JPS6143689A - El element - Google Patents

Abstract

PURPOSE:To provide an EL element emitting luminescence in high luminance even at a low voltage, and producible easily at a low cost, and composed of a luminescent layer having triple-layered structure, wherein each layer is composed of a thin film made of a highly oriented electroluminescent organic compound molecule having relatively different electronegativity from the other adjacent layer. CONSTITUTION:The objective EL element is composed of a triple-layered luminescent layer 2 and a pair of electrode layers 1, 3 sandwiching said luminescent layer, wherein at least one of the electrode layers is transparent. The first and the third luminescent layers are made of a monomolecular film (or its built-up film) composed of electroluminescent organic compounds 4, 6 having higher electron affinity than the second luminescent layer. The second luminescent layer is made of a monomolecular film (or its built-up film) composed of an electroluminescent organic compound 5 having higher electron-donative property than the first and the third luminescent layers. EFFECT:It can be produced easily.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an EL element using electrical light emission, that is, EL, and more specifically, the present invention relates to an EL element using electrical light emission, that is, EL, and more specifically, the light emitting layer has a three-layer structure,
each layer comprises at least one electroluminescent organic compound having a different electronegativity relative to other adjacent layers;
E consists of a thin film arranged with highly ordered molecular orientation.
Regarding L elements.

(Prior art) Conventional EL elements are made of Mn'l) or Cu or Re.
It consists of a luminescent layer whose luminescent base material is ZnS containing F3 (Re; rare earth ion) etc. as an activator,
Due to the difference in the basic structure of the light emitting layer, there are two types: powder type EL and thin film type E.
It is structurally classified into L.

Among devices that have been put into practical use, thin-film ELs generally have higher brightness than powder-type ELs, but thin II! Since the light-emitting layer of EL is formed by vapor-depositing a light-emitting base material onto a substrate, it has drawbacks such as difficulty in manufacturing large-area devices and extremely high manufacturing costs.

For this reason, powder-type EL, in which a light-emitting base material, that is, ZnS, is dispersed in an organic binder, which is most easily mass-produced and costs only a few tenths of that of S-film type devices, has attracted attention. . In general.

In EL light emission, the thinner the thickness of the light emitting layer, the better the light emission characteristics. However, in the case of the powder type EL, since the luminescent base material is a non-continuous powder, when one luminescent layer is made thin, pinholes are likely to occur in the luminescent layer, making it difficult to reduce the layer thickness. Therefore, it has a major drawback in that sufficient brightness characteristics cannot be obtained. Recently, an improved device in which an intermediate dielectric layer made of vinylidene fluoride polymer is disposed within the light-emitting layer of the powder type EL has been disclosed in Japanese Patent Application Laid-Open No. 1] B58-17.
However, it has not yet achieved sufficient performance in terms of luminance and power consumption.On the other hand, recently, new optical and Research and development into materials for electronics is being actively carried out, and materials such as EC elements, piezoelectric elements, pyroelectric elements, non-radiometer optical elements, and strong electrostatic liquid crystals are comparable to metals and S mechanical materials. lol them! Compelling organic materials have been announced. As described above, there is a demand for the development of functional organic materials as new functional materials that surpass inorganic materials, and a cumulative film of monomolecular layers of anthracene derivatives and pyrene derivatives, which have a parent tree group and a hydrophobic group in the molecule, is being used as an electrode. An EL element formed on a substrate is proposed in Japanese Patent Laid-Open No. 52-35587. However, these EL devices have not yet achieved sufficient performance as a real EL device in terms of brightness, power consumption, etc. Furthermore, in the case of organic EL devices, the density of carrier electrons or holes is extremely low. The probability of excitation of mechanical molecules due to carrier recombination or the like becomes extremely small, and efficient light emission cannot be expected.

(Disclosure of the Invention) Therefore, the purpose of Unexposed 11 is to eliminate the drawbacks of the prior art as described above, to provide an EL element that can emit light with sufficiently high brightness even when driven at a low voltage, is inexpensive, and is easy to manufacture. The goal is to provide the following.

The above object of the present invention has been achieved by forming a light emitting layer of an EL element by combining specific materials and having a specific configuration.

In other words, 1 is an EL device consisting of a light emitting layer with a three-layer laminated structure and two electrode layers in which at least one layer sandwiching the light emitting layer is transparent, in which the first and third light emitting layers are is composed of a monomolecular film made of at least one electroluminescent organic compound that is electron-accepting relative to the second emissive layer, or a cumulative film thereof, and the second emissive layer is
and a monomolecular film made of at least one electroluminescent organic compound that is electron-donating relative to the third light-emitting layer, or a cumulative film thereof.

To explain the present invention in detail, the electroluminescent organic compound used in the present invention and which mainly characterizes the present invention has a high luminescence quantum efficiency and is easily susceptible to external perturbation.
It is a compound that has an electronic system and can be electrically excited. For example, it basically includes fused polycyclic aromatic hydrocarbons, p-terphenyl, 2.5-diphenyloxazole, l, 4-
Bis(2-methylstyryl)-benzene, xanthine,
Examples include coumarin, acridine, cyanine dyes, benzophenone, phthalocyanine and its metal complexes, porphyrin and its metal complexes, 8-hydroxyquinoline and its metal complexes, organic ruthenium complexes, organic rare earth complexes, and derivatives of these compounds. . Furthermore, compounds that can serve as electron acceptors or electron donors for the above compounds include heterocyclic compounds other than those mentioned above and derivatives thereof, aromatic amines and aromatic polyamines, compounds with a quinone structure, and tetracyanoquinodimethane. and tetracyanoethylene.

Particularly useful compounds in the present invention are those obtained by chemically modifying the electroluminescent compound as described above by a known method if necessary, and having at least one hydrophobic moiety and at least one hydrophilic moiety in its structure. It is a compound having a sexual moiety (all of these are in a relative sense), and includes, for example, a compound represented by the following general formula CI) and other compounds.

[(X-R,), 2], L-$-R2(I) In the above formula, X is a hydrogen atom, a halogen atom, an alkoxy group,
Alkyl ether group, nitro group; carpoxyl group, sulfonic acid group, phosphorus group.

Silicic acid group, primary to tertiary amino group; these gold Ii! salt.

Primary to tertiary amine salts, acid salts; ester groups, sulfamide groups, amide groups, imino groups, quaternary amine groups and their salts, water-based groups, etc.; R9 has 4 to 30 carbon atoms, preferably 10 to 30 carbon atoms; 25 alkyl groups, preferably linear alkyl groups; m is 1 or a group (R is any substituent such as a hydrogen atom, an alkyl group, or an aryl); φ is as exemplified later is a residue of an electroluminescent compound; R1, like X, is a hydrogen atom or any other substituent; at least one of one or more of X, φ and R2 is a hydrophilic moiety; , and at least one is a hydrophobic moiety.

Preferred examples of the compound φ of the general formula (1) and other compounds are as follows.

(Margin below) Z=NH1O, S Z=CO, NHZ=CO1N
H%O,5Z=NH,0,SZ=NH%0,SZ=NH
,0,5Z=Ss Se Z=S%Se
'Z=Ss 5eZ=NH,OlS Z=
NH1αS Z=NH, O1SM=MgsZnsSn
hAtC1M=HzsBe*MghCa*CdSn, f
ilch% YbCI M=Ers Tm Sm, Eu, Tb,
Z = 0, Nm, -' M=A4 Gas Irs Tab a=3 PJ
I-Ers Smb EuDA-Zns Cd b M
g s pb s a=2 Gd 1Tb %D
yTm, Yb Tb, Dy, Tm, Yb Gd, T
b, DyTm, Yb Z=O,S, Se O<p≦2 The above luminescent compounds can be used alone or as a mixture in each luminescent layer in the present invention. In addition,
These compounds are examples of preferred compounds, and it goes without saying that other rust conductors or other compounds may be used as long as the same purpose is achieved.

In the present invention, the luminescent compounds as described above are used in the first to third stages of the EL device of the present invention, depending on their electronegativity.
The light emitting layer is divided into three light emitting layers, and the light emitting layer has a three-layered structure.

That is, since the above-mentioned light-emitting compounds have different electronegativity, when one or more of the above-mentioned compounds are employed as the light-emitting compounds for forming the first and third light-emitting layers, these employed A second luminescent compound is a luminescent compound having a different electronegativity.
Among such light-emitting compounds that may be selected as compounds for forming a light-emitting layer, particularly preferable electron-donating compounds include 1-tiSS class amino amino groups, alkoxy groups, alkyl ether groups, etc. The main ones are those having an electron-donating group or nitrogen heterocyclic compounds, and the electron-accepting ones include electron-withdrawing groups such as carbonyl group, sulfonyl group, nitro group, and quaternary amino group. The main compounds are those having In the present invention, such luminescent compounds can be used alone or in combination in each luminescent layer.

The other elements forming the EL element of the present invention, that is, the two electrode layers that sandwich the light emitting layer, can use any conventionally known electrode layer, but at least one of the layers is transparent. There is a need. As the transparent electrode, any desired transparent electrode layer can be used as in the past, and preferred ones are 1, for example, transparent synthetic resins such as polymethyl methacrylate and polyester, transparent films or sheets such as glass, etc. A transparent conductive material such as indium oxide, tin oxide, or indium tin oxide (ITo) is coated on the entire surface or in a pattern. When using opaque electrodes on one side, these opaque electrodes may be of conventionally known types, and are generally and preferably made of aluminum, silver, gold, etc. with a thickness of about 0.1 to 0.3 pm. This is the vapor-deposited film. Further, the shape of the transparent electrode or the opaque electrode may be any shape such as a plate, a belt, or a cylinder, and can be selected depending on the purpose of use. The thickness of the transparent electrode is preferably about 0.01 to 0.21 Lm. If the thickness is less than this range, the physical strength and electrical properties of the element itself will be insufficient, and if the thickness is more than the above range, Otherwise, problems may arise in terms of transparency, light weight, compactness, etc.

In the EL element of the present invention, between the two electrode layers as described above,
Using electroluminescent compounds with relatively different electronegativities as described above, 3F! ), in which the molecules constituting the three-layered emissive layer are arranged in a monomolecular film or a cumulative film thereof with highly ordered molecular arrangement. It is characterized by certain things.

In the present invention, a particularly preferred method for forming such a monomolecular film or a cumulative film thereof is the Langmuir-Blodgett method (LB method). When a molecule with a structure that has a hydrophobic group maintains an appropriate balance between the two (amphiphilic balance), the molecule forms a monomolecular layer on the water surface with the hydrophilic group facing down. This method utilizes this fact to form a monomolecular film or a cumulative film thereof. Specifically, in order to prevent the monomolecular film spread on the water layer from freely diffusing and spreading too much, a partition plate (or float) is provided to limit the spread area and control the aggregated state of the film material. is controlled, the surface pressure is gradually increased, and a surface pressure suitable for manufacturing a monomolecular film or a cumulative film thereof is set. By gently lifting or lowering the clean substrate vertically while maintaining this surface pressure, the monomolecular film is transferred onto the substrate. A monomolecular film is produced in the above manner, and a cumulative film having a desired degree of accumulation can be formed by repeating the above-mentioned operations.

In addition to the above-mentioned vertical dipping method, the monomolecular film can be transferred onto the substrate by methods such as a horizontal deposition method, a single rotation cylinder method, and the like. The horizontal deposition method is a method in which the substrate is brought into contact with the water surface horizontally and transferred, and the rotating cylinder method is a method in which a cylindrical substrate is rotated above the water surface and the monomolecular film is transferred onto the surface of the substrate.

In the vertical immersion method described above, when a substrate with a hydrophilic surface is pulled out of water in a direction transverse to the water surface, a monomolecular film is formed on the substrate with the tree-philic groups of the molecules facing the substrate. As mentioned above, when the substrate is moved up and down, one monomolecular film is overlapped in each process.The direction of the film-forming molecules is reversed between the lifting process and the dipping process, so according to this method, the molecules between each layer are A Y-type film is formed in which the hydrophilic group of the molecule and the hydrophobic group of one molecule of the hydrophilic group face each other. On the other hand, in the horizontal attachment method, the substrate is placed horizontally on the water surface. By this method, a monomolecular film with the hydrophobic groups of the molecules facing the substrate is formed on the substrate. In this method, even if monomolecular films are accumulated, there is no change in the orientation of the film molecules, and in all layers an X-shaped film is formed with the hydrophobic groups facing the substrate. In all layers, the hydrophilic groups face the substrate side.
The 0-rotation cylinder method, in which M is referred to as a Z-type membrane, is a method in which the monomolecular film is transferred to the surface of the substrate by rotating the cylinder above the water surface of the substrate. The method of transferring the monomolecular film onto the substrate is not limited to these methods; in other words, when using a large-area substrate, a method of extruding the substrate from a substrate roll into a water layer may also be used. Furthermore, the directions of the above-mentioned hydrophilic groups and hydrophobic groups toward the substrate are in principle, and can be changed by surface treatment of the substrate, etc.

In the EL device of the present invention, the above-mentioned light-emitting layer forming material is preferably formed by the above-mentioned LB method, and between the above-mentioned two electrode layers, three compounds having different electronegativities are formed between the two electrode layers.
This can be obtained by forming it as a layered structure.

As described in the section on a conventional technique, it is known to form an EL element by the LB method, but with this known method, an EL element with sufficient performance cannot be obtained.

As a result of various studies, the present inventor has constructed a three-layer structure for one light-emitting layer, and each light-emitting layer has a different electronegativity as described above.
- It has been discovered that the performance of conventional EL elements can be significantly improved by forming a monomolecular film or a cumulative film of these compounds using a compound.

One important aspect of the present invention is that each light-emitting layer is a monomolecular film made of the above-mentioned light-emitting material. In the EL device of this embodiment, first, a material that is relatively electron-accepting to the second layer to be formed as an intermediate layer is dissolved in a suitable organic solvent such as chloroform, dichloromethane, dichloroethane, etc. to a concentration of about 10 to IO, and the solution is
It is developed on an aqueous phase of an appropriate pH (e.g., pH about 1 to 8) which may contain various metal ions, and the solvent is evaporated to form a monomolecular film. A material having electron donating properties relative to the first layer formed in this way was then transferred in the same manner to the first layer formed in this manner. and transfer it as a monomolecular film to the surface of the first light emitting layer to form a second layer,
A third layer is formed on the surface of the second calendar in the same manner as above, and is made of a compound that is reciprocally electron-accepting to the second layer, and finally, an electrode material such as aluminum, silver, gold, etc. is formed on the surface of the second layer. , preferably by vapor deposition or the like to form a back electrode layer.

The thickness of the luminescent layer consisting of three monomolecular layers of the EL device thus obtained varies depending on the type of material used, but generally a thickness of about 0.01-1 μm is suitable. be.

Another important aspect is that at least one layer, preferably all three layers, of the three layers constituting the light emitting layer of the EL device of the present invention is a cumulative film of the above-mentioned monomolecular film. This embodiment can be obtained by accumulating monolayers as described above in various ways up to the required number of layers by using the LB method described above.

The thickness of the light-emitting layer of the EL device thus obtained, that is, the cumulative number of monolayers, can be changed arbitrarily, but in the present invention, the cumulative number of the three layers is about 4 to 400. is suitable.

Note that the adhesion between one or both electrode layers used as a substrate and the light-emitting layer is sufficiently strong in the LB method, and the light-emitting layer will not peel or fall off. In order to strengthen the adhesion, the surface of the substrate may be treated in advance, or an appropriate adhesive layer may be provided between the substrate and the light emitting layer. The adhesive strength can also be strengthened by adjusting various conditions such as the pH of the layer, ionic species, water temperature, transfer rate of the monomolecular film, or surface pressure of the monomolecular film.

Since the performance of the EL element formed as described above may deteriorate due to the influence of moisture and oxygen in the air, it is made moisture resistant by conventionally known means.

It is desirable to use a sealed JIfI structure that is S* resistant.

In the EL device of the present invention as described above, the structure of the light emitting layer is as follows:
It is an ultra-thin film, has a high degree of molecular order and functionality necessary for the operation of an EL device, and has excellent light-emitting performance. In addition, in terms of manufacturing, 1. The thickness of the 5 light-emitting layers is uniform over a large area.

Since the EL element can be made without defects and can be produced at room temperature, normal pressure, or conditions close to it, there is an advantage that light-emitting functional materials with relatively low heat resistance can be used.

Furthermore, as schematically shown in FIG. 1, the light-emitting layer of the EL device of the present invention is different from the light-emitting layer of the prior art consisting of a single calendar, as schematically shown in FIG. ~Since the third light-emitting layer has a uniform interface with each other, various interactions between these three layers with different electronegativities are extremely easy, to a degree that cannot be achieved with conventional technology. It exhibits excellent light emitting performance. That is, the first to third
By variously changing the difference in electronegativity between the light emitting layer and the light emitting layer, the light emission intensity can be improved, the light emission color can be arbitrarily changed, and the service life can be significantly extended.

Furthermore, the prior art has excellent luminescence.

Materials with insufficient film formability or film strength could not be used in practice, but in the present invention, such IIIk, ll!
Even if the material is inferior in bipolar properties and film strength, but has excellent luminescence,
By using a material with excellent film-forming properties in at least one layer, a light-emitting layer with excellent luminescence properties, film-forming properties, and film strength can be obtained.

The ELF device of the present invention described above can achieve excellent EL luminescence by applying electrical energy such as alternating current, pulse, or direct current between the electrode layers so that electrical energy such as a suitable electric field acts on the light emitting layer. This shows that.

Next, the present invention will be explained in more detail with reference to Examples. Note that the words in the middle of the text are based on weight.

Example 1 A transparent electrode was formed by depositing an ITO layer with a thickness of 1500 Å on the surface of a 501 square glass plate by sputtering. After thoroughly cleaning this one-layer substrate, Joyce-L
Langair-Traugh4 made by oebe1
(1) Zero-order immersed in an aqueous phase adjusted to pH 6.5.

A BThe above compound A
and B were dissolved in chloroform at a molar ratio of l=1 (10-jmol/ml), and then developed on the aqueous phase. After the solvent chloroform was removed by evaporation, the surface pressure was increased (30 dyne/cm) to precipitate the above mixed molecules in the form of a film. Thereafter, while keeping the surface pressure constant, the film-forming substrate was gently moved up and down in the direction across the water surface (vertical speed 2 cm/xin), and the mixed monomolecular film was transferred onto the substrate. .5, 10 and 15 layers of accumulated monolayers! Created IIQ. In this cumulative process.

Each time the substrate was taken out of the water tank, it was allowed to stand for 30 minutes or more to evaporate and remove the water adhering to the substrate.

Next, the mixed monomolecular film remaining on the surface of the aqueous phase was completely removed and newly dissolved in chloroform (10-3 mol
/fL) was developed on the aqueous phase. By the same method as above, new functional monolayers and two-layer cumulative films were formed on the surfaces of the monolayers and monolayer cumulative films that had already been produced.

Once again, the monomolecular film on the surface of the aqueous phase was completely removed, and a single layer of 8 g of monomolecules and 3, 5
, 10.15W to form a monomolecular cumulative film, which was used as the third layer.

Finally, the substrate having [formed as described above] was placed in a vapor deposition tank, and the nuclide was once reduced to a vacuum level of 10 Torr, and then the vacuum level was adjusted to 10 Torr, and the vapor deposition rate was increased to 20 Torr.
At A/sea, a film thickness of 1500 A was deposited on the Alt thin film to form a back electrode.The prepared EL element was sealed with a sealing glass as shown in FIG. 3, and then purified according to a conventional method. and degassed and dehydrated silicone oil is injected into the seal to form the four ELs of the present invention.
A light emitting cell was formed. 5V, 5 to these EL light emitting cells
When an alternating current voltage of 0 Hz was applied, EL light emission having a color unique to the material used was obtained. The evaluation results are shown in Table 1.

The above-mentioned EL element of the present invention had a lower driving voltage and better luminance characteristics than the conventional EL element using ZnS as a light emitting matrix.

Comparative Example 1 In Example 1, except that only Compound A was used as the luminescent compound and a mono-calendar was used, the rest was the same as that of Example 1.
A comparative EL device was obtained in the same manner as in Example 1, and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

Cumulative degree Supervision ■ Pressure 1 Disaster prevention 1 layer 2 Calendar 3
! J 正辷口 (Shl-1115V
, 400Hz 3 0.183 2 3
10V, 400Hz 11 0.135 2
5 10V, 400Hz 20 0.11
10 2 10 10V, 400Hz 18
0. H2S 2 15 LOW, 400Hz
17 0.07 Niwa Mosquito Isamu” Cumulative degree 3 10V, 40011z 1 or less 0
．． 218 10V, 400Hz 1 or less
0.112 10V, 400Hz 1 or less 0.122 10V, 400Hz
1 or less 0.0332 10V, 400Hz
1 or less 0.08 Example 2 In place of compounds A, B, and C in Example 1, the following compounds R, E, and F were used, and D E
F The other parts were the same as in Example 1.1 EL element of the present invention (however,
The cumulative number of each was 5.2.5), and when evaluated under the same conditions as Example 1, the current density was 0913 A/cm
', and the brightness (Ft-L) was 18.

[Brief explanation of drawings]

FIG. 1 diagrammatically shows an EL device based on the prior art LB method, FIG. 2 diagrammatically shows an EL device according to the present invention, and FIG. It is a diagram schematically showing a cross section of an EL element. l; transparent itt electrode 2; light emitting layer 3; back electrode
4; Luminescent compound 5; Luminescent compound 6;
Luminescent compound 7; Seal glass 8: Silicone insulating oil 9; Glass plate Patent applicant Canon Co., Ltd. agent Burying earth 1) Katsuhiro Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] In an EL device consisting of a light emitting layer with a three-layer stacked structure and two electrode layers sandwiching the light emitting layer, at least one of which is transparent, the first and third light emitting layers are connected to the second light emitting layer. consisting of a monomolecular film or a cumulative film thereof made of at least one electroluminescent organic compound that is relatively electron-accepting to The above-mentioned EL device is characterized in that it is made of a monomolecular film or a cumulative film thereof made of at least one relatively electron-donating electroluminescent organic compound.