JPH04126790A - Luminescent element - Google Patents

Abstract

PURPOSE:To obtain a thin-film type luminescent element, having a positive hole transport layer which is a specific m-phenylenediamine-based compound, improved in deterioration of emission brightness with time, having the high emission brightness and usable as light sources, etc., for illumination, display, indication and optical communication. CONSTITUTION:The objective luminescent element having a positive hole transport layer which is an m-phenylenediamine-based compound expressed by formula I [R1 to R5 are H, halogen or alkyl or alkoxy which may be respectively substituted; M is H, alkyl, alkoxy, halogen or formula II (R6 and R7 are H, halogen or alkyl or alkoxy which may be respectively substituted)].

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thin film light emitting element used for illumination such as a backlight of a liquid crystal and various decorators, a display, a light source for optical communication, and the like.

C. Prior Art] A high-brightness charge injection type organic electroluminescent device has recently been announced.
These are surface-emitting devices, and are expected to be applied to matrix movable displays.

Regarding these charge injection type electroluminescent devices, for example,
Applied Physics Letter (Appl, Phys.
S, Let,) Ll 913 (1987) and Japanese Journal of Applied Physics (Jpn, J, Appl, Phys,) U 1269
(1988), etc. The laminated structure of the thin film device that has been published is to create a transparent electrode on a transparent substrate such as glass, and on top of that is a hole transport layer made of an organic compound such as diamine, and a light emitting layer. It can be an 1il1 light-emitting element consisting of layers and electrodes and having a total thickness of several μm or less.

[Invention tries to solve it! ! [Iff] In the organic electroluminescent device described above, a problem is a phenomenon in which the luminescence intensity decreases over time, that is, the luminance deteriorates over time. Therefore, it is desired to improve the deterioration of luminance over time and improve the luminance.

[Means for Solving the Problems] In order to solve the above problems, the present inventors, as a result of intensive studies, used m-phenylenediamine-based compounds as diamine derivatives used in the hole transport layer made of organic compounds. I got the idea that a highly efficient thin-film light-emitting device could be obtained by doing this, and when I tried this, I realized a thin-film light-emitting device that not only has high luminous efficiency but also has little deterioration over time. completed.

In research on electrophotographic photoreceptors, triphenylamine-based diamine derivatives are known as materials for hole transport layers. Among these, regarding m-phenylenediamine compounds, for example, as seen in the presentation by Kuninaka and Sendai et al. at the 56th Spring Annual Meeting of the Chemical Society of Japan, 3XII C39,
m-phenylenediamine compounds have been studied as carrier transport materials in resin dispersion systems for electrophotographic photoreceptors, and have higher drift mobility than other amine compounds. The reason for this is that derivatives in which phenylenediamine is attached to the m-position have a small deviation in electron density within the molecule. For this reason, we propose that the ion radical state, which is an intermediate state that moves holes, is not localized within the molecule and provides high drift mobility.

In an electrophotographic photoreceptor, a hole transporting material is usually used by being dispersed in a resin, and is used together with a charge-generating material that generates charges when exposed to light.

In addition, the hole transport layer used in electrophotographic photoreceptors is 20
It is formed with a thickness of about μm and functions to transport a small amount of holes generated in the charge-generating material and erase corona-charged surface charges.

On the other hand, in the light-emitting device of the present invention, unlike the electrophotographic device, erasing of the electrical charges is not possible, and not only does a continuous direct current flow directly, but also a high electric field is applied to the hole transport layer. A very thin film is formed and no resin is used.

However, the delocalization of the ionic radical state that transports holes in m-phenylenediamine-based compounds results in high hole transport ability even in devices such as those in the present invention.
I thought that it might improve luminous efficiency. Moreover, surprisingly, m-phenylenediamine-based compounds have never been used in light-emitting devices.

Surprisingly, it was found that when m-phenylenediamine-based compounds were used in the hole transport layer, not only high luminance was obtained, but also the deterioration of luminescence over time was reduced. Since this is a substituent at the m-position, the symmetry is broken compared to a substituent at the 2-position, and it is difficult to form domains even in a thin film without a binder or other constituents as used in the present invention. It is thought that.

It is thought that this resulted in a stable hole transport layer having high hole transport ability.

The present invention has a structure in which a hole transport layer made of an organic compound, a light emitting layer, and an electrode are laminated in this order on at least a transparent electrode, and the hole transport layer made of an organic compound is formed by -Equation (1) [Formula (1) In, R1, R2, R1, R4, and R3 represent a hydrogen atom, an alkyl group, an alkoxyl group, or a halogen atom, and may be substituted as long as each can be substituted, and all substituents may be the same or different from each other. You can. M is a hydrogen atom, an alkyl group, an alkoxyl group, a halogen atom, or - Formula (2) [In Formula (2), R-1R7 represents a hydrogen atom, an alkyl group, an alkoxyl group, or a halogen atom, and each is substituted as much as possible. and all substituents may be the same or different from each other.] A light-emitting element, a light-emitting layer, and an electrode, characterized by being an m-phenylenediamine-based compound represented by The present invention relates to the above-mentioned light emitting element in which an electron transport layer is laminated therebetween.

In other words, it is a thin film type light emitting element with high brightness and low deterioration using an m-phenylenediamine compound as a hole transport layer.

In addition, in formulas (1) and (2), the meaning of "each can be substituted" means that each benzene ring in the formula has 1 to 5 substituents.

FIG. 1 is a diagram illustrating the configuration of the present invention. In FIG. 1, reference numeral 100 represents a transparent substrate, which is used for manufacturing purposes and for the purpose of protecting the mechanical components of the device, but may not be necessary depending on the case. The transparent substrate only needs to be transparent to incident light, and suitable examples include glass and plastic resin substrates. Additives such as inorganic or organic pigments or dyes may be added to these substrates to partially remove the emitted light. Also, optical filter 4ill! A functional membrane may be inserted or laminated.

The transparent electrode in the present invention is indicated by 101 in FIG.

The material used may be any material as long as it has sufficient optical transparency for incident light or output light.For example, a material that can easily inject holes into the hole transport layer is preferred. Thin films of metals with large electron work functions, alloys, metal oxides, and other metal compounds, and thin films made of stacked layers of these metals are used for fishing. For example, platinum, gold, selenium, palladium,
Preferred examples include metals and alloy compounds such as nickel, tungsten, tantalum, and tellurium, and laminated films thereof, and thin films and laminated films of metal compounds such as CuI.

In the present invention, a hole transport layer made of an organic compound is formed on a transparent electrode. In FIG. 1, a hole transport layer made of an organic compound is indicated by 102. The feature of the present invention is that the hole transport layer material made of this organic compound has the following formula:
It is to use m-phenylenediamine type compound shown by.

For example, suitable examples include N, N, N'', N''-tetraphenyl-1,3-diaminotonzene (m-PDA) C formula % formula % [formula (12)), N, N, N', N'-tetrakis (
3-methylphenyl')-3,5-diaminotoluene (
5Me-m-PDA)C formula (13)) , N, N, N'
, N', N", N"-hexakis(4-methylphenyl)-1,3,5-triaminobenzene (6Me-1,3
, 5-DPAB)C formula (14)E. The structural formulas of these examples are expressed as formulas (11) to (14)
Shown below.

(I2) Furthermore, methods for synthesizing these m-phenylenediamine compounds are disclosed in, for example, JP-A-1-142642 and are generally known.

The thickness of the hole transport layer made of an organic compound in the present invention is not particularly limited, but is usually 5 nm to 2 μm.

Methods for manufacturing the hole transport layer in the present invention include vacuum evaporation method, sublimation method, molecular beam epitaxy method, L
Physical or chemical thin film forming methods such as Method B, coating methods such as dipping and spin cording can be used.

A light emitting layer is formed in contact with the hole transport layer made of the above organic compound. In FIG. 1, 103 indicates a light emitting layer. Organic compounds used in the light emitting layer in the present invention include:
Organic compounds that have a high emission quantum yield, have a π-electron system that is susceptible to external perturbations, and are easily excited are preferably used.

Examples of such organic compounds include fused polycyclic aromatic hydrocarbons such as anthracene, coronene, and perylene, polyphenyl 12.5-diphenyloxazole, 1,4 -Bis-(2-methylstyryl)-benzene and other distylphenses, cyclopentagenes, perinones, xanthines, coumarins, acridines, NK1952 (
Forms complexes in an excited state in cyanine dyes such as Nippon Photosensitive Color Products), hensifenones, phthalocyanine dyes, as well as heterocyclic compounds other than those listed above, aromatic amines, aromatic polyamines, and compounds with a quinone structure. Examples of such compounds include polyacetylene, polysilane, etc. A preferred example is a metal complex compound consisting of a metal and an organic ligand. As a specific example, the metal species include ^1, Ga, I
r, Zn, Cd, Mg, Pb, τa, etc. are preferable, and examples of the organic ligand include porphyrin, chlorophyll, 8-hydroxyquinoline (oxine), phthalocyanine, salicylaldehyde oxime, 1
-Nitroso-2-naphthol, couferone, dithizone,
Acetylacetone and the like are used. More specifically,
For example, oxine complex, 5,7-dibromooxine complex, 5,7-diiodooxine complex, thioxin complex,
Examples include methyloxine complexes, more specifically aluminum oxine complexes, lead oxine complexes, lead dibromooxine complexes, lead (5,7-diiodooxine) complexes, lead thioxine complexes, lead selenooxine complexes, and bismuth methyloxine complexes. Preferred examples include complexes.

Representative examples include tris(8-hydroxyquinoline)aluminum shown in 2 (21) and formulas (22) to (26).
) include polycyclic compounds such as those shown in

Moreover, a mixture of these compounds may be used.

Additives called dopants are added to these light-emitting layers.
By adding in an amount of 1wtχ to 30-tχ, the color of the emitted light can be changed. For example, by adding coumarin to tris(8-hydroxyquinoline)aluminum shown in formula (21), the original green light emission changes to blue-green light emission. Furthermore, it is known that an orange luminescent color can be obtained by adding a styryl dye. The light emission when an additive is added is the light emission from the additive, which shows that the light emission can be changed by changing the additive.

The light-emitting layer in the present invention is an amorphous layer of these organic compounds,
It is an amorphous, polycrystalline, or single crystal layer containing microcrystals or microcrystals. The thickness of the layer is not particularly limited, but is usually between 5 nm and 2 nm.
μm is adopted.

As a manufacturing method of the light emitting layer in the present invention, physical or chemical thin film forming methods such as vacuum evaporation method, sublimation method, molecular beam epitaxy method, LB method, coating method such as dipping or spin cord can be used. .

Furthermore, an electrode is provided in contact with the light emitting layer. In FIG. 1, an example illustrating the invention, the electrode is indicated at 104. Furthermore, an electron transport layer may be provided between the electrode and the light emitting layer.

In the present invention, the electrode in contact with the light-emitting layer or electron-transporting layer may be transparent or translucent, or may not be transparent. The electrode used here is preferably one that easily injects electrons into the light-emitting layer or electron-transporting layer, and -i For example, metals with small electron work functions, alloy thin films, and laminated films thereof are used. For example, metal thin films such as magnesium, lithium, potassium, calcium, rubidium, strontium, and cerium, alloys such as magnesium-silver, and CCs-0- A, C5z
Examples include metal compound thin films such as SbSNaJSbSCsNaJSb, and laminated thin films thereof. In the present invention, examples of materials used for the electron transport layer that may be present between the light emitting layer and the electrode include cross-conjugated compounds such as diphenoquinones as shown in formula (31) and formula (32), and benzophenone. Suitable examples include hydrazone-based compounds, 2,4.7-)dinitro-9-fluorenone, and fluorene-based compounds such as the compound represented by formula (33).

Cat, CI" The method for manufacturing the electron transport layer in the present invention includes vacuum evaporation method, sublimation method, molecular beam epitaxy method, L
Physical or chemical thin film forming methods such as Method B, coating methods such as dipping and spin cording can be used. There is no particular limit to the film thickness, but it is from 10 nm to 2 μm.
degree is used.

[Effects of the Invention] By using an m-phenylenediamine compound in the hole transport layer, the light-emitting element of the present invention is a light-emitting element in which deterioration of luminance over time is improved and has high luminance.

C Example] Hereinafter, the present invention will be specifically explained with reference to Examples, but the embodiments of the present invention are not limited thereto.

Example I A thin film of m-PDA, which is an m-phenylenediamine compound, was formed by vacuum evaporation on a glass substrate 1 (manufactured by Matsuzaki Shinku Co., Ltd.) which had been pattern-etched to a thickness of 200 nm using ITO as a transparent electrode. Degree of vacuum 10-'To
The frequency of the crystal oscillation film thickness meter is 0.5 kHz under the conditions of rr.
Vapor deposition was stopped when the change occurred, and tris(8-hydroxyquinoline) aluminum was further vapor-deposited on this layer under the same conditions. The film thickness was set to a point where the crystal oscillation film thickness meter changed by 0.4k)Iz. Furthermore, on top of this, the degree of vacuum is 2
Mg was vacuum deposited to a thickness of 200 nm under the conditions of Xl0-6 Torr.

When a voltage was applied with the ITO side of the electrode of the laminated thin film thus prepared being positive and the Mg side being negative, light emission was observed.

No light emission was observed when the voltage was applied in the opposite direction.

FIG. 2 shows the luminance characteristics with respect to voltage. 2000cd
Emission brightness close to /m'' was obtained, indicating that the device has high emission brightness.

This sample was allowed to emit light continuously in a dry box while a voltage was applied to it. In this case, the luminance is initially 12
7cd/+” was the same 12V after 100 hours.
The voltage was 113 cd/m'' when a voltage of

Comparative Example 1 According to Example 1, ITO was used as a transparent electrode and the thickness was 200 nm.
N,N'-diphenyl-N,N'-bis, which is a phenylenediamine compound but is not a substituent at the m position, was deposited on a glass substrate (manufactured by Matsuzaki Vacuum Co., Ltd.), which was pattern-etched to a thickness of , by vacuum evaporation. (3-methylphenyl)-
A thin film of 1,4-diaminobenzene (p-PDA) was created. At a vacuum level of 10-'Torr, the evaporation was stopped when the frequency of the crystal oscillation film thickness meter changed to Q, 5kHz.
Further, tris(8-hydroxyquinoline)aluminum was evaporated onto this layer under the same conditions. The film thickness was set to a point where the crystal oscillation film thickness meter changes by 0.4 kHz. Furthermore, Mg was vacuum-deposited onto this to a thickness of 200 nm under the condition of a vacuum degree of 2×10 −' Torr.

p-PDA used here was synthesized as follows.

N,N'-diphenyl-1,4-diaminobenzene (
After a reflux reaction of 21.8 g of Tokyo Kasei, 8.5 g of potassium carbonate, 1.1 g of copper powder, and nitrobenzene 100II+1 for 24 hours, the solvent and unreacted raw materials were removed by steam distillation. Wash the residue with water and add benzene 400
-sl, dried over magnesium sulfate, and insoluble matter was removed by filtration. This solution was separated using activated alumina column chromatography using a benzene-hexane solution of 1:1 (volume ratio), and the first fraction eluted was separated. The solvent was distilled off to obtain a pale yellow solid. Yield 9
．． 8g, yield 44Z. Recrystallization from benzene-methanol gave pale yellow plate crystals. This crystal was further purified by sublimation to form a white solid, which was then used. Melting point 170-1
The luminance characteristics versus voltage of the laminated thin-M sample prepared at 71°C are shown in FIG. 3 by a solid line.

This sample was allowed to emit light continuously in a dry box while a voltage was applied to it. In this case, the luminance is initially 18
What was 118 cd/m” when a voltage of V was applied became 100 cd/m”
After some time, the voltage decreased to 70 cd/+'' by applying the same voltage of 18 V.

When compared with Example 1, it can be seen that the voltage-luminance characteristics are inferior and there is a large difference in luminance deterioration over time.

Comparative Example 2 Similar to Comparative Example 1, in accordance with Example 1, ITO was used as a transparent electrode on a glass substrate (manufactured by Matsuzaki Vacuum Co., Ltd.) on which a pattern was etched to a thickness of 200 nm. created a thin film of nickel phthalocyanine (Tokyo Kasei), which is known as a hole transport material. Vapor deposition was stopped when the frequency of the crystal oscillation film thickness meter changed by 0.4 kHz under the vacuum condition of 10-' Torr, and then the deposition of tris(8-hydroxyquinoline) was continued under the same conditions.
Aluminum was evaporated onto this layer. The S thickness was set to a point where the crystal oscillation film thickness meter changes by 0.4 kHz. Furthermore, on top of this, M
g was vacuum deposited to a thickness of 200 nm. The luminance characteristics of the produced laminated thin film sample with respect to voltage are shown in FIG. 3 by broken lines.

A comparison with Example 1 shows that the voltage-luminance characteristics are significantly inferior.

Example 2 N, N, N', N', which are m-phenylenediamine compounds, were deposited by vacuum evaporation on a glass substrate (manufactured by Hiho Shinku Co., Ltd.) on which a pattern of 200 nm thick was etched using ITO as a transparent electrode. , N”, N”-hexakis (4-
A thin film of methylphenyl)-1,3,5-triaminobenzene (6Me-1,3,5-DPAB) was prepared.

The vapor deposition was stopped when the frequency of the crystal oscillation film thickness meter changed by 0.6 kHz under the vacuum condition of 10-' Torr, and tris(8-hydroxyquinoline) aluminum was further vapor-deposited on this layer under the same conditions.

The film thickness was set to a point where the crystal oscillation film thickness meter changes by 0.4 kHz. Furthermore, on top of this, a vacuum degree of 2X10-'Tor is applied.
Mg was vacuum-deposited to a thickness of 200 nm under conditions of r.

6Me-1,3,5-DPAB used here was synthesized as follows. Phloroglucinol (Gyudon Chemical) 2
g and p+ p'-ditolylamine (Tokyo Kasei) 14.5
g, 0.6 g of iodine at 250°C in an autoclave.
The reaction was allowed to proceed for 0 hours. After the reaction, the mixture was poured into 1 ml of benzene, 5 g each of sodium carbonate and sodium sulfate were added, and the mixture was stirred for 2 hours. Insoluble matter was removed by filtration, and the solution was subjected to active alumina column filtration using benzene-hexane (l:1 (volume ratio)) as a developing solution. The solvent was distilled off, and p,p'-ditolylamine and oil were removed using a sublimation tube to obtain a pale brown solid. Yield 0.66g, Yield 6.3
χ. It was recrystallized from Hensen-methanol to obtain white needle-shaped crystals, which were used. Melting point: 234-236°C0 Figure 4 shows the luminance characteristics of the prepared laminated thin film sample versus voltage. Similar to Example 1, high luminance was exhibited.

While voltage was applied to this sample, nine consecutive lights were emitted in a dry box. In this case, the luminance is initially I
What was 115 cd/m2 with OV voltage application was 10
105 cd/m” by applying the same IOV voltage after 0 hours
Met. As with Example 1, it is shown that the stability is excellent.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a configuration example of the present invention. 100: Transparent substrate 101: Transparent electrode 102: Hole transport layer 103: Light emitting layer 104: Electrode FIGS. 2 and 4 are graphs showing the voltage-luminance characteristics of Examples 1 and 2, respectively. FIG. 3 is a graph showing voltage-luminance characteristics of a comparative example. □: Comparative example 1 ------・-: Comparative example 2 Patent applicant
Mitsui Toatsu Chemical Co., Ltd.Figure 1 Brightness (cd/m2) Brightness (cd/m2)

Claims (2)

[Claims] 1. It consists of a structure in which a hole transport layer made of an organic compound, a light emitting layer, and an electrode are laminated in this order on at least a transparent electrode, and the hole transport layer made of an organic compound has the general formula (1) ▲There are mathematical formulas, chemical formulas, tables, etc. ▼ [In formula (1), R_1, R_2, R_3, R_4
, R_5 represents a hydrogen atom, an alkyl group, an alkoxyl group, or a halogen atom, each of which may be substituted as long as it can be substituted, and all substituents may be the same or different from each other. M is a hydrogen atom, an alkyl group,
Alkoxyl group, halogen atom, or general formula (2) ▲ Numerical formulas, chemical formulas, tables, etc. A light-emitting element characterized by being an m-phenylenediamine-based compound represented by the following formula. 2. 2. The light emitting device according to claim 1, wherein an electron transport layer is laminated between the light emitting layer and the electrode.