KR20080011623A - Light emitting device and fabrication method of the same - Google Patents

Abstract

A light emitting device and a fabrication method thereof are provided to improve the light emitting efficiency and the reliability of the device by having a second electrode made of silver or an alloy of silver with low specific resistance and high physical properties. A light emitting device includes a substrate(100), a first electrode(110), a light emitting layer(140), an electron injection layer(160), and a second electrode(170). The first electrode is located on the substrate. The light emitting layer is located on the first electrode. The electron injection layer is located on the light emitting layer. The second electrode is located on the electron injection layer. The electron injection layer is composed of a first layer made of a halogen metal compound and a second layer made of metal.

Description

Electroluminescent device and method of manufacturing the same {Light emitting device and fabrication method of the same}

1 is a cross-sectional view showing the structure of an electroluminescent device according to an embodiment of the present invention.

2 is a graph showing the J-V characteristics of the electroluminescent device according to an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

100 substrate 110 first electrode

120: hole injection layer 130: hole transport layer

140: light emitting layer 150: electron transport layer

160: electron injection layer 170: second electrode

The present invention relates to an electroluminescent device and a method of manufacturing the same.

Flat panel displays (FPDs) are becoming more important with the development of multimedia. In response, various liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), light emitting devices (Light Emitting Devices), etc. Flat panel displays have been put into practical use.

Among them, the electroluminescent display has a high response time with a response speed of 1 ms or less, low power consumption, and no self-emission, so that there is no problem in viewing angle.

In particular, the organic light emitting device includes an anode, an organic light emitting layer positioned on the anode, and a cathode located on the organic light emitting layer, and when voltage is applied to the anode and the cathode, holes are injected from the anode into the organic light emitting layer, and the organic material from the cathode Electrons are injected into the light emitting layer. The holes and electrons injected into the organic light emitting layer recombine to produce excitons, which emit light as the excitons transition from the excited state to the ground state.

Here, as a cathode, aluminum (Al) having a low work function is mainly used, and aluminum (Al) is a material having high specific resistance and having good electron migration, which easily moves aluminum atoms according to the direction of current movement. there is a problem. Therefore, the cathode made of aluminum has a high possibility of causing a wiring defect due to the formation of a hillock due to mass movement when heat is applied when the electroluminescent device is driven. In addition, since aluminum has higher moisture and oxygen permeability and stronger oxidizing power than other metals, aluminum oxide films are easily formed on the surface of the cathode or at the interface between the cathode and other layers. This increases the driving voltage of the electroluminescent device by increasing the resistance of the cathode.

Accordingly, an object of the present invention is to provide an electroluminescent device and a method of manufacturing the same, which can improve the reliability and luminous efficiency of the device.

In order to achieve the above object, the present invention, a substrate, a first electrode located on the substrate, a light emitting layer located on the first electrode, an electron injection layer and an electron injection layer containing a halogen metal compound and a metal located on the light emitting layer Provided is an electroluminescent device comprising a second electrode located on a layer.

The electron injection layer may include a first layer made of a halogen metal compound and a second layer made of metal located on the first layer.

The thickness of the first layer can be 0.3 to 10 nm.

The electron injection layer may be a co-deposited metal and a halogen metal compound.

The halogen metal compound may be lithium fluoride (LiF), sodium fluoride (NaF), cesium fluoride (CsF), magnesium fluoride (MgF ₂ ), calcium fluoride (CaF ₂ ), or the like.

The metal may be a metal having a low work function and high reactivity with a halogen element.

The metal may be aluminum or magnesium.

The second electrode may be made of silver or silver alloy.

The present invention also provides a substrate, forming a first electrode on the substrate, forming a light emitting layer on the first electrode, forming an electron injection layer containing a halogen metal compound and a metal on the light emitting layer And it provides a method of manufacturing an electroluminescent device comprising the step of forming a second electrode on the electron injection layer.

The forming of the electron injection layer may include forming a first layer including a halogen metal compound on the emission layer; And forming a second layer of metal on the first layer.

The forming of the electron injection layer may be performed by co-depositing a halogen metal compound and a metal.

The second electrode can be formed of silver or silver alloy.

Hereinafter, with reference to the accompanying drawings, it will be described embodiments of the present invention;

1 is a cross-sectional view showing the structure of an electroluminescent device according to an embodiment of the present invention.

Referring to FIG. 1, the first electrode 110, the hole injection layer 120, the hole transport layer 130, the emission layer 140, the electron transport layer 150, the electron injection layer 160, and the substrate 100 may be disposed on the substrate 100. The electroluminescent device including the second electrode 170 is positioned.

In detail, the first electrode 110 is positioned on the substrate 100 made of glass, plastic, or metal. The first electrode 110 may be an anode for providing holes, and may be a transparent conductive film such as indium tin oxide (ITO), indium zinc oxide (IZO), indium cerium oxide (ICO), or zinc oxide (ZnO). Can be formed.

The hole injection layer 120 is positioned on the first electrode 110. The hole injection layer 120 may be formed of a material having a high hole injection efficiency from the first electrode 110, that is, a small ionization potential and a material capable of maintaining a stable interface with the first electrode 110.

Representative examples of the material that can be used as the hole injection layer 120 is copper phthalocyanine (CuPc), a porphyrin-based copper complex, and starburst type aromatic aryl amine compounds may be used.

The hole transport layer 130 is positioned on the hole injection layer 120. The hole transport layer 130 receives holes from the hole injection layer 120 and transports the holes to the light emitting layer 140. The hole transport layer 130 has high hole mobility and stability to holes and blocks electrons. Since the hole transport layer 130 requires heat resistance to the device, a material having a glass transition temperature (Tg) of 80 ° C. or higher is preferable.

Materials that can be used for the hole transport layer 130 include spiro-arylamine compounds, perylene-arylamine compounds, azacycloheptatriene compounds, bis (diphenylvinylphenyl) anthracene, silicon germanium oxide compounds, and silicon-based aryls Amine compounds and the like.

The emission layer 140 is positioned on the hole transport layer 130. The light emitting layer 140 is a layer for emitting light by recombining holes and electrons injected from the anode and the cathode, respectively, and made of a material having high quantum efficiency.

The organic monomolecule for the light emitting layer in which holes and electrons combine to emit light is largely divided into a host material and a guest material in terms of function. Generally, the host or the guest material may be used alone, but when used alone, the efficiency and brightness are low, and the excimer characteristic due to self-packing is exhibited. Thus, the host may be used by doping the guest. Can be.

As the green light emitting layer, 8-hydroxyquinoline aluminum salt (Alq ₃ ) is used exclusively, and as the blue light emitting layer, aromatic hydrocarbons, spiro-type materials, organometallic compounds including aluminum, and heterocyclic compounds having imidazole groups Fused aromatic compounds and the like may be used.

In the case of the red light emitting layer, a small amount of red light emitting material is doped into a large amount of green light emitting material due to the characteristic of red light emission with a small band gap, and the red light emitting layer may use a carbazole-based organic material as a host material. As the dopant, PIQIr (acac), PQIr (acac), PQIr ({tris (1-phenylquinoline) iridium}), DCJTB, DCDDC, AAAP, DPP and BSN can be used.

The electron transport layer 150 is positioned on the emission layer 140. The electron transport layer 150 may be made of a material having a high electron affinity, a high electron transfer speed, and excellent stability to electrons so as to efficiently transport the injected electrons to the light emitting layer. Aromatic compounds such as tetraphenyl butadiene, metal complexes such as aluminum of hydroxy quinoline, cyclopentadiene derivatives and bis styryl benzene derivatives may be used. Among organic monomolecular substances, 8- Hydroxyquinoline aluminum salt (Alq ₃ ) is mainly used.

The electron injection layer 160 is positioned on the electron transport layer 150. The electron injection layer 160 may include a halogen metal compound and a metal. Examples of the halogen metal compound may include lithium fluoride (LiF), sodium fluoride (NaF), cesium fluoride (CsF), magnesium fluoride (MgF ₂ ) or calcium fluoride (CaF ₂ ). Has a low work function and high reactivity with the halogen element. For example, aluminum (Al) or magnesium (Mg) is mentioned.

Here, the metal is for reacting with the halogen metal compound to lower the injection barrier with the cathode. For example, in the electron injection layer made of lithium fluoride (LiF) and aluminum (Al), since aluminum (Al) is highly reactive with florin, lithium is removed and reacted with florin (F). Therefore, lithium (Li) having a low work function is present alone in the electron injection layer 160, thereby lowering an energy barrier of electron injection, thereby improving electron injection characteristics. Therefore, even when a metal having a low reactivity with the halogen metal compound is used in the formation of the subsequent second electrode, the electron injection characteristics are excellent, and thus there is an advantage in that the selection of materials can be widened when the second electrode is formed.

The electron injection layer 160 may include a first layer made of a halogen metal compound and a second layer made of a metal on the first layer. Here, the thickness of the first layer made of a halogen metal compound may be 0.3 to 10 nm. When the thickness of the first layer is 0.3 nm or more, the thickness of the first layer may be uniformly formed, and when the thickness of the first layer is 10 nm or less, electrical failure due to the insulating properties of the halogen metal compound may be prevented.

Alternatively, the electron injection layer 160 may be formed as one layer by co-depositing a halogen metal compound and a metal.

The electron injection layer 160 may be formed by e-beam deposition, thermal evaporation, or sputtering.

The second electrode 170 is positioned on the electron injection layer 160. The second electrode 170 may be made of silver (Ag) or silver alloy. Silver (Ag) or silver alloy (Ag alloy) has a low work function and excellent reflectance, there is an advantage to increase the luminous efficiency of the electroluminescent device. In addition, silver (Ag) or silver alloy (Ag alloy) has a lower specific resistance than aluminum and has high molecular weight and high physical properties. Therefore, there is an advantage that can lower the voltage required for driving the electroluminescent device.

In an embodiment of the present invention, the first electrode is formed as an anode, but the first electrode may be formed as a cathode. In this case, the stacking order of organic layers such as a hole transport layer may be reversed. In addition, the hole injection layer, the hole transport layer and the electron transport layer described in an embodiment of the present invention may be selectively formed.

Experimental Example

A first electrode was formed on the substrate using indium tin oxide, and an organic light emitting layer was formed on the first electrode. Then, an electron transport layer was formed using 8-hydroxyquinoline aluminum salt (Alq ₃ ) on the organic light emitting layer, and then lithium fluoride (LiF) and aluminum (Al) were sequentially stacked to form an electron injection layer. . Here, lithium fluoride (LiF) and aluminum (Al) were each formed to a thickness of 5 kPa. Thereafter, a second electrode was formed of silver (Ag) on the electron injection layer to manufacture an electroluminescent device.

(Comparative Example 1)

On the organic light emitting layer, an electron transport layer made of 8-hydroxyquinoline aluminum salt (Alq ₃ ) and an electron injection layer made of lithium fluoride (LiF) were sequentially formed, and then a second electrode was formed using silver (Ag). Except one, an electroluminescent device was manufactured in the same manner as in Experimental Example. Herein, the electron injection layer was formed to a thickness of 5 GPa.

(Comparative Example 2)

An electroluminescent device was formed in the same manner as in Experimental Example except that an electron transport layer was formed on the organic light emitting layer using 8-hydroxyquinoline aluminum salt (Alq ₃ ), and then a second electrode was formed using silver (Ag). Was prepared.

2 is a graph illustrating J-V characteristics of the electroluminescent devices according to Experimental Examples and Comparative Examples 1 and 2 of the present invention.

Referring to FIG. 2, it can be seen that the electroluminescent device A according to the experimental example has a lower driving voltage than the electroluminescent devices B and C according to Comparative Examples 1 and 2.

In Comparative Example 1, the electron injection layer was formed of lithium fluoride (LiF), which is a halogen metal compound. However, since the reactivity between silver (Ag) and the halogen element (F) is weak, the electron injection effect is reduced, thereby forming the electron injection layer. It can be seen that it has a high driving voltage similar to Comparative Example 2 not.

However, when the electron injection layer is formed of lithium fluoride (LiF) and aluminum (Al), which are halogen metal compounds as in the experimental example of the present invention, the energy barrier is lowered during electron injection, thereby improving the electron injection effect. Therefore, it can be seen that the driving voltage of the electroluminescent element is lowered.

As described above, the electroluminescent device according to an embodiment of the present invention includes an electron injection layer including a halogen metal compound and a metal, thereby lowering an energy barrier of electron injection, thereby lowering a driving voltage of the electroluminescent device. Therefore, the luminous efficiency of the electroluminescent element can be improved.

In addition, the electroluminescent device according to an embodiment of the present invention includes a second electrode made of silver or a silver alloy having a low specific resistance and excellent physical properties, thereby increasing luminous efficiency and ensuring device reliability.

While the invention has been shown and described with reference to certain preferred embodiments, the invention is not so limited, and the invention is not limited to the scope and spirit of the invention as defined by the following claims. It will be readily apparent to one of ordinary skill in the art that various modifications and variations can be made.

The present invention has the advantage of ensuring the reliability of the device, it is possible to provide an electroluminescent device with high luminous efficiency.

Claims (19)

Board; A first electrode on the substrate; A light emitting layer on the first electrode; An electron injection layer disposed on the emission layer and including a halogen metal compound and a metal; And Electroluminescent device comprising a second electrode located on the electron injection layer. The method of claim 1, The electron injection layer is an electroluminescent device comprising a first layer made of a halogen metal compound and a second layer made of metal located on the first layer. The method of claim 2, The first layer has a thickness of 0.3 to 10 nm or less. The method of claim 1, The electron injection layer is an electroluminescent device in which a metal halide and a metal co-deposited. The method of claim 1, The halogen metal compound is any one selected from the group consisting of lithium fluoride (LiF), sodium fluoride (NaF), cesium fluoride (CsF), magnesium fluoride (MgF ₂ ) and calcium fluoride (CaF ₂ ) Light emitting element. The method of claim 1, The metal is an electroluminescent device having a low work function and a metal having high reactivity with a halogen element. The method of claim 6, The metal is an electroluminescent device is aluminum or magnesium. The method of claim 1, The second electrode is an electroluminescent device made of silver or silver alloy. The method of claim 1, An electroluminescent device having an electron transport layer interposed between the light emitting layer and the electron injection layer. The method of claim 1, And at least one of a hole injection layer and a hole transport layer interposed between the first electrode and the light emitting layer. The method of claim 1, The anode is an electroluminescent device consisting of a transparent conductive film. The method of claim 1, The light emitting layer is an electroluminescent device comprising an organic material. Providing a substrate; Forming a first electrode on the substrate; Forming a light emitting layer on the first electrode; Forming an electron injection layer including a halogen metal compound and a metal on the light emitting layer; And Forming a second electrode on the electron injection layer manufacturing method of an electroluminescent device. The method of claim 13, Forming the electron injection layer, Forming a first layer including a halogen metal compound on the light emitting layer; And forming a second layer made of a metal on the first layer. The method of claim 13, Forming the electron injection layer A method of manufacturing an electroluminescent device which is carried out by co-depositing the halogen metal compound and a metal. The method of claim 13, The halogen metal compound is any one selected from the group consisting of lithium fluoride (LiF), sodium fluoride (NaF), cesium fluoride (CsF), magnesium fluoride (MgF ₂ ) and calcium fluoride (CaF ₂ ) Method of manufacturing a light emitting device. The method of claim 13, The metal has a low work function and is a metal having high reactivity with a halogen element. The method of claim 17, The metal is aluminum or magnesium manufacturing method of the electroluminescent device. The method of claim 13, The second electrode is a method of manufacturing an electroluminescent device formed of silver or silver alloy.

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