KR101801291B1 - Organic electroluminescent diode - Google Patents

Abstract

The present invention relates to a positive electrode and a negative electrode facing each other; A light emitting material layer disposed between the first and second surfaces of the anode and the cathode, the light emitting material layer including red, green and blue organic emission patterns; A hole transport layer disposed between the anode and the light emitting material layer; An electron transport layer positioned between the cathode and the light emitting material layer; A capping layer located on a second side of the cathode and including first and second capping layers; And a light control layer disposed between the first and second capping layers and made of a metal material, wherein the first capping layer is positioned between the cathode and the light control layer. do.
Thereby, it has excellent light absorption and light scattering characteristics, and it is possible to prevent a color shift problem due to an increase in power consumption and a viewing angle.

Description

[0001] The present invention relates to an organic electroluminescent diode

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an organic light emitting diode, and more particularly, to an organic light emitting diode capable of reducing power consumption and minimizing a color shift problem depending on a viewing angle.

Until recently, CRT (cathode ray tube) was mainly used as display equipment. However, in recent years, flat panel display devices such as a plasma display panel (PDP), a liquid crystal display device (LCD), and an organic electroluminescent device (OELD) Have been widely studied and used.

Among the above flat panel display devices, the organic electroluminescent device is a self-luminous device, and lightweight and thin can be used because a backlight used in a liquid crystal display device which is a non-luminous device is not required.

In addition, it is advantageous in terms of power consumption as compared with liquid crystal display devices, has advantages of being able to drive DC low voltage, fast response speed, strong internal components, and high temperature resistance.

In particular, since the manufacturing process is simple, it is advantageous in that the production cost can be saved more than the conventional liquid crystal display equipment.

1 is a view showing a basic pixel structure of a general active matrix organic electroluminescent device.

As shown, one pixel of the active matrix type organic electroluminescent device includes a switching thin film transistor STr, a driving thin film transistor DTr, a storage capacitor StgC, and an organic light emitting diode E, .

That is, a gate line GL is formed in a first direction, a data line DL is formed in a second direction intersecting the first direction, and a voltage is applied to the data line DL, A power supply line PL is formed.

A switching thin film transistor STr is formed at the intersection of the data line DL and the gate line GL and a driving thin film transistor DTr electrically connected to the switching thin film transistor STr is formed have.

At this time, the driving thin film transistor DTr is electrically connected to the organic light emitting diode E. That is, the first electrode, which is one terminal of the organic electroluminescent diode E, is connected to the drain electrode of the driving thin film transistor DTr, and the second electrode, which is the other terminal, is connected to the power supply line PL. At this time, the power supply line (PL) transfers the power supply voltage to the organic light emitting diode (E). A storage capacitor StgC is formed between the gate electrode and the source electrode of the driving thin film transistor DTr.

Therefore, when a signal is applied through the gate line GL, the switching thin film transistor STr is turned on and the signal of the data line DL is transmitted to the gate electrode of the driving thin film transistor DTr, The thin film transistor DTr is turned on so that light is output through the organic light emitting diode E. At this time, when the driving thin film transistor DTr is turned on, a level of a current flowing from the power supply line PL to the organic light emitting diode E is determined. Accordingly, the organic light emitting diode E The storage capacitor StgC is capable of maintaining a constant gate voltage of the driving thin film transistor DTr when the switching thin film transistor STr is turned off The level of the current flowing through the organic light emitting diode E can be kept constant until the next frame even if the switching thin film transistor STr is turned off.

2, the organic light emitting diode E includes an anode 10 formed on each of the red, green, and blue pixel regions Rp, Gp, and Bp, and an anode 10 formed on the hole transport layer 12, emitting material layer including a hole transporting layer, a red organic emission pattern 14, a green organic emission pattern 16 and a blue organic emission pattern 18, an electron transporting layer 20, And a cathode. Although not shown, a hole injection layer may be positioned between the anode 10 and the hole transport layer 12, and an electron injection layer may be positioned between the cathode 22 and the electron transport layer 20. [

When a voltage is applied to the anode 10 and the cathode 22 in the organic electroluminescent diode E having such a structure, holes and electrons are injected through the hole transport layer 12 and the electron transport layer 20, respectively, And are combined with each other in the light emitting material layer to emit light. However, conventional organic light emitting diodes have limitations in light output efficiency and color characteristics.

In addition, since a polarizing plate must be attached to prevent deterioration of visibility due to external light, there is a problem that power consumption is increased.

In the present invention, the light output efficiency and the color characteristic of the organic electroluminescent diode are improved. It is also intended to prevent an increase in power consumption by the polarizing plate.

Thereby providing a high-efficiency organic electroluminescent device capable of providing a high-quality image.

In order to solve the above-mentioned problems, there are provided a positive electrode and a negative electrode facing each other; A light emitting material layer disposed between the first and second surfaces of the anode and the cathode, the light emitting material layer including red, green and blue organic emission patterns; A hole transport layer disposed between the anode and the light emitting material layer; An electron transport layer positioned between the cathode and the light emitting material layer; A capping layer located on a second side of the cathode and including first and second capping layers; And a light control layer disposed between the first and second capping layers and made of a metal material, wherein the first capping layer is positioned between the cathode and the light control layer. do.

And the first capping layer is formed of a material having a hole mobility higher than an electron mobility.

And the hole mobility of the material of the first capping layer is 10 ^-9 to 10 ^-1 m ² / V · s.

The light control layer may be formed of any one of silver, magnesium-silver alloy, and samarium.

The light control layer is characterized by having a metal cluster shape.

And the thickness of the first capping layer is smaller than the thickness of the second capping layer.

The hole transport layer may include a first hole transport layer corresponding to all the red, green and blue organic emission patterns, a second hole transport layer corresponding to the red organic emission pattern, and a third hole transport layer corresponding to the green organic emission pattern .

And the thickness of the second hole transporting layer is larger than the thickness of the third hole transporting layer.

Since the organic electroluminescent diode according to the present invention can improve the visibility even without a polarizing plate, power consumption can be reduced.

Also, an attempt is made to solve the problem of color shift depending on the viewing angle in an organic light emitting diode.

In addition, the light output efficiency and color characteristics of the organic light emitting diode can be improved by utilizing the microcavity effect.

1 is a view showing a basic pixel structure of a general active matrix organic electroluminescent device.
2 is a schematic cross-sectional view of a general organic light emitting diode.
3 is a schematic cross-sectional view of an organic light emitting diode according to a first embodiment of the present invention.
4 is a schematic cross-sectional view of an organic light emitting diode according to a second embodiment of the present invention.
5 is a schematic cross-sectional view for explaining a light control layer in an organic light emitting diode according to a second embodiment of the present invention.
6 is a graph for explaining a color shift problem by an organic light emitting diode according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings.

3 is a schematic cross-sectional view of an organic light emitting diode according to a first embodiment of the present invention.

The organic light emitting diode includes an anode 110 formed on each of red, green and blue pixel regions Rp, Gp and Bp, a first hole transporting layer 112 and a second electrode formed on the red pixel region Rp. A hole transport layer 114, a third hole transport layer 116 formed on the green pixel region Gp, and a red organic emission pattern 122, a green organic emission pattern 124, and a blue organic emission pattern 126, An electron transport layer 130, a cathode 140, and a capping layer 150. The electron transport layer 130 may be formed of a material having a high crystallinity. Although not shown, a hole injecting layer may be disposed between the anode 110 and the first hole transporting layer 112, and an electron injecting layer may be disposed between the cathode 140 and the electron transporting layer 130 have.

Although not shown, in the organic electroluminescent device, power supply lines extending in parallel with any one of a gate wiring and a data wiring which intersect each other on the substrate and define the respective pixel regions Rp, Gp, Bp are located And a switching thin film transistor connected to the gate wiring and the data wiring and a driving thin film transistor connected to the switching thin film transistor are disposed in the respective pixel regions Rp, Gp and Bp. The driving thin film transistor is connected to the anode 110.

The anode 110 is a reflective electrode and includes a layer of a transparent conductive material having a high work function such as indium-tin-oxide (ITO) and a layer of a reflective material such as silver or silver alloy can do.

The first and second hole transporting layers 114 and 116 are formed on the red, green, and blue pixel regions Rp, Gp, and Bp, respectively, (Rp, Gp).

In addition, the cathode 140 is made of an alloy of magnesium and silver (Mg: Ag) and has a transflective property. That is, the light emitted from the light emitting material layer is displayed to the outside through the cathode 140. Since the cathode 140 has a transflective property, some of the light is directed to the anode 110 again.

Thus, repeated reflection occurs between the anode 110 and the cathode 140 acting as a reflective layer, which is referred to as a microcavity effect. That is, light is repeatedly reflected in the cavity between the anode 110 and the cathode 140, thereby increasing the light efficiency.

Since the wavelengths of light emitted from the red, green and blue organic emission patterns 122, 124 and 126 are different, the thickness of the cavity defined by the distance between the anode 110 and the cathode 140 is Different. That is, in the red pixel region Rp in which red light having the longest wavelength is emitted, the anode 110 and the cathode 140 are separated from each other by the first distance d1, and the blue light, The anode 110 and the cathode 140 are spaced apart from each other by a third distance d3 in the pixel region Bp and the anode 110 and the cathode 140 are separated from each other in the green pixel region Gp, ) Is smaller than the first distance (d1) and larger than the third distance (d3). (d1 > d2 > d3)

Accordingly, the first hole transport layer 112 is formed on the entire surface of the red, green, and blue pixel regions Rp, Gp, and Bp based on the wavelength of the green light, and the second hole transport layer 112 is formed on the red pixel region Rp. A hole transport layer 114 is further formed and a third hole transport layer 116 having a thickness smaller than that of the second hole transport layer 114 is formed in the green pixel region Gp.

The capping layer 150 is formed for increasing the light extracting effect and is formed of a host material of the hole transporting layer 112, 114, 116 and the electron transporting layer 130 and the organic light emitting patterns 122, 124, .

The organic light emitting diode having the above-described structure has an effect of increasing the light output efficiency and obtaining a clear color characteristic by utilizing the microcavity effect.

However, the organic light emitting diode has a problem that the visible light is deteriorated due to reflection of external light, and a polarizing plate for preventing the organic light emitting diode is formed on the capping layer 150. In the case of using a polarizing plate, power consumption is increased in order to obtain the same luminance due to loss of light. In addition, the above-described organic light emitting diode has a color shift problem depending on the viewing angle.

The organic light emitting diode of the second embodiment for solving the above problem will be described.

FIG. 4 is a schematic cross-sectional view of an organic light emitting diode according to a second embodiment of the present invention, FIG. 5 is a schematic cross-sectional view illustrating an organic light emitting diode according to a second embodiment of the present invention, to be.

Referring to FIG. 4, the organic light emitting diode according to the second embodiment of the present invention includes a cathode 210 formed on each of the red, green, and blue pixel regions Rp, Gp, and Bp, a first hole transport layer 212 A second hole transport layer 214 formed on the red pixel region Rp, a third hole transport layer 216 formed on the green pixel region Gp, a red organic emission pattern 222, An electron transport layer 230, a cathode 240, a light control layer 260, and a first and a second capping layer (not shown) 252, and 254, respectively.

Although not shown, a hole injection layer may be located between the anode 210 and the first hole transport layer 212, and an electron injection layer may be positioned between the anode 240 and the electron transport layer 230 have.

The anode 210 is a reflective electrode. The anode 210 may include a transparent conductive material layer having a high work function such as indium-tin-oxide (ITO) and a reflective material such as silver (Ag) Layer.

The first and second hole transporting layers 214 and 216 are formed on the red, green, and blue pixel regions Rp, Gp, and Bp, respectively, (Rp, Gp).

In addition, the cathode 240 is made of an alloy of magnesium and silver (Mg: Ag) and has a transflective property. That is, the light emitted from the light emitting material layer is displayed to the outside through the cathode 240. Since the cathode 240 has a transflective property, a part of the light is directed to the anode 210 again.

Thus, repeated reflection occurs between the anode 210 and the cathode 240 acting as a reflective layer, which is referred to as a microcavity effect. That is, light is repeatedly reflected in the cavity between the anode 210 and the cathode 240, thereby increasing the light efficiency.

Since the wavelengths of light emitted from the red, green and blue organic emission patterns 222, 224 and 226 are different from each other, the thickness of the cavity defined by the distance between the anode 210 and the cathode 240 is Different. That is, in the red pixel region Rp in which red light having the longest wavelength is emitted, the anode 210 and the cathode 240 are spaced apart from each other by a first distance (d1 in FIG. 3) The anode 210 and the cathode 240 are spaced apart from each other by a third distance d3 in the blue pixel region Bp and the green pixel region Gp in which green light is emitted, ) And the cathode 240 is smaller than the first distance d1 and larger than the third distance d3 in Fig. 3).

Accordingly, the first hole transport layer 212 is formed on the entire surface of the red, green, and blue pixel regions Rp, Gp, and Bp based on the wavelength of the green light, and the second hole transport layer 212 is formed on the red pixel region Rp. A hole transport layer 214 is further formed and a third hole transport layer 216 having a thickness smaller than that of the second hole transport layer 214 is formed in the green pixel region Gp.

The capping layer 250 is formed to increase the light extracting effect and includes a first capping layer 252 located on the cathode 240 and a second capping layer 254 located on the light control layer 260 ). That is, the light control layer 260 is positioned between the first and second capping layers 252 and 254.

In this case, the first capping layer 252 is formed of a material having a hole mobility greater than an electron mobility. For example, the first capping layer 252 may include any of host materials of the first through third hole transporting layers 212, 214, and 216 and the red, green, and blue organic light emitting patterns 222, 224, and 226 It can be made of the same material as one. The first capping layer 252 may be formed of an anthracene-based material, a fluorene-based material, or a pyrene-based material. For example, the material of the first capping layer 252 has a hole mobility of 10 ^-9 to 10 ^-1 m ² / V · s.

Meanwhile, the second capping layer 254 may be made of a material having the same characteristics as the first capping layer 252, or may be made of a material having a high electron mobility. For example, the second capping layer 254 may be formed of an organic material having good hole mobility, that is, the first to third hole transporting layers 212, 214, 216 and the red, , 224, and 246, or may be made of a material having excellent electron mobility characteristics such as the electron transport layer 230.

The light control layer 260 is disposed on the first capping layer 252 and is made of a metal material.

For example, a transition metal, an alkali metal, an alkaline earth metal, a rare earth metal, and an alloy thereof. For example, silver (Ag), magnesium-silver alloy (Mg: Ag), and samarium (Sm). When the light control layer 260 is made of a magnesium-silver alloy (Mg: Ag), the content of silver may be about 5 to 10% by weight. The light control layer 260 has a thickness of about 20 to 200 A, preferably 60 to 120 A.

As described above, the first capping layer 252 is made of a material having a hole mobility higher than that of the electron mobility. When the metal material is deposited on the first capping layer 252, 260 are formed in the form of metal clusters or metal grains without forming a film form.

5, the light control layer 260 located between the first capping layer 252 and the second capping layer 254 may have a hole mobility higher than the electron mobility, Is deposited on the pinning layer 252 to form a cluster.

According to the shape of the light control layer 260, light scattering and absorption are simultaneously increased. That is, surface plasmon resonance occurs in the optical control layer 260 of the above-described type, so that the optical field increases around the grain, thereby causing scattering of light. In addition, the optical field increased by surface plasmon resonance increases the light absorption by the organic film, i.e., the first and second capping layers 252 and 254, which are located close to the metal clusters.

Light absorption by the light control layer 260 is proportional to the thickness of the light control layer 260 and light scattering by the light control layer 260 is inversely proportional to the thickness of the light control layer 260 .

That is, the light control layer 260 of the present invention has a thickness of about 20 to 200 A. For example, if the light control layer 260 has a thickness of 20 A, the light scattering property becomes strong. If the light control layer 260 has a thickness of about 200 A, It becomes.

Meanwhile, the thickness of the first capping layer 252 is smaller than that of the second capping layer 254. The first capping layer 252 has a thickness of about 50 to 150 A and the second capping layer 254 has a thickness of about 450 to 650 A.

If the thickness of the first capping layer 252 is too small, the light control layer 260 is not formed in a cluster shape due to the electron mobility characteristic of the cathode 240. Also, if the first capping layer 252 is too thick, the distance between the light control layer 260 and the cathode 240 increases, and blurring due to diffuse reflection occurs. Therefore, the thickness of the first capping layer 252 can be adjusted to a thickness of about 20 to 150 A. The thickness of the second capping layer 254 may be about the thickness of the first capping layer 252 because the capping layer 250 needs to have a thickness of about 500 to 800 A in order to obtain a light extraction effect. Can be adjusted accordingly.

As described above, the organic light emitting diode according to the second embodiment of the present invention deposits a metal material on the first capping layer 252 having a hole mobility higher than that of the electron mobility to form a light control layer 260 are formed, the light absorption and scattering characteristics can be improved.

In the conventional organic light emitting diode, a polarizing plate is used to improve the visibility and power consumption is increased. However, in the present invention, since the visibility is improved by the light control layer 260 having excellent light absorption characteristics, a polarizing plate is not required. Accordingly, the power consumption can be reduced as compared with the conventional organic light emitting diode. On the other hand, an anti-reflection film may be formed on the second capping layer 254 to further improve the visibility and suppress the increase of the power consumption.

Also, in the conventional organic light emitting diode, color shift problem occurs according to the viewing angle. In the present invention, the light control layer 260 having excellent light scattering characteristics can also solve the color shift problem according to the viewing angle.

Hereinafter, the characteristics of the light control layer will be compared with each other through comparative examples and experimental examples.

Comparative Example

The first hole transport layer 1160A is laminated on the reflective anode connected to the thin film transistor.

A second hole transport layer 680A corresponding to the red pixel region and a third hole transport layer 350A corresponding to the green pixel region are formed on the hole transport layer in order to obtain a micro cavity effect by adjusting the optical distance in accordance with each color, And a red organic emission pattern 360A, a green organic emission pattern 200A, and a blue organic emission pattern 200A were sequentially deposited. Thereafter, an electron transport layer 360A was deposited for electron entry.

Mg: Ag (110A: 10%) was deposited as a transflective cathode on the electron transport layer. A capping layer 630A and a polarizing plate for improving visibility were attached on the cathode to improve light extraction efficiency.

1-4 Experimental Example

The first to third hole transporting layers, the red, green and blue organic emission patterns, the electron transporting layer and the cathode were laminated under the same conditions as the first comparative example, and the first capping layer 100A, 1 capping layer, and a second capping layer 530A on the light control layer were continuously deposited on the light controlling layer. The thickness of the light control layer was 60 (Experimental Example 1), 80 (Experimental Example 2), 100 (Experimental Example 3) and 120 (Experimental Example 4) A.

5-7 Experimental Example

The first to third hole transporting layers, the red, green and blue organic emission patterns, the electron transporting layer and the cathode were laminated under the same conditions as the first comparative example, and the first capping layer 100A, 1 capping layer, and a second capping layer 530A on the light control layer were continuously deposited on the light controlling layer. The thickness of the light control layer was 80 (Experimental Example 5), 100 (Experimental Example 6) and 120 (Experimental Example 7) A.

The experimental results of Comparative Example and Experimental Examples 1 to 7 are summarized in Table 1 below.

Color coordinates
efficiency
Power Consumption
[mW] Rx Gx By white red green blue Comparative Example 0.669 0.187 0.058 10.7 15.8 22.8 1.7 866 Experimental Example 1 0.660 0.184 0.054 21.8 31.7 48.8 3.2 450 Experimental Example 2 0.658 0.179 0.051 20.2 29.9 44.9 2.8 483 Experimental Example 3 0.659 0.179 0.052 18.9 28.5 41.1 2.7 512 Experimental Example 4 0.653 0.161 0.045 14.9 23.3 33.6 1.8 632 Experimental Example 5 0.658 0.173 0.049 19.4 30.6 43.3 2.5 503 Experimental Example 6 0.656 0.164 0.046 17.4 27.4 38.4 2.1 558 Experimental Example 7 0.652 0.151 0.042 14.1 22.4 31.9 1.6 662

As can be seen from Table 1, in the case of Experimental Example 1-7 using the light control layer, it is understood that the power consumption is reduced as compared with the Comparative Example while maintaining the visibility. This is because the visibility can be maintained without the polarizing plate by the light absorption property of the light control layer, and the increase in the power consumption by the polarizing plate is prevented.

6 is a graph showing the color shift phenomenon of Comparative Example and Experimental Example 1-4. Referring to FIG. 6, it can be seen that color shifts according to viewing angles are suppressed in Experimental Examples 1 to 3 (graph BD) including a light control layer as compared with a comparative example (Graph A) which does not include a light control layer .

This is because the viewing angle dependence is weakened by the scattering property of the light control layer.

As described above, the organic light emitting diode of the present invention includes a light control layer in the form of a metal cluster to improve light scattering and light absorption characteristics. The polarizing plate for improving the visibility is not required by the improvement of the light absorption property, so that the power consumption can be reduced.

Further, the color shift problem due to the viewing angle can be solved by the light scattering characteristic.

The present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention.

210: anode 212, 214, 214: hole transport layer
222, 224, 226: organic light emission pattern
230: electron transport layer 240: cathode
250: capping layer 260: light control layer

Claims (8)

An anode and a cathode opposing each other;
A light emitting material layer disposed between the first and second surfaces of the anode and the cathode, the light emitting material layer including red, green and blue organic emission patterns;
A hole transport layer disposed between the anode and the light emitting material layer;
An electron transport layer positioned between the cathode and the light emitting material layer;
A capping layer located on a second side of the cathode and including first and second capping layers;
And a light control layer disposed between the first and second capping layers and made of a metal material,
Wherein the first capping layer is positioned between the cathode and the light control layer.
The method according to claim 1,
Wherein the first capping layer is made of a material having a hole mobility higher than an electron mobility.
3. The method of claim 2,
And the hole mobility of the material of the first capping layer is in the range of 10 ^-9 to 10 ^-1 m ² / V · s.
The method according to claim 1,
Wherein the light control layer is made of silver, magnesium-silver alloy, or samarium.
The method according to claim 1,
Wherein the light control layer has a metal cluster shape or a metal grain shape.
The method according to claim 1,
Wherein the thickness of the first capping layer is less than the thickness of the second capping layer.
The method according to claim 1,
The negative electrode has a semi-permeable property,
The hole transport layer may include a first hole transport layer corresponding to all the red, green and blue organic emission patterns, a second hole transport layer corresponding to the red organic emission pattern, and a third hole transport layer corresponding to the green organic emission pattern The organic electroluminescent device comprising:
8. The method of claim 7,
And the thickness of the second hole transporting layer is greater than the thickness of the third hole transporting layer.

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