JP2003249381A - Organic electroluminescence element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To offer simple construction achieving high output efficiency and bright display. <P>SOLUTION: The organic electroluminescence element comprises a number of protruded portions 10B provided on a transparent substrate 1 using a colorless transparent resin layer 2. The protruded portion 10B satisfies L=2 to 100 μm, L/H=2 to 20, where L is the diameter of the protruded portion 10B in the surface direction of the substrate and H is the height in the direction of its thickness. An alkali barrier film 3, a transparent conductive film 4, a luminous layer 5 and a light deflective electrode 6 are laminated in sequence thereon. An observer 20 can view that a number of recessed portions 10A are formed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-luminous organic electroluminescence device (hereinafter also referred to as an organic EL device).

[0002]

2. Description of the Related Art Appl. Phys. Lett. , 5
1,913 (1987), an organic material is adopted as a light emitting layer, and a hole transport layer and a light emitting layer / electron transport layer are laminated.
An organic EL device having a layer structure and using tris (8-quinolinolato) aluminum (hereinafter referred to as Alq) for a light emitting layer and an electron transporting layer is disclosed.

This organic EL device emits green light at a driving voltage of 10 V or less, has a luminance of 1000 cd / m ² and a luminous efficiency of 1.5 lumen / W.

In contrast to liquid crystal display devices, PDPs, LED display devices, fluorescent display devices and the like which are widely used at present, the organic EL device can provide a bright display in principle, and has high definition and excellent visibility. Therefore, it is expected as a next-generation display element capable of displaying high information quality.

Therefore, in putting an organic EL element into practical use, it is strongly demanded that it be bright and have low power consumption. In order to realize the characteristics, it is necessary to select a good combination of the light emitting material and the electrode of the organic EL element and improve the light emitting efficiency itself. Further, it is important to improve the extraction efficiency of spontaneously emitted light.

In a general organic EL device, about 80% of the light emitted isotropically from the light emitting layer having a simple planar structure is reflected at the substrate interface and further emitted from the end face of the substrate to the outside. Or is absorbed by the constituent material of the organic EL element. As a result, the light L _O emitted to the front surface of the organic EL element and visible to the observer is calculated to be about 20% (see FIG. 4).

In the current organic EL device, most of the spontaneously emitted light is lost, and the ratio of contribution to display is considerably low. Therefore, in order to improve the light extraction efficiency of the organic EL element, a method of incorporating an optical element into the substrate of the organic EL element is known. For example, Japanese Patent Application Laid-Open No. 10-172756 discloses a method of incorporating a flat plate microlens into a transparent substrate itself.

In addition, OPTICS LETTERS V
ol. 22, No. 6,396 (1997), a prototype example in which an organic EL element is formed on the upper surface of a glass substrate whose surface is processed into a mesa type is announced.

[0009]

As described above, in the conventional examples, attempts have been made to improve the extraction efficiency of spontaneously emitted light. However, there is a problem that the device structure for improving the extraction efficiency and the manufacturing process are complicated, and it cannot be applied to a large-area substrate.

Further, there is a problem that the manufacturing cost of the organic EL element is basically high and it is not suitable for mass production.

[0011]

That is, the first aspect of the present invention is provided with a substantially flat transparent substrate, and the light emitting layer and the light-reflecting electrode are provided on the substrate of the transparent substrate. Assuming that a large number of recesses are provided in the light-reflective electrode and the diameter of the recesses in a plane substantially parallel to the substrate surface is L and the height of the recesses in the thickness direction of the substrate is H, L = 5 to 100 μm.
Provided is an organic electroluminescence device satisfying m and L / H = 2 to 20.

Aspect 2 provides the organic electroluminescent element according to Aspect 1, wherein the convex portions are provided on the substrate surface so as to correspond to the concave portions substantially one-to-one.

Aspect 3 provides the organic electroluminescence display element according to Aspect 2, wherein the convex portions are formed of a colorless transparent material.

Aspect 4 provides the organic electroluminescence display element according to Aspect 2, wherein a coloring material or a fluorescence conversion material is used for at least a part of the constituent material of the convex portion.

Aspect 5 provides the organic electroluminescent device according to Aspect 1, 2, 3 or 4, wherein the occupancy of the plane portion of the recess is 20 to 80% in the plane of the transparent substrate.

Aspect 6 is the organic electroluminescent device according to Aspect 1, 2, 3, 4 or 5, wherein the cross section of the recess in the substrate surface direction is selected from any of a circle, a triangle, a quadrangle, a hexagon and an octagon. A luminescent element is provided.

Aspect 7 is a method for manufacturing an organic electroluminescent device, in which a light emitting layer and a light-reflecting electrode are formed on a substrate of a substantially flat transparent substrate, wherein a large number of convex portions are formed on the substrate surface, and the convex portions are formed. A light-emitting layer and a light-reflective electrode are formed on the light-reflective electrode, and a large number of recesses are formed in the light-reflective electrode in a one-to-one correspondence with the protrusions. Provided is L, where H is the height of the concave portion in the thickness direction of the substrate, and L = 5 to 100 μm and L / H = 2 to 20 are satisfied, and a method for manufacturing an organic electroluminescence device is provided.

Further, in the above-mentioned organic electroluminescence device, the concave portion or the convex portion is 10 ⁴ to 1 in the plane.
0 ⁶ / cm is ^{preferably 2} is formed comprising.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the basic configuration of the present invention, a large number of recesses 10A are provided in a light reflecting electrode 6 on a transparent substrate (see FIG. 1). The light-reflective electrode 6 is provided on the opposite side of the observer 20.
Are placed. That is, a large number of aggregates of the recesses 10A are formed in the light reflective electrode 6 located on the non-observer side.

The recess 10A is formed on the substrate 1 in advance.
This can be formed by forming a large number of convex portions 10B made of a colorless transparent resin, and forming the alkali barrier layer 3, the transparent electrode 4, the light emitting layer 5, and the light reflective electrode 6 on the convex portions 10B. Alternatively, each layer may be sequentially formed so as to transfer the shape.

FIG. 2 shows a convex surface portion 10 formed by assembling a large number of convex portions on the surface of the substrate 1. In the case of adopting a simple structure, as shown in FIG. 2, a convex portion made of a colorless transparent resin is prepared corresponding to the required size of the display surface, and a transparent conductive film and a light emitting layer are provided thereon. Organic E provided with an organic layer including a light-reflecting electrode and a light-reflecting electrode 6 having a recess 10A when viewed from the observer 20 side.
An L element is formed.

The light-emitting layer and the light-reflective electrode are preferable because they can be easily formed in accordance with the convex portions provided in advance on the substrate surface. In this case, the light emitting layer and the light reflective electrode have substantially the same curved surface shape.

The concave portion 10A of the light-reflective electrode 6 positioned so as to sandwich the light emitting layer between the convex portion on the substrate 1 and the convex portion substantially functions as a concave mirror (see FIG. 5). Light emitting layer 5
The light spontaneously emitted by is reflected by the concave portion 10A of the light reflective electrode 6 located on the non-observer side, and the probability of the light L _O passing through the substrate 1 can be increased.

In this way, the light from the organic EL element is positively emitted forward, and the light extraction efficiency of the entire organic EL element can be improved. That is, the light L _O that can be visually recognized by the observer and can contribute to the display can be dramatically increased. Next, the operation of the present invention will be described.

First, assume that the surface of the glass substrate is flat. The refractive index of the glass is 1.5 and the refractive index of the transparent electrode / organic layer is 1.8. The critical angle for total internal reflection at the glass / air interface is 41.8 °.

The incident angle of light on the transparent electrode / glass interface corresponding to this critical angle is 33.7 °. Of the light emitted in all directions from the light emitting layer, even if the light emitted toward the direction of the cathode (reflective electrode) located on the non-observer side is 100% reflected by the cathode, this angle condition is satisfied. The probability of satisfaction of light is only about 17%.

Next, in the present invention, it will be described that the light extraction efficiency can be improved by providing the light reflecting electrode with a concave structure. A trial calculation was performed on the light emitted from the vicinity of the center of the recess. Alternatively, it is assumed that the observer 20 sees the center of spontaneous light emission at the crown of the convex portion 10B.

FIG. 8 shows the case where H = L / 2. The material of the substrate is glass. In the figure, θ = 0 to 3
A light ray having an emission angle in the range of 3.7 ° is emitted from the surface of the glass substrate to the outside. However, the emitted light in the range of θ = 33.7 ° and φ = 45 ° is totally reflected at the glass / air interface, propagates laterally in the glass substrate, and is not emitted to the display surface side.

Therefore, the light becomes ineffective light which cannot contribute to the display. Emitted light having an angle larger than θ = 45 ° is reflected by the electrode functioning as a concave mirror. Then, since it enters the inside of the glass substrate at a deep angle with respect to the surface of the glass substrate, it can be effectively extracted to the outside as light that can contribute exclusively to the display.

The emitted light (T _{L in the} shaded area) in the range of θ = 33.7 ° and φ = 45 ° is mainly ineffective light.
This angular range (and its 180 ° of all radial directions
The probability of entering the angular range (in the opposite direction) is about 12%. Therefore, in this case, the light extraction efficiency in this recess is 88%.

FIG. 9 shows an example in which the shape of the recess is shallow and the aspect ratio L / H = 10 is set. By the same calculation method as above, with respect to the light emitted from the vicinity of the central portion of the recess, the light emitted in the range of θ = 33.7 ° to φ = 78.7 ° becomes invalid, and the light extraction efficiency becomes 37%. .

It is difficult to make a highly accurate trial calculation of all the light emitted from the side wall of the recess, but the higher the height of the recess, the more the light emitted at a “deep angle” with respect to the surface of the glass substrate. It can be estimated that the ratio increases (see FIGS. 8 and 9).

Therefore, as described above, the light emitted from the central portion of the concave portion may be mainly subjected to the approximate trial calculation.
By this method, it is possible to know the emission state of the display light or the effective usage rate of the entire organic EL element.

Table 1 below shows the calculated value of the light extraction efficiency in one pixel when the ratio of the recessed portion in the pixel is changed. For example, 2 recesses with a diameter of 10 μm
When they are arranged at a pitch of 0 μm, the relative ratio (occupancy ratio) of the cross-sectional area occupied by the recesses on the surface of the transparent substrate is 20%.
The right column of Table 1 shows the case of a conventional example in which a complete planar structure is formed without providing a recess. The recesses are arranged in the plane at substantially equal pitches in the XY directions.

At this time, the height of the recess is 2 μm and L = 10.
If μm (H = L / 5) is set, the light extraction efficiency in one pixel is calculated to be 24%. The light extraction efficiency is improved by about 40% as compared with the comparative example in which only the flat surface is provided without providing the convex portion on the surface of the glass substrate. This is almost in agreement with the results of Examples described later.

[0036]

[Table 1]

Although the case of the glass substrate has been described, the present invention can be applied to the case of a material having flexibility and capable of changing into a curved surface such as a plastic substrate. It is more preferable to use the present invention than the case of glass because of the relative relationship of the refractive index.

Further, it is preferable that the entire convex surface portion provided with a large number of convex portions is made of a colorless transparent material. For example, a pattern of convex portions made of transparent resin can be formed on the transparent substrate by resin molding. Alternatively, transparent spheres such as silica beads may be embedded in the transparent film. Alternatively, the transparent substrate itself may be press-molded to form a convex portion on the surface on which the organic EL element is formed.

The size of the convex portion is configured to be a diameter sufficiently larger than the emission wavelength of the organic EL element so that the influence of changes in color and intensity due to light interference is reduced. And,
The diameter is set to be sufficiently smaller than the size of one pixel of the organic EL element.

In the present invention, it is preferable that the diameter L of the concave portion of the light reflecting electrode in the plane direction is in the range of 5 to 100 μm. Further, the closer the shape of the recess is to the hemisphere, the higher the light extraction efficiency is. However, when the manufacturing method of forming the convex portion as described above and forming the concave portion on the convex portion is adopted, it is necessary to continuously provide a large number of convex portions in the plane direction of the substrate. However, it becomes difficult to uniformly form the entire convex portion.

Therefore, as the dimension of the convex portion, the aspect ratio of the height H to the diameter L = H / L is set to be 2 to 20. Further, it is more preferable that H / L = 3 to 10. The diameter L does not have to have an accurate shape such as a circle, a triangle, or a quadrangle, which is a dimension that functions as a diameter in the plane direction.

In general, in order to form a pixel, convex portions of the same size are uniformly arranged in a plane so as to form an aggregate of convex portions. FIG. 6 shows an example of a substantially hexagonal plane shape, and FIG. 7 shows an example of a substantially octagonal plane shape.

A curved body of the light-reflective electrode is formed by covering the light emitting layer on the convex portion and further having a concave portion acting as a concave mirror. It may be configured to have a shape that substantially functions as a concave mirror so that the light does not escape in the lateral direction and is condensed on the observer side.

Further, a part of the convex portion may be formed of a coloring material such as a color filter material or a wavelength conversion material such as a fluorescence conversion material, that is, a colored transparent body. In this aspect, the chromaticity of the spontaneous emission light of the organic EL element can be adjusted together. That is, it is possible to simultaneously achieve the function of condensing spontaneous emission and the function of adjusting chromaticity. FIG. 3 shows a schematic cross-sectional view of an organic EL element having a colored layer 7 formed using a color filter material and an overcoat layer 8.

To form the organic EL device of this aspect,
The convex portions may be formed by covering the pattern of the color filter material or the fluorescence conversion material with the overcoat film. Hereinafter, specific embodiments of the present invention will be described with reference to Examples 1 to 3. The invention is not limited to these examples.

[0046]

EXAMPLE 1 Example 1 will be described with reference to FIG.
The convex portion 1 is formed by using a layer of the colorless transparent resin 2 on the glass substrate 1.
OB was formed. A clear resist (CFPR manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied on the glass substrate 1, and a circular pattern having a diameter of 10 μm was spread by photolithography at a pitch of 20 μm. This circular pattern was configured to be sufficiently smaller than the size of the pixel of the organic EL element to be finally formed.

The film thickness was 2 μm at the central part of the circular pattern, and the film was formed so as to have a curved surface shape in which the film thickness gradually decreases toward the outer peripheral part of the circular pattern. Further, a SiO ₂ film (having a film thickness of 2) is formed as an alkali barrier film 3 on the convex portion, which is an aggregate of the circular patterns, by sputtering.
0 nm), an ITO film (film thickness 200 n as the transparent electrode film 4
m) was continuously formed, and the ITO film was further patterned to form an anode.

On this anode, copper phthalocyanine (film thickness 10 nm), 4,4'-bis [N-
(1-Naphthyl) -N-phenylamino] biphenyl (hereinafter referred to as α-NPD) is formed into a film (film thickness 40n.
m), and further Alq (film thickness 50 nm) and LiF (film thickness 0.5 nm) were formed into the light emitting layer 5. Finally, 100 nm of Al was vapor-deposited as a metal film serving as a cathode to form an organic EL element. In this way, the light-reflective electrode 6 having the recesses 10A having substantially the same shape and arrangement pitch as the projections 10B could be formed.

When the organic EL device of this example was made to emit light and the light emitting surface was observed with a microscope, it was observed that a circular pattern having a diameter of 10 μm was emitting light brightly. When the voltage-luminance characteristics were compared with the organic EL element of the comparative example formed in the same manner except that the light emitting portion was completely flat, it was found that the luminance was improved by 50 to 60% in this example. confirmed.

Example 2 This example will be described with reference to FIGS. 2 and 3. A red color resist layer 7 (V259 manufactured by Nippon Steel Chemical Co., Ltd.) was applied on a glass substrate, and a circular pattern having a diameter of 10 μm was formed by photolithography so as to be spread on a plane at a pitch of 20 μm.

The film thickness of the circular pattern formed on the substrate was 2.5 μm. A clear resist (CFPR manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied thereon as an overcoat film 8. As a result, the steps of the color resist pattern having a large number of protrusions were flattened to some extent, resulting in a smooth surface shape.

Furthermore, a 20 nm SiO ₂ film as an alkali barrier film 3 and an ITO film having a film thickness of 200 nm as a transparent electrode film 4 are continuously formed thereon by sputtering, and the ITO film is patterned to form an anode. Formed.

Copper phthalocyanine was deposited to a thickness of 10 nm and α-NPD was deposited to a thickness of 40 nm on this anode by a vacuum deposition method, and rubrene 2% -doped Alq was added.
(Film thickness 30 nm), Alq (film thickness 30 nm), LiF
A film having a thickness of 0.5 nm was formed as a light emitting layer 5.

Finally, as the light-reflecting electrode 6 serving as the cathode, 1
Al was vapor-deposited to a film thickness of 00 nm to form an organic EL device. Similarly to the first example, the concave section 20A of the present example also substantially corresponds to the previously formed convex section 10B in a one-to-one correspondence.

A predetermined current was supplied to the organic EL device of this example to cause it to emit light. When observing the light emitting surface with a microscope, it was observed that a circular pattern having a diameter of 10 μm emitted red light, and a flat portion around the circular pattern emitted yellow light. The luminescent color looked orange with the naked eye.

(Example 3) In the same manner as in Example 1, an organic EL element having a pattern in which one pattern is substantially hexagonal as shown in FIG. 6 was formed. L = 10 μm, H = 1 μm
(Aspect ratio L / H = 10) was set. Then, the emission rate of light toward the front of the organic EL device of this example was improved by about 70%.

[0057]

As described above, according to the present invention,
With a relatively simple structure, increase the rate of light emission to the front,
An organic EL device having high light extraction efficiency can be obtained.
Due to the high light extraction efficiency, a brighter display device can be formed with the same power consumption. Further, if the same brightness is displayed, a display device with low power consumption can be realized.

Further, in the organic EL element of the present invention, the surface area on the substrate surface on which the organic EL element is formed is slightly larger than the pixel area as compared with the conventional example. Since the light emitting layers that contribute to the display are formed to increase per unit area, the brightness is basically increased as compared with the conventional planar organic EL element. Then, the drive voltage of the organic EL element can be lowered. It can be easily applied to large-area display devices.

Further, the organic EL element of the present invention has the effect that since the metal electrode is not a flat surface, it does not become a mirror surface and the reflection of the pixel when it is not emitting light is less likely to occur.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a first configuration example of an organic EL element of the present invention.

FIG. 2 is a schematic plan view of a first configuration example of the organic EL element of the present invention.

FIG. 3 is a cross-sectional view of an example in which a convex portion is formed using a coloring material or a fluorescence conversion material.

FIG. 4 is a schematic optical path diagram in a conventional organic EL element.

FIG. 5 is a schematic optical path diagram of the organic EL element of the present invention.

FIG. 6 is a schematic plan view of a second configuration example of the organic EL element of the present invention.

FIG. 7 is a schematic plan view of a third configuration example of the organic EL element of the present invention.

FIG. 8 is an optical path diagram in the vicinity of a recess according to the present invention.

FIG. 9 is an optical path diagram in the vicinity of a recess according to the present invention.

[Explanation of symbols] 1: substrate 2: colorless transparent resin 3: Alkali barrier film 4: Transparent electrode 5: Light emitting layer 6: Light reflective electrode (metal electrode) 7: Coloring material or fluorescence conversion material 8: Overcoat film

Claims (7)

[Claims] 1. A substantially flat transparent substrate, a light emitting layer and a light-reflecting electrode are provided on the transparent substrate, and a large number of recesses are provided in the light-reflecting electrode when viewed from an observer side. , L = 5 to 10 where L is the diameter of the recess in a plane substantially parallel to the substrate surface and H is the height of the recess in the thickness direction of the substrate.
An organic electroluminescence device satisfying 0 μm and L / H = 2 to 20. 2. The organic electroluminescence device according to claim 1, wherein the convex portions are arranged on the substrate surface so as to correspond to the concave portions substantially one-to-one. 3. The organic electroluminescence display device according to claim 2, wherein the convex portion is formed of a colorless transparent material. 4. The organic electroluminescence display element according to claim 2, wherein a coloring material or a fluorescence conversion material is used for at least a part of the constituent material of the convex portion. 5. The organic electroluminescence device according to claim 1, wherein the occupancy of the concave portion with respect to the flat surface portion in the plane of the transparent substrate is 20 to 80%. 6. A cross section of the recess in the substrate surface direction is circular,
The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device is selected from a triangle, a quadrangle, a hexagon, and an octagon. 7. A method of manufacturing an organic electroluminescence device, comprising: forming a light emitting layer and a light-reflecting electrode on a substrate of a substantially flat transparent substrate; A light-emitting layer and a light-reflective electrode are formed on the light-reflective layer, a large number of recesses are formed in the light-reflective electrode in a one-to-one correspondence with the protrusions, and the diameter of the recess is L in a plane substantially parallel to the substrate surface. When the height of the concave portion in the thickness direction of the substrate is H, L = 5 to 100 μm, L / H = 2
To 20 are satisfied, The manufacturing method of the organic electroluminescent element characterized by the above-mentioned.