JP4495978B2 - ORGANIC ELECTROLUMINESCENT ELEMENT AND SURFACE LIGHT SOURCE AND DISPLAY DEVICE USING THIS ELEMENT - Google Patents

Description

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

Electroluminescent elements that provide light emission layers by providing a light emitting layer between electrodes are not only used for display display devices, but also for various types such as flat illumination, light sources for optical fibers, backlights for liquid crystal displays, and backlights for liquid crystal projectors. As a light source, research and development is actively progressing.

In particular, the organic electroluminescence element is excellent in terms of light emission efficiency, low voltage driving, light weight, and low cost, and has attracted much attention in recent years. In these light source applications, the greatest concern is the improvement of luminous efficiency, and improvements in device configuration, materials, driving methods, manufacturing methods, etc. are being studied with the aim of luminous efficiency comparable to fluorescent lamps.

However, in an in-solid 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 output medium is totally reflected and confined inside. And lost as guided light.

In the calculation based on the classical law of refraction (Snell's law), if the refractive index of the light emitting layer is n, the light extraction efficiency η for extracting the generated light to the outside is approximated by η = 1 / (2n ² ) Is done. If the refractive index of the light emitting layer is 1.7, η is about 17%, and 80% or more of light is lost as guided light and lost in the side face direction of the device.

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

In recent years, as a method for increasing the light emission efficiency of the light emitting layer itself, development of a light emitting material capable of obtaining light emission from phosphorescence from triplet excitons (Japanese Patent Laid-Open No. 2001-313178) is also progressing, and quantum efficiency is dramatically increased. There is also a possibility that it can be improved.

However, even if the quantum efficiency is improved, the light extraction efficiency is reduced in such a way that the extraction efficiency is multiplied by that. In other words, if the take-out efficiency is improved, there remains room for a dramatic improvement in efficiency as a synergistic effect.

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

For example, as a method of improving the extraction efficiency, a method of improving the extraction efficiency by giving the substrate itself a light condensing property (Japanese Patent Laid-Open No. Sho 63-314795), or a light emitting layer formed with discotic liquid crystal A method of improving the front 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, etc. on the element itself (Japanese Patent Laid-Open Nos. 11-214162 and 11-214163) JP-A-11-283951, etc.) have been proposed.

However, these proposals have problems such as a complicated configuration 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 diffusing layer is formed to change the refraction angle of light to reduce light under total reflection conditions.

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

These proposals have found characteristics such as the characteristics of the 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 made of glass exclusively from the viewpoint of excellent transparency, strength, low cost, gas barrier property, chemical resistance, heat resistance, etc. Has a refractive index of about 1.52.

A transparent electrode is used as the electrode on the light extraction surface side. As 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, and the like, but is approximately 1.9 to 2.0, and is a very high refractive index material.

In addition, the refractive index of organic layers such as light-emitting materials, electron-transporting materials, and hole-transporting materials used in the light-emitting layers of organic electroluminescence devices generally has a π-conjugate that contains many benzene rings in its molecular structure. Since it is a coupled system, its refractive index is higher than that of a general organic material, and there are many that are about 1.65 to 1.75.

In such an organic electroluminescence element, the emitted light generated in the light emitting layer is emitted to the entire space. When the refractive index relationship is as described above, total reflection occurs not only at the glass substrate / air layer interface but also at the ITO layer / glass substrate.

That is, in FIG. 7 to be described later, 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. When light is transmitted from the ITO 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 the 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 confined inside the device. The light that enters the glass substrate is totally reflected at the interface between the glass and air, and is confined inside the device. When these ratios are calculated in consideration of the solid angle, about 20% of light can be emitted to the outside, about 35% of light reflected at the glass / air interface, and about 45 of 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 for the light reflected at the ITO / glass interface, It can not show any effect. Moreover, as described above, in the classical calculation, about 45% of the emitted light is lost at the interface.

By the way, in the organic electroluminescence device, when an electric field is applied, holes injected from the anode and electrons injected from the cathode are recombined to form excitons, and the fluorescent material (or phosphorescent material) emits light. It uses the principle to do. Therefore, in order to increase the quantum efficiency, this recombination needs to be performed efficiently.

A method generally used as the method is a method in which the element has a laminated structure. Examples of the laminated structure include a two-layer type of hole transport layer / electron transporting light-emitting layer, and a three-layer type of hole transport layer / light-emitting layer / electron transport layer. In order to increase efficiency, a number of stacked elements having a double hetero structure have been proposed.

In such a laminated structure, recombination occurs almost concentrated in a certain region.

For example, in the case of the two-layer type organic electroluminescence element, as shown in FIG. 10, it 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 formed interface layer between the hole transport layer 4 and the electron transporting light emitting layer 5 is intensively generated in the region 6 on the side of the electron transporting light emitting layer, approximately 10 nm (Takuya Ogawa, et al, “IEICE TRANS ELECTRON”). Vol.E85-C, No. 6, pages 1239, 2002).

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

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

In FIG. 11, only the radiated light in the front direction is described, but light in the oblique direction actually exists, and the interference condition varies depending on the angle of the radiated light depending on the distance d and the emission wavelength λ. As a result, light in the front direction can be intensified and light in the wide angle direction can be intensified, or vice versa. That is, the light emission luminance varies depending on the viewing angle. Of course, as the distance d increases, the light intensity changes significantly depending on the angle.

Therefore, the film thickness is usually set so that the distance d is about 1/4 wavelength of the emission wavelength so that the light in the front direction strengthens each other.

Further, when the distance d is thinner than about 50 nm, for example, light is remarkably absorbed in the reflective electrode in which metal is usually used, and the emission intensity is reduced and the intensity distribution is affected. That is, in the organic electroluminescence element, the radiated light distribution changes remarkably depending on the distance d between the light emitting region and the reflective electrode, and the above-described waveguide light component changes greatly accordingly.

Furthermore, the emission spectrum of the organic electroluminescence element has a broad characteristic over a relatively wide wavelength. Therefore, as a result of the wavelength range that strengthens depending on the distance d changing, the emission peak wavelength changes. Also, depending on the distance d, the emission spectrum also changes depending on the viewing angle.

In order to solve these problems, a proposal has been made to select a film thickness so as to suppress a phenomenon in which the emission color varies depending on the viewing angle (see Patent Document 1). However, there is no description regarding guided light in this proposal, and the film thickness that can suppress the viewing angle dependence of the emission color by this proposal is clearly different from the scope of the present invention described later.

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

That is, the guided light component also changes significantly depending on the element configuration. For example, M.M. H. According to a report by Lu et al. (J. Appl. Phys., Vol. 91, No. 2, p. 595, 2002), a guided light component by an element configuration is obtained by a quantum theoretical calculation method considering a microcavity effect. A detailed study of changes in
Japanese Patent Laid-Open No. 5-3081 (pages 2 to 4)

In view of the conventional technology as described above, the present invention provides loss light confined as guided light inside the element, particularly loss light totally reflected at the interface between the transparent electrode and the glass substrate, which has been difficult to extract conventionally. In addition, an object of the present invention is to provide an organic electroluminescence element that is efficiently extracted and has excellent external extraction efficiency, and also to provide a highly efficient surface light source and display device using this element.

As a result of intensive studies in order to solve the above problems, the present inventors have obtained the following knowledge. This will be described with reference to FIGS.

First, FIG. 7 shows a schematic diagram of the two-layered organic electroluminescence element shown in FIG. 10 when emitted light from the light emitting region is emitted to the outside, only for the upper hemisphere. Is. Actually, there is emitted light in the direction of the reflective electrode, but it is omitted here.

In FIG. 7, as described above, the emitted light emitted in all directions is first totally reflected at the interface between the transparent electrode and the glass substrate and 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. If 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 in the classical calculation.

Next, the light transmitted to the glass substrate is further totally reflected at the air interface and confined inside. The loss at this interface corresponds to about 35% of the total emitted light in the same calculation. Therefore, only 20% is actually emitted to the outside and reaches the observer.

Therefore, in the two-layer type organic electroluminescence element shown in FIG. 7 (FIG. 10), as shown in FIG. 8, the region 8 in which the reflection / refraction angle of light is disturbed on the support substrate (glass substrate) 1 is shown. As for the light totally reflected at the air / glass interface, some of the light can be guided to the outside by diffusing the transmitted light under the total reflection condition. However, the light that can be extracted by this method is only the total reflection light at the air / glass interface, and the light that is totally reflected at the glass substrate / transparent electrode interface cannot even be incident on the region 8, so that it can be extracted outside. No effect on efficiency improvement.

As a result of further investigation to overcome the above problems, the inventors of the present invention formed a transparent layer having a refractive index equal to or higher than that of the light emitting layer adjacent to the transparent electrode, and then emitted light. By diffusing and refracting the light, the light totally reflected at the glass substrate / transparent electrode interface can be guided to the outside. As a result, it is effective for light corresponding to about 80% of the whole. It turns out that it 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. 7 (FIG. 10) in order to understand this point. It shows the state of. As described above, all the emitted light generated from the light emitting layer is transmitted to the transparent electrode having a high refractive index. Next, when entering the support substrate, if the refractive index is lower than that of the light emitting layer, total reflection occurs, but if it is greater than the refractive index of the light emitting layer, there is no critical angle according to Snell's law, and all light is It becomes possible to enter the support substrate.

Here, when the refractive index of the support substrate is increased, the critical angle at the air / support substrate interface is decreased, and the light extracted to the outside is only 20% of the whole. However, unlike light confined in an extremely thin thin film having a total thickness of only a few hundred nm, if the light can be guided to a relatively thick layer such as a support substrate, the organic electroluminescent device They can be taken out without damaging the properties.

Further, as described above, in an actual organic electroluminescence element, a light interference effect occurs. Usually, the element configuration is usually determined so that light in the front direction that can be emitted to the outside is strengthened. In this case, since the guided light interferes so as to be weakened, even if a region that causes disturbance in the reflection / refraction angle of the light is formed, a large brightness improvement effect cannot be expected.

However, unlike the conventional methods described above, the inventors of the present invention purposely determine the element configuration so that light in the front direction is weakened and light of a wide angle component normally confined inside the element as guided light is strengthened. Then, after amplifying the waveguide light in which the most amount of light is distributed, an area that causes disturbance in the reflection / refraction angle of the light is formed. I found out that

In other words, the area where light reflection / refraction angle is not disturbed is not provided, and the luminous efficiency is lowered with ordinary organic electroluminescence elements. However, when the above areas are provided, the above-mentioned areas are provided in the conventional element. As a result, it was found that a highly efficient organic electroluminescence device was finally obtained.

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

That is, the present invention relates to an organic electroluminescence device having at least one organic layer including a light emitting layer and a pair of electrodes each including at least one of an anode electrode and a cathode 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 light is reflected adjacent to or inside the light extraction surface side of the transparent layer. A region that causes disturbance in the refraction angle is provided , and the above-described region that causes disturbance in the reflection / refraction angle of light has an average particle diameter of 0.2 to 20 μm in the transparent material, which has a different refractive index. A transparent material or a non-transparent material having a light diffusible portion dispersed therein, a lens structure, or an uneven surface having a surface roughness of 1 μm or more, and a pair with the organic layer. The front luminance value of the emitted light radiated from the light extraction surface to the observer side is 50 ° to 70 ° in a state where the electrode does not have the above-described transparent layer and a region in which the reflection / refraction angle of light is disturbed. The organic electroluminescence element (hereinafter simply referred to as “light emitting value in the direction of the angle”) is formed so as to satisfy the relationship of the formula (1); the luminance value in the front direction <the luminance value in the direction of 50 degrees to 70 degrees. (Referred to as organic EL element) .

Further, according to the present invention, 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) In the above polycarbodiimide resin, 10 mol% or more of R (organic diisocyanate residue) in the formula (I) is a naphthalene diisocyanate residue, and R ¹ in the formula (I) (organic monoisocyanate residue). The present invention relates to an organic EL device having the above-described structure, in which (isocyanate residue) is a 1-naphthyl isocyanate residue.

The present invention also relates to an organic EL device having the above-described 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 a transparent layer.

Further, in the present invention, as a particularly preferable embodiment of such an organic EL element, a pair of electrodes composed of an anode electrode and a cathode electrode is composed of a reflective electrode and a transparent electrode, and a hole-electron recombination light-emitting region is formed. The distance between the central portion and the reflective electrode is d (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. In this case, the organic EL element has the above-described configuration that satisfies the relationship of the formula (2): (0.3 / n) λ <d <(0.5 / n) λ.

The present invention also relates to a surface light source comprising the organic EL elements having the above-described configurations, and to a display device comprising the organic EL elements having the respective configurations. It is.

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

In addition, by applying this organic EL element to a surface light source or a display device, it is possible to reduce power consumption and reduce the current flowing to the element, thereby reducing the deterioration of organic materials and extending the life of the element. Is also connected.

In addition, by forming a region that causes disturbance in the reflection / transmission angle of light, even if a gark spot seen in an organic EL element is generated, it is almost invisible and the organic has no change in appearance over a long period of time. The effect which can provide an EL element is also acquired.

Embodiments of the present invention will be described below with reference to the drawings.

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

In other words, the organic layer composed of the hole transport layer 4 and the electron transport light-emitting layer 5 is sandwiched between a pair of electrodes composed of the transparent electrode (anode) 2 and the reflective electrode (cathode) 3. During operation, recombination occurs in a region on the side of the electron transporting light emitting layer of about 10 nm from the interface layer between the hole transporting layer 4 and the electron transporting light emitting layer 5, and light emission is concentrated in the illustrated light emitting region 6. Arise.

Note that, for example, in a three-layer type organic EL element of a hole transport layer / light emitting layer / electron transport layer different from the two-layer type, when a voltage is applied between the electrodes, holes are generated from the anode and from the cathode. Electrons are injected, they move through the respective carrier transport layers and recombine in the light emitting layer to generate excitons, and EL light emission occurs as described above.

Further, in the above-mentioned organic EL element, in order to make the effects of the present invention better, the light emission in the front direction is particularly weakened as the above basic structure, but the guided light confined inside the element is intensified. 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 angular distribution of the luminance of the organic EL element having only the above-described basic configuration (that is, before providing a transparent layer and a region in which the reflection / refraction angle of light described below is disturbed) as 0 ° in front. It is a characteristic view measured every 10 degrees from 80 degrees to 80 degrees. In the figure, curve -a is the one according to the present invention, and curve -b is the conventional one.

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 (according to the present invention) and 60 nm (conventional one). It is. The current applied to the element is measured by applying a voltage so that the current of the present invention is 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 ° front direction, and the luminance value is substantially constant over a relatively wide range, and shows a preferable luminance distribution of a perfect diffusion type. . On the other hand, the thing of this invention has the characteristic that a brightness | luminance becomes high, so that a front luminance value is low and it becomes a wide angle.

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

This relationship is achieved in the above example due to the difference in thickness of the electron-transporting light-emitting layer 5, but the material and thickness of the organic layer including the light-emitting layer 5 and the pair of electrodes are appropriately determined. By selecting, it can be achieved arbitrarily.

In a more 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 light-emitting layer (in this case, the electron-transporting light-emitting layer 5) is used. When the peak wavelength of the fluorescence emission spectrum of the material is λ and the refractive index of the organic layer (in this case, the electron-transporting light-emitting layer 5) between the light-emitting layer and the reflective electrode 3 is n, formula (2); It is desirable to be configured so as to satisfy the relationship (0.3 / n) λ <d <(0.5 / n) λ.

For example, in the above example, if the electron transporting light emitting layer 5 is green light having a peak fluorescence emission 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 in the range.

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 is more important in actual lighting applications. For 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, and a blue light emitting layer, a green light emitting layer, a red light emitting layer, and a yellow light emitting layer, There are many other types such as a method of laminating separately and a method using a material that emits white light.

These organic EL elements have a plurality of emission peaks in each wavelength region, like fluorescent lamps. In this case, depending on the emission wavelength, the recombination region, and the distance between the reflective electrodes, the case where the emitted light in the front direction strengthens and the case where it weakens significantly change depending on the wavelength region.

For example, in the white light-emitting organic EL element described above, a type in which blue, green, and red light emitting materials are dispersed in one light emitting layer, and the respective emission peak wavelengths are 450 nm, 540 nm, and 630 nm, The distance d satisfying the formula (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, assuming that the refractive index of the light emitting layer is 1.65. And each will be different.

In the present invention, the basic structure satisfying the relationship of the formula (1), more preferably the relationship of the formula (2) is used, and the refractive index is adjacent to the light extraction surface side of the transparent electrode 2. Is provided as a region 8 that is provided with a transparent layer 7 that is equal to or more than the light emitting layer and that is substantially adjacent to the light extraction surface side of the transparent layer 7 and that substantially disturbs the reflection / scattering angle of light. The transparent layer is a matrix, and a light diffusion layer in which diffusion particles having a different refractive index are dispersed is provided. Thereby, there is no total reflected light at the interface between the transparent layer 7 and the transparent electrode 2, 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. As a result, Luminous brightness is greatly improved.

In the present invention, regarding the transparent layer 7 described above, the refractive index equal to or higher than that of the light emitting layer is 0.95 times or more with respect to the refractive index of the light emitting layer, 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 drawn as if it was extracted to the outside, but in reality, the light that has passed through the light diffusion layer 8 is also at the interface of the support substrate 1. Received total reflection and trapped. However, the light totally reflected at the interface between the support substrate 1 and the air layer is finally extracted outside by repeating the reflection at the reflective electrode 3 and the light diffusion layer 8 again and again. become.

Further, in the configuration shown in FIG. 1, the region 8 that causes the reflection / scattering angle of the light to be 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. That is, the transparent layer 7 itself may be constituted by the light diffusion layer 8 described above. Furthermore, as shown in FIG. 4, a support substrate 1 made of a transparent layer material can be used, and the substrate 1 itself can be used as the transparent layer 7.

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

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

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 transporting layer 4 and a transparent electrode 2 are provided in this order on a support substrate 1, A so-called upper surface extraction type organic EL element that extracts emitted light from the opposite surface side of the support substrate 1 by further sequentially providing the transparent layer 7 and the light diffusion layer 8 as described above may be used. In this case, the support substrate 1 does not particularly need to be transparent.

Furthermore, the present invention can also be applied to a double-sided organic EL element in which both are formed of transparent electrodes instead of the reflective electrodes. In this case, the light emission intensity on both sides can be improved by forming the transparent layer and the light diffusion layer on both transparent electrodes. Thus, in the case of the organic EL element of the double-side extraction type without a reflective electrode, it is not necessary to satisfy the above-mentioned formulas (1) and (2).

In addition, the organic EL element of the present invention is provided with a transparent layer 7 adjacent to the light extraction surface side of the transparent electrode 2 having a high refractive index, and adjacent to the light extraction surface side of the transparent layer 7 or of the transparent layer 7. It suffices if the region 8 that substantially disturbs the reflection / scattering angle of light is provided inside, and various embodiments can be taken in addition to the above examples. Further, 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 thus two or more transparent layers having different functions may be formed.

In the organic EL element of the present invention, the organic material, electrode material, layer structure and film thickness of each layer as the basic structure are not particularly limited, and the conventional technique can be applied as it is. The organic layer may be formed by vacuum deposition of a low molecular weight material, or a high molecular weight material may be formed by a coating method or the like, and is not particularly limited.

Specifically, the anode / hole transport layer / electron transporting light-emitting layer / cathode, which is the above-described two-layer organic EL element, and the anode / hole transport layer, which is a three-layer 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 elements can be selected, and there is no particular limitation.

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

As the electrode material, an optimal material can be 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. For the cathode, those in which Mg and Ag are co-deposited at an atomic ratio of about 10: 1, a Ca electrode, an Al electrode doped with a small amount of Li, etc. are preferable from the viewpoint of improving the electron injection efficiency by lowering the work function of the cathode. Although 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 the method of using a glass substrate and extracting light emission through the transparent electrode to the glass substrate side, as described above, an opaque metal plate is used for the support substrate, and light is extracted from the opposite side of the support substrate. It is good also as such a structure.

In addition to using the anode as a transparent electrode, a thin metal electrode capable of maintaining translucency of several nanometers to several tens of nanometers from the interface of the organic layer is formed as a cathode, and then ITO is formed. Thus, the cathode may be a transparent electrode.

Furthermore, a flexible material such as a polymer film may be used for the support substrate, and as described above, the support substrate itself may constitute a transparent layer, and light may be emitted from the support substrate itself. A region in which the reflection / refraction angle is disturbed may be formed.

Regardless of an organic material or an inorganic material, the material of the transparent layer in the present invention can be suitably used as long as its refractive index is equal to or higher than that of the light emitting layer.

For example, high refractive index glass containing sulfur atoms, polyethylene terephthalate resin having a refractive index of 1.65, polyethersulfone resin, or the like having a refractive index of 0.95 times or more with respect to the refractive index of the light emitting layer The effect of the present invention can be exhibited to some extent. From the viewpoint of processability, a resin material is desirable.

However, characteristics other than the refractive index such as molding processability, heat resistance, thermal expansion coefficient, moisture resistance, adhesion to the transparent electrode, and transparency are also important, and these characteristics are satisfied. Many materials are not satisfactory. In order to maximize the effects of the present invention, it is desirable that the refractive index be 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 refractive index higher than this 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 in order 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 , other sulfides such as ZnS, selenides, tellurides, etc. There are no particular restrictions. The shape of these fine particles may be spherical or not, and can be widely used as long as scattering does not occur in the visible light region.

The particle diameter of these fine particles must be sufficiently smaller than the wavelength of visible light and not larger than the size that does not cause light scattering in the visible light region, and the average particle diameter is 1 to 100 nm, preferably It is good that it is 1-50 nm.

The amount of these fine particles added is not particularly limited, but it is preferable that the amount of 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 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 present 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 that of the light emitting layer. The refractive index of the light-emitting layer varies depending on its molecular structure, but some of the higher ones exceed 1.75. In this case, the refractive index of ordinary resin materials is usually 1.7 or less, and in order to sufficiently increase the refractive index, it is necessary to add a large amount of fine particles as described above.

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

However, the refractive index of a general resin is about 1.49 to 1.65. Except for a special one such as a resin containing a sulfur atom, which is used for a plastic lens of eyeglasses, the resin alone of the present invention is used. There are few that can be suitably used.

As a result of intensive studies in view of such a situation, the present inventors, as a material applied to the transparent layer, have 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 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 mixed group of two or more. Especially, it is desirable to occupy 10 mol% or more of naphthalene diisocyanate residues in all organic diisocyanate residues. The organic monoisocyanate residue (R ¹ ) is particularly preferably a 1-naphthyl isocyanate group.

Such polycarbodiimide resin uses, for example, several kinds of organic diisocyanates, and these are subjected to a carbodiimidization reaction in the presence of a carbodiimidization catalyst and a solvent at 0 to 150 ° C., preferably 10 to 120 ° C. It can be obtained by end-capping with isocyanate. The end-capped polycarbodiimide resin is excellent in storage stability of the solution.

Here, the end-capping with the organic monoisocyanate can be carried out by adding the organic monoisocyanate to the reaction system at the final stage, the middle stage, or the initial stage of the polymerization reaction or throughout the polymerization reaction. The end point of the reaction can be confirmed by observing the absorption (2,140 cm ⁻¹ ) derived from the carbodiimide group by IR measurement and the disappearance of the absorption derived from the isocyanate group (2,280 cm ⁻¹ ).

Organic diisocyanates include hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, cyclohexyl diisocyanate, 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] hexafluorobropan, 2, One type or two or more types such as 2-bis [4- (4-isocyanatophenoxy) phenyl] propane may be mentioned.

In particular, it is desirable to use 10% by mole or more of naphthalene diisocyanate. 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, 1-naphthyl isocyanate are preferable. Species or two or more are used.

Among these organic monoisocyanates, it is particularly preferable to use 1-naphthyl isocyanate because the monoisocyanates do not react with each other and the end-capping of polycarbodiimide can proceed efficiently.

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 mole, the molecular weight of the polycarbodiimide resin becomes too large, or the viscosity of the solution increases due to the crosslinking reaction or the solution is solidified, so that 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 film well when forming a film by coating and drying.

When an organic diisocyanate is used as an aliphatic diisocyanate and an aromatic diisocyanate and both 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 0 to 50 ° C, more preferably 10 to 40 ° C. When the reaction temperature is higher than 50 ° C., the reaction between the aromatic diisocyanates proceeds preferentially, and the reaction between the aliphatic diisocyanate and the aromatic diisocyanate does not proceed sufficiently.

Moreover, when the aromatic diisocyanate which exists excessively in the reaction system is further reacted with the polycarbodiimide resin obtained by the polymerization reaction in this way, the reaction temperature is preferably 40 to 150 ° C, and preferably 50 to 120 ° C. More preferably. If the reaction temperature is less than 40 ° C., the reaction takes time and is not practical, and if it exceeds 150 ° C., it becomes difficult to select a reaction solvent.

The organic solvent used as the reaction solvent and the dilute solution of the resulting polycarbodiimide resin may be a conventionally known one.

Specifically, halogenated hydrocarbons such as tetrachloroethylene, 1,2-dichloroethane, 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 aromatic hydrocarbon solvents. One of these organic solvents may be used alone, or two or more thereof may be mixed and used.

The concentration of the organic diisocyanate in the reaction system is desirably 5 to 80% by weight. If it is lower than 5% by weight, the carbodiimidization reaction may not proceed, and if it exceeds 80% by weight, it may be difficult to control the reaction.

Any known phosphorus-based catalyst is preferably used as the carbodiimidization catalyst. Specifically, 1-phenyl-2-phospholene-1-oxide, 3-methyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, 3-methyl-1-phenyl-2 Mention may be made of phospholene oxides such as phospholene-1-oxide and their 3-phospholene isomers.

After completion of the carbodiimidization reaction, the reaction solution may be put into a poor solvent such as methanol, ethanol, isopropyl alcohol, hexane, and the polycarbodiimide resin is precipitated and precipitated, and unreacted monomers and catalysts may be removed.

In order to prepare a polycarbodiimide resin solution, the precipitated polymer is washed and dried by a predetermined operation, and then dissolved again in an organic solvent. 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 being adsorbed on an appropriate adsorbent or the like. As the adsorbent, alumina gel, silica gel, activated carbon, zeolite, activated magnesium oxide, activated bauxite, frath earth, activated clay, molecular sieve carbon and 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 above-mentioned fine particles to the polycarbodiimide resin, the effect of the present invention can be more effectively exhibited as a transparent layer that is almost close to the refractive index of the transparent electrode without impairing the original characteristics of the resin. it can.

In the present invention, the region that causes disturbance in the reflection / refraction angle of light can basically efficiently disturb the transmission angle of light that is greater than or equal to the total reflection angle to a transmission angle that is less than or equal to the total reflection angle, The formation method is not particularly limited as long as it is formed so that more guided light confined inside the element can be emitted to the outside. That is, what has been proposed conventionally can be applied as it is.

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

There is no limitation on the refractive index, refractive index difference, particle size, etc., but from the viewpoint of causing light scattering, the particle size is 0.2 to 20 μm, preferably 0.3 to 10 μm, more preferably 0. It is preferable that the refractive index difference is 0.05 or more.

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

Specific examples include lenticular lenses, Fresnel lenses, corner cube lenses, fly-eye lenses, cat-eye lenses, double fly-eye lenses, double lenticular lenses, radial lenticular lenses, prism lenses, and microprism lenses. Or a lens obtained by changing the convex surface of these lenses to a concave surface, or a transparent sphere or a semi-transparent sphere arranged in a planar shape. Alternatively, the direction of light may be changed by carving a groove such as a V-shaped groove.

Furthermore, you may form a physical uneven surface in the support substrate surface or each interface. Specifically, it can be formed by transferring a periodic uneven structure. Further, the size of the uneven surface is preferably larger than the wavelength of light, specifically, 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 rainbow-colored glare occurs due to the interference effect of light.

In the present invention, a surface light source characterized by comprising an organic EL element having such a structure 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.

In addition, 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. Moreover, IR measurement was performed using FT / IR-230 (made by JEOL Ltd.).

<Synthesis Example 1>
To 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 stirred at 100 ° C. The temperature was raised and held 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 clinching apparatus, 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) Mmol), 44.87 g (266.76 mmol) of hexamethylene diisocyanate and 216.56 g of toluene were added and mixed. To this were added 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, and the mixture was stirred at 25 ° C. for 3 hours. After that, the temperature was raised to 100 ° C. with stirring, and 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 above. That is, the 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-like sample having a thickness of 50 μm was produced.

This sample was cut into a size of 1 cm × 2 cm, cured for 1 hour in a curing furnace at 120 ° C., 150 ° C., and 175 ° C., and then its refractive index was measured using a multiwavelength upe refractometer (DR-M4 manufactured by ASTAGO). Measured with

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 application 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│
└────┴───────┴───────┴───────┘

A toluene solution containing 70% by weight of silica particles having an average particle size of 0.5 μm was added to the polycarbodiimide resin solution obtained in Synthesis Example 1 at a ratio of 20% by weight with respect to the polycarbodiimide resin and stirred. . This dispersion is applied on a glass substrate with an applicator and cured at 150 ° C. for 1 hour to form a transparent layer that doubles 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. When the haze value of this sample was measured with a reflection / transmittance meter (“HR-100” manufactured by Murakami Color Research Laboratory Co., Ltd.), it was 87.3%.

Next, from the ITO ceramic target (In ₂ O ₃ : SnO ₂ = 90% by weight: 10% by weight) on the surface of the transparent layer that also serves as the light diffusion layer, in order to produce the organic EL element shown in FIG. An ITO layer having a thickness of 100 nm was formed by sputtering, and a transparent electrode (anode) was formed. Separately, in order to produce the organic EL device shown in FIG. 7, a transparent layer that also serves as a light diffusion layer is not formed, but an ITO layer is formed directly on the glass substrate in the same manner as described above, and a transparent electrode ( Anode).

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

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

Thereafter, 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 with a thickness of 100 nm. From the viewpoint of preventing MgAg oxidation, Ag is further deposited thereon. A reflective electrode (back electrode) (cathode) was formed to a thickness of 50 nm.

After taking out from the vacuum evaporation system, drop an ultraviolet curable epoxy resin on the cathode electrode side, cover it with a slide glass, and when the epoxy resin spreads sufficiently, cure the epoxy resin with a high pressure ultraviolet lamp, Sealed.

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

About the organic EL element which does not form the transparent layer which serves as a light-diffusion layer, the brightness | luminance was measured every 10 degree | times from 0 degree to 80 degree | times with the commercially available luminance meter (Product name "BM9" by Topcon Co., Ltd.). Each luminance value is 0 degree: 126 cd / m ² , 10 degree: 138 cd / m ² , 20 degree: 154 cd / m ² , 30 degree: 181 cd / m ² , 40 degree: 225 cd / m ² , 50 degree: 272 cd / m ² , 60 degrees: 307 cd / m ² , 70 degrees: 386 cd / m ² , 80 degrees: 339 cd / m ² .

As is clear from this result, the organic EL element in which the transparent layer serving also as the light diffusion layer is not formed sufficiently satisfies the relationship of the formula (1) of the present invention.

In this organic EL device, the recombination of holes and electrons occurs 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. Moreover, the peak wavelength λ of the fluorescence spectrum when the black light was used as the excitation light source and the Alq thin film deposited on the glass substrate was irradiated was about 530 nm.

Furthermore, the refractive index n of the Alq film measured using a spectroscopic ellipsometer was approximately 1.67 at a wavelength of 590 nm. Therefore, said organic EL element was also satisfying the relationship of Formula (2) of this invention.

Next, as a result of measuring the front luminance when a voltage of 15 V was applied to the organic EL element of the present invention in which a transparent layer that also serves as a light diffusion layer was formed, the result was 387 cd / m ^2. It was.

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

As is apparent from the results, in accordance with the present invention, an organic EL device, in particular, the above transparent electrode, is formed by forming on the ITO transparent electrode a transparent layer that also serves as a light diffusing layer using a polycarbodiimide resin having a high refractive index as a matrix. According to the organic EL element whose characteristics when the layer is not formed satisfy the relationship of the formulas (1) and (2) of the present invention, the value of the front luminance is large from 126 cd / m ² to 387 cd / m ^2. It was confirmed that this was an increase.

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 produced in the same procedure as in Example 1.

When a voltage of 15 V was applied to the organic EL element 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 a dispersion containing silica particles on a glass substrate, the dispersion containing the silica particles was applied onto a polyethylene terephthalate (PET) film having a surface peel-treated at 150 ° C. After curing for 1 hour, a light diffusion layer having a thickness of 25 μm was formed. Next, the polycarbodiimide resin solution obtained in Synthesis Example 1 itself (that is, a resin solution to which no silica particles are added) is applied on this light diffusion layer, and cured at 150 ° C. for 1 hour, A 25 μm transparent layer was formed.

Peeling from the PET film gave a film layer (light diffusion layer and transparent layer) having an overall thickness of 50 μm. This film layer was adhered and laminated on a glass substrate, and 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 543 cd / m ² , and it was confirmed that the luminance was greatly increased.

A polyethersulfone (PES) resin was dissolved in 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 size of 0.5 μm was dissolved in PES. The mixture was added at a ratio of 20% by weight and stirred. This dispersion was applied onto a glass substrate with an applicator and dried at 150 ° C. for 15 minutes to form a transparent layer having a thickness of 25 μm and 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. When the haze value of this sample was measured with a reflection / transmittance meter (“HR-100” manufactured by Murakami Color Research Laboratory Co., Ltd.), it was 84.7%.

Thereafter, the organic EL element shown in FIG. 3 was produced in the same procedure as in Example 1. When a voltage of 15 V was applied to the organic EL element and the front luminance was measured, it was 356 cd / m ² , and it was confirmed that the luminance increased.

Comparative Example 1
A toluene solution containing 70% by weight of silica particles having an average particle size of 0.5 μm was added to the polycarbodiimide resin solution obtained in Synthesis Example 1 at a ratio of 20% by weight with respect to the polycarbodiimide resin and stirred. . This dispersion is applied on a glass substrate with an applicator and cured at 150 ° C. for 1 hour to form a transparent layer that doubles as a 25 μm thick light diffusion layer on a 1.1 mm thick glass substrate. did.

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

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

Thereafter, the organic EL element shown in FIG. 8 was produced in the same procedure as in Example 1. When a voltage of 15 V was applied to this device and the front luminance was measured, it was 278 cd / m ² . In this way, when a glass substrate with a low refractive index exists on the ITO transparent electrode, even if a light diffusing layer using a polycarbodiimide resin having a high refractive index as a matrix is formed, the luminance is increased. Compared to Example 1, it was small.

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

As a result, 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 , 80 degrees: 202 cd / m ² .

As is clear from this result, the organic EL element described above did not satisfy the relationship of the formula (1) of the present invention. Further, in this organic EL element, the distance d between the central portion of the hole-electron recombination light-emitting region and the reflective electrode in the present invention is approximately 60 nm, so the relationship of the formula (2) of the present invention is also satisfied. It was not something.

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 as described above. When a voltage of 8.2 V was applied to the organic EL element 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, There was almost no increase.

An acrylate UV curable resin with a refractive index of 1.65 ("GRANDIC PC2-720 series" manufactured by Dainippon Ink & Chemicals, Inc.) is applied to a mold in which a regular pyramid structure with a side of 10 μm is formed without gaps. The film was applied using an applicator, and cured by irradiating with 200 mJ / cm ² of ultraviolet light with a high-pressure ultraviolet lamp.

On the surface, for the purpose of increasing the film strength, a solution obtained by dissolving PES resin in DMAc solvent at a concentration of 25% by weight was further applied, dried at 120 ° C. for 20 minutes, and then peeled off from the mold. A resin sheet having an uneven structure was formed.

Next, ITO was formed to a thickness of 100 nm on the PES resin surface opposite to the surface on which the pyramid structure of the resin sheet was formed. Thereafter, the organic EL element shown in FIG. 5 was produced in the same procedure as in Example 1.

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

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

When a voltage of 15 V was applied to this organic EL element and the front luminance was measured, it was 312 cd / m ² , which was lower than that in Example 5, but the luminance improvement effect was still recognized. It was.

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

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

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

It is sectional drawing which shows the 1st example of the organic electroluminescent element of this invention. It is a characteristic view which shows the angle dependence of the brightness | luminance about the basic composition of this invention and the conventional organic electroluminescent element. It is sectional drawing which shows the 2nd example of the organic electroluminescent element of this 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. It is a principle explanatory view of the present invention. It is another principle explanatory drawing of this invention. It is another principle explanatory view of the present invention. It is explanatory drawing which shows the light emission area | region of an organic electroluminescent element. It is explanatory drawing about the brightness | luminance of an organic electroluminescent element.

Explanation of symbols

1 Support substrate 2 Transparent electrode (anode)
3 Reflective electrode (cathode)
4 hole transport layer 5 electron transporting light emitting layer 6 light emitting region 7 transparent layer 8 region that causes disturbance in reflection and refraction angle of light

Claims (8)

In an organic electroluminescence device having at least one organic layer including a light emitting layer and a pair of electrodes each including at least one of an anode electrode and a cathode electrode sandwiching the organic layer, the light extraction surface side of the transparent electrode adjacent to, the refractive index is provided with the light-emitting layer and equal to or more transparent layers, and the turbulence within the adjacent light extraction surface side or the transparent layer of the transparent layer to the reflection and refraction angle of light The above-described region where the reflection / refraction angle of the light is disturbed is a transparent material or an opaque material having an average particle diameter of 0.2 to 20 μm different from the refractive index in the transparent material. Of the organic layer and the pair of electrodes are made of the above-mentioned transparent layer. The front luminance value of the emitted light emitted from the light extraction surface to the observer side and the luminance value in the direction of 50 degrees to 70 degrees in a state where the layer and the region that causes the disturbance of the reflection / refraction angle of light are not provided, An organic electroluminescent element characterized by being formed so as to satisfy the relationship of formula (1): front luminance value <luminance value in the direction of 50 degrees to 70 degrees .
The transparent layer has the following formula (I):
^{R 1 -N = C = N (} -R-N = C = N-) n-R 1 ... (I)
The organic electroluminescent device according to claim 1, comprising a polycarbodiimide resin represented by the formula: wherein R is an organic diisocyanate residue, R ¹ is an organic monoisocyanate residue, and n is an integer of 1 to 100.
3. The organic electroluminescence device according to claim 2 , wherein the polycarbodiimide resin is one in which 10 mol% or more of R (organic diisocyanate residue) in the formula (I) is a naphthalene diisocyanate residue.
The organic electroluminescence device according to claim 2 or 3 , wherein the polycarbodiimide resin is ^one in which R ¹ (organic monoisocyanate residue) in the formula (I) is a 1-naphthyl isocyanate residue.
The organic electroluminescence device according to any one of claims 1 to 4 , wherein 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.
A pair of electrodes consisting of an anode electrode and a cathode electrode consists of a reflective electrode and a transparent electrode. The distance between the center of the hole-electron recombination light-emitting region and the reflective electrode is d (nm), When 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 electroluminescent element according to claim 1, satisfying a relationship of <d <(0.5 / n) λ.
A surface light source, characterized by comprising the organic electroluminescence device according to any one of claims 1-6.
Display device characterized by comprising the organic electroluminescence device according to any one of claims 1-6.

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