JP2011049000A - Organic el light-emitting device - Google Patents

Abstract

Light extraction efficiency is improved in an organic EL light emitting device.
An organic EL light emitting device includes a plurality of light emitting units and a light transmitting substrate. The light emitting unit 2 is disposed on one surface 31 of the substrate 3. Light from the light emitting unit 2 is extracted through the substrate 3. The light emitting device 1 has a lens structure 5 having a refractive index equivalent to that of the substrate 3 corresponding to each of the light emitting portions 2 on the light extraction surface 32 side of the substrate 3. Each of the lens structures 5 is arranged such that the optical axis 51 passes through the center 20 of the light emitting unit 2, and the bottom area of the lens structure 5 is larger than the area of the light emitting unit 2. Thereby, most of the light incident on the substrate 3 from the light emitting unit 2 enters the lens structure 5, and the light extraction efficiency of the organic EL light emitting device 1 is improved.
[Selection] Figure 2

Description

  The present invention relates to an organic EL light emitting device using light emission of an organic light emitting layer.

  2. Description of the Related Art Conventionally, an organic EL element (an organic electroluminescence element) that obtains a surface light source by emitting an organic substance is known. An organic EL element has features such as being self-luminous, exhibiting a relatively high-efficiency light emission characteristic, and being capable of emitting light in various colors, for example, a light emitter of a display device such as a flat panel display Or, it is expected to be used as a backlight of a liquid crystal display, a light source for illumination, etc., and some have already been put into practical use.

  As shown in FIG. 5, a general organic EL device 100 includes a light-transmitting electrode 102 serving as an anode, a hole transport layer 103, a light-emitting layer 104, an electron transport layer 105, a cathode on a light-transmitting substrate 101. The light reflective electrode 106 is formed in this order. In addition, each layer other than the board | substrate 101 of the organic EL element 100 is expanded and shown in the thickness direction. The hole transport layer 103, the light emitting layer 104, and the electron transport layer 105 constitute an organic layer 107. In the organic EL element 100, by applying a voltage between the electrodes 102 and 106, electrons are injected into the light emitting layer 104 through the electron transport layer 105, and holes are injected into the light emitting layer 104 through the hole transport layer 103. In the light emitting layer 104, electrons and holes are recombined to emit light. Light emitted from the light-emitting layer 104 is extracted into the atmosphere through the light-transmissive electrode 102 and the substrate 101.

  The light emitted from the light emitting layer 104 is totally reflected at the interface due to the refractive index difference between the electrode 102 and the substrate 101 and between the substrate 101 and the atmosphere 109, and within the light emitting layer 104, the organic layer 107 other than the light emitting layer 104, and the electrode 102. The phenomenon of being confined within the substrate 101 occurs. According to a simple estimate, of the light emitted from the light emitting layer 104, the light confined in the organic layer 107 or the electrode 102 is about 50%, and the light confined in the substrate 101 is about 30%, which is extracted into the atmosphere. It is said that only about 20% of light is emitted.

  In order to solve this problem, there is a light emitting device in which a lens structure is provided on the light extraction surface side of the substrate and the light in the substrate is extracted into the atmosphere (see, for example, Patent Document 1). The apparatus shown in this document has a light emitting part, a substrate, and a lens structure. The thickness of the substrate is d1, the distance from the substrate surface to the apex of the lens structure is d2, and the radius of curvature of the lens structure is R3. A relationship of ≦ R3 is defined. Further, this document stipulates that the center of curvature of the lens structure is the center of the light emitting part. It is said that the light extraction efficiency of the apparatus can be increased to 50% by the above two points. However, in an apparatus that satisfies only these regulations, the light extraction efficiency is still insufficient because there is light that does not enter the lens structure among the light emitted from the light emitting section.

Japanese Patent Laid-Open No. 9-171892

  The present invention solves the above-described problems, and an object of the present invention is to improve light extraction efficiency in an organic EL light emitting device using light emission of an organic light emitting layer.

  In order to achieve the above object, the invention of claim 1 comprises a plurality of light emitting portions having an organic light emitting layer and a translucent substrate, and the light emitting portion is disposed on one surface of the substrate, An organic EL light emitting device in which light from a light emitting unit is extracted through the substrate, and a lens structure having a refractive index equivalent to that of the substrate corresponding to each of the light emitting units on the light extraction surface side of the substrate, Each of the lens structures is arranged such that its optical axis passes through the center of the light emitting part, and the bottom area of the lens structure is larger than the area of the light emitting part.

  According to a second aspect of the present invention, in the organic EL light emitting device according to the first aspect, the lens structure is bonded to the substrate through an adhesive layer having a refractive index equivalent to that of the substrate.

  According to a third aspect of the present invention, in the organic EL light emitting device according to the first aspect, the lens structure is formed integrally with the substrate.

  According to the first aspect of the present invention, since there is almost no difference in refractive index between the substrate and the lens structure, there is no critical angle at the interface between the substrate and the lens structure, and light incident on the substrate from the light emitting portion Therefore, the light is incident on the lens structure without being totally reflected at the interface, and thus the light extraction efficiency of the organic EL light emitting device is improved. In addition, since each light emitting portion concentrically opposes a lens structure having a larger bottom area than the area, most of the light incident on the substrate from the light emitting portion enters the lens structure, and the organic EL light emitting device The light extraction efficiency is improved.

  According to the invention of claim 2, since the adhesive layer has a refractive index equivalent to that of the substrate, the lens structure has a refractive index equivalent to that of the substrate. For this reason, there is no critical angle at the interface between the substrate and the adhesive layer and between the adhesive layer and the lens structure, total reflection does not occur at the interface, and the light extraction efficiency of the organic EL light emitting device is improved.

  According to the invention of claim 3, since no interface exists between the substrate and the lens structure, the light extraction efficiency of the organic EL light emitting device is improved.

The top view which looked at the organic electroluminescent light emitting device which concerns on the 1st Embodiment of this invention from the light extraction surface side. XX sectional drawing of FIG. Sectional drawing of the light emission part of the apparatus. The top view which looked at the organic electroluminescent light-emitting device which concerns on the 2nd Embodiment of this invention from the light extraction surface side. Sectional drawing of the conventional organic EL element.

(First embodiment)
An organic EL light emitting device (hereinafter referred to as a light emitting device) according to a first embodiment of the present invention will be described with reference to FIGS. As shown in FIGS. 1 and 2, the light emitting device 1 includes a plurality of light emitting units 2 having an organic light emitting layer 21 (hereinafter referred to as a light emitting layer), a translucent substrate 3, and the light emitting units 2. A wiring 4 for connecting to an external power source 1 and a plurality of lens structures 5 are provided. The light emitting unit 2 is disposed on one surface 31 of the substrate 3. Light from the light emitting unit 2 is extracted through the substrate 3. The lens structure 5 is arranged on the light extraction surface 32 side of the substrate 3 so as to correspond to each of the light emitting units 2 and has a refractive index equivalent to that of the substrate 3. Here, the same refractive index means that the refractive index difference is within plus or minus 0.2. Each of the lens structures 5 is arranged such that the optical axis 51 passes through the center 20 of the light emitting unit 2, and the bottom area of the lens structure 5 is larger than the area of the light emitting unit 2.

  The optical axis 51 of the lens structure 5 is in the normal direction of the substrate 3. The ratio of the bottom area of the lens structure 5 to the area of the light emitting portion 2 is preferably as large as possible, and more preferably 80 or more. Each of the lens structures 5 is adjacent to each other at a polygonal side 52. The polygon is, for example, a hexagon and may be a rectangle. The lens structure 5 has a convex shape having a substantially semicircular cross section. However, since the lens structure 5 is a polygonal shape in plan view, the lens structure 5 has a convex shape having a ridge line 53 instead of a hemispherical shape.

  As shown in FIG. 3, the light emitting unit 2 is an organic EL element in which an anode 22 made of a transparent electrode, an organic layer 24, and a light reflective cathode 23 are stacked in this order. In addition, each layer of the light emission part 2 is expanded and illustrated by the appropriate magnification in the thickness direction. The organic layer 24 has at least a light emitting layer 21 containing a light emitting material, and an appropriate organic layer such as an electron injection layer, an electron transport layer 25, a hole block layer, a hole injection layer, a hole transport layer 26, or the like is laminated as necessary. Configured. In the present embodiment, an electron transport layer 25 is interposed between the cathode 23 and the light emitting layer 21, and a hole transport layer 26 is interposed between the anode 22 and the light emitting layer 21. The light emitting layer 21 may be a stack of a plurality of light emitting layers. Each of these layers of the light emitting unit 2 is formed on the substrate 3 by, for example, a vacuum deposition method.

  The planar shape of the light emitting unit 2 is made point-symmetric with respect to the center 20 such as a circle by the mask used when forming the light emitting unit 2 (see FIG. 1). The light emitting units 2 are arranged in a plane on the one surface 31 of the substrate 3 at substantially equal intervals. The board | substrate 3 consists of an insulator which has translucency, for example, shape | molds resin, such as glass or a polystyrene, in plate shape. The wiring 4 is formed on the substrate 3 and connected to the anode 22 and the cathode 23 of the light emitting unit 2.

  The lens structure 5 is formed by molding, for example, a glass or a translucent resin such as polystyrene or acrylic. In order to make the refractive index of the lens structure 5 equal to the refractive index of the substrate 3, the material of the lens structure 5 is the same material as the substrate 3, or a resin to which a refractive index adjusting agent such as molybdenum oxide is added.

  The lens structure 5 is bonded to the substrate 3 via a substrate 3 and an adhesive layer (not shown). The adhesive layer is made of, for example, matching oil and has a refractive index equivalent to that of the substrate 3. The lens structure 5 may be formed integrally with the substrate 3 by resin molding or the like.

  In the light emitting device 1 configured as described above, a voltage is applied to the anode 22 and the cathode 23 of the light emitting unit 2 via the wiring 4, and the light emitting unit 2 emits light. The light emitted from the light emitting unit 2 enters the substrate 3, enters the lens structure 5 through the substrate 3, and is extracted from the lens structure 5 into the atmosphere.

  According to the light emitting device 1 according to the present embodiment, since there is almost no difference in refractive index between the substrate 3 and the lens structure 5, there is no critical angle at the interface between the substrate 3 and the lens structure 5. The incident light enters the lens structure 5 without being totally reflected at the interface between the substrate 3 and the lens structure 5, and thus the light extraction efficiency of the light emitting device 1 is improved. Further, each light emitting unit 2 concentrically opposes the lens structure 5 having a larger bottom area than the area thereof, so that most of the light incident on the substrate 3 from the light emitting unit 2 enters the lens structure 5, The light extraction efficiency of the light emitting device 1 is improved.

  Further, when the lens structure 5 is bonded to the substrate 3, the adhesive layer has the same refractive index as that of the substrate 3, so that the lens structure 5 also has the same refractive index. For this reason, there is no critical angle at the interface between the substrate 3 and the adhesive layer and between the adhesive layer and the lens structure 5, and total reflection at the interface does not occur, and the light extraction efficiency of the light emitting device 1 is improved. Further, when the substrate 3 and the lens structure 5 are integrally formed, there is no interface between the substrate 3 and the lens structure 5, so that the light extraction efficiency of the light emitting device 1 is improved.

(Second Embodiment)
A light emitting device 10 according to a second embodiment of the present invention will be described with reference to FIG. In the light emitting device 10 of the present embodiment, the lens structure 15 has a substantially hemispherical shape instead of the polygonal lens structure 5 in plan view in the first embodiment. Since the lens structure 15 has a substantially hemispherical shape, the diameter of the bottom surface is approximately twice the height. Each of the lens structures 15 is disposed adjacent to each other. Similarly to the first embodiment, the optical axis 151 of the lens structure 15 is disposed so as to pass through the center 20 of the light emitting unit 2, and the bottom area of the lens structure 15 is made larger than the area of the light emitting unit 2. The planar shape of the light emitting unit 2 is a circle that is point-symmetric with respect to the center 20 thereof, and may be a polygon that is rotationally symmetric with respect to the center 20 such as a regular hexagon, a regular pentagon, or a square. The centers 20 are arranged in a hexagonal lattice shape. You may arrange | position the center 20 of the light emission part 2 in tetragonal lattice form.

  The light emitting device 10 configured as described above can obtain the same effects as the light emitting device 1 of the first embodiment. Further, since the lens structure 15 has a substantially hemispherical shape, molding is easy.

  Two light-emitting devices as examples of the present invention and two light-emitting devices as comparative examples were manufactured and subjected to evaluation tests.

As the substrate, a non-alkali glass plate (Corning, No. 1787) having a thickness of 0.7 mm was used. On the substrate, ITO as the anode has a thickness of 150 nm, the hole transport layer has 4,4′-bis [N- (naphthyl) -N-phenyl-amino] biphenyl (α-NPD) as the thickness of 40 nm, and the light emitting layer is Alq3. 6% doped with rubrene, 30 nm thick as the electron transport layer, 65 nm thick as the TpPyPhB electron transport layer, 1 nm thick LiF as the electron injection layer, 80 nm thick as the cathode, and the light emitting portion Obtained. The light emitting part has a square shape in a plan view and has a side of 2 mm and an area of 4 mm ² .

The lens structure is made of non-alkali glass, which is the same as the material of the substrate, in a hemispherical shape with a diameter of 4 mm, and is arranged so that the optical axis of this lens structure passes through the center of the light emitting part. Bottom area of the lens structure is about 12.6 mm ^2, greater than the area 4 mm ² of the light-emitting portion. The lens structure and the substrate were bonded with matching oil having a refractive index equivalent to that of the substrate.

  Using a non-alkali glass as a material, a substrate having a thickness of 0.7 mm and a hemispherical lens structure having a diameter of 4 mm were integrally formed. The light emitting part was produced in the same manner as in Example 1.

(Comparative Example 1)
Comparative Example 1 corresponds to the apparatus described in Patent Document 1. The lens structure has a curvature centered on the center of the light emitting portion. The thickness (d1) of the substrate was 0.7 mm, the distance (d2) from the substrate surface to the apex of the lens structure was 0.7 mm, and the radius of curvature (R3) of the lens structure was 2.0 mm. The relationship between d1, d2, and R3 is d1 + d2 <R3. Other than that, it was the same as Example 1.

(Comparative Example 2)
Comparative Example 1 was performed except that the distance (d2) from the substrate surface of the lens structure to the apex of the lens structure was 1.3 mm. Comparative Example 2 corresponds to the apparatus described in Patent Document 1, and is different from Comparative Example 1 in that the relationship between d1, d2, and R3 is d1 + d2 = R3.

(Evaluation test)
In the light emitting devices of each of the above examples and comparative examples, a current is passed between the anode and the cathode so that the current density is 10 mA / cm ^2, and the extracted light (emitted light) is measured by an integrating sphere (flux meter). did. Table 1 shows the current efficiency [lm / A] (lumen / ampere) of the light flux calculated based on this measurement result. Since the current density is the same, the light extraction efficiency is higher as the current efficiency of the light emitting device is higher.

  As can be seen from Table 1, Comparative Example 2 had higher current efficiency than Comparative Example 1. That is, in the apparatus described in Patent Document 1, the light extraction efficiency is higher when the distance (d2) from the substrate surface to the apex of the lens structure is larger. Example 1 of the present invention had higher current efficiency than Comparative Example 2. In addition, the current efficiency of Example 2 was higher than that of Example 1. That is, it was confirmed that Example 1 and Example 2 of the present invention have higher light extraction efficiency than the apparatus described in Patent Document 1. It was also found that the light extraction efficiency is higher when the substrate and the lens structure are integrally formed than when the lens structure is bonded to the substrate.

  In addition, this invention is not restricted to the structure of said embodiment, A various deformation | transformation is possible in the range which does not change the summary of invention. For example, the lens structure may be a hemisphere cut into a regular hexagonal planar shape, and this lens structure may be arranged on the substrate in a honeycomb shape.

DESCRIPTION OF SYMBOLS 1, 10 Organic EL light-emitting device 2 Light-emitting part 20 Center of light-emitting part 21 Organic light-emitting layer (light-emitting layer)
3 Substrate 32 Light extraction surface 5, 15 Lens structure 51, 151 Optical axis of lens structure

Claims (3)

An organic EL light emitting device comprising a plurality of light emitting portions having an organic light emitting layer and a translucent substrate, wherein the light emitting portion is disposed on one surface of the substrate, and light from the light emitting portion is extracted through the substrate. A device,
A lens structure having a refractive index equivalent to that of the substrate corresponding to each of the light emitting portions on the light extraction surface side of the substrate,
Each of the lens structures is arranged such that its optical axis passes through the center of the light emitting unit,
2. An organic EL light emitting device, wherein a bottom area of the lens structure is larger than an area of the light emitting part.   The organic EL light-emitting device according to claim 1, wherein the lens structure is bonded to the substrate via an adhesive layer having a refractive index equivalent to that of the substrate.   2. The organic EL light emitting device according to claim 1, wherein the lens structure is formed integrally with the substrate.

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