JP2005339927A - Organic electroluminescence device - Google Patents

Abstract

【Task】
An organic EL element having a simple configuration and improved light extraction efficiency, and further, the light emitted from the substrate to the outside has almost the same brightness without being colored regardless of the emission angle. To provide such an organic EL element.
[Solution]
The organic EL element has a transparent substrate in which an antireflection film is formed on one surface and a transparent anode layer, organic EL layer, and cathode layer are sequentially stacked on the other surface. The refractive index decreases from the transparent substrate side to the element external side.
[Selection] Figure 1

Description

  The present invention relates to an organic electroluminescence element (hereinafter referred to as an organic EL element) which is a planar solid-state light-emitting element that can be used as a multicolor display device or a light source.

  In recent years, organic EL elements are superior to other solid-state light emitting elements in that they can be driven by a low voltage, have a wide viewing angle, have high visibility, and have high-speed response. Have excellent performance. Organic EL elements have been put into practical use in various technical fields because of the excellent performance as described above.

  The organic EL element is configured by sequentially laminating a conductive film (anode layer), an organic EL layer, and a metal conductive film (cathode layer) on a substrate. And by applying a voltage between both electrodes, an electric current flows into an organic EL layer and light is generated. In an organic EL element that has been widely used in recent years, light generated in an organic EL layer is irradiated to the outside through a transparent anode layer and a substrate.

  Here, before the light generated in the organic EL layer is irradiated to the outside, the light is generated by the interface between the organic EL layer and the anode layer, the interface between the anode layer and the substrate, and the interface between the substrate and the outside (air). Partially reflected. Furthermore, when light is transmitted from a layer having a high refractive index to a layer having a low refractive index, light incident at an angle greater than the critical angle causes total reflection. Therefore, the light extraction efficiency in the conventional organic EL element is less than about 15%. In the present text, the ratio of the amount of light actually irradiated from the substrate to the outside with respect to the amount of light generated in the organic EL layer is referred to as light extraction efficiency (unit:%). Therefore, in order to improve the light extraction efficiency, organic EL elements exemplified in the following Patent Documents 1 to 3 have been proposed.

JP 2003-86353 A JP 2003-109749 A JP 2003-31374 A

  In the organic EL element described in Patent Document 1, the light extraction efficiency is improved by disposing a light collecting layer between the anode layer and the substrate. The condensing layer is composed of a structure having a light condensing property and a transparent resin having a higher refractive index than that of the structure. Moreover, the organic EL element described in Patent Document 2 aims to improve the light extraction efficiency by forming the interface between the anode layer and the substrate as an uneven surface.

  However, when manufacturing the organic EL element described in each of Patent Documents 1 and 2, a process for forming a complex structure such as a condensing layer in Patent Document 1 and an uneven interface in Patent Document 2 Will be newly added. For this purpose, introduction of a new processing device or the like and work with extremely high accuracy are required. Therefore, the practicality is poor from the viewpoint of cost and labor.

  In addition, the organic EL element described in Patent Document 3 improves the light extraction efficiency by providing an antireflection film on both surfaces of the substrate, that is, the interface between the anode layer and the substrate and the interface between the substrate and the outside (air). ing.

  However, the antireflection film used in Patent Document 3 uses a film that can reduce the reflectance most when the emission angle is 0 °. For this reason, as the emission angle increases, the change in reflectance due to the wavelength increases. In other words, it is not preferable because the color changes or darkens depending on the viewing angle of the light irradiated from the substrate to the outside.

  Accordingly, in view of the above circumstances, the present invention is an organic EL element having a simple configuration and improved light extraction efficiency, and further, the light emitted to the outside from the substrate can be emitted regardless of the exit angle. An object of the present invention is to provide an organic EL element which is not colored and has substantially the same brightness.

  In order to achieve the above object, the organic EL device according to claim 1 has an antireflection film formed on one surface, and a transparent anode layer, organic EL layer, and cathode layer are sequentially stacked on the other surface. The antireflection film is configured such that the refractive index decreases from the transparent substrate side toward the element external side.

  According to the organic EL element of the first aspect, by using the antireflection film as described above, it is possible to effectively prevent a phenomenon in which the transmittance decreases as the emission angle of light emitted from the element increases. be able to.

  Here, light having an emission angle of 0 ° has the highest luminance and hardly undergoes a color change. On the other hand, as the emission angle increases, the brightness of the light decreases and the color changes. Therefore, the conventional antireflection film exemplified in Patent Document 3 cannot effectively prevent a decrease in luminance or color change of light having a large emission angle. On the other hand, the transmittance of the antireflection film as described above does not change greatly depending on the emission angle. Therefore, the organic EL device according to claim 1 guarantees the luminance of light emitted with a large emission angle, and has a light extraction efficiency as a result, even though the antireflection film is provided. The improvement is realized.

  Preferably, an antireflection film is used in which the refractive index at the portion closest to the transparent substrate is smaller than the refractive index of the transparent substrate. Thereby, the reflectance at the interface between the antireflection film and the transparent substrate can be effectively reduced.

Specifically, the antireflection film described above can be configured by laminating a plurality of thin films having different refractive indexes. In this case, in order to achieve the above-described effect that the transmittance can be maintained even when the emission angle becomes large, the antireflection film has a thickness t (unit: nm) of each thin film that satisfies the following condition (1), and It is desirable that the refractive index difference | Δn | between adjacent thin films satisfies the following condition (2).
30 ≦ t ≦ 200 (1)
0.02 ≦ | Δn | ≦ 0.3 (2)

  Condition (1) is a condition for preventing color change while ensuring light transparency. In condition (1), if the film thickness t is lower than the lower limit, the film thickness becomes too thin with respect to the wavelength of light. Therefore, the effect obtained by stacking two films having different refractive indexes even when light is incident thereon. Is not preferable because it is not obtained. In condition (1), when the film thickness t exceeds the upper limit, the effect of gradually changing the refractive index from the transparent substrate to the air decreases, and the interference effect on the thick film becomes significant. For this reason, the reflectance changes greatly, that is, a color change occurs, which is not preferable.

  Condition (2) is a condition for enhancing the effectiveness of the antireflection effect. If the refractive index difference | Δn | is less than the lower limit in the condition (2), it is difficult to obtain an antireflection effect using the refractive index difference, which is not preferable. On the other hand, if the refractive index difference | Δn | exceeds the upper limit in the condition (2), the interference effect at the interface between adjacent thin films becomes remarkable, and the transmittance cannot be sufficiently secured, which is not preferable. .

Further, the refractive index ne of the outermost layer (hereinafter referred to as the outermost layer) in the antireflection film has the following condition (3):
1.02 ≦ ne ≦ 1.38 (3)
It is desirable to satisfy (Claim 4). In this way, by making the refractive index of the outermost layer closer to the refractive index of the outside (air), the reflectance at the interface with the outside can be kept small for light emitted with any exit angle. it can.

  In addition, by making the outermost layer porous, a layer having a refractive index closer to the outside can be obtained. In addition, a multilayer film structure in which the refractive index gradually changes can be configured by films made of different materials, but even with the same material, porous films with different degree of pore formation are used. Even so, the multilayer film structure can be formed.

  Further, the outermost layer requiring a low refractive index is preferably composed of any one of MgO, Al 2 O 3, SiO 2, MgF 2, and CaF 2.

  The antireflection film can also be configured as a single layer film whose refractive index continuously changes.

Furthermore, the organic EL element according to claim 8 is characterized in that the refractive index n1 of the transparent substrate and the refractive index n2 of the anode layer satisfy the following conditions (4) to (6), respectively.
1.60 <n1 <2.15 (4)
1.60 <n2 <2.15 (5)
| N1-n2 | <0.4 (6)

  According to the eighth aspect of the present invention, the reflectance at the interface between the transparent substrate and the anode layer is effectively reduced by making the range of the refractive index that can be taken by the transparent substrate and the anode layer substantially the same. At the same time, by providing an antireflection film at the interface between the transparent substrate and the outside, the reflectance at the interface is also effectively reduced. Accordingly, the light extraction efficiency can be improved by suppressing the reflectance at each interface without complicating the configuration as in the organic EL elements described in Patent Documents 1 and 2 described above.

Further, according to the invention described in claim 9, the refractive index n3 of the organic EL layer further satisfies the following conditions (7), (8):
1.60 <n3 <1.80 (7)
| N2-n3 | <0.4 (8)
It is desirable to satisfy. Thereby, the reflectance at the interface between the organic EL layer and the anode layer can also be suppressed, and the light extraction efficiency can be further improved.

  As described above, the organic EL element according to the present invention effectively reduces the reflectance at the interface by providing the antireflection film having a predetermined design at the interface between the transparent substrate and the outside. Furthermore, the reflectance at the interface between the transparent substrate and the anode layer is also reduced by making the refractive indexes of at least the transparent substrate and the anode layer substantially the same. As described above, the organic EL element according to the present invention can improve the light extraction efficiency while having a simple configuration in which each layer is configured with an appropriate refractive index.

  Furthermore, the organic EL device according to the present invention can maintain luminance and suppress color change even with light having a large emission angle at the interface between the transparent substrate and the outside by the antireflection film.

  FIG. 1 is a diagram showing a schematic configuration of an organic EL element 10 according to an embodiment of the present invention. As shown in FIG. 1, the organic EL element 10 has a transparent substrate 1. On one surface of the transparent substrate 1, an anode layer 2, an organic EL layer 3, and a cathode layer 4 are stacked in this order from the one surface side. An antireflection film 5 is provided on the other surface of the transparent substrate 1. The dimensions of the members 1 to 5 shown in FIG. 1 are exaggerated for convenience of explanation, and are different from the dimensions of the actual organic EL element 10.

The transparent substrate 1 is made of glass having a refractive index n1 that satisfies the following condition (4).
1.60 <n1 <2.15 (4)
The anode layer 2 is made of a transparent electrode layer such as an ITO (Indium Tin Oxide) film, an ATO (antimony doped tin dioxide) film, or a ZnO (zinc oxide) film. The refractive index n2 of the anode layer 2 satisfies the following condition (5).
1.60 <n2 <2.15 (5)
In this embodiment, the refractive index of the transparent substrate 1 and the refractive index of the anode layer 2 satisfy the condition (4) or the condition (5), respectively, and are set so that the difference in refractive index between them becomes small. That is, the following condition (6) is satisfied.
| N1-n2 | <0.4 (6)
In this way, by suppressing the difference in refractive index between the transparent substrate 1 and the anode layer 2, the reflectance at the interface between the transparent substrate 1 and the anode layer 2 is suppressed to improve the light extraction efficiency.

The organic EL layer 3 is composed of Alq3 (aluminum quinolinol complex), Almq (methylaluminum quinolole complex), Beq2 (beryllium-quinoline complex), or the like. More specifically, the organic EL layer 3 is configured by laminating a light emitting layer and an electron transport layer in order from the anode layer 2 side. In addition, although the layer for making light emission last longer, such as a positive hole injection layer and a positive hole transport layer, is arrange | positioned between the anode layer 2 and the organic electroluminescent layer 3, description and illustration are abbreviate | omitted here. The refractive index n3 of the organic EL layer 3 satisfies the following conditions (7) and (8).
1.60 <n3 <1.80 (7)
| N2-n3 | <0.4 (8)

  The cathode layer 4 is a metal conductive film made of Al, Ag, In, Mg, Au, or the like. By applying a voltage to the anode layer 2 and the cathode layer 4, a current flows through the organic EL layer 3 to emit light. Light generated in the organic EL layer 3 is irradiated to the outside (here, air) through the anode layer 2 and the transparent substrate 1.

The antireflection film 5 is provided on the transparent substrate 1 by a technique such as vapor deposition, sputtering, CVD, spin, dip, spray, or pasting. The antireflection film 5 is configured such that the refractive index gradually decreases from the transparent substrate 1 side toward the outside. Specifically, the antireflection film 5 of the present embodiment is configured by laminating a plurality of thin films having different refractive indexes. Each thin film satisfies the following condition (1). Condition (1) is a condition for preventing color change while ensuring light transparency.
30 ≦ t ≦ 200 (1)

  FIG. 2 is a graph showing the antireflection effect of the antireflection film for light incident at an incident angle of 5 ° when the thickness t of each thin film constituting the antireflection film is changed. In the graph, the horizontal axis indicates the wavelength of incident light, and the vertical axis indicates the reflectance.

  As shown in FIG. 2, each antireflection film composed of a thin film having a film thickness that does not satisfy the condition (1) such as 210 nm or 20 nm has a high reflectance in the visible region, and the reflection The rate also varies from wavelength to wavelength. Therefore, if an antireflection film composed of a thin film having a film thickness that does not satisfy the condition (1) is used, not only the light extraction efficiency is lowered, but also visibility may be deteriorated due to occurrence of a color change. is there.

  On the other hand, the antireflection film 5 of the present embodiment configured with a thin film having a thickness of 135 nm that satisfies the condition (1) has a reflectivity in the visible region as compared with a configuration that does not satisfy the condition (1). It is relatively low and uniformly suppressed. That is, the organic EL element 10 including the antireflection film 5 that satisfies the condition (1) has high light extraction efficiency while effectively suppressing color change.

Further, in order to obtain the effect of gradually changing the reflectance, the antireflection film 5 is configured so that the refractive index difference | Δn | between two adjacent films satisfies the following condition (2). The By configuring the refractive index difference | Δn | to satisfy the condition (2), the antireflection effect of the antireflection film 5 can be effectively obtained.
0.02 ≦ | Δn | ≦ 0.3 (2)

  In the antireflection film 5 configured to satisfy the conditions (1) and (2), the reflectance reduction effect does not depend on the exit angle, unlike the antireflection film disclosed in Patent Document 1. . Therefore, the organic EL element 10 of this embodiment can obtain high light extraction efficiency in a wide emission range.

  In addition, in order to keep the reflectance at the interface between the transparent substrate 1 and the antireflection film 5 low, the film in contact with the transparent substrate in the antireflection film 5 has a refractive index smaller than the refractive index of the transparent substrate 1. Is done.

Further, in order to keep the reflectance at the interface between the outside and the antireflection film 5 low, the refractive index ne of the outermost layer in the antireflection film 5 is as follows:
1.02 ≦ ne ≦ 1.38 (3)
It is set to satisfy. As a thin film satisfying the condition (3), a porous film using a predetermined material is suitable. Examples of the predetermined material include materials having a small refractive index and relatively durability, such as MgO, Al2O3, SiO2, MgF2, and CaF2.

  Specific examples of the organic EL element 10 configured as described above will be described below. Table 1 shows a specific numerical configuration of the organic EL element 10 of the example of the above embodiment. In Table 1, the outermost layer of the antireflection film 5 is a porous film of SiO2.

  As shown in Table 1, in the organic EL element 10 of the example, the thickness t of each thin film constituting the antireflection film 5 is all 135 nm. Further, the refractive index difference | Δn | between the thin films is 0.08 or 0.16. Further, the refractive index ne of the outermost layer is 1.20. That is, the organic EL element 10 of the example satisfies all the conditions (1) to (3) regarding the antireflection film 5. Further, n1 = 1.81, n2 = 2.00, and n3 = 1.75, which satisfy the conditions (4) to (8), respectively.

  Next, as Comparative Example 1, specific numerical configurations of conventional organic EL elements are shown in Table 2. In addition, as Comparative Example 2, specific numerical configurations relating to substantially the same elements as the organic EL element described in Patent Document 3 are shown in Table 3. The antireflection films of Comparative Examples 1 and 2 shown in Tables 2 and 3 are designed to have a film thickness that provides the lowest reflectance for light having an emission angle of 0 ° at the interface between the glass substrate and the outside. .

  The performance of the organic EL element 10 of the example and the organic EL elements of Comparative Examples 1 and 2 will be described. FIG. 3 is a graph showing the light extraction efficiency for each wavelength in each organic EL element. In FIG. 3, the horizontal axis represents the wavelength of light emitted to the outside, and the vertical axis represents light extraction efficiency. In addition, regarding the distribution of the light extraction efficiency shown in FIG. 3, the organic EL element 10 of an Example is shown with a continuous line, and the organic EL element of Comparative Examples 1 and 2 is shown with a dotted line and a dashed-dotted line, respectively. The same applies to FIG. 4 shown below. As shown in FIG. 3, compared to the organic EL elements of Comparative Examples 1 and 2, the organic EL element 10 of the example has a flat distribution and high light extraction efficiency over almost the entire wavelength range. That is, in the organic EL element 10 of the example, the color change of the light irradiated to the outside is suppressed to be smaller than that of the organic EL elements of Comparative Examples 1 and 2.

  FIG. 4 is a graph showing the emission angle of light (wavelength 550 nm) emitted from the organic EL layer 3 and the transmittance of the light from the transparent substrate 1 to the outside in each organic EL element. In FIG. 4, the horizontal axis represents the emission angle, and the vertical axis represents the transmittance. As shown in FIG. 4, compared with the organic EL elements of Comparative Examples 1 and 2, the organic EL element 10 of the example has a flat and high transmittance distribution over a wide range of emission angles. That is, the organic EL element 10 of the example ensures high luminance and a stable light amount even when the light emission angle (in other words, the emission angle at the substrate 1) increases.

  The above is the embodiment of the present invention. The organic EL device according to the present invention is not limited to the above configuration. For example, the antireflection film 5 of the example has a structure in which the refractive index gradually changes according to the numerical structure (film thickness, etc.) as shown in Table 1 to enhance the antireflection effect. With this configuration, the antireflection effect can be improved.

  For example, in the above embodiment, the antireflection film 5 is configured by laminating a plurality of thin films having different refractive indexes. However, the antireflection film in the organic EL element of the present invention is a single layer whose refractive index continuously changes. A layer film may be used. Moreover, in the said Example, the refractive index was changed by using a different material for another layer, and the porous film | membrane is used only for the outermost layer which needs to keep the refractive index low most. Here, the porous film has a feature that the refractive index can be changed even if the film is made of the same material by changing the density of the pores. Therefore, if this feature is used, the antireflection film can be made of as few kinds of materials as possible. Thereby, an organic EL element having a simpler and cheaper configuration is provided.

  Moreover, in the said embodiment, the structure which the refractive index (n1, n2) of the transparent substrate 1 and the anode layer 2 became substantially the same was shown. The organic EL element according to the present invention can be configured so that the refractive index n3 of the organic EL layer 3 is substantially the same as the refractive index of the transparent substrate 1 and the anode layer 2. Thereby, since the reflectance of the light inject | emitted from the organic EL layer 3 to the anode layer 2 can be suppressed, the further increase in the light quantity of the light irradiated to the exterior is implement | achieved.

It is a figure which shows schematic structure of the organic EL element of embodiment of this invention. It is a graph showing the antireflection effect of the antireflection film with respect to light incident at an incident angle of 5 ° when the thickness of each thin film constituting the antireflection film is changed. It is a graph which shows the light extraction efficiency for every wavelength in the organic EL element of an Example, and the organic EL element of each comparative example 1 and 2. It is a graph showing the emission angle of the light (wavelength 550nm) inject | emitted from an organic EL layer in the organic EL element of an Example, and the organic EL element of each comparative example 1 and 2, and the transmittance | permeability of this light.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Anode layer 3 Organic EL layer 4 Cathode layer 5 Antireflection film 10 Organic EL element

Claims (9)

An organic electroluminescence device having a transparent substrate in which an antireflection film is formed on one surface and a transparent anode layer, an organic electroluminescence layer, and a cathode layer are sequentially laminated on the other surface,
The organic electroluminescence device, wherein the antireflection film is configured such that the refractive index decreases from the transparent substrate side toward the device outer side. The organic electroluminescent device according to claim 1,
An organic electroluminescence device, wherein a refractive index of the antireflection film at a portion closest to the transparent substrate is smaller than a refractive index of the transparent substrate. In the organic electroluminescent element according to claim 1 or 2,
The antireflection film is formed by laminating a plurality of thin films having different refractive indexes,
The film thickness t (unit: nm) of the thin film satisfies the following condition (1), and the refractive index difference | Δn | between the adjacent thin films is the following condition (2):
30 ≦ t ≦ 200 (1)
0.02 ≦ | Δn | ≦ 0.3 (2)
An organic electroluminescent element characterized by satisfying the above. In the organic electroluminescent element according to claim 3,
The refractive index ne of the layer on the outermost side of the element in the antireflection film has the following condition (3):
1.02 ≦ ne ≦ 1.38 (3)
An organic electroluminescent element characterized by satisfying In the organic electroluminescent element according to claim 3 or 4,
In the antireflection film, at least the layer on the outermost side of the element is porous, and the organic electroluminescence element. In the organic electroluminescent element in any one of Claims 3-5,
An organic electroluminescence element, wherein the layer on the outermost side of the antireflection film is made of any one of MgO, Al2O3, SiO2, MgF2, and CaF2. In the organic electroluminescent element according to claim 1 or 2,
The organic electroluminescence device according to claim 1, wherein the antireflection film is a single layer film whose refractive index continuously changes. In the organic electroluminescent element in any one of Claims 1-7,
The refractive index n1 of the transparent substrate and the refractive index n2 of the anode layer are the following conditions (4) to (6)
1.60 <n1 <2.15 (4)
1.60 <n2 <2.15 (5)
| N1-n2 | <0.4 (6)
An organic electroluminescent element characterized by satisfying the above. The organic electroluminescent device according to claim 8, wherein
Conditions (7) and (8) where the refractive index n3 of the organic electroluminescence layer is as follows:
1.60 <n3 <1.80 (7)
| N2-n3 | <0.4 (8)
An organic electroluminescent element characterized by satisfying

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