JPH04212287A - Organic membranous electro-luminescence(el) element - Google Patents

Abstract

PURPOSE:To provide an organic membranous EL element high in brightness and long in service life. CONSTITUTION:In an organic membranous EL element composed of at least an anode 2, a positive hole pouring and transport layer 3, an organic electron transport luminous layer 4, and a cathode 5, or at least an anode 2, a positive hole pouring and transport layer 3, an organic luminous layer 7, an electron pouring and transport layer 8, and a cathode 5 in this order, the cathode 5 contacting with the organic electron transport luminous layer 4 or the electron pouring and transport layer 8 is made of an alloy including an alkaline metal element of 6mol% or more as the specific feature of this organic membranous EL element. By using a relatively stable alloy of a low work function which consists of an alkaline metal element and some other metals, the electron pouring amount to the organic electron transport luminous layer can be increased, effective in higher brightness of the organic membranous EL element.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an EL device using electrical light emission, that is, electroluminescence (hereinafter simply referred to as EL), and more specifically relates to at least an anode, a hole injection transport layer, an organic electron transport layer, and an organic electron transport layer. The present invention relates to an organic thin film EL device that is composed of a light emitting layer, a cathode, or at least an anode, a hole injection transport layer, an organic light emitting layer, an electron injection transport layer, and a cathode.

[Prior art]

[0002] Conventional EL devices are mainly AC drive type devices in which a high-resistance insulating layer is provided between electrodes, and they are broadly classified into distributed type EL devices and thin film type EL devices. The structure of a dispersed EL element is to coat an aluminum foil, which will serve as a back electrode, to a thickness of several tens of micrometers with powder such as barium titanate, which has a high dielectric constant and is dispersed in a resin binder, to form an insulating layer. A zinc sulfide-based luminescent layer dispersed in a resin binder is provided on top of the phosphor, and a transparent electrode is further laminated thereon. This type of element is inexpensive, has a large area, and has a thickness of 1 mm.
The following surface light emitters can be obtained and are used as backlights for liquid crystal display devices, but the brightness tends to decrease.

Thin-film EL devices are made by depositing several thousand dielectric thin film layers such as yttrium oxide as an insulating layer on a transparent electrode substrate made of a glass plate coated with indium oxide to tin oxide (hereinafter simply referred to as ITO) by sputtering or the like. On top of this, a ZnS-based, ZnSe-based, SrS-based, CaS-based, etc. phosphor thin film is laminated to a thickness of several thousand angstroms by electron beam evaporation, sputtering, etc., and then a dielectric thin film layer and a back electrode such as aluminum are formed. It has a structure in which the layers are stacked in this order. The film thickness between the electrodes is 1 to 2 μm or less. Thin-film EL elements have a long life and are capable of high-definition display, and are suitable for applications such as portable computer displays, but are expensive.

[0004] In the case of either type of EL element, an AC high voltage of 100 V or more is required to obtain sufficient brightness. However, for example, when a battery is used to cause an EL element to emit light, a step-up transformer is required, so even if the EL element is as thin as 1 mm or less, it is difficult to reduce the thickness of the entire device in which it is incorporated.

[0005] In recent years, therefore, research has been conducted aiming at low voltage direct current driven EL elements that do not require step-up transformers, and one example of which is research on organic thin film EL elements.

[0006] JP-A-57-51781, JP-A-5
9-194393, JP 63-264692, JP 63-295695, Japanese Journal of Applied Physics No.
Vol. 9, p. 773 (1986), Applied Physics Letters, Vol. 51, No. 12, p. 913 (1987)
According to the Journal of Applied Physics, Vol. 65, No. 9, p. 3610 (1989), this type of organic thin film EL device has conventionally been manufactured as follows.

First, copper phthalocyanine or poly(3-methyl) is deposited as a hole injection transport layer on an anode of a transparent conductive film of gold or ITO formed by vapor deposition or sputtering on a transparent insulating substrate such as glass. Thiophene, or
Compound represented by formula 1:

[0008]

[Chemical formula 1]

1,1-bis(4-di-para-tolylaminophenyl)cyclohexane (melting point: 181.4°C to 18°C)
2.4°C) or a compound represented by "Chemical formula 2":

0
010]

[Case 2]

N,N'-diphenyl-N,N'-bis(
3-methylphenyl)-1,1'-biphenyl-4,4
A layer of a tetraphenyldiamine derivative such as '-diamine (melting point 159°C to 163°C) is formed by vapor deposition or electrolytic polymerization.
It is formed as a single layer or a laminated layer to a thickness of about μm or less.

Next, tetraphenylbutadiene, anthracene, perylene, coronene, 12
-phthaloperinone derivative, tris(8-quinolinol)
An organic electron-transporting light-emitting layer is formed to a thickness of about 1.0 μm or less by coating an organic phosphor such as aluminum by vapor deposition or by dispersing it in a resin binder. Finally, single metals such as Mg, In, and Al, or an alloy of Mg and Ag (atomic ratio 10:1), etc. are deposited thereon as a cathode.

In the device manufactured as described above, holes and electrons are injected into the light-emitting layer by applying a low DC voltage of 20 to 30 V or less with the transparent electrode side as the anode, and the recombination causes light emission of 1000 cd. /m2 brightness was obtained.

Furthermore, according to Applied Physics Letters Vol. 57, No. 6, p. 531 (1990), Adachi et al. as N,N'-diphenyl-N,N'-
Bis(3-methylphenyl)-1,1'-biphenyl-
4,4'-diamine, 1-[4 as organic light emitting layer (7)
-N,N-bis(P-methoxyphenyl)aminostyryl]naphthalene, 2-(4
-biphenyl)-5-(4-t-butylphenyl)-1
, 3,4-oxadiazole (hereinafter simply referred to as BPBD), and an alloy of Mg and Ag as the cathode (5) were sequentially laminated to produce an organic thin film EL device, and similarly low DC voltage of 20 to 30 V or less was made. EL emission of about 1000 cd/m2 was obtained.

[0015] Now, considering the preferable conditions for the cathode material used in the organic thin film EL element, (1) it has good adhesion to the organic thin film. ■Difficult to oxidize and stable. ■It has a low work function so that electrons can be easily injected into the energy level of the lowest unoccupied molecular orbital (hereinafter simply referred to as LUMO) of the organic thin film material. etc. can be mentioned.

Conventionally, the cathode material Mg-Ag alloy (atomic ratio 10:1, work function approximately 3.8 eV) that has been most used is C.I. W. Developed by Tang et al., the adhesion of low work function Mg (work function approximately 3.6 eV) to an organic thin film and the smoothness of the deposited film are improved by adding Ag. However, this means that corrosion progresses more easily to the inside of the metal film in air than in the case of Mg alone.

[0017] Organic thin film EL elements are susceptible to heat during heat sealing and to adhesives containing organic solvents, so no adequate sealing method has been developed so far. Therefore, devices are stored and driven in vacuum or in an inert atmosphere such as dry Ar gas, and there has been a need to develop a stable cathode material with a low work function.

Furthermore, the energy level of the LUMO of tris(8-quinolinol) aluminum, which is conventionally known as a typical electron-transporting luminescent material that can provide the highest brightness, is the same as the work function measured by the photoelectron emission method in the atmosphere. Subtracting the optical energy gap (2.75 eV) from the value yields approximately 3.1 eV, and in the case of BPBD, which is used as an electron injection transport material, it is 2.7 eV. Therefore, by efficiently injecting electrons into these materials, 100
As a cathode material for obtaining an organic thin film EL device with a high luminance of 00 cd/m2 or more, Li (work function 2.0 cd/m2), which has a work function smaller than 3.1 eV and a high Fermi level, is used.
9eV), Na (2.75eV), K (2.1eV),
Although alkali metals such as 5 eV) are promising, single metals are extremely susceptible to oxidation and are unstable, so they could not be used as cathodes.

[0019]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems.
- To provide a high-brightness organic thin film EL device using a cathode material that has a lower work function than an Ag alloy and is relatively stable;
This invention was made with the aim of providing an organic thin film EL element that does not easily deteriorate even in the air.

[0020]

[Means for Solving the Problems] That is, the present invention provides at least an anode, a hole injection transport layer, an organic electron transport light emitting layer, a cathode, or at least an anode, a hole injection transport layer, an organic light emitting layer, an electron injection transport layer, Organic thin film E consisting of cathode
The organic thin film EL element is characterized in that the cathode in contact with the organic electron transport light emitting layer or the electron injection transport layer is an alloy containing 6 mol % or more of an alkali metal element.

Furthermore, on the cathode containing an alkali metal element of an organic thin film EL element formed from an anode on a substrate, a non-corrosive metal cathode layer containing no alkali metal element is formed.
This is an organic thin film EL device characterized in that it is formed with a thickness of 00 Å or more.

An embodiment of the present invention will be explained below with reference to FIGS. 1 and 2 of the drawings. FIG. 1 shows an organic thin film EL device according to the present invention, which is formed on a substrate (1), an anode (2), a hole injection transport layer (3), an organic electron transport light emitting layer (4), and a cathode (5).
), a sealing layer (6), and a glass plate (15) is bonded and sealed with an adhesive (16). In the example of FIG. 2, a cathode (5) is formed on a substrate (1). ) in reverse order,
This is a case where the glass plate (15) is bonded and sealed with an adhesive (16).

Furthermore, as shown in FIG.
The functions are separated into a substrate (1), an anode (2), a hole injection transport layer (3), an organic light emitting layer (7), an electron injection transport layer (
8), cathode (5), and sealing layer (6), or as shown in FIG.
) can also be constructed in the reverse order starting from the cathode (5).

[0024] The anode (2) has a surface resistance of 10 to 50 Ω/cm by coating a transparent conductive material such as ITO or zinc aluminum oxide on a transparent insulating substrate (1) such as glass by vacuum deposition or sputtering. Square, visible light transmittance 80%
The above-mentioned transparent electrodes or semi-transparent electrodes with a thin layer of gold or platinum deposited are desirable.

However, in other cases, the anode (2) is opaque and has a high capacity for hole injection into the organic electron transport emissive layer (4) or the organic emissive layer (7) through the hole injection transport layer (3). A metal plate with a large function such as gold, platinum, or nickel, or a semiconductor substrate with a work function of 4.8 eV or more such as silicon, gallium phosphide, or amorphous silicon carbide, or these metals or semiconductors is placed on an insulating substrate (1). The cathode (5) can also be a transparent electrode or a translucent electrode. If the cathode (5) is also opaque, at least one end of the organic electron-transporting light-emitting layer (4) or the organic light-emitting layer (7) needs to be transparent.

Next, a hole injecting and transporting layer (3) is formed on the transparent anode (2), and the preferable conditions for the hole injecting and transporting material are that it is stable against oxidation, has high hole mobility, and is ionizable. The energy must be between that of the anode material and the light-emitting layer material, the film must have good film formability, and it must be substantially transparent at least in the fluorescence wavelength region of the light-emitting layer material. Specifically, phthalocyanines such as copper phthalocyanine and metal-free phthalocyanine, or tetraphenyldiamine derivatives are used in a single layer or in a stacked manner. Typical materials for tetraphenyldiamine derivatives include 1,1-bis(4-di-para-
tolylaminophenyl)cyclohexane, N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1
, 1'-biphenyl-4,4'-diamine, N,N'-
Diphenyl-N,N'-bis(para-tolyl)-1,1
'-Biphenyl-4,4'-diamine, N,N,N'N
Examples include '-tetra(para-tolyl)-4,4'-diaminobiphenyl, but are not particularly limited to the above examples.

Hole injection transport layer using these compounds (
The film 3) is mainly formed on the anode (2) of the transparent electrode by vapor deposition, but it is also dispersed in a resin such as polyester, polycarbonate, polymethylphenylsilane, etc. and coated by a method such as spin coating. It is also possible to form it by The film thickness of the hole injection transport layer (3) is 1 μm even when formed as a single layer or a laminated layer.
or less, preferably 0.03 to 0.1 μm.

When using a hole injection transport material that melts when heated, such as a tetraphenyldiamine derivative,
During or after the vapor deposition of the hole injection/transport material, the substrate may be heated at a temperature below the melting point in a vacuum or in an inert gas atmosphere to remove defects in the vapor deposited film. Also,
When using a hole injecting and transporting material such as copper phthalocyanine, which is crystalline and tends to make the surface of the deposited film uneven, it is also possible to obtain an amorphous deposited film by cooling the substrate during deposition.

Next, an organic electron transport luminescent layer (4) is formed on the hole injection transport layer (3).
The phosphor used in 4) can be any phosphor that has fluorescence in the visible region and can be formed into a film by an appropriate method. for example,
Anthracene, salicylate, pyrene, coronene, perylene, tetraphenylbutadiene, 9,10-bis(phenylethynyl)anthracene, 8-quinolinollithium, tris(8-quinolinol)aluminum, tris(5,7-dichloro,8-quinolinol) ) aluminum, tris(5-chloro-8-quinolinol)aluminum, bis(8-quinolinol)zinc, tris(5-fluoro-8-quinolinol)aluminum, bis[8-
(para-tosyl)aminoquinoline] zinc complex and cadmium complex, 1,2,3,4-tetraphenylbutadiene, pentaphenylbutadiene, and the like.

[0030] The phosphor in the organic electron transporting light emitting layer (4) is
In order to convert the emission wavelength and improve luminous efficiency, two or more types of phosphors may be mixed, or two or more emitting layers of multiple types of phosphors may be laminated, one of which fluoresces in the infrared or ultraviolet region. It may also indicate.

The method for forming the organic electron transporting light emitting layer (4) is as follows:
This is carried out by vacuum evaporation method, cumulative film method, or by dispersing it in a suitable resin binder and coating it by a method such as spin coating. The film thickness of the organic electron-transporting light-emitting layer (4) is 1 μm or less, preferably 0.03 to 0.1 μm, even when formed as a single layer or a laminated layer.

[0032] Next, when the organic electron-transporting and emitting layer (4) is functionally separated into the organic emitting layer (7) and the electron-injecting and transporting layer (8), the preferable condition for the electron-injecting and transporting material is that the electron mobility is is large, the energy level of LUMO is between the same level as the LUMO energy level of the organic light-emitting layer material and the Fermi level of the cathode material, the work function is larger than that of the organic light-emitting layer material, and the film formability is good. Further, in an element configured such that the anode (2) is opaque and light is extracted from a transparent or translucent cathode (5), the element must be substantially transparent at least in the fluorescence wavelength region of the organic light-emitting layer material. Examples include BPBD, 3,4,9,10-
Examples include perylenetetracarboxyl-bis-benzimidazole, but are not particularly limited to the above examples.

The electron injection transport layer (8) is formed by a vacuum evaporation method, a cumulative film method, or by dispersing it in a suitable resin binder and coating it by a method such as spin coating. The film thickness of the electron injection transport layer (8) is
It is 1 μm or less, preferably 0.01 to 0.1 μm.

[0034] Furthermore, a hole injection transport layer, an electron transport light emitting layer,
In order to increase the heat resistance of the electron injection transport layer, vinyl groups, allyl groups, methacryloyloxymethyl groups, methacryloyloxy groups, methacryloyloxyethyl groups, acryloyl groups, and acryloyloxymethyl groups are added to the organic molecules listed as examples of the constituent materials of each layer. It is also possible to introduce one or more polymerizable substituents such as acryloyloxyethyl groups and polymerize each layer during or after film formation, or to improve the film formability of the constituent materials of each layer and form a smooth film. One or more alkyl groups such as methyl groups and ethyl groups may be introduced into the organic molecules listed as examples of the constituent materials of each layer.

[0035] Furthermore, in order to improve the adhesion between the ITO glass substrate and the hole injection transport layer, the hole injection transport layer may be provided after the ITO film is treated with a silane-based or titanate-based coupling agent. . Further, when forming the organic electron transporting and emitting layer (4) or the organic emitting layer (7) and the electron injecting and transporting layer (8) by a vacuum evaporation method, hydrogen,
It is also possible to introduce a non-electron-withdrawing or electron-donating gas such as ammonia into the vacuum chamber and make it adsorb onto the organic molecules, thereby preventing the organic molecules from adsorbing oxygen in the air and increasing the electrical resistance of the film.

Next, a cathode (5) according to the present invention is formed on the organic electron transport/emissive layer (4) or the electron injection/transport layer (8). The main components of the cathode alloy according to claim 1 of the present invention are alkali metal elements such as Li, Na, and K, and more stable elements other than the alkali metal elements such as Mg, Al, In, Sn, Zn,
Although it is a metal such as Ag or Zr, it may contain impurities and additives within several mol % in addition to the main components. The work functions of alkali metal elements are, for example, 2.9 eV for Li, 2.75 eV for Na, and 2.15 eV for K, so Tris (
The Fermi level is sufficiently higher than the LUMO level of aluminum (8-quinolinol), and efficient electron injection can be expected, but since alkali metal alone is extremely easily oxidized in air, it is difficult to use it as a cathode in organic thin-film EL devices. Ta.

Therefore, in the present invention, the alkali metal element is Mg.
It is stabilized by alloying with one or more metals other than alkali metal elements such as , Al, In, Sn, Zn, Zr, and Ag. Even when the device is exposed to the atmosphere from a vacuum after forming the cathode by a method such as co-evaporation, rapid corrosion to the inside of the cathode in contact with the organic electron-transporting light-emitting layer is prevented. This is thought to be because a dense oxide film is formed on the cathode surface that is exposed to air due to alloying. The proportion of the alkali metal element in the cathode alloy of the present invention is preferably 6 mol % to 30 mol %, and if it is 30 mol % or more, oxidation and corrosion will easily progress to the inside of the cathode when exposed to humid air.

Therefore, since the thickness of the low work function cathode layer for effective electron injection is 500 Å or less, it is sufficient to first reduce the thickness of the cathode layer (9) containing an alkali metal element to about 500 Å or less. As shown in FIG. 5, a non-corrosive metal cathode layer containing no alkali metal (1
The cathode may be formed by laminating the layers 0) to a thickness of 500 Å or more. Examples of non-corrosive metals include Mg, Sn,
Examples include Al, In, Ni, Cu, Ag, Au, Pt, Zn, etc., but in addition to the above, any metal element other than alkali metal elements and alkaline earth metal elements larger than 4th period can be used. .

The cathode (5) is formed by codeposition using a resistance heating method under a degree of vacuum of the order of 10 -5 Torr or less from separate deposition sources for each component while monitoring with a crystal resonator type film thickness meter. At this time, even in the case of a single layer or a stack, the film is formed with a thickness of about 0.1 to 0.3 μm, but the film is formed using an alloy target instead of co-evaporation by electron beam evaporation or sputtering method. You can also do it.

Next, a sealing layer (6) is formed on the device to prevent oxidation of the organic layer and electrodes of the device. The sealing layer (6) is formed immediately after the formation of the cathode (5). Examples of sealing layer materials include oxides such as SiO2, SiO, GeO, MoO3, MgF2, LiF, BaF2, AlF3,
Examples include inorganic compounds with high barrier properties such as fluorides such as FeF3 and sulfides such as GeS and SnS, but are not limited to the above examples. A single film or a combination of these materials is formed by vapor deposition, sputtering, or the like. In the case of vapor deposition using a resistance heating method, GeO is superior because it can be vapor deposited at a low temperature.

Furthermore, in order to prevent moisture from entering, a low hygroscopic photocurable adhesive, epoxy adhesive, etc. (15) is used.
The glass plate (16) is glued and sealed. In addition to glass plates, metal plates, plastic plates, etc. can also be used. In order to prevent deterioration of the organic layer due to ultraviolet rays and extend the life of the EL element, we provide an ultraviolet absorbing layer made of a ZnO film etc. on the glass surface of the ITO glass substrate, and in order to change the spectrum of EL emission, color filter layer, EL
It is also possible to provide a layer of material that absorbs the emitted light and emits fluorescence.

[0042] Furthermore, by using an anode in which a translucent film of a single metal or an alloy such as gold, platinum, or alloy for visible light is laminated on an ITO glass substrate as an anode, and a cathode that is opaque and has a high reflectance in visible light, The distance between the anode and cathode is E
By laminating a hole injection transport layer, an organic electron transport light emitting layer, etc. to a thickness equal to an integer multiple of 1/2 of the L emission wavelength corrected by the refractive index of the organic thin film to form an optical resonator. It is also possible to obtain an EL spectrum with a narrow half-width in the EL emission wavelength region.

The organic thin film EL device constructed as described above is connected to a power source (11) with a lead wire (12) with the hole injection transport layer (3) side as positive, and air is removed by applying a DC voltage. Although it stably emits light inside, it emits light even when an alternating current voltage is applied while a positive voltage is applied to the electrode on the hole injection transport layer (3) side. In addition, the organic thin film EL device configured as above generates a photovoltaic force by irradiating the absorption region of the organic thin film with light so that the electrode on the hole injection transport layer side becomes positive, and functions as a photovoltaic cell. do.

[0044]

【Example】

<Example 1> Hereinafter, an example of the EL element of the present invention will be described with reference to FIG. First, a transparent insulating substrate (1) with a thickness of 1.
A 1 mm glass plate is used, and 1200 Å of ITO is placed on top of it.
was coated to form an anode (2). After thoroughly cleaning this transparent conductive glass substrate, N, N,
N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine with 5
00 Å was deposited. Next, tris(8-quinolinol)aluminum was evaporated to a thickness of 500 Å as an organic electron-transporting light-emitting layer (4), and an Mg-Na alloy was co-evaporated on its upper surface as a cathode (5) to a thickness of 95 Å so that the proportion of Na was 23 mol%. After the deposition, Mg alone was deposited to a thickness of 2140 Å. The work function of the cathode (5) was 3.2 eV as measured by photoelectron emission method.

Finally, as the sealing layer (6), GeO was added to 1.8
After μm deposition, the glass plate (15) is bonded with ultraviolet curing adhesive (1
6) was adhered and sealed. This element emits yellow-green light when a DC voltage of 3V or more is applied, and at 13V it emits 10200
It exhibited a brightness of cd/m2. The current density at this time is 5
It was 36 mA/cm2.

<Example 2> Similar to Example 1, a hole injection transport layer (3) and an organic electron transport light emitting layer (4) were sequentially deposited on a transparent conductive glass, and then a Mg- A Li alloy was deposited to a thickness of 2200 Å by co-evaporation so that the proportion of Li was 26 mol %. The work function of the cathode (5) was approximately 3.1 eV as measured by photoelectron emission method. Finally, as a sealing layer (6), Li
F was deposited to a thickness of 1 μm.

[0047] This element emits yellow-green light when a DC voltage of 3V or more is applied, and emits light of 11123 cd/m at 17V.
It showed a brightness of 2. The current density at this time is 399mA/
cm2.

Example 3 As in Example 2, a hole injection transport layer (3), an organic electron transport light emitting layer (4), and a cathode (5) were formed in this order on transparent conductive glass.

When an adhesive tape was pasted on the cathode surface of this device and a peel test was performed, it was found that unlike the case where an Mg-Ag alloy was used for the cathode, the organic electron transporting light emitting layer (4) was attached to the cathode (
5), it was shown that the adhesion between the organic electron transporting light emitting layer and the cathode was stronger than when an Mg-Ag alloy was used for the cathode.

<Example 4> After depositing the hole injection transport layer (3) on transparent conductive glass in the same manner as in Example 1, tris(8-quinolinol) aluminum containing 0.5 mol% of coumarin 540 was deposited. 500Å
100% by co-evaporation of a Mg-Li alloy as a cathode (6) on the top surface so that the proportion of Li is 26 mol%.
After the deposition of 2100 Å, Mg alone was subsequently deposited to a thickness of 2100 Å. Finally, GeO was deposited to a thickness of 2 μm as a sealing layer (6), and then a glass plate (15) was bonded and sealed with an ultraviolet curing adhesive (16). This element emitted green light in the air at 3V or higher, and exhibited a luminance of 40,000 cd/m2 at 14V. The current density at this time was 510 mA/cm2. Note that this element exhibited uniform surface emission with almost no deterioration even after being exposed to air for more than three months.

[0051]

[Example 5] As in Example 1, a hole injection transport layer (3) and an organic electron transport light emitting layer (4) were sequentially deposited on transparent conductive glass, and then an Al-Li alloy was deposited as a cathode (5). A thickness of 2200 Å was deposited by co-evaporation so that the proportion of Li was 28 mol %. The work function of the cathode (5) was about 3.2 eV as measured by photoelectron emission method. Finally, the sealing layer (6
) was deposited with a thickness of 0.7 μm. This element is 3V
Above, it emits yellow-green light, and the maximum brightness is 10V at 17V.
The current density was 322 cd/m2 and 341 mA/cm2.

<Comparative Example 1> Similar to Example 1, a hole injection transport layer (3) and an organic electron transport light emitting layer (4) were sequentially deposited on a transparent conductive glass, and then Mg- was deposited as a cathode (5). An Ag alloy was formed by co-evaporation so that the proportion of Ag was 12 mol %. The work function of the cathode (5) was approximately 3.8 as measured by photoelectron emission method.
It was eV. Finally, MgF2 was deposited to a thickness of 0.3 μm as a sealing layer (6). This element emits yellow-green light at 3V or higher, and the maximum brightness is 5990 cd/m2 at 17V.
The current density was 268 mA/cm2.

[0053]

As described above, according to the present invention, organic electron The amount of electrons injected into the transport light emitting layer can be increased compared to the case where a conventional cathode made of an Mg-Ag alloy is used, which is effective in increasing the brightness of an organic thin film EL device.

Furthermore, laminating a non-corrosive metal cathode layer that does not contain an alkali metal on a cathode that contains an alkali metal is effective in extending the life of the organic thin film EL device.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of an organic thin film EL element of the present invention.

FIG. 2 is an explanatory diagram showing another embodiment of the organic thin film EL device of the present invention.

FIG. 3 is an explanatory diagram showing another embodiment of the organic thin film EL device of the present invention.

FIG. 4 is an explanatory diagram showing another embodiment of the organic thin film EL device of the present invention.

FIG. 5 is an explanatory diagram showing another embodiment of the organic thin film EL device of the present invention.

[Explanation of symbols]

(1) Substrate (2) Anode (3) Hole injection transport layer (4) Organic electron transport light emitting layer (5) Cathode (6) Sealing layer (7) Organic light emitting layer (8) Electron injection transport layer (9) Cathode layer containing alkali metal (10) Corrosion-resistant cathode layer (11) Power supply (12) Lead wire (13) Cathode outlet (14) Anode outlet (15) Glass plate (16) Adhesive

Claims (2)

[Claims] 1. An organic thin film comprising at least an anode, a hole injection transport layer, an organic electron transport light emitting layer, and a cathode, or at least an anode, a hole injection transport layer, an organic light emitting layer, an electron injection transport layer, and a cathode. An organic thin film EL device, wherein the cathode in contact with the organic electron transport light emitting layer or the electron injection transport layer is an alloy containing 6 mol % or more of an alkali metal element. Claim 2: Organic thin film EL formed from an anode on a substrate.
2. The organic thin film EL device according to claim 1, further comprising a corrosion-resistant metal cathode layer not containing an alkali metal element and having a thickness of 500 Å or more on the cathode containing an alkali metal element.