JPS6137876A - Electroluminescent element - Google Patents

Abstract

PURPOSE:The titled element having a good light emission efficiency by low-voltage driving, made by providing a light emitting layer in which an electron- accepting org. compd. layer, an electron-donating org. compd. layer and an electrical insulating layer are laminated at least two-folds between two transparent electrode layers. CONSTITUTION:A first layer 5-1, 5-2 of thickness <=500Angstrom comprising a relatively electron-accepting org. compd. and another org. compd. serving as an electron- accepting compd. thereto, a second layer 6-1, 6-2 of thickness <=300Angstrom comprising a monomolecular film or monomolecular cumulative film of a relatively electron- donating org. compd. and another org. compd. serving as an electron-donating compd. thereto, and a third layer 4-1, 4-2 of thickness <=300Angstrom comprising a monomolecular film or monomolecular cumulative film of an electrical insulating compd. are laminated in the order of the third layer 4-1, the first layer 5-1, the second layer 6-1 and the third layer 4-2 at least two-folds between electrode layers 1 and 2 each having a thickness of 0.01-0.3mum of which at least one is transparent to form a light emitting layer 3 of thickness <=1mum.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to an electroluminescent (EL) device that performs electroluminescence. The present invention relates to an EL element having a layer having an EL function in combination with thin films, which can emit light efficiently even when driven at a low voltage, and has sufficient brightness.

[Prior art]

An EL element has a structure in which a light-emitting layer containing a material with EL@ ability, that is, a material that has the function of emitting light when placed in an electric field, is placed between two electrodes, and a voltage is applied between these electrodes. A light-emitting element that generates light by applying an electric field and converting electrical energy directly into light.
For example, unlike traditional light emitting methods, such as incandescent light bulbs where a filament is heated to emit light, or fluorescent light, where electrically excited gas imparts energy to a phosphor and causes it to emit light, thin panels are used. Possibility of realizing light-emitting bodies such as lamps, lines, diagrams, images, etc., or as components of display media such as lamps, lines, diagrams, images, etc., or as light-emitting bodies such as large-area panel lamps. It is attracting attention as having the following.

These EL devices differ in their light emission methods; one is an intrinsic EL method that performs field-excited light emission due to the movement of carriers within the light-emitting layer, and the other is an intrinsic EL method that performs field-excited light emission by injecting carriers into the light-emitting layer from an electrode. There are two main types: the carrier injection EL method and the carrier injection EL method.

Furthermore, due to the differences in the structure of the light-emitting layer of the device, EL devices are divided into thin film types, which have a thin film made of a material that has an EL function as a light-emitting layer, and light-emitting devices that have a material that has an EL function dispersed in a binder. It is broadly classified into two types: a powder type with layers and a powder type with layers.

In addition, conventionally, as a material having the above-mentioned EL function, M
Inorganic metal materials such as ZnS containing .eta., Cu, or ReF3 (Re represents a rare earth) as an activator have been mainly used.

Thin n-type EL elements can have a thin light-emitting layer, making the distance between the electrodes sufficiently short, and can generate a stronger electric field within the light-emitting layer, making it possible to operate at low voltages. , has a structure suitable for obtaining high brightness and good light emission.

However, if this type of EL device is manufactured by forming a thin light-emitting layer using the above-mentioned inorganic metal material mainly consisting of ZnS using a thin film forming method such as vapor deposition, the manufacturing cost becomes extremely high. In addition, since it is extremely difficult to form a light-emitting layer made of a uniform thin film over a large area, it has not been possible to mass-produce high-quality, large-area EL elements.

On the other hand, E
As an L element, an intrinsic E in which a light-emitting layer is formed by dispersing the above-mentioned ZnS-based EL inorganic material in an organic binder.
An L-type organic powder type EL element is known.

However, in this powder type EL element, when the layer thickness is formed thin, defects such as pinholes are likely to occur in the light emitting layer. There are structural limits to making it thinner, making it impossible to obtain sufficient light emission, especially high brightness, and because the layer thickness is relatively thick, power consumption increases to generate a stronger electric field. It had the following problems. In order to generate a stronger electric field in the light-emitting layer of this powder-type EL element, an improved powder-type EL element was developed, in which an intermediate dielectric layer made of vinylidene fluoride polymer was provided.
Although it is known from the publication No. 172891, it is currently not possible to obtain satisfactory performance in terms of brightness, power consumption, etc.

On the other hand, recently, various thin film forming methods have been used to control the chemical structure and higher-order structure of organic compound materials, which enable the formation of thin films with high precision. It is attracting attention for its application as a material for electrochromic elements, piezoelectric elements, pyroelectric elements, nonlinear optical elements, ferroelectric liquid crystals, etc. Furthermore, it is also possible to use these materials to form the light emitting layer of EL elements. It is expected to be used as a material.

Among these, anthracene, pyrene, perylene, or their derivatives are known as organic materials for the light-emitting layer of EL devices, and carriers using monomolecular cumulative films of these materials as the light-emitting layer are known. An injection EL type device is known from Japanese Unexamined Patent Publication No. 52-35587.

However, in this EL device, although the light-emitting layer is formed as a thin film with high precision, the density of electrons or holes, which are carriers, is very low, and the probability of excitation of functional molecules due to carrier movement or recombination is low. low,
At present, it is not possible to obtain efficient light emission, and the results are not particularly satisfactory in terms of power consumption and brightness.

[Purpose of the invention]

An object of the present invention is to provide a novel EL element that has good luminous efficiency, can provide sufficiently high luminance even when driven at low voltage, is inexpensive, and has a structure that is easy to manufacture.

Another object of the present invention is to enable EL devices to be formed by appropriately selecting various organic compound materials and combining the optimal thin film formation method for the material, and to easily impart desired light emitting characteristics. An object of the present invention is to provide an EL element having a structure that allows for.

[Structure of the invention]

That is, the electroluminescent device of the present invention has two electrodes, at least one of which is transparent, and a luminescent layer provided between these electrode layers, in which the luminescent layer is relatively A first compound containing an organic compound exhibiting acceptability, and a second compound containing an organic compound exhibiting relative electron donating property.
and a third layer having electrical insulation properties, further comprising another compound capable of becoming an electron acceptor for the organic compound relatively exhibiting electron acceptability in the first layer. ,
and the second layer contains another compound that can serve as an electron donor for the relatively electron-donating organic compound, and these layers extend from one side of the electrode layer to the other. The first layer, the second layer, and the third layer are stacked in this order twice or more on the third layer, and the second layer and the third layer are further stacked, It is characterized by being composed of a monomolecular film or a monomolecular cumulative film of a compound capable of forming each of these layers.

The light-emitting element of the present invention basically has two electrodes, at least one of which is transparent, and a light-emitting layer with an EL function provided between these electrode layers with an insulating layer interposed therebetween. It is a thin film type EL element, and its feature lies in the structure of the light emitting layer.

The light-emitting layer of the EL device of the present invention includes an organic compound (hereinafter abbreviated as EA compound) that exhibits a relatively electron-accepting property;
A compound that can become an electron acceptor for the EA compound (hereinafter referred to as an EA-a compound) is placed in a position where organic compounds that are relatively electron-donating (hereinafter referred to as ED compounds) are in contact with each other and around the EA compound. (abbreviated as E), but also the above E
It has a structure in which compounds (hereinafter referred to as Ell-d compounds) that can serve as electron donors for the compound are arranged around the D compound, and when these compounds are placed in an electric field, the relationship between these compounds is Due to the interaction of Among them, the main light emission source is a light-emitting effect based on the formation of an exciplex accompanying the transfer of electrons between the ED compound and the EA compound, and moreover, such an exciplex is efficiently formed with the generation of an electric field. It is characterized by having a structure suitable for being used.

Hereinafter, the EL element of the present invention will be explained in more detail using the drawings.

FIG. 1 is a schematic cross-sectional view of an example of the EL element of the present invention.

1 and 2 are electrodes for generating an electric field by applying a voltage, and 1 is a transparent electrode for extracting the generated light. 3 is a light emitting layer having an EL function;
between the layers 4-1.4-3, the first layer 5-1.5-2,
It has a multilayer structure in which the second layers El-1, 6-2 and the third layer 4-2 are alternately stacked. Layer 4-1, 4-2, 4-3
is formed from a monomolecular film of a compound capable of forming each layer or a cumulative film thereof.

The first layer 5-1 of the light-emitting layer 3 contains as a main component a compound that can be an EA compound with respect to the above-mentioned ED compound contained in the second layer 6-1, and this first layer 5-1 The second layer 6-1 is laminated in direct contact with the first layer 5-1.
The main component is a compound that can be an ED compound compared to the EA compound contained in 1.

The interface 7- between the first layer 5-1 and the second layer B-1
1 is the contact surface between the EA compound and the ED compound.

The relationship between the first layer 5-2 and the second layer 8-2 is similar to this, and an interface 7-2 is uniquely formed by these layers.

At these interfaces 7-1 and 7-2, when a voltage is applied to the electrodes 1 and 2 and an electric field is applied to the light emitting layer 3, E
A compound and ED compound form a complex in an excited state,
When this exciplex returns to the ground state, excitation energy is generated as light from the complex, EA compound, and/or ED compound in the excited state. In this way, the EL of the present invention
Is this interface the source of light emission in the device? -1 and 7-2 are the main light sources.

Furthermore, 11 layers 5-! , 5-2 contains EA-, which can act as an electron acceptor for the EA compound that is the main component of these layers.
a compound is mixed, and this EA-a compound is E
It mainly has the function of increasing the electric field excitation efficiency of the EA compound through interaction with the EA compound, such as receiving electrons from the A compound.

In addition, the second layer 6-1.8-2 contains ED-, which can act as an electron donor for the ED compound that is the main component of these layers.
d compound is mixed, and this ED-d compound also mainly has the function of increasing the electric field excitation efficiency of the ED compound through interaction with the ED compound such as donating electrons to the ED compound. .

The ED-d and EA-a compounds can control the electrochemical properties of the first layer and the second layer as desired, such as controlling the emission color, by interacting with the EA compound and the ED compound. In addition to the above-mentioned functions, the controller may also have a function of controlling the above-mentioned functions.

First layer 5 constituting the light emitting layer of the EL element of the present invention
-1.5-2 and the second layer e-t, 6-2 contain compound molecules directly involved in the formation of the field-excited complex as shown below, or at least one of the compounds as a functional moiety. The second layer 6-
1.6-2 is formed from a monomolecular film or a monomolecular cumulative film.

Furthermore, the first layer 5-1.5-2 contains EA-a, which can act as an electron acceptor for the EA compound that is the main component of these layers.
a compound is included as a subcomponent, the second layer e-t,
8-2 contains the main components of these layers as well as an ED-d compound that can serve as an electron donor for a certain ED compound as a subcomponent.

A light emitting layer 3 of a compound molecule directly involved in the formation of an electric field excited complex contained as a main component in the first layer and the second layer.
As for the arrangement within, the following combinations can be cited as typical ones.

(a) First layer 5-1.5-2 and second layer 8-1.6-
Compound molecules (having an EL function (mainly emitting light)) are arranged in each of 2 on the basis of exciplex formation.

(b) Based on exciplex formation in the first layer 5-1.5-2<
A compound molecule with EL function is arranged.

Compound (ED compound) molecules that can serve as electron donors for these compound molecules are included in the second layer 8-1. B-
It is located at 2.

(c) Based on exciplex formation in the second layer 6-1.6-2
Compound molecules having an EL function are arranged, and compound (EA compound) molecules that can serve as electron acceptors for these compounds are arranged in the first layer 5-1, 5-2.

As the compound having the EL function based on the formation of an exciplex, an organic compound that has a high luminescence quantum efficiency, has a π-electron system that is easily susceptible to external perturbation, and is easily excited by an electric field is preferably used.

Examples of such compounds include fused polycyclic aromatic hydrocarbons, p-terphenyl, 2,5-diphenyloxazole, 1,4-bis-(2-methylstyryl)-benzene, xanthine, coumarin, acridine, and cyanine. Pigments, benzophenone, phthalocyanine, metal complexes of phthalocyanine, porphyrin, metal complexes of porphyrin, 8-hydroxyquinoline, metal complexes of 8-hydroxyquinoline, ruthenium complexes, rare earth complexes, and derivatives of these compounds, and heterocycles other than those listed above. Based on exciplex formation, <EL
411! Among these compounds, compounds that can relatively become EA compounds can be listed.
A light-emitting layer having the above-described structure (L) of the first layer and second layer is formed by appropriately selecting and combining at least one type of ED compound and one or more substances that can become an ED compound, and the first layer is formed by a vapor deposition method. The second layer can be formed using a single molecule accumulation method, which will be described later.

Furthermore, compounds that can act as electron acceptors or electron donors for compounds having an EL function based on exciplex formation as described above include heterocyclic compounds other than the compounds mentioned above, derivatives thereof, and aromatic amines. , aromatic polyamines, compounds having a quinone structure, tetracyanoquinodimethane, tetracyanoethylene, etc., and by appropriately selecting and combining the above-mentioned compounds and these compounds, the first layer described above can be formed. A light emitting layer having the second layer structure (b) or (C) can be formed.

Furthermore, EA which is the main component of the first layer contained in the first layer
an EA-a compound that can serve as an electron acceptor for the compound;
The ED-d compound that can act as an electron donor for the ED compound that is the main component of the second layer and is included in the second layer has <EL function (mainly Compounds that emit light), compounds that can act as electron donors or acceptors for such compounds, compounds that can become light emitters due to excitation energy transfer, and compounds that have at least one of these compound molecules as a functional moiety. I can do it. When forming the first layer and the second layer, these EAs are selected depending on the compound used as the main component of the first layer and the second layer.
-a and ED-d compounds may be appropriately selected and used so as to have the above-mentioned functions. The dimensions of the EA-a compound relative to the EA compound and the ED-d compound relative to the ED compound vary depending on the compounds used in the first and second layers, and - although not generally defined - are usually −
For compound a, lO mol% of EA compound ~ 0.1
For the ED-d compound, it is about 10 mol% to 0.1 mol% of the ED compound.

Note that the compounds mentioned above that can be used as ED and EA compounds may be compounds that have a function of emitting light that is not based on the formation of an exciplex, and furthermore, EA-a and ED.
The compound that can become the -d compound may also have an EL function, and the light emission in the EL element of the present invention is caused by the first
The light emission is not limited to only at the interface 7-1.7-2 between the layer 5-1.5-2 and the second layer 8-1. .8-2 may also include the case where light is emitted.

In order to form a monomolecular film or a monomolecular cumulative film containing the above-mentioned compound or a compound having the compound molecule as a functional part, it is necessary to enable highly ordered molecular orientation and arrangement and to easily form an ultra-thin film layer. The so-called single molecule accumulation method can be suitably applied.

This single molecule accumulation method is based on the following principle. In other words, for example, in a molecule that has a hydrophilic part and a hydrophobic part, when the balance between the two (amphipathic balance) is maintained appropriately, many of these molecules will be hydrophilic and hydrophobic on the water surface. Form a monomolecular layer with the sexual part facing down.

This monomolecular layer has the characteristics of a two-dimensional system, and when these molecules are sparsely dispersed, the two-dimensional ideal gas equation between the area A per molecule and the surface pressure ■, nA = kT. (
k, Portzmann's constant, T: absolute temperature), and these molecules form a "gas film"; however, when A is made sufficiently small, intermolecular interactions become stronger, and these molecules form a two-dimensional solid "condensed film" (or solid form a film)′. This condensed film can be transferred to the surface of a substrate such as glass, and an ultra-thin monomolecular film or a cumulative film thereof can be formed on the substrate.

According to this method, the orientation of the molecules forming the monolayer is such that, for example, almost all of the tree-like parts of the constituent molecules are oriented toward the substrate in a highly ordered manner. It can be uniform. Therefore, by forming the second layer of the light emitting layer of the EL element of the present invention into a monomolecular film or a monomolecular cumulative film, the functionality consisting of compound molecules directly involved in the formation of an exciplex contained in the second layer can be improved. It becomes possible to arrange the portions at high density at the interface between the first layer and the second layer.

Various solutions can be used as a solution for forming a single molecule in this single molecule accumulation method, and depending on the solution used, a well-balanced number of molecules having different affinity for the solution can be used. A monomolecular film can be formed by appropriately selecting a compound for forming a molecular film. Among such solutions for forming a monomolecular film, water or a solution containing water as a main component is preferably used because it is inexpensive, easy to handle, and safe.

The structure of the light-emitting layer of the EL device of the present invention will be described below, taking as an example the case where a single molecule accumulation method using water or a solution containing water as a main component is applied.

Basically, the compounds contained in the first layer and the second layer of the light-emitting layer of the EL device of the present invention include the above-mentioned ED, EA,
, ED-d and EA-a compounds, or a compound having at least one of these compounds as a functional moiety. Among such compounds, monolayer-forming compounds have, for example, monolayer-forming compounds that have one functional moiety, depending on the position within the molecule of the functional moiety, As shown in the schematic diagram of the structure,
(a) The functional part 21 is located in the woody part 22, - Figure 2 (a) (b) The functional part 21 is located in the hydrophobic part 23, - Figure 2 (b) (C) The functional part 21 is a hydrophobic part 23 and a wood-loving part 22
- It is broadly classified into the three types shown in Figure 2 (C).

The components of the hydrophilic portion 22 of these compounds include:
For example, carboxyl groups and their metal salts, amine salts and esters, sulfonic acid groups and their metal salts and amine salts, sulfonamide groups, amide groups, amino groups, imino groups,
Examples include a hydroxyl group, a quaternary amino group, an oxyamino group, an oximino group, a diazonium group, a guanidine group, a hydrazine group, a phosphoric acid group, a silicate group, and an aluminate group.

Each can be used alone or in combination to constitute the hydrophilic moiety 22 in the above compound.

Further, as the constituent elements of the hydrophobic portion 23, linear or branched alkyl groups, vinylene, vinylidene,
Examples include olefinic hydrocarbons such as acetylene, fused polycyclic phenyl groups such as phenyl, naphthyl, anthranyl, and chain polycyclic phenyl groups such as dophenyl; or in combination can constitute the hydrophobic moiety 23 in the above compound.

On the other hand, the interface between the first layer and the second layer of the light emitting layer of the EL device of the present invention? The orientation and arrangement of the ED compound contained in the monomolecular film at points -1 and 7-2 (parts where light is mainly emitted) are shown in the schematic cross-sectional partial view near the interface 7-1 in Figure 3 (this figure In the case of , the second layer is formed from a monomolecular film containing compound molecules each having one functional moiety consisting of an ED compound molecule, and for molecules having a functional moiety consisting of ED-d compound molecules 35, (Illustration of functional parts is omitted) As shown in (1) (E
A hydrophilic portion 32 having a functional portion 31 (composed of compound D) is oriented at the interface 7-1.

(2) The molecular (E) forming the monomolecular film of the second layer 8-1
A hydrophobic portion 33 having a functional portion 31 (composed of compound D) is oriented at the interface 7-1.

Figure 3 (b) It can be basically divided into two patterns.

In order to form such an interface pattern of the light-emitting layer, compounds belonging to type a and type b of the monomolecular film forming compound containing the ED compound molecule as a functional moiety listed above are preferably used. . Hereinafter, in order to form the above-mentioned interface pattern (1), the above-mentioned type a is applied to the second layer.
Furthermore, in order to form the above-mentioned interface pattern (2), it is suitable to use a compound belonging to the above-mentioned type b in the second layer.

The types of molecules having a functional portion consisting of the ED-d compound molecules 35 (not shown) are the interface pattern (1), E used in (2)
A suitable type may be appropriately selected depending on the D compound.

The example explained above is a case where the second layer is formed from a monomolecular film, but even when the second layer 8-1.6-2 is formed from a monomolecular cumulative film, the first The monomolecular film of the second layer constituting the interface 7-1. Just form it.

In addition, when the second layer 8-1.8-2 is composed of a monomolecular cumulative film, each monomolecular film constituting the cumulative film may be the same, or the monomolecular film One or more of these may be different from other monolayers. Furthermore, the structure based on the orientation state of the molecules forming each monomolecular film of the monomolecular cumulative film is so-called Y-type (between each film, there are a woody part and a woody part, or a hydrophobic part and a hydrophobic part). (structures in which the hydrophobic parts of each layer face each other), x-type (structures in which the hydrophobic parts of each layer face the substrate side), Z-type (structures in which the wood-loving parts of each layer face the substrate side), and various other variations of these structures. The structure can be as follows. Furthermore, the monomolecular film forming the second layer constituting the light-emitting layer of the EL device of the present invention contains one or more compounds having EI) compound molecules as a functional moiety as a main component;
It may be a multi-component monomolecular film containing one or more compounds other than one or more compounds having the ED-d compound molecules as a functional moiety as a subcomponent. In such cases, other compounds may include compounds that do not have a functional moiety but can control the electrochemical properties of the emissive layer through interaction with compounds that do, and even monolayers. Compounds that can increase the strength of the layer or improve adhesion to other layers can be mentioned.

The structure of the monomolecular film or monomolecular cumulative film as described above depends on the desired electrical characteristics of the second layer.
For example, monomolecular films made of compounds belonging to type a, b, or type C of the above-mentioned monomolecular film-forming compounds may be combined and accumulated to form a monomolecular film. It is possible to control the potential curve of π electrons in the direction perpendicular to the surface direction of the film.

Compounds that can be used to form the second layer 8-1.6-2 include the above-mentioned compounds capable of forming a functional part, or having one or more of these compounds. Among the compounds, those that have a well-balanced tree-philic moiety and hydrophobic moiety can be used as they are for forming a monolayer, while those that do not have a tree-philic moiety and/or hydrophobic moiety can be used as is. Alternatively, a hydrophobic group can be newly introduced into the molecule to form a monolayer-forming compound.

Examples of such compounds include compounds represented by the following structural formulas.

In addition, in the structural formula shown below, X and Y represent the parent wood group as mentioned above, but when both of these exist in one molecule, even if either one is the parent wood group, In such a case, the other one will be hydrogen. Further, R represents an alkyl group having a linear or side chain having about 4 to 30 carbon atoms, preferably about 10 to 25 carbon atoms.

5.6゜6≦m+n 7, 8゜21,
22.
27゜6≦n≦20 28゜241゜0≦n≦2 25゜M=H2, Be, Mg, Ca, Cd, 5rAICI, Y
bC1 82゜M=Er, Sm, Eu, Gd, Tb, Dy, Tm, Yb
34゜M=Er, Sm, Eu, Gd, 'I'b, Dy, "I"
m, YbM-Er, Sm, Eu, Gd, 〒b, Dy,'
I'm, YbRI-H, -CH3, -CF3, ()8
6, 87. 3B.

39・40゜4・8.
4.4゜H (aH2) Based on the formation of an exciplex among the above-mentioned compounds capable of forming a functional moiety, a compound having an EL function is modified with a hydrophobic group and/or a parent group to form a monolayer-forming compound. It is.

In addition, the compounds having the structural formulas of 鐅42 to 54 and 85 to 86 have structures in which an alkyl chain is directly bonded to a functional moiety, but the bonding of an alkyl chain to a functional moiety is, for example, It may be an ether bond, a bond via a carbonyl group, or the like.

Furthermore, among the monolayer-forming compounds exemplified here,
Compounds that can be used in other thin film formation methods such as vapor deposition methods include
It can also be used to form layers. In addition, the first layer also contains an EA compound as a main component and one or more compounds having as a molecular functional moiety, similar to the second layer in -F.
It may also contain one or more compounds other than one or more compounds having the EA-a compound molecule as a functional moiety, which is a subcomponent, and in such a case, the other compound may contain a functional moiety. Compounds that can control the electrochemical properties of the light-emitting layer by interacting with compounds that have a functional moiety, and also increase the strength of the first layer and the adhesion with other layers. Examples include compounds that can improve the

The third layer 4-1.4-2, 4-3, which is another layer of the light-emitting layer of the EL element of the present invention, is a layer having an insulating property, and in particular, the third layer 4-1. 4-3 is the EL of the present invention
It has the function of increasing the insulation of the element's capacitor structure,
The third layer 4-2 has the function of confining the movement of electrons within a necessary minimum area and emitting light by efficiently transferring and receiving electrons. As a material that can form these third layers, the general formula that can form a monomolecular film having accurate and uniform insulation properties is: % formula %) (In the above formula, n is 10 ≦n≦30, and X
-COOH, -CONH2, -GOOR, -N” (
CH3)3 □ C1-.

Examples include compounds represented by (representing a group such as).

This third layer may also be a monomolecular film or a monomolecular cumulative film, and in the case of a monomolecular cumulative film, each monomolecular film may be the same or one or more of each monomolecular film may be It may be different from other monolayers. Further, the monomolecular film forming the third layer may be a monomolecular film made of one type of compound, or may be a multicomponent monomolecular film made of two or more types of compounds.

Although the EL element of the present invention having two interfaces formed by the first layer and the second layer shown in FIG. 1 has been described so far, the EL element of the present invention has two interfaces. The number is not limited to this, and may be three or more.

The thickness of each layer constituting the light-emitting layer of the EL device of the present invention having the above structure varies depending on the number of interfaces the EL device has and the structure of each layer itself, but for the first layer,
50OA or less, preferably 200A or less, for the second layer, 300A or less, preferably 100A or less, the third layer
For the layer, it is desirable that the thickness of the entire light emitting layer be 300 A or less, preferably 100 A or less, and the thickness of the entire light emitting layer be 1 μs or less, preferably 3000 A or less, in order to obtain a good light emitting state even in low voltage driving. .

At least one of the two electrode layers 1 and 2 of the EL element of the present invention is provided as a transparent electrode in order to extract light.

When forming an electrode layer as a transparent electrode, PMMA,
InO2, 5n02, insium tin oxide (1,7,0), etc. are laminated by a vapor deposition method on a transparent substrate such as a polyester film or sheet, or a glass plate, or these materials are used as a light emitting layer. It can be formed by direct lamination.

In addition, it is possible to directly deposit AI on a thin plate made of a material that can form a normal electrode with sufficient conductivity, or on a suitable substrate or on a light-emitting layer formed on a non-transparent electrode.
, Ag, Au, etc. can be laminated by a vapor deposition method or the like.

The thickness of these electrode layers is 0. OI - about 0.3μ, preferably 0.05μ, 0.2. It is considered to be a degree.

Note that the shape and size of the EL element of the present invention can be made into various shapes as desired. For example, when forming a transparent electrode, the substrate is used as a substrate for forming a light emitting layer, and this substrate may be shaped like a plate, a belt, etc. A desired shape and size can be obtained by using, for example, a cylindrical shape. Further, the two electrode layers may be patterned into various shapes as desired.

In the EL element of the present invention having the above configuration, the EL
Between the two electrodes 1 and 2 of the device, for example, a 1×1
By applying direct current, alternating current, or pulse voltage so that an electric field of about 05 to 3 x 106 is applied, good light emission can be obtained from the light emitting layer 3 through the transparent electrode.

Hereinafter, typical operations of the single-molecule accumulation method represented by the Langmuir-Blodgett method (LB method) applied to the formation of the second layer and the third layer of the light-emitting layer of the EL device of the present invention will be explained. explain.

An aqueous phase for forming a monomolecular film is provided in a water tank, and a clean substrate is immersed in the aqueous phase. Next, a predetermined amount of a solution of a monomolecular film-forming compound dissolved or dispersed in a suitable solvent is spread in the aqueous phase, and this compound is deposited in the form of a film on the surface of the aqueous phase. At this time, in order to prevent the precipitates from freely diffusing on the water phase and spreading too much, a partition plate (or float) is provided to limit the area of development and control the aggregation state of the membrane material.
Obtain a surface pressure (■) proportional to the aggregate state. Then, activate the partition plate to reduce the expansion area.

Gradually increase the surface pressure (■) and set it to a surface pressure (■) suitable for forming a monomolecular film. Now, if the substrate that has already been immersed is gently lowered once in the direction perpendicular to the aqueous phase surface while maintaining this surface pressure, the upward and downward movement of the substrate will cause a single drop. The molecular film is transferred onto a substrate to form a monomolecular cumulative film 4'.

In order to transfer a monomolecular film to a substrate, in addition to the vertical immersion method described above, there is also a horizontal deposition method in which the substrate's aqueous phase surface is kept parallel and in contact with it horizontally, and a cylindrical substrate is rotated on the water surface. Various methods can be applied, such as a rotating cylinder method in which the monomolecular film is transferred onto the surface of the substrate, or a method in which the substrate is extruded from a substrate roll into an aqueous phase. In the vertical dipping method, the orientation of the film-forming molecules is usually reversed between the substrate pulling process and the dipping process, so that a so-called Y-shaped film is formed. Further, according to the horizontal deposition method, a monomolecular film with hydrophobic groups facing the substrate side is formed, and when a cumulative film is formed, a so-called X-type film is formed. However, the orientation of such parent tree groups and hydrophobic groups is
It is also possible to change it by surface treatment of the substrate, etc.

Furthermore, the pH of the aqueous phase when forming the second layer and the third layer of the light emitting layer of the EL device of the present invention by the single molecule accumulation method.
1. The type of additive and its acid for adjusting the pH of the aqueous phase, the temperature of the aqueous phase, the operating conditions such as the rate of raising and lowering the substrate or the surface pressure, etc., are determined by the type of monolayer-forming compound used,
It may be selected as appropriate depending on the characteristics of the film to be formed.

The light-emitting layer of the present invention can be formed, for example, in the following manner using the single molecule accumulation method as described above and other thin film forming methods such as vapor deposition.

First, a third layer consisting of a monomolecular film or a monomolecular cumulative film having a desired configuration is formed using the third layer forming material described above on the substrate on which the transparent electrode layer is provided. Next, a first layer having a desired structure is formed on this third layer by vapor deposition or the like using a material capable of forming the first layer described above. Further, on this first layer, a second layer consisting of a monomolecular film or a monomolecular cumulative film having a desired configuration is laminated using a material capable of forming the above-described second layer.

Furthermore, a third layer is laminated on the second layer, and the first to third layers are stacked according to the desired number of interfaces between the first layer and the second layer.
Repeat the layer formation operation twice or more.

Finally, on this third layer, A1. The EL element of the present invention can be formed by laminating metal materials such as Ag and Au by a vapor deposition method or the like.

If a substrate with a non-transparent electrode plate or electrode layer is used as the substrate for forming the first light-emitting layer, the final
．． Materials for forming a transparent electrode layer, such as T and O, may be laminated onto the light emitting layer by vapor deposition or the like. In addition, when both electrodes are transparent, a transparent electrode layer is formed using the above-mentioned material on a transparent substrate for forming a light emitting layer, and another transparent electrode layer is laminated after the formation of the light emitting layer is completed. good.

Note that the plurality of first layers included in the light emitting layer of the EL element of the present invention may each have the same structure, and the structure of one or more of the plurality of first layers may be different from each other. The structure of the first layer may be different from that of the other first layers.
The same applies to the layer and the third layer. Further, an adhesive layer may be provided between each layer constituting the EL element of the present invention in order to improve the adhesiveness of each layer. Furthermore, it is desirable that the EL element of the present invention be provided with a protective structure for protecting the element from the effects of moisture and oxygen in the air.

The EL device of the present invention as described above mainly emits light at the interface between two layers having different electrochemical properties, and has a structure in which a plurality of such interfaces are provided in the light extraction direction of the EL device. The amount of light emitted per unit of the light extraction surface is greatly increased compared to conventional EL elements.

Furthermore, in the EL element of the present invention, for a plurality of interfaces that mainly emit light, the composition of the two layers constituting the interface is changed for each interface, and these are combined to achieve a desired emission color, etc. It is now possible to control accordingly.

Further, the light emitting layer of the EL element of the present invention is mainly formed by combining an organic compound material and a thin film formation suitable for the material, and in particular, the second layer and the third layer of each layer constituting the light emitting layer. Although the layer is formed from a monomolecular film or a monomolecular cumulative film, it has a multilayer structure with multiple interfaces that emit light, as shown in
The overall thickness of the light-emitting layer is formed to be thin, and an efficient light-emitting state can be obtained even when driven at a low voltage, and sufficient brightness can be obtained.

Moreover, in the EL device of the present invention, since the second layer that is involved in the direct light emission of the light emitting layer is formed by a monomolecular layer or a monomolecular cumulative film, the functionality of the compound that is directly involved in light emission is The light-emitting layer contains a compound whose portions are oriented and arranged toward the interface with high order and precision, and which can serve as an electron acceptor and a compound that can serve as an electron donor for compounds directly involved in light emission. This makes it possible to emit light based on the formation of an exciplex through more efficient electron transfer.

In addition, monomolecular films can be formed at almost normal temperature and pressure, and the second and third layers constituting the light emitting layer cannot be formed by conventional vapor deposition methods. It has become possible to use heat-sensitive organic compounds as constituent materials.

Furthermore, each layer of the light-emitting layer of the EL device of the present invention can be easily formed as a thin film with high precision using various organic compound materials, and even when the EL device of the present invention is formed as an EL device with an area of approximately 9 mm, it does not emit light. The layers were formed with high precision and had good functionality as a large-area EL device, and the EL device of the present invention was an inexpensive and mass-producible EL device.

Hereinafter, the EL device of the present invention will be explained in more detail according to Examples.

Example 1 5f) A 1. A T and 0 layer was formed to obtain a transparent electrode plate. This electrode plate was placed in a Langmuir-Trough 4 manufactured by Joyce-Loebe 1.
10'+aol#! The sample was immersed in an aqueous phase whose pH was adjusted to 6.5 by containing CdCl2.

Next, add stearic acid to chloroform. IXIO-3m
0.5 n/! of a solution dissolved at a concentration of ol/Il! of,
It was developed on the aqueous phase. After chloroform was removed by evaporation from the surface of the aqueous phase, the surface pressure of the aqueous phase was adjusted to 3 Qdyne/am, and a film of stearic acid was precipitated on the surface of the aqueous phase.

Furthermore, while keeping the surface pressure constant, the electrode plate was gently pulled across the water surface at a speed of 20 cm/sin.
A monomolecular film consisting of stearic acid molecules as a layer is formed on the electrode layer of the electrode plate, and this is pulled out of the aqueous phase.
It was left to dry at room temperature for 0 minutes or more. Furthermore, this operation was repeated twice to form a monomolecular cumulative film in which three monomolecular films made of stearic acid molecules were laminated as a third layer on the electrode layer of the electrode plate. Note that the stearic acid remaining on the surface of the water phase was completely removed from the surface of the water phase.

Next, this electrode plate was set at a predetermined position in the vapor deposition tank of the resistance heating vapor deposition apparatus, and anthracene (ALP, 216°C) was placed in one of the resistance heating ports, and indazole (layer) was placed in the other one. After first reducing the pressure in the tank to a vacuum level of 10' Torr, the current flowing to the port containing indazole was kept constant so that the indazole deposition rate was about 0.2 people/see. and the current flowing through the port containing anthracene was adjusted so that the deposition rate of the entire vapor deposition layer made of a mixture of anthracene and indazole was 2 people/see, and the current flowing through the port containing anthracene was adjusted to 200. The layer was formed on an insulating layer as a third layer which was previously formed as a first layer. Note that the degree of vacuum in the tank during vapor deposition was maintained at 9 x 1 O-6 Torr, and the temperature of the substrate holder was 20°C.

After forming the first layer in this way, the electrode substrate was immersed in the aqueous phase from which the remaining stearic acid had been completely removed, and then freshly added these at a ratio of 100 mol: 1 mol. The total amount is 1×10'n+ol/j! of a solution dissolved in chloroform with a degree of filtration of 0.5 + aj! was spread on this water phase, the surface pressure was adjusted to 30 dyne/cm, and when a monomolecular film of the above compound was formed on the water phase, the electrode plate was gently moved in the direction across the water surface at a speed of 2 cm/win. 2 up and down
By reciprocating, a monomolecular cumulative film consisting of four monomolecular films made of the above compound molecules was formed at an angle of 52° as a second layer on top of the previously formed first layer. Next, this electrode plate is pulled out of the water phase,
It was again left to dry at room temperature for 30 minutes or more.

Thereafter, according to the method described above, a third layer consisting of two monomolecular films made of stearic acid was laminated on the second layer,
A light-emitting layer C having four interfaces between the first layer and the second layer is obtained by repeating the formation operations from the first layer to the third layer described above four times.
A layer thickness of about 150 OA) was formed.

The electrode plate on which the light-emitting layer was formed in this way was placed into the vapor deposition tank again, and the pressure inside the tank was first reduced to a vacuum level of 104 Torr, and then the vacuum level was further adjusted to 10' Torr, and then the vacuum level was adjusted to 20 A. /5ecc7) Deposition rate: 1500A
(7) An EL element of the present invention was formed by depositing an A1 layer on the last formed third layer as a back electrode. This EL
As shown in FIG. 4, after the device is sealed with a sealing glass 41, silicone oil 42 that has been purified, degassed, and dehydrated according to a conventional method is injected into the seal to seal the EL cell 43.
was formed.

KO (7) , J: EL X E L SE/I/ (7) Electrode 44.45, AC voltage of 20 V, 400 Hz was applied to emit light, and the brightness and current density in the emitted light were measured. , current density 0.09 mA/c+s2te28
The brightness of Ft-L was measured.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an example of the EL element of the present invention, and FIG.
The figure is a schematic diagram of the molecular structure of the monolayer-forming compound, and Figure 3 is a schematic diagram showing a typical example of the arrangement of molecules at the interface between the first layer and the second layer of the EL device of the present invention. , FIG. 4 is a schematic cross-sectional view of an EL nacelle incorporating the EL element of the present invention. l, 44: Transparent electrode layer 2.45: Electrode layer 3: Luminescent layer 4-1.4-2.4-3: Third layer 5-1.5-2.5-3: First layer 8 -1.6-2.8-3: Second layer? -1.7-2: Interface 21.31: Functional part 22.32: Hydrophilic part 23.33: Hydrophobic part 35: Compound molecule having ED-d compound as a functional part 40: EL element 41 Nigaras Seal 42: Silicone oil 43: EL Cell 5 [; Section 1 Section 2 Fig. 4

Claims (1)

[Claims] 1) In an electroluminescent element having two electrode layers, at least one of which is transparent, and a light-emitting layer provided between these electrode layers, the light-emitting layer is an organic compound that relatively exhibits electron-accepting properties. a first layer containing an organic compound having relatively electron-donating properties, and a third layer having electrically insulating properties.
furthermore, the first layer contains another compound that can serve as an electron acceptor for the relatively electron-accepting organic compound, and the second layer contains the relatively contains another compound that can serve as an electron donor for an organic compound exhibiting electron donating properties, and these layers are arranged on the third layer from one of the electrode layers to the other. The first layer, the second layer, and the third layer are laminated in this order twice or more, and the second layer and the third layer are made of a compound capable of forming each of these layers. An electroluminescent device comprising a monomolecular film or a monomolecular cumulative film.