Horology: time measuring systems or devices – Power supply details – Electrical
Reexamination Certificate
1998-03-27
2001-05-08
Roskoski, Bernard (Department: 2859)
Horology: time measuring systems or devices
Power supply details
Electrical
Reexamination Certificate
active
06229766
ABSTRACT:
The present invention concerns a dial formed of a solar cell and arranged, in particular, to supply a timepiece horometric circuit or an electric circuit for an apparatus such as a measuring apparatus. The invention more particularly concerns a dial wherein the face seen by the user has a metal appearance or aspect.
Timepieces, in particular watches, whose horometric circuit is supplied by one or more a-Si:H
-i-p or p-i-n amorphous silicon solar cells connected in series are already known. These cells, which use photovoltaic conversion to generate electric power, are generally made on a metal substrate on which an insulating layer, a transparent or opaque inner conductive layer, successive n-i-p amorphous silicon layers and a transparent outer conductive layer are successively deposited. The use of the insulating layer allows the subsequent connection in series of several photovoltaic elements on the same metal substrate. The transparent conductive layers are generally made of indium oxide (ITO) or tin oxide (SnO
2
) or doped zinc oxide (ZnO). The use of ITO, Sn O
2
or ZnO for making the transparent conductive layer has several drawbacks. The ITO layer exposed to light gives way to interference phenomenon which leads to undesirable coloured iridescence on the surface of the dial, in particular in the case of a watch dial. In order to overcome this problem, covering the ITO with lacquer is known, however, this additional layer of lacquer gives a blackish appearance to the dial, which is also unsatisfactory when one wishes to use such a dial for a watch, insofar as the dial interferes in a dominant manner in the ornamental function of the watch. Moreover, the resistivity of ITO is relatively high (in the order of 8×10
−4
&OHgr;cm), which leads to a significant impedance drop in the cell, in particular when the cell is exposed to light of strong intensity.
Patent Document WO-A-96/12989 attempts to overcome these problems. According to this Document, the dial is formed of a solar cell masked by a translucent ceramic film made of Al
2
O
3
so that the solar cell is hidden from the user's view. However, this cell's appearance is milky white and consequently unattractive to the consumer. Patent Document WO-A-96/31810 further proposes to modify the appearance of such a dial by adding a coloured layer onto the face of the dial seen by the user. However, the result obtained with this additional transmissive layer remains lustreless and does not allow the aesthetic appearance of the dial to be significantly enhanced.
A principal object of the invention is thus to overcome the drawbacks of the aforementioned prior art by providing a dial fitted with a solar cell which presents an intense brilliance to the user particularly suited to making decorative dials, for example for timepieces, while maintaining acceptable electric capacities for application to the cell used as a power source, with a simple and economic cell structure.
The invention therefore concerns a dial, in particular for a timepiece, formed of a solar cell including a substrate, at least one plurality of superposed layers defining at least one n-i-p or p-i-n element and a conductive layer forming a first electrode arranged to be exposed to luminous radiation or light, characterised in that said electrode is formed of a partially reflective metal layer.
Thus one obtains a dial formed of a solar cell, which has an improved external appearance, insofar as the metal layer reflects a fraction of the incident light and offers an aesthetic metal brilliance while allowing a sufficient fraction of incident light to pass for the photovoltaic effect to occur.
It will be noted that this use of a partially reflecting layer to form the conductive layer exposed to the light goes against the principle currently employed in this field by the man skilled in the art, who tends constantly to make such layers with maximum transmission and to reduce to a minimum any incident light reflection on the conductive layer.
Such a dial also has the advantage of being monolithic and consequently of performing the dual function of dial and source of electric power for a timepiece or suchlike.
According to an advantageous feature of the invention, at a wavelength of 550 nm, the first electrode has light reflectivity comprised between 90% and 50% and preferably between 85% and 60%.
With such reflectivity and weak light, for example 100 lux, and with a silver layer of a thickness of approximately 30 nm, the dial according to the invention can provide a current of the order of 1 &mgr;A or more, which is sufficient to supply the time-keeping circuit of an electronic timepiece.
The partially reflective metal also has a higher conductivity level than ITO which, in the event of exposure to high intensity light, leads to a lower voltage drop in the metal than in ITO.
It will also be noted that this reflectivity easily allows the use of a solar cell to be disguised by giving the dial the appearance of a conventional dial.
According to another preferred feature, the metal of the first electrode is selected from the group comprising gold, aluminium, silver, platinum, palladium, rhodium, nickel, titanium and copper.
These metals have the significant advantage of having sufficient reflection coefficients for the applications in question in the visible wavelengths while having sufficiently high electric conductivity.
REFERENCES:
patent: 5438556 (1995-08-01), Dinger et al.
patent: 5761158 (1998-06-01), Azuma et al.
patent: 0 697 636 (1996-02-01), None
patent: WO96/12989 (1996-05-01), None
patent: WO96/31810 (1996-10-01), None
Fischer Diego
Saurer Eric
Asulab S.A.
Griffin & Szipl, P.C.
Roskoski Bernard
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