JP2003332065A - Organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent reduction of visibility in a liquid crystal panel (LCD) in turning off a back light for the LCD, when an organic electroluminescence (EL) element is used as the back light. <P>SOLUTION: In the organic EL element 101 having a transparent substrate 12 and pinching an organic electroluminescence (EL) layer 16 between a pair of electrodes formed of an anode 14 and a cathode 20 disposed in the transparent substrate 12, a light emitting surface 26 of the transparent substrate 12 is provided with a light scattering layer 30 for backwardly scattering visible light coming from the outside. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence element (hereinafter referred to as an organic EL element) used as a light source of a backlight for a liquid crystal panel (hereinafter referred to as LCD).

[0002]

2. Description of the Related Art Organic EL devices are light emitting devices which are expected in the future because they emit light at a relatively low voltage and have a simple device structure. The device life, which has been regarded as a practical problem, has been improved considerably in recent years.

FIG. 4 is an explanatory diagram showing an example of the configuration of a conventional organic EL element 10. The organic EL element 10 is formed by sequentially depositing indium oxide (ITO: Indi), which is a transparent electrode, on an element substrate 12 such as transparent glass.
um.Tin.Oxide), an anode 14, a hole injection layer (not shown), a hole transport layer, an organic EL layer 16 made of an electron transporting light emitting layer, and a cathode 20 are laminated. Organic EL
The element 10 has, for example, (1) anode / light emitting layer / cathode, (2) anode / light emitting layer / electron transporting layer / cathode, and (3) anode / hole transporting layer / light emitting layer in addition to the configuration shown in FIG. / Cathode, (4) anode / hole transport layer / light emitting layer / electron transport layer / cathode, and other various structures.

Further, the cathode 20 can be formed of a multi-layer structure of a metal or a metal compound having a small work function. still,
Since the cathode 20 is soft and easily damaged, the take-out electrode 18 is usually formed on the transparent substrate 12, and the cathode 20 is formed so as to be connected to the take-out electrode 18. An ITO film is often used for the extraction electrode 18.

It is known that the organic EL layer 16 is deteriorated by water vapor, oxygen and the like in the air. Therefore, Ar
In an atmosphere of (argon) or N ₂ (nitrogen), the organic EL is formed on the sealing substrate 24 such as stainless steel (SUS).
It is common to cover the layer 16 and adhere the sealing substrate 24 with the adhesive 22 applied to the peripheral portion of the transparent substrate 12 to form an airtight structure. A desiccant such as calcium oxide (CaO) may be provided on the inner surface of the sealing substrate 24.

For light emission of the organic EL device 10, holes and electrons are injected into the organic EL layer 16 by applying a DC voltage to the anode 14 and the cathode 20 facing the anode 14, and these are recombined and recombined. The energy generated by the binding excites the fluorescent substance and emits light when the excited fluorescent substance returns to the ground state.

This emitted light is transmitted through the transparent substrate 12 and is taken out. In the above structure, the surface opposite to the film forming surface of the transparent substrate 12 becomes the light emitting surface 26. If the element configuration is changed and a transparent sealing substrate 24 is used, the sealing substrate 24
Light can also be taken out with the side as the light emitting surface 26.

The organic EL layer 16 includes an electron-transporting light-emitting layer (not shown). By doping the light-emitting layer with various dyes, light emission of red, blue, green, etc. can be obtained. It is also possible to obtain white light by arranging organic EL elements that emit red, blue, and green in fine stripes or a matrix.

The above-mentioned organic EL element 10 can also be used as a backlight for an LCD. The organic EL element 10 has an excellent feature that it is possible to obtain surface emission with high brightness and no brightness unevenness, as compared with a backlight using a conventional LED.

[0010]

Generally, in a liquid crystal display device, a backlight is provided on the back surface of the LCD in order to improve the visibility and the like. However, in electronic devices such as mobile phones, the backlight is often turned off except when necessary for the purpose of suppressing the consumption of a battery that is a power source and extending the usable time of the device.

In the organic EL element 10, the constituent organic EL element 16 is often doped with a dye, and copper phthalocyanine (CuPc) exhibiting a green-blue color is often used as a hole injecting layer. In the light emitting state,
It has a unique color. Such an organic E
When the L element 10 is used as a backlight of an LCD, since the LCD is achromatic and semitransparent, the unique color of the organic EL element 10 will be observed through the LCD.

Here, the coloring mechanism of light when the organic EL element 10 is used for a planar backlight of an LCD when it is not lit will be described. External light transmitted through an LCD (not shown) is from the X direction shown in FIG.
0 from the upper surface side, the transparent substrate 12, the transparent electrode 14
Through in order. Then, this external light is emitted from the organic EL layer 1
Although it is incident on 6, the light is transmitted by being colored with a dye or the like doped in the light emitting layer, and reflected by the mirror-shaped cathode 20. The reflected return light passes through the respective constituent members in the reverse order of the above and is emitted from the organic EL element 10.

After passing through the LCD, it reaches the eyes of the observer. As a result, the LCD when the backlight is turned off is colored with a color peculiar to the organic EL element 10, and there is a problem that the visibility of the originally displayed image is deteriorated.

The present invention has been made in view of this problem, and an object thereof is to backscatter the light incident from the outside so as to eliminate the deterioration of the visibility of the LCD when the backlight is off. It is to provide an EL element.

[0015]

In order to achieve the above object, in the present invention, visible light incident on the organic EL element from the outside is controlled. Then, it was found that by controlling this light by a method of backscattering on the surface of the element and efficiently suppressing the light incident on the organic EL layer, the coloring at the time of non-light emission as described above can be eliminated. The present invention has been completed.

The present invention is an organic EL device comprising a transparent substrate, and an organic electroluminescence (EL) layer sandwiched between a pair of electrodes consisting of an anode and a cathode provided on the transparent substrate. The light emitting surface is provided with a light scattering layer for backscattering visible light incident from the outside.

In the organic EL device of the present invention thus constructed, the device surface is not affected by the color of the coloring organic substance such as copper phthalocyanine used in the hole injecting layer or the colorant of the organic EL layer. It looks cloudy. Therefore, when the organic EL device according to the present invention is used as a backlight of an LCD, the LCD is not colored as described above even when the backlight is turned off, and the visibility due to coloring, which has been a problem in the past, is reduced. The drop can be resolved.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In addition, each figure used in the following description is
It should be understood that the present invention has been shown in a schematic manner to the extent that it can be understood, and thus the present invention is not limited to the illustrated examples. Further, in each drawing used for the description, the same constituent components are denoted by the same reference numerals, and the overlapping description may be omitted.

(First Embodiment) An embodiment of the organic EL device according to the present invention will be described with reference to FIG. The structure of the organic EL element 101 of this example is shown in FIG. Organic EL
The element 101 has a transparent substrate 12, and the transparent substrate 12 is provided with a pair of electrodes including an anode 14 and a cathode 20. The organic EL layer 16 is sandwiched between the electrodes. Specifically, on one main surface of the transparent substrate 12, the anode 14, which is a transparent electrode, the organic EL layer 16, and the cathode 20 are sequentially stacked. The structures of the transparent substrate 12, the anode 14, the organic EL layer 16, the cathode 20, the adhesive 22, and the sealing substrate 24 in this embodiment are the same as those of the conventional example already described with reference to FIG. Therefore, the description of the overlapping description is omitted.

Further, the organic EL element 101 of this embodiment
On the other main surface of the transparent substrate 12, that is, the light emitting surface 26,
Light scattering layer 30 for backscattering visible light incident from the outside
Is provided. Here, as described above, the light emitting surface 26 is the transparent substrate 1 from which the light emitted from the organic EL layer 16 is emitted.
2 is the outer surface and is usually a flat surface. In this embodiment, the organic E emitted from the light emitting surface 26 is
The light emitted from the L layer 16 passes through the light scattering layer 30 and is emitted to the outside.

Next, the structure of the light scattering layer 30 will be described. The light scattering layer 30 is preferably formed by using a transparent filter that transmits light. This filter 30 has a flat surface on one side. The filter 30 is provided on the transparent substrate 12 with its flat surface in contact with the light emitting surface 26 of the transparent substrate 12. In addition, filter 3
At 0, the surface opposite to the flat surface facing the light emitting surface 26 has an uneven surface 107, which is an uneven surface 107. The surface roughness of the uneven surface 107 of the filter 30 is preferably 1 to 5 μm. In other words, the height difference w between the convex portion 103 and the concave portion 105 shown in FIG. 1 is optimally set to 1 to 5 μm.

Furthermore, the filter 30 is preferably made of a light-transmissive material having a refractive index different from that of the transparent substrate 12. The filter 30 is preferably composed of a glass substrate. In that case, it is preferable to form irregularities of uniform shape on one surface of the glass substrate by a sand plast method so as to have a surface roughness of 1 to 5 μm.
Further, preferably, the filter 30 may be formed by corroding one surface of the glass substrate with a hydrogen fluoride solution. In this case, it is preferable to use soda glass as the glass substrate. Incidentally, in FIG.
Shows a configuration having a rectangular cross section. But,
The configuration of the uneven surface 107 is not limited to the configuration shown in FIG. 1, and any shape may be used as long as it has an uneven shape that causes backscattering.

The organic EL element 101 having the above-mentioned structure
Will be described as an example of using as a backlight for an LCD in a mobile phone. When the backlight is on, the organic E
In the L element 101, a DC voltage is applied between the transparent electrode 14 and the cathode 20, and the organic EL layer 16 emits light.
On the other hand, when the backlight is off, the transparent electrode 14 and the cathode 2
Since a DC voltage does not flow between 0 and 0, the organic EL layer 16 does not emit light.

Since the liquid crystal element in the LCD is transparent, it transmits external light. According to this embodiment, external light enters the light scattering layer 30 from the X direction shown in FIG. 1, that is, from the upper surface side of the organic EL element 101. The visible light contained in this incident light is backscattered in the light scattering layer 30. Therefore, visible light that is incident from the outside, transmits the light scattering layer 30, and irradiates the organic EL layer 16 through the transparent substrate 12 can be suppressed. In other words, according to this embodiment, the returning light from the organic EL layer 16 can be efficiently suppressed. Therefore, the organic EL layer 16
The surface of the organic EL element 101 looks whitish irrespective of the color of the dye doped in.

In other words, it can be said that the return light that passes through the light scattering layer 30 when the backlight is turned off does not substantially exist on the liquid crystal element side. As a result, the background of the liquid crystal element of the LCD is not colored with the color unique to the organic EL layer 16 when the backlight is turned off. Therefore, the liquid crystal image formed in the display window is not buried in the background color,
Clearly visible. That is, according to this embodiment, it is possible to solve the problem of the visibility of the LCD when the backlight is turned off, which has been a problem in the past.
In addition, in order to obtain a visibility that does not cause a problem in practical use, in the organic EL element 101, the uneven surface 107 has a surface roughness of 1
It is preferable that the thickness is 5 μm.

(Second Embodiment) Next, the organic E of this embodiment is used.
The configuration of the L element 201 is shown in FIG. The organic EL element 201 according to the present embodiment is the organic EL element of the first embodiment shown in FIG.
It has almost the same configuration as the element 101. Therefore, the description of the overlapping description is omitted.

The light-scattering layer 32 included in the organic EL element 201 according to the present embodiment is different in form from the light-scattering layer according to the first embodiment. That is, as shown in FIG. 2, the light scattering layer 32 is composed of a fine particle film. This fine particle film 3
2 is formed of fine particles 34 having a particle diameter R of 1 to 5 μm, and the constituent material of these fine particles 34 is preferably a light transmissive material having a refractive index different from that of the transparent substrate 12. For the fine particles 34, for example, a material such as plastic or glass is preferably used.

The organic EL element 201 having the above-mentioned structure
When used as a backlight for an LCD in a mobile phone, even when visible light enters the organic EL element 201 from the outside, for example, the X direction shown in FIG. 2, the same operation as in the first embodiment is performed. The same effect can be obtained.

(Third Embodiment) FIG. 3 shows the structure of an organic EL element 301 of this embodiment. Organic EL element 3 of this example
In No. 01, the transparent substrate 12 itself in the organic EL element 101 of the first embodiment is configured as the light scattering layer 36. That is, in the transparent substrate 36, the organic EL layer 16
The surface on the side opposite to the surface on which is stacked is the light emitting surface 303. Therefore, as shown in FIG.
6 is directly formed on the light emitting surface 303. FIG. 3 shows an example in which the light scattering layer 36 is formed on the light emitting surface 303 as an uneven surface.

The other constitution of the organic EL element 301 according to this embodiment is the same as that of the organic EL element 1 of the first embodiment shown in FIG.
The configuration is substantially the same as 01. Therefore, the description of the overlapping description is omitted. The structure and the method of forming the light scattering layer 36 are the same as those of the light scattering layer 30 described with reference to FIG.

The organic EL element 301 having the above-mentioned structure
When used as a backlight for an LCD in a mobile phone, even when visible light enters the organic EL element 301 from the outside, for example, the X direction shown in FIG. 3, the same operation as in the first embodiment is performed. , The same effect can be obtained. In addition, since the organic EL element 301 has a structure in which the transparent substrate and the light scattering layer are also used, the manufacturing process of the organic EL element is easier than that of the organic EL elements 101 and 201 of the first and second embodiments. It can be simplified.

[0032]

As is apparent from the above description, according to the present invention, the visibility of the LCD when the backlight is off, which is a problem when the organic EL element is used as a backlight for an LCD, is reduced. It can be resolved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing the configuration of an organic EL element of an example according to the present invention.

FIG. 2 is a cross-sectional view schematically showing the structure of an organic EL device of Example 2 according to the present invention.

FIG. 3 is a cross-sectional view schematically showing the structure of an organic EL element of Example 3 according to the present invention.

FIG. 4 is a sectional view schematically showing a configuration of a conventional organic EL element.

[Explanation of symbols]

10, 101, 201, 301: Organic EL element 12: Transparent substrate 14: Transparent electrode (ITO) 16: Organic EL layer 18: Extraction electrode (ITO) 20: cathode 22: Adhesive 24: Sealing substrate (SUS) 26: Light emitting surface 30, 32, 36: Light scattering layer 34: Fine particles 103: convex portion 105: recess 107: uneven surface

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshio Iwata             1-8 Nakase, Nakase, Mihama-ku, Chiba City, Chiba Prefecture             Ico Instruments Co., Ltd. (72) Inventor Mitsuru Suginoya             1-8 Nakase, Nakase, Mihama-ku, Chiba City, Chiba Prefecture             Ico Instruments Co., Ltd. (72) Inventor Yusuke Izumisawa             10-2 Otosetsu-cho, Kanazawa-ku, Yokohama-shi, Kanagawa (72) Inventor Toshihiro Koike             2-19-5 Nakanoshima, Tama-ku, Kawasaki City, Kanagawa Prefecture             issue (72) Inventor Hidefumi Omori             10-3 Otosetsu-cho, Kanazawa-ku, Yokohama-shi, Kanagawa F-term (reference) 3K007 AB17 BB01 BB06 DB03

Claims (6)

[Claims] 1. An organic EL device in which an organic EL layer is sandwiched between a pair of electrodes consisting of an anode and a cathode provided on a transparent substrate, wherein visible light incident from the outside is emitted to the light emitting surface side of the transparent substrate. An organic EL device comprising a light scattering layer for scattering. 2. The anode, which is a transparent electrode, the organic EL layer, and the cathode are laminated on one main surface of the transparent substrate, and the light scattering layer is on the other main surface of the transparent substrate. The organic EL device according to claim 1, wherein the organic EL device is installed in. 3. The organic EL element according to claim 2, wherein the light scattering layer is directly formed on the light emitting surface. 4. The light-scattering layer comprises a light-transmissive, uneven surface having a surface roughness of 1 to 5 μm.
Alternatively, the organic EL device according to item 3. 5. The light-scattering layer is light-transmissive and has a particle size of 1 to 1.
The organic EL element according to claim 2, comprising a fine particle film formed of fine particles of 5 μm. 6. The organic EL device according to claim 4, wherein the light scattering layer has a refractive index different from that of the transparent substrate.