JPS6143685A - El element - Google Patents

Abstract

PURPOSE:To provide an EL element having high luminance and long service life, and composed of a luminescent layer having double-layered structure, wherein each layer is composed of a thin film made of an oriented electroluminescent organic compound molecule having relatively different electronegativity from the other adjacent layer. CONSTITUTION:The objective EL element is composed of a double-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 luminescent layer is made of a mixed monomolecular film (or its built-up film) composed of a mixture of (i) an electroluminescent organic compound having higher electron affinity than the second layer and (ii) an electron donative organic compound having higher electron donative property than the above compound. The second luminescent layer is made of a mixed monomolecular film (or its built-up film) composed of a mixture of (iii) an electroluminescent organic compound having higher electron donative property than the first layer and (iv) an organic compound having higher electron affinity than the above compound.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) 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 two-layer structure,
each layer comprises at least one electroluminescent organic compound that differs in 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, Cu or Re F3.
ZnS containing (Re; rare earth ion) etc. as an activator
It consists of a light-emitting layer made of a light-emitting Bt material, and is structurally classified into powder type EL and S-molded EL depending on the basic structure of the light-emitting layer.

Among devices that have been put into practical use, thin 111EL generally has higher brightness than powder-type EL, but thin 11aEL has a light-emitting layer formed by vapor-depositing a light-emitting base material on a substrate, so it is not suitable for large-area devices. It has the drawbacks that it is difficult to manufacture and the manufacturing cost is very high.

For this reason, powder-type EL, in which a light-emitting base material, that is, ZnS, is dispersed in an organic binder, which has the highest 41:LC properties and costs only a few tenths of the cost of thin-film devices, is attracting attention. Ta. 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 discontinuous powder, when the luminescent layer is thinned, pinholes are likely to occur in the luminescent layer, making it difficult to reduce the layer thickness. The major drawback is 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. 58-17289.
However, it has not yet achieved sufficient performance in terms of luminance, power consumption, etc. However, recently, new optical and electronic devices have been developed by controlling the chemical structure and higher-order structure of organic materials. Research and development into materials for EC elements, piezoelectric elements, pyroelectric elements,
Organic materials, such as nonradiometric optical elements and ferroelectric liquid crystals, 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 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 Unexamined Patent Application Publication No. 1998-11-112 S2-3 S5 A7 V+. However, these EL elements have not yet achieved sufficient performance in terms of brightness, power consumption, etc. as actual EL elements, and furthermore, in the case of the fiEL elements, the density of carrier electrons or holes is very small. The probability of excitation of functional molecules due to carrier recombination or the like 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 purpose of the present invention is to provide a light-emitting layer of an EL device with special features.
This was achieved by combining certain materials and forming them into a specific configuration.

That is, 1 the present invention provides an EL device comprising a two-layered light emitting layer and two electrode layers sandwiching the light emitting layer, at least one of which is transparent, in which the light emitting layer of the tjsl has a second
consisting of a mixed monomolecular film or a cumulative film thereof consisting of a mixture of an electroluminescent organic compound that is electron-accepting relative to the light-emitting layer and an organic compound that is electron-donating relative to the compound; A mixed monomolecule in which the second light-emitting layer is composed of a mixture of an electroluminescent organic compound that is electron-donating relative to the first light-emitting layer and an organic compound that is electron-accepting relative to the compound. The above-mentioned EL element is characterized in that it is made of a film 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, 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 (I) and other compounds.

[(X-R,)YnZ], -φ-12(r) In the above formula, X is a hydrogen atom, a halogen atom, an alkoxy group, an alkyl ether group, a 21. phosphate group.

Silicic acid group, primary to tertiary amino group; metal salts thereof.

Primary to tertiary amine salts, acid salts; ester groups, sulfamide groups, amide groups, imino groups, quaternary amino groups, their mounds, hydroxyl groups, etc.; R1 has 4 to 30 carbon atoms, preferably 10 to 25 carbon atoms; is an alkyl group, preferably a linear alkyl group; m is 1 or a group (ILa is any substituent such as a hydrogen atom, an alkyl group, or an aryl group); φ
is a residue of an electroluminescent compound as exemplified later; R
Like X, 2 is a hydrogen atom or any other substituent; at least one of the one or more X, φ and R2 is a hydrophilic moiety, and at least one is a hydrophobic moiety. be.

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

(Margin below) Z=NH1O,S Z=CO,NHZ=CO,N
Hlo, 5Z=NH, 01S z = NH, O15Z=NH10, 5Z=S1Se
Z=Sb Se Z=S, SeZ
=NHlo,S Z=NH1αS Z=NH1
0, SM=Er, Tm Sm, Eu, Tb,
Z = 0, N true Ru M=A4 Ga, Ir, Ta, a=3 M=
Er, Sms EuM=Zn, Cd, Mg, p
b%a=2 Gd, Tb, DyTm, Yb M=Ers Sm, Eu, Gd M=Er,
Sm, EuTb, Dy % 1 unit], Yb
Gd% Tb, DyTm%y
b 2 = 0, S, SeO≦1)≦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 trainers or other compounds may be used as long as the same purpose is achieved.

The present invention is characterized in that the luminescent compounds as described above are used separately in the first luminescent layer and the second luminescent layer of the EL device of the present invention, depending on their electronegativity. That is, since the above-mentioned luminescent compounds have different electronegativities, when one or more of the above-mentioned compounds is employed as a luminescent compound for forming the first luminescent layer, one luminescence of these employed The luminescent compound is a compound that is particularly preferable as an electron donating compound among such luminescent compounds, which may be selected from the luminescent compounds having different electronegativity as the compound for forming the second luminescent layer. are mainly those having electron-donating groups such as primary-tertiary amine groups, hydroxyl groups, alkoxy groups, alkyl ether groups, or nitrogen heterocyclic compounds,
The electron-accepting compounds are mainly compounds having an electron-withdrawing group such as a carbonyl group, a sulfonyl group, a nitro group, or a quaternary amino group. In the present invention, such luminescent compounds can be used alone or in combination in each luminescent layer.

The present invention further provides an organic compound (hereinafter referred to as a donor) that is relatively more electron-donating than the luminescent compound forming the first layer as described above, preferably about tiJi! is added at a ratio of 1/10 to 1/100 mole to increase the electron acceptability of the first layer. i and the luminescent compound forming the second layer, an organic compound (hereinafter referred to as acceptor) that is relatively more electron-accepting than the second layer, preferably about 171
It is characterized in that it is added in a proportion of 0 to 17,100 moles to adjust the electron donating property of the second layer.

The above-mentioned acuhipter may be selected from the above-mentioned luminescent compounds, or may be selected from other organic compounds with high electron-withdrawing properties other than the above-mentioned ones.

In addition, the donor may be selected from the above-mentioned luminescent compounds, or may be selected from other organic compounds with large electron-donating properties other than those mentioned above.6For example, as the acceptor, the above-mentioned electron-withdrawing Similarly, the donor can be selected from various organic compounds having a large electron-donating substituent as described above.

The other elements forming the EL* element of the present invention, that is, the two electrode layers sandwiching one light emitting layer, can use any conventionally known elements, but at least the lIgJ
needs to be transparent. As the transparent electrode layer, any desired transparent electrode layer can be used, and preferred examples include transparent synthetic resins such as polymethyl methacrylate and polyester, and transparent films or sheets made of glass or the like with oxidation on the surface. indium, tin oxide,
It is coated entirely or in a pattern with a transparent conductive material such as indium tin oxide (ITO). When opaque electrodes are used on one side, these opaque electrodes may be conventionally known ones, and are preferably made of aluminum with a thickness of about 0.1 to 0.3 g, m. 8 coatings of silver, gold, etc. Further, the shape of the transparent #J 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. Moreover, the thickness of the transparent electrode layer is about 0. O1~0.
Approximately 2 pm is preferable; 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, problems will arise with transparency, lightness, compactness, etc. There is a risk.

In the EL element of the present invention, between the two electrode layers as described above,
It is obtained by forming a luminescent layer consisting of two layers using separately the electroluminescent compounds (containing an acceptor or a donor) having relatively different electronegativities as described above, and the formed two It is characterized in that the molecules constituting the layered light-emitting layer are arranged in 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 moderately maintained in a molecule with a structure that has a hydrophobic group, 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 to gradually increase the surface pressure to set a surface pressure suitable for producing a monomolecular film or a cumulative film thereof. By gently raising 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 of a monomolecular film is formed as a cumulative film having a desired degree of accumulation by repeating the operations described in i) η.

In addition to the above-mentioned vertical dipping method, the monomolecular film can be transferred to the substrate by methods such as the horizontal attraction method and the 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 above-mentioned vertical immersion method, when a substrate having a hydrophilic surface is pulled out of water in a direction across the water surface, a monomolecular film with the hydrophilic groups of the molecules facing the substrate is formed on the substrate. As mentioned above, when the substrate is moved up and down, the monomolecular film is piled up one by one 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 distance between each layer is A Y5 film is formed in which the hydrophilic group of the molecule and the hydrophobic group of one molecule (and the hydrophobic group face each other).On the other hand, in the horizontal attachment method, the substrate is attached horizontally to the water surface and transferred. in,
A monolayer is formed on the substrate with the hydrophobic groups of the molecules facing toward the plate side. In this method, even if the monolayers are accumulated,
There is no alteration in the orientation of the film-forming molecules, and an X-type film is formed in which the hydrophobic groups face the substrate in all layers.9On the contrary, a cumulative a film is formed in which the hydrophilic groups face the substrate in all layers. The 0-rotation cylinder method, which is called a Z-type membrane, is a method in which a monomolecular film is transferred to the surface of a 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 includes the above-mentioned acceptor or donor and uses materials for forming a light-emitting layer having different electronegativities, preferably by the above-mentioned 2F! This is obtained by forming a two-layer structure light-emitting layer between two electrode layers.

As mentioned in the section of the prior art, it is known that an EL element can be formed by the LB method, but the known method cannot produce an EL element with sufficient performance, and the inventor has conducted various research. As a result, the light-emitting layer has a two-layer structure, and each light-emitting layer is formed as a mixed monomolecular film or a cumulative film thereof using compounds with different degrees of air negativity containing acceptors or donors as described above. It has been found that the performance of the EL element is significantly improved.

One key feature of the present invention is that each light-emitting layer is
This embodiment is a mixed monomolecular film made of the luminescent material containing an acceptor or a donor. The EL device of this embodiment is prepared by first dispersing about 1 liter of the relatively electron-accepting material, including the donor, in a suitable organic solvent, such as chloroform, dichloromethane, dichloroethane, etc.
O~10゛2M concentration, and the solution is adjusted to an appropriate pH (for example, pt
1 to 8) on an aqueous phase, the solvent is removed by evaporation to form a mixed monomolecular film, and the mixture is transferred onto one electrode substrate using the LB method as described above to form the first layer. Dry thoroughly 1
Next, for the first layer thus formed, a relatively electron-donating material containing an acceptor is similarly transferred as a mixed monolayer onto the surface of the first light-emitting layer. The back electrode layer is obtained by depositing an electrode material such as aluminum, silver, or gold on the surface of the second layer, preferably by vapor deposition or the like. 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 monomolecular film of the EL device obtained in this way varies depending on the materials and types used, but is generally about 0.01 to 1 μm thick. suitable.

Another important aspect constitutes the light emitting layer of the EL device of the present invention. At least one of the two layers.

Preferably, both are cumulative films of the above-mentioned mixed single molecules 11. This embodiment can be obtained by accumulating the above-mentioned mixed single molecules 11 in various ways up to the required number of molecules by using the LB method described above.

The thickness of the light-emitting layer of the EL device obtained in this way, 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 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 water layer, ionic species, water temperature, monomolecular film transfer rate, or monomolecular film surface pressure.

The performance of the EL element formed as described above may deteriorate due to the influence of moisture and oxygen in the air, so it is best to make it into a moisture- and oxygen-resistant hermetically sealed structure using conventional means. Delicious.

The structure of the emissive layer of the undeveloped IJJ EL device described above is a super-S film, and it has a high degree of molecular order and functionality necessary for the operation of the EL device, and has excellent light emitting performance. It is something that you have. In addition, in terms of manufacturing, over a large area,
The thickness of the luminescent layer is uniform.

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 consisting of a single layer in the prior art, as schematically shown in FIG. light emitting layer and second
Since the light-emitting layer has a uniform interface, various interactions between these two layers with different electronegativity are extremely easy, and it exhibits excellent light-emitting performance that cannot be achieved with conventional technology. It is something to do. 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 extended significantly.

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 if a material has excellent luminescence properties, by using a material with excellent formation properties in one of the layers, it is possible to obtain a luminescent layer with excellent luminescence properties, film formability, and film strength. .

The EL device of the present invention described above can achieve excellent EL emission 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^ on the top surface of a 50 m square glass plate by sputtering. After thoroughly cleaning this film-forming substrate, Jayce -
Langmurr-Trough manufactured by Laebe1
A B The above compounds A and B were then dissolved in chloroform in a molar ratio of 100:l (10 mol /i) and then developed on the above water phase. After the solvent chloroform was removed by evaporation, the surface pressure was increased (30 dyne/am) 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 2C/■in), the mixed monomolecular film was transferred onto the substrate, and the mixed monomolecular IQ Only, 3, 5.9. and 1
A monomolecular cumulative film with five layers was created. 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, completely remove the mixed monomolecular film remaining on the surface of the aqueous phase and add a new one.

(Left below) Dissolve CD in chloroform at a molar ratio of 100:1.
3 mol/i) solution was developed on the aqueous phase. By the same method as above, a new I/%a easily mixable mixed monolayer film was deposited on the surface of the mixed monomolecular film and medium molecule cumulative film that had already been prepared in 3.5°9 and 15-layer stacks. A dense cumulative film was formed.

The substrate with the thin film formed as described above was placed in a vapor deposition tank, and the nuclide was once depressurized to a vacuum level of 10 Torr, and then the vacuum level was adjusted to 10 Tarr and the vapor deposition rate was set to 20λ/se.
In a, the fabricated EL device was evaporated onto the thin film with a thickness of 1500λ and used as a back electrode.The fabricated EL device was sealed with sealing glass as shown in FIG. 3, and then purified and desorbed according to conventional methods. The dehydrated silicone oil was injected into the seal to form four EL cells of the present invention. When an alternating current voltage 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 device of the present invention was an EL device with a lower driving voltage and good two-emission luminance characteristics compared to a conventional EL device using ZnS as a light emitting matrix.

Comparative Example 1 Example 1 except that only compound A was used as the luminescent compound in Example 1 and a mono-calendar was used.
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.

, lj [- Trap Eisei] Cumulative degree Enka Yu BE! LJf IJ11
! ! 1st layer 2nd layer 辡辷Ll (m
A/lηyu1 1 5V, 400Hz 4-0
0.303 3 10V, 400Hz
18 0.115 5 10V, 400Hz
25 0.1011 8 10V, 4
00Hz 28 0.0815 15
10V, 400Hz 27 0.
10 stop 1 starvation cumulative degree 2 5V, 400Hz 1 or less 0.
218 10V, 400Hz 5 or less
0.110 10V, 400Hz 5
Below 0.118 10V, 400Hz
5 or less 0.0830 1 (IV, 400
Hz 5 or less 0.08 Example 2 In place of compounds A, B, C and p in Example 1,
Using the following compounds E, F, G and H
FG
H and others were the same as in Example 1, and one EL element of the present invention (
However, when each cumulative number was 15) and evaluated under the same conditions as in Example 1, the luminance (Ft-L) was 36 at a current density of 0.13 mA/cta'.

[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 E'L element. l; transparent electrode 2; luminescent layer 3; back electrode 4; luminescent compound 4'; acceptor 5-luminescent compound 5'; donor 6
;Seal glass 7;Silicon insulating oil 8.Ni glass plate patent applicant Canon Co., Ltd. (""Nee representative patent attorney and 1) Katsuhiro 7! +? Snake;:V
τ;;f))A Figures 1 and 3

Claims (1)

[Claims] In an EL device consisting of a two-layered light-emitting layer and two electrode layers sandwiching the light-emitting layer, at least one of which is transparent, the first light-emitting layer is opposite to the second light-emitting layer. a mixed monomolecular film consisting of a mixture of an electroluminescent organic compound that is relatively electron-accepting and an organic compound that is electron-donating relative to the compound;
A mixed monomolecular film in which the light-emitting layer is made of a mixture of an electroluminescent organic compound that is electron-donating relative to the first light-emitting layer and an organic compound that is electron-accepting relative to the first light-emitting layer; The above-mentioned EL device is characterized in that it is made of a cumulative film thereof.