JPH07228865A - Organic thin-film luminescent element - Google Patents

Abstract

PURPOSE:To obtain the subject element, using a specific (di)styryl compound as a new hole injection substance, capable of realizing the light emission, having a high luminance and excellent in life stability and durability, good in film- forming properties and improved in mass productivity. CONSTITUTION:This element is an organic thin-film luminescent element comprising a pair of electrodes of a positive pole 2 and a negative pole 5, a luminous layer 4 sandwiched therebetween and a charge injection layer composed of a hole injection layer 3 laminated onto an insulating transparent substrate 1. The hole injection layer 3 comprises a layer containing at least one of a distyryl compound expressed by formula T [X is S or O; R1 and R2 each is H, an alkyl, etc.; Ar1 and Ar2 each is an (substituted)aryl or a heterocyclic ring] and a styryl compound expressed by formula II (R3 and R4 each R1; Ar3 is Ar1). The element is obtained by forming a transparent electrically conductive film of an indium tin oxide as the positive pole 2, then successively forming the hole injection layer 3 and the luminous layer 4 composed of (8- hydroxyquinoline)aluminum on the substrate 1 composed of, e.g. glass and finally forming Mg/Ag as the negative pole 5 according to a vacuum deposition method.

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 substance used for a hole injection layer.

[0002]

2. Description of the Related Art With the increasing demand for flat displays replacing conventional cathode ray tubes, various display devices have been vigorously developed and put into practical use. An electroluminescence element (hereinafter referred to as an EL element) meets these needs, and is particularly attracting attention as an all-solid-state spontaneous light-emitting element because of its high resolution and high visibility not found in other displays.

What has been put into practical use at present is that the light emitting layer has a Z layer.
It is an EL element using an nS / Mn-based inorganic material. However, since the driving voltage required for light emission of this type of inorganic EL element is as high as about 200 V, the driving method is complicated, the manufacturing cost is high, and the efficiency of blue light emission is low. In order to apply it as a display, characteristics such as low voltage drive, high brightness, long life and full color are required. On the other hand, thin-film EL elements using organic materials can drastically reduce the driving voltage required for light emission and have full potential for full-color application by applying various light-emitting materials. There is.

In particular, Tang et al. Reported that a high brightness of 1000 cd / m ² or more was obtained at a low applied voltage of 10 V in a laminated EL device using a quinolinol compound as a light emitting material and a diamine compound as a charge injection material ( Appl.Phys.Lett.Vol.51, No.12,913, (1987))
Since then, research has been actively conducted for practical use.

However, an organic thin film E which meets all the requirements
L element is not currently available. Therefore, organic EL materials and charge injection materials are being energetically searched for along with EL element structures and manufacturing methods. As an organic light-emitting material, it is required to have excellent film-forming properties, high luminous efficiency, and stability.
Further, the charge injection material is required to have excellent film-forming properties, high charge transportability, and high charge injection efficiency into the light emitting layer and be stable, as disclosed in JP-A-2-311591 and JP-A-5959.
The materials disclosed in, for example, the publication of 194393 are known.

The layer structure will be described with reference to FIGS. 1 and 2 are typical structural cross-sectional views of an EL device according to the present invention. FIG. 1 shows a pair of electrodes of a positive electrode 2 and a negative electrode 5 between which a hole injection layer 3 and a light emitting layer 4 are sequentially laminated. In FIG. 2, the positive electrode 2 and the negative electrode 5 have a pair of electrodes, and the hole injection layer 3, the light emitting layer 4, and the electron injection layer 7 are sequentially stacked between them.

[0007]

As described above, although the thin film EL element using an organic material strongly suggests the possibility of low voltage driving and full colorization, it is particularly weak in blue and blue-green light emission. However, there are still many problems to be solved in terms of performance. In particular, the problem of characteristic deterioration due to long-term driving is a problem that must be overcome.
Further, since the thickness of this organic thin film is submicron or less, it is necessary to develop a material having good film-forming property and stability. Further, from the viewpoint of mass production, development of an organic material which is easy to mass produce and is inexpensive, and improvement of a device forming method are also important technical issues.
Further, development of many kinds of light emitting layer materials and charge injection layer materials has been desired in order to obtain light emission of various colors.

The present invention has been made in view of the above points, and an object thereof is to develop a novel hole injecting substance to realize light emission with high brightness and excellent life stability and to have a good film forming property. In order to provide an organic thin film light emitting device having excellent durability.

[0009]

According to the present invention, the above-mentioned object is to provide a pair of electrodes, a positive electrode and a negative electrode, and a light emitting layer sandwiched between the electrodes, an electron injection layer and a hole injection layer on an insulating transparent substrate. In the organic thin film light-emitting device, the charge injection layer is formed of at least a hole injection layer, and the hole injection layer is a distyryl compound represented by the following general formula (I) or the following general formula: This is achieved by comprising a layer containing at least one of the styryl compounds represented by the formula (II).

[0010]

[Chemical 3]

[Wherein X represents a sulfur atom or an oxygen atom, R ₁ and R ₂ represent a hydrogen atom, an alkyl group or a substituted or unsubstituted aryl group, and Ar ₁ and Ar ₂ represent a substituted or unsubstituted aryl group] Represents a group or a heterocyclic group. ]

[0012]

[Chemical 4]

[Wherein X represents a sulfur atom or an oxygen atom, R ₃ and R ₄ represent a hydrogen atom, an alkyl group or a substituted or unsubstituted aryl group, and Ar ₃ represents a substituted or unsubstituted aryl group or a heterocyclic group. Represents a ring group. It is effective that the light emitting layer combines the injected electrons and holes to emit light.

[0014]

There is no known example of using the distyryl compound represented by the general formula (I) or the styryl compound represented by the general formula (II) as a hole injecting material. These inventors have conducted a number of experiments on these compounds in the course of extensive studies on various organic materials in order to achieve the above-mentioned object, and as a result, their technical elucidation has not yet been sufficiently conducted. By using the compounds represented by the formulas (1) and (II) as a hole injection material,
A good film is formed and there are few electrical defects such as pinholes generated in the film, and stable light emission with high brightness is realized.Furthermore, this hole injection material can be mass-produced inexpensively and easily. We also found that it is suitable for mass production.

Since the light emitting layer is designed to combine the injected electrons and holes to emit light, when electrons or holes are respectively injected from the electrode, the light emitting layer is thinned to form a light emitting layer. The recombination of the confined carriers becomes strong and the light is emitted from the light emitting layer, and the light emission from the charge injection layer is reduced.

[0016]

EXAMPLES The compounds of the general formula (I) used in the present invention can be synthesized by a known method. For example, the general formula (I-1) is represented by the compound (a) shown in the following reaction.
And (b).

[0017]

[Chemical 5]

The compound (II-7) of the general formula (II) can be obtained by carrying out a known reaction using the compounds (c) and (d) shown in the following reaction.

[0019]

[Chemical 6]

Specific examples of the compound represented by the general formula (I) include the following.

[0021]

[Chemical 7]

[0022]

[Chemical 8]

[0023]

[Chemical 9]

The following are specific examples of the compound represented by the general formula (II).

[0025]

[Chemical 10]

[0026]

[Chemical 11]

[0027]

[Chemical 12]

[0028]

[Chemical 13]

FIG. 1 is an EL showing an embodiment of the present invention.
FIG. 1 is a typical structural cross-sectional view of an element, in which a pair of electrodes of a positive electrode 2 and a negative electrode 5 and a hole injection layer 3 and a light emitting layer 4 are sequentially laminated between them (emitted light is indicated by an arrow in the figure). Go in the direction.). On a transparent transparent substrate 1 made of glass or the like, a positive electrode 2 made of a semi-permeable film such as gold or nickel, or a transparent conductive film such as indium tin oxide (hereinafter referred to as ITO) or tin oxide (hereinafter referred to as SnO ₂ ) is used as a resistor. It is formed by heating vapor deposition, electron beam vapor deposition, or sputtering. The positive electrode 2 preferably has a thickness of 10 to 300 nm in order to have transparency. Next, an organic thin film is sequentially formed as the hole injection layer 3 and the light emitting layer 4. Both layers may be a single material or a mixed film of additives and a resin binder. As a film forming method, both layers are spin coated, cast, LB method,
A film can be formed by resistance heating vapor deposition, electron beam vapor deposition, or the like.
The film thickness of both layers is 10 to 300 nm, preferably 20 to 100 nm. Finally, the negative electrode 5 is formed by vapor deposition. As the material of the negative electrode 5, Mg, Mg / Ag, In, Ca, Al or the like having a small work function is used.

FIG. 2 is a typical structural sectional view of an EL device showing another embodiment of the present invention, in which a positive electrode 2 and a negative electrode 5 are used.
And a hole injecting layer 3, a light emitting layer 4, and an electron injecting layer 7 are sequentially laminated between them (the emitted light proceeds in the direction shown by the arrow in the figure). A semi-permeable film such as gold or nickel or IT on an insulating transparent substrate 1 such as glass
The positive electrode 2 made of a transparent conductive film such as O.SnO _{2 is} formed by resistance heating vapor deposition, electron beam vapor deposition, or sputtering.
The positive electrode 2 has a transparency of 10 to 300 n in order to have transparency.
A thickness of m is desirable. Next, an organic thin film is sequentially formed as the hole injection layer 3, the light emitting layer 4, and the electron injection layer 7. The three layers may be a single material or a mixed film with an additive and a resin binder. As a film forming method, all three layers can be formed by spin coating, casting, LB method, resistance heating vapor deposition, electron beam vapor deposition and the like. The thickness of each layer is 10 to 300 nm, preferably 20 to 1
00 nm. Finally, the negative electrode 5 is formed by vapor deposition. As the material of the negative electrode 5, Mg having a small work function,
Mg / Ag, In, Ca, Al or the like is used.

The following are specific examples of the compound used in the light emitting layer 4.

[0032]

[Chemical 14]

[0033]

[Chemical 15]

[Example 1] A glass of 50 mm square in which ITO having a thickness of about 100 nm was provided as a positive electrode 2 on an insulating transparent substrate 1 was used as a substrate, and this substrate was placed in a resistance heating vapor deposition apparatus (hereinafter referred to as a vacuum chamber). After mounting, the hole injection layer 3 and the light emitting layer 4 were sequentially formed as shown in FIG. During film formation, the internal pressure of the vacuum chamber was reduced to 1 × 10 ⁻⁴ Pa. The compound (I-1) is used for the hole injection layer 3, and the evaporation source temperature is 220 to 280 ° C.
Heating in the range of 6 and a film forming rate of about 0.2 nm / sec.
It was formed to 0 nm. Next, without breaking the vacuum of the vacuum chamber, structural formula (III-1) of a specific example of the compound used for the light emitting layer 4 as the light emitting layer 4 is shown (8-hydroxyquinoline).
Aluminum was heated at an evaporation source temperature of 220 to 250 ° C. to form 60 nm at a film forming rate of about 0.2 nm / sec. After that, the substrate was taken out of the vacuum chamber and had a diameter of 5 mm.
Attach a stainless mask consisting of the dot pattern, and mount it in the vacuum chamber again, and then place the negative electrode 5 on the upper part of the substrate.
Mg / Ag (weight ratio of 10: 1) as 100 nm
Formed.

In Example 1 above, this compound (I-
The hole injection layer 3 composed of 1) was a uniform vapor deposition film, and when a DC voltage of 10 V was applied to this organic thin film EL element having a diameter of 5 mm, green light emission was obtained. At this time, the emission center wavelength was 520 nm and the maximum luminance was 1000 cd / m ² or more. Further, it showed good stability even in continuous light emission over 1000 hours. [Example 2] A film thickness of about 1 as the positive electrode 2 on the insulating transparent substrate 1.
A glass of 50 mm square provided with ITO of 00 nm was used as a substrate, this substrate was mounted in a vacuum chamber, and a hole injection layer 3, a light emitting layer 4, and an electron injection layer 7 were sequentially formed as shown in FIG.
During film formation, the internal pressure of the vacuum chamber was reduced to 1 × 10 ⁻⁴ Pa. The compound (I-3) was used for the hole injection layer 3 and heated at an evaporation source temperature of 230 to 290 ° C. to form a film having a film formation rate of about 0.2 nm / sec and a thickness of 60 nm. Next, the (8-hydroxyquinoline) aluminum is used as the light emitting layer 4 without breaking the vacuum of the vacuum chamber, and the evaporation source temperature 220 to
The film was heated to a temperature of 250 ° C. with hydroxy, and the film formation rate was set to about 0.2 nm / sec to form 60 nm. Further, similarly, without breaking the vacuum of the vacuum chamber, 30 nm of a perylene tetracarboxylic derivative represented by the following structural formula (IV) was continuously formed as the electron injection layer 7. 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 the vacuum chamber. It was formed to 100 nm.

In Example 2 above, this compound (I-
The hole injection layer 3 composed of 3) was a uniform vapor deposition film, and when a DC voltage of 10 V was applied to this organic thin film EL element having a diameter of 5 mm, green light emission was obtained. At this time, the emission center wavelength was 530 nm and the maximum luminance was 1000 cd / m ² or more. In addition, good stability was exhibited even in continuous light emission over 1000 hours.

[0037]

[Chemical 16]

Example 3 An organic thin film EL device was manufactured under the same conditions as in Example 1, except that the compound (II-1) was used for the hole injection layer 3 and heating was performed at an evaporation source temperature of 150 to 250 ° C. Was produced. Also in Example 3 above, when a DC voltage of 10 V was applied, green light emission was obtained. At this time, the emission center wavelength is 530 nm and the maximum brightness is 1000 cd.
/ M ² or more. In addition, good stability was exhibited even in continuous light emission over 1000 hours. [Example 4] An organic thin film EL device was produced under the same conditions as in Example 2, except that the compound (II-5) was used for the hole injection layer 3 and heating was performed at an evaporation source temperature of 120 to 230 ° C. .

Also in the fourth embodiment, the DC voltage is 10V.
Was applied, a green light emission was obtained. At this time, the emission center wavelength was 530 nm and the maximum luminance was 1000 cd / m ² or more. In addition, good stability was exhibited even in continuous light emission over 1000 hours.

[0040]

According to the present invention, in an organic thin film light emitting device in which a light emitting layer made of an organic material and a charge injection layer made of an electron injection layer and a hole injection layer are laminated, the charge injection layer is at least positive. By forming the hole injecting layer and using the compounds represented by the general formulas (I) and (II) in the hole injecting layer, the effects described in Examples 1 to 4 can be obtained, and the brightness is high and the life is stable. The organic thin film light emitting device that realizes excellent light emission, can form a good film with good film formability and excellent durability, has few electrical defects such as pinholes, has high brightness, has a long life and is stable. can get.

[Brief description of drawings]

FIG. 1 is a typical structural sectional view of an EL device showing an embodiment of the present invention.

FIG. 2 is a typical structural sectional view of an EL device showing 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 Negative Electrode 6 Driving DC Power Supply 7 Electron Injection Layer

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masami Kuroda 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Osamu Nabeta 1 Nitta Tanabe, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 inside Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. An organic thin-film light emitting device comprising a pair of positive and negative electrodes, a light emitting layer sandwiched therebetween, and a charge injection layer, which are stacked on an insulating transparent substrate, wherein the charge injection layer is a hole injection layer. The organic thin film light emitting device is characterized in that the hole injection layer is formed of a layer containing at least one of a distyryl compound represented by the following general formula (I) or a styryl compound represented by the following general formula (II). element. 2. An organic thin film light emitting device comprising a pair of positive and negative electrodes, a light emitting layer sandwiched therebetween, and a charge injection layer, which are laminated on an insulating transparent substrate. The hole injecting layer is formed of a layer containing at least one of a distyryl compound represented by the following general formula (I) or a styryl compound represented by the following general formula (II): Organic thin film light emitting device. 3. The organic thin film light emitting device according to claim 1 or 2, wherein the light emitting layer combines the injected electrons and holes to emit light. [Chemical 1] [In the formula, X represents a sulfur atom or an oxygen atom, and R ₁ , R ₂
Represents a hydrogen atom, an alkyl group or a substituted or unsubstituted aryl group, and Ar ₁ and Ar ₂ represent a substituted or unsubstituted aryl group or heterocyclic group. ] [Chemical 2] [In the formula, X represents a sulfur atom or an oxygen atom, and R ₃ , R ₄
Represents a hydrogen atom, an alkyl group or a substituted or unsubstituted aryl group, and Ar ₃ represents a substituted or unsubstituted aryl group or heterocyclic group. ]