JP2006100257A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element capable of displaying an image of high luminance and high contrast and in which rainbow color due to diffraction of the reflecting light is not visible. <P>SOLUTION: This is the organic electroluminescent element which has a first electrode, a second electrode, at least one layer of organic layer containing a luminous layer between the first electrode and the second electrode, a transparent substrate, and a prism structure between the first electrode or second electrode and the transparent substrate. The prism structure is located with the apex of the prism facing the transparent electrode side, and the coefficient of variation of the pitch between apexes of the prism is 1% or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescent element (hereinafter also referred to as “organic EL element”, “light emitting element”, or “EL element”) that can emit light by converting electric energy into light.

  Organic EL elements are attracting attention as promising display elements because they can emit light with high luminance at a low voltage. However, generally, organic EL elements have lower luminous efficiency than inorganic LED elements and the like. Furthermore, there is a demand for organic EL devices with improved luminous efficiency and brightness.

  The external energy efficiency indicating the light emission efficiency of the organic EL element is represented by the product of the internal energy efficiency of the element and the light extraction efficiency (see, for example, Non-Patent Document 1). In order to improve the luminous efficiency of the organic EL element, it is necessary to improve the light extraction efficiency in addition to improving the internal energy efficiency.

  The light extraction efficiency is a ratio of light emitted from the front surface of the transparent substrate into the atmosphere with respect to light emitted from the device. In order for the light emitted from the light-emitting layer to be emitted into the atmosphere, it must pass through the interfaces of several media with different refractive indexes, but according to Snell's law of refraction, each interface has a critical angle above its critical angle. Light incident at an angle is totally reflected at the interface and guided through the layer and disappears or is emitted from the side surface of the layer, and the light emission from the front of the device is reduced accordingly. As a result, for example, when the device is applied to a display, the front luminance is lowered.

As a method for improving the reduction in front luminance, a method is known in which a diffraction grating composed of dots, grooves, and the like is formed at the interface, and light is diffracted and extracted (see, for example, Patent Document 1). In this case, in addition to insufficient improvement in frontal brightness, rainbow colors are generated due to interference of reflected light, which is not preferable when applied to a display.
Recently, an attempt to eliminate this rainbow color with random dots has been reported (see, for example, Non-Patent Document 2), and although light interference has disappeared, the degree of improvement in luminance has decreased and remains insufficient.

As a method for improving the decrease in front luminance, a method of providing a prism at the interface is also known (see, for example, Patent Document 2). In this method, since the prism has a light collecting function, the degree of improvement in front luminance is large.
Japanese Patent No. 2911183 JP 2003-86353 A “Optics Letters”, 1997, Vol. 22, No. 6, p. 396 "Preliminary Proceedings of the 51st Joint Conference on Applied Physics", 2004, 30a-ZN-13

The image passing through the prism has a problem that the contrast is lowered due to blurring, but it can be improved by reducing the distance between the light emitting layer and the prism and the distance (pitch) between the apexes of the prism.
However, if the prisms are regularly formed and the pitch thereof is reduced, the same problem as that of the diffraction grating described above, that is, the rainbow color problem due to interference of reflected light occurs. On the other hand, no method has been found that can solve the rainbow color problem without lowering the brightness improvement degree.

  The present invention has been made in view of the above problems, and it is an object of the present invention to provide an organic electroluminescent element that can display a high-brightness and high-contrast image and that does not show a rainbow color due to diffraction of reflected light.

In view of the above circumstances, the present inventors have conducted intensive research and found that the prism apex of the prism structure provided on the electrode and the transparent substrate is directed toward the transparent substrate, and the prisms are arranged randomly. The present invention has been completed by finding out that the above problems can be solved.
That is, the present invention is achieved by the following means.

<1> First electrode, second electrode, at least one organic layer including a light emitting layer between the first electrode and the second electrode, a transparent substrate provided on the light extraction side, and the first electrode Or an organic electroluminescent element having a prism structure between the second electrode and the transparent substrate, the prism structure being located with the apex of the prism facing the transparent substrate, and the apex of the prism An organic electroluminescent element having a pitch variation coefficient of 1% or more.

<2> The organic electroluminescent element as described in <1> above, wherein a coefficient of variation in pitch of the prism is 3% or more.
<3> The organic material according to <1> or <2>, wherein the first electrode is an anode, the second electrode is a cathode, and the prism structure is provided on an anode side of the first electrode. Electroluminescent device.

<4> The organic material according to <1> or <2>, wherein the first electrode is an anode, the second electrode is a cathode, and the prism structure is provided on a cathode side of the second electrode. Electroluminescent device.

<5> The organic electroluminescent element according to any one of <1> to <4>, wherein an average value of the pitch between the apexes of the prisms is 0.4 μm or more and 20 μm or less.

<6> The organic electroluminescent element according to any one of <1> to <5>, wherein the apexes of the prisms are aligned on the same plane and bonded to the transparent substrate.

  ADVANTAGE OF THE INVENTION According to this invention, an organic electroluminescent element which can display a high-intensity and high-contrast image, and cannot see the iridescent color by diffraction of reflected light can be provided.

The organic electroluminescent element of the present invention includes a first electrode, a second electrode, at least one organic layer including a light emitting layer between the first electrode and the second electrode, a transparent substrate, and the first electrode or the An organic electroluminescent element having a prism structure between a second electrode and the transparent substrate, the prism structure being positioned with the apex of the prism facing the transparent substrate, and between the apexes of the prism The variation coefficient of the pitch is 1% or more.
By configuring the organic electroluminescent element of the present invention as described above, it is possible to obtain an organic electroluminescent element that can display a high-brightness and high-contrast image and that does not cause a rainbow color problem due to diffraction of reflected light.

<Prism structure>
The prism structure of the present invention refers to a structure having a plurality of prisms, and is formed, for example, at a pitch with V-shaped grooves on the surface of a metal oxide layer.
The prism generally means a transparent body having two or more optical planes, and at least one set of surfaces is not approximately parallel.
Since the prism has a light collecting effect, it is applied to an optical member. For example, a material in which a large number of regular V-shaped grooves are formed on the entire surface of one surface of a plastic film at a pitch of several tens to several hundred microns is known as a prism sheet. However, a sheet having a wave shape and a prism having a slightly rounded apex are also used as a prism sheet, and the present invention includes such a shape.

According to the inventor's research, when the prism pitch (distance between vertices) is reduced to about 20 μm, the prism functions as a reflection type diffraction grating, and diffracts the reflected light of external light. A noticeable rainbow color is visible. Therefore, it becomes a problem particularly when an EL element having the prism is used for a display.
Here, if the prism is randomized so that the variation coefficient of the pitch of the prism is 1% or more, this rainbow color problem can be reduced, while the brightness improvement degree is equivalent to the case where the prism is not randomized. The present invention has been found and completed.
The coefficient of variation is preferably 1 to 350%, more preferably 3 to 250%, from the viewpoint of preventing contrast reduction, improving luminance, and reducing rainbow colors. The larger the coefficient of variation, the greater the effect of reducing the rainbow color, but this range is also preferred from the viewpoint of ease of prism production.
The coefficient of variation referred to here means the ratio of the standard deviation of the pitch to the average value of the pitch.

  The randomization means that prisms included in the prism structure are arranged in the prism structure so that the pitch (distance between vertices) is random, and the degree of randomness is defined as follows.

  In the present invention, the degree of randomness is defined using a coefficient of variation (= standard deviation ÷ average value). The standard deviation σ is expressed by the following equation.

Here, x _i is the prism pitch, μ is the average value of the prism pitch, and n is the total number of prism peaks −1.

Therefore, the variation coefficient q is represented by the following equation.

Here, x _i is the prism pitch, μ is the average value of the prism pitch, and n is the total number of prism peaks −1.

Hereinafter, as an example of a method for determining a random prism pitch, a case where the pitch is a uniform distribution and a case where the pitch is a normal distribution will be described, but the present invention is not limited thereto.
1. Uniform distribution (the pitch frequency is uniform between the minimum value and the maximum value)
The specific value of the random pitch is obtained by using the Excel 2000 RAND function of Microsoft Corporation. This RAND function is a function for generating a random number in the range of 0-1. With this value as R _i , x _i calculated by the following equation is adopted as the pitch value.
x _i = R _i × (P _max −P _min ) + P _min
(P _min is the minimum pitch value, P _max is the maximum pitch value)

2. Normal distribution (pitch appearance frequency is normally distributed around the average pitch μ)
1 above. Similarly to (Uniform distribution), random numbers are generated in the range of 0 to 1, and the value is R _i . Using the NORMINV function of Excel2000, the pitch Yi was determined as Yi = NORMINV (Ri, μ, σ). Where μ is the average pitch and σ is the target standard deviation.
This was repeated to obtain (number of peaks-1) Yi. If it is desired to set an upper limit and a lower limit for the pitch distribution, Yi outside the range may be ignored.

In the present invention, a prism structure is provided between the transparent substrate on the light extraction side and the electrode (first electrode or second electrode) on the light extraction side, and the apex of the prism faces the transparent substrate side. In this case, it is desirable in terms of mechanical strength that the apexes (mountains) of the prisms are aligned on the same plane and bonded to the transparent substrate.
That is, it is preferable that the prism structure is formed to be randomized so that the variation coefficient is 1% or more, and the levels of the apexes (mountains) of the prism are the same.
In addition, the average value of the prism pitch is preferably 0.4 μm or more and 20 μm or less, more preferably 1 μm or more and 15 μm or less, and particularly preferably 2 μm or more and 10 μm or less from the viewpoint of preventing a decrease in contrast and improving luminance. When the average value of the prism pitch is less than or equal to the visible light wavelength of 0.4 μm, the light condensing effect is insufficient.
These preferred combinations are the most preferred embodiments.

Hereinafter, the creation of the prism structure will be described.
The random pitch prism may be directly cut by the following method, but it is generally preferable to first make a die using Ni or the like.

First, an example of programming when machining a V-groove array having an apex angle θ, the pitch of which varies randomly from Pmin to Pmax μm will be described.
The processing of the V-groove array having the apex angle θ is preferably performed by hail processing using a diamond tool, but the concept of this processing can also be applied to other processing methods (fly cutting) and the like.
The value of the pitch Pmin depends on the accuracy of the processing machine and the material of the workpiece, but is preferably 0.1 to 10 μm, and more preferably 0.1 to 1 μm from the viewpoint of machining accuracy.
The value of Pmax is larger than Pmin, and in order to reduce the processing load, it is preferable to set the maximum value for obtaining a desired resolution to Pmax.
Further, it is necessary that V-grooves with a random pitch can be processed within the range of the resolution of the processing machine between Pmax and Pmin.
In order to avoid an unnecessarily narrow pitch, the relationship between Pmax and Pmin is preferably set to a value of 1.05 × Pmin ≦ Pmax ≦ 5 × Pmin.

Hereinafter, a method of dispersing the desired pitch width P (n) using the random number R (n) will be described.
First, as described above, the random number R (n) is generated using the calculation table software of the personal computer. Here, R (n) is given by the size of 0-1. When the following formula (1) is used, R (n) can be dispersed in a desired pitch width P (n).

P (n) = R (n) × (Pmax−Pmin) + Pmin (1)
Here, n is a numerical value determined according to the required area area.

For example, when processing an area of 300 mm in the pitch direction with Pmax = 5 μm and Pmin = 1 μm, since the average pitch is 3 μm, approximately 300 / 0.003 = 10 ⁵ V-grooves are required.

  Based on P (n), the absolute coordinate Pab (n) of the V-groove is determined.

  Pab (n) = ΣP (n) (2)

  Next, the cutting depth d is set by the equation (3).

  d = (1/2) · P (n) / tan (θ / 2) (3)

  In the case of easy-cutting materials, it is possible to perform V-groove machining with the incision value of equation (3), but in the case of electroless nickel frequently used in fine molds, the incision is divided into several degrees and processed little by little It is preferable to prevent the edge from sagging. In this case, it is preferable to reduce the cutting amount d (m) as the cutting becomes deeper. Furthermore, in order to obtain a good machined surface, it is possible to create a better shape by performing spark-out (no cutting depth) at the end.

The above method is a case where the pitch distribution is uniformly distributed from Pmin to Pmax.
In the present invention, the pitch distribution may not be uniform. For example, in the case of a normal distribution, a method for creating a desired random pitch is as described above.

  In general, the processing speed (the traveling speed of the diamond bite) is preferably high in terms of the quality of the processed surface and the processing efficiency. However, in the hail processing method in which the tool reciprocates with respect to the workpiece, since there is a limit to speeding up, about 1000 to 5000 mm / min is preferable.

  When processing is performed by the above-described method, the levels of the vertices (mountains) of the mold coincide with each other, but by setting d (m) to a constant value, it is possible to form a pattern in which the level of the valleys is constant.

  After completing the random pitch V-groove array, change the tool movement direction or the direction of the workpiece by 90 degrees, and then perform random pitch V-groove processing to form a random pitch square pyramid array (pyramid array). ) Can be created. In the present invention, such a pyramidal array can also be preferably used.

-Creation of prism structure-
The target prism structure can be made by transfer from the above mold.
That is, when a solution-like medium is poured into the mold, cured by the action of light or heat, or simply cooled, and then removed from the mold, the prism pattern is transferred. A prism structure can be prepared by including the material for forming the prism structure in the solution-like medium.

  The solution medium to be poured may be one that finally forms a prism structure, or may be an intermediate transfer medium such as a silicone elastomer. That is, the transfer may be repeated as necessary.

Hereinafter, a case of creating by transferring will be described.
When a mold with the same level of peaks is transferred an even number of times, a prism structure with the same level of peaks is formed. When a mold with the same level of valleys is transferred with an odd number of times, the level of peaks is obtained. A prism structure with the same can be obtained. In general, it is preferable that a prism structure having finally the same level of peaks is formed. Which mold is used can be selected in consideration of the ease of the manufacturing process.
However, in the case of pyramids, the odd-numbered transfer creates a female mold with a concave top, so the pyramid structure (prism structure) with the same level of peaks is transferred from the mold with the same level of peaks. It is necessary to obtain a pyramid structure (prism structure) having the same level of the peaks by transferring an odd number of times from a female mold created by transfer from the mold.

  As the apex angle of the prism is sharper, the luminance is improved more, but the contrast is also lowered. Conversely, when the angle is obtuse, the decrease in contrast is reduced, but the degree of improvement in brightness is also reduced. Therefore, the apex angle is preferably 60 to 120 degrees, more preferably 70 to 110 degrees, and still more preferably 80 to 100 degrees.

  Examples of the substance constituting the prism structure include organic polymer materials such as acrylic resin, epoxy resin, polyimide resin, and polycarbonate resin, and inorganic materials made of metal oxides. In the case of an organic polymer material, a prism structure can be easily formed because a method of hot pressing on a mold can be applied. In the case of a metal oxide, a prism structure having a large refractive index can be created.

When forming the organic EL device of the present invention, the distance from the prism-side surface of the light emitting layer to the lowest surface of the prism (the surface including the deepest V-groove) is preferably 100 μm or less, more preferably from the viewpoint of contrast. It is preferable that a prism structure as described above is prepared so as to be 50 μm or less, and the prism apex is placed on a transparent substrate to obtain a substrate with a prism structure. The prism structure can be directed to the transparent substrate by attaching the prism structure using a UV curable adhesive or the like.
An organic EL element is obtained by providing a light-transmitting anode, an organic layer including a light emitting layer, and a cathode on the substrate with the prism structure.
In addition, when used in a method known as so-called top emission, after providing an anode, an organic layer, and a light-transmitting cathode on another substrate, the above-mentioned substrate with a prism structure is attached to the prism structure. The organic EL element can be obtained by bonding the electrodes on the cathode side or installing them through a spacer.
The organic EL device thus produced has high brightness, can display a high-contrast image, and does not cause a rainbow color problem due to diffraction of reflected light.

  Examples of the transparent substrate in the organic electroluminescence device of the present invention include quartz glass, alkali-free glass, soda lime glass, and plastic film. The organic electroluminescent device may be either a fluorescent device or a phosphorescent device. Regarding other components such as an electrode and an organic layer in the electroluminescent element, for example, JP-A No. 2004-221068, JP-A No. 2004-214178, JP-A No. 2004-146067, JP-A No. 2004-103577, and JP-A No. 2004-103577 are disclosed. Those described in JP-A No. 2003-323987, JP-A No. 2002-305083, JP-A No. 2001-172284, JP-A No. 2000-186094, and the like can be similarly applied to the present invention.

  Hereinafter, although the present invention is explained using an example, the present invention is not limited to these.

Example 1
By cutting the surface of Ni with a diamond tool, eight molds -1 to 8 having a pitch shown in Table 1 were prepared.
Molds -1 to 3 are comparative pitches having a regular pitch (coefficient of variation <1%), and molds -4 to 8 are randomized with the pitches shown in Table 1 and the apex ( The level of (mountain) is the same.

  Silicone elastomer was poured onto each mold and cured, and then removed from the mold to create a prism pattern (8 types) made of silicone.

A UV curable epoxy resin was applied to glass having a thickness of 30 μm in an amount of 12 ml / m ² . However, it was set to 24 ml / m ² only for the element-3. The silicone prism pattern was pressed onto this, and UV light was irradiated from the glass substrate side to cure the resin. Next, the silicone pattern was removed to form a glass substrate with a prism.

  This prism-attached glass substrate was placed on a glass substrate having a thickness of 0.7 mm so that the prism surface faced the glass substrate and bonded together. On this, an anode (thickness 0.15 μm) of indium tin oxide (ITO, indium / tin = 95/5 molar ratio) was formed by sputtering using a DC power source. The surface resistance of this anode was 10Ω / □.

An organic compound layer was placed on the anode.
As the organic hole transport layer, N, N′-dinaphthyl-N, N′-diphenylbenzidine was provided in a thickness of 0.04 μm by vacuum deposition.
Further thereon, tris (8-hydroxyquinolino) aluminum was provided as an organic light emitting layer in a thickness of 0.06 μm by vacuum deposition.
A patterned mask is placed on the organic compound layer, magnesium: silver = 10: 1 (molar ratio) is deposited in a thickness of 0.25 μm in a deposition apparatus, and silver is further deposited by 0.3 μm to form a cathode. Was provided. Aluminum lead wires were respectively emitted from the anode and the cathode to prepare organic EL elements 1 to 8.

  On the other hand, a comparative organic EL element-9 was prepared in exactly the same manner except that no prism structure was included.

  A DC voltage of 12 V was applied to each of these elements to emit light, and the front luminance was measured. Table 1 shows the ratio of the luminance to the element-9 as the luminance improvement degree.

  In addition, a repetitive pattern of light emitting lines / non-light emitting lines having a width of 200 μm was displayed on the screen, and the visibility of the line image was observed. The results are shown in Table 1, where the image blur could not be recognized as ◯ and the image blur could be recognized as x.

Next, a circularly polarizing plate was provided on the device, and the degree of rainbow color was evaluated from various angles by the following five-point method in a state where light was emitted. The results are shown in Table 1.
The evaluation criterion is “5 points: the rainbow color is not visible. 4 points: the rainbow color is hardly visible. 3 points: the rainbow color is slightly visible. 2 points: the rainbow color is visible. 1 point: the rainbow color is visible. It is clearly visible. ” If it is 3 points or more, there is no practical problem, but 4 points or more is more preferable.

  As is apparent from Table 1, elements -1 to 3 and 9 having a coefficient of variation of less than 1% and no prism are defective in any of the above evaluation items, and the elements -4 to 4 of the present invention exhibit 1% or more. It can be seen that 8 is good in all cases, although there is variation.

(Example 2)
A die-9 was created by cutting the surface of Ni with a diamond tool. Mold-9 has an apex angle of 90 degrees and the valley levels are the same. When viewed in the valley portion, the pitch is randomized between 5 and 10 μm, and the coefficient of variation is 5% at an average pitch of 7.5 μm.

  A silicone elastomer was poured onto this, cured, and then removed from the mold to create a silicone prism pattern.

A UV curable epoxy resin was applied to an alkali-free glass having a thickness of 0.7 mm in an amount of 12 ml / m ² . The silicone prism pattern was pressed onto this, and UV light was irradiated from the glass substrate side to cure the resin. Subsequently, when the silicone pattern was removed, a pattern of minute random prisms was formed on the glass.
This was irradiated with an excimer lamp (172 nm) in the atmosphere for 10 minutes to make the surface hydrophilic.

Tainoc A-6 (manufactured by Taki Chemical Co., Ltd., titanium oxide sol) is mixed with PVA102 (Kuraray Co., Ltd., 30% by weight of titanium oxide) aqueous solution and sodium dodecylbenzenesulfonate (0.05% of coating solution). Then, this aqueous liquid was applied on the above-mentioned micro random prism (as titanium oxide, an amount of 20 g / m ² ) and dried.
The obtained coated material was heat-treated at 600 ° C. for 1 hour using an electric furnace.
By this heat treatment, the epoxy resin and PVA disappeared, and a structure placed on an alkali-free glass substrate with the apex of the random prism made of titanium oxide facing on the glass was formed.

  On this, an anode of indium tin oxide (ITO, indium / tin = 95/5 molar ratio) was formed by sputtering using a direct current power source (thickness 0.15 μm). The surface resistance of this anode was 10Ω / □.

An organic compound layer was placed on the anode.
As the organic hole transport layer, N, N′-dinaphthyl-N, N′-diphenylbenzidine was provided in a thickness of 0.04 μm by vacuum deposition. Further thereon, tris (8-hydroxyquinolino) aluminum was provided as an organic light emitting layer in a thickness of 0.06 μm by vacuum deposition.

  A patterned mask is placed on the organic compound layer, magnesium: silver = 10: 1 (molar ratio) is deposited in a thickness of 0.25 μm in a deposition apparatus, and silver is further deposited by 0.3 μm to form a cathode. Was provided. An organic EL device 10 was prepared by emitting aluminum lead wires from the anode and the cathode, respectively.

A DC voltage of 12 V was applied to the EL element-10 to emit light. The luminance was 2.5 times the measured luminance value of the comparative element-9 measured in Example 1.
Further, when a repetitive pattern of light-emitting lines and non-light-emitting lines having a width of 200 μm was displayed on the screen of the element-10 and the visibility of the line image was observed, it showed a satisfactory contrast.
Further, the element provided with the circularly polarizing plate was caused to emit light and observed from various angles, but no rainbow color due to diffraction of reflected light was observed.

It is a bottom emission type layer block diagram which is one aspect | mode of the organic electroluminescent element of this invention. It is a layer block diagram of the top emission system which is one aspect | mode of the organic electroluminescent element of this invention. It is another layer block diagram of the top emission system which is one aspect | mode of the organic electroluminescent element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Prism structure 3 1st electrode 4 Organic layer 5 2nd electrode 6 Board | substrate 7 Spacer

Claims (6)

A first electrode, a second electrode, at least one organic layer including a light emitting layer between the first electrode and the second electrode, a transparent substrate provided on a light extraction side, and the first electrode or the first electrode An organic electroluminescent element having a prism structure between two electrodes and the transparent substrate, the prism structure being positioned with the apex of the prism facing the transparent substrate, and the pitch between the apexes of the prism The organic electroluminescent element characterized by having a coefficient of variation of 1% or more. The organic electroluminescence device according to claim 1, wherein a variation coefficient of a pitch of the prism is 3% or more. 3. The organic electroluminescent element according to claim 1, wherein the first electrode is an anode, the second electrode is a cathode, and the prism structure is provided on an anode side of the first electrode. 3. The organic electroluminescent element according to claim 1, wherein the first electrode is an anode, the second electrode is a cathode, and the prism structure is provided on a cathode side of the second electrode. 5. The organic electroluminescent element according to claim 1, wherein an average value of the pitches between the prism vertices is 0.4 μm or more and 20 μm or less. The organic electroluminescent element according to claim 1, wherein apexes of the prisms are aligned on the same plane and bonded to the transparent substrate.

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