JPS6147787A - El element - Google Patents

Abstract

PURPOSE:An inexpensive and easily producible EL element capable of providing emission with high luminance even by low-voltage drive, having luminous layers consisting of a three layer structure, wherein each layer consists of a thin layer of an electrically luminous organic compound. CONSTITUTION:The aimed EL element consisting of the luminous layer 2 having a three layer lamination structure, and the two electrode layers 1 and 3 wherein at least one is transparent, sandwiching it in between, the first luminous layer consists of a molecule piled layer comprising the electrically luminous organic compound 4, and the organic compound 4' having electron donor properties relatively based on the compound, the second luminous layer consists of a molecule piled layer comprising the compound 4 or the electrically luminous organic compound 5 having the same electronegativity as that of the compound, and the third luminous layer consists of a molecule piled layer comprising the compound 4 or the electrically luminous organic compound 6 having the same electronegativity as that of the compound 4, and the organic compound 6' having electron donor properties relatively based on the compound.

Description

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

(Prior art) Conventional EL elements are made of Mn, Cu or Re F3.
Zn containing (Re; i 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, which is most easily mass-produced and costs only a few tenths of the cost of thin-film devices, has become available in which a light-emitting base material, that is, ZnS, is dispersed in an organic binder. . 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.
It has not yet achieved sufficient performance in terms of luminance, power consumption, etc. On the other hand, recently, research and development has been actively conducted to control the chemical structure and higher-order structure of organic materials to create new materials for optical and electronics.
Organic materials, such as 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, there is a demand for the development of functional organic materials as new functional materials that surpass inorganic materials, and a cumulative film of monomolecular layers of anthracene derivatives and pyrene derivatives, which have a parent tree group and a hydrophobic group in the molecule, is being used as an electrode. The EL element formed on the 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 comprising a light emitting layer having a three-layer stacked structure and two electrode layers sandwiching the light emitting layer, at least one of which is transparent, in which the first light emitting layer is electrically The second light-emitting layer is composed of a molecular deposited film consisting of a light-emitting organic compound (A) and at least one organic compound that is electron-donating relative to the compound (A) (hereinafter referred to as donor), and the second light-emitting layer is a molecular deposited film consisting of an electroluminescent organic compound (A) or an electroluminescent organic compound having a similar electronegative charge as compound (A), and the third layer is composed of the electroluminescent organic compound described above. Compound (A) or Compound (A
) and an electroluminescent organic compound with an electronegative charge in the opposite direction, and at least one organic compound (hereinafter referred to as acceptor) that is relatively electron-accepting to compound (A). The above-mentioned EL element is characterized by the following.

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 electron acceptors or electron donors for the above compounds include #i elementary cyclic compounds other than those mentioned above and derivatives thereof, aromatic amines and aromatic polyamines,
Compounds having a quinone structure, such as tetracyanoquinodimethane and tetracyanoethylene, can be mentioned.

In the present invention, compounds useful for forming the first to third light-emitting layers are appropriately selected and used from the electroluminescent compounds described above depending on their electronegativity.

Examples of basic skeletons of compounds and other compounds useful for forming the first to third layers are as follows.

(However, the basic skeletons illustrated below include alkyl groups having 1 to 4 carbon atoms, alkoxy groups, alkyl ether groups, halogen atoms, nitro groups, primary to tertiary amine groups, hydroxyl groups, carboxamide groups, sulfoamide groups, etc.) (May have common substituents.) (Hereinafter blank) Z=N)(,0,S Z-CO, NHZ=CO1
NH10, SZ = NH,0,5 Z=NH,0,S Z=NH1
0, SZ= S, Se Z= S, Se
Z=S, ' 5eZ=NH, OlS
Z=NF(%Q S Z=NH, O1SM= Er
%Tm Sm, Eu, Tb, Z = 0.
N true u M=A4 Ga, Ir, Ta, a=3 M-Er
, Sm, EuM=Zn, Cd, 'Mg, pb, a=2
Gd, Tb, DyTm, Yb Tb, Dy, Tm, Yb Gd, Tb, D
ymi Yb Z=O,S; Se O≦p≦2 The above luminescent compounds can be used alone or as a mixture in each luminescent layer in the present invention. In addition,
These compounds are examples of preferred compounds, and it goes without saying that other derivatives or other compounds may be used as long as the same purpose is achieved.

In the present invention, at least one specific preferred compound (A) is selected from the luminescent compounds described above, a donor is combined with the compound (A) to form a first layer, and then the compound (A) or forming the second M from an electroluminescent organic compound with the same electronegative charge as the compound (A), and finally an electroluminescent organic compound with the same electronegative charge as the compound (A) or the compound (A); The third layer is formed by combining a chemical organic compound with an acceptor, and the light-emitting layer has a three-layer stacked structure.

Among such luminescent compounds, compounds preferred as compound (A) are those having intermediate electronegativity and excellent luminous efficiency among the above-mentioned exemplified compounds.

In addition, particularly preferable compounds as donors are first to third
The main compounds are the above-mentioned luminescent compounds or other organic compounds having electron-donating groups such as amine groups, hydroxyl groups, alkoxy groups, alkyl ether groups, or nitrogen heteroatoms, and acceptors include carbonyl groups and sulfonyl groups. The luminescent compounds or other organic compounds having an electron-withdrawing group such as , nitro group, or quaternary amine group are mainly used. In the present invention, such luminescent compounds, donors, or acceptors can be used alone or in combination in each luminescent layer.

The other elements forming the EL element of the present invention, that is, the two electrode layers sandwiching one light emitting layer, can use any conventionally known elements, but at least one of the layers must be transparent. There is a need. As the transparent electrode, any desired transparent electrode layer can be used as in the past, and preferred examples include transparent synthetic resins such as polymethyl methacrylate and polyester, and transparent films or sheets such as glass that have oxidized surfaces. The entire surface or pattern is coated with a transparent conductive material such as indium, tin oxide, or indium-tin-oxide (ITo). If opaque electrodes are used on one side, these opaque electrodes may be of conventionally known types, and are generally and preferably made of aluminum with a thickness of approximately 0.1 to 0.3 JLm;
It is a vapor deposited film of silver, gold, etc. Further, the shape of the transparent electrode or the opaque electrode may be any shape such as a plate, a belt, or a cylinder, and can be selected depending on the purpose of use. Also,
The thickness of the transparent electrode is preferably about 0.01 to 0.2 pLm. 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, However, there may be problems with transparency, lightness, compactness, etc.

In the present invention, particularly preferred methods for forming the molecular deposition films constituting the first to third light emitting layers are resistance heating evaporation method and CVD method. For example, in the evaporation method,
Each can form a thin film for about 500 people.

For example, when using the resistance heating vapor deposition method, the material is placed in a tungsten board placed in a vacuum chamber, and the material is placed 30 cm from the substrate.
Otherwise, resistance heating is performed, and sublimable materials are set at the sublimation temperature, and meltable materials are vapor deposited at a temperature higher than the melting point. The pre-vacuum level is set to 2×10 Torr or less, the port is closed with a shutter before vapor deposition, the port is heated and the air is allowed to air for 2 minutes, and then the shutter is opened to perform vapor deposition.

The speed during deposition is measured using a crystal oscillator film thickness monitor, but the preferred speed is 0°1λ/sec.
It is performed between looλ/see. In order to prevent oxidation and the like, the degree of vacuum at that time is maintained at 10-3 Torr or less, preferably about 10-gTorr.

In the EL device of the present invention, the above-mentioned material for forming a light-emitting layer is preferably formed using the above-mentioned molecular deposition film between the above-mentioned two electrode layers as a three-layer structure having different electronegativities. This is obtained by In the prior art, it is known that an EL device is formed by a molecular deposition method, but this known method cannot provide an EL device with sufficient performance, and as a result of various studies, the present inventors It has been found that the performance of the conventional EL element can be significantly improved by forming the EL element into a three-layer structure and forming the first to third layers as molecular deposited films having different electronegativities as described above.

In the EL device of the present invention, first, at least one compound (A) as described above is selected, and the compound (A) and the donor are preferably mixed in a molar ratio of 1:1/lo to 1:1/Zoo. The compound (A) or an electroluminescent organic material having a similar electronegative charge as the compound (A) is formed as a first layer by a molecular deposition method as described above. A molecular deposition film is formed from the compound by the molecular deposition method as described above to form a second layer, and the surface of the second layer is similarly coated with the h-containing compound (A) or the same electrical potential as the compound (A). A third layer is formed by combining a negatively charged electroluminescent organic compound and an acceptor, preferably in a molar ratio of about 121/10 N1 = 1/100, and finally a third layer is formed, such as aluminum, silver, gold, etc. The back electrode layer is obtained by depositing an electrode material such as, preferably, by vapor deposition or the like.

The thickness of the light-emitting layer made of the EL element thin film obtained in this way varies depending on the type of material used, but generally the first layer has a thickness of about 0.000 m to 0.400 m. So, the second
Preferably, the layers are about o,oi to 0.47 zm thick and the third layer is about o,oi to 0.47 zm thick.

Note that the adhesion between the electrode layer used as a substrate and the light-emitting layer is sufficiently strong in the molecular deposition method, and the light-emitting layer will not peel or fall off, but the adhesion may be strengthened. For this purpose, the surface of the substrate may be pretreated 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 has excellent light-emitting performance.

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 of the prior art that is a single layer, as schematically shown in FIG. Since the third light-emitting layer and the third light-emitting layer are stacked with uniform interfaces, various interactions between the three layers with different electronegativities are extremely easy, which is impossible to achieve with conventional technology. It exhibits excellent light emitting performance. That is, by variously changing the electric negative difference between the first to third light-emitting layers by 1 degree, etc., it is possible to improve the luminous intensity or change the luminous color as desired, and also to significantly extend its service life. can be done.

Furthermore, although the conventional technology has excellent luminescence, it is difficult to form a film.
Materials with insufficient film strength could not be practically used, but in the present invention, although such materials have poor film formability and film strength,
Even if a material has excellent luminescence properties, by using a material with excellent film-forming properties in at least one layer, a luminescent layer with excellent luminescence properties, film-forming properties, and film strength can be obtained.

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

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

Example 1 A transparent electrode was formed by depositing an ITO layer with a thickness of 1500 nm on the surface of a 50+*g square glass plate by sputtering.

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

216°C) and anthraquinone CB) (mp.

286° C.) to a thickness of 55 OA to form a t51 layer. This vapor deposition was carried out by first reducing the pressure in the vapor deposition tank to a vacuum level of 10 Torr, gradually increasing the temperature of the resistance heating board (Mo), and keeping it constant at a temperature close to the respective melting points.
Furthermore, adjust the pumping speed to bring the degree of vacuum to 9 x 10-'
Torr and anthraquinone deposition rate lλ/s
The current flowing through the anthraquinone-loaded board was adjusted so that the total deposition rate was 5 A/s.
A vapor deposited film was formed by adjusting the current flowing through the board containing anthracene so that ec was obtained. The degree of vacuum during vapor deposition is
It was 9 x 10-'Torr. Further, the temperature of the substrate holder was kept constant by circulating 20° C. water.

Next, in the same manner as above, only anthracene was added to 25OA
The second layer was formed by vapor deposition to a film thickness of .

Furthermore, in the same manner as above, anthracene and indazole CC) (mp, 146° C.) was deposited to a thickness of 550 μm to form the third layer.

Finally, the substrate with the thin film formed as described above was placed in a vapor deposition tank, and the nuclide was once depressurized to a vacuum level of 10 Torr, and then the vacuum level was adjusted to 10 Torr, and the vapor deposition rate was increased to 2.
Figure 3 shows an EL element fabricated by depositing Al on the thin film at 0λ/sec to a thickness of 1 soo as a back electrode.
As illustrated in , after sealing with a sealing glass, purified, degassed, and dehydrated silicone oil was injected into the seal according to a conventional method to form an EL light emitting cell of the present invention. IOV, 400Hz for these EL light emitting cells
When an alternating current voltage of 0.16 mA/
cnf with a brightness of 23.5ft-Li2) EL emission was observed.

The above-mentioned EL element of the present invention had a lower driving voltage and better luminance characteristics than the conventional EL element using ZnS as a light emitting matrix.

Comparative Example 1 In Example 1, except that only Compound A was used as the luminescent compound and a single layer was used, the rest was Example 1.
An EL element for comparison was obtained in the same manner as in Example 1, and evaluated in the same manner as in Example 1. As a result, the luminance was 1 ft-L or less at a current density of 0.2 mA/crn'.

Example 2 The following compounds R and E were used in place of Compounds B and C in Example 1, and D, E and others were carried out in the same manner as in Example 1 to obtain an EL device of the present invention. - When evaluated under the conditions, the current density was 0.
The luminance (Ft-L) was 21.8 in 09 Yu A/c Go.

[Brief explanation of drawings]

FIG. 1 schematically shows an EL device using the conventional 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. 1; Transparent electrode 2; Luminescent layer 3; Back electrode 4; Luminescent compound 4'; Donor -5: Luminescent compound 6: Luminescent compound 6
;'Acceptor 7; Seal glass 8; Silicone insulating oil 9 Ni glass plate

Claims (1)

[Claims] In an EL device comprising a light emitting layer with a three-layer stacked structure and two electrode layers sandwiching the light emitting layer, at least one of which is transparent, the first light emitting layer is made of an electroluminescent organic compound (A ) and at least one organic compound that is electron-donating relative to compound (A), and the second light-emitting layer is composed of the electroluminescent organic compound (A).
) or compound (A), and the third layer is composed of the electroluminescent organic compound (A) or the compound (A), and the third layer is composed of the electroluminescent organic compound (A) or compound (A). ) and the above-mentioned molecular deposited film comprising an electroluminescent organic compound having the same electronegative charge as in (A) and at least one organic compound relatively electron-accepting to compound (A). EL element.