Method for preparing PN junction and application thereof

Abstract

The invention discloses a method for preparing a PN junction and application thereof, and belongs to the technical field of solar cells. The method comprises the following steps: S1, a printing procedure: printing slurry containing a boron element and phosphorus slurry containing a phosphorus element on the front surface and / or the back surface of a to-be-processed material, and drying to form a plurality of printing areas; wherein the printing area covers the to-be-doped area; s2, a laser doping process: laser doping treatment is carried out on the doped region, and a laser spot of the laser doping treatment meets one or more of the following conditions: 1) the shape of the laser spot is a parallelogram; 2) the monopulse energy of the middle part of the light spot accounts for more than 90% of the total monopulse energy of the light spot, the monopulse energy of the marginal area of the light spot accounts for less than 10% of the total monopulse energy of the light spot, and the width and power of the marginal area meet certain conditions; and 3) only one layer of laser spots exists in the to-be-doped region, or multiple layers of laser spots are uniformly overlapped in the to-be-doped region. The application of the method in the preparation of the solar cell can solve the problem that the performance and the stability of the existing cell are reduced.

Description

Technical Field

[0001] The present application belongs to the technical field of solar cells, and specifically relates to a method for preparing a PN junction and its application. Background Art

[0002] A solar cell is a device that converts solar energy directly into electrical energy. Its core component is the photoelectric conversion material. Currently, silicon-based solar cells occupy a large share of the global photovoltaic market due to their high efficiency, stability, and environmental friendliness. In the manufacturing process of solar cells, doping is a key step. Doping refers to the process of introducing impurity atoms into semiconductor materials to change their electrical properties. Usually, doping can be achieved through high-temperature diffusion or ion implantation. In the traditional solar cell manufacturing process, high-temperature diffusion is usually used for doping. However, this method is not only complicated and time-consuming in operation, but also has high requirements for equipment and processes, and is relatively expensive. In addition, the uniformity of doping is poor.

[0003] To solve this problem, some researchers have proposed using laser doping to replace high-temperature diffusion. The advantage of this method is that the size and shape of the doped area can be precisely controlled. For example, Chinese patent application publication number CN103441190A, published on December 11, 2013, discloses a method for making a PN junction in a solar cell. After the solar silicon wafer undergoes a texturing process, a certain concentration of phosphoric acid is sprayed on the surface of the silicon wafer, and then laser scanning is performed. This method can replace the high-temperature diffusion method for making a PN junction and is suitable for industrial production. However, this method also has some problems, mainly the low uniformity of doping. Low doping uniformity will lead to reduced performance and stability of the cell.

[0004] Therefore, finding a PN junction preparation method that improves doping uniformity is an urgent problem to be solved in the current solar cell manufacturing process. Summary of the Invention

[0005] 1. Problem to be solved

[0006] The present application provides a method for preparing a PN junction, the purpose of which is to solve the problem of low doping uniformity in the prior art. Furthermore, the method of the present application is applied in the preparation of solar cells to solve the problem of reduced performance and stability of existing solar cells.

[0007] 2. Technical solution

[0008] In order to solve the above problems, the technical solutions adopted in this application are as follows:

[0009] As a first aspect of the present application, the present application provides a method for preparing a PN junction, comprising the following steps:

[0010] S1. Printing process: printing a slurry containing boron and a phosphorus slurry containing phosphorus on the front and / or back of the material to be processed, and drying to form multiple printing areas; alternatively, forming multiple BSG layers and PSG layers as printing areas on the front and / or back of the material to be processed; wherein the printing areas cover the area to be doped;

[0011] S2. Laser doping process: performing laser doping treatment on the doping area, wherein the laser spot of the laser doping treatment meets one or more of the following conditions:

[0012] 1) The shape of the laser spot is a parallelogram. Furthermore, the internal angle of the laser spot is 70-110°, and the aspect ratio of the laser spot is (3-1):1. Those skilled in the art will understand that a square is a special rectangle, and a rectangle is a special parallelogram. In this application, a parallelogram includes a rectangle, and a rectangle includes a square.

[0013] 2) The single pulse energy in the middle of the spot accounts for more than 90% of the total single pulse energy of the spot, and the single pulse energy in the edge of the spot accounts for less than 10% of the total single pulse energy of the spot. In order to seek the best spot uniformity, that is, doping uniformity, the width and power of the edge area meet the following conditions:

[0014] The width of the edge area is 0 to 5 μm (including 5 μm), and the single pulse energy of the edge area accounts for 5% to 10% of the total single pulse energy of the spot;

[0015] The width of the edge region is 5 to 10 μm (excluding 5 μm), and the single pulse energy of the edge region accounts for less than 5% of the total single pulse energy of the light spot.

[0016] The more uniform the energy distribution of the laser spot, the better the doping uniformity. When the edge energy of the laser spot cannot be evenly distributed, ensuring that the energy distribution in the middle is uniform and has a large gap with the edge energy can also ensure the uniformity of doping.

[0017] 3) There is only one layer of laser spot in the area to be doped, or there are two or more layers of laser spots uniformly overlapping in the area to be doped; laser doping requires higher energy per unit area, so laser doping is usually performed by overlapping laser spots. When the overlapping conditions of the laser spots are set as in the present application, it can not only ensure the doping of the doping source, but also improve the uniformity of doping.

[0018] Furthermore, the material to be processed is a semiconductor substrate or a semiconductor substrate with a ploy layer attached thereto.

[0019] Furthermore, the inner angle of the laser spot is 80-100°. Furthermore, the inner angle of the laser spot is 90°, which is a rectangle.

[0020] Furthermore, the length ratio of two adjacent sides of the laser spot is 1:1.

[0021] Furthermore, the ratio of the lengths of the two adjacent sides of the laser spot is 1:1, and the internal angle is 90°, which is a square. The closer the shape of the laser spot is to a square, the better the uniformity of the doping surface.

[0022] As a second aspect of the present application, the present application also provides the application of the above-mentioned method for preparing a PN junction in the manufacture of a solar cell.

[0023] As the third aspect of the present application, the present application also provides the application of the above-mentioned method for preparing a PN junction in the manufacture of a BC battery. In the laser doping process, the wavelength of the laser is 300 to 680 nanometers; further, the wavelength of the above-mentioned laser is 532 nm.

[0024] Furthermore, the power of the above laser is 30-45W, at which point the doping effect is good and it is not easy to cause damage. When the power is lower than 30W, the doping concentration is low.

[0025] Furthermore, the width of the doped region is greater than 150 microns, and the optimal spot size is 50 to 100 microns in side length.

[0026] Furthermore, the width of the doped region is greater than 250 micrometers, and the optimal spot size is 100 to 200 micrometers in side length.

[0027] 3. Beneficial effects

[0028] Compared with the prior art, the present application has the following advantages:

[0029] (1) The method for preparing a PN junction in this application improves the uniformity of slurry doping by changing the shape, energy distribution and overlapping conditions of the laser spot. This method is applied in the preparation of solar cells, thereby improving the cell efficiency and thus the performance of the cell.

[0030] (2) The method for preparing a PN junction of the present application improves the uniformity of slurry doping, thereby effectively avoiding the problem of unstable product performance caused by uneven doping, thereby improving the performance stability of the product;

[0031] (3) The method for preparing a PN junction in the present application is simple in manufacturing and improves manufacturing efficiency, and is therefore more suitable for large-scale applications, which helps promote the large-scale popularization of solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the locations of the slurry area and the doping area;

[0033] Figure 2 is a schematic diagram of the laser spot;

[0034] Figure 3 Schematic diagram of light spot arrangement in Example 3 and Comparative Example 1;

[0035] Figure 4 The battery having a partial P or N structure in Example 4;

[0036] Figure 5 Schematic diagram of light spot arrangement in Example 7 and Comparative Example 2;

[0037] Figure 6 Schematic diagram of light spot arrangement in Example 8 and Comparative Example 3;

[0038] Figure 7 Schematic diagram of the center area a, edge area c and overlapping area b of the light spot. DETAILED DESCRIPTION

[0039] The present application is further described below with reference to specific embodiments.

[0040] It should be noted that the terms such as "upper," "lower," "left," "right," and "middle" cited in this specification are only for the convenience of description and are not used to limit the scope of implementation. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of this application without substantially changing the technical content.

[0041] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0042] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents or instruments used, if the manufacturer is not specified, are commercially available conventional products.

[0043] As used herein, the term "about" is used to provide flexibility and imprecision associated with a given term, measurement, or value. One skilled in the art can readily determine the degree of flexibility for a particular variable.

[0044] As used herein, the term "at least one of" is intended to be synonymous with "one or more of." For example, "at least one of A, B, and C" explicitly includes only A, only B, only C, and combinations of each thereof.

[0045] Concentration, amount and other numerical data can be presented in range format in this article.Should be understood that such range format is only used for convenience and brevity, and should be flexibly interpreted as not only including the numerical value clearly described as range limit, but also including all independent numerical values ​​or subranges encompassed within the scope, just as each numerical value and subrange are clearly described.For example, the numerical range of about 1 to about 4.5 should be interpreted as not only including the limit value of 1 to about 4.5 clearly described, but also including independent numerals (such as 2,3,4) and subranges (such as 1 to 3,2 to 4 etc.).The same principle is applicable to the scope of only narrating a numerical value, such as "less than about 4.5," which should be interpreted as including all above-mentioned values ​​and scopes.In addition, no matter how the breadth of described scope or feature is, this explanation should be applicable.

[0046] In this application, the size of the laser spot is detected or defined by the following method: a single-pulse laser scan is performed on the front side of the cell on the relatively smooth silicon nitride surface, and the size of the single laser spot is observed and measured under a 3D microscope (the thickness of the silicon nitride is 70 to 80 nm, and the reflectivity of the suede is 1.5 to 1.8).

[0047] In this application, TOPCon refers to Tunnel Oxide Passivated Contact (Tunnel Oxide Passivated Contact technology).

[0048] Poly-Si refers to polycrystalline silicon.

[0049] BSG refers to Boron Silicate Glass.

[0050] PSG refers to Phospho Silicate Glass.

[0051] Average power: Average power = single pulse energy × repetition rate - the laser energy output per unit time in one repetition cycle. (1W = 1J / s).

[0052] In a specific embodiment, the present invention provides a method for preparing a PN junction, comprising the following steps:

[0053] S1. Printing process: Printing a slurry containing iodine and a phosphorus slurry containing phosphorus on the front and / or back of the material to be processed, and drying to form multiple printing areas; alternatively, forming multiple BSG layers and PSG layers as printing areas on the front and / or back of the material to be processed; wherein the printing areas cover the area to be doped;

[0054] S2. Laser doping process: performing laser doping treatment on the doping area, wherein the laser spot of the laser doping treatment meets one or more of the following conditions:

[0055] 1) The shape of the laser spot is a parallelogram, the internal angle of the laser spot is 70-110°, and the aspect ratio of the laser spot is (3-1):1;

[0056] 2) The single pulse energy in the middle of the spot accounts for more than 90% of the total single pulse energy of the spot, and the single pulse energy in the edge of the spot accounts for less than 10% of the total single pulse energy of the spot. In order to seek the best spot uniformity, that is, doping uniformity, the width and power of the edge area meet the following conditions:

[0057] The width of the edge area is 0 to 5 μm, and the single pulse energy in the edge area accounts for 5% to 10% of the total single pulse energy of the spot;

[0058] The width of the edge region is 5 to 10 μm, and the single pulse energy of the edge region accounts for less than 5% of the total single pulse energy of the light spot.

[0059] 3) There is only one layer of laser spot in the area to be doped, or there are two or more layers of laser spots uniformly overlapping in the area to be doped.

[0060] Taking the preparation of a PN junction of a solar cell as an example, the specific solar cell is a BC cell. The present invention provides a method for preparing a BC cell, comprising the following steps:

[0061] S1. Printing process:

[0062] S11, preparing a silicon-based substrate, wherein the resistivity of the substrate is 1 to 10 ohm·cm (Ω·cm) and the thickness is 0.05 to 0.5 mm;

[0063] S12, using screen printing, printing boron paste containing boron element and phosphorus paste containing phosphorus element on the back of the silicon-based substrate to form multiple paste areas; Figure 1 As shown, the dotted box is the slurry area, and the solid box is the doping area. The area of ​​these slurry areas is slightly larger than the area required for doping. After printing, drying is performed. Laser doping can not only use boron slurry and phosphorus slurry, but also films containing doping sources such as BSG and PSG.

[0064] S2. Laser doping process:

[0065] Laser doping is performed using a laser with a wavelength of 300 to 680 nanometers. The laser conditions used in the doping area are high power (30 to 45 W). To ensure the uniformity of doping, the laser spot conditions are limited according to at least one of 1) to 3):

[0066] 1) Define the shape of the laser spot: The closer the shape of the laser spot is to a square, the better the doping uniformity (when the aspect ratio of the spot is close to 1:1 and the angles of the four corners are close to 90°, the doping uniformity is better);

[0067] 2) Limit the energy distribution of the laser spot: The more uniform the energy distribution of the laser spot, the better the doping uniformity. When the energy distribution at the edge of the spot cannot be uniform, ensuring that the energy distribution in the middle is uniform and the energy gap with the edge is large can also ensure the uniformity of doping (when the laser energy is reduced, the edge area of ​​the spot becomes blurred, that is, the blurred area is not counted as the spot area. At this time, there is an obvious color change at the edge of the spot, such as Figure 2 The light blue part of the edge of the light spot is the edge area).

[0068] In order to achieve the best spot uniformity, that is, doping uniformity, the width and power of the edge area meet the following conditions. The spot uniformity is good and the doping uniformity is excellent:

[0069] The width of the edge area is 0 to 5 μm (including 5 μm), and the single pulse energy of the edge area accounts for 5% to 10% of the total single pulse energy of the spot;

[0070] The width of the edge region is 5 to 10 μm (excluding 5 μm), and the single pulse energy of the edge region accounts for less than 5% of the total single pulse energy of the light spot.

[0071] 3) Limit the overlapping conditions of the laser spots: Because laser doping requires a high energy per unit area, generally only one layer of laser spots is used in the area to be doped, or multiple layers of laser spots are evenly overlapped in the area to be doped. This can ensure the slurry doping and improve the uniformity of doping. The non-doped area or low-doped area of ​​the printing area is irradiated with laser conditions of low laser power to ensure that the slurry is removed when it is undoped or low-doped.

[0072] S3, cleaning process: After using laser to remove the slurry, use acid solution or alkaline solution to clean, generally cleaning time is less than 30 minutes, to remove impurities and residues on the surface of the substrate forming the P-type region and N-type region to ensure the performance and quality of the solar cell;

[0073] S4, annealing process: the cleaned substrate is annealed at a temperature of 800-1000°C for 5-120 minutes to activate the doped area and achieve local P+ or N+ doping. Through the above steps, the slurry residue in the non-laser doped area can be effectively removed to avoid contamination and technical problems affecting subsequent processes. At the same time, the uniformity of slurry doping is enhanced, and the performance and stability of the battery cell are improved. When an oxide layer and a polysilicon layer (Poly) are formed on the surface of the silicon substrate, annealing is performed to promote the doping of Poly, the oxide layer and the silicon substrate.

[0074] S5, texturing and removing PSG and BSG: texturing the front surface of the device obtained in step S4, and then placing it in acid solution to remove BSG and PSG generated by annealing; then performing RCA standard cleaning on the device to remove surface contaminants;

[0075] S6, depositing a first passivation layer on the front and back sides using an ALD process;

[0076] S7, depositing a first anti-reflection layer and a second anti-reflection layer on the front and back surfaces in sequence by a PECVD process;

[0077] S8. Screen-print the first electrode and the second electrode on the back side and perform sintering.

[0078] Example 1

[0079] In a method for manufacturing a BC battery in this embodiment, laser doping is performed on a silicon-based substrate, and the width of the doping region is 450 microns. The laser wavelength is a green nano laser of 532 nm, the power is 35 W, the frequency is 50 kHz, the spot shape is a parallelogram, the internal angle is 70°, the aspect ratio is 1:1, the side length of the spot is 150 microns, the single pulse energy in the middle part of the laser spot accounts for more than 90% of the total single pulse energy of the spot, the shape of the middle area of ​​the laser spot is the same as the laser spot, the single pulse energy at the edge of the spot accounts for less than 10% of the total single pulse energy of the spot, the width of the edge area is 0 to 5 μm, and the single pulse energy of the edge area accounts for 5% to 10% of the total single pulse energy of the spot; this embodiment selects a 1 μm width for the edge area, and the single pulse energy of the edge area accounts for 10% of the total single pulse energy of the spot. At this time, the spot uniformity is better and the doping uniformity is better. The spots are arranged tangentially, such as Figure 3 As shown on the right, the target area is doped, and the square resistance of the boron-doped area after annealing is 150±10Ω / sqr, and the square resistance of the phosphorus-doped area after annealing is 40±10Ω / sqr.

[0080] Example 2

[0081] In a method for manufacturing a BC battery in this embodiment, laser doping is performed on a silicon-based substrate. The width of the doping area is 450 microns, the laser wavelength is 532 nm, the power is 35 W, the frequency is 50 kHz, the spot shape is rectangular, the inner angle is 90°, the aspect ratio is 3:1, the length and width of the spot are 300 microns and 150 microns respectively, the single pulse energy in the middle part of the laser spot accounts for more than 90% of the total single pulse energy of the spot, the shape of the middle area of ​​the laser spot is the same as the laser spot, the single pulse energy at the edge of the spot accounts for less than 10% of the total single pulse energy of the spot, the width of the edge area is 0 to 5 μm, and the single pulse energy of the edge area accounts for 5% to 10% of the total single pulse energy of the spot; this embodiment selects a width of 5 μm for the edge area, and the single pulse energy of the edge area accounts for 5% of the total single pulse energy of the spot. At this time, the spot uniformity is better and the doping uniformity is better. The spots are arranged tangentially, such as Figure 3 As shown on the right, the target area is doped, and the square resistance of the boron-doped area after annealing is 150±10Ω / sqr, and the square resistance of the phosphorus-doped area after annealing is 40±10Ω / sqr.

[0082] Example 3

[0083] In a method for manufacturing a BC battery in this embodiment, laser doping is performed on a silicon-based substrate, and the width of the doping region is 450 microns. The laser wavelength is 532nm, the power is 35W, the frequency is 50kHz, and the spot shape is square, that is, the inner angle is 90°, the aspect ratio is 1:1, the side length of the spot is 150 microns, and the single pulse energy in the middle part of the laser spot accounts for more than 90% of the total single pulse energy of the spot. The shape of the middle area of ​​the laser spot is the same as the laser spot, and the single pulse energy at the edge of the spot accounts for less than 10% of the total single pulse energy of the spot. The width of the edge area is 5-10μm, and the single pulse energy of the edge area accounts for less than 5% of the total single pulse energy of the spot. This embodiment selects a width of 10μm for the edge area, and the single pulse energy of the edge area accounts for 1% of the total single pulse energy of the spot. At this time, the spot uniformity is better and the doping uniformity is better. The spots are arranged tangentially, such as Figure 3 As shown on the right, the target area is doped, and the square resistance of the boron-doped area after annealing is 150±10Ω / sqr, and the square resistance of the phosphorus-doped area after annealing is 40±10Ω / sqr.

[0084] Example 4

[0085] This embodiment is the same as embodiment 3, except that LPCVD is used to deposit a tunnel oxide layer and a poly layer on the back of the silicon wafer, and then a boron paste containing boron elements and a phosphorus paste containing phosphorus elements are printed on the poly layer by screen printing to form multiple paste areas; the area of ​​these paste areas is slightly larger than the area required for doping; and drying is performed after printing. Figure 4The schematic diagram of the BC battery structure of this embodiment shows that the target area is doped with laser. The sheet resistance of the boron-doped area after annealing is 150±10Ω / sqr, and the sheet resistance of the phosphorus-doped area after annealing is 40±10Ω / sqr.

[0086] Example 5

[0087] This example is similar to Example 3, differing only in that a layer of BSG and PSG is deposited on the backside of the silicon wafer using PECVD instead of a dried doping slurry. Laser doping is performed in the target area, achieving a sheet resistance of 150±10Ω / sqr in the boron-doped area and 40±10Ω / sqr in the phosphorus-doped area after annealing.

[0088] Example 6

[0089] This embodiment is the same as Example 3, with the only difference being that LPCVD is used to deposit a tunnel oxide layer and a poly layer on the back of the silicon wafer, and then PECVD is used to deposit a layer of BSG and PSG on the back of the silicon wafer. Instead of the dried doping slurry, the target area is doped with a laser. The square resistance of the boron-doped area after annealing is 150±10Ω / sqr, and the square resistance of the phosphorus-doped area after annealing is 40±10Ω / sqr.

[0090] The doping of the present invention is applicable to the backlight side of the cell (relative to the velvet on the front side, the velvet on the back side is smaller in area, or the bumps on the back side are more gentle, which will not cause excessive absorption of light during laser irradiation, thereby causing damage to the velvet structure and avoiding an increase in the reflectivity of the front structure); the doping of the present invention is applicable to the poly surface (reducing direct damage to the silicon wafer substrate caused by the laser, while helping to increase the doping concentration and reduce the contact resistance of the electrode contact area), at which time the uniformity, doping concentration and depth of doping are better controlled).

[0091] Example 7

[0092] This embodiment is the same as embodiment 3, except that the laser frequency is 100kHz and the light spot arrangement is different. Multiple layers of laser spots are evenly overlapped in the area to be doped. The light spot arrangement of this embodiment is as follows: Figure 5 As shown on the right, the laser doped the target area. After annealing, the sheet resistance of the boron-doped area was 150±10Ω / sqr, and the sheet resistance of the phosphorus-doped area was 40±10Ω / sqr.

[0093] Example 8

[0094] This embodiment is the same as embodiment 3, except that the laser frequency is 150kHz and the light spot arrangement is different. Multiple layers of laser spots are evenly overlapped in the area to be doped. The light spot arrangement of this embodiment is as follows: Figure 6As shown on the right, the laser doped the target area. After annealing, the sheet resistance of the boron-doped area was 150±10Ω / sqr, and the sheet resistance of the phosphorus-doped area was 40±10Ω / sqr.

[0095] Comparative Example 1

[0096] Comparative Example 1 is the same as Example 3, except that the shape of the light spot is circular. Figure 3 As shown on the left, the light spots are tangent to each other and do not overlap. The laser dopes the target area. At this time, the single pulse energy at the center and the edge of the spot is different. The center single pulse energy is high and the edge is low, as shown in the figure below. Figure 7 As shown, the single pulse energy in the central area a is guaranteed to meet the standard. At this time, the single pulse energy in the edge area c is about 30% of the central area. The square resistance of the boron-doped central area after annealing is 150±10Ω / sqr, and the square resistance of the edge area after annealing is 450±10Ω / sqr; the square resistance of the phosphorus-doped central area after annealing is 40±5Ω / sqr, and the square resistance of the edge area after annealing is 150±10Ω / sqr.

[0097] Comparative Example 2

[0098] Comparative Example 2 is the same as Example 7, except that the shape of the light spot is circular. Figure 5 As shown on the left, the light spots are tangent to each other and overlap by 50%. The laser dopes the target area. At this time, the single pulse energy at the center and edge of the light spot is different. The single pulse energy at the center is high and low at the edge. Figure 7 As shown, the energy density in the central region a is guaranteed to meet the standard. The energy density in the edge region c is approximately 30% of the central region. The energy density in the overlapping region b is equivalent to the effect of two laser exposures, and the non-overlapping region d is equivalent to no laser exposure. The square resistance of the boron-doped central region after annealing is 150±10Ω / sqr, the square resistance of the edge region after annealing is 450±10Ω / sqr, and the square resistance of the overlapping region after annealing is 60±10Ω / sqr. The non-overlapping region is not laser-doped. The square resistance of the phosphorus-doped central region after annealing is 40±5Ω / sqr, the square resistance of the edge region after annealing is 150±10Ω / sqr, and the square resistance of the overlapping region after annealing is 15±10Ω / sqr. The non-overlapping region is not laser-doped.

[0099] Comparative Example 3

[0100] Comparative Example 3 is the same as Example 8, except that the shape of the light spot is circular. Figure 6 As shown on the left, the light spots overlap 50% up, down, left, and right. The laser dopes the target area. At this time, the single pulse energy at the center and the edge of the spot is different. The center single pulse energy is high and the edge is low. Figure 7As shown, the energy density in the central region a is guaranteed to meet the standard. The energy density in the edge region c is approximately 30% of the central region. The energy density in the overlapping region b is equivalent to the effect of three laser exposures, and the non-overlapping region d is equivalent to no laser exposure. The square resistance of the boron-doped central region after annealing is 150±10Ω / sqr, the square resistance of the edge region after annealing is 450±10Ω / sqr, and the square resistance of the overlapping region after annealing is 30±10Ω / sqr. The non-overlapping region is not laser-doped. The square resistance of the phosphorus-doped central region after annealing is 40±5Ω / sqr, the square resistance of the edge region after annealing is 150±10Ω / sqr, and the square resistance of the overlapping region after annealing is 10±10Ω / sqr. The non-overlapping region is not laser-doped.

[0101] Comparative Example 4

[0102] Comparative Example 4 is identical to Example 3, differing only in that the distinction between the center and edge regions of the spot is no longer made, and the edge region area is assumed to be the same as the spot area. In this case, the single pulse energy at the edge of the spot accounts for less than 40% of the total single pulse energy of the spot, and the width of the edge region is 20 μm. Laser doping is performed in the target area, and the sheet resistance of the boron-doped region after annealing is 150 ± 5 Ω / sqr, while the sheet resistance of the phosphorus-doped region after annealing is 40 ± 5 Ω / sqr. The sheet resistance at the edge of the spot is significantly greater than that at the center, indicating significant doping non-uniformity.

[0103] Combining the above specific embodiments and comparative examples, it can be seen that in the specific embodiments, the square resistance of the laser doped area using the method of the present invention changes evenly; in comparative examples 1, 2, 3, and 4, the processing area using a general circular spot will have uneven energy distribution, such as Figure 7 As shown, different square resistance values ​​are formed in the center region a, edge region c, and overlapping region b of the spot, while the non-overlapping region d is undoped. This difference cannot be eliminated by changing the laser processing parameters. In Comparative Examples 2 and 3, the center and overlapping regions pose a risk of burn-through when high energy is applied. In contrast, the edge regions are processed with insufficient energy, resulting in substandard doping concentrations, while the non-overlapping regions are undoped. This significantly reduces the photoelectric conversion efficiency of the doped photovoltaic cell.

[0104] The electrical performance tests of the cells obtained in the above examples and comparative examples are shown in Table 1.

[0105] Table 1 BC battery performance test of each embodiment and comparative example

[0106]

[0107] As shown in Table 1, Examples 1 to 8 employ the method of the present invention to improve doping uniformity, thereby increasing the open-circuit voltage and short-circuit current of the battery, and thus improving the battery's conversion efficiency. Combining the Examples with Comparative Example 4, it can be seen that grading the spot energy in the edge region can further improve doping uniformity and thus improve the battery's conversion efficiency.

[0108] The above description is only an illustration of some preferred embodiments of the present disclosure and the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the above-mentioned inventive concept. For example, the above-mentioned features are replaced with (but not limited to) technical features with similar functions disclosed in the embodiments of the present disclosure.

Claims

1. A method for preparing a PN junction, characterized in that: The steps are: S1. Printing process: printing a slurry containing boron element and a phosphorus slurry containing phosphorus element on the front and / or back of the material to be processed, and drying to form a plurality of printing areas; Alternatively, a plurality of BSG layers and PSG layers are formed on the front side and / or the back side of the material to be processed as the printing area; wherein the printing area covers the area to be doped; S2, laser doping process: laser doping treatment is performed on the doping area, wherein the laser spot of the laser doping treatment meets one or more of the following conditions: 1) The shape of the laser spot is a parallelogram; 2) The single pulse energy in the middle part of the spot accounts for more than 90% of the total single pulse energy of the spot, and the single pulse energy in the edge area of ​​the spot accounts for less than 10% of the total single pulse energy of the spot. The width and power of the edge area meet the following conditions: The width of the edge area is 0 to 5 μm, and the single pulse energy in the edge area accounts for 5% to 10% of the total single pulse energy of the spot. The width of the edge area is 5 to 10 μm, and the single pulse energy in the edge area accounts for less than 5% of the total single pulse energy of the spot; 3) There is only one layer of laser spot in the area to be doped, or there are two or more layers of laser spots uniformly overlapping in the area to be doped.

2. A method for preparing a PN junction according to claim 1, characterized in that: In step S2, the inner angle of the laser spot is 70-110°, and the aspect ratio of the laser spot is (3-1):

1.

3. A method for preparing a PN junction according to claim 2, characterized in that: In step S2, the inner angle of the laser spot is 90°, and the aspect ratio of the laser spot is 1:

1.

4. A method for preparing a PN junction according to claim 1, characterized in that: In step S1, the material to be processed is a semiconductor substrate or a semiconductor substrate with a ploy layer attached thereto.

5. A method for preparing a solar cell, characterized in that: The invention comprises the method for preparing a PN junction as described in any one of claims 1 to 4.

6. A method for preparing a BC battery, characterized in that: The method for preparing a PN junction comprises the method according to any one of claims 1 to 4, wherein in the laser doping process of step S2, the wavelength of the laser is 300 to 680 nanometers.

7. The method for preparing a BC battery according to claim 6, characterized in that: The wavelength of the laser is 532nm.

8. The method for preparing a BC battery according to claim 6, characterized in that: The power of the laser is 30 to 45W.

9. The method for preparing a BC battery according to claim 6, characterized in that: The width of the doped region is more than 150 microns, and the side length of the light spot is 50 to 100 microns.

10. The method for preparing a BC battery according to claim 6, characterized in that: The width of the doped region is more than 250 microns, and the side length of the light spot is 100 to 300 microns.

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