A method for manufacturing a single crystal silicon cell and a single crystal silicon cell

Abstract

The present application provides a kind of monocrystalline silicon cell and its preparation method, including the following steps: texturing on at least one surface of monocrystalline silicon wafer substrate, obtain the monocrystalline silicon wafer with a plurality of continuous pyramid structure of pyramid surface on the at least one surface;At least one pyramid surface of the obtained monocrystalline silicon wafer is doped with diffuser, obtain the monocrystalline silicon wafer with PN junction;Using slurry containing spherical metal particles on the side of the monocrystalline silicon wafer with PN junction with the at least one pyramid surface electrode grid printing and sintering, so that spherical metal particles form ohmic contact with pyramid surface.The present application further includes by laser SE process to enhance the ohmic contact of metal particles and pyramid tip.The present application improves fill factor, reduces open circuit voltage loss, increases battery conversion efficiency;Meet the dual needs of reducing contact area contact resistance and reducing non-contact area carrier recombination, reduce the electrical loss of solar cell.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, specifically, it relates to a method for preparing monocrystalline silicon solar cells and a monocrystalline silicon solar cell. Background Technology

[0002] As is well known, with the continuous improvement of solar cell efficiency, it is necessary to conduct in-depth research on various factors affecting efficiency in order to achieve higher conversion efficiency. The contact resistance between the semiconductor and metal grid lines, a significant factor in electrical losses, is a crucial factor. Therefore, existing manufacturing processes utilize selective emission regions to divide the front surface into two different doping regions to meet the different requirements of the emission region. In the grid line region at the electrode contact, a high dopant concentration is required to achieve good ohmic contact between the metal and semiconductor, thereby reducing contact resistance; therefore, heavy and deep doping is necessary in this region. In the light-absorbing region, a low dopant concentration is required to reduce carrier recombination; therefore, light doping is used in the non-electrode contact region.

[0003] Currently, the commonly used method for fabricating selective emission regions (SEPR) involves simultaneously preparing a pn junction via diffusion and then creating an oxide layer with a high dopant concentration on the front surface of the silicon wafer. A high-energy laser is then applied to directly drive the dopant into the gate contact areas where electrodes will be fabricated. The dopant in non-electrode contact areas remains in the oxide layer, unaffected by the laser. Subsequent etching removes the oxide layer on the front surface, achieving selective emission regions with different doping concentrations in different areas. During screen printing, the electrode gate pattern is matched to the SEPR to achieve the dual advantages of reduced contact resistance and reduced carrier recombination. However, on textured silicon wafer surfaces, the pyramid-like structure with its apex and valleys means that during laser-driven selective emission region electrode gate printing, the paste will preferentially etch the apex, forming contact with it. In this case, the high-concentration dopant in the valleys cannot effectively reduce contact resistance; instead, its high doping concentration leads to high carrier recombination, negatively impacting the cell efficiency.

[0004] In existing production processes, lasers simultaneously advance dopants at the top and bottom of the tower. This results in higher carrier recombination in the valley regions where the dopants are not corroded by the slurry, thus affecting efficiency. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing monocrystalline silicon solar cells, a method for laser differential propulsion of dopants, and monocrystalline silicon solar cells.

[0006] Specifically, the present invention relates to the following aspects:

[0007] 1. A method for preparing monocrystalline silicon solar cells, characterized in that the method comprises the following steps:

[0008] A single-crystal silicon wafer is texturized on at least one surface of a single-crystal silicon substrate to obtain a single-crystal silicon wafer with a pyramidal textured surface having a plurality of continuously arranged pyramidal structures on the at least one surface, wherein

[0009] Let L be the average length of the base of the triangular cross-section obtained by cutting through the apex of the pyramid structure in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid.

[0010] The average angle between the side of the triangular cross-section obtained by cutting through the pyramid tip in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid structure and the base is defined as θ.

[0011] At least one pyramidal textured surface of the obtained single-crystal silicon wafer is subjected to dopant diffusion to obtain a single-crystal silicon wafer with a PN junction;

[0012] Electrode grid lines are printed and sintered on one side of a single-crystal silicon wafer with a PN junction having at least one pyramidal textured surface using a paste containing spherical metal particles, so that the spherical metal particles form an ohmic contact with the pyramidal textured surface.

[0013] The spherical metal particles contained in the slurry have a D90 ≥ L / (4sinθ).

[0014] 2. The method according to item 1, characterized in that the D90 range of the metal particles is L / (4sinθ)≤D90≤2L.

[0015] 3. The method according to item 1, wherein θ is 45-75°, preferably 50-65°, and more preferably 54.75-60°.

[0016] 4. The method according to item 3, wherein L is 0.5-5 μm, preferably 1-3 μm, and more preferably 1.2-1.8 μm.

[0017] 5. The method according to item 4, characterized in that the D90 range of the metal particles is 1μm≤D90≤4μm.

[0018] 6. The method according to item 1, characterized in that obtaining a doped single-crystal silicon wafer comprises the following steps:

[0019] A dopant diffusion process is performed on a single-crystal silicon wafer with a pyramidal textured surface to form a dopant-containing silicon dioxide layer on the surface of the pyramidal textured surface.

[0020] The dopants in the silicon dioxide layer are propelled by laser, and the concentration of the dopants at the top of the pyramid is higher than that at the bottom of the pyramid.

[0021] 7. The method according to item 6, characterized in that the power of the laser in laser propulsion is 18-32W.

[0022] 8. The method according to item 7, characterized in that the marking speed in laser propulsion is 20000-30000 mm / s and the laser frequency is 200-300 Hz.

[0023] 9. The method according to item 1, wherein the dopant is phosphorus.

[0024] 10. A monocrystalline silicon solar cell, characterized in that at least one surface of the monocrystalline silicon solar cell has a pyramidal textured surface with a plurality of continuously arranged pyramidal structures forming a PN junction.

[0025] Let L be the average length of the base of the triangular cross-section obtained by cutting through the apex of the pyramid structure in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid.

[0026] The average angle between the side of the triangular cross-section obtained by cutting through the pyramid tip in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid structure and the base is defined as θ.

[0027] The pyramid-shaped textured surface has electrode grid lines, in which spherical metal particles are distributed to form ohmic contact with the pyramid-shaped textured surface, and the D90 of the spherical metal particles is ≥ L / (4sinθ).

[0028] 11. The monocrystalline silicon solar cell according to item 10, characterized in that the D90 range of the metal particles is L / (4sinθ)≤D90≤2L.

[0029] 12. The monocrystalline silicon solar cell according to item 10, characterized in that θ is 45-75°, preferably 50-65°, and more preferably 54.75-60°.

[0030] 13. The monocrystalline silicon solar cell according to item 10, wherein L is 0.5-5 μm, preferably 1-3 μm, and more preferably 1.2-1.8 μm.

[0031] 14. The monocrystalline silicon solar cell according to item 10, characterized in that the D90 range of the metal particles is 1μm≤D90≤4μm.

[0032] 15. The monocrystalline silicon solar cell according to item 10, characterized in that the apex of the pyramidal textured surface is laser-driven to form a chamfered structure.

[0033] 16. The solar cell according to claim 10, characterized in that the monocrystalline silicon solar cell is prepared by any one of claims 1-9.

[0034] This invention improves the selective emission stage process by utilizing the different degrees of dopant propagation by the laser at the apex and trough of the pyramid, thereby achieving different dopant concentrations in the apex region (in contact with the slurry) and the non-contact trough region. This improves the fill factor, reduces open-circuit voltage loss, and increases cell conversion efficiency. Compared to existing technologies, it does not impose higher requirements on the selective emission process and meets the dual requirements of reducing contact resistance in the contact area and reducing carrier recombination in the non-contact area, thus reducing the electrical losses of the solar cell. Attached Figure Description

[0035] Figure 1 A top view of the pyramid-shaped pile structure formed after pile processing;

[0036] Figure 2 This is a side view of the pyramid-shaped pile structure formed after pile fabrication.

[0037] Figure 3 A schematic diagram illustrating the calculation of the relationship between the size of metal particles in the slurry and the size of the pyramid.

[0038] Figure 4 This is a schematic diagram showing metal particles in the slurry in contact with the top of the pyramid but not with the bottom.

[0039] Figure 5 This is a schematic diagram illustrating the differential propulsion of a laser at the top and bottom of a pyramid.

[0040] Figure 6 This is a scanning electron microscope (SEM) image of the pyramid textured surface according to an embodiment of the present invention;

[0041] Figure 7 This is a scanning electron microscope (SEM) image showing the laser propulsion of the pyramid tip in Embodiment 1 of the present invention;

[0042] Figure 8 This is a scanning electron microscope (SEM) image showing the laser propulsion of the pyramid tip in Embodiment 2 of the present invention;

[0043] Figure 9 The image shows the scanning electron microscope (SEM) results of the slurry in Example 1 after contact sintering with the pyramid.

[0044] Figure 10 The image shows the scanning electron microscope (SEM) results of the slurry in Comparative Example 1 after contact sintering with the pyramid.

[0045] Figure 11 The results show the differences in series resistance and fill factor of the monocrystalline silicon solar cells prepared in Example 3 and Comparative Example 1. Detailed Implementation

[0046] The present invention will be further described below with reference to embodiments. It should be understood that the embodiments are only used to further illustrate and explain the present invention, and are not intended to limit the present invention.

[0047] Unless otherwise defined, technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art. While similar or identical methods and materials may be applied in experimental or practical applications, materials and methods are described herein. In case of conflict, the definitions included herein shall prevail. Furthermore, materials, methods, and examples are for illustrative purposes only and are not intended to be limiting. The invention is further described below with reference to specific embodiments, but is not intended to limit the scope of the invention.

[0048] This invention provides a method for preparing monocrystalline silicon solar cells, the method comprising the following steps:

[0049] Step 1: Texturing is performed on at least one surface of a monocrystalline silicon wafer substrate to obtain a monocrystalline silicon wafer with a pyramidal textured surface having multiple continuously arranged pyramidal structures on the at least one surface, wherein...

[0050] Let L be the average length of the base of the triangular cross-section obtained by cutting through the apex of the pyramid structure in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid.

[0051] The average angle between the side of the triangular cross-section obtained by cutting through the pyramid tip in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid structure and the base is defined as θ.

[0052] Step 2: At least one pyramidal textured surface of the obtained single-crystal silicon wafer is subjected to dopant diffusion to obtain a single-crystal silicon wafer with a PN junction;

[0053] Step 3: Using a paste containing spherical metal particles, electrode grid lines are printed and sintered on one side of a single-crystal silicon wafer with a PN junction that has at least one pyramidal textured surface, so that the spherical metal particles form an ohmic contact with the pyramidal textured surface.

[0054] In step one, the monocrystalline silicon wafer substrate can be either a P-type or an N-type monocrystalline silicon wafer; this invention does not limit the type. In one specific embodiment, the monocrystalline silicon wafer substrate used is a boron-doped monocrystalline silicon wafer. Before texturing, the monocrystalline silicon wafer substrate can be cleaned to remove impurities adsorbed on the surface of the silicon substrate during processes such as slicing, grinding, chamfering, and polishing.

[0055] The texturing method can employ methods known in the prior art. Texturing can be performed on one surface or both surfaces of a monocrystalline silicon wafer substrate. Specific process conditions can be adjusted by those skilled in the art according to actual needs. For example, texturing can be performed in a tank-type texturing equipment using an etching solution of NaOH and isopropanol. In one specific embodiment, the texturing conditions are as follows: Hydrogen peroxide in the pre-cleaning tank oxidizes organic matter on the silicon wafer surface, and sodium hydroxide dissolves the oxidation products while removing some of the mechanically damaged layer; then, the wafer is rinsed with deionized water in a water tank to remove desorbed impurities and residual alkali; in the texturing tank, a certain proportion of sodium hydroxide and additive solution is used to etch the monocrystalline silicon wafer, forming an uneven textured surface to increase light absorption; then, the wafer enters a post-cleaning tank to remove some organic matter remaining in the additives on the silicon wafer surface; next, it passes through a water washing tank to rinse with deionized water to remove desorbed impurities and residual alkali; finally, a slow lifting process removes desorbed impurities and residual acid, completing the entire texturing process.

[0056] The top view of the "pyramid" in this invention is as follows: Figure 1 As shown, the side view is as follows Figure 2 As shown, this is a regular square pyramid with a square base and four isosceles triangles on its sides sharing a common vertex. Figure 3 and Figure 4 As shown, the average length of the base of the triangular cross-section obtained by cutting through the pyramid tip in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid is considered as L, that is, the average length of the base of the regular square pyramid is L. The average angle between the side and the base of the triangular cross-section obtained by cutting through the pyramid tip in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid is considered as θ.

[0057] In step two, at least one pyramidal textured surface of the obtained single-crystal silicon wafer is subjected to dopant diffusion to obtain a single-crystal silicon wafer with a PN junction. Dopant diffusion can be performed using methods known in the prior art, and the specific process conditions can be adjusted by those skilled in the art according to actual needs. In one specific embodiment, the dopant is phosphorus.

[0058] In one specific implementation, the conditions for phosphorus doping can be as follows: using a tubular diffusion furnace from Naura Technology Group, the monocrystalline silicon wafer is first inserted into a quartz boat and then placed on a silicon carbide paddle, followed by feeding into the inlet tube; after ensuring the furnace tube is properly sealed, nitrogen gas is introduced into liquid phosphorus oxychloride and connected to the furnace tube, and phosphorus diffusion is performed on the monocrystalline silicon wafer under high temperature; then high-temperature propulsion is carried out to diffuse the impurity source into the silicon wafer, increasing the junction depth and reducing the concentration on the silicon wafer surface; after cooling, oxygen is introduced to completely react and remove any unreacted phosphorus source, preventing contamination of the external air after opening the furnace door; finally, nitrogen gas is introduced to purge the furnace tube while balancing the pressure, and the furnace door is opened to remove the diffused monocrystalline silicon wafer from the furnace tube.

[0059] In step three, during the electrode grid line printing process, the glass frit in the paste first dissolves into a liquid, which etches the silicon dioxide and silicon nitride layers generated in step two, thereby exposing the emitter silicon surface. Depending on the desired electrode grid lines, pastes containing different metal particles can be selected, such as pastes containing silver particles.

[0060] like Figure 3 As shown, given θ and L, the average height H of the pyramid can be determined, i.e., H = (L / 2) * tanθ. If the metal particles in the slurry are tangent to the pyramid's hypotenuse at a point one-quarter of the total length of the hypotenuse from the bottom upwards, and let a be the vertical height from the point of tangency to the bottom of the pyramid, then a = H / 4 = (L / 8) * tanθ. Let b be the average distance between the center point of the metal particles in the slurry and the contact points between the two hypotenuses of the pyramid, then b / 2 = a * tan(90° - θ) = (L / 8) * tanθ * tan(90° - θ) = L / 8, b = L / 4. The corresponding diameter of the metal particles is D = 2r = b / sinθ = L / (4sinθ).

[0061] Because the apex of the pyramid is higher than the valley floor, the metal particles in the slurry will preferentially contact the apex, where the laser-driven dopant concentration is higher. Meanwhile, the organic matter in the slurry, due to its density, will aggregate and flow to the valley floor, forming a protective layer. Furthermore, the size of the metal particles is generally greater than or equal to the distance between the apex points, making it difficult for particles to fall into the valley floor where the laser-driven dopant concentration is lower, thus preventing poor contact. A schematic diagram is shown below. Figure 4As shown; next, after high-temperature sintering in the sintering furnace, the metal particles form a good ohmic contact with the pyramid tip with low contact resistance, resulting in a reduction in series resistance, an increase in fill factor, and a positive gain in efficiency; the valley region has virtually no metal particles, and organic matter will volatilize under high temperature, reducing carrier recombination and open-circuit voltage loss, thus positively impacting efficiency. Therefore, the metal particles should be appropriately matched to the pyramid size, with the particle size D90 ideally such that approximately 90% or more of the metal particles are in roughly tangential contact with more than a quarter of the pyramid's hypotenuse. In other words, the D90 range of the metal particles should be D90 ≥ L / (4sinθ) to ensure reduced carrier recombination in the valley region.

[0062] More preferably, the D90 range of the metal particles is D90≤2L, that is, L / (4sinθ)≤D90≤2L. This is because, in the ideal case where the pyramid size distribution is extremely concentrated, four adjacent pyramid structures correspond to at most one metal particle, thus forming a good ohmic contact between the top of each pyramid and the metal particle. When a large number of metal particles exceed the average size of the pyramid base 2L, compression will occur between adjacent metal particles, causing some pyramid tips to be unable to contact the top of the pyramid, thereby deteriorating the ohmic contact between the metal particles and the pyramid surface and increasing the contact resistance.

[0063] Theoretically, any acute angle θ (0-90 degrees) can be used. However, to ensure that the laser propulsion is more focused on the pyramid tip of the textured surface, and to guarantee sufficient contact between the metal particles and the area from the valley to the pyramid tip, the preferred angle is 45-75°. Examples include 45°, 50°, 55°, 60°, 65°, 70°, and 75°, with 50-65° being more preferred to further enhance the combination of contact performance and laser propulsion. Within this angle range, 54.75°-60° is even more preferred, representing the conventional tilt angle for alkaline etching of the pyramid textured surface. This tilt angle can be obtained through conventional alkaline etching without requiring additional complex textured surface angle adjustment processes.

[0064] The average length L can be 0.5-5 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm, preferably 1-3 μm, and more preferably 1.2-1.8 μm. In some embodiments, L can be selected in the range of 1-2 μm. Under the minimum or maximum value of L within this range, the corresponding range of D90 of the silver paste particles is 0.5-2 μm and 1-4 μm, respectively. With the above-mentioned size matching, this application can ensure sufficient ohmic contact between the silver paste particles and the pyramid textured surface of the PN junction, while significantly reducing carrier recombination at the bottom of the pyramid.

[0065] It should be noted that although the length of the base of each pyramid in the pyramid textured surface, and the angle formed by the side of the triangular cross-section obtained by cutting the pyramid tip and the base, may fluctuate somewhat relative to the average length L and average angle θ, this does not affect the implementation of the embodiments of the present invention. Existing texturing methods do not result in particularly large dispersions in the aforementioned lengths and angles. Furthermore, the metal paste actually used contains a certain amount of low-melting-point conductive material and glass frit, and the distribution of metal particles has a certain degree of dispersion. Therefore, when the D90 of the metal particles in the metal paste meets the requirements, a large number of pyramid structures can already form sufficient ohmic contact with metal particles of suitable size at a relatively high position above the base, such as above 1 / 4 of the pyramid height. In addition, smaller metal particles can supplement the ohmic contact near the top of smaller pyramid structures, and the low-melting-point conductive material fuses between the metal particles during sintering to form conductive connections. Therefore, although the pyramid-patterned surface of the present invention may ultimately result in a small number of pyramid structures and small-sized metal particles forming ohmic contact at the bottom of the pyramid, as can be seen from the above analysis, this will not lead to the situation described in the prior art. Figure 10 The diagram shows that many of the pyramid bases exhibit deteriorated ohmic contact.

[0066] In a preferred embodiment, the step of obtaining a doped single-crystal silicon wafer may include the following steps:

[0067] Dopant diffusion is performed on at least one pyramidal textured surface of the obtained single-crystal silicon wafer to form a dopant-containing silicon dioxide layer on the surface of at least one pyramidal textured surface.

[0068] The dopants in the silicon dioxide layer are propelled by laser, and the concentration of the dopants at the top of the pyramid is higher than that at the bottom of the pyramid.

[0069] When using laser propulsion, such as Figure 5 As shown, this invention employs appropriate laser power to enhance the fit between the original metal particles and the pyramid size. The laser further accentuates the doping effect at the pyramid tip, forming N...++ The doped region improves the conductivity at the pyramid tip, while also making the tip smoother and less sharp, forming a chamfered structure. This increases the effective ohmic contact area between the metal particles and the pyramid, reducing the ohmic contact resistance, thus lowering the series resistance, increasing the fill factor, and positively impacting efficiency.

[0070] Specifically, when using lasers to propel dopants, the atoms at the apex of the pyramid have more dangling bonds, lower bond energies, and four exposed interfaces. At this point, the atoms at the apex have higher energy and are in an active, unstable state. Therefore, during laser propulsion, the laser more easily drives the dopant into the apex, resulting in a higher dopant concentration there. Conversely, the atoms at the valleys of the pyramid have higher bond energies and only two exposed interfaces. The probability of these atoms being in a stable state is much higher than at the apex, and the area of ​​the valleys is much larger. Therefore, under the same laser energy, much less dopant is driven into the valleys compared to the apex.

[0071] Choosing the right laser propulsion conditions is crucial. Excessive laser power will not only drive in the active dopant atoms at the top of the cell, but also have enough energy to activate and drive in the stable dopant atoms at the bottom. In this case, the high dopant concentration at the top of the cell will be beneficial for reacting with the screen printing paste and forming good contact, while the high dopant concentration at the bottom of the cell will lead to more carrier recombination, which will have a negative impact on the efficiency of the cell. On the other hand, if the laser power is too low, due to insufficient energy, the dopant atoms at the top of the cell may not be driven in sufficiently, and the concentration required to form good ohmic contact with the paste may not be achieved.

[0072] To achieve the best doping effect, in one specific embodiment, the power of the laser in laser propulsion is 18-32W, for example, it can be 18W, 19W, 20W, 21W, 22W, 23W, 24W, 25W, 26W, 27W, 28W, 29W, 30W, 31W, or 32W.

[0073] In one specific implementation, a laser manufactured by Wuhan Teil is used, and the marking speed during laser propulsion is 20,000-30,000 mm / s, for example, 20,000 mm / s, 21,000 mm / s, 22,000 mm / s, 23,000 mm / s, 24,000 mm / s, 25,000 mm / s, 26,000 mm / s, 27,000 mm / s, 28,000 mm / s, 29,000 mm / s, or 30,000 mm / s.

[0074] In one specific implementation, the laser frequency in laser propulsion is 200-300Hz, for example, it can be 200Hz, 210Hz, 220Hz, 230Hz, 240Hz, 250Hz, 260Hz, 270Hz, 280Hz, 290Hz, or 300Hz.

[0075] In one specific implementation, the laser power in laser propulsion is 18-32W, the marking speed is 20000-30000mm / s, and the laser frequency is 200-300Hz.

[0076] The damage caused by the laser to the pyramid textured surface after laser propulsion, as well as the effect of dopant propulsion, can be observed using a scanning electron microscope.

[0077] The present invention also provides a monocrystalline silicon solar cell, wherein at least one surface of the monocrystalline silicon solar cell has a pyramidal textured surface with multiple continuously arranged pyramidal structures forming a PN junction.

[0078] Let L be the average length of the base of the triangular cross-section obtained by cutting through the apex of the pyramid structure in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid.

[0079] The average angle between the side of the triangular cross-section obtained by cutting through the pyramid tip in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid structure and the base is defined as θ.

[0080] The pyramid-shaped textured surface has electrode grid lines, in which spherical metal particles are distributed to form ohmic contact with the pyramid-shaped textured surface, and the D90 of the spherical metal particles is ≥ L / (4sinθ).

[0081] More preferably, the D90 range of the metal particles is D90≤2L, that is, L / (4sinθ)≤D90≤2L.

[0082] The θ angle can theoretically be any acute angle, i.e., 0-90 degrees, but is preferably 45-75°, for example, 45°, 50°, 55°, 60°, 65°, 70°, 75°, and even more preferably 50-65°.

[0083] The length L can be 0.5-5 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, preferably 1-3 μm, and more preferably 1.2-1.8 μm. In some embodiments, L can be selected in the range of 1-2 μm. Under the minimum or maximum value of L in this range, the corresponding range of D90 of the silver paste particles is 0.5-2 μm and 1-4 μm, respectively.

[0084] Furthermore, due to the laser propulsion effect, the apex of the pyramidal textured surface of the monocrystalline silicon solar cell of the present invention becomes smoother and less sharp, forming a chamfered structure.

[0085] Furthermore, the monocrystalline silicon solar cell can be prepared by the above method.

[0086] Example

[0087] Example 1

[0088] 1. Using boron-doped monocrystalline silicon wafers as experimental wafers, a pyramidal textured surface was prepared in a Jiejia Weichuang trough-type texturing equipment: First, hydrogen peroxide in the pre-cleaning tank oxidizes the organic matter on the silicon wafer surface, while sodium hydroxide dissolves the oxidation products and removes some of the mechanically damaged layer. Next, the wafer is rinsed with deionized water in a water tank to remove the desorbed impurities and residual alkali. In the texturing tank, a certain proportion of sodium hydroxide and additive solution is used to corrode the monocrystalline silicon wafer, forming an uneven textured surface to increase light absorption. Then, the wafer enters the post-cleaning tank to remove some organic matter from the additives remaining on the silicon wafer surface. It then passes through a water washing tank 2 to rinse with deionized water to remove the desorbed impurities and residual alkali. Finally, a slow lifting process removes the desorbed impurities and residual acid, completing the entire texturing process.

[0089] The scanning electron microscope results of the prepared pyramid textured surface are as follows: Figure 6 As shown, the average length L of the base of the triangular cross-section obtained by cutting through the pyramid tip in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid is 1.7 μm, the average angle θ between the side and the base of the triangular cross-section obtained by cutting through the pyramid tip in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid is 54.75°, and the height is 1.1 μm.

[0090] 2. The texturized silicon wafer is placed in a tube diffusion furnace for phosphorus diffusion to prepare a pn junction. Simultaneously, a phosphorus-containing silicon dioxide layer of phosphorus-silicon glass is prepared on the surface of the silicon wafer. Using a tube diffusion furnace from Naura Technology Group, the monocrystalline silicon wafer is first inserted into a quartz boat and then placed on a silicon carbide paddle, followed by feeding into the inlet tube. After ensuring the furnace tube is properly sealed, nitrogen gas is introduced into liquid phosphorus oxychloride and connected to the furnace tube. Phosphorus diffusion of the monocrystalline silicon wafer is carried out at a high temperature (750℃-880℃). This is followed by high-temperature propulsion. The impurity source is diffused into the silicon wafer to increase the junction depth and reduce the concentration on the silicon wafer surface. Then, the temperature is lowered (750℃-780℃), and then phosphorus oxychloride is introduced again for diffusion to replenish the phosphorus doping concentration on the surface, providing a phosphorus source for subsequent SE laser propulsion. After that, oxygen is introduced to completely react and remove any unreacted phosphorus oxychloride to prevent contamination of the outside air after the furnace door is opened. Finally, nitrogen is introduced to purge the furnace tubes and balance the pressure before opening the furnace door to remove the diffused monocrystalline silicon wafer from the furnace tubes.

[0091] 3. Selective emission regions were prepared on the diffused silicon wafer. Laser propulsion was used to advance the dopant in the silicon dioxide layer. Specifically, the laser propulsion operating conditions were: laser power of 32W, marking speed of 28000mm / s, and laser frequency of 250Hz. The laser-propulsed single-crystal silicon wafer was characterized by scanning electron microscopy to observe its pyramidal textured morphology. The results are as follows: Figure 7 As shown, the greater damage at the top of the pyramid allows for the introduction of more dopant, resulting in a significant decrease in resistance. Most of the dopant introduction points are located at the apex of the pyramid, and the damage to the apex makes its shape less sharp, which can enhance the ohmic contact between the apex and the silver particles in the subsequent sintering silver paste. However, a higher laser power will further damage the apex of the pyramidal surface, leading to a deterioration of the original light-trapping structure. Therefore, the laser power should not exceed 32W; otherwise, the final solar cell will have increased light reflectivity due to the deterioration of the light-trapping effect, resulting in a decrease in the cell's conversion efficiency.

[0092] 4. The laser-driven monocrystalline silicon wafers undergo etching, annealing, and coating. A Jiejia Weichuang tank etching machine is used, employing HF acid and nitric acid to etch the front and rear surfaces. This removes the phosphorus-containing silicon dioxide layer formed on the front surface during the diffusion process and the pyramid structure formed on the rear surface during texturing, polishing the rear surface to facilitate better growth of the silicon nitride passivation layer. A Naura tube annealing machine is used to anneal the silicon wafer in a furnace tube. Oxygen is used in a high-temperature environment (650℃-780℃) to oxidize the laser-driven diffusion surface, generating a silicon dioxide film for passivation. Finally, a Naura tube coating machine is used to coat the silicon wafer in a furnace tube. Ammonia and silane react under vacuum to grow silicon nitride films on both the front and rear surfaces of the annealed monocrystalline silicon wafer, achieving passivation and anti-reflection effects.

[0093] 5. A Maiwei chain printing press is used to screen print the solar cells. The back electrode is revealed by screen printing the aluminum paste on the back side, and the front electrode is revealed by screen printing the silver paste on the front side. The electrodes printed on the monocrystalline silicon wafer are then sintered in a Maiwei sintering furnace. During sintering, the glass phase in the silver paste softens and melts, wetting the silicon wafer surface and etching the anti-reflection film, followed by etching the silicon emitter. At this time, silicon reacts with metal oxides in a redox reaction, releasing metallic silver particles and forming corrosion pits. During cooling, Ag particles recrystallize near these corrosion pits, meaning silver particles grow onto the silicon wafer surface. The reacted glass and organic matter volatilize in the high-temperature environment. After sintering, the metal and silicon wafer form an ohmic contact with low contact resistance, thus producing the finished monocrystalline silicon solar cell. The D90 of the silver particles in the front silver paste is greater than or equal to 1 μm and less than or equal to 4 μm. The scanning electron microscope (SEM) image of the final monocrystalline silicon solar cell is shown below. Figure 9 As shown in the figure, the size of the silver particles in the slurry is much larger than the distance between the apex of the pyramid. The silver particles cannot fall into the valley area, so they will directly contact each other at the apex of the adjacent pyramid, while there is no contact in the valley area.

[0094] Example 2

[0095] The difference between Example 2 and Example 1 lies in the operating conditions of laser propulsion in step 3. Specifically, the laser propulsion operating conditions are: laser power of 18W, marking speed of 28000mm / s, and laser frequency of 250Hz.

[0096] The laser-driven single-crystal silicon wafer was characterized by scanning electron microscopy to observe its pyramidal textured surface. The results are as follows: Figure 8 As shown, the damage is smaller and less dopant is introduced. In contrast to Example 1, under this laser propulsion process, the damage range at the pyramid tip is smaller, and the pyramid textured surface maintains a better light-trapping texture. However, due to less dopant introduced at the pyramid tip, the resistance reduction is smaller, and the sharper pyramid tip shape is not conducive to ohmic contact with conductive particles. Therefore, the ohmic contact between the pyramid tip and the silver particles in the subsequent sintered silver paste is weakened compared to Example 1. Thus, the laser power should not be lower than 18W; otherwise, the final solar cell will experience increased series resistance due to the deterioration of the paste ohmic contact, resulting in a decrease in the cell's conversion efficiency.

[0097] Example 3

[0098] The difference between Example 3 and Example 1 lies in the operating conditions of laser propulsion in step 3. Specifically, the laser propulsion operating conditions are: laser power of 27W, marking speed of 26000mm / s, and laser frequency of 250Hz.

[0099] Comparative Example 1

[0100] The difference between Comparative Example 1 and Example 3 lies in the D90 of the silver particles in the silver paste in step 5. Specifically, the D90 of the silver particles in the silver paste is less than 1 μm. Because the size of the silver particles in the paste is less than 1 μm, these silver particles fall into the valley of the pyramid. At the valley, due to the selective propulsion of the laser, the concentration of the dopant phosphorus is lower, resulting in a larger contact resistance after contact with the paste, causing an increase in the series resistance of the solar cell and a decrease in the fill factor. This contact of the silver particles is like... Figure 10 As shown in Table 1, the specific operating conditions for each embodiment and comparative example are as follows:

[0101] Table 1

[0102]

[0103] Test case

[0104] The differences in series resistance and fill factor were measured in the monocrystalline silicon solar cells prepared in Example 3 and Comparative Example 1. The results are as follows: Figure 11 As shown, solar cells made from monocrystalline silicon wafers through texturing, diffusion, SE, etching, annealing, coating, screen printing, and sintering are subjected to illumination tests using an IV testing instrument simulating sunlight. Calculations are then performed to output various parameters, including series resistance and fill factor. The main differences in conversion efficiency between solar cells stem from differences in series resistance and fill factor. The results in the figure show that, compared to the solar cell of Comparative Example 1, the solar cell of this invention has a 0.33% higher fill factor and a 0.13 milliohm lower series resistance.

[0105] The series resistance mainly consists of the base region resistance, the lateral resistance of the emitter region, the contact resistance between the silver electrode and the emitter region, and the line resistance of the silver grid lines. With other battery manufacturing processes unchanged, reducing the contact resistance between the silver electrode and the emitter region leads to a decrease in series resistance and an increase in the fill factor, thereby improving the cell's conversion efficiency. The contact resistance between the silver electrode and the emitter region is mainly determined by the doping concentration of the emitter region. In the cell of this invention, the series resistance is lower than in existing processes, thus achieving the goal of reducing series resistance and increasing the fill factor. Simultaneously, the selective advancement of the SE (Sediment Electrode) maintains a low concentration in the valley region not in contact with the slurry, further improving the open-circuit voltage.

Claims

1. A method of preparing a single crystal silicon cell, characterized by, The method includes the following steps: A single-crystal silicon wafer is texturized on at least one surface of a single-crystal silicon substrate to obtain a single-crystal silicon wafer with a pyramidal textured surface having a plurality of continuously arranged pyramidal structures on the at least one surface, wherein Let L be the average length of the base of the triangular cross-section obtained by cutting through the apex of the pyramid structure in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid. The average angle between the side of the triangular cross-section obtained by cutting through the pyramid tip in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid structure and the base is defined as θ. Dopant diffusion is performed on at least one pyramidal textured surface of the obtained single-crystal silicon wafer to obtain a single-crystal silicon wafer with a PN junction, wherein the concentration of dopant at the pyramid apex is higher than the concentration at the pyramid trough. Electrode grid lines are printed and sintered on one side of a single-crystal silicon wafer with a PN junction having at least one pyramidal textured surface using a paste containing spherical metal particles, so that the spherical metal particles form an ohmic contact with the pyramidal textured surface. The spherical metal particles contained in the slurry have a D90 ≥ L / (4sinθ); The D90 range of the metal particles is 1μm≤D90≤4μm.

2. The method of claim 1, wherein, The D90 range of the metal particles is L / (4sinθ)≤D90≤2L.

3. The method of claim 1, wherein, θ is 45-75°.

4. The method of claim 3, wherein, θ is 50-65°.

5. The method of claim 3, wherein, θ is 54.75-60°.

6. The method of claim 3, wherein, L is 0.5-5μm.

7. The method of claim 6, wherein, L is 1-3 μm.

8. The method of claim 6, wherein, L is 1.2-1.8 μm.

9. The method of claim 1, wherein, Obtaining a single-crystal silicon wafer with a PN junction includes the following steps: Dopant diffusion is performed on at least one pyramidal textured surface of the obtained single-crystal silicon wafer to form a dopant-containing silicon dioxide layer on the surface of at least one pyramidal textured surface. The dopants in the silicon dioxide layer are propelled by laser.

10. The method of claim 9, wherein, The power of the laser used in laser propulsion is 18-32 W.

11. The method of claim 10, wherein, The marking speed in laser propulsion is 20,000-30,000 mm / s, and the laser frequency is 200-300 Hz.

12. The method of claim 1, wherein, The dopant is phosphorus.

13. A single crystal silicon cell, characterized by At least one surface of the monocrystalline silicon solar cell has a pyramidal textured surface with multiple continuously arranged pyramidal structures forming a PN junction, wherein the concentration of dopant at the apex of the pyramid is higher than the concentration at the trough of the pyramid. Let L be the average length of the base of the triangular cross-section obtained by cutting through the apex of the pyramid structure in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid. The angle between the side of the triangular cross-section obtained by cutting through the pyramid tip in a direction perpendicular to the silicon wafer substrate and parallel to the base of the pyramid structure and the base edge is defined as θ. The pyramid-shaped textured surface has electrode grid lines, in which spherical metal particles are distributed to form ohmic contact with the pyramid-shaped textured surface, and the D90 of the spherical metal particles is ≥ L / (4sinθ). The D90 range of the metal particles is 1μm≤D90≤4μm.

14. The single crystal silicon solar cell of claim 13, wherein, The D90 range of the metal particles is L / (4sinθ)≤D90≤2L.

15. The monocrystalline silicon solar cell according to claim 14, characterized in that, θ is 45-75°.

16. The single crystal silicon slice of claim 15, wherein, θ is 50-65°.

17. The monocrystalline silicon solar cell according to claim 15, characterized in that, θ is 54.75-60°.

18. The single crystal silicon slice of claim 13 wherein, L is 0.5-5μm.

19. The single crystal silicon solar cell of claim 18, wherein, L is 1-3 μm.

20. The single crystal silicon slice of claim 18, wherein, L is 1.2-1.8 μm.

21. The single crystal silicon slice of claim 13 wherein, The pyramid's textured surface is laser-driven to create a chamfered structure at its apex.

22. The cell defined in claim 13, wherein The monocrystalline silicon solar cell is prepared by the method according to any one of claims 1-12.

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