JPS6137891A - El element - Google Patents

Abstract

PURPOSE:To obtain high luminance by low-voltage driving, by forming a light- emitting layer into dual-layer structure and forming each layer as mixed monomolecular films or monomolecular cumulative films from compounds different in electronegativity from each other including an acceptor or donor. CONSTITUTION:A light-emitting layer 2 of dual-layer structure is formed between a transparent electrode 1 and a rear electrode 3. The first light-emitting layer is formed as mixed monomolecular films or monomolecular cumulative films consisting of a mixture of an electron-accepting, electroluminescent org. compd. 4 such as a compd. of the formula I and an org. compd. 4', such as a compd. of the formula II, which is more electron-accepting than the compd. 4. The second light-emitting layer is formed as mixed monomolecular films or monomolecular cumulative films consisting of a mixture of an electron-donating, electroluminescent org. compd. 5, such as a compd. of the formula III, and an org. compd. 5', such as a compd. of the formula IV, which is more electron- donating than the compd. 5, to obtain the purpose EL element.

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 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, Cu or Re F3.
ZnS containing (Re; rare earth ion) etc. as an activator
It consists of a light-emitting layer having a light-emitting base material, and the light-emitting layer is broadly classified into powder type EL and thin film type EL depending on the basic structure of the light emitting layer.

Among devices that have been put into practical use, thin-film ELs generally have higher brightness than powder-type ELs, but because thin-film ELs form a light-emitting layer by vapor-depositing a light-emitting base material onto a substrate, they are 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 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 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, pinholes are likely to occur in the luminescent layer when the luminescent layer is thinned.
It has a major drawback in that it is difficult to reduce the layer thickness, and therefore sufficient brightness characteristics cannot be obtained. Recently, an improved type of element 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 JP-A-58-172891.
It has not yet achieved sufficient performance in terms of luminance, power consumption, etc. On the other hand, 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.
Organic materials, such as piezoelectric elements, pyroelectric elements, nonradiometric optical elements, and ferroelectric liquid crystals, have been announced that are comparable to or superior to metals and inorganic materials. 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. The EL element formed on the substrate was disclosed in Japanese Patent Application Laid-Open No. 52-35587.
It is proposed in the Publication No. However, these EL devices have not achieved sufficient performance in terms of brightness, power consumption, etc. as actual EL devices, and furthermore, in the case of organic EL devices, the density of carrier electrons or holes is very low. 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, it is an object of the present invention to solve the above-mentioned drawbacks of the prior art, to provide an EL element that is inexpensive and easy to manufacture, which can provide sufficiently moderate light emission even when driven at a low voltage. 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.

That is, 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. A mixed monomolecular film consisting of a mixture of an electroluminescent organic compound that is electron-accepting relative to the layer and an organic compound that is electron-accepting relative to the compound, or a cumulative film thereof, and a second A mixed monomolecular film in which the 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-donative relative to the first 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, 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, tomato earth complexes, and derivatives of these compounds. can. 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 parenteral moiety in its structure. It is a compound having a woody part (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,), Zl, -φ-R2(I) In the above formula, X is a hydrogen atom, a halogen atom, an alkoxy group,
Alkyl ether groups, nitro groups; carboxyl groups, sulfonic acid groups, phosphoric acid groups, silicic acid groups, primary to tertiary amino groups; metal salts thereof, primary to tertiary amine salts, acid salts: ester groups,
Sulfoamide group, amide group, imino group, quaternary amine group and their salts, hydroxyl group, etc.: R has 4 to 30 carbon atoms
, preferably 10 to 25 alkyl groups, preferably linear alkyl groups: m is 1 or 2, n is an integer of 1 to 4; Z is a direct bond or 10-1-s-1 -Zan R-CH2 Crystal R5--SOYN R3, -CO-1-c
A linking group such as oo- (R3 is a hydrogen atom, an alkyl group,
8
At least one of one or more of X, φ and R2
Each is a woody moiety, and at least one is a hydrophobic moiety.

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

(Margin below) Z=N)T, 0.5Z=CO, NHZ=CO1NH,0
1SO・Z=NH,01S Z=NH10,S Z=NH,01
SZ=S% Se Z=S, Se
Z=S%5ez=NH,0,S Z=NH
,Q S Z=NH,0,S1'i? A4 Ga+
Tr* Ta, a=3 M: Er, Sm, Eu
M2Zn, Cd, Mg, pb, a=2
Gd, Tb, DyTm, Yb M2Er+ Sm, Eu, Gd M=Ert
Smi EuTb, Dy, Tm, Yb G
d%Tb%DyTm, Yb-2-O, 51SeO≦p≦2 The following luminescent compounds can be used alone or as a mixture in each luminescent layer in the present invention. Note that these compounds are examples of preferable compounds, and it goes without saying that other derivatives or other compounds may be used as long as the same purpose is achieved.

The present invention is characterized in that luminescent compounds such as those listed in L 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 luminescent compounds as described in 1- above have different electronegativities, when one or more of the above compounds is employed as the luminescent compound for forming the first luminescent layer, As for the luminescent compound, the luminescent compounds having different electronegativities may be selected as the compound for forming the second luminescent layer. Among such luminescent compounds, particularly preferable electron-donating compounds are electron-donating compounds such as primary to tertiary amine groups, hydroxyl groups, alkoxy groups, alkyl ether groups, etc. The main ones are those having a j-group or nitrogen heterocyclic compounds, and examples of electron-accepting groups include electron-withdrawing groups such as carbonyl groups, sulfonyl groups, cotro groups, and quaternary amine groups. 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 present invention further preferably includes an organic compound (hereinafter referred to as an acceptor) that is relatively more electron-accepting than the luminescent compound forming the first layer as described above, preferably about In addition, in a proportion of 1710 to 17100 mol, to further strengthen the electron-accepting property of the first layer, and to the luminescent compound forming the second layer, an organic compound that is relatively more electron donating than the luminescent compound forming the second layer. (hereinafter referred to as donor) is preferably about 1,710 to 1,710 per mole of the former.
It is characterized in that it is added at a ratio of 1/100 mol to further strengthen the electron donating property of the second layer.

The acceptor as described above may be selected from the above-mentioned luminescent compounds, or may be selected from other organic compounds with high electron-withdrawing properties other than those mentioned above. Further, the donor may also be selected from the above-mentioned luminescent compounds, or may be selected from other organic compounds with high electron-donating properties other than the above-mentioned ones. for example,
The acceptor is selected from various compounds having a large electron-withdrawing substituent as mentioned above, and the donor is selected from various organic compounds having a large electron-donating substituent as mentioned above. be able to.

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, and preferred examples include 1, 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. 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 be of conventionally known types, and are generally and preferably made of aluminum, silver, or gold with a thickness of about 0.1 to 0.3 pm. This is a vapor-deposited film such as Further, the shape of the transparent electrode layer or the opaque electrode layer may be any shape such as a plate shape, a belt shape, or a cylindrical shape, and can be selected depending on the purpose of use. Moreover, the thickness of the transparent electrode layer is about 0. A thickness of about O1 to 0.2Ii, m 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, transparency, lightness, and compactness will be insufficient. There is a risk that problems may occur.

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 mixed monomolecular film or a cumulative film thereof, in which the molecules are 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). In this LB method, when a molecule has a structure that has a lignophilic group and a hydrophobic group in the molecule, and the balance between the two (balance of amphiphilicity) is maintained appropriately, the molecule is placed on the water surface. This is a method of forming a monomolecular film or a cumulative film thereof by utilizing the fact that the wood group faces downward to form a monomolecular layer. Specifically, to prevent the monomolecular film spread on the water layer from spreading too much by freely diffusing the water phase, a partition plate (or float) is provided to limit the spread area and allow the film material to gather. 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. A monomolecular film is manufactured in the following two steps, and a cumulative film of a monomolecular film is formed by repeating the above-described operations as a cumulative film having a desired degree of accumulation.

In addition to the vertical dipping method described in -1-, 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 above-mentioned vertical immersion method, when a substrate with a hydrophilic surface is pulled out of water in a direction across the water surface, a monomolecular film is formed on the substrate with the tree-philic groups of the molecules facing the substrate. When the substrate is moved up and down as described above, one monolayer layer is overlapped with each step. Since the direction of the film-forming molecules is reversed between the pulling process and the dipping process, this method creates a Y-shaped film in which the wood-loving groups and wood-loving groups of the molecules and the hydrophobic groups of the molecules face each other. is formed. 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 accumulated, there is no change in the direction of the film-forming molecules, and an X-shaped film is formed in which the hydrophobic groups face the substrate side in all layers. On the other hand, a cumulative film in which the hydrophilic groups in all layers face the substrate side is called a Z-type film. The rotating cylinder method 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 to 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 uses a material for forming a light emitting layer which contains the acceptor or donor as described above and has a different electronegativity, and preferably forms two electrode layers as described above by the LB method as described above. This is obtained by forming a light emitting layer with a two-layer structure between them.

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 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 electronegativities containing acceptors or donors as described above, thereby improving the EL of the conventional technology. It was discovered that the performance of the device was significantly improved.

One important embodiment of the present invention is an embodiment in which each luminescent layer is a mixed monolayer of the luminescent material containing an acceptor or donor. The EL device of this embodiment is prepared by first adding a material that is electron-accepting relative to the other layer containing the acceptor in a suitable organic solvent such as chloroform, dichloromethane, dichloroethane, etc.
The solution is dissolved at a concentration of about 0 to 16M, and the solution is adjusted to an appropriate pH (for example, pH about 1), which may contain various metal ions.
~8) Develop it on the human face, remove the solvent by evaporation to form a mixed monomolecular film, transfer it to one electrode substrate as the first layer using the LB method as described above, and dry it thoroughly. Then, for the first layer formed in this way, a relatively electron-donating material containing a donor is similarly transferred to the surface of the first light-emitting layer as a mixed monolayer. Then, an electrode material such as aluminum, silver, or gold is deposited on the surface of the second layer, preferably by vapor deposition, to form a back electrode layer. In addition, the first
The formation order of the layer and the second layer may be reversed to the same effect.

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 17 Lm 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 is obtained by accumulating the mixed 1i molecular films as described above in a systematic manner 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 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 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 adhesive force, the surface of the substrate may be treated in advance, or a suitable adhesive layer may be provided between the substrate and the light emitting layer. Furthermore, the adhesive force can be strengthened by adjusting various conditions such as the material for forming the light-emitting layer, the pH of the water layer used, the ion species, the water temperature, the transfer rate of the monomolecular film, or the surface pressure of the monomolecular film. can.

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 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 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 if a material has excellent luminescence properties, 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 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 Å on the surface of a 50 mm square glass plate by sputtering. After thoroughly cleaning this film-forming substrate, Joyce-L
Langmiur-Trough4 manufactured by oebe1
containing 4×10-' mol of Cdcff2 at pH 6,5
immersed in an aqueous phase prepared in next.

A B The above compounds A and B were dissolved in chloroform at a ratio of Zoo:1 (10 mol/a), and then developed into a "water phase". After the solvent chloroform was removed by evaporation, the surface pressure was increased (30 dyne/am) 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/n+in), and the i-coated monomolecular film was transferred onto the substrate, and only the monomolecular film was 3.5.9, and mixed monomolecular cumulative films with 15 layers were 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 monomolecular film remaining on the surface of the aqueous phase, and newly dissolve CD in chloroform at a mixing ratio of 10:1.
l/Jj): The solution was developed on the aqueous phase.

By the same method as above, a new functional mixed monomolecular film, a cumulative film of 3.5.9 and 15 layers of mixed monomolecular film was deposited on the surface of the mixed monomolecular film and mixed monomolecular cumulative film that had already been created. Formed.

The substrate having the thin film 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 105 Torr, and the vapor deposition rate was 20A/2.
sec, AI was evaporated onto the thin film to a thickness of 1500 nm to form a back electrode. As illustrated in FIG. 3, the produced EL element is sealed with a sealing glass, and then purified, degassed, and dehydrated silicone oil is injected into the seal according to the conventional method to produce the five EL elements of the present invention. formed a cell.

When an alternating current voltage was applied to these EL cells, total EL light emission having a color unique to the dye was obtained. Table 1 shows the evaluation results.
Shown below.

The EL element of the present invention described in -F 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.
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.

``Shinongou'' Cumulative level 1 luxury II 1 delivery IL Toyoto 1st layer 2nd layer 0shi1↓〕(mA/cm')1
1 3V, 400Hz 3.0
0.183 3 10V, 400Hz
20 0.145 5 10V, 400Hz
28 0.139 9 10V, 40
0Hz 32 0.1115 15
10V, 400Hz 33 0.
10 Flood Remains” Cumulative Table 2 3V, 400Hz 1 or less B
IOV, 400Hz 5 or less 10 10V, 4
00Hz tt18 10V, 4001(z
tt30 10V, 400■z〃Example 2 In place of compounds A and B in Example 1, the following compounds E and F were used, and E ,
The cumulative number of each was 15) and evaluated under the same conditions as in Example 1. At a current density of 0.09 mA/cm2, the luminance (
Ft-L) was 35.

[Brief explanation of drawings]

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. l; Transparent electrode 2; Luminescent layer 3; Back electrode 4; Luminescent compound 4'; Acceptor 5; Luminescent compound 5': Donor 6
; Seal glass 7; Silicone insulating oil 8 Glass plate M1 Figure 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 relatively electron-accepting to the compound, or a cumulative film thereof, and a second
A mixed monomolecular film in which the 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-donating relative to the compound. or a cumulative film thereof.
L element.