JP7600771B2 - Organic EL display device - Google Patents

Description

The present invention relates to a technology that enables improved brightness in organic electroluminescence (EL) display devices.

Organic EL display devices are self-emitting display devices that use organic light-emitting diodes (OLEDs), and there are two known light-emitting methods. One is the RGB method, and the other is the color filter method.

In the RGB system, one pixel is formed by sub-pixels made of red (R), green (G), and blue (B) light-emitting diode elements. Since no color filters are used, the light-emitting efficiency is high and it is also possible to increase color purity.

The color filter method is a method of forming a color image by combining red (R), green (G), and blue (B) color filters with a white OLED. Since the light emission intensity of the white OLED element corresponding to each color can be controlled independently, it is possible to increase the color purity of dark areas (black) and also to display a high contrast.

Although the color filter method has the disadvantage of low light emission efficiency, it has the advantage of a simple manufacturing process, low cost, and favorable miniaturization. For this reason, in fields such as microdisplays and large TVs, the color filter method is used, and white OLEDs are produced by vacuum deposition.

Organic EL display devices using the color filter method have the problem of low light-emitting efficiency in principle, but they also have the problem of high power consumption because high brightness is achieved by increasing the output of the white OLED. For this reason, there is a demand for technology that can reduce power consumption while maintaining brightness in color filter organic EL display devices.

As a prior art that solves such a problem, for example, Patent Document 1 discloses a technology that enables a low-temperature curing process that does not damage the white organic EL layer when forming a color filter on a white organic EL layer in a color filter type organic EL display device that has a color filter on a white organic EL light-emitting layer, and enables the formation of a color filter with a high color material concentration made of a thin layer that enables high color reproducibility.

JP 2019-153389 A

However, in this technology, the color filters are formed with a high color material concentration, so the fluorescence emitted from the color materials is absorbed inside the color filters and cannot be extracted to the outside, and therefore the fluorescence cannot be used to improve the brightness of the organic EL display device.
In view of the above circumstances, an object of the present invention is to provide a technique that enables improvement in the luminance of a color filter type organic EL display device.

As a means for solving the above problems, a first aspect of the present invention is an organic electroluminescence display device comprising, in this order, at least a white organic electroluminescence light-emitting layer, a planarization layer for planarizing a surface of the white organic electroluminescence light-emitting layer, and color filters for forming red, green, and blue pixels,
the planarization layer contains at least one coloring material that emits fluorescence,
The organic electroluminescence display device is characterized in that the concentration of the fluorescent color material is lower than the concentration of the color material in the color filter.

The second aspect is the organic electroluminescence display device according to the first aspect, characterized in that the light transmittance of the planarization layer is 90% or more.

The third aspect is the organic electroluminescence display device according to the first or second aspect, characterized in that the fluorescent coloring material contains at least one of Pigment Red 254 and Acid Red 289.

According to the organic EL display device of the present invention, the planarization layer that planarizes the surface of the white organic electroluminescence light-emitting layer contains at least one color material that emits fluorescence. Since the concentration of the fluorescent color material is lower than the concentration of the color material in the color filter, the fluorescence generated by the excitation of the color material in the planarization layer is not absorbed by the color material in the planarization layer, but passes through the color filter and can be observed from outside the organic EL display device. Therefore, the brightness of the organic EL display device can be improved by the fluorescence emitted from the planarization layer.

FIG. 1 is a cross-sectional view illustrating an organic EL display device of the present invention.

The organic EL display device of the present invention will be described with reference to FIG.

The organic EL display device 10 of the present invention is an organic electroluminescence display device that includes, in this order, a drive circuit board 1 on which a drive circuit using semiconductor elements is formed, and at least a white organic electroluminescence light-emitting layer 2, a planarization layer 3 that planarizes the surface of the white organic electroluminescence light-emitting layer 2, and a color filter 4 that forms red, green, and blue pixels on the drive circuit board 1. Furthermore, a glass plate 6 is attached to the surface of the color filter 4 opposite the planarization layer 3 via an adhesive layer 5, for example, to form the organic EL display device 10.

(Planarization Layer)
The planarization layer 3 of the organic EL display device 10 of the present invention is characterized in that it contains at least one color material that emits fluorescence. This color material generates fluorescence when excited by the white light emitted from the white organic electroluminescence light-emitting layer 2. The concentration of the color material in the planarization layer 3 is lower than the concentration of the color material in the color filter 4. Therefore, the fluorescence generated in the planarization layer 3 is partly absorbed by the color material in the planarization layer 3, but most of it passes through the planarization layer 3 and further passes through the color filter 4, and can be observed from outside the organic EL display device 10. Therefore, the brightness of the organic EL display device 10 can be improved.

In addition, in the organic EL display device 10 of the present invention, the light transmittance of the planarization layer 3 is preferably 90% or more. Such a high light transmittance allows the concentration of the color material in the planarization layer 3 to be sufficiently low, and most of the fluorescence generated in the planarization layer 3 to reach the outside of the planarization layer 3 without being absorbed by the color material in the planarization layer 3.

In addition, in the organic EL display device 10 of the present invention, the color material contained in the planarization layer 3 preferably contains at least one of Pigment Red 254 and Acid Red 289. These color materials can emit fluorescence with high efficiency, and therefore can provide an excellent effect of improving the brightness of the organic EL display device 10.

(White organic EL light-emitting layer)
The white organic EL light-emitting layer 2 is made of a laminate in which a plurality of layers including an organic semiconductor light-emitting layer are laminated, and is a light-emitting layer made of a so-called organic light-emitting diode (OLED) that emits white light.

(Color Filter)
The color filter 4 is formed with pixels 7 each including at least a red sub-pixel R, a green sub-pixel G, and a blue sub-pixel B as a constituent unit.

The color filter 4 is usually produced by preparing a colored photosensitive composition of black, red, green, or blue, in which a colored composition consisting of fine black, red, green, or blue pigments is uniformly dispersed in a photosensitive transparent resin, applying the composition to a substrate, drying the composition, and then patterning the composition by photolithography.

Specifically, first, a black matrix 8 (see FIG. 1) is formed on a substrate using a black photosensitive composition that serves as a reference pattern. The black matrix 8 forms partitioned regions for forming red, green, and blue sub-pixels R, G, and B. Next, colored layers, for example, of red, green, and blue colors are formed in sequence to form the color filter 4.

In the organic EL display device 10 shown in FIG. 1, the above substrate is a white organic EL light-emitting layer 2 formed on a drive circuit board 1.

(Drive circuit board)
The driving circuit board 1 is a substrate in which a driving circuit for OLED is formed on the surface of a silicon wafer by, for example, processing the silicon wafer. The driving circuit for OLED is a current maintaining circuit. For example, when an image displayed by an organic EL display device is 30 frames per second, after one image is displayed, the next image is displayed 1/30 seconds later. That is, since the OLED, which is the light-emitting element of the organic EL display device, is a current-driven light-emitting element, it is necessary to maintain a current value required for emitting one image for 1/30 seconds. Since the liquid crystal element used in the liquid crystal display device is a voltage-driven type, one transistor is sufficient as a switching element, but at least two transistors are required for one subpixel in the organic EL display device.

(Adhesive layer)
The adhesive layer 5 is not particularly limited as long as it is an adhesive material capable of adhering the color filter 4 and the glass plate 6 with a sufficiently strong adhesive strength to form an organic EL display device, and is a transparent material having a high light transmittance of 80% or more in the entire visible light range. Any adhesive having optical specifications that is commonly used can be used.

(Glass plate)
The glass plate 6 can be suitably used as long as it has a high performance of blocking moisture and oxygen, has excellent performance as a protective layer for protecting the white organic EL light-emitting layer 2, has high surface hardness, and is made of transparent glass.

Next, we will explain an example of the present invention.

(Formation of White Organic EL Light Emitting Layer)
A silicon wafer on which a drive circuit for an organic EL element was formed was used to form a white organic EL element by a vapor deposition method on the side of the silicon wafer on which the drive circuit was formed. Finally, a passivation layer made of silicon nitride was formed by a plasma CVD (Chemical Vapor Deposition) method, and the element was sealed to produce a substrate on which a white organic EL light-emitting layer was formed.

(Preparation of Colored Composition)
Next, the preparation of a coloring composition for producing a planarizing layer and a color filter will be described.
(1) Colored Composition for Planarizing Layer The following colorants (coloring materials) were used in the colored resin composition.
Red pigment: C.I. Pigment Red 254
(BASF "Ilgarfor Red B-CF")
Purple dye: Acid Red 289
(Tokyo Chemical Industry Co., Ltd.)

Using the above coloring materials, the following colored composition for a flattening layer was prepared.
The mixture of the following composition was stirred and mixed to be homogeneous, and then filtered through a 5 μm filter to obtain a coloring material for flattening layer (PL-1).
Red pigment: C.I. Pigment Red 254 10 parts by weight Purple dye: Acid Red 289 10 parts by weight Acrylic varnish (solid content 20%) 67 parts by weight

Then, the coloring material (PL-1) was used to prepare a photosensitive coloring composition (PL-1) for the flattening layer according to the composition shown in Table 1.

(2) Photosensitive Black Composition and Pigment for Black Composition The following coloring materials (pigments) were used in the colored (resin) composition.
Blue pigment: C.I. Pigment Blue 15:6
("LIONOL BLUE ES" manufactured by Toyo Color Co., Ltd.
Purple pigment: C.I. Pigment violet 23
("LIONOGEN VIOLET RL" manufactured by Toyo Color Co., Ltd.)
Yellow face: C.I. Pigment Yellow 139
(BASF Blue "Paliotol Yellow 2146HD"

Preparation of Black Colored Composition A black colored composition (black composition) was prepared using the above pigment.
Blue pigment: C.I. Pigment Blue 15:6 11 parts by weight Purple pigment: C.I. Pigment violet 23 11 parts by weight Yellow face: C.I. Pigment Yellow 139 6 parts by weight Acrylic varnish (solid content 20%) 170 parts by weight

Then, the above mixture was stirred and mixed uniformly, dispersed in a sand mill using glass beads with a diameter of 1 mm for 5 hours, and then filtered through a 5 μm filter to obtain a black pigment black colorant (BLK-1).

The colorant (BLK-1) was used to prepare a black photosensitive black composition (photosensitive black composition) (BLK-1) with the composition shown in Table 1.

(3) Photosensitive red composition Pigment for red coloring composition Red pigment: C.I. Pigment Red 254
(BASF "Ilgarfor Red B-CF")
Yellow pigment: C.I. Yellow 139
(BASF "Palioto Yellow L 2146HD")

Preparation of Red Colored Composition The mixture of the following composition was stirred and mixed uniformly, and then dispersed in a sand mill using glass beads having a diameter of 1 mm. The mixture was then filtered through a 5 μm filter to prepare a red colorant (R-1).
Red pigment: C.I. Pigment Red 254 78 parts by weight Yellow pigment: C.I. Pigment Yellow 139 22 parts by weight Acrylic varnish (solid content 20%) 215 parts by weight Using the colorant (R-1), a red photosensitive coloring composition (photosensitive red composition) (RR-1) was prepared according to the formulation shown in Table 1.

(4) Pigment for photosensitive green composition and green coloring composition Green pigment: C.I. Pigment Green 58
(DIC "FASTOGEN GREEN A110"
Yellow pigment: C.I. Pigment Yellow 185
(BASF "Paliotol Yellow L 1155"

Preparation of Green Colored Composition Using the above pigment, the mixture of the following composition was stirred and mixed to a uniform consistency, and then filtered through a 5 μm filter to obtain a green colored composition (G-1).
Green pigment: C.I. Pigment Green 58 65 parts by weight Yellow pigment: C.I. Pigment Yellow 185 35 parts by weight Acrylic varnish (solid content 20%) 215 parts by weight Then, using the coloring composition (G-1), a green photosensitive coloring composition (photosensitive green composition) (GR-1) was prepared so as to have the composition described in Table 1.

(5) Blue coloring composition Pigment for blue coloring composition Blue pigment: C.I. Pigment Blue 15:6
("LIONOL BLUE ES" manufactured by Toyo Color Co., Ltd.)
Purple pigment: C.I. Pigment Violet 23
("LIONOGEN VIOLET RL" manufactured by Toyo Color Co., Ltd.)

Preparation of Blue Colored Composition A blue colored resin composition was prepared using the above pigment.
The mixture having the following composition was stirred and mixed to be homogeneous, and then filtered through a 5 μm filter to obtain a blue colored composition (B-1).
Blue pigment: C.I. Pigment Blue 15:6 63 parts by weight Purple pigment: C.I. Pigment Violet 23 37 parts by weight Acrylic varnish (solid content 20%) 215 parts by weight Using the coloring composition, a blue photosensitive coloring composition (photosensitive blue composition) (BR-1) was prepared according to the formulation shown in Table 1.

(Fabrication of Color Filter and Organic EL Display Device)
Next, the photosensitive coloring composition PL-1 for the planarization layer was applied by a spinner onto the substrate on which the white organic EL light-emitting layer was formed so that the film thickness of the cured product was 0.1 μm. After that, the coating was cured by heating at 100° C. for 10 minutes using a heating oven, and the formation of the planarization layer was completed.

Next, a photosensitive black composition was applied onto the flattening layer using a spinner so that the film thickness of the cured finished product was 1.0 μm, and the composition was exposed to ultraviolet light through a pattern mask, developed with an alkali, washed with water, and dried to provisionally form a black layer (black matrix) of a color filter with a pixel size of 2.4 μm x 2.4 μm. The composition was then heated in a heating oven at 80°C for 10 minutes to cure, completing the formation of the black layer (black matrix) of the color filter.

Next, a green photosensitive resin composition was applied onto the black matrix using a spinner so that the film thickness after curing was 1.0 μm. The composition was then exposed to ultraviolet light through a pattern mask, developed with an alkali, washed with water, and dried to provisionally form a green layer (G) of a color filter with a pixel size of 2.4 μm x 2.4 μm. The composition was then heated in a heating oven at 80°C for 10 minutes for curing, completing the formation of the green layer (G) of the color filter.

Next, in the same manner as in the method for forming the green layer (G) of the color filter described above, a red photosensitive resin composition was applied with a spinner so that the film thickness of the cured finished product would be 1.0 μm, and the red layer (R) of the color filter with a pixel size of 2.4 μm x 2.4 μm was provisionally formed through a pattern mask through ultraviolet light exposure, alkaline development, water washing and drying processes. After that, it was heated in a heating oven at 80°C for 10 minutes to cure, and the formation of the red layer (R) of the color filter was completed.

Furthermore, in the same manner as in the method for forming the green layer (G) of the color filter described above, a blue photosensitive resin composition was applied with a spinner so that the film thickness of the cured finished product would be 1.0 μm, and the blue layer (B) of the color filter with a pixel size of 2.4 μm x 2.4 μm was provisionally formed through a pattern mask, UV exposure, alkaline development, water washing and drying processes. After that, it was heated in a heating oven at 80°C for 10 minutes for curing, and the formation of the blue layer (B) of the color filter was completed, and the color filter was produced.

After forming the color filter, the cover glass was attached using the sealant Structbond XMF-T107 (Mitsui Chemicals) to create an organic EL display device.

Comparative Example
Next, a comparative example will be described.

An organic EL display device was fabricated in the same manner as in the example, except that a color filter was formed on the white organic EL light-emitting layer without forming a planarizing layer.

(Brightness Evaluation)
The organic EL display devices produced in the examples and the comparative examples were turned on, and the luminance was compared relative to each other. The luminance was measured using a CS-1000A manufactured by Konica Minolta.

The measurement results of the luminance of the organic EL device are shown in Table 2. When the luminance of the comparative example was taken as 100%, the luminance of the example was 105%.
From the results in Table 2, it is found that the brightness of the Examples is relatively improved compared to the Comparative Examples. This result is considered to be due to the fact that the planarizing layer converts the light emitted from the white organic EL light-emitting layer, reducing the loss of light in the wavelength range that is originally absorbed by the color filter, leading to the improvement in brightness.

The present invention can be used as an organic EL display device for electronic devices such as smart glasses, head-mounted displays, and electronic viewfinders.

DESCRIPTION OF SYMBOLS 1: Drive circuit board 2: White organic EL light-emitting layer 3: Planarization layer 4: Color filter 5: Adhesive layer 6: Glass plate 7: Pixel 8: Black matrix 10: Organic EL display device R: Red subpixel G: Green subpixel B: Blue subpixel

Claims (3)

An organic electroluminescence display device comprising at least a white organic electroluminescence light-emitting layer, a planarization layer for planarizing a surface of the white organic electroluminescence light-emitting layer, and color filters for forming red, green, and blue pixels, in this order,
the planarization layer contains at least one coloring material that emits fluorescence,
2. An organic electroluminescence display device, wherein a concentration of the fluorescent color material is lower than a concentration of the color material in the color filter. The organic electroluminescent display device according to claim 1, characterized in that the light transmittance of the planarization layer is 90% or more. The organic electroluminescence display device according to claim 1 or 2, characterized in that the fluorescent coloring material contains at least one of Pigment Red 254 and Acid Red 289.

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