JP2758660B2 - Dispersion type electroluminescent device using zinc oxide as transparent electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a dispersion-type electroluminescent device (hereinafter, referred to as an EL device) used as, for example, a planar light source.

[Prior Art] As a transparent electrode of a conventional dispersion type EL element, an indium tin oxide thin film (hereinafter referred to as an ITO film) formed by sputtering or vapor deposition is known and widely used.

[Problems to be Solved by the Invention] However, the dispersion type EL device in which the ITO film is a transparent electrode has the following problems.

When lighted for a long time, as will be described in detail later, the ITO film undergoes a phenomenon of blackening at the interface with the light emitting layer, further deteriorating the light emitting layer, thereby reducing the luminance and shortening the life. .

In particular, when the lamp is lit in a high-temperature, high-humidity or sunlight-irradiated state, a blackening phenomenon occurs at an early stage, which limits the field of use.

Further, the above blackening phenomenon impairs the appearance of the product and lowers the commercial value.

[Means for solving the problem]

The present invention uses a zinc oxide (ZnO) transparent conductive film or III instead of an ITO film conventionally used for a transparent electrode of a dispersion type EL element.
It has been found that the above problem can be improved by using a zinc oxide transparent conductive film containing a group IV element and / or a group IV element (hereinafter, both are collectively referred to as a ZnO-based film). Further, the dispersion type EL device can be manufactured by a known manufacturing technique using the above-mentioned ZnO-based film as a transparent electrode on the front surface or a transparent electrode on the back surface of the device or as both electrodes.

Next, an outline of each component of the present invention will be described.

I as an element contained as an impurity in the ZnO transparent conductive film
Specific examples will be described using group II element aluminum (Al) and group IV element silicon (Si). Al and / or
The content of Si is 0.1 to 20% by atomic% based on zinc (Zn).
It is desirable that Al and / or Si content
If the content is less than 0.1 atomic%, it is generally difficult to obtain the effect of addition. If the content is more than 20%, the crystallinity of the transparent conductive film is significantly deteriorated, and the low efficiency tends to increase.
The preferred content of Si and Si is 1 to 15 atomic%. Of course, the present invention can be used alone ZnO, these III
The group element, group IV element, and the like are not particularly limited as long as a predetermined amount is added as necessary.

The ZnO-based film can be manufactured by a sputtering method, a spray method, or any other known film forming technique.However, in the case of a transparent electrode, the ZnO-based film also serves as a base for the EL light-emitting layer, and has crystallinity and particularly smoothness of the surface. It is desirable to use a sputtering method because a high quality film having excellent uniformity is desired.

In addition, gallium (G
a), indium (In) and boron (B) etc. or Si
Examples of group IV elements other than the above include germanium (Ge), titanium (Ti), zirconium (Zr), hafnium (Hf), and the like, and the amounts of addition thereof can be the same as those of Al and Si. Of course, a group III element and a group IV element may be used in combination.

Examples of the substrate on which the transparent electrode according to the present invention is formed include transparent glass, transparent plastic films, sheets, and plates, and are not particularly limited.

The luminous body forming the luminescent layer can be exemplified by a known mixture containing a main agent, an activator and, if necessary, an activator, such as ZnS, SrS, and CaS as the main agent, and Cu, Mn, Ce, and E as the activator.
Examples of activators such as u, Tb, Ce and the like include Cl, Al, F and the like, but are not particularly limited.

Examples of the organic polymer binder forming the light emitting layer include organic compounds having a high dielectric constant such as cyanoethyl cellulose, cyanoethyl saccharose, and cyanoethyl pullulan, but there is no particular limitation. The body is in a dispersed state.

As the insulating layer according to the present invention, Ba is contained in an organic polymer binder.
TiO ₃ , SrTiO ₃ , PbTiO ₃ (there are no particular restrictions and examples are merely examples) dispersed therein, or high dielectric constants such as polyethylene terephthalate and polyvinylidene fluoride (these examples are no particular restrictions and examples) Can be exemplified, but there is no particular limitation. In this case, the organic polymer binder may be the same as the binder exemplified above in the light emitting layer, but is not particularly limited. In addition, examples of the composition mainly composed of the thermoplastic resin include a film and a sheet, but there is no particular limitation.

Although the back electrode according to the present invention is not particularly limited, it is more advantageous to adopt the following configuration depending on the configuration of the insulating layer, for example. That is, an organic polymer binder is used in the insulating layer.
When using a compound such as BaTiO ₃ , a metal foil such as Al is preferable, while when the insulating layer is mainly composed of a thermoplastic resin having a high dielectric constant, a paste containing Ag, C, Ni, and other conductive materials is used. A conductive paint or the like on the insulating layer, or
It is desirable to form Al, Ag, and other metal deposits on the insulating layer. In this case, examples of the conductive paint include a paste in which fine powder of a conductive substance is dispersed in a binder of a polyester resin or other appropriate resin. Of course, it is needless to say that a preferred embodiment other than the above examples can be appropriately used as the back electrode.

The transparent conductive film in the present invention is provided with a ZnO-based film.A ZnO film and Zn doped with at least one element selected from the group consisting of a group III element and a group IV element as impurities.
A multilayer having at least two O films can also be used. In this case, either of the films may be in contact with the light-emitting layer, or two or more layers may be used, and the order of the structures is not particularly limited.

Further, the transparent conductive film of the present invention, between the ZnO-based film and the substrate,
The provision of a transparent conductive film made of another metal, a metal oxide, or the like is inevitable. In particular, an ITO film is preferable. Such an ITO film may be effective in improving the adhesion and the conductivity of the ZnO-based film.

The present invention has a structure in which a ZnO-based film transparent electrode, a light emitting layer, an insulating layer, and a back electrode are laminated in this order, but if necessary, another third light emitting layer is provided between the light emitting layer and the insulating layer, and between the insulating layer and the back electrode. It is absolutely inevitable that a layer composed of the components will enter. Of course, if necessary, a layer made of another third component may be added to the outside of the base or the back electrode.

The above has been an exemplary description of each component related to the present invention, and it goes without saying that the present invention is not limited to these descriptions.

[Operation] In general, a dispersion-type EL element contains water (H ₂ O) at least in a light-emitting layer or the like. When a voltage is applied to this dispersion-type EL element, an electrolysis phenomenon of H ₂ O occurs at the interface between the transparent electrode and the light emitting layer, and hydrogen generated by the electrolysis reduces the oxide thin film of the transparent electrode. Metallization is considered to be one factor in the above-described blackening phenomenon.

In addition, since the current moisture-proofing method of the dispersion-type EL element is not perfect, H ₂ O intrudes from the outside into the interface between the transparent electrode and the light emitting layer, especially in a humid environment, and further hydrogen is generated by the electrolysis of H ₂ O. Is presumed to promote the blackening phenomenon.

Furthermore, under conditions of exposure to sunlight, electrolysis and photochemical reaction promote the blackening and also promote the deterioration of the light emitting layer.

The above blackening phenomenon depends on the binding energy between the metal of the transparent electrode, which is an oxide, and oxygen.

At present, in a tin oxide thin film (referred to as a SnO ₂ film), an ITO film, and a ZnO-based film of the present invention which are generally used as a transparent electrode, the SnO ₂ film is most easily reduced, followed by an ITO film and a ZnO film.
It becomes difficult to be reduced in the order of the base film. This is because the oxygen binding energy of each metal is 290 KJ / mol for tin (Sn),
Indium (In): 308KJ / mol, Zinc (Zn): 348KJ / mol
From this value, it can be inferred that the ZnO-based film is most difficult to be reduced.

Further, looking at the band gap inherent to the material between indium tin oxide and zinc oxide, the former is 3.75 to 4.3 eV and the latter is 3.2 to 3.4 eV.
It is considered that the system film absorbs and blocks all the ultraviolet rays from the ultraviolet light on the visible light side more than the ITO film.

For this reason, in the dispersion type EL device, the transparent electrode is
By replacing the film with a ZnO-based film, the progress speed of the blackening phenomenon of the transparent electrode due to sunlight exposure can be suppressed, and furthermore, the deterioration of the light emitting layer itself due to sunlight exposure can be suppressed.

The high-performance EL characteristics of the dispersion-type EL element using the ZnO-based film transparent electrode are considered to be due to the familiarity of the interface between ZnO and ZnS.

Examples Hereinafter, the present invention will be described with reference to Examples.

Example 1 As shown in FIG. 1, 10 parts by weight of cyanoethyl cellulose and 60 parts by weight of cyanoethyl saccharose were heated and dissolved in 150 parts by weight of a dimethylformamide solution on a back electrode 5 made of Al foil (thickness: about 50 μm). An insulating layer 4 in which 200 parts by weight of BaTiO ₃ (particle size: about 1 μm) was dispersed in an organic polymer binder was prepared by a screen printing method to a thickness of 10 to 20 μm, and the same organic layer as above was formed thereon. Molecular binder (cyanoethylcellulose: cyanoethylsaccharose: dimethylformamide solution containing 10: 60: 150 parts by weight) 100
A luminescent layer 3 in which 80 to 90 parts by weight of ZnS: Cu phosphor was dispersed with respect to parts by weight was laminated by screen printing at a thickness of 50 to 60 μm. On the other hand, a polyester film (about 100 μm in thickness) was used as the transparent substrate 1, and a ZnO: Al film (8
A transparent electrode 2 having a thickness of 100 to 1000 ° and a transmittance of 550 nm of 82% and an Al atom of 3.6% with respect to the Zn atom is deposited. The transparent electrode 2 is overlaid on the light emitting layer 3 and passed through a heating roller. Then, the organic polymer binder exerts an adhesive force by heat, and the transparent electrode 2 and the light emitting layer 3 are bonded. An EL element obtained by sealing a moisture-proof film on the dispersion-type EL element thus produced, and an ITO film (thickness: 4
And a dispersion-type EL element manufactured in the same manner as described above except that the dispersion EL element is used in the same manner as above.
The device was continuously lit by applying a sine wave voltage of 400 Hz and 100 V, and the change over time in luminance was compared. The results are shown as driving environment conditions in three environments: a normal temperature and normal humidity environment in FIG. 2, a 30 ° C., 95% environment in FIG. 3, and a sunlight irradiation environment in FIG. The curves shown by solid lines 6, 8, and 10 are the dispersion-type EL devices in which the transparent electrodes are ZnO: Al films, and the curves shown by broken lines 7, 9, and 11 are the dispersion-type EL devices in which the transparent electrodes are ITO films. The following table shows the luminance retention ratio after each elapsed time.

Under any of the environmental conditions, the blackening phenomenon occurred early in the ITO film, but did not occur in the EL element using the ZnO: Al film as the transparent electrode. It was also found that the luminance decreased slowly with time, and the life was long.

On the other hand, a transparent electrode made of an ITO film and a transparent electrode made of a ZnO: Al film were used on the glass used as the transparent substrate 1,
When a dispersion type EL device is manufactured, the dispersion type EL using a transparent electrode composed of a ZnO: Al film under the above three driving environments is also used.
The element did not suffer from blackening, and was superior in terms of luminance reduction.

Further, the superiority was also observed when a ZnS: Mn phosphor powder was used instead of the ZnS: Cu phosphor powder of the light emitting layer.

The superiority of the above ZnO: Al film is that gallium (Ga), indium (In), boron (B), silicon (Si), germanium (Ge), titanium (Ti), hafnium (Hf), and It was also confirmed in a zinc oxide film to which zirconium (Zr) was added.

Further, in forming an insulating layer and a light emitting layer, a solvent is used in this example. However, the type of such a solution is not particularly limited, and may be omitted if it can be formed without a solution. At this time, in this example, the solution evaporates appropriately after screen printing.

Example 2 As shown in FIG. 5, an ITO film 2a (thickness: about 100 μm) was used on a polyester film (thickness: about 100 μm) used as a transparent substrate.
400-500mm) and then a ZnO film 2b (thickness 400
A transparent electrode having only an ITO film (thickness: 800 to 900 mm) was formed on the transparent substrate 1 in the same manner as in the case where a dispersion-type EL element was manufactured using the transparent electrode having a thickness of When a dispersion-type EL element was similarly manufactured using the same method, the deterioration when continuously lit by applying a sine wave voltage of 400 Hz and 100 V under three driving environments in Example 1 was compared. In the case of only one, the blackening phenomenon occurred early, but the dispersion type using the two-layered transparent electrode according to the present invention was used.
In the EL element, the blackening phenomenon did not occur even after 1000 hours.

This indicates that even if the ITO film exists in the transparent electrode, it is not reduced unless it is in contact with the light emitting layer, that is, the blackening phenomenon occurs at the interface between the light emitting layer and the transparent electrode. This indicates that a ZnO film to which a Group III or Group IV element is not added as an impurity can also be used as a protective film.

Further, even when a zinc oxide film to which a group III or IV element is added as an impurity is formed into a multilayer, its effectiveness as a protective film was confirmed.

Example 3 In forming an insulating layer, 10 parts by weight of cyanoethyl pullulan as an organic polymer binder, 20 parts by weight of cyanoethyl sucrose dissolved in 40 parts by weight of a dimethylformamide solution, and 70 parts by weight of BaTio ₃ were used. In forming the light-emitting layer, 100 parts by weight of the same organic polymer binder as described above (10:20:40 parts by weight of cyanoethyl pullulan: cyanoethyl saccharose: dimethylformamide) and Zn
S: 80 to 90 parts by weight of a Cu phosphor, and a dispersion type EL element was prepared in the same manner as in Example 1 except that the transparent electrode was an ITO film and a ZnO: Al film. In the three driving environments of Example 1, when the sine wave voltage of 400 Hz and 100 V is applied and the lamp is continuously lit, a comparison is made.
The blackening phenomenon occurred early in the dispersed EL device using the film, but the blackening phenomenon did not occur even after 1000 hours had passed in the device using the ZnO: Al film. This indicates that the superiority of the ZnO: Al film is recognized regardless of the type of the polymer binder.

Example 4 A polyester film (thickness: 6 to 7 μm) was used as the insulating layer 4 in FIG. 1, and an Ag paste (Ag fine particles were dispersed in a polyester resin binder and an organic solvent) as a back electrode 5 on the polyester film insulating layer. Example 1 was prepared by using a paste-like conductive paint) applied by screen printing (organic solvent is vaporized).
In the case where a dispersion-type EL element is produced in the same manner as in the above, there are two cases in which the transparent electrode is an ITO film and a case where the transparent electrode is a ZnO: Al film.
400Hz, 100V under the three driving environments of Example 1
Comparing the degradation during continuous lighting by applying a sinusoidal voltage of, the blackening phenomenon occurred early in the dispersion type EL device using the ITO film, but the device using the ZnO: Al film No blackening phenomenon occurred even after the lapse of time. This indicates that the superiority of the ZnO: Al film is recognized regardless of the type of the insulating layer.

[Effects of the Invention] In a conventional dispersion type EL device using an ITO film as a transparent electrode, a blackening phenomenon occurs at an interface with a light emitting layer when the device is continuously lit. However, by using a ZnO-based film instead of the ITO film, such a blackening phenomenon is suppressed, the aging of the luminance is slowed down, the life can be extended, and very excellent characteristics are obtained. A distributed EL element can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a distributed EL device according to the present invention, and FIGS. 2, 3, and 4 are EL devices shown in FIG.
FIG. 5 is a diagram showing a change over time in luminance under three environments of the device. FIG. 5 is a cross-sectional view showing another embodiment of the dispersion type EL device according to the present invention. 1 ... Transparent substrate, 2 ... Transparent electrode, 2a ... ITO film, 2b ... ZnO film,
Reference numeral 3 represents a light emitting layer, 4 represents an insulating layer, and 5 represents a back electrode.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shunsuke Hirano 163 Morikawaramachi, Moriyama City, Shiga Prefecture Gunze Moriyama Plant (56) References JP-A-62-122011 (JP, A) JP-A-61-198592 (JP, A) JP-A-63-245889 (JP, A) JP-A-61-76695 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B 33/28

Claims (2)

(57) [Claims] A zinc oxide transparent conductive film, a group III element and an IV
A transparent electrode comprising a two-layer or a multilayer of two or more layers with a zinc oxide transparent conductive film to which at least one element selected from the group of group elements is added as an impurity, and having a configuration in which the stacking order of the layers is not limited Is formed on a substrate, and on the transparent electrode, a light-emitting layer, an insulating layer, and a back electrode each formed by dispersing a phosphor in an organic polymer binder are laminated in this order. element. 2. An indium tin oxide thin film is formed on a substrate, and a zinc oxide transparent conductive film or at least one element selected from the group consisting of a group III element and a group IV element is added as an impurity on the thin film. 2. The dispersion-type electroluminescence device according to claim 1, wherein the dispersion-type electroluminescence device has a configuration in which a zinc oxide transparent conductive film or a multilayer film including two or more layers thereof is formed and these are used as transparent electrodes.