KR20110034800A - Organic light emitting display device - Google Patents

Abstract

PURPOSE: An organic light emitting display device is provided to improve a lifetime by improving the number of electrons which moves to a light emitting layer and removing a radical ion. CONSTITUTION: A cell driving unit is formed between a first substrate and a second substrate. An organic light emitting display device includes a first electrode(132), a second electrode(138), and a light emitting layer(135) comprised of host, dopant, and electron transport materials. An hole injection layer(133) and a hole transport layer(134) are successively formed between the first electrode and the light emitting layer. An electron transport layer(136) and an electron injection layer(137) are successively formed between the second electrode and the light emitting layer.

Description

Organic Light Emitting Display Device

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 capable of lowering a driving voltage and improving luminous efficiency and lifetime.

In recent years, with the development of the information society, various types of demands on display devices have increased, such as liquid crystal display (LCD), plasma display panel (PDP), electro luminescent display (ELD), field emission display (FED), and VFD ( Research on flat panel display devices such as Vacuum Fluorescent Display is being actively conducted. Flat display devices that realize various information as screens are the core technology of the information and communication era, and are developing in a direction that is thinner, lighter, portable, and high performance.

Accordingly, as a flat panel display device that can reduce the weight and volume, which is a disadvantage of the cathode ray tube (CRT), an organic light emitting display device that displays an image by controlling the amount of light emitted from the organic light emitting layer has been in the spotlight. An organic light emitting display device is a self-luminous device using a thin light emitting layer between electrodes, and has an advantage of thinning like a paper.

In the active matrix organic light emitting display device (AMOLED), pixels composed of three color (R, G, B) sub-pixels are arranged in a matrix to display an image. Each sub pixel includes an organic light emitting element and a cell driver for independently driving the organic light emitting element. The cell driver includes at least two thin film transistors and a storage capacitor to control the amount of current supplied to the organic light emitting diode according to the data signal to control the brightness of the organic light emitting diode.

The conventional organic light emitting device is composed of a cathode electrode, an organic light emitting layer, and an anode electrode, the organic light emitting layer emits light by the combination of electrons and holes from the cathode electrode and the anode electrode. In order to obtain an optimal luminous efficiency, holes and electrons must be balanced in the light emitting layer. Due to the rapid movement speed of the holes, the number of holes in the light emitting layer is excessively increased, resulting in an unbalanced density of holes and electrons.

The imbalance between the hole and the electron density decreases the recombination ratio between the hole and the electron, and thus does not exhibit excellent luminous efficiency. In order to improve the luminous efficiency, the driving voltage is increased. In addition, radical ions generated at the interface of the light emitting layer interfere with the coupling of holes and electrons, thereby degrading the life characteristics of the organic light emitting device.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an organic light emitting display device capable of lowering a driving voltage and improving light emission efficiency and lifespan.

The organic light emitting diode display according to the present invention includes a first substrate and a second substrate bonded to each other, a cell driver formed between the first substrate and the second substrate, and an organic light emitting diode driven by the cell driver. The organic light emitting diode may include a first electrode, a second electrode, and a light emitting layer formed between the first electrode and the second electrode and formed of a host, a dopant, and an electron transporting material. Up to 10 wt% of the host is injected into the light emitting layer.

The organic light emitting diode further includes a hole injection layer and a hole transport layer sequentially formed between the first electrode and the light emitting layer, and an electron transport layer and an electron injection layer sequentially formed between the second electrode and the light emitting layer.

The electron transport material is injected into the light emitting layer at 3 wt% of the host.

Alternatively, the electron transport material is injected into the light emitting layer at 6 wt% of the host.

The dopant is injected into the light emitting layer at 6 wt% of the host.

The organic light emitting diode may include the first electrode electrically connected to the cell driver, a hole injection layer formed on the first electrode, a hole transport layer formed on the hole injection layer, and a hole transport layer. And a light emitting layer, an electron transporting layer formed on the light emitting layer, an electron injection layer formed on the electron transporting layer, and the second electrode formed on the electron injection layer.

The electron transporting material is the same material as the material forming the electron transporting layer.

The hole injection layer is made of HAT (CN) ₆ .

The first electrode is formed of a transparent conductive layer, and the second electrode is formed of Al.

The organic light emitting diode display according to the present invention balances the density of holes and electrons in the light emitting layer to increase the coupling ratio, thereby exhibiting an optimum luminous efficiency and reducing a driving voltage.

Furthermore, the organic light emitting display device according to the present invention eliminates radical ions generated at the interface of the light emitting layer and improves the number of electrons moving into the light emitting layer, thereby improving the life characteristics of the organic light emitting device.

Hereinafter, an organic light emitting display device according to the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, an organic light emitting display device according to an exemplary embodiment of the present invention includes a cell driver 120 and an organic light emitting device 130 formed between a first substrate 110 and a second substrate 140 bonded to a material 150. ).

The cell driver 120 formed on the first substrate 110 includes a plurality of signal lines, a thin film transistor, and a protective layer, and is mainly a switch transistor (not shown), a driving transistor (not shown), and a storage capacitor (not shown). City).

The switching transistor supplies a data signal from the data line in response to the scan signal of the gate line, and the driving transistor flows in the organic light emitting element 130 through the connection electrode in response to the data signal from the switching transistor. To control. The storage capacitor causes a constant current to flow through the driving transistor even when the switching transistor is turned off. The driving transistor is electrically connected to the organic light emitting diode 130 through the connection electrode.

2 and 3, the organic light emitting diode 130 includes an organic light emitting layer formed between the first electrode 132 and the second electrode 138. The organic emission layer is a layer in which light is emitted as the axtone formed by combining holes and electrons injected from the first electrode 132 and the second electrode 138 falls to the ground state.

The organic light emitting layer includes a hole injection layer (HIL) 133, a hole transporting layer (HTL) 134, an emission layer (EML) 135, and an electron transporting layer (ETL) 136. And an electron injection layer (EIL) 137.

The first electrode 132 is an anode for hole injection, and has a high work function and is formed of a conductive layer. The first electrode 132 is electrically connected to the driving transistor of the cell driver and is formed of a transparent conductive layer in sub pixel units. As the transparent conductive layer, indium tin oxide (ITO), tin oxide (TO), indium zinc oxide (IZO), indium tin zinc oxide (ITZO), or these May be used.

The hole injection layer 133 and the hole transport layer 134 are for transferring the holes supplied from the first electrode 132 to the light emitting layer 135, and serves to lower the driving voltage by increasing quantum efficiency. The hole injection layer 133 is formed of HAT (CN) ₆ (hexa-azatriphenylenehexacarbonitrile) or a known hole injection material on the first electrode 132, and the hole transport layer 134 is known on the hole injection layer 133. Formed of a hole transport material. The hole injection layer 133 and the hole transport layer 134 may form a hole injection layer and a transport layer as one layer with adjacent layers, and may be selectively formed respectively.

The emission layer 135 is a layer that generates light of a specific wavelength by the combined electrons and holes, and is formed on the hole transport layer 134. The light emitting layer 135 may be formed of only a host or a dopant, but due to its low efficiency and brightness and self-packing of each molecule, It is undesirable because the cymer properties occur simultaneously. Therefore, the light emitting layer 135 is mainly formed by doping the dopant to the host, wherein the excitons are generated in the host and transferred to the dopant, and emit light while falling to the bottom in the dopant.

Therefore, in order to obtain the maximum efficiency, the electron and the hole injection have to be balanced, and the movement speed of the hole is high, so that the number of holes in the light emitting layer is larger than the electrons. In particular, when HAT (CN) ₆ is used as the hole injection layer 133, the driving voltage is lowered, but the movement speed of the holes from the first electrode 132 is further improved, and the number of holes in the light emitting layer is excessively increased.

In order to prevent this, the emission layer 135 of the present invention further includes an electron transport material (ETM). The electron transport material (ETM) injected into the light emitting layer 135 lowers the energy barrier of electron injection to facilitate the transport of electrons, thereby enhancing the injection of electrons in the light emitting layer 135 as much as possible. In this case, when the electron transport material (ETM) is injected into the light emitting layer by more than 10 wt% of the host material, the quality of the color coordinates is deteriorated. Therefore, the electron transport material (ETM) is injected by 10 wt% or less of the host material forming the light emitting layer 135. And the dopant is injected at 6 wt% of the host material.

When 10 wt% or less of an electron transport material (ETM) is injected into the light emitting layer 135, the density of holes and electrons is balanced in the light emitting layer 135, thereby increasing the coupling ratio of holes and electrons, and increasing the organic light emitting device ( 130 indicates an optimal luminous efficiency and reduces the driving voltage. In addition, since the radical ions generated at the interface of the light emitting layer 135 dissociate with the ions generated in the electron transport layer 136, the number of electrons moved into the light emitting layer 135 is improved, and holes are formed in the center of the light emitting layer 135. And electrons are combined to improve the life characteristics of the organic light emitting device 130.

The electron transport layer 136 lowers the energy barrier of electron injection to facilitate electron injection and transport, and is formed on the light emitting layer 135. The material constituting the electron transport layer 136 functions to stably transport electrons injected from the cathode, and includes an oxazole compound, an isoxazole compound, a triazole compound, an isothiazole compound, and an oxadiazole compound. , Thiadiazole compounds, perylene compounds, aluminum complexes such as Alq3 (tris (8-quinolinolato) -aluminum) BAlq, SAlq, Known materials such as Almq3, gallium complexes such as Gaq'2OPiv, Gaq'2OAc, 2 (Gaq'2), etc. can be used, etc. Materials used in the electron transport layer 136 are electrons injected into the light emitting layer 135 It may be the same material as the transport material or different materials.

The electron injection layer 137 is for easily injecting electrons from the second electrode 138 into the light emitting layer 135 and is formed on the electron transport layer 136. As the electron injection layer 137, any material known as an electron injection layer forming material such as LiF, NaCl, CsF, Li ₂ O, BaO, CsCO _3, and BCP mixture can be used.

The second electrode 138 is a cathode for supplying electrons to the light emitting layer 135, and a metal, an alloy, an electrically conductive compound, or a mixture thereof having a low work function may be used. Specific examples include lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), magnesium-silver (Mg-Ag), and the like. Can be mentioned.

In the organic light emitting diode display having the above-described structure, a driving voltage is applied from the cell driver 120 between the first electrode 132 and the second electrode 138. At this time, holes are injected from the first electrode 132 into the hole injection layer and the hole transport layer to move to the light emitting layer 135. Then, electrons are injected into the electron injection layer and the electron transport layer from the second electrode 138 and move to the emission layer 135. At this time, the electrons move into the light emitting layer 135 at a high speed by the electron transport material (ETM) in the light emitting layer 135. The moved holes and electrons are combined in the emission layer 135 to generate light, and emit light through the first electrode 132 and the first substrate 110 to implement an image.

Looking at the effects of the present invention through specific comparative examples and examples are as follows. The efficiency and the lifespan are compared by fabricating a general organic light emitting device that does not doped with an electron transporting material in a light emitting layer and a blue organic light emitting device which doped an electron transporting material in a light emitting layer.

(Comparative Example)

After forming the driving transistor, ITO (320Å) / HIL (50Å) / HTL (700Å) / EML (Blue Host 300Å + Blue Dopant 6 wt%) / ETL (200Å) / EIL (LIF, 10Å) are deposited in this order. After the Al was deposited by Cathode. In this case, the current efficiency was 4.5cd / A (3.7V), the voltage efficiency was 3.8 Im / W, and the CIE (Commision Internationale de L'Eclairage) was x = 0.147 and y = 0.065.

Experimental Example 1

After forming the driving transistor, ITO (320kW) / HIL (50kW) / HTL (700kW) / EML (Blue Host 300kW + Blue Dopant 6wt% + ETM 3wt%) / ETL (200kW) / EIL (LIF, 10Å) was sequentially deposited and then Al was deposited by Cathode. In this case, the current efficiency was 4.7 cd / A (3.6 V), the voltage efficiency was 4.0 Im / W, and the CIE (Commision Internationale de L'Eclairage) was x = 0.147 and y = 0.066.

(Experimental Example 2)

After forming the driving transistor, ITO (320kW) / HIL (50kW) / HTL (700kW) / EML (Blue Host 300kW + Blue Dopant 6wt% + ETM 5wt%) / ETL (200kW) / EIL (LIF, 10Å) was sequentially deposited and then Al was deposited by Cathode. In this case, the current efficiency was 4.8 cd / A (3.6V), the voltage efficiency was 4.1 Im / W, and the CIE (Commision Internationale de L'Eclairage) was x = 0.147 and y = 0.067.

Experimental Example 3

After forming the driving transistor, ITO (320kW) / HIL (50kW) / HTL (700kW) / EML (Blue Host 300kW + Blue Dopant 6wt% + ETM 10wt%) / ETL (200kW) / EIL (LIF, 10Å) was sequentially deposited and then Al was deposited by Cathode. In this case, the current efficiency was 4.7 cd / A (3.5V), the voltage efficiency was 4.2 Im / W, and the CIE (Commision Internationale de L'Eclairage) was x = 0.147 and y = 0.069.

Table 1 below summarizes the results of measuring the electro-optical characteristics of the organic light emitting device according to Comparative Examples to Experimental Example 4 described above.

Emission Layer (EML) V cd / A Im / W CIEx CIEy Comparative Example (A) Blue Host 300Å + Blue Dopant 6 wt% 3.7 4.5 3.8 0.147 0.065 Experimental Example 1
(B) Blue Host 300Å + Blue Dopant 6 wt% + ETM 3 wt% 3.6 4.7 4.0 0.147 0.066 Experimental Example 2
(C) Blue Host 300Å + Blue Dopant 6 wt% + ETM 5 wt% 3.6 4.8 4.1 0.147 0.067 Experimental Example 3
(D) Blue Host 300Å + Blue Dopant 6 wt% + ETM 10 wt% 3.5 4.7 4.2 0.147 0.069

Comparing the devices A, B, C, and D manufactured as described above, a graph as shown in FIG. 4 appears. That is, it can be seen that the lifespan of the experimental devices B, C, and D, which is further doped with an electron transporting material, is further improved in the light emitting layer, as compared with the comparative device A. As described above, the present invention improves the efficiency and lifespan of the organic light emitting device by mixing the electron transport material in the light emitting layer, thereby improving the electron transport ability to balance the holes and electrons in the light emitting layer.

The above-described techniques represent presently preferred embodiments, and the present invention is not limited to the above-described embodiments and the accompanying drawings. Modifications and other uses of the embodiments will be apparent to those skilled in the art, and such changes and other uses are defined by the scope of the claims contained within or appended to the spirit of the invention.

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

FIG. 2 is a cross-sectional view illustrating an organic light emitting display device of the organic light emitting display device of FIG. 1.

3 is an energy band diagram of the organic light emitting diode of FIG. 2.

4 is a graph showing the conventional structure and the lifetime of the organic light emitting device according to the present invention.

<< Explanation of symbols for main part of drawing >>

110: first substrate 120: cell driver

130: organic light emitting element 132: first electrode

133: hole injection layer 134: hole transport layer

135: light emitting layer 136: electron transport layer

137: electron injection layer 138: second electrode

140: second substrate 150: real

Claims (9)

A first substrate and a second substrate bonded to each other; A cell driver formed between the first substrate and the second substrate; And An organic electroluminescent device driven by the cell driver; The organic light emitting diode includes a first electrode, a second electrode, and a light emitting layer formed between the first electrode and the second electrode and made of a host, a dopant, and an electron transporting material. And the electron transport material is injected into the light emitting layer at 10 wt% or less of the host. The organic light emitting device of claim 1, further comprising: a hole injection layer and a hole transport layer sequentially formed between the first electrode and the light emitting layer; And an electron transporting layer and an electron injection layer sequentially formed between the second electrode and the light emitting layer. The organic light emitting display device of claim 1, wherein the electron transport material is injected into the light emitting layer at 3 wt% of the host. The organic light emitting display device of claim 1, wherein the electron transport material is injected into the light emitting layer at 6 wt% of the host. The organic light emitting display device of claim 1, wherein the dopant is injected into the light emitting layer at 6 wt% of the host. The method of claim 1, wherein the organic light emitting device, The first electrode electrically connected to the cell driver; A hole injection layer formed on the first electrode, A hole transport layer formed on the hole injection layer; The light emitting layer formed on the hole transport layer; An electron transport layer formed on the light emitting layer; An electron injection layer formed on the electron transport layer; And the second electrode formed on the electron injection layer. The organic light emitting display device of claim 2, wherein the electron transport material is the same material as the material forming the electron transport layer. The organic light emitting display device of claim 2, wherein the hole injection layer is formed of HAT (CN) ₆ . The method of claim 1, wherein the first electrode is electrically connected to the cell driver and is formed of a transparent conductive layer. And the second electrode is made of Al.

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