KR100280962B1 - Organic light-emitting diode having high efficiency - Google Patents

Abstract

The present invention relates to an organic electroluminescent device having a high luminous efficiency, the organic electroluminescent device comprising an anode transparent electrode, a hole transport layer, an organic light emitting layer and an electron injection electrode, wherein the hole transport layer is a polymer material, a hole transport material and an organic It is characterized by consisting of a light emitting material. The organic electroluminescent device of the present invention can be driven at low voltage, and has high stability and long life.

Description

High efficiency organic electroluminescent device {ORGANIC LIGHT-EMITTING DIODE HAVING HIGH EFFICIENCY}

The present invention relates to an organic electroluminescent device of high efficiency which can be driven at low voltage and is stable and long life.

In general, electron and hole transport materials are used to improve electron and hole injection in fabricating an organic electroluminescent device. In addition, a technique of doubling the luminous effect during low voltage driving by reducing the potential difference generated during electron injection in the cathode part by using an alkali-based metal having a low work function value as a cathode is also used.

In the related art, the luminous efficiency is increased by band matching in the bonding between the hole transport layer and the light emitting layer. However, even in the case of the same organic material, it is difficult to obtain the best bonding state in a situation where heterogeneous materials are bonded. This causes a problem of high voltage driving because holes are not easily injected into the organic light emitting layer when the organic light emitting diode is driven. However, under high voltage, the light emitting diode becomes unstable and has a short lifespan.

Accordingly, an object of the present invention is to provide a highly efficient organic electroluminescent device capable of driving at low voltage and having a high stability and a long lifetime in order to solve the above problems.

1 shows the structure of an organic electroluminescent device according to an embodiment of the present invention,

Figure 2 shows the current-voltage (Fig. 2a) and light emission intensity-voltage (Fig. 2b) characteristics of the organic electroluminescent device of the present invention,

3 shows the electroluminescence characteristics according to the applied voltage of the organic light emitting device of the present invention,

4 is a light emission photograph according to the applied voltage of the organic light emitting device of the present invention (4a: 9 volts, 4b: 10 volts, 4c: 11 volts, 4d: 12 volts).

* <Description of the symbols for the main parts of the drawings>

1: flat glass 2: ITO transparent anode

3: hole transport layer 4: light emitting and electron transport layer

5: cathode

In the present invention to achieve the above object, in the organic electroluminescent device comprising an anode transparent electrode, a hole transport layer, an organic light emitting layer and an electron injection electrode, the hole transport layer is made of a polymer material, a hole transport material and an organic light emitting material An organic electroluminescent device is provided.

Hereinafter, the present invention will be described in detail.

The organic electroluminescent device of the present invention includes four components as follows. The first is an anode transparent electrode substrate prepared by etching ITO (Indium Tin Oxide) -glass into an appropriate shape. The second is a hole transport layer in which a hole transport material, which is a guest, is dispersed in a polymer host material, and additionally contains an organic light emitting material. Third is an organic light emitting layer prepared by depositing an organic light emitting material. The fourth is an electron injection electrode manufactured by depositing a metal electrode. In addition, an electron transport layer may be inserted between the organic light emitting layer and the metal electrode. Representative electron transport materials include 2- (4-biphenyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (PBD), 2,5-bis (4-naphthyl) -1,3,4-oxadiazole (BND), oxadiazole derivatives (OXD).

In manufacturing the hole transport layer of the organic electroluminescent device, in order to maintain stability, a host-guest structure using a polymer as a host is used. In general, as a host material, a polymer (eg, polyimide) having thermal and structural stability is used as a matrix, a hole transport material is used as a guest, mixed, and a hole transport layer is applied through a wet process (eg, spin coating). Can be produced.

A feature of the present invention is to improve the contact surface between the organic light emitting material layer and the hole transport layer by mixing a predetermined amount of the organic light emitting material in the hole transport layer to develop a high efficiency organic light emitting device that can be driven under low voltage. When the electrotransport layer is used in the electroluminescent device of the present invention, the contact surface may be improved by adding an organic light emitting material to the electrotransport layer.

Examples of the polymer host material used in the hole transport layer of the present invention include poly (ether imide) having a repeating unit represented by the following Chemical Formula 1. It is preferable that the glass transition temperature of the said poly (etherimide) is 250 degreeC or more, and molecular weight is 30,000 or more.

Examples of the hole transport material include N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-diphenyl-4,4'-diamine (TPD) and poly (N) -Vinylcarbazole) (PVK), 4,4 ', 4 "-tri (N-carbazolyl) triphenylamine (TCTA), 4,4', 4" -tris (3-methylphenylamino) triphenylamine ( m-MTDATA), and TPD is most preferred.

Examples of the organic light emitting material used in the present invention include tris (8-hydroxyquinolinolato) aluminum (Alq ₃ ) and 4- (dicyanomethylene) -2-methyl-6- (4-dimethylamino Styryl) -4H-pyran (DCM), 1,4-distyrylbenzene, anthracene, tetracene, pentrasene, coronene, perylene, pyrene, bis (8-quinolinolato) zinc (II), 9 , 10-diphenylanthracene, tris (4,4,4-trifluoro-1- (2-thienyl) -1,3-butanediono) -1,10-phenathroline europium (III) ( Eu (TTFA) 3Phen), Tris (2,4-pentadiono) -1,10-phenathroline terbium (III) (Tb (ACAC) 3Phen), Tris (4,4,4-trifluoro- 1- (2-thienyl) -1,3-butanediono) -1,10-phenathroline disprosium (III) (Dy (TTFA) 3Phen) and the like.

The poly (ether imide), hole transport material and organic light emitting material are mixed so that the weight ratio of poly (ether imide): hole transport material: organic light emitting material is 4: 3: 3 to 5: 4: 1. The mixture is dispersed in a solvent at a concentration of 0.5-2 wt% to prepare a coating solution. In this case, chloroform, N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAC), or the like may be used as the solvent, and chloroform is preferable.

A solution of the hole transport material and the light emitting material dispersed in the polyimide was spin-coated for 1 to 3 minutes at 3000 to 6000 rpm on the ITO-glass transparent electrode, and dried at 50 to 80 ° C. for 30 minutes to 1 hour to form a hole transport layer. Manufacture.

The organic light emitting material is vacuum-deposited on the hole transport layer to prepare a light emitting layer.

The organic light emitting layer-coated substrate is placed in a vacuum chamber, and aluminum is deposited on the organic thin film to manufacture an 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, poly (etherimide) having a repeating unit of formula 1 (molecular weight: about 45,000), N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-diphenyl-4 , 4'-diamine and tris (8-hydroxyquinolinolato) aluminum were mixed so that the weight ratio was 50:40:10. The solution prepared by dissolving in chloroform so that the concentration of the mixture was 0.5% by weight was spin-coated at 5000 rpm for 1 minute on an ITO-glass transparent electrode, and dried at 60 ° C. for 1 hour to prepare a hole transport layer.

After vacuum depositing tris (8-hydroxyquinolinolato) aluminum on the hole transport layer, an aluminum electrode serving as a cathode was vacuum deposited on the organic thin film. The structure of the organic electroluminescent device of the present invention prepared as described above is shown in FIG.

Figure 2 shows the current-voltage characteristic (Fig. A) and the light emission intensity-voltage characteristic (Fig. B) of the organic light emitting device of the present invention. As shown in FIG. 2A, the current required for electroluminescence is injected at about 9 V, which is consistent with the result of the emission intensity-voltage characteristic curve. In addition, typical light emitting diode characteristics are shown, which is essential for the development of low voltage and high efficiency light emitting devices.

3 shows an electroluminescence spectrum obtained by analyzing a light emission phenomenon according to an applied voltage for each wavelength. As the voltage increased, the oscillator strength (which can be calculated from the area of the electroluminescence spectrum for each applied voltage) coincided with the increase in the emission intensity of FIG. 2. This indicates that unnecessary work loss during the light emission process is small.

FIG. 4 is a light emission photograph (4a: 9 volts, 4b: 10 volts, 4c: 11 volts, 4d: 12 volts) of the red organic electroluminescent device prepared above, and showed an absolute brightness of 1000 Cd / m 2 or more at 12V.

As described above, in the present invention, by mixing the light emitting material in the hole transport layer, while improving the contact resistance through homogeneous bonding, the organic light emitting material mixed in the hole transport layer receives the electrons and serves to transfer the electrons to the hole transport layer organic material In addition to the inorganic material and the inorganic material as well as the bonding between different organic materials can improve the contact resistance, and due to the above mixed layer it can increase the hole and electron injection efficiency during driving. As a result, it was possible to manufacture a stable and long life organic electroluminescent device.

In addition, the organic light emitting layer of the present invention can be used in the development of various optoelectronic devices.

Claims (7)

An organic electroluminescent device comprising an anode transparent electrode, a hole transport layer, an organic light emitting layer, and an electron injection electrode, wherein the hole transport layer is made of a polymer material, a hole transport material and an organic electroluminescent material used in the organic light emitting layer Electric light emitting device. The method of claim 1, The polymer material is an organic electroluminescent device, characterized in that the poly (ether imide) having a repeating unit of the formula (1). Formula 1

The method of claim 1, The organic light emitting material is tris (8-hydroxyquinolinolato) aluminum (Alq ₃ ), 4- (dicyanomethylene) -2-methyl-6- (4-dimethylaminostyryl) -4H-pyran (DCM ), 1,4-distyrylbenzene, anthracene, tetracene, pentracene, coronene, perylene, pyrene, bis (8-quinolinolato) zinc (II), 9,10-diphenylanthracene, tris ( 4,4,4-trifluoro-1- (2-thienyl) -1,3-butanediono) -1,10-phenathroline europium (III) (Eu (TTFA) 3Phen), tris ( 2,4-pentadiono) -1,10-phenathroline terbium (III) (Tb (ACAC) 3Phen) and tris (4,4,4-trifluoro-1- (2-thienyl)- An organic electroluminescent device, characterized in that it is selected from the group consisting of 1,3-butanediono) -1,10-phenathroline disprosium (III) (Dy (TTFA) 3Phen). The method of claim 1, The hole transport material is N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-diphenyl-4,4'-diamine (TPD), poly (N-vinylcarbazole ) (PVK), 4,4 ', 4 "-tri (N-carbazolyl) triphenylamine (TCTA) and 4,4', 4" -tris (3-methylphenylamino) triphenylamine (m-MTDATA) An organic electroluminescent device, characterized in that selected from the group consisting of. The method of claim 1, The hole transport layer is mixed with a polymer material, a hole transport material and a light emitting material in a weight ratio of 4: 3: 3 to 5: 4: 1, and the prepared mixture is dissolved in an organic solvent at a concentration of 0.5 to 2% by weight to coat An organic electroluminescent device, characterized in that it is prepared by obtaining a solution and coating the prepared coating solution. The method of claim 1, An organic electroluminescent device further comprising an electron transport layer between the organic light emitting layer and the cathode. The method of claim 6, An organic electroluminescent device, characterized in that the electron transport layer contains an organic light emitting material.

Images