JPH01233427A - Electrochromic display element - Google Patents

Abstract

PURPOSE:To assure a long cycle life even under driving conditions including a pause state by incorporating cerium oxide into tungsten oxide. CONSTITUTION:Transparent display electrodes 2 and insulating protective films 3 are provided respectively to prescribed patterns on the surface of a transparent glass plate 1 by which a tungsten oxide substrate 4 is formed. An electrochromic material film 5 consisting of the tungsten oxide contg. the cerium oxide is provided on the display electrodes 2 of the prescribed display segment parts of the display electrode substrate 4 where the protective films 3 are not formed, by which the display electrodes 6 are formed. The yellowing of the tungsten oxide, known as 'burn' is prevented by adding the cerium oxide to the tungsten oxide in such a manner, by which the display element having the long cycle life is obtd. even under the driving conditions including the pause state.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an electrochromic display element.

[Conventional technology]

Electrochromic display elements that use tungsten oxide (WO) as an electrochromic substance and an organic solvent-based electrolyte containing lithium ions in an organic solvent have only recently been commercialized, but they are becoming more and more popular. Initially, it was used with a colored charge amount of about 4s+C/c+i. Later, due to the desire for higher quality, a colored charge amount of 6 mC/cd, and furthermore a colored charge amount of 8 to 10 mC/c-, came to be required. However, it has become possible to meet this demand by improving the method of forming tungsten oxide films. At the same time, cycle life was also investigated; for example, Ando et al.
If the tungsten oxide film thickness is 5,000 in lays Jan PP3 ('85), the amount of colored charge is 6 mC/cd.
We confirmed the lifespan of 10'' cycles by repeating coloring and decoloring.Furthermore, the inventors confirmed that the coloring charge amount was 8.511IC.
An electrochromic display element was obtained in which no problem occurred after 107 cycles even when a cycle life test was carried out at an increased temperature of /c11. However, when we conducted a practical test to apply the above electrochromic display element to stock price display boards, etc., we found that tungsten oxide was generated during the enemy cycle despite being used with a colored charge amount of about 8 to 10 mC/c+1. The inventors analyzed this yellow-brown tungsten oxide film using X-ray photoelectron spectroscopy. It was discovered that the tungsten oxide film contained tetravalent tungsten. - Generally, the coloring mechanism of tungsten oxide is said to be as follows, and it is reported that reversibility is lost when the value of χ exceeds 0.3.

However, the amount of colored charge at 10 mC/c+a is about 0.095 based on the value of χ above, and the inventors of the present invention have never encountered such troubles in the past.
This phenomenon of yellowing and browning of tungsten oxide was named "staining." The difference between the conventional cycle life test and the driving method in the practical test is as shown in Figures 2 and 3. In the case of the practical test, as shown in Figure 3, It is driven in a mode in which the electrodes are opened for a minute, the coloring state is maintained using the memory function of the electrochromic display element (referred to as the resting state), the color is erased, and the color is colored again. In other words, the difference between conventional cycle life tests and practical tests is that, as shown in Figure 2, in the case of conventional cycle life tests, coloring and decoloring occur in a short time and in the same amount of time; does not have the above-mentioned dormant state.

[Problem to be solved by the invention]

This invention is based on the problem that conventional electrochromic display elements suffer from a yellowing phenomenon of tungsten oxide called "fading" under operating conditions that include the above-mentioned rest state, resulting in loss of display function and shortened cycle life. It is an object of the present invention to solve this problem and provide an electrochromic display element that has a long cycle life even under driving conditions including a rest state.

[Means to solve the problem]

In order to solve the above problems, the present invention has investigated electrochromic materials, and by adding cerium oxide to tungsten oxide, provides an electrochromic display element that has a long cycle life even under operating conditions including a rest state. It has been made possible.

This is detailed as follows.

As a result of intensive research into the mechanism of yellowing of tungsten oxide, known as "staining," and its countermeasures, we have not fully elucidated the mechanism, but we are currently thinking as follows. As mentioned above, the amount of colored charge has been increased in order to improve the quality, but in addition to this, the present inventors have also improved the response speed and are now able to generate 8 to 10 mC within a short time of 0.6 seconds. It has been achieved to obtain a colored charge amount of /c.

Diffusion of lithium ions into tungsten oxide particles proceeds from the outermost surface of the tungsten oxide particles toward the center of the particles, but when a charge is injected for 0.6 seconds, lithium ions fully penetrate into the tungsten oxide particles. Unable to diffuse, lithium ions exist near the surface of the tungsten oxide particles, and when this is immediately decolored, all lithium ions are extracted from the tungsten oxide particles.

However, when a dormant state exists, the lithium ions diffuse into the center of the tungsten oxide particle and become almost uniformly distributed within the particle. Therefore, when erasing this,
If the decoloring time is short, the lithium ions cannot be sufficiently diffused, so a small amount of lithium ions remain within the tungsten oxide particles.

As a result, as the coloring and decoloring cycle is repeated, lithium ions accumulate within the tungsten oxide particles, and a large amount of pentavalent tungsten oxide exists within the particles, making them sufficiently transparent even after decoloring. Instead, a blue color remains. When the cycle is repeated further, the pentavalent tungsten oxide becomes tetravalent, which is the cause of the yellowish brown color.Furthermore, the tetravalent tungsten oxide does not exhibit electrochromic properties, which is the reason why it does not become colored. In order for tungsten oxide to change from pentavalent to tetravalent, a potential of approximately 1■ is required, and tungsten oxide does not change from hexavalent to pentavalent to tetravalent in a general coloring-decoloring cycle. This is because such an energy barrier must be overcome.

Based on the above, it is thought that the best way to prevent the yellowing phenomenon of tungsten oxide, which is called "°° discoloration," is to increase the decoloring voltage and lengthen the decoloring time. .It has been found that increasing the decoloring time to 2 seconds or more is effective in preventing the occurrence of "fading," but such a long decoloring time results in a lack of speed as a display device. Therefore, as a result of further study, the present inventors discovered that by adding cerium oxide to tungsten oxide, it is possible to prevent the yellowing-browning phenomenon of tungsten oxide called "fading". He found out.

In other words, by adding cerium oxide to tungsten oxide to make the tungsten oxide contain cerium oxide, the diffusion of lithium ions in tungsten oxide becomes faster, and lithium ions are quickly released from tungsten oxide particles during decolorization. It is believed that the lithium ions are removed and no longer remain in the tungsten oxide particles, preventing the tungsten oxide from turning blue during decolorization, and preventing the tungsten oxide from changing into a tetravalent state. The amount of cerium oxide added to tungsten oxide, that is, the concentration of cerium oxide in the electrochromic material consisting of a mixture of tungsten oxide and cerium oxide constituting the electrochromic material film is 0.2 to 20 at% ( atomic%), that is, when the cerium oxide concentration in the electrochromic material is less than 0.2 atomic%.
On the other hand, if the cerium oxide concentration exceeds 20 at %, the electrochromic properties will deteriorate, such as the amount of colored charge decreasing due to the accompanying decrease in tungsten oxide.Especially. The concentration of cerium oxide in the electrochromic material is preferably in the range of 1 to 10 at%.The thickness of the electrochromic material film made of tungsten oxide containing cerium oxide is 3,000 atomic percent
~io, ooo is preferable, and if the film thickness is less than 3,000 and the amount of colored charge is 1 OLIIC/cd or more,
On the other hand, when the film thickness is 10,000
When it exceeds the human body, the membrane becomes blueish, making it difficult to visually recognize the color change of the electrochromic substance.

The electrochromic display element of the present invention is characterized by containing cerium oxide in tungsten oxide, but the structure of this element other than the electrochromic material composition may be the same polarity as the conventional element. An example of the electrochromic display element of the present invention, including its configuration, will be explained with reference to FIG.

In the figure, l is a transparent glass plate, and a display electrode substrate 4 is formed by providing a transparent display electrode 2 and an insulating protective film 3 in a predetermined pattern on the surface of this transparent glass plate l. An electrochromic material film 5 made of tungsten oxide containing cerium oxide is provided on the display electrode 2 in a predetermined display segment portion of the display electrode substrate 4 where the protective film 3 is not formed, thereby forming a display electrode 6. ing.

7 is a counter electrode substrate, and a counter electrode material layer 9 made of an activated carbon material is provided on the surface of the counter homopolar substrate 7 via a counter electrode 8 to form a counter electrode 10. The display electrode substrate 4 and the counter electrode substrate 7 are arranged facing each other with their respective processed surfaces inward through a spacer 11 made of synthetic resin, glass, etc., and perchlorate as an electrolyte is added to an organic solvent such as propylene carbonate inside. It is filled with an electrolytic solution 12 in which a lithium salt such as lithium oxide is appropriately dissolved.

The electrochromic material film 5 made of tungsten oxide containing cerium oxide is formed using, for example, a vacuum evaporation apparatus as shown in FIG. To explain FIG. 4, 21 is a heater, 22 is a substrate,
23 is cerium oxide, 24 is tungsten oxide, 2
5 is an electron beam heating device, and 26 is an exhaust port.

This vacuum evaporation device produces an electrochromic material film 5.
To form the display electrode substrate 4 on which the display electrode 2 has been formed, the display electrode substrate 4 is placed at the location indicated by base +ff122 in FIG. It is heated by the beam heating device 25 to vaporize it, and is deposited on the display electrode 2 of the display electrode substrate 4.

The electrode 2 is made of a transparent conductive material such as indium-tin composite oxide (hereinafter referred to as ITO), and is usually formed using existing thin film forming techniques such as vacuum evaporation and sputtering. Formed to the thickness of a human being. The insulating protective film 3 is generally made of a transparent insulating material such as SiO□, and is usually formed to a thickness of about 3,000 to 10,000 by vacuum evaporation, coating, etc. A colored insulating material may be used depending on the intended use of the element. Also, depending on the durability of the display electrode 2 and the driving conditions of the electrochromic display element, In some cases, one film 3 is not provided. The method for forming the pattern of the electrochromic material film 5 is to form a resist film used for manufacturing semiconductors on the display electrodes 2 and the protective film 3 other than the display segment portions, and then apply the electrochromic material over the entire surface as described above. After forming by a vacuum evaporation method or the like, the resist film is removed and the electrochromic material film 5 is left only on the display segment portion using a lift-off method, or after the electrochromic material 1195 is formed on the entire surface of the display electrode 2 and the protection 113, There is an etching method in which a resist film is formed on the electrochromic material film 5 in the display segment portion, and the portions of the electrochromic material not covered with the resist film are removed by etching.

A glass plate is generally used as the counter homopolar substrate 7, but a non-transparent synthetic resin plate or the like may be used as the counter electrode 8.
A metal such as gold, platinum, or tungsten or the same material as the display electrode 2 is used. In addition to the thin film forming technique described above, in the case of metal, the counter electrode substrate 7 is formed by pressing or bonding a foil-like material. Usually 1,000~s on the surface
, is formed to a thickness of about the size of an ooo person, and its surface resistance is 10
A value of Ω/mouth or less is favorable, and a value of 5 Ω/mouth or less is particularly desirable.

The homopolar material layer 9 made of activated carbon material usually has a thickness of 1
It is formed by pasting an activated carbon fiber cloth of about 00 to 500 μm on the counter electrode B with a conductive adhesive, but it is not limited to this cloth, and any activated carbon fiber cloth can be used as long as activated carbon is used as the counter electrode material. , may be formed by any method.

Note that 13 and 14 are lead terminals on the display electrode side and lead terminals on the opposite electrode side fixed to the side edge of the display electrode substrate 4,
Reference numeral 15 denotes a conductive layer made of a material such as conductive paste or metal foil constituting the external lead-out portion of the counter electrode 8, and 16 is a background material that hides the counter electrode 10 and uses its own color tone as the background of the display. It is composed of an electrolyte-impregnated sheet molded product in which a pigment that develops the color tone is dispersed in a binder component such as polytetrafluoroethylene.

〔Example〕

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

Example 1 ITO with a thickness of 2,500 mm to serve as a display electrode was placed on the surface of a transparent glass plate measuring 5 mm in length, 165 mm in width, and 1.1 a+m thick.
After forming a film by vacuum evaporation and processing it into a predetermined pattern, a protective film of silicon dioxide (
A Sing) film was provided by vacuum evaporation and processed into a predetermined pattern to form a display electrode substrate.

Using the vacuum evaporation apparatus shown in FIG. 4 on this display electrode substrate,
The power of each electron beam was adjusted so that the composition of tungsten oxide and cerium oxide in the film reached a predetermined concentration under the conditions of a substrate temperature of 150°C and a deposition rate of 10 people/sec.
An electrochromic material film was deposited to a thickness of 1,000 mm, and formed into a figure-8 pattern for displaying numbers using a lift-off method to form a display electrode.

On the other hand, on the entire surface of the counter-polar substrate, which is made of a transparent glass plate of 45au+ in length and 16(is) in width (1.1m-thick),
A counter electrode made of ゜000 ITO film was formed by vacuum evaporation method, and activated carbon fiber cloth (trade name: CH-20, manufactured by Kuraray Co., Ltd.) was applied on top of the counter electrode (trade name: PR-10, manufactured by Tokurikisha Co., Ltd.). 2 at 180℃.
A counter-homopolar material layer was formed by heat treatment for a period of time to form a counter-homopolar material layer. Then, the above-mentioned two substrates were placed in such a manner that the electrochromic material film and the opposing seed material layer faced each other, and between them, a sheet-shaped molded mixture of titanium dioxide powder and polytetrafluoroethylene powder (manufactured by Sumitomo Electric Industries, Ltd.) was formed. A background material made of Poalon (trade name) is interposed, and rectangular annular spacers made of polyester resin with a thickness of 1 mm are placed on the periphery to face each other, and the interior is sealed with an epoxy resin adhesive. Dissolve 1 + sol/l of lithium perchlorate in propylene carbonate,
6 ml of electrolytic method with addition of 0.1% by weight of pure water
was enclosed. Next, lead terminals were attached and a conductive layer was formed by attaching a silver base l to produce the electrochromic display element shown in FIG. 1.

Example 2 An electrochromic display element was produced under the same conditions as in Example 1, except that the composition of the electrochromic material film was kept constant at a cerium oxide concentration of 5 at % and the film thickness was changed.

Comparative Example 1 An electrochromic display element was produced under the same conditions as in Example 1, except that an electrochromic material film was formed using only tungsten oxide without adding cerium oxide.

The electrochromic display elements of Examples 1 and 2 and the electrochromic display element of Comparative Example 1 were heated at 20°C.
At a constant temperature, the rest state as shown in Fig. 3 was maintained for 1 minute, coloring applied voltage: -1.2V, coloring voltage application time 20.6 seconds, decoloring applied voltage: +1.4V. ,
Coloring and decoloring was carried out by applying a decoloring voltage for 20.6 seconds, and the initial amount of colored charge was measured, and a cycle life test was conducted at room temperature. Evaluation of "fading" was carried out by observing the electrochromic material film during decolorization with a color difference meter and using b(a), and the number of cycles when the value became 2 or more was defined as the cycle life.

As shown in Table 1, the electrochromic display elements of Examples containing cerium oxide all had a longer cycle life than the electrochromic display element of Comparative Example 1, which corresponds to the conventional product, and especially the cerium oxide concentration. is 0.
When the content was 2 atomic % or more, the cycle life became longer. but,
As the amount of colored charge decreases as the concentration of cerium oxide increases, it is preferable that the upper limit of the concentration of cerium oxide is 20 atomic %. Also, the thickness of the electrochromic material film is determined from the relationship of the amount of colored charge. , 3,000 Å or more.

〔Effect of the invention〕

As explained above, in the present invention, by incorporating cerium oxide into tungsten oxide, it was possible to provide an electrocomic display element with a long cycle life even under driving conditions including a rest state.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of an electrochromic display element according to the present invention. FIG. 2 is a time chart of a conventional cycle life test, and FIG. 3 is a time chart of a practical cycle life test including a rest state. Fourth
The figure is a schematic diagram showing an example of a vacuum deposition apparatus for forming an electrochromic material film. 2...Display electrode, 4...Display electrode substrate, 2...Electrochromic material film, 12...Electrolyte solution Fig. 1 2...Display electrode 4...Display electrode substrate 5...Electrochromic material film Mink material film 12... Electrolyte Figure 2 Coloring voltage application time Figure 3 Coloring voltage application time

Claims (2)

[Claims] (1) In an electrochromic display element in which an electrochromic material film is formed on the display electrode of the display electrode substrate and an organic solvent-based electrolyte solution containing lithium ions is used, the electrochromic material is an oxide containing cerium oxide. An electrochromic display element characterized by being made of tungsten. (2) 0.0% cerium oxide in the electrochromic material.
The electrochromic display element according to claim 1, wherein the content is 2 to 20 atomic %.