Optical: systems and elements – Optical modulator – Light wave temporal modulation
Patent
1998-10-13
2000-05-23
Sugarman, Scott J.
Optical: systems and elements
Optical modulator
Light wave temporal modulation
359269, 359272, 359273, 359274, 359275, G02F 1155
Patent
active
06067184&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to an electrochromic or photoelectrochromic device, particularly suitable for reversible storage and display of data and for the control of light transmission, making use of one or two electrodes made of semiconductor having high specific surface area.
2. Brief Description of the Related Art
In order to prepare an electrochromic device in which the changing of visible light absorption is greater than 90% (for example from 5 to 95%), and which uses molecules as electrochromic units, it is necessary for the surfaces to have densities reaching the value of .GAMMA.0.sup.-8 mol/cm.sup.2 if the extinction coefficient of these molecules varies from .DELTA.IAUX 101 .backslash.f "Symbol"}=20'000 when changing oxidation state. Up to now, this requirement has been met in the following manner when preparing electrochromic devices:
the electrochromic compound is present in solution contacting the electrode. The requirement is fulfilled with a 0.25 M concentration and a layer thickness of the solution of 2 .mu.m;
the electrochromic compound is electrochemically precipitated in a thin layer on an electrode;
the electrochromic compound is polymerised or incorporated into a film of polymer or composite material on the surface.
SUMMARY OF THE INVENTION
A description is provided hereunder of a new type of electrochromic and photoelectrochromic devices, which, in order to attain the performance characteristics indicated earlier, make use of electrodes made of nanocrystalline semiconductor having very high specific surface area on the surface from which electrodes the electrochromic molecules are adsorbed. These devices are rapid, with switching times of less than 3 s for an absorption change of at least 90%, and allowing for brilliant colours to be obtained.
The invention relates to electrochemical systems comprising at least two electrodes, each of which may be transparent or opaque, and at least one of which changes colour depending on: source;
Furthermore, the colour change engendered by the light may be of the lighting.
Furthermore, the colour change engendered by the external voltage may be: (structured surface of the electrode).
This results in the following applications: transmission, governed by an external voltage-current source; external voltage-current source; reversible data storage, controlled by a light beam (writing) and by an external voltage-current source (storage and deletion); automatically to the intensity of the light received.
All these colour changes, easy to observe with the naked eye except in the case of III-A when data storage is on micrometric and sub-micrometric scale, correspond to chemical reactions which are well defined on the molecular level, namely oxidations or reductions of an electrochromic compound, usually grafted onto the whole of the surface of an electrode made of nanocrystalline semi-conductor accessible to such molecules. Such an electrode is prepared by sol-gel process such as the one described in detail by Stalder and Augustynski in J. Electrochem. Soc. 1979, 126, 2007, while maintaining the relative humidity of the ambient air at a value of between 50 and 80%, without a variation of more than 5%, during the hydrolysis of the metal alcoholate of which metal the oxide is being prepared. The thickness of the nanocrystalline layer is between 0.1 and 10 .mu.m or more, leading to a roughness factor of between about 10 and 1000, for example 700, meaning that the electrode surface area which is accessible to molecules having a typical diameter of 1 nm is 10 to 1000 times the value of the projected layer surface; e.g. 700 times. The result of this is that any change in the optical properties of a layer of molecules adsorbed on the surface of the semiconductor will engender macroscopic effects amplified by the roughness factor. Accordingly, the light absorption by a monolayer of coloured molecules will be stronger by a factor equal to the roughness factor on a nanocrystalline electrode than
REFERENCES:
patent: 5724187 (1998-03-01), Varaprasad et al.
Abstract No. 848 "Nanocrystalline TiO.sub.2 Electrodes Modified by Redox Active Organic Monolayers" by Pierre Bonhote, Michael Gratzel, Lorenz Walder, Extended Abstracts, vol. 95-2, (Oct. 8-13, 1995), pp. 1345-1346.
Nanostructured TiO.sub.2 Semiconductor Electrodes Modified with Surface Attached Viologens: Applications for Displays and Smart Windows. By Anders Hagfeldt, Lorenz Walder and Michael Gratzel, Institut de Chimie Physique, Lausanne, Switzerland, SPIE vol. 2531, pp 60-69 pub. 1995.
Towards Large-Area Photovoltaic Nanocells: Experiences learned from Smart Window Technology. By Carl M. Lampert, Lawrence Berkeley Laboratory, University of California, Berkeley, California, Sep. 1, 1993.
New Complimentary Electrochromic Display Utilizing Polymeric YbPc.sub.2 and Prussian Blue Films. By Naoya Kashiwazaki, Tokyo Denki University, Saitama, Japan, Mar. 4, 1991.
Bonhote Pierre
Gratzel Michael
Walder Lorenz
Browning Clifford W.
Burke Margaret
Ecole Polytechnique Federale de Lausanne
Sugarman Scott J.
LandOfFree
Electrochromic or photoelectrochromic device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrochromic or photoelectrochromic device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrochromic or photoelectrochromic device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1841147