KR100390727B1 - Organic electroluminescent device comprising crosslinked polyimide layer as inter organic layer - Google Patents

Abstract

The present invention provides an organic electroluminescent device comprising an electrode, an organic intermediate layer and a metal electrode sequentially formed on a substrate, wherein the organic intermediate layer comprises a crosslinked polyimide of formula (1) Provided is an element.

Where

A, B and X are selected from the group consisting of alkyl, aryl, alkylaryl, heterocyclic, alkoxy, aryloxy, carbon, hydrogen, nitrogen, sulfur and phosphorus,

y is an integer from 3 to 8,

n and m are integers greater than or equal to 1 (m has a value less than nym).

Description

Organic electroluminescent device comprising a cross-linked polyimide layer as an organic intermediate layer {ORGANIC ELECTROLUMINESCENT DEVICE COMPRISING CROSSLINKED POLYIMIDE LAYER AS INTER ORGANIC LAYER}

The present invention relates to an organic electroluminescent device having excellent heat resistance, and more particularly to an organic electroluminescent device comprising a crosslinked polyimide layer as an organic intermediate layer.

Recently, in order to increase the stability of an organic electroluminescent device (OELD), polyimide having the highest thermal stability among polymers has been applied to OELD. For example, Japanese Patent Application Laid-Open No. 3-274693 forms an organic light emitting layer and a charge transport layer by vacuum deposition polymerization of two types of monomers, and Japanese Patent Application Laid-open No. Hei 4-93389 reports a polyimide organic charge transport layer. It was. In addition, Japanese Patent Application Laid-open No. Hei 7-230881 reports a hole transport layer containing polyimide containing silicon, and Japanese Patent Laid-Open No. Hei 9-153641 discloses monomolecular molecules having a hole transporting or luminescence ability and general insulating polyimide. A hole transport layer and a light emitting layer made of a thin film in which the mixture is disclosed are disclosed.

However, the polyimide used in these patents is a linear polymer prepared by a general method of producing a precursor thin film by mixing or vacuum-depositing dianhydride and diamine by wet or dry at the same time, followed by heat treatment. Therefore, the linear polyimide thus prepared has a large change in glass transition temperature, which is an indicator of stability, depending on the kind of dianhydride or diamine constituting the main chain, so that the heat resistance is weakened, and thus the desired electrical properties (electron or hole mobility), There is a disadvantage that it is difficult to obtain a monomer having excellent emission color and luminous efficiency. In addition, in the case of a composite thin film as well as a single polyimide thin film, the stability of the thin film is changed depending on the content and type of the functional organic monomolecule added.

Therefore, in the present invention, a polyimide thin film was prepared by adding a crosslinking agent having a trifunctional or higher functional group when producing polyimide to develop a device having higher stability and excellent heat resistance.

An object of the present invention is to provide an organic electroluminescent device comprising a polyimide thin film excellent in heat resistance.

1 shows a schematic structure of an organic electroluminescent device according to an aspect of the present invention.

<Explanation of symbols for the main parts of the drawings>

a: substrate b: anode electrode

c: organic intermediate layer d: cathode electrode

In order to achieve the above object, in the present invention, in the organic electroluminescent device comprising an anode, an organic intermediate layer and a cathode sequentially formed on a transparent substrate, the organic intermediate layer comprises a cross-linked polyimide of the formula It provides an organic electroluminescent device, characterized in that:

Formula 1

Where

A, B and X are selected from the group consisting of alkyl, aryl, alkylaryl, heterocyclic, alkoxy, aryloxy, carbon, hydrogen, nitrogen, sulfur and phosphorus,

y is an integer from 3 to 8,

n and m are integers greater than or equal to 1 (m has a value less than nym).

The crosslinked polyimide thin film of the present invention may be formed as in Scheme 1 below, and generally may be prepared by two methods, a wet process and a dry process.

Wherein x, A, and B are as defined in Formula 1, and m is an integer smaller than nym.

First, in the wet process, diamine (4) dissolved in a reaction solvent such as N-methyl-2-pyrrolidine (NMP) or dimethyl acetate (DMAc), a crosslinking agent (2) solution, and dianhydride (3) are mixed with each other. To prepare a crosslinked polyimide precursor (5) solution, and then to prepare a crosslinked precursor solution obtained by using a transparent electrode coated substrate or an organic or polymer coated with a hole injection layer, a hole transport layer, or a light emitting layer. Polyimide (1) thin film crosslinked by thermal imidization at a suitable temperature of 150 ° C or higher after coating with a conventional method such as spin coating, doctor-blading, roll coating, etc. on the thin film Can be prepared. In the preparation of the crosslinked polyimide precursor solution, the degree of crosslinking may vary depending on the relative reaction rate of diamine and dianhydride in the initial stage of the reaction.

In the dry process, the crosslinking agent (2), the dianhydride (3) and the diamine (4) are respectively attached to an evaporation source of a vacuum chamber or a vaporization source mounted in a chemical vapor deposition (CVD) chamber, A crosslinked precursor (5) thin film was prepared by a CVD reaction in the presence of a vacuum deposition crosslinking polymerization (VDXP) or a carrier gas at high vacuum on a transparent electrode coated substrate. Then, thermally imidized at a temperature of 150 ° C. or higher may be used to prepare a crosslinked polyimide (1) thin film.

Crosslinking agents used in the present invention include melamine, tris (aminophenyl) amine, tetraaminophenylsilicone and tetraaminophenyltin. Examples of dianhydrides and diamines are as described in Korean Patent Application Laid-Open No. 2000-33543, the inventors of which are the inventors of the present invention, and in particular, dianhydrides are 4.4 '-(4,4'-isopropylidediphenoxy). Bis (phthalic anhydride) and pyromellitic acid dianhydride are preferred, and as diamine, N, N'-diphenyl-N, N'-bis (4-aminobiphenyl)-(1,1'-biphenyl) -4,4'-diamine (DBABBD) is preferred. In addition, diacid chloride, a salt derivative, or a derivative having a photosensitive group introduced therein may be used instead of dione hydride.

The crosslinking agent, dianhydride and diamine may preferably be used in a ratio of 0.02: 1: 0.98 to 0.3: 1: 0.7.

When preparing a crosslinked polyimide thin film according to the present invention, a single molecule or a polymer functional material, for example, a hole injection material, a hole transport material, a light emitting material, an electron transport material, or the like may be mixed to form a composite thin film.

The organic electroluminescent device may be manufactured by coating the organic thin film layer, the cathode, and the like on a polyimide thin film prepared as described above in a conventional manner.

The crosslinked polyimide thin film according to the present invention can greatly increase the stability of the device when used in the organic intermediate layer of the organic electroluminescent device.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are only for illustrating the present invention and the present invention is not limited thereto.

Example 1

A crosslinked polyimide thin film was prepared by the wet method.

Ie, N, N'-diphenyl-N, N'-bis (4-aminobiphenyl)-(1,1'-biphenyl) -4,4 'in a glove box filled with argon. NMP dissolved in 8.5 mmol of diamine (DBABBD) and 1 mmol of melamine in NMP, and then slowly added dropwise to NMP in which 10 mmol of 4.4 '-(4,4'-isopropylidediphenoxy) bis (phthalic anhydride) was dissolved. To prepare a precursor solution. The total concentration of the solution was about 2 wt%. The solution was coated on a pre-prepared ITO glass substrate at a rate of 3,000 rpm, then soft-baked at 80 ° C. for 30 minutes and thermally imidized at 300 ° C. for 1 hour to crosslink the crosslinked material having a thickness of about 30 nm. Polyimide hole injection and transport thin films were prepared.

Aluminum as the negative electrode was thermally deposited on the crosslinked polyimide thin film under vacuum of about 1 × 10 ⁻² torr.

Subsequently, in order to measure the heat resistance of the obtained composite thin film, any relaxation behavior corresponding to the glass transition temperature up to 400 ° C. as a result of scanning to 400 ° C. using a capacitance-temperature (CT) method was obtained. Did not appear. That is, the prepared thin film was found to be stable as the glass transition temperature is 400 ℃ or more.

Example 2

After preparing a cross-linked polyimide hole injection and transport thin film according to the method of Example 1, vacuum deposition of tris (8-hydroxyquinolinolato) aluminum (Alq ₃ ), a green light emitting material thereon to 40nm Then, a lithium-aluminum alloy (lithium content: 0.02%) was vacuum-deposited as a negative electrode to prepare an organic electroluminescent device.

The turn-on voltage of the device thus manufactured was about 3V, and a high luminance of 12,000 cd / m ² was obtained at about 14V.

Example 3

A crosslinked polyimide thin film was prepared by the dry method. That is, the pyromellitic acid dianhydride, DBABBD, and tris (aminophenyl) amine crosslinking agents are each contained 0.2 g in three resistance heating crucibles in a vacuum chamber, and the deposition rate is controlled to control the crosslinking agent: dianhydride: diamine. The deposition was performed such that the ratio was 0.1: 1: 0.9, and the deposition was stopped when the total thickness became about 50 nm. The resulting crosslinked precursor thin film was imidated in the same manner as in Example 1 and the final thickness of the obtained thin film was about 27 nm, and C-T measurement showed no relaxation behavior below 400 ° C. That is, it was confirmed that the glass transition temperature of the prepared vacuum thin film is also very stable thin film at 400 ℃ or more.

Example 4

After preparing the cross-linked polyimide hole injection and transport thin film according to the method of Example 3, vacuum deposition of tris (8-hydroxyquinolinolato) aluminum (Alq ₃ ), a green light emitting material thereon to 40nm Then, a lithium-aluminum alloy (lithium content: 0.02%) was vacuum deposited to manufacture an organic electroluminescent device.

The turn-on voltage of the fabricated device was about 2.5V, and high luminance of 20,500cd / m ² was obtained at about 16V.

The glass transition temperature of the organic electroluminescent device including the crosslinked polyimide thin film of the present invention is 400 ℃ or more, the glass transition temperature of the organic electroluminescent device comprising a linear polyimide containing the existing flexible molecules is 200 ℃ or less Compared to the above, stability and heat resistance can be improved to make flexible molecules of various structures stable.

In addition, the crosslinked polyimide thin film of the present invention can be used not only in organic electroluminescent devices but also in organic semiconductor devices such as organic transistors and solar cells.

Claims (5)

An organic electroluminescent device comprising an anode, an organic intermediate layer and a cathode sequentially formed on a transparent substrate, wherein the organic intermediate layer comprises a crosslinked polyimide thin film of Formula 1 below: Formula 1 Where A, B and X are selected from the group consisting of alkyl, aryl, alkylaryl, heterocyclic, alkoxy, aryloxy, carbon, hydrogen, nitrogen, sulfur and phosphorus, y is an integer from 3 to 8, n and m are integers greater than or equal to 1 (m has a value less than nym). The method of claim 1, The crosslinked polyimide thin film is an organic electroluminescent device, characterized in that formed using a cross-linking agent, dianhydride and diamine in the ratio of 0.02: 1: 0.98 to 0.3: 1: 1.7. The method of claim 1, The crosslinked polyimide thin film is formed by coating a crosslinked polyimide precursor solution by adding dianhydride to a mixed solution of diamine and a crosslinking agent and thermally imidating the organic electroluminescent device. The method of claim 1, The crosslinked polyimide thin film is formed by simultaneously vacuum depositing a crosslinking agent, dianhydride and diamine to form a crosslinked polyimide precursor thin film, and then thermally imidating the organic electroluminescent device. The method of claim 1, The crosslinked polyimide thin film is an organic electroluminescent device, characterized in that the composite film formed by mixing a hole injection material, a hole transport material, a light emitting material or an electron transport material.