KR20120076255A - White organic light emitting device - Google Patents

Abstract

PURPOSE: A white organic light-emitting device is provided to improve viewing angle by being formed into a multi- stack structure which includes a first stack and a second stack laminated between a first electrode and a second electrode. CONSTITUTION: A first electrode(110) and a second electrode(150) are faced with each other on a substrate(100). A first stack(120) is located between the first electrode and the second electrode. The first stack comprises a first common level(122), a first light-emitting layer(124), and an electron-transport layer(126). A second stack(140) is located between the first stack and the second electrode. The second stack comprises a hole-transport layer(142), a second light-emitting layer(144), and a second common layer(146).

Description

White organic light emitting element {WHITE ORGANIC LIGHT EMITTING DEVICE}

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

In recent years, the display field for visually expressing electrical information signals has been rapidly developed as the information age has been developed, and various flat panel display devices having excellent performance of thinning, light weight, and low power consumption have been developed. Flat Display Device has been developed and is rapidly replacing the existing Cathode Ray Tube (CRT).

Specific examples of such a flat panel display include a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), and an organic light emitting display. (Organic Light Emitting Device: OLED) and the like.

Among them, the organic light emitting diode display is considered as a competitive application for the compactness of the device and the vivid color display without requiring a separate light source.

In the organic light emitting diode display, it is essential to form an organic light emitting layer. In order to form the organic light emitting layer, a deposition method using a shadow mask is used.

However, in the case of a large area, the shadow mask has a drooping phenomenon due to its load, which makes it difficult to use it many times, and a defect occurs in the formation of the organic light emitting layer pattern, thereby requiring an alternative method.

There is a white organic light emitting display device as one of several methods that have been proposed to replace the shadow mask.

Hereinafter, a white organic light emitting diode display will be described.

The white organic light emitting diode display is to deposit each layer between the anode and the cathode without a mask when forming a light emitting diode, characterized in that to deposit the organic layers with different components including the organic light emitting layer in a vacuum state in order. The white organic light emitting diode display is an element that is used for various purposes, such as a thin light source, a backlight of a liquid crystal display, or a full color display employing a color filter.

Nowadays, a white organic light emitting diode display uses a duplex light stack structure in which a first stack using a blue fluorescent element as a light emitting layer and a second stack structure using a yellow-green phosphorescent element as a light emitting layer are stacked. It is becoming. In the white organic light emitting diode, white light is realized by a mixing effect of blue light emitted from a blue fluorescent device and yellow light emitted from a yellow phosphorescent device.

In this case, the fluorescent blue light emitted from the first stack changes according to the viewing angle, whereas the phosphorescent yellow light emitted from the second stack does not change in the viewing angle, thereby shifting the white color coordinates. As such, a problem arises in that the white color coordinate is shifted to have a narrow viewing angle characteristic.

The present invention has been made to solve the above problems, to provide a white organic light emitting device that can improve the characteristics of the viewing angle.

To this end, in the white organic light emitting diode according to the present invention, a first common layer, a second emission electrode, and a first common layer, a first emission layer, and an electron transporting layer which are opposed to each other on a substrate are sequentially disposed between the first and second electrodes. A first stack stacked between the first stack and a second stack in which a hole transporting layer, a second light emitting layer, and a second common layer are sequentially stacked between the first stack and the second electrode, and between the first stack and the second stack And a charge generation layer for controlling charge balance between the stacks, wherein the thickness of the first common layer is in a range of 100 nm to 200 nm.

Here, the first light emitting layer is formed as a single light emitting layer doped with a fluorescent blue dopant in one host.

In addition, the second light emitting layer is formed by doping a phosphorescent yellow-green dopant (phosphorescence yellow-phosphorescence green) to one host, or by doping a phosphorescent yellow-green dopant to two hosts.

The first common layer is positioned between the first electrode and the first light emitting layer to serve as hole injection or hole transport, and is configured as a hole injection layer or a hole transport layer.

In addition, the second common layer is positioned between the second electrode and the second light emitting layer to serve as an electron injection or electron transport layer, and is composed of an electron injection layer or an electron transport layer.

The thickness of the first stack, the second stack, and the charge generating layer is 300 nm to 600 nm.

The first common layer is positioned at 0 nm to 300 nm from the first electrode, and the first common layer is located at 100 nm to 600 nm from the second electrode.

The first light emitting layer is located at 100 to 400 nm from the first electrode, and the second light emitting layer is located at 100 to 600 nm from the second electrode.

According to the present invention, a white organic light emitting device includes a first stack stacked between a first common layer, a first light emitting layer, and an electron transporting layer between a first electrode and a second electrode, and a charge generating layer, between a first stack, and a charge generating layer. And a second stack stacked with a hole transport layer, a second light emitting layer, a second common layer, and a second electrode.

The emission peak of the organic laminate is shifted by controlling the thickness of each organic layer and the overall organic layer of such a structure so that the reduction rate according to the viewing angle of the fluorescent blue light emitting layer and the reduction rate according to the viewing angle of the phosphorescent yellow-green light emitting layer are made to be the same ratio. It has the characteristics of the viewing angle.

1 is a perspective view illustrating a white organic light emitting diode according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view for describing the thickness of each layer of the white organic light emitting diode according to the first embodiment of the present invention illustrated in FIG. 1.
3 is a graph illustrating emission peaks of the conventional white organic light emitting diode.
4 illustrates an emission peak of the organic laminate according to the first embodiment of the present invention.
5 is a graph showing an emission peak (EL Peak) according to a first embodiment of the present invention.
6 is a graph comparing a white organic light emitting diode according to a first embodiment of the present invention with a conventional white organic light emitting diode.
7 (a) is a graph showing a photoluminescence peak according to the first embodiment of the present invention and Figure 7 (b) is an emission peak of the organic laminate in the organic light emitting device structure. .
8 is a perspective view illustrating a white organic light emitting diode according to a second embodiment of the present invention.
FIG. 9 is a cross-sectional view for describing a thickness of each layer of the white organic light emitting diode according to the second exemplary embodiment of the present invention illustrated in FIG. 8.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The configuration of the present invention and the operation and effect thereof will be clearly understood through the following detailed description. Before describing the present invention in detail, the same components are denoted by the same reference symbols as possible even if they are displayed on different drawings. In the case where it is judged that the gist of the present invention may be blurred to a known configuration, do.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 1 to 9.

FIG. 1 is a perspective view illustrating a white organic light emitting diode according to a first embodiment of the present invention, and FIG. 2 illustrates a thickness of each layer of the white organic light emitting diode according to the first embodiment of the present invention shown in FIG. 1. It is a section for.

1 and 2, a white organic light emitting diode according to a first exemplary embodiment of the present invention may include a first electrode 110, a second electrode 150, and a first electrode facing each other on a substrate 100. A first stack 120, a charge generation layer 130, and a second stack 140 stacked between the 110 and the second electrode 150 are included. The multi-stack white organic light emitting device includes a light emitting layer having a different color in each stack, and light of different colors emitted from the light emitting layer of each stack is mixed to realize white light. At this time, the total thickness of the organic layer of the white organic light emitting device has a range of 300nm to 600nm. The overall thickness H1 of the organic layer may include the first stack 120 except for the first electrode 110, the substrate 100, and the second electrode 150, the charge generation layer 130, and the second stack 140. It means the thickness included.

The first electrode 110 is a transparent conductive material such as transparent conductive oxide (TCO) as an anode, and is formed of indium tin oxide (ITO), indium zinc oxide (IZO), or IZO (IZO). .

The second electrode 150 is a cathode, and is formed of gold (Au), aluminum (AL), molybdenum (MO), chromium (Cr), copper (Cu), or the like as a reflective metal material such as aluminum.

The first stack 120 includes a first common layer 122, a first emission layer 124, and an electron transport layer (ETL) 126 between the first electrode 110 and the charge generation layer 130. They are stacked one by one.

The first common layer 122 is positioned between the first electrode 110 and the first emission layer 124 to serve as hole injection or hole transport. To this end, the first common layer may be configured of at least one hole transport layer (HTL) or hole injection layer (HIL). In this case, the number of stacked layers of the hole transport layer or the hole injection layer may be changed according to the characteristics of the device. In addition, the first common layer 122 is positioned at 0 nm to 300 nm (H3) from the first electrode 110 and is positioned at 100 nm to 600 nm (H2) from the second electrode 150. In addition, the thickness of the first common layer 122 is formed to have a range of 100 nm to 200 nm.

The first light emitting layer 124 is a single light emitting layer doped with a fluorescent blue dopant in one host. At this time, the wavelength band of the fluorescent blue dopant has a range of 400 nm to 500 nm. In addition, the first emission layer 124 is positioned between 100 nm and 400 nm (H5) from the first electrode 110.

A charge generation layer (CGL) 130 is formed between the stacks to control charge balance between the stacks. The charge generation layer 130 is positioned adjacent to the first stack 120 and adjacent to the N type organic layer 132 and the second stack 140 which inject electrons into the first stack 120. It is made of a P-type organic layer 134 positioned to inject holes into the second stack 140.

The N type organic layer 132 is formed of an organic layer containing alkali metals such as lithium (Li), sodium (Na), K (potassium), rubidium (Rb), Cs (cesium), and Fr (franxium). The P type organic layer 134 may be formed of an organic material.

In the second stack 140, a hole transport layer 142, a second light emitting layer 144, and a second common layer 146 are sequentially stacked between the second electrode 150 and the charge generation layer 130.

The second common layer 146 is positioned between the second electrode 150 and the second emission layer 146 to serve as electron injection or electron transport. To this end, the second common layer 146 may be configured of at least one Electron Transport Layer (ETL) or Electron Injection Layer (EIL). In this case, the stacking number of the electron transporting layer or the electron injection layer may be changed according to the characteristics of the device.

The second light emitting layer 144 may be a single light emitting layer formed by doping phosphorescent yellow-green dopant on one host or a single light emitting layer doped by phosphorescent yellow-green dopant on two hosts. At this time, the wavelength band of the phosphorescent yellow-green dopant has a range of 540 nm to 580 nm. As illustrated in FIG. 1, the white organic light emitting diode emits blue light from the first stack 120, and emits yellow light (YG) from the second stack 140, thereby implementing white light. The second light emitting layer 144 is positioned at 10 nm to 100 nm from the second electrode 150.

On the other hand, the improvement of the viewing angle according to the thickness (Cavity) of the entire organic layer and the thickness (Cavity) of each organic layer according to the first embodiment of the present invention will be described with reference to FIGS.

3 is a graph showing emission peaks of the conventional white organic light emitting diode, and FIG. 4 illustrates emission peaks of the organic laminate according to the first embodiment of the present invention. 5 is a graph illustrating an emission peak according to the first embodiment of the present invention. 6 is a graph comparing a white organic light emitting diode according to a first embodiment of the present invention with a conventional white organic light emitting diode.

First, the EL peak of the white organic light emitting device including the fluorescent blue light emitting layer of the first stack and the phosphorescent yellow-green light emitting layer of the second stack is a peak of photoluminescence indicating a unique color of each light emitting layer material. (Photoluminesecence Peak; hereinafter referred to as PL Peak) is determined by the product of the emission peak (hereinafter referred to as EM Peak) of the organic laminate in the organic light emitting device structure.

In this case, the characteristics of the viewing angle vary according to the overlapping area of the PL peak of the photoluminescence peak and the EM peak of the organic laminate. That is, as the area of overlap between the peak of the photoluminescence (PL Peak) and the emission peak (EM Peak) of the organic laminate increases, the light emission characteristic does not change according to the viewing angle, and the peak of the photoluminescence peak (PL Peak) and the emission peak of the organic laminate are As the area of overlap of the (EM Peak) decreases, the light emission characteristic decreases according to the viewing angle.

In general, the area where the PL peak of the fluorescent blue light emitting layer and the EM peak of the organic laminate overlap, the PL peak of the phosphorescent yellow-green light emitting layer, and the emission peak of the organic laminate ( The area where the EM peaks overlap is different. In other words, the area where the PL peak of the fluorescent blue light emitting layer and the EM peak of the organic laminate overlap is small and fluctuates depending on the viewing angle, and the photoluminescent peak of the phosphor yellow-green light emitting layer is PL peak. ) And the emission peak (EM Peak) of the organic laminate are large, and thus there is no variation depending on the viewing angle.

In the case of a multi-stack white organic light emitting device, light of different colors emitted from the light emitting layers of each stack is mixed to realize white light. When the light emitted from each light emitting layer has a different viewing angle, The corresponding white color coordinate is shifted.

Specifically, FIG. 3 illustrates a light emission peak for a fluorescent blue light emitting layer emitted from a first stack of a conventional white organic light emitting device and a light emission peak for a phosphorescent yellow-green light emitting layer emitted from a second stack. EL Peak) is shown. In this case, the conventional white organic light emitting diode displays an emission peak when the thickness of the common layer of the first stack is 100 nm or less. In addition, the first curves 20 and 20a show a viewing angle of 0 ° (front), the second curves 22 and 22a show a viewing angle of 15 degrees, and the third curves 24 and 24a show a viewing angle of 30 degrees and a fourth curve. (26, 26a) shows a viewing angle of 45 degrees, and the 5th curves 28 and 28a show a viewing angle of 60 degrees.

As shown in FIG. 3, the emission peaks of the fluorescent blue light emitting layers emitted from the first stack of the conventional white organic light emitting diodes (Blue EL Peak; 20, 22, 24, 26, 28) gradually decrease with the viewing angle. On the other hand, the emission peak (Yellow-Green EL Peak; 20a, 22a, 24a, 26a, 28a) for the yellow-green light emitting layer emitted from the second stack does not change with the viewing angle.

Accordingly, the blue EL peak gradually decreases as the angle range changes with the front side at 0 °, and the yellow-green EL peak becomes strong, and the color coordinate of white is shifted severely, resulting in viewing angle characteristics. Degrades.

As such, the overlapping area of the blue PL peak of the fluorescent blue light emitting layer and the EM peak of the organic laminate and the yellow-green PL peak of the phosphorescent yellow-green light emitting layer and the organic laminate Since the area where the EM peaks overlap, the viewing angles of the light emitting layers are different, thereby displaying uneven white light.

Accordingly, the white organic light emitting diode according to the first embodiment of the present invention shifts the emission peak (EM Peak) of the organic laminate as shown in FIG. 4 by controlling the overall thickness of the organic layer or the thickness of the organic material of each layer. The overlapping area between the light emission peak (Yellow-Green PL Peak) of the phosphorescent yellow-green light emitting layer and the emission peak (EM Peak) of the organic laminate is reduced. 4 shows an emission peak (EM Peak) 44 of the organic laminate according to the first embodiment of the present invention, and compared to the emission peak Max1 of the organic laminate according to the conventional white organic light emitting device. It can be seen that the emission peak of the organic laminate (Max2) according to the first embodiment is significantly shifted.

As such, the overlapping area of the light-emitting PL peak of the phosphorescent yellow-green light-emitting layer and the EM peak of the organic layered laminate becomes small and varies according to the viewing angle.

In other words, the white organic light emitting diode according to the first embodiment of the present invention has a light emission peak for a blue light emitting layer emitted from the first stack 120 as shown in FIG. 5 (Blue EL Peak; 10, 12, 14). (16,18) is gradually decreasing with the viewing angle, and the yellow-green EL peak (10a, 12a, 14a, 16a, 18a) for the yellow-green light emitting layer emitted from the second stack gradually increases with the viewing angle. Going down. The first curves 10 and 10a shown in FIG. 5 show a viewing angle of 0 ° (front), the second curves 12 and 12a show a viewing angle of 15 °, and the third curves 14 and 14a show a viewing angle of 30 °, The fourth curves 16 and 16a show a viewing angle of 45 degrees, and the fifth curves 18 and 18a show a viewing angle of 60 degrees.

In other words, the graphs of the blue EL peaks 10, 12, 14, 16 and 18 of the fluorescent blue light emitting layer emitted from the first stack 120 are reduced according to the viewing angle, and the phosphorescent yellow-green emitted from the second stack. The graph of the emission layer (Yellow-Green EL Peak; 10a, 12a, 14a, 16a, 18a) is also reduced according to the viewing angle, thereby realizing uniform white light even if the viewing angle is varied.

This, it can be seen that the viewing angle is improved as shown in FIG. The first curve 30 shown in FIG. 6 is a change curve according to the viewing angle of the conventional white organic light emitting device, and the second curve 32 is a viewing angle of the white organic light emitting device according to the first embodiment of the present invention. Along the curve. In this case, the conventional organic light emitting device is a change curve according to the viewing angle when the thickness of the first common layer of the first stack is less than 100 nm.

7 (a) and 7 (b) are diagrams for describing the light emission peak of the fluorescent blue light emitting layer and the light emission peak of the phosphorescent yellow-green light emitting layer according to the first embodiment of the present invention shown in FIG. 5, and FIG. (b) is a graph showing the multiplication of the photoluminescence peak (PL Peak) (Fig. 7 (a)) and the emission peak (EM Peak) (Fig. 7 (b)) of the organic laminate according to the first embodiment of the present invention admit.

Referring to FIGS. 7A and 7B, the first curve 40 illustrated in FIG. 7A shows a unique photoluminescence peak PL of the material of the blue light emitting layer according to the first embodiment of the present invention. Peak, and the second curve 42 shown in FIG. 7 (a) shows the inherent photoluminescence peak (PL Peak) of the material of the yellow-green light emitting layer according to the first embodiment of the present invention. In addition, the graph 44 illustrated in FIG. 7B illustrates an emission peak (EM Peak) of the organic laminate in the white organic light emitting diode structure according to the first embodiment of the present invention.

The photoluminescence peak (PL PeaK) 40 of the blue light emitting layer shown in FIG. 7 (a) and the photoluminescence peak (PL PeaK) 42 of the yellow-green light emitting layer shown in FIG. 7 (a) and the organic laminate shown in FIG. By multiplying the EM peak 44, the emission peak of the blue emission layer and the yellow-green emission layer of the first stack illustrated in FIG. 5 are displayed.

FIG. 8 is a perspective view illustrating a white organic light emitting diode according to a second exemplary embodiment of the present invention, and FIG. 9 illustrates the thickness of each layer of the white organic light emitting diode according to the second exemplary embodiment of the present invention illustrated in FIG. 8. It is a section for.

8 and 9, a white organic light emitting diode according to a second exemplary embodiment of the present invention may include a first electrode 110, a second electrode 150, and a first electrode facing each other on a substrate 100. A first stack 160, a charge generation layer 130, and a second stack 170 stacked between the 110 and the second electrode 150 are included. The multi-stack white organic light emitting device includes a light emitting layer having a different color in each stack, and light of different colors emitted from the light emitting layer of each stack is mixed to realize white light. At this time, the total thickness of the organic layer of the white organic light emitting device has a range of 300nm to 600nm. The overall thickness H1 of the organic layer may include the first stack 120 except for the first electrode 110, the substrate 100, and the second electrode 150, the charge generation layer 130, and the second stack 140. It means the thickness included.

In this case, since the first electrode 110, the second electrode 150, and the charge generation layer 130 are the same as the white organic light emitting diode according to the first embodiment of the present invention, a description thereof will be omitted.

The first stack 160 includes a hole injection layer (HIL) 162 and a first hole transport layer (HTL) 164 between the first electrode 110 and the charge generation layer 130. The second hole transport layer 165, the first emission layer 166, and the first electron transport layer (ETL) 168 are sequentially stacked. In this case, the first light emitting layer 166 is a single light emitting layer doped with a fluorescent blue dopant in one host. At this time, the wavelength band of the fluorescent blue dopant has a range of 400 nm to 500 nm. In addition, the first emission layer 166 is positioned between 100 nm and 400 nm (H5) from the first electrode 110. The hole injecting layer 162, the first hole transporting layer 164, and the second hole transporting layer 165 are formed to have a thickness ranging from 100 nm to 200 nm. In addition, the hole injection layer 162 is positioned at 0 nm to 300 nm (H3) from the first electrode, and is located at 100 nm to 600 nm (H2) from the second electrode.

The second stack 170 may include a third hole transport layer 172, a second light emitting layer 174, a second electron transport layer 176, and an electron injection layer 178 between the second electrode 150 and the charge generation layer 130. ) Are stacked one by one. In this case, as shown in FIGS. 8 and 9, the second light emitting layer 174 may be a single light emitting layer formed by doping a phosphorescent yellow-green dopant to one host, or a phosphorescent yellow-green to two hosts. It may be a single light emitting layer formed by doping the dopant. As illustrated in FIG. 1, the white organic light emitting diode emits blue light from the first stack 160 and emits yellow light YG from the second stack 170, thereby implementing white light. At this time, the wavelength band of the phosphorescent yellow-green dopant has a range of 540 nm to 580 nm. In addition, the second emission layer 174 is positioned at 10 nm to 100 nm from the second electrode 150.

The foregoing description is merely illustrative of the present invention, and various modifications may be made by those skilled in the art without departing from the spirit of the present invention. Accordingly, the embodiments disclosed in the specification of the present invention are not intended to limit the present invention. The scope of the present invention should be construed according to the following claims, and all the techniques within the scope of equivalents should be construed as being included in the scope of the present invention.

100 substrate 110: first electrode
120,160: first stack 122: first common layer
124,166 first light emitting layer 126 electron transport layer
130: charge generation layer 132: N type organic layer
134: P-type organic layer 140170: second stack
142 hole transport layer 144,174 second light emitting layer
146: second common layer 150: second electrode
162: hole injection layer 164: first hole transport layer
165: second hole transport layer 168: first electron transport layer
172: third hole transport layer 176: second electron transport layer
178: electron injection layer

Claims (8)

First and second electrodes opposed to each other on a substrate;
A first stack in which a first common layer, a first light emitting layer, and an electron transporting layer are sequentially stacked between the first electrode and the second electrode;
A second stack in which a hole transport layer, a second light emitting layer, and a second common layer are sequentially stacked between the first stack and the second electrode;
A charge generation layer formed between the first stack and the second stack to control charge balance between the stacks;
The thickness of the first common layer is a white organic light emitting device is formed in the range of 100nm ~ 200nm. The white organic light emitting diode of claim 1, wherein the first emission layer is formed of a single emission layer doped with a fluorescent blue dopant in one host. 2. The white organic light emitting diode of claim 1, wherein the second light emitting layer is formed by doping a phosphorescent yellow-green dopant to one host or by doping a phosphorescent yellow-green dopant to two hosts. . The white organic light emitting diode of claim 1, wherein the first common layer is positioned between the first electrode and the first light emitting layer to serve as hole injection or hole transport, and is formed of a hole injection layer or a hole transport layer. The white organic light emitting diode of claim 1, wherein the second common layer is positioned between the second electrode and the second light emitting layer to serve as an electron injection or electron transport layer, and is configured as an electron injection layer or an electron transport layer. The white organic light emitting diode of claim 1, wherein a thickness of the first stack, the second stack, and the charge generating layer is 300 nm to 600 nm. The white organic light emitting diode of claim 1, wherein the first common layer is positioned at 0 nm to 300 nm from the first electrode, and the first common layer is located at 100 nm to 600 nm from the second electrode. The white organic light emitting diode of claim 1, wherein the first emission layer is positioned at 100 to 400 nm from the first electrode, and the second emission layer is located at 100 to 600 nm from the second electrode.

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