JP2003229279A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an organic electroluminescent element having improved driving durability by changing the element composition. <P>SOLUTION: For the organic electroluminescent element comprising a pair of electrodes composed of a positive electrode 2 and a negative electrode 7 and at least more than one layer of organic layers 4, 5, 6 laid between the above, a positive electrode interface thin film layer 3 made of a specific compound or a material having a specific nature is formed between the positive electrode 2 and the organic layer. By the above, the organic electroluminescent element having improved driving durability in comparison with a previous element, concretely, the electroluminescent element restrained from the lowering of brightness and the increase of driving voltage at the continuous driving, is obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device which is widely used as various display devices and has excellent continuous driving durability.

[0002]

2. Description of the Related Art An electroluminescent device is brighter and clearer than a liquid crystal device due to self-luminous display.
It has been studied by many researchers since ancient times. As an electroluminescent device that has reached a practical level, Z, which is an inorganic material, is currently used.
There is an element using nS. However, such an inorganic electroluminescent device requires a driving voltage of 50 V or higher for light emission, and thus has not been widely used.

On the other hand, an electroluminescent element using an organic material
The organic electroluminescent device, which is a child
It was far from, but in 1987 Eastman
・ CW Tan of Kodak Company
g) The characteristics of the laminated structure element developed by
Has made great strides. They have a stable vapor-deposited film structure
Layer consisting of a phosphor that can transport
Light emitting layer) and an organic substance capable of transporting holes.
Layer (hole-transporting layer) to stack holes and electrons in the phosphor.
It was succeeded in injecting into and making it emit light. By this
The luminous efficiency of the electroluminescent device is improved and the voltage is 10 V or less.
1000 cd / m²The above light emission can be obtained
It was After that, the electron-transporting light-emitting layer was formed into a light-emitting layer and an electron-transporting layer.
The functional separation of the layers that make up the device was promoted.
As a result, at present 10,000 cd / m ²The above emission characteristics
Has been obtained.

In order to further improve the luminous efficiency of the organic electroluminescent device, it has been studied to insert a hole injection layer between the anode and the hole transport layer. Examples of materials being studied for the hole injection layer include phthalocyanine described in JP-A-63-295695, quinacridone derivative described in JP-A-8-325564, and JP-A-2000-150.
Ansanthuron derivatives described in Japanese Patent No. 167 and the like can be mentioned.

[0005]

However, although such an organic electroluminescent device has a high light emitting property immediately after the device is manufactured, it does not have sufficient stability during driving. Phenomenon such as a decrease in brightness and an increase in drive voltage with continuous driving is seen, which is a problem for practical use.

An object of the present invention is to realize an organic electroluminescent device having improved driving durability by improving the device structure of the organic electroluminescent device.

[0007]

An organic electroluminescent device of the present invention has a pair of electrodes composed of an anode and a cathode and at least one layer composed of an organic material sandwiched therebetween, and an anode and an organic layer. Between the anode and the anode interfacial thin film layer made of a specific compound or a material having a specific property. According to the present invention, it is possible to obtain an organic electroluminescence device in which driving durability, specifically, reduction in luminance and increase in driving voltage during continuous driving are suppressed as compared with conventional ones.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The invention described in claims 1 to 3 is
A pair of electrodes consisting of an anode and a cathode, and a layer made of at least two or more organic substances including a hole transport layer therebetween,
An organic electroluminescence device characterized in that an anode interfacial thin film layer composed of a compound having a carbazole ring is provided between the anode and the organic layer, and the present invention suppresses a decrease in luminance during continuous driving. be able to.

The inventions according to claims 4 to 6 have a pair of electrodes composed of an anode and a cathode, and a layer composed of at least two layers of organic materials including a hole transport layer between them, and the anode and the organic material. An OLED compound, an oxazine compound, an organic electroluminescent device characterized by providing an anode interface thin film layer composed of any of a phenanthroline compound between layers, according to the present invention to increase the driving voltage during continuous driving. Can be suppressed.

The invention according to claim 7 is characterized in that, in the electroluminescent device according to any one of claims 1 to 6, a triphenylamine derivative is used in the hole transport layer. According to the present invention, a device with higher efficiency can be obtained.

According to an eighth aspect of the present invention, there is provided a pair of electrodes composed of an anode and a cathode and at least one layer made of an organic material sandwiched between the electrodes, and an anode interface is provided between the anode and the organic layer. Having a thin film layer, the ionization potential or work function of the material forming the anode interface thin film layer is greater than the ionization potential or work function of the material forming the organic layer in contact with the anode and the anode interface thin film layer. According to the present invention, it is possible to significantly suppress an increase in driving voltage during continuous driving.

The invention according to claim 9 has a pair of electrodes composed of an anode and a cathode, and a layer composed of at least one organic material sandwiched between the electrodes, and the anode interface is provided between the anode and the organic layer. Organic electroluminescence having a thin film layer, characterized in that the hole mobility of the material forming the anode interface thin film layer is smaller than the hole mobility of the organic layer in contact with the anode interface thin film layer. This is an element, and the present invention can suppress an increase in drive voltage during continuous driving.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a schematic structure of an organic electroluminescent device according to the present invention. An anode 2 is formed on a glass substrate 1, and an anode interface thin film layer 3, a hole transport layer 4, a light emitting layer 5, an electron transport layer 6 and a cathode 7 are formed on the anode 2.

For the anode 2, indium tin oxide (ITO) as a transparent electrode or a gold thin film as a semitransparent electrode can be used.

The hole-transporting layer 4 and the electron-transporting layer 6 constitute a charge-transporting layer, which facilitates the injection of charges from the electrodes and transports the injected charges to the light-emitting region. As the hole transport layer 4, a material having a strong hole transport property is used, and specifically, N, N′-diphenyl-
N, N'-bis (3-methylphenyl) 1,1'-biphenyl-4,4'-diamine (TPD), 4,4'-bis [N- (1-naphthyl) -N-phenyl-amino] A triphenylamine derivative such as biphenyl (α-NPD), a thiophene derivative, or a stilbene derivative can be used. On the other hand, a material having a strong electron transporting property can be used for the electron transporting layer 6, and specifically, a quinolinol metal typified by a phenanthroline derivative, an oxadiazole derivative, tris (8-hydroxyquinolinol) aluminum (Alq), or the like. The use of complexes and the like is being considered.

A large number of compounds have been studied for the light emitting layer 5, but basically any substance capable of injecting electrons / holes and having fluorescence / phosphorescence can be used. In addition, it has been studied to use a film in which a small amount of a dye is dispersed in a material having excellent film-forming properties as a light emitting layer to improve the efficiency of the device, prolong the life of the device, and adjust the emission color. This method is very effective for fluorescent dyes that are easily crystallized or cause concentration quenching by themselves.

The cathode 7 needs to be capable of injecting electrons into the organic film, and an alkali metal, an alkaline earth metal or a compound thereof is often used as one of the constituent materials. Specifically, lithium, magnesium and calcium,
Alternatively, these metals and compounds can be used in combination with other metals.

According to the present embodiment, by providing the anode interface thin film layer 3 between the anode 2 and the hole transport layer 4, it is possible to suppress the decrease in brightness or the increase in drive voltage during continuous driving, The driving durability can be greatly improved.

As a main material constituting the anode interface thin film layer 3, a compound having a carbazole ring represented by the following formulas (4), (5) and (6), particularly represented by (7) and (9) The compound can be used.

[0020]

[Chemical 4] (Ar represents a divalent group represented by the following (A) to (H).)

[0021]

[Chemical 5] (In the formula, R ₁ is a hydrogen atom, an alkyl group, an alkoxy group,
It represents a halogen atom, and n represents an integer of 1 to 5. )

[0022]

[Chemical 6] (In the formula, R ₂ is a hydrogen atom, an alkyl group, an alkoxy group,
Represents a halogen atom, A represents a nitrogen atom, a carbon atom, a substituted or unsubstituted aromatic hydrocarbon ring, and m represents 3 or 4
Indicates. )

Since the carbazole ring easily forms an association state with other carbazole rings, it is considered that it is easy to form a dense film when formed into a thin film. Since a strong electric field is generated in the organic film for transporting charges, when the element contains ionic impurities, these impurities may move and accumulate in the film. However, by inserting such a dense film at the interface of the anode, it is possible to suppress the diffusion of ionic impurities on the ITO surface, particularly indium ions, which is one of the factors that causes a decrease in brightness during continuous driving, into the film. it can. Further, the same effect can be obtained by using an imidazole compound, an oxazine compound or a phenanthroline compound.

As a main material for forming the anode interface thin film layer 3, a material having an ionization potential or work function larger than the ionization potential or work function of the material forming the organic layer in contact with the anode 2 and the anode interface thin film layer 3. Can be used. When such a material is used for the anode interface thin film layer 3, a strong electric field is formed near the anode interface. It is considered that this facilitates injection of holes from the anode 2 into the organic layer, and makes it less susceptible to changes in the anode interface state due to continuous driving. Anode interface thin film layer 3
The same effect can be obtained by using a material having a hole mobility lower than the hole mobility of the organic layer in contact with the anode interface thin film layer 3.

The anode interface thin film layer 3 may be a mixture of two or more suitable materials. For the film formation, a generally used method, specifically, a vacuum vapor deposition method (resistance heating, electron beam, sputtering, etc.) or a wet film formation method (cast method, spin coating method, etc.) can be used.

The anode interface thin film layer 3 according to the present invention has a thickness of 1 to 50.
A film having a film thickness of nm can be used, but a film thickness of 1 to 10 nm is preferable in order to obtain a higher effect.

Although the case where the organic layer is composed of the three layers of the hole transport layer 4, the light emitting layer 5 and the electron transport layer 6 has been described here, the case where one layer also has the function of two layers is described. Alternatively, when each layer is composed of a plurality of materials, it can be similarly implemented. It is also possible to insert a layer having a new function.

[0028]

EXAMPLES Next, specific examples of the present invention will be described. (Example 1) As a transparent anode on a glass substrate,
Coat a tin-tin oxide film (ITO work function 4.8 eV)
Used by caulking and patterning in the shape of electrodes
It was After cleaning this substrate thoroughly, put it together with the material to be evaporated.
Set in the vacuum device at^-FourExhausted to Pa. So
And then the compound shown in (Chemical Formula 7) as a thin film layer at the anode interface.
(1) (Ionization potential 6.0 eV) at 5 nm
The film was formed. Further thereon, N, N'- as a hole transport layer is formed.
Bis [4 '-(N, N-diphenylamino) -4-bif
[Enyryl] -N, N'-diphenylbenzidine (TPT
  Ionization potential 5.4eV) 50nm film formation
did. After that, as a light emitting layer and an electron transport layer
Alq was formed into a film of 50 nm. Then Al as the cathode
/ Li mixed film is formed with a thickness of 150 nm to create a device
did. These films are continuous without breaking the vacuum.
I went. The film thickness is monitored by a crystal oscillator.
did. Immediately after manufacturing the device, take out the electrode in dry nitrogen.
Then, the characteristics were measured. The device obtained is charged.
When pressure was applied, uniform yellow-green light emission was observed.
In this device, the current density was 50 mA / c in dry nitrogen.
m²When driven at a brightness of 1360 cd / m²,Voltage
It was 6.3V. Further current density 50mA / cm ²so
The luminance when driven with a constant current for 500 hours is 750 cd /
m²The voltage was 6.5V.

[0029]

[Chemical 7]

[0030]

[Chemical 8]

Example 2 An element was prepared in the same manner as in Example 1 except that the compound (2) shown in (Chemical Formula 9) was used for the anode interface thin film layer. This element is used at a current density of 50 mA / cm ²
When driven at a luminance of 1550 cd / m ² , a voltage of 6.
It was 8V. 50 at a current density of 50 mA / cm ²
The luminance when driven with a constant current for 0 hours was 780 cd / m ² , and the voltage was 7.1V.

[0032]

[Chemical 9]

Example 3 As an anode interface thin film layer (Chemical formula 1)
A device was produced in the same manner as in Example 1 except that the compound (3) shown in 0) was used. Current density of this device is 50mA /
When driven at cm ² , the luminance was 1390 cd / m ² and the voltage was 6.5V. Furthermore, the brightness when driven at a constant current for 500 hours at a current density of 50 mA / cm ² is 750 cd / m 2.
² , the voltage was 6.8V.

[0034]

[Chemical 10]

Example 4 An element was prepared in the same manner as in Example 1 except that Nile Red which was a laser dye was used as the anode interface thin film layer. This device has a current density of 50 mA / c
When driven at m ² , the brightness was 1310 cd / m ² and the voltage was 6.4V. Furthermore, the brightness when driven with a constant current for 500 hours at a current density of 50 mA / cm ² is 680 cd / m 2.
² , the voltage was 6.6V.

Example 5 As an anode interface thin film layer (Chemical formula 1)
Example 1 except that bathocuproin shown in 1) was used.
A device was prepared in the same manner as in. Current density of this device is 50mA
When driven at / cm ² , the luminance was 1400 cd / m ² and the voltage was 6.2V. Furthermore, the current density is 50 mA / cm ²
The brightness when driven with a constant current for 500 hours at 720 cd /
m ² and voltage were 6.6V.

[0037]

[Chemical 11]

(Example 6) As a substrate, an indium tin oxide film (ITO) was previously formed on a glass as a transparent anode and patterned into an electrode shape. After thoroughly washing this substrate, it was set in a vacuum apparatus together with the material to be vapor-deposited and evacuated to 10 ⁻⁴ Pa. Then, the compound (1) was formed into a film of 5 nm as an anode interface thin film layer. Further, TPT having a thickness of 50 nm was formed thereon as a hole transport layer. Then, a mixed layer in which 1 mol% of DCM as a laser dye was added to Alq as a light emitting layer with a thickness of 25 nm and Alq as an electron transport layer with a thickness of 25 nm was formed. Alq and DCM
The mixed layer of was prepared by a co-evaporation method in which two kinds of materials are evaporated from independent evaporation sources. These film formations were continuously performed without breaking the vacuum even once. The film thickness was monitored by a crystal oscillator. Immediately after the device was manufactured, the electrode was taken out in dry nitrogen, and then the characteristics were measured. When a voltage was applied to the obtained device, uniform orange light emission was obtained. Current density of this element is 50m
When driven at A / cm ² , the brightness was 2070 cd / m ² ,
The voltage was 6.4V. Further current density 50mA / cm
Brightness of ² 500 hours constant current when driven 1130c
The d / m ² and the voltage were 6.5V.

Example 7 An indium tin oxide film (ITO) was formed in advance as a transparent anode on glass, and a substrate patterned in the shape of an electrode was thoroughly washed, and then it was placed in a vacuum apparatus together with a material to be deposited. Set to 10 ^-4 Pa
Exhausted to. Then, as an anode interface thin film layer (Chemical formula 1
Compound (4) shown in 2) (hole mobility 5 × 10 ⁻⁶ cm
² / V · sec) was formed into a film of 5 nm. Further, a compound (5) (hole mobility: 3 × 10 ⁻⁵ cm ² / V · sec) shown in (Chemical Formula 13) as a hole transport layer was formed thereon to a thickness of 50 nm. Then, Alq was formed as an electron transporting light emitting layer. After that, an Al / Li mixed film as a cathode is formed to a thickness of 150 nm.
A film was formed with a thickness of 1 to prepare a device. These film formations were continuously performed without breaking the vacuum even once. The film thickness was monitored by a crystal oscillator. Immediately after the device was manufactured, the electrode was taken out in dry nitrogen, and then the characteristics were measured. When a voltage was applied to the obtained device, uniform yellow-green light emission was obtained. Current density of this element is 50m
When driven at A / cm ² , the brightness was 1300 cd / m ² ,
The voltage was 6.1V. Further current density 50mA / cm
The brightness when driven with constant current for ² hours at 730 cd
/ M ² and the voltage was 6.3V.

[0040]

[Chemical 12]

[0041]

[Chemical 13]

Comparative Example 1 As Comparative Example 1, an element was prepared in the same manner as in Example 1 except that the anode interface thin film layer was not provided. When a voltage was applied to this device, uniform yellow-green light emission was obtained. Current density of this device is 50mA /
When driven at cm ² , the luminance was 1170 cd / m ² and the voltage was 6.5V. Furthermore, the brightness when driven with a constant current for 500 hours at a current density of 50 mA / cm ² is 500 cd / m 2.
² , the voltage was 7.2V.

(Comparative Example 2) As Comparative Example 2, an element was prepared in the same manner as in Example 5 except that the anode interface thin film layer was not provided. When a voltage was applied to this device, uniform orange light emission was obtained. This device has a current density of 50 mA / c
When it was driven at m ² , the brightness was 1880 cd / m ² and the voltage was 6.6 V. Further, the luminance when driven at a constant current for 500 hours at a current density of 50 mA / cm ² is 1040 cd /
m ² and voltage were 7.1V.

From the results shown in Examples 1 to 5 and Comparative Examples 1 and 2, it was found that the element obtained in this example was suppressed in the decrease in luminance and the increase in voltage during continuous driving.

[0045]

As described above, according to the present invention, it is possible to improve the durability during continuous driving.

[Brief description of drawings]

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

[Explanation of symbols]

1 substrate 2 anode 3 Anode interface thin film layer 4 Hole transport layer 5 Light emitting layer 6 Electron transport layer 7 cathode

Claims (9)

[Claims] 1. An organic electroluminescence device having a pair of electrodes composed of an anode and a cathode and a layer composed of at least two layers including an organic material containing a hole transport layer therebetween, wherein the anode and the hole transport layer are An organic electroluminescence device having an anode interfacial thin film layer in between, wherein the anode interfacial thin film layer is a compound having a carbazole ring. 2. The organic electroluminescence device according to claim 1, wherein the anode interface thin film layer is a compound represented by the formula (1). [Chemical 1] (Ar represents a divalent group represented by the following (A) to (H).) (In the formula, R ₁ is a hydrogen atom, an alkyl group, an alkoxy group,
It represents a halogen atom, and n represents an integer of 1 to 5. ) 3. The organic electroluminescent device according to claim 1, wherein the anode interface thin film layer is represented by the following general formula. [Chemical 3] (In the formula, R ₂ is a hydrogen atom, an alkyl group, an alkoxy group,
Represents a halogen atom, A represents a nitrogen atom, a carbon atom, a substituted or unsubstituted aromatic hydrocarbon ring, and m represents 3 or 4
Indicates. ) 4. An organic electroluminescence device having a pair of electrodes composed of an anode and a cathode and at least two or more layers containing an organic material including a hole transport layer between the electrodes, wherein the anode and the hole transport layer are An organic electroluminescent device having an anode interface thin film layer between the anode interface thin film layer and the anode interface thin film layer being an imidazole compound. 5. An organic electroluminescence device having a pair of electrodes composed of an anode and a cathode, and a layer composed of at least two organic layers including a hole transport layer between them, wherein the anode and the hole transport layer are An organic electroluminescent device comprising an anode interfacial thin film layer between the anode interfacial thin film layer and an oxazine compound. 6. An organic electroluminescence device having a pair of electrodes composed of an anode and a cathode and a layer composed of at least two organic layers including a hole transport layer therebetween, wherein the anode and the hole transport layer are An organic electroluminescent device having an anode interface thin film layer between the anode and the anode interface thin film layer being a phenanthroline compound. 7. The organic electroluminescent device according to claim 1, wherein the hole transport layer in contact with the anode interface thin film layer is a triphenylamine derivative. 8. An organic electroluminescent device having a pair of electrodes composed of an anode and a cathode and at least one layer made of an organic material sandwiched between the electrodes, wherein an anode interface thin film layer is provided between the anode and the organic layer. And the ionization potential or work function of the material forming the anode interface thin film layer is larger than the ionization potential or work function of the material forming the organic layer in contact with the anode and the anode interface thin film layer. Characterized organic electroluminescent device. 9. An organic electroluminescent device having a pair of electrodes composed of an anode and a cathode and at least one layer made of an organic material sandwiched therebetween, wherein an anode interface thin film layer is provided between the anode and the organic layer. And a hole mobility of a material forming the anode interface thin film layer is smaller than a hole mobility of an organic layer in contact with the anode interface thin film layer.