KR19990024683A - Manufacturing method of green organic electroluminescent device using polyaniline / aromatic polyimide - Google Patents

Abstract

The present invention relates to a low-voltage organic electroluminescent device having improved stability, comprising: an organic electroluminescent device including an anode transparent electrode, a p-type thin film, an electron transport layer, and an n-type thin film serving as an organic light emitting layer, and a cathode metal electrode. In the production method, a mixture of the doped polyaniline prepared by doping the poly-aniline having a repeating unit of formula (I) with the p-type thin film layer and the aromatic polyimide precursor having a repeating unit of formula (II) Coating to prepare a thin film, it characterized in that it is prepared by thermal imidization.

Description

Manufacturing method of green organic electroluminescent device using polyaniline / aromatic polyimide

The present invention relates to a method for manufacturing a green organic electroluminescent device having low driving voltage and improved stability.

Conventional organic electroluminescent devices are largely manufactured in four types according to the manufacturing method of the organic thin film. The first is to deposit monomolecular fluorescent materials in vacuum to make single and multiple layers, and the second is to produce spin-coated light emitting polymers in single or multiple layers. Third, the monomolecular fluorescent material is dispersed in a polymer and spin-coated, and the fourth method is to produce a hole transport thin film layer by dispersing the electrotransmitter in the polymer, and then vacuum-depositing the monomolecular light emitting material. Generally, the anode uses transparent ITO, and the cathode uses aluminum, magnesium, calcium, silver, and the like.

Since 1992, several studies using polyaniline have been published after fabricating low voltage devices using polyaniline, an electrically conductive polymer ( Jpn. J. Appl. Phys. , 34, L260-L263 (1995); Synthetic Metals , 80, 111). -117 (1996); J. Appl. Phys. , 77, 294-698 (1995); and Nature , 357, 477-479 (1992)). However, in this case, since only polyaniline is mainly used as the hole transport layer or a mixture with a thermoplastic polymer having low thermal stability, stability and driveability at low voltage cannot be achieved at the same time. In addition, since a single layer or a double layer is mainly made of only a polymer, it is difficult to manufacture a precise double layer structure.

Accordingly, an object of the present invention is to provide a method of manufacturing a green organic electroluminescent device having high stability and capable of driving at low voltage.

1 shows a structure of a green organic electroluminescent device manufactured according to the present invention,

FIG. 2 shows the current-voltage characteristics of the green organic electroluminescent device when the doped polyaniline / polyamic acid mixture was dried only (a) and converted to doped polyaniline / polyimide by thermal imidization (b). Indicate,

FIG. 3 shows the emission intensity-voltage of the green organic electroluminescent device when the doped polyaniline / polyamic acid mixture is dried only (a) and when it is thermally imidized to convert into a doped polyaniline / polyimide (b). b) exhibit properties,

Figure 4 shows the vacuum deposition of the luminescent material on the p-type thin film when the doped polyaniline / polyamic acid mixture is dried only (a) and converted to doped polyaniline / polyimide by thermal imidization (b). The photoluminescence spectrum of the case,

FIG. 5 shows the electroluminescence spectra of the green organic electroluminescent device when the doped polyaniline / polyamic acid mixture was dried only (a) and converted to doped polyaniline / polyimide by thermal imidization (b). .

Explanation of symbols for main parts of the drawings

1: flat glass 2: ITO layer

3: p-type thin film 4: n-type thin film

5: aluminum electrode 6: green light emitted from organic electroluminescent element

According to the above object, in the present invention, in the method of manufacturing an organic electroluminescent device comprising an anode transparent electrode, a p-type thin film, an electron transport layer and an n-type thin film serving as an organic light emitting layer, a cathode metal electrode, the p- A thin film was prepared by coating a combination of a doped polyaniline prepared by doping polyaniline having a repeating unit of formula (I) and an aromatic polyimide precursor having a repeating unit of formula (II), Provided is a method of manufacturing a green organic electroluminescent device, characterized in that it is prepared by thermal imidation:

Formula 1

Formula 2

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

The organic electroluminescent device of the present invention comprises a doped polyaniline, which is a hole transport layer material prepared by doping a polyaniline having a repeating unit of formula (I), with a repeating unit of formula (II), a precursor of aromatic polyimide. A solution prepared by dispersing in a polyamic acid having a weight average molecular weight of 20,000 to 70,000 was coated on a positive electrode transparent electrode, dried, and then thermally imidized to prepare a p-type thin film. The n-type thin film, which serves, is vacuum deposited. Subsequently, a cathode metal layer is laminated to produce an element.

Indium tin oxide (ITO) -glass is generally used as the anode transparent electrode.

Doped polyaniline, which is used as a hole transport material to form a p-type thin film, is used in a polyaniline-emeraldine base (PANI-EB) having a repeating unit of formula (I) in the presence of a solvent. Prepared by doping.

The solvent includes chloroform, N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), and the like. Doping materials include dodecylbenzenesulfonic acid (DBSA), camphor sulfonic acid (CSA) ((+) and (-)), benzenesulfonic acid, p-toluenesulfonic acid (PTSA), and 5-sulfosalicylic acid (SSA). And the like, and their structural formulas are as follows.

For example, polyaniline doped with dodecylbenzenesulfonic acid has a repeating unit of formula (III)

The polyamic acid of Structural Formula (II), a precursor of polyimide, a heat resistant polymer, may be synthesized by reacting 4,4-oxyphenylenediamine and pyromellitic dianhydride at 0 to 60 ° C. for 24 to 48 hours in the presence of a solvent. Can be. The solvent may be N-methyl-2-pyrrolidine (NMP), DMAc, THF, DMF, DMSO and the like.

The doped polyaniline prepared as described above is dispersed in a polyamic acid having a repeating unit of formula (II) at a weight ratio of 2:98 to 95: 5. If the weight ratio is less than 2:98, there is little conductivity and hole transport ability, and if it exceeds 95: 5, it is not preferable because it is the same as the case of using only doped polyaniline.

The doped polyamide / polyamic acid mixture is dispersed in a solvent at a concentration of 0.5 to 3% by weight, wherein the solvent used is N-methyl-2-pyrrolidine (NMP), which can dissolve the polyamic acid well, Preference is given to using weak basic solvents such as DMAc, dimethylsulfoxide (DMSO).

The doped polyaniline / polyamic acid solution is spin coated onto the positive electrode transparent electrode for 2-5 minutes at 500-8,000 rpm. The coated thin film is dried at 40 to 90 ° C. for at least 30 minutes, and then thermally imidized at 180 to 300 ° C. for at least 1 hour to convert the polyamic acid to a polyimide having a repeating unit of formula (IV).

Subsequently, the light emitting material is vacuum-deposited at a rate of 0.01 to 0.1 nm / sec in the vacuum chamber so that the final light emitting layer thin film thickness is 5 to 10 nm. The metal is vacuum deposited on the organic thin film at a rate of 0.5 to 1 nm / sec so that the thickness of the final metal layer is 300 nm or more. The structure of the organic electroluminescent device manufactured as described above is shown in FIG. 1.

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

Example

An ITO layer 2 was coated on the flat glass 1 to prepare an anode transparent electrode.

Dodecylbenzenesulfonic acid (DBSA) was doped into a non-conductive polyaniline-emeraldine base (PANI-EB) having repeat units of formula (I) in the presence of N-methyl-2-pyrrolidine (NMP) solvent. Doped polyaniline having a repeating unit of formula (III) was prepared. PANI-EB before doping was blue, and after doping turned green. Subsequently, it was filtered through a 0.5 μm Teflon filter to obtain a clear solution.

4,4-oxyphenylenediamine and pyromellitic dianhydride were reacted at 5 to 60 ° C. for 36 to 48 hours to prepare a polyamic acid of formula (II), a precursor of polyimide.

The weight ratio of the prepared doped polyaniline and polyamic acid was 20/80, and the concentration of the doped polyaniline / polyamic acid was 1% by weight to disperse in 50 ml of a solvent to prepare a solution blend.

The doped polyaniline / polyamic acid solution was spin coated on the positive electrode transparent electrode at 5,000 rpm for about 3 minutes. The spin-coated thin film 3 was dried at 85 ° C. for 1 hour and then thermal imidized at 200 ° C. for 1 hour. Subsequently, Alq3, which is a light emitting material, was vacuum-deposited at a rate of 0.02 nm / sec in the vacuum chamber so that the thickness of the final light emitting layer thin film 4 was 5 nm. Aluminum was vacuum-deposited on the organic thin film at a rate of 0.5 nm / sec so that the thickness of the final cathode metal layer 5 was 300 nm. The structure of the organic electroluminescent device manufactured as described above is shown in FIG. 1.

Comparative example

The organic electroluminescent device was manufactured by repeating the procedure of Example except that the coating of the doped polyaniline / polyamic acid formulation was not thermally imidized.

FIG. 2 shows the current-voltage characteristics of the green organic electroluminescent device when the doped polyaniline / polyamic acid mixture is dried only (a) and when it is thermally imidized and converted into doped polyaniline / polyimide (b). It is shown. In the comparative example, in which only the drying was performed without thermal imidization (a), the injection of current started at about 4 volts, whereas in the thermally imidized example (b), injection of the current was started at about 3 volts. FIG. 3 shows the emission intensity-voltage of the green organic electroluminescent device when the doped polyaniline / polyamic acid mixture is dried only (a) and when it is thermally imidized and converted into doped polyaniline / polyimide (b). b) characterization. The turn on voltage at which green light was observed was about 6 volts for the comparative example dried only and about 5 volts for the heat imidized example (b).

Figure 4 shows the vacuum deposition of a luminescent material on the p-type thin film when the doped polyaniline / polyamic acid mixture is dried only (a) and when it is converted to doped polyaniline / polyimide by thermal imidization (b). Photoluminescence spectrum of the case, and FIG. 5 is their electroluminescence spectrum. In the case of drying only, the peak wavelength in the photoluminescence spectrum when excited at 365 nm and the electroluminescence spectrum at 8 volts are almost identical, whereas in the case of thermal imidization, the peak wavelength in the electroluminescence spectrum is slightly toward the short wavelength side. Moved.

Both drying and heat imidization showed a brightness of 150 Cd / m 2 at 8 volts.

In the conventional organic electroluminescent device, since polyaniline and a thermoplastic film having low thermal stability are mainly used, low voltage and thermal stability cannot be satisfied at the same time. However, in the present invention, the doped polyaniline having high electrical conductivity and the polyimide having excellent thermal stability and mechanical strength can be used as the hole transport layer to simultaneously achieve stability and low voltage driveability of the organic electroluminescent device. In addition, the present invention may be used for conducting lines and electromagnetic wave shielding, solar cells, optoelectronic devices and the like of organic electroluminescent devices as well as other electronic devices.

Claims (6)

In the method for manufacturing an organic electroluminescent device comprising an anode transparent electrode, a p-type thin film, an electron transport layer and an n-type thin film serving as an organic light emitting layer, and a cathode metal electrode, the p-type thin film layer is represented by the following structural formula (I To prepare a thin film by coating a mixture of a doped polyaniline prepared by doping polyaniline having a repeating unit of (A) and an aromatic polyimide precursor having a repeating unit of the following structural formula (II), and thermal imidization thereof Characterized in that the manufacturing method of the green organic electroluminescent device. Formula 1 Formula 2 The method of claim 1, The polyaniline having a repeating unit of formula (I) is doped with a doping material selected from the group consisting of dodecylbenzenesulfonic acid, camphor sulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and 5-sulfosalicylic acid. Way. The method of claim 1, The doped polyaniline is dispersed in a polyimide precursor at a weight ratio of 2:98 to 95: 5. The method of claim 3, wherein Dispersing the blend of the doped polyaniline and polyimide precursor in a solvent at a concentration of 0.5 to 3% by weight to prepare a solution. The method of claim 1, And manufacturing the n-type thin film by vacuum depositing a material serving as an electron transport layer and an organic light emitting layer. The method of claim 1, Aluminum, silver, calcium, magnesium, copper and alloys of these metals as the cathode metal electrode.