JP2016018189A - Electrochromic device, and driving method of electrochromic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochromic device in which the decoloring response is improved while the drive voltage is reduced.SOLUTION: An AC voltage is applied to an electrochromic element during a decoloring operation of the electrochromic element. With the AC voltage, a maximum voltage (E) is between a positive-side coloring threshold voltage (E) and a negative-side coloring threshold voltage (E), and a minimum voltage (E) is the negative-side coloring threshold voltage (E) or lower. The period (PW) in which the voltage of the negative-side coloring threshold voltage or lower is applied is shorter than the charge transfer period.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an electrochromic device and a method for driving an electrochromic element.

  In recent years, there is an increasing demand for a variable ND filter that can adjust an optical density steplessly in a moving image shooting apparatus using a solid-state imaging device. Many optical elements using liquid crystals or inorganic electrochromic thin films have been proposed so far, but they are widely used because they are inferior to conventional ND filters in terms of light amount adjustment range and reliability. Not reached. On the other hand, those using organic electrochromic molecules are particularly promising for use as a variable ND filter mounted in an imaging apparatus because the light amount adjustment range is wide and the spectral transmittance design is relatively easy.

  An electrochromic device using organic electrochromic molecules includes an electrochemically active anodic material and an electrochemically active cathodic material between a pair of electrodes. In many cases, at least one of the anodic material and the cathodic material is configured as a material that exhibits electrochromic properties, that is, a material that exhibits an absorption band in the visible light region by electrochemical oxidation and reduction. At this time, the oxidation reaction of the anodic material and the reduction reaction of the cathodic material occur simultaneously on the pair of electrodes, whereby a closed circuit is formed in the element and a current flows.

  In an element in which the reaction current of the anodic material is complementarily ensured by the reaction current of the cathodic material, the driving voltage of the element is between the oxidation potential of the anodic electrochromic material and the reduction potential of the cathodic electrochromic material. It is determined by the potential difference. For this reason, in order to obtain a large optical density change as an element, it is necessary to apply a larger potential difference than this potential difference to flow a current. However, application of a large potential difference causes corrosion of the transparent electrode, side reaction of the electrochromic material, and the like, and the durability of the element is remarkably impaired. Therefore, an element configuration that obtains a large current by applying a smaller potential difference has been desired.

  In addition, in an element configuration in which an anodic material and a cathodic material are used in a complementary manner, the reaction of each material occurs only on the electrode surface during coloring. It is known that the reaction also occurs between the oxidant and the reductant of the cathode material. In Patent Document 1, a reverse voltage is applied to the element to form an oxidant of an anodic material and a reductant of a cathodic material in the vicinity of a pair of electrodes, and the decolorization response can be improved by decoloring between these materials. Have been described.

JP-T 2009-540376

  However, in the method of Patent Document 1, since a reverse voltage pulse in the Faraday current region that is longer than the charge transfer time is applied, there is a problem that coloring occurs during decoloring driving and the maximum transmittance is reduced. .

  By the way, in order to apply an organic electrochromic molecule and an element using an anodic material and a cathodic material in a complementary manner to a variable ND filter application, a reduced form of an anodic material and an oxidized form of a cathodic material. Any of them preferably has no absorption band in the visible light region. However, the oxidation-reduction potential difference between materials having such characteristics is generally large, and it is necessary to drive the device with a large voltage (potential difference). A large driving voltage (potential difference) causes reductive corrosion of the transparent electrode and a side reaction of the anodic material and the cathodic material, which greatly impairs the reliability of the device.

  Therefore, the present inventors adopt a relatively small driving voltage (potential difference) if an electrode material having a reversible redox potential between the redox potential of the anodic material and the redox potential of the cathode material is employed. It has been noted that the element can be driven by. For example, an electrode having a porous structure formed of tin oxide nanoparticles has a redox potential between the anodic material and the cathodic material. And since it does not color by oxidation-reduction reaction, if this is employ | adopted as an electrode, an element can be driven with a comparatively small drive voltage (potential difference).

  However, the redox reaction of an electrode having a porous structure is accompanied by adsorption / desorption or insertion / release of cations present in the electrochromic medium. Therefore, it is generally slow with respect to the redox reaction of organic electrochromic molecules, and it may take time for the transmittance to recover, especially when decolored, and may cause a color residue of the anodic material.

  In view of the above problems, an object of the present invention is to provide an electrochromic device and a method for driving an electrochromic element that have improved decolorization response while reducing drive voltage.

The electrochromic device of the present invention is
An electrochromic element having a pair of electrodes and an electrochromic medium disposed between the pair of electrodes, and a driving means for driving the electrochromic element,
The electrochromic medium is composed of a liquid containing at least one kind of anodic electrochromic material and at least one kind of cathodic electrochromic material,
The pair of electrodes are a first electrode that performs redox of the anodic electrochromic material and a second electrode that performs redox of the cathodic electrochromic material, and at least the second electrode The surface facing the electrochromic medium has a porous structure, and the redox potential of the second electrode is between the redox potential of the anodic electrochromic material and the redox potential of the cathodic electrochromic material. Yes,
The driving means applies an AC voltage to the electrochromic element during a decoloring operation of the electrochromic element, and the AC voltage has a maximum voltage between a positive color threshold voltage and a negative color threshold voltage. The minimum voltage is equal to or lower than the negative coloring threshold voltage, and the time during which the voltage equal to or lower than the negative coloring threshold voltage is applied is less than the charge transfer time.

The driving method of the electrochromic device of the present invention is as follows.
A method for driving an electrochromic device having a pair of electrodes and an electrochromic medium disposed between the pair of electrodes,
The electrochromic medium is composed of a liquid containing at least one kind of anodic electrochromic material and at least one kind of cathodic electrochromic material,
The pair of electrodes are a first electrode that performs redox of the anodic electrochromic material and a second electrode that performs redox of the cathodic electrochromic material, and at least the second electrode The surface facing the electrochromic medium has a porous structure, and the redox potential of the second electrode is between the redox potential of the anodic electrochromic material and the redox potential of the cathodic electrochromic material. Yes,
During the decoloring operation of the electrochromic element, an AC voltage is applied to the electrochromic element, and the AC voltage has a maximum voltage between a positive coloring threshold voltage and a negative coloring threshold voltage, and a minimum voltage. Is equal to or lower than the negative coloring threshold voltage, and the time during which a voltage equal to or lower than the negative coloring threshold voltage is applied is less than the charge transfer time.

  According to the present invention, since the driving voltage can be reduced, reductive corrosion of the electrode and side reaction of the electrochromic material can be avoided, and the decoloring response can be improved. Therefore, for example, the reliability can be greatly improved as an optical element for use in a variable ND filter.

It is typical sectional drawing which shows an example of the electrochromic element which the electrochromic apparatus of this invention has. It is a figure which shows the cyclic voltammogram characteristic of an electrochromic material and a 2nd electrode. It is typical sectional drawing which shows the other example of the electrochromic element which the electrochromic apparatus of this invention has. It is a figure which shows the relationship between the coloring threshold voltage of an anodic electrochromic material, and the specific surface area of a 2nd electrode. FIG. 4 is a diagram showing characteristics of the electrochromic element of Example 1. It is the figure which showed an example of the drive voltage waveform at the time of erasing operation. FIG. 3 is a diagram showing a change over time in the transmittance of the electrochromic device of Example 1. It is the figure which normalized and showed the decoloration response time of the electrochromic element of Example 1 by the comparative example. It is the figure which showed the time change of the transmittance | permeability of the electrochromic element of Example 2. FIG. It is the figure which normalized and showed the decoloration response time of the electrochromic element of Example 2 by the comparative example. It is a figure which shows an example of the imaging device of this invention. It is a figure which shows the other example of the imaging device of this invention. It is a figure which shows an example of the window material of this invention.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the configuration, relative arrangement, and the like described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified.

≪Electrochromic device≫
FIG. 1 is a schematic cross-sectional view showing one embodiment of an electrochromic element included in the electrochromic device of the present invention. The element in FIG. 1 is a transmissive complementary electrochromic element using organic electrochromic molecules. In FIG. 1, 1a and 1b are substrates, 2 is a first electrode, 3 is a second electrode, and 4 is an electrochromic medium. As shown in FIG. 1, the electrochromic device of the present invention has a pair of electrodes (first electrode 2 and second electrode 3) and an electrochromic medium 4 disposed between the pair of electrodes.

<Substrate 1a, 1b>
As the substrates 1a and 1b, for example, glass substrates such as quartz glass, white plate glass, borosilicate glass, alkali-free glass, and chemically tempered glass are preferably used. Particularly, alkali-free glass substrates are preferably used from the viewpoint of durability. It is preferable to do.

  Here, the optical characteristics of the substrates 1a and 1b will be described. The electrochromic device of the present invention preferably has a high visible light transmittance and a low haze in order to be disposed in an optical path of an imaging optical system, an imaging device or the like. Therefore, the visible light transmittance of the substrates 1a and 1b is preferably 80% or more, and more preferably 90% or more. Moreover, it is preferable that the haze value of the board | substrates 1a and 1b is 1% or less, More preferably, it is 0.5% or less.

<First electrode 2>
The first electrode 2 is an electrode that performs redox of the anodic electrochromic material. In FIG. 1, the first electrode 2 is formed on a substrate 1a. At least the surface of the first electrode 2 facing the electrochromic medium 4 does not have a porous structure, but has a flat or substantially flat structure (hereinafter abbreviated as “substantially flat”), and has a specific surface area. A structure that can be regarded as approximately 1 cm ² / cm ² is preferable.

Here, the specific surface area in the present invention is a specific surface area (S _B / S _A : cm ² / cm ² ) as an effective area (S _B : cm ² ) relative to the geometric area (S _A : cm ² ) of the electrode. ). The geometric area (S _A ) is synonymous with the projected area and represents the apparent area (cm ² ) when the substrate is projected. The effective area (S _B ) represents the surface area (cm ² ) inside the porous body calculated by measurement by nitrogen gas adsorption method (BET method) and measurement of membrane weight.

  Examples of the first electrode 2 include tin-doped indium oxide (ITO), zinc oxide, gallium-doped zinc oxide (GZO), aluminum-doped zinc oxide (AZO), tin oxide, antimony-doped tin oxide (ATO), and fluorine-doped oxidation. A thin film made of a so-called transparent conductive oxide such as tin (FTO) or niobium-doped titanium oxide (TNO) can be used. Further, in consideration of conductivity and high transparency, it is possible to adopt a laminated structure of these. The thickness of the first electrode 2 is preferably 100 nm or more and 1000 nm or less, and more preferably 200 nm or more and 500 nm or less. In particular, as a material having both high visible light transmittance and chemical stability, an FTO thin film having a thickness of about 200 nm can be suitably used. The film formation method of the first electrode 2 is not particularly limited, and examples thereof include vapor phase film formation methods such as sputtering, vapor deposition, and CVD, and liquid phase film formation methods such as sol-gel, spin coating, printing, and plating. Can be mentioned.

  Here, the optical characteristics of the first electrode 2 will be described. The electrochromic device of the present invention preferably has a high visible light transmittance and a low haze in order to be disposed in an optical path of an imaging optical system, an imaging device or the like. Therefore, the visible light transmittance of the first electrode 2 is preferably 80% or more, and more preferably 90% or more. Moreover, it is preferable that the haze value of the 1st electrode 2 is 1% or less, More preferably, it is 0.5% or less.

<Second electrode 3>
The second electrode 3 is an electrode that performs redox of the cathodic electrochromic material. In FIG. 1, the second electrode 3 is formed on a substrate 1b.

  The surface of the second electrode 3 facing at least the electrochromic medium 4 has a porous structure. The redox potential of the second electrode 3 is between the redox potential of the anodic electrochromic material and the redox potential of the cathodic electrochromic material. Hereinafter, the reason why such a second electrode 3 is used will be described with reference to FIG.

FIG. 2 is a diagram showing an example of cyclic voltammogram characteristics of the anodic electrochromic material, the cathodic electrochromic material, and the second electrode 3. The potential reference on the horizontal axis is a non-aqueous solvent system reference electrode (Ag / Ag ⁺ ). In FIG. 2, the potential at which the anode current of the anodic electrochromic material begins to flow is about +0.31 V, and the potential at which the cathode current of the cathodic electrochromic material begins to flow is about −0.70 V. Therefore, an element in which an electrochromic medium containing these materials is sandwiched between the first electrodes 2 has a threshold voltage (potential difference) ΔE of 1.01V. On the other hand, since the reduction potential of the second electrode 3 is about +0.02 V, in an element in which an electrochromic medium including only an anodic electrochromic material is sandwiched between the first electrode 2 and the second electrode 3, The threshold voltage (potential difference) ΔE ′ is 0.29V. That is, the device of the present invention can greatly reduce the drive voltage (potential difference) of the device as compared with the device in which the anodic electrochromic material and the cathodic electrochromic material are sandwiched between the first electrodes 2. Furthermore, in the device of the present invention, if the voltage is further increased while maintaining ΔE ′ = 0.29 V, a larger current is guaranteed by the reduction current of the cathodic electrochromic material.

  As the second electrode 3, in addition to the transparent conductive oxide exemplified as the first electrode 2, a porous film made of tungsten oxide, cerium oxide, or a composite oxide thereof can be used. There is no restriction | limiting in particular in the shape and manufacturing method of the 2nd electrode 3, Nano structure bodies, such as a nanoparticle film | membrane which has a through-hole, a nanorod, a nanowire, and a nanotube, etc. can be used. Among these, a nanoparticle film is preferable, and in particular, a nanoparticle film having an average particle diameter of 40 nm or less, an average pore diameter of 30 nm or less, and an arithmetic average roughness of 50 nm or less can realize optical characteristics described later, and can be suitably used. it can. Furthermore, a tin oxide nanoparticle film having a large specific surface area per unit volume and excellent optical properties can be suitably used. The thickness of the second electrode 3 is 1500 nm or more, preferably 3000 nm or more.

  Here, the optical characteristics of the second electrode 3 will be described. The electrochromic device of the present invention preferably has a high visible light transmittance and a low haze in order to be disposed in an optical path of an imaging optical system, an imaging device or the like. Therefore, the visible light transmittance of the first electrode 2 is preferably 80% or more, and more preferably 90% or more. The haze value of the second electrode 3 is preferably 1% or less, more preferably 0.5% or less.

  As shown in FIG. 3, the second electrode 3 may have a laminated structure of a layer 5 having a porous structure and a transparent conductive layer 6. This is configured such that when the surface resistance of the layer 5 having a porous structure is high, this is compensated by the transparent conductive layer 6 having a low resistance.

The specific surface area of the surface of the second electrode 3 facing the electrochromic medium 4 is preferably 300 cm ² / cm ² or more, more preferably 600 cm ² / cm ² or more. If the specific surface area is 300 cm ² / cm ² or more, it is preferable that the threshold voltage at which current starts to flow through the device is sufficiently lowered. FIG. 4 is a diagram showing the relationship between the oxidation coloring threshold voltage of the anodic electrochromic material A represented by the following structural formula (A) and the specific surface area of the second electrode 3. The first electrode 2 was a fluorine-doped tin oxide (FTO) thin film having a specific surface area of approximately 1 cm ² / cm ² .

Here, the coloring threshold voltage is an optical density change ΔOD (= −log (T / T ₀ )) at the absorption wavelength of the electrochromic material (T represents transmittance, and T ₀ represents initial transmittance) of 0.01. The voltage at which T / T ₀ = 97.7% was obtained. As shown in FIG. 3, when the specific surface area of the second electrode 3 is 300 cm ² / cm ² or more, the threshold voltage is 2.23 V when the specific surface area of the second electrode 3 is approximately 1 cm ² / cm ^2. It can be seen that when the specific surface area is 1 cm or less and further the specific surface area is 600 cm ² / cm ² or more, it can be reduced to 0.5 V or less.

<Electrochromic medium 4>
The electrochromic medium 4 is made of a liquid containing at least one kind of anodic electrochromic material and at least one kind of cathodic electrochromic material.

  The anodic electrochromic material and the cathodic chromic material are preferably transparent materials that do not absorb in the visible light region in a neutral state, and the anodic electrochromic material is oxidized to a specific wavelength in the visible light region. A material that absorbs light, a canode-like electrochromic material, is a material that absorbs a specific wavelength in the visible light region by being reduced. By mixing a plurality of materials each having a different absorption band in the visible light region, the device can have flat absorption characteristics. Specific examples of the anodic electrochromic material include organic electrochromic molecules such as thiophenes, and specific examples of the cathodic chromic material include organic electrochromic molecules such as viologens.

  A supporting electrolyte may be added to the electrochromic medium 4. The supporting electrolyte is not particularly limited as long as it has low reactivity with the electrode material and can be used stably, and a plurality of supporting electrolytes can be used in combination. A salt composed of an alkali cation such as lithium or an organic cation such as a quaternary ammonium cation and an inorganic anion such as a perchlorate anion can be used.

  As a solvent for dissolving the electrochromic material, etc., considering solubility, vapor pressure, viscosity, potential window, etc., propylene carbonate, γ-butyrolactone, benzonitrile, N-methylpyrrolidone, 3-methoxypropionitrile, N, A polar aprotic solvent such as N-dimethylacetamide can be used.

  In addition to the constituent materials described above, a dehydrating agent, a stabilizer, a thickener, and the like may be added to the electrochromic medium.

  Next, a process of injecting the electrochromic medium 4 into the element will be described.

  The glass substrate 1a on which the first electrode 2 is formed and the glass substrate 1b on which the second electrode 3 is formed are bonded together with a sealing material with the electrode inside and leaving an opening in part. As the sealing material, a material that is chemically stable, does not transmit gas or water, and does not inhibit the oxidation-reduction reaction of the electrochromic material, such as glass frit, epoxy resin, metal, or the like can be used. A member that defines a pair of glass substrate intervals may be mixed with the sealing material, or a substrate interval defining member may be disposed separately. The element bonded with the opening remaining in part is sealed after injecting the electrochromic medium 4 from the opening by a vacuum injection method.

<Drive means and drive method>
5A and 5B are diagrams showing characteristics of the electrochromic element used in Example 1 described later. FIG. 5A is a current-voltage characteristic, and FIG. 5B is a diagram showing transmittance-voltage characteristics. is there.

First, when the potential applied to the first electrode 2 is swept in the positive direction, an oxidation reaction of the anodic electrochromic material occurs in the first electrode 2. At the same time, ion rearrangement in the second electrode 3, a reduction reaction of the second electrode 3 itself, and a reduction reaction of the cathodic electrochromic material occur, and a closed circuit is formed in the device and coloring starts. As shown in FIG. 5, the coloring threshold voltage E _th ⁺ on the positive side is + 1.1V.

Next, when the potential applied to the first electrode 2 is swept in the negative direction, a reduction reaction of the cathodic electrochromic material occurs at the first electrode 2. At the same time, an oxidation reaction of the anodic electrochromic material occurs in the second electrode 3, a closed circuit is formed in the element, and coloring starts. As shown in FIG. 5, the coloring threshold voltage E _th ⁻ on the negative side is −1.4V.

Usually, when coloring an element, it is desired to flow more current at a low voltage, so a positive voltage larger than E _th ⁺ is applied to the first electrode 2. When the color is to be erased, a voltage between E _th ⁺ and E _th ⁻ is applied to the first electrode 2. Typically, both electrodes are short-circuited and grounded. The reason for this is that in the anodic electrochromic material and cathodic electrochromic material both comprise elements, since a large reverse voltage is applied when the reverse reaction resulting in coloration occurred, the range of voltage that can be applied during discoloring E _th ^This is because it is limited between ⁺ and E _th ⁻ .

  On the other hand, the redox reaction of the second electrode 3 itself is a cation adsorption or insertion reaction (reduction reaction) when the element is colored, and a cation desorption or release reaction (oxidation reaction) at the time of decoloration. There is nothing else. Since the redox reaction of the second electrode 3 itself is slower than the redox reaction of the electrochromic material, the paired electrode reaction is rate-determined particularly during decoloring, and the recovery of transmittance is delayed, or the anodic electrochromic A color residue of the material may occur. In order to improve the speed of the oxidation-reduction reaction of the second electrode 3 itself, particularly the oxidation reaction during decoloring, it is preferable to apply a reverse voltage as large as possible during decoloring. However, as described above, a large reverse voltage cannot be applied to the element of the present invention including both an anodic electrochromic material and a cathodic electrochromic material.

Therefore, the driving means (not shown) applies an AC voltage to the electrochromic element during the decoloring operation of the electrochromic element. FIG. 6 is a conceptual diagram showing an example of a drive voltage waveform during the decoloring operation. In the waveform shown in FIG. 6, the maximum voltage E _high is between E _th ⁺ and E _th ⁻ , and the minimum voltage E _lo is below E _th ⁻ . Furthermore, the modulation voltage waveform is such that the time PW _lo during which a voltage equal to or less than E _th ⁻ is applied is less than the charge transfer time. Here, it is preferable that PW _lo is 0.2 ms or less, the duty ratio of E _lo is 2% or less, and E _lo is −3 V or more. Further, it is preferable that the driving means applies an alternating voltage until at least the transmittance of the electrochromic element reaches 80%. Note that the driving voltage waveform may be other than the rectangular waveform during the decoloring operation, and a sine wave, a triangular wave, a trapezoidal wave, or the like can be applied.

When a direct current voltage equal to or less than E _th ⁻ is applied, a Faraday current flows through the element to start coloring, but a certain time is required until the Faraday current starts to flow. This time is called the charge transfer time. When a voltage is applied for less than the charge transfer time, the electrochromic molecule does not react with the electrode, and it is considered that the formation of an electric double layer on the electrode surface, the orientation of the electrochromic molecule, etc. are occurring. Therefore, if the voltage application is stopped at this stage, it is possible to improve the substantial decoloring response speed by promoting only the movement of cations without coloring the element. This charge transfer time largely depends on the element configuration, but is about 0.1 ms.

≪Imaging optical system and imaging device≫
FIG. 11 is a schematic diagram showing an imaging device having an imaging optical system using the electrochromic device of the present invention as an optical filter. As shown in FIG. 11, the imaging optical system 102 is detachably connected to the imaging device 103 via a mount member (not shown).

  The imaging optical system 102 is a unit having a plurality of lenses or lens groups. For example, in FIG. 11, the imaging optical system 102 represents a rear focus zoom lens that performs focusing after the stop. The first lens group 104 having a positive refractive power, the second lens group 105 having a negative refractive power, the third lens group 106 having a positive refractive power, and a positive refractive power in order from the subject side (left side as viewed in the drawing). The fourth lens group 107 has four lens groups. Zooming is performed by changing the distance between the second lens group 105 and the third lens group 106, and focusing is performed by moving a part of the fourth lens group 107. The imaging optical system 102 has, for example, an aperture stop 108 between the second lens group 105 and the third lens group 106, and an optical element between the third lens group 106 and the fourth lens group 107. A filter 101 is included. Light passing through the imaging optical system 102 is arranged so as to pass through the lens groups 102 to 107, the aperture stop 108, and the optical filter 101, and the amount of light can be adjusted using the aperture stop 108 and the optical filter 101. it can.

  The configuration in the imaging optical system 102 can be changed as appropriate. For example, the optical filter 101 can be arranged in front of the aperture stop 108 (subject side) or behind (imaging apparatus 103 side), and the first lens group. It may be arranged before 104 or after the fourth lens group 107. If it is arranged at a position where light converges, there is an advantage that the area of the optical filter 101 can be reduced. Also, the form of the imaging optical system 102 can be selected as appropriate. In addition to the rear focus type, an inner focus type in which focusing is performed before the stop may be used, or other methods may be used. In addition to the zoom lens, a special lens such as a fisheye lens or a macro lens can be selected as appropriate.

  The glass block 109 included in the imaging apparatus is a glass block such as a low-pass filter, a face plate, or a color filter. The imaging device 110 is a sensor unit that receives light that has passed through the imaging optical system 102, and an imaging device such as a CCD or CMOS can be used. In addition, an optical sensor such as a photodiode may be used, and an optical sensor that acquires and outputs light intensity or wavelength information can be used as appropriate.

  As shown in FIG. 11, when the optical filter 101 is incorporated in the imaging optical system 102, the driving unit may be disposed inside the imaging optical system 102 or may be disposed outside the imaging optical system 102. When arranged outside the imaging optical system 102, the electrochromic element inside and outside the imaging optical system 102 is connected to the driving means through wiring, and drive control is performed.

  As shown in FIG. 12, the imaging device 103 itself may include the electrochromic device (optical filter 101) of the present invention. FIG. 12 is a schematic diagram of an imaging apparatus having an optical filter. The optical filter 101 may be disposed at an appropriate location inside the imaging device 103, and the imaging element 110 may be disposed so as to receive light that has passed through the optical filter 101. In FIG. 12, for example, the optical filter 101 is disposed immediately before the image sensor 110. When the imaging device 103 itself includes the optical filter 101, the connected imaging optical system 102 itself does not need to have the optical filter 101, so that a dimmable imaging device using an existing imaging optical system is configured. It becomes possible.

  Such an image pickup apparatus can be applied to a product having a combination of light amount adjustment and an image pickup element. For example, it can be used for a camera, a digital camera, a video camera, a digital video camera, and can also be applied to a product incorporating an imaging device such as a mobile phone, a smartphone, a PC, or a tablet.

  By using the electrochromic device of the present invention as a dimming member, the dimming amount can be appropriately changed by one filter, and there are advantages such as reduction in the number of members and space saving.

≪Window material≫
FIG. 13 is a view showing a window member using the electrochromic device of the present invention, FIG. 13 (a) is a perspective view, and FIG. 13 (b) is a cross-sectional view taken along line XX ′ of FIG. 13 (a). .

  A window material 111 in FIG. 13 is a dimming window, and includes the electrochromic element 10, a transparent plate 113 that sandwiches the electrochromic element 10, and a frame 112 that surrounds and integrates the whole. Reference numeral 7 denotes a spacer. The driving means may be integrated in the frame 112 or may be disposed outside the frame 112 and connected to the electrochromic element 10 through wiring.

  The transparent plate 113 is not particularly limited as long as it is a material having high light transmittance, and is preferably a glass material in consideration of use as a window. In FIG. 13, the electrochromic element 10 is a component independent of the transparent plate 113, but for example, the substrates 1 a and 1 b of the electrochromic element 10 may be regarded as the transparent plate 113.

  The material of the frame 112 is not limited, but it may be considered that the whole of the electrochromic element 10 covering at least a part and having an integrated form is a frame.

  Such a light control window can be applied to, for example, an application for adjusting the amount of sunlight entering the room during the daytime. Since it can be applied to the adjustment of the amount of heat in addition to the amount of sunlight, it can be used to control the brightness and temperature of the room. In addition, the present invention can also be applied as a shutter for blocking the view from the outside to the room. Such a light control window can be applied to a window of a vehicle such as an automobile, a train, an airplane, a ship, a filter of a display surface of a clock or a mobile phone, in addition to a glass window for a building.

  Examples of the present invention will be described below.

<Example 1>
(1) Production of electrochromic element The electrochromic element shown in FIG. 4 was produced.

  First, as a substrate 1a, a glass substrate (EAGLE XG (registered trademark) manufactured by Corning) having a thickness of 0.7 mm was prepared. A 200 nm-thick fluorine-doped tin oxide (FTO) thin film having a substantially flat surface structure was formed on the substrate 1a as the first electrode 2. Here, the substrate 1a having the first electrode 2 had an average visible light transmittance of 85%, a haze of 0.1%, and a sheet resistance of 40Ω / □.

Next, the same glass substrate as the substrate 1a was prepared as the substrate 1b, and the second electrode 3 having a laminated structure of the transparent conductive layer 6 and the porous layer 5 was formed thereon. Specifically, the same FTO thin film as the first electrode 2 was formed as the transparent conductive layer 6 on the substrate 1b. Next, a tin oxide nanoparticle slurry with an average particle size of 21 nm (SNAP15WT% -G02 manufactured by CIK Nanotech) and a zinc oxide nanoparticle slurry with an average particle size of 34 nm (ZNAP15WT% -G0 manufactured by CIK Nanotech) were oxidized with tin oxide: oxidation. Mixing was performed so that the volume ratio of zinc was 2: 1. To this mixture, a small amount of an inorganic binder was further added to improve the flatness of the film surface and prevent peeling to obtain a nanoparticle mixed slurry. This mixed slurry was applied onto the transparent conductive layer 6 and baked at 500 ° C. for 30 minutes. Thereafter, only zinc oxide was etched with dilute hydrochloric acid to obtain a porous layer 5 made of a tin oxide nanoparticle film. The specific surface area of the porous layer 5 was 653cm ² / cm ^2. The visible light transmittance of the substrate 1b having the second electrode 3 was 87%, and the haze was 0.6%.

  Next, the substrates 1a and 1b were bonded with an epoxy resin with the electrodes inside, leaving an opening for injecting the electrochromic medium. At this time, a PET film having a thickness of 50 μm (Teijin (registered trademark) Tetron (registered trademark) film G2 manufactured by Teijin DuPont Films Ltd.) was used as a spacer.

  Next, as the electrochromic medium 4, an anodic electrochromic material A shown in the structural formula (A) and a cathodic electrochromic material B shown in the following structural formula (B) are dissolved in a propylene carbonate solvent. Was made. At this time, the concentrations of the anodic electrochromic material A and the cathodic electrochromic material B were 30 mM.

  The electrochromic medium 4 was injected from the opening by vacuum injection to the element prepared by leaving the opening prepared previously, and the opening was sealed with an epoxy resin to produce an electrochromic element.

(2) Driving of electrochromic element The obtained element was installed in an apparatus including an irradiation light source and a photodiode for detecting transmitted light, and was driven while monitoring the transmittance of the element. As described above (see FIG. 5), E _th ⁺ = 1.1 V and E _th ⁻ = −1.4 V of the obtained element.

The coloring drive was performed at + 1.8V1s. During the decoloring operation, a rectangular voltage waveform (E _high = 0 V, E _lo = −2 V, 100 Hz) shown in FIG. 6 was applied. The width PW _lo was as shown in Table 1.

  FIG. 7 shows the time change of the transmittance of the element in each driving method. For comparison, the case where a DC voltage of 0 V was applied during the decoloring operation was shown as a comparative example. Further, FIG. 8 shows the decolorization response times of the driving methods (a) to (c) normalized by the decolorization response time of the comparative example (x mark in the figure).

From FIG. 7, it can be seen that as PW _lo is increased, the rise of the decoloring response is improved with respect to the comparative example. However, in the driving methods (c) and (d), coloring occurs during decoloring driving, so that the maximum transmittance is lowered. Further, FIG. 8 shows that the driving method (b) can improve the decoloring response by about 50% with respect to the comparative example. Therefore, the preferred PW _lo is 0.2 ms.

When the charge transfer time of the device was confirmed, if PW _lo was 0.2 ms or less, there was no decrease in transmittance per single pulse of the device, and the decrease in transmittance was about 0.2% per single pulse at 0.5 ms. In 1.0 ms, the transmittance decrease was about 0.5% per single pulse. Therefore, it can be said that the charge transfer time of this element is larger than 0.2 ms and shorter than 0.5 ms.

<Example 2>
Example 1 is the same as Example 1 except that the driving method during the erasing operation is changed as follows. In this example, a rectangular voltage waveform (E _high = 0 V, 100 Hz, PW _lo = 0.1 ms) shown in FIG. 6 was applied during the decoloring operation. _Elo was as shown in Table 2.

  FIG. 9 shows the time change of the transmittance of the element in each driving method. For comparison, the case where a DC voltage of 0 V was applied during the decoloring operation was shown as a comparative example. FIG. 10 shows the decolorization response times of the driving methods (a) to (e) normalized by the decolorization response time of the comparative example (x mark in the figure).

9 and 10, when gradually increasing the E _lo, it is seen that continue to improve the rise of the erasing response to Comparative Example. However, in the driving method (e), since the coloring is slightly caused during the erasing driving, the erasing response time is reduced. Therefore, _Elo is preferably −3 V or higher, more preferably −2.5 V or higher. From this, it can be seen from FIG. 10 that the maximum decoloring response can be improved by about 40% compared to the comparative example.

1a, 1b: substrate, 2: first electrode, 3: second electrode, 4: electrochromic medium, 5: porous layer, 6: transparent conductive layer

Claims (19)

An electrochromic element having a pair of electrodes and an electrochromic medium disposed between the pair of electrodes, and a driving means for driving the electrochromic element,
The electrochromic medium is composed of a liquid containing at least one kind of anodic electrochromic material and at least one kind of cathodic electrochromic material,
The pair of electrodes are a first electrode that performs redox of the anodic electrochromic material and a second electrode that performs redox of the cathodic electrochromic material, and at least the second electrode The surface facing the electrochromic medium has a porous structure, and the redox potential of the second electrode is between the redox potential of the anodic electrochromic material and the redox potential of the cathodic electrochromic material. Yes,
The driving means applies an AC voltage to the electrochromic element during a decoloring operation of the electrochromic element, and the AC voltage has a maximum voltage between a positive color threshold voltage and a negative color threshold voltage. The electrochromic device is characterized in that the minimum voltage is equal to or lower than the negative coloring threshold voltage, and the time during which a voltage equal to or lower than the negative coloring threshold voltage is applied is less than the charge transfer time.   2. The electrochromic device according to claim 1, wherein a time for applying a voltage equal to or lower than the negative coloring threshold voltage is 0.2 ms or less.   The electrochromic device according to claim 1, wherein a duty ratio of the minimum voltage in the AC voltage is 2% or less.   The electrochromic device according to claim 1, wherein the minimum voltage is −3 V or more.   The electrochromic device according to any one of claims 1 to 4, wherein the driving unit applies the alternating voltage until at least a transmittance of the electrochromic element reaches 80%. 6. The electrochromic device according to claim 1, wherein a specific surface area of a surface of the second electrode facing the electrochromic medium is 300 cm ² / cm ² or more.   The electrochromic device according to any one of claims 1 to 6, wherein the porous structure is formed of nanoparticles.   The electrochromic device according to claim 7, wherein the nanoparticles are tin oxide nanoparticles.   An imaging optical system comprising the electrochromic device according to any one of claims 1 to 8.   An image pickup apparatus comprising: the electrochromic device according to claim 1; and an image pickup device that receives light that has passed through an electrochromic element included in the electrochromic device.   A window member comprising the electrochromic device according to claim 1. A method for driving an electrochromic device having a pair of electrodes and an electrochromic medium disposed between the pair of electrodes,
The electrochromic medium is composed of a liquid containing at least one kind of anodic electrochromic material and at least one kind of cathodic electrochromic material,
The pair of electrodes are a first electrode that performs redox of the anodic electrochromic material and a second electrode that performs redox of the cathodic electrochromic material, and at least the second electrode The surface facing the electrochromic medium has a porous structure, and the redox potential of the second electrode is between the redox potential of the anodic electrochromic material and the redox potential of the cathodic electrochromic material. Yes,
During the decoloring operation of the electrochromic element, an AC voltage is applied to the electrochromic element, and the AC voltage has a maximum voltage between a positive coloring threshold voltage and a negative coloring threshold voltage, and a minimum voltage. Is a negative coloring threshold voltage or less, and the time during which a voltage equal to or less than the negative coloring threshold voltage is applied is less than the charge transfer time.   13. The method of driving an electrochromic device according to claim 12, wherein a time for applying a voltage equal to or lower than the negative coloring threshold voltage is 0.2 ms or less.   The method of driving an electrochromic device according to claim 12 or 13, wherein a duty ratio of the minimum voltage in the AC voltage is 2% or less.   The method of driving an electrochromic device according to claim 12, wherein the minimum voltage is −3 V or more.   16. The method of driving an electrochromic element according to claim 12, wherein the driving unit applies the AC voltage until at least the transmittance of the electrochromic element reaches 80%. The electrochromic element driving according to any one of claims 12 to 16, wherein a specific surface area of the surface of the second electrode facing the electrochromic medium is 300 cm ² / cm ² or more. Method.   The method of driving an electrochromic device according to any one of claims 12 to 17, wherein the porous structure is formed of nanoparticles.   The method of driving an electrochromic device according to claim 18, wherein the nanoparticles are tin oxide nanoparticles.

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