JP2004296429A - Organic electroluminescent element and surface light source and display using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element capable of efficiently extracting loss light confined in the element as waveguide light. <P>SOLUTION: In this organic electroluminescent element having at least one layer of organic layers 4, 5 including a luminescent layer 5, and a pair of electrodes comprising a reflective electrode (cathode) 3 and a transparent electrode (anode) 2 to sandwich the layer, a transparent layer 7 having a refractive index equal to or larger than the refractive index of the luminescent layer is provided adjacently to the light extracting surface side of the transparent electrode 2. In addition, a region 8 practically causing disturbance in reflection/scattering angles of light adjacently to the light extracting surface of the transparent layer 7 or in the transparent layer 7 is provided, and the transparent layer 7 is made of a polycarbodiimides resin. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to an organic electroluminescence element having excellent luminous efficiency, particularly excellent external light extraction efficiency, and a highly efficient surface light source and a display device using this element.

Electroluminescent elements that provide a light-emitting layer between electrodes to obtain electrical light emission can be used not only for display devices, but also for various types of devices such as flat panel lighting, optical fiber light sources, backlights for liquid crystal displays, and backlights for liquid crystal projectors. R & D is also actively progressing as a light source.

In particular, organic electroluminescent elements are excellent in terms of luminous efficiency, low-voltage driving, light weight, and low cost, and have been receiving much attention in recent years. In these light source applications, the greatest concern is the improvement of the luminous efficiency. Improvements in the element configuration, materials, driving methods, manufacturing methods, and the like are being studied with the goal of luminous efficiency comparable to that of fluorescent lamps.

However, in a solid-state light-emitting device that extracts light from the light-emitting layer itself, such as an organic electroluminescence device, light emitted above the critical angle determined by the refractive index of the light-emitting layer and the refractive index of the emission medium is totally reflected and confined inside. And is lost as guided light.

In the calculation based on the classical law of refraction (Snell's law), assuming that the refractive index of the light emitting layer is n, the light extraction efficiency η at which the generated light is extracted outside is approximated by η = 1 / (2n ² ). Is done. If the refractive index of the light emitting layer is 1.7, η ≒ approximately 17%, and light of 80% or more is lost as guided light and lost light in the side direction of the element.

In the case of an organic electroluminescence device, among the excitons generated by the recombination of electrons and holes injected from the electrodes, only singlet excitons contribute to light emission, and the generation probability is 1%. / 4. That is, even if only this is taken into consideration, the efficiency is extremely low at 5% or less.

In recent years, as a method of increasing the luminous efficiency of the luminescent layer itself, development of a luminescent material that can also emit light from phosphorescence from triplet excitons (JP-A-2001-313178) has been advanced, and quantum efficiency has been dramatically increased. Has also been found to be possible.

However, even if the quantum efficiency is improved, the light extraction efficiency is reduced by the extraction efficiency. In other words, if the extraction efficiency is improved, there is still room for a synergistic effect to improve the efficiency.

In order to extract the guided light to the outside, a region is formed between the light emitting layer and the exit surface that disturbs the reflection and refraction angles, breaking Snell's law and changing the transmission angle of the light that is originally totally reflected as guided light. It is necessary to make the light emission itself have a light collecting property. However, it is not easy to form a region in which all of these guided lights can be emitted to the outside. Therefore, many proposals have been made to extract as much guided light as possible.

For example, as a method of improving the extraction efficiency, a method of improving the extraction efficiency by imparting light condensing properties to the substrate itself (Japanese Patent Application Laid-Open No. 63-31479), or a method of forming a light-emitting layer from discotic liquid crystal and emitting light A method of improving the directivity of light itself (Japanese Patent Laid-Open No. 10-321371), a method of forming a three-dimensional structure, an inclined surface, a diffraction grating, and the like on the element itself (Japanese Patent Application Laid-Open Nos. 11-214162 and 11-214163). And Japanese Patent Application Laid-Open No. 11-283751).

However, these proposals have problems such as a complicated structure and low luminous efficiency of the light emitting layer itself.

Further, as a relatively simple method, a method has been proposed in which a light diffusion layer is formed to change the refraction angle of light to reduce light under total reflection conditions.

For example, a method using a diffusion plate in which particles having a refractive index distribution structure having different refractive indices between the inside and the surface are dispersed in a transparent substrate (Japanese Patent Application Laid-Open No. 6-347617). Many proposals have been made, such as a method using a diffusion member in which layers are arranged (Japanese Patent Application Laid-Open No. 2001-356207), a method of dispersing scattering particles in the same material as the light emitting layer (Japanese Patent Application Laid-Open No. 6-151061), and the like.

These proposals have found characteristics such as the characteristics of scattering particles, the difference in refractive index from the dispersion matrix, the dispersion form of the particles, and the location where the scattering layer is formed.

By the way, the transparent substrate used for the organic electroluminescence element is mainly made of glass from the viewpoint of excellent transparency, strength, low cost, gas barrier property, chemical resistance, heat resistance, etc., and general soda lime glass and the like. Has a refractive index of about 1.52.

Further, a transparent electrode is used as the electrode on the light extraction surface side. For the transparent electrode, indium tin oxide (ITO) in which indium oxide is doped with tin oxide is widely used because of its excellent transparency and electrical conductivity. The refractive index of ITO varies depending on its composition, film formation method, crystal structure, etc., but is about 1.9 to 2.0, which is a very high refractive index material.

In addition, the refractive index of an organic layer such as a light-emitting material, an electron-transporting material, and a hole-transporting material used for a light-emitting layer of an organic electroluminescence element generally has a π-conjugation containing a large number of benzene rings in its molecular structure. Since it is a bonding system, its refractive index is higher than that of general organic materials, and it is often about 1.65 to 1.75.

In such an organic electroluminescence device, light emitted from the light emitting layer is emitted to the entire space. In the case of the above-described refractive index relationship, total reflection occurs not only at the interface between the glass substrate and the air layer but also at the ITO layer and the glass substrate.

That is, assuming that the refractive index of the light emitting layer is 1.7, the refractive index of ITO is 1.9, the refractive index of the glass substrate is 1.52, and the refractive index of the air layer is 1 in FIG. When light is transmitted from the light emitting layer to the ITO layer, since the refractive index of the ITO layer is higher than that of the light emitting layer, total reflection does not occur, and all light except for light reflected on the surface enters the ITO layer. However, since the refractive index of the light emitting layer is higher than the refractive index of the glass substrate, there is a critical angle.

Therefore, light having a transmission angle greater than the critical angle is totally reflected at the interface between the ITO and the glass substrate and is confined inside the device. Light entering the glass substrate is totally reflected at the interface between glass and air, and is confined inside the element. When these ratios are calculated in consideration of the solid angle, about 20% of the light can be emitted to the outside, about 35% of the light reflected at the glass / air interface, and about 45% of the light reflected at the ITO / glass interface. %.

Therefore, even if a light diffusion layer or the like is formed on the glass substrate, the light that can be extracted is only the light reflected at the glass / air interface, and the light reflected at the ITO / glass interface is No effect can be demonstrated. Moreover, as described above, according to classical calculations, about 45% of the emitted light is lost at the interface.

Meanwhile, in an organic electroluminescence element, when an electric field is applied, holes injected from an anode and electrons injected from a cathode recombine to form excitons, and a fluorescent substance (or a phosphorescent substance) emits light. It uses the principle of doing. Therefore, this recombination needs to be performed efficiently in order to increase the quantum efficiency.

As a general method, there is a method in which the element has a laminated structure. Examples of the laminated structure include a two-layer type of a hole transport layer / an electron transporting light-emitting layer, and a three-layer type of a hole transport layer / light-emitting layer / electron transport layer. Further, in order to increase the efficiency, many stacked devices having a double hetero structure have been proposed.

In the case of such a laminated structure, recombination occurs almost in a certain area.

For example, in the case of the two-layer type organic electroluminescent device, as shown in FIG. 10, the organic electroluminescent device is sandwiched between a pair of electrodes composed of a reflective electrode (cathode) 3 and a transparent electrode (anode) 2 on a support substrate 1. From the interface layer between the hole transport layer 4 and the electron transporting light emitting layer 5, about 10 nm is concentratedly generated in the region 6 on the electron transporting light emitting layer side (Takuya Ogawa, et al, “IEICE TRANS ELECTRON”). Vol.E85-C, No. 6, page 1239, 2002).

Light generated in the light emitting region 6 is emitted in all directions. As a result, as shown in FIG. 11, an optical path difference occurs between the light emitted toward the light extraction surface on the transparent electrode 2 side and the light emitted toward the reflective electrode 3 and reflected and emitted toward the light extraction surface. .

In FIG. 11, the thickness of the electron transporting light emitting layer of the organic electroluminescence element is usually several tens to one hundred and several tens nm, which is on the order of the wavelength of visible light. Therefore, the light finally emitted to the outside causes interference, and the light is strengthened or weakened depending on the distance d between the light emitting region and the reflective electrode.

In FIG. 11, only the emitted light in the front direction is described. However, light in an oblique direction actually exists, and the interference condition differs depending on the distance d and the emission wavelength λ depending on the angle of the emitted light. As a result, light in the front direction may be strengthened, and light in the wide angle direction may be weakened, or vice versa. That is, the emission luminance changes depending on the viewing angle. Of course, when the distance d increases, the light intensity changes significantly depending on the angle.

Therefore, normally, the film thickness is set such that the distance d is approximately １ ／ wavelength of the emission wavelength so that the lights in the front direction reinforce each other.

Further, when the distance d is smaller than, for example, about 50 nm, light absorption becomes remarkable in the reflective electrode that usually uses a metal, and the emission intensity decreases and the intensity distribution is affected. That is, in the organic electroluminescence element, the distribution of emitted light changes significantly depending on the distance d between the light emitting region and the reflective electrode, and the above-mentioned guided light component also changes greatly with it.

Further, the emission spectrum of the organic electroluminescence element has broad characteristics over a relatively wide wavelength. Therefore, as a result of the change of the wavelength range that is strengthened depending on the distance d, the emission peak wavelength changes. Further, depending on the distance d, the emission spectrum also changes with the viewing angle.

In order to solve these problems, proposals have been made for selecting a film thickness so as to suppress a phenomenon that a light emission color varies depending on a viewing angle (see Patent Document 1). However, this proposal does not describe waveguided light, and the film thickness that can suppress the viewing angle dependence of the emission color in this proposal is clearly different from the scope of the present invention described later.

For the above reasons, the classical calculation that about 80% of the emitted light is confined inside the device as guided light cannot accurately estimate the external extraction efficiency of the stacked organic electroluminescence device.

That is, the guided light component also changes significantly depending on the element configuration. For example, M. H. According to a report by Lu et al. (J. Appl. Phys., Vol. 91, No. 2, p. 595, 2002), a guided light component due to an element configuration is obtained by a quantum calculation method considering a microcavity effect. Detailed studies have been made on the changes in
JP-A-5-3081 (pages 2-4)

In view of the above-described conventional techniques, the present invention reduces loss light confined as guided light inside the element, especially loss light totally reflected at the interface between the transparent electrode and the glass substrate, which was conventionally difficult to extract. It is another object of the present invention to provide an organic electroluminescent element having high efficiency of external extraction and excellent external extraction efficiency, and to provide a highly efficient surface light source and a display device using this element.

The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, have obtained the following findings. This will be described with reference to FIGS.

First, FIG. 7 shows a schematic diagram of the two-layer type organic electroluminescent element shown in FIG. 10 when light emitted from the light emitting region thereof is emitted to the outside, with respect to only the upper hemisphere. Things. Actually, emitted light in the direction of the reflective electrode also exists, but is omitted here.

In FIG. 7, as described above, the emitted light radiated in all directions is first totally reflected at the interface between the transparent electrode and the glass substrate and is confined inside. This is because the refractive index of the glass substrate is usually about 1.52, which is lower than the refractive index of the light emitting layer. Assuming that the refractive index of the light emitting layer is 1.7 and the refractive index of the glass substrate is 1.52, the loss at this interface corresponds to about 45% of the total emitted light by classical calculation.

Next, the light transmitted to the glass substrate undergoes total reflection at the air interface, and is confined inside. The loss at this interface corresponds to about 35% of the total emitted light by a similar calculation. Therefore, only 20% of the light is actually emitted outside and reaches the observer.

Therefore, in the two-layer type organic electroluminescence device shown in FIG. 7 (FIG. 10), as shown in FIG. 8, a region 8 on the support substrate (glass substrate) 1 where the reflection / refraction angle of light is disturbed. When the light diffusion layer is formed as described above, for light totally reflected at the air / glass interface, some light can be guided to the outside by diffusing the transmission light under the condition of total reflection. However, the light that can be extracted by this method is only the totally reflected light at the air / glass interface, and the light that is totally reflected at the glass substrate / transparent electrode interface cannot even enter the region 8, so that it can be extracted outside. It has no effect on improving efficiency.

The present inventors have further studied to overcome the above problem, and as a result, formed a transparent layer having a refractive index equal to or higher than the refractive index of the light-emitting layer adjacent to the transparent electrode. By diffusing and refracting the light, the light totally reflected at the interface between the glass substrate and the transparent electrode can also be guided to the outside, and as a result, the light corresponding to about 80% of the whole is effectively treated. It turned out to be something that can be demonstrated.

FIG. 9 shows a case where the refractive index of the support substrate 1 is made equal to the refractive index of the light emitting layer in the two-layer type organic electroluminescence element shown in FIG. It shows the state of. All of the light emitted from the light emitting layer is transmitted to the transparent electrode having a high refractive index as described above. Next, when the light is incident on the support substrate, total reflection occurs when its refractive index is lower than that of the light-emitting layer.If the refractive index is equal to or higher than the refractive index of the light-emitting layer, there is no critical angle according to Snell's law, and all light is emitted. It becomes possible to enter the support substrate.

Here, as the refractive index of the supporting substrate increases, the critical angle at the interface between the air and the supporting substrate decreases, and as a result, only 20% of the light is extracted outside. However, unlike light confined in an extremely thin thin film having a thickness of only a few hundred nm in total, if light can be guided to a relatively thick layer such as a supporting substrate, an organic electroluminescent element They can be taken out without impairing the properties.

Further, as described above, in an actual organic electroluminescence element, a light interference effect occurs. Normally, the element configuration is usually determined so that frontal light that can be emitted to the outside is enhanced. In this case, the guided light interferes with each other so as to weaken each other. Therefore, even if a region where the reflection and refraction angles of the light are disturbed is formed, a large brightness improvement effect cannot be expected.

However, the present inventors, unlike the above-described conventional method, intentionally determine the element configuration such that light in the front direction is weakened and light of a wide-angle component that is usually confined inside the element as guided light is strengthened. Then, after amplifying the guided light in which most of the light amount is distributed, and forming a region where the reflection and refraction angles of the light are disturbed, the luminous efficiency is remarkably improved as compared with the above conventional method. It turned out to be.

In other words, a light emitting efficiency is rather reduced in a normal organic electroluminescent element which does not have a region that causes disturbance in the angle of reflection and refraction of light. It was found that a highly efficient organic electroluminescent device was finally obtained.

The present invention has been completed based on the above findings.

That is, the present invention relates to an organic electroluminescent device having at least one organic layer including a light-emitting layer, and a pair of electrodes comprising an anode electrode and a cathode electrode, at least one of which is a transparent electrode sandwiching the organic layer. A transparent layer having a refractive index equal to or higher than that of the light emitting layer is provided adjacent to the light extraction surface side of the electrode, and substantially adjacent to or inside the light extraction surface side of the transparent layer. The present invention relates to an organic electroluminescence device (hereinafter, simply referred to as an organic EL device), which is provided with a region that causes disturbance in light reflection and scattering angles.

In particular, in the present invention, a region in which the reflection and refraction angles of light are disordered is obtained by dispersing and dispersing a transparent material or an opaque material having a different refractive index from the transparent material and having an average particle diameter of 0.2 to 20 μm in the transparent material. The present invention relates to the organic EL device having the above-mentioned structure, which comprises a light diffusing portion, a lens structure, or an uneven surface having a surface roughness of 1 μm or more.

Further, in the present invention, the above transparent layer preferably has the following formula (I):
^{R 1 -N = C = N (} -R-N = C = N-) n-R 1 ... (I)
(Wherein R is an organic diisocyanate residue, R ¹ is an organic monoisocyanate residue, and n is an integer of 1 to 100). the polycarbodiimide resin is one or more 10 mol% of formula (I) in the R (organic diisocyanate residue) consists naphthalene diisocyanate residues, also, R ¹ in formula (I) (organic monocarboxylic (Isocyanate residue) comprises a 1-naphthyl isocyanate residue.

Further, the present invention relates to the organic EL device having the above-mentioned structure, in which at least one kind of fine particles having an average particle diameter of 1 to 100 nm is dispersed and distributed in the transparent layer.

Furthermore, the present invention, as a particularly preferred embodiment of such an organic EL element, provides a light extraction in a state where the organic layer and the pair of electrodes do not have a transparent layer and a region that causes disturbance in the reflection and scattering angles of light. The front luminance value of the emitted light emitted from the surface to the observer side and the luminance value in the direction of 50 ° to 70 ° satisfy Expression (1); the front luminance value <the luminance value in the direction of 50 ° to 70 °. The present invention relates to an organic EL device having the above-mentioned structure formed as described above.

In particular, according to the present invention, a pair of electrodes including an anode electrode and a cathode electrode includes a reflective electrode and a transparent electrode, and the distance between the reflective electrode and the center of the hole-electron recombination light emitting region is d ( Equation (2): (0.nm), the peak wavelength of the fluorescence emission spectrum of the material used for the light emitting layer is λ (nm), and the refractive index of the organic layer between the light emitting layer and the reflective electrode is n. 3 / n) λ <d <(0.5 / n) λ.

Further, the present invention relates to a surface light source provided with the organic EL elements of the above-described configurations, and to a display device provided with the organic EL elements of the above-described configurations. It is.

As described above, according to the present invention, guided light that is originally confined as loss light inside the device can be efficiently extracted, and an organic EL device having excellent luminous efficiency can be provided. In particular, it is significantly different from a conventional organic EL element in that total reflection light at the interface between a transparent electrode and a glass substrate can be extracted, which was difficult to extract in the past.

In addition, by applying this organic EL element to a surface light source or a display device, power consumption can be reduced, and current flowing through the element can be reduced, so that deterioration of organic materials is reduced and the life of the element is extended. Also leads.

In addition, by forming a region that causes disturbance in the light reflection / transmission angle, even if a gark spot observed in the organic EL element is generated, it is hardly visually recognized, and the organic light having no change in appearance for a long time. The effect of providing an EL element is also obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a two-layer type organic EL device of the present invention. This has a basic configuration in which a transparent electrode (anode) 2, a hole transport layer 4, an electron transportable light emitting layer 5, and a reflective electrode (cathode) 3 are sequentially laminated on a support substrate 1.

That is, an organic layer including the hole transport layer 4 and the electron transporting light emitting layer 5 is sandwiched between a pair of electrodes including the transparent electrode (anode) 2 and the reflective electrode (cathode) 3. During operation, recombination occurs in a region of about 10 nm from the interface layer between the hole transporting layer 4 and the electron transporting light emitting layer 5 on the side of the electron transporting light emitting layer, and light emission is concentrated in the light emitting region 6 shown in the figure. Occurs.

In addition, in a three-layer organic EL device different from the two-layer type, for example, a hole transport layer / light-emitting layer / electron transport layer, when a voltage is applied between the electrodes, holes are emitted from the anode and from the cathode. Electrons are injected, and these move in the respective carrier transport layers and recombine in the light emitting layer to generate excitons, thereby generating EL light emission as described above.

Further, in the above-mentioned organic EL device, in order to better exhibit the effects of the present invention, as the above-mentioned basic configuration, particularly, the emitted light in the front direction is weakened, but the light guide light confined inside the device is enhanced. It is desirable to have such a configuration. This will be described in more detail with reference to the characteristic diagram of FIG.

FIG. 2 shows the luminance angle distribution of an organic EL element consisting of only the above-described basic configuration (that is, before a transparent layer and a region where the reflection and refraction angles of light, which will be described later, are disturbed). FIG. 10 is a characteristic diagram measured every 10 degrees from degrees to 80 degrees. In the figure, curve-a is for the present invention, and curve-b is for the prior art.

However, in the basic configuration, the thickness of the transparent electrode 2 is 100 nm, the thickness of the hole transport layer 4 is 50 nm, and the thickness of the electron transporting light emitting layer 5 is 140 nm (of the present invention) and 60 nm (conventional). It is. The current flowing through the element was measured by applying a voltage so that the current of the present invention was the same as that of the conventional one.

From FIG. 2, the conventional one has a high front luminance value, that is, a luminance value in the 0-degree front direction, and has a substantially constant luminance value over a relatively wide range, indicating a favorable luminance distribution of a perfect diffusion type. . On the other hand, according to the present invention, the front luminance value is low, and the luminance increases as the angle increases.

That is, the present invention is configured so as to satisfy the relationship of Expression (1); front luminance value <luminance value in the direction of 50 to 70 degrees in the angle dependence of luminance.

Note that this relationship is achieved by the difference in the thickness of the electron transporting light emitting layer 5 in the above example, but the material and thickness of the organic layer including the light emitting layer 5 and the pair of electrodes are appropriately adjusted. The selection can be achieved arbitrarily.

In a further preferred embodiment of the present invention, the distance between the center of the hole-electron recombination light-emitting region 6 and the reflective electrode 3 is d, and the distance is used for the light-emitting layer (in this case, the electron-transport light-emitting layer 5). Where λ is the peak wavelength of the fluorescence emission spectrum of the material being used, and n is the refractive index of the organic layer (the electron transporting light emitting layer 5 in this case) between the light emitting layer and the reflective electrode 3; It is desirable to be configured to satisfy the relationship of (0.3 / n) λ <d <(0.5 / n) λ.

For example, in the above example, if the peak wavelength of fluorescence emission of the electron transporting light emitting layer 5 is green light having a wavelength of 540 nm and its refractive index is 1.65, the distance d is 98.2 to 163.6 nm. It is good to be set in the range of.

In the above description, the case where the emitted light is green light is taken as an example. However, an organic EL element that emits white light becomes more important in actual lighting applications and the like. In the method of emitting white light, a method of dispersing a plurality of light-emitting materials such as blue and yellow, blue and green and red, respectively, and a blue light-emitting layer, a green light-emitting layer, a red light-emitting layer, and a yellow light-emitting layer, There are various other uses such as a method of laminating them separately and a method of using a material that emits white light.

These organic EL elements have a plurality of emission peaks in each wavelength region, similarly to a fluorescent lamp or the like. In this case, depending on the wavelength range, the case where the light emitted in the front direction is strengthened and the case where the light emitted is weakened remarkably change depending on the wavelength, the recombination region, and the distance between the reflective electrodes.

For example, in the above-described white light-emitting organic EL element, a type in which blue, green, and red light-emitting materials are dispersed in one light-emitting layer is considered, and respective light emission peak wavelengths are 450 nm, 540 nm, and 630 nm. Assuming that the refractive index of the light emitting layer is 1.65, the distance d that satisfies the expression (2) is 81.8 to 136 nm for blue, 98.2 to 163.6 nm for green, and 114.6 to 190.9 nm for red. And each will be different.

In the present invention, the basic structure that satisfies the relationship of the expression (1), more preferably the relationship of the expression (2) is used, and the refractive index is adjacent to the light extraction surface side of the transparent electrode 2. Is provided with a transparent layer 7 equal to or more than the light emitting layer, and adjacent to the light extraction surface side of the transparent layer 7 as a region 8 which substantially disturbs the light reflection / scattering angle as described above. And a light diffusion layer in which diffusion particles having different refractive indices are dispersed is provided. As a result, the totally reflected light at the interface between the transparent layer 7 and the transparent electrode 2 disappears, all the emitted light is scattered by the light diffusion layer 8, and the ratio of the guided light emitted to the outside is increased. Light emission luminance is greatly improved.

In the present invention, the refractive index of the transparent layer 7 is equal to or higher than that of the light emitting layer, which means that the refractive index of the light emitting layer is 0.95 times or more, preferably the refractive index of the light emitting layer or more. It means that it is 1.05 times or more.

In FIG. 1, all the light that has passed through the light diffusion layer 8 is depicted as being extracted to the outside. However, actually, the light that has passed through the light diffusion layer 8 also remains at the interface of the support substrate 1. Receives total reflection and is confined. However, the light totally reflected at the interface between the support substrate 1 and the air layer is finally extracted to the outside by repeating the reflection at the reflective electrode 3 and passing through the light diffusion layer 8 again and again. become.

In the configuration of FIG. 1, the region 8 where the reflection and scattering angles of light are disturbed is provided adjacent to the light extraction surface side of the transparent layer 7, but as shown in FIG. May be provided partially or entirely inside the. That is, the transparent layer 7 itself may be constituted by the light diffusion layer 8 described above. Further, as shown in FIG. 4, a substrate made of a transparent layer material may be used as the support substrate 1, and the substrate 1 itself may be used as the transparent layer 7.

Further, in FIG. 4, the same light diffusion layer 8 as described above is formed adjacent to the light extraction surface side of the support substrate 1 also serving as the transparent layer 7, but instead of this light diffusion layer 8, FIG. As shown in (1), a lens array may be formed on the light extraction surface side of the support substrate 1 which also serves as the transparent layer 7, or a physical uneven surface may be formed.

Note that, in FIGS. 3 to 5 described above, other components are the same as those in FIG. 1, and are denoted by the same reference numerals and description thereof is omitted.

Further, in the organic EL device of the present invention, as shown in FIG. 6, a reflective electrode 3, an electron transporting light emitting layer 5, a hole transport layer 4, and a transparent electrode 2 are provided in this order on a support substrate 1. By providing the transparent layer 7 and the light diffusion layer 8 as described above in this order, a so-called top emission type organic EL element may be obtained in which emission light is extracted from the opposite surface side of the support substrate 1. In this case, the support substrate 1 does not particularly need to be transparent.

Further, the present invention can be applied to an organic EL element of a double-sided take-out type in which both are formed of transparent electrodes instead of the reflective electrodes. In this case, by forming the transparent layer and the light diffusion layer on both transparent electrodes, the light emission intensity on both surfaces can be improved. As described above, in the case of a double-sided organic EL element without a reflective electrode, it is not necessary to satisfy the above-described formulas (1) and (2).

In addition, in the organic EL device of the present invention, a transparent layer 7 is provided adjacent to the light extraction surface side of the transparent electrode 2 having a high refractive index, and the transparent layer 7 is adjacent to the light extraction surface side of the transparent layer 7 or the transparent layer 7 What is necessary is just to provide the region 8 in which the reflection and scattering angles of light are substantially disturbed inside, and various embodiments other than the above-described examples can be adopted. In addition, another layer may be provided between the transparent electrode 2 and the transparent layer 7 for the purpose of surface smoothness, adhesion, prevention of diffusion of residual impurities, improvement of gas barrier properties, and the like. However, it is necessary that this other layer also constitutes a transparent layer, and two or more transparent layers having another function may be formed as described above.

In the organic EL device of the present invention, there is no particular limitation on the organic material, the electrode material, the layer structure, and the film thickness of each layer as the basic structure, and the conventional technology can be applied as it is. The organic layer may be formed by vacuum-depositing a low-molecular material or a high-molecular material by a coating method or the like, and there is no particular limitation.

Specifically, the anode / hole transporting layer / electron transporting light emitting layer / cathode, which is the above-described two-layer type organic EL element, and the anode / hole transporting layer / three-layer type organic EL element, Various configurations such as a light-emitting layer / electron transport layer / cathode and an anode / light-emitting layer / cathode different from these stacked devices can be selected, and there is no particular limitation.

A configuration may be adopted in which a hole injection layer is provided at the anode interface, an electron injection layer is provided at the cathode interface, or an electron block layer and a hole block layer are inserted for improving recombination efficiency. Basically, when a structure, a material, and a formation method that increase the luminous efficiency are selected, EL light emission with high power can be obtained with low power consumption, and the effect of the present invention is further enhanced.

The electrode material can also be appropriately selected as appropriate. For the anode, a transparent conductive film such as indium tin oxide (ITO), antimony-doped tin oxide, or zinc oxide is used. Since the refractive index of this transparent conductive film is about 1.9 or more, the effect of the present invention is exhibited. The cathode is preferably formed by co-evaporation of Mg and Ag at an atomic ratio of about 10: 1, a Ca electrode, an Al electrode doped with a small amount of Li, and the like, from the viewpoint of improving the electron injection efficiency by reducing the work function of the cathode. Although it is used, it is not particularly limited as described above.

As the support substrate in the present invention, a general substrate can be used regardless of the presence or absence of transparency. In addition to using a glass substrate and extracting light to the glass substrate side through a transparent electrode, as described above, an opaque metal plate is used as a support substrate and light is extracted from the opposite side to the support substrate Such a configuration may be adopted.

In addition to forming the anode as a transparent electrode, as the cathode, a metal electrode having a thickness of several nm to several tens of nm from the interface of the organic layer and capable of maintaining light transmission is formed, and thereafter, ITO is formed. The cathode may be a transparent electrode.

Further, a flexible material such as a polymer film may be used for the support substrate, or as described above, the support substrate itself may constitute the transparent layer, and the support substrate itself may transmit light. A region in which the reflection and refraction angles are disturbed may be formed.

Regarding the material of the transparent layer in the present invention, regardless of an organic material or an inorganic material, a material having a refractive index equal to or higher than that of the light emitting layer can be suitably used.

For example, high refractive index glass containing a sulfur atom, polyethylene terephthalate resin having a refractive index of 1.65, polyether sulfone resin, or the like having a refractive index of at least 0.95 times the refractive index of the light emitting layer. The effect of the present invention can be exhibited to some extent. From the viewpoint of workability, a resin material is preferable.

However, properties other than the refractive index such as moldability, heat resistance, coefficient of thermal expansion, moisture resistance, adhesion to a transparent electrode, and transparency are also important, and these properties are satisfied. There are many materials that are not satisfactory. In order to maximize the effects of the present invention, the refractive index is preferably 1.05 times or more the refractive index of the light emitting layer. From these viewpoints, it is desirable to further increase the refractive index by adding fine particles having a higher refractive index and a particle diameter smaller than the wavelength of light to the transparent layer. Conversely, fine particles having a low refractive index can be dispersed and distributed to adjust the refractive index.

The fine particles used for such _{purpose, TiO 2, ZrO 2, ZnO} , Y 2 O 3, SnO 2, CdO, PbO, SiO 2, Sb 2 O 5, Al 2 O 3, CeO 2, In 2 O ₃ , metal oxides such as HfO ₂ , In ₂ O ₃ doped with SnO ₂ , SbO ₂ doped with Sb ₂ O ₅ , sulfides such as ZnS, selenides, tellurides, etc. No particular limitation. The shape of these fine particles may or may not be a true sphere, and they can be widely used as long as scattering does not occur in the visible light region.

The particle diameter of these fine particles is required to be sufficiently smaller than the wavelength of visible light and not more than a size that does not cause light scattering in the visible light region, and the average particle diameter is 1 to 100 nm, preferably The thickness is preferably 1 to 50 nm.

The amount of these fine particles to be added is not particularly limited, but it is preferable that the amount of the fine particles be 10 to 500 parts by weight with respect to 100 parts by weight of the resin. By changing the refractive index and addition amount of the fine particles, the refractive index can be controlled to an arbitrary value within a certain range.

The method for producing these fine particles is not limited, and may be subjected to some surface treatment or surface modification in order to improve the dispersibility of the fine particles.

As described above, the refractive index of the transparent layer in the invention is at least 0.95 times the refractive index of the light emitting layer, preferably at least the refractive index of the light emitting layer, more preferably at least 1.05 times the light emitting layer. The refractive index of the light-emitting layer varies depending on its molecular structure, but a high one may exceed 1.75. In this case, the ordinary resin material usually has a refractive index of 1.7 or less, and in order to sufficiently increase the refractive index, it is necessary to add a large amount of the fine particles as described above.

In the present invention, when forming a light diffusion layer, it is necessary to add diffusion particles for scattering light in addition to the fine particles added for increasing the refractive index. In addition, when forming the lens structure or the concave-convex structure, if the proportion of the fine particles is increased too much, not only the inherent workability of the resin is impaired, but also the strength may be reduced, and the properties as the resin may be impaired. For this reason, it is preferable that the refractive index of the resin itself serving as the matrix is as high as possible, and a material that is higher than the refractive index of the light emitting layer by itself is preferable.

However, the refractive index of a general resin is about 1.49 to 1.65, and except for a special resin such as a resin containing a sulfur atom, which is used for plastic lenses of eyeglasses, the resin alone of the present invention is used. Few can be found to be suitable.

In view of such a situation, the present inventors have made intensive studies and as a result, as a material applied to the transparent layer, the following formula (I);
^{R 1 -N = C = N (} -R-N = C = N-) n-R 1 ... (I)
(Wherein, R represents an organic diisocyanate residue, R ¹ represents an organic monoisocyanate residue, and n is represented by an integer of 1 to 100). I found it.

In the formula (I), the organic diisocyanate residue (R) includes tolylene diisocyanate residue, diphenylmethane diisocyanate residue, naphthalene diisocyanate residue, hexamethylene diisocyanate residue, dodecamethylene diisocyanate residue and the like. It may be a group or a mixture of two or more. In particular, it is desirable that the naphthalene diisocyanate residue accounts for 10 mol% or more of the total organic diisocyanate residue. The organic monoisocyanate residue (R ¹ ) is particularly preferably a 1-naphthyl isocyanate group.

Such a polycarbodiimide resin uses, for example, several kinds of organic diisocyanates, and carries out a carbodiimidation reaction at 0 to 150 ° C., preferably 10 to 120 ° C. in the presence of a carbodiimidation catalyst and a solvent to obtain an organic monoisocyanate. It can be obtained by blocking the terminal with an isocyanate. The polycarbodiimide resin whose terminal is blocked in this way has excellent storage stability of the solution.

Here, the terminal blocking with the organic monoisocyanate can be carried out by adding the organic monoisocyanate to the reaction system at any of the last stage, the middle stage, the initial stage, or the whole of the polymerization reaction. The end point of the reaction can be confirmed by observing absorption (2,140 cm ^-1 ) derived from a carbodiimide group by IR measurement and disappearance of absorption (2,280 cm ^-1 ) derived from an isocyanate group.

Examples of the organic diisocyanate include hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, xylylene diisocyanate, tetramethyl xylylene diisocyanate, isophorone diisocyanate, cyclohexyl diisocyanate, and lysine. Diisocyanate, methylcyclohexane-2,4-diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene diisocyanate, 1-methoxyphenyl -2,4-diisocyanate, 3,3'-dimethoxy-4,4-diph Nylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 3,3'-dimethyl-4,4'-diphenyl ether diisocyanate, 2,2-bis [4- (4-isocyanatophenoxy) phenyl] hexafluoropropane, One or two or more of 2-bis [4- (4-isocyanatophenoxy) phenyl] propane and the like can be mentioned.

In particular, it is desirable to use naphthalenediisocyanate at 10 mol% or more. In addition, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate and the like are also preferable.

As the organic monoisocyanate, aromatic monoisocyanates such as phenyl isocyanate, p-nitrophenyl isocyanate, p- or m-tolyl isocyanate, p-formylphenyl isocyanate, p-isopropylphenyl isocyanate and 1-naphthyl isocyanate are preferable. Species or two or more are used.

Among these organic monoisocyanates, use of 1-naphthyl isocyanate is preferred, since the monoisocyanates do not react with each other and can efficiently block the terminal of polycarbodiimide.

Such an organic monoisocyanate is used in a ratio of 1 to 10 mol per 100 mol of the organic diisocyanate. When the amount is less than 1 mol, the molecular weight of the polycarbodiimide resin becomes too large, the solution viscosity increases due to a cross-linking reaction, and the solution is solidified, and the storage stability of the polycarbodiimide resin solution tends to decrease. On the other hand, when the amount exceeds 10 mol, the solution viscosity of the polycarbodiimide resin solution is too low, so that it is difficult to form a good film upon forming a film by coating and drying.

When an aliphatic diisocyanate and an aromatic diisocyanate are used as the organic diisocyanate and the two are reacted in the presence of a carbodiimidization catalyst, the reaction is preferably performed at a low temperature. That is, the reaction temperature is preferably from 0 to 50C, more preferably from 10 to 40C. When the reaction temperature is higher than 50 ° C., the reaction between aromatic diisocyanates proceeds preferentially, and the reaction between aliphatic diisocyanate and aromatic diisocyanate does not proceed sufficiently.

When the polycarbodiimide resin obtained by the polymerization reaction is further reacted with an aromatic diisocyanate excessively present in the reaction system, the reaction temperature is preferably set to 40 to 150 ° C, and 50 to 120 ° C. More preferably, If the reaction temperature is lower than 40 ° C., the progress of the reaction takes a long time to be impractical, and if it exceeds 150 ° C., it becomes difficult to select a reaction solvent.

The organic solvent used as the reaction solvent and the diluted solution of the obtained polycarbodiimide resin may be a conventionally known organic solvent.

Specifically, halogenated hydrocarbons such as tetrachloroethylene, 1,2-dichloroethane and chloroform; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; cyclic ether solvents such as tetrahydrofuran and dioxane; toluene, xylene and the like And the like. These organic solvents may be used alone or in a combination of two or more.

The concentration of the organic diisocyanate in the reaction system is preferably from 5 to 80% by weight. When the amount is lower than 5% by weight, the carbodiimidization reaction may not proceed, and when it exceeds 80% by weight, the control of the reaction may be difficult.

As the carbodiimidization catalyst, any known phosphorus-based catalyst is suitably used. Specifically, 1-phenyl-2-phospholene-1-oxide, 3-methyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, 3-methyl-1-phenyl-2 And phosphorene oxides such as -phospholene-1-oxide and their 3-phospholene isomers.

After completion of the carbodiimidization reaction, the reaction solution may be poured into a poor solvent such as methanol, ethanol, isopropyl alcohol, or hexane to precipitate and precipitate the polycarbodiimide resin, thereby removing unreacted monomers and catalyst.

In order to prepare a polycarbodiimide resin solution, a polymer precipitated and precipitated may be washed and dried by a predetermined operation, and then dissolved in an organic solvent again. By performing such an operation, the solution stability of the polycarbodiimide resin can be improved.

The by-product contained in the polycarbodiimide resin solution may be purified by adsorbing it on a suitable adsorbent or the like. As the adsorbent, alumina gel, silica gel, activated carbon, zeolite, activated magnesium oxide, activated bauxite, frase earth, activated clay, molecular sieve carbon, or the like can be used alone or in combination.

Since the polycarbodiimide resin thus obtained has a very high refractive index, it can be used as it is as a material for the transparent layer.

Further, by adding the fine particles further to the polycarbodiimide resin, without impairing the inherent characteristics of the resin, as a transparent layer substantially close to the refractive index of the transparent electrode, it is possible to better exert the effects of the present invention. it can.

In the present invention, the region that causes disturbance in the angle of reflection and refraction of light can basically disturb the transmission angle of light at an angle equal to or greater than the total reflection angle to a transmission angle equal to or less than the total reflection angle, What is necessary is just to be formed so that more guided light confined inside the element can be emitted to the outside, and there is no particular limitation on the forming method. That is, the conventionally proposed one can be applied as it is.

For example, as the light diffusion layer, a light diffusion portion in which a transparent material or an opaque material having a different refractive index from the transparent material is dispersed and dispersed may be formed. Specifically, there is a dispersion in which silica particles, titania particles, zirconia particles, plastic particles, liquid crystal particles, bubbles, and the like are dispersed in polycarbodiimide resin, which is a transparent layer material.

The refractive index, the refractive index difference, and the particle size of the particles are not limited. However, from the viewpoint of causing light scattering, the particle size is 0.2 to 20 μm, preferably 0.3 to 10 μm, and more preferably 0 to 10 μm. 0.5 to 5 μm, and the difference in refractive index is preferably 0.05 or more.

Further, a lens structure can also be suitably used. The lens structure is a thin, plate-shaped transparent member that changes the direction of light traveling straight through a plurality of lenses, prisms, V-shaped grooves, and the like arranged or formed in concentric circles, a plurality of parallel lines, a lattice, or the like. Means substance.

Specific examples include lenticular lenses, Fresnel lenses, corner cube lenses, fly's eye lenses, cat's eye lenses, double fly's eye lenses, double lenticular lenses, radial lenticular lenses, prism lenses, microprism lenses And a lens in which the convex surface of these lenses is changed to a concave surface, a transparent sphere or a translucent sphere arranged in a plane, and the like. Further, the direction of light may be changed by carving a groove such as a V-shaped groove.

Further, a physical uneven surface may be formed on the support substrate surface or each interface. Specifically, it can be formed by transferring a periodic uneven structure. The size of the uneven surface is preferably larger than the wavelength of light, and more specifically, is preferably 1 μm or more. If the uneven surface is smaller than that, there is a problem that the reflection / transmission angle of light cannot be efficiently disturbed, and iridescent glare occurs due to the light interference effect.

In the present invention, a surface light source comprising an organic EL element having such a configuration as a light emitting element, and a display device comprising the organic EL element as a light emitting element are provided. it can. Thus, a surface light source and a display device with high luminous efficiency can be provided.

Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited only to the following examples.

The polycarbodiimide resin used in the following examples was synthesized according to Synthesis Examples 1 and 2 below. Both synthesis examples were performed under a nitrogen stream. The IR measurement was performed using FT / IR-230 (manufactured by JEOL Ltd.).

<Synthesis example 1>
In a 500 ml four-necked flask equipped with a stirrer, a dropping funnel, a reflux condenser and a thermometer, 29.89 g (171.6) of tolylene diisocyanate (isomer mixture: "T-80" manufactured by Mitsui Takeda Chemical Co., Ltd.) Mmol), 94.48 g (377.52 mmol) of 4,4'-diphenylmethane diisocyanate, 64.92 g (308.88 mmol) of naphthalene diisocyanate, and 184.59 g of toluene were mixed. To this were added 8.71 g (51.48 mmol) of 1-naphthyl isocyanate and 0.82 g (4.29 mmol) of 3-methyl-1-phenyl-2-phospholene-2-oxide, and the mixture was heated to 100 ° C. while stirring. The temperature was raised and maintained for 2 hours.

The progress of the reaction was confirmed by infrared spectroscopy. Specifically, to observe an increase in absorption of reduced and N-C-N stretching vibration of the carbodiimide absorption of N-C-O stretching vibration of the isocyanate ^{(2,270cm -1) (2,135cm -1)} . The end point of the reaction was confirmed by IR, and the reaction solution was cooled to room temperature to obtain a polycarbodiimide resin solution.

<Synthesis Example 2>
In a 500 ml four-necked flask equipped with a binding device, a dropping funnel, a reflux condenser and a thermometer, 89.01 g (355.68 mmol) of 4,4'-diphenylmethane diisocyanate and 24.92 g of naphthalene diisocyanate (118.56) were added. Mmol), 44.87 g (266.76 mmol) of hexamethylene diisocyanate and 216.56 g of toluene were added and mixed. 7.52 g (44.46 mmol) of 1-naphthyl isocyanate and 0.71 g (3.705 mmol) of 3-methyl-1-phenyl-2-phospholene-2-oxide were added thereto, and the mixture was stirred at 25 ° C. for 3 hours. Thereafter, the temperature was raised to 100 ° C. while stirring, and the temperature was further maintained for 2 hours.

The progress of the reaction was confirmed by infrared spectroscopy. Specifically, to observe an increase in absorption of reduced and N-C-N stretching vibration of the carbodiimide absorption of N-C-O stretching vibration of the isocyanate ^{(2,270cm -1) (2,135cm -1)} . The end point of the reaction was confirmed by IR, and the reaction solution was cooled to room temperature to obtain a polycarbodiimide resin solution.

The following refractive index tests were performed on the polycarbodiimide resins obtained in Synthesis Examples 1 and 2 described above. That is, a polycarbodiimide resin solution was applied on a separator made of a polyethylene terephthalate film having a thickness of 50 μm treated with a release agent, heated at 130 ° C. for 1 minute, and then heated at 150 ° C. for 1 minute to obtain a thickness. A film sample having a thickness of 50 μm was prepared.

This sample was cut into a size of 1 cm × 2 cm, cured in an oven at 120 ° C., 150 ° C., and 175 ° C. for 1 hour, and then its refractive index was measured with a multi-wavelength Ape refractometer (DR-M4 manufactured by ASTAGO). Was measured.

The results were as shown in Table 1. From these results, the polycarbodiimide resins obtained in Synthesis Examples 1 and 2 had a higher refractive index than general polymer resins, and were preferable for adaptation to the present invention.

Table 1
┌────┬───────────────────────┐
│ │ Refractive index (wavelength: 587.6 nm) │
│ ├───────┬───────┬───────┤
│ │120 ℃ cure│150 ℃ cure│175 ℃ cure│
├────┼───────┼───────┼───────┤
│Synthesis Example 1│ 1.7571│ 1.7479│ 1.7443│
│Synthesis Example 2│ 1.7343│ 1.7245│ 1.7230│
└────┴───────┴───────┴───────┘

To the polycarbodiimide resin solution obtained in Synthesis Example 1, a toluene solution containing 70% by weight of silica particles having an average particle diameter of 0.5 μm was added at a ratio of 20% by weight based on the polycarbodiimide resin, followed by stirring. . This dispersion is applied on a glass substrate by an applicator and cured at 150 ° C. for 1 hour to form a transparent layer serving also as a 25 μm-thick light diffusion layer on a 1.1 mm-thick glass substrate. did.

The refractive index of the glass substrate measured with an Abbe refractometer was 1.517 at a wavelength of 587.6 nm. The haze value of this sample was measured with a reflection / transmittance meter (“HR-100” manufactured by Murakami Color Research Laboratory) and found to be 87.3%.

Next, in order to fabricate the organic EL device shown in FIG. 3, a DC layer was formed on a surface of a transparent layer also serving as a light diffusion layer from an ITO ceramic target (In ₂ O ₃ : SnO ₂ = 90% by weight: 10% by weight). An ITO layer having a thickness of 100 nm was formed by a sputtering method, and a transparent electrode (anode) was formed. Separately, in order to manufacture the organic EL device shown in FIG. 7, an ITO layer is formed directly on a glass substrate in the same manner as described above without forming a transparent layer also serving as a light diffusion layer, and a transparent electrode ( Anode).

Thereafter, the ITO layer was etched using a photoresist with respect to both of the transparent electrodes, and a pattern was formed so that the light emitting area became 15 mm × 15 mm. After performing ultrasonic cleaning, ozone cleaning was performed using a low-pressure ultraviolet lamp.

Next, organic layers were sequentially formed on the ITO surface by a vacuum evaporation method. First, as a hole injection layer, CuPc represented by the formula (3) was formed at a deposition rate of 0.3 nm / s to a thickness of 15 nm. Next, as a hole transport layer, α-NPD represented by the formula (4) was formed to a thickness of 50 nm at a deposition rate of 0.3 nm / s. Finally, as the electron transporting light emitting layer, Alq represented by the formula (5) was formed at a deposition rate of 0.3 nm / s to a thickness of 140 nm.

Then, Mg is co-deposited at a deposition rate of 1 nm / s and Ag at a deposition rate of 0.1 nm / s to form MgAg having a thickness of 100 nm. From the viewpoint of preventing oxidation of MgAg, Ag is further deposited thereon. The reflective electrode (back electrode) (cathode) was formed to a thickness of 50 nm.

After taking out from the vacuum deposition apparatus, ultraviolet curable epoxy resin is dropped on the cathode electrode side, a slide glass is put on it, and when the epoxy resin has spread sufficiently, the epoxy resin is cured with a high-pressure ultraviolet lamp, and the element is Sealed.

When a voltage of 15 V was applied to the organic EL device thus manufactured, a current was passed through the device at a current density of 10.5 mA / cm ² , and light emission was observed.

With respect to the organic EL element in which the transparent layer also serving as the light diffusion layer was not formed, the luminance was measured every 10 degrees from 0 degree to 80 degrees using a commercially available luminance meter (trade name "BM9" manufactured by Topcon Corporation). The luminance values are 0 degree: 126 cd / m ² , 10 degrees: 138 cd / m ² , 20 degrees: 154 cd / m ² , 30 degrees: 181 cd / m ² , 40 degrees: 225 cd / m ² , and 50 degrees: 272 cd / m ² m ² , 60 degrees: 307 cd / m ² , 70 degrees: 386 cd / m ² , and 80 degrees: 339 cd / m ² .

As is clear from these results, the organic EL device having no transparent layer also serving as the light diffusion layer sufficiently satisfied the relationship of the formula (1) of the present invention.

In this organic EL device, recombination of holes and electrons occurs almost at the interface between α-NPD and Alq. Therefore, the distance d between the central portion of the hole-electron recombination light-emitting region and the reflective electrode in the present invention was about 140 nm. The peak wavelength λ of the fluorescence spectrum when the Alq thin film deposited on the glass substrate was irradiated with black light as the excitation light source was about 530 nm.

Further, the refractive index n of the Alq film measured using a spectroscopic ellipsometer was about 1.67 at a wavelength of 590 nm. Therefore, the above-mentioned organic EL device also satisfied the relationship of the formula (2) of the present invention.

Next, the front luminance of the organic EL device of the present invention, on which a transparent layer also serving as a light diffusing layer was formed when a voltage of 15 V was applied, was measured in the same manner as described above, to be 387 cd / m ^2. Was.

In the transparent layer also serving as the light diffusion layer, the polycarbodiimide resin obtained in Synthesis Example 1 which was used as a matrix resin had a refractive index of 1.7479 when cured at 150 ° C. It was about 1.05 times the refractive index of a certain Alq, satisfying the conditions of the present invention.

As is clear from the results, according to the present invention, an organic EL device comprising a transparent layer also serving as a light diffusion layer using a polycarbodiimide resin having a high refractive index as a matrix on an ITO transparent electrode, According to the organic EL element whose characteristics when no layer is formed satisfy the relationship of the formulas (1) and (2) of the present invention, the value of the front luminance is as large as 126 cd / m ² to 387 cd / m ^2. It was confirmed that it increased.

A transparent layer serving also as a light diffusion layer was formed in the same manner as in Example 1 except that the polycarbodiimide resin solution obtained in Synthesis Example 2 was used instead of the polycarbodiimide resin solution obtained in Synthesis Example 1. Thereafter, an organic EL element was manufactured in the same procedure as in Example 1.

When a voltage of 15 V was applied to the organic EL device and the front luminance was measured, it was 367 cd / m ² , and it was confirmed that the luminance was also increased.

In Example 1, instead of applying the dispersion containing silica particles on a glass substrate, the dispersion containing silica particles was applied on a polyethylene terephthalate (PET) film whose surface was subjected to a release treatment, and the dispersion was applied at 150 ° C. After curing for 1 hour, a light diffusion layer having a thickness of 25 μm was formed. Then, the polycarbodiimide resin solution itself obtained in Synthesis Example 1 (that is, a resin solution to which silica particles were not added) was applied onto the light diffusion layer, and cured at 150 ° C. for 1 hour to obtain a thickness. A 25 μm transparent layer was formed.

By peeling from the PET film, a film layer (light diffusion layer and transparent layer) having a total thickness of 50 μm was obtained. This film layer was adhered and laminated on a glass substrate, and thereafter, the same procedure as in Example 1 was followed to produce the organic EL device shown in FIG.

When a voltage of 15 V was applied to this organic EL device and the front luminance was measured, it was 543 cd / m ² , and it was confirmed that the luminance was greatly increased.

A polyethersulfone (PES) resin is dissolved in an N, N-dimethylacetamide (DMAc) solvent at a concentration of 25% by weight, and a DMAc solution containing 70% by weight of silica particles having an average particle diameter of 0.5 μm is dissolved in a PES solution. At a ratio of 20% by weight to the mixture and stirred. This dispersion was applied on a glass substrate by an applicator and dried at 150 ° C. for 15 minutes to form a transparent layer having a thickness of 25 μm and also serving as a light diffusion layer.

The refractive index of PES measured with an Abbe refractometer was 1.649 at a wavelength of 587.6 nm. The haze value of this sample was measured with a reflection / transmittance meter (“HR-100” manufactured by Murakami Color Research Laboratory) and found to be 84.7%.

After that, the organic EL element shown in FIG. When a voltage of 15 V was applied to this organic EL element and the front luminance was measured, it was 356 cd / m ² , and it was confirmed that the luminance was increased.

Comparative Example 1
To the polycarbodiimide resin solution obtained in Synthesis Example 1, a toluene solution containing 70% by weight of silica particles having an average particle diameter of 0.5 μm was added at a ratio of 20% by weight based on the polycarbodiimide resin, followed by stirring. . This dispersion is applied on a glass substrate by an applicator and cured at 150 ° C. for 1 hour to form a transparent layer serving also as a 25 μm-thick light diffusion layer on a 1.1 mm-thick glass substrate. did.

Next, on a glass substrate opposite to the transparent layer also serving as a light diffusion layer, a thickness is formed by a DC sputtering method from an ITO ceramic target (In ₂ O ₃ : SnO ₂ = 90% by weight: 10% by weight). A 100 nm ITO layer was formed, and a transparent electrode (anode) was formed.

Thereafter, the ITO layer was etched using a photoresist on the transparent electrode, and a pattern was formed so that a light emitting area was 15 mm × 15 mm. After performing ultrasonic cleaning, ozone cleaning was performed using a low-pressure ultraviolet lamp.

Thereafter, an organic EL device shown in FIG. When a voltage of 15 V was applied to this device and the front luminance was measured, it was 278 cd / m ² . As described above, when a glass substrate having a low refractive index is present on the ITO transparent electrode, even if a light diffusion layer using a polycarbodiimide resin having a high refractive index as a matrix is formed, an increase in luminance cannot be achieved. It was smaller than in Example 1.

Comparative Example 2
An organic EL device was manufactured in the same manner as in Example 1, except that a transparent layer also serving as a light diffusion layer was not formed, and Alq was formed as an electron transporting light emitting layer to a thickness of 60 nm at a deposition rate of 0.3 nm / s. Produced. A voltage of 8.2 V was applied to the organic EL device, a current was applied at a current density of 10.5 mA / cm ² to emit light, and the angle dependence of luminance was examined.

The results show that each luminance value is 0 degree: 323 cd / m ² , 10 degree: 323 cd / m ² , 20 degree: 319 cd / m ² , 30 degree: 315 cd / m ² , 40 degree: 302 cd / m ² , 50 degree : 286 cd / m ² , 60 degrees: 269 cd / m ² , 70 degrees: 244 cd / m ² , and 80 degrees: 202 cd / m ² .

As is clear from the results, the above organic EL device did not satisfy the relationship of the formula (1) of the present invention. In addition, in this organic EL device, the distance d between the center of the hole-electron recombination light-emitting region and the reflective electrode according to the present invention is about 60 nm, so that the relationship of the formula (2) of the present invention is satisfied. Did not do.

Next, an organic EL device was produced in the same manner as in Comparative Example 1 except that the Alq layer was formed to a thickness of 60 nm in the same manner as described above. When a voltage of 8.2 V was applied to this organic EL device, and the front luminance was measured, it was 335 cd / m ² .

That is, when a light diffusion layer using a polycarbodiimide resin having a high refractive index as a matrix is not formed on the ITO transparent electrode, and the relationship of the formulas (1) and (2) of the present invention is not satisfied, the luminance is not improved. There was little increase.

An acrylate-based ultraviolet-curable resin ("GRANDIC PC2-720 series" manufactured by Dainippon Ink and Chemicals, Inc.) having a refractive index of 1.65 is placed in a mold in which a square pyramid structure having a side of 10 μm is formed without gaps. The composition was applied using an applicator, and irradiated with ultraviolet rays of 200 mJ / cm ² from a high-pressure ultraviolet lamp to be cured.

On the surface, a solution in which a PES resin was dissolved in a DMAc solvent at a concentration of 25% by weight was further applied for the purpose of increasing the film strength, dried at 120 ° C. for 20 minutes, and then peeled from the mold to obtain the pyramid. A resin sheet having a structure having irregularities was prepared.

Next, ITO was deposited to a thickness of 100 nm on the PES resin surface of the resin sheet opposite to the surface on which the pyramid structure was formed. Thereafter, the organic EL device shown in FIG.

When a voltage of 15 V was applied to the organic EL element and the front luminance was measured, it was 402 cd / m ² , and it was found that a high luminance was obtained.

A Cargill standard refraction liquid having a refractive index of 1.40 was dropped on a concave and convex surface having a pyramid structure of the organic EL element manufactured in Example 5 so as to cover a 15 mm × 15 mm area which is a light emitting portion of the organic EL element. Apparently, the uneven surface having a pyramid structure was smoothed.

When a voltage of 15 V was applied to this organic EL element, the front luminance was measured. As a result, the luminance was 312 cd / m ² , which was lower than that of Example 5; however, the effect of improving the luminance was still recognized. Was done.

Comparative Example 3
The surface of the quartz glass substrate (refractive index: 1.47) was subjected to a surface roughening treatment by an inverse sputtering method using an argon gas until the average surface roughness became 0.05 μm. The glass surface was coated with the polycarbodiimide resin solution obtained in Synthesis Example 1 by spin coating, and cured at 150 for 1 hour to form a transparent layer having a thickness of 3 μm.

Next, a film of ITO was formed to a thickness of 100 nm on the transparent layer. Thereafter, an organic EL element was manufactured in the same procedure as in Example 1. When a voltage of 15 V was applied to the organic EL device and the front luminance was measured, it was 138 cd / m ² .

As is apparent from the results, when the surface roughness of the glass substrate was smaller than the range of the present invention, the effect of improving the luminance was hardly recognized.

FIG. 2 is a cross-sectional view illustrating a first example of the organic electroluminescence element of the present invention. FIG. 5 is a characteristic diagram showing the angle dependence of luminance for the basic configuration of the present invention and a conventional organic electroluminescence element. FIG. 4 is a cross-sectional view illustrating a second example of the organic electroluminescence element of the present invention. It is sectional drawing which shows the 3rd example of the organic electroluminescent element of this invention. It is sectional drawing which shows the 4th example of the organic electroluminescent element of this invention. It is sectional drawing which shows the 5th example of the organic electroluminescent element of this invention. FIG. 2 is a diagram illustrating the principle of the present invention. It is another principle explanatory drawing of this invention. FIG. 11 is a diagram illustrating still another principle of the present invention. FIG. 3 is an explanatory diagram showing a light emitting region of the organic electroluminescence element. FIG. 3 is an explanatory diagram of luminance of an organic electroluminescence element.

Explanation of reference numerals

1 support substrate 2 transparent electrode (anode)
3 reflective electrode (cathode)
Reference Signs List 4 hole transport layer 5 electron transporting light emitting layer 6 light emitting area 7 transparent layer 8 area causing disorder in light reflection / refraction angle

Claims (12)

In an organic electroluminescence device having at least one organic layer including a light emitting layer and a pair of electrodes including an anode electrode and a cathode electrode at least one of which is a transparent electrode, a light extraction surface side of the transparent electrode , A transparent layer having a refractive index equal to or higher than that of the light-emitting layer is provided, and the light reflection / scattering angle is substantially adjacent to the light extraction surface side of the transparent layer or inside the transparent layer. An organic electroluminescence device, wherein a region causing disturbance is provided.
The area where the reflection and refraction angles of light are disturbed is from a light diffusive part in which a transparent material or an opaque material having an average particle diameter of 0.2 to 20 μm having a different refractive index is dispersed in a transparent material. The organic electroluminescence device according to claim 1.
2. The organic electroluminescence device according to claim 1, wherein the region where the reflection and refraction angles of light are disturbed has a lens structure.
2. The organic electroluminescence device according to claim 1, wherein the region in which the reflection and refraction angles of light are disturbed comprises an uneven surface having a surface roughness of 1 μm or more.
The transparent layer has the following formula (I):
^{R 1 -N = C = N (} -R-N = C = N-) n-R 1 ... (I)
(Wherein R is an organic diisocyanate residue, R ¹ is an organic monoisocyanate residue, and n is an integer of 1 to 100), and is a polycarbodiimide resin represented by the formula: Organic electroluminescent element.
The organic electroluminescence device according to claim 5, wherein the polycarbodiimide resin is such that at least 10 mol% of R (organic diisocyanate residue) in the formula (I) is composed of naphthalenediisocyanate residue.
The organic electroluminescent device according to claim 5, wherein R ¹ (organic monoisocyanate residue) in the formula (I) comprises a 1-naphthyl isocyanate residue in the polycarbodiimide resin.
The organic electroluminescence device according to any one of claims 1 to 7, wherein at least one kind of fine particles having an average particle size of 1 to 100 nm is dispersed and distributed in the transparent layer.
In a state where the organic layer and the pair of electrodes do not have a transparent layer and a region that causes disturbance in the reflection and scattering angles of light, the front luminance value of emitted light emitted from the light extraction surface to the observer side and 50 degrees. The organic material according to any one of claims 1 to 8, wherein the luminance value in the direction of -70 degrees is formed so as to satisfy the following relationship: Expression (1); front luminance value <luminance value in the direction of 50 to 70 degrees. Electroluminescent element.
A pair of electrodes consisting of an anode electrode and a cathode electrode is composed of a reflective electrode and a transparent electrode, and the distance between the center of the hole-electron recombination light-emitting region and the reflective electrode is d (nm). Assuming that the peak wavelength of the fluorescence emission spectrum of the material used is λ (nm) and the refractive index of the organic layer between the light emitting layer and the reflective electrode is n, the formula (2): (0.3 / n) λ The organic electroluminescence device according to claim 9, wherein a relationship of <d <(0.5 / n) λ is satisfied.
A surface light source comprising the organic electroluminescence device according to claim 1.
A display device comprising the organic electroluminescence element according to claim 1.

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