JP2009110873A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spontaneous emission display device, capable of improving light takeout efficiency from a light emitting layer, and achieving high front luminance, and high resolution. <P>SOLUTION: On a substrate 1, a light emitting element comprising an anode 2, the light emitting layer 3, and a cathode 4 is laminated, and the light emitting element is sealed with a sealing film 5. On the light emitting surface side of the sealing film 5, a light takeout layer 7 is integrated with the sealing film. On the light incident surface side of the light takeout layer 7, projections are formed in one-to-one correspondence to the position of the light emitting element. In a gap 6 between the projection and the projection, material of a lower index of refraction than the index of refraction of the light takeout layer is filled. Light advancing in diagonal directions which is totally reflected on the surface of each layer without being taken out in conventional devices is totally reflected on the projections on the light takeout layer to be directed upward, so that the light can be taken out. Due to the presence of the projections, mixture of light from adjoining picture elements is hard to occur, thereby resolution can be improved compared to conventional display devices. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light emitting element such as an organic EL element and a display device using the same, and relates to an improvement for improving the extraction efficiency of the light emitting element.

In general, an organic EL element is a self-luminous element, and thus has high visibility and can be thinned. Therefore, application to a flat panel display is expected. Research on EL using organic materials is old, and various researches have been made, but at first, due to poor luminous efficiency, it was not practically used.
However, in 1987, CWTang of Kodak Co., Ltd. proposed a functionally separated organic EL device that was divided into a hole transport layer and a light-emitting layer, and it was possible to obtain much higher light emission efficiency than conventional ones. became. Since then, research on organic EL devices has become very active. In particular, organic EL devices can emit light with high brightness at a voltage as low as several volts, and emit light of any color tone by selecting a fluorescent material. Since it can be performed, development aimed at practical use as a flat panel display, a liquid crystal display backlight, and a light source for illumination has been energetically performed.

  For example, as shown in FIG. 4, a general organic EL element has a structure in which a light-transmitting ITO film 110 is formed on a glass substrate 100 by sputtering, and a photosensitive resist is applied to the surface of the ITO film 110 to perform exposure. After development, the ITO film is etched into a stripe shape with an etchant such as hydrochloric acid to form a transparent electrode pattern. Then, a hole transport layer 120 made of a triphenylamine-based material (TPD) is provided on the surface, and a light emitting layer 130 also serving as an electron transport layer 140 made of an aluminum complex such as Alq3 is laminated thereon to form an organic layer. To do. Further, the cathode 150 made of Al, Li, Ag, Mg, In, or an alloy thereof is formed in a stripe shape in a direction perpendicular to the transparent electrode pattern by a method such as vacuum deposition.

Here, when a voltage is applied to the transparent electrode 110 and the back electrode 150, holes from the hole transport layer 120 in the direction of the back electrode 150 and electrons in the electron transport layer 140 in the direction of the transparent electrode 110 at the intersection of both electrodes. It moves and emits light by combining electrons and holes near the boundary between both layers. The emitted light travels in all directions, and the light traveling toward the transparent electrode 110 is transmitted as it is and emitted from the glass substrate 100 to the outside. The light traveling toward the back electrode 150 is reflected by the electrode 150, travels toward the transparent electrode 110, and is emitted to the outside.
JP-A 64-7635 JP-A-6-32307

  By the way, when a general organic EL structure that transmits through the glass substrate 100 and takes out to the outside is used, the energy conversion efficiency is very low. The luminous efficiency of the organic EL is that the phosphor has a luminous efficiency of about 25%, and the light extraction efficiency that is the ratio of the light emitted from the phosphor that is extracted outside the organic EL element is about 20%. Together, the energy conversion efficiency of the organic EL element is only about 5%.

  In particular, in the conventional organic EL structure, as shown in FIG. 5, for example, the light emitted from the phosphor is entirely caused by the difference in refractive index between the organic layers 140 to 120, the transparent electrode 110, and the glass substrate 100. Since the light is confined by the reflection effect, the light cannot be efficiently extracted outside the device. For example, when the refractive index of the organic layers 140 to 120 is N = 1.7, the refractive index of the transparent electrode 110 is N = 2.0, and the refractive index of the glass substrate 100 is N = 1.5, the organic layers 140 to 120 are used. The light transmitted from the transparent electrode 110 to the transparent electrode 110 is about 47% of the total emitted light, the light transmitted from the transparent electrode 110 to the glass substrate 100 is 34%, and the light extracted from the glass substrate 100 to the atmospheric layer is 19%, 80%. Near rays of light are lost in vain due to total reflection at the interface (Technical Information Association “Technology for High Brightness, High Efficiency, and Long Life in Organic EL Displays” P106). As described above, the configuration of the conventional organic EL element has a problem that light extraction efficiency is low and light from the light emitting layer cannot be effectively used.

Therefore, conventionally, various methods have been proposed to improve such light extraction efficiency. For example, an attempt has been made to improve light extraction efficiency by sandwiching a light emitting layer between reflective electrodes, extracting light guided through the light emitting layer from an end surface, and reflecting the light in the front direction by a micromirror placed on the substrate.
However, this method is effective when the size of the light-emitting element is large, but if the light-emitting element is miniaturized like a dot matrix display, it becomes very difficult to form a micromirror corresponding to each element.

In addition, for example, a method of suppressing a waveguide mode in a substrate by forming mesa-shaped unevenness on a glass substrate and forming an organic EL element on the top of the unevenness has been proposed.
However, in this case, there is a problem that it is difficult to process the substrate.

As another method, a method of forming a microlens on the surface of a glass substrate has been proposed. If this method is used, light having a critical angle or more that was originally totally reflected on the surface of the glass substrate can be extracted to the outside due to the refractive effect of the lens, so that the light extraction efficiency is improved.
However, in this case, if a light beam greatly tilted from the normal direction of the substrate is incident on the lens, the condensing effect of the lens does not work, and light is lost in the side direction, so the front luminance is not sufficiently increased. . In addition, light from adjacent pixels enters the same lens and mixes colors, causing a reduction in screen resolution.

  Accordingly, an object of the present invention is to provide a display device that can solve the above-described problems and can realize an organic EL light-emitting element with high extraction efficiency and high front luminance and resolution.

  In order to achieve the above object, a display device of the present invention includes a substrate, a self-luminous element formed on the substrate, a light extraction layer disposed to face the light emitting surface of the self-luminous element, A transparent sealing film that is filled between the substrate and the light extraction layer and surrounds the self-light-emitting element and integrates the substrate and the light extraction layer; and the light extraction layer includes the self-light-emitting layer. A convex portion on a surface facing the mold element, a concave portion between adjacent convex portions, and the concave portion filled with a material having a refractive index lower than that of the light extraction layer. It has a refractive material layer.

  According to the display device of the present invention, a convex portion is formed on the light incident surface of the light extraction layer disposed opposite to the light emitting surface of the self light emitting element corresponding to the position of the self light emitting element, and the adjacent convex Since the low refractive material layer having a refractive index lower than the refractive index of the light extraction layer is filled in the concave portion between the convex portion and the convex portion, the oblique light emitted from the light emitting element is fronted by the inclined surface of the light extraction layer. The screen can be refracted in the direction, and the front luminance of the screen can be improved and the extraction efficiency can be improved.

Hereinafter, embodiments of the present invention will be described in detail.
1 to 3 are cross-sectional views showing a laminated structure of a display device according to an embodiment of the present invention, and FIG. 1 shows a case where a light emission surface side of a light extraction layer is a plane (first example). Shows a case where the convex inclined surface on the light incident surface side of the light extraction layer partially includes a curved surface (second example). FIG. 3 shows a case where a convex portion is provided on the light exit surface side of the light extraction layer (third example).

As shown in FIG. 1, in the display device of the first example according to the present embodiment, a self-luminous element comprising an anode 2, a light emitting layer 3 and a cathode 4 is formed on the surface of a substrate 1, and these elements are formed. Is sealed with a sealing film 5 made of a transparent medium.
A light extraction layer 7 is provided on the viewer side of the sealing film 5, and the light extraction layer 7 and the substrate 1 are integrated via the sealing film 5.
Further, a convex portion 7a is formed on the light-emitting element side of the light extraction layer 7 corresponding to the position of the light-emitting element, and the refractive index lower than the light extraction layer 7 is between the convex portion 7a and the convex portion 7a. It is filled with a material having a refractive index (low refractive material layer).

In such a display device, the light emitted from the self-luminous element on the substrate 1 travels in all directions, but conventionally, it is totally reflected at the interface with the atmospheric layer and cannot be extracted outside. Since the light beam L2 traveling in the oblique direction is totally reflected by the inclined surface of the convex portion 7a of the light extraction layer 7, light can be extracted to the outside.
The convex shape is desirably inclined so as to open to the light exit surface side in order to effectively reflect light from the element in the front direction. For example, by giving a pyramid such as a cone, a triangular pyramid, a quadrangular pyramid, a truncated cone or a truncated pyramid shape at the element position, or a convex curved surface shape on the element side, oblique light emitted from the element is reflected on the inclined surface. It can be taken out effectively by total reflection. Alternatively, the same effect can be obtained by forming a V-shaped groove (concave portion) on the light incident surface side of the light extraction layer 7.
In addition, since light rays from adjacent pixels are blocked by the inclined surface of the convex portion 7a, color mixing is unlikely to occur, and a display with good resolution can be provided by using the configuration of this example.

  Further, the display device of the second example according to the present embodiment shown in FIG. 2 has a curved surface of the inclined surface of the convex portion 7a shown in FIG.

  Furthermore, as shown in FIG. 3, in the display device of the third example according to the present embodiment, a convex portion 8 is formed on the light emission surface side of the light extraction layer 7 corresponding to the position of the light emitting element. . By forming the convex portion 8, the oblique light emitted from the light emitting element can be refracted in the front direction, and the front luminance of the screen can be increased. The convex shape includes a lens structure such as a microlens, a lenticular lens, and a Fresnel lens, a pyramid structure such as a triangular frustum and a quadrangular pyramid, a pyramid such as a triangular pyramid and a quadrangular pyramid, and a cone like a cone. The body is mentioned.

  In the first example shown in FIG. 1, the space between the convex portions 7a on the light incident surface side of the light extraction layer 7 and the convex portions 7a may be filled with an air layer. By making the low refractive index layer an air layer, the critical angle of the interface becomes small, so that light from the light emitting element can be totally reflected more efficiently.

Hereinafter, the detailed configuration and operation of the present embodiment will be specifically described.
First, in FIG. 1, light emitted from the light emitting elements on the substrate 1 travels in all directions as diffused light. In that case, the light beam L1 traveling at an angle not so inclined from the normal direction of the substrate reaches the light exit surface as it is after entering the light extraction layer 7 and is emitted to the outside. Further, the light L2 tilted by a certain inclination angle or more from the normal direction of the substrate 1 is totally reflected by the inclined surface 7b of the convex portion 7a of the light extraction layer 7, and then reaches the light emission surface 7c of the light extraction layer 7. Refracted at the interface and emitted to the outside.
Here, the shape of the inclined surface 7b may be a planar shape as shown in FIG. 1 (first example), or may be a shape including a part of a curved surface as shown in FIG. 2 (second example). There may be. When the inclined surface 7b is a flat surface, a part of light rays whose incident angle with respect to the inclined surface does not reach the critical angle is transmitted to the low refractive index material layer. Exceeds the critical angle, the light from the light emitting element can be reflected efficiently.

  FIG. 3 (third example) shows a case where a lens structure (convex portion 8) is provided on the observer side of the light extraction layer 7 corresponding to the position of the light emitting element. Of the light emitted from the light emitting element, the light L4 traveling in the normal direction of the substrate 1 or in the vicinity of the normal direction enters the lens (convex portion 8) without being reflected by the inclined surface 7a of the convex portion 7. Then, it is refracted and taken out to the outside. The light L5 inclined by a certain inclination angle or more from the normal direction of the substrate 1 is totally reflected by the inclined surface 7a of the convex portion 7, and then enters the lens (convex portion 8) and is refracted on the lens surface to be external. Is taken out.

  However, a part of the light ray L6 incident near the skirt of the lens (convex portion 8) is totally reflected on the lens surface and returned to the substrate 1, but in this case, a highly reflective material is applied to the electrode of the light emitting element. It can be used again by using it. Alternatively, by designing the diameter of the lens to be larger than the diameter of the light emitting element, the incident angle of the light beam with respect to the lens surface can be reduced, so that total reflection inside the lens can be suppressed.

  In the case of a general organic EL, in order to extract light from the light emitting layer through the substrate to the outside, a light transmissive glass substrate, a highly smooth plastic plate, a film, or the like is used as the substrate. However, in this embodiment, since the light is extracted to the opposite side of the substrate, the substrate is not limited to such a light transmissive material, and an opaque material such as a metal plate can be used. It is.

In addition, a transparent electrode such as ITO is generally used for the anode, but in the present embodiment, light is emitted to the cathode side, and therefore, the anode is made of a metal such as Mg, Al, Ag, or an alloy thereof. It is more suitable to use a reflective electrode.
In addition, a reflective electrode is generally used for the cathode. However, in this embodiment, a light transmissive electrode such as ITO or a thin metal foil having a high light transmittance is used because of the configuration in which light is emitted to the cathode side. Use.

In addition, the sealing film 5 serves as an adhesive layer for integrating the light extraction layer and the substrate while preventing the light emitting layer from being deteriorated in light emission due to moisture contained in the outside air.
The sealing film material is composed of a thermosetting resin made of an epoxy resin, an acrylic resin, a urethane resin, or the like, or a photocurable resin. Since the light-emitting element is vulnerable to heat, it is necessary to select a resin that cures at a temperature as low as Tg as much as possible. In addition, since the light-emitting element is easily damaged by ultraviolet rays, it is preferable to use a light-curing resin that is cured with visible light rather than UV light.

  The light extraction layer 7 is manufactured separately from the EL element, and then the EL element and the light extraction layer are bonded and integrated.

  The unevenness formed on the light incident surface side of the light extraction layer 7 and the unevenness formed on the light exit surface side are, for example, PET (polyethylene terephthalate), PC (polycarbonate), PMMA (polymethyl methacrylate), COP ( It can be formed from a monolithic molded body that is molded on both sides by press molding or extrusion molding using a thermoplastic resin using a cycloolefin polymer). Alternatively, by an ultraviolet curing molding method in which an ultraviolet solidified resin is disposed on a base material of PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), PMMA (polymethyl methacrylate), PE (polyethylene), etc. Both sides may be formed.

  As another method, when a microlens shape is provided, an ultraviolet curable resin is dropped at a predetermined position by an ink jet method, and the resin that has become a lens shape by surface tension is irradiated with UV light and cured. A lens can be created. Alternatively, a lens shape can be obtained by surface tension by creating a cylindrical resist pattern on a base material by photolithography and heating the base material to melt the resist. Alternatively, the microlens can be formed by repeating exposure and etching of the resist using a photomask.

  Alternatively, a method in which the unevenness on the light incident surface side and the unevenness on the light emission surface side are separately manufactured by the above-described method and bonded together with an adhesive or an adhesive to produce them integrally is also possible.

As a method of providing a low refractive index material layer between the convex portions on the light incident surface side of the light extraction layer, a low refractive index photocuring is performed so as to cover the irregularities on the light incident surface side of the light extraction layer. A method is used in which the functional material is coated by a method such as roll coating, bar coating, or curtain coating, and then the resin remaining on the convex surface is removed by a doctor blade. Alternatively, an adhesive material made of a low refractive index material is applied to the transparent substrate, and the transparent substrate and the light extraction layer are pressure-bonded so that the adhesive material embeds the gap between the protrusions, and then sealed with the transparent substrate. For example, there is a method in which a stop film is bonded and integrated.
In addition, when the low refractive index material layer is an air layer, by setting the thickness of the sealing film thinner than the thickness of the convex portion, the gap between the convex portion and the convex portion is sealed when the light extraction layer is bonded. This can be achieved by performing integration so as not to be buried by the stop film.

It is sectional drawing which shows the laminated structure of the display apparatus by embodiment of this invention, and has shown the case where the light-projection surface side of a light extraction layer is a plane (1st example). It is sectional drawing which shows the laminated structure of the display apparatus by embodiment of this invention, and the case where the convex inclined surface by the side of the light-incidence surface of a light extraction layer contains a curved surface partially (2nd example) is shown. It is sectional drawing which shows the laminated structure of the display apparatus by embodiment of this invention, and shows the case where the convex part is provided in the light-projection surface side of the light extraction layer (3rd example). It is sectional drawing which shows the laminated structure of a general conventional organic EL element. FIG. 5 is a cross-sectional view for explaining that light from the light emitting layer undergoes total reflection in each layer of the element in the stacked structure shown in FIG. 4.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Anode, 3 ... Light emitting layer, 4 ... Cathode, 5 ... Sealing film, 7 ... Light extraction layer.

Claims (8)

A substrate,
A self-luminous element formed on the substrate;
A light extraction layer disposed opposite to the light emitting surface of the self-luminous element;
A transparent sealing film that is filled between the substrate and the light extraction layer, surrounds the self-luminous element, and integrates the substrate and the light extraction layer;
The light extraction layer has a convex portion on the surface facing the self-luminous element, and has a concave portion between adjacent convex portions, and the concave portion has a lower refractive index than the light extraction layer. Having a low refractive material layer filled with a refractive index material,
A display device characterized by that.   The display according to claim 1, wherein a plurality of self-luminous elements are disposed on the substrate, and a convex portion of the light extraction layer is provided in one-to-one correspondence with the plural self-luminous elements. apparatus.   The display device according to claim 1, wherein the convex portions and the side walls of the concave portions of the light extraction layer are formed by flat inclined surfaces.   The display device according to claim 1, wherein a side wall of the convex portion and the concave portion of the light extraction layer is formed by an inclined surface including a partially curved surface.   3. The display device according to claim 1, wherein the low refractive material layer of the light extraction layer is an air layer.   The display device according to claim 1, further comprising a lens portion on a surface of the light extraction layer opposite to the self-luminous element.   The display device according to claim 1, wherein the self-luminous element is an organic EL element.   The self-luminous element is a laminate having an anode provided on the upper surface of the substrate, a light emitting layer provided on the anode, and a cathode provided on the light emitting layer. The display device according to 1.

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