EP0902339A1 - Dial consisting of a solar-cell, especially for a timepiece - Google Patents

Abstract

The dial comprises an upper substratum (2) which is translucid and has an electrode (6) on its lower surface and also a lower substratum (4) which has an electrode (8) on its upper surface. A physicochemical system comprises a semiconducting layer (12) with a monomolecular colorant (14) and an electrolyte (16) is enclosed between the substrata (2, 4).

Description

The present invention relates to a dial formed of a solar cell, especially of the photoelectrochemical type regenerative, the dial being intended to power a time circuit of a timepiece or a electrical circuit of a device such as a measure or the like. The invention relates more particularly a dial whose face shown at the user presents an original aesthetic aspect such than an opalescent or metallic appearance.

We already know from document WO-A-96/12989 a dial for a watch whose horometric circuit is powered by a conventional silicon solar cell. The dial described in this document is formed of a translucent ceramic sheet, such as Al ₂ O ₃ , placed above the solar cell so that it is hidden from the view of the user. The translucent nature of the dial allows a sufficient amount of light energy to pass through to illuminate the cell below.

According to this document the solar cell and the dial which the covers are made up of two separate parts which must be carried out and assembled independently. This structure has many drawbacks. In effect, such a structure increases the number of parts involved in the manufacture of a device in front of be equipped, such as a watch, and therefore complicates the construction of such a device and increases its cost price. In addition, the superimposition of the ceramic sheet and the cell solar leads to an increase in the thickness of the watch. This superimposed structure also leads to create an interface where reflections occur parasites from the incident light, which is harmful to overall efficiency of the solar cell.

The main aim of the invention is therefore to remedy the disadvantages of the aforementioned prior art in providing a dial formed by one or more cells integrated into it, the dial presenting the user an original opalescent or metallic appearance, particularly suitable for making dials decorative, for example for timepieces, everything maintaining acceptable electrical performance for the application of the cell used as source of energy and this using a cell structure simple and economical.

To this end, according to a first aspect, the invention has for the purpose of a dial, in particular for a timepiece, formed of at least one solar cell of the type regenerative photoelectrochemical comprising a first substrate intended to be exposed to light radiation and a second substrate, said substrates bearing, on their opposite, electrodes between which is arranged a physicochemical system capable of absorbing light and generate an electrical voltage to terminals of said electrodes, characterized in that said first substrate is formed of a translucent material.

According to a second aspect, the invention also for the purpose of a dial, in particular for a timepiece, formed of a substrate having a first face on which extends at least a plurality of overlapping layers defining at least one interleaved n-i-p or p-i-n element between two electrodes, and a second face intended for be exposed to light radiation, characterized in that said substrate is formed of a translucent material.

According to a third aspect, the invention also for the purpose of a dial, in particular for a timepiece, formed of a substrate having a first face on which extends at least a plurality of overlapping layers defining at least one interleaved n-i-p or p-i-n element between two electrodes, and a second face intended for be exposed to light radiation, characterized in that said substrate is formed of a transparent material and in that a partially transparent metallic layer and partially reflective is deposited on said second side of the substrate.

According to a fourth aspect, the subject of the invention is a dial, in particular for a timepiece, formed of minus a solar cell of the photoelectrochemical type regenerative comprising a first substrate intended for be exposed to light radiation and a second substrate, said substrates carrying, on their face in gaze, electrodes between which is arranged a physicochemical system capable of absorbing light and to generate an electrical voltage across said terminals electrodes, characterized in that said first substrate is made of a transparent material and in that a layer partially transparent and partially metallic reflective is deposited on said second face of the substrate.

Thanks to the characteristics presented by the four aspects of this invention we get a dial monolithic formed of a solar cell which achieves the dual function of dial and power source electric, for example for a timepiece or similar. By translucent material we understand everything material which lets in part of the light incident and backscatter or reflect another part while concealing from the observer the elements behind the substrate made of such a material.

According to an advantageous characteristic common to first two aspects of the invention, the substrate intended to be exposed to light radiation has a light reflectivity between 50% and 90% and preferably between 60% and 85% in the field of lengths visible waves.

With such reflectivity and illumination low, for example 200 to 300 lux, the dial depending the invention can provide a power of the order of 1 μW or more, which is still enough to power the timepiece circuit of an electronic timepiece under these lighting conditions.

Note also that this reflectivity allows easily conceal the appearance and structure of underlying solar cells by giving the dial a much more aesthetic appearance.

According to another preferred characteristic common to first two aspects of the invention, the substrate intended to be exposed to light radiation is made based aluminum oxide, zirconium oxide or a glass opalescent.

According to another preferred characteristic common to last two aspects of the invention, the metal of the metallic layer is chosen from the set comprising gold, aluminum, silver, platinum, palladium, nickel, titanium, rhodium and copper.

• la figure 1 est une représentation schématique en perpective d'un cadran formant une cellule solaire selon un premier aspect de l'invention;
• la figure 2 est une coupe longitudinale partielle de la figure 1;
• la figure 3 est une coupe longitudinale partielle d'un cadran formant une cellule solaire selon un deuxième aspect de l'invention; et
• la figure 4 est une coupe longitudinale partielle d'un cadran formant une cellule solaire selon un troisième aspect de l'invention.

Other characteristics and advantages of the invention will appear more clearly on reading the following description of an embodiment of the invention given purely by way of non-limiting illustration, this description being made in conjunction with the drawings in which:

• Figure 1 is a schematic perspective view of a dial forming a solar cell according to a first aspect of the invention;
• Figure 2 is a partial longitudinal section of Figure 1;
• Figure 3 is a partial longitudinal section of a dial forming a solar cell according to a second aspect of the invention; and
• Figure 4 is a partial longitudinal section of a dial forming a solar cell according to a third aspect of the invention.

The description of the invention will be made in the part of an application to a dial for a part of watchmaking such as a watch, however it goes without saying that the invention is in no way limited to this application and that it could be advantageously used as part of any other application to low-consumption electrical instruments, in particular portable, including a dial.

Referring first to Figure 1, we see a watch dial formed by a solar cell according to a first aspect of the invention and designated by the reference general 1. Dial 1 is capable of transforming a light radiation into an electric current by a process called photo-conversion to feed, via a power circuit, a timepiece circuit of the watch. These circuits and their connections (not shown) are well known to those skilled in the art and will not be therefore not described here in more detail. For a detailed description of the photo-conversion process, we refer to pages 303 to 312 of the book entitled "Solar Photopiles" by A. Ricaud and published by Éditions French polytechnic and university presses, ISBN 2-88074326-5 .

Dial 1 according to the first aspect of the invention is formed by a solar cell of the type regenerative photoelectrochemical. Dial 1 includes a first substrate 2 and a second substrate 4 comprising respectively over the entire surface of their face opposite an electrode 6 respectively 8.

A physico-chemical system 10 capable of absorbing light and generate an electrical voltage to electrode terminals is arranged between the two substrates 2 and 4.

This system 10 comprises a layer 12 of a semiconductor oxide, deposited on electrode 8. Layer 12 is for example formed of a layer of titanium oxide textured. This system 10 further comprises a layer 14 monomolecular dye that is adsorbed on the surface of layer 12. System 10 comprises an electrolyte 16, based on non-aqueous solvent containing a redox couple, for example the iodine / iodide redox couple, this electrolyte being directly in contact with the dye layer 14. Finally, the electrolyte 16 is in turn in contact with a thin layer 18 of an electrocatalyst, for example a thin layer of platinum which is deposited on electrode 6.

The substrates 2 and 4 are joined together, by example, by a sealing frame 20 to define a space in which the system extends 10.

According to the invention, one of the two substrates 2, 4 is made of a translucent material, it being understood that the substrate intended to produce the visible face of the dial (or exposed to light radiation) will be realized in such material. In the example shown, it is the substrate 2 which is intended to be exposed to light radiation and which is made of a translucent material, layer 18 being of course transparent.

Note in this connection that when the substrate 4 is intended to form the visible face of the dial, the electrode 8 will also be transparent.

According to the invention, the material forming the substrate 2 has a reflectivity of the incident light radiation between 50% and 90% in the field of lengths visible waves, which gives the appearance aesthetic sought for the dial.

Advantageously, the substrate 2 can be produced based on aluminum oxide, zirconium oxide or opalescent glass.

To obtain the desired reflectivity, we act essentially on the thickness of substrate 2 taking also takes into account, if necessary, the diffusing power of material used.

Preferably, the first substrate 2 has a reflectivity between 60% and 85% in the field of visible wavelengths.

It has been found that with a thickness of the substrate 2 of the order of 0.5 mm and preferably 0.3 mm, a cell having a surface corresponding to that of a conventional watch face (of the order of 5 cm ² ), even in low-light conditions (200 to 300 lux) delivers an electrical power allowing to power a timepiece circuit of an electronic watch, namely typically a power of 1 µW to 1.5 µW in average.

The electrode 6 carried by the substrate 2 is indeed heard formed of a conductive layer transparent to the light at wavelengths that correspond to absorption of the dye. This electrode is made of preferably in the form of a thin layer of a mixture indium oxide and tin oxide or tin oxide and antimony oxide. It goes without saying that the skilled person may choose any other transparent conductive layer equivalent.

The substrate 4, which is not intended a priori to to pass a light radiation, can be realized made of an opaque and advantageously reflective material.

It should also be noted that all of the materials used likely to come into contact with the electrolyte 16, in particular the two substrates 2, 4 and the electrodes 6 and 8, are materials chemically compatible with the electrolyte of the physico-chemical system 10. By chemically compatible, we mean inert materials that is to say who do not react vis-à-vis the electrolyte, in particular with respect to the redox couple.

The dial 1 finally includes a hole 22 located substantially in its center to allow the passage of axes on which the watch hands are fixed intended to move above the dial 1.

Note that the drawing does not reflect the dimensions exact dial, these dimensions having been strongly exaggerated for clarity.

In the context of the application described, the substrate which is exposed to light radiation can also have hour markers 24 (figure 1) forming a round of hours or other inscriptions, these indexes or inscriptions can be attached or engraved on the face of the substrate exposed to light radiation.

In the example in Figure 2, layer 12 comprising the monomolecular layer of dye 14 is deposited on the substrate 4. It is understood that according to an alternative embodiment, this layer 12 could be deposited on the substrate 2 (translucent). In this realization the electrocatalytic layer 18 can be opaque or reflective.

In Figure 3, we see a partial section of a dial 26 according to a second aspect of the invention. The dial 26 comprises a substrate 28 formed of a plate rigid having the same characteristics as those of substrate 2 which has just been described in connection with the Figures 1 and 2. The substrate 28 comprises a first face 30 on which a plurality of layers are deposited 32a, 32b, 32c successive thin p, i, n respectively sandwiched between two conductive layers 34, 36 respectively forming electrodes.

Of course, the electrode 34 which is arranged between layer 32c and in contact with it and the substrate 28 is transparent, this electrode 34 being the element of the cell which is intended to be directly exposed to light radiation through the substrate 28. As for example, electrode 34 like electrode 36 can be formed by a thin layer of an oxide mixture indium and tin oxide (ITO).

The three layers 32a, 32b and 32c, forming a elementary solar cell 32, therefore define a diode, i.e. a p-i-n junction diode with an intrinsic zone, inserted between a zone p and a zone n, which can be exposed to light radiation. This elementary solar cell 32 consists of three layers of hydrogenated amorphous silicon (a-Si: H) having different conductivity types to form the diode p-i-n. Layer 32a of the elementary cell 32 is doped for example with phosphorus to obtain a n type conductivity. The thickness of this layer is preferably of the order of 10 to 20 nm. The next layer 32b of the elementary cell 32 is a layer intrinsic i which is thicker than the previous one and in which electron-hole pairs are generated when the cell is exposed to light radiation. The layer 32b has for example a thickness of the order of 200 to 500 nm. Layer 32c of the elementary cell is for example doped with boron to obtain a p-type conductivity. The thickness of this layer is preferably of the order of 10 to 30 nm.

In this example, the p-type layer 32c is the most close to substrate 28, but it is understood that according to an alternative embodiment the layer closest to the substrate 28 could be an n-type layer.

Referring now to Figure 4, we see a partial section of a dial 40 according to a third aspect of the invention, in which the elements identical to those described in conjunction with Figure 3 have been designated by the same reference numbers.

Unlike the embodiment shown in Figure 3, the substrate 28 of the dial 40 is transparent and a partially reflective metal layer 42 is deposited on an outer face 44 of the substrate, opposite side 30.

This layer 42 has a reflectivity of the incident light radiation between 50% and 90% in the visible wavelength range, which provides the metallic luster and therefore the appearance aesthetic sought for the dial. To get this reflectivity, we essentially act on the thickness of the metal of layer 32. Preferably, this layer metallic 42 has a reflectivity of between 60% and 85% in the visible wavelength range.

It has also been found that, depending on the metal used for the layer 42, a thickness of the order of 20 nm and preferably 35 nm of this layer, allows sufficient light to pass through even in low-light conditions (200 to 300 lux ) so that an elementary cell having a surface of a conventional watch face (of the order of 5 cm ² ) provides electrical power making it possible to supply a time-keeping circuit of an electronic watch, namely typically a power 1 µW on average.

In any event, layer 42 will present a minimum thickness between 2 and 10 nm and a maximum thickness between 15 and 40 nm.

The metal layer 42 can be formed of a metal chosen from the group comprising gold, copper, aluminum, silver, platinum, palladium, nickel, titanium and rhodium. Of course others metals with reflectivity characteristics of the same order may also be suitable.

Note also that depending on the nature of the layer 42, an intermediate layer could be provided of attachment between the face 44 and the layer 42.

The deposition of the metal from layer 42 can be carried out conventionally by sputtering, evaporation thermal vacuum or using a barrel electrons. This deposit can be made through a mask defining the contours of layer 42 or delimited according to photolithography techniques classics.

According to a fourth aspect of the invention, not shown, the translucent substrate of the dial according to the first aspect of the invention is replaced by a substrate made of transparent material on the outside from which a layer having characteristics has been deposited identical to those of layer 44 described in connection with figure 4.

According to a variant of the invention, the dials shown in Figures 2 and 3 may include on the outer face of their respective translucent substrate a metallic layer such as that described in connection with Figure 4.

Claims (10)

Dial, in particular for a timepiece, formed at least one solar cell of the type regenerative photoelectrochemical comprising a first substrate intended to be exposed to light radiation and a second substrate, said substrates bearing, on their opposite, electrodes between which is arranged a physicochemical system capable of absorbing light and generate an electrical voltage to terminals of said electrodes, characterized in that said first substrate is formed of a translucent material. Dial, in particular for a timepiece, formed a substrate having a first face on which extends at least a plurality of superimposed layers defining at least one n-i-p or p-i-n element inserted between two electrodes, and a second side intended to be exposed to light radiation, characterized in that said substrate is formed of a translucent material. Dial according to claim 1 or 2, characterized in that said substrate intended to be exposed to light radiation has a reflectivity of the light between 50% and 90% and preferably between 40% and 85% in the field of visible wavelengths. Dial according to claim 1 or 2, characterized in that the substrate intended to be exposed to radiation light is made from aluminum oxide, oxide zirconium or opalescent glass. Dial according to claim 1 or 2, characterized in that the substrate intended to be exposed to radiation light has a thickness between 0.3 and 0.5 mm. Dial, in particular for a formed timepiece a substrate having a first face on which extends at least a plurality of superimposed layers defining at least one n-i-p or p-i-n element inserted between two electrodes, and a second side intended to be exposed to light radiation, characterized in that said substrate is formed of a transparent material and in this that a partially transparent metallic layer and partially reflective is deposited on said second side of the substrate. Dial, in particular for a timepiece, formed at least one solar cell of the type regenerative photoelectrochemical comprising a first substrate intended to be exposed to light radiation and a second substrate, said substrates bearing, on their opposite, electrodes between which is arranged a physicochemical system capable of absorbing light and generate an electrical voltage to terminals of said electrodes, characterized in that said first substrate is formed of a transparent material and what a partially transparent metallic layer and partially reflective is deposited on said second side of the substrate. Dial according to claim 6 or 7, characterized in that said metal layer has a light reflectivity between 50% and 90% and preferably between 60% and 85% in the field of lengths visible waves. Dial according to claim 6 or 7, characterized in that the metal of the metallic layer is chosen among the set including gold, aluminum, silver, platinum, palladium, nickel, titanium, rhodium and copper. Dial according to claim 6 or 7, characterized in that the metal layer has a thickness minimum between 2 and 10 nm and a maximum thickness between 15 and 40 nm.

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