Organic compounds -- part of the class 532-570 series – Organic compounds – Nitrogen attached directly or indirectly to the purine ring...
Reexamination Certificate
2002-06-07
2004-05-11
Lester, Evelyn (Department: 2873)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitrogen attached directly or indirectly to the purine ring...
C546S257000, C252S586000, C359S265000
Reexamination Certificate
active
06734305
ABSTRACT:
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.
PREAMBLE
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 &Ggr;>5×10
−8
mol/cm
2
if the extinction coefficient of these molecules varies from &Dgr;&egr;=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 &mgr;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.
A description is provided hereunter 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.
DESCRIPTION OF THE INVENTION
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:
I. the voltage applied between the two electrodes by a current-voltage source;
II. the intensity of the light to which the system is exposed;
III. the combined influence of I and II.
Furthermore, the colour change engendered by the light may be
A. local: only the lit location changes colour;
B. global: the entire system changes colour, irrespective of the location of the lighting.
Furthermore, the colour change engendered by the external voltage may be:
a. global: the entire system changes colour;
b. local: only the electrically addressed location changes colour (structured surface of the electrode).
This results in the following applications:
I-a: reversible electrochromic systems for the control of light transmission, governed by an external voltage-current source;
I-b: electrochromic systems for the reversible data display, governed by an external voltage-current source;
III-A: reversible photoelectrochromic systems for the optical writing and reversible data storage, controlled by a light beam (writing) and by an external voltage-current source (storage and deletion);
II-B: systems (filters, glazing), of which the transmission adapts 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 semiconductor 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 &mgr;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 on a flat surface.
Semiconductors which are particularly suitable for the preparation of the nanocrystalline electrodes must possess a large band gap. They may be chosen from among the oxides of the elements from Group IV of the periodic system, e.g. titanium, zirconium, or hafnium, from Group V, e.g. vanadium, niobium, or tantalum, from Group VI, e.g. chromium, molybdenum, or tungsten, or from other groups, e.g. silver, zinc, strontium, iron, or nickel. They may equally be of the perovskite type, such as SrTiO
3
or CaTiO
3
.
In particular, the invention relates to an electrochromic or photoelectrochromic device possessing the property of changing colour under the effect of an electric voltage and/or of a variation in the intensity of a light radiation, this device comprising at least one cathode and one anode, at least one of these electrodes being constituted at least in part of a transparent or translucent substrate bearing an electrically conductive coating, and an electrolyte arranged between these electrodes, and an electric circuit connecting said cathode and anode, this device being characterised in that at least one of these electrodes carries a coating constituted of at least one nanocrystalline layer of at least one semiconductive material, having a roughness factor equal to at least 20, and a monolayer of electrically active molecules or of an electrically active polymer, said monolayer being adsorbed on the surface of this coating, and in that the device contains at least one auxiliary electrically active compound, possibly dissolved in the electrolyte, having the property of being capable of being oxidised or reduced in a reversible manner.
It is in particular possible to envisage embodiments which present one or more of the following specific features:
a. the semiconductor is a titanium-, zirconium-, hafnium-, vanadium-, niobium-, tantalum-, molybdenum-, tungsten-, zinc-, strontium-, iron-, nickel-, silver-oxide or a perovskite of the said metals;
b. the electrical circuit comprises a current-voltage source;
c. the device comprises a small auxiliary electrode in addition to the anode and the cathode;
It is in particular also possible to achieve a number of variants of the electrochromic device according to the invention, each of these variants presenting special features according to one of the following points:
1. variant in which the cathode carries an adsorbed monolayer of at least one type of electrochromophoric molecules, which molecules comprise at least one adsorbable attachment group, possibly a polymerisable or condensible group, and at least one type n electrochromophoric group of which the property is to be colourless in the oxidised state and coloured in the reduced state, the auxiliary electroactive compound being fixed at the anode in the form of an electroactive coating, the electrolytic solution between the electrodes containing at least one electrochemically inert salt in solution in a solvent;
2. variant according to point 1, in which the electrochromophoric molecules comprise, as the electrochromophoric group, N,N′-dialkylbipyridinium or the diimide derivative of naphthalene-1,4,5,8-tetracarboxylic acid;
3. variant according to point 1, in which the electrochromophoric molecules comprise, as the attachment group, the carboxylate, salicylate, catecholate or phosphonate group, and, if applicable, as the polymerisable group, the vinyl or pyrrole group, or,
Lorenz Walder
Michael Grätzel
Pierre Bonhôte
Browning Clifford W
Ecole Polytechnique Federale de Lausanne
Lester Evelyn
Woodard Emhardt Moriarty McNett & Henry LLP
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