JPH09157642A - Light emitting element and back light or display using the same element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light emitting element containing a specific substance between positive and negative electrodes of element emitted by electric energy, capable of providing blue coloring having high brightness even at a low voltage under low electric current voltage and useful for flat panel display apparatus, back light, etc. SOLUTION: This light emitting element contains a substance having a tropolone skeleton e.g. a chelating complex of the formula [R<1> to R<5> are each H, a halogen, OH, a 1-10C alkyl (R'), a 1-10C alkoxy(carbonyl), a 1-10C trialkylsilyloxy, a (R'-substituted)amino a 1-10C acyl, cyano, nitro, a (substituted) aromatic hydrocarbon group or a heterocyclic group, especially H; M is a center atom of aluminum, gallium, beryllium, etc.; (n) is a valence of M]} as a luminescent layer, a host material for the luminescent layer and a doping material, etc., of the luminescent layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element capable of converting electric energy into light to emit light in a planar manner, and can be used in display elements, flat panel displays, backlights, lighting, interiors, signs, signboards, electrophotographic machines, etc. The present invention relates to a light emitting device that can be suitably used in the field.

[0002]

2. Description of the Related Art An organic laminated thin film element in which an electron injected from a negative electrode and a hole injected from a positive electrode emit light when recombined in an organic phosphor sandwiched between both electrodes is thin and has a low driving voltage. The feature is the light emission at the bottom. The fact that this organic laminated thin film element emits light with high brightness is due to Tang of Kodak;
C. W. For the first time (Appl. Phy
s. Lett. 1987, 51 (12), 913).

A typical organic laminated thin film light emitting device presented by Kodak is a positive electrode, an ITO glass substrate, a diamine compound as a hole transport layer, tris (8-quinolinolato) aluminum as a light emitting layer, and a negative electrode. And magnesium and silver are sequentially provided as 10
Green light emission of 1000 cd / m ² was possible at a driving voltage of about V. This organic laminated thin film light emitting device is characterized in that a diamine compound, which is a hole transport layer, is provided between tris (8-quinolinolato) aluminum, which is a light emitting body, and ITO, which is a positive electrode. Although the emission brightness was improved as compared with that of Example 1, the emission brightness was not always sufficient.

A luminous body used in such an organic laminated thin film light emitting device is, for example, Tris (8) shown in Tang et al.
-Quinolinolato) aluminum, benzoperylenedicarboxylic acid derivative (JP-A-5-163488), coumarin derivative (JP-A-5-78655), vinyl biphenyl derivative (JP-A-5-308)
0), divinylbenzene derivative (JP-A-6-10085).
7), oxadiazole derivatives, distyrylbenzene derivatives and the like, polymer-based polyphenylene vinylene derivatives (JP-A-5-247460) and arylamine-based polycarbonate derivatives (JP-A-5-247).
No. 459), polythiophene derivatives, polyparaphenylene derivatives and the like are known, and at present, multi-color light emission is possible to some extent.

Oxadiazole derivatives, tris (8-quinolinolato) aluminum and the like are specifically known as materials for the electron transport layer, but there are not many findings. If the blocking of holes and the injection efficiency of electrons can be improved by selecting the material, it is possible to make a very high performance light emitting device.

[0006]

However, the conventionally used light-emitting body is capable of multicolor light emission, but the light-emitting performance,
In particular, since the luminous efficiency is insufficient, it was not possible to obtain high-luminance light emission, particularly blue light emission, under low voltage and low current.

The present inventors have conducted studies for the purpose of providing a device capable of emitting blue light with high brightness even under a low voltage and a low current, by improving the light emitting performance, particularly the light emitting efficiency.

[0008]

Means for Solving the Problems As a result of intensive investigations by the present inventors on a blue light emitting device having high luminous efficiency, a light emitting device containing a substance having a tropolone skeleton between a positive electrode and a negative electrode has a low voltage and The present inventors have found that high-luminance blue light emission is possible even under an electric current, and completed the present invention.

The present invention is characterized in that an element which emits light by electric energy contains a substance having a tropolone skeleton between a positive electrode and a negative electrode, and preferably contains a chelate complex of a tropolone derivative.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The substance having a tropolone skeleton of the present invention preferably forms a 5-membered ring with a tropolone derivative and a central element to form a chelate complex, and more preferably, the central atom is divalent or trivalent. It is a cation. Examples of the central atom of the chelate complex of the tropolone derivative include aluminum, calcium, gallium, strontium, barium, beryllium, boron and magnesium, with aluminum, gallium and beryllium being particularly preferred.

The chelate complex of the tropolone derivative preferably used in the present invention has the following general formula:

Embedded image (In the formula, R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each a hydrogen atom, a halogen atom, a hydroxyl group, or a carbon number of 1 to 1
An alkyl group having 0 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a trialkylsilyloxy group having 1 to 10 carbon atoms, an amino group having 1 to 10 carbon atoms and optionally having an alkyl substituent,
It is selected from an acyl group having 1 to 10 carbon atoms, an alkoxycarbonyl group having 1 to 10 carbon atoms, a cyano group, a nitro group, an aromatic hydrocarbon group or a heterocyclic group which may have a substituent, and they are the same as each other. Or it may be different. M represents a central atom, and n represents the valence number of M. ) Is a chelate complex of a tropolone derivative represented by the formula (1), and more preferably R ¹ , R ² , R ³ , R ⁴ and R ⁵ are hydrogen atoms.

The chelate complex of the tropolone derivative of the present invention can be obtained, for example, by adding an aqueous solution in which the central atom is dissolved to a tropolone derivative solution in which the corresponding tropolone derivative is dissolved in an organic solvent, and neutralizing with an alkali if necessary. However, the present invention is not limited to this. Examples of the aqueous solution in which the central atom is used for the synthesis of the chelate complex of the tropolone derivative include aluminum chloride, gallium chloride and beryllium sulfate.

The light emitting device of the present invention can be used as a light emitting device of various hues, and is particularly suitable as a blue light emitting device.

In the light emitting device of the present invention, the light emitting layer preferably contains a substance having a tropolone skeleton.
A substance with a tropolone skeleton has a tropolone skeleton 1
It is possible to use different kinds of substances, and if necessary, it is possible to use a plurality of substances having a tropolone skeleton.

Further, it is possible to use a substance having a tropolone skeleton as a host material of the light emitting layer, and to add a small amount of a coumarin derivative, a perinone derivative, a perylene derivative, a quinacridone derivative, a vinylbiphenyl derivative, a divinylbenzene derivative or the like as a dopant. is there. In this case, the tropolone derivative or the chelate complex thereof is usually 85% to 99.99% of the entire light emitting layer, and preferably,
95% to 99.99%, more preferably 99% to 9
9.9% used.

Further, known are bisstyrylanthracene derivatives, tetraphenylbutadiene derivatives, oxadiazole derivatives, distyrylbenzene derivatives, pyrrolopyridine derivatives, cyclopentadiene derivatives, thiadiazolopyridine derivatives, and polymers such as polyparaphenylene derivatives. The chelating complex of the tropolone derivative of the present invention can be added to the above light emitting layer material in a small amount as a dopant and used. In this case, the chelate complex of the tropolone derivative is usually 0.01% to 15% of the entire light emitting layer,
Preferably 0.01% to 5%, more preferably 0.
1% to 1% is used.

The method for forming the light emitting layer containing the substance having a tropolone skeleton of the present invention is not particularly limited, but methods such as resistance heating vapor deposition, electron beam, sputtering, molecular lamination method and coating method are used. Especially,
From the viewpoint of characteristics, resistance heating vapor deposition and electron beam vapor deposition are preferable.

Further, the thickness of the light emitting layer is not particularly limited, but is usually 10 to 100 nm.

In the present invention, the positive electrode is not particularly limited as long as it is a transparent electrode for extracting light. For example, tin oxide, indium oxide, indium tin oxide (ITO).
Conductive metal oxides such as, or metals such as gold, silver, and chromium, and further, laminates of these metals and ITO, inorganic conductive substances such as copper iodide and copper sulfide, polythiophene, polypyrrole, polyaniline, etc. Conductive polymer,
Also, a laminate of these and ITO is used, and ITO glass or Nesa glass is preferably used.

The resistance of such a transparent electrode is not particularly limited as long as it can supply a sufficient current for light emission of the element, but it is desirable that the resistance is low in terms of power consumption of the element. For example, as a transparent electrode, an ITO substrate of 300 Ω / □ or less works well, but preferably 20 Ω / □.
The following low resistance substrates are selected.

The thickness of ITO of the transparent electrode can be arbitrarily selected depending on the resistance value, but is usually 50 nm to 300 nm.
Often used in the range of.

As the substrate of the transparent electrode such as ITO, soda lime glass, non-alkali glass, transparent resin or the like is used. When using glass, regarding the material,
It is preferable to use non-alkali glass in order to reduce the amount of ions eluted from the glass. When soda lime glass is used, it is preferable to use soda lime glass coated with a barrier coat such as SiO ₂ .

The thickness of the transparent electrode substrate is not particularly limited as long as it is sufficient to maintain mechanical strength, but in the case of ITO glass, a substrate having a thickness of 0.7 mm or more is usually used.

The ITO film is formed by a method such as an electron beam method, a sputtering method or a chemical reaction method.
Furthermore, it is possible to lower the driving voltage of the element by subjecting ITO to UV-ozone treatment.

In the present invention, the negative electrode supplies electrons to the electron transport layer, the light emitting layer and the like. The negative electrode is selected in consideration of the adhesion between the negative electrode such as the electron transport layer and the light emitting layer and a substance adjacent to the negative electrode, adjustment of ionization potential, and stability. In order to maintain stable performance over long-term use, it is desirable to use a material that is relatively stable in the atmosphere, but it is also possible to improve stability by using a protective film or the like.

The substance used for the negative electrode is, for example,
Metals such as indium, gold, silver, aluminum, lead, and magnesium, rare earths, alkali metals, and alloys of these metals can be used. From the viewpoint of device characteristics, magnesium, lithium, sodium, potassium, and the like can be used. It is preferable to use a low work function metal. Further, in order to enhance the stability of these low work function metals, an alloy with silver, aluminum or the like can be used.

Further, a resistance heating method, an electron beam method, a sputtering method, a coating method or the like is used for producing the negative electrode, and the metal can be vapor-deposited alone, or two or more components can be vapor-deposited simultaneously. Furthermore, it is possible to vapor-deposit a plurality of metals simultaneously to form an alloy electrode, or vapor-deposit an alloy prepared beforehand.

The structure of the light emitting device of the present invention includes, in addition to the positive electrode and the negative electrode, a light emitting layer alone, a hole transport layer / light emitting layer, a hole transport layer / light emitting layer / electron transport layer, a light emitting layer / electron transport. It may have a multi-layered structure of layers or a form in which a light emitting material and a hole transport material and / or an electron transport material are mixed to form a single layer.

The hole transport layer in the present invention is a layer for efficiently transporting holes from the positive electrode, and is, for example, a carbazole dimer derivative, 4,4'-bis [N- (3-methylphenyl)-. N-phenylamino] biphenyl (TP
D), 4,4 ', 4 "-tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine (m
-MTDATA), poly (N-vinylcarbazole),
Known hole transporting materials such as polysilane can be laminated or mixed and used.

The formation of these hole transport layers is mainly carried out by a vacuum vapor deposition method. The method of coating the above hole transport material by dissolving it in a solution or the above hole transport material in a solvent together with a resin component. A method of coating by dissolving or dispersing is also possible.

As the resin component for dissolving or dispersing the hole transporting material, for example, polyvinyl chloride, polycarbonate, polystyrene, poly (N-vinylcarbazole), polymethyl methacrylate, polybutyl methacrylate, polyester, polysulfone, polyphenylene oxide, Polybutadiene, hydrocarbon resin, ketone resin, phenoxy resin, polyamide, ethyl cellulose,
Examples thereof include vinyl acetate, ABS resin, polyurethane resin, melamine resin, unsaturated polyester resin, alkyd resin, epoxy resin and silicone resin.

From the viewpoint of driving voltage, it is preferable that the thickness of the hole transport layer is as thin as the limit film thickness where the leak current of the device starts to increase, but the practical film thickness considering the durability of the device is limited. It is preferable to make it slightly thicker than the film thickness. The preferable thickness of the hole transport layer is not limited because it varies depending on the surface state of the ITO substrate, the constituent material of the hole transport layer, and the like, but is preferably about 20 to 120 nm, and 80 to
100 nm is more preferable.

The electron transport layer in the present invention is a layer for efficiently transporting electrons from the negative electrode, and preferably has high electron injection efficiency. Therefore, it is desirable that the electron transport layer is a substance having a high electron affinity, a high electron mobility, an excellent stability, and an impurity that becomes a trap is hard to be generated at the time of manufacturing and during use. As such an electron transport layer, the substance having the tropolone skeleton of the present invention can be used.

Further, as an electron transport layer, tris (8-
A metal chelate complex of a quinolinol derivative such as quinolinolato) aluminum, a perylene derivative, a perinone derivative, a naphthalene derivative, a coumarin derivative, a tetraphenylbutadiene derivative, an oxadiazole derivative, a bisstyrylbenzene derivative, a pyrazine derivative, and a phenanthroline derivative can be used. However, it is not particularly limited thereto.

The electron-transporting material can take any form of single layer, layered layer and mixed layer, and can take an optimal state in combination with the light emitting layer and the negative electrode.

By using a light emitting device containing a substance having a tropolone skeleton, a display and a backlight suitable for high-luminance blue light emission can be newly manufactured.

[0037]

The present invention will be described below with reference to examples.
The present invention is not limited to this.

Example 1 A glass substrate (15 Ω / □) on which an ITO transparent electrode film was deposited to a thickness of 150 nm as a positive electrode was cut into a predetermined size, etched and washed. The ITO substrate was vertically dipped in a dichloroethane solution of 0.85 wt% poly (N-vinylcarbazole) and pulled up at a speed of 50 mm / min to dip-coat the hole transport layer. This was evacuated by a vacuum vapor deposition machine until the degree of vacuum became 5 × 10 ⁻⁶ Torr or less.

The light emitting layer has the following chemical formula:

Embedded image The tris (troporonato) gallium shown by 100n
m and then 3n of lithium was used as a negative electrode.
m and silver were vapor-deposited to a thickness of 150 nm to produce a 5 × 5 mm square device.

This light emitting element exhibits uniform blue light emission,
The maximum brightness was 168 cd / m ² (16 V, 37 mA).

Example 2 A glass substrate (15 Ω / □) on which an ITO transparent electrode film was deposited to a thickness of 150 nm as a positive electrode was cut into a predetermined size, etched and washed. The ITO substrate was vertically dipped in a dichloroethane solution of 0.85 wt% poly (N-vinylcarbazole) and pulled up at a speed of 50 mm / min to dip-coat the hole transport layer. This was evacuated by a vacuum vapor deposition machine until the degree of vacuum became 5 × 10 ⁻⁶ Torr or less.

The light emitting layer has the following chemical formula:

Embedded image Tris (troporonato) aluminum shown by 10
Laminated to a thickness of 0 nm, and then, as a negative electrode, lithium was vapor-deposited to a thickness of 3 nm and silver to a thickness of 150 nm, and then 5 × 5 mm.
A corner element was made.

This light emitting element exhibits uniform blue light emission,
The maximum brightness was 83 cd / m ² (13 V, 30 mA).

[0044]

By incorporating the substance having a tropolone skeleton of the present invention into a light emitting device, blue light emission of high brightness can be obtained even under a low voltage and a low current, and a high performance light emitting device can be manufactured. .

Claims (14)

[Claims] 1. A light emitting device, which emits light by electric energy, containing a substance having a tropolone skeleton between a positive electrode and a negative electrode. 2. The light emitting device according to claim 1, wherein the substance having a tropolone skeleton is a chelate complex of a tropolone derivative. 3. The light emitting device according to claim 1, wherein a substance having a tropolone skeleton and a central atom form a 5-membered ring to form a chelate complex. 4. The light emitting device according to claim 3, wherein the central atom is a divalent or trivalent cation. 5. The light-emitting device according to claim 2, wherein the chelate complex of the tropolone derivative is represented by the following general formula: (In the formula, R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each a hydrogen atom, a halogen atom, a hydroxyl group, or a carbon number of 1 to 1
An alkyl group having 0 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a trialkylsilyloxy group having 1 to 10 carbon atoms, an amino group having 1 to 10 carbon atoms and optionally having an alkyl substituent,
It is selected from an acyl group having 1 to 10 carbon atoms, an alkoxycarbonyl group having 1 to 10 carbon atoms, a cyano group, a nitro group, an aromatic hydrocarbon group or a heterocyclic group which may have a substituent, and they are the same as each other. Or it may be different. M represents a central atom, and n represents the valence number of M. ) A chelating complex of a tropolone derivative represented by the formula (1). 6. The light emitting device according to claim 5, wherein R ¹ , R ² , R ³ , R ⁴ and R ⁵ in the general formula are hydrogen atoms. 7. The light emitting device according to claim 5, wherein M in the general formula is aluminum, gallium or beryllium. 8. The device according to claim 1, which emits blue light.
The light-emitting device according to item 1. 9. The light emitting device according to claim 1, wherein a substance having a tropolone skeleton is used in a light emitting layer. 10. The light emitting device according to claim 1,
A light emitting device, wherein a substance having a tropolone skeleton is used as a host material of a light emitting layer. 11. The light emitting device according to claim 1, wherein
A light emitting device, wherein a substance having a tropolone skeleton is used as a doping material for a light emitting layer. 12. The light emitting device according to claim 1, wherein
A light emitting device having a hole transport layer and / or an electron transport layer in addition to the light emitting layer. 13. A display device comprising the light emitting device according to claim 1. 14. A backlight using the light emitting device according to claim 1.