JP2006351211A - Surface emitting light source and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface emitting light source with improvement of brightness aimed at through enhancement of light extraction efficiency. <P>SOLUTION: The surface emitting light source 10 has a light-emitting element 11 made of a laminated body of a transparent electrode 13, a light-emitting layer 14 including an organic EL layer formed on the surface 12a of a transparent substrate 12, and the light-emitting element 11 has a prism-structure face 11A of a polyhedral structure on the surface of the transparent substrate 12. With this, the light-emitting layer 14 is given a bent part, so as to enable to effectively take out total reflection light inside the light-emitting layer 14 from the bent part. Further, by making the light-emitting element 11 in a polyhedral structure, substantial improvement in brightness due to increase in a light-emitting area is aimed at. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface-emitting light source including an electroluminescent element such as an organic electroluminescent element (hereinafter also referred to as “organic EL element”) and a liquid crystal display device including the same.

  Conventionally, cold cathode fluorescent lamps have been widely used for backlights of liquid crystal display devices. Although the cold cathode fluorescent lamp has excellent characteristics in terms of emission wavelength range, brightness, etc., it requires a reflector, a light guide plate, etc. to illuminate the entire surface, which increases the cost of components and consumes power. There are some points that need to be improved.

  Therefore, in recent years, a liquid crystal display device using a surface light emitting device such as an organic EL element as a backlight has been proposed (see, for example, Patent Document 1 below). The organic EL element is a self-luminous element, and can be manufactured by a thin film process, has many excellent points such as low power consumption and a wide wavelength selection range.

  FIG. 9 shows a basic configuration of the organic EL element. In general, the organic EL element 1 has a configuration in which a transparent electrode 3 as an anode, a light emitting layer 4 including an organic EL layer, and a reflective electrode 5 as a cathode are laminated on a transparent substrate 2 such as a glass substrate. The transparent electrode 3 is formed of an ITO (Indium Tin Oxide) film or the like, and the reflective electrode 5 is formed of an aluminum film or the like. Various structures are known for the light emitting layer 4. For example, the light emitting layer 4 is composed of a three-layer type including a hole transport layer 6, an organic EL layer 7, and an electron transport layer 8.

  In the organic EL element 1 having such a configuration, by applying a direct current voltage between the transparent electrode 3 and the reflective electrode 5, holes injected from the transparent electrode 3 cause the hole transport layer 6 to be in contact. Then, electrons injected from the reflective electrode 5 are introduced into the organic EL layer 7 through the electron transport layer 8. In the organic EL layer 7, light having a predetermined wavelength is generated by recombination of the introduced holes and electrons, and the generated light is emitted to the outside through the transparent electrode 3 and the transparent substrate 2. .

  By the way, this kind of organic EL element 1 has a problem that extraction efficiency of light generated in the light emitting layer 4 is low for the following reason.

  That is, the light emission efficiency in the light emitting layer 4 depends on the excited state of the organic EL layer molecules excited by the recombination of holes and electrons. The light emission from the organic EL layer is divided into light emission from the excited singlet state (fluorescence) and light emission from the excited triplet state (phosphorescence). These excited states are determined by the direction of the electron spin of the organic molecule, and the generation probability is estimated to be 25% for the excited singlet state and 75% for the excited triplet state. However, since most of the organic EL layer 7 is prohibited from emitting light (phosphorescence) from the excited triplet state, the excitation energy is lost as thermal energy. Therefore, in the light emitting layer 4, only light emission from the excited singlet state can be obtained.

  The light generated in the light emitting layer 4 is extracted outside through the anode (transparent electrode) 3 and the transparent substrate 2. However, under the influence of the refractive index of the light emitting layer 4 and the transparent electrode 3, the transparent substrate 2 and the air layer, the light generated in the light emitting layer 4 is transmitted between the light emitting layer 4 and the transparent electrode 3 as shown in FIG. Due to the total reflection action at the interface and the total reflection action at the interface between the transparent electrode 3 and the transparent substrate 2, the emission efficiency to the outside is reduced. For example, when the refractive index of the light emitting layer 4 is 1.7, the extraction efficiency is 20% or less.

In order to solve such a problem, in the conventional organic EL element,
(1) A prism or a semi-cylindrical microlens is formed on the light extraction side (see Patent Documents 2 and 3 below),
(2) An optical element such as a diffraction grating is provided between the transparent substrate and the light emitting layer (see Patent Document 4 below). (3) Particles that diffuse light in the light emitting layer are dispersed or light is adjacent to the light emitting layer. Providing a diffusion layer (see Patent Document 5 below);
(4) A low refractive index layer is provided between the transparent substrate and the light emitting layer (see Patent Document 6 below),
(5) Attempts have been made to increase the light extraction efficiency by a method such as sandwiching the light emitting layer between a reflective layer and a half mirror to cause a cavity effect (see Patent Document 7 below).

JP-A-10-125461 Japanese Patent No. 2670572 JP 2004-227929 A Japanese Patent No. 2911183 JP 11-329742 A JP 2003-77647 A JP-A-9-190883

  However, the methods (1) and (4) are effective for taking out the totally reflected light in the transparent substrate, but have no effect on the totally reflected light in the light emitting layer. Further, in (2), there is a problem in the processing of the interface between the anode and the light emitting layer, which makes it difficult to implement.

  Furthermore, in the method (3) for introducing light diffusing particles into the light emitting layer, foreign matter is put into the light emitting layer which is required to be smooth and thin, and there is a concern that the device performance is deteriorated. Even when the diffusion layer is formed adjacent to the light emitting layer, there is a problem of smoothness of the surface, and there is a possibility that the device performance such as lifetime is deteriorated. The case where the diffusion layer is formed outside the transparent substrate is essentially the same as the case of providing the microlens (1).

  On the other hand, the method (4) has no effect on the total reflection at each inner layer, and the method (5) improves the light extraction efficiency in the front direction, but the resonance wavelength changes depending on the viewing angle. There is a problem of causing a color change.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a surface-emitting light source and a liquid crystal display device capable of improving luminance by increasing light extraction efficiency.

  In solving the above-described problems, a surface-emitting light source of the present invention is a surface-emitting light source in which a light-emitting element composed of a laminate of a transparent electrode, a light-emitting layer, and a reflective electrode is formed on the surface of a substrate. Has a polyhedral structure on the substrate surface.

  In the present invention, the light emitting element has a polyhedral structure so that the light emitting layer has a bent portion, and the total reflected light in the light emitting layer can be effectively extracted from the bent portion. As a result, the light extraction efficiency is increased and the luminance can be improved.

  Further, by making the light emitting element have a multi-face structure, the luminance can be substantially improved by increasing the light emitting area. Furthermore, the radiation pattern of light can be controlled by variously changing the structure of the polyhedron. For example, when the light emitting element has a prism structure with an apex angle of 90 degrees, the light irradiation intensity in the front direction can be increased.

  The light emitting device according to the present invention can be formed on the substrate surface by using a vacuum thin film process such as a vacuum deposition method or a sputtering method. And the light emitting element which concerns on this invention can be easily formed by making the surface of the said board | substrate into a polyhedral structure. In this case, since the inclined surface of the light emitting element can be formed in a smooth plane or curved surface, it is possible to suppress a decrease in element performance such as lifetime.

  The light emitting element according to the present invention has a polyhedral structure including an inclined surface, so that the light extraction efficiency can be improved. Specifically, a three-dimensional structure having periodicity in at least one direction, for example, a prism structure, a semi-cylindrical structure, a trapezoidal structure, or a composite structure thereof can be adopted as the polyhedral structure of the light emitting element. Further, a pyramid structure such as a triangular pyramid, a quadrangular pyramid, a hexagonal pyramid, or a cone having periodicity in two orthogonal directions may be used.

  Note that the light emitting element according to the present invention can be composed of an organic EL element, an electroluminescent element such as an inorganic EL element, or another self-light emitting element such as a light emitting diode.

As described above, according to the surface emitting light source of the present invention, since the light emitting element on the substrate has a multi-face structure, the total reflected light in the layer can be effectively extracted to the outside. Thereby, the light extraction efficiency can be increased and the luminance can be improved.
Further, according to the liquid crystal display device of the present invention, since the surface light source having the above-described configuration is provided in the backlight, it is possible to reduce the thickness and weight of the device, reduce the component cost, and the like.

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

(First embodiment)
FIG. 1 shows the configuration of a surface-emitting light source 10 according to the first embodiment of the present invention. The surface-emitting light source 10 of the present embodiment is used for a backlight for a liquid crystal display device, for example. Here, FIG. 1A is a perspective view schematically showing a form of the surface-emitting light source 10 when viewed from the light emitting element 11 side, and FIG. 1B is a schematic cross-sectional view of an essential part thereof.

  The surface emitting light source 10 has a structure in which a transparent electrode 13 as an anode, a light emitting layer 14 and a reflecting electrode 15 as a cathode are sequentially laminated on a surface 12a of a transparent substrate 12. The laminate 11 of the transparent electrode 13, the light emitting layer 14, and the reflective electrode 15 constitutes a “light emitting element” according to the present invention, and in particular, in the present embodiment, constitutes an organic EL element.

  As the transparent substrate 12, a transparent substrate having a light transmittance of 70% or more such as glass or plastic is used. As the plastic substrate, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polycarbonate (PC), or the like can be used. The transparent substrate 12 is not limited to a rigid (self-supporting) material and may be composed of a flexible material.

  The surface 12a of the transparent substrate 12 has a polyhedral structure including an inclined surface. In particular, in the present embodiment, a prism structure having a triangular cross section formed with periodicity in one direction is formed. The prism-shaped structural surface can be formed, for example, by pressing the surface 12a of the transparent substrate 12 at a high temperature. On the other hand, in this Embodiment, the back surface 12b of the transparent substrate 12 is formed in the flat plane.

  The surface 12a of the transparent substrate 12 is not limited to being formed in a prism structure, but may be a semi-cylindrical structure, a trapezoidal structure, or a composite structure thereof. Moreover, the uneven | corrugated shape which does not contain an inclined surface may be sufficient.

  The transparent electrode 13, the light emitting layer 14, and the reflective electrode 15 are formed on the surface 12 a of the transparent substrate 12 by using a vacuum film forming means such as a vacuum evaporation method or a sputtering method. The light emitting element 11 composed of these laminates is formed with a constant film thickness following the surface 12 a of the transparent substrate 12, whereby a prism structure surface 11 </ b> A having a polyhedral structure including the inclined surface P on the surface of the transparent substrate 12. Is formed.

  As the transparent electrode 13, a light-transmitting conductive oxide film such as an ITO film or a tin oxide film is used. On the other hand, the reflective electrode 15 has light reflectivity in order to direct light generated in the light emitting layer 4 toward the transparent substrate 12, and is formed of, for example, aluminum, platinum, gold, chromium, tungsten, nickel, or the like.

  The light emitting layer 14 is configured by a three-layer type including, for example, a hole transport layer / organic EL layer / electron transport layer, but in addition to this, a single layer type, a hole injection layer, and an electron injection layer are provided. Other element structures such as a five-layer type may be adopted. The light emitting layer 14 may be formed in a solid shape on the surface 12a of the substrate 12, or may be distributed in a pattern. The pattern shape is not particularly limited, and various shapes such as a mass shape and a stripe shape can be employed.

  The material of the light emitting layer 14 is selected according to the light emission color. The emission color may be white monochromatic light or RGB (red, green, blue) monochromatic light. The constituent material of the light emitting layer 14 can use a well-known material, The illustration is abbreviate | omitted here.

  In the surface-emitting light source 10 of the present embodiment, by applying a DC voltage between the transparent electrode 13 and the reflective electrode 15, holes are introduced from the transparent electrode 13 to the light-emitting layer 14, and from the reflective electrode 15. Electrons are introduced into the light emitting layer 14. In the light emitting layer 14, organic EL molecules are excited by recombination of the introduced holes and electrons, and light having a predetermined wavelength is generated. The generated light is emitted in a planar shape to the outside (downward in FIG. 1B) through the transparent electrode 13 and the transparent substrate 12.

  In the present embodiment, the light emitting element 11 is formed on the surface 12a of the transparent substrate 12 in a multi-faceted prism structure having a top (ridge) T and a bottom (valley) B as shown in FIG. 1B. Therefore, a bent portion is generated at a portion where the light emitting layer 14 corresponds to each of the top portion T and the bottom portion B. As a result, of the light emitted from the light emitting layer 14, the total reflected light generated at each interface of the transparent electrode 13, the reflective electrode 15, and the transparent substrate 12 is emitted from the bent portion of the light emitting layer 14. Although the emitted light is refracted and transmitted through the adjacent prism surface, a part of the light is totally reflected by the back surface 12b of the transparent substrate 12, and then reflected by the prism surface of the substrate surface 12a, and finally emitted from the substrate back surface 12b. The

  As described above, according to the present embodiment, the light totally reflected by the inner layer of the light emitting element 11 can be effectively extracted to the outside, so that the light extraction efficiency can be improved as compared with the conventional case. Further, by making the light emitting element 11 have a multi-face structure, the luminance can be substantially improved by increasing the light emitting area.

  For example, FIG. 2 is a luminance distribution diagram (simulation result) showing an example of the orientation characteristic of the surface-emitting light source 10 having the above configuration. FIG. 2 shows luminance data measured over 90 degrees on the left and right sides with the direction of 180 degrees as the film front direction. The axis in the radial direction indicates the magnitude of luminance. For comparison, FIG. 4B shows a luminance distribution in the case of the organic EL element 1 having a conventional structure with a flat light emitting surface as shown in FIGS. 4A and 9. According to the present embodiment, the effect of improving the luminance in the front direction is recognized, and it has been confirmed that the overall light emission intensity can be increased 1.28 times compared to the conventional case.

  In this example, the transparent substrate has a thickness of 1 μm (refractive index of 1.5), the transparent electrode has a thickness of 150 nm (refractive index of 2.0), the light emitting layer has a thickness of 150 nm (refractive index of 1.7), The thickness of the reflective electrode was 150 nm, the prism apex angle θ (see FIG. 1A) of the substrate surface 12a was 90 degrees, and the prism formation pitch d (see FIG. 1A) was 20 μm.

  In the configuration of the transparent substrate 12 described above, the apex angle θ and the formation pitch d of the prism formed on the surface 12a are the coverage of the transparent electrode layer 13, the light emitting layer 14, and the reflective electrode layer 15 formed thereon. The size is not particularly limited as long as the size can be secured.

  Specifically, the apex angle θ is 10 degrees to 170 degrees, preferably 30 degrees to 150 degrees, and more preferably 40 degrees to 140 degrees. If the apex angle θ is less than 10 degrees, the prism apex is too sharp and there is a risk of short circuit between the transparent electrode and the reflective electrode laminated thereon. When the apex angle θ exceeds 170 degrees, the light emitting element is substantially the same as when the light emitting element is flat.

The formation pitch d of the top (ridge) and bottom (valley) of the prism is selected in the range of, for example, 50 nm or more and 500 μm or less. The inclined surface P that connects the top (ridge) and the bottom (valley) is a flat surface, but it may be a curved surface. In particular, according to the present embodiment, since the light emitting element 11 is formed using the vacuum thin film forming process, the inclined surface P can be formed on a smooth surface, thereby suppressing a decrease in element performance such as lifetime. .
In addition, when forming each constituent thin film of the light emitting element 11, the in-plane film thickness uniformity can be enhanced by causing the substrate 12 to perform a planetary motion in a vacuum chamber.

  By applying the surface emitting light source 10 having the above configuration to the backlight of the liquid crystal display device, the entire liquid crystal display device can be reduced in thickness and weight, and the cost of the backlight components can be reduced. be able to.

  Further, when the surface 12a of the substrate 12 has a prism structure as described above, a low refractive index material and a high refractive index are provided between the surface 12a of the transparent substrate 12 and the transparent electrode 13, for example, as shown in FIG. By interposing the dielectric multilayer film 16 in which a plurality of materials are alternately stacked, a polarization separation function for separating the light emitted from the light emitting layer 14 into a P-wave polarization component and an S-wave polarization component can be provided. In this case, by arranging the transmission axis of the polarizing plate of the liquid crystal panel in parallel with the outgoing polarization direction, the light use efficiency in the liquid crystal panel can be improved and the luminance can be further improved.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. Here, FIG. 5A is a perspective view schematically showing a form of the surface emitting light source 20 according to the second embodiment of the present invention when viewed from the light emitting element 11 side, and FIG. 5B is a schematic cross-sectional view of an essential part thereof. . In the figure, portions corresponding to those of the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the surface emitting light source 20 of the present embodiment, the surface 12a of the transparent substrate 12 has a prism structure, and the light emitting element 11 stacked thereon also forms the prism structure surface 11A. It is common with the form. However, this embodiment is different from the first embodiment in that a similar prism structure is formed on the back surface 12b of the transparent substrate 12.

  By making the back surface 12b of the transparent substrate 12 into a prism structure, the light generated in the light emitting layer 14 and emitted from the transparent substrate 12 is emitted in the front direction by the refractive transmission action by the prism surface on the substrate back surface 12b side. Is possible. Thereby, the brightness | luminance of a front direction can be aimed at.

  FIG. 6 is a luminance distribution diagram (simulation result) showing an example of orientation characteristics of the surface-emitting light source 20 configured as described above. In the figure, the solid line indicates the luminance distribution in the horizontal direction, and the broken line indicates the luminance distribution in the horizontal direction. As apparent from the comparison with FIG. 4B, according to the present embodiment, the front luminance is greatly increased. In addition, it was confirmed that the overall light emission intensity increased by 2.24 times as compared with the conventional structure.

  In the present embodiment, the prism apex angle and pitch of the back surface 12b of the transparent substrate 12 are configured to be equivalent to the prism structure on the front surface 12a side, but of course not limited thereto. Further, although both prism structures are formed in such a relationship that the top and bottom of the prism are opposite to each other on the front surface 12a side and the back surface 12b side of the substrate 12, other configurations may be adopted. Furthermore, the extending direction of the prisms may be orthogonal to the front surface 12a side and the back surface 12b side.

(Third embodiment)
7 and 8 show a third embodiment of the present invention. Here, FIG. 7 is a perspective view schematically showing a form of the surface-emitting light source 30 of the present embodiment when viewed from the light emitting element 11 side, and FIG. 8 is a luminance distribution diagram showing an example of the orientation characteristic (simulation result). ). In the figure, portions corresponding to those of the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, each of the above-described embodiments is that the light emitting element 11 formed on the surface 12a of the transparent substrate 12 is a quadrangular pyramid-shaped polyhedral structure 11B having periodicity in two orthogonal directions. Is different. The light emitting element 11 </ b> B having such a configuration can be formed by forming the surface of the transparent substrate 12, which is a base, into a similar quadrangular pyramid two-dimensional array structure. In the present embodiment, a similar quadrangular pyramid two-dimensional array structure is also formed on the back surface 12 b side of the transparent substrate 12.

  Also with the surface emitting light source 30 having such a configuration, it is possible to improve the light extraction efficiency similar to the above-described embodiments, and to improve the in-plane luminance. Further, by arranging a large number of cone-shaped structural surfaces on the back surface 12b side of the transparent substrate 12, it is possible to enhance the condensing property of the extracted light and to improve the luminance in the front direction. From the simulation results of FIG. 8, it was confirmed that the in-plane emission intensity can be increased to 1.89 times that of the prior art by the above configuration.

  The polyhedral structure 11B of the light emitting layer 11 is not limited to the quadrangular pyramid-shaped two-dimensional array structure described in the above example, but other polygonal pyramid shapes such as a triangular pyramid, a hexagonal pyramid, and a conical two-dimensional array. You may form with a structure. Also, the back surface 12b side of the transparent substrate 12 may have a prism structure as described in the second embodiment.

  As mentioned above, although each embodiment of this invention was described, of course, this invention is not limited to these, A various deformation | transformation is possible based on the technical idea of this invention.

  For example, in the above embodiment, the light-emitting element 11 formed on the transparent substrate 12 is configured by an organic EL element. However, instead of this, it may be configured by another electroluminescent element, that is, an inorganic EL element. . The present invention can also be applied to other self-luminous elements such as light-emitting diodes.

  In the above embodiment, the light generated in the light emitting layer 14 is extracted to the outside through the transparent electrode 13 and the transparent substrate 12. Instead, the cathode 15 side is made of a transparent electrode material. Thus, it is possible to adopt a so-called top emission type in which light is emitted from the cathode side. In this case, the substrate 12 is not limited to a light transparent one.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the surface emitting light source 10 by the 1st Embodiment of this invention, A is a perspective view when it sees from the light emitting element 11, and B is principal part sectional drawing. It is a simulation result of the luminance distribution showing an example of the orientation characteristic of the surface emitting light source 10. It is a principal part cross-sectional schematic diagram which shows the modification of the 1st Embodiment of this invention. It is a figure explaining the surface emitting light source which consists of the conventional organic EL element, A is a perspective view, B is a simulation result which shows an example of luminance distribution. It is a figure which shows typically the surface emitting light source 20 by the 2nd Embodiment of this invention, A is a perspective view when it sees from the light emitting element 11, and B is principal part sectional drawing. It is the simulation result of the luminance distribution which shows an example of the orientation characteristic of the surface emitting light source 20. It is a perspective view when the surface emitting light source 30 by the 3rd Embodiment of this invention is seen from the light emitting element 11 side. It is a simulation result of luminance distribution showing an example of the orientation characteristic of the surface emitting light source 30. It is sectional drawing explaining the structure of the conventional organic EL element. It is sectional drawing explaining the problem of the conventional organic EL element.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10, 20, 30 ... Surface emitting light source, 11 ... Light emitting element (organic EL element), 11A, 11B ... Structural surface, 12 ... Transparent substrate, 12a ... Front surface, 12b ... Back surface, 13 ... Transparent electrode (anode), 14 ... Light emitting layer, 15 ... reflective electrode (cathode), 16 ... dielectric multilayer film, P ... inclined surface.

Claims (10)

A surface emitting light source in which a light emitting element composed of a laminate of a transparent electrode, a light emitting layer, and a reflective electrode is formed on a substrate surface
The surface-emitting light source, wherein the light-emitting element has a polyhedral structure on the surface of the substrate. The surface-emitting light source according to claim 1, wherein the light-emitting element has a polyhedral structure including an inclined surface. The surface-emitting light source according to claim 1, wherein the substrate is made of a light-transmitting material. The surface-emitting light source according to claim 1, wherein the inclined surface is a flat surface or a curved surface. The surface emitting light source according to claim 1, wherein the light emitting element has a three-dimensional structure having periodicity in at least one direction. At least the surface side of the substrate has a polyhedral structure including an inclined surface;
The surface emitting light source according to claim 1, wherein the light emitting element is formed on a surface of the substrate. 7. The surface light emitting device according to claim 6, wherein a dielectric multilayer film in which a high refractive index material and a low refractive index material are alternately laminated is formed between the substrate surface and the light emitting element. light source. The surface-emitting light source according to claim 1, wherein the light-emitting element is an electroluminescent element. The surface-emitting light source according to claim 8, wherein the light-emitting element is an organic electroluminescence element. In a liquid crystal display device provided with a liquid crystal panel and a surface-emitting light source that is disposed on the back side of the liquid crystal panel and emits illumination light,
The surface-emitting light source has a light emitting element formed of a laminate of a transparent electrode, a light emitting layer, and a reflective electrode formed on a substrate surface,
The liquid crystal display device, wherein the light emitting element has a polyhedral structure on the surface of the substrate.

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