Patent Application
20150315035
The present invention relates an electrochromic film and the method of making the film. The film may be used for optical modulation.
The U.S. Department of Energy has estimated that the use of smart windows could reduce peak electric loads in buildings by 20-30%, but cost and unsatisfactory performance are two issues that limit wider adoption of this technology. Smart glass, also referred to as switchable, dimmable, or dynamic glass or glazing, varies the light transmittance and thermal properties of windows depending on changing ambient conditions and the needs of users and occupants. This class of high-performance glazing products offers significant energy efficiency, aesthetic, and user comfort and wellbeing benefits as compared to conventional “static” glazing. As benefits this industry, building and automotive design trends are showing a greater use of smart glass. Concurrently, changes in building codes and increased adoption of green building standards point to design challenges in managing heat gain and glare from increased glazing area ratios. Smart glass addresses these various market drivers.
Starting from a low base, smart glass for use in architectural and transportation facades, windows, and privacy screens is forecast to become a nearly $700 million sector of the flat glass market by 2020. The market will be dominated by architectural applications, mirroring overall market figures for flat glass globally, which are heavily skewed toward the buildings sector. Significant new production capacity entering the market in the near term will help drive down production costs and reduce the substantial price premium between static and dynamic glass, contributing to increased market share.
Tungsten Oxide (WO3) is a transition metal oxide which is well-known for its non-stoichiometric properties that enable its use in numerous applications including electrochromics, photocatalysis, and sensor technology. Among these applications is electrochromic windows for both aesthetics and energy efficiency, which are the most highly developed applications with commercial products entering the market. The buildings sector consumes more energy than transportation or industry, accounting for 40% of energy expenditures in the US. Windows are responsible for a significant fraction, strongly influencing the cooling, heating and lighting requirements. Smart windows employing electrochromics have the potential to significantly reduce this energy footprint by controlling solar heat gain and lighting through modulation of their optical characteristics (i.e. transmittance, reflectance).
Tungsten oxide is the leading cathodic electrochromic material due to its excellent optical properties and reversibility in response to an applied voltage. There have been significant progress in the forty years since Deb's pioneering studies (S. K. Deb, Philosophical Magazine, 1973, 27, 801). Current applications for electrochromatic materials are mostly limited to niche markets such as dimmable rear view mirrors and the windows of Boeing's Dreamliner. Further improvements in both performance and cost reduction are required to enable widespread deployment of this technology. For example, a minor complaint about the Dreamliner is that the windows do not get dark enough. However, cost remains the main driver that must be addressed, particularly for energy efficient window applications.
Numerous techniques have been developed for the synthesis of WO3 thin films. Physical vapor deposition techniques such as sputtering and thermal evaporation have been used extensively, but a drawback of these deposition techniques is the requirement for high vacuum chambers. In addition, these techniques typically produce dense films, and it can be challenging to efficiently introduce nanostructure or porosity.
Sol-gel chemistries combined with sacrificial templating agents can be used to create mesoporous structures that promote fast and efficient ion intercalation. Originally pioneered for silica, these strategies have been developed for numerous metal oxides as well as other materials through functionalization of silica. Application of these techniques to mesoporous WO3 have demonstrated remarkably improved electrochromic properties.
Critical performance metrics for electrochromic materials include optical modulation, coloration efficiency, switching speed, and durability. The optical modulation (ΔT) is the difference in transmission between the bleached and colored states. The highest value reported to date for tungsten oxide is ΔT=85%, which in both cases was achieved in films deposited using sol gel chemistry. Coloration efficiency (CE) is based on the transmission change normalized by the amount of charge insertion as described by Equation (1):
where Q is the amount of charge inserted and A is the area of the sample. Leading films report coloration efficiencies on the order of 50 cm2/C, and the highest reported to date of CE=64 cm2/C was obtained using a proton containing electrolyte. There is no established standard for quantifying switching speed, but the most common metric employed is the time required to obtain 90% of full optical modulation, and time scales on the order of 10 s are commonly reported for nanostructured WO3 films for small samples (˜1 cm2). These values are not suitable for comparison with the performance in an actual window. In addition, the switching speed will be different for samples that are not measured with a solid state electrolyte (which will impede switching speed in a fully integrated material). Crystallinity is a key metric impacting durability. Nanocrystalline WO3 films have displayed better coloration efficiency and cycling stability than either amorphous WO3 or bulk crystal WO3 films. Mesoporous, crystalline WO3 films provide an ideal morphology that imparts durability along with high surface specific area for efficient ion intercalation.
Sol-gel approaches have produced high performance material, but the techniques employed to produce these results such as dip coating, spin coating, or evaporation induced self assembly are generally quite slow and not amenable to large scale, in line manufacturing. The present invention addresses these and other issues.
Electrochromic WO3 films are generally produced by ultrasonic spray deposition techniques using templated sol-gel chemistry. By optimizing the sol (solution) composition mesoporous films are produced whose transparency in the visible may be modulated from about 0 to 100% during electrochemical cycling. The films display fast switching kinetics, producing an about 75% change in absolute transmission in about 3 seconds and about 27 second during coloration and bleaching, respectively. Optimum electrochromic performance can be achieved by controlling the sol concentration and/or the application thickness in this robust process. The excellent performance is attributed to the nanocrystalline nature of the films, which provides high specific surface area (>about 100 m2/g) for efficient lithium ion intercalation.
Smart windows are solar control devices that can electronically regulate the flow of sunlight and heat. The present invention includes a series of thin films deposited onto a glass substrate, one on top of the other, to form a functional electrochromic stack. The outermost layers can be transparent conductors, which can be used to apply a voltage to the active layers sandwiched between them. The active layers include an electrochromic (EC) layer, an ion conductor (IC) layer, and a counter electrode layer (CE). The EC layer is responsible for the majority of optical modulation, and the material of the EC layer is tungsten oxide that is commonly employed in commercial devices, including architectural product devices.
The present invention describes a unique chemistry and fabrication approach that produces mesoporous tungsten oxide films capable of modulating optical transmission up to the theoretical limit of about 100% in the visible regime (>about 550 nm). The novel process is based on adopting established sol-gel chemistry to ultrasonic spray deposition (USD). USD is performed under ambient conditions as opposed to high vacuum sputtering (the standard commercial process), and as such is more amenable to in-line, high volume, low cost manufacturing. Though the focus of the present invention is electrochromics, mesoporous thin films are employed in a number of applications including membranes, batteries, and filters, and solar cells. The process described here is expected to be highly amenable to a wide range of mesoporous materials.
This process is distinct from conventional spray pyrolysis, where a heated substrate is used to drive the chemistry involved in film formation. Advantages of USD include low capital requirements and materials utilization that approaches about 100%. Moreover, the use of benign solvents such as water and alcohol enables processing under ambient conditions. USD has also been used to produce high performance nickel oxide, a leading counter electrode in the electrochromic stack, and as such one could envision employing USD for in-line production of complete devices.
The baseline process employed in the present invention is nearly identical to conventional sol-gel processing, with the exception that the sol is deposited by USD onto an unheated substrate instead of by spin coating. The sol is comprised of WCl6 and an organic templating agent (P123) dissolved in ethanol. Films are then placed into a humidified environment to facilitate hydrolysis and gelation. Lastly, a high temperature calcination step is used to remove the organic template, complete the oxidation process, and induce crystallinity. The annealing step is critical, and that best results were obtained with rapid annealing in which the substrates directly on a hot plate maintained at 350° C. Under these conditions films displayed about 75% optical modulation, in some embodiments up to about 100% optical modulation, a coloration efficiency of about 50 cm2/C, and very fast switching times (<10 s).
Performance of the coating correlates with the nanostructure and the specific surface area of the nanocrystalline films. The shape and size of the mesoporous networks may be directed through the control of parameters such as sol composition. The volume fraction of the block copolymer can be used for the rationale control of nanostructure, and optimization of this critical parameter has been used successfully to control porosity and increase specific surface area in a number of material systems.
The present invention relates an electrochromic film and the method of making the film. The film may be used for optical modulation.
Sol-gel: is shorthand for solution gelation chemistry, which generally means a liquid solution that evolves into a gel like state through stirring and/or drying.
An aspect of the invention is a method to produce an electrochromic film. The method includes providing sol, wherein the sol comprises WCl6 and an organic templating agent dissolved in an alcohol. The baseline solution was prepared by dissolving 1 g of Triblock polymer Pluronic P123 (poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene), EO20PO70EO20) into 10 ml of anhydrous ethanol. The sol was completed by adding about 0.595 g of WCl6 (≧99.9%) followed by 12 hours of stirring. The sol is deposited by ultrasonic spray deposition onto an unheated substrate, which does not require spin coating. The films are placed into an approximately 100% humidified environment to facilitate hydrolysis and gelation. The films are then subjected to a high temperature calcination step to remove the organic template, complete the oxidation process, and induce crystallinity. The resulting WO3 films may greater than about 85% optical modulation across the visible spectrum. In some embodiments, the films may display about 100% optical modulation across the visible spectrum through optimization of the sol composition.
The mass ratio (WCl6:Organic templating agent) may be between about 0.1 and about 5. In some embodiments, the ratio may be between about 0.2 to about 2, in some embodiments between about 0.3 to about 1. In some embodiments, the reagent ratio may be about 0.595.
The organic templating agent may be any suitable organic templating agent, including but not limited to Pluronic P123 (poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene), EO20PO70EO20), or another agent that includes a triblock copolymer. The alcohol may be any suitable alcohol, including but not limited to ethanol, methanol, isopropanol, propanol, combinations thereof, or the like.
The reagent ratio will impact of the total concentration in alcohol. The concentration of the WCl6 in the alcohol may be between about 0.5 mM to about 5 mM, in some embodiments about 1.5 mM to about 3 mM. In some embodiments, the concentration may be about 1.5 mM, about 2.25 mM, or about 3 mM. Concentrated sols at 1.5, 2.25 and 3 mM, are denoted in the description as 1C, 1.5C and 2C, respectively. The sol concentration significantly impacts the morphology and nanostructure of the mesoporous films as well as their electrochromic performance.
The calcining step may occur at a temperature between about 300° C. and about 400° C. In some embodiments, the calcining step may occur at a temperature of about 300° C., about 310° C., about 320° C., about 330° C., about 340° C., about 350° C., about 360° C., about 370° C., about 380° C., about 390° C., or about 400° C. In some embodiments, the substrate with the sol is calcined for between about 30 minutes to about 20 hours, about 4 hours to about 15 hours, or about 8 hours to about 10 hours.
The sol may be applied to the substrate by ultrasonic spraying. The ultrasonic spray nozzle may be operated at a flow rate between about 0.05 mL/min to about 2 mL/min, in some embodiments about 0.25 mL/min. In some embodiments, the flow rate may be between about 0.5 mL/min to about 1 mL/min. In some embodiments, the flow rate may be about 0.05 mL/min, about 0.8 mL/min, about 0.9 mL/min, about 1.0 mL/min, about 1.1 mL/min, about 1.2 mL/min, about 1.3 mL/min, about 1.4 mL/min, about 1.5 mL/min, about 1.6 mL/min, about 1.7 mL/min, about 1.8 mL/min, about 1.9 mL/min, or about 2 mL/min.
The frequency of the ultrasonic spray nozzle during application may be between about 10 kHz to about 1000 kHz, in some embodiments about 120 kHz. In some embodiments, the frequency may be about 10 kHz, about 20 kHz, about 30 kHz, about 40 kHz, about 50 kHz, about 100 kHz, about 200 kHz, about 300 kHz, about 400 kHz, about 500 kHz, about 600 kHz, about 700 kHz, about 800 kHz, about 900 kHz, or about 1000 kHz.
The sol may be entrained in a gas, wherein the gas is selected from the group consisting of nitrogen, argon, helium, combinations thereof, or similar inert gases. In some embodiments, the gas may be nitrogen. The flow rate of the gas provided to the nozzle may be between about 1 to about 10 slm. In some embodiments, the flow rate may be about 1 slm, about 2 slm, about 3 slm, about 4 slm, about 5 slm, about 6 slm, about 7 slm, about 8 slm, about 9 slm, or about 10 slm.
The substrate may be any suitable material, including but not limited to, a glass material, a membrane, and a filter, and combinations thereof. The substrate may be positioned between about 1 cm to about 20 cm from the tip of the ultrasonic spray nozzle. In some embodiments, the distance between the substrate and the tip of the ultrasonic spray nozzle may be about 1 cm, about 5 cm, about 10 cm, about 15 cm, or about 20 cm. The substrate may be cleaned prior to applying the sol using any suitable method. In some embodiments, the substrates may be cleaned by soaking in alcohol, wiped dry, blown dry with a gas then placed into an oxygen plasma prior to use.
The parameters discussed above are for one spray orifice. One skilled in the art would understand that multiple spray orifices may be used by scaling the amounts and flow rates of the materials. Another aspect of the present invention is a method to apply a film to a substrate. The method includes preparing a sol, wherein the sol includes tungsten hexachloride and an organic templating agent dissolved in an alcohol to produce a film precursor. The film precursor is applied to at least one substrate to form a coated substrate. The coated substrate is exposed to a humidified environment to produce film gelation. The film gelation is calcined to produce a film. The resulting WO3 films display greater than about 85% optical modulation across the visible spectrum through optimization of the sol composition.
The mass ratio (WCl6:Organic templating agent) may be between about 0.1 and about 5. In some embodiments, the ratio may be between about 0.2 to about 2, between about 0.4 and about 1, in some embodiments between about 0.3 to about 1. In some embodiments, the ratio may be about 0.597.
The alcohol may be any suitable alcohol, including but not limited to ethanol, methanol, isopropanol, propanol, combinations thereof or the like.
The reagent ratio will impact of the total concentration in alcohol. The concentration of the WCl6 in the alcohol may be between about 0.5 mM to about 5 mM, in some embodiments be between 1.5 mM to about 3 mM. In some embodiments, the concentration may be about 1.5 mM, about 2.25 mM, or about 3 mM. Concentrated sols at 1.5, 2.25 and 3 mM, are denoted in the description as 1C, 1.5C and 2C, respectively. The sol concentration significantly impacts the morphology and nanostructure of the mesoporous films as well as their electrochromic performance.
The calcining step may occur at a temperature between about 300° C. and about 400° C. In some embodiments, the calcining step may occur at a temperature of about 300° C., about 310° C., about 320° C., about 330° C., about 340° C., about 350° C., about 360° C., about 370° C., about 380° C., about 390° C., or about 400° C. Calcining occurs for between about 10 minutes to about 24 hours. In some embodiments, the substrate with the sol is calcined for between about 30 minutes to about 20 hours, about 4 hours to about 15 hours, or about 8 hours to about 10 hours.
The templating agent may be a triblock copolymer. In some embodiments, the triblock copolymer may include poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene), EO20PO70EO20. In some embodiments, the triblock copolymer is Pluronic P123.
The sol may be applied to the substrate by ultrasonic spraying. The flow rate of ultrasonic spray nozzle may be between about 0.5 mL/min to about 2 mL/min, in some embodiments about 0.25 mL/min. In some embodiments, the flow rate may be about 0.05 mL/min, about 0.8 mL/min, about 0.9 mL/min, about 1.0 mL/min, about 1.1 mL/min, about 1.2 mL/min, about 1.3 mL/min, about 1.4 mL/min, about 1.5 mL/min, about 1.6 mL/min, about 1.7 mL/min, about 1.8 mL/min, about 1.9 mL/min, or about 2 mL/min.
The frequency of the ultrasonic spray nozzle during application may be between about 10 kHz to about 1000 kHz, in some embodiments about 120 kHz. In some embodiments, the frequency may be about 10 kHz, about 20 kHz, about 30 kHz, about 40 kHz, about 50 kHz, about 100 kHz, about 200 kHz, about 300 kHz, about 400 kHz, about 500 kHz, about 600 kHz, about 700 kHz, about 800 kHz, about 900 kHz, or about 1000 kHz.
The sol may be entrained in a gas, wherein the gas is selected from the group consisting of nitrogen, argon, helium, combinations thereof, or similar materials. In some embodiments, the gas may be nitrogen. The flow rate of the gas provided to the nozzle may be between about 1 to about 10 slm. In some embodiments, the flow rate may be about 1 slm, about 2 slm, about 3 slm, about 4 slm, about 5 slm, about 6 slm, about 7 slm, about 8 slm, about 9 slm, or about 10 slm.
The substrate may be any suitable material, including but not limited to, a glass material, a membrane, and a filter, and combinations thereof. The substrate may be positioned between about 1 cm to about 20 cm from the tip of the ultrasonic spray nozzle. In some embodiments, the distance between the substrate and the tip of the ultrasonic spray nozzle may be about 1 cm, about 5 cm, about 10 cm, about 15 cm, or about 20 cm. The substrate may be cleaned prior to applying the sol using any suitable method. In some embodiments, the substrates may be cleaned by soaking in alcohol, wiped dry, blown dry with a gas then placed into an oxygen plasma prior to use.
Another aspect of the invention is a film. The film comprises tungsten oxide, where the tungsten oxide has greater than about 85% optical modulation across a visible spectrum. In some embodiments, the optical modulation across the visible spectrum may be greater than about 85%, greater than about 90%, greater than about 95%, greater than about 97%, greater than about 98%, greater than about 99% or about 100%. In some embodiments, the optical transmission may be about 85%, about 90%, about 95%, about 95%, about 97%, about 98%, about 99% or about 100%. The film may be used for coating a substrate to reduce the transmission of light.
The film thickness may be controlled as it is a product of the sol concentration and the number of passes (P) through a deposition zone. In some embodiments, the film thickness may be between about 200 nm and about 2000 nm. In some embodiments, the film thickness may be about 200 nm, about 300 nm, about 400 nm, about 500 nm, about 600 nm, about 700 nm, about 800 nm, about 900 nm, about 1000 nm, about 1100 nm, about 1200 nm, about 1300 nm, about 1400 nm, about 1500 nm, about 1600 nm, about 1700 nm, about 1800 nm, about 1900 nm, or about 200 nm.
The structure of the deposited film may be mesoporous. The particle size of the individual nanocrysallites in the film may be between about 3 nm to about 15 nm. In some embodiments, may be about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, or about 15 nm. The average pore size in the mesoporous film may be between 2 nm and 12 nm. In some embodiments, the average pore size may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, or about 12 nm.
The optical transmission of the film may be greater than 85% across the visible spectrum (about 550 nm to about 950 nm). In some embodiments, the optical modulation across the visible spectrum may be greater than about 85%, greater than about 90%, greater than about 95%, greater than about 97%, greater than about 98%, greater than about 99% or about 100%. In some embodiments, the optical transmission may be about 85%, about 90%, about 95%, about 95%, about 97%, about 98%, about 99% or about 100%.
The film may be in a colored state or the film may be in a bleached state. The film may be colored in about 3 seconds by application of appropriate voltage in an Li+-containing electrolyte solution. The film may be bleached in about 20-60 seconds by application of appropriate voltage in an Li+-containing electrolyte solution. In some embodiments, the film may be transparent. In some embodiments, the film may be less than about 90% transparent.
Triblock polymer Pluronic P123 (poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene), EO20PO70EO20), anhydrous ethanol and tungsten hexachloride (WCl6) were all purchased from Sigma-Aldrich and used without further purification. An inert glove box was used for reagent storage and sol preparation, due to the moisture sensitivity of these components. Sol solution preparation began by separately dissolving about 1 grams, about 1.5 grams and about 2 grams of the triblock copolymer P123 in 10 ml anhydrous ethanol (≧99.5%) for 1C, 1.5C and 2C concentration levels, respectively. The sol was completed by adding about 0.595 grams, about 0.8925 grams, and about 1.19 g of WCl6 (≧99.9%) to the 1C, 1.5C and 2C triblock copolymer/ethanol solution and followed by 12 hours of stirring to produced sols that were then used for ultrasonic spray deposition.
The stable sols was transferred to a syringe and delivered to the ultrasonic spray nozzle at a flow rate of 0.25 ml/min using Fluid Metering Inc. VMP TRI Pulseless “Smoothflow” pump. The ultrasonic spray system was obtained from Sono-Tek Corporation and consisted of a model 8700-120 spray head that operated at a frequency of 120 kHz. The spray nozzle had a 0.230 in. diameter conical tip and 0.015 in. diameter orifice that was fitted with the impact system for gas-driven spray delivery. The atomized mist was entrained in a stream of nitrogen whose flowrate was fixed at 6.9 slm using an electronic mass flow controller (Omega FMA 1818). This aerosol was directed onto fluorinated tin oxide (FTO) coated glass (TEC-15, Pilkington) positioned 5 cm below the nozzle under ambient conditions. Other suitable materials include transparent conducting oxide (TCO) and TCO like materials, including ZnO:Al. Before deposition, all substrates were cleaned with an isopropanol-soaked clean-room wipe, blown dry with nitrogen, and then placed in an oxygen plasma (800 mtorr, 155 W) for 5 minutes. Samples were mounted on a computer controlled stage which rastered them through the deposition zone for the desired number of spray passes, producing uniform, iridescent blue films. Samples were then transferred into a chamber saturated with water vapor for hydrolysis.
The final step is calcination, where samples are heated in air to remove residual solvent and the polymer template while completing the oxidation and crystallization of the WO3. Samples were placed directly onto a hot plate set at maintained at about 350° C. After 1 hour on the hot plate the samples were removed and allowed to naturally cool down to room temperature.
The nanoscale morphology was examined by transmission electron microscopy (TEM, Philips CM200). Selected area diffraction (SAD) patterns were carried out by using 200 kV electrons. Samples for transmission electron microscopy (TEM) and selected area diffraction (SAD) were produced by suspending scraped tungsten oxide powder in ethanol using sonication and placing a drop on a TEM grid and allowing the solvent to evaporate. FESEM characterization of the films was performed on a JEOL JSM-7000F microscope operating at 2 keV. The crystallinity of final tungsten oxide films were assessed by X-ray diffraction (XRD) using CuKα radiation over a range of 20=20-65° using 0.05° steps. Raman spectroscopy was performed using the about 488 nm line of a 15 mW argon ion laser. N2 physisorption was performed using a Micrometrics ASAP 2020 after samples were degassed at 250° C. under vacuum for 4 h.
The film thickness may be proportional to the sol concentration (C) multiplied by the number of passes (P) made through the deposition zone.
At the intermediate concentration (1.5C), the surface of the films becomes somewhat wavy, and at 2C there are surface cracks are visible in some regions. These macroscopic changes in morphology are attributed to the viscosity of the sol, which increases linearly with sol concentration from about 3.4 cP at 1C to about 7 cP at 2C. At higher viscosity the size of the droplets produced by the ultrasonic nebulizer increases, as does their distribution. The 2C concentration was the highest used with the present equipment, as clogging was observed at higher concentrations.
The structural changes described above are manifested through significant improvements in the specific surface area of the mesoporous films.
Electrochromic performance was evaluated by cycling films in an electrolyte composed of about 1 M LiClO4 dissolved in propylene carbonate in a test cell housed in an Ar-purged glovebox. Cyclic voltammetry and potential cycling measurements were made using a BioLogic VMP3 multichannel potentiostat. Cyclic voltammetry (CV) was performed using an about 20 mV/s scan rate between about 2 and 4 V vs. Li/Li+. Switching kinetics was measured using chronoamperometric cycling between about 1.7 and 4.2 V vs. Li/Li+, and the switching speed is defined as the time required to achieve 75% of the full optical change. A diode laser (about 670 nm) coupled to a detector (Thor Labs, Inc. DET100A) was used to collect optical transmission in direct registry during cycling. For analysis of the full transmission spectra the laser and detector were replace by a broadband halogen light source and an Ocean Optics USB 4000 fiber optic spectrometer, respectively. In both cases contribution of a clean FTO substrate was background subtracted, so that the reported optical response reflects only contributions from the WO3 film. In addition, both still images and videos of the transmission change were acquired by illuminating the cell with a standard incandescent flashlight and recording the transmission with a fiber-optic based camera (General Tools Model DCS050).
In the cyclic voltammetry analysis, the electrochromic performance was found to primarily be a function of the film thickness, and nominally independent of the sol concentration. Representative plots of CVs and optical transmission from the 1C and 2C levels are illustrated in
The electrochromic performance during cyclic voltammetry was nominally identical at the three concentration levels (1C, 1.5C, and 2C). The lithium ion intercalation rate during CV is relatively slow, and as such the coloration efficiency reflected the charge capacity of the material. To assess the dynamics of switching, the films were exposed to alternating step potentials with a period of about 120 seconds.
Switching speed was quantified by the time required to modulate the absolute transmission by about 75%.
The optical response reported in
The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiment described hereinabove is further intended to explain the best mode known for practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.
This application claims priority and the benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/986,279 filed Apr. 30, 2014, which is incorporated herein in its entirety by reference.
This invention was made with government support under grant number DMR-0820518 awarded by the National Science Foundation and Contract No. DE-AC36-08GO28308 between the United States Department of Energy and the Alliance for Sustainable Energy, LLC, the Manager and Operator of the National Renewable Energy Laboratory. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61986279 | Apr 2014 | US |
