JPH03110786A - Organic electroluminescence device - Google Patents

Abstract

PURPOSE:To exercise a stable performance even in the repeating service by providing a device to apply a power of the polarity reverse to the polarity in the luminous time. CONSTITUTION:A device to apply a negative voltage to an electrode 1 being the positive electrode in the luminous time, and a positive voltage to an electrode 4 being the negative electrode in the luminous time, from a power source 9, by turning on a switch 8 after a luminous process is finished and a switch 6 is turned off, is provided. A reduction of the luminous intensity owing to the repeated service is considered to be resulting from a cause accumulating the charge by a trap or the like at the interface between an organic hole pouring layer 2 and an organic luminous layer 3. Consequently, the charge accumulated by the repeated service is removed by feeding a power of the polarity reverse to the polarity in the luminous time. The repeating performance is improved extensively, accordingly.

Description

[Detailed description of the invention] Industrial applications The present invention relates to organic electroluminescent devices.

BACKGROUND OF THE INVENTION Organic electroluminescent devices are devices that emit light in response to electrical signals and are constructed using organic compounds as light-emitting substances.

An organic electroluminescent device basically consists of a pair of opposing electrodes sandwiching an organic light-emitting layer and a nucleus layer. Light emission occurs when electrons are injected from one electrode and holes are injected from the other electrode, which excites the luminescent material in the luminescent layer to a higher energy level, and the excited luminescent material returns to its original state. This is a phenomenon in which excess energy is released as light when returning to the ground state.

In order to increase luminous efficiency, in addition to the above basic configuration, a hole injection layer is further provided in the electrode for injecting holes.

An example of an organic electroluminescent device is one that uses single crystal anthracene as a light emitting material.
It is described in the specification of P3530325.

Further, Japanese Patent Application Laid-Open No. 59-194393 proposes a combination of a hole injection layer and an organic light emitting layer.

JP-A-63-295695 proposes a combination of an organic hole injection transport layer and an organic electron injection transport layer.

However, although the emission intensity of organic electroluminescent devices has been improved by improving the structure,
On the other hand, it has a major problem of poor stability during repeated use.

Therefore, there is currently a desire to develop an organic electroluminescent device that has good characteristics such as stronger emission intensity and excellent repeat stability.

Problems to be Solved by the Invention The present invention has been made in view of the above circumstances, and its purpose is to provide an organic electroluminescence device that exhibits stable performance even when used repeatedly. It is in.

Means for Solving the Problems The present invention provides an organic electroluminescence device including at least one set of counter electrodes, an organic hole injection transport layer, and an organic light emitting layer, which includes means for applying electric power with a polarity opposite to that of light emission. The present invention relates to an organic electroluminescence device characterized by the following.

FIG. 1 schematically shows the basic configuration of the electroluminescence device of the present invention. In the figure, (1) is an electrode that becomes an anode during light emission, and on top of it are an organic hole injection transport layer (2), an organic light emitting layer (3), and an electrode (4) that becomes a cathode during light emission. It has a sequentially laminated structure.

When making an organic electroluminescent device emit light,
Connect the switch (6) and connect the electrode (
A positive voltage is applied to electrode (1) and a negative voltage is applied to electrode (4).

To stop the light emission, just disconnect the switch (6) and stop the power supply. Usually, if the light is emitted again and then extinguished, the above procedure is repeated.

In addition to the above-mentioned power supply means at the time of light emission, the present invention further provides:
Means for applying power of the opposite polarity to that when power is supplied during light emission, that is, after the light emission process is completed and the switch (6) is disconnected, the switch (8) is connected and the power supply source (9
), a negative voltage is applied to the electrode (1) which is used as an anode during light emission.
It is characterized by being provided with means for applying a positive voltage to the electrode (4) which serves as a cathode during light emission.

By adding such means, it is possible to improve the reduction in luminescence intensity due to repeated use.

The decrease in luminescence intensity due to repeated use is thought to be caused by charge accumulation due to traps, etc. at the interface between the organic hole injection layer and the organic light emitting layer. This can be removed by supplying power with a polarity opposite to that used when emitting light, and by doing so, the repeatability can be significantly improved.

The magnitude of the voltage applied with the opposite polarity to that at the time of light emission may be lower than the voltage applied at the time of light emission, and if the magnitude is too large, deterioration will progress instead.

The power supply source (8) may be a DC voltage power supply or an AC voltage power supply.

The conductive material used for the electrode (1) used as an anode during light emission of an organic electroluminescence device is 4
Those with a work function larger than eV are preferred, and carbon, aluminum, vanadium, iron, cobalt, nickel, copper, zinc, tungsten, silver, tin, gold, and their alloys, tin oxide, and indium oxide value are used. .

The metal forming the electrode (4) used as a cathode during light emission is preferably a metal with a work function smaller than 4eV, such as magnesium, calcium, titanium, yttrium, lithium, gadolinium, ytterbium, ruthenium, manganese, and their like. Alloys are used.

In an organic electroluminescent device, at least an electrode (1) or an electrode (2) is provided so that light emission can be observed.
) is a transparent electrode. At this time, an electrode (
If a transparent electrode is used in 4), the transparency is likely to be impaired, so it is preferable that the electrode (1), which serves as an anode during light emission, be a transparent electrode.

When forming a transparent electrode, a conductive material such as that described above may be used on a transparent substrate, and the electrode may be formed by vapor deposition, sputtering, or the like to ensure desired translucency.

The transparent substrate is not particularly limited as long as it has appropriate strength, is not adversely affected by heat caused by vapor deposition, etc. during the production of the electroluminescent device, and is transparent. Examples of such substrates include glass substrates, transparent substrates, etc. It is also possible to use resins such as polyethylene, polypropylene, polyether sulfone, polyether ether ketone, etc.

IT has transparent electrodes formed on a glass substrate.
Commercially available products such as OlNESA are known and may be used.

When forming the electroluminescent device of the present invention, an organic hole injection and transport layer (2) is formed on the electrode (1) which serves as an anode at the time of sale.

Compounds used in the organic hole injection transport layer include triphenylamine compounds, pyrazoline compounds, stilbene compounds, oxadiazole compounds, oxatriazole compounds, hydrazone compounds, butadiene compounds, triphenylmethane compounds, tetraphenylbenzidine compounds, and these compounds. Derivatives of etc. are used. Among these, a butadiene compound represented by the following general formula [11] is particularly preferred.

rl Ars [wherein Ar, , Ar, and Ars are each an aryl group which may have a substituent, and at least one has a di-substituted amino group; Ar is hydrogen, an alkyl group,
Each represents an aralkyl group, an aryl group, or a heterocyclic group which may have a substituent. ] In the general formula [11], Ar, , Ar2 and Ar.

each represents an aryl group such as phenyl or naphthyl,
The aryl group may have a substituent such as a halogen atom, an alkyl group, an alkoxy group or a di-substituted amino group.

At least one of the substituents Ar and ~Ar preferably has a di-substituted amino group, and examples of the di-substituted amino group include a dialkylamino group, a dialkylamino group, a diarylamino group, and a diallylamino group. .

Ar is a hydrogen atom, a methyl group, an alkyl group such as ethyl,
It represents an aralkyl group such as benzyl or 7-enethyl, an aryl group such as phenyl or naphthyl, or a heterocyclic residue such as thiophene, dioxindane, or pyridine.

Examples of substituents for Ar4 include halogen atoms, alkyl groups, alkoxy groups, and di-substituted amino groups.

The organic hole transport layer (2) may be formed by vapor depositing the above compound, or may be formed by spin-coding a suitable resin solution of the above compound.

When formed by vapor deposition, the thickness is usually 0°O1~0
．． 3 μm, and when formed by the spin cord method, the butadiene compound etc. is 20 to 80% by weight based on the binder resin.
The thickness is 0.05 to 1.0 μm so that the content is about
It is sufficient to form it to a certain extent.

An organic light emitting layer is formed on the organic hole transport layer (2) thus formed.

As the organic light-emitting substance used in the organic light-emitting layer, known ones can be used, such as evitridine, 2,5-bis[5,7-di-t-pentyl-2-benzoxazolyl 1
Thiophene, 2.2'-(1,4-] dinylene divinylene) bisbenzothiazole, 2.2'(4,4'-biphenylene) bisbenzothiazole, 5-methyl-2-(
2-[4-(5-methyl-2-benzoxazolyl)phenyl]vinyl)benzoxazole, 2,5-bis(5
-Methyl-2-benzoxazolyl)thiophene, anthracene, naphthalene, phenanthrene, pyrene, chrysene, perylene, perinone, 1,4-diphenylbutadiene, tetraphenylbutadiene, coumarin, macridinestilbene, 2-(4-biphenyl)- 6-7enylbenzoxazole, aluminum trisoxine, magnesium bisoxine, bis(benzo-8-quinolitool)zinc, bis(2-methyl-8quinolinolado) aluminum oxide, indium trisoxine, aluminum tris(5-methyloxine), Lithium oxine, gallium trioxin, calcium bis(5-chlorooxine), polyzinc-bis(8-hydroxy-5
-quinolinonyl)methane)dilithium epindolidione, zinc bisoxine, 1.2-phthaloperinone, 1.2
- Su7ri loperinone and the like can be mentioned. Also,
- Intrashell fluorescent dyes such as fluorescent coumarin dyes, fluorescent perylene dyes, fluorescent pyran dyes, fluorescent thiopyran dyes, fluorescent polymethine dyes, fluorescent merocyanine dyes, fluorescent imidazole dyes, etc. can also be used. Among these, particularly preferred are chelated oxinoid compounds.

The organic light-emitting layer may have a single layer structure of the above-mentioned light-emitting substance, or
A multilayer structure may be used to adjust characteristics such as the color of the emitted light and the intensity of the emitted light.

Next, an electrode is formed on the organic light-emitting layer to serve as a cathode during the above-described light emission.

The case where an organic luminescent device is formed by sequentially stacking an organic hole injection transport layer (2), a light-emitting layer (3), and a cathode (4) on an electrode (1) that functions as an anode at the time of sale has been described above. The device may be manufactured by sequentially laminating a light emitting layer (3), an organic hole injection transport layer (2) and an anode on an electrode (4) which serves as a cathode at the time of sale.

One set of electrodes is made by connecting a suitable lead wire (5) such as nichrome wire, gold wire, copper wire, platinum wire, etc. to each electrode, and applying a positive voltage to electrode (1) and electrode (4) when emitting light as described above. ) and a means for turning on and off a negative voltage to the electrode (1) after the completion of light emission.
A means is provided for turning on and off a negative voltage on the electrode (4) and a positive voltage on the electrode (4).

The organic electroluminescent device of the present invention can be applied to various display devices or display devices.

The present invention will be explained below with reference to Examples.

A butadiene compound represented by the following structural formula was deposited on glass coated with indium tin oxide to form a thin film with a thickness of 500 mm.

Next, 500% of aluminum trisoxine was deposited by vapor deposition.
A thin film was formed to have the thickness of a human.

Next, a thin film with a thickness of 200 OA was formed using Mg and Ag at an atomic ratio of 10:1 as a cathode.

In this way, an organic electroluminescent device was produced.

Evaluation Example The obtained electroluminescent device was heated for 5 minutes while applying a bias voltage using its glass electrode as an anode.
It was operated for 1 hour at a current density of mA/cm''.

The initial output is from 0.1 mW/cm” to 0.09 mW/
c+++”. After operating for another hour, the temperature dropped to 0.
．． It decreased to 085 mW/cm''.

Next, short-circuit both poles and apply a bias voltage of - opposite to that used when emitting light.
After applying 20V for 30 minutes, it was operated again at a current density of 5mA/cm2; however, the initial output was O, 1mW.
/cm”.

COMPARATIVE EXAMPLE After operating the electroluminescent device obtained in Example for 2 hours, the picture electrode was short-circuited and an additional 5 mA was applied.
When operated at a current density of 0.09 mW/cm”
The output only recovered to "cm".

Effects of the Invention According to the present invention, an organic electroluminescent device can be used with good durability while maintaining the initial luminescence intensity by providing a means for supplying power of opposite polarity to the time of light emission.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an electroluminescent device of the present invention. 1: Electrode 2: Organic hole injection transport layer 3: Light emitting layer 4: Electrode 5: Lead wire 6: Switch 7: Power supply source 8: Switch 9: Power supply source

Claims (1)

[Claims] 1. What is claimed is: 1. An organic electroluminescent device comprising at least one set of counter electrodes, an organic hole injection transport layer, and an organic light emitting layer, the organic electroluminescent device comprising means for applying electric power having a polarity opposite to that of light emission.