An all solid-state variable transmission electrochromic device has a source of charge compensating ions. An inorganic oxide counterelectrode film which on reduction with the accompanying insertion of the charge compensating ions increases its transmission of light of predetermined wavelength is separated from a primary electrochromic film which on reduction with the accompanying insertion of the charge compensating ions decreases its transmission of light of predetermined wavelength by an insulating electrolyte film that transports the charge compensating ions. First and second electrodes are contiguous with the inorganic oxide counter electrode film and the primary electrochromic film, respectively, and separated by the three films.
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1. A solid-state variable transmission electrochromic device comprising,
a source of charge compensating ions, an inorganic oxide electrochromic counter electrode film composed of a mixture of at least two oxides with a first of said oxides an oxide of a metal from the group consisting of vanadium and chromium and a second of said oxides an oxide of a different metal from the group consisting of V, Cr, Nb, Ta and ti which on reduction with the accompanying insertion of said charge compensating ions increases its transmission of light of predetermined wavelength, a primary electrochromic film which on reduction with the accompanying insertion of said charge compensating ions decreases its transmission of light of said predetermined wavelength, an insulating electrolyte film contiguous with and separating said inorganic oxide counter electrode film and said primary electrochromic film for the transport of said charge compensating ions therebetween, first and second electrodes contiguous with said inorganic oxide counter electrode film and said primary electrochromic film respectively and separated by said inorganic oxide counter electrode film, said insulating electrolyte film and said primary electrochromic film, said first and second electrodes being for receiving an electric potential therebetween for producing a current flow such that electrons flow into one of said electrodes and out of the other and said charge compensating ions flow through said insulating electrolyte film from that one of said inorganic oxide counter electrode and said primary electrochromic film being oxidized to that one thereof being reduced for modulating said device between states of minimum and maximum transmission at said predetermined wavelength with the direction of transmission change being determined by the direction of current flow.
2. The device of
wherein the reflectivity of said device may be modulated between a state of maximum reflectivity and a state of minimum reflectivity by controlling the absorption of said device with a potential applied between said first and second electrodes.
3. The device of
wherein the transmittance of said device may be controlled between a state of maximum transmittance and a state of minimum transmittance in response to a potential applied between said first and second electrodes.
4. A device in accordance with
said inorganic oxide counter electrode film is a mixture (V2 O5)1-x (Nb2 O5)x (x═0.01-0.99) prereduced with Li, said insulating electrolyte film is sputtered from a composite target of 42% Li2 O, 25% SiO2 and 32% ZrO2, said charge compensating ions are lithium, said first electrode is reflective aluminum, (X═ and said second electrode is transparent and tin-doped indium oxide on a substrate.
5. A device in accordance with
said inorganic oxide counter electrode film is a mixture (V2 O5)1-x(Nb2 O5)x(x═0.01-0.99) (V2 O5)1-x (Nb2 O5)x (x═0.01-0.99) prereduced with Li, said insulating electrolyte film is sputtered from a composite target of 42% Li2 O, 26% SiO2 and 32% ZrO2, said charge compensating ions are lithium, said first electrode is reflective aluminum, and said second electrode is transparent and tin-doped indium oxide on a substrate.
6. A device in accordance with
said inorganic oxide counter electrode film is a mixture (V2 O5)1-x (Nb2 O5)x, X═0.01-0.99) prereduced with Li, said insulating electrolyte film is sputtered from a composite target of 42% Li2 O, 26% SiO2 and 32% ZrO2, said charge compensating ions are lithium, said first electrode is reflective aluminum, and said second electrode is transparent and tin-doped indium oxide on a substrate, wherein the reflectance of said device may be controlled between a state of maximum transmittance and a state of minimum transmittance in response to a potential applied between said first and second electrodes.
7. A device in accordance with
8. A device in accordance with
said counter electrode is a mixture (V2 O5)1-x(Nb2 O5) x (x═0.01-0.99) (V2 O5)1-x (Nb2 O5)x (x═0.01-0.99) prereduced with Li, said insulating electrolyte film is poly (bismethoxyethoxymethoxide) phosphazine doped with LiCF3 SO3, and said first and second electrodes are tin-doped indium oxide deposited upon glass.
9. A device in accordance with claim 1 3 wherein said primary electrochromic film is tungsten trioxide,
said counter electrode is a mixture (V2 O5)1-x (Nb2 O5)x (x═0.01-0.99) prereduced with Li, said insulating electrolyte film is poly(bismethoxyethoxymethoxide) phosphazine doped with LiCF3 SO3, and said first and second electrodes are tin-doped indium oxide deposited upon glass, wherein one of said electrodes is a thin film transmissive at said predetermined wavelength and the other of said electrodes is reflective at said predetermined wavelength,
wherein the reflectivity transmissivity of said device may be modulated between a state of maximum reflectivity transmissivity and a state of minimum reflectivity transmissivity by controlling the adsorption absorption of said device with a potential applied between said first and second electrodes. 10. A device in accordance with
said counter electrode is a mixture (V2)5)1-x(Nb2 O5)x (x═0.01-0.99) (V2 O5)1-x (Nb2 O5)x (x═0.01-0.99) prereduced with Li, said insulating electrolyte film is poly (bismethoxyethoxymethoxide) phosphazine doped with LiCF3 SO3, and said first and second electrodes are tin-doped indium oxide deposited upon glass.
11. A device in accordance with
said counter electrode is a mixture (V2 O5)1-x(Nb2 O5)x (x═0.01-0.99) (V2 O5)1-x (Nb2 O5)x (x═0.01-0.99) prereduced with Li, said insulating electrolyte film is poly (bismethoxyethoxymethoxide) phosphazine doped with LiCF3 SO3, and one of said electrodes is tin-doped indium oxide deposited onto glass and the other of said electrodes is a reflective aluminum film on glass.
12. A device in accordance with
said counter electrode is a mixture (V2 O5)1-x(Nb2 O5)x (x═0.01-0.99) (V2 O5)1-x (Nb2 O5)x (x═0.01-0.99) prereduced with Li, said insulating electrolyte film is poly (bismethoxyethoxymethoxide) phosphazine doped with LiCF3 SO3, and one of said electrodes is tin-doped indium oxide deposited onto glass and the other of said electrodes is a reflective aluminum film on glass.
13. A device in accordance with
said counter electrode is a mixture (V2 O5)1-x (Nb2 O5)x (x═0.01-0.99) prereduced with Li, said insulating electrolyte film is poly(bismethoxyethoxymethoxide) phosphazine doped with LiCF3 SO3, and one of said electrodes is tin-doped indium oxide, deposited onto glass and the other of said electrodes is a reflective aluminum film on glass, wherein the reflectance of said device may be controlled between a state of maximum transmittance and a state of minimum transmittance in response to a potential applied between said first and second electrodes. 14. A device in accordance with claim 1 wherein said primary electrochromic film is tungsten trioxide, said inorganic oxide counter electrode film is a mixture (V2 O5)1-x (Nb2 O5)x (x═0.01-0.99) prereduced with Li, said insulating electrolyte film is sputtered from a composite target of 42% Li2 O, 26% SiO2 and 32% ZrO2, said charge compensating ions are lithium said first electrode is reflective aluminum, said second electrode is transparent tin-doped indium oxide, one of said first and second electrodes being on a substrate.
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This invention was made with Government support under Contract No. DE-AC03-87SF16733 awarded by the Department of Energy. The Government has certain rights to this invention.
This application is a S2 O4 ═ S2 O4.dbd. for the H-inserted form. Alternatively, it may be accomplished by vacuum processing in a separate step, such as sputtering from a Li target or a target which decomposes to give Li atoms in the vapor phase, or exposing to an H2 plasma for H-insertion. Further, the layer may be produced by vapor deposition of the reduced material directly using a source or target of the desired composition, or a reducing reactive atmosphere to transform the source or target to the desired composition during the deposition process.
The above procedure enables the device to be assembled with one electrode in fully oxidized state and the other fully reduced, which would represent either the extreme colored or extreme bleached state of the device. Alternatively, layers 16 and 18 may be prepared in some intermediate state of oxidation, e.g., by shorting out fully oxidized and fully reduced layers in the presence of electrolyte prior to assembly. This procedure reduces the chemical activity of either layer, rendering either less susceptible to chemical reaction during the assembly procedure.
The structures are assembled by laminating layer 20 between the substrates coated with contiguous layers 12 and 16 on one substrate and 12' and 18 on the other.
In operation, layers 12 and 12' are connected to an external current source. If electrons are supplied through layer 12, layer 16 will become reduced, with the accompanying insertion of a charge compensating cation from the electrolyte. Simultaneously, electrons will be withdrawn from layer 18, with the accompanying expulsion of a charge compensating cation into the electrolyte. The electrolyte conducts ions from layer 18 to layer 16. If the polarity of the current is reversed, layer 16 18 16 and layer 16 18 become oxidized and reduced, respectively, and the flow of charge compensating cations through the electrolyte is reversed in direction. When all of the charge compensating ions from layer 16 have been transferred to layer 18, or when layer 18 is reduced as far as possible and has accepted as many charge compensating ions as possible, the device is in its fully colored state. Similarly, the device is in its fully colorless state when the maximum charge compensating ions have been transferred from layer 18 to layer 16.
Since device 10 has a well-defined relationship between voltage and state of charge, a voltage may be imposed between 12 and 12' and a current be allowed to flow to adjust to that voltage difference, the resulting transmittance being predictable from that voltage difference alone. This feature of truly reversible electrochromic devices allows for simplified control electronics, especially with the relationship between transmittance and voltage difference.
Referring to FIG. 2, there is shown a device substantially similar to that of FIG. 1, but with a thin film solid electrolyte, 0.01 to 10 μm thick, preferably 0.1 μm. This device comprises a multilayer thin film stack. Corresponding reference symbols identify identical elements in FIGS. 1 and 2. Device 30 is prepared by sequential deposition of the layers by thin film processes, preferably vacuum sputtering. The solid electrolyte 32 is a ceramic which conducts ions, but not electrons. Suitable Li+ conductors for layer 32 are ternary mixtures of Li2 O, ZrO2 and SiO2, and simple compounds of Li which behave as electrolytes, such as LiNbO3, LiTaO3, Li3 N, LiI, Li2 WO4 and LiA1F4, and variants and mixtures thereof. Suitable proton conductors are partially hydrated electronically insulating inorganic oxides or fluorides, such as SiO2, A12 O3, Ta2 O5, Nb2 O5, and MgF2. The device in FIG. 2 also may be made with layers 16 and 18 reversed.
In the Li-based device, one of the layers is prepared in the Li-inserted, reduced form while the other layer is prepared in the fully oxidized form. For Example Lix WO3 may be prepared by sputtering from a Li2 WO4 target in a reducing atmosphere, from a Li/W alloy target in a partially oxidizing atmosphere, or by sputtering metallic Li directly onto a WO3 layer. In the H-based device, hydrogenated electrode layers may be produced by introducing the fully oxidized layer into a hydrogen plasma. By preparing the device in this way, the finished device will be either in its fully colored or fully bleached state, depending on whether the primary electrochromic layer 18 on the counter electrode layer 16 is initially reduced.
The operation of the embodiment in FIG. 2 is identical to that in FIG. 1.
FIG. 3 shows a spectrum of transmittance versus wavelength for a typical structure in its two extreme states, also referred to in the examples. The difference in transmission at the wavelength of modulation between these two extreme states represents the dynamic range of the device at that wavelength. All intermediate values of light transmission within that dynamic range are possible. When any coloration state is reached, the current source may be removed and that state is retained until current is resumed in either direction.
Applications of devices 10 and 30 include windows with adjustable transmittance for glare reduction and energy efficiency, and solar panels. They can be used as light attenuators for active information displays, such as electroluminescent displays. They can be incorporated into photographic equipment, e.g., as variable grey scale filters and as lens diaphragms. If applied to reflective substrates, these devices may be used as a variable reflectance mirror, e.g., for rearview automotive mirrors. By eliminating electrolyte 32, which will allow under some conditions switching but eliminate substantial open circuit optical memory, device 30 can be used for high frequency (<1 Hz) as light modulation under the excitation of an ac electrical current. The invention may thus be useful for analog or digital modulation of optical frequency carriers.
PAC EXAMPLE 1The first example demonstrates the effect of increased transmittance during reduction and decreased transmittance during oxidation for two members of a group of counter electrode materials according to the invention. The effect is described by the use of colorization efficiencies which relate the optical density change (ΔOD) to the quantity of lithium intercalated into the film (q, in coulombs/cm2) through the equation,
OD(λ)═CE(λ)q (1)
wherein CE(λ) is the wavelength dependent coloration efficiency. In equation (1), a negative value of q is defined to represent deintercalation of lithium (i.e., oxidation) from the electrochromic layer. A negative value of CE(λ) represents a film which becomes increasingly transmissive during reduction with lithium.
An ITO-coated glass substrate was coated further with a thin film of the mixed oxide counter electrode material. These coatings were deposited by reactive radio frequency (rf) magnetron sputtering from a composite target of the parent metals. In this way, one counter electrode film was prepared from a mixed target containing 50 mole percent Cr and 50 mole percent V, while another was prepared from a 35:65 Nb, V target. The metal composition of the deposit reflected that of the targets, as determined by surface spectroscopic analysis. Conditions for the desired reduced-state visible transmittance were similar for both oxides: a sputter gas composition of 10% oxygen in argon was introduced into the vacuum chamber at a flow rate of 10 sccm and maintained at a total pressure of 35 μm. An rf power density of 5 watts/cm2 at the metal target was employed during the deposition and the substrate was allowed to thermally equilibrate with the plasma to a typical substrate temperature of 120°C The distance between the target and the substrate was 5 cm. A typical as-deposited film thickness is 0.15 μm, with a reversible lithium capacity of 15 mC/cm2.
The coloration efficiencies of the films were determined as a function of wavelength by electrochemical reduction and oxidation with lithium in a spectrophotometer. The coloration efficiencies are shown in FIG. 4. The coloration efficiencies of both materials are small and negative over the entire wavelength range of interest, indicating that reduction with lithium causes them to become increasingly transmissive over a 350 to 1400 nm wavelength range. Furthermore, multicycle electrochemical reduction-oxidation testing of the mixed oxides over 2000 cycles has demonstrated that these materials undergo a large number of optical switching cycles without degradation or accompaniment of irreversible side reactions.
The second example comprises electrochromic light modulators employing a Li+ -conducting polymer electrolyte and the mixed oxide counter electrodes. The primary electrochromic layer, amorphous WO3, was first deposited onto ITO-coated glass by reactive rf magnetron sputtering. A reactive sputter gas composition of 10% oxygen in argon was employed in the vacuum chamber at a flow rate of 10 sccm and maintained at a total pressure of 100 μm. The deposition was carried out at an rf power density of 5 watts/cm2 at the target with a substrate to target distance of 5 cm. The temperature of the substrate was controlled by thermal equilibrium with the plasma and is typically 120°C The deposition was carried out for a sufficient length of time that the thickness of the WO3 film was 0.2 μm, and the film was capable of reversible reduction and oxidation with the alkali insertion ion to a level of 15 mC/cm2.
A second ITO-coated glass substrate was coated with a counter electrode material comprised of a thin sputtered film of amorphous (Cr0.5 V0.5)Oy or (Nb0.35 V0.65)Oz, as described in the first Example. The counter electrode film was electrochemically reduced with lithium by the double injection process (Li+ and electron) in an electrolyte of 1N LiClO4 /propylene carbonate so that the film contains 15 mC/cm2 of intercalated lithium. The resulting counter electrode film thus had the composition Lix (Cr0.5 V0.5)Oy or Lix (Nb0.35 V0.65)Oz, with x approximately equal to unity in the fully reduced state. The lithium acts as the charge compensating ion during electrochemical reduction of the primary and counter electrode layers.
An electrochromic light modulator was then fabricated by laminating the substrates containing the WO3 and reduced counter electrode films together with a Li+ conducting polymer that is transparent over the wavelength range of desired transmittance modulation. The Li+ conducting polymer in this example, was a mixture of N-methyl pyrrolidone (PVP) and polyethylene glycol (PEG) doped with LiCF3 SO3. The PVP/PEG mixture had the weight ratio of 40/60 and the ratio of LiCF3 SO3 /PVP-mer was 3:1. The application of a voltage between the ITO electrodes caused the transmittance of the light modulator to be controlled as a unique function of the applied voltage. FIG. 3 shows the transmittance spectra for the two extreme optical states of the device described with the V:Nb:O counter electrode. The device with the V:Cr:O counter electrode gave nearly identical performance. In both cases, the most transmissive state was obtained with an applied voltage of 1.5 volts with respect to the WO3 layer and the least transmissive at a voltage of -2.0 volts with respect to the WO3 layer.
In the third example, an all solid-state electrochromic light modulator was fabricated by sequential RF sputtering of an active electrochromic material (a-WO3), an oxide-based Li+ conductor (Li2 O.SiO2.ZrO2), and a V:Nb:O counter electrode as described in the previous examples. Lithium was electrochemically intercalated into the a-WO3 layer and an aluminum top-contact was evaporated onto the counter electrode layer. The light modulator has the following structure, glass/ITO/aLi x WO3 /Li2 O.SiO2.ZrO2 /(Nb0.035 V0.65)Oy /aluminum In the as-fabricated condition the light modulator exhibited a deep blue coloration and low specular reflectance when viewed through the glass side. When a potential of -2.0 volts with respect to the aluminum layer was applied between the aluminum and ITO contacts the WO3 layer, the modulator became highly reflecting as viewed through the glass. A charge transfer of only 10 mC/cm2 was required to achieve this optical modulation.
Other embodiments are within the appended claims.
Cogan, Stuart F., Rauh, R. David
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