JPH08330074A - Electroluminescence light emitting element - Google Patents

Abstract

PURPOSE: To heighten initial brightness, and suppress brightness deterioration resulting from long time luminescence by using indium oxide containing 15 to 50wt.% of tin oxide for a transparent conductive layer. CONSTITUTION: At least a transparent conductive layer 20, a light emitting body layer 30, and a back face electrode 40 are laminated in this order on one side face of a transparent base body 10. Indium oxide containing 15 to 50wt.% of tin oxide is used for a transparent conductive layer 20. Zinc sulfide is used for the light emitter layer 30 as a light emitter, and a transparent high polymer molding is used for the transparent base body 10. For the high polymer molding, polyethylene terephthalate, or the like is used, and the same is lighter, is hardly broken, and can be formed into thinner comparing with glass. When the transparent conductive layer 20 contains the indium oxide less than 15wt.% of the tin oxide, it is impossible to obtain sufficient durability. When its containing amount is more than 50 percentage, transparency is deteriorated in a visible light area so that it is impossible to take out emitted light from the light emitter layer 30 effectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent light emitting device, and more particularly to an electroluminescent light emitting device which suppresses a decrease in luminance during continuous light emission and has excellent durability.

[0002]

2. Description of the Related Art Conventionally, an electroluminescent light emitting element has been used in applications such as a backlight of a liquid crystal display and a light emitting element for decoration because a thin light emitting body can be obtained. There are two types of electroluminescence light emitting elements, an AC driving type and a DC driving type, depending on the driving method, and the former is widely used in spite of the necessity of an AC driving circuit because a strong light emission intensity can be obtained. On the other hand, the latter has the advantage that the drive circuit is simplified because the emission intensity is inferior to the AC drive system, but DC drive is possible, and these two types of drive systems are used properly according to the application.

An electroluminescent light-emitting element is based on a transparent conductive substrate having a transparent conductive film formed on a transparent substrate, and a light emitting layer, a dielectric layer, and a back electrode are sequentially formed on the transparent conductive film. It is known that the whole structure is covered with a transparent moisture-proof layer. Tin oxide, indium oxide, or the like is used for the transparent conductive film. It is known that zinc sulfide is doped with fluoride as the light emitting layer, and the emission color can be changed by selecting an appropriate fluoride material. For example, when neodymium fluoride (NdF ₃ ) is used as the doping material, it emits orange light, and when terbium fluoride (TbF ₃ ) is used, it emits green light. It is also common to provide a dielectric layer between the transparent electrode layer and the light emitting layer, between the light emitting layer and the back electrode, or both in order to effectively apply an electric field to the light emitting layer. Is done in a regular manner. The dielectric layer is made of yttrium oxide, silicon nitride, thallium oxide or the like having a high dielectric constant, and aluminum is used for the back electrode.

Conventionally, indium oxide containing about 5% by weight of tin oxide has been used for a transparent conductive layer of an electroluminescence light emitting device. The transparent conductive layer has excellent transparency in order to efficiently emit visible light emitted from the light emitting layer to the outside, has a low resistance value to some extent in terms of driving voltage, and is used for a long time. However, indium oxide containing tin oxide in an amount of about 5% by weight was excellent in transparency and a transparent conductive layer satisfying a sufficient resistance value was obtained.

[0005]

As described above, the indium oxide film containing about 5% by weight of tin oxide is conventionally used for the transparent conductive layer of the electroluminescent light emitting device. This is because the sheet resistance value can be minimized and the visible light transmittance can be increased by adding about 5% by weight of tin oxide to indium oxide. It is necessary to lower the sheet resistance value
It is necessary to reduce the power consumption required for light emission, and a high visible light transmittance is necessary to effectively take out the emitted light without allowing the transparent conductive layer to absorb the emitted light. In order to practically use it as an electroluminescence light emitting element, it is necessary to have an emission luminance of about 1500 (candelas / m ² ) or more. If the transparent conductive layer has a high sheet resistance value and a low visible light transmittance, the emission luminance cannot be obtained for the reason described above. As for the indium oxide containing about 5% by weight of tin oxide, the indium oxide satisfying the conditions was obtained. However, when indium oxide containing about 5% by weight of tin oxide is used for the transparent conductive layer of the electroluminescence light emitting element,
The contact with zinc sulfide, which is a light-emitting body, deteriorates the interface, and there is a problem that the emission brightness is significantly reduced when light emission is continued.

Therefore, as a method of suppressing the deterioration of the interface between the light emitting layer and the transparent conductive film, a metal thin film is laminated on the transparent conductive layer mainly composed of indium oxide, which causes deterioration, and the transparent conductive layer is the light emitting layer. There is disclosed a method of preventing direct contact with the (Japanese Patent Laid-Open No. 6-71804). However, the lamination of the metal thin film not only complicates the process, but also causes a decrease in visible light transmittance,
It was not always the best solution.

In view of the above circumstances, the present invention improves the durability of the transparent conductive film itself with respect to the light emitting layer, improves the durability of the electroluminescent light emitting device, and has a single transparent conductive layer structure. It is possible to provide an electroluminescent element having a sufficiently high initial luminance and a significant reduction in luminance deterioration for long-term light emission by a simple process due to the effect of simplifying the process and preventing the reduction of visible light transmittance. Has an aim.

[0008]

DISCLOSURE OF THE INVENTION As a result of intensive studies to solve the above problems, the present inventors have found that indium oxide containing 15 to 50% by weight of tin oxide is preferable zinc sulfide as a light emitting material. It has excellent durability against
When this was used as a transparent conductive layer of an electroluminescence light emitting element, it was found that a decrease in luminance during continuous light emission was significantly suppressed, and the present invention was completed.

That is, the present invention provides (1) a transparent substrate (A)
In the electroluminescent light-emitting device, in which at least the transparent conductive layer (B), the light emitting layer (C), and the back electrode (D) are laminated on one surface in the order of ABCD, tin oxide is formed on the transparent conductive layer (B). Of indium oxide containing 15 to 50% by weight is used, and (2) zinc sulfide is mainly used as a light emitter in the light emitter layer (C) ( 1) The electroluminescent light emitting device according to 1) or 2), wherein the transparent base material (A) is a transparent polymer molding. It is a thing.

The present invention will be described with reference to FIG. 1 of the accompanying drawings. On one main surface of a transparent substrate (A) 10, a transparent conductive layer made of indium oxide containing 15 to 50% by weight of tin oxide (first The present invention relates to an electroluminescent light emitting device in which a layer) (B) 20, a light emitting layer (second layer) (C) 30 preferably made of zinc sulfide, and a back electrode layer (D) 40 are sequentially formed.

The transparent substrate 10 used in the present invention can be used as long as it has transparency in the visible light region, its surface is smooth to some extent, and its heat resistance is about 100 ° C. or higher. Specifically, transparent glass or a transparent polymer molding can be used. Since glass has excellent transparency, surface smoothness, and heat resistance in the visible light region, it can be suitably used as the transparent substrate of the present invention.

As the polymer molded article, polyethylene terephthalate, polyether sulfone, polyether ether ketone, polycarbonate, polypropylene, polyimide and the like are listed as those satisfying the above conditions in terms of transparency and heat resistant temperature. The polymer molded body is lighter than glass and is less likely to break, and can be made thinner, so that it can be more suitably used as the transparent substrate of the present invention. These polymer molded bodies may be plate-shaped or film-shaped as long as the main surface forming the transparent conductive layer is smooth. Since the plate-shaped polymer substrate is excellent in dimensional stability and mechanical strength, it can be suitably used especially when it is required.
Further, the polymer film has flexibility, and since the transparent conductive layer can be continuously formed by the roll-to-roll method, it is possible to efficiently produce a transparent conductive substrate when using this. , Which can also be preferably used. In this case, a film having a thickness of 10 to 250 μm is usually used. When the thickness of the film is less than 10 μm, the mechanical strength as a base material is insufficient, and when it is more than 250 μm, the flexibility is insufficient, and therefore the film is not suitable for being rolled up and used.

Among the above-mentioned transparent polymer moldings, polyethylene terephthalate is excellent in transparency and processability, and can be used more preferably. Further, since polyether sulfone has excellent heat resistance, heat treatment is required when heat treatment is required after preparation of the transparent conductive laminate, or when assembling an electroluminescent display using the transparent conductive laminate. It can be used more suitably when it is necessary.

The surface of this transparent polymer substrate is previously subjected to sputtering treatment, corona treatment, flame treatment, ultraviolet irradiation,
Etching treatment such as electron beam irradiation, undercoating treatment, etc.
You may perform the process which improves the adhesiveness with respect to the said film of the transparent conductive layer which consists mainly of indium oxide formed on this. Further, before forming the transparent conductive layer mainly made of indium oxide, a dustproof treatment such as solvent cleaning or ultrasonic cleaning may be performed, if necessary.

In the present invention, a transparent conductive layer made of indium oxide containing 15 to 50% by weight of tin oxide is formed as a first layer on one main surface of such a transparent substrate. By containing tin oxide in an amount of 15% by weight or more, the chemical stability of indium oxide is improved, and the durability of the electroluminescent light emitting material is improved. Since indium oxide having a tin oxide content of less than 15% by weight cannot provide durability, sufficient durability cannot be obtained even if an electroluminescent light emitting device is formed using such a transparent conductive layer. . If tin oxide is contained in excess of 50% by weight, excellent durability can be obtained, but transparency in the visible light region is impaired and the light emitted from the light emitting layer cannot be effectively extracted. In addition to
Since the resistance value also becomes high and sufficient emission brightness cannot be obtained when it is used as an electroluminescence light emitting element,
This is also undesirable.

The thickness of the transparent conductive layer made of indium oxide containing 15 to 50% by weight of tin oxide is usually 10 nm to
200 nm is preferred. The thickness of the transparent conductive layer affects its sheet resistance value and visible light transmittance. In order to reduce the sheet resistance value, the transparent conductive layer may be made as thick as possible, but if it is too thick, the visible light transmittance will decrease. Therefore, the thickness of the transparent conductive layer is determined by the required sheet resistance value and visible light transmittance. If the thickness of the transparent conductive layer is less than 10 nm, the sheet resistance value becomes high, and it is unsuitable for use as a transparent electrode of an electroluminescence light emitting device.
In order to reduce the sheet resistance value, the film thickness may be increased, but if it is much thicker than 200 nm, the visible light transmittance becomes low, which is also not preferable.

Thus, by forming a transparent conductive layer of indium oxide containing 15 to 50% by weight of tin oxide, preferably 10 to 200 nm in thickness, on one main surface of the transparent substrate, the electro Since it is possible to obtain a sheet having a sheet resistance value and a visible light transmittance required for the transparent conductive layer of the luminescent light emitting element, an electroluminescent light emitting element is formed using it, and the sheet is provided between the transparent conductive layer and the back electrode. Electroluminescence emission that has sufficiently suppressed the decrease in luminance when the light emission is continued because the transparent conductive layer has excellent durability in addition to the sufficient light emission luminance when a voltage is applied to emit light. The device is obtained.

As a method for forming the transparent conductive layer made of indium oxide containing 15 to 50% by weight of tin oxide, any of conventionally known physical vapor deposition methods such as vacuum deposition method, sputtering method and ion plating method can be used. Can be adopted. In the sputtering method, a direct current (DC) using indium oxide containing a predetermined amount of tin oxide as a target or an inert gas such as argon as a sputtering gas
Alternatively, a radio frequency (RF) magnetron sputtering method can be used. Further, in order to increase the transparency and conductivity of the transparent conductive layer, oxygen gas of 0.1 to 20 flow rate% may be mixed in the sputtering gas. Further, a direct current or high frequency reactive sputtering method using a tin-indium alloy having a predetermined composition ratio as a target, an inert gas such as argon as a sputtering gas, and an oxygen gas as a reactive gas can also be suitably used. In this method, the transmittance and conductivity of the transparent conductive layer very sensitively influence the partial pressure of oxygen gas, which is a reactive gas, so it is preferable to strictly control the partial pressure. Any of the above-mentioned sputtering methods can be suitably used because a transparent conductive layer excellent in transparency and conductivity can be easily obtained.

The transparent conductive film obtained by the above method is
Heat treatment (annealing) may be performed to further improve the environment resistance. The heat treatment temperature is usually 100 to 2
It is about 00 ° C.

In the present invention, the phosphor layer is then formed. A light emitting material mainly composed of zinc sulfide can be used for the light emitting layer. By adding to the zinc sulfide, a rare earth fluoride, which is a luminescent center, such as praseodymium fluoride (PrF ₃ ), neodymium fluoride (NdF ₃ ), terbium fluoride (TbF ₃ ), etc., in an amount of about 0.01 to 10 wt%. The emission color can be changed. The thickness of the light emitting layer may be set to such a level that sufficient emission brightness can be obtained.
It is about 100 μm.

The light emitting layer can be formed by a conventionally known vacuum deposition method or coating method. In the vacuum vapor deposition method, preferably, a luminescent material obtained by adding a predetermined additive to zinc sulfide is heated in a vacuum apparatus to evaporate, and adhered onto a transparent substrate on which a transparent conductive layer is disposed oppositely. A phosphor layer can be formed. In the coating method, in a suitable solvent such as acetone,
For example, zinc sulfide and an additive powder are dispersed, coated on a transparent substrate on which a transparent conductive layer is formed, and heated to vaporize the solvent to form a light emitting layer. This coating method is preferably used because the phosphor layer can be obtained by a relatively simple process.

In order to effectively apply an electric field to the phosphor layer, a dielectric layer may be provided between the transparent electrode and the phosphor layer, between the phosphor layer and the back electrode, or both. it can. By providing the dielectric layer, the luminous efficiency can be increased and the luminous brightness can be improved. As a material for the dielectric layer, a material having a high dielectric constant is preferable in order to effectively apply an electric field to the light emitting layer, and for example, yttrium oxide, silicon nitride, thallium oxide, barium titanate or the like can be used. Among them, barium titanate is well known as a high dielectric constant material and can be preferably used. The thickness of the dielectric layer is generally about 500 to 3000Å.

For forming the dielectric layer, a vacuum deposition method or a coating method can be used as in the method for forming the light emitting layer. In the coating method, the powder of a predetermined material is dispersed in an appropriate solvent such as acetone and then coated, and the dielectric layer can be formed by a simple process of heating and vaporizing the solvent, and thus it is also preferably used here.

A back electrode is further formed on the light emitting layer (or dielectric layer) formed as described above. For the back electrode, a metal having a high reflectance in the visible region is preferably used in order to effectively guide the light emitted from the light emitting layer to the transparent substrate side. Among them, aluminum is suitable because it has a relatively high reflectance, excellent stability, and is inexpensive.

As the method of forming the back electrode, any of conventionally known physical film-forming vapor phase growth methods such as a vacuum deposition method and a sputtering method can be used. More simply, a metal foil may be laminated on the light emitting layer or the dielectric layer. The thickness of the back electrode should be such that it can sufficiently reflect visible light,
It is about 0.1 to 100 μm. When the electroluminescent light emitting element is used as a display, the back electrode may be patterned if necessary.

Further, in order to prevent the deterioration of the electroluminescent light emitting element due to moisture, the electroluminescent light emitting element produced as described above may be sealed by sandwiching it with a transparent moisture-proof film such as ethylene trifluoride chloride. The atomic composition of the transparent conductive layer formed by the above method can be measured by Auger electron spectroscopy (AES), inductively coupled plasma method (ICP), Rutherford backscattering method (RBS), or the like. Further, these film thicknesses can be measured by observation in the depth direction of Auger electron spectroscopy, cross-section observation by a transmission electron microscope, or the like.

[0027]

EXAMPLES Next, the present invention will be specifically described with reference to Examples. Example 1 On one surface of a polyethylene terephthalate film (thickness 188 μm), indium oxide containing 15% by weight of tin oxide as a target, argon gas as a sputtering gas, and oxygen gas as a reactive gas (flow ratio,
3 mTorr using Argon: Oxygen = 10: 0.1)
Under an atmosphere of r, a 50-nm-thick transparent conductive layer was formed by a DC magnetron reactive sputtering method. Furthermore, a solution in which a fluorescent powder containing neodymium fluoride (2 wt%) added to zinc sulfide is dispersed in an acetone solvent is coated on the roll coater, and then heat-treated at 150 ° C. for 3 minutes to vaporize the acetone to make it thick. A 30 μm thick phosphor layer was obtained. Further, a solution in which barium titanate powder was dispersed in an acetone solvent was applied thereon by a roll coater, and most of the acetone was vaporized by heating at 60 ° C. for 120 minutes, and then an aluminum foil having a thickness of 25 μm was applied. The resultant was laminated and further heat-treated at 150 ° C. for 3 minutes to completely vaporize acetone in the dielectric layer and at the same time, to adhere the aluminum foil. This was further sandwiched with a transparent moisture-proof film, trifluoroethylene chloride, and the ends were brought into close contact with each other to obtain an electroluminescence light-emitting device.

[Examples 2 to 4] When a transparent conductive layer was produced, the content of tin oxide was 20% by weight (Example 2),
Alternatively, an electroluminescent light emitting device was produced by the same method as in Example 1 except that a target of 35% by weight (Example 3) or 50% by weight (Example 4) was used.

[Comparative Examples 1 and 2] When a transparent conductive layer is produced, the content of tin oxide is 10% by weight (Comparative Example 1),
Alternatively, an electroluminescent light emitting device was produced in the same manner as in Example 1 except that a target of 75% by weight (Example 2) was used.

The tin content of the transparent conductive layer, the sheet resistance, the visible light transmittance, the initial light emission luminance, and the durability of the electroluminescent light emitting device produced as described above were evaluated by the following methods.

Tin oxide content of the transparent conductive layer [SnO ₂
(Wt%)]: Measured by Auger electron spectroscopy. Sheet resistance [R (Ω / □)]: Measured by a four-terminal method when a transparent conductive layer was formed on one main surface of a transparent substrate. Visible light transmittance [Tvis (%)]: A transparent conductive layer is formed on one main surface of a transparent substrate, which is manufactured by Hitachi, Ltd.
Manufactured by a spectrophotometer U-3400. Initial Luminance [I ₀ (Candela / m ² )]: Temperature 50
AC 100V (frequency:
A voltage of 1 kHz) was applied between the transparent electrode and the back electrode to cause the electroluminescence element to emit light, and the emission luminance thereof was measured using luminance: LS-110 manufactured by Minolta Co., Ltd. Environmental resistance [I / I _0]: the light-emitting luminance measured after it emission luminance I after continued emission 3000 hours (candela / m ²⁾ and a Minolta Co., Ltd. luminance meter: LS-110
Was used to evaluate the change rate I / I ₀ . Table 1 shows the above measurement results.

[0032]

[Table 1]

As is clear from the results in the above table, the electroluminescence light-emitting device of the present invention has a high initial luminance and is excellent in durability with little reduction in luminance when light emission is continued. .

[0034]

As described above, in the present invention, by using a transparent conductive layer made of indium oxide containing 15 to 50% by weight of tin oxide as a transparent electrode on one main surface of the transparent substrate, initial light emission is achieved. It is possible to provide an electroluminescent light emitting element having high brightness and excellent in durability that suppresses a decrease in brightness when light emission is continued.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a transparent conductive laminate of the present invention.

[Explanation of symbols]

10 Transparent Substrate 20 Transparent Conductive Layer Made of Indium Oxide Containing 15 to 50% by Weight of Tin Oxide 30 Luminescent Layer 40 Back Electrode

Claims (3)

[Claims] 1. An electroluminescent light-emitting device in which at least a transparent conductive layer (B), a light-emitting layer (C), and a back electrode (D) are laminated on one surface of a transparent substrate (A) in the order of ABCD, An electroluminescent light-emitting device, characterized in that indium oxide containing 15 to 50% by weight of tin oxide is used for the transparent conductive layer (B). 2. The electroluminescent light emitting device according to claim 1, wherein zinc sulfide is mainly used as a light emitting body in the light emitting body layer (C). 3. The electroluminescent light emitting device according to claim 1, wherein a transparent polymer molding is used for the transparent substrate (A).