KR100581918B1 - Organic electroluminescence display - Google Patents

Abstract

The present invention provides an organic electroluminescent device having a light emitting layer comprising a phosphorescent dopant between a pair of electrodes, wherein the light emitting layer includes a hole transport material and an electron transport material as a host. . In the organic electroluminescent device of the present invention, efficiency and lifespan characteristics are improved by using a mixture of a hole transporting material and an electron transporting material as a host of an optical device in forming a light emitting layer.

Description

Organic electroluminescence display

1 is a cross-sectional view of an organic electroluminescent device according to an embodiment of the present invention.

The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent device having improved efficiency and lifespan by employing a light emitting layer containing a phosphorescent dopant.

The light emitting material of the organic electroluminescent device is classified into a fluorescent material using excitons in a singlet state and a phosphorescent material using a triplet state according to its light emitting mechanism.

Phosphorescent materials generally have a structure of organometallic compounds containing heavy atoms, and when such phosphorescent materials are used, excitons in the triplet state, which were originally forbidden transitions, emit light through an allowable transition. The phosphorescent material can use triplet excitons with a 75% generation probability and can have a much higher luminous efficiency than fluorescent materials using singlet excitons with a 25% generation probability.

The light emitting layer using the phosphorescent material is composed of a host material and a dopant material that emits light by transferring energy therefrom. As the dopant material, various materials using iridium metal compounds have been reported at Princeton University and the University of Southern California. In particular, as the blue light emitting material, Ir compounds based on (4,6-F ₂ ppy) ₂ Irpic or fluorinated ppy ligand structures have been developed, and the host material of these materials is CBP (4,4'-). N, N'-dicarbazole-biphenyl) materials are widely used. The CBP molecule has sufficient energy transfer in the triplet state of the energy gap of green and red materials, but it is less than the energy gap of blue materials, resulting in a very inefficient endothermic transition rather than exothermic energy transfer. Is being reported. As a result, the CBP host is pointed out as a cause of problems of low blue light emission efficiency and short lifespan due to insufficient energy transfer to the blue dopant.

Recently, a method of using a carbazole compound having a triplet energy band gap larger than CBP as a host when forming an emission layer using a phosphorescent material is known.

However, when the carbazole compound known to date is used, there is much room for improvement because the efficiency and lifespan characteristics of the phosphorescent device do not reach a satisfactory level.

Accordingly, the technical problem to be achieved by the present invention is to provide an organic EL device having improved efficiency and lifetime characteristics by solving the above problems.

In order to achieve the above technical problem, in the present invention, in the organic electroluminescent device having a light emitting layer comprising a phosphorescent dopant between a pair of electrodes,

The light emitting layer provides an organic electroluminescent device comprising a hole transport material and an electron transport material as a host.

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

In the present invention, when the light emitting layer including the phosphorescent dopant is formed, a material having a hole transporting property and a material having an electron transporting property are used together to improve the luminous efficiency and lifespan of the organic EL device.

A carbazole compound is used as the hole transport material having the hole transport property, and an organic metal complex including a metal and an organic ligand is used as the material having the electron transport property.

As an example of the carbazole compound, the carbazole compound may be 1,3,5-tricarbazolylbenzene, 4,4'-biscarbazolylbiphenyl, m-biscarbazolylphenyl 4,4'-biscarbazolyl- 2,2'-dimethylbiphenyl, 4 ', 4 "-tri (N-carbazolyl) triphenylamine, 1,3,5-tri (2-carbazolylphenyl) benzene, 1,3,5-tris ( One or more polyvinylcarbazoles selected from the group consisting of 2-carbazolyl-5-methoxyphenyl) benzene and bis (4-carbazolylphenyl) silane; examples of the organometallic complex include bis (8- Hydroxyquinolato) biphenoxy metals {bis (8-hydroxyquinolato) biphenoxy metals}, bis (8-hydroxyquinolato) phenoxy metals {bis (8-hydroxyquinolato) phenoxy metals}, bis (2-methyl -8-hydroxyquinolato) biphenoxy metal {bis (2-methyl-8-hydroxyquinolato) biphenoxy metal}, bis (2-methyl-8-hydroxyquinolato) phenoxy metal) {bis (2 -methyl-8-hydroxyquinolato) phenoxy metal} and bis (2- (2-hydroxy Cyphenyl) quinolato) metal and is at least one selected from the group consisting of bis (2- (2-hydroxyphenyl) quinolato) metal, and the metal is aluminum (Al), zinc (Zn), beryllium (Be), or Gallium (Ga) The electron transporting materials are in particular bis (8-hydroxyquinolato) biphenoxy aluminum, bis (8-hydroxyquinolato) phenoxy aluminum, bis (2-methyl-8-hydride Preference is given to oxyquinolato) biphenoxy aluminum, bis (2-methyl-8-hydroxyquinolato) phenoxy aluminum or bis (2- (2-hydroxyphenyl) quinolato) zinc.

The content of the host in the light emitting layer is preferably 80 to 99 parts by weight based on 100 parts by weight of the total weight of the light emitting layer forming material (ie, the total weight of the host and the dopant). If the content of the host is less than 80 parts by weight, the quenching phenomenon of the triplet occurs and the efficiency is lowered. If the content of the host exceeds 99 parts by weight, the light emitting material is insufficient and the efficiency and life is lowered, which is not preferable.

The content of the electron transporting material constituting the host is preferably 5 to 2000 parts by weight based on 100 parts by weight of the hole transporting material. If the content of the electron transporting material is less than 5 parts by weight, the property is not improved compared to a single host, and if it exceeds 2000 parts by weight, it is not preferable because the property improvement effect does not appear.

The phosphorescent dopant used in forming the light emitting layer of the present invention is a light emitting material, and non-limiting examples thereof include bisthienylpyridine acetylacetonate iridium, bis (benzothienylpyridine) acetylacetonate iridium {bis benzothienylpyridine) acetylacetonate Iridium}, bis (2-phenylbenzothiazole) acetylacetonate iridium {Bis (2-phenylbenzothiazole) acetylacetonate Iridium}, bis (1-phenylisoquinoline) iridium acetylacetonate {bis (1-phenylisoquinoline) Iridium acetylacetonate}, tris (1-phenylisoquinoline) iridium {tris (1-phenylisoquinoline) Iridium} and the like.

Hereinafter, the manufacturing method of the organic EL device of the present invention will be described.

Referring to Figure 1 describes a method for manufacturing an organic EL device according to an embodiment of the present invention.

First, an anode is formed on a substrate by coating an anode material, which is a first electrode. Herein, a substrate used in a conventional organic electroluminescent device is used, and an organic substrate or a transparent plastic substrate having excellent transparency, surface smoothness, ease of handling, and waterproofness is preferable. As the anode material, indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO ₂ ), zinc oxide (ZnO), and the like, which are transparent and have excellent conductivity, are used.

A hole injection layer (HIL) is selectively formed by vacuum thermal evaporation or spin coating of the hole injection layer material on the anode. It is preferable that the thickness of a hole injection layer is 50-1500 kPa here. If the thickness of the hole injection layer is less than 50 kV, the hole injection characteristic is lowered, and if the thickness of the hole injection layer is more than 1500 kV, it is not preferable because of the increase of the driving voltage.

The hole injection layer material is not particularly limited, and copper phthalocyanine (CuPc) or starburst type amines such as TCTA, m-MTDATA, IDE406 (Idemitsu Corp.), and the like may be used as the hole injection layer.

A hole transport layer (HTL) is selectively formed by vacuum thermal evaporation or spin coating of the hole transport layer material on the hole injection layer formed by the above process. The hole transport layer material is not particularly limited, and N, N'-bis (3-methylphenyl) -N, N'-diphenyl- [1,1-biphenyl] -4,4'-diamine (TPD), N, N'-di (naphthalen-1-yl) -N, N'-diphenyl benzidine, N, N'-di (naphthalen-1-yl) -N, N'-diphenyl-benxidine: α-NPD) , IDE320 (Idemitsu Co., Ltd.), etc. are used. It is preferable that the thickness of a hole transport layer is 50-1500 kPa here. If the thickness of the hole transport layer is less than 50 kV, the hole transfer property is deteriorated.

Subsequently, the light emitting layer EML is formed on the hole transport layer by using a mixture of the above-described electron transport material and hole transport material as a host and a phosphorescent dopant together. The light emitting layer forming method is not particularly limited, but a method such as vacuum deposition, inkjet printing, laser transfer, photolithography, or the like is used.

It is preferable that the thickness of the said light emitting layer is 100-800 GPa. If the thickness of the light emitting layer is less than 100 kW, the efficiency and lifetime are lowered. If the thickness of the light emitting layer is more than 800 kW, the driving voltage increases, which is not preferable.

The hole blocking layer HBL is selectively formed on the light emitting layer by vacuum deposition or spin coating a material for hole blocking. The material for the hole blocking layer used at this time is not particularly limited, but should have ionization potential higher than that of the light emitting compound while having electron transport ability, and typically, Balq, BCP, TPBI, and the like are used. If the thickness of the hole blocking layer is preferably 30 to 500 kPa. If the thickness of the hole blocking layer is less than 30 kW, the hole blocking property is not good, and thus the efficiency is lowered.

An electron transport layer forms an electron transport layer (ETL) on the hole blocking layer as a vacuum deposition method or a spin coating method. It does not restrict | limit especially as an electron carrying layer material, Alq3 can be used. It is preferable that the thickness of the said electron carrying layer is 50-600 GPa. If the thickness of the electron transport layer is less than 50 kW, the lifespan characteristics are lowered. If the electron transport layer is more than 600 kW, it is not preferable to increase the driving voltage.

In addition, an electron injection layer EIL may be selectively stacked on the electron transport layer. As the electron injection layer forming material, materials such as LiF, NaCl, CsF, Li ₂ O, BaO, and Liq can be used. It is preferable that the thickness of the said electron injection layer is 1-100 kPa. If the thickness of the electron injection layer is less than 1 kW, the driving voltage is not high because it does not serve as an effective electron injection layer, and if it exceeds 100 kW, the driving voltage acts as an insulating layer.

Subsequently, the organic electroluminescent device is completed by forming a cathode, which is a second electrode, by vacuum-heat deposition of a cathode metal, which is a second electrode, on the electron injection layer.

The cathode metal is lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), magnesium-silver (Mg-Ag ) And the like are used.

The organic electroluminescent device of the present invention may further form an intermediate layer of one or two layers according to the needs of the anode, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, the electron injection layer, and the cathode. In addition to the above-mentioned layers, a hole blocking layer and an electron blocking layer may also be included.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited only to the following examples.

Example 1

The anode cuts a corning 15Ω / cm ² (1200Å) ITO glass substrate to 50mm x 50mm x 0.7mm and ultrasonically cleans for 5 minutes in isopropyl alcohol and pure water, followed by UV and ozone cleaning for 30 minutes. Was used.

N, N'-di (1-naphthyl) -N, N'-diphenylbenzidine (NPD) was vacuum deposited on the substrate to form a hole transport layer having a thickness of 600 kPa.

50 parts by weight of bis (2-methyl-8-hydroxyquinolato) biphenoxy aluminum, which is a host electron transport material, and 50 parts by weight of 4,4'-biscarbazolyl biphenyl, a hole transport material, on the hole transport layer 10 parts by weight of bis (benzothiethylylpyridine) acetylacetonate iridium (phosphate dopant) was co-deposited to form a light emitting layer having a thickness of about 400 GPa.

Alq3, an electron transporting material, was deposited on the emission layer to form an electron transporting layer having a thickness of about 300 kHz.

LiF 10 전극 (electron injection layer) and Al 1000 Å (cathode) were sequentially vacuum deposited on the electron transport layer to form a LiF / Al electrode, thereby manufacturing an organic EL device as shown in FIG. 1.

Comparative Example 1

The anode was cut to a corning 15 □ / cm ² (1200Å) ITO glass substrate 50 mm x 50 mm x 0.7 mm, ultrasonically cleaned in isopropyl alcohol and pure water for 5 minutes, and then UV, ozone for 30 minutes. It was used by washing.

NPD was vacuum deposited on the substrate to form a hole transport layer having a thickness of 600 mm3. A light emitting layer was formed by co-depositing 10 parts by weight of a phosphorescent dopant bis (benzothienylpyridine) acetylacetonate iridium on a host 4,4'-biscarbazolylbiphenyl on the hole transport layer.

Alq3, an electron transporting material, was deposited on the emission layer to form an electron transporting layer having a thickness of about 300 kHz.

LiF 10 전극 (electron injection layer) and Al 1000 Å (cathode) were sequentially vacuum deposited on the electron transport layer to form a LiF / Al electrode, thereby manufacturing an organic EL device as shown in FIG. 1.

In the organic EL device manufactured according to Example 1 and Comparative Example 1, the efficiency and lifespan characteristics were investigated.

As a result, the efficiency of the organic electroluminescent device of Comparative Example 1 was about 4.3 cd / A, the efficiency of the organic electroluminescent device of Example 1 was 5.0 cd / A, which was improved as compared with the case of Comparative Example 1.

In addition, as a result of the life characteristics investigation, it was confirmed that the organic electroluminescent device of Example 1 is improved compared to the case of Comparative Example 1.

The organic electroluminescent device of the present invention improves efficiency and lifespan characteristics by using a mixture of a hole transporting material and an electron transporting material as a host of a phosphorescent device in forming a light emitting layer.

Claims (9)

In an organic electroluminescent device having a light emitting layer comprising a phosphorescent dopant between a pair of electrodes, The light emitting layer includes a hole transport material and an electron transport material as a host, The hole transport material is a carbazole compound, the electron transport material is an organometallic complex, The carbazole compound is 1,3,5-tricarbazolylbenzene, 4,4'-biscarbazolylbiphenyl, m-biscarbazolylphenyl 4,4'-biscarbazolyl-2,2'-dimethylbiphenyl , 4 ', 4 "-tri (N-carbazolyl) triphenylamine, 1,3,5-tri (2-carbazolylphenyl) benzene, 1,3,5-tris (2-carbazolyl-5-meth At least one selected from the group consisting of methoxyphenyl) benzene and bis (4-carbazolylphenyl) silane or polyvinyl carbazole. delete delete delete The method of claim 1, wherein the organometallic complex is a bis (8-hydroxyquinolato) biphenoxy metal, a bis (8-hydroxyquinolato) phenoxy metal, bis (2-methyl-8-hydroxy Quinolato) biphenoxy metal, bis (2-methyl-8-hydroxyquinolato) phenoxy metal) and bis (2- (2-hydroxyphenyl) quinolato) metal Above, the metal is Al, Zn, Be, or Ga characterized in that the organic electroluminescent device. The organometallic complex of claim 1, wherein the organometallic complex is bis (8-hydroxyquinolato) biphenoxy aluminum, bis (8-hydroxyquinolato) phenoxy aluminum, bis (2-methyl-8-hydroxy Quinolato) biphenoxy aluminum, bis (2-methyl-8-hydroxyquinolato) phenoxy aluminum or bis (2- (2-hydroxyphenyl) quinolato) zinc Light emitting element. The organic electroluminescent device according to claim 1, wherein the content of the host in the light emitting layer is 80 to 99 parts by weight based on 100 parts by weight of the total weight of the light emitting layer forming material. The organic electroluminescent device according to claim 1, wherein the content of the electron transporting material in the light emitting layer is 5 to 2000 parts by weight based on 100 parts by weight of the hole transporting material. The method of claim 1, wherein the phosphorescent dopant in the light emitting layer, Bisthienylpyridine acetylacetonate iridium, bis (benzothienylpyridine) acetylacetonate iridium, bis (2-phenylbenzothiazole) acetylacetonate iridium, bis (1-phenylisoquinoline) iridium acetylacetonate, tris ( 1-phenylisoquinoline) is at least one selected from the group consisting of lithium.

Images