Laser processing method and preparation method of solar cell and laser device

Abstract

A laser processing method of a solar cell comprises the steps that a silicon substrate is provided, the surface of the silicon substrate is provided with a film layer to be processed, and the film layer to be processed comprises at least one of a silica glass layer and a dielectric layer; laser is adopted to irradiate the local area of the to-be-processed film layer so as to remove the local area of the to-be-processed film layer, light spots of the laser are strip-shaped, the length-width ratio of the light spots is 2: 1 or above, the length of the light spots is larger than or equal to 200 micrometers, the laser is pulse laser, the pulse width ranges from 100 fs to 10 ps, the monopulse energy is larger than or equal to 100 microJ, and the wavelength ranges from 300 nm to 1200 nm. Through configuration of the strip-shaped laser spots with a certain length-width ratio, the effect of locally removing the film layer of the solar cell is achieved, and compared with an existing large-size square spot laser film opening process, the method has the advantages of being low in single-pulse energy requirement, good in process uniformity, high in stability and large in productivity improvement space. The invention also provides a preparation method of the solar cell and a laser device.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic material manufacturing and processing, and more specifically, to a laser processing method for solar cells, a method for preparing solar cells, and a laser device. Background Art

[0002] In the current preparation process of photovoltaic cells, laser technology is widely used in the patterning of the film materials to be processed in the battery. There are two main methods of laser patterning technology. The first is laser film opening, which removes the film materials to be processed in the laser area through the characteristics of laser instantaneous heating, and then selectively etches by wet method to retain the non-laser area; the second is laser oxidation, which forms an etching-resistant in-situ mask on the surface of the film material to be processed through laser induction, and then selectively etches by wet method to retain the laser area. In the laser film opening method, based on the removal of large areas of film layers to be processed and the need for high production capacity, a larger shaped spot is usually used to meet the film opening requirements. In order to ensure the appropriate pulse energy density to achieve instantaneous heating and removal of the film materials to be processed, a large spot means a correspondingly larger single pulse energy, which places high demands on both lasers and optical components. As far as the existing technology is concerned, it can achieve 250×250μm 2 The shaping square spot is used to remove the film layer to be processed, but when the width of the film is required to be 500μm or more, it is necessary to use the light spot splicing method to achieve the process effect, which will lead to a decrease in production capacity. Summary of the invention

[0003] In view of this, the present application provides a laser processing method for a solar cell, comprising: Providing a silicon substrate, wherein a film layer to be processed is disposed on a surface of the silicon substrate, and the film layer to be processed includes at least one of a silicon glass layer and a dielectric layer; Laser is used to irradiate a local area of ​​the film layer to be processed to remove the local area of ​​the film layer to be processed. The shape of the laser spot is a strip, the aspect ratio of the spot is 2:1 or above, the length is ≥200μm, the laser is a pulsed laser, the pulse width is 100fs~10ps, the single pulse energy is ≥100μJ, and the wavelength is 300~1200nm.

[0004] This application achieves the effect of local removal of the film layer of the solar cell through a specific strip-shaped laser spot configuration. Compared with the existing large-sized square spot laser film opening process, it has the advantages of low single pulse energy requirements, good process uniformity, high stability, and large room for capacity improvement, and reduces the requirements for lasers and optical components, thereby reducing the difficulty and cost of industrial mass production. By compressing the laser pulse energy into a narrow and long strip spot instead of a large-sized square spot, the pulse energy density requirement for film removal can be relatively easily achieved, and the production capacity can be ensured to be unaffected by simply increasing the pulse repetition frequency. Thanks to the setting of the aspect ratio of the strip spot, the technical effect of a large film opening line width can be achieved at one time without the need for spot splicing, with better uniformity, precision and stability.

[0005] In some embodiments, the laser has a wavelength of 300-600 nm.

[0006] In some embodiments, the moving speed of the laser along the processing direction is ≥40 m / s; and the length direction of the laser spot is perpendicular to the moving direction of the laser.

[0007] The present application also provides a method for preparing a TOPCon solar cell, comprising: Providing a silicon substrate, wherein the silicon substrate is an N-type silicon substrate and comprises a front side and a back side opposite to each other, and performing pre-processing on the silicon substrate; forming a tunneling oxide layer and an intrinsic amorphous silicon layer in sequence on the back side of the silicon substrate; Diffusion of phosphorus is performed on the intrinsic amorphous silicon layer to form a phosphorus-doped polysilicon layer. In this step, a phosphorus-silicate glass layer is formed on the outermost side of the back side. The back side includes a grid line area and a non-grid line area, and a laser is used to remove the phosphorus silicon glass layer on the back side located in the non-grid line area, the laser spot is in a strip shape, the aspect ratio of the laser spot is 2:1 or more, the length is ≥200 μm, the laser is a pulse laser, the pulse width is 100 fs~10 ps, ​​the single pulse energy is ≥100 μJ, and the wavelength is 300~1200 nm; Using wet etching to thin or remove the portion of the phosphorus-doped polysilicon layer located in the non-gate line area; and The silicon substrate is post-processed to form a solar cell.

[0008] By using a laser with a specific strip-shaped spot, the outermost phosphosilicate glass layer on the surface of the solar cell is selectively removed. The phosphosilicate glass layer in the gate line area can be used as a mask layer for subsequent etching of the phosphorus-doped polysilicon layer, thereby effectively etching, thinning or removing the phosphorus-doped polysilicon layer in the non-gate line area.

[0009] In some embodiments, after the wet etching, the thickness of the phosphorus-doped polysilicon layer in the non-gate line area is reduced to less than 50 nm.

[0010] In some embodiments, the moving speed of the laser along the processing direction is ≥40 m / s, and the length direction of the laser spot is perpendicular to the moving direction of the laser.

[0011] In some embodiments, the post-processing includes: Pickling to remove the remaining phosphosilicate glass layer and borosilicate glass layer; Forming a passivation layer and an anti-reflection layer on the front surface and the back surface in sequence; Conductive metal paste is printed on the gate line region on the back side and the front side and cured to form metal electrodes.

[0012] In some embodiments, the pre-processing includes: Cleaning and texturing the silicon substrate; Boron is diffused into the silicon substrate to form an emitter on the front side. In this step, a borosilicate glass layer is formed on the back side and the front side. The borosilicate glass layer formed on the back side is removed.

[0013] The present application also provides a method for preparing a back-contact solar cell, comprising: Providing a silicon substrate, wherein the silicon substrate is an N-type silicon substrate and includes a front side and a back side opposite to each other; forming a tunneling oxide layer and an intrinsic amorphous silicon layer in sequence on the back side; Diffusion of boron is performed on the intrinsic amorphous silicon layer to form a boron-doped polysilicon layer. In this step, a borosilicate glass layer is formed on the outermost side of the back side. The back side includes an N-region fine gate region, an N-region main gate region, a P-region fine gate region, and a P-region main gate region. The borosilicate glass layer located in the N-region fine gate region and the N-region main gate region on the back side is removed by laser. The N-region fine gate region and the N-region main gate region are cross-connected. The shape of the laser spot is a stripe. The aspect ratio of the laser spot is 2:1 or more, and the length is ≥200μm. The laser is a pulsed laser with a pulse width of 100fs~10ps, a single pulse energy ≥100μJ, and a wavelength of 300~1200nm. Wet etching is used to remove the portion of the boron-doped polysilicon layer on the back side located in the N-region fine gate region and the N-region main gate region; and post-processing is performed on the silicon substrate to form a solar cell.

[0014] By using a laser with a specific strip-shaped spot, the outermost silicon glass layer (phosphosilicate glass layer or borosilicate glass layer) on the surface of the solar cell is selectively removed. The retained silicon glass layer can be used as a mask layer for subsequent etching of the doped polysilicon layer, thereby effectively etching the doped polysilicon layer in the corresponding area, thereby realizing the preparation of a patterned P region or N region.

[0015] In some embodiments, the preparation method further comprises: forming a tunneling oxide layer and an intrinsic amorphous silicon layer again in sequence on the back side of the silicon substrate; Diffusion of phosphorus into the intrinsic amorphous silicon layer to form a phosphorus-doped polysilicon layer, wherein a phosphorus-silicate glass layer is formed on the outermost side of the back side in this step; The laser is used to remove the phosphorus silicon glass layer located at the P region fine gate region and the P region main gate region on the back side, and the P region fine gate region and the P region main gate region are cross-connected; The portion of the phosphorus-doped polysilicon layer located in the P-region fine gate region and the P-region main gate region is removed by wet etching.

[0016] In some embodiments, the post-processing includes: removing the phosphosilicate glass layer and the borosilicate glass layer on the back side; removing the film layer formed on the front surface; Forming a passivation layer and an anti-reflection layer on the front surface and the back surface in sequence; Conductive metal paste is printed on the N-region fine gate region, the N-region main gate region, the P-region fine gate region and the P-region main gate region on the back side and cured to form metal electrodes.

[0017] In some embodiments, the moving speed of the laser along the processing direction is ≥40 m / s, and the length direction of the laser spot is perpendicular to the moving direction of the laser.

[0018] The present application also provides a laser device, comprising: a laser, a reflector, a beam expander, a shaping element, a galvanometer, and a field mirror arranged in sequence along an optical path; The laser is used to emit pulsed laser; The reflector is used to reflect the pulsed laser from the laser and adjust and collimate it to the beam expander; The beam expander is used to expand the pulse laser; The shaping element is used to adjust the intensity distribution of the laser light, and forms a strip-shaped light spot with an aspect ratio after focusing; The galvanometer and the field lens are used to reflect and focus the laser light respectively, so as to project the strip-shaped spot of the laser light to a designated position; The laser device is used to emit laser, the shape of the laser spot is strip-shaped, the aspect ratio of the spot is 2:1 or above, the length is ≥200μm, the laser is a pulse laser, the pulse width is 100fs~10ps, the single pulse energy is ≥100μJ, and the wavelength is 300~1200nm.

[0019] In some embodiments, the shaping element is one of a diffractive optical element, a liquid crystal spatial modulator, and a microlens array.

[0020] In some embodiments, the laser device further comprises an optical adjustment frame, the shaping element is rotatably disposed on the optical adjustment frame, and the orientation of the laser spot is adjusted by rotating the shaping element; or The laser device further comprises an optical adjustment frame, wherein the laser device comprises at least two shaping elements arranged on the optical adjustment frame, and the orientation of the laser spot is changed by switching the at least two shaping elements in the optical path. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 FIG. 1 is a schematic diagram of a laser device for processing a solar cell according to an embodiment of the present application.

[0022] Figure 2 FIG. 1 is a schematic diagram of laser processing of a solar cell according to an embodiment of the present application.

[0023] Description of main component symbols: 100, laser device; 10, laser; 20, reflector; 30, beam expander; 40, shaping element; 50, galvanometer; 60, field lens; 42, optical adjustment frame; 11, strip light spot; 200, solar cell; 210, first processing area; 220, second processing area. DETAILED DESCRIPTION

[0024] The present application provides a laser processing method for a solar cell, which selectively removes a part of a film layer to be processed on the surface of a silicon substrate of a solar cell by using a laser with a strip-shaped spot having a certain aspect ratio, thereby realizing patterning of the film layer to be processed.

[0025] A laser processing method for a solar cell, comprising: Providing a silicon substrate, wherein a film layer to be processed is disposed on the surface of the silicon substrate, and the film layer to be processed includes at least one of a glass layer and a dielectric layer; Laser is used to irradiate a local area of ​​the film layer to be processed to remove the local area of ​​the film layer to be processed. The laser spot is a shaped flat top spot in a strip shape. The aspect ratio of the laser spot is 2:1 or more, and the length is ≥200μm. The preferred spot length is 200μm, 250μm, 300μm, 350μm, 400μm, 450μm, 500μm, 600μm. The aspect ratio of the laser spot is preferably 2:1-10:1, for example, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1.

[0026] The laser is a pulsed laser with a pulse width of 100fs~10ps and a single pulse energy ≥100μJ. Preferably, the single pulse energy is 100-500μJ, such as 100μJ, 200μJ, 300μJ, 400μJ, 500μJ, so as to achieve instantaneous removal of the film material to be processed and minimize laser-induced damage. Single pulse energy is the laser energy carried by a single pulse, pulse width is the time of a single pulse, and peak power is the maximum power reached by a single pulse. Since peak power = single pulse energy / pulse width, by limiting the range of pulse width and single pulse energy, a peak power suitable for film material removal can be obtained, which can avoid excessive peak power damaging the material under the film to be processed, resulting in performance degradation, and can also avoid incomplete removal of the film to be processed due to too low peak power.

[0027] The present application sets a strip-shaped laser spot with a certain length and width range, that is, the area size range of the laser spot can be determined. In addition, the present application also sets the pulse width and single pulse energy range of the laser, that is, the energy range of the laser can also be determined. In this way, the present application can roughly determine the range of the pulse energy density. The present application indirectly controls the pulse energy density of the laser through process parameters to ensure that the laser can effectively remove the film layer.

[0028] The wavelength of the laser is 300-1200 nm. In some embodiments, the laser is a laser with a wavelength of 300-600 nm to adapt to the penetration depth and thermal impact on the film material to be processed. For example, the laser is an ultraviolet laser with a wavelength of 355 nm, a green laser of 532 nm or 540 nm.

[0029] The length direction of the laser strip spot is perpendicular to the moving direction of the laser. The strip spot can significantly reduce the time of laser jumping and alignment per unit time, thereby improving the processing efficiency per unit time. It can also reduce the error during jumping and alignment and improve the uniformity of film processing.

[0030] By setting the size of the strip spot, the same pulse energy density can be achieved at a relatively low single pulse energy, thereby ensuring the film removal effect and reducing the difficulty of process implementation; or by setting the aspect ratio of the strip spot at the same single pulse energy and pulse energy density, the processing efficiency can be optimized to improve accuracy and productivity.

[0031] The moving speed of the laser along the processing direction is ≥40m / s. Generally, the increase in the moving speed of the laser will improve the processing efficiency of the laser. However, if the movement of the laser is not too large, otherwise the effect of laser removal of the film layer will be insufficient. Therefore, the present application sets a suitable moving speed, which not only matches the configuration of the laser spot, but also ensures the removal effect of the film layer. The preferred moving speed of the laser along the processing direction is 40-100m / s, such as 40m / s, 50m / s, 60m / s, 70m / s, 80m / s, 90m / s, 100m / s.

[0032] The orientation of the stripe light spot can be changed to meet the needs of different processing directions. Figure 2 For example, Figure 2 The first processing area 210 and the second processing area 220 intersect vertically, Figure 2 The middle dotted line indicates the moving direction of the stripe light spot 11. When the irradiation scanning of the first processing area 210 is completed, the orientation of the laser light spot needs to be changed and adjusted to irradiate and scan the second processing area 220. The present application has no limitation on the method of changing the orientation of the laser light spot.

[0033] In some embodiments, in addition to the film layer to be processed, other layers are provided on the surface of the silicon substrate of the solar cell, such as an N-type or P-type doped layer, and at least one of a glass layer and a dielectric layer is stacked on the N-type or P-type doped layer.

[0034] In some embodiments, the material of the glass layer is borosilicate glass (BSG) or phospho-silicate glass (PSG). The material of the dielectric layer is SiN x and / or SiO 2 .

[0035] The present application achieves the effect of local removal of the film layer of a solar cell by configuring a strip-shaped laser spot with a certain aspect ratio. Compared with the existing laser film opening process with a large-size square spot, it has the advantages of low single-pulse energy requirement, good process uniformity, high stability, and large room for capacity improvement. It also reduces the requirements for lasers and optical components, thereby reducing the difficulty and cost of industrial mass production.

[0036] By compressing the laser pulse energy into a narrow strip spot instead of a large square spot, the pulse energy density required for film removal can be relatively easily achieved, and the production capacity can be ensured to be unaffected by simply increasing the pulse repetition frequency. Thanks to the setting of the aspect ratio of the strip spot, the technical effect of large film opening line width can be achieved at one time without spot splicing, with better uniformity, accuracy and stability.

[0037] The present application also provides a method for preparing a tunnel oxide passivating contact (TOPCon) solar cell, which includes the above-mentioned laser processing method. The method for preparing a TOPCon solar cell includes the following steps S1 to S6.

[0038] S1: providing a silicon substrate, wherein the silicon substrate is an N-type silicon substrate and includes a front side and a back side opposite to each other, and performing pre-processing on the silicon substrate.

[0039] In some embodiments, in step S1, the pre-processing further includes: Cleaning and texturing the silicon substrate; Diffusion of boron into the silicon substrate to form a P-type emitter on the front side. In this step, a borosilicate glass layer is formed on the outermost sides of the back side and the front side. Back polishing removes the back structure, that is, polishing the back to remove the structure (such as the boron diffusion layer) formed on the back in the previous step, so that the back of the silicon substrate is exposed.

[0040] Boron diffusion is a conventional boron diffusion process. In some embodiments, the boron source used for boron diffusion can be selected from BCl 3 , BBr 3 , B 2 H 6 , trimethyl boron and other precursors. Under certain temperature conditions, boron source gas, oxygen, diluent gas (such as nitrogen) and the like are introduced to deposit boron on the surface of the silicon substrate; then high temperature is applied to promote the diffusion of boron into the silicon substrate.

[0041] In addition to the front and back sides, the silicon substrate also includes the side surfaces connected between the front and back sides. After boron diffusion, the outermost sides of each surface of the silicon substrate have a higher boron concentration, forming a BSG layer. The BSG layer formed on the side of the silicon substrate is prone to short circuits, and the BSG layer formed on the back of the silicon substrate will affect subsequent passivation, so both need to be removed.

[0042] In some embodiments, the BSG layer may be removed by etching using a chain BSG removal machine with a hydrofluoric acid solution to remove the BSG on the back and side surfaces.

[0043] S2: forming a tunneling oxide layer and an intrinsic amorphous silicon layer in sequence on the back side of the silicon substrate.

[0044] In some embodiments, step S2 is to form a tunnel oxide layer on the back of the silicon substrate by low pressure chemical vapor deposition (LPCVD), and to form an intrinsic amorphous silicon layer on the tunnel oxide layer, but the preparation method is not limited to LPCVD, and other preparation methods may also be used. The tunnel oxide layer is usually a silicon oxide layer with a thickness not exceeding 3 nm.

[0045] S3: Phosphorus is diffused into the intrinsic amorphous silicon layer to form a phosphorus-doped polysilicon layer, wherein a phosphorus-silicate glass layer is formed on the outermost side of the back side in this step.

[0046] The phosphorus diffusion in step S3 is a conventional phosphorus diffusion process. In some embodiments, after step S3, a phosphorus-silicate glass (PSG) layer is formed on the outermost side of each surface of the silicon substrate due to the high concentration of phosphorus. Usually, the PSG layer will be completely removed in subsequent steps. After the phosphorus diffusion, a phosphorus-doped polysilicon layer will also be formed on the front side, which can be removed in subsequent steps.

[0047] S4: The back side includes a grid line area and a non-grid line area. Laser is used to remove the phosphosilicate glass layer in the non-grid line area on the back side. The laser spot is a shaped flat-top spot in a strip shape with an aspect ratio of 2:1 or above and a length ≥200μm. The laser is a pulsed laser with a pulse width of 100fs~10ps, a single pulse energy ≥100μJ, and a wavelength of 300~1200nm.

[0048] In step S4, the PSG layer in the non-gate line area on the back is removed by utilizing the characteristics of laser instantaneous heating, and the phosphorus-doped polysilicon layer in the non-gate line area on the back is exposed, while the PSG in the gate line area is retained, and the retained PSG covers the phosphorus-doped polysilicon layer in the gate line area.

[0049] S5: using wet etching to reduce or remove the portion of the phosphorus-doped polysilicon layer located in the non-gate line region.

[0050] In step S5, wet etching is adopted, and alkaline etching liquid can be selected to etch and thin or remove the phosphorus-doped polysilicon layer in the non-gate line area. The phosphorus-doped polysilicon layer in the gate line area on the back side will not be etched by the etching liquid due to the protection of the PSG layer, so the thickness of the phosphorus-doped polysilicon layer in the gate line area on the back side will not change.

[0051] Before thinning, the thickness of the phosphorus-doped polysilicon layer is 100-200 nm; after etching, the thickness of the phosphorus-doped polysilicon layer in the non-gate line area is thinned to less than 50 nm.

[0052] Due to the characteristics of the polysilicon layer material, it will cause more optical absorption, resulting in a decrease in light energy utilization, which in turn leads to low conversion efficiency of the battery. By thinning the thickness of the phosphorus-doped polysilicon layer in the non-gate line area, the parasitic absorption of the polysilicon layer material can be effectively reduced, thereby improving the conversion efficiency of the battery to a certain extent.

[0053] S6: performing post-processing on the silicon substrate.

[0054] In some embodiments, in S6, post-processing includes: Pickling to remove the remaining phosphosilicate glass layer and borosilicate glass layer; Forming a passivation layer and an anti-reflection layer on the front and back sides in sequence; Conductive metal paste is printed on the gate line area on the back side and the front side and cured to form metal electrodes.

[0055] In some embodiments, an atomic layer deposition (ALD) technique may be used to form a passivation layer on the front surface, but the present invention is not limited thereto. In some embodiments, the thickness of the passivation layer is 2-8 nm, and the passivation layer may be aluminum oxide.

[0056] In some embodiments, plasma enhanced atomic layer deposition (PEALD) can be used to form an anti-reflection layer on the front and back surfaces, but the invention is not limited thereto. In some embodiments, the anti-reflection layer is Si y N x or Si z N x O y At least one of the anti-reflection layer has the function of reducing reflection and increasing transmission. In some embodiments, the deposition thickness of the anti-reflection layer is controlled to be 70-90nm.

[0057] In some embodiments, conductive metal paste is printed on both the front and back sides, and the conductive metal paste is solidified by sintering to form metal gate lines, and the metal atoms in the conductive metal paste are in contact with the silicon substrate.

[0058] It is understandable that both the pre-processing and the post-processing may also include some necessary steps for forming a solar cell, although not specifically described in this application.

[0059] By using a laser with a specific strip-shaped spot, the outermost phosphosilicate glass layer on the surface of the solar cell is selectively removed. The remaining phosphosilicate glass layer in the gate line area can be used as a mask layer for subsequent etching of the phosphorus-doped polysilicon layer, thereby effectively etching and thinning the phosphorus-doped polysilicon layer in the non-gate line area.

[0060] The present application also provides a method for preparing a back contact (BC) solar cell, which includes the above-mentioned laser processing method. The method for preparing a BC solar cell includes the following steps M1 to M11.

[0061] M1: providing a silicon substrate, wherein the silicon substrate is an N-type silicon substrate and comprises a front side and a back side opposite to each other, and performing pre-processing on the silicon substrate.

[0062] In some embodiments, in step M1, the pre-treatment further includes: cleaning and texturing the silicon substrate.

[0063] M2: forming a tunneling oxide layer and an intrinsic amorphous silicon layer in sequence on the back side of the silicon substrate.

[0064] In some embodiments, step M2 is to sequentially form a tunneling oxide layer and an intrinsic amorphous silicon layer on the back of the silicon substrate by LPCVD, but this is not limited to this, and other preparation methods may also be used. The tunneling oxide layer is usually a silicon oxide layer with a thickness of no more than 3nm.

[0065] M3: Boron is diffused into the intrinsic amorphous silicon layer to form a boron-doped polysilicon layer. In this step, a BSG layer will be formed on the outermost side of the back side.

[0066] Boron diffusion is a conventional boron diffusion process. In some embodiments, the boron source used for boron diffusion can be selected from BCl 3 , BBr 3 , B 2 H 6 , trimethyl boron and other precursors. Under certain temperature conditions, boron source gas, oxygen, diluent gas (such as nitrogen) and the like are introduced to deposit boron on the surface of the silicon substrate; then high temperature is applied to promote the diffusion of boron into the silicon substrate.

[0067] After boron diffusion, the outermost surface of each surface of the silicon substrate has a higher boron concentration, forming a BSG layer. The BSG layer formed on the side of the silicon substrate is prone to short circuit, and the BSG layer formed on the back of the silicon substrate will affect the subsequent passivation, so both need to be removed.

[0068] M4: The back side includes independent N-region fine gate region and P-region fine gate region, independent N-region main gate region and P-region main gate region, and laser is used to remove the BSG layer of the N-region fine gate region and the N-region main gate region on the back side.

[0069] The aspect ratio of the laser spot is 2:1 or above, and the length is ≥200μm; the laser is a pulsed laser with a pulse width of 100fs~10ps, a single pulse energy ≥100μJ, and a wavelength of the laser is 300~1200nm.

[0070] The N region fine gate region is cross-connected with the N region main gate region, the P region fine gate region is cross-connected with the P region main gate region, and the N region fine gate region and the P region fine gate region, the N region main gate region and the P region main gate region are independent and spaced apart from each other.

[0071] In step M4, the BSG layer in the N region fine gate region and the N region main gate region on the back side is removed by utilizing the characteristic of laser instantaneous heating, while the BSG layer in other regions (eg, the P region fine gate region and the P region main gate region) is retained.

[0072] A laser with a stripe spot is used to remove the BSG layer located in the fine gate area of ​​the N region, and then the orientation of the stripe spot is changed to remove the BSG layer located in the main gate area of ​​the N region.

[0073] M5: Use wet etching to remove the portion of the boron-doped polysilicon layer on the back side located in the N-region fine gate region and the N-region main gate region.

[0074] In step M5, wet etching is adopted, and alkaline etching liquid can be selected to etch and remove the portion of the boron-doped polysilicon layer located in the N-region fine gate region and the N-region main gate region, that is, the boron-doped polysilicon layer is patterned. The boron-doped polysilicon layer in other areas on the back (such as the P-region fine gate region and the P-region main gate region) will not be etched by the etching liquid due to the coverage and protection of the BSG layer, and thus it is retained.

[0075] M6: forming a tunneling oxide layer and an intrinsic amorphous silicon layer again in sequence on the back side of the silicon substrate.

[0076] In some embodiments, step M6 is the same as step M2, which is to form a tunneling oxide layer and an intrinsic amorphous silicon layer on the back of the silicon substrate in sequence by LPCVD, but this is not limited to other preparation methods. The tunneling oxide layer is usually a silicon oxide layer with a thickness of no more than 3nm.

[0077] M7: Phosphorus is diffused into the intrinsic amorphous silicon layer to form a phosphorus-doped polysilicon layer. In this step, a phosphorus-silicate glass (PSG) layer is formed on the outermost side of the back side.

[0078] Phosphorus diffusion is a conventional phosphorus diffusion process. In some embodiments, after step M7, after phosphorus diffusion, the outermost surfaces of each surface of the silicon substrate have a higher phosphorus concentration, forming a PSG layer.

[0079] M8: Continue to use the above laser to remove the phosphorus silicon glass layer in the P region fine gate area and the P region main gate area on the back side.

[0080] In step M8, the PSG layer in the P region fine gate region and the P region main gate region on the back side is removed by utilizing the characteristic of laser instantaneous heating, while the PSG layer in other regions (eg, the N region fine gate region and the N region main gate region) is retained.

[0081] A laser with a stripe-shaped spot is used to remove the PSG layer located in the fine gate area of ​​the P region, and then the orientation of the stripe-shaped spot is changed to remove the PSG layer located in the main gate area of ​​the P region.

[0082] M9: Use wet etching to remove the phosphorus-doped polysilicon layer on the back side located in the P-region fine gate area and the P-region main gate area.

[0083] In step M9, wet etching is adopted, and alkaline etching liquid can be selected to etch and remove the phosphorus-doped polysilicon layer located in the P-region fine gate region and the P-region main gate region, that is, the phosphorus-doped polysilicon layer is patterned. The phosphorus-doped polysilicon layer in other regions on the back side (such as the N-region fine gate region and the N-region main gate region) will not be etched by the etching liquid due to the protection of the PSG layer, and thus it is retained.

[0084] Thus, after step M9, the boron-doped polysilicon layer of the P region fine gate region and the P region main gate region, and the phosphorus-doped polysilicon layer of the N region fine gate region and the N region main gate region are retained on the back side, and PN region isolation is achieved by controlling the laser overlapping area.

[0085] The order of M3 to M5 and M7 to M9 can be adjusted, that is, in other embodiments, phosphorus-doped polysilicon layer+etching can be performed first, and then boron-doped polysilicon layer+etching can be performed.

[0086] M10: Remove the remaining PSG layer and BSG layer on the back side of the silicon substrate.

[0087] An acidic etching solution, such as a hydrofluoric acid solution, may be used to remove the PSG layer and the BSG layer remaining on the back side.

[0088] M11: Post-processing the silicon substrate to form a back-contact solar cell.

[0089] The post-processing includes: The doped polysilicon layer, the PSG layer and the BSG layer formed on the front side are removed by wet etching.

[0090] Forming a passivation layer and an anti-reflection layer on the front and back sides in sequence; Conductive metal paste is printed on the N-region fine gate region and the N-region main gate region, the P-region fine gate region and the P-region main gate region on the back side and cured to form metal electrodes.

[0091] It is understandable that both the pre-processing and the post-processing may also include some necessary steps for forming a solar cell, although not specifically described in this application.

[0092] By using a laser with a specific strip-shaped spot, the outermost silicon glass layer (phosphosilicate glass layer or borosilicate glass layer) on the surface of the solar cell is selectively removed. The retained silicon glass layer can be used as a mask layer for subsequent etching of the doped polysilicon layer, thereby effectively etching the doped polysilicon layer in the corresponding area, thereby realizing the preparation of a patterned P region or N region.

[0093] Compared with the existing laser mold opening technology, the laser patterning technology of the present application has relatively low implementation difficulty and the same production capacity, or has similar implementation difficulty and higher production capacity, while achieving the same technical effect goals, and is more suitable for large-scale mass production.

[0094] See also Figure 1 The present application also provides a laser device 100 for the laser processing method of the solar cell of the present application. The laser device 100 includes a laser 10, a reflector 20, a beam expander 30, a shaping element 40, a galvanometer 50 and a field lens 60 arranged in sequence along the laser light path. The laser device 100 is used to emit laser light, the shape of the laser spot is a strip, the aspect ratio of the spot is 2:1 or more, the length is ≥200μm, the laser is a pulsed laser, the pulse width is 100fs~10ps, the single pulse energy is ≥100μJ, and the wavelength is 300~1200nm The laser 10 is an ultrafast pulse laser, which is used to emit pulsed laser light, and the laser light is a Gaussian beam. The reflector 20 is used to reflect the laser light from the laser 10 and adjust and collimate it to the beam expander 30. Figure 1 As shown, in the embodiment of the present application, the laser device 100 includes two reflectors 20 arranged at an interval, but this is not limited to this. The number and angle of the reflectors 20 can be adjusted and designed as needed.

[0095] The beam expander 30 is used to expand the laser beam to form a parallel beam.

[0096] The shaping element 40 is used to adjust the intensity distribution of the laser, for example, to shape a parallel laser beam with Gaussian distribution so that the laser has a specific intensity distribution and forms a strip-shaped light spot with a flat top distribution and a certain aspect ratio on the working plane after focusing.

[0097] The galvanometer 50 and the field lens 60 are used to reflect and focus the laser light respectively, so as to project the laser light spot to a designated position. A reflective lens (not shown) is arranged in the galvanometer 50, and the movement of the laser light spot is realized by rotating the reflective lens.

[0098] The shaping element 40 is one of a diffractive optical element, a liquid crystal spatial modulator, and a microlens array.

[0099] The laser device 100 further includes an optical adjustment frame 42 , and the shaping element 40 is disposed on the optical adjustment frame 42 .

[0100] In some embodiments, the shaping element 40 is rotatably disposed on the optical adjustment frame 42. The shaping element 40 can be driven by a motor (not shown) to rotate around its own axis to adjust the orientation of the laser stripe spot.

[0101] In some embodiments, the laser device 100 includes at least two shaping elements 40, which are respectively mounted on an optical adjustment frame 42. Each shaping element 40 allows the laser spot to have a different initial orientation angle, and the shaping element 40 can be driven by a motor to achieve switching between the shaping elements 40 in the laser light path to switch the orientation of the stripe light spot.

[0102] The laser device 100 of the present application obtains a strip-shaped laser spot with a flat-top distribution through a shaping element 40. In addition, the shaping element 40 can be rotatably set on an optical adjustment frame 42 to achieve a change in the orientation of the strip-shaped spot, or different shaping elements 40 can be set to achieve laser spots with different orientations, thereby adapting to different laser processing directions. Laser patterning of complex graphics can be achieved without the need for multiple sets of configurations and repeated positioning, avoiding the problem that the orientation of the strip-shaped spot is fixed, resulting in the advantage of laser mold opening processing only along a specific direction.

[0103] like Figure 2 As shown, the stripe light spot 11 of the laser can be irradiated in the first processing area 210 and the second processing area 220 of the solar cell 200. Taking the back contact solar cell as an example, the first processing area 210 can correspond to the N-region or P-region fine grid area, and the second processing area 220 can correspond to the N-region or P-region main grid area. The width of the first processing area 210 is equal to the length of the stripe light spot 11, and the length extension of the first processing area 210 is consistent with the moving direction of the stripe light spot 11. The width of the second processing area 220 is equal to the length of the stripe light spot 12, the stripe light spot 12 is the same as or different from the stripe light spot 11, and the length extension of the second processing area 220 is consistent with the moving direction of the stripe light spot 12. Figure 2 The middle dotted line indicates the moving direction of the stripe light spot 11 . Figure 2 The second processing area 220 intersects the first processing area 210 perpendicularly. When the irradiation scanning of the first processing area 210 is completed, the orientation of the laser spot needs to be changed and adjusted to irradiate and scan the second processing area 220.

[0104] This application achieves the effect of local removal of the film layer of the solar cell by configuring a strip-shaped laser spot with a certain aspect ratio. Compared with the existing laser film opening process with a large-sized square spot, it has the advantages of low single-pulse energy requirements, good process uniformity, high stability, and large room for capacity improvement, and reduces the requirements for lasers and optical components, thereby reducing the difficulty and cost of industrial mass production. By compressing the laser pulse energy into a narrow and long strip spot instead of a large-sized square spot, the pulse energy density requirement for film removal can be relatively easily achieved, and the production capacity can be ensured to be unaffected by simply increasing the pulse repetition frequency. Thanks to the setting of the aspect ratio of the strip spot, the technical effect of a large film opening line width can be achieved at one time without the need for spot splicing, with better uniformity, precision and stability.

[0105] The above implementation modes are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the above preferred implementation modes, a person skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A laser processing method for a solar cell, characterized in that: include: Providing a silicon substrate, wherein a film layer to be processed is disposed on a surface of the silicon substrate, and the film layer to be processed includes at least one of a silicon glass layer and a dielectric layer; Laser is used to irradiate a local area of ​​the film layer to be processed to remove the local area of ​​the film layer to be processed. The shape of the laser spot is a strip, the aspect ratio of the spot is 2:1 or above, the length is ≥200μm, the laser is a pulsed laser, the pulse width is 100fs~10ps, the single pulse energy is ≥100μJ, and the wavelength is 300~1200nm.

2. The laser processing method of a solar cell according to claim 1, characterized in that: The laser has a wavelength of 300-600 nm.

3. The laser processing method of a solar cell according to claim 1, characterized in that: The moving speed of the laser along the processing direction is ≥40m / s; The length direction of the laser spot is perpendicular to the moving direction of the laser.

4. A method for preparing a TOPCon solar cell, characterized in that: include: Providing a silicon substrate, wherein the silicon substrate is an N-type silicon substrate and comprises a front side and a back side opposite to each other, and performing pre-processing on the silicon substrate; forming a tunneling oxide layer and an intrinsic amorphous silicon layer in sequence on the back side of the silicon substrate; Diffusion of phosphorus is performed on the intrinsic amorphous silicon layer to form a phosphorus-doped polysilicon layer. In this step, a phosphorus-silicate glass layer is formed on the outermost side of the back side. The back side includes a grid line area and a non-grid line area, and a laser is used to remove the phosphorus silicon glass layer on the back side located in the non-grid line area, the laser spot is in a strip shape, the aspect ratio of the laser spot is 2:1 or more, the length is ≥200 μm, the laser is a pulse laser, the pulse width is 100 fs~10 ps, ​​the single pulse energy is ≥100 μJ, and the wavelength is 300~1200 nm; Using wet etching to thin or remove the portion of the phosphorus-doped polysilicon layer located in the non-gate line area; and The silicon substrate is post-processed to form a solar cell.

5. The method for preparing a TOPCon solar cell according to claim 4, characterized in that: After the wet etching, the thickness of the phosphorus-doped polysilicon layer in the non-gate line area is reduced to less than 50 nm.

6. The method for preparing a TOPCon solar cell according to claim 4, characterized in that: The moving speed of the laser along the processing direction is ≥40 m / s, and the length direction of the laser spot is perpendicular to the moving direction of the laser.

7. The method for preparing a TOPCon solar cell according to claim 4, characterized in that: The post-processing includes: Pickling to remove the remaining phosphosilicate glass layer and borosilicate glass layer; Forming a passivation layer and an anti-reflection layer on the front surface and the back surface in sequence; Conductive metal paste is printed on the gate line region on the back side and the front side and cured to form metal electrodes.

8. The method for preparing a TOPCon solar cell according to claim 4, characterized in that: The pre-treatment includes: Cleaning and texturing the silicon substrate; Diffusion of boron is performed on the silicon substrate to form an emitter on the front side. In this step, a borosilicate glass layer is formed on the back side and the front side. The back surface is polished to remove the structure formed on the back surface in the previous step.

9. A method for preparing a back contact solar cell, characterized in that: include: Providing a silicon substrate, wherein the silicon substrate is an N-type silicon substrate and includes a front side and a back side opposite to each other; forming a tunneling oxide layer and an intrinsic amorphous silicon layer in sequence on the back side; Diffusion of boron is performed on the intrinsic amorphous silicon layer to form a boron-doped polysilicon layer. In this step, a borosilicate glass layer is formed on the outermost side of the back side. The back side includes an N-region fine gate region, an N-region main gate region, a P-region fine gate region, and a P-region main gate region. The borosilicate glass layer located in the N-region fine gate region and the N-region main gate region on the back side is removed by laser. The N-region fine gate region and the N-region main gate region are cross-connected. The shape of the laser spot is a stripe. The aspect ratio of the laser spot is 2:1 or more, and the length is ≥200μm. The laser is a pulsed laser with a pulse width of 100fs~10ps, a single pulse energy ≥100μJ, and a wavelength of 300~1200nm. The portion of the boron-doped polysilicon layer on the back side located in the N region fine gate region and the N region main gate region is removed by wet etching.

10. The method for preparing a back contact solar cell according to claim 9, characterized in that: The preparation method further comprises: forming a tunneling oxide layer and an intrinsic amorphous silicon layer again in sequence on the back side of the silicon substrate; Diffusion of phosphorus is performed on the intrinsic amorphous silicon layer to form a phosphorus-doped polysilicon layer. In this step, a phosphorus-silicate glass layer is formed on the outermost side of the back side. The laser is used to remove the phosphorus silicon glass layer located at the P region fine gate region and the P region main gate region on the back side, and the P region fine gate region and the P region main gate region are cross-connected; Using wet etching to remove the portion of the phosphorus-doped polysilicon layer located in the P-region fine gate region and the P-region main gate region; The silicon substrate is post-processed to form a solar cell.

11. The method for preparing a back contact solar cell according to claim 10, characterized in that: The post-processing includes: removing the phosphosilicate glass layer and the borosilicate glass layer on the back side; removing the film layer formed on the front surface; Forming a passivation layer and an anti-reflection layer on the front surface and the back surface in sequence; Conductive metal paste is printed on the N-region fine gate region, the N-region main gate region, the P-region fine gate region and the P-region main gate region on the back side, and cured to form metal electrodes.

12. The method for preparing a back contact solar cell according to claim 9, characterized in that: The moving speed of the laser along the processing direction is ≥40 m / s, and the length direction of the laser spot is perpendicular to the moving direction of the laser.

13. A laser device, characterized in that: include: A laser, a reflector, a beam expander, a shaping element, a galvanometer and a field mirror are sequentially arranged along the optical path; The laser is used to emit pulsed laser; The reflector is used to reflect the pulsed laser from the laser and adjust and collimate it to the beam expander; The beam expander is used to expand the laser beam; The shaping element is used to adjust the intensity distribution of the pulsed laser to form a stripe-shaped light spot with an aspect ratio after focusing; The galvanometer and the field lens are used to reflect and focus the laser light respectively, so as to project the strip-shaped spot of the laser light to a designated position; The laser device is used to emit laser, the shape of the laser spot is strip-shaped, the aspect ratio of the spot is 2:1 or above, the length is ≥200μm, the laser is a pulse laser, the pulse width is 100fs~10ps, the single pulse energy is ≥100μJ, and the wavelength is 300~1200nm.

14. The laser device according to claim 13, characterized in that The shaping element is one of a diffractive optical element, a liquid crystal spatial modulator, and a microlens array.

15. The laser device according to claim 13, characterized in that The laser device further comprises an optical adjustment frame, the shaping element is rotatably arranged on the optical adjustment frame, and the orientation of the laser spot is adjusted by rotating the shaping element; or The laser device further comprises an optical adjustment frame, wherein the laser device comprises at least two shaping elements arranged on the optical adjustment frame, and the orientation of the laser spot is changed by switching the at least two shaping elements in the optical path.

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