Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-03-07
2003-07-01
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S269000, C359S270000, C359S275000
Reexamination Certificate
active
06587250
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electrochromic devices, and in particular to electrochromic devices comprising an electrically conducting, electrochromic element and at least one layer of solidified electrolyte, and two or more electrodes for connection to an electric voltage supply. The invention also relates to addressing of an electrochemically active element.
BACKGROUND OF THE INVENTION
Electrochromic materials exhibit colour changes or changes in optical density as a result of electrochemical reduction and/or oxidation reactions. An electrochromic material can either be present as a solid, or exist as molecular, neutral or ionic species in an electrolyte solution. These materials have been used for the creation of electrochromic cells, where the passage of electric charge causes colour changes in the materials. Electrochromic cells are used in electrochromic devices of different kinds, and two principal categories of these devices can be distinguished. The two-categories differ from each other mainly in the arrangement of the elements of the electrochromic cell.
The first category of electrochromic devices utilises a sandwich construction, and is used in applications such as automobile windows, building windows, sunglasses, large billboards, mirrors with variable reflectance, sunroofs etc. In this type of electrochromic device, continuous layers of electrochromic material and electrolyte (as well as other layers of e.g. ion reservoir material) are confined between two electrodes that completely cover the layers of electrochromic material and electrolyte. For the electrochromic device to be of use, at least one of said electrodes has to be transparent to let light through the device. This requirement is met in the prior art through the use of electrode materials such as indium-doped tin oxide (ITO), tin dioxide or fluorine-doped tin dioxide. The electrochromic-materials used in these applications vary, but are often based on heavy metal oxides such as WO
3
or conducting polymers such as polyaniline or polypyrrole. The conducting, electrochromic polymer poly-(3,4-ethylendioxythiophene) (PEDOT) has attracted much study, and sandwich devices incorporating this polymer have been realised.
The second category of electrochromic devices aim at providing an electrically updateable display for realisation on a flexible support, U.S. Pat. No. 5,754,329 describes such a display, in which the electrodes of the electrochromic device are placed in one and the same plane, contacting a layer of electrochromic material for the generation of local colour effects at the interface between the electrochromic material and the electrodes. U.S. Pat. No. 5,877,888 represents a further development of this device, describing a two-sided display. However, the arrangement of the component layers of the electrochromic device is similar to that of the device of the U.S. Pat. No. 5,754,329 patent, considering that the electrodes on either side of the display support contact electrochromic material only, and the generation of electrochromic effects is confined to the area of the electrodes. The electrochromic materials that are used in these devices are described in detail in U.S. Pat. No. 5,812,300.
The electrochromic devices of the prior art have limitations in that any colour change effects are essentially confined to the area of electrodes. Prior art devices offer no versatility in the addressing of electrochromic material. As a result, the prior art suffers drawbacks as to the potential for generating innovative and versatile electrochromic devices. Furthermore, the materials used in electrochromic devices of the prior art suffer drawbacks as to environmental friendliness, processability and economy. Thus, there is a demand for electrochromic devices that improve the art and do not suffer the disadvantages of the prior art.
SUMMARY OF THE INVENTION
An object of the present invention is to meet this demand, by providing an electrochromic device that allows the electrochromic material to be addressed via the electrolyte, so that the electrode architecture is not limited by the requirement that the electrodes of the voltage supply be in direct electrical contact with the electrochromic material for electrochromic effects to occur. In embodiments of the invention, the electrochromic material used should exhibit colour change at locations distant from the immediate area of the electrodes, in response to an electric field within the electrolyte between the electrodes.
Another object of the present invention is to advance the art of electrochromic devices, by providing an electrochromic device, for example an electrochromic display, which utilises a combination of materials that are simple to use, compatible with a flexible support such as a sheet or web of a polymer or of paper and with conventional printing methods, and that cause as few environmental problems as possible upon manufacture, use, disposal and destruction of the device.
Another object of the present invention is to provide an electrochromic device, in which the utilised electrochromic material is in itself electrically conducting.
Another object of the present invention is to provide a combination of electrochromic systems for displays of more than one colour.
Still another object of the invention is to provide a bi-stable electrochromic display, wherein the induced colour changes remain after removal of the applied potential difference.
A further object of the invention is to provide a process for the manufacture of such an electrochromic device, which process utilises conventional printing methods or other deposition techniques that are well known, relatively unexpensive and easily scaled up.
The aforementioned and other objects are realised by the electrochromic device according to the present invention. Thus, a supported or self-supporting electrochromic device is provided, comprising:
at least one electrochromic element comprising (i) at least one material that is electrically conducting in at least one oxidation state and (ii) at least one electrochromic material, wherein said materials (i) and (ii) can be the same or different,
at least one layer of a solidified electrolyte which is in direct electrical contact with said electrochromic element, and
at least two electrodes adapted to be electrically connected to a voltage supply so as to create a difference in potential therebetween;
each of said electrodes being in direct electrical contact with at least one of said electrolyte layer(s) and not in direct electrical contact with said electrochromic element.
The electrochromic device according to the invention is particularly advantageous in that a display can be realised were the electrodes only cover a fraction of the solidified electrolyte with which they are in direct electrical contact, offering a substantial freedom when designing devices. Thus, in preferred embodiments of the invention, the electrodes cover between 0,01% and 50% of the area of the electrolyte layer(s), for example between 0,01% and 25%, or between 0,01% and 10%.
In one embodiment of the invention, an electrochromic device is provided, in which-the electrodes are arranged side by side in a plane. The electrodes then form an electrode layer, which can be deposited on a support in a conventional manner, and patterned in any desirable fashion. This is of special interest in the realisation of electrochromic displays. Also, when this arrangement of electrodes is used, the connections formed with the electrolyte are preferably made with only one layer of said electrolyte.
The invention provides an electrochromic device, where the external circuit supplying voltage to the device is not in electrical contact with the electrochromic element. The voltage applied to the electrodes induces an electric field in the electrolyte, which then surprisingly gives rise to an electrochromic colour change in the electrochromic element. This surprising possibility of addressing an electrochromic element through an electrolyte opens up many applications for the
Armgarth Mårten
Berggren Rolf M.
Kugler Thomas
Remonen Tommi M.
Acreo AB
Ben Loha
Burns Doane Swecker & Mathis L.L.P.
Hasan M.
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