KR20150036908A - Organic light emitting display - Google Patents

Abstract

Provided is an organic light emitting device which lowers driving voltage and extends lifetime. The organic light emitting display device according to the present invention comprises a first and second electrode facing each other on a substrate; at least two light emitting units formed on the first and second electrodes; a first P type charge generating layer including an N type charge generating layer and a P type charge generating layer formed by sequentially laminated between the light emitting units, wherein the P type charge generating layer is characterized by including a first P type charge generating layer formed on the N type charge generating layer and including a P type dopant; and a second P type charge generating layer formed on a first P type charge generating layer and including an electron drawing group.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an organic light-

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an organic light emitting display capable of lowering a driving voltage and improving lifetime.

Recently, as the information age has come to the information age, a display field for visually expressing electrical information signals has been rapidly developed. In response to this, a variety of flat display devices having excellent performance such as thinning, light weight, and low power consumption have been developed. Device) is being developed.

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).

Particularly, the organic light emitting display device is advantageous in that it has a higher response speed and a larger light emitting efficiency, luminance, and viewing angle than other flat panel display devices. Such an OLED display includes a cathode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode.

In such an organic light emitting diode display, a single light emitting unit including a hole injecting layer, a hole transporting layer, a light emitting layer, an electron transporting layer, and an electron injecting layer may be disposed between the first and second electrodes. Emitting unit in which a plurality of single light-emitting units are formed between the light-emitting units.

However, in the case of the structure of the conventional multi-emission unit, the number of organic layers increases between the first and second electrodes, which increases the driving voltage. In addition, the OLED display device having a conventional multi-emission unit has a problem in that the efficiency is not as high as that of the OLED display device as compared with the OLED display device having a single emission unit, and the lifetime and efficiency are reduced.

In order to solve the above-described problems, the present invention provides an organic light emitting diode display capable of lowering a driving voltage and improving lifetime.

According to an aspect of the present invention, there is provided an organic light emitting diode display comprising: first and second electrodes opposing each other on a substrate; At least two light emitting units formed between the first and second electrodes; An N-type charge generation layer and a P-type charge generation layer sequentially formed between the light emitting units, wherein the P-type charge generation layer is formed on the N-type charge generation layer and includes a P-type dopant A first P-type charge generation layer; And a second P-type charge generation layer formed on the first P-type charge generation layer and including an electron attracting group.

The first P-type charge generation layer is made of only the P-type dopant, or is composed of the P-type dopant and the P-type host.

When the first P-type charge generation layer comprises the P-type dopant and the P-type host, the volume ratio of the P-type dopant in the first P-type charge generation layer is 1 to 10%.

The P-type dopant of the second P-type charge generation layer is formed of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), and the P- And the host is formed of at least one of NPB, CBP, NPD, TPD, TBA, and TTA.

Wherein the electron attracting group is formed of at least one of CN, NO2, F, Cl, Br, and I, and the second P-type charge generating layer has a lowest unoccupied molecular orbital (LUMO) Value.

And the second P-type charge generation layer is formed of HATCN.

The first and second P-type charge generation layers each have a thickness of 50 Å to 500 Å, and the total thickness of the P-type charge generation layer composed of the first and second P-type charge generation layers is 100 Å to 1000 Å do.

In the organic light emitting display according to the present invention, a charge generation layer comprising an N-type charge generation layer and first and second P-type charge generation layers is formed between a plurality of light emitting units. That is, since the two charge separation regions and one charge recombination region are formed in the organic light emitting display device according to the present invention, more holes and electrons are generated than conventional organic light emitting display devices having a single-layer P-type charge generation layer can do. Accordingly, in the organic light emitting diode display according to the present invention, the injection of charges is smooth and the driving voltage is lowered, and the amount of holes and electrons in the light emitting layer becomes uniform, so that the luminous efficiency is increased and the lifetime is improved. As a result, the efficiency of white can be increased and power consumption can be lowered.

1 is a perspective view illustrating an organic light emitting display according to an embodiment of the present invention.
2 is a diagram showing a band diagram of the organic light emitting display shown in FIG.
FIGS. 3A to 3C are views for explaining the characteristics of the organic light emitting diode display according to Comparative Examples 1 and 2 and the embodiment of the present invention.
4 is a cross-sectional view illustrating an OLED display device having a color filter according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings and embodiments.

1 is a cross-sectional view illustrating an organic light emitting display according to an embodiment of the present invention.

1 includes first and second electrodes 102 and 104 facing each other on a substrate 101, first and second light emitting units 110 and 120 formed between the first and second electrodes 102 and 104, And a charge generation layer 130 located between the first and second light emitting units 110 and 120. [

At least one of the first and second electrodes 102 and 104 is formed as a transflective electrode. When the first electrode 102 is a transflective electrode and the second electrode 104 is a reflective electrode, the light is emitted to the bottom. When the second electrode 104 is a transflective electrode and the first electrode 102 is a reflective electrode, it is a top emission structure that emits light to the top. Meanwhile, both the first and second electrodes 102 and 104 may be a double-sided light emitting structure which is formed as a transmitting electrode and emits light to upper and lower portions.

As the semi-transparent electrode, a transparent conductive material such as indium tin oxide (ITO) and indium zinc oxide (IZO), and a conductive material such as aluminum (Al), gold (Au), molybdenum (MO) (Al), gold (Au), molybdenum (MO), chromium (Cr), copper (Cu), or copper (Cu) is used as the reflective electrode. , LiF, or the like, or a multi-layered structure using them.

In the embodiment of the present invention, the first electrode 102 is formed as a transflective electrode as an anode, and the second electrode 104 is formed as a cathode as a reflective electrode.

The first light emitting unit 110 is formed between the first electrode 102 and the N-type charge generating layer 132. The first light emitting unit 110 includes a hole injection layer (HIL) 112, a first hole transport layer (HTL1) 114, a first light emitting layer (EML1) 116, And a first electron transport layer (ETL1) 118. The first hole transport layer 114 supplies holes from the first electrode 102 to the first emission layer 116 and the first electron transport layer 118 supplies electrons from the N-type charge generation layer 132 to the first Light is supplied to the light emitting layer 116. In the first light emitting layer 116, holes supplied through the first hole transporting layer 114 and electrons supplied through the first electron transporting layer 118 are recombined to generate light.

The second light emitting unit 120 is formed between the second electrode 104 and the P-type charge generating layer 134. The second light emitting unit 120 includes a second hole transport layer 124 (HTL2), a second light emitting layer 126 (EML2), and a second electron transport layer 128 (ETL2) sequentially formed on the P-type charge generation layer 134, Respectively. The second hole transport layer 124 supplies holes from the P-type charge generation layer 134 to the second light emitting layer 126 and the second electron transport layer 128 supplies electrons from the second electrode 104 to the second Light is supplied to the light emitting layer 126. In the second light emitting layer 126, the holes supplied through the second hole transporting layer 124 and the electrons supplied through the second electron transporting layer 128 are recombined to generate light.

Here, the first light emitting layer 116 emits blue light into a light emitting layer containing a fluorescent or phosphorescent blue dopant and a host, and the second light emitting layer 126 emits yellow light with a phosphorescent or phosphorescent yellow-green dopant and a host- So that white light can be realized. In addition, other fluorescent or phosphorescent dopants can be used to realize white light.

The charge generation layer 130 includes an N-type charge generation layer 132 and a P-type charge generation layer 134 which are sequentially stacked.

The N-type charge generating layer 132 is disposed on the first electron transporting layer 118 closer to the first electrode 102 than the P-type charge generating layer 134. The N-type charge generation layer 132 is formed between the interface between the first P-type charge generation layer 134a and the second P-type charge generation layer 134b and the interface between the second P-type charge generation layer 134b and the second hole And attracts electrons which are n-type electric charges separated at the interface between the light-emitting layer 124 and the light- The N-type charge generation layer 132 is formed by doping alkali metal particles into an organic material.

The P-type charge generation layer 134 is disposed closer to the second electrode 104 than the N-type charge generation layer 132. The P-type charge generation layer 134 includes a first P-type charge generation layer 134a and a second P-type charge generation layer 134b which are sequentially stacked on the N-type charge generation layer 132.

The first P-type charge generation layer 134a draws holes at the interface with the N-type charge generation layer 132 to generate holes. To this end, the first P-type charge generation layer 134a is formed by a mixture of a P-type host and a P-type dopant that attracts holes, or is formed of only a P-type dopant. Here, the volume ratio of the P-type dopant in the first P-type charge generation layer 134a is 1 to 100%, preferably 1 to 10%. At this time, if the volume ratio of the P-type dopant is less than 1% or exceeds 100%, holes and electrons are not properly generated in the first P-type charge generation layer 134a.

The P-type dopant is formed, for example, with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). The P-type dopant doped in the first P-type charge generating layer 134a can fill the pores of the N-type charge generating layer 132 having a plate-like structure adjacent to the first P-type charge generating layer 134a, Can be improved.

The P-type host is formed of the same or different material as at least one of the first and second hole transporting layers 114 and 124. For example, the P-type host is formed of at least one of NPB, CBP, NPD, TPD, TBA, and TTA.

The second P-type charge generation layer 134b attracts electrons at the interface with the second hole transport layer 124 to generate electrons. To this end, the second P-type charge generation layer 134b is formed of a material including an electron withdrawing group which is an n-type organic material. Here, the electron attracting group is formed of at least one of CN, NO2, F, Cl, Br, For example, the second P-type charge generation layer 134b is formed of HAT-CN. The second P-type charge generation layer 134b has a lowest unoccupied molecular orbital (LUMO) level of -5 eV or less.

Each of the first and second P-type charge generation layers 134a and 134b has a thickness of 50 to 500 ANGSTROM and a P-type charge generation layer (first and second P-type charge generation layers 134a and 134b) 134 are formed to have a total thickness of 100 ANGSTROM to 1000 ANGSTROM. Here, when the total thickness of the P-type charge generation layer 134 is less than 100 Å or exceeds 1000 Å, holes and electrons are not properly generated in the first and second P-type charge generation layers 134a and 134b.

The interface between the first P-type charge generation layer 134a and the N-type charge generation layer 134b and the interface between the second P-type charge generation layer 134b and the second hole transport layer 124 are formed in the charge separation region (CS), electrons as an n-type charge and holes as a p-type charge are generated and separated as shown in Fig. The interface between the first and second P-type charge generation layers 134a and 134b is a charge recombination region CR, and holes and electrons are recombined.

The electrons separated in the charge separation region CS are transferred to the first light emitting unit 110 through the N-type charge generating layer 132 and are emitted from the first light emitting layer 116 of the first light emitting unit 110 to the first electrode 102) to form excitons and emit visible light while emitting energy.

The holes separated in the charge separation region CS move to the second light emitting unit 120 and combine with electrons moved from the second electrode 104 in the second light emitting layer 126 to form excitons, It can emit light in the ray area.

Thus, in the present invention, the interface between the first P-type charge generation layer 134a and the N-type charge generation layer 134b and the interface between the second P-type charge generation layer 134b and the second hole transport layer 124 Two charge separation regions CS are formed at each interface and one charge recombination region CR at the interface between the first and second P-type charge generation layers 134a and 134b is formed. Accordingly, the present invention can generate more holes and electrons than conventional organic light emitting display devices having a single-layer P-type charge generation layer, and the injection of charge is smooth, thereby lowering the driving voltage. In particular, when any one of the first and second light emitting layers 116 and 126 is formed as a blue light emitting layer, the amount of electrons transferred to the blue light emitting layer increases, so that the amount of holes and electrons in the blue light emitting layer becomes uniform, . As a result, the efficiency of white can be increased and power consumption can be lowered.

Table 1 shows the characteristics of Comparative Examples 1 and 2 and the white organic light emitting device according to the embodiment of the present invention.

Current density
(mA / cm ² ) Driving voltage
(V) efficiency
(cd / A) Quantum efficiency
QE (%) Color coordinates
CIEx Color coordinates
CIEy life span
(T95) Comparative Example 1
10 3.6 75.3 22.3 0.448 0.541 100%
50 4.2 63.3 18.6 0.445 0.544 Comparative Example 2
10 3.7 74.1 22.0 0.449 0.541 113.9%
50 4.5 62.1 18.3 0.445 0.544 Example
10 3.5 75.3 22.3 0.449 0.541 152.1%
50 4.1 62.8 18.5 0.445 0.544

In Table 1, Comparative Example 1 is an organic electroluminescent device having a single-layer P-type charge generation layer made of HATCN. In Comparative Example 2, an organic electric field including a first P type charge generation layer made of HATCN and a second P type charge generation layer made of a P type charge generation layer made of a P type dopant of F4TCNQ and a P type type host of NPD Emitting device. An embodiment of the present invention is a multi-layer P-type charge control layer comprising a first P-type charge generation layer 134a made of a P-type dopant of F4TCNQ and a P-type host of NPD, and a second P-type charge generation layer 134b made of HATCN And an organic electroluminescent element having a charge generation layer. The embodiment of Table 1 is only an example for helping to understand the characteristics of the present invention, but the present invention is not limited thereto.

As shown in Table 1 and FIG. 3A, the embodiment of the present invention shows that the driving voltage for obtaining a current density of 10 mA / cm ^{2 and} a current density of 50 mA / cm ² is lower by 0.1 V than that of Comparative Example 1 . Further, in the embodiment of the present invention, the driving voltage for obtaining a current density of 10 mA / cm ^{2 and} a current density of 50 mA / cm ² is 0.2 V and 0.4 V lower than that of Comparative Example 2, and the quantum efficiency is increased by 0.3% . In addition, it can be seen that the embodiment of the present invention increases life span by about 13.9% and 52.1%, respectively, as compared with Comparative Examples 1 and 2 as shown in Table 1. As described above, it can be seen that the driving voltage of the embodiment of the present invention is lowered by 0.1 to 0.4 V and the lifetime is increased by about 13.9% to 52.1% in comparison with the comparative examples 1 and 2.

As shown in FIG. 3B, it can be seen that the embodiment of the present invention has a maximum intensity of light in comparison with Comparative Examples 1 and 2 at a wavelength of about 564 nm that emits yellow-green (YG) As shown in the figure, the efficiency of the embodiment of the present invention is similar to that of Comparative Example 1 and is higher than that of Comparative Example 2.

The organic light emitting diode display according to the present invention is also applicable to a structure having a driving thin film transistor connected to the first electrode and red, green and blue color filters 150R, 150G and 150B as shown in FIG. 4 . That is, the white light generated through the charge generation layer 130 and the first and second light emitting units 110 and 120 is emitted while passing through the sub pixel region where the red color filter 150R is formed, and the green color filter 150G And blue light is emitted while passing through the sub pixel region in which the blue color filter 150B is formed and white light is emitted while passing through the sub pixel region in which the color filter is not formed.

On the other hand, in the present invention, the case where two light emitting units are used is described as an example, but the light emitting units may be formed further. That is, between the plurality of light emitting units, a charge generating layer comprising the N-type charge generating layer 132 and the first and second P-type charge generating layers 134a and 134b is formed.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Will be clear to those who have knowledge of.

102: first electrode 104: second electrode
110, 120: light emitting unit 132; N-type charge generation layer
134: P-type charge generation layer

Claims (7)

First and second electrodes facing each other on a substrate;
At least two light emitting units formed between the first and second electrodes;
An N-type charge generation layer and a P-type charge generation layer sequentially formed between the light emitting units,
The P-type charge generation layer
A first P-type charge generation layer formed on the N-type charge generation layer and including a P-type dopant;
And a second P-type charge generation layer formed on the first P-type charge generation layer and including an electron attracting group. The method according to claim 1,
Wherein the first P-type charge generation layer is made of only the P-type dopant. 3. The method of claim 2,
Wherein the first P-type charge generation layer comprises the P-type dopant and the P-type host, and the volume ratio of the P-type dopant in the first P-type charge generation layer is 1 to 10% Device. The method according to claim 2 or 3,
Wherein the P type dopant is formed of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), and the P type host is NPB, CBP, NPD, TPD , TBA, and TTA. The method according to claim 1,
The electron attracting group is formed of at least one of CN, NO2, F, Cl, Br, and I, and the second P-type charge generating layer has a lowest unoccupied molecular orbital (LUMO) level of -5.0 eV or less Lt; RTI ID = 0.0 > OLED. ≪ / RTI > 6. The method of claim 5,
And the second P-type charge generation layer is formed of HATCN. The method according to claim 1,
The thickness of each of the first and second P-type charge generation layers is 50 Å to 500 Å,
Wherein the total thickness of the P-type charge generation layer including the first and second P-type charge generation layers is 100 ANGSTROM to 1000 ANGSTROM.

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