KR101849583B1 - White organic light emitting display device - Google Patents

Abstract

The present invention relates to a white organic light emitting display capable of improving a color viewing angle by placing a stack for emitting long wavelength light on the anode side and a stack for emitting short wavelength light on the cathode side, And a second electrode; A charge generation layer formed between the first electrode and the second electrode; A first stack formed between the first electrode and the charge generating layer; And a second stack formed between the charge generating layer and the second electrode, wherein a wavelength of light emitted from the first stack is longer than a wavelength of light emitted from the second stack.

Description

WHITE ORGANIC LIGHT EMITTING DISPLAY DEVICE [0001]

The present invention relates to a white organic light emitting display, and more particularly, to a white organic light emitting display capable of improving a color viewing angle.

Recently, as the information age has come to a full-fledged information age, a display field for visually expressing electrical information signals has been developed rapidly. In response to this, various flat panel display devices having excellent performance of thinning, light weight, (Flat Display Device) has been developed to replace CRT (Cathode Ray Tube).

Specific examples of such flat panel display devices include a liquid crystal display device (LCD), a plasma display panel (PDP), a field emission display (FED) (Organic Light Emitting Device) (OLED).

Among these, an organic light emitting display device is attracting attention as a competitive application for not requiring a separate light source and for compacting a device and displaying a clear color. In such an OLED display, formation of an organic light emitting layer is essential. Conventionally, a deposition method using a shadow mask has been used for forming an organic light emitting layer.

However, in the case of a large area of the shadow mask, a phenomenon of sagging due to the load is generated and it is difficult to use the shadow mask many times, and an alternative method is required because defects are formed in the formation of the organic light emitting layer pattern. As one of the various methods for replacing such a shadow mask, there is a white organic light emitting display.

The white organic light emitting display device is characterized in that each layer between an anode and a cathode is deposited without a mask at the time of forming a light emitting diode, thereby sequentially depositing organic layers having different components including an organic light emitting layer in a vacuum state. Such a white organic light emitting display device is used for various purposes such as a thin light source, a backlight of a liquid crystal display device, or a full color display device employing a color filter.

Hereinafter, a typical white organic light emitting display will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of a conventional white organic light emitting display device.

1, a conventional white organic light emitting display device includes a first electrode 110 and a second electrode 150 opposed to each other on a substrate 100, a first electrode 110 and a second electrode 150 between the first electrode 110 and the second electrode 150, A first stack 120 formed between the first electrode 110 and the charge generating layer 130 and a second stack 120 formed between the charge generating layer 130 and the second electrode 150. The charge generating layer 130 is formed between the first electrode 110 and the charge generating layer 130, And a second stack (140).

In the conventional white OLED display device, the first stack 120 uses a blue fluorescent element as a light emitting layer, the second stack 140 uses a yellow-green phosphor element as a light emitting layer, The blue (B) light emitted from the first stack 120 and the yellow green (YG) light emitted from the second stack 140 are mixed to realize white light.

However, in general, the efficiency of the blue light (B) is significantly lower than that of the yellowish green (YG) light. Therefore, in a typical white organic light emitting diode display, the PL (Photoluminescence) peak of the first stack 120, which emits blue (B) light having a low efficiency, (YG) light, the emittance peak is formed in the long wavelength region, which is much deviated from the PL peak of the yellow green (YG) light. Therefore, as the viewing angle increases, the luminance of the blue (B) light decreases sharply as compared with the yellow-green (YG) light.

Further, since the width of the blue (B) light of the first stack 120 is narrower than the width of the emissive peak of the yellow (YG) light of the second stack 140, the blue (B) As the viewing angle is larger, the luminous efficiency is significantly lowered. As a result, as the viewing angle increases, a yellowish white color, that is, a white color expressed as warm white is realized, and the display quality is degraded.

SUMMARY OF THE INVENTION The present invention has been conceived in order to solve the above-mentioned problems, and it is an object of the present invention to provide a white color display device capable of improving the color viewing angle by providing Cool White by placing a stack for emitting long wavelength light on the anode side and a stack for emitting short- And an organic light emitting display device.

According to an aspect of the present invention, there is provided a white organic light emitting diode display comprising: a first electrode and a second electrode opposing each other on a substrate; A charge generation layer formed between the first electrode and the second electrode; A first stack formed between the first electrode and the charge generating layer; And a second stack formed between the charge generating layer and the second electrode, wherein a wavelength of light emitted from the first stack is longer than a wavelength of light emitted from the second stack.

And emits green light and red light or yellow-green light in the first stack, and blue light in the second stack.

Light emitted from the first and second stacks is emitted downward through the substrate.

The first stack includes a first common layer and a first light emitting layer sequentially stacked, and the first common layer includes a first hole injection layer and a first hole transport layer.

Wherein the second stack comprises a second common layer, a second light emitting layer and a third common layer stacked in turn, the second common layer comprising a second hole injection layer and a second hole transport layer, Includes a first electron injection layer and a first electron transport layer.

The white organic light emitting display of the present invention has the following effects.

First, by placing a stack emitting a long wavelength light on the anode side and a stack emitting short wavelength light on the cathode side, Cool White can be implemented to improve the color viewing angle.

Second, the charge generating layer formed on the stack for emitting long wavelength light functions as an electron transporting layer and an electron injecting layer to remove the electron transporting layer and the electron injecting layer of the stack for emitting long wavelength light, And the driving voltage is lowered.

1 is a cross-sectional view of a conventional white organic light emitting display device.
2 is a cross-sectional view of a white organic light emitting display device of the present invention.
Figure 3a is a cross-sectional view of the first stack of Figure 2;
Figure 3b is a cross-sectional view of the second stack of Figure 2;
FIG. 4 is a graph illustrating the luminance reduction rate of each of the white organic light emitting display device and the white organic light emitting display device according to the present invention. FIG.

Hereinafter, a white OLED display device according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a cross-sectional view illustrating a white organic light emitting display device according to the present invention. Figure 3a is a cross-sectional view of the first stack of Figure 2, and Figure 3b is a cross-sectional view of the second stack of Figure 2;

2, the white organic light emitting display of the present invention includes a first electrode 210 and a second electrode 250, a first electrode 210 and a second electrode 250 opposed to each other on a substrate 200, A first stack 220 formed between the first electrode 210 and a charge generation layer 230 and a second stack 220 formed between the charge generation layer 230 and the second charge storage layer 230. [ And a second stack (240) formed between the electrodes (250).

The multi-stack white organic light emitting device includes light emitting layers of different colors in each stack, and light of different colors emitted from the light emitting layers of each stack is mixed to realize white light. In particular, the white organic light emitting display of the present invention has the wavelength of the light emitted from the first stack 220 longer than the wavelength of the light emitted from the second stack 240.

Specifically, the substrate 200 is formed of a transparent glass, plastic, or the like so that the light generated in the first and second stacks 220 and 240 is emitted to the outside through the substrate 200. The first electrode 210 formed on the substrate 200 may be formed of an oxide such as tin oxide (ITO), indium tin oxide (ITO), indium zinc oxide (IZO) , Indium Tin Zinc Oxide (ITZO), or the like.

The second electrode 250 is a cathode formed of an opaque conductive material such as magnesium (Mg), silver (Ag), aluminum (Al), calcium (Ca) May be formed. In particular, the second electrode 250 may be formed of a metal having a high reflectance so that light emitted from the first and second stacks 220 and 240 may be emitted to the bottom through the substrate 200.

The charge generation layer 230 between the first and second stacks 220 and 240 provides charge balancing between the first and second stacks 220 and 240. Although not shown, the charge generating layer 230 is positioned adjacent to the first stack 220 and is located adjacent to the N-type organic layer and the second stack 240 for injecting electrons into the first stack 220, And a P-type organic layer injecting holes into the stack 240.

In general, a white organic light emitting display having a plurality of stacks formed on a substrate has a wavelength shorter than a wavelength of light emitted from a stack having a cathode located on the anode side. For example, blue (B) light is emitted from the stack positioned on the anode side, and yellow-green (YG) light is emitted from the stack located on the cathode side. In this case, however, the color viewing angle may be reduced.

In general, the EL spectrum of a white organic light emitting display is determined by the product of the photoluminescence (PL) peak and the emission peak of the light emitting substance. In this case, the emittance is determined by the refractive index and the thickness of each layer, and represents the degree of exiting the excitons generated through the recombination of electrons and holes through the substrate 200 to the outside.

However, when a first stack for emitting light having a short wavelength is disposed on the anode side and a second stack for emitting light having a long wavelength is disposed on the cathode side as in a general white organic light emitting display device, a PL peak is applied to the emittance peak for each wavelength It is hard to match. Specifically, PL (Photoluminescence) of short wavelength light is distributed in a narrow wavelength band and PL of long wavelength light is distributed in a relatively wide wavelength band as compared with PL of short wavelength light. Therefore, an EL spectrum determined by the product of PL peak and Emittance peak is also narrow It is distributed in the wavelength band, and it is distributed in the wide wavelength band with respect to the long wavelength light.

Therefore, a typical white organic light emitting display device forms a stack for emitting short wavelength light on an anode to match a PL (Photoluminescence) peak with a resonance period of short wavelength light, and forms a stack that emits long wavelength light, An emittance peak in the form of an offset is formed in the long wavelength region. As a result, as the viewing angle increases, the intensity of the lowered EL spectrum of the short wavelength light and the long wavelength light is different, and a color shift phenomenon occurs in which the color coordinates change depending on the viewing angle.

Further, when white light is implemented with three stacks, it is difficult to match the PL peak with the resonance period of the long wavelength region, so that a color shift phenomenon occurs in which the color coordinates of the viewing angle are changed.

Accordingly, the white organic light emitting display of the present invention has a wavelength of light emitted from the first stack 220 is longer than a wavelength of light emitted from the second stack 240. That is, a first stack 220 for emitting long wavelength light is formed on the first electrode 210 to form a second stack 240 that emits short wavelength light after matching the PL peak with the resonance period of the long wavelength light, The phenomenon that the luminance of the short wavelength light is further decreased according to the change of the viewing angle is changed to the phenomenon that the luminance of the long wavelength light is further reduced.

Specifically, the first stack 220 formed on the first electrode 210 includes a first common layer 222 and a first light emitting layer 224 which are sequentially stacked, as shown in FIG. 3A. In this case, the first light-emitting layer 224 may be a single light-emitting layer doped with a phosphorescence yellow + phosphorescence green to one host or a single light-emitting layer doped with a phosphorescent yellow-green dopant to two hosts have. Also, although not shown, the first light emitting layer 224 may be a single light emitting layer formed by doping phosphorescence green and phosphorescence red together with phosphorescence green and phosphorescence red into one host.

The first common layer 222 is formed by sequentially stacking the first hole injection layer and the first hole transport layer. In particular, the N type organic layer of the charge generation layer 230 functions as an electron injection layer and an electron transport layer. Thus, there is no need to further form an electron transport layer and an electron injection layer on the first light emitting layer 224 of the first stack 220, simplifying the process and reducing manufacturing costs, The thickness can be reduced. As a result, the driving voltage of the first stack 220 can be reduced.

The second stack 240 formed on the charge generating layer 230 includes a second common layer 242, a second light emitting layer 244 and a third common layer 246 stacked in order as shown in FIG. 3B do. At this time, the second light emitting layer 244 is a single light emitting layer containing a dopant of a blue fluorescent component in one host.

Accordingly, in the white organic light emitting display of the present invention, yellow (YG) light is emitted from the first stack 220 and blue (B) light is emitted from the second stack 240 to realize white light. In addition, when the second light emitting layer 244 is a single light emitting layer formed by doping phosphorescence green and phosphorescence Red together in one host, red (R) and green (R) light are emitted from the first stack 220 G) light is emitted from the second stack 240, and blue (B) light is emitted from the second stack 240 to realize white light.

Although not shown, the second common layer 242 is formed by sequentially laminating the second hole injection layer and the second hole transport layer, and the third common layer 246 is formed by stacking the first electron injection layer and the first electron injection layer Layer are sequentially stacked.

In the white OLED display of the present invention, the total thickness d of the first stack 220, the charge generating layer 230, and the second stack 240 is 3000 ANGSTROM to 8000 ANGSTROM. In order to satisfy the resonance period of the light emitted from the first and second light emitting layers 224 and 244 of the first and second stacks 220 and 240, the first light emitting layer 224 and the second light emitting layer 244 (N is a positive integer) times of λ (peak wavelength of light emitted from the light-emitting layer) / 4 on the substrate 200. For example, when d is 3000 Å and the peak wavelength of light emitted from the first light emitting layer 224 is 600 nm, the first light emitting layer 224 has a wavelength of 600 nm / 4 = 150 nm, for example, ≪ / RTI > When the peak wavelength of the light emitted from the second light emitting layer 244 is 400 nm, the second light emitting layer 244 is located at 400 nm / 4 = 100 nm, for example, 1000 Å and 2000 Å from the substrate 200 .

That is, as described above, the light emitting layer that emits a short wavelength light has more positions that can satisfy the resonance period between the first electrode 210 and the second electrode 250 than the light emitting layer that emits the long wavelength light. Accordingly, the white organic light emitting display of the present invention may include a second stack 244 that emits a short-wavelength light after matching a resonance period and a PL (photoluminescence) peak by first forming a first light emitting layer 224 that emits long- The phenomenon that the luminance of the short wavelength light is further reduced in accordance with the change of the viewing angle is changed to the phenomenon that the luminance of the long wavelength light is further reduced.

4 is a graph illustrating luminance reduction rates of the white organic light emitting display according to the present invention and the conventional white organic light emitting display according to viewing angles according to wavelengths.

As shown in FIG. 4, a typical white organic light emitting display device has a remarkably reduced brightness compared to yellow-green (YG) light even when the viewing angle is 20 ° or more. That is, in a general white organic light emitting display device, when the viewing angle becomes large, there arises a problem that the white light becomes yellowish. However, in the white organic light emitting display of the present invention, the yellowish green (YG) light significantly decreases in luminance as compared with the blue (B) light at a viewing angle of 40 degrees or more.

In general, the display device is advantageous in screen display as compared with the above-described whiteish of yellowish color, that is, the white color expressed as warm white, in which the color temperature is high and the so-called Cool White, Therefore, as in the white OLED display of the present invention, Cool White can be realized when the luminance of blue (B) light is higher than that of yellow-green (YG) light.

That is, a stack for emitting long wavelength light is disposed close to the anode to match the long wavelength light to the emittance peak, and a stack for emitting short wavelength light is disposed close to the cathode. Therefore, the white organic light emitting display according to the present invention changes the phenomenon that the luminance of the existing blue (B) light is further decreased according to the change of the viewing angle into the phenomenon that the yellow green (YG) The color viewing angle can be improved.

Further, the charge generating layer formed on the stack for emitting the long wavelength light functions as the electron transporting layer and the electron injecting layer, thereby removing the electron transporting layer and the electron injecting layer of the stack for emitting the long wavelength light, And the driving voltage is lowered.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Will be apparent to those of ordinary skill in the art.

200: substrate 210: first electrode
220: first stack 222: first common layer
224: first light emitting layer 230: charge generation layer
240: second stack 242: second common layer
244: second light emitting layer 246: third common layer
250: second electrode

Claims (5)

An anode electrode disposed on the substrate;
A first stack on the anode electrode, the first stack including a first light emitting layer;
A charge generation layer located on the first stack and in direct contact with the first light emitting layer;
A second stack located on the charge generating layer and including a second light emitting layer; And
And a cathode electrode located on the second stack,
The wavelength of light emitted from the first light emitting layer is longer than the wavelength of light emitted from the second light emitting layer,
Wherein light emitted from the first light emitting layer and the second light emitting layer is emitted downward through the substrate,
Wherein a resonance period of the first stack corresponds to a PL (Photo-Luminescence) peak of light emitted from the first light emitting layer. The method according to claim 1,
Wherein the first light emitting layer emits green light and red light or yellow-green light, and the second light emitting layer emits blue light. . The method according to claim 1,
The substrate and the n-fold of (where, λ ₁ of the distance λ _2/4 of the distance between the λ _1/4 for n times, the substrate and the second light-emitting layer between the first light-emitting layer of the light peak emission from the first light-emitting layer Wavelength,? ₂ is a peak wavelength of light emitted from the second light emitting layer, and n is a positive integer). The method according to claim 1,
Wherein the first stack further comprises a first hole injection layer and a first hole transport layer sequentially disposed between the substrate and the first light emitting layer. The method according to claim 1,
Wherein the second stack comprises a second hole-injecting layer and a second hole-transporting layer sequentially positioned between the charge generating layer and the second light-emitting layer, and a second electron-injecting layer disposed sequentially between the second light- Layer and a first electron transport layer. ≪ RTI ID = 0.0 > 18. < / RTI >

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