JPS6222138B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for driving an electrochromic device. In general, a certain element is colored when it is energized, and the color is erased (i.e., it returns to its original color) by energization with the polarity opposite to that of the energization, heating, or a combination of these operations. In other words, a reversible coloring/decoloring phenomenon that depends on electrical polarity is called an electrochromy phenomenon. The mechanism that causes the electrochromy phenomenon is not necessarily single, but in many cases it is considered to be a so-called redox reaction between an electrolyte and a color-forming substance.
In this case, the electrolyte and the color-forming substance are not necessarily distinguished from each other in terms of materials. In some cases, the same substance can be a color-forming substance and an electrolyte at the same time. In addition, from another perspective, it is considered that the light absorption characteristics change due to the injection of injected electrons into the color center, as in the case of photochromy phenomenon, and in reality, electrochromy phenomenon is caused by a combination of these two phenomena. It is understood that this is occurring. Since the electrochromy phenomenon electrically changes the original color of a material, the combination of colors is diverse. Furthermore, whether a material can transmit light, reflect light, or scatter light is not determined by the properties of the material itself, but rather by the method of forming the layers. It has the property of being able to form either type. In addition to these configurations and the above-mentioned diversity, there are also materials that have a memory property in which the colored state persists after coloring or development occurs until it is erased, and there are also materials whose color tone changes in response to the applied voltage value. Since various applications can be considered, research has been actively conducted in recent years, mainly in the field of image display. Among these, the phenomenon based on the electrolysis of substances by electric current, that is, the oxidation and reduction reactions (redox reactions) of substances, is particularly referred to as electrochemicomism. This is what it says. The features of devices that apply electrochemical microscopy are that they are so-called passive displays, have low driving voltage, have memory characteristics, have good contrast, have a wide viewing angle, and have colorful displays. It is possible, etc., and conventionally,
It has advantageous characteristics compared to liquid crystal display elements and LED display elements that are in practical use. However, in devices to which such electrochemistry is applied, the problem of device life remains the most important issue in the process of putting them into practical use. In other words, when the write-memory-erase cycle is repeated, coloring defects on the electrodes, erasing defects, generation of yellow precipitates, uneven coloring, color tone changes, etc. occur. This significantly shortens the lifespan of the product, and is a major obstacle to commercialization. Thus, the present invention focuses on extending the life of electrochemical cells based on electrochemochemical microscopy. That is, the main purpose of the present invention is to write-memory-
An object of the present invention is to provide an electrochemical cell with improved durability against repeated erase cycles. The present invention, which has achieved such an object, provides a method for driving an electrochromic device having two electrically insulating substrates provided with electrodes and an electrolyte layer disposed between the two electrically insulating substrates. , the electrodes provided on the two electrically insulating substrates are both laminated electrodes having a low resistance metal layer and a metal oxide layer with a thickness of 200 Å to 15000 Å coated thereon, and writing is performed between the laminated electrodes. The method of driving the electrochromic device is characterized by applying direct current pulses of opposite polarity during the step and during the erase step. Display devices based on electrochemical microscopy consist of a light-transmissive or reflective working electrode, its counter electrode, and its oxidation/reduction state reversibly changed by the passage of electric current. Using a cell containing an electro-responsive color-bleaching medium consisting of an electrochemical dye-bleaching substance and an electrolyte and a solvent thereof capable of effecting a detectable change in the appearance of the electrode. It is known.
Both electrodes and the electrolyte are housed in a suitable housing with means for seeing through the working electrode. The electrochemical color-developing material in such devices is capable of accepting or donating electrons, thereby converting it into a radical ion with high absorbance, usually in the visible region of the spectrum, and
At the same time, these radical ions combine with anions present in the medium to form a medium-insoluble colored body on the working electrode. Its general structure is as shown in FIG. 1, in which a working electrode 1 and a counter electrode 2 are arranged in a cell 3 made of glass or the like, and both electrodes are connected to a power source 4 by conducting wires 5 and 6. Inside the cell 3, an electrically responsive coloring/decoloring medium 7 is enclosed. Note that, apart from the illustrated example, a cell may also be constructed in which the electrodes 1 and 2 are arranged on the same plane. Next, the driving method of such a device is as follows. That is, first, writing to the working electrode occurs when applying a DC voltage from the outside so that the working electrode is negative and the counter electrode is positive, and second, the memory effect (that occurs when the external voltage is turned off and the circuit is opened). (The writing on the working electrode continues.), and thirdly, the polarity is reversed from when writing, so that the working electrode side is positive,
There are three driving steps in which writing on the working electrode is erased by applying a DC voltage from the outside so that the opposite electrode becomes negative. Note that writing may be performed with the working electrode side facing positive. Figure 2 shows a typical drive pulse application method,
8 is a write step, 9 is a memory step, 1
0 represents an erase step. By the way, as the electrode shown above, conventionally,
It has been proposed to use metals such as gold and platinum or metal oxides such as tin oxide alone. However,
When a metal is used alone, it is difficult to obtain chemical stability against a coloring/decoloring medium, and the generation of by-products during repeated cell use is unavoidable, resulting in a shortened cell life in many cases. On the other hand, when using metal oxides, although they have better chemical stability than metals, they have considerably higher electrical resistance.
This is disadvantageous in practical terms because the responsiveness deteriorates, high-density coloring cannot be obtained, and the power consumption of the cell increases. In contrast, in the present invention, by improving the electrode constituent materials, it is possible to extend the life of the cell, that is, improve its durability for repeated use, without causing a decrease in cell responsiveness or coloring density. This is what I did. Here, each element constituting the electrochemical cell of the present invention will be explained in detail. First, the structure of the electrode and its material are particularly important in the present invention. FIG. 3 is a schematic diagram illustrating the structure of an electrode according to the present invention, in which an electrode 12 is arranged on an electrically insulating substrate 11 made of glass or plastic. The electrode 12 is formed by laminating a low resistance metal layer 13 and a metal oxide layer 14 which are electrically connected to each other. In the illustrated example, one layer each of 13 and 14 is laminated, but the present invention is not limited to this embodiment, and each or either one may have a multilayer structure. . The metal oxide layer 14 is provided on the low-resistance metal layer 13 by a known method such as vapor deposition, coating, or sputtering. In the present invention, care should be taken to prevent the low resistance metal layer 13 from being exposed and coming into direct contact with the coloring/decoloring medium housed in the cell. For example, as shown in FIG. 4, if the end of the low-resistance metal layer 13 is exposed without being completely covered with the metal oxide layer, the end may be separately coated with an electrically insulating material that is stable against the coloring/decoloring medium. It is preferable to mask 15 with a substance (for example, resin, glass, metal oxide, etc.). by the way,
According to the knowledge obtained by the present inventors, in the electrochemical cell of the present invention, the electrode has a sheet resistance of approximately 50Ω or less, preferably 10Ω or less, from the viewpoint of its responsiveness or coloring density. It turns out that it needs to be configured like this. Therefore, it is preferable that the thickness of the metal oxide layer 14, which has higher electrical resistance than metal, be as thin as possible. In the present invention, the metal oxide layer 14 is preferably provided with a thickness in the range of approximately 200 Å to 15,000 Å, although there are some differences depending on the material used. The constituent material of the low resistance metal layer 13 is not particularly limited, but generally includes aluminum, copper,
Silver, palladium, platinum, gold, etc. are preferably used. Furthermore, the constituent materials of the metal oxide layer 14 include indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), tungsten oxide (WO ₃ ), lead oxide (PbO ₂ ), titanium oxide (TiO ₂ ), Bismuth oxide (Bi ₂ O ₃ ) and the like are particularly preferred. Further, the mask 15 is generally made of SiO ₂ , SiO, Al ₂ O ₃ , epoxy resin, or the like. It is well known that the chemical stability of metal oxides is superior to that of simple metals. but,
The display effect based on electrochemicomism is
Because it is highly dependent on the amount of current (charge amount), if a metal oxide, which has significantly higher electrical resistance than metal, is used as an electrode, the response of the coloring/decoloring process may be delayed, and the coloring may be delayed. This causes serious problems in cell characteristics, such as uneven decoloring and deterioration of the coloring/decoloring medium due to increased applied voltage. In the present invention, the chemical instability of low resistance metals is
This is supplemented by a thin coating of metal oxide, and the thickness of the metal oxide is approximately 200 Å to 15,000 Å.
If the film is formed with a thickness of 1.5 Å, the low resistance of the metal can be effectively utilized, and the increase in resistance of the entire electrode can be suppressed within the allowable range. Note that the electrodes satisfying the above conditions can be arbitrarily arranged in the cell container according to the specifications of the device. Next, other components related to the electrochemical cell of the present invention will be explained. The electro-responsive coloring and decoloring medium to be housed in the cell container is mainly composed of an electrochemical coloring and decoloring substance (which can also be seen as a redox-reactive organic substance), an electrolyte, and further contains various additives. In addition, these are usually used after being dissolved in a solvent such as water. The electrochemical coloring/decolorizing substance used in the present invention is not particularly limited, and a wide range of redox-reactive organic substances can be mentioned. However, among them, pyridinium compounds having a quaternary ammonium salt structure can be cited as a good example. As a specific example, 1,1'-dimethyl-4,4'-bipyridinium dibromide 1,1'-diethyl-4,4'-bipyridinium dibromide 1,1'-diheptyl-4,4'-bipyridinium
dibromide 1,1'-dibenzyl-4,4'-bipyridinium
dibromide N,N'-di(p-cyanophenyl)-4,4'-bipyridinium dichloride 2,2'-(diethyl)bipyridinium dichloride N,N'-diethyl-2,7-diazapyrenium dichloride N-benzyl-4-cyano-pyridinium bromide and the like can be mentioned. In addition, the following compounds used as redox indicators can also be used. For example, Safranin T neutral red Indigo monosulfur oxide Diphenyl amine Diphenyl amine-P-sulfuronic acid p-nitro diphenyl amine Diphenyl amine-2,3'-dicarboxylic acid Diphenyl amine-2,2'-dicarboxylic acid etc. can be mentioned. Next, regarding the electrolyte, potassium bromide, potassium chloride, etc. are typical ones, but ferrous ammonium sulfate, etc. can also be used as a good electrolyte. Water is generally used as a solvent, but depending on the type of electrochemical coloring/decolorizing substance, a mixed solvent of water and an organic solvent such as methyl alcohol or dimethyl form amide may be used. is sometimes used. Furthermore, the effects of the present invention will be explained with reference to the following examples. Example A working electrode and a counter electrode configured as shown in the table below were placed in a glass cell with a spacing of 2 mm between each electrode.
It was arranged so that The size of each electrode is 2mm x 3
It was made into a rectangle of mm. 1 in distilled water in each such cell.
It was filled with a solution of 1'-diheptyl-4,4'-bipyridium dibromide (0.05 molar concentration) and potassium bromide (0.3 normal concentration). For each cell obtained above, apply +2V by DC power supply.
The driving operation was continuously repeated in a potential cycle of (2 sec) → OV (0.5 sec) → −2 V (2 sec). The numerical values shown in the table below represent the number of cycles the above operation can be repeated until unnecessary deposits accumulate on the electrode. In addition, the response of coloring and decoloring and the uniformity of coloring density were evaluated.

【table】

[Table] However, the response evaluations in the above are: ◎...Very fast, 〇...Fast, △...Slow, ×...Very slow.
Accordingly, the density uniformity was evaluated according to the following criteria: ◎...Very good, 〇...Fair, △...Poor, ×...Very poor. Examples 10 to 11, Comparative Examples 5 to 9 A cell was prepared in the same manner as in Example 1, except that the working electrode and counter electrode used in the cell had the configuration shown in the table below. Driving was performed in the same manner as above, and the coloring/decoloring state during driving and its response were evaluated. These results are also listed in the table below.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining an example of the configuration of a device that applies electrochemical microscopy, FIG. 2 is an explanatory diagram showing an overview of the driving system of the device shown in FIG. and FIG. 4 are schematic cross-sectional views illustrating the outline of the electrode structure according to the present invention.
In the figure, 1, 2, 12...electrode, 3...cell container, 4...
...Power source, 13...Low resistance metal layer, 14...Metal oxide layer, 15...Mask.

Claims (1)

[Claims] 1 two electrically insulating substrates provided with electrodes;
In a method for driving an electrochromic device having an electrolyte layer disposed between two electrically insulating substrates, the electrodes provided on the two electrically insulating substrates are both coated with a low resistance metal layer and an electrolyte layer thereon. An electrochromic device comprising a metal oxide layer with a thickness of 200 Å to 15,000 Å, and a DC pulse of opposite polarity is applied between the laminated electrodes during a writing step and an erasing step. Driving method of Tsuku element.