JP2006041558A - Organic electroluminescent device and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroliminescent device, having a stable luminescence property for a long time, and to proivde a method of manufacturing the same. <P>SOLUTION: An organic electroluminescent device includes a layered structure, in which an anode, a hole transport layer and an electron transport layer sandwiched by the anode and the cathode therebetween are sequentially stacked on a substrate. The hole transport layer contains 0.1-20 wt.% of an electron transport compound contained in the electron transport layer. Additionally, the organic electroluminescent device includes a layered structure in which the anode, a hole injection layer, a hole transport layer and an electron transport layer, sandwiched by the anode and the cathode therebetween are sequentially stacked on the substrate. The hole transport layer contains 0.1-20 wt.% of an electron transport compound contained in the electron transport layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescent element and a method for manufacturing the same, and more particularly to a thin film device that emits light by applying an electric field to a light emitting layer made of an organic compound.

Conventionally, as a thin film type electroluminescent (EL) element, there are ZnS, CaS, SrS, etc. which are inorganic material II-VI compound semiconductors, Mn which is an emission center, rare earth elements (Eu, Ce, Tb, Sm, etc.) ) Is generally used, but an EL device manufactured from the above inorganic material is required to be 1) AC driven (50 to 1000 Hz),
2) High driving voltage (~ 200V),
3) Full color is difficult (especially blue is a problem)
4) The cost of the peripheral drive circuit is high.
Has the problem.

  However, in recent years, EL devices using organic thin films have been developed to improve the above problems. In particular, in order to increase the luminous efficiency, the type of electrode is optimized for the purpose of improving the efficiency of carrier injection from the electrode, and the organic hole transport layer composed of an aromatic diamine and the organic light emitting composed of an aluminum complex of 8-hydroxyquinoline. With the development of an organic electroluminescent device provided with a layer (Non-patent Document 1), the luminous efficiency has been greatly improved as compared with a conventional EL device using a single crystal such as anthracene, which is close to practical characteristics. .

  In addition to the electroluminescent device using the low molecular material as described above, as a material for the organic light emitting layer, poly (p-phenylene vinylene) (Non-patent Document 2 and others), poly [2-methoxy-5- (2 -Ethylhexyloxy) -1,4-phenylenevinylene] (Non-Patent Document 3 and others), poly (3-alkylthiophene) (Non-Patent Document 4 and others) and other electroluminescent device development and polyvinyl An element (Non-Patent Document 5) in which a low-molecular light-emitting material and an electron transfer material are mixed with a polymer such as carbazole has also been developed.

  The biggest problem of the organic electroluminescent device is the stability of the device. There are several factors that shorten the lifetime of the device, but the dominant factor is the deterioration of the thin film shape of the organic light emitting layer. This deterioration of the thin film shape is thought to be due to crystallization (or aggregation) of the organic amorphous film due to heat generation during element driving. Organic thin films formed from molecules with low molecular weight (molecular weight of about 400 to 600) cause crystallization through van der Waals force during or after thin film formation, resulting in island-like aggregated structures There are many.

  In the two-layer device (see Non-Patent Document 1) composed of a hole transport layer and a light-emitting layer, the two-layer stack structure is disturbed due to the above-described crystallization deterioration, and constituent molecules of each layer migrate between layers. Wake up and interdiffuse as a result. The diffusion of the hole transport material into the light emitting layer causes quenching of light emission and causes a decrease in luminance. At the same time, when diffused in the light emitting layer at a high concentration, a route for holes passing through the light emitting layer without recombination is formed, and the light emission efficiency is lowered. Further, the hole transport material diffuses into the light emitting layer that is the recombination light emitting region, so that trap levels are formed and drive voltage is increased.

  In order to prevent the deterioration due to the crystallization, several attempts have been made so far. Usually, an organic electroluminescent device is manufactured by a vacuum deposition method, but a stable crystalline thin film is obtained during vacuum deposition (Patent Document 1), and a uniform thin film is obtained by cooling a substrate (Non-Patent Document). 6) Heating the substrate when depositing phthalocyanine as a hole transport layer (85 ° C., 100 ° C.) (Patent Document 2) has been performed, but the thin film state of the organic light emitting layer has not been improved sufficiently. It was. Although the light emitting layer and the charge transport layer are thinned while being irradiated with light (Patent Document 3), the vacuum deposition apparatus is complicated and the effect is sufficient for irradiation from the substrate side. There wasn't. In order to improve the stability of each layer, mixing of a hole transport layer (Patent Documents 4 and 5) and mixing of a light-emitting layer (Patent Document 6) has been attempted, but it is sufficient for interdiffusion between layers. The effect is not acquired. In addition, a mixed layer of both layers is provided between the hole transport layer and the light emitting layer (Patent Document 7, Patent Document 8, Patent Document 9, and Patent Document 10), an inclined structure (Patent Document 11), and the like have been studied. However, it cannot be said that a sufficient effect is obtained with respect to the above-described decrease in luminance and increase in driving voltage, and it is a further problem that the manufacturing method is complicated for the inclined structure.

On the other hand, attempts to use a polymer material instead of a low-molecular material as a light-emitting layer of an organic electroluminescent device have been made as described above. However, since a thin film is formed by a wet method called coating, impurities can be controlled. It is difficult, and at present both the luminous efficiency and stability of the device are insufficient.
For the above-mentioned reasons, for practical use of organic electroluminescent elements, the actual situation is that the stability of the elements has a big problem, and it is a large light source for backlights of facsimiles, copying machines, liquid crystal displays, etc. This is a problem and is undesirable for a display element such as a flat panel display.
Appl. Phys. Lett. 51, 913, 1987 Nature, 347, 539, 1990 Appl. Phys. Lett. 58, 1982 Jpn. J. et al. Appl. Phys, 30, vol. 1938 Applied Physics, 61, 1044, 1992 Jpn. J. et al. Appl. Phys. , 30, L864, 1991 Japanese Patent Laid-Open No. 3-173095 JP-A-2-12795 JP-A-4-167395 JP-A-4-161480 JP-A-4-161482 Japanese Patent Laid-Open No. 7-312289 JP-A-3-114197 Japanese Patent Laid-Open No. 3-190088 JP-A-4-334894 JP-A-5-182762 JP-A-4-357694

  In view of the above circumstances, the present inventors have intensively studied for the purpose of providing an organic electroluminescent device exhibiting stable light emission characteristics for a long period of time and a manufacturing method thereof.

As a result, it has been found that the inclusion of the main component of the electron transport layer material in the hole transport layer stabilizes the stability of the device, particularly the interface between the hole transport layer and the electron transport layer, and the present invention is completed. It came.
That is, the gist of the present invention is an organic including a laminated structure of an anode / hole transport layer / electron transport layer in which a hole transport layer and an electron transport layer sandwiched between an anode and a cathode are laminated in this order on a substrate. An electroluminescent device, wherein the hole transport layer contains 0.1 to 20 wt% of an electron transport compound contained in the electron transport layer, and on the substrate, Organic electroluminescence including a laminated structure of anode / hole injection layer / hole transport layer / electron transport layer in which a hole injection layer, a hole transport layer and an electron transport layer sandwiched between an anode and a cathode are laminated in this order It is an element, Comprising: It exists in the organic electroluminescent element characterized by containing 0.1-20 weight% of electron transport compounds contained in the said electron carrying layer in the said positive hole transport layer.

According to the organic electroluminescent element of the present invention, an element exhibiting stable emission characteristics for a long time can be obtained.
Accordingly, the organic electroluminescent device according to the present invention is a flat panel display (for example, for OA computers or wall-mounted televisions) or a light source (for example, a light source for a copying machine, a backlight for a liquid crystal display or instrument). Applications to light sources), display boards, and marker lamps are conceivable, and their technical value is great.

Hereinafter, the organic electroluminescent element of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing a structural example of a general organic electroluminescent device used in the present invention. 1 is a substrate, 2 is an anode, 3 is a hole transport layer, 4 is an electron transport layer, Each represents a cathode.

  When the hole transport layer 3 has a light emitting function, 3 becomes a light emitting layer (see Appl. Phys. Lett., 55, 1489, 1989). When the electron transport layer 4 has a light emitting function, 4 becomes a light emitting layer (see Appl. Phys. Lett., 51, 913, 1987). Furthermore, the hole transport layer 3 and the electron transport layer 4 may have a light emitting function at the same time, and both may be light emitting layers.

  The substrate 1 serves as a support for the organic electroluminescent element, and a quartz or glass plate, a metal plate or a metal foil, a plastic film, a sheet, or the like is used. In particular, a glass plate or a transparent synthetic resin plate such as polyester, polymethacrylate, polycarbonate, or polysulfone is preferable. When using a synthetic resin substrate, it is necessary to pay attention to gas barrier properties. If the gas barrier property of the substrate is too small, the organic electroluminescent element may be deteriorated by the outside air that has passed through the substrate, which is not preferable. For this reason, a method of providing a gas barrier property by providing a dense silicon oxide film or the like on at least one surface of the synthetic resin substrate is also a preferable method.

  An anode 2 is provided on the substrate 1, and the anode 2 plays a role of hole injection into the hole transport layer. This anode is usually made of metal such as aluminum, gold, silver, nickel, palladium, platinum, metal oxide such as oxide of indium and / or tin, metal halide such as copper iodide, carbon black, or poly It is composed of conductive polymers such as (3-methylthiophene), polypyrrole, and polyaniline. In general, the anode 2 is often formed by sputtering, vacuum deposition, or the like. Further, in the case of metal fine particles such as silver, fine particles such as copper iodide, carbon black, conductive metal oxide fine particles, and conductive polymer fine powders, they are dispersed in an appropriate binder resin solution and placed on the substrate 1. It is also possible to form the anode 2 by applying to. Further, in the case of a conductive polymer, a thin film can be directly formed on the substrate 1 by electrolytic polymerization, or the anode 2 can be formed by applying a conductive polymer on the substrate 1 (Appl. Phys. Lett. , 60, 2711, 1992). The anode 2 can also be formed by stacking different materials. The thickness of the anode 2 varies depending on the required transparency. When transparency is required, the visible light transmittance is usually 60% or more, preferably 80% or more. In this case, the thickness is usually 5 to 1000 nm, preferably 10 to 10%. It is about 500 nm. If it may be opaque, the anode 2 may be the same as the substrate 1. Furthermore, it is also possible to laminate different conductive materials on the anode 2 described above.

  A hole transport layer 3 is provided on the anode 2. The material of the hole transport layer 3 needs to be a material that has high hole injection efficiency from the anode 2 and can efficiently transport the injected holes. For this purpose, it is required that the ionization potential is low, the hole mobility is high, the stability is high, and impurities that become traps are not easily generated during production or use.

  As such a hole transport material, for example, an aromatic diamine compound in which a tertiary aromatic amine unit such as 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane is linked (Japanese Patent Laid-Open No. 59-86). No. 194393), including two or more tertiary amines represented by 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl, and two or more condensed aromatic rings are nitrogen atoms Aromatic amines substituted with the above (Japanese Patent Laid-Open No. 5-234681), triphenylbenzene derivatives and aromatic triamines having a starburst structure (US Pat. No. 4,923,774), N, N′-diphenyl-N , N′-bis (3-methylphenyl) biphenyl-4,4′-diamine and the like (US Pat. No. 4,764,625), α, α, α ′, α′-tetrame Ru-α, α'-bis (4-di-p-tolylaminophenyl) -p-xylene (Japanese Patent Laid-Open No. 3-269084), a sterically asymmetric triphenylamine derivative as a whole molecule (Japanese Patent Laid-Open No. 129271), a compound in which a plurality of aromatic diamino groups are substituted on a pyrenyl group (Japanese Patent Laid-Open No. 4-175395), an aromatic diamine in which a tertiary aromatic amine unit is linked by an ethylene group (Japanese Patent Laid-Open No. 4-264189) Gazette), aromatic diamines having a styryl structure (JP-A-4-290851), those obtained by linking aromatic tertiary amine units with a thiophene group (JP-A-4-304466), starburst aromatic triamines ( JP-A-4-308688), a benzylphenyl compound (JP-A-4-364153), a fluorene group having a tertiary amino group. (Japanese Patent Laid-Open No. 5-25473), triamine compounds (Japanese Patent Laid-Open No. 5-239455), bisdipyridylaminobiphenyl (Japanese Patent Laid-Open No. 5-320634), N, N, N-triphenylamine derivatives (JP-A-6-1972), aromatic diamine having a phenoxazine structure (JP-A-7-138562), diaminophenylphenanthridine derivative (JP-A-7-252474), hydrazone compound (JP-A-2 -311591), silazane compounds (US Pat. No. 4,950,950), silanamine derivatives (JP-A-6-49079), phosphamine derivatives (JP-A-6-25659), quinacridone compounds and the like. It is done.

  Among the above compounds, an aromatic amine is preferable, and specifically, an aromatic diamine compound in which a tertiary aromatic amine unit is linked, 4,4′-bis [N- (1-naphthyl) -N-phenyl. An aromatic amine containing two or more tertiary amines represented by amino] biphenyl and having two or more condensed aromatic rings substituted with nitrogen atoms, an aromatic triamine having a starburst structure with a derivative of triphenylbenzene, N , N′-diphenyl-N, N′-bis (3-methylphenyl) biphenyl-4,4′-diamine, etc., compounds in which a plurality of aromatic diamino groups are substituted on the pyrenyl group, starburst fragrance Group triamine compounds, N, N, N-triphenylamine derivatives, and aromatic diamine derivatives having a phenoxazine structure.

These compounds may be used alone or in combination as necessary.
In addition to the above compounds, as the material of the hole transport layer 3, polyvinyl carbazole and polysilane (Appl. Phys. Lett., 59, 2760, 1991), polyphosphazene (Japanese Patent Laid-Open No. 5-310949), Polyamide (JP-A-5-310949), polyvinyltriphenylamine (JP-A-7-53953), a polymer having a triphenylamine skeleton (JP-A-4-133055), and a triphenylamine unit as a methylene group Polymers (Synthetic Metals, 55-57, 4163, 1993) and polymethacrylates containing aromatic amines (J. Polym. Sci., Polym. Chem. Ed., 21, 969) , 1983).

The hole transport layer 3 is formed by laminating the above hole transport material on the anode 2 by a coating method or a vacuum deposition method.
In the case of the coating method, one or more hole transport materials and, if necessary, additives such as a binder resin and a coating property improving agent that do not trap holes are added and dissolved to prepare a coating solution. Then, it is applied onto the anode 2 by a method such as spin coating, and dried to form the hole transport layer 3. Examples of the binder resin include polycarbonate, polyarylate, and polyester. When the binder resin is added in a large amount, the hole mobility is lowered. Therefore, it is desirable that the binder resin be less, and usually 50% by weight or less is preferable.

In the case of the vacuum evaporation method, the hole transport material is put in a crucible installed in a vacuum vessel, the inside of the vacuum vessel is evacuated to about 10 ⁻⁴ Pa with a suitable vacuum pump, and then the crucible is heated, The hole transport material is evaporated and a hole transport layer 3 is formed on the anode 2 on the substrate 1 placed facing the crucible.

When the hole transport layer 3 is formed, as an acceptor, a metal complex and / or metal salt of an aromatic carboxylic acid (Japanese Patent Laid-Open No. 4-320484), a benzophenone derivative and a thiobenzophenone derivative (Japanese Patent Laid-Open No. 5-295361) No.), fullerenes (JP-A-5-331458) and the like are doped at a concentration of 10 ⁻³ to 10% by weight to generate holes as free carriers, thereby enabling low voltage driving. be able to.
The thickness of the hole transport layer 3 is usually 10 to 300 nm, preferably 30 to 100 nm. In order to uniformly form such a thin film, a vacuum deposition method is generally used.

  The hole injection layer 3a may be inserted between the hole transport layer 3b and the anode 2 for the purpose of further improving the efficiency of hole injection and improving the adhesion of the whole organic layer to the anode. (See FIG. 2). The material used for the hole injection layer 3a is preferably a material that has a low ionization potential, high conductivity, and forms a thermally stable thin film on the anode, and is preferably a phthalocyanine compound or a porphyrin compound (Japanese Patent Laid-Open No. 57-51781). And Japanese Patent Application Laid-Open No. 63-295695). By inserting the hole injection layer 3a, the driving voltage of the initial element is lowered, and at the same time, an increase in voltage when the element is continuously driven with a constant current is suppressed. The conductivity can be improved by doping the hole injection layer 3a with an acceptor in the same manner as the hole transport layer 3a.

The film thickness of the hole injection layer 3a is usually 2 to 100 nm, preferably 5 to 50 nm. In order to uniformly form such a thin film, a vacuum deposition method is generally used.
An electron transport layer 4 is provided on the hole transport layer 3. The electron transport layer 4 is formed of a compound capable of efficiently transporting electrons from the cathode in the direction of the hole transport layer 3 between electrodes to which an electric field is applied.

  The electron transporting compound used for the electron transport layer 4 needs to be a compound that has high electron injection efficiency from the cathode 5 and can efficiently transport the injected electrons. For this purpose, it is required to be a compound that has a high electron affinity, a high electron mobility, and excellent stability and prevents trapping impurities from being produced or produced during use.

  Materials satisfying such conditions include aromatic compounds such as tetraphenylbutadiene (Japanese Patent Laid-Open No. 57-51781) and metal complexes such as aluminum complexes of 8-hydroxyquinoline (Japanese Patent Laid-Open No. 59-194393). Cyclopentadiene derivatives (JP-A-2-289675), perinone derivatives (JP-A-2-289676), oxadiazole derivatives (JP-A-2-216791), bisstyrylbenzene derivatives (JP-A-1-245087). No. 2-22484), perylene derivatives (JP-A-2-189890, JP-A-3-791), coumarin compounds (JP-A-2-191694, JP-A-3-792), rare earths Complex (Japanese Patent Laid-Open No. 1-256584), Distyrylpyrazine derivative (Japanese Patent Laid-Open No. 2-252) 93), p-phenylene compounds (JP-A-3-33183), thiadiazolopyridine derivatives (JP-A-3-37292), pyrrolopyridine derivatives (JP-A-3-37293), naphthyridine derivatives ( JP-A-3-203982). Among the above compounds, a metal complex of 8-hydroxyquinoline such as an aluminum complex of 8-hydroxyquinoline is preferable.

In general, the electron transport layer 4 using these compounds often simultaneously plays a role of transporting electrons and a role of emitting light upon recombination of holes and electrons.
For the purpose of improving the luminous efficiency of the device and changing the emission color, for example, doping a fluorescent dye for lasers such as coumarin with an aluminum complex of 8-hydroxyquinoline as a host material (J. Appl. Phys., Volume 65). 3610 (1989)). Also in the present invention, the light emission characteristics of the device can be further improved by doping various fluorescent dyes with 10 ⁻³ to 10 mol% using the electron transport material as a host material. Similar dye doping is possible for the hole transport layer (see Jpn. J. Appl. Phys., Vol. 34, page L824 and JP-A-4-335087). The film thickness of the electron transport layer 4 is usually 10 to 200 nm, preferably 30 to 100 nm.

The electron transport layer can also be formed by the same method as the hole transport layer, but a vacuum deposition method is usually used.
In an organic electroluminescent device including at least a hole transport layer and an electron transport layer, the stability of the interface between the hole transport layer and the electron transport layer is important. In the structure of FIG. 1, since the hole transport layer is provided below the electron transport layer, the stability of the thin film shape of the hole transport layer affects the stability of the device. This indicates that even if the electron transport layer itself can maintain a thermally stable thin film state, it does not make sense without the shape stability of the hole transport layer.

For the above reasons, it is very important for the heat resistance, storage stability, and driving stability of the device to form a thermally stable hole transport layer.
It is an object of the present invention to prevent deterioration due to mutual diffusion of thermally induced compounds constituting both layers at the interface between the hole transport layer and the electron transport layer. In order to achieve this object, 0.1 to 20% by weight of the electron transport compound contained in the electron transport layer in the hole transport layer (however, in the case of using a binder, the weight is excluded from the calculation) It has been found that the inclusion is effective. The electron transport compound is a main component compound that usually occupies 80% by weight or more of the electron transport layer (however, when the binder is used, the weight of the binder is excluded). It is called a material.

  Interdiffusion at the hole transport layer / electron transport layer interface is mainly due to the fact that the glass transition temperature of the hole transport material is not sufficiently high and the hole transport molecules easily move as the temperature rises. It is considered that the constituent molecules of the electron transport layer, which is the upper layer, are diffused during hole transport along with the movement of the molecules. In general, the hole transport layer is in an amorphous state, but tends to move toward a crystallization state, which is a more stable state by molecular movement. For this reason, it is effective to contain other types of molecules in order to make the amorphous state more stable, but it has been found that it is most effective to use the constituent molecules of the electron transport layer. This results in a kind of parking problem. Voids due to molecular movement in the hole transport layer promote diffusion of molecules constituting the electron transport layer. This void is considered to strongly reflect the shape of the molecule, so if the constituent molecules of the electron transport layer are already contained in the hole transport layer, the same kind of molecules will not be able to diffuse later. It is. For the above reasons, it is considered that inclusion of an electron transport compound as a main component of the electron transport layer in the hole transport layer is very effective for preventing mutual diffusion at the interface.

  The amount of the electron transport compound contained in the hole transport layer is preferably in the range of 0.1 to 20% by weight, and particularly preferably in the range of 0.5 to 20% by weight. If the content is less than 0.1% by weight, it is insufficient to prevent mutual diffusion. If the content exceeds 20% by weight, an electron conduction path is formed by the electron transport material itself by percolation, and the hole transport layer is formed. The number of electrons passing without recombination increases and the luminous efficiency decreases, which is not preferable.

The concentration of the electron transport compound contained in the hole transport layer may be uniform or non-uniform in the film thickness direction as long as it is within the range of 0.1 to 20% by weight, It is preferable that the manufacturing process is uniform in terms of simplicity.
As a method for containing the electron transport compound in the hole transport layer, the above-described vacuum deposition method or coating method is used.

In the case of the vacuum evaporation method, a hole transport material mixed with an electron transport material of a predetermined concentration may be put into a crucible as an evaporation source, or the hole transport material and the electron transport material may be placed in separate crucibles. Two-way simultaneous vapor deposition may be performed.
In the case of the coating method, a hole transport material, an electron transport material having a predetermined concentration, and additives such as a binder resin and a coating property improver that do not trap holes are added if necessary and dissolved to form a coating solution. The positive hole transport layer 3 is prepared by applying it on the anode 2 by a method such as spin coating or dipping and drying. Examples of the binder resin include polycarbonate, polyarylate, and polyester. When the binder resin is added in a large amount, the hole mobility is lowered. Therefore, it is desirable that the binder resin be less, and usually 50% by weight or less is preferable.

  As a method for further improving the luminous efficiency of the organic electroluminescent element, an electron injection layer 4b can be further laminated on the electron transport layer 4a. The compound used for the electron injection layer 4b is required to be capable of easily injecting electrons from the cathode and further having an electron transport capability. Examples of such an electron transport material include oxadiazole derivatives (Appl. Phys. Lett., 55, 1489, 1989, etc.) and systems in which they are dispersed in a resin such as polymethyl methacrylate (PMMA) (Appl. Phys., Lett., 61, 2793, 1992), phenanthroline derivatives (JP-A-5-331459), quinoxaline compounds (JP-A-6-207169), or n-type hydrogenated amorphous carbonization. Examples thereof include silicon, n-type zinc sulfide, and n-type zinc selenide. The thickness of the electron injection layer 4b is usually 5 to 200 nm, preferably 10 to 100 nm.

  The cathode 5 serves to inject electrons into the electron transport layer 4. The material used for the cathode 5 can be the material used for the anode 2, but a metal having a low work function is preferable for efficient electron injection, such as tin, magnesium, indium, calcium, A suitable metal such as aluminum or silver or an alloy thereof is used. The film thickness of the cathode 5 is usually the same as that of the anode 2. For the purpose of protecting the cathode made of a low work function metal, further laminating a metal layer having a high work function and stable to the atmosphere on the cathode increases the stability of the device. For this purpose, metals such as aluminum, silver, nickel, chromium, gold and platinum are used.

In addition to the structure shown in FIGS. 1 to 3, an organic electroluminescent device having the following layer structure is used in the present invention;
Anode / hole transport layer / electron transport layer / interface layer / cathode,
Anode / hole transport layer / electron transport layer / electron injection layer / interface layer / cathode,
Anode / hole injection layer / hole transport layer / electron transport layer / interface layer / cathode,
Anode / hole injection layer / hole transport layer / electron transport layer / electron injection layer / interface layer / cathode.

  In the above layer structure, the interface layer is for improving the contact between the cathode and the organic layer, and includes an aromatic diamine compound (JP-A-6-267658), a quinacridone compound (JP-A-6-330031), naphthacene. Derivatives (JP-A-6-330032), organosilicon compounds (JP-A-6-325871), organophosphorus compounds (JP-A-6-325872), compounds having an N-phenylcarbazole skeleton (Japanese Patent Application No. 6) -199562), an N-vinylcarbazole polymer (Japanese Patent Application No. 6-200942) and the like. The thickness of the interface layer is usually 2 to 100 nm, preferably 5 to 30 nm. Instead of providing the interface layer, a region containing 50% by weight or more of the material of the interface layer may be provided in the vicinity of the cathode interface between the organic light emitting layer and the electron transport layer.

  The present invention can be applied to any of an organic electroluminescent element having a single element, an element having a structure arranged in an array, and a structure having an anode and a cathode arranged in an XY matrix.

  EXAMPLES Next, although an Example demonstrates this invention further more concretely, this invention is not limited to description of a following example, unless the summary is exceeded.

Example 1
The organic thin film was produced with the following method using the vacuum evaporation method by resistance heating.
As a hole transport layer material, N, N′-diphenyl-N, N ′-(3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (H1) shown below

As an electron transport material having a light emitting function, 8-hydroxyquinoline complex of aluminum represented by the following structural formula, Al (C ₉ H ₆ NO) ₃ (E1)

Was put in a separate tungsten boat provided in the vacuum deposition apparatus, and a 120 nm thick indium tin oxide (ITO) transparent conductive film was deposited on a glass substrate (made by HOYA; sputter film formation) with acetone. After ultrasonic cleaning, washing with pure water, ultrasonic cleaning with isopropyl alcohol, and drying with dry nitrogen, they were placed at a distance of 30 cm facing the boat in the vacuum deposition apparatus. The apparatus was evacuated using an oil diffusion pump equipped with a liquid nitrogen trap until the degree of vacuum in the apparatus was 2 × 10 ⁻⁶ Torr (about 2.7 × 10 ⁻⁴ Pa) or less.

  Each of the tungsten boats was heated to perform binary simultaneous vapor deposition. The vapor deposition rate of the hole transport material (H1) was 0.2 to 0.3 nm / second. By controlling the evaporation amount of the aluminum 8-hydroxyquinoline complex (E1) at this time, a hole transport layer containing 2% by weight of the electron transport material (E1) was formed with a film thickness of 50 nm. Next, the aluminum 8-hydroxyquinoline complex (E1) was deposited as an electron transport layer in the same manner as the hole transport layer. At this time, the deposition rate was 0.2 to 0.3 nm / second, and an electron transport layer having a film thickness of 50 nm was laminated on the hole transport layer.

  The sample obtained in this manner was taken out from the vacuum deposition apparatus, stored at 80 ° C. for 10 hours, and then observed with a microscope. As a result, the uniform thin film shape after deposition was maintained, and crystallization was observed. Was not. Further, when the surface roughness Ra (JIS B0601) was measured with a contact-type surface roughness meter, no change was observed between 4 nm and before and after the heat treatment.

Comparative Example 1
A thin film sample was prepared on an ITO glass substrate in the same manner as in Example 1 except that the electron transport material (E1) was not contained in the hole transport layer (H1). When this sample was stored at a temperature of 60 ° C. for 24 hours in the same manner as in Example 1 and observed under a microscope, it was observed that many dendritic crystallization patterns were generated. The surface roughness Ra was 50 nm, which was large compared to 4 nm before the heat treatment, and the smoothness was lost.

Examples 2 to 4 and Comparative Example 2
An organic electroluminescent element having the structure shown in FIG. 1 was produced by the following method using a vacuum evaporation method by resistance heating.
As a hole transport layer material, N, N′-diphenyl-N, N ′-(3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (H1) is used for electron transport having a light emitting function. As a material, an 8-hydroxyquinoline complex of aluminum (E1) was put in a separate tungsten boat provided in the vacuum deposition apparatus, and an indium tin oxide (ITO) transparent conductive film was deposited to 120 nm on a glass substrate. The object (manufactured by HOYA; sputtered film) was ultrasonically cleaned with acetone, washed with pure water, ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen, and 30 cm away from the crucible in the vacuum deposition apparatus. Installed. The apparatus was evacuated using an oil diffusion pump equipped with a liquid nitrogen trap until the degree of vacuum in the apparatus was 2 × 10 ⁻⁶ Torr (about 2.7 × 10 ⁻⁴ Pa) or less.

Each of the tungsten boats was heated to perform binary simultaneous vapor deposition. The vapor deposition rate of the hole transport material (H1) was 0.2 to 0.3 nm / second. By controlling the evaporation amount of the aluminum 8-hydroxyquinoline complex at this time, a hole transport layer having a composition shown in Table 1 was formed with a film thickness of 50 nm.
Next, the aluminum 8-hydroxyquinoline complex (E1) was deposited as an electron transport layer in the same manner as the hole transport layer. At this time, the deposition rate was 0.2 to 0.3 nm / second, and an electron transport layer having a film thickness of 50 nm was laminated on the hole transport layer.

Here, the element on which the electron transport layer has been deposited is once taken out from the vacuum deposition apparatus into the atmosphere, and a 5 mm wide stripe-shaped shadow mask is orthogonal to the ITO stripe of the anode as a mask for cathode deposition. In close contact with the element, it is placed in another vacuum deposition apparatus, and the degree of vacuum in the apparatus is 2 × 10 ⁻⁶ Torr (about 2.7 × 10 ⁻⁴ Pa) or less in the same manner as the organic layer. Was exhausted. Subsequently, aluminum was deposited as a cathode so as to have a film thickness of 50 nm. Deposition was performed using a tungsten boat at a degree of vacuum of 1 × 10 ⁻⁵ Torr (about 1.3 × 10 ⁻³ Pa) and a deposition rate of 1 nm / second.

  The results of measuring the emission characteristics by applying a forward voltage to each electrode of the organic electroluminescence device having a size of 5 mm × 5 mm obtained as described above, a positive voltage to the ITO anode, and a negative voltage to the Al cathode are shown. -1.

Example 5
An organic electroluminescent element having the structure shown in FIG. 1 was produced by the following method.
An indium tin oxide (ITO) transparent conductive film deposited on a glass substrate with a thickness of 120 nm (manufactured by Geomat Corp .; electron beam film-formed product; sheet resistance 15 Ω) is 2 mm wide using ordinary photolithography technology and hydrochloric acid etching. The anode was formed by patterning into stripes. The patterned ITO substrate is cleaned in the order of ultrasonic cleaning with acetone, water with pure water, and ultrasonic cleaning with isopropyl alcohol, then dried with nitrogen blow, and finally with ultraviolet ozone cleaning. installed. After performing rough evacuation of the apparatus with an oil rotary pump, an oil diffusion pump equipped with a liquid nitrogen trap is used until the vacuum in the apparatus becomes 2 × 10 ⁻⁶ Torr (about 2.7 × 10 ⁻⁴ Pa) or less. Exhausted.

  Next, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (H2) shown below, placed in a ceramic crucible placed in the above apparatus.

The hole transport layer was formed by heating and evaporating with a tantalum wire heater around the crucible and simultaneously evaporating the aluminum 8-hydroxyquinoline complex contained in another ceramic crucible. At this time, the temperature of the H2 crucible was controlled in the range of 200 to 211 ° C, and the temperature of the E1 crucible was controlled in the range of 210 to 220 ° C. A hole transport layer having a film thickness of 60 nm was obtained at a vacuum degree of 2 × 10 ⁻⁶ Torr (about 2.7 × 10 ⁻⁴ Pa) at the time of vapor deposition and a vapor deposition rate of H 2 of 0.2 to 0.5 nm / second. At this time, the amount of E1 contained in H2 was 0.9% by weight.

Subsequently, an 8-hydroxyquinoline complex of aluminum (E1) was deposited on the hole transport layer in the same manner as a material for the electron transport layer having a light emitting function. At this time, the temperature of the crucible was controlled in the range of 280 to 290 ° C. The degree of vacuum during vapor deposition is 2 × 10 ⁻⁶ Torr (about 2.7 × 10 ⁻⁴ Pa), the vapor deposition rate is 0.2 to 0.6 nm / second, and the thickness of the deposited electron transport layer is 75 nm. there were.

The substrate temperature during vacuum deposition of the hole transport layer and the electron transport layer was kept at room temperature. Here, the element on which the electron transport layer has been deposited is once taken out from the vacuum deposition apparatus into the atmosphere, and a 2 mm wide stripe-shaped shadow mask is orthogonal to the ITO stripe of the anode as a mask for cathode deposition. In close contact with the element, it is placed in another vacuum deposition apparatus, and the degree of vacuum in the apparatus is 2 × 10 ⁻⁶ Torr (about 2.7 × 10 ⁻⁴ Pa) or less in the same manner as the organic layer. Was exhausted. Subsequently, an alloy electrode of magnesium and silver was deposited as a cathode so as to have a film thickness of 80 nm by a binary simultaneous deposition method. Vapor deposition was performed using a molybdenum boat, the degree of vacuum was 8 × 10 ⁻⁶ Torr (about 1.1 × 10 ⁻³ Pa), the deposition rate of magnesium was 0.5 nm / second, and the obtained alloy cathode was composed of magnesium and silver. The atomic ratio was 10: 1.2.

  Luminescence characteristics were measured by applying a forward voltage to each electrode of the organic electroluminescence device having a size of 2 mm × 2 mm obtained as described above, a positive voltage to the ITO anode, and a negative voltage to the magnesium / silver alloy cathode. The results are shown in Table-2.

  The area of the amorphous light emitting portion (called a dark spot) measured using a CCD camera after storing this device in a nitrogen atmosphere at room temperature for 90 days showed a good storage stability of about 2% of the total area. .

Comparative Example 3
A device was fabricated in the same manner as in Example 2 except that the main component of the electron transport layer was not included in the hole transport layer. The results of measuring the light emission characteristics of this device are shown in Table-2.
The dark spot was measured after storing the above device at room temperature for 90 days in the same manner as in Example 2 and found to be 30%.

Example 6
A device was fabricated in the same manner as in Example 2 except that the amount of aluminum 8-hydroxyquinoline complex (E1) contained in the hole transport layer was changed to 1.9% by weight. Table 3 shows the results of measuring the luminous efficiency after holding the device at a temperature of 110 ° C. in a nitrogen atmosphere. No deterioration in luminous efficiency was observed.

Comparative Example 4
A device was fabricated in the same manner as in Example 2 except that the main component of the electron transport layer was not included in the hole transport layer. The results of measuring the luminous efficiency after storing this device at 110 ° C. in a nitrogen atmosphere in the same manner as in Example 3 are shown in Table 4. A decrease in luminous efficiency was observed in 1 hour.

The schematic cross section which showed an example of the organic electroluminescent element. The schematic cross section which showed another example of the organic electroluminescent element. The schematic cross section which showed another example of the organic electroluminescent element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3, 3b Hole transport layer 4, 4a Electron transport layer 5 Cathode 3a Hole injection layer 4b Electron injection layer

Claims (6)

  An organic electroluminescent device comprising a laminated structure of an anode / hole transport layer / electron transport layer, wherein a hole transport layer and an electron transport layer sandwiched between an anode and a cathode are laminated in this order on a substrate, An organic electroluminescence device comprising 0.1 to 20 wt% of an electron transport compound contained in the electron transport layer in the hole transport layer.   A laminated structure of anode / hole injection layer / hole transport layer / electron transport layer in which a hole injection layer, a hole transport layer and an electron transport layer sandwiched between an anode and a cathode are laminated in this order on a substrate. An organic electroluminescence device comprising: an organic electroluminescence device comprising 0.1 to 20 wt% of an electron transport compound contained in the electron transport layer in the hole transport layer.   The organic electroluminescent element according to claim 1 or 2, wherein the hole transport layer contains an aromatic amine.   The organic electroluminescent element according to claim 1, wherein the electron transport compound is a metal complex of 8-hydroxyquinoline.   The organic electroluminescent element according to claim 1, wherein the concentration of the electron transport compound in the hole transport layer is uniform in the film thickness direction.   In the manufacturing method of the organic electroluminescent element of any one of Claims 1-5, the said positive hole transport layer is formed by carrying out binary evaporation of the positive hole transport compound and the electron transport compound simultaneously. A method for producing an organic electroluminescent element.

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