NL2026389B1

NL2026389B1 - Method for producing a multitude of electrically interconnected photovoltaic cells.

Info

Publication number: NL2026389B1
Application number: NL2026389A
Authority: NL
Inventors: Kornelius Dijken Durandus
Original assignee: Atlas Technologies Holding Bv
Priority date: 2020-09-01
Filing date: 2020-09-01
Publication date: 2022-05-04

Abstract

The invention relates to a method for producing a multitude of electrically interconnected photovoltaic cells, the method comprising: . Providing a polygonal segment (300) freed from a semiconductor wafer, the segment showing a photosensitive side and a backside opposite to the photosensitive side, the backside comprising a multitude of cathode electrodes and anode electrodes, the segment showing fracture lines between the cells (302, 304) on or in the photosensitive side and/or the backside of the segment, Characterized in that the method comprises . A step of electrically interconnecting a number of the electrodes, and . A subsequent step of breaking the segment along fracture lines, thereby forming the multitude of electrically interconnected photovoltaic cells. Interconnections are preferably made using a back-contact foil (306) with a connection pattern on it, to which anodes and cathodes are soldered of conductively glued..

Description

Method for producing a multitude of electrically interconnected photovoltaic cells. Technical field of the invention.

[0001] The invention relates to a method for producing a multitude of electrically interconnected photovoltaic cells, the method comprising: ° Providing a polygonal segment freed from a semiconductor wafer, the segment showing a photosensitive side and a backside opposite to the photosensitive side, the backside comprising a multitude of cathode electrodes and anode electrodes, the segment showing fracture lines on or in the photosensitive side or the backside of the segment. Acknowledgement.

[0002] The project leading to this application has received funding from the European Union'’s Horizon 2020 research and innovation program under grant agreement No.

848820. Background of the invention.

[0003] Solar cells, further referred to as cells, have two sides of which one side is a photo-sensitive side. Cells further comprise an anode and a cathode. Typically, the anode is arranged at one side of the cell and the cathode to an opposite side, but cells having an anode and a cathode at only one side {typically the side opposite to the photosensitive side) are known. The cells are cut out from a wafer, such as a silicon wafer.

[0004] If the cell must be curved, the cell is thinned to a thickness of, for example, 60 um. A lower thickness leads to an increased transparency of the cell, and thus a lower efficiency, while a higher thickness leads to increased stiffness and thus a higher risk of fracturing. Although the cell can then bend in one direction, and even in two directions as long as the bending lines do not intersect (thus a local curvature in one direction only), bending in two directions such that the bending lines intersect (for example in a saddle point) is almost impossible: even a slight local bending in two directions results in fracture. Only for very small cells some bending/curvature in two directions is possible before the mechanical stress exceeds the fracture limit.

[0005] Notwithstanding the above-mentioned limitations, for certain applications there is a demand for cells that can be curved in two directions. An example thereof are cells used in a curved roof of a solar car, where such cells are adhered to a curved roof of, for example, glass. An example is the roof of the Lightyear One, a product of Atlas

Technologies B.V., Helmond, the Netherlands. As mentioned, this is possible by using a multitude of small cells.

[0008] It is noted that the curvature of the surface can be concave, convex, or at some places concave and at other places convex. Also saddle points are possible, and (local) flat planes.

[9007] Interconnections can be made with wires {including ribbons and so-called finger wires) or with a flexible foil, a so-called back-contact foil, the flexible foil having a conductive pattern on it to which the cells are connected. There being so many cells implies that many cells must be positioned, either to a transparent surface (a glass roof, bonnet, or such like), with respect to each other or to a flexible foil, and interconnected. A method of mounting the cells to the roof of a vehicle is given in, for example, international patent application publication WQ2020064474A1.

[0008] That a large number of cells is needed that are separately placed on e.g. a transparent surface implies that there are many areas in between the cells, leading to a loss of photosensitive area and thus loss of efficiency

[0009] The invention intends to provide a simpler solution where less positioning is required, and with a higher efficiency. Summary of the invention.

[0010] To that end the method according to the invention is characterized in that the method comprises e A step of electrically interconnecting a number of the electrodes, and » After the step of electrically interconnecting a number of the electrodes, a step of breaking the segment along fracture lines, thereby forming the multitude of electrically interconnected photovoltaic cells.

[0011] By breaking the segment in small cells after connecting the electrodes on the wafer no positioning among the cells (of the segment) is needed. Interconnection of the cells (interconnecting them in series, in parallel, or combinations thereof) can be done on the segment.

[9012] It is noted that a cell may have more than one anode electrode and one cathode electrode, However, for a cell to be used a connection to at least one cathode and one anode of a cell is sufficient.

[0013] It is noted that not all fracture lines need to be broken. The cells will be pressed or adhered to a surface, such as a transparent glass or polycarbonate surface. If the local curvature of the surface is small, or only occurs in one direction, no breaking of (a part of) the fracture lines at the corresponding location is needed.

[0014] As the cells are separated by a small area, only the area needed to break them apart, the photosensitive area is almost identical to the area of the segment.

[0015] In an embodiment a flexible foil is provided with a connection pattern thereon, and the method further comprises a step of positioning the segment to the flexible foil, and the interconnections are formed by soldering or conductive gluing of the electrodes to the connection pattern.

[0016] The interconnections can be formed via a flexible foil (often referred to as a back- contact foil or BCF) with an interconnection pattern on it. Only the BCF and the segment need to be aligned, instead of the multitude of cells and the BCF. This simplifies the positioning by reducing the amount of positionings needed. Soldering and electrically connecting using a conductive glue are methods known as such.

[0017] It is noted that the flexible foil can have a little play by not connecting the electrodes with straight connections to each other, but by connecting them with a slightly meandering pattern between the electrodes.

[0018] In another embodiment the interconnections are made by bonding, soldering or conductive gluing of wires to the electrodes.

[0019] By interconnecting the electrodes on the segment by wires (including ribbons).

Here as well alignment is easier. Bonding, soldering and electrically connecting using a conductive glue are methods known as such.

[0020] In another embodiment, before the segment is broken along fracture lines the segment is at least at one side of the segment adhered to a laminate or encapsulant.

[0021] By adhering at least one side to a laminate or encapsulant, such as EVA (Ethylene Vinyl Acetate) or POE (PolyOlefin Elastomer), a more easily handled slab is obtained. The laminate/encapsulant can be (partly) cured (cross-linked), leaving it flexible, or, especially when applied to both sides of the segment, fully cured. Attachment of the segment to the laminate or encapsulant may take place before interconnecting a number of the electrodes of the segment or after forming the interconnections.

[0022] It is noted that it is also possible to adhere a number of segments to one film of laminate/encapsulant, for example all segments that form the cells for a roof of a vehicle.

[0023] The slab can comprise all segments needed for the panel {curved surface, roof, bonnet), or only a part of the segments needed for the panel.

[0024] It is noted that, after breaking the segment, the laminate may be slightly stretched to create sufficient electrical insulation between the cells.

[0025] In an embodiment the fracture lines are scratches or grooves or a series of notches on or in a side of the segment.

[0026] By forming scratches, grooves and/or notches on or in a side (a surface) of the segment, or on the wafer where the segment is freed from, under mechanical strain the scratches, grooves and/or notches will propagate to the other side of the segment, thereby breaking the segment into smaller parts.

Preferable at least two sets of scratches, grooves or notches are provided, each set consisting of parallel lines, the two sets intersecting each other.

The scratches, grooves and/or notches can be made by lithography and etching, or, for example, by mechanical scratching, laser ablation, etc. Such techniques are well-known to the skilled artisan.

[0027] In another embodiment the step of breaking the segment along the fracture lines involves bending the segment.

[0028] By bending the segment, for example over a cylinder or subsequently over two non-parallel cylinders, the segment is broken in smaller parts.

[0029] The skilled artisan will recognize that each of the axis of the cylinders should be parallel or almost parallel to a set of fracture lines.

[0030] In another embodiment the step of breaking the segment along the fracture lines involves exposing the wafer to a temperature shock.

[0031] By first heating the segment to a high temperature of, for example, 100°C and then dipping it in a fluid with a low temperature of, for example, -40 °C, the temperature shock results in breaking of the segment into cells. Dependent on the thickness of the segment, and its thermal properties, a smaller or larger temperature shock may be necessary.

[0032] In another embodiment the breaking of the segment is performed by pressing the segment against a curved, transparent or translucent surface.

[0033] By pressing the segment against a curved and transparent or translucent surface, such as a glass, plexiglass or polycarbonate (typically the roof of a vehicle), the segment is broken into a multitude of cells. It is noted that this is preferable combined with the segment being adhered to a laminate or encapsulated with, for example EVA. Also other curved transparent parts can be used, such as bonnets, door panels, etc.

Pressing the segment against a curved surface can be achieved by the laminate and the segments being pressed to the transparent or translucent surface by vacuum force (comparable to vacuum forming), or overpressure (comparable to blow moulding).

The panels can be part of, for example cars, coaches, boats, trucks, trains, building element, etc.

[0034] In a further embodiment, after pressing the segment against the curved 5 transparent or translucent surface at least one fracture line is not broken

[0035] If the curved material (the panel, for example a roof, a bonnet, or a door panel) is locally insufficiently curved, one or more of the fracture lines may stay intact (unbroken). This does not offer a problem if the neighbouring cells that are thus not divided by a broken fracture line, are connected in parallel, as for parallelized cells no voltage difference occurs between the surfaces of the adjacent cells.

[00386] In a still further embodiment all cells of a segment are connected in parallel.

[0037] By connecting all cells in parallel, it becomes from an electrical point of view irrelevant if the fracture lines are there or not. This is especially attractive if the panel (vehicle roof, bonnet or such like) is covered with only one type of segments, or a very limited number of versions, and some are broken (where the curvature is relatively large) and some are not or only partly {where the curvature is less or lacking) broken.

[0038] In another embodiment more than one segment is connected to one flexible foil and/or more than one flexible foil is connected to one segment.

[0039] In another embodiment the fracture lines are formed during breaking, the breaking due to laser cleavage or laser ablation.

[0040] Laser cleavage is the processes where a laser locally dumps so much energy in the segment that the segment forms a crack in the segment. Using laser ablation, the material of the material of the segment is locally evaporated.

[0041] The invention further relates to a panel comprising cells manufactured according to any of the preceding claims.

[0042] This relates to vehicles (cars, trucks, coaches, trains, boats, planes) with a panel comprising cells manufactured according to any of the before-mentioned embodiments. Such a panel may thus be a car roof, a boat deck, a train roof, a car bonnet, wings of a (glider) plane, etc., comprising cells manufactured according to any of the before- mentioned embodiments.

Brief description of the drawings.

[0043] The invention is now elucidated using figures, in which identical reference signs indicate corresponding features. To that end:

[0044] Figure 1 schematically shows a wafer from which a segment can be freed,

[0045] Figure 2 schematically shows the photosensitive side of a segment with scratches on its surface,

[0046] Figure 3 schematically shows a flexible foil attached to the backside of the segment.

Detailed description of the invention.

[0047] Figure 1 schematically shows a wafer from which a segment can be freed.

[0048] A wafer 100 showing a photosensitive side (shown) and an opposite with anodes and cathodes, shows a multitude of fracture lines on a surface of wafer. These fracture lines can be formed on the photosensitive side, the opposite side, or both sides. The fracture lines can be lines etched into the surface, they can be made by laser ablation, they can be scratches, or a series of notches. These and alternative methods are known to the skilled artisan. Important is that the fracture lines, when exposed to a mechanical stress below the fracture limit of the bulk material (the non-scratched material), will form a propagating fracture that divides the parts bordering the fracture lines.

[0049] The wafer 100 shows fracture lines 102, 104, 106, 108 that border a segment to be freed from the wafer. The segment is preferable a polygonal segment, so that when laying several of these segments against each other, a plane can be covered. The segment can be triangular, square, rectangular, hexagonal, or another shape.

[0050] First now the segment is freed from other parts of the wafer not being part of the segment, such as part 116.

[0051] It is noted that horizontal and vertical fracture lines (110, 112, 114) for breaking the cells apart may already be present on the wafer, or they may be added to the segment in a later stage. If the fracture lines for the cells are already present on the wafer, they may be limited to the area of the segment (as is the case for fracture lines 110, 112) or they may extend into the parts that are not part of the segment, such as fracture line 114. Breaking the segment out of the wafer may be done by bending the wafer locally at the border of the segment in a manner known to the skilled artisan.

[0052] Figure 2 schematically shows the photosensitive side of a segment with fracture lines on its surface.

[0053] Figure 2 shows a rectangular segment with a multitude of solar cells that are not yet freed from each other. Other forms of segments, such as triangular, hexagonal, octagonal, etc., segments can be used as well, preferably formed such that all segments fit into each other to form a as well as any segment in a shape that fits to the shape of other segments. In this example the cells have different sizes. This is especially useful when locally, for example cell 204, must be fitted to a high curvature location, while cell 206 is to be fitted to a flat or very little curved location.

[0054] The fracture lines may be placed on the photo-sensitive side or on the opposite side. The fracture lines may be shallow, so that the cells at the side where the fracture lines are placed are still electrically interconnected, or sufficiently deep to result in a side where the individual cells are not interconnecting anymore.

[0055] All cells need to have at least one cathode and one anode (here not shown as this is a schematic drawing of the photosensitive side and cathodes and anodes are on the opposite side), but more than one cathode and/or anode on one cell is permitted.

[0056] Itis noted that preferably cells should not be too small, as the border of a cell (roughly a border with a width in the order of the thickness of the cell) does not contribute to its working. A small cell thus shows a lower efficiency than a large cell.

[0057] Figure 3 schematically shows the backside of the segment of figure 2 with a flexible foil soldered thereon.

[0058] Figure 3 schematically shows a segment 300 on which a flexible foil 306 is mounted (soldered, glued with conductive glue). The flexible foil comprises a conductive pattern and the connections between the cells (for example cells 302 and 304) connect these cells in parallel or in series. As an example in this figure all cells in a row along the x-axis can be serialized (connected in series) by a horizontal strip of the flexible foil in the x-axis, while all horizontal strips of the flexible foil are connected in parallel. In another example all cells are parallelized. Other interconnection patterns are possible, resulting in different voltages and currents at a given irradiance. On the flexible foil other components, such as bypass diodes, may be added. The flexible foil may show a flap 308 for easy connection to electronics, such as to a Maximum Power Point Tracker.

[0059] It is noted that one segment may be contacted to several flexible foils, or that one flexible foil may contact several segments, or any combination thereof. A segment is formed from a wafer. Wafer size is nowadays typically 22 cm (9 inch) in diameter. The roof of a vehicle, for example two meters wide and for example three meters long, may thus comprises many segments. It may thus be attractive to have one flexible foil extend over several segment.

[0060] The skilled person will recognize that interconnections can also be made with wires or ribbons. The connections can be formed by bonding, soldering or conductive gluing.

[0061] It is further noted that, if the curved surface is locally not or only slightly curved, the fracture lines will locally not fracture, and several cells may not be divided from each other. This is no problem as long as the cells are connected in parallel, as the voltages on the cells is then identical and the cells operate as one large cell: a low voltage combined with a high current.

[0062] In an extreme example of that a curved surface, such as a roof of a vehicle, is covered with many segments having an identical lay-out. Dependent on the local curvature of the surface, some fracture line will fracture, and some will not. This enables the manufacturing of such a solar cell covered surface with one version of segments, or a limited number of versions of segments.

[0063] If the fracture lines are broken, for example by bending the segments over cylinders, the cells can be connected in series, resulting in a higher voltage combined with a low current.

[0064] It is noted that in the embodiments discussed, often panels with cells having smaller spacing between them can be realized, resulting in higher efficiency per square meter.

[0065] It is noted that some embodiments are illustrated using panels for cars, such as a car roof, a bonnet, or a door panel. The invention is not limited to such panels only, and extend to any surface to be covered with a multitude of photovoltaic cells. This includes, for example, panels for boats, coaches, trucks, trains, building elements, etc.

Claims

Conclusions.

1. A method of producing a plurality of electrically interconnected photovoltaic cells, the method comprising: . providing a polygonal segment (200) freed from a semiconductor wafer (100), the segment having a photosensitive side and a backside opposite the photosensitive side, the backside including a plurality of cathode electrodes and anode electrodes, the segment has fracture lines (102, 104, 108, 108, 110, 112) on or in the photosensitive side or back of the segment, characterized in that the method comprises . a step of electrically connecting a plurality of electrodes together, and . a next step in which the segment is broken along fault lines, thereby forming the plurality of electrically interconnected photovoltaic cells.

The method of claim 1, wherein the method further comprises providing a flexible foil having a bonding pattern thereon, the method further comprising a step of positioning the segment on the flexible foil, and the interconnections are formed by soldering or conductive gluing of the electrodes to the connection cartridge.

Method according to claim 1, characterized in that the mutual connections are made by connecting, soldering or conductively gluing wires to the electrodes.

The method of any preceding claim, wherein before the segment is fractured along fracture lines, the segment is bonded to a laminate or encapsulant on at least one side of the segment.

The method of claim 4, wherein the laminate or encapsulant is a laminate or encapsulant from the group of EVA (ethylene vinyl acetate) or POE (polyolefin elastomer).

A method according to any one of the preceding claims, wherein the fracture lines are scratches or grooves or a series of indentations or on or in a surface of the segment.

A method according to any preceding claim, wherein the step of breaking the segment along the fracture lines includes bending the segment.

The method of claim 7, wherein the bending comprises bending the segment over a cylinder, the cylinder having a longitudinal axis parallel to a portion of the fracture lines.

The method of any preceding claim, wherein the step of breaking the segment along the fracture lines includes exposing the wafer to a temperature shock.

The method of claim 7, wherein bending of the segment is performed by pressing the segment against a curved, transparent or translucent surface.

Method according to claim 10, wherein after pressing the segment against the curved transparent surface at least one fracture line is not interrupted.

The method of claim 11, wherein all cells of a segment are connected in parallel.

A method according to any one of claims 10-12, wherein the curved transparent material is a material from the group consisting of glass, polycarbonate and plexiglass.

The method of claim 2, wherein more than one segment is bonded to one flexible film.

The method of claim 2, wherein more than one flexible film is bonded to one segment.

The method of claim 1, wherein the fracture lines are formed during fracturing, fracturing as a result of laser cleavage or laser ablation.

Vehicle comprising a panel with cells made according to any one of the preceding claims.