KR20160076461A - Organic electro luminescence device - Google Patents

Abstract

In the present invention, provided is an organic electroluminescent device representing high efficiency by improving properties of driving voltage, light emitting efficiency, and durability. The organic electroluminescent device comprises: a positive electrode; a negative electrode; and an organic material layer with one or more layers, interposed between the positive electrode and the negative electrode. At least one of the organic material layers with one or more layers includes: a first host; a second host; and a dopant.

Description

TECHNICAL FIELD [0001] The present invention relates to an organic electroluminescence device,

The present invention relates to an organic electroluminescent device including at least one organic material layer.

In order to increase the luminous efficiency of the organic electroluminescent device, it is necessary to increase the color purity and to transfer the energy. This can be achieved by applying a light emitting layer in which a host material and a dopant material are mixed in an organic material layer included in the organic electroluminescent device.

The dopant material can be divided into a fluorescent dopant and a phosphorescent dopant using an organic material. Since the phosphorescent material can theoretically improve the luminous efficiency up to 4 times as compared with the fluorescent material, studies on the phosphorescent host as well as the phosphorescent dopant are being carried out variously.

As phosphorescent dopant materials currently applied to the light emitting layer, metal complex compounds including Ir such as Firpic, Ir (ppy) ₃ , (acac) Ir (btp) ₂ and the like are known, and CBP and mCP are known as phosphorescent host materials . Specifically, it has been known to apply the mCP as a blue phosphorescent host while applying the Firpic as a blue phosphorescent dopant, or to apply the CBP as a green phosphorescent host while applying Ir (ppy) ₃ as a green phosphorescent dopant.

However, since the phosphorescent dopant and the phosphorescent host emit light using triplet energy, the phosphorescent dopant and phosphorescent host emit phosphorescent dopants and phosphorescent phosphors, There is a limit to obtaining devices. Accordingly, development of an organic electroluminescent device including a light emitting layer to which a phosphorescent material having a large bandgap and easy charge carrier injection / transportation and a large binding power for excitons is required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an organic electroluminescent device having improved characteristics such as a driving voltage, a luminescent efficiency, and a lifetime, in order to solve the above problems.

In order to achieve the above object, cathode; And an organic material layer interposed between the anode and the cathode, wherein the organic material layer includes at least one selected from the group consisting of a hole injecting layer, a hole transporting layer, a light emitting layer and an electron transporting layer, And a dopant, wherein energy levels of the first host, the second host, and the dopant satisfy the following relational expression.

HOMO _D > HOMO _1host > HOMO _2host

LUMO _D <LUMO _2host <LUMO _1host

The meaning of each in the above equation is as follows.

HOMO _D : HOMO energy level of the dopant

HOMO _1host : HOMO energy level of the first host

HOMO _2host : HOMO energy level of the second host

LUMO _D : LUMO energy level of the dopant

LUMO _1host : The LUMO energy level of the first host

LUMO _2host : LUMO energy level of the second host

Since the organic electroluminescent device of the present invention includes an electron dominant first host, a hole dominant second host and a dopant in the light emitting layer, the conventional organic electroluminescent device includes a light emitting layer to which one kind of host is applied Characteristics such as a driving voltage, a luminous efficiency and a lifetime can be further improved as compared with an organic electroluminescent device. Therefore, the organic electroluminescent device of the present invention can exhibit high efficiency, and when the display panel is manufactured using such an organic electroluminescent device, a display panel having improved performance and lifetime can be provided.

Hereinafter, the present invention will be described.

The organic electroluminescent device of the present invention includes at least one anode, an anode, and at least one organic layer sandwiched between the anode and the cathode, and the organic layer includes a hole injection layer, a hole transport layer, And an electron transport layer. The light emitting layer includes a first host, a second host, and a dopant, and will be described in detail as follows.

The anode included in the organic electroluminescent device of the present invention injects holes into an organic material layer. The material to be applied to such an anode is not particularly limited, but includes, but not limited to, metals such as vanadium, chromium, copper, zinc, gold, or alloys thereof; Metal oxides such as zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); ZnO: Al or SnO _2: a combination of a metal and an oxide such as Sb; Conductive polymers such as polythiophene, poly (3-methylthiophene), poly [3,4- (ethylene-1,2-dioxy) thiophene] (PEDT), polypyrrole and polyaniline; And carbon black. The method of producing the anode is not particularly limited, but a method of coating a cathode material on a substrate made of a material such as a silicon wafer, quartz, glass plate, metal plate, or plastic film can be mentioned as a non-limiting example.

The cathode included in the organic electroluminescent device of the present invention injects electrons into the organic material layer. Materials to be applied to such an anode include, but are not limited to, metals such as magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, ; And multilayer structure materials such as LiF / Al or LiO ₂ / Al. The method for producing the negative electrode is not particularly limited as long as it is a method known in the art.

The organic material layer included in the organic electroluminescent device of the present invention includes at least one selected from the group consisting of a hole injecting layer, a hole transporting layer, a light emitting layer and an electron transporting layer. In consideration of the characteristics of the organic electroluminescent device, .

The hole injection layer and the hole transport layer included in the organic material layer of the present invention serve to transfer holes injected from the anode to the light emitting layer. The material to be applied to the hole injection layer is not particularly limited, but a material capable of receiving holes from the anode smoothly at a low voltage, wherein a highest occupied molecular orbital (HOMO) value is a function of a material to be applied to the anode, , The light-emitting layer). Specific examples of the material to be applied to the hole injection layer include, but are not limited to, metal porphyrine, oligothiophene, arylamine-based organic materials, hexanitrile hexaazatriphenylene-based organic materials, quinacridone series Organic materials of perylene series, anthraquinone, conductive polymers of polyaniline and polythiophene series, and the like.

Also, the material to be applied to the hole transport layer is not particularly limited. However, it is preferable that the hole transport layer is a material capable of transporting holes from the anode or the hole injection layer to the light emitting layer, and having high hole mobility. Specifically, non-limiting examples of the material to be applied to the hole transporting layer include an arylamine-based organic material, a conductive polymer, and a block copolymer having a conjugated portion and a non-conjugated portion together.

The light emitting layer included in the organic material layer of the present invention is a layer in which holes and electrons meet to form an exciton. Specifically, holes injected into the light emitting layer use the HOMO energy level of the first host, and electrons injected into the light emitting layer use the LUMO energy level of the second host to form excitons. The light emitting layer of the present invention includes an electron conduction first host, a hole conduction second host and a dopant, wherein the first host, the second host and the dopant satisfy the following formula.

HOMO _D > HOMO _1host > HOMO _2host

LUMO _D <LUMO _2host <LUMO _1host

The meaning of each in the above equation is as follows.

HOMO _D : HOMO energy level of the dopant

HOMO _1host : HOMO energy level of the first host

HOMO _2host : HOMO energy level of the second host

LUMO _D : LUMO energy level of the dopant

LUMO _1host : The LUMO energy level of the first host

LUMO _2host : LUMO energy level of the second host

The HOMO energy level of the first host is not particularly limited as long as it is lower than the HOMO energy level of the dopant, but it is preferably 5.0 to 7.0 eV. Further, the HOMO energy level of the second host is not particularly limited as long as it is lower than the HOMO energy level of the first host. Preferably, the difference between HOMO _1host and HOMO _2host may be between 0.1 and 0.5 eV.

The LUMO energy level of the second host is not particularly limited as long as it is higher than the LUMO energy level of the dopant, but it is preferably 1.0 to 3.0 eV. Also, the LUMO energy level of the first host is not particularly limited as long as it is higher than the LUMO energy level of the second host. Preferably, the difference between LUMO 1 _host and LUMO _2host may be between 0.1 and 0.5 eV.

The HOMO energy level of the dopant is higher than that of the first host and the second host, thereby improving hole injection efficiency into the light emitting layer. As described above, when the hole injection efficiency is improved, the formation of excitons in the light emitting layer becomes smooth, and therefore, high luminous efficiency can be exhibited.

On the other hand, the triplet energy of the first host and the second host is not particularly limited as long as it is higher than the triplet energy of the dopant, but is preferably 2.0 to 3.5 eV. To facilitate energy transfer from the host to the dopant, the first host and second host material in the phosphorescent light emitting layer must have a singlet and triplet energy level higher than the singlet term and triplet energy of the dopant material. This is because the excitons in the triplet of the dopant can be prevented from reversing to the host again, and the luminous efficiency, driving voltage and lifetime of the organic electroluminescent device can be further improved.

Specifically, when the light emitting layer is red phosphorescence, the triplet energy of the first host and the second host is preferably 2.0 eV or more, and when the light emitting layer is green phosphorescence, the triplet energy of the first host and the second host is 2.3 eV or more When the light emitting layer is blue phosphorescent, the triplet energy of the first host and the second host is preferably 2.5 eV or more. Further, when the triplet energies of the first host and the second host each exceed 3.5 eV, the driving voltage may rise, so that the triplet energies of the first host and the second host are preferably 2.0 to 3.5 eV, respectively Do.

Here, the triplet energy means the energy difference between the base state and the triplet state.

It is preferable that the electron mobility of the first host is 1 × ^{10 -6} cm ² / V · s at room temperature and the hole mobility of the second host is ¹ × ^{10 -6} cm ² / V · s or more at room temperature. When the electron mobility of the first host and the hole mobility of the second host are in the above range, electrons and holes can be effectively injected into the light emitting layer.

The first host and the second host included in the light emitting layer may be a triphenylene compound, a dibenzofuran compound, a dibenzothiophene compound, an azepine compound, a carbazole compound, a phosphine oxide compound, And a nitrogen-containing heterocyclic compound (for example, a pyrimidine-based compound).

Since the triphenylene type compound, the dibenzofuran type compound, the dibenzothiophene type compound, the azepine type compound and the carbazole type compound each have a triplet energy of 3.0 eV or more, not only the red and green phosphorescent host but also the blue phosphorescent host Can be applied. In addition, the thermal stability is very excellent and the stability of the device can be improved. Specific examples of such triphenylene-based compounds, dibenzofuran-based compounds, dibenzothiophene-based compounds, azepine-based compounds and carbazole-based compounds include, but are not limited to, the following compounds represented by H1 to H25.

In the above H1 to H25

X ₁ is NAr ₁ , O, or S,

X ₂ is NAr ₂ , O, S, or CR ₂₄₈ R ₂₄₉ ,

X ₁ and X ₂ are the same or different and at least one is NAr ₁ ,

Each of Ar ₁ and Ar ₂ is independently a C ₆ to C ₄₀ aryl group or a heteroaryl group having 5 to 40 nuclear atoms,

R ₁ to R ₂₄₉ are each independently hydrogen, a C ₁ to C ₄₀ alkyl group, a C ₆ to C ₄₀ aryl group, and a heteroaryl group having 5 to 40 nuclear atoms, or may be bonded to adjacent groups to form a condensed ring (specifically, A condensed aromatic ring, a condensed heteroaromatic ring)

The aryl group and heteroaryl group of Ar ₁ and Ar _{2 and} the alkyl group, aryl group and heteroaryl group of R ₁ to R ₂₄₉ are each independently a substituted or unsubstituted C ₆ to C ₄₀ aryl group, Is substituted or unsubstituted with a heteroaryl group having 5 to 40 ring atoms.

On the other hand, the phosphine oxide-based compound can also be applied as a green / red / blue phosphorescent host since it has a large band gap due to interference of π-π conjugation due to phosphine oxide group and triple energy of 3.0 eV or more have. Further, since the electron transporting property is excellent, the efficiency and stability of the organic electroluminescent device can be improved.

In addition, since the nitrogen-containing heterocyclic compound (triplet energy greater than 2.8 eV) has a HOMO-LUMO band gap and an electron absorbing property and is excellent in electron transporting property, the efficiency and stability of the organic electroluminescent device can be improved. Specific examples of such nitrogen-containing heterocyclic compounds include, but are not limited to, the compounds represented by the following C1 to C19.

The dopant included in the light emitting layer is not particularly limited, but may be a metal; Metal oxides; And metal complex compounds, among which metal complex compounds are preferably used.

The metal complex compound is not particularly limited, but examples thereof include a platinum-containing metal complex compound, a zinc-containing metal complex compound, and an iridium-containing metal complex compound. Among them, a metal complex compound containing iridium (Ir) . At this time, examples of the iridium-containing metal complex compound include Firpic, Ir (ppy) ₃ , (acac) Ir (btp) ₂ and the like.

In the meantime, the mixing ratio of the first host and the second host in the light emitting layer of the present invention is not particularly limited, but it is preferable that the first host and the second host are mixed in a weight ratio of 1:99 to 99: 1. In addition, although the mixing ratio of the dopant to the first host and the second host is not particularly limited, it is preferable that the first host and the second host: dopant are mixed in a weight ratio of 99: 1 to 70:30.

The method for producing the light emitting layer of the present invention is not particularly limited, but examples thereof include a co-evaporation method, a vacuum evaporation method, and a solution coating method. In the co-deposition method, the first host and the second host are disposed in the first and second heat sources, respectively, and the dopant is placed in the third heat source, and simultaneously heat is applied thereto to form the light emitting layer.

Specifically, a first host having a high electron mobility and a high electron injection efficiency is disposed in a first heat source at a vacuum degree of 1 x 10 ^-0.6 torr or less, and a hole mobility is high and a hole injection efficiency A good second host is disposed in the second heat source, a dopant is disposed in the third heat source, and the evaporation rate per second of each material is controlled simultaneously, thereby co-depositing at a proper ratio. At this time, the number of co-deposited hosts may be two or more depending on the characteristics of the light emitting layer.

In addition, a host having similar deposition temperatures in the host may be mixed in an appropriate ratio and disposed in a single heat source, followed by coagulation by heating to form a light emitting layer. Specifically, a mixed host (e.g., a first host and a second host) is disposed in a first heat source at a degree of vacuum of 1X10 ^-0.6 torr or less, a dopant is disposed in a second heat source, The speed is controlled at the same time to produce the light emitting layer.

In this way, when the host mixed with the first heat source is disposed to produce the light emitting layer, the error of the host mixing ratio of one or more kinds can be reduced, and the light emitting layer can be formed using a small number of heat sources. Specifically, when the deposition temperature of the first host and the second host is ± 10 ° C, they can be mixed and placed in one heat source.

The electron transport layer included in the organic material layer of the present invention serves to transfer electrons injected from the cathode to the light emitting layer. The material to be applied to such an electron transporting layer is not particularly limited. However, it is preferable that the electron transporting layer is a material which can transfer electrons from the cathode well to the light emitting layer and has high mobility to electrons. Specifically, non-limiting examples of the material to be applied to the electron transporting layer include Al complex of 8-hydroxyquinoline; Complexes containing Alq ₃ ; Organic radical compounds; Hydroxyflavone-metal complexes, and the like, but are not limited thereto.

Meanwhile, the organic material layer of the present invention may further include an electron injection layer on the electron transporting layer.

The method for preparing the organic layer except for the light emitting layer of the present invention is not particularly limited, but examples thereof include vacuum deposition, solution coating and the like. Examples of the solution coating method include a spin coating method, a dip coating method, a doctor blading method, an ink jet printing method, a thermal transfer method, and the like.

The organic electroluminescent device of the present invention may have a structure in which a cathode, an organic layer, and a cathode are sequentially stacked, and an insulating layer or an adhesive layer may be further included between the anode and the organic layer or between the cathode and the organic layer.

The organic electroluminescent device of the present invention may be manufactured by forming an organic material layer and an electrode using materials and methods known in the art, except for a light emitting layer.

Hereinafter, the present invention will be described in detail with reference to Examples. However, the present invention is not limited by the following Examples.

[Preparation Example] Compounds PGH1-1 to PGH2-4, CBP and Ir (ppy) ₃  Ready

Compounds represented by the following PGH1-1 to PGH1-4 as the first host of the present invention and PGH2-1 to PGH2-4 as the second host were prepared. The HOMO and LUMO of the above compounds, CBP and Ir (ppy) ₃ , were measured by methods known in the art and are shown in Table 1 below.

compound HOMO (eV) LUMO (eV) PGH1-1 -5.33 -1.93 PGH1-2 -5.59 -2.24 PGH1-3 -5.66 -2.28 PGH1-4 -5.52 -2.15 PGH2-1 -5.85 -2.58 PGH2-2 -5.88 -2.51 PGH2-3 -5.90 -2.53 PGH2-4 -5.79 -2.46 CBP -5.90 -2.50 Ir (ppy) ₃ -5.30 -3.00

[Examples 1 to 9] Preparation of Organic Electroluminescent Device

The glass substrate coated with ITO (Indium tin oxide) thin film with thickness of 1500 Å was ultrasonically cleaned with distilled water. After the distilled water was washed, it was ultrasonically washed with a solvent such as isopropyl alcohol, acetone, or methanol, dried, transferred to a UV OZONE cleaner (Power sonic 405, Hoshin Tech), and then the substrate was cleaned using UV for 5 minutes The substrate was transferred to a vacuum evaporator.

On the ITO transparent substrate (electrode) prepared above, a phosphorescent host (first host + second host) of the following Table 2 + 10% Ir (m-MTDATA 60 nm) / TCTA the ppy) stacked in _{3 (30 nm) / BCP (} 10 nm) / Alq 3 (30 nm) / LiF (1 nm) / Al (200 nm) in order to prepare an organic electroluminescent device.

The m-MTDATA, TCTA, Ir (ppy) ₃ and BCP used were as follows.

[Comparative Example 1] Production of organic electroluminescent device

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that CBP was used as a phosphorescent host in the formation of the light emitting layer. At this time, the CBP used is as follows.

[Comparative Example 2] Production of organic electroluminescent device

An organic electroluminescent device was manufactured in the same manner as in Example 1 except that PGH1-1 was used as a phosphorescent host in the formation of the light emitting layer.

[Experimental Example 1]

The organic EL devices manufactured in Examples 1 to 9 and Comparative Examples 1 and 2 were measured for driving voltage, EL peak and current efficiency at a current density of 10 mA / cm 2. The results are shown in Table 2 below. .

Host (mixing ratio) The driving voltage (V) EL peak (nm) Current efficiency (cd / A) Example 1 PGH1-1 + PGH2-1 (5: 5) 6.40 516 43.1 Example 2 PGH1-1 + PGH2-2 (5: 5) 6.45 516 43.2 Example 3 PGH1-1 + PGH2-3 (5: 5) 6.20 516 43.6 Example 4 PGH1-1 + PGH2-4 (5: 5) 6.40 516 42.8 Example 5 PGH1-2 + PGH2-3 (5: 5) 6.40 516 42.6 Example 6 PGH1-3 + PGH2-3 (5: 5) 6.45 516 43.1 Example 7 PGH1-4 + PGH2-3 (5: 5) 6.25 516 43.0 Example 8 PGH1-1 + PGH2-3 (3: 7) 6.45 516 43.2 Example 9 PGH1-1 + PGH2-3 (7: 3) 6.35 516 42.7 Comparative Example 1 CBP 6.93 516 38.2 Comparative Example 2 PGH1-1 6.50 516 40.9

The organic electroluminescent devices according to the present invention (Embodiments 1 to 9) using the light emitting layer including the first host, the second host and the dopant (Organic Electroluminescent Devices) using the light emitting layer including a single host It was confirmed that the current efficiency and the driving voltage were superior to those of Examples 1 and 2.

Claims (6)

anode; cathode; And an organic layer interposed between the anode and the cathode,
The organic material layer includes at least one selected from the group consisting of a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer,
Wherein the light emitting layer comprises a first host, a second host and a dopant,
Wherein the energy level of the first host, the second host, and the dopant satisfy the following relational expression.
HOMO _D > HOMO _1host > HOMO _2host
LUMO _D <LUMO _2host <LUMO _1host
Each of the meanings in the above formula is as follows;
HOMO _D : HOMO energy level of the dopant
HOMO _1host : HOMO energy level of the first host
HOMO _2host : HOMO energy level of the second host
LUMO _D : LUMO energy level of the dopant
LUMO _1host : The LUMO energy level of the first host
LUMO _2host : LUMO energy level of the second host The method according to claim 1,
Wherein the triplet energies of the first host and the second host are respectively greater than triplet energy of the dopant and 2.0 to 3.5 eV. The method according to claim 1,
Wherein the electron mobility of the first host is 1 × ^{10 -6} cm ² / V · s at room temperature and the hole mobility of the second host is ¹ × ^{10 -6} cm ² / V · s or more at room temperature. The method according to claim 1,
Wherein the first host and the second host are each selected from the group consisting of a triphenylene compound, a dibenzofuran compound, a dibenzothiophene compound, an azepine compound, a carbazole compound, a phosphine oxide compound, and a nitrogen- Wherein the organic electroluminescent device is selected from the group consisting of organic electroluminescent devices. The method according to claim 1,
Wherein each of the first host and the second host is any one of compounds represented by the following H1 to H25.

In the above H1 to H25
X ₁ is NAr ₁ , O, or S,
X ₂ is NAr ₂ , O, S, or CR ₂₄₈ R ₂₄₉ ,
X ₁ and X ₂ are the same or different and at least one is NAr ₁ ,
Each of Ar ₁ and Ar ₂ is independently a C ₆ to C ₄₀ aryl group or a heteroaryl group having 5 to 40 nuclear atoms,
R ₁ to R ₂₄₉ each independently represent a hydrogen atom, a C ₁ to C ₄₀ alkyl group, a C ₆ to C ₄₀ aryl group, and a heteroaryl group having 5 to 40 nuclear atoms, or may be bonded to adjacent groups to form a condensed ring,
The aryl group and heteroaryl group of Ar ₁ and Ar _{2 and} the alkyl group, aryl group and heteroaryl group of R ₁ to R ₂₄₉ are each independently a substituted or unsubstituted C ₆ to C ₄₀ aryl group, Is substituted or unsubstituted with a heteroaryl group having 5 to 40 ring atoms. The method according to claim 1,
Wherein the dopant is an iridium-containing metal complex compound.