ELECTROCHROMIC THIN-FILM MATERIAL
One exemplary embodiment of an electrochromic thin-film material comprises a metal-chalcogen compound; and/or a mixture or solid solution of one or more metal-rich metal-chalcogen compounds and/or lithium. One or more of the metals comprise Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Sb, or Bi, or combinations thereof; and one or more of the chalcogens comprise O, S, Se, or Te, or combinations thereof.
The subject matter disclosed herein relates to thin-film materials that can be utilized in reflection-controllable electrochromic windows (i.e., light-control glass) for buildings, vehicles, aircraft and watercraft. More particularly, the subject matter disclosed herein relates to reflection-controllable electrochromic thin-film materials comprising a metal-chalcogen compound in which one or more of the metals comprise Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Sb, or Bi, or combinations thereof, and one or more of the chalcogens comprise O, S, Se, or Te, or combinations thereof.
Windows and other openings are generally the place where the most heat enters and escapes buildings. For example, during the winter about 48% of the heat produced by a heating system of a building escapes through windows of the building. During the summer, the proportion of heat that enters an air-conditioned room through the windows can reach about 71%. A tremendous energy savings can, therefore, be realized by effectively controlling light and heat entering and escaping through windows. Light-control glass has been developed to control the bi-directional flow of light and heat through a window.
There are several ways that light is controlled by light-control glass. One way is to form an electrochromic material on the glass in which the transmissivity of the electrochromic material reversibly changes upon application of a current or a voltage. Another way is to form a thermochromic material on the glass in which the transmissivity of the thermochromic material changes with temperature. Yet another way is to use a gasochromic material that changes its transmissivity by controlling the atmosphere gas. Of these, electrochromic-based light-control glass has been researched in which a tungsten-oxide thin film is used for the light-control layer. Some commercial products based on this type of electrochromic light-control glass have already appeared.
Conventional electrochromic-based light-control glass, including tungsten-oxide-based versions, all control light by absorbing the light using a light-control layer. A drawback with absorbing the light is that heat is produced and radiated into a room when the light-control layer absorbs light, thereby diminishing the energy-saving effect of the conventional electrochromic light-control glass. To eliminate this drawback, another approach of reflecting light rather than absorbing light has been considered. Accordingly, a material capable of reversibly switching between a mirror state and a transparent state would be useful.
For a long time, such a material capable of switching between a mirror state and a transparent state was not found, but in 1996 a group in the Netherlands discovered a hydride of a rare earth, such as yttrium or lanthanum, switches between a mirror state and a transparent state under the influence of hydrogen. Such a material is conventionally referred to as a “switchable mirror”. See, for example, J. N. Huiberts et al., Nature, 380, 1996, 231. The rare-earth hydrides undergo a large change in transmissivity, and have excellent light-control mirror characteristics. Nevertheless, because a rare-earth element is used in the material, there are problems in terms of resources and cost when rare-earth-hydride-based switchable mirrors are used for window coatings and other applications.
Additionally, conventional metal-hydride-based mirrors suffer from poor cycle life due to the reactive nature of the metal film, which is readily attacked by air or water. Notably, water is one component of the electrolyte in electrochromic hydride mirrors, and may be produced during removal of hydrogen from the mirror film in both electrochromic and gasochromic devices. The life-cycle degradation is conventionally inhibited by using additional barrier layers for protecting the active materials and by sealing devices for preventing access of environmental air and water. The former approach of adding barrier layers is difficult to achieve and may not be effective after long periods of use. The latter approach of sealing does not address the problem of internal sources of water or oxygen.
More recently, U.S. Pat. No. 6,647,166 B2 to T. J. Richardson discloses alloys of magnesium and transitional-metals that can be used as switchable-mirror materials, thereby significantly reducing the cost of materials for electrochromic-based light-control glass.
U.S. Pat. No. 7,042,615 B2 to T. J. Richardson discloses the use of a semi-metal, such as antimony, as a switchable-mirror thin-film material based on alloying and de-alloying of the semi-metal with lithium: Sb+3Li++3e−=Li3Sb. Such elements-based thin-film materials, however, suffer from several severe drawbacks for the following reasons. (1) The electrochromic reaction does not take place until very low potential (about 0.7 V vs. Li/Li+), thus preventing the use of known transparent conducting oxides, such as ITO and FTO, as the transparent electrodes in an electrochromic device. (2) The reaction involves a very large percentage of volume expansion/contraction upon full lithiation/delithiation (about 136% for pure Sb), causing problems of pulverization and de-lamination of the reflective layers. (3) Low-resistivity metals (e.g., Ni and Co) need to be added to the reflective layers to reduce the percentage of volume change and increase the conductivity of the matrix, but the added metal absorbs a significant portion of the incident light and lowers the maximum transmission of an electrochromic window. (4) The electrochromic reaction involving the extruding and re-admission of the non-active metal is a non-topotactic and, thus, poorly reversible reaction. (5) A direct-current voltage higher than about 4 V is needed to drive an electrochromic device employing such an electrochromic material, which accelerates the degradation of an electrochromic device during long-term use or cycling due to side reactions associated with high driving-voltages.
Therefore, there is an urgent need in the electrochromic fields to discover reflection-controllable electrochromic thin-film materials based on intercalation compounds with intrinsic open structures for highly reversible electro-optical switching at a potential compatible with known transparent conducting oxide electrodes.
In U.S. Pat. No. 7,042,615 B2, T. J. Richardson discloses the use of transition-metal dichalcogenides (including TiS2, NbSe2, and NbTe2) as switchable-mirror thin-film materials, based on the contemplation that these semiconducting solids become metallic upon lithium insertion or intercalation (CATHODIC electrochromism). These chalcogen-rich transition-metal chalcogenides, however, show too narrow electro-optical switching ranges or too low coloration efficiencies, if any, to be useful in practical electrochromic devices.
The subject matter disclosed herein is illustrated by way of example and not by limitation in the accompanying figures in which like reference numerals indicate similar elements and in which:
As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not to be construed as necessarily preferred or advantageous over other embodiments. The term “topotactic” refers to solid-state reactions that are characterized by the fact that defined lattice matrix elements specific to the original solid phase remain unaltered in the course of the reaction with respect to their structural organization. The term “chalcogen” refers to any of the elements of O, S, Se, and Te. The term “chalcogen-rich metal chalcogenide” refers to a metal chalcogenide with a chalcogen/metal atomic ratio equal to or greater than about 2. The term “metal-rich metal chalcogenide” refers to a metal chalcogenide with a chalcogen/metal atomic ratio less than about 2. The abbreviation of “ITO” refers to “indium tin oxide”, and the abbreviation of “FTO” refers to “fluorine-doped tin oxide”.
The subject matter disclosed herein relates to thin-film materials that can be utilized in a reflection-controllable electrochromic window (i.e., a light-control window) for controlling the spectral transmissivity of the window of, for example, a building, a vehicle, an aircraft and a watercraft, without using blinds or curtains. More particularly, the subject matter disclosed herein relates to highly durable reflection-controllable electrochromic thin-film materials that can be used as an electrochromically active layer. One exemplary embodiment of a highly durable reflection-controllable electrochromic thin-film material comprises metal-rich metal-chalcogenide compounds that comprise tellurium, a transition metal, and lithium. Another exemplary embodiment of a highly durable reflection-controllable electrochromic thin-film material comprises metal-rich metal-chalcogenide compounds that comprise tellurium, a main-group metal, and lithium. Suitable transition metals comprise Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn and combinations thereof. Suitable main-group metals comprise Sb, Bi, and mixture thereof. One exemplary embodiment of a metal-rich metal-chalcogenide thin-film material comprising tellurium, a transition metal, and lithium, has survived cycling tests in an all-solid-state reflective device for over one thousand cycles with the switching range of transmission degraded less than 10%.
The subject matter disclosed herein also relates to thin-film materials that can also be utilized as anode materials in thin-film lithium-ion batteries. One exemplary embodiment of a metal-rich metal-chalcogenide thin-film material comprising tellurium, a transition metal, and lithium, has exhibited a large charge capacity (about 27000 Coulomb per cubic centimeter) and a high reversibility (over 100 cycles) on charge-discharge cycling between 1.0 V and 2.6 V versus Li+/Li.
In a highly reversible manner, the thin-film materials disclosed herein become transparent upon lithiation, and become reflective and/or absorptive upon delithiation.
The thin-film materials of metal-rich metal chalcogenides disclosed herein show intense and highly reversible ANODIC electrochromism. Specifically, the thin-film materials turn from semi-metallic or metallic (reflective and/or absorptive) into insulators (transparent) in a highly reversible manner upon lithium insertion or intercalation.
Exemplary embodiments of a highly durable reflection-controllable electrochromic thin-film metal-rich metal-chalcogenide material comprise compounds of tellurium, selenium, a transition metal, and lithium. The addition of selenium into the metal-rich metal-chalcogenide material widens the optical absorption band-gap of the material, and significantly increases the visible-light transmittance of the thin-film material in its bleached state. Addition of other chalcogen elements (such as O and S) shows the same effect of optical band-gap widening. The optical band-gap of the thin-film material increases with the electronegativity of the constituent chalcogen elements in the order of O>S>Se>Te.
The subject matter disclosed herein is described in specific terms by several working examples in which a metal-rich metal-chalcogenide thin film formed from one or more metals, one or more chalcogens, and lithium was produced by co-sputtering in a multi-source magnetron sputtering apparatus. The thin film for each example was formed on a glass sheet substrate having a thickness of about 3 mm. The glass sheet substrate was degreased, washed, dried, placed in a vacuum apparatus, and then subjected to vacuum evacuation. The thin film deposition took place in a high vacuum chamber with a base pressure of about 3×10−7 Torr in the plasma of argon at close to room temperature, except as otherwise stated. The freshly deposited thin film had a typical metallic gloss and was in a mirror state. It should be understood that the subject matter disclosed herein is not limited by the following several working examples.
In one exemplary embodiment of the subject matter disclosed herein, a reflection-switchable thin-film material was formed by co-sputtering Te and Nb at close to room temperature to form a metal-rich metal-chalcogenide thin film having a composition of Nb3Te2. Depending upon the embodiment, the thickness of the thin film material formed can be between about 1 nm and about 500 nm. Curves 1 and 4 in
In one exemplary embodiment of the subject matter disclosed herein, a reflection-switchable thin-film material was formed by co-sputtering Te, Nb and Li at close to room temperature to form a lithiated metal-rich metal-chalcogenide thin film having a composition of Nb3Te2Li0.4. Depending upon the embodiment, the thickness of the thin film material formed can be between about 1 nm and about 500 nm. Selection of a particular thin-film material thickness is a tradeoff between a relatively thin film, which provides a generally higher transmittance, but a generally lower reflectance and durability, and a relatively thick film, which provides a generally lower transmittance, but a generally higher reflectance and better durability. Curves 2 and 3 in
In one exemplary embodiment of the subject matter disclosed herein, a reflection-switchable thin-film material was formed by co-sputtering Te, Nb and Li onto an ITO-coated glass substrate heated at about 275 degree Celsius to form a metal-rich metal-chalcogenide thin film having a composition of Nb3Te2Li0.4. Depending upon the embodiment, the thickness of the thin film material formed can be between about 1 nm and about 500 nm. Selection of a particular thin-film material thickness is a tradeoff between a relatively thin film, which provides a generally higher transmittance, but a generally lower reflectance and durability, and a relatively thick film, which provides a generally lower transmittance, but a generally higher reflectance and better durability.
In one exemplary embodiment of the subject matter disclosed herein, a reflection-switchable thin-film material was formed by co-sputtering Te with Mo and Li at close to room temperature to form a metal-rich metal-chalcogenide thin film having a composition of MoTeLi0.2. Depending upon the embodiment, the thickness of the thin film material formed can be between about 1 nm and about 500 nm.
In one exemplary embodiment of the subject matter disclosed herein, a reflection-switchable thin-film material was formed by co-sputtering Te with Ti and Li at close to room temperature to form a metal-rich metal-chalcogenide thin film having a composition of Ti3Te2Li0.4. Depending upon the embodiment, the thickness of the thin film material formed can be between about 1 nm and about 500 nm.
In one exemplary embodiment of the subject matter disclosed herein, a reflection-switchable thin-film material was formed by co-sputtering Te with W and Li at close to room temperature to form a metal-rich metal-chalcogenide thin film having a composition of W3Te2Li0.4. Depending upon the embodiment, the thickness of the thin film material formed can be between about 1 nm and about 500 nm.
In one exemplary embodiment of the subject matter disclosed herein, a reflection-switchable thin-film material was formed by co-sputtering Te with Cr and Li at close to room temperature to form a metal-rich metal-chalcogenide thin film having a composition of Cr3Te2Li0.4. Depending upon the embodiment, the thickness of the thin film material formed can be between about 1 nm and about 500 nm.
In one exemplary embodiment of the subject matter disclosed herein, a reflection-switchable thin-film material was formed by co-sputtering Te with Sb, Co, and Li at close to room temperature to form a metal-rich metal-chalcogenide thin film having a composition of SbTeCo0.5Li0.4. Depending upon the embodiment, the thickness of the thin film material formed can be between about 1 nm and about 500 nm.
Although the foregoing disclosed subject matter has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced that are within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the subject matter disclosed herein is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.
Claims
1. An electrochromic thin-film material, comprising a metal-rich metal-chalcogen compound of at least one metal and at least one chalcogen, in which an atomic ratio of a total amount of chalcogens to a total amount of metals other than lithium is less than about 2:1.
2. The electrochromic thin-film material according to claim 1, wherein the at least one metal comprises Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Sb, or Bi, or combinations thereof.
3. The electrochromic thin-film material according to claim 2, wherein the at least one chalcogen comprises O, S, Se, or Te, or combinations thereof.
4. The electrochromic thin-film material according to claim 1, wherein a thickness of the thin-film material is between about 1 nm and about 1000 nm.
5. The electrochromic thin-film material according to claim 4, wherein a thickness of the thin-film material is between about 5 nm and about 50 nm.
6. The electrochromic thin-film material according to claim 1, wherein the at least one chalcogen comprises O, S, Se, or Te, or combinations thereof.
7. The electrochromic thin-film material according to claim 1, wherein the thin-film material comprises NbxTeLiy, in which 0.5≦x≦20, and 0≦y≦20.
8. The electrochromic thin-film material according to claim 1, wherein the thin-film material comprises MoxTeLiy, in which 0.5≦x≦20, and 0≦y≦20.
9. The electrochromic thin-film material according to claim 1, wherein the thin-film material comprises TixTeLiy, in which 0.5≦x≦20, and 0≦y≦20.
10. The electrochromic thin-film material according to claim 1, wherein the thin-film material comprises WxTeLiy, in which 0.5≦x≦20, and 0≦y≦20.
11. The electrochromic thin-film material according to claim 1, wherein the thin-film material comprises CrxTeLiy, in which 0.5≦x≦20, and 0≦y≦20.
12. The electrochromic thin-film material according to claim 1, wherein the thin-film material comprises SbxTeCoyLiz, in which 0.5≦x≦20, 0.01≦y≦20, and 0≦z≦20.
13. An all-solid-state electrochromic device, comprising:
- a transparent base material; and
- an electrochromic multilayer-stack structure formed on the transparent base material, the electrochromic multilayer-stack structure comprising: a first transparent-conductive film; an ion-storage layer formed on the first transparent-conductive film; a solid-electrolyte layer formed on the ion-storage layer; and an electrochromic layer formed on the solid-electrolyte layer, the electrochromic layer comprising an electrochromic thin-film material comprising a metal-rich metal-chalcogen compound of at least one metal and at least one chalcogen, in which an atomic ratio of a total amount of chalcogens to a total amount of metals other than lithium is less than about 2:1.
14. The all solid-state electrochromic device according to claim 13, wherein the at least one metal comprises Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Sb, or Bi, or combinations thereof.
15. The all solid-state electrochromic device according to claim 14, wherein the at least one chalcogen comprises O, S, Se, or Te, or combinations thereof.
16. The all solid-state electrochromic device according to claim 13, wherein a thickness of the thin-film material is between about 1 nm and about 1000 nm.
17. The all solid-state electrochromic device according to claim 16, wherein a thickness of the thin-film material is between about 5 nm and about 50 nm.
18. The all solid-state electrochromic device according to claim 13, wherein the at least one chalcogen comprises O, S, Se, or Te, or combinations thereof.
19. The all solid-state electrochromic device according to claim 13, wherein the thin-film material comprises at least one of NbxTeLiy, MoxTeLiy, TixTeLiy, WxTeLiy, or CrxTeLiy, or combinations thereof, in which 0.5≦x≦20, and 0≦y≦20.
20. The all solid-state electrochromic device according to claim 13, wherein the thin-film material comprises SbxTeCoyLiz, in which 0.5≦x≦20, 0.01≦y≦20, and 0≦z≦20.
Type: Application
Filed: Mar 20, 2009
Publication Date: Sep 23, 2010
Inventors: Zhongchun Wang (Santa Rosa, CA), Paul P. Nguyen (San Jose, CA), Jeremy A. Dixon (Santa Rosa, CA)
Application Number: 12/407,950
International Classification: G02F 1/153 (20060101); C09K 9/00 (20060101);