JPH04230997A - Thin film electrode for element, electroluminescence element with it, and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide an element with high homogeneity and density and with high intensity and high efficiency at the low voltage by constituting a thin film electrode for the element with an electron-injectable metal and an organic substance. CONSTITUTION:A metal such as Gd, Zn, In, Ta, Ba, Ca, Ce, Er, Eu, Hf, La, Mg, Nd, Sc, Sm, Y, Yb and an electro-conductive compound are used for an electron-injectable metal. Organic low-molecule and organic high-molecule compounds with the feature to be stuck or bound to the electron-injectable metal can be used for the organic substance, and an organic compound having the capability to form a complex with the electron-injectable metal or an acceptor organic compound is preferable. The electron-injectable metal and the organic substance are deposited on a substrate to form a thin film electrode for an element, thus the element with increased homogeneity and density, decreased volume resistivity, and high intensity and efficiency is obtained.

Description

[Detailed description of the invention]

0001

[Industrial application field]

The present invention relates to a thin film electrode for an element, an electroluminescent (hereinafter referred to as EL) element having the same, and a method for manufacturing the same, and more specifically, a thin film electrode for an element particularly suitable for use as a cathode of an organic EL element and a method for manufacturing the same. In addition, EL provides high brightness and high efficiency light emission.
This invention relates to an element and its manufacturing method.

BACKGROUND OF THE INVENTION Focusing on the high fluorescence efficiency of organic compounds, research into devices that utilize the EL performance of organic compounds has been conducted for a long time. for example,
Helfrish, Dresner, William
et al. used anthracene crystals to obtain blue light emission (
J. Chem. Phys. ,44, 2902 (1
966)). Furthermore, Vincett, Barlow et al. have fabricated light emitting devices using a vacuum evaporation method using fused polycyclic aromatic compounds (Thin Solid Film).
s, 99, 171 (1982)).

However, in either case, only low luminance and low luminous efficiency can be obtained. Recently, it has been reported that blue light emission of 100 cd/m2 was obtained using tetraphenylbutadiene as a luminescent material (Japanese Patent Laid-Open No. 59-1943
Publication No. 93). Furthermore, it has been reported that a green light-emitting organic thin film EL device with a luminance of 1000 cd/m2 or more was developed by laminating a hole-conducting diamine compound and a fluorescent aluminum chelate complex as a light-emitting material (Appl. Phys. Lett., 51,
913 (1987)). In addition, distyrylbenzene compounds, which are famous as laser dyes, have high fluorescence in the blue to blue-green region, and when used as a light-emitting material in a single layer, 80 cd
It has been reported that an EL emission of about 1/m2 could be obtained (European Patent No. 0319881).

[0003] Here, as the cathode in the organic thin film EL element, US Pat.
Alkali metals such as Na
: K alloys are known, but devices using these electrodes have a maximum quantum yield of 0.01 to 0.08% (RCA
Review, vol30, p. 322), which has a significantly low work function and is easy to inject electrons, but is highly active and unstable, making it impractical. Also, a tunnel injection cathode (U.S. Pat. No. 3,710,167, Proceedin
gs of IEEE, p. 1863, 1970
(2003), SiO2 was deposited on a wafer made of n-type Si.
A cathode covered with a thickness of 0 to 40 Å, or an Al
The cathode is formed by covering the top with Al2O3 to a thickness of 50 Å, and anthracene is used as the light emitting layer to obtain a quantum yield of 0.01 to 0.04%. However, although these cathodes are more stable than the above-mentioned alkali metals, they require the formation of an extremely thin oxide film, which poses a problem in reproducibility. Furthermore, US Pat. No. 4,539,507 uses In for the cathode, ITO/1,1-bis(4-di-p-tolylaminophenyl)cyclohexane (hole transport layer)/4,4
'-bis(5,7-di-t-pentyl-2-benzoxazolyl)stilbene (electron transport layer)/In composition
When the L element has an applied voltage of 22V and a current density of 140mA/cm2, the current density is 340cd/cm2 with a peak of 520nm.
m2 emission (quantum yield 1.2%, power conversion efficiency 0.1
4%). Although this EL element has achieved reduction in applied voltage and increased brightness of the element, In of the cathode has weak electron injection properties, and there remains room for improvement. EP0278757 also describes cathodes made of multiple metals other than alkali metals, at least one of which has a work function of 4 eV or less, such as Mg, Ag, I
It has been shown that a cathode that is uniform, dense, and has a good sheet resistance value can be obtained by vapor-depositing any of n, Sn, Sb, Te, and Mn onto an organic material. Specifically, using Mg and Ag, an Al complex of ITO/1,1-bis(4-di-p-tolylaminophenyl)cyclohexane/oxine/
0.05mW/cm2 when 5V is applied with Mg:Ag configuration
(approximately 50 cd/m2), light emission (green) with a power conversion efficiency of 0.45% was obtained.

[0004] The cathode of this EL element has improved adhesion, uniformity, and density to the organic film, and has improved stability, reduced sheet resistance, and
Although the luminous efficiency has been improved, this cathode also has a volume resistivity of 3, for example in Mg:Ag (atomic ratio 10:1).
．． It is 4 to 6×10 −5 Ω·cm, which is 8 to 13 times larger than the volume resistivity of Mg bulk (polycrystalline), which is 4.45×10 −6 Ω·cm. This is thought to be because the thin film still lacks uniformity and density, but this lack of uniformity and density leads to oxidation in the atmosphere. In addition, in some cases, the adhesion with the organic layer was poor, resulting in non-uniform light emission. Ag, In, Al for the second metal
etc., the vapor deposition source reaches a high temperature of 800° C. or higher during vapor deposition, and the underlying organic film is often damaged by radiant heat. Therefore, the present inventors have developed a thin film that is more uniform, dense, and has good adhesion to the organic layer, while retaining the characteristics of the electrode made of a metal with a small work function other than the alkali metal and other metals. We conducted intensive research to develop a thin film electrode that has a good sheet resistance value and does not damage the underlying organic film during film formation.

[0005]

[Problems to be Solved by the Invention] As a result, it has been found that the above object can be achieved by using a specific metal and an organic substance. The present invention was completed based on this knowledge.

That is, the present invention provides a thin film electrode for an element made of an electron-injecting metal and an organic substance. The present invention also provides a method for manufacturing a thin film electrode for an element, in which an electron-injecting metal and an organic substance are co-deposited. Furthermore, the present invention provides an EL device using the above thin film electrode for the device as a cathode. Furthermore, the present invention provides a method for manufacturing an EL element in which a cathode is formed by co-evaporating a metal with easy electron injection and an organic substance.

[0007] The above-mentioned metal capable of injecting electrons preferably has a work of 4.1 eV or less in order to inject electrons into an electron transport band such as a light emitting layer or an electron injection layer (electron transport layer) made of an organic substance in an organic thin film EL device. It is made of a metal and an electrically conductive compound that has a function. Such electron-injecting metals are described in "Chemistry Handbook" 3rd edition, Basic Edition II.
, Maruzen, 1982, II-493.Ba, Ca, Ce, Cs, Er, Eu, Gd, Hf,
K, La, Mg, Na, Nd, Sc, Sm, Y, Yb,
Examples include Zn and Li. However, among these, Group I metals such as Cs and Na, which have particularly small work functions, have extremely high reactivity and are difficult to stabilize. Therefore, preferable metals used for the thin film electrode of the present invention are Gd, Zn, In
, Ta, Ba, Ca, Ce, Er, Eu, Gd, Hf,
These include La, Mg, Nd, Sc, Sm, Y, Yb, and Zn. By using such an easily electron-injecting metal as a constituent material of a thin film electrode, it is possible to lower the operating voltage of the device, improve the luminescence quantum yield of the device, and improve the luminous efficiency of the device.

[0008] On the other hand, the organic substance can be of various types, but organic low molecules and organic polymer compounds that have the property of adhering to or bonding to the electron-injecting metal, preferably the electron-injecting metal. It is an organic compound that has the ability to form a complex with or an acceptor organic compound. Acceptor organic compounds are described in "Chemistry of Conductive Low-dimensional Materials", Gakkai Publishing Center, 1983, p61.
As shown in

[0009]

[Chemical formula 1]

(In the formula, X is a halogen atom, R is an alkyl group, an aryl group, an alkyl-substituted aryl group, an alkoxy-substituted aryl group, or a hydrogen atom.) is a compound that has a quinoid structure. Preferred compounds include those shown in the following structural formulas (a) to (e).

[0011]

[Case 2]

In the above general formula (I), R1, R2,
R3 and R4 independently represent an alkyl group, an alkoxy group, a halogen atom, a nitro group, a cyano group, an alkoxycarbonyl group, and an aryl group; They may be combined to form a saturated or unsaturated 6-membered ring or 5-membered ring. R5 and R6 are each an electron-withdrawing group, such as a dicyanomethylene group, a dicyanocarbonylmethylene group,
Indicates an oxygen atom, a cyanoimino group, a cyanoalkoxycarbonylmethylene group, a dialkoxycarbonylmethylene group, a dicarboxylic acid methylene group, or a cyanocarboxylic acid methylene group. Furthermore, in the above general formula (II), R5
and R6 are electron-withdrawing groups having the same meaning as in general formula (I), and R1, R2, R3, R4, R7, R8, R9, R
10 is the same group as R1 to R4 in general formula (I). Specific compounds with such a structure include:

[0013]

[Chemical formula 3]

[0014]

[C4]

[0015] etc. (Japanese Unexamined Patent Publication No. 57-14925
No. 9, No. 61-225151, No. 61-233750
(see U.S. Pat. Nos. 4,869,984 and 4,869,985).

[0016]

[C5]

In the compound represented by the above general formula (III), R
11 to R14 are independently an acyl group, alkoxycarbonyl group, nitro group, alkylamino group, carbonyl group, arylalkyl group, aryloxycarbonyl group, benzyloxycarbonyl group, phenethyloxycarbonyl group, or aminocarbonyl group, and R15 is electron-withdrawing group,
Examples include a dicyanocarbonylmethylene group, an oxygen atom, a dicyanomethylene group, a cyanoimino group, a cyanoalkoxycarbonylmethylene group, a dialkoxycarbonylmethylene group, a dicarboxylic acid methylene group, or a cyanocarboxylic acid methylene group. in particular,

[0018]

[C6]

[0019] etc. (Japanese Patent Application Laid-Open No. 60-69657
No. 61-143764, No. 61-148159). (c) 4H,- represented by the following general formula (IV)
Thiopyran-1,1-dioxide derivatives (Japanese Patent Application Laid-Open No. 1983-1999-
(See Publication No. 222477).

[0020]

[C7]

Here, R23 represents an electron-withdrawing group, and R23 represents an electron-withdrawing group.
1, R25 independently represents an alkyl group or an aryl group, R
22 and R24 independently represent hydrogen or an alkoxycarbonyl group, and the carbon atoms constituting R21 and R22, R24 and R25 may together form a fused unsaturated 6-membered ring. The thiopyrane dioxide derivative represented by the general formula (IV) also exhibits a half-wave reduction potential on the positive side of −0.5 V and is used as a preferred acceptor molecule. in particular

[0022]

[Chemical formula 8]

Aromatic ring compounds and heterocyclic compounds having a dicarboxylic acid imide structure represented by (R represents an alkyl group, an aryl group, an alkyl group-substituted aryl group, an alkoxy group-substituted aryl group, etc.) are also acceptor molecules. . These are a particularly preferred group of compounds. in particular

[0024]

[Chemical formula 9]

[0025] etc.

[0026]

[Chemical formula 10]

(wherein, Ar1, Ar2, Ar4, A
r5 independently represents an aryl group, an alkyl-substituted aryl group, or a cyano-substituted aryl group, and Ar3 represents an arylene group, an alkyl-substituted arylene group, or a cyano-substituted arylene group. in particular

[0028]

[Chemical formula 11]

[0029] etc. The above compound groups (a) to (e) can be preferred compounds of the present invention as long as they are organic compounds having an electron-withdrawing group. It is not limited. In addition, as long as the attachment or bonding (including complex formation) of metal and organic substance can be maintained, alkyl groups, alkoxy groups, aryl groups, alkoxyalkyl groups, allyloxyalkyl groups, hydroxy groups, hydroxyalkyl groups, aralkyl groups , alkylamino group, arylamino group, nitroalkyl group, alkylcarbonyl group, alkoxycarbonyl group, etc. may be substituted with an organic substance. Further, polymers containing the above-mentioned organic low molecular structures, such as polymers having these as pendant groups, or polymers having these in the main chain structure, may also be used. This is because even if the polymer is used, it maintains the property of adhering to or bonding with an easily electron-injecting metal. Next, the organic compound forming the complex is preferably a porphyrin or phthalocyanine compound having the following structural formula (VI).

[0030]

[Chemical formula 12]

Here, Q is -N= or -C(R)=, R is hydrogen, an alkyl group, an aralkyl group, an aryl group, a heterocyclic group, and T1 and T2 represent hydrogen or
Alternatively, they may be bonded together to complete an unsaturated 6-membered ring, and further substituents such as an alkyl group, an aryl group, a halogen atom, or a heterocyclic group may be added. Further, the compound (VI) may already form a complex with a metal atom. Such complex-forming organic compounds can also be used as the organic substance of the present invention, even if they are not acceptor molecules, as long as they have the ability to form a complex with an electron-injecting metal. Another type of organic compound that has the property of adhering to an electron-injecting metal can also be used. Examples of such are chelated oxinoid compounds, which have been found to form good electron-injecting metal:organic compound cathodes. Here, preferred ones include those of the following formula.

[0032]

[Chemical formula 13]

(wherein Me represents a metal and n is an integer from 1 to 3; Z independently in each case represents the atom completing the nucleus with at least two fused aromatic rings).
From the above it is clear that the metal can be a monovalent, divalent or trivalent metal. Examples of metals include alkali metals such as lithium, sodium, or potassium;
Alkaline earth metals such as magnesium or calcium, or earth metals such as boron or aluminum may be mentioned. Generally, any monovalent, divalent, or trivalent metal known to be a useful chelating metal can be used. Also, Z is at least 2
complete the heterocyclic nucleus containing fused aromatic rings, in one of which is an azole or azine ring. Additional rings, including both aliphatic and aromatic rings, can be fused with these two required rings if desired. Furthermore, the number of Z is preferably 18 or less to avoid adding molecular bulk without improving functionality. Examples of the above useful chelated oxinoid compounds include aluminum trisoxine, magnesium bisoxine,
Bis[benzo(f)-8-quinolinol]zinc, bis(
2-methyl-8-quinolinolate) aluminum oxide, indium trisoxine, aluminum tris(5-methyloxine), lithium oxine, gallium trioxine, calcium bis(5-chlorooxine)
, poly[zinc(II)-bis(8-hydroxy-5-quinolinonyl)methane], dilithium epindolidione, and the like. Among the above preferred compounds, particularly preferred are the groups of compounds (a), (b), (d), and (e),
For example, the following TCNQ, TNF, NTDI, PTDI,
Alloxazine and the like.

[0034]

[Chemical formula 14]

[0035] Furthermore, the general formula (
In I) to (VII), preferable alkyl groups have 1 to 10 carbon atoms, and specific examples include methyl group, ethyl group,
Examples include propyl group and butyl group. Similarly, preferred aryl groups have 6 to 20 carbon atoms, and specific examples include phenyl, naphthyl, anthonyl, pyrenyl, perylenyl, etc., and preferred alkoxy groups have 1 to 10 carbon atoms. , specific examples include methoxy group,
Examples include ethoxy group, propoxy group, butoxy group, and the like.

Next, a method of forming a thin film electrode using the above-mentioned electron-injecting metal and organic substance will be explained. Various methods can be used to form a thin film, but in order to obtain a uniform and dense thin film, which is the preferred cathode form when used as a cathode for an EL device, it is possible to form a thin film by deposition from a gas phase. It is preferable to use a method of forming a , that is, a vapor deposition method. In particular, since the temperature at which an organic substance becomes a gas phase and the temperature at which a metal becomes a vapor phase are significantly different, it is necessary to separate the metal vapor deposition source and the organic substance vapor deposition source and deposit them simultaneously using a binary simultaneous vapor deposition method. is preferred. During actual vapor deposition, the metal vapor deposition source and the organic material vapor deposition source are set at a temperature that sufficiently increases their respective vapor pressures, and when the organic material and metal reach the intended vapor deposition rate, the shutter above the vapor deposition source is opened and the vapor deposition begins. Start. When the desired film thickness value is reached, the shutter is closed to stop the production. The preferred degree of vacuum during vapor deposition is 10 -5 Torr or less, and the substrate temperature is not particularly limited, but should be set at a temperature that does not destroy the thin film properties of the underlying organic film. The thin film properties of organic films are due to melting,
Because it may be lost due to crystallization, etc.,
The temperature is preferably 0°C, and preferably about room temperature. still,
Care should be taken not to reach the decomposition temperature when depositing organic matter. Furthermore, in some cases, organic substances may release gas during heating, but this is often due to residual solvent used in cleaning and may not be related to decomposition.

The composition ratio of the electron-injecting metal and the organic substance is homogeneous, dense, and has a very small and good sheet resistance value even if the organic substance is in a small amount of about 1/30 by weight of the metal. A thin metal film (cathode) can be produced. The weight ratio of the organic substance to the metal can be preferably used up to 30%, since the substance as a metal has priority. Particularly preferably, the weight ratio is 1 to 10, which can maintain a particularly good sheet resistance value.
% range. The above 1/30 is about 1% or less when converted to a molar ratio, which means that only a small amount of organic matter can give the above good results. Usually, an organic substance is one component, but if necessary, it is also possible to produce an electrode made of two or more components and a metal. It is also possible to use a plurality of metal components (for example, Mg and Yb). The film thickness is preferably 10 nm to 500 nm.
It is. If it is too thin (10 nm or less), the sheet resistance value will increase and it will be easily oxidized. Moreover, if it is too thick, it will take time to manufacture it. Particularly preferably from 50nm to 300nm
It is. Further, the metal vapor deposition rate is preferably 0.1 nm.
/second to 10nm/second, particularly preferably 0.5 to 5nm/second
Seconds. Additionally, some metals degas during processing, and the composition of this degas was determined by quadrupole mass spectrometry to be adsorbed gases such as CO, CO2, H2O, and H2. . Since H2O, CO, CO2, etc. are undesirable because they oxidize the metal during vapor deposition, it is desirable to remove the adsorbed gas by cleaning, melting, etc. the metal vapor deposition source in advance.

The production mechanism of the thin film electrode of the present invention will now be described as follows. Mg, Zn, rare earth metals (Yb, E
When a metal such as u, etc. is deposited alone, it hardly adheres to an organic thin film or glass, and a metal thin film suitable as an electrode cannot be obtained. On the other hand, if we use an organic low molecule that has the property of adhering to or bonding to these metals, preferably an acceptor compound or a complex-forming compound, and perform two-source co-evaporation of this and the metal, it can also be deposited on organic thin films or glass. It is easy to adhere and can produce complete metal films. This means that even if metal alone does not adhere to the surface, an organic compound will first adhere to it, and then this organic compound and metal will adhere or bond.
It is estimated that a thin film will be formed. Further, metal alone tends to aggregate and form a significantly discontinuous and non-uniform film, but organic substances inhibit this cohesiveness and produce a uniform and dense film. In addition, metals that easily adhere to organic thin films, glass, etc.
By using the method of the present invention, even if the metal film is made of aluminum (for example, Al), the density will be increased, the sheet resistance value will be reduced, and a good metal thin film can be obtained. Further, a uniformly dense thin film made of an electron-injecting metal and an organic substance is significantly less likely to be oxidized than a metal-only film. Furthermore, as an advantage in producing a thin film made of an electron-injectable metal and an organic substance, since the temperature of the organic substance vapor deposition source is 500° C. or lower, the organic film is not damaged at all by the radiant heat of this vapor deposition source. Note that, since there are metals with easy electron injection properties such as Mg, Yb, and Eu, which have a low evaporation source temperature, it is possible to almost completely prevent damage to the organic film by selecting the metal type.

EL using the thin film electrode of the present invention as a cathode
There are various configurations of the device, but basically, a light emitting layer is sandwiched between a pair of electrodes (anode and cathode), and if necessary, a hole injection layer or an electron injection layer is added. A layer may be provided. Specifically, (1) anode/emitting layer/cathode,
(2) Anode/hole injection layer/light emitting layer/cathode, (3) anode/
Hole injection layer/light emitting layer/electron injection layer/cathode, (4) anode/
Examples include structures such as a light emitting layer/electron injection layer/cathode. Although the hole injection layer and electron injection layer are not necessarily required, the presence of these layers further improves the light emitting performance. In addition, in the above-mentioned elements, it is preferable that each element is supported by a substrate, and the substrate is not particularly limited, and is made of a material conventionally used for EL elements, such as glass, transparent plastic, quartz, etc. can be used.

The light-emitting layer in the EL device of the present invention can be formed by forming a film using various conventionally used light-emitting materials by a known method (vacuum deposition, LB method, spin coating, casting method, etc.). I can do it. This light-emitting layer has an injection function that can inject holes from the hole injection transport layer when an electric field is applied, and electrons from the cathode or electron injection transport layer. It has three functions: a transport function that moves by the force of an electric field, and a light emitting function that provides a field for recombination of electrons and holes, which leads to light emission.

[0041] However, there may be a difference in the ease with which holes are injected and the ease with which electrons are injected, and there may also be a difference in the transport capacity expressed by the mobility of holes and electrons, but either It is preferable to move one charge. Regarding the above-mentioned light-emitting materials, various materials can be used as the light-emitting materials as long as they have both the above-mentioned functions and exhibit fluorescence in a solid state. There are various known ones, for example 3-
(2'-N-methylbenzimidazolyl)-7-N,N
- Coumarins represented by diethylaminocoumarin (Coumarin 30) (see JP-A-2-191694),
Phthaloperinone series (J. Appln. Phys. 2nd
7, L713 (1988)), benzoxazolyl or benzthiazole series (JP-A-59-19439)
3), metal chelated oxinoid compounds (see Publication No. 3), metal chelated oxinoid compounds (
JP-A-63-295695), stilbene compounds (EP031988 or EP0373582)
(see Publication No.), dimethylidine compound (EP03887)
68) and perylene compounds.

[0042] The thickness of the light-emitting layer can also be appropriately determined depending on the situation, but is usually in the range of 5 nm to 5 μm. Further, as the anode, an electrode material containing a metal having a large work function (4.1 eV or more), an alloy, an electrically conductive compound, or a mixture thereof is preferably used. Specific examples of such electrode materials include metals such as Au, CuI,
Examples include dielectric transparent materials such as ITO, SnO2, and ZnO. The anode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. When emitting light from this electrode, it is desirable that the transmittance be greater than 10%, and the sheet resistance of the electrode is preferably several hundred Ω/□ or less. Furthermore, the film thickness depends on the material, but is usually 10nm.
m to 1 μm, preferably from 10 to 200 nm. Note that in this EL element, it is advantageous for either the anode or the cathode to be transparent or semi-transparent so that the emitted light is transmitted through the element, and the efficiency of extracting the emitted light is high.

As described above, the structure of the EL device of the present invention has various aspects, and the hole injection layer (hole injection transport layer) in the EL device having the structure (2) or (3) above is: This layer is made of a hole transport compound and has the function of transmitting holes injected from the anode to the light emitting layer. By interposing this hole injection layer between the anode and the light emitting layer, Many holes are injected into the emissive layer by the electric field, and electrons injected into the emissive layer from the cathode or electron injection layer are suppressed by the electron barrier existing at the interface between the emissive layer and the hole injection layer. It accumulates near the interface within the layer and improves luminous efficiency, etc.
This results in an element with excellent light-emitting performance.

[0044] When the hole transfer compound used in the hole injection layer is placed between two electrodes to which an electric field is applied and holes are injected from the anode, the hole transfer compound is used to properly transfer the holes to the light emitting layer. A compound capable of transmitting, for example 104 to 106 V
/cm when an electric field of at least 10 −6 cm2 is applied.
A material having a hole mobility of /V·sec is preferable. There are no particular limitations on such hole transport compounds as long as they have the above-mentioned preferable properties. Any material can be selected from among the known materials used for the injection layer. Examples of the charge transport material include triazole derivatives (described in U.S. Pat. No. 3,112,197, etc.), oxadiazole derivatives (U.S. Pat. No. 3,189,447), etc.
(described in Japanese Patent Publication No. 37-16096), imidazole derivatives (described in Japanese Patent Publication No. 37-16096), polyarylalkane derivatives (U.S. Pat. No. 3,615,40)
Specification No. 2, Specification No. 3,820,989, No. 3
, 542,544 specification, Japanese Patent Publication No. 45-555, Japanese Patent Publication No. 51-10983, Japanese Patent Publication No. 51-9322
Publication No. 4, Publication No. 55-17105, Publication No. 56-414
Publication No. 8, Publication No. 55-108667, Publication No. 55-15
6953, US Pat. No. 56-36656), pyrazoline derivatives and pyrazolone derivatives (US Pat. No. 3,180,729, US Pat. No. 4,278)
, 746 specification, JP-A-55-88064,
No. 55-88065, No. 49-105537, No. 55-51086, No. 56-80051, No. 56-88141, No. 57-45545
Publication No. 54-112637, Publication No. 55-745
46), phenylenediamine derivatives (U.S. Patent No. 3,615,404, Japanese Patent Publication No. 51-10105, Japanese Patent Publication No. 46-3712,
JP-A No. 47-25336, JP-A No. 54-53435, JP-A No. 54-110536, JP-A No. 54-1199
No. 25, etc.), arylamine derivatives (U.S. Pat. No. 3,567,450, No. 3, 1)
Specification No. 80,703, Specification No. 3,240,597, Specification No. 3,658,520, Specification No. 4,232
, Specification No. 103, Specification No. 4,175,961, Specification No. 4,012,376, Japanese Patent Publication No. 49-357
Publication No. 02, Publication No. 39-27577, Japanese Unexamined Patent Publication No. 1983-
No. 144250, No. 56-119132, No. 56-22437, West German Patent No. 1,110,51
8), amino-substituted chalcone derivatives (as described in U.S. Pat. No. 3,526,501, etc.), oxazole derivatives (as described in U.S. Pat. No. 3,501, etc.),
257,203, etc.), styryl anthracene derivatives (described in JP-A-56-46234, etc.), fluorenone derivatives (described in JP-A-56-46234, etc.), fluorenone derivatives (described in JP-A-56-46234, etc.),
-110837, etc.), hydrazone derivatives (U.S. Pat. No. 3,717,462, JP-A-54-59143, JP-A-55-52063)
Publication No. 55-52064, Publication No. 55-4676
Publication No. 0, Publication No. 55-85495, Publication No. 57-113
50, 57-148749, etc.), stilbel derivatives (JP-A-61-21
No. 0363, No. 61-228451, No. 61
-14642 publication, 61-72255 publication, 6
No. 2-47646, No. 62-36674, No. 62-10652, No. 62-30255, No. 60-93445, No. 60-94462, No. 60-174749, No. 60 -1750
Examples include those described in Publication No. 52, etc.).

Although these compounds can be used as hole transport compounds, the following porphyrin compounds (
those described in JP-A No. 63-295695, etc.) and aromatic tertiary amine compounds and styrylamine compounds (U.S. Pat. No. 4,127,412, JP-A-Sho 53)
-27033 publication, 54-58445 publication, 5
No. 4-149634, No. 54-64299,
No. 55-79450, No. 55-144250, No. 56-119132, No. 61-29555
Publication No. 8, Publication No. 61-98353, Publication No. 63-295
It is preferable to use the aromatic tertiary amine compound (described in Japanese Patent No. 695, etc.), especially the aromatic tertiary amine compound.

Representative examples of the porphyrin compounds include:
Porphyrin; 1,10,15,20-tetraphenyl-21H,23H-porphyrin copper(II); 1,10
, 15,20-tetraphenyl-21H,23H-porphyrin zinc (II); 5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin; silicon phthalocyanine oxide; aluminum phthalocyanine chloride; metal); dilithium phthalocyanine; copper tetramethyl phthalocyanine; copper phthalocyanine; chromium phthalocyanine; zinc phthalocyanine; lead phthalocyanine; titanium phthalocyanine oxide; magnesium phthalocyanine; copper octamethyl phthalocyanine. Representative examples of the aromatic tertiary compound and styrylamine compound include N,N,N',N'-tetraphenyl-4,4'-diaminobiphenyl;N,N'-diphenyl-N,N'-di(3-methylphenyl)-4,4'-
Diaminobiphenyl;2,2-bis(4-di-p-tolylaminophenyl)propane; 1,1-bis(4-di-
p-tolylaminophenyl)cyclohexane; N, N,
N',N'-tetra-p-tolyl-4,4'-diaminobiphenyl;1,1-bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane; bis(4-
Dimethylamino-2-methylphenyl)phenylmethane; bis(4-di-p-tolylaminophenyl)phenylmethane; N,N'-diphenyl-N,N'-di(4-methoxyphenyl)-4,4'-diaminobiphenyl; N
,N,N',N'-tetraphenyl-4,4'-diaminodiphenyl ether; 4,4'-bis(diphenylamino)quaterphenyl;N,N,N-tri(p-tolyl)amine; 4-( di-p-tolylamine)-4'
-[4(di-p-tolylamine)styryl]stilbene; 4-N,N-diphenylamino-(2-diphenylvinyl)benzene; 3-methoxy-4'-N,N-diphenylaminostilbene; N-phenylcarbazole Examples include.

The hole injection layer in the EL element may be composed of a single layer made of one or more of these hole transfer compounds, or may be composed of a hole injection layer made of a compound different from the above layer. It may also be one in which layers are laminated.

On the other hand, the electron injection layer (electron injection transport layer) in the EL element having the configuration (3) is made of an electron transfer compound and has the function of transferring electrons injected from the cathode to the light emitting layer. have. There are no particular limitations on such electron transfer compounds, and any one can be selected and used from conventionally known compounds. Preferred examples of the electron transfer compound include:

[0049]

[Chemical formula 15]

Nitro-substituted fluorenone derivatives such as

[
0051

[Chemical formula 16]

Thiopyrane dioxide derivatives such as

0
053]

[Chemical formula 17]

Diphenylquinone derivatives such as [Polymer Preprint
Second), Japan” Volume 37, No. 3, Page 681 (
(1988)], or

[0055]

[Chemical formula 18]

Compounds such as [J.Apply.Physics]
s), Vol. 27, p. 269 (1988)], anthraquinodimethane derivatives (Japanese Patent Application Laid-Open No.
-149259, 58-55450, 61-225151, 61-233750, 63-104061, etc.)
Fleorenylidene methane derivative (JP-A-60-6965
Publication No. 7, Publication No. 61-143764, Publication No. 61-14
8159), anthrone derivatives (JP-A-61-225151, JP-A-61-2337)
Examples include those described in Japanese Patent No. 50, etc.). Also, the formula which is a dioxazole derivative

[0057]

[Chemical formula 19]

Compounds represented by the following can also be used. Next, an example of a suitable method for manufacturing an EL element using the thin film electrode of the present invention will be explained for each element of each structure. To explain the method for manufacturing the EL device consisting of the above-mentioned anode/emitting layer/cathode, first, a thin film of a desired electrode material, for example, an anode material, is deposited on a suitable substrate to a thickness of 1 μm or less, preferably in the range of 10 to 200 nm. Formed by a method such as vapor deposition or sputtering to have a film thickness of
After creating the anode, a luminescent material with the general formula (
A thin film of the compound represented by I) is formed to provide a light-emitting layer. Methods for making the luminescent material into a thin film include, for example, spin coating, casting, and vapor deposition, but the vapor deposition method is preferable because a homogeneous film is easily obtained and pinholes are less likely to be generated. . To make the luminescent material thinner,
When this vapor deposition method is adopted, the vapor deposition conditions vary depending on the type of organic compound used in the light-emitting layer, the intended crystal structure and association structure of the molecular deposited film, but generally the boat heating temperature is 50 to 400°C, Vacuum degree 10-5 to 10-
It is preferable to appropriately select a film thickness of 3 Pa, a deposition rate of 0.01 to 50 nm/sec, a substrate temperature of -50 to +300° C., and a film thickness of 5 nm to 5 μm. Next, after forming this light-emitting layer, a thin film made of the above-mentioned electron-injecting metal and an organic substance is formed thereon to a thickness of 1 μm or less, preferably in the range of 50 to 200 nm, and a cathode is provided. In this way, a desired EL element can be obtained. Note that in manufacturing this EL element, it is also possible to reverse the manufacturing order and manufacture the cathode, the light emitting layer, and the anode in this order.

Next, a method for manufacturing an EL device consisting of an anode/hole injection layer/light emitting layer/cathode will be explained. First, the anode is formed in the same manner as in the case of the EL device described above, and then,
A hole injection layer is provided thereon by forming a thin film made of a hole transport compound by vapor deposition or the like. The vapor deposition conditions at this time may be based on the vapor deposition conditions for forming a thin film of the luminescent material. Next, on this hole injection layer, a light emitting layer and a cathode are sequentially placed.
A desired EL element can be obtained by providing it in the same manner as in the case of manufacturing the EL element. Note that in the fabrication of this EL element, the fabrication order is reversed, and the cathode, light emitting layer,
It is also possible to fabricate the hole injection layer and the anode in this order. Furthermore, to explain the method for manufacturing an EL device consisting of an anode/hole injection layer/light emitting layer/electron injection layer/cathode, first, the anode, hole injection layer, After sequentially providing the light-emitting layers, a thin film made of an electron transfer compound is formed on the light-emitting layer by a vapor deposition method, etc.
A desired EL device can be obtained by providing an electron injection layer and then providing a cathode thereon in the same manner as in the production of the EL device. Note that in the production of this EL element, the production order may be reversed and the cathode, electron injection layer, light emitting layer, hole injection layer, and anode may be produced in this order. When applying a DC voltage to the EL element obtained in this way, when applying a voltage of about 5 to 40 V with the anode as + and the cathode as -, light emission can be observed from the transparent or translucent electrode side. can. Furthermore, even if a voltage with the opposite polarity is applied, no current flows and no light is emitted at all. Furthermore, when applying an alternating voltage, light is emitted only when the anode is in a positive state and the cathode is in a negative state. Note that the waveform of the applied alternating current may be arbitrary.

As explained above, the thin film electrode of the present invention has increased uniformity and density, can significantly reduce volume resistivity, and has improved adhesion to the underlying organic film and glass. In addition, it can be easily formed into a film by a vapor deposition method, and furthermore, the organic film is not damaged during film formation. In particular, by using it as a cathode for an EL element, it can increase its luminous efficiency and provide uniformity of luminescence.
High brightness and high efficiency EL light emission can be obtained at low voltage. Therefore, the EL element using the thin film electrode of the present invention is expected to be effectively used as a light emitting material for various display devices.

[0061]

EXAMPLES Next, the present invention will be explained in more detail based on Examples and Comparative Examples.

Example 1 A white plate glass was ultrasonically cleaned using isopropyl alcohol for 30 minutes, immersed in isopropyl alcohol, taken out, and blown dry with dry nitrogen gas. This was used as a substrate and attached to the substrate holder of a vapor deposition apparatus manufactured by Japan Vacuum Technology Co., Ltd. Further, an Mg ribbon cleaned with dilute hydrochloric acid was placed in a resistance heating boat made of molybdenum, and this resistance heating boat was attached to a terminal of a vapor deposition apparatus. In addition, 200 mg of the above-mentioned TNF was placed in another resistance heating boat made of molybdenum and attached to another terminal. Then, the vacuum chamber was set to 6×10-6To
After evacuation to rr, the boat containing TNF was first energized and heated to a deposition rate of 0.1 nm/sec. Next, heat the resistance heating boat containing Mg, and
The deposition rate was set to 1.5 nm/sec. After this,
Vapor deposition was started by opening the shutter covering the substrate, and the film was deposited using a corrected crystal oscillator until the film thickness reached 120 nm. The vacuum chamber was returned to atmospheric pressure and a thin film made of Mg:TNF was taken out. After confirming that the mirror surface was uniform, the sheet resistance value was measured by the four-probe method, and as a result, an extremely excellent value of 0.85Ω/□ was obtained. Further, the film thickness near the measurement point was found to be 130 nm using a stylus type film thickness meter. The volume resistivity obtained from this is 1.1 x 10-5 Ωcm, and TNF
As a core, we were able to create a uniform, dense thin film. In addition, "Chemistry Handbook" 3rd edition; Basic Edition II, Maruzen, 1932.
According to 1999, the volume resistivity obtained from Mg polycrystals is
It is 4.45×10 −6 Ω·cm. Therefore, the metal thin film obtained in this example has a value about twice as good as this. Also, the sheet resistance value of the Mg:Ag film described in EP0278757 is 3.36Ω/□
(100 nm conversion).

Comparative Example 1 Mg alone was evaporated in the same manner as in Example 1, except that the boat containing TNF was not energized. The obtained Mg thin film was blackish gray in color and had a sheet resistance value of 1 kΩ/□ or more. This indicates that Mg alone is difficult to adhere to glass and is difficult to form a uniform thin film.

Examples 2 to 10 The type of organic substance (acceptor compound and complex-forming compound), the vapor deposition rate ratio of Mg/organic substance, and the film thickness were
M
g: A thin film made of an organic substance was produced. The results are shown in Table 1.

[0065]

[Table 1]

[0066]

[Table 2]

As shown in Table 1, excellent thin films for electrodes made of Mg:organic substance could be obtained using various acceptor compounds and complex-forming organic compounds.

Example 11 A thin film consisting of Mg:organic material was prepared in the same manner as in Example 1 except that the above-mentioned TCNQ was used as the organic material and the film thickness was 18 to 19 nm. As a result, despite the extremely thin film thickness, the sheet resistance was extremely low at 4.3Ω/□.
It showed excellent value. The volume resistivity converted from this is 7
．． It was 9×10 −6 Ω·cm, and a good value was obtained even with an extremely thin film thickness. This indicates that the obtained thin film is uniform and dense. As is well known, the volume resistivity of vapor deposited films is often significantly different from the bulk value (for example, because thin films tend to form island-like structures). (See “Thin Film” by Kanehara, 4th edition, Shokabo Publishing, p.166-175)
.

Examples 12 to 14 The organic substance was TCNQ, and the metal was Yb, Z as shown in Table 2.
A thin film made of an electron-injecting metal/organic substance was prepared in the same manner as in Example 1 except that n and In were used. The results are shown in Table 2. According to the above-mentioned "Chemical Handbook," the volume resistivity of Yb, Zn, and In is 2.9 x 10-6, respectively.
They are 8.92×10 −6 and 8.37×10 −6 Ω·cm.

[0070]

[Table 3]

Example 15 A white plate glass with ITO (manufactured by HOYA) was ultrasonically cleaned with isopropyl alcohol for 30 minutes, then ultrasonically cleaned with pure water for 1 minute, and further immersed in isopropyl alcohol. It was taken out and blown dry with N2. Furthermore, this substrate was cleaned for 120 seconds using a UV and ozone cleaning device manufactured by Samco International Co., Ltd. This substrate was attached to a substrate holder of a vacuum evaporation device manufactured by Nippon Vacuum Technology Co., Ltd. In addition, TPD (a compound with the structural formula below) is added to the Mo resistance heating boat.

[0072]

[C20]

200 mg of [0073] was added and attached to the current terminal. Furthermore, another Mo boat has Al(Ox)3 (
Compounds with the following structural formula)

[0074]

[C21]

200 mg of [0075] was put in and attached to another current-carrying terminal. The vacuum chamber was evacuated to 10-5 Torr, and the Mo boat containing the TPD was energized to a temperature of 0.1 to 0.3 Torr.
The film was deposited to a film thickness of 600 Å at a deposition rate of nm/sec. Next, electricity was applied to the boat containing Al(Ox)3, which was deposited at a deposition rate of 0.1 to 0.3 nm/sec to a thickness of 600 Å.
The film was deposited to a film thickness of . Next, the vacuum chamber was returned to the atmosphere, and a stainless steel vapor deposition mask was attached on the substrate/TPD bath/Al(Ox) layer, and further attached to the substrate holder. In addition, Mg whose surface was cleaned by dilute hydrochloric acid treatment was placed in a Mo resistance heating boat, and PTDI (a compound with the following structural formula) was placed in another Mo resistance heating boat.

[0076]

[C22]

200 mg of [0077] was added, and each of these boats was attached to a current terminal. After evacuating the vacuum chamber to 10-5 Torr, the terminal is energized and the Mg deposition rate is 1.
．． 3-1.4 nm/sec, PTDI deposition rate 0.1-1.
The rate was adjusted to 0.3 nm/sec, and binary simultaneous evaporation was performed until the electrode thin film consisting of Mg:PTDI reached a thickness of 100 nm, and the vacuum chamber was returned to the atmosphere and the glass/ITO
/TPD layer/Al(Ox)3/Mg: An EL element made of an organic substance was produced. The ITO of this element is the positive electrode, Mg:
As a result of applying 6V to an electrode made of PTDI as a negative electrode, a current of 7.3mA/cm2 flows and a brightness of 330cd/
A yellow-green luminescence of m2 was obtained. The luminous efficiency at this time is 2.
It was 4 lumens/watt (lm/W). When the voltage was further increased to 8V, the current was 37mA/cm2.
brightness of 1570 cd/m2 (luminous efficiency 1
．． 7 (lm/W)).

Comparative Example 2 Similar to Example 15, substrate/ITO layer/Al(Ox)
After producing the three layers, an Mg:Ag electrode was produced in place of the Mg:PTDI electrode. The deposition rate is Mg 1
．． 2-1.4 nm/sec, Ag 0.09-0.11 nm
/second, and the film thickness was 100 nm. As a result of conducting a current test in the same manner as in Example 13, when 6V was applied, a current of 15.7mA/cm2 flowed, and the brightness was 324c.
d/m2 was obtained. Luminous efficiency is 1.1 (lm/W)
Met.

Example 16 Al in which the organic substance is an aluminum complex with three oxine coordinations
(Ox)3, the Mg and organic matter deposition rates were 2 nm/sec and 0.1 to 0.3 nm/sec, respectively, and the Mg
: A cathode thin film made of organic matter was created. The sheet resistance value of the obtained thin film was 2Ω/□.

Example 17 Stilbene derivative in which the organic substance was substituted with cyanogen (compound with the following structural formula)

[0081]

[C23]

##STR2## and the vapor deposition rates of Mg and organic matter are 1 to 2 nm/sec and 0.1 to 0.3 nm/sec, respectively,
A cathode thin film made of Mg:organic material was created in the same manner as in Example 16, except that the film thickness was 120 nm. The sheet resistance value of the obtained thin film was 1.0Ω/□.

Example 18 Copper phthalocyanine (CuPc) on Mo resistance heating boat
, TPD and DPVBi (compounds with the following structural formula)

00
84]

[C24]

Put 200 mg of each of [0085] into the vacuum chamber for 10
-3Pa, CuPc, TPD and DPVBi
Vapor deposition was carried out until each tank had a film thickness of 20 nm, 40 nm, and 40 nm, respectively. Next, Al(Ox) as an organic substance
A cathode thin film made of Mg:organic substance was prepared using Here, the vapor deposition rates of Mg and Al(Ox)3 are 1.0 to 2.0 nm/sec and 0.1 to 0.3 nm/sec, respectively.
It was seconds. ITO of this element is used as the positive electrode, Mg:Al(O
x) As a result of applying 10V to an electrode consisting of 3 as a negative electrode, a current of 6.7mA/cm2 flows and a brightness of 230cd.
/m2 blue luminescence was obtained. The luminous efficiency at this time is 1.
1 (lm/W). When the voltage was further increased to 15V, the current was 93m
A current of A/cm2 was obtained, and a brightness of 2040 cd/m2 was obtained.

Comparative Example 3 A cathode thin film was prepared in the same manner as in Example 15, except that the cathode was made of Mg:Ag in the same manner as in Comparative Example 2. As a result of applying 15V to this device, with ITO as the positive electrode and the Mg:Ag electrode as the negative electrode, the current was 231mA/c.
m2 flow and blue luminescence with a brightness of 1100 cd/m2 was obtained. The luminous efficiency at this time was 0.1 (lm/W). At this time, the light emission was significantly non-uniform. This is Mg
: Indicates that the Ag cathode is non-uniformly deposited on the DPVBi layer. In the above, as can be seen by comparing Example 15 and Comparative Example 2, the luminous efficiency of the device using the Mg:PTDI electrode is significantly improved. In addition, Example 1
As can be seen by comparing Comparative Example 8 and Comparative Example 3, the Mg:PTDI cathode significantly improved the adhesion to the organic layer and was able to provide uniformity of light emission and improved luminous efficiency.

[0087]

[Effects of the Invention] As explained above, the thin film electrode of the present invention has improved uniformity and density, can significantly reduce volume resistivity, and has good adhesion to underlying organic films and glass. In addition, the film can be easily formed by a vapor deposition method, and the organic film is not damaged during film formation. In particular, by using it as a cathode for EL elements,
The luminous efficiency can be increased and uniformity of luminescence can be provided, and high-luminance, high-efficiency EL luminescence can be obtained at low voltage. Therefore, the EL element using the thin film electrode of the present invention is expected to be effectively used as a light emitting material for various display devices.

Claims (8)

[Claims] 1. A thin film electrode for an element, comprising an electron-injecting metal and an organic substance. 2. The thin film electrode for an element according to claim 1, wherein the thin film electrode is a thin film electrode for an organic electroluminescent element. 3. The thin film electrode for an element according to claim 1, wherein the organic substance has a property of adhering to or bonding to a metal capable of injecting electrons. 4. The thin film electrode for an element according to claim 1, wherein the organic substance is an acceptor compound. 5. The thin film electrode for an element according to claim 1, wherein the organic substance has the ability to form a complex with a metal capable of injecting electrons. 6. A method for manufacturing a thin film electrode for an element, comprising co-evaporating an electron-injecting metal and an organic substance. 7. An electroluminescent device characterized in that the thin film electrode for device according to any one of claims 1 to 5 is used as a cathode. 8. A method for manufacturing an electroluminescent device, comprising forming a cathode by co-evaporating an electron-injecting metal and an organic substance.