KR100721429B1 - Organic light emitting diode and the method for preparing the same - Google Patents

Abstract

The present invention includes an organic light emitting diode having an anode, a cathode, and an emission layer interposed between the anode and the cathode, and an electron injection layer including at least one material selected from the group consisting of metal nitrides and metal oxides between the cathode and the emission layer. And to a method for producing the same. The organic light emitting diode has excellent electrical characteristics, and thus, a flat panel display having improved reliability may be obtained.

Organic light emitting diode

Description

Organic light emitting diode and method for preparing the same

1A and 1B are cross-sectional views schematically illustrating a structure of an organic light emitting diode according to an embodiment of the present invention.

2A and 2B are graphs showing current-voltage characteristics of organic light emitting diodes according to the present invention manufactured according to various N ₂ plasma powers and N ₂ plasma treatment times.

3 is a graph showing the current-voltage characteristics of an organic light emitting diode according to the present invention having LiF layers having various thicknesses.

4 is a graph showing current-voltage characteristics of an organic light emitting diode according to the present invention having MgO layers having various thicknesses.

5 is a graph showing current-voltage characteristics of one embodiment of an organic light emitting diode according to the present invention,

6 is a graph showing luminance characteristics of one embodiment of the organic light emitting diode according to the present invention.

The present invention relates to an organic light emitting diode and a method of manufacturing the same, and more particularly, to an organic light emitting diode having an electron injection layer containing at least one of a metal nitride and a metal oxide and a method of manufacturing the same. The organic light emitting diode according to the present invention has excellent electrical properties, and by using this, a flat panel display having improved reliability can be obtained.

In the 21st century, the movement to the information society is accelerating, and accordingly, the information display is gradually shifting from the conventional CRT display to the flat display according to the necessity to exchange information anytime and anywhere. Among them, liquid crystal displays (LCDs) are most commonly used as flat panel displays because of their lightness and low power consumption.However, since they are light emitting devices instead of self emitting devices, brightness, contrast ratio, viewing angle, Due to technical limitations such as large area, efforts are being made to develop new flat panel displays that can overcome these shortcomings. One of these new flat panel displays is an organic light emitting diode (OLED), which is capable of low voltage driving, has a wide viewing angle and a fast response speed, and is light-emitting as a self-luminous type. Therefore, Japan, Korea, and the United States have recently accelerated the practical use.

Since the introduction of OLED by Tang and Van Slyke in 1987, indium tin oxide (ITO), which is transparent, has good conductivity and has a work function of 4.7 eV, is commonly used as the anode material of OLED. In the case of a general OLED using the anode made of ITO, the light generated from the light emitting layer becomes a bottom-emitting OLED which is taken out through the anode, that is, ITO. However, in the case of an active matrix OLED, since two or more transistors are required to drive one OLED, such a transistor has a disadvantage in that the light generated in the light emitting layer of the OLED is extracted, that is, the aperture ratio is reduced. .

In order to solve this problem, research on transparent OLED (TOLED) using both cathode and anode as ITO, which is a transparent conductive oxide, has been started. After that, 90% reflectivity of Ag, Al, etc. is used as the bottom electrode. Research into improving the efficiency of TOLED by using a material larger than this has been conducted. Inverted top-emission OLEDs (ITEOLEDs), which use a cathode as the back electrode, are among ATOLED's n-channel transistors, which have excellent electrical characteristics, especially charge mobility. It is very attractive in that it can be applied to.

One of the important problems in manufacturing such a TOLED is the improvement of the hole or electron injection ability from the hole injection electrode or the electron injection electrode to the light emitting layer. Ag and Al are mainly used as the back electrode of TOLED and ITEOLED, respectively. These materials have excellent reflectivity of 90% or more, but Ag has a small work function because it is used as an anode (~ 4.7 eV), and Al is used as a cathode. Since the work function is relatively large (~ 4.3 eV), when they are used as anodes or cathodes of TOLEDs or ITEOLEDs, respectively, the charge injection barrier between the electrode and the organic material layer (e.g., the light emitting layer) is large, so that the effective hole or electron injection Has the disadvantage of falling ability. Therefore, there is a need for improvement thereof.

The present invention is designed to solve the above problems, and an object thereof is to provide an organic light emitting diode having an electron injection layer including at least one of a metal nitride and a metal oxide and a method of manufacturing the same.

In order to achieve the above object of the present invention, a first aspect of the present invention comprises an anode, a cathode and a light emitting layer interposed between the anode and the cathode, and selected from the group consisting of metal nitride and metal oxide between the cathode and the light emitting layer Provided is an organic light emitting diode having an electron injection layer including one or more materials.

In order to achieve the another object of the present invention, the second aspect of the present invention, forming a cathode on the substrate, and the electron injection layer made of at least one material selected from the group consisting of metal nitride and metal oxide on the cathode Forming a light emitting layer; forming a light emitting layer on the electron injection layer; and forming an anode on the light emitting layer.

The organic light emitting diode according to the present invention has excellent electrical characteristics, and by using this, a flat panel display having improved reliability can be obtained.

Hereinafter, the present invention will be described in more detail.

The organic light emitting diode according to the present invention includes an anode, a cathode, and a light emitting layer interposed between the anode and the cathode, wherein the electron injection layer including at least one material selected from the group consisting of metal nitrides and metal oxides between the cathode and the light emitting layer. Intervened.

Since the electron injection layer increases the electron injection ability by the tunneling effect, it is possible to improve the electron injection ability from the cathode to the light emitting layer. More specifically, a dipole is formed between the cathode and the light emitting layer to cause a potential drop, thereby effectively matching the lowest-unoccupied molecular orbital (LUMO) energy level and the Fermi energy level of the material forming the light emitting layer. You can. As a result, the tunneling barrier of the electrons can be reduced to improve the electron injection. As such materials, the inventors have found that metal nitrides and / or metal oxides may be used.

More specifically, the metal nitride that may be included in the electron injection layer may be selected from the group consisting of Mg nitride, Al nitride, Ti nitride, Ag nitride and Ta nitride, but is not limited thereto. Preferably, the metal nitride may be TaN, TiN or AlNx (x ≧ 1).

Meanwhile, the metal oxide that may be included in the electron injection layer may be selected from the group consisting of Mg oxide, Al oxide, Ti oxide, Ag oxide, and Ta oxide, but is not limited thereto. Preferably, the metal oxide may be Al ₂ O ₃ , TiO ₂ , Ta ₂ O ₃ or MgO.

The electron injection layer according to the present invention may further include halides of alkali metals in addition to metal nitrides and / or metal oxides. Specific examples of the halide of the alkali metal include, but are not limited to, LiF, NaCl, CsF, and the like.

The thickness of the electron injection layer according to the present invention may be 0.1 nm to 10 nm. When the thickness of the electron injection layer is less than 0.1 nm, a satisfactory degree of electron injection effect cannot be obtained, and when the thickness of the electron injection layer exceeds 10 nm, the driving voltage increases, which is not preferable.

The electron injection layer according to the present invention may have a single layer structure made of one material or two or more multilayer structures made of different materials. More specifically, the electron injection layer according to the present invention has a multi-layer structure such as AlNx (x≥1) layer / LiF layer, AlNx (x≥1) layer / MgO layer, MgO layer / LiF layer, or LiF layer / MgO layer. It may have, but is not limited thereto. Among them, AlN _x and MgO have a large bandgap (˜6.2, 7.8 eV) and a large dielectric constant (˜10.7, 9.96), and thus the AlNx (x ≧ 1) layer / MgO layer structure. The electron injection layer having H can significantly lower the electron injection barrier due to a potential drop due to dipole formation between the cathode and the light emitting layer.

In the organic light emitting diode according to the present invention, the anode is an electrode for injecting holes and the cathode is an electrode for injecting electrons. Any of the above anode and cathode can be used as the back electrode. Preferably the cathode may be a back electrode.

The cathode is Al, Ca, Ce, Co, Cr, Cu, Fe, Ga, Gd, Ge, In, La, Ni, Mg, Mn, Na, Pb, Pd, Pt, Sb, Se, Si, Sn, Te , Ti, Zn, and may include one or more selected from the group consisting of alloys thereof, but is not limited thereto. In addition, the cathode according to the invention may have a multi-layered structure composed of two or more different materials among them.

According to an embodiment of the present invention, the cathode of the present invention may have a Ti layer / Al layer structure. Al has a high reflectance, high conductivity, has a relatively small work function, and is suitable as a cathode material, and Ti allows the Al layer to be better adsorbed onto the substrate.

The organic light emitting diode according to the present invention may have various laminated structures. For example, an electron transport layer may be further included between the electron injection layer and the emission layer. At this time, in the case of using a material having electron transport capability as the light emitting layer material, it is not necessary to provide a separate electron transport layer. Alternatively, the light emitting layer may further include at least one of a hole injection layer and a hole transport layer between the anode.

Accordingly, as shown in FIG. 1A, the cathode, the electron injection layer, the light emitting layer, and the anode are stacked in order, or as shown in FIG. 1B, the cathode, the electron injection layer, the light emitting layer, the hole transport layer, the hole injection layer, and the like. The anode may have a stacked structure in order, but is not limited thereto. 1A and 1B are organic light emitting diodes according to the present invention, which briefly illustrate an embodiment of an ITEOLED whose cathode is a cathode, but is not limited thereto. For example, it is also possible to use an anode as a back electrode by stacking in the reverse order of the stacking order as shown in FIGS. 1A and 1B.

One embodiment of the method of manufacturing an organic light emitting diode according to the present invention comprises the steps of forming a cathode on the substrate; Forming an electron injection layer made of at least one material selected from the group consisting of metal nitrides and metal oxides on the cathode; Forming a light emitting layer on the electron injection layer; And forming an anode on the light emitting layer. Among them, at least one of a hole transport layer forming step and a hole injection layer forming step may be further included between the light emitting layer forming step and the anode forming step.

On the other hand, there is also provided a method for producing an organic light emitting diode using an anode as a back electrode. That is, another embodiment of the method of manufacturing an organic light emitting diode according to the present invention comprises the steps of forming an anode on the substrate; Forming a light emitting layer on the anode; Forming an electron injection layer made of at least one material selected from the group consisting of metal nitrides and metal oxides on the light emitting layer; And forming a cathode on the electron injection layer.

Hereinafter, a method of manufacturing an organic light emitting diode according to the present invention will be described in detail with reference to the organic light emitting diode as shown in FIG. 1B.

First, a cathode is formed on the substrate. As the substrate, a substrate used in a conventional organic light emitting diode is used, and a glass substrate or a transparent plastic substrate excellent in mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and waterproofness is preferable. When manufacturing an AMOLED, the substrate may be provided with a transistor. For the material constituting the cathode, see the above. The cathode may be formed using various known deposition methods.

Next, an electron injection layer HIL is formed on the cathode. For the material, thickness, structure, etc. of the electron injection layer, refer to the foregoing.

The electron injection layer forming step may be performed by N ₂ , O ₂ or N ₂ O plasma treatment of the cathode surface. For example, when the surface of the cathode is Al, by treating the surface with N ₂ plasma, an electron injection layer made of AlNx (x ≧ 1) may be formed on the Al layer, which is the cathode.

The conditions for plasma treatment of the cathode surface are different depending on the thickness of the electron injection layer to be formed. Specifically, the plasma power may be 25W to 75W, and the plasma processing time may be 15 seconds to 60 seconds. If the plasma power and the plasma treatment time do not reach the above-mentioned bar, the thickness of the electron injection layer is too thin to obtain a satisfactory electron injection effect, and when the plasma power and plasma treatment time exceeds the above-mentioned bar, the electron injection The thickness of the layer may be too thick and the driving voltage may rise.

Apart from this, the electron injection layer can be formed by depositing metal nitride and / or metal oxide on the cathode by using a known deposition method, a sputtering method, or the like as described above. When the electron injection layer is formed by the sputtering method, the sputtering conditions vary depending on the compound used as a material of the electron injection layer, the structure and thermal properties of the target electron injection layer, and the like. It can select suitably from the range of the pressure of -10 mTorr and the sputtering power of 50-200W.

Meanwhile, after the electron injection layer is formed, the surface of the electron injection layer may be further treated with O ₂ , N ₂ , N ₂ O or Ar plasma. As a result, various impurities associated with the formation of the electron injection layer may be removed to obtain an organic light emitting diode having more excellent electrical characteristics.

Thereafter, an electron transport layer (not shown in FIG. 1B) is selectively formed on the electron injection layer using various methods such as vacuum deposition, spin coating, and casting. Subsequently, if the light emitting layer material to be described also has electron transporting properties, the electron transporting layer may not be provided separately, but if electron transporting properties are additionally required, an electron transporting layer may be selectively formed.

When the electron transport layer is formed by the vacuum deposition method, the conditions vary depending on the compound used, but generally in the range of deposition temperature of 100 to 500 ° C, vacuum degree of 10 ^-8 to 10 ^-3 torr, and deposition rate of 0.01 to 100 mW / sec. You can choose appropriately.

On the other hand, in the case of forming the electron transport layer by the spin coating method, the coating conditions are different depending on the compound used as the material of the electron transport layer, the structure and thermal properties of the desired electron transport layer, the coating speed of about 2000rpm to 5000rpm, coating The heat treatment temperature for post solvent removal may be appropriately selected in the temperature range of about 80 ℃ to 200 ℃.

The electron transport layer material functions to stably transport electrons injected from the cathode, and a quinoline derivative, in particular, a known material such as tris (8-quinolinorate) aluminum (Alq ₃ ), TAZ, Balq, or the like may be used.

The electron transport layer may have a thickness of about 100 kPa to 1000 kPa, preferably 200 kPa to 500 kPa. This is because when the thickness of the electron transport layer is less than 100 kV, the electron transport characteristic may be degraded, and when the thickness of the electron transport layer exceeds 1000 kW, the driving voltage may increase.

The emission layer EML may be formed on the electron injection layer (the electron transport layer if the electron transport layer is formed separately) using a vacuum deposition method, a spin coating method, a cast method, an LB method, or the like. When the light emitting layer is formed by a vacuum deposition method or a spin coating method, the deposition conditions vary depending on the compound used, but are generally selected from the ranges of conditions almost the same as that of the electron transport layer.

As the light emitting layer material, as a variety of known materials, a single material or a mixture of a host and a dopant may be used. For example, Alq ₃ or CBP (4,4'-N, N'-dicarbazole-biphenyl), PVK (poly (n-vinylcarbazole)), etc. can be used. In the case of the dopant material, IDE102, IDE105, and C545T available from Hayashibara, Inc. can be used as fluorescent dopants, and red phosphorescent dopants PtOEP, UD's RD 61, and green phosphorescent dopants can be used as phosphorescent dopants. Ir (PPy) ₃ (PPy = 2-phenylpyridine), F2Irpic which is a blue phosphorescent dopant, and a red phosphorescent dopant RD 61 manufactured by UDC.

In particular, when forming the light-emitting layer as Alq _3, Alq ₃ may not be provided ttaroyi the bar, an electron transport layer that can serve as a light emitting layer and the electron transporting layer at the same time.

The thickness of the light emitting layer may be about 100 kPa to 1000 kPa, preferably 200 kPa to 600 kPa. This is because, when the thickness of the light emitting layer is less than 100 kW, the light emission characteristics may be reduced, and when the thickness of the light emitting layer exceeds 1000 kW, the driving voltage may increase.

The hole transport layer (HTL) may be formed on the emission layer by using various methods such as vacuum deposition, spin coating, casting, and LB. When the hole transport layer is formed by the vacuum deposition method and the spinning method, the deposition conditions and the coating conditions vary depending on the compound used, but are generally selected from a range of conditions substantially the same as the formation of the electron transport layer.

As the hole transport material, a known hole transport material may be used. Examples of such hole transport materials include carbazole derivatives such as N-phenylcarbazole and polyvinylcarbazole, N, N'-bis (3-methylphenyl) -N, N'-diphenyl- [1, Having an aromatic condensed ring such as 1-biphenyl] -4,4'-diamine (TPD), N, N'-di (naphthalen-1-yl) -N, N'-diphenyl benzidine (α-NPD) Conventional amine derivatives and the like are included, but are not limited thereto.

The hole transport layer may have a thickness of about 50 kPa to 1000 kPa, preferably 100 kPa to 600 kPa. This is because when the thickness of the hole transport layer is less than 50 kV, hole transport characteristics may be degraded, and when the thickness of the hole transport layer exceeds 1000 kW, the driving voltage may increase.

The hole injection layer may be formed on the hole transport layer by using various methods such as vacuum deposition, spin coating, casting, and LB. When the hole injection layer is formed by the vacuum deposition method and the spinning method, the deposition conditions and the coating conditions vary depending on the compound used, and are generally selected from the ranges of conditions substantially the same as those of the formation of the electron transport layer.

As the hole injection layer material, various well-known hole injection materials may be used. For example, phthalocyanine compounds such as copper phthalocyanine (CuPc) disclosed in US Pat. No. 4,356,429, or starburst type amine derivatives described in Advanced Material, 6, p.677 (1994), TCTA, m-MTDATA, m -MTDAPB, Pani / DBSA (Polyaniline / Dodecylbenzenesulfonic acid: polyaniline / dodecylbenzenesulfonic acid) or PEDOT / PSS (Poly (3,4-ethylenedioxythiophene) / Poly (4-styrenesulfonate): poly (3, 4-ethylenedioxythiophene) / poly (4-styrenesulfonate)), Pani / CSA (Polyaniline / Camphor sulfonic acid: polyaniline / camphorsulfonic acid) or PANI / PSS (Polyaniline) / Poly (4-styrenesulfonate): polyaniline) / Poly (4-styrenesulfonate)) and the like can be used.

Thereafter, an anode may be formed on the hole injection layer. As the anode material, indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO ₂ ), zinc oxide (ZnO), and the like, which are transparent and have excellent conductivity, may be used. Apart from this, Au, Mg, Ag, Al and the like can also be used.

Such organic light emitting diodes can be used in a variety of flat panel displays. Or it can be used also as a light source, such as LCD. In particular, when the cathode is a back electrode, an n-channel transistor can be used as the transistor provided under the substrate, whereby a flat panel display having better electrical characteristics can be obtained.

Hereinafter, the present invention will be described in more detail using examples.

Example

Production Example  A ( Comparative example )

An organic light emitting diode having the following structure was fabricated: glass substrate / cathode (Ti 20 nm, Al 150 nm) / light emitting layer (Alq ₃ 22 nm) / hole transport layer (α-NPD 35nm) / hole injection layer (CuPc 18nm) / anode (Au 30 nm).

Glass substrates were prepared and purified using acetone, isopropyl alcohol and deionized water. A pattern of the region where the cathode is to be formed on the glass substrate is formed by using conventional lithography, and then loaded into a thermal evaporator having a pressure of 2 × 10 ⁻⁶ Torr. The cathode was formed by depositing Ti 20 nm and Al 150 nm in order. Thereafter, Alq ₃ , α-NPD, and CuPc were deposited to have thicknesses of 22 nm, 35 nm, and 18 nm, respectively, to form a light emitting layer, a hole transport layer, and a hole injection layer, and then, Au was deposited at 30 nm to form an anode. The organic light emitting diode was completed. This is called sample A.

Production Example  B

An organic light emitting diode having the following structure was fabricated: glass substrate / cathode (Ti 20 nm, Al 150 nm) / electron injection layer (AlNx) / light emitting layer (Alq ₃ 22 nm) / hole transport layer (α-NPD 35nm) / hole injection Layer (CuPc 18 nm) / anode (Au 30 nm).

Glass substrates were prepared and purified using acetone, isopropyl alcohol and deionized water. A pattern of the region where the cathode is to be formed on the glass substrate is formed by using conventional lithography, and then loaded into a thermal evaporator having a pressure of 2 × 10 ⁻⁶ Torr. The cathode was formed by depositing Ti 20 nm and Al 150 nm in order. After loading it into a plasma treatment chamber, it was exposed to N ₂ plasma (N ₂ injection rate: 10 sccm) under 100 mTorr and 35 W for 30 seconds, thereby depositing an electron injection layer made of AlN _x on the cathode. Formed. This was again loaded into a thermal evaporator, and Alq ₃ , α-NPD and CuPc were deposited to have thicknesses of 22 nm, 35 nm, and 18 nm, respectively, to form a light emitting layer, a hole transport layer, and a hole injection layer. Thereafter, Au was deposited at 30 nm to form an anode, thereby completing an organic light emitting diode. This is called sample B1.

Production Example  C ( Comparative example )

Among the Preparation Example A, except that LiF was further deposited to a thickness of 0.5nm on the cathode, using the same method as Preparation Example A, an organic light emitting diode having the following structure was manufactured: Glass substrate / cathode (Ti 20nm, Al 150nm) / electron injection layer (LiF 0.5nm) / light emitting layer (Alq ₃ 22nm) / hole transport layer (α-NPD 35nm) / hole injection layer (CuPc 18nm) / anode (Au 30nm) . This is called sample C.

Production Example  D

An organic light emitting diode having the following structure was fabricated: glass substrate / cathode (Ti 20nm, Al 150nm) / electron injection layer (MgO 1nm) / light emitting layer (Alq ₃ 22nm) / hole transport layer (α-NPD 35nm) / hole Injection layer (CuPc 18 nm) / anode (Au 30 nm).

Glass substrates were prepared and purified using acetone, isopropyl alcohol and deionized water. A pattern of the region where the cathode is to be formed on the glass substrate is formed by using conventional lithography, and then loaded into a thermal evaporator having a pressure of 2 × 10 ⁻⁶ Torr. Then, Ti 20 nm and Al 150 nm were sequentially deposited to form a cathode, and then MgO was deposited to a thickness of 1 nm to form an electron injection layer. MgO deposition was performed using RF magnetron sputtering under conditions of room temperature, Ar: O ₂ = 20: 5 sccm, 5 mTorr, 100W. This was again loaded into a thermal evaporator, and Alq ₃ , α-NPD and CuPc were deposited to have thicknesses of 22 nm, 35 nm, and 18 nm, respectively, to form a light emitting layer, a hole transport layer, and a hole injection layer. Thereafter, Au was deposited at 30 nm to form an anode, thereby completing an organic light emitting diode. This is called sample D.

Production Example E1

An organic light emitting diode having the following structure was fabricated: glass substrate / cathode (Ti 20 nm, Al 150 nm) / electron injection layer (AlNx, LiF 0.5 nm) / light emitting layer (Alq ₃ 22 nm) / hole transport layer (α-NPD 35 nm) ) / Hole injection layer (CuPc 18 nm) / anode (Au 30 nm).

Glass substrates were prepared and purified using acetone, isopropyl alcohol and deionized water. A pattern of the region where the cathode is to be formed on the glass substrate is formed by using conventional lithography, and then loaded into a thermal evaporator having a pressure of 2 × 10 ⁻⁶ Torr. Then, Ti 20 nm and Al 150 nm were deposited one by one to form a cathode. After loading it into a plasma treatment chamber, it was exposed to 100 mTorr and 35 W of N ₂ plasma (N ₂ inflow rate: 10 sccm) for 30 seconds to form an AlN _x layer on top of the cathode, LiF was deposited to a thickness of 0.5 nm on the AlNx layer to form an electron injection layer. This was again loaded into a thermal evaporator, and Alq ₃ , α-NPD and CuPc were deposited to have thicknesses of 22 nm, 35 nm, and 18 nm, respectively, to form a light emitting layer, a hole transport layer, and a hole injection layer. Thereafter, Au was deposited at 30 nm to form an anode, thereby completing an organic light emitting diode. This is called sample E1.

Production Example E2  To E8

Samples E2 to E8 were prepared in the same manner as in Preparation Example B1, except that N ₂ plasma treatment conditions in Preparation Example E1 were adjusted as in Table 1 below. Samples E2 to E5 were prepared by changing plasma power to 0 W, 25 W, 65 W, and 75 W, respectively, with the N ₂ plasma treatment time fixed at 30 seconds, and samples E6 to E8 being plasma treated with the plasma power fixed. The time was changed to 15 seconds, 20 seconds, and 60 seconds, respectively.

Sample No. N ₂ injection rate (sccm) Plasma Power (W) Plasma Treatment Time (sec) E1 10 35 30 E2 10 0 30 E3 10 25 30 E4 10 65 30 E5 10 75 30 E6 10 35 15 E7 10 35 20 E8 10 35 60

The current-voltage characteristics of the organic light emitting diode according to the N ₂ plasma power and plasma treatment time for forming the AlNx layer as the electron injection layer by evaluating the current-voltage characteristics of the samples E1 to E8 are shown in FIGS. 2A and 2B. It was. Hewlett Packard's 4156 A device was used to evaluate the current-voltage characteristics of the organic light emitting diode.

Figure 2a shows the current-voltage characteristics of the samples E1 to E5, the N ₂ plasma treatment time is 30 seconds, the N ₂ injection rate is fixed at 10 sccm, the current-voltage characteristics when the N ₂ plasma power is changed It is shown. It can be seen from FIG. 2A that the best current-voltage characteristics are shown when the N ₂ plasma power is 35W.

2B shows the current-voltage characteristics of samples E1 and E6 to E8, and the current-voltage when the N ₂ plasma treatment time is changed after fixing the N ₂ plasma power at 35 W and the N ₂ injection rate at 10 sccm. It is characteristic. It can be seen from FIG. 2B that the best current-voltage characteristics are shown when the N ₂ plasma treatment time is 30 seconds.

Production Example E9  And E10

Samples E9 and E10 were prepared in the same manner as in Preparation Example E1 except that the thickness of the LiF layer was adjusted as shown in Table 2 in Preparation Example E1.

Sample No. LiF layer thickness (nm) E9 0.8 E10 One

The current-voltage characteristics of Sample B (ie, the thickness of the LiF layer is 0 nm), E1, E9, and E10 were evaluated to evaluate the effect of the thickness of the LiF layer on the current-voltage characteristics of the organic light emitting diode in addition to the AlNx layer. . Hewlett Packard's 4156 A device as described above was used to evaluate the current-voltage characteristics, and the results are shown in FIG. 3.

According to FIG. 3, the current-voltage characteristics of samples E1, E9, and E10 including LiF layers were better than those of sample B without further LiF layers, and the current-voltage characteristics were excellent in the order of E10, E9, and E1. Can be.

Production Example  F1

An organic light emitting diode having the following structure was fabricated: glass substrate / cathode (Ti 20 nm, Al 150 nm) / electron injection layer (AlNx, MgO 1 nm) / light emitting layer (Alq ₃ 22 nm) / hole transport layer (α-NPD 35nm) / Hole injection layer (CuPc 18 nm) / anode (Au 30 nm).

Glass substrates were prepared and purified using acetone, isopropyl alcohol and deionized water. A pattern of the region where the cathode is to be formed on the glass substrate is formed by using conventional lithography, and then loaded into a thermal evaporator having a pressure of 2 × 10 ⁻⁶ Torr. Then, Ti 20 nm and Al 150 nm were deposited one by one to form a cathode. After loading it into a plasma treatment chamber, it was exposed to 100 mTorr and 35 W of N ₂ plasma (N ₂ inflow rate: 10 sccm) for 30 seconds to form an AlN _x layer on top of the cathode, MgO was deposited to a thickness of 1 nm on the AlNx layer to form an electron injection layer. MgO deposition was performed using RF magnetron sputtering under conditions of room temperature, Ar: O ₂ = 20: 5 sccm, 5 mTorr, 100W. This was again loaded into a thermal evaporator, and Alq 3, α-NPD and CuPc were deposited to have thicknesses of 22 nm, 35 nm, and 18 nm, respectively, to form a light emitting layer, a hole transport layer, and a hole injection layer. Thereafter, Au was deposited at 30 nm to form an anode, thereby completing an organic light emitting diode. This is called sample F1.

Production Example  F2 and F3

Samples F2 and F3 were prepared in the same manner as in Preparation Example F1, except that the thickness of the MgO layer was adjusted as in Table 3 in Preparation Example F1.

Sample No. Thickness of MgO Layer (nm) F2 0.5 F3 2

The current-voltage characteristics of the samples F1 to F3 were evaluated to evaluate the effect of the thickness of the MgO layer on the current-voltage characteristics of the organic light emitting diode in addition to the AlNx layer. Hewlett Packard's 4156 A device as described above was used to evaluate the current-voltage characteristics, and the results are shown in FIG. 4.

According to FIG. 4, it can be seen that Sample F1 including the MgO layer having a thickness of 1 nm among Samples F1 to F3 has the best current-voltage characteristics.

Production Example  G

After the formation of the preparation of F1, AlNx / MgO electron injection layer, an electron injection layer, thereby completing the organic light emitting diode is a point of the surface was N ₂ plasma treatment in the same manner as in Preparative F1 negative. This is called sample G.

Evaluation example

The current-voltage characteristics of samples A, B, C, D, E1, F1 and G were evaluated and the results are shown in FIG. 5. According to FIG. 5, it can be seen that, among the seven samples, the current-voltage characteristic of the sample A without the electron injection layer is the worst. Sample A had an operating voltage of about 12.6 V at a current density of 50 mA / cm ² . Samples B, C, and D using AlN _x , LiF, and MgO as the electron injection layers, respectively, showed better current-voltage characteristics than sample A, and the operating voltages were about 10.8, about 11.1, and about 10.7 at 50 mA / cm ² , respectively. Similar results were obtained with V. As a result, it can be seen that electron injection can be performed more effectively by performing an N ₂ plasma treatment on the Al surface, which is part of the cathode, as in Sample B, and further forming an AlN x layer. Sample E1 using AlN _x / LiF and sample F1 using AlN _x / MgO showed operating voltages of 10.5 and 8.9 V at 50 mA / cm ² , respectively, indicating excellent current-voltage characteristics.

On the other hand, the sample E1, and F1 with respect to G, exhibited a luminance (cd / m ²⁾ corresponding to a current density (mA / cm ²⁾ in Fig. 6 by evaluation. Yokokawa instrument 3298F device was used for brightness evaluation. At 200 mA / cm ² , sample E1 exhibited a luminance of 840 cd / m ² , sample F1 exhibited a luminance of 950 cd / m ² , and sample G exhibited a luminance of 1030 cd / m ² .

The organic light emitting diode according to the present invention has an electron injection layer made of a metal nitride or a metal oxide between the cathode and the light emitting layer, so that electron injection can be easily performed, thereby having excellent current-voltage characteristics and luminance.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (19)

An anode, a cathode and a light emitting layer interposed between the anode and the cathode, the cathode is an electron injection electrode, the cathode is Al, Ca, Ce, Co, Cr, Cu, Fe, Ga, Gd, Ge, In, La At least one selected from the group consisting of Ni, Mg, Mn, Na, Pb, Pd, Pt, Sb, Se, Si, Sn, Te, Ti, Zn, and alloys thereof, between the cathode and the light emitting layer. Two or more multi-layered structures comprising a) at least one material selected from the group consisting of metal nitrides and metal oxides, and b) at least two of the alkali metal halides, wherein the electron injection layers are made of different materials. An organic light emitting diode having a. delete The method of claim 1, wherein the metal nitride is selected from the group consisting of Mg nitride, Al nitride, Ti nitride, Ag nitride and Ta nitride, the metal oxide is Mg oxide, Al oxide, Ti oxide, Ag oxide and Ta oxide An organic light emitting diode, characterized in that selected from the group consisting of. The organic light emitting diode of claim 1, wherein the electron injection layer is formed by N ₂ , O _2, or N ₂ O plasma treatment on a cathode surface. The organic light emitting diode of claim 1, wherein the metal nitride is TaN, TiN, or AlNx (x ≧ 1), and the metal oxide is Al ₂ O ₃ , TiO ₂ , Ta ₂ O _3, or MgO. The organic light emitting diode of claim 1, wherein the electron injection layer has a thickness of 0.1 nm to 10 nm. delete The method of claim 7, wherein the electron injection layer has a structure of AlNx (x≥1) layer / LiF layer, AlNx (x≥1) layer / MgO layer, MgO layer / LiF layer or LiF layer / MgO layer. Organic light emitting diode. delete The organic light emitting diode of claim 1, wherein the cathode has a Ti layer / Al layer structure. The organic light emitting diode of claim 1, further comprising at least one of a hole injection layer and a hole transport layer between the light emitting layer and the anode. Al, Ca, Ce, Co, Cr, Cu, Fe, Ga, Gd, Ge, In, La, Ni, Mg, Mn, Na, Pb, Pd, Pt, Sb, Se, Si as electron injection electrodes on the substrate Forming a cathode comprising at least one selected from the group consisting of Sn, Te, Ti, Zn and alloys thereof; An electron injection layer having at least two multi-layered structures comprising a) at least one material selected from the group consisting of a) metal nitrides and metal oxides, and b) halides of alkali metals, and comprising different materials on top of the cathode; Forming; Forming a light emitting layer on the electron injection layer; And Forming an anode on the light emitting layer; Method for manufacturing an organic light emitting diode comprising a. The method of claim 12, wherein the forming of the electron injection layer is performed by treating the surface of the cathode with O ₂ , N _2, or N ₂ O plasma. The method of claim 12, wherein the forming of the electron injection layer is performed by depositing one or more selected from the group consisting of metal nitrides and metal oxides on the cathode. The method of claim 12, further comprising, after forming the electron injection layer, treating the surface of the electron injection layer with O ₂ , N ₂ , N ₂ O, or Ar plasma. . The method of claim 12, further comprising at least one of a hole transport layer forming step and a hole injection layer forming step between the light emitting layer forming step and the anode forming step. The organic light emitting diode of claim 1, wherein the metal nitride or metal oxide is a nitride or oxide of a metal included in the cathode. The method of claim 13, wherein the plasma power is 25W to 75W during the plasma treatment. The method of claim 13, wherein the plasma treatment time is 15 seconds to 60 seconds during the plasma treatment.

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