KR100313912B1 - Organic Electroluminescent Device - Google Patents

Abstract

The present invention relates to an organic electroluminescent device, by forming a double layer consisting of a first layer and a second layer or a mixed layer in which these first and second layers are mixed between an organic laminated film and a cathode. At the same time has a long life. Here, the first layer is composed of a compound having a structure of formula (1) or at least one porphyrinic compound, the second layer is composed of at least one of alkali metal, alkaline earth metal and compounds thereof.

Formula 1

Description

Organic EL device

TECHNICAL FIELD The present invention relates to display elements, and more particularly to organic EL elements.

Recently, as the size of the display device increases, the demand for a flat display device having less space occupancy is increasing. As one of the flat display devices, an electroluminescent device is attracting attention.

This electroluminescent element is largely divided into inorganic electroluminescent element and organic EL element according to the material used.

In general, an inorganic electroluminescent device is a device that emits light by applying a high electric field to a light emitting part, accelerating electrons in the high electric field, and colliding with the light emitting center to thereby excite the light emitting center.

In addition, the organic EL device has an exciton generated by combining electrons and holes injected by injecting electrons and holes into a light emitting part from an electron injection electrode and a hole injection electrode, respectively, from an excited state to a ground state. It is a device that emits light when falling.

The inorganic electroluminescent device having the above operating principle requires a high voltage of 100 to 200 V as a driving voltage because a high electric field is required, while an organic EL device can be driven at a low voltage of about 5 to 20 V. Because of this, research is being actively conducted.

In addition, the organic EL element has excellent characteristics such as wide viewing angle, high speed response and high contrast, so it can be used as a pixel of a graphic display, a pixel of a television image display or a surface light source. It is thin, light, and has good color, making it suitable for next-generation flat panel displays.

Looking at the structure of the organic EL device having such a use, as shown in Figure 1, the anode 2 formed on the transparent substrate 1, and the hole injection layer (HIL: hole injecting layer formed on the anode 2) (3) and hole transport layer (HTL) (4), light emitting layer (5) formed on the hole transport layer (4), and electron transport layer (ETL: electron transport layer) formed on the light emitting layer ( 6) and an electron injecting layer (EIL) 7 and a cathode 8 formed on the electron injecting layer 7.

Here, one or more of the hole injection layer 3, the hole transport layer 4, the electron transport layer 6, the electron injection layer 7 may be omitted.

The cathode 8 of the organic EL device thus formed injects electrons into the light emitting layer 5 through the electron transport layer 6 or the electron injection layer 7, and the anode 2 is the hole injection layer 3 or the hole. By injecting holes into the light emitting layer 5 through the transport layer 4, electron-holes are paired in the light emitting layer 5, and the light is emitted by emitting energy as it disappears.

In most organic EL devices, electron injection is much more difficult than hole injection. In general, the smaller the work function of the cathode, the easier the electron injection.

However, in general, materials having a small work function are difficult to use as electrodes because of their high reactivity.

Therefore, one or more stable metals such as Mg: Ag and Al: Li are often used in the form of an alloy and used as a cathode.

However, these alloys are less stable than aluminum and are expensive to manufacture and difficult to deposit uniformly.

When using materials with low work functions such as Mg: Ag or Al: Li as electrodes, a more serious problem is that Mg ions or Li ions diffuse into the organic film, causing cross-talk or leakage between pixels. The current often occurs.

However, the above problems can be alleviated by using the anode material as aluminum, but aluminum has a poor electron injecting capability, and thus a method of improving the problem is needed.

Therefore, in recent years, in order to improve the electron injection ability, an insulating material such as LiF, MgF ₂ , Li ₂ O between an aluminum electrode and a light emitting layer or between an aluminum electrode and an electron transport layer may be formed into a very thin (about 0.3 to 1.0 nm) ultra thin film. Examples have been reported. [IEEE Transactions on Electronic Devices, Vol. 44, No. 8, p 1245-1248 (1997)]

In this case, Li ₂ O is an insulator with a very low work function.

Alkaline metals are generally known to have a low work function and lower when oxidized.

For example, the work function of Cs is 2.1 eV, but the work function of Cs ₂ O decreases to about 1 eV.

In order to lower the electron injection barrier, various alkali metal compounds such as Li ₂ O, LiBO ₂ , NaCl, KCl, K ₂ SiO ₃ , RbCl, and Cs ₂ O have been used in the form of an insulating buffer layer.

However, despite the above improvement, the introduction of the insulating buffer layer has revealed new problems.

That is, the adhesion between the organic laminated film and aluminum was not good, and the lifetime of the device was reduced.

As a result, the adhesion between the buffer layer and the aluminum and the interface between the buffer layer and the organic layer was poor due to the difference between the materials.

SUMMARY OF THE INVENTION The present invention has been made to improve the above-mentioned conventional problems, and an object of the present invention is to provide an organic EL device capable of significantly increasing the luminous efficiency and lifetime of the device by inserting a new material between the organic laminated film and the cathode. have.

1 is a structural cross-sectional view showing a general organic EL device,

2 is a structural cross-sectional view showing an organic EL device according to the present invention.

Explanation of symbols for main parts of the drawings

21: transparent substrate 22: anode

23 organic laminated film 24 cathode

25: protective film 26: the first layer

27: second layer

In order to achieve the above object, the present invention provides a buffer layer including an anode on a substrate, an organic electroluminescent layer having at least one organic layer stacked on the anode, an organic electroluminescent layer formed on the organic electroluminescent layer, and a first layer made of a material of Formula 1 below. And it provides an organic EL device comprising a cathode formed on the buffer layer.

R ₁ to R ₄ is a material selected from the group consisting of hydrogen, an alkyl group (1-5 carbon atoms), an alkoxy group (1-5 carbon atoms), an aryl group, an aryloxyl group and a halogen group, wherein A is hydrogen, an alkyl group ( 1-5) and an aryl group.

Preferably, in the substance of Chemical Formula 1, R ₁ to R ₄ are each hydrogen, an alkyl group (1-5 carbon atoms), an alkoxy (1-5 carbon atoms) group, a phenoxyl group, a phenyl group, a naphthyl group, F, Cl, and Br It is a material selected from the group consisting of, wherein A is a material selected from the group consisting of methyl group, ethyl group, phenyl group and hydrogen.

More preferably, R ₁ is a substance selected from the group consisting of an alkyl group (1-5 carbon atoms), an alkoxy group (1-5 carbon atoms), a phenoxyl group, and a phenyl group, and R ₂ , R ₃ , R ₄ and A material wherein A is each hydrogen can be applied to the organic EL device.

In addition, the compound having the formula 1 of the present invention is a compound in which at least one of R ₁ and R ₂ , R ₂ and R ₃ and R ₃ and R ₄ are interconnected to form a pentagonal or hexagonal conjugated cyclic ring Can be selected. At this time, the skeleton of the ring may be selected from C, N and S.

Another feature of the present invention provides an organic EL device in which the buffer layer further comprises a second layer made of at least one of an alkali metal, an alkaline earth metal and a compound thereof.

In this case, the cathode may be formed of aluminum, and a layer made of Li ₂ O may be selected as the _second layer. The thickness of the second layer made of at least one of the alkali metal, the alkaline earth metal, and a compound thereof may be 0.2 nm to 3 nm, and the thickness of the first layer made of the material of Formula 1 may be 0.5 nm to 50 nm.

In addition, another feature of the present invention is that the buffer layer of the material constituting the first layer, that is, the compound of formula (1), and the material constituting the second layer, that is, at least one of the alkali metal, alkaline earth metal and compounds thereof It is to provide an organic EL device in which the material is a mixed layer in the form of co-deposition.

The mixing ratio between the material of formula 1 and at least one material of alkali metals, alkaline earth metals and compounds thereof in the mixed layer can be fixed or varied as a function of position. In addition, the thickness of the mixed layer may be selected within 0.5nm ~ 10nm, at this time, the cathode may be formed of aluminum. Meanwhile, Li ₂ O may be used as at least one material of the alkali metal, alkaline earth metal, and compounds thereof.

On the other hand, the present invention is an organic EL device comprising at least one organic electroluminescent layer between an anode and a cathode, the organic EL, characterized in that it comprises a first layer made of at least one porphyrinic compound (porphyrinic compound) Provided is an element.

The porphyrinic compound is characterized in that it has a structure of formula (2).

Wherein A is -N = or -C (R) =, wherein R is a substance selected from the group consisting of H, alkyl, alkoxy, aralkyl, alkaryl, aryl and heterocyclic groups, and M is a periodic table Is selected from the group consisting of elements of groups IA, IIA, IIIA, IVA, 3, 4, 5 and 6 cycles, wherein Y is an alkoxy group, phenoxyl group, alkylamino group, arylamino group , An alkylphosphine group, an arylphosphine group, an alkylsulfur group, or an arylsulfur group, or a substance selected from the group consisting of elements of the VIA and VIIA groups of the periodic table, wherein n is 0, 1, 2 It is an integer which is one of, and the B ₁ to B ₈ is hydrogen, alkyl group, aryl group, alkoxy group, aryloxyalkyl group, hydroxy group, hydroxyalkyl group, aralkyl group, alkylamino group, arylamino group, alkylthiol group, arylthiol Group, nitroalkyl , An alkylcarbonyl group, an alkoxycarbonyl group, a phenyl group, an amino group, a cyano group, a naphthyl group, an alkaryl group, or a substance selected from the halogen group, and a heterocyclic group consisting of a click, the B ₁ and B _2, B ₃ and B _4, B ₅ And one or more of B ₆ and B ₇ and B ₈ may be connected to each other to form any of an unsaturated or saturated pentagonal, hexagonal and heptagonal ring.

In the material of Formula 2, preferably M is 2Li, 2Na, Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Pt, Cu, 2Ag, Zn, Pd, Al, Ga, In , Si, Sn, Pb, 2H and TiO, and may be selected from the group consisting of, Y in the formula 2 is O, F, Cl, Br, alkoxy group (C1-10) and phenoxyl group from the group May be the selected material.

In addition, as the material of Formula 2, preferably one or more of the B1 and B2, B3 and B4, B5 and B6 and B7 and B8 are each interconnected to be any one of an unsaturated or saturated pentagonal, hexagonal and hexagonal ring The backbone of the ring may consist of elements selected from C, N, S and O, wherein the unsaturated or saturated pentagonal, hexagonal or heptagonal ring may be hydrogen, alkyl, aryl, alkoxy, aryloxyalkyl, hydroxy or hydroxy. Group consisting of alkyl group, aralkyl group, alkylamino group, arylamino group, alkylthiol group, arylthiol group, nitroalkyl group, alkylcarbonyl group, alkoxycarbonyl group, phenyl group, amino group, cyanyl group, naphthyl group, alkaryl group, halogen group and heterocyclic group It can be formed including a material selected from. In this case, a compound having the structure of Formula 3 or Formula 4 below may be selected.

Wherein A is -N = or -C (R) =, wherein R is a substance selected from the group consisting of H, alkyl, alkoxy, aralkyl, alkaryl, aryl and heterocyclic groups, and M is a periodic table Is selected from the group consisting of elements of groups IA, IIA, IIIA, IVA, 3, 4, 5 and 6 cycles, wherein Y is an alkoxy group, phenoxyl group, alkylamino group, arylamino group , An alkylphosphine group, an arylphosphine group, an alkylsulfur group and an arylsulfur group, or a substance selected from the group consisting of elements of the VIA and VIIA groups of the periodic table, wherein n is 0, 1, 2 And each of X ₁ to X ₈ is hydrogen, an alkyl group, an aryl group, an alkoxy group, an aryloxyalkyl group, a hydroxy group, a hydroxyalkyl group, an aralkyl group, an alkylamino group, an arylamino group, an alkylthiol group, or an arylthiol. Group, nitroalkyl It is a substance selected from the group consisting of a group, an alkylcarbonyl group, an alkoxycarbonyl group, a phenyl group, an amino group, a cyanyl group, a naphthyl group, an alkali group, a halogen group and a heterocyclic group. At this time, M of Formulas 3 and 4 is preferably 2Li, 2Na, Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Pt, Cu, 2Ag, Zn, Pd, Al, Ga, In , Si, Sn, Pb, 2H and TiO, and may be a material selected from the group consisting of, Y in the formula 3 and 4 is O, F, Cl, Br, alkoxy group (1 to 10 carbon atoms) and phenoxyl group It may be a material selected from. Also more preferably, the porphyrinic compound may be at least one of materials having the structures of Formulas 5 and 6.

In this case, M is a material selected from the group consisting of Co, AlCl, Cu, 2Li, Fe, Pb, Mg, SiCl ₂ , 2Na, Sn, Zn, Ni, Mn, VO, 2Ag, MnCl, SnCl ₂ and TiO.

The present invention also provides an organic EL device to which the porphyrinic compounds described above are applied, comprising: a second made of at least one of an alkali metal, an alkaline earth metal and a compound thereof between the cathode and the first layer made of the porphyrinic compound; The layer may be formed. In this case, the cathode may be formed of aluminum, and the second layer may be formed of Li ₂ O. In addition, the thickness of the second layer made of at least one of the alkali metal, alkaline earth metal and compounds thereof may be selected within 0.2 nm to 3 nm, and the thickness of the first layer made of the porperic compound is 0.5 nm to 50 nm. Can be selected within.

The present invention also provides an organic EL device in which the first layer is present in the form of a mixed layer in which at least one material of an alkali metal, an alkaline earth metal and a compound thereof is further included in the form of co-deposition. to provide. In this case, the mixing ratio between the porphyrin compound and at least one material of the alkali metal, alkaline earth metal and their compounds in the mixed layer may be fixed or changed as a function of position, and the thickness of the mixed layer is within 0.5 nm to 10 nm. Can be selected from. The cathode is preferably formed of aluminum, and Li ₂ O may be selected as at least one material of the alkali metal, alkaline earth metal, and compounds thereof.

The organic EL device having the above characteristics will be described below with reference to the accompanying drawings. FIG. 2 is a structural cross-sectional view showing an organic EL device according to the present invention. As shown in FIG. It is formed on a laminated structure having a transparent substrate 21, an anode 22, an organic laminated film (composed of a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer) 23, and a cathode 24, and a laminate structure. The first layer 26 and the second layer 27 are stacked between the passivation layer 25 and the organic layer layer 23 and the cathode 24 having a laminate structure to improve electron injection and adhesion.

Here, the materials used as the first layer 26 and the second layer 27 are as mentioned above.

Meanwhile, in order to improve electron injection, the material of the second layer 27 is made of at least one of an alkali metal, an alkaline earth metal, and a compound thereof, such as Li, Cs, Li ₂ O, LiF, and the like.

The cathode 24 is made of a metal such as Al or an alloy thereof.

As described above, in the present invention, the first layer 26 and the second layer 27 made of the above materials are laminated between the organic multilayer film 23 and the cathode 24 to improve the luminous efficiency of the device and at the same time, the lifetime. Greatly increase.

Here, the thicknesses of the first layer 26 and the second layer 27 are about 0.5 nm to 50 nm and 0.2 nm to 3 nm, respectively.

In order to investigate the characteristics of the organic EL device of the present invention having such a structure, the device according to the present invention and the device according to the prior art were analyzed.

Here, elements A and B are organic EL elements according to the prior art, and elements C and D are organic EL elements according to the present invention.

First, the basic device structure that emits green light is (1) 150 nm thick, an anode made of ITO (Indium Tin Oxide), (2) a buffer layer made of CuPc (copper phthalocyanine) having a thickness of about 10 nm to 20 nm, ( 3) A hole having a thickness of about 30 nm to 50 nm and consisting of N, N'-diphenyl-N, N'-bis (3-methylphenyl)-(1,1'-biphenyl) -4,4'-diamine (TPD) (4) A light emitting layer having a thickness of 40 nm to 60 nm and consisting of tris (8-hydroxy-quinolate) aluminum (Alq ₃ ).

Device A is a structure in which an aluminum cathode is formed directly on the organic laminated film (device structure: ITO / CuPc / TPD / Alq ₃ / Al), and device B is made of Li ₂ O having an thickness of about 1 nm between the organic laminated film and the cathode. The structure in which the second layer was inserted (element structure: ITO / CuPc / TPD / Alq ₃ / Li ₂ O (1 nm) / Al).

And device C is ITO / CuPc / TPD / Alq ₃ / CuPc (2nm) / Li ₂ O (1nm) / Al, and device D is ITO / CuPc / TPD / Alq ₃ / Li ₂ O (1nm) / CuPc ( 2 nm) / Al.

In other words, the stacking order of Li ₂ O (1 nm) and CuPc (2 nm) is reversed for the device C and the device D.

Finally, all devices are encapsulated in an inert gas.

When a current density of 3 mA / cm 2 was applied to each of the four types of devices, the voltages, luminances, and lifetimes applied to the cathodes and the anodes of the devices are shown in Table 1 below.

Voltage (V) Luminance (cd / ㎡) life span Element A 6 50 Short (less than 1 hour) Element B 6 100 Short (less than 1 hour) Element C 6 150 Long (more than 2000 hours) Element D 8 130 Medium (about 100 hours)

Here, the lifetime quoted in Table 1 means the time when the luminance drops to half of the initial value.

Thus, as shown in Table 1, it can be seen that the luminance of the elements C and D of the present invention is improved, and in particular, the life is greatly increased, rather than the elements A and B having the conventional structures.

The reason why the life is increased is as follows.

In the case of Li ₂ O, not only the adhesion between Alq ₃ and Al is poor, but the Li ₂ O layer having a thickness of 1 nm is not a completely uniform layer but rather has an island-like structure.

However, if there is a CuPc layer between Alq ₃ and Li ₂ O, like device C, a portion of the CuPc layer is in direct contact with the Al layer through open spaces in the Li ₂ O layer.

This phenomenon increases the adhesion at the interface between the organic film and the metal and increases the life of the device.

That is, the copper ions of the CuPc layer bond relatively strongly between CuPc and Al.

In addition, as shown in Table 1, it can be seen that the device D has a higher driving voltage than the device C.

The reason for this is that CuPc is present between Li ₂ O and Al, which increases the electron injection barrier.

The resulting increase in electrical and thermal stress shortens the lifetime compared to device C.

Meanwhile, the present invention uses a mixed layer in which the first layer and the second layer are mixed between the organic laminated film and the cathode instead of the double layer including the first layer 26 and the second layer 27 as shown in FIG. 2. It may be.

The mixed layer is formed by co-deposition of (1) an alkali metal, an alkaline earth metal, at least one of the compounds thereof, and (2) at least one of the compound having the formula (1) or the porperic compound.

This mixed layer improves adhesion but is poorly injected.

And in the mixed layer, the mixing ratio between these two groups of materials is fixed or varied as a function of position.

Among them, the mixing ratio is (1) Alkali metals, alkaline earth metals and compounds selected from the group consisting of these compounds almost 0% at the interface with the organic laminated film, the concentration of alkali metals or alkaline earth metals gradually increases toward the cathode (2) It is most preferable to have a structure in which at least one of the materials having the formula (1) or at least one of the porperic compounds is 0% at the interface with the cathode and the concentration of the porperic compound is increased toward the organic laminate. Do.

The thickness of this mixed layer is about 0.5-10 nm.

The organic EL device according to the present invention has the following effects.

A double layer consisting of a first layer and a second layer or a mixed layer of these two layers is formed between the organic layer and the cathode to greatly increase not only the luminance but also the life of the device.

Claims (13)

Anode on substrate, An organic light emitting layer in which at least one organic layer is stacked on the anode, A buffer layer formed on the organic light emitting layer, the buffer layer comprising a first layer made of a material of the following formula: An organic EL device comprising a cathode formed on the buffer layer: R ₁ to R ₄ are hydrogen, an alkyl group (1-5 carbon atoms), an alkoxy group (1-5 carbon atoms), an aryl group, an aryloxy group and a material selected from the group consisting of a halogen group, the R ₁ and R ₂ , At least one of R ₂ and R ₃ and R ₃ and R ₄ are interconnected to form a pentagonal or hexagonal conjugated cyclic ring; A is a substance selected from the group consisting of hydrogen, an alkyl group (1-5 carbon atoms) and an aryl group. The method of claim 1, The skeleton of the conjugated cyclic ring of pentagonal or hexagonal structure in which at least one of R ₁ and R ₂ , R ₂ and R _3, and R ₃ and R ₄ are interconnected is an element selected from C, N and S. An organic electroluminescent element characterized by the above-mentioned. The method of claim 1, R ₁ to R ₄ are each selected from the group consisting of hydrogen, an alkyl group (1-5 carbon atoms), an alkoxy (1-5 carbon atoms) group, a phenoxyl group, a phenyl group, a naphthyl group, F, Cl, and Br; A is an organic EL device, characterized in that the material selected from the group consisting of methyl, ethyl, phenyl and hydrogen. The method of claim 3, wherein R ₁ is a substance selected from the group consisting of an alkyl group (1-5 carbon atoms), an alkoxy group (1-5 carbon atoms), a phenoxyl group, and a phenyl group; And each of R ₂ , R ₃ , R ₄ and A is hydrogen. The method of claim 1, And the buffer layer further comprises a second layer made of at least one of an alkali metal, an alkaline earth metal and a compound thereof. The method of claim 1, And the buffer layer further comprises a second layer made of at least one of an alkali metal, an alkaline earth metal and a compound thereof, and wherein the cathode is made of aluminum. The method of claim 5, And the second layer is Li ₂ O. The method of claim 5, The thickness of the said 2nd layer is 0.2 nm-3 nm, and the thickness of the said 1st layer is 0.5 nm-50 nm, The organic electroluminescent element characterized by the above-mentioned. The method of claim 1, The buffer layer is an organic EL device, characterized in that the mixture of the material of the formula and at least one of the alkali metal, alkaline earth metal and their compounds in the form of co-deposition (co-deposition). The method of claim 9, And the mixing ratio in the mixed layer is fixed or varied as a function of position. The method of claim 9, The thickness of the said mixed layer is 0.5 nm-10 nm, The organic electroluminescent element characterized by the above-mentioned. The method of claim 1, The buffer layer is a mixed layer formed by co-deposition of a material of the chemical formula and an alkali metal, an alkaline earth metal and a compound thereof, and the cathode is an organic EL device, wherein the cathode is formed of aluminum. . The method of claim 9, At least one of the alkali metals, alkaline earth metals and compounds thereof is Li ₂ O.