JPS6143686A - El element - Google Patents

Abstract

PURPOSE:To provide an EL element emitting luminescence in high luminance even at a low voltage, and producible easily at a low cost, by using a double- layered luminescent layer, wherein each of the first and the second luminescent layers is made of a thin film of an electroluminescent organic compound having different electronegativity from each other. CONSTITUTION:The first luminescent layer placed opposite to the transparent electrode layer 1 is made of a mixed monomolecular film or its built-up film composed of a mixture of an electroluminescent compound 5 having higher electron affinity than the second luminescent layer and an organic compound 5' having higher electron donative property than the compound 5. The second luminescent layer is placed opposite to the back electrode layer 3, and is made of a mixed built-up film composed of a mixture of an electroluminescent organic compound 4 having higher electron donative property than the first luminescent layer and an organic compound 4' having higher electron affinity than the organic compound 4.

Description

[Detailed Description of the Invention] (Industrial Field of Application) Shukanmei relates to an EL element using electrical light emission, that is, EL, and more specifically, the light emitting layer has a two-layer structure,
The present invention relates to an ELi device comprising a thin film of at least one electroluminescent organic compound, each layer having a different electronegativity relative to the other adjacent layers.

(Prior art)', Conventional EL elements are made of Mn, Cu or □Re.
It consists of a light-emitting layer whose light-emitting material is ZnS' containing F3 (Re: rare ion) etc. as an activator, and due to the difference in the basic structure of the light-emitting layer, powder type EL
and thin type IIi type EI.

Among devices that have been put into practical use, thin #ELs generally have higher brightness than powder-type ELs, but thin-film ELs have a large area because the light-emitting layer is formed by vapor-depositing a light-emitting base material on the substrate. The youngest element is difficult to manufacture and has drawbacks such as extremely high manufacturing costs.Therefore, it is the most mass-producible and only a few tenths of the cost of an 11-layer element! Powder type EL, in which a luminescent base material, ie, Zn'S, is dispersed in an organic binder that requires only 3M has started to attract attention. Generally, in an EL device, the thinner the light emitting layer is, the better the light emitting characteristics will be. However, in the case of the powder type EL, the luminescent base material is a discontinuous powder, so if the luminescent layer is thinned,
This has the major disadvantage that pinholes are likely to occur in the light-emitting layer, making it 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 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. 58-17.
2.891, but it has not yet achieved sufficient performance in terms of luminance brightness, power consumption, etc.
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 ferroelectric liquid products that are comparable to or superior to metals and inorganic materials have been announced. In this way, as there is a 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 a parent group and a hydrophobic group in one molecule, has been developed as an electrode. An EL element formed on a substrate is proposed in Japanese Patent Laid-Open No. 52-35587. 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, the purpose of the single light source 11 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 L1 objective of the present invention was achieved by forming the light emitting layer of the EL element by combining specific materials and having a specific configuration.

That is, one aspect of the present invention is an EL device consisting of a two-layered light emitting layer, and a VL Meiden electrode layer and a back electrode layer sandwiching the light emitting layer.
In the bird, the first light-emitting layer faces the transparent electrode layer and includes an electroluminescent organic compound that is electron-accepting relative to the second light-emitting layer and an electroluminescent organic compound that is electron-accepting relative to the second light-emitting layer. The second light emitting layer is made of a mixed monomolecular film made of a mixture with a donating organic compound or a stack thereof, and the second light emitting layer faces the back electrode layer and has an electron density relative to the first light emitting layer. The above-mentioned EL device is characterized in that it is composed of a mixed molecule deposited film consisting of a mixture of a donating electroluminescent organic compound and an electron-accepting organic compound relative to the donor electroluminescent organic compound.

To explain the present invention in detail, 1. The electroluminescent organic compound used in the present invention and which mainly characterizes the present invention has a high luminous quantum efficiency and also has a π-electron system that is easily susceptible to external perturbations. It is a compound that can be electrically excited,
For example, basically fused polycyclic aromatic hydrocarbon, p-terphenyl.

2,5-diphenyloxazole, 1,4-bis(2-
methylstyryl) - benzene, xanthine, coumarin,
Examples include acridine, cyanine dyes, benzophenone, tuthalocyanine and metal complexes thereof, porphyrin and gold H complexes thereof, 8-hydroxyquinoline and metal complexes thereof, 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 compound useful for forming the first light-emitting layer is obtained by chemically modifying the electroluminescent compound as described above by a known method as necessary.

It is a compound that has at least one hydrophobic part and at least one woody part (all of which are in a relative sense) in its structure. Compounds of formula CI) and other compounds are included.

[(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.; Rμ±C4-3
0, preferably 10 to 25 alkyl groups, preferably linear alkyl groups: m is 1 or -5o2NR,
, -CO-1-〇〇〇-, etc. (R3 is a hydrogen atom, an alkyl group, an arbitrary substituent such as aryl), and φ is a residue of an electroluminescent compound as exemplified later. R2, like X, is a hydrogen atom or any other substituent; at least one of one or more characters, φ and R2 is a hydrophilic moiety, and at least one is It is a hydrophobic part.

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 compounds of the general formula (I) useful for forming the first layer, and compounds useful for forming the second layer (this skeleton and other compounds are exemplified by:
It is as follows. (However, φ(], (
This main skeleton includes an alkyl group having 1 to 4 carbon atoms, an alkoxy group, an alkyl ether group, a halogen atom, a nitro group, a primary
~ It may have general substituents such as tertiary amino group, hydroxyl group, carboxamide group, sulfoamide group, etc. ) (Margin below) Z=NH10, S Z=CO%NHZ=CO1N
H,01SZ=NH%O% S z = NH1O15Z=NH,0,5Z=S%Se
Z=S, Se Z=Ss Se
Z = Nf(, OlS Z = NH1Q S Z
=NH,O,SM= Mgs Zns Sns ALC
L M= Hz%Bes Mg, Ca b Cd
Sn, ALCL, YbC2 M= Er, T turtle Sm+ Eu, Tb, Z
= 0, Nnu M=A4Ga, Ir, Ta, a=3 M=Er, S
m, EuM-Zns Cd * Mat pb +
a-2Gd s Tb s DyTm%Yb M=Er, Sm, Eu%Gd M=Er,
Sm, EuTb, Dy, Tl1l, Yb
, Gd, Tb, DyTm%yb Z=0, S, Se O.; It should be noted that 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.

The present invention is characterized in that the luminescent compounds as described above are used separately in the first luminescent layer and the second luminescent MJ of the EL device of the present invention, depending on their electronegativity. That is, since the above-mentioned luminescent compounds have different electronegativities, among them, the compound that is relatively electron-accepting is selected as the luminescent compound for forming the first luminescent layer. However, the light-emitting compound that is relatively electron-donating to these compounds may be selected as the second light-emitting layer forming compound.

Among these luminescent compounds, electron-donating problems,
Particularly preferred compounds include a 1-i tertiary amino group,
The main ones are those with electron-donating groups such as hydroxyl group, alkoxy group, alkyl ether group, or nitrogen heterocyclic compounds, and the electron-accepting ones include carbonyl group, sulfonyl group, nitro group, Compounds having an electron-withdrawing group such as a quaternary amine 7 group are the main ones.

In the present invention, such luminescent compounds can be used alone or in combination in each luminescent layer.

The present invention further provides that, for the luminescent compound forming the f51 layer as described above, an organic compound (hereinafter referred to as donor) which is relatively more electron-donating than the compound is preferably added per mole of the former. , in a proportion of about 17 Zoo to 1/10 mole to adjust the electron acceptability of the first layer, and the second layer.
An organic compound (hereinafter referred to as acceptor) that is relatively more electron-accepting than the luminescent compound forming the layer, preferably about 1/10 per mol of the former.
It is characterized in that it is added at a ratio of ~1/100 mole to reduce the electron donating property of the second layer to tJR.

The acceptor as described above may be selected from the above-mentioned luminescent compounds, or may be selected from other organic compounds with large electron-withdrawing properties other than the above-mentioned, and the donor may also be selected from the above-mentioned luminescent compounds. For example,
The acceptor is selected from various compounds having a large electron-withdrawing substituent as mentioned above, and the donor is selected from various organic compounds having a large electron-donating substituent as mentioned above. be able to.

The other elements forming the EL element of the present invention, namely the transparent electrode layer and the back electrode layer, sandwich the light emitting layer, and
Any conventionally known calendar can be used, but at least the calendar needs to be transparent. As the transparent electrode layer, any desired transparent electrode layer can be used, and preferred examples include 1, for example, transparent synthetic resins such as polymethyl methacrylate and polyester, and transparent films or sheets made of glass or the like. indium oxide,
b coated with a transparent conductive material such as tin oxide, indium-tin-oxide CITo) on the entire surface or in a pattern.
It is. If an opaque back electrode layer is used on one side, these opaque electrode layers may also be of conventionally known types, and typically and preferably have a thickness of about 0.1-0.3
)bm vapor-deposited film of aluminum, silver, gold, etc. The shape of the transparent electrode layer or the back electrode layer 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 layer is approximately 0
．． 01 to 0.2 m is preferable, and H below this range
Otherwise, the physical strength and electrical properties of the element itself will be insufficient, and if the thickness exceeds the above-mentioned range vIJ, problems may occur with respect to transparency, lightness, compactness, etc.

The EL device of the present invention uses electroluminescent compounds (containing acceptors or donors) having relatively different electronegativities as described above between the 2Fj electrode layers as described above, thereby forming two layers. The first layer constituting the two-layered emissive layer faces the transparent electrode layer and has electron-accepting properties relative to the second layer. It is a mixed monomolecular film or a composite aS composed of a compound that is arranged with a highly ordered molecular orientation, and the second layer faces the back-type S layer and is electron-donating relative to the first layer. It is characterized by being a mixed molecule deposited film consisting of a chemical compound.

In the present invention, a particularly preferable method for forming such a first layer monomolecular film or its accumulation is the Langmuir-Prodgett method (LB method). When a molecule with a structure that has a hydrophilic group and a hydrophobic group maintains an appropriate balance between the two (amphiphilic balance), the molecule forms a single molecule on the water surface with the hydrophilic group facing downward. This is a method of forming a monomolecular film or a cumulative film thereof by utilizing the presence of carbon atoms.

Specifically, to prevent the monomolecular film spread on the water layer from spreading too much by freely diffusing the water phase, a partition plate (or float) is provided to limit the spread area and allow the film material to gather. The conditions are controlled and the surface pressure is gradually increased to set a surface pressure suitable for producing a monomolecular film or a cumulative film thereof. 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 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 above-mentioned vertical dipping method, when a substrate having a hydrophilic surface is pulled out of water in a direction transverse to the water surface, a monomolecular film is formed on the substrate with the tree-philic groups of the molecules facing the substrate. As mentioned above, when the substrate is lowered one step, the monomolecular film is overlapped one by one in each process.The direction of the film-forming molecules is reversed in the lifting process and the dipping process, so this method Between each layer, the hydrophilic group of the molecule and the hydrophobic J of one molecule of the hydrophilic group,
(A Y-shaped film is formed in which the hydrophobic groups face each other.On the other hand, in the horizontal attachment method, the substrate is attached horizontally to the water surface and transferred, and one molecule of the hydrophobic group faces the substrate side.) The film is formed on the board. In this method, even if a monomolecular film is accumulated, there is no change in the orientation of the film-forming molecules, and in all layers, the #aqueous groups face the substrate; On the contrary, in all cases, the cumulative film in which the hydrophilic groups face the substrate is called a Z-type film. This is a method of transferring a monomolecular film onto a substrate surface.The method of transferring a monomolecular film onto a substrate is not limited to these methods.In other words, when using a large-area substrate, the substrate is pushed out from a substrate roll into a water layer. In addition, the directions of the above-mentioned woodphilic groups and hydrophobic groups toward the substrate are in principle, and can be changed by surface treatment of the substrate, etc.

In the present invention, particularly preferred methods for forming the mixed molecule deposited film constituting the second light-emitting layer are resistance heating evaporation method and CVD method.
An S film of about 5ooA can be formed as a light emitting layer.

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.
In the following, 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 speed during deposition is measured using a crystal oscillator film thickness monitor, but a suitable speed is 0゜λ/sec.
~100λ/sec, and the degree of vacuum at that time is 1OTarr or less, preferably l to prevent oxidation etc.
This is done by keeping it at about OTart.

In the EL element of the present invention, among the two electrode layers as described above,
As the first layer facing the transparent electrode layer, a relatively electron-accepting compound and an appropriate donor are selected from the above compounds, and a mixture is prepared.1 For example, by the LB method, a mixed monomolecular film or a cumulative film thereof is formed. forming a mixture of a relatively electron-donating compound and an appropriate acceptor selected from among the above-mentioned compounds as the second layer facing the back electrode layer;
This can be obtained by forming a mixed molecule deposited film using the method described above, and forming a light-emitting layer with a two-layer 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 two-layer structure, and the first light-emitting layer is formed as a mixed monomolecular film or its cumulative Mi11% using a relatively electron-accepting compound containing a donor as described above, In addition, it has been discovered that the performance of the conventional EL element can be significantly improved by forming the second layer as a mixed molecule deposited film from a compound that is relatively electron-donating and contains an acceptor with respect to the first NI. It is.

One embodiment of the present invention is an embodiment in which the first light-emitting layer is a mixed monomolecular film made of the luminescent material containing a donor. The EL device of this embodiment is prepared by first preparing a mixture of a donor and a material that is relatively electron-accepting for the second layer in a suitable organic solvent such as chloroform, dichloromethane, dichloroethane, etc. 10--1 (ii
"M", and the solution is adjusted to an appropriate pH (e.g., pEI of about 1 to 8), which may contain various metal ions.
), and the solvent was evaporated to form a mixed monomolecular film, which was then transferred onto one transparent electrode substrate as the first layer using the LB method as described above, and thoroughly dried. .

Next, a second layer is formed as a mixed molecular deposition film using a mixture of a material that is electron-donating relative to the first layer formed in this way and seven receptors by the molecular deposition method as described above. , then on the surface of this second layer 2, e.g. aluminum, silver.

The back electrode layer is obtained by depositing an electrode material such as gold, preferably by vapor deposition or the like.

The thickness of the two-layer light emitting layer of the EL device thus obtained varies depending on the type of material used, but is generally preferably about 0.01 to 1 ILm thick.

Another important aspect is that the first layer constituting the light emitting layer of the EL device of the present invention is a cumulative film of the above mixed monomolecular film. This embodiment can be obtained by accumulating the above I20 mixed monolayer in various ways to the required number of layers using the LB method described above, and then forming the second layer as described above.

The thickness of the light-emitting layer of the EL device of the present invention obtained in this way can be changed arbitrarily, but in the present invention, the cumulative number of mixed monomolecular films in the first layer is about 4 to 200. , the thickness of the second layer is about 0.001~0.5 pm, and the thickness of the entire light emitting layer is about 0.02~1.0 pm. It is preferable to set it to m.

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 molecular deposition method, and the light-emitting layer does not peel or fall off. However, in order to strengthen the adhesive strength, the substrate surface may be treated in advance, or an appropriate adhesive layer may be provided between the substrate and the light emitting layer.Furthermore, in the LB method, one light emitting layer may be The adhesive strength can also be strengthened by adjusting various conditions such as the type of material used to form the adhesive, 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.

Since the performance of the EL element formed as described above may deteriorate due to the influence of moisture and oxygen in the air, it is made moisture resistant by conventionally known means.

Oxygen resistant’! It is desirable to have an E-sealed structure.

Trees like the above: 5? ! In the EL device No. 1, the structure of the light emitting layer is an ultra-thin film, and the first layer has a high degree of molecular order and function necessary for the operation of the EL device, and
The $2 layer and the first layer exhibit excellent light emitting performance through various electrical interactions.

Furthermore, the emissive layer of the device for the EI of unreleased rJ1 is different from the emissive layer consisting of a single layer in the prior art, as schematically shown in FIG. Since the first light-emitting layer and the second light-emitting layer have a uniform interface, various interactions between these two 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 between the first light-emitting layer and the second light-emitting layer, the light emission intensity can be improved or the light emission color can be changed arbitrarily, and the service life can also be changed. It can be significantly extended.

Furthermore, the conventional technology has excellent luminescence properties.

Materials with insufficient film-forming properties or film strength could not be practically used, but in the present invention, even materials with poor film-forming properties or film strength but excellent luminescence properties can be used. By using a material with excellent film-forming properties for the layer, it is possible to obtain a light-emitting layer that is excellent in all of luminescent 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 811 in the text is based on weight.

Example 1 A transparent electrode was formed by depositing an ITO layer with a thickness of 1500 Å on the surface of a 50 ia square glass plate by sputtering. After thoroughly cleaning this film-forming substrate, Joyce -
Langmuir-Trough manufactured by Loebe1
Pi(6,
0 order immersed in an aqueous phase adjusted to 5.

(A) (B) The above compounds (A) and CB) were dissolved in chloroform at a molar ratio of 1O:l (10”” mol/fL
), the solution was poured onto the aqueous phase. After the solvent chloroform was removed by evaporation, the surface pressure was increased (30 dyne/cm).
), the above mixed molecules were deposited in the form of a film. Thereafter, while keeping the surface pressure constant, the film-forming substrate was gently moved up and down in a direction across the water surface (vertical speed 2 crn/win).
, transfer the mixed monolayer onto the substrate.

A mixed monomolecular cumulative film with five layers was created. In this cumulative process, each time the substrate is pulled up from the water tank,
The moisture adhering to the substrate was evaporated by leaving it for more than a minute.

Next, using a resistance heating evaporation device, anthracene (B
) (mp, 216°C) and indasol (D) (mp, 1
46° C.) was deposited to a film thickness of 50 OA. This vapor deposition is
The vapor deposition tank was once depressurized to a vacuum level of 10-'Tart, and the temperature of the resistance heating board (MO) was gradually raised so that the indazole vapor deposition rate was approximately IA/sec.
Keeping the current flowing through the resistance heating board constant, the total deposition rate is 5 A/! A deposited film was formed by adjusting the current flowing through the board containing anthracene so that eC.

The degree of vacuum during vapor deposition was 9 X I O-' Torr. Further, the temperature of the substrate holder was kept constant by circulating 20° C. water.

Finally, the thin film formed as described above was placed in a steaming tank 27, and the nuclide was once depressurized to a vacuum level of 10 Torr.
Vacuum level adjusted to 10 Torr and deposition rate 20λ/se
c Te, 1500λ(7) II! The fabricated EL device was made by depositing AI on the thin film to form a back electrode, and as illustrated in FIG. Oil was injected into the seal to form the EL light emitting cell of the present invention. IOV, 400 for these EL light emitting cells
When an AC voltage of Hz was applied, the current density was 0, 10
It exhibited EL light emission with a brightness of 27 ft-L at mA/c1f.

The EL devices of the present invention described above had lower driving voltages and better luminance characteristics than conventional EL devices using ZnS as a light emitting matrix.

Comparative Example 1 A comparative EL element was obtained in the same manner as in Example 1 except that the second layer was not formed.
Moreover, when evaluated in the same manner as in Example 1, the current density was 0.1
The brightness was 1 ft-L or less at 1 mA/c♂.

Example 2 In place of compounds A, B, C and D in Example 1,
The following compounds E, F, G and H were used, and E F G H and others were used in the same manner as in Example 1 to obtain an EL device of the present invention (however, the cumulative number was 5), and under the same conditions as Example 1. When evaluated,
Brightness (Ft-L) at current density 0, 12mA/c 2
was 28.

[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 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.

Claims (1)

[Claims] In an EL device consisting of a two-layered light-emitting layer, a transparent electrode layer and a back electrode layer sandwiching the light-emitting layer, the first light-emitting layer faces the transparent electrode layer and the second light-emitting layer faces the second light-emitting layer. consisting of a mixed monomolecular film or a cumulative film thereof consisting of a mixture of an electroluminescent organic compound that is electron-accepting relative to the compound and an organic compound that is electron-donating relative to the compound;
A second light-emitting layer faces the back electrode layer and includes an electroluminescent organic compound that is electron-donating relative to the first light-emitting layer and an electroluminescent organic compound that is electron-accepting relative to the first light-emitting layer. The above-mentioned EL device is made of a mixed molecule deposited film made of a mixture with an organic compound.