JPH0379692A - Electroluminescent element - Google Patents

Abstract

PURPOSE:To obtain an easily producible electroluminescent element having high luminance and durability to keep the luminous performance over a long period by using a luminescent layer containing a specific polycyclic aromatic organic compound. CONSTITUTION:The objective luminescent element is produced by forming an organic compound of formula 1 (R is alkyl, alkoxy, halogen or nitro) in the form of a thin film by vacuum deposition, solution coating, etc., and sandwiching a luminescent layer containing the above thin film between an anode and a cathode. The organic compound having electron-transfer capability is preferably an oxadiazole derivative of formula II-VI.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has a light-emitting layer made of a light-emitting substance, and can directly convert electrical energy into light energy by applying an electric field. 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]

Electroluminescent devices differ in their emission excitation mechanisms.

(1) An intrinsic electroluminescent device that excites a light emitter through local movement of electrons and holes within the light emitting layer and emits light only in an alternating current electric field; (2) Injection of electrons and holes from electrodes and their There are two types of electroluminescent devices: carrier injection type electroluminescent devices that excite the luminescent material through recombination within the light emitting layer and operate with a direct current electric field. (
I) Intrinsic electroluminescence type light emitting devices are generally made of ZnS and Mn.
, which uses an inorganic compound doped with Cu, etc. as a light emitting body, but it requires a high AC electric field of 200 V or more to drive, is expensive to manufacture, and has insufficient brightness and durability. It has the following problems.

The carrier injection type electroluminescent device (2) has become capable of achieving high luminance since thin film-like organic compounds have been used as the light emitting layer. For example, JP-A-59-19
4393 and U.S. Pat. No. 4,720,432, green light emitting devices are disclosed in Jpn, Journal of Appli.
ed Physics.

Vol, 27. P713-715 discloses a chromophoric light-emitting element, which usually emits high-intensity light under a DC electric field of less than toov.

However, research on carrier injection type electroluminescent devices using organic materials as light emitters, including the above examples, is limited.

It cannot be said that sufficient research into materials and device development has been carried out yet, and the reality is that there are currently many challenges to be solved, such as further improvement of brightness, control of emission wavelength, and improvement of durability. It is.

[Problem to be solved by the invention]

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide an electroluminescent element with excellent durability and long-lasting luminous performance.

[Means to solve the problem]

As a result of intensive studies on the constituent elements of a light-emitting layer to solve the above problems, the present inventors found that the light-emitting layer includes an anode, a cathode, and one or more layers of organic compound thin film sandwiched between the anode and the cathode. The present inventors have discovered that an electroluminescent device in which the light-emitting layer contains a compound represented by the following general formula (1) is effective in solving the above problems, and the present invention has been completed. .

(R represents an alkyl group, an alkoxy group, a halogen, or a nitro group.) That is, the electroluminescent device of the present invention has a light-emitting layer made of one or more organic compound thin films sandwiched between an anode and a cathode. In particular, an organic compound represented by the above general formula (I) is used as the main compound constituting the light emitting layer.

The electroluminescent device in the present invention has the general formula (
It is constructed by forming the organic compound shown in 1) into a thin film by vacuum evaporation, solution coating, etc., and sandwiching it between an anode and a cathode. At that time, a plurality of other substances may be added to the compound as additives. Further, in order to improve the efficiency of charge injection from the electrode, it is also possible to separately provide a charge injection transport layer between the electrode and the charge injection transport layer. The anode materials include nickel, gold, platinum, palladium, alloys thereof, metals with large work functions such as tin oxide (S, O□), indium tin oxide (ITO), iodide steel, and alloys and compounds thereof. For example, conductive polymers such as poly(3-methylthiophene) and polypyrrole can be used. on the other hand,
As the cathode material, silver, tin, lead, magnesium, manganese, aluminum, or an alloy thereof, which has a small work function, is used. It is desirable that at least one of the materials used as the anode and the cathode be sufficiently transparent in the emission wavelength region of the device, specifically, it is desirable that the material has a light transmittance of 80% or more.

Hereinafter, the present invention will be explained along with the drawings.

FIG. 1(a), FIG. 1(b), and FIG. 1(c) are schematic cross-sectional views 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 a light-emitting layer of an organic compound represented by the general formula (1) having a hole transport ability and a light-emitting function, and its film thickness is from 100 Å to 200 Å.
OA is preferable, more preferably 200 to 1000 people
It is in. 3b is a thin film layer of an organic compound having electron transport ability, and its thickness is preferably from 100 Å to 1500 Å, more preferably from 200 Å to 1000 Å.
3c is the general formula (1) having hole transport ability and light emitting function.
) The light emitting layer is a thin film made of a mixture of an organic compound represented by () and an organic compound having an electron transport ability, and the film thickness is preferably 200 Å to 3000 Å, more preferably 400 to 1500 Å. In this case, the mixed composition of both components can be varied in the range of 10/90 to 90/lO by weight. Furthermore, 3d is a thin film layer of another organic compound having hole transport ability.

The film thickness is preferably 100 Å to 1500 Å, more preferably 200 Å to 1000 Å.

In the present invention, the compound represented by the general formula (1) is used as the compound contained in the light emitting layer, and representative examples thereof are shown below.

As an organic compound with electron transport ability, it has an excellent electron injection effect in one light emitting layer, prevents the movement of excitons generated in the light emitting layer to the electron transport layer, and has the ability to form thin films by vacuum evaporation. There are some excellent compounds. Specifically, the oxadiazole derivatives shown below are desirable.

C,H.

When such a compound is used, most of the organic compounds having hole transport ability and light emitting function can be made to emit light by considering the energy levels of the light emitting layer and the electron transport layer.

In the present invention, when a thin film of a mixture of an organic compound having a hole transporting ability and a light emitting function and an organic compound having an electron transporting ability is used as a light emitting layer, the composition is 10/90 to 90% by weight as described above. / Can be changed up to 10. Formation of mixture thin film.

This can be carried out by a vacuum evaporation method, a coating method, a melting method, or the like. In the case of a vacuum evaporation method, simultaneous evaporation can be performed from two resistance heating evaporation sources whose heating temperatures can be independently measured and the evaporation rate can be controlled. In addition, a mixture of fine powders of both substances is placed in one resistance heating evaporation source,
A good mixture thin film can also be created by vapor deposition. Furthermore, it is also possible to create a mixed film with a compositional change in the film thickness direction by using two independent heating evaporation sources and depositing the two substances while independently changing the deposition rate.

The electroluminescent device of the present invention has improved durability.

In order to improve luminous efficiency, one to several organic layers may be inserted between the luminescent layer and the electrode. For example, Figure 1 (C)
As shown in FIG. 3, a thin N! It is also possible to improve the luminous efficiency by providing J3d.

〔Example〕

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

Example 1 Indium-tin oxide (I) with a thickness of 500 Å was used as an anode.
A glass substrate (110 YA!) on which a thin film of TO) was formed was washed with a neutral detergent, and then washed in ethanol for about 10 minutes.
Ultrasonic cleaning was performed for 1 minute. This was placed in boiling ethanol for about 1 minute, and after being taken out, it was immediately blown dry.

Next, a fluorescent organic compound layer (luminescent M) was formed on the glass substrate by vapor depositing a compound represented by the following formula (E-1) using a resistance heating source whose heating temperature was set and whose vapor deposition rate could be controlled. That is, a tantalum boat containing the compound represented by formula (E4) was controlled by a temperature controller, and the deposition rate was maintained at 2 A/S. The accuracy during vapor deposition was 0.7×10 −@torr, and the substrate temperature was 20° C. The thickness of the deposited layer formed on the ITO was 500 Å.

Next, an electron transport substance of the following formula (T
The oxadiazole derivative represented by -1).

An electron transport layer having a thickness of 500 nm was formed by vapor deposition using a resistance heating source with a heating temperature set and a controllable vapor deposition rate. That is, the temperature of the boat containing the compound represented by the following formula (T-1) was controlled, and the deposition rate was maintained at 2λ/S.

Next, a film Jg, tsoo Mg-
A cathode of Ag was deposited. When an external power source was connected to the light emitting device thus obtained and a current was passed through it, clear light emission was observed when a positive bias voltage was applied to the anode side. Furthermore, the device could be operated in air with sufficient humidity removed.

(E-1) (T-1) Example 2 A light-emitting device was produced in the same manner as in Example 1 except that a compound represented by the following formula (E-2) was used as a light-emitting substance.

The obtained light emitting device exhibited clear light emission when a positive bias voltage was applied to the anode side.

Furthermore, this light emitting device could be operated in air with sufficient humidity removed.

Example 3 A light emitting device was produced in the same manner as in Example 1 except that a compound represented by the following formula (E-3) was used as a light emitting substance.

The obtained light emitting device exhibited clear light emission when a positive bias voltage was applied to the anode side.

Furthermore, this light emitting device could be operated in air with sufficient humidity removed.

(E-3) Example 4 Same as Example 1 except that the compound represented by the following formula (E-4) was used as the luminescent substance and the compound represented by the following formula (T-2) was used as the electron transport substance. A light emitting device was manufactured using the following steps. The obtained light emitting device exhibited clear light emission when a positive bias voltage was applied to the anode side.

Furthermore, this light emitting device could be operated in air with sufficient humidity removed.

(E-4) (T-2) [Effects of the Invention] Since the electroluminescent device of the present invention has the above-mentioned configuration, it is easy to manufacture, has high brightness, and is durable so that its luminous performance lasts for a long period of time. It has excellent characteristics.

[Brief explanation of drawings]

FIGS. 1(a) to 1(C) are schematic cross-sectional views of typical electroluminescent devices of the present invention. ■... Substrate, 2, 4... Electrode, 3a, 3c... Light emitting layer, 3b... Electron transport layer, 3d... Hole transport layer. Engraving of the drawings (no change in content) Figure (a) Figure (b) Figure (C) Procedural amendment (method) 1. Indication of the case 1999 Patent Application No. 214203 2. Name of the invention Electroluminescence Element 3: Relationship with the case of the person making the amendment Patent applicant address: 3-6 Nakamagome Ko-chome, Ota-ku, Tokyo Name
(674) Ricoh Co., Ltd. - Representative Hama 1) Hiro 4, Agent 〒151 5, Date of amendment order November 13, 1999 (Shipping date: November 28, 1999)

Claims (1)

[Claims] (1) An electroluminescent device comprising an anode and a cathode, and a light-emitting layer made of one or more organic compound thin films sandwiched between the anode and the cathode, wherein the light-emitting layer has the following general formula (I
) An electroluminescent device characterized by containing a compound represented by: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (R represents an alkyl group, an alkoxy group, a halogen, or a nitro group.)