JPH0451491A - Multicolor electroluminescent element - Google Patents

Abstract

PURPOSE:To efficiently take out emitted light from each of luminous layers while increasing also the luminous area of the layer to some degree and obtaining a multicolor electroluminescent element of not only high brightness but also very compactness by dividing the luminous layers respectively into plural parts, and also making up the divided regions respectively of materials having luminous spectra different from one another. CONSTITUTION:Anodes 2, at least one or plural luminous layers 4, 4', 4'' and cathodes 6 each having its light reflecting ability are laminatedly formed in this order respectively on both obverse and reverse faces of a transparent substrate 1 while the luminous layers 4, 4', 4'' formed on either the obverse or reverse of, or respectively on both surfaces of the substrate 1 are divided respectively into plural parts and they are made up respectively of materials having luminous spectra different from one another. The luminous layers 4, 4', 4'' are respectively 50 to 5,000Angstrom thick, and preferably 100 to 1,000Angstrom thick. Positive- hole transport layers 3, 3' and electron transport layers 5, 5' on the other hand are respectively 200 to 5,000Angstrom thick, and preferably 500 to 1,000Angstrom thick.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electroluminescent device that has a luminescent layer made of a luminescent substance and can directly convert electrical energy into light energy by applying an electric field.

[Conventional technology]

Conventionally, this type of electroluminescent device, ie, the Elec-1 to Luminescence (hereinafter abbreviated as EL) device, uses at least one of the electrodes as a transparent electrode, as shown in FIG. 2, and the light emitted from the light emitting layer is It was taken out through the board. However, since the EL light emitted from the light-emitting layer is emitted uniformly in all directions, the EL light is emitted from the interfaces of the insulating layer, transparent electrode, and glass substrate due to differences in the refractive index before it exits the device. (According to Japanese Patent Laid-Open No. 57-60691, the proportion of the amount of light extracted to the outside through the substrate is at most 10% of the total amount of light emitted). In order to improve this point, an edge-emitting type EL element as shown in FIG. 3 has been proposed. In this device, both of the electrodes that sandwich the light-emitting layer are metal electrodes with high reflectance, and the EL light emitted from the light-emitting layer undergoes total internal reflection between both electrodes, and is extracted from the end face of the light-emitting layer to the outside of the device. . Therefore, in the case of this type, most of the total amount of light emitted is emitted to the outside except for the part absorbed inside the element, so that EL light can be extracted efficiently.

By the way, the thickness of the light emitting layer of an EL element is generally 1, .
000 to 10,000, and it is even thinner than this for organic EL devices that use organic thin films as light-emitting layers, which have been attracting attention in recent years, and have been attracting attention in recent years. ．． Approximately 000 people. For this reason, when the organic EL element is of the edge-emitting type, although the efficiency of emitting light is certainly increased, the light-emitting area becomes significantly smaller, which may cause severe inconvenience depending on the application. For example, when used as a light source for an image reading device (image sensor), the irradiation area of the document is small, which limits the reading speed and makes it difficult to control the color tone of the light emitted from the edge. A problem occurs.

[Problem to be solved by the invention]

The present invention has been made in view of the above-mentioned drawbacks of the prior art.
The purpose is to provide an extremely compact electroluminescent device that can efficiently extract light emitted to the outside, has a relatively large light emitting area, has high brightness, and is extremely compact.

Still another object of the present invention is to provide a light emitting device that can control the color tone of light emitted from the end face.

Still another object of the present invention is to provide a small and simple electroluminescent device capable of producing high-intensity white light.

[Means to solve the problem]

As a result of intensive studies to achieve the above object, the present inventors have found that an electroluminescent device in which the light-emitting layer is divided into a plurality of parts and each divided region is made of a material having a different emission spectrum is effective. They discovered this and completed the present invention.

That is, according to the present invention, an anode,
At least one or more layers of a light emitting layer and a cathode having light reflecting ability are laminated in this order, and the light emitting layer formed on one or both of the front and back surfaces of the substrate is divided into a plurality of parts, and A multicolor electroluminescent device is provided in which the light emitting layers are each made of a material having a different emission spectrum.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view of a main part of a typical electroluminescent device of the present invention. In this example, a case is taken in which the light emitting layer formed on one side of the substrate is divided into two parts in a direction perpendicular to the light emission direction. In Figure 1, 1
is a substrate, and is made of a transparent material in the wavelength range of light emitted from the light emitting layer. -For boat fishing, use glass or various translucent resin sheets (polyethylene terephthalate, polyimide, etc.). 1 also serves as the rear end of the light guide path for the light emitted from the light emission, as will be described later, so it is desirable that it be as transparent as possible. 2 is a transparent electrode that serves as an anode, and is made of nickel, gold, platinum, palladium, alloys of these, tin oxide (Sn02), indium tin oxide (ITO), etc.
), metals with large work functions such as copper iodide, and their alloys and compounds are used.

The thickness of the anode is 100 to 5,000, preferably 200
~1,500 people.

3.3' is a hole transport layer, which transports holes injected from the anode to the light emitting layer.

Examples of the organic compound having a hole transporting ability include 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 I.liphenylamines, stilbene derivatives, oxadiazoles, etc. Specific examples thereof include the following.

The same compound may be used for the hole transport layers 3 and 3',
Different compounds may also be used.

4.4', 4'' are light-emitting layers, and fluorescent organic compounds that are excited by recombination of holes and electrons and emit light are used.Specific compound examples include light-emitting layers N4,4',4''. Compounds each having a different emission spectrum are used.

5.5' is an electron transport layer, which transports the electrons injected from the cathode to the electrostimulant luminescence layer.

As the electron injection/transport material, various conventionally known materials can be used. For example, oxadiazole derivatives as shown below can be used.

C,,H5 The same compound may be used for the electron transport layers 5 and 5',
Different compounds may be used.

6 is a cathode, and a metal having a small work function such as silver, tin, lead, magnesium, manganese, aluminum, or an alloy thereof is used. The cathode also serves as a reflective layer for reflecting light emitted from the light emitting layer and confining it within the device, so it is formed relatively thick. Usually more than 800Å,
Preferably 1. ．． It is better to have a thickness of 500 Å or more.

The following two layers are usually formed by vacuum evaporation, but the electrodes may also be formed by sputtering or the like.

The thickness of the luminescent layer is 50 to 5,000, preferably 10
The thickness of the hole transport layer and the electron transport layer is 200 to 5,000, preferably 500 to 1,000.
, 000 people.

Depending on the compound used as the light emitting layer, either one or both of the hole transport layer and the electron transport layer may be omitted. Further, a protective layer may be provided on the cathode 6 if necessary.

Next, the operation of the electroluminescent device of the present invention will be explained. When a power source is connected between the anode and the cathode and a voltage is applied, when the anode side becomes a high potential with respect to the cathode, holes are injected from the anode and electrons from the cathode are injected into the light emitting layer through their respective transport layers. The injected holes and electrons recombine and lead molecules in the light emitting layer to an excited state. A part of the energy released when the excited molecules return to the ground state is emitted as El light. El light is emitted in all directions, but
It is totally reflected by the cathode 6, and its traveling direction is aligned in the direction of the end face.

At this time, the substrate 1 functions as a light guide path, and most of the light is emitted from the cross section of the substrate 1 at the element end face. Since the cross-sectional area of the substrate 1 is much larger than that of the light emitting layer 4,
The light emission area also increases accordingly.

FIG. 4 shows the compound (E-8), compound (E-9), and compound (E
-10) are shown, respectively.

In the figure, the solid line is the compound (E-10), and the dashed-dotted line is the compound (E-10).
E-8), the broken line is the emission spectrum of compound (E-9). Compound (E-1,0) has an emission peak wavelength of 630n
Compound (E-8) emits green light at 520 nm, and compound (E-9) emits blue light at 460 nm. Therefore, it can be seen that when these light-emitting layers are made to emit light while adjusting the brightness, the light emitted from the device is observed as white.

Conversely, if the brightness of each light-emitting layer is controlled by changing the voltage applied to the electrodes, the frequency, the duty ratio, etc., the light emitted from the device can be changed to any color in the visible range. Since the luminous efficiency varies depending on the compound used in the luminescent layer, it is also possible to correct the brightness by changing the area of the luminescent layer.

In the second example below, a case has been described in which an organic thin film is used as a light-emitting layer for an El element, but it goes without saying that the present invention can also be applied to a type in which an inorganic thin film is used as a light-emitting layer. Further, the light-emitting layer on not only one side of the substrate but also both sides can be divided into a plurality of parts, and a different compound can be used as the light-emitting layer for each part.

〔Effect of the invention〕

In the electroluminescent device of the present invention, luminescent layers are provided on both sides of the transparent substrate, and the substrate itself is configured to serve as a light guide, so it has extremely high brightness compared to conventional edge-emitting electroluminescent devices. In addition, the light emitting area can also be increased.

Furthermore, since a plurality of light emitting layers with different emission spectra are formed on both sides of the substrate, the light emitting layers of the device can be changed as desired. Furthermore, by selecting a material that emits light in three primary colors as the light-emitting layer compound, a light-emitting element that emits light in all visible ranges including white can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a main part of a typical electroluminescent device of the present invention. FIGS. 2 and 3 are schematic cross-sectional views of conventional electroluminescent devices. FIG. 4 shows the luminescence spectra of the compounds contained in the luminescent layer in the present invention. 1: Substrate 2: Anode 3.3': Hole transport J'l 4,4', 4'': Light emitting layer 5.5': Electron transport layer 6: Cathode Patent applicant Rico Co., Ltd.

Claims (2)

[Claims] (1) An anode, at least one or more light emitting layers, and a cathode having light reflecting ability are laminated in this order on both the front and back surfaces of a transparent substrate, and are also formed on one or both of the front and back surfaces of the substrate. A multicolor electroluminescent device characterized in that a light emitting layer is divided into a plurality of parts, and each of the light emitting layers is made of a material having a different emission spectrum. (2) The multicolor electroluminescent device according to claim (1), wherein the light-emitting layer is composed of a plurality of materials having emission peak wavelengths near the three primary colors.