JPS6155182A - El element - Google Patents

Abstract

PURPOSE:The title element which has high luminance even on low-voltage drive and excellent emission quantum efficiency, and is low-priced, made by placing a luminescent layer of a specified two-layer constitution between two electrode layers at least one of which is transparent. CONSTITUTION:A luminescent layer 2 which has a thickness of 0.01-1mum and has a two-layer constitution consisting of the first luminescent layer comprising a mixed unimolecular (cumulative) film of a mixture of 1mol of an electroluminescent organic compound 5 (A) and 0.1-0.01mol of an organic compound 5' (B) which is electron accepting relative to component A; and the second luminescent layer comprising a mixed unimolecular (cumulative) film of a mixture of 1mol of component A or an electroluminescent organic compound 4 (C) having the same degree of electronegativity is component A and 0.1-0.01mol of an organic compound 4' (D) which is electron donating relative to component A or C, is formed between a transparent electrode 1 of a thickness of 0.01-0.2mum and an opaque back electrode 3 of a thickness of 0.1-0.3mum.

Description

Detailed Description of the Invention (Industrial Use ¥f) The present invention relates to an EL element using electrical light emission, that is, EL, and more specifically, the light emitting layer has a two-layer structure,
The present invention relates to an EL device comprising a thin film in which each layer is arranged with highly ordered molecular orientation and has a different electronegativity relative to other adjacent layers.

(Prior art) Conventional EL elements are made of 1Mn, Cu or ReF7 (
It consists of a light-emitting layer whose light-emitting base material is ZnS containing Re (rare earth ions) as an activator, and is structurally divided into powder-type EL and thin-film EL, depending on the basic structure of the light-emitting layer. Ru.

Among devices that have been put into practical use, Q-film ELs generally have higher brightness than powder-type ELs, but thin-film ELs have a large area because the light-emitting layer is formed by vapor-depositing a light-emitting base material on the substrate. This method has drawbacks such as difficulty in manufacturing the device and extremely high manufacturing cost.

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 the cost of thin-film devices, has attracted attention. Generally, in EL light emission, the thinner the JA optical layer, the better the light emission characteristics. However, in the case of the powder type EL, since the luminescent base material is a discontinuous powder,
When the light-emitting layer is made thinner, pinholes are likely to occur in the light-emitting layer, making it difficult to reduce the layer thickness, and therefore having a major drawback in that sufficient brightness characteristics cannot be obtained. Recently, an improved device in which an intermediate dielectric layer made of a 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. 172891/1982, but it has not yet been reported. However, recently, research and development has been actively conducted to control the chemical structure and higher order structure of organic materials to create new materials for optical and electronics. , EC elements, piezoelectric elements, pyroelectric elements, nonradiometric optical elements, ferroelectric liquid crystals, and other organic materials that are comparable to or superior to metals and inorganic 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 conductors, which have a parent group and a hydrophobic group in the molecule, has been developed. The EL element formed on the electrode substrate was published in Japanese Patent Application Laid-Open No. 52-3558.
This is proposed in Publication No. 7. 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 functional molecules due to carrier recombination etc. becomes extremely small, and efficient light emission cannot be expected.

(Disclosure of the Invention) Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art, and 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. It is to provide.

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.

That is, the present invention provides an EL device comprising a two-layered light-emitting layer and two electrode layers in which at least one layer sandwiching the light-emitting layer is transparent, in which the first light-emitting layer is electrically emissive. organic compound (A) and an organic compound that is relatively electron-accepting to compound (A) (hereinafter referred to as acceptor)
The second light-emitting layer consists of a mixed monomolecular film or a cumulative film of a mixture of an electroluminescent organic compound (
A) or a mixed unit consisting of a mixture of an electroluminescent organic compound having the same electronegativity as the compound (A) and an organic compound relatively electron-donating to the compound (A) (hereinafter referred to as a donor). The above-mentioned EL device is characterized in that it is made of a molecular film or a molecule film thereof.

To explain the present invention in detail, 1. 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, 1.4-
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 (1) and other compounds.

[(X-R,), Z], -φ-R2 (1) In the above formula, X is a hydrogen atom, a halogen atom, an alkoxy group, an alkyl ether group, a nitro group; a carboxyl group, a sulfone! group, phosphate group.

Kay#! i# group, 1st to 3rd amino groups: metal salts of these,
Primary to tertiary amine salts, acid salts; ester groups, sulfamide groups, amide groups, imino groups, quaternary amino groups and their salts, hydroxyl groups, etc.; R1 has 4 to 30 carbon atoms, preferably 10 to 25 carbon atoms; an alkyl group, preferably a straight-chain alkyl group; m is 1 or -S O, N R,, -co-
, -coo-, etc. (R, is an arbitrary substituent such as a hydrogen atom, an alkyl group, an aryl, etc.); φ is a residue of an electroluminescent compound as exemplified later; R2
Like X, is a hydrogen atom or any other substituent; at least one of the one or more X, φ and R□ is a lignophilic moiety, and at least one is a hydrophobic moiety It is.

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

(Margin below) Z=NH, O, S Z=CO, NHZ=CO, NH
,01SZ=NH,01S Z=Su,0,S Z=NH,O%5
Z=S%5eZ=S%5eZ=S1SeZ=Su, O%S
Z=NH1αS Z=NH,O1S1VpA4G
a, Ir+Ta, a=3 M=Er, Sm, EuM
=Zn, Cd, Mgb pb, a=2G
d, Tb, DyTm, Yb M==Er, Sms Eu, Gd M=Er
, Smb EuTb, Dy, Tm%Yb
Gd%Tb, DyTm%Yb 2=0, S, SeO≦p≦2 The above luminescent compounds can be used alone in each luminescent layer in the present invention, or a mixture can be used as long as the electronegativity is the same. It can also be used as Incidentally, these compounds are examples of preferred compounds, and it goes without saying that other derivatives or other compounds may be used as long as the same purpose is achieved.

In the present invention, a luminescent compound (A) having a specific electronegativity or a luminescent compound having a similar electronegativity to the compound (A) is selected from the luminescent compounds as described above, and the EL element of the present invention is used as the main emissive compound of the first emissive layer and the second emissive layer of It is said that

Among the luminescent compounds and non-luminescent compounds, compounds are particularly preferred as acceptors.

Compounds having an electron-withdrawing group such as a carbonyl group, a sulfonyl group, a nitro group, or a quaternary amine group are the main ones, and particularly preferable compounds as donors include first to third groups.
The main ones are those having an electron-donating group such as an amino group, a hydroxyl group, an alkoxy group, or an alkyl ether group, or a nitrogen heterocyclic compound.

The acceptor as described above is preferably about 171 moles of the luminescent compound forming the first layer as described above.
The donor is preferably added in a proportion of about 1/10 to 1/100 to reduce the electronegativity of the first layer.
100 moles to increase the electronegativity of the second layer.

As described above, the acceptor may be selected from the above-mentioned luminescent compounds or non-luminescent compounds, or may be selected from other organic compounds with high electron-accepting properties, and the donor may be selected from the above-mentioned luminescent compounds or non-luminescent compounds. The acceptor may be selected from the above-mentioned luminescent compounds or non-luminescent compounds, or may be selected from other highly electron-donating organic compounds other than the above-mentioned ones. It is preferable to select from various compounds having a large substituent group, and also as a donor, from various organic compounds having a large electron-donating substituent as described above (1).

The other elements forming the EL element of the present invention, that is, the two electrode layers sandwiching the light emitting layer, can be any conventionally known element, but at least one of the layers must be transparent. There is a need. As the transparent electrode layer, any desired transparent electrode layer can be used as in the past, and preferred examples include transparent synthetic resins such as polymethyl methacrylate and polyester, and transparent films or sheets such as glass that have oxidized surfaces. A transparent conductive material such as indium, tin oxide, or indium-tin-oxide (ITO) is coated on the entire surface or in a pattern. If opaque electrodes are used on one side, these opaque electrodes may also be of conventionally known type, and are generally and preferably about 0.0 mm thick. Aluminum of L~0.3ALm,
It is a vapor deposited film of silver, gold, etc. Further, the shape of the transparent electrode layer or the opaque electrode layer may be any shape such as a plate, a belt, or a cylinder, and can be selected depending on the purpose of use. Further, the thickness of the transparent electrode layer is preferably about 0.01 to 0.2 gm. If the thickness is less than this range, the physical strength and electrical properties of the element itself will be insufficient; The thickness may cause problems in transparency, lightness, compactness, etc.

In the EL element of the present invention, between the two electrode layers as described above,
It can be obtained by changing the electronegativity of an electroluminescent compound with a specific electronegativity as described above by adding an acceptor or donor, and forming a luminescent layer consisting of two layers with different electronegativity. It is characterized in that the molecules constituting the formed two-layer structure light-emitting layer are a monomolecular film or a cumulative film thereof, each of which is arranged with highly ordered molecular orientation.

In the present invention, a particularly preferred method for forming such a monomolecular film or a cumulative film thereof is the Langmuir-Prodgett method (LB method). When the balance between the two (amphiphilic balance) is maintained at an appropriate level, the molecule forms a monomolecular layer on the water surface with the hydrophilic group facing downward. 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 installed to limit the spreading surface and to collect the film material. The conditions are 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 raising or lowering the clean substrate vertically while maintaining this surface pressure, the monolayer is transferred onto the substrate. Although a monomolecular film is manufactured in the above manner, a cumulative film of a monomolecular film is formed by repeating the above-described operations as a cumulative film with a desired degree of precision.

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 and a rotating cylinder method. The horizontal deposition method is a method in which the substrate is brought into horizontal contact with the water surface and transferred, and the rotating cylinder method is a method in which a cylindrical substrate is rotated on the water surface to transfer the monomolecular film onto the surface of the substrate. In the vertical immersion method described above, when a substrate with a hydrophilic surface is lifted 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 toward the substrate. As mentioned above, when the substrate is moved up and down, the monomolecular film becomes oriented one by one in each process.The direction of the film-forming molecules is reversed in the lifting process and the dipping process, so according to this method, the distance between each layer is A Y-shaped film is formed in which the hydrophilic groups and the lignophilic groups of the molecules, and the hydrophobic groups and the hydrophobic groups of the molecules face each other. On the other hand, the horizontal adhesion method is a method in which a substrate is attached horizontally to the water surface and then transferred, and 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 repeated, there is no change in the orientation of the film-forming molecules, and an X-shaped film is formed in which the hydrophobic groups face the substrate in all layers. A cumulative film in which the hydrophilic groups in the layers face the substrate side is called an X-type film.The zero-rotation cylinder method is a method in which a 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 woodphilic groups and hydrophobic groups toward the substrate are in principle, and can be changed by surface treatment of the substrate, etc.

The EL device of the present invention is produced by adding an acceptor or donor as described above to a luminescent compound having a specific electronegativity.
It is obtained by forming a two-layer structure of a light emitting layer between two electrode layers as described above, using materials for forming a light emitting layer having different electronegativities, preferably by the LB method as described above. be.

As mentioned in the prior art section, it is known to form an EL element by the LB method, but this known method does not allow for obtaining an EL element with sufficient performance, and the present inventor has conducted various research studies. As a result, the performance of the conventional EL device can be improved by forming the light emitting layer into a two-layer structure and forming each light emitting layer as a mixed monomolecular film or a cumulative film thereof containing acceptors or donors with different electronegativities as described above. We have found that this results in a significant improvement.

One important embodiment of the present invention is that each emissive layer is a mixed moiety film of the emissive material containing an acceptor or donor. The EL element of this aspect is
First, a luminescent compound of a specific electronegativity containing an acceptor is dissolved in a suitable organic solvent, such as chloroform,
It is dissolved in dichloromethane, dichloroethane, etc. to a concentration of about 1O to IOM, and the solution is mixed with a suitable p)I (for example, pi (about 1 to 8 ) on the aqueous phase, and the solvent is evaporated to form a mixed monomolecular film.
Using the LB method as described above, the first layer is transferred onto one electrode substrate, dried sufficiently, and then a specific electronegative layer containing a donor is applied to the first layer formed in this way. Similarly, a mixed monomolecular film of a luminescent compound is transferred onto the surface of the first luminescent layer. Next, an electrode material such as aluminum, silver, or gold is applied to the surface of the second layer. , preferably by vapor deposition or the like to form a back electrode layer. Note that the same effect can be obtained even if the order of forming the first layer and the second layer is reversed.

The thickness of the light-emitting layer made of the two-layer mixed monolayer of the EL device thus obtained varies depending on the type of material used, but generally a thickness of about 0.01 to IBm is suitable. It is.

Another important aspect is that at least one, preferably both, of the two layers constituting the light-emitting layer of the EL device of the present invention is a cumulative film of the above-mentioned mixed monomolecular film. This embodiment can be obtained by accumulating the mixed monolayer as described above in various ways up to the required number of layers 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 mixed monolayers, can be changed arbitrarily, but in the present invention, the total thickness of the two layers is about 4 to 400.
A cumulative number of is preferred.

Note that the attachment 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 adhesive strength, 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 force can also be strengthened by adjusting various conditions such as the pH of the water layer, ionic species, water temperature, monomolecular film transfer rate, or surface pressure of the monomolecular film.

The performance of the EL element formed as described above may deteriorate due to the influence of moisture and oxygen in the air if left as is, so it is desirable to create a moisture- and oxygen-proof hermetically sealed structure using conventionally known means. .

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, it is possible to produce an EL device with a uniform thickness of the light-emitting layer over a large area and no defects, and it can be manufactured at room temperature, normal pressure, or near normal temperature, so it is relatively heat resistant. There is an advantage that even a neutral luminescent functional material 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 layer, as schematically shown in FIG. Since the light-emitting layer and the second light-emitting layer have a uniform interface, various interactions between these two layers with different electronegativities are extremely easy, and a level of interaction that cannot be achieved with conventional technology is achieved. It exhibits excellent luminous performance. That is, by variously changing the difference in electronegativity between the first light-emitting layer and the second light-emitting layer, the light emission intensity can be improved or the light emission color can be changed arbitrarily, and the service life can also be changed. It can be significantly extended.

Furthermore, in the conventional technology, it was virtually impossible to use materials that had excellent luminescence but insufficient film formability or film strength; however, in the present invention, materials with poor film formability or film strength could not be used. but,
Even materials that have been affected by luminescence.

By using a material with excellent film-forming properties for one of the layers, a light-emitting layer with excellent luminescence properties, film-forming properties, and film strength can be obtained.

The EL device of the present invention described below can achieve excellent EL 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 full luminescence.

Next, the present invention will be explained in more detail with reference to Examples. Note that the middle part of one sentence is based on weight.

Example 1 A transparent electrode was formed by depositing an ITO layer with a thickness of 1,500 nm on the surface of a 50+ am square glass plate by the snog tuttering method. After thoroughly cleaning this film-forming substrate,
-Langmuir manufactured by Loebe1 -Troug
A then immersed in an aqueous phase containing 4X10M CdCl, adjusted to pH 6.8, of the above compounds A and B in a molar ratio of 100:l.

Dissolved in chloroform (10-' mol/Jl)
rear.

It was developed on the above water phase. After the solvent chloroform was removed by evaporation, the surface pressure was increased by 1 (30 dyne/c+*) to precipitate the above-mentioned 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/m1n), and the mixed monomolecular film was transferred onto the substrate. A monomolecular cumulative film of 5, 10 and 15 layers was prepared to serve as the first acceptor layer. In this cumulative process, each time the substrate was pulled 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 is completely removed and a new layer is added.

The compound A and the compound C are dissolved in loloform at a molar ratio of 100:1 (10 mat/day),
The solution was spread on the aqueous phase. By the same method as above,
5.10 Add only a new mixed monolayer or mixed monolayer on the surface of the already created mixed monolayer and monolayer cumulative film.
Then, a 15W cumulative film was formed to form a second donor group.

The substrate with the thin film formed as described above was placed in a vapor deposition tank, and the tank was once depressurized to a vacuum level of 10 Torr, and then TA was adjusted to a vacuum level of 10 Tarr, and the vapor deposition rate was 20λ/s.
EC was used to deposit AI with a thickness of 1500λ onto the thin film and use it as a back electrode.The fabricated EL device was sealed with a sealing glass as illustrated in Figure 3, and then purified and purified according to conventional methods. Degassed and dehydrated silicone oil was injected into the seal to form four EL cells of the present invention. When an alternating current voltage of 400 Hz was applied to these EL cells, total EL light emission having a color unique to the compound 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 single layer was used, the rest was Example 1.
An EL device for comparison was obtained in the same manner as above, and evaluated in the same manner as the actual artist. The evaluation results are shown in Table 1.

1st = E layer weight "■degree fox beans uLU 虱且present" 1st layer 2nd layer stop Ω (ridge group 虻) 1
1 3V, 400) 1z 5 0.34
5 5 5V, 400Hz 20 0.
1110 to 5V, 400Hz 28
0.1115 15 10V, 400Hz
33 0.10 凰劰■” Cumulative degree 2 5V, 400Hz 5 or less 0.30
10 5V, 400Hz 5 or less 0.1
120 5V, 400Hz 5 or less 0.
1030 5V, 400Hz 5 or less 0
．． 10 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 EL element of the present invention was prepared in the same manner as in Example 1 (however,
The cumulative number of each was 15) and evaluated under the same conditions as Example 1. At a current density of 0.12 mA/am'', the brightness (
Ft-L) was 35.

[Brief explanation of the drawing]

FIG. 1 schematically shows an EL device using the LB method of the prior art, FIG. 2 schematically shows an EL device according to the present invention, and FIG. 3 schematically shows an EL device according to the present invention. It is a diagram schematically showing a cross section of an EL element. 1; Transparent electrode 2: Luminescent layer 3: Back electrode 4: Luminescent compound 4': Donor 5; Luminescent compound 5' near axebuter-6
; Seal glass 7; Silicone insulating oil 8; Glass plate patent applicant
Canon Co., Ltd. Figure 1 5' Figure 3

Claims (1)

[Claims] In an EL device consisting of a two-layered light-emitting layer and two electrode layers in which at least one layer sandwiching the light-emitting layer is transparent, the first light-emitting layer is made of an electroluminescent organic compound (
A) and an organic compound relatively electron-accepting to compound (A) or a cumulative film thereof, and the second light-emitting layer is composed of an electroluminescent organic compound ( A) or a mixed monomolecular film consisting of a mixture of an electroluminescent organic compound having the same level of electronegativity as compound (A) and an organic compound that is electron-donating relative to compound (A), or an accumulation thereof. The above E, characterized in that it consists of a membrane.
L element.