JPH0337293A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE:To enable an organic electroluminescent element comprising a pair of electrodes each comprising at least two conductive layers and, disposed between said electrodes, an organic hole injection transportation layer and an organic light-emitting layer to emit light of improved luminance at a low voltage by incorporating a specific compound in the organic light-emitting layer. CONSTITUTION:An organic electroluminescent element comprising a pair of electrodes each comprising two conductive layers and, disposed between said electrodes, an organic hole injection transportation layer and an organic light- emitting layer, wherein the organic light-emitting layer contains a compound represented by formula I [wherein A to D each represent a substituted or unsubstituted aromatic hydrocarbon group; X represents a substituted or unsubstituted nitrogen atom, a sulfur atom, an oxygen atom or a selenium atom; and Y represents a hydrogen atom, a cyano group, an amide group, an ester group, an alkyl group, a carboxyl group, a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group] (e.g. a compound represented by formula II).

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an organic electroluminescent device, and more specifically, an electric field is applied by a combination of a hole injection transport layer and a light emitting layer made of an organic compound. This invention relates to a thin film device that emits light.

(Prior art) Conventionally, as a thin film type electroluminescent device, if
-ZnS, CaS, which are Vl group compound semiconductors.

Mn and rare earth elements (Bu, Bu,
Generally, electroluminescent devices doped with Ce, Tb, S-) are doped, but electroluminescent devices made from the above inorganic materials require: 1) alternating current driving (~1 kHz); 2) high driving voltage (~1 kHz);
200V), 3) It is difficult to achieve full color, and 4) The cost of peripheral drive circuits is high.

However, in recent years, in order to improve the above problems, electroluminescent devices using organic materials have been developed. Pigment (J, Che+s,
Soc, + Chell, Com+sun, +5
57 +1985), pyrazoline (Mo1. Cry
st, Liq, Cryst, +135, 355
(1986) ), perylene (Jpn, J, A
ppl.

Phys, 25 L773. (1986))
Alternatively, coumarin-based compounds and tetraphenylbutadiene (Japanese Unexamined Patent Publication No. 57-51781) have been reported; Optimization and creation of a light-emitting layer consisting of a hole injection transport layer and an organic phosphor (Japanese Patent Application Laid-Open No. 57-51781.59-194393)
．． 63-295695) etc. are being carried out.

(Problems to be Solved by the Invention) However, the organic electroluminescent devices disclosed by these methods still have insufficient luminous performance, and further improvement studies are desired.

An object of the present invention is to provide an organic electroluminescent device using an organic light-emitting substance that can emit light with high brightness even at a low driving voltage.

(Means for Solving the Problems) That is, the gist of the present invention is to provide an electroluminescent device in which a hole injection transport layer and a light emitting layer are provided between electrodes consisting of two conductive layers, in which the light emitting layer has the following general formula: () (In the formula, A, B, C1, and D represent an aromatic hydrocarbon group that may have a substituent, and X is a nitrogen atom, a sulfur atom, or an oxygen atom that may have a substituent. , or a selenium atom, and Y is a hydrogen atom, a cyano group, an amide group, an ester group, an alkyl group, a carboxyl group, an optionally substituted aromatic hydrocarbon group, or an optionally substituted aromatic heterocycle An organic electroluminescent device characterized by containing a compound represented by the following.

Hereinafter, the electroluminescent device of the present invention will be explained with reference to the accompanying drawings. 1 and 2 are cross-sectional views schematically showing an example of the structure of an electroluminescent device of the present invention, where l is a substrate, 2a,
2b represents a conductive layer, 3 represents a hole injection transport layer, 4 represents a light emitting layer, and 5 represents an electron injection transport layer.

The substrate l serves as a support for the electroluminescent device of the present invention, and may be a quartz or glass plate, a metal plate or metal foil, a plastic film or sheet, and may be a glass plate, polyester, polymethacrylate, Transparent synthetic resin substrates such as polycarbonate and polysulfone are preferred.
A conductive layer 2a is provided on the substrate l;
A is usually a metal such as aluminum, gold, silver, nickel, palladium, or tellurium, a metal oxide such as indium and/or tin oxide, copper iodide, carbon black, or poly(3-methylthiophene). It is made of conductive resin such as.

The conductive layer is usually formed by sputtering, vacuum evaporation, etc., but it can also be formed using fine metal particles such as silver, copper iodide, carbon black, conductive metal oxide fine particles, conductive resin fine powder, etc. In some cases, it can also be formed by dispersing it in a suitable binder resin solution and coating it on the substrate. Furthermore, in the case of conductive resin, a thin film can be formed directly on the substrate by electric field polymerization.

The above conductive layer can also be laminated with two or more different materials. The thickness of the conductive layer 2a varies depending on the required transparency, but if transparency is required, it is desirable that the visible light transmittance is 60% or more, preferably 80% or more. The number is about 50 to too many people, preferably about 100 to 5000 people. If opaqueness is acceptable, the conductive layer 2a may be the same as the substrate 1. Furthermore, the conductive layer 2a may be laminated with two or more different materials. In the example shown in FIG. 1, the conductive layer 2a serves as an anode to inject holes. on the other hand,
The conductive layer 2b serves as a cathode to inject electrons into the light emitting layer 4.

The material used for the conductive layer 2b can be the material for the conductive layer 2a, but in order to efficiently inject electrons, a metal with a low work function is preferable.
Appropriate metals such as tin, magnesium, indium, aluminium, silver, or alloys thereof are used. The thickness of the conductive layer 2b is usually the same as that of the conductive layer 2a. Further, although not shown in FIGS. 1 and 2, a substrate similar to substrate 1 may be further provided on the conductive layer 2b.

However, as an electroluminescent device, it is necessary that at least one of the conductive layers 2a and 2b has good permeability.

From this, one of the conductive layers 2a and 2b has a 100 to 5
It is preferable that the film has a thickness of 0.000 mm, and that it has good transparency.

A genuine tag injection transport N3 is provided on the conductive layer 2a,
The hole injection transport layer 3 is formed of a compound that can efficiently transport holes from the anode toward the light emitting layer between the electrodes to which an electric field is applied.

The hole injecting and transporting compound needs to be a compound that has high injection efficiency from the conductive layer 2a and can efficiently transport the injected holes. To this end, it is required that the compound has a low ionization potential, high hole mobility, excellent stability, and is unlikely to generate trapping impurities during production or use.

Such hole injection and transport compounds are described, for example, in JP-A-59-
194393, pages 5-6 and U.S. Patent No. 417596.
Examples include those explained in columns 13 to 14 of No. 0. Preferred specific examples of these compounds include N, N'
-diphenyl-N.

N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-cyan ξ:t,t'-bis(4-diP
-) lyluanξnophenyl)cyclohexane: 4.4'-
Examples include aromatic amine compounds such as bis(diphenylacetate))quatrophenyl.

The hole injection transport layer 3 is formed by laminating it on the conductive layer 2a by a coating method or a vacuum evaporation method.

In the case of coating, a coating solution containing one or more hole-injecting and transporting compounds and, if necessary, additives such as a binder resin that does not trap holes and a coating properties improver such as a leveling agent, is used. It is adjusted, coated on the conductive layer 2a by a method such as a spin code method, and dried to form the hole injection transport layer 3. Examples of the binder resin include polycarbonate, polyarylate, polyester, and the like. If the binder resin is added in a large amount, it will reduce the mobility of the original tag, so a small amount is desirable, and 50% by weight or less is preferable.

The thickness of the hole injection transport layer is usually 100 to 3000, preferably 300 to 1000. Vacuum deposition is often used to uniformly form such thin films.

In FIG. 1, an organic light-emitting layer 4 is typically laminated on a hole injection transport layer 3. This layer simultaneously serves the role of transporting electrons from the conductive layer 2b toward the hole injection transport layer 3 and the role of causing light emission when holes and electrons are recombined. Materials that meet such conditions include aromatic compounds such as tetraphenylbutadiene and coumarin (Japanese Patent Application Laid-open No.
51'781) and metal complexes such as aluminum complexes of 8-hydroxyquinoline (Japanese Unexamined Patent Publication No. 59-194393).

In FIG. 2, an electron injection transport layer 5 is provided between the organic light emitting layer 4 and the conductive layer 2b as a measure to increase the efficiency of light emission. It is thought that the electron injection and transport layer 5 plays the role of efficiently injecting electrons from the conductive layer 2b and simultaneously transporting the injected electrons toward the light emitting layer 4. In this structure, the compound used for the light-emitting layer 4 does not need to have an electron transport ability, and the degree of freedom in material selection is increased.

The electroluminescent device of the present invention is characterized in that the above organic light emitting compound is selected from the compounds represented by the above general formula (1).

In the general formula (I), A, B, C and D represent an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, or a phenanthryl group which may have a substituent, and the substituent is a chlorine atom. , halogen atoms such as bromine atoms and iodine atoms,
Alkyl groups having 1 to 6 carbon atoms such as methyl group and ethyl group; Alkoxy groups having 1 to 6 carbon atoms such as methoxy group and ethoxy group; Alkoxy groups having 1 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group Alkoxycarbonyl groups having an alkoxysulfonyl group such as a methoxysulfonyl group and an ethoxysulfonyl group; examples include a cyano group, an amino group, a dimethylamino group, and a nitro group.

X represents a nitrogen atom, sulfur atom, oxygen atom, or selenium atom which may have a substituent, and examples of the substituent bonded to the nitrogen atom include an alkyl group such as an alkyl group having 1 to 28 carbon atoms; methoxyethyl alkoxyalkyl groups such as methoxy-ethoxyethyl group and n-butoxyethoxyethyl group; alkoxyalkoxyalkoxyalkyl groups such as methoxyethoxyethoxyethyl group and ethoxyethoxyethoxyethyl group S: phenyl Oxyethyl group, naphthyloxyethyl L, optionally substituted aryloxyalkyl group such as p-chlorophenyloxyethyl group; substituted aryloxyalkyl group such as benzyl group, phenethyl group, p-chlorobenzyl group, p-nitrobenzyl group, etc. Cycloalkylalkyl groups such as dichlorohexylmethyl group, cyclohexylethyl group, cyclopentylethyl group; optionally substituted alkenyloxyalkyl groups such as allyloxyethyl group and 3-bromoallyloxyethyl group; Cyanoalkyl groups such as cyanomethyl group and cyanomethyl group; Hydroxyalkyl groups such as hydroxyethyl group and hydroxymethyl group; Tetrahydrofuryl group,
Substituted or unsubstituted alkyl groups such as tetrahydrofuryl alkyl groups such as tetrahydrofurylethyl groups, substituted or unsubstituted alkenyl groups such as allyl groups, 2-chloroallyl groups, phenyl L p-methylphenyl groups, naphthyl groups, m- Examples include substituted or unsubstituted aryl groups such as a methoxyphenyl group, and cycloalkyl groups such as a cyclohexyl group and a cyclopentyl group.

Y is a hydrogen atom, a cyano group, an amide group represented by the following formula: C0NHz, -CONHR, -CONRR' (in the above formula, R and R' are an aromatic hydrocarbon group such as a phenyl group or an optionally substituted alkyl group) ), an ester group represented by the following formula! -COOR (in the above formula, R represents an aromatic hydrocarbon group such as a phenyl group or an optionally substituted alkyl group), an alkyl group having 1 to 28 carbon atoms, a carboxyl group, even if substituted good phenyl group,
Aromatic hydrocarbon groups such as naphthyl group and phenanthryl group:
It is selected from aromatic heterocyclic groups such as optionally substituted chenyl group, pyrrolyl group, thiazolyl group, furyl group, oxacylyl group, benzochenyl group, benzofuranyl group, indolyl group, and pyridyl group.

The synthesis method of these compounds was described by Mataga et al. in J. He
terocyclic, Chew, Volume 18, 107
3 (1981).

A specific example of the compound thus obtained is shown by the following formula (I
I) to (XIX) are examples.

H3 DiU (J CHs These compounds exhibit strong fluorescence and are suitable as compounds for the organic light-emitting layer.

The thickness of the organic light emitting layer 4 is usually 100 to 2000, preferably 300 to 1000.

The organic light emitting layer 4 can also be formed by the same method as the hole injection transport layer, but usually a vacuum evaporation method is used. Organic thin films formed by vacuum evaporation often aggregate and deteriorate after being left for a long period of time, but the organic light-emitting compound of the present invention is also excellent in this respect.

The thickness of the electron injection transport layer 5 further provided on the organic light emitting layer is usually 30 to 1000, preferably 50 to 300.
It's a person. Examples of the compound used in the electron injection transport layer 5 include the aforementioned tetraphenylbutadiene and the Alti form of 8-hydroxyquinoline.

Incidentally, the electroluminescent device of the present invention can also have a structure opposite to that shown in FIG. 1, that is, the conductive layer 2b, the organic light emitting layer 4, the hole injection/transport 13, and the conductive layer 2a can be laminated in this order on the substrate. ,
As described above, it is also possible to provide the electroluminescent device of the present invention between two substrates, at least one of which is highly transparent.

Similarly, the structure may be reversed to that shown in FIG. 2, that is, the conductive layer 2b, the electron injection transport layer 5, the organic light emitting layer 4, the hole injection transport layer 3, and the conductive layer 2a may be laminated in this order on the substrate. It is possible.

(Effect of the invention) According to the electroluminescent device of the invention, conductive N (anode)/
Hole injection transport layer / light emitting layer / conductive layer (cathode) or conductive layer (anode) / hole injection transport JW / light emitting layer / electron injection transport layer / conductive layer (cathode) are sequentially rolled over the substrate. Moreover, since a specific compound is employed in the light-emitting layer, when a voltage is applied using the recirculation layer as an electrode, luminescence with sufficient luminance for practical use can be obtained with a low driving voltage.

Therefore, the electroluminescent device of the present invention can be used in the field of flat panel displays (for example, wall-mounted TVs) and light sources that take advantage of its characteristics as a surface light emitting device (for example, light sources for copying machines, liquid crystal displays, and backlight sources for instruments). ), display boards, and marker lights, and its technical value is great.

(Examples) Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the description of the following Examples unless it exceeds the gist thereof.

Example 1 An electroluminescent device having the structure shown in FIG. 1 was manufactured.

A transparent conductive film of 1,000 indium tin oxide (ITO) deposited on a glass substrate was ultrasonically cleaned with toluene and isopropyl alcohol, and then heated with Ar in a vacuum container.
The surface was cleaned by exposing it to a glow discharge for 1 minute. Thereon, as a hole injection transport layer, an aromatic amine compound represented by the following structural formula (1) was deposited to a thickness of 750 nm by vacuum evaporation.

In the vapor deposition, the aromatic amine compound is placed in a ceramic crucible, the area around the crucible is heated with a Ta ray heater, and the vapor deposition source is evaporated in a vacuum container. The degree of vacuum during vapor deposition is lXl0
”It was Torr.

Next, as an organic light-emitting layer, a compound represented by formula (It) was deposited to a thickness of 776 nm in the same manner as the hole injection transport layer.

Finally, as a cathode, an alloy electrode of magnesium and silver was deposited to a thickness of 2,000 yen by simultaneous evaporation so that the film thickness ratio was 10:1. A molybdenum boat was used for the evaporation, the degree of vacuum was 1X10-'Torr, and a glossy electrode was obtained.

In this way, an electroluminescent device having the structure shown in FIG. 1 was produced, and the ITO electrode (anode) of this device was coated with magnesium-1! When a negative DC voltage of 25V was applied to the electrode (cathode), the voltage was 15cd/m"
Uniform light emission was confirmed at a brightness of . This emission was green and had a peak wavelength of 525 nm. Also, the current density flowing through the element at this time was 1.2 x 10-”A/CI+”
So, the luminous efficiency is 0.016j! m/W. The threshold for light emission is a voltage of 20. It was IV. Note that the threshold voltage indicates a voltage at which the luminance becomes 1 (cd/m'').

Example 2 After 750 people deposited a hole injection transport layer and 505 people deposited an organic light emitting layer in the same manner as in Example 1, 100 people deposited an 8-hydroxyquinoline hel complex represented by the following structural formula (2). Finally, a cathode electrode was formed to produce an electroluminescent device having the structure shown in FIG.

The characteristics of this device were evaluated in the same manner as in Example 1. 24
Uniform light emission with a brightness of 1128 cd/m" was obtained by applying a DC voltage of
The wavelength was 25 nm, and the peak profile matched the fluorescence spectrum of the vapor-deposited film of the compound used for the organic light-emitting layer.

The current density flowing through the element at this time was 0.17 A/c+a
"The luminous efficiency was 0.094!m/W.The threshold voltage for luminescence was 14.0 V.

Example 3 The first step was carried out in the same manner as in Example 1 and Example 2, except that the compound represented by formula (IV) was used as the material for the organic light emitting layer.
An electroluminescent device having the structure shown in the figure and FIG. 2 was manufactured.

The film thicknesses of the light-emitting layers at this time were 650 and 500, respectively.

Uniform light emission was obtained in all elements.

The characteristics of each element are shown in the table below.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views of examples of the electroluminescent device of the present invention, in which l represents the substrate and 2 a s 2
b represents a conductive layer, 3 represents a hole injection transport layer, 4 represents a light emitting layer, and 5 represents an electron injection transport layer.

Claims (1)

[Claims] In an organic electroluminescent device in which an organic hole injection transport layer and an organic light emitting layer are provided between electrodes consisting of two conductive layers, the organic light emitting layer has the following general formula, ▲ mathematical formula, chemical formula, or table. etc.▼ (In the formula, A, B, C, and D represent an aromatic hydrocarbon group that may have a substituent, and X is a nitrogen atom or a sulfur atom that may have a substituent. , oxygen atom, or selenium atom, and Y is a hydrogen atom, a cyano group, an amide group, an ester group, an alkyl group, a carboxyl group, an optionally substituted aromatic hydrocarbon group, or an optionally substituted aromatic group. An organic electroluminescent device characterized by containing a compound represented by (representing a group heterocyclic group).