GB2190760A - Electrochromic element - Google Patents

Abstract

An electrochromic element has a two-dimensional substrate, an upper electrode A, an electrochromic layer, and a lower electrode B. Electrode terminal regions CA, CB are formed on two opposite regions of the substrate, preferably extending such that between them they encompass substantially all of the active area of the cell, in order to avoid non- uniformity of operation over the area and reduce response times. The invention is applicable to mirrors for automobiles. <IMAGE>

Description

SPECIFICATION Electrochromic element BACKGROUND OF THE INVENTION: Field of the invention The present invention relates to a new and improved electrochromic element ("electrochromic" is referred to as an EC and an EC element is referred to as an ECD hereinafter).

Related Background Art A conventional ECD comprises a pair of electrode layers, at least one of which is transparent, and an EC layer sandwiched between the pair of electrode layers. When a voltage having a magnitude of a voltage from a dry cell is applied across the pair of electrode layers of the ECD, the ECD emits light. When the reverse voltage is applied to the ECD, the ECD is extinguished and becomes transparent again. Extensive studies have been made on ECDs for display devices and, in particular, 7-segment numerical display devices, transmitting or reflecting control devices, and other devices.

When an EC material such as W03 emits light, electrons (e-) and cations (X+) are simultaneously injected, and general reaction formulas for emission and extinction are represented as follows: Extinction State: W03+ne-+nX+

Emission State: XnWO3 H' or Li ions are mainly used as cations (X') since they have a small ion radius and good mobility. Cations (X') need not constantly be cations. A material which is converted into cations upon application of a voltage and hence an electric field thereto can be used. In particular, water is used as a cation source for H'. In this case, an amount of water can be very small, and moisture naturally permeated into the EC layer from air upon exposure of the ECD to air is enough.

However, even if the WO, layer is sandwiched by a pair of electrodes and causes emissions, emission cannot be immediately interrupted. Even if a reverse extinction voltage is applied to the pair of electrode layers, electrons (e ) are supplied from the electrode contacting the cathode and the following reaction occurs in the presence of H': WO3+ne +HnWO3 A conventional ECD is known which has an insulating layer made of SiO2 or MgF2 between a W03 layer and one electrode, as proposed by S.K. Deb et al. This insulating layer prevents free movement of electrons but allows that of ions such as H' or OH . The H' and OH ions carry electric changer (in this sense, this layer cannot be called the insulating layer but must be correctly called an ionic conduction layer).The following reaction of OH ions occurs at the interface between the ionic conduction layer and the anode: OH 1/2H,0+1/40,Tt-e The electrons are emitted toward the anode.

In the emission state, the following reactions can be assumed: Cathode: W03+ne +nH'-HnWO, Anode: nOH n/2H2O+n/402f+ne In the extinction state, the following reactions can be assumed: Cathode: HnWO3~WO3+ne +nH' Anode: nH2O+ne -nOH +n/2H2t As is apparent from the above reaction formulas, since water is consumed during emission and extinction of the ECD proposed by S.K. Deb et al, emission cannot be performed without smooth supply of water from air. In addition, O2 and H2 gases are generated upon driving, and peeling between the layers tend to occur.

In U.S. Patent No. 4,350,414, and ECD is proposed wherein an EC emission oxide layer is formed between an ionic conduction layer and an electrode layer. In this ECD, iridium oxide is used for the EC emission oxide layer. During emission of W03, the following reactions are assumed to occur in the anode: Transparent: Ir(OH)m+n(OH-)

Colored: Ir(OH)p.qH,O+ rH,O+S(e-) During extinction of W03, the following reactions are assumed to occur in the cathode: lr(OH)p.qH2O+rH2O+S(e-)

lr(OH)m+n(OH-) Therefore, water is regenerated and is not consumed. In addition, upon operation of the ECD, 2 and H2 gases are not generated.

Other conventional ECDs are exemplified by a combination of an EC layer and a lithium solidstate electrolytic layer and a combination of an EC layer and a proton-containing solid material, a proton-emissive solid material, or a semi-solid resin layer.

In any case, the ECD must be sealed in favor of reliability and durability of the ECD. In particular, in an ECD using water as a proton source, sealing must be performed not to leak water from the ECD layer. Epoxy resin or any other resin is generally used for sealing.

When the ECD is sealed, a drive voltage must be applied across a pair of electrode layers.

The electrode layers are partially exposed to use the exposed portions as electrode connecting terminals. External wires are bonded to these terminals.

Example of a transparent electrode material used in such an ECD are SnO2, In203, and ITO (a mixture of SnO2, and In203). These materials have relatively high electrical resistances. For this reasons, if the display area is large and emission extinction is caused, it takes a long period of time to cause emission/extinction of the entire area, and thus only a nonuniform emission/extinction distribution is obtained.

SUMMARY OF THE INVENTION: It is, therefore, an object of the present invention to provide an electrochromic element which eliminates the problems of nonuniform emission/extinction of the conventional element.

In order to achieve the above object of the present invention, there is provided an electrochromic element having a two-dimensional substrate, an upper electrode, an electrochromic layer, and a lower electrode, with at least the upper electrode, the electrochromic layer, and the lower electrode being formed on the substrate, characterized in that electrode terminals are formed in two opposite regions of the substrate.

Examples of the material for the upper and lower electrodes and the electrode terminals are a metal (e.g. Al, Ag, Ni, Pt, Au, Pd, Cr, Ir, Ru, and Rh), a transparent conductive oxide, e.g., SnO2, In203, an ITO (a mixture of SnO2 and In203), and carbon.

Electrode formation or lamination can be performed by a thin film formation method such as vacuum deposition, reactive deposition, ion plating, reactive ion plating, sputtering, reactive sputtering, or CVD (Chemical Vapor Deposition). A thick film formation method (a solution of an organic metal compound such as a metal alcolato or its olygomer is applied to a substrate and the resultant structure is baked to form a thick film) may be used as needed.

The thickness of the electrode varies depending on the resistances of the transparent conductive oxides but generally falls within the range of 0.01 to 0.5 Xtm. If a metal is used for the electrode, its thickness preferably falls within the range of 8 x 10 5 to 10 1 mm.

It is preferable to simultaneously form the electrode terminals of the upper and lower electrodes.

According to a first embodiment of the present invention, the electrode terminals are respectively formed along the long sides of a rectangular substrate. No terminals are formed along the short sides of the rectangular substrate. If the terminals are formed along the short sides, a distance between the short sides, that is, the distance substantially corresponding to the length of the long side becomes long and nonuniform emission/extinction tends to occur. However, according to a third embodiment of the present invention, the electrode terminals are formed along both short and long sides of a rectangular substrate.

A material for the EC layer is an EC emission reduced or oxide material. Examples of the EC reduced material are an inorganic oxide such as W03 and MoO3 and an organic material.

Examples of the EC emission oxide material are an inorganic material (e.g., iridium hydroxide or oxide, nickel hydroxide or oxide, chromium hydroxide or oxide, vanadium hydroxide or oxide, tellurium hydroxide or oxide, or rhodium hydroxide or oxide) and an organic material.

The EC layer can be used singly or in a two-layer structure consisting of the EC emission reduced and oxide layers. Alternatively, the EC layer may be additionally used together with an ionic conduction layer. The most preferable structure is a three-layer structure as EC emission reduced layer/ionic conduction layer/EC emission oxide layer (reversible electrolytic oxidation may be utilized although distinct emission does not occur).

The thickness of each of these EC layers is normally 0.01 to several ,um. The layer is generally formed by the thin film formation method described above.

The ionic conduction layer, formed if required, serves as an insulator for electrons but as a conductor for protons (H+) and hydroxyl ions (OH-). The ionic conduction layer is formed to provide a memory function to the ECD. In other words, even after the ECD is deenergized, the emission state is preserved. Examples of the ionic conduction layer are given as follows: (1) a thin film of inorganic dielectric, e.g., tantalum oxide (Ta205), niobium oxide (Nb2OS), zirconium oxide (ZrO2), titanium oxide (TiO2), hafnium oxide (HfO2), yttrium oxide (Y303), lanthanum oxide (La203), silicon oxide (SiO2), magnesium fluoride, zirconium phosphate, or a mixture thereof (these materials are insulators for electrons but conductors for protons (H+) and hydroxyl ions (OH-)). The thickness of the solid-state thin ECD can be very small.In addition, no liquid leakage occurs. In this case, the above inorganic dielectric is preferably used to form the ionic conduction layer; (2) a solid electrolyte such as sodium chloride, potassium chloride, sodium bromate, potassium bromate, Na3Zr2Si2PO,2, Na,+xZrSixP3xO,2, Na5YSi4O,2, or PbAg4l5; (3) water or a proton-source containing synthetic resin such as a copolymer bf methacrylic acid fi-hydroxyethyl and 2-acrylamide-2-methylpropane-sulfonate, a water-containing vinyl polymer such as a water-containing methacrylate copolymer, or water-containing polyester;; (4) an electrolytic solution such as an acid (e.g. sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, butyric acid, or oxalic acid), an aqueous solution thereof, an alkali solution (e.g., sodium hydroxide or potassium hydroxide), or an aqueous solution of a solid-state strong electrolyte (e.g., sodium chloride, lithium chloride, potassium chloride, or lithium sulfate); and (5) a semi-solid gel electrolyte such as a material obtained by gelating an electrolytic solution by a gelling agent such as polyvinyl alcohol, CMC, agar-agar, or gelatin.

The ionic conduction layer can be formed by a vacuum thin film formation technique, a thick film formation method, sealing, injection, coating, or any other method. The thickness of the ionic conduction layer falls within the range of 0.01 /zm to 1 mm.

Furthermore, the EC emission oxide layer, a reversible electrolytic oxide layer, or a catalyst layer may be used. Examples of such a material are an inorganic material (e.g., iridium hydroxide or oxide, nickel hydroxide or oxide, tellurium hydroxide or oxide, chromium hydroxide or oxide, vanadium hydroxide or oxide, or tellurium hydroxide or oxide) and an organic material. Such a material may be dispersed in another ionic conduction layer or a transparent electrode.

BRIEF DESCRIPTION OF THE DRA WINGS: Figure 1 is a schematic sectional view of an ECD according to a first embodiment of the present invention; Figures 2A, 2B, and 2C are respectively plan views for explaining steps in manufacturing the ECD shown in Fig. 1; Figures 3A, 3B, and 3C are respectively sectional views of the ECD shown in Fig. 2A to 2C taken along the lines thereof; Figure 4 is a schematic view showing electrical connections of a drive system to the ECD shown in Fig. 1; Figures 5A, 5B, and 5C are respectively plan views for explaining the steps in manufacturing an ECD according to a second embodiment of the present invention; Figures 6A and 6B are respectively schematic views showing a third embodiment of the present invention;; Figures 7A, 7B, 7C, and 8 are respectively plan views for explaining the steps in manufacturing the ECD of the third embodiment of the present invention; Figures 9A and 9B are respectively schematic views of a fourth embodiment of the present invention; Figure 10 is a sectional view of a fifth embodiment of the present invention; Figure 11 is a plan view of a sixth embodiment of the present invention; and Figure 12 is a view showing an improved laminated structure according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS: The present invention will be described in detail with reference to preferred embodiments of the present invention.

Fig. 1 is a sectional view of an ECD according to a first embodiment, and the steps in manufacturing this ECD are illustrated in Figs. 2A, 2B, and 2C (plan views) and Figs. 3A, 3B, and 3C (sectional views taken along the lines of Figs. 2A, 2B, and 2C).

(1) As shown in Fig. 2A, an ITO film was formed on a glass substrate S and was photoetched to obtain an ITO pattern, thereby forming a lower electrode B, its terminal B1, and an upper electrode terminal C. The lower electrode B and its terminal B1 were integrally formed.

They are not physically separated but conceptually classified for illustrative convenience.

Another means such as mask deposition may be employed in place of patterning by photoetching so as to obtain a desired pattern from the beginning. After the electrode is formed on the entire surface of the substrate S, the electrode layer may be patterned not by photoetching but by laser cutting.

The characteristic feature of the first embodiment of the present invention lies in the fact that strip-like electrode terminals are respectively formed along the long sides of the substrate. For this reason, a groove for isolating the upper electrode terminal C from the lower electrode B is parallel to the long sides of the substrate S.

(2) As shown in Figs. 2B and 3B, an iridium oxide-tin oxide mixture layer D, a tantalum oxide layer E, and tangsten oxide layer F were sequentially formed on the substrate S in the order named.

(3) As shown in Figs. 2C and 3C, an Al electrode A was formed by mask deposition. In this case, part of the Al electrode A was electrically connected to one end of the terminal C.

(4) As shown in Fig. 1, finally, the resultant structure was sealed with epoxy resin R, except for its parts contacting the edges of the electrode terminal C and the electrode B. At the same time, a protective glass plate G having a size slightly smaller than the size of the substrate S was adhered to the epoxy resin to prepare an ECD.

The preparation process and conditions of each layer are summarized in Table 1.

Only the exposed ECD portions outside the sealing region R are parts of the ITO electrodes C and B1. As shown in Fig. 4, external wires LA and LB are bonded to the exposed portions, respectively. When a coloring voltage (+ 1.35 V) was supplied from a drive supply (Su) to the electrodes C and B1, the reflectance of light L having a wavelength of 633 nm and incident on the substrate S of the ECD was decreased to 15% (one second after the voltage application).

The reflectance was maintained even if the ECD was deenergized. When an extinction voltage (- 1.35 V) was then applied to the ECD, the reflectance was recovered to 65% (one second after the voltage application).

The resultant ECD was dipped in warm water at 70"C for 100 hours. The electrodes B and C did not peel from the substrate S and exhibited substantially the same characteristics as in the state prior to dipping.

The best effect was obtained when a ratio of the short sides to the long sides is 1:2. Table 1

Layer Vacuum Thin Condition Film Film formation Film Formation Thick- Technique Substrate Vacuum Rate Symbol Material ness Temperature (#/second) (#) ( C) (Torr.) B ) O ITO 1000 Vacuum deposition 300 O2 : 2x10-4 2 Iridium oxide D tin monoxide 1200 RP ion plating Room O2 : 4x10-4 1 Mixture film Temperature E Tantalum 10000 " " O2 : 4x10-4 6 oxide F Tungsten 5000 Vacuum deposition " Ar : 4x10-4 6 oxide A Al 1000 " " 2 x 10-5 4 A second embodiment exemplifies an anti-glare mirror serving as a rear-view mirror in an automobile. The structure of the second embodiment is substantially the same as that of the first embodiment, except that the sectional shape of the substrate is elliptical. Fig. 5A corresponds to Fig. 2A; Fig. 5B, to Fig. 2B; and Fig. 5C, to Fig. 2C.

In a third embodiment of the present invention, as shown in Figs. 6A and 6B, the outer edge of a strip-like supplementary terminal C of an upper electrode and an inverted U-shaped outer edge of a lower electrode B are exposed with an appropriate size.

A bucket-like clip CA having a substantially U-shaped section and a length substantially corresponding to one side of a substrate S is prepared for the supplementary electrode terminal of the upper electrode A having a low electrical resistance. A U-shaped conductive clip CB having sides each with a length corresponding to each of the remaining sides of the substrate is prepared for the lower electrode B having a high electrical resistance. As shown in Fig. 7C, the clip CA is mounted on the strip-like outer edge of the supplementary electrode terminal. The clip CB is mounted on the U-shaped outer edge of the lower electrode B, thereby obtaining the electrode terminals.

Each clip is prepared such that a 0.05- to 2-mm thick plate made of a metal such as phosphor bronze and having elasticity is bent to obtain a U-shaped member. The electrical resistance of the upper electrode is greatly higher than that of the lower electrode.

External wires LA and LB are respectively bonded to the clips CA and CB by soldering or a conductive adhesive.

The electrical connections of the external wires need not be made at opposite positions of Fig. 6A. However, the positions of the external wires may be close to each other.

Furthermore, epoxy resin (R) is applied to the surface of the resultant structure, and a protective glass plate G having the size defined by the clips CA and CB is placed on the epoxy resin R. The resin R is then cured to seal the ECD. The resin R and the glass plate G are omitted in Figs. 6A and 6B.

When the size of the ECD was given as 9.2 cmx 19.2 cm and a coloring voltage (+ 1.35 V) was applied from a drive supply to the external wires LA and LB, the reflectance of the ECD was decreased to 15% (10 second after the voltage application) when light having a wavelength 633 nm was incident on the substrate S. Even if the ECD was deenergized, the reflectance was maintained for a given period of time. When an extinction voltage (- 1.35 V) was applied to the wires LA and LB, the reflectance was recovered to 65% (10 seconds after the voltage application).

In the third embodiment, when an Al electrode A as an upper electrode was formed by mask deposition, the mask shape was changed to simultaneously form the upper Al electrode A and a strip-like terminal CA continuous therewith as well as a U-shaped terminal CB and an ITO terminal of a lower electrode B. The clips used in the third embodiment were not used in the fourth embodiment.

The resultant ECD is illustrated in the plan view of Fig. 9A and the sectional view of Fig. 9B.

In the fourth embodiment, an ITO supplementary electrode terminal Al of an upper Al electrode A was not formed on the substrate. At the time of mask deposition of the Al electrode A as the upper electrode, the shape of the mask was changed to simultaneously form the Al electrode A and a strip-like electrode terminal CA continuous therewith as well as a U-shaped electrode terminal CB separated from the upper electrode A and an ITO electrode terminal of the lower electrode. Therefore, the clips used in the third embodiment were not used in the fifth embodiment.

The resultant ECD is illustrated in the sectional view of Fig. 10.

A sixth embodiment exemplifies an anti-glare mirror serving as a side-view mirror in an automobile, as shown in Fig. 11. The structure of the sixth embodiment is substantially the same as that of the third embodiment, except that the shape of an aluminium electrode A corresponding to the reflecting surface of the mirror is not rectangular.

Fig. 12 shown an improved laminated structure according to the present invention. Some of the layers described above are inverted.

Claims (19)

1. An electrochromic element including: a) a substrate; b) a first electrode; c) an electrochromic layer; d) a second electrode, said first electrode being formed on said substrate in the order named; e) a first conductive portion formed on said substrate, said first conductive portion being electrically connected to said first electrode such that a first region electrically connected to said first electrode extends along substantially one direction; and f) a second conductive portion formed on said substrate, said second conductive portion being electrically connected to said second electrode such that a second region electricaly connected to said second electrode extends along substantially said one direction and that said first and second regions sandwich said first electrode.

2. An element according to claim 1, further including means for giving a potential difference between said first and second conductive portions.

3. An element according to claim 2, wherein said substrate transmits at least part of radiation, said first electrode transmits at least part of radiation, and said second electrode reflects at least part of radiation.

4. An element according to claim 2, wherein said substrate has a substantially rectangular shape, said first region is formed along one long side of said substrate, and said second region is formed along the other long side of said substrate.

5. An element according to claim 4, wherein said substrate transmits at least part of radiation, said first electrode transmits at least part of radiation, said first electrode transmits at least part of radiation, and said second electrode reflects at least part of radiation.

6. An element according to claim 5, wherein said first electrode has an electrical resistance higher than that of said second electrode, and each of said first and second conductive portions has an electrical resistance lower than that of said first electrode.

7. An element according to claim 2, wherein said substrate has a substantially rectangular shape, said first region is formed along three continuous side of said substrate, and said second region is formed along a remaining one side of said substrate.

8. An element according to claim 7, wherein said substrate transmits at least part of radiation, said first electrode transmits at least part of radiation, and said second electrode reflects at least part of radiation.

9. An element according to claim 8, wherein said first electrode has an electrical resistance higher than that of said second electrode, and each of said first and second conductive portions has an electrical resistance lower than that of and said first electrode.

10. An element according to claim 2, wherein said substrate has a shape extending along one direction, and said first and second regions are formed so as to extend along said one direction.

11. An element according to claim 10, wherein said substrate transmits at least part of radiation, said first electrode transmits at least part of radiation and said second electrode reflects at least part of radiation.

12. An element according to claim 11, wherein said first electrode has an electrical resistance higher than that of said second electrode, and each of said first and second conductive portions has an electrical resistance lower than that of said first electrode.

13. An element according to claim 2, wherein said substrate transmits at least part of radiation, said first electrode transmits at least part of radiation, and said second electrode reflects at least part of radiation, and wherein said first electrode has an electrical resistance higher than that of said second electrode, and each of said first and second conductive portions has an electrical resistance lower than that of said first electrode.

14. An element according to claim 13, wherein said first electrode and said first conductive portion are connected such that said first region is larger than said second region.

15. An electrochromic element comprising an electrochromic layer sandwiched between upper and lower electrodes and defining an electrochromically active area of the element, and terminals contacting said upper and lower electrodes throughout elongate opposed and spaced apart regions encompassing therebetween the said active area.

16. An electrochromic element comprising a substrate, a first electrode formed on said substrate, an electrochromic layer overlying said first electrode, a second electrode overlying said photochromic layer, said overlying electrode and photochromic layers defining an active area of the element, and first and second terminals formed on said substrate and contacting said first and second electrodes respectively in each case over an extensive region thereof with the respective regions encompassing therebetween substantially all of said active area.

17. An electrochromic element comprising a substrate having a two-dimensional surface, an upper electrode, an electrochromic layer, and a lower electrode, at least part of the upper electrode, the electrochromic layer, and the lower electrode being formed on the substrate, and electrode terminals contacting said upper and lower electrodes formed on two opposite regions of the substrate.

18. An electrochromic element having terminals of a higher electrical conductivity than the electrodes of the element overlying the said electrodes throughout areas thereof which substantially encompass therebetween the active area of the element.

19. An electrochromic element substantially as hereinbefore described with reference to any of the accompanying drawings.