JPS6137885A - El element - Google Patents

Abstract

PURPOSE:An EL element which emit light with very high luminance even by low-voltage driving and can be easily manufactured, which is constituted of a light-emitting layer contg. a molecular film using both an electroluminescent org. compd. and an org. compd. different in electronegativity, and an electrode layer. CONSTITUTION:An EL element comprising the hereinafter described light-emitting layer and two electrode layers holding it, of which at least one layer is transparent. Said light-emitting layer comprises a mixed monomolecular film or monomolecular cumulative film consisting of a mixture of an electroluminescent org. compd. and an org. compd. different in electronegativity. Said electroluminescent org. compd. is a compd. having high light emitting quantum effect and a pi-electron system readily affected by external perturbation, and being capable of electrical excitation, such as a condensed polycyclic aromatic hydrocarbon, a cyanine dyestuff or benzophenone. As said org. compd. different in electronegativity, any compd. electron-donating to or electron-accepting from the light-emitting compd. may be used.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an EL device using electroluminescence, that is, EL, and more specifically, the present invention relates to an EL device using electroluminescence, that is, EL. The present invention relates to an EL element comprising a thin film in which a mixture of the organic compound and at least one organic compound having a different electronegativity is arranged with highly ordered molecular orientation.

(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, nonradiometer 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 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 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 object of the present invention is to use together at least one type of electroluminescent organic compound and at least one type of organic compound having a different electronegativity from the organic compound as a material for forming a light-emitting layer of an EL element, and to This was achieved by employing thin film production technology to arrange the molecules of the above-mentioned mixed material in a highly ordered structure to form the light-emitting layer of the EL device.

That is, the present invention provides an EL element comprising a light-emitting layer and two electrode layers sandwiching the light-emitting layer, in which at least one of the electrode layers is transparent, wherein the light-emitting layer has at least one type of electroluminescent material. The above-mentioned EL device is characterized in that it is composed of a mixed monomolecular H composed of a mixture of an organic compound and at least one kind of organic compound in which the organic compound has a different electronegativity, 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-terfecol, 2.5-diphenyloxazole, 1.4-
Bis(2-methylstyryl)-benzene, xanthine,
Examples include coumarin, acridine, cyanine dye, pentuphenone, phthalocyanine and its gold JIM form, porphyrin and its metal complex, 8-hydroxyquinoline and its metal complex, organic lutecholam complex, organic rare earth complex, and derivatives of these compounds. be able to. 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 having a quinone structure, such as tetracyanoquinodimethane and tetracyanoethylene, can be mentioned.

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-u,)T, 1ZITL-φ-Rz
(1) X in the above formula is a hydrogen atom,
Halogen atoms, alkoxy groups, alkyl ether groups, nitro groups; carboxyl groups, sulfonic acid groups, phosphoric acid groups, silicic acid groups, primary to tertiary amino groups: metal salts, primary to tertiary amine salts, acid salts thereof; Ester group, sulfamide group, amide group, imino group, quaternary amine group and their salts, hydroxyl group, etc.: R1 has 4 to 30 carbon atoms, preferably 10 to 2 carbon atoms.
5 alkyl groups, preferably a linear alkyl group; m is 1 or a group (R3 is any substituent such as a hydrogen atom, an alkyl group, or an aryl); φ is an electric field as exemplified later. is a residue of a luminescent compound; like X, R2 is a hydrogen atom or any other substituent, and at least one of the 81 or more X, φ and R2 is a phyllophilic moiety; And at least one is a hydrophobic moiety.

Examples of preferable compounds and other compounds of general formula CI) are as follows.

(Margin below) Z=NH, O, S Z=CO, NHZ=CO, NH
,0,5Z=NH,0,3 Z=NH,0,S Z=NH,
01SZ-5i Se 725% Se
Z-8s 5eZ=NH,0,S Z=N
H, αS Z=NH, O, SM=Mg i Z n
* S n s AtCl M : Hz * B
e * Mgi Ca * CdSn, AlC1,
YbC1 u M=A4 Gab Ir%Ta, a=3 1'i!
Erb Sm, EuM-Zn, Cd, Mgv pb%a
=2 Gd, Tb, Dyms Yb Tb, Dy, Tm, Yb Gd, Tb, D
yTm, Yb 2=0, S, SeO≦p≦2 The above luminescent compounds can be used alone or as a mixture 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.

In the present invention, the organic compound used in combination with the luminescent compound as described above (hereinafter referred to as a co-acting compound) has a different electronegativity from the luminescent compound and has less electrical energy than the luminescent compound. Any compound that can electrically interact with the luminescent compound under loaded conditions and can donate electrons to or accept electrons from the luminescent compound But that's fine. For example, the co-acting compound can be selected from the above-mentioned luminescent compounds and other non-luminescent compounds.

That is, since the above-mentioned luminescent compounds have different electronegativity, when one or more of the above-mentioned compounds are employed as a luminescent compound, the employed luminescent compounds are different in electronegativity. A different luminescent compound or another compound may be selected as the co-acting compound. Particularly preferred compounds as such co-acting compounds include those having electron donating groups such as primary-tertiary amine groups, hydroxyl groups, alkoxy groups, and alkyl ether groups; The main compounds are ring compounds, and the main electron-accepting compounds are compounds having electron-withdrawing groups such as carbonyl groups, sulfonyl groups, nitro groups, and quaternary amine groups. Such co-acting compounds are preferably used in the present invention in a molar ratio of about 0.1 to about 10 per mole of luminescent compound, preferably in a molar ratio of 1:1. Such co-acting compounds can also be used in the present invention alone or as a mixture of two or more.

The other elements forming the EL element of the present invention, that is, the two electrode layers sandwiching the light emitting layer, can use any conventionally known elements, but at least one layer must be transparent. There is. As the transparent electrode, 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, etc. with indium oxide on the surface. , tin oxide, indium-tin-oxide (ITO), or the like, on the entire surface or in a pattern. When using opaque electrodes on one side, these opaque electrodes may also be of conventionally known types, and the general and preferred ones are:
The thickness is about 0.1~0. ．． 3iLm aluminum, silver,
It is a vapor-deposited film of gold, etc. 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 0.21 Lm. If the thickness is less than this range, the physical strength and electrical properties of the element itself will be insufficient, and if the thickness is more than the above range, Otherwise, problems may arise in terms of transparency, light weight, compactness, etc. □The EL device of the present invention can be obtained by forming a light-emitting layer between the two electrode layers as described above using a mixture of the electroluminescent compound as described above and the synergistic compound as described above. It is characterized in that the molecules constituting the formed light-emitting layer are a mixed monomolecular film or a cumulative film thereof, in which 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 hydrophilic 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 monomolecular layer is formed with the functional groups facing downward. 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 producing 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 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 across the water surface, a monomolecular film with the hydrophilic groups of the molecules facing the substrate is formed on 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, according to this method, between each layer, the wood-loving group and wood-loving group of the molecule, the hydrophobic group of the molecule, and the Y where the hydrophobic group faces each other. A mold film is formed. On the other hand, the horizontal attachment method is a method in which the substrate is attached horizontally to the water surface and transferred.
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 tree-philic 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 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.

The EL element of the present invention is obtained by forming the above-mentioned light-emitting layer forming material between the above-mentioned two electrode layers, preferably by the above-mentioned LB method.

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, even if a composite material having different electronegativity and at least one of which is luminescent as described above is used instead of a single material for forming the luminescent layer, a monomolecular film or a cumulative film thereof can be easily formed. Furthermore, the inventors have found that the performance of prior art EL devices can be significantly improved by using materials with such a configuration.

Next, important aspects of the present invention will be explained. A first aspect of the present invention is an aspect in which the light-emitting layer is a monomolecular film made of the composite material. The EL device of this embodiment is prepared by dissolving the necessary materials in the necessary proportions in an appropriate organic solvent such as chloroform, dichloromethane, dichloroethane, etc. to a concentration of about 10 to IOM, and adding various metal ions to the solution. Developed on an aqueous phase with an appropriate pH (for example, pH about 1 to 8) that may contain the solvent, and evaporated off the solvent to form a mixed monomolecular film,
Transferred onto one electrode substrate using the LB method as described above,
It is obtained by sufficiently drying, and then depositing an electrode material such as aluminum, silver, or gold, preferably by vapor deposition, on the surface of the monomolecular layer to form a back electrode layer. The thickness of the light-emitting layer of the EL device thus obtained varies depending on the type of material used, but is generally about 0.01 to I11. A thickness of m is preferred.

Another important aspect is that the light-emitting layer of the EL device of the present invention is a cumulative film of the above-mentioned mixed monolayer. This embodiment can be obtained by using the LB method described above and by accumulating the above mixed monomolecular film by various methods up to the required number of layers. 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 thickness of the light emitting layer of the EL element obtained in this way is about 4
A cumulative number of ˜400 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 y 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, the light emitting layer of the EL device of the present invention is as shown in FIGS. 1 and 2.
As schematically shown in the figure, unlike the prior art light-emitting layer made of a single substance, as schematically shown in FIGS. 3 and 4, the main light-emitting material and the co-acting material molecules are Since they are uniformly mixed in the monomolecular film, various interactions between these different molecules are extremely easy, and they exhibit excellent luminescent performance that cannot be achieved with conventional techniques. That is, the difference in electronegativity between the main emissive material and the co-acting material,
Alternatively, by variously changing the combination thereof, the luminous intensity can be improved, the luminous color can be arbitrarily changed, and the service life 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 as the co-acting material, 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 performance 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. It shows luminescence.

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 1500λ on the surface of a 50 mm glass plate by sputtering. After thoroughly cleaning this transparent electrode, it is used as a film-forming substrate.
It was immersed in an aqueous phase containing 4X 10M CdCl from Joyce-Loebe 1 and adjusted to pH 6.5.

AB Next, the above compounds A and B were dissolved in chloroform at a molar ratio of 1:1 (10 mol/l), and then developed on the above water phase. After the solvent chloroform was removed by evaporation, the surface pressure was increased (30 dyne/Cm) to precipitate the above-mentioned mixed molecules in the form of a film. Then, while keeping the surface pressure constant,
Gently raise or lower the film-forming substrate in a direction across the water surface (vertical speed 2 cm/min), 111
+ Transfer the combined monomolecular film onto the substrate, 1 layer of monomolecular film, 1
A mixed monomolecular cumulative film of 0.15, 20, 25 and 30 layers was fabricated on the substrate. In this cumulative process,
Each time the substrate was taken out of the water tank, it was left to stand for 30 minutes or more to evaporate and remove the water adhering to the substrate.

The substrate with the six types of thin films formed as described above was placed in a vapor deposition tank, and the nuclide was once depressurized to a vacuum level of 10 Torr, then the vacuum level was adjusted to 1 O-Torr, and the vapor deposition rate was 20 A/sec. , 1500A thick was deposited on each of the thin films in a pattern to form a back electrode. After sealing the six EL elements of the present invention produced as described above with a sealing glass as illustrated in FIG. to form six sealed EL light emitting cells of the present invention. E of each of these
When an alternating current voltage of lO2 and 400 Hz was applied to the L light emitting cell, six EL lights having colors unique to the dye were obtained. The evaluation results are shown in Table 1.

Such EL elements of the present invention are all made of Zn of the conventional example.
Compared to an EL element using S as a luminescent matrix, the driving voltage was lower and the EL element had good emission brightness characteristics.

Example 2 A mixed homomonolayer film containing the above compounds C and D in a molar ratio of 1:1 and a cumulative film thereof (10, 15, 20, 2
Six EL devices of the present invention were fabricated, each having 5 and 30 layers) as light-emitting layers.

Such EL elements of the present invention are all made of Zn of the conventional example.
Compared to an EL element using S as a luminescent matrix, the driving voltage was lower and the EL element had good emission brightness characteristics. The evaluation results are shown in Table 1.

Comparative Example 1 A comparative EL device was obtained in the same manner as in Example 1, except that only the following compound was used as the luminescent compound, and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

(Left below) -11-↓-Tori-L1! LM1 2 0.810
10 0, 115
12 0, 120 20
0.0925 20
0.0930 18 0.07
Yo” U starving LJ! LM1 2 0.510
11 0.0915
15 0.0920
22 0.0825 25
0.0?30 24
0.07 ratio "L example" 2 LLM 1 1 or less 0.210 1 or less 0.1 15 1 or less 0.08 20 1 or less 0.08 25 1 or less 0.08 30 1 or less 0.07 Example 3 Others In the same manner as in Example 1, the EL element of the present invention (however,
When the cumulative number was 15) and evaluated under the same conditions as in Example 1, the brightness (Ft
-L) was 28.

[Brief explanation of drawings]

1 and 2 schematically show the light-emitting layer of an EL device using the LB method of the prior art, and FIGS. 3 and 4 schematically show the light-emitting layer of the EL device of the present invention. FIG. 5 schematically shows a cross section of the EL element of the present invention. 1; Hydrophobic part 2; Hydrophilic part 3; Light-emitting layer
4; Substrate 5; Luminescent compound 6; Cooperative compound 7; Seal glass 8: Back electrode 9; Silicon insulating oil 10; Transparent electrode 11; Glass plate

Claims (1)

[Claims] Consisting of a light emitting layer and two electrode layers sandwiching the light emitting layer,
In the EL device in which at least one of the electrode layers is transparent, the light emitting layer is a mixture of at least one electroluminescent organic compound and at least one organic compound whose electronegativity is different from that of the organic compound. The above-mentioned EL device is characterized in that it is made of a mixed monomolecular film or a cumulative film thereof.