Solar cell and preparation method thereof

Abstract

According to the solar cell piece and the preparation method thereof, an emitting electrode is formed on the front face of the solar cell piece, and the doping degree of the emitting electrode in the edge area of the front face is larger than the doping degree of the emitting electrode in the middle area of the front face. By improving the doping degree of the edge area, the square resistance of the edge of the silicon wafer is reduced, the edge area is easier to react with the glass powder in the grid line slurry, and the influence of aluminum oxide formed by winding plating on the front surface when aluminum oxide is deposited on the back surface on the contact of the grid line slurry and the silicon wafer can be relatively reduced or compensated; and the edge EL reject ratio of the solar cell is reduced.

Description

Technical Field

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

[0002] In the existing process, the EL at the edge of the solar cell often darkens. The inventors found that the aluminum oxide deposition on the back of the silicon wafer usually adopts a tubular ALD device. Two silicon wafers are placed in one slot of the aluminum boat, and the two silicon wafers are inserted back to back. Therefore, during the deposition process, the aluminum oxide will be plated around the edge of the front. When the slurry is screen-printed and sintered, the EL at the edge of the solar cell is dark because the slurry has a weak ability to penetrate the aluminum oxide. 。

[0003] In view of this, it is necessary to provide an improved solar cell and a preparation method thereof to solve the above technical problems. Summary of the invention

[0004] In order to solve one of the above problems, the present invention provides a solar cell and a method for preparing the same, which specifically adopts the following technical solutions:

[0005] A solar cell sheet has an emitter formed on its front side, wherein the doping degree of the emitter in the edge region of the front side is greater than the doping degree of the emitter in the middle region of the front side.

[0006] Furthermore, the doping degree includes at least one of doping concentration, doping depth, and change in silicon wafer resistance.

[0007] Furthermore, the doping degree of part of the emitters in the edge region is the same as that of at least part of the emitters in the middle region, and the doping degree of another part of the emitters in the edge region is greater than that of the emitters in the middle region.

[0008] Further, the emitter is a selective emitter, and the selective emitter includes:

[0009] The lightly doped region is located in the non-metallized area on the front side;

[0010] A heavily doped region is located in the front metallization region, and the heavily doped region includes an edge doped region located in the edge region and a middle doped region located in the middle region, and the doping degree of the edge doped region is greater than the doping degree of the middle doped region.

[0011] Furthermore, the square resistance of the edge doped region is 70Ω / sq±10Ω / sq, and the square resistance of the middle doped region is 90Ω / sq±10Ω / sq.

[0012] Furthermore, the junction depth of the edge doping region is 0.26 μm to 0.30 μm, and the junction depth of the middle doping region is 0.20 μm to 0.24 μm.

[0013] Furthermore, the solar cell comprises a plurality of heavily doped regions arranged along a first direction, and the heavily doped regions extend along a second direction perpendicular to the first direction; wherein the edge doped region comprises 2 to 4 heavily doped regions close to the edge of the solar cell in the first direction and ends of the other heavily doped regions in the second direction.

[0014] Furthermore, the width of the edge region is 1 cm to 2.5 cm; or, the edge of the front side of the solar cell has aluminum oxide coated around it, and the width of the edge region is not less than the width of the aluminum oxide.

[0015] A method for preparing a solar cell comprises: performing doping on the front side of a silicon slice, wherein the doping degree of an edge region is greater than the doping degree of a middle region.

[0016] Furthermore, the doping degree includes at least one of doping concentration, doping depth, and change in silicon wafer resistance.

[0017] Furthermore, the width of the edge area is 1 cm to 2.5 cm.

[0018] Furthermore, the method for preparing the solar cell comprises the following steps:

[0019] Diffusion is performed on the front side of the silicon wafer;

[0020] Performing a first laser doping on a metallized area at an edge area of ​​the silicon wafer to form an edge doping area;

[0021] A second laser doping is performed on the metallized area in the middle area of ​​the silicon wafer to form a middle doping area, and the doping degree of the edge doping area is greater than the doping degree of the middle doping area.

[0022] Further, the power of the first laser is greater than the power of the second laser;

[0023] Or, the first laser power is 45W±5W, and the second laser power is 32W±5W.

[0024] Furthermore, the wavelength of the first laser is 530nm, the laser power is 45W±5W, the laser spot is 85μm-100μm, the laser irradiation frequency is 400KHZ-500KHZ, and the laser scanning speed is 40000mm

[0025] / s~60000mm / s, scanning time is 0.8s~1.0s;

[0026] The wavelength of the second laser is 530, the laser power is 32W±5W, the laser spot is 85μm~100μm, the laser irradiation frequency is 300KHZ~400KHZ, the laser scanning speed is 20000mm / s~40000m / s, and the scanning time is 0.4s~0.6s.

[0027] Furthermore, the silicon wafer includes a plurality of metallized regions arranged along a first direction, and the metallized regions extend along a second direction perpendicular to the first direction; the metallized regions in the edge area include 2 to 4 metallized regions close to the edge of the silicon wafer in the first direction and the ends of the other metallized regions in the second direction.

[0028] Further, the square resistance of the edge doped region is 70Ω / sq±10Ω / sq, and the square resistance of the middle doped region is 90Ω / sq±10Ω / sq; and / or, the junction depth of the edge doped region is 0.26μm~0.30μm, and the junction depth of the middle doped region is 0.20μm~0.24μm.

[0029] Furthermore, the method for preparing the solar cell also includes the following steps: diffusion on the front side of the silicon wafer;

[0030] At least a portion of the edge region of the silicon wafer is doped with laser.

[0031] Furthermore, the parameters of laser doping are: the wavelength of the first laser is 530nm, the laser power is 45W±5W, the laser spot is 85μm~100μm, the laser irradiation frequency is 400KHZ~500KHZ, and the laser scanning speed is 40000mm.

[0032] Furthermore, the method for preparing the solar cell further comprises the following step: performing laser doping on at least a portion of the middle region of the silicon wafer, wherein the power of the laser doping on the edge region is greater than the power of the laser doping on the middle region.

[0033] Beneficial effects of the present invention: The solar cell and its preparation method of the present invention reduce the square resistance of the silicon wafer edge by increasing the doping degree of the edge area, and the edge area is more likely to react with the glass powder in the grid line paste, which can relatively reduce or compensate for the influence of aluminum oxide formed by the front side coating when aluminum oxide is deposited on the back side on the contact between the grid line paste and the silicon wafer, thereby reducing the edge EL defect rate of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0035] Figure 1 1 is a cross-sectional structural diagram of a solar cell, (a) is a conventional cell formed by a conventional process; (b) is a solar cell with an emitter in one embodiment of the present invention; (c) is a solar cell with an SE structure in another embodiment of the present invention;

[0036] Figure 2 A schematic diagram of the front side of a solar cell with a SE structure in one embodiment of the present invention, showing an edge doping region and a middle doping region;

[0037] Figure 3 Schematic diagram of the effect of solar cells, (a) is a traditional cell formed by traditional technology; (b) is the solar cell of the present invention.

[0038] Among them, 1-silicon wafer, 11-edge region, 12-middle region, 2-emitter, 21-heavily doped region, 211-edge doped region, 212-middle doped region, 22-lightly doped region. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0040] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0041] In view of the fact that existing ALD equipment cannot solve the problem of aluminum oxide wrapping, the present invention provides a solar cell and a preparation method thereof, which optimizes the emitter on the front side of the silicon wafer to improve the problem of dark EL at the edge of the solar cell.

[0042] The present invention provides a solar cell having an emitter 2 formed on the front side, wherein the doping level of the emitter 2 in the edge region of the front side is greater than the doping level of the emitter 2 in the middle region of the front side, that is, the doping level of at least part of the emitter 2 in the edge region 11 is greater than the doping level of the emitter 2 in the middle region 12.

[0043] The solar cell reduces the square resistance of the edge of the silicon wafer 1 by increasing the doping degree of the edge region 11, and the edge region 11 is more likely to react with the glass powder in the gate line paste, which can relatively reduce or compensate for the influence of the aluminum oxide formed by the front side coating when the aluminum oxide is deposited on the back side on the contact between the gate line paste and the silicon wafer 1, thereby reducing the edge EL defect rate of the solar cell.

[0044] The edge region 11 is a width range extending a certain distance inward from the edge of the solar cell, and the middle region 12 is a general term for all regions inside the frame region; that is, the edge region 11 is arranged around the middle region 12 .

[0045] Preferably, the edge of the front side of the solar cell has aluminum oxide coated around it, and the width of the edge region 11 is not less than the width of the aluminum oxide, so the conductivity of the entire aluminum oxide covered area is improved, reducing the edge EL defect rate.

[0046] The width of the edge region 11 is 1 cm to 2.5 cm, preferably 2 cm or more. This width design can cover the width of the aluminum oxide plated in the general process, so it can greatly reduce the edge EL defect rate of the solar cell; if the width is too small, it cannot cover the aluminum oxide plated area and has no effect; if the width is too large, there will be too much velvet surface damaged by the laser, affecting the reflection effect.

[0047] In the present invention, the doping degree includes at least one of doping concentration, doping depth (junction depth), and change in the square resistance of the silicon wafer 1. The following will be described in conjunction with a specific structure or doping process.

[0048] The doping level of the edge region 11 is greater than that of the middle region 12, which is measured from the perspective of the average doping of this region, including but not limited to: the doping level at any position of the edge region 11 is greater than that at any position of the middle region 12. Or, the doping level at any position of the edge region 11 is greater than that at any position of the middle region 12. The doping level of part of the emitter 2 in the edge region 11 is the same as that of at least part of the emitter 2 in the middle region 12, while the doping level of another part of the emitter 2 in the edge region 11 is greater than that of the emitter 2 in the middle region 12; therefore, the doping level of the entire edge region 11 is greater than that of the middle region 12.

[0049] Preferably, the emitter 2 is a selective emitter 2 (SE), the area where the gate line is preformed on the front of the silicon wafer 1 is called the metallization area, which is heavily doped to form a heavily doped area 21; the non-gate line area is a non-metallization area, which is lightly doped to form a lightly doped area 22; that is, the selective emitter 2 includes a lightly doped area 22 located in the non-metallization area and a heavily doped area 21 located in the metallization area. This can ensure good contact between the metal gate line and the silicon wafer 1, increase the minority carrier lifetime, and improve the efficiency of the solar cell.

[0050] Furthermore, the heavily doped region 21 includes an edge doped region 211 located in the edge region 11 and a middle doped region 212 located in the middle region 12. In a specific embodiment, the metallization region includes a plurality of heavily doped regions 21 arranged along a first direction, and the heavily doped regions 21 extend along a second direction perpendicular to the first direction. The edge doped region 211 includes 2 to 4 heavily doped regions 21 close to each edge of the solar cell in the first direction and ends of other heavily doped regions 21 in the second direction. That is, the 2 to 4 heavily doped regions 21 close to the edge of the solar cell in the first direction are all edge doped regions 211, the two ends of the heavily doped region 21 in the middle in the first direction in the second direction are all edge doped regions 211, and the area between the two ends is the middle doped region 212.

[0051] The doping levels of the lightly doped regions 22 at all positions on the entire solar cell are substantially the same, the doping level of the edge doped region 211 is greater than that of the middle doped region 212 , and thus the doping level of the entire edge region 11 is higher than that of the middle region 12 .

[0052] In a preferred embodiment, the square resistance of the edge doped region 211 is 70Ω / sq±10Ω / sq, and the square resistance of the middle doped region 212 is 90Ω / sq±10Ω / sq.

[0053] In a preferred embodiment, the junction depth of the edge doping region 211 is 0.26 μm to 0.30 μm, and the junction depth of the middle doping region 212 is 0.20 μm to 0.24 μm.

[0054] The present invention also provides a method for preparing a solar cell, comprising performing doping on the front side of a silicon wafer 1, wherein the doping degree of an edge region 11 is greater than the doping degree of a middle region 12; the square resistance of the edge of the silicon wafer 1 is reduced, and the edge region 11 is more likely to react with glass powder in a gate wire paste, which can relatively reduce or compensate for the influence of aluminum oxide formed by coating on the front side when aluminum oxide is deposited on the back side on the contact between the gate wire paste and the silicon wafer 1, thereby reducing the edge EL defect rate of the solar cell.

[0055] The edge region 11 and the doping degree are as described above and will not be elaborated here.

[0056] The edge region 11 and the middle region 12 may be doped in any of dozens of existing methods, such as doping the two regions separately, or doping the two regions simultaneously and then doping the edge region 11 a second time.

[0057] Preferably, the method for preparing the solar cell comprises the following steps: diffusion on the front side of the silicon wafer 1 to form an emitter 2; and then laser doping at least a portion of the edge region 11 of the silicon wafer 1. The silicon wafer 1 in the laser irradiation region is partially melted, so that the phosphorus atoms of the PSG layer in the region are further advanced, the doped phosphorus elements are enriched, and the phosphorus is further diffused, thereby forming a local high-concentration phosphorus doping, so that the square resistance value of the region is further reduced.

[0058] The diffusion process is as follows: POCl3 and O2 are introduced into the diffusion furnace, the flow rate of POCl3 is 800sccm-1500sccm, the flow rate of O2 is 400sccm-800sccm, and the time is 400s-600s; the advancement process is 830℃-860℃ high temperature advancement for 900s. After diffusion, the square resistance of the front side of the silicon wafer 1 is 180±10Ω / sq.

[0059] Laser doping parameters of edge area 11: the laser is a pulsed laser or a continuous laser, and the parameters of laser doping are that the wavelength of the first laser is 530nm, the laser power is 45W±5W, the laser spot is 85μm~100μm, the laser irradiation frequency is 400KHZ~500KHZ, and the laser scanning speed is 40000mm.

[0060] Of course, at least a portion of the middle region 12 of the silicon wafer 1 can also be laser doped, and the laser doping power of the edge region 11 is greater than the laser doping power of the middle region 12, which can still ensure that the doping level of the edge region 11 is higher than the doping level of the middle region 12.

[0061] Preferably, the emitter 2 is a selective emitter 2. The method for preparing the solar cell comprises the following steps: firstly, diffusion is performed on the front side of the silicon wafer 1; a first laser doping is performed on the metallized area located in the edge area 11, that is, a first laser is used to irradiate the metallized area in the edge area 11 to form an edge doped area 211; a second laser doping is performed on the metallized area located in the middle area 12, that is, a second laser is used to irradiate the metallized area in the middle area 12 to form a middle doped area 212; wherein the doping degree of the edge doped area 211 is greater than the doping degree of the middle doped area 212.

[0062] In a preferred embodiment, the silicon wafer 1 includes a plurality of metallized regions arranged along a first direction, and the metallized regions extend along a second direction perpendicular to the first direction; the metallized regions of the edge region 11 include 2 to 4 metallized regions close to each edge of the silicon wafer 1 in the first direction and the ends of the other metallized regions in the second direction.

[0063] Preferably, the power of the first laser is greater than the power of the second laser, so that the doping concentration and / or doping depth of the edge doping region 211 is higher than the doping concentration and / or doping depth of the middle doping region 212. In a preferred embodiment, the first laser power is 45W±5W, and the second laser power is 32W±5W.

[0064] Specifically, the wavelength of the first laser is 530nm, the laser power is 45W±5W, the laser spot is 85μm-100μm, the laser irradiation frequency is 400KHZ-500KHZ, the laser scanning speed is 40000mm / s-60000mm / s, and the scanning time is 0.8s-1.0s. The wavelength of the second laser is 530, the laser power is 32W±5W, the laser spot is 85μm-100μm, the laser irradiation frequency is 300KHZ-400KHZ, the laser scanning speed is 20000mm / s-40000m / s, and the scanning time is 0.4s-0.6s.

[0065] The solar cell obtained by this method has a square resistance of 70Ω / sq±10Ω / sq in the edge doping region 211, and a square resistance of 90Ω / sq±10Ω / sq in the middle doping region 212. The junction depth of the edge doping region 211 is 0.26μm to 0.30μm, and the junction depth of the middle doping region 212 is 0.20μm to 0.24μm.

[0066] In addition, the method for preparing the solar cell further comprises the following steps:

[0067] Silicon wafer 1 texturing;

[0068] Choose any of the above methods to make emitter 2;

[0069] Remove PSG from the surface and edges and prepare a silicon oxide layer on the front side;

[0070] Aluminum oxide is deposited on the back side;

[0071] Front and back PECVD deposition of passivation layer and anti-reflection layer;

[0072] Screen-printed metal electrodes;

[0073] sintering;

[0074] test;

[0075] Sorting.

[0076] In summary, the solar cell and the preparation method thereof of the present invention reduce the square resistance of the edge of the silicon wafer 1 by increasing the doping degree of the edge region 11, and the edge region 11 is more likely to react with the glass powder in the gate line paste, which can relatively reduce or compensate for the influence of the aluminum oxide formed by the front side coating when the aluminum oxide is deposited on the back side on the contact between the gate line paste and the silicon wafer 1, thereby reducing the edge EL defect rate of the solar cell.

[0077] It should be understood that although the present specification is described according to embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0078] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A solar cell having an emitter formed on its front side, characterized in that: The doping degree of the emitter in the front edge region is greater than the doping degree of the emitter in the front middle region.

2. The solar cell according to claim 1, characterized in that: The doping degree includes at least one of doping concentration, doping depth, and change in silicon wafer resistance.

3. The solar cell according to claim 1, characterized in that: The doping degree of part of the emitters in the edge region is the same as that of at least part of the emitters in the middle region, and the doping degree of another part of the emitters in the edge region is greater than that of the emitters in the middle region.

4. The solar cell according to any one of claims 1 to 3, characterized in that: The emitter is a selective emitter, and the selective emitter includes: The lightly doped region is located in the non-metallized area on the front side; A heavily doped region is located in the front metallization region, and the heavily doped region includes an edge doped region located in the edge region and a middle doped region located in the middle region, and the doping degree of the edge doped region is greater than the doping degree of the middle doped region.

5. The solar cell according to claim 4, characterized in that: The square resistance of the edge doping region is 70Ω / sq±10Ω / sq, and the square resistance of the middle doping region is 90Ω / sq±10Ω / sq.

6. The solar cell according to claim 4, characterized in that: The junction depth of the edge doping region is 0.26 μm to 0.30 μm, and the junction depth of the middle doping region is 0.20 μm to 0.24 μm.

7. The solar cell according to claim 4, characterized in that: The solar cell comprises a plurality of heavily doped regions arranged along a first direction, and the heavily doped regions extend along a second direction perpendicular to the first direction; wherein the edge doped region comprises 2 to 4 heavily doped regions close to the edge of the solar cell in the first direction and ends of the other heavily doped regions in the second direction.

8. The solar cell according to claim 1, characterized in that: The width of the edge area is 1 cm to 2.5 cm; Alternatively, the edge of the front side of the solar cell has aluminum oxide coated around it, and the width of the edge area is not less than the width of the aluminum oxide.

9. A method for preparing a solar cell, characterized in that: include: Doping is performed on the front side of the silicon wafer, wherein the doping level in the edge region is greater than that in the middle region.

10. The method for preparing a solar cell according to claim 9, characterized in that: The doping degree includes at least one of doping concentration, doping depth, and change in silicon wafer resistance.

11. The method for preparing a solar cell according to claim 9, characterized in that: The width of the edge area is 1 cm to 2.5 cm.

12. The method for preparing a solar cell according to any one of claims 9 to 11, characterized in that: The steps include: Diffusion is performed on the front side of the silicon wafer; Performing a first laser doping on a metallized region at an edge region of the silicon wafer to form an edge doping region; A second laser doping is performed on the metallized area in the middle area of ​​the silicon wafer to form a middle doping area, and the doping degree of the edge doping area is greater than the doping degree of the middle doping area.

13. The method for preparing a solar cell according to claim 12, characterized in that: The power of the first laser is greater than the power of the second laser; Or, the first laser power is 45W±5W, and the second laser power is 32W±5W.

14. The method for preparing a solar cell according to claim 12, characterized in that: The wavelength of the first laser is 530nm, the laser power is 45W±5W, the laser spot is 85μm-100μm, the laser irradiation frequency is 400KHZ-500KHZ, the laser scanning speed is 40000mm / s-60000mm / s, and the scanning time is 0.8s-1.0s; The wavelength of the second laser is 530, the laser power is 32W±5W, the laser spot is 85μm~100μm, the laser irradiation frequency is 300KHZ~400KHZ, the laser scanning speed is 20000mm / s~40000m / s, and the scanning time is 0.4s~0.6s.

15. The method for preparing a solar cell according to claim 12, characterized in that: The silicon wafer includes a plurality of metallized regions arranged along a first direction, and the metallized regions extend along a second direction perpendicular to the first direction; the metallized regions in the edge area include 2 to 4 metallized regions close to the edge of the silicon wafer in the first direction and ends of the other metallized regions in the second direction.

16. The method for preparing a solar cell according to claim 12, characterized in that: The square resistance of the edge doping region is 70Ω / sq±10Ω / sq, and the square resistance of the middle doping region is 90Ω / sq±10Ω / sq; And / or, the junction depth of the edge doping region is 0.26 μm to 0.30 μm, and the junction depth of the middle doping region is 0.20 μm to 0.24 μm.

17. The method for preparing a solar cell according to any one of claims 9 to 11, characterized in that: The steps include: Diffusion is performed on the front side of the silicon wafer; At least a portion of the edge region of the silicon wafer is doped with laser.

18. The method for preparing a solar cell according to claim 17, characterized in that: The parameters of laser doping are: the wavelength of the first laser is 530nm, the laser power is 45W±5W, the laser spot is 85μm~100μm, the laser irradiation frequency is 400KHZ~500KHZ, and the laser scanning speed is 40000mm.

19. The method for preparing a solar cell according to claim 17, characterized in that: The method comprises the following steps: performing laser doping on at least a part of the middle region of the silicon wafer, wherein the power of the laser doping on the edge region is greater than the power of the laser doping on the middle region.

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