Silicon substrate and preparation method thereof, and back contact solar cell

Abstract

The invention provides a silicon substrate, a preparation method and a back contact solar cell, the silicon substrate comprises a first surface and a second surface, the second surface comprises at least one smooth curved surface area, the smooth curved surface area comprises a plurality of smooth curved surfaces, and the plurality of smooth curved surfaces are in irregular or array distribution in the smooth curved surface area. According to the method, the smooth curved surface region is formed after the second surface of the silicon wafer is subjected to laser processing and auxiliary chemical smoothing treatment, the smooth curved surface region comprises the irregular or array-distributed smooth curved surfaces, and after the functional layer is prepared in the smooth curved surface region, the surface area of PN and NN + junctions of the solar cell can be increased, so that the double-sided rate of the solar cell is improved, passivation is facilitated, and the service life of the solar cell is prolonged. The invention is suitable for back-contact solar cells.

Description

Technical Field

[0001] This invention belongs to the field of solar cell processing technology, specifically relating to a silicon substrate and its preparation method, and a back-contact solar cell. Background Technology

[0002] Currently, in the fabrication process of back-contact solar cells, due to the difference in passivation effect between the P and N poly passivation layers on the back side, and the fact that the P and N electrodes are located on the same side, the back side of the silicon substrate is designed to be polished. Although this facilitates the control of wet process on the production line and simplifies the process, and is beneficial for surface passivation treatment, the relatively small area of ​​the PN and NN+ junction regions affects the quantum efficiency of the long-wavelength band on the back surface. Furthermore, the polished surface results in a small contact area between the gate lines and the substrate, affecting adhesion, and the high reflectivity on the back side affects the bifaciality.

[0003] In existing technologies, although methods such as planarizing the back pyramid, designing an inverted pyramid, and fabricating a new pyramid on the pyramid surface are used to increase the specific surface area, the difference in surface state magnitude caused by crystal orientation differences still cannot be avoided. For example, after surface planarization... <100> After crystal orientation passivation, the surface state density can be reduced to 1E10cm. -2 Below, the edge of the pyramid <111> After crystal orientation passivation, the surface state density can be reduced to 1E11 cm⁻¹. -2 Around, but still higher <100> The surface state density and dihedrality of the crystal orientation cannot be improved. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the prior art, the present invention proposes a silicon substrate and its preparation method, and a back contact solar cell.

[0005] To achieve the above objectives, according to a first aspect of the present invention, a silicon substrate is provided, comprising a first surface and a second surface disposed opposite to each other, the second surface comprising at least one smooth surface region, the smooth surface region comprising a plurality of smooth surfaces, the plurality of smooth surfaces being irregularly or arrayed in the smooth surface region.

[0006] According to the above scheme, the smooth surface region includes a bowl-shaped smooth surface, a groove-shaped smooth surface, or a mixture of a bowl-shaped smooth surface and a groove-shaped smooth surface; The diameter of the opening side of the bowl-shaped smooth curved surface is 2~50µm, the depth is 1~15µm, and the longitudinal section is arc-shaped; The groove-shaped smooth curved surface has a groove width of 2~50µm and a groove depth of 1~15µm on the open side, and its longitudinal section is arc-shaped, and / or... The surface roughness Sa of the smooth surface ranges from 0.2 to 1 µm; and / or, The projected area of ​​the smooth surface on the second surface accounts for 80% or more of the projected area of ​​the smooth surface region on the second surface; and / or, The smooth curved surface regions are continuously distributed on the second surface; or, the smooth curved surface regions are spaced apart on the second surface, and the space between two adjacent smooth curved surface regions is a smooth plane.

[0007] According to a second aspect of the present invention, a method for preparing a silicon substrate is provided, wherein a laser is used to pattern the second surface of a silicon wafer to form a curved area, the curved area comprising a plurality of curved surfaces, the plurality of curved surfaces being irregularly distributed or arrayed in the curved area; The first and second surfaces of the silicon wafer are chemically smoothed, wherein the first surface forms a smooth plane and the second surface forms a smooth curved surface region at the patterned processing position. The smooth curved surface region includes multiple smooth curved surfaces formed by smoothing the curved surface, and the multiple smooth curved surfaces are irregularly distributed or arrayed in the smooth curved surface region.

[0008] When performing the patterning process according to the above method, the pattern of the patterning process includes a bowl-shaped curved surface, a groove-shaped curved surface, or both a bowl-shaped curved surface and a groove-shaped curved surface. The diameter of the opening side of the bowl-shaped curved surface is 2.5~62.5µm, the depth is 1~18.75µm, and the longitudinal section is arc-shaped; The groove width on the open side of the groove-shaped curved surface is 2.5~62.5m, the groove depth is 1~18.75µm, and the longitudinal section is arc-shaped.

[0009] According to a third aspect of the present invention, another method for preparing a silicon substrate is provided, wherein a first surface and a second surface of a silicon wafer are polished. The first and second surfaces of the silicon wafer are masked. A laser is used to pattern the second surface, remove the mask, and form a curved area on the silicon wafer. The curved area includes multiple curved surfaces, which are irregularly or arrayed in the curved area. Chemical smoothing treatment forms a smooth surface region in the patterned area. The smooth surface region includes multiple smooth surfaces formed by surface smoothing. The multiple smooth surfaces are irregularly distributed or arrayed in the smooth surface region. Remove the mask from the first and second surfaces.

[0010] According to the other method described above, when performing the patterning process, the pattern of the patterning process includes a bowl-shaped surface, a groove-shaped surface, or both a bowl-shaped surface and a groove-shaped surface. The diameter of the opening side of the bowl-shaped curved surface is 2~50µm, the depth is 1~15µm, and the longitudinal section is arc-shaped; The groove width on the open side of the groove-shaped curved surface is 2~50µm, the groove depth is 1~15µm, and the longitudinal section is arc-shaped.

[0011] According to the above method and another method, the surface roughness Sa within the smooth surface ranges from 0.2 to 1 µm, and / or, The projected area of ​​the smooth surface on the second surface accounts for 80% or more of the projected area of ​​the smooth surface region on the second surface.

[0012] According to the above method and another method, the smooth curved surface region is continuously distributed on the second surface; or, the smooth curved surface region is distributed at intervals on the second surface, and the interval region between two adjacent smooth curved surface regions is a smooth plane; The smooth surfaces in the smooth surface region are either continuous or intermittently distributed.

[0013] According to a fourth aspect of the present invention, a back-contact solar cell is provided, comprising a silicon substrate, wherein the back surface of the silicon substrate includes at least one smooth curved surface region, the smooth curved surface region including a plurality of smooth curved surfaces, the plurality of smooth curved surfaces being irregularly or arrayed in the smooth curved surface region; It also includes a P-region functional layer and an N-region functional layer spaced apart on the back side of the silicon substrate, a GAP region is provided between adjacent P-region functional layers and N-region functional layers, a passivation layer and an electrode are provided on the P-region functional layer and the N-region functional layer, a passivation layer is provided on the GAP region of the silicon substrate, and a passivation layer is provided on the front side of the silicon substrate. The P-region functional layer and the N-region functional layer are at least partially disposed in the smooth curved surface region of the silicon substrate.

[0014] According to the above scheme, the smooth surface region includes a bowl-shaped smooth surface, a groove-shaped smooth surface, or a mixture of bowl-shaped and groove-shaped smooth surfaces. The diameter of the opening side of the bowl-shaped smooth curved surface is 2~50µm, the depth is 1~15µm, and the longitudinal section is arc-shaped; The groove width on the open side of the groove-shaped smooth curved surface is 2~50µm, the groove depth is 1~15µm, and the longitudinal section is arc-shaped.

[0015] According to the above scheme, the surface roughness Sa of the smooth surface ranges from 0.2 to 1 µm, and / or, The orthographic projection area of ​​the smooth surface on the back side accounts for 80% or more of the orthographic projection area of ​​the smooth surface region on the second surface.

[0016] According to the above scheme, the silicon substrate at the GAP region location has a pyramid structure.

[0017] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: 1. This invention, by processing the second surface of a silicon wafer and assisting in chemical smoothing treatment, forms an irregular or array-distributed smooth curved surface, which can increase the surface area of ​​the PN and NN+ junctions of the solar cell, thereby improving the bifaciality of the solar cell, and is conducive to surface passivation treatment, and is suitable for solar cells with back passivation contact structures.

[0018] 2. This invention obtains the basic shape of a curved surface through laser processing, and then obtains a smooth curved surface through chemical smoothing treatment. The process is simple and easy to implement. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a back-contact solar cell structure in the prior art.

[0020] Figure 2 This is a schematic diagram of a back-contact solar cell structure provided in an embodiment of the present invention.

[0021] Figure 3 An optical microscope image of a silicon wafer processed by laser to form multiple spaced pits, according to an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of a second surface structure of a silicon substrate provided in an embodiment of the present invention.

[0023] Figure 5 yes Figure 4 A cross-sectional schematic diagram of a silicon substrate.

[0024] Figure 6 This is a schematic diagram of another silicon substrate second surface structure provided in an embodiment of the present invention.

[0025] Figure 7 yes Figure 6 A cross-sectional schematic diagram of a silicon substrate.

[0026] Figure 8-13 These are schematic diagrams of several other silicon substrate second surface structures provided in embodiments of the present invention.

[0027] In the figure: 1-silicon substrate, 2-front passivation layer, 301-P-region functional layer, 302-N-region functional layer, 4-electrode, 101-smooth curved surface region, 102-smooth planar region. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0029] Figure 1 This is a schematic diagram of a back-contact solar cell structure in the prior art, including a silicon substrate 1. The front side of the silicon substrate has a pyramid structure, and a passivation layer 2 is disposed on the front side of the silicon substrate 1. The area on the back side of the silicon substrate 1 corresponding to the P-region functional layer 301 and the N-region functional layer 302 is a polished structure. A passivation layer (not shown in the figure) and a back electrode 4 are disposed on the P-region functional layer 301 and the N-region functional layer 302. It can be seen that the contact surfaces between the silicon substrate 1 and the P-region functional layer 301 and the N-region functional layer 302 are all polished planes. The relatively small area of ​​the PN and NN+ junction regions affects the quantum efficiency of the long-wavelength band on the back side. Furthermore, the polished planes result in a small contact area between the grid lines and the silicon substrate, and the reflectivity is above 25%, affecting the bifaciality. This invention mainly addresses the structural characteristics of back-contact solar cells by performing laser patterning processing on the back surface of the silicon wafer, followed by chemical smoothing treatment, to form an irregular or arrayed smooth curved surface, such as... Figure 2 As shown, the contact surfaces between the silicon substrate 1 and the P-region functional layer 301 and the N-region functional layer 302 of the present invention include smooth curved surfaces. The smooth curved surfaces increase the surface area of ​​the PN and NN+ junctions and the metallization contact area, while improving the bifaciality of the solar cell and facilitating surface passivation.

[0030] On one hand, the present invention provides a silicon substrate including a first surface and a second surface disposed opposite to each other, wherein the second surface includes at least one smooth surface region, the smooth surface region including a plurality of smooth surfaces, the plurality of smooth surfaces being irregularly or arrayed in the smooth surface region.

[0031] It should be noted that array distribution refers to a smooth surface that is arranged in a regular array, while irregular distribution refers to a smooth surface that is arranged in an irregular pattern.

[0032] In some embodiments, the smooth surface is a bowl-shaped smooth surface or a groove-shaped smooth surface. The bowl-shaped smooth surface has an opening diameter of 2-50 µm, a depth of 1-15 µm, and an arc-shaped longitudinal section. The groove-shaped smooth surface has an opening width of 2-50 µm, a groove depth of 1-15 µm, and an arc-shaped longitudinal section. The smooth surface region includes a bowl-shaped smooth surface, a groove-shaped smooth surface, or both.

[0033] Preferably, the surface roughness of the smooth curved surface is... <100> The surface roughness is relatively uniform across crystal orientations; in this invention, Sa ranges from 0.2 to 1 µm, where the values ​​are specific to a point or range. The projected area of ​​the smooth surface on the second surface accounts for 80% or more of the projected area of ​​the smooth surface region on the second surface. Specifically, adjacent smooth surfaces can be connected or spaced apart. When smooth surfaces are connected, the projected area of ​​the smooth surface on the second surface can account for 100% of the projected area of ​​the smooth surface region on the second surface.

[0034] Furthermore, the smooth curved surface regions are continuously distributed on the second surface, or the smooth curved surface regions are spaced apart on the second surface, with the spacer region between two adjacent smooth curved surface regions being a smooth plane. Preferably, the smooth curved surface regions are distributed parallel to each other on the second surface. When fabricating a back contact solar cell, the P-region functional layer and the N-region functional layer can be set corresponding to the spaced smooth curved surface regions, and the GAP region can be set corresponding to the spacer region.

[0035] Furthermore, the first surface of the silicon substrate is a smooth plane.

[0036] On the other hand, the present invention provides a back-contact (BC) solar cell, which is fabricated on the aforementioned silicon substrate. Specifically, the back-contact solar cell includes a silicon substrate, the back side of which includes at least one smooth curved surface region, the smooth curved surface region including multiple smooth curved surfaces, the multiple smooth curved surfaces being irregularly or arrayed in the smooth curved surface region.

[0037] It should be noted that array distribution refers to a smooth surface that is arranged in a regular array, while irregular distribution refers to a smooth surface that is arranged in an irregular pattern.

[0038] It also includes a P-region functional layer and an N-region functional layer spaced apart on the back side of the silicon substrate, a GAP region between the P-region functional layer and the N-region functional layer, a passivation layer and a back electrode on the P-region functional layer and the N-region functional layer, a passivation layer on the GAP region of the silicon substrate, and a textured surface on the front side of the silicon substrate with a passivation layer thereon; wherein, the P-region functional layer and the N-region functional layer are at least partially disposed in the smooth curved surface region of the silicon substrate.

[0039] As will be understood by those skilled in the art, the P-region functional layer and the N-region functional layer can be tunneling passivation structures. For example, the P-region functional layer includes a tunneling oxide layer and a boron-doped polysilicon layer sequentially disposed on the back side of the silicon substrate, and the N-region functional layer includes a tunneling oxide layer and a phosphorus-doped polysilicon layer sequentially disposed on the back side of the silicon substrate.

[0040] Furthermore, in a back-contact solar cell of the present invention, the smooth surface is either a bowl-shaped smooth surface or a groove-shaped smooth surface; the diameter of the opening side of the bowl-shaped smooth surface is 2~50µm, the depth is 1~15µm, and the longitudinal section is arc-shaped; the groove width of the opening side of the groove-shaped smooth surface is 2~50µm, the groove depth is 1~15µm, and the longitudinal section is arc-shaped; the smooth surface region includes a bowl-shaped smooth surface, a groove-shaped smooth surface, or both a bowl-shaped smooth surface and a groove-shaped smooth surface.

[0041] Furthermore, in a solar cell with a back-side passivated contact according to the present invention, the surface roughness Sa of the smooth curved surface ranges from 0.2 to 1 µm, where the values ​​are specific to a point or range. The orthographic projection area of ​​the smooth curved surface on the second surface accounts for 80% or more of the orthographic projection area of ​​the smooth curved surface region on the second surface. Specifically, adjacent smooth curved surfaces can be connected or spaced apart. When smooth curved surfaces are connected to each other, the orthographic projection area of ​​the smooth curved surface on the second surface can account for 100% of the area of ​​the smooth curved surface region.

[0042] Furthermore, in a back-contact solar cell of the present invention, the GAP region can be disposed on a smooth plane of the silicon substrate, or at least partially disposed on a smooth curved surface region. Preferably, the P-region functional layer and the N-region functional layer are disposed on the smooth curved surface region of the silicon substrate, and the GAP region is disposed on a smooth plane on the back side of the silicon substrate. It is understood that when texturing the front side of the back-contact solar cell, texturing of the corresponding position of the GAP region on the back side of the silicon substrate is also completed simultaneously. Correspondingly, the silicon substrate at the position corresponding to the GAP region is a planar textured surface, or a combination of a smooth curved textured surface and a planar textured surface. In other words, the silicon substrate at the position corresponding to the GAP region has a pyramid structure.

[0043] On the other hand, the present invention also provides a method for preparing the aforementioned silicon substrate and back contact solar cell, thereby forming the aforementioned silicon substrate and back contact solar cell.

[0044] To enable those skilled in the art to better understand the embodiments of the present invention, the following examples are provided for description.

[0045] Example 1: This embodiment provides a method for preparing a silicon substrate, including the following steps: S1. The second surface of the silicon wafer is patterned using a laser.

[0046] In this process, a laser is used to pattern the second surface of the silicon wafer, forming pits (bowl-shaped surfaces) and / or grooves (grooves) of a certain depth. Specifically, the patterning process can produce bowl-shaped pit patterns, groove patterns, or patterns that include both bowl-shaped pits and grooves.

[0047] See Figure 3 , Figure 3This is an optical microscope image showing multiple spaced pits created by laser processing on the second surface of a silicon wafer. As can be seen from the image, the diameter gradually decreases from the opening side towards the depth direction, and the longitudinal cross-section of the pit is arc-shaped; in other words, it has a bowl-shaped structure.

[0048] In this invention, the diameter of the opening side of the bowl-shaped curved surface is 2~62.5µm, the depth is 1~18.75µm, and the longitudinal section is arc-shaped.

[0049] The groove-shaped curved surface has a groove width of 2~62.5µm and a groove depth of 1~18.75µm on the open side, and its longitudinal section is arc-shaped. The groove width gradually decreases from the open side to the depth direction.

[0050] Laser energy density is 15,000~90,000 mJ / cm² 2 The point value or range value is specified. During processing, a pulsed laser is used, with one or more pulses acting on the same position to process the aforementioned curved surface. More specifically, when processing pits, one or more pulses act on the same position to form a pit, with the optimal method being a single pulse to form a single pit. During laser scanning, the laser spots are controlled to prevent overlap, resulting in multiple pits. When processing grooves, the laser scans along the length of the groove, controlling the laser spot overlap rate to be greater than 0, thus forming a groove. It should be noted that those skilled in the art, based on the technical concept of this invention, can control the laser energy density and the number of pulses to process the aforementioned curved surface pattern. When the energy is too high or the number of pulses is too large, the depth will increase, forming flat pits or grooves.

[0051] As a typical embodiment, the laser energy density used in this invention is 23000 mJ / cm². 2 Each position is processed by a single pulse to form such as Figure 3 The pit shown.

[0052] When patterning the second surface using a laser, the patterned areas can be continuously distributed or spaced apart on the second surface. When spaced apart, the P-region functional layers and N-region functional layers can be fabricated on the spaced patterned areas during subsequent solar cell fabrication; the spaced areas correspond to the gaps (GAPs).

[0053] S2. The first and second surfaces are chemically smoothed, forming smooth curved surfaces and smooth planes. In this way, the first surface becomes a smooth plane, and the patterned area of ​​the second surface becomes a smooth curved surface area. Each smooth curved surface area forms multiple smooth curved surfaces formed by the surface smoothing treatment. The smooth curved surfaces are irregularly or in an array distribution in the smooth curved surface area.

[0054] It should be noted that array distribution refers to a smooth surface that is arranged in a regular array, while irregular distribution refers to a smooth surface that is arranged in an irregular pattern.

[0055] After this chemical smoothing process, the surface roughness Sa within the smoothed surface ranges from 0.2 to 1 µm. Here, surface roughness refers to the roughness of the surface within the smoothed surface. The orthographic projection area of ​​the smoothed surface on the second surface accounts for 80% or more of the orthographic projection area of ​​the smoothed surface region on the second surface. Specifically, adjacent smoothed surfaces can be connected or spaced apart. When smoothed surfaces are connected, the orthographic projection area of ​​the smoothed surface on the second surface can account for 100% of the orthographic projection area of ​​the smoothed surface region on the second surface.

[0056] After this chemical smoothing process, the resulting smooth surface is either a bowl-shaped smooth surface or a groove-shaped smooth surface. The bowl-shaped smooth surface is a depression similar to a bowl, with a diameter of 2~50µm on the open side, a depth of 1~15µm, and an arc-shaped longitudinal section. It is formed by the chemical smoothing process of the depression.

[0057] The resulting groove-shaped smooth curved surface is a groove with a groove width of 2~50µm and a groove depth of 1~15µm on the open side. Its longitudinal section is arc-shaped and is formed by the chemical smoothing treatment of the groove.

[0058] Furthermore, the chemical smoothing treatment uses an alkaline solution, specifically: chemical smoothing treatment is performed using an alkaline wet process solution. The alkaline wet process solution includes an alkaline substance, with the mass ratio of the alkaline substance in the stock solution being 45%, and the volume ratio of the alkaline substance stock solution to water in the prepared alkaline wet process solution being 2%~50%. In some embodiments, the chemical smoothing treatment time is 10~600s, and the temperature is 50~90℃. Preferably, an alkaline polishing additive with polishing properties can also be used to enhance the smoothing effect; for example, a commercially available alkaline polishing additive is used, and its volume percentage in the total alkaline wet process solution is 2~5%. It should be noted that when using alkaline solutions for smoothing treatment, the concentration of alkaline substances in the alkaline solution, the smoothing treatment time, and the temperature must be within the above-mentioned ranges to achieve the smoothing effect. Excessive concentration, excessively long smoothing treatment time, or excessively high temperature may lead to over-corrosion, forming square lattices or pyramids, and failing to achieve the effect of smooth curved surfaces.

[0059] The etching rate at laser-processed areas is lower than that at non-laser-processed areas, resulting in less roughness in the resulting pits and / or grooves. Those skilled in the art, based on the technical concept of this invention, can obtain smooth curved surfaces and smooth flat surfaces by controlling the alkali content of the alkaline solution, the processing time, and the temperature.

[0060] In a typical implementation, the volume ratio of the alkaline substance stock solution is 5%, and the solution is applied at 75°C for 150 seconds.

[0061] In addition, chemical smoothing treatment can also use an acid solution, specifically: chemical smoothing treatment is performed using an acidic wet solution. In some embodiments, the mass ratio of HF in the HF stock solution is 49%, the mass ratio of HNO3 in the HNO3 stock solution is 69%, and the volume ratio of each stock solution in the prepared acid solution is: HF:HNO3:H2O = 1:(1~3):(1~10). Preferably, an acid polishing additive with polishing effect can also be used to enhance the smoothing effect. For example, the acid polishing additive is a commercially available additive, which accounts for 0.2~2% of the total volume of the acidic wet solution.

[0062] In a typical implementation, the original liquid volume ratio is HF:HNO3:H2O = 1:1:8.

[0063] It should be noted that when the first and second surfaces are chemically smoothed, due to the chemical thinning effect, the diameter or width of the opening side and the depth of the curved surface will be reduced to a certain extent after the chemical smoothing treatment, not exceeding 20%.

[0064] See Figures 4 to 13 Figure 4 This is a schematic diagram of a second surface structure of a silicon substrate provided in an embodiment of the present invention. Figure 5 yes Figure 4 A cross-sectional schematic diagram. Figure 6 This is a schematic diagram of another silicon substrate second surface structure provided in an embodiment of the present invention. Figure 7 yes Figure 6 A cross-sectional schematic diagram. Figure 8-13 These are schematic diagrams of several other silicon substrate second surface structures provided in embodiments of the present invention.

[0065] A silicon substrate structure obtained by the above method is as follows: Figure 4 and Figure 5 As shown, the device includes a silicon substrate 1 having a first surface and a second surface. The first surface is a smooth plane, and the second surface includes a plurality of parallel and spaced smooth curved surface regions 101. Each smooth curved surface region 101 includes a plurality of arrayed bowl-shaped smooth curved surfaces, the interior of which is a smooth surface. A smooth plane region 102 is formed between adjacent smooth curved surface regions 101.

[0066] Another silicon substrate structure obtained by the above method is as follows: Figure 6 and Figure 7As shown, the device includes a silicon substrate 1 having a first surface and a second surface. The first surface is a smooth plane, and the second surface includes a plurality of parallel and spaced smooth curved surface regions 101. Each smooth curved surface region 101 includes a plurality of arrayed groove-shaped smooth curved surfaces, the interior of which is a smooth surface. A smooth plane region 102 is formed between adjacent smooth curved surface regions 101.

[0067] A smooth surface in a smooth surface region can be like... Figures 4 to 7 The array can be distributed on the second surface, or it can be distributed irregularly on the second surface. It can also include a combination of bowl-shaped smooth surfaces and groove-shaped smooth surfaces, for example, bowl-shaped smooth surfaces and groove-shaped smooth surfaces can be distributed alternately.

[0068] The grooved smooth surface can be continuously set in its extension direction, such as... Figure 6 As shown, it can also be set intermittently, such as... Figure 8 As shown, it can also be a combination of the two, such as Figure 9 As shown. The combination of bowl-shaped smooth surfaces and groove-shaped smooth surfaces can be arranged in blocks with intervals, such as... Figure 10 As shown, they can also be mixed and arranged in the same area, such as... Figure 11 As shown. When a bowl-shaped smooth surface, a groove-shaped smooth surface, or both bowl-shaped and groove-shaped smooth surfaces are included, they can be a regular array, such as... Figure 12 As shown, it can also be arranged irregularly, such as... Figure 13 As shown. and Figures 4 to 7 The smooth curved surface regions with multiple interval settings are different. Figures 8 to 13 It consists of a smooth curved surface region.

[0069] It should be noted that, Figures 4 to 13 The image roughly shows the location of the smooth surface region and the smooth surface itself, but it is not drawn to scale. In fact, the points in the image correspond to the bowl-shaped smooth surface, and the lines correspond to the groove-shaped smooth surface.

[0070] Furthermore, in the silicon substrate of the present invention, the surface roughness Sa within the smooth curved surface ranges from 0.2 to 1 µm, wherein the point value or range value indicates that the orthographic projection area of ​​the smooth curved surface on the second surface accounts for 80% or more of the total area of ​​the smooth curved surface region. Specifically, adjacent smooth curved surfaces can be connected or spaced apart. When smooth curved surfaces are connected to each other, the orthographic projection area of ​​the smooth curved surface on the second surface can account for 100% of the area of ​​the smooth curved surface region. In this embodiment, the roughness is data obtained using laser confocal microscopy.

[0071] Example 2: This embodiment provides a method for preparing a silicon substrate, including the following steps: S1. Perform chemical polishing on the first and second surfaces of the silicon wafer.

[0072] In this design, the first and second surfaces of the silicon wafer are two surfaces that are positioned opposite each other. During the subsequent fabrication of the solar cell, the first and second surfaces correspond to the front and back sides of the solar cell, respectively.

[0073] S2, Double-sided mask: Masking the first and second surfaces of the polished silicon wafer.

[0074] The mask can be SiN x SiO x SiON x Or, a multilayer membrane of two or more of them, etc.

[0075] S3. The second surface is patterned using a laser.

[0076] When patterning the second surface using a laser, the laser removes the mask and creates a curved area on the silicon wafer. Specifically, the patterning process can create bowl-shaped recesses (curved surfaces), grooves (grooved curved surfaces), or patterns that include both bowl-shaped recesses and grooves.

[0077] The diameter of the opening side of the bowl-shaped curved surface is 2~50µm, the depth is 1~15µm, and the longitudinal section is arc-shaped.

[0078] The groove width on the open side of the groove-shaped curved surface is 2~50µm, the groove depth is 1~15µm, and the longitudinal section is arc-shaped.

[0079] In this step, the laser energy density is ≥10000mJ / cm². 2 The point value or range value is specified. As a typical embodiment, the laser energy density used in this invention is 15000 mJ / cm². 2 Each position is processed with a single pulse.

[0080] When patterning the second surface using a laser, the patterned areas can be continuously distributed or spaced apart on the second surface. When spaced apart, the P-region functional layers and N-region functional layers can be fabricated on the spaced patterned areas during subsequent solar cell fabrication; the spaced areas correspond to the gaps (GAPs).

[0081] S4. Chemical smoothing treatment: curved surfaces are formed into smooth curved surfaces, and flat surfaces are formed into smooth flat surfaces. A smooth curved surface area is formed in the patterned area. The smooth curved surface area includes multiple smooth curved surfaces formed by chemical smoothing treatment of curved surfaces. The multiple smooth curved surfaces are irregularly distributed or arrayed in the smooth curved surface area.

[0082] It should be noted that array distribution refers to a smooth surface that is arranged in a regular array, while irregular distribution refers to a smooth surface that is arranged in an irregular pattern.

[0083] After this chemical smoothing process, the surface roughness Sa within the smoothed surface ranges from 0.2 to 1 µm. Here, surface roughness refers to the roughness of the surface within the smoothed surface. The orthographic projection area of ​​the smoothed surface on the second surface accounts for 80% or more of the orthographic projection area of ​​the smoothed surface region on the second surface. Specifically, adjacent smoothed surfaces can be connected or spaced apart. When smoothed surfaces are connected, the orthographic projection area of ​​the smoothed surface on the second surface can account for 100% of the orthographic projection area of ​​the smoothed surface region on the second surface.

[0084] After this chemical smoothing process, the resulting smooth surface is either a bowl-shaped smooth surface or a groove-shaped smooth surface. The bowl-shaped smooth surface is a depression similar to a bowl, with a diameter of 2~50µm on the open side, a depth of 1~15µm, and an arc-shaped cross-section, formed by the chemical smoothing process of the depression.

[0085] The resulting groove-shaped smooth curved surface is called a groove. The groove width on the open side is 2~50µm, the groove depth is 1~15µm, and its cross-section is arc-shaped. It is formed by the groove chemical smoothing treatment.

[0086] Furthermore, the chemical smoothing treatment uses an alkaline solution, specifically an alkaline wet process. The alkaline wet process solution includes an alkaline substance, with the mass ratio of the alkaline substance in the stock solution being 45%. In the prepared alkaline wet process solution, the volume ratio of the stock alkaline substance to water is 2%–10%. In some embodiments, the chemical smoothing treatment time is 10–600 s, and the temperature is 50–90°C. Preferably, an alkaline polishing additive with polishing properties can be used to enhance the smoothing effect. For example, a commercially available polishing agent can be used as the alkaline polishing additive, accounting for 2–5% of the total volume of the alkaline wet process solution. It should be noted that when using alkaline solutions for chemical smoothing, the concentration of alkaline substances in the alkaline solution, the chemical smoothing treatment time, and the temperature must be within the above-mentioned ranges to achieve the smoothing effect. Excessive concentration, excessively long smoothing treatment time, or excessively high temperature may lead to over-corrosion, resulting in square lattices or pyramids, and failing to achieve the effect of smooth curved surfaces.

[0087] In a typical implementation, the volume ratio of the alkaline substance stock solution is 4%, and the solution is reacted at 75°C for 120 seconds.

[0088] In addition, chemical smoothing treatment can also be performed using an acid solution, specifically an acidic wet solution. In some embodiments, the mass ratio of HF in the HF stock solution is 49%, and the mass ratio of HNO3 in the HNO3 stock solution is 69%. The volume ratio of each stock solution in the prepared acid solution is HF:HNO3:H2O = 1:(1~3):(1~10). Preferably, an acid polishing additive with polishing properties can also be used to enhance the smoothing effect. For example, a commercially available polishing agent can be used as the acid polishing additive, and its volume ratio in the total acidic wet solution is 0.2~2%.

[0089] In a typical implementation, the original liquid volume ratio is HF:HNO3:H2O = 1:1.5:8.

[0090] In this embodiment, due to the presence of the mask, the diameter or width and depth of the opening side of the curved surface remain essentially unchanged.

[0091] S5. Remove the masks from the first and second surfaces to obtain the silicon substrate.

[0092] Specifically, the mask can be removed using an HF acid solution. The mask on the first and second surfaces is removed, exposing the polished surfaces of the first and second surfaces. It should be noted that, for ease of description, the terms "smooth surface area" and "smooth surface" are used in step S4; however, the actual smooth surface area, smooth surface, and smooth plane all refer to the surfaces after mask removal.

[0093] In addition, when acid solution treatment is used in step S4, the mask removal steps of the first and second surfaces are completed simultaneously.

[0094] The silicon substrate structure obtained by the above method is the same as the silicon substrate structure obtained in Example 1. The polished planes of the first and second surfaces are equivalent to the smooth planes of Example 1, and the roughness is not much different.

[0095] Example 3 This embodiment also provides a method for preparing a TBC solar cell, which is prepared using a silicon substrate formed in Example 1 or Example 2, including, S11. A tunneling oxide layer and an intrinsic amorphous silicon layer are prepared on the back side of a silicon substrate, and boron diffusion is performed to form a boron-doped polycrystalline silicon layer and a BSG layer.

[0096] S12. Laser process the N-region and GAP region on the back side of the silicon substrate to remove the BSG layer at the corresponding positions.

[0097] S13, alkaline chemical etching, to remove the boron-doped polysilicon layer and tunnel oxide layer in the N-region and GAP region.

[0098] S14. A tunneling oxide layer and an intrinsic amorphous silicon layer are prepared on the back side of a silicon substrate, and phosphorus diffusion is performed to form a phosphorus-doped polycrystalline silicon layer and a PSG layer.

[0099] S15. Laser process the P-area and GAP-area on the back of the silicon wafer to remove the PSG layer at the corresponding positions.

[0100] S16. Chemical etching (chain cleaning equipment): Removes the phosphorus-doped polysilicon layer and boron-doped polysilicon layer plated around the front edge, removes the phosphorus-doped polysilicon layer and tunneling oxide layer in the P area and GAP area, and the N area on the back is protected by PSG and the P area is protected by BSG, so there will be no further etching.

[0101] S17, Alkali texturing (tank equipment): Alkali texturing is performed to form a pyramid structure on the front side of the silicon substrate, while a GAP area is formed between the P and N regions on the back side.

[0102] Understandably, during alkaline texturing, if the GAP region is located in the smooth planar region 102 of the silicon substrate, then the back side of the silicon substrate corresponding to the GAP region, like the front side, forms a pyramid structure on the plane. If the GAP region corresponds to the smooth curved surface region 101 of the silicon substrate, then the smooth curved surface includes a pyramid structure, and the non-smooth curved surface positions of the smooth curved surface region also have pyramid structures. Thus, the silicon substrate at the GAP region location can have a pyramid structure on the plane, a pyramid structure on the smooth curved surface, or a combination of pyramid structures on the plane and the smooth curved surface. In other words, the back side of the silicon substrate corresponding to the GAP region has a pyramid structure.

[0103] Remove the PSG and BSG layers on the back surface in S18 and HF solutions.

[0104] S19, AlO2 deposited on the front and back sides x / SiN x passivation layer, or AlO x / SiN x / SiON x Multilayer passivation layers, etc.

[0105] S20, screen-printed grid line electrodes, sintered to form a battery.

[0106] It should be noted that the P-region functional layer and the N-region functional layer are at least partially disposed on the smooth curved surface region of the silicon substrate, and preferably all disposed on the smooth curved surface region. This can increase the surface area of ​​the PN and NN+ junctions and the metallization contact area, while improving the bifaciality of the solar cell and facilitating surface passivation treatment.

[0107] In this embodiment, steps S11-S20 are all conventional steps. TBC solar cells can also be fabricated using other conventional steps on the silicon substrate of this invention. It is understood that other back-contact solar cells, such as HBC, can also be fabricated.

[0108] It should be noted that, when describing the fabrication of the solar cell, the front side of the silicon substrate corresponds to the aforementioned first surface, and the back side of the silicon substrate corresponds to the aforementioned second surface. Here, the back side refers to the back surface of the solar cell, and the front side refers to the light-receiving surface of the solar cell.

[0109] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A silicon substrate comprising a first surface and a second surface disposed opposite to each other, characterized in that: The second surface includes at least one smooth surface region, which includes multiple smooth surfaces that are irregularly or arrayed in the smooth surface region.

2. The silicon substrate according to claim 1, characterized in that: The smooth surface region includes a bowl-shaped smooth surface, a groove-shaped smooth surface, or a mixture of bowl-shaped and groove-shaped smooth surfaces; The diameter of the opening side of the bowl-shaped smooth curved surface is 2~50µm, the depth is 1~15µm, and the longitudinal section is arc-shaped; The groove-shaped smooth curved surface has a groove width of 2~50µm and a groove depth of 1~15µm on the open side, and its longitudinal section is arc-shaped, and / or... The surface roughness Sa of the smooth curved surface ranges from 0.2 to 1 µm; And / or, The orthographic projection area of ​​the smooth surface on the second surface accounts for 80% or more of the orthographic projection area of ​​the smooth surface region on the second surface; and / or, The smooth curved surface regions are continuously distributed on the second surface; or, the smooth curved surface regions are spaced apart on the second surface, and the space between two adjacent smooth curved surface regions is a smooth plane.

3. A method for preparing a silicon substrate, characterized in that: A laser is used to pattern the second surface of a silicon wafer to form a curved area. The curved area includes multiple curved surfaces, which are irregularly or arrayed in the curved area. The first and second surfaces of the silicon wafer are chemically smoothed, wherein the first surface forms a smooth plane and the second surface forms a smooth curved surface region at the patterned processing position. The smooth curved surface region includes multiple smooth curved surfaces formed by smoothing the curved surface, and the multiple smooth curved surfaces are irregularly distributed or arrayed in the smooth curved surface region.

4. The method for preparing a silicon substrate according to claim 3, characterized in that: When performing the patterning process, the pattern includes a bowl-shaped surface, a groove-shaped surface, or both a bowl-shaped surface and a groove-shaped surface. The diameter of the opening side of the bowl-shaped curved surface is 2~62.5µm, the depth is 1~18.75µm, and the longitudinal section is arc-shaped; The groove width on the open side of the groove-shaped curved surface is 2~62.5m, the groove depth is 1~18.75µm, and the longitudinal section is arc-shaped.

5. A method for preparing a silicon substrate, characterized in that: The first and second surfaces of the silicon wafer are polished. The first and second surfaces of the silicon wafer are masked. A laser is used to pattern the second surface, remove the mask, and form a curved area on the silicon wafer. The curved area includes multiple curved surfaces, which are irregularly or arrayed in the curved area. Chemical smoothing treatment forms a smooth surface region in the patterned area. The smooth surface region includes multiple smooth surfaces formed by surface smoothing. The multiple smooth surfaces are irregularly distributed or arrayed in the smooth surface region. Remove the mask from the first and second surfaces.

6. The method for preparing a silicon substrate according to claim 5, characterized in that: When performing the patterning process, the pattern of the patterning process includes a bowl-shaped surface, a groove-shaped surface, or both a bowl-shaped surface and a groove-shaped surface; The diameter of the opening side of the bowl-shaped curved surface is 2~50µm, the depth is 1~15µm, and the longitudinal section is arc-shaped; The groove width on the open side of the groove-shaped curved surface is 2~50µm, the groove depth is 1~15µm, and the longitudinal section is arc-shaped.

7. A method for preparing a silicon substrate according to any one of claims 3 to 6, characterized in that: The surface roughness Sa within the smooth curved surface ranges from 0.2 to 1 µm, and / or, The projected area of ​​the smooth surface on the second surface accounts for 80% or more of the projected area of ​​the smooth surface region on the second surface.

8. A method for preparing a silicon substrate according to any one of claims 3 to 6, characterized in that: The smooth curved surface regions are continuously distributed on the second surface; or, the smooth curved surface regions are spaced apart on the second surface, and the space between two adjacent smooth curved surface regions is a smooth plane. The smooth surfaces in the smooth surface region are either continuous or intermittently distributed.

9. A back-contact solar cell, characterized in that: The device includes a silicon substrate, the back side of which includes at least one smooth curved surface region, the smooth curved surface region including multiple smooth curved surfaces, the multiple smooth curved surfaces being irregularly or arrayed in the smooth curved surface region; It also includes a P-region functional layer and an N-region functional layer spaced apart on the back side of the silicon substrate, a GAP region is provided between adjacent P-region functional layers and N-region functional layers, a passivation layer and an electrode are provided on the P-region functional layer and the N-region functional layer, a passivation layer is provided on the GAP region of the silicon substrate, and a passivation layer is provided on the front side of the silicon substrate. The P-region functional layer and the N-region functional layer are at least partially disposed in the smooth curved surface region of the silicon substrate.

10. A back-contact solar cell according to claim 9, characterized in that, The smooth surface region includes a bowl-shaped smooth surface, a groove-shaped smooth surface, or a mixture of bowl-shaped and groove-shaped smooth surfaces. The diameter of the opening side of the bowl-shaped smooth curved surface is 2~50µm, the depth is 1~15µm, and the longitudinal section is arc-shaped; The groove width on the open side of the groove-shaped smooth curved surface is 2~50µm, the groove depth is 1~15µm, and the longitudinal section is arc-shaped.

11. A back-contact solar cell according to claim 9, characterized in that: The surface roughness Sa of the smooth surface ranges from 0.2 to 1 µm, and / or, The orthographic projection area of ​​the smooth surface on the back side accounts for 80% or more of the orthographic projection area of ​​the smooth surface region on the second surface.

12. A back-contact solar cell according to any one of claims 9 to 11, characterized in that, The silicon substrate at the location of the GAP area has a pyramid structure.

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