JPS6143690A - El element - Google Patents

Abstract

PURPOSE:To provide an EL element emitting luminescence in high luminance even at a low voltage, and composed of a luminescent layer having triple-layered structure, wherein each of the first and the third layers is composed if a thin film made of a highly oriented electroluminescent organic compound molecule having different electronegativity from the adjacent second layer. CONSTITUTION:The objective EL element is composed of a triple-layered luminescent layer 2 and a pair of electrode layers 1, 3 sandwiching said luminescent layer, wherein at least one of the electrode layers is transparent. The first and the third luminescent layers are made of a monomolecular film (or its built-up film) composed of electroluminescent organic compounds 4, 6 having higher electron affinity than the second luminescent layer. The second luminescent layer is made of a molecular built-up film composed of an electroluminescent organic compound 5 having higher electron-donative property than the first and the third higher electron-donative property than the first and the third luminescent layers. EFFECT:It can be produced easily at a low cost.

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,
An EL device in which the first and third layers are thin films in which at least one electroluminescent organic compound having a different electronegativity relative to the adjacent second layer is arranged with highly ordered molecular orientation. Regarding elements.

(Prior art) Conventional EL elements are made of Mn, Cu or l1ls.
Z containing F3 (Re; rare earth ion) etc. as an activator
It consists of a light-emitting layer using nS as a material for emitting light, and due to the difference in the basic structure of the light-emitting layer, there are two types: powder type EL and thin film EL.
It is structurally classified into L.

Among devices that have been put into practical use, thin film ELs generally have higher brightness than powder type ELs, but thin ELs have a light emitting layer formed by vapor depositing a light emitting base material on a substrate. It is difficult to manufacture a large-area device, and the manufacturing cost is extremely 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 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, one luminescent base material is a discontinuous powder, so if one luminescent layer is made thin, pinholes are likely to occur in the luminescent layer.
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 device 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 Japanese Patent Application Laid-open No. 11i58-172891, but it is still difficult to emit light. However, 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 EC elements, piezoelectric elements, pyroelectric elements, non-radiometer optical elements, and ferroelectric liquid products, have been announced that are comparable to or superior to metals and inorganic materials. in this way,
Amid the demand for the development of functional organic materials as new functional materials that surpass inorganic materials, a cumulative film of monomolecular layers of anthracene derivatives and pyrene derivatives, which have parent wood groups and hydrophobic groups in their molecules, has been developed as an electrode substrate. The formed EL element was published in Japanese Patent Application Laid-Open No. 52-35.
5871-; Proposed in the publication. However, these EL devices have not achieved sufficient performance as a real EL device in terms of brightness, power consumption, etc.
In the case of an L element, the density of carrier electrons or holes is very low, and the probability of excitation of functional molecules due to carrier recombination is very small, so efficient light emission cannot be expected.

(Disclosure of the Invention) Therefore, the object of the present invention is to eliminate the drawbacks of the prior art as described above, 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 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 with 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 and third light emitting layers are: The second light emitting layer is composed of a monomolecular film or a cumulative film thereof made of at least one electroluminescent organic compound that is electron-accepting relative to the second light emitting layer, and the second light emitting layer The above-mentioned EL device is characterized in that it is made of a molecular deposited film made of at least one electroluminescent organic compound that is electron-donating relative to the light-emitting 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.
Basically, it is a compound that has an electronic system and can be electrically excited.

Fused polycyclic aromatic hydrocarbon, p-terphenyl, 2.5-
diphenyloxazole, l,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, 41!1 rare earth rust bodies, 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;
Mention may be made of aromatic amines and aromatic polyamines, compounds with quinone aAl, tetracyanoquinodimethane, tetracyanoethylene, and the like.

In the present invention, the compounds useful for forming the first and third light-emitting layers are obtained by chemically modifying the electroluminescent compounds as described above by a known method as necessary, and having at least It is a compound that has one hydrophobic part and at least one wood-loving part (all of these are in a relative sense), and is represented by the following general formula CI). Compounds and other compounds.

[(X-R,), Z]? L-φ-R2 (I) 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, a silicic acid group, 1 to 3 Ami 7 groups;
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.; RI has 4 to 4 carbon atoms;
30, preferably 10 to 25 alkyl groups, preferably linear alkyl groups; m is 1 or a group (R, is an arbitrary substituent such as a hydrogen atom, an alkyl group, aryl, etc.); φ is a residue of an electroluminescent compound as exemplified later; R2, like X, is a hydrogen atom or any other substituent; l or more X, φ and R
At least 14N of 2 is a hydrophilic moiety, and at least one is a hydrophobic moiety.

Further, in the present invention, the organic compound useful for forming the second light-emitting layer is selected from the same types of compounds as above, except for those chemically modified.

Preferred examples of compounds of general formula (I) useful for forming the first and third layers, basic skeletons of compounds useful for forming the second layer, and other compounds include:
It is as follows. (However, φ (basic skeleton) illustrated below is an alkyl group having 1 to 4 carbon atoms, (, alkoxy group, alkyl ether group, halogen atom, nitro group,
- It may have general substituents such as a tertiary amino group, a hydroxyl group, a carboxamide group, a sulfoamide group, etc. )(below
Margin) Z=NH, O, S Z=CO, NHZ=CO1N
H,O%SZSeNH,01S z=N'H101SZ=NH%o%5 z=S%Sez;51sez=s%5eZ=N■■,0
．． S Z=NH1αS Z=NH%0. SM-Mg
s Z n s S n s AtCl M
=Hz s Be % Mgs Ca s CdSn,
ALCI% YbCI M= Er, Tm, Sm, Eu, Tb, z
=o, N group u M=A4 Gas 1r, Ta, a=3 M=E
r%Sm, EuM=Zn, CdtMg, pbn a=2
Gd, Tbs DyTm, Yb M= Er, Sm, Ell, Gd
M= Ers Sms EuTb %
Dy h i”m * Yb Gd +
The luminescent compounds such as Tb + DyTm%yb Z = O* Sn Se 0Sp52 or more can be used alone or as a mixture in each luminescent layer in the present invention. Note that these compounds are examples of preferable compounds, and it goes without saying that other conductor-visitors 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 in the first to ti
It is characterized in that the light emitting layer of S3 is used separately to form a three-layer laminated structure.

That is, since the above-mentioned light-emitting compounds have different electronegativity, when one or more of the above-mentioned compounds are employed as the light-emitting compounds for forming the first and third light-emitting layers, these employed A second luminescent compound is a luminescent compound having a different electronegativity.
Among such light-emitting compounds that can be selected as compounds for forming a light-emitting layer, particularly preferable electron-donating compounds include primary to tertiary amine groups, hydroxyl groups,
Those with electron-donating groups such as alkoxy groups and alkyl ether groups, or nitrogen heterocyclic compounds are the main ones, and those with electron-accepting properties include carbonyl groups, sulfonyl groups, nitro groups, and quaternary amino groups. Compounds having electron-withdrawing groups such as , (, etc.) are the main compounds. In the present invention, such luminescent compounds can be used alone or as a single-layer composite in each luminescent layer.

The other elements forming the EL structure of the present invention, namely the two electrode layers, sandwich the light emitting layer, and any conventionally known electrode layer can be used, but at least the IH thereof must be transparent. There needs to be. 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.

It is coated entirely or in a pattern with a transparent conductive material such as indium tin oxide (ITO). If opaque electrodes are used on one side, these opaque electrodes may be of conventionally known type, and generally and preferably have a thickness of about 0.1 to 0.3. It is a vapor deposited film of aluminum, silver, gold, etc. of wm. 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 layer m. If the thickness is less than this range, the physical strength and electrical properties of the element itself will be insufficient; , there is a risk of problems with 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 using separately the electroluminescent compounds having relatively different electronegativities as described above, and among the light emitting layers of the formed 3Ji3 structure, t51 and The third layer is characterized in that the molecules constituting the third layer are each arranged in a monomolecular film or a cumulative film thereof with highly ordered molecular orientation, and the second layer is a molecular deposition film.

In the present invention, a particularly preferred method for forming such a monomolecular film or a cumulative film thereof is the Langmuir-Blodgett method (LB method).
In this method, when a molecule has a structure that has a lignophilic group and a hydrophobic group within the molecule, and the balance between the two (balance of amphiphilicity) is maintained appropriately, the molecule will absorb the hydrophilic group on the water surface. This is a method of forming a monomolecular film or a cumulative film thereof by utilizing the fact that the film turns downward into a monomolecular layer. 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 its cumulative mass is set. The monolayer is transferred onto the substrate by gently lifting or lowering the clean substrate vertically while maintaining this surface pressure. 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 one-turn 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 toward the substrate. As mentioned above, when the substrate is moved up and down, the monomolecular film is overlapped one by one in each process.The direction of the film-forming molecules is reversed between the lifting process and the dipping process, so according to this method, each living room A Y-shaped film is formed in which the woody groups of the molecules face each other, and the hydrophobic groups of the molecules 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 in all layers. In the 0-rotation cylinder method, a cumulative Mi film in which the hydrophilic groups face the substrate is called a type 2 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, methods such as extruding a plate from a substrate roll into a water layer are also available. In addition, the orientation of the xylemophilic group and hydrophobic group to the substrate described in ii;i is a general rule and can be changed by surface treatment of the substrate, etc.'
Particularly preferable methods for forming the molecular deposition film constituting the light-emitting layer of ff52 are resistance heating evaporation and CVD.
A thin film about 0.000 years old can be formed.

For example, when using the resistance heating evaporation method, the material is placed in a tungsten board placed in a vacuum chamber, and 30 cm
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, the port was closed with a shutter, the port was heated, and the air was allowed to air for 2 minutes.

Open the shutter and deposit.

The speed during deposition is measured using a crystal oscillator film thickness monitor, but a suitable speed is 0°I A/sec.
In order to prevent oxidation, etc., the degree of vacuum is maintained at 1 O Torr or less, preferably about 1 O'' Tart.

In the EL device of the present invention, the material for forming the emissive layer as described above is preferably formed by the LB method and the molecular deposition film as described above, and between the two electrode layers as described above, compounds having different electronegativities are formed. It is obtained by forming it as a structure.

As mentioned in the prior art section, it is known to form an EL element by the LB method, but this known method does not allow for obtaining an EL element with sufficient performance, and the present inventor has conducted various research studies. As a result, the light-emitting layer has a 3Fr: structure, and the first and third light-emitting layers in contact with both outer Ai layers are made of compounds with different electronegativities as described above, and are made of single molecules or a cumulative film thereof. It has been found that by forming the t5z layer as a molecular deposition film, the performance of the prior art EL device can be significantly improved.

One important aspect of the present invention is an aspect in which the first and third light-emitting layers are monomolecular films made of the above-mentioned light-emitting material. In the EL device of this embodiment, first, a material that is relatively electron-accepting to the second layer to be formed as an intermediate layer is mixed in a suitable organic solvent such as chloroform, dichloromethane, dichloro-b-thane, etc. Approximately 16゛～x6-t146
The solution is developed on an aqueous phase of an appropriate pH (for example, pH about 1 to 8) that may contain various metal ions, and the solvent is evaporated off to form a monomolecular film. was formed and transferred onto one electrode substrate to form the rtS1 layer by the LB method as described above, sufficiently dried, and then the tJ51 layer formed in this way is relatively electron-donating to the W. A molecular deposition film is formed using the material by the molecular deposition method as described above to form a second layer, and an electron-accepting compound relative to the second layer is coated on the surface of the second layer in the same manner as described above. Form the third layer.

Finally, 1. electrode material such as aluminum, silver, gold, etc.
Preferably, the back electrode layer is obtained by vapor deposition or the like.

The thickness of the emissive layer consisting of three monomolecular layers of the EL device thus obtained varies depending on the type of material used, but is generally about 0.01 to 1 m thick. suitable.

Another important aspect is an aspect in which at least one layer, preferably both layers, of the first and third layers constituting the light-emitting layer of the EL device of the present invention is a cumulative film of the above-mentioned monomolecular film. be. This embodiment can be obtained by accumulating the above monomolecular film by various methods to the required number of layers and forming a molecular deposition film using the LB method and molecular deposition method.

The thickness of the light-emitting layer of the EL device thus obtained, that is, the cumulative number of monolayers, can be changed arbitrarily, but in the present invention, the total thickness of the first and third layers is approximately 2.
A cumulative number between 00 and 300 is preferred, with a total of about 0
．． 5-0.75. The thickness of the ring is suitable.

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 one light emitting layer will not peel or fall off. In order to strengthen the adhesive strength, the surface of the substrate may be pretreated or an appropriate adhesive layer may be provided between the substrate and the light emitting layer. The pH of the layer, the ionic species, the water temperature, the transfer rate of the monolayer, or? The adhesive strength can also be strengthened by adjusting various conditions such as the surface pressure of the 11-molecular film.

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 above-mentioned EL device with undeveloped IJJ, the structure of the light-emitting layer is an ultra-thin film, and the first and third layers facing the electrode layer are
The polymer has a high degree of molecular order and functionality necessary for the operation of an EL device, and has excellent light-emitting performance.

Furthermore, the light emitting layer of the EL element of the present invention is different from the light emitting layer of the prior art consisting of a single calendar, as schematically shown in Fig. m1, and as shown schematically 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, 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, the prior art has excellent luminescence.

Materials with insufficient film-forming properties and film strength could not be used in practice, but in the present invention, even materials with poor film-forming properties and film strength but excellent luminescence properties can be used.

By using a material with excellent film-forming properties in at least one layer, it is possible to obtain a light-emitting layer with excellent luminescence properties, film-forming properties, and film strength.

The EL device of the present invention described above can achieve excellent EL emission by applying electrical energy such as alternating current, pulse, or direct current between the electrode layers so that electrical energy such as a suitable electric field acts on the light emitting layer. This shows that.

Next, the present invention will be explained in more detail with reference to Examples. Note that the words in the middle of the text are based on weight.

Example 1 ITOW with a thickness of 1500λ was deposited on the surface of a 50 mm square glass plate by sputtering to form a transparent electrode. After thoroughly cleaning this film-forming substrate, Joyce -
Langmuir-Troug manufactured by Loel+e1
Next, the above compound A was dissolved in chloroform (10-
'mol/l) and then developed on the above aqueous phase. After removing the solvent chloroform by evaporation, the surface pressure was increased (30
dyne/ci+), the above molecules were deposited in a film.

Thereafter, while keeping the surface pressure constant, the film-forming substrate is gently moved up and down in the direction across the water surface (vertical speed 2 cra).
/win), transfer the monolayer onto the substrate.

A monomolecular cumulative VI film with four monolayer layers was created. In this cumulative process, each time the substrate was pulled out of the water tank, it was allowed to stand for 30 minutes or more to evaporate and remove the water adhering to the substrate.

Next, using a resistance heating evaporation apparatus, Andracef (B) (mp, 216°C) was evaporated to a thickness of 500λ on the transparent electrode substrate provided with the monomolecular film and its cumulative film. layered. During this deposition, the deposition tank was heated to 10-'T.
The pressure was reduced to a degree of vacuum of orr, the temperature of the resistance heating board (MO) was gradually increased, and the temperature was kept constant at 216℃, and the pumping speed was adjusted to gJ to reduce the degree of vacuum to 9X10.
Torr and at a deposition rate of 5 A/sec.
A deposited film was formed by adjusting the current flowing through the board containing anthracene. The degree of vacuum during vapor deposition was 9 x 10-
'It was Torr. In addition, the temperature of the substrate holder is
Water at 20°C was circulated and kept constant.

Again, the same material used to form the first layer was used at the same concentration and in the same manner to form a third layer by accumulating one monomolecular film and four layers on the surface of the second layer.

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'' Tarr, and then the vacuum level was adjusted to 10 Torr and the vapor deposition rate was 20 A/sec. After evaporating AI with a thickness of 1,500 yen on the thin film and using it as a back electrode, the fabricated EL element was sealed with a sealing glass as shown in Fig. 3.
Purified, degassed, and dehydrated silicone oil was injected into the seals to form four EL light emitting cells of the present invention according to conventional methods. lOv, 5 for these EL light emitting cells.
When an AC voltage of 0 Hz was applied, t51 and tj
When the S3 layer is a monolayer, the current density is 0-17mA.
An EL idea with a brightness of 1.3 ft-L is observed in /C Go, and when the first and third layers are cumulative films, the current density is 0.
．． EL emission with a brightness of 2.2 ft-L was observed at 09 mA/Crn''.

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.
An EL element for comparison was obtained in the same manner as in Example 1, and evaluated in the same manner as in Example 1. The current density was 0 and 19 mA/ct.
The luminance at r+' was less than 1 ft-L - Example 2 Compounds C and D below were used in place of compounds A and B in Example 1.

The EL element of the present invention was prepared in the same manner as in Example 1 except for CD (however,
The cumulative number of each was 4) and evaluated under the same conditions as in Example 1.
Ft-L) was 3.2.

[Brief explanation of the drawing]

FIG. 1 schematically shows an EL device using the LB method of the prior art, FIG. 2 schematically shows an EL device of the present invention, and the ftIJs diagram schematically shows the EL device of the present invention It is a diagram schematically showing a cross section of the element. l; 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

Claims (1)

[Claims] In an EL device consisting of 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 and third light emitting layers are connected to the second light emitting layer. consisting of a monomolecular film or a cumulative film thereof made of at least one electroluminescent organic compound that is relatively electron-accepting to The above-mentioned EL device, characterized in that it is made of a molecular deposited film made of at least one relatively electron-donating electroluminescent organic compound.