JP2007095444A - Organic electroluminescence display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device capable of improving color reproducibility and of reducing power consumption, in an organic electroluminescence display device for making an organic layer emit light by arranging the organic layer including a luminescent layer between a positive electrode and a negative electrode and by applying a voltage between the positive electrode and the negative electrode. <P>SOLUTION: The display device is characterized in that one pixel is composed of: a first sub-pixel emitting red light; a second sub-pixel emitting green light; a third sub-pixel emitting blue light; and a fourth sub-pixel emitting intermediate color light (for instance, yellow light) between the red light of the first sub-pixel and the green light of the second sub-pixel. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic electroluminescence display device (organic EL display device) including a plurality of organic electroluminescence elements (organic EL elements).

  In recent years, with the diversification of information equipment, there is an increasing demand for a thin display device capable of thin and full color display. As one of them, an organic EL element having features such as high efficiency, thinness, light weight, and low viewing angle dependency has attracted attention.

The organic EL device has an advantage that high emission luminance of 100 to 100,000 cd / m ² or more can be obtained at a low voltage of about 2.5 to 12 V. For this reason, the application to the full color display of an organic EL element is anticipated.

  As a full color technology for a display device using an organic EL element, a white light emitting organic EL element is used as a light source (backlight), and color filters of three primary colors red (R), green (G), and blue (B) are used. A filter system that emits light through the substrate, a system that uses a color conversion layer (CCM) using a blue organic EL element as a light source, and a three-color independent light-emitting system that arranges three primary color organic EL elements in parallel on a substrate have been proposed. Yes.

The above three-color independent light emitting method can optimize materials, element structures, etc. for each color, and has advantages in terms of power consumption and color reproducibility compared to a filter method with poor light utilization efficiency. . As a method for reducing power consumption, four colors of red (R), green (G), blue (B), and white (W) that use white light with high light use efficiency in the filter method are used. There has been proposed an organic EL display device that drives (Patent Document 1, etc.).
JP 2004-31440 A

  However, in the above three-color independent light emission method, when the color reproducibility of each color is improved, there is a tendency that the light emission efficiency tends to be lowered, and the power consumption of the entire apparatus increases.

  Although such a problem also has a problem of the light emitting material itself, the part that depends on human visibility is strong, and it is difficult to fundamentally improve it.

  Human vision is known to have different visual sensitivities for each color, and a plot of this for each wavelength is the standard relative luminous sensitivity, which is 555 nm as shown in FIG. The light with the highest wavelength has the best visibility, and the light with a wavelength shorter and longer than 555 nm is monotonously deteriorated.

  Red light is usually obtained from a light emitting layer having a peak wavelength of about 580 nm to 700 nm. In order to obtain red light with good chromaticity, a light emitting material having a peak wavelength on the long wavelength side is required. However, in such a case, light emission efficiency tends to decrease because light in a long wavelength region with poor visibility is used.

  Blue light is usually obtained from a light emitting layer having a peak wavelength of about 400 nm to 500 nm. In order to obtain blue light with good chromaticity, a light emitting material having a peak wavelength on the shorter wavelength side is required. However, even in such a case, the light emission efficiency tends to decrease because light in a short wavelength region with poor visibility is used.

  Green light is usually obtained from a light emitting layer having a peak wavelength of about 480 nm to 560 nm. Since a wavelength region with relatively good visibility is used, the light emission efficiency is improved compared to red light and blue light, but the single wavelength light of 555 nm with the best visibility actually exhibits a color close to yellowish green. When green light required for a display or the like is emitted, a light emitting material having a peak wavelength on the shorter wavelength side is usually used. In such a case, naturally, light in a wavelength region with poor visibility is used, and the light emission efficiency tends to decrease.

  Such a phenomenon appears more prominently in an organic EL display device using a polymer material. This is because many polymer materials tend to exhibit a broad emission spectrum in which there are more components longer than the peak wavelength than components shorter than the low-molecular materials due to chemical structural reasons. It is thought that there is.

  In such a spectral shape, even when the emission peak wavelength is the same, the color of the longer wavelength is exhibited as compared with a narrow emission spectrum. For example, in a polymer material having a peak wavelength near 555 nm, The color becomes closer to yellow than green. For the same reason, in order to obtain green light with good chromaticity, it is necessary for the polymer material to have a peak wavelength on the shorter wavelength side, and in this case, light in a wavelength region with further poor visibility is used. As a result, the luminous efficiency tends to decrease.

  In an organic EL element using a polymer material, there is almost no green material having relatively excellent chromaticity and luminous efficiency.

  An object of the present invention is to provide an organic EL display device capable of solving the above-described conventional problems and reducing power consumption while maintaining good color reproducibility.

  The organic EL display device of the present invention is an organic EL display device in which an organic layer including a light emitting layer is disposed between an anode and a cathode, and the organic layer emits light by applying a voltage between the anode and the cathode. A first subpixel that emits light, a second subpixel that emits green light, a third subpixel that emits blue light, a red light and a second subpixel of the first subpixel. One pixel is composed of a fourth sub-pixel emitting an intermediate color of green light.

  According to the present invention, by using a fourth subpixel that emits an intermediate color between the red light of the first subpixel and the green light of the second subpixel, the fourth subpixel has a wavelength region with the best visibility. Therefore, the luminous efficiency can be increased, and the power consumption can be reduced while maintaining good color reproducibility.

  Visibility is added to the illuminance of cd (candela) and lm (lumen) used for the evaluation of luminous efficiency. Therefore, the light emission efficiency can be increased by effectively utilizing the wavelength region with good visibility according to the present invention.

  In the present invention, the emission peak wavelength of the fourth subpixel is preferably in the range of 500 nm to 580 nm. More preferably, it has an emission peak wavelength in the range of 540 nm to 560 nm, which is the wavelength region with the best visibility.

  In the present invention, the fourth subpixel emits an intermediate color between the red light of the first subpixel and the green light of the second subpixel. Hereinafter, the light emitting layer constituting the fourth subpixel is referred to as a yellow light emitting layer for the sake of convenience, and the intermediate color generated from the fourth subpixel is referred to as yellow light.

  In the present invention, it is preferable that the fourth subpixel is superior to the first subpixel in luminous efficiency. The fourth subpixel is preferably superior to the second subpixel in terms of luminous efficiency. In general, many luminescent materials that emit yellow light emitted from the fourth subpixel are known to have high luminous efficiency. Further, as described above, the fourth sub-pixel emits light in a wavelength region with good visibility, and thus high light emission efficiency is easily obtained.

  By using a subpixel having higher light emission efficiency than the first subpixel and / or the second subpixel as the fourth subpixel, the light emission efficiency of the entire display device can be increased.

  In the present invention, the fourth subpixel preferably emits light having a smaller x value and a larger y value than the first subpixel in the CIE chromaticity coordinates. In the present invention, it is preferable that the fourth subpixel emits light having a larger x value and a smaller y value than the second subpixel in the CIE chromaticity coordinates.

  FIG. 7 is a diagram showing CIE chromaticity coordinates of the fourth subpixel as described above. The area of the fourth subpixel indicated by hatching in FIG. 7 is an area having a smaller x value than the first subpixel and a larger y value, and a larger x value than the second subpixel and a smaller y value. It has become. In the present invention, it is preferable that the fourth sub-pixel emits light within the range of such a region in the CIE chromaticity coordinates.

  Therefore, the light emission peak wavelength of the second subpixel emits light having a shorter wavelength than that of the fourth subpixel. In the CIE chromaticity coordinates, green light having a smaller x value and a larger y value than the fourth subpixel is emitted.

  In the present invention, the peak wavelength of light emission of the first subpixel is preferably in the range of 580 nm to 700 nm.

  In the present invention, the emission peak wavelength of the third subpixel is preferably in the range of 400 nm to 500 nm.

  In the present invention, each of the first subpixel to the fourth subpixel preferably includes an organic layer (organic EL element) that emits each emission color, and the organic EL element is configured independently of each other. Preferably, each subpixel can be driven independently. The light emitting layer of the organic EL element may be a light emitting layer that emits the light emission color of each subpixel, or the light emission color of the light emitting layer of the organic EL element is converted by a color filter or a color conversion layer (CCM). May emit light.

  In particular, for the second subpixel, an organic layer (organic EL element) that emits substantially the same emission color as the fourth subpixel is provided, and a color filter that attenuates light of a component in a long wavelength region is disposed. By passing through this color filter, it is possible to emit light instead of green light. Since the organic EL element that emits yellow light of the fourth subpixel exhibits high luminous efficiency, the same light emitting efficiency as that of the fourth subpixel is used in the second subpixel. Can be increased.

  According to the present invention, since the fourth subpixel having a peak wavelength in a wavelength region with good visibility and having high luminous efficiency is used, the power consumption of the entire organic EL display device while maintaining good color reproducibility. And the lifetime characteristics of the entire organic EL display device can be improved.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to a following example.

  FIG. 1 is a schematic sectional view showing an organic EL display device according to an embodiment of the present invention.

As shown in FIG. 1, on a transparent substrate 1 made of glass, plastic or the like, a laminated film 11 of a layer made of, for example, silicon oxide (SiO ₂ ) and a layer made of silicon nitride (SiNx) is formed.

  A TFT (thin film transistor) 20 is provided on the laminated film 11, and the TFT includes a polycrystalline silicon layer 12, a source electrode 13 s, a drain electrode 13 d, a gate oxide film 14, and a gate electrode 15.

  A drain electrode 13d and a source electrode 13s are provided on the polycrystalline silicon layer 12, the drain electrode 13d of the TFT 20 is connected to the hole injection electrode 2, and the source electrode 13s of the TFT 20 is connected to a power line (not shown). It is connected.

A first interlayer insulating film 16 made of, for example, silicon oxide (SiO ₂ ) and silicon nitride (SiNx) is formed on the gate oxide film 14 so as to cover the gate electrode 15. A second interlayer insulating film 17 made of, for example, silicon oxide (SiO ₂ ) and silicon nitride (SiNx) is formed on the first interlayer insulating film 16 so as to cover the drain electrode 13d and the source electrode 13s.

  A planarizing layer 18 made of, for example, acrylic resin is formed on the second interlayer insulating film 17, and a transparent hole injection electrode 2 is formed on the planarizing layer 18 for each pixel. Further, a partition wall 19 made of, for example, polyimide that defines the area of each pixel is formed so as to cover the hole injection electrode 2. The hole injection electrode 2 is formed of a transparent conductive film such as indium tin oxide (ITO), for example.

  A hole injection layer 3 is formed on the hole injection electrode 2 and the partition wall 19. On the hole injection layer 3, a red light emitting layer 41, a green light emitting layer 42, corresponding to the light emission color of each pixel, A blue light emitting layer 43 and a yellow light emitting layer 44 are formed. The hole injection layer 3 and the light emitting layers 41 to 44 are sequentially stacked by a method such as an ink jet method.

  The region where the red light emitting layer 41 is formed corresponds to the region of the first subpixel of the present invention, and the region where the green light emitting layer 42 is formed is the region of the second subpixel of the present invention. The region where the blue light emitting layer 43 is formed corresponds to the region of the third subpixel of the present invention, and the region where the yellow light emitting layer 44 is formed is the first region of the present invention. This corresponds to an area of 4 subpixels.

  In this example, a two-layer type (hole injection layer / light-emitting layer) organic EL element using a general polymer material is shown, but the organic light-emitting layer is a single-layer type (light-emitting layer), two layers. Type (hole injection layer / light emitting layer), three layer type (hole injection layer / hole transport layer / light emitting layer), four layer type (hole injection layer / hole transport layer / light emitting layer / electron transport layer), five layer type ( Any structure of hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer) may be used. The material constituting the organic layer may be a polymer material or a low molecular material, or a combination of a polymer material and a low molecular material may be used.

  Calcium is vapor-deposited as the electron transport layer 5 so as to cover the red light-emitting layer 41, the green light-emitting layer 42, the blue light-emitting layer 43, the yellow light-emitting layer 44 and the partition wall 19, and aluminum is vapor-deposited thereon as the electron injection electrode 6. Yes.

  Examples of the polymer light-emitting material that can be used for the red light-emitting layer 41 include MEH-PPV and PF-BT-BTT2-TPD that have the following structures.

  Examples of the polymer light emitting material that can be used for the green light emitting layer 42 include F8BT + PFO and PF-DSB-TPD having the following structure.

  Examples of the polymer light-emitting material that can be used for the blue light-emitting layer 43 include PFO and PF-TPD having the following structure.

  Examples of the polymer light emitting material that can be used for the yellow light emitting layer 44 include PF8-BT-TPD and Yellow-PPV having the following structure.

  Examples of the polymer material that can be used for the hole injection layer 3 include PEDOT-PSS and PAni having the following structure.

  Examples of the polymer material that can be used for the hole transport layer include PF8-TPA and PF8-TPD having the following structure.

  FIG. 2 is a schematic sectional view showing a display device of another embodiment according to the present invention. The organic EL display device shown in FIG. 2 uses the yellow light emitting layer 44 similar to the fourth subpixel emitting yellow light in the region of the second subpixel emitting green light. A green color filter layer CF is provided on the second interlayer insulating film 17 on the light extraction side below the yellow light emitting layer 44. The yellow light emitted from the yellow light emitting layer 44 is emitted as green light by passing through the green color filter layer CF. The other configuration of the organic EL display device shown in FIG. 2 is basically the same as that of the organic EL display device shown in FIG.

  In this embodiment, since the organic EL element (organic layer) of the fourth sub-pixel capable of obtaining high luminous efficiency is used for the second sub-pixel, the luminous efficiency of the organic EL display device as a whole is increased. Can do.

  FIG. 3 is a plan view showing an example of the arrangement of the first sub-pixel (R), the second sub-pixel (G), the third sub-pixel (B), and the fourth sub-pixel (Y). . In the arrangement state shown in FIG. 3, the first subpixel to the fourth subpixel are arranged in parallel. The aperture ratio of each subpixel is about 20%.

  In the embodiment shown in FIGS. 1 and 2, the subpixel arrangement state shown in FIG. 3 is adopted. However, the subpixel arrangement and the aperture ratio may be appropriately changed in consideration of the performance of the element. it can. When four types of subpixels are used, the aperture ratio of each subpixel is about three-quarters compared to the case where three color subpixels are used. Therefore, when obtaining monochromatic light, the required luminance of each color is approximately four-thirds when considered simply. In organic EL elements, it is generally known that the lifetime of red light and blue light is worse than that of green light, and it is generally considered to increase the aperture ratio of blue light and red light.

  FIG. 4 shows an arrangement example of each subpixel when the aperture ratio of blue light and red light is increased. In this case, the aperture ratio for each subpixel is about 30% for red light and blue light, and about 15% for green light and yellow light. Since the aperture ratios of red light and blue light are about the same as those in the case of three colors, the same lifetime can be obtained. On the other hand, since the aperture ratio of green light and yellow light is about half that of the case of three colors, the brightness when a single green light is turned on is about doubled. Since yellow light has good visibility, it is known that it has a longer lifetime than red light and blue light. Further, in an actual display or the like, in the case of three colors, it is possible to use yellow light with better efficiency and longer life even for the part of the color that had to use green light. The efficiency and lifetime of the entire device are hardly a problem.

  In the organic EL display device of the present invention, the arrangement of the sub-pixels is not limited to that shown in FIGS. 3 and 4, and may be in an arrangement state as shown in FIGS. 5 and 6, for example.

  Moreover, in the organic EL display device shown in the above embodiment, a bottom emission type organic EL display device that extracts light emitted from the light emitting layer of the organic EL element from the substrate side is shown. However, the organic EL display device of the present invention is shown. Is applicable to a top emission type organic EL display device that extracts light from the side opposite to the substrate.

[Evaluation of organic EL display devices]
The characteristics of the organic EL display device shown in FIG. 1 were evaluated. As a comparative example, in the organic EL display device shown in FIG. 1, there is no fourth subpixel, the first to third subpixels are arranged in parallel, and the aperture ratio of each subpixel is about 30%. The thing of was used.

  In the comparison of power consumption, in the organic EL display device of this embodiment and the organic EL display device of the comparative example, the x value in the CIE chromaticity coordinates, which is standard white light, is 0.31, and the y value is 0.33. The power consumption of the panel portion when white light having the same intensity was lit was compared.

When red light is obtained from the first sub-pixel using the organic EL display device in the present embodiment, the chromaticity of the red light is CIE chromaticity coordinates (0.69, 0.31), and the luminous efficiency is 100 cd. It was 2.31 lm / W when / m ^{2 was} lit.

When green light is obtained from the second sub-pixel using the organic EL display device according to the present embodiment, the chromaticity of the green light is CIE chromaticity coordinates (0.39, 0.59), and the luminous efficiency is 100 cd. 13.8 lm / W at / m ² lighting.

When blue light is obtained from the third sub-pixel using the organic EL display device according to the present embodiment, the chromaticity of the blue light is CIE chromaticity coordinates (0.16, 0.14), and the luminous efficiency is 100 cd. When turned on / m ² , it was 2.5 lm / W.

When yellow light is obtained from the fourth subpixel using the organic EL display device according to the present embodiment, the chromaticity of the yellow light is CIE chromaticity coordinates (0.49, 0.50), and the luminous efficiency is 100 cd. It was 18.0 lm / W when / m ^{2 was} lit.

  FIG. 8 is a CIE chromaticity diagram showing the position of the chromaticity of the emission color in each of the sub-pixels.

  As described above, yellow light obtained from the fourth subpixel has higher luminous efficiency than red light obtained from the first subpixel and green light obtained from the second subpixel.

  Since the luminous efficiency of each sub-pixel in the organic EL display device of the comparative example has the same configuration as that of the embodiment according to the present invention, its chromaticity and luminous efficiency are the same as those of the above-described embodiment. It is. In the organic EL display device of the embodiment according to the present invention and the organic EL display device of the comparative example, white having x value in the CIE chromaticity coordinates of 0.31 and y value of 0.33, which is standard white light. It was found that the power consumption of the panel portion when the light was lit at the same intensity was about 70% in the organic EL display device of the embodiment according to the present invention as compared with the comparative example.

  As is clear from the above results, according to the present invention, by using the fourth subpixel, the light emission efficiency of the entire organic EL display device can be increased, the power consumption can be reduced, and the long lifetime can be achieved. Can be achieved.

1 is a schematic cross-sectional view showing an organic EL display device of one embodiment according to the present invention. The schematic sectional drawing which shows the organic electroluminescence display of other embodiment according to this invention. The top view which shows an example of the arrangement | positioning state of the 1st subpixel-the 4th subpixel in this invention. The top view which shows the other example of the arrangement | positioning state of the 1st subpixel-the 4th subpixel in this invention. The top view which shows the further another example of the arrangement | positioning state of the 1st subpixel-the 4th subpixel in this invention. The top view which shows the further another example of the arrangement | positioning state of the 1st subpixel-the 4th subpixel in this invention. FIG. 10 is a CIE chromaticity diagram showing a preferable region of the emission color of the fourth subpixel in the present invention. The CIE chromaticity diagram showing the chromaticity of the emission color of each sub-pixel in the organic EL display device of one embodiment according to the present invention. The figure which shows the relationship between a wavelength and visibility.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Hole injection electrode 3 ... Hole injection layer 5 ... Electron transport layer 6 ... Electron injection electrode 11 ... Laminated film 12 ... Polycrystalline silicon layer 13s ... Source electrode 13d ... Drain electrode 14 ... Gate oxide film 15 ... Gate electrode DESCRIPTION OF SYMBOLS 16 ... 1st interlayer insulation film 17 ... 2nd interlayer insulation film 18 ... Planarization layer 19 ... Partition 20 ... Thin-film transistor (TFT)
41 ... Red light emitting layer 42 ... Green light emitting layer 43 ... Blue light emitting layer 44 ... Yellow light emitting layer CF ... Green color filter layer

Claims (7)

An organic electroluminescence display device in which an organic layer including a light emitting layer is disposed between an anode and a cathode, and the organic layer emits light by applying a voltage between the anode and the cathode,
A first sub-pixel emitting red light;
A second sub-pixel emitting green light;
A third sub-pixel emitting blue light;
An organic electroluminescence display device, wherein one pixel is composed of a fourth subpixel that emits an intermediate color of red light of the first subpixel and green light of the second subpixel.   The organic electroluminescence display device according to claim 1, wherein the fourth subpixel is superior to the first subpixel in terms of luminous efficiency.   The organic electroluminescence display device according to claim 1, wherein the fourth subpixel is superior to the second subpixel in luminous efficiency.   4. The light emitting device according to claim 1, wherein the fourth sub-pixel emits light having a smaller x value and a larger y value than the first sub-pixel in CIE chromaticity coordinates. Organic electroluminescence display device.   5. The light emitting device according to claim 1, wherein the fourth subpixel emits light having a larger x value and a smaller y value than the second subpixel in CIE chromaticity coordinates. Organic electroluminescence display device.   6. The organic electroluminescence display device according to claim 1, wherein an emission peak wavelength of the fourth subpixel is in a range of 500 nm to 580 nm. The second subpixel includes the organic layer exhibiting substantially the same emission color as the fourth subpixel, and transmits a color filter that attenuates light of a component in a long wavelength range, The organic electroluminescence display device according to claim 1, wherein light emitted from the organic layer is changed to green light to emit light.

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