KR20100022638A - Organic light emitting display - Google Patents

Abstract

PURPOSE: An organic light emitting display device is provided to improve luminous efficiency by improving an reaction speed of a hole and an electron. CONSTITUTION: An anode(110) is formed on a substrate. An organic layer is formed on the anode and includes a hole injection layer(130), a hole transport layer(140), a light emitting layer(150), an electron transport layer(160), and an electron injection layer(170). A cathode is formed on the organic layer. The electron transport layer is comprised of first to fourth electron transport layers. The second to fourth transport layers are doped with the material to promote electron mobility. The density of the material to promote the electron mobility increases from the second electron transport layer to the fourth electron transport layer.

Description

Organic light emitting display device {ORGANIC LIGHT EMITTING DISPLAY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device for improving luminous efficiency and lifetime.

Recently, among the various display devices that implement various information on the screen, an organic light emitting display device that can be thinned like a paper has attracted attention.

Such an organic light emitting display device is a self-luminous device using a thin organic light emitting layer between electrodes, which is called an organic EL or organic light emitting diode (OLED) display device and uses an OLED display device hereinafter. OLED displays have advantages such as low power consumption, thinness, and self-luminous, compared to liquid crystal displays, but have shortcomings.

OLED displays are being developed based on an active matrix type suitable for displaying moving images by independently driving each of three color (R, G, B) sub-pixels constituting one pixel.

Each subpixel of an active matrix OLED (hereinafter, AMOLED) display device includes an OLED composed of an organic light emitting layer between an anode and a cathode, and a subpixel driver for driving the OLED independently. The sub-pixel driver includes at least two thin film transistors and a storage capacitor to control the brightness of the OLED by controlling the amount of current supplied to the OLED according to the data signal. The OLED includes a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer laminated with an organic material between an anode and a cathode.

When a forward voltage is applied between the anode and the cathode, electrons from the cathode move to the light emitting layer through the electron injection layer and the electron transport layer, and holes from the anode move to the light emitting layer through the hole injection layer and the hole transport layer. The light emitting layer emits light by recombination of electrons from the electron transport layer and holes from the hole transport layer, and brightness is proportional to the amount of current flowing between the anode and the cathode.

1A and 1B are cross-sectional views schematically illustrating a general organic light emitting display device.

As shown in FIGS. 1A and 1B, a general organic light emitting display device includes an anode 20 and a cathode 30 formed by being sequentially stacked on a transparent substrate 10, and the anode 20. And an organic layer formed between the cathodes 30. Here, the organic layer is a hole injection layer (HIL) 61, a hole transporting layer (HTL) 62, an emission layer (EML) 40, sequentially from the anode 20 An electron transporting layer (ETL) 51 and an electron injection layer EIL 52 are stacked and formed.

In the general organic light emitting display device configured as described above, when a driving voltage is applied to the anode 20 and the cathode 30, holes in the hole injection layer 61 and electrons in the electron injection layer 52 are respectively directed toward the light emitting layer 40. Proceeds to flow into the light emitting layer (40). When electrons and holes flow into the emission layer 40, excitons are generated.

Subsequently, the excitons fall from the excited state to the ground state to generate visible light corresponding to the energy difference.

Most of the light generated in the light emitting layer 40 of the general organic light emitting display device is trapped inside the organic light emitting display device due to internal reflection and does not contribute to the amount of light output. Therefore, a method of improving light extraction efficiency is required.

Accordingly, a method of improving light extraction efficiency by controlling the thickness of each organic film, that is, the hole transport layer or the hole injection layer, for each of the R, G, and B sub-pixels has been proposed.

However, when the thickness of the organic layer, such as the hole injection layer or the hole transport layer of the organic layer, is adjusted for each sub-pixel, the carrier balance in each sub-pixel is changed and the device characteristic itself is changed so that it is difficult to obtain desired characteristics, which causes a decrease in efficiency. If the thickness of the organic layer is increased, the amount of material consumption increases accordingly, and there is a problem in that a condition occurs in consideration of the tac time of the process.

In addition, since most of the light generated by the light emitting layer 40 is trapped inside the organic light emitting diode display due to internal reflection and does not contribute to the light output amount, a method of improving light extraction efficiency is required.

In addition, when a driving voltage is applied to the anode 20 and the cathode 30, the holes in the hole injection layer 61 and the electrons in the electron injection layer 52 proceed toward the emission layer 40, respectively. There is a problem that the light emission efficiency is lowered because the electron is faster than the mobility of electrons and the rate at which electrons and holes react in the light emitting layer is slow.

The present invention is to solve the conventional problems as described above to provide an organic light emitting display device to improve the luminous efficiency and lifespan by sequentially increasing the concentration of the material to promote electron mobility in the electron transport layer to form a multi-layer. There is a purpose.

An organic light emitting display device according to the present invention for achieving the above object is sequentially stacked between an anode formed on a substrate, a cathode formed to correspond to the anode at regular intervals to form an electric field, and between the anode and the cathode And an organic layer including a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer, wherein the electron transport layer is formed of a material that promotes mobility of electrons gradually from the interface of the light emitting layer to the electron injection layer. It is characterized in that the material is doped in multiple layers so as to increase.

An organic light emitting display device according to the present invention has the following effects.

That is, by sequentially increasing the concentration of a substance that promotes electron mobility in the electron transport layer and forming the multilayer, light emission efficiency and lifespan may be improved by improving the reaction rate between electrons and holes.

FIG. 2 is a schematic cross-sectional view of an organic light emitting display device according to the present invention, and FIG. 3 is a schematic cross-sectional view of the electron transport layer of FIG. 2.

As shown in FIG. 2, the organic light emitting diode display according to the present invention includes an anode 110 and a cathode 120 sequentially formed on a transparent or opaque substrate 100 with a predetermined space therebetween. And an organic layer formed between the anode 110 and the cathode 120.

Here, the organic layer is a hole injection layer (HIL) 130, a hole transporting layer (HTL) 140, an emission layer (EML) 150, sequentially from the anode 110 An electron transporting layer (ETL) 160 and an electron injection layer EIL 170 are stacked and stacked.

In addition, the anode 110 is formed of a metal having high reflectivity such as Al, Al / Li, Ma / Ag, Al / Nd, and the cathode 120 is formed of a conductive material having a transmissive or semi-transparent material, and a transparent material. Indium Tin Oxide (ITO), Tin Oxide (TO), Indium Zinc Oxide (IZO) or Indium Tin Zinc Oxide (ITZO) is used as the furnace. As the semi-permeable material, forming a thin film of LiF / Al, CsF / Al, Mg: Ag, Ca / Ag, Ca: Ag, LiF / Ma: Ag, LiF / Ca / Ag, LiF / Ca: Ag desirable.

In addition, when the cathode 120 is formed of a transparent conductive layer, an auxiliary electrode (not shown) may be provided on the cathode 120 to lower the resistance of the cathode 120. The auxiliary electrode (not shown) is a conductive metal material having a lower resistance value than that of the cathode 120, and includes silver (Ag), aluminum (Al), chromium (Cr), molybdenum (Mo), and the light emitting layer 160. Is formed in the non-luminescing region of.

The hole injection layer 130 forms CuPc (copper phthalocyanine) in a thickness of 10 to 30 nm, and the hole transport layer 140 is N, N'-dipheny1-N, N'-bis (3-methylpheny1)-( 1-1'-bipheny1) 4,4'-diamine (TPD) or 4,4'-bis [N- (1-naphthy1) -N-pheny1-amino] bipheny (NPD) to form a thickness of 30-60 nm do.

The electron injection layer 170 coats LiF or Li 2 O thinly by about 5 μs or by applying an alkali metal or alkaline earth metal such as Li, CA, Mg, Sm to 200 μs or less to improve the injection of electrons.

In addition, in bonding the upper and lower elements, one of the two is also used an encapsulation substrate, and in bonding the upper and lower elements, an electrical buffer layer is provided for electrical contact between the upper and lower elements. It is also possible to operate the two elements of the upper plate and the lower plate using one driving chip, and when using the single driving chip, the lower plate element is not driven when driving the upper element, and the upper element is not driven when driving the lower element. Do not.

In addition, as shown in FIG. 3, the electron transport layer 160 has a multilayer structure by sequentially increasing a concentration of a material for promoting electron mobility from the lower side to the upper side.

That is, the electron transport layer 160 may be a pure first electron transport layer 161 and a second electron transport layer 162 doped with 0 to 5% of a material causing electron promotion on the first electron transport layer 161. And a third electron transport layer 163 doped with a material that induces electron promotion on the second electron transport layer 162 by 5 to 10%, and promotes electrons on the third electron transport layer 163. And a fourth electron transport layer 164 doped with 10-20% of the material.

Here, the electron transport layer 160 is formed to a thickness of 200 Å, the first electron species layer 161 is formed to a thickness of about 100 Å, the first to third electron transport layer (162, 163, 164) is about 33 Å It is formed in the thickness of.

In the embodiment of the present invention, four electron transport layers have been described. However, the present invention is not limited thereto and may be formed of four or more electron transport layers.

Herein, the substance for promoting electron mobility may include a substituted or unsubstituted Al complex, a substituted or unsubstituted Be complex, a substituted or unsubstituted Zn complex, a substituted or substituted substance having the electron transporting property. Unsubstituted oxidiazole derivatives, substituted or unsubstituted triazole derivatives, substituted or unsubstituted thiophene derivatives, substituted or unsubstituted pyrrole derivatives, substituted or unsubstituted sila-cyclopentadiene derivatives, substituted or unsubstituted anthracene derivatives, substituted or substituted It is selected from unsubstituted pyrene derivatives and substituted or unsubstituted perylene derivatives.

More specifically, materials for promoting electron mobility are described below. That is, Alq3 [Tris- (8-hydroxyquinolinolato) -aluminium], BeBq ₂ [bis (10-hydroxybenzofhgqinolinato) beryllium], Zn (oxz) ₂ [Bis (2- (2-hydroxyphenyl0-benz-1,3-oxadiazoleato) zinc], PBD [2- (4-biphenylyl) -5- (4-tert-butyl-phenyl0-1,3,4-oxadiazole], TAZ [3- (4-Biphenylyl) -4-phenyl-5-tert -butylphenyl-, 2,4-triazole], Liq [8-Quinolinolato Lithium], Mgq ₂ [Bis (8-Quinolinolato) Magnesium], Znq ₂ [Bis (8-Quinolinolato) Zinc].

In addition, since the lifespan of the organic light emitting display device of the present invention is greatly reduced by external oxygen or moisture, an upper substrate (not shown) and a sealant (not shown) to which an absorbent (not shown) is attached to block the life. Encapsulation is performed to complete an organic light emitting display device having a top-emission method.

In the organic light emitting diode display according to the present invention configured as described above, when a driving voltage is applied to the anode 110 and the cathode 120, holes in the hole injection layer 130 and electrons in the electron injection layer 170 are respectively light emitting layer 150. Proceed toward) and flows into the light emitting layer 150. When electrons and holes are introduced into the emission layer 150, excitons are generated, and the excitons fall from the excited state to the ground state to generate visible light corresponding to the energy difference. The visible light generated from the light emitting layer 150 emits light on the entire surface in the upper direction of the cathode 120.

Here, the present invention improves the light extraction efficiency by changing the light properties by differently doping concentration of the electron transport layer 160 of the organic layer to the electron transport layer 160 in the electron transport layer 160 from different doping concentration from the top to the bottom. .

That is, in the embodiment of the present invention, the electron transport layer 160 is doped with Liq to promote electron mobility so that the electron mobility becomes 1.0 × 10 ⁻⁵ cm 2 V −1 or more, and the doping of the Liq is a light emitting layer. Doping is gradually increased from the interface 150 to the electron injection layer 170.

Table 1 below shows the results of measuring efficiency and life time when Liq is doped into the electron transport layer. Here, the measurement conditions were 20 mW / cm 2, and the life measurement conditions were performed at B (1500 nit), 25 ° C., and 50%.

V cd / A lm / W Lifetime Reference 3.6 4.9 4.3 300 ETL + Liq 3.9 4.7 3.8 500 Multilayer ETL 3.6 5.3 4.8 500

As shown in Table 1, the voltage (V) applied to the anode and the cathode in the electron transport layer (Multilayer ETL) and the conventional electron transport layer (Ref) of the present invention is the same, while the conventional luminous efficiency (cd / A) is 4.9 It can be seen that the efficiency of the present invention is 5.3, and the brightness (lm / W) is also conventionally 4.3, but the present invention is 4.8.

In addition, the conventional lifetime (Lifetime) is 300, it can be seen that in the present invention 500.

4A and 4B are graphs of current density (mA / cm 2) and light emission efficiency (cd / A) of the organic light emitting diode display based on Table 1.

As shown in FIGS. 4A and 4B, the electron transport layer (Multilayer ETL) of the present invention can increase the luminous efficiency and lifespan of the organic light emitting display device of the conventional electron transport layer (Ref).

5 is a graph illustrating a result of measuring life of an organic light emitting display device based on Table 1. FIG.

As shown in FIG. 5, it can be seen that in the electron transporting layer of the present invention, Liq for promoting electron mobility is formed in a multi-layered structure, and thus lifespan is longer than that of the conventional (Ref).

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be apparent to those who have knowledge.

1A and 1B are cross-sectional views schematically illustrating a general organic light emitting display device.

2 is a schematic cross-sectional view of an organic light emitting display device according to an exemplary embodiment of the present invention.

3 is a schematic cross-sectional view of the electron transport layer of FIG. 2.

4A and 4B are graphs showing current density (mA / cm 2) and luminous efficiency (cd / A) of an organic light emitting display device based on Table 1;

5 is a graph illustrating a result of measuring lifetime of an organic light emitting display device based on Table 1;

* Description of the symbols for the main parts of the drawings *

100: substrate 110: anode

120 cathode 130 hole injection layer

140: hole transport layer 150: light emitting layer

160: electron transport layer 170: electron injection layer

Claims (4)

An anode formed on the substrate, A cathode formed to correspond to the anode at regular intervals to form an electric field; An organic layer including a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer, which are sequentially stacked between the anode and the cathode; The electron transport layer is an organic light emitting display device, characterized in that the material is doped in multiple layers so that the material that promotes the mobility of electrons gradually increases from the interface of the light emitting layer to the electron injection layer. The organic light emitting display device of claim 1, wherein the material doped with the electron transport layer is Liq. The organic light emitting display device of claim 1, wherein the electron transport layer is formed of a multi-layered material. The method of claim 3, wherein the electron transport layer A first electron transport layer formed on the light emitting layer, A second electron transport layer doped with 0 to 5% of a material causing electron promotion on the first electron transport layer; A third electron transport layer doped with 5-10% of a material causing electron promotion on the second electron transport layer; And a fourth electron transporting layer doped with 10-20% of a material causing electron promotion on the third electron transporting layer.

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