Solar cell and method for manufacturing the same

Abstract

The present invention provides a solar cell and a preparation method thereof, which belongs to the technical field of solar cells, and can at least partially solve the problem that the back electrode formed by electroplating in the existing solar cells has poor adhesion, or the preparation process is complicated and the efficiency is reduced. The solar cell preparation method of the present invention comprises: forming a passivation structure on the contact silicon layer on the back side of the silicon substrate; the back side is the side opposite to the light incident side; using a laser to remove the passivation structure at least part of the position of the electrode area to form a contact opening, using a laser to melt at least part of the contact silicon layer at the contact opening, and solidifying the melted contact silicon layer to form a re-solidified structure; the electrode area is an area for forming a back electrode; electroplating is performed to form a back electrode in the electrode area on the back side of the contact silicon layer.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cells, and in particular relates to a solar cell and a preparation method thereof. Background Art

[0002] In a passivated contact solar cell, such as a TOPCon (tunneling oxide passivation) solar cell or a HJT (silicon heterojunction) solar cell, a back electrode can be formed on the back side thereof using an electroplating process.

[0003] However, the existing back electrodes formed by electroplating have poor adhesion, or the preparation process is complicated and the efficiency is reduced. Summary of the invention

[0004] The present invention at least partially solves the problem that the back electrode formed by electroplating in existing solar cells has poor adhesion, or the preparation process is complicated and the efficiency is reduced, and provides a solar cell and a preparation method thereof that can make the back electrode formed by electroplating have strong adhesion without increasing the preparation steps and reducing the cell efficiency.

[0005] In a first aspect, an embodiment of the present invention provides a method for preparing a solar cell, comprising:

[0006] A passivation structure is formed on the contact silicon layer on the back side of the silicon substrate; the back side is the side opposite to the light incident side;

[0007] Using a laser to remove the passivation structure at least partially at the electrode region to form a contact opening, using a laser to melt at least partially the contact silicon layer at the contact opening, and solidifying the melted contact silicon layer to form a re-solidified structure; the electrode region is a region for forming a back electrode;

[0008] Electroplating is performed to form a back electrode in the electrode region on the back side of the contact silicon layer.

[0009] Optionally, removing the passivation structure at least partially at the electrode region by laser to form a contact opening, and melting at least partially the contact silicon layer at the contact opening by laser comprises:

[0010] Using laser to irradiate the passivation structure at least partially in the electrode region, and evaporate and remove the irradiated passivation structure to form a contact opening;

[0011] The contact silicon layer is irradiated with laser light at least at a portion of the contact opening to melt the contact silicon layer.

[0012] Optionally, the pulse duration of the laser used to evaporate and remove the passivation structure is 1 ps to 30 ps, ​​and the energy density is 0.2 J / cm 2 Up to 1.2J / cm2 ;

[0013] The pulse duration of the laser used to melt the contact silicon layer is between 1 ns and 50 ns, and the energy density is between 0.1 J / cm 2 Up to 0.5J / cm 2 .

[0014] Optionally, the pattern of the laser used to evaporate and remove the passivation structure includes a plurality of non-overlapping first light spots, and the radial size of each of the first light spots is between 40 μm and 60 μm;

[0015] The pattern of the laser used to melt the contact silicon layer includes a second spot located at the center of each of the first spots, and the radial size of each of the second spots is between 20 μm and 40 μm and is smaller than the radial size of the first spot where it is located.

[0016] Optionally, the step of removing at least a portion of the passivation structure at the electrode region using a laser to form a contact opening comprises:

[0017] irradiating the passivation structures at a plurality of spaced positions of the electrode region with a laser, removing the irradiated passivation structures to form contact openings, and causing the edge portions of the remaining passivation structures close to the contact openings to warp;

[0018] Wherein, the thickness of the back electrode is greater than the thickness of the passivation structure.

[0019] Optionally, an angle between a raised edge portion of the passivation structure closest to the contact silicon layer and the contact silicon layer is in a range of 15° to 60°.

[0020] Optionally, a maximum distance between the raised edge portion of the passivation structure and the contact silicon layer is in a range of 250 nm to 2000 nm.

[0021] Optionally, along a direction from the raised edge portion of the passivation structure to the center of the passivation structure, a size of an orthographic projection of the raised edge portion of the passivation structure on the contact silicon layer is in a range of 1 μm to 4 μm.

[0022] Optionally, the raised edge portion of the passivation structure is a curved surface structure.

[0023] Optionally, the distance between two adjacent spacing positions is between 1 μm and 20 μm.

[0024] Optionally, the thickness of the passivation structure is between 50 nm and 200 nm;

[0025] The thickness of the back electrode is 1 μm to 12 μm.

[0026] Optionally, the depth of the resolidified structure is between 30 nm and 1000 nm.

[0027] Optionally, a tunneling layer is provided on the back side of the silicon substrate;

[0028] The contact silicon layer is a polysilicon layer located at the back side of the tunnel layer.

[0029] Optionally, before forming the passivation structure on the contact silicon layer on the back side of the silicon substrate, the method further includes:

[0030] The back side of the contact silicon layer is polished.

[0031] In a second aspect, an embodiment of the present invention provides a solar cell, comprising:

[0032] A silicon substrate, wherein the back side of the silicon substrate has a contact silicon layer; the back side is the side opposite to the light incident side;

[0033] A passivation structure is provided on the back side of the contact silicon layer, wherein the passivation structure has a contact opening formed by laser at at least a portion of the electrode region, and at least a portion of the contact silicon layer at the contact opening is a resolidified structure; the electrode region is a region for forming a back electrode, and the resolidified structure is a structure formed by solidifying the contact silicon layer after being melted by laser;

[0034] A back electrode is arranged at the electrode region; the back electrode is located at a side of the passivation structure away from the silicon substrate and is formed by electroplating on the contact silicon layer.

[0035] Optionally, there are a plurality of spaced contact openings in the electrode region, and edge portions of the passivation structure close to the contact openings are raised;

[0036] The thickness of the back electrode is greater than the thickness of the passivation structure.

[0037] Optionally, the solar cell further satisfies at least one of the following conditions:

[0038] The angle between the raised edge of the passivation structure closest to the contact silicon layer and the contact silicon layer is 15° to 60°;

[0039] The maximum distance between the raised edge portion of the passivation structure and the contact silicon layer is 250nm to 2000nm;

[0040] Along the direction from the raised edge portion of the passivation structure to the center of the passivation structure, the size of the orthographic projection of the raised edge portion of the passivation structure on the contact silicon layer is 1 μm to 4 μm;

[0041] The raised edge portion of the passivation structure is a curved surface structure;

[0042] The distance between two adjacent contact openings is 1 μm to 20 μm.

[0043] Optionally, the thickness of the passivation structure is between 50 nm and 200 nm;

[0044] The thickness of the back electrode is 1 μm to 12 μm.

[0045] Optionally, the depth of the resolidified structure is between 30 nm and 1000 nm.

[0046] Optionally, a tunneling layer is provided on the back side of the silicon substrate;

[0047] The contact silicon layer is a polysilicon layer located at the back side of the tunnel layer.

[0048] According to an embodiment of the present invention, when or after the passivation structure on the back side of the solar cell is laser grooved to form a contact opening, the contact silicon layer at the contact opening is melted by laser, and the re-solidified structure is formed after solidification again, and then the back electrode is formed by electroplating on the re-solidified structure; wherein, the re-solidified structure is not specially grown and has not been polished, so its surface is rough and the contact area with the back electrode is large, so the electroplated back electrode can ensure strong adhesion; at the same time, the re-solidified structure and the contact opening are both formed by laser, so it can be achieved by simply changing the process parameters of the laser groove, etc., without adding a separate step, so the preparation process is simple; in addition, only the back side of the contact silicon layer corresponding to the back electrode forms a relatively rough re-solidified structure, while most of the back side of the contact silicon layer remains smooth, and the proportion of the rough surface is very small, so it will not affect the battery efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A schematic diagram of a process for preparing a solar cell according to an embodiment of the present invention;

[0050] Figure 2 A schematic diagram of a process of another method for preparing a solar cell according to an embodiment of the present invention;

[0051] Figure 3 is a schematic cross-sectional structure diagram of a solar cell according to an embodiment of the present invention;

[0052] Figure 4 It is a schematic diagram of a partial cross-sectional structure of a middle electrode region of another solar cell according to an embodiment of the present invention;

[0053] Figure 5 It is a schematic diagram of a local cross-sectional structure of an electrode region after a passivation structure is formed in another solar cell according to an embodiment of the present invention;

[0054] Figure 6A schematic diagram of a local cross-sectional structure of an electrode region after a contact opening is formed in another solar cell according to an embodiment of the present invention;

[0055] Figure 7 A schematic diagram of a local cross-sectional structure of an electrode region after a resolidified structure is formed in another solar cell according to an embodiment of the present invention;

[0056] Figure 8 A schematic diagram of a partial cross-sectional structure of a raised edge portion of a passivation structure in another solar cell according to an embodiment of the present invention;

[0057] Fig. 9 A schematic diagram of the distribution of laser spots during the preparation of another solar cell according to an embodiment of the present invention;

[0058] Fig.10 A schematic diagram of a pattern of a back electrode in another solar cell according to an embodiment of the present invention;

[0059] Among them, the figure markings are: 1, silicon substrate; 11, resolidification structure; 2, passivation structure; 21, contact opening; 3, back electrode; 31, main grid line; 32, fine grid line; 5, contact silicon layer; 91, first light spot; 92, second light spot. DETAILED DESCRIPTION

[0060] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0061] It should be understood that the specific embodiments and drawings described herein are only used to explain the present invention rather than to limit the present invention.

[0062] It can be understood that, in the absence of conflict, the various embodiments of the present invention and the various features therein can be combined with each other.

[0063] It can be understood that, for the convenience of description, the drawings of the present invention only show the parts related to the embodiments of the present invention, while the parts unrelated to the embodiments of the present invention are not shown in the drawings.

[0064] TOPCon (tunneling oxide passivation) solar cells, HJT (silicon heterojunction) solar cells, etc. are passivated contact solar cells, that is, one or more passivation layers that play a field passivation role are formed on the back side of the solar cell. Therefore, compared with PERC (passivated emitter and back side) solar cells, the cell efficiency of the passivated contact solar cell is further improved, for example, its cell efficiency can exceed 25%.

[0065] If the passivated contact solar cell adopts the silver paste sintering method to form the electrode (grid line), the proportion of silver paste cost will increase significantly (from 10-11% of PERC cells to 16-24%), thus limiting its wider application.

[0066] To this end, in some related technologies, grooves can be formed in the passivation layer on the back side of the passivated contact solar cell by laser to expose a conductive structure for contacting the back electrode (such as a contact silicon layer), and a back electrode is formed on the exposed contact silicon layer by electroplating to reduce costs.

[0067] However, the back side of the solar cell is not used for light entry, so the back side of the silicon layer in contact is usually not chemically textured, and even needs to be polished, so it is a smooth surface, resulting in a small contact area with the electrode, and the back electrode formed by electroplating has poor adhesion and is easy to fall off.

[0068] If the back side of the contact silicon layer is also chemically textured to increase the contact area and improve the adhesion of the back electrode, on the one hand, it is necessary to increase the texturing step, which makes the preparation process complicated. On the other hand, the formation of the textured surface on the back side will lead to increased optical parasitic absorption and reduced battery efficiency.

[0069] First, refer to Figures 1 to 10 , an embodiment of the present invention provides a method for preparing a solar cell.

[0070] The method for preparing a solar cell according to an embodiment of the present invention is used to form a solar cell, especially a passivated contact solar cell (ie, a solar cell having a passivation layer on the back side), such as a TOPCon solar cell, a HJT solar cell, etc.

[0071] Reference Figure 1 , the method for preparing a solar cell according to an embodiment of the present invention comprises:

[0072] S101 , forming a passivation structure 2 on the contact silicon layer 5 on the back side of the silicon substrate 1 .

[0073] The back side is the side opposite to the light incident side.

[0074] S102 , using a laser to remove at least a portion of the passivation structure 2 in the electrode region to form a contact opening 21 , using a laser to melt at least a portion of the contact silicon layer 5 at the contact opening 21 , and solidifying the melted contact silicon layer 5 to form a re-solidified structure 51 .

[0075] The electrode region is a region for forming the back electrode 3 .

[0076] S103 , performing electroplating to form a back electrode 3 in the electrode region on the back side of the contact silicon layer 5 .

[0077] Reference Figure 3The solar cell has a "silicon substrate 1" made of a silicon-based material, and one side of the silicon substrate 1 is a light-entering side facing the sunlight, and the other side is a back side opposite to the light-entering side.

[0078] A contact silicon layer 5 for contacting the back electrode 3 is disposed on the back side of the silicon substrate 1 . The contact silicon layer 5 is also made of a silicon-based material.

[0079] On the back side of the contact silicon layer 5 , one or more passivation layers need to be formed, and all the passivation layers constitute a passivation structure 2 as a whole.

[0080] After forming the passivation structure 2 , at least part of the passivation structure 2 in the area (electrode area) where the back electrode 3 is to be formed is removed by laser grooving to expose the conductive contact silicon layer 5 , that is, a “contact opening 21 ” is formed in the passivation structure 2 .

[0081] While or after forming the contact opening 21 , the contact silicon layer 5 at the contact opening 21 is locally heated by using laser, so that the heated contact silicon layer 5 melts (but does not evaporate), and after solidifying again, a re-solidified structure 51 is formed.

[0082] After the resolidified structure 51 is formed, electroplating is performed using the conductive contact silicon layer 5 (the resolidified structure 51 ) exposed at the contact opening 21 to form the back electrode 3 in the electrode region on the back side of the contact silicon layer 5 .

[0083] The specific electroplating solution, electroplating parameters, etc. used in the electroplating process can be set according to the material and parameters of the back electrode 3, and will not be described in detail here.

[0084] According to an embodiment of the present invention, when or after the passivation structure 2 (passivation layer) on the back side of the solar cell is laser grooved to form the contact opening 21, the contact silicon layer 5 at the contact opening 21 is also melted by laser, and the re-solidified structure 51 is formed after solidification again, and then the back electrode 3 is electroplated on the re-solidified structure 51; wherein, the re-solidified structure 51 is not specially grown and has not been polished, so its surface is rough and the contact area with the back electrode 3 is large, so the electroplated back electrode 3 can ensure strong adhesion; at the same time, the re-solidified structure 51 and the contact opening 21 are both formed by laser, so it can be achieved by simply changing the process parameters of the laser groove, etc., without adding a separate step, so the preparation process is simple; in addition, only the back side of the contact silicon layer 5 corresponding to the back electrode 3 forms a relatively rough re-solidified structure 51, while most of the back side of the contact silicon layer 5 remains smooth, and the proportion of the rough surface is very small, so it will not affect the battery efficiency.

[0085] Optionally, a tunneling layer 59 is disposed on the back side of the silicon substrate 1 ; the contact silicon layer 5 is a polysilicon layer located on the back side of the tunneling layer 59 .

[0086] Reference Figure 4 As one embodiment of the present invention, a tunneling layer 59 of a material such as silicon oxide (SiOx) may be formed on the back side of the silicon substrate 1, and a polycrystalline silicon (poly-Si) layer is provided outside the tunneling layer 59, and the polycrystalline silicon layer is the partially melted contact silicon layer 5 mentioned above.

[0087] When the molten contact silicon layer 5 solidifies again to form the re-solidified structure 51 , the environment is difficult to control precisely, so the re-solidified structure 51 is usually polycrystalline. Therefore, a contact silicon layer 5 made of polycrystalline silicon (Poly-Si) can also be used accordingly.

[0088] It should be understood that the contact silicon layer 5 may also be in other forms.

[0089] For example, if the back electrode 3 is in direct contact with the silicon substrate 1 , the back side region of the silicon substrate 1 itself is also in contact with the silicon layer 5 at the same time.

[0090] Optional, see Figure 2 , using a laser to remove at least a portion of the passivation structure 2 at the electrode region to form a contact opening 21, and using a laser to melt at least a portion of the contact silicon layer 5 at the contact opening 21 (S102) includes:

[0091] S1021 , using laser to irradiate at least a portion of the passivation structure 2 in the electrode region, and evaporating and removing the irradiated passivation structure 2 to form a contact opening 21 .

[0092] S1022 , using laser to irradiate at least a portion of the contact silicon layer 5 at the contact opening 21 to melt the contact silicon layer 5 .

[0093] As one embodiment of the present invention, reference may be made to Figure 5 First, a complete passivation structure 2 is formed on the back side of the contact silicon layer 5; then, referring to Figure 6 , irradiate the passivation structure 2 at the position to be removed with a laser, evaporate the passivation structure 2 to form a contact opening 21; then, refer to Figure 7 , changing the laser parameters (such as reducing the laser energy and changing the shape, size, energy distribution, etc. of the light spot), melting (but not evaporating) the contact silicon layer 5 at least partially in the contact opening 21, so that it solidifies again to form a re-solidified structure 51.

[0094] It should be understood that due to the limitation of process precision, the removed passivation structure 2 (contact opening 21) may exceed the range of laser irradiation, and the melted contact silicon layer 5 (re-solidified structure 21) may also exceed the area irradiated by the laser, and the back electrode 3 may also slightly exceed the range of the electrode area.

[0095] It should be understood that in the process of removing the passivation structure 2 and melting the contact silicon layer 5 , it is not necessarily guaranteed that the contact silicon layer 5 is absolutely intact, that is, a part of the contact silicon layer 5 may also be lost by evaporation.

[0096] It should be understood that it is also feasible if the contact silicon layer 5 is heated and melted while the passivation structure 2 is being evaporated.

[0097] Optionally, the pulse duration of the laser used to evaporate and remove the passivation structure 2 is 1 ps to 30 ps, ​​and the energy density is 0.2 J / cm 2 Up to 1.2J / cm 2 ;

[0098] The pulse duration of the laser used for melting the contact silicon layer 5 is 1 ns to 50 ns, and the energy density is 0.1 J / cm 2 Up to 0.5J / cm 2 .

[0099] As one embodiment of the present invention, the laser for treating the passivation structure 2 needs to evaporate the passivation structure 2, so its intensity should be relatively large, for example, its pulse duration can be 1 to 30 ps, ​​and its energy density can be 0.2 J / cm 2 Up to 1.2J / cm 2 Furthermore, the pulse duration can be between 3 and 10 ps, ​​and the energy density can be between 0.3 J / cm 2 Up to 0.8J / cm 2 .

[0100] In contrast, although the laser for treating the contact silicon layer 5 will partially melt the contact silicon layer 5, it should not cause obvious evaporation of the contact silicon layer 5. Therefore, the intensity of the laser should be relatively low, for example, the pulse duration can be 1 to 50 ns, and the energy density can be 0.1 J / cm 2 Up to 0.5J / cm 2 Furthermore, the pulse duration can be between 3 and 30 ns, and the energy density can be between 0.1 J / cm 2 Up to 0.3J / cm 2 .

[0101] Among them, lasers that play different roles may have different energies, wavelengths, energy distributions, spot sizes, shapes, etc.

[0102] For example, the wavelength of the laser used to remove the passivation structure 2 may be shorter, such as 355 nm; while the wavelength of the laser used to melt the contact silicon layer 5 may be longer, such as 532 nm or 1064 nm.

[0103] For another example, the energy of the laser used to remove the passivation structure 2 may be a flat top distribution, while the energy of the laser used to melt the contact silicon layer 5 may be a Gaussian distribution.

[0104] For another example, optionally, the pattern of the laser used to evaporate and remove the passivation structure 2 includes a plurality of non-overlapping first light spots 91, and the radial dimension of each first light spot 91 is between 40 μm and 60 μm;

[0105] The pattern of the laser for melting the contact silicon layer 5 includes a second light spot 92 located at the center of each first light spot 91 . The radial dimension of each second light spot 92 is between 20 μm and 40 μm and is smaller than the radial dimension of the first light spot where it is located.

[0106] Reference Fig. 9 In the embodiment of the present invention, the laser light spots (first light spots 91) used to remove the passivation structure 2 may not overlap (including having intervals), and the radial dimension of each first light spot 91 is 40 to 60 μm, and may further be 40 to 50 μm. For example, referring to Fig. 9 The first light spot 91 may be a square (such as a square flat-top laser), and the side length of the rounded square may be 40 to 60 μm.

[0107] Relative, reference Fig. 9 After the contact opening 21 is obtained, a second light spot 92 which is "smaller" than the first light spot 91 can be used to irradiate the center of the first light spot 91, so as to melt the contact silicon layer 5 from the center of the contact opening 21, and the radial dimension of each second light spot 92 is 20 to 40 μm, and can further be 30 to 40 μm. For example, referring to Fig. 9 The second light spot 92 may be circular (such as using a circular Gaussian laser), and the diameter of the circle may be between 20 and 40 μm.

[0108] For example, after each first light spot 91 is used to remove the passivation structure 2, the pattern and energy distribution of the light spot are changed by diffraction, etc., and the energy of the laser is reduced, so that the first light spot 91 is transformed into the second light spot 92, and the contact silicon layer 5 at the corresponding position is melted.

[0109] It should be understood that the laser used in the embodiment of the present invention may also be in other forms. For example, a plurality of first light spots 91 may overlap, or the second light spot 92 may be the same as the first light spot 91 in size, shape, and position.

[0110] Optionally, the depth of the re-solidified structure 51 is between 30 nm and 1000 nm.

[0111] As one embodiment of the present invention, since the re-solidified structure 51 is mainly used to change the structure of the surface in contact with the back electrode 3, its depth (the dimension along the direction perpendicular to the back side of the silicon substrate 1) should not be too large so as not to affect the properties of the main body of the contact silicon layer 5. For example, the depth of the re-solidified structure 51 can be 30 to 1000 nm, and further can be 30 to 100 nm.

[0112] Optionally, using a laser to remove at least a portion of the passivation structure 2 in the electrode region to form the contact opening 21 (S102) includes:

[0113] S1029 , using laser to irradiate the passivation structures 2 at multiple spaced positions in the electrode region, removing the irradiated passivation structures 2 to form contact openings 21 , and causing edge portions of the remaining passivation structures 2 close to the contact openings 21 to rise.

[0114] The thickness of the back electrode 3 is greater than the thickness of the passivation structure 2 .

[0115] As one embodiment of the present invention, refer to Figure 4 , Figure 6 , Figure 7 Instead of removing all the passivation structure 2 in the electrode region, the passivation structure 2 may be removed separately at a plurality of spaced locations, thereby forming a plurality of spaced contact openings 21 in the electrode region, while the passivation structure 2 is "retained" at the intervals between the contact openings 21.

[0116] Reference Figure 4 , Figure 6 , Figure 7 When the passivation structure 2 is removed by laser, due to the effects of thermal stress, thermal expansion and contraction, the edge portion of the remaining passivation structure 2 close to the contact opening 21 will "lift up" and form a gap with the contact silicon layer 5.

[0117] Therefore, refer to Figure 4 , Figure 8 The passivation structure 2 retained in the electrode region is divided into two parts, namely, an "attached part" located in the center and attached to the contact silicon layer 5, and a "raised part" located at the edge and relative to the contact silicon layer 5.

[0118] Since the structure obtained by electroplating grows from the substrate, refer to Figure 4 , the back electrode 3 prepared by electroplating will "extend" between the "raised" part of the edge of the passivation structure 2 and the contact silicon layer 5. Further, since the thickness of the back electrode 3 (the dimension along the direction perpendicular to the back side of the silicon substrate 1) is greater than the thickness of the passivation structure 2 (the dimension along the direction perpendicular to the back side of the silicon substrate 1), Figure 4 , the back electrode 3 in the electrode region will cover the remaining passivation structure 2. Thus, referring to Figure 4 The “raised” portion of the passivation structure 2 retained in the electrode region is equivalent to being able to “stuck” the back electrode 3 located between it and the silicon contact silicon layer 5 , further improving the adhesion of the back electrode 3 .

[0119] It should be understood that, in addition to the edge of the passivation structure 2 being lifted when the contact opening 21 is formed, the thermal effect when the contact silicon layer 5 in the contact opening 21 is melted may further aggravate the lifting of the edge of the passivation structure 2 .

[0120] Among them, refer to Fig. 9 Specifically, multiple first light spots 91 used to remove the passivation structure 2 may be spaced apart (i.e., the light spot overlap rate is 0), thereby removing only the passivation structure 2 at the position irradiated by the first light spot 91. Therefore, the position of the first light spot 91 forms the contact opening 21, and the position between the first light spots 91 is the passivation structure 2 retained above.

[0121] Optionally, the angle between the raised edge portion of the passivation structure 2 (ie, the raised portion) closest to the contact silicon layer 5 and the contact silicon layer 5 is in a range of 15° to 60°.

[0122] Reference Figure 8 There is an angle a between the "rootmost part (the part closest to the attached part)" of the raised part of the passivation structure 2 and the surface of the contact silicon layer 5 where it is located, and the angle of the angle a can be specifically 15 to 60°, and further 15 to 45°.

[0123] Optionally, the maximum distance between the raised edge portion of the passivation structure 2 and the contact silicon layer 5 is in a range of 250 nm to 2000 nm.

[0124] Reference Figure 8 It is obvious that the closer the raised portion of the passivation structure 2 is to the "end", the farther it is from the contact silicon layer 5, and the distance between the end of the raised portion and the contact silicon layer 5 can be regarded as the "height d1" of the raised portion, and the raised height d1 can be 250 to 2000nm, and further can be 500 to 1000nm.

[0125] Optionally, along the direction from the raised edge portion of the passivation structure 2 to the center of the passivation structure 2 , the size of the orthographic projection of the raised edge portion of the passivation structure 2 on the contact silicon layer 5 is in a range of 1 μm to 4 μm.

[0126] Reference Figure 8 Only a part of the edge area of ​​the passivation structure 2 is warped, and the size of this part in the direction from the edge to the center of the passivation structure 2 is the "width d2" of the warped part, and the width d2 can be 1 to 4 μm, and further can be 2 to 3 μm.

[0127] Optionally, the raised edge portion 3 of the passivation structure 2 is a curved surface structure.

[0128] Reference Figure 8 , the raised portion of the passivation structure 2 may form a “cambered surface”.

[0129] For example, the raised portion may be a smooth curved surface; wherein the curvatures of various portions of the curved surface may be the same or different (including gradual changes along a certain direction); wherein the "root" of the raised portion of the curved surface may be "smoothly transitioned" to the attached portion of the passivation structure 2, or may be bent at a certain angle.

[0130] It should be understood that the specific form of the raised edge portion of the passivation structure 2 is not limited to the above example.

[0131] For example, the raised part can also be a reference Figure 4 It is basically "flat", or has other shapes; for example, the raised parts on both sides of a passivation structure 2 can be basically symmetrical, or have different structures (including shape and size).

[0132] Optionally, the distance between two adjacent spacing positions is 1 μm to 20 μm.

[0133] Reference Fig. 9 The gap between the interval positions (first light spot 91) of the laser irradiation to remove the passivation structure 2 (that is, the gap between the contact openings 21) can be 1 to 20 μm, and further can be 4 to 10 μm, which can not only play a better role in improving the adhesion, but also avoid adverse effects on the conductive properties (such as ohmic resistance) of the back electrode 3.

[0134] It should be understood that the specific forms of the contact opening 21 in the electrode area and the retained passivation structure 2 are not limited thereto; and the specific distribution of the first light spot 91 used to remove the passivation structure 2 is also not limited thereto. For example, a plurality of first light spots 91 may overlap to form a "large" contact opening 21, and different "large" contact openings 21 may be spaced apart.

[0135] It should be understood that the passivation structure 2 at the edge of the electrode region may also form the above-mentioned “lifted” structure, and the back electrode 3 may also enter between the “lifted” structure and the contact silicon layer 5 .

[0136] Optionally, the thickness of the passivation structure 2 is between 50 nm and 200 nm;

[0137] The thickness of the back electrode 3 is 1 μm to 12 μm.

[0138] The thickness of the passivation structure 2 (the total thickness of all passivation layers) may be 50-200 nm, and further may be 70-120 nm; correspondingly, the thickness of the back electrode 3 may be 1-12 μm, and further may be 3-8 μm.

[0139] Optional, see Figure 2, before forming the passivation structure 2 on the contact silicon layer 5 on the back side of the silicon substrate 1 (S101), it also includes:

[0140] S100 , polishing the back side of the contact silicon layer 5 .

[0141] It can be seen that the back electrode 3 is actually in contact with the surface of the resolidified structure 51, so whether the back side of the contact silicon layer 5 is originally smooth does not affect the adhesion of the back electrode 3. To this end, as a method of an embodiment of the present invention, the entire contact silicon layer 5 on the back side of the silicon substrate 1 can be polished first to further improve the battery efficiency.

[0142] It should be understood that the specific forms of the various structures in the embodiments of the present invention are diverse.

[0143] For example, the silicon substrate 1 may also be made of polycrystalline silicon, single crystal silicon, amorphous silicon, etc., and may be doped into an N-type or P-type semiconductor, or have a doping layer on the surface.

[0144] For example, the back electrode 3 (electrode area) can be specifically referred to Fig.10 , including relatively thick main grid lines 31, and thin grid lines 32 connected between the main grid lines 31 (in the related art, the main reason is that the adhesion of the thin grid lines 32 is insufficient), which can specifically be an emitter.

[0145] If the size of the thin gate line 32 is appropriate, a plurality of first light spots 91 arranged in a row may be used to form an electrode region corresponding to one thin gate line 32 .

[0146] For another example, the specific material of the back electrode 3 may be an alloy of one or more of silver (Ag), nickel (Ni), and copper (Cu), or a composite structure of different materials.

[0147] For another example, a textured surface (such as a large number of micro-pyramid structures) can be formed on the light incident side of the silicon substrate 1 by chemical texturing, and a front passivation layer made of materials such as aluminum oxide and silicon nitride can also be formed.

[0148] For another example, a front electrode, such as a base electrode, may be formed on the outer side of the front passivation layer through a silver paste sintering process.

[0149] For another example, in the process of preparing solar cells, other steps of forming the silicon substrate 1, the tunneling layer 59, the contact silicon layer 5, the light incident side structure, etc. may also be included, which will not be described in detail here.

[0150] Second, refer to Figures 1 to 10 , an embodiment of the present invention provides a solar cell.

[0151] The solar cell of the embodiment of the present invention is prepared by the above method and thus has a corresponding structure.

[0152] The solar cell according to the embodiment of the present invention comprises:

[0153] A silicon substrate 1, wherein the back side of the silicon substrate 1 has a contact silicon layer 5; the back side is the side opposite to the light incident side;

[0154] A passivation structure 2 is provided on the back side of the contact silicon layer 5, wherein the passivation structure 2 has a contact opening 21 formed by laser at at least a portion of the electrode region, and at least a portion of the contact silicon layer 5 at the contact opening 21 is a resolidified structure 51; the electrode region is a region for forming the back electrode 3, and the resolidified structure 51 is a structure formed by solidifying the contact silicon layer 5 after being melted by laser;

[0155] A back electrode 3 is provided at the electrode region; the back electrode 3 is located at a side of the passivation structure 2 away from the silicon substrate 1 and is formed by electroplating on the contact silicon layer 5 .

[0156] Optionally, there are a plurality of spaced contact openings 21 in the electrode region, and edge portions of the passivation structure 2 close to the contact openings 21 are raised;

[0157] The thickness of the back electrode 3 is greater than the thickness of the passivation structure.

[0158] Optionally, the solar cell in the embodiment of the present invention further satisfies at least one of the following:

[0159] The angle between the raised edge of the passivation structure 2 closest to the contact silicon layer 5 and the contact silicon layer 5 is 15° to 60°;

[0160] The maximum distance between the raised edge portion of the passivation structure 2 and the contact silicon layer 5 is 250 nm to 2000 nm;

[0161] Along the direction from the raised edge portion of the passivation structure 2 to the center of the passivation structure 2 , the size of the orthographic projection of the raised edge portion of the passivation structure 2 on the contact silicon layer 5 is 1 μm to 4 μm;

[0162] The raised edge portion 3 of the passivation structure 2 is a curved surface structure;

[0163] The distance between two adjacent contact openings 21 is 1 μm to 20 μm.

[0164] Optionally, the thickness of the passivation structure 2 is between 50 nm and 200 nm;

[0165] The thickness of the back electrode 3 is 1 μm to 12 μm.

[0166] Optionally, the depth of the re-solidified structure 51 is between 30 nm and 1000 nm.

[0167] Optionally, a tunneling layer 59 is disposed on the back side of the silicon substrate 1 ; the contact silicon layer 51 is a polysilicon layer located on the back side of the tunneling layer.

[0168] Comparative Example 1:

[0169] As a comparison, a TOPCon solar cell is provided, which includes an N-type doped single crystal silicon substrate.

[0170] The light-entering side of the silicon substrate 1 is chemically textured to form a front passivation layer of a composite material of silicon oxide / silicon nitride / aluminum oxide; the front passivation layer away from the silicon substrate 1 is sintered with silver paste to form a front electrode (base) that penetrates the front passivation layer and contacts the silicon substrate 1.

[0171] The back side of the silicon substrate 1 is chemically textured, and a tunneling layer 51 of silicon oxide and a polysilicon layer (contact silicon layer 5) are formed in sequence.

[0172] A passivation structure 2 is formed on the back side of the polysilicon layer; the thickness of the passivation structure 2 is 100 nm, and the material is a composite material of silicon oxide / silicon nitride.

[0173] All passivation structures 2 in the electrode area are removed by laser grooving to form a contact opening 21. A back electrode 3 (emitter) is formed on the polysilicon layer at the contact opening 21 by electroplating. The back electrode 3 is 5 μm thick and is made of nickel-copper-silver alloy.

[0174] According to the test, the cell efficiency of the solar cell of Comparative Example 1 is 24.2%, and the adhesion of the back electrode 3 is 0.3 N / cm.

[0175] Comparative Example 2:

[0176] The solar cell of this comparative example is similar to the solar cell of comparative example 1, except that the back side of its silicon substrate 1 is not textured, and the polysilicon layer (contact silicon layer 5) is polished.

[0177] According to the test, the cell efficiency of the solar cell of Comparative Example 2 is 24.5%, and the adhesion of the back electrode 3 is 0.1 N / cm.

[0178] Embodiment 1:

[0179] A solar cell is provided in an embodiment of the present invention, which is similar to the solar cell of comparative example 2, except that after a contact opening 21 is formed in the passivation structure 2 by laser grooving, the polysilicon layer (contact silicon layer 5) at the contact opening 21 is melted by laser and solidified again to form a re-solidified structure 51, so that the back electrode 3 is in contact with the re-solidified structure 51.

[0180] The slotting laser is realized by a plurality of continuous first light spots 91. The first light spot 91 is a square flat-top laser with a side length of 45 μm and an energy of 0.5 J / cm 2Each first light spot 91 is then melted by a second light spot 92 at its center. The second light spot 92 is a circular Gaussian laser with a diameter of 35 μm and an energy of 0.2 J / cm 2 .

[0181] According to the test, the cell efficiency of the solar cell of Example 1 is 24.45%, and the adhesion of the back electrode 3 is 0.3 N / cm.

[0182] It can be seen that, relative to the solar cell in which the back side of the silicon substrate 1 is also textured (Comparative Example 1), the preparation process of the solar cell in the embodiment of the present invention is simple (without textured step), the cell efficiency is higher, and the adhesion of its back electrode 3 is not reduced; and relative to the solar cell in which the back side of the silicon substrate 1 is not textured (Comparative Example 2), the adhesion of the back electrode 3 of the solar cell in the embodiment of the present invention is significantly higher, and the cell efficiency is not reduced.

[0183] Therefore, the embodiment of the present invention can improve the adhesion of the back electrode 3, and the preparation process is simple and the battery efficiency is high.

[0184] Embodiment 2:

[0185] The solar cell of this embodiment is similar to the solar cell of embodiment 1, except that the passivation structure 2 in the electrode region is not completely removed, but a plurality of spaced contact openings 21 are formed.

[0186] Among them, in the embodiment of the present invention, the interval between each second light spot 92 is 6μm; and the edge portion of the passivation structure 2 in the electrode area forms the above-mentioned "warping", and the angle a between the edge portion of the warping (warping portion) and the surface of the polysilicon layer (contact silicon layer 5) is 30°, the height d1 is 500nm, the width d2 is 2μm, and it is basically a curved surface.

[0187] As before, the thickness of the passivation structure 2 is 100 nm, and the thickness of the back electrode 3 is 5 μm, so the thickness of the back electrode 3 is greater than the thickness of the passivation structure 2 .

[0188] According to the test, the cell efficiency of the solar cell of Example 2 is 24.5%, and the adhesion of the back electrode 3 is 0.4 N / cm.

[0189] It can be seen that, compared with the method of removing all the passivation structure 2 in the electrode region, when a part of the passivation structure 2 is retained in the electrode region, the adhesion of the back electrode 3 can be further improved.

[0190] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a solar cell, characterized in that: include: forming a passivation structure on the contact silicon layer on the back side of the silicon substrate; The back side is the side opposite to the light incident side; Using a laser to remove the passivation structure at least partially at the electrode region to form a contact opening, using a laser to melt at least partially the contact silicon layer at the contact opening, and solidifying the melted contact silicon layer to form a re-solidified structure; the electrode region is a region for forming a back electrode; Electroplating is performed to form a back electrode in the electrode region on the back side of the contact silicon layer.

2. The preparation method according to claim 1, characterized in that: The step of removing the passivation structure at least partially at the electrode region by laser to form a contact opening, and melting at least partially the contact silicon layer at the contact opening by laser comprises: Using laser to irradiate the passivation structure at least partially in the electrode region, and evaporate and remove the irradiated passivation structure to form a contact opening; The contact silicon layer is irradiated with laser light at least at a portion of the contact opening to melt the contact silicon layer.

3. The preparation method according to claim 2, characterized in that: The pulse duration of the laser used for evaporating and removing the passivation structure is 1 ps to 30 ps, ​​and the energy density is 0.2 J / cm 2 Up to 1.2J / cm 2 ; The pulse duration of the laser used to melt the contact silicon layer is between 1 ns and 50 ns, and the energy density is between 0.1 J / cm 2 Up to 0.5J / cm 2 .

4. The preparation method according to claim 2, characterized in that: The pattern of the laser used for evaporating and removing the passivation structure includes a plurality of non-overlapping first light spots, and the radial size of each of the first light spots is between 40 μm and 60 μm; The pattern of the laser used to melt the contact silicon layer includes a second spot located at the center of each of the first spots, and the radial size of each of the second spots is between 20 μm and 40 μm and is smaller than the radial size of the first spot where it is located.

5. The preparation method according to claim 1, characterized in that: The step of removing at least a portion of the electrode region by laser to form a contact opening comprises: irradiating the passivation structures at a plurality of spaced positions of the electrode region with a laser, removing the irradiated passivation structures to form contact openings, and causing the edge portions of the remaining passivation structures close to the contact openings to warp; Wherein, the thickness of the back electrode is greater than the thickness of the passivation structure.

6. The preparation method according to claim 5, characterized in that: The angle between the raised edge portion of the passivation structure closest to the contact silicon layer and the contact silicon layer is 15° to 60°.

7. The preparation method according to claim 5, characterized in that: The maximum distance between the raised edge portion of the passivation structure and the contact silicon layer is 250nm to 2000nm.

8. The preparation method according to claim 5, characterized in that: Along the direction from the raised edge portion of the passivation structure to the center of the passivation structure, a size of an orthographic projection of the raised edge portion of the passivation structure on the contact silicon layer is in a range of 1 μm to 4 μm.

9. The preparation method according to claim 5, characterized in that: The raised edge portion of the passivation structure is a curved surface structure.

10. The preparation method according to claim 5, characterized in that: The distance between two adjacent spacing positions is 1 μm to 20 μm.

11. The preparation method according to claim 5, characterized in that: The thickness of the passivation structure is between 50nm and 200nm; The thickness of the back electrode is 1 μm to 12 μm.

12. The preparation method according to claim 1, characterized in that: The depth of the resolidified structure is between 30 nm and 1000 nm.

13. The preparation method according to claim 1, characterized in that: A tunneling layer is provided on the back side of the silicon substrate; The contact silicon layer is a polysilicon layer located at the back side of the tunnel layer.

14. The preparation method according to claim 1, characterized in that: Before forming the passivation structure on the contact silicon layer on the back side of the silicon substrate, the method further comprises: The back side of the contact silicon layer is polished.

15. A solar cell, characterized in that: include: A silicon substrate, wherein the back side of the silicon substrate has a contact silicon layer; the back side is the side opposite to the light incident side; A passivation structure is provided on the back side of the contact silicon layer, wherein the passivation structure has a contact opening formed by laser at at least a portion of the electrode region, and at least a portion of the contact silicon layer at the contact opening is a resolidified structure; the electrode region is a region for forming a back electrode, and the resolidified structure is a structure formed by solidifying the contact silicon layer after being melted by laser; A back electrode is arranged at the electrode region; the back electrode is located at a side of the passivation structure away from the silicon substrate and is formed by electroplating on the contact silicon layer.

16. The solar cell according to claim 15, characterized in that: There are a plurality of contact openings spaced apart from each other in the electrode region, and edge portions of the passivation structure close to the contact openings are warped; The thickness of the back electrode is greater than the thickness of the passivation structure.

17. The solar cell according to claim 16, characterized in that: The solar cell further satisfies at least one of the following: The angle between the raised edge of the passivation structure closest to the contact silicon layer and the contact silicon layer is 15° to 60°; The maximum distance between the raised edge portion of the passivation structure and the contact silicon layer is 250nm to 2000nm; Along the direction from the raised edge portion of the passivation structure to the center of the passivation structure, the size of the orthographic projection of the raised edge portion of the passivation structure on the contact silicon layer is 1 μm to 4 μm; The raised edge portion of the passivation structure is a curved surface structure; The distance between two adjacent contact openings is 1 μm to 20 μm.

18. The solar cell according to claim 16, characterized in that: The thickness of the passivation structure is between 50nm and 200nm; The thickness of the back electrode is 1 μm to 12 μm.

19. The solar cell according to claim 15, characterized in that: The depth of the resolidified structure is between 30 nm and 1000 nm.

20. The solar cell according to claim 15, characterized in that A tunneling layer is provided on the back side of the silicon substrate; The contact silicon layer is a polysilicon layer located at the back side of the tunnel layer.

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