Impurity-absorbing slurry as well as preparation method and application thereof

Abstract

The invention discloses gettering slurry as well as a preparation method and application thereof. The gettering slurry comprises resin, a gettering agent, a thickening agent and a solvent, and the gettering agent comprises silicon dioxide. According to the method, the gettering slurry is coated on the surface of the silicon wafer, and silicon dioxide can enable precipitates to preferentially nucleate in the gettering slurry on the surface of the silicon wafer and in a high-defect-density region related to a damaged layer on the surface of the silicon wafer, so that the concentration of impurities in a silicon wafer substrate is obviously reduced; according to the method, impurities have enough opportunities to diffuse from a silicon wafer substrate to a damaged area and a gettering slurry area at the edge, and then conventional texturing and other processes are carried out to remove gettering slurry and a damaged layer, so that the quality of the silicon wafer is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, and relates to a getter paste, its preparation method and application. Background Technology

[0002] Most solar cells are made of silicon. During the casting process, it is difficult to avoid a large number of impurities in the raw materials dissolving in the melt and eventually remaining in the silicon wafer, which reduces the minority carrier lifetime of the silicon wafer.

[0003] To reduce or eliminate residual impurities within silicon wafers, existing technologies offer several solutions. For example, CN114551636A provides a high-efficiency heterojunction solar cell and its fabrication method. This method adds a gettering step before the conventional heterojunction solar cell fabrication process. This gettering step is completed through a full-chain gettering process, specifically including: chain-like pre-cleaning of the silicon wafer, chain-like coating of gettering sources on the silicon wafer surface, and chain-like high-temperature gettering of the silicon wafer. This method can reduce the metal impurity content of N-type monocrystalline silicon wafers, improve the quality level of silicon wafers, reduce the differences between silicon wafers, and improve the conversion efficiency of heterojunction solar cells. However, the gettering agents used in this method are phosphoric acid solutions, phosphorus-containing pastes, or boron-containing pastes. These substances pose environmental problems. Moreover, although impurity atoms can migrate and diffuse to the surface N+ doped layer or P doped layer, they may flow back into the silicon substrate during the subsequent cooling process, leading to a reduction in the impurity removal effect.

[0004] Therefore, providing a highly efficient getter paste that can effectively remove impurities from silicon wafers to improve their performance is a pressing technical problem that needs to be solved. Summary of the Invention

[0005] In view of the above-mentioned problems existing in the prior art, the purpose of the present invention is to provide a pickling slurry, its preparation method and application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a slurry for removing impurities, the slurry comprising a resin, an impurity absorber, a thickener, and a solvent, wherein the impurity absorber comprises silica.

[0008] The getter agent in the getter paste of this invention is mainly composed of silicon dioxide, which purifies impurities in the silicon wafer substrate by attracting and removing them. The resin acts as an adhesive, fully fusing with the other components and ensuring thorough contact and adhesion to the silicon wafer during the coating process. It also allows for rapid removal during the cleaning process after the getter reaction. By coating the getter paste onto the surface of the silicon wafer, the silicon dioxide causes precipitates to preferentially nucleate within the getter paste on the wafer surface and in high-defect-density areas associated with the damaged layer on the wafer surface. This significantly reduces the concentration of impurities in the silicon wafer substrate, allowing them sufficient opportunity to diffuse from the substrate to the damaged areas at the edges and the getter paste area. Subsequently, conventional texturing and other processes remove the getter paste and damaged layer, thereby effectively improving the quality of the silicon wafer.

[0009] Compared to using getters such as phosphorus and boron, the advantages of this invention are: 1. The getter of this invention avoids the use of harmful chemicals, and the getter paste of this invention is environmentally friendly, with advantages in safety and environmental protection; 2. The getter paste of this invention can retain impurity ions in the high defect density region to the maximum extent, without flowing back into the silicon wafer substrate in large quantities during the subsequent cooling process; 3. Since silicon dioxide is sensitive to temperature and cooling rate, the adsorption and removal of impurities can be maximized by using the process parameters of high-temperature annealing (such as peak temperature, isothermal time, and cooling rate).

[0010] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0011] Preferably, the silica is nano-silica powder, wherein nano refers to a particle size in the range of 1nm to 100nm, and the particle size can be, for example, 1nm, 3nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm or 100nm, etc.

[0012] Preferably, the resin includes at least one of epoxy resin, phenolic resin, or acrylic resin.

[0013] Preferably, the thickener includes at least one of cellulose, polyvinyl alcohol, and polyacrylamide.

[0014] Preferably, the solvent includes at least one of acetone, ethylene glycol, diethyl ether, and dimethyl sulfoxide.

[0015] Preferably, the absorbent slurry also includes additives.

[0016] Preferably, the additives include at least one of a thickener, a leveling agent, and a dispersant. The thickener increases the viscosity of the absorbent slurry and improves the resin viscosity; the leveling agent facilitates the leveling of the slurry and improves the uniformity of the coating; the dispersant facilitates the uniform distribution of nano-silica in the slurry.

[0017] Preferably, the thickener includes at least one of cellulose, polyvinyl alcohol, and polyacrylamide.

[0018] Preferably, the leveling agent includes at least one of silicone oil, ethylene glycol monobutyl ether, and organosilicon resin.

[0019] Preferably, the dispersant comprises at least one of sodium hexametaphosphate and alkylbenzene sulfonate.

[0020] Preferably, based on the total mass of the absorbent slurry as 100%, the composition of the absorbent slurry includes:

[0021] Resin 15%–40%

[0022] Adsorbent 5%–10%

[0023] Thickener 1%–15%

[0024] Solvent 30%–50%

[0025] Leveling agent and / or dispersant 0.5% to 5%.

[0026] In the absorbent slurry of the present invention, the resin content is 15% to 40%, for example 15%, 16%, 18%, 20%, 21%, 23%, 24%, 25%, 26%, 28%, 30%, 32%, 33%, 35%, 36%, 37%, 38%, or 40%.

[0027] In the absorbent slurry of the present invention, the content of absorbent is 5% to 10%, for example 5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%.

[0028] In the absorbent slurry of the present invention, the content of thickener is 1% to 15%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc.

[0029] In the absorbent slurry of the present invention, the solvent content is 30% to 50%, for example 30%, 32%, 33%, 35%, 36%, 37%, 38%, 40%, 42%, 43%, 45%, 47%, 48%, or 50%.

[0030] In the impurity absorbent slurry of the present invention, the content of leveling agent and / or dispersant is 0.5% to 5%, for example 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc.

[0031] In a second aspect, the present invention provides a method for preparing the impurity absorbent slurry as described in the first aspect, the method comprising the following steps:

[0032] After the resin and solvent are stirred evenly once, the impurity absorber and optional additives are added and stirred a second time to obtain the impurity absorbent slurry.

[0033] Preferably, the conditions for stirring the resin and solvent are: at a temperature of 100℃ to 300℃, and at a speed of 50 rpm to 200 rpm for 10 min to 30 min. The temperature can be, for example, 100℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 220℃, 240℃, 260℃, 280℃, or 300℃, the speed can be, for example, 50 rpm, 60 rpm, 70 rpm, 80 rpm, 100 rpm, 120 rpm, 130 rpm, 150 rpm, 170 rpm, 180 rpm, or 200 rpm, and the time can be, for example, 10 min, 15 min, 20 min, 25 min, or 30 min.

[0034] Preferably, the secondary stirring conditions are: at a temperature of 100℃ to 300℃, stirring and dispersing at a speed of 50 rpm to 200 rpm for 20 min to 40 min. The temperature can be, for example, 100℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 220℃, 240℃, 260℃, 280℃, or 300℃, the speed can be, for example, 50 rpm, 60 rpm, 70 rpm, 80 rpm, 100 rpm, 120 rpm, 130 rpm, 150 rpm, 170 rpm, 180 rpm, or 200 rpm, and the time can be, for example, 20 min, 25 min, 30 min, 35 min, or 40 min.

[0035] Preferably, an additive is added during the secondary stirring stage.

[0036] In one embodiment, after the resin and solvent are stirred evenly once, a getter absorbent and an additive are added separately, and the mixture is stirred a second time to obtain the getter absorbent slurry.

[0037] Thirdly, the present invention provides a method for gettering a silicon wafer, the method comprising the following steps:

[0038] The gettering paste described in the first aspect is coated on the surface of the silicon wafer, annealed at high temperature, and after the gettering paste is removed, texturing is performed. The texturing process includes a texturing pre-cleaning step to remove the gettering paste containing impurities and the silicon wafer damage layer containing impurities, thereby completing the silicon wafer gettering.

[0039] As those skilled in the art know, silicon wafers are generally obtained by slicing, during which a damaged layer inevitably forms. This invention employs a new technique: surface damage gettering and getter paste impurity removal. First, a getter paste is uniformly coated onto the silicon wafer surface, followed by high-temperature annealing to dissolve most metallic impurity precipitates. Then, cooling is performed, and the precipitates preferentially nucleate within the getter paste on the silicon wafer surface and in high-defect-density regions associated with the damaged layer. This significantly reduces the concentration of impurities remaining in the silicon wafer substrate, allowing sufficient opportunity for impurities to diffuse from the substrate to the damaged areas at the edges and the getter paste area. Therefore, impurities in the silicon wafer after gettering are mainly concentrated in these areas. When using this getter-treated silicon wafer to prepare crystalline silicon solar cells, only conventional texturing processes are needed to remove the getter paste and damaged layer, significantly reducing the residual impurity concentration on the silicon wafer. This effectively improves silicon wafer quality, minority carrier lifetime, and increases the open-circuit voltage and short-circuit current of the solar cell, thereby improving cell quality and efficiency.

[0040] This invention uses a specific gettering slurry to getter silicon wafers, resulting in a significant gettering effect. When the silicon wafers obtained after gettering are used in the fabrication of crystalline silicon solar cells, the efficiency improvement of different cell technologies ranges from 0.05% to 0.15%.

[0041] The getter paste of the present invention is used to getter silicon wafers and prepare crystalline silicon solar cells. The getter paste removal is simple, the process is simplified, and it is more conducive to mass production.

[0042] Preferably, the coating method includes any one of spin coating, brush coating, or spray coating.

[0043] Preferably, the thickness of the gettering slurry coating formed by coating is 200nm to 5μm, such as 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm.

[0044] Preferably, the high-temperature annealing is performed using a chain annealing device.

[0045] Conventional getter removal typically employs high-temperature tubular equipment and cleaning equipment. Compared to conventional getter removal equipment, this invention mainly adds slurry and chain annealing equipment. It requires fewer devices, has lower costs, and is suitable for industrial production.

[0046] In this invention, the cleaning equipment can be a chain cleaning device or a tank cleaning device, and can be integrated with the high-temperature annealing equipment of this invention, or it can be a separate device.

[0047] Preferably, the silicon wafer channels in the chain annealing equipment are 5 to 10, for example, 5, 6, 7, 8 or 10 channels.

[0048] Preferably, the high-temperature annealing includes: heating to the annealing temperature and maintaining the temperature.

[0049] Preferably, the high-temperature annealing temperature is 850℃~950℃, such as 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃. Here, the annealing temperature refers to the peak temperature. Within this temperature range, a better gettering effect can be achieved.

[0050] Preferably, the isothermal time for the high-temperature annealing is 5 min to 15 min, such as 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 12 min, or 15 min.

[0051] Preferably, the heating is a rapid heating, and the heating rate of the rapid heating is 6℃ / min to 10℃ / min, such as 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min.

[0052] Preferably, after the heat preservation, cooling is performed, and the cooling is a medium-speed cooling, with a cooling rate of 3℃ / min to 4℃ / min, such as 3℃ / min, 3.5℃ / min, or 4℃ / min.

[0053] Preferably, the cooling time is 5 min to 15 min, for example, 5 min, 6 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min or 15 min.

[0054] By controlling at least one of the following: peak temperature, constant temperature time, rapid heating, medium-speed cooling, and cooling time, it is possible to maximize the retention of impurities in the damaged layer and the impurity-absorbing slurry zone.

[0055] As a preferred embodiment of the gettering method for silicon wafers according to the present invention, the silicon wafer is pretreated before being coated with gettering paste, and the surface of the silicon wafer after the surface pretreatment has a surface damage layer.

[0056] Preferably, the surface pretreatment uses a mixed solution of hydrogen peroxide and alkali. The alkali may be sodium hydroxide and / or potassium hydroxide.

[0057] Preferably, the reagent used for the pre-cleaning of the texturing process is a mixture of alkali and hydrogen peroxide, wherein the alkali may be sodium hydroxide and / or potassium hydroxide.

[0058] Preferably, the temperature of the pre-washing of the flocking process is 45℃ to 65℃, for example, 45℃, 50℃, 55℃, 60℃ or 65℃.

[0059] Preferably, the pre-washing time for the flocking process is 30s to 50s, such as 30s, 35s, 40s, 45s, or 50s.

[0060] Preferably, the removal of impurity slurry is carried out in the following manner: the treated silicon wafer is washed with water and acid-washed, wherein the acid used for acid washing is HF with a mass concentration of 5% to 10%, and the mass concentration may be, for example, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9% or 10%.

[0061] Fourthly, the present invention provides a crystalline silicon solar cell, which is prepared by processing a silicon wafer using the gettering method described in the third aspect. The crystalline silicon solar cell includes any one of polycrystalline solar cells, PERC solar cells, TOPCon solar cells, HJT solar cells, IBC solar cells, TBC solar cells, HBC solar cells, and perovskite tandem solar cells.

[0062] In one embodiment, the present invention provides a method for preparing a crystalline silicon solar cell, comprising the following steps:

[0063] S1 performs front-side boron diffusion on the texturized silicon wafer, with a diffusion sheet resistance of 80Ω to 300Ω (e.g., 80Ω, 100Ω, 120Ω, 130Ω, 150Ω, 160Ω, 180Ω, 200Ω, 220Ω, 240Ω, 260Ω, 280Ω, or 300Ω, etc.) and a diffusion depth of 0.3μm to 2.4μm (e.g., 0.3μm, 0.6μm, 1μm, 1.5μm, 2μm, or 2.4μm, etc.).

[0064] S2 performs laser SE redoping on the gate region using a laser. The diffusion sheet resistance of the laser region is 70Ω to 160Ω (e.g., 70Ω, 80Ω, 90Ω, 100Ω, 110Ω, 120Ω, 135Ω, 150Ω or 160Ω, etc.), and the diffusion depth is 0.6μm to 2.6μm (e.g., 0.6μm, 0.8μm, 1μm, 1.3μm, 1.5μm, 1.6μm, 1.8μm, 2μm, 2.3μm or 2.6μm, etc.).

[0065] 8) Secondary diffusion, with a secondary diffusion temperature of 950℃~1100℃ (e.g., 950℃, 970℃, 1000℃, 1050℃ or 1100℃, etc.).

[0066] 9) Alkali polishing: The edge etching and back alkaline polishing are performed using a chain + tank type equipment to facilitate the formation of a better passivation layer in the future.

[0067] 10) The back tunneling oxide layer and doped polysilicon are prepared by LPCVD + phosphorus diffusion or PECVD + annealing. The thickness of the tunneling oxide layer is 1nm to 3nm (e.g., 1nm, 2nm or 3nm), and the thickness of the doped polysilicon is 70nm to 160nm (e.g., 70nm, 80nm, 100nm, 110nm, 130nm, 150nm or 160nm), with a doping concentration of 1E20-1E21.

[0068] 11) Chain-type + tank-type cleaning is used to remove the silicon layer coated on the front side and to clean the semi-finished product.

[0069] 12) Use ALD to deposit alumina on the front side with a deposition thickness of 4nm to 12nm (e.g., 4nm, 6nm, 8nm, 10nm or 12nm) to enhance the field passivation effect.

[0070] 13) Passivation and light trapping are performed by depositing one or more of SiN / SiON / SiO on the front and back sides using PECVD.

[0071] 14) Screen printing and light injection.

[0072] 15) Laser contact enhancement treatment.

[0073] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0074] Compared with existing technologies, the present invention has the following beneficial effects:

[0075] (1) The present invention coats the surface of the silicon wafer with getter paste. Silica can cause the precipitates to nucleate preferentially in the getter paste on the surface of the silicon wafer and in the high defect density area associated with the damaged layer on the surface of the silicon wafer. This significantly reduces the concentration of impurities in the silicon wafer substrate, giving the impurities a sufficient opportunity to diffuse from the silicon wafer substrate to the damaged area at the edge and the getter paste area. Then, conventional texturing and other processes are performed to remove the getter paste and the damaged layer, thereby effectively improving the quality of the silicon wafer.

[0076] (2) This invention employs a new technology, namely surface damage gettering and gettering slurry impurity removal technology. First, the gettering slurry is uniformly coated on the silicon wafer surface, and then high-temperature annealing is performed to dissolve most of the metal impurity precipitates. Then, cooling is performed, and the precipitates preferentially nucleate in the gettering slurry on the silicon wafer surface and in the high defect density area associated with the silicon wafer surface damage layer. This significantly reduces the concentration of impurities remaining in the silicon wafer substrate, giving impurities sufficient opportunity to diffuse from the silicon wafer substrate to the damaged area at the edge and the gettering slurry area. Therefore, the impurities in the silicon wafer after gettering treatment are mainly concentrated in the above-mentioned areas. When using the silicon wafer after gettering treatment to prepare crystalline silicon cells, only conventional texturing processes are needed to remove the gettering slurry and damage layer, which significantly reduces the residual impurity concentration of the silicon wafer, thereby effectively improving the silicon wafer quality, improving the minority carrier lifetime of the silicon wafer, and increasing the open-circuit voltage and short-circuit current of the cell, thereby achieving the purpose of improving cell quality and increasing cell efficiency. Attached Figure Description

[0077] Figure 1 This is a process flow diagram of a method for preparing crystalline silicon according to an embodiment of the present invention;

[0078] Among them, 1-N-type silicon wafer, 2-getter paste, 3-front boron diffusion layer, 4-back tunneling and doped polycrystalline silicon layer, 5-front alumina, 6-passivation layer SiN, 7-electrode. Detailed Implementation

[0079] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0080] The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0081] Example 1

[0082] This embodiment provides a slurry for removing impurities, comprising a resin, an impurity absorbent, a solvent, and additives. The resin is epoxy resin, the impurity absorbent is nano-silica (particle size in the range of 1nm to 100nm), the solvent is acetone, and the additives are a thickener and a leveling agent. The thickener is cellulose, and the leveling agent is silicone oil.

[0083] The composition of the absorbent slurry is shown in Table 1, taking the total mass of the absorbent slurry as 100%.

[0084] The method for preparing the impurity absorbent slurry provided in this embodiment includes the following steps:

[0085] After the resin and solvent are stirred evenly once, the impurity absorber and additives are added and stirred a second time to obtain the impurity absorbent slurry.

[0086] The preparation conditions for the impurity absorbent slurry are shown in Table 2.

[0087] Example 2

[0088] This embodiment provides a slurry for removing impurities, comprising a resin, an impurity absorbent, a solvent, and additives. The resin is a phenolic resin, the impurity absorbent is nano-silica (particle size in the range of 1nm to 100nm), the solvent is ethylene glycol, and the additives are a thickener and a leveling agent. The thickener is cellulose, and the leveling agent is ethylene glycol monobutyl ether.

[0089] The composition of the absorbent slurry is shown in Table 1, taking the total mass of the absorbent slurry as 100%.

[0090] The method for preparing the impurity absorbent slurry provided in this embodiment includes the following steps:

[0091] After the resin and solvent are stirred evenly once, the impurity absorber and additives are added and stirred a second time to obtain the impurity absorbent slurry.

[0092] The preparation conditions for the absorbent slurry are shown in Table 2.

[0093] Example 3

[0094] This embodiment provides a slurry for removing impurities, comprising a resin, an impurity absorbent, a solvent, and additives. The resin is an acrylic resin, the impurity absorbent is nano-silica (particle size in the range of 1nm to 100nm), the solvent is acetone, and the additives are a thickener, a leveling agent, and a dispersant. The thickener is cellulose, the leveling agent is ethylene glycol monobutyl ether, and the dispersant is sodium hexametaphosphate.

[0095] The composition of the absorbent slurry is shown in Table 1, taking the total mass of the absorbent slurry as 100%.

[0096] The method for preparing the impurity absorbent slurry provided in this embodiment includes the following steps:

[0097] After the resin and solvent are stirred evenly once, the impurity absorber and additives are added and stirred a second time to obtain the impurity absorbent slurry.

[0098] The preparation conditions for the absorbent slurry are shown in Table 2.

[0099] Example 4

[0100] This embodiment provides a slurry for removing impurities, comprising a resin, an impurity absorbent, a solvent, and additives. The resin is an acrylic resin, the impurity absorbent is nano-silica (particle size in the range of 1nm to 100nm), the solvent is acetone, and the additives are a thickener and a leveling agent. The thickener is cellulose, and the leveling agent is silicone resin.

[0101] The composition of the absorbent slurry is shown in Table 1, taking the total mass of the absorbent slurry as 100%.

[0102] The method for preparing the impurity absorbent slurry provided in this embodiment includes the following steps:

[0103] After the resin and solvent are stirred evenly once, the impurity absorber and additives are added and stirred a second time to obtain the impurity absorbent slurry.

[0104] The preparation conditions for the absorbent slurry are shown in Table 2.

[0105] Table 1

[0106]

[0107] Table 2

[0108]

[0109]

[0110] Application Example 1

[0111] This application example provides a method for fabricating crystalline silicon solar cells. See the process flow diagram below. Figure 1 This includes the following steps:

[0112] 1) such as Figure 1 As shown in (a), a mixed aqueous solution of hydrogen peroxide and sodium hydroxide (where the concentration of sodium hydroxide is 0.9% and the concentration of hydrogen peroxide is 3.5%) is used to pretreat the surface of the silicon wafer to remove surface oil. Note that only slight etching is performed to preserve the damaged layer on the surface of the silicon wafer.

[0113] 2) such as Figure 1 As shown in (b), a getter paste (Example 1) was coated on the surface of a silicon wafer by brushing, and the coating thickness was 500 nm.

[0114] 3) such as Figure 1 As shown in (c), a chain annealing machine is used to rapidly heat the silicon wafer to 900°C (heating rate of 10°C / min), and hold it at the temperature for 8 min for high-temperature annealing and gettering. During the high-temperature process, the organic solvent evaporates, the impurities dissolve and preferentially nucleate in the damaged layer and gettering slurry area. After the high temperature, the wafer is cooled for 10 min at a rate of 4°C / min.

[0115] 4) The impurity-absorbing slurry with high concentrations of dissolved impurities is removed by water washing and acid washing tanks. The acid used for acid washing is HF with a mass concentration of 10%.

[0116] 5) such as Figure 1 As shown in (d), the silicon wafer is cleaned and texturized using an alkaline texturing method. The texturing process includes texturing pre-cleaning to remove the silicon wafer damage layer containing high concentrations of impurities, thus completing the silicon wafer gettering.

[0117] The reagent used for the pre-cleaning of the texturing process is a mixed aqueous solution of hydrogen peroxide and sodium hydroxide (where the concentration of sodium hydroxide is 1% and the concentration of hydrogen peroxide is 6%).

[0118] 6) such as Figure 1 As shown in (e), a boron diffusion machine is used to perform front-side boron diffusion on the silicon wafer, with a diffusion sheet resistance of 200Ω and a diffusion depth of 1.5μm.

[0119] 7) Laser SE redoping is performed on the gate line region by laser. The diffusion sheet resistance of the laser region is 100Ω and the diffusion depth is 2μm.

[0120] 8) Secondary diffusion, secondary diffusion temperature 1000℃.

[0121] 9) such as Figure 1 As shown in (f), alkaline polishing is performed using a chain + tank type equipment for edge etching and back-side alkaline polishing, which facilitates the formation of a better passivation layer in the future.

[0122] 10) such as Figure 1 As shown in (g), the back tunneling oxide layer and doped polysilicon were prepared by LPCVD + phosphorus diffusion. The thickness of the tunneling oxide layer was 2 nm, the thickness of the doped polysilicon was 100 nm, and the doping concentration was 1E20-1E21.

[0123] 11) such as Figure 1 As shown in (h), a chain-type + tank-type cleaning method is used to remove the silicon layer deposited on the front side and to clean the semi-finished product.

[0124] 12) For example Figure 1 As shown in (i), ALD is used for front-side alumina deposition with a thickness of 8 nm to enhance the field passivation effect.

[0125] 13) such as Figure 1 As shown in (j), PECVD is used to deposit SiN on both the front and back sides for passivation and light trapping.

[0126] 14) For example Figure 1 As shown in (k) in the figure, screen printing and light injection.

[0127] 15) Laser contact enhancement treatment.

[0128] Application Example 2

[0129] This application example provides a method for preparing a crystalline silicon solar cell, which differs from Application Example 1 in steps 2) and 3), specifically:

[0130] 2) A getter paste was coated on the surface of a silicon wafer (Example 2). The coating method was spin coating, and the coating thickness was 1 μm.

[0131] 3) A chain annealing machine is used to rapidly heat the silicon wafer to 850°C (heating rate of 10°C / min), and hold it at the temperature for 15 minutes for high-temperature annealing and gettering. During the high-temperature process, the organic solvent evaporates, the impurities dissolve and preferentially nucleate in the damaged layer and gettering slurry area. After the high temperature, the wafer is cooled for 5 minutes at a rate of 4°C / min.

[0132] Application Example 3

[0133] This application example provides a method for preparing a crystalline silicon solar cell, which differs from Application Example 1 in steps 2) and 3), specifically:

[0134] 2) A gettering paste was coated on the surface of a silicon wafer (Example 3). The coating method was spraying, and the coating thickness was 2 μm.

[0135] 3) The silicon wafer is rapidly heated to 950°C (8°C / min) using a chain annealing machine and held at that temperature for 5 minutes for high-temperature annealing and gettering. During the high-temperature process, the organic solvent evaporates, the impurities dissolve and preferentially nucleate in the damaged layer and gettering slurry area. After the high temperature, the wafer is cooled for 15 minutes at a rate of 3°C / min.

[0136] Application Example 4

[0137] This application example provides a method for preparing a crystalline silicon solar cell, which differs from Application Example 1 in steps 2) and 3), specifically:

[0138] 2) A getter paste was coated on the surface of a silicon wafer (Example 3). The coating method was spin coating, and the coating thickness was 5 μm.

[0139] 3) The silicon wafer is rapidly heated to 920℃ at a rate of 9℃ / min using a chain annealing machine and held at that temperature for 7min for high-temperature annealing and gettering. During the high-temperature process, the organic solvent evaporates, the impurities dissolve and preferentially nucleate in the damaged layer and gettering slurry area. After the high temperature, the wafer is cooled for 10min at a rate of 4℃ / min.

[0140] Application Example 5

[0141] This application example provides a method for preparing a crystalline silicon solar cell. The difference from application example 1 is that the cooling rate in step 3) is 8°C / min.

[0142] Application Example 6

[0143] This application example provides a method for preparing a crystalline silicon solar cell. The difference from application example 1 is that in step 3), the temperature is kept constant at 800°C.

[0144] Application Example 7

[0145] This application example provides a method for preparing a crystalline silicon solar cell. The difference from application example 1 is that in step 3), the temperature is kept constant at 970°C.

[0146] Application Example 8

[0147] This application example provides a method for preparing a crystalline silicon solar cell. The difference from application example 1 is that in step 3), the heating rate is 12°C / min.

[0148] Application Example 9

[0149] This application example provides a method for preparing a crystalline silicon solar cell. The difference from application example 1 is that the coating thickness in step 2) is 100 nm.

[0150] Application Example 10

[0151] This application example provides a method for preparing a crystalline silicon solar cell, which differs from Application Example 1 in that the coating thickness in step 2) is 5.1 μm.

[0152] Application Comparative Example 1

[0153] This application provides a comparative method for preparing a crystalline silicon solar cell. The difference between this method and Application Example 1 is that step 2) does not involve setting a coating.

[0154] Performance testing:

[0155] This test was conducted using the HALM tester for electrical performance IV testing.

[0156] The test results are shown in Table 3.

[0157] Table 3

[0158]

[0159]

[0160] As shown in Table 1, the present invention uses a specific getter paste to getter silicon wafers, and the gettering effect is obvious. When the silicon wafers after gettering are used to prepare crystalline silicon cells, compared with Comparative Example 1 (which does not use getter paste for gettering), the open-circuit voltage and short-circuit current of the cells are improved, and the efficiency of the cells is improved.

[0161] A comparison of Application Example 1 and Application Example 5 shows that adjusting the cooling rate within the preferred range of 3-4 °C / min is beneficial for increasing the voltage and current.

[0162] By comparing Application Example 1 with Application Examples 6-7, it can be seen that the preferred temperature range for constant temperature is 850℃~950℃. If the temperature is too low, it is not conducive to the flow of impurities; if the temperature is too high, it is not conducive to the retention of impurities in the absorbent slurry.

[0163] A comparison of Application Example 1 and Application Example 8 shows that by controlling the heating rate within the preferred range of 8 to 10°C, it is beneficial for impurities to flow to the impurity-absorbing slurry.

[0164] By comparing Application Example 1 with Application Examples 9-10, it can be seen that the coating thickness has an optimal range of 100nm to 5μm. If the thickness is too small, it is not conducive to the full absorption of impurities; if the thickness is too large, it is not conducive to the flow of impurities and it is easy to introduce new impurities.

[0165] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A slurry for absorbing impurities, characterized in that, The getter slurry includes a resin, a getter agent, and a solvent, wherein the getter agent includes silica.

2. The absorbent slurry according to claim 1, characterized in that, The silica is nano-silica powder; Preferably, the resin includes at least one of epoxy resin, phenolic resin, or acrylic resin; Preferably, the solvent includes at least one of acetone, ethylene glycol, diethyl ether, and dimethyl sulfoxide.

3. The absorbent slurry according to claim 1 or 2, characterized in that, The impurity absorbent slurry also includes additives; Preferably, the additives include at least one of thickeners, leveling agents, and dispersants; Preferably, the thickener comprises at least one of cellulose, polyvinyl alcohol, and polyacrylamide; Preferably, the leveling agent comprises at least one of silicone oil, ethylene glycol monobutyl ether, and organosilicon resin; Preferably, the dispersant comprises at least one of sodium hexametaphosphate and alkylbenzene sulfonate.

4. The absorbent slurry according to claim 3, characterized in that, Based on the total mass of the absorbent slurry being 100%, the absorbent slurry comprises: Resin 15%–40% Adsorbent 5%–10% Thickener 1%–15% Solvent 30%–50% Leveling agent and / or dispersant 0.5% to 5%.

5. A method for preparing the absorbent slurry as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: After the resin and solvent are stirred evenly once, the impurity absorber and optional additives are added and stirred a second time to obtain the impurity absorbent slurry. Preferably, the conditions for stirring the resin and solvent are: at a temperature of 100℃ to 300℃, and at a speed of 50 rpm to 200 rpm for 10 min to 30 min. Preferably, the conditions for the secondary stirring are: stirring and dispersing at a temperature of 100℃~300℃ and a speed of 50rpm~200rpm for 20min~40min; Preferably, an additive is added during the secondary stirring stage.

6. A method for gettering silicon wafers, characterized in that, The gettering method for the silicon wafer includes the following steps: The gettering paste according to any one of claims 1-4 is coated on the surface of a silicon wafer, annealed at high temperature, and after the gettering paste is removed, texturing is performed. The texturing process includes a texturing pre-cleaning step to remove the gettering paste containing impurities and the silicon wafer damage layer containing impurities, thereby completing the silicon wafer gettering.

7. The gettering method for silicon wafers according to claim 6, characterized in that, The coating method includes any one of spin coating, brush coating or spray coating; Preferably, the thickness of the gettering slurry coating formed by the coating process is 200 nm to 5 μm; Preferably, the high-temperature annealing is performed using a chain annealing device; Preferably, the silicon wafer channels in the chain annealing equipment are 5 to 10 channels; Preferably, the high-temperature annealing includes: heating to the annealing temperature and maintaining the temperature at that temperature; Preferably, the annealing temperature for the high-temperature annealing is 850℃~950℃; Preferably, the isothermal time for the high-temperature annealing is 5 min to 15 min; Preferably, the heating is a rapid heating, and the heating rate of the rapid heating is 6℃ / min to 10℃ / min; Preferably, after the heat preservation, cooling is performed, and the cooling is a medium-speed cooling, with a cooling rate of 3℃ / min to 4℃ / min. Preferably, the cooling time is 5 min to 15 min.

8. The gettering method for silicon wafers according to claim 6 or 7, characterized in that, Before coating the silicon wafer with the gettering slurry, the silicon wafer undergoes surface pretreatment, and the surface of the silicon wafer after surface pretreatment has a surface damage layer. Preferably, the reagent used for the surface pretreatment is a mixed solution of hydrogen peroxide and alkali.

9. The gettering method for silicon wafers according to claim 6, characterized in that, The reagent used for the pre-cleaning of the texturing process is a mixed solution of alkali and hydrogen peroxide; Preferably, the temperature of the pre-washing of the flocking process is 45℃~65℃; Preferably, the pre-washing time for the flocking process is 30s to 50s; Preferably, the removal of impurity slurry is carried out in the following manner: the treated silicon wafer is washed with water and acid-washed, wherein the acid used for acid washing is HF with a mass concentration of 5% to 10%.

10. A crystalline silicon solar cell, characterized in that, The crystalline silicon solar cell is prepared by processing a silicon wafer using the gettering method described in any one of claims 6-9. The crystalline silicon solar cell includes any one of polycrystalline cells, PERC cells, TOPCon cells, HJT cells, IBC cells, TBC cells, HBC cells, and perovskite tandem cells.

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