JPH04298989A - Organic thin film type electroluminescence element - Google Patents

Abstract

PURPOSE:To suppress deterioration of an organic thin film by ultraviolet rays so as to maintain stable characteristic over a long period by providing an ultraviolet-ray absorbing layer in any location of a light emitting layer and an element surface. CONSTITUTION:An anode 2, hall transport layer 3, light emitting layer 4, electron transport layer 5 and a cathode 6 are successively formed on a substrate 1 consisting of glass or resin film, in an element of a layer 4, and an ultraviolet- ray absorbing layer is provided in any location of the layer 4 and an element surface. As the ultraviolet-ray absorbing layer, an ultraviolet-ray absorbing film and a glass or the like, coated with glass or zinc oxide crystal grains containing an ultraviolet-ray absorbing agent of CeO2, CdS, etc., are used. In this way, ultraviolet-rays from the outside of the element are interrupted and suppressed from reaching the light emitting layer, and stable characteristic can be maintained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device, and more particularly to an organic light emitting device containing an organic compound as a component in its light emitting layer.

0002

2. Description of the Related Art Hitherto, electroluminescent devices have been known that have a laminated structure of thin films made of inorganic compounds. . This inorganic thin film type electroluminescent device generally has a transparent electrode (ITO) and an insulating layer (Si3) on a glass substrate as shown in FIG.
N4), light emitting layer (ZnS:Mn), insulating layer (Si3N4
) and metal electrode (Al) layers are sequentially formed. Although such an inorganic thin film type electroluminescent device 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.

On the other hand, in recent years, attempts have been made to produce electroluminescent devices in which organic thin films are laminated. For example, as disclosed in Japanese Unexamined Patent Publication No. 57-51781, a thin layer of an organic compound that is to become a luminescent material is
Alternatively, it has a structure in which holes are sandwiched between thin layers of material that selectively conducts holes, and electrodes are provided 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.

By the way, it is known that the compounds used as the light emitting layer of such organic thin film electroluminescent devices generally have fluorescence. These compounds are usually
It absorbs light in the short wavelength range (violet to blue) of ultraviolet and visible light, and emits fluorescence in a wavelength range specific to each compound. The wavelength range of fluorescence is almost the same as the wavelength range when an electric field is applied to emit EL light, so when an organic thin-film light-emitting element using this type of compound as a light-emitting layer is used, for example, as a display device, it can be used indoors. It absorbs lights and outdoor light, and even non-lit parts to which no electric field is applied emit some light. As a result, display contrast decreases, resulting in poor visibility.

Furthermore, according to experiments conducted by the present inventors, when an organic thin film electroluminescent device was forcibly irradiated with ultraviolet rays,
It was confirmed that the luminance was significantly reduced. Although the detailed reason for this is not clear at present, it is thought that absorption of ultraviolet rays causes a structural change in the organic compound used, resulting in a decrease in its light-emitting function. As described above, electromagnetic waves in the wavelength range typified by ultraviolet rays are extremely harmful to organic thin film electroluminescent devices, and its removal is essential from the viewpoint of improving device performance.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned state of the prior art, and is capable of exhibiting normal contrast without decreasing luminance even when exposed to indoor light or outdoor light. Another object of the present invention is to provide an organic thin film type electroluminescent device in which deterioration of the organic thin film due to ultraviolet rays is suppressed and stable characteristics can be maintained over a long period of time.

[0007]

[Means for Solving the Problems] As a result of intensive studies to achieve the above object, the present inventors found that providing an ultraviolet absorbing layer, etc. on the substrate, light emitting layer, element surface, etc. can solve the above problems. They have found that this is effective and have completed the present invention.

That is, according to the present invention, in an organic thin film type electroluminescent device having a light emitting layer consisting of an anode and a cathode formed on a substrate and one or more layers of organic compounds sandwiched between these, the light emitting An organic thin film type electroluminescent device is provided, characterized in that an ultraviolet absorbing layer is provided on either the layer or the surface of the device, and also absorbs ultraviolet rays and transmits at least 80% or more of light in the visible wavelength range. An organic thin film type electroluminescent device is provided that has an anode and a cathode formed on a substrate, and one or more layers of organic compound sandwiched between them as a light emitting layer, and further includes an anode and a cathode formed on a substrate. In an organic thin film type electroluminescent device whose light emitting layer is a cathode and one or more layers of organic compounds sandwiched between them, the entire light emitting surface of the device is covered with an ultraviolet absorbing film or sheet. An organic thin film type electroluminescent device having characteristics is provided.

The present invention will be explained in more detail below.

FIG. 1 is a sectional view of an organic thin film type electroluminescent device according to the present invention. In the figure, numeral 1 represents a substrate, which is generally made of glass, resin film, or the like. 2 is an anode, and 6 is a cathode.

[0011] As the anode material, nickel, gold, platinum, palladium, alloys thereof, metals with large work functions such as tin oxide (SnO2), indium tin oxide (ITO), copper iodide, alloys and compounds thereof, and For example, conductive polymers such as poly(3-methylthiophene) and polypyrrole can be used. On the other hand, as cathode materials, silver, tin, lead, magnesium, manganese,
Aluminum or an alloy thereof is used. It is desirable that at least one of the materials used for the anode and the cathode be sufficiently transparent in the emission wavelength region of the device. Specifically, it is desirable to have a light transmittance of 80% or more.

Further, 3 is a hole transport layer, which has a function of transporting holes injected from the anode to the light emitting layer.

[0013] As the organic compound used in the hole transport layer, there may be mentioned a high molecular compound having an excellent hole transporting ability such as polyvinylcarbazole, and a low molecular compound having an excellent hole transporting ability. Examples of low molecular weight compounds include triphenylamines, stilbene derivatives, oxadiazoles, etc. Specific examples thereof include the following.

[0014]

[Table 1-(1)]

[Table 1-(2)]

Reference numeral 4 denotes a light-emitting layer, which emits light by recombining energy of injected holes and electrons. The organic compound used has fluorescence. A specific example is shown below.

[0016]

[Table 2-(1)]

[Table 2-(2)]

Further, 5 is an electron transport layer, which has a function of transporting electrons injected from the cathode to the light emitting layer. As the organic compound used in the electron transport layer, any compound exhibiting electron transport properties such as perylene derivatives and oxadiazole derivatives can be used. Examples of compounds preferably used in the present invention are shown below.

[0018]

[Table 3]

The organic thin film type electroluminescent device of the present invention is produced by applying the above-described organic compound to a thickness of less than 2 μm in total, more preferably from 0.05 μm to 0.5 μm, by vacuum evaporation, solution coating, etc. It is constructed by forming an organic compound layer by reducing the thickness and sandwiching it between an anode and a cathode.

Now, in order to mainly suppress ultraviolet rays from reaching the light-emitting layer in an organic thin-film electroluminescent device having such a structure, in the present invention, as described above, a film is applied to either the light-emitting layer or the surface of the device. It is characterized by the provision of an ultraviolet absorbing layer.

Specifically, in the case of a type that extracts light from the substrate side, an ultraviolet absorbing layer is provided on the outside of the substrate, or the substrate itself is provided with an ultraviolet absorbing function. On the other hand, in the case of a type that extracts light from the opposite side of the substrate, an ultraviolet absorbing layer is provided on the electrode formed in the uppermost layer (the cathode 6 in the example of FIG. 1).

As the ultraviolet absorbing layer used for this purpose, it is preferable to use a resin film to which a compound having ultraviolet absorbing ability is added, or a glass containing an ultraviolet absorbing component.

As a specific example, 2-hydroxyalkoxy-4-alkoxybenzophenone, 2,
4-dihydroxybenzophenone or benzotriazole added, 2-hydroxy-4 to polyolefin
Examples include ultraviolet absorbing films such as those added with -octoxybenzophenone, glasses containing ultraviolet absorbers such as CeO2 and CdS, and glasses coated with zinc oxide crystal fine particles.

By using these as a substrate or laminating them on a substrate or electrode, it is possible to block ultraviolet rays from outside the device and prevent them from reaching the light emitting layer. The organic thin film type electroluminescent device according to the present invention includes not only the type having a three-layer structure of organic compounds as shown in FIG. 1, but also the type shown in FIG. 2 and FIG. An organic two-layer type as shown in Figure 3, an organic single-layer type (not shown) in which both are omitted and only the emissive layer is used, and an organic/inorganic laminated type (not shown) in which an inorganic compound is used in some layers. It can also be applied to

[0025] Depending on the material used, if left in the atmosphere, it may gradually oxidize or absorb moisture, resulting in deterioration of its properties. The entire device may be placed in a cell and silicone oil or the like may be sealed therein.

[0026]

[Examples] The present invention will be explained in more detail with reference to Examples below. Example 1 Ultraviolet absorbing glass containing approximately 2% by weight of CeO2 was used as a substrate, and indium tin oxide (ITO) was sequentially deposited on this glass.
) an anode (thickness 1200 Å), a hole transport layer (thickness 750 Å) made of the following compound (Chemical formula 1), a light emitting layer (thickness 500 Å) made of the following compound (Chemical formula 2), and a cathode made of aluminum (thickness 1000 Å), respectively. It was formed by vacuum evaporation, and an element as shown in FIG. 3 was created. The degree of vacuum during deposition is approximately 7×1
06 Torr, and the substrate temperature is room temperature.

[Chemical formula 1]

[Case 2]

Comparative Example 1 Same as Example 1 except that general alkali glass was used as the substrate.
The device was created in exactly the same manner as above.

When a DC power source was connected to the anode and cathode of these two types of elements and a current was passed through them, there was almost no difference in the brightness of the light emitting part in either element. As a result, in the element of Comparative Example 1, fluorescence was generated due to the action of the ultraviolet component of the indoor light, whereas in the element of Example 1, no such fluorescence was observed, and the visibility was excellent. Also, from the substrate side of these elements, the peak wavelength is 313 nm and the energy intensity is 110 μW.
When irradiated with ultraviolet light of /cm2, the device of Comparative Example 1 had a luminance of about 20% of the initial value after 5 minutes of irradiation, which was a significant decrease, whereas the device of Example had a luminance of about 80% of the initial value.
The brightness was maintained.

Example 2, Comparative Example 2 Example 1 except that general alkali glass was used as the substrate.
Two devices were created in the same manner as above. A polyester film containing 1.0% by weight of 2,4-dihydroxybenzophenone was bonded to the outside of the substrate of one of the elements to create an element as shown in FIG. 3, which was designated as Example 2. In the figure, 7 indicates the ultraviolet absorbing layer made of the polyester film. Comparative Example 2 was the one in which no film was attached. When these elements were evaluated in the same manner as in Example 1, it was confirmed that the elements of Example 2 were superior in both visibility during operation and brightness change upon irradiation with ultraviolet light.

[0030]

Effects of the Invention In the organic thin film electroluminescent device of the present invention, (1) an ultraviolet absorbing layer is provided on either the light emitting layer or the surface of the device, (2) a substrate having ultraviolet absorbing ability is used, or (3) Since the entire light-emitting surface of the device is coated with an ultraviolet absorbing film, it suppresses fluorescence emission from the light-emitting layer due to ultraviolet components contained in indoor lights and outdoor light, and allows the light-emitting and non-light-emitting parts to be separated. Decrease in contrast can be prevented. It also prevents deterioration of organic thin films due to ultraviolet rays,
An organic thin film electroluminescent device that can maintain stable characteristics over a long period of time can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a typical electroluminescent device of the present invention.

FIG. 2 is a schematic cross-sectional view of an electroluminescent device according to another embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of an electroluminescent device according to still another embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of a conventional electroluminescent device.

Claims (3)

[Claims] 1. In an organic thin film electroluminescent device having a light-emitting layer consisting of an anode and a cathode formed on a substrate and one or more layers of organic compounds sandwiched between them, either the light-emitting layer or the surface of the device is An organic thin film type electroluminescent device characterized by having an ultraviolet absorbing layer provided in said part. 2. An anode and a cathode formed on a substrate that absorbs ultraviolet rays and transmits at least 80% of visible wavelength light, and one or more layers of organic compounds sandwiched between them. Organic thin film type electroluminescent device. 3. In an organic thin-film electroluminescent device whose light-emitting layer is an anode and a cathode formed on a substrate and one or more layers of organic compounds sandwiched between them, the entire light-emitting surface of the device is exposed to ultraviolet rays. An organic thin film type electroluminescent device characterized by being coated with an absorbent film or sheet.