KR100603404B1 - Organic electroluminescence display - Google Patents

Abstract

The present invention includes a light emitting layer including a phosphorescent dopant and a phosphorescent host between a first electrode and a second electrode, wherein the phosphorescent host has a triplet energy of 2.3 to 3.5 eV and a first phosphorescent host and a second phosphorescent host. It includes, wherein the difference between the energy level of the HOMO (Highest Occupied Molecular Orbital) and the HOMO of the second phosphorescent host of the first phosphorescent host is not zero or LUMO (Lowest Unoccupied Molecular Orbital) and the second phosphor of the first phosphorescent host The organic electroluminescent device is characterized in that the difference in the energy level of the LUMO of the host is not zero. The organic electroluminescent device of the present invention uses two kinds of phosphorescent hosts and phosphorescent dopants having desirable triplet energy, HOMO and LUMO energy level characteristics in forming a light emitting layer. As a result, the efficiency of recombination of holes and electrons in the vicinity of the light emitting layer is increased, thereby improving light emission efficiency and lifespan characteristics.

Description

Organic electroluminescence display

1A is a view showing energy levels in a light emitting layer of an organic EL device according to the present invention,

1B is a diagram showing energy levels in the organic EL device structure of the present invention,

2 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 life characteristics while 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 an organometallic compound structure 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 4,4'-biscarba. Zolylbiphenyl (CBP) is 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.

 The technical problem to be achieved by the present invention is to solve the above problems to provide an organic electroluminescent device having a very improved luminous efficiency and lifespan characteristics.

In order to achieve the above technical problem, the present invention includes a light emitting layer including a phosphorescent dopant and a phosphorescent host between the first electrode and the second electrode,

The phosphorescent host includes a first phosphorescent host having a triplet energy of 2.3 to 3.5 eV and a second phosphorous host,

The energy level difference between the first Occupied Molecular Orbital (HOMO) and the second phosphor host is not 0 or the lower unoccupied molecular orbital (LUMO) of the first phosphor host and the LUMO of the second phosphor host The organic electroluminescent device is characterized in that the energy level difference is not zero.

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

In the present invention, a phosphorescent dopant is used to form an emission layer, and as a host, the emission layer includes a first phosphorescent host having a triplet energy of 2.3 to 3.5 eV and a second phosphorous host, and a HOMO (first phosphorescent host) of the first phosphorescent host. The energy difference between the high Occupied Molecular Orbital and the second phosphor host is not zero, or the energy difference between the low phosphorus host's LUMO (Lowest Unoccupied Molecular Orbital) and the second phosphor host is nonzero. The luminous efficiency is improved by increasing the recombination efficiency of holes and electrons. Here, the triplet energy of the host is the difference in energy level between the ground state and the triplet state .

If the triplet energy of the phosphorescent host constituting the light emitting layer is less than 2.3 eV, energy transfer to the dopant is not efficient), and if it exceeds 3.5 eV, the driving voltage increases, which is not preferable. In addition, when the energy difference between the HOMO of the first phosphorescent host and the HOMO of the second phosphorescent host is 0 and / or the energy difference between the LUMO of the first phosphorescent host and the LUMO of the second phosphorescent host is 0, the luminous efficiency is lowered, which is undesirable. Can not do it.

The HOMO energy level of the first phosphorescent host is 5.5 to 7.0 eV, and the LUMO energy level is 2.1 to 3.5 eV. The HOMO energy level of the second phosphorescent host is 5.5 to 7.0 eV, and the LUMO energy level of 2.1 to 3.5eV. The first phosphorescent host and the second phosphorescent host are selected to satisfy the above-described HOMO and LUMO energy level conditions.

Further, the triplet energy of the first phosphorescent host is selected to be smaller than the triplet energy of the second phosphorescent host. The energy band gap between the HOMO and LUMO energy levels of the first phosphorescent host and the second phosphorescent host is preferably 2.5 to 4.0 eV, respectively.

1A and 1B, the principle of the present invention will be described, but tris (2-phenylpyridine) Iridium} (Ir (ppy) ₃ ) is used as an example of a dopant. do.

The triplet energy of the host must be greater than 2.3 eV because the triplet energy of the host must be larger than the triplet energy of the dopant in order for the energy transition to occur in the light emitting layer using the phosphorescent material. . In the present invention, since the energy level between the first phosphorescent host and the second phosphorescent host is not the same, when the holes and the electrons are injected and moved, they move along a more stable energy level. Does not move out of the light emitting layer.

On the other hand, the above-described effect with the same energy level between the first phosphorescent host and the second phosphorescent host does not appear. Therefore, the charge may move along the stable energy level when at least one of the HOMO energy level and the LUMO energy level of the first phosphor host and the second phosphor host is different.

In FIG. 1A, S ₁ ^H denotes the singlet excited state of the host, S ₀ ^H denotes the singlet ground state of the host, T ₁ ^H denotes the triplet excited state of the host, and S ₁ ^G denotes the singlet excited state of the dopant. , S ₀ ^G represents the singlet bottom state of the dopant, and T1 and T2 represent the triplet excited state of the dopant, respectively.

Specific examples of the first phosphorescent host and the second phosphorescent host include 4,4′-biscarbazolylbiphenyl (CBP) (triplet energy: 2.56 eV, HOMO = 3.0 eV, LUMO = 5.8 eV), 2,9-dimethyl -4,7-diphenyl-9,10-phenanthroline (BCP) (triplet energy: 2.5 eV, HOMO = 3.0 eV, LUMO = 6.3 eV), BAlq3 (triplet energy: 2.4 eV, HOMO = 2.8 eV, LUMO = 5.9 eV).

The mixing weight ratio of the first phosphorescent host and the second phosphorescent host is preferably 10:90 to 90:10.

The content of the host in the light emitting layer is 70 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) and the content of the dopant is 1 to 30 parts by weight. If the content of the host is less than 70 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 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 (2-phenylpyridine) iridium {Ir (PPy) ₃ }, tris (2-biphenylpyridine) iridium, tris ( 3-biphenyl pyridine) iridium, tris (4-biphenyl pyridine) iridium, etc. are mentioned.

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), etc., 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 (NPD), IDE320 (Idemitsu Co., Ltd.), N, N`-diphenyl-N, N`-bis (1-naphthyl)-(1,1`-biphenyl) -4,4`-diamine (NPB) do. 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, on the hole transport layer, a light emitting layer EML is formed by using a first phosphorescent host, a second phosphorescent host, and a phosphorescent dopant together as a host that satisfy the above-described energy conditions. 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.

The thickness of the light emitting layer is preferably 100 to 800 kPa, particularly 300 to 400 kPa. If the thickness of the light emitting layer is less than 100 kW, the efficiency and lifetime are lowered, and if the thickness of the light emitting layer exceeds 800 kW, the driving voltage increases, which is not preferable.

When the phosphorescent dopant is used to form the light emitting layer, a hole blocking layer (HBL) (not shown) may be formed as needed by vacuum deposition or spin coating a material for hole blocking on the light emitting layer.

An electron transport layer forms an electron transport layer (ETL) on the light emitting 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 layers mentioned above, an electron blocking layer may 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.

75 parts by weight of CBP, 25 parts by weight of BCP and 5 parts by weight of IrPPy3 were co-deposited on the hole transport layer 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 Å (electron injection layer) and Al 1000 Å (cathode) were sequentially vacuum deposited on the electron transport layer to form a LiF / Al electrode to manufacture an organic EL device.

Comparative Example 1

An organic electroluminescent device was manufactured in the same manner as in Example 1, except that Alq3 (triplet energy: 2.0 eV, HOMO = 3.0 eV, LUMO = 5.8 eV) was used instead of BCP to form the emission layer.

Reference Example 1

An organic electroluminescent device was manufactured in the same manner as in Example 1, except that BCP was not used in forming the emission layer.

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

As a result, the luminous efficiency of the organic electroluminescent device of Comparative Example 1 was about 10 cd / A, the lifetime was 1000 h (@ 1000 cd / m ² ), and the luminous efficiency of the organic electroluminescent device of Reference Example 1 was about 24 cd / A. , The lifetime is 5,000h (@ 1000 cd / m ² ), while the organic electroluminescent device of Example 1 has a luminous efficiency of 32 cd / A, a lifetime of 10,000 h (@ 1000 cd / m ² ), Comparative Example 1 Compared to the case, the efficiency and life characteristics are improved.

The organic electroluminescent device of the present invention uses two kinds of phosphorescent hosts and phosphorescent dopants having desirable triplet energy, HOMO and LUMO energy level characteristics in forming a light emitting layer. As a result, the efficiency of recombination of holes and electrons in the vicinity of the light emitting layer is increased, thereby improving light emission efficiency and lifespan characteristics. In addition, by mixing the two host materials can improve the fairness by solving the problem of crystallization that can occur in a single material.

Claims (12)

A light emitting layer comprising a phosphorescent dopant and a phosphorescent host between the first electrode and the second electrode, The phosphorescent host includes a first phosphorescent host having a triplet energy of 2.3 to 3.5 eV and a second phosphorous host, The energy level difference between the first Occupied Molecular Orbital (HOMO) and the second phosphor host is not 0 or the lower unoccupied molecular orbital (LUMO) of the first phosphor host and the LUMO of the second phosphor host An organic electroluminescent device, characterized in that the energy level difference is not zero. The organic electroluminescent device according to claim 1, wherein the triplet energy of the first phosphorescent host is smaller than the triplet energy of the second phosphorescent host. The organic electroluminescent device according to claim 1, wherein an energy band gap between HOMO and LUMO energy levels of the first phosphorescent host and the second phosphorescent host is 2.5 to 4.0 eV, respectively. The organic electroluminescent device according to claim 1, wherein a mixing weight ratio of the first phosphorescent host and the second phosphorescent host is 10:90 to 90:10. The method of claim 1, wherein the first phosphorescent host and the second phosphorescent host are 4,4′-biscarbazolylbiphenyl (CBP), 2,9-dimethyl-4,7-diphenyl-9,10-phenanthrole An organic electroluminescent device, each of which is selected from the group consisting of lean (BCP) and BAlq. The organic electroluminescent device according to claim 1, wherein the light emitting layer contains 70 to 99 parts by weight of the host and 1 to 30 parts by weight of the phosphorescent dopant. The method of claim 1, wherein the phosphorescent dopant is bisthienylpyridine acetylacetonate iridium, bis (benzothienylpyridine) acetylacetonate iridium {bis (benzothienylpyridine) acetylacetonate Iridium}, bis (2-phenylbenzo Thiazole) 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 (2-phenylpyridine) iridium, tris (2-biphenylpyridine) iridium, tris (3-biphenyl pyridine) iridium, tris (4-biphenyl pyridine) 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 first phosphorescent host is CBP, the second phosphorescent host is Balq, and the mixed weight ratio thereof is 10:90 to 90:10. The organic electroluminescent device according to claim 8, wherein the phosphorescent dopant used with the first phosphorescent host and the second phosphorescent host is tris (2-phenylpyridine) iridium. The organic electroluminescent device according to claim 9, 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. The organic electroluminescent device according to claim 1, further comprising at least one selected from a hole injection layer and a hole transport layer between the first electrode and the light emitting layer. The organic electroluminescent device according to claim 1, further comprising at least one selected from a hole blocking layer, an electron transport layer, and an electron injection layer between the light emitting layer and the second electrode.

Images