KR20060080765A - Organic electroluminescent device having increased lifetime - Google Patents

Abstract

The present invention relates to an organic electroluminescent device. According to the present invention, when the organic layer of the organic light emitting device includes a hole blocking material-doped emitting layer, thermal stability and lifespan of the device may be improved.

Description

Organic Electroluminescent Device with Extended Lifetime {ORGANIC ELECTROLUMINESCENT DEVICE HAVING INCREASED LIFETIME}             

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

<Description of Signs of Major Parts of Drawings>

11 transparent electrode (anode) 12 hole injection layer

13 hole transport layer 14 light emitting layer doped with a hole blocking material

15 electron transport layer 16 electron injection layer

17 metal electrode (cathode)

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device having an increased lifespan, including a light emitting layer doped with a hole blocking material.

Flat panel displays play a very important role in supporting a highly visual information society, centered on the internet, which is rapidly growing in recent years. In particular, organic electroluminescent devices (organic EL devices) capable of low voltage driving with self-luminous type have superior viewing angles and contrast ratios compared to liquid crystal displays (LCDs), which are mainstream flat panel displays, and require no backlight. Light weight and thinness are possible, and it has an advantage in terms of power consumption. In addition, the fast response speed and wide color reproduction range have attracted attention as a next generation display device.

In general, an organic EL device is formed on a glass substrate in order of an anode made of a transparent electrode, an organic thin film including a light emitting region, and a metal electrode. In this case, the organic thin film may include a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL), or an electron injection layer (electron injection) in addition to the emitting layer (EML). layer, EIL), and may further include an electron blocking layer (EBL) or a hole blocking layer (HBL) due to light emission characteristics of the light emitting layer.

When an electric field is applied to the organic EL device having such a structure, holes are injected from the anode and electrons are injected from the cathode, and the injected holes and electrons are recombined in the emission layer through the hole transport layer and the electron transport layer, respectively, to emit light excitons. To form. The formed light exciter emits light while transitioning to the ground state. In this case, the light emitting layer (guest) may be doped into the light emitting layer (host) to increase the efficiency and stability of the light emitting state.

Recently, it has been known that not only fluorescent light emitting materials but also phosphorescent materials can be used as light emitting materials for organic EL devices (DF O'Brien et al., Applied Physics Letters , 74 ( 3 ), 442-444, 1999; MA Baldo et al. , Applied Physics letters , 75 ( 1 ), 4-6, 1999), and these phosphorescences are characterized by the transition of electrons from the ground state to the excited state, and then through intersystem crossing, After the light emission transition, the triplet excitons are composed of a mechanism that emits light while transitioning to the ground state. At this time, the transition to the triplet excitons does not directly transition to the ground state (spin forbidden), since the process of transition to the ground state after the flipping of the electron spin proceeds (lifetime) than fluorescence (lifetime) It has a longer characteristic. That is, the emission duration of fluorescence emission is only several nanoseconds, but the phosphorescence emission corresponds to several micro seconds, which is a relatively long time.

In the organic EL device, when the holes injected from the anode and the electrons injected from the cathode recombine to form luminescent excitons, the quantum mechanical assumption shows that the ratio of the singlet and triplet is 1: 3. This means that triplet emission excitons are generated three times more than singlet emission excitons in the device. Therefore, when phosphorescent light emitting materials are used, the emission efficiency is about three times higher than when fluorescent light emitting materials are used. There is an advantage to this.

In the case of a phosphorescent light emitting device, the luminous efficiency is high, but the life of the excitons is long, so that diffusion into layers other than the light emitting layer occurs easily, and thus the efficiency of the device is reduced. To solve this problem, Korean Patent Application Publication No. 2001-79818 discloses A hole blocking layer is inserted in front of the transport layer to confine the excitons to the light emitting insect. However, this method has a problem in that the lifetime of the device is low due to the low thermal stability of the hole blocking material used in the hole blocking layer.

Accordingly, it is an object of the present invention to provide an organic electroluminescent device having excellent electrical stability, high luminous efficiency characteristics, and an increased lifetime.

In order to achieve the above object, in the present invention, an organic electroluminescent device comprising an anode and a cathode and an organic layer therebetween, the organic electroluminescent device comprising a light emitting layer doped with a hole blocking material as the organic layer to provide.

Hereinafter, the present invention will be described in detail.

The present invention is to solve the problem that the hole blocking layer used in the conventional organic light emitting device, in particular phosphorescent light emitting device has a high hole blocking ability, but shortens the life of the device due to low thermal stability, the hole blocking material separately It is characterized in that it is used by doping the light emitting layer without forming a layer of.

An embodiment of the organic electroluminescent device according to the present invention has a structure in which a transparent anode, a hole injection layer, a hole transport layer, a light emitting layer doped with a hole blocking material, an electron transport layer, an electron injection layer, and a cathode are sequentially stacked. The hole blocking material-doped light emitting layer, which is used in the present invention, serves to prevent the excitons generated in the light emitting layer from diffusing to other layers to perform high efficiency light emission.

This embodiment according to the present invention is shown in FIG. 1, wherein layer 14 represents the hole blocking material-doped light emitting layer described above. In the present invention, a light emitting layer may be a host material and a dopant material, which are commonly used, and as the hole blocking material, bassocuproin (BCP), 3- (4-biphenylyl) -4-phenyl-5- Materials such as) 4-t-butylphenyl) -1,2,4-triazole (TAZ), bis (8-hydroxy2-methylquinolinato) aluminum biphenoxide (BAlq), and the like can be used. It is not limited to.

As shown in FIG. 1, the organic electroluminescent device of the present invention includes a transparent electrode (anode) 11, a hole injection layer 12, a hole transport layer 13, a hole blocking material-doped light emitting layer 14, and an electron transport layer. 15, the electron injection layer 16 and the metal electrode (cathode) 17 may be sequentially stacked.

In the organic electroluminescent device according to the present invention, the transparent electrode (anode) 11 and the metal electrode (cathode) 17 are conventional electrode materials, for example, the transparent electrode is indium tin oxide (ITO) or With SnO ₂ , the metal electrode may be formed of metals such as Li, Mg, Ca, Ag, Al, and In or alloys thereof, and the metal electrode may have a single layer or a multilayer structure of two or more layers.

In addition, the hole injection layer 12 may be composed of a conventional hole injection material, for example, copper phthalocyanine (CuPc) of the general formula (1) alone or in combination of two or more kinds, or two or more layers in which other layers are laminated. It may be.

The hole transport layer 13 is a conventional hole transport material, for example 4,4-bis [N- (1-naphthyl) -N-phenyl-amine] biphenyl (α-NPD) 4, N, N-diphenyl-N, N-bis (3-methylphenyl) -1,1-biphenyl-4,4-diamine (TPD) and poly- (N-vinylcarbazole) (PVCz) and the like It can contain individually or in mixture of 2 or more types, and can also laminate | stack two or more layers as a separate layer.

In addition, the hole blocking material-doped light emitting layer 14 may be formed of an iridium-based light emitting material, for example, tris (2-) in a host material such as 4,4-dicarbazole bisphenyl (CBP) of Chemical Formula 4 below. Phenylpyridine) iridium (Ir (ppy) 3) may be included as a light emitting material and may have a single layer or a multilayer structure of two or more layers. The hole blocking material doped in the light emitting layer is Bastocuproine (BCP) of Chemical Formula 6, 3- (4-biphenylyl) -4-phenyl-5- (4-t-butylphenyl) ) -1,2,4-triazole (TAZ) and bis (8-hydroxy-2-methylquinolinato) -aluminum biphenoxide (BAlq) of formula (8).

The doping amount of the hole blocking material in the hole blocking material-doped light emitting layer 14 may be in the range of 1 to 50% by weight based on the sum of the light emitting material and the hole blocking material, and 10 to 20% by weight is optimal in efficiency and lifetime. Is preferable.

In addition, the electron transporting material used for the electron transporting layer 15 may be, for example, a material such as tris (8-quinolinolato) aluminum (Alq 3) of general formula (9).

In addition, the electron injection layer 16 may include a conventional electron injection material including LiF.

The above-mentioned anode, cathode and various organic thin films can be formed by a conventional deposition method.

According to the present invention, the organic electroluminescent device having the hole blocking material-doped light emitting layer has high thermal stability, and thus, life and efficiency can be greatly improved.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are not intended to limit the invention only.

Example: Fabrication of Organic Electroluminescent Device with Hole-blocking Material-doped Light-Emitting Layer

An organic electroluminescent device having a structure as shown in FIG. 1 was manufactured by the following process.

150nm first ITO (Indium Tin Oxide) -coated glass substrate (Asahi Glass Co., Ltd., sheet resistance 8 Ω / cm ² ) was ultrasonically cleaned with water-based detergent, ultrapure water, isopropyl alcohol and methanol in sequential order. (11) was produced.

Copper phthalocyanine (CuPc) was deposited on the transparent electrode 11 to form a hole injection layer 12 having a thickness of 20 nm, and then 4,4-bis [N- (1-naphthyl)-on the hole injection layer 12. N-phenyl-amine] biphenyl (α-NPD) was deposited to form a hole transport layer 13 at 20 nm. Subsequently, 4,4-dicarbazole bisphenyl (CBP), BCP and tris (2-phenylpyridine) iridium (Ir (ppy) 3) were added in amounts of 100-x: x: 10 to give the doping amounts shown in Table 1 below. It was deposited on the hole transport layer 13 at a rate of 1 nm / second using a weight ratio to form a light emitting layer 14 of 30 nm. After co-deposition, tris (8-quinolinolato) aluminum (Alq3) was deposited on the light emitting layer 14 at a rate of 1 nm / sec to form an electron transport layer 15 of 40 nm, followed by LiF deposition. Electron injection layer 16 was formed. An organic electroluminescent device was manufactured by depositing Al on the electron injection layer 16 to form a cathode 17 of 150 nm.

The prepared organic electroluminescent device is, in summary, an ITO transparent electrode (150 nm) / CuPc hole injection layer (20 nm) / α-NPD hole transport layer (40 nm) / CBP + BCP + Ir (ppy) 3 hole blocking material-doped Light emitting layer (30 nm) / Alq3 electron transport layer (40 nm) / LiF electron injection layer (1 nm) / Al electrode (150 nm)] was laminated in order from the bottom.

Comparative Example: An organic electroluminescent device having a hole blocking layer / electron transport layer

For comparative experiments, separately, an ITO transparent electrode (150 nm) / CuPc hole injection layer (20 nm) / α-NPD hole transport layer (40 nm) / CBP + Ir (ppy) 3 light emitting layer was prepared by a deposition process similar to Example 1 above. (30 nm) / BCP hole blocking layer (10 nm) / Alq3 electron transport layer (40 nm) / LiF electron injection layer (1 nm) / Al electrode (150 nm)].

Device performance evaluation

The electroluminescent (EL) characteristics of the organic electroluminescent device manufactured as described above were applied to the PR-650 of Photo Research, and the life test was performed at an initial luminance of 500 cd / m ² . . As a result, the results as shown in Table 1 below according to the doping amount of BCP.

From the above results, the organic electroluminescent device including the light emitting layer doped with the hole blocking material according to the present invention, while maintaining the luminous efficiency and color purity as compared to the organic electroluminescent device including the light emitting layer and the hole blocking layer separately as in the comparative example It can be seen that the service life is significantly improved.

As described above, the organic electroluminescent device according to the present invention having the organic layer doped with the hole blocking material in the light emitting layer provides an effect of improving the lifespan when compared to the light emitting device having the respective layers composed of separate layers according to the conventional method. do.

Claims (6)

An organic electroluminescent device comprising an anode and a cathode and an organic layer therebetween, wherein the organic layer comprises a hole blocking material-doped emitting layer. The method of claim 1, An organic electroluminescent device, characterized in that the organic layer has a structure including a hole injection layer, a hole transport layer, a hole blocking material-doped light emitting layer, an electron transport layer and an electron injection layer. The method according to claim 1 or 2, Organic electroluminescent device, characterized in that the doping amount of the hole blocking material ranges from 1 to 50% by weight. The method of claim 3, wherein Organic electroluminescent device, characterized in that the doping amount of the hole blocking material ranges from 10 to 20% by weight. The method according to claim 1 or 2, The hole blocking material is vasocuproin (BCP), 3- (4-biphenylyl) -4-phenyl-5-) 4-t-butylphenyl) 1,2,4-triazole (TAZ), bis (8-hydroxy2-methylquinolinato) aluminum biphenoxide (BAlq), or a mixture thereof. The method according to claim 1 or 2, An organic electroluminescent device, wherein the hole blocking material-doped light emitting layer comprises a phosphorescent light emitting material.

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