Patent Publication Number: US-2021191214-A1

Title: Faster switching low-defect electrochromic windows

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     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 its entirety and for all purposes. 
     FIELD 
     The disclosure generally relates to electrochromic devices and in particular to material layers in electrochromic devices. 
     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. 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. However, advances in electrochromic technology, apparatus, and related methods of making and/or using them, are needed because conventional electrochromic windows suffer from, for example, high defectivity and low versatility. 
     SUMMARY 
     Certain embodiments pertain to electrochromic devices comprising first and second conductors, wherein at least one of the first and second conductors is a multi-layered conductor. The electrochromic devices further comprising an electrochromic stack between the conductors adjacent a substrate. The at least one multi-layer conductor comprises a metal layer sandwiched between a first non-metal layer and a second non-metal layer such that the metal layer does not contact the electrochromic stack. 
     Certain embodiments pertain to electrochromic devices comprising in the following order: a) a glass substrate, b) a first TCO layer, c) a first defect mitigating insulating layer, d) a first metal layer, e) a second defect mitigating insulating layer, f) an EC stack comprising a cathodically coloring electrode layer and an anodically coloring electrode layer sandwiching an ion conductor layer, g) a second TCO layer, h) a second metal layer, and i) a third TCO layer. 
     Certain embodiments pertain to an electrochromic device comprising, in the following order, a substantially transparent substrate, a first multi-layer conductor disposed on the substantially transparent substrate. The first multi-layer conductor comprises, in order, a first conductive material layer, a first defect mitigating insulating layer, a second conductive material layer, and a second defect mitigating insulating layer. The electrochromic device further comprising an electrochromic stack and a second multi-layer conductor disposed on the electrochromic stack. The second multi-layer conductor comprises, in order, a third defect mitigating insulating layer, a third conductive material layer, a fourth defect mitigating insulating layer, and a fourth conductive material layer. 
     Certain embodiments pertain to an electrochromic device comprising, in the following order, a substantially transparent substrate and a first multi-layer conductor disposed on the substantially transparent substrate. The first multi-layer conductor comprises, in order, a first transparent conductive oxide layer, a first metal layer, a second transparent conductive oxide layer, and a first defect mitigating insulating layer. The electrochromic device further comprises an electrochromic stack and a second multi-layer conductor disposed on the electrochromic stack. The second multi-layer conductor comprises, in order, a third transparent conductive oxide layer, a second metal layer, and a fourth transparent conductive oxide layer. 
     Certain embodiments pertain to An electrochromic device comprising, in the following order a substantially transparent substrate and a first multi-layer conductor disposed on the substantially transparent substrate. The first multi-layer conductor comprising, in order, a first transparent conductive oxide layer, a first metal layer, a second transparent conductive oxide layer, one or more blocking layers, a first defect mitigating insulating layer. The electrochromic device further comprising an electrochromic stack and a second multi-layer conductor disposed on the electrochromic stack, the second multi-layer conductor comprising, in order, a third transparent conductive oxide layer, a second metal layer, and a fourth transparent conductive oxide layer. 
     Certain embodiments pertain to An electrochromic device comprising, in the following order a substantially transparent substrate and a first multi-layer conductor disposed on the substantially transparent substrate. The first multi-layer conductor comprises, in order, a first transparent conductive oxide layer, a first metal layer, a protective cap layer, and a second transparent conductive oxide layer. The electrochromic device further comprises an electrochromic stack and a second multi-layer conductor disposed on the electrochromic stack. The second multi-layer conductor comprises, in order, a third transparent conductive oxide layer, a second metal layer, and a fourth transparent conductive oxide layer. 
     These and other features and embodiments will be described in more detail below with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  depicts a schematic illustration of a cross section of an electrochromic device, according to aspects. 
         FIGS. 2A and 2B  depict schematic illustrations of a cross section of an electrochromic device, according to certain aspects. 
         FIG. 3  depicts a schematic illustration of a cross section of an electrochromic device comprising in order a substrate, a diffusion barrier, a first composite conductor with a first conductive (metal or TCO) material layer, a first DMIL, a second conductive (metal or TCO) material layer, and a second DMIL and a second composite conductor with mirrored layers to first composite conductor, according to embodiments. 
         FIG. 4  depicts a schematic illustration of a cross section of an electrochromic device with a composite conductor having one or more color tuning layers, according to aspects. 
         FIG. 5A  depicts a schematic illustration of a cross section of an electrochromic device with a composite conductor having a DMIL between a TCO/Metal/TCO stack and the electrochromic stack, according to aspects. 
         FIG. 5B  depicts a schematic illustration of a cross section of an electrochromic device with a composite conductor having a DMIL between a TCO/Metal/TCO stack and the electrochromic stack, according to aspects. 
         FIG. 6  depicts a schematic illustration of a cross section of an electrochromic device with one or more barrier/blocking layer, according to aspects. 
         FIG. 7  depicts a schematic illustration of a cross section of an electrochromic device with a protective cap, according to aspects. 
         FIG. 8  depicts a schematic illustration of a cross section of an electrochromic device with multi-layer conductors, according to embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Certain aspects pertain to electrochromic devices configured not only for faster switching, but also for high quality low-defect count. In some cases, the electrochromic devices have multi-layer conductors of differing materials. The different conductor material layers are configured for faster switching relative to conventional single-layer conductors, while also being optically and materially compatible with the other device layers. In other aspects, electrochromic devices are configured with one or more barrier/blocking layer and/or one or more metal alloy layers to help prevent migration of the metal into the electrochromic device for improved durability. These and other aspects are described below. 
     I. Electrochromic Device Structure 
     Before turning to a more detailed description on conductor designs and other improvements in layers of an electrochromic device, examples of the structure of an electrochromic device are provided. An electrochromic device generally comprises two conductors that sandwich an electrochromic stack. The electrochromic stack typically includes an electrochromic (EC) layer, a counter electrode (CE) layer, and optionally one or more ion conducting (IC) layers that allow ion transport but are electrically insulating. Electrochromic devices are typically deposited on a substrate, and oftentimes are depicted as fabricated on a horizontally oriented substrate, and thus for the purposes of this disclosure, the conductors of the electrochromic device are sometimes referred to as “upper” and “lower” conductors where the description makes reference to drawings that depict the conductors in this manner. In other cases, the conductors are referred to as “first” and “second” conductors. 
       FIG. 1  is a schematic illustration of a cross-section of an electrochromic device  100 , according to embodiments. The electrochromic device  100  comprises a substrate  102  (e.g., glass), a first conductor  110 , an electrochromic stack  120 , and a second conductor  130 . A voltage source,  20 , operable to apply an electric potential across electrochromic stack  120  effects the transition of the electrochromic device  100  between tint states such as, for example, between a bleached state and a colored state. In certain implementations, the electrochromic device  100  further comprises a diffusion barrier of one or more layers between the substrate  102  and the first conductor  110 . In some cases, the substrate  102  may be fabricated with the diffusion barrier. 
     In certain embodiments, the electrochromic stack is a three-layer stack including an EC layer, optional IC layer that allows ion transport but is electrically insulating, and a CE layer. The EC and CE layers sandwich the IC layer. Oftentimes, but not necessarily, the EC layer is tungsten oxide based and the CE layer is nickel oxide based, e.g., being cathodically and anodically coloring, respectively. In one embodiment, the electrochromic stack is between about 100 nm and about 500 nm thick. In another embodiment, the electrochromic stack is between about 410 nm and about 600 nm thick. For example, the EC stack may include an electrochromic layer that is between about 200 nm and about 250 nm thick, an IC layer that is between about 10 and about 50 nm thick, and a CE layer that is between about 200 nm and 300 nm thick. 
       FIGS. 2A and 2B  are schematic cross-sections of an electrochromic device  200 , according to embodiments. The electrochromic device  200  comprises a substrate  202 , a first conductor  210 , an electrochromic stack  220 , and a second conductor  230 . The electrochromic stack  220  comprises an electrochromic layer (EC)  222 , an optional ion conducting (electronically resistive) layer (IC)  224 , and a counter electrode layer (CE)  226 . A voltage source  22  is operable to apply a voltage potential across the electrochromic stack  220  to effect transition of the electrochromic device between tint states such as, for example, between a bleached state (refer to  FIG. 2A ) and a colored state (refer to  FIG. 2B ). In certain implementations, the electrochromic device  200  further comprises a diffusion barrier located between the substrate  202  and the first conductor  210 . 
     In certain implementations of the electrochromic device  200  of  FIGS. 2A and 2B , the order of layers in the electrochromic stack  220  may be reversed with respect to the substrate  202  and/or the position of the first and second conductors may be switched. For example, in one implementation the layers may be in the following order: substrate  202 , second conductor  230 , CE layer  226 , optional IC layer  224 , EC layer  222 , and first conductor  210 . 
     In certain implementations, the CE layer may include a material that is electrochromic or not. If both the EC layer and the CE layer employ electrochromic materials, one of them is a cathodically coloring material and the other an anodically coloring material. For example, the EC layer may employ a cathodically coloring material and the CE layer may employ an anodically coloring material. This is the case when the EC layer is a tungsten oxide and the counter electrode layer is a nickel tungsten oxide. The nickel tungsten oxide may be doped with another metal such as tin, niobium or tantalum. 
     During an exemplary operation of an electrochromic device (e.g. electrochromic device  100  or electrochromic device  200 ), the electrochromic device can reversibly cycle between a bleached state and a colored state. For simplicity, this operation is described in terms of the electrochromic device  200  shown in  FIGS. 2A and 2B , but applies to other electrochromic devices described herein as well. As depicted in  FIG. 2A , in the bleached state, a voltage is applied by the voltage source  22  at the first conductor  210  and second conductor  230  to apply a voltage potential across the electrochromic stack  220 , which causes available ions (e.g. lithium ions) in the stack to reside primarily in the CE layer  226 . If the EC layer  222  contains a cathodically coloring material, the device is in a bleached state. In certain electrochromic devices, when loaded with the available ions, the CE layer can be thought of as an ion storage layer. Referring to  FIG. 2B , when the voltage potential across the electrochromic stack  220  is reversed, the ions are transported across optional IC layer  224  to the EC layer  222 , which causes the material to transition to the colored state. Again, this assumes that the optically reversible material in the electrochromic device is a cathodically coloring electrochromic material. In certain embodiments, the depletion of ions from the counter electrode material causes it to color also as depicted. In other words, the counter electrode material is anodically coloring electrochromic material. Thus, the EC layer  222  and the CE layer  226  combine to synergistically reduce the amount of light transmitted through the stack. When a reverse voltage is applied to the electrochromic device  200 , ions travel from the EC layer  222 , through the IC layer  224 , and back into the CE layer  226 . As a result, the electrochromic device  200  bleaches i.e. transitions to the bleached states. In certain implementations, electrochromic devices can operate to transition not only between bleached and colored states, but also to one or more intermediate tint states between the bleached and colored states. 
     Some pertinent examples of electrochromic devices are presented in the following US patent applications, each of which is hereby incorporated by reference in its entirety: U.S. patent application Ser. No. 12/645,111, filed on Dec. 22, 2009; U.S. patent application Ser. No. 12/772,055, filed on Apr. 30, 2010; U.S. patent application Ser. No. 12/645,159, filed on Dec. 22, 2009; U.S. patent application Ser. No. 12/814,279, filed on Jun. 11, 2010; and U.S. patent application Ser. No. 13/462,725, filed on May 2, 2012. 
     Electrochromic devices such as those described with reference to  FIGS. 1, 2A and 2B  can be incorporated, for example, in electrochromic windows. In these examples, the substrate is a transparent or substantially transparent substrate such as glass. For example, the substrate  102  or the substrate  202  may be architectural glass upon which electrochromic devices are fabricated. Architectural glass is glass that can be 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. In some embodiments, architectural glass can be as large as about 72 inches by 120 inches. 
     As larger and larger substrates are used in electrochromic window applications, it becomes more desirable to reduce the number and extent of the defects in the electrochromic devices, otherwise performance and visual quality of the electrochromic windows may suffer. Certain embodiments described herein may reduce defectivity in electrochromic windows. 
     In some embodiments, one or more electrochromic devices are integrated into an insulating glass unit (IGU). An insulated glass unit comprises multiple panes (also referred to as “lites”) with a spacer sealed between panes to form a sealed interior region that is thermally insulating and can contain a gas such as an inert gas. In some embodiments, an IGU includes multiple electrochromic lites, each lite having at least one electrochromic device. 
     In certain embodiments, an electrochromic device is fabricated by thin film deposition methods such as, e.g., sputter deposition, chemical vapor deposition, pyrolytic spray on technology and the like, including combinations of thin film deposition technologies known to one of ordinary skill in the art. In one embodiment, the electrochromic device is fabricated using all plasma vapor deposition. 
     In certain embodiments, an electrochromic device may further comprise one or more bus bars for applying voltage to the conductors of the electrochromic device. The bus bars are in electrical communication with a voltage source. The bus bars are typically located at one or more edges of the electrochromic device and not in the center region, for example, the viewable central area of an IGU. In some cases, the bus bars are soldered or otherwise connected to the first and second conductors to apply a voltage potential across the electrochromic stack. For example, ultrasonic soldering, which makes a low resistance connection, may be used. Bus bars may be, for example, silver ink based materials and/or include other metal or conductive materials such as graphite and the like. 
     II. Conductor and Other Electrochromic Device Materials 
     Recently, there has been increased attention paid to improving conductors for applications such as large-area electrochromic devices. Conventionally, single-layer conductors with transparent conductive oxides (TCOs) based on In 2 O 3 , ZnO, aluminum zinc oxide (AZO), fluorinated tin oxide (FTO), indium tin oxide (ITO) have been used, but advanced and/or large-area electrochromic devices require new conductors with lower resistivities than previously achieved, e.g., for faster switching speeds. A TCO/metal/TCO three-layer structure can serve as an alternative since it may provide superior electrical characteristics to that of a conventional single-layer conductor and may have improved optical properties. However, improvements are still needed with regards to this structure. For example, incorporating a TCO/metal/TCO three-layer structure into advanced electrochromic devices introduces problematic issues such as addressing optical and material compatibility with other layers of the advanced electrochromic devices. Generally speaking, recent advancements in electrochromic device design have necessitated improvements in conductors compatible with these advanced designs. 
     In some embodiments, electrochromic devices are configured not only for faster switching, but also to take into account the need for high quality, low-defect count electrochromic devices. In some cases, the electrochromic device conductors are configured for faster switching relative conventional single-layer TCO conductors, while also being optically and materially compatible with the other device layers. 
     The conductors described herein generally include one or more metal layers or one or more TCO layers, and in some embodiments, include both one or more metal layers and one or more TCO layers. The conductors having two or more layers of differing composition are sometimes referred to herein as “composite conductors” or “multi-layer conductors.” In some cases, a composite conductor has two or more metal layers of differing composition. In other cases, a composite conductor has one or more metal layers and one or more TCO layers. In yet other cases, a composite conductor has two or more TCO layers. Generally, but not necessarily, the TCO materials used in conductors are high band gap metal oxides. 
     Some examples of TCO materials used in a TCO layer of a conductor include, but are not limited to, fluorinated tin oxide (FTO), indium tin oxide (ITO), aluminum zinc oxide (AZO) and other metal oxides, doped with one or more dopants or not, for example. In some cases, the TCO layer is between about 200 nm and 500 nm thick. In some cases, the TCO layer is between about 100 nm and 500 nm thick. In some cases, the TCO layer is between about 10 nm and 100 nm thick. In some cases, the TCO layer is between about 10 nm and 50 nm thick. In some cases, the TCO layer is between about 200 nm and 500 nm thick. In some cases, the TCO layer is between about 100 nm and 250 nm thick. 
     Some examples of metals used in a metal layer of a conductor include, but are not limited to, silver, copper, aluminum, gold, platinum, and mixtures, intermetallics and alloys thereof. In one embodiment, the metal layer has a thickness in the range of between about 1 nm and 5 nm thick. In one embodiment, the metal layer has a thickness in the range between about 5 nm to about 30 nm. In one embodiment, the metal layer has a thickness in the range between about 10 nm and about 25 nm. In one embodiment, the metal layer has a thickness in the range between about 15 nm and about 25 nm. 
     In some embodiments, a metal layer of a conductor may be comprised of a “metal sandwich” construction of two or more different metal sublayers. For example, a metal layer may comprise a “metal sandwich” construction of Cu/Ag/Cu sublayers instead of a single layer of, for example, Cu. In another example, a metal layer may comprise a “metal sandwich” construction of NiCr/metal/NiCr, where the metal sublayer is one of the aforementioned metals. 
     In some embodiments, a metal layer of a conductor comprises a metal alloy. Electromigration resistance of metals can be increased through alloying. Increasing the electromigration resistance of metal layers in a conductor reduces the tendency of the metal to migrate into the electrochromic stack and potentially interfere with operation of the device. By using a metal alloy, the migration of metal into the electrochromic stack can be slowed and/or reduced which can improve the durability of the electrochromic device. Certain aspects pertain to using a metal alloy in a metal layer of a conductor to help reduce the tendency of migration of the metal into the electrochromic stack and potentially improve the durability of the electrochromic device. For example, addition of small amounts of Cu or Pd to silver can substantially increase the electromigration resistance of the silver material. In one embodiment, for example, a silver alloy with Cu or Pd is used in a conductor to reduce the tendency of migration of silver into the electrochromic stack to slow down or prevent such migration from interfering with normal device operation. In some cases, the metal layer may be comprised of an alloy whose oxides have low resistivity. In one example, the metal layer may further comprise another material (e.g., Hg, Ge, Sn, Pb, As, Sb, or Bi) as compound during the preparation of the oxide to increase density and/or lower resistivity. 
     In some embodiments, the one or more metal layers of a composite conductor are transparent. Typically, a transparent metal layer is less than 10 nm thick, for example, about 5 nm thick or less. In other embodiments, the one or more metal layers of a composite conductor are opaque or not entirely transparent. 
     In certain embodiments, a composite conductor includes a layer of material of “opposing susceptibility” adjacent a dielectric or metal layer. A material of “opposing susceptibility,” referring to the material&#39;s electric susceptibility, generally refers to a material that has susceptibility to having an opposing sign. Electric susceptibility of a material refers to its ability to polarize in an applied electric field. The greater the susceptibility, the greater the ability of the material to polarize in response to the electric field. Including a layer of “opposing susceptibility” can change the wavelength absorption characteristics to increase the transparency of the dielectric or metal layer and/or shift the wavelength transmitted through the combined layers. For example, a composite conductor can include a high-index dielectric material layer (e.g., TiO 2 ) of “opposing susceptibility” adjacent a metal layer to increase the transparency of the metal layer. In some cases, the added layer of “opposing susceptibility” adjacent a metal layer can cause a not entirely transparent metal layer to be more transparent. For example, a metal layer (e.g., silver layer) that has a thickness in the range of from about 5 nm to about 30 nm, or between about 10 nm and about 25 nm, or between about 15 nm and about 25 nm, may not be entirely transparent by itself, but when coated with a material of “opposing susceptibility” (e.g., TiO 2  layer on top of the silver layer), the transmission through the combined layers is higher than the metal or dielectric layer alone. Certain aspects pertain to selecting a dielectric or metal layer and an adjacent layer of “opposing susceptibility” to color tune the electrochromic device to transmit certain wavelengths of a desired spectrum. 
     In certain embodiments, a composite conductor includes one or more metal layers and one more “color tuning” layers also referred to as “index matching” layers. These color tuning layers are generally of a high-index, low-loss dielectric material of “opposing susceptibility” to the one or more metal layers. Some examples of materials that can be used in “color tuning” layers include silicon oxide, tin oxide, indium tin oxide, and the like. In these embodiments, the thickness and/or material used in the one or more color tuning layers changes the absorption characteristics to shift the wavelength transmitted through the combination of the material layers. For example, the thickness of the one or more color tuning layers can be selected to tune the color of light transmitted through the electrochromic device in a bleached state to a desired spectrum (e.g., more blue over green or red). In another example, tuning layers are chosen and configured to reduce transmission of certain wavelengths (e.g., yellow) through the electrochromic device, and thus e.g. a window which includes the device coating. 
     Although the first and second composite conductors generally have the same or substantially similar layers and the order of the layers in the first composite conductor mirrors the order of the layers of the second composite conductor in described implementations, the disclosure is not so limiting. For example, the first composite conductor may have different layers than the second composite conductor in other embodiments. As another example, the first composite conductor may have the same layers as the second composite conductor but the order of the layers may not mirror each other. 
     In certain embodiments, the first and second conductors have matched sheet resistance, for example, to provide optimum switching efficiency of the electrochromic device and/or a symmetric coloration front. Matched conductors have sheet resistances that vary from each other by no more than 20% in some embodiments, in other embodiments by no more than 10%, and in yet other embodiments by no more than 5%. 
     For large-area electrochromic devices, e.g., those devices disposed on architectural scale substrates, that is, substrates at least 20×20 inches and up to 72×120 inches, the overall sheet resistance of each of the multi-layer conductors (including all layers of the conductor such as metal, TCO, and DMIL, if present) is typically less than 15 Ω/□, less than 10 Ω/□, less than 5 Ω/□, less than 3 Ω/□, or less than 2 Ω/□. This allows for faster switching relative to conventional devices, particularly when the sheet resistance is less than 5 Ω/□, or less than 3 Ω/□, or less than 2 Ω/□. Resistivities of conductors described herein are typically measured in Ω-cm. In one example, the resistivity of one or more of the multi-layer conductors may be between about 150 Ω-cm and about 500 Ω-cm. One or more of the layers of a multi-layer conductor, such as a metal layer, may have a lower resistivity. 
     Ideally, at least the lower conductor&#39;s topography should be smooth for better conformal layers in the deposited stack thereon. In certain embodiments, one or both of the conductors is a substantially uniform conductor layer that varies by about ±10% in thickness in some cases, or about ±5% in thickness in some cases, or even about ±2% in thickness in some cases. Although typically the thickness of conductors is about 10-800 nm, the thickness will vary depending upon the materials used, thickness of individual layers and how many layers are in the conductor. For example, for composite conductors that include one or more TCOs, the TCO components can be between about 50 nm and about 500 nm thick while the conductor also includes one or more metal layers. In one example, the thickness of the metal layer(s) is in the range of between about 0.1 nm and about 5 nm thick. In one example, the thickness of the metal layer(s) is in the range of between about 1 nm and about 5 nm thick. In one example, the thickness of the metal layer(s) is in the range of about 5 nm to about 30 nm. In one example, the thickness of the metal layer(s) is in the range of between about 10 nm and about 25 nm. In one example, the thickness of the metal layer(s) is in the range of or between about 15 nm and about 25 nm. 
     In certain cases, the one or more metal layers of a conductor are fabricated sufficiently thin so as to be transparent in a transmissive electrochromic device. In other cases, a metal layer of a conductor is fabricated sufficiently thin to be almost transparent and then a material of “opposing susceptibility” is disposed adjacent the almost transparent metal to increase the transparency of the metal layer in transmissive electrochromic device. In cases with reflective devices, the one or more metal layers may have non-transparent metal layers without adding an adjacent layer of material of “opposing susceptibility.” 
     Electrochromic devices described herein may include one or more defect mitigating insulating layers (DMILs) such as those described in U.S. patent application Ser. No. 13/763,505, titled “DEFECT MITIGATION LAYERS IN ELECTROCHROMIC DEVICES” and filed on Feb. 8, 2013, which is hereby incorporated by reference in its entirety. DMIL technology includes devices and methods employing the addition of at least one DMIL. A DMIL prevents electronically conducting layers and/or electrochromically active layers from contacting layers of the opposite polarity and creating a short circuit in regions where certain types of defects form. In some embodiments, a DMIL can encapsulate particles and prevent them from ejecting from the electrochromic stack and possibly cause a short circuit when subsequent layers are deposited. In certain embodiments, a DMIL has an electronic resistivity of between about 1 and 5×10 10  Ohm-cm. 
     In certain embodiments, a DMIL contains one or more of the following metal oxides: cerium oxide, titanium oxide, aluminum oxide, zinc oxide, tin oxide, silicon aluminum oxide, tungsten oxide, nickel tungsten oxide, tantalum oxide, and oxidized indium tin oxide. In certain embodiments, a DMIL contains a nitride, carbide, oxynitride, or oxycarbide such as nitride, carbide, oxynitride, or oxycarbide analogs of the listed oxides, e.g., silicon aluminum oxynitride. As an example, the DMIL may include one or more of the following metal nitrides: titanium nitride, aluminum nitride, silicon nitride, and tungsten nitride. The DMIL may also contain a mixture or other combination of oxide and nitride materials (e.g., a silicon oxynitride). 
     The general attributes of a DMIL include transparency in the visible range, weak or no electrochromism, electronic resistance comparable to or higher than that of undoped electrode material (electrochromic and/or counter electrode), and physical and chemical durability. In certain embodiments, the DMIL has a density of at most about 90% of the maximum theoretical density of the material from which it is fabricated. 
     As discussed above, one of the properties of a DMIL is its electronic resistivity. Generally, a DMIL should have an electronic resistivity level that is substantially greater than that of the transparent conductive layer in the conductor, and in certain cases orders of magnitude greater. In some embodiments, the material of a DMIL has an electronic resistivity that is intermediate between that of a conventional ion conducting layer and that of a transparent conductive layer (e.g., indium doped tin oxide). In some cases, the material of a DMIL has an electronic resistivity is greater than about 10 −4  Ω-cm (approximate resistivity of indium tin oxide). In some cases, the material of a DMIL has an electronic resistivity is greater than about 10 −4  Ω-cm. In some cases, a DMIL has an electronic resistivity between about 10 −4  Ω-cm and 10 14  Ω-cm (approximate resistivity of a typical ion conductor for electrochromic devices). In some cases, the material of a DMIL has an electronic resistivity between about 10 −5  Ω-cm and 10 12  Ω-cm. In certain embodiments, the electronic resistivity of the material in the DMIL is between about 1 and 5×10 13  Ω-cm. In certain embodiments, the electronic resistivity of the material in the DMIL is between about 10 2  and 10 12  Ω-cm. In certain embodiments, the electronic resistivity of the material in the DMIL is between about 10 6  and 5×10 12  Ω-cm. In certain embodiments, the electronic resistivity of the material in the DMIL is between about 10 7  and 5×10 9  Ω-cm. In some embodiments, the material in the DMIL will have a resistivity that is comparable (e.g., within an order of magnitude) of that of the material of the electrochromic layer or the counter electrode layer of the electrochromic stack. 
     The electronic resistivity is coupled to the thickness of the DMIL. This resistivity and thickness level will together yield a sheet resistance value which may in fact be more important than simply the resistivity of the material alone (a thicker material will have a lower sheet resistance). When using a material having a relatively high resistivity value, the electrochromic device may be designed with a relatively thin DMIL, which may be desirable to maintain the optical quality of the device. In certain embodiments, the DMIL has a thickness of about 100 nm or less or about 50 nm or less. In one example, the DMIL has a thickness of about 5 nm, in another example, the layer has a thickness of about 20 nm, and in another example, the layer has a thickness of about 40 nm. In certain embodiments, the DMIL has a thickness of between about 10 nm and about 100 nm. In one case, a DMIL is about 50 nm thick. In certain embodiments, the electronic sheet resistance of the DMIL is between about 40 and 4000 Ω per square or between about 100 and 1000 Ω per square. In some cases, the insulating material is electrically semiconducting having a sheet resistance that cannot be easily measured. 
     In certain embodiments, particularly those in which a DMIL is disposed on the substrate, a thicker layer of a DMIL is sometimes employed. The thickness of the DMIL may be, for example, between about 5 and 500 nm, between about 5 and 100 nm, between 10 and 100 nm, between about 15 and 50 nm, between about 20 and 50 nm, or between about 20 and 40 nm. 
     In certain embodiments, the material making up the DMIL has a relatively low charge capacity. In the context of an electrochromic device, a material&#39;s charge capacity represents its ability to reversibly accommodate lithium ions during normal electrochromic cycling. Charge capacity is the capacity of the material to irreversibly accommodate lithium ions that it encounters during fabrication or during initial cycling. Those lithium ions that are accommodated as charge are not available for subsequent cycling in and out of the material in which they are sequestered. If the insulating material of the DMIL has a high charge capacity, then it may serve as a reservoir of nonfunctional lithium ions (typically the layer does not exhibit electrochromism so the lithium ions that pass into it do not drive a coloring or bleaching transition). Therefore, the presence of this additional layer requires additional lithium ions to be provided in the device simply to be taken up by this additional layer. This is of course a disadvantage, as lithium can be difficult to integrate into the device during fabrication. In certain embodiments, the charge capacity of the DMIL is between about 10 and 100 milliCoulomb/cm 2 *um. In one example, the charge capacity of the DMIL is between about 30 and 60 milliCoulomb/cm 2 . For comparison, the charge capacity of a typical nickel tungsten oxide electrochromic layer is approximately 120 milliCoulomb/cm 2 *um. In certain embodiments, the charge capacity of a DMIL is between about 30 and 100 milliCoulomb/cm 2 *um. In one example, the charge capacity of the DMIL is between about 100 and 110 milliCoulomb/cm 2 *um. For comparison, the charge capacity of a typical nickel tungsten oxide electrochromic layer is typically less than about 100 milliCoulomb/cm 2 *um. 
     In certain embodiments, the DMIL is ionically conductive. This is particularly the case if the layer is deposited before the counter electrode layer. In some of these embodiments, the DMIL has an ionic conductivity of between about 10 −7  Siemens/cm and 10 −12  Siemens/cm. In other of these embodiments, the DMIL has an ionic conductivity of between about 10 −8  Siemens/cm and 10 −11  Siemens/cm. In other of these embodiments, the DMIL has an ionic conductivity of between about between 10 −9  Siemens/cm and 10 −10  Siemens/cm. 
     In some implementations, the DMIL exhibits little or no electrochromism during normal operation. Electrochromism may be measured by applying a defined voltage change or other driving force and measuring the change in optical density or transmissivity of the device. 
     According to certain implementations, the material of the DMIL should have favorable optical properties. For example, the material of the DMIL should have a relatively low optical density such as, for example, an optical density below about 0.1 or an optical density below about 0.05. Additionally in certain cases, the material of the DMIL has a refractive index that matches that of adjacent materials in the stack so that it does not introduce significant reflection. The material should also adhere well to other materials adjacent to it in the electrochromic stack. 
     As discussed above, a DMIL can serve to encapsulate particles that deposit on the device during fabrication in certain embodiments. By encapsulating these particles, they are less likely to eject and potentially cause defects. In certain implementations, the fabrication operation that deposits the DMIL is performed immediately after or soon after the process operation or operations that likely introduces particles into the device. These implementations may be useful to improve encapsulating the particles and reduce defectivity in electrochromic devices. In certain implementations, thicker layers of DMILs are used. Using thicker DMILs may be particularly useful to increase encapsulating of particles and reduce defectivity in electrochromic devices. 
     Various insulating materials may be used in DMILs. Some of these insulating materials include various transparent metal oxides such as, for example, aluminum oxide, zinc oxide, tin oxide, silicon aluminum oxide, silicon oxide, cerium oxide, stoichiometric tungsten oxide (e.g., WO 3 , wherein the ratio of oxygen to tungsten is exactly 3), variations of nickel tungsten oxide, and highly oxidized indium tin oxide (ITO). In some cases, the insulating material of the DMIL is selected from aluminum oxide, zinc oxide, silicon aluminum oxide, tantalum oxide, and nickel tungsten oxide (typically a non-electrochromic type). In addition, some nitrides, carbides, oxynitrides, oxycarbides, and fluorides having medium to high resistance and optical transparency can be used. For example, nitrides such as titanium nitride, tantalum nitride, aluminum nitride, silicon nitride, and/or tungsten nitride may be used. Further, carbides such as titanium carbide, aluminum carbide, tantalum carbide, silicon carbide, and/or tungsten carbide may be used. Oxycarbides and/or oxynitrides may also be used in certain embodiments. Unless otherwise specified, each of these compositions may be present in various stoichiometries or ratios of elements. For DMILs containing nickel and tungsten, the ratio of nickel to tungsten may be controlled such that relatively high ratios are employed. For example the Ni:W (atomic) ratio may be between about 90:10 and 50:50 or between about 80:20 and 60:40. 
     In some cases, the material chosen for the DMIL is a material that integrates well (i.e. compatible) with electrochromic stack. The integration may be promoted by (a) employing compositions similar to those of materials in layers adjacent to DMIL in the stack (promotes ease of fabrication), and (b) employing materials that are optically compatible with the other materials in the stack and reduce quality degradation in the overall stack. 
     In certain embodiments, the electrochromic device includes a diffusion barrier between the lower conductor and the transparent substrate (e.g., a glass substrate such as soda lime glass). The diffusion barrier may include one or more layers. The diffusion barrier layer or layers keep sodium ions from diffusing into the electrochromic device layers above it and may also, optionally, be optically tuned to enhance various optical properties of the entire construct, e.g., % optical transmission (% T), haze, color, reflection and the like. 
     In one embodiment, the diffusion barrier includes one or more layers including one more of, for example, silicon dioxide, silicon oxide, tin oxide, FTO and the like. In certain aspects, the diffusion barrier is a three-layer stack of SiO 2 , SnO 2 , and SiO x , wherein the SiO 2  layer has a thickness in the range of between 20 nm and 30 nm, the a SnO 2  layer has a thickness in the range of between 20 and 30 nm, and the SiO x  layer has a thickness in the range of 2 nm to 10 nm. In one aspect, the SiO x  layer of the tri-layer diffusion barrier is a monoxide or a mix of the monoxide with SiO 2 . In one aspect, the tri-layer diffusion barrier may be sandwiched between an FTO and the substrate. In certain aspects, the diffusion barrier is in a bi-layer or tri-layer construction of SnO 2 , SiO 2  and SiO x  in various combinations. In one embodiment, thicknesses of individual diffusion barrier layers may be in the range between about 10nm and 30 nm. In certain cases, thicknesses of individual diffusion barrier layers may be in the range of 20 nm-30 nm. In some cases, the diffusion barrier may be a sodium diffusion barrier and/or an anti-reflection or anti-iridescent layer. 
     In certain implementations, the electrochromic device has a diffusion barrier between the lower conductor and the substrate. In other implementations, the electrochromic device does not have a diffusion barrier. In some cases, a diffusion barrier may not be necessary and is not used. For example, if the substrate is a sodium free substrate such as plastic or alkali free glass, the diffusion barrier is optional. In other examples, an electrochromic device may have one or more color tuning layers over the substrate that function as a diffusion barrier. 
     III. Composite Conductors Examples 
     This section includes examples of electrochromic devices having one or more composite conductors, according to embodiments. In certain implementations, the electrochromic stacks and other layers of the electrochromic devices described in this section may have similar characteristics to layers described in the sections above. For example, the layers of the electrochromic stacks described in this section may be similar in some respects to the layers described with reference to 
       FIGS. 2A and 2B  in Section I. As another example, the characteristics of the DMILs described in this section are described in detail in Section II. 
     Conductive Material/DMIL 1 /Conductive Material/DMIL 2   
     In certain embodiments, a composite conductor comprises material layers with the order of: a first conductive material layer, a first DMIL adjacent the first conductive material layer, a second conductive material layer adjacent the first DMIL, and a second DMIL adjacent the second conductive material layer. In these embodiments, the first conductive material layer is a metal layer or a TCO layer and the second conductive material layer is a metal layer or a TCO layer. In certain examples, both the first and second conductive material layers are metal layers. In other examples, both the first and second conductive material layers are a TCO layers. In other examples, the first or second conductive material layer is a TCO layer and the other conductive material layer is a metal layer. An example of a composite conductor with material layers, in order, of: a first conductive material layer, a first DMIL, a second conductive material layer, and a second DMIL is shown in  FIG. 3 . 
       FIG. 3  depicts a schematic illustration of the material layers of an electrochromic device  300 , according to embodiments. The electrochromic device  300  comprises a substrate  302 , one or more diffusion barrier layers  304  disposed on the substrate  302 , a first composite conductor  310  disposed on the diffusion barrier layer(s)  304 , an electrochromic stack  320  disposed on the first composite conductor  310 , and a second composite conductor  330  disposed on the electrochromic stack  320 . The first composite conductor  310  comprises a first conductive material layer  312 , a first DMIL  314 , a second conductive material layer  316 , and a second DMIL  318 . The second composite conductor  330  comprises a third DMIL  314 , a third conductive material layer  334 , a fourth DMIL  336 , and a fourth conductive material layer  338 . The first conductive material layer  312  and the fourth conductive material layer  338  are either a metal layer or a TCO layer. The second conductive material layer  316  and the third conductive material layer  334  are either a metal layer or a TCO layer. In one example, the first conductive material layer  312  is a TCO layer and the second conductive material layer  316  is a metal layer. In another example, the first conductive material layer  312  is a metal layer and the second conductive material layer  316  is a TCO layer. In another example, both the first conductive material layer  312  and the second conductive material layer  316  are made of metal. In another example, both the first conductive material layer  312  and the second conductive material layer  316  are made of a TCO. 
     If the first conductive material layer  312  is made of a TCO, then the layer is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. If the first conductive material layer  312  is made of a metal, then the layer may be made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment where the first conductive material layer  312  is made of a metal, the thickness is between about 1 nm and 5 nm thick. In one embodiment where the first conductive material layer  312  is made of a metal, the thickness is between about 5 nm to about 30 nm. In one embodiment where the first conductive material layer  312  is made of a metal, the thickness is between about 10 nm and about 25 nm. In one embodiment where the first conductive material layer  312  is made of a metal, the thickness is between about 15 nm and about 25 nm. In one embodiment, the first conductive material layer  312  is made of a silver metal. The first DMIL  314  may be made of any of the materials described above for DMILs and has the associated electrical, physical and optical properties of the DMIL materials as described above. In one embodiment, the first DMIL  314  is of TiO 2 . In one case, the first DMIL  314  of TiO 2  is between 10 nm and 100 nm thick. In another case, the first DMIL  314  of TiO 2  is between 25 nm and 75 nm thick. In another case, the first DMIL  314  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the first DMIL  314  of TiO 2  is about 50 nm thick. 
     If the second conductive material layer  316  is made of a TCO, then the layer is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. If the second conductive material layer  316  is made of a metal, then the layer may be made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment where the second conductive material layer  316  is made of a metal, the thickness is between about 1 nm and 5 nm thick. In one embodiment where the second conductive material layer  316  is made of a metal, the thickness is between about 5 nm to about 30 nm. In one embodiment where the second conductive material layer  316  is made of a metal, the thickness is between about 10 nm and about 25 nm. In one embodiment where the second conductive material layer  316  is made of a metal, the thickness is between about 15 nm and about 25 nm. In one embodiment, the second conductive material layer  316  is made of a silver metal. 
     The second DMIL  318  may be made of any of the materials described above for DMILs and has the associated electrical, physical and optical properties of the DMIL materials as described above. In one embodiment, the second DMIL  318  is of TiO 2 . In one case, the second DMIL  318  of TiO 2  is between 10 nm and 100 nm thick. In another case, the second DMIL  318  of TiO 2  is between 25 nm and 75 nm thick. In another case, the second DMIL  318  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the second DMIL  318  of TiO 2  is about 50 nm thick. 
     The third DMIL  314  may be made of any of the materials described above for DMILs and has the associated electrical, physical and optical properties of the DMIL materials as described above. In one embodiment, the third DMIL  314  is of TiO 2 . In one case, the third DMIL  314  of TiO 2  is between 10 nm and 100 nm thick. In another case, the third DMIL  314  of TiO 2  is between 25 nm and 75 nm thick. In another case, the third DMIL  314  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the third DMIL  314  of TiO 2  is about 50 nm thick. 
     The fourth DMIL  336  may be made of any of the materials described above for DMILs and has the associated electrical, physical and optical properties of the DMIL materials as described above. In one embodiment, fourth DMIL  336  is of TiO 2 . In one case, fourth DMIL  336  of TiO 2  is between 10 nm and 100 nm thick. In another case, the fourth DMIL  336  of TiO 2  is between 25 nm and 75 nm thick. In another case, the fourth DMIL  336  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the fourth DMIL  336  of TiO 2  is about 50 nm thick. 
     If the third conductive material layer  334  is made of a TCO, then the layer is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. If the third conductive material layer  334  is made of a metal, then the layer may be made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment where the third conductive material layer  334  is made of a metal, the thickness is between about 1 nm and 5 nm thick. In one embodiment where the third conductive material layer  334  is made of a metal, the thickness is between about 5 nm to about 30 nm. In one embodiment where the third conductive material layer  334  is made of a metal, the thickness is between about 10 nm and about 25 nm. In one embodiment where the third conductive material layer  334  is made of a metal, the thickness is between about 15 nm and about 25 nm. In one embodiment, the third conductive material layer  334  is made of a silver metal. 
     If the fourth conductive material layer  338  is made of a TCO, then the layer is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. If the fourth conductive material layer  338  is made of a metal, then the layer may be made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one case, the fourth conductive material layer  338  is silver and is between about 1 nm and 5 nm thick. In one embodiment where the fourth conductive material layer  338  is made of a metal, the thickness is between about 1 nm and 5 nm thick. In one embodiment where the fourth conductive material layer  338  is made of a metal, the thickness is between about 5 nm to about 30 nm. In one embodiment where the fourth conductive material layer  338  is made of a metal, the thickness is between about 10 nm and about 25 nm. In one embodiment where the fourth conductive material layer  338  is made of a metal, the thickness is between about 15 nm and about 25 nm. In one embodiment, the fourth conductive material layer  338  is made of a silver metal. 
     In the illustrated embodiment, the first and second composite conductors  310  and  330  have the same or substantially similar material layers as each other with a mirrored layout. That is, the third DMIL  332  is the same or substantially similar to the second DMIL  318 , the fourth DMIL  336  is the same or substantially similar to the first DMIL  314 , the first conductive material layer  312  is the same or substantially similar to the fourth conductive material layer  338 , and the second conductive material layer  316  is the same or substantially similar to the third conductive material layer  334 . In other embodiments, the first and second composite conductors  310  and  330  may have different orders of the same layers. In yet other embodiments, the first and second composite conductors  310  and  330  have different material layers. Although the electrochromic device  300  is shown in with diffusion barrier layer(s)  304 , another embodiment omits it. 
     In certain aspects, the first composite conductor  310  of the electrochromic device  300  shown in  FIG. 3  further comprises one or more color tuning layers located between the substrate  302  and the first conductive material layer  312 . In these aspects, the first conductive material layer  312  is made of metal. In some of these aspects, the color tuning layer(s) is substituted for the diffusion barrier  304 . In these color tuning embodiments, the one or more color tuning layers may be selected to increase transparency of the conductor and/or to modify the wavelength of light passing through the electrochromic device to change the color of light transmitted. Some examples of materials that can be used in color tuning layers are silicon oxide, tin oxide, indium tin oxide, and the like. 
     Various Layers With “Opposing Susceptibility” 
     In certain embodiments, the materials used in one or more of the diffusion barrier layer(s), color tuning layer(s) and DMIL layer(s) are selected based on “opposing susceptibility” to adjacent layers to increase the transparency of the electrochromic device and/or tune the wavelength of light transmitted through the electrochromic device to a desired spectrum. For example, the materials may be selected to transmit a range of wavelengths associated with blue light through the electrochromic device. In some cases, the materials are selected to shift the range of wavelengths away from green or red. An example of a construction of an electrochromic device with a composite conductor comprising one or more color tuning layers is shown in  FIG. 4 . In this example, the electrochromic device  400  does not have a separate diffusion barrier disposed on the substrate  402 . 
       FIG. 4  depicts a schematic illustration of an electrochromic device  400  comprising a substrate  402 , a first composite conductor  410  disposed on the substrate  402 , an electrochromic stack  420  disposed on the first composite conductor  410 , and a second composite conductor  430  disposed on the electrochromic stack  420 . The first composite conductor  410  comprises one or more color tuning layers  411 , a metal layer (e.g., silver)  412  disposed on the one or more color tuning layers  411 , and a first DMIL (e.g., TiO 2 )  424  disposed on the metal layer  412 . The second composite conductor  420  comprises a second DMIL  432  disposed on the EC stack  420 , and a second metal layer  433 . In another embodiment, the order of the layers in either or both of the composite conductors  410  and  430  may be reversed. 
     In certain implementations, the second DMIL  432  is the same or substantially similar to the first DMIL  424  and/or the second metal layer  433  is the same or substantially similar to the first metal layer  412 . In other embodiments, the first composite conductor  410  and/or the second composite conductor  430  have additional layers. For example, one or more color tuning layers may be added to the second composite conductor  430 . As another example, a diffusion barrier may be added between the one or more color tuning layers  411  and the substrate  402 . 
     The one or more color tuning layers  411  is made of any of the materials described above for color tuning layers. The first metal layer  412  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the first metal layer  412  has a thickness in a range of between about 1 nm and about 5 nm. In one embodiment, the first metal layer  412  has a thickness in a range of between about 5 nm and about 30 nm. In one embodiment, the first metal layer  412  has a thickness in a range of between about 10 nm and about 25 nm. In one embodiment, the first metal layer  412  has a thickness in a range of between about 15 nm and about 25 nm. In one embodiment, the first metal layer  412  is made of silver. 
     The first DMIL  424  may be made of any of the materials described above for DMILs and has the associated electrical, physical and optical properties of the DMIL materials as described above. In one embodiment, the first DMIL  424  is of TiO 2 . In one case, first DMIL  424  of TiO 2  is between 10 nm and 100 nm thick. In another case, the first DMIL  424  of TiO 2  is between 25 nm and 75 nm thick. In another case, the first DMIL  424  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the first DMIL  424  of TiO 2  is about 50 nm thick. 
     The second metal layer  433  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the second metal layer  433  is silver, for example, having a thickness between about 1 nm and 5 nm thick. In one embodiment, the second metal layer  433  has a thickness between about 1 nm and about 5 nm thick. In one embodiment, the second metal layer  433  has a thickness between about 5 nm and about 30 nm. In one embodiment, the second metal layer  433  has a thickness between about 10 nm and about 25 nm. In one embodiment, the second metal layer  433  has a thickness between about 15 nm and about 25 nm. 
     The second DMIL  432  may be made of any of the materials described above for DMILs and has the associated electrical, physical and optical properties of the DMIL materials as described above. In one embodiment, the second DMIL  432  is of TiO 2 . In one case, second DMIL  432  of TiO 2  is between 10 nm and 100 nm thick. In another case, the second DMIL  432  of TiO 2  is between 25 nm and 75 nm thick. In another case, the second DMIL  432  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the second DMIL  432  of TiO 2  is about 50 nm thick. 
     In certain embodiments, one or more of the layers of materials describe herein can serve multiple functions. For example, in one embodiment, a layer disposed on the substrate function both as a diffusion barrier and an opposite susceptibility layer. Also, a layer can function both as a DMIL layer and an opposite susceptibility layer. 
     DMIL Between TCO/Metal/TCO Conductor and Electrochromic Stack 
     In certain embodiments, an electrochromic device has a lower composite conductor comprising a TCO (e.g., ITO)/Metal/TCO (e.g., ITO) stack also referred to as an “IMI stack” and a DMIL (e.g., TiO 2 ) between the IMI stack and the electrochromic stack. An example of such an electrochromic device is shown in  FIG. 5 . In these embodiments, the DMIL layer may improve durability of the electrochromic device. There may be a DMIL between each IMI, of two, and an EC stack that is sandwiched therebetween, that is, IMI/DMIL/EC stack/DMIL/IMI, optionally with color tuning and/or diffusion barrier layers between that structure and the substrate. 
       FIG. 5A  depicts a schematic illustration of an electrochromic device  500  comprising a substrate  502 , a first composite conductor  510  disposed on the substrate  502 , a DMIL  504  disposed on the first composite conductor  510 , an electrochromic stack  520  disposed on the DMIL  504 , and a second composite conductor  530  disposed on the electrochromic stack  520 . The first composite conductor  510  comprises a first TCO layer  512  disposed on the substrate  502 , a first metal layer (e.g., silver)  514  disposed on the first TCO layer  512 , and a second TCO layer  516  disposed on the first metal layer  514 . The second composite conductor  530  comprises a third TCO layer  532  disposed on the electrochromic stack  520 , a second metal layer (e.g., silver)  534  disposed on the third TCO layer  532 , and a fourth TCO layer  536  disposed on the second metal layer  534 . Another embodiment also includes a second DMIL between EC stack and the third TCO layer as shown in  FIG. 5B . 
     In one implementation, the first and second composite conductors  510  and  530  have the same or substantially similar material layers in a mirrored arrangement. That is, the fourth TCO  536  is the same or substantially similar to the first TCO layer  512 , the third TCO layer  532  is the same or substantially similar to the second TCO layer  516 , and the first metal layer  514  is the same or substantially similar to the second metal layer  534 . In other embodiments, the first and second composite conductors  510  and  530  may have different orders of the same layers. In yet other embodiments, the first and second composite conductors  510  and  530  may have one more different material layers. In certain aspects, the first composite conductor  510  and/or the second composite conductor  530  have one or more color tuning layers. 
     The first TCO layer  512  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the first TCO layer  512  is a FTO layer between about 200 nm and 500 nm thick. The first metal layer (e.g., silver)  514  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the first metal layer  514  is silver. In one embodiment, the first metal layer  514  has a thickness in the range of about 1 nm and about 5 nm. In one embodiment, the first metal layer  514  has a thickness in the range of about 5 nm to about 30 nm. In one embodiment, the first metal layer  514  has a thickness in the range of about 10 nm and about 25 nm. In one embodiment, the first metal layer  514  has a thickness in the range of about 15 nm and about 25 nm. 
     The second TCO layer  516  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the second TCO layer  516  is a FTO layer between about 200 nm and 500 nm thick. The third TCO layer  532  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the third TCO layer  532  is a FTO layer between about 200 nm and 500 nm thick. The second metal layer  534  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the second metal layer  534  is silver. In one embodiment, the second metal layer  534  has a thickness in the range of between about 1 nm and about 5 nm thick. In one embodiment, the second metal layer  534  has a thickness in the range of between about 5 nm to about 30 nm. In one embodiment, the second metal layer  534  has a thickness in the range of between about 10 nm and about 25 nm. In one embodiment, the second metal layer  534  has a thickness between about 15 nm and about 25 nm. 
     The fourth TCO layer  536  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the fourth TCO layer  536  is a FTO layer between about 200 nm and 500 nm thick. The first DMIL  504  may be made of any of the materials described above for DMILs and has the associated electrical, physical and optical properties of the DMIL materials as described above. In one embodiment, the first DMIL  504  is of TiO 2 . In one case, the first DMIL  504  of TiO 2  is between 10 nm and 100 nm thick. In another case, the first DMIL  504  of TiO 2  is between 25 nm and 75 nm thick. In another case, the first DMIL  504  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the first DMIL  504  of TiO 2  is about 50 nm thick. 
       FIG. 5B  depicts a schematic illustration of an electrochromic device  500  comprising a substrate  552 , a first composite conductor  560  disposed on the substrate  552 , a first DMIL  554  disposed on the first composite conductor  550 , an electrochromic stack  570  disposed on the first DMIL  554 , a second DMIL  572  disposed on the electrochromic stack  520 , and a second composite conductor  580  disposed on the second DMIL  572 . The first composite conductor  560  comprises a first TCO layer  562  disposed on the substrate  552 , a first metal layer (e.g., silver)  564  disposed on the first TCO layer  562 , and a second TCO layer  566  disposed on the first metal layer  564 . The second composite conductor  580  comprises a third TCO layer  582  disposed on the second DMIL  572 , a second metal layer (e.g., silver)  584  disposed on the third TCO layer  582 , and a fourth TCO layer  586  disposed on the second metal layer  584 . 
     In one implementation, the first and second composite conductors  560  and  580  have the same or substantially similar material layers in a mirrored arrangement. That is, the fourth TCO  586  is the same or substantially similar to the first TCO layer  562 , the third TCO layer  532  is the same or substantially similar to the second TCO layer  566 , and the first metal layer  564  is the same or substantially similar to the second metal layer  584 . In other embodiments, the first and second composite conductors  560  and  580  may have different orders of the same layers. In yet other embodiments, the first and second composite conductors  560  and  580  may have one more different material layers. In certain aspects, the first composite conductor  560  and/or the second composite conductor  580  have one or more color tuning layers. 
     The first TCO layer  562  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the first TCO layer  562  is a FTO layer between about 200 nm and 500 nm thick. The first metal layer (e.g., silver)  564  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the first metal layer  564  is silver. In one embodiment, the first metal layer  564  has a thickness in the range of about 1 nm and about 5 nm. In one embodiment, the first metal layer  564  has a thickness in the range of about 5 nm to about 30 nm. In one embodiment, the first metal layer  564  has a thickness in the range of about 10 nm and about 25 nm. In one embodiment, the first metal layer  564  has a thickness in the range of about 15 nm and about 25 nm. 
     The second TCO layer  570  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the second TCO layer  570  is a FTO layer between about 200 nm and 500 nm thick. The third TCO layer  582  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the third TCO layer  582  is a FTO layer between about 200 nm and 500 nm thick. The second metal layer  584  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the second metal layer  584  is silver. In one embodiment, the second metal layer  584  has a thickness in the range of between about 1 nm and about 5 nm thick. In one embodiment, the second metal layer  584  has a thickness in the range of between about 5 nm to about 30 nm. In one embodiment, the second metal layer  584  has a thickness in the range of between about 10 nm and about 25 nm. In one embodiment, the second metal layer  584  has a thickness between about 15 nm and about 25 nm. 
     The fourth TCO layer  586  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the fourth TCO layer  586  is a FTO layer between about 200 nm and 500 nm thick. The first DMIL  584  may be made of any of the materials described above for DMILs and has the associated electrical, physical and optical properties of the DMIL materials as described above. In one embodiment, the first DMIL  584  is of TiO 2 . In one case, the first DMIL  584  of TiO 2  is between 10 nm and 100 nm thick. In another case, the first DMIL  584  of TiO 2  is between 25 nm and 75 nm thick. In another case, the first DMIL  584  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the first DMIL  584  of TiO 2  is about 50 nm thick. 
     The second DMIL  572  may be made of any of the materials described above for DMILs and has the associated electrical, physical and optical properties of the DMIL materials as described above. In one embodiment, the second DMIL  572  is of TiO 2 . In one case, the second DMIL  572  of TiO 2  is between 10 nm and 100 nm thick. In another case, the second DMIL  572  of TiO 2  is between 25 nm and 75 nm thick. In another case, the second DMIL  572  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the second DMIL  572  of TiO 2  is about 50 nm thick. In one embodiment, the second DMIL  572  has the same characteristics of first DMIL  554 . 
     Barrier/Blocking Layer(s) 
     In certain embodiments, an electrochromic device includes one or more barrier or blocking layers disposed between the lower conductor and the electrochromic stack to help prevent diffusion of metal into the electrochromic stack. Some examples of materials that can be used in such barrier or blocking layers are tantalum nitride, titanium nitride, silicon nitride, silicon oxynitride and the like, which can serve to block migration of silver from the lower conductor into the electrochromic stack. Titanium nitride and tantalum nitride, e.g., are particularly good barrier layers to prevent metal migration. An example of an electrochromic device with one or more barrier or blocking layers disposed between the lower conductor and the electrochromic stack is shown in  FIG. 6 . 
       FIG. 6  depicts a schematic illustration of an electrochromic device  600 , according to embodiments. The electrochromic device  600  comprises a substrate  602 , one or more diffusion barrier layers  604  disposed on the substrate  602 , a first composite conductor  610  disposed on the diffusion barrier layer(s)  604 , one or more barrier/blocking layers  618  (e.g., material layers of TaN or TiN) disposed on the a first composite conductor  610 , a first DMIL  619  (e.g., TiO 2 ) disposed on the one or more barrier/blocking layers  618 , an electrochromic stack  620  disposed on the first DMIL  619 , and a second composite conductor  630  disposed on the electrochromic stack  620 . The first composite conductor  610  comprises a first TCO layer  612  (e.g., ITO layer) disposed on the one or more diffusion barrier layers  604 , a first metal layer  614  (e.g., silver layer) disposed on the first TCO layer  612 , and a second TCO layer  616  disposed on the first metal layer  614 . The second composite conductor  630  comprises a third TCO layer  632  disposed on electrochromic stack  620 , a second metal layer  634  disposed on the third TCO layer  632 , and a fourth TCO layer  636  disposed on the second metal layer  634 . The one or more barrier/blocking layers  618  are between the first DMIL  619  and the second TCO layer  616  to provide a barrier for diffusion into the electrochromic stack  620 . For example, if the metal layer  614  is a silver layer and the one or more barrier/blocking layers  618  comprise TaN or TiN, then the TaN or TiN barrier/blocking layers  618  can block migration of silver into the electrochromic stack  620 . 
     The first TCO layer  612  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the first TCO layer  612  is a FTO layer between about 200 nm and 500 nm thick. The first metal layer  614  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the first metal layer  614  is silver. In one embodiment, the first metal layer  614  has a thickness in the range of between about 1 nm and 5 nm thick. In one embodiment, the first metal layer  614  has a thickness in the range of between about is about 5 nm to about 30 nm. In one embodiment, the first metal layer  614  has a thickness in the range of between about 10 nm and about 25 nm. In one embodiment, the first metal layer  614  has a thickness in the range of between about 15 nm and about 25 nm. 
     The second TCO layer  616  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the second TCO layer  616  is a FTO layer between about 200 nm and 500 nm thick. The third TCO layer  632  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the third TCO layer  632  is a FTO layer between about 200 nm and 500 nm thick. The second metal layer  634  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the second metal layer  634  is silver. In one embodiment, the second metal layer  634  has a thickness in the range of between about 1 nm and 5 nm thick. In one embodiment, the second metal layer  634  has a thickness in the range of between about 5 nm and about 30 nm. In one embodiment, the second metal layer  634  has a thickness in the range of between about 10 nm and about 25 nm. In one embodiment, the second metal layer  634  has a thickness in the range of between about 15 nm and about 25 nm. 
     The fourth TCO layer  636  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the fourth TCO layer  636  is a FTO layer between about 200 nm and 500 nm thick. The barrier/blocking layers  618  is made of materials described above for barrier/blocking layers and has all the associated electrical, physical and optical properties of the barrier/blocking layers. The first DMIL  619  may be made of any of the materials described above for DMILs and has the associated electrical, physical and optical properties of the DMIL materials as described above. In one embodiment, the first DMIL  619  is of TiO 2 . In one case, the first DMIL  619  of TiO 2  is between 10 nm and 100 nm thick. In another case, the first DMIL  619  of TiO 2  is about 50 nm thick. In one case, the first DMIL  619  of TiO 2  is between 10 nm and 100 nm thick. In another case, the first DMIL  619  of TiO 2  is between 25 nm and 75 nm thick. In another case, the first DMIL  619  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the first DMIL  619  of TiO 2  is about 50 nm thick. 
     In one implementation, the first and second composite conductors  610  and  630  have the same or substantially similar material layers with the illustrated mirrored layout. That is, the first TCO layer  612  is the same or substantially similar to the fourth TCO layer  636 , the first metal layer  614  is the same or substantially similar to the second metal layer  634 , and the second TCO layer is the same or substantially similar to the third TCO layer  632 . In other embodiments, the first and second composite conductors may have different orders of the same layers. In yet other embodiments, the first and second composite conductors may have one more different material layers. In certain implementations, the electrochromic device  600  omits the diffusion barrier  604 . In certain aspects, the first and/or second composite conductor  610 ,  630  of the electrochromic device  600  shown in  FIG. 6  further comprises one or more color tuning layers adjacent the metal layers. 
     Protective Cap 
     In certain embodiments, an electrochromic device includes a protective cap layer on top of a key conductive layer (e.g., metal layer) to protect it from being damaged during one or more fabrication operations. For example, a key conductive layer may be of aluminum, which is readily oxidized to aluminum oxide during fabrication operations such as those that include high temperature such as a heat treatment process. Oxidation of an aluminum conductive layer can make it a poor conductor, particularly if the aluminum layer is thin. Certain aspects pertain to fabricating a protective cap layer, such as a titanium protective cap layer, over the aluminum conductive layer to protect it during fabrication. Using titanium metal as a protective cap layer has the benefit that the titanium oxidized to TiO 2 , which generates a DMIL layer while simultaneously protecting the underlying aluminum from oxidation. 
       FIG. 7  depicts a schematic illustration of an electrochromic device  700  comprising a substrate  702 , one or more diffusion barrier layers  704  disposed on the substrate  702 , a first composite conductor  710  disposed on the diffusion barrier layer(s)  704 , an electrochromic stack  720  disposed on the first composite conductor  710 , and a second composite conductor  730  disposed on the electrochromic stack  720 . The first composite conductor  710  comprises a first TCO layer  712  disposed on the one or more diffusion barrier layers  704 , a first metal layer (e.g., silver)  714  disposed on the first TCO layer  712 , a protective cap layer  716  disposed on the first metal layer  714 , and a second TCO layer  718  disposed on the protective cap layer  716 . If the protective cap layer is of material such as titanium that oxidizes to generate a DMIL during a fabrication operation, then a DMIL layer (not shown) may be formed at the interface to the second TCO  718 . The second composite conductor  530  comprises a third TCO layer  732  disposed on the electrochromic stack  720 , a second metal layer (e.g., silver)  734  disposed on the third TCO layer  732 , and a fourth TCO layer  736  disposed on the second metal layer  734 . 
     The first TCO layer  712  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the first TCO layer  712  is a FTO layer between about 200 nm and 500 nm thick. The first metal layer  714  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the first metal layer  714  is silver. In one embodiment, the first metal layer  714  has a thickness in the range of between about 1 nm and 5 nm thick. In one embodiment, the first metal layer  714  has a thickness in the range of between about 5 nm and about 30 nm. In one embodiment, the first metal layer  714  has a thickness in the range of between about 10 nm and about 25 nm. In one embodiment, the first metal layer  714  has a thickness in the range of between about 15 nm and about 25 nm. 
     The protective cap layer  716  may be made of any of the materials described above for protective cap materials and has the associated electrical, physical and optical properties of the protective cap materials as described above. The second TCO layer  718  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the second TCO layer  718  is a FTO layer between about 200 nm and 500 nm thick. The third TCO layer  732  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the third TCO layer  732  is a FTO layer between about 200 nm and 500 nm thick. The second metal layer  734  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the second metal layer  734  is silver. In one embodiment, the second metal layer  734  has a thickness in the range of between about 1 nm and 5 nm thick. In one embodiment, the second metal layer  734  has a thickness in the range of between about 5 nm and about 30 nm. In one embodiment, the second metal layer  734  has a thickness in the range of between about 10 nm and about 25 nm. In one embodiment, the second metal layer  734  has a thickness in the range of between about 15 nm and about 25 nm. 
     The fourth TCO layer  736  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the fourth TCO layer  736  is a FTO layer between about 200 nm and 500 nm thick. 
     In one implementation, the first and second composite conductors  710  and  730  have the same or substantially similar material layers in a mirrored arrangement. That is, the fourth TCO  736  is the same or substantially similar to the first TCO layer  712 , the third TCO layer  732  is the same or substantially similar to the second TCO layer  716 , and the first metal layer  714  is the same or substantially similar to the second metal layer  734 . In other embodiments, the first and second composite conductors  710  and  730  may have different orders of the same layers. In yet other embodiments, the first and second composite conductors  710  and  730  may have one more different material layers. In certain aspects, the first composite conductor  710  and/or the second composite conductor  740  have one or more color tuning layers. 
     Other examples of Multi-layer Lower Conductors 
       FIG. 8  is an example used to illustrate various other embodiments of multi-layer conductors.  FIG. 8  depicts a schematic illustration of the material layers of an electrochromic device  800 , according to embodiments. The electrochromic device  800  comprises a substrate  802 , one or more diffusion barrier layers  804  disposed on the substrate  802 , a first composite conductor  810  disposed on the diffusion barrier layer(s)  804 , an electrochromic stack  820  disposed on the first composite conductor  810 , and a second composite conductor  830  disposed on the electrochromic stack  820 . The first composite conductor  810  comprises a first TCO layer  812  disposed over the one or more diffusion barrier layers  804 , a first DMIL  814  disposed over the first TCO layer  812 , a first metal layer  816  disposed over the first DMIL  814 , and a second DMIL  818  disposed over the first metal layer  816 . The second composite conductor  830  comprises an optional third DMIL  832  shown disposed over the electrochromic stack  820 , a second TCO  833  disposed over the third DMIL  832 , a second metal layer  834  disposed over the second TCO  833 , a third TCO  836  disposed over the second metal layer  834 , an optional third metal layer  837  disposed over the third TCO  836 , and an optional fourth TCO  838  disposed over the third metal layer  837 . 
     In certain aspects, the first composite conductor  810  of the electrochromic device  800  shown in  FIG. 8  further comprises one or more color tuning layers located adjacent one or more of the metal layers. In these color tuning embodiments, the one or more color tuning layers may be selected to increase transparency of the conductor and/or to modify the wavelength of light passing through the electrochromic device to change the color of light transmitted. Some examples of materials that can be used in color tuning layers are silicon oxide, tin oxide, indium tin oxide, and the like. 
     The first TCO layer  812  is made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the first TCO layer  812  is a FTO layer between about 200 nm and 500 nm thick. 
     The first DMIL  814  may be made of any of the materials described above for DMILs and has the associated electrical, physical and optical properties of the DMIL materials as described above. In one embodiment, the first DMIL  814  is of TiO 2 . In one case, the first DMIL  814  of TiO 2  is between 10 nm and 100 nm thick. In another case, the first DMIL  814  of TiO 2  is between 25 nm and 75 nm thick. In another case, the first DMIL  814  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the first DMIL  814  of TiO 2  is about 50 nm thick. 
     The first metal layer  816  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the first metal layer  816  is silver. In one embodiment, the first metal layer  816  has a thickness in the range of between about 1 nm and 5 nm thick. In one embodiment, the first metal layer  816  has a thickness in the range of between about 5 nm and about 30 nm. In one embodiment, the first metal layer  816  has a thickness in the range of between about 10 nm and about 25 nm. In one embodiment, the first metal layer  816  has a thickness in the range of between about 15 nm and about 25 nm. 
     A function of the second DMIL  818  is to prevent metal from the first metal layer  816  from migrating and exposure to the electrochromic stack  820 . For example, the electrochromic device  800  may be lithium, proton or other ion based in some cases. Such electrochromic devices undergo oxidation/reduction reactions at their electrode layers. The second DMIL  818  protects the first metal layer  816  from oxidation and reduction reactions, particularly oxidation. The second DMIL  818  can be made of any of the materials described above for DMILs and has the electrical, physical and optical properties of DMILs as described above. In one embodiment, the second DMIL  818  is TiO 2 . In one case, the second DMIL  818  of TiO 2  is between 10 nm and 100 nm thick. In another case, the second DMIL  818  of TiO 2  is between 25 nm and 75 nm thick. In another case, the second DMIL  818  of TiO 2  is between 40 nm and 60 nm thick. In yet another case, the second DMIL  818  of TiO 2  is about 50 nm thick. 
     The third DMIL  832  is an optional layer. The third DMIL  832  may function to prevent the second TCO layer  833  from exposure to the electrochromic stack  820  and/or may function as a traditional DMIL. In one embodiment, the third DMIL  832  is NiWO and is between about 10 nm and about 100. In another embodiment, the third DMIL  832  is NiWO and is between about 10 nm and about 50 nm thick. 
     The second TCO layer  833  may be made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the second TCO layer  833  is ITO and is between about 10 nm and about 100 nm thick. In one embodiment, the second TCO layer  833  is ITO and is between about 25 nm and about 75 nm thick. In one embodiment, the second TCO layer  833  is ITO and is about 50 nm thick. 
     The second metal layer  834  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the second metal layer  834  is silver. In one embodiment, the second metal layer  834  has a thickness in the range of between about 1 nm and 5 nm thick. In one embodiment, the second metal layer  834  has a thickness in the range of between about 5 nm and about 30 nm. In one embodiment, the second metal layer  834  has a thickness in the range of between about 10 nm and about 25 nm. In one embodiment, the second metal layer  834  has a thickness in the range of between about 15 nm and about 25 nm. 
     The third TCO layer  836  may be made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the third TCO layer  836  is ITO and is between about 50 nm and about 500 nm thick. In one embodiment, the third TCO layer  836  is ITO and is between about 100 nm and about 500 nm thick. In one embodiment, the third TCO layer  836  is ITO and is between about 100 nm thick and about 250 nm thick. 
     The third metal layer  837  is optional. If this third metal layer  837  is included, then the optional fourth TCO layer  838  is also included. The third metal layer  837  is made of any of the metal materials as described above for metal layers, including alloys, intermetallics, mixtures and/or layers of metals, and having the electrical, physical and optical properties of the metals as described above. In one embodiment, the third metal layer  837  is silver. In one embodiment, the third metal layer  837  has a thickness in the range of between about 1 nm and 5 nm thick. In one embodiment, the third metal layer  837  has a thickness in the range of between about 5 nm and about 30 nm. In one embodiment, the third metal layer  837  has a thickness in the range of between about 10 nm and about 25 nm. In one embodiment, the third metal layer  837  has a thickness in the range of between about 15 nm and about 25 nm. 
     The fourth TCO layer  838  is optional. If the fourth TCO layer  838  is included, then the third metal layer  837  is also included. The fourth TCO layer  838  may be made of any of the materials described above for TCOs and has the associated electrical, physical and optical properties of the TCO materials as described above. In one embodiment, the fourth TCO layer  838  is ITO and is between about 50 nm and about 500 nm thick. In one embodiment, the fourth TCO layer  838  is ITO and is between about 100 nm and about 500 nm thick. In one embodiment, the fourth TCO layer  838  is ITO and is between about 100 nm thick and about 250 nm thick. 
     In certain aspects, an electrochromic device comprises two conductors, at least one of which is a multi-layer conductor, and an electrochromic stack between the conductors, disposed on a substrate (e.g., glass). Each multi-layer conductor comprises a metal layer sandwiched between at least two non-metal layers such as, for example, a metal oxide layer, a transparent conductive oxide (TCO) layer and/or a DMIL. That is, a metal layer is not in direct contact with the electrochromic stack. In some cases, one or both of the conductors further comprises one or more additional metal layers. In these aspects, the additional metal layers are also sandwiched between layers and not in contact with the electrochromic stack. In some aspects, the one or more metal layers of a multi-layer conductor are not in contact with a TCO layer. For example, a metal layer of a multi-layer conductor may be sandwiched between two DMILs. 
     In certain aspects, a multi-layer conductor may comprise a metal layer sandwiched between a DMIL and a non-metal layer. In some cases, the sandwiched metal layer may comprise of one of silver, gold, copper, platinum, and alloys thereof In some cases, the metal layer may be comprised of an alloy whose oxides have low resistivity. In one example, the metal layer may further comprise another material (e.g., Hg, Ge, Sn, Pb, As, Sb, or Bi) as compound during the preparation of the oxide to increase density and/or lower resistivity. 
     Layers of Multi-Layer Lower Conductors With Multiple Functions 
     In certain embodiments, one or more of the layers of materials described herein can serve multiple functions. For example, in one embodiment, a layer disposed on the substrate function both as a diffusion barrier and an opposite susceptibility layer. Also, a layer can function both as a DMIL layer and as an opposite susceptibility layer. 
     Although the foregoing embodiments have 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 above description and the appended claims.