that were not seen in the bulk state, and among them, "localized plasmon resonance" is expected to be applied. .. Plasmon is a coarse and dense wave of free electrons generated by the collective vibration of free electrons in a metal nanostructure.

In recent years, the technical field dealing with the above plasmons has attracted a great deal of attention and is being actively researched as "plasmonics". Such research is a light emitting element utilizing the localized plasmon resonance phenomenon of metal nanoparticles. Including those for the purpose of improving the light emission efficiency of.

For example, Patent Document 1 discloses a technique for enhancing fluorescence by utilizing a localized plasmon resonance phenomenon and a photoexcited light emitting element using the technique. Patent Document 2 discloses an organic EL device utilizing plasmon resonance of a metal-based particle aggregate. Non-Patent Document 1 discloses a study on localized plasmon resonance by silver nanoparticles and a photoexcited light emitting element having a monomolecular film whose light emission is enhanced by utilizing localized plasmon resonance as a light emitting layer.

JP-A-2007-139540 Japanese Unexamined Patent Publication No. 2013-179017

T. Fukuura and M. Kawasaki, "Long Range Enhancement of Molecular Fluorescence by Closely Packed Submicro-scale Ag Islands", e-Journal of Surface Science and Nanotechnology, 2009, 7, 653

However, although the organic EL element described in Patent Document 2 exhibits higher luminance efficiency and luminance than the organic EL element having no metal-based particle aggregate, there is room for further improvement.
Therefore, an object of the present invention is to provide an organic EL element capable of exhibiting good luminance efficiency and luminance.

［式中、
Ｍは、前記カソード層と前記アノード層との間の光学的共振器長（ｎｍ）を表す。
ｍは、任意の自然数を表す。
λは、有機エレクトロルミネッセンス素子の発光スペクトルの最大ピークにおける極大波長（ｎｍ）を表す。］
［２］ 前記カソード層、前記発光層、前記アノード層及び前記金属系粒子集合体層をこの順に含む、［１］に記載の有機エレクトロルミネッセンス素子。
［３］ 前記カソード層、前記発光層、前記アノード層、前記金属系粒子集合体層及び基板をこの順に含む、［１］又は［２］に記載の有機エレクトロルミネッセンス素子。
［４］ 前記アノード層と前記金属系粒子集合体層との間に絶縁層をさらに含む、［２］又は［３］に記載の有機エレクトロルミネッセンス素子。
［５］ 前記金属系粒子が、紫外～可視光領域においてプラズモン共鳴可能な金属系材料で構成されている、［１］～［４］のいずれかに記載の有機エレクトロルミネッセンス素子。
［６］ 前記発光層の厚みが１０ｎｍ以上である、［１］～［５］のいずれかに記載の有機エレクトロルミネッセンス素子。
［７］ 前記アスペクト比が１を超える、［１］～［６］のいずれかに記載の有機エレクトロルミネッセンス素子。 The present invention provides an organic EL element and a method for enhancing light emission of the organic EL element shown below.
[1] An organic electroluminescence element including a basic organic electroluminescence element and a metal-based particle aggregate layer attached to the basic organic electroluminescence element.
The metal-based particle aggregate layer is formed by arranging 30 or more metal-based particles two-dimensionally apart from each other, and the average particle size of the metal-based particles is within the range of 200 nm or more and 1600 nm or less, and the average. The height is in the range of 55 nm or more and 500 nm or less, the aspect ratio defined by the ratio of the average particle size to the average height is in the range of 1 or more and 8 or less, and the average distance between adjacent metal particles. Is in the range of 1 nm or more and 150 nm or less,
The basic organic electroluminescence device includes a cathode layer, a light emitting layer containing an organic light emitting material, and an anode layer in this order.
The basic organic electroluminescence element has a ratio A / B of light emission intensity A from the cathode layer side and light emission intensity B from the anode layer side of 0.2 or more.
An organic electroluminescence element in which the optical cavity length M (nm) between the cathode layer and the anode layer satisfies the following formula (1) in any natural number m.

[During the ceremony,
M represents the optical cavity length (nm) between the cathode layer and the anode layer.
m represents an arbitrary natural number.
λ represents the maximum wavelength (nm) at the maximum peak of the emission spectrum of the organic electroluminescence device. ]
[2] The organic electroluminescence element according to [1], which comprises the cathode layer, the light emitting layer, the anode layer, and the metal-based particle aggregate layer in this order.
[3] The organic electroluminescence element according to [1] or [2], which comprises the cathode layer, the light emitting layer, the anode layer, the metal-based particle aggregate layer, and the substrate in this order.
[4] The organic electroluminescence device according to [2] or [3], further comprising an insulating layer between the anode layer and the metallic particle aggregate layer.
[5] The organic electroluminescence element according to any one of [1] to [4], wherein the metal particles are made of a metal material capable of plasmon resonance in the ultraviolet to visible light region.
[6] The organic electroluminescence device according to any one of [1] to [5], wherein the light emitting layer has a thickness of 10 nm or more.
[7] The organic electroluminescence device according to any one of [1] to [6], wherein the aspect ratio exceeds 1.

It is possible to provide an organic EL element capable of exhibiting good luminance efficiency and luminance.
The organic EL element according to the present invention can be suitably applied to a display (image display device) or a lighting device.

It is sectional drawing which shows typically the example of the organic EL element which concerns on this invention. It is sectional drawing which shows typically another example of the organic EL element which concerns on this invention. 6 is an SEM image (10000 times and 50,000 times scale) when the metal-based particle aggregate layer in the laminate obtained in Experimental Example 1 is viewed from directly above. It is an AFM image of the metal-based particle aggregate layer in the laminated body obtained in Experimental Example 1. 6 is an absorption spectrum of the laminate obtained in Experimental Example 1, Experimental Example 2 and Experimental Example 3.

<Organic EL element>
The organic EL element according to the present invention includes a basic organic electroluminescence element and a metal-based particle aggregate layer attached to the basic organic electroluminescence element.
The basic organic electroluminescence device includes a cathode layer, a light emitting layer containing an organic light emitting material, and an anode layer in this order.
Hereinafter, the present invention will be described in more detail with reference to embodiments.

(1) Structure of Organic EL Element FIG. 1 is a cross-sectional view schematically showing an example of the organic EL element according to the present invention. The organic EL element 1 shown in FIG. 1 includes a cathode layer (cathode electrode) 10; a light emitting layer 20 containing an organic light emitting material; an anode layer (anode electrode) 30; an insulating layer 40; and a metal-based particle aggregate layer 50. Include in order. The metal-based particle aggregate layer 50 is a layer in which 30 or more metal-based particles 51 are two-dimensionally arranged apart from each other.
In the organic EL element 1, the basic organic EL element includes a cathode layer 10, a light emitting layer 20, an anode layer 30, and an insulating layer 40.
In the organic EL element 1, light is taken out from at least the cathode layer 10 side, and is usually taken out from both sides of the cathode layer 10 side and the anode layer 30 side. However, as will be described later, the intensity A of light emission from the cathode layer 10 side and the intensity B of light emission from the anode layer 30 side have a predetermined relationship.

The organic EL element according to the present invention may contain other components. For example, the organic EL element according to the present invention is arranged on the side opposite to the insulating layer 40 in the metal-based particle aggregate layer 50, as in the organic EL element 2 shown in FIG. 2, and is arranged on the opposite side to the insulating layer 40. A substrate (supporting substrate) 60 for supporting the above may be included.
Further, the organic EL element according to the present invention can include one or more layers other than the light emitting layer 20 arranged between the cathode layer 10 and the anode layer 30. Specific examples of other layers will be described later.

In the basic organic electroluminescence element included in the organic EL element according to the present invention, the intensity A of light emission from the cathode layer 10 side and the intensity B of light emission from the anode layer 30 side have a predetermined relationship. Specifically, in the basic organic electroluminescence element, the ratio A / B of the emission intensity A from the cathode layer 10 side and the emission intensity B from the anode layer 30 side is usually 0.2 or more, preferably 0. It is .22 or more, more preferably 0.23 or more, still more preferably 0.24 or more.

The position of the metal-based particle aggregate layer 50 in the organic EL element is such that the light emission from the cathode layer 10 side is absorbed by the metal-based particle aggregate layer 50 from the viewpoint of increasing the intensity A of the light emission from the cathode layer 10 side. It is preferable that the anode layer 30 is arranged on the opposite side of the light emitting layer 20 so that there is no such thing. In the organic EL element according to the present invention, the cathode layer 10, the light emitting layer 20, the anode layer 30, and the metal-based particle aggregate layer 50 are more preferably arranged in this order, and more preferably, the cathode layer 10, the light emitting layer 20, and the like. The anode layer 30, the insulating layer 40, and the metal-based particle aggregate layer 50 are arranged in this order. When the substrate 60 for supporting the metal particle aggregate layer 50 is included as in the organic EL element 2 shown in FIG. 2, the cathode layer 10, the light emitting layer 20, the anode layer 30, the insulating layer 40, and the metal system are included. It is preferable that the particle aggregate layer 50 and the substrate 60 are arranged in this order.
Hereinafter, each layer constituting the organic EL element will be described.

(2) Metal-based particle aggregate layer The metal-based particle aggregate layer 50 is a layer in which 30 or more metal-based particles 51 are two-dimensionally arranged apart from each other.
The metal-based particle aggregate layer 50 is a layer made of a metal-based particle aggregate having a predetermined shape, which is particularly advantageous for enhancing the light emission of the organic EL element. That is, the average particle size of the metal-based particles 51 constituting the metal-based particle aggregate layer 50 is in the range of 200 nm or more and 1600 nm or less, the average height is in the range of 55 nm or more and 500 nm or less, and the ratio of the average particle size to the average height. The aspect ratio defined in is in the range of 1 or more and 8 or less, and the average distance between adjacent metal-based particles 51 (hereinafter, also referred to as “average particle distance”) is in the range of 1 nm or more and 150 nm or less. Is.

Since the metal-based particle aggregate layer 50 having the above-mentioned predetermined structure can exhibit strong plasmon resonance, the light emission of the light emitting layer 20 can be effectively enhanced in the organic EL element including the metal-based particle aggregate layer 50, whereby the light emission of the light emitting layer 20 can be effectively enhanced. The brightness efficiency and brightness of the organic EL element can be improved.
The strength of the plasmon resonance exhibited by the metal-based particle aggregate layer 50 is not merely the sum of the localized plasmon resonances exhibited by the individual metal-based particles 51 at a specific wavelength, but is stronger than that. That is, when 30 or more metal-based particles 51 having a predetermined shape are densely arranged at a predetermined average particle distance, the individual metal-based particles 51 interact with each other to develop strong plasmon resonance. It is considered that this was expressed by the interaction between the localized plasmons of the metallic particles 51.

Generally, when the absorption spectrum of a plasmon material is measured by absorptiometry, a plasmon resonance peak (hereinafter, also referred to as "plasmon peak") is observed as a peak in the ultraviolet to visible light region, and the maximum of this plasmon peak is observed. The strength of the plasmon resonance of the plasmon material can be roughly evaluated from the magnitude of the absorbance value at the wavelength.
When the absorption spectrum of the metal-based particle aggregate layer 50 having the above-mentioned predetermined structure is measured by absorptiometry in a state where it is laminated on a glass substrate, the plasmon peak on the longest wavelength side in the ultraviolet to visible light region is obtained. The absorbance at the maximum wavelength of is 1 or more, further 1.5 or more, and further can be about 2.

The absorption spectrum of the metal-based particle aggregate layer 50 can be measured by an absorptiometry using a measurement sample formed on a glass substrate. Specifically, the absorption spectrum is on the back surface side of the glass substrate on which the metal-based particle aggregate layer 50 is laminated (the side opposite to the metal-based particle aggregate layer 50), and is ultraviolet from the direction perpendicular to the substrate surface. -The intensity I of the transmitted light in all directions transmitted to the metal-based particle aggregate layer 50 side by irradiating the incident light in the visible light region, and the substrate of the same thickness and material as the substrate of the measurement sample, which is made of metal. The same incident light as before is irradiated from the direction perpendicular to the surface of the substrate on which the system particle aggregate layer 50 is not laminated, and the intensity I ₀ of the transmitted light in all directions transmitted from the opposite side of the incident surface is integrated. Obtained by measurement using a spherical spectrophotometer. At this time, the absorbance on the vertical axis of the absorption spectrum is calculated by the following equation:
Absorbance = -log ₁₀ (I / I ₀ )
It is represented by.
The absorption spectrum can be measured using a general spectrophotometer.

Further, in measuring the maximum wavelength of the plasmon peak on the longest wavelength side in the ultraviolet to visible light region and its absorbance, an objective lens and a spectrophotometer may be used to narrow the measurement field and measure the absorbance spectrum. ..

In the emission enhancement using the localized plasmon resonance phenomenon of the conventional plasmon material (metal nanoparticles or aggregates thereof), the action range of the localized plasmon resonance is limited to an extremely narrow range of 10 nm or less from the surface of the metal nanoparticles. There was a problem. This is because when the distance between the metal nanoparticles and the excited molecule is increased, the localized plasmon resonance does not effectively affect the organic EL element, and the light emission enhancing effect gradually weakens, and the energy of the Felster mechanism is reduced. This is because when the movement exceeds the range in which the movement is exhibited (1 nm to 10 nm), the light emission enhancing effect can hardly be obtained.
For example, Patent Document 1 discloses that a particle aggregate composed of a large number of flat metal particles independent of each other is used as a fluorescence enhancing element by utilizing a localized plasmon resonance phenomenon. Also, the distance between the metal nanoparticles effective for obtaining the effective emission enhancing effect and the excited molecule is 10 nm or less.

Therefore, the light emission enhancing effect of the organic EL element utilizing the conventional localized plasmon resonance phenomenon of the metal nanoparticles or their aggregate is not always sufficiently satisfactory due to the limitation of the range of action of the localized plasmon resonance. .. For example, when the organic EL element has a light emitting layer having a thickness of several tens of nm or more, even if the metal nanoparticles can be arranged close to or inside the light emitting layer, they are localized. Since the direct emission enhancing effect by plasmon resonance can be obtained only in a part of the light emitting layer, the effect of improving the brightness efficiency and the brightness is partial.

On the other hand, the metal-based particle aggregate layer 50 having the above-mentioned predetermined structure is a particle having a relatively large particle size in which the metal-based particle 51 constituting the metal-based particle aggregate layer 50 is generally considered to have a small emission enhancing effect. Nevertheless (see paragraphs 0010 and 0011 of Patent Document 1), strong plasmon resonance is caused by the fact that the metal-based particles 51 having a specific shape are arranged apart from each other at a specific average particle distance. In addition to showing, the range of action of the extended plasmon resonance (the range of the enhancing effect by the plasmon) is shown.
According to the metal-based particle aggregate layer 50 having the above-mentioned predetermined structure, the range of action of the plasmon resonance, which was conventionally limited to the range of the Felster distance (about 10 nm or less), is extended to, for example, about several hundred nm. can do. By extending the range of action, the entire light emitting layer 20 is enhanced even when the thickness of the light emitting layer 20 is large or the position where the metal-based particle aggregate layer 50 is arranged is far from the light emitting layer 20. This makes it possible to improve the brightness efficiency and brightness of the organic EL element.
The effect of extending the range of action of the plasmon resonance as described above is also the interaction between the localized plasmons of the metallic particles 51 caused by densely arranging 30 or more metallic particles 51 having a predetermined shape at predetermined intervals. It is considered that it was expressed by.

The metal-based particle aggregate layer 50 having the above-mentioned predetermined structure exhibits strong plasmon resonance, and further, since the range of action of the plasmon resonance is extended, for example, 10 nm or more, further 20 nm or more, and further 30 nm or more. It may have the ability to enhance the whole of the light emitting layer 20 having the thickness of.
Further, the light emitting layer 20 arranged at a position of, for example, 10 nm or more, further several tens of nm (for example, 20 nm, 30 nm, or 40 nm) or more, and further several hundred nm or more, may have the ability to enhance light emission.

Further, the metal-based particle aggregate layer 50 having the above-mentioned predetermined structure has a maximum wavelength of plasmon peak in the absorption spectrum in the ultraviolet to visible light region, depending on the average particle size of the metal-based particles 51 and the distance between the average particles. Can show a peculiar shift.
Specifically, as the average particle size of the metal-based particles 51 is increased by keeping the average particle distance constant, the maximum wavelength of the plasmon peak on the longest wavelength side in the ultraviolet to visible light region shifts to the short wavelength side (). Blue shift). Similarly, when the metal-based particles 51 are relatively large, as the average particle size of the metal-based particles 51 is kept constant and the distance between the average particles is reduced (when the metal-based particles 51 are arranged more densely), the ultraviolet rays are emitted. -The maximum wavelength of the plasmon peak on the longest wavelength side in the visible light region shifts to the short wavelength side. This peculiar phenomenon is the Mie scattering theory generally accepted for plasmon materials [according to this theory, the maximum wavelength of the plasmon peak shifts (red shift) to the long wavelength side as the particle size increases. ] Is contrary to.

The peculiar blue shift as described above is also caused by the mutual arrangement of the metal-based particles 51 having a specific shape at a distance between the localized plasmons of the metal-based particles 51 due to the arrangement of the metal-based particles 51 having a specific shape at a distance between the specific average particles. It is considered that this is due to the action.
The metal-based particle aggregate layer 50 (in a state of being laminated on a glass substrate) has an absorption spectrum in the ultraviolet to visible light region measured by an absorptiometry according to the shape of the metal-based particles 51 and the distance between average particles. The plasmon peak on the longest wavelength side may exhibit a maximum wavelength in a wavelength region of, for example, 350 nm or more and 550 nm or less or 350 nm or more and 500 nm or less. Further, the metal-based particle aggregate layer 50 is typically 30 nm or more and 500 nm or less (for example, 30 nm or more) as compared with the case where the metal-based particles 51 are arranged at a sufficiently long inter-particle distance (for example, 1 μm). A blue shift of (250 nm or less) can occur.

Such a metal-based particle aggregate layer 50 in which the maximum wavelength of the plasmon peak is blue-shifted as compared with the conventional one, for example, the metal-based particle aggregate layer 50 having the plasmon peak in the wavelength region of blue or its vicinity is It is particularly useful when ultraviolet light or purple light is used as an excitation light source and a light emitting layer 20 containing an organic light emitting material that emits light in a wavelength region of blue or its vicinity is used. That is, it is possible to effectively enhance the light emission in the wavelength region of blue or its vicinity.

Next, the specific configuration of the metal-based particle aggregate layer 50 will be described in more detail.
The metallic material constituting the metallic particles 51 is a material capable of plasmon resonance in the ultraviolet to visible light region. A material capable of plasmon resonance in the ultraviolet to visible light region means a material showing a plasmon peak appearing in the ultraviolet to visible light region in absorption spectrum measurement by absorptiometry when nanoparticles or aggregates thereof are used. do.
As the metal-based material capable of plasmon resonance in the ultraviolet to visible light region, for example, precious metals such as gold, silver, copper, platinum, and palladium; metals other than precious metals such as aluminum and tantalum; the precious metals and metals other than precious metals are selected. Alloys containing the metals to be used; metal compounds containing metals selected from the noble metals and metals other than the noble metals (metal oxides, metal salts, etc.) can be mentioned. Among them, noble metals such as gold, silver, copper, platinum, and palladium are preferable as the metal-based material capable of plasmon resonance in the ultraviolet to visible light region, and they are inexpensive and have small absorption (the imaginary part of the dielectric function is small in the visible light wavelength). ), It is more preferable to use silver.

The average particle size of the metal-based particles 51 is in the range of 200 nm or more and 1600 nm or less, and in order to effectively obtain the effect of enhancing the light emission of the light emitting layer 20, it is preferably 200 nm or more and 1200 nm or less, more preferably 250 nm or more and 500 nm or less. More preferably, it is in the range of 300 nm or more and 500 nm or less.
It is preferable that the average particle size of the metal-based particles 51 is appropriately selected according to the type of the metal-based material constituting the metal-based particles 51.

The average particle size of the metal-based particles 51 is defined as the average particle size of 10 particles randomly selected from the SEM observation image from directly above the metal-based particle aggregate layer 50 in which the metal-based particles 51 are two-dimensionally arranged. Five tangent diameters are randomly drawn in the particle image (however, any straight line having a tangent diameter can pass only inside the particle image, and one of them passes only inside the particle and is the longest straight line that can be drawn. (Assuming), the average value (hereinafter, this average value is also referred to as "tangent diameter average value") is the average value of the particle size of the selected 10 particles when the particle size of each particle is used. be. The tangent diameter is defined as a perpendicular line connecting the interval (Nikkan Kogyo Shimbun, "Particle Measurement Technology", 1994, p. 5) when the contour (projected image) of a particle is sandwiched between two parallel lines in contact with it. ..

More specifically, the method for measuring the average particle size will be described. First, the SEM observation image is measured using a scanning electron microscope "JSM-5500" manufactured by JEOL Ltd. Next, the obtained observation image is read by using the free image processing software "ImageJ" manufactured by the National Institutes of Health in the United States with a width of 1280 pixels and a height of 960 pixels. Next, using the random number generation function "RANDBETWEEN" of the spreadsheet software "Excel" manufactured by Microsoft, 10 random numbers (x ₁ , x ₂ , x ₃ , x ₄ , x ₅ , x ₆ ) from 1 to 1280. , X ₇ , x ₈ , x ₉ , x ₁₀ ), 1 to 960 to 10 random numbers (y ₁ , y ₂ , y ₃ , y ₄ , y ₅ , y ₆ , y ₇ , y ₈ , y ₉ , y ₁₀ ) are obtained respectively. 10 sets of random number combinations (x ₁ , y ₁ ), (x ₂ , y ₂ ), (x ₃ , y ₃ ), (x ₄ , y ₄ ), (x ₅ ,) from each of the obtained 10 random numbers. y ₅ ), (x ₆ , y ₆ ), (x ₇ , y ₇ ), (x ₈ , y ₈ ), (x ₉ , y ₉ ) and (x ₁₀ , y ₁₀ ) are obtained. 10 sets of coordinate points (x ₁ , y ₁ ), (x ₂ , y ₂ ), where the numerical value of the random number generated from 1 to 1280 is the x coordinate and the numerical value of the random number generated from 1 to 960 is the y coordinate. (X ₃ , y ₃ ), (x ₄ , y ₄ ), (x ₅ , y ₅ ), (x ₆ , y ₆ ), (x ₇ , y ₇ ), (x ₈ , y ₈ ), (x) ₉ , y ₉ ) and (x ₁₀ , y ₁₀ ) are obtained. Then, the above-mentioned average value of the tangential diameters is obtained for each of the total of 10 particle images including the coordinate points, and then the average particle size is obtained as the average value of the average values of the 10 tangent diameters. If at least one of the 10 coordinate points, which is a set of 10 random number combinations, is not included in the particle image, or if two or more coordinate points are included in the same particle, this random number combination is discarded. Then, random number generation is repeated until all 10 coordinate points are included in different particle images.

The average height of the metal-based particles 51 is in the range of 55 nm or more and 500 nm or less, and in order to effectively obtain the effect of enhancing the light emission of the light emitting layer 20, it is preferably 55 nm or more and 300 nm or less, more preferably 70 nm or more and 150 nm. It is within the following range. The average height of the metal-based particles 51 is 10 when 10 particles are randomly selected in the AFM observation image of the metal-based particle aggregate layer 50 and the heights of these 10 particles are measured. It is the average value of the measured values.

The aspect ratio of the metal-based particles 51 is in the range of 1 or more and 8 or less, and in order to effectively obtain the effect of enhancing the light emission of the light emitting layer 20, it is preferably 2 or more and 8 or less, more preferably 2.5 or more and 8. It is within the following range. The aspect ratio of the metal-based particles 51 is defined by the ratio of the average particle size to the average height (average particle size / average height). The metal-based particles 51 may be spherical, but in order to effectively obtain the effect of enhancing the light emission of the light emitting layer 20, it is preferable that the metal particles 51 have a flat shape having an aspect ratio of more than 1.

From the viewpoint of exciting highly effective plasmons, the metal-based particles 51 preferably have a smooth curved surface, and more preferably have a flat shape having a smooth curved surface. The metal particles 51 may have some minute irregularities (roughness), and in this sense, the metal-based particles 51 may have an irregular shape.

In view of the uniformity of the intensity of plasmon resonance in the plane of the metal-based particle aggregate layer 50, it is preferable that the size variation among the metal-based particles 51 is as small as possible. However, even if there is some variation in the particle size, it is not preferable that the distance between the large particles is large, and it is preferable that the small particles fill the space between them to facilitate the interaction between the large particles.

In the metal-based particle aggregate layer 50, the metal-based particles 51 are arranged so that the average distance (average inter-particle distance) from the adjacent metal-based particles 51 is within the range of 1 nm or more and 150 nm or less. By densely arranging the metal-based particles 51 in this way, it is possible to exert effects such as strong plasmon resonance and extension of the action range of plasmon resonance.
The average interparticle distance is preferably in the range of 1 nm or more and 100 nm or less, more preferably 1 nm or more and 50 nm or less, and further preferably 1 nm or more and 20 nm or less in order to effectively obtain the effect of enhancing the light emission of the light emitting layer 20. .. If the average interparticle distance is less than 1 nm, electron transfer based on the Dexter mechanism occurs between the particles, which is disadvantageous in terms of deactivation of localized plasmons.

The metal-based particle aggregate layer 50 in which the metal-based particles 51 are arranged apart from each other preferably does not exhibit conductivity as the layer, and specifically, the metal-based particle aggregate layer 50 has a metal-based particle aggregate layer 50. When a pair of tester probes of a multimeter [tester ("E2378A" manufactured by Hewlett-Packard Co., Ltd.)] are brought into contact with each other at a distance of 10 mm to 15 mm, the resistance value is 30 MΩ or more under the measurement conditions when the range setting is "30 MΩ". As a result, it is preferable that "overload" is displayed.
When electrons can be exchanged between some or all of the metal-based particles 51, the plasmon resonance effect tends to decrease. Therefore, it is preferable that the metal-based particles 51 are surely separated from each other and that no conductive substance is interposed between the metal-based particles 51.

The average inter-particle distance is an SEM observation image from directly above the metal-based particle aggregate layer 50 in which the metal-based particles 51 are two-dimensionally arranged, and 30 particles are randomly selected and each of the selected particles is selected. Is the average value of the interparticle distances of these 30 particles when the interparticle distances with the adjacent particles are obtained. The inter-particle distance between adjacent particles is a value obtained by measuring the distances between all adjacent particles (distances between surfaces) and averaging them.

More specifically, the method for measuring the average particle distance will be described. First, the SEM observation image is measured using a scanning electron microscope "JSM-5500" manufactured by JEOL Ltd. Next, the obtained observation image is read by using the free image processing software "ImageJ" manufactured by the National Institutes of Health in the United States with a width of 1280 pixels and a height of 960 pixels. Next, using the random number generation function "RANDBETWEEN" of the spreadsheet software "Excel" manufactured by Microsoft, 1 to 1280 to 30 random numbers (x ₁ to x ₃₀ ) and 1 to 960 to 30 random numbers (y). ₁ to y ₃₀ ) are obtained respectively. From each of the obtained 30 random numbers, 30 sets of random number combinations (x ₁ , y ₁ ) are used to obtain (x ₃₀ , y ₃₀ ). 30 sets of coordinate points (x ₁ , y ₁ ) to (x ₃₀ , y ₃₀ ) are set with the numerical value of the random number generated from 1 to 1280 as the x coordinate and the numerical value of the random number generated from 1 to 960 as the y coordinate. obtain. Then, for each of the total of 30 particle images including the coordinate points, the interparticle distance between the particle and the adjacent particle is obtained, and then the average particle is used as the average value of the interparticle distance between the 30 adjacent particles. Get the distance. If at least one of the 30 coordinate points, which is a combination of 30 random numbers, is not included in the particle image, or if two or more coordinate points are included in the same particle, this random number combination is discarded. Then, random number generation is repeated until all 30 coordinate points are included in different particle images.

The number of the metal-based particles 51 contained in the metal-based particle aggregate layer 50 is 30 or more, preferably 50 or more. By forming a particle aggregate containing 30 or more metal-based particles 51, strong plasmon resonance and extension of the action range of plasmon resonance are exhibited by the interaction between the localized plasmons of the metal-based particles 51.

In light of the general element area of the organic EL element, the number of the metal-based particles 51 contained in the metal-based particle aggregate layer 50 can be, for example, 300 or more, further 17,500 or more. The number density of the metal-based particles 51 in the metal-based particle aggregate layer 50 is preferably 7 particles / μm ² or more, and more preferably 15 particles / μm ² or more.

In the organic EL element according to the present invention, the metal-based particle aggregate layer 50 is an organic EL as a laminate in which the metal-based particle aggregate layer 50 is laminated on a substrate (support substrate) 60, as shown in FIG. It may be incorporated in the element. In the organic EL element, the substrate 60 is arranged on the side opposite to the light emitting layer 20 side of the metal-based particle aggregate layer 50. The forming substrate that can be used in the manufacturing method for forming the metal-based particle aggregate layer 50 can also be used as it is as the substrate 60.
In the above laminated body, it is preferable that the metal-based particle aggregate layer 50 is directly laminated on the substrate 60.

In the metal-based particle aggregate layer 50 included in the organic EL element according to the present invention, the metal-based particles 51 are insulated from each other, that is, they are non-conductive with respect to the adjacent metal-based particles 51. Is preferable.
When electrons can be exchanged between some or all of the metal-based particles 51, the plasmon resonance effect tends to decrease. Therefore, when the laminate in which the metal-based particle aggregate layer 50 is laminated on the substrate 60 is incorporated in the organic EL element, the substrate 60 is preferably made of a non-conductive material.
Examples of the non-conductive material constituting the substrate 60 include mica, SiO ₂ , ZrO ₂ , inorganic insulating materials such as glass, and thermoplastic resins. The surface of the substrate 60 on which the metallic particle aggregate layer 50 is formed is preferably smooth.
The substrate 60 may be a translucent substrate or an optically transparent substrate, or may be non-translucent (light-absorbing).
When light is taken out from the anode layer 30 side, the substrate 60 is preferably a translucent substrate or an optically transparent substrate. In this case, the substrate 60 preferably has a light transmittance of 80% or more, and more preferably 90% or more, with respect to the light emitted from the light emitting layer 20.
The thickness of the substrate 60 is not particularly limited, and is, for example, 10 μm or more and 10 mm or less, preferably 20 μm or more and 5 mm or less, and more preferably 30 μm or more and 1 mm or less.

In the organic EL device according to the present invention, a protective layer may be provided that covers the surface of the metal-based particles 51 or further fills the gaps between the metal-based particles 51. In order to ensure the electrical insulation between the metal particles 51, the protective layer is preferably made of an insulating material. As for the insulating material constituting the protective layer, the description below regarding the insulating material constituting the insulating layer 40 is quoted.
As shown in FIG. 1, the insulating layer 40 described later may also serve as the protective layer.

It is preferable that the maximum emission wavelength of the light emitted from the light emitting layer 20 is equal to or close to the maximum wavelength of the plasmon peak of the metal-based particle aggregate layer 50. Thereby, the enhancing effect by the plasmon resonance can be enhanced more effectively. The maximum wavelength of the plasmon peak of the metal-based particle aggregate layer 50 can be controlled by adjusting the constituent materials, the average particle size, the average height, the aspect ratio and / or the average inter-particle distance of the metal-based particles 61 constituting the plasmon peak. be.

The metal-based particle aggregate layer 50 can be produced, for example, by the following method.
[A] A bottom-up method for growing metal-based particles 51 from minute seeds on a substrate (for example, substrate 60).
[B] After coating the metal-based particles 51 having a predetermined shape with a protective layer made of an amphipathic material having a predetermined thickness, this is placed on a substrate (for example, a substrate 60) by an LB (Langmuir Bloodget) film method. How to make a film,
[C] In addition, a method of post-treating a thin film produced by vapor deposition or sputtering, resist processing, etching processing, a casting method using a dispersion liquid in which metal-based particles are dispersed, and the like.

For example, International Publication No. 2013/042449 describes, as an example of the above [a], a manufacturing method for growing metallic particles on a substrate by sputtering ring or the like. Further, for example, in International Publication No. 2014/045852, as an example of the above [c], a dispersion liquid in which metal-based particles are dispersed is applied on a substrate, and the obtained thin film is morphologically changed into a metal-based particle aggregate layer. The manufacturing method for making the particles is described. Also in the present invention, these production methods can be preferably used. Further, as another example of the above [a], the metal cation is reduced in a state where the substrate is in contact with the liquid containing the metal cation constituting the metal particle, whereby the metal particle aggregate layer is formed on the substrate. You can also list how to do it.

(3) Cathode layer and anode layer The organic EL element according to the present invention has a microcavity structure. For this reason, the cathode layer 10 and the anode layer 30 usually have reflection performance with respect to the light emitted by the light emitting layer 20.
Examples of the material constituting the cathode layer 10 include alkali metals, alkaline earth metals, transition metals and Group 13 metals of the Periodic Table, such as lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium and strontium. , Barium, aluminum, scandium, vanadium, zinc, ittrium, indium, cerium, samarium, europium, terbium, itterbium, lanthanoid elements and other metals; two or more alloys selected from the metals; 1 selected from the metals Alloys of more than one species and one selected from gold, silver, platinum, copper, palladium, manganese, titanium, cobalt, nickel and tungsten; gold, platinum, silver, copper; indium oxide, zinc oxide, tin oxide, Indium tin oxide (ITO), indium zinc oxide (IZO); organic substances such as polyaniline and its derivatives, polythiophene and its derivatives; or graphite or graphite interlayer compounds are preferred.
Examples of the alloy include magnesium-silver alloy, magnesium-indium alloy, magnesium-aluminum alloy, indium-silver alloy, lithium-aluminum alloy, lithium-magnesium alloy, lithium-indium alloy, and calcium-aluminum alloy.
The cathode layer 10 may have a multilayer structure of two or more layers made of different materials.

The thickness of the cathode layer 10 is usually 1 nm or more and 500 nm or less, preferably 5 nm or more and 60 nm or less, and more preferably 10 nm or more and 40 nm or less.

Examples of the method for forming the cathode layer 10 include a vacuum vapor deposition method, a sputtering method, an ion plating method, a plating method, a laminating method in which a metal thin film is thermocompression bonded, and a coating method. As the coating method, spin coating method, casting method, micro gravure coating method, gravure coating method, bar coating method, roll coating method, wire bar coating method, dip coating method, spray coating method, screen printing method, flexographic printing method, Examples thereof include an offset printing method and an inkjet printing method.

Examples of the material constituting the anode layer 30 include indium oxide, zinc oxide, tin oxide, indium tin oxide (ITO), indium zinc oxide (IZO), gold, platinum, silver, copper and the like. Among these, ITO, IZO, or tin oxide is preferably used. As the anode layer 30, a transparent conductive film of an organic substance such as polyaniline and its derivative, polythiophene and its derivative may be used.
The anode layer 30 may have a multilayer structure of two or more layers made of different materials.

The thickness of the anode layer 30 is, for example, 1 nm or more and 200 nm or less, preferably 5 nm or more and 50 nm or less, and more preferably 10 nm or more and 30 nm or less.
Examples of the method for forming the anode layer 30 include the same method as the method for forming the cathode layer 10.

In the organic EL element according to the present invention, the optical cavity length M (nm) between the cathode layer 10 and the anode layer 30 satisfies the above formula (1) at any natural number m. By satisfying the above equation (1), it is possible to obtain the effect of improving the luminance efficiency and the luminance due to the inclusion of the microcavity structure.
From the viewpoint of improving the luminance efficiency and the luminance, the organic EL element according to the present invention preferably has an optical cavity length M (nm) of any natural number m, preferably satisfying the formula (2), and more preferably the formula. It satisfies (3), more preferably the formula (4), even more preferably the formula (5), and particularly preferably the formula (6). In equations (2) to (6), the meanings of m and λ are the same as those in equation (1).

In the formulas (1) to (6), the optical resonator length M (nm) between the cathode layer 10 and the anode layer 30 is expressed by the following formula.

In the formula (7), M1 is the optical path length between the cathode layer 10 and the anode layer 30 (that is, the sum of the optical path lengths (nm) of each layer interposed between the cathode layer 10 and the anode layer 30). It is expressed by the equation (8). In equation (8), λ has the same meaning as in equation (1), _n (λ) represents the refractive index of each of the above layers for light having a wavelength of λ (nm), and Li represents the above. Represents the thickness (nm) of each layer.
In the formula (7), M2 is the sum of the phase shifts (nm) that occur when light is reflected at the interface of each layer interposed between the cathode layer 10 and the anode layer 30, and is represented by the formula (9). To. In equation (9), λ has the same meaning as in equation (1), _{n s} represents the real part of the refraction coefficient of the material on the light incident / reflecting side with respect to the reflecting surface, and nm represents the real part of the refraction coefficient of the material on the reflecting surface. Represents the real part of the refraction of the material on the opposite side of the light incident / reflecting side, and _km represents the imaginary part of the refraction of the material on the opposite side of the light incident / reflecting side with respect to the reflecting surface.

The optical cavity length M between the cathode layer 10 and the anode layer 30 adjusts the refractive index (material) and / or the thickness of one or more layers interposed between the cathode layer 10 and the anode layer 30. Can be controlled by.

(4) Light-emitting layer The light-emitting layer 20 is a layer having a function of emitting light and contains an organic light-emitting material. The light emitting layer 20 can be made of a material conventionally known in the art. The organic light emitting material is, for example, a conventionally known organic phosphorescent light emitting material (phosphorescent light emitting polymer or the like), an organic fluorescent light emitting material (fluorescent light emitting polymer or the like), or the like.
The organic EL element according to the present invention may have one layer or two or more light emitting layers.

More specifically, examples of the organic light emitting material include a light emitting small molecule and a light emitting polymer. Examples of the luminescent small molecule include a tris (8-quinolinolato) aluminum complex [tris (8-hydroxyquinoline) aluminum complex; Alq ₃ ], a bis (benzoquinolinolato) beryllium complex [BeBq], and the like. The light emitting layer 20 containing a light emitting small molecule can be obtained by, for example, a dry film forming method such as a spin coating method or a vapor deposition method, or a wet film forming method.

Examples of the luminescent polymer include π-conjugated polymers such as poly (9,9-dioctylfluorene-alt-benzothiadiazole), poly (p-phenylene vinylene), and polyalkylthiophene. The light emitting layer 20 containing the light emitting polymer can be obtained by a wet film forming method using a light emitting polymer-containing liquid, for example, a spin coating method.
The light emitting layer 20 may be a layer in which a light emitting small molecule or a light emitting polymer is dispersed in a matrix. As the matrix material, a transparent polymer such as a conductive polymer and a semiconductor polymer can be used.

The light emitting layer 20 may be made of a monolayer of dye molecules or have dye molecules dispersed in a matrix. The light emitting layer 20 made of a monolayer can be obtained by spin-coating a dye molecule-containing liquid and then removing the solvent. Examples of the dye molecule include Rhodamine 101, Rhodamine 110, Rhodamine 560, Rhodamine 6G, Rhodamine B, Rhodamine 640, Rhodamine 700 and the like sold by Rhodamine, and Coumarin 503 and the like sold by Rhodamine. Examples include system pigments.

The light emitting layer 20 in which the dye molecules are dispersed in the matrix can be obtained by a method of spin-coating a liquid containing the dye molecules and the matrix material and then removing the solvent. As the matrix material, a transparent polymer such as a conductive polymer and a semiconductor polymer can be used.

According to the present invention, the light emitting layer 20 has a light emitting layer of, for example, 10 nm or more because the metal-based particle aggregate layer 50 is provided with a strong plasmon resonance and an extended range of action of the plasmon resonance (range of the enhancement effect by the plasmon). Further, even when the thickness is 20 nm or more, and further, even when the thickness is 30 nm or more, it is possible to enhance the light emission of the entire light emitting layer 20 and to improve the luminance efficiency and the luminance. The upper limit of the thickness of the light emitting layer 20 is not particularly limited, but is preferably 300 nm, more preferably 200 nm.
According to the present invention, the metal-based particle aggregate layer 50 is provided with a metal-based particle aggregate layer 50 showing strong plasmon resonance and having an extended range of action of plasmon resonance (range of enhancement effect by plasmon), so that the metal-based particle aggregate of the light emitting layer 20 is provided. Even when the distance between the surface on the body layer 50 side and the surface on the light emitting layer 20 side of the metal-based particle aggregate layer 50 is, for example, 10 nm or more, further 20 nm or more, and further 30 nm or more. It is possible to enhance the light emission of the light emitting layer 20 and to improve the brightness efficiency and the brightness.

In the organic EL element according to the present invention, even if the distance between the surface of the light emitting layer 20 on the metal-based particle aggregate layer 50 side and the surface of the metal-based particle aggregate layer 50 on the light emitting layer 20 side is 20 nm or more. , Organic having the same configuration except that the photoluminescence quantum yield (number of emitted photons / number of absorbed photons) of the organic light emitting material contained in the light emitting layer 20 does not have the metal-based particle aggregate layer 50. Compared with the EL element (basic organic EL element), it can be 1.5 times or more, further 2 times or more, and further 3 times or more.
In the organic EL element according to the present invention, even if the distance between the surface of the light emitting layer 20 on the metal-based particle aggregate layer 50 side and the surface of the metal-based particle aggregate layer 50 on the light emitting layer 20 side is 20 nm or more. , Organic having the same configuration except that the photoluminescence quantum yield (number of emitted photons / number of absorbed photons) of the organic light emitting material contained in the light emitting layer 20 does not have the metal-based particle aggregate layer 50. Compared with the EL element (basic organic EL element), it can be 1.5 times or more, further 2 times or more, and further 3 times or more.
In order to obtain a photoluminescence quantum yield of 1.5 times or more, the distance is preferably 150 nm or less, more preferably 100 nm or less, and further preferably 80 nm or less.

The effect of enhancing light emission due to plasmon resonance of the metal-based particle aggregate layer 50 tends to decrease as the distance between the light-emitting layer 20 and the metal-based particle aggregate layer 50 increases. From this point of view, the distance between the surface of the light emitting layer 20 on the metal-based particle aggregate layer 50 side and the surface of the metal-based particle aggregate layer 50 on the light emitting layer 20 side is, for example, 200 nm or less, preferably 150 nm or less. , More preferably 100 nm or less.

(5) Insulating layer The insulating layer 40 that can be arranged between the anode layer 30 and the metal-based particle aggregate layer 50 is intended to provide electrical insulation between the anode layer 30 and the metal-based particle aggregate layer 50. Layer. By ensuring the electrical insulation between the anode layer 30 and the metal-based particle aggregate layer 50, a current may flow through the metal-based particle aggregate layer 50 and the effect of enhancing light emission by plasmon resonance may not be sufficiently obtained. Can be prevented.
As shown in FIG. 1, the insulating layer 40 may be formed so as to fill the gap between the metal-based particles 51, and in this case, the insulating layer 40 provides electrical insulation between the metal-based particles 51. It also plays a role in securing.

The organic EL device according to the present invention may have one or more insulating layers between the anode layer 30 and the metal-based particle aggregate layer 50. When having two or more insulating layers, they may be made of different materials from each other. For example, the insulating layer 40 is formed by laminating the above-mentioned protective layer that covers the surface of the metal-based particles 51 or further fills the gaps between the metal-based particles 51, and one or more layers made of an insulating material laminated on the protective layer. It may be a structure.

The material constituting the insulating layer 40 is not particularly limited as long as it has good insulating properties, and is, for example, spin _- on glass (SOG; for example, a material containing an organic siloxane material), SiO ₂ or Si 3N. _4. A resin (for example, a thermoplastic resin, a cured resin) or the like can be used.

The thickness of the insulating layer 40 is preferably 20 nm or more, more preferably 30 nm or more, from the viewpoint of ensuring the desired insulating property.
Further, the thickness of the insulating layer 40 is preferably set from the viewpoint of reducing the distance between the surface of the light emitting layer 20 on the metal-based particle aggregate layer 50 side and the surface of the metal-based particle aggregate layer 50 on the light emitting layer 20 side. It is 200 nm or less, more preferably 150 nm or less, still more preferably 100 nm or less, and even more preferably 80 nm or less.

(6) Other Components that the Organic EL Element may Have The organic EL element according to the present invention includes one or more layers other than the light emitting layer 20 arranged between the cathode layer 10 and the anode layer 30. Can include.
Examples of the other layer include a layer provided between the cathode layer 10 and the light emitting layer 20, and a layer provided between the anode layer 30 and the light emitting layer 20.

Examples of the layer provided between the cathode layer 10 and the light emitting layer 20 include an electron injection layer, an electron transport layer, and a hole block layer. Two or more layers may be provided for each of these layers.
The electron injection layer is a layer having a function of improving the electron injection efficiency from the cathode layer 10, and the electron transport layer has a function of improving electron injection from the electron injection layer or the electron transport layer closer to the cathode layer 10. It is a layer.

Further, when the electron injection layer or the electron transport layer has a function of blocking the transport of holes, these layers may be referred to as a hole block layer.
Having a function of blocking the transport of holes makes it possible to fabricate, for example, an element that allows only a hole current to flow, and to confirm the effect of blocking by reducing the current value.

Examples of the layer provided between the anode layer 30 and the light emitting layer 20 include a hole injection layer, a hole transport layer, an electron block layer, and the like. Two or more layers may be provided for each of these layers.
The hole injection layer is a layer having a function of improving the hole injection efficiency from the anode layer 30, and the hole transport layer is a hole from the hole injection layer or the hole transport layer closer to the anode layer 30. It is a layer having a function of improving injection.

Further, when the hole injection layer or the hole transport layer has a function of blocking the transport of electrons, these layers may be referred to as an electron block layer.
Having a function of blocking the transport of electrons makes it possible to fabricate, for example, an element that allows only an electron current to flow, and to confirm the effect of blocking by reducing the current value.

Examples of the layer structure from the anode layer 30 to the cathode layer 10 are as follows.
a) Anode layer 30 / light emitting layer 20 / cathode layer 10
b) Anode layer 30 / hole injection layer / light emitting layer 20 / cathode layer 10
c) Anode layer 30 / hole injection layer / light emitting layer 20 / electron injection layer / cathode layer 10
d) Anode layer 30 / hole injection layer / light emitting layer 20 / electron transport layer / cathode layer 10
e) Anode layer 30 / hole transport layer / light emitting layer 20 / electron injection layer / cathode layer 10
f) Anode layer 30 / hole transport layer / light emitting layer 20 / electron transport layer / electron injection layer / cathode layer 10
g) Anode layer 30 / hole injection layer / light emitting layer 20 / electron transport layer / electron injection layer / cathode layer 10
h) Anode layer 30 / hole injection layer / hole transport layer / light emitting layer 20 / cathode layer 10
i) Anode layer 30 / hole injection layer / hole transport layer / light emitting layer 20 / electron injection layer / cathode layer 10
j) Anode layer 30 / hole injection layer / hole transport layer / light emitting layer 20 / electron transport layer / cathode layer 10
k) Anode layer 30 / hole injection layer / hole transport layer / light emitting layer 20 / electron transport layer / electron injection layer / cathode layer 10
l) Anode layer 30 / light emitting layer 20 / electron injection layer / cathode layer 10
m) Anode layer 30 / light emitting layer 20 / electron transport layer / electron injection layer / cathode layer 10
The symbol "/" indicates that the layers sandwiching the symbol "/" are laminated adjacent to each other.

(7) Ratio of the intensity of light emission from the cathode layer side to the intensity of light emission from the anode layer side In the basic organic EL element included in the organic EL element according to the present invention, the intensity A of light emission from the cathode layer 10 side and The ratio A / B to the intensity B of the light emitted from the anode layer 30 side is 0.2 or more, preferably 0.22 or more, more preferably 0.23 or more, and further preferably 0.24 or more. If the metal-based particle aggregate layer 50 is arranged on the side of the anode layer 30 opposite to the light emitting layer 20 with respect to the basic organic EL element having such light emitting characteristics, the intensity of light emission from the cathode layer 10 side can be increased. can do.

The ratio A / B is usually 3 or less, typically 2 or less, and more typically 1.5 or less.
The ratio A / B can be controlled by adjusting the refractive index (material) and / or the thickness of one or more layers interposed between the cathode layer 10 and the anode layer 30.

The basic organic EL element has a partial structure in which the metal-based particle aggregate layer 50 is removed from the organic EL element having the metal-based particle aggregate layer 50, and includes at least a cathode layer 10, a light emitting layer 20, and an anode layer 30 in this order. Typically, it includes a laminated structure extending from the cathode layer 10 to the anode layer 30.
For example, in an organic EL device in which a cathode layer 10, a light emitting layer 20, an anode layer 30, an insulating layer 40, a metal-based particle aggregate layer 50, and a substrate 60 are arranged in this order, the ratio A / B of the basic organic EL element is. Ratio A of the organic EL element when an organic EL element having no metal-based particle aggregate layer 50 is produced in the same manner as the above organic EL element except that the metal-based particle aggregate layer 50 is not formed on the substrate 60. It can be calculated as / B.

［式中、
Ｍは、前記カソード層と前記アノード層との間の光学的共振器長（ｎｍ）を表す。
ｍは、任意の自然数を表す。
λは、有機エレクトロルミネッセンス素子の発光スペクトルの最大ピークにおける極大波長（ｎｍ）を表す。］ <Method of enhancing light emission of organic EL element>
As described above, the cathode layer, the light emitting layer containing the organic light emitting material, and the anode layer are included in this order, and the ratio A / B of the light emission intensity A from the cathode layer side to the light emission intensity B from the anode layer side is 0. The organic EL element is configured by arranging a metal-based particle aggregate layer having a predetermined structure with respect to the basic organic EL element having a predetermined structure of 2 or more, and the optical resonator length between the cathode layer and the anode layer. By configuring the organic EL element so that M (nm) satisfies the formula (1) in any of the natural numbers m, the light emission of the organic EL element can be enhanced, whereby the brightness efficiency of the organic EL element and the brightness efficiency of the organic EL element can be enhanced. The brightness can be improved.
That is, the present invention also relates to a method for enhancing light emission of an organic EL element shown below.
The cathode layer, the light emitting layer containing the organic light emitting material, and the anode layer are included in this order, and the ratio A / B of the light emission intensity A from the cathode layer side to the light emission intensity B from the anode layer side is 0.2. For the basic organic EL element described above,
Thirty or more metal-based particles are arranged two-dimensionally apart from each other, and the average particle size of the metal-based particles is in the range of 200 nm or more and 1600 nm or less, and the average height is in the range of 55 nm or more and 500 nm or less. The aspect ratio defined by the ratio of the average particle size to the average height is in the range of 1 or more and 8 or less, and the average distance between adjacent metal particles is in the range of 1 nm or more and 150 nm or less. A certain metal-based particle aggregate layer is attached, and the optical resonator length M (nm) between the cathode layer and the anode layer satisfies the following formula (1) at any natural number m. A method for enhancing light emission of an organic EL element, which comprises forming an organic EL element.

[During the ceremony,
M represents the optical cavity length (nm) between the cathode layer and the anode layer.
m represents an arbitrary natural number.
λ represents the maximum wavelength (nm) at the maximum peak of the emission spectrum of the organic electroluminescence device. ]

Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to these specific examples.

<Experimental Example 1: Fabrication of Metallic Particle Aggregate Layer>
Using a DC magnetron sputtering device, silver particles are grown extremely slowly on a non-alkali glass substrate (0.7 mm thick) as a support substrate under the following conditions, and metal-based particle aggregates are grown on the entire surface of the support substrate. A thin film was formed to obtain a laminate of a support substrate and a metal-based particle aggregate layer.
Gas used: Argon Chamber pressure (sputter gas pressure): 10 Pa
Distance between board and target: 100 mm
Spatter power: 4W
Average particle size growth rate (average particle size / spatter time): 0.9 nm / min Average height growth rate (= average deposition rate = average height / spatter time): 0.25 nm / min Substrate temperature: 300 ° C.
Board size and shape: 7 mm x 11 mm rectangle

FIG. 3 is an SEM image when the metal-based particle aggregate layer in the obtained laminate is viewed from directly above. FIG. 3A is a 10000x scale magnified image, and FIG. 3B is a 50000x scale magnified image. Further, FIG. 4 is an AFM image showing the metal-based particle aggregate layer in the obtained laminate. "VN-8010" manufactured by KEYENCE CORPORATION was used for AFM image photographing (the same applies hereinafter). The size of the image shown in FIG. 4 is 5 μm × 5 μm.

From the AFM image, the "average height" of the silver particles constituting the metallic particle aggregate layer of Experimental Example 1 was obtained. Further, from the SEM image, the "average particle size" and the "average particle distance" of the silver particles constituting the metal-based particle aggregate layer of Experimental Example 1 were obtained according to the above measurement method, and the obtained average particle size and the average particle size were obtained. The "aspect ratio" (average particle size / average height) was calculated from the average height. As a result, the average particle size was 335 nm, the average interparticle distance was 16.7 nm, the average height was 96.2 nm, and the aspect ratio was 3.48. Further, from the SEM image, it can be seen that the metal-based particle aggregate layer of this production example has about 1.93 × ^{109 (about 25 / μm 2 )} silver particles.
When the presence or absence of conductivity of the metallic particle aggregate layer of Experimental Example 1 was confirmed by the above-mentioned method using a tester [multimeter ("E2378A" manufactured by Hewlett-Packard Co., Ltd.)], resistance was obtained under the above-mentioned measurement conditions. As a result of the value being 30 MΩ or more, "overload" was displayed. It was confirmed that the metal-based particle aggregate layer of Experimental Example 1 did not have conductivity.

<Experimental Examples 2 and 3: Preparation of Metallic Particle Aggregate Layer>
Two types of laminates of the support substrate and the metal-based particle aggregate layer were produced in the same manner as in Experimental Example 1 except that the sputtering time of the DC magnetron sputtering method was changed (Experimental Example 2 and Experimental Example 3). The metallic particle aggregate layer of Experimental Example 2 has substantially the same particle shape, aspect ratio, and average interparticle distance as Experimental Example 1 except that the average height of the metallic particles is about 10 nm, and Experimental Example 3 has. The metal-based particle aggregate layer of No. 1 had substantially the same particle shape, aspect ratio, and average inter-particle distance as in Experimental Example 1 except that the average height of the metal-based particles was about 30 nm.

[Measurement of absorption spectrum of metallic particle aggregate layer laminated substrate]
FIG. 5 is an absorption spectrum measured by an absorptiometry of a laminate having a metal-based particle aggregate layer obtained in Experimental Example 1, Experimental Example 2 and Experimental Example 3 (the method for measuring the absorption spectrum is described above. Street). Shown in non-patent literature (K. Lance Kelly, et al., "The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment", The Journal of Physical Chemistry B, 2003, 107, 668) As described above, the flat-shaped silver particles as in Experimental Example 1 generally have a plasmon peak near about 550 nm when the average particle size is 200 nm, and around 650 nm when the average particle size is 300 nm. (Both are cases of silver particles alone).

On the other hand, the laminate of Experimental Example 1 has the longest wavelength in the ultraviolet to visible light region as shown in FIG. 5, although the average particle size of the silver particles constituting the laminate is about 300 nm (335 nm). It can be seen that the maximum wavelength of the plasmon peak on the side is around 450 nm, which is shifted to the short wavelength side.
The maximum wavelength of the plasmon peak also depends on the average particle size of the metallic particles. For example, Experimental Example 2 and Experimental Example 3 have a plasmon peak on the considerably longer wavelength side as compared with Experimental Example 1 due to the small average particle size, and their maximum wavelengths are about 510 nm and about 470 nm, respectively. be.
Further, in Experimental Example 1, the absorbance at the maximum wavelength of the plasmon peak on the longest wavelength side in the ultraviolet to visible light region is about 1.9, which is extremely higher than that of Experimental Example 2 and Experimental Example 3, which is higher than that of Experimental Example 1. It can be seen that the metal-based particle aggregate layer of the above exhibits extremely strong plasmon resonance.

<Example 1: Fabrication of organic EL element>
Immediately after preparing the laminate according to Experimental Example 1, a spin-on glass (SOG) solution was spin-coated on the metal-based particle aggregate layer, and an insulating layer having an average thickness of 30 nm was laminated. As the SOG solution, "OCD T-7 5500T" manufactured by Tokyo Ohka Kogyo Co., Ltd., which is an organic SOG material, diluted with ethanol was used.

Next, an ITO layer (thickness 20 nm) as an anode layer is laminated on the insulating layer by an ion sputtering method, and then a hole injection layer forming solution is spin-coated on the anode layer to form holes having an average thickness of 20 nm. The injection layers were laminated. As the hole injection layer forming solution, a solution obtained by diluting the trade name "Plexcore AQ 1200" manufactured by PLEXTRONICS with ethanol was used.

Then, a xylene solution containing a hole transport material was spin-coated on the hole injection layer to form a hole transport layer having a thickness of 20 nm. The hole transport material is a polymer compound synthesized according to Japanese Patent Application Laid-Open No. 2013-47315.
Next, Alq ₃ as a light emitting layer was formed on the hole transport layer by a vacuum vapor deposition method to a thickness of 30 nm.

Then, by a vacuum vapor deposition method, a NaF layer (4 nm thickness) as an electron injection layer, an Mg layer (4 nm thickness) and an Ag layer (16 nm thickness) as a cathode layer are laminated on the light emitting layer in this order, and a desiccant is attached. It was sealed with glass to obtain an organic EL element.

<Example 2: Fabrication of organic EL element>
An organic EL device was produced in the same manner as in Example 1 except that the thickness of Alq ₃ as a light emitting layer was 45 nm.

<Comparative Examples 1 to 4: Fabrication of Organic EL Element>
Organic as in Example 1 except that the thickness of Alq ₃ as a light emitting layer was 65 nm (Comparative Example 1), 80 nm (Comparative Example 2), 120 nm (Comparative Example 3), and 145 nm (Comparative Example 4), respectively. An EL element was manufactured.

<Reference Examples 1 and 2, Comparative Reference Examples 1 and 4>
An insulating layer, an anode layer, a hole injection layer, a hole transport layer, a light emitting layer, an electron injection layer and a cathode layer without forming a metal-based particle aggregate layer on a non-alkali glass substrate (0.7 mm thick). The organic EL elements of Reference Examples 1 and 2 and Comparative Reference Examples 1 to 4 having no metal-based particle aggregate layer were prepared in the same manner as in Examples 1 and 2 and Comparative Examples 1 and 4, respectively, except that the holes were formed in order. (Reference Examples 1 and 2 and Comparative Reference Examples 1 and 4 correspond to Examples 1 and 2 and Comparative Examples 1 and 4, respectively).

(Calculation of optical cavity length M)
For the organic EL devices of Examples 1 and 2 and Comparative Examples 1 to 4, the optical cavity length M between the cathode layer and the anode layer is set according to the above equations (7) to (9) based on the following numerical values. Calculated. The results are shown in Table 1.
λ: 530 nm
n (λ): 1.4 (insulating layer)
1.9 (anode layer)
1.63 (hole injection layer)
1.75 (light emitting layer)
1.4 (electron injection layer)
Li (thickness of hole injection layer, hole transport layer, light emitting layer, electron injection layer): as described above _{n s} : 1.4
nm: _0.176
km : 3.291

(Obtaining the ratio A / B of the emission intensity A from the cathode layer side and the emission intensity B from the anode layer side)
The above ratios A / B were obtained for the organic EL devices having no metal-based particle aggregate layer produced in Reference Examples 1 and 2 and Comparative Reference Examples 1 and 4, and these were used in Examples 1 and 2 and Comparative Examples 1 and 4, respectively. The ratio A / B of the basic organic EL element contained in the organic EL element of. The A / B values are shown in Table 1.
The intensity A of light emission from the cathode layer side is the maximum when the organic EL element is set in the device so that the cathode layer side faces the detector and a voltage of 0 to 12 V is swept and applied to the organic EL element. It was measured as the luminance efficiency (Cd / A) and the luminance (Cd / m ² ) when a voltage was applied, which was the maximum luminance efficiency.
For the intensity B of light emission from the anode layer side, an organic EL element having no metal-based particle aggregate layer is set in the apparatus so that the anode layer side (non-alkali glass substrate side) faces the detector, and the organic EL is set. It was measured as the maximum luminance efficiency (Cd / A) when a voltage of 0 to 12 V was swept and applied to the element and the luminance (Cd / m ² ) when a voltage was applied, which was the maximum luminance efficiency.

(Evaluation of the maximum luminance efficiency of the organic EL element and the luminance when a voltage is applied, which is the maximum luminance efficiency)
For the organic EL elements of Examples 1 and 2 and Comparative Examples 1 to 4, the brightness (maximum brightness) when a voltage is applied, which is the maximum brightness efficiency and the maximum brightness efficiency of the light emitted from the cathode layer side, is determined according to the following method. Measured and evaluated.
Using a brightness measuring device, the voltage was swept to measure the brightness (Cd / m ² ) observed in the vertical upper surface direction from the substrate light emitting surface of the organic EL element.
The current value (unit: A) when the observed brightness was 1000 Cd / m ² was measured, and the brightness was divided by the current value to obtain Cd / A @ 1000 Cd / m ² .
The results are shown in Table 1. The brightness at the time of applying a voltage, which is the maximum luminance efficiency and the maximum luminance efficiency of the organic EL elements of Examples 1 and 2, was significantly improved as compared with the organic EL elements of Comparative Examples 1 to 4.

<Example 3: Fabrication of organic EL element>
Instead of forming an Alq ₃ having a thickness of 30 nm, a xylene solution containing a light emitting material was spin-coated on the hole transport layer to form a light emitting layer having a thickness of 145 nm. An EL element was manufactured. The light emitting material is a blue fluorescent light emitting polymer material synthesized according to the method described in Japanese Patent Application Laid-Open No. 2012-216815.

<Comparative Example 5: Fabrication of Organic EL Element>
An organic EL element was formed in the same manner as in Example 3 except that an Ag continuous film having a thickness of 100 nm was formed on a non-alkali glass substrate (thickness 0.7 mm) instead of the metal-based particle aggregate layer by a vacuum vapor deposition method. Made.

<Reference example 3>
An insulating layer, an anode layer, a hole injection layer, a hole transport layer, a light emitting layer, an electron injection layer and a cathode layer without forming a metal-based particle aggregate layer on a non-alkali glass substrate (0.7 mm thick). The organic EL element of Reference Example 3 having no metal-based particle aggregate layer was produced in the same manner as in Example 3 except that the particles were formed in order.

(Calculation of optical cavity length M)
For the organic EL element of Example 3, the optical cavity length M between the cathode layer and the anode layer was calculated according to the above equations (7) to (9) based on the following numerical values. The results are shown in Table 2.
λ: 475 nm
n (λ): 1.4 (insulating layer)
1.9 (anode layer)
1.63 (hole injection layer)
1.8 (hole transport layer)
1.8 (light emitting layer)
1.4 (electron injection layer)
Li (thickness of hole injection layer, hole transport layer, light emitting layer, electron injection layer): as described above _{n s} : 1.4
nm: _0.176
km : 3.291

(Obtaining the ratio A / B of the emission intensity A from the cathode layer side and the emission intensity B from the anode layer side)
The above ratio A / B was obtained for the organic EL element having no metal-based particle aggregate layer produced in Reference Example 3, and this was used as the ratio A / B of the basic organic EL element contained in the organic EL element of Example 3. .. The A / B values are shown in Table 2. The measurement methods for A and B are the same as described above.

(Evaluation of maximum brightness, maximum brightness efficiency and external quantum efficiency (EQE) of organic EL element)
The maximum luminance, maximum luminance efficiency and external quantum efficiency (EQE) of the light emitted from the cathode layer side were measured and evaluated for the organic EL elements of Example 3 and Comparative Example 5.
The method for measuring the maximum luminance and the maximum luminance efficiency is the same as described above. For the external quantum efficiency (EQE), EQE @ 1000 Cd / m ² was obtained from the brightness, emission spectrum, applied voltage, and current amount when the observed brightness was 1000 Cd / m ² .
The results are shown in Table 2. The maximum luminance, maximum luminance efficiency, and EQE of the organic EL element of Example 3 were significantly improved as compared with the organic EL element of Comparative Example 5.

1, 2, organic EL element, 10 cathode layer, 20 light emitting layer, 30 anode layer, 40 insulating layer, 50 metal-based particle aggregate layer, 51 metal-based particles, 60 substrate.

Claims (8)

An organic electroluminescence element including a basic organic electroluminescence element and a metal-based particle aggregate layer attached to the basic organic electroluminescence element.
The metal-based particle aggregate layer is formed by arranging 30 or more metal-based particles two-dimensionally apart from each other, and the average particle size of the metal-based particles is within the range of 200 nm or more and 1600 nm or less, and the average. The height is in the range of 55 nm or more and 500 nm or less, the aspect ratio defined by the ratio of the average particle size to the average height is in the range of 1 or more and 8 or less, and the average distance between adjacent metal particles. Is in the range of 1 nm or more and 150 nm or less,
The basic organic electroluminescence device includes a cathode layer, a light emitting layer containing an organic light emitting material, and an anode layer in this order.
The basic organic electroluminescence element has a ratio A / B of light emission intensity A from the cathode layer side and light emission intensity B from the anode layer side of 0.2 or more.
An organic electroluminescence element in which the optical cavity length M (nm) between the cathode layer and the anode layer satisfies the following formula (1) in any natural number m.

[During the ceremony,
M represents the optical cavity length (nm) between the cathode layer and the anode layer.
m represents an arbitrary natural number.
λ represents the maximum wavelength (nm) at the maximum peak of the emission spectrum of the organic electroluminescence device. ] The organic electroluminescence element according to claim 1, further comprising the cathode layer, the light emitting layer, the anode layer, and the metal-based particle aggregate layer in this order. The organic electroluminescence element according to claim 1 or 2, further comprising the cathode layer, the light emitting layer, the anode layer, the metal-based particle aggregate layer, and the substrate in this order. The organic electroluminescence device according to claim 2 or 3, further comprising an insulating layer between the anode layer and the metallic particle aggregate layer. The organic electroluminescence element according to any one of claims 1 to 4, wherein the metal-based particles are made of a metal-based material capable of plasmon resonance in the ultraviolet to visible light region. The organic electroluminescence device according to any one of claims 1 to 5, wherein the light emitting layer has a thickness of 10 nm or more. The organic electroluminescence device according to any one of claims 1 to 6, wherein the aspect ratio exceeds 1. The organic electroluminescence device according to any one of claims 1 to 7, wherein the light emitting layer is arranged at a position separated from the metallic particle aggregate layer by 30 nm or more.

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