JPS6160776A - EL element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an EL device using electrical light emission, that is, EL, and more specifically, the present invention relates to an EL device that uses electrical light emission, that is, EL, and more specifically, a light emitting layer having a multilayer structure,
Each calendar has at least [1 electroluminescent organic compound,
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 ReF.
Z containing y (Re; rare earth ion) etc. as an activator
It consists of a light-emitting layer using nS as a light-emitting base material, and due to the difference in the basic structure of the light-emitting layer, there are two types: powder type EL and eight-film type EL.
It is broadly categorized structurally.

Among the elements that have been put into practical use, Thin II! EL generally has higher brightness than powder-type EL, but since fl@EL forms a light-emitting layer by vapor-depositing a light-emitting base material onto a substrate, it is difficult to manufacture large-area devices, and the manufacturing cost is high. It had the disadvantage that it became 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. In general.

In full EL light emission, the thinner the thickness of one light emitting layer, the better the light emission characteristics. However, in the case of the powder type EL, since one luminescent base material is a discontinuous powder, when the luminescent layer is thinned, pinholes tend to occur in the luminescent layer, making it difficult to reduce the thickness of one layer. The major drawback is that sufficient brightness characteristics cannot be obtained. Recently, an improved device in which an intermediate current conductor layer made of a vinylidene heptafluoride 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 products, that are comparable to or surpass metals and inorganic materials have been developed. 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"J# children have not achieved sufficient performance as a real EL element in terms of brightness, power consumption, etc. Furthermore, in the case of organic EL elements, the density of carrier electrons or holes is extremely low. Therefore, the probability of excitation of functional molecules due to carrier recombination is extremely small, and efficient light emission cannot be expected.

(Disclosure of the Invention) Therefore, one object of the present invention is to eliminate the drawbacks of the prior art as described above, 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. 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 multilayered light emitting layer and two electrode layers sandwiching the light emitting layer, at least one of which is transparent. The above-mentioned EL element is characterized in that it is formed by alternating two layers with 4F3 or more edges.

First calendar: A monomolecular film or a cumulative film thereof comprising at least one electroluminescent organic compound that is electron-accepting relative to the second calendar.

Second layer: A monomolecular film or a cumulative film thereof comprising at least one electroluminescent organic compound that is electron-donating relative to the first layer.

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 has an electronic system and TI! It is a compound that can be excited gaseously, for example, basically fused polycyclic aromatic hydrocarbons, p-
Terphenyl, 2,5-diphenyloxazole, 1.
4-bis(2-methylstyryl)-benzene, xanthine, coumarin, acridine, cyanine dye, benzophenone, phthalocyanine and its metal complex, porphyrin and its metal complex, 8-hydroxyquinoline and its gold-am compound, organic ruthenium complex, #! Examples include 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.

can be given.

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,), Z ]]? L-φ-R, (I) In the above formula, X is a hydrogen atom, a halogen atom, an alkoxy group, a 7-alkyl ether, a carboxyl group, a sulfonic acid group, a phosphoric acid group, a geic acid group, or a 1-3 amino acid group. Groups; metal salts of these, primary to tertiary amine salts, salts: ester groups, sulfamide groups, amide groups,
imino group, quaternary amine group, salts thereof, hydroxyl group, etc.; R is an alkyl group having 4 to 30 carbon atoms, preferably 10 to 25 carbon atoms, preferably a linear alkyl group; m
is a linkage such as 1 or 1SO1N R,, -CO-, -COO-, etc. (R, is a hydrogen atom, an alkyl group, an arbitrary substituent such as a 7-aryl): φ is exemplified later. Like! is a residue of an electroluminescent compound; R2, like X, is a hydrogen atom or any other substituent; at least one of one or more of X, φ and R2 is a phyllophilic moiety and at least 1 is a hydrophobic moiety.

Preferred examples of compound b of general formula CI) and other compounds as φ are as follows (
Bottom margin) Z=NH. O. SZ=
C.O. NH Z=CO, NH. O. SZ=NH
,O%S -NH,O,S Z=NH. O
．． SZ=S%Se z==sl Sez
= NH, O. S Z = NH, αS Z
=NH,0. S5 mouth, AtC1, YbC1 M=Er, Tm Sm, Eui Tb, z=
o, NnM=A4 Ga, Ir, Ta, a=3
M=Er, Sm, EuP? Zn, Cd, Mg,
pb, a=2 Gd, Tb, DyTm,
Yb M=Er, Sm, Eu, Gd M=Er, Sm
, EuTb, Dy, Tm, Yb Gd, T
b, DyTm, Yb Z=Ot 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 derivatives 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 separately in the first luminescent layer and the second luminescent layer of the EL device of the present invention according to their electronegativity, and these layers are alternately used. 4
It is characterized by forming a multilayered light-emitting layer by laminating more than one layer.

That is, since the above-mentioned luminescent compounds each have different TL air negativity, when one or more of the above-mentioned compounds is employed as a luminescent compound for forming the first luminescent layer, the employed luminescent 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 to tertiary amino groups, hydroxyl groups, alkoxy groups, alkyl ether groups, etc., or nitrogen heterocyclic compounds, and electron-accepting ones include: Compounds having electron-withdrawing groups such as carbonyl groups, sulfonyl groups, nitro groups, and quaternary amine groups are the main ones. 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 sandwiching one light emitting layer, can use any conventionally known elements, but at least one of the layers must be transparent. There is a need. As the transparent electrode, any transparent type G4W that has the same purpose as before can be used, and the preferred one is 1, for example, a transparent synthetic resin such as polymethyl methacrylate or polyester, or a transparent film or sheet made of glass or the like. indium oxide, tin oxide,
The entire surface or pattern is coated with a transparent conductive material such as indium-tin-oxide (rTo). If opaque electrodes are used on one side, these opaque electrodes may be of conventionally known opaque electrodes, and are generally and preferably made of aluminum, silver, gold, etc. with a thickness of about 0.1-0.3 gm. Steaming! 1III. 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. Further, the thickness of the transparent electrode 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, 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,
The first layer and the second R are formed using electroluminescent compounds having relatively different electronegativity as described above, and four or more layers of these are alternately laminated to form a multilayer light emitting layer. It is characterized in that the molecules constituting the light emitting layer of the formed multilayer structure are a monomolecular film or a 8I 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 Φ-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, 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 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 its composite MFN 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 produced in the above manner, a cumulative film of a monomolecular film is formed by repeating the above-mentioned operations as a cumulative film having a desired degree of accumulation.

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 the substrate side. As mentioned above, when the substrate is moved up and down, one monomolecular film is overlapped in each step.The direction of the film-forming molecules is reversed between the lifting step and the dipping step, so according to this method, the distance between each layer is A Y-shaped film is formed in which the woody groups of the molecules and the hydrophobic groups of one molecule of the woody groups 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 when monomolecular films are accumulated, there is no change in the orientation of the film-forming molecules, and in all layers, an X-type IKI with hydrophobic groups facing the substrate is formed. In the 0-rotation cylinder method, a $ stack in which the wood-philic group faces the substrate is called a Z-type film, 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 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 material for forming a light-emitting layer is preferably formed into a multilayer structure consisting of compounds having different electronegativities between the two electrode layers as described above, using the above-mentioned LB method. It is obtained by forming .

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 inventors of the present invention conducted various research. As a result, the light emitting layer has a multilayer structure of four or more layers, and each light emitting layer is formed as a monomolecular film or a cumulative film thereof using compounds with different electronegativities as described above.
It has been found that the performance of the conventional EL element is significantly improved.

One important embodiment of the present invention is an embodiment in which each luminescent layer is a monomolecular film made of the luminescent material. The EL device of this embodiment is prepared by first dispersing a material that is relatively electron-accepting to the second layer in a suitable organic solvent such as chloroform, dichloromethane, dichloroethane, etc.
~IOM, and the solution is adjusted to an appropriate pH (e.g., pH about 1~IOM), which may contain various metal ions.
8) was developed on the aqueous phase, the solvent was evaporated to form a monomolecular film, and the monomolecular film was transferred onto one electrode substrate using the LB method as described above. ! 1, sufficiently dried, and then the material relatively electron-donating to the first R formed in this way was similarly formed into a monomolecular film.
It is transferred to the surface of the light-emitting layer and laminated as a second layer. This operation is repeated twice to form a multilayer light emitting layer, and then an electrode material such as aluminum, silver, gold, etc. is deposited on the surface of the second layer, preferably by vapor deposition or the like. This can be obtained by forming a back electrode layer on the back electrode layer.

The number of laminated layers of the light-emitting layer composed of a multilayer monomolecular film of ELK molecules thus obtained is generally preferably about 4 to 400, and the total thickness of the light-emitting layer depends on the material used. Although it varies depending on the type, a thickness of about 0.01 to lpm is generally suitable.

Another important aspect is that at least one of the layers constituting the light emitting layer of EL511 of the present invention! , preferably all layers are r8-like, which is a cumulative film of the monolayers described above. This embodiment can be obtained by accumulating the above monomolecular film layer by layer in various ways up to the required number of layers using the LB method.

vL of each layer of the light emitting layer of the EL device obtained in this way
The number of MJ is preferably about 4 to 400, and the cumulative number of each layer is preferably about 2 to 200, and the total thickness can be changed arbitrarily, but in the present invention, the total thickness is 1. The preferred range is about 0.01 to 17 zm.

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, 1. 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.1. Various conditions such as the pH of the water layer, ionic species, water temperature, monomolecular film transfer rate, or monomolecular film surface pressure! $! The adhesive strength can also be strengthened by the I part.

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 recommended to make it into a moisture-resistant, enzymatically sealed structure using conventionally known means. desirable.

In the EL device of the present invention as described above, the structure of the light emitting layer is as follows:
! It is a thin film and has a high degree of molecular order and functionality necessary for the operation of an EL device, and provides excellent light emitting performance. In terms of manufacturing, the thickness of one emitting layer is uniform over a large area, making it possible to produce an EL element without defects, and it can be manufactured at room temperature, normal pressure, or under conditions close to that, making it comparatively This method has the advantage that it is possible to use light-emitting functional materials that are not particularly heat resistant.

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 that is a single layer, as shown schematically in FIG. luminescent layer and t
Since the light-emitting layer of JS2 has a uniform interface and these layers are stacked in four layers, various interactions between the two living rooms with different electronegativities are extremely easy, and compared to conventional technology. It exhibits an excellent luminous performance that cannot be achieved with other materials. In other words, by variously changing the difference in electronegativity between the first light-emitting layer and the second light-emitting layer, the luminescence intensity can be improved, or the luminescence color can be arbitrarily changed, and the service life can also be improved. It can be lengthened 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. is 1
Even if the material is excellent in luminescence, by using a material with excellent film-forming properties in one of the layers, a luminescent layer with excellent luminescence, 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. It should be noted that the middle part of the sentence is based on the amount of fi.

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 a sputter-linda method. After thoroughly cleaning this film-forming substrate, Joyce-L
Langmuir-Trough4 manufactured by oebe1
The sample was immersed in an aqueous phase whose pH was adjusted to 6.5.

(A) Next, the carbazole compound (A) was dissolved in chloroform (10 layers/Jl), and then developed in the aqueous phase. After removing the solvent chloroform by evaporation, the surface pressure was increased (30 dyne/c intestine).1. The above molecules were deposited in the form of a film. Furthermore, 4XIO of/41 CdC:I
, and adjusted to pH 8,0.
muir-Trough4 (1) On the aqueous phase, (B) a chloroform solution (10 mo
lXJL) was developed and a monomolecular film was deposited in the same manner as above. Thereafter, while keeping the surface pressure constant, the film-forming substrate was gently raised in a direction across the water surface (rising rate of 2 cw/sin), and the monomolecular film was transferred onto the substrate.

Next, the substrate was left to stand for 30 minutes, dried, and then gently immersed in the aqueous phase in which the carbazole monolayer had been deposited at a lowering rate of 2'cI/sin), thereby converting the monolayer into the pre-precipitated monolayer. By repeating 0 or more operations of layering grains on a pyrene film, pyrene monomolecular films and carbazole monomolecular films were alternately laminated in 4 layers, 7 layers, 9 layers, and 15 layers.

The substrate with the thin film formed as described above was placed in a vapor deposition tank, and the nuclide was heated to a vacuum level of 10 Torr at 20λ/s.
At ea, At was evaporated onto the thin layer M1h with a film thickness of L500A to form a back electrode.9 The fabricated EL element was sealed with a sealing glass as illustrated in FIG. 3, and then purified and purified according to the conventional method. Degassed and dehydrated silicone oil was injected into the seal to form four EL light emitting cells of the present invention. When evening wave voltage was applied to these EL cells, EL light emission having a color characteristic of the dye 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 better luminance characteristics than the conventional EL device using ZnS as a light emitting matrix.

Example 2 An EL device of the present invention was produced in the same manner as in Example 1, except that CD was used and the other procedures were the same as in Example 1. The evaluation results are shown in the first page.

Example 3 The EL of the present invention was produced in the same manner as in Example 1, except that the carbazole layer and pyrene layer in Example 1 were each made into a cumulative film with a cumulative degree of 5, and the number of laminated layers was 4,7,9,15. I got the element. Table 1 shows the results of evaluation in the same manner as in Example 1.

Comparative Example 1 In Example 1, except that only Compound B was used as the luminescent compound and a single layer was used, the rest was Example 1.
Comparative EL Miko was obtained in the same manner as in Example 1, and 3f valence was obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

Comparative Example 2 In Example 2, except that Compound Rino was used as the luminescent compound and a single layer was used, the other changes were as in Example 2.
A comparative EL device was obtained in the same manner as in Example 2, and evaluated in the same manner as in Example 2. The evaluation results are shown in Table 1.

Itto-ran-1-J Ara-1 shift] Yuyte degree 1111 u IL Kasa" square plate giant red! 4 4V, 400Hz 20 0.1
07 5V, 400Hz 28 0.
109 7V, 400Hz 32 0
．． 1115 10V, 400Hz 38
4 4V, 400Hz 22 0.0
137 5V, 400Hz 24
0.109? V, 40
0Hz 28 0.1O1510V,
400Hz 32 0.09 笈亙亘】(
The cumulative degree of each layer is 5) 4 10V, 400Hz 25
0.097 18V, 400Hz
35 0.088 20V
, 400) 1z 40 0.0815
30V, 400Hz 50
0.08 no Higashijo” (cumulative degree) 4 4V, 400Hz 10 0.1
07 5V, 400Hz 14
0.109 7V, 400H
z 20 0.1115 1
0V, 400Hz 25 0.12 (cumulative degree) 4 4V, 400Hz 12
0.107 5V, 400Hz
13 0.108 7V, 400H
z 15 0.0915
10V, 400Hz 20 0.
09

[Brief explanation of drawings]

FIG. 1 diagrammatically shows an EL element based on the LB method of the prior art, FIG. 1 schematically shows a cross section of an EL element of the invention. 1: Transparent electrode 2: Luminescent layer 3: Back electrode 4; Luminescent compound 5: Luminescent compound 6: Luminescent compound 7; Seal glass 8
: Silicone insulating oil 9; Glass plate Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] In an EL device comprising a multilayered light emitting layer and two electrode layers sandwiching the light emitting layer, at least one of which is transparent, the above light emitting layer has the following first layer and the following first layer. The above-mentioned EL device is characterized in that it is formed by repeatedly laminating four or more layers of two layers alternately. First layer: a monomolecular film or a cumulative film thereof consisting of at least one electroluminescent organic compound that is electron-accepting relative to the second layer. Second layer: a monomolecular film or a cumulative film thereof comprising at least one electroluminescent organic compound that is electron-donating relative to the first layer.