KR100263756B1 - Process for preparation of red light-emitting device using high-performance polyimide - Google Patents

Abstract

PURPOSE: A method for fabricating a red organic electric light emitting device using a high performance polyimide is provided to improve a thermal stability and to have a long life time by dispersing a monomer red light emitting material to a polyimide having a heat resistance and a chemical resistance and a good mechanical physical property in a solid thin film state. CONSTITUTION: The organic electrical light emitting device includes an anode transparent electrode(1,2), an organic light emitting layer and an electron implantation electrode(4). The organic light emitting layer is fabricated by coating a solution made by dispersing a red light emitting material into an etherimide. The red light emitting material is dispersed into the etherimide with a weight ratio of 5:95 or 50:50, and a chloroform is used as a dispersion solvent. And the thickness of the red organic light emitting layer is 50 - 200 nm.

Description

Manufacturing method of red organic electroluminescent device using high performance polyimide {PROCESS FOR PREPARATION OF RED LIGHT-EMITTING DEVICE USING HIGH-PERFORMANCE POLYIMIDE}

The present invention relates to a method of manufacturing a red organic electroluminescent device having improved stability and long life.

In fabricating a conventional organic electroluminescent device, a method of dispersing a monomolecular fluorescent material in a polymer, spin-coating it, drying it, putting it in a vacuum chamber, and depositing a metal electrode has been mainly used.

However, acrylic polymers and vinyl polymers used in conventional light emitting layers are generally inferior in heat resistance and film resistance, and thus have difficulty in thin film processing, low solution formability, and low reliability. In other words, when a thin film is manufactured by a thin film processing method such as spin-coating, the polymer chain spreads in the direction of centrifugal force to obtain a radial rough surface, thereby degrading the stability of the device, and due to low heat resistance, it is easily deteriorated due to Joule heat generated during operation. The device is easily destroyed.

Accordingly, the present invention can be processed in a solution state in order to solve the above problems, while in a solid thin film state redistribute monomolecular red light emitting material to the polyimide excellent in heat resistance, chemical resistance, mechanical properties, etc. at the molecular level, excellent red organic An object of the present invention is to provide a method of manufacturing an organic electroluminescent device having improved thermal stability and long life by manufacturing a light emitting layer.

1 is 4- (dicyanomethylene) -2-methyl-6- (4-dimethylaminostyryl) -4H-pyran (DCM) / poly (etherimide) (PEI) (50/50) Light absorption (a) and photoluminescence (b) spectra of the thin film,

Figure 2 shows the energy band structure of the DCM / PEI (50/50) thin film before (a) and (b) before applying a DC voltage,

3 shows a structure of a red organic electroluminescent device according to an embodiment of the present invention,

4 is a light emission photograph of a red organic electroluminescent device according to an embodiment of the present invention (4a: 10 volts, 4b: 15 volts, 4c: 18 volts, 4d: 20 volts),

FIG. 5 shows the current voltage characteristics of the left (a), middle (b) and right (c) cells of the device of FIG.

6 shows a change curve of the current density (a) and the electroluminescence intensity (b) in the device according to the application of a direct current voltage,

7 shows the linear relationship of current density-electroluminescent intensity at low current densities (a) and high (b), the minimum current density (c) and linearity of current density-electroluminescent intensity required to turn on the device. This changing current density,

8 shows a change in electroluminescence efficiency according to applied DC voltage of a device,

9 shows the change in electroluminescent intensity according to the power density of the device.

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

1: flat glass 2: ITO layer

3: DCM / PEI thin film 4: aluminum thin film layer

5: power supply 6: red light

In order to achieve the above object, in the present invention, a method of manufacturing an organic electroluminescent device including an anode transparent electrode, an organic light emitting layer, and an electron injection electrode, wherein the organic light emitting layer has a red light emitting material having a repeating unit represented by the following Chemical Formula 1 Provided is a method of manufacturing an organic electroluminescent device, which is prepared by coating a solution dispersed in (etherimide).

Formula 1

In the above formula

n is an integer of 30 to 150.

Hereinafter, the present invention will be described in detail.

The organic electroluminescent device of the present invention includes three components as follows. The first is an anode transparent electrode substrate prepared by etching ITO (Indium Tin Oxide) -glass into an appropriate shape. Second is a red organic light emitting layer prepared by spin-coating a solution prepared by mixing a red light emitting material and a polyimide at a predetermined weight ratio, applying a thin film on a transparent electrode, and drying to completely remove the solvent. Third is an electron injection electrode manufactured by depositing an aluminum electrode.

A feature of the present invention is to coat a solution prepared by mixing a red luminescent material and a polyimide at a predetermined weight ratio in manufacturing a light emitting layer on the transparent electrode and then drying.

The light emitting material used in the manufacture of the organic electroluminescent device of the present invention is 4- (dicyanomethylene) -2-methyl-6- (4-dimethylaminostyryl) -4H-pyran (DCM), coronene, fer Reylene, Tris (4,4,4-trifluoro-1- (2-thienyl) -1,3-butanediono) -1,10-phenathroline europium (III) (Eu (TTFA) 3Phen ), And their structural formula is as follows.

As the soluble polyimide used in the production of the organic electroluminescent device of the present invention, poly (etherimide) having a repeating unit of the above formula (I) is used. It is preferable that the glass transition temperature of the said poly (etherimide) is 170 degreeC or more, and molecular weight is 20,000 or more.

The light emitting material is dispersed in the polyimide in a weight ratio of 5:95 to 50:50. Examples of the solvent used at the time of dispersing include low boiling point methylene chloride, chloroethane, chloroform, and the like, of which chloroform is most preferred.

The light emitting material solution dispersed in the polyimide is spin coated on the ITO-glass transparent electrode at 1,000 to 5,000 rpm for 1 to 5 minutes, and dried at 30 to 70 ° C. for 30 minutes to 2 hours to prepare an organic light emitting layer.

It is preferable that the thickness of the said light emitting layer is 50-200 nm. By controlling the thickness of the thin film, the voltage emitted can be controlled.

The substrate coated with the organic light emitting layer is placed in a vacuum chamber, and aluminum is deposited on the organic thin film to manufacture a red organic electroluminescent device.

The present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited only to the following examples.

Example 1

First, the red phosphor DCM was dispersed in chloroform by adjusting the weight ratio to 10/90, 30/70 and 50/50 in poly (etherimide) having a repeating unit of formula (I) (molecular weight: about 50,000). The solution was spin coated on the ITO-glass transparent electrodes (1, 2) at about 3000 rpm for at least 3 minutes. The spin-coated thin film 3 was then dried at 50 ° C. for 1 hour. The substrate was placed in a vacuum chamber and an aluminum electrode 4 as a cathode was deposited on the organic thin film. The structure of the red organic electroluminescent device manufactured as described above is shown in FIG. 3.

1 shows the light absorption spectrum (a) and the light emission spectrum (b) of the DCM / PEI thin film. Absorption peaks were observed around 480 nm, which is that of the red luminescent material, DCM, and the photoluminescent properties of the film measured with excitation light at 480 nm were also inherent in DCM and the maximum peak was observed near 620 nm. Thus, it can be seen that the DCM / PEI thin film of the present invention becomes red light.

Figure 2 shows the energy band structure of the DCM / PEI (50/50) thin film before (a) and (b) before applying a DC voltage. When a DC voltage is not applied, an energy band structure as shown in FIG. 2A is applied. When voltage is applied, electrons are injected into an organic electrode and holes are injected into an organic thin film as shown in FIG. 2B. The injected electrons and holes excite DCM, a luminescent material in the organic thin film, to give red light emission.

Figure 4 is a light emission photograph of the red organic electroluminescent device (4a: 10 volts, 4b: 15 volts, 4c: 18 volts, 4d: 20 volts), a very faint red light is difficult to see at 10 volts, At 15 volts a noticeable red color was observed. At 18 volts a vivid red color was seen, and at 20 volts it was very bright, saturated and white.

Each current density-voltage characteristic of the three cells of the multiple device of FIG. 4 is shown in FIG. 5. The left cell (a) showed much higher current density at the same voltage than the other cells because of the change in film thickness during spin-coating.

Example 2

An organic electroluminescent device was manufactured in which the red light emitting layer had a thickness of about 100 nm by repeating the same procedure as in Example 1 except for spin-coating DCM / PEI (specifying weight ratio) at 2000 rpm for 3 minutes.

6 shows the current density-voltage characteristic (a) and the electroluminescence intensity-voltage characteristic (b) of the device. As you can see, at about 20 volts, the current flows rapidly. The “turn-on” voltage at which electroluminescence was observed was found to be about 15-16 volts.

7 shows the change in electroluminescence intensity according to the current density when driving the device. The minimum current density for " on " is about 10 mA / cm &lt; 2 &gt;, and after &quot; on &quot;, electroluminescent intensity changes with current densities of about 35 mA / cm &lt; 2 &gt; This suggests that there is a change in the light emitting area or mechanism below and above a certain current density.

8 shows a change in light emission quantum efficiency of a device according to an applied voltage when the device is driven. This light emission quantum efficiency is not an absolute value but a relative value and thus cannot be compared with data of other documents and patents. The quantum efficiency gradually increased from about 13 volts, but increased above about 17 volts, almost linearly proportional to the applied voltage.

9 shows a change in electroluminescence intensity according to the power density consumed when driving the device. It can be seen that light emission starts only when the power density is about 80-90mA / cm 2, and the light emission intensity increases as the power density increases. In general, as the power density increases about 2 times, the electroluminescent intensity increases about 3 times.

In the conventional organic electroluminescent device, when the mono-molecule light emitting material is dispersed in a polymer medium as an organic light emitting layer, acrylic and vinyl polymers which are commonly used are short in heat resistance and mechanical properties, thereby shortening the life of the device. There is this. In the present invention, an organic light emitting device having improved stability can be manufactured by manufacturing an organic light emitting layer from a method in which a red light emitting material is dispersed in a soluble polyimide having excellent heat resistance, chemical resistance, and mechanical properties.

In addition, the organic light emitting layer according to the present invention can be applied to solar cells, FET devices, organic thin film sensors, etc., which are organic semiconductor devices in addition to the organic electroluminescent device. In particular, when the thin film is coated on various structures using chloroform having a low boiling point to disperse the red fluorescent material in the soluble polyimide, a thin film laser of various structures is possible.

Claims (4)

In the method of manufacturing an organic electroluminescent device comprising an anode transparent electrode, an organic light emitting layer and an electron injection electrode, the organic light emitting layer is a solution in which a red light emitting material is dispersed in a poly (etherimide) having a repeating unit Method for producing a red organic light emitting device, characterized in that the coating is prepared: Formula 1

(I) In the above formula n is an integer of 30 to 150. The method of claim 1, The red light emitting material is 4- (dicyanomethylene) -2-methyl-6- (4-dimethylaminostyryl) -4H-pyran (DCM), coronene, perylene and tris (4,4,4-tri Fluoro-1- (2-thienyl) -1,3-butanediono) -1,10-phenathroline europium (III) (Eu (TTFA) 3Phen), characterized in that it is selected from the group consisting of Way. The method of claim 1, Dispersing the red light-emitting material in a poly (etherimide) at a weight ratio of 5:95 to 50:50 and preparing a solution using chloroform as a dispersion solvent. The method of claim 1, The red organic light emitting layer has a thickness of 50 to 200nm.

Images