JPS6144987A - 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 (Field of Industrial Application) 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 three-layer structure,
The present invention relates to an EL device in which each layer is a thin film in which at least one electroluminescent organic compound is arranged with highly ordered molecular orientation.

(Prior art) Conventional EL elements are made of Mn, Cu or ReFa.
Zn containing (Re; rare earth ion) etc. as an activator
It consists of a light-emitting layer using S as a light-emitting base material, and is broadly classified structurally 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.

Therefore, powder-type EL, in which a light-emitting base material, that is, Zn'''S, 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, is attracting attention. In general, in EL light emission, the thinner the light emitting layer, the better the light emitting characteristics.However,
In the case of powder type EL, since the luminescent base material is a discontinuous powder, pinholes are likely to occur in one luminescent layer when the luminescent layer is thinned, making it difficult to reduce the layer thickness. It has a major drawback in that brightness characteristics cannot be obtained. Recently, an improved type of powder type EL in which an intermediate dielectric layer made of a vinylidene fluoride polymer is disposed within the light emitting layer 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 comparable to or superior to metals and inorganic materials have been announced, such as C elements, piezoelectric elements, pyroelectric elements, non-radiometer optical elements, and ferroelectric liquid crystals. 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 hydrophilic and hydrophobic groups in their molecules, is being used as an electrode substrate. The EL element formed on the top is
□ is proposed in Publication No. 5587. However, these EL devices have not achieved sufficient performance in terms of brightness, power consumption, etc. as actual E and L devices, and furthermore, in the case of organic EL devices, the density of carrier electrons or holes is extremely low. Because of their small size, 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, an object of the present invention is to eliminate the drawbacks of the prior art as described above, and to provide an E1 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 0 to provide.

The above object of the present invention has been achieved by forming a light emitting layer of an EL element by combining specific materials and having a specific configuration.

That is, the present invention provides an EL device comprising a light emitting layer having a three-layer stacked structure and two electrode layers sandwiching the light emitting layer, at least one of which is transparent, in which the first light emitting layer is electrically It consists of a monomolecular film or a cumulative film thereof consisting of a luminescent organic compound (A) and at least one organic compound that is electron-donating relative to the compound (A) (hereinafter abbreviated as donor), and a second The light-emitting layer is composed of a monomolecular film or a cumulative film thereof made of the electroluminescent organic compound (A) or an electroluminescent compound having the same electronegativeity as the compound (A), and the third layer is The above electroluminescent organic compound (
A) or a compound consisting of an electroluminescent compound having the same electronegativity as compound (A) and at least one organic compound relatively electron-accepting to compound (A) (hereinafter abbreviated as acceptor); The above EL device is characterized in that it is made of a molecular 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.
Basically, it is a compound that has an electronic system and can be electrically excited.

Fused polycyclic aromatic hydrocarbon, 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,
Examples include 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 parenteral moiety in its structure. It is a compound having a woody part (all of these are relative terms), and includes, for example, a compound represented by the following general formula CI) and other compounds.

[(X-R,), , Z], -φ-R, (I) In the above formula, X is a hydrogen atom, a halogen atom, an alkoxy group,
Alkyl ether group, nitro group; carboxyl group, sulfonic acid group, phosphoric acid group, silicic acid group, primary to tertiary amino group; metal salts thereof, primary to tertiary amine salts, acid salts; ester group,
Sulfoamide group, amide group, imino group, quaternary amino group and their salts, hydroxyl group, etc.; R1 has 4 to 3 carbon atoms.
0, preferably 10 to 25 alkyl groups, preferably linear alkyl groups; m is 1 or 2, n is 1 to 4
is an integer; Z is a direct bond or -0-1-S-1-
N R,, -CH2N R, -1-S O2N R3,
A linking group such as -CO-1-COO- (R is a hydrogen atom,
φ is a residue of an electroluminescent compound as exemplified later; R1, like X, 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 part.

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

(Margin below) Z=NH10, sz=co, NHZ=CO1N
H, O, SZ = NHlo, 5 Z = NH10, S Z =
NHlo, 5Z=S, Se Z=S,
Se Z=S, SeZ2NH%O,S
Z=NI ball QS Z2NH,0%SM=Mg,Z
n, Sn, A/Cj M-=Hz, Be, Mg,
Ca, CdSn, AtC1, YbCI M=Er, Tm, Sm, Eu, Tb,
Z=O1N1M=A4 Gai Ir, Tas
a=3 M=Ers Sm, EuM=Zn,
Cd, Mg%pb, a=2 Gd, Tb,
DyTm, Yb M2Ert Sm+ Eu, Gd M=Er%
Sm+ EuTb, Dy, Tm, Yb
Gd, Tb, DyTm, Yb Z=O,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, at least one specific preferred compound (A) is selected from the luminescent compounds described above, a donor is combined with the compound (A) to form a first layer, and then the compound (A) or forming a second layer from an electroluminescent compound having the same electronegativity as the compound (A), and finally forming a second layer from the compound (A) or an electroluminescent compound having the same electronegativity as the compound (A); It is characterized in that the third layer is formed by combining the and an acceptor, and the light emitting layer has a three-layer laminated structure.

Among such luminescent compounds, compounds preferred as compound (A) are those having intermediate electronegativity and excellent luminous efficiency among the above-mentioned exemplified compounds.

In addition, particularly preferable compounds as donors are first to third
The luminescent compounds or other organic compounds having an electron-donating group such as an amino group, a hydroxyl group, an alkoxy group, or an alkyl ether group or a nitrogen heteroatom are the main ones, and as an acceptor, a carbonyl group or a sulfonyl group is used. The luminescent compounds or other organic compounds having an electron-withdrawing group such as , nitro group, or quaternary amino group are mainly used.

In the present invention, such luminescent compounds can be used alone or in a mixture of two or more in each luminescent layer.

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, 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), etc., on the entire surface or in a pattern. If opaque electrodes are used on one side, these opaque electrodes may also be of conventionally known opaque electrodes, and are generally and preferably made of aluminum with a thickness of about 0.0, I NO, 3 JLm;
It is a vapor deposited film of silver, 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. Also,
The thickness of the transparent electrode is approximately 0. A thickness of about 0.0 to 0.2 μm 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, compactness, etc. will be deteriorated. 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 light-emitting layer consisting of three layers with relatively different electronegativities as described above, and the molecules constituting the light-emitting layer of the three-layer structure each have a highly ordered molecular orientation. It is characterized by being a monomolecular film or a cumulative film thereof arranged with

In the present invention, a particularly preferred method for forming such a monomolecular film or a cumulative film thereof is the Langmuir-Blodgett method. j (LB method). This LB
In this method, when a molecule has a structure that has a hydrophilic group and a hydrophobic group within the molecule, when the balance between the two (amphiphilic balance) is maintained appropriately, the molecule has a hydrophilic group on the water surface. This is a method of forming a monomolecular film or its cumulative MW by utilizing the fact that the monomolecular layer forms downward. 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, the surface pressure is gradually increased, and a surface pressure suitable for manufacturing a monomolecular film or a cumulative film thereof is set. By gently raising or lowering the clean substrate vertically while maintaining this surface pressure, the monolayer is transferred onto the substrate. Although a monomolecular film is manufactured in the above manner, a cumulative film of a monomolecular film is formed by repeating the above-described operations as a cumulative film 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 having one surface that is hydrophilic is lifted out of water in a direction transverse to 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, in this method, between each layer, a Y-shaped film is formed in which the wood-loving groups of the molecules face each other, 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 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 direction of the film-forming molecules, and an X-shaped film is formed in which the hydrophobic groups face the substrate 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 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 hydrophilic groups and hydrophobic groups described above 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 luminescent layer is formed between the two electrode layers as described above using the material for forming the luminescent layer, preferably by the LB method as described above, as a three-layer structure having different electronegativities. It is something that can be obtained by doing.
□ 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 inventor has conducted two types of research. As a result, it has been found that the performance of conventional EL devices can be significantly improved by forming the emissive layer into a three-layer structure and forming each emissive layer as a monomolecular film or a cumulative film thereof having different electronegativities as described above. This is what I found out.

One important embodiment of the present invention is an embodiment in which each luminescent layer is a monomolecular film made of the luminescent material. In the EL device of this embodiment, at least one compound (A) as described above is first selected, and the compound (A) and the donor are preferably mixed in a molar ratio of 1:1/10 to 1:1/100. The solution is dissolved in a suitable organic solvent such as chloroform, dichloromethane, 4-z dichloroethane, etc. to a concentration of about 10 to 100 ml, and the solution is mixed with a suitable solvent which may contain various total ions. The mixed monomolecular film is developed by evaporating the solvent and transferring it onto one electrode substrate using the LB method as described above. Then, Compound (A) or an electroluminescent compound having a similar electronegativity to Compound (A) is similarly transferred as a monolayer onto the surface of the first luminescent layer. to form a second layer, and the above compound (A) or an electroluminescent compound having the same electronegativity as compound (A) and an acceptor are preferably applied to the surface of the second layer in the same manner as described above.
: 1/10 N1 : 1/100 molar ratio to form the third layer, and finally, for example, aluminum,
The back electrode layer is obtained by depositing an electrode material such as , silver, or gold, preferably by vapor deposition or the like. Note that the above method has the same effect even if the order of forming the first to third layers is reversed.

The thickness of the light-emitting layer made of three monolayers of the EL device thus obtained varies depending on the type of material used, but is generally about 0.01 to . A thickness of l well m is suitable.

Another important aspect is that at least one layer, preferably three layers, of the three layers constituting the light emitting layer of the EL device of the present invention,
In this embodiment, both are cumulative films of the above-mentioned monomolecular films. This embodiment can be obtained by accumulating monolayers as described above in various ways up to the required number of layers by using the LB method described above.

The thickness of the luminescent layer of the EL device thus obtained, that is, the cumulative number of monolayers, can be changed arbitrarily, but in the present invention, the first layer has a cumulative number of about 4 to 150 layers. The second layer has a cumulative number of about 4 to 150, and the third layer has a cumulative number of about 4 to 150, and the total of the three layers is about 1
Cumulative numbers from 2 to 450 and thicknesses from about 0.03 to l#Lm are 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 of the prior art that is a single layer, as schematically shown in FIG. Since the third light-emitting layer and the third light-emitting layer are stacked with uniform interfaces, various interactions between the three layers with different electronegativities are extremely easy, to a degree that cannot be achieved with conventional technology. It exhibits excellent light emitting performance. That is, by variously changing the difference in electronegativity with the first to fifth third photoexhibiting layers, the luminous intensity can be improved or the luminescent color can be arbitrarily changed, and its service life can also be significantly extended. can be done.

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 a material has excellent luminescence properties, by using a material with excellent film-forming properties in at least one layer, a luminescent 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 a 1,500-layer ITO layer on the surface of a 50-layer glass plate by sputtering.

After thoroughly cleaning this film-forming substrate, Joyce-Loebe
Manufactured by 1 company (7) Langmuir-Trough4 of 4
It was immersed in an aqueous phase containing X 10-" mol/1 (DGdtl: l) and adjusted to pH 6.5. Next, the above compounds A and B were dissolved in chloroform at a molar ratio of 10:1. (10-3mat/41) and then developed on the above aqueous phase.After removing the solvent chloroform by evaporation,
The surface pressure was increased (30 dyne/cm) to precipitate the above mixed molecules in the form of a film. °Then, 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/win), and the mixed monomolecular film was transferred onto the substrate, leaving only the monomolecular film alone. , 4.6.8.
A monomolecular cumulative film of 10 layers was created and used as the first layer (acceptor single layer). In this accumulation process, each time the substrate was pulled 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.

Next, the mixed monomolecular film remaining on the surface of the aqueous phase was completely removed and newly dissolved in chloroform (10-3 mol
/l) of Compound A was spread on the aqueous phase. By the same method as above, only a new functional monomolecular film was formed on the surface of the monomolecular film and the monomolecular cumulative film, and a cumulative film of four layers was formed as a second layer.

Once again, the monomolecular film on the surface of the aqueous phase was completely removed, and the compound A and the compound C were newly used at a molar ratio of 10:1, and at the same concentration as used for forming the first layer. A monolayer of one layer and 4.6.8
．． A monomolecular cumulative film was obtained by accumulating 10 layers, and a third layer (donor single layer) was formed.

Finally, 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.The vacuum level was then adjusted to 10-' Torr, and the vapor deposition rate was set to 20λ/ sec, AI was evaporated on the thin film to a thickness of 1500 nm to form a back electrode.The fabricated EL device was sealed with a sealing glass as illustrated in Fig. 3, and then purified and purified according to conventional methods. Degassed and dehydrated silicone oil was injected into the seal to form four EL light emitting cells of the present invention.
When an alternating current voltage of oV and 400 Hz was applied, full EL light emission having a color unique to the material used was obtained. The evaluation results are shown in Table 1.

The above-mentioned EL element of the present invention had a lower driving voltage and better luminance characteristics than the conventional EL element using ZnS as a light emitting matrix.

Comparative Example 1 In Example 1, except that only Compound A was used as the luminescent compound and a single layer was used, the rest was Example 1.
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.

Cumulative i11 [Lll! E Ij[LILI1
1st layer 2nd layer 3M Tomoe" ■/ crn')
1 1 1 5V, 400Hz 5.1 0
．． 304 4 4 10V, 400Hz 22
0.126 4 8 10V, 400Hz
22 0.118 4 8 1QV, 400Hz
2B 0.1110 4 10 10V
, 400Hz 211 0.10 Arashi Tsuyuki” Cumulative degree 3 10V, 400Hz 1 or less 0
．． 1112, IOV, 400H21 or less 0.1018 10V, 400Hz
1 or less 0.1020 10V, 400H
z 1 or less 0.0924 10V, 4
00Hz 1 or less 0.08 Example 2 The following compounds were used instead of compounds A, B and C in Example 1, and D
E F and others are Example 1
In the same manner as above, an EL element of the present invention (however, the cumulative number of each is to, 4.10) was obtained and evaluated under the same conditions as in Example 1. At a current density of 0 and 1 mA/crn', the luminance (Ft-L) was 22.4.

[Brief explanation of drawings]

FIG. 1 diagrammatically shows an EL device according to the prior art LB method, FIG. 2 diagrammatically shows an EL device according to the present invention, and FIG. 3 diagrammatically 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'; Donor 5; Luminescent compound 6; Luminescent compound 6
'; Acceptor 7; Seal glass 8: Silicone insulating oil 9; Glass plate ゛ Fig. 1 6' Fig. 3

Claims (1)

[Claims] In an EL device comprising a light emitting layer with a three-layer stacked structure and two electrode layers sandwiching the light emitting layer, at least one of which is transparent, the first light emitting layer is made of an electroluminescent organic compound (A ) and at least one organic compound that is electron-donating relative to compound (A), or a cumulative film thereof, and the second light-emitting layer is composed of the electroluminescent organic compound (A). ) or an electroluminescent compound having the same electronegativity as compound (A), or a cumulative film thereof, and the third layer is composed of the electroluminescent organic compound (A) or compound (A). It is characterized by consisting of a monomolecular film or a cumulative film thereof consisting of an electroluminescent compound having the same electronegativity as A) and at least one organic compound relatively electron-accepting to compound (A). The above EL
element.