JPH05114486A - Electroluminescent element - Google Patents

Abstract

PURPOSE:To enable the luminous state of high brightness to be kept for a long time by constituting the radiation layer of an electroluminescent element of a fluorocarbon oil sealed layer. CONSTITUTION:An anode 2 formed with a thin oxide film is provided on a glass substrate 1, and a luminous layer 3 comprising a combination of a hole transport compound and an electron transport compound is formed on the anode 2. In addition, a cathode 4 is formed on the layer 3, using an alloy of Mg, Al or the like. Also, a radiation layer 5 is provided on the cathode 4, and the outside thereof is covered with a seal glass layer 6. Then, cooling media are sealed inside the layer 6. Fluorocarbon oil is used as a material of the layer 5. This oil has a heat transfer rate two times as large as that of silicone oil, and the rate is improved by approximately five times, when the air is forcibly supplied to the oil. Also, when a humidity absorption agent such as zeolite and silica gel is sealed in the layer 5, the ingress of moisture from the air can be prevented, and the radiation effect of the layer 5 can be all the more improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a light emitting layer made of a light emitting material, and can directly convert electric energy into light energy by applying an electric field, which is different from conventional incandescent lamps, fluorescent lamps or light emitting diodes. Differently, the present invention relates to an electroluminescent device that enables realization of a large-area planar light-emitting body.

[0002]

2. Description of the Related Art In electroluminescence devices, due to the difference in their light emission excitation mechanism, (1) Intrinsic electroluminescence which excites a light emitter by local movement of electrons and holes in a light emitting layer and emits light only in an AC electric field. The element is divided into (2) a carrier injection type electroluminescent element which operates by a DC electric field by injecting electrons and holes from an electrode and recombining the electrons and holes in the emitting layer to excite a luminescent body. The intrinsic electroluminescence type light emitting device of (1) generally uses an inorganic compound in which Mn, Cu, etc. are added to ZnS as a light emitting body, but requires a high AC electric field of 200 V or more for driving, There are problems such as high cost and insufficient brightness and durability. In the carrier injection type electroluminescent device of (2), a thin film organic compound has been used as a light emitting layer, and a high brightness device has been obtained. For example, JP-A-59-194
393, U.S. Pat. No. 4,539,507, JP-A-63-2
95695, U.S. Pat.
3-264692 includes an anode, an organic hole injection transporter,
An electroluminescent device composed of an organic electron injecting luminescent material and a cathode is disclosed, and materials used for these are:
For example, aromatic tertiary amines are cited as typical examples of organic hole injecting and transporting materials, and aluminum trisoxine and the like are cited as typical examples of organic electron injecting light emitting materials.

In addition, Jpn. Journal of Ap
plied Physics, vol. 27, p713
In -715, an electroluminescent device including an anode, an organic hole transport layer, a light emitting layer, an organic electron transport layer, and a cathode is reported. Materials used for these are N as an organic hole transport material, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-biphenyl-4,
4'-diamine is also an organic electron transport material,
Bisbenzimidazole 3,4,9,10-perylenetetracarboxylic acid is exemplified, and phthaloperinone is exemplified as the light emitting material. In these examples, in order to use an organic compound as a hole transport material, a light emitting material, and an electron transport material, it is necessary to explore various characteristics of these organic compounds and effectively combine these characteristics to form an electroluminescent device. In other words, it means that research and development of a wide range of organic compounds is necessary. Further, including the above examples, the carrier injection type electroluminescent device using an organic compound as a light emitter has a short history of research, and it cannot be said that the material research and device research have been sufficiently conducted. At present, there are many problems such as further improvement of brightness and diversification of emission wavelength or improvement of durability for precise selection of emission hues of blue, green and red when considering full color display. The reality is that they are holding.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and an object thereof is an electroluminescent device having high emission brightness, exhibiting various emission hues, and excellent durability. To provide.

[0005]

The inventors of the present invention have found that the short life of conventional electroluminescent devices is caused by heat generated when a current is applied and moisture in the air by which an organic electron transport layer and an organic hole transport layer are formed. It was found that the cause is to promote crystallization of the layer and peeling of the film.

In order to solve the above-mentioned problems, the inventors of the present invention promote the heat dissipation of an element in an electroluminescent element composed of an anode and a cathode, and an organic compound of one layer or a plurality of layers sandwiched between them. Therefore, it has been found that an electroluminescent element featuring an element having a layer in which fluorocarbon oil is sealed as a heat dissipation layer is effective for the above problems. Further, in the fluorocarbon oil enclosed as a heat dissipation layer in order to prevent the inclusion of water in the air, it was found that the electroluminescent element mixed with a hygroscopic agent shows a further excellent effect on the above problems, the present invention It came to completion.

That is, according to the present invention, in an electroluminescent device having a heat dissipation layer on at least one of an anode and a cathode, and composed of one or more organic layer compounds sandwiched therebetween, An electroluminescent device is provided in which the heat dissipation layer is a layer in which fluorocargon oil is encapsulated, and a hygroscopic agent is mixed in the fluorocarbon oil encapsulated as the heat dissipation layer. The electroluminescent device according to 1. is provided.

The fluorocarbon oil used in the heat dissipation layer in the present invention has a heat transfer property of about 0.00017 cal / cm · s.
It is ec · ° C. (25 ° C.), shows twice the heat transfer property of silicone oil, and is a compound having an extremely excellent heat transfer property with the property that the heat transfer property is improved by about 5 times when forced air is blown. Furthermore, the fluorocarbon oil exhibits excellent thermal stability and chemical inertness, does not attack the electrodes or organic compounds, and the fluorocarbon oil itself is stable to these materials. Further, the dielectric strength of the fluorocarbon oil is 35 kV or more per 2.54 mmgap, which is extremely large, and therefore exhibits excellent electrical insulation. Therefore, the use of fluorocarbon oil as the heat dissipation layer of the electroluminescent device is extremely effective in promoting heat dissipation of the device.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a typical electroluminescent device of the present invention. Reference numeral 1 is a glass substrate or synthetic resin substrate, and 2 is an anode formed on the substrate. 2 is formed by vapor deposition of a metal such as gold, platinum or palladium, a sputtered film or a thin oxide film (ITO) of tin or indium tin oxide, and is preferably transparent in the wavelength region of 400 nm or more in order to take out light emission. Reference numeral 3 is a light emitting layer made of a combination of a hole transporting compound and an electron transporting compound.

Examples of the electron-donating organic compound having a hole-transporting ability include a polymer compound having an excellent hole-transporting ability such as polyvinylcarbazole and a low-molecular compound having an excellent hole-transporting ability. Examples of the low molecular weight compound include triphenylamines, stilbene derivatives, oxadiazoles and the like, and specific examples thereof include the following.

[0011]

[Table 1]

As the light emitting organic compound, a substance having an electron transporting property or a hole transporting property and emitting strong fluorescence in a solid state is used. Examples of the electron-transporting substance include a perinone derivative and a quinoline complex derivative, and specific examples thereof include the following substances.

[0013]

[Table 2]

Examples of the hole-transporting substance include triphenylamine derivatives, oxadiazole derivatives, and triphenylamine derivatives. Specific examples thereof include the following substances.

[0015]

[Table 3]

The light-emitting layer is a single layer in which a compound having a hole-transporting property, an electron-transporting property and a light-emitting property is used alone, or a multi-layer comprising a combination of a hole-transporting compound, a light-emitting compound or an electron-transporting compound. It may be formed of.
Reference numeral 4 denotes a cathode, which is formed on the light emitting layer by vacuum vapor deposition of a metal, and any metal capable of being vacuum vapor deposited can be used as the material, but a metal having a small work function, particularly Mg, Al, Ag, It is desirable to use In, Sn, Pb, Mn, or an alloy thereof.

Reference numeral 5 is a heat dissipation layer, which is formed by covering the outside with a sealing glass 6 and enclosing a cooling solvent. As described above, the fluorocarbon oil is used as the material of the heat dissipation layer to prevent the temperature rise of the element. If a moisture absorbent such as zeolite or silica gel is further enclosed in the heat dissipation layer of No. 5, it is possible to prevent the ingress of water from the air, so that the effect is further exerted. In FIG. 1, the heat dissipation layer is provided on only one of the glass substrates, but the heat dissipation layer may be provided on both sides as in FIG. In this case, it is desirable that the hygroscopic agent is mixed in the layer opposite to the transparent electrode so as not to interfere with light emission.

[0018]

EXAMPLES The present invention will be described more specifically below based on examples. Example 1 Size 3 mm × 3 mm, thickness 1000Å on a glass substrate
Forming an anode of indium tin oxide (ITO)
On top of that, 1,1-bis (4-N, N-) is formed as a hole transport layer.
Ditrylaminophenyl) cyclohexane 500Å, tris (8-hydroxyquinoline) aluminum 500Å as an electron transport layer, and a cathode 1500 made of aluminum
Å was laminated in this order by vacuum vapor deposition to fabricate a device. The degree of vacuum during vapor deposition is about 6 × 10 ⁻⁶ torr, and the substrate temperature is room temperature. The thus-produced element was covered with a seal glass as shown in 6 of FIG. 1 and the fluorocarbon oil therein was used as Fluorinert (trade name) manufactured by Sumitomo 3M Limited.
By enclosing FC-70, an element having a structure as shown in FIG. 1 was produced. When a DC power source was connected to the anode and cathode of this device through a lead wire and a voltage of 20 V was applied in the atmosphere at 25 ° C, a current with a current density of 78.9 mA / cm ² flowed through the device and the yellowish green color was clear. It was confirmed that various light emission. The initial luminance at this time was 1900 cd / m ² . When continuous driving was performed under these conditions, the time until the luminance decreased to 50% was 300 minutes.

Example 2 A device was manufactured in the same manner as in Example 1 except that zeolite dried in vacuum at 150 ° C. was mixed in the solvent for the heat dissipation layer. A direct current power supply was connected to the anode and cathode of the device thus produced via lead wires, and a voltage of 20 V was applied in the atmosphere at 25 ° C. to obtain a current density of 79.2.
A current of mA / cm ² was passed through the device, and clear emission of yellowish green was confirmed. The initial luminance at this time was 1920 cd / m ² . Next, after leaving the device at 25 ° C. in saturated water vapor for 10 days and applying a voltage of 20 V in the atmosphere at 25 ° C., a current having a current density of 75.2 mA / cm ² was passed through the device and a clear yellowish green color was obtained. Luminescence was confirmed. The brightness at this time is 1810
It was cd / m ² .

Example 3 An element was manufactured in the same manner as in Example 1 except that zeolite dried in vacuum at 150 ° C. was mixed in the solvent of the heat dissipation layer. A DC power source was connected to the anode and cathode of the device thus produced through lead wires, and a voltage of 20 V was applied in an atmosphere of 25 ° C. saturated water vapor, and a current density of 79.8 mA / cm ² was obtained. After flowing through the device, clear yellow-green light emission was confirmed. The initial brightness at this time is 192
It was 0 cd / m ² . When continuous driving was performed under these conditions, the time until the luminance decreased to 50% was 300 minutes.

Comparative Example 1 A device was prepared in the same manner as in Example 1 except that the heat dissipation layer was omitted. When a direct current power supply was connected to this element through a lead wire and a voltage of 20 V was applied in the atmosphere at 25 ° C., a current with a current density of 75.9 mA / cm ² was passed through the element, and clear yellow-green light emission was confirmed. It was The initial luminance at this time was 1980 cd / m ² . When continuous driving is performed under these conditions, the time until the brightness drops to 50% is
It was 10 minutes. Further, when such a device was left in saturated steam at 25 ° C. for 10 days and then a voltage of 20 V was applied in the atmosphere at 25 ° C., a current having a current density of 42.2 mA / cm ² flowed through the device and a clear yellowish green color was observed. Luminescence was confirmed, but the brightness at this time was 510 cd / m ² .

[0022]

(1) Operation and effect corresponding to claim 1 The electroluminescent device according to claim 1 uses fluorocarbon oil as a heat dissipation layer, so that heat generation of the device can be suppressed and the electroluminescent device can have a long driving voltage. It is possible to emit light with high brightness over time. (2) Operation and Effect Corresponding to Claim 2 In the electroluminescent device according to claim 2, since the moisture absorbing agent is further enclosed in the heat dissipation layer, it is possible to perform both cooling and water absorbing functions in a single layer. As compared with the case where the water absorption layer and the water absorption layer are separately provided, the element can be made thinner and the manufacturing process can be simplified.

[Brief description of drawings]

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

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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yota Sakon 1-3-3 Nakamagome, Ota-ku, Tokyo Stock company Ricoh Co., Ltd. (72) Toshihiko Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo Shares Company Ricoh

Claims (3)

[Claims] 1. An electroluminescent device comprising a heat-dissipating layer on at least one of an anode and a cathode, and comprising one or a plurality of organic compound layers sandwiched therebetween, wherein the heat-dissipating layer is a fluorocarbon oil. An electroluminescent device, which is a layer in which is encapsulated. 2. The electroluminescent device according to claim 1, wherein a hygroscopic agent is mixed in fluorocarbon oil sealed as a heat dissipation layer. 3. The light emitting layer is an electroluminescent layer comprising a combination of a hole transporting compound and an electron transporting compound.
The electroluminescent element described.