A method for preparing a selective emitter and a method for preparing a solar cell sheet

Abstract

The present application discloses a method for preparing a selective emitter and a method for preparing a solar cell sheet, belonging to the technical field of solar cells. The method comprises: lightly doping a silicon wafer after texturing to form a lightly doped p-n junction; coating a boron slurry on the surface of the silicon wafer after light doping; oxidizing the boron slurry on the surface of the silicon wafer to remove C and H elements of organic matter in the boron slurry, wherein the oxidation method is chain oxidation and the oxidation temperature is greater than 600°C; heavily doping the oxidized silicon wafer to form a selective emitter; and by performing an oxidation reaction on the boron slurry before heavy doping, the C and H elements in the boron slurry are reacted to generate CO2 and H2O and then removed, thereby avoiding the problem of subsequent heavy doping pushing the C element into the silicon wafer and causing pollution and leakage.

Description

Technical Field

[0001] The present application relates to the technical field of solar cells, and in particular to a method for preparing a selective emitter and a method for preparing a solar cell sheet. Background Art

[0002] The selective emitter (SE) structure is one of the most promising methods for achieving high efficiency in the production process of crystalline silicon solar cells. In order to take into account the needs of open circuit voltage, short circuit current and fill factor (affected by contact resistance) at the same time, heavy doping is performed at the electrode contact part through the boron paste printing process to reduce the contact resistance, and light doping is performed between the electrodes through the tubular diffusion process to reduce Auger recombination and increase the open voltage and current.

[0003] However, the effect of heavy doping on improving battery efficiency through the boron paste printing process currently varies significantly. Summary of the invention

[0004] The purpose of the present application is to provide a method for preparing a selective emitter and a method for preparing a solar cell sheet, so as to solve the problem that the current heavy doping through the boron paste printing process has an uneven effect on improving the cell efficiency.

[0005] During the invention process, the applicant discovered that the silicon wafers of the battery heavily doped using the boron paste printing process contained the element C, which caused contamination and led to leakage problems. The applicant analyzed that the reason may be that the boron paste contains the element C, which is pushed into the silicon wafer together with the element B during the heavy doping process.

[0006] In a first aspect, an embodiment of the present application provides a method for preparing a selective emitter, the method comprising:

[0007] Lightly doping the textured silicon wafer to form a lightly doped pn junction;

[0008] Apply boron slurry on the surface of the lightly doped silicon wafer;

[0009] Oxidizing the boron slurry on the surface of the silicon wafer to remove C and H elements of organic matter in the boron slurry, wherein the oxidation method is chain oxidation and the oxidation temperature is greater than 600° C.;

[0010] The oxidized silicon wafer is heavily doped to form a selective emitter.

[0011] By performing an oxidation reaction on the boron slurry before heavy doping, the C and H elements in the boron slurry are reacted to generate CO2 and H2O and then removed, thereby avoiding the problem of subsequent heavy doping pushing the C element into the silicon wafer, causing pollution and leakage. At the same time, when drying at a conventional temperature of about 200°C, only the moisture in the boron slurry can be removed, and at this time the boron slurry will only produce a certain volatilization, and will not be pushed forward, resulting in a waste of boron. When the temperature reaches above 600°C, the boron slurry will be pushed forward to a certain extent, thereby reducing the waste of boron. The oxidation is carried out by chain oxidation, which cleverly combines oxidation and drying, effectively shortening the time of the entire process. At the same time, the applicant found that the conversion efficiency of the solar cell prepared by chain oxidation is higher, which can produce unexpected technical effects.

[0012] In combination with the first aspect, in an optional embodiment of the present application, the oxidation temperature is greater than 700° C.; optionally, the oxidation temperature is 700-900° C.; and / or

[0013] The oxidation time is less than 60 min;

[0014] Optionally, the oxidation time is 5-40 min;

[0015] Optionally, the oxidation time is 15-30 minutes.

[0016] The higher the oxidation temperature, the better the boron propulsion effect. Therefore, controlling the oxidation temperature to >700°C can achieve better oxidation and propulsion effects. The purpose of controlling the time is to completely eliminate the carbon-containing organic matter in the boron slurry. Most boron slurries can completely eliminate the carbon-containing organic matter within 60 minutes. The applicant believes that controlling the oxidation temperature to 700-900°C and the oxidation time to 15-30 minutes is a better choice.

[0017] In combination with the first aspect, in an optional embodiment of the present application, the oxidizing atmosphere is saturated pure oxygen.

[0018] The use of pure oxygen atmosphere can fully remove the C and H elements of organic matter in the boron slurry, and can reduce the reaction between other gases and silicon wafers to avoid affecting battery performance.

[0019] In combination with the first aspect, in an optional embodiment of the present application, the boron slurry includes boric acid; and / or

[0020] The volume concentration of the boron slurry is 5%-9%;

[0021] Optionally, the volume concentration of the boron slurry is 6%-8%.

[0022] In the above implementation process, those skilled in the art may select the boron slurry and its concentration according to actual conditions. For example, the volume concentration of the boron slurry is 5%, 6%, 7%, 8% and 9%.

[0023] In combination with the first aspect, in an optional embodiment of the present application, the texturing is performed using alkaline solution;

[0024] Optionally, the volume concentration of the alkali solution is 0.5% to 1.5%.

[0025] In combination with the first aspect, in an optional implementation of the present application, lightly doping the silicon wafer after texturing to form a lightly doped pn junction specifically includes:

[0026] BCl3 is deposited on the surface of the silicon wafer after texturing to form a lightly doped pn junction.

[0027] In combination with the first aspect, in an optional embodiment of the present application, the heavy doping method includes high temperature propulsion or laser propulsion;

[0028] Optionally, the temperature of the high temperature propulsion is 900-1100°C;

[0029] Optionally, the high temperature advancement time is 20-40 minutes.

[0030] In the above implementation process, technicians in this field can select the heavy doping method and its parameters according to actual conditions. For example, the high temperature advancement temperature is 900°C, 1000°C and 1100°C, and the high temperature advancement time is 20min, 30min and 40min.

[0031] In combination with the first aspect, in an optional implementation manner of the present application, the sheet resistance of the heavily doped region formed by heavy doping is 40-80Ω / sq; and / or

[0032] The junction depth of the heavily doped region formed by heavy doping is 1-1.6 μm.

[0033] In a second aspect, the present application also provides a method for preparing a solar cell sheet, the method comprising:

[0034] Forming a selective emitter on a silicon wafer using the above selective emitter preparation method;

[0035] alkaline polishing the silicon wafer on which the selective emitter is formed;

[0036] Prepare polysilicon film on the back of the silicon wafer after alkali polishing, and then clean it;

[0037] The surface of the cleaned silicon wafer is subjected to film preparation, and then electrode preparation is performed to obtain a solar cell wafer.

[0038] In the above implementation process, a selective emitter is formed by boron paste printing + high-temperature thermal oxidation, which can effectively reduce the contact resistance of the electrode contact area, improve the fill factor, and increase the battery efficiency. By oxidizing the boron paste before heavy doping, the C and H elements in the organic matter are removed, leaving only B, which effectively prevents the C element from being pushed into the silicon wafer during subsequent heavy doping to cause pollution and leakage. At the same time, the drying and oxidation steps are cleverly combined together without adding additional steps, saving process equipment and preparation time.

[0039] In conjunction with the second aspect, in an optional embodiment of the present application, the step of preparing a film on the cleaned surface of the silicon wafer includes:

[0040] Depositing an aluminum oxide film for passivation and a silicon nitride film for anti-reflection on the front side of the cleaned silicon wafer;

[0041] A silicon nitride film for back film hydrogen passivation is deposited on the back side of the cleaned silicon wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 A flow chart of a method for preparing a selective emitter provided in an embodiment of the present application;

[0044] Figure 2 A flow chart of a method for preparing a solar cell sheet provided in an embodiment of the present application. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0046] Please refer to Figure 1 , the present application embodiment provides a method for preparing a selective emitter, the method comprising:

[0047] S0. Use N-type silicon wafers, use 1% alkaline solution NaOH for texturing and use 20%-40% volume concentration of hydrogen peroxide and 1%-5% volume concentration of alkaline solution KOH to clean the silicon wafers

[0048] S1. Lightly doping the textured silicon wafer to form a lightly doped pn junction;

[0049] S2. Applying boron slurry on the surface of the lightly doped silicon wafer;

[0050] In some embodiments, the silicon wafer after texturing is lightly doped to form a lightly doped pn junction, specifically including:

[0051] BCl3 is deposited on the surface of the silicon wafer after texturing to form a lightly doped pn junction.

[0052] Specifically, in this embodiment, a tubular boron diffusion furnace is used to directly deposit BCl3 at a high temperature to form a lightly doped pn junction.

[0053] In some embodiments, the boron slurry includes boric acid, and the volume concentration of the boron slurry is 5%-9%. Preferably, the volume concentration of the boron slurry is 6%-8%. Furthermore, the volume concentration of the boron slurry is 7%.

[0054] S3. oxidizing the boron slurry on the surface of the silicon wafer to remove impurities in the boron slurry;

[0055] In order to reduce the steps and preparation time, the applicant cleverly combines oxidation and drying by chain oxygen. In some embodiments, the oxidation temperature is greater than 600°C; the oxidation time is less than 60min. The applicant found that when drying at a conventional temperature of about 200°C, only the water in the boron slurry can be removed, and the boron slurry will also volatilize to a certain extent at this time, and no waste of boron will occur due to advancement. When the temperature reaches above 600°C, the boron slurry will be advanced to a certain extent, thereby reducing the waste of boron. The control time is to completely eliminate the carbon-containing organic matter in the boron slurry. Most of the boron slurries can completely eliminate the carbon-containing organic matter within 60min; in order to further enhance the advancement effect of boron, preferably, the oxidation temperature is greater than 700°C; the oxidation time is 5-40min. However, the advancement effect of boron has a certain limit value. When the limit value is reached, it is difficult to further enhance it through temperature factors. At the same time, considering the energy consumption of product preparation, the oxidation temperature is 700-900°C; the oxidation time is 15-30min.

[0056] In some embodiments, the oxidizing atmosphere is saturated pure oxygen. It should be noted that this is to avoid introducing other impurity elements as much as possible, but it is difficult to ensure 100% pure oxygen in actual production, so the pure oxygen here refers to pure oxygen close to 100%, such as an atmosphere with an oxygen volume fraction of 99%, 98%, etc. It can be understood by those skilled in the art that adding an inert gas that does not react is also achievable, so the atmosphere needs to satisfy that the gas participating in the reaction is only oxygen as much as possible.

[0057] S4. Heavy doping is performed on the oxidized silicon wafer to form a selective emitter.

[0058] In some embodiments, the heavy doping method includes high temperature propulsion and laser propulsion; the temperature of high temperature propulsion is 900-1100°C, and the time of high temperature propulsion is 20-40min; the power of laser propulsion is 30-40W, and the time of laser propulsion is 5-10s.

[0059] Specifically, in this embodiment, a tubular diffusion furnace is used for high-temperature advancement at 1000°C for 30 minutes, or a 35W, 10s nanosecond doping laser is used for advancement to form a heavily doped area in the boron paste printing area, and finally a BSG layer of more than 100nm is formed on the front side of the silicon wafer.

[0060] In some embodiments, the sheet resistance of the heavily doped region formed by heavy doping is 40-80Ω / sq; the junction depth of the heavily doped region formed by heavy doping is 1-1.6 μm.

[0061] By subjecting the boron slurry to an oxidation reaction before heavy doping, the C and H elements in the boron slurry are reacted to generate CO2 and H2O and then removed, thus avoiding the problem of subsequent heavy doping pushing the C element into the silicon wafer and causing contamination and leakage.

[0062] Please refer to Figure 2 The present application also provides a method for preparing a solar cell sheet, the method comprising:

[0063] S0. Use N-type silicon wafers, use alkali solution with a volume concentration of 1% for texturing, and then use hydrogen peroxide and alkali to clean the silicon wafers.

[0064] S1. Lightly doping the textured silicon wafer to form a lightly doped pn junction;

[0065] In some embodiments, the silicon wafer after texturing is lightly doped to form a lightly doped pn junction, specifically including:

[0066] BCl3 is deposited on the surface of the silicon wafer after texturing to form a lightly doped pn junction.

[0067] Specifically, in this embodiment, a tubular boron diffusion furnace is used to directly deposit BCl3 at a high temperature of 800°C-900°C to form a lightly doped pn junction.

[0068] S2. Applying boron slurry on the surface of the lightly doped silicon wafer;

[0069] In some embodiments, the boron slurry includes boric acid, and the volume concentration of the boron slurry is 5%-9%. Preferably, the volume concentration of the boron slurry is 6%-8%. Furthermore, the volume concentration of the boron slurry is 7%.

[0070] S3. oxidizing the boron slurry on the surface of the silicon wafer to remove impurities in the boron slurry;

[0071] In order to reduce the steps and preparation time, the applicant cleverly combines oxidation and drying by chain oxygen. In some embodiments, the oxidation temperature is greater than 600°C; the oxidation time is less than 60min. The applicant found that when drying at a conventional temperature of about 200°C, only the water in the boron slurry can be removed, and the boron slurry will also volatilize to a certain extent at this time, and no waste of boron will occur due to advancement. When the temperature reaches above 600°C, the boron slurry will be advanced to a certain extent, thereby reducing the waste of boron. The control time is to completely eliminate the carbon-containing organic matter in the boron slurry. Most of the boron slurries can completely eliminate the carbon-containing organic matter within 60min; in order to further enhance the advancement effect of boron, preferably, the oxidation temperature is greater than 700°C; the oxidation time is 5-40min. However, the advancement effect of boron has a certain limit value. When the limit value is reached, it is difficult to further enhance it through temperature factors. At the same time, considering the energy consumption of product preparation, the oxidation temperature is 700-900°C; the oxidation time is 15-30min.

[0072] In some embodiments, the oxidation method is chain oxidation, and the oxidation atmosphere is saturated pure oxygen. It should be noted that this is to avoid introducing other impurity elements as much as possible, but it is difficult to ensure 100% pure oxygen in actual production, so the pure oxygen here refers to pure oxygen close to 100%, such as an atmosphere with an oxygen volume fraction of 99%, 98%, etc. It can be understood by those skilled in the art that adding an inert gas that does not react is also achievable, so the gas in the atmosphere that needs to participate in the reaction must be only oxygen as much as possible.

[0073] In some embodiments, oxidation can also be performed in a tubular annealing furnace. When oxidation is performed in a tubular annealing furnace, oxygen needs to be introduced into the tubular annealing furnace, and the volume flow rate of oxygen is about 1000 sccm, such as 800-1200 sccm. When oxidation is performed in a tubular annealing furnace, the boron slurry can be dried before oxidation, and the drying temperature is about 200°C, such as 150°C-250°C, and the drying time is about 30s, such as 20s-60s.

[0074] S4. Heavy doping is performed on the oxidized silicon wafer to form a selective emitter.

[0075] In some embodiments, the heavy doping method includes high temperature propulsion and laser propulsion; the temperature of high temperature propulsion is 900-1100° C., the time of high temperature propulsion is 20-40 minutes, the power of laser propulsion is 30-40W, and the time of laser propulsion is 5-10 seconds.

[0076] Specifically, in this embodiment, a tubular diffusion furnace is used for high-temperature advancement at 1000°C for 30 minutes, or a 35W, 10s nanosecond doping laser is used for advancement to form a heavily doped area in the boron paste printing area, and finally a BSG layer of more than 100nm is formed on the front side of the silicon wafer.

[0077] In some embodiments, the sheet resistance of the heavily doped region formed by heavy doping is 40-80Ω / sq; the junction depth of the heavily doped region formed by heavy doping is 1-1.6 μm.

[0078] S4. Alkali polishing of the silicon wafer forming the selective emitter;

[0079] Specifically, in this embodiment, a chain HF machine is used to remove the back boron expansion plated BSG, and then a slot alkaline polishing machine is used to remove the boron slurry on the back and edge pn junctions and the front lightly doped area.

[0080] S5. Preparation of polysilicon film on the back of the alkali-polished silicon wafer, followed by cleaning;

[0081] Specifically, in this embodiment, a tubular PECVD device is used to achieve thin film deposition on the back of the silicon wafer; then a tubular annealing furnace is used to use nitrogen (N2) or oxygen (O2) to transform the crystal structure of the deposited amorphous silicon thin film to form a polycrystalline silicon thin film poly-Si; then a chain HF machine is used to remove the oxide layer plated to the front side during deposition and the oxide layer generated during annealing, and then a tank alkali polishing machine is used to remove the front poly coating and the boron paste printed on the front side.

[0082] S6. Perform film preparation on the surface of the cleaned silicon wafer, and then perform electrode preparation to obtain a solar cell wafer.

[0083] The film preparation includes front film preparation and back film preparation. The front film preparation includes: front aluminum oxide film and silicon nitride film deposition. Specifically, aluminum oxide (AlO x ) film is used for passivation, PECVD deposited silicon nitride (SiN x ) film is used for anti-reflection; the preparation of the back film includes PECVD deposition of a back silicon nitride film, specifically, PECVD deposition of a SiNx film is used for back film hydrogen passivation.

[0084] The printing of the electrode preparation adopts screen printing of the front and back slurry. After the electrode preparation is completed, light injection, efficiency testing and sorting are carried out to obtain the solar cell sheet.

[0085] By adopting the above design, a selective emitter is formed by boron paste printing + high-temperature thermal oxidation, which can effectively reduce the contact resistance of the electrode contact area, improve the fill factor, and increase the battery efficiency. By oxidizing the boron paste before heavy doping, the C and H elements in the organic matter are removed, leaving only B, which effectively prevents the C element from being pushed into the silicon wafer during subsequent heavy doping to cause pollution and leakage. At the same time, the drying and oxidation steps are cleverly combined together without adding additional steps, saving process equipment and preparation time.

[0086] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0087] Example 1

[0088] A method for preparing a solar cell sheet, the method comprising:

[0089] (1) Texturing: N-type silicon wafers were used, and NaOH with a volume concentration of 1% was used for texturing, and hydrogen peroxide with a volume concentration of 30% and KOH with a volume concentration of 3% were used for cleaning the silicon wafers;

[0090] (2) Light doping: Using a tubular boron diffusion furnace, BCl3 is directly deposited at a high temperature of 800°C to form a lightly doped pn junction;

[0091] (3) Boron paste printing: Boron paste with a volume concentration of 7% is printed on the surface of the silicon wafer using a screen printer;

[0092] (4) Pre-oxidation: oxidation with chain oxygen at 700°C for 15 minutes;

[0093] (5) Heavy doping: A tubular diffusion furnace is used for high temperature advancement at 1000°C for 30 minutes to form a heavily doped area in the boron paste printing area and form a BSG layer of more than 100nm on the front side of the silicon wafer;

[0094] (6) Alkali polishing: Use a chain HF machine to remove the BSG on the back side, and then use a slot alkali polishing machine to remove the boron slurry on the back side and edge pn junction and the lightly doped area on the front side;

[0095] (7) Doped oxide layer and polysilicon passivation film on the back: thin film deposition is achieved on the back of the silicon wafer using tubular PECVD equipment;

[0096] (8) Annealing: Using a tubular annealing furnace, nitrogen (N2) is used to transform the crystal structure of the deposited amorphous silicon film to form a polycrystalline silicon film poly-Si;

[0097] (9) RCA cleaning: Use a chain HF machine to remove the oxide layer plated on the front side during deposition in step (8) and the oxide layer generated during annealing, and then use a tank alkali polishing machine to remove the front poly coating and the boron paste printed on the front side;

[0098] (10) Front aluminum oxide film and silicon nitride film deposition: Aluminum oxide (AlO x ) film is used for passivation, PECVD deposited silicon nitride (SiN x ) Films are used for anti-reflection;

[0099] (11) PECVD deposition of back silicon nitride film: PECVD deposition of SiN x Thin film, used for back film hydrogen passivation;

[0100] (12) Screen printing the front and back slurries to make electrodes;

[0101] (13) Light injection, test efficiency and sorting.

[0102] Example 2

[0103] A method for preparing a solar cell sheet, the method comprising:

[0104] (1) Texturing: N-type silicon wafers were used, and NaOH with a volume concentration of 1% was used for texturing, and hydrogen peroxide with a volume concentration of 30% and KOH with a volume concentration of 3% were used for cleaning the silicon wafers;

[0105] (2) Light doping: Using a tubular boron diffusion furnace, BCl3 is directly deposited at a high temperature of 800°C to form a lightly doped pn junction;

[0106] (3) Boron paste printing: Boron paste with a volume concentration of 7% is printed on the surface of the silicon wafer using a screen printer;

[0107] (4) Pre-oxidation: oxidation with chain oxygen at 800°C for 15 minutes;

[0108] (5) Heavy doping: A tubular diffusion furnace is used for high temperature advancement at 1000°C for 30 minutes to form a heavily doped area in the boron paste printing area and form a BSG layer of more than 100nm on the front side of the silicon wafer;

[0109] (6) Alkali polishing: Use a chain HF machine to remove the BSG on the back side, and then use a slot alkali polishing machine to remove the boron slurry on the back side and edge pn junction and the lightly doped area on the front side;

[0110] (7) Doped oxide layer and polysilicon passivation film on the back: thin film deposition is achieved on the back of the silicon wafer using tubular PECVD equipment;

[0111] (8) Annealing: Using a tubular annealing furnace, nitrogen (N2) is used to transform the crystal structure of the deposited amorphous silicon film to form a polycrystalline silicon film poly-Si;

[0112] (9) RCA cleaning: Use a chain HF machine to remove the oxide layer plated on the front side during deposition in step (8) and the oxide layer generated during annealing, and then use a tank alkali polishing machine to remove the front poly coating and the boron paste printed on the front side;

[0113] (10) Front aluminum oxide film and silicon nitride film deposition: Aluminum oxide (AlO x ) film is used for passivation, PECVD deposited silicon nitride (SiN x ) Films are used for anti-reflection;

[0114] (11) PECVD deposition of back silicon nitride film: PECVD deposition of SiN x Thin film, used for back film hydrogen passivation;

[0115] (12) Screen printing the front and back slurries to make electrodes;

[0116] (13) Light injection, test efficiency and sorting.

[0117] Example 3

[0118] A method for preparing a solar cell sheet, the method comprising:

[0119] (1) Texturing: N-type silicon wafers were used, and NaOH with a volume concentration of 1% was used for texturing, and hydrogen peroxide with a volume concentration of 30% and KOH with a volume concentration of 3% were used for cleaning the silicon wafers;

[0120] (2) Light doping: Using a tubular boron diffusion furnace, BCl3 is directly deposited at a high temperature of 800°C to form a lightly doped pn junction;

[0121] (3) Boron paste printing: Boron paste with a volume concentration of 7% is printed on the surface of the silicon wafer using a screen printer;

[0122] (4) Pre-oxidation: oxidation with chain oxygen at 700°C for 30 minutes;

[0123] (5) Heavy doping: A tubular diffusion furnace is used for high temperature advancement at 1000°C for 30 minutes to form a heavily doped area in the boron paste printing area and form a BSG layer of more than 100nm on the front side of the silicon wafer;

[0124] (6) Alkali polishing: Use a chain HF machine to remove the BSG on the back side, and then use a slot alkali polishing machine to remove the boron slurry on the back side and edge pn junction and the lightly doped area on the front side;

[0125] (7) Doped oxide layer and polysilicon passivation film on the back: thin film deposition is achieved on the back of the silicon wafer using tubular PECVD equipment;

[0126] (8) Annealing: Using a tubular annealing furnace, nitrogen (N2) is used to transform the crystal structure of the deposited amorphous silicon film to form a polycrystalline silicon film poly-Si;

[0127] (9) RCA cleaning: A chain HF machine is used to remove the oxide layer plated on the front side during deposition in step (8) and the oxide layer generated during annealing, and then a tank alkaline polishing machine is used to remove the poly coating on the front side and the boron paste printed on the front side;

[0128] (10) Front aluminum oxide film and silicon nitride film deposition: Aluminum oxide (AlO x ) film is used for passivation, PECVD deposited silicon nitride (SiN x ) Films are used for anti-reflection;

[0129] (11) PECVD deposition of back silicon nitride film: PECVD deposition of SiN x Thin film, used for back film hydrogen passivation;

[0130] (12) Screen printing the front and back slurries to make electrodes;

[0131] (13) Light injection, test efficiency and sorting.

[0132] Example 4

[0133] A method for preparing a solar cell sheet, the method comprising:

[0134] (1) Texturing: N-type silicon wafers were used, and NaOH with a volume concentration of 1% was used for texturing, and hydrogen peroxide with a volume concentration of 30% and KOH with a volume concentration of 3% were used for cleaning the silicon wafers;

[0135] (2) Light doping: Using a tubular boron diffusion furnace, BCl3 is directly deposited at a high temperature of 800°C to form a lightly doped pn junction;

[0136] (3) Boron paste printing: Boron paste with a volume concentration of 7% is printed on the surface of the silicon wafer using a screen printer;

[0137] (4) Pre-oxidation: Oxidation was performed by introducing 1000 sccm of oxygen at 700°C for 30 min in a tubular annealing furnace;

[0138] (5) Heavy doping: A tubular diffusion furnace is used for high temperature advancement at 1000°C for 30 minutes to form a heavily doped area in the boron paste printing area and form a BSG layer of more than 100nm on the front side of the silicon wafer;

[0139] (6) Alkali polishing: Use a chain HF machine to remove the BSG on the back side, and then use a slot alkali polishing machine to remove the boron slurry on the back side and edge pn junction and the lightly doped area on the front side;

[0140] (7) Doped oxide layer and polysilicon passivation film on the back: thin film deposition is achieved on the back of the silicon wafer using tubular PECVD equipment;

[0141] (8) Annealing: Using a tubular annealing furnace, nitrogen (N2) is used to transform the crystal structure of the deposited amorphous silicon film to form a polycrystalline silicon film poly-Si;

[0142] (9) RCA cleaning: A chain HF machine is used to remove the oxide layer plated on the front side during deposition in step (8) and the oxide layer generated during annealing, and then a tank alkaline polishing machine is used to remove the poly coating on the front side and the boron paste printed on the front side;

[0143] (10) Front aluminum oxide film and silicon nitride film deposition: Aluminum oxide (AlO x ) film is used for passivation, PECVD deposited silicon nitride (SiN x ) Films are used for anti-reflection;

[0144] (11) PECVD deposition of back silicon nitride film: PECVD deposition of SiN x Thin film, used for back film hydrogen passivation;

[0145] (12) Screen printing the front and back slurries to make electrodes;

[0146] (13) Light injection, test efficiency and sorting.

[0147] Example 5

[0148] A method for preparing a solar cell sheet, the method comprising:

[0149] (1) Texturing: N-type silicon wafers were used, and NaOH with a volume concentration of 1% was used for texturing, and hydrogen peroxide with a volume concentration of 30% and KOH with a volume concentration of 3% were used for cleaning the silicon wafers;

[0150] (2) Light doping: Using a tubular boron diffusion furnace, BCl3 is directly deposited at a high temperature of 800°C to form a lightly doped pn junction;

[0151] (3) Boron paste printing: Boron paste with a volume concentration of 7% is printed on the surface of the silicon wafer using a screen printer;

[0152] (4) Drying: Drying at 200°C for 30 seconds;

[0153] (5) Pre-oxidation: Oxidation was performed by introducing 1000 sccm of oxygen at 800°C for 30 min in a tubular annealing furnace;

[0154] (6) Heavy doping: A tubular diffusion furnace is used for high temperature advancement at 1000°C for 30 minutes to form a heavily doped area in the boron paste printing area and form a BSG layer of more than 100nm on the front side of the silicon wafer;

[0155] (7) Alkali polishing: Use a chain HF machine to remove the BSG on the back side, and then use a slot alkali polishing machine to remove the boron slurry on the back side and edge pn junction and the lightly doped area on the front side;

[0156] (8) Doped oxide layer and polysilicon passivation film on the back: thin film deposition is achieved on the back of the silicon wafer using tubular PECVD equipment;

[0157] (9) Annealing: Using a tubular annealing furnace, nitrogen (N2) is used to transform the crystal structure of the deposited amorphous silicon film to form a polycrystalline silicon film poly-Si;

[0158] (10) RCA cleaning: A chain HF machine is used to remove the oxide layer plated on the front side during the deposition in step (8) and the oxide layer generated during the annealing process, and then a tank alkaline polishing machine is used to remove the front poly plating layer and the boron paste printed on the front side;

[0159] (11) Front aluminum oxide film and silicon nitride film deposition: Aluminum oxide (AlO x ) film is used for passivation, PECVD deposited silicon nitride (SiN x ) Films are used for anti-reflection;

[0160] (12) PECVD deposition of back silicon nitride film: PECVD deposition of SiN x Thin film, used for back film hydrogen passivation;

[0161] (13) Screen printing the front and back slurries to make electrodes;

[0162] (14) Light injection, test efficiency and sorting.

[0163] Example 6

[0164] A method for preparing a solar cell sheet, the method comprising:

[0165] (1) Texturing: N-type silicon wafers were used, and NaOH with a volume concentration of 1% was used for texturing, and hydrogen peroxide with a volume concentration of 30% and KOH with a volume concentration of 3% were used for cleaning the silicon wafers;

[0166] (2) Light doping: Using a tubular boron diffusion furnace, BCl3 is directly deposited at a high temperature of 800°C to form a lightly doped pn junction;

[0167] (3) Boron paste printing: Boron paste with a volume concentration of 7% is printed on the surface of the silicon wafer using a screen printer;

[0168] (4) Pre-oxidation: oxidation with chain oxygen at 500°C for 30 minutes;

[0169] (5) Heavy doping: A tubular diffusion furnace is used for high temperature advancement at 1000°C for 30 minutes to form a heavily doped area in the boron paste printing area and form a BSG layer of more than 100nm on the front side of the silicon wafer;

[0170] (6) Alkali polishing: Use a chain HF machine to remove the BSG on the back side, and then use a slot alkali polishing machine to remove the boron slurry on the back side and edge pn junction and the lightly doped area on the front side;

[0171] (7) Doped oxide layer and polysilicon passivation film on the back: thin film deposition is achieved on the back of the silicon wafer using tubular PECVD equipment;

[0172] (8) Annealing: Using a tubular annealing furnace, nitrogen (N2) is used to transform the crystal structure of the deposited amorphous silicon film to form a polycrystalline silicon film poly-Si;

[0173] (9) RCA cleaning: A chain HF machine is used to remove the oxide layer plated on the front side during deposition in step (8) and the oxide layer generated during annealing, and then a tank alkaline polishing machine is used to remove the poly coating on the front side and the boron paste printed on the front side;

[0174] (10) Front aluminum oxide film and silicon nitride film deposition: Aluminum oxide (AlO x ) film is used for passivation, PECVD deposited silicon nitride (SiN x ) Films are used for anti-reflection;

[0175] (11) PECVD deposition of back silicon nitride film: PECVD deposition of SiN x Thin film, used for back film hydrogen passivation;

[0176] (12) Screen printing the front and back slurries to make electrodes;

[0177] (13) Light injection, testing efficiency and sorting.

[0178] Example 7

[0179] A method for preparing a solar cell sheet, the method comprising:

[0180] (1) Texturing: N-type silicon wafers were used, and NaOH with a volume concentration of 1% was used for texturing, and hydrogen peroxide with a volume concentration of 30% and KOH with a volume concentration of 3% were used for cleaning the silicon wafers;

[0181] (2) Light doping: Using a tubular boron diffusion furnace, BCl3 is directly deposited at a high temperature of 800°C to form a lightly doped pn junction;

[0182] (3) Boron paste printing: Boron paste with a volume concentration of 7% is printed on the surface of the silicon wafer using a screen printer;

[0183] (4) Pre-oxidation: Oxidation was performed by introducing 1000 sccm of oxygen at 500°C for 30 min in a tubular annealing furnace;

[0184] (5) Heavy doping: A tubular diffusion furnace is used for high temperature advancement at 1000°C for 30 minutes to form a heavily doped area in the boron paste printing area and form a BSG layer of more than 100nm on the front side of the silicon wafer;

[0185] (6) Alkali polishing: Use a chain HF machine to remove the BSG on the back side, and then use a slot alkali polishing machine to remove the boron slurry on the back side and edge pn junction and the lightly doped area on the front side;

[0186] (7) Doped oxide layer and polysilicon passivation film on the back: thin film deposition is achieved on the back of the silicon wafer using tubular PECVD equipment;

[0187] (8) Annealing: Using a tubular annealing furnace, nitrogen (N2) is used to transform the crystal structure of the deposited amorphous silicon film to form a polycrystalline silicon film poly-Si;

[0188] (9) RCA cleaning: A chain HF machine is used to remove the oxide layer plated on the front side during deposition in step (8) and the oxide layer generated during annealing, and then a tank alkaline polishing machine is used to remove the poly coating on the front side and the boron paste printed on the front side;

[0189] (10) Front aluminum oxide film and silicon nitride film deposition: Aluminum oxide (AlO x ) film is used for passivation, PECVD deposited silicon nitride (SiN x ) Films are used for anti-reflection;

[0190] (11) PECVD deposition of back silicon nitride film: PECVD deposition of SiN x Thin film, used for back film hydrogen passivation;

[0191] (12) Screen printing the front and back slurries to make electrodes;

[0192] (13) Light injection, testing efficiency and sorting.

[0193] Comparative Example 1

[0194] A method for preparing a solar cell sheet, the method comprising:

[0195] (1) Texturing: N-type silicon wafers were used, 1% alkaline solution NaOH was used for texturing, and 30% volume concentration of hydrogen peroxide and 3% volume concentration of alkaline solution KOH were used to clean the silicon wafers;

[0196] (2) Boron diffusion: using a tubular boron diffusion furnace, BCl3 is diffused at high temperature to form a lightly doped pn junction;

[0197] (3) Alkali polishing: Use a chain HF machine to remove the BSG with boron expansion on the back side, and then transfer it to a slot-type alkaline polishing machine through a robot to remove the pn junction on the back side and edge;

[0198] (4) Doped oxide layer and polysilicon passivation film on the back: thin film deposition is achieved on the back of the silicon wafer using tubular PECVD equipment;

[0199] (5) Annealing: Using a tubular annealing furnace, nitrogen (N2) is used to transform the crystal structure of the deposited amorphous silicon film to form a polycrystalline silicon film poly-Si;

[0200] (6) RCA cleaning: Use a chain HF machine to remove the oxide layer plated on the front side during deposition in step (4) and the oxide layer generated during annealing, and then use a tank alkaline polishing machine to remove the poly coating on the front side;

[0201] (7) Front aluminum oxide film and silicon nitride film deposition: Aluminum oxide (AlO x ) film 2 is used for passivation, PECVD deposited silicon nitride (SiN x ) Films are used for anti-reflection;

[0202] (8) PECVD deposition of back silicon nitride film: PECVD deposition of SiN x Thin film, used for back film hydrogen passivation;

[0203] (9) Screen printing the front and back slurries to make electrodes;

[0204] (10) Electrical injection, test efficiency and sorting.

[0205] The batteries provided in the examples and comparative examples were tested, and the process parameters and results of each example are shown in the following table:

[0206]

[0207]

[0208]

[0209] It can be seen from the above table that by adopting the method provided in the embodiment of the present application, the boron slurry is oxidized before heavy doping. Compared with the BSL process in the prior art, as shown in Comparative Example 1, the conversion efficiency can be improved by at least 0.08%. It can be seen from the comparison between Examples 1-5 and 6-7 that when the oxidation temperature is further controlled, the conversion efficiency can be further improved, and the open-voltage circuit is also positively affected to a certain extent, which is increased by about 0.002V relative to Examples 6-7. It can be seen from the comparison between Examples 1-3 and 4-5 that the conversion efficiency of the chain oxidation process is more significantly improved than that of the oxidation method using a tubular annealing furnace, which can be increased by at least 0.04% relative to Examples 4-5. At the same time, the open-circuit voltage is also further improved, which is increased by about 0.001V relative to Examples 4-5, and it also has a certain positive effect on the fill factor.

[0210] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a selective emitter, characterized in that: The method comprises: Lightly doping the textured silicon wafer to form a lightly doped pn junction; Applying boron slurry on the surface of the lightly doped silicon wafer; Oxidizing the boron slurry on the surface of the silicon wafer to remove C and H elements of organic matter in the boron slurry, the oxidation method is chain oxidation, the oxidation temperature is 700-900° C., the oxidation time is 15-30 minutes, and the oxidation atmosphere is saturated pure oxygen; The oxidized silicon wafer is heavily doped to form a selective emitter.

2. The method for preparing a selective emitter according to claim 1, characterized in that: The boron slurry comprises boric acid; and / or The volume concentration of the boron slurry is 5%-9%.

3. The method for preparing a selective emitter according to claim 2, characterized in that: The volume concentration of the boron slurry is 6%-8%.

4. The method for preparing a selective emitter according to claim 1, characterized in that: The texturing is carried out by using alkaline solution.

5. The method for preparing a selective emitter according to claim 4, characterized in that: The volume concentration of the alkali solution is 0.5% to 1.5%.

6. The method for preparing a selective emitter according to claim 1, characterized in that: The lightly doping the textured silicon wafer to form a lightly doped pn junction comprises: BCl3 is deposited on the surface of the silicon wafer after texturing to form a lightly doped pn junction.

7. The method for preparing a selective emitter according to claim 1, characterized in that: The heavy doping method includes high temperature propulsion or laser propulsion.

8. The method for preparing a selective emitter according to claim 7, characterized in that: The temperature of the high temperature advancement is 900-1100°C.

9. The method for preparing a selective emitter according to claim 7, characterized in that: The high temperature advancement time is 20-40 minutes.

10. The method for preparing a selective emitter according to claim 1, characterized in that: The sheet resistance of the heavily doped region formed by the heavy doping is 40-80Ω / sq; and / or The junction depth of the heavily doped region formed by the heavy doping is 1-1.6 μm.

11. A method for preparing a solar cell sheet, characterized in that: The method comprises: Forming a selective emitter on a silicon wafer using the method for preparing a selective emitter according to any one of claims 1 to 10; alkaline polishing the silicon wafer on which the selective emitter is formed; Preparing a polysilicon thin film on the back of the silicon wafer after alkali polishing, and then cleaning it; The cleaned silicon wafer surface is subjected to film preparation, and then electrode preparation is performed to obtain a solar cell wafer.

12. The method for preparing a solar cell sheet according to claim 11, characterized in that: The step of preparing a film on the cleaned surface of the silicon wafer comprises: Depositing an aluminum oxide film for passivation and a silicon nitride film for anti-reflection on the front side of the cleaned silicon wafer; A silicon nitride film for back film hydrogen passivation is deposited on the back side of the cleaned silicon wafer.

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