JPH08188773A - Organic electroluminescence element - Google Patents

Abstract

PURPOSE: To provide an organic electroluminescence element which has a layer containing a specific hole-transporting polymer, thus can be readily produced, manifests sufficient luminance and excellent durability and easily enables the enlargement of the display area. CONSTITUTION: This electroluminescent element is given by arranging a layer of an organic substance between a couple of electrodes of which at least one is transparent or translucent where the organic layer comprises a hole- transporting polymer of the formula (R<1> , R<2> are each H, an alkyl; X is a (substituted) divalent aromatic group; Y is a residue of a divalent alcohol; Z is a residue of a divalent carboxylic acid; l, m are each 1-5; n, k are each 0, 1; p is 5-500). In an embodiment, a transparent insulator base such as glass 1, transparent electrodes made of tin indium oxide 2, a hole-transporting layer 31 containing the polymer of the formula, a luminescent layer which can transport electrons and the back electrode 5 are laminated in turns to give this element.

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, and more specifically, by using a specific hole-transporting polymer, the device can be easily manufactured, the stability of the device can be further improved, and the area can be easily increased. Flat light emitting device.

[0002]

2. Description of the Related Art An electroluminescent device (hereinafter referred to as "EL device") is a self-luminous all-solid-state device, has high visibility and is resistant to impact, and is therefore expected to be widely applied. At present, inorganic fluorescent materials are mainly used and widely used, but since they require an AC voltage of 200 V or more for driving, they have problems such as high manufacturing cost and insufficient brightness. ing. On the other hand, research on an EL device using an organic compound was first started using a single crystal such as anthracene, but there was a problem that the film thickness was as thick as about 1 mm and a driving voltage of 100 V or more was required. Therefore, thin film formation by the vapor deposition method has been attempted (Thin Solid F
ilms, 94, 171 (1982). However,
The drive voltage is still as high as 30 V, the carrier density of electrons and holes in the film is low, and the excitation probability due to recombination of carriers is low, so that there is a problem that sufficient brightness cannot be obtained.

In recent years, in a function-separated device in which a hole-transporting organic compound and an organic fluorescent substance having an electron-transporting ability are sequentially laminated by a vacuum vapor deposition method to form a thin film, a voltage of 1000 cd / It has been reported that a high brightness of m ² or more can be obtained (Appl. Phys. Lett., 51,
913 (1987), active research is being conducted. However, this device uses a vacuum deposition method and
Since the following thin film is formed, pin holes are easily generated, and in order to obtain sufficient performance, it is necessary to perform film formation under strictly controlled conditions, productivity is low, and it is difficult to increase the area. There is a problem. In addition, this element has several mA / cm
^Since it is driven in a high current density state of ² , a large amount of heat is generated and the tetraphenyldiamine derivative, which is preferably used as a hole transport material, is gradually crystallized, leading to a decrease in brightness. There was a problem with.

In order to solve the problem of stability, starburst amine which can obtain a stable amorphous state is used as a hole transport material (Proceedings of the 65th Annual Meeting of the Chemical Society of Japan 3-C2-34 (1993)). ), Using a polymer in which triphenylamine has been introduced into the side chain of polyphosphazene (Proceedings of the 42nd Symposium on Polymers 20J21 (1)
993)) has been reported, but it does not satisfy the hole injecting property from the anode or the hole injecting property to the light emitting layer due to the ionization potential of the hole transporting material. Further, when a polymer is used, a high current density cannot be obtained and sufficient brightness cannot be obtained.

On the other hand, light emission by a polymer single layer structure, which is expected to improve productivity, has been studied, and conductive polymers such as polyphenylene vinylene have been used (Nature, Vol.
357, 477 (1992)), a mixture of an electron-transporting material and a fluorescent dye in a hole-transporting polyvinylcarbazole (The 38th Applied Physics Association Joint Lecture Proceedings 31p-
G-12 (1991)) has been proposed, but the brightness, the luminous efficiency, etc. are still inferior to those of the laminated EL device. Incidentally, the hole-transporting polymer represented by the following general formula (I) has been developed as a material for electrophotography (JP-A-5-232727), but it has not yet been reported to be applied to EL devices. Absent.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and its purpose is to facilitate manufacture, obtain sufficient brightness, and provide an EL having excellent durability.
It is to provide an element.

[0007]

Means for Solving the Problems As a result of intensive investigations by the present inventors regarding a hole transport material in order to achieve the above object,
It was found that the hole transporting polymer represented by the following general formula (I) has suitable ionization potential, hole mobility and thin film forming ability for organic EL devices, and has completed the present invention. That is, the EL device of the present invention comprises an organic compound layer sandwiched between a pair of electrodes, at least one of which is transparent or semitransparent, and the organic compound layer has the following general formula (I): It is characterized by having a layer containing a hole transporting polymer represented by.

Embedded image (In the formula, R ¹ and R ² are each independently a hydrogen atom,
An alkyl group, an alkoxy group, a substituted amino group, a halogen atom, or a substituted or unsubstituted aryl group, X
Represents a substituted or unsubstituted divalent aromatic group, Y represents a divalent alcohol residue, Z represents a divalent carboxylic acid residue,
l and m each independently represent an integer of 1 to 5,
n and k each independently represent an integer of 0 or 1, and p represents an integer of 5 to 5000. )

The present invention will be described in detail below. The hole-transporting polymer represented by formula (I) is disclosed in
It can be easily synthesized by using the synthesis method described in Japanese Patent No. 232727. Specific examples of X, Y and Z in the above general formula (I) include those selected from the following structures.

Examples of X include those selected from the following groups.

Embedded image [In the formula, Ar represents a group represented by the following formula,

[Chemical 4] (R ⁵ represents an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms or a halogen atom.) R ³ and R ⁴ are each a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, and a substituent. Alternatively, it represents an unsubstituted phenyl group or a substituted or unsubstituted aralkyl group, Y represents a dihydric alcohol residue, and s represents an integer of 0 to 3. ]

Examples of Y and Z include those selected from the following groups.

Embedded image [R ⁶ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, q and r each represent an integer of 1 to 10, t represents an integer of 1 or 2, and W represents a group below. Represents one selected from.

[Chemical 6] (S 'means an integer of 1 to 3)]

1 and 2 show the structure of the organic EL device according to the present invention. 1 is an insulating substrate, 2 is a transparent electrode, 31 and 32 are layers composed of a hole transporting polymer represented by the general formula (I), 31 acts as a hole transporting layer, and 32 is a light emitting layer. The numeral 4 denotes a light emitting layer having an electron transporting function, and 5 denotes a back electrode. The insulator substrate 1 is preferably transparent for taking out light emission, and glass, plastic film, or the like is used. The transparent electrode 2 is preferably transparent so as to take out light emission similarly to the insulating substrate and has a large work function for injecting holes, and is preferably indium tin oxide (ITO), tin oxide (NESA), indium oxide. , Oxide film such as zinc oxide,
Alternatively, vapor-deposited or sputtered gold, platinum, palladium or the like is used.

In the case of the device structure shown in FIG. 1, the layer 31 acting as a hole transporting layer is formed of the hole transporting polymer represented by the general formula (I) alone, or adjusts the hole mobility. For this purpose, the tetraphenyldiamine derivative may be dispersed in an amount of 1 to 50% by weight.
In addition, the light-emitting layer 4 having an electron transporting property emits fluorescence in a solid state, and a good thin film can be formed by a vacuum vapor deposition method, and a strong electron interaction with the adjacent hole transporting polymer represented by the general formula (I) is obtained. It is formed using an organic compound that does not act. The following compounds (1) to (13) are preferably used, but not limited thereto. In addition,
The compound exhibiting electron interaction can be distinguished from the fact that the fluorescence wavelength shifts to the long wavelength side when dispersed in the hole transporting polymer represented by the general formula (I).

[0013]

[Chemical 7]

[0014]

Embedded image

When the light emitting material is one that can be vacuum-deposited but does not form a good thin film or does not show a clear electron transporting property, it is used as a light emitting layer for the purpose of improving the durability of the device and the light emitting efficiency. An electron transport layer may be inserted between the back electrodes 5. As the electron transport material used in such an electron transport layer, a compound capable of forming a good thin film by a vacuum vapor deposition method is used, and preferably an oxadiazole derivative, a nitro-substituted fluorenone derivative, a diphenoquinone derivative, A thiopyran dioxide derivative, a fluorenylidene methane derivative and the like are used, and the following compounds (14) to (16) are preferably used, but not limited thereto.

[0016]

[Chemical 9]

In the case of the device structure shown in FIG. 2, the layer 32 acting as a light emitting layer contains 50% by weight or less, preferably 0.01% or less of the light emitting material in at least the hole transporting polymer represented by the general formula (I). It is a layer dispersed in the range of -40% by weight. The compound (1) to the compound (10) are preferably used as the light emitting material, but an electron transporting material is used in order to adjust the balance between holes and electrons injected into the device.
% To 50% by weight, light emitting layer and back electrode 5
An electron transport layer may be inserted between them. As such an electron transporting material, a compound which does not show strong electron interaction with the hole transporting polymer represented by the general formula (I) is used, and the following compound (17) is preferably used. It is not limited. Similarly, in order to adjust the hole mobility, a predetermined amount of the tetraphenylenediamine derivative may be simultaneously dispersed and used.

[Chemical 10]

For the back electrode 5, a metal having a small work function is used because it can be vacuum-deposited and injects electrons, but magnesium, aluminum, silver, indium and alloys thereof are particularly preferable.

These organic EL elements are represented by the general formula (I).
The hole-transporting polymer represented by the formula (1) or a hole-transporting polymer represented by the general formula (I) and a light-emitting material, and if necessary, an electron-transporting material and a hole-transporting material are dispersed in an organic solvent. A solution is used to form a film on the transparent electrode by a spin coating method, a dipping method, or the like.
The film thickness is preferably about 0.03 to 0.2 μm. The dispersed state of the light emitting material may be a molecular dispersed state or a fine particle dispersed state. In order to obtain a molecular dispersion state, it is necessary to use a common solvent for the hole-transporting polymer, the light-emitting material, the electron-transporting material and the hole-transporting material as the dispersion solvent. It is necessary to select in consideration of dispersibility of the material and solubility of the electron transport material, the hole transport material and the hole transport polymer. In order to disperse in fine particles, a ball mill, a sand mill, a paint shaker,
Attritor, ball mill, homogenizer, ultrasonic method, etc. can be used. Then, the light emitting layer, the electron transporting layer, and the like, and the back electrode may be formed by a vacuum vapor deposition method depending on the intended device configuration. Thereby EL
The element can be easily manufactured. A light emitting layer to be laminated,
The thickness of each electron transport layer is preferably 0.1 μm or less.

[0020]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. The life was measured as follows. That is, the element was driven in constant current with a current flowing when the element was 100 cd / m ² in dry nitrogen, and the half life of the emission luminance was adopted as the element life.

Example 1 A 5% by weight dichloroethane solution of a hole-transporting polymer (molecular weight 80,000) consisting of repeating structural units represented by the following structural formula (I-1) was prepared,

[Chemical 11] It was filtered through a 0.1 μm PTFE filter (manufactured by ADVANTEC). Using this solution, a hole transport layer having a thickness of about 0.1 μm was formed by a dipping method on a glass substrate on which a strip-shaped ITO electrode having a width of 2 mm was formed by etching. After sufficiently drying, the exemplified compound (1) purified by sublimation as a light emitting material was put into a tungsten boat, and a film thickness of 0.05 μm was formed on the hole transport layer by a vacuum deposition method.
The light emitting layer of was formed. The vacuum degree at this time is 10 ^-5 Tor
The boat temperature was 300 ° C. Then Mg-Ag
The alloy is used as a back electrode with a width of 2 mm and a thickness of 0.15 μm.
It was formed by co-evaporation so as to intersect with the O electrode. The effective area of the device was 0.04 cm ² . When a DC voltage of 15 V was applied to the device manufactured as described above in a vacuum (10 ⁻³ Torr) with the ITO electrode side being positive and the Mg—Ag alloy side being negative, a green of 240 cd / m ² (wavelength maximum 530 nm ) Emission was observed, and the current density at this time was 42 mA / cm ² . In addition, constant current (18
The half-life of light emission under mA / cm ² ) drive was about 12 hours.

Example 2 1 part by weight of the hole-transporting polymer (I-1) used in Example 1 and 1 part by weight of the exemplified compound (1) as a light emitting material were mixed to obtain a 10% by weight dichloroethane solution. Prepared,
It was filtered through a 0.1 μm PTEE filter. Using this solution, a hole transport layer having a film thickness of about 0.15 μm was formed by a dipping method on a glass substrate on which a strip-shaped ITO electrode having a width of 2 mm was formed by etching. After sufficiently drying, a Mg-Ag alloy was formed by co-evaporation as a back electrode having a width of 2 mm and a thickness of 0.15 μm so as to intersect with the ITO electrode. The effective area of the device is 0.04 cm ² . When a DC voltage of 15 V was applied to the device thus produced in a vacuum (10 ⁻³ Torr) with the ITO electrode side being positive and the Mg—Ag alloy side being negative, a green of 160 cd / m ² (wavelength maximum 530 nm) was obtained. Was observed, and the current density at this time was 31 mA / cm ² . The half-life of light emission at a constant current (19 mA / cm ² ) drive is about 10
It was time.

Example 3 2 parts by weight of the hole transporting polymer (I-1) used in Example 1 and 0.1 of the exemplified compound (10) as a light emitting material.
By weight, 1 part by weight of the exemplified compound (17) as an electron transport material was mixed to prepare a 10 wt% dichloroethane solution, which was filtered through a 0.1 μm PTEE filter. Using this solution, a hole transport layer having a film thickness of about 0.15 μm was formed by a dipping method on a glass substrate on which a strip-shaped ITO electrode having a width of 2 mm was formed by etching. After sufficiently drying, a Mg-Ag alloy was formed by co-evaporation as a back electrode having a width of 2 mm and a thickness of 0.15 μm so as to intersect with the ITO electrode. The effective area of the device is 0.04 cm ² . The device manufactured in this manner was placed in a vacuum (10 ⁻³ To
In rr), when the ITO electrode side is positive and the Mg—Ag alloy side is negative and a direct current of 10 V is applied, it is 150 cd.
/ M ² red emission was observed, and the current density at this time was 22
It was mA / cm ² . In addition, constant current (15 mA / cm
² ) The half-life of light emission during driving was about 9 hours.

Comparative Example 1 1 part by weight of the hole transport material represented by the following structural formula (18), and 1 part by weight of the exemplified compound (1) as a light emitting material,

[Chemical 12] As a binder resin, 1 part by weight of PMMA is mixed and 10
Prepare a wt% dichloroethane solution and add 0.1 μm PT
It was filtered with an EE filter. 2 mm with this solution
A hole transport layer having a film thickness of about 0.15 μm was formed by a dipping method on a glass substrate on which a strip-shaped ITO electrode having a width was formed by etching. After being sufficiently dried, a Mg-Ag alloy was used as a back electrode having a width of 2 mm and a thickness of 0.15 μm and ITO.
It was formed by co-evaporation so as to intersect the electrodes. The effective area of the device was 0.04 cm ² . The element manufactured as described above was subjected to a direct current of 2 in a vacuum (10 ⁻³ Torr) with the ITO electrode side being positive and the Mg—Ag alloy side being negative.
When 0 V was applied, green emission of 130 cd / m ² was observed, and the current density at this time was 28 mA / cm ² . The half-life of light emission under constant current (22 mA / cm ² ) drive was about 6 hours.

Comparative Example 2 Polyvinylcarbazole was used as the hole-transporting polymer.
1 part by weight of the exemplified compound (10) as a light emitting material, and 1 part of the exemplified compound (14) as an electron transport material.
Parts by weight were mixed to prepare a 10% by weight dichloroethane solution, which was filtered through a 0.1 μm PTEE filter. Using this solution, a hole transport layer having a film thickness of about 0.15 μm was formed by a dipping method on a glass substrate on which a strip-shaped ITO electrode having a width of 2 mm was formed by etching. After sufficiently drying, a Mg-Ag alloy was formed by co-evaporation as a back electrode having a width of 2 mm and a thickness of 0.15 μm so as to intersect with the ITO electrode. The effective area of the device was 0.04 cm ² . The element produced as described above was placed in a vacuum (10 ⁻³
Torr), when the ITO electrode side is positive and the Mg-Ag side is negative and a direct current of 15 V is applied, 110 cd
/ M ² red emission was observed, and the current density at this time was 24
It was mA / cm ² . In addition, constant current (23 mA / cm
² ) The half-life of light emission during driving was about 4 hours.

[0026]

INDUSTRIAL APPLICABILITY In the organic EL device of the present invention, since the layer containing the hole transporting polymer represented by the above general formula (I) is formed, the spin coating method, the dipping method, etc. are used in the production thereof. It is possible to form a good thin film by using it, and it has an ionization potential and hole mobility suitable for an organic EL device. Further, since the film thickness can be set to be relatively large, defects such as pinholes are few, and it is easy to increase the area, and it is possible to increase the brightness of the element and improve the durability.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an example of an organic EL element of the present invention.

FIG. 2 is a schematic cross-sectional view of another example of the organic EL element of the present invention.

[Explanation of symbols]

1 ... Insulator substrate, 2 ... Transparent electrode, 31 ... Hole transport layer, 3
2 ... Emitting layer, 4 ... Emitting layer having electron transporting ability, 5 ... Back electrode,

Claims (4)

[Claims] 1. An electroluminescent device comprising an organic compound layer sandwiched between a pair of electrodes, at least one of which is transparent or semitransparent, wherein the organic compound layer is a positive electrode represented by the following general formula (I). An organic electroluminescent device having a layer containing a hole transporting polymer. Embedded image (In the formula, R ¹ and R ² are each independently a hydrogen atom,
An alkyl group, an alkoxy group, a substituted amino group, a halogen atom, or a substituted or unsubstituted aryl group, X
Represents a substituted or unsubstituted divalent aromatic group, Y represents a divalent alcohol residue, Z represents a divalent carboxylic acid residue, and l and m each independently represent an integer of 1 to 5. And n and k each independently represent an integer of 0 or 1, and p represents an integer of 5 to 5000. ) 2. The organic electroluminescent device according to claim 1, wherein the hole transporting polymer layer represented by the general formula (I) and the light emitting layer are sequentially formed on the transparent electrode. 3. The organic electroluminescent device according to claim 1, wherein a light emitting layer containing the hole transporting polymer represented by the general formula (I) and a light emitting material is formed on the transparent electrode. 4. The organic electroluminescent device according to claim 3, wherein the light emitting layer contains an electron transporting compound.