JPH04772A - Electroluminescent element - Google Patents

Abstract

PURPOSE:To make drividing by AC power possible and increase durability of light emission performance by a method wherein two kinds of electrode elements are laminated in a light transmitting electrode, a work function of an electrically conductive substance contained in each electrode element is different, and the electrode elements are arranged periodically so as to face each other via an organic compound layer in a pair of facing electrodes. CONSTITUTION:An electroluminescent device comrises an electrode element 5 formed of light transmitting base 1,2, light transmitting electrodes 3, 4, and a first conductive substance, an electrode element 6 formed of a second conductive substance having a work function different from that of the first conductive substance, an organic compound layer 7, and a power supply 8. Any shape can be taken for the electrode element 5, for example, stripe or mosaic shape, if they can be arranged in a periodic manner. The electrode elements 6 should preferably be arranged in such a way that they are alternately arranged periodically together with the electrode elements 5 on each interface with the organic compound layer 7, and that they are arranged facing the electrode elements 5 with the organic compound layer 7 provided therebetween.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has a light-emitting layer made of a light-emitting substance, and by applying an electric field, the applied energy of the electric field can be directly converted into light energy. The present invention relates to an electroluminescent device that, unlike fluorescent lamps or light emitting diodes, enables the realization of large-area planar light emitters.

[Conventional technology]

There are two types of electroluminescent devices: (1) intrinsic electroluminescent devices, which excite the emissive layer to emit light by local movement of electrons and holes within the emissive layer using an alternating current electric field, and (2) a direct current electric field. There are two types of electroluminescent devices: carrier-injection type electroluminescent devices, which inject electrons and holes from an electrode and recombine them in a light-emitting layer to excite a light-emitting substance and cause it to emit light. (1) Intrinsic electroluminescence type light-emitting elements generally use an inorganic compound such as ZnS with Cu or Cu and a substance added thereto as a light emitting body, but require a high alternating current electric field of 200 μm or more for driving. However, there are many problems such as insufficient brightness and luminous lifetime.

Examples of the carrier injection type electroluminescent device (2) include JP-A No. 59-194393 and U.S. Pat. No. 4,720,4.
No. 32 or Japanese Journal o
f Applied Physics (Vol. 27, 71
3 pages, published in 1988) are publicly known. These technologies are characterized by a structure in which a thin organic compound light emitting layer and an electron and/or hole transport layer are sandwiched between an anode and a cathode, and emit light with high brightness in a DC driving electric field of 100 V or less.

However, carrier injection type electroluminescent devices, including the above-mentioned known technology, have a luminous intensity of 1 luminous efficiency, a lifetime of luminescent state,
The reality is that there are many problems such as the selectivity of the emission wavelength, and so far there are no known examples of this being put to practical use. In particular, carrier injection type electroluminescent devices are driven by direct current, so
The injected charge carriers are captured and localized in the organic compound layer and at the interface between the organic compound layer and the electrode, affecting properties such as luminance brightness, luminous efficiency, and lifetime of the luminescent state.
There was a problem that the properties of the element were deteriorated.

[Problem to be solved by the invention]

The present invention has been made in view of the above circumstances, and its first purpose is to provide a carrier injection type electroluminescent device with a novel electrode configuration, and another purpose is to provide a carrier injection type electroluminescent device that can be driven by AC. An object of the present invention is to provide a type electroluminescent device.

A third object of the present invention is to provide a carrier injection type electroluminescent device with excellent durability and long-lasting luminous performance.

[Means to solve the problem]

The present inventors have conducted extensive studies on a novel electroluminescent device to solve the above problems, and have found that in an electroluminescent device consisting of a pair of translucent electrodes and an organic compound layer sandwiched between them, each electrode an electrode element A made of a first conductive material provided in a periodic arrangement on each layer of an organic compound layer, and a first conductive material provided on the layer containing the electrode element A; and an electrode element B made of a second conductive substance having a different work function, and further characterized in that in a pair of opposing electrodes, each electrode component is arranged to face each other with an organic substance in between. They discovered that an electroluminescent device is effective for solving the above problems and completed the present invention.In other words, according to the present invention, an electroluminescent device in which an organic compound layer is sandwiched between a pair of transparent electrodes In the element, the light-transmitting electrode is a stack of two types of electrode elements, and the work functions of conductive substances contained in each electrode element are different, and further, in a pair of opposing electrodes, each electrode element has a different work function. Provided is an electroluminescent device characterized in that the organic compound layers are periodically arranged opposite to each other with an organic compound layer interposed therebetween.

Hereinafter, the electroluminescent device according to the present invention will be explained in detail.

FIG. 1 is a schematic cross-sectional view showing the structure of the electroluminescent device of the present invention. In the electroluminescent device shown in FIG. 1, 1 and 2 are transparent substrates, 3 and 4 are transparent electrodes, 5 is an electrode element A made of a periodically arranged first conductive material, and 6 is a transparent substrate. Electrode element B is made of a first conductive material and a second conductive material having a different work function, 7 is an organic compound layer, and 8 is a power source.

In the electroluminescent device of the present invention, the electrodes are formed of two types of conductive materials having different work functions, as described above.

Gold, gold, and other conductive materials with large work functions include gold;
Beryllium, cobalt, chromium, indium, molybdenum, nickel, palladium, platinum, rhodium, tungsten, tin oxide, indium oxide, indium oxide-tin oxide (ITO), zinc oxide, cadmium sulfide, cadmium oxide-tin oxide, iodide network , poly(3-methylthiophene), polypyrrole, and the like.

Examples of conductive substances having a small work function include silver, aluminum, bismuth, gallium, indium, lithium, magnesium, manganese, niobium, lead, strontium, and zinc.

When providing electrode element A using a substance with a small work function, it is desirable to use a substance with a large work function as electrode element B, and when using a substance with a large work function as electrode element A, it is desirable to use a substance with a large work function as electrode element B. It is desirable to use a material with a small work function as element B.

In the present invention, when two types of electrode elements are arranged periodically and the work functions of the conductive substances contained in each electrode element are different, alternating current driving becomes possible, and light emission becomes possible. Although the reason for the effects such as improved performance durability is not clear at present, it is presumed to be due to the following reasons. Electrode elements A with different work functions
and B are periodically arranged facing each other with an organic compound layer interposed therebetween, making AC driving possible. In addition, localized charge carriers trapped in the organic compound layer and at the interface between the organic compound layer and the electrode are released by the action of the applied alternating current electric field.

Further, the shape of the electrode elements A may be any shape as long as it can be arranged periodically, such as a stripe shape or a mosaic shape.

It is appropriate that the shape of the electrode elements B is such that they are arranged periodically and alternately with the electrode elements A at each interface of the organic compound layer, and are arranged opposite to the electrode elements A with the organic compound layer interposed therebetween. be.

Methods for forming electrodes include vacuum evaporation, sputtering,
Conventionally known techniques such as electrolytic polymerization and screen printing can be used.

Further, the electrode according to the present invention needs to be transparent to light emitted from the organic compound layer. Various methods can be employed to ensure transparency to visible light, including a method of selecting the type of conductive material used for the electrode or a method of regulating the film thickness of the formed electrode.

For the organic compound layer of the electroluminescent device of the present invention, an organic compound exhibiting charge transporting properties and luminescent properties can be used.

Specific examples of compounds applicable to the present invention are shown below.

Structural Formula The organic compound layer in the electroluminescent device of the present invention is formed, for example, by coating a layer containing the above-mentioned exemplified compounds on a transparent electrode. As a coating method, conventionally known film forming techniques such as a dry method such as a vacuum evaporation method, a wet method such as a spin coating method, and a dip coating method can be applied. The thickness of the organic compound layer is approximately 300 ~
A range of about 5,000 people is preferred.

When an organic compound layer is provided using a wet film forming method, a coating liquid obtained by dispersing or dissolving the above-mentioned exemplified compounds in a suitable solvent may be coated on the transparent electrode. Usable solvents include water, alcohols such as methanol, ethanol, and isopropanol, ketones such as acetone, 2-butanone, and cyclohexanone, amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl. Sulfoxides such as sulfoxide, ethyl compounds such as tetrahydrofuran, dioxane, and ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, chloroform, methylene chloride, dichloroethane, 1, 1. , aliphatic halogenated hydrocarbons such as 2-trichloroethane, or aromatics such as benzene, toluene, xylene, ligroin, monochlorobenzene, dichlorobenzene and the like. It is also possible to add a film-forming binder to the coating solution.

Such binders include polyvinyl butyral, polycarbonate, polyarylate, polysulfone, polyethersulfone, polyester, phenoxy resin, polyvinyl acetate, acrylic resin, polyacrylamide resin, polyamide, polyvinylpyridine, styrene resin, vinyl chloride resin. , epoxy resin, urethane resin, cellulose resin, casein, gelatin, polyvinyl alcohol, polyvinylpyrrolidone, and the like.

〔Example〕

EXAMPLES Next, the present invention will be explained in detail with reference to Examples, but the present invention is not limited thereto.

Example 1 A 50 mm x 50 m1+ Pyrex glass was ultrasonically cleaned with a neutral detergent, distilled water, and hot ethanol, and dried in a clean booth. Gold was vacuum-deposited on this Pyrex glass to provide electrode element B with a thickness of 400 mm, and aluminum was further deposited using the same method (film thickness of 1.000 mm).
Then, striped electrode elements A having a width of 1 mm and periodically arranged at intervals of 1 mm were provided to form a translucent electrode 3. Exemplary compound E-12 was vacuum-deposited on the electrode thus prepared to form an organic compound layer with a thickness of 600 ml. Next, a mask is provided on the organic compound layer, and the electrode element B of the translucent electrode 3 is
Aluminum is vacuum-deposited in a position opposite to the film thickness 1.
, 000 people), and finally the mask was removed and the gold layer was coated with a thickness of 400 mm.
The light-transmitting electrode 4 was vacuum-deposited to form a transparent electrode 4, and an electroluminescent device of the present invention was produced. An alternating current voltage with a frequency of 50 Hz was applied to the electroluminescent device thus produced. Light emission begins as the applied voltage increases, and the linear current increases to 30 mA/c.
Clear green light emission with a brightness of 40 cd/m2 was observed over a long period of time.

Examples 2 to 7 Elements having the same structure as in Example 1 were fabricated using the electrode materials and organic compounds shown in Table 1.

All electrodes were manufactured by vacuum evaporation using resistance heating.

Next, an alternating voltage with a frequency of 50 Hz was applied to these samples. All samples began to emit light as the applied voltage increased, and light emission for a long period of time was confirmed.

Table 1 shows the wear conditions and luminescence behavior of each sample.

Example 8 An element of the present invention was produced in the same manner as in Example 2 except that the organic compound layer was provided by the wet film forming method described below.

Creation of organic compound layer by wet film formation method> Exemplary compound E
(
Rotation speed 2. OOOrpm) film thickness 1,000 on transparent electrode
0 organic compound layers were provided.

The light emitting characteristics of the thus obtained device were examined in the same manner as in Example 1. As a result, the drive current is 60m
Clear light emission with a brightness of 50 cd/m'' at A/cm'' could be observed for a long time.

〔effect〕

Since the electroluminescent device of the present invention has electrodes having a specific configuration as described above, it can be activated by alternating current and has excellent durability with long-lasting luminescent performance.

[Brief explanation of drawings]

1.2...Transparent substrate 5... Electrode element A 7...Organic compound layer 3.4...Transparent electrode 6... Electrode element B 8...Electric power source Patent applicant Rico Co., Ltd.

Claims (1)

[Claims] (1) In an electroluminescent device in which an organic compound layer is sandwiched between a pair of transparent electrodes, the transparent electrode is a stack of two types of electrode elements, and each electrode element contains a conductive substance. 1. An electroluminescent device having different work functions, and further comprising a pair of opposing electrodes in which each electrode element is periodically arranged opposite to each other with an organic compound layer interposed therebetween.