KR100669777B1 - Organic electroluminescence display - Google Patents

Abstract

The present invention provides an organic electroluminescent device having a light emitting layer comprising a phosphorescent host and a phosphorescent dopant between a first electrode and a second electrode, wherein the phosphorescent dopant is present to have a gradual concentration gradient along the thickness of the light emitting layer. To provide. In the organic electroluminescent device of the present invention, efficiency and lifespan characteristics are improved by using a concentration gradient of the phosphorescent dopant in forming the emission layer.

Description

Organic electroluminescence display

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

2 is a view showing the results of efficiency characteristics according to the Examples and Comparative Examples of the present invention.

3 is a view showing the results of life characteristics according to the Examples and Comparative Examples 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.

Electroluminescent devices (EL devices) are self-luminous display devices that have a wide viewing angle, excellent contrast, and fast response time. EL elements are classified into inorganic EL elements and organic EL elements according to materials for forming an emitting layer. Herein, the organic EL device has an advantage of excellent luminance, driving voltage, and response speed, and multicoloring, compared to the inorganic EL device.

A typical organic electroluminescent device has an anode formed on the substrate, and the hole transport layer (HTL), the light emitting layer (EML), the electron transport layer (ETL) and the cathode (cathode) are sequentially formed on the anode. Have Here, the hole transport layer, the light emitting layer, and the electron transport layer are organic thin films made of an organic compound.

The driving principle of the organic EL element is that when a voltage is applied between the anode and the cathode, holes injected from the anode are moved to the light emitting layer via the hole transport layer. On the other hand, electrons are injected into the light emitting layer from the cathode via the electron transport layer, and carriers are recombined in the light emitting layer to generate excitons. The exciton is changed from the excited state to the ground state, whereby the fluorescent molecules in the light emitting layer emit light to form an image. At this time, the excited state falls to the ground state through the singlet excited state and emits light is called 'fluorescence', and the triplet excited state falls to the ground state through the excited state is called 'phosphorescence'. In the case of fluorescence, the probability of singlet excited state is 25% (triple state 75%) and there is a limit of luminous efficiency, whereas phosphorescence can be used to triplet 75% and singlet excited state 25%. Can be up to 100% internal quantum efficiency.

Phosphorescent materials generally have an organometallic compound structure containing heavy atoms, and when such phosphorescent materials are used, the excitons in the triplet state, which were originally forbidden transitions, emit light through an allowable transition. The phosphorescent material may use triplet excitons with a 75% generation probability and thus 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 light emitting material, Ir compounds based on (4,6-F ₂ ppy) ₂ Irpic or fluorinated ppy ligand structures have been developed, and CBP (4,4 ') is a host material for these light emitting materials. -N, N'-dicarbazole-biphenyl) is widely used.

Recently, a method of using a carbazole compound having a triplet energy band gap larger than CBP as a host when forming a light emitting layer using a phosphorescent material has been known. However, even when a carbazole compound known to date is used, the efficiency and lifespan characteristics of the phosphorescent device have been improved. There was a lot of room for improvement because it did 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, the present invention,

In an organic electroluminescent device having a light emitting layer comprising a phosphorescent host and a phosphorescent dopant between a first electrode and a second electrode,

The phosphorescent dopant provides an organic electroluminescent device that exists to have a gradual concentration gradient along the thickness of the light emitting layer.

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

In the present invention, the phosphorescent dopant has a concentration gradient according to the thickness of the light emitting layer when forming the light emitting layer including the phosphorescent host and the phosphorescent dopant, thereby improving the luminous efficiency and lifespan characteristics of the organic EL device.

According to one embodiment of the present invention, the phosphorescent host may include a low molecular hole transport material, and the phosphorescent dopant may be distributed to increase gradually along the thickness direction from the electron transport layer of the light emitting layer to the hole transport layer.

According to another embodiment of the present invention, the phosphorescent host may include an electron transport material, and the phosphorescent dopant may be distributed to increase gradually in the thickness direction from the hole transport layer of the light emitting layer to the electron transport layer.

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}, tris (phenylpyridine) Iridium}, tris (2-biphenylpyridine) iridium {tris (2- phenylpyridine) Iridium}, tris (3-biphenylpyridine) Iridium}, or tris (4-biphenylpyridine) Iridium {tris (4-biphenylpyridine) Iridium}. .

The concentration of the phosphorescent dopant is preferably in the range of 1 to 30 parts by weight based on 100 parts by weight of the total weight of the light emitting layer forming material in a portion in contact with the electron transport layer along the thickness of the light emitting layer. If it is less than 1 part by weight, the light emitting material is insufficient and the efficiency and life is lowered, which is not preferable. If it exceeds 30 parts by weight, the triplet quenching phenomenon occurs and the efficiency is lowered, which is not preferable.

According to one embodiment of the invention, the hole transport material is preferably a carbazole compound. Non-limiting examples of the carbazole compound, 1,3,5-tricarbazolylbenzene (4,4'-biscarbazolylbiphenyl {4,4'-biscarbazolylbiphenyl (CBP)) }, m-biscarbazolylphenyl, 4,4'-biscarbazolyl-2,2'-dimethylbiphenyl {(4,4'-biscarbazolyl-2,2'-dimethylbiphenyl) [dmCBP] }, 4,4 ', 4 "-tri (N-carbazolyl) triphenylamine {4,4', 4" -tri (N-carbazolyl) triphenylamine}, 1,3,5-tri (2-carbazolyl Phenyl) benzene {1,3,5-tris (2-carbazolylphenyl) benzene}, 1,3,5-tris (2-carbazolyl-5-methoxyphenyl) benzene {1,3,5-tris (2- carbazolyl-5-methoxyphenyl) benzene} and bis (4-carbazolylphenyl) silane {bis (4-carbazolylphenyl) silane} is preferably at least one selected from the group consisting of.

In another embodiment of the present invention, the phosphorescent host includes an electron transporting material, and although the content of the phosphorescent host is constant, the phosphorescent dopant may be distributed to increase gradually in the thickness direction from the hole transporting layer of the light emitting layer to the electron transporting layer. Can be.

The electron transporting material having electron transporting properties may include at least one selected from an organometallic complex including a metal and an organic ligand, a spirofluorene compound, an oxadiazole compound, a phenanthroline compound, a triazine compound, and a triazole compound. Compound.

Non-limiting examples of the organometallic complex include bis (8-hydroxyquinolato) biphenoxy metal and bis (8-hydroxyquinolato) phenoxy metal. (8-hydroxyquinolato) phenoxy metal}, 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}, bis (2-methyl-8-quinolinolato) (para-phenyl-phenololato) metal {Bis ( 2-methyl-8-quinolinolato) (para-phenyl-phenolato) metal}, and bis (2- (2-hydroxyphenyl) quinolato) metal {bis (2- (2-hydroxyphenyl) quinolato) metal} At least one selected from the group consisting of, the metal is aluminum (Al), zinc (Zn), beryllium (Be), or gallium (Ga).

The electron transporting materials are particularly preferably bis (8-hydroxyquinolato) biphenoxy aluminum, bis (8-hydroxyquinolato) phenoxy aluminum, bis (2-methyl-8-hydroxyquinolato) Phenoxy aluminum, bis (2-methyl-8-hydroxyquinolato) phenoxy aluminum, bis (2-methyl-8-quinolinolato) (para-phenyl-phenololato) aluminum (BAlq), or bis Preference is given to (2- (2-hydroxyphenyl) quinolato) zinc.

The spirofluorene-based compound is a structure having a linking ring between two spirofluorenes, the linkage is triazole, oxadiazole, naphthalene, anthracene Or phenyl, or the like, and the position 9 of each fluorene is substituted with O, S, Se, NR, PR, or the like, or NR or PR is substituted between two spirofluorenes. It can be a structure that directly connects. Each R is H, or a C 6 to C 20 alkyl group, a C 5 to 20 aryl group having 1 to 20 carbon atoms, a C 2 to 20 heteroaryl group, and a C 1 to 20 alkoxy group having 6 carbon atoms It is a substituent selected from the group which consists of an aryl group of 20. Preferably, the spirofluorene-based compound is 2,5-disspirobifluorene-1,3,4-oxadiazole (2,5-Dispirobifluorene-1,3,4-oxadiazole).

Examples of the oxadiazole-based compound include (4-biphenylyl) -5- (4-tertbutylphenyl) -1,3,4-oxadiazole and the like, and examples of the phenanthroline-based compound include 2,9-dimethyl-4,7-diphenyl-9,10-phenanthroline (BCP), and the like. Examples of the triazine-based compound include 2,4,6-tris (diphenylamino) -1. , 3,5-triazine, 2,4,6-tricarbazolo-1,3,5-triazine, 2,4,6-tris (N-phenyl-2-naphthylamino) -1,3, 5-triazine or 2,4,6-tris (N-phenyl-1-naphthylamino) -1,3,5-triazine, etc. are mentioned. Examples of the triazole-based compound include 3-phenyl-4- (1'-naphthyl) -5-phenyl-1,2,4-triazole.

According to the present invention, the phosphorescent dopant material of the constituent material of the light emitting layer is changed in concentration, but the material used as the phosphorescent host is constant without changing the concentration. In general, the content of the phosphorescent host that may be used in the light emitting layer is preferably 1 to 30 parts by weight based on 100 parts by weight of the total weight of the light emitting layer forming material. If the content of the host is less than 1 part by weight, the quenching phenomenon of the triplet occurs and the efficiency is lowered. If the content of the host exceeds 30 parts by weight, the light emitting material is insufficient and the efficiency and lifespan are deteriorated.

At least one selected from a hole injection layer, a hole transport layer, a hole blocking layer, an electron transport layer, and an electron injection layer may be further provided between the first electrode or the second electrode and the light emitting layer.

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, but a glass or 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.

Thermal evaporation of the hole injection layer material in high vacuum on the anode, or depending on the type of material used, spin-coating and dip-coating , Doctor-blading, inkjet printing, or thermal transfer, organic vapor deposition (OVPD), or the like. The hole injection layer HIL is selectively formed using the above-described method. 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.

The hole transport layer material is coated on the hole injection layer formed according to the above process to selectively form the hole transport layer HTL. 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, an emission layer EML is formed on the hole transport layer by using a phosphorescent dopant and a phosphorescent host together. The light emitting layer forming method is not particularly limited, but methods such as vacuum deposition, inkjet printing, laser transfer, photolithography, organic vapor deposition (OVPD) and the like are used as described above. .

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. Organic vapor phrase deposition technology is used to form the light emitting layer having a concentration gradient of the dopant of the present invention. Source temperature, carrier gas flow rate, and chamber pressure are adjusted to precisely control the concentration of organic matter in the carrier gas to accurately reproduce the light emitting layer at various deposition rates. In the manufacturing method, it is possible to directly control the deposition rate of the organic material doped by the flow rate of the carrier gas. Since the flow rate of the gas can be controlled even in a very short time, a desired doping rate can be obtained, and a light emitting layer having a concentration gradient can be produced when the doping rate is continuously changed.

The hole blocking material HBL is selectively formed on the light emitting layer by using a vacuum deposition method, a spin coating method, or the like. 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 mA, the hole blocking property is not good, and the efficiency is lowered.

An electron transport layer forms an electron transport layer (ETL) on the hole blocking layer as the vacuum deposition method and the 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 is deteriorated. 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.

10 parts by weight of phosphorus dopant tris (2-biphenylpyridine) iridium [Ir (ppy) ₃ ] in 90 parts by weight of 4,4'-biscarbazolylbiphenyl (CBP) as a host on the hole transport layer Vacuum deposition was started by organic vapor deposition (OVPD), and the concentration of the dopant was continuously changed to form a light emitting layer having a concentration gradient such that the dopant was 5 parts by weight in the portion where the light emitting layer having a thickness of about 300 kPa was in contact with the electron 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.

Comparative example 1 (when there is no concentration gradient)

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.

NPD was vacuum deposited on the substrate to form a hole transport layer having a thickness of 600 mm3. 5 parts by weight of a phosphorescent dopant tris (2-biphenylpyridine) iridium [Ir (ppy) ₃ ] was deposited on 95 parts by weight of the host 4,4'-biscarbazolylbiphenyl (CBP) on the hole transport layer, The light emitting layer was formed in the thickness of 300 kPa.

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.

FIG. 2 shows an example of the case where a light emitting layer having a concentration gradient of phosphorescent dopant is used. Compared with the comparative example 1 which does not have a concentration gradient, Example 1 has shown that the efficiency characteristic was excellent.

In detail, the organic electroluminescent device of Comparative Example 1 has an efficiency of about 32.4 cd / A, and the organic electroluminescent device of Example 1 has an efficiency of 41.8 cd / A, which is more efficient than that of Comparative Example 1. This was improved.

3 shows an example of the case where a light emitting layer having a concentration gradient of phosphorescent dopant is used. Compared with the comparative example 1 which does not have a concentration gradient, Example 1 has shown the outstanding lifetime characteristic.

In addition, the lifespan characteristics are represented by the time when the initial emission luminance decreases by 50%. The organic electroluminescent device of Example 1 is 800 hours at 5,000 cd / m2, and the organic electroluminescent device of Comparative Example 1 is 5,000 cd / m2. As shown by 550 hours, Example 1 was confirmed to improve the life characteristics compared to the case of Comparative Example 1.

The organic electroluminescent device of the present invention improves the efficiency and lifespan characteristics of the phosphorescent device by having a concentration gradient of the phosphorescent dopant in forming the light emitting layer.

Claims (9)

In an organic electroluminescent device having a light emitting layer comprising a phosphorescent host and a phosphorescent dopant between a first electrode and a second electrode, The phosphorescent host includes a low molecular weight hole transport material, and the phosphorescent dopant is present to have a gradual concentration gradient that increases in the thickness direction from the electron transport layer of the light emitting layer to the hole transport layer. delete delete The phosphine dopant of claim 1, wherein the phosphorescent dopant is bisthienylpyridine acetylacetonate iridium, bis (benzothienylpyridine) acetylacetonate iridium, bis (2-phenylbenzothiazole) acetylacetonate iridium, bis (1-phenyl Isoquinoline) iridium acetylacetonate, tris (1-phenylisoquinoline) iridium, tris (phenylpyridine) iridium, tris (2-biphenylpyridine) iridium, tris (3-biphenylpyridine) iridium, and tris (4- Biphenylpyridine) Iridium organic electroluminescent device, characterized in that at least one selected from the group consisting of. The organic electroluminescent device according to claim 1, wherein the phosphorescent dopant is 1 to 30 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 hole transport material is a carbazole compound. The method of claim 6, wherein the carbazole compound is 1,3,5-tricarbazolylbenzene, 4,4'-biscarbazolyl biphenyl, m-biscarbazolylphenyl, 4,4'-biscarbazolyl-2 , 2'-dimethylbiphenyl, 4,4 ', 4 "-tri (N-carbazolyl) triphenylamine, 1,3,5-tri (2-carbazolylphenyl) benzene, 1,3,5-tris An organic electroluminescent device, characterized in that at least one selected from the group consisting of (2-carbazolyl-5-methoxyphenyl) benzene, and bis (4-carbazolylphenyl) silane. delete The organic electroluminescence device of claim 1, further comprising at least one selected from a hole injection layer, a hole transport layer, a hole blocking layer, an electron transport layer, and an electron injection layer between the first electrode or the second electrode and the light emitting layer. device.

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