A high-efficiency solar PERC-SE cell and its frequency-division laser fabrication process

Abstract

This invention discloses a high-efficiency solar PERC-SE cell and its frequency-division laser fabrication process; comprising: S1, mixing alkaline solution and hydrogen peroxide to obtain a cleaning solution, and cleaning a silicon wafer in the cleaning solution; S2, texturing the cleaned silicon wafer in a texturing solution; S3, introducing nitrogen, oxygen, and phosphorus sources to diffuse the silicon wafer and prepare a phosphorus diffusion layer; S4, chemically etching to remove the P-N junction on the back side of the silicon wafer after diffusion; S5, depositing a silicon nitride antireflection film on the front side of the silicon wafer; S6, depositing an aluminum oxide passivation film on the back side of the silicon wafer; S7, using a laser to open the passivation film on the back side of the silicon wafer, printing electrode paste, and sintering to form ohmic contacts; after completing S1 to S7, the silicon wafer can be fabricated into a battery substrate to be laser-SE treated, the front side of the battery substrate including a fine grid line region and a MARK point region; S8, performing low-power laser SE treatment on the fine grid line region; S9, performing high-power laser SE treatment on the MARK point region; and fabricating a high-efficiency solar PERC-SE cell from the laser-SE treated battery substrate.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, specifically to a high-efficiency solar PERC-SE cell and its frequency-division laser fabrication process. Background Technology

[0002] SE-PERC (Selective Emitter) solar cells are currently the mainstream high-efficiency cells on the market. Their main characteristics are high phosphorus doping concentration in the metallization region and low phosphorus doping concentration in the illumination region. The metallization region has a deep diffusion junction, making it difficult for impurities such as metals to enter the depletion region and form deep energy levels during sintering. The illumination region has a low doping concentration, resulting in good short-wavelength response. The lateral diffusion of the high and low junctions has a significant front-field effect, which is beneficial for the collection of photogenerated carriers. This structure reduces the emitter contact resistance and emitter dark saturation current, improves the fill factor, short-circuit current, and open-circuit voltage, and significantly increases the cell's conversion efficiency.

[0003] Among the various SE (Self-Polymer) preparation methods, the laser-induced phosphorus silicate glass (PSG) doping method is low in cost and highly compatible with production lines, so it has been adopted by major solar cell manufacturers. The principle of the SE laser PSG doping method is as follows: After diffusion on a p-type silicon wafer, a phosphorus-rich PSG layer is formed on the surface of the silicon wafer. The SE laser emitter uses this phosphorus-rich PSG layer as a doping source and emits laser pulses at high frequency to melt the surface of the silicon wafer, causing phosphorus atoms in the PSG layer to be pushed to the surface of the silicon wafer. After the doped phosphorus atoms solidify, they will quickly replace the positions of silicon atoms, thereby achieving the purpose of diffusion and propagation of doped atoms.

[0004] In this process, in order to dope more "P" (i.e. phosphorus atoms) in the PSG layer into silicon, we tried to prepare solar cells under different laser power doping conditions. However, the adjustment of the overall power of the SE laser has a significant impact on the morphology of the mark points. Reducing the power affects the overall alignment and registration of the screen printing, and ensuring the alignment and registration of the screen printing will greatly limit the adjustment space of the fine grid area. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a high-efficiency solar PERC-SE cell and its frequency-division laser fabrication process. This invention has the advantages of low cost, strong compatibility and specificity, and large development potential.

[0006] This invention is achieved through the following technical solution:

[0007] A frequency-division laser fabrication process for high-efficiency PERC-SE solar cells, characterized by comprising the following steps:

[0008] S1. Silicon wafer cleaning: Alkali solution and hydrogen peroxide are mixed to obtain a cleaning solution. The silicon wafer is placed in the cleaning solution for cleaning to remove the damaged layer on the surface of the silicon wafer and reduce the recombination rate of photogenerated carriers.

[0009] S2. Alkali texturing: The cleaned silicon wafer is placed in a texturing solution for anisotropic alkaline texturing to form a pyramidal textured surface.

[0010] S3. Diffusion preparation of PN junction: Nitrogen, oxygen and phosphorus source are introduced to thermally diffuse the silicon wafer to prepare a phosphorus diffusion layer using the thermal diffusion process, and the sheet resistance of the diffusion layer is 40-80Ω.

[0011] S4. Chemical etching: A chemical etching solution is used to etch away the PN junction on the back of the diffused silicon wafer and remove the phosphosilicate glass to form a polished surface.

[0012] S5. Preparation of front antireflective film: A silicon nitride antireflective film with a refractive index of 1.1-1.8 is deposited on the front side of the silicon wafer using the PECVD process.

[0013] S6. Preparation of back passivation film: A layer of aluminum oxide passivation film is deposited on the back of the silicon wafer using a chemical vapor deposition process.

[0014] S7. Laser grooving: A laser is used to open the passivation film on the back of the silicon wafer, and then electrode paste is printed and sintered to form an ohmic contact. After completing the above S1 to S7 steps, the silicon wafer can be made into a solar cell substrate to be laser SE treatment, and the front side of the solar cell substrate includes: a fine grid line area and a MARK point area.

[0015] S8. Laser processing of fine grid line region: Perform low-power laser SE processing on the fine grid line region;

[0016] S9. Laser processing of the MARK point area: High-power laser SE processing is performed on the MARK point area; the laser SE-processed solar cell substrate is then used to make a high-efficiency solar PERC-SE cell.

[0017] Specifically, the frequency-division laser fabrication process for high-efficiency solar PERC-SE cells provided by this invention includes: (1) processing the MARK point region of the semi-finished silicon wafer (i.e., the cell substrate) after diffusion process using a high-power laser; (2) processing the fine grid line region of the semi-finished silicon wafer after diffusion process using a low-power laser; and (3) obtaining a selective emitter product with low surface concentration from the semi-finished silicon wafer processed in multiple steps. The method described in this invention optimizes the current SE laser doping process and has the characteristics of low cost, strong compatibility and specificity, and large development space. Without affecting the normal production of the production line, it does not increase equipment costs. It focuses on two aspects: ensuring the alignment of the screen camera and reducing the damage to the silicon wafer surface. It opens up the adjustable space of the sub-grid while further reducing the CT time of the process and improving the laser SE production capacity. By modifying the laser processing process, the damage of laser grooving is reduced, the passivation damage of the cell surface is further reduced, the defect density of the silicon wafer surface is optimized, a lower surface recombination rate is obtained, and the short-wavelength response is improved, thereby optimizing the electrical performance and improving the cell conversion efficiency.

[0018] Furthermore, a frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell includes: Step S1, silicon wafer cleaning: wherein the silicon wafer is a P-type monocrystalline or polycrystalline silicon wafer, and the thickness of the silicon wafer is 200-400μm and the resistivity is 0.5-10Ω·cm.

[0019] Furthermore, a frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell includes the following steps: Step S1, silicon wafer cleaning: Alkali solution and hydrogen peroxide are mixed to obtain a cleaning solution. The silicon wafer is placed in the cleaning solution at 55-65°C for 80-110 seconds to remove the damaged layer on the surface of the silicon wafer. The volume ratio of the alkali solution to the hydrogen peroxide is 1:(5-8). The alkali solution is a sodium hydroxide solution or potassium hydroxide solution with a concentration of 0.5-1.5wt%.

[0020] Furthermore, a frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell includes: Step S2, alkaline texturing: The cleaned silicon wafer is placed in a texturing agent for 60-120 seconds of anisotropic alkaline texturing to form a pyramidal textured surface structure; wherein: the texturing solution is prepared from inorganic alkali, anhydrous ethanol, texturing additives, and water; the inorganic alkali is sodium hydroxide or potassium hydroxide; the texturing additive is a monocrystalline silicon texturing additive.

[0021] Furthermore, a frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell includes: Step S2, alkaline texturing: The texturing solution comprises the following components by mass fraction: 1.5-3.5 wt% inorganic alkali, 5-10 wt% anhydrous ethanol, 0.5-1.5 wt% texturing additive, and the balance being water.

[0022] Furthermore, a frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell includes: Step S3, phosphorus diffusion: nitrogen, oxygen, and a phosphorus source are introduced, and the silicon wafer is thermally diffused in a diffusion furnace at 820-850°C to prepare a phosphorus diffusion layer, with a sheet resistance of 40-80Ω; wherein the phosphorus source used is phosphorus oxychloride, or the phosphorus source is a mixture of ammonium dihydrogen phosphate, isopropanol, and water.

[0023] Furthermore, a frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell includes: Step S4, chemical etching: using a chemical etching solution to etch and remove the PN junction on the back of the diffused silicon wafer, remove the phosphosilicate glass, and polish; wherein: the temperature of the chemical etching is 60-70℃, and the etching time is 100-150 seconds; the chemical etching solution is a mixed solution of hydrofluoric acid and nitric acid.

[0024] Furthermore, a frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell includes: Step S8, laser processing of the fine grid line region: performing 50% power laser SE processing on the fine grid line region; Step S9, laser processing of the MARK point region: performing 100% power laser SE processing on the MARK point region. Specifically, this includes: using a single SE laser line to perform laser SE processing on the fine grid line region. In the step of performing laser SE processing on the fine grid line region, the laser engraving speed is 25000-30000 mm / s, the laser on / off rate is in the range of 95-105%, and the laser frequency is in the range of 160-210 kHz.

[0025] Furthermore, a frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell is described: the laser spot used for laser SE treatment is square in shape, with a side length of 80-95μm and a laser power of 15-20W.

[0026] A high-efficiency solar PERC-SE cell is characterized by being manufactured using the above-mentioned process.

[0027] This invention features low cost, strong compatibility and specificity, and ample room for development. Without affecting normal production line operations or increasing equipment costs, it addresses two key aspects: ensuring screen camera alignment and reducing silicon wafer surface damage. It expands the adjustability of the sub-gate while further reducing the CT time and increasing laser SE throughput. By modifying the laser processing technology, it reduces damage from laser grooving, further minimizing passivation damage to the cell surface, optimizing the defect density of the silicon wafer surface, achieving a lower surface recombination rate, and improving short-wavelength response, thereby optimizing electrical performance and increasing cell conversion efficiency.

[0028] The beneficial effects of this invention are:

[0029] The improvements of the frequency-division laser fabrication process for high-efficiency solar PERC-SE cells provided by this invention are as follows: the laser process is changed from a one-step same-power processing to a two-step power-division processing, the power of the MARK point remains unchanged, the power of the fine grid region can be reduced independently, the alignment of the screen printing grippers is guaranteed, the doping damage of the sub-grid is reduced, and the overall CT time of the laser SE is reduced synchronously after the overall laser power is reduced. In the laser processing, in order to dope more "P" (i.e., phosphorus atoms) in the PSG layer into silicon, we tried to fabricate solar cells under different laser power doping conditions and compared their electrical performance. We found that when the laser power is within a certain range, the series resistance of the SE solar cell decreases with the increase of laser power; however, when the laser power reaches a threshold, the concentration of phosphorus atoms on the silicon wafer surface decreases with the increase of power, resulting in poor ohmic contact between the emitter and the metal electrode. At the same time, observation of the laser-doped silicon wafer surface under a scanning microscope also shows that lower laser power causes less damage to the textured tip, while stronger laser power destroys the entire textured structure. The method provided by this invention adjusts the laser power of the sub-gate to the optimal threshold, while the MARK point uses the lowest processing power while ensuring that the screen camera can recognize it.

[0030] The process of this invention is only applicable to the optimization of the laser processing steps of solar PERC-SE cells. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] A frequency-division laser fabrication process for high-efficiency PERC-SE solar cells includes the following specific steps:

[0034] S1. Silicon wafer cleaning: A 1.0 wt% potassium hydroxide solution and hydrogen peroxide are mixed at a volume ratio of 1:5 to obtain a cleaning solution. The silicon wafer is placed in the cleaning solution at 60°C for 90 seconds to remove the damaged layer on the surface of the silicon wafer. The silicon wafer is a P-type monocrystalline silicon wafer with a thickness of 220 μm and a resistivity of 0.5-10 Ω·cm.

[0035] S2. Alkaline texturing: The cleaned silicon wafer is placed in a texturing solution for 80 seconds of anisotropic alkaline texturing to form a pyramidal texturing structure; wherein: the texturing solution comprises the following components by mass fraction: sodium hydroxide 2.5wt%, anhydrous ethanol 8.0wt%, monocrystalline silicon texturing additive 1.2wt%, and the balance being water;

[0036] S3. Diffusion preparation of PN junction: Control the amount of nitrogen, oxygen, and phosphorus source, and perform thermal diffusion on the silicon wafer at 830°C in a diffusion furnace to prepare a phosphorus diffusion layer using the thermal diffusion process, and the sheet resistance of the diffusion layer is 40-80Ω; wherein: the phosphorus source used is phosphorus oxychloride.

[0037] S4. Chemical etching: Using a chemical etching solution (a mixture of hydrofluoric acid and nitric acid), the PN junction on the back of the diffused silicon wafer is removed at 60°C for 120 seconds, the phosphosilicate glass is removed, and a polished surface is formed.

[0038] S5. Preparation of front antireflection film: A silicon nitride antireflection film with a refractive index of 1.76 is deposited on the front side of the silicon wafer using the PECVD process.

[0039] S6. Preparation of back passivation film: A layer of aluminum oxide passivation film is deposited on the back of the silicon wafer using a chemical vapor deposition process.

[0040] S7. Laser grooving: A laser is used to open the passivation film on the back of the silicon wafer, then electrode paste is printed, and then sintered to form an ohmic contact; after completing the above S1 to S7 steps, the silicon wafer can be made into a solar cell substrate to be laser SE treatment, and the front side of the solar cell substrate includes: a fine grid line area and a MARK point area.

[0041] S8. Laser processing of the fine grid line region: The fine grid line region is subjected to 50% low-power laser SE processing;

[0042] S9. Laser processing of the MARK point area: The MARK point area is subjected to 100% high-power laser SE processing; the laser spot of the laser SE processing is square in shape, and the side length of the laser spot is 80-95μm, and the laser power is 15-20W; the solar cell substrate after laser SE processing is made into a high-efficiency solar PERC-SE cell.

[0043] Example 2

[0044] A frequency-division laser fabrication process for high-efficiency PERC-SE solar cells is described below:

[0045] S1. Silicon wafer cleaning: A 1.0 wt% sodium hydroxide solution and hydrogen peroxide are mixed at a volume ratio of 1:8 to obtain a cleaning solution. The silicon wafer is placed in the cleaning solution at 65°C for 105 seconds to remove the damaged layer on the surface of the silicon wafer. The silicon wafer is a P-type polycrystalline silicon wafer with a thickness of 380 μm and a resistivity of 0.5-10 Ω·cm.

[0046] S2. Alkaline texturing: The cleaned silicon wafer is placed in a texturing solution for 110 seconds of anisotropic alkaline texturing to form a pyramidal texturing structure; wherein: the texturing solution comprises the following components by mass fraction: 1.5 wt% potassium hydroxide, 9.0 wt% anhydrous ethanol, 1.5 wt% monocrystalline silicon texturing additive, and the balance being water.

[0047] S3. Diffusion preparation of PN junction: Control the amount of nitrogen, oxygen, and phosphorus source, and perform thermal diffusion on the silicon wafer at 850°C in a diffusion furnace to prepare a phosphorus diffusion layer using the thermal diffusion process, and the sheet resistance of the diffusion layer is 40-80Ω; wherein: the phosphorus source used is a mixture of ammonium dihydrogen phosphate, isopropanol and water.

[0048] S4. Chemical etching: Using a chemical etching solution (a mixture of hydrofluoric acid and nitric acid), the PN junction on the back of the diffused silicon wafer is removed at 70°C for 110 seconds, the phosphosilicate glass is removed, and a polished surface is formed.

[0049] S5. Preparation of front antireflection film: A silicon nitride antireflection film with a refractive index of 1.35 is deposited on the front side of the silicon wafer using the PECVD process.

[0050] S6. Preparation of back passivation film: A layer of aluminum oxide passivation film is deposited on the back of the silicon wafer using a chemical vapor deposition process.

[0051] S7. Laser grooving: A laser is used to open the passivation film on the back of the silicon wafer, then electrode paste is printed, and then sintered to form an ohmic contact; after completing the above S1 to S7 steps, the silicon wafer can be made into a solar cell substrate to be laser SE treatment, and the front side of the solar cell substrate includes: a fine grid line area and a MARK point area.

[0052] S8. Laser processing of the fine grid line region: The fine grid line region is subjected to 50% low-power laser SE processing;

[0053] S9. Laser processing of the MARK point area: The MARK point area is subjected to 100% high-power laser SE processing; the laser spot of the laser SE processing is square in shape, and the side length of the laser spot is 80-95μm, and the laser power is 15-20W; the solar cell substrate after laser SE processing is made into a high-efficiency solar PERC-SE cell.

[0054] The above-described preferred embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of the invention. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A frequency-division laser fabrication process for high-efficiency solar PERC-SE cells, characterized in that, The process includes the following steps: S1. Silicon wafer cleaning: Alkali solution and hydrogen peroxide are mixed to obtain a cleaning solution. The silicon wafer is placed in the cleaning solution for cleaning to remove the damaged layer on the surface of the silicon wafer. S2. Alkali texturing: The cleaned silicon wafer is placed in a texturing solution for anisotropic alkaline texturing to form a pyramidal textured surface. S3. Diffusion preparation of PN junction: Nitrogen, oxygen and phosphorus source are introduced to thermally diffuse the silicon wafer to prepare a phosphorus diffusion layer using the thermal diffusion process, and the sheet resistance of the diffusion layer is 40 to 80 Ω. S4. Chemical etching: A chemical etching solution is used to etch away the PN junction on the back of the diffused silicon wafer and remove the phosphosilicate glass to form a polished surface. S5. Preparation of front antireflective film: Deposit a silicon nitride antireflective film with a refractive index of 1.1 to 1.8 on the front side of the silicon wafer; S6. Preparation of back passivation film: Deposit an aluminum oxide passivation film on the back of the silicon wafer; S7. Laser grooving: A laser is used to open the passivation film on the back of the silicon wafer, and then electrode paste is printed and sintered to form an ohmic contact. After completing the above S1 to S7 steps, the silicon wafer can be made into a solar cell substrate to be laser SE treatment, and the front side of the solar cell substrate includes: a fine grid line area and a MARK point area. S8. Laser processing of fine grid line region: Perform low-power laser SE processing on the fine grid line region; S9. Laser processing of the MARK point area: High-power laser SE processing is performed on the MARK point area; the laser SE-processed solar cell substrate is then used to fabricate a high-efficiency solar PERC-SE cell. In step S8, the fine grid line region is subjected to 50% power laser SE processing; in step S9, the MARK point region is subjected to 100% power laser SE processing.

2. The frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell according to claim 1, characterized in that, Step S1, silicon wafer cleaning: The silicon wafer is a P-type monocrystalline or polycrystalline silicon wafer, and the thickness of the silicon wafer is 200-400μm and the resistivity is 0.5-10Ω·cm.

3. The frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell according to claim 1, characterized in that, Step S1, silicon wafer cleaning: Mix alkaline solution and hydrogen peroxide to obtain a cleaning solution, and place the silicon wafer in the cleaning solution at 55-65°C for 80-110 seconds to remove the damaged layer on the surface of the silicon wafer; wherein: the volume ratio of the alkaline solution to the hydrogen peroxide is 1:(5-8); the alkaline solution is a sodium hydroxide solution or potassium hydroxide solution with a concentration of 0.5-1.5wt%.

4. The frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell according to claim 1, characterized in that, Step S2, Alkali texturing: The cleaned silicon wafer is placed in a texturing agent for 60-120 seconds for anisotropic alkali texturing to form a pyramidal texturing structure; wherein: the texturing solution is prepared from inorganic alkali, anhydrous ethanol, texturing additive and water; the inorganic alkali is sodium hydroxide or potassium hydroxide; the texturing additive is a monocrystalline silicon texturing additive.

5. The frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell according to claim 4, characterized in that, Step S2, Alkali Texturing: The texturing solution comprises the following components by mass fraction: 1.5-3.5 wt% inorganic alkali, 5-10 wt% anhydrous ethanol, 0.5-1.5 wt% texturing additive, and the balance being water.

6. The frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell according to claim 1, characterized in that, Step S3, Phosphorus diffusion: Nitrogen, oxygen, and phosphorus source are introduced, and the silicon wafer is thermally diffused in a diffusion furnace at 820-850°C to prepare a phosphorus diffusion layer, and the sheet resistance of the diffusion layer is 40-80Ω; wherein the phosphorus source used is phosphorus oxychloride, or the phosphorus source is a mixture of ammonium dihydrogen phosphate, isopropanol and water.

7. The frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell according to claim 1, characterized in that, Step S4, Chemical Etching: Using a chemical etching solution, the PN junction on the back side of the diffused silicon wafer is etched away, the phosphosilicate glass is removed, and the wafer is polished; wherein: the temperature of the chemical etching is 60-70℃, and the etching time is 100-150 seconds; the chemical etching solution is a mixed solution of hydrofluoric acid and nitric acid.

8. The frequency-division laser fabrication process for a high-efficiency solar PERC-SE cell according to claim 1, characterized in that, The laser spot in the laser SE treatment is square in shape, with a side length of 80–95 μm and a laser power of 15–20 W.

9. A high-efficiency solar PERC-SE cell, characterized in that, It is prepared by the process described in any one of claims 1 to 8.