Back contact solar cell and back coarsening method thereof

Abstract

The invention relates to the photovoltaic field, and discloses a back contact solar cell and a back side coarsening method thereof. In the first direction, first type regions and second type regions which are alternately distributed at intervals are arranged on the back surface of the substrate; in the second direction, a dielectric layer and a first type polycrystalline silicon layer are sequentially arranged on the back surface of the substrate in the first type region from inside to outside, and a dielectric layer and a second type polycrystalline silicon layer are sequentially arranged on the back surface of the substrate in the second type region; the surfaces, deviating from the substrate, of the first type polycrystalline silicon layer and the second type polycrystalline silicon layer are rough surfaces; a first type region electrode and a second type region electrode. The surface roughness of the first type polycrystalline silicon layer and the second type polycrystalline silicon layer away from the substrate is large, the adhesive force of the first type region electrode and the second type region electrode can be improved, meanwhile, the local current density and the contact resistance are reduced, the light scattering capacity of the surface of the first type polycrystalline silicon layer and the second type polycrystalline silicon layer away from the substrate can be improved, and the service life of the device is prolonged. And the cell conversion efficiency is improved.

Description

Technical Field

[0001] This application relates to the photovoltaic field, and in particular to a back-contact solar cell and a method for roughening the back side thereof. Background Technology

[0002] Back-contact solar cells are a type of solar cell that integrates all positive and negative metal contacts on the back side. Their grid-free design on the front side can absorb more sunlight, combining aesthetics with high power generation efficiency.

[0003] IBC (Interdigitated Back Contact) cells are a type of high-efficiency back contact cell. TOPCon (Tunnel Oxide Passivated Contact) cells have an ultra-thin silicon oxide layer formed on the back side of the substrate as a tunneling oxide layer. A doped polycrystalline silicon layer is superimposed on the surface of the silicon oxide layer. The silicon oxide layer and the doped polycrystalline silicon layer form a passivated contact structure, which can improve the conversion efficiency of the cell.

[0004] TBC (TOPCon Back Contact) solar cells are a high-efficiency solar cell technology that combines the passivation contact technology of TOPCon with the back contact electrode structure of IBC. It inherits the characteristics of IBC cells—no grid lines on the front and a fully back-electrode configuration—while utilizing the tunneling oxide layer and polycrystalline silicon layer of TOPCon to achieve excellent passivation. The back of a TBC cell has alternating Type I and Type II regions. The smooth surfaces of the polycrystalline silicon layers in both regions result in weak adhesion of the silver paste to the electrodes (<1.5 N / mm), making them prone to delamination.

[0005] Therefore, how to solve the above-mentioned technical problems should be a key focus for those skilled in the art. Summary of the Invention

[0006] The purpose of this application is to provide a back-contact solar cell and a method for roughening the back side thereof to improve the adhesion between the electrode and the polycrystalline silicon layer.

[0007] To address the aforementioned technical problems, this application provides a back-contact solar cell, comprising:

[0008] Substrate; in a first direction, the back side of the substrate is provided with alternating first-type regions and second-type regions;

[0009] In the second direction, a dielectric layer and a first-type polysilicon layer are sequentially disposed from the inside to the outside on the back side of the substrate in the first-type region, and a dielectric layer and a second-type polysilicon layer are sequentially disposed from the inside to the outside on the back side of the substrate in the second-type region; the surfaces of the first-type polysilicon layer and the second-type polysilicon layer facing away from the substrate are rough surfaces;

[0010] A first-type region electrode located in the first-type region and a second-type region electrode located in the second-type region;

[0011] The first direction is along the length of the back-contact solar cell, the second direction is along the thickness of the back-contact solar cell, and the first direction is perpendicular to the second direction.

[0012] Optionally, the rough surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are uneven surfaces, and the depth of the recessed areas on the rough surfaces ranges from 15nm to 50nm.

[0013] Optionally, the thickness of the damaged layer in the first type of polysilicon layer and the second type of polysilicon layer is less than or equal to 50 nm.

[0014] Optionally, the surface roughness of the first type polysilicon layer and the second type polysilicon layer facing away from the substrate ranges from 0.3 μm to 1.2 μm.

[0015] Optionally, it also includes:

[0016] A passivation repair layer located on the surfaces of the first type polysilicon layer and the second type polysilicon layer facing away from the substrate.

[0017] This application also provides a method for roughening the back side of a back-contact solar cell, including:

[0018] Prepare a substrate in a first direction, wherein the back side of the substrate is provided with alternating first-type regions and second-type regions;

[0019] In a second direction, a dielectric layer and a first-type polycrystalline silicon layer are grown sequentially from the inside to the outside in a first-type region of the substrate, and a dielectric layer and a second-type polycrystalline silicon layer are grown sequentially from the inside to the outside in a second-type region of the substrate; the first direction is along the length direction of the back-contact solar cell, the second direction is along the thickness direction of the back-contact solar cell, and the first direction is perpendicular to the second direction.

[0020] The surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened by at least one of liquid sandblasting, gas sandblasting and brushing a roughening layer, so that the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened.

[0021] A first-type region electrode is grown in the first-type region, and a second-type region electrode is grown in the second-type region.

[0022] Optionally, the abrasive particles in the blasting slurry and / or blasting airflow include a first particle with a size in the nanometer range and a second particle with a size in the micrometer range.

[0023] Optionally, roughening the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate by at least one of liquid blasting, gas blasting, and applying a roughening layer includes:

[0024] A mask is fabricated on the back side of the back contact solar cell, and the mask is located in the isolation area between the first type region and the second type region;

[0025] Under the action of the mask, the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened by liquid sandblasting and / or gas sandblasting.

[0026] Optionally, roughening the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate by at least one of liquid blasting, gas blasting, and applying a roughening layer includes:

[0027] A first mask is fabricated on the back side of the back contact solar cell. The first mask is located in the isolation area between the first type region and the second type region, as well as in the first type region.

[0028] Under the action of the first mask, at least one of liquid sandblasting, gas sandblasting and brushing roughening layer is used to roughen the surface of the second type polysilicon layer away from the substrate, so that the surface of the second type polysilicon layer away from the substrate is a rough surface.

[0029] Remove the first mask and fabricate a second mask on the back side of the solar cell. The second mask is located in the isolation area between the first type region and the second type region, as well as in the second type region.

[0030] Under the action of the second mask, the surface of the first type polysilicon layer away from the substrate is roughened by at least one of liquid sandblasting, gas sandblasting and brushing a roughening layer, so that the surface of the first type polysilicon layer away from the substrate is a rough surface; wherein, the roughness of the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate is different.

[0031] Optionally, it also includes:

[0032] The back side of the substrate located in the isolation region between the first type region and the second type region is roughened by at least one of liquid sandblasting, gas sandblasting and applying a roughening layer.

[0033] The back-contact solar cell of this application includes a substrate. A dielectric layer and a first-type polycrystalline silicon layer are sequentially disposed from the inside out in a first-type region, and a dielectric layer and a second-type polycrystalline silicon layer are sequentially disposed from the inside out in a second-type region. The surfaces of the first-type and second-type polycrystalline silicon layers facing away from the substrate are rough surfaces. This high surface roughness improves the adhesion between the first-type and second-type region electrodes and reduces the possibility of detachment. Simultaneously, the increased contact area between the first-type and second-type region electrodes and the first-type polycrystalline silicon layer reduces local current density and contact resistance. Furthermore, the rough surfaces of the first-type and second-type polycrystalline silicon layers facing away from the substrate increase light scattering capability, reduce light reflection loss, improve the bifaciality and light absorption efficiency of the cell, and ultimately enhance the cell's conversion efficiency.

[0034] In addition, this application also provides a method for roughening the back side of a back-contact solar cell with the above-mentioned advantages. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the structure of a back-contact solar cell provided in an embodiment of this application;

[0037] Figure 2 A flowchart illustrating a method for roughening the back surface of a back-contact solar cell provided in this application embodiment;

[0038] In the figure, 1. Substrate, 11. Type I region, 12. Type II region, 13. Isolation region, 2. Dielectric layer, 3. Type I polysilicon layer, 4. Type II polysilicon layer, 5. Type I region electrode, 6. Type II region electrode, 7. Textured structure. Detailed Implementation

[0039] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0040] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0041] As described in the background section, the polycrystalline silicon layer surfaces in the first and second type regions on the back of the prior art of back-contact solar cells are smooth, resulting in weak adhesion of the click silver paste and easy delamination.

[0042] In view of this, this application provides a back-contact solar cell, please refer to... Figure 1 ,include:

[0043] Substrate 1; In the first direction X, the back side of the substrate 1 is provided with alternating first type region 11 and second type region 12;

[0044] In the second direction Y, a dielectric layer 2 and a first-type polysilicon layer 3 are sequentially disposed from the inside to the outside on the back side of the substrate 1 in the first-type region 11, and a dielectric layer 2 and a second-type polysilicon layer 4 are sequentially disposed from the inside to the outside on the back side of the substrate 1 in the second-type region 12; the surfaces of the first-type polysilicon layer 3 and the second-type polysilicon layer 4 facing away from the substrate 1 are rough surfaces.

[0045] A first-type region electrode 5 located in the first-type region 11 and a second-type region electrode 6 located in the second-type region 12;

[0046] The first direction X is along the length of the back-contact solar cell, and the second direction Y is along the thickness of the back-contact solar cell. The first direction X is perpendicular to the second direction Y.

[0047] The substrate 1 can be a silicon substrate 1, etc., and is not limited in this application. The front side of the substrate 1 can be a textured structure 7 to increase the light trapping effect, increase the number of reflections of light on the front side of the substrate 1, and improve the absorption of light, thereby improving the battery efficiency.

[0048] In this application, the first type region 11 is a P-region, and the second type region 12 is an N-region; the first type polysilicon layer 3 is a P-type polysilicon layer, and the second type polysilicon layer 4 is an N-type polysilicon layer. The dielectric layer 2 is a silicon dioxide layer.

[0049] An isolation region 13 is formed between the first type region 11 and the second type region 12 to isolate the first type region 11 and the second type region 12. The back side of the substrate 1 of the isolation region 13 is not limited in this application and depends on the specific circumstances.

[0050] As one possible implementation, the back surface of the substrate 1 located in the isolation region 13 is a rough surface, which can increase the light trapping effect, increase the number of light reflections in the isolation region 13, and improve the light absorption on the back surface of the substrate 1.

[0051] As another possible implementation, the back side of the substrate 1 located in the isolation region 13 is a smooth surface. In this case, no additional processing is required on the back side of the substrate 1 located in the isolation region 13, which is very simple.

[0052] As another possible implementation, an isolation membrane layer located in the isolation region 13 is also included, that is, an isolation membrane layer is provided in the isolation region 13. This application does not limit the isolation membrane layer, as long as it serves to isolate the first type region 11 and the second type region 12.

[0053] The first type polysilicon layer 3 and the second type polysilicon layer 4 have uneven surfaces away from the rough surface of the substrate 1. In this application, the depth of the depressions in the rough surface is not limited and can be set by the user. For example, the rough surfaces of the first type polysilicon layer 3 and the second type polysilicon layer 4 away from the substrate 1 are uneven surfaces, and the depth of the depression area on the rough surface ranges from 15nm to 50nm. If the depression depth is less than 15nm, the roughness of the rough surface is too small, resulting in a small contact area between the first type regional electrode 5 and the second type regional electrode 6, and limited improvement in adhesion. If the depression depth is greater than 50nm, the first type regional electrode 5 and the second type regional electrode 6 may not be able to completely fill the depression area, resulting in the first type regional electrode 5 and the second type regional electrode 6 being disconnected at some positions.

[0054] For example, the recess depth can be 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 50nm, etc.

[0055] It should be noted that this application does not limit the surface roughness of the first type polysilicon layer 3 and the second type polysilicon layer 4 away from the substrate 1, but depends on the specific circumstances.

[0056] As one possible implementation, the surfaces of the first type polycrystalline silicon layer 3 and the second type polycrystalline silicon layer 4 facing away from the substrate 1 have the same roughness. In this case, when roughening the back side of the solar cell, both the first type polycrystalline silicon layer 3 and the second type polycrystalline silicon layer 4 can be processed simultaneously, reducing the complexity of the process.

[0057] As another possible implementation, the surfaces of the first type polycrystalline silicon layer 3 and the second type polycrystalline silicon layer 4 facing away from the substrate 1 have different roughnesses. In this case, when roughening the back of the solar cell, the first type polycrystalline silicon layer 3 and the second type polycrystalline silicon layer 4 are processed separately to obtain the required roughness.

[0058] When the surface roughness of the first type polysilicon layer 3 and the second type polysilicon layer 4 facing away from the substrate 1 is not the same, the difference in roughness can be greater than or equal to 0.2.

[0059] It should also be noted that the roughness of the surfaces of the first type polysilicon layer 3 and the second type polysilicon layer 4 facing away from the substrate 1 is not limited in this application, but depends on the specific circumstances.

[0060] As one possible implementation, the surface roughness of the first type polysilicon layer 3 and the second type polysilicon layer 4 facing away from the substrate 1 is in the range of 0.3μm~1.2μm. This can both increase the contact area between the first type regional electrode 5 and the first type polysilicon layer 3, and between the second type regional electrode 6 and the second type polysilicon layer 4, reducing the possibility of electrode detachment, and ensure that the electrode paste fills the recessed area of ​​the rough surface, avoiding electrode breakage.

[0061] When a rough surface is formed on the surface of the first type polysilicon layer 3 and the second type polysilicon layer 4 away from the substrate 1, it will cause certain damage to the first type polysilicon layer 3 and the second type polysilicon layer 4, forming a damage layer. In order to reduce the adverse effect of the damage layer on the contact between the first type regional electrode 5 and the first type polysilicon layer 3, and between the second type regional electrode 6 and the second type polysilicon layer 4, and to improve the battery efficiency, in one embodiment of this application, the thickness of the damage layer in the first type polysilicon layer 3 and the second type polysilicon layer 4 is less than or equal to 50 nm.

[0062] Compared to the prior art where the surface reflectance of the first type polysilicon layer 3 and the second type polysilicon layer 4 away from the substrate 1 is greater than 25% when the roughening is not performed, the surface reflectance of the first type polysilicon layer 3 and the second type polysilicon layer 4 away from the substrate 1 in this application is reduced to 9%~20%.

[0063] In this embodiment, the back-contact solar cell includes a substrate 1. A dielectric layer 2 and a first-type polycrystalline silicon layer 3 are sequentially disposed from the inside to the outside in a first-type region 11, and a dielectric layer 2 and a second-type polycrystalline silicon layer 4 are sequentially disposed from the inside to the outside in a second-type region 12. The surfaces of the first-type polycrystalline silicon layer 3 and the second-type polycrystalline silicon layer 4 facing away from the substrate 1 are rough surfaces. Therefore, the large surface roughness of the first-type polycrystalline silicon layer 3 and the second-type polycrystalline silicon layer 4 facing away from the substrate 1 can improve the adhesion with the first-type region electrode 5 and the second-type region electrode 6, and reduce the possibility of the first-type region electrode 5 and the second-type region electrode 6 detaching. At the same time, since the contact area between the first-type region electrode 5 and the first-type polycrystalline silicon layer 3 and the second-type region electrode 6 and the second-type polycrystalline silicon layer 4 is increased, the local current density can be reduced and the contact resistance can be reduced. In addition, since the surfaces of the first type polysilicon layer 3 and the second type polysilicon layer 4 facing away from the substrate 1 are rough, the light scattering ability of the surfaces of the first type polysilicon layer 3 and the second type polysilicon layer 4 facing away from the substrate 1 can be increased, light reflection loss can be reduced, the bifaciality and light absorption efficiency of the cell can be improved, and the cell conversion efficiency can be increased.

[0064] Based on the above embodiments, in one embodiment of this application, the back-contact solar cell may further include: a passivation repair layer located on the surfaces of the first type polycrystalline silicon layer 3 and the second type polycrystalline silicon layer 4 that are away from the substrate 1.

[0065] In this embodiment, the passivation repair layer is not limited and can be set by the user. For example, the passivation repair layer can be an aluminum oxide layer and / or a silicon nitride layer.

[0066] The alumina layer directly performs chemical passivation and field-effect passivation on the surfaces of the first type polycrystalline silicon layer 3 and the second type polycrystalline silicon layer 4 that are away from the substrate 1; during the fabrication of the silicon nitride layer, the reaction precursors (such as SiH4 and NH3) decompose to generate a large number of hydrogen atoms. During deposition and subsequent sintering and annealing, these hydrogen atoms diffuse into the silicon bulk, achieving bulk passivation and surface passivation.

[0067] This application also provides a method for roughening the back side of a back-contact solar cell; please refer to [reference needed]. Figure 2 The method may include:

[0068] Step S101: Prepare a substrate. In a first direction, the back side of the substrate is provided with alternating first-type regions and second-type regions.

[0069] Step S102: In the second direction, a dielectric layer and a first type polysilicon layer are grown sequentially from the inside to the outside in the first type region of the substrate, and a dielectric layer and a second type polysilicon layer are grown sequentially from the inside to the outside in the second type region of the substrate.

[0070] The first direction is along the length of the back-contact solar cell, the second direction is along the thickness of the back-contact solar cell, and the first direction is perpendicular to the second direction.

[0071] The dielectric layer is a silicon dioxide layer. The thickness of the first type of polycrystalline silicon layer can range from 150 nm to 350 nm, and the thickness of the second type of polycrystalline silicon layer can range from 80 nm to 300 nm.

[0072] Step S103: The surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened by at least one of liquid sandblasting, gas sandblasting and applying a roughening layer, so that the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened.

[0073] When roughening is performed by liquid blasting, the roughening process is carried out by spraying a blasting fluid containing abrasive particles. When roughening is performed by gas blasting, the roughening process is carried out by spraying a blasting airflow containing abrasive particles.

[0074] The function of abrasive particles is to micro-cut / micro-fracture the surfaces of the first and second type polycrystalline silicon layers facing away from the substrate under high-speed impact, forming an uneven, rough surface. The type of abrasive particles used in this application is not limited and depends on the specific circumstances. For example, abrasive particles include, but are not limited to, any one or any combination of silica particles, alumina particles, titanium dioxide particles, silicon carbide particles, glass beads, and plastic particles. Nano-sized silica particles are preferred as they do not introduce other impurities.

[0075] It should be noted that this application does not limit the shape of the abrasive particles, and the shape can be set by the user. For example, the shape of the abrasive particles can be spherical, and the size range of the abrasive particles can be 20nm~100nm.

[0076] The abrasive particles are nanoscale in size and spherical in shape, which can reduce damage to the first and second type polycrystalline silicon layers and reduce the thickness of the damaged layer.

[0077] Nanoscale abrasive particles have limited roughening effect on the surfaces of the first and second type polycrystalline silicon layers facing away from the substrate. To improve the roughening effect, in one embodiment of this application, the abrasive particles in the blasting slurry and / or blasting airflow include first particles with a size of nanometers and second particles with a size of micrometers. The size range of the second particles can be 0.1 μm to 1.5 μm.

[0078] When using liquid blasting, the liquid dispersant in the blasting slurry can be an alcohol or ether liquid. The abrasive concentration in the blasting slurry is 10wt%~30wt%, the water-based suspension pressure is 0.1Mpa~0.5Mpa, and a slurry circulation system (agitator and pump) is provided to ensure that the abrasive particles are uniformly suspended in the liquid and do not settle.

[0079] When using gas blasting, the gas can be compressed air or compressed nitrogen. A fluidized bed system is used to ensure uniform mixing of abrasive particles and gas, and stable concentration. The blasting pressure range can be 0.05 MPa to 0.3 MPa. If the blasting pressure is greater than 0.3 MPa, the damage layer thickness will be too large. If it is less than 0.05 MPa, it is impossible to effectively roughen the surfaces of the first and second type polysilicon layers facing away from the substrate.

[0080] When the injection time is the same and the injection pressure is 0.05 MPa, 0.2 MPa and 0.4 MPa respectively, the relevant battery parameters are shown in Table 1.

[0081] Table 1

[0082]

[0083] As shown in Table 1, when the spraying pressure is 0.05 MPa, the surfaces of the first and second type polysilicon layers facing away from the substrate cannot be effectively roughened. When the spraying pressure is 0.4 MPa, the thickness of the damaged layer on the surfaces of the first and second type polysilicon layers facing away from the substrate is greater than 50 nm. Therefore, in this application, the spraying pressure is set between 0.05 MPa and 0.3 MPa to ensure effective roughening while avoiding excessively thick damaged layers, and also to obtain better reflectivity and cell efficiency.

[0084] During the roughening process, the nozzle that sprays out the sandblasting fluid and sandblasting airflow includes multiple nozzles, which can be array nozzles or slit nozzles.

[0085] As one possible implementation, the angle between the nozzle and the normal to the back of the solar cell is in the range of 30° to 90°, preferably 45° to 70°. If the angle is too small, the roughening efficiency will be insufficient. If the angle is too large, the surface of the first type polycrystalline silicon layer and the second type polycrystalline silicon layer away from the substrate will be sprayed almost perpendicularly or perpendicularly, which will easily cause a large depth of breakdown damage.

[0086] As one possible implementation, the distance between the nozzle and the back of the solar cell is 5mm to 100mm, and the blasting time is 5s to 60s. Too close a distance will result in significant damage to the surfaces of the first and second polycrystalline silicon layers facing away from the substrate; too large a distance will affect the roughening efficiency. Too short a blasting time will result in relatively low surface roughness of the first and second polycrystalline silicon layers facing away from the substrate, affecting electrode adhesion; a blasting time greater than 60s is too long and will increase the thickness of the damaged layer by 30%.

[0087] When roughening is performed by brushing a roughening layer, a coating liquid containing particles is brushed onto the surfaces of the first and second type polycrystalline silicon layers facing away from the substrate, and then dried by heating, thereby forming a brushed roughening layer on the surfaces of the first and second type polycrystalline silicon layers facing away from the substrate. The particles include, but are not limited to, any one or any combination of silicon dioxide particles, alumina particles, titanium dioxide particles, and silicon carbide particles, and the liquid medium of the coating liquid can be an alcohol or an ether, etc.

[0088] During the roughening process, parameters such as the pressure of the compressed gas, the flow rate of the blasting slurry, and the spray angle are monitored and adjusted in real time to ensure that they remain constant during the blasting process.

[0089] Step S104: Grow a first type region electrode in the first type region and grow a second type region electrode in the second type region.

[0090] The growth processes of the first and second type regional electrodes are well known to those skilled in the art and will not be described in detail here.

[0091] In this embodiment, the back-side roughening method for a back-contact solar cell involves growing a dielectric layer and a first-type polycrystalline silicon layer sequentially from the inside out in a first-type region of the substrate, and then growing a dielectric layer and a second-type polycrystalline silicon layer sequentially from the inside out in a second-type region of the substrate. The surfaces of the first and second-type polycrystalline silicon layers facing away from the substrate are then roughened, resulting in rough surfaces. This improves adhesion to the first and second type region electrodes, reducing the likelihood of detachment. Simultaneously, the increased contact area between the first and second type region electrodes and their respective polycrystalline silicon layers reduces local current density and contact resistance. Furthermore, the rough surfaces of the first and second-type polycrystalline silicon layers increase their light scattering ability, reducing light reflection loss, improving the bifaciality and light absorption efficiency of the cell, and ultimately enhancing the cell's conversion efficiency. In addition, the roughening method in this embodiment does not cause a loss of open-circuit voltage, while improving the fill factor and short-circuit current, thereby improving the battery conversion efficiency. Compared with the etching roughening method in the prior art, the sandblasting process in this embodiment has significant advantages in terms of equipment cost, operating cost, and process time.

[0092] Based on the above embodiments, in one embodiment of this application, roughening the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate by at least one of liquid sandblasting, gas sandblasting, and applying a roughening layer includes:

[0093] A mask is fabricated on the back side of the back contact solar cell, and the mask is located in the isolation area between the first type region and the second type region;

[0094] Under the action of the mask, the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened by at least one of liquid sandblasting, gas sandblasting and brushing a roughening layer.

[0095] The mask has a perforated pattern that exposes the first type region and the second type region. The mask can be photoresist, stainless steel, polyimide film or special alloy, etc., and no specific limitation is made in this application.

[0096] When the mask is photoresist, it is directly coated on the back of the back-contact solar cell. A standard photolithography process, involving ultraviolet light exposure and development, precisely exposes the first and second type regions that require sandblasting. When the mask is made of stainless steel, polyimide film, or a special alloy, openings that perfectly match the patterns of the first and second type regions are cut using precision etching or laser processing.

[0097] In this embodiment, a mask is fabricated on the back of the battery to expose the first type region and the second type region simultaneously. Then, the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened simultaneously to make the roughness of the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate the same.

[0098] Based on the above embodiments, in one embodiment of this application, roughening the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate by at least one of liquid sandblasting, gas sandblasting, and applying a roughening layer includes:

[0099] A first mask is fabricated on the back side of the back contact solar cell. The first mask is located in the isolation area between the first type region and the second type region, as well as in the first type region.

[0100] Under the action of the first mask, at least one of liquid sandblasting, gas sandblasting and brushing roughening layer is used to roughen the surface of the second type polysilicon layer away from the substrate, so that the surface of the second type polysilicon layer away from the substrate is a rough surface.

[0101] Remove the first mask and fabricate a second mask on the back side of the solar cell. The second mask is located in the isolation area between the first type region and the second type region, as well as in the second type region.

[0102] Under the action of the second mask, the surface of the first type polysilicon layer away from the substrate is roughened by at least one of liquid sandblasting, gas sandblasting and brushing a roughening layer, so that the surface of the first type polysilicon layer away from the substrate is a rough surface; wherein, the roughness of the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate is different.

[0103] The first mask and the second mask can be any of photoresist, stainless steel, polyimide film or special alloy, etc. The first mask and the second mask can be the same or different, and no specific limitation is made in this application.

[0104] In this embodiment, by using a first mask and a second mask, the surfaces of the second type polysilicon layer away from the substrate and the first type polysilicon layer away from the substrate are roughened respectively, which can make the surfaces of the second type polysilicon layer away from the substrate and the first type polysilicon layer away from the substrate have different roughnesses, and achieve independent control of the first type region and the second type region.

[0105] Based on any of the above embodiments, in one embodiment of this application, the back surface roughening method of the back contact solar cell may further include: roughening the back surface of the substrate located in the isolation region between the first type region and the second type region by at least one of liquid sandblasting, gas sandblasting and brushing a roughening layer.

[0106] In this embodiment, the surface of the isolation region is also roughened to form an uneven surface, which can increase the light trapping effect, increase the number of light reflections in the isolation region, and improve the light absorption on the back side of the substrate.

[0107] Based on any of the above embodiments, in one embodiment of this application, the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened by at least one of liquid sandblasting, gas sandblasting and brushing a roughening layer, so that the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened, and further includes: growing a passivation repair layer on the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate.

[0108] The growth process of the passivation repair layer may include: low-temperature annealing at 200°~300° in a nitrogen atmosphere for 10min~20min in an ALD (atomic layer deposition) equipment to completely volatilize the alcohol or ether organic matter in the sandblasting slurry, and the nitrogen carries away the impurity gas. An aluminum oxide layer is grown on the surface of the first type polycrystalline silicon layer and the second type polycrystalline silicon layer away from the substrate using the ALD process. Then, a silicon nitride layer is grown on the surface of the aluminum oxide layer using the PECVD (plasma enhanced chemical vapor deposition) process.

[0109] The passivation repair layer can repair damage to the surfaces of the first and second type polysilicon layers that are away from the substrate, and can also achieve bulk passivation and surface passivation.

[0110] Based on any of the above embodiments, in one embodiment of this application, the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened by at least one of liquid sandblasting, gas sandblasting and brushing a roughening layer, so that the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened. After this, the process may further include cleaning the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate, so that the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are clean.

[0111] This application does not specify the specific cleaning method, as long as the cleaning effect can be achieved.

[0112] As one possible implementation, cleaning the surfaces of the first type polysilicon layer and the second type polysilicon layer facing away from the substrate includes:

[0113] Step S201: Use high-pressure blowing and / or high-pressure spray rinsing to perform preliminary cleaning on the surfaces of the first type polysilicon layer and the second type polysilicon layer that are away from the substrate.

[0114] This step uses physical cleaning to remove most of the abrasive particles adhering to the surface. High-pressure blowing is particularly suitable for gas blasting, using inert gases such as nitrogen; high-pressure spray rinsing is particularly suitable for liquid blasting, using extremely fine, high-pressure deionized water at an angle (e.g., 15°) to blow away particles using the shear force of the water flow.

[0115] Step S202: Place the pre-cleaned battery structure in a mixed solution cleaning tank and clean the surfaces of the first type polycrystalline silicon layer and the second type polycrystalline silicon layer that are away from the substrate again.

[0116] This step uses chemical cleaning to remove residual or electrostatically adsorbed particles and other contaminants from the surface.

[0117] The mixed solution in the cleaning tank is a mixture of HF, HCl, H2O2, and H2O, with a ratio of HF:HCl:H2O2:H2O = 2:1:0.5:6. After initial cleaning, the battery structure is cleaned in the mixed solution cleaning tank for 120-420 seconds. HCl primarily removes metal ion contaminants such as Al from the abrasive particles. 3+ H2O2 has strong oxidizing properties, which causes an oxide layer to form on the surface of polycrystalline silicon and can effectively remove organic contaminants such as alcohols and ethers in the grinding fluid. HF slightly corrodes the oxide layer, thereby "lifting" the adsorbed particles off the surface, while also dissolving metal oxides and silica impurities. Then, it is washed in a low-concentration 0.5%~2% pure HF bath for 60s~150s to completely remove the chemical oxide layer grown in the above process, exposing a clean polycrystalline silicon surface.

[0118] Step S203: Clean the battery structure again with deionized water.

[0119] The HF solution was washed away with deionized water and dried in a drying tank to avoid watermarks, resulting in clean, impurity-free battery cells with micro-pit structures in the first and second type regions.

[0120] The method for roughening the back side of the back contact solar cell of this application is described below using a specific case.

[0121] Step 1: Using an N-type silicon wafer as a substrate, texturing is performed on the front side of the substrate to form a textured structure, while the back side is a smooth surface;

[0122] Step 2: Grow a silicon dioxide dielectric layer and a type 1 polysilicon layer in the type 1 region on the back side of the substrate, and grow a silicon dioxide dielectric layer and a type 2 polysilicon layer in the type 2 region. An isolation region is formed between the type 1 region and the type 2 region.

[0123] Step 3: The battery cell is advanced using a chain roller with its back side facing upwards until it reaches the sandblasting position. Roughening is achieved using liquid sandblasting. The sandblasting nozzles are evenly distributed directly above the battery cell, 20mm from the surface. The sandblasting is performed at a pressure of 0.15 MPa and a 45° angle for 30 seconds. The abrasive particles in the sandblasting slurry consist of spherical silica particles with a diameter of 20 nm to 50 nm, mixed with particles of 0.5 μm to 0.8 μm in diameter. The abrasive particles are uniformly dispersed in the suspension. The dispersion solvent is 98% methanol, and the abrasive particle concentration is 25 wt%.

[0124] Step 4: Clean the sandblasted battery cells;

[0125] Step 5: Using the ALD process, grow an aluminum oxide layer on the surface of the first and second type polysilicon layers facing away from the substrate; then use the PECVD process to grow a silicon nitride layer on the surface of the aluminum oxide layer to form a passivation repair layer.

[0126] Step 6: Coat the first type region and the second type region with electrode paste and sinter them to form the first type region electrode and the second type region electrode.

[0127] This application also provides a photovoltaic module, which includes the back-contact solar cell described in any of the above embodiments.

[0128] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0129] The foregoing has provided a detailed description of the back-contact solar cell and its back-side roughening method provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the solution and core ideas of this application. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of this application.

Claims

1. A back-contact solar cell, characterized in that, include: Substrate; in a first direction, the back side of the substrate is provided with alternating first-type regions and second-type regions; In the second direction, a dielectric layer and a first-type polysilicon layer are sequentially disposed from the inside to the outside on the back side of the substrate in the first-type region, and a dielectric layer and a second-type polysilicon layer are sequentially disposed from the inside to the outside on the back side of the substrate in the second-type region; the surfaces of the first-type polysilicon layer and the second-type polysilicon layer facing away from the substrate are rough surfaces; A first-type region electrode located in the first-type region and a second-type region electrode located in the second-type region; The first direction is along the length of the back-contact solar cell, the second direction is along the thickness of the back-contact solar cell, and the first direction is perpendicular to the second direction.

2. The back-contact solar cell as described in claim 1, characterized in that, The rough surfaces of the first type polycrystalline silicon layer and the second type polycrystalline silicon layer away from the substrate are uneven surfaces, and the depth of the recessed areas on the rough surfaces ranges from 15nm to 50nm.

3. The back-contact solar cell as described in claim 1, characterized in that, The thickness of the damaged layer in the first type of polycrystalline silicon layer and the second type of polycrystalline silicon layer is less than or equal to 50 nm.

4. The back-contact solar cell as described in claim 1, characterized in that, The surface roughness of the first type polycrystalline silicon layer and the second type polycrystalline silicon layer away from the substrate ranges from 0.3 μm to 1.2 μm.

5. The back-contact solar cell according to any one of claims 1 to 4, characterized in that, Also includes: A passivation repair layer located on the surfaces of the first type polysilicon layer and the second type polysilicon layer facing away from the substrate.

6. A method for roughening the back surface of a back-contact solar cell, characterized in that, include: Prepare a substrate in a first direction, wherein the back side of the substrate is provided with alternating first-type regions and second-type regions; In the second direction, a dielectric layer and a first-type polycrystalline silicon layer are grown sequentially from the inside to the outside in the first-type region of the substrate, and a dielectric layer and a second-type polycrystalline silicon layer are grown sequentially from the inside to the outside in the second-type region of the substrate; the first direction is along the length direction of the back-contact solar cell, the second direction is along the thickness direction of the back-contact solar cell, and the first direction is perpendicular to the second direction. The surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened by at least one of liquid sandblasting, gas sandblasting and brushing a roughening layer, so that the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened. A first-type region electrode is grown in the first-type region, and a second-type region electrode is grown in the second-type region.

7. The back-side roughening method for a back-contact solar cell as described in claim 6, characterized in that, The abrasive particles in the blasting fluid and / or blasting airflow include a first particle with a size in the nanometer range and a second particle with a size in the micrometer range.

8. The method for roughening the back side of a back-contact solar cell as described in claim 6, characterized in that, Roughening the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate by at least one of liquid blasting, gas blasting, and applying a roughening layer includes: A mask is fabricated on the back side of the back contact solar cell, and the mask is located in the isolation area between the first type region and the second type region; Under the action of the mask, the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate are roughened by at least one of liquid sandblasting, gas sandblasting and brushing a roughening layer.

9. The method for roughening the back side of a back-contact solar cell as described in claim 6, characterized in that, Roughening the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate by at least one of liquid blasting, gas blasting, and applying a roughening layer includes: A first mask is fabricated on the back side of the back contact solar cell. The first mask is located in the isolation area between the first type region and the second type region, as well as in the first type region. Under the action of the first mask, at least one of liquid sandblasting, gas sandblasting and brushing roughening layer is used to roughen the surface of the second type polysilicon layer away from the substrate, so that the surface of the second type polysilicon layer away from the substrate is a rough surface. Remove the first mask and fabricate a second mask on the back side of the solar cell. The second mask is located in the isolation area between the first type region and the second type region, as well as in the second type region. Under the action of the second mask, the surface of the first type polysilicon layer away from the substrate is roughened by at least one of liquid sandblasting, gas sandblasting and brushing a roughening layer, so that the surface of the first type polysilicon layer away from the substrate is a rough surface; wherein, the roughness of the surfaces of the first type polysilicon layer and the second type polysilicon layer away from the substrate is different.

10. The method for roughening the back side of a back-contact solar cell as described in claim 6, characterized in that, Also includes: The back side of the substrate located in the isolation region between the first type region and the second type region is roughened by at least one of liquid sandblasting, gas sandblasting and applying a roughening layer.

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