OPTIMISED SOLAR CELL, SOLAR CELL MODULE AND METHOD OF MANUFACTURING THEREOF

Abstract

The present invention concerns a bifacial solar cell (1) comprising a front side (10) and a back side (20), said front and back sides (10, 20) having a respective outer layer (34) made of transparent conductive oxide, on which is placed a respective metallization grid (11, 21), each metallization grid (11, 21) comprising first collectors (111, 211) running parallel to each other in a horizontal direction (x) of said solar cell (1) and second collectors (112, 212) crossing said first collectors (111, 211), each second collector (112, 212) comprising two vertical elements (112a, 112b, 212a, 212b) and at least one horizontal element (112c, 212c) every one or two first collectors (111) or 3 or 6 first collectors (211) connecting said two vertical elements (112a, 112b, 212a, 212b), said solar cell module being characterized in that said metallization grids (11, 21) furtherly comprise at least one respective front or back area (113, 213), said front or back area (113, 213) comprising said at least one horizontal element (112c, 212c) and a portion of the underlying outer layer (34) made of transparent conductive oxide, so that a cell connector can be attached to said solar cell (1) by means of an electrically conductive adhesive deposited on said front or back area (113, 213) without needing a physical barrier for said electrically conductive adhesive. The present invention also concerns a solar cell module and a method of manufacturing thereof.

Claims

1. Solar cell module comprising a first and a second bifacial solar cell (1), each solar cell (1) comprising a front side (10) and a back side (20), said front and back sides (10, 20) having a respective outer layer (34) made of transparent conductive oxide, on which is placed a respective metallization grid (11, 21), each metallization grid (11, 21) comprising first collectors (111, 211) running parallel to each other in a horizontal direction (x) of said solar cell (1), and second collectors (112, 212) crossing said first collectors (111, 211), each second collector (112, 212) comprising two vertical elements (112a, 112b, 212a, 212b) and at least one horizontal element (112c, 212c), connecting said two vertical elements (112a, 112b, 212a, 212b), wherein said metallization grid (11, 21) furtherly comprises respective front or back areas (113, 213), said front or back areas (113, 213) comprising said at least one horizontal element (112c, 212c) and a portion of the underlying outer layer (34) made of transparent conductive oxide, and being apart from each other of a distance, said solar cell module being characterised in that it comprises a cell connector, said cell connector comprising a first portion connected in a non-continuous way to said front areas (113) of said first solar cell (1) by means of an electrically conductive glue deposited in spots on said front areas (113), said cell connector comprising also a second portion connected in a non-continuous way to said back areas (213) of said second solar cell (1) by means of an electrically conductive glue deposited in spots on said back areas (213).

2. Solar cell module according to claim 1, characterized in that each vertical element (112a, 112b, 212a, 212b) comprises protrusions (112d, 212d) in correspondence of each first collector (111, 211), said protrusions (112d, 212d) horizontally protruding from said vertical elements (112a, 112b, 212a, 212b) so as to extend the total horizontal size of said second collectors (112, 212) in order to guarantee reliable current measurements on said solar cell (1).

3. Solar cell module according to claim 1, characterized in that said solar cell (1) is a HJT solar cell.

4. Solar cell module according to claim 1, characterized in that each horizontal element (112c, 212c) crosses said two vertical elements (112a, 112b, 212a, 212b) and is placed in correspondence of a respective first collector (111, 211).

5. Solar cell module according to claim 1, characterized in that said first collectors (211) on said back side (20) are triple the number of said first collectors (111) on said front side (10).

6. Solar cell module according to claim 1, characterized in that on said front side (10) there is one horizontal element (112c) for each first collector (111) or every two first collectors (111).

7. Solar cell module according to claim 1, characterized in that on said back side (20) there is one horizontal element (212c) every three first collectors (211) or every six first collectors (211).

8. Solar cell module according to claim 1, characterized in that said back area (213) is greater in size than said front area (113).

9. (canceled)

10. Method for connecting a first and a second bi-facial solar cells (1) in a solar cell module, each solar cell (1) comprising a front side (10) and a back side (20), said front and back sides (10, 20) having a respective outer layer (34) made of transparent conductive oxide, on which is placed a metallization grid (11, 21), each metallization grid (11, 21) comprising first collectors (111, 211) running parallel to each other in a horizontal direction (x) of said solar cell (1) and second collectors (112, 212) crossing said first collectors (111, 211), each second collector (112, 212) comprising two vertical elements (112a, 112b, 212a, 212b) and at least one horizontal element (112c, 212c) connecting said two vertical elements (112a, 112b, 212a, 212b), said solar cell module comprising furtherly a cell connector, said method being characterized by comprising the following steps: a) deposit spots of electrically conductive glue on the front side (10) of said first solar cell (1) in a non-continuous way, each spot being deposited in correspondence of said horizontal element (112c), said adhesive covering said horizontal element (112c) and a portion of said outer layer (34) comprised between said two vertical elements (112a, 112b); b) deposit spots of electrically conductive glue on the back side (20) of said second solar cell (1) in a non-continuous way, each spot being deposited in correspondence of said horizontal element (212c), said adhesive covering said horizontal element (212c) and a portion of said outer layer (34) comprised between said two vertical elements (212a, 212b); c) attach a first portion of said cell connector to said electrically conductive glue deposited in step a) and a second portion of said cell connector to said electrically conductive adhesive deposited in step b), so as to connect said front side (10) of said first solar cell (1) to said back side (20) of said second solar cell (1).

11. Method according to claim 10, characterized in that said electrically conductive glue deposited in step a) does not extend beyond said two vertical elements (112a, 112b).

12. Method according to claim 10, characterized in that said electrically conductive glue deposited in step b) extends beyond said two vertical elements (212a, 212b).

13. (canceled)

Description

[0053] The present invention will now be described, for illustrative but not limitative purposes, according to its preferred embodiment, with particular reference to the figures of the accompanying drawings, wherein:

[0054] FIG. 1 shows a transversal section of a known HJT solar cell;

[0055] FIG. 2 shows the front view of a known solar cell metallization grid;

[0056] FIG. 3a shows the front view of a portion of the front side of a solar according to the invention;

[0057] FIG. 3b shows an enlargement of FIG. 3a;

[0058] FIG. 4a shows the rear view of a portion of the back side of the solar of FIG. 3a;

[0059] FIG. 4b shows an enlargement of FIG. 4a;

[0060] FIG. 5 shows the front view of a portion of the front side of a solar cell according to the invention, wherein has been marked, with a rectangular shape, the front area where an electrically conductive adhesive will be placed according to the present invention;

[0061] FIG. 6 shows the rear view of a portion of the back side of the solar cell of FIG. 5, wherein has been marked, with a rectangular shape, the back area where an electrically conductive adhesive will be placed according to the invention;

[0062] FIG. 7 shows a front view of a portion of the front side of a solar cell according to the invention wherein the electrically conductive adhesive has been already applied, the image was obtained through an optical microscope.

[0063] With reference to FIGS. 3-7, a solar cell 1 according to the present invention has a front side 10 and a rear side 20.

[0064] The solar cell 1 is preferably a HJT solar cell 1, similar to the HJT solar cells 1 known in the state of the art, comprising a central layer 3 made of c-Si, preferably n-type c-Si, or c-Si(n), two middle layers 31 made of hydrogenated amorphous Silicon a-Si:H, surrounding said central layer 3; a first front layer 32 made of n+ hydrogenated amorphous Silicon a-Si:H(n+) and a first back layer 33 made of p+ hydrogenated amorphous Silicon a-Si:H(p+), in contact with one respective middle layer 31, said first front layer 32 being in correspondence of the front side 10 of the solar cell 1 and said first back layer 33 being in correspondence of the back side 20 of the solar cell 1, both said first front and back layers 32, 33 being covered by an outer layer 34 made of conductive material, preferably TCO.

[0065] Each side 10, 20 of the solar cell 1 comprises also a respective external metallization grid 11, 21, comprising first collectors 111, 211, or fingers 111, 211, running parallel to each other in a horizontal direction x of said solar cell.

[0066] Preferably, the distance between each finger 111, 211 on the respective side 10, 20 is constant.

[0067] In particular, the number of fingers 211 on the back side 20 is greater than the number of fingers 111 on the front side 10, preferably triple, in order to decrease the electrical resistance of the fingers, without excessively limiting the active area of the cell.

[0068] Each side 10, 20 of the solar cell 1 comprises also second collectors 112, 212, or bus bars 112, 212, running in a vertical direction y of said solar cell, said vertical direction y being transversal to said horizontal direction x.

[0069] Specifically, each bus bar 112, 212 of each side 10, 20 comprises two vertical elements 112a, 112b, 212a, 212b and a plurality of horizontal elements 112c, 212c, or pads 112c, 212c, which connect said two vertical elements 112a, 112b, 212a, 212b.

[0070] In particular, each horizontal element 112c, 212c is placed in correspondence of a finger 111, 211. However, on the front side 10 one horizontal element 112c is preferably placed at each finger 111 or every two fingers 111, while on the back side 20 the number of said horizontal elements 212c is less than the number of fingers 211, preferably one third the number of fingers 211, more preferably one horizontal element 211c being placed every three or six fingers 211.

[0071] In particular, the preferred distance between two consecutive vertical elements 112a, 112b, 212a, 212b of each bus bar 112, 212 on each side 10, 20 can vary between 0.055-0.065 mm, preferably being equal to 0.6 mm, while the preferred distance between two consecutive pads 112c, 212c on each side 10, 20 is in the range between 1.795-1.805 mm, preferably equal to 1.8 mm.

[0072] Furthermore, the preferred distance between two consecutive fingers on the back side is equal to 0.6 mm.

[0073] Additionally, each bus bar 112, 212 comprises a plurality of protrusions 112d, 212d, or micro-pads 112d, 212d, which protrude horizontally from said vertical elements 112a, 112b, 212a, 212b, increasing the horizontal size of said bus bars 112, 212.

[0074] Preferably, the total horizontal size of each bus bar 112, 212 with said protrusions 112d, 212d is equal to 0.9 mm.

[0075] In particular, the horizontal size of each micro-pad 112d, 212d can vary between 0.895-0.905 mm.

[0076] Specifically, each bus bar 112, 212 on the front 10 and on the back side 20 of the cell 1 comprises a protrusion 112d, 212d for each finger 111, 211 connected to said bus bar 112, 212.

[0077] The above-described layout allows an easy gluing of a cell connector, or ribbon, which connect two adjacent solar cells 1 between each other.

[0078] In particular, a ribbon usually connects the front side 10 of a first solar cell 1 to the back side 20 of a second solar cell 1.

[0079] In fact, an electrically conductive adhesive, preferably an electrically conductive glue, can be placed on the front side 10 and/or on the back side 20 of the cell in correspondence of each pad 112c, 212c, so as to partially overlap the conductive layer 34 made of TCO underlying the metallization grid.

[0080] When such adhesive is placed on the cell 1, it will therefore cover a front area 113 on the front side 10 of the cell 1 and/or a back area 213 on the back side 20 of the cell 1.

[0081] Therefore, the cell 1 is provided with non-continuous front areas 113 and back areas 213 and the electrically conductive glue will be deposited in spots on said front areas 113 and/or on said back areas 213 of the cell 1 in a non-continuous way.

[0082] In particular, the front areas 113 will be distanced from one another of a first distance and the back areas 213 will be distanced from one another of a second distance.

[0083] Therefore, in such configuration, the ribbon will be attached only to said intermittent areas 113, 213 of the cell 1, reducing the total consumption of electrically conductive adhesive, if compared to the use of electrically conductive tape, which completely covers the bus-bar.

[0084] The preferred size of the areas 113, 213 covered by electrically conductive adhesive is 0.5×0.7 mm.sup.2 for the front side 10 and 0.7×0.7 mm.sup.2 for the back side 20 of the cell 1, wherein 0.5 mm and 0.7 mm respectively represent the horizontal and the vertical edges of such areas.

[0085] In fact, due to possibly less accurate positioning systems for said electrically conductive adhesive on the back side 20 of the cell 1, the back area 213 covered by electrically conductive adhesive should be greater in size than the front area 113 covered by electrically conductive adhesive.

[0086] Advantageously, the proposed shape of the bus bar 112, 212 acts as a pilot hole for the electrically conductive adhesive, limiting the total thickness of a solar cell module made by different stacked layers (e.g. silver contact+ ECA+ribbon). This also reduces the mechanical stresses induced on the solar cells 1 during the encapsulation process and therefore the possible crack that can be formed on the cells 1. Stress reduction may also lead to a better module reliability during the module life.

[0087] Also, said layout advantageously allows maintaining high electrical performances of said solar cells 1. In particular, cell electrical performance measurements can be done by means of a set of micro-tips placed on the bus bars 112, 212 on both sides 10, 20. Specifically, such micro-tips can be placed either on the pads 112c, 212c or on the vertical elements 112b, 212b. In fact, the pads 112c, 212c and vertical elements 112b, 212b sizes have been selected in order to achieve precise measurements also is case of possible tips misalignments.

[0088] Therefore, thanks to the proposed metallization layout of the cell, the silver paste consumption can be reduced, maintaining the cell electrical performance.

[0089] In fact, in order to have a reliable measurement of the cell 1 electrical performance, a good contact is needed between the tips and the measured bus bar 112, 212, together with an accurate placement of the tips on said bus bar 112, 212.

[0090] Therefore, tips size and position on cell 1 have been optimized in order to maintain a good electrical contact between each tip and the aforementioned bus bar 112, 212.

[0091] It is worth to notice that the bus bar 112, 212 metallization layout can be applied to different kinds of solar cell 1. Therefore, also the proposed method of gluing a ribbon to the bus bars 112, 212 for connecting together a plurality of solar cells 1 can be applied to different kind of solar cells 1.

[0092] However, in case of HJT solar cells 1 such solution is particularly advantageous.

[0093] In fact, the adhesion of electrically conductive adhesive performs better on TCO rather than on silver paste. Such better adhesion results in better peel strength within limited areas 113, 213 of the cell 1.

[0094] Furthermore, because of such better adhesion the adhesive consumption can be reduced, leading to a reduction of the production costs. In fact, electrically conductive adhesive usually comprises silver, and is therefore an expensive element. The good adhesion of ECA on TCO, allowed by the proposed metallization layout, advantageously does not require any kind of physical barrier for the adhesive, such as the presence of a separated auxiliary bus bar made of two additional external vertical lines surrounding the main bus bar 112, 212. Therefore, the proposed layout does not lead to any interruption of the current, and reduces the overall resistance of the cell 1. Furthermore, such good adhesion does not require the presence of any extra non-conductive layer in the solar cell 1, maximizing the areas exposed to light.

EXAMPLE 1

[0095] The above described metallization layout was tested on HJT solar cells 1 and solar cell modules. The following results were obtained: [0096] comparable solar cell 1 and solar cell module performance to other known HJT cell; [0097] reduced silver consumption, of at least 10%, if compared with other known HJT cells; [0098] reliable cell electrical performance measurement (with appropriate tool settings); and [0099] reliable peel strength after ribbon adhesion.

[0100] The tests were made on a large number of solar cells 1 (more than 50,000 solar cells were processed with good electrical performances).

[0101] The measured peel force of a ribbon attached on said front or back areas 113, 213 by means of said electrically conductive adhesive was always greater than 1 N/mm. This value is comparable with values obtained on straight bus bars or straight ECA dispensing.

[0102] The present invention has been described for illustrative but not limitative purposes, according to its preferred embodiment, but it is to be understood that variations and/or modifications can be made by those skilled in the art without departing from the scope of the claims, as defined by the annexed claims.