JPH0867872A - Organic electroluminescence element - Google Patents

Abstract

PURPOSE: To obtain the subject element excellent in heat resistance, brightness, luminous efficiency and color purity of luminous color by providing a hole- injecting layer comprising a specific quinacridone or a specific quinazoline compound between anode and a hole transporting layer. CONSTITUTION: This element is obtained by laminating (A) an anode, (B) a hole transporting layer comprising an organic compound, (C) a luminous compound comprising an organic compound and (D) a cathode in this order and providing a hole-injecting layer comprising a quinacridone compound of formula I [R1 to R4 are each H, a halogen, an alkyl or alkoxy or a benzene ring or an N-alkylindoline ring in which R1 and R2 or R3 and R4 are together bonded; a ring A is benzene ring or 1,4-cyclohexadiene ring) or a ring of the formula II (a ring B is benzene ring or 1,4-cyclohexadiene ring)] or a quinazoline compound of formula III between the layers A and B.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light emitting device provided with a light emitting layer formed by layering such a substance by utilizing electroluminescence of a substance which emits light when an electric current is injected, and particularly, the light emitting layer is constituted by an organic compound as a light emitter. The present invention relates to an organic electroluminescent device.

[0002]

BACKGROUND ART As an organic electroluminescence device of this type, as shown in FIG. 1, a metal cathode 1 and a transparent anode 2 are used.
, A two-layer structure in which a phosphor thin film 3 made of an organic compound and laminated with each other, that is, a light emitting layer and a hole transporting layer 4, is arranged, and as shown in FIG.
There is known a three-layer structure in which an electron transporting layer 5, which is made of an organic compound, a light emitting layer 3 and a hole transporting layer 4 are laminated between a transparent anode 2 and a transparent anode 2. Here, the hole transport layer 4 has a function of facilitating injection of holes from the anode and a function of blocking electrons, and the electron transport layer 5 has a function of facilitating injection of electrons from the cathode.

In these organic electroluminescent elements, a glass substrate 6 is arranged outside the transparent anode 2 and contains electrons injected from the metal cathode 1 and holes injected from the transparent anode 2 to the light emitting layer 3. Excitons are generated by the recombination, and the excitons emit light in the process of radiation deactivation, and the light is emitted to the outside through the transparent anode 2 and the glass substrate 6. However, in the conventional devices, there are still few devices which are sufficiently satisfactory in terms of durability because of short emission half-life.

Further, as disclosed in JP-A-63-295695, an organic electroluminescence device having a two-layer structure and having a hole injection layer such as copper phthalocyanine inserted between the anode and the hole transport layer is also available. Being developed.

[0005]

In the organic electroluminescence device having such a hole injection layer, it is known that the hole injection layer is made of copper phthalocyanine represented by the following chemical formula (3).

[0006]

[Chemical 3]

However, the organic electroluminescence device using this copper phthalocyanine in the hole injection layer is still not sufficiently satisfactory in terms of luminous efficiency. Therefore, there is a demand for an organic electroluminescence device having high durability and high luminous efficiency that emits light with high brightness. It is an object of the present invention to provide a highly durable organic electroluminescence device that can emit light with high brightness and high luminous efficiency.

[0008]

The organic electroluminescent device according to the present invention is an organic electroluminescent device comprising an anode, a hole transport layer made of an organic compound, a light emitting layer made of an organic compound, and a cathode, which are sequentially stacked. The following chemical formula 1 is provided between the anode and the hole transport layer.
A quinacridone compound having a structure represented by:
A quinazoline compound having the structure shown by

[0009]

[Chemical 4]

[0010]

[Chemical 5]

(Wherein ring A is

[0012]

[Outside 4]

And ring B is

[0014]

[Outside 5]

[0015] represents, R ₁ to R ₄ independently of one another are hydrogen, a halogen atom, an alkyl group or alkoxy group, or R ₁ and R ₂ or R ₃ and R ₄ are a benzene ring or bonded to each other

[0016]

[Outside 6]

And R ₅ represents an alkyl group) is provided.

[0018]

According to the present invention, since the hole injecting layer composed of the quinacridone derivative or the quinazoline derivative is provided between the hole transporting layer and the anode, the quinacridone derivative of the hole injecting layer is
Due to its excellent heat resistance and robustness, the device driving life is improved, and there is almost no absorption of light with a wavelength of 600 nm or more, and orange to red light emission can be effectively extracted to the outside, and high brightness light emission can be achieved with a low applied voltage. An organic electroluminescence device is obtained.

[0019]

The present invention will be described below with reference to the drawings. As shown in FIG. 3, the organic electroluminescence device of the present invention comprises a light emitting layer 3, a hole transporting layer 4 and a hole injecting layer 4a which are laminated as a thin film between a pair of a metal cathode 1 and a transparent anode 2 to form a thin film. As shown in FIG. 4, or as shown in FIG. 4, an electron transport layer 5, a light emitting layer 3, a hole transport layer 4 and a hole injection layer 4a were deposited between a pair of metal cathode 1 and transparent anode 2. The structure is fine. In either case, one of the electrodes 1 and 2 may be transparent. For example, for the cathode 1, aluminum,
A metal having a low work function such as magnesium, indium, silver, or an alloy of each and having a thickness of about 100 to 5000 angstroms can be used. Further, for example, the anode 2 is made of a conductive material having a large work function such as indium tin oxide (hereinafter referred to as ITO) and has a thickness of 1
000 to 3000 angstroms or gold with a thickness of 800 to 1500 angstroms can be used. When gold is used as the electrode material, the electrode becomes semitransparent.

First, the quinacridone compound having the structure represented by the chemical formula 1 or the quinazoline compound having the structure represented by the chemical formula 2 used for the hole injection layer 4a formed on the anode of the substrate is represented by the following chemical formula 4. Quinacridone compound.

[0021]

[Chemical 6]

A 2,9-dichloroquinacridone compound represented by the following chemical formula 5,

[0023]

[Chemical 7]

Is used for the hole injection layer. As other quinacridone halides, 3,10-dichloro body, 4,11-dichloro body, 3,4,10,11-tetrachloro body, 1,4,8,11-tetrachloro body, 2,4,9, 11-tetrachloro body, 2,3,9,10-tetrachloro body (Japanese Patent Publication No. 36-14383), 1,2,8,9-tetrachloro body, 1,3,8,10-tetrachloro body, 2,9-dibromo form,
3,10-dibromo compound, 4,11-dibromo compound, 2,4,9,11-tetrabromo compound, 1,4,8,11-tetrabromo compound, 2,8,9,11-tetrabromo compound, 1,3 , 8,10-Tetrabromo body, 4,11-difluoro body, 2,9-difluoro body, 3,10-difluoro body, 2,4,9,11-
Tetrafluoro body, 1,4,8,11-tetrafluoro body, 2,4,
Examples include 9,11-tetraiodo form and 2,9-diiodo form.

Further, the hole injection layer is also formed of a 2,9-dimethylquinacridone compound represented by the following chemical formula 6.

[0026]

Embedded image

Further, other quinacridone compounds used as the hole injecting layer include 3,10-dimethyl compound, 4,11-dimethyl compound, 1,4,8,11-tetramethyl compound, 2,4,9. There are 1,11-tetramethyl body, 1,2,8,9-tetramethyl body and 1,3,8,10-tetramethyl body. Further, a 1,8-dichloro-4,11-dimethylquinacridone compound represented by the following chemical formula 7 is also used in the hole injection layer.

[0028]

[Chemical 9]

Further, 2,9-dimethyl-3,10-dichloro body,
3,10-Dichloro-4,11-dimethyl body, 1,8-dimethyl-3,10-
Dichloro form, 2,9-dichloro-4,11-dimethyl form, and 2,9-
A quinacridone compound of a dimethyl-4,11-dichloro body is also used in the hole injection layer. In addition, 2, which is represented by the following chemical formula 8,
The 9-dimethyl-4,11-diethoxy form is also used in the hole injection layer.

[0030]

[Chemical 10]

Further, a 2,9-diethoxy-4,11-dimethyl compound and a 2,4,9,11-tetramethoxy compound are also used in the hole injection layer. In all of the above quinacridone derivatives, these 6,13-dihydro derivatives are also used. For example, in the case of the above chemical formula 8, 2,9-dimethyl-4,11-diethoxy- The 6,13-dihydro form is used for the hole injection layer.

[0032]

[Chemical 11]

Furthermore, in the hole injection layer, 3,4,10,11-dibenzo compound represented by the following chemical formula 10

[0034]

[Chemical 12]

Further, 1,2,8,9-dibenzo compound and 2,3,
The 9,10-dibenzo form is used. In addition, the following chemical formula 11
And a quinazoline compound represented by the following chemical formula 12 (Yokoyama et al., Nikkashi, 382, 1977 )
Is also used for the hole injection layer.

[0036]

[Chemical 13]

[0037]

Embedded image

Furthermore, a quinacridone derivative condensed through a benzene ring represented by the following chemical formula 13,

[0039]

[Chemical 15]

Is also used for the hole injection layer. Also in these quinacridone derivatives, dihydro derivatives can be used in the hole injection layer. Next, in the hole transport layer 4 formed on the hole injection layer, a substance represented by the general formula (14), for example, NPD represented by the following chemical formula 15 called TPD,
N′-diphenyl-N, N′-bis (3methylphenyl) -1,1′-biphenyl-4,4′-diamine is preferably used, and CTMs represented by the following chemical formulas 16 to 25 are used.
The compounds known as (Carrier Transport Materials) may be used alone or as a mixture.

[0041]

Embedded image

[0042]

[Chemical 17]

[0043]

[Chemical 18]

[0044]

[Chemical 19]

[0045]

Embedded image

[0046]

[Chemical 21]

[0047]

[Chemical formula 22]

[0048]

[Chemical formula 23]

[0049]

[Chemical formula 24]

[0050]

[Chemical 25]

[0051]

[Chemical formula 26]

[0052]

[Chemical 27]

For example, a quinoline derivative is used for the light emitting layer 3, and an aluminum complex of 8-hydroxyquinoline represented by the following chemical formula 26, that is, an Al oxine chelate (hereinafter referred to as Alq ₃ ),

[0054]

[Chemical 28]

In addition to these, for example, bis (8-quinolinol) magnesium, bis (benzo {f} -8-quinolinol) zinc and bis (2-methyl-) are preferably used.
8-quinolinol) aluminum oxide, tris (8-quinolinol) indium, tris (5-methyl-8-quinolinol) aluminum, 8-quinolinol lithium, tris (5-chloro-8-quinolinol) gallium, bis (5-chloro-). 8-quinolinol) calcium and poly [zinc (II) -bis (8-hydroxy-5-quinolinyl) methane] can be used.

Further, the light emitting layer 3 composed of a guest substance and a host substance may be used, and the guest substance of the light emitting layer 3 is a dicyanomethylenepyran compound represented by the chemical formula 27.

[0057]

[Chemical 29]

(Hereinafter referred to as DCM) or a dicyanomethylenepyran compound represented by the chemical formula 28

[0059]

[Chemical 30]

(Hereinafter referred to as DCM2) is used.
The guest substance is selected from fluorescent dyes having a high fluorescence quantum yield, and 0.01 wt. % To 10 wt. It is preferably contained at a concentration of%. This is because light emission with high brightness can be obtained with a low applied voltage.
Although the light emitting layer 3 and the organic hole transport layer 4 are arranged between the cathode 1 and the anode 2 in the above embodiment, for example, the organic electron transport layer 5 is arranged between the cathode 1 and the light emitting layer 3 as shown in FIG. The same effect can be obtained as an organic electroluminescence device having the above structure. As the electron transport layer 5, the above 8-hydroxyquinoline Alq ₃ can be used. Further, as the electron transport layer 5, t-Bu- represented by the following chemical formula 29 is used.
PBD [2- (4'-tert-Butylphenyl) -5- (biphenyl) -1,3,4
-oxadiazole] is preferably used, and the following chemical formula 3
The compounds represented by 0 to 35 can also be used.

[0061]

[Chemical 31]

[0062]

[Chemical 32]

[0063]

[Chemical 33]

[0064]

Embedded image

[0065]

Embedded image

[0066]

Embedded image

[0067]

Embedded image

Example 1 On a glass substrate on which an anode made of ITO having a film thickness of 2000 angstrom was formed,
Each thin film was vacuum-deposited to a vacuum degree of 1.0 × 10 ⁻⁵ Torr.
First, quinacridone represented by the chemical formula 4 was deposited as a hole injection material on ITO in a higher vacuum to form a hole injection layer with a thickness of 350 Å at a deposition rate of 3 Å / sec. Next, TPD represented by Chemical Formula 15 was similarly formed as a hole transport layer to have a thickness of 350 Å. Alq _{3 represented} by the chemical formula 26 as a host material of the light emitting layer and DCM2 represented by the chemical formula 28 as a guest material are formed on different layers from different deposition sources at a weight ratio of Alq ₃ : DCM2 = 10: 1 and a thickness of 500 Å. It vapor-deposited and formed the light emitting layer. On top of that, only Alq ₃ was vapor-deposited to a thickness of 500 Å as an electron transport layer, and magnesium and silver were used as cathodes on this electron transport layer from different vapor deposition sources to obtain an atomic ratio Mg: Ag.
= 10: 1 and co-deposited to a thickness of 1600 angstroms.

The electroluminescence device as shown in FIG. 4 thus produced has chromaticity coordinates x = 0.61, y = 0.
At 38,300 cd / m ² , luminous efficiency of 1.1 lm / W and external quantum efficiency of 3.6% were obtained. A constant current (3.
When driven at 6 mA / cm ² ), the initial brightness was 220 cd / m ²
It took 508 hours to reach half brightness.

(Comparative Example 1) The hole injection layer made of a quinacridone derivative was not formed, and the film thickness of the hole transport layer of TPD was set to 50.
An electroluminescence device was prepared in the same manner as in Example 1 except that the electroluminescence device was formed to have a thickness of 0 angstrom. The element created in this way has chromaticity coordinates x = 0.61, y = 0.38,
A luminous emission efficiency of 300 cd / m ² of 1.5 lm / W and an external quantum efficiency of 3.6% were obtained.

When this device was driven at a constant current (3.6 mA / cm ² ), the time required to reduce the initial brightness from 218 cd / m ² to half the brightness was 315 hours, which was shorter than in Example 1. (Comparative Example 2) hole injection and for the use of copper phthalocyanine represented by the chemical formula 3 in place of the quinacridone derivative material, Alq ₃ and DCM2 weight ratio of Alq _3: DCM2 =
An electroluminescent element was produced in the same manner as in Example 1 except that the electroluminescence element was changed to 10: 2.

The element thus produced has a chromaticity x = 0.
61, y = 0.38, luminous luminous efficiency 0.8 at 300 cd / m ²
0 lm / w and external quantum efficiency of 2.0%, which are inferior to those of Example 1. For this reason, the power consumption when driving the device increases. When this device was driven at a constant current (6.5 mA / cm ² ), the time required to reduce the initial brightness from 218 cd / m ² to half the brightness was 485 hours, which was about the same as in Example 1.

Example 2 An electroluminescence device was prepared in the same manner as in Example 1, but the hole injection layer incorporated different quinacridone derivative or quinazoline derivative. That is, 3,4,10,11-dibenzoquinacaridone represented by the chemical formula 10 (formula 10), 2,9-dimethylquinacridone represented by the formula 6 (formula 6) and quinazoline represented by the formula 12
The characteristics of the electroluminescent elements each having a hole injection layer made of (Chemical Formula 12) were measured.

[0074] Table 1, in each electroluminescent device listed and the chromaticity, 300 cd / m ² o'clock luminous emission efficiency, external quantum efficiency, the half-life from the initial luminance 200 cd / m ^2.

[0075]

[Table 1]

Comparative Example 3 An electroluminescence device was prepared in the same manner as in Example 1 except that the hole transport layer of TPD was not formed. The element created in this way is
Chromaticity coordinates x = 0.61, y = 0.38, luminous efficiency 0.3 lm / w at 300 cd / m ² and external quantum efficiency 0.4% were obtained.
It can be seen that it is inferior to that of Example 1. When this device was driven at a constant current (32 mA / cm ² ), the half-life from the initial luminance of 190 cd / m ² was 5 hours, which was very short. (Evaluation) As described above, the quinacridone derivative is heat resistant,
Since it is a pigment having excellent fastness and sufficiently withstands a shock generated at the time of injecting holes from ITO, the driving life of an element using this as a hole injecting layer is significantly improved.

Copper phthalocyanine has a wavelength of 600 to 700 n.
m absorbs light and absorbs orange to red light emission, which changes the chromaticity of the element used for the hole injection layer and reduces the external quantum efficiency. However, in the case of the quinacridone derivative, there is almost no absorption of light having a wavelength of 600 nm or more, and orange to red emission can be effectively taken out to the outside in a device using this as a hole injection layer.

The quinacridone derivative has a wavelength of 600
It has a high light transmittance of nm or more, has a hole transporting property, and is excellent in heat resistance.

[0079]

As described above, according to the present invention, since the hole injection layer made of the quinacridone derivative or the quinazoline derivative is provided between the hole transport layer and the anode, it has heat resistance,
An organic electroluminescence device capable of emitting high brightness light at a low applied voltage can be obtained. Further according to the invention,
The luminous efficiency of the organic electroluminescence device is improved, the emission spectrum distribution is sharpened, and the color purity of the emitted color is improved.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an organic electroluminescence device having a two-layer structure.

FIG. 2 is a structural diagram showing an organic electroluminescence device having a three-layer structure.

FIG. 3 is a structural diagram showing an organic electroluminescence device of the present invention.

FIG. 4 is a structural diagram showing an organic electroluminescence device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal electrode (cathode) 2 Transparent electrode (anode) 3 Light emitting layer 4 Organic hole transport layer 4a Hole injection layer 5 Electron transport layer 6 Glass substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Nomura 3-26-8 Shimo, Kita-ku, Tokyo Nippon Kayaku Co., Ltd.

Claims (2)

[Claims] 1. A positive electrode, a hole transport layer comprising an organic compound,
An organic electroluminescence device comprising a light emitting layer made of an organic compound and a cathode, which are sequentially stacked, wherein a quinacridone compound having a structure represented by the following chemical formula 1 or a structure represented by the following chemical formula 2 is provided between the anode and the hole transporting layer. Quinazoline compound of Embedded image (In the formula, ring A is And the ring B is R _{1 to} R ₄ independently of one another are a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group, or a benzene ring in which R ₁ and R ₂ or R ₃ and R ₄ are bonded to each other or Wherein R ₅ represents an alkyl group), and a hole injection layer made of R ₅ is provided. 2. The organic electroluminescence device according to claim 1, wherein an electron transport layer made of an organic compound is disposed between the cathode and the light emitting layer.