JP2003282235A - Organic electroluminescence display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress loss of white balance caused by degradation of red, green, and blue organic EL elements and to reduce coloring of a display device with the lapse of time. <P>SOLUTION: The display device includes an optically transparent member wherein the transmittance of light emitted from the element in which relative luminance decreases most rapidly among red, green, and blue luminescence elements is larger than the transmittance of light emitted from the other elements. <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 display device having a plurality of organic electroluminescence elements.

[0002]

2. Description of the Related Art An organic electroluminescence display device (hereinafter, also simply referred to as "organic EL display device") is expected as a display device to replace a liquid crystal display device which is currently widespread, and is being developed for practical use. There is. In particular, an active matrix type organic EL display device provided with a thin film transistor (TFT) as a switching element is considered to be a main role of a next-generation flat panel display device.

Generally, an organic EL device provided in an organic EL display device
In the L element, electrons and holes are injected into the light emitting layer from the electron injecting electrode and the hole injecting electrode, respectively, and these are recombined at the interface between the light emitting layer and the hole transporting layer or inside the light emitting layer near the interface to form an organic molecule. Becomes an excited state, and when this organic molecule returns from the excited state to the ground state, it emits fluorescence.

Here, a light emitting element which emits a proper color can be obtained by selecting a material used for the light emitting layer. A color display device can be realized by appropriately selecting such a light emitting element. Red, which is generally the three primary colors of light,
A light emitting element which emits green and blue light has been developed and used.

The organic EL display device is provided with an organic electroluminescence element (hereinafter, simply referred to as "organic EL element") in which each pixel emits red, green and blue light.

FIG. 2 is a diagram schematically showing a cross section of a general organic EL device having three types of light emitting layers of red, green and blue.

On the glass substrate 10, the hole injection electrode 12,
The intervening layer 14 and the hole transport layer 16 are sequentially formed,
Subsequently, the red light emitting layer 22, the green light emitting layer 24, and the blue light emitting layer 26 which respectively emit red, green, and blue light.
Are formed so as to be adjacent to each other in respective predetermined regions on the hole transport layer 16.

Subsequently, an electron transport layer 28, an electron injection layer 30, and an electron injection electrode 32 are commonly formed in this order on these three types of light emitting layers.

Here, in FIG. 2, the members located above the glass substrate 10 are generally substantially transparent in the visible region except for the electron injection electrode 32 in which metal is used. Therefore, because of the mirror-like structure, the external light incident on the glass substrate 10 from below in FIG. 2 is reflected by the electron injection electrode 32, and the reflected light is emitted from the glass substrate 10.
When the image is displayed in such a state, the black image becomes whitish due to the reflection of external light, and the contrast deteriorates. In order to suppress this, a phase difference plate 34 and a linear polarizing plate 36 are attached to the surface of the glass substrate 10 opposite to the surface on which the hole injection electrode 12 is formed, and the above-mentioned reflection of external light is performed. Is shut off. Further, the retardation plate 34 and the linear polarizing plate 36 also affect the light emitted from the organic EL element, and transmit about 45%.

[0010]

By the way, it is known that an organic EL element is generally deteriorated with time. Furthermore, since the materials and compositions of the red, green, and blue organic EL elements are different from each other, the deterioration characteristics of the above three elements may be different from each other. In such a case, there is a problem in that the white balance adjusted at the beginning of manufacturing the display device is destroyed due to a change with time, so that the display device is colored with time.

The present invention has been made on the basis of such recognition, and its purpose is to provide organic EL elements of red, green and blue.
It is to suppress the breakage of white balance due to the deterioration of the element and reduce the coloring over time of the display device.

[0012]

According to the present invention for solving the above problems, a light emitting element that emits red light, a light emitting element that emits green light, a light emitting element that emits blue light, and a light transmitting member. In the organic electroluminescence display device including, the transmittance of light emitted by the light-transmissive member of the three light-emitting elements having the fastest relative luminance decrease is the most relative of the light-transmissive members. Provided is an organic electroluminescent display device, which is characterized by having a transmittance higher than that of light emitted from an element other than an element having a rapid decrease in luminance.

Deterioration of the organic EL element can be known by, for example, a decrease in relative luminance after 2000 hours of light emission. Here, the relative intensity _{I r,} when the manufacturing initial luminance _{I 0,} the brightness at an arbitrary time t was set to _{I t, I r = I t} / I 0
It is represented by.

When the deterioration characteristics of the red, green, and blue organic EL elements are different, the white balance is lost over time as described above. According to the present invention, regarding the transmittance of the light transmitting member, the transmittance of the light emitted by the element of the three light emitting elements having the lowest relative luminance decrease is made relatively higher than the transmittance of the other light. It is possible to prevent the white balance from breaking down over time.

For example, as shown in the schematic view of FIG. 3A, when the deterioration of the blue element is faster than that of the red and green elements, the brightness of the blue decreases with time and the white balance is increased. Collapse. At this time, for example, even if a light transmitting member having an optical spectrum as shown in FIG. 4A is used, light is transmitted at a constant rate regardless of the wavelength, and the white balance is lost.

The material for the circularly polarizing member, which is a kind of light transmitting member provided in the conventional organic EL display device, has been selected only from the viewpoint of measures against external light reflection.

In the case of the above example, according to the invention, FIG.
With the light transmitting member having the optical spectrum as shown in (b), the luminous efficiency of the blue element can be made relatively higher than the luminous efficiency of red and green. By doing so, the current flowing through the blue element can be reduced, so that the load on the element can be reduced. Therefore, as shown in the schematic diagram of FIG. 4B, the deterioration characteristics of the blue light emitting elements are close to those of the red and green light emitting elements. As a result, it is possible to suppress the deterioration of the white balance over time.

The light transmitting member may be a circularly polarizing member. Thereby, in addition to the effect of suppressing the collapse of the white balance, the effect of reducing the influence of external light can be obtained.

The circularly polarizing member may include a linear polarizing plate and a retardation plate.

Further, according to the present invention, there is provided an organic electroluminescence display device including a light emitting element which emits red light, a light emitting element which emits green light, a light emitting element which emits blue light, and a light transmitting member. The light transmitting member includes a substance that absorbs light, and the absorptivity of the substance that absorbs the light is the absorption rate of the light emitted by the one of the three light emitting devices that has the fastest decrease in relative luminance. There is provided an organic electroluminescence display device characterized in that the absorption rate of light emitted from an element other than the element whose relative luminance is most rapidly lowered is smaller than that of the substance.

As a result, the white balance is lost over time by making the transmittance of the light emitted by the one of the three light emitting elements, which has the lowest relative luminance decrease, relatively higher than the transmittance of the other light. Can be suppressed.

The light transmitting member may be a circularly polarizing member. Thereby, in addition to the effect of suppressing the collapse of the white balance, the effect of reducing the influence of external light can be obtained.

The circularly polarizing member may include a linear polarizing plate and a retardation plate.

Either the linear polarizing plate or the retardation plate may contain a substance that absorbs the light. Further, both the linearly polarizing plate and the retardation plate may contain a substance that absorbs the light.

The light emitting device may be composed of two or more kinds of light emitting devices. For example, consider the case of a light emitting element that emits red light.By combining a light emitting element that emits yellow light and a light emitting element that emits blue light, white light is emitted, and this is covered with a red color filter. It can emit red light.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION In this embodiment, the organic EL elements of adjacent pixels of an active matrix type organic EL display device are arranged.
The boundary between the L elements is set appropriately. Here, in particular, the boundary is provided in a region that does not affect the display of pixels.

FIG. 1 shows an outline of a plan view of the above-mentioned three-color pixel regions of an organic EL display device in which one pixel includes organic EL elements which emit red, green, and blue light, respectively.
In order from the left, a red pixel Rpix including a red light emitting layer,
A green pixel Gpix including a green light emitting layer and a blue pixel Bpix including a blue light emitting layer are provided.

The configuration of each pixel is the same in plan view. One pixel is formed in a region surrounded by the gate signal line 51 and the drain signal line 52. A first TFT 130, which is a switching element, is formed near the intersection on the upper left of both signal lines, and a second TFT 140 that drives the organic EL element is formed near the center. In addition, indium tin oxide (Indium Tin Oxi
An organic EL element is formed in an island shape in a region where the hole injection electrode 12 made of de: ITO) is formed. Since such a configuration is adopted, the current flowing through each organic EL element is independently controlled.

FIG. 5 shows a sectional structure of an organic EL display device having red, green and blue pixels according to the present embodiment, and particularly shows a sectional structure taken along the line AA shown in FIG. There is. A red pixel Rpix, a green pixel Gpix, and a blue pixel Bpix are provided in order from the left.

On the surface of the glass substrate 10 opposite to the surface to which the active layer 11 to be described later is bonded, a circular polarization member 44 formed by bonding a retardation plate 40 and a linear polarization plate 42 is bonded. There is. Generally, a circularly polarizing member can be obtained by combining a retardation plate and a linear polarizing plate. The circular polarization member 44 and the glass substrate 10 may be bonded to each other by using a hot-melt adhesive or a photo-curing adhesive to obtain a predetermined bonding strength within a few minutes, thereby improving the positioning accuracy. It is preferable from the viewpoint of improving the production rate. Further, in order to avoid the loss such as absorption and scattering of light due to the adhesive, it is preferable to apply the adhesive only to the peripheral portion of the retardation plate 40 and adhere it to the glass substrate 10.

At this time, the circularly polarizing member 44 is selected which can relatively increase the transmittance of light emitted by the element having the fastest relative luminance decrease among the three light emitting elements as compared with the transmittance of the other light.

If an appropriate circularly polarizing member 44 exhibiting a desired optical spectrum cannot be obtained, for example, the retardation plate 40 or the linear polarizing plate 42 is coated with a substance that absorbs light of a specific wavelength. By doing so, the circularly polarizing member 44 exhibiting a desired optical spectrum can be obtained. Further, by attaching an optical filter having a desired optical spectrum to the circularly polarizing member 44, the circularly polarizing member 44 having the desired optical spectrum can be obtained.

The active layer 11 is formed on the glass substrate 10, and a part of the active layer 11 is formed as the second TFT 140 necessary for driving the organic EL element. in addition,
The insulating film 13 and the first planarizing layer 15 are formed. A transparent hole injecting electrode 12 and an insulating second planarizing layer 18 are formed thereon.

ITO is used as the material of the hole injecting electrode 12.
In addition, tin oxide (SnO ₂ ) and indium oxide (In ₂
O ₃ ) can be exemplified. An acrylic resin can be used as an example of the material of the first flattening layer 15.

The second TFT 140 is composed of the second planarization layer 1
It is formed under 8. Here, the second flattening layer 18 is not formed on the entire surface of the hole injecting electrode 12 but covers the region where the second TFT 140 is formed and injects holes in the shape of the second flattening layer 18. The electrode 12 and each film layer described later are locally formed so as not to be broken.

Next, the hole transport layer 16 is formed so as to cover the hole injection electrode 12 and the second flattening layer 18. On top of that, a red light emitting layer 22 and a green light emitting layer 2 are further provided.
4 and the blue light emitting layer 26 are formed in predetermined regions.

Here, as the material of the hole transport layer 16,
N, N'-Di (naphthalene-1-yl) -N, N'-diphenyl-benzidine (N, N'-Di (naphthalene-1-yl) -N, N'-diphenyl-benz
idine: NPB) or 4,4 ', 4''-tris (3-methylphenylphenylamino) triphenylamine (4,4', 4 ''-tris (3-m
ethylphenylphenylamino) triphenylamine: MTDAT
A) and N, N'-diphenyl-N, N'-di (3-methylphenyl)-
1,1'-biphenyl-4,4'-diamine (N, N'-diphenyl-N, N'-
di (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine: T
PD) etc. can be illustrated.

[0038]

[Chemical 1]

[0039]

[Chemical 2]

As a host material of the red light emitting layer 22 and the green light emitting layer 24, for example, one metal ion such as aluminum quinoline complex (Alq ₃ ) or bis (benzoquinolinolato) beryllium complex (BeBq ₂ ) is used. Chelate metal complexes in which a plurality of ligands are coordinated are widely used.

[0041]

[Chemical 3]

[0042]

[Chemical 4]

Generally, an organic EL element formed by using a chelate metal complex as a material for a light emitting layer has a problem in light emission of a color having a short wavelength, that is, blue light. Therefore, a blue light emitting layer is disclosed in JP-A-2002-25770. Disclosed in the gazette
tert-butyl substituted dinaphthyl anthracene (TBAD
N) and the like, anthracene and its derivatives, and distilbenzene and its derivatives may be used as the host.

[0044]

[Chemical 5]

Further, each of the light emitting layers uses the above-mentioned chelate metal complex or condensed polycyclic aromatic compound as a host to form Rubrene.
Desired emission characteristics can be obtained by doping a dopant such as e).

[0046]

[Chemical 6]

The boundary region between the light emitting layers is provided on the surface of the second flattening layer 18 in a region parallel to the glass substrate. Further, the electron transport layer 28 is independently formed on each light emitting layer. Examples of the material of the electron transport layer 28 include chelate metal complexes such as Alq3 and BeBq2. Further, an electron injection layer 30 and an electron injection electrode 32 are sequentially formed in common on each electron transport layer 28.
Therefore, the boundary generated between the electron transport layers 28 is provided so as to overlap the boundary generated between the light emitting layers. Here, examples of the material of the electron injection electrode 32 include aluminum, an aluminum alloy containing a trace amount of lithium, a magnesium indium alloy, a magnesium silver alloy, and the like.

[0048]

EXAMPLE In this example, a three-color organic EL element having the structure shown in FIG. 5 was used, in which the red light emitting layer 22, the green light emitting layer 24, and the blue light emitting layer 26 were made of the following materials. I was there. The red light emitting layer 22 uses Alq3 as a host, and
% DCJTB and 10% rubrene are doped. In addition, the green light emitting layer 24 uses Alq3 as a host and 1% of quinacridone derivative and 1% of quinacridone derivative.
It is doped with 0% TBADN. The blue light emitting layer 26 is doped with 2% tert-butyl-substituted perylene (TBP) using TBADN as a host.

Further, the red light emitting layer 22, the green light emitting layer 24,
The thickness of the blue light emitting layer 26 is 37.5 nm, and the electron transport layer 28 is further 37.5 n thick on each light emitting layer.
It is formed by m.

The red light emitting layer 22, the green light emitting layer 24,
And the wavelength regions of light emitted by the blue light emitting layer 26 are 600 to 660 nm, 490 to 530 nm, and 43, respectively.
It was 0 to 470 nm.

[0051]

[Chemical 7]

[0052]

[Chemical 8]

A circularly polarizing plate having the optical spectrum shown in FIG. 6A was used as the circularly polarizing member 44. This circularly polarizing plate has a transmittance in the wavelength region (430 to 470 nm) of the light emitted by the blue light emitting layer 26, a wavelength region (600 to 660 nm) of the light emitted by the red light emitting layer 22 and the light emitted by the green light emitting layer 24. It is characterized in that it is higher than the transmittance in the wavelength region (490 to 530 nm).

Table 1 shows the change in the luminance of each organic EL element after 2000 hours, with the luminance at the initial stage being 100%. The luminance of each of the red, green and blue organic EL elements after the lapse of 2000 hours is 76, 75 and 73%, respectively,
The white balance was almost maintained.

[0055]

[Table 1]

(Comparative Example) In the comparative example, the configuration was the same as that of the above-mentioned example except for the circularly polarizing member 44. As the circularly polarizing member 44, a circularly polarizing plate having the optical characteristics shown in FIG. 6B was used. This circularly polarizing plate transmits red, green, and blue light with almost the same transmittance.

Table 2 shows the change in the luminance of each organic EL element after 2000 hours, with the luminance at the initial stage being 100%. The brightness of each of the red, green, and blue organic EL elements after the lapse of 2000 hours is 74, 72, and 58%, respectively,
The brightness of the blue organic EL element was significantly reduced as compared with the brightness of other colors. As a result, the white balance was lost and the screen was colored.

[0058]

[Table 2]

From the above comparative example, it is understood that the deterioration rate of the blue organic EL element is higher than the deterioration rates of the other organic EL elements. In consideration of the deterioration characteristics of these three-color organic EL elements, in the above-described embodiment, a circularly polarizing plate that transmits blue light more efficiently than others is used. As a result, the current flowing through the blue organic EL element can be reduced, so that the load on the element can be reduced. From this, the deterioration characteristics of the blue element can be made close to the deterioration characteristics of the red and green elements, so that it is possible to suppress the collapse of the white balance after 2000 hours.

[0060]

According to the present invention, it is possible to prevent the white balance from being disturbed due to the deterioration of the red, green and blue organic EL elements. As a result, it is possible to reduce coloration of the display device over time.

[Brief description of drawings]

FIG. 1 is a plan view of an active matrix type organic EL display device according to an embodiment of the present invention, in particular red,
It is the figure which showed the area | region of 3 pixels of green and blue.

FIG. 2 is a sectional view schematically showing a structure of a conventional organic EL display device.

FIG. 3 is a schematic diagram for explaining a decrease in relative luminance of an organic EL element including three types of light emitting layers that emit red, green, and blue.

FIG. 4 is a schematic diagram for explaining an optical spectrum of a circularly polarizing member and a light transmitting member.

FIG. 5 shows a structure of an organic EL device including three types of light emitting layers that emit red, green, and blue light when applied to an active matrix display device according to an embodiment of the present invention. FIG.

FIG. 6 is a graph showing an optical spectrum of a circularly polarizing plate used in Examples of the present invention and an optical spectrum of a circularly polarizing plate used in Comparative Examples.

[Explanation of symbols]

10 glass substrate, 11 active layer, 12 hole injection electrode, 13 insulating film, 14 intermediate layer, 15 first planarizing layer, 16 hole transport layer, 18 second planarizing layer, 22 red light emitting layer, 24 green light emitting layer, 26
Blue light emitting layer, 28 electron transport layer, 30 electron injection layer, 32 electron injection electrode, 34 retardation plate, 36
Linear polarizing plate, 40 Phase difference plate, 42 Linear polarizing plate, 4
4 circular polarization member, 51 gate signal line, 52 drain signal line, 130 first TFT, 140 second TF
T, Rpix red pixel, Gpix green pixel, B
pix Blue pixel.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yukio Mori             2-5-3 Keihan Hondori, Moriguchi City, Osaka Prefecture             Within Yo Denki Co., Ltd. F-term (reference) 3K007 AB04 AB11 BB06 DB03

Claims (7)

[Claims] 1. An organic electroluminescent display device comprising a light emitting element that emits red light, a light emitting element that emits green light, a light emitting element that emits blue light, and a light transmitting member, wherein Among the three light emitting elements of the member, the transmittance of light emitted by the element having the fastest decrease in relative luminance is the transmittance of light emitted by the element of the light transmitting member other than the element having the fastest decrease in relative luminance. Organic electroluminescence display device characterized by being larger than. 2. The organic electroluminescence display device according to claim 1, wherein the light transmitting member is a circularly polarizing member. 3. The organic electroluminescence display device according to claim 2, wherein the circularly polarizing member includes a linear polarizing plate and a retardation plate. 4. An organic electroluminescence display device comprising a light emitting element which emits red light, a light emitting element which emits green light, a light emitting element which emits blue light, and a light transmitting member. The member includes a substance that absorbs light, and the absorptivity of light emitted by an element of the three light-emitting elements that has the fastest decrease in relative luminance of the substance that absorbs light is An organic electroluminescence display device characterized by being smaller than the absorptance of light emitted from an element other than the element whose relative luminance decreases most rapidly. 5. The organic electroluminescent display device according to claim 4, wherein the light transmitting member is a circularly polarizing member. 6. The organic electroluminescence display device according to claim 5, wherein the circularly polarizing member includes a linear polarizing plate and a retardation plate. 7. The organic electroluminescence display device according to claim 6, wherein either the linear polarizing plate or the retardation plate contains a substance that absorbs the light. apparatus.