JPH03296595A - Organic thin film electroluminescent element - Google Patents

Abstract

PURPOSE:To improve driving voltage and luminance by incorporating a specific luminescent material into a luminescent layer. CONSTITUTION:A transparent electrode base 3 consists of a transparent base 1 and a transparent electroconductive material layer 2 which is 0.01-1mum thick and formed on the base 1. A luminescent layer 4 which is 0.001-10mum thick and comprises an organic trifunctional compound of the formula (where R1, R1' and R1'' are each H, (non)substituted linear or branched alkyl group or (non)substituted aryl group; R2, R3, R2', R3', R2'' and R3'' are each R1, (non) substituted alkenyl or (non)substituted heterocyclic group or R2 and R3 and/or R2' and R3' and/or R2' and R2'' may form a ring with an adjacent C atom; and A is a trivalent group comprising an aromatic hydrocarbon) and back electrode 5 which is 0.01-1mum thick are formed in thin-film form on the transparent electrode base 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electroluminescent device, and more particularly to an organic thin film electroluminescent device containing an organic compound that emits light in response to an electrical signal.

[Prior art and problems to be solved by the invention] Conventional electroluminescent device (hereinafter referred to as E-device)
In this structure, a transparent electrode is formed on a transparent substrate, and a light emitting layer and an insulating layer are arranged between the transparent electrode and the back electrode (Japanese Patent Laid-Open No. 122092/1982).

As the light-emitting layer, an inorganic light-emitting layer whose light-emitting material is ZnS containing Mn, Cu, or ReF3 (Re is a rare earth ion) on the inactive side is preferably used (Japanese Patent Application Laid-Open No. 1-23
No. 9795), and the basic structure of the light-emitting layer is classified into a powder type and a thin film type. Powder-type EL devices have a light-emitting material dispersed in an organic binder, making them easy to mass-produce and reducing costs, but they have the problem of short lifespan. Furthermore, since the luminescent material is a discontinuous powder, pinholes are likely to occur in the luminescent layer when the luminescent layer is made thinner, making it difficult to reduce the thickness of the luminescent layer, which is a major disadvantage in that sufficient brightness characteristics cannot be obtained. have. On the other hand, thin film EL elements generally have high brightness because they form a light emitting layer by depositing a light emitting material on a transparent electrode, but the driving voltage is 100 V or more, making the driving method complicated.

On the other hand, organic thin film EL devices can reduce the driving voltage and emit light with high brightness, so research has been active in recent years, and many organic thin film EL devices have been developed (Ap.
pl, Phys, Lett,, 51.12°913
(19B?), Japanese Unexamined Patent Publication No. 194395/1983). These organic thin film EL devices are of a laminated type including a transparent electrode/hole injection layer/light emitting layer/back electrode, and the film thickness between the electrodes must not exceed 1, s. As a result, pinholes are likely to occur, making it difficult to manufacture large-area devices, resulting in a very high manufacturing cost. In addition, organic thin film EL devices that emit light with high brightness at low voltage have been fabricated using thin films using the Langmuir-Prodgett method (LB method).
JP-A-52-35587, JP-A-61-4368
Publication No. 2). However, the LB method has problems in that it is difficult to manufacture and lacks practicality. Furthermore, organic thin film EL devices that are easy to manufacture have recently been developed (Japanese Patent Application Laid-Open No. 1-245
No. 087) has insufficient brightness.

[Means to solve the problem]

The present inventors have solved the above problems, and have developed an organic thin film E that can be driven at low voltage, emit high-brightness light, is inexpensive, and is easy to manufacture.
Develop an L element (as a result of intensive studies, we found that an organic thin film EL element that is inexpensive and easy to manufacture, has excellent driving voltage and brightness by incorporating a specific organic trifunctional compound as a luminescent material in the luminescent layer) The present invention was based on the discovery that the following can be obtained.

That is, the present invention provides an organic thin film electroluminescent device having a light emitting layer between a transparent electrode and a back electrode formed on a transparent substrate, in which the light emitting layer contains the general formula (1) (where RI+R+ZR1' is Rz+ R3+ RZZI?l°, which are the same or different and represent any one of a hydrogen atom, an optionally substituted linear or branched alkyl group, and an optionally substituted aryl group.

R2'' and R3'' are the same or different and each represents a hydrogen atom, an optionally substituted linear or branched alkyl group, an optionally substituted aryl group, an optionally substituted alkenyl group, or an optionally substituted alkenyl group. or R7 and R8 and/or R, l and R
, l and/or R2'' and R3'' together with adjacent carbon atoms form a ring.

^ represents a trivalent group consisting of an aromatic hydrocarbon. ) The present invention provides an organic thin film electroluminescent device characterized by containing the organic trifunctional compound shown in ) as a light emitting material.

In the present invention, the light-emitting layer contains a compound in which three substituted vinyl groups such as styryl groups are bonded to a trivalent group consisting of an aromatic hydrocarbon represented by the general formula (1).

Examples of the above trivalent groups include those represented by the following formulas.

(C) Furthermore, (d) naphthalene, (e) anthracene, (ge) phenanthrene, ((to) pyrene, (c) naphthacene, (
Also included are trivalent groups composed of polynuclear aromatic hydrocarbons such as i) 1°2-benzoanthracene, 1) 3,4-benzophenanthrene, (b) chrysene, and (1) 1-liphenylene.

Among the above trivalent groups, those whose raw materials are easily available are preferred.

In general formula (1), R1+ R+'+ R+" is
They may be the same or different and represent either a hydrogen atom, an optionally substituted linear or branched alkyl group, or an optionally substituted aryl group, but the ease of production, performance of the resulting compound, etc. From the point of RI+ RI'+ R1"
are the same and are preferably any one of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group. Examples of the alkyl group and aryl group include a methyl group, an ethyl group, and a phenyl group.

Also, in the case of - large amount (1), R1+ R3+ R2'
+ R3ZR3"J2" is the same or different and represents a hydrogen atom, an optionally substituted linear or branched alkyl group, an optionally substituted aryl group, an optionally substituted alkenyl group, an unsubstituted or R2 and R3 and/or R
21 and R31 and/or R21'' and R1'' form a ring together with adjacent carbon atoms.

Among these, especially R2+ R2'+ RZ'' and R
3+R3'+R3' are each the same and each is an alkyl group, aryl group, alkenyl group, or heterocyclic group having 1 to 12 carbon atoms, or together with adjacent carbon atoms, each has 4 to 12 carbon atoms. Those forming 12 rings are preferred.

Examples of the alkyl group, aryl group, and heterocyclic group include methyl group, ethyl group, phenyl group, naphthyl group, pyridyl group, carbazole group, and substituted ones thereof, and examples of the alkenyl group include.

The method for synthesizing the above-mentioned compound is not particularly limited, but it can be synthesized according to the method normally used for synthesizing styryl compounds. For example, it can be synthesized by condensing triacylated A with triphenylphosphonium halide or phosphonic acid ester, or by condensing (here R4 represents a lower alkyl group) with a carbonyl compound.

Although it is possible to introduce three identical substituted vinyl groups into the trivalent group A, it is also possible to obtain a trifunctional compound having different substituted vinyl groups in one molecule by arbitrarily selecting the reaction raw materials.

Specific examples of the compounds used in the present invention include those shown in the following formulas, but the present invention is not limited thereto.

LIZJ (13) (15) CH3 (17) (18) (19) (22) (20) (21) (30) (31) (37) (38) (39) (48) (43) (4b) υH3 (49) (50) (51) (56) (57) (52) (53) (54) (55) (58) (60) gHs N (61) (64) (62) (63) These compounds can be used alone or in combination of two or more.

Further, the above organic trifunctional compound can also be used as a luminescent material in a luminescent layer of a stacked organic thin film EL device having a transparent electrode/hole injection layer/luminescent layer/back electrode. Since the hole injection layer is placed between the transparent electrode and the light emitting layer, the hole injection layer is 400n-
It is preferable to transmit 80 to 100% of the above wavelengths.

Therefore, the hole transfer compound in the hole injection layer is preferably an aromatic amine that is a colorless solid at room temperature, can appropriately inject holes into the light emitting layer, and can be easily and reversibly oxidized. Examples of such aromatic amines include 1,1-bis(
4-di-p-tolylaminophenyl)cyclohexane,
Bis(4-dimethylamino-2-methylphenyl)phenylmethane, N,N,N-)ly(p-tolyl)amine, N,N'-diphenyl-N,N"-bis(3-methylphenyl)-1 ,1°-biphenyl”) −4,
Examples include 4'-diamine.

In producing the organic thin film EL device of the present invention, a transparent electrode, a light emitting layer, and a back electrode are sequentially formed in the form of a thin film on a transparent substrate.

Any conventionally known transparent electrode can be used as the transparent electrode, and preferred examples include indium oxide, indium tin oxide (ITO) on a transparent substrate such as a transparent resin such as polymethyl methacrylate or polyester, glass, or quartz. It is coated with a transparent conductive material such as tin oxide, aluminum, nickel, or gold to a thickness of 0.01 to 1.0 am.

Methods for thinning a light-emitting layer using the organic trifunctional compound represented by the general formula (1) as a light-emitting material include spin cording, vapor deposition, LB method, etc., which may be selected depending on the light-emitting material used. Vapor deposition is preferred in order to make the film uniform. Conditions for forming a thin film by vapor deposition vary depending on the luminescent material used, but the heating temperature is set above the sublimation temperature for sublimable materials, and above the melting point for meltable materials. Preferably, the heating temperature is 100 to 400° C1, the transparent electrode substrate temperature is -20 to AOO"C, the degree of vacuum is 10-7 to 10" Torr to prevent oxidation, and the deposition rate is between 0.1 to 100 people/sec. conduct. The thickness of the light-emitting layer is not particularly limited and may be selected depending on the situation, but 0.0
01-10-1, preferably 0.01-5-.

The back electrode may be of a conventionally known type, such as a vapor-deposited film of aluminum, silver, gold, magnesium, manganese, tin, etc., and the film thickness is preferably 0.01 to 11 m.

The above-described transparent substrate, transparent electrode, light-emitting layer, and back electrode can be similarly used when producing a stacked organic thin-film EL device including a hole injection layer.

The same method as for forming the light-emitting layer can be used to make the hole injection layer thin, and the method may be selected depending on the hole transfer compound used, but a vapor deposition method is preferable in order to make the film uniform. The thickness of the hole injection layer is not particularly limited and may be selected depending on the situation, but it is 0.001 to 10A, preferably 0.001 to 10A.
．． 01-5J1!1.

When using the organic thin film EL device thus obtained, the transparent electrode and back electrode are each connected to a power source. By applying a voltage to this, it emits blue-green or green light.

〔Example〕

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

Synthesis Example-2135-Tsu-(-N, N stirring device,
77.4 g (0.3 mol) of phosphonic acid jetyl/1z synthesized from p-chloromethylanisole was placed in a 214-hole flask equipped with a cooling tube, a nitrogen inlet tube, and a dropping funnel, and dissolved in 500 wLl of dimethylformamide. Methanol 200@7 in which 40 g of sodium hydroxide was dissolved was added thereto at room temperature. 400-dimethylformamide in which 716.2 g (0.1 mol) of 1.3.5-)riformylbenze was dissolved was slowly added dropwise at room temperature. After the dropwise addition was completed, the mixture was stirred at room temperature for 1 hour, and the yellow crystals that had formed were filtered. The crystals were washed 3 times with water and 2 times with methanol, and recrystallized with ethanol.
Lis(β-(P-methoxystyryl))benzene at 36
8 (yield 78%) was obtained.

1 equipped with a stirring device, cooling tube, nitrogen introduction tube, and thermometer.
3 g of diethyl phosphonate synthesized from 1.3.5-tris(chloromethyl)benzene in 4 ff flasks
(5,7 mmol), p-N,N diethylaminobenzaldehyde 3 g (17 mmol), sodium hydride 1.2 g, 1,2-dimethoxyethane 300 WLl
and stirred at 85°C for 3 hours without introducing nitrogen. Thereafter, the reaction mixture was cooled to room temperature and poured into 22 portions of water. Furthermore, ethyl acetate 11 was added and mixed well, and the ethyl acetate layer was separated. This ethyl acetate solution was washed twice with water and dried over anhydrous sodium sulfate. After drying, ethyl acetate was distilled off under reduced pressure to obtain a yellow solid, which was recrystallized from n-hexane/ethyl acetate (4/1) to obtain 3 g of yellow crystals (yield 90%).

Synthesis Example-324-1S - -NN 1 equipped with a stirring device, cooling tube, nitrogen introduction tube, and thermometer
5 g of diethyl phosphonate synthesized from 1.2.4- ) lis(bromomethyl)benzene in 24 flasks.
(9.5 mmol) and 300 mmol of ethylene glycol dimethyl ether were added and dissolved, and 3.0 g of sodium hydride was added thereto at room temperature. After stirring for 30 minutes, p-N
, N-diethylaminobenzaldehyde 5g (28,
5 mmol) of ethylene glycol dimethyl ether solution was added dropwise at room temperature. After the dropwise addition was completed, the temperature was raised to 85°C and stirred at that temperature for 5 hours.

Thereafter, the reaction mixture was cooled to room temperature and 2! poured into the water. Furthermore, add ethyl acetate 11 (mix and separate the ethyl acetate layer. This ethyl acetate solution was washed twice with water and dried over anhydrous sodium sulfate. After drying, ethyl acetate was distilled off under reduced pressure. A yellow solid was obtained, purified once using a silica gel column (ethyl acetate), and further recrystallized using isopropanol to obtain 4.7 g of yellow crystals (yield: 83%).

Example-1 An organic thin film EL device as shown in FIG. 1 was manufactured.

That is, I
A transparent electrode 2 having a film thickness of 0.1 - was formed by sputtering using TO to obtain a transparent electrode substrate 3. On this transparent electrode substrate 3, 200a+g of the luminescent material (4) obtained in Synthesis Example-1 was placed in a tantalum boat heated to 250°C, and 2X
Deposition rate of 5 people/at 10-' TorrO system pressure
The light emitting layer 4 having a film thickness of 0.4 mm was obtained by vapor deposition for 20 seconds. The substrate temperature at this time was room temperature.

Next, a shadow masking layer is placed on this luminescent layer 4, and gold 2 is applied.
00 mg was placed in a tantalum boat heated to 1300° C., and the film was deposited at a deposition rate of 10 people/sec at an internal system pressure of I x 10 -'' Torr to obtain a back electrode 5 with a film thickness of 0.1!m.

The transparent electrode 3 and back electrode 5 of the organic thin film EL device thus obtained were connected to a power source 7 through lead wires 6, and when a DC voltage of 15 V was applied, a current density of 611
A brightness of 150 cd/m'' was obtained at A/CI+''. The emission color at this time was blue-green at 500 nm.

Example-2 In Example-1, a luminescent material (6) was used instead of the luminescent material (4), and the material was placed in a tantalum boat heated to 280°C, and vapor-deposited at an internal system pressure of I x 10-'Torr. At a speed of 1 person/see, the film thickness is 1. An organic thin film EL device was produced in exactly the same manner except that a light emitting layer of 0- was obtained.

When a DC voltage of 20 V was applied to the organic thin film EL device thus obtained, a luminance of 250 cd/m'' was obtained at a current density of 1 o-^/Cal''. The emission color at this time was green at 530 nm.

Example-3 In Example-1, a luminescent material (41) was used instead of the luminescent material (4), and the material was placed in a tantalum boat heated to 300"C, and the deposition rate was adjusted at an internal system pressure of 4 x 10-bTorr. An organic thin film EL device was produced in exactly the same manner except that a light emitting layer with a film thickness of 0.8 - was obtained at a rate of 4 people/sec.

When a DC voltage of 18 V was applied to the organic thin film EL device obtained in this way, a luminance of 300 cd/m'' was obtained at a current density of l{^/cIII2.The luminance color at this time was green at 540 nm. Met.

Example-4 In Example-1, a luminescent material (42) was used instead of the luminescent material (4), and the material was placed in a tantalum boat heated to 320°C and deposited at an internal system pressure of 7 x 10-'Torr. An organic thin film EL device was produced in exactly the same manner except that a light emitting layer with a thickness of 0.2 - was obtained at a speed of 2 persons/sec.

When a DC voltage of 20 V was applied to the organic thin film EL device thus obtained, the current density was 5IIIA/cIll!
A luminance of 200 cd/m'' was obtained at this time.The emission color at this time was green at 545 nm.

Example-5 In Example-1, a luminescent material (65) was used instead of the luminescent material (4), and the material was placed in a tantalum boat heated to 280°C, and vapor-deposited at an internal system pressure of 2 x 10-” Torr. An organic thin film EL device was produced in exactly the same manner except that a light emitting layer with a thickness of 1.2 m was obtained at a speed of 4 persons/sec.

When a DC voltage of 20 V was applied to the organic thin film EL device thus obtained, a luminance of 250 cd/m'' was obtained at a current density of 15 mA/cm''. The emitted light color at this time was 535n- green.

Comparative Example-1 In Example-1, 14-bis(2-methylstyryl)benzene was used instead of the luminescent material (4), and 300'
Place in a tantalum boat heated to C, 5 x 1f
Deposition rate 10 people/se at l'TorrO system pressure
An organic thin 111 EL device was produced in exactly the same manner except that a light emitting layer with a thickness of 0.5 μm was obtained in step c.

When a DC voltage of 15 V was applied to the organic thin film EL device thus obtained, the luminance was as low as 20 cd/m'' at a current density of 20 mA/cm''.

Comparative Example-2 In Example-1, instead of the luminescent material (4), 1°4-
Using bis(2-ethylstyryl)benzene at 320°C
6 x 10-
Deposition rate 5 people/sec at system pressure of 'Torr
An organic thin film EL device was produced in exactly the same manner except that a light emitting layer with a film thickness of 0.7 layers was obtained.

When a DC voltage of 20 V was applied to the organic thin film EL device thus obtained, the luminance was as low as 35 cd/m'' at a current density of 25 mA/cm''.

〔Effect of the invention〕

The organic thin film EL device of the present invention, which is characterized by containing an organic trifunctional compound as a light emitting material in its light emitting layer, can emit light with high brightness when driven at low voltage, and its structure also includes a transparent electrode/
Since it is a light emitting layer/back electrode, it is inexpensive and easy to manufacture.

Therefore, it can be applied to computer terminal display devices, etc.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a state in which the organic El film εL element obtained in Example 1 is connected to a power source. 1: Transparent glass substrate 2: Transparent electrode 3: Transparent electrode substrate 4: Luminescent layer 5: Back electrode 6: Lead wire 7: Power source Fig. 1

Claims (3)

[Claims] 1. In an organic thin film electroluminescent device having a light-emitting layer between a transparent electrode and a back electrode formed on a transparent substrate, the light-emitting layer contains the general formula (1) (where R_1, R_1', R_1'', R_1'' are the same or different and represent a hydrogen atom, an optionally substituted linear or branched alkyl group, an optionally substituted aryl group, and R_2, R_3, R_2'R_3', R_
2"R_3" are the same or different hydrogen atoms,
Represents any of an optionally substituted linear or branched alkyl group, an optionally substituted aryl group, an optionally substituted alkenyl group, an optionally substituted heterocyclic group, or R_2 and R_3 and/or R_2'
and R_3' and/or R_2'' and R_3'' form a ring together with adjacent carbon atoms. A represents a trivalent group consisting of aromatic hydrocarbon. ) An organic thin film electroluminescent device comprising an organic trifunctional compound represented by the following as a light-emitting material. 2. 2. The organic thin film electroluminescent device according to claim 1, wherein in general formula (1), A is a trivalent group represented by the formula ▲, which includes a mathematical formula, a chemical formula, a table, etc. ▼. 3. 2. The organic thin film electroluminescent device according to claim 1, wherein in general formula (1), A is a trivalent group represented by the formula ▲, which includes a mathematical formula, a chemical formula, a table, etc. ▼.