A solar cell and a method of manufacturing the same

Abstract

The application relates to the technical field of solar cells, and particularly discloses a solar cell and a preparation method thereof. The solar cell comprises a silicon substrate, the silicon substrate comprises a front surface and a back surface, the front surface comprises a first laser contact area, a second laser contact area and a third laser contact area, the first laser contact area and the third laser contact area are alternately and spacedly arranged on the front surface of the silicon substrate; the second laser contact area and the first laser contact area are overlapped in a vertical direction, the width of the second laser contact area is smaller than that of the first laser contact area, the front surface further comprises a front surface metal electrode, the front surface metal electrode is in contact with the second laser contact area, and the crystallization rate of the second laser contact area is higher than that of a non-overlapping area in the first laser contact area. The solar cell has the advantages that the contact resistance of the metal grid line is reduced through gradient crystallization treatment, filling gain is brought, and the photoelectric conversion efficiency of the solar cell is further improved.

Description

Technical Field

[0001] This application relates to the technical field of solar cells, and in particular to a solar cell and a method for its fabrication. Background Technology

[0002] With the gradual depletion of fossil fuels, various renewable energy devices have emerged, and solar cells, as a new energy alternative, are being used more and more widely. Photovoltaic cells are used to convert solar energy into electrical energy and are widely used in various applications utilizing renewable energy. Current efficiency improvement efforts mainly focus on edge passivation, back-side poly local structuring, grid line optimization, passivation film structure design, etc. However, the photoelectric conversion efficiency of photovoltaic cells still needs to be improved.

[0003] Currently, the fabrication methods for solar cells using related technologies include the following steps:

[0004] (1) Take several experimental pieces after the boron expansion process and perform local front-side laser treatment;

[0005] (2) Then, a texturing process is performed to remove the oxide layer in the laser contact area;

[0006] (3) Boron diffusion followed by oxidation (1020 ~ 1030 ℃) for 3000 s to further advance the junction depth in the non-laser region. The thickness of the oxidized boron diffusion layer is slightly higher than the thickness of the initial boron diffusion layer (i.e. the initial boron diffusion layer generated before boron).

[0007] (4) The experimental piece is alkali polished to remove the borosilicate glass on the back side, and then a tunneling oxide layer and a phosphorus diffusion layer are deposited.

[0008] (5) Deposit an alumina film and a silicon nitride film on the front and back of the experimental piece.

[0009] In related technologies, after boron-induced oxidation, boron atoms in the BSG (borosilicate glass oxide) layer on the silicon wafer surface continue to move into the wafer's interior, redistributing impurities in the lightly and heavily doped regions to form an ideal junction. During this post-oxidation process, SiO2 segregation increases sheet resistance, reduces recombination, and makes the oxidized boron-rich layer easier to remove. Without post-oxidation, surface recombination surges, turnaround voltage decreases, boron activation is insufficient, and doping uniformity is poor.

[0010] Directly applying a laser beam to the initial boron-rich layer makes it difficult to achieve a complete film opening effect. Furthermore, high-power lasers are required for high-power localized processing, which carries the risk of severe laser thermal effects, often leading to edge laser damage, poor passivation, and lower-than-expected photoelectric conversion efficiency gains. Simultaneously, a post-oxidation process is essential to improve sheet resistance and reduce recombination; otherwise, surface recombination will surge, leading to a decrease in on-state voltage, insufficient boron activation, poor doping uniformity, and high temperatures and long overall process flow, resulting in significant industrial losses.

[0011] In addition, solar cells manufactured using related solar cell fabrication processes have a high recombination center and a large charge depletion region on the front side, resulting in a lower open-circuit voltage. At the same time, the high contact resistance between the metal grid lines and the front side leads to poor photoelectric conversion efficiency of the cell. Summary of the Invention

[0012] In order to eliminate the high-temperature post-oxidation process in the boron expansion process, shorten the process time, and at the same time improve the crystallinity of the boron-doped amorphous silicon layer, reduce the contact resistance between the metal grid lines and their front side by forming a gradient crystallization treatment, thereby bringing fill gain and further improving the photoelectric conversion efficiency of the cell, this application provides a solar cell and its fabrication method.

[0013] In a first aspect, this application provides a solar cell, which adopts the following technical solution:

[0014] A solar cell includes a silicon substrate, the silicon substrate having a front side and a back side opposite to the front side, the front side of the silicon substrate having a first laser contact area, a second laser contact area and a third laser contact area, the first laser contact area and the third laser contact area being alternately arranged on the front side of the silicon substrate, and a height difference existing between the first laser contact area and the third laser contact area.

[0015] The projections of the second laser contact area and the first laser contact area in the vertical direction coincide, and the width of the second laser contact area is smaller than the width of the first laser contact area. The front side of the silicon substrate also includes a front metal electrode, which forms contact with the second laser contact area. The crystallinity of the second laser contact area is higher than that of the non-overlapping area in the first laser contact area.

[0016] By adopting the above technical solution, gradient crystallization is set in the area in contact with the front metal electrode, thereby reducing the contact resistance. The front metal electrode forms contact with the second laser contact area with a higher crystallinity, and the crystallinity of the non-overlapping area in the first laser contact area is lower than that of the second laser contact area, which reduces the contact resistance between the metal grid line and its front side, resulting in fill gain and further improving the photoelectric conversion efficiency of the battery. The height difference between the third laser contact area and the first laser contact area causes the third laser contact area to form a groove structure, which allows light to undergo multiple reflections and scatterings after entering the groove, increasing the path length of light inside the battery and improving the light absorption efficiency.

[0017] Optionally, the second laser contact area is a first crystallinity region, and the non-overlapping area in the first laser contact area is a second crystallinity region. The crystallinity of the second crystallinity region is 60% to 80%, and the crystallinity of the first crystallinity region is 90% to 95%.

[0018] By adopting the above technical solution, the crystallization rate of the first laser contact area is higher than that after the initial low-temperature boron expansion. Reducing the post-oxidation temperature and time can also shorten the post-oxidation steps. The crystallization rate of the second laser contact area after laser crystallization is higher than that after the first laser crystallization treatment. This can reduce the contact resistance of the fine grid line contact area and bring about filling gain.

[0019] Optionally, the height difference between the first laser contact area and the third laser contact area is 2-5 μm.

[0020] Optionally, the width of the first laser contact area is denoted as A1, and the width of the second laser contact area is denoted as A2, wherein the ratio of A2 to A1 is 1:(3~5).

[0021] Optionally, the ratio of A2 to A1 can be 1:3, 1:4, or 1:5, etc.

[0022] Optionally, the width of the third laser contact area is denoted as A3, where A3 = 400~480 μm, and A3 can be 400 μm, 420 μm, 450 μm, 460 μm, 480 μm, etc. The crystallinity of the third laser contact area is 91%~93%.

[0023] Secondly, this application provides a method for preparing a solar cell, employing the following technical solution:

[0024] A method for preparing a solar cell includes the following steps:

[0025] Pretreatment: The front side of the silicon substrate is texturized;

[0026] Pre-boron process: Boron diffusion is performed on the front side of the pretreated silicon substrate to sequentially generate a boron diffusion layer and a phosphosilicate glass oxide layer;

[0027] Laser crystallization and film opening process: The first and second laser contact areas of the silicon substrate after the pre-boron process are sequentially subjected to laser crystallization, and then the third laser contact area is subjected to laser film opening process.

[0028] Texturing: The front side of the silicon substrate after laser crystallization and film opening is wet texturing to remove the boron diffusion layer and phosphosilicate glass oxide layer in the first laser contact area, and to form a groove in the third laser contact area with a pyramid textured surface.

[0029] Polishing and deposition: The back side of the texturized silicon substrate is cleaned to form a polished structure, and a tunneling oxide layer and a phosphorus diffusion layer are sequentially prepared on the back side of the cleaned silicon substrate;

[0030] Passivation: After depositing a first passivation layer on the front side of the silicon substrate, a second passivation layer is deposited on both the front and back sides of the silicon substrate;

[0031] Printing fine grids: Fine grid paste is printed on the passivated silicon substrate, and the metal electrode is prepared by sintering.

[0032] By adopting the above technical solution, this application achieves gradient crystallization, eliminating the need for the post-oxidation high-temperature process step in existing boron diffusion technology. The initial low-temperature boron diffusion process generates a boron diffusion layer and a borosilicate glass oxide layer. First, laser crystallization is performed on the first laser contact area, allowing the laser to directly contact the borosilicate glass oxide layer and improve the crystallinity of the underlying polycrystalline silicon layer. Then, laser crystallization is performed on the second laser contact area to further improve the crystallinity of this area and reduce the contact resistance of the gate contact area. Next, a localized boron diffusion layer of a certain width is formed in the third laser contact area. After wet texturing and cleaning, a residue-free, highly stable groove with controllable etching depth is formed. Subsequent generation of a new textured surface allows light to undergo multiple reflections and scatterings after entering the groove, increasing the path length of light within the cell and improving light absorption efficiency.

[0033] The reason why the first crystallinity region is obtained by two lasers instead of a single high-power laser is that high-power lasers can damage the silicon substrate (and ozone repair cannot completely improve it), which means that the region cannot be adequately passivated and repaired in the future. The third laser contact area directly uses high laser power to open the film. Since the region is subsequently wet-cleaned, the damage layer caused by the high-energy laser to the silicon substrate can be washed away, which also brings a certain improvement in crystallinity.

[0034] Optionally, in the pretreatment, the silicon substrate is an n-type single-crystal silicon wafer with a thickness of 130 μm and a resistivity of 1~5 Ω·cm. The silicon substrate with the textured surface is a pyramidal textured surface, with an average pyramidal texture size of 2~5 μm, an average texture height of 1~2 μm, and a specific surface area of ​​1~2 m². 2 / g, pile density 35000-38000 pieces / mm 2 ;

[0035] Optionally, in the pre-boron process, boron diffusion is performed at a temperature of ≤900℃ to form an inner boron diffusion layer and an outer borosilicate glass oxide layer. The thickness of the boron diffusion layer is denoted as D1, and the thickness of the borosilicate glass oxide layer is denoted as D2. D1 = 25~40nm, and D2 = 40~60nm.

[0036] Optionally, D1 can be 25 nm, 28 nm, 30 nm, 35 nm, 38 nm, 40 nm, etc., and D2 can be 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, etc.

[0037] By adopting the above technical solution and controlling the thickness of the boron diffusion layer and the borosilicate glass oxide layer, the thicknesses of the two are better matched for subsequent laser film opening. When the boron diffusion layer is combined with the matched borosilicate glass oxide layer, the laser beam can fully open the film during laser film opening, the laser film opening window is large, laser damage can be reduced, and positive gain is brought to the passivation effect.

[0038] Optionally, the laser beam can be a purple nano laser, a purple picosecond laser, a green nano laser, a green picosecond laser, or a green nano laser. The third laser contact area uses a UV picosecond laser.

[0039] Optionally, in the laser crystallization and film-opening process, the laser power of the second laser contact area is greater than that of the first laser contact area, and the laser power of the third laser contact area is greater than that of the second laser contact area.

[0040] Optionally, the laser parameters of the first laser contact area are: wavelength 250 ~ 370 nm, pulse width 1 ~ 5 ps, frequency 15 ~ 30 kHz, power 4 ~ 6 W, and laser processing time 5 ~ 10 s;

[0041] The laser parameters for the second laser contact area are: wavelength 250 ~ 370 nm, pulse width 1 ~ 5 ps, frequency 15 ~ 30 kHz, power 10 ~ 15 W, and laser processing time 20 ~ 30 s;

[0042] The laser parameters of the third laser contact area are ultraviolet picosecond laser, wavelength 250~370 nm, spot size 200~300 μm, frequency: 600 kHz, speed: 45000 mm / s, pulse width 1~2 ps, single pulse energy 1~5 μJ, and laser overlap rate controlled at 47~50%.

[0043] By adopting the above technical solution, this application uses low-temperature boron diffusion to match the crystallization treatment (4~6 W) of the first laser contact area. This results in low laser power, minimal damage, and a low-crystallinity boron diffusion layer. The second laser crystallization treatment further increases the crystallinity of this boron diffusion layer region, reducing the contact resistance with the fine gate line contact area and bringing a fill factor (FF) gain. The power P = F*S (where F is the frequency and S is the spot area) can be preliminarily calculated using the laser overlap rate (47~50%) of the third laser contact area. Its relatively large overlap rate results in an actual power of approximately 17 W, ensuring that the actual power of the third laser is greater than that of the first and second lasers, thus achieving the film-opening effect.

[0044] Optionally, in the laser crystallization and film opening process, after the first laser contact area is laser crystallized, ozone remediation treatment is also included.

[0045] Optionally, the specific parameters for ozone remediation treatment are: ozone concentration set at 1000 ppm to 10000 ppm, and treatment time at 1 to 30 minutes.

[0046] By adopting the above technical solution, an ozonation treatment is required after the first laser crystallization process to repair the laser damage caused by the first laser treatment and avoid damage to the polycrystalline silicon layer during the wet texturing process.

[0047] Optionally, in the texturing process, the groove depth formed by the third laser contact area is denoted as D3, where D3 = 2 ~ 5 μm, the average size of the pyramidal texturing surface is 2 ~ 4 μm, the average height of the texturing surface is 1 ~ 2 μm, and the specific surface area is 1 ~ 2 m². 2 / g, pile density is 32000-36000 / mm 2 At this point, the number of naps in area A1 is 35,000~38,000 per mm. 2 .

[0048] Optionally, D3 can be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, etc.

[0049] By adopting the above technical solution, by adding a borosilicate glass oxide layer with controllable thickness in the pre-boron process, and combining it with a smaller laser power range, the initial passivation layer can be accurately removed with low thermal damage, stable wet process, and complete film opening. The textured grooves formed by etching further allow light to be reflected and scattered multiple times, increasing the internal path length and improving light absorption efficiency.

[0050] Optionally, in the polishing and deposition process, a poly layer with a thickness of 130-150 nm is deposited on the back side of the silicon substrate, followed by oxidation to form a phosphosilicate glass oxide layer with a thickness of 40-50 nm.

[0051] Optionally, the first passivation layer is an aluminum oxide layer, and the second passivation layer is a silicon nitride layer.

[0052] In summary, this application has the following beneficial effects:

[0053] 1. The front metal electrode makes contact with the second laser contact area, which has a higher crystallinity. The crystallinity of the non-overlapping area in the first laser contact area is lower than that of the second laser contact area, which reduces the contact resistance between the metal grid line and its front side, resulting in fill gain and further improving the photoelectric conversion efficiency of the battery. The height difference between the third laser contact area and the first laser contact area causes the third laser contact area to form a groove structure, which allows light to undergo multiple reflections and scatterings after entering the groove, increasing the path length of light inside the battery and improving the light absorption efficiency.

[0054] 2. This application employs low-temperature boron diffusion to match the crystallization treatment of the first laser contact area (4 ~ 6 W). The laser power is low, resulting in less damage. After treatment, a boron diffusion layer with high crystallinity is formed. The second laser crystallization treatment further improves the crystallinity of the boron diffusion layer region, reduces the contact resistance with the fine gate line contact area, and brings a fill factor FF gain.

[0055] 3. The crystallization rate of the first laser contact area is higher than that after the initial low-temperature boron expansion. Reducing the post-oxidation temperature and time can also shorten the post-oxidation steps. The crystallization rate of the second laser contact area after laser crystallization is higher than that after the first laser crystallization treatment. This can reduce the contact resistance of the fine grid line contact area and bring about fill gain. Attached Figure Description

[0056] Figure 1 This is a diagram illustrating the solar cell structure forming process of Embodiment 1 of this application.

[0057] Figure 2 This is a flowchart illustrating the solar cell manufacturing process for Comparative Example 1.

[0058] Explanation of reference numerals in the attached figures: 111, silicon substrate; 112, textured structure; 113, boron diffusion layer; 114, borosilicate glass oxide layer; 115, second crystallinity region; 116, first crystallinity region; 117, tunneling oxide layer; 118, phosphorus diffusion layer; 119, first passivation layer; 120, second passivation layer; 121, front metal electrode. Detailed Implementation

[0059] Experimental methods in the following embodiments of this application that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. All commonly used chemical reagents used in the embodiments are commercially available products.

[0060] The present application will be further described in detail below with reference to the accompanying drawings.

[0061] Example 1

[0062] like Figure 1 As shown, a method for preparing a solar cell includes the following steps:

[0063] S1. Pretreatment: An n-type single-crystal silicon wafer with a resistivity of 3 Ω·cm and a thickness of 130 μm is selected as the silicon substrate 111. The front side of the silicon substrate 111 is texturized to form a silicon substrate 111 with a pyramid textured surface structure 112. The average size of the pyramid textured surface is 3 μm, the average height of the textured surface is 1 μm, and the specific surface area is 1.5 m². 2 / g, pile density 37,000 / mm 2 ;

[0064] S2. Pre-boron process: A pre-boron process is performed on the front side of the pretreated silicon substrate 111 to dope boron atoms. The surface concentration is 5E18, the annealing time is 1000 s, the temperature is 900℃, and the holding time is 50 s to activate the doped ions and simultaneously repair lattice defects introduced by laser processing. The surface doping concentration and junction depth are controlled by adjusting the annealing time. An inner boron diffusion layer 113 and an outer phosphosilicate glass oxide layer are formed sequentially. The thickness of the boron diffusion layer 113 is denoted as D1, and the thickness of the borosilicate glass oxide layer 114 is denoted as D2. D2 is always greater than D1, where D1 is 30 nm and D2 is 50 nm.

[0065] S3. Laser crystallization and film opening treatment: The front side of the silicon substrate 111 includes a first laser contact area, a second laser contact area and a third laser contact area. The first laser contact area of ​​the silicon substrate 111 after the pre-boron process is subjected to laser crystallization treatment, and then the first laser contact area is subjected to ozone repair treatment. The specific parameters of the ozone repair treatment are: the ozone concentration is set to 6000 ppm and the treatment time is 15 minutes.

[0066] Then, the second laser contact area is subjected to laser crystallization treatment to form a second crystallization rate region 115 with a low crystallization rate and a first crystallization rate region 116 with a high crystallization rate. The second laser contact area is the first crystallization rate region, and the non-overlapping area in the first laser contact area is the second crystallization rate region 115. The crystallization rate of the second crystallization rate region is 70%, and the crystallization rate of the first crystallization rate region is 93%.

[0067] Finally, laser film-opening treatment is performed on the third laser contact area to make the crystallization rate of the third laser contact area close to that of the first crystallization rate region, with the crystallization rate of the third laser contact area reaching 92%.

[0068] The first and third laser contact areas are alternately arranged on the front side of the silicon substrate 111. The second laser contact area partially overlaps with the first laser contact area, and the center positions of the second laser contact area and the first laser contact area are aligned. The width of the first laser contact area is denoted as A1, the width of the second laser contact area is denoted as A2, and the width of the third laser contact area is denoted as A3. The width ratio of A2 to A1 is 1:4, A1 is 400 μm, A2 is 100 μm, and A3 is 450 μm.

[0069] The laser beam uses an ultraviolet picosecond laser. The laser parameters of the first laser contact area are: wavelength 250 ~ 370 nm, pulse width 1 ~ 5 ps, frequency 15 ~ 30 kHz, power 4 ~ 6 W, and laser processing time 5 ~ 10 s.

[0070] The laser parameters for the second laser contact area are: wavelength 250 ~ 370 nm, pulse width 1 ~ 5 ps, frequency 15 ~ 30 kHz, power 10 ~ 15 W, and laser processing time 20 ~ 30 s.

[0071] The laser parameters for the third laser contact area are: ultraviolet picosecond laser, wavelength 250 ~ 370 nm, spot size 200 ~ 300 μm, frequency: 600 kHz, velocity: 45000 mm / s, pulse width 1.5 ps, single pulse energy 3 μJ, and laser overlap rate controlled at 47 ~ 50%.

[0072] S4. Texturing: The front side of the silicon substrate 111 after laser crystallization and film opening treatment is wet-textured to remove the boron diffusion layer 113 and the phosphosilicate glass oxide layer in the first laser contact area, forming a new textured surface. A groove is formed in the third laser contact area, and the etching depth of the groove is denoted as D3, where D3 is 3 μm. The groove surface has a pyramid textured structure 112. The average size of the pyramid textured surface is 3 μm, the average height of the textured surface is 2 μm, and the specific surface area is 2 m². 2 / g, pile density 36000 / mm2 .

[0073] S5. Polishing and Deposition: The back side of the texturized silicon substrate 111 is cleaned by chain hydrofluoric acid and then etched by alkaline wet etching to remove the phosphorus silicate glass oxide layer on the back side of the silicon substrate 111 to form a polished structure. A tunneling oxide layer 117 and a phosphorus diffusion layer 118 are sequentially prepared on the back side of the cleaned silicon substrate 111 using LPCVD. A poly layer with a thickness of 140 nm is deposited on the back side of the silicon substrate 111 and then oxidized to form a 45 nm phosphorus silicate glass oxide layer.

[0074] S6. Passivation: After depositing a first passivation layer 119 on the front side of the silicon substrate 111, a second passivation layer 120 is deposited on the front and back sides of the silicon substrate 111; the first passivation layer 119 is an aluminum oxide layer with a thickness of 5 nm, and the second passivation layer 120 is a silicon nitride layer.

[0075] S7. Printing fine grids: Fine grid paste is printed on the front and back sides of the passivated silicon substrate 111, and the printing position of the fine grid paste on the front side is aligned with the second laser contact area. After sintering, the preparation of the front metal electrode 121 and the back metal electrode (not shown in the figure) is completed.

[0076] Example 2-3

[0077] A method for preparing a solar cell differs from Example 1 in that the process parameters are different, but all other aspects are the same.

[0078] The fabrication process parameters of the solar cells in Examples 1-3 are shown in Table 1.

[0079] Table 1. Fabrication process parameters of solar cells in Examples 1-3

[0080] Example 4

[0081] A method for preparing a solar cell differs from Example 1 in that the crystallinity of the second crystallinity region is 50%, while the rest is the same as in Example 1.

[0082] Example 5

[0083] A method for preparing a solar cell differs from Example 1 in that the crystallinity of the second crystallinity region is 85%, while the rest is the same as in Example 1.

[0084] Example 6

[0085] A method for preparing a solar cell differs from Example 1 in that the crystallinity of the first crystallinity region is 80%, while the rest are the same as in Example 1.

[0086] Example 7

[0087] A method for preparing a solar cell differs from Example 1 in that the crystallinity of the first crystallinity region is 98%, while the rest are the same as in Example 1.

[0088] Comparative Example 1

[0089] Reference Figure 2 A method for preparing a solar cell includes the following steps:

[0090] 1) Take the experimental piece after the boron diffusion process and perform localized front-side laser treatment;

[0091] 2) Then, a texturing process is performed to remove the oxide layer in the laser contact area;

[0092] 3) Boron diffusion followed by oxidation (1020 ~ 1030 ℃) for 3000 s. This further deepens the junction in the non-laser region, and the thickness of the subsequently oxidized boron diffusion layer is slightly higher than the initial boron diffusion layer thickness (i.e., the initial boron diffusion layer generated before boron diffusion).

[0093] 4) The experimental piece is subjected to alkaline polishing to remove the borosilicate glass on the back side, and then a tunneling oxide layer and a phosphorus diffusion layer are deposited.

[0094] The experimental piece was then subjected to further deposition of an alumina film and a silicon nitride film on both the front and back surfaces.

[0095] Comparative Examples 2-3

[0096] A method for fabricating a solar cell differs from Example 1 in that, in S2, the thickness D1 of the boron diffusion layer and the thickness D2 of the borosilicate glass oxide layer are different.

[0097] In Comparative Example 2, the thickness of the boron diffusion layer, D1, is 10 nm, and the thickness of the borosilicate glass oxide layer, D2, is 30 nm.

[0098] In Comparative Example 3, the thickness of the boron diffusion layer, D1, is 50 nm, and the thickness of the borosilicate glass oxide layer, D2, is 70 nm.

[0099] Comparative Example 4

[0100] A method for preparing a solar cell differs from Example 1 in that, in steps S3, laser crystallization, and film opening, the first laser contact area is not subjected to laser crystallization treatment, i.e., the second crystallization region and the first crystallization region are not formed.

[0101] Comparative Example 5

[0102] A method for preparing a solar cell differs from Example 1 in that, in steps S3, laser crystallization, and film opening, the second laser contact area is not subjected to laser crystallization treatment, i.e., the second crystallization rate region and the first crystallization rate region are not formed.

[0103] Comparative Example 6

[0104] A method for fabricating a solar cell differs from Example 1 in that, in steps S3, laser crystallization, and film-opening treatment, the third laser contact area is not laser-opened. That is, a groove structure is not formed in the third laser contact area after texturing.

[0105] Performance testing experiment

[0106] The battery structures of Examples 1-3 and Comparative Examples 1-6 were tested, and the test results are shown in Table 2.

[0107] Table 2. Test results of solar cells in Examples 1-3 and Comparative Examples 1-6

[0108] The test results of Examples 1-3 and Comparative Examples 1-6 show that Examples 1-3 are superior to Comparative Examples 1-6, indicating that this application uses gradient crystallization, which can eliminate the need for the post-oxidation high-temperature process step in the prior art. An initial low-temperature boron diffusion process generates a boron diffusion layer and a borosilicate glass oxide layer. First, laser crystallization is performed on the first laser contact area to allow the laser to directly contact the borosilicate glass oxide layer, improving the crystallinity of the underlying polycrystalline silicon layer. Then, laser crystallization is performed on the second laser contact area to further improve the crystallinity of this area and reduce the contact resistance of the gate contact area. Next, a localized boron diffusion layer of a certain width is formed in the third laser contact area. After wet texturing and cleaning, a residue-free, highly stable groove with controllable etching depth is formed. Subsequent generation of a new textured surface allows light to undergo multiple reflections and scatterings after entering the groove, increasing the path length of light inside the battery and improving light absorption efficiency.

[0109] Combining Examples 1 and 4-7 with the test results in Table 2, it can be seen that Example 1 is superior to Examples 4-7. This indicates that by controlling the crystallinity of the first crystallinity region and the second crystallinity region, this application can help reduce the contact resistance of the grid line region and improve the conversion efficiency of the battery.

[0110] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A solar cell, characterized in that: The silicon substrate includes a front side and a back side opposite to the front side. The front side of the silicon substrate includes a first laser contact area, a second laser contact area and a third laser contact area. The first laser contact area and the third laser contact area are alternately arranged on the front side of the silicon substrate, and there is a height difference between the first laser contact area and the third laser contact area. The projections of the second laser contact area and the first laser contact area in the vertical direction coincide, and the width of the second laser contact area is smaller than the width of the first laser contact area. The front side of the silicon substrate also includes a front metal electrode, which forms contact with the second laser contact area. The crystallinity of the second laser contact area is higher than that of the non-overlapping area in the first laser contact area.

2. A solar cell according to claim 1, characterized in that: The second laser contact area is the first crystallization rate region, and the non-overlapping area in the first laser contact area is the second crystallization rate region. The crystallization rate of the second crystallization rate region is 60% to 80%, and the crystallization rate of the first crystallization rate region is 90% to 95%.

3. A solar cell according to claim 1, characterized in that: The height difference between the first laser contact area and the third laser contact area is 2-5 μm.

4. A solar cell according to claim 1, characterized in that: The width of the first laser contact area is denoted as A1, and the width of the second laser contact area is denoted as A2. The ratio of A2 to A1 is 1:(3~5).

5. A solar cell according to claim 1, characterized in that: The width of the third laser contact area is denoted as A3, where A3 = 400~480μm.

6. A method for preparing a solar cell according to any one of claims 1-5, characterized in that, Includes the following steps: Pretreatment: The front side of the silicon substrate is texturized; Pre-boron process: Boron diffusion is performed on the front side of the pretreated silicon substrate to sequentially generate a boron diffusion layer and a phosphosilicate glass oxide layer; Laser crystallization and film opening process: The first and second laser contact areas of the silicon substrate after the pre-boron process are sequentially subjected to laser crystallization, and then the third laser contact area is subjected to laser film opening process. Texturing: The front side of the silicon substrate after laser crystallization and film opening is wet texturing to remove the boron diffusion layer and phosphosilicate glass oxide layer in the first laser contact area, and to form a groove in the third laser contact area with a pyramid textured surface. Polishing and deposition: The back side of the texturized silicon substrate is cleaned to form a polished structure, and a tunneling oxide layer and a phosphorus diffusion layer are sequentially prepared on the back side of the cleaned silicon substrate; Passivation: After depositing a first passivation layer on the front side of the silicon substrate, a second passivation layer is deposited on both the front and back sides of the silicon substrate; Printing fine grids: Fine grid paste is printed on the passivated silicon substrate, and the metal electrode is prepared by sintering.

7. The method for preparing a solar cell according to claim 6, characterized in that: In the aforementioned pre-boron process, boron diffusion is performed at a temperature ≤900℃ to form an inner boron diffusion layer and an outer borosilicate glass oxide layer. The thickness of the boron diffusion layer is denoted as D1, and the thickness of the borosilicate glass oxide layer is denoted as D2. D1 = 25 ~ 40 nm, and D2 = 40 ~ 60 nm.

8. The method for preparing a solar cell according to claim 6, characterized in that: In the laser crystallization and film-opening process, the laser power of the second laser contact area is greater than that of the first laser contact area, and the laser power of the third laser contact area is greater than that of the second laser contact area.

9. A method for preparing a solar cell according to claim 6, characterized in that: In the laser crystallization and film opening process, after the first laser contact area is subjected to laser crystallization treatment, ozone remediation treatment is also included.

10. A method for preparing a solar cell according to claim 6, characterized in that: In the texturing process, the groove depth formed by the third laser contact area is denoted as D3, where D3 = 2~5μm.

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