JP2786038B2 - EL device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device, and more particularly to an organic electroluminescent device (organic EL device) using a novel organic material for a hole transport layer.

[0002]

2. Description of the Related Art In recent years, with the diversification of information devices, CR
There is an increasing need for a flat display element that consumes less power and has a smaller space occupation volume than T. As such a flat display element, there are a liquid crystal, a plasma display, and the like. Particularly, recently, a self-luminous electroluminescent element (electroluminescence (EL) element) which has a clear display attracts attention.

[0003] The above-mentioned EL elements can be roughly classified into inorganic EL elements and organic EL elements depending on the constituent materials, and inorganic EL elements have already been put to practical use. However, since the driving method of the inorganic EL element is so-called “collision excitation light emission” in which accelerated electrons collide with the application of a high electric field to cause the emission center to emit light, it is necessary to drive the inorganic EL element at a high voltage. There is. For this reason, there has been a problem that the cost of peripheral devices is increased. On the other hand, the organic EL element is of a so-called “injection light emission type” in which charges (holes and electrons) injected from an electrode are recombined in a light emitting body to emit light. Can be. In addition, there is an advantage that any emission color can be easily obtained by changing the molecular structure of the organic compound. Therefore, the organic EL element is very promising as a future display element.

Here, the organic EL device generally has a two-layer structure (a structure in which a hole transport layer and a light emitting layer are formed between a hole injection electrode and an electron injection electrode (SH-A structure), or a hole injection structure). A structure in which a light emitting layer and an electron transport layer are formed between an electrode and an electron injection electrode (SH-B structure)] or a three-layer structure [a hole transport layer is provided between a hole injection electrode and an electron injection electrode. (DH structure) in which a light emitting layer and an electron transport layer are formed]. An electrode material having a large work function such as gold or ITO (indium-tin oxide) is used as the hole injection electrode, and an electrode material having a small work function such as Mg is used as the electron injection electrode. An organic material is used for the hole transport layer, the light emitting layer, and the electron transport layer. A material having the property of a p-type semiconductor is used for the hole transport layer, and a material having the property of an n-type semiconductor is used for the electron transport layer. For the light emitting layer, a material having the property of an n-type semiconductor in the SH-A structure, the property of a p-type semiconductor in the SH-B structure, and the property close to neutral in the DH structure is used. In any case, the holes injected from the hole injection electrode and the electrons injected from the electron injection electrode recombine at the interface between the light emitting layer and the hole (or electron) transport layer and within the light emitting layer to emit light. is there.

[0005] In the above-mentioned organic EL devices, many luminescent materials exhibit an electron transporting property. For example, a typical luminescent material, 8-quinolinol aluminum complex (CW Tang)
and SA VanSlyke, Appl. Phys. Lett., Vol. 51, N
o. 12, P913 (1987)), perinone derivative (C. Adachi,
S. Tokito, T. Tsutsui, and S. Saito, Jpn. J. Appl.
Phys., Vol. 27, No. 4, L713 (1988)). In this case, the optimum structure of the device is the SH-A structure or the DH structure, and in any case, a stable hole transport material is required.

At present, several kinds of materials are known as the hole transport material. As typical examples, compounds having one oxadiazole ring in the molecular skeleton,
Or a diamine derivative. These compounds are very excellent in hole transport properties,
Proven as an organic EL material.

[0007]

However, compounds conventionally used as hole transport layer materials have the property of being easily crystallized, and after film formation, crystals are precipitated and the element itself is destroyed. There is a problem. In view of the above problems, an object of the present invention is to provide an electroluminescent element having a long light-emitting life, having a hole transporting material that does not easily crystallize.

[0008]

According to the present invention, in order to achieve the above object, an invention according to claim 1 is characterized in that an organic hole transport layer, an organic light emitting layer and an organic light emitting layer are provided between a hole injection electrode and an electron injection electrode. An organic three-layer device structure in which the electron transport layer is formed in order from the hole injection electrode side, or between the hole injection electrode and the electron injection electrode, the organic hole transport layer and the organic emission layer are sequentially formed from the hole injection electrode side. In the formed electroluminescent device having an organic two-layer device structure, the organic hole transport layer includes:
The number of oxadiazole rings is 2, and an oxadiazole-based compound having an alkyl chain having n (n = 1 to 10) carbon atoms between oxadiazole rings is used.

The invention of claim 2 is characterized in that the oxadiazole compound is selected from the following chemical formulas 1 and 2. The invention according to claim 3 is an organic three-layer element structure in which an organic hole transport layer, an organic light emitting layer, and an organic electron transport layer are sequentially formed from the hole injection electrode side between the hole injection electrode and the electron injection electrode. Is an organic electroluminescent device having an organic two-layer device structure in which an organic hole transport layer and an organic light emitting layer are sequentially formed from a hole injection electrode side between a hole injection electrode and an electron injection electrode. Is characterized in that an oxadiazole-based compound having three oxadiazole rings and three oxadiazole rings substituted on the benzene ring is used.

The invention of claim 4 is characterized in that the 1,3,5-position of the benzene ring in the oxadiazole compound is substituted by an oxadiazole ring. The invention of claim 5 is characterized in that the oxadiazole-based compound is selected from the following chemical formula (3) or (4).

According to a sixth aspect of the present invention, there is provided an organic three-layer device in which an organic hole transport layer, an organic light emitting layer, and an organic electron transport layer are sequentially formed between a hole injection electrode and an electron injection electrode. An electroluminescent device having a structure or an organic two-layer device structure in which an organic hole transport layer and an organic light emitting layer are sequentially formed from a hole injection electrode side between a hole injection electrode and an electron injection electrode. For the transport layer,
An oxadiazole-based compound having two oxadiazole rings, wherein the oxadiazole ring is substituted at the ortho position (1,2 position) of the benzene ring. The invention of claim 7 is characterized in that the oxadiazole-based compound is selected from the following chemical formulas (5) and (6).

The invention according to claim 8 is an organic three-layer element in which an organic hole transporting layer, an organic light emitting layer and an organic electron transporting layer are formed in order from the hole injection electrode side between the hole injection electrode and the electron injection electrode. An electroluminescent device having a structure or an organic two-layer device structure in which an organic hole transport layer and an organic light emitting layer are sequentially formed from a hole injection electrode side between a hole injection electrode and an electron injection electrode. For the transport layer,
2,2 ′ of a biphenyl group having two oxadiazole rings, and the oxadiazole ring is composed of two benzene rings.
Characterized in that an oxadiazole-based compound substituted at the position is used. A ninth aspect of the present invention is characterized in that the oxadiazole-based compound is selected from the following chemical formulas (7) and (8).

[0013]

[0014]

The oxadiazole-based compound having a plurality of oxadiazole rings has better film-forming properties than experiments.
It was confirmed that crystallization was difficult. Therefore, in an electroluminescent device using the oxadiazole-based compound for the hole transport layer, no crystal is precipitated even when stored or operated for a long time. As a result, the life of the electroluminescent element can be extended.

The fluorescence of the oxadiazole-based compound is in the range of 460 to 530 nm, and even when all the blue to red light-emitting materials are used for the light-emitting layer, the excitation energy from the light-emitting layer is reduced. Excitons can be confined in the light emitting layer without moving to the hole transport layer. Here, the oxadiazole compound is
In general, the compound is synthesized by a method as shown in the following chemical formula 17 or chemical formula 18. The reaction time differs depending on each compound.

[0016]

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[0017]

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Here, Ar is selected from the group consisting of the following formulas (19) to (24).

[0019]

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[0020]

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[0021]

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[0022]

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[0023]

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[0024]

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[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. (Embodiment 1) FIG. 1 is a sectional view of an electroluminescent device according to an embodiment of the present invention.
Hole injection electrode (anode) composed of tin oxide (ITO)
2, an organic hole transport layer 3 (thickness: 500 °) made of an oxadiazole compound (shown in the following Chemical Formula 25), and 8-
An organic light emitting layer 4 (thickness: 500 °) composed of a quinolinol aluminum complex (shown in the following Chemical Formula 26) and Mg and Ag are 1
Electron injection electrodes (cathodes) 6 (thickness: 2000 °) mixed at a ratio of 0: 1 are sequentially formed.

[0026]

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[0027]

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Here, the electroluminescent device having the above structure was manufactured as follows. First, the substrate having indium-tin oxide (ITO) formed on the glass substrate 1 was washed with a neutral detergent, and then ultrasonically washed in acetone for 20 minutes and in ethanol for about 20 minutes. Next, the substrate was placed in boiling ethanol for about 1 minute, taken out, and immediately blow-dried. Thereafter, an oxadiazole compound is vacuum-deposited on the hole injecting electrode 2 made of ITO to form a hole transport layer 3, and then an 8-quinolinol aluminum complex is vacuum-deposited on the organic hole transport layer 3. Thus, the organic light emitting layer 4 was formed. Furthermore, Mg and Ag were co-deposited on the organic light emitting layer 4 at a ratio of 10: 1,
An electron injection electrode 5 was formed. All of these depositions were performed under the conditions of a degree of vacuum of 1 × 10 ⁻⁶ Torr, a substrate temperature of 20 ° C., and a deposition rate of an organic layer of 2 ° / sec.

The oxadiazole compound was prepared through the steps of synthesis of a precursor of the oxadiazole compound and synthesis of the oxadiazole compound as described below. 1. Synthesis of Precursor of Oxadiazole Compound First, 4-Dimethine was placed in a three-necked flask (capacity: 500 ml).
ylaminobenzhydrazide 10.31 g (57.53 mmo
l), and further add 100 ml of dehydrated pyridine. Next, a cooling pipe is attached to the above-mentioned mouth, N ₂ gas is introduced into the flask, the atmosphere in the flask is changed to an N ₂ atmosphere, and the mixture is stirred at room temperature to dissolve 4-dimethylaminobenzhydrazide in pyridine. In addition, from the side tube of the three-necked flask,
6.26 g (30.83 mmol) of haloyl Chloride is added to the reaction system, and then the pyridine is refluxed for 8 hours. After the reaction is completed, pyridine is removed from the reaction system by distillation. The reaction is washed well with water and dried in a vacuum desiccator under vacuum. This produces an oxadiazole precursor. The above reaction is shown in the following formula.

[0030]

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2. Synthesis of Oxadiazole Compound In a three-necked flask (capacity: 500 ml), 13.23 g of the oxadiazole precursor described above is added, and 100 ml of phosphorus oxochloride (POCl 3) is further added. Next, a cooling pipe is attached to the above-mentioned mouth, and the phosphorus oxochloride is refluxed for 6 hours. After the completion of the reaction, phosphorus oxochloride is removed from the reaction system by distillation. While reacting the remaining phosphorus oxochloride remaining in the reaction system with water, the reactants are thoroughly washed with water. The reaction is vacuum dried in a vacuum desiccator. Thereby, an oxadiazole compound is synthesized. The oxadiazole is purified by sublimation purification. The purification yield in this case was 23%. The above reaction is shown in the following formula.

[0032]

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The results of the elemental analysis of the above oxadiazole are shown below. The values in parentheses are theoretical values. H: 5.37% (5.35%) C: 69.00% (69.01%) N: 16.66% (18.57%) The melting point was 329 ° C.

The organic electroluminescent device manufactured as described above is hereinafter referred to as (A ₁ ) device. (Example 2) Except that an oxadiazole compound represented by the following chemical formula 29 is used as a material of the hole transport layer, the above-mentioned Example 1 is used.
In the same manner as in the above, an organic electroluminescent device was produced.

[0035]

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Hereinafter, this element is referred to as an (A ₂ ) element. (Example 3) An organic electric field was formed in the same manner as in Example 1 except that an oxadiazole compound represented by the following formula (30) was used as a material of the hole transport layer, and a perinone derivative represented by the following formula (31) was used as a material of the light emitting layer. A light-emitting element was manufactured.

[0037]

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[0038]

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Hereinafter, this element is referred to as an (A ₃ ) element. (Example 4) An organic electric field was used in the same manner as in Example 1 except that an oxadiazole compound represented by the following formula (32) was used as a material of the hole transport layer and a perylene derivative represented by the following formula (33) was used as a material of the light emitting layer. A light-emitting element was manufactured.

[0040]

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[0041]

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Hereinafter, this element is referred to as an (A ₄ ) element. (Comparative Example 1) An organic electroluminescent device was produced in the same manner as in Example 1 except that a compound containing one oxadiazole ring shown in the following Chemical Formula 34 was used as a material for the hole transport layer.

[0043]

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Hereinafter, this element is referred to as an (X ₁ ) element. Comparative Example 2 An organic electroluminescent device was produced in the same manner as in Example 3 except that a diamine derivative represented by Chemical Formula 35 below was used as a material for the hole transport layer.

[0045]

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Hereinafter, this element is referred to as an (X ₂ ) element. (Experiment) For the (A ₁ ) to (A ₄ ) elements of this example and the comparative examples (X ₁ ) and (X ₂ ) elements, the DC was obtained by biasing the hole injection electrode to plus and the electron injection electrode to minus. A current was applied, and the luminance, the peak wavelength of EL light emission, and the life when continuous light emission was performed were measured.

Table 1 shows the driving voltage, current density, and measurement results at the time of measurement. FIG. 2 shows an emission spectrum diagram of the (A ₁ ) element.

[0048]

[Table 1]

As is clear from Table 1, the (A ₁ ) to (A ₄ ) elements of this embodiment are comparative examples (X ₁ ) and (X ₂ ).
It was found that the life was longer and more stable than the element. When the surface of the comparative example (X ₁ ) element was observed with a microscope,
Precipitation of fine crystals was observed. From these facts, it was found that the hole transport material of this example had better film-forming properties and higher stability during element driving. (Other Examples) In the above Examples, although no measurement was performed, an oxadiazole-based compound having an alkyl chain having n carbon atoms between oxadiazole rings, as shown in Chemical formula 1, was used. An oxadiazole-based compound in which the ortho position (1,2-position) of a benzene ring is substituted by an oxadiazole ring as shown in the above formula 5, and a biphenyl group as shown in the above formula 6 The same effect can be expected by using an oxadiazole-based compound in which the 2,2′-position is substituted with an oxadiazole ring for the hole transport layer.

The number of carbon atoms between the oxadiazole rings is n.
As the oxadiazole-based compound having two alkyl chains, those having n = 0 to 10 carbon atoms can be used, and among them, those having 1 to 6 carbon atoms in the alkyl chain are more desirable.

[0051]

As described above, according to the present invention,
An oxadiazole-based compound having a plurality of oxadiazole rings was excellent in film-forming properties, and was able to extend the life of an electroluminescent device using the compound as an organic hole transport layer.

[Brief description of the drawings]

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

FIG. 2 is a spectrum diagram of the device of Example 1 of the present invention.

[Explanation of symbols]

 Reference Signs List 1 glass substrate 2 hole injection electrode 3 organic hole transport layer 4 organic light emitting layer 5 electron injection electrode

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Hamada 2-18-18 Keihanhondori Moriguchi City Sanyo Electric Co., Ltd. (56) References The Chemical Society of Japan, The Chemical Society of Japan November 10, 1991, 1991, No. 11. P1540-1547 (58) Fields surveyed (Int. Cl. ⁶ , DB name) C09K 11/06

Claims (9)

(57) [Claims] An organic three-layer device structure in which an organic hole transport layer, an organic light emitting layer, and an organic electron transport layer are sequentially formed from a hole injection electrode side between a hole injection electrode and an electron injection electrode, or a hole injection. between the electrode and the electron injection electrode, the electroluminescent device in which an organic hole transporting layer and the organic light-emitting layer has an organic two-layer device structure formed in this order from the hole injecting electrode side, into the organic hole transport layer, Okisajiazo
And the number of carbon atoms between the oxadiazole rings is 2.
Has n (n = 1 to 10) alkyl chains
An electroluminescent device using an azole compound . 2. The oxadiazole compound has the following formula:
The electroluminescent device according to claim 1, wherein the device is selected from the group consisting of (1) and (2). Embedded image Embedded image The above R, R ₁ , R ₂ , R ₃ are NH ₂ , N (CH
₂ ) selected from the group consisting of ₂ and N (C ₂ H ₅ ) ₂ .
R ′ is H, C _n H _{2n + 1} (n = 1 to 10), OC
H ₃ , OC ₂ H ₅ , phenyl, cyclohexyl and oxo
It is selected from the group consisting of a sadiazole ring. 3. Between a hole injection electrode and an electron injection electrode.
The organic hole transport layer, the organic light emitting layer, and the organic electron transport layer
Are formed in order from the hole injection electrode side.
Between the hole injection electrode and the electron injection electrode
The hole transport layer and the organic light emitting layer are arranged in order from the hole injection electrode side.
Electroluminescent device with organic two-layer device structure formed in
In the organic hole transport layer, oxadiazole
The number of rings is 3, and oxadiazo is
Oxadiazole-based compounds with a substituted aryl ring
An electroluminescent device, comprising: 4. The method according to claim 1, wherein the oxadiazole compound is a benzene
1,3- and 5-positions of the ring are substituted by oxadiazole rings
4. The electroluminescent element according to claim 3, wherein
Child. 5. The oxadiazole compound according to claim 1 ,
Characterized by being selected from Chemical Formula 3 or Chemical Formula 4.
The electroluminescent device according to claim 4, wherein Embedded image Embedded image The above R, R ₁ , R ₂ , R ₃ are NH ₂ , N (CH
₂ ) selected from the group consisting of ₂ and N (C ₂ H ₅ ) ₂ .
R ′ is H, C _n H _{2n + 1} (n = 1 to 10), OC
H ₃ , OC ₂ H ₅ , phenyl, cyclohexyl and oxo
It is selected from the group consisting of a sadiazole ring. 6. Between a hole injection electrode and an electron injection electrode.
The organic hole transport layer, the organic light emitting layer, and the organic electron transport layer
Are formed in order from the hole injection electrode side.
Between the hole injection electrode and the electron injection electrode
The hole transport layer and the organic light emitting layer are arranged in order from the hole injection electrode side.
Electroluminescent device with organic two-layer device structure formed in
In the organic hole transport layer, two oxadia
Having a sol ring, wherein the oxadiazole ring is a benzene ring
Oxadiazole substituted at the ortho position (1,2 position)
An electroluminescent device, comprising a base compound. 7. The oxadiazole compound according to claim 1 ,
Characterized in that it is selected from Chemical Formula 5 or Chemical Formula 6.
The electroluminescent device according to claim 6, wherein Embedded image Embedded image The above R, R ₁ , R ₂ , R ₃ are NH ₂ , N (CH
₂ ) selected from the group consisting of ₂ and N (C ₂ H ₅ ) ₂ .
R ′ is H, C _n H _{2n + 1} (n = 1 to 10), OC
H ₃ , OC ₂ H ₅ , phenyl, cyclohexyl and oxo
It is selected from the group consisting of a sadiazole ring. 8. Between a hole injection electrode and an electron injection electrode.
The organic hole transport layer, the organic light emitting layer, and the organic electron transport layer
Are formed in order from the hole injection electrode side.
Between the hole injection electrode and the electron injection electrode
The hole transport layer and the organic light emitting layer are arranged in order from the hole injection electrode side.
Electroluminescent device with organic two-layer device structure formed in
In the organic hole transport layer, two oxadia
Having a sol ring, wherein the oxadiazole ring has two
Substitution at 2,2'-position of biphenyl group consisting of zen ring
Oxadiazole-based compounds
An electroluminescent device to be characterized. 9. The oxadiazole compound according to claim 1
Characterized by being selected from Chemical Formula 7 or Chemical Formula 8
The electroluminescent device according to claim 8, wherein Embedded image Embedded image The above R, R ₁ , R ₂ , R ₃ are NH ₂ , N (CH
₂ ) selected from the group consisting of ₂ and N (C ₂ H ₅ ) ₂ .
R ′ is H, C _n H _{2n + 1} (n = 1 to 10), OC
H ₃ , OC ₂ H ₅ , phenyl, cyclohexyl and oxo
It is selected from the group consisting of a sadiazole ring.