A screen printing method of SE-TOPCon cell

Abstract

The application relates to a screen printing method of an SE-TOPCon cell and belongs to the technical field of photovoltaic cell preparation. The method comprises the following steps: performing etching and boron diffusion treatment on the front surface and the back surface of an N-type cell silicon wafer; performing SE laser redoping treatment on the front surface of the N-type cell silicon wafer after the boron diffusion treatment is completed, so as to obtain a plurality of SE laser lines, a rectangular mark and a positioning pattern; comparing and positioning the pattern of a screen printing screen plate with the plurality of SE laser lines, the rectangular mark and the positioning pattern, and performing screen printing according to the comparison and positioning result. Through the arrangement, when screen printing is performed, the screen printing screen plate can firstly capture the positioning pattern to perform preliminary positioning, then the coverage of the pattern of the screen printing screen plate on the rectangular mark and the plurality of SE laser lines is observed, the screen plate is accurately positioned on the N-type cell silicon wafer, the position deviation between the pattern of the screen plate and the plurality of SE laser lines is reduced, and the photoelectric conversion efficiency of the SE-TOPCon cell is improved.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic cell manufacturing technology, and in particular to a screen printing method for SE-TOPCon cells. Background Technology

[0002] In recent years, SE-TOPCon cells, formed by combining selective emitter (SE) technology with tunneling oxide passivation contact technology, have become the mainstream product for crystalline silicon photovoltaic cells. The P++ region in an SE-TOPCon cell is created by using SE technology to melt the silicon wafer surface with high-energy laser pulses, forming SE laser lines that dope phosphorus atoms from the PSG into the molten region, achieving heavy doping. When the screen-printed metal grid lines come into contact with the SE laser lines, it reduces the contact resistance between the front electrode and the silicon wafer, and also lowers the surface recombination rate of the silicon wafer, thereby increasing the short-circuit current and open-circuit voltage of the SE-TOPCon cell, ultimately improving its conversion efficiency.

[0003] However, during the screen printing process of SE-TOPCon batteries, inaccurate positioning between the screen printing stencil and the P++ area often results in misalignment between the front SE laser lines in the P++ area and the metal grid lines of the screen printing stencil. This causes the SE laser lines to be exposed or overlapped, and the coverage of the metal grid lines and SE laser lines to be low. Consequently, SE-TOPCon batteries exhibit problems such as a dark EL image after sintering, and low short-circuit current, open-circuit voltage, fill factor, and conversion efficiency. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a screen printing method for SE-TOPCon batteries that reduces screen printing deviation. The technical solution of this invention is as follows:

[0005] A screen printing method for SE-TOPCon batteries includes the following steps:

[0006] S1, texturing and boron expansion processing are performed on the front and back sides of the N-type solar cell silicon wafer; S2, SE laser heavy doping processing is performed on the front side of the N-type solar cell silicon wafer after boron expansion processing to obtain multiple SE laser lines, four rectangular marks and four positioning patterns, forming the P++ region; S3, the pattern of the screen printing stencil is compared and positioned with the multiple SE laser lines, four rectangular marks and four positioning patterns of the P++ region, and screen printing is performed according to the comparison and positioning results to obtain the front electrode and the back electrode.

[0007] Optionally, when performing texturing on the front and back sides of the N-type solar cell wafer, S1 includes: after removing organic dirt, metal impurities, and mechanical damage layers generated during the wire cutting process from the surface of the N-type solar cell wafer, forming an uneven textured surface on the front and back sides of the N-type solar cell wafer through a texturing process.

[0008] Optionally, S1, when performing boron diffusion processing, includes: diffusing P-type elements on the front and back sides of the N-type solar cell wafer after texturing to form a P+ layer on the front side of the N-type solar cell wafer and an N+ layer on the back side of the N-type solar cell wafer.

[0009] Optionally, when S2 performs SE laser heavy doping treatment on the front side of the N-type solar cell silicon wafer that has undergone boron diffusion treatment to obtain multiple SE laser lines, four rectangular markers, and four positioning patterns to form the P++ region, it includes the following steps:

[0010] S21, Set the laser wavelength, power, and scanning speed of the laser device, and etch multiple SE laser lines on the front side of the N-type battery silicon wafer after boron diffusion treatment using the set laser wavelength, power, and scanning speed; S22, Perform multiple laser engravings on the upper and lower ends of the two SE laser lines near the two sides of the N-type battery silicon wafer to form four rectangular markings; S23, Etch four cross-shaped positioning patterns on the inner side of the four rectangular markings to form the P++ area.

[0011] Optionally, before comparing and positioning the pattern of the screen printing stencil with the multiple SE laser lines, four rectangular markers, and four positioning patterns in the P++ area, step S3 further includes: performing an oxidation treatment on the front side of the N-type solar cell silicon wafer forming the P++ area to form a silicon oxide layer on the P++ area; performing a BSG removal-alkali polishing treatment on the back side of the oxidized N-type solar cell silicon wafer to remove BSG from the edges and back side of the N-type solar cell silicon wafer while retaining BSG on the front side of the N-type solar cell silicon wafer, removing the damage layer, etching textured layer, and polishing textured layer on the front and back sides of the N-type solar cell silicon wafer to form a mirror effect on the surface of the N-type solar cell silicon wafer; and performing an EP-poly treatment on the back side of the oxidized N-type solar cell silicon wafer to form a silicon oxide layer on the N-type solar cell silicon wafer. A tunneling oxide layer, a silicon oxide thin film layer, and an in-situ doped amorphous silicon layer are prepared on the back side of the N-type solar cell wafer. The N-type solar cell wafer undergoes annealing after EP-poly processing, causing the in-situ doped amorphous silicon layer to transform into an N-type polycrystalline silicon thin film layer on the back side of the N-type solar cell wafer. The annealed N-type solar cell wafer undergoes RCA processing, specifically etching the front and edges of the N-type solar cell wafer using hydrofluoric acid solution, sodium hydroxide solution, and auxiliary additives to remove silicon oxide and BSG on the front side and PSG on the back side. The front side of the RCA-processed N-type solar cell wafer undergoes ALD processing to form an aluminum oxide thin film layer on the P+ layer. A silicon nitride thin film layer is deposited on both the front and back sides of the ALD-processed N-type solar cell wafer.

[0012] Optionally, when comparing and positioning the pattern of the screen printing plate with the multiple SE laser lines, four rectangular markers and four positioning patterns in the P++ area, step S3 includes: the screen printing plate first grabs the four positioning patterns in the P++ area for preliminary positioning, and then observes the coverage of the pattern of the screen printing plate with the four rectangular markers and multiple SE laser lines in the P++ area for precise positioning.

[0013] Optionally, when performing screen printing based on the comparison and positioning results to obtain the front electrode and the back electrode, S3 includes: after confirming that the pattern of the screen printing stencil covers the four rectangular marks and multiple SE laser lines of the P++ area, applying material to the front side of the N-type battery silicon wafer to print multiple metal grid lines to form the front electrode, and applying material to the back side of the N-type battery silicon wafer to print multiple metal grid lines to form the back electrode.

[0014] Optionally, after step S3, the process further includes: performing a metallization treatment on the screen-printed N-type battery silicon wafer by sintering in a sintering furnace to form ohmic contacts.

[0015] All of the above-mentioned optional technical solutions can be combined arbitrarily, and the present invention will not provide a detailed description of the structure after each combination.

[0016] By means of the above solution, the beneficial effects of the present invention are as follows:

[0017] By performing SE laser heavy doping on the front side of the N-type solar cell silicon wafer that has undergone boron diffusion treatment, multiple SE laser lines, four rectangular markers, and four positioning patterns are obtained, forming a P++ region. During screen printing, the screen printing stencil first grasps the four positioning patterns in the P++ region for initial positioning. Then, the operator observes the coverage of the stencil's patterns on the four rectangular markers and multiple SE laser lines, allowing for precise positioning within the P++ region. This reduces the positional deviation between the stencil's patterns and the multiple SE laser lines during screen printing, improving the coverage of the stencil's patterns and the multiple SE laser lines. This, in turn, improves the short-circuit current, open-circuit voltage, fill factor, and photoelectric conversion efficiency of the SE-TOPCon cell, and solves the problem of a dark EL image after sintering in SE-TOPCon cells.

[0018] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0019] Figure 1 This is a flowchart of the present invention;

[0020] Figure 2 This is a schematic diagram of the P++ region in this invention;

[0021] Figure 3 for Figure 2 A magnified view of a section at point A in the middle;

[0022] Figure 4 This is a schematic diagram showing the coverage of the SE laser line and the metal grid line.

[0023] Explanation of icon numbers:

[0024] 1. P++ area; 2. SE laser line; 3. Rectangular mark; 4. Positioning graphic; 5. Metal grid line. Detailed Implementation

[0025] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0026] like Figures 1 to 3 As shown, the present invention provides a screen printing method for SE-TOPCon batteries, comprising the following steps:

[0027] S1, texturing and boron expansion processing are performed on the front and back sides of the N-type solar cell silicon wafer; S2, SE laser heavy doping processing is performed on the front side of the N-type solar cell silicon wafer after boron expansion processing to obtain multiple SE laser lines 2, four rectangular marks 3 and four positioning patterns 4, forming P++ region 1; S3, the pattern of the screen printing stencil is compared and positioned with the multiple SE laser lines 2, four rectangular marks 3 and four positioning patterns 4 of P++ region 1, and screen printing is performed according to the comparison and positioning results to obtain the front electrode and the back electrode.

[0028] Of course, in actual implementation, the number of rectangular markers 3 can also be set to six, eight, etc. Just ensure that a pair of rectangular markers 3 are located on a single SE laser line 2.

[0029] In a specific implementation, the front side of the N-type solar cell silicon wafer that has undergone boron diffusion treatment is subjected to SE laser heavy doping treatment to obtain multiple SE laser lines 2, four rectangular markers 3, and four positioning patterns 4, forming a P++ area 1. This allows the screen printing stencil to be initially positioned by grasping the four positioning patterns 4 in the P++ area 1 during screen printing. Then, the operator observes the coverage of the pattern on the four rectangular markers 3 and multiple SE laser lines 2, enabling the screen printing stencil to be precisely positioned in the P++ area 1. This reduces the positional deviation between the pattern on the screen printing stencil and the multiple SE laser lines 2 during screen printing, and improves the coverage of the pattern on the screen printing stencil and the multiple SE laser lines 2.

[0030] Optionally, when performing texturing on the front and back sides of the N-type solar cell wafer, S1 includes: after removing organic dirt, metal impurities, and mechanical damage layers generated during the wire cutting process from the surface of the N-type solar cell wafer, forming an uneven textured surface on the front and back sides of the N-type solar cell wafer through a texturing process.

[0031] Optionally, S1, when performing boron diffusion processing, includes: diffusing P-type elements on the front and back sides of the N-type solar cell wafer after texturing to form a P+ layer on the front side of the N-type solar cell wafer and an N+ layer on the back side of the N-type solar cell wafer.

[0032] Optionally, when S2 performs SE laser heavy doping treatment on the front side of the N-type battery silicon wafer that has undergone boron diffusion treatment to obtain multiple SE laser lines 2, four rectangular markers 3, and four positioning patterns 4 to form the P++ region 1, it includes the following steps:

[0033] S21, set the laser wavelength, power and scanning speed of the laser equipment, and etch multiple SE laser lines 2 on the front side of the N-type battery silicon wafer after boron diffusion treatment with the set laser wavelength, power and scanning speed; S22, perform multiple laser engravings on the upper and lower ends of the two SE laser lines 2 near the two sides of the N-type battery silicon wafer to form four rectangular marks 3; S23, etch four cross-shaped positioning patterns 4 on the inner side of the four rectangular marks 3 to form P++ area 1.

[0034] Specifically, in this invention, the etching width of the SE laser line 2 is 70-100μm, and the etching width of the rectangular mark 3 is 75-150μm.

[0035] In a specific implementation, the edge of the N-type battery silicon wafer can be initially located by using a camera, and then SE laser heavy doping treatment can be performed using a laser device.

[0036] In a specific implementation, the parameters set for the laser equipment when performing SE laser heavy doping treatment on N-type battery silicon wafers can be as shown in Table 1.

[0037] Table 1

[0038]

[0039] Laser is used to melt the textured surface of the N-type battery silicon wafer, creating a mirror effect at position 3 of the rectangular mark. Because the reflectivity of position 3 of the rectangular mark is significantly different from that of other positions, it enables visual observation by staff.

[0040] Optionally, before comparing and positioning the pattern of the screen printing stencil with the multiple SE laser lines 2, four rectangular markers 3, and four positioning patterns 4 of the P++ area 1, step S3 further includes: oxidizing the front side of the N-type solar cell silicon wafer forming the P++ area 1 to form a silicon oxide layer on the P++ area 1; performing a BSG removal-alkali polishing process on the back side of the oxidized N-type solar cell silicon wafer to remove BSG from the edges and back side of the N-type solar cell silicon wafer while retaining BSG on the front side, removing the damage layer, etching textured layer, and polishing textured layer on the front and back sides of the N-type solar cell silicon wafer to create a mirror effect on the surface of the N-type solar cell silicon wafer; and performing an EP-poly process on the back side of the oxidized N-type solar cell silicon wafer to achieve a mirror effect on the surface of the N-type solar cell silicon wafer. A tunneling oxide layer, a silicon oxide thin film layer, and an in-situ doped amorphous silicon layer are prepared on the back side of an N-type solar cell silicon wafer. The N-type solar cell silicon wafer that has undergone EP-poly processing is then annealed to transform the in-situ doped amorphous silicon layer into an N-type polycrystalline silicon thin film layer on the back side of the N-type solar cell silicon wafer. The annealed N-type solar cell silicon wafer undergoes RCA processing, specifically by etching the front and edges of the N-type solar cell silicon wafer with hydrofluoric acid solution, sodium hydroxide solution, and auxiliary additives to remove silicon oxide and BSG on the front side and PSG on the back side. The front side of the RCA-processed N-type solar cell silicon wafer undergoes ALD processing to form an aluminum oxide thin film layer on the P+ layer. A silicon nitride thin film layer is deposited on both the front and back sides of the ALD-processed N-type solar cell silicon wafer.

[0041] Oxidation treatment improves the ohmic contact of N-type silicon wafers and reduces contact resistance. BSG removal-alkali polishing increases reflection from the back of the N-type silicon wafer, allowing light to return to the wafer for reuse and improving light utilization. This increases short-circuit current, thereby improving the conversion efficiency of SE-TOPCon cells. EP-poly treatment prevents direct contact between the surface of the N-type silicon wafer and the metal grid lines 5, improving passivation. Depositing an aluminum oxide film on the front side of the N-type silicon wafer provides passivation. Depositing silicon nitride films on both the front and back sides of the N-type silicon wafer acts as an anti-reflective coating, protecting the wafer.

[0042] Optionally, when comparing and positioning the pattern of the screen printing stencil with the multiple SE laser lines 2, four rectangular markers 3, and four positioning patterns 4 in the P++ area 1, step S3 includes: the screen printing stencil first grabs the four positioning patterns 4 in the P++ area 1 for preliminary positioning, and then observes the coverage of the pattern of the screen printing stencil with the four rectangular markers 3 and multiple SE laser lines 2 in the P++ area 1 for precise positioning.

[0043] In a specific implementation, during precise positioning, the operator first observes the coverage of the screen printing pattern between the multiple SE laser lines 2 in the P++ area. Since the etching width of the SE laser lines 2 is relatively narrow, when observing the pattern of the screen printing pattern and the coverage of the multiple SE laser lines 2, the operator can further observe the coverage of the four rectangular markers 3 with the screen printing pattern with wider etching width, thereby completing the precise positioning of the screen printing pattern in the P++ area.

[0044] Optionally, when performing screen printing based on the comparison and positioning results to obtain the front electrode and the back electrode, S3 includes: after confirming that the pattern of the screen printing stencil covers the four rectangular marks 3 and multiple SE laser lines 2 of the P++ area 1, applying material to the front side of the N-type battery silicon wafer to print multiple metal grid lines 5 to form the front electrode, and applying material to the back side of the N-type battery silicon wafer to print multiple metal grid lines 5 to form the back electrode.

[0045] like Figure 4 As shown, if the coverage of the metal grid line 5 and the SE laser line 2 is as follows... Figure 4 As shown in Figure (a), the coverage is good, and no manual adjustment is required. If the coverage of the metal grid line 5 and the SE laser line 2 is as shown... Figure 4 The situation shown in Figure (b) indicates poor coverage, requiring manual adjustments by staff until the metal grid line 5 and the SE laser line 2 achieve high coverage.

[0046] Optionally, after S3, the process includes: performing a metallization treatment on the screen-printed N-type battery silicon wafer by sintering in a sintering furnace to form ohmic contacts.

[0047] To verify the effect of the screen printing method for SE-TOPCon batteries provided by this invention on the photoelectric conversion efficiency of SE-TOPCon batteries, multiple sets of experiments with different coverage of metal grid lines 5 and SE laser lines 2 were set up for data comparison. The experimental data are shown in Table 2.

[0048] Table 2

[0049]

[0050]

[0051] As shown in Table 2, multiple experiments were conducted by varying the coverage between the metal grid line 5 and the SE laser line 2. This demonstrated that a higher coverage between the metal grid line 5 and the SE laser line 2 improves the electrical parameters of the SE-TOPCon battery, including short-circuit current, open-circuit voltage, and fill factor. Furthermore, the screen printing method for SE-TOPCon batteries provided by this invention, by adding four rectangular markers 3, allows the screen printing plate to first capture the four positioning patterns 4 of the P++ area 1. The operator then observes the coverage between the metal grid line 5, the four rectangular markers 3 of the P++ area 1, and the SE laser line 2. This makes it easier to achieve high coverage between the metal grid line 5 and the SE laser line 2 during screen printing, thereby improving the short-circuit current, open-circuit voltage, fill factor, and conversion efficiency of the SE-TOPCon battery. It also solves the problem of a dark EL image after sintering in SE-TOPCon batteries, thus improving the photoelectric conversion efficiency of SE-TOPCon batteries.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A screen printing method for SE-TOPCon batteries, characterized in that, include: S1, texturing and boron diffusion processes are performed on the front and back sides of the N-type solar cell silicon wafer; S2, SE laser heavy doping treatment is performed on the front side of the N-type battery silicon wafer that has completed boron expansion treatment to obtain multiple SE laser lines (2), four rectangular marks (3) and four positioning patterns (4) to form the P++ region (1). S3, compare and position the pattern of the screen printing plate with the multiple SE laser lines (2), four rectangular marks (3) and four positioning patterns (4) of the P++ area (1), and perform screen printing according to the comparison and positioning results to obtain the front electrode and the back electrode; The positioning pattern (4) is cross-shaped, and the rectangular mark (3) is etched on the upper and lower ends of the two SE laser lines (2) near the N-type battery silicon wafer, and the etching width of the rectangular mark (3) is greater than the etching width of the SE laser line (2). When comparing and positioning the pattern of the screen printing plate with the multiple SE laser lines (2), four rectangular marks (3) and four positioning patterns (4) of the P++ area (1), the S3 process includes: the screen printing plate first grabs the four positioning patterns of the P++ area (1) for preliminary positioning, and then observes the coverage of the pattern of the screen printing plate with the four rectangular marks (3) and multiple SE laser lines (2) of the P++ area (1) for precise positioning; When performing screen printing based on the comparison and positioning results to obtain the front electrode and the back electrode, S3 includes: after confirming that the pattern of the screen printing stencil covers the four rectangular marks (3) and multiple SE laser lines (2) of the P++ area (1), multiple metal grid lines (5) are printed on the front side of the N-type battery silicon wafer to form the front electrode, and multiple metal grid lines (5) are printed on the back side of the N-type battery silicon wafer to form the back electrode.

2. The screen printing method for an SE-TOPCon battery according to claim 1, characterized in that, The S1 process, when texturing the front and back sides of an N-type solar cell wafer, includes: After removing organic dirt, metal impurities, and mechanical damage layers generated during the wire cutting process from the surface of the N-type solar cell silicon wafer, an uneven textured surface is formed on the front and back sides of the N-type solar cell silicon wafer through a texturing process.

3. The screen printing method for a SE-TOPCon battery according to claim 1, characterized in that, The S1 process, during boron diffusion treatment, includes: P-type elements are diffused on the front and back sides of the N-type solar cell wafer after texturing to form a P+ layer on the front side of the N-type solar cell wafer and an N+ layer on the back side of the N-type solar cell wafer.

4. The screen printing method for an SE-TOPCon battery according to claim 1, characterized in that, When S2 performs SE laser heavy doping treatment on the front side of the N-type battery silicon wafer that has undergone boron expansion treatment to obtain multiple SE laser lines (2), four rectangular markers (3) and four positioning patterns (4) to form the P++ region (1), it includes: S21, set the laser wavelength, power and scanning speed of the laser device, and etch multiple SE laser lines on the front side of the N-type battery silicon wafer after boron diffusion treatment with the set laser wavelength, power and scanning speed (2). S22, multiple laser engravings are performed on the upper and lower ends of the two SE laser lines (2) near the N-type battery silicon wafer to form four rectangular marks (3). S23, four cross-shaped positioning patterns (4) are laser-engraved on the inner side of the four rectangular marks (3) respectively to form the P++ area (1).

5. The screen printing method for a SE-TOPCon battery according to claim 1, characterized in that, Before comparing and positioning the pattern of the screen printing stencil with the multiple SE laser lines (2), four rectangular markers (3), and four positioning patterns (4) of the P++ area (1), step S3 further includes: The front side of the N-type battery silicon wafer forming the P++ region (1) is oxidized to form a silicon oxide layer on the P++ region; The back side of the N-type solar cell silicon wafer that has undergone oxidation treatment is subjected to BSG removal-alkali polishing treatment to remove BSG from the edges and back side of the N-type solar cell silicon wafer, while retaining BSG on the front side of the N-type solar cell silicon wafer. This process removes the damage layer, etched textured layer, and polished textured layer from the front and back sides of the N-type solar cell silicon wafer, resulting in a mirror-like surface on the N-type solar cell silicon wafer. The back side of the N-type solar cell silicon wafer that has undergone BSG-alkali polishing is subjected to EP-poly treatment to prepare a tunneling oxide layer, a silicon oxide thin film layer and an in-situ doped amorphous silicon layer on the back side of the N-type solar cell silicon wafer. The N-type solar cell silicon wafer that has undergone EP-poly treatment is annealed to transform the in-situ doped amorphous silicon layer into an N-type polycrystalline silicon thin film layer on the back side of the N-type solar cell silicon wafer. The N-type solar cell silicon wafer that has undergone annealing is subjected to RCA treatment, specifically by etching the front and edges of the N-type solar cell silicon wafer with hydrofluoric acid solution, sodium hydroxide solution and auxiliary additives to remove silicon oxide, BSG on the front and PSG on the back of the N-type solar cell silicon wafer. The front side of the N-type battery silicon wafer that has undergone RCA treatment is subjected to ALD treatment to form an aluminum oxide thin film layer on the P+ layer; A silicon nitride thin film layer is deposited on both the front and back sides of the N-type solar cell wafer that has undergone ALD treatment.

6. The screen printing method for an SE-TOPCon battery according to claim 1, characterized in that, Following S3, the following also includes: The N-type solar cell silicon wafers that have completed screen printing are subjected to metallization treatment by sintering in a sintering furnace to form ohmic contacts.

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