JP2003229269A - Organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element having efficient electron injection electrodes and good working stability to improve a visual field effect better than that of previous EL elements. <P>SOLUTION: For the organic EL composed of a positive electrode, a base board, and an organic EL layer comprising a negative electrode, a negative electrode buffer layer, an electron carrier layer, a light emitting layer, a hole carrier layer, and a positive electrode buffer layer, an electron carry efficiency is accurately controlled depending on the element structure alternately laminating the electron carrier layers and the negative electrode buffer layers more than twice. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic EL device, and more particularly to an inorganic / organic junction structure used in a device that emits light by applying an electric field to a thin film of an organic compound.

[0002]

2. Description of the Related Art Organic light emitting devices (e.g., organic EL devices such as light emitting displays and laser devices) have positive and negative polarities from an anode and a cathode when a DC voltage is applied to electrodes attached to both sides of an organic insulator thin film having strong fluorescence. Charge is injected,
Positive and negative charges move in the thin film due to the generated electric field, and with a certain probability, the energy released during recombination is consumed to form the singlet excited state (molecular exciton) of the fluorescent molecule, and its emission quantum efficiency is increased. Light is emitted to the outside in a proportion to return to the ground state, and the light emitted at this time is used.

The above organic insulator thin film is composed of, for example, an electron injection layer, an electron transport layer, a light emitting layer, a hole transport layer, etc., and is generically called an organic EL layer. Aluminum or magnesium alloy (MgAg, MgCa, etc.) is often used for the cathode, and ITO is used for the anode to extract EL light emission.
Often transparent electrodes such as are used. A buffer layer is often formed between each of the cathode and the anode and the organic EL layer.

A cathode structure used in an organic EL device has a cathode structure as disclosed in JP-A-10-74586.
Those having a layered structure are known. According to this, the cathode is composed of a fluoride layer in contact with the organic EL layer and a conductive layer in contact with the fluoride layer. It is desirable to use a metal having a low work function as the cathode that controls the electron injection function. However, metals with low work functions are always subject to atmospheric oxidation. Therefore, by forming an ultrathin layer such as a fluoride film between the conductive layer and the organic EL layer, it is possible to fabricate an element that exhibits high device efficiency at low operating voltage and low current density while improving oxidation resistance. Have been successful.

[0005]

However, at present, in order to further improve the visual field efficiency, an organic EL element having an efficient electron injecting electrode and good operational stability is demanded, and it is necessary to use the conventional organic EL material. In terms of electron transport performance, it is insufficient in view of high efficiency and high reliability of the device.

In the organic EL device, the material most commonly used for the anode is ITO, but ITO is basically a polycrystalline film and has surface irregularities of about 20 nm. As shown in FIG. 3, the organic EL layer 9 including the electron transport layer 3, the light emitting layer 4, the hole transport layer 5, and the anode buffer layer 6, the cathode 1, and the cathode buffer layer 2 while leaving the surface of the anode 7 uneven. When the two-layer cathode 11 made of is formed into a film, the organic EL layer becomes discontinuous, and when the device is actually operated, the electric field is nonuniformly applied, and a non-emission point called a dark spot ( Surface is formed, which is a serious problem in terms of device light emission characteristics. It is possible to reduce the discontinuous portion of the organic EL layer by increasing the thickness of the entire organic EL layer 9 or to increase the spatial distance between the cathode and the anode, but consider the electronic physical properties of the organic EL layer material. Then, although the reliability is improved, the element light emission characteristics are not improved.
It is possible to prevent the formation of dark spots due to non-uniformity of the electric field by polishing the ITO surface to reduce the surface roughness, but this causes problems of time loss and cost.

Moreover, since the fluoride layer of the conventional organic EL element is an extremely thin layer of about 0.5 to 1 nm, the film is likely to be discontinuous depending on the film forming conditions. As a result, as shown in FIG. 4, the contact between the organic EL layer 9 and the two-layer cathode 11 is insufficient, so that the cathode floats up, or the oxygen generated by the deterioration of the organic EL layer 9 due to the heat generated during driving. Impurities of 10,
Alternatively, impurities 10 such as moisture and oxygen in the atmosphere that enter due to the unevenness of the surface of the anode 7 diffuse by the uneven application of an electric field and reach the two-layer cathode 11, resulting in the phenomenon that the cathode floats. There is. The peeling of the cathode from the organic EL layer directly results in a dark spot, which impairs the reliability of light emission of the organic EL element without limit.

In order to solve the above problems, the present invention proposes an organic EL device in which an electron transport layer and a cathode buffer layer are alternately laminated at least twice or more.

[0009]

The present invention is directed to a cathode, a cathode buffer layer, an organic EL layer including an electron transport layer, a light emitting layer, a hole transport layer, and an anode buffer layer, an anode, and an organic layer including a substrate. In the EL element, the electron transport layer and the cathode buffer layer are alternately laminated at least twice or more.

The organic EL device of the present invention is characterized in that the number of electrons injected into the light emitting layer is arbitrarily controlled by the thicknesses and the numbers of the cathode buffer layers and the electron transport layers which are alternately laminated.

The organic EL device of the present invention is characterized in that at least one of the alternately stacked cathode buffer layers is a halogen compound such as a fluoride.

The organic EL device of the present invention is characterized in that at least one of the cathode buffer layers alternately laminated is an oxide.

The organic EL device of the present invention is characterized in that the cathode buffer layers which are alternately laminated each have a thickness of 0.2 to 15 nm.

The organic EL device of the present invention is characterized in that the electron transport layers which are alternately laminated each have a thickness of 10 to 1000 nm.

In the organic EL device, the formation of 1: 1 electron-hole pairs in the light emitting layer is very important, and the excess carriers impair the light emitting efficiency and reliability of the device. A structure that can handle a combination of an electron transport material and a hole transport material is required. The present invention is particularly characterized in that the electron transport efficiency is accurately controlled from the device structure. Specifically, the number of electrons injected into the light emitting layer is arbitrarily controlled by the thickness of each of the cathode buffer layer and the electron transport layer which are alternately stacked and the number of stacks.

Further, by making the structure in which the electron transport layer and the cathode buffer layer are alternately laminated at least twice or more, that is, by positively incorporating the organic / inorganic interface structure into the device, the electron injection effect is achieved. The characteristic is that the spatial distance between the cathode and the anode is increased while improving the efficiency. Separation of the spatial distance prevents current leaks and dark spots due to non-uniform electric field during device operation due to external pressure, cathodes, and structural protrusions on the surface of the anode, and prevents repeated organic / inorganic interfaces. In addition, diffusion of water and oxygen existing in the atmosphere, reaction of cathode, anode components, components of the organic EL layer such as the hole transport layer, peeling of the cathode due to diffusion, and device deterioration are prevented.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The organic EL device of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic view of an organic EL device according to the present invention, where 1 is a cathode, 2 is a cathode buffer layer, 3 is an electron transport layer, 4 is a light emitting layer, 5 is a hole transport layer, and 6
Is an anode buffer layer, 7 is an anode, and 8 is a substrate.

The material used for the cathode 1 is generally preferably a low work function metal, and is preferably a metal such as tin, magnesium, indium, calcium, aluminum or silver, or an alloy containing these as the main components. It is also possible to use a material in which a metal that is relatively stable in the air is slightly doped with a metal having a low work function. The thickness of the cathode is usually 0.1 nm to 10 μm, preferably 50 nm to 1
μm. The cathode is a vacuum deposition method, a sputtering method,
It is often formed by an electron beam evaporation method, a plasma CVD method, and a coating method. In the vacuum deposition method, the crucible containing the material is placed in a vacuum container, and the
After evacuation to about 0 ^-4 Pa, the crucible is heated to sublimate or evaporate the material to a desired film thickness, and in the coating method, conductive metal fine particles dispersed in an appropriate binder resin solution or coatability improving material. Is applied to a desired place by spin coating, ink jet, or the like to be formed.

The cathode buffer layer 2 has the functions of improving the adhesion between the cathode and the organic EL layer, preventing the diffusion of the cathode material to the organic light emitting layer side, and further improving the efficiency of electron injection from the cathode. . The material used for the cathode buffer layer is an alkali metal halogen compound, an alkaline earth metal halogen compound, and various oxides. Halogen is five elements of fluorine, chlorine, bromine, iodine and astatine, and as the halogen compound used in the present invention, fluoride, chloride, bromide and iodide are preferable. Specific preferred halogen compounds are listed below: lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride, calcium fluoride, magnesium fluoride, strontium fluoride, barium fluoride, lithium chloride, calcium chloride, sodium chloride. , Magnesium chloride, strontium chloride, barium chloride, lithium bromide, calcium bromide, magnesium bromide, strontium bromide, barium bromide and the like. Specific examples of preferable oxides for use in the present invention include lithium oxide, rubidium oxide, potassium oxide, sodium oxide, cesium oxide, strontium oxide, magnesium oxide, and calcium oxide. The same material or different materials may be used for each cathode buffer layer. The cathode buffer layer is usually formed by a vacuum vapor deposition method, a sputtering method, or an electron beam vapor deposition method, and each layer has a thickness of 0.
2 nm to 30 nm, preferably 0.2 to 15 nm
Is.

The electron transport layer 3 is formed of a compound capable of efficiently transporting electrons from the cathode in the direction of the hole transport layer between the electrodes to which an electric field is applied. These compounds have high electron affinity, high electron mobility,
It is required that it has excellent stability and that impurities that become electron traps are unlikely to be generated during manufacturing or use. As a compound material satisfying such a condition, an aromatic compound such as tetraphenylbutadiene, a metal complex such as Alq ₃ or 10-
Hydroxybenzo [h] quinoline metal complex, mixed ligand aluminum chelate complex, cyclopentadiene derivative, perinone derivative, oxadiazole derivative, bisstyrylbenzene derivative, perylene derivative, coumarin compound, rare earth complex, distyrylpyrazine derivative, Examples thereof include p-phenylene compounds, thiadiazolopyridine derivatives, pyrrolopyridine derivatives, and naphthyridine derivatives. One kind or a plurality of kinds of the above materials may be used for each electron transport layer. The electron transport layer is often formed by using a vacuum deposition method or a coating method, and the thickness of each layer is usually 5 to 1000 nm, preferably 10 to 100 nm.
nm.

The greatest feature of the present invention is that the cathode buffer layer 2 and the electron transport layer 3 are controlled and stacked alternately on the order of nanometers or less.

The light emitting layer 4 is formed for the purpose of changing the color of emitted light in addition to improving the light emitting efficiency of the device. As an example of changing the emission color, it is known to use Alq ₃ as a host material and dope a fluorescent dye for laser such as coumarin. Doping a fluorescent dye with the electron transport layer as a host material is also important for the purpose of improving the driving life of the device. For example, Alq ₃ is used as a host material, and a fused polycyclic aromatic ring such as a naphthacene derivative represented by rubrene, a quinacridone derivative, and a perylene derivative is doped in an amount of 0.1 to 10% by weight with respect to the host material. It is possible to greatly improve the light emission characteristics, particularly the driving stability. These light emitting layers are formed by vacuum vapor deposition,
Often formed by a coating method, the layer thickness is usually 5 to 2
It is 00 nm, preferably 10 to 100 nm.

The hole transport layer 5 is required to efficiently transport the holes injected from the anode to the light emitting layer side. Therefore, the ionization potential is small, the transparency to visible light is high, the hole mobility is large, the stability is good,
It is desirable to use a material having a glass transition temperature of 70 ° C. or higher and having excellent heat resistance, in which impurities that become hole traps are unlikely to be generated during production or use. Materials that meet these requirements are
For example, aromatic diamine compounds such as 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane, 4,
Aromatic amines such as 4'-bis [(N-1-naphthyl) -N-phenylamino] biphenyl and derivatives of triphenylbenzene, aromatic triamines having a starburst structure, N, N'-diphenyl-N, N Aromatic diamines such as'-bis (3-methylphenyl) biphenyl-4,4'-diamine, N, N, N-triphenylamine derivatives, α,
Examples include α, α ′, α′-tetramethyl-α, α′-bis (4-di-p-tolylaminophenyl) -p-xylene. The hole transport layer is often formed by a vacuum vapor deposition method or a coating method, and the layer thickness is usually 5 to 200 nm, preferably 10 to 100 nm.

The material used for the anode buffer layer 6 has good contact with the anode and can form a uniform thin film.
Thermal stability with a melting point of 300 ° C or higher and a glass transition point of 100 ° C or higher is required. Further, it is desirable that the ionization potential is low, holes can be easily injected from the anode, and the hole mobility is high. Examples of materials that satisfy such requirements include porphyrin derivatives and phthalocyanine compounds. The anode buffer layer 6 is formed by a vacuum vapor deposition method or a coating method, and the layer thickness is usually 3 to 100 nm, preferably 10 to 50 nm.

The anode 7 serves to inject holes into the light emitting layer. The anode is usually a metal oxide such as indium and / or tin oxide, a metal such as aluminum, gold, silver, nickel, palladium, platinum, a halogenated metal such as copper iodide, carbon black, or poly (3-methyl). (Thiophene), polypyrrole, polyaniline, and other conductive polymers. When transparency is required, the thickness of the anode should be such that the visible light transmittance is 60% or more, preferably 8%.
0% or more is desirable, usually 5 to 1000 nm
And preferably 10 to 500 nm. If transparency is not required and opacity is acceptable, the same material as the substrate 8 may be used. The anode is often formed by a sputtering method, a vacuum vapor deposition method, an electron beam vapor deposition method, a plasma CVD method, and a coating method. Among them, the sputtering method and the coating method can form a large area at a time, and thus are relatively good. Used.

The substrate 8 serves as a support for the organic EL device, and glass, quartz, a metal plate, a metal foil, a plastic film, a sheet, or the like is used. In particular, glass plates and transparent synthetic resins such as polyester, polymethacrylate, polycarbonate, and polysulfone are desirable.

In the organic EL device of the present invention in which the cathode buffer layer 2 and the electron transport layer 3 are repeatedly laminated four times in FIG.
The case where the thickness of the cathode buffer layer 2 is sequentially increased from the cathode side to the anode side is shown. With such a structure, electrons are amplified and generated in an avalanche shape at each cathode buffer layer / electron transport layer interface, and a very highly efficient electron injection effect is exhibited toward the light emitting layer 4 side. When it is desired not to inject more electrons than necessary or when the reliability of the device is to be considered first, as shown in FIG. 5, the cathode side is a thick buffer layer, and the cathode side is thinly laminated in order to the anode side. Basically, it is desirable that the number of injected electrons and the number of injected holes are 1: 1. However, since the electron transporting ability of the material itself of the hole transport layer 5 and the light emitting layer 4 is poor, the number of injected holes is It may be lower than the number. In such a case, the excessively injected electrons serve as ineffective carriers, which may cause a decrease in quantum efficiency in light emission of the organic EL element. In the present invention, the thickness of the cathode buffer layer and the electron transport layer and the number of repetition cycles of the cathode buffer layer and the electron transport layer are predicted by a device simulation technique or the like by the combination of each material, and from the light emission characteristics and the element driving stability. Since the advantage can be arbitrarily set, it is possible to prevent the quantum efficiency from being lowered due to the generation of invalid carriers.

Further, as shown in FIG. 6, even when the cathode buffer layer 2 is formed to have a constant thickness and the thickness of the electron transport layer 3 is arbitrarily changed, the organic EL layer becomes thick as a whole. Since many inorganic / organic interfaces are incorporated in the device, the organic EL has good reliability such as light emission characteristics and environmental resistance.
The device is obtained. (Examples) Next, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. Further, in order to confirm the layer structure of the organic EL elements produced in the following Examples and Comparative Examples, an Auger electron spectrometer, an ultraviolet photoelectron spectrometer, an X-ray photoelectron spectrometer, an atomic force microscope, an energy filter transmission electron microscope are used. Using. (Example 1) 150 transparent ITO conductive films were formed on a glass substrate.
Laminated to a thickness of nm. This ITO film-coated substrate is 2 m by using ordinary photolithography technology and hydrochloric acid etching.
After forming an m-width stripe pattern (anode), ultrasonic cleaning with acetone, ultrasonic cleaning with pure water, ultrasonic cleaning with isopropyl alcohol was performed, and the resultant was dried by nitrogen blow. Finally, ultraviolet ozone cleaning was carried out, and after installation in a vacuum vapor deposition apparatus, it was evacuated by a vacuum pump until it ^reached 1 × 10 ⁻⁴ Pa. Hereinafter, vapor deposition is performed using this apparatus. First, as the anode buffer layer, copper phthalocyanine (Chemical formula 1)

[0029]

[Chemical 1]

The temperature is 150 ° C., the degree of vacuum is 2 × 10 ^-4 Pa,
Vapor deposition was performed at a vapor deposition rate of 0.1 nm / sec to obtain a 15 nm anode buffer layer. Next, as a hole transport layer, 4,4 '
-Bis [N- (1-naphthyl) -N-phenylamino]
Biphenyl

[0031]

[Chemical 2]

At a temperature of 120 ° C. and a vacuum degree of 2 × 10 ^-4 P
a, vapor deposition at a vapor deposition rate of 0.1 nm / sec, 30 nm
A hole transport layer of Subsequently, as a light emitting layer, Alq ₃
(Chemical formula 3)

[0033]

[Chemical 3]

And a quinacridone derivative (Chemical formula 4)

[0035]

[Chemical 4]

While the quinacridone derivative was accurately monitored by a separate film thickness monitor so that the quinacridone derivative was 2% by weight relative to Alq ₃ , the vacuum degree was 2 × 10 ^-4 Pa and the Al
q ₃ was vapor-deposited under the conditions of a temperature of 160 ° C., a vapor deposition rate of 0.2 nm / sec, and a quinacridone derivative at a temperature of 120 ° C. and a vapor deposition rate of 0.1 nm / sec to obtain a light-emitting layer having a thickness of 30 nm. Further, Alq ₃ is used as an electron transport layer at a temperature of 160 ° C. and a vacuum degree of 2 ×.
10 ⁻⁴ Pa, vapor deposition rate of 0.2 nm / second
An electron transport layer of nm was obtained. Subsequently, as a cathode buffer layer, lithium fluoride (LiF) was vapor-deposited under the conditions of a temperature of 570 ° C., a vacuum degree of 2 × 10 ⁻⁴ Pa and a vapor deposition rate of 0.1 nm / sec to obtain a cathode buffer layer having a film thickness of 1 nm. . Again, under the same conditions, the electron transport layer Alq ₃ and the cathode buffer layer LiF were alternately formed twice, three times in total. Finally, as a cathode, a 2 mm wide shadow mask mask made of aluminum for vapor deposition is placed at a position 5 μm away from the device surface so as to be orthogonal to the anode.
It was installed using a manipulator, and aluminum was vapor-deposited to a thickness of 100 nm. Thus, an organic EL device having a 2 mm × 2 mm size light emitting area portion was obtained. The cross-sectional structure of the device of Example 1 is the same as the schematic view shown in FIG.

The device characteristics of Example 1 were evaluated by applying a DC voltage with the positive polarity of the anode and the negative polarity of the cathode. As a result, when the luminance exceeded 1 cd / m ² , the applied voltage was 2 V and 250 mA.
The applied voltage was 8 V when the current density of / cm ² was obtained, and the brightness at that time was 9,210 cd / m ² . When this element was driven at a DC constant current density of 15 mA / cm ² , the initial luminance was 620 cd / m ² , the initial driving voltage was 2.5 V,
The half-life was 25,000 hours. (Example 2) The electron transport layer Alq3 was set to 10 nm, and the cathode buffer layers LiF to be alternately stacked were set to 5, _{3, 1} , and 0.5 nm in order from the light emitting layer side, and stacked repeatedly 4 times. An element manufactured in the same manner as in Example 1 is called Example 2. The cross-sectional structure of the device of Example 2 is the same as the schematic view shown in FIG.

The device characteristics of Example 2 were evaluated under the same conditions as in Example 1. As a result, in the device thus manufactured, the anode was positive and the cathode was negative, and a DC voltage was applied. When applied, the applied voltage was 1.5 V when the brightness exceeded 1 cd / m ² , the applied voltage was 6 V when a current density of 250 mA / cm ² was obtained, and the brightness at that time was 107,5.
It was 10 cd / m ² . This element is a DC constant current density 1
Initial brightness is 750 cd when driven at 5 mA / cm ^2.
/ M ² , the initial drive voltage was 2 V, and the half-life was 26,000 hours. (Example 3) An element manufactured in the same manner as in Example 1 except that lithium oxide was used for the cathode buffer layer is referred to as Example 3.

The device characteristics of Example 3 were evaluated under the same conditions as in Example 1. The applied voltage is 2.0 V when the brightness exceeds 1 cd / m ² , the applied voltage is 7.7 V when the current density of 250 mA / cm ² is obtained, and the brightness at that time is 9,098 cd.
/ M ² . This element has a DC constant current density of 15 mA /
The initial luminance when driven at cm ² was 605 cd / m ² , the initial driving voltage was 2.5 V, and the half-life was 25,000 hours. (Example 4) An element manufactured in the same manner as in Example 1 except that the film thickness of the cathode buffer layer LiF was 5, 3, and 1 nm in order from the cathode side is set as Example 4. The cross-sectional structure of the device of Example 4 is the same as the schematic diagram shown in FIG.

The device characteristics of Example 4 were evaluated under the same conditions as in Example 1. The applied voltage when the brightness exceeds 1 cd / m ² is 2.8 V, the applied voltage is 8 V when the current density of 250 mA / cm ² is obtained, and the brightness at that time is 8,820 cd / m 2.
^{Was 2} . This element was set to a DC constant current density of 15 mA / cm ²
The initial luminance was 595 cd / m ² , the initial driving voltage was 2.5 V, and the half-life was 32,000 hours. (Example 5) as an electron transporting layer in Example 5 the element manufactured in the same manner as in Example 1 except that the film thickness of Alq ₃ was 5,10,30nm in order from the cathode side. The sectional structure of the element of Example 5 is the same as the schematic view shown in FIG.

The device characteristics of Example 5 were evaluated under the same conditions as in Example 1. The applied voltage is 3.0 V when the brightness exceeds 1 cd / m ² , the applied voltage is 8.5 V when a current density of 250 mA / cm ² is obtained, and the brightness at that time is 9,610 cd.
/ M ² . This element has a DC constant current density of 15 mA /
The initial luminance when driven at cm ² was 580 cd / m ² , the initial driving voltage was 2.5 V, and the half-life was 31,000 hours. Comparative Example 1 An element manufactured in the same manner as in Example 1 except that the electron transport layer Alq ₃ is formed to a thickness of 30 nm and the cathode buffer layer LiF is formed to a thickness of 1 nm only once is set as Comparative example 1. The cross-sectional structure of the element of Comparative Example 1 is the same as the schematic diagram shown in FIG.

The device characteristics of Comparative Example 1 were evaluated under the same conditions as in Example 1. The applied voltage is 5.0 V when the brightness exceeds 1 cd / m ² , the applied voltage is 18 V when the current density of 250 mA / cm ² is obtained, and the brightness at that time is 2,110 cd / m ^2.
It was m ² . This element has a DC constant current density of 15 mA / c
When driven at m ² , initial luminance was 210 cd / m ² , initial driving voltage was 7.5 V, and half-life was 115 hours. (Comparative Example 2) An element manufactured in the same manner as in Comparative Example 1 except that the cathode buffer layer LiF has a thickness of 0.5 nm is referred to as Comparative Example 2. The cross-sectional structure of the element of Comparative Example 2 is the same as the schematic diagram shown in FIG.

In order to evaluate the device characteristics of Comparative Example 2, 15
When the device was made to emit light after being driven at a current density of mA / cm ² for 30 minutes, there were 4 dark spots in the light emitting area.
0% was present. Therefore, when the cross-sectional structure was observed, it was found that a space was formed between the cathode and the cathode buffer layer. In another device manufactured under the same conditions, the space between the cathode and the cathode buffer layer, and the hole transport layer 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl is the moisture content. It was also observed that it was crystallized by mixing.

[0044]

According to the present invention, it is possible to obtain an advantageous effect that it is possible to provide an element structure having a highly efficient electron injection ability in an organic EL element and good operation stability.

[Brief description of drawings]

FIG. 1 is an organic E of Example 1, which is an embodiment of the present invention.
L element schematic cross-sectional view

FIG. 2 is a schematic cross-sectional view of an organic EL element of Example 2 which is another mode of the present invention.

FIG. 3 is a schematic cross-sectional view showing a cause of current leakage during operation of an organic EL element having a conventional organic EL layer structure.

FIG. 4 is a schematic cross-sectional view showing a cause of generation of impurities during operation of an organic EL element having a conventional organic EL layer structure.

FIG. 5 is a schematic cross-sectional view of an organic EL element of Example 4, which is another mode of the present invention.

FIG. 6 is a schematic cross-sectional view of an organic EL device of Example 5, which is another mode of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cathode 2 ... Cathode buffer layer 3 ... Electron transport layer 4 ... Emitting layer 5 ... Hole transport layer 6 ... Anode buffer layer 7 ... Anode 8 ... Substrate 9 ... Conventional organic EL layer 10 ... Discontinuous portion of organic EL layer , And passage of impurities such as oxygen and water 11 ... Two-layer cathode

Claims (6)

[Claims] 1. An organic EL layer including a cathode, a cathode buffer layer, an electron transport layer, a light emitting layer, a hole transport layer, and an anode buffer layer, and an electron transport layer in an organic EL device including an anode and a substrate. An organic EL device characterized in that a cathode buffer layer is alternately laminated at least twice or more. 2. The organic E according to claim 1, wherein the number of electrons injected into the light emitting layer is arbitrarily controlled by the thickness of each of the electron transport layer and the cathode buffer layer and the number of laminations.
L element. 3. The organic EL device according to claim 1, wherein at least one of the cathode buffer layers is a halogen compound. 4. The organic E according to claim 1, wherein at least one of the cathode buffer layers is an oxide.
L element. 5. The cathode buffer layers each have a thickness of 0.2 to
It is 30 nm, The organic EL element of Claim 1 characterized by the above-mentioned. 6. The electron transport layer has a thickness of 5 to 1000.
The organic EL according to claim 1, wherein
element.