JPH0361169B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an electrochromic display element used, for example, in calculators, watches, various numeric displays, various displays related to home appliances, and the like. Conventional configurations and their problems Compared to liquid crystal displays, electrochromic displays have no viewing angle dependence, and their colors are bright and clear. As electrochromic materials, WO ₃ is well known as an inorganic material, and viologen, pyrazoline, anitraquinone, and dyes of styryl-based analog compounds are well known as organic materials. A thin film of WO ₃ is formed on a transparent electrode by vapor deposition or the like, and an electrolytic solution, a dielectric film, etc. are provided between the counter electrodes to form an element. WO ₃
Practical problems include the display life, color unevenness between display segments, and the type of coloring, which is a single blue color. In addition, in order to stabilize the counter electrode reaction, special efforts must be made in the material of the counter electrode, and there are also problems in that a reflector or the like must be incorporated into the element. Organic pigments such as viologen-based pigments develop color when reduced, and return to their decolored state when oxidized.
The problem with viologen dyes is that they have a short display life. The reason for this is that since the dye in the coloring state becomes insolubilized in the solvent, the phenomenon of soluble and insoluble dyes occurs depending on whether the color fades or develops, but there is a problem with the reversibility of this phenomenon.
Furthermore, since ions are involved in these redox reactions, there are problems in that they may have an adverse effect on the ionic transparent electrode and that power consumption is large. The characteristics that current electrochromic displays are inferior to liquid crystal displays are display life and response speed. The present applicant has previously proposed an electrochromic display element using a dye, which is a type of styryl-like compound, as an electrochromic material. The basic structure of the electrochromic display element is shown in Figure 1. 1 is a glass substrate, 2 is a display electrode, 3 is a counter electrode, 4 is a sealing material, 5 is a sealing material, 6
indicates a displayable substance. The glass substrate 1 may be made of a material in which at least one side is transparent. As the electrode material for the display electrode 2 and the counter electrode 3, In ₂ O ₃
A transparent electrode such as SnO 2 or SnO ₂ is used. In terms of area, the display electrode 2 is smaller than the counter electrode 3.
As the sealing material 4 and the pore sealing material 5, epoxy resin, low melting point glass solder, etc. are used. The displayable substance 6 is a solution in which a dye is dissolved in a non-aqueous organic solvent together with a supporting electrolyte. As the electrochromic material, a styryl-based compound dye was used. In such an electrochromic display element, when a DC voltage V ₁ is applied between the display electrode 2 and the counter electrode 3 so that the display electrode 2 side is positive, the changes in current and coloring density with respect to voltage application time are expressed as a second equation.
As shown in the figure. a represents the applied voltage, b represents the current value, and c represents the temporal change in color density. In such a configuration, the current value i _L flowing through the element increases, and the coloring density decreases.
There was a drawback that high D _O could not be obtained. OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional drawbacks, and aims to improve the display life and response speed of electrochromic display elements, improve display quality, and faithfully reproduce display electrode patterns. Structure of the Invention The present invention achieves the above-mentioned object by providing a display electrode on one side of two transparent substrates facing each other and a counter electrode on the other, wherein both the display electrode and the counter electrode are made of a transparent conductive film. The electrical resistance of the conductive film in the first region facing the display electrode of the counter electrode is equal to or less than 10 ⁶ Ω/unit, and the electrical resistance of the conductive film in the second region not opposed to the conductive film in the first region is The object of the present invention is to provide an electrochromic display element characterized in that the electrical resistance is lower by one order of magnitude or more than the electrical resistance of . DESCRIPTION OF EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. FIG. 3 shows the structure of an electrochromic display element which is an embodiment of the present invention. A is a side sectional view, and b is a plan view of the counter electrode. In the figure, 1 is a transparent substrate such as glass, 2 is a display electrode, 3 is a counter electrode, 4 is a sealing material, and 6 is a displayable substance.The feature of this embodiment is that both the display electrode 2 and the counter electrode 3 are transparent. The counter electrode 3 is composed of two types of conductive films having different electrical resistances, such as a first conductive film 7 and a second conductive film 8. A solution having the following configuration was used as the displayable substance 6 sealed inside the display element. As an electrochromic material, 3,3-dimethyl-2-(P-dimethylaminostyryl)-indolino[1,2-b]-oxazoline (abbreviated as IRPDM), which is one of the dyes of styryl-like compounds, is used.
This was dissolved in a propylene carbonate solution together with tetrabutylammonium perchlorate as a supporting electrolyte to a concentration of 0.03M/ and 0.3M/, respectively. IRPDM is colorless until electrical stimulation is applied, but when electrical stimulation is applied, it becomes colored red with a light absorption peak around 550 nm. SnO ₂ film or In ₂ O ₃ −SnO ₂ (ITO) is used as the first conductive film 7 of the counter electrode 3, and as the second conductive film 8
In ₂ O ₃ -SnO ₂ (ITO) was used, and the following three types of counter electrodes were used to compare the characteristics, including the case where the first and second conductive films 7 and 8 were only the same ITO film. I conducted an experiment. The contents are shown in Table 1 below. In this case, the area of the first conductive film 7 is the display electrode 2.
It shall be exactly the same as, or slightly larger than, and located in the opposite position. It is assumed that the area ratio between the display electrode 2 and the counter electrode 3 is 1/2 or more.

[Table] For these three types of display elements, the current value i _L after applying 1.3V for 3 minutes at the DC voltage shown in Figure 2
The color density was determined by measuring the light absorption rate at 550 nm. In addition, the indicated lifespan is at 60℃.
We performed a continuous application test of 1.3V and investigated. The characteristic results are shown in Table 2.

[Table] From the conventional case (No. 1) in which the electrical resistance of the first conductive film 7 is equal to that of the second conductive film 8 and is R _O ,
The electrical resistance of the first conductive film 7 is R ₁ (No. 2) and R ₂ (No. 2).
3), the time characteristics of the current and coloring density become as shown in FIGS. 4a and 4b. In other words, the leakage current i _L
As the electrical resistance of the first conductive film 7 increases,
On the contrary, the coloring density becomes larger. The characteristics of the display element tend to be desirable in terms of power consumption and coloring contrast. When the electrical resistance of the first conductive film 7 is in an insulating state, the current value is the smallest and the coloring density is the highest. However, in this case, the display pattern is not uniquely determined by the display electrode pattern, but the counter electrode The influence of the pattern (the pattern of the first conductive film 7) appears. Therefore,
Considering this influence, the electrical resistance of the first conductive film 7 is preferably smaller than 10 ⁶ Ω/hole. Furthermore, as shown in Table 2, as the electrical resistance of the first conductive film 7 increases, the display life also increases. Next, a second embodiment will be described. As the displayable substance 6, the same substance as in the first example was used. For the counter electrode 3, SnO ₂ (10KΩ/hole) was used as the first conductive film 7 in FIG. 3, and three types of ITO with different electrical resistances were used as the second conductive film 8. . The contents are shown in Table 3 below.

[Table] The coloring start-up characteristics were investigated when a DC voltage of 1.3 V was applied to these three types of display elements. The rise characteristics were compared based on the time it takes to reach 90% of the saturated color density. The results are shown in Table 4.

[Table] In this embodiment, the electrical resistance of the first conductive film 7 is kept constant, and the electrical resistance of the second conductive film 8 is varied from R _O ′ (No. 4) to R ₁ ′ (No. 5), R ₂ ' (No. 6), the time characteristics of the current and coloring density hardly change. However, as shown in FIGS. 5a and 5b, the response characteristics change. That is, as the electrical resistance of the second conductive film 8 becomes lower, the rise characteristics become better. As the difference in electrical resistance between the first and second conductive films becomes smaller than an order of magnitude, the saturated coloring density becomes lower and the contrast decreases. Therefore, in view of display quality, it is necessary that the electrical resistances of the first and second conductive films differ by at least one order of magnitude. This tendency holds true even when decoloring is performed by reversing the polarity of the applied voltage between the display electrode 2 and the counter electrode 3. A side sectional view of an electrochromic device according to a third embodiment of the present invention is shown in FIG. This example has the same configuration as the first and second examples except for the configuration of the counter electrode. The counter electrode 3 of this embodiment is a first electrode with high electrical resistance.
The second conductive film 7 is embedded in a second conductive film 8 having low electrical resistance, and in this case as well, the same characteristics as in the embodiment described above can be obtained. These examples increase electrical coloring efficiency, reduce leakage current when voltage is applied, and cause electrochemical side reactions (reactions not directly related to coloring reactions).
, and the display life can be greatly improved. Note that the transparent electrode materials used for the counter electrode of the present invention include SnO ₂ and In ₂ O ₃ − shown in this example.
In addition to SnO ₂ (ITO), In ₂ O ₃ , V ₂ O ₅ , TiO ₂ ,
One or more composites of metal oxides such as InO ₂ , MoO ₃ , and WO ₃ are used. Effects of the Invention In summary, the present invention provides a display electrode on one of two transparent substrates provided facing each other and a counter electrode on the other, both of the display electrode and the counter electrode being made of a transparent conductive film, and Electrical resistance of the conductive film in the first region of the counter electrode facing the display electrode
To provide an electrochromic display element, characterized in that the electrical resistance of the electrically conductive film in the non-opposing second region is lower than the electrical resistance of the electrically conductive film in the first region by at least one order of magnitude, 10 ⁶ Ω/unit or less. This has the advantages of long display life, reduced power consumption, improved response characteristics, improved color contrast, and improved faithful reproducibility of display electrode patterns.

[Brief explanation of drawings]

Figure 1 is a side sectional view showing the basic structure of a conventional electrochromic display element, Figures 2 a to c are diagrams showing changes in applied voltage, current, and color density over time in the display element, and Figure 3 a. 3 is a side sectional view of an electrochromic display element according to an embodiment of the present invention, FIG. 3b is a plan view of a counter electrode of the same display element, and FIGS. Figures 5a and 5b show the time characteristics of current and coloring density when the electrical resistance of the first conductive film is increased while keeping the electrical resistance constant. Figure 6 shows the temporal characteristics of current and coloring density when the electrical resistance is kept constant and the electrical resistance of the second conductive film is lowered.
The figure is a side sectional view of an electrochromic display element according to another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Transparent substrate, 2...Display electrode, 3...Counter electrode, 4...Sealing material, 6...Displayable substance, 7...
...First conductive film, 8...Second conductive film.

Claims (1)

[Claims] 1 A display electrode is provided on one of two transparent substrates provided facing each other, and a counter electrode is provided on the other, the display electrode and the counter electrode are both made of a transparent conductive film, and the display electrode of the counter electrode is opposed to the display electrode. The electrical resistance of the electrically conductive film in the first region is 10 ⁶ Ω/mouth or less, and the electrical resistance of the electrically conductive film in the non-opposed second region is lower than the electrical resistance of the electrically conductive film in the first region by at least one order of magnitude. Electrochromic display element.