JPS5860731A - Electrochromic display device - Google Patents

Abstract

PURPOSE:To eliminate the need for counter electrodes and to make the density of coloring constant by applying a voltage between plural pieces of conductive films provided on a transparent substrate to oxidize the conductive films thereby coloring the electrodes of the electrochemical coloring material on the conductive films. CONSTITUTION:An upper substrate 1 of transparent glass and a lower substrate 2 of a recessing shape are combined to provide a cell space. An electrolyte 7 of a lithium perchlorate soln. or the like is packed in the cell space. Plural pieces of transparent conductive films 4 such as indium oxide are provided on the inner side surface in the cell of the substrate 1 and electrodes 5 of an electrochemical coloring material such as tungsten oxide are formed thereon, whereby an intended electrochromic display device is obtained. In the stage of driving, a voltage by which oxidation reaction is effected in the films 4 is applied between plural pieces of the transparent conductive films. Thus the cations in the electrolyte 7 and the electrons from the films 4 are implanted into the electrodes 5, whereby the electrochemical coloring material is colored and displaying is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to driving for maintaining a predetermined contrast in an electrochromic display device that utilizes an electrochemical coloring phenomenon.

Conventional electroxemic displays have drawbacks, such as difficulty in maintaining constant contrast and the need for a counter electrode in addition to the electrochemical colorant.

The general structure of a conventional electrochromic display device is shown in FIG.

The two upper and lower substrates 1 and 2 face each other with a spacer 3 in between,
constitutes a cell. The upper substrate 1 is made of transparent glass, and a transparent conductive film 4 made of indium oxide, tin oxide, etc. is provided on the inner side of the cell, and furthermore, an electrode 5 made of an electrochemically colored substance such as tungsten oxide, molybdenum oxide, etc. is formed thereon. ing. The lower substrate 2 may be opaque, and may be made of ceramic or glass, for example, and a counter electrode 6 made of a metal such as gold or platinum or a conductive material such as indium oxide or tin oxide is provided on the inner side of the cell. The cell space between the upper and lower two groups @1 and 2 is filled with an electrolyte 7 in which an electrolyte such as sulfuric acid or lithium perchlorate is dissolved in a solvent. In some cases, white powder such as aluminum or porous white rice 8 is added.

In the electrochromic display device with the T structure described above, when voltage is applied with the electric rod 5 at a negative potential with respect to the counter electrode B, both the positive ions (M+) in the electrolytic solution 7 and the electrons in the transparent conductive film 4 is injected into the electrode 5, and if the electrochemical coloring material is tungsten oxide, the tungsten bronze is released and colored. When a voltage is applied with the polarity of the potential reversed, positive ions and electrons are extracted from the electric wire 5 and the color is erased.

xM"+WOs+xe-, l: MXWO8(1) (decolorization) (coloration) A colored electrochemical material maintains its colored state even when the applied voltage is cut off. That is, it has memory properties. However, it is known that the optical density of coloring when no voltage is applied gradually decreases.Memory characteristics are determined by the insulation resistance of the panel container, the amount of impurities in the panel, and the characteristics of the counter electrode. Display contrast is not stable because it is affected by changes over time.Also, because the potential range in which the transparent conductive film does not cause a chemical reaction is narrow, the driving voltage range is limited, making it difficult to obtain sufficient contrast. There are drawbacks such as slow response.As mentioned above, the instability of contrast and the limitation of the 11IJt pressure range are major problems in the practical application of electrochromic display devices.

The present invention significantly improves these drawbacks and facilitates the practical use of electrochromic display devices.

In the electrochromic mink display device of the present invention, during or before driving the panel, between the plurality of transparent conductive films,
■The transparent conductor tM on the terminal side applies a voltage that causes an electrochemical reaction. At this time, ■On the terminal side, a reaction occurs in which cations in the electrochemical colored substance are extracted into the electrolytic solution, and an oxidation reaction occurs in the transparent conductive film.

An anode current flows due to discharge of the electric double layer at the interface between the two and the electrolyte solution. On the other hand, on the e terminal side, a cathode current flows due to the injection reaction of cations into the electrochemical coloring substance, the reduction reaction of the transparent conductive film, and the charging of the electric double layer at the interface between the two and the electrolyte solution. Naturally, the anode current and cathode current are equal. Here, if the applied voltage is sufficiently large, the current due to oxidation of the transparent conductive film will be larger than the current due to reduction, and accordingly, the cathode current due to cation injection into the electrochemically colored substance will be greater than the current due to cation extraction. is larger than the anode current due to In other words, the amount of charge injected into the electrochemical coloring material on the e-terminal side is greater than the amount of charge extracted from the electrochemical coloring material on the e-terminal side.

When the above voltage application operation is repeated for any segment, the amount of charge involved in coloring in the electrochemical coloring substance of the panel as a whole increases, and the coloring density (coloring density) becomes higher.

At this time, the transparent conductive film is a heavy source of electrochemical coloring material. When the amount of charge in the electrochemical coloring substance reaches a certain level, the oxidation reaction and reduction reaction of the transparent conductive film panel as a whole reach equilibrium, and the coloring density becomes constant. Therefore, the contrast can be kept constant at a predetermined value.

Further, the contrast can be controlled by the magnitude of the applied voltage.

Hereinafter, the present invention will be explained in detail with reference to Examples.

Embodiment In an electrochromic display device having the structure shown in FIG. 2, the upper substrate 1 is a transparent glass substrate, an indium oxide transparent conductive film is provided on the inner side of the cell by electron beam evaporation, and tungsten oxide is coated on top of the indium oxide transparent conductive film. X 10"-'
Vapor deposition was carried out in a vacuum of Torr at a substrate temperature of 100°C, and approximately [l
Form an electrode using an electrochemical color-forming substance exclusively for L6μ membranes.

The lower substrate is formed into a spacer with the lower substrate using concave glass, and by combining this concave glass and the upper substrate, a cell space of ~115tIIk is provided. The electrolyte filling the cell space is a 1M propylene carbonate solution of lithium perchlorate, with a white plate of aluminum oxide as a white background.

When a voltage of tov is applied between arbitrary transparent conductive films and coloring and decoloring are repeated between the electrochemically colored substances, the coloring density of the electrochemically colored substance in the colored state is expressed as the reflectance.
FIG. (a) shows the case where the initial reflectance is 100%, and (b) shows the case where the initial reflectance is started from 40%. 1.6
FIG. 4 shows the reflectance when v is applied. Applied voltage 1
．． In OV, the transparent conductive film is not oxidized, so all electrochemically colored substances are almost completely decolored. On the other hand, applied voltage 1
．． At 6 V, a reaction occurs in which the transparent conductive film is oxidized, so that the reflection "4" of the electrochemical coloring substance remains constant.

As described in detail above, the present invention is an electrochromic film that has a constant coloring density, has a simple structure that does not require a counter electrode, and is easy to drive, by driving with applied pressure that causes a chemical reaction in a transparent conductive film. This is what made the display device possible.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional electrochromic display device with a general 411 structure, Figure 2 is a cross-sectional view of an electrochromic display device of the present invention, and Figure 3 is driven with a voltage that does not cause the transparent conductive film to react. FIG. 4 is a characteristic diagram showing the change in reflectance over time of the electrochromic display device of the present invention. 1... Upper substrate 2... Lower substrate 3... Spacer 4... Transparent conductive film 5...'w11 Colored substance of vaporized chemical vapor/Counter electrode 7... Electrolyte 8... White Applicant for background treason or more Dai-ni Seikosha Co., Ltd. Figure 1 Figure 2 2ゝ4 Sub■ Application t'Tile food + i Kiribake cycle & Mouth) r
Figure 4

Claims (1)

[Claims] An electrolyte is sandwiched between a pair of substrates, at least one of which is transparent, and a portion of an electrode of an electrochemically colored substance formed on a plurality of conductive films provided on at least one substrate serves as a display pixel. An electrochromic display device comprising an electrochromic display device characterized in that a voltage that causes a chemical reaction in the conductive film is applied to the conductive film.