JP2006303030A - Electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroluminescent element (EL) of which luminance is improved by efficiently picking up a light from a light emitting layer (2) to the observation surface side outside a surface substrate (11). <P>SOLUTION: The EL element is provided with at least a light emitting layer (5) between facing two electrodes (2 and 11), and the light pick-up side includes color conversion layers (13a, 13b and 13c). An electrode (7) on the side of the surface substrate (11) of the two electrodes is formed into a transparent electrode, and the surface of the side of the transparent electrode (7) in the color conversion layers (13a, 13b and 13c) is made smooth. Thus, irregular reflection of a light is prevented on the boundary between the transparent electrode (7) and the color conversion layers (13a, 13b and 13c), and a light from the light emitting layer is efficiently picked up to the side of the observation surface outside the surface substrate so as to improve luminance. The smooth surface of the color conversion layer is preferably 200 nm or less in arithmetic average height (Ra). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electroluminescence (EL) element used for a display device or the like.

  In recent years, flat displays have attracted attention as display devices, and plasma displays have been put into practical use as an example. Plasma displays are attracting attention because they can be easily enlarged, have high brightness, and have a wide viewing angle. However, since the structure of the display is complicated and the manufacturing process is also complicated, the improvement is progressing, but it is still expensive at present.

  In addition, a display using an electroluminescence (EL) phenomenon has been proposed. In inorganic EL, an electrode is disposed on a semiconductor inorganic phosphor, and light is emitted by recombination or excitons of electrons and holes of the inorganic phosphor when voltage is applied, or accelerated electrons in the semiconductor collide with the emission center, When the atom or ion that becomes the emission center is excited and returns to its original state, it emits light. The EL element displays characters and images (hereinafter referred to as “images”) using the principle of emitting light by sandwiching a phosphor layer between upper and lower electrodes and applying an electric field to the phosphor layer. Of course, single light display is possible, but single light can be color-converted by a color conversion layer to display full color. However, when performing color conversion, there is a problem that the light extraction efficiency is lowered and the luminance is lowered.

In order to solve this problem, a translucent layer and a color conversion layer are provided on the light emitting surface side, the refractive index of the color conversion layer is made larger than the refractive index of the translucent layer, and the color conversion layer, the translucent layer, There is a proposal to make the interface of the surface uneven (Patent Document 1 below). As another proposal, there is an example in which the refractive index from the electrode on the light extraction side of the organic EL to the substrate is arranged in a specific order (Patent Document 2 below).
JP 2000-284705 A International Publication WO 02 / 17689A1

  However, the color conversion layer is basically based on a resin. If the surface of the color conversion layer on the transparent electrode side is rough, the light from the light emitting layer is diffusely reflected, improving the light extraction efficiency. There is a problem that it is not.

  In order to solve the above-described conventional problems, the present invention provides an EL element that improves the luminance by efficiently extracting light from a light-emitting layer to the observation surface outside the surface substrate.

  The EL device of the present invention includes at least a light emitting layer between two opposing electrodes, includes a color conversion layer and a surface substrate on the light extraction side, and the surface substrate side electrode of the two electrodes is a transparent electrode. In the element, the transparent electrode side surface of the color conversion layer is a smooth surface.

  The present invention smoothes the surface of the color conversion layer on the transparent electrode side, thereby preventing irregular reflection of light at the interface between the color conversion layer and the transparent electrode light-emitting layer, and observing light from the light-emitting layer on the outside of the surface substrate. It is possible to provide an EL element that is efficiently taken out to the surface side and improved in luminance.

  The EL element of the present invention includes at least a light emitting layer between two opposing electrodes. The light emitting layer is formed by layering a light emitting object such as an inorganic or organic phosphor. An electric insulating layer (dielectric layer) may be disposed on both sides or one side of the light emitting layer. In the case of an inorganic phosphor, a dielectric layer is provided between two opposing electrodes, and light is emitted by an electric field using the principle of a capacitor.

  The color conversion layer is formed on the observation surface side substrate with respect to the light emitting layer. A transparent electrode is interposed between the color conversion layer and the light emitting layer. The surface of the color conversion layer on the transparent electrode side is preferably smoothed so as to have an arithmetic average height (Ra) of 200 nm or less. Thereby, irregular reflection of light at the interface between the color conversion layer and the transparent electrode light emitting layer can be prevented. The reason why the arithmetic average height of the surface of the color conversion layer on the transparent electrode side is 200 nm or less is that light is scattered if the irregularity is λ / 2 or less of visible light (wavelength 400 nm to 750 nm). This is because there is not. Here, the arithmetic average height (Ra) refers to the arithmetic average height (Ra) defined in JIS B 0601-2001.

  The smooth surface of the color conversion layer is formed by adopting means such as hot pressing, moving and polishing while being hot pressed. In this case, a color conversion layer may be formed on the surface of the observation side glass substrate, and smoothing may be performed in this state. As another method, one or both surfaces of the color conversion layer may be smoothed and transferred to a glass substrate or a transparent electrode by a transfer method. When the transfer method is employed, the color conversion layer is integrally attached to the glass substrate or the transparent electrode using an adhesive, an ultraviolet curable resin, or the like. In the case of polishing, polishing cloth, polishing paper, polishing slurry or the like is used. When the polishing slurry is used, a general water slurry for resin polishing may be used, and a slurry composed of abrasive particles such as alumina, silica, cerium oxide and water is used.

  It is preferable to further provide a translucent resin smooth layer between the transparent electrode and the color conversion layer. In this case, the interface between the transparent electrode and the translucent resin smooth layer and the interface between the translucent resin smooth layer and the color conversion layer are both smoothed so that the arithmetic average height (Ra) is 200 nm or less. It is preferable to do this. Furthermore, when the refractive index of the transparent electrode is n1, the refractive index of the color conversion layer is n2, and the refractive index of the transparent resin smooth layer is n3, the refractive index of each layer satisfies the relationship of n1> n3> n2. Is preferred. Thereby, it is possible to prevent reflection caused by a large change in the refractive index, efficiently extract light from the light emitting layer to the observation surface side outside the surface substrate, and provide an EL element with improved luminance.

  The refractive index of the translucent resin smooth layer is preferably 1.5 or more and 2 or less. As the translucent resin smooth layer, polystyrene (refractive index 1.59), epoxy resin (refractive index 1.55 to 1.60), polyvinylidene chloride (refractive index 1.60 to 1.63), polysulfone (refractive index). 1.63), a phenol-formaldehyde resin (refractive index 1.70), a silicon resin layer (refractive index 1.70) such as polysilane and polysilazane, and the like can be used.

  A black matrix may be disposed in the color conversion layer. For example, a resin material such as polymethyl methacrylate (PMMA) having a thickness of about 5 to 20 μm is used for the color conversion layer. In this case, the refractive index n2 is 1.49.

  As the transparent electrode, a transparent electrode layer made of an indium-tin oxide alloy (ITO) having a thickness of 200 to 300 μm is used. In this case, the refractive index n1 is 2.1. When light from the light emitting layer is directly input to the color conversion layer through the transparent electrode layer, the light is reflected due to a large difference in refractive index. For this reason, for example, a polystyrene layer having a refractive index n3 of 1.59 or a silicon resin layer such as polysilane or polysilazane having a refractive index n3 of 1.70 is interposed between the transparent electrode layer and the color conversion layer. Thereby, reflection of light entering the color conversion layer can be suppressed.

As the dielectric layer, Y ₂ O ₃ , Li ₂ O, MgO, CaO, BaO, SrO, Al ₂ O ₃ , SiO ₂ , MgTiO ₃ , CaTiO ₃ , BaTiO ₃ , SrTiO ₃ , ZrO ₂ , TiO ₂ , At least one of B ₂ O ₃ , PbTiO ₃ , PbZrO ₃ , and PbZrTiO ₃ (PZT) can be used. Further, a ferroelectric layer may be interposed between both electrodes, and a means for further increasing the luminous efficiency may be taken.

Examples of the light-emitting substance that can be used in the light-emitting layer include ZnS: Ag, ZnS: Cu, ZnS: Mn, SrS: Ce: Eu, ZnS: Sm: Cl, CaS: Eu, ZnS: Tb: F, and CaS: Ce. _{ZnMgS: Mn, CaGa 2 S 4} : Ce, SrS: Cu, CaS: Pb, BaAl 2 S 4: Eu, Y 2 O 3: Eu, Ca 2 Ge 2 O 7: generally known as a phosphor, such as Mn Can be used.

(Embodiment 1)
(1) Formation of color conversion layer (1-1) Preparation of coating material paste The following components were mixed at 90 ° C for 1 hour to prepare a coating material paste.
(A) Solvent N-methyl-2-pyrrolidone: 5 g
Benzyl alcohol: 5g
(B) Transparent binder resin Polymethylmethacrylate powder (PMMA: manufactured by Sumitomo Chemical Co., Ltd., refractive index 1.49): 3 g
(C) Pigment Green: Coumarin 540 (Exciton): 40 mg
Red: DCM (Exciton): 40mg
Blue: No additive (because the light emitting layer emits blue light)
(1-2) Coating Method A black matrix containing graphite and PMMA and having a thickness of 2 μm, a width of 50 μm, and a pitch interval of 150 μm was formed on the surface of the glass substrate. On the black matrix, the green, red and colorless pastes are printed in the order of G, B (colorless) and R by screen printing method over the pitch interval, and the solvent is gradually evaporated to 170 ° C. , Dried in 60 minutes. The film thickness after drying was 30 μm.

  This will be described below with reference to the drawings. FIG. 1 is a perspective view showing a manufacturing process of a light extraction portion 20 composed of a transparent substrate and a color conversion layer of an EL element in one embodiment of the present invention. The light extraction unit 20 is formed by forming the black matrix 12 on a glass transparent substrate 11 and color conversion comprising G and B (colorless and transparent, the light emitting layer emits blue light and does not require color conversion) and R. Layers 13a, 13b, and 13c are formed. A metal hot press plate 15 was placed on the color conversion layers 13a, 13b, and 13c, and a pressure of 100 Pa was applied at a temperature of 200 ° C., followed by sliding in the arrow direction. Thereby, the arithmetic average height (Ra) prescribed | regulated by JISB0601-2001 became 150 nm on the upper surface of each color conversion layer. The thickness of each color conversion layer was 15 μm.

FIG. 2 is a cross-sectional view showing the light emitting unit 10 from the back side substrate of the EL element to the translucent resin protective layer on the transparent electrode in one embodiment of the present invention. First, a back electrode 2 made of copper wiring having a thickness of 10 μm was formed on the back glass 1 in parallel in a stripe shape. Furthermore, a dielectric layer 3 made of BaTiO ₃ with a thickness of 30 μm, a smooth layer 4 made of a BaTiO ₃ organic acid with a thickness of 0.6 μm, and a fluorescent light made of BaAl ₂ S ₄ : Eu with a thickness of 0.6 μm thereon. A body light emitting layer 5 and a diffusion preventing layer 6 made of Al ₂ O ₃ having a thickness of 0.5 μm were formed. A transparent electrode 7 made of an indium-tin oxide alloy (ITO) layer (refractive index n1 = 2.1) having a thickness of 0.5 μm and a width of 150 μm is formed in parallel in a stripe shape in a direction perpendicular to the back electrode 2. did. The back electrode 2 to the transparent electrode 7 were formed by sputtering.

  Next, as shown in FIG. 3, the light extraction unit 20 is aligned and placed on the light emitting unit 10, and the display element 30 is assembled by sealing the periphery with an epoxy resin.

  When an alternating voltage of 1 kHz, 10 μA, and 180 V was applied to the EL element 30, a luminance improvement of about 15% was recognized as compared with the color conversion layer that was not subjected to the smoothing process.

(Embodiment 2)
In Embodiment 1, a polishing method was used instead of the hot press method for the smoothing treatment of the color conversion layer. That is, alumina particles having an average particle diameter of 10 μm are used as an abrasive, water is added by 40% by weight to form a slurry, the slurry is applied to a cloth, and the polishing pressure is 6.9 × 10 ³ Pa to 20.7. Polishing was performed at a pressure of × 10 ³ Pa. The polished surface had an arithmetic average height (Ra) defined by JIS B0601-2001 of 30 nm. This was made into the light extraction part.

  Thereafter, the display element 30 was assembled in the same manner as in the first embodiment.

  When an alternating voltage of 1 kHz, 10 μA, and 180 V was applied to the EL element 30, a luminance improvement of about 20% was recognized compared to the color conversion layer that was not smoothed.

(Embodiment 3)
3 g of polystyrene (trade name “GPPS” manufactured by PS Japan Co., Ltd., refractive index: 1.59): 3 g was dissolved in 10 g of N-methyl-2-pyrrolidone as a solvent to obtain a coating material paste. This coating material paste was coated on a glass substrate with a doctor blade, and the solvent was gradually evaporated, followed by drying at 170 ° C. for 60 minutes. The film thickness after drying was 40 μm. This was polished on both sides by the same method as in the second embodiment. The polished surface had an arithmetic average height (Ra) defined by JIS B0601-2001 of 30 nm. The film thickness after polishing was 325 μm.

  The obtained translucent resin smooth layer 14 is interposed between the light extraction portion 20 polished as in the second embodiment and the light emitting portion 10 obtained in the same manner as in the first embodiment, and pressed from above and below. The display element 30 was assembled by sealing the periphery with an epoxy resin.

  When an alternating voltage of 1 kHz, 10 μA, and 180 V was applied to the EL element 30, a brightness improvement of about 5% was recognized as compared with the display element of the second embodiment.

It is a perspective view which shows the smoothing process of the color conversion layer surface in Embodiment 1 of this invention. It is sectional drawing which shows the light emission part of the EL element in embodiment of this invention. It is sectional drawing of the EL element in Embodiment 1 of this invention. It is sectional drawing of the EL element in Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Back glass 2 Back electrode 3 Dielectric layer 4 Smooth layer 5 Phosphor light emitting layer 6 Diffusion prevention layer 7 Transparent electrode 10 Light extraction part 11 Transparent substrate 12 Black matrix 13a, 13b, 13c Color conversion layer 14 Translucent resin smooth layer 15 Hot press board 20 Light emission part 30 EL element

Claims (4)

In an electroluminescent device comprising at least a light emitting layer between two opposing electrodes, including a color conversion layer and a surface substrate on the light extraction side, and using the electrode on the surface substrate side of the two electrodes as a transparent electrode,
The surface of the color conversion layer on the transparent electrode side is a smooth surface.   The electroluminescent device according to claim 1, wherein the smooth surface of the color conversion layer has an arithmetic average height (Ra) of 200 nm or less.   The electroluminescent element according to claim 1, further comprising a translucent resin smooth layer between the transparent electrode and the color conversion layer. The interface between the transparent electrode and the translucent resin smooth layer and the interface between the translucent resin smooth layer and the color conversion layer are all smoothed so that the arithmetic average height (Ra) is 200 nm or less. The electroluminescent device according to claim 3.

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