KR100605112B1 - Organic light emitting diodes - Google Patents

Abstract

 The present invention relates to a multicolor organic light emitting device, comprising a plurality of subpixels stacked in order of a hole transport layer, a light emitting layer, an electron transport layer, and a metal electrode on a light-transmitting first electrode, wherein the light emitting layer of each subpixel is red light. And an organic light emitting material emitting green light, blue light and white light.

Organic light emitting, white light emitting, blue light emitting, red light emitting

Description

Organic light emitting diodes

Figure 1. Conventional organic light emitting device of the RGB independent light emitting method

Figure 2. Conventional organic light emitting device of the color conversion method

Figure 3. A conventional organic light emitting device of the white light emitting method with a color filter

Figure 4. W-RGB type conventional organic light emitting device with RGBW color filter

Figure 5. Color coordinate distribution used in 13,000 images

Figure 6. Power consumption graphs of RGB and RGBW displays for different images

7. Organic light emitting device of the RGBW independent light emitting method according to the present invention

8. Subpixel structure in which white light is emitted according to the present invention

9. Emission Spectrum of White OLED

10. Light emission color purity of white OLED according to the present invention

11. Current density-voltage characteristics of white OLED

12. Luminance-voltage characteristics of white OLED

13. Luminous efficiency-luminance characteristics of white OLED

Explanation of symbols on the main parts of the drawing

11-first electrode

12-hole injection layer (HIL)

13-hole transport layer (HTL)

14-light emitting layer (LEL)

15-electron transport layer (ETL)

16-electron injection layer (EIL)

17-metal electrode

18-blue light emitting layer

19-Red Light Emitting Layer

20-color conversion layer

21-color filter

22-white light emitting layer

23-liquid crystal

Organic light emitting diodes (OLEDs) are attracting attention as next-generation flat panel displays suitable for moving images due to their characteristics such as light weight, low power consumption and fast response speed. Nowadays, commercialization is progressing fast enough to be adopted as the basic panel of external windows in mobile phones, and the development speed of the technology is rising rapidly, and recently, 20-inch OLED has been developed, and it is a medium and large screen within 3-4 years. Is expected to encounter OLED TV. In particular, as Asian countries such as Korea, Japan, and Taiwan are speeding up their technology development based on their experiences in developing advanced display devices such as semiconductors and LCDs, it is expected that competition for display market leadership will intensify in the future.

In order to realize full-color display using such OLED, development of light emitting material, which is a core component material, will be very important factor, but the speed of improvement of performance of light emitting material is very slow considering the target of medium and large screen. . Therefore, a new concept must be introduced in terms of panel structure in order to drastically improve OLED performance. For this reason, many concepts for panel companies to change the panel structure to realize a commercialized display have been announced.

The following three methods are known as a full color display using OLED.

(1) RGB independent light emission method

As shown in FIG. 1, an independent light emission method using subpixels having light emitting layers each of organic light emission in RGB, which is the most common OLED panel structure, and all commercially available panels adopt the RGB independent light emission method. .

In the conventional RGB independent light emission method, the white color of the CIE coordinates (0.33, 0.33) should be adjusted to RGB. Therefore, even if the loss of electrical efficiency or pure chromaticity is prioritized, the color harmony is prioritized more than the RGB element device. The OLED structure had to be designed. For example, if the efficiency or chromaticity of pure blue drops, the pure red may be implemented.

(2) color conversion method

As shown in FIG. 2, a blank subpixel for blue and a subpixel having a red and green color conversion layer are disposed on the blue light emitting device, and in the color conversion method, development of a high performance blue light emitting material is very important. In particular, blue has a large energy gap and is disadvantageous in the device than other colored light emitting materials in terms of stability of the material. In the case of the blue light emitting material developed to date, application is possible to some extent in terms of color purity and luminous efficiency, but application of the method (2) has not been announced yet due to disadvantages in terms of lifespan.

(3) White light emitting system with color filter

As shown in FIG. 3, an RGB color filter is placed on the white OLED, and whether to adopt this method depends on the development of a white OLED having a clear, high brightness, high efficiency spectrum of the RGB tricolor region. Although many researchers are working on the development of high-efficiency white OLEDs aiming at such a structure, many problems are emerging.

White OLEDs are known using two light emitting materials and three light emitting materials. While the method using two light emitting materials has a wide process margin and easy implementation of white color coordinates, there is a disadvantage in that light emission efficiency is significantly reduced when using an RGB color filter. In fact, no matter how much light-emitting materials having a broad emission wavelength range are used, the luminous efficiency of each RGB that has passed through the color filter can only be about 1/5 of the white luminous efficiency. On the other hand, the method adopting the three light emitting materials does not show a large loss in the luminous efficiency of white even after passing through the RGB color filter. However, the process is very difficult and the change of the white color coordinate according to the driving voltage is very severe. Have.

On the other hand, as a modification of the white light emitting method with the color filter, the RGBW color filter is attached on the white OLED having the structure as shown in FIG. 4 at the International Display Society "IMID 2004" held in August 2004 by Kodak. It has been proposed a method, which is also known in the Republic of Korea Patent Publication No. 2003-77430 and the Republic of Korea Patent Publication No. 2004-74958.

According to Kodak's video image analysis, as shown in the color coordinate distribution graph of FIG. 5, pure RGB is rarely used in most video images, and intermediate colors including white are much higher. As can be seen from the power consumption graphs of RGB and RGBW displays, the RGB color filler can be obtained by using a RGBW color filter that adds a white filter that uses the color of the white OLED instead of the RGB color filter. It is reported that power consumption can be reduced by 50% compared to using.

However, Kodak's RGBW color filter adopts a full-color display using a color filter on a white OLED, which adopts an LCD display that does not emit light. The disadvantage is that power consumption is greatly increased. Since OLED, which is self-luminous, can emit a variety of high-efficiency emission colors, the color filter type full color implementation method of the method (3) and Kodak's RGBW color filter adoption method are more disadvantages in terms of power consumption.

Accordingly, an object of the present invention is to provide an organic light emitting device of RGBW independent light emitting method, which can fully utilize the advantages of OLED which is self-emitting as a method of transforming RGB independent light emitting method, and has low power consumption. Another object of the present invention is to provide an independent white light emitting subpixel without using a white color as RGB, and is relatively free from white balance problems, so that the organic light emitting light of the RGBW independent light emitting method can adopt a light emitting material or a light emitting device structure. It is to provide an element.

The present invention relates to an organic light emitting device of RGBW independent light emitting method that can fully utilize the advantages of OLED that is self-luminous and has low power consumption as a modification method of RGB independent light emitting method. Comprising a plurality of sub-pixels stacked in the order of a hole transporting layer, a light emitting layer, an electron transporting layer, a metal electrode, the light emitting layer of each subpixel is characterized in that the organic light emitting material that emits red light, green light, blue light and white light .

In the organic light emitting device of the RGBW independent light emitting method according to the present invention, a method of reducing power consumption by turning on only two subpixels of RW, GW, or BW without turning on all three RGB subpixels in an intermediate color that takes up the majority of colors. Adopted. By adopting the RGBW independent light emission method, it is possible to overcome the color balance problem that should always be considered when using only three subpixels of RGB. Therefore, the problem that occurs in the conventional RGB independent light emission method by adopting the RGBW independent light emission method of the present invention. It is now possible to select the light emitting material and the device structure more freely.

Hereinafter, the present invention will be described in detail.

The organic light emitting diode of the RGBW independent light emitting method according to the present invention is composed of a plurality of subpixels stacked in the order of a hole transporting layer, a light emitting layer, an electron transporting layer, a metal electrode on the first electrode having a light transmitting property, as shown in FIG. The light emitting layer of each subpixel is made of an organic light emitting material emitting red light, green light, blue light and white light.

The light emitting layer in which the red light, the green light, and the blue light are emitted is provided as an organic light emitting material obtained by doping a second organic light emitting material to an organic light emitting material film formed of an organic light emitting material or a first organic light emitting material made of the same component. The conventional organic light emitting material employed in the conventional RGB independent light emission method can be employed. The light emitting layer of the subpixel emitting white light is preferably provided by laminating a blue organic light emitting material and a red organic light emitting material, and the light emitting layer employs a doping system that uses a second light emitting material to dope the first organic light emitting material. Preferably, the blue and red light emitting materials can each be composed of two compounds.

Applicant has a light emitting efficiency of up to 13 cd / A and a maximum luminance of 50,000 cd using a light emitting layer in which a blue light emitting material composed of the following Chemical Formulas 1 and 2 and a red light emitting material composed of the following Chemical Formulas 3 and 4 are laminated: Invented a white OLED exhibiting excellent performance of / m ² , and therefore, using the RGB OLED adopted in the conventional RGB independent light emitting method together with the white OLED invented by the applicant, an excellent RGBW independent light emitting OLED can be realized. Can be.

[Formula 1]

[Formula 2]

[Formula 3]

[Formula 4]

The light emitting layer of the white subpixel in the multi-color organic light emitting device of the RGBW independent light emitting method according to the present invention is preferably laminated on the hole transport layer in the order of blue light emitting material / red light emitting material, and the luminous efficiency of the blue light emitting material and the red light emitting material. In consideration of the light emission efficiency and the luminance of the desired RGBW can be adjusted by adjusting the thickness of each light emitting material.

The first electrode, the hole transport layer (HTL), the electron transport layer (ETL), and the metal electrode, which are provided above and below the light emitting layer LEL and constitute a subpixel, may employ conventionally known ones. The first electrode and the hole transport layer may be employed. The hole injection layer HIL may be further provided between the HTLs.

The first electrode is a conductive and transparent electrode, and common transparent materials used in the present invention are indium tin oxide (ITO), indium zinc oxide (IZO) and tin oxide, but aluminum- or indium-doped zinc oxide, Magnesium-indium oxide and nickel-tungsten oxide may be deposited by any suitable means such as, but not limited to, evaporation, sputtering, chemical vapor deposition, or electrochemical means.

The hole injection material used in the hole injection layer (HIL) provided if necessary serves to improve the deposition characteristics of the organic layer and facilitate the injection of holes into the hole transport layer (HTL). Suitable materials for use in the hole injection layer are arylamine based compounds comprising at least two aromatic tertiary amine residues, porphyrin based compounds as described in US Pat. No. 4,720,432, and plasma-deposited fluorine as described in US Pat. No. 6,208,075. Carboxyl polymers and the like.

A hole transport material useful as a hole transport layer (HIL) is well known compounds such as aromatic tertiary amines, particularly those comprising two or more aromatic tertiary amine residues described in US Pat. Nos. 4,720,432 and 5,061,569. However, it is not limited to the range of the said compound.

The electron transport layer (ETL) is deposited on the light-emitting layer mentioned above by the use of any means such as evaporation, sputtering, chemical vapor deposition or electrochemical means, and the preferred material for use in the electron transport layer is a metal chelating compound, Benzazole, polyphenylenevinylene derivatives, poly-para-phenylene derivatives, and the like.

The metal electrode is composed of a transparent conductive layer made of metal or a metal oxide and an electron injection layer (EIL) in contact with the light emitting layer under the transparent conductive layer.

Hereinafter, the light emission characteristics of the device will be described in an embodiment of a subpixel in which white light used in the organic light emitting device of the RGBW independent light emission method is emitted.

As the structure of the subpixel in which white light is emitted according to the present invention, the following conventional subpixel structure is used.

ITO / HIL (60) / HTL (20) / BlueEML (14) / RedEML (19) / ETL (30) / EIL (2) / Al (unit: nm)

First, a transparent electrode ITO thin film (15 Ω / □) obtained from an OLED glass (Samsung Corning Co.) was subjected to ultrasonic cleaning using trichloroethylene, acetone, ethanol, and distilled water sequentially, and then stored in isopropanol. It was used after.

The ITO substrate was installed in the substrate folder of the vacuum deposition apparatus, and the 4,4 ', 4 "-tris (N, N- (2-naphthyl) -phenylamino) triphenylamine (Formula 5) was placed in a cell in the vacuum deposition apparatus. 4,4 ', 4 "-tris (N, N- (2-naphthyl) -phenylamino) triphenylamine, 2-TNATA) was added and evacuated until the vacuum in the chamber reached 10 ^-6 torr. A current was applied to evaporate 2-TNATA to deposit a 60 nm thick hole injection layer on the ITO substrate.

Next, N , N' -bis (α-naphthyl) -N , N' -diphenyl-4,4'-diamine ( N , N'- bis (α-) naphthyl) -N , N' -diphenyl-4,4'-diamine, NPB) was added, and NPB was evaporated by applying a current to the cell to deposit a 20 nm thick hole transport layer on the hole injection layer.

After depositing the hole transport layer, a light emitting material was formed into two layers to form a white light emitting layer. First, the compound of Formula 1 and the compound of Formula 2 were each placed in different cells, and the first light emitting layer having a thickness of 14 nm was deposited by simultaneously evaporating at a molar% ratio of 2: 100. Thereafter, the compound of Formula 3 and the compound of Formula 4 were evaporated simultaneously at a molar% ratio of 4: 100 on the first emission layer to deposit a second emission layer having a thickness of 19 nm to form a white emission layer.

Subsequently, tris (8-hydroxyquinoline) -aluminum (Alq) of Chemical Formula 7 was deposited on the light emitting layer in the same manner as in NPB as an electron transporting layer. Lithium quinolate (Liq) of Formula 8 was deposited to a thickness of 2 nm as an injection layer.

After the organic layer 7 was formed as described above, an aluminum (Al) metal cathode was deposited to a thickness of 150 nm by using another vacuum deposition apparatus to fabricate a white organic light emitting device.

[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]

The light emitting layer of the white light-emitting subpixel manufactured in the above step was produced white OLED using blue and red light emitting materials having luminous efficiency of 15 cd / A and 18 cd / A, respectively. The efficiency was 12 cd / A at the luminance of / m ² , and pure white was realized in all luminance regions.

9 to 13 illustrate light emission characteristics of a subpixel emitting white light used in an organic light emitting device of the RGBW independent light emitting method according to the present invention. From the above, the white OLED having a simple light emitting device structure is a conventional RGB OLED. The structure and common layer can be used together, so it is fully compatible, there is little change in white purity due to luminance change, very high luminous efficiency, and long device life compared to other RGB devices, and it is very suitable for commercialization for RGBW pattern. It can be seen that it has excellent characteristics.

Although the preferred embodiments of the present invention have been shown and described above, the present invention is not limited to the above-described embodiments, and the present invention is not limited to the above-described embodiments without departing from the spirit of the present invention as claimed in the claims. Various modifications can be made by those skilled in the art, and such modifications are intended to fall within the scope of the appended claims.

 When OLED full color display is realized using RGBW independent light emitting device, only two subpixels, RW, GW, and BW, are used for most intermediate colors, which consumes about 50% of power consumption compared to RGB subpixel systems. Since there is no need to reduce the white implementation to RGB, there is an advantage that the light emitting material or the light emitting element structure can be adopted relatively free from the white balance problem.

Claims (4)

The light emitting layer comprises a plurality of subpixels stacked in order of a hole transporting layer, a light emitting layer, an electron transporting layer, and a metal electrode. The light emitting layer of each subpixel includes organic light emitting red, green, blue, and white light. A multicolor organic light emitting device comprising a material. The method of claim 1, The light emitting layer in which the red light, the green light, and the blue light are emitted is composed of an organic light emitting material or two or more organic light emitting materials of the same component, and the light emitting layer of the subpixel in which the white light is emitted is composed of a blue organic light emitting material and a red organic light emitting material. Multi-color organic light emitting device. The method of claim 2, The light emitting layer emitting white light is a multi-color organic light emitting device, characterized in that the blue light emitting material composed of the following formula (1) and (2) and a red light emitting material composed of the following formula (3) and (4). [Formula 1]

[Formula 2]

[Formula 3]

[Formula 4]

The method of claim 3, wherein A light emitting layer in which white light is emitted is a multi-color organic light emitting device, characterized in that laminated in the order of blue light emitting material and red light emitting material.

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