JPS6147785A - El element - Google Patents

Abstract

PURPOSE:An inexpensive and easily producible EL element capable of providing emission with high luminance even by low-voltage drive, consisting of a luminous layer of a specific three layer lamination structure comprising thin layers of electrically luminous organic compounds, and electrode layers sandwiching them in between. CONSTITUTION:In an EL element consisting of the luminous layers 4-6 having a three layer lamination structure, and the two electrode layers 1 and 3 wherein at least 1 is transparent, sandwiching the layers 4-6 in between, the first luminous layer 4 consists of a molecule piled layer comprising the electrically luminous organic compound A and one or more organic compounds having electron donor properties relatively based on the compound A, the second luminous layer 5 consists of a monomolecular layer comprising the compound A or an electrically luminous organic compound having the same electronegativity as that of the compound A or its accumulated layer, and the third layer 6 consists of a molecule piled layer comprising the compound A or the electrically luminous organic compound having the same electronegativity as that of the compound A, and the organic compound having electron donor properties relatively based on the compound A, to give the aimed EL element.

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, one light emitting layer has a three-layer structure,
The present invention relates to an EL device, each layer comprising a thin film of at least one electroluminescent organic compound.

(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 a functional molecule due to carrier recombination or the like becomes extremely small, and efficient light emission can be expected.

(Disclosure of the Invention) Accordingly, an object of the present invention is to provide an EL element that eliminates the drawbacks of the prior art as described above, can emit light with sufficiently high brightness even when driven at a low voltage, is inexpensive, and is easy to manufacture. 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 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 The second light-emitting layer is composed of a molecular deposited film consisting of a light-emitting organic compound (A) and at least one organic compound that is electron-donating relative to the compound (A) (hereinafter referred to as donor), and the second light-emitting layer is The third layer consists of a monomolecular film or a cumulative film thereof consisting of the electroluminescent organic compound (A) or an electroluminescent organic compound having the same electricality as the compound (A), and the third layer is the electroluminescent organic compound described above. an electroluminescent organic compound having the same electrophilicity as the organic compound (A) or compound (A); and at least one organic compound that is relatively electron-accepting to the compound (A). The above-mentioned EL device is characterized in that it is made of a molecular deposited film consisting of a molecule (hereinafter referred to as an acceptor).

To explain the present invention in detail, the electroluminescent organic compound used in the present invention and which mainly characterizes the present invention has a high luminescence quantum efficiency and is easily susceptible to external perturbation.
It is a compound that has an electronic system and can be electrically excited. For example, it basically includes fused polycyclic aromatic hydrocarbons, p-terphenyl, 2.5-diphenyloxazole, 1.4-
Bis(2-methylstyryl)-benzene, xanthine,
Examples include coumarin, acridine, cyanine dyes, benzophenone, phthalocyanine and its metal complexes, porphyrin and its metal complexes, 8-hydroxyquinoline and its metal complexes, organic ruthenium complexes, organic rare earth complexes, and derivatives of these compounds. . Furthermore, compounds that can serve as electron acceptors or electron donors for the above compounds include heterocyclic compounds other than those mentioned above and derivatives thereof, aromatic amines and aromatic polyamines, compounds with a quinone structure, and tetracyanoquinodimethane. and tetracyanoethylene.
'' In the present invention, the organic compounds useful for forming the first and third light-emitting layers are preferably selected from the above-mentioned compounds, or, depending on the case, the following compounds.

In the present invention, the compound useful for forming the second light-emitting layer is obtained by chemically modifying the electroluminescent compound as described above by a known method as necessary, and having at least one light-emitting layer in its structure. It is a compound that has both a hydrophobic part and at least one hydrophilic part (all of these are in a relative sense), for example, the following general formula (
It includes the compound represented by I) and other compounds.

[(X-R, Z]Tl-$-R2 (1) In the above formula, X is a hydrogen atom, a halogen atom, an alkoxy group, an alkyl ether group, a nitro group: a carboxyl group, a sulfonic acid group, a phosphoric acid group , silicic acid group, 1st to 3rd amino group;
These metal salts, primary to tertiary amine salts, acid salts: ester groups, sulfamide groups, amide groups, imino groups, quaternary amino groups and their salts, hydroxyl groups, etc.: R 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
Z is a direct bond or -0-1-3-, -
NR,, -CH2N R, -1-S O:, N R,,
A linking group such as -CO-1-COO- (R, is an arbitrary substituent such as a hydrogen atom, an alkyl group, or an aryl group); φ is a residue of an electroluminescent compound as exemplified later. Like X, R1 is a hydrogen atom or any other substituent; at least one of the one or more X, φ and R2 is a hydrophilic moiety, and at least one is a hydrophobic moiety; It is.

Preferred examples of the basic skeleton of the compound useful for forming the first layer and the third layer, φ of the compound of general formula CI) useful for forming the second layer, and other compounds are as follows. It is.

(However, the basic skeleton (φ) illustrated below has 1 to 1 carbon atoms.
4 alkyl group, alkoxy group, alkyl ether group,
It may have general substituents such as a halogen atom, a nitro group, a primary to tertiary amino group, a hydroxyl group, a carboxamide group, a sulfoamide group, and the like. ) (Margin below) Z=NH, Ols z=co, NHZ=CO1N
H,01SZ=NH,0% 5 Z=NH,O,S Z=NH,
01Sz=S1 Se z-5%Sc
zfu S,5eZ=NH,OlS Z=NH,Q
S Z = NH, 0, SM = Mg, Zn, Sn + AtC
1M-=H2, Be, Mg, Ca, CdSn, AtC1
, YbCI M= Er, Tm Sm, Eu, Tb, z
=o, NmM=A4 Ga, Ir, Ta, a=3
+14Er, Sm, EuM=Zn, Cd, Mg,
pb, a=2 Gd, Tb, DyTm,
Yb M=Er+ 5m, Eu, Gd M=Eri
Smt EuTb, Dy, Tm, Yb
Gd, Tb, DyTm, Yb Z-0, S, SeO≦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) Alternatively, a second layer is formed from compound (A) or an electroluminescent organic compound having the same degree of electroconductivity as that of compound (A), and finally an electroluminescent organic compound having the same degree of conductivity as compound (A) or It is characterized in that the third layer is formed by combining a luminescent organic compound with 7 receptors, and the luminescent 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 main compounds are the above-mentioned luminescent compounds or other organic compounds having an electron-donating group such as an amino group, a hydroxyl group, an alkoxy group, an alkyl ether group, or a nitrogen heteroatom, and acceptors include ', carbonyl group, sulfonyl group, etc. The luminescent compounds or other organic compounds having an electron-withdrawing group such as a nitro group, a nitro group, or a quaternary amino group are mainly used. In the present invention, such luminescent compounds, donors, or acceptors 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 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 as in the past, and preferred ones include (1) a transparent synthetic resin such as polymethyl methacrylate or polyester, a transparent film or sheet such as 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 be of conventionally known types, and are generally and preferably made of aluminum, silver, gold, etc. with a thickness of about 0.1 to 0.31 Lm. This is the vapor-deposited film. 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. The thickness of the transparent electrode is preferably about 0.01 to 0.24 m. 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,
It is obtained by forming a light-emitting layer consisting of three layers with relatively different electronegativity as described above, and of the three-layer light-emitting layer formed, the first and third layers are formed by molecular deposition. The second layer is characterized by being a monomolecular film or a cumulative film thereof, in which the molecules constituting the second layer are arranged with highly ordered molecular orientation.

In the present invention, particularly preferred methods for forming the molecular deposition films constituting the first and third light emitting layers are resistance heating evaporation and CVD. 500 each as three light emitting layers.
A thin film of about λ can be formed.

For example, when using the resistance heating vapor deposition method, the material is placed in a tungsten board placed in a vacuum chamber, and the material is placed 30 cm from the substrate.
Otherwise, resistance heating is performed, and sublimable materials are set at the sublimation temperature, and meltable materials are vapor deposited at a temperature higher than the melting point. The pre-vacuum level was set to 2 x 10-' Torr or less, and the port was closed with a shutter before vapor deposition, and the port was heated and left in the air for 2 minutes.

Open the shutter and deposit.

The rate during deposition is measured using a film thickness monitor using a crystal oscillator, but a suitable rate is 0, l A /
B a C"' l U (J A / se C1
7) Il+ TE"IT g 7 *In order to prevent oxidation, etc., the degree of vacuum at that time is maintained at 101 Torr or less, preferably about 10-' Torr.

In the present invention, a particularly preferred method for forming the monomolecular film or the cumulative film thereof constituting the second light-emitting layer is the Langmuir-Prodgett method (LB method).
This LB method is a method that uses a molecule with a structure that has a hydrophilic group and a hydrophobic group within the molecule to maintain an appropriate balance between the two (amphiphilic balance''). is a method of forming a monomolecular film or a cumulative film thereof by using the layer of polymer molecules on the water surface with the woody group facing downward.Specifically, on the water layer To prevent the developed monomolecular film from spreading freely on the water phase and spreading too much, a partition plate (or float) is provided to limit the developed area and control the state of aggregation of the film material, gradually reducing the surface pressure. By raising or lowering the clean substrate gently vertically while maintaining the surface pressure, the monolayer is deposited on the substrate. A monomolecular film is produced in the above manner, and a cumulative film of a monomolecular film having a desired degree of accumulation is formed by repeating the above operations.

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 with the hydrophilic groups of the molecules facing the substrate is formed on the substrate. As mentioned above, when the substrate is lowered 7 times, the monomolecular film overlaps one layer at each step.The direction of the film-forming molecules is reversed between the lifting step and the dipping step, so this method In this case, a Y-shaped film is formed in which the molecule's woody groups and molecule's woody groups and the molecule's hydrophobic groups and hydrophobic groups face each other. On the other hand, in the horizontal adhesion method, a substrate is attached horizontally to the water surface and transferred, and a monomolecular film with one molecule of hydrophobic group 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 an X-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.

In the EL device of the present invention, the emissive layer forming material as described above is formed into a three-layer structure having different electronegativity between the two electrode layers as described above, preferably by the molecular deposition method and the LB method as described above. 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 present inventor has conducted various research studies. As a result, by forming the light emitting layer as a three-layer structure, forming the first layer and the third layer as a molecular deposition film, and forming the second light emitting layer as a monomolecular film or a cumulative film thereof, the conventional EL element can be manufactured. It was discovered that the performance of the system was significantly improved.

One important aspect of the present invention is an aspect in which the second light-emitting layer is a monomolecular film made of the above-mentioned light-emitting material. The ET:element of this embodiment first comprises at least one
A seed compound (A) is selected and the compound (A) and donor are combined in a molar ratio of preferably 1:1/10 to 1:1/Zoo and deposited by a molecular deposition method as described above. As the first layer, compound (A) or an electroluminescent organic compound of similar electroconductivity as compound (^) is added in a suitable organic solvent such as chloroform, dichloromethane, dichloroethane, etc. to about 10- The solution is developed on an aqueous phase of an appropriate pH (e.g., pH approximately 1 to 8) that may contain various metal ions, and the solvent is removed by evaporation. Form a monomolecular film and transfer it onto one electrode substrate using the LB method as described above? Then, in the same manner as above, the compound (A) or an electroluminescent organic compound having a similar electroconductivity as the compound (A) and an acceptor are mixed, preferably in a ratio of about 1:l/ 10
: 1/100 molar ratio to form a third layer, and finally, an electrode material such as aluminum, silver, gold, etc. is deposited, preferably by vapor deposition, to form a back electrode layer. can get.

The thickness of the light-emitting layer consisting of three thin films of the EL element thus obtained varies depending on the type of material used, but generally a thickness of about 0.01-1 #Lm is suitable. be.

Another important aspect is that the second layer constituting the light emitting layer of the EL device of the present invention is a cumulative film of the above monomolecular film. This embodiment is to form a molecular deposition film as described above by using the molecular deposition method and LB method, and to form a light-emitting layer by accumulating the monomolecular film to a required number of times using various methods. obtained by.

Although the thickness of the light emitting layer of the EL element obtained in this way can be changed arbitrarily, in the present invention,
The layer is about 0. The thickness of O1~0.4pm and the second layer is about 4~0.4pm.
With a cumulative number of 150, the third layer is about 0. O1~0.47zm
, and a total thickness of about 0.03 lpm for the three layers is preferred.

Note that the adhesion between the electrode layer used as a substrate and the light emitting layer is as follows.
In the molecular deposition method, it is sufficiently strong and the light emitting layer will not peel or fall off, but in order to strengthen the adhesion, the substrate surface may be pre-treated or the light emitting layer may be bonded to the substrate. A suitable adhesive layer may be provided between the layers. Furthermore, the first layer and the second layer and the 882nd layer and the third layer
Adhesion to the layer is sufficient, but in the LB method, various conditions such as the material for forming the emissive layer, the pH of the water layer used, ion species, water temperature, monomolecular film transfer rate, or monomolecular film surface pressure, etc. The adhesion force can also be strengthened by adjusting the

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, and the second layer has a high degree of molecular order and function necessary for the operation of an EL device, and has excellent light-emitting performance.

Furthermore, as schematically shown in Figure 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 Figure 2. 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, which is impossible to achieve with conventional technology. It exhibits excellent luminous performance. That is, the first to third
By variously changing the difference in electronegativity between the light emitting layer and the light emitting layer, the light emission intensity can be improved, the light emission 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 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 exhibit excellent EL by applying electrical energy such as alternating current, pulse, or direct current between the electrode layer and the electrode layer 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 1500 nm on the surface of a 50 m glass plate with a zero angle by sputtering.

Next, anthracene (A) (mp, 216°C) and anthraquinone (B) (mp, 286°C) were deposited on the transparent electrode substrate at 500°C using a resistance heating evaporation apparatus.
It was deposited to a film thickness of A to form an i1 layer. This vapor deposition was carried out by first reducing the pressure in the vapor deposition tank to a vacuum level of 10 Torr, gradually increasing the temperature of the resistance heating board (Mo) and keeping it constant near the melting point of each, and then adjusting the pumping speed. The vacuum level was maintained at 9XIO Tart, the current flowing through the board containing anthraquinone was adjusted so that the anthraquinone evaporation rate was IA/sec, and anthracene was added so that the total evaporation rate was 5λ/sec. A deposited film was formed by adjusting the current flowing through the board.

The degree of vacuum during vapor deposition was 9 X IO-'T orr. Further, the temperature of the substrate holder was kept constant by circulating 20° C. water.

Next, a solution of the above compound C and Dt-1 dissolved in chloroform at a molar ratio of 1:1 (i o"
,5 adjusted to Jo7ce-L made by Loebe1 company.
angsru.

It was developed in the aqueous phase of ir-Trough4. After removing the solvent chloroform by evaporation, the surface pressure was increased (:30
dy −=−ne/cm), the above molecules were deposited in the form of a film. Thereafter, while keeping the surface pressure constant, the film-forming substrate on which the first layer was already formed was gently moved up and down in the direction across the water surface (at a speed of 2C layer/in) to form a monomolecular film. Monomolecular film 8, which was transferred onto the substrate and accumulated into 8 layers, only the monomolecular film! A membrane was made to serve as the second 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.

Then anthracene and indazole (E) (mp
, 145° C.) in a molar ratio of about 10:1, and the first
Similar to the formation of the layer, the third M layer was deposited to a thickness of 50 OA on the above monomolecular film and its cumulative film. : Closed.

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, and then the vacuum level was adjusted to lσ'T o r r, and the vapor deposition rate was set to 20λ/sec. Then, as shown in Fig. 3, the fabricated EL device was made by vapor depositing Al on the thin film to a thickness of 1,500 mm and used as a back electrode.After sealing with a sealing glass, it was purified and desorbed according to the conventional method. The dehydrated silicone oil was injected into the seal to form the EL light emitting cell of the present invention. These EL light emitting cells have l OV, 4
00HzO) When an AC voltage was applied, when the second layer was a monomolecular film, 81 light emission with a brightness of 2.4 ft-L was observed at a current density of 0.16 mA/crn', indicating that the WS2 layer was a cumulative film. When, the current density is 0.15mA/crn'
Emissions with a brightness of 23.8 ft-L(7)81 were observed.

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 C was used as the luminescent compound and a single layer was used, the rest was the same as Example 1.
A comparative EL element was obtained in the same manner as in Example 1, and evaluated in the same manner as in Example 1, and the luminance was 1 ft-L or less at a current density of 0.2 mA/cm'.

Example 2 In place of compounds B and E in Example 1, the following compounds F and G were used, and the other conditions were the same as in Example 1 to prepare an EL device of the present invention (however,
The cumulative number of each sample was 8), and when evaluated under the same conditions as in Example 1, the current density was 0.09 A/ClT1' and the brightness (Ft-L) was 20.5.

[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. 1; 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 Fig. 2 4' 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 the compound (A), and the second light-emitting layer is made of the electroluminescent organic compound (A).
or consisting of a monomolecular film or a cumulative film thereof made of an electroluminescent organic compound having the same electricality as that of the compound (A), and the third layer is the electroluminescent organic compound (A).
or a molecular deposited film consisting of an electroluminescent organic compound having the same electronegativity as the compound (A) and at least one organic compound that is relatively electron-accepting to the compound (A). The above EL element.