JPH0337292A - 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 the 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 the 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 and B 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 nitrogen atom or a substituted or unsubstituted carbon atom] (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, inorganic material II
- ZnS and CaS which are Vl group compound semiconductors.

Mn and rare earth elements (Eu,...
Electroluminescent devices made from the above-mentioned inorganic materials are generally doped with Ce, TbSSm), but the electroluminescent devices made from the above-mentioned 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. Dyes (J, Chem, Soc
, ,Chem,C.

mmun, 557.1985), pyrazoline (Mol
,Cryst, Liq,Cryst,.

Upper Yui, 355. (1986)), perylene (JPn,
J, App 1. Ph)', S,, ii, L77
3.1986)), coumarin-based compounds, and tetraphenylbutadiene (Japanese Patent Application Laid-Open No. 57-51781), etc., have been reported, and furthermore, in order to increase luminous efficiency, the injection efficiency of carriers from the electrode is improved. As a result, optimization of the electrode type and creation of a light emitting layer consisting of a hole injection transport layer and an organic phosphor (Japanese Patent Laid-Open No. 57-51781.59
-194393.63-295695), etc.

(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.

That is, 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 organic electroluminescent element in which an organic hole injection transport layer and an organic light emitting layer are provided between electrodes consisting of two conductive layers. is the following general formula (1
) (In the formula, A and B represent an aromatic hydrocarbon group that may have a substituent, and X represents a nitrogen atom, a sulfur atom, an oxygen atom, or a selenium atom that may have a substituent. Indicate, Y
represents a nitrogen atom or a carbon atom which may have a substituent.

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

The substrate 1 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, A transparent synthetic resin substrate such as polycarbonate or polysulfone is preferred.

A conductive layer 2a is provided on the substrate l;
a is usually a metal such as argonium, gold, silver, nickel, palladium, tellurium, a metal oxide such as indium and/or tin oxide, copper iodide, carbon black, or poly(3-methyl It is made of conductive resin such as thiophene).

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 different materials. The thickness of the conductive layer 2a varies depending on the required transparency, but if transparency is required, the visible light transmittance is 6.
It is desirable to transmit 0% or more, preferably 80% or more, and in this case, 50 to 10,000 people, preferably 100
~5000 people. Conductive layer 2 if opaque is acceptable
a may be the same as the substrate l. Furthermore, it is also possible to laminate the above conductive layers using 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 plays a role of injecting electrons into the light emitting layer 4 as a cathode. The material used for the conductive layer 2b can be the same as the material for the conductive layer 2a, but in order to efficiently inject electrons, metals with a low work function are preferred, such as tin, magnesium, and indium. , Al≧Nium, Silver, or an alloy thereof. The thickness of the conductive layer 2b is usually the same as that of the conductive layer 2a. Further, although not shown in FIG. 1, a substrate similar to the 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 transparency. For this reason, one of the conductive layers 2a and 2b preferably has a thickness of 100 to 5000 layers, and is desired to have good transparency.

A genuine tag injection transport layer 3 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 injection/transport compound needs to be a compound that has high hole 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 a genuine tag injection transport compound is, for example, disclosed in Japanese Patent Application Laid-open No. 1983-
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'-diamine: t,t'-bis(4-'
;-p-)lylaminophenyl)cyclohexane: 4,
Examples include aromatic amine compounds such as 4'-bis(diphenylamino)quadrophenyl.

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, the hole mobility will be reduced, so a smaller amount is preferable, 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.
51781) and metal complexes such as aluminum complexes of 8-hydroxyquinoline (Japanese Unexamined Patent Publication No. 194393/1983).

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 (I).

In the general formula (1), A and B represent an aromatic hydrocarbon group which may have a substituent, and are selected from a phenyl group, a naphthyl group, a phenanthrene group, etc., and examples of the substituent include a chlorine atom, Halogen atoms such as bromine atoms and iodine atoms; alkyl groups having 1 to 6 carbon atoms such as methyl groups and ethyl groups;
Alkoxy groups with 1 to 6 carbon atoms such as methoxy and ethoxy groups; alkoxycarbonyl groups having alkoxy groups with 1 to 6 carbon atoms such as methoxycarbonyl and ethoxycarbonyl groups; carbon atoms such as methoxysulfonyl and ethoxysulfonyl groups 1 to 6 alkoxysulfonyl groups; examples include cyano group, amino group, dimethylamino group, and nitro group.

X represents a nitrogen atom, sulfur atom, oxygen atom, or selenium atom that may have a substituent, and examples of the substituent bonded to the nitrogen atom include a hydrogen atom and an alkyl group such as an alkyl group having 1 to 28 carbon atoms. ; Alkoxyalkyl groups such as methoxyethyl group and ethoxyethyl group; methoxy-ethoxyethyl group,
Alkoxyalkoxyalkyl groups such as n-butoxyethoxyethyl group; alkoxyalkoxyalkoxyalkyl groups such as methoxyethoxyethoxyethyl group and ethoxyethoxyethoxyethyl group; phenyloxyethyl group,
Optionally substituted aryloxyalkyl group such as naphthyloxyethyl group, P-chlorophenyloxyethyl group: benzyl group, phenethyl L, optionally substituted arylalkyl group such as p-chlorobenzyl group, p-nitrobenzyl group, etc. Group; cycloalkylalkyl group such as cyclohexylmethyl group, cyclohexylethyl group, cyclopentylethyl group; optionally substituted alkenyloxyalkyl group such as allyloxyethyl group, 3-bromoallyloxyethyl group; cyanoethyl group, cyanomethyl group cyanoalkyl groups such as hydroxyethyl groups, hydroxymethyl groups; substituted or unsubstituted alkyl groups such as tetrahydrofuryl groups, tetrahydrofurylethyl groups, allyl groups, 2-chloroallyl groups; Substituted or unsubstituted alkenyl groups, phenyl groups, p-methylphenyl groups,
Examples include substituted or unsubstituted aryl groups such as naphthyl group and m-methoxyphenyl group, and cycloalkyl groups such as cyclohexyl group and cyclopentyl group.

Y is a nitrogen atom or a carbon atom which may have a substituent, and examples of the substituent include a hydrogen atom, a cyano group, and an amide group represented by the following formula: C0NH, -CONHR, -CONRR' (in the above formula, R , R' represents 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, an aromatic hydrocarbon group such as an optionally substituted phenyl group, a naphthyl group, or a phenanthryl group. ; Aromatic heterocyclic groups such as optionally substituted thienyl group, pyrrolyl group, thiazolyl group, furyl group, oxasilyl group, benzothienyl group, benzofuranyl group, indolyl group, pyridyl group, etc.

Synthesis methods for these compounds are described by Mataga et al., J.

Heterocycle 1c, Chem, Volume 18, 1
p. 073 (1981); vol. 26, p. 215 (1981)
, 9).

The above-mentioned compounds obtained in this manner are specifically exemplified by the following formulas (n) to (XVI).

0Cz)Is QC, H.S. (Vl) (■) C.I.

(■) (X) (IX) (XI) (XI) (XIV) (XV) Due to the resonance structure of the compounds shown in formulas (XIV) to (XVI), the NH group of the 5-membered ring is There is no problem even if it is in the position of a nitrogen atom.

All of these compounds (I[) to (XVI) 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.

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 layer 3, and the conductive layer 2a can be laminated in this order on the substrate. can be,
As described above, it is also possible to provide the electroluminescent element of the present invention between two substrates, at least one of which is highly transparent.

(Effect of the invention) According to the electroluminescent device of the invention, the conductive layer (anode)/
The hole injection transport layer/emissive layer/conductive layer (cathode) are sequentially provided on the substrate, and since a specific compound is used in the emissive layer, when a voltage is applied using both thermoelectric layers as electrodes. , 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 televisions) and as a light source that takes advantage of its characteristics as a surface light emitting device (for example, a light source for copying machines, a backlight source for liquid crystal displays, and instruments). , display board,
It can be applied to 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.

That is, indium tin oxide (I
To) After 1000 transparent conductive films were deposited and ultrasonically cleaned with toluene and isopropyl alcohol, an aromatic amine compound represented by the following structural formula (1) was vacuum evaporated on top of the transparent conductive film as a hole injection transport layer. The film was deposited to a thickness of 500 mm using the method.

The degree of vacuum during vapor deposition was 6×10-'Torr.

Next, as an organic light-emitting layer, a compound represented by the structural formula (II) was deposited to a thickness of 500 nm in the same manner as the name plate injection transport layer.

0Cd(.

Finally, as a cathode, an alloy electrode of magnesium and silver was deposited to a film thickness of 1500 ml by simultaneous vapor deposition so that the film thickness ratio was 10:1. The degree of vacuum during vapor deposition is 6X 1
A shiny electrode was obtained at 0-'Torr.

Furthermore, electroluminescent devices were similarly produced for the compounds represented by structural formulas (III) and (IV), respectively.

Regarding the electroluminescent device thus obtained having the structure shown in FIG.
The table below shows the results of evaluating the light emitting characteristics by applying a negative DC voltage to the magnesium-silver electrode (cathode). Note that the threshold voltage indicates a voltage at which the luminance becomes 1 (cd/rrf).

Uniform light emission with high brightness was obtained at low voltage in all cells.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the structure of the electroluminescent device of the present invention, in which 1 represents a substrate, 2a and 2b a conductive layer, 3 a hole injection transport layer, and 4 a light emitting 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 and B represent an aromatic hydrocarbon group that may have a substituent, and X is a nitrogen atom, a sulfur atom, an oxygen atom that may have a substituent, or Indicates a selenium atom, Y
represents a nitrogen atom or a carbon atom that may have a substituent.