JPH0790255A - Organic electroluminescent device - Google Patents

Abstract

(57) [Summary] [Structure] An organic electroluminescence device comprising an organic layer sandwiched by an anode and a cathode on a substrate, the organic layer comprising at least an organic hole transporting substance, an electron transporting substance and a fluorescent substance. And an organic electroluminescent device comprising a polyvinyl triarylamine having a repeating unit represented by the following general formula (I) as the organic hole transporting substance. [Chemical 1] [Effect] By using polyvinyl triarylamine as the organic hole transporting material, it is possible to obtain a device having heat resistance and exhibiting stable light emission characteristics even after long-term driving.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device, and more particularly to a thin film type device which emits light by applying an electric field to a light emitting layer made of an organic compound.

[0002]

2. Description of the Related Art Conventionally, as a thin film type electroluminescent (EL) element, Zn which is a II-VI group compound semiconductor of an inorganic material has been used.
It is general that S, CaS, SrS, etc. are doped with Mn or a rare earth element (Eu, Ce, Tb, Sm, etc.), which is the emission center, but the EL element made from the above inorganic material is 1). AC drive is required (50 to 1000 Hz), 2) high drive voltage (up to 200 V), 3) full colorization is difficult (especially blue is a problem), and 4) peripheral drive circuit costs are high. ing.

However, in recent years, in order to improve the above problems,
EL devices using organic thin films have been developed. In particular, the electrode type was optimized for the purpose of improving the efficiency of carrier injection from the electrode in order to increase the light emission efficiency, and the organic hole transport layer made of an aromatic diamine and the organic light emission made of an aluminum complex of 8-hydroxyquinoline. Of an organic electroluminescent device having a layer (Appl. Phy
s. Lett. , 51, p. 913, 1987), the luminous efficiency is greatly improved as compared with the conventional electroluminescent device using a single crystal such as anthracene, and is close to practical characteristics.

In addition to the above materials, poly (p-phenylene vinylene) (Natur is used as a material for the organic light emitting layer).
e, 347, 539, 1990; Appl. Ph
ys. Lett. , 61, 2793, 1992
Year), poly [2-methoxy, 5- (2'-ethylhexoxy) -1,4-phenylenevinylene] (Appl.P).
hys. Lett. , 58, 1982, 1991.
Year; Thin Solid Films, Volume 216, 9
6 1992; Nature, 357, 477.
P., 1992), poly (3-alkylthiophene)
(Jpn. J. Appl. Phys, 30 volumes, L193
8 pages, 1991; Appl. Phys. , 72
Vol., P. 564, 1992), etc.
A device in which a light emitting material and an electron transfer material are mixed with a polymer such as polyvinylcarbazole (Applied Physics, 61, 1044
Page, 1992) is also being developed.

[0005]

The biggest problem of the organic electroluminescent device is the service life during driving. Although there are several factors that shorten the life of the device, the deterioration of the thin film shape of the organic layer is dominant. It is considered that the deterioration of the shape of the thin film is caused by crystallization (or aggregation) of the organic amorphous film due to heat generated when the device is driven.

Many low molecular weight compounds (having a molecular weight of about 400 to 600), especially low molecular weight compounds used as hole transport materials, have a low glass transition temperature (Tg). For example, in an aromatic diamine compound, -23 to 8
2 ° C. (US Pat. No. 4,127,412), 39-78
° C (The 51st Japan Society of Applied Physics, 28a-PB-3, 199)
A Tg of 0 years) has been reported. In many organic amorphous thin films formed from the above compounds, crystallization is accelerated by the temperature rise, and as a result, an island-like aggregate structure is exhibited. If such crystallization occurs, phenomena such as a decrease in light emission efficiency, the occurrence of a non-light emitting portion called a dark spot, a short circuit, etc. appear as deterioration of the light emitting characteristics of the device, and finally the driving life is shortened. It is desirable that the Tg is 100 ° C. or higher because the temperature is expected to rise in the steps of vapor deposition, baking (annealing), wiring, encapsulation, etc. when the element is manufactured, other than when the element is driven.

On the other hand, it has been attempted to use a polymer material as an organic hole transport material of an organic electroluminescence device instead of a low molecular weight compound. Polyvinylcarbazole (Technical report of IEICE, OME90-38, 1990)
Year), polysilane (Appl. Phys. Lett.,
59, 2760, 1991), Polyphosphazene (The 42nd Annual Meeting of the Polymer Society of Japan, I-8-07 and I)
-8-08, 1993) and the like have been reported, but polyvinylcarbazole (PVK) has a high Tg of 200 ° C., but has a problem such as a trap and the like, and has low durability, and polysilane has a driving life due to photodegradation or the like. As short as a few seconds, polyphosphazene has a high ionization potential and does not exhibit properties superior to conventional aromatic diamines. A hole transport layer in which an aromatic diamine compound is dispersed in polycarbonate or polymethylmethacrylate (PMMA) in an amount of 30 to 80% by weight has also been studied (Jpn. J. App.
l. Phys. , 31, L960, 1992),
The low molecular weight compound acts as a plasticizer to lower the Tg, and the device characteristics are lower than those of the aromatic diamine compound. In addition to this, an element in which PVK or the like is mixed with an electron transporting material, a fluorescent material, or the like to form a film by a wet coating method, but as described above, PVK has a problem such as a trap and the like, and thus is not practical. Can be said.

For the above-mentioned reasons, the organic electroluminescence device has a serious problem in driving life of the device for practical use.

[0009]

In view of the above situation, the present inventors have aimed to provide an organic electroluminescent device which exhibits stable light emission characteristics over a long period of time, and is inexpensive and easy to manufacture. As a result of diligent studies, it was found that it is preferable to use polyvinyl arylamine as the organic hole transporting material in the integrated device of the light emitting layer and the charge transporting layer, and the present invention has been completed.

That is, the gist of the present invention is an organic electroluminescence device comprising an organic layer sandwiched by an anode and a cathode on a substrate, the organic layer being at least an organic hole transporting substance and an electron transporting substance. And a polyvinyl triarylamine containing a fluorescent substance and having a repeating unit represented by the following general formula (I) as the organic hole transporting substance.

[0011]

[Chemical 2]

(In the formula, Ar ¹ represents an arylene group which may have a substituent, Ar ² and Ar ³ represent an aryl group which may have a substituent, and the substituents are each independently. , An alkyl group, an alkenyl group, an allyl group, an alkoxycarbonyl group, an alkoxy group and an amino group.) Hereinafter, the organic electroluminescent device of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view schematically showing an example of the structure of the organic electroluminescence device of the present invention, in which 1 is a substrate, 2a and 2b.
Represents a conductive layer and 3 represents an organic light emitting layer. The substrate 1 serves as a support for the organic electroluminescent element of the present invention, and is usually a quartz or glass plate, a metal plate or metal foil, a plastic film or sheet, and the like. Polymethacrylate, polycarbonate,
A transparent synthetic resin substrate such as polysulfone is preferable.

A conductive layer 2a is provided on the substrate 1,
This conductive layer 2a is usually a metal such as aluminum, gold, silver, nickel, palladium, tellurium, indium and / or
Alternatively, a metal oxide such as tin oxide, copper iodide, carbon black, or a conductive polymer such as poly (3-methylthiophene) is used. The conductive layer is usually formed by a sputtering method, a vacuum deposition method or the like, but fine particles of metal such as silver or copper iodide, carbon black, fine particles of conductive metal oxide, fine powder of conductive polymer, etc. In this case, it can also be formed by dispersing it in an appropriate binder resin solution and applying it on a substrate. Further, in the case of a conductive polymer, a thin film can be directly formed on the substrate by electrolytic polymerization, or can be formed by coating on the substrate (Appl. Phys. Lett., 60).
Vol. 2711, 1992). The thickness of the conductive layer 2a is
Although it depends on the required transparency, when the transparency is required, the visible light transmittance is 60% or more, preferably 8%.
It is desirable to transmit 0% or more, and in this case, the thickness is
Usually 5 to 1000 nm, preferably 10 to 500 nm
It is a degree. The conductive layer 2a may be the same as the substrate 1 if it is opaque. The conductive layer 2a may be formed by stacking different substances.

In the example of FIG. 1, the conductive layer 2a plays a role of hole injection as an anode. on the other hand,
The conductive layer 2b functions as a cathode to inject electrons into the organic light emitting layer 4. As the material used for the conductive layer 2b, the material for the conductive layer 2a can be used, but a metal having a low work function is preferable for efficient electron injection, and tin, magnesium, indium, and aluminum are preferable. A suitable metal such as silver, silver, or an alloy thereof is used. The thickness of the conductive layer 2b is usually the same as that of the conductive layer 2a. Also, although not shown in FIG.
A substrate similar to the substrate 1 can be further provided on the conductive layer 2b. However, it is necessary for the EL element that at least one of the conductive layers 2a and 2b has good transparency. From this, one of the conductive layers 2a and 2b is 10 to 500
The film thickness is preferably nm, and it is desired that the film has good transparency. Further, like the conductive layer 2a, the conductive layer 2b may be formed by stacking different substances.

The organic layer 3 is provided on the conductive layer 2a. As the organic hole transporting material contained in the organic layer, the hole injection efficiency from the conductive layer 2a is high and the injected positive hole is positive. It must be a material that can efficiently transport the pores. For that purpose, it is required that the ionization potential is small, the hole mobility is large, the stability is excellent, and impurities that serve as traps are hard to be generated during manufacturing or use.

The present invention is characterized by containing a polyvinyltriarylamine having a repeating unit represented by the general formula (I) as an organic hole transporting substance. In the general formula (I), Ar ¹ is preferably a phenylene group which may have a substituent, and Ar ² and Ar ³ are optionally substituted phenyl groups, naphthyl groups and anthryl. A fused aromatic ring group which may have a substituent such as a group is shown. Each of the above substituents independently has an alkyl group having 1 to 6 carbon atoms such as a methyl group or an ethyl group; an alkenyl group such as a vinyl group; an allyl group; a carbon number 1 to 6 such as a methoxycarbonyl group or an ethoxycarbonyl group. Alkoxycarbonyl group: C1 such as methoxy and ethoxy groups
~ 6 alkoxy group; selected from amino groups such as dimethylamino group and diethylamino group.

The number average molecular weight of the polymer having the repeating unit represented by the general formula (I) is preferably 500 to
2,000,000, particularly preferably 1,000 to 10,000
00 is desirable. In the present invention, the hole mobility can be increased by introducing triarylamine as a side chain of polyvinyl, and at the same time, T
It is possible for g to be 100 ° C. or higher.

The polyvinyltriarylamine represented by the above general formula (I) is, for example, JP-A-1-10595.
It is synthesized by the method disclosed in Japanese Patent No. 4 publication. Specific preferred examples of the polyvinyltriarylamine represented by the general formula (I) are shown in Tables 1 and 2 below.
It is not limited to these.

[0020]

[Table 1]

[0021]

[Table 2]

Further, the polyvinyltriarylamine used in the present invention may have a copolymerization part other than the polyvinyltriarylamine of the general formula (I). Examples of the electron transport material include oxadiazole derivatives (Appl. Phys. Lett., 5
5: 1489, 1989; Jpn. J. App
l. Phys. , Vol. 31, p. 1812, 1992) and the like.

[0023]

[Chemical 3]

[0024]

[Chemical 4]

The mixing ratio of the electron transport layer material in the organic layer may be any ratio as long as it does not cause precipitation.
Usually, it is 5 to 80 parts by weight, preferably 10 to 70 parts by weight. Examples of the fluorescent substance that can be used in the present invention include:
Dyes such as coumarins, dyes for laser, fluorescent brightening agents, dyes for scintillation counter, and the like, which can be arbitrarily used from compounds exhibiting fluorescence.

As a film forming method, a wet coating method, a vacuum vapor deposition method and the like can be considered. In the case of the wet coating method, the polyvinyltriarylamine, the electron transporting material and the fluorescent material are chloroform, dichloroethane, tetrahydrofuran ( THF), dissolved in an organic solvent such as toluene, and then the conductive layer 2a is formed by a method such as spin coating or dipping.
The organic layer 3 is formed by coating the above and heating and drying. At this time, it is desirable not to use a binder resin or the like. In particular,
The spin coating method is preferable in order to form a uniform thin film on the submicron order without defects such as pinholes. In addition, it is also possible to form a film by ternary simultaneous vapor deposition of polyvinyltriarylamine, an electron transport substance and a fluorescent substance using a vacuum vapor deposition method or the like.

The thickness of the organic hole transport layer 3 formed as described above is usually 10 to 300 nm, preferably 3
It is 0 to 100 nm. In the present invention, by using polyvinyl triarylamine as the organic hole transporting material, it is possible to obtain an element having heat resistance and exhibiting stable light emission characteristics even after long-term driving.

[0028]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the description of the following examples unless it exceeds the gist. Example 1 First, polyvinyl triphenylamine (No. (1) in Table 1) represented by the following structural formula was synthesized according to the method disclosed in JP-A-1-105954.

[0029]

[Chemical 5]

The number average molecular weight of this polymer (1) is 9,
It was 300 and the weight average molecular weight was 20,200. When DSC measurement (using Seiko DSC-20) was performed, Tg was 116 ° C. Indium tin oxide (ITO) transparent conductive film 120n on glass substrate
m The deposited material is ultrasonically cleaned with acetone, washed with pure water, ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen, and further UV / ozone cleaned to perform IT.
An O substrate was obtained.

1.2 parts by weight of the polymer (1) obtained above and 2- (4'-tert-butylphenyl) -5 (4 "-biphenyl) -1,3,4-oxa as an electron-transporting substance. A 1,2-dichloroethane solution containing 0.55 part by weight of diazole (hereinafter referred to as tBu-PBD) and 0.02 part by weight of perylene as a fluorescent substance was prepared, and spin-coated on the obtained ITO substrate. A film having a thickness of 63 nm was formed by the method.

Finally, as a cathode, an alloy electrode of magnesium and silver was vapor-deposited with a film thickness of 150 nm by a binary vapor deposition method. The vapor deposition was performed using a molybdenum boat, the degree of vacuum was 4 × 10 ⁻⁶ Torr, and the vapor deposition time was 4 minutes and 20 seconds. A glossy film was obtained. The atomic ratio of magnesium to silver was 10: 1.5. When a positive DC voltage is applied to the ITO electrode (anode) of the organic electroluminescent device thus manufactured and a negative DC voltage is applied to the magnesium-silver alloy electrode (cathode), the device emits blue light and its brightness is 304 cd / m at 25 V, 11 mA / cm ^{2
Was 2} . Example 2 1.3 parts by weight of the polymer (1) obtained in Example 1, 0.58 parts by weight of tBu-PBD as an electron transport material, and 3- (2'- represented by the following structural formula as a fluorescent material. A 1,2-dichloroethane solution containing 0.02 part by weight of benzothiazolyl) -7-diethylaminocoumarin was prepared, and an organic electroluminescence device was produced by the same method as in Example 1.

[0033]

[Chemical 6]

When a voltage of 24 V was applied to the organic electroluminescent device thus produced, 69.5 mA / cm ²
And a current density of 340 cd / m ² was obtained. Example 3 1.2 parts by weight of the polymer (1), 0.55 parts by weight of tBu-PBD as an electron transporting substance, and 4- (dicyanomethylene) -2-methyl-6 represented by the following structural formula as a fluorescent substance. A 1,2-dichloroethane solution containing 0.02 parts by weight of (p-dimethylaminostyryl) -4H-pyran was prepared, and an organic electroluminescence device was produced by the same method as in Example 1.

[0035]

[Chemical 7]

When a voltage of 30 V was applied to the organic electroluminescent device thus produced, a current density of 42 mA / cm ² was obtained and a luminance of 53 cd / m ² was exhibited.

[0037]

The organic electroluminescent device of the present invention, which contains polyvinyltriarylamine as an organic hole transporting substance, has a high glass transition temperature, has a thermally stable thin film structure, and is excellent. Excellent emission characteristics can be exhibited. Further, when the coating method is used as the method of forming the organic hole transport layer, it can be easily manufactured at a lower cost than the vacuum deposition method.

Therefore, the organic electroluminescent element of the present invention is a light source (for example, a light source of a copying machine, a liquid crystal display, and instruments) which makes the best use of the characteristics of a flat panel display (for example, for OA computers and wall-mounted televisions) and a surface light emitter. It can be applied to backlights, display boards, and marker lights, and its technical value is great.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of an organic electroluminescent device according to the present invention.

[Explanation of symbols]

 1 substrate 2a, 2b conductive layer 3 organic light emitting layer

Claims (1)

[Claims] 1. An organic electroluminescent device comprising an organic layer sandwiched by an anode and a cathode on a substrate, the organic layer containing at least an organic hole transporting substance, an electron transporting substance and a fluorescent substance. An organic electroluminescent device comprising a polyvinyl triarylamine having a repeating unit represented by the following general formula (I) as the organic hole transporting substance. [Chemical 1] (In the formula, Ar ¹ represents an arylene group which may have a substituent, Ar ² and Ar ³ represent an aryl group which may have a substituent, and the substituents are each independently an alkyl group. , An alkenyl group, an allyl group, an alkoxycarbonyl group, an alkoxy group and an amino group.)