Solar cell and preparation method thereof

Abstract

The present invention provides a solar cell comprising a silicon wafer; a diffusion layer located on the surface of the silicon wafer, the diffusion layer comprising a lightly doped region, a buffer doped region, and a heavily doped region, the heavily doped region being located within the buffer doped region, the sheet resistance of the lightly doped region being greater than the sheet resistance of the buffer doped region and greater than the sheet resistance of the heavily doped region; and an electrode, the electrode being located on the heavily doped region and forming an ohmic contact with the heavily doped region. The solar cell of the present invention, by providing a buffer doped region with a sheet resistance between the lightly doped region and the heavily doped region, can form an ohmic contact with the offset electrode when the electrode and the heavily doped region cannot completely overlap due to process errors. Due to its moderate doping, the buffer doped region does not result in a severely reduced minority carrier lifetime, thereby significantly improving the efficiency of the cell.

Description

Technical Field

[0001] The present application relates to the technical field of solar cell manufacturing, and in particular to a solar cell with high cell efficiency and a preparation method thereof. Background Art

[0002] In solar cell manufacturing, diffusion doping to create a PN junction is a key process. During the phosphorus doping process to create the emitter, light doping can reduce minority carrier recombination and increase minority carrier lifetime. However, this light doping leads to poor contact between the silver metal electrode and the silicon, increasing contact resistance. Selective emitter technology involves heavy doping in the metal electrode region and light doping in the non-metallic region, ensuring contact between the silver and silicon while also increasing minority carrier lifetime.

[0003] Laser-doped selective emitters (LDSEs) utilize a laser beam to selectively illuminate the silicon surface, molten the substrate, and allow dopant atoms to rapidly enter the molten silicon. When the laser beam is removed, the molten silicon cools and crystallizes, allowing the dopant atoms to enter the silicon crystal, forming heavily doped regions. The fabrication process for a laser-doped selective emitter is as follows: texturing → diffusion → laser doping → etching → PECVD coating → screen printing → sintering and testing.

[0004] In the laser doping process, the laser performs light doping according to the screen printing pattern, and forms heavy doping in the subsequent screen printing pattern area. Figure 1 As shown, the surface of silicon wafer 1' has lightly doped regions 11' and heavily doped regions 13'. Due to factors such as partial offset of the silicon wafer 1' during screen printing and the gradual widening of the gate lines 2' over the life of the screen, the width of the laser-heavily doped regions 13' must be significantly greater than the width of the gate lines 2'. In a typical example, the laser-doped width is 80μm and the silver gate lines are 40μm wide. Because the heavily doped regions are wider than the silver gate lines, recombination is severe in the heavily doped regions not in contact with the silver gate lines, resulting in a short minority carrier lifetime and affecting the efficiency of battery 100'.

[0005] In view of this, it is necessary to provide an improved solar cell and a preparation method thereof to solve the above problems. Summary of the Invention

[0006] The object of the present invention is to provide a solar cell with high cell efficiency and a preparation method thereof.

[0007] To achieve the above-mentioned object of the invention, the present invention provides a solar cell, which includes a silicon wafer; a diffusion layer located on the surface of the silicon wafer, the diffusion layer including a lightly doped region, a buffer doped region, and a heavily doped region, the heavily doped region being located within the buffer doped region, and the square resistance of the lightly doped region being greater than the square resistance of the buffer doped region and being greater than the square resistance of the heavily doped region; and an electrode, the electrode being located on the heavily doped region and forming an ohmic contact with the heavily doped region.

[0008] As a further improvement of the present invention, the width of the buffer doping regions located on both sides of the heavily doped region in the width direction is between 1 / 4 and 3 / 4 of the width of the heavily doped region.

[0009] As a further improvement of the present invention, widths of the buffer doping regions located on both sides of the heavily doped region in a width direction are the same or different.

[0010] As a further improvement of the present invention, the width of the heavily doped region is 0.8 to 1.2 times the width of the electrode.

[0011] As a further improvement of the present invention, the sheet resistance of the lightly doped region is 130 ohm / sq±20 ohm / sq, the sheet resistance of the buffer doped region is 100 ohm / sq±20 ohm / sq, and the sheet resistance of the heavily doped region is 60 ohm / sq±10 ohm / sq.

[0012] As a further improvement of the present invention, the silicon wafer is P-type silicon, and the diffusion layer is a phosphorus diffusion layer; or the silicon wafer is N-type silicon, and the diffusion layer is a boron diffusion layer.

[0013] In order to achieve the above-mentioned purpose of the invention, the present invention also provides a method for preparing a solar cell, comprising the following steps: providing a silicon wafer after texturing, and performing diffusion on the surface of the silicon wafer to form a lightly doped region; performing doping in a first region of the silicon wafer to form a buffer doped region; and performing doping in a second region of the silicon wafer to form a heavily doped region; wherein the second region is located in the first region, and the square resistance of the lightly doped region is greater than the square resistance of the buffer doped region and greater than the square resistance of the heavily doped region.

[0014] As a further improvement of the present invention, the steps of forming a buffer doping region are specifically as follows: in the first region, a laser beam is used to irradiate doping, the laser power is 10 W ~ 20 W, the laser irradiation frequency is 1000 KHZ ~ 2000 KHZ, the laser scanning speed is 30 m / s ~ 50 m / s, and the diameter of the laser beam is the width of the first region ± 10 μm.

[0015] As a further improvement of the present invention, the step of forming a heavily doped region is specifically as follows: in the second region, a laser beam is used to irradiate the doping, the laser power is 20 W ~ 30 W, the frequency is 1000 KHZ ~ 2000 KHZ, the scanning speed is 30 m / s ~ 50 m / s, and the diameter of the laser beam is the width of the second region ± 10 μm.

[0016] As a further improvement of the present invention, the width of the first region located on both sides of the second region in the width direction is between 1 / 4 and 3 / 4 of the width of the second region.

[0017] As a further improvement of the present invention, the widths of the first regions located on both sides of the second region in the width direction are the same or different.

[0018] As a further improvement of the present invention, the method for preparing a solar cell further includes the following step: preparing an electrode above the heavily doped region.

[0019] As a further improvement of the present invention, the width of the heavily doped region is 0.8 to 1.2 times the width of the electrode.

[0020] As a further improvement of the present invention, the sheet resistance of the lightly doped region is 130 ohm / sq±20 ohm / sq, the sheet resistance of the buffer doped region is 100 ohm / sq±20 ohm / sq, and the sheet resistance of the heavily doped region is 60 ohm / sq±10 ohm / sq.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: the solar cell of the present invention is provided with a buffer doping region, and the square resistance of the buffer doping region is between the lightly doped region and the heavily doped region. When the electrode and the heavily doped region cannot completely overlap due to process errors, the buffer doping region can form an ohmic contact with the offset electrode. Since its doping is moderate, it will not cause the minority carrier lifetime to be seriously low, thereby greatly improving the efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a cross-sectional view of a selective emitter of an existing solar cell, and does not illustrate other structures of the solar cell;

[0023] Figure 2 is a cross-sectional view of a selective emitter of a solar cell according to a preferred embodiment of the present invention, and does not illustrate other structures of the solar cell;

[0024] Figure 3a to Figure 3e It is a process flow chart of a method for preparing a selective emitter of a solar cell in a preferred embodiment of the present invention. Specific embodiments

[0026] The present application will be described in detail below with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present application, and any structural, methodological, or functional changes made by a person skilled in the art based on these embodiments are included within the scope of protection of the present application.

[0027] In the various drawings of the present application, for the sake of convenience, some sizes of structures or parts are exaggerated relative to other structures or parts. Therefore, they are only used to illustrate the basic structure of the subject matter of the present application.

[0028] Additionally, terms used herein to indicate spatial relative positions, such as “upper,” “above,” “lower,” and “below,” are used for ease of description to describe the relationship of one unit or feature relative to another unit or feature as shown in the accompanying drawings. Terms of spatial relative position may be intended to encompass different orientations of the device in use or operation in addition to the orientation shown in the drawings. For example, if the device in the drawings were turned over, units described as being “below” or “beneath” other units or features would be “above” the other units or features. Thus, the exemplary term “below” may encompass both above and below orientations. The device may be otherwise oriented (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein interpreted accordingly.

[0029] like Figure 2 As shown, a solar cell 100 according to a preferred embodiment of the present invention includes a silicon wafer 1; a diffusion layer located on the surface of the silicon wafer 1, the diffusion layer including a lightly doped region 11, a buffer doped region 12, and a heavily doped region 13, the heavily doped region 13 is located within the buffer doped region 12, and the square resistance of the lightly doped region 11 is greater than the square resistance of the buffer doped region and greater than the square resistance of the heavily doped region 13; an electrode 2, the electrode 2 is located on the heavily doped region 13 and forms an ohmic contact with the heavily doped region 13.

[0030] The other structures of the solar cell 100 are the same as those in the prior art and are not described again here.

[0031] Those skilled in the art will understand that the phrase "the heavily doped region 13 is located within the buffer doped region 12" mentioned in the present invention means that, excluding process errors, the width of the buffer doped region 12 is greater than the width of the heavily doped region 13, and along a direction perpendicular to the silicon wafer 1, the projection of the heavily doped region 13 on the silicon wafer 1 is located within the buffer doped region 12. Specifically, this means that one side edge of the heavily doped region 13 in the width direction is located within the buffer doped region 12, or both side edges are located within the buffer doped region 12. This also includes the situation where one side edge of the heavily doped region 13 in the width direction inevitably slightly exceeds the buffer doped region 12 due to process errors.

[0032] The square resistance of the buffer doped region 12 of the present invention is between that of the lightly doped region 11 and the heavily doped region 13. When the electrode 2 and the heavily doped region 13 cannot completely overlap due to process errors, the buffer doped region can form an ohmic contact with the offset electrode 2. Since its doping is moderate, it will not cause the minority carrier lifetime to be seriously low, thereby greatly improving the efficiency of the battery.

[0033] Specifically, when the silicon wafer 1 is P-type silicon, phosphorus diffusion is used; when the silicon wafer 1 is N-type silicon, boron diffusion is used. The sheet resistance of the lightly doped region 11 is 130 ohm / sq ± 20 ohm / sq, the sheet resistance of the buffer doped region is 100 ohm / sq ± 20 ohm / sq, and the sheet resistance of the heavily doped region 13 is 60 ohm / sq ± 10 ohm / sq.

[0034] In the present invention, portions of the buffer doped regions 12 are provided on both sides of the heavily doped region 13 in the width direction. When printing gate lines to form the electrode 2, ohmic contact can be formed with the buffer doped regions 12 by shifting to either side. The widths of the buffer doped regions 12 on both sides of the heavily doped region 13 in the width direction may be the same or different. Considering that the probability of the gate lines of the electrode 2 shifting to both sides is substantially the same, the widths of the buffer doped regions 12 are preferably the same or substantially the same.

[0035] The width of the buffer doping region 12 located on both sides of the heavily doped region 13 in the width direction is between 1 / 4 and 3 / 4 of the width of the heavily doped region 13; this width design can compensate for the defect of low minority carrier lifetime caused by the offset caused by the current printing process.

[0036] Preferably, the width of the buffer doped regions 12 on both sides of the heavily doped region 13 in the width direction is 1 / 2 of the width of the heavily doped region 13. For example, if the width of the electrode 2 is 40 μm, the width of the heavily doped region 13 is 40 μm, and the width of the buffer doped regions 12 on both sides of the heavily doped region 13 in the width direction is 20 μm.

[0037] Furthermore, the width of the heavily doped region 13 is designed to be 0.8 to 1.2 times the width of the electrode 2, so that, within the process error range, the width of the heavily doped region 13 is the same as the width of the electrode 2, that is, the two are substantially completely overlapped. Preferably, the width of the heavily doped region 13 is the same as the width of the electrode 2, which maximizes the efficiency of the solar cell.

[0038] like Figure 3a to Figure 3e As shown in FIG. 1 , a method for preparing a solar cell 100 according to a preferred embodiment of the present invention includes the following steps: Figure 3a , providing a silicon wafer 1 after texturing. Figure 3b, diffuses on the surface of the silicon wafer 1 to form a lightly doped region 11, that is, to form a PN junction; when the silicon wafer 1 is P-type silicon, phosphorus diffusion is used, and when the silicon wafer 1 is N-type silicon, boron diffusion is used. Figure 3c , doping is performed in the first region of the silicon wafer 1 to form a buffer doping region 12. Figure 3d , doping is performed in the second region of the silicon wafer 1 to form a heavily doped region 13; wherein the second region is located in the first region, and the square resistance of the lightly doped region 11 is greater than the square resistance of the buffer doped region and greater than the square resistance of the heavily doped region 13.

[0039] The order of the steps for forming the buffer doped region 12 and the heavily doped region 13 can be interchanged, and the interchange will not affect the structure of the formed solar cell 100 .

[0040] Those skilled in the art will appreciate that the aforementioned method for preparing a solar cell 100 is intended to form a solar cell 100 having a selective emission electrode. Therefore, the position and shape of the second region are designed to be consistent with the preformed electrode 2. The second region is located within the first region, so the width of the first region is greater than that of the second region, and the heavily doped region 13 is located within the buffer doped region 12. The effects achieved by this method are described in the aforementioned description of the solar cell 100 and will not be further elaborated here.

[0041] Specifically, the sheet resistance of the lightly doped region 11 is 130 ohm / sq±20 ohm / sq, the sheet resistance of the buffer doped region is 100 ohm / sq±20 ohm / sq, and the sheet resistance of the heavily doped region 13 is 60 ohm / sq±10 ohm / sq.

[0042] In the present invention, portions of the first region are present on both sides of the second region in the width direction, and the widths of the first regions on both sides of the second region in the width direction are the same or different. Therefore, portions of the buffer doped region 12 are present on both sides of the heavily doped region 13 in the width direction, and the widths of the buffer doped regions 12 on both sides of the heavily doped region 13 in the width direction are the same or different. Considering that the probability of the gate line of the electrode 2 shifting to both sides is basically the same, it is preferred that the buffer doped regions 12 be the same or substantially the same.

[0043] Specifically, the width of the first region on both sides of the second region in the width direction is between 1 / 4 and 3 / 4 of the width of the second region. Therefore, the width of the buffer doping region 12 on both sides of the heavily doped region 13 in the width direction is between 1 / 4 and 3 / 4 of the width of the heavily doped region 13.

[0044] Preferably, the width of the first region on both sides of the second region in the width direction is 1 / 2 of the width of the second region. Therefore, the width of the buffer doped region 12 on both sides of the heavily doped region 13 in the width direction is 1 / 2 of the width of the heavily doped region 13. For example, if the width of the electrode 2 is 40 μm, the width of the second region is 40 μm, the width of the first region is 80 μm, and the width of the first region on both sides of the second region in the width direction is 20 μm.

[0045] Furthermore, the method for preparing the solar cell 100 further includes the following steps: Figure 3e As described above, the electrode 2 is prepared above the heavily doped region 13. Specifically, it can also include: etching the silicon wafer 1 forming the lightly doped region 11, the buffer doped region 12, and the heavily doped region 13 in sequence to remove the phosphorus silicon glass layer, preparing silicon nitride by PECVD, screen printing the electrode 2, and sintering; during the screen printing of the electrode 2, the position of the electrode 2 needs to be the same as the position of the heavily doped region 13, and the width of the electrode 2 is designed to be substantially the same as the width of the heavily doped region 13. Therefore, "preparing the electrode 2 above the heavily doped region 13" means that the electrode 2 is located above the heavily doped region 13, and does not specifically mean that the electrode 2 is directly made on the heavily doped region 13.

[0046] All the preparation processes mentioned in the present invention, except for the preparation process of the heavily doped region 13 and the buffer doped region 12 of the diffusion layer, can be referenced by existing processes and will not be described in detail here.

[0047] The width of the second region is designed to be 0.8 to 1.2 times the width of the electrode 2, preferably the same as the width of the electrode 2. Accordingly, the width of the heavily doped region 13 formed is 0.8 to 1.2 times the width of the electrode 2, preferably the same as the width of the electrode 2.

[0048] In a preferred embodiment of the present invention, the buffer doping region 12 is formed by irradiating the first region with a laser beam. The laser power is 10 W to 20 W, the laser irradiation frequency is 1000 kHz to 2000 kHz, the laser scanning speed is 30 m / s to 50 m / s, and the laser beam diameter is the width of the first region ±10 μm. This step is applicable to phosphorus diffusion in P-type silicon and boron diffusion in N-type silicon.

[0049] In a preferred embodiment of the present invention, the step of forming the heavily doped region 13 is as follows: within the second region, a laser beam is used for doping. The laser power is 20 W to 30 W, the frequency is 1000 kHz to 2000 kHz, the scanning speed is 30 m / s to 50 m / s, and the diameter of the laser beam is the width of the second region ±10 μm. This step is applicable to phosphorus diffusion in P-type silicon and boron diffusion in N-type silicon.

[0050] Different from the above embodiment, other conventional doping processes may also be used to form the buffer doping region 12 and the heavily doped region 13 in the first region and the second region respectively. The conventional doping processes will not be described in detail.

[0051] In summary, the solar cell 100 of the present application is provided with a buffer doping region 12, and the square resistance of the buffer doping region 12 is between the lightly doped region 11 and the heavily doped region 13. When the electrode 2 and the heavily doped region 13 cannot completely overlap due to process errors, the buffer doping region 12 can form an ohmic contact with the offset electrode 2. Since its doping is moderate, it will not cause the minority carrier lifetime to be seriously low, thereby greatly improving the efficiency of the battery.

[0052] It should be understood that although this specification is described in terms of implementation methods, not every implementation method 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 implementation method can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0053] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of this application. They are not intended to limit the scope of protection of this application. Any equivalent implementation methods or changes that do not deviate from the technical spirit of this application should be included in the scope of protection of this application.

Claims

1. A solar cell, characterized in that: The solar cell comprises silicon wafers; a diffusion layer located on the surface of the silicon wafer, the diffusion layer comprising a lightly doped region, a buffer doped region, and a heavily doped region, the buffer doped region being located within the lightly doped region, the heavily doped region being located within the buffer doped region, and the sheet resistance of the lightly doped region being greater than the sheet resistance of the buffer doped region and greater than the sheet resistance of the heavily doped region; an electrode, the electrode being located on the heavily doped region and forming an ohmic contact with the heavily doped region; There are partial buffer doping regions on both sides of the heavily doped region in the width direction, and the width of the buffer doping regions on both sides of the heavily doped region in the width direction is between 1 / 4 and 3 / 4 of the width of the heavily doped region; the width of the heavily doped region is 0.8 times to 1.2 times the width of the electrode.

2. The solar cell according to claim 1, wherein: The width of the buffer doping regions located on both sides of the heavily doped region in the width direction is between 1 / 2 of the width of the heavily doped region.

3. The solar cell according to claim 1, wherein: The widths of the buffer doping regions located on both sides of the heavily doped region in a width direction are the same or different.

4. The solar cell according to claim 1, wherein: The width of the heavily doped region is the same as the width of the electrode.

5. The solar cell according to claim 1, wherein: The sheet resistance of the lightly doped region is 130 ohm / sq±20 ohm / sq, the sheet resistance of the buffer doped region is 100 ohm / sq±20 ohm / sq, and the sheet resistance of the heavily doped region is 60 ohm / sq±10 ohm / sq.

6. The solar cell according to claim 1, wherein: The silicon wafer is P-type silicon, and the diffusion layer is a phosphorus diffusion layer; or the silicon wafer is N-type silicon, and the diffusion layer is a boron diffusion layer.

7. A method for preparing a solar cell, characterized in that: The process includes the following steps: Provide a silicon wafer after texturing, and diffuse on the surface of the silicon wafer to form a lightly doped area; Doping is performed in the first region of the silicon wafer to form a buffer doping region, wherein the buffer doping region is located in the lightly doped region; Doping is performed in the second region of the silicon wafer to form a heavily doped region; preparing an electrode above the heavily doped region; Among them, the second region is located in the first region, and the square resistance of the lightly doped region is greater than the square resistance of the buffer doped region and greater than the square resistance of the heavily doped region; the width of the first region located on both sides of the second region in the width direction is between 1 / 4 and 3 / 4 of the width of the second region; the width of the heavily doped region is 0.8 times to 1.2 times the width of the electrode.

8. The method for preparing a solar cell according to claim 7, wherein: The steps of forming the buffer doping region are specifically as follows: in the first region, use a laser beam to irradiate the doping, the laser power is 10 W ~ 20 W, the laser irradiation frequency is 1000 KHZ ~ 2000 KHZ, the laser scanning speed is 30 m / s ~ 50 m / s, and the diameter of the laser beam is the width of the first region ± 10 μm.

9. The method for preparing a solar cell according to claim 7, wherein: The steps of forming the heavily doped region are as follows: in the second region, use a laser beam to irradiate the doping, the laser power is 20 W ~ 30 W, the frequency is 1000 KHZ ~ 2000 KHZ, the scanning speed is 30 m / s ~ 50 m / s, and the diameter of the laser beam is the width of the second region ± 10 μm.

10. The method for preparing a solar cell according to claim 7, wherein: The width of the first region located on both sides of the second region in the width direction is between 1 / 2 of the width of the second region.

11. The method for preparing a solar cell according to claim 7, wherein: The widths of the first regions located on both sides of the second region in the width direction are the same or different.

12. The method for preparing a solar cell according to claim 7, wherein: The width of the heavily doped region is the same as the width of the electrode.

13. The method for preparing a solar cell according to claim 7, wherein: The sheet resistance of the lightly doped region is 130 ohm / sq±20 ohm / sq, the sheet resistance of the buffer doped region is 100 ohm / sq±20 ohm / sq, and the sheet resistance of the heavily doped region is 60 ohm / sq±10 ohm / sq.

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