JPH06271847A - Organic thin film luminescent element - Google Patents

Abstract

PURPOSE:To obtain the subject element useful for a display device, etc., providing a stable yellowish green emission, high luminance, excellent film-forming properties and mass productivity, comprising an electron injecting layer and a luminous layer containing a specific styryl-thiophene compound between electrodes of an anode and a cathode. CONSTITUTION:This element comprises a charge injecting layer composed of at least one of an electron injecting layer 5 and a positive hole injecting layer 3 and a luminous layer 4 containing a styryl-thiophene compound of formula I[R1 and R2 are each alkyl, alkoxy or (substituted)aryl; R3 and R6 are each H or alkyl; R4 and R5 are each H, alkyl or aryl; R7 is H, alkyl, halogen, etc.; R8 is H, alkyl, aryl, etc.; (n) is 1 or 2] such as a compound of formula II between a pair of electrodes of an anode 2 and a cathode 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic thin film light emitting device used as a light emitting source of various display devices, and more particularly to a light emitting substance used for a light emitting layer of the device.

[0002]

2. Description of the Related Art With the rapid increase in demand for flat displays replacing conventional cathode ray tubes, various display elements have been vigorously developed and put into practical use. An electroluminescence element (hereinafter referred to as an EL element) is also adapted to such a need, and in particular, as an all solid state spontaneous light emitting element,
It attracts attention due to its high resolution and high visibility that other displays do not have. At present, what has been put into practical use is an EL element made of an inorganic material using a ZnS / Mn system in the light emitting layer. However, this type of inorganic EL element has a problem that the driving method is complicated and the manufacturing cost is high because the driving voltage required for light emission is as high as 100 V or more. Also,
Since the efficiency of blue light emission is low, full colorization is difficult. On the other hand, a thin film light emitting device using an organic material is
Since the driving voltage required for light emission can be significantly reduced and the potential for full color conversion can be sufficiently obtained by applying various light emitting materials, research has been actively conducted in recent years.

In particular, in the laminated type composed of electrode / hole injection layer / light emitting layer / electrode, tris (8-hydroxyquinoline) aluminum is used as the light emitting material and 1,1 is used as the hole injection material.
Since the use of -bis (4-N, N-ditolylaminophenyl) cyclohexane gave a brightness of 1000 cd / m ² or more at an applied voltage of 10 V or less, the development was spurred. (Appl.Phys.Let
t. 51 , 913, (1987)).

[0004]

As described above, although the thin film light emitting device using an organic material strongly suggests the possibility of low voltage driving and full colorization, the problem to be solved in terms of performance. There are many left. In particular, the problem of characteristic deterioration due to long-time driving of about 10,000 hours is a problem that must be overcome. In addition, RGB in full color
Development of light-emitting material that enables emission of three primary colors, and because the organic layer has a thickness of 1 μm or less, film formation is good, there are no electrical defects such as pinholes, and electron and hole transporting ability Development of excellent organic materials, selection of electrode materials with excellent charge injection properties into organic layers, etc.

Further, from the viewpoint of mass productivity, the development of inexpensive organic materials that can be mass-produced and the improvement of the element forming method are important issues. The present invention has been made in view of the above points, and an object thereof is to provide an organic thin-film light emitting device that is highly bright and excellent in stability, inexpensive and easily manufactured by developing a novel yellow-green light emitting material. .

[0006]

According to the present invention, the above-mentioned object has a pair of electrodes consisting of a positive electrode and a negative electrode, and a charge injection layer and a light emitting layer sandwiched therebetween, and the charge injection layer is an electron. The light emitting layer is composed of at least one of an injection layer and a hole injection layer. The light emitting layer recombines injected electrons and holes to emit light, and contains a styryl-thiophene compound represented by the following general formula (I). This is achieved by assuming that it is a waste.

[0007]

[Chemical 2]

[In the formula (I), R ₁ and R ₂ are each an alkyl group, an alkoxy group, a substituted or unsubstituted aryl group, R ₃ and R ₆ are hydrogen atoms and an alkyl group, and R ₄ and R ₅ are hydrogen. Atom, alkyl group, aryl group, R ₇ is a hydrogen atom,
An alkyl group, a halogen atom, an alkoxy group, a dialkylamino group, a diarylamino group, R ₈ is a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, and n is 1 or 2. ] Specific examples of the styryl-thiophene compound represented by the general formula (I) are shown below.

[0009]

[Chemical 3]

[0010]

[Chemical 4]

[0011]

[Chemical 5]

[0012]

[Chemical 6]

[0013]

[Chemical 7]

[0014]

The present inventors have conducted many experiments on various substances in order to achieve the above-mentioned object. As a result, the styryl-thiophene compound represented by the general formula (I) is effective, although the details are unknown. I found a thing.

[0015]

EXAMPLES Specific examples of the organic thin film light emitting device using the styryl-thiophene compound in the present invention will be described.
A description will be given with reference to the drawings. The styryl-thiophene compound represented by the general formula (I) can be synthesized by the Wittig reaction of the compound represented by the following (A) and the compounds represented by the following (B) and (C).

[0016]

[Chemical 8]

[Wherein R ₁ and R ₂ are an alkyl group, an alkoxy group, a substituted or unsubstituted aryl group, R ₃ and R ₂ , respectively]
₆ is a hydrogen atom, an alkyl group, R ₄ and R ₅ are a hydrogen atom, an alkyl group, an aryl group, R ₇ is a hydrogen atom, an alkyl group,
A halogen atom, an alkoxy group, a dialkylamino group, a diarylamino group, R ₈ is a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, and n is 1 or 2. The styryl-thiophene compound of the present invention is a Witt of the compound shown in (D) below and the compound shown in (E) below.
The following (F) is synthesized by ig reaction and then (F) is Vils
The following (G) can be synthesized by the meirer reaction, and this (G) can be synthesized by the Wittig reaction with the compound shown in the following (H).

[0018]

[Chemical 9]

[R ₁ and R ₂ are each an alkyl group, an alkoxy group, a substituted or unsubstituted aryl group, R ₃ and R 2
₆ is a hydrogen atom, an alkyl group, R ₄ and R ₅ are a hydrogen atom, an alkyl group, an aryl group, R ₇ is a hydrogen atom, an alkyl group,
A halogen atom, an alkoxy group, a dialkylamino group, a diarylamino group, R ₈ is a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, and n is 1 or 2. FIG. 1 is a sectional view showing an organic thin film light emitting device according to an embodiment of the present invention.

FIG. 2 is a sectional view showing an organic thin film light emitting device according to another embodiment of the present invention. FIG. 3 is a sectional view showing an organic thin film light emitting device according to another embodiment of the present invention. 1 is an insulating substrate, 2 is a positive electrode, 3 is a hole injection layer,
4 is a light emitting layer, 5 is an electron injection layer, and 6 is a negative electrode. The insulating substrate 1 is made of glass, resin or the like as a support for the element. A transparent material is used for the light emitting surface.

The positive electrode 2 is made of a semi-permeable film of gold, nickel or the like or a transparent conductive film of indium tin oxide (ITO), tin oxide (SnO ₂ ) or the like, and is formed by resistance heating vapor deposition, electron beam vapor deposition, or sputtering. To do. It is desirable that the positive electrode 2 has a thickness of 100 to 3000 Å in order to have transparency. The hole injection layer 3 is required to efficiently transport and inject holes, and it is desirable that the hole injection layer 3 be as transparent as possible in the emission maximum region of the emitted light. Spin coating, casting, LB method, resistance heating vapor deposition,
Although there are electron beam vapor deposition and the like, resistance heating vapor deposition is general. The film thickness is 200 to 5000Å, preferably 3
It is 00 to 800Å. As a hole injection material, a hydrazone compound, a pyrazoline compound, a stilbene compound,
An amine compound or the like is used. Typical hole-injecting substances are represented by chemical formulas (IV-1) to (IV-7).

[0022]

[Chemical 10]

The light emitting layer 4 efficiently emits light by recombination of holes injected from the hole injection layer or the positive electrode and electrons injected from the negative electrode or the electron injection layer. Film forming methods include spin coating, casting, LB method, resistance heating evaporation, electron beam evaporation and the like, but resistance heating evaporation is common.
The film thickness is 200 to 5000 Å, but preferably 300
Or 800Å.

It is desirable that the electron injection layer 5 efficiently injects electrons into the light emitting layer. Film forming methods include spin coating, casting, LB method, resistance heating evaporation, electron beam evaporation and the like, but resistance heating evaporation is common. The film thickness is 200 to 5000Å, preferably 300 to 800Å
Is. An oxadiazole derivative, a perylene derivative, etc. are used as an electron injection substance. Chemical formula (V-
Representative electron injecting substances are shown in 1) to the chemical formula (V-4).

[0025]

[Chemical 11]

The negative electrode 6 needs to efficiently inject electrons into the organic layer. As a film forming method, resistance heating evaporation, electron beam evaporation, or sputtering method is used. As the material for the negative electrode 6, Mg, Ag, In, Ca, which has a small work function,
Al and the like, alloys of these and laminated bodies are used. Example 1 Using a glass of 50 mm square provided with ITO having a film thickness of about 1000 Å as a substrate, the substrate was set in a resistance heating vapor deposition apparatus, and a hole injection layer and a light emitting layer were sequentially formed as shown in FIG. . During film formation, the internal pressure of the vacuum chamber was 8 × 10 ⁻⁴ Pa. The hole injection layer was formed to a thickness of 600Å using the compound represented by the chemical formula (IV-1). Subsequently, the styryl-thiophene compound represented by the chemical formula (I-4) was used as a light emitting layer and heated at a boat temperature of about 270 to 300 ° C. to form a film of 600 Å at a film forming rate of about 2 Å / s. After that, the substrate was taken out from the vacuum chamber, a stainless mask for a dot pattern with a diameter of 5 mm was attached, and the substrate was newly set in a resistance heating vapor deposition device to use Mg / In (1
A weight ratio of 0: 1) was formed.

In Example 1, the light emitting layer made of the styryl-thiophene compound is a uniform vapor deposition film,
Moreover, when a DC voltage was applied to the organic thin film light emitting device having a diameter of 5 mm, it was yellowish green (emission center wavelength 540 to 555 n
A uniform light emission of m) was obtained. Also, the emission brightness is 100 cd
A stability of 100 h or more was confirmed at / m ² . Example 2 A glass of 50 mm square provided with ITO having a film thickness of about 1000 Å was used as a substrate, the substrate was set in a resistance heating vapor deposition apparatus, and a light emitting layer and an electron injection layer were sequentially formed. During film formation, the internal pressure of the vacuum chamber was 8 × 10 ⁻⁴ Pa. For the light emitting layer, the compound represented by the chemical formula (I-4) is used and the boat temperature is about 270.
To 300 ° C. to form 600 Å at a film forming rate of about 2 Å / s. Subsequently, the compound represented by the chemical formula (V-4) was used as an electron injection layer to form 600 Å.
After that, the substrate was taken out from the vacuum chamber, a stainless mask for a dot pattern with a diameter of 5 mm was attached, and the substrate was newly set in a resistance heating vapor deposition device to form Mg / In as a negative electrode 6.
(10: 1 weight ratio).

In Example 2, the light emitting layer made of the styryl-thiophene compound was a uniform vapor deposition film,
Moreover, when a DC voltage was applied to the organic light-emitting device having a diameter of 5 mm, a uniform emission of yellowish green light (emission center wavelength 540 to 560 nm) was obtained. Further, it was confirmed that the light emission luminance was 80 cd / m ² and the stability was 90 hours or more. Example 3 Using a glass of 50 mm square provided with ITO having a film thickness of about 1000 Å as a substrate, the substrate was mounted in a resistance heating vapor deposition apparatus, and a hole injection layer, a light emitting layer, and an electron injection layer were formed as shown in FIG. The films were sequentially formed. The internal pressure of the vacuum chamber was 8 × 10 ⁻⁴ Pa. The hole injection layer was formed to a thickness of 600Å using the compound represented by the chemical formula (IV-1). Then, as the light emitting layer, the styryl-
Of the thiophene compounds, a compound represented by the chemical formula (I-4) was used and heated at a boat temperature of about 270 to 300 ° C. to form a film of 600 Å at a film forming rate of about 2 Å / s.
Further, subsequently, 600 Å was formed as the electron injection layer by using the compound represented by the chemical formula (V-4). After that, the substrate was taken out from the vacuum chamber and the dot pattern with a diameter of 5 mm was used.
Attached to the stainless steel mask, and newly installed in the resistance heating vapor deposition device to form the negative electrode 6 with Mg / In (1
0: 1 ratio) was formed.

In Example 3, the light emitting layer made of the styryl-thiophene compound was a uniform vapor deposition film,
Moreover, when a DC voltage was applied to the organic thin film light emitting device having a diameter of 5 mm, it was yellowish green (emission center wavelength 540 to 555 n
A uniform light emission of m) was obtained. Luminous intensity 150 cd
A stability of 120 h or more was confirmed at / m ² . Example 4 A glass of 50 mm square provided with ITO having a film thickness of about 1000 Å was used as a substrate and the substrate was set in a resistance heating vapor deposition apparatus, and as shown in FIG. 1, a hole injection layer and a light emitting layer were sequentially formed. . During film formation, the internal pressure of the vacuum chamber was 8 × 10 ⁻⁴ Pa. The hole injection layer was formed to a thickness of 600Å using the compound represented by the chemical formula (IV-1). Subsequently, a styryl-thiophene compound represented by the above chemical formula (I-13) was used as a light emitting layer and heated at a boat temperature of about 260 to 290 ° C. to form a film of 600 Å at a film forming rate of about 2Å / s.
After that, the substrate was taken out from the vacuum chamber, a stainless mask for a dot pattern with a diameter of 5 mm was attached, and the substrate was newly set in a resistance heating vapor deposition device to form Mg / In as a negative electrode 6.
(10: 1 weight ratio).

In Example 4, the light emitting layer made of the styryl-thiophene compound was a uniform vapor deposition film,
Moreover, when a direct current voltage was applied to the organic thin film light emitting element having a diameter of 5 mm, it was yellowish green (emission center wavelength 545 to 560 n
A uniform light emission of m) was obtained. Also, the emission brightness is 90 cd /
A stability of 110 h or longer was confirmed at m ² . Example 5 A glass of 50 mm square provided with ITO having a film thickness of about 1000 Å was used as a substrate, the substrate was set in a resistance heating vapor deposition apparatus, and a light emitting layer and an electron injection layer were sequentially formed. During film formation, the internal pressure of the vacuum chamber was 8 × 10 ⁻⁴ Pa. For the light emitting layer, the compound represented by the chemical formula (I-13) is used and the boat temperature is about 26.
It was heated at 0 to 290 ° C. to form 600 Å at a film forming rate of about 2 Å / s. Subsequently, the compound represented by the chemical formula (V-4) was used as an electron injection layer to form 600 Å.
After that, the substrate was taken out from the vacuum chamber, a stainless mask for a dot pattern with a diameter of 5 mm was attached, and the substrate was newly set in a resistance heating vapor deposition device to form Mg / In as a negative electrode 6.
(10: 1 weight ratio).

In Example 5, the light emitting layer made of the styryl-thiophene compound was a uniform vapor deposition film,
Moreover, when a DC voltage was applied to the organic light-emitting device having a diameter of 5 mm, a uniform emission of yellowish green light (emission center wavelength 540 to 560 nm) was obtained. Also, the emission brightness is 100 cd / m ²
It was confirmed that the stability was 95 h or more. Example 6 Using a glass of 50 mm square provided with ITO having a film thickness of about 1000 Å as a substrate, the substrate was mounted in a resistance heating vapor deposition apparatus, and a hole injection layer, a light emitting layer and an electron injection layer were formed as shown in FIG. The films were sequentially formed. The internal pressure of the vacuum chamber was 8 × 10 ⁻⁴ Pa. The hole injection layer was formed to a thickness of 600Å using the compound represented by the chemical formula (IV-1). Then, as the light emitting layer, the styryl-
Of the thiophene-based compounds, the compound represented by the chemical formula (I-13) was used and heated at a boat temperature of about 260 to 290 ° C., and the film formation rate was about 2Å / s to form 600Å. Further, the above chemical formula (V-
Using the compound shown in 4), 600Å was formed. After that, the substrate was taken out of the vacuum chamber, a stainless mask made of a dot pattern having a diameter of 5 mm was attached, and the substrate was newly mounted in a resistance heating vapor deposition apparatus to form Mg / In as a negative electrode 6.
(10: 1 ratio).

In Example 6, the light emitting layer made of the styryl-thiophene compound was a uniform vapor deposition film,
Moreover, when a direct current voltage was applied to the organic thin film light emitting element having a diameter of 5 mm, it was yellowish green (emission center wavelength 545 to 560 n
A uniform light emission of m) was obtained. Also, the emission brightness is 140 cd
A stability of 130 h or more was confirmed at / m ² .

[0033]

According to the present invention, it has a pair of electrodes consisting of a positive electrode and a negative electrode, and a charge injection layer and a light emitting layer sandwiched therebetween, and the charge injection layer is composed of an electron injection layer and a hole injection layer. The light emitting layer is composed of at least one of the following general formula (I) and emits light by recombining injected electrons and holes.
Since it contains the styryl-thiophene-based compound (1), high-luminance and stable yellow-green light emission is realized. Further, since it has excellent film-forming properties and is inexpensively and easily synthesized, it is possible to obtain an organic thin film light emitting device that can be easily mass-produced.

[0034]

[Chemical 12]

[In the formula (I), R ₁ and R ₂ are each an alkyl group, an alkoxy group, a substituted or unsubstituted aryl group, R ₃ and R ₆ are hydrogen atoms and an alkyl group, and R ₄ and R ₅ are hydrogen. Atom, alkyl group, aryl group, R ₇ is a hydrogen atom,
An alkyl group, a halogen atom, an alkoxy group, a dialkylamino group, a diarylamino group, R ₈ is a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, and n is 1 or 2. ]

[Brief description of drawings]

FIG. 1 is a sectional view showing an organic thin film light emitting device according to an embodiment of the present invention.

FIG. 2 is a sectional view showing an organic thin film light emitting device according to another embodiment of the present invention.

FIG. 3 is a sectional view showing an organic thin film light emitting device according to still another embodiment of the present invention.

[Explanation of symbols]

 1 Insulating transparent substrate 2 Positive electrode 3 Hole injection layer 4 Light emitting layer 5 Electron injection layer 6 Negative electrode

Claims (3)

[Claims] 1. A pair of electrodes consisting of a positive electrode and a negative electrode, and a charge injection layer and a light emitting layer sandwiched therebetween, wherein the charge injection layer comprises at least one of an electron injection layer and a hole injection layer. The organic thin film light emitting device is characterized in that the light emitting layer recombines the injected electrons and holes to emit light, and contains the styryl-thiophene compound represented by the following general formula (I). [Chemical 1] [In the formula (I), R ₁ and R ₂ are each an alkyl group, an alkoxy group, a substituted or unsubstituted aryl group, R ₃ and R 2
₆ is a hydrogen atom, an alkyl group, R ₄ and R ₅ are a hydrogen atom, an alkyl group, an aryl group, R ₇ is a hydrogen atom, an alkyl group,
A halogen atom, an alkoxy group, a dialkylamino group, a diarylamino group, R ₈ is a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, and n is 1 or 2. ] 2. The device according to claim 1, wherein R ₃ ,
An organic thin film light emitting device, wherein R ₄ , R ₆ and R ₈ are hydrogen atoms, R ₁ and R ₂ are phenyl groups, R ₅ is a methyl group, and R ₇ is a diphenylamino group. 3. The device according to claim 1, wherein R ₄ ,
R _5, R _6, R ₈ is a hydrogen atom, R ₁ is tolyl, R ₂ is a phenyl group, R ₃ is a methyl group, an organic thin film light emitting element, wherein R ₇ is dimethylamino group.