Patent Publication Number: US-2021191215-A1

Title: Electrochromic devices

Description:
INCORPORATION BY REFERENCE 
     An Application Data Sheet is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed Application Data Sheet is incorporated by reference herein in their entireties and for all purposes. 
     FIELD 
     This disclosure relates to electrochromic devices, methods of fabrication, associated apparatus and the like. 
     BACKGROUND 
     Electrochromism is a phenomenon in which a material exhibits a reversible electrochemically-mediated change in an optical property when placed in a different electronic state, typically by being subjected to a voltage change. The optical property is typically one or more of color, transmittance, absorbance, and reflectance. One well known electrochromic material, for example, is tungsten oxide (WO 3 ). Tungsten oxide is a cathodic electrochromic material in which a coloration transition, transparent to blue, occurs by electrochemical reduction. 
     Electrochromic materials may be incorporated into, for example, windows and mirrors. The color, transmittance, absorbance, and/or reflectance of such windows and mirrors may be changed by inducing a change in the electrochromic material. One well known application of electrochromic materials, for example, is the rear view mirror in some cars. In these electrochromic rear view mirrors, the reflectivity of the mirror changes at night so that the headlights of other vehicles are not distracting to the driver. 
     While electrochromism was discovered in the 1960&#39;s, electrochromic devices still unfortunately suffer various problems and have not begun to realize their full commercial potential. Advancements in electrochromic technology, apparatus and related methods of making and/or using them, are needed. 
     SUMMARY 
     A typical electrochromic device includes an electrochromic (“EC”) electrode layer and a counter electrode (“CE”) layer, separated by an ionically conductive (“IC”) layer that is highly conductive to ions and highly resistive to electrons. In other words, the ionically conductive layer permits transport of ions but blocks electronic current. As conventionally understood, the ionically conductive layer therefore prevents shorting between the electrochromic layer and the counter electrode layer. The ionically conductive layer allows the electrochromic and counter electrodes to hold a charge and thereby maintain their bleached or colored states. In conventional electrochromic devices, the components form a stack with the ion conducting layer sandwiched between the electrochromic electrode and the counter electrode. The boundaries between these three stack components are defined by abrupt changes in composition and/or microstructure. Thus, the devices have three distinct layers with two abrupt interfaces. 
     Quite surprisingly, the inventors have discovered that high quality electrochromic devices can be fabricated without depositing an ionically-conducting electronically-insulating layer. In accordance with certain embodiments, the counter electrode and electrochromic electrodes are formed immediately adjacent one another, often in direct contact, without separately depositing an ionically-conducting layer. It is believed that various fabrication processes and/or physical or chemical mechanisms produce an interfacial region between contacting electrochromic and counter electrode layers, and this interfacial region serves at least some functions of an ionically conductive electronically-insulating layer in conventional devices. Certain mechanisms that may be key to forming the interfacial region are described below. 
     The interfacial region typically, though not necessarily, has a heterogeneous structure that includes at least two discrete components represented by different phases and/or compositions. Further, the interfacial region may include a gradient in these two or more discrete components. The gradient may provide, for example, a variable composition, microstructure, resistivity, dopant concentration (for example, oxygen concentration), and/or stoichiometry. 
     In addition to the above discoveries, the inventors have observed that in order to improve device reliability, two layers of an electrochromic device, the electrochromic (EC) layer and the counter electrode (CE) layer, can each be fabricated to include defined amounts of lithium. Additionally, careful choice of materials and morphology and/or microstructure of some components of the electrochromic device provide improvements in performance and reliability. In some embodiments, all layers of the device are entirely solid and inorganic. 
     Consistent with above observations and discoveries, the inventors have discovered that formation of the EC-IC-CE stack need not be done in the conventional sequence, EC→IC→CE or CE→IC→EC, but rather an ion conducting electronically-insulating region, serving as an IC layer, can be formed after formation of the electrochromic layer and the counter electrode layer. That is, the EC-CE (or CE-EC) stack is formed first, then an interfacial region serving some purposes of an IC layer is formed between the EC and CE layers using components of one or both of the EC and CE layers at the interface of the layers. Methods described herein not only reduce fabrication complexity and expense by eliminating one or more process steps, but provide devices showing improved performance characteristics. 
     Thus, one embodiment is a method of fabricating an electrochromic device, the method including: forming an electrochromic layer including an electrochromic material; forming a counter electrode layer in contact with the electrochromic layer without first providing an ion conducting electronically-insulating layer between the electrochromic layer and the counter electrode layer; and forming an interfacial region between the electrochromic layer and the counter electrode layer, where the interfacial region is substantially ion conducting and substantially electronically-insulating. The electrochromic layer and counter electrode layer are typically, but not necessarily, made of one or more materials more electronically conductive than the interfacial region but may have some electronically resistive character. The interfacial region can contain component materials of the EC layer and/or the CE layer, and in some embodiments, the EC and CE layers contain component materials of the interfacial region. In one embodiment, the electrochromic layer includes WO 3 . In some embodiments, the EC layer includes WO 3 , the CE layer includes nickel tungsten oxide (NiWO), and the IC layer includes lithium tungstate (Li 2 WO 4 ). 
     Heating may be applied during deposition of at least a portion of the electrochromic layer. In one embodiment, where the EC layer includes WO 3 , heating is applied after each of a series of depositions via sputtering in order to form an EC layer with a substantially polycrystalline microstructure. In one embodiment, the electrochromic layer is between about 300 nm and about 600 nm thick, but the thickness may vary depending upon the desired outcome which contemplates formation of the interfacial region after deposition of the EC-CE stack. In some embodiments, the WO 3  is substantially polycrystalline. In some embodiments, an oxygen rich layer of WO 3  can be used as a precursor to the interfacial region. In other embodiments the WO 3  layer is a graded layer with varying concentrations of oxygen in the layer. In some embodiments, lithium is a preferred ion species for driving the electrochromic transitions, and stack or layer lithiation protocols are described. Specifics of the formation parameters and layer characteristics are described in more detail below. 
     Another embodiment is a method of fabricating an electrochromic device, the method including: (a) forming either an electrochromic layer including an electrochromic material or a counter electrode layer including a counter electrode material; (b) forming an intermediate layer over the electrochromic layer or the counter electrode layer, where the intermediate layer includes an oxygen rich form of at least one of the electrochromic material, the counter electrode material and an additional material, where the additional material includes distinct electrochromic and/or counter electrode material, the intermediate layer not substantially electronically-insulating; (c) forming the other of the electrochromic layer and the counter electrode layer; and (d) allowing at least a portion of the intermediate layer to become substantially electronically-insulating and substantially ion conducting. Specifics of the formation parameters and layer characteristics for this method are also described in more detail below. 
     In other embodiments, a substantially electronically-insulating and ion conducting region is formed on, and after formation of, the electrochromic or the counter electrode layer, as a result of heating a superstoichiometric oxygen form of the electrochromic or the counter electrode layer in the presence of lithium. The other of the electrochromic or the counter electrode layer is formed after, and on, the substantially electronically-insulating and ion conducting region thus formed. In one example, the electrochromic layer is formed first, for example on a glass substrate having a transparent conductive oxide thereon. The electrochromic layer can have a first sub-layer of a metal oxide that is stoichiometric or sub-stoichiometric in oxygen and a top layer that is superstoichiometric in oxygen, or the electrochromic layer can be a graded composition with at least a superstoichiometric upper portion. Superstoichiometric metal oxides are exposed to lithium and heated to form the substantially electronically-insulating and ion conducting region. The counter electrode is formed thereon as part of fabrication of a functioning electrochromic stack. Further details of these methods are described below. 
     In other embodiments, a substantially electronically-insulating and ion conducting interfacial region is formed after formation of the electrochromic or the counter electrode layer, as a result of exposing a superstoichiometric oxygen form of the electrochromic or the counter electrode layer to lithium, followed by formation of the other of the electrochromic or the counter electrode layer. That is, during formation of the second electrode, a lithium flux is driven from the first formed electrode layer (having been exposed to lithium) into the second formed, or forming, electrode layer. It is believed that this lithium flux may drive formation of the substantially electronically-insulating and ion conducting interfacial region. In one example, the electrochromic layer is formed first, for example on a glass substrate having a transparent conductive oxide thereon. The electrochromic layer can have a first sub-layer of a metal oxide that is stoichiometric or sub-stoichiometric in oxygen and a top layer that is superstoichiometric in oxygen, or the electrochromic layer can be a graded composition with at least a superstoichiometric upper portion. Superstoichiometric metal oxides are exposed to lithium, for example sputtering lithium. The counter electrode is formed thereon where the aforementioned lithium flux forms the substantially electronically-insulating and ion conducting interfacial region between the electrochromic and counterelectrode layers. Further details of these methods are described below. 
     Another embodiment is an apparatus for fabricating an electrochromic device, including: an integrated deposition system including: (i) a first deposition station containing a material source configured to deposit an electrochromic layer including an electrochromic material; and (ii) a second deposition station configured to deposit a counter electrode layer including a counter electrode material; and a controller containing program instructions for passing the substrate through the first and second deposition stations in a manner that sequentially deposits a stack on the substrate, the stack having an intermediate layer sandwiched in between the electrochromic layer and the counter electrode layer; where either or both of the first deposition station and the second deposition station are also configured to deposit the intermediate layer over the electrochromic layer or the counter electrode layer, and where the intermediate layer includes an oxygen rich form of the electrochromic material or the counter electrode material and where the first and second deposition stations are interconnected in series and operable to pass a substrate from one station to the next without exposing the substrate to an external environment. In one embodiment, apparatus are operable to pass the substrate from one station to the next without breaking vacuum and may include one or more lithiation stations operable to deposit lithium from a lithium-containing material source on one or more layers of the electrochromic device. In one embodiment, apparatus are operable to deposit the electrochromic stack on an architectural glass substrate. Apparatus need not have a separate target for fabrication of an ion conducting layer. 
     Another embodiment is an electrochromic device including: (a) an electrochromic layer including an electrochromic material; (b) a counter electrode layer including a counter electrode material; and (c) an interfacial region between the electrochromic layer and the counter electrode layer, where the interfacial region includes an electronically-insulating ion conducting material and at least one of the electrochromic material, the counter electrode material and an additional material, where the additional material includes distinct electrochromic and/or counter electrode material. In some embodiments the additional material is not included; in these embodiments the interfacial region includes at least one of the electrochromic material and the counter electrode material. Variations in the composition and morphology and/or microstructure of the interfacial region are described in more detail herein. Electrochromic devices described herein can be incorporated into windows, in one embodiment, architectural glass scale windows. 
     Another embodiment is an EC element which is a single layer graded composition including an EC region, an IC region and a CE region, respectively. In certain embodiments, the EC element is all solid-state and inorganic. The EC element can be described in a number of ways, as detailed below. The EC element functions as an EC device, but is a single layer, not multiple layers, one stacked upon the other, as in conventional practice. In certain embodiments, the EC element includes transition metal oxides, alkali metals and mixed transition metal oxides. One embodiment is an EC device including a first transparent electrode, a second transparent electrode, and the EC element sandwiched in between the first and second transparent electrodes. In one embodiment, described in more detail in relation to  FIG. 4G , an EC element includes transparent conducting regions as well, i.e. a fully functioning EC element that is a single coating on a substrate. 
     Another embodiment is a method of fabricating a single layer EC element on a substrate in a sputter system, including: a) sputter coating an EC material including a first transition metal and a first oxygen concentration onto the substrate; b) increasing from the first oxygen concentration to a second oxygen concentration, higher than the first, during a); c) introducing lithium into the sputter system; and, d) sputter coating a CE material including a second transition metal and oxygen; wherein the fabrication is a substantially continuous process and the concentration of the first transition metal is decreased from a) to d), and the concentration of the second transition metal is increased from a) to d). In certain embodiments the first transition metal is tungsten and the second transition metal is nickel. Lithium may be introduced into the sputter system in a variety of ways including sputtering, evaporation and the like. 
     Yet another embodiment is a method of fabricating a single layer EC element on a substrate in a sputter system, including sputter coating materials from a plurality of closely associated sputter targets such that there is mixing of materials sputtered from each target in the region where two targets are proximate each other; wherein the single layer EC element is fabricated upon a single pass of the substrate and the plurality of closely associated sputter targets past each other. 
     Another embodiment is a method of fabricating a single layer EC element on a substrate in a sputter system, including sputter coating materials from a single sputter target including a composition reflective of the single layer EC element; wherein the single layer EC element is fabricated upon a single pass of the substrate and the single sputter target past each other. 
     These and other features and advantages will be described in further detail below, with reference to the associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description can be more fully understood when considered in conjunction with the drawings in which: 
         FIG. 1A  is a schematic cross-section depicting conventional formation of an electrochromic device stack. 
         FIG. 1B  is a graph showing composition of EC, IC and CE layers in a conventional electrochromic stack. 
         FIGS. 2A-F  are graphs showing representative component compositions for electrochromic devices. 
         FIGS. 3A and 3B  are process flows in accord with embodiments described herein. 
         FIGS. 4A-4D  are schematic cross-sections depicting formation of electrochromic devices in accord with specific embodiments described herein. 
         FIGS. 4E-4G  depict sputter targets and aspects of sputtering methods in accord with embodiments described herein. 
         FIG. 4H  depicts a schematic cross section of an electrochromic element. 
         FIGS. 4I-4L  depict sputter targets and aspects of sputtering methods in accord with embodiments described herein. 
         FIGS. 4M, 4N, 4P and 4Q  are schematic representations of sputtering according to embodiments described herein. 
         FIG. 5  depicts an integrated deposition system in a perspective view. 
         FIG. 6  is a graph showing how process parameters and endpoint readouts correlate during formation of an electrochromic stack in accord with embodiments described herein. 
         FIGS. 7 and 8A -C are actual cross-sections of electrochromic devices made using methods in accord with embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  is a schematic cross-section depicting a conventional electrochromic device stack,  100 . Electrochromic device  100  includes a substrate  102 , a conductive layer (CL)  104 , an electrochromic (EC) layer  106 , an ion conducting (IC) layer  108 , a counter electrode (CE) layer  110 , and a conductive layer (CL)  112 . Elements  104 ,  106 ,  108 ,  110 , and  112  are collectively referred to as an electrochromic stack  114 . Typically, the CL layers are made of a transparent conductive oxide, and are commonly referred to as “TCO” layers. Since the TCO layers are transparent, the coloring behavior of the EC-IC-CE stack is observable through the TCO layers, for example, allowing use of such devices on a window for reversible shading. A voltage source  116 , operable to apply an electric potential across electrochromic stack  114 , effects the transition of the electrochromic device from, for example, a bleached state (i.e., transparent) to a colored state. The order of the layers may be reversed with respect to the substrate. That is, the layers can be in the following order: substrate, transparent conductive layer, counter electrode layer, ion conducting layer, electrochromic material layer and (another) transparent conductive layer. 
     Again referring to  FIG. 1A , in conventional methods of fabricating an electrochromic stack, the individual layers are deposited one atop the other in a sequential format as depicted in the schematic on the left side of  FIG. 1A . That is, TCO layer  104  is deposited on substrate  102 . Then EC layer  106  is deposited on TCO  104 . Then IC layer  108  is deposited on EC layer  106 , followed by deposition of CE layer  110  on IC layer  108 , and finally TCO layer  112  on CE layer  110  to form electrochromic device  100 . Of course, the order of steps can be reversed to make an “inverted” stack, but the point is that in conventional methods the IC layer is necessarily deposited on the EC layer followed by deposition of the CE layer on the IC layer, or the IC layer is deposited on the CE layer followed by deposition of the EC layer on the IC layer. The transitions between the layers of material in the stack are abrupt. 
     One notable challenge with above procedure is the processing required to form the IC layer. In some prior approaches it is formed by a sol gel process which is difficult to integrate into a CVD or PVD process employed to form the EC and CE layers. Further, IC layers produced by sol gel and other liquid-based processes are prone to defects that reduce the quality of the device and may need to be removed by, for example, scribing. In other approaches, the IC layer is deposited by PVD from a ceramic target, which can be difficult to fabricate and use. 
       FIG. 1B  is a graph depicting material % composition versus position in the electrochromic stack of  FIG. 1A , namely layers  106 ,  108  and  110 , that is, the EC, IC and CE layers. As mentioned, in conventional electrochromic stacks, the transitions between the layers of material in the stack are abrupt. For example, EC material  106  is deposited as a distinct layer with little or no compositional bleed over to the adjacent IC layer. Similarly, IC material  108  and CE material  110  are compositionally distinct with little or no bleed over to adjacent layers. Thus, the materials are substantially homogeneous (except for certain compositions of CE material described below) with abrupt interfaces. Conventional wisdom was that each of the three layers should be laid down as distinct, uniformly deposited and smooth layers to form a stack. The interface between each layer should be “clean” where there is little intermixing of materials from each layer at the interface. 
     One of ordinary skill in the art would recognize that  FIG. 1B  is an idealized depiction, and that in a practical sense there is inevitably some degree of material mixing at layer interfaces. The point is, in conventional fabrication methods any such mixing is unintentional and minimal. The inventors have found that interfacial regions serving as IC layers can be formed where the interfacial region includes significant quantities of one or more electrochromic and/or counter electrode materials by design. This is a radical departure from conventional fabrication methods. In certain embodiments, there are no distinct layers as in conventional EC devices, that is, the conventional EC device is replaced with an EC element, that is, a single layer of graded materials that serves the function of an EC device. Various methods of forming these novel constructs are described in more detail below. 
     For the purposes of this disclosure, an EC device is an electrochromic stack construct, i.e., having more than one layer. An EC element is a single layer graded composition that serves the function of an EC device. It its most basic form, an EC element includes an EC region, an IC region and a CE region, in the form of a single layer graded composition. Thus supplied with, e.g, appropriate ions and when a field is applied across it, an EC element would color or bleach as an EC device would. If such an EC element is sandwiched between two electrode layers, then this would, collectively, constitute an EC device. However, if the EC element itself comprises not only EC, IC and CE regions, but also, e.g., transparent electrode regions, then it is not an EC device, it is an EC element because it is a single layer graded composition serving the function of an EC device. Certain embodiments described herein relate to EC devices, where there are at least two distinct layers in a stack format, while other embodiments relate to EC elements where there is only a single layer graded composition that serves the function of an EC device. 
     As mentioned above, the inventors have discovered that formation of the EC-IC-CE stack need not be conducted in the conventional sequence, EC→IC→CE or CE→IC→EC, but rather an interfacial region serving as the ion conducting layer can be formed after deposition of the electrochromic layer and the counter electrode layer. That is, the EC-CE (or CE-EC) stack is formed first, then an interfacial region, which may possess at least some functions of an IC layer, is formed between the EC and CE layers using components of one or both of the layers (and or another electrochromic or counter electrode material in some embodiments) at the interface of the layers. In some embodiments, the EC or CE is formed, including a superstoichiometric portion which may include an upper layer, and then exposed to lithium and heat to form an ionically-conducting substantially electronically-insulating region, followed by formation of the other of the EC and the CE. The ionically-conducting substantially electronically-insulating region then serves as the interfacial region between the EC and CE. In other embodiments, the EC or the CE is formed, including a superstoichiometric portion or upper layer, and then exposed to lithium, for example, via sputtering lithium. The other of the EC and CE is then formed thereon. It is believed that formation of the second electrode drives a lithium flux from the first formed electrode toward the second electrode. In turn, this flux of lithium drives formation of an ionically-conducting substantially electronically-insulating interfacial region between the EC and CE layers. In other embodiments a single layer graded composition, an EC element, is fabricated. The EC element includes an EC region, an IC region (the interfacial region) and a CE region (an ion storage region that may or may not also be electrochromic). The interfacial region serves at least some function of a conventional IC layer because it is substantially ion conducting and substantially electronically-insulating. It should be noted, however, that interfacial regions as described can have higher than conventionally accepted leakage currents but the devices show good performance nonetheless. 
     In one embodiment the electrochromic layer is formed with an oxygen rich region which is converted to the interfacial region or layer serving as an IC layer upon subsequent processing after the counter electrode layer is deposited. In some embodiments, a distinct layer which includes an oxygen rich version of an electrochromic material is used to (ultimately) form an interfacial layer serving as an IC layer between the EC and CE layers. In other embodiments, a distinct layer which includes an oxygen rich version of a counter electrode material is used to (ultimately) form an interfacial region serving as an IC layer between the EC and CE layers. All or a portion of the oxygen rich CE layer is converted to the interfacial region. In yet other embodiments, a distinct layer which includes an oxygen rich version of a counter electrode material and an oxygen rich form of an electrochromic material is used to (ultimately) form an interfacial region serving as an IC layer between the EC and CE layers. In other words, some or all of oxygen rich material serves as a precursor to the interfacial region that serves as an IC layer. Methods described herein can not only reduce process steps, but produce electrochromic devices showing improved performance characteristics. 
     As mentioned, it is believed that some of the EC and/or CE layer in an interfacial region is converted to a material that provides one or more functions of an IC layer, notably high conductivity for ions and high resistivity for electrons. The IC functional material in the interfacial region may be, for example, a salt of the conductive cations; for example, a lithium salt. 
       FIGS. 2A, 2B and 2C  show composition graphs of three possible examples of electrochromic device stacks (each containing an EC layer, a CE layer and an interfacial region serving as an IC layer), where the EC material is tungsten oxide (denoted here as WO 3 , but meant to include WO x , where x is between about 2.7 and about 3.5, in one embodiment x is between about 2.7 and about 2.9), the CE material is nickel tungsten oxide (NiWO) and the interfacial region primarily comprises lithium tungstate (denoted here as Li 2 WO 4 , in another embodiment, the interfacial region is a nanocomposite of between about 0.5 and about 50 (atomic) % Li 2 O, between about 5 and about 95% Li 2 WO 4 , and about 5 and about 70% WO 3 ) with some amount of the EC and/or the CE material. In more general terms, the interfacial region typically, though not necessarily, has a heterogeneous structure that includes at least two discrete components represented by different phases and/or compositions, which phases or compositions vary in concentration over the width of the interfacial region. Because of this the interfacial region that serves as an IC layer is sometimes referred to herein as a “gradient region,” a “heterogeneous IC layer” or a “dispersed IC layer.” The illustrations in  FIGS. 2A, 2B and 2C , although described in terms of specific materials, are more generally representative of composition variations of any suitable materials for electrochromic devices described herein. 
       FIG. 2A  depicts an electrochromic stack where the EC material is a significant component of the interfacial region that functions as an IC layer, while the CE material is not a significant component. Referring to  FIG. 2A , starting at the origin and moving from left to right along the x-axis, one can see that a portion the EC material, WO 3 , which is substantially all tungsten oxide, serves as the EC layer. There is a transition into the interfacial region where there is gradually less tungsten oxide and correspondingly gradually more of lithium tungstate, up to and including near the end of the interfacial region where there is a portion that is substantially all lithium tungstate with some minor amounts of tungsten oxide. Although the transition from the EC layer to the interfacial region is demarked at a composition of substantially all tungsten oxide and de minimus amounts of lithium tungstate, it is clear that the transition is not abrupt as in conventional devices. In this example, effectively the transition begins to occur where the composition has sufficient quantity of lithium tungstate to enable the material to serve at least some functions of an IC layer, for example, ion conduction and electronic insulation. Certainly the composition much closer to the CE layer, where the composition is substantially lithium tungstate, serves the function of an IC layer, as lithium tungstate is known to exhibit these properties. But there is also some IC layer function in other parts of interfacial region. The inventors have found that such “heterogeneous IC layers” improve switching characteristics and perhaps thermal cycling stability of electrochromic devices as compared to conventional devices with abrupt transitions. The CE layer in this example contains primarily nickel tungsten oxide as the active material, and has a relatively abrupt transition to the nickel tungsten oxide composition at the edge of the interfacial region. Methods for making stacks with such interfacial regions are described in more detail below. 
     It should be noted that, for example, that the nickel tungsten oxide CE layer in  FIG. 2A  is depicted as having about 20% lithium tungstate. Without wishing to be bound by theory, it is believed that the nickel tungsten oxide CE layer exists as nickel oxide cores or particles surrounded by a shell or matrix of lithium tungstate which imparts moderately good ionic conductivity to the CE layer, and thereby aids in the electrochromic transition of the CE layer during operation of the electrochromic stack. The exact stoichiometry of lithium tungstate in the CE layer may vary significantly from embodiment to embodiment. In some embodiments, there may also be some tungsten oxide in the CE layer. Also, because lithium ions travel to and from the EC and CE layers via the interfacial region serving as the IC layer, there may be significant amounts of lithium tungstate in the EC layer, for example as depicted in  FIG. 2A . 
       FIG. 2B  depicts an electrochromic stack where the CE material is a significant component of the interfacial region that functions as an IC layer, while the EC material is not a significant component. Referring to  FIG. 2B , starting at the origin and moving from left to right along the x-axis, one can see that in this case, the EC material, which is substantially all tungsten oxide, serves as the EC layer. There is an abrupt transition into the interfacial region where there is little if any tungsten oxide, but there is a large amount of lithium tungstate and at least some nickel tungsten oxide (CE material). The composition of the interfacial region changes along the x-axis with progressively less and less lithium tungstate and correspondingly more and more nickel tungsten oxide. The transition from the interfacial region to the CE layer is demarked arbitrarily at a composition of about 80% nickel tungsten oxide and about 20% of lithium tungstate, but this is merely an example of where the transition occurs in a graded composition. The interfacial region may be viewed as ending when no, or little, additional change in composition occurs when progressing further through the stack. In addition, the transition effectively ends where the composition has sufficient quantity of nickel tungsten oxide such that the material no longer serves at least some function that a distinct IC layer would serve. Certainly the composition much closer to the CE layer as demarked, where the composition is 80% nickel tungsten oxide, serves the function of a CE layer. Likewise, the composition of the interfacial region much closer to the EC layer, where lithium tungstate is the substantial component, serves as an ion conducting electronically-insulating material. 
       FIG. 2C  depicts an electrochromic stack where both the EC material and the CE material are significant components of the interfacial region that functions as an IC layer. Referring to  FIG. 2C , starting at the origin and moving from left to right along the x-axis, one can see that a portion the EC material, WO 3 , which is substantially all tungsten oxide, serves as the EC layer. There is a transition into the interfacial region where there is gradually less tungsten oxide and correspondingly gradually more lithium tungstate. In this example, about a third of the way through what is (arbitrarily) demarked as the interfacial region, there is also a growing amount of nickel tungsten oxide counter electrode material. At about midway through what is demarked as the interfacial region, there is about 10% each of tungsten oxide and nickel tungsten oxide and 80% lithium tungstate. In this example there is no abrupt transition between an EC layer and an IC layer or between an IC layer and a CE layer, but rather an interfacial region which has a continuous graded composition of both the CE and EC materials. In fact, there is no abrupt boundary or distinct layer present, so this example is not actually a stack of materials, but rather a single graded layer comprising an EC region, and IC region and a CE region. This is an example of an EC element. In this example, the lithium tungstate component peaks at about half way through the interfacial region, and so this region is likely the strongest electronically-insulating portion of the interfacial region. 
     As mentioned above in the Summary section, the EC and CE layers may include material components that impart some electrical resistivity to the EC and CE layers; the lithium tungstate in described in  FIGS. 2A-C  that spans all three regions, at least in some quantity, is an example of such materials that impart electrical resistivity to the EC and CE layers. 
       FIGS. 2A-C  represent only three non-limiting examples of graded compositions of interfacial regions that serve as IC layers in electrochromic devices described herein. One of ordinary skill in the art would appreciate that many variations are possible without escaping the scope of the description. In each of the examples in  FIGS. 2A-C  there is at least one layer where there are only two material components and one of the components not present or present only at a level that is de minimus. The invention is not limited in this way. Thus, one embodiment is an electrochromic device including a electrochromic layer, an interfacial region serving as an IC layer, and a counter electrode layer, where at least one material component of each of the aforementioned two layers and one region of the device is present in each of the electrochromic layer, the interfacial region and the counter electrode layer in a concentration of at least about 25% by weight, in another embodiment at least about 15% by weight, in another embodiment at least about 10% by weight, in another embodiment at least about 5% by weight, in yet another embodiment at least about 2% by weight. In another embodiment, the material component is present at any of these concentration ranges in only two of the three layers and region. In the depicted embodiments, the interface between at least two of the three component layers/regions is not abrupt but exhibits substantial variation in composition over a region of, for example, at least about 20 nm and/or at least about 2% of the total thickness of the EC element. 
     The amount of electrochromic and/or counter electrode material in the interfacial region can be significant, in one embodiment as much as 50% by weight of the interfacial region. However, in many embodiments, the ion-conducting electronically-insulating material is typically the majority component, while the remainder of the interfacial region is electrochromic and/or counter electrode material. In one embodiment, the interfacial region includes between about 60% by weight and about 95% by weight of the ion-conducting electronically-insulating material while the remainder of the interfacial region is electrochromic and/or counter electrode material. In one embodiment, the interfacial region includes between about 70% by weight and about 95% by weight of the ion-conducting electronically-insulating material while the remainder of the interfacial region is electrochromic and/or counter electrode material. In one embodiment, the interfacial region includes between about 80% by weight and about 95% by weight of the ion-conducting electronically-insulating material while the remainder of the interfacial region is electrochromic and/or counter electrode material. 
     In some embodiments, interfacial regions in devices described herein may be relatively distinct, that is, when analyzed, for example by microscopy, there are relatively distinguishable boundaries at adjoining layers, even though the interfacial region contains amounts of the electrochromic and/or counter electrode material. In such embodiments the interfacial region&#39;s thickness can be measured. In embodiments where the interfacial region is formed from an oxygen-rich (super-stoichiometric) region of an EC and/or CE layer, the ratio of the thickness of the interfacial region as compared to the layer or layers it is formed from is one metric for characterizing the interfacial region. For example, an electrochromic layer is deposited with an oxygen-rich upper layer. The EC layer may include a single metal oxide or two or more metal oxides mixed homogenously or heterogeneously in layers or more diffuse regions. The EC layer is 550 nm thick, including the oxygen-rich layer (or region). If about 150 nm of the EC layer is converted to interfacial region, then about 27% of the EC is converted to interfacial region, that is, 150 nm divided by 550 nm. In another example, the EC layer includes a first metal oxide region (or layer) and a second metal oxide layer (or region) that is oxygen-rich. If all or a portion of the oxygen-rich metal oxide layer is converted to interfacial region, then the thickness of the interfacial region divided by the total thickness of the first and second metal oxide layers (prior to formation of the interfacial region) is a metric for the interfacial region. In one embodiment, the interfacial region includes between about 0.5% and about 50% by thickness of a precursor region (EC and/or CE, including oxygen-rich portion) used to form it, in another embodiment, between about 1% and about 30%, in yet another embodiment, between about 2% and about 10%, and in another embodiment between about 3% and about 7%. 
     The inventors have discovered that graded compositions serving as the IC layer have many benefits. While not wishing to be bound by theory, it is believed that by having such graded regions, the efficiency of the electrochromic transitions is improved dramatically. There are other benefits as described in more detail below. 
     While not wishing to be bound to theory, it is believed that one or more of the following mechanisms may affect the transformation of EC and/or CE material to an IC functioning material in the interfacial region. However, the performance or application of embodiments described herein is not limited to any of these mechanisms. Each of these mechanisms is consistent with a process in which IC layer material is never deposited during fabrication of the stack. As is made clear elsewhere herein, apparatus described herein need not have a separate target comprising material for an IC layer. 
     In a first mechanism, the direct lithiation of the electrochromic material or the counter electrode material produces an IC material (for example, a lithium tungstate) in the interfacial region. As explained more fully below various embodiments employ direct lithiation of one of the active layers at a point in the fabrication process between the formation of the EC and CE layers. This operation involves exposure of the EC or CE layer (whichever is formed first) to lithium. According to this mechanism, a flux of lithium passing through the EC or CE layer produces an ionically conductive, electronically resistive material such as a lithium salt. Heating or other energy can be applied to drive this flux of lithium. This described mechanism converts the top or exposed portion of the first formed layer (EC or CE layer) prior to formation of the second layer (CE or EC layer). 
     Thus, one embodiment is a method of fabricating an electrochromic device including: (a) forming either an electrochromic layer including an electrochromic material or a counter electrode layer including a counter electrode material; (b) forming an intermediate layer over the electrochromic layer or the counter electrode layer, where the intermediate layer includes an oxygen rich form of at least one of the electrochromic material, the counter electrode material and an additional material, where the additional material includes distinct electrochromic or counter electrode material, the intermediate layer not substantially electronically-insulating; (c) exposing the intermediate layer to lithium; and (d) heating the stack formed in order to convert at least part of the intermediate layer to a region, coextensive with the area of the intermediate layer, including an electronically-insulating ionically-conducting material and the material of the intermediate layer. The region can include a heterogeneous mixture of the electronically-insulating ionically-conductive material and the material of the intermediate layer. The additional material mentioned relates to the fact that sometimes it is desirable to use mixed metal oxides in an electrochromic and/or a counter electrode layer, rather than a single metal oxide, for example. The nature of mixed metal oxides in accord with methods and devices described herein is described in more detail below. 
     In one embodiment, the electrochromic layer is formed first. In one embodiment, the electrochromic layer is deposited tungsten oxide. In one embodiment, depositing tungsten oxide includes sputtering using a tungsten target and a first sputter gas including between about 40% and about 80% O 2  and between about 20% Ar and about 60% Ar, to reach a thickness of between about 350 nm and about 450 nm, and heating, at least intermittently, to between about 150° C. and about 450° C. during formation of the electrochromic layer. In one embodiment, the electrochromic layer is substantially polycrystalline WO 3 . 
     In one embodiment, the intermediate layer is a superstoichiometric oxygen form of WO 3 . In one embodiment, the superstoichiometric tungsten oxide is deposited via sputtering a tungsten target and a second sputter gas including between about 70% and 100% O 2  and between 0% Ar and about 30% Ar, to reach a thickness of between about 10 nm and about 200 nm, without heating. 
     In one embodiment, (c) includes sputtering lithium onto the intermediate layer until the blind charge is satisfied and (d) includes heating the stack to between about 100° C. and about 450° C. In another embodiment, (d) includes heating the stack to between about 200° C. and about 350° C., for between about 2 minutes and about 30 minutes. In either of the former two embodiments, (d) can be performed under an inert atmosphere and/or an oxidizing atmosphere. Examples of inert atmospheres include argon, nitrogen and the like; oxidizing atmospheres include oxygen and other oxidizing agents. 
     In some embodiments, rather than two layers of EC or CE material, one near or at stoichiometric oxygen, a single layer is used, where the layer has at least a portion that is superstoichiometric in oxygen. In one embodiment, a graded layer is used where the layer has a gradually varying composition with at least a superstoichiometric oxygen upper portion. Thus, another embodiment is a method of fabricating an electrochromic device including: (a) forming either an electrochromic layer including an electrochromic material or a counter electrode layer including a counter electrode material, where the layer formed includes a superstoichiometric oxygen portion in an upper region of, and coextensive with, the area of the layer; (b) exposing the superstoichiometric oxygen portion to lithium; and (c) heating to convert at least part of the superstoichiometric oxygen portion to a region, coextensive with the area of the superstoichiometric oxygen portion and including an electronically-insulating ionically-conducting material and the material of the superstoichiometric oxygen portion. In one embodiment, the region includes a non-homogeneous mixture of the electronically-insulating ionically-conducting material and the material of the superstoichiometric oxygen portion. 
     In one embodiment, (a) includes forming the electrochromic layer by depositing tungsten oxide. In one embodiment, depositing tungsten oxide includes sputtering using a tungsten target and a sputter gas, where the sputter gas includes between about 40% and about 80% O 2  and between about 20% and about 60% Ar at the start of sputtering the electrochromic layer, and the sputter gas includes between about 70% and 100% O 2  and between 0% and about 30% Ar at the end of sputtering the electrochromic layer, and heating, at least intermittently, to between about 200° C. and about 350° C. at the beginning of formation of the electrochromic layer but not heated during deposition of at least a final portion of the electrochromic layer. 
     In one embodiment, (b) includes sputtering, or otherwise delivering, lithium onto the intermediate layer until the blind charge is satisfied and (c) includes heating the stack to between about 100° C. and about 450° C. In another embodiment, (c) includes heating the stack to between about 200° C. and about 350° C., for between about 2 minutes and about 30 minutes. In either of the former two embodiments, (c) can be performed under an inert atmosphere and/or an oxidizing atmosphere. Examples of inert atmospheres include argon, nitrogen and the like; oxidizing atmospheres include oxygen and other oxidizing agents. 
     In either of the two aforementioned methods, that is, using an electrochromic material having either an intermediate superstoichiometric oxygen layer or a single layer with a superstoichiometric oxygen upper region, further processing include forming the counter electrode layer on the region. In one embodiment, the counter electrode layer includes NiWO, between about 150 nm and about 300 nm thick. In one embodiment, the NiWO is substantially amorphous. Further processing can include sputtering, or otherwise delivering, lithium onto the counter electrode layer until the counter electrode layer is substantially bleached and sputtering an additional amount of lithium onto the counter electrode layer, between about 5% and about 15% excess based on the quantity required to bleach the counter electrode layer. A transparent conducting oxide layer, such as indium tin oxide, can be deposited on top of the counter electrode layer. 
     In one embodiment, stacks formed in this way are heated, before or after depositing the transparent conducting oxide, at between about 150° C. and about 450° C., for between about 10 minutes and about 30 minutes under Ar, and then for between about 1 minute and about 15 minutes under O 2 . After this processing, the stack is processed further by heating the stack in air at between about 250° C. and about 350° C., for between about 20 minutes and about 40 minutes. Flowing a current between the electrochromic layer and the counter electrode layer, as part of an initial activation cycle of the electrochromic device, can also be performed. 
     Referring again to the interfacial region formation mechanisms, in a second mechanism, lithium diffusing from one of the EC or CE to the other layer, after both layers have formed and/or during formation of a second layer upon a lithiated first layer, causes conversion of part of one of the EC and/or CE at their interface to the interfacial region having the IC functioning material. The lithium diffusion may take place after all the second layer has formed or after only some fraction of the second layer has formed. Further, the diffusion of lithium and consequent conversion to IC functional material take place in either the first or second deposited layers and in either the EC or CE layer. In one example, the EC layer is formed first and then lithiated. As the CE layer is subsequently deposited on top of the EC layer, some lithium diffuses from the underlying EC layer toward and/or into the CE layer causing a transformation to an interfacial region which contains an IC functioning material. In another example, the EC layer formed first (optionally with an oxygen rich upper region), then the CE layer is formed and lithiated. Subsequently some lithium from the CE layer diffuses into the EC layer where it forms the interfacial region having the IC functioning material. In yet another example, the EC layer is deposited first and then lithiated to produce some IC functioning material according to first the mechanism described above. Then, when the CE layer is formed, some lithium diffuses from the underlying EC layer toward the CE layer to produce some IC material in an interfacial region of the CE layer. In this manner, the IC functioning material nominally resides in both the CE and EC layers proximate their interface. 
     Thus, another embodiment is a method of fabricating an electrochromic device including: (a) forming either an electrochromic layer including an electrochromic material or a counter electrode layer including a counter electrode material; (b) forming an intermediate layer over the electrochromic layer or the counter electrode layer, where the intermediate layer includes an oxygen rich form of at least one of the electrochromic material, the counter electrode material and an additional material, where the additional material includes distinct electrochromic or counter electrode material, the intermediate layer not substantially electronically-insulating; (c) exposing the intermediate layer to lithium; and (d) depositing the other of the electrochromic layer and the counter electrode layer on the intermediate layer thereby converting at least part of the intermediate layer to a region, coextensive with the area of the intermediate layer and including an electronically-insulating ionically-conducting material and the intermediate layer material. In one embodiment, the region includes a non-homogeneous mixture of the electronically-insulating ionically-conducting material and the intermediate layer material. 
     In one embodiment, the electrochromic layer is formed first and includes depositing tungsten oxide. In one embodiment, depositing tungsten oxide includes sputtering using a tungsten target and a first sputter gas including between about 40% and about 80% O 2  and between about 20% Ar and about 60% Ar, to reach a thickness of between about 350 nm and about 450 nm, and heating, at least intermittently, to between about 150° C. and about 450° C. during formation of the electrochromic layer. In one embodiment, the electrochromic layer is substantially polycrystalline WO 3 . In this embodiment, the intermediate layer is a superstoichiometric oxygen form of WO 3 , for example, in one embodiment, (b) includes sputtering WO 3  using a tungsten target and a second sputter gas including between about 70% and 100% O 2  and between 0% Ar and about 30% Ar, to reach a thickness of between about 10 nm and about 200 nm, without heating. 
     In some embodiments, rather than two layers of EC or CE material, one near or at stoichiometric oxygen, a single layer is used, where the layer has at least a portion that is superstoichiometric in oxygen. In one embodiment, a graded layer is used where the layer has at least a superstoichiometric oxygen upper portion. Thus, another embodiment is a method of fabricating an electrochromic device including: (a) forming either an electrochromic layer including an electrochromic material or a counter electrode layer including a counter electrode material, where the layer formed includes a superstoichiometric oxygen portion in an upper region of, and coextensive with, the area of the layer; (b) exposing the superstoichiometric oxygen portion to lithium; and (c) depositing the other of the electrochromic layer and the counter electrode layer on the superstoichiometric oxygen portion thereby converting at least part of the superstoichiometric oxygen portion to a region, coextensive with the area of the superstoichiometric oxygen portion and including an electronically-insulating ionically-conducting material and the material of the superstoichiometric oxygen portion. In one embodiment, the region includes a non-homogeneous mixture of the electronically-insulating ionically-conducting material and the material of the superstoichiometric oxygen portion. 
     In one embodiment, the electrochromic layer is formed first. In one such embodiment, the electrochromic layer includes depositing tungsten oxide. In one embodiment, depositing tungsten oxide includes sputtering using a tungsten target and a sputter gas, where the sputter gas includes between about 40% and about 80% O 2  and between about 20% and about 60% Ar at the start of sputtering the electrochromic layer, and the sputter gas includes between about 70% and 100% O 2  and between 0% and about 30% Ar at the end of sputtering the electrochromic layer, and heating, at least intermittently, to between about 200° C. and about 350° C. at the beginning of formation of the electrochromic layer but not heated during deposition of at least a final portion of the electrochromic layer. This EC layer may also be substantially polycrystalline. 
     In either of the two aforementioned methods, that is, using an electrochromic material having either an intermediate superstoichiometric oxygen layer or a single layer with a superstoichiometric oxygen upper region, exposing either the intermediate layer or the superstoichiometric oxygen portion to lithium can include sputtering, or otherwise delivering, lithium onto the aforementioned layer or portion. Depositing the other of the electrochromic layer and the counter electrode layer includes forming the counter electrode layer on the intermediate layer or the superstoichiometric oxygen portion. In one embodiment, the counter electrode layer includes NiWO, between about 150 nm and about 300 nm thick. In one embodiment, the NiWO is substantially amorphous. Further processing can include sputtering, or otherwise delivering, lithium onto the counter electrode layer until the counter electrode layer is substantially bleached and sputtering an additional amount of lithium onto the counter electrode layer, between about 5% and about 15% excess based on the quantity required to bleach the counter electrode layer. A transparent conducting oxide layer, such as indium tin oxide, can be deposited on top of the counter electrode layer. 
     In one embodiment, stacks formed in this way are heated, before or after depositing the transparent conducting oxide, at between about 150° C. and about 450° C., for between about 10 minutes and about 30 minutes under Ar, and then for between about 1 minute and about 15 minutes under O 2 . After this processing, the stack is processed further by heating the stack in air at between about 250° C. and about 350° C., for between about 20 minutes and about 40 minutes. Flowing a current between the electrochromic layer and the counter electrode layer as part of an initial activation cycle of the electrochromic device can also be performed. 
     In a third mechanism, the EC and CE layers are formed to completion (or at least to the point where the second formed layer is partially complete). Then, the device structure is heated and the heating converts at least some of the material in the interfacial region to an IC functioning material (for example, a lithium salt). Heating, for example as part of a multistep thermochemical conditioning (MTCC) as described further herein, may be performed during deposition or after deposition is completed. In one embodiment, the heating is performed after a transparent conductive oxide is formed on the stack. In another embodiment, heating is applied after the second layer is partially or wholly complete, but before a transparent conductive oxide is applied thereto. In some cases, the heating is directly and primarily responsible for the transformation. In other cases, the heating primarily facilitates the diffusion or flux of lithium ions that creates the IC-functioning material region as described in the second mechanism. 
     Finally, in a fourth mechanism, current flowing between the EC and CE layers drives the transformation of at least one of the electrochromic material and the counter electrode material to the IC-functioning material in the interfacial region. This may occur because, for example, an ion flux associated with the flowing current is so large it drives a chemical transformation of EC and/or CE material to IC material in the interfacial region. For example, as explained below, a large lithium flux through tungsten oxide in an EC layer may produce lithium tungstate, which serves as an IC material. The lithium flux may be introduced during, for example, an initial activation cycle of a newly formed device. In one embodiment, the current flow in the initial activation cycle is used, in lieu of heating, to drive the chemical transformation. However, this need not be the case, as other opportunities for driving high ionic fluxes may be more appropriate for effecting the conversion. More generally it is the application of an energy form, for example heat and/or electric current that drives the conversion of the materials to the ionically conductive electronically insulating interfacial region. Other energy forms such as vibrational energy, radiant energy, acoustic energy, mechanical energy and the like can be used. Methods described herein can be performed by one of ordinary skill in the art without resort to any one or more of the above mechanisms. 
     As described in relation to  FIG. 2C , an EC element has no abrupt transition between an EC layer and an IC layer or between an IC layer and a CE layer, but rather is a single layer graded composition having an EC region, which transitions to an IC region (the interfacial region), which transitions to a CE region. Since an EC element is a single layer of graded composition, EC elements can be described in a number of ways including those below. The following description is meant to illustrative of certain embodiments of EC elements. 
     One embodiment is an EC element which is a single layer graded composition including an EC region, an IC region and a CE region, respectively. In one embodiment, the EC element is all solid-state and inorganic. A single EC element can be described in a number of ways in order to understand the graded composition of which it is comprised. In various embodiments, the single layer graded composition EC element has no abrupt boundaries between EC/IC or between IC/CE. Rather both of these interfaces are characterized by graded compositions as discussed herein. In some cases, the single layer graded composition EC element has a continuously variable composition across all regions of the element. In other cases, the element has at least one region, or at least two regions, of constant composition.  FIGS. 2D, 2E and 2F  are examples of how one can metric the composition of one type of EC element. In these particular examples, the EC element&#39;s EC region includes a first transition metal; the IC region includes an alkali metal, and the CE region comprises a mixed transition metal oxide. In this particular example, the mixed transition metal oxide includes the first transition metal and an additional transition metal, although in other examples, the mixed transition metal oxide does not include the first transition metal. In some devices,  FIGS. 2D-F  are describing the same EC element, but in different ways. Each of these ways exemplify how one might describe any number of EC elements in accord with embodiments described herein. In this example, some of the components depicted in the graphs are present throughout the graded composition, some are not. For example, one transition metal is continuously present in significant concentration across the entire device, from the EC region, through the CE region. The invention is not limited in this way. In some embodiments some or all the components are present at least in some de minimus amount (or even a significant amount) throughout the EC element. In certain examples within the realm of  FIGS. 2D-F , each component has at least some presence in each region of the EC element. 
     Referring to  FIG. 2D , the EC element is described in terms of the mole fraction of elemental components from which it is composed as a function of the region, EC, IC or CE in which the components occur. Starting from the origin and moving from left to right across the graph, in the EC region, there is a higher mole fraction of oxygen (O) than the first transition metal (TM 1 ). For example, this could represent tungsten oxide in approximately a 3:1 ratio of oxygen to tungsten. Moving further to the right, the mole fraction of oxygen and the first transition metal decline starting somewhere in the EC region and through the IC region and into the CE region. At some point in the CE region, the mole fraction of oxygen and the first transition metal level off. For example, this could represent nickel tungsten oxide of stable composition in the CE region. In this example, a second transition metal (TM 2 ) is present throughout the EC element, in this particular example having a higher mole fraction in the CE region than the other regions of the EC element. Also, an alkali metal (M alk ) is present in the EC element. For the purposes of this description, “alkali metal” is meant to encompass both neutral elemental alkali metal and cations thereof, e.g. bound in a material matrix or mobilely associated with the matrix and thus able to intercalate/transport during device operation. In this example the alkali metal has the highest mole fraction in the IC region. This might correspond to lithium of lithium tungstate existing in this region in one example. It is important to note that the mole fraction of components depicted in  FIG. 2D  are those components fixed in the EC element, e.g., the alkali metal component does not include mobile lithium ions that might be used to drive the EC element to color or bleach (as such ions are mobile and their position in the EC element will change depending upon an applied charge, for example). This example is illustrative of how one might describe the composition of an EC element. 
     One embodiment is an EC element including: a) a first transition metal having a higher mole fraction of the composition in the EC region than a second transition metal, if present, in the EC region, b) an alkali metal having a maximum mole fraction of the composition in the IC region as compared to the EC region and the CE region; and c) the second transition metal having its maximum mole fraction, of the composition of any region of the EC element, in the CE region. 
     Referring to  FIG. 2E , if one were to consider the composition of the same EC element as described in relation to  FIG. 2D , but without considering oxygen content, that is another way to describe embodiments described herein. For example, in this graph the y-axis is not mole fraction, but rather metal concentration; that is, the concentration of each metal, TM 1 , M alk , and TM 2 , in each region of the graded composition. In this example, each of the first transition metal and the alkali metal are described in terms of their concentration relative to the other two metals. The second transition metal is described in terms of its absolute concentration. Referring to  FIG. 2E , in the EC region, the first transition metal has its maximum concentration, relative to the other metals. The alkali metal has its maximum concentration in the IC region, relative to the other metals. The second transition metal has its maximum (absolute) concentration in the CE region. In this example, TM 1  and TM 2  have substantially the same concentration in the CE region, e.g., this might represent NiWO. 
     One embodiment is an EC element, including: a) a first transition metal having a maximum concentration, relative to other metals in the EC element, in the EC region, b) an alkali metal having a maximum concentration, relative to other metals in the EC element, in the IC region, and c) a second transition metal having its absolute maximum concentration in the CE region of the EC element. 
       FIG. 2F  describes the composition of the same EC element as described in relation to  FIGS. 2D and 2E , but looking at the actual composition, e.g. compounds, that make up each region. For example, in this graph the y-axis is % composition of each compound, oxide of the first transition metal (TM 1 -oxide), an oxide mixture which includes the alkali metal, along with the first and second transition metals (M alk -TM 1 -TM 2  oxide mixture) and a mixed transition metal oxide (TM 1 -TM 2  oxide), in each region of the graded composition. As mentioned the mixed transition metal oxide need not include the first transition metal (e.g. it can include a second and third transition metal), but it does in this example. The graph in  FIG. 2F  represents devices including those represented by the specific example described in relation to  FIG. 2C . In this example, the TM 1 -oxide is most abundant in the EC region, and it is the primary constituent of the EC region. The M alk -TM 1 -TM 2  oxide mixture is the primary constituent of the IC region and the TM 1 -TM 2  oxide is the primary constituent of the CE region. Note that the M alk -TM 1 -TM 2  oxide mixture may include more than one compound in a matrix of materials, e.g. this could represent a graded mixture of lithium tungstate, tungsten oxide and nickel tungsten oxide. The morphology of the EC element may vary across the layer, i.e. the graded region may have amorphous portions, crystalline portions and/or mixed amorphous crystalline portions in any one or more of the regions. In some embodiments, the CE region is substantially amorphous. 
     One embodiment is an EC element, including: a) a first transition metal oxide which is the primary constituent of the EC region, b) a mixed transition metal oxide which is the primary constituent of the CE region, and c) a mixture including the first transition metal and the mixed transition metal oxide, the mixture being the primary constituent of the IC region. One embodiment is an EC element, including: a) a first transition metal oxide which is the primary constituent of the EC region, b) a mixed transition metal oxide which is the primary constituent of the CE region, and c) a mixture including an alkali metal compound, the first transition metal and the mixed transition metal oxide, the mixture being the primary constituent of the IC region. In one embodiment, the mixed transition metal oxide includes the first transition metal and a second transition metal selected from the group consisting of nickel, tantalum, titanium, vanadium, chromium, cerium, cobalt, copper, iridium, iron, manganese, molybdenum, niobium, palladium, praseodymium, rhodium and ruthenium. In one embodiment, the mixed transition metal oxide does not include the first transition metal. In one embodiment, the alkali metal is lithium cation, either associated with a compound or associated with the material matrix as a transportable ion during operation of the EC element. 
     One embodiment is an EC element as described herein in which the first transition metal is tungsten and the alkali metal is lithium. In one embodiment, the EC region is cathodically coloring and the CE region is anodically coloring. In one embodiment, the second transition metal is nickel. In certain embodiments, the EC element includes oxygen in each of the EC, IC and CE regions. In one embodiment, EC elements described herein are configured to operate by transport of lithium ions from the CE region, through the IC region and into the EC region, or, from the EC region, through the IC region and into the CE region, when a potential is applied across the EC element. In one embodiment, the first transition metal oxide is tungsten oxide and the mixed transition metal oxide is nickel tungsten oxide. 
     One embodiment is an EC device including: a) a first transparent electrode, b) a second transparent electrode, and c) the EC element as described herein sandwiched therebetween. In one embodiment, the first and second transparent electrodes include tin oxide based materials. The EC device may be fabricated on a substrate as described herein; in one embodiment, the substrate is glass. In one embodiment, the glass includes a sodium diffusion barrier. 
     One embodiment is an EC element which is a single layer graded composition including: a) an EC region including primarily tungsten oxide, b) a CE region including primarily nickel tungsten oxide; and, therebetween, c) an IC region including a mixture of lithium tungstate, tungsten oxide and nickel tungsten oxide. One embodiment is an EC device including the aforementioned EC element. In one embodiment, the EC device comprises the EC element sandwiched between two transparent conductive electrodes. 
     One embodiment is an EC element which is a single layer graded composition including: a) an EC region including a tungsten oxide rich matrix which transitions to a matrix with increasingly more lithium tungstate, the EC region transitioning to; b) an IC region including a mixture of lithium tungstate, tungsten oxide and nickel tungsten oxide, the IC region transitioning, moving away from the EC region, i. from more to less tungsten oxide; ii. from less to more nickel tungsten oxide; and, iii. having a lithium tungstate rich matrix near a central portion of the IC region; and c) a CE region which transitions, moving away from the IC region, from more to less lithium tungstate to a nickel tungsten oxide rich matrix. One embodiment is an EC device including the aforementioned EC element. In one embodiment, the EC device comprises the EC element sandwiched between two transparent conductive electrodes. 
     One embodiment is an EC element as described herein, further including, abutting one of the EC or the CE face of the EC element, a reflective coating, a thermochromic coating, a photovoltaic coating or a photochromic coating. One embodiment is an EC device including the aforementioned EC element. In one embodiment, the EC device comprises the EC element sandwiched between two transparent conductive electrodes. In one embodiment, the EC device includes the EC element having only the reflective coating abutting the CE face of the EC element, the EC element-reflective coating two-layer structure sandwiched between two transparent conductive electrodes. In one embodiment, the reflective coating is an EC coating that becomes reflective anodically and transparent cathodically. Examples of reflective coatings that may be used for this purpose are described in U.S. Pat. Nos. 7,646,526 and 8,031,389, filed Sep. 30, 2008 and Oct. 1, 2008, respectively, which are herein incorporated by reference in their entirety. In one embodiment, the aforementioned EC device is configured to operate by migration of lithium ions from the CE region, through the IC region and into the EC region, or, from the EC region, through the IC region and into the CE region, when a potential is applied across the EC element. 
     Additional EC functionality need not be a discrete layer added onto (abutting) one or both faces of an EC element. One embodiment is an EC element as described herein, further including, at least one additional region selected from the group consisting of a reflective region, a thermochromic region and a photochromic region. In one embodiment, the at least one of a reflective region, a thermochromic region or a photochromic region are on either side of the EC region-IC-region-CE-region core graded construct. In one embodiment, an anodically-coloring reflective region is included in the EC element either between the IC and CE regions or graded into the CE region, opposite the IC region. Exemplary, but non-limiting, anodically coloring reflective materials for this region are described above. In one embodiment the EC element also includes at least one ion transport region between the reflective region and neighboring regions, e.g. as a buffer region if the reflective material is somehow incompatible with the IC region and/or the CE region. 
     Methods of fabricating EC devices and EC elements are described in more detail below. 
       FIG. 3A  is a process flow,  300 , in accord with methods described herein. Specifically, an EC layer is deposited (on a CL, for example a TCO), see  305 . Then a CE layer is deposited, see  310 . After the EC and CE layers are deposited, then an interfacial region serving as an IC layer is formed therebetween, see  315 . One embodiment is an analogous method (not depicted) where steps  305  and  310  are reversed. The thrust of the method being that the interfacial region, functioning as an IC layer, is formed after the EC and CE layers, in some embodiments using at least part of one of the EC and CE layers to make the interfacial region. For this reason, interfacial regions formed in this way are sometimes referred to as “intrinsic” IC layers. In other embodiments a distinct layer is formed between the EC and CE layers, for example using an oxygen-enriched version of the EC material or the CE material, where the layer is converted whole or in part to the interfacial region, but again, after formation of the EC and CE layers. Various methods to form the interfacial region after the EC-CE stack is formed are described below. 
     Thus, as mentioned, one embodiment is a method of fabricating an electrochromic device, the method including: forming an electrochromic layer including an electrochromic material; forming a counter electrode layer in contact with the electrochromic layer without first providing an ion conducting electronically-insulating layer between the electrochromic layer and the counter electrode layer, where the counter electrode layer includes a counter electrode material; and forming an interfacial region between the electrochromic layer and the counter electrode layer, where the interfacial region is substantially ion conducting and substantially electronically-insulating. The interfacial region can contain component materials of the EC layer, the CE layer or both. The interfacial region can be formed in a number of ways, as described in more detail below. 
       FIG. 3B  is a process flow,  320 , showing a process flow in accord with the method described in relation to  FIG. 3A , in particular, a process flow for depositing an EC layer, then a CE layer and ultimately forming an interfacial region, functioning as an IC layer therebetween. Even more particularly, in this embodiment, the EC layer includes WO 3  with various amounts of oxygen, in particular compositions and configurations; the CE layer includes NiWO, the interfacial region includes Li 2 WO 4 , and TCO materials such as indium tin oxide and fluorinated tin oxide are used. It should be noted that the layers of the electrochromic devices are described below in terms of solid state materials. Solid state materials are desirable because of reliability, consistent characteristics and process parameters and device performance. Exemplary solid state electrochromic devices, methods and apparatus for making them and methods of making electrochromic windows with such devices are described in U.S. Non-provisional patent application Ser. No. 12/645,111, entitled “Fabrication of Low Defectivity Electrochromic Devices,” by Kozlowski et al., and U.S. Non-provisional patent application Ser. No. 12/645,159, entitled “Electrochromic Devices,” by Wang et al., both of which are incorporated by reference herein for all purposes. In particular embodiments, the electrochromic devices described herein are all solid state and made in apparatus that allow deposition of one or more layers of the stack in a controlled ambient environment. That is, in apparatus where the layers are deposited without leaving the apparatus and without, for example, breaking vacuum between deposition steps, thereby reducing contaminants and ultimately device performance. In a particular embodiment, apparatus do not require a separate target for depositing an IC layer, as is required in conventional apparatus. As one of ordinary skill in the art would appreciate, the invention is not limited to these materials and methods, however, in certain embodiments, all of the materials making up electrochromic stacks and precursor stacks (as described below) are inorganic, solid (i.e., in the solid state), or both inorganic and solid. 
     Because organic materials tend to degrade over time, for example when exposed to ultraviolet light and heat associated with window applications, inorganic materials offer the advantage of a reliable electrochromic stack that can function for extended periods of time. Materials in the solid state also offer the advantage of not having containment and leakage issues, as materials in the liquid state often do. It should be understood that any one or more of the layers in the stack may contain some amount of organic material, but in many implementations one or more of the layers contains little or no organic matter. The same can be said for liquids that may be present in one or more layers in small amounts. It should also be understood that solid state material may be deposited or otherwise formed by processes employing liquid components such as certain processes employing sol-gels or chemical vapor deposition. 
     Referring again to  FIG. 3B , first an EC layer of WO 3  is deposited, see  325 .  FIGS. 4A-4C  are schematic cross-sections depicting formation of electrochromic devices in accord with specific methods and apparatus described herein, and specifically in accord with process flow  320 . Specifically,  FIGS. 4A-4C  are used to show three non-limiting examples of how an EC layer including WO 3  can be formed as part of a stack, where an interfacial region serving as an IC layer is formed after the other layers of the stack are deposited. In each of  FIGS. 4A-4C , the substrate  402 , the first TCO layer  404 , the CE layer  410  and the second TCO layer  412  are essentially the same. Also, in each of the three embodiments, a stack is formed without an IC layer, and then the stack is further processed in order to form an interfacial region that serves as an IC layer within the stack, that is between the EC and the CE layer. 
     Referring to each of  FIGS. 4A-4C , layered structures,  400 ,  403  and  409 , respectively are depicted. Each of these layered structures includes a substrate,  402 , which is, for example, glass. Any material having suitable optical, electrical, thermal, and mechanical properties may be used as substrate  402 . Such substrates include, for example, glass, plastic, and mirror materials. Suitable plastic substrates include, for example acrylic, polystyrene, polycarbonate, allyl diglycol carbonate, SAN (styrene acrylonitrile copolymer), poly(4-methyl-1-pentene), polyester, polyamide, etc. and it is preferable that the plastic be able to withstand high temperature processing conditions. If a plastic substrate is used, it is preferably barrier protected and abrasion protected using a hard coat of, for example, a diamond-like protection coating, a silica/silicone anti-abrasion coating, or the like, such as is well known in the plastic glazing art. Suitable glasses include either clear or tinted soda lime glass, including soda lime float glass. The glass may be tempered or not. In some embodiments, commercially available substrates such as glass substrates contain a transparent conductive layer coating. Examples of such glasses include conductive layer coated glasses sold under the trademark TEC Glass™ by Pilkington of Toledo, Ohio, and SUNGATE™ 300 and SUNGATE™ 500 by PPG Industries of Pittsburgh, Pa. TEC Glass™ is a glass coated with a fluorinated tin oxide conductive layer. 
     In some embodiments, the optical transmittance (i.e., the ratio of transmitted radiation or spectrum to incident radiation or spectrum) of substrate  402  is about 90 to 95%, for example, about 90-92%. The substrate may be of any thickness, as long as it has suitable mechanical properties to support the electrochromic device. While the substrate  402  may be of any size, in some embodiments, it is about 0.01 mm to 10 mm thick, preferably about 3 mm to 9 mm thick. 
     In some embodiments, the substrate is architectural glass. Architectural glass is glass that is used as a building material. Architectural glass is typically used in commercial buildings, but may also be used in residential buildings, and typically, though not necessarily, separates an indoor environment from an outdoor environment. In certain embodiments, architectural glass is at least 20 inches by 20 inches, and can be much larger, for example, as large as about 72 inches by 120 inches. Architectural glass is typically at least about 2 mm thick. Architectural glass that is less than about 3.2 mm thick cannot be tempered. In some embodiments with architectural glass as the substrate, the substrate may still be tempered even after the electrochromic stack has been fabricated on the substrate. In some embodiments with architectural glass as the substrate, the substrate is a soda lime glass from a tin float line. The percent transmission over the visible spectrum of an architectural glass substrate (i.e., the integrated transmission across the visible spectrum) is generally greater than 80% for neutral substrates, but it could be lower for colored substrates. Preferably, the percent transmission of the substrate over the visible spectrum is at least about 90% (for example, about 90-92%). The visible spectrum is the spectrum that a typical human eye will respond to, generally about 380 nm (purple) to about 780 nm (red). In some cases, the glass has a surface roughness of between about 10 nm and about 30 nm. In one embodiment, substrate  402  is soda glass with a sodium diffusion barrier (not shown) to prevent sodium ions from diffusing into the electrochromic device. For the purposes of this description, such an arrangement is referred to as “substrate  402 .” 
     Referring again to layered structures,  400 ,  403  and  409 , on top of substrate  402  is deposited a first TCO layer,  404 , for example made of fluorinated tin oxide or other suitable material, that is, among other things, conductive and transparent. Transparent conductive oxides include metal oxides and metal oxides doped with one or more metals. Examples of such metal oxides and doped metal oxides include indium oxide, indium tin oxide, doped indium oxide, tin oxide, doped tin oxide, zinc oxide, aluminum zinc oxide, doped zinc oxide, ruthenium oxide, doped ruthenium oxide and the like. In one embodiment this second TCO layer is between about 20 nm and about 1200 nm thick, in another embodiment, between about 100 nm and about 600 nm thick, in another embodiment about 350 nm thick. The TCO layer should have an appropriate sheet resistance (R s ) because of the relatively large area spanned by the layers. In some embodiments, the sheet resistance of the TCO layers is between about 5 and about 30 Ohms per square. In some embodiments, the sheet resistance of TCO layers is about 15 Ohms per square. In general, it is desirable that the sheet resistance of each of the two conductive layers be about the same. In one embodiment, the two layers, for example  404  and  412 , each have a sheet resistance of about 10-15 Ohms per square. 
     Each of layered structures  400 ,  403  and  409 , include a stack  414   a ,  414   b  and  414   c , respectively, each of which include the first TCO layer  404  on top of substrate  402 , a CE layer  410 , and a second TCO layer  412 . The difference in each of layered structures  400 ,  403  and  409  is how the EC layer was formed, which in turn affects the morphology of the resultant interfacial region in each scenario. 
     Consistent with process flow  325  of  FIG. 3B , each of stacks  414   a ,  414   b  and  414   c  include an electrochromic layer deposited on top of the first TCO layer  404 . The electrochromic layer may contain any one or more of a number of different electrochromic materials, including metal oxides. Such metal oxides include tungsten oxide (WO 3 ), molybdenum oxide (MoO 3 ), niobium oxide (Nb 2 O 5 ), titanium oxide (TiO 2 ), copper oxide (CuO), iridium oxide (Ir 2 O 3 ), chromium oxide (Cr 2 O 3 ), manganese oxide (Mn 2 O 3 ), vanadium oxide (V 2 O 5 ), nickel oxide (Ni 2 O 3 ), cobalt oxide (Co 2 O 3 ) and the like. In some embodiments, the metal oxide is doped with one or more dopants such as lithium, sodium, potassium, molybdenum, niobium, vanadium, titanium, and/or other suitable metals or compounds containing metals. Mixed oxides (for example, W—Mo oxide, W—V oxide) are also used in certain embodiments, that is, the electrochromic layer includes two or more of the aforementioned metal oxides. An electrochromic layer including a metal oxide is capable of receiving ions transferred from a counter electrode layer. 
     In some embodiments, tungsten oxide or doped tungsten oxide is used for the electrochromic layer. In one embodiment, the electrochromic layer is made substantially of WO x , where “x” refers to an atomic ratio of oxygen to tungsten in the electrochromic layer, and x is between about 2.7 and 3.5. It has been suggested that only sub-stoichiometric tungsten oxide exhibits electrochromism; i.e., stoichiometric tungsten oxide, WO 3 , does not exhibit electrochromism. In a more specific embodiment, WO x , where x is less than 3.0 and at least about 2.7 is used for the electrochromic layer. In another embodiment, the electrochromic layer is WOx, where x is between about 2.7 and about 2.9. Techniques such as Rutherford Backscattering Spectroscopy (RBS) can identify the total number of oxygen atoms which include those bonded to tungsten and those not bonded to tungsten. In some instances, tungsten oxide layers where x is 3 or greater exhibit electrochromism, presumably due to unbound excess oxygen along with sub-stoichiometric tungsten oxide. In another embodiment, the tungsten oxide layer has stoichiometric or greater oxygen, where x is 3.0 to about 3.5. In some embodiments, at least a portion of the EC layer has an excess of oxygen. This more highly oxygenated region of the EC layer is used as a precursor to formation of an ion conducting electron insulating region which serves as an IC layer. In other embodiments a distinct layer of highly oxygenated EC material is formed between the EC layer and the CE layer for ultimate conversion, at least in part, to an ion conducting electronically-insulating interfacial region. 
     In certain embodiments, the tungsten oxide is crystalline, nanocrystalline, or amorphous. In some embodiments, the tungsten oxide is substantially nanocrystalline, with grain sizes, on average, from about 5 nm to 50 nm (or from about 5 nm to 20 nm), as characterized by transmission electron microscopy (TEM). The tungsten oxide morphology or microstructure may also be characterized as nanocrystalline using x-ray diffraction (XRD) and/or electron diffraction, such as selected area electron diffraction (SAED) For example, nanocrystalline electrochromic tungsten oxide may be characterized by the following XRD features: a crystal size of about 10 to 100 nm, for example, about 55 nm. Further, nanocrystalline tungsten oxide may exhibit limited long range order, for example, on the order of several (about 5 to 20) tungsten oxide unit cells. 
     Thus, for convenience, the remainder of process flow  320 , in  FIG. 3B , will be further described in relation to a first embodiment, including formation of EC layer  406 , represented in  FIG. 4A . Then a second and third embodiment, represented in  FIGS. 4B and 4C , respectively, will be described thereafter with particular emphasis on formation and morphology and/or microstructure of their respective EC layers. 
     As mentioned with reference to  FIG. 3B , an EC layer is deposited, see  325 . In a first embodiment (represented in  FIG. 4A ), a substantially homogeneous EC layer,  406 , including WO 3  is formed as part of stack  414   a , where the EC layer is in direct contact with a CE layer  410 . In one embodiment, the EC layer includes WO 3  as described above. In one embodiment, heating is applied during deposition of at least a portion of the WO 3 . In one particular embodiment, several passes are made past a sputter target, where a portion of the WO 3  is deposited on each pass, and heating is applied, for example to substrate  402 , after each deposition pass to condition the WO 3  prior to deposition of the next portion of WO 3  of layer  406 . In other embodiments, the WO 3  layer may be heated continually during deposition, and deposition can be done in a continuous manner, rather than several passes with a sputter target. In one embodiment, the EC layer is between about 300 nm and about 600 nm thick. As mentioned, the thickness of the EC layer depends on upon the desired outcome and method of forming the IC layer. 
     In embodiments described in relation to  FIG. 4A , the EC layer is WO 3 , between about 500 nm and about 600 nm thick, that is sputtered using a tungsten target and a sputter gas including between about 40% and about 80% O 2  and between about 20% Ar and about 60% Ar, and where the substrate upon which the WO 3  is deposited is heated, at least intermittently, to between about 150° C. and about 450° C. during formation of the EC layer. In a particular embodiment, the EC layer is WO 3 , about 550 nm thick, sputtered using the tungsten target, where the sputter gas includes about 50% to about 60% O 2  and about 40% to about 50% Ar, and the substrate upon which the WO 3  is deposited is heated, at least intermittently, to between about 250° C. and about 350° C. during formation of the electrochromic layer. In these embodiments, the WO 3  layer is substantially homogenous. In one embodiment, the WO 3  is substantially polycrystalline. It is believed that heating the WO 3 , at least intermittently, during deposition aids in formation of a polycrystalline form of the WO 3 . 
     As mentioned, a number of materials are suitable for the EC layer. Generally, in electrochromic materials, the colorization (or change in any optical property—for example, absorbance, reflectance, and transmittance) of the electrochromic material is caused by reversible ion insertion into the material (for example, intercalation) and a corresponding injection of a charge balancing electron. Typically some fraction of the ion responsible for the optical transition is irreversibly bound up in the electrochromic material. As described herein, some or all of the irreversibly bound ions are used to compensate “blind charge” in the material. In most electrochromic materials, suitable ions include lithium ions (Li + ) and hydrogen ions (H + ) (i.e., protons). In some cases, however, other ions will be suitable. These include, for example, deuterium ions (D + ), sodium ions (Na + ), potassium ions (K + ), calcium ions (Ca ++ ), barium ions (Ba ++ ), strontium ions (Sr ++ ), and magnesium ions (Mg ++ ). In various embodiments described herein, lithium ions are used to produce the electrochromic phenomena. Intercalation of lithium ions into tungsten oxide (WO 3−y  (0&lt;y≤˜0.3)) causes the tungsten oxide to change from transparent (bleached state) to blue (colored state). In a typical process where the EC layer includes or is tungsten oxide, lithium is deposited, for example via sputtering, on EC layer  406  to satisfy the blind charge (as will be discussed in more detail below with reference to  FIGS. 6 and 7 ), see  330  of the process flow in  FIG. 3B . In one embodiment, the lithiation is performed in an integrated deposition system where vacuum is not broken between deposition steps. It should be noted that in some embodiments, lithium is not added at this stage, but rather can be added after deposition of the counter electrode layer or in other embodiments lithium is added after the TCO is deposited. 
     Referring again to  FIG. 4A , next a CE layer,  410 , is deposited on EC layer  406 . In some embodiments, counter electrode layer  410  is inorganic and/or solid. The counter electrode layer may include one or more of a number of different materials that are capable of serving as reservoirs of ions when the electrochromic device is in the bleached state. During an electrochromic transition initiated by, for example, application of an appropriate electric potential, the counter electrode layer transfers some or all of the ions it holds to the electrochromic layer, changing the electrochromic layer to the colored state. Concurrently, in the case of NiO and/or NiWO, the counter electrode layer colors with the loss of ions. 
     In some embodiments, suitable materials for the counter electrodes include nickel oxide (NiO), nickel tungsten oxide (NiWO), nickel vanadium oxide, nickel chromium oxide, nickel aluminum oxide, nickel manganese oxide, nickel magnesium oxide, chromium oxide (Cr 2 O 3 ), manganese oxide (MnO 2 ) and Prussian blue. Optically passive counter electrodes include cerium titanium oxide (CeO 2 —TiO 2 ), cerium zirconium oxide (CeO 2 —ZrO 2 ), nickel oxide (NiO), nickel-tungsten oxide (NiWO), vanadium oxide (V 2 O 5 ), and mixtures of oxides (for example, a mixture of Ni 2 O 3  and WO 3 ). Doped formulations of these oxides may also be used, with dopants including, for example, tantalum and tungsten. Because counter electrode layer  410  contains the ions used to produce the electrochromic phenomenon in the electrochromic material when the electrochromic material is in the bleached state, the counter electrode preferably has high transmittance and a neutral color when it holds significant quantities of these ions. The counter electrode morphology may be crystalline, nanocrystalline, or amorphous. 
     In some embodiments, where the counter electrode layer is nickel-tungsten oxide, the counter electrode material is amorphous or substantially amorphous. Substantially amorphous nickel-tungsten oxide counter electrodes have been found to perform better, under some conditions, in comparison to their crystalline counterparts. The amorphous state of the nickel-tungsten oxide may be obtained though the use of certain processing conditions, described below. While not wishing to be bound to any theory or mechanism, it is believed that amorphous nickel-tungsten oxide is produced by relatively higher energy atoms in the sputtering process. Higher energy atoms are obtained, for example, in a sputtering process with higher target powers, lower chamber pressures (i.e., higher vacuum), and smaller source to substrate distances. Under the described process conditions, higher density films, with better stability under UV/heat exposure are produced. 
     In certain embodiments, the amount of nickel present in the nickel-tungsten oxide can be up to about 90% by weight of the nickel tungsten oxide. In a specific embodiment, the mass ratio of nickel to tungsten in the nickel tungsten oxide is between about 4:6 and 6:4, in one example, about 1:1. In one embodiment, the NiWO is between about 15% (atomic) Ni and about 60% Ni, and between about 10% W and about 40% W. In another embodiment, the NiWO is between about 30% (atomic) Ni and about 45% Ni, and between about 15% W and about 35% W. In another embodiment, the NiWO is between about 30% (atomic) Ni and about 45% Ni, and between about 20% W and about 30% W. In one embodiment, the NiWO is about 42% (atomic) Ni and about 14% W. 
     In one embodiment, CE layer  410  is NiWO as described above, see  335  of  FIG. 3B . In one embodiment, the CE layer is between about 150 nm and about 300 nm thick, in another embodiment between about 200 nm and about 250 nm thick, in another embodiment about 230 nm thick. 
     In a typical process, lithium is also applied to the CE layer until the CE layer is bleached. It should be understood that reference to a transition between a colored state and bleached state is non-limiting and suggests only one example, among many, of an electrochromic transition that may be implemented. Unless otherwise specified herein, whenever reference is made to a bleached-colored transition, the corresponding device or process encompasses other optical state transitions such non-reflective-reflective, transparent-opaque, etc. Further the term “bleached” refers to an optically neutral state, for example, uncolored, transparent or translucent. Still further, unless specified otherwise herein, the “color” of an electrochromic transition is not limited to any particular wavelength or range of wavelengths. As understood by those of skill in the art, the choice of appropriate electrochromic and counter electrode materials governs the relevant optical transition. 
     In a particular embodiment, lithium, for example via sputtering, is added to a NiWO CE layer, see  340  of  FIG. 3B . In a particular embodiment, an additional amount of lithium is added after sufficient lithium has been introduced to fully bleach the NiWO, see  345  of  FIG. 3B  (this process is optional, and in one embodiment excess lithium is not added at this stage in the process). In one embodiment this additional amount is between about 5% and about 15% excess based on the quantity required to bleach the counter electrode layer. In another embodiment, the excess lithium added to the CE layer is about 10% excess based on the quantity required to bleach the counter electrode layer. After CE layer  410  is deposited, bleached with lithium and additional lithium is added, a second TCO layer,  412 , is deposited on top of the counter electrode layer, see  350  of  FIG. 3B . In one embodiment, the transparent conducting oxide includes indium tin oxide, in another embodiment the TCO layer is indium tin oxide. In one embodiment this second TCO layer is between about 20 nm and about 1200 nm thick, in another embodiment, between about 100 nm and about 600 nm thick, in another embodiment about 350 nm thick. 
     Referring again to  FIG. 4A , once layered structure  400  is complete, it is subjected to thermochemical conditioning which converts at least a portion of stack  414   a  to an IC layer (if it was not already converted due to lithium diffusion or other mechanism). Stack  414   a  is a precursor, not an electrochromic device, because it does not yet have an ion conducting/electronically-insulating layer (or region) between EC layer  406  and CE layer  410 . In this particular embodiment, in a two step process, a portion of EC layer  406  is converted to IC layer  408  to make a functional electrochromic device  401 . Referring to  FIG. 3B , layered structure  400  is subjected to an MTCC, see  355 . In one embodiment, the stack is first subjected to heating, under inert atmosphere (for example argon) at between about 150° C. and about 450° C., for between about 10 minutes and about 30 minutes, and then for between about 1 minutes and about 15 minutes under O 2 . In another embodiment, the stack is heated at about 250° C., for about 15 minutes under inert atmosphere, and then about 5 minutes under O 2 . Next, layered structure  400  is subjected to heating in air. In one embodiment the stack is heated in air at between about 250° C. and about 350° C., for between about 20 minutes and about 40 minutes; in another embodiment the stack is heated in air at about 300° C. for about 30 minutes. The energy required to implement MTCC need not be radiant heat energy. For example, in one embodiment ultraviolet radiation is used to implement MTCC. Other sources of energy could also be used without escaping the scope of the description. 
     After the multistep thermochemical conditioning, process flow  320  is complete and a functional electrochromic device is created. As mentioned, and while not wishing to be bound by theory, it is believed that the lithium in stack  414   a  along with a portion of EC layer  406  and/or CE layer  410  combine to form interfacial region  408  which functions as an IC layer. Interfacial region  408  is believed to be primarily lithium tungstate, Li 2 WO 4 , which is known to have good ion conducting and electronically-insulating properties relative to traditional IC layer materials. As discussed above, precisely how this phenomenon occurs is not yet known. There are chemical reactions that must take place during the multistep thermochemical conditioning to form the ion conducting electronically-insulating region  408  between the EC and CE layers, but also it is thought that an initial flux of lithium traveling through the stack, for example provided by the excess lithium added to the CE layer as described above, plays a part in formation of IC layer  408 . The thickness of the ion conducting electronically-insulating region may vary depending on the materials employed and process conditions for forming the layer. In some embodiments, interfacial region  408  is about 10 nm to about 150 nm thick, in another embodiment about 20 nm to about 100 nm thick, and in other embodiments between about 30 nm to about 50 nm thick. 
     As mentioned above, there are a number of suitable materials for making the EC layer. As such, using, for example lithium or other suitable ions, in the methods described above one can make other interfacial regions that function as IC layers starting from oxygen rich EC materials. Suitable EC materials for this purpose include, but are not limited to SiO 2 , Nb 2 O 5 , Ta 2 O 5 , TiO 2 , ZrO 2  and CeO 2 . In particular embodiments where lithium ions are used, ion conducting materials such as but not limited to, lithium silicate, lithium aluminum silicate, lithium aluminum borate, lithium aluminum fluoride, lithium borate, lithium nitride, lithium zirconium silicate, lithium niobate, lithium borosilicate, lithium phosphosilicate, and other such lithium-based ceramic materials, silicas, or silicon oxides, including lithium silicon-oxide can be made as interfacial regions that function as IC layers. 
     As mentioned, in one embodiment, the precursor of the ion conducting region is an oxygen-rich (super-stoichiometric) layer that is transformed into ion-conducting/electron-insulating region via lithiation and MTCC as described herein. While not wishing to be bound to theory, it is believed that upon lithiation, the excess oxygen forms lithium oxide, which further forms lithium salts, that is, lithium electrolytes, such as lithium tungstate (Li 2 WO 4 ), lithium molybdate (Li 2 MoO 4 ), lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), lithium titanate (Li 2 TiO 3 ), lithium zirconate (Li 2 ZrO 3 ) and the like. In one embodiment, the interfacial region comprises at least one of tungsten oxide (WO 3+x , 0≤x≤1.5), molybdenum oxide (MoO 3+x , 0≤x≤1.5), niobium oxide (Nb 2 O 5+x , 0≤x≤2), titanium oxide (TiO 2+x , 0≤x≤1.5), tantalum oxide (Ta 2 O 5+x , 0≤x≤2), zirconium oxide (ZrO 2+x , 0≤x≤1.5) and cerium oxide (CeO 2+x , 0≤x≤1.5). 
     Any material, however, may be used for the ion conducting interfacial region provided it can be fabricated with low defectivity and it allows for the passage of ions between the counter electrode layer  410  to the electrochromic layer  406  while substantially preventing the passage of electrons. The material may be characterized as being substantially conductive to ions and substantially resistive to electrons. In one embodiment, the ion conductor material has an ionic conductivity of between about 10 −10  Siemens/cm (or ohm −1  cm −1 ) and about 10 −3  Siemens/cm and an electronic resistivity of greater than 10 5  ohms-cm. In another embodiment, the ion conductor material has an ionic conductivity of between about 10 −8  Siemens/cm and about 10 −3  Siemens/cm and an electronic resistivity of greater than 10 10  ohms-cm. While ion conducting layers should generally resist leakage current (for example, providing a leakage current of not more than about 15 μA/cm 2 , it has been found that some devices fabricated as described herein have surprising high leakage currents, for example, between about 40 μA/cm and about 150 μA/cm, yet provide good color change across the device and operate efficiently. 
     As mentioned above, there are at least two other ways of creating an ion conducting electronically-insulating region between the EC and CE layers, after formation of the stack. These additional embodiments are described below with reference to a particular example where tungsten oxide is used for the EC layer. Also, as mentioned above, the interfacial region with IC properties may form in situ during fabrication of the stack when, for example, lithium diffusion or heat converts some of the EC and/or CE layer to the interfacial region. 
     In general, there are certain benefits to creating the ion conducting region later in the process. First, the ion conducting material may be protected from some of the harsh processing that occurs during deposition and lithiation of the EC and CE layers. For example, the deposition of these layers by a plasma process is often accompanied by a large voltage drop proximate the stack, frequently in the neighborhood of 15-20 volts. Such large voltages can damage or cause break down of the sensitive ion conducting material. By shifting the IC material formation to later in the process, the material is not exposed to potentially damaging voltage extremes. Second, by forming the IC material later in the process, one may have better control over some process conditions that are not possible prior to completion of both the EC and CE layers. These conditions include lithium diffusion and current flow between electrodes. Controlling these and other conditions late in the process provides additional flexibility to tailor the physical and chemical properties of the IC material to particular applications. Thus, not all of the benefits described herein are due to the unique interfacial region acting as an IC layer, that is, there are manufacturing and other benefits as well. 
     It has been observed that ion conducting materials formed in accordance with some of the embodiments described herein have superior performance when compared to devices fabricated using conventional techniques for forming an IC layer (for example, PVD from an IC material target). The device switching speed, for example, has been found to be very fast, for example less than 10 minutes, in one example about eight minutes, to achieve about 80% of end state compared to 20-25 minutes or more for traditional devices. In some instances, devices described herein have switching speeds orders of magnitude better than conventional devices. This is possibly attributable to the greater amounts of readily transferable lithium disposed in the interfacial region and/or the graded interfaces, for example between the EC and interfacial region and/or between the CE and the interfacial region. Such lithium may be in the EC and/or CE phases intermixed with the IC phase present in the interfacial region. It is also due possibly to the relatively thin layer or network of IC material present in the interfacial region. In support of this view, it has been observed that some devices fabricated in accordance with the teachings herein have high leakage currents, yet surprisingly exhibit good color change and good efficiency. In some cases, the leakage current density of solidly performing devices has been found to be at least about 100 μA/cm. In some embodiments, EC devices and EC elements may have leakage currents as low as 10 μA/cm or less. 
     Referring now to  FIG. 4B , in a second embodiment, the initially laid down EC material of stack  414   b  is really two layers: a first WO 3  layer,  406 , analogous to layer  406  in  FIG. 4A , but between about 350 nm and about 450 nm thick, that is sputtered using a tungsten target and a first sputter gas including between about 40% and about 80% O 2  and between about 20% Ar and about 60% Ar, and a second WO 3  layer,  405 , between about 100 nm and about 200 nm thick, that is sputtered using the tungsten target and a second sputter gas including between about 70% and 100% O 2  and between 0% Ar and about 30% Ar. In this embodiment, heat is applied, for example by heating substrate  402 , at least intermittently, to between about 150° C. and about 450° C. during deposition of the first WO 3  layer,  406 , but not, or substantially not, heated during deposition of the second WO 3  layer  405 . In a more specific embodiment, layer  406  is about 400 nm thick and the first sputter gas includes between about 50% and about 60% O 2  and between about 40% and about 50% Ar; the second WO 3  layer  405  is about 150 nm thick and the second sputter gas is substantially pure O 2 . In this embodiment, heat is applied, at least intermittently, to between about 200° C. and about 350° C. during formation of the first WO 3  layer,  406 , but not, or substantially not, heated during formation of the second WO 3  layer  405 . In this way, the first WO 3  layer is substantially polycrystalline, while the second WO 3  layer is not necessarily so. 
     Referring again to  FIG. 4B , as described above in relation to  FIGS. 3B and 4A , the stack is completed by lithiation of EC layer(s)  406  and  405  to approximately or substantially satisfy the blind charge, deposition of CE layer  410 , lithiation of the CE layer to bleach state, addition of additional lithium, and deposition of the second TCO layer  412  to complete layered stack  403 . Analogous thermochemical conditioning is performed on layered stack  403  to provide layered stack  407 , a functional electrochromic device including an ion conducting electronically-insulating region  408   a . While not wishing to be bound by theory, in this example, it is believed that the oxygen rich layer  405  of WO 3  serves primarily as the source of precursor material to form interfacial region  408   a . In this example, the entire oxygen rich WO 3  layer is depicted as converting to interfacial region  408   a , however it has been found that this is not always the case. In some embodiments, only a portion of an oxygen rich layer is converted to form an interfacial region that serves the function of an IC layer. 
     Referring now to  FIG. 4C , in a third embodiment, layered stack  409  includes an EC layer,  406   a , which has a graded composition of WO 3  and is formed as part of a stack,  414   c , where the graded composition includes varying levels of oxygen. In one non-limiting example, there is a higher concentration of oxygen in EC layer  406   a  at the EC-CE layer ( 410 ) interface than, for example, at the interface of TCO layer  404  with EC layer  406   a.    
     In one embodiment, EC layer  406   a  is a graded composition WO 3  layer, between about 500 nm and about 600 nm thick, that is sputtered using a tungsten target and a sputter gas, where the sputter gas includes between about 40% and about 80% O 2  and between about 20% Ar and about 60% Ar at the start of sputtering the electrochromic layer, and the sputter gas includes between about 70% and 100% O 2  and between 0% Ar and about 30% Ar at the end of sputtering the electrochromic layer, and where heat is applied, for example to substrate  402 , at least intermittently, to between about 150° C. and about 450° C. at the beginning of formation of EC layer  406   a  but not, or substantially not, applied during deposition of at least a final portion of EC layer  406   a . In a more specific embodiment, the graded composition WO 3  layer is about 550 nm thick; the sputter gas includes between about 50% and about 60% O 2  and between about 40% and about 50% Ar at the start of sputtering the electrochromic layer, and the sputter gas is substantially pure O 2  at the end of sputtering the electrochromic layer; and where heat is applied, for example to substrate  402 , at least intermittently, to between about 200° C. and about 350° C. at the beginning of formation of the electrochromic layer but not, or substantially not, applied during deposition of at least a final portion of the electrochromic layer. In one embodiment heat is applied at the described temperature ranges at the onset of deposition and gradually decreased to no applied heat at a point where about half of the EC layer is deposited, while the sputter gas composition is adjusted from between about 50% and about 60% O 2  and between about 40% and about 50% Ar to substantially pure O 2  along a substantially linear rate during deposition of the EC layer. 
     More generally, the interfacial region typically, though not necessarily, has a heterogeneous structure that includes at least two discrete components represented by different phases and/or compositions. Further, the interfacial region may include a gradient in these two or more discrete components such as an ion conducting material and an electrochromic material (for example, a mixture of lithium tungstate and tungsten oxide). The gradient may provide, for example, a variable composition, microstructure, resistivity, dopant concentration (for example, oxygen concentration), stoichiometry, density, and/or grain size regime. The gradient may have many different forms of transition including a linear transition, a sigmoidal transition, a Gaussian transition, etc. In one example, an electrochromic layer includes a tungsten oxide region that transitions into a superstoichiometric tungsten oxide region. Part, or all, of the superstoichiometric oxide region is converted to the interfacial region. In the final structure, the tungsten oxide region is substantially polycrystalline and the microstructure transitions to substantially amorphous at the interfacial region. In another example, an electrochromic layer includes a tungsten oxide region that transitions into a niobium (superstoichiometric) oxide region. Part, or all, of the niobium oxide region is converted to the interfacial region. In the final structure, the tungsten oxide region is substantially polycrystalline and the microstructure transitions to substantially amorphous at the interfacial region. 
     Referring again to  FIG. 4C , as described above in relation to  FIGS. 3B and 4A , the stack is completed by lithiation of EC layer  406   a  to approximately or substantially satisfy the blind charge, deposition of CE layer  410 , lithiation of the CE layer to bleach state, addition of additional lithium, and deposition of the second TCO layer  412  to complete layered stack  409 . Analogous multistep thermochemical conditioning is performed on layered stack  409  to provide layered stack  411 , a functional electrochromic device including an ion conducting electronically-insulating region  408   b  and at least a portion of original graded EC layer  406   a  which serves as the EC layer in the functional electrochromic device  411 . While not wishing to be bound by theory, in this example, it is believed that uppermost oxygen rich portion of the graded layer of WO 3  primarily forms graded interfacial region  408   b . While not wishing to be bound by theory, there is the possibility that formation of the interfacial region is self-limiting and depends on relative amounts of oxygen, lithium, electrochromic material and/or counter electrode material in the stack. 
     In various embodiments described herein, the electrochromic stack is described as not, or substantially not, being heated during certain processing phases. In one embodiment, the stack is cooled, actively or passively (for example using a heat sink), after a heating step. Apparatus described herein include active and passive cooling components, for example, active cooling can include platens that are cooled via fluid circulation, cooling via exposure to cooled (e.g. via expansion) gases, refrigeration units and the like. Passive cooling components can include heat sinks, such as blocks of metal and the like, or simply removing the substrate from exposure to heat. 
     Another embodiment is a method of fabricating an electrochromic device, the method including: (a) forming either an electrochromic layer including an electrochromic material or a counter electrode layer including a counter electrode material; (b) forming an intermediate layer over the electrochromic layer or the counter electrode layer, where the intermediate layer includes an oxygen rich form of at least one of the electrochromic material, the counter electrode material and an additional material, where the additional material includes distinct electrochromic or counter electrode material, where the intermediate layer is not substantially electronically-insulating; (c) forming the other of the electrochromic layer and the counter electrode layer; and (d) allowing at least a portion of the intermediate layer to become substantially electronically-insulating. In one embodiment, the electrochromic material is WO 3 . In another embodiment, (a) includes sputtering WO 3  using a tungsten target and a first sputter gas including between about 40% and about 80% O 2  and between about 20% Ar and about 60% Ar, to reach of thickness of between about 350 nm and about 450 nm, and heating, at least intermittently, to between about 150° C. and about 450° C. during formation of the electrochromic layer. In another embodiment, (b) includes sputtering WO 3  using a tungsten target and a second sputter gas including between about 70% and 100% O 2  and between 0% Ar and about 30% Ar, to reach a thickness of between about 100 nm and about 200 nm, without heating. In yet another embodiment, the method further includes sputtering lithium onto the intermediate layer until the blind charge is approximately or substantially satisfied. In one embodiment, the counter electrode layer includes NiWO, between about 150 nm and about 300 nm thick. In another embodiment, lithium is sputtered onto counter electrode layer until the counter electrode layer is bleached. In another embodiment, an additional amount of lithium, between about 5% and about 15% excess based on the quantity required to bleach the counter electrode layer, is sputtered onto the counter electrode layer. In another embodiment, a transparent conducting oxide layer is deposited on top of the counter electrode layer. In one embodiment the transparent conducting oxide includes indium tin oxide, in another embodiment, the transparent conducting oxide is indium tin oxide. In another embodiment, the stack formed from the above embodiments is heated at between about 150° C. and about 450° C., for between about 10 minutes and about 30 minutes under Ar, and then for between about 1 minutes and about 15 minutes under O 2 , and then heated in air at between about 250° C. and about 350° C., for between about 20 minutes and about 40 minutes. 
     In another embodiment, (a) includes sputtering a first electrochromic material of formula MO x , where M is a metal or metalloid element and x indicates stoichiometric oxygen to M ratio, and (b) includes sputtering a second electrochromic material of formula NO y  as the intermediate layer, where N is the same or a different metal or metalloid element and y indicates a superstoichiometric amount of oxygen to N ratio. In one embodiment, M is tungsten and N is tungsten. In another embodiment, M is tungsten and N is selected from the group consisting of niobium, silicon, tantalum, titanium, zirconium and cerium. 
     Another embodiment is an electrochromic device including: (a) an electrochromic layer including an electrochromic material; (b) a counter electrode layer including a counter electrode material; and (c) an interfacial region between the electrochromic layer and the counter electrode layer, where the interfacial region includes an electronically-insulating ion conducting material and at least one of the electrochromic material, the counter electrode material and an additional material, where the additional material includes distinct electrochromic or counter electrode material. 
     In one embodiment, the electronically-insulating ion conducting material and at least one of the electrochromic materials, the counter electrode material and the additional material are substantially evenly distributed within the interfacial region. In another embodiment, the electronically-insulating ion conducting material and at least one of the electrochromic material, the counter electrode material and the additional material include a composition gradient in a direction perpendicular to the layers. In another embodiment, consistent with either of the two aforementioned embodiments, the electronically-insulating ion conducting material includes lithium tungstate, the electrochromic material includes a tungsten oxide and the counter electrode material includes nickel tungsten oxide. In a specific implementation of the aforementioned embodiment, there is no additional material. In one embodiment, the electrochromic layer is between about 300 nm and about 500 nm thick, the interfacial region is between about 10 nm and about 150 nm thick, and the counter electrode layer is between about 150 nm and about 300 nm thick. In another embodiment, the electrochromic layer is between about 400 nm and about 500 nm thick; the interfacial region is between about 20 nm and about 100 nm thick, and the counter electrode layer is between about 150 and about 250 nm thick. In yet another embodiment, the electrochromic layer is between about 400 nm and about 450 nm thick; the interfacial region is between about 30 nm and about 50 nm thick, and the counter electrode layer is about 200 nm and about 250 nm thick. 
     Another embodiment is a method of fabricating an electrochromic device, the method including: depositing an electrochromic layer by sputtering a tungsten target with a sputter gas comprising between about 40% and about 80% O 2  and between about 20% Ar and about 60% Ar to produce WO 3  to a thickness of between about 500 nm and about 600 nm, where the substrate upon which the WO 3  is deposited is heated, at least intermittently, to between about 150° C. and about 450° C. during formation of the electrochromic layer; sputtering lithium onto the electrochromic layer until the blind charge is satisfied; depositing a counter electrode layer on the electrochromic layer without first providing an ion conducting electronically-insulating layer between the electrochromic layer and the counter electrode layer, where the counter electrode layer includes NiWO; sputtering lithium onto the counter electrode layer until the counter electrode layer is substantially bleached; and forming an interfacial region between the electrochromic layer and the counter electrode layer, where the interfacial region is substantially ion conducting and substantially electronically-insulating. In one embodiment, forming the interfacial region includes MTCC of the stack, alone or along with substrate, conductive and/or encapsulation layers. 
     The description in relation to  FIGS. 4A-C  was in relation to EC devices, that is, in terms of at least two distinct layers existing in the device architecture. As described, certain embodiments include EC elements where there is only a single layer of graded material that serves the function of an EC device or stack.  FIG. 4D  depicts one such EC element,  421 , which is part of an EC device  413 . The EC element  421  is a single layer graded composition, having a cathodically coloring EC region,  417 , which transitions to an IC region,  418  (an interfacial region as described herein), which transitions to an anodically coloring CE region,  419 . The EC element  421  is sandwiched between two transparent conducting oxide (TCO) electrodes,  404  and  412 . Device fabrication in this example includes depositing TCO  404  on substrate  402 , the depositing EC element  421  on TCO  404 , followed by deposition of TCO  412  on EC element  421 . Thus, EC device  413  has only three layers, EC element  421  sandwiched between TCO&#39;s  404  and  412 . Fabrication of EC elements is described in more detail below. 
     In a broad sense, an EC element is a single layer EC device stack having successive functional regions as opposed to distinct layers where there is an abrupt material change between layers and de minimus material mixing between successive layers. Rather, an EC element has successive functional regions where there is more than de minimus material mixing between each successive functional region. In certain embodiments, e.g. as described in relation to possible mechanisms for formation of an interfacial region serving as an IC layer, fabrication of an EC element can include judicious choice of materials, where the materials are laid down in a conventional sense, in layers, but where the material choice and/or subsequent processing promotes material mixing and/or chemical and/or morphological changes that transform the interfaces between successive layers into graded regions, and thus, what starts as a stack of layers is transformed into an EC element. 
     In other embodiments, fabrication of an EC element includes depositing, e.g. sputtering, materials in the vapor phase to deposit successive functional regions in an EC element, where there is more than de minimus material mixing between successive functional regions during the deposition process, that is, in the vapor phase, e.g. materials for successive functional regions are co-sputtered at least for a period between sputtering of the first material and sputtering of the second material. In the example of all sputter deposited materials, this result may be accomplished by, e.g., using sputter targets having the appropriate composition and configuration such that material mixing is limited to some fraction of each of the successive functional regions. That is, the functional regions are composed primarily of some material (which itself may be a graded composition) and this material is deposited to form the bulk of the function region. For example, material mixing occurs during transition from sputtering a first material, from which a first functional region is comprised, to sputtering a second material, from which the next successive functional region is comprised. There is some mixing (co-sputtering) during this transition between the two materials, which ceases at some point, and then the second material is sputtered for a period, followed by a transition where the second material is sputtered along with a third material. The transition from the second functional region to the third function region includes co-sputter of the second and third materials. The third material is sputtered alone for a period, followed by the next transition if there is a fourth material, and so on. In certain embodiments, the material mixing occurs in the vapor phase, prior to the materials being deposited (although there may be further mixing and/or morphological changes after deposition). Particular embodiments for achieving sputtering profiles for creating EC elements are described below. 
     One embodiment is a method of fabricating a single layer graded composition EC element on a substrate in a sputter system, including: a) sputter coating an EC material including a first transition metal and a first oxygen concentration onto the substrate; b) increasing from the first oxygen concentration to a second oxygen concentration, higher than the first, during a); c) introducing lithium into the sputter system; and d) sputter coating a CE material including a second transition metal and oxygen; wherein the fabrication is a substantially continuous process and the concentration of the first transition metal is decreased from a) to d), and the concentration of the second transition metal is increased from a) to d). In one embodiment, the first transition metal is tungsten. In one embodiment, the second transition metal is nickel. In one embodiment, introducing lithium into the sputter system includes sputtering target comprising a lithium compound. In one embodiment, the lithium compound is lithium tungstate. 
     Methods of fabricating EC elements described herein can be performed, for example, using a sputter system having capability of introducing targets and/or target materials during plasma sputter. Another way to accomplish these methods is to arrange a series of targets, in substantially contiguous fashion, where the targets&#39; composition reflects the composition of the desired graded EC element, and pass the substrate pass the targets during sputter (and/or pass the targets past the substrate during sputter). Yet another way of performing these methods is to sputter from a single a target, the composition of which reflects the composition of the desired graded EC element. These embodiments are described in more detail below. 
     One embodiment is a method of fabricating a single layer graded composition EC element on a substrate in a sputter system, including sputter coating materials from a plurality of closely associated sputter targets such that there is mixing of materials sputtered from each target in the region where two targets are proximate each other; where the single layer EC element is fabricated upon a single pass of the substrate and the plurality of closely associated sputter targets past each other. 
       FIG. 4E  depicts a target assembly,  421 , which may be used to fabricate an EC element as described herein. Target assembly  421  includes a backing plate,  420 , on which are affixed three target sections, an EC target section,  425 , an IC target section,  430 , and a CE target section,  435 . Each of the target sections comprises a material reflective of the majority constituent of the deposited region to which they correspond. A substrate,  431 , is translated past target assembly  421  as depicted by the heavy dashed arrow. One of ordinary skill in the art would appreciate that three separate targets, each with their own power supply and backing plate, for example, would also work, so long as the targets were proximate during sputter deposition such that there was some mixing of materials from the sputter plasmas in the areas near contiguous target edges. For the purposes of this description the term “closely associated sputter targets” is meant to include these possibilities. Also, although  FIG. 4E  depicts linear edges of the target sections proximate and parallel to each other, this need not be so. For example, the adjoining (or proximate) edges of targets could be curved, zig zag or other complementary (or not) shapes to enhance plasma and thus material mixing in the deposited layer. Also, although in this example there are three target sections, this need not be so. For example there may be many target sections, reflective of the graded composition along the sputter deposition path, for example, of varying widths, shapes and compositions depending upon the desired outcome. The width of the target, speed of translation of the substrate and/or target past each other, sputter power, etc. will determine the characteristics of the deposited single film graded composition. The plurality of closely associated sputter targets need not be planar targets, but may be rotary targets or combinations of planar, rotary and other target types and/or shapes appropriate to effect the desired outcome in the graded composition. 
     Referring again to  FIG. 4E , as indicated by the heavy dashed arrow, substrate  431  and target assembly are translated relative to each other, for example the substrate is passed along and in front of the target assembly, during sputter deposition. As the substrate moves along the target, a single layer graded composition that functions as an EC device is deposited on the substrate. In one embodiment, a plurality of closely associated sputter targets includes a target including an EC material, a target including an IC material and a target including a CE material. In one embodiment, the EC material includes tungsten oxide. In one embodiment, the IC material includes lithium tungstate. In one embodiment, the CE material includes nickel tungsten oxide. 
     As described above, another embodiment is a method of fabricating a single layer graded composition EC element on a substrate in a sputter system, including sputter coating materials from a single sputter target including a composition substantially reflective of the single layer EC element; wherein the single layer EC element is fabricated upon a single pass of the substrate and the single sputter target past each other. This is illustrated in  FIG. 4F . Target assembly  422  includes a backing plate  420 , to which is affixed a sputter target,  440 . Sputter target  440  has a composition reflective of the desired EC element to be deposited. During sputtering, a substrate is translated past sputter target  440  in a single pass, during which the EC element is deposited. The single target can be manufactured, e.g., by sintering together materials for each of the respective regions of the EC element. In one embodiment, target sub-sections are sintered together; that is, smaller pre-formed target sections are sintered and/or fused together into the single target. The individual target sections that are sintered into a single target may have straight edges prior to sintering together, e.g. target sections as depicted in relation to  FIG. 4E . In other embodiments, the individual target sub-sections are interleaved at the abutting edges, e.g. as depicted in  FIG. 4F , line  421 , prior to sintering. That is, the target sub-sections may fit together, e.g. like postage stamps, having interleaved edges. In certain embodiments, interleaving provides for bettering mixing of materials at the transition between two materials in the EC element (thus in one embodiment, the interleaving obviates the need for sintering sections into a single target). The interleaving can be of any shape, e.g. curved as line  421  suggests, or zig-zag, rectangular interlocking, and the like. Also, the interleaving can be gross, having large interleaving features and/or very fine or small interleaving features, e.g. prismatically interleaved surfaces are abutted and the target sub-sections sintered together. 
     In one embodiment, the single sputter target includes a region of EC material, which is graded into a region of IC material, which is graded into a region of CE material. In one embodiment, the region of EC material includes tungsten oxide. In one embodiment, the region of IC material includes lithium tungstate. In one embodiment, the region of CE material includes nickel tungsten oxide. 
     In the description above, an EC element is often described in terms of a single layer graded composition having an EC region, an IC region and a CE region. In certain embodiments, this EC element is described as being sandwiched between two transparent conducting oxide (TCO) electrodes in order to form an EC device.  FIG. 4G  illustrates a target arrangement,  423 , that can be used to fabricate such an EC device. In this arrangement, target assembly  422 , as described in relation to  FIG. 4F , is situated between two separate targets,  450  having a backing plate  445 , and  460  having a backing plate  455 . Assuming there is no mixing of materials between targets  450 ,  440  and  460  during sputtering, an EC element sandwiched between two TCO layer electrodes will be formed in a single pass sputter deposition. However, if targets  450  and  460  are proximate target  440  such that there is material mixing by design during sputtering, then an EC element such as described in relation to  FIG. 4H  is formed. 
       FIG. 4H  is a cross section schematic of an EC element,  442 . EC element  442  is a single layer graded composition having a first TCO region,  404   a , a cathodically coloring EC region,  417   a , an IC region,  418   a , an anodically coloring CE region,  419   a  and a second TCO region,  412   a . Once appropriately lithiated (during formation of EC element  442 , or not), as depicted, a potential can be applied across EC element  442  and it will function as a conventional EC device. However, EC element  442  is a single layer graded composition, deposited in a single pass on a substrate. This is a radical departure from conventional fabrication methods and EC structure. Using the methods described herein, one can coat a single layer of material on a substrate, where the material behaves as a conventional EC device would. This saves considerable processing steps and the result is highly desirable—a single layer film switchable coating, e.g. one that includes complementary coloring functional regions. One advantage of such a construct is that delamination resulting from adhesion issues between material layers is avoided. Of course, as described above, there are various target arrangements that can accomplish these methods. 
     As described in relation to  FIG. 4G , if the target sections are appropriately spaced one can fabricate an EC element such as that described in relation to  FIG. 4H . Alternatively, a target assembly,  424 , as depicted in  FIG. 4I  could be used. Target assembly  424  includes a single backing plate,  465 , on which are mounted a plurality of target sections,  470 - 490 , whose composition correspond to the regions of the desired EC element on the substrate post sputter. In this example, the neighboring target sections are abutting or in close proximity with each other. The abutting or closely neighboring edges may not be straight as depicted, but may include interleaving as described in relation to  FIG. 4F . One embodiment is a method of fabricating an EC element including five successive functional regions: a first transparent conductor region, a cathodically coloring electrochromic region, an ion conducting region, an anodically coloring electrochromic region and a second transparent conductor region; the method comprising substantially continuous sputtering during formation of the five successive functional regions. 
       FIG. 4J  shows yet another alternative, sputter target assembly  426 , which is a plurality of closely associated sputter targets,  491 - 495 , e.g. each with their own backing plate and associated power supply and magnetic source, whose composition correspond to the regions of the desired EC element on the substrate post sputter. Targets  491 - 495  are configured so that there is material mixing by design of the plasmas for each target in the regions between the targets. Conventional thought is to have complete isolation and control of sputter plasma geometry such that a substrate can be passed by the sputter target and a film of highly uniform composition, reflecting the target and sputter gas composition is deposited. In embodiments described herein, material mixing of adjacent plasma and/or material deposited on a substrate is by design so that a single layer graded composition results. One of ordinary skill in the art would appreciate that various target arrangements and materials are possible without deviating from the scope of the description. For example, rather than five target sections as depicted in  FIG. 4I , the first TCO target section may be obviated if the substrate is, e.g., float glass with a TCO, e.g. a fluorinated tin oxide pyrolytic coating, already deposited (the result would be in this example, an EC device because there are two layers, the TCO and an EC element with four regions). In another example, rather than five sputter targets, as depicted in  FIG. 4J , one might choose to use ten targets, e.g., of less width but having overall substantially the same collective width, for more material mixing throughout the deposition and thus in the deposited single layer graded composition. Lithium sputter targets (not depicted) may also be included at various positions in the target arrangement. In yet another example, a reflective region, a thermochromic region, a photochromic region, and/or a photovoltaic region may be desired. In this example, targets are configured and/or arranged so that corresponding reflective, thermochromic, photochromic and/or photovoltaic regions are incorporated in the EC element. 
       FIG. 4K  shows yet another alternative, sputter target assembly  427 , which is a plurality of closely associated rotary sputter targets,  472 ,  473 ,  474 ,  476  and  478 , e.g. each with their own associated power supply and magnetic source, whose composition correspond to the regions of the desired EC element on substrate  431  post sputter. The rotary targets are configured so that there is material mixing by design of the plasmas for each target in the regions between the targets. In this example, there are baffles,  471 , between each rotary target. Baffles  471  may be movable, in order to attenuate or augment material mixing in the region between neighboring rotary targets. The baffles may be moved perpendicular to the substrate, toward or away from the substrate and/or along an axis parallel to the substrate, between two rotary targets, such that the separation between the baffle and any two targets on either side can be controlled. By being able to move the baffles in this manner, the material mixing in the region between neighboring targets can be controlled and designed for the desired result. The baffles may not have straight edges as depicted, i.e., they may have edges with curved edges, jagged edges, rectangular cuts, etc. in order to mediate material mixing in the region between targets. In addition to, or in the alternative to baffles, sputter targets (planar or rotary) may be configured to move toward and away from each other and/or toward and away from the substrate during sputter deposition. The rotary targets in  FIG. 4K  are depicted as rotating in the same direction, but this is but one embodiment. In other embodiments, the rotary targets may turn in alternating directions or in any combination, e.g., two clockwise, one counter clockwise, two clockwise, etc. 
       FIG. 4L  shows yet another alternative, sputter target assembly  428 , which is a plurality of closely associated sputter targets,  482 ,  483 ,  484 ,  485  and  486 , e.g. each with their own associated power supply and magnetic source, whose composition correspond to the regions of the desired EC element on a substrate post sputter. This example shows a mixture of planar sputter targets and rotary targets. In this example, rotary targets  483  and  485  rotate opposite each other. The neighboring targets may have baffles as described above or not. The order and number of rotary and planar targets may vary, depending upon the desired sputter outcome. For example, there may be two planar targets and three rotary targets or four planar targets and one rotary target. Mixing rotary and planar targets allows for greater flexibility in process design and control. Parameters related to sputter deposition of an EC element are described in more detail below. 
     Certain embodiments described herein include using a plurality of separate sputter targets arranged in close proximity in order to create overlapping zones of different material plasmas which allows fabrication of an EC element.  FIG. 4M  depicts various geometries as they relate to process parameters in relation to two planar sputter targets in close proximity and a substrate translating past the targets. The distance between the sputter targets, a, is one factor that affects material mixing in the sputter plasmas. The distance between the sputter targets will be a factor in the amount of overlap of plasma densities (as depicted by the curved dotted lines radiating from each target. Also, the shape and density of the plasma from each target will be affected by the magnetic field shape and strength (the black rectangles represent the magnets of the cathode) as well as the pressure and power density used to generate the plasma. The distance between the sputter target and the substrate, β, is another parameter that affects how proximate sputter plasmas will mix. The distance between the target and the substrate will determine how dense the plasma impinging on the substrate will be. The distance β can be varied to increase or decrease the density of the plasma impinging on the substrate, for example, by moving the targets toward, or away from, the substrate; moving the substrate toward, or away from the targets, or both. 
     In certain embodiments, the relationship between distances α and β are chosen to impact the density and shape of the plasmas as well as the desired deposition profile. In one embodiment, for deposition using optimally-mixed plasmas between two targets, the ratio of β to a is between about 1 and about 10, in another embodiment between about 1.5 and about 5, and in another embodiment between about 2 and about 5. The plasma densities depicted in  FIG. 4M  are merely representative. In this example, the plasma densities are drawn as symmetrical and equivalent in shape. This is not necessary. For example, as described, the plasmas are of different materials (as reflected by the target compositions) and therefore may require different energies, pressures, etc. to be created and maintained. As well, the magnets of the cathodes may be configured in various ways to shape the plasmas and create varying densities appropriate for a particular deposition profile for a desired EC element. As depicted in  FIG. 4M , this configuration creates three zones. Zone 1 is a material deposition zone that is substantially comprised of the material from which target 1 is made. Zone 3 is a material deposition zone that is substantially comprised of the material from which target 2 is made. Zone 2 is a material deposition zone that is substantially a mixture of the two target materials. The relative concentrations of the plasma from target 1 and the plasma from target 2 in zone 2 is generally a gradient along the length (parallel to translation of the substrate) of zone 2. The gradient can be manipulated by, e.g., configuring the plasma densities and shapes of two successive targets. The plasma densities, material properties, magnetic coils, and the like are factors that allow these zones to be established and maintained in a steady state so that varying compositions can be deposited on the substrate as it translates past the targets. 
     Another parameter that affects the deposition is the speed at which the substrate and the target assembly pass by one another. For example, the speed of translation of the substrate past the targets will be a factor in how much material is deposited onto the substrate. In one embodiment the translation speed of the substrate past the targets is constant, in another embodiment it varies. In one embodiment, the translation speed of the substrate past the targets is between about 0.1 meters per second and about 1 meter per second, in another embodiment between about 0.1 meters per second and about 0.5 meters per second, and in another embodiment between about 0.2 meters per second and about 0.5 meters per second. The speed of the substrate will determine the travel distance, that is, how far a particular point on the substrate must traverse in each deposition zone, or collectively, across the target assembly that creates the EC element. The thickness of the EC element, and of each material or mixture of materials deposited in each deposition zone, will directly depend on the translation speed, the travel distance, as well as the plasma density, shape, etc. as described above. 
       FIGS. 4N and 4P  depict arrangements with two rotary targets and one planar and one rotary target, respectively. For these configurations, the distances α and β are as described above in relation to  FIG. 4M . Referring to  FIG. 4N , rotary targets 1 and 2 are depicted as having their internal magnets (depicted as dark curved structures in the interior of each target) configured to generate plasmas at different angles with respect to the substrate surface. This is another example of how plasma densities and shapes can be manipulated in order to create material deposition zones 1-3. The rotation of the targets can be in the same direction or not. Referring to  FIG. 4P , planar target 1 and rotary target 2 are proximate each other. This arrangement produces another unique plasma deposition profile across three zones.  FIGS. 4M, 4N and 4P  depict the three possible combinations of two proximate planar and/or rotary targets. As described herein, various combinations of successive planar and rotary targets are possible. Considering any three successive targets in an assembly for depositing an EC element, a planar target may be flanked by two planar targets, two rotary targets, or one planar and one rotary target. Likewise a rotary target may be flanked by two planar targets, two rotary targets, or one planar and one rotary target. As discussed above, baffles may also be used in between targets, planar or rotary, to further shape and control plasma mixing between two targets. 
     As described herein in relation to fabrication of an EC element, multiple targets may be arranged proximate each other and a substrate passed by the sputter plasmas emanating from the targets, including mixing between successive targets, in order to deposit an EC element on the substrate. One of ordinary skill in the art would appreciate that the more disparate the characteristics of the materials of each target, the more variables there are to be considered when configuring a particular system to deposit an EC element, particularly creating contiguous plasmas from each target. This is true because of the different power requirements, pressures, temperatures and the like that are required for each of the target materials. In certain embodiments, the target materials are selected so that the conditions used to create plasmas from each are similar. In one embodiment, each of the assembly of sputter targets comprises a metal oxide. In one embodiment, each of the assembly of sputter targets comprises a transition metal oxide. Each target may also include a compound that contains a transition metal and an alkali metal, e.g., lithium tungstate. By using targets that each have a metal oxide, the process conditions for sputtering each of the successive targets are more closely matched. This aids in sputtering an EC element, because, e.g., the pressure, temperature, power etc. are more normalized across the targets. This allows for less complication in the configuration of the sputter chamber that contains the targets, e.g., less baffles or other measures to accommodate pressure, temperature or power density differentials in successive target zones. For example, in one embodiment the temperature across the deposition zones does not vary by more than about 150° C., in another embodiment the temperature across the deposition zones does not vary by more than about 100° C., in another embodiment the temperature across the deposition zones does not vary by more than about 50° C. In another example, the pressure across the deposition zones does not vary by more than about 10 mTorr, in another embodiment the pressure across the deposition zones does not vary by more than about 5 mTorr, in another embodiment the pressure across the deposition zones does not vary by more than about 2 mTorr. In one embodiment an EC element is fabricated using a tungsten target, a lithium tungstate target and a nickel tungsten target. The EC element is fabricated using argon or other inert sputter gas along with oxygen as described herein. In one embodiment, the EC element is lithiated via lithium sputter using a lithium metal target downstream from the target assembly used to fabricate the EC element. 
     In certain embodiments, as described above, rather than using a plurality of separate sputter targets arranged in close proximity in order to create overlapping zones of different material plasmas, one can use a single target with varying composition across the target (e.g. see  FIGS. 4F and/or 4G  and associated description) or a plurality of abutting targets on a single backing plate (e.g. see  FIGS. 4E and/or 4I  and associated description) to fabricate an EC element. For example, taking the example from  FIG. 4I , target assembly  424 , where five target sections,  470 ,  475 ,  480 ,  485  and  490 , are affixed to a backing plate  465 ,  FIG. 4Q  depicts a single plasma geometry across the five targets. In this example, the sputter target sections are abutted together or very close together so, α, is very small or non-existent. The relative widths of the targets are only representative, they may in reality be much wider or narrower than each other, depending upon the plasma density, amount of material desired in the deposition, thickness of regions, etc. The distance β is shown, which is, again, important due to the plasma densities, etc. as the substrate passes by the target assembly. The shape and density of the plasma across the target sections will be affected by the magnetic field shape and strength (the black rectangles represent the magnets of the cathode) as well as the pressure and power density used to generate the plasma. In this example, the target sections are of different widths and the cathode magnets are arranged asymmetrically, depending upon the desired plasma density profile. 
     In this example, since there are five target sections, nine deposition zones are established during sputter. As the leading edge of the substrate enters zone 1, TCO material is deposited. This deposition is continued until zone 2 is reached, where a graded mixture of TCO and electrochromic material are deposited. Zone 3 is where electrochromic material is deposited, followed by zone 4 where a mixture of electrochromic material and ion conducting material is deposited. Next, in zone 5, ion conducting material is laid down, followed by zone 6, where a mixture of ion conducting material and counter electrode material is deposited. In zone 7, counter electrode material is deposited, followed by zone 8, where a mixture of counter electrode material and a second TCO material are deposited. Finally, in zone 9, the second TCO material is laid down. 
     As the substrate exits zone 9, a single layer of material, which comprises five functional regions, a first transparent conducting region, an electrochromic region, an ion conducting region, a counter electrode region and a second transparent conducting region, respectively, has been deposited on the substrate. The functional regions may comprise any of the materials described herein for their respective functions. In one embodiment, the first and second transparent conducting regions comprise ITO, the electrochromic region comprises tungsten oxide, the counter electrode region comprises NiWO, and the ion conducting region comprises at least one of lithium tungstate, silicon-aluminum-oxide lithium silicate, lithium aluminum silicate, lithium aluminum borate, lithium aluminum fluoride, lithium borate, lithium nitride, lithium zirconium silicate, lithium niobate, lithium borosilicate, lithium phosphosilicate and lithium phosphorous oxynitride. 
     The EC devices and EC elements described herein can include one or more additional layers or regions, respectively, such as one or more passive layers or regions, for example to improve certain optical properties, providing moisture or scratch resistance, to hermetically seal the electrochromic device and the like. Typically, but not necessarily, a capping layer is deposited on an EC stack or EC element. In some embodiments, the capping layer is SiAlO. In some embodiments, the capping layer is deposited by sputtering. In one embodiment, the thickness of a capping layer is between about 30 nm and about 100 nm. 
     From the discussion above, it should be appreciated that EC devices and EC elements described herein can be made in a single chamber apparatus, for example a sputter tool that has, for example, a tungsten target, a nickel target and a lithium target along with oxygen and argon sputter gases. As mentioned, due to the nature of the interfacial regions formed to serve the purpose of a conventional distinct IC layer, a separate target for sputtering an IC layer is not necessary. For example in certain embodiments, an EC and CE layer are deposited in contact with each other and an interfacial region serving as an IC layer is formed thereafter. In other embodiments a single layer graded composition is fabricated from a target having a composition that substantially reflects the composition of the graded layer. Of particular interest to the inventors is fabricating electrochromic devices and/or EC elements described herein, for example, in a high throughput fashion, therefore it is desirable to have apparatus that can fabricate EC devices and/or EC elements sequentially as substrates pass through an integrated deposition system. For example, the inventors are particularly interested in fabricating electrochromic devices on windows, particularly architectural glass scale windows (supra). 
     Thus, another embodiment is an apparatus for fabricating an electrochromic device, including: an integrated deposition system including: (i) a first deposition station containing a material source configured to deposit an electrochromic layer including an electrochromic material; and (ii) a second deposition station configured to deposit a counter electrode layer including a counter electrode material; and a controller containing program instructions for passing the substrate through the first and second deposition stations in a manner that sequentially deposits a stack on the substrate, the stack having an intermediate layer sandwiched in between the electrochromic layer and the counter electrode layer; where either or both of the first deposition station and the second deposition station are also configured to deposit the intermediate layer over the electrochromic layer or the counter electrode layer, and where the intermediate layer includes an oxygen rich form of the electrochromic material or the counter electrode material and where the first and second deposition stations are interconnected in series and operable to pass a substrate from one station to the next without exposing the substrate to an external environment. In one embodiment, apparatus described herein are operable to pass the substrate from one station to the next without breaking vacuum and may include one or more lithiation stations operable to deposit lithium from a lithium-containing material source on one or more layers of the electrochromic device. In one embodiment, apparatus described herein are operable to deposit the electrochromic stack on an architectural glass substrate. 
     In one embodiment, the apparatus is operable to pass the substrate from one station to the next without breaking vacuum. In another embodiment, the integrated deposition system further includes one or more lithiation stations operable to deposit lithium from a lithium-containing material source on at least one of the electrochromic layer, the intermediate layer and the counter electrode layer. In yet another embodiment, the integrated deposition system is operable to deposit the stack on an architectural glass substrate. In one embodiment, the apparatus is operable to pass the substrate across a plurality of closely associated sputter targets such that a single layer graded composition, EC element, is deposited on the substrate in a single pass. In another embodiment, the integrated deposition system further includes a substrate holder and transport mechanism operable to hold the architectural glass substrate in a vertical orientation while passing through the integrated deposition system. In another embodiment, the apparatus further includes one or more load locks for passing the substrate between an external environment and the integrated deposition system. In another embodiment, the apparatus further includes at least one slit valve operable to permit isolation of the one or more lithium deposition stations from at least one of the first deposition station and the second deposition station. In one embodiment, the integrated deposition system includes one or more heaters configured to heat the substrate. 
       FIG. 5  depicts a simplified representation of an integrated deposition system  500  in a perspective view and with more detail including a cutaway view of the interior. In this example, system  500  is modular, where entry load lock  502  and exit load lock  504  are connected to deposition module  506 . There is an entry port,  510 , for loading, for example, architectural glass substrate  525  (load lock  504  has a corresponding exit port). Substrate  525  is supported by a pallet,  520 , which travels along a track,  515 . In this example, pallet  520  is supported by track  515  via hanging but pallet  520  could also be supported atop a track located near the bottom of apparatus  500  or a track, for example mid-way between top and bottom of apparatus  500 . Pallet  520  can translate (as indicated by the double headed arrow) forward and/or backward through system  500 . For example during lithium deposition, the substrate may be moved forward and backward in front of a lithium target,  530 , making multiple passes in order to achieve a desired lithiation. This function is not limited to lithium targets, however, for example a tungsten target may pass multiple times past a substrate, or the substrate may pass by via forward/backward motion path in front of the tungsten target to deposit, for example, an electrochromic layer. Pallet  520  and substrate  525  are in a substantially vertical orientation. A substantially vertical orientation is not limiting, but it may help to prevent defects because particulate matter that may be generated, for example, from agglomeration of atoms from sputtering, will tend to succumb to gravity and therefore not deposit on substrate  525 . Also, because architectural glass substrates tend to be large, a vertical orientation of the substrate as it traverses the stations of the integrated deposition system enables coating of thinner glass substrates since there are fewer concerns over sag that occurs with thicker hot glass. 
     Target  530 , in this case a cylindrical target, is oriented substantially parallel to and in front of the substrate surface where deposition is to take place (for convenience, other sputter means are not depicted here). Substrate  525  can translate past target  530  during deposition and/or target  530  can move in front of substrate  525 . The movement path of target  530  is not limited to translation along the path of substrate  525 . Target  530  may rotate along an axis through its length, translate along the path of the substrate (forward and/or backward), translate along a path perpendicular to the path of the substrate, move in a circular path in a plane parallel to substrate  525 , etc. Target  530  need not be cylindrical, it can be planar or any shape necessary for deposition of the desired layer with the desired properties. Also, there may be more than one target in each deposition station and/or targets may move from station to station depending on the desired process. The various stations of an integrated deposition system described herein may be modular, but once connected, form a continuous system where a controlled ambient environment is established and maintained in order to process substrates at the various stations within the system. 
     More detailed aspects of how electrochromic materials are deposited using integrated deposition system  500  are described in US Non-Provisional patent applications, Ser. Nos. 12/645,111 and 12/645,159, supra. 
     Integrated deposition system  500  also has various vacuum pumps, gas inlets, pressure sensors and the like that establish and maintain a controlled ambient environment within the system. These components are not shown, but rather would be appreciated by one of ordinary skill in the art. System  500  is controlled, for example, via a computer system or other controller, represented in  FIG. 5  by an LCD and keyboard,  535 . One of ordinary skill in the art would appreciate that embodiments described herein may employ various processes involving data stored in or transferred through one or more computer systems. Embodiments described herein also relate to the apparatus, such computers and microcontrollers, for performing these operations. These apparatus and processes may be employed to deposit electrochromic materials of methods described herein and apparatus designed to implement them. The control apparatus described herein may be specially constructed for the required purposes, or it may be a general-purpose computer selectively activated or reconfigured by a computer program and/or data structure stored in the computer. The processes presented herein are not inherently related to any particular computer or other apparatus. In particular, various general-purpose machines may be used with programs written in accordance with the teachings herein, or it may be more convenient to construct a more specialized apparatus to perform and/or control the required method and processes. 
     Embodiments that describe fabrication of single layer graded composition EC elements can be made in a similar apparatus to that described in relation to  FIG. 5 , with appropriate configuration of target assemblies and the like. One embodiment is an integrated deposition system for fabricating an electrochromic window, the system comprising: a plurality of closely associated sputter targets operable to pass a substrate from one sputter to the next without exposing the substrate to an external environment, wherein the plurality of closely associated sputter targets comprise (i) a first sputter target containing a material source for depositing an electrochromic material; (ii) a second sputter target containing a material source for depositing an ion conducting material; and (iii) a third sputter target containing a material source for depositing a counter electrode material; and a controller containing program instructions for passing the substrate by the plurality of closely associated sputter targets in a manner that deposits on the substrate a single layer graded composition including: (i) an electrochromic region, (ii) an ion conducting region, and (iii) a counter electrode region. In one embodiment, the system is operable to pass the substrate past the plurality of closely associated sputter targets without breaking vacuum. In one embodiment, the system is configured to deposit the single layer graded composition on an architectural glass substrate of at least six feet by ten feet. In another embodiment, the system further includes a substrate holder and transport mechanism operable to hold the architectural glass substrate in a substantially vertical orientation while in the system. The system may further include one or more load locks for passing the substrate between an external environment and the integrated deposition system. In one embodiment, the system further includes one or more lithium deposition stations, each comprising a lithium-containing material source. These stations can be used to lithiate the EC element should that be desirable. In one embodiment, the system includes at least two lithium deposition stations. The system may therefore include at least one slit valve operable to permit isolation a lithium deposition station, apart from the plurality of closely associated sputter targets. In one embodiment, the system can be configured to accommodate a target having a composition that substantially reflects the composition of an EC element to be deposited. Such targets are contemplated to be wider in some instances that a traditional sputter target, depending upon the desired thickness of the single layer graded composition film and the switching characteristics desired. 
     From the description above, particularly of  FIGS. 3A-3B , it can be seen that with methods described herein, one can not only make electrochromic devices, but also prefabricate a layered stack, for example  400 ,  403  and  409 , that can in some cases be converted through subsequent processing, for example as described herein, to an electrochromic device. Though not functional electrochromic devices, by virtue of not having an ion conducting and electronically-insulating region between the EC and CE layers, such “electrochromic device precursors” can be of particular value. This is especially true if the device precursors are manufactured in a high purity, integrated processing apparatus as described herein, where the material layers are all deposited under a controlled ambient environment where, for example, vacuum is never broken. In that way, high purity, low-defect materials are stacked and essentially “sealed,” for example, by the final TCO layer and/or a capping layer prior to leaving the integrated system. 
     Like the electrochromic devices described above, electrochromic device precursors can also include one or more additional layers (not shown) such as one or more passive layers, for example to improve certain optical properties, providing moisture or scratch resistance, to hermetically seal the device precursor and the like. In one embodiment, a capping layer is deposited on the TCO layer of the precursor stack. In some embodiments, the capping layer is SiAlO. In some embodiments, the capping layer is deposited by sputtering. In one embodiment, the thickness of a capping layer is between about 30 nm and about 100 nm. Subsequent processing with the cap layer in place forms the IC layer without contamination from the environment, that is, with the additional protection of the capping layer. 
     Conversion of an EC device precursor to a functional electrochromic device can occur outside the integrated system if desired, since the internal stack structure is protected from the outside environment and somewhat less stringent purity conditions are necessary for the last conditioning steps to convert the precursor stack to the functional device. Such stacked electrochromic device precursors can have advantages, for example, longer lifespan due to conversion to the electrochromic device only when needed, flexibility by having, for example, a single precursor stack that can be stored and used when conversion parameters are improved or fed to different conversion chambers and/or customer sites for conversion depending on the needs of the final product and quality standards that must be met. Also such precursor stacks are useful for testing purposes, for example, quality control or research efforts. 
     Accordingly, one embodiment is an electrochromic device precursor including: (a) a substrate; (b) a first transparent conducting oxide layer on the substrate; (c) a stack on the first transparent conducting oxide layer, the stack including: (i) an electrochromic layer including an electrochromic material, and (ii) a counter electrode layer including a counter electrode material; where the stack does not include an ion conducting and electronically-insulating region between the electrochromic layer and the counter electrode layer; and (d) a second transparent conducting oxide layer on top of the stack. In one embodiment, the electrochromic layer includes tungsten oxide and the counter electrode layer comprises nickel tungsten oxide. In one embodiment, at least one of the stack and the electrochromic layer contain lithium. In another embodiment, the electrochromic layer is tungsten oxide with superstoichiometric oxygen content at least at the interface with the counter electrode layer. In another embodiment, the stack includes an IC precursor layer between the counter electrode layer and the electrochromic layer, the IC precursor layer including tungsten oxide with higher oxygen content than that of the electrochromic layer. In one embodiment, where there is no IC precursor layer between the EC and CE layers, the electrochromic layer is between about 500 nm and about 600 nm thick and the counter electrode layer is between about 150 nm and about 300 nm thick. In another embodiment, where there is an IC precursor layer between the EC and CE layers, the electrochromic layer is between about 350 nm and about 400 nm thick, the IC precursor layer is between about 20 nm and about 100 nm thick, and the counter electrode layer is between about 150 nm and about 300 nm thick. In one embodiment, precursor devices described herein are exposed to heating to convert them to functional electrochromic devices. In one embodiment, the heating is part of an MTCC. 
     Another embodiment is an electrochromic device including: (a) an electrochromic layer including an electrochromic material, and (b) a counter electrode layer including a counter electrode material, where the device does not contain a compositionally homogeneous layer of electronically-insulating, ion conducting material between the electrochromic layer and the counter electrode layer. In one embodiment, the electrochromic material is tungsten oxide, the counter electrode material is nickel tungsten oxide, and between the electrochromic layer and the counter electrode layer is an interfacial region including a mixture of lithium tungstate and at least one of tungsten oxide and nickel tungsten oxide. In another embodiment, the electrochromic layer is between about 300 nm and about 500 nm thick; the interfacial region is between about 10 nm and about 150 nm thick, and the counter electrode layer is between about 150 nm and about 300 nm thick. 
     Examples 
       FIG. 6 , is a graph of a process flow used as a protocol for fabricating electrochromic devices. The y axis units are optical density and the x axis units are time/process flow. In this example, an electrochromic device is fabricated analogous to that described in relation to  FIG. 4A , where the substrate is glass with fluorinated tin oxide as the first TCO, the EC layer is WO 3  with excess oxygen in the matrix (for example, sputtered using the tungsten target, where the sputter gas is about 60% O 2  and about 40% Ar), the CE layer is formed atop the EC layer and is made of NiWO and the second TCO is indium tin oxide (ITO). Lithium is used as the ion source for the electrochromic transition. 
     Optical density is used to determine endpoints during fabrication of the electrochromic device. Starting at the origin of the graph, optical density is measured as the EC layer, WO 3 , is deposited on the substrate (glass+TCO). The optical density of the glass substrate has a baseline value optical density of about 0.07 (absorbance units). The optical density increases from that point as the EC layer builds, because tungsten oxide, although substantially transparent, absorbs some visible light. For a desired thickness of the tungsten oxide layer about 550 nm thick, as described above, the optical density rises to about 0.2. After deposition of the tungsten oxide EC layer, lithium is sputtered on the EC layer as indicated by the first time period denoted “Li.” During this period, the optical density increases along a curve further to about 0.4, indicating that the blind charge of the tungsten oxide has been satisfied, as tungsten oxide colors as lithium is added. The time period denoted “NiWO” indicates deposition of the NiWO layer, during which the optical density increases because NiWO is colored. The optical density increases further during NiWO deposition from about 0.4 to about 0.9 for the addition of a NiWO layer about 230 nm thick. Note that some lithium may diffuse from the EC layer to the CE layer as the NiWO is deposited. This serves to maintain the optical density at a relatively lower value during the NiWO deposition, or at least during the initial phase of the deposition. 
     The second time period denoted “Li” indicates addition of lithium to the NiWO EC layer. The optical density decreases from about 0.9 to about 0.4 during this phase because lithiation of the NiWO bleaches the NiWO. Lithiation is carried out until the NiWO is bleached, including a local minima at about 0.4 optical density. The optical density bottoms out at about 0.4 because the WO 3  layer is still lithiated and accounts for the optical density. Next, as indicated by time period “extra Li” additional lithium is sputtered onto the NiWO layer, in this example about 10% additional lithium as compared to that added to the NiWO to bleach it. During this phase the optical density increases slightly. Next the indium tin oxide TCO is added, as indicated by “ITO” in the graph. Again, the optical density continues to rise slightly during formation of the indium tin oxide layer, to about 0.6. Next, as indicated by time period denoted “MSTCC” the device is heated to about 250° C., for about 15 minutes under Ar, and then about 5 minutes under O 2 . Then the device is annealed in air at about 300° C. for about 30 minutes. During this time, the optical density decreases to about 0.4. Thus optical density is a useful tool for fabricating devices, for example for determining layer thickness based on material deposited and morphology, and especially for titrating lithium onto the various layers for satisfying blind charge and/or reaching a bleached state. 
       FIG. 7  shows a cross section TEM of an electrochromic device  700  fabricated using methods described herein, consistent with the protocol as described in relation to  FIG. 6 . Device  700  has a glass substrate  702  upon which an electrochromic stack,  714 , is formed. Substrate  702  has an ITO layer,  704 , which serves as the first TCO. A tungsten oxide EC layer,  706 , is deposited on TCO  704 . Layer  706  was formed at a thickness of about 550 nm, that is, WO 3  formed via sputtering tungsten with oxygen and argon as described above in relation to  FIG. 6 . To the EC layer was added lithium. Then a CE layer,  710 , of NiWO, about 230 nm thick, was added followed by addition of lithium to bleach and then about 10% excess. Finally an indium tin oxide layer,  712 , was deposited and the stack was subjected to multistep thermochemical conditioning as described above in relation to  FIG. 4A . After the MSTCC, this TEM was taken. As seen, a new region,  708 , which is ion conducting electronically-insulating, was formed. 
       FIG. 7  also shows five selected area electron diffraction (SAED) patterns for the various layers. First,  704   a , indicates that the ITO layer is highly crystalline. Pattern  706   a  shows that the EC layer is polycrystalline. Pattern  708   a  shows that the IC layer is substantially amorphous. Pattern  710   a  shows that the CE layer is polycrystalline. Finally, pattern  712   a  shows that the indium tin oxide TCO layer is highly crystalline. 
       FIG. 8  is a cross section of a device,  800 , analyzed by scanning transmission electron microscopy (STEM). In this example, device  800  was fabricated using methods described herein, consistent with the protocol as described in relation to  FIG. 4B . Device  800  is an electrochromic stack formed on a glass substrate (not labeled). On the glass substrate is a fluorinated tin oxide layer,  804 , which serves as the first TCO (sometimes called a “TEC” layer, for transparent electronic conductor”). A tungsten oxide EC layer,  806 , was deposited on TCO  804 . In this example, layer  806  was formed at a thickness of about 400 nm, that is, WO 3  formed via sputtering tungsten with oxygen and argon as described above in relation to  FIG. 6 , then an oxygen rich precursor layer,  805 , was deposited to a thickness of about 150 nm. To layer  805  was added lithium. Then a CE layer,  810 , of NiWO, about 230 nm thick, was added followed by addition of lithium to bleach and then about 10% excess. Finally an indium tin oxide layer,  812 , was deposited and the stack was subjected to multistep thermochemical conditioning as described above in relation to  FIG. 4B . After the MSTCC, this STEM was taken. As seen, a new region,  808 , which is ion conducting electronically-insulating, was formed. The difference between this example and the embodiment described in relation to  FIG. 4B , is that here the oxygen rich layer  805 , unlike analogous layer  405  in  FIG. 4B , was only partially converted to the interfacial region  808 . In this case only about 40 nm of the 150 nm of oxygen rich precursor layer  405  was converted to the region serving as the ion conducting layer. 
       FIGS. 8B and 8C  show a “before and after” comparison of device,  800 , ( FIG. 8C ) and the device precursor ( FIG. 8B ) before multistep thermochemical conditioning as analyzed by STEM. In this example, only layers  804 - 810 , EC through CE, are depicted. The layers are numbered the same as in  FIG. 8A , with a few exceptions. The dotted line in  FIG. 8B  is used to approximately demark the interface of EC layer  806  and oxygen rich layer  805  (this is more apparent in  FIG. 8C ). Referring again to  FIG. 8B , it appears that at least there is lithium, as indicated by  808   a , concentrated (approximately 10-15 nm thick region) at the interface of oxygen rich layer  805  and CE layer  810 . After MTCC,  FIG. 8C , it is clear that interfacial region  808  has formed. 
     Although the foregoing has been described in some detail to facilitate understanding, the described embodiments are to be considered illustrative and not limiting. It will be apparent to one of ordinary skill in the art that certain changes and modifications can be practiced within the scope of the appended claims.