Patent Publication Number: US-10331003-B2

Title: Electrochromic privacy window

Description:
FIELD 
     The present invention is generally directed to electrochromic (EC) windows configured to provide privacy through light modulation. 
     BACKGROUND OF THE INVENTION 
     Residential and commercial buildings represent a prime opportunity to improve energy efficiency and sustainability in the United States. The buildings sector alone accounts for 40% of the United States&#39; yearly energy consumption ( 40  quadrillion BTUs, or “quads”, out of 100 total), and 8% of the world&#39;s energy use. Lighting and thermal management each represent about 30% of the energy used within a typical building, which corresponds to around twelve quads each of yearly energy consumption in the US. Windows cover an estimated area of about 2,500 square km in the US and are a critical component of building energy efficiency as they strongly affect the amount of natural light and solar gain that enters a building. Recent progress has been made toward improving window energy efficiency through the use of inexpensive static coatings that either retain heat in cold climates (low emissive films) or reject solar heat gain in warm climates (near-infrared rejection films). 
     Currently, static window coatings can be manufactured at relatively low cost. However, these window coatings are static and not well suited for locations with varying climates. A window including an electrochromic (EC) device overcomes these limitations by enhancing window performance in all climates. 
     However, one of the shortcomings of conventional EC windows is the inability to achieve a sufficiently dark state to allow for use in privacy applications. Accordingly, there is a need for smart windows suitable for privacy applications. 
     SUMMARY 
     According to various embodiments, provided is an electrochromic (EC) window that includes an EC device and a privacy device. 
     According to various embodiments, an electrochromic (EC) privacy window comprises an EC pane unit comprising a first EC device having a bright state and a dark state, and a privacy device facing the EC pane unit and having a bright state and a privacy state configured to attenuate visible radiation transmitted through the window. In some embodiments, when the privacy device is in the privacy state the window has transmitted haze of greater that 80%. In other embodiments, when the privacy device is in the privacy state and the first EC device is in the dark state, the window has a visible transmittance of about 0.1% or less. 
     According to other embodiments, an electrochromic (EC) privacy window comprises an EC pane unit comprising a first EC device having a bright state and a dark state, and a privacy device facing the EC pane unit and having a bright state and a privacy state configured to attenuate visible radiation transmitted through the window, where the privacy device comprises a switchable mirror device or film, a polymer-dispersed liquid crystal device or film, or a tunable liquid crystal filter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  are schematic representations of EC devices according to various embodiments. 
         FIG. 2  is a schematic representation of an electrochromic device that may be tuned to produce a particular color, according to various embodiments or the present disclosure. 
         FIGS. 3A to 3D  are sectional views of a smart window, according to various embodiments of the present disclosure. 
         FIG. 4  is a sectional view of a smart window, according to various embodiments of the present disclosure. 
         FIG. 5  is a sectional view of a smart window, according to various embodiments of the present disclosure. 
         FIG. 6  is a sectional view of a smart window, according to various embodiments of the present disclosure. 
         FIG. 7  is a sectional view of a smart window, according to various embodiments of the present disclosure. 
         FIG. 8  is a sectional view of a smart window, according to various embodiments of the present disclosure. 
         FIG. 9  is a sectional view of a smart window, according to various embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     The invention is described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure is thorough, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like reference numerals in the drawings denote like elements. 
     It will be understood that when an element or layer is referred to as being disposed “on” or “connected to” another element or layer, it can be directly on or directly connected to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being disposed “directly on” or “directly connected to” another element or layer, there are no intervening elements or layers present. It will be understood that for the purposes of this disclosure, “at least one of X, Y, and Z” can be construed as X only, Y only, Z only, or any combination of two or more items X, Y, and Z (e.g., XYZ, XYY, YZ, ZZ). 
     Various embodiments disclosed herein provide electrochromic nanostructured materials capable of selectively modulating radiation in near-infrared (NIR) and visible spectral regions. The material may include nanostructured doped transition metal oxides with ternary compounds of the type A x M z O y . In various embodiment A x M z O y  compounds, if it is assumed that z=1, then 0.08≤x≤0.5 (preferably 0.25≤x≤0.35), and 2≤y≤3. In various embodiments, since the nanostructures may be non-uniform as a function of depth, x may represent an average doping content. To operate, the subject material may be fabricated into an electrode that will change optical properties after driven by an applied voltage. 
     In order to improve the performance of EC window coatings, selective modulation of NIR and visible spectra radiation, and avoidance of degrading effects of UV radiation, may be desired. Various embodiments may provide single-component electrochromic nanostructured materials capable of selectively modulating NIR and visible spectral regions. Further, since certain spectral regions may damage the electrochromic nanostructured material, the various embodiments may incorporate at least one protective material and/or protective layer to prevent such damage. 
     The various embodiments provide devices and methods for enhancing optical changes in windows using electrochromic nanostructured materials fabricated into an electrode to form an electrochromic device. In various embodiments, the material may undergo a reversible change in optical properties when driven by an applied potential. Based on the applied potential, the electrochromic nanostructured materials may modulate NIR radiation (wavelength of around 780-2500 nm), as well as visible radiation (wavelength of around 400-780 nm). In an example, the device may include a first nanostructured material that modulates radiation in a portion of the NIR spectral region and in the visible spectral region, and a second nanostructured material that modulates radiation in an overlapping portion of the NIR spectral region such that the NIR radiation modulated by the device as a whole is enhanced and expanded relative to that of just the first nanostructured material. In various embodiments, the material may operate in multiple selective modes based on the applied potential. 
     Further, the various embodiments may include at least one protective material to prevent or reduce damage to an electrochromic nanostructured material that may result from repeated exposure to radiation in the UV spectral region. In an example, a protective material may be used to form at least one barrier layer in the device that is positioned to block UV radiation from reaching the first nanostructured material and electrolyte. In another example, a protective material may be used to form a layer that is positioned to block free electron or hole charge carriers created in the electrolyte due to absorption of UV radiation by the nanostructured electrode material from migrating to that material, while allowing conduction of ions from the electrolyte (i.e., an electron barrier and ion conductor). 
     In various embodiments, control of individual operating modes for modulating absorption/transmittance of radiation in specific spectral regions may occur at different applied biases. Such control may provide users with the capability to achieve thermal management within buildings and other enclosures (e.g., vehicles, etc.), while still providing shading when desired. 
       FIGS. 1A-1C  illustrate embodiment electrochromic devices. It should be noted that such electrochromic devices may be oriented upside down or sideways from the orientations illustrated in  FIGS. 1A-1C . Furthermore, the thickness of the layers and/or size of the components of the devices in  FIGS. 1A-1C  are not drawn to scale or in actual proportion to one another other, but rather are shown as representations. 
     In  FIG. 1A , an embodiment electrochromic device  100  may include a first transparent conductor layer  102   a , a working electrode  104 , a solid state electrolyte  106 , a counter electrode  108 , and a second transparent conductor layer  102   b . Some embodiment electrochromic devices may also include one or more optically transparent support layers  110   a ,  110   b  respectively positioned in front of the first transparent conductor layer  102   a  and/or positioned behind the second transparent conductor layer  102   b . The support layers  110   a ,  110   b  may be formed of a transparent material such as glass or plastic. 
     The first and second transparent conductor layers  102   a ,  102   b  may be formed from transparent conducting films fabricated using inorganic and/or organic materials. For example, the transparent conductor layers  102   a ,  102   b  may include inorganic films of transparent conducting oxide (TCO) materials, such as indium tin oxide (ITO) or fluorine doped tin oxide (FTO). In other examples, organic films in transparent conductor layers  102   a ,  102   b  may include graphene and/or various polymers. 
     In the various embodiments, the working electrode  104  may include nanostructures  112  of a doped or undoped transition metal oxide bronze, and optionally nanostructures  113  of a transparent conducting oxide (TCO) composition shown schematically as circles and hexagons for illustration purposes only. As discussed above, the thickness of the layers of the device  100 , including and the shape, size and scale of nanostructures is not drawn to scale or in actual proportion to each other, but is represented for clarity. In the various embodiments, nanostructures  112 ,  113  may be embedded in an optically transparent matrix material or provided as a packed or loose layer of nanostructures exposed to the electrolyte. 
     In the various embodiments, the doped transition metal oxide bronze of nanostructures  112  may be a ternary composition of the type AxMzOy, where M represents a transition metal ion species in at least one transition metal oxide, and A represents at least one dopant. Transition metal oxides that may be used in the various embodiments include, but are not limited to any transition metal oxide which can be reduced and has multiple oxidation states, such as niobium oxide, tungsten oxide, molybdenum oxide, vanadium oxide, titanium oxide and mixtures of two or more thereof. In one example, the nanostructured transition metal oxide bronze may include a plurality of undoped tungsten oxide (WO 3-x ) nanoparticles, where 0≤x≤0.33, such as 0≤x≤0.1. 
     In various embodiments, the at least one dopant species may be a first dopant species that, upon application of a particular first voltage range, causes a first optical response. The applied voltage may be, for example, a negative bias voltage. Specifically, the first dopant species may cause a surface plasmon resonance effect on the transition metal oxide by creating a significant population of delocalized electronic carriers. Such surface plasmon resonance may cause absorption of NIR radiation at wavelengths of around 780-2000 nm, with a peak absorbance at around 1200 nm. In various embodiments, the specific absorbances at different wavelengths may be varied/adjusted based other factors (e.g., nanostructure shape, size, etc.), discussed in further detail below. In the various embodiments, the first dopant species may be an ion species selected from the group of cesium, rubidium, and lanthanides (e.g., cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium). 
     In various embodiments, the dopant may include a second dopant species that causes a second optical response based upon application of a voltage within a different, second particular range. The applied voltage may be, for example, a negative bias voltage. In an embodiment, the second dopant species may migrate between the solid state electrolyte  106  and the nanostructured transition metal oxide bronze of the working electrode  104  as a result of the applied voltage. Specifically, the application of voltage within the particular range may cause the second dopant species to intercalate and deintercalate the transition metal oxide structure. In this manner, the second dopant may cause a change in the oxidation state of the transition metal oxide, which may cause a polaron effect and a shift in the lattice structure of the transition metal oxide. This shift may cause absorption of visible radiation, for example, at wavelengths of around 400-780 nm. 
     In various embodiments, the second dopant species may be an intercalation ion species selected from the group of lanthanides (e.g., cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium), alkali metals (e.g., lithium, sodium, potassium, rubidium, and cesium), and alkali earth metals (e.g., beryllium, magnesium, calcium, strontium, and barium). In other embodiments, the second dopant species may include a charged proton species. 
     In various embodiments, nanostructures  113  may optionally be mixed with the doped transition metal oxide bronze nanostructures  112  in the working electrode  104 . In the various embodiments, the nanostructures  113  may include at least one TCO composition, which prevents UV radiation from reaching the electrolyte and generating electrons. In an example embodiment, the nanostructures  113  may include an indium tin oxide (ITO) composition, which may be a solid solution of around 60-95 wt % (e.g., 85-90 wt %) indium(III) oxide (In 2 O 3 ) and around 5-40 wt % (e.g., 10-15 wt %) tin(IV) oxide (SnO 2 ). In another example embodiment, the nanostructures  113  may include an aluminum-doped zinc oxide (AZO) composition, which may be a solid solution of around 99 wt % zinc oxide (ZnO) and around 2 wt % aluminum(III) oxide (Al 2 O 3 ). Additional or alternative TCO compositions that may be used to form nanostructures  113  in the various embodiments include, but are not limited to, indium oxide, zinc oxide and other doped zinc oxides such as gallium-doped zinc oxide and indium-doped zinc oxide. 
     The TCO composition of nanostructures  113  may be transparent to visible light/radiation and, upon application of the first voltage, may modulate absorption of NIR radiation at wavelengths of around 1200-2500 nm, with peak absorbance around 2000 nm (e.g., at a longer peak wavelength than the bronze nanoparticles  112 , but with overlapping absorption bands). In particular, application of the first voltage may cause an increase in free electron charge carriers, and therefore cause a surface plasmon resonance effect in at least one TCO composition of nanostructures  113 . In an embodiment in which the TCO composition is ITO, the surface plasmon resonance effect may be caused by oscillation of free electrons produced by the replacement of indium ions (In 3+ ) with tin ions (Sn 4+ ). Similar to the transition metal oxide bronze, such surface plasmon resonance may cause a change in absorption properties of the TCO material. In some embodiments, the change in absorption properties may be an increase in absorbance of NIR radiation at wavelengths that overlaps with that of the nanostructures  112 . Therefore, the addition of TCO composition nanostructures  113  to the working electrode  104  may serve to expand the range of NIR radiation absorbed (e.g., at wavelengths of around 780-2500 nm) compared to that of the nanostructures  112  alone (e.g., at wavelengths of around 780-2000 nm), and to enhance absorption of some of that NIR radiation (e.g., at wavelengths of around 1200-2000 nm). 
     Based on these optical effects, the nanostructure  112  and optional nanostructure  113  of the working electrode may progressively modulate transmittance of NIR and visible radiation as a function of applied voltage by operating in at least three different modes. For example, a first mode may be a highly solar transparent (“bright”) mode in which the working electrode  104  is transparent to NIR radiation and visible light radiation. A second mode may be a selective-IR blocking (“cool”) mode in which the working electrode  104  is transparent to visible light radiation but absorbs NIR radiation. A third mode may be a visible blocking (“dark”) mode in which the working electrode  104  absorbs radiation in the visible spectral region and at least a portion of the NIR spectral region. In an example, application of a first voltage having a negative bias may cause the electrochromic device to operate in the cool mode, blocking transmittance of NIR radiation at wavelengths of around 780-2500 nm. In another example, application of a second negative bias voltage having a higher absolute value than the first voltage may cause the electrochromic device to operate in the dark state, blocking transmittance of visible radiation (e.g., at wavelengths of around 400-780 nm) and NIR radiation at wavelengths of around 780-1200 nm. In another example, application of a third voltage having a positive bias may cause the electrochromic device to operate in the bright state, allowing transmittance of radiation in both the visible and NIR spectral regions. In various embodiments, the applied voltage may be between −5V and 5V, preferably between −2V and 2V. For example, the first voltage may be −0.25V to −0.75V, and the second voltage may be −1V to −2V. In another example, the absorbance of radiation at a wavelength of 800-1500 nm by the electrochromic device may be at least 50% greater than its absorbance of radiation at a wavelength of 450-600 nm. 
     Alternatively, the nanostructure  112  and optional nanostructure  113  of the working electrode may modulate transmittance of NIR and visible radiation as a function of applied voltage by operating in two different modes. For example, a first mode may be a highly solar transparent (“bright”) mode in which the working electrode  104  is transparent to NIR radiation and visible light radiation. A second mode may be a visible blocking (“dark”) mode in which the working electrode  104  absorbs radiation in the visible spectral region and at least a portion of the NIR spectral region. In an example, application of a first voltage having a negative bias may cause the electrochromic device to operate in the dark mode, blocking transmittance of visible and NIR radiation at wavelengths of around 780-2500 nm. In another example, application of a second voltage having a positive bias may cause the electrochromic device to operate in the bright mode, allowing transmittance of radiation in both the visible and NIR spectral regions. In various embodiments, the applied voltage may be between −2V and 2V. For example, the first voltage may be −2V, and the second voltage may be 2V. 
     In various embodiments, the solid state electrolyte  106  may include at least a polymer material and a plasticizer material, such that electrolyte may permeate into crevices between the transition metal oxide bronze nanoparticles  112  (and/or nanoparticles  113  if present). The term “solid state,” as used herein with respect to the electrolyte  106 , refers to a polymer-gel and/or any other non-liquid material. In some embodiments, the solid state electrolyte  106  may further include a salt containing, for example, an ion species selected from the group of lanthanides (e.g., cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium), alkali metals (e.g., lithium, sodium, potassium, rubidium, and cesium), and alkali earth metals (e.g., beryllium, magnesium, calcium, strontium, and barium). In an example embodiment, such salt in the solid state electrolyte  106  may contain a lithium and/or sodium ions. In some embodiments, the solid state electrolyte  106  may initially contain a solvent, such as butanol, which may be evaporated off once the electrochromic device is assembled. In some embodiments, the solid state electrolyte  106  may be around 40-60 wt % plasticizer material, preferably around 50-55 wt % plasticizer material. In an embodiment, the plasticizer material may include at least one of tetraglyme and an alkyl hydroperoxide. In an embodiment, the polymer material of the solid state electrolyte  106  may be polyvinylbutyral (PVB), and the salt may be lithium bis(trifluoromethane). In other embodiments, the solid state electrolyte  106  may include at least one of lithium phosphorus oxynitride (LiPON) and tantalum pentoxide (Ta 2 O 5 ). 
     In some embodiments, the electrolyte  106  may include a sacrificial redox agent (SRA). Suitable classes of SRAs may include, but are not limited to, alcohols, nitrogen heterocycles, alkenes, and functionalized hydrobenzenes. Specific examples of suitable SRAs may include benzyl alcohol, 4-methylbenzyl alcohol, 4-methoxybenzyl alcohol, dimethylbenzyl alcohol (3,5-dimethylbenzyl alcohol, 2,4-dimethylbenzyl alcohol etc.), other substituted benzyl alcohols, indoline, 1,2,3,4-tetrahydrocarbazole, N,N-dimethylaniline, 2,5-dihydroanisole, etc. In various embodiments, the SRA molecules may create an air stable layer that does not require an inert environment to maintain charge. 
     Polymers that may be part of the electrolyte  106  may include, but are not limited to, poly(methyl methacrylate) (PMMA), poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVB), poly(ethylene oxide) (PEO), fluorinated co-polymers such as poly(vinylidene fluoride-co-hexafluoropropylene), poly(acrylonitrile) (PAN), poly(vinyl alcohol) (PVA), etc. Plasticizers that may be part of the polymer electrolyte formulation include, but are not limited to, glymes (tetraglyme, triglyme, diglyme etc.), propylene carbonate, ethylene carbonate, ionic liquids (1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl) imide, 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethane sulfonyl)imide, etc.), N,N-dimethylacetamide, and mixtures thereof. 
     In some embodiments, the electrolyte  106  may include, by weight, 10-30% polymer, 40-80% plasticizer, 5-25% lithium salt, and 0.5-10% SRA. 
     The counter electrode  108  of the various embodiments should be capable of storing enough charge to sufficiently balance the charge needed to cause visible tinting to the nanostructured transition metal oxide bronze in the working electrode  104 . In various embodiments, the counter electrode  108  may be formed as a conventional, single component film, a nanostructured film, or a nanocomposite layer. 
     In some embodiments, the counter electrode  108  may be formed from at least one passive material that is optically transparent to both visible and NIR radiation during the applied biases. Examples of such passive counter electrode materials may include CeO 2 , CeVO 2 , TiO 2 , indium tin oxide, indium oxide, tin oxide, manganese or antimony doped tin oxide, aluminum doped zinc oxide, zinc oxide, gallium zinc oxide, indium gallium zinc oxide, molybdenum doped indium oxide, Fe 2 O 3 , and/or V 2 O 5 . In other embodiments the counter electrode  108  may be formed from at least one complementary material, which may be transparent to NIR radiation but which may be oxidized in response to application of a bias, thereby causing absorption of visible light radiation. Examples of such complementary counter electrode materials may include Cr 2 O3, MnO 2 , FeO 2 , CoO 2 , NiO 2 , RhO 2 , or IrO 2 . The counter electrode materials may include a mixture of one or more passive materials and/or one or more complementary materials described above. 
     Without being bound to any particular theory, it is believed that the application of a first voltage in the various embodiments may cause the interstitial dopant species (e.g., cesium) in the crystal structure of the transition metal oxide bronze to have a greater amount of free carrier electrons and/or to cause the interstitial dopant species (e.g., lithium ions from the electrolyte) to perform non-faradaic capacitive or pseudo-capacitive charge transfer on the surface of the nanostructures  112 , which may cause the surface plasmon resonance effect to increase the absorption of NIR radiation. In this manner, the absorption properties of the transition metal oxide bronze characteristics may change (i.e., increased absorption of NIR radiation) upon application of the first voltage. Further, application of a second voltage having a higher absolute value than the first voltage in the various embodiments may cause faradaic intercalation of an intercalation dopant species (e.g., lithium ions) from the electrolyte into the transition metal oxide nanostructures. It is believed that the interaction of this dopant species provides interstitial dopant atoms in the lattice which creates a polaron effect. In this manner, the lattice structure of transition metal oxide nanoparticles may experience a polaron-type shift, thereby altering its absorption characteristics (i.e., shift to visible radiation) to block both visible and near infrared radiation. 
     In some embodiments, in response to radiation of certain spectral regions, such as UV (e.g., at wavelengths of around 10-400 nm) may cause excitons to be generated in the polymer material of the solid state electrolyte  106 . The UV radiation may also excite electrons in the doped transition metal oxide bronze to move into the conduction band, leaving holes in the valence band. The generated excitons in the polymer material may dissociate to free carriers, the electrons of which may be attracted to the holes in the valence band in the doped transition metal oxide bronze (e.g., cesium-doped tungsten trioxide (Cs x WO 3 )) of nanoparticles  112 . Since electrochemical reduction of various transition metal oxide bronzes by such free electron charge carriers may degrade their performance (i.e., from unwanted coloration of the transition metal oxide bronze), embodiment devices may include one or more layer of a protective material to prevent UV radiation from reaching the solid state electrolyte  106 , in addition to or instead of nanostructures  113  mixed into the working electrode. 
       FIG. 1B  illustrates an embodiment electrochromic device  150  that addresses degradation of the doped transition metal oxide bronze nanostructures  112 . Similar to device  100  shown in  FIG. 1A , device  150  may include a first transparent conductor layer  102   a , a working electrode  104 , a solid state electrolyte  106 , a counter electrode  108 , a second transparent conductor layer  102   b , and one or more optically transparent support layers  110   a ,  110   b . In addition, device  150  may include one or more protective layers  116   a ,  116   b  made of a material that absorbs UV radiation. In an example embodiment, the device  150  may include a first protective layer  116   a  disposed between a first support layer  110   a  and the first transparent conductor layer  102   a . The device may optionally include a second protective layer  116   b  disposed between a second support layer  110   b  and the second transparent conductor layer  102   b . Alternatively, the UV protective layer  116   a  may be disposed on the exterior surface of the first support layer  110   a , or may be disposed between the first transparent conductor  102   a  and the working electrode  104 . In other words, the first and/or second UV protective layers  116   a ,  116   b  may be disposed between any of the layers of the electrochromic device  150 , such that UV radiation is substantially prevented from reaching the working electrode  104 . 
     The UV radiation absorbing material of the one or more protective layers  116   a ,  116   b  of the various embodiments may be any of a number of barrier films. For example, the one or more protective layers  116   a ,  116   b  may be a thin film of at least one TCO material, which may include a same as or different from TCO compositions in the nanostructures  113 . In an example embodiment, a protective layer  116   a  of the device  150  may be an ITO thin film, and therefore capable of absorbing UV radiation by band-to-band absorption (i.e., absorption of a UV photon providing enough energy to excite an electron from the valence band to the conduction band). In another example embodiment, the device may include the TCO nanostructures  113  made of ITO, as well as a protective layer  116   a  composed of an ITO thin film. Alternatively, the TCO nanostructures  113  may form a separate thin film layer  116   b  disposed between the transition metal oxide bronze nanoparticles  112  and the transparent conductor  102   a . In some embodiments, the UV radiation absorbing materials of protective layers  116   a ,  116   b  may include organic or inorganic laminates. 
     In another embodiment, at least one UV protective layer, such as protective layer  116   a  in  FIG. 1B , may be a UV radiation reflector made of a high index transparent metal oxide. Since birds can see radiation in the UV range, a UV reflector may be implemented in embodiments positioned as outside windows in order to prevent birds from hitting the windows. In some other embodiments, UV radiation absorbing organic molecules and/or inorganic UV radiation absorbing nanoparticles (e.g., zinc oxide, indium oxide, ITO, etc.) may be incorporated within the electrolyte  106  material. 
       FIG. 1C  illustrates another embodiment electrochromic device  170  that addresses degradation of the doped transition metal oxide bronze nanostructures  112  by controlling the effects of the electron charge carriers generated in the electrolyte from exposure to UV radiation. Similar to devices  100  and  150  discussed above with respect to  FIGS. 1A and 1B  respectively, device  170  may include a first transparent conductor layer  102   a , a working electrode  104 , a solid state electrolyte  106 , a counter electrode  108 , a second transparent conductor layer  102   b , and one or more optically transparent support layers  110   a ,  110   b . In addition, device  170  may include a protective layer  118  positioned between the working electrode  104  and the electrolyte  106 . The protective layer  118  may be composed of one or more ionically conductive and electrically insulating material. 
     As discussed above, without being bound to any particular theory, it is believed that the migration of intercalation ions between the electrolyte  106  and the working electrode  104  is responsible for at least some of the device&#39;s capability to modulate spectral absorption. Therefore, in order to maintain operability of the device, the electrically insulating material used to form the protective layer  118  should also be ionically conductive. That is, the material of the protective layer  118  may prevent or reduce free electrons in the solid state electrolyte layer  106  from reducing the transition oxide bronze of nanoparticles  112 , while allowing the diffusion of ions of an intercalation dopant species (e.g., Na, Li, etc.) between the electrolyte  106  and working electrode  104 . In an example embodiment, the electrically insulating material that makes up the protective layer  118  may be tantalum oxide, such as tantalum pentoxide (Ta 2 O 5 ), which blocks migration of electrons from the electrolyte  106  while allowing diffusion of the intercalation dopant species ions (e.g., lithium ions) from the electrolyte  106 . In this manner, degradation of the transition metal oxide bronze is reduced or prevented by controlling the effect of the absorbed UV radiation in addition to or instead of instead of blocking its absorption. Other example materials that may be used to form the protective layer  118  in addition to or instead of tantalum pentoxide may include, without limitation, strontium titanate (SrTiO 3 ), zirconium dioxide (ZrO 2 ), indium oxide, zinc oxide, tantalum carbide, niobium oxide, and various other dielectric ceramics having similar electrical and/or crystalline properties to tantalum pentoxide. 
     In an alternative embodiment, instead of or in addition to the protective layer  118 , the nanostructures  112  may each be encapsulated in a shell containing an electrically insulating and ionically conductive material, which may be the same as or different from the material of the protective layer  118  (e.g., tantalum oxide, strontium titanate, zinc oxide, indium oxide, zirconium oxide, tantalum carbide, or niobium oxide). 
     In an example embodiment, each nanostructure  112  may have a core of cubic or hexagonal unit cell lattice structure tungsten bronze, surrounded by a shell of tantalum pentoxide. 
     In some embodiments, the electrolyte  106  may include a polymer that reduces damage to the device due to UV radiation. The polymer may be any of a number of polymers that are stable upon absorption of UV radiation (e.g., no creation of proton/electron pairs). Examples of such polymers may include, but are not limited to, fluorinated polymers without hydroxyl (—OH) groups (e.g., polyvinylidene difluoride (PVDF)). 
     In another embodiment, a positive bias may be applied to the counter electrode  108  to draw UV radiation generated electrons from the electrolyte  106  to the counter electrode  108  in order to reduce or prevent electrons from the electrolyte  106  from moving to the working electrode  104  to avoid the free electron-caused coloration of the doped transition metal oxide bronze in the working electrode  104 . 
     In another embodiment, a device may include more than one of, such as any two of, any three of, or all four of: (i) a protective layer of electrically insulating material (e.g., protective layer  118  or protective material shells around the bronze nanoparticles), (ii) one or more protective layer of UV radiation absorbing material (e.g., protective layer(s)  116   a  and/or  116   b  in  FIG. 1B  and/or UV radiation absorbing organic molecules and/or inorganic UV radiation absorbing nanoparticles incorporated within the electrolyte  106  material), (iii) electrolyte polymer that is stable upon absorption of UV radiation, and/or (iv) application of positive bias to the counter electrode  108 . In various embodiments, the nanostructures  113  may be included in or omitted from electrochromic devices  150 ,  170 . 
     In another embodiment, the protective layer(s)  116   a  and/or  116   b  may comprise a stack of metal oxide layers. Alternatively, the stack may comprise a separate component that is provided instead of or in addition to the layer(s)  116   a  and/or  116   b . The stack may provide improvement in the reflected color of the electrochromic device. Prior art devices generally have a reddish/purplish color when viewed in reflection. The stack may comprise index-matched layers between the glass and transparent conductive oxide layer to avoid the reddish/purplish reflected color. As noted above, the index-matched layer can serve as the UV absorber or be used in addition to another UV absorber. The stack may comprise a zinc oxide based layer (e.g., ZnO or AZO) beneath an indium oxide based layer (e.g., indium oxide or ITO). 
     Compared to nanocomposite electrochromic films, the various embodiments may involve similar production by utilizing a single nanostructured material in the working electrode to achieve the desired spectral absorption control in both NIR and visible regions, and another nanostructured material to enhance and expand such control in the NIR region. Further, the various embodiments may provide one or more additional layer(s) of a protective material to minimize degradation of the single nanostructured material. 
     In some embodiments, the working electrode and/or the counter electrode may additionally include at least one material, such as an amorphous nano structured material, that enhances spectral absorption in the lower wavelength range of the visible region. In some embodiments, the at least one amorphous nanostructured material may be at least one nanostructured amorphous transition metal oxide. 
     In particular, the amorphous nano structured materials may provide color balancing to the visible light absorption that may occur due to the polaron-type shift in the spectral absorption of the doped-transition metal oxide bronze. As discussed above, upon application of the second voltage having a higher absolute value, the transition metal oxide bronze may block (i.e., absorb) radiation in the visible range. In various embodiments, the absorbed visible radiation may have wavelengths in the upper visible wavelength range (e.g., 500-700 nm), which may cause the darkened layer to appear blue/violet corresponding to the un-absorbed lower visible wavelength range (e.g., around 400-500 nm). In various embodiments, upon application of the second voltage, the at least one nanostructured amorphous transition metal oxide may absorb complementary visible radiation in the lower visible wavelength range (e.g., 400-500 nm), thereby providing a more even and complete darkening across the visible spectrum with application of the second voltage. That is, use of the amorphous nanostructured material may cause the darkened layer to appear black. 
     In some embodiments, at least one nanostructured amorphous transition metal oxide may be included in the working electrode  104  in addition to the doped-transition metal oxide bronze nanostructures  112  and the optional TCO nanostructures  113 . An example of such material in the working electrode  104  may be, but is not limited to, nanostructured amorphous niobium oxide, such as niobium(II) monoxide (NbO) or other niobium oxide materials (e.g., NbO x ). In some embodiments, the counter electrode  108  may include, as a complementary material, at least one nanostructured amorphous transition metal oxide. That is, in addition to optically passive materials, the counter electrode  108  may include at least one material for color balancing (i.e., complementing) the visible radiation absorbed in the working electrode (i.e., by the transition metal oxide bronze. An example of such material in the counter electrode  108  may be, but is not limited to, nanostructured amorphous nickel oxide, such as nickel(II) oxide (NiO) or other nickel oxide materials (e.g., NiO x ). 
     In the various embodiments, nanostructures that form the working and/or counter electrode, including the at least one amorphous nanostructured material, may be mixed together in a single layer. An example of a mixed layer is shown in  FIG. 1A  with respect to transition metal oxide bronze nanostructures  112  and TCO nanostructures  113 . Alternatively, nano structures that form the working and/or counter electrode, including the at least one amorphous nanostructured material, may be separately layered according to composition. For example, a working electrode may include a layer of amorphous NbO x  nanostructures, a layer of transition metal oxide bronze nanostructures, and a layer of ITO nanostructures, in any of a number of orders. 
     The nanostructured transition metal oxide bronzes that may be part of the working electrode  104  in various embodiment devices can be formed using any of a number of low cost solution process methodologies. For example, solutions of Nb:TiO 2  and Cs x WO 3  may be synthesized using colloidal techniques. Compared to other synthetic methodologies, colloidal synthesis may offer a large amount of control over the nanostructure size, shape, and composition of the nanostructured transition metal oxide bronze. After deposition, a nanostructured transition metal oxide bronze material in the working electrode  104  may be subjected to a thermal post treatment in air to remove and cap ligands on the surface of the nanostructures. 
     In various embodiments, nanostructured amorphous transition metal oxide materials may be formed at room temperature from an emulsion and an ethoxide precursor. For example, procedures used to synthesize tantalum oxide nanoparticles that are described in “Large-scale synthesis of bioinert tantalum oxide nanoparticles for X-ray computed tomography imaging and bimodal image-guided sentinel lymph node mapping” by M H Oh et al. (J Am Chem Soc. 2011 Apr. 13; 133(14):5508-15), incorporated by reference herein, may be similarly used to synthesize amorphous transition metal oxide nanoparticles. For example, an overall synthetic process of creating the nanoparticle, as described in Oh et al., may adopted from the microemulsion synthesis of silica nanoparticles. In such process, a mixture of cyclohexane, ethanol, surfactant, and a catalysis for the sol-gel reaction may be emulsified. The ethoxide precursor may be added to the emulsion, and uniform nanoparticles may be formed by a controlled-sol gel reaction in the reverse micelles at room temperature within around 5 minutes. The sol-gel reaction may be catalyzed, for example, by NaOH. 
     In some embodiments, the nanostructured amorphous transition metal oxide may be sintered at a temperature of at least 400° C. for at least 30 minutes, such as 400 to 600° C. for 30 to 120 minutes to form a porous web. In an example embodiment, the porous web may be included in a working electrode  104 , with the tungsten bronze nanoparticles and ITO nanoparticles incorporated in/on the web. Alternatively, the sintering step may be omitted and the nano structured amorphous transition metal oxide may remain in the device in the form of nanoparticles having amorphous structure. In this embodiment, the device containing the nanostructured amorphous transition metal oxide may include or may omit the protective layer(s)  116   a ,  116   b , and  118 , the UV stable electrolyte polymer, and the application of positive bias to the counter electrode. 
     Electrochromic responses of prepared nano structured transition metal oxide bronze materials (e.g., Cs x WO 3 , Nb:TiO 2 , etc.) may be demonstrated by spectro-electrochemical measurements. 
     In various embodiments, the shape, size, and doping levels of nanostructured transition metal oxide bronzes may be tuned to further contribute to the spectral response by the device. For instance, the use of rod versus spherical nanostructures  112  may provide a wider level of porosity, which may enhance the switching kinetics. Further, a different range of dynamic plasmonic control may occur for nanostructures with multiple facets, such as at least 20 facets. 
     Various embodiments may also involve alternation of the nanostructures  112  that form the working electrode  104 . For example, the nanostructures may be nanoparticles of various shapes, sizes and/or other characteristics that may influence the absorption of NIR and/or visible light radiation. In some embodiments, the nanostructures  112  may be isohedrons that have multiple facets, preferably at least 20 facets. 
     In some embodiments, the transition metal oxide bronze nanostructures  112  may be a combination of nanoparticles having a cubic unit cell crystal lattice (“cubic nanoparticles”) and nanoparticles having a hexagonal unit cell crystal lattice (“hexagonal nanoparticles”). Each unit cell type nanoparticle contributes to the performance of the working electrode  104 . For example, the working electrode  104  may include both cubic and hexagonal cesium doped tungsten oxide bronze nanoparticles. In alternative embodiments, the working electrode  104  may include either cubic or hexagonal cesium doped tungsten oxide nanoparticles. For example, the working electrode  104  may include cubic cesium-doped tungsten oxide (e.g. Cs 1 W 2 O 6-X ) nanoparticles and amorphous niobium oxide nanoparticles or hexagonal cesium-doped tungsten oxide (e.g. Cs 0.29 W 1 O 3 ) nanoparticles without niobium oxide. In alternative embodiments, the working electrode  104  may include undoped tungsten oxide (e.g. WO 3-x ) nanoparticles where 0≤x≤0.33, such as 0&lt;x≤0.17, including 0&lt;x≤0.1. 
     For example, upon application of the first (i.e., lower absolute value) voltage described above, the hexagonal bronze nanostructures  112  may block NIR radiation having wavelengths in the range of around 800-1700 nm, with the peak absorption at the mid-NIR wavelength of around 1100 nm. The cubic bronze nanostructures  112  may block NIR radiation having wavelengths in the close-NIR range with the peak absorption of around 890 nm. The indium oxide based (including ITO) and/or zinc oxide based (including AZO) nanostructures  113  may be included in the working electrode  104  to block the higher wavelength IR radiation upon application of the first voltage. Thus, the cubic bronze and hexagonal bronze nanostructures may block respective close and mid-NIR radiation (e.g., using the Plasmon effect), while the nanostructures  113  may block the higher wavelength IR radiation. 
     Upon application of the second (i.e., higher absolute value) voltage described above, the cubic bronze nanostructures  112  may block visible and NIR radiation having wavelengths in the range of around 500-1500 nm, with the peak absorption at the close-NIR wavelength of around 890 nm (e.g., using the polaron effect). Optionally, the amorphous niobium oxide may also be added to the working electrode  104  to block the short wavelength visible radiation (e.g., 400 to 500 nm wavelength). 
     The cubic bronze nanostructures block visible radiation via the polaron effect at a lower applied voltage than the hexagonal bronze nanostructures. Thus, the second voltage may have an absolute value which is below the value at which the hexagonal bronze nano structures block visible radiation via the polaron effect such that these nanostructures do not contribute to blocking of visible radiation. Alternatively, the second voltage may have an absolute value which is above the value at which the hexagonal bronze nanostructures block visible radiation via the polaron effect such that these nanostructures also contribute to blocking of visible radiation. 
     Embodiment nanoparticles that form the working electrode  104  may be around 4-6 nm in diameter, and may include 40 to 70 wt %, such as around 50 wt % cubic tungsten bronze nanostructures, 15 to 35 wt %, such as around 25 wt % hexagonal tungsten bronze nanostructures, and optionally 15 to 35 wt %, such as around 25 wt % ITO nanostructures. In some embodiments, in order to achieve color balancing as described above, the nanoparticles that form the working electrode  104  may optionally include around 5-10 wt % amorphous NbO x  nanostructures in place of cubic tungsten bronze nanostructures. In this embodiment, the device containing two types of bronze nanoparticles may include or may omit the protective layer(s)  116   a ,  116   b , and  118 , the UV stable electrolyte polymer, the application of positive bias to the counter electrode, and the amorphous niobium oxide. 
     In summary, the working electrode  104  may include one or more of the following components:
         (a) metal oxide bronze nanostructures  112  having (i) a cubic, (ii) hexagonal, or (iii) a combination of cubic and hexagonal unit cell lattice structure;   (b) protective (i) indium oxide based (including ITO) and/or zinc oxide based (including AZO) nanostructures  113 ;   (c) amorphous niobium oxide nanoparticles and/or web; and/or   (d) additional nanostructures selected from undoped tungsten oxide, molybdenum oxide, titanium oxide, and/or vanadium oxide.       

     The counter electrode  108  may include one or more of the following components:
         (a) passive electrode material selected from cerium(IV) oxide (CeO 2 ), titanium dioxide (TiO 2 ), cerium(III) vanadate (CeVO 2 ), indium(III) oxide (In 2 O 3 ), tin-doped indium oxide, tin(II) oxide (SnO 2 ), manganese-doped tin oxide, antimony-doped tin oxide, zinc oxide (ZnO), aluminum-doped zinc oxide (AZO), iron(III) oxide (Fe 2 O 3 ), and vanadium(V) oxide (V 2 O 5 );   (b) an active electrode material selected from chromium(III) oxide (Cr 2 O 3 ), manganese dioxide (MnO 2 ), iron(II) oxide (FeO), cobalt oxide (CoO), nickel(II) oxide (NiO), rhodium(IV) oxide (RhO 2 ), and iridium(IV) oxide (IrO 2 );   (c) amorphous nickel oxide nanoparticles and/or web; and/or   (d) conductivity enhancer nanoparticles selected from indium oxide, ITO, and zinc oxide.       

     While the various embodiments are described with respect to electrochromic windows, the embodiment methods, systems, and devices may also be used in materials for other types of smart windows. Such smart windows may include, but are not limited to, polymer-dispersed liquid crystals (PLDD), liquid crystal displays (LCDs), thermochromics, etc. 
     Color Tunability 
     Color tunability of electrochromic devices is applicable to a variety of applications. According to various embodiments, the present disclosure provides electrochromic devices having the capability of achieving a multitude of colors that may not currently be available in the market. The technique for achieving color tunability in one embodiment is based on the selection of the composition and the deposition of the active materials. While colored glass may be achieved by the use of doped glass (e.g., glass with metal impurities added to impart color), this is a non-standard product from most primary glass manufacturers on their float lines, and this entails cost premium. By contrast, the presently disclosed color tunability can be achieved in a nearly cost-neutral fashion, as the nanostructures can be synthesized for approximately the same cost for devices of different colors. 
     According to various embodiments, the present disclosure allows color of electrochromic devices to be tuned by utilizing various nanostructure compositions, or mixtures thereof, in the active, i.e. working, electrode of an electrochromic device. In particular, depending on the nanostructure components used and/or a ratio therebetween, a wide range of colors may be achieved, such as, for example, gray, blue, green, purple, and brown, but the present disclosure is not limited thereto. For example, an electrochromic device may include a working electrode including a variety of metal oxide nanostructures, such as nanocrystals and amorphous metal oxide nanoparticles. Such nanostructures may include WO 3 , Cs x WO 3  (where 0.2≤x≤0.4, e.g., 0.29≤x≤0.31), Cs 1 WO 6-σ  (where 0≤σ≤0.3), NbO x , TiO 2 , MoO 3 , NiO 2 , V 2 O 5 , or combinations thereof. 
       FIG. 2  is a schematic representation of an electrochromic device  180  that may be configured to produce a particular color, according to various embodiments or the present disclosure. The electrochromic device  180  is similar to the electrochromic device  150  of  FIG. 1B , so only the differences therebetween will be discussed in detail. 
     Referring to  FIG. 2 , the electrochromic device  180  includes a working electrode  104 . In particular, the working electrode  104  may include various nanostructures as discussed above, in order to produce corresponding colors. For example, the working electrode may include first nanostructures  115  and/or second nanostructures  117 , according to a particular color the working electrode  104  is configured to form. In other words, the second nanostructures  117  may be omitted, or additional nanostructures may be added. 
     For example, in order to produce a blue color, the working electrode  104  may include about 100 wt. % of WO 3  as the first nanostructures  115  and may omit the second nanostructures  117 . In order to produce a green color, the working electrode  104  may include about 60 wt. % of Cs x WO 3 , such as Cs 0.29 WO 3 , hexagonal crystal lattice structure nanocrystals as the first nanostructures  115 , and about 40 wt. % of indium tin oxide (e.g., Sn:In 2 O 3 ) nanocrystals as the second nanostructures  117 . 
     In order to produce a brown color, the working electrode  104  may include about 100 wt. % NbO x  nanoparticles (e.g., Nb 2 O 5-σ  where 0≤σ≤0.1) as the first nanostructures  115  and may omit the second nanostructures  117 . In order to produce a purple color, the working electrode  104  may include about 100 wt. % Nb:TiO 2  nanocrystals as the first nanostructures  115  and may omit the second nanostructures  117 . 
     According to various embodiments, the present inventors discovered that electrochromic devices that produce a neutral gray color may be unexpectedly advantageous. In particular, since the human eye is less sensitive with respect to detecting variations in neutral gray colors, as compared to variations in other colors, color variations in adjacent electrochromic devices that produce neutral gray colors are less noticeable to the human eye. As such, tone variations between adjacent electrochromic devices producing a neutral gray color may be greater than for other colors, without being noticeable to the human eye. 
     For example, in order to produce a neutral gray color, the first nanostructures  115  may include amorphous niobium oxide (“NbO x ”) nanoparticles (e.g., Nb 2 O 5-σ  where 0≤σ≤0.1), and the second nanostructures  117  may include cesium doped tungsten oxide (“CWO”) nanoparticles having a cubic crystal lattice structure (e.g., CsW 2 O 6-σ  nanocrystals, where 0≤σ≤0.3). Herein, the CWO nanoparticles may be referred to as “nanocrystals”, due to their crystalline structure. The relative amounts of the NbO x  nanoparticles and CWO nanocrystals included in the working electrode  104  may result in variations in the color of the working electrode  104 . 
     In particular, the working electrode  104  may include a nanostructured layer comprising from about 40 to about 80 wt. % of the NbO x  nanoparticles and from about 60 to about 10 wt. % of the CWO nanocrystals. In other embodiments, the working electrode  104  may include from about 65 to about 80 wt. % of the NbO x  nanoparticles and from about 35 to about 20 wt. % of the CWO nanocrystals. In some embodiments, the working electrode may include from about 40 to 50 wt. % of the NbO x  nanoparticles and from about 60 to about 50 wt. % of the CWO nanocrystals. 
     According to various embodiments, the NbO x  nanoparticles may have an average particle size of from about 2 to about 6 nm, such as from about 3 to about 5 nm. For example, the NbO x  nanoparticles may have an average particle size of about 4 nm. The CWO nanocrystals may have an average particle size of from about 3 to about 7 nm, such as from about 4 to about 6 nm. For example, the CWO nanocrystals may have an average particle size of about 5 nm. 
     According to other embodiments, the working electrode  104  may include a nanostructured layer comprising a mixture of amorphous molybdenum oxide nanoparticles (“MoO 3 ”) and tungsten oxide nanocrystals (“WO 3 ”), in order to produce a neutral gray color. In particular, the working electrode  104  may include a nanostructured layer comprising from about 40 to about 80 wt. % of the MoO 3  nanoparticles and from about 60 to about 10 wt. % of the WO 3  nanocrystals. In other embodiments, the working electrode  104  may include from about 65 to about 80 wt. % of the MoO 3  nanoparticles and from about 35 to about 20 wt. % of the WO 3  nanocrystals. In some embodiments, the working electrode may include from about 40 to 50 wt. % of the MoO 3  nanoparticles and from about 60 to about 50 wt. % of the WO 3  nanocrystals. 
     According to some embodiments, the working electrode  104  may include a nanostructured layer comprising molybdenum doped tungsten oxide nanocrystals. For example, the molybdenum doped tungsten oxide nanocrystals may be represented by the general formula Mo x WO 3  (where 0.1≤x≤0.75, e.g., 0.2≤x≤0.5). 
     According to various embodiments, the working electrode  104  may include a nanostructured layer comprising a mixture of amorphous niobium oxide (e.g., NbO x  described above) nanoparticles and undoped tungsten oxide nanocrystals, in order to produce a neutral gray color. In some embodiments, when the tungsten oxide is initially manufactured, the tungsten oxide may be dark blue in color. This may indicate oxygen vacancies in the tungsten oxide, meaning that the tungsten oxide is oxygen deficient (i.e., non-stoichiometric). The tungsten oxide may be annealed in air after initial manufacturing (e.g., before or after being placed into the electrochromic device), which may result in the tungsten oxide becoming transparent. The air-annealing may result in the filling of oxygen deficiencies in the tungsten oxide nanocrystals, which may result in the tungsten oxide being stoichiometric or less non-stoichiometric. 
     For example, the tungsten oxide may be represented by WO 3-x , where 0≤x≤0.33, such as 0≤x≤0.17. The tungsten oxide may be oxygen deficient, such that 0&lt;x≤0.33, such as 0&lt;x≤0.17. The tungsten oxide (e.g., undoped tungsten oxide) may have a cubic crystal structure. In particular, the working electrode  104  may include from about 85 to about 95 wt. % NbO x  nanoparticles and from about 15 to about 5 wt. % WO 3-x  nanocrystals. In other embodiments, the working electrode  104  may include from about 88 to about 93 wt. % NbO x  nanoparticles and from about 13 to about 7 wt. % WO 3-x  nanocrystals. In other embodiments, the working electrode  104  may include about 90 wt. % NbO x  nanoparticles and about 10 wt. % WO 3-x  nanocrystals. 
     In some embodiments, the working electrode  104  may have a thickness ranging from about 1200 to about 1800 nm. For example, the working electrode  104  may have a thickness ranging from about 1300 to about 1700 nm, or a thickness ranging from about 1400 to about 1600 nm. In other embodiments, the working electrode  104  may have a thickness of about 1500 nm and may include about 90 wt. % NbO x  nanoparticles and about 10 wt. % oxygen deficient WO 3-x  nanocrystals. 
     In various embodiments, the working electrode  104  comprises from about 40 to about 95 wt. % of amorphous niobium oxide nanoparticles and from about 60 to about 5 wt. % of cesium doped tungsten oxide nanoparticles having a cubic crystal lattice structure, or undoped, oxygen deficient tungsten oxide, based on the total weight of the nano structures. 
     EC Privacy Windows 
     Privacy applications are especially important for various EC window applications, such as residential window applications, for example. To insure privacy, an EC privacy window should have a dark state visible radiation transmission amount of about 0.1% or less, such as 0.01 to 0.1%, or an optical density of about 3.0 or more, such as 3.0 to 5.0. However, conventional EC devices generally have a dark state visible radiation transmittance of about 3-5%. 
     In order to provide privacy without providing such low levels of visible radiation transmittance, an EC privacy window may be configured to scatter light transmitted there through or thereto. In particular, such an EC window should have a degree of scattering, as measured by a transmitted haze, of about 80% or more, such as 80% to 99%. 
     According to various embodiments, EC windows that are configured for privacy applications are provided. In particular, provided are EC windows that include a light control layer or device (e.g., privacy device) in addition to an EC device. For example, as discussed below, various embodiments provide EC windows that include a second EC device, a polymer-dispersed liquid crystal (PDLC) layer, a switchable mirror, and/or a liquid crystal (LC) layer that behaves like a notch filter having a high optical density in a wavelength range of interest. 
       FIG. 3A  is a top schematic view of an EC privacy window  300  (e.g., insulated glass unit, (IGU)), according to various embodiments of the present disclosure. Referring to  FIG. 3A , the window  300  includes an EC pane unit  302 , a sealing separator  310 , a first pane  312 , a privacy device  340 , a control unit  350 , and optionally a low emissivity (Low-E) coating  330 . The EC pane unit  302  and the first pane  312  may be separated by a void or space  306 . Herein, a “pane” refers to a substantially transparent substrate, such as a glass or plastic substrate. 
     EC privacy windows components may be referred to as having “inner” and “outer” surfaces. Herein, the “inner” surfaces face the space  306 , and the “outer” surfaces face away from the space  306  toward the interior of a structure, such as a building or vehicle. As shown in  FIG. 3A , a privacy window may be depicted as having a particular orientation with respect to an external environment (outdoor environment depicted by the sun) and an internal environment (indoor environment of the structure). Thus, the EC pane unit  302  faces the Sun and the first pane  312  faces the interior of the structure. However, the orientation of an EC privacy window may be reversed in some embodiments, such that the EC pane unit  302  faces the interior of the structure and the first pane  312  faces the Sun. 
     The sealing separator  310  extends along the perimeter of the window  300  and may be configured to hermetically seal a space  306  between the EC pane unit  302  and the first pane  312 . The space  306  may be charged with an inert gas such as argon or nitrogen. In one embodiment, the space  306  is substantially liquid free. In one embodiment the space  306  is charged with an inert gas and is substantially liquid (e.g., moisture) free. In one embodiment, the space  306  has a moisture content of less than about &lt;0.1 ppm. 
     The Low-E coating  330  may be configured to minimize the amount of ultraviolet and infrared light that can pass through the EC window  300 , without substantially compromising the amount of visible radiation that is transmitted there through. In  FIG. 3A , the Low-E coating  330  is disposed on an inner surface of the EC pane unit  302 . However, the Low-E coating  330  may be disposed on an outer of the EC pane unit  302 , or may be disposed on inner or outer surfaces of the first pane  312 . In some embodiments, one or more panes of the EC pane unit  302 , may be formed of Low-E glass, and/or the first pane  312  may be formed of Low-E glass, and the Low-E coating  330  may be omitted. 
     The EC pane unit  302  may include a third pane  316 , a fourth pane  318 , and an EC device  320  disposed there between. The EC device  320  may include the transparent conductors, counter electrodes, electrolytes, insulating materials, working electrodes, and/or Bragg reflectors as described above with regard to  FIGS. 1A-2C . 
     The EC device  320  may be any of the EC devices  100 ,  150 ,  170 ,  180  described above, for example. The EC device  320  may have a dark state visible radiation transmittance ranging from about 3% to about 7%, such as from about 4% to about 6%, or about 5%. The EC device  320  may have a bright state visible radiation transmittance ranging from about 60% to about 70%, such as from about 63% to about 67%, or about 65%. In various embodiments, the EC device  320  may have a neutral gray color. 
     The privacy device  340  may be disposed on an inner surface of the first pane  312 , as shown in  FIG. 3A . However, the present disclosure is not limited to such a location. For example, the privacy device may be disposed on inner or outer surfaces of the first pane  312  or the EC device  320 , as shown in  FIGS. 3B-3D , for example. 
     The privacy device  340  may be configured to actively or passively modulate light transmitted thereto, such as light received from the external environment through the EC device  320 . In particular, the privacy device may absorb, reflect, filter, and/or scatter light transmitted thereto. For example, the privacy device  340  may include a liquid crystal (LC) device, a tunable filter LC device, a reflective LC device, a polymer-dispersed liquid crystal (PDLC) device, an EC device, a transition metal switchable mirror (TMSM) device, a one-way mirror, or the like. 
     In some embodiments, the privacy device  340  may be configured such that, when used alone or in conjunction with the EC device  320 , the window  300  has an optical density of greater than about 3.0, and/or a visible radiation transparency of about 0.1% or less, in a privacy state. In other embodiments, the privacy device  340  may be configured such that, when used alone or in conjunction with the EC device  320 , the window  300  has a transmitted haze of greater than 80%, in a privacy state. Herein, a “privacy state” refers to when at least a privacy device of an EC privacy window is in a dark state. 
     The control unit  350  may be configured to control the operation of the EC device  320  and/or the privacy device  340 . 
       FIG. 3B  is a top schematic view of an EC privacy window  301 , according to various embodiments of the present disclosure. The window  301  is similar to the window  300 , so only the differences therebetween will be discussed in detail. 
     Referring to  FIG. 3B , the privacy device  340  may be disposed on an inner surface of the EC pane unit  302 . The Low-E coating  330  may be disposed on an inner surface of the first pane  312 . 
       FIG. 3C  is a top schematic view of an EC privacy window  303 , according to various embodiments of the present disclosure. The window  303  is similar to the window  301 , so only the differences therebetween will be discussed in detail. 
     Referring to  FIG. 3C , the privacy device  340  may be disposed on an inner surface of the first pane  312 . The Low-E coating  330  may be disposed on an outer surface of the first pane  312 . 
       FIG. 3D  is a top schematic view of an EC privacy window  305 , according to various embodiments of the present disclosure. The window  305  is similar to the window  303 , so only the differences therebetween will be discussed in detail. 
     Referring to  FIG. 3D , the privacy device  340  may be disposed on an outer surface of the first pane  312 . The Low-E coating  330  may be disposed on an inner surface of the first pane  312 . In addition, the window  305  may optionally include a second pane  314  disposed on an outer surface of the first pane  312 , with the privacy device  340  being disposed therebetween. 
       FIG. 4  is a top schematic view of an EC privacy window  400 , according to various embodiments of the present disclosure. The window  400  is similar to the window  300 , so only the differences therebetween will be discussed in detail. 
     Referring to  FIG. 4 , the window  400  includes a first EC pane unit  302 , an opposing second EC pane unit  304 , a sealing separator  310 , and optionally a Low-E coating  330 . The second EC pane unit  304  includes a first pane  312 , a second pane  314 , and a privacy device  440  disposed therebetween. The privacy device  440  may be an EC device that includes multiples layered elements, such as the transparent conductors, counter electrodes, electrolytes, insulating materials, working electrodes, and/or Bragg reflectors described above with regard to  FIGS. 1A-2 . 
     The sealing separator  310  is disposed about peripheral regions of the first and second EC pane units  302 ,  304 , without substantially obscuring a viewable region of the window  400 . The sealing separator  310  may be configured to hermetically seal a space or chamber  306  that is at least partially defined by opposing surfaces of the EC pane units  302 ,  304 . The space  306  may be charged with an inert gas such as argon or nitrogen. In one embodiment, the space  306  is substantially liquid free. In one embodiment the space  306  is charged with an inert gas and is substantially liquid (e.g., moisture) free. In one embodiment, the space  306  has a moisture content of less than about &lt;0.1 ppm. 
     The Low-E coating  330  may be configured to minimize the amount of ultraviolet and infrared light that can pass through the EC window  400 , without compromising the amount of visible radiation that is transmitted there through. In  FIG. 3 , the Low-E coating  330  is disposed on an exterior surface (e.g., a surface facing the outdoor environment) of the second EC pane unit  304 . However, the Low-E coating  330  may be disposed on interior or exterior surfaces of either of the EC pane units  302 ,  304 . In some embodiments, one or more panes of the EC pane units  302 ,  304  may be formed of Low-E glass and the Low-E coating  330  may be omitted. 
     In some embodiments, one or both of the EC pane units  302 ,  304  may include any of the EC devices described above. In various embodiments, at least one of the EC pane units  302 ,  304  may have a neutral gray color. Herein, “visible transmittance” refers to an amount of visible radiation is transmitted through an element, with 0% visible transmittance referring to no visible light transmission, and with 100% visible light transmittance referring to complete or nearly complete transparency. 
     For example, the EC pane units  302 ,  304  may each have a dark state visible transmittance of about 3% or less, such as about 2.9%, or about 2.8% and may each have a bright state visible transmittance ranging from about 60% to about 70%, such as from about 63% to about 67%, or about 65%. Herein, the dark state of the second EC pane unit  304  may also be referred to as a privacy state. In addition, the window  400  may be referred to as having a bright state, where both the EC pane units  302 ,  304  are in the bright state, and a privacy or dark state, where both the EC pane units  302 ,  304  are in the dark or privacy state. 
     Accordingly, when the first EC pane unit  302  is in the dark state, and the second EC unit  304  is in the privacy/dark state, the window may assume a privacy state. In the privacy state, the window  400  may have a visible transmittance of about 0.1% or less, such as 0.09% or 0.08% or less, e.g., 0.05 to 0.09%. The inclusion of two EC pane units may also provide for improved sound isolation characteristics, as measured by a sound transfer coefficient. 
     In other embodiments, the EC pane units  302 ,  304  may have different visible transmittance values. For example, the first EC pane unit  302  may include a general EC device, and the second EC pane unit  304  may be a low-transmittance EC device. 
     In particular, the first EC pane unit  302  may have a dark state visible transmittance ranging from about 3% to about 7%, such as from about 4% to about 6%, or about 5%, and may have bright state visible transmittance ranging from about 60% to about 70%, such as from about 63% to about 67%, or about 65%. 
     The second EC pane unit  304  may have a dark/privacy state visible transmittance of ranging from about 0.5% to about 3%, such as from about 0.75% to about 2%, or about 1%, and may have a bright state visible transmittance ranging from about 35% to about 45%, such as from about 37% to about 43%, or about 40%. As such, the window  400  may have a total dark or privacy state visible transmittance of about 0.05% and a bright state visible transmittance of about 26%. 
       FIG. 5  is a sectional view of an EC privacy window  500 , according to various embodiments of the present disclosure. The window  500  is similar to the window  400 , so only the differences therebetween will be discussed in detail. 
     Referring to  FIG. 5 , the window  500  includes an EC pane unit  302 , a sealing separator  310 , a privacy device  540 , a first pane  312 , an opposing second pane  314 , and an optional Low-E coating  330 . The privacy device  540  is disposed between the first and second panes  312 ,  314 . As such, the privacy device  540  may have improved structural stability, physical protection, and/or environmental protection, as compared to a privacy device that is adhered to a single pane. 
     The privacy device  540  may include first and second electrodes  546 A,  546 B respectively disposed on opposing surfaces of the first and second panes  312 ,  314 , and an active region  542  disposed between the first and second electrodes  546 A,  546 B. The first and second electrodes  546 A,  546 B may be connected to a voltage source. The privacy device  540  may be configured to absorb, reflect, filter, and/or scatter light transmitted thereto, such as visible radiation. 
     In some embodiments, the privacy device  540  may be configured such that, when used in conjunction with the EC pane unit  302 , the window  500  has an optical density of greater than about 3.0, and/or a visible transmittance of about 0.1% or less, in a privacy state. In other embodiments, the privacy device  540  may be configured such that, when used in conjunction with the EC pane unit  302 , the window  500  has a transmitted haze of greater than 80% in a privacy state. 
     In some embodiments, the active region  542  may include a polymer-dispersed liquid crystal (PDLC) layer. The PDLC layer may be formed by dissolving or dispersing liquid crystals into a liquid polymer, followed by solidification or curing of the polymer. During the change of the polymer from a liquid to solid, the liquid crystals may become incompatible with the solid polymer and may form droplets throughout the solid polymer. The curing conditions affect the size of the droplets, which affects the final optical properties of the PDLC layer. The electrodes  546 A,  546 B may be formed of transparent, conductive materials, as described above with regard to transparent electrodes of the EC devices. 
     When no voltage is applied to the electrodes  546 A,  546 B, the PDLC layer assumes a translucent privacy state (e.g., dark state), where the liquid crystals are randomly arranged in the droplets. This results in scattering of light as it passes through the window  500 , producing a hazy “milky white” appearance. When a voltage is applied to the electrodes  546 A,  546 B, the PDLC layer assumes a transparent state, where the electric field formed between the electrodes  546 A,  546 B causes the liquid crystals to align, allowing light to pass through the droplets with very little scattering. The degree of transparency (e.g., haze amount) can be controlled by the magnitude of the applied voltage. 
     In other embodiments, the active region  542  may include a liquid crystal layer configured to operate as a tunable notch filter with high optical density in a wavelength range of interest. The liquid crystal layer may be tuned according to a voltage applied to the electrodes  546 A,  546 B. For example, the liquid crystal layer may be tuned to absorb visible radiation, and/or other wavelength ranges such as NIR radiation. The liquid crystal layer may have a dark state visible transmittance, that ranges from about 0.005% to about 1%, such as from about 0.05% to about 0.5%, or about 0.1%, and may have a bright state visible transmittance ranging from about 75% to about 85%, such as from about 77% to about 83%, or about 80%. For example, the tunable liquid crystal filter  542  has optical transmittance of about 0.1% over a wavelength range of from about 650 nm to about 890 nm. 
     In other embodiments, the active region  542  may include a reflective liquid crystal layer. For example, the privacy device  540  may include a switchable mirror, such as an e-TransFlector™ switchable mirror available from Kent Optronics, Inc, which switches between reflective and transmissive (i.e., bright) states. As such, the privacy device  540  may have a reflective (i.e., “dark”) state visible transmittance of about 0.1% and a bright state visible transmittance of between about 40 and 87%. In this case, when the privacy device  540  and the EC pane unit  302  are operated concurrently, the window  500  may have a dark state visible transmittance of about 0.005% and a bright state visible transmittance of about 59%. 
       FIG. 6  is a sectional view of an EC privacy window  600 , according to various embodiments of the present disclosure. The window  600  is similar to the window  500 , so only the differences therebetween will be described in detail. 
     Referring to  FIG. 6 , the window  600  includes a first pane  312 , a second pane  314 , and a privacy device  640  disposed therebetween. The privacy device  640  may include a first transparent electrode  646 A, a second transparent electrode  646 B, a mirror electrode  648 , and an electrolyte layer  650 . 
     The privacy device  640  may operate as a transition-metal switchable mirror (TMSM). The mirror electrode  648  may include magnesium and one or more transition metals, such as titanium and/or nickel. The electrolyte layer  650  may include ionic species, such as lithium ions. The mirror electrode  648  may be converted from a transparent to a reflecting state and back again, by application of current or voltage to the electrodes  646 A,  646 B, which causes the migration of ions from the electrolyte layer  650  into the mirror electrode  648 . As a result, the reflectivity of the mirror electrode  648  may be controlled according to the applied voltage. 
     In a bright (i.e., transmissive) state, the TMSM privacy device  640  may have a visible radiation transparency of about 50% and reflectivity of about 10%. In a reflective (i.e., “dark”) state, the TMSM privacy device  640  may have a visible radiation transparency of about 0.5% and reflectivity of about 75%. 
     The EC pane unit  302  and the TMSM privacy device  640  may be operated independently or concurrently. The window  600  may have a total visible radiation transmittance ranging from about 0.005% (dark state) to about 59% (bright state). 
     In one embodiment, the privacy devices  340 ,  440 ,  540  and/or  640  may be operated independently of the EC device in the EC pane unit  302 . In one embodiment, the window is configured to operate in the following three states: (i) a bright state where the EC device is in the bright state and the privacy device is in the bright state; (ii) a dark state where the EC device is in the dark state and the privacy device is in the bright state; and (iii) a privacy state where the privacy device is in the privacy state and the first EC device is in the dark state. 
     In another embodiment, the EC window is configured to operate in the following four states: (1) a bright state where the EC device is in the bright state and the privacy device is in the bright state; (2) a dark state where the EC device is in the dark state and the privacy device is in the bright state; (3) a bright privacy state where the privacy device is in the privacy state and the EC device is in the bright state; and (4) a dark privacy state where the privacy device is in the privacy state the EC device is in the dark state. For example, when the EC device is in the dark state, the visible transmittance of the window may be reduced from about 2% to about 0.1% or less, such as about 0.01%, by switching the privacy device from the bright state to the privacy state. 
     In various embodiments, the EC window may be configured to operate in more than four states. For example, in addition to the above four states, the EC window may include a number of intermediate states between the bright state and the dark privacy state. In particular, the EC device and/or the privacy device may be configured to have multiple different levels of visible transmittance and/or haze. For example, the EC device may have multiple intermediate states between bright and dark states, and the privacy device may have a bright state and a privacy state. In an embodiment, the control unit may also be configured to control the EC device to be in a plurality of additional intermediate states between the bright state and the dark state such that the window is further configured to operate in a plurality of additional intermediate states between the bright state and the dark privacy state. The control unit may control the EC device to be in the plurality of additional intermediate states by applying intermediate values of control voltage or current to the EC device. 
     For example, the EC device may have intermediate states that have a visible transmittance of one or more of 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, and/or 80%, etc. When the privacy device is configured to be in the bright state, then the EC window may have intermediate states having visible transmittance of one or more of 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, and/or 80%, etc. 
       FIG. 7  is a top schematic view of an EC privacy window  700 , according to various embodiments of the present disclosure. Referring to  FIG. 7 , the window  700  includes a first pane  702 , a first EC device  704 , and a second EC device  706 . Each EC device  704 ,  706  may include a first electrode  710 , a second electrode  714 , and an electrolyte layer  712  disposed therebetween. Herein, either of the EC devices  704 ,  706  maybe referred to, or operate as, a privacy device. The first and second electrodes  710 ,  714  may be different ones of a working electrode and a counter electrode. For example, the second electrodes  714  may be working electrodes, and the first electrodes  710  may be counter electrodes. 
     The window  700  may also include a second pane  720  and a third pane  722 . The second pane  720  may be configured to protect the second EC device  706 , and the third pane  722  may be configured to protect the first EC device  704 . The first pane  702  is located between the second and third panes  720 ,  730  and may separate the first and second EC devices  704 ,  706  from each other. Although not shown, the window  700  may include a sealing frame. 
       FIG. 8  is a top schematic view of an EC privacy window  800 , according to various embodiments of the present disclosure. Referring to  FIG. 8 , the window  800  may be a triple glazed window including, an EC pane unit  810 , a LC pane unit  820  (e.g., privacy device), and a first pane  802  disposed therebetween. The window  800  may also include a sealing separator  804  configured to support the EC pane unit  810 , the first pane  802 , and the LC pane unit  820 , such that a space  806  is formed between the EC pane unit  810  and the first pane  802 , and a space  806  is formed between the first pane  802  and the LC pane unit  820 . The spaces  806  may be charged with air or an inert gas, such as argon or nitrogen. 
     The EC pane unit  810  may include a second pane  812 , a third pane  814 , and an EC device  816  disposed therebetween. The LC pane unit  820  may include a fourth pane  822 , a fifth pane  824 , and a LC device  826  disposed therebetween. The EC pane unit  810  may form an exterior surface of the window  800 , and the LC pane unit  820  may form an interior surface of the window  800 , according to various embodiments, since the EC pane unit is less sensitive to cold than the LC pane unit. Locating the LC pane unit  820  on the interior side of the window  800  may beneficially protect the LC device  826  from temperature extremes, such as cold temperatures that may negatively affect the performance of the EC device  826 . The LC pane unit  820  typically has a faster switching time than the EC pane unit  810  to quickly set the privacy state by blocking visible light. In contrast, the EC pane unit  810  typically blocks heat (i.e., infrared radiation) and UV radiation. Thus, the EC and LC pane units located in series in the EC window are capable of fast privacy state switching as well as blocking heat and UV radiation. 
     The window  800  may also include a Low-E layer or coating  830  disposed on the first pane  802 . While shown on the exterior surface of the first pane  802 , the Low-E coating  830  may be disposed on the interior surface thereof, in some embodiments. In other embodiments, the first pane  802  may be a double or triple silver pane, such as a SuperNeutral 68 pane from Guardian Inc. 
       FIG. 9  is a top schematic view of an EC privacy window  801 , according to various embodiments of the present disclosure. The window  801  is similar to the window  800 , so only the difference therebetween will be discussed in detail. 
     Referring to  FIG. 9 , the window  801  is configured such that the first pane  802  forms the interior surface of the window  801 , the EC pane unit  810  forms the exterior surface of the window  801 , and the LC pane unit  820  is disposed therebetween. The Low-E coating  830  may be disposed on the exterior surface of the first pane  802 . 
     The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The description was chosen in order to explain the principles of the invention and its practical application. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.