Photovoltaic cell with specific arrangement of energy collectors

Abstract

The utility model relates to a photovoltaic cell (1). The photovoltaic cell (1) comprises a first front collector layer (4), an amorphous silicon layer (6) on the first layer (4), and a second conductive layer (8) on the amorphous silicon layer (6). An electrical connection from the second electrically conductive layer (8) to the first layer (4) is made through the amorphous silicon layer (6). The electrical connection of the second electrically conductive layer (8) to the first layer (4) is made at the periphery of the photovoltaic cell through the amorphous silicon layer (6), the electrically conductive layer (8) comprising a positive peripheral bus (8 ') connected to the TCO first layer (4) and at least one positive connection terminal at one end of the positive peripheral bus, and a negative peripheral bus connected to a negative connection terminal, the positive peripheral bus (8') being connected to the TCO first layer (4) and at least one negative connection terminal at one end of the positive peripheral bus. And the positive peripheral bus bar and the negative peripheral bus bar are asymmetric with respect to each other, wherein the positive peripheral bus bar is longer than the negative peripheral bus bar.

Description

Technical Field

[0001] The present invention relates to a photovoltaic cell having a specific arrangement of collectors for collecting energy in the form of electric current, and to a method for producing such a photovoltaic cell.

[0002] Therefore, the present invention includes optimizing the efficiency of photovoltaic cells used in portable electronic objects, such as wristwatches. Background Technology

[0003] Each photovoltaic cell has a general shape adapted to the shape of the portable object that houses it. Typically, it can be a cylindrical cell arranged on the inner surface of the glass of the portable object that houses it, or arranged on the dial surface visible from the outside of the portable object.

[0004] This type of photovoltaic cell is produced using a series of layers, particularly a first front layer that is transparent to ambient light, called the front collector. This front layer can be produced using a layer of zinc oxide (ZnO:Al or AZO) doped with aluminum. This first layer can be arranged on the inner surface of the glass of a portable object facing the dial, and typically deposited thereon a pin-like sequence of thin layers of amorphous silicon (a-Si) (p-doped, intrinsically i, n-doped), called the absorber, which converts the absorbed light radiation into positive charge carriers (holes) and negative charge carriers (electrons). The structure typically terminates in a second conductive layer (e.g., aluminum or another metal combination), called the back collector.

[0005] In this configuration, positive charge carriers drift towards the front collector, where they are neutralized by electrons from the external circuitry. Negative charge carriers drift towards the back collector, where they supply electrons to the external circuitry and create a negative charge current between the back and front collectors. By convention, this involves a (positive) current flowing between the positive and negative terminals; therefore, in the configuration just described, the charge current is negative.

[0006] Initially, for a technology using only one metal layer, an embodiment for producing photovoltaic cells has been proposed based on existing technology, such as... Figure 1 As shown. In this embodiment, a symmetrical design is proposed for the current collector or peripheral bus, that is, using peripheral buses of more or less the same length, width, and thickness to form two semicircles or arcs around the circumference of the circular cell. Generally speaking, the bus must be as long as possible to promote the most homogeneous current distribution in the front collector of the photovoltaic cell, which reduces resistive losses.

[0007] In the case of homogeneous photovoltaic cells (referred to as single-segment cells), such as Figure 1 As shown, the current lines follow an approximately straight and parallel path between the two peripheral busbars. Using current transparent conductive layer technology for forming the front collector, it should be noted that the layer resistance is at least one to two orders of magnitude greater than the resistance of the thin layer deposited at the rear of the cell to form the rear collector.

[0008] When current flows through the front and back collectors, this difference in layer resistance causes the potential gradient in the front collector to be significantly higher than that in the back collector, and the power loss also increases with the increase of the current value. Summary of the Invention

[0009] Therefore, the present invention proposes a photovoltaic cell with a specific arrangement of current collectors or peripheral buses that significantly reduces the voltage drop in the front collector caused by the current generated by the absorption layer after light capture.

[0010] Therefore, the present invention relates to a photovoltaic cell arranged to significantly reduce the voltage drop across the front collector.

[0011] To provide electrical contact on only one side of a photovoltaic cell, a portion of the back collector is typically separated by chemical etching or another method, making it usable as a positive terminal. This positive terminal is electrically connected to the front collector via a metal busbar deposited in an opening previously formed through a sequence of thin amorphous silicon layers (absorbers). The front collector is transparent and conductive (TCO) and can be made using a layer of aluminum-doped zinc oxide (ZnO:Al or AZO). The conductivity of the front collector is much lower than that of the back collector, which can be, for example, a metal layer made of aluminum. This difference in conductivity is approximately 30 times.

[0012] Under these conditions, according to the invention, at least one metal peripheral busbar connected to the front collector is provided, which is significantly longer than the metal peripheral busbar provided in the rear collector. Preferably, the length of the front peripheral busbar should be at least 10 times the length of the rear peripheral busbar. This asymmetry in length, for example, between peripheral buses of the same width and thickness, makes it possible to limit or reduce the potential drop within the front collector to less than 100 mV. This represents a gain of almost 50 mV compared to the potential drop observed in a photovoltaic cell with a symmetrical peripheral busbar. The potential drop within the front collector can be less than 100 mV, which makes it possible to limit the power loss of a photovoltaic cell that produces a voltage of no more than 600 mV to 700 mV before processing in the electronic modules of portable objects.

[0013] Advantageously, the connection from the front collector to a portion of the rear collector (preferably an aluminum layer on opposite surfaces) can provide two asymmetrical busbars that connect to the front collector on one side and to the aluminum layer defining the negative terminal on the other side.

[0014] In addition, two peripheral busbar segments can be provided from the connection point of the aluminum layer to the front collector. These two peripheral busbar segments connect to the positive terminal, thereby depicting a defined angle on either side of the connection point of the front collector. The angle described by the positive peripheral busbar of the front collector is much larger than the angle of the negative terminal of the aluminum layer. For the peripheral busbar connected to the front collector, a coverage of 330° is expected, while for the negative terminal portion of the aluminum layer, this angle may be less than 30°.

[0015] Advantageously, each free end of the positive peripheral busbar connected to the front collector includes a connecting end to further reduce the current flowing through the metal peripheral busbar. Therefore, the two positive terminals connected to the peripheral busbar connected to the front collector are intended to be connected in parallel via a flexible connector, for example, to an electronic data processing module. Thus, the current flowing to each end of the metal peripheral busbar is half the total current flowing to the negative terminal. This also means that two positive terminals and one negative terminal are connected to an electronic module, which is primarily located below the dial of the portable object. Attached Figure Description

[0016] The objectives, advantages, and features of a photovoltaic cell with a specific arrangement of energy harvesters, as well as the objectives, advantages, and features of methods for producing such photovoltaic cells, will become clearer in the following non-limiting description given with reference to the accompanying drawings, in which:

[0017] Figure 1 A bottom view of a photovoltaic cell according to the prior art is shown, the photovoltaic cell having symmetrical peripheral busbars for negative and positive terminals.

[0018] Figure 2 A bottom view of a photovoltaic cell according to the present invention is shown, the photovoltaic cell having asymmetrical peripheral busbars of different lengths for connecting a front collector to a positive terminal and a rear collector to a negative terminal, the busbars being made of a metal layer already used to form the rear collector.

[0019] Figure 3a , 3b Figures 3c and 3d show cross-sections of four steps of the method for producing photovoltaic cells in the first embodiment, which retain a region of conductive layer without openwork in the central reading region of the photovoltaic cell, while clearly delineating the boundaries between the positive and negative regions.

[0020] Figure 4 The invention is shown in Figure 3d The cross-section shown is a bottom view of a photovoltaic cell of a first alternative embodiment, which has an asymmetrical peripheral busbar, i.e., a different length relative to the peripheral busbar of the negative region. Figure 5a , 5b Figures 5c and 5d show cross-sections of four steps in a method for producing a photovoltaic cell according to a second alternative embodiment of the photovoltaic cell, and

[0021] Figure 6a , 6b Figures 6c and 6d show cross-sections of four steps in a method for producing a photovoltaic cell according to a third alternative embodiment of the photovoltaic cell. Detailed Implementation

[0022] The following description primarily describes a single-segment photovoltaic cell with a specific arrangement of current collectors, which includes an asymmetrical peripheral bus or collector to reduce the voltage drop between at least one positive terminal and one negative terminal of the photovoltaic cell.

[0023] This single-segment photovoltaic cell mainly consists of a first front layer, transparent to ambient light, called the front collector, which can be fabricated using a layer of aluminum-doped zinc oxide (ZnO:Al or AZO). This first layer can be arranged on the inner surface of the glass of a portable object facing the dial, and on it, typically deposited, a pin-type sequence (p-doped, impurity-free i, n-doped) of amorphous silicon (a-Si) thin layers, called the absorber, which generates positive charge carriers (holes) and negative charge carriers (electrons) under illumination. The structure typically terminates in a second conductive layer, which can be a metallic layer, for example made of aluminum or a combination of other metals, called the back collector.

[0024] The single-segment photovoltaic cell may include a base layer formed thereon. One side of the glass of a portable object, or a portion of the dial of a portable object, can be used as the base layer of the photovoltaic cell. In the remainder of this description, it will be preferred to produce the complete photovoltaic cell on the inner surface of the glass.

[0025] Compared with existing technologies Figure 1 In comparison, it can be noted that Figure 2 A relatively generalized embodiment is shown, which has an asymmetrical peripheral bus or collector, thereby allowing the positive peripheral bus 8' connected to the defined positive terminals 8'a and 8'b to be fixed at a quasi-constant potential on the largest portion of the periphery of the front layer of the photovoltaic cell to which it is connected.

[0026] This modification—aimed at maintaining a nearly constant potential over a large portion of the outer periphery of the photovoltaic cell's front layer—makes it possible to force a quasi-radial configuration of the current lines, such as... Figure 2 As shown, this reduces the potential difference between the highest value at the center and the lowest value at the periphery.

[0027] The rear collector connected to the defined negative terminal 8 consists of a low-resistivity metal layer. Although the geometry of the rear collector is unfavorable, it limits the potential difference between terminal 8 and its diametrically opposed end to a negligible value compared to the front collector.

[0028] Photovoltaic cell 1 is typically in the form of a cylinder. This part of the cylinder can be designed to be fastened to the underside of the glass of a portable object, or above the dial of a portable object. For example, the portable object could be a watch.

[0029] exist Figure 2 In the configuration shown, the positive peripheral bus 8' connected to the front collector of the photovoltaic cell describes a portion of an arc with an angle of at least 330°. On the other hand, the arc of the negative peripheral bus 8 describes an angle of approximately 30° or less. For the positive peripheral bus, an arc of almost 350° can even be envisioned, and for the negative peripheral bus 8, an arc of less than 10° can be envisioned.

[0030] The outer peripheral busbar 8' is connected to the front collector (not in this) on its longest portion and preferably along its entire length. Figure 2 (As shown in the diagram). This means that the positive peripheral bus terminates at a first positive terminal 8'a and, conversely, at a second positive terminal 8'b, so that they can subsequently be connected via a specific connector to an electronic module located below the dial of the portable object. The negative terminal of the negative peripheral bus will also subsequently be connected to the electronic module via a specific connector. The two positive terminals 8'a and 8'b of the positive peripheral bus 8' make it possible to reduce the voltage drop on the positive peripheral bus by three-quarters by placing the two sectors of the bus in parallel and then connecting them to the electronic module, dividing the collected current by half on the one hand and the distance to be covered by half on the other.

[0031] Figure 3a , 3b Figures 3c and 3d illustrate the various steps of a method for producing photovoltaic cells according to the first embodiment. As in the initial... Figure 3a As can be seen, there is a base layer 2, which is a glass layer and forms part of the actual photovoltaic cell in this case. However, multiple layers, one on top of another, can be used as the base layer 2, and these layers can consist of at least one glass layer, on or under which one or more transparent material layers are placed, or at the end of the method, a sapphire layer is deposited on one or more glass layers.

[0032] More typically, the photovoltaic cell 1 includes a first front collector layer 4 as a base layer, which is defined as the front collector at the end of the production process. A pin-type sequence (p-doped, impurity-free i, n-doped) of amorphous silicon (a-Si) thin layers—referred to as absorbers or defined as amorphous silicon layer 6—is deposited on the first front collector layer, and a second conductive layer 8, preferably a metal layer such as an aluminum layer, is added to the amorphous silicon layer 6.

[0033] The following uses glass 2, a portable object serving as the base layer, to describe all the steps involved in the production and patterning of the photovoltaic cell 1, on which the three connecting layers mentioned above, namely the first front collector layer 4, the amorphous silicon layer 6, and the second conductive layer 8, are produced and patterned.

[0034] This means that photovoltaic cell 1 can include both glass layer 2 and the three layers specified above, or only the three layers specified above.

[0035] It should also be noted that the photovoltaic cell 1 can also be mounted or fastened to the dial of a portable object. However, in this case, the front collector layer 8 is directly used as the base layer because, at the end of the method for producing a single-segment photovoltaic cell 1, the latter is mounted or fastened to the dial of the portable object on the side of the second conductive layer (back collector), which can be a metallic layer. This first layer of the front collector can advantageously be a zinc oxide (ZnO) layer or a layer of aluminum-doped zinc oxide (ZnO:Al or AZO).

[0036] Since a glass layer, or a layer of glass and sapphire, is typically used as the glass 2 of a portable object, various subsequent steps are performed on the inner surface of the glass 2 of the portable object. The glass layer 2 is shown as a base layer on which various other layers of the single-segment photovoltaic cell 1 are deposited.

[0037] Figure 3aAs shown, a weakly conductive first pre-collector layer 4 is first deposited on one side of the glass layer 2. This can be a first pre-layer 4, which is zinc oxide (ZnO) or a first zinc oxide layer doped with aluminum (ZnO:Al or AZO). Above this first pre-layer 4, a pin-type sequence (p-doped, impurity-free i, n-doped) of amorphous silicon (a-Si) thin layers is provided, referred to as the placed absorber or deposited amorphous silicon layer 6, which is used to capture electromagnetic waves, i.e., light, so as to convert them into electrical energy through layers arranged above and below the amorphous silicon layer 6. The general shape of the pre-layer 4 and the amorphous silicon layer 6 depends primarily on the general shape of the glass on which they are produced or deposited. Primarily in the embodiment shown, when viewed from above, the base layer of the glass 2, as a portable object (such as a watch), is generally circular in shape or forms part of a glass bell to enclose the watch case. Therefore, the first pre-layer 4 adopts a general cylindrical shape for deposition or fastening to the inner surface of the watch glass 2. Similarly, a thin amorphous silicon layer 6 is arranged or deposited on the first front layer 4 and is similar in shape to the first front layer 4.

[0038] Figure 3b The second step of the method shown is to typically create openings 12 in the peripheral location of the photovoltaic cell 1, through a sequence of pins (p-doped, i-undoped, n-doped) across a thin amorphous silicon (a-Si) layer (defined as amorphous silicon layer 6), which indicate an entrance to the first front layer. Each opening 12 created to connect to the first front collector layer can be fabricated using a laser or other etching techniques such as those used in microelectronics. Then, in Figure 3c In the third step of the method shown for producing photovoltaic cell 1, a second conductive layer 8 is deposited on top of the amorphous silicon layer 6. This second conductive layer 8 is preferably a metal layer, such as an aluminum layer. This metal layer is preferably made of aluminum and extends through… Figure 3b The opening 12 created in the method steps shown is for contact with the first front layer 4.

[0039] at last, Figure 3d The final step of the manufacturing method shown includes separating a second conductive layer 8 (which may be, for example, a metal layer 8 made of aluminum) to contact the portion of the metal layer connected to at least one negative terminal of the photovoltaic cell on one side and on the other side. For this purpose, an opening 12' is made in and through the conductive layer 8, which may be an aluminum layer 8, and is formed in such a way that the aluminum metal layer 8' connected, for example, to the first front layer 4 is separated from the aluminum metal layer 8 connected to the negative terminal of the photovoltaic cell 1.

[0040] exist Figure 3dAt the end of the method of this first alternative embodiment of the photovoltaic cell 1 shown, the photovoltaic cell 1 can capture a light beam or light 10. It will be explained below that the photovoltaic cell 1 is intended to be connected to an electronic module typically located below the dial of a portable object in order to convert light into electrical energy.

[0041] Figure 4 The diagram shows a view from below at the end of the manufacturing process, illustrating the separation of the second metal layer (e.g., made of aluminum) to connect the front collector layer on one side and the negative terminal of the photovoltaic cell 1 on the other. Figure 4 The asymmetric peripheral busbars of the present invention are clearly shown, namely the positive peripheral busbar connected to the front collector layer and the negative peripheral busbar connected to the negative connection terminal of the photovoltaic cell.

[0042] One or more openings created in the second conductive layer 8 (such as an aluminum layer) allow for the creation of a positive peripheral busbar 8' for subsequent connection to an electronic module beneath the dial of the portable object. These openings allow the view of the amorphous silicon layer 6 beneath the conductive layer (which is the aluminum layer 8).

[0043] Each positive peripheral busbar from the connection to the first front collector layer terminates on a first positive terminal 8'a on a first side and on a second positive terminal 8'b on a second side. The two peripheral busbar sectors together describe a total arc defined at least 330°. The negative peripheral busbar of the aluminum layer is represented only by the negative terminal 8 facing both positive terminals 8'a and 8'b. The negative peripheral busbar has an arc of less than 30°, which illustrates the asymmetry between the positive and negative peripheral busbars sought by the present invention.

[0044] The two positive peripheral bus sectors 8' together are approximately 10 times larger than the negative peripheral bus 8, which provides the advantage of reduced voltage drop as described above, especially under higher illumination conditions that generate stronger currents.

[0045] Furthermore, in this first alternative embodiment, the negative terminal 8 is directly connected to the remainder of the metal layer 8, which has no cutout portion and is surrounded by two positive peripheral bus sectors 8'.

[0046] Figure 5a , 5b Figures 5c and 5d show cross-sections of four steps in a method for producing photovoltaic cells according to a second alternative embodiment. Figure 6a , 6b Figures 6c and 6d show cross-sections of four steps in a method for producing a photovoltaic cell according to a third alternative embodiment of the photovoltaic cell.

[0047] It should be noted that all steps in the methods used to generate this method in these second and third alternative embodiments will not be repeated, as they are substantially similar to those in the references. Figure 3a , 3b The steps described in 3C and 3D.

[0048] In a second alternative embodiment of the method for producing photovoltaic cell 1, Figure 5d In the fourth step shown, chemical etching is performed to etch both the conductive layer 8 (such as the metal layer 8) and the amorphous silicon layer 6, thereby obtaining an opening that is given reference number 12' and defines the cutout portion.

[0049] Similarly, in a third alternative embodiment of the method for producing photovoltaic cell 1, in Figure 6d In the fourth step shown, chemical etching is performed to etch both the conductive layer 8 (such as the metal layer 8) and the amorphous silicon layer 6, as well as the first front layer 4 above the substrate, which may be the glass 2 of a portable object.

[0050] If the cutout is used to make the photovoltaic cell semi-transparent, the cutaway can be chosen between 75% and 95%, that is, up to 25% PV coverage (which becomes too visible) and at least 5% PV coverage (which is difficult to design because the cell power becomes too low).

[0051] However, as indicated at the beginning of the specific embodiments, the method for producing photovoltaic cells can begin directly with the first front collector layer 4 forming the base layer. From this base layer, other layers are arranged sequentially from one side of the first front collector layer 4. The first front collector layer 4 can advantageously consist of a zinc oxide (ZnO) layer or a first layer of aluminum-doped zinc oxide (ZnO:Al or AZO).

[0052] In the above case, the produced photovoltaic cell 1 is not bonded to the glass of the portable object, or is not directly located on the dial of the portable object. In the case of the photovoltaic cell 1 consisting only of the above three layers, it must be possible to subsequently connect the connection terminals of the positive peripheral bus and the negative peripheral bus to an electronic module that is usually located below the dial of the portable object in order to manage the signals received via its connection terminals having positive peripheral bus and negative peripheral bus.

[0053] It should be noted that, in order to connect these positive and negative peripheral bus terminals to the electronic module of the portable object, flexible connections of the FPC (flexible printed circuit) type bonded to ACF (anisotropic conductive film), connectors with spring bars, also known as pogos, or even Zebra-type connectors (containing elastic blocks with regularly spaced conductive areas) can be used. However, the connection between the photovoltaic cell and the electronic module of the portable object will not be described in more detail because the present invention is mainly based on the difference in length between the positive and negative peripheral buses in order to optimize the efficiency of such photovoltaic cells. In this case, thanks to the specific arrangement of the positive and negative peripheral buses, there is a reduction in potential drop in the connection with the low-conductivity TCO layer compared to photovoltaic cells in the prior art.

[0054] Various other forms of photovoltaic cells can be conceived by those skilled in the art without departing from the scope of the invention as defined by the claims.

Claims

1. A photovoltaic cell (1) intended to be disposed on the inner surface of the glass of a portable object or on the dial of the portable object, the photovoltaic cell (1) comprising a transparent and conductive front collector layer (4), an amorphous silicon layer (6) on the front collector layer (4), and a conductive layer (8) on the amorphous silicon layer (6), the conductive layer (8) constituting a rear collector, the electrical connection from the conductive layer (8) to the front collector layer (4) being made through the amorphous silicon layer (6), Its features are, The electrical connection from the conductive layer (8) to the front collector layer (4) is made through the amorphous silicon layer (6) at the periphery of the photovoltaic cell. The conductive layer (8) includes a positive peripheral bus (8') and a negative peripheral bus. The positive peripheral bus (8') is connected to the front collector layer (4) and to at least one positive connection terminal (8'a, 8'b) at one end of the positive peripheral bus. The negative peripheral bus is connected to a negative connection terminal. The positive peripheral bus and the negative peripheral bus are asymmetrical relative to each other, wherein the length of the positive peripheral bus is greater than the length of the negative peripheral bus.

2. The photovoltaic cell (1) according to claim 1, characterized in that, The thickness and width of the positive outer busbar are basically the same as those of the negative outer busbar, and the length of the positive outer busbar is at least 10 times that of the negative outer busbar.

3. The photovoltaic cell (1) according to claim 1 or 2, characterized in that, The electrical connection from the conductive layer (8) to the front collector layer (4) is made across the entire length of the positive peripheral busbar through the amorphous silicon layer (6), which will be formed on the conductive layer (8), which is a metal layer.

4. The photovoltaic cell (1) according to claim 3, characterized in that, The metal layer is an aluminum layer.

5. The photovoltaic cell (1) according to claim 3, wherein the photovoltaic cell is a cylinder in plan view, characterized in that, The positive peripheral bus describes a total arc of 330°, which has an electrical connection to the periphery of the front collector layer (4) over the entire length of the positive peripheral bus. The positive peripheral bus terminates at a first positive connection terminal (8'a) on a first side and at a second positive connection terminal (8'b) on a second opposite side. The negative peripheral bus, including a negative connection terminal, follows an arc of less than 30°, which has a first positive connection terminal (8'a) and a second positive connection terminal (8'b) of the positive peripheral bus on the first side and the second opposite side.

6. The photovoltaic cell (1) according to claim 3, wherein the photovoltaic cell is a cylinder in plan view, characterized in that, The positive peripheral bus describes a total arc of 350°, which has an electrical connection to the periphery of the front collector layer (4) over the entire length of the positive peripheral bus. The positive peripheral bus terminates at a first positive connection terminal (8'a) on a first side and at a second positive connection terminal (8'b) on a second opposite side. The negative peripheral bus, including a negative connection terminal, follows an arc of less than 10°, which has a first positive connection terminal (8'a) and a second positive connection terminal (8'b) of the positive peripheral bus on the first side and the second opposite side.

7. The photovoltaic cell (1) according to claim 1 or 2, characterized in that, Various successive layers, starting from the front collector layer (4), are produced on the inner surface of the glass of the portable object in order to form a single-segment photovoltaic cell assembly together with the glass (2) of the portable object, which forms part of the photovoltaic cell.

8. The photovoltaic cell (1) according to claim 1 or 2, characterized in that, The conductive layer (8) is a metal layer that includes a hollow portion in the central part of the negative connection terminal connected to the negative peripheral busbar so that the photovoltaic cell is semi-transparent.

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