JPH03216998A - Electro-luminescent element - Google Patents

Abstract

PURPOSE:To obtain a luminescent performance having a hightened element breakdown voltage and a long stability, by forming in the electric field polymerization method at least one layer out of other organic compound thin films supported between a positive electrode and a negative electrode. CONSTITUTION:Organic compound layers 3a, 3b are supported between a positive electrode 2 and a negative electrode 3. At least one of the layers 3a is formed in the electric field polymerization method. The layer film 3a, obtained in the electric field polymerization method is polymerized, and more dense than a monomer film formed by a vacuum vapor deposition method or by spin coating method and also higher in withstand voltage. The film 3 is difficult to crystalize, as a result it can help prevent element breakdown and improve element durability in use for a part of an electro-luminescent element. In this method, an electro-luminescent element is obtained which can functions at a low voltage, continues a luminescent performance for many hours, and is easy to control the luminescent wave length with excellent durability.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention can directly convert electrical energy into light energy by applying an electric field, and unlike conventional incandescent lamps, fluorescent lamps, or light emitting diodes, it can be used on a large surface area. The present invention relates to an electroluminescent device capable of realizing a shaped light emitting body.

[Conventional technology]

2. Description of the Related Art Hitherto, as an electroluminescent device, one having a laminated structure of thin films made of inorganic compounds is known. This inorganic thin film electroluminescent device generally has a transparent electrode (ITO), an insulating layer (S13N4), a light emitting layer (ZnS:Mn), an evergreen layer (Sl3N4), and a metal electrode on a glass substrate, as shown in Figure 2. (
Each layer of AI2) is formed in sequence. Although such an inorganic thin film type electroluminescent element has high luminance, the driving voltage is as high as 100 to 200 V, and a dedicated high-voltage driving IC is required. Furthermore, materials that can be used as the base material for the light-emitting layer and the activator are limited, and it is not always possible to obtain a device with high brightness at a desired emission wavelength.

In response to this, in recent years attempts have been made to produce electroluminescent devices in which organic thin films are laminated. For example, as disclosed in JP-A-57-51781, a thin layer of an organic compound to serve as a light emitter is supported by a thin layer of a material that selectively conducts electrons and/or holes. It has a structure with electrodes on both sides.

In such organic thin film electroluminescent devices, the range of materials for the light emitting layer can be selected from a wider range than in inorganic thin film electroluminescent devices, and devices having various emission wavelengths have been found.

In addition, the driving voltage is generally low, about 5 to 60 V, and the large area ratio is easy, so it is expected to be applied to various light emitting and display devices including full color displays.

However, research on electroluminescent devices using organic compounds as light emitters, including the examples mentioned above, is limited, and it cannot be said that sufficient material research and device development have been carried out. The reality is that there are many challenges to be solved, such as improving light emission, controlling emission wavelength, and improving durability.

In particular, in conventional organic thin-film electroluminescent devices, the monomer organic compound is made into a thin film using vacuum evaporation, etc., so there is a problem with the dielectric strength of the device against applied voltage, and even a slight excessive voltage can destroy the device. Furthermore, the life of the device is limited by the progress of crystallization of the organic compound layer.

[Problem to be solved by the invention]

The present invention overcomes the drawbacks of the prior art as described above, and has a structure that can be driven at low voltage, maintains luminous performance for a long time, allows easy control of the luminous wavelength, and has excellent durability. The object is to provide an electroluminescent device.

[Means to solve the problem]

As a result of intensive studies on the constituent elements of the light-emitting layer to solve the above problems, the present inventors found that in an electroluminescent element composed of one or more layers of organic compounds sandwiched between two electrodes, The inventors have also found that the above-mentioned problems can be solved by making at least one of the compound layers an electropolymerized film, and have completed the present invention.

That is, according to the present invention, in an electroluminescent element composed of an anode, a cathode, and one or more organic compound layers sandwiched between them, at least one of the organic compound layers is formed by electropolymerization. An electroluminescent device is provided.

The present invention is characterized in that at least one of the organic compound thin film layers constituting the electroluminescent device is composed of an electropolymerized film. The electrolytic polymerization method is a method in which an electrolyte and heptamer are dissolved in water or a suitable organic solvent, a pair of electrodes are inserted into the solution, and a current is applied to deposit a thin polymer film on the electrode surface. . Since the resulting film is polymerized, it is extremely dense compared to monomer films formed by vacuum evaporation or spin coating, has a higher dielectric strength, and is less likely to crystallize, making it suitable for use in some electroluminescent devices. When used for this purpose, it can contribute to preventing dielectric breakdown and improving durability of the device.

Materials that can be formed into films by the electric field polymerization method include five-membered heterocycles such as pyrrole and thiophene, aromatic amines such as aniline and aminopyrene, aromatic hydrocarbons such as benzene, pyrene, and fluorene, and vinyl compounds such as N-vinyl rubber. In particular, the compounds shown below are materials suitable as constituent elements of electroluminescent devices and are preferably used. I C, H, 1C2H, 《C,H, 2n= C2H. 1 CHJ l CH2CH, H, N-◎-0-◎1NH2 02N101S101NH2 HyoN-◎-O-◎-NH1◎ H2N-◎1S1◎-NH1◎ ◎ -NH101010-NH-◎ ◎-NH-◎1S-◎-NH1◎ ◎-NH-◎-O-◎1N {O)). ◎-NH-◎-s-Q-N-{o)2 (qmasuN-◎-0-◎-N-C))2 A specific electrolytic polymerization film is produced, for example, as follows. First, the monomers of these organic compounds are mixed with a solvent that has a high dielectric constant and dissolves the electrolyte well, such as alcohols such as acetonitrile, penzonitrile, propylene carbonate, and methyl alcohol, dimethylformamide, nitrobenzene, N-methylpyrrolidone, and tetrahydrofuran. , dissolve in dimethyl sulfoxide, etc., and add an appropriate amount of electrolyte. As the electrolyte, organic or inorganic salts or double salts, complex salts, ionic dyes, etc., which are soluble in organic solvents and easily ionically dissociated, are used. Specifically, (n-C4Hs) JCRO4. (C2H5)4NB
F4, (C.}I,)N}IsO. ．． (n-C.H9
)4N-CH, {TOSO,, (C2HS). NPFG.
LiCQ04. NaAsF, AgBF, . Rose Bengal etc. are used. It is desirable to use these electrolytes after purification and vacuum drying. In this case, the concentration of electrolyte in the polymerization reaction is 0. Ol~1.0+soQ/Q,
Preferably it is in the range of 0.05 to 0.3 moQ/R.

The concentration of the heptanomer depends on its solubility in the solvent used, but generally one serving of tmoQ/Q to IIIloQ/Q
is within the range of In the electrolytic polymerization method of the present invention, 2,6-lutidine, pyridine, etc., which are hydrogen acceptors, are added to promote the production of the polymer. 2,4,6-collidine and the like can be added. Although the concentration of the additive is arbitrary, it is preferably from equimolar to 20 times the molar amount of the monomer. Although the electric field polymerization reaction can be carried out using a bipolar system or a bipolar system, it is preferable to perform the electrolytic polymerization reaction using a bipolar system because constant potential or constant current polymerization can be performed. In the case of the bipolar method, a general reference electrode can be used, but a saturation force Romel electrode (SC
E) or silver/silver chloride is often used. Electrolysis voltage is SC
Polymerization is possible at 1 V or more with respect to H, but constant potential, constant current, or cyclic potential may also be used for polymerization. By dedoping the obtained polymer film to remove cationic active species, it is possible to obtain a nearly transparent and electrically stable film.The present invention will be explained below with reference to the drawings.

FIG. 1(a) is a schematic cross-sectional view of the electroluminescent device of the present invention. 1 is a glass substrate or a synthetic resin substrate, 2 is an anode electrode layer formed on the substrate, and 4 is a cathode electrode layer. 3a is an electropolymerized film having a hole transport ability, and its thickness is preferably from 100 to 2,000, more preferably from 200 to 1,000. 3b is a thin film layer of an organic compound having an electron transport ability and a light emitting function, and its thickness is preferably from 100 to 1,500, more preferably from 200 to 1,000.

The anode materials include nickel, gold, platinum, palladium, alloys of these, metals with large work functions such as tin oxide (SnO), indium tin oxide (ITO), copper iodide, their alloys and compounds, and even polyester. (3-methylthiophene), a conductive polymer such as polypyrrole, etc. can be used. On the other hand, as the cathode material, a metal with a small work function such as silver, tin, lead, magnesium, manganese, aluminum, or an alloy thereof is used. At least one of the materials used as the anode and the cathode is
It is desirable that the material be sufficiently transparent in the emission wavelength region of the device. Specifically, it is preferable to have a light transmittance of 80% or more.

FIG. 1(b) is a schematic cross-sectional view showing another embodiment of the electroluminescent device of the present invention. 1, 2, 3a, 3b, 4 are shown in Figure 1 (
Same as a). 3c is a thin film layer of an organic compound having electron transport ability.

The electroluminescent device according to the present invention uses such an electropolymerized film as a component such as a hole transport layer, a light emitting layer, an electron transport layer, or an electrode. For example, when using it as a hole transport layer, the device is manufactured by the following procedure. That is, for example, indium tin oxide (ITO) is placed on the substrate as an anode.
is formed by sputtering, electron beam evaporation, spraying, etc.

After etching into a predetermined pattern, a solution is prepared by dissolving a suitable one of the monomer materials mentioned above in a solvent together with an electrolyte and additives, and the solution is placed on the anode side. Using SCE as the reference electrode and platinum as the cathode, a polymer film is deposited on the ITO when a current is passed for a predetermined period of time. The obtained polymer film is dedoped from electrolyte ions by applying a reverse electric field as necessary, and then washed with acetone and methanol and dried in vacuum. By sequentially forming an electron-transporting light-emitting layer and a cathode on the hole-transporting layer thus formed by, for example, a vacuum evaporation method, an electroluminescent device as shown in FIG. 1(a) is created. .

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 A glass substrate on which a 500-thick ITO thin film was formed as an anode was washed for seven minutes, and then a hole transport layer was formed on the anode using the following solution. Acetonitrile 20-2,6-lutidine 0.05■oQ/QN,N
'-Diphenylbenzidine 4,5mmoR/fl
◎-NH1◎-◎1NH-◎ That is, a solution having the above composition was placed in an electrolytic cell, and a glass substrate with a 1-piece 0 was used as the anode, a platinum wire as the cathode, and an SCE as the reference electrode. OV-+2 for SCH
V-+OV. Polymerization was performed by applying a triangular wave at a sweep rate of 50 mV/see. After applying electricity for 20 seconds, take out the glass substrate with ITO and add propylene carbonate/Tetra n.
-Ptylammonium perkate rate (0.1mol12
IQ) Voltage of SCH in solution, OV-+-0.8V-
+OV. 1! Dedoping was carried out by applying a triangular wave with a drawing rate of 50 V/see. The resulting polymer film has a thickness of 1
, 200 It was a smooth, pale yellow film that was almost transparent. After thorough cleaning with acetone and methanol and vacuum drying, about 750 of the following materials were deposited on the polymer film by vacuum evaporation to form an electron-transporting light-emitting layer.

Further, as a cathode, magnesium and silver were binary-evaporated onto the cathode to form an alloy film, thereby producing an element having the structure as shown in FIG. 1(a). When an external power source was connected to the thus obtained light emitting device and a voltage was applied so that the anode side had a high potential, yellow-green light emission was observed.

As a comparative example, devices were fabricated using the same materials by vacuum evaporation. When an external power supply was connected in the same way and voltage was applied, yellow-green light was emitted in the same way, but
Compared to the element of this example, dielectric breakdown occurred at a lower voltage and the brightness decreased in a shorter time.

Example 2 A hole transport layer was formed on the same ITO-coated glass substrate as in Example 1 using the following solution.

Nitrobenzene 20+all
2,6-lutidine 0.05+soQ/Q 1 C2H. The polymerization conditions and post-treatment were the same as in Example 1 to obtain a smooth electropolymerized film. Next, 250 perylene derivatives and 750 perylene derivatives were formed as a hexaphenylbenzene electron transporting layer as a light emitting layer, respectively, by vacuum deposition in this order. Finally, a magnesium/silver cathode was dual-evaporated to produce an element having the structure shown in FIG. 1(b). Next, we compared the characteristics of the electroluminescent devices with electroluminescent devices that were all fabricated using the vacuum evaporation method in the same manner as in Example 1. Although yellow-orange light emission was observed in all of the devices, the breakdown voltage and the In terms of longevity,
It was confirmed that the device of this example using an electrolytic polymer film was superior.

Note that in the above examples, the electric field polymerization method was employed to form the hole transport layer, but when a fluorescent monomer was used, the light emitting layer could be formed by the electric field polymerization method.

〔Effect of the invention〕

In the electroluminescent device of the present invention, at least one layer of the organic compound thin film sandwiched between the anode and the cathode is formed by an electrolytic polymerization method, thereby increasing the dielectric strength of the device and obtaining stable light emission characteristics over a long period of time. be able to. In addition, when multiple electrodes are separated from each other on the same substrate, a different polymer film can be formed for each electrode by appropriately selecting the electrodes during polymerization.
Light emitting characteristics can be changed.

[Brief explanation of drawings]

1(.) and 1(b) are schematic cross-sectional views of an electroluminescent device according to the present invention, and FIG. 2 is a schematic cross-sectional view of a conventional electroluminescent device.

Claims (3)

[Claims] (1) An electroluminescent device comprising an anode, a cathode, and one or more organic compound layers sandwiched between them, characterized in that at least one of the organic compound layers is formed by electropolymerization. electroluminescent device. (2) The electroluminescent device according to claim (1), wherein at least one of the organic compound layers is an electropolymerized film. (3) The anode and/or cathode are composed of a plurality of sub-electrodes separated from each other, and at least one of each sub-electrode is
3. The electroluminescent device according to claim 1, wherein one of the sub-electrodes is formed with an electropolymerized film different from that of the other sub-electrodes.