Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-08-11
2003-07-01
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S150000, C349S152000
Reexamination Certificate
active
06587175
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns an electro-optical cell, in particular a liquid crystal cell, or an improved electrochemical photovoltaic cell, in particular for a timepiece, and more particularly connecting means intended to establish an electric connection between the electrodes of the cell and an electric supply or control circuit. The present invention also concerns a manufacturing method for the aforementioned cell.
A first known category of photovoltaic cells converts light into electricity by exploiting the photovoltaic effect which appears at the junction of semi-conductors. The semi-conductor material fulfils at the same time the functions of light absorption and separation of the resulting electric charges (electrons and holes). As the material must have a high level of purity and be free of defects, failing which the electrons and holes would be combined again before having been able to be separated, the manufacturing costs are high.
The present invention is intended for a second type of photovoltaic cell called an electrochemical cell, a schematic diagram of which is shown in
FIG. 1
annexed to this application.
Such a cell, designated as a whole by the general numerical reference
1
, includes a first transparent front strip
2
and a second rear strip
4
which is also transparent. These two strips
2
and
4
each include, on their facing faces, a first electrode
6
also called a counter-electrode, and a second electrode
8
also called a photoelectrode. These electrodes
6
and
8
are usually made in the form of a thin layer of an indium/tin or tin oxide/antimony mixture.
Strip
4
further includes a layer
10
made in the form of a porous structure
12
having a large effective surface formed of particles of an active semi-conductor oxide such as, for example, titanium dioxide TiO
2
, the role of which will be described hereinafter.
Strips
2
and
4
are joined to each other by a sealing frame
14
which extends along, the perimeter thereof and which defines a volume
16
filled with an electrolyte
18
containing a mediator such as the redox couple iodide-tri-iodide I
−
/I
3−
.
Titanium oxide TiO
2
which constitutes layer
10
is a semi-conductor which is normally not sensitive to visible light because of the width of its forbidden band, and which only begins to absorb close to ultraviolet. It can nonetheless be sensitised by adsorption of a colouring agent such as a complex compound of a transition metal, in particular ruthenium or osmium, which allows an incident photon/electron conversion rate approaching the unit. The light absorption, symbolised by arrows in
FIG. 1
, is assured by the colouring agent chemically adsorbed at the surface of semi-conductive material layer
10
. After having been excited by the absorption of a light photon, the colouring agent can transfer an electron into the conduction band of the semi-conductor of layer
10
. The electric field present within the semi-conductive layer
10
allows the extraction of this electron. After transferring the electron, the colouring agent returns to the fundamental oxidised state. The recombination between the electron in the conduction band and the hole on the oxidised colouring agent is much slower than the reduction of the oxidised colouring agent by the mediator. Consequently, the charge separation is efficient. The oxidised mediator is reduced to counter-electrode
6
.
The present invention is also intended for so-called electro-optical display cells, in particular liquid crystal cells which, like electrochemical photovoltaic cells, include.
a first transparent front strip whose upper surface constitutes the front face of said cell;
a second rear strip whose lower surface constitutes the rear face of said cell;
each of the strips including on their facing faces at least one electrode, these electrodes being intended to be connected to a display control circuit and partially coming level with the edge of the corresponding strip to define an electric contact zone in distinct locations on the cell perimeter;
the strips being separated by a sealing frame defining a volume for the confinement of an optically active medium, and
connecting means for establishing the electric connection between each electrode and said display control circuit.
A constant problem in the field of electrochemical cells of the kind described hereinbefore lies in the connecting means to be used for establishing a reliable electric contact between the electrodes of the cell and an electric supply circuit. This problem is also encountered with electro-optical display cells wherein the electrodes of the cell have to be connected to a device for generating electric control signals which modify the electro-optical characteristics of the material confined between the strips of the cell.
The Applicant has already provided a response to this problem by proposing, in his French Patent No. FR-B1-2 637 110, an improved electro-optical cell wherein each of the two cell strips carries a transparent electrode over its entire surface, this electrode partially coming level with the edge of the strip onto which it has been deposited to define a lateral electric contact zone. In this Patent, the connecting means include a contact pad made of an adhesive synthetic material charged with conductive particles which are added onto the edge of each strip, to the right of the contact zone, and which assure the electric connection with the electric control circuit of the cell.
During use, this connection technique has nonetheless exhibited several drawbacks. On the one hand, the strips of the cell must be staggered in relation to each other, in order to provide access to the electrodes and to make the electric connections. Such an arrangement makes series manufacturing of the cells difficult, in particular when the cells are circular, and requires additional time-consuming operations.
On the other hand, as recalled hereinbefore, the connection between the electrodes and the control circuit is made via the electric contact zone where each of the electrodes of the cell comes level with the edge of the strip onto which it has been deposited. The thickness of this contact zone is very small, typically of the order of a thousand angstroms. Problems of electric contact or even breakage of the mechanical connection between the electrodes and the contact pads thus appear.
Moreover, timepieces such as wristwatches are known wherein an electrochemical photovoltaic cell of the aforementioned type is conventionally arranged under the crystal so as to be sufficiently exposed to light. By conversion of the visible light into an electric current, the photovoltaic cell powers, via an electric circuit, the horometric means of the watch.
Arranged underneath the watch crystal, the photovoltaic cell covers the time indicators (minute and hour hands, etc.) as well as the dial of the watch. Nonetheless, since this cell is quasi transparent, the indicators and the dial remain visible through the cell.
The electric connections of an electrochemical cell, arranged in two distinct locations on the cell perimeter, must however be masked in order to made them invisible from the exterior when one looks through the watch crystal. In order to overcome this problem, the only known solution is to increase the size of the bezel to mask the electrodes, and thus to reduce the useful surface of the crystal and the dial, which is detrimental to the aesthetic appearance of the watch and to the ability to read the information displayed on the dial. Another solution consists in reducing the dimensions of the photovoltaic cell, which is detrimental to its efficiency.
Another solution is known from the unexamined Japanese Patent Application No. 61-201289 which concerns a liquid crystal cell including a first front transparent plate
1
a
, and a second back plate
1
b
which is also transparent. These two plates
1
a
and
1
b
each include on their opposite faces a set of electrodes, respectively
2
a
and
2
b
, said electrodes being flush with
Born Jean-Jacques
Ruedin Yves
Sallin Michel
Asulab S.A.
Dudek James
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