Method for coating separating edges of a plurality of separated partial solar cells, and partial solar cell

Abstract

The invention relates to a method for coating separating edges (11a) of a plurality of separated partial solar cells (1) each having a front side (12), a back side (14) and edges (11) extending between the front side (12) and the back side (14), comprising a separating edge (11a), the method comprising the following steps: – providing the plurality of separated partial solar cells (1) in a manner stacked in a carrier element (2) having at least one pocket (21) for receiving the plurality of stacked partial solar cells (1), – coating the separating edges (11a) of the plurality of separated partial solar cells with an a-Si:H passivation layer (3). Furthermore, the invention relates to a partial solar cell (1) which is obtained according to the method, and a partial solar cell (1) which comprises a separating edge (11a) coated with an a-Si:H passivation layer.

Description

[0001] Method for coating separating edges of a plurality of separated partial solar cells and partial solar cells

[0002] The invention relates to a method for coating separating edges of a plurality of separate partial solar cells and to a partial solar cell obtained by such a method. In particular, the invention relates to a method for coating separating edges of a plurality of separate partial solar cells, which are coated with a passivation layer, and to a partial solar cell obtained by the method, and to a partial solar cell having a separating edge with a passivation layer according to the method.

[0003] Partial solar cells are smaller solar cells created by splitting a so-called full solar cell. Solar modules composed of electrically interconnected partial solar cells are also called partial-cell solar modules and have several advantages over solar modules composed of full solar cells. For example, a partial-cell solar module exhibits better low-light performance, offers higher yields in shaded areas, and lower power losses. Splitting full solar cells into two or more partial solar cells is achieved by splitting the full solar cell. However, this process creates at least one exposed, unpassivated separation edge. These unpassivated edges reduce the efficiency of the partial solar cells.

[0004] CN 111430506 A describes a method for passivating separation edges with Al2O3, for example by means of an ALD (atomic layer deposition) process, in which Al2O3 is deposited on the separation edge and the sub-cell is subsequently annealed at up to 500°C to achieve a good passivation effect. There is a need to optimize the subsequent passivation of sub-cell separation edges, since high temperatures during deposition of the Al2O3 and / or annealing can damage the sub-solar cell, e.g. by impairing electrical contacts such as increasing the contact resistance. It is an object of the invention to provide a method for coating separation edges of a large number of separate sub-solar cells and a sub-solar cell that increases the efficiency of the sub-solar cells coated in this way in a cost-effective manner.

[0005] According to the invention, the object is achieved by a method having the features of patent claim 1 and by a partial solar cell having the features of patent claim 12. Advantageous further developments and modifications are specified in the subclaims.

[0006] The invention relates to a method for coating separating edges of a plurality of separate partial solar cells, each having a front side, a back side and edges extending between the front side and the back side, comprising a separating edge, the method comprising the following steps:

[0007] Providing the plurality of separated partial solar cells stacked in a carrier element having at least one pocket for receiving the plurality of stacked partial solar cells, coating the separating edges of the plurality of separated partial solar cells with an a-Si:H passivation layer.

[0008] The a-Si:H layer combines the property of doping-independent, very good chemical passivation effective at a pn junction with a low deposition temperature that is harmless to finished partial solar cells and no or sufficiently low activation temperature. The passivation layer at the separation edge increases the lifetime of the partial solar cell. The a-Si:H layer is preferably 20 to 80 nm thick, more preferably 40 to 80 nm thick. The layer thickness preferably depends on the roughness of the separation edge. The a-Si:H layer is preferably an intrinsic, preferably undoped, a-Si:H layer. For the purposes of the invention, an intrinsic or undoped layer is a layer that is free of foreign atoms, with the exception of any impurities that are technically unavoidable due to the manufacturing process.The coating is applied to a stack of partial solar cells, thus avoiding coating the front and back of the cells, which has no disadvantages in terms of efficiency or later processing, and eliminating the need to separate the partial solar cell stack after the full cells have been separated by a separation process. This makes the process particularly cost-effective and has a high yield. A high throughput of partial solar cells in correspondingly small systems is possible, which leads to comparatively low process costs. With the process, a large number of partial solar cells can be treated simultaneously in a device such as a moderate vacuum apparatus, where the term "moderate" refers to a chamber volume. Deposition processes on individual partial solar cells can also have negative effects due to the coating being applied to the front or back of the cell, for example:Unwanted absorption on the cell surface (loss of efficiency, optical appearance), shadowing at solder contact areas, which can affect further processing. Therefore, coating the separation edges of a stack of partial solar cells is particularly advantageous.

[0009] The term "partial solar cell" refers to a part of a separated solid solar cell. The part comprises a processed and coated substrate, for example in the form of a semiconductor wafer, wherein the surface structures of the semiconductor wafer have at least one front-side electrode and one back-side electrode. The separated solid solar cell is preferably designed such that it is ready for use in a solar module. The partial solar cells subjected to the method according to the invention are then also suitable for direct use in a solar module. The front side of the substrate is a side facing the incident light during operation, and the back side is a side facing away from the incident light. The front side electrode is preferably designed as an electrode finger structure. The edges extend between the front side and the back side and can have one or more separating edges, which are preferably designed as laser separating edges.The separation edges represent open edges after the separation of the full solar cells. Edges that are not separation edges are preferably coated with a layer such as a passivation layer, e.g. made of SiNx.

[0010] In a preferred embodiment, the coating of the separating edges of the plurality of separate sub-solar cells with the a-Si:H passivation layer is carried out at a temperature of less than 250°C, preferably less than 200°C. The passivation of the separating edges with amorphous silicon or a-Si:H is preferably carried out at temperatures of less than 250°C, i.e. in a low-temperature process. As a result, the sub-solar cells are not subjected to as great thermal stress during the coating process as at higher temperatures. At higher process temperatures, in particular above 400°C, there is a risk of degradation effects, e.g. due to activation of recombination centers or material changes, such as oxidation of metal contacts and / or impairment of electrical contacts.

[0011] The coating step preferably comprises a plasma-enhanced coating, more preferably a PECVD (plasma-enhanced chemical vapor deposition) process. This allows the thermal stress on the solar cells to be further reduced. Furthermore, parasitic coating of the front and back sides of the solar cells during the coating process is prevented, since the plasma required for deposition cannot penetrate the narrow micrometer-sized gaps between the stacked cells. Even more preferably, the coating process comprises a capacitively coupled PECVD process with a gas temperature of <200°C.This reduces the stress on the partial solar cells due to ion bombardment and radiation, and the thermal stress on the partial solar cell stack is also significantly lower than, for example, in an inductive low-pressure plasma or a microwave plasma with high plasma power, i.e. plasmas that can reach gas temperatures of > 300 °C due to the higher electron density and high number of collisions between electrons, ions, and neutral particles. The PECVD process is preferably carried out capacitively at 13.56 MHz or using a microwave plasma at 2.45 GHz, so that the partial solar cells are not part of a plasma electrode. Alternatively, the coating preferably comprises a sputtering process. This achieves good adhesion of the deposited passivation layer, while the thermal stress during the coating process is also low. Sputtering is used, for example,from a silicon target, preferably from a planar or rotary target in a hydrogen-containing atmosphere.

[0012] In a further preferred embodiment, the partial solar cells in the PECVD process are first transported through a vacuum door into an infeed and heating chamber in a vacuum system, where they are heated to 200 to 250°C. This is done, for example, using an IR radiator over a period of 2 to 5 minutes. They are then transported to a PECVD chamber where they are plasma-coated with a-Si:H at a maximum temperature of 200 - 250°C. This is done, for example, using a wall heater and at a pressure of, for example, 0.12 to 0.3 mbar, before they are transported out of the system through a vacuum door into an outfeed chamber.

[0013] In a preferred embodiment, the plurality of separate partial solar cells are stacked such that all their separating edges point in the same direction. Preferably, the separating edges to be coated point in the direction of the plasma during plasma coating. The plasma can be, for example, a microwave plasma or a capacitive plasma.

[0014] Preferably, the plurality of separate partial solar cells comprises 100 to 1000 separate partial solar cells per pocket of the carrier element, and the pockets are filled with separate partial solar cells. If the front-side electrode is designed as an electrode finger structure, gaps approximately 20 to 50 μm wide are present between the stacked partial solar cells due to the electrode fingers raised on the surface. A PECVD plasma does not usually penetrate into such narrow gaps due to the plasma edge layer, so that deposition on the front and / or back of the stacked partial solar cells is prevented or at least reduced to a peripheral minimum. Such a parasitic coating on the front and back of the partial solar cells is thereby prevented or at least greatly reduced.

[0015] In a preferred embodiment, the plurality of separate partial solar cells is a plurality of half-cells, third-cells, or quarter-cells. Partial solar cells reduce the current per cell and thus the series resistance losses in the cell connectors connecting the partial solar cells in a solar module. The series resistance losses scale with the square of the current, so that losses are reduced to a quarter by halving the cells and to a ninth by dividing the cells into thirds. Quarter cells have the advantage of improving the current flow in the solar module and increasing efficiency. These solar modules are also less susceptible to cracks and damage because they are smaller and have a higher density of quarter-solar cells. Half-cells preferably each have one separation edge. Quarter cells preferably each have two separation edges. Third-cells can have one or two separation edges.

[0016] Preferably, the depth of the at least one pocket is selected depending on a length dimension of the front and / or rear sides of the plurality of stacked partial solar cells. Preferably, the depth of the at least one pocket is greater for half cells than for third cells, and greater for third cells than for quarter cells. For example, the depth of the at least one pocket for half cells is in the range of 83 to 105 mm. Preferably, the depth of the at least one pocket is selected such that the separating edges to be coated of the partial solar cells stacked in the pocket are flush or substantially flush with the pocket.

[0017] The pocket may have an opening for receiving and coating a separating edge. If the partial solar cells have two separating edges to be coated, the pocket may also be configured to have two openings to allow the two separating edges to be coated to be coated simultaneously. The two openings are preferably configured such that the partial solar cells to be coated are held only at their outer corners and at the edges not to be coated.

[0018] In a preferred embodiment, the number of stacked partial solar cells is selected such that the width of the pocket is filled by more than 80%, preferably more than 90%, of the stacked partial solar cells. This prevents plasma from penetrating gaps between the front and back sides of the stacked partial solar cells, thus preventing or at least greatly reducing parasitic coating on the front and back sides of the partial solar cells.

[0019] Preferably, the coating of the separating edges of the plurality of partial solar cells is carried out using SiH4 and H2 as process gases. Advantageously, the process gases are supplied laterally relative to the separating edges to be coated, or alternatively, preferably in a "showerhead" design, in which the process gases are also supplied centrally relative to the separating edges to be coated.

[0020] In a preferred embodiment, the plurality of separate partial solar cells are stacked such that the front and back sides of all partial solar cells are arranged parallel to each other. This ensures that the separating edges to be coated point in the same direction. Preferably, the front and back sides are aligned parallel to the depth of the pocket.

[0021] Preferably, the partial solar cells of the plurality of separate partial solar cells are designed as TopCon (Tunnel Oxide Passivated Contact) solar cells or PERC (Passivated Emitter and Rear Cell) partial solar cells. TopCon partial solar cells have a relatively high efficiency, a high open circuit voltage, and also low degradation. PERC partial solar cells also have a relatively high efficiency and also efficient low-light behavior. Preferably, the method further comprises a step of arranging a SiNx cover layer on the a-Si:H passivation layer. The SiNx cover layer serves as a protective and / or barrier layer, e.g., against the penetration of moisture into the a-Si:H passivation layer.

[0022] The invention further relates to a partial solar cell obtained by a method according to one or more of the previously described embodiments. The partial solar cell has a higher efficiency than a partial solar cell not subjected to the method according to the invention.

[0023] The invention further relates to a partial solar cell having a separating edge coated with an a-Si:H passivation layer. Alternatively, the partial solar cell has two separating edges, each coated with an a-Si:H passivation layer. Embodiments and advantages described for the method apply accordingly to the partial solar cell. The separating edge represents an edge of the partial solar cell that arises when a full solar cell is divided, for example by laser separation or “thermal laser separation”. The partial solar cell is preferably designed as a TopCon or as a PERC partial solar cell. The a-Si:H passivation layer is preferably intrinsic, i.e. undoped. A SiNx cover layer is preferably arranged on the a-Si:H passivation layer as a protective and / or barrier layer, e.g. against the penetration of moisture into the a-Si passivation layer.

[0024] The invention will be further explained in the following detailed description and the accompanying figures. The figures are purely schematic and not drawn to scale.

[0025] It shows:

[0026] Fig. 1a is a schematic representation of structural elements of a method according to the invention; Fig. 1b is a schematic representation of a variant of the structural elements of the method shown in Fig. 1a

[0027] Fig. 2 is a sketched representation of a variant of the carrier element used in the method shown in Fig. 1a;

[0028] Fig. 3 is a cross-sectional view of a partial solar cell before carrying out the process shown in Fig. 1a;

[0029] Fig. 4 is a cross-sectional view of a partial solar cell after carrying out the method shown in Fig. 1a;

[0030] Fig. 5 is a schematic representation of a variant of the method shown in Fig. 1a.

[0031] Fig. 1a shows a schematic representation of structural elements of a method according to the invention. The method serves to coat separating edges 11a of a plurality of separated partial solar cells 1, each having a front side (not shown), a back side (not shown), and edges 11 extending between the front and back sides, comprising a separating edge 11a. The method comprises the following steps:

[0032] Providing the plurality of separate partial solar cells 1 stacked in a carrier element 2 with at least - here purely by way of example - one pocket 21 for receiving the plurality of stacked partial solar cells 1, coating the separating edges 11a of the plurality of separate partial solar cells with an a-Si:H passivation layer 3.

[0033] The method is carried out in a sealed plasma chamber 23 in which a microwave plasma or a capacitively or inductively coupled high-frequency plasma 4 is generated. The plasma can be generated, for example, by means of a plasma device with the aid of an exchangeable tube 5. The plasma chamber 23 has gas outlets 6 for introducing SiH4 and H2, as indicated by dashed arrows, which serve as process gases for coating the separating edges 11a with the a-Si:H passivation layer 3. The plurality of separated partial solar cells 1 is stacked such that all of their separating edges 11a point in the same direction R. The plurality of separated partial solar cells 1 is, for example, a plurality of half-cells, third-cells, or quarter-cells whose front and back sides have the same length dimension. The pocket 21 is filled with separated partial solar cells 1.A depth T of the at least one pocket 21 is selected depending on a length dimension of the front and / or rear sides of the plurality of stacked partial solar cells 1. A number of stacked partial solar cells 1 is selected such that a width B of the pocket 21 is filled by more than 90% of the stacked partial solar cells 1. For example, 100 half-cells are stacked in the pocket 21. In this case, the pocket 21 has, for example, a width B of 21 to 22 mm, a depth T of 83 mm, and a length (not shown) of 166 mm, relating to the M6 ​​format. For format M10 with an edge length of 200 mm or M12 with an edge length of 210 mm, the depth of the pockets is 100 or 105 mm for half solar cells or 50 / 55 mm for quarter solar cells, whereby the length of the pockets is then 200 or 210 mm.

[0034] Fig. 1b shows a schematic representation of a variant of the structural elements of the process shown in Fig. 1a. The schematic representation of the structural elements corresponds to the schematic representation of the structural elements with the difference that the pocket 21 is open not only on one side, but on two sides, so that partial solar cells 1, which have two separating edges 11a, can be coated with the a-Si-H passivation layer 3 on both separating edges 11a simultaneously in one process step. Furthermore, the plasma chamber, the gas inlets, and the tube have been omitted for the sake of clarity, and the plasma devices generate a plasma 4 to the left and right of the separating edges. However, they can also be located above and below the separating edges 11a.

[0035] Fig. 2 shows a sketched representation of a variant of the carrier element used in the method shown in Fig. 1a. The carrier element 2 shown in Fig. 2 has several pockets 21, each of which can be filled with partial solar cells (not shown). The carrier element 2 has a height H of approximately 100-120 mm. The pockets 21 each have a depth T of 83 to 105 mm, which is designed to accommodate half-cells. The pockets 21 each have a width B, which depends on the number of partial solar cells to be coated. It is selected such that the half-cells are compactly stacked in the pockets 21.

[0036] Fig. 3 shows a cross-sectional view of a partial solar cell before carrying out the method explained in Fig. 1a. The partial solar cell has a substrate 9 in the form of a semiconductor wafer. A p+ layer 8 is formed on a front side 12 of the substrate 9. An n-tail 10, an oxide 15, and an n-poly Si layer 16 are provided on the back side 14 of the substrate 9. A SiNx passivation layer is arranged on the front side 12, the back side 14, and an edge 11 extending between the front side 12 and the back side 14, of which a separating edge 11a extending between the front side 12 and the back side 14 is free. Furthermore, metal contacts 7 are arranged on both the front side 12 and the back side 14 as front and back electrodes in the form of electrode finger structures.

[0037] Fig. 4 shows a cross-sectional view of a partial solar cell after performing the process shown in Fig. 1a. The partial solar cell 1 shown in Fig. 4 corresponds to the partial solar cell 1 shown in Fig. 3, with the difference that the separating edge 11a is coated with an a:Si:H passivation layer 3.

[0038] Fig. 5 shows a sketch of a variant of the process shown in Fig. 1a. In this variant, the carrier element 2 shown in Fig. 2 with partial solar cells (not shown) is transported in a transport direction TR. In a PECVD process, the carrier element 2 is first transported through a vacuum door 18 into an infeed and heating chamber 22, in which the partial solar cells are heated to approximately 200 °C using an IR radiator for a period of 2 to 20 minutes. Then, the carrier element 2 together with the partial solar cells is transported through a transfer gate 19 into a PECVD chamber 23, in which the partial solar cells are plasma-coated with a-Si:H at a temperature of 150 - 250 °C, using a wall heater and at a pressure of, for example, 0.1 to 0.3 mbar.Subsequently, the carrier element 2 together with the partial solar cells is transported through a further transfer gate 19 into an ejection chamber 24 and then ejected from the system through a further vacuum door 18.

[0039] The support element 2 shown here has ten pockets 21, with each pocket 21 containing, for example, 100 partial solar cells stacked in the form of half-cells, so that a total of 1000 partial solar cells can be accommodated in the support element 2. The pockets 21 each have a width B of 166 mm. The support element 2 has a support element length TL in the range of 300 to 350 mm and a support element width TB in the range of 400 to 450 mm.

[0040] List of reference symbols:

[0041] B Width

[0042] H Height

[0043] TB support element width

[0044] TL support element length

[0045] R direction

[0046] TR transport direction

[0047] T Depth

[0048] 1 partial solar cells

[0049] 2 support element

[0050] 3 Passivation layer

[0051] 4 Plasma

[0052] 5 pipe

[0053] 6 Gas outlet

[0054] 7 Metal contact

[0055] 8 p+ layer

[0056] 9 Substrat

[0057] 10 n-tail

[0058] 11 edge

[0059] 11a Separating edge

[0060] 12 Front

[0061] 14 Back

[0062] 15 Oxide

[0063] 16 n-poly Si layer

[0064] 17 SiN coating

[0065] 18 Door

[0066] 19 Transfer Gate

[0067] 21 bag

[0068] 22 Inlet chamber

[0069] 23 PECVD chamber

[0070] 24 Discharge chamber

Claims

Patent claims: 1 . Method for coating separating edges (11a) of a plurality of separate partial solar cells (1 ) each having a front side (12), a back side (14) and edges (11 ) extending between the front side (12) and the back side (14), comprising a separating edge (11a), the method comprising the following steps: Providing the plurality of separate partial solar cells (1) stacked in a carrier element (2) with at least one pocket (21) for receiving the plurality of stacked partial solar cells (1), coating the separating edges (11a) of the plurality of separate partial solar cells with an a-Si:H passivation layer (3).

2. Method according to claim 1, characterized in that the coating of the separating edge (11a) of the plurality of separated partial solar cells with the a-Si:H passivation layer (3) is carried out at a temperature of less than 250° C, preferably less than 200° C.

3. The method according to claim 1 or 2, characterized in that the coating comprises a plasma coating, preferably a PECVD process, more preferably a capacitively coupled PECVD process or sputtering.

4. Method according to one of the preceding claims, characterized in that the plurality of separated partial solar cells (1) are stacked such that all their separating edges (11a) point in a same direction (R).

5. Method according to one of the preceding claims, characterized in that the plurality of separate partial solar cells (1) has 100 to 1000 separate partial solar cells (1) per pocket (21) of the carrier element (2) and the pockets (21) are filled with separate partial solar cells (1).

6. Method according to one of the preceding claims, characterized in that the plurality of separate partial solar cells (1) is a plurality of half cells, third cells or quarter cells.

7. Method according to one of the preceding claims, characterized in that a depth (T) of the at least one pocket (21) is selected as a function of a length dimension of the front and / or rear sides (12, 14) of the plurality of stacked partial solar cells (1).

8. Method according to one of the preceding claims, characterized in that a number of stacked partial solar cells (1) is selected such that a width (B) of the pocket (21) is filled by the stacked partial solar cells (1) to more than 80%, preferably to more than 90%.

9. Method according to one of the preceding claims, characterized in that the coating of the separating edges (11a) of the plurality of partial solar cells (1) is carried out using SiH4 and H? as process gases.

10. Method according to one of the preceding claims, characterized in that the plurality of separate partial solar cells (1) are provided stacked in such a way that the front and rear sides (12, 14) of all partial solar cells (1) are each arranged parallel to one another.

11. Method according to one of the preceding claims, characterized in that the partial solar cells (1) of the plurality of separate partial solar cells (1) are designed as TopCon solar cells or PERC partial solar cells.

12. Method according to one of the preceding claims, characterized by arranging a SiNx cover layer on the a-Si:H passivation layer (3).

13. Partial solar cell (1) obtained by a method according to one of the preceding claims.

14. Partial solar cell (1), comprising one or two separating edges (11a), each of which is or are coated with an a-Si:H passivation layer, preferably each coated with an intrinsic a-Si:H passivation layer, wherein the a-Si:H passivation layer(s) are preferably coated with a SiN x - top layer is or are covered.

15. Partial solar cell (1) according to claim 13 or 14, which is designed as a TopCon or as a PERC partial solar cell.

16. Partial solar cell (1) according to one of claims 13 to 15, characterized in that the a:Si passivation layer (3) has a layer thickness in the range of 20 to 80 nm, preferably 40 to 80 nm.

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