JPH0446311B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to an electroluminescent device (electroluminescent (EL) device) that performs electroluminescence.
In detail, it has a layer with an EL function that combines two types of thin films made of organic compounds with different electrochemical properties, and in particular, a two-terminal EL that provides efficient light emission even when driven at low voltage and has sufficient brightness. Regarding elements. [Prior Art] An EL element has a structure in which a light-emitting layer containing a material with an EL function, that is, a material that emits light when placed in an electric field, is arranged between two electrodes. A light-emitting element that generates light by applying a voltage to generate an electric field and converting electrical energy directly into light.
Alternatively, unlike conventional light emitting methods such as fluorescent lamps, in which electrically excited gas imparts energy to a phosphor to cause it to emit light, various shapes such as a thin panel, belt, cylinder, etc. It is attracting attention as a component of a display medium used for displaying lamps, lines, figures, images, etc., or as a material that has the potential to realize light emitting bodies such as large-area panel lamps. These EL devices differ in their light emitting 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, which performs Furthermore, due to the differences in the structure of the light-emitting layer of the device, there are two types of EL devices: a thin-film type that has a thin film made of a material that has an EL function as a light-emitting layer, and a light-emitting type that has 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, the materials with the above EL function include:
Conventionally, inorganic metal materials such as ZnS containing Mn, Cu, or ReF ₃ (Re represents a rare earth) as an activator have been mainly used. Thin-film EL elements have a thin light-emitting layer,
It has a structure suitable for making the distance between the electrodes sufficiently short, generating a stronger electric field within the light-emitting layer, and obtaining good light emission with high brightness even when driven at low voltage. ing. However, the above
When manufacturing this type of EL element by forming a thin film emitting layer using an inorganic metal material mainly composed of ZnS using a thin film formation method such as vapor deposition, there is a problem in that the manufacturing cost becomes extremely high. Furthermore, since it is extremely difficult to form a light-emitting layer consisting of a uniform thin film over a large area, it has been impossible to mass-produce high-quality, large-area EL elements. On the other hand, as an EL element that is easy to mass-produce and is advantageous in terms of cost, the above-mentioned ZnS is mainly used.
An organic powder type EL element of an intrinsic EL type is known, in which a light-emitting layer is formed by dispersing an EL inorganic material in an organic binder. However, in this powder type EL element,
If the layer thickness is thin, defects such as pinholes are likely to occur in the light-emitting layer.There are structural limits to reducing the layer thickness of the light-emitting layer beyond a certain level in order to sufficiently improve the light-emitting characteristics. It is not possible to emit light, especially high brightness, and since the layer thickness is relatively thick, there have been problems such as increased power consumption in order to generate a stronger electric field. This is an improved powder type EL device that has an intermediate dielectric layer made of vinylidene fluoride polymer in the light emitting layer of this powder type EL element to generate a stronger electric field.
Although a device is known from Japanese Patent Application Laid-Open No. 172891/1989, the device currently does not have 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 scientific structure and higher-order structure of organic compound materials, which can form thin films with high precision, and are being used in optical and electronic materials instead of conventionally used metals and inorganic materials. It is attracting attention for its application as a material for electrochromic elements, piezoelectric elements, pyroelectric elements, nonlinear optical elements, ferroelectric liquid crystals, etc., and furthermore, it is being used to form the light emitting layer of EL elements using these materials. It is expected that it will be used as a material for Among these, anthracene, pyrene, perylene, or their derivatives are known as organic materials for the light-emitting layer of EL devices, and carrier injection using a monomolecular cumulative film of these materials as the light-emitting layer is known. The EL type element was published in Japanese Patent Application Laid-Open No. 1986.
It is known from the publication No.-35587. However, in this EL element, although the light emitting layer is formed as a thin film with high precision,
The density of carrier electrons or holes is very low, and the probability of excitation of functional molecules due to carrier movement or recombination is low, making it difficult to obtain efficient light emission, which is particularly unsatisfactory in terms of power consumption and brightness. The current situation is that it has not become familiar. [Object of the Invention] An object of the present invention is to provide a novel EL element that has good luminous efficiency, can obtain 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 be able to appropriately select various organic compound materials for EL devices and to form thin films by combining them with optimal thin film formation methods, thereby easily imparting desired light emitting characteristics. The object of the present invention is to provide an EL element having a structure that allows the above. [Structure of the Invention] That is, the two-terminal electroluminescent device of the present invention includes two electrode layers, at least one of which is transparent, and a light-emitting layer provided between these electrode layers. The layers include a first layer containing an organic compound that relatively exhibits electron-accepting properties, a second layer containing an organic compound that relatively exhibits electron-donating properties, and a third layer having an electrically insulating layer. and these layers are stacked by repeating the first layer, the second layer, and the third layer in this order two or more times on the third layer from one side of the electrode layer to the other. the first layer, the second layer and the third layer.
The layer is characterized in that it consists of a monomolecular film or a monomolecular cumulative film of a compound capable of forming each of these layers. The two-terminal electroluminescent device (hereinafter simply EL) of the present invention
The device basically has two electrode layers, 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. This is a so-called intrinsic EL type thin film 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 that exhibits a relatively electron-accepting property (hereinafter referred to as an EA compound) and an organic compound that exhibits a relatively electron-donating property (hereinafter referred to as an ED compound). It has a structure in which these compounds are placed in contact with each other, and has a luminescence effect as a main light source based on the formation of an exciplex due to the transfer of electrons between these compounds when they are placed in an electric field. Moreover, such an exciplex is characterized by having a structure suitable for being efficiently formed with the generation of an electric field. 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. Reference numerals 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, and between the third layer 4-1, 4-3 which functions as an insulating layer laminated on both the upper and lower ends, the first layer 5-1, 5-2, Second layer 6-
It has a multilayer structure in which layers 1, 6-2 and the third layer 4-2 are alternately stacked, and each layer is a monomolecular film of a compound capable of forming the respective layer or a monomolecular film thereof. It is formed from a cumulative film. The first layer 5-1 of the light-emitting layer 3 has EA for the above-mentioned ED compound contained in the second layer 6-1.
This first layer 5 contains a compound that can be a compound.
-1, the second layer 6-1 is laminated in direct contact with
ED for the EA compound contained in the first layer 5-1
The interface 7-1 between the first layer 5-1 and the second layer 6-1 is a contact surface between the EA compound and the ED compound. The relationship between the first layer 5-2 and the second layer 6-2 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, the EA compound and the 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. As described above, the main source of light emission in the EL element of the present invention is light emission at the interfaces 7-1 and 7-2. First layers 5-1, 5-2 and second layers 6-1, 6- constituting the light emitting layer of the EL element of the present invention
2 is formed from a monomolecular film or a monomolecular cumulative film containing a compound molecule directly involved in the formation of an electric field excited complex as shown below, or a compound molecule having at least one of the compound molecules as a functional part. ing. As for the arrangement of compound molecules directly involved in the formation of such an electric field excited complex in the light emitting layer 3, the following combinations can be cited as typical examples. (a) first layer 5-1, 5-2 and second layer 6-1,
EL based on exciplex formation for each of 6-2
Compound molecules with functions (mainly emitting light) are arranged. (b) Compound molecules having an EL function based on exciplex formation are arranged in the first layers 5-1 and 5-2,
Compound (ED compound) molecules that can serve as electron donors for these compound molecules are arranged in the second layers 6-1 and 6-2, respectively. (c) Compound molecules having an EL function based on exciplex formation are arranged in the second layers 6-1 and 6-2,
Molecules of compounds (EA compounds) that can act as electron acceptors for these compounds are formed in the first layer 5, respectively.
-1 and 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 susceptible to external perturbation, and is easily excited by an electric field is suitably used. Examples of such compounds include fused polycyclic aromatic hydrocarbons, p-terphenyl, 2,5-diphenyloxazole, 1,4-bis-(2-methylstyryl)-benzene, xanthine, coumarin,
Acridine, cyanine dye, benzophenone, phthalocyanine, metal complex of phthalocyanine, porphyrin, metal complex of porphyrin, 8-hydroxyquinoline, metal complex of 8-hydroxyquinoline, ruthenium complex, rare earth complex, and derivatives of these compounds, and other than the above Among the heterocyclic compounds and their derivatives, aromatic amines, aromatic polyamines, and compounds with a quinone structure, compounds having an EL function based on exciplex formation can be mentioned.
One or more compounds that can be an EA compound and one or more compounds that can be an ED compound are appropriately selected and combined to form a light-emitting layer having the above-described structure (a) of the first layer and second layer. It can be formed using the single molecule accumulation method described. Furthermore, compounds that can serve as electron acceptors or electron donors for the above-mentioned compounds having an EL function based on exciplex formation include heterocyclic compounds other than the above-mentioned compounds and their derivatives, aromatic amines, and aromatic polyamines. , a compound having a quinone structure, tetracyanoquinodimethane, tetracyanoethylene, etc., and by appropriately selecting and combining the above-mentioned compounds and these compounds, the above-mentioned first layer and second layer can be formed. Layer composition (b) or
A light emitting layer having (c) can be formed. Note that the compounds that can form the functional moieties mentioned above may be compounds that have a function of emitting light that is not based on exciplex formation, and the light emission in the EL element of the present invention is caused by the The light emission is not limited to only at the interfaces 7-1 and 7-2 between the first layer 5-1 and the second layer.
5-2 and/or the second layer 6-1, 6-2 may also include a 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 at least one of the compound molecules as a functional moiety, it is possible to achieve highly ordered molecular orientation and arrangement, and to easily form an ultra-thin film layer. A so-called single molecule accumulation method, which can be used to form a single molecule, 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 is expressed between the area A per molecule and the surface pressure π;
πA=kT (k: Boltzmann constant, T: absolute temperature)
holds true, and these molecules form a "gas film"; however, when A is made sufficiently small, the intermolecular interaction becomes stronger, and these molecules form a two-dimensional solid "condensation film (or solid 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 molecules forming the monolayer are arranged in such a way that, for example, almost all of the hydrophilic parts of the constituent molecules are oriented toward the substrate in a highly ordered manner.
It can be made uniform within one monolayer. Therefore, by making the interface between the first layer and the second layer of the EL element of the present invention an interface made of a monomolecular film,
It becomes possible to arrange functional parts consisting of compound molecules directly involved in exciplex formation, which are contained in the first layer and the second layer, respectively, at a 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 ET 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 compound that can form the first layer and the second layer of the light-emitting layer of the EL device of the present invention is a compound that can form the above-mentioned functional portion or a compound that can function as a compound molecule. For example, in the case of a monolayer-forming compound having one functional moiety, these compounds have at least one functional moiety, depending on the position within the molecule containing the functional moiety. As shown in the schematic diagram of the molecular structure in Figure 2, (a) the functional part 21 is on the hydrophilic part 22 side, - Figure 2a (b) the functional part 21 is on the hydrophobic part 23 side, - Fig. 2b (c) Functional part 21 is located approximately midway between hydrophobic part 23 and hydrophilic part 22 - It is broadly classified into three types as shown in Fig. 2c. Components of the hydrophilic portion 22 of these compounds include, for example, carboxyl groups and metal salts thereof;
Amine salts and esters, sulfonic acid groups and their metal salts and amine salts, sulfonamide groups, amide groups, amino groups, imino groups, hydroxyl groups, 4
grade amino group, oxyamino group, oxyimino group,
Diazonium group, guanidine group, hydrazine group,
Examples include a phosphoric acid group, a silicic acid group, and an aluminate group, each of which can be used alone or in combination to constitute the hydrophilic moiety 22 in the above compound. Furthermore, the constituent elements of the hydrophobic portion 23 include linear or branched alkyl groups, olefinic hydrocarbons such as vinylene, vinylidene, and acetylene, fused polycyclic phenyl groups such as phenyl, naphthyl, and anthranyl, and biphenyl groups. Examples include hydrophobic groups such as chain polycyclic phenyl groups, and these groups can also constitute the hydrophobic moiety 23 in the above compound either singly or in combination. On the other hand, the orientation and arrangement of the monomolecular film at the interfaces 7-1 and 7-2 (where light emission mainly occurs) between the first layer and the second layer of the light-emitting layer of the EL device of the present invention are as follows: A schematic cross-sectional partial view near the interface 7-1 in Figures 3a and 3b (in this figure, the first layer and the second layer
As shown in (1) the functional part 31 of the molecules forming the monomolecular film of the first layer 5-1 is and a hydrophilic portion 32' having a functional portion 31' of the molecules forming the monomolecular film of the second layer 6-1 are oriented at the interface 7-1. - Figure 3a a (2) Forming a monomolecular film of the second layer 6-1 with a hydrophobic part 33 having a functional part 31 of molecules forming a monomolecular film of the first layer 5-1 A hydrophobic portion 33' with a functional portion 31' of the molecule is oriented at the interface 7-1. - Figure 3a b (3) Forming a monomolecular film of the second layer 6-1 with a hydrophobic part 33 having a functional part 31 of molecules forming a monomolecular film of the first layer 5-1 A hydrophilic portion 32' with a functional portion 31' of the molecule is oriented at the interface 7-1. - Figure 3b a (4) Forming a monomolecular film of the second layer 6-1 with a hydrophilic part 32 having a functional part 31 of molecules forming a monomolecular film of the first layer 5-1 A hydrophobic portion 33' with a functional portion 33' of the molecule is oriented at the interface 7-1. - It is basically divided into four patterns as shown in Figure 3b. In order to form such an interface pattern of the light-emitting layer, compounds belonging to types a and b of the monomolecular film-forming compounds listed above are preferably used. In addition, in order to form the above-mentioned interface pattern (1), it is preferable to use a compound belonging to the type a in the first layer and the second layer.
In order to form (2), it is preferable to use a compound belonging to the type b mentioned above for the first layer and the second layer. Furthermore, in order to form the above-mentioned interface pattern (3), it is preferable to use the compound belonging to the type a in the first layer and the compound belonging to the type b in the second layer, and form the above-mentioned interface pattern (3). In order to form 4), it is preferable to use a compound belonging to type b in the first layer and a compound belonging to type a in the second layer. In the example explained above, the first layer and the second layer are formed from a monomolecular film, but the first layer 5-1, 5-2 and/or the second layer 6-1 ，
Even when 6-2 is composed of a monomolecular cumulative film,
The interface between the first layer and the second layer 7-
What is necessary is to form a monomolecular film constituting 1 and 7-2. In addition, when the first layer 5-1, 5-2 and/or the second layer 6-1, 6-2 consists of a monomolecular cumulative film, each monomolecular film constituting the cumulative film is may be the same, or one or more of the monolayers may be different from the other monolayers. Furthermore, the structure of the monomolecular cumulative film due to the orientation state of the molecules forming each monolayer is the so-called Y type (between each film, a hydrophilic part and a hydrophilic part or a hydrophobic part and a hydrophobic part are mutually separated). Various types of structures are available, such as the X-type (a structure in which the hydrophobic part of each film faces the substrate side), the Z-type (a structure in which the hydrophilic part of each film faces the substrate side), and variations thereof. It can be a structure. Furthermore, the monomolecular film constituting the light-emitting layer of the present invention may be a multicomponent monomolecular film formed of two or more kinds of compounds. In such a case, the first layer and the second layer may be a combination of two or more compounds having functional moieties to increase the strength of the monomolecular layer constituting the emissive layer or to improve the adhesion between each layer. It may be formed by adding other ingredients to improve the properties. The structure of such a monomolecular film or a monomolecular cumulative film depends on the desired electrical properties of the first layer or the second layer, that is, the structure of the compound forming the first layer or the second layer or An appropriate selection may be made depending on the combination of compounds, for example, end molecular films made of compounds belonging to types a, b, or c of the monolayer-forming compounds are combined and accumulated to form a film perpendicular to the surface direction of the monolayer. It is possible to control the potential curve of π electrons in various directions. The above first layer 5-1, 5-2 and second layer 6
Compounds that can be used to form -1,6-2 include the above-mentioned compounds capable of forming a functional moiety, or compounds having one or more of the above-mentioned compounds, which have hydrophilic properties. Compounds that have a good balance of hydrophilic and hydrophobic moieties can be used as is for forming monolayers, and those that do not have hydrophilic and/or hydrophobic moieties as mentioned above newly added to the molecule. It can be used as a compound for forming a monomolecular film. Examples of such compounds include compounds represented by the following structural formulas. In addition, in the structural formula shown below, X and Y
represents a hydrophilic group as mentioned above, but when both of these exist in one molecule, it is sufficient that one of them is a hydrophilic group, and in such a case, the other one is hydrogen. Further, R represents a linear or side chain alkyl group having about 4 to 30 carbon atoms, preferably about 10 to 25 carbon atoms. Among these compounds, the compounds with structural formulas No. 1 to No. 35 are compounds that have an EL function based on the formation of an exciplex among the compounds that can form the functional moiety listed above, by combining them with hydrophobic groups and/or It is modified with a hydrophilic group to form a monomolecular film-forming compound.
In addition, the compounds of structural formulas No. 42 to No. 54 and No. 85 to No. 86 have structures in which an alkyl chain is directly bonded to a functional moiety; The bond may be, for example, an ether bond, a bond via a carbonyl group, or the like. 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 insulating properties, and in particular, the third layer 4-1, 4
-3 has a function of increasing the insulation of the capacitor structure of the EL element of the present invention, and the third layer 4-2 confines the movement of electrons within the minimum necessary area, and emit light through efficient exchange of electrons. It has the function of making it perform. The materials that can form these third layers include the following general formula that can form a monomolecular film with precise and uniform insulation: CH ₃ (-CH ₂ )- _o X, or (In the above formula, n is 10≦n≦30, and
are −COOH, −CONH ₂ , −COOR, −N ⁺ (CH ₃ ) ₃・
^Cl-

[Formula] Cl ^- ,

Examples include compounds represented by the following formula: This third layer may also be a monomolecular film or a monomolecular cumulative film, and in the case of a monomolecular cumulative film, even if each monomolecular film is the same, one of each monomolecular film
One or more of the monolayers may be different from other monolayers. Furthermore, the monomolecular film forming this third layer is
It may be a monomolecular film consisting of one type of compound,
Further, a multi-component monomolecular film composed of two or more kinds of compounds may be used. Note that up until now, the first layer and the second layer have been described using FIG.
The EL device of the present invention having two interfaces formed by layers has been described.
The number of interfaces that the element has 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.
For the first layer, 300 Å or less, preferably 100 Å
Å or less, the second layer is 300 Å or less, preferably 100 Å or less, the third layer is 500 Å or less, preferably 200 Å or less, and the total layer thickness of the light emitting layer is 1 μm or less, preferably 3000 Å or less This is desirable in order to obtain a good light emission state even when driven at a low voltage. Two electrode layers 1 and 2 of the EL element of the present invention
At least one of these is provided as a transparent electrode to extract light. When forming an electrode layer as a transparent electrode,
InO ₂ on a film or sheet such as PMMA, polyester, or a transparent substrate such as a glass plate.
SnO ₂ , indium tein oxide (ITO)
The light emitting layer can be formed by laminating these materials by a vapor deposition method or the like, or by directly laminating these materials on the light emitting layer. In addition, non-transparent electrode layers can be formed by thin plates made of materials that can form normal electrodes with sufficient conductivity, or by directly depositing Al, Ag, Au, etc. on a suitable substrate or on a light-emitting layer formed. It can be formed by laminating layers by a vapor deposition method or the like. The thickness of these electrode layers is about 0.01 to 0.3 μm, preferably about 0.05 to 0.2 μm. Note that the shape and size of the EL element of the present invention are as follows:
It can be made into various shapes as desired, for example, by using a substrate for forming a monomolecular film as a substrate for forming a transparent electrode, and using a plate-shaped, belt-shaped, or cylindrical substrate as the substrate, the desired shape can be obtained. and size. Moreover, the two electrode layers may be patterned into various shapes as desired. In the EL element of the present invention having the above configuration,
By applying direct current, alternating current, or pulse voltage between the two electrodes 1 and 2 of the EL element, for example, so that an electric field of about 1×10 ⁵ to 3×10 ⁶ is applied to the light emitting layer 3, a good condition can be obtained. Light emission can be obtained from the light emitting layer 3 through the transparent electrode. Hereinafter, typical operations of the single-molecule accumulation method, typified by the Langmuir-Prodget method (LB method), applied to the formation of the light-emitting layer of the EL device of the present invention will be explained. 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 an appropriate solvent is spread into the aqueous phase,
This compound is deposited in the form of a film on the surface of the aqueous phase. At this time, in order to prevent this precipitate 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 state of aggregation of the membrane substance. Obtain a proportional surface pressure π. Then, activate the partition plate to reduce the expansion area,
The surface pressure π is gradually increased and set to a surface pressure π suitable for forming a monomolecular film. Here, this surface pressure π
When the previously immersed substrate is gently moved up and down in a direction perpendicular to the aqueous phase surface while maintaining the temperature, the monomolecular film is transferred onto the substrate as the substrate moves upward and downward. , a monomolecular cumulative film is formed. To transfer a monomolecular film onto a substrate, in addition to the vertical immersion method mentioned above, there are also horizontal attachment methods in which the substrate is brought into contact with the water phase horizontally while keeping it parallel to the surface, and a cylindrical substrate is rotated on the water surface. Various methods can be applied, such as a rotating cylinder method in which a monomolecular film is transferred to the surface of a substrate using a rotating cylinder method, 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. In addition, according to the horizontal deposition method, a monomolecular film with the hydrophobic groups facing the substrate side is formed, and when it is made into a cumulative film, the so-called
A mold film is formed. However, the orientation of such hydrophilic groups and hydrophobic groups can also be changed by surface treatment of the substrate. Furthermore, the PH of the aqueous phase when forming the light-emitting layer of the EL device of the present invention by the single molecule accumulation method, the type and amount of additives for adjusting the PH of the aqueous phase, the temperature of the aqueous phase, and the substrate. The operating conditions, such as the rate of raising and lowering or the surface pressure, depend on the type of monolayer-forming compound used,
An appropriate selection may be made depending on the characteristics of the film to be formed. By the single molecule accumulation method as described above, the light emitting layer of the present invention can be formed, for example, in the following manner. 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 and a second layer consisting of a monomolecular film or a monomolecular cumulative film having a desired configuration are formed in this order using a material capable of forming the first layer and second layer described above. Laminated on the previously formed third layer. Furthermore, a third layer is laminated on the second layer, and the forming operation of the first layer to the third layer is repeated depending on the desired number of interfaces between the first layer and the second layer. Repeat more than once. Finally, a metal such as Al, Ag, or Au is laminated on this third layer by a vapor deposition method or the like to form the EL of the present invention.
elements can be formed. If a substrate with a non-transparent electrode plate or electrode layer is used as the substrate for initial monolayer formation, a material for forming a transparent electrode layer such as ITO is finally laminated by vapor deposition, etc. Good.
Also, if both electrodes are transparent,
A transparent electrode layer may be formed using the above-mentioned material on a transparent substrate for forming a monomolecular film, and the transparent electrode layer may be laminated after the formation of the light emitting layer is completed. 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 may be different from that of other first layers, and the same applies to the second and third layers. 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, the present invention
It is desirable that the EL element be provided with a protective structure to protect 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 higher than that of conventional EL.
The size was significantly increased compared to that of the element. Furthermore, in the EL element of the present invention, the composition of the two layers constituting the interface is changed for each interface, and these are combined to change the luminescent color as desired for the plurality of interfaces that mainly emit light. It became possible to control the Furthermore, although the light-emitting layer of the EL element of the present invention is composed of a plurality of monomolecular films and has a multilayer structure with a plurality of interfaces that emit light as described above, the entire light-emitting layer is The thickness is extremely thin, and even when driven at low voltage, an efficient light emitting state can be obtained, and sufficient brightness can be obtained. Moreover, in the EL device of the present invention, each layer of the light emitting layer is formed of a monomolecular film, so
The functional parts of the compound that are directly involved in light emission are highly ordered and precisely oriented and arranged toward the interface, making it possible to emit light based on the formation of exciplexes due to more efficient electron transfer. can be formed at approximately room temperature and pressure, and even heat-sensitive organic compounds that could not be used in conventional vapor deposition methods can be used as constituent materials, and the EL device of the present invention is inexpensive. It became an EL element that could be mass-produced. Furthermore, even when the EL device of the present invention is formed as a large-area EL device, the large-area light-emitting layer is formed with high precision by the single-molecule accumulation method, and it has good functionality. . Hereinafter, the EL device of the present invention will be explained in more detail according to Examples. Example 1 An ITO layer with a thickness of 1500 Å was formed on a 50 mm square glass surface by sputtering to obtain a transparent electrode plate. This electrode plate was manufactured by Joyce-Loebel.
4×10 ^-4 mol/in Langmuir−Trough4
It was immersed in an aqueous phase whose pH was adjusted to 6.5 by containing CdCl ₂ . Next, add arachidic acid to chloroform 1x
0.5 ml of the solution dissolved at a concentration of 10 ^-3 mol/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 30 dyne/cm, and a film of arachidic acid was precipitated on the surface of the aqueous phase. Furthermore, while keeping the surface pressure constant, the electrode plate was gently pulled up at a speed of 2 cm/min in the direction across the water surface, and the third layer, a monomolecular film insulating layer made of arachidic acid molecules, was applied to the electrode layer of the electrode plate. This was pulled out of the aqueous phase and left to dry at room temperature for 30 minutes or more. Here, the arachidic acid remaining on the surface of the aqueous phase is completely removed from the surface of the aqueous phase, and the electrode plate on which the monomolecular insulating layer of arachidic acid has been formed is immersed again in the aqueous phase, and then the electrode plate is re-immersed into the aqueous phase. 0.5 ml of a chloroform solution containing a concentration of 1 x 10 ^-3 mol/was developed on this aqueous phase, and the surface pressure was increased.
After adjusting to 30 dyne/cm, gently pull the electrode plate across the water surface at a speed of 2 cm/min.
A monomolecular film made of the above compound molecules was formed as a second layer on the insulating layer. Next, this electrode plate was taken out of the aqueous phase and left to dry again at room temperature for 30 minutes or more. Furthermore, the above compounds left on the surface of the water phase are completely removed, the electrode plate is immersed in the water phase, and a new one is prepared. 0.5 ml of a chloroform solution containing a concentration of 1 x 10 ^-3 mol/was developed on this aqueous phase, and the surface pressure was increased.
After adjusting to 30 dyne/cm, gently pull the electrode plate across the water surface at a speed of 2 cm/min.
A monomolecular film composed of the above compound molecules was formed as a first layer on the second layer. Thereafter, the above-described formation operation from the third layer to the first layer is repeated four times, and finally the third layer is laminated to form a light-emitting layer having four interfaces between the first layer and the second layer ( A layer thickness of approximately 400 Å) was formed. The electrode plate with the luminescent layer formed in this way is
The tank was placed in a vapor deposition tank, and the pressure inside the tank was first reduced to a vacuum level of 10 ^-6 Torr, and then the vacuum level was further adjusted to 10 ^-5 Torr, and an Al layer of 1500 Å was finally deposited at a evaporation rate of 20 Å/sec. The EL element of the present invention was formed as a back electrode by vapor deposition on the formed third layer. As shown in FIG. 4, after this EL element 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.
An EL cell 43 was formed. 10V to electrodes 44 and 45 of such an EL cell,
An AC voltage of 400 Hz was applied to emit light, and the luminance and current density of the emitted light were measured. The results are shown in Table 1. Examples 2 to 4 Same as Example 1 except that the forming operation from the third layer to the first layer is repeated 8 times (Example 2), 12 times (Example 3), or 16 times (Example 4) first
8 interfaces between the layer and the second layer (Example 2), 12
(Example 3) or 16 (Example 4) EL elements of the present invention were respectively formed, and further, EL cells were created using these. Each EL cell was caused to emit light in the same manner as in Example 1,
The brightness and current density at that time were measured. The results are shown in Table 1. Example 5 An ITO layer with a thickness of 1500 Å was formed on a 50 mm square glass surface by sputtering to obtain a transparent electrode plate. This electrode plate was manufactured by Joyce-Loebel.
4×10 ^-4 mol/in Langmuir−Trough4
It was immersed in an aqueous phase whose pH was adjusted to 6.5 by containing CdCl ₂ . Next, add arachidic acid to chloroform 1x
0.5 ml of the solution dissolved at a concentration of 10 ^-3 mol/was developed on the aqueous phase. After evaporating chloroform from the surface of the water phase, the surface pressure of the water phase was reduced to 30dyne/cm.
arachidic acid in the form of a film was precipitated on the surface of the aqueous phase. Furthermore, while keeping the surface pressure constant, the electrode plate was gently reciprocated vertically twice at a speed of 2 cm/min across the water surface to form an insulating layer consisting of four monolayers of arachidic acid. A third layer was formed on the electrode layer of the electrode plate, pulled out of the aqueous phase, and left to dry at room temperature for 30 minutes or more. Here, the arachidic acid remaining on the surface of the aqueous phase is completely removed from the surface of the aqueous phase, and the electrode plate on which the monomolecular insulating layer of arachidic acid has been formed is immersed again in the aqueous phase, and then the electrode plate is re-immersed into the aqueous phase. 0.5 ml of a chloroform solution containing a concentration of 1 x 10 ^-3 mol/was developed on the aqueous phase, and the surface pressure was increased.
After adjusting the electrode plate to 30 dyne/cm, the electrode plate was gently pulled up at a speed of 2 m/min across the water surface, and then pulled down and pulled up once each.
The first layer consists of three layers of monomolecular films made of the above compound.
layer was formed on the insulating layer. Next, this electrode plate was taken out of the aqueous phase and left to dry again at room temperature for 30 minutes or more. Next, the above compounds left on the surface of the water phase are completely removed, the electrode plate is immersed in the water phase, and a new one is prepared. 0.5 ml of a chloroform solution containing a concentration of 1 x 10 ^-3 mol/was developed on the aqueous phase, and the surface pressure was increased.
Once adjusted to 30 dyne/cm, the electrode plate was gently pulled up across the water surface at a speed of 2 cm/min, and then pulled down and pulled up once each.
The second layer has three layers of monomolecular films made of the above compound.
was formed on the first layer of the layers. Thereafter, the above-described formation operation from the third layer to the second layer is repeated four times, and finally the third layer is further laminated to form a light-emitting layer having four interfaces between the first layer and the second layer. (layer thickness: about 1000 Å) was formed. The electrode plate with the luminescent layer formed in this way is
The tank was placed in a vapor deposition tank, and the pressure inside the tank was first reduced to a vacuum level of 10 ^-6 Torr, and then the vacuum level was further adjusted to 10 ^-5 Torr, and an Al layer of 1500 Å was finally deposited at a evaporation rate of 20 Å/sec. The EL element of the present invention was formed as a back electrode by vapor deposition on the formed third layer. As shown in FIG. 4, after this EL element 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.
An EL cell 43 was formed. To the electrodes 44 and 45 of such an EL cell, 10V,
An AC voltage of 400 Hz was applied to emit light, and the luminance and current density of the emitted light were measured. The results are shown in Table 1.

【table】 [Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an example of the EL device of the present invention, FIG. 2 is a schematic diagram of the molecular structure of a monolayer-forming compound, and FIGS. 3a and 3b are diagrams showing the structure of the EL device of the present invention. FIG. 4 is a schematic diagram showing a typical example of the arrangement of molecules at the interface between the first layer and the second layer.
FIG. 2 is a schematic cross-sectional view of an EL cell incorporating an EL element. 1,44: transparent electrode layer, 2,45: electrode layer,
3: Light emitting layer, 4-1, 4-2, 4-3: Third layer, 5-1, 5-2, 5-3: First layer, 6-
1,6-2,6-3: second layer, 7-1,7-
2: Interface, 21, 31, 31': Functional part, 2
2,32,32': Hydrophilic part, 23,33,3
3': hydrophobic part, 40: EL element, 41: glass seal, 42: silicone oil, 43: EL cell.

Claims (1)

[Claims] 1. In an electroluminescent device 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 contains a first organic compound that relatively exhibits electron-accepting properties. with a layer of
A second compound containing a relatively electron-donating organic compound
and a third layer having electrical insulation properties,
These layers are formed by stacking the first layer, second layer and third layer in this order two or more times on the third layer from one side of the electrode layer to the other. , and further characterized in that these first layer, second layer, and third layer are composed of a monomolecular film or a monomolecular cumulative film of a compound capable of forming each of these layers. Light emitting element.