JPS6155185A - El element - Google Patents

Abstract

PURPOSE:The titled element which has high luminance even on low-voltage drive and excellent emission quantum efficiency, and is low-priced, made by placing a luminescent layer of a specified two-layer constitution between two electrode layers at least one of which is transparent. CONSTITUTION:A luminescent layer 2 which has a thickness of 0.01-1mum and has a two-layer constitution consisting of the first layer comprising an accumulated mixed molecular film of a thickness of about 500Angstrom , of a mixture of 1mol of an electroluminescent organic compound 4 (A) and 0.1-0.01mol of an organic compound 4' (B) that is electron accepting relative to component A; and the second luminescent layer comprising an accumulated mixed molecular film of a thickness of about 500Angstrom , of a mixture of 1mol of component A or an electroluminescent organic compound 5 (C) having the same degree of electronegativity as component A and 0.1-0.01mol of an organic compound (D) that is electron donating relative to component A or C, is formed between a transparent electrode 1 of a thickness of 0.01-0.2mum and an opaque back electron 3 of a thickness of 0.1-0.3mum.

Description

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

(Prior art) Conventional EL elements are made of Mn, Cu or Re F3.
Zn containing (Re; rare earth ion) etc. as an activator
It consists of a light-emitting layer using S as a light-emitting base material, and is broadly classified structurally into powder-type EL and thin-film type EL, depending on the basic structure of the light-emitting layer.

Among devices that have been put into practical use, thin-film ELs generally have higher brightness than powder-type ELs, but because thin-film ELs form a light-emitting layer by vapor-depositing a light-emitting base material onto a substrate, they are not suitable for large-area devices. It has the drawbacks that it is difficult to manufacture and the manufacturing cost is very high.

For this reason, powder-type EL, in which a light-emitting base material, that is, ZnS, is dispersed in an organic binder, which is most easily mass-produced and costs only a few tenths of the cost of thin-film devices, has attracted attention. Generally, in EL light emission, the thinner the thickness of the light emitting layer, the better the light emission characteristics. However, in the case of the powder type EL, since the luminescent base material is a discontinuous powder, pinholes are likely to occur in the luminescent layer when the luminescent layer is thinned.
It has a major drawback in that it is difficult to reduce the layer thickness, and therefore sufficient brightness characteristics cannot be obtained. Recently, an improved type of element in which an intermediate dielectric layer made of a vinylidene fluoride polymer is disposed within the light emitting layer of the powder type EL has been disclosed in JP-A-58-172891.
Although sufficient performance in terms of luminance and power consumption has not yet been achieved, recent research and development efforts have been actively conducted to control the chemical structure and higher-order structure of organic materials to create new materials for optical and electronics applications. EC element,
Organic materials, such as piezoelectric elements, pyroelectric elements, nonradiometer optical elements, and ferroelectric liquid crystals, have been announced that are comparable to or superior to metals and inorganic materials. As described above, amid the demand for the development of functional organic materials as new functional materials that surpass inorganic materials, we have developed a cumulative film of monomolecular layers of anthracene derivatives and pyrene conductors, which have a parent group and a hydrophobic group in one molecule. The EL element formed on the electrode substrate was disclosed in Japanese Patent Application Laid-Open No. 52-35587.
It is proposed in the Publication No. However, these EL devices have not yet achieved sufficient performance as a real EL device in terms of brightness, power consumption, etc. Furthermore, in the case of organic EL devices, the density of carrier electrons or holes is extremely low. The probability of excitation of functional molecules due to carrier recombination or the like becomes extremely small, and efficient light emission cannot be expected.

(Disclosure of the Invention) Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide an EL element that can emit light with sufficiently high brightness even when driven at a low voltage, is inexpensive, and is easy to manufacture. It is to provide.

The above object of the present invention has been achieved by forming a light emitting layer of an EL element by combining specific materials and having a specific configuration.

That is, the present invention provides an EL device consisting of a two-layered light-emitting layer and two electrode layers sandwiching the light-emitting layer, at least one of which is transparent, in which the first light-emitting layer has electroluminescent properties. The film is made of a mixed molecular salt 8I film consisting of a mixture of an organic compound (A) and an organic compound relatively electron-accepting to the compound (A) (hereinafter referred to as an acceptor), and the second light-emitting layer is electrically A luminescent organic compound (A) or an electroluminescent organic compound having the same electronegativity as the compound (A) and an organic compound that is electron donating relative to the compound (A) (hereinafter referred to as a donor). The above EL device is characterized in that it is made of a mixed molecule deposited film made of a mixture.

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

In the present invention, preferred examples of basic skeletons of compounds useful for forming the light-emitting layer are as follows. (However, φ (basic skeleton) illustrated below has 1 carbon number
It may have general substituents such as ~4 alkyl groups, alkoxy groups, alkyl ether groups, halogen atoms, nitro groups, primary to tertiary amino groups, hydroxyl groups, carboxamide groups, and sulfoamide groups. ) (Margin below) Z-N) f, OlS Z=CO, NHZ=CO, N
H,0,5Z=NH,01S Z=NH1O%S Z=NH,O,
5Z=S1Sez=s1sez=s%5eZ=W,Ol
S Z=NH1αS Z=NH,0%SSn,At
C4YbCt M=Er, Trrl Sm, Eu, Tb,
Z = O1N brutality M = A4 Gas Ir%Ta
, a=3 M=Er, Sm, E, uM=Zn%C
d%Mgs pb, a=2 Gd%Tb, Dy
ms Yb M=Er+ Sm+ Eu, Gd M=Er
1Smi EuTb, Dy, Tm%Yb
Gd, Tb%DyTm%yb Z=0, S, SeO≦p≦2 The above luminescent compounds can be used alone in each luminescent layer in the present invention, or a mixture can be used as long as they have the same electronegativity. It can also be used as Note that these compounds are examples of preferable compounds, and it goes without saying that other derivatives or other compounds may be used as long as the same purpose is achieved.

In the present invention, a luminescent compound (A) having a specific electronegativity or a luminescent compound having a similar electronegativity to the compound (A) is selected from the luminescent compounds as described above, and one EL element of the present invention is prepared. It is used as the main emissive compound of the first emissive layer and the second emissive layer, an acceptor is added to these to form the first layer, and a donor is mixed to form the second layer. It is said that

Among the luminescent compounds or non-luminescent compounds, particularly preferable compounds as acceptors include carbonyl groups,
Compounds having electron-withdrawing groups such as sulfonyl groups, nitro groups, and quaternary amino groups are the main ones, and particularly preferred compounds as donors include primary to tertiary amine groups, hydroxyl groups, alkoxy groups, and alkyl ethers. The main ones are those having an electron-donating group such as a nitrogen-donating group, or nitrogen heterocyclic compounds.

The acceptor as described above is preferably about 1/1 per mole of the luminescent compound forming the first layer as described above.
The donor is preferably added in a proportion of about 1/10 to 1/100 to reduce the electronegativity of the first layer.
/100 mol to increase the electronegativity of the second layer.

The acceptor as described above may be selected from the above-mentioned luminescent compounds or non-luminescent compounds, or may be selected from other organic compounds with high electron-accepting properties other than those mentioned above.

In addition, the donor may be selected from the above-mentioned luminescent compounds or non-luminescent compounds, or may be selected from other organic compounds with large electron donating properties other than those mentioned above.For example, as the acceptor, the above-mentioned It is preferable to select from various compounds having a large electron-accepting substituent such as the above, and also, as a donor, from various organic compounds having a large electron-donating substituent as described above.

The other elements forming the EL element of the present invention, namely the transparent electrode layer and the back electrode layer, sandwich the light emitting layer, and
Any conventionally known material can be used, but at least one layer thereof must be transparent. As the transparent electrode layer, any desired transparent electrode layer can be used as in the past, and preferred examples include polymethyl methacrylate,
A transparent conductive material such as indium oxide, tin oxide, or indium tin oxide coated entirely or in a pattern on the surface of a transparent film or sheet such as transparent synthetic resin such as polyester or glass. It is. When using an opaque back electrode layer on one side, these opaque 82 layers may also be of conventionally known type, and JIQ and preferred ones have a thickness of about 0.1 to 0.
．． It is a vapor deposited film of aluminum, silver, gold, etc. with a thickness of 3 pm. Further, the shape of the transparent electrode layer or the back electrode layer may be any shape such as a plate, a belt, or a cylinder, and can be selected depending on the purpose of use. Further, the thickness of the transparent electrode layer is approximately 0
．． It is preferably about 0.01 to 0.2 m.

If the thickness is less than this range, the physical strength and electrical properties of the element itself will be insufficient, and if the thickness is more than the above range, problems may arise in transparency, lightness, compactness, etc.

In the EL element of the present invention, between the two electrode layers as described above,
It can be obtained by changing the electronegativity of an electroluminescent compound with a specific electronegativity as described above by adding an acceptor or donor, and forming a luminescent layer consisting of two layers with different electronegativity. The first layer constituting the luminescent layer of the formed two-layer structure is a mixed molecule deposited film consisting of an electroluminescent compound (A) of a specific electronegativity containing an acceptor, and the second layer is It is characterized by being a mixed molecule deposited film consisting of a compound (A) containing a donor or an electroluminescent compound having the same electronegativity as the compound.

In the present invention, particularly preferred methods for forming the mixed molecule deposited films constituting the first and second light-emitting layers include resistance heating evaporation method and CVD method, such as evaporation-X
With this method, a thin film of about 5008 can be formed as each light-emitting layer.

For example, when using the resistance heating evaporation method, the material 1 is placed in a tungsten board placed in a vacuum chamber, and 30C is removed from the substrate.
If the material is II+ or higher, resistance heating is performed, and if the material is sublimable, the temperature is set to the sublimation temperature, and if the material is meltable, the temperature is set to the melting point or higher. The pre-vacuum level should be 2 x 10'Torr or less.
Before vapor deposition, the boat is closed with a shutter, heated, and left in the air for 2 minutes, then the shutter is opened and vapor deposition begins.

Motowaka medium speed is measured while measuring with a crystal oscillator film thickness monitor, but a suitable speed is 0.1 in/SeC ~
This is carried out at a rate of 100λ/sec.

The degree of vacuum at that time was 10 Torr to prevent oxidation etc.
Hereinafter, the pressure is preferably maintained at about 10 Torr.

The E L' element of the present invention has an electroluminescent compound (A) with a specific electronegativity selected from the above compounds and an appropriate acceptor as the first layer of the two electromagnetic layers as described above. A mixed molecule deposited film is formed by the above-described molecular deposition method, and as a second layer, the above-mentioned compounds are mixed with compound (A) or an electroluminescent compound having a similar electronegativity. Select a suitable donor and make a mixture,
Similarly, a mixed molecule deposited film is formed and the light emitting layer has a two-layer structure.

In the prior art, it is known that an EL element is formed by a molecular deposition method, but an EL element with sufficient performance cannot be obtained by this known method, and as a result of various researches, the present inventors
The light-emitting layer has a 21-layer structure, the first light-emitting layer is formed as a mixed molecule deposited film using an electroluminescent compound of a specific electronegativity containing the acceptor as described above, and the second light-emitting layer is
By forming the layer as a mixed molecular deposit from a donor-containing compound (A) or an electroluminescent compound of comparable electronegativity to compound (A), the performance of prior art EL devices is significantly improved. This is what we found out.

The thickness of the light-emitting layer of the EL device of the present invention obtained in this way can be changed arbitrarily, but in the present invention, the thickness of the entire light-emitting layer is about 0-+01 to 18 Lm. is suitable.

Note that the adhesion between one or both electrode layers used as a substrate and the light-emitting layer is sufficiently strong in the molecular deposition method and the LB method, and one light-emitting layer may peel or fall off. However, in order to strengthen the adhesion, the surface of the substrate may be treated in advance, or a suitable adhesive layer may be provided between the substrate and the light emitting layer.

The performance of the EL element formed as described above may deteriorate due to the influence of moisture and oxygen in the air if left as is, so it is desirable to create a moisture- and oxygen-proof hermetically sealed structure using conventionally known means. .

In the EL device of the present invention as described above, the structure of the light emitting layer is as follows:
It is an ultra-thin film, and exhibits excellent light-emitting performance through various electrical interactions between the first layer and the second layer.

Furthermore, as schematically shown in FIG. 1, the light-emitting layer of the EL device of the present invention is different from the light-emitting layer consisting of a single layer in the prior art, as schematically shown in FIG. light emitting layer and second
Since the light-emitting layer has a uniform interface, various interactions between these two layers with different electronegativity are extremely easy, and it exhibits excellent light-emitting performance that cannot be achieved with conventional technology. It is something to do. That is, by variously changing the difference in electronegativity between the first light-emitting layer and the second light-emitting layer, the light emission intensity can be improved or the light emission color can be changed arbitrarily, and the service life can also be changed. It can be significantly extended.

Furthermore, the prior art has excellent luminescence.

Materials with insufficient film-forming properties or film strength could not be used in practice, but in the present invention, even materials with poor film-forming properties or film strength but excellent luminescence properties can be used. By using materials with excellent film-forming properties for the layer, luminescence,
A light-emitting layer having excellent film formability and film strength can be obtained.

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

Next, the present invention will be explained in more detail with reference to Examples. Note that the middle part of one sentence is based on weight.

Example 1 A transparent electrode was formed by depositing an ITO layer with a thickness of 1500 nm on the surface of a 501111 square glass plate by sputtering.

Next, anthracene (A) (mp) was deposited on the transparent electrode substrate using a resistance heating evaporation apparatus.

216°C) and indazole (B) (mp, L46'O)
was deposited to a film thickness of 550λ. In this vapor deposition, the pressure of the vapor deposition tank is once reduced to a vacuum level of 10 Tarr, and the temperature of the resistance heating board (M o ) is gradually raised until the vapor deposition rate of indazole reaches 0. The current flowing through the resistance heating board is kept constant so that the total deposition rate is about Lλ/sec.
A vapor deposited film was formed by adjusting the current flowing through the board containing anthracene so that the current was 100 m/sec. The degree of vacuum during vapor deposition was 9×10 Torr. Further, the temperature of the substrate holder was kept constant by circulating 20° C. water.

Next, after returning the vapor deposition tank to normal pressure, the vapor deposition compounds were anthracene (C) (mp, 216°C) and anthraquinone (
D) (mp, 286°C). 1 time in the vapor deposition tank
Reduce the pressure to a vacuum level of 0 Torr and use a resistance heating board (M
o) Gradually raise the temperature so that the anthraquinone deposition rate is about 0.1λ/see, and keep the current flowing through the resistance heating board constant so that the total deposition rate is 2 people/sec. The current flowing through the board containing anthracene was adjusted to form a 550-layer deposited layer.

Finally, the substrate with the thin film formed as described above is placed in a vapor deposition tank, and the tank is once depressurized to a vacuum level of 10 Torr, and then the vacuum level is adjusted to 10 Torr, and the vapor deposition rate is increased to 2.
At 0λ/sec, 1500% Al was evaporated onto the thin film to form a back electrode.The fabricated EL element was sealed with a sealing glass as shown in Fig. 3, and then evaporated according to the conventional method. The EL light emitting cell of the present invention was formed by injecting purified, degassed, and dehydrated silicone oil into the seal.
When an AC voltage (Hzcy) was applied, the current density was 0.
18mA/c, brightness 26ft-L (7) ELJA at m'
Showed the light. The EL device of the present invention described above is based on the conventional Zn
Compared to an EL element using S as a luminescent matrix, the driving voltage was lower and the EL element had good emission brightness characteristics.

Comparative Example 1 A comparative EL element was obtained in the same manner as in Example 1 except that the second layer was not formed.
In addition, when evaluated in the same manner as in Example 1, the current density G,
The brightness was 5 ft-L or less at 14 mA/crn'.

Example 2 In place of compounds A, B, C and D in Example 1,
Using the following compounds E, F, G and H, E F G
H and others were the same as in Example 1, and the EL of the present invention was prepared.
When the device was obtained and evaluated under the same conditions as in Example 1, the current density was 0, 17 mA/cm'te, and the brightness (Ft-L) was 30.

[Brief explanation of drawings]

FIG. 1 schematically shows an EL device based on the prior art molecular deposition method, FIG. 2 schematically shows an EL device according to the present invention, and FIG. 3 schematically shows an EL device according to the present invention. FIG. 2 schematically shows a cross section of an EL element.

Claims (1)

[Claims] In an EL device consisting of a two-layered light-emitting layer and two electrode layers sandwiching the light-emitting layer, at least one of which is transparent, the first light-emitting layer is made of an electroluminescent organic compound (A).
and an organic compound that is electron-accepting relative to compound (A), and the second light-emitting layer is composed of a mixture of electroluminescent organic compound (A) or compound (A). ) The above-mentioned EL is characterized in that it is made of a mixed molecule deposited film consisting of a mixture of an electroluminescent organic compound having the same electronegativity as the compound (A) and an organic compound that is electron-donating relative to the compound (A). element.