JP2002151272A - Electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroluminescent element excellent in heat resistance and durability by restraining thermal deterioration of an organic electroluminescent element. SOLUTION: With the electroluminescent element composed of consisting of a positive and a negative electrodes, and organic compounds of one or a plurality of layers pinched between them, a conductive thin film formed of an oligoaniline derivative as represented in a formula (1), an electron-accepting dopant and salt as a carrier transport sub-layer between the positive electrode and the organic layer. In the formula, R1, R2 and R3 denote, each independently, non-substitute or substitute univalent carbon hydride group, or organooxy group, A and B each independently bivalent group as represented in formula (2) or (3), and R4 to R11 denote, each independently, hydrogen atom, a hydroxyl group, a non-substitute or substitute univalent carbon hydride group or organooxy group, acyl group, or sulfonic group. 'm' and 'n' denote, each independently, an integer of 1 or more, and satisfy m+n<=20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device having a light-emitting layer made of a light-emitting substance and capable of directly converting an applied voltage to luminous energy by applying an electric field.
The present invention relates to an electroluminescent device in which a conductive polymer layer is formed at an interface between an inorganic electrode and an organic layer to improve hole injection efficiency.

[0002]

2. Description of the Related Art An electroluminescent phenomenon of an organic material has been observed with an anthracene single crystal (J. Chem. Phys. 3).
8 (1963) 2042). Thereafter, the use of a solution electrode having good injection efficiency led to the observation of a relatively strong luminescence phenomenon (Phys. Rev. Lett. 14 (19)
65) 226). Thereafter, research was conducted to form an organic light-emitting substance with a conjugated organic host substance and a conjugated organic activator having a condensed benzene ring (US Pat. No. 3,172,172).
862, USP3, 172,050, USP3,71
0,167; Chem. Phys. 44 (196
6) 2902, J. Mol. Chem. Phys. 50 (196
9) 14364). However, each of the organic light-emitting substances mentioned here has a disadvantage that the film thickness is large and the electric field required for light emission is high.

[0003] On the other hand, a study of a thin film element by a vapor deposition method has been conducted, and an effect has been brought about in reducing a driving voltage. However, it has not been possible to obtain a practical level of luminance (Polymer
24 (1983) 748, Jpn. J. Appl. P
hys. 25 (1986) L773).

In recent years, Eastman Kodak Company has proposed a device in which a charge transport layer and a light emitting layer are formed between electrodes by a vapor deposition method, and high luminance at a low driving voltage has been realized (Ap.
pl. Phys. Lett. 51 (1987) 913,
USP 4,356,429). The research has been further intensified, and a three-layer type device in which carrier transport and a light emitting group are separated has been studied, and an organic electroluminescent device has entered a practical stage (Jpn. J. Appl. Phys. 27).
(1988) L269, L713).

[0005]

However, it has been found that these devices are susceptible to peeling due to moisture adsorption or thermal degradation, and that the dark spots increase significantly after long use. These deteriorations are mainly caused by peeling at the interface between the inorganic electrode and the organic layer, but these problems have not been sufficiently solved.

Accordingly, it is an object of the present invention to provide an electroluminescent device which suppresses thermal degradation of these organic electroluminescent devices and has excellent heat resistance and durability.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, an inorganic electrode as a buffer layer between an inorganic electrode (ITO electrode) as an anode and an organic hole transport layer. It has been found that providing one layer of an oligoaniline derivative represented by the following general formula (1) having excellent adhesion and conductivity as a carrier transport auxiliary layer is extremely effective for durability. Invented the invention.

At this time, conductivity is imparted by doping the oligoaniline derivative with a sulfonic acid derivative of the following general formula (4) to impart performance as an electrode and to maintain the hole transporting ability. In addition, the affinity between the inorganic electrode and the hole transport layer, which is an organic layer, is improved, and interface phenomena such as peeling are suppressed, and the durability of the element itself is improved.

That is, the present invention relates to an electroluminescent device comprising an anode and a cathode and one or more layers of an organic compound sandwiched between the anode and the cathode. General formula (1) as auxiliary layer

[0010]

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(Wherein R ¹ , R ² and R ³ each independently represent an unsubstituted or substituted monovalent hydrocarbon group or an organooxy group, and A and B each independently represent a group represented by the general formula (2) or General formula (3)

[0012]

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Wherein R ^{4 to} R ¹¹ are each independently a hydrogen atom, a hydroxyl group, an unsubstituted or substituted monovalent hydrocarbon group or an organooxy group, an acyl group,
Or a sulfonic acid group, wherein m and n are each independently 1
With the above positive numbers, m + n ≦ 20 is satisfied. The present invention relates to an electroluminescent device using an electrically conductive thin film formed by forming a salt with the oligoaniline derivative represented by the formula (1) and an electron-accepting dopant.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The method for synthesizing an oligoaniline derivative in the present invention is not particularly limited. For example, it can be synthesized by the following method.

That is, a method in which an aromatic amine and a phenol are subjected to a condensation reaction by a dehydration condensation reaction, or a method in which an aromatic amine and an aromatic amine hydrochloride are reacted in a molten state are generally used.

The substituents R ¹ and R ^{3 to} R ¹¹ in the oligoaniline moiety of the general formula (1) are generally hydrogen, but are preferably alkyl, alkoxy, cyclohexyl, biphenyl to increase the solubility in solvents. Group, bicyclohexyl group,
A phenylcyclohexyl group is suitable. For example, an alkyl group generally includes a methyl group, an ethyl group, a propyl group, and the like. The number of carbon atoms is generally 1 to 4, but it is possible to introduce up to 20 carbon atoms. The number of m and n in the oligoaniline moiety is independently a positive number of 1 or more, but preferably 2 or more in consideration of its conductivity, and 20 or less in consideration of its solubility in a solvent.

The substituent R ² is a hydrogen atom, a hydroxyl group, an unsubstituted or substituted monovalent hydrocarbon group or an organooxy group,
An acyl group, an alkyl group having 1 to 20 carbon atoms, or 1 carbon atom
-20 alkoxy groups are suitable. For example, as an alkyl group, there are generally a methyl group, an ethyl group, a propyl group and the like, and a carbon number of 1 to 4 is generally used.
It is possible to introduce up to 20 carbon atoms.

Regarding the doping (salt formation) of the oligoaniline derivative of the present invention represented by the general formula (1) and the dopant obtained by the above-described production method,
Formula (4) as an acid

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[0019] (D represents a benzene ring, a naphthalene ring, Atorasen ring, a phenanthrene ring or a heterocyclic ring, R ^12, R
¹³ each independently represents a carboxyl group or a hydroxyl group. The sulfonic acid derivative which easily causes the intermolecular interaction represented by the formula (1) is desirable. Such molecules include, for example, sulfosalicylic acid derivatives such as 5-sulfosalicylic acid and sulfophthalic acid derivatives such as 4-sulfophthalic acid. Although the doping concentration varies depending on the molecular weight of the oligoaniline derivative, it is generally preferable to add the dopant so that one or less nitrogen atom in the oligoaniline derivative becomes one dopant or less.

The coating film of the oligoaniline derivative is not particularly limited as long as it can dissolve the oligoaniline derivative. Specific examples of these solvents include N-methylpyrrolidone, N, N-dimethylacetamide, N, N-
Dimethylformamide and the like can be mentioned. These may be used alone or as a mixture. Furthermore, even if a solvent which cannot obtain a homogeneous solvent by itself is used, the solvent may be added to the extent that a homogeneous solvent can be obtained. Examples thereof include ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, ethyl carbitol acetate, ethylene glycol and the like.

The oligoaniline coating film can be formed on the substrate by applying the solution on the substrate and evaporating the solvent. The temperature at this time should just evaporate a solvent, and 80-150 degreeC is sufficient normally.

The coating method for forming the oligoaniline thin film of the present invention includes a dipping method, a spin coating method,
Examples include a transfer printing method, roll coating, and brush coating, but are not particularly limited. Alternatively, after the oligoaniline derivative already doped with the general formula (4) is isolated, the oligoaniline derivative can be laminated by a vacuum evaporation method. The film thickness is not particularly limited, but is preferably as thin as possible to improve external luminous efficiency, and is usually preferably 0.5 to 1000 °.

As for the shape of the electroluminescent element, the above-mentioned oligoaniline thin film is first formed on ITO which is an inorganic electrode. At this time, generally, ITO is used which has been subjected to a cleaning treatment such as reverse sputtering, ozone treatment and acid treatment to remove foreign substances such as organic substances on the surface. An organic material for electroluminescence is laminated on the substrate with electrodes thus obtained. Currently, the laminated structure has various shapes, but is not particularly limited, but generally, a hole transport layer, a light emitting layer,
An element laminated in the order of the carrier transport layer is used.

The hole transporting material is not particularly limited, but is generally a tertiary aromatic amine such as N, N, N
-Tris (p-toluyl) amine (TPD), 1,1-
Bis [(di-4-toluylamine) phenyl] cyclohexane, N, N′-diphenyl-N, N′-bis (3-
Methylphenyl) (1,1′-biphenyl) 4,4′-
Diamine, N, N, N ', N'-tetrakis (4-methylphenyl) (1,1'-biphenyl) -4,4'-diamine, N, N'-bis (1-naphthyl) -N, N '-
Diphenyl-1,1′-bisphenyl-4,4′-diamine (α-NPD), 4,4 ′, 4 ″ -tris (3-methylphenylamino) triphenylamine and the like. A pyrazoline derivative is used.

There is no particular limitation on the carrier transporting material, but generally an aromatic condensed ring compound or a metal complex compound is often used. For example, Tris (8
Metal complex systems such as -hydroxyquinoline) aluminum (Alq), bis (10-hydroxybenzo [h] quinolate) beryllium (BeBq2), 1,3,4-oxathiazole derivatives, 1,2,4-triazole derivatives, Bis (benzimidazole) derivatives of perylenedicarboxyimide, thiopyransulfone derivatives, and the like can be given.

Examples of the light emitting material include Alq and tris (5-cyano-8-hydroxyquinoline) aluminum (Al (Q-CN)) as metal complex-based materials, and oxathiazole-based dyes such as biphenyl Examples include -p- (t-butyl) phenyl-1,3,4-oxathiazole, triazoles, allylenes, coumarins, and the like, but are not particularly limited.

These materials are sequentially laminated by a vacuum vapor deposition method, and a MgAg alloy is vapor-deposited thereon as a cathode. By applying an electric field to the device thus obtained, an electroluminescent device that emits light of a specific wavelength can be obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples, but it should not be construed that the invention is limited thereto.

[0029]

EXAMPLES Example 1 Aniline pentamer

[0030]

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Was dissolved in DMF solvent and doped with 5-sulfosalicylic acid. Table 1 shows the doping amount and varnish preparation conditions.

[0032]

[Table 1] Table 1 Varnish preparation conditions ─────────────────────────── Run No. Aniline pentamer dopant DMF mmol g mmol gg ─────────────────────────── ────────────────────────── 1 2.2595 1.00 2.260 0.574 29.91 2 2.2595 1.00 4.519 1.148 40.81 3 2.2595 1.00 6.779 1.723 51.74 4 2.2595 1.00 9.038 2.297 62.64電 気 The electrical properties of the obtained thin film are shown in Table 2 below.

[0033]

[Table 2] Table 2 Electrical properties of conductive thin film ──────────────────────────────── Run No. 1 2 3 4 ──────────────────────────────── Mobility --- 9.19 13.7 2.61 Carrier density --- 4.52 × 10 ¹² 8.23 × 10 ¹¹ 2.19 × 10 ¹⁰ Conductivity --- 2.12 × 10 ⁶ 8.15 × 10 ⁷ 1.26 × 10 ⁸ Ionization potential 5.11 5.08 5.00 4.94 ワ The varnish described above was formed by spin coating. Thereafter, firing was performed to obtain a conductive thin film. The obtained thin film was immediately converted into a light emitting element by vapor deposition. The element structure was such that α-NPD and Alq were each stacked on the ITO electrode by 500 °, and MgAg was stacked on the ITO electrode as a 2000 ° electrode.

The luminance characteristics of the device thus manufactured were measured. Table 3 shows the results.

[0035]

[Table 3] Table 3 Characteristics of electroluminescent device ──────────────────────────────── Run 1 2 3 4 ─── ───────────────────────────── Flash start voltage (V) --- 2.5 2.5 2.5 Maximum brightness (cd / m ² )- -16460 (11V) 17540 (11V) 13440 (11V) Current efficiency (cd / A) --- 6.40 (11V) 8.56 (11V) 7.27 (11V) ────────────── Example 2 Aniline hexamer was dissolved in a DMF solvent and doped with 5-sulfosalicylic acid. Table 4 shows doping amounts and varnish preparation conditions.

[0036]

[Table 4] Table 4 Varnish preparation conditions {Run No. Aniline hexamer dopant DMF mmol g mol gg} ────────────────────────── 1 1.8738 1.00 1.874 0.476 28.04 2 1.8738 1.00 3.748 1.953 37.11 3 1.8738 1.00 5.621 2.429 46.15 4 1.8738 1.00 7.495 2.905 55.20 5 1.8738 1.00 9.369 3.381 64.24 電 気 The electrical properties of the obtained thin film are shown in Table 5 below.

[0037]

[Table 5] Table 5 Electrical properties of conductive thin film ────────────────────────────── Run No. 1 35 ── ──────────────────────────── Mobility 6.00 21.4 19.1 Carrier density 1.78 × 10 ¹¹ 5.10 × 10 ¹⁰ 1.44 × 10 ⁹ Conductivity 1.72 × 10 ⁷ 1.74 × 10 ⁷ 3.78 × 10 ⁸ Ionization potential 5.13 4.98 5.00 ──────────────────────────────

The varnish described above was formed by spin coating. Thereafter, firing was performed to obtain a conductive thin film. The obtained thin film was immediately converted into a light emitting element by vapor deposition. The element structure is I
On the TO electrode, α-NPD and Alq were each laminated by 500 °, and MgAg was laminated thereon as a 2000 ° cathode electrode. The luminance characteristics of the device thus manufactured were measured. Table 6 shows the results.

[0039]

[Table 6] Table 6 Characteristics of electroluminescent device ────────────────────────── Run 1 3 5 ────────── ──────────────── Emission start voltage (V) --- 2.5 2.5 Maximum brightness (cd / m ² ) --- 16540 (11V) 17440 (11V) Current efficiency (cd / A) --- 5.40 (11V) 5.27 (11V) ──────────────────────────

COMPARATIVE EXAMPLE 1 As a comparative example, an element structure ITO / α having no auxiliary layer was used.
The emission characteristics of -NPD / Alq / MgAg were measured. Each layer other than ITO was formed by a vacuum deposition method. Run 1 Light emission start voltage (V) 2.75 Maximum brightness (cd / m ² ) 6000 (14.75V) Current efficiency (cd / A) 5.00 (8V)

COMPARATIVE EXAMPLE 2 As a comparative example, an element structure using a conductive polymer in which polyphenetidine is doped with camphorsulfonic acid as an auxiliary layer ITO / auxiliary layer / α-NPD / Alq / MgA
g was measured for its emission characteristics. The auxiliary layer was formed by a spin coating method. Each layer other than ITO was formed by a vacuum evaporation method. Run 1 Light emission start voltage (V) 2.75 Maximum brightness (cd / m ² ) 10300 (15.5V) Current efficiency (cd / A) 5.38 (12.25V)

[0042]

The oligoaniline derivative used in the present invention is easy to synthesize, and is used as a raw material to form a coating having excellent heat resistance, coating strength, coating properties and antistatic properties or low charge accumulation. Is obtained. By using such an oligoaniline derivative as a charge injection auxiliary layer of an electroluminescent device, a highly reliable electroluminescent device can be obtained.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K007 AB02 AB03 AB06 AB11 AB15 AB18 CA01 CB01 DA01 DB03 EA02 EB00 FA01 4J043 PA04 PC016 PC066 PC116 PC186 QB02 ZB21

Claims (5)

[Claims] 1. An electroluminescent device comprising an anode, a cathode, and one or more layers of an organic compound sandwiched between the anode and the cathode, which is generally used as a carrier transport auxiliary layer between the anode and the organic layer. Formula (1) (Wherein R ¹ , R ² and R ³ each independently represent an unsubstituted or substituted monovalent hydrocarbon group or an organooxy group, and A and B each independently represent the general formula (2) or the general formula ( 3) Wherein each of R ^{4 to} R ¹¹ is independently a hydrogen atom, a hydroxyl group, an unsubstituted or substituted monovalent hydrocarbon group or an organooxy group, an acyl group, or a sulfonic acid group. , M and n are each independently 1 or more positive numbers, and satisfy m + n ≦ 20. An electroluminescent device using an electrically conductive thin film formed by forming a salt with the oligoaniline derivative represented by the formula (1) and an electron-accepting dopant. R ² in the general formula (1) is a hydrogen atom, a hydroxyl group, an unsubstituted or substituted monovalent hydrocarbon group or an organooxy group, an acyl group, an alkyl group having 1 to 20 carbon atoms,
The electroluminescent device according to claim 1, which is an alkoxy group having 1 to 20 carbon atoms. 3. A compound represented by the following general formula (4): (D represents a benzene ring, a naphthalene ring, an athracene ring, a phenanthrene ring or a heterocyclic ring, and R ¹² and R ¹³ each independently represent a carboxyl group or a hydroxyl group.) The electroluminescent device according to claim 1, wherein: 4. The conductive thin film according to claim 1, wherein the thin film is obtained by dispersing or dissolving an oligoaniline derivative of the general formula (1) and a sulfonic acid derivative of the general formula (4) in an organic solvent. The electroluminescent device according to claim 1, wherein the electroluminescent device is formed by dipping. 5. The conductive thin film according to claim 1, wherein the thin film is doped with an oligoaniline derivative represented by the general formula (1) and a sulfonic acid derivative represented by the general formula (4) dispersed or dissolved in an organic solvent. 4. The electroluminescent device according to claim 1, wherein the isolated device is formed by a vapor deposition method.