Display element

Abstract

To provide a display element excellent in repetition stability of coloring and decoloring.SOLUTION: The display element comprises: a first electrode formed on a first substrate; a second electrode formed on a second substrate and arranged facing the first electrode; an electrolyte layer arranged between the first electrode and the second electrode; and voltage application means for applying voltage to the first electrode and the second electrode. The second electrode is modified with low potential oxidation-reduction substance that causes oxidation-reduction by more cathodic potential than reaction progressing by the first electrode.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a display element utilizing electrochromism.

Background Art

[0002] As an example of a display element utilizing electrochromism, i.e., a phenomenon in which a reversible color change occurs due to an electrochemical oxidation-reduction reaction, a smart window (ECSW) that creates a transparent state and a colored state by an electrochemical oxidation-reduction reaction and can achieve electronic dimming is known.

[0003] Patent Document 1 describes a display element in which an electrolyte layer containing tetrabutylammonium bromide (TBAB) is sandwiched between a pair of indium tin oxide (ITO) transparent conductive glass electrodes, and a reversible white coloring reaction can occur by performing electrochemical oxidation-reduction, and it can be applied to a white display ECSW that does not absorb sunlight and can solve the problem of heat release.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the display element of Patent Document 1, the voltage required to cause a white coloring reaction is large, and a large potential is applied to the counter electrode facing the display electrode that causes a reversible color tone change between the white state and the transparent state. Therefore, deterioration accompanied by an increase in electrical resistance progresses, and there is a problem that the coloring and fading do not last long for repeated color tone changes.

[0006] The present invention has been made paying attention to such problems, and an object thereof is to provide a display element excellent in the repeated stability of coloring and decoloring.

Means for Solving the Problems

[0007] The display element of the present invention for solving the above problems is a first electrode formed on a first substrate, a second electrode formed on a second substrate and disposed opposite to the first electrode, an electrolyte layer disposed between the first electrode and the second electrode, a display element in which a voltage is applied to the first electrode and the second electrode by a voltage applying means, characterized in that the second electrode is modified with a low-potential redox substance that undergoes oxidation-reduction at a more cathodic (more base) potential than the reaction proceeding at the first electrode. According to this feature, when causing a coloring and decoloring reaction at the first electrode, the potential applied to the second electrode can be reduced, and deterioration accompanied by an increase in electrical resistance can be suppressed. Therefore, it is excellent in the repeated stability of coloring and decoloring.

[0008] The low-potential redox substance is characterized in that it undergoes oxidation-reduction at a more anodic (more noble) potential than substances other than the second electrode constituent substance and the substance that reacts at the first electrode contained in the electrolyte layer. According to this feature, the potential applied to the second electrode can be further reduced, and deterioration accompanied by an increase in electrical resistance can be suppressed. Therefore, it is further excellent in the repeated stability of coloring and decoloring.

[0009] a nanoparticle film of the second electrode constituent substance is formed on the second electrode, characterized in that the low-potential redox substance is modified on the nanoparticle film. According to this feature, the nanoparticle film formed on the second electrode can increase the actual surface area of the second electrode and increase the modification amount of the low-potential redox substance. Therefore, the amount of energized electricity, the maximum absorption degree, and the repeated durability of coloring and decoloring in the display element can be enhanced.

[0010] The second electrode constituent material is indium tin oxide (ITO). According to this feature, since ITO has a more cathodic potential for oxidation-reduction than general oxidation-reduction substances, many substances can be selected as low-potential oxidation-reduction substances.

[0011] The low-potential oxidation-reduction substance is characterized by being Prussian blue (PB). According to this feature, the stability of coloring and decoloring can be enhanced.

[0012] The electrolyte layer is characterized by being made of hydrogel. According to this feature, the driving voltage range of the display element can be narrowed, the repetitive durability of coloring and decoloring can be enhanced, and liquid leakage from the display element can be suppressed by increasing the viscosity of the electrolyte layer.

Brief Description of the Drawings

[0013]

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Embodiment for Carrying out the Invention

[0014] An embodiment for carrying out the display element according to the present invention will be described below based on examples.

Example

[0015] As shown in FIG. 1, the display element according to the present invention includes, for example, an ITO display electrode in which a transparent ITO electrode (first electrode) is formed on a transparent glass substrate (first substrate), and a transparent ITO electrode (second electrode) on a transparent glass substrate (second substrate). On the formed ITO counter electrode, further, an oxidation-reduction reaction occurs at a more anodic potential than a substance other than the substance that reacts with the first electrode contained in the ITO (second electrode constituent substance) and the electrolyte layer, and an oxidation-reduction reaction occurs at a more cathodic potential than the reaction proceeding at the first electrode. A PB-modified ITO counter electrode modified with PB (low-potential redox substance), and an electrolyte layer disposed (sandwiched) between the ITO display electrode and the PB-modified ITO counter electrode. The ITO display electrode and the PB-modified ITO counter electrode are applied with a voltage by a voltage application means. That is, the display element in the present Example 1 has a structure of a two-electrode cell (PB cell) using an ITO display electrode and a PB-modified ITO counter electrode. In addition, the display element of the present Example 1 contains TBAB in the electrolyte layer, and the ITO display electrode can be used as a white display ECSW that causes a reversible color tone change between a white state and a transparent state. Further, in the display element of the present Example 1, the substance that reacts with the first electrode contained in the electrolyte layer is a bromide ion.

[0016] (PB Modification Method) Here, a method for modifying PB on the ITO counter electrode will be described. First, potassium ferricyanide (K 3 [Fe(CN) 6 , manufactured by Kanto Chemical Co., Inc., purity 99% or more) and iron(III) chloride (FeCl 3 ·6H 2O (manufactured by FUJIFILM Wako Pure Chemical Corporation, purity 99% or higher) was each dissolved at 0.1 M, and further 0.1 M of concentrated hydrochloric acid (manufactured by Kanto Chemical Co., Inc., HCl content 35 - 37%) was added to prepare an electrolytic solution. In this electrolytic solution, a washed ITO substrate (manufactured by Diomatik Co., Ltd., 10 Ω / sq) was immersed as the negative electrode, and a platinum plate was immersed as the positive electrode, and a voltage of 0.6 V was applied between the electrodes for 140 seconds to deposit PB on the ITO counter electrode on the ITO substrate.

[0017] Next, an electrolytic solution containing 0.1 M each of potassium chloride (KCl, manufactured by Kanto Chemical Co., Inc., purity 99.5% or higher) and hydrogen chloride (HCl) was prepared. The ITO counter electrode on which PB was deposited, a platinum electrode, and an Ag / AgCl reference electrode (manufactured by BAS, RE-1B) were immersed in this electrolytic solution, and a potential sweep treatment (sweep rate: 20 mV / s) was performed on the ITO counter electrode on which PB was deposited in a voltage range of -0.05 V to 0.35 V (vs Ag / AgCl) for 10 cycles.

[0018] Finally, by drying at 100 °C for 1 hour in a hot air dryer, the PB-modified ITO counter electrode shown in Figure 2 is obtained.

[0019] Note that the ITO substrate used in Example 1 has an ITO film formed by a sputtering method.

[0020] (Electrolytic cell) Next, the fabrication of a two-electrode type electrolytic cell will be described. First, a rectangular tubular rubber sheet (thickness 5 mm) with a 1.4 cm × 1.4 cm hole was placed on the conductive surface of an ITO substrate (manufactured by Diomatik Co., Ltd., 10 Ω / sq) on which a 2.0 cm × 2.5 cm ITO film was formed, and its internal space was filled with an electrolytic solution in which 0.1 M of TBAB (manufactured by Tokyo Chemical Industry Co., Ltd., purity 98% or higher) and 0.5 M of potassium bromide (KBr, manufactured by FUJIFILM Wako Pure Chemical Corporation, purity 98% or higher) were dissolved. Next, another ITO substrate was placed on top of it and clamped with a double clip to fabricate a two-electrode type electrolytic cell.

[0021] As shown in FIG. 1, in the electrolytic cell of the first embodiment, the counter electrode is a PB-modified ITO counter electrode, and hereinafter, this electrolytic cell will be referred to as a "PB cell".

[0022] (Photoelectrochemical properties of the PB cell) Here, the photoelectrochemical properties when an aqueous solution is used as the electrolyte solution filled in the electrolyte layer of the PB cell will be described with reference to FIGS. 5 and 6. FIG. 5 shows the cyclic voltammogram (CV) when the PB cell is used, and FIG. 6 shows the change in absorbance (wavelength: 450 nm) (absorption spectrum and its color development efficiency) when the absorbance is measured simultaneously. The measurement conditions are a potential sweep rate of 20 mV / s, a sweep range of -1.0 V to 2.0 V, and the number of repetitions is 10 times. Also, the change in absorbance is measured by the measurement system shown in FIG. 3.

[0023] As shown in FIG. 5, when a voltage of about 1 V or more is applied to the ITO display electrode side, it can be confirmed that an oxidation current corresponding to the white coloring reaction (oxidation reaction) of (1) to (3) in the chemical reaction formula of FIG. 4 showing the reaction mechanism of TBAB contained in the electrolyte layer flows. On the other hand, when a voltage of about 0 V or less is applied, it can be confirmed that a reduction current corresponding to the white decoloring reaction (reduction reaction), which is the reverse process of the white coloring reaction of (1) to (3) in the chemical reaction formula of FIG. 4, flows.

[0024] Also, as shown in FIG. 6, when a voltage of about 1.5 V or more is applied to the ITO display electrode side, the white coloring reaction of (1) to (3) in the chemical reaction formula of FIG. 4 proceeds, and it can be confirmed that the absorbance increases due to the formation of a white film on the ITO display electrode. On the other hand, when a voltage of about -0.5 V or less is applied, the white decoloring reaction, which is the reverse process of the white coloring reaction of (1) to (3) in the chemical reaction formula of FIG. 4, occurs, and the white film dissolves, resulting in a decrease in absorbance and the ITO display electrode becoming transparent.

[0025] In this way, it was confirmed that the repeated behavior of white coloring and decoloring and the electrochemical stability on the ITO display electrode are good. The reason why the voltage at which the oxidation current starts to flow (about 1 V) is different from the voltage at which whitening occurs (about 1.5 V) is presumably due to the fact that any one of the reactions (1) to (3) in the chemical reaction formula of Fig. 4 is slow (rate-determining step), and there is a time lag between voltage application and whitening.

[0026] (CV Comparison between PB Cell and PB-Unmodified Cell) Next, Fig. 7 shows the results of a comparative study of the CVs of a PB cell and a cell using a conventional ITO counter electrode (PB-unmodified) (hereinafter referred to as "PB-unmodified cell").

[0027] As shown in Fig. 7, when comparing the coloring voltages (oxidation voltages), in the case of the PB-unmodified cell, the oxidation peak is 2.3 V, while in the case of the PB cell, the oxidation peak can be confirmed to be reduced to 1.6 V. Next, when comparing the decoloring voltages (reduction voltages), in the case of the PB-unmodified cell, the reduction peak is -2.3 V, while in the case of the PB cell, the reduction peak can be confirmed to be reduced to -0.7 V. Due to this change in the oxidation-reduction voltage, it can be confirmed that in the case of the PB-unmodified cell, the driving voltage range is -2.5 V to 2.5 V, while in the case of the PB cell, the driving voltage range is narrowed to -1 V to 2 V.

[0028] In this way, it was confirmed that the PB cell using the PB-modified ITO electrode on the counter electrode side has a 0.5 V decrease in the coloring voltage and a 1.5 V decrease in the decoloring voltage compared to the conventional PB-unmodified cell. In particular, the decrease in the decoloring voltage leads to preventing the reduction degradation of the counter electrode and improving the repeated stability of coloring and decoloring.

[0029] (Measurement of Unipolar Potentials of PB Cell and PB-Unmodified Cell) As described above, by using the PB cell, it was confirmed that the driving voltage was significantly reduced. However, the driving voltage is the voltage applied across the entire cell. Therefore, in order to confirm how the cell voltage is distributed between the display electrode side and the counter electrode side while the cell is driving, the potential applied to the display electrode side and the counter electrode side of the PB-unmodified cell and the PB cell is measured. As shown in Fig. 8, this measurement is performed by inserting a silver wire into the cell and measuring the potential with respect to this silver wire (single-pole potential measurement).

[0030] Fig. 9(a) shows the results of the single-pole potential measurement of the PB-unmodified cell, and Fig. 9(b) shows the results of the single-pole potential measurement of the PB cell. In Fig. 9, the voltage on the horizontal axis represents the voltage applied to the counter electrode with respect to the display electrode of the two-electrode electrolytic cell. The potential on the vertical axis represents the potential applied to the ITO display electrode (refer to the solid line), the ITO counter electrode, or the PB-modified ITO counter electrode (refer to the dashed line) with respect to the silver wire, which is the reference for the potential.

[0031] As shown in Fig. 9(a), it can be confirmed that in the PB-unmodified cell, a negative potential of up to -1.03 V is applied to the ITO counter electrode. On the other hand, as shown in Fig. 9(b), in the PB cell, it can be confirmed that a negative potential of only up to -0.54 V is applied to the PB-modified ITO counter electrode.

[0032] Thus, by modifying the ITO counter electrode with PB, the negative potential applied to the ITO counter electrode can be reduced, and as a result, the reduction degradation of the ITO counter electrode can be prevented.

[0033] (Repeated durability comparison between PB cell and PB-unmodified cell) Next, a comparison of the repeated durability of coloring and bleaching between the PB cell and the unmodified PB cell is performed. For the unmodified PB cell, a cell voltage of 2.2 V (coloring voltage) is applied for 20 seconds to form a white film on the ITO display electrode, and the absorbance at 450 nm is measured. Then, a cell voltage of -2.2 V (bleaching voltage) is applied for 20 seconds to dissolve and disappear the white film on the ITO display electrode, and the absorbance measurement step at 450 nm is repeated 50 cycles. On the other hand, for the PB cell, measurements are performed in the same manner as for the unmodified PB cell, except that the coloring voltage is 1.7 V and the bleaching voltage is -0.8 V.

[0034] As shown in Fig. 10(a), in the case of the unmodified PB cell, the maximum achievable absorbance (initial absorbance) increased to around 1.4, but the absorbance gradually decreased as coloring and bleaching were repeated, and it was confirmed that the absorbance retention rate after 50 cycles was 58%. On the other hand, as shown in Fig. 10(b), in the case of the PB cell, the maximum achievable absorbance (initial absorbance) was around 0.76, but the absorbance retention rate after 50 cycles was 84%, and it was confirmed that the repeated durability of coloring and bleaching was significantly improved. This is presumably because the PB film on the counter electrode is responsible for a stable redox reaction, and the reduction degradation of the ITO electrode is suppressed.

Example

[0035] Next, the display element according to Example 2 will be described with reference to Figs. 11 to 16. Note that descriptions of configurations that are the same as those in the above examples and are redundant will be omitted.

[0036] (Examination of increasing the amount of PB modification) In the comparison of the repeated durability between the PB cell and the unmodified PB cell in Example 1 above, the absorbance obtained with the PB cell was small and the whiteness was insufficient. This is presumably because the amount of PB modification was not sufficient and the white film formation reaction occurring on the ITO display electrode was not sufficiently compensated. Therefore, in this Example 2, an examination is performed to increase the amount of PB modification in the PB-modified ITO counter electrode.

[0037] In Example 2, as a method for increasing the amount of PB modification in the PB-modified ITO counter electrode, as shown in FIG. 12, an ITO nanoparticle film is formed on the same ITO substrate (manufactured by Geomatech, 10 Ω / sq) as used in Example 1, and a PB-modified ITO nanoparticle counter electrode with PB modified thereon is fabricated (see FIG. 11). Specifically, first, 0.375 g of ITO nanoparticles (manufactured by Nanotech, average particle size 30 nm) is dispersed in 4.5 g of 1-butanol, and the dispersion is prepared by stirring for 30 minutes. 40 μL of the dispersion is applied to the ITO substrate so that the coating area is 2.0 cm × 0.8 cm. Next, sintering is performed at 300 °C for 1 hour to fabricate an ITO nanoparticle substrate. In this way, by further coating the smooth surface of the ITO substrate with ITO nanoparticles, the actual surface area can be increased due to porosity, and by modifying PB on the ITO nanoparticle film, the amount of PB modification can be increased as a result. Note that the ITO substrate used in Example 2 is formed by sputtering, and ITO is deposited in an atomically seamless manner, having a smooth surface with a small surface roughness.

[0038] (Verification measurement of the increase in surface area of the ITO nanoparticle substrate) The ITO nanoparticle substrate and the platinum plate, and the ITO substrate and the platinum plate were each immersed in a 0.1 M lithium bromide aqueous solution, and cyclic voltammetry was performed to measure the surface area according to the electric double layer model. As a result, it was confirmed that the ITO nanoparticle substrate (see FIG. 13(a)) had a 214-fold increase in current, that is, a 214-fold increase in surface area, compared to the original ITO substrate (see FIG. 13(b)).

[0039] (Photoelectrochemical properties of the PB / ITO nanoparticle cell) Next, in addition to the PB cell and the PB-unmodified cell of Example 1, the results of comparing the CV and absorbance changes of the PB / ITO nanoparticle cell using the PB-modified ITO nanoparticle counter electrode are shown in FIGS. 14(a) and (b). Note that the PB-modified ITO nanoparticle counter electrode was fabricated by modifying PB on the ITO nanoparticle substrate in the same manner as described in Example 1.

[0040] As shown in Fig. 14(a), from the CV results, it was confirmed that the PB / ITO nanoparticle cell can obtain an energized charge amount (C) more than twice that of the PB cell.

[0041] Also, from the absorbance change shown in Fig. 14(b), it was confirmed that the PB / ITO nanoparticle cell shows a maximum achievable absorbance of 1.5 or more and can achieve sufficient white display comparable to that of the PB-unmodified cell. Fig. 15(a) shows the transparent state (-1.1 V applied for 20 seconds) of the PB / ITO nanoparticle cell, and Fig. 15(b) shows the white state (1.8 V applied for 20 seconds). The rectangular thick frame portion in the figure shows the coloring and erasing of the ITO display electrode.

[0042] (Repeated durability of PB / ITO nanoparticle cell) Next, the results of measuring the repeated durability of the PB / ITO nanoparticle cell are shown in Fig. 16. The coloring voltage is 1.8 V, the erasing voltage is -1.1 V, and the voltage application time is 20 seconds.

[0043] As shown in Fig. 16, the maximum achievable absorbance (initial absorbance) increased up to around 1.3, and the absorbance retention rate was 93% even after 50 cycles and 100 cycles. This value of the absorbance retention rate is improved compared to the values of the PB-unmodified cell and the PB cell (see Figs. 10(a) and (b)), and it was confirmed that the repeated durability is significantly improved.

[0044] Thus, as reasons for the improvement of the repeated durability of the PB / ITO nanoparticle cell, it is presumed that the redox of PB was stably performed, the anchoring effect of the nanoparticles made PB less likely to desorb from the electrode substrate, and a larger amount of PB could be supported compared to the PB cell.

Example

[0045] Next, the display element according to Example 3 will be described with reference to Figs. 17 to 19. The description of the configuration that is the same as that of the above example and overlaps is omitted.

[0046] (Study on Using Hydrogel for the Electrolyte Layer) In Example 3, for the study of preventing liquid leakage from the electrolytic cell, a PB / ITO nanoparticle hydrogel cell using a hydrogel with water as the solvent instead of the electrolytic solution (aqueous solution) in Examples 1 and 2 was fabricated as the electrolyte layer. The electrolyte layer of the PB / ITO nanoparticle hydrogel cell is composed of 0.4 M TBAB, 0.5 M KBr, and 1.6 wt% polyacrylamide (PAAm), and the pH was adjusted to 3 by adding HCl. The hydrogel is composed of an electrochromic material, a supporting electrolyte, a gelling substance, and a solvent (water).

[0047] (Measurement of Coloring and Bleaching Voltages of PB / ITO Nanoparticle Hydrogel Cell) First, Fig. 17 shows the results of measuring the coloring and bleaching voltages that occur on the ITO display electrode of the PB / ITO nanoparticle hydrogel cell by CV. The scanning rate is 20 mV / s.

[0048] As shown in Fig. 17, it can be confirmed that the oxidation peak of the coloring voltage at which whitening occurs on the ITO display electrode is 1.8 V, and the reduction peak of the bleaching voltage at which it becomes transparent is -0.8 V. That is, compared with the results when using the PB-unmodified cell shown in Fig. 7 (oxidation peak: 2.3 V, reduction peak: -2.3 V), it was confirmed that the PB / ITO nanoparticle hydrogel cell can significantly narrow the driving voltage range despite using a hydrogel with a higher electrical resistance.

[0049] (Coloring and Bleaching Repeated Characteristics of PB / ITO Nanoparticle Hydrogel Cell) Next, for the PB / ITO nanoparticle hydrogel cell, a white film was formed on the ITO display electrode by applying a cell voltage of 2.4 V for 25 seconds (coloring), and the absorbance at 450 nm was measured. Then, a cell voltage of -1.2 V was applied for 40 seconds to dissolve and disappear the white film on the ITO display electrode (bleaching), and the absorbance at 450 nm was measured. Fig. 18 shows the results of repeating these steps 100 cycles.

[0050] As shown in Fig. 18, it was confirmed that the PB / ITO nanoparticle hydrogel cell can achieve stable repetitive durability of 100 cycles, similar to the PB / ITO nanoparticle cell using the above-described electrolyte. Also, in the case of the PB / ITO nanoparticle hydrogel cell, the initial absorbance was around 1.3, and it was confirmed that the absorbance did not decrease even after 100 cycles, and the absorbance retention rate was 100%. Also, it was confirmed that there was no reduction degradation of the counter electrode.

[0051] (Comparison of response times) The number of cycles on the horizontal axis of the graphs of the absorbance-cycle relationships for the PB-unmodified cell, PB cell, PB / ITO nanoparticle cell, and PB / ITO nanoparticle hydrogel cell (corresponding to Figs. 10(a), 10(b), 16, and 18) was converted to time, and a single coloring and bleaching curve at an arbitrary time was extracted. Then, the coloring time, which is the time until the absorbance change for coloring reaches 90%, and the bleaching time, which is the time until the absorbance change for bleaching reaches 90%, were measured as the coloring and bleaching response times of each display element. Figs. 19(a) to (d) show the coloring and bleaching extraction curves for the PB-unmodified cell, PB cell, PB / ITO nanoparticle cell, and PB / ITO nanoparticle hydrogel cell. Also, the coloring and bleaching times calculated from these coloring and bleaching extraction curves are shown in Table 1.

[0052] [Table 1]

[0053] As shown in Figs. 19(a) to (d) and Table 1, it was confirmed that the coloring times of the PB-unmodified cell, PB cell, and PB / ITO nanoparticle hydrogel cell were approximately 10 seconds. This is too slow for application to electronic paper, but it is presumed to be within an acceptable time range for application to smart windows.

[0054] In addition, in the PB / ITO nanoparticle cell, it was confirmed that a relatively fast response of about 5 seconds was observed. This indicates that by making the counter electrode porous and increasing the loading amount of PB, the white coloring reaction proceeding at the display electrode can be accelerated. It is presumed that by further examining the material and structure of the counter electrode in the future, the coloring reaction rate at the display electrode can be further improved.

[0055] In addition, it was confirmed that the bleaching rates of the PB-unmodified cell, the PB cell, and the PB / ITO nanoparticle cell are faster than the coloring rates, and the bleaching time is approximately 6 seconds. This is because during the coloring reaction, bromide ions need to diffuse from the electrode interface to the electrode ((1) in the chemical reaction formula of FIG. 4), which takes time, whereas in bleaching, the tribromide ions responsible for bleaching ((3) in the chemical reaction formula of FIG. 4) exist in a state adsorbed on the electrode, so no diffusion process is required.

[0056] In addition, in the PB / ITO nanoparticle hydrogel cell, it was confirmed that the bleaching rate is extremely fast and the cell bleaches in 2.5 seconds. It is presumed that the hydrogel has some effect during the process of the tribromide ions being reduced back to bromide ions.

[0057] As described above, in the display element according to the present invention, a composite material modified with a low-potential redox substance (PB) that undergoes oxidation-reduction at a more anodic (nobler) potential than substances other than the second electrode constituent material (ITO) and the substance (bromide ions) that reacts with the first electrode in the electrolyte layer, and undergoes oxidation-reduction at a more cathodic (baser) potential than the reaction proceeding at the first electrode, is used. When causing the coloring and bleaching reactions at the display electrode, the potential applied to the counter electrode can be reduced, and deterioration accompanied by an increase in electrical resistance can be suppressed. Therefore, it has excellent repeat stability of coloring and bleaching.

[0058] In addition, a nanoparticle film of a second electrode constituent material (ITO) is formed on the counter electrode, and a structure in which a low-potential redox substance (PB) is modified on the nanoparticle film is adopted, so that the actual surface area can be increased and the modification amount of the low-potential redox substance can be increased. Therefore, the amount of electric charge passed, the maximum absorbance reached, and the repeated durability of coloring and bleaching in the display element can be enhanced.

[0059] In addition, as the second electrode constituent material, since ITO has a more cathodic potential for redox reaction than general redox substances, many substances can be selected as the low-potential redox substance.

[0060] In addition, since an inexpensive substance such as PB is used as the low-potential redox substance to enhance the stability of coloring and bleaching, the manufacturing cost of the display element can be reduced.

[0061] In addition, since the electrolyte layer is made of a hydrogel instead of an electrolytic solution (aqueous solution), the driving voltage range of the display element can be narrowed, the repeated durability of coloring and bleaching can be enhanced, and by increasing the viscosity of the electrolyte layer, liquid leakage from the display element can be suppressed. Furthermore, the bleaching speed can be increased compared with the case where the electrolyte layer is an electrolytic solution (aqueous solution).

[0062] As described above, the embodiments of the present invention have been described with reference to the drawings. However, the specific configuration is not limited to these embodiments, and modifications and additions within the scope not departing from the gist of the present invention are also included in the present invention.

[0063] For example, in the above-described Examples 1 to 3, the configuration of a display element that can be used as a white display ECSW in which the display electrode causes a reversible color tone change between a white state and a transparent state has been described. However, the present invention is not limited thereto, and it goes without saying that the display element of the present invention can be applied to various display elements using electrochromism including conventional ECSW.

[0064] In Examples 1 to 3 described above, the mode in which a glass substrate is used as the first substrate constituting the display electrode has been described. However, the present invention is not limited to this, and a known substrate having light transmissivity other than the glass substrate may be used as the first substrate.

[0065] In Examples 1 to 3 described above, the mode in which a glass substrate is used as the second substrate constituting the counter electrode has been described. However, the present invention is not limited to this, and a known substrate having light transmissivity other than the glass substrate may be used as the second substrate. Further, depending on the use of the display element, a known substrate having no light transmissivity may be used as the second substrate.

[0066] In Examples 1 to 3 described above, the mode in which a transparent ITO electrode is formed as the first electrode on the first substrate has been described. However, the present invention is not limited to this, and the first electrode may be composed of a transparent electrode material such as, for example, fluorine-doped tin oxide (FTO), zinc oxide (ZnO), tin oxide (SnO 2 ), titanium oxide (TiO 2 ), polyethylenedioxythiophene (PEDOT), polyaniline, a metal nanowire dispersion film, a carbon nanotube dispersion film, graphene, or the like.

[0067] In Examples 1 to 3 described above, the mode in which a transparent ITO electrode is formed as the second electrode on the second substrate has been described. However, the present invention is not limited to this, and the second electrode may be composed of a transparent electrode material such as, for example, fluorine-doped tin oxide (FTO), zinc oxide (ZnO), tin oxide (SnO 2 ), titanium oxide (TiO 2 ), polyethylenedioxythiophene (PEDOT), polyaniline, a metal nanowire dispersion film, a carbon nanotube dispersion film, graphene, or the like, or platinum, gold, an alloy thereof, carbon, diamond, or the like.

[0068] In Examples 1 to 3 described above, the display element in which the substrates and electrodes constituting the display electrode and the counter electrode have the same configuration (glass substrate and ITO electrode) has been described. However, the present invention is not limited to this, and the configurations of the substrates and electrodes constituting the display electrode and the counter electrode may be different.

[0069] In Examples 1 to 3, the mode in which PB is modified as a low-potential redox substance on the ITO electrode constituting the counter electrode has been described. However, the present invention is not limited to this, and the low-potential redox substance is a substance that undergoes oxidation-reduction at a more cathodic potential than the reaction proceeding at the first electrode. More preferably, it undergoes oxidation-reduction at a more cathodic potential than the reaction proceeding at the first electrode, and undergoes oxidation-reduction at a more anodic potential than substances other than the substance (bromide ion) that reacts at the first electrode included in the second electrode constituent material and the electrolyte layer. In addition to PB, for example, carbon materials such as tungsten oxide, viologen compounds, quinone compounds, molybdenum oxide, vanadium oxide, niobium oxide, titanium oxide, and activated carbon may be used.

[0070] In Example 2, the mode in which the nanoparticle film of ITO, which is the second electrode constituent material, is formed on the ITO electrode constituting the counter electrode has been described. However, the present invention is not limited to this, and the nanoparticle film formed on the second electrode may be a substance different from the second electrode constituent material.

[0071] In Example 2, the mode in which a three-layer laminated structure (see FIG. 11) in which an ITO nanoparticle film is formed on the ITO electrode constituting the counter electrode and PB is modified on the ITO nanoparticle film has been described. However, the present invention is not limited to this, and the counter electrode may be configured, for example, as a two-layer laminated structure in which an ITO nanoparticle film is directly formed on a glass substrate and PB is modified thereon. In this case, it is necessary to configure the structure so that electrical conduction can be achieved between the ITO nanoparticle film and the power source by connection. That is, in the counter electrode of FIG. 11, it is necessary to expand the coating portion of the ITO nanoparticle film to the wire connection position.

[0072] The counter electrode may also be configured as a single-layer structure in which the second electrode constituent material (for example, ITO) and the low-potential redox substance (for example, PB) are arranged randomly or in a stripe shape.

[0073] In Example 3, an example was described in which polyacrylamide was used as a gelling component of the hydrogel constituting the electrolyte layer. However, the present invention is not limited to this, and as the gelling component, one or more known water-soluble polymers can be mixed and used.

[0074] In Examples 1 to 3, the electrochromic material, supporting electrolyte, and solvent constituting the electrolyte layer have a configuration of a display element that can be used as a white display ECSW. However, the present invention is not limited to this, and it goes without saying that known materials can be combined and used according to the application of the display element. [Industrial Applicability]

[0075] The present invention modifies a counter electrode in a display element using electrochromism with a low-potential redox substance (e.g., PB) that undergoes oxidation-reduction at a more anodic potential than substances other than the counter electrode constituent substance (e.g., ITO) and the substance (e.g., bromide ion) that reacts with the first electrode contained in the electrolyte layer. By doing so, when causing a coloring / bleaching reaction in the display electrode, the potential applied to the counter electrode can be reduced, and deterioration accompanied by an increase in electrical resistance can be suppressed. Therefore, the present invention is a very useful technology that can be widely applied to the field of electrochromic displays such as smart windows and electronic paper. In particular, when the present invention is applied to a white display smart window (ECSW), in addition to excellent power-saving performance due to the memory property that is a characteristic of electrochromic materials, excellent energy-saving performance by not absorbing sunlight due to white display and solving the problem of heat release, it can provide a highly practical white display ECSW with excellent repeat stability and durability of coloring / bleaching that has never been achieved before.

Claims

1. a first electrode formed on a first substrate, a second electrode formed on a second substrate and disposed opposite to the first electrode, an electrolyte layer disposed between the first electrode and the second electrode, a display element to which a voltage is applied to the first electrode and the second electrode by voltage applying means, wherein the second electrode is modified with a low-potential redox substance that undergoes oxidation-reduction at a more cathodic (more base) potential than the reaction proceeding at the first electrode.

2. The display element according to claim 1, wherein the low-potential redox substance undergoes oxidation-reduction at a more anodic (more noble) potential than substances other than the second electrode constituent substance and the substance that reacts at the first electrode contained in the electrolyte layer.

3. a nanoparticle film of the second electrode constituent substance is formed on the second electrode, The display element according to claim 1, wherein the low-potential redox substance is modified on the nanoparticle film.

4. The display element according to claim 1, wherein the second electrode constituent substance is indium tin oxide (ITO).

5. The display element according to any one of claims 1 to 4, wherein the low-potential redox substance is Prussian blue (PB).

6. The display element according to claim 1, wherein the electrolyte layer is made of a hydrogel.

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