JPH08273831A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE: To provide an organic electroluminescent element which can maintain stable electroluminescent properties for a long duration and of which driving voltage can be lowered by forming an anode on a substrate and then treating the anode with an acid and then with an alkali before organic electroluminescent layer formation. CONSTITUTION: An anode 2 made of an indium and/or tin oxide is formed on a substrate 1. An organic electroluminescent layer 3 and a cathode 4 are layered on the anode to give an organic electroluminescent element. At that time, before the organic electroluminescent layer 3 is formed on the anode 2, the anode 2 is treated with an acid and then with an alkali. As the acid for the acid treatment, an inorganic acid or an organic acid with pH about 5 or lower is used. As the alkali, ammonia or amines or their aq. solutions with pH about 8 or higher are used. With the treatment, impurities in the interfaces can be removed and the resulting element can be driven stably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device, and more particularly, to a thin film type device which emits light by applying an electric field to a light emitting layer made of an organic compound.

[0002]

2. Description of the Related Art Conventionally, as a thin film type electroluminescence (EL) element, Z which is a II-IV group compound semiconductor of an inorganic material has been used.
In general, nS, CaS, SrS, etc. are doped with Mn or a rare earth element (Eu, Ce, Tb, Sm, etc.), which is the emission center, but EL elements made from the above inorganic materials are 1). AC drive is required (50 to 1000 Hz), 2) high drive voltage (up to 200 V), 3) full colorization is difficult (especially blue is a problem), and 4) peripheral drive circuit costs are high. ing.

In recent years, in order to improve the above problems, EL devices using organic thin films have been developed. In particular, the electrode type was optimized for the purpose of improving the efficiency of carrier injection from the electrode in order to increase the light emission efficiency, and the organic hole transport layer made of an aromatic diamine and the organic light emission made of an aluminum complex of 8-hydroxyquinoline. Of an organic electroluminescence device having a layer (Appl. Phys. Let
t. , 51, p. 913, 1987), the luminous efficiency has been greatly improved as compared with the conventional EL device using a single crystal such as anthracene, and is close to practical characteristics.

However, these devices have a problem that the voltage rises when they are driven at a constant current density. Therefore, it is necessary to lower the initial drive voltage, and attempts have been made to improve the luminous efficiency and the current-voltage characteristics. As for the improvement of luminous efficiency, coumarin 540 and DC are added to the luminous layer.
M1 (J. Appl. Phys. 65 (9) 1989p.
3610-3616), rubrene (Japanese Patent Laid-Open No. 4-3350).
87), quinacridone (JP-A-3-255190).
Japanese Patent Laid-Open No. 3-255190) has been attempted to significantly improve the light emission characteristics by doping with a dye known under the common name (Japanese Patent Laid-Open Publication No. 3-255190). In order to improve the current-voltage characteristics, a method of lowering the driving voltage by treating the surface of the substrate with an acid has been tried (Japanese Patent Laid-Open No. 14795/1992). The current situation is that it has not reached it.

[0005]

The organic electroluminescent elements disclosed so far have a problem that the driving voltage is high and it is difficult to obtain stable driving characteristics for a long period of time.

[0006]

In view of the above situation, the present inventors provide an organic electroluminescent device capable of maintaining stable light emitting characteristics for a long period of time and lowering driving voltage. As a result of intensive studies for the purpose, it was found that the above problem can be solved by treating the electrode on the substrate with an acid and then with an alkali, and completed the present invention.

That is, the gist of the present invention is to provide an organic electroluminescent device having an anode, a cathode, and at least an organic light emitting layer between them, provided on a substrate, wherein the anode is an oxide of indium and / or tin. And an organic electroluminescent device characterized by being treated with an acid and then with an alkali. Hereinafter, the organic electroluminescent device of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view schematically showing a structural example of the organic electroluminescence device of the present invention, in which 1 is a substrate, 2 is an anode, and 3 is a substrate.
Represents an organic light emitting layer, and 4 represents a cathode. The substrate 1 serves as a support for the organic electroluminescent element of the present invention, and a plate of quartz or glass, a metal plate or a metal foil, a plastic film or a sheet, etc. is used. In particular, glass plate, polyester, polymethylmethacrylate, polycarbonate,
A transparent synthetic resin plate such as polysulfone is preferred.

An anode 2 is provided on the substrate 1. Anode 2
Plays a role of injecting holes into the organic light emitting layer 3. This anode is made of indium and / or tin oxide, and the thickness of the anode 2 depends on the required transparency. When transparency is required, it is desirable that the visible light transmittance be 60% or more, preferably 80% or more. In this case, the thickness is usually 5 to 1000 nm, preferably about 10 to 500 nm. is there.

These anodes are usually subjected to some cleaning before laminating the organic light emitting layer. For example, after cleaning with a commercially available detergent, ultrasonic cleaning is performed with deionized water and isopropyl alcohol (hereinafter abbreviated as "IPA"), and finally exposed to toluene vapor (Japanese Patent Laid-Open No. 4-233195).
Gazette), after washing with a neutral detergent, acetone, I
Ultrasonic cleaning is performed in PA, and finally it is immersed in boiling IPA for natural drying (Japanese Patent Laid-Open No. 5-299174).
Etc. have been reported. In addition to this, plasma treatment (JP-A-5-135877), ultraviolet / ozone cleaning (JP-A-6-88072), and an attempt to treat the surface of the anode with an acid (JP-A-4-14795) Etc. are also carried out, and various treatments have been applied.

As a result of intensive studies, the present inventors have found that it is preferable to treat the anode with an acid and then with an alkali before the usual cleaning. The acid for acid treatment in the present invention is an inorganic acid or an organic acid having a pH of 5 or less, preferably pH 2 or less, and particularly preferably pH 1 or less. As the inorganic acid, hydrochloric acid, hydrofluoric acid,
Examples thereof include hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, perchloric acid, phosphoric acid, boric acid, and aqueous solutions thereof. Organic acids include acetic acid, oxalic acid, benzoic acid, formic acid, citric acid, and succinic acid. Acid etc. are mentioned. The above acid can be treated by bringing it into contact with the surface of the anode in a liquid or vapor state, and a method such as spraying or dipping in the liquid is preferable. In particular, it is preferable to carry out the contact treatment by immersing it in an acid solution. The treatment temperature with an acid may be any temperature so long as it is not violently etched, and is usually 0 to 60.
° C. The treatment time with an acid is usually 5 seconds to 10 hours, preferably 30 seconds to 5 hours. More preferably, it is 1 minute to 3 hours.

After the acid treatment, it is washed with water and then treated with alkali. Any alkali can be used as long as it has a pH of 8 or more. Preferred inorganic alkalis are ammonia; alkali metals such as sodium hydroxide, potassium hydroxide and barium hydroxide. , Hydroxides of alkaline earth metals; alkali metals such as potassium carbonate; carbonates of alkaline earth metals; alkali metals such as potassium hydrogen carbonate and sodium hydrogen carbonate; hydrogen carbonates of alkaline earth metals; alkali metals and alkalis An aqueous solution of an earth metal hypochlorite or the like can be mentioned. In the organic system, acyclic amines such as ethylamine, diethylamine, triethylamine, methylamine, dimethylamine and trimethylamine, cyclic amines such as pyridine and piperidine, and quaternary ammonium salts such as tetramethylammonium hydroxide can be mentioned. . Of these alkalis, ammonia or amines or aqueous solutions thereof are preferable, and ammonia water or acyclic amines or aqueous solutions thereof are particularly preferable.
The alkali treatment can be carried out by bringing it into contact with the acid-treated anode surface in a liquid or vapor state, and a method such as spraying or dipping in a liquid is preferable. In particular, it is preferable to carry out the contact treatment by immersing it in an alkaline solution. In addition, ultrasonic waves may be applied to the alkaline liquid or stirring may be performed. The treatment temperature with alkali is usually 0 to 100.
C., preferably 0 to 70.degree. The treatment time with alkali is usually 5 seconds to 10 hours, preferably 30 seconds to 5 hours. More preferably, it is 1 minute to 3 hours. After the alkali treatment, the usual cleaning as described above is performed.

The acid treatment improves the roughness of the substrate and makes it smoother, so that the probability of short-circuiting of the device is reduced, the uneven brightness of the light emitting surface is eliminated, and a more stable organic electroluminescent device can be manufactured. . Table 1 shows examples of anodes whose roughness is improved by acid treatment. Table 1 shows an indium tin oxide (ITO) anode manufactured by a conventional method at a temperature of 40.
This is an example when treated with a sulfuric acid aqueous solution having a concentration of 1 N (0.5 mol / l) at 0 ° C.

[0014]

[Table 1] Acid treatment solution: aqueous sulfuric acid solution having a concentration of 1 N and a temperature of 40 ° C Ra: center line average roughness (JIS B0601) Rz: 10-point average roughness (JIS B0601)

Further, by treating with an alkali after the acid treatment, a trace amount of the acid component remaining on the surface is neutralized, whereby impurities at the interface can be removed, and the element can be stably driven.

An organic light emitting layer is laminated on the anode 2 treated in this way, but if the materials responsible for charge injection, transport and light emission are different, the structure shown in FIG. 2 may be used. It is possible.

Hereinafter, FIG. 2 will be described. In FIG.
Reference numeral 1 is a substrate, 2 is an anode, 3a is a hole injection layer, 3b is a hole transport layer, 3c is an electron transport layer, and 4 is a cathode. The hole injection layer 3a is required to have a function of facilitating the injection of holes from the anode into the hole transport layer and, at the same time, have an adhesiveness with the anode.
Examples of these materials include porphyrin derivatives (Japanese Patent Laid-Open Publication No.
3-295695 gazette) and Starburst amine (Proceedings of the 54th Annual Meeting of the Applied Physics Society of Japan, 29p-AC-
15) and the like are used. If sufficient characteristics can be obtained without the hole injection layer, this layer can be omitted.

A hole transport layer 3b is formed on the hole injection layer 3a or the anode 2. The hole-transporting layer is required to have high hole mobility, excellent stability, and resistance to generation of trapping impurities during manufacture or use. As a material of the hole transport layer suitable for obtaining such characteristics, for example, an aromatic compound in which a tertiary aromatic amine unit such as 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane is linked is used. Group diamine compounds (JP-A-59
No. 194393), 4,4′-bis [N- (1-
Aromatic amines containing two or more tertiary amino groups represented by naphthyl) -N-phenylamino] biphenyl and having two or more fused aromatic rings substituted by nitrogen atoms (Japanese Patent Laid-Open No. 5-211 / 1993).
34681), an aromatic triamine having a starburst structure as a derivative of triphenylbenzene (US Pat. No. 4,923,774), N, N'-diphenyl-
N, N'-bis (3-methylphenyl) biphenyl-
Aromatic diamines such as 4,4′-diamine (US Pat. No. 4,764,625), α, α, α ′, α′-tetramethyl-α, α′-bis (4-di-p-tolyl) Aminophenyl) -p-xylene (JP-A-3-269084), a triphenylamine derivative which is sterically asymmetric as a whole molecule (JP-A-4-12971), and a pyrenyl group substituted with a plurality of aromatic diamino groups. Compound (JP-A-4-175395), an aromatic diamine in which a tertiary aromatic amine unit is linked with an ethylene group (JP-A-4-175395).
264189), aromatic diamines having a styryl structure (JP-A-4-290851), those in which aromatic tertiary amine units are linked by a thiophene group (JP-A-4-304466), and starburst type aromatics. Triamine (JP-A-4-308688), benzylphenyl compound (JP-A-4-364153), and tertiary amine linked by a fluorene group (JP-A 5-2).
5473), triamine compounds (JP-A-5-23)
9455), bisdipyridylaminobiphenyl (JP-A-5-320634), N, N, N-triphenylamine derivative (JP-A-6-1972),
Aromatic diamine having phenoxazine structure (Japanese Patent Application No.
-290728) and diaminophenylphenanthridine derivatives (Japanese Patent Application No. 6-45669), hydrazone compounds (Japanese Patent Application Laid-Open No. 2-311).
591), a silazane compound (US Pat. No. 4,955).
No. 0,950), silanamin derivatives (JP-A-6-4).
No. 9079), phosphamine derivatives (JP-A-6-2).
5659), quinacridone compounds and the like. These compounds may be used alone or, if necessary, may be mixed and used. In addition to the above compounds, polyvinyl carbazole and polysilane (Appl. Phys. Lett.
9, vol. 2760, 1991), polyphosphazene (JP-A-5-310949), polyamide (JP-A-5-310949), polyvinyltriphenylamine (Japanese Patent Application No. 5-205377), triphenylamine. A polymer having a skeleton (Japanese Unexamined Patent Publication No. 4-133065), a polymer in which triphenylamine units are linked by a methylene group or the like (Synthetic Metals, 55-
57, 4163, 1993), polymethacrylates containing aromatic amines (J. Polym. Sc.
i. , Polym. Chem. Ed. , Volume 21, 969
P., 1983) and the like.

The hole transport layer 3b is formed by laminating the above-mentioned material for the hole transport layer on the anode 2 or the hole injection layer 3a by a coating method or a vacuum deposition method. In the case of coating, a coating solution is prepared by dissolving one or more materials for the hole transport layer and, if necessary, a binder resin that does not become a hole trap, and additives such as a coating improver such as a leveling agent. The organic hole transporting layer 3b is formed by preparing, coating on the anode 2 or the hole injecting layer 3a by a method such as spin coating, and drying. As a binder resin,
Examples thereof include polycarbonate, polyarylate, polyester and the like. The addition amount of the binder resin decreases the hole mobility when it is too large, and therefore it is preferable that the addition amount be small.
It is preferably 50% by weight or less. When the hole injection layer 3a is present, it is necessary to properly select the solvent so that the solvent used does not reduce the surface roughness of the hole injection layer 3a.

In the case of the vacuum vapor deposition method, the material of the hole transport layer is put in a crucible installed in a vacuum container, and the inside of the vacuum container is about 10 ⁻⁶ Torr (about 10 ⁻⁴ Pa) by an appropriate vacuum pump.
After evacuating to a certain degree), the crucible is heated to evaporate the material of the hole transport layer and form the hole transport layer 3b on the substrate placed facing the crucible.

When the hole transport layer 3b is formed, further, as an acceptor, a metal complex and / or a metal salt of an aromatic carboxylic acid (JP-A-4-320484), a benzophenone derivative and a thiobenzophenone derivative (JP-A-4-32048). No. 5-295361) and fullerenes (Japanese Patent Laid-Open No. 5-331458) are doped at a concentration of 10 ⁻³ to 10 wt% to generate holes as free carriers, and low voltage driving is also possible. It is possible.

The thickness of the hole transport layer 3b is usually 10-3.
00 nm, preferably 30 to 100 nm. In order to uniformly form such a thin film, the vacuum evaporation method is often used. As the material of the hole transport layer 3b, it is possible to use an inorganic material instead of the organic compound. The conditions required for the inorganic material are the same as those for the organic hole transport layer. Examples of the inorganic material used for the hole transport layer 3b include p-type hydrogenated amorphous silicon, p-type hydrogenated amorphous silicon carbide, p-type hydrogenated microcrystalline silicon carbide, p-type zinc sulfide, and p-type zinc sulfide. Examples include type zinc selenide.
These inorganic hole transport layers are formed by CVD method, plasma CVD
Method, vacuum deposition method, sputtering method or the like.

The thickness of the inorganic hole transporting layer is generally 10 to 300 nm, preferably 30 to 1 as in the organic hole transporting layer.
00 nm. The electron transport layer 3 is formed on the hole transport layer 3b.
c is provided, but the electron transport layer 3c is formed of a compound capable of efficiently transporting electrons from the cathode toward the hole transport layer 3b between the electrodes to which an electric field is applied.

The material for the electron transport layer must be a compound that has a high electron injection efficiency from the cathode 4 and can efficiently transport the injected electrons.
For that purpose, it is required that the compound has a high electron affinity, a high electron mobility, excellent stability, and an impurity that becomes a trap and is less likely to be generated at the time of production or use.

As materials satisfying such conditions, aromatic compounds such as tetraphenyl butadiene (Japanese Patent Laid-Open No. Sho 5 (1999) -58138)
7-51781), a metal complex such as an aluminum complex of 8-hydroxyquinoline (JP-A-59-1943).
93), a cyclopentadiene derivative (JP-A-2-
289675), perinone derivatives (JP-A-2-2)
No. 89676), an oxadiazole derivative (JP-A-2-216791), a bisstyrylbenzene derivative (JP-A 1-245087, etc.), a perylene derivative (JP-A-2-189890, etc.), a coumarin compound ( Japanese Unexamined Patent Publication (Kokai) No. 2-191694), rare earth complex (Japanese Unexamined Patent Publication No. 1-256584), distyrylpyrazine derivative (Japanese Unexamined Patent Publication No. 2-252793), p-phenylene compound (Japanese Unexamined Patent Publication No. 3-33183), Thiadiazolopyridine derivative (JP-A-3-37292), pyrrolopyridine derivative (JP-A-3-37293), naphthyridine derivative (JP-A-3-203982)
Issue).

Electron transport layer 3c using these compounds
Usually plays a role of transporting electrons and a role of producing light emission upon recombination of holes and electrons. When the organic hole transport layer 3b has a light emitting function, the electron transport layer 3
c plays only the role of transporting electrons. For the purpose of improving the luminous efficiency of the element and changing the color of emitted light, for example,
Doping fluorescent dyes for laser such as coumarin using aluminum complex of 8-hydroxyquinoline as a host material (J. Appl. Phys., Vol. 65, 3610).
P., 1989). Also in the present invention, the emission characteristics of the device can be further improved by using the above-mentioned material for the electron transport layer as a host material and doping various fluorescent dyes at 10 ⁻³ to 10 mol%. The thickness of the electron transport layer 3c is usually 10 to 200 nm, preferably 3
It is 0 to 100 nm.

The electron transport layer 3c can also be formed by the same method as the hole transport layer 3a, but a vacuum deposition method is usually used. As a method for further improving the luminous efficiency of the organic electroluminescent device, it is conceivable to stack another electron transport layer 3d on the electron transport layer 3c as shown in FIG. The compound used for the electron transport layer 3d is required to be capable of easily injecting electrons from the cathode and further having an electron transporting ability. As such an electron transport material,

[0028]

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[0029]

Embedded image

Oxadiazole derivatives such as (App
l. Phys. Lett. , 55, 1489, 19
1989 etc.) or a system in which they are dispersed in a resin such as polymethylmethacrylate (Appl. Phys. Lett., 6
1 volume, page 2793, 1992), or n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, n-type zinc selenide, and the like. The thickness of the electron transport layer 3d is usually 5 to
It is 200 nm, preferably 10 to 100 nm.

It is also possible to further provide an interface layer 3e between the electron transport layer 3d and the cathode 4 as shown in FIG. The role of the interface layer is that the organic light emitting layer and the cathode have affinity with the organic light emitting layer and at the same time have good adhesion to the cathode, and are chemically stable, and during and / or after formation of the cathode. It has an effect of suppressing the reaction. It is also important to provide a uniform thin film shape from the viewpoint of adhesion with the cathode. As a material that plays such a role, an aromatic amine compound (JP-A-5-048075) is disclosed.
(Japanese Patent Application No. 6-009492), compounds having a phenylcarbazole skeleton (Japanese Patent Application No. 6-199562), polyvinylcarbazole derivatives (Japanese Patent Application No. 6-200942), and the like.

Further, the interface layer 3e is provided without providing the electron transport layer 3d.
It is also possible to provide. When forming the interface layer 3e shown above, these compounds may be mixed and used. Further, other fluorescent dyes, light emitting materials and the like may be mixed for the purpose of improving the stability of the film of the interface layer. Examples of the materials to be mixed include compounds consisting of aromatic amines, laser dyes such as coumarin derivatives, polycyclic aromatic dyes such as perylene and rubrene, organic pigments such as quinacridone, and 8-hydroxyquinoline metal complexes. Can be mentioned.

A cathode 4 is provided on the organic light emitting layer, the electron transport layer or the interface layer. The cathode is required to form a stable film because it is easy to inject electrons into the electron transport layer and the interface layer described above. Therefore, a metal having a low work function is usually used, and a metal having a work function of 4 eV or less is usually applied. Preferred metals include beryllium,
Magnesium, calcium, scandium, titanium, manganese, gallium, strontium, yttrium, indium, barium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, Hafnium, radium, actinium, thorium, uranium and the like can be mentioned, and magnesium, calcium, scandium and indium are particularly preferable. However, if a low work function cathode is used alone, it is easily oxidized and easily deteriorates. Therefore, these elements usually contain an element having a work function of 4 eV or more as the second metal. The second metal is usually aluminum, vanadium, chromium, iron, cobalt, nickel, copper, zinc, germanium, arsenic, selenium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, tin, antimony, tellurium, tantalum. , Tungsten, rhenium, osmium, iridium, platinum, gold, mercury, lead, bismuth, polonium and the like, and preferably aluminum, copper, silver, gold, tin, lead, bismuth, tellurium and antimony. It is also possible to further stack a metal on the cathode to stabilize the cathode. As a preferred combination of the interface layer and the cathode, there can be mentioned an interface layer containing phenylcarbazole and silver, or a cathode mainly composed of silver (JP-A-6-199562, JP-A-6-220343). Issue).

The thickness of the cathode 4 is usually the same as that of the anode 2. However, it is necessary for the EL element that at least one of the anode 2 and the cathode 4 has good transparency. From this, it is preferable that one of the anode 2 and the cathode 4 has a film thickness of 10 to 500 nm. Further, a substrate similar to the substrate 1 can be further provided on the cathode 4.

[0035]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited by the following description of the examples as long as the gist thereof is not exceeded. Example 1 An organic electroluminescent device was produced by the following method. An ITO transparent conductive film (manufactured by Geomatec Co., Ltd .: manufactured by EB method) having a thickness of 120 nm was deposited on a glass substrate to a concentration of 1 N (0.5).
Mol / l) was immersed in a sulfuric acid solution at a temperature of 40 ° C. for 30 minutes, washed with water, and then ultrasonically washed with 28% ammonia water for 10 minutes. After that, it is washed with demineralized water, ultrasonically washed with acetone and isopropyl alcohol for 10 minutes, and then dried by blowing dry nitrogen, and after UV / ozone cleaning, it is installed in a vacuum deposition apparatus and the vacuum degree in the apparatus is adjusted. Is 1 × 10 ^-6 To
It was evacuated using an oil diffusion pump until it became rr or less.

An aromatic amine compound (H1) was used as an organic hole transport layer material on this substrate.

[0037]

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[0038] was placed in a ceramic crucible and heated by a tantalum wire heater around the crucible for vapor deposition. The temperature of the crucible at this time was controlled in the range of 180 to 230 ° C. The degree of vacuum during vapor deposition was 1.4 × 10 ⁻⁶ Torr, and the organic hole transport layer 3b having a film thickness of 60 nm was obtained with the vapor deposition time of 2 minutes and 30 seconds. Then, as the material of the organic electron-transporting layer 3c, 8- hydroxyquinoline complex of aluminum shown in the following structural _{formula, Al (C 9 H 6 NO} ) 3 (E1),

[0039]

[Chemical 4]

The above was vapor-deposited on the organic hole transport layer 3b in the same manner. The temperature of the crucible at this time is 330-3
Control was performed in the range of 80 ° C. Degree of vacuum during vapor deposition is 1.8 × 1
0 ^-6 Torr, evaporation time 2 minutes 20 seconds, film thickness 75 nm
Met. This layer serves as a light emitting layer.

Finally, an alloy electrode of magnesium and silver was vapor-deposited as a cathode by a binary vapor deposition method so as to have a film thickness of 150 nm. A molybdenum boat was used for vapor deposition, and a glossy film was obtained at a vacuum degree of 7 × 10 ⁻⁶ Torr and a vapor deposition time of 2 minutes. The atomic ratio of magnesium to silver is 10: 1.2.
Met. I of the organic electroluminescent device produced in this way
It was measured by applying a positive DC voltage to the TO electrode (anode) and a negative DC voltage to the magnesium-silver alloy electrode (cathode). Table 2 shows the results.

Comparative Example 1 Example 1 except that sulfuric acid treatment and ammonia water treatment were not performed.
Same as. Table 2 shows the results. Comparative Example 2 The procedure of Example 1 was repeated, except that only the sulfuric acid treatment was performed and the ammonia water treatment was not performed. Table 2 shows the results.

Example 2 Aqueous sodium hydroxide solution (0.
01N) was used, and the same as in Example 1. Table 2 shows the results.

Example 3 The same procedure as in Example 1 was carried out except that the treatment was carried out with hydrochloric acid having a concentration of 1 N and a temperature of 40 ° C. instead of sulfuric acid. Table 2 shows the results. Example 4 The same as Example 3 except that a mixed solution of dimethylamine and water was used instead of ammonia. Table 2 shows the results.

[0045]

[Table 2] Vth: 1cd / m ² to over voltage η100: 100cd / m ² o'clock luminous efficiency V100: 100cd / m ² o'clock voltage

[0046]

According to the organic electroluminescent device of the present invention, an anode, an organic light emitting layer, and a cathode are sequentially provided on a substrate, the anode is indium oxide and / or tin oxide, and the anode is treated with an acid. As a result, the surface is smoothed and further treated with alkali to neutralize the trace amount of acid component remaining on the surface, whereby impurities at the interface can be removed, and the effect of acid treatment is further improved. It appears significantly, sufficient brightness can be obtained at a relatively low voltage, and stable light emission characteristics can be obtained for a long period of time.

Therefore, the EL device of the present invention is used in the field of flat panel displays (for example, OA computers and wall-mounted televisions) and light sources (for example, light sources for copiers, liquid crystal displays and instruments) which make the best use of the characteristics as a surface light emitter. It can be applied to backlights, display boards, and marker lights, and its technical value is great.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of the structure of an organic electroluminescent device of the present invention.

FIG. 2 is a schematic cross-sectional view showing another structural example of the organic electroluminescent element of the present invention.

FIG. 3 is a schematic cross-sectional view showing another structural example of the organic electroluminescent element of the present invention.

FIG. 4 is a schematic cross-sectional view showing another structural example of the organic electroluminescent element of the present invention.

[Explanation of symbols]

1 Substrate 2 Anode 3 Organic Light Emitting Layer 3a Hole Injection Layer 3b Hole Transport Layer 3c Electron Transport Layer 3d Organic Electron Transport Layer 3e Composed of a Compound Different from 3c 3e Interface Layer 4 Cathode

Claims (2)

[Claims] 1. In an organic electroluminescent device having an anode, a cathode, and at least an organic light emitting layer interposed therebetween, which is provided on a substrate, the anode is an oxide of indium and / or tin, and is treated with an acid. An organic electroluminescent device characterized by being treated with an alkali after being treated. 2. The organic electroluminescent device according to claim 1, wherein the alkali is ammonia or amine or an aqueous solution thereof.