KR20090041040A - Organic light emitting device - Google Patents

Abstract

An organic electroluminescent device is provided to extend a lifetime by using material having a high heat resistance and an optimum glass transition temperature as a hole injection layer material. An anode(2) is formed on a transparent substrate(1) by a sputtering method. A hole injection layer(3) and a hole transport layer(4) are successively formed on the anode by a vacuum deposition. A light emitting layer(5) and an electron transport layer(6) are successively formed on the hole transport layer. An electron injection layer(7) and a cathode(8) are formed on the electron transport layer. A glass transition temperature of a hole injection layer material is 110~250°C, and is higher than a glass transition temperature of a hole transport layer material. The anode is an ITO(Indium Thin Oxide) electrode.

Description

Organic Light Emitting Device

The present invention relates to an organic electroluminescent device.

Organic light emitting diodes (OLEDs) emit light by injecting charges into the organic light emitting layer formed between the electron injection electrode (cathode) and the hole injection electrode (anode) and then disappear after pairing electrons and holes. to be.

Organic electroluminescent devices not only form devices on flexible transparent substrates such as plastics, but also operate at lower voltages of 10V or less than plasma display panels or inorganic electroluminescent (EL) displays. This is possible, the power consumption is relatively low, the color is excellent. In addition, the organic electroluminescent device can display three colors of green, blue, and red, and thus, has become a subject of much interest as a next generation rich color display device.

The development of the organic electroluminescent device is to optimize the type of electrode for the purpose of improving the charge injection efficiency in the electrode, and to provide a thin film between the electrode and the hole transport layer made of aromatic diamine and the light emitting layer made of 8-hydroxyquinoline aluminum complex. The development has been directed toward practical use as a high-performance flat panel having characteristics such as self-luminous and high-speed response in that the light emission efficiency is drastically improved compared to a device using a single crystal such as anthracene.

In order to further improve the efficiency of such an organic EL device, the above-described configuration of the anode / hole transporting layer / light emitting layer / cathode is used, and a hole injection layer, an electron injection layer or an electron transporting layer is appropriately provided, for example It is known to be composed of anode / hole injection layer / hole transport layer / light emitting layer / cathode, anode / hole injection layer / light emitting layer / electron transport layer / cathode, anode / hole injection layer / light emitting layer / electron transport layer / electron injection layer / cathode have. The hole transport layer has a function of transferring holes injected from the hole injection layer to the light emitting layer, and the electron transport layer has a function of transferring electrons injected from the cathode to the light emitting layer.

Along with the function of these constituent layers, many organic materials have been developed so far. However, these organic electroluminescent devices cannot be said to have satisfactory performance yet. The main reason is the short life of the device.

One of the major causes of the short life span of the organic EL device is deterioration such that the hole injection layer in contact with the anode is decomposed by heat by heat generated from the electrode, particularly the ITO anode. The inventors found that at the end of each effort, the parameter closely related to degradation is the glass transition temperature (Tg) of the hole injection layer material.

In other words, when the glass transition temperature is low, the hole injection layer material is deteriorated by the heat of the anode generated during driving, and thus the glass transition temperature should be high. On the other hand, if the glass transition temperature is too high, there is a problem that the deposition process for forming the hole injection layer becomes difficult due to the increase in the sublimation temperature of the material.

SUMMARY OF THE INVENTION The present invention aims to provide the optimum glass transition temperature of a hole injection layer material for improving the above problems, and having no high difficulty in the manufacturing process while having high heat resistance.

As a means for achieving the above object,

The present invention is an organic electroluminescent device comprising an anode, a hole injection layer, a hole transport layer, a light emitting layer, a cathode, the glass transition temperature (Tg) of the hole injection layer material is in the range of 110 ℃ to 250 ℃ organic electroluminescent device To provide.

In addition, an example of a hole injection layer material that satisfies the glass transition temperature is provided.

Hereinafter, the present invention will be described in detail.

The organic electroluminescent device of the present invention is an organic electroluminescent device comprising an anode, a hole injection layer, a hole transport layer, a light emitting layer, a cathode, the glass transition temperature (Tg) of the hole injection layer material ranges from 110 ℃ to 250 ℃. It is characterized by being mine.

In addition, since the hole injection layer is in direct contact with the anode, the glass transition temperature (Tg) of the hole injection layer material is preferably higher than the glass transition temperature (Tg) of the hole transport layer material.

In the present invention, the conditions required as the material of the hole injection layer are good in contact with the anode and can form a uniform thin film, and particularly, must be thermally stable. Therefore, the glass transition temperature should be more than 110 ℃. If lower than this, it can be seen that the material of the hole injection layer in contact with the anode is easily deteriorated and the life is significantly shortened. In addition, the glass transition temperature of the material of the hole injection layer is 250 ℃ or less there is no difficulty in deposition.

Any material that satisfies the above requirements can be used as the hole injection layer and all are included in the present invention. For example, hole injection layer materials such as phthalocyanine compounds such as phthalocyanine, organic compounds such as polyaniline and polythiophene, metal oxides such as sputtered carbon film, vanadium oxide, ruthenium oxide, and molybdenum oxide Any material satisfying the above requirements is included in the present invention.

As a specific example, the compound represented by following formula (1) is mentioned.

[Formula 1]

Wherein Ar ₁ , Ar ₂ , Ar ₃ , and Ar ₄ are each independently selected from C ₂ to C ₃₀ aromatic groups (which may include a heteroaromatic ring) with or without a substituted hydrogen position.

The aromatic group may be free of heteroaromatic rings, all heteroaromatic rings, or part of heteroaromatic rings. A heteroaromatic ring is a vent containing N, O, S, etc. which are hetero elements, and means having aromaticity. Examples include pyridine, pyrrole, furan, thiophene, pyrazole, imidazole, oxazole, isoxazole, thiazole, isothiazole, and aromatic groups bonded in combination with these. R ₂ , R ₃ may be the same or different.

The aromatic group of C ₄₂ to C ₃₀ may be substituted with some or all of hydrogen, and is not limited to a substituent, aryl, alkyl, alkoxy, halogen, cyan It may be selected from the group consisting of cyano and silyl. Specifically, methyl, ethyl, propyl, isopropyl, butyl, t-butyl, methoxy, ethoxy and butoxy , Trimethylsilyl, fluorine and chlorine.

Ar ₁ , Ar ₂ , Ar ₃ , and Ar ₄ may be each independently selected from those represented by the following Chemical Formula 2. However, the present invention is not limited thereto, and those known to the aryl group of the light emitting material structure in the art may be selected as long as they can achieve the object of the present invention and are included in the present invention.

[Formula 2]

The organic electroluminescent device of the present invention is not limited to its structure as long as the device is provided with a hole injection layer having the above-mentioned characteristics, and is included in the present invention. Specific examples of the structure include (1) anode / hole injection layer / hole transport layer / light emitting layer / cathode, (2) anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / cathode, (3) anode / hole Injection layer / hole transport layer / light emitting layer / transmission embroidery layer / electron injection layer / cathode.

1 is a cross-sectional view of an organic electroluminescent device according to an embodiment of the present invention. Briefly described as follows. First, the anode 2 is formed on the transparent substrate 1 by a method such as sputtering, and the hole injection layer 3 and the hole transport layer 4 are sequentially vacuum deposited on the anode. After forming the organic light emitting layer 5 and the electron transport layer 6 on the hole transport layer 4 again by vacuum deposition, an electron injection layer 7 and a cathode 8 are formed on the electron transport layer 6.

The light emitting layer 5 may be monochromatic or multicolor light emission, and may have a multilayer structure. Examples of the light emitting material include singlet light emitting materials and triplet light emitting materials. In addition to Alq3 and its derivatives, the singlet luminescent material may be a known luminescent material such as daylight luminescent material, luminescent whitening material, laser dye, organic scintillator, and various fluorescence analysis reagents.

Specifically, polycyclic condensed compounds such as anthracene, pyrene, chrysene, perylene, coronene, rubrene, quinacridone, oligophenylene compounds such as quarterphenyl, 1,4-bis (2-methylstyryl) benzene , 1,4-bis (4-methyl-5-phenyl-2-oxazolyl) benzene, 1,4-bis (5-phenyl-2-oxazolyl) benzene, 2,5-bis (5-tertiary- Butyl-2-benzoxazolyl) thiophene, 1,4-diphenyl-1,3-butadiene, 1,6-diphenyl-1,3,5-hexatriene, 1,1,4,4-tetra Scintillators for liquid scintillation such as phenyl-1,3-butadiene, metal complexes of auxin derivatives, coumarin dyes, dicyano methylenepyran dyes, dicyano methylenethiopyran dyes, polymethine dyes, oxobenzanthracene dyes, xanthene dyes , Carbostyryl dyes and perylene dyes, oxadine-based compounds, stilbene derivatives, spiro compounds, oxadiazole-based compounds and the like.

On the other hand, noble metal complexes, such as a metal complex which uses platinum as a center metal, and a metal complex which uses iridium as a center metal, are mentioned as a triplet light emitting material. The amount of the metal complex contained in the light emitting layer is preferably in the range of 0.1 to 30% by weight. If it is 0.1 weight% or less, it cannot contribute to the improvement of the luminous efficiency of an element, and when it exceeds 30 weight%, concentration quenching, such as an organometallic complex forming a dimer, will arise, and it will fall in luminous efficiency. In the element using the conventional glimmer (single term), the one which is slightly larger than the amount of the whitish pigment | dye contained in a light emitting layer tends to be preferable.

The substrate 1 is not particularly limited, and those commonly used in organic electroluminescent devices, for example, glass, transparent plastic, quartz, and the like may be used.

As the material of the positive electrode 2 mentioned above, ITO or IZO can be generally used, and as the material of the hole injection layer 3, copper (II) phthalocyanine is usually used. The hole transport layer 4 may be a triphenylamine or diphenylamine derivative such as NPD (N, N-di (naphthalen-1-yl) -N, N'-diphenylbenzidine), and the dopant may be used in the light emitting layer 5. In the case of using a general blue dopant may be used, for example CBP (4,4'-N, N-dicarbazole-biphenyl) may be used. In addition, Alq3 can be used as the electron transport layer 6 because of its excellent electron transport properties, and another material that can be used as the electron transport layer 6 is 2- (4-non-phenyl) -5- (4-tert. Oxadiazole and triazole derivatives such as -butylphenyl) -1,3,4-oxadiazole. Alkali metal (Cs, Rb, K, Na, Li) derivatives (Li ₂ O, etc.) may be used as the material of the electron injection layer, and Mg / Ag, Al, Al / Li, Al / Nd as the cathode material. Etc. are possible.

Each layer constituting the organic electroluminescent element of the present invention can be formed by applying a known method, such as a vapor deposition method, a spin coating method, a cast method, or the like, to a material which should constitute each layer, to form a thin film. The film thickness of each of the layers thus formed, for example, the light emitting layer, is not particularly limited and can be appropriately selected depending on the situation.

The organic electroluminescent device of the present invention has improved lifespan by using a material having a glass transition temperature as a hole injection layer material having high heat resistance and no significant difficulty in the manufacturing process.

Hereinafter, the present invention will be described in more detail with reference to Examples. The following examples are specific examples of the present invention, but the present invention is not limited thereto even though there is a certain or definite expression.

Compound 1 was synthesized by the following scheme.

[Scheme]

                                                      Compound 1

Synthesis Example 1

Synthesis of 2,6-dinitrodibenzodioxin

60 g (0.326 mol) of dibenzodioxin was added to 1600 ml of acetic acid, and 280 ml of fuming nitric acid was added dropwise over 1 hour while stirring at room temperature. After completion of the dropwise addition, stirring was further continued for 2 hours, and the obtained precipitate was collected by filtration. After slurrying with methanol, 85.7 g (0.313 mol, yield 96.0%) of 2,6-dinitrodibenzodioxin was obtained by drying under reduced pressure. The purity of the obtained product was 96.5area% (HPLC, 254 nm).

Synthesis Example 2

Synthesis of 2,6-diaminodibenzodioxin

81 g (0.295 mol) of 2,6-dinitrodibenzodioxin and 25 g of 10% palladium carbon were added to the mixed solution of 1000 ml of anisole and 1000 ml of THF, and hydrogen gas was vented for 8 hours under room temperature stirring. The 10% palladium carbon was filtered off and further the 10% palladium carbon was rinsed with THF. The filtrate and rinse were mixed and concentrated, and then 61.9 g (0.289 mol, 98.0%) of 2,6-diaminodibenzodioxin was obtained by drying under reduced pressure. The purity of the obtained product was 94.2area% (HPLC, 254 nm).

Synthesis Example 3

Synthesis of N, N'-Diacetyl-2,6-diaminodibenzodioxin

50.0 mg (0.233 mol) of 2,6-diaminodibenzodioxin and 55.3 g (0.699 mol) of pyridine were added to a mixed solution of 900 ml of toluene and 900 mL of THF, and 59.5 g (0.583 mol) of acetic anhydride was added at room temperature with stirring. It was dripped over 10 minutes. After dropping, the mixture was stirred overnight, and the precipitate was collected by filtration. After slurrying with toluene (250 ml × 2), 57.0 g (0.191 mol, yield 82.0%) of N, N′-diacetyl-2,6-diaminodibenzodioxin were obtained by drying under reduced pressure. The purity of the obtained product was 99.3area% (HPLC, 254 nm).

Synthesis Example 4

Synthesis of N, N'-diacetyl-N, N'-diphenyl-2,6-diaminodibenzodioxin

N, N'-diacetyl-2,6-diaminodibenzodioxin 34.3 g (0.115 mol), 96.4 g (0.576 mol) iodine benzene, 48.2 g (0.253 mol) copper iodide (I), 63.6 g potassium carbonate (0.460 mol) and a slurry solution of 1500 ml of quinoline were heated and stirred at 170 ° C. for 48 hours. After cooling to room temperature, 500 ml of methylene chloride and 500 ml of water were added, and the precipitate was separated by filtration. 500 ml of water was further added to the filtrate, and the oil and water were separated. The organic layer was concentrated and then dried under reduced pressure to obtain 79.4 g of crude product. This was used for the next reaction without purification.

Synthesis Example 5

Synthesis of N, N'-diphenyl-2,6-diaminodibenzodioxin

79.4 g of the diacetoamide compound obtained in Synthesis Example 4 was added to a mixed solution of 500 g of methanol and 100 g of a 24% sodium hydroxide aqueous solution, followed by heating to reflux for 20 hours. After cooling to room temperature, 1000 ml of water was added, and the precipitate was collected by filtration. After rinsing with water, 44.3 g of N, N'-diphenyl-2,6-diaminodibenzodioxin was obtained by drying under reduced pressure. The crude product obtained was purified by heating lithography with methanol. Yield 31.8g (0.087mol, yield 75.7% (2steps)), purity 98.4area% (HPLC, 254nm).

Synthesis Example 6

Synthesis of N, N'-di (9-phenanthryl) -N, N'-diphenyl-2,6-diaminodibenzodioxin (Compound 1)

0.445 g (2.2 mmol) of tritert-butylphosphines were added to 0.12 g (0.55 mmol) xylene (10 ml) solution of palladium acetate (II), and it stirred for 30 minutes by heating at 80 degreeC. This solution was heated to 80 ° C. with N, N'-diphenyl-2,6-diaminodibenzodioxin 4.03 g (0.011 mol), 9-bromophenanthrene 7.07 g (0.0275 mol) and tert-butoxy It was sent in a solution of 4.44 g (0.0462 mol) of xylene (200 ml) sodium. Then, it heated up to 135 degreeC and heated and stirred for 4 hours at the same temperature. After cooling to room temperature, 150 ml of water was added, and the precipitate was filtered off. The mother liquor was separated by oil and water, the water bath was washed with 200 ml of toluene, the organic layers were mixed, concentrated and dried under reduced pressure to give 13.0 g of a crude product. N, N'-di (9-phenanthryl) -N, N'-diphenyl-2,6-diaminodibenzodioxine 3.85 by crystallization with ethyl acetate / hexane solvent after treatment with activated carbon g (0.00536 mol, yield 48.7%) was obtained. The purity of the obtained product was 98.6area% (HPLC, 254 nm). Sublimation purification was further performed.

The glass transition temperature of the compound 1 was 149 ° C.

<Example 1>

The light emitting area of the ITO gliss was patterned to have a size of 3 mm × 3 mm and then washed. After placing the substrate in the vacuum chamber, the basic pressure was 1 X 10 ^-6 torr, and then Compound 1 (650Å) / NPD (400Å) / ADN + CBP (3%) (250Å) / Alq3 (350Å) / The film was formed in the order of LiF (5 Pa) / Al (1,000 Pa). That is, Compound 1 was used as a material for the hole injection layer.

<Example 2>

Except for using the HI-204 product (glass transition temperature of 119 ℃) of LG Chemical Co., Ltd. as the material of the hole injection layer in Example 1.

Comparative Example 1

Except for using the compound 1 in the NPD (glass transition temperature 98 ℃) as the material of the hole injection layer in Example 1 was carried out in the same manner.

The lifespan of the organic EL device manufactured by Examples and Comparative Examples was measured by fixing the efficiency of the spectrum over time and injecting a constant current. 1500nit was constantly adjusted and the corresponding current was injected into DC, and the measurement results are shown in FIG. 2.

As shown in FIG. 2, Examples 1 and 2 had a small change in intensity, that is, brightness over time, but Comparative Example 1 showed a significant difference and the luminance decreased. It shows that it is significantly superior to the comparative example. Therefore, it can be seen that the lower limit of the glass transition temperature of the present invention is 110 ° C.

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

2 is a graph measuring the life characteristics of the Examples and Comparative Examples of the present invention.

** Description of the main symbols in the drawings **

1: substrate 2: anode

3: hole injection layer 4: hole transport layer

5: light emitting layer 6: electron transport layer

7: electron injection layer 8: cathode

Claims (5)

An organic electroluminescent device comprising an anode, a hole injection layer, a hole transport layer, a light emitting layer, a cathode, The glass transition temperature (Tg) of the hole injection layer material is in the range of 110 ℃ to 250 ℃ organic electroluminescent device. The organic electroluminescent device according to claim 1, wherein the glass transition temperature (Tg) of the hole injection layer material is higher than the glass transition temperature (Tg) of the hole transport layer material. The organic electroluminescent device according to claim 1, wherein the anode is an ITO electrode. The organic electroluminescent device according to any one of claims 1 to 3, wherein the hole injection layer material is selected from compounds represented by the following general formula (1). [Formula 1]

(Wherein Ar ₁ , Ar ₂ , Ar ₃ , and Ar ₄ are each independently selected from an aromatic group of C ₂ to C ₃₀ , which may be substituted or unsubstituted with a hydrogen position, which may include a heteroaromatic ring.) The organic electroluminescent device according to claim 4, wherein Ar ₁ , Ar ₂ , Ar ₃ , and Ar ₄ are each independently one of the following Chemical Formulas 2. [Formula 2]

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