Preparation equipment and preparation method of tunneling oxidation passivation contact structure of solar cell

Abstract

The invention belongs to the technical field of solar cells, and particularly relates to preparation equipment and a preparation method of a tunneling oxidation passivation contact structure of a solar cell. The preparation equipment of the tunneling oxidation passivation contact structure of the solar cell comprises a base, wherein a first conveying belt, a silicon wafer dipping assembly and a second conveying belt are arranged on the base from left to right; the first conveying belt is used for conveying the silicon wafers into the silicon wafer dipping device; the second conveying belt is used for conveying the impregnated silicon wafers; the silicon wafer dipping assembly comprises a nitric acid pool, the nitric acid pool is a cuboid with an open top surface, and a plurality of rollers are rotatably connected in the nitric acid pool; the rotating speeds of the rollers are the same, and when each roller rotates, the silicon wafer moves in the horizontal direction. The equipment provided by the invention is simple in structure, low in equipment cost, simple to operate in the use process, and capable of efficiently preparing the high-quality tunneling oxidation passivation contact structure.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cells, and in particular relates to a preparation device and a preparation method of a tunneling oxidation passivation contact structure of a solar cell. Background Art

[0002] The over-exploitation and utilization of non-renewable energy such as oil, coal, and natural gas not only makes it difficult to meet human needs, but also destroys the environment on which humans depend for survival. Therefore, new clean energy such as wind energy, solar energy, and geothermal energy have received widespread attention from the society. Among them, solar energy has been favored by social energy development due to its small limiting factors and wide sources. Solar cells are a type of photoelectric semiconductor wafer that directly generates electricity using sunlight. They have the advantages of simple energy conversion process, simple operation, simple battery structure, and green environmental protection. However, the performance and stability of solar cells need to be further improved.

[0003] In the fields of materials science, semiconductor technology and surface engineering, the interaction between interfaces has a crucial impact on the performance of materials, especially in the preparation of semiconductor devices such as solar cells. The interface properties between semiconductor materials and dielectric materials directly affect the performance and stability of the device. The tunneling oxide passivation contact (TOPCon) structure based on the "selective barrier effect" (i.e. selectively blocking one carrier while effectively transmitting another carrier) is an effective method to provide a passivation contact to improve the performance of the device.

[0004] In the prior art, physical vapor deposition, chemical vapor deposition and thermal oxidation methods are often used to prepare tunneling oxidation passivation contact structures. Among them, the thermal oxidation method needs to be carried out at high temperature, and the controllability of the high-temperature furnace tube reaction is poor, and it is difficult to accurately control the thickness and uniformity of the SiOx layer. The use of this method increases the complexity and cost of the preparation equipment, and may also cause thermal damage to the Si substrate, which may affect the interface passivation performance. Although methods such as physical vapor deposition and chemical vapor deposition can accurately control the thickness and uniformity of the SiOx layer, their equipment cost is high and the process is complicated.

[0005] Therefore, how to economically and efficiently prepare high-quality tunneling oxide passivation contact structures for solar cells is an important challenge facing current technology. Summary of the invention

[0006] Based on this, the purpose of the present invention is to provide a preparation device and a preparation method for a tunneling oxidation passivation contact structure of a solar cell, so as to solve the problems of high equipment cost and poor passivation performance of solar cells in the preparation process of the tunneling oxidation passivation contact structure of solar cells in the prior art.

[0007] To achieve the above object, the present invention adopts the following technical solution.

[0008] The present invention provides a preparation device for a tunnel oxidation passivation contact structure of a solar cell, comprising: a base, on which a first conveyor belt, a silicon wafer dipping assembly and a second conveyor belt are arranged from left to right;

[0009] The first conveyor belt is used to transport the silicon wafer to the silicon wafer dipping device;

[0010] The second conveyor belt is used to transport the silicon wafers after impregnation;

[0011] The silicon wafer dipping assembly comprises: a nitric acid tank, which is a rectangular parallelepiped with an open top surface, and a plurality of rollers are rotatably connected in the nitric acid tank; each of the rollers rotates at the same speed, and when each of the rollers rotates, the silicon wafer moves in a horizontal direction;

[0012] The driving assembly is used to drive the plurality of rollers to move.

[0013] In some embodiments of the present invention, the nitric acid pool has a length of 2.5 to 2.9 m, a width of 1.0 to 1.5 m, and a height of 8 to 12 cm; the roller has a diameter of 4.0 cm to 4.5 cm, and a length of 95 cm to 145 cm.

[0014] In some embodiments of the present invention, the roller passes through the inner wall of the nitric acid pool and is rotatably connected to the nitric acid pool; a cylindrical gear is fixedly connected to one end of the roller passing through the nitric acid pool, and a first bevel gear is also fixedly connected to the outside of the cylindrical gear;

[0015] The driving assembly comprises: a rotating shaft, which is rotatably connected to the side wall of the nitric acid tank; a second bevel gear and a first sprocket are fixedly connected to the rotating shaft, and the second bevel gear is meshed with the first bevel gear;

[0016] The rotary motor comprises a fixed end and an output end; the fixed end is connected to the base, the output end is fixedly connected with a second sprocket, and the first sprocket and the second sprocket are connected through a chain transmission.

[0017] In some embodiments of the present invention, the distance between the first conveyor belt and the second conveyor belt and the nitric acid pool is less than 1 / 3 of the length of the battery cell.

[0018] The present invention also provides a method for preparing a tunneling oxidation passivation contact structure of a solar cell, comprising: placing a silicon wafer on the preparation equipment for the tunneling oxidation passivation contact structure of a solar cell, contacting the back side of the silicon wafer with the preparation equipment for the tunneling oxidation passivation contact structure of a solar cell, immersing the silicon wafer in the nitric acid solution, and forming a tunneling oxidation passivation contact structure on the back side of the silicon wafer after the immersion is completed;

[0019] The concentration of the nitric acid solution is 8 moL / L to 9 moL / L; the immersion temperature is 20° C. to 25° C.; and the immersion time is 5 min to 10 min.

[0020] In some embodiments of the present invention, the silicon wafer is placed on the preparation equipment of the tunneling oxidation passivation contact structure of the solar cell after being pretreated;

[0021] The pre-processing comprises:

[0022] S1, cleaning and texturing the silicon wafer;

[0023] S2, after the texturing is completed, a front emitter is prepared on the front side of the silicon wafer;

[0024] S3, after the emitter is prepared, alkaline polishing is performed on the back side of the silicon wafer.

[0025] In some embodiments of the present invention, in S1, the texturing conditions are: using a mixed solution of a NaOH solution with a volume fraction of 1% to 3% and an isopropanol solution with a volume fraction of 5% to 7%, the process is carried out at 75°C, and the corrosion depth is 3μm to 6μm; the volume ratio of the NaOH solution to the isopropanol solution is 3 to 4:1.

[0026] In some embodiments of the present invention, in S2, after the texturing is completed, the silicon wafer is placed in the tube furnace for boron diffusion to form p + Emitter.

[0027] In some embodiments of the present invention, in S3, a hydrofluoric acid solution with a volume fraction of 4% to 5% is used to remove the residual BSG layer, and a mixed solution of hydrofluoric acid with a volume fraction of 45% to 55% and nitric acid with a volume fraction of 60% to 65% is used to etch the edge of the silicon wafer, and then a mixed solution of hydrofluoric acid and nitric acid is used to polish the back of the silicon wafer; the volume ratio of hydrofluoric acid with a volume fraction of 45% to 55% and nitric acid with a volume fraction of 60% to 65% in the mixed solution is 1:2 to 3;

[0028] The back side polishing conditions are: polishing time 300s-400s, polishing temperature 65°C-75°C.

[0029] The present invention also provides a solar cell, comprising a tunneling oxidation passivation contact structure prepared by the method.

[0030] In some embodiments of the present invention, the thickness of the tunneling oxide passivation contact structure is 1.45 nm to 1.55 nm.

[0031] Based on the technical solution of the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) Compared with the equipment used in physical vapor deposition and chemical vapor deposition methods, the equipment for preparing the tunneling oxidation passivation contact structure of a solar cell provided by the present invention is simple to operate and has low equipment cost. Moreover, when used for preparing the tunneling oxidation passivation contact structure of a solar cell, it can be carried out at room temperature, thus avoiding the problem of poor controllability of high-temperature furnace tube reaction when the thermal oxidation method is carried out at high temperature. Therefore, it can be conveniently and quickly used for preparing the tunneling oxidation passivation contact structure of a solar cell.

[0033] (2) The method for preparing the tunneling oxidation passivation contact structure of a solar cell provided by the present invention can be carried out at room temperature, and the concentration and immersion time of the HNO3 solution can be precisely controlled. The tunneling oxidation passivation contact structure (SiOx layer) can be efficiently prepared, and the thickness and uniformity of the SiOx layer can be ensured, thereby improving the interface passivation performance and thus improving the performance of the solar cell.

[0034] (3) In the present invention, a wet chemical nitric acid oxidation method is used instead of a thermal oxidation method: compared with the commonly used thermal oxidation method for generating a tunneling oxide passivation layer, the method provided by the present invention can produce a tunneling oxide passivation contact with higher quality in a short time, and has higher economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a top view of the equipment for preparing the tunneling oxidation passivation contact structure for a solar cell provided in Example 1.

[0036] Figure 2 This is a front view of the equipment for preparing the tunneling oxidation passivation contact structure of a solar cell provided in Example 1.

[0037] Figure 3 This is the main process flow chart of TOPCon battery.

[0038] Figure 4 This is a schematic diagram of the TOPCon battery structure.

[0039] Reference numerals:

[0040] 1-base, 2-first conveyor belt, 3-second conveyor belt, 4-nitric acid tank, 5-roller, 6-cylindrical gear, 7-first bevel gear, 8-rotating shaft, 9-second bevel gear, 10-rotating motor, 11-chain. DETAILED DESCRIPTION

[0041] The experimental methods in the following examples of the present invention without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturers.

[0042] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0043] The terms "including" and "having" and any variations thereof of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, device, product or equipment comprising a series of steps is not limited to the listed steps or modules, but may optionally include steps not listed, or may optionally include other steps inherent to these processes, methods, products or equipment.

[0044] In the present invention, the term "multiple" refers to two or more than two. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0045] The following describes the invention in conjunction with specific embodiments.

[0046] Example 1: A preparation device for a solar cell tunneling oxidation passivation contact structure

[0047] A preparation device for a solar cell tunneling oxidation passivation contact structure, such as Figure 1 and Figure 2 As shown, it comprises: a base 1, on which a first conveyor belt 2, a silicon wafer dipping assembly and a second conveyor belt 3 are arranged from left to right;

[0048] A first conveyor belt 2, used for transporting silicon wafers to a silicon wafer dipping device;

[0049] The second conveyor belt 3 is used to transport the silicon wafers after impregnation;

[0050] The silicon wafer dipping assembly includes: a nitric acid tank 4 for storing nitric acid that reacts with the silicon wafer; the nitric acid tank 4 is in the shape of a rectangular parallelepiped with an open top, and the long side of the rectangular parallelepiped is higher than the wide side of the nitric acid tank 4; a plurality of rollers 5 are also rotatably connected in the nitric acid tank 4; each roller 5 rotates at the same speed, and when each roller 5 rotates, the battery cell moves in a horizontal direction; to ensure that the back side of the silicon wafer can be completely exposed to the nitric acid, the nitric acid liquid level in the nitric acid tank 4 is 5 mm higher than the highest point of the roller 5.

[0051] Furthermore, the nitric acid pool 4 has a length of 2.5 to 2.9 m, a width of 1.0 to 1.5 m, and a height of 8 to 12 cm; the roller 5 has a diameter of 4.0 cm to 4.5 cm, and a length of 95 cm to 145 cm.

[0052] Specifically, in the present invention, the nitric acid pool 4 is 2.9 m long, 1.3 m wide and 10 cm high; the roller 5 is made of polyvinylidene fluoride (PVDF) or tetrafluoroethylene (PTFE), and the roller 5 has a diameter of 4.5 cm and a length of 110 cm.

[0053] Further, the roller 5 passes through the inner wall of the nitric acid pool 4 and is rotatably connected to the nitric acid pool 4; a cylindrical gear 6 is fixedly connected to one end of the roller 5 passing through the nitric acid pool 4, and a first bevel gear 7 is also fixedly connected to the outside of the cylindrical gear 6; further, the length of the roller 5 is parallel to the wide side of the nitric acid pool 4;

[0054] The driving assembly includes: a rotating shaft 8, which is rotatably connected to the side wall of the nitric acid tank 4; a second bevel gear 9 and a first sprocket are also fixedly connected to the rotating shaft 8, and the second bevel gear 9 is meshed with the first bevel gear 7; specifically, the rotating shaft 8 is rotatably connected to the outer side wall of the nitric acid tank 4, and the length of the rotating shaft 8 is parallel to the long side of the nitric acid tank 4;

[0055] The rotating motor 10 includes a fixed end and an output end; the fixed end is connected to the base 1 , and a second sprocket is fixedly connected to the output end. The first sprocket and the second sprocket are connected through a chain 11 .

[0056] Furthermore, in order to avoid jamming between the conveyor belt and the nitric acid pool 4 during the silicon wafer conveying process, the distance between the first conveyor belt 2 and the second conveyor belt 3 and the nitric acid pool 4 is less than 1 / 3 of the length of the battery cell.

[0057] The equipment for preparing the tunneling oxidation passivation contact structure of a solar cell provided by the present invention has a simple structure and low equipment cost. When in use, the cleaned silicon wafer is placed on the first conveyor belt 2, and the first conveyor belt 2 can convey the silicon wafer to the nitric acid pool 4. By adjusting the rotation speed of the roller 5 in the nitric acid pool 4, the time for the silicon wafer to stay in the nitric acid pool 4 can be controlled, so that the tunneling oxidation passivation contact structure is prepared on the back of the silicon wafer. After the preparation is completed, the silicon wafer with the prepared tunneling oxidation contact is transported out of the nitric acid pool 4 through the second conveyor belt 3, which is convenient for the next step. The equipment is simple to operate, can be used at room temperature for the preparation of the tunneling oxidation passivation contact structure of the solar cell, and can be used for the preparation of the tunneling oxidation passivation contact structure of the solar cell conveniently and quickly.

[0058] Example 2: A method for preparing a tunneling oxidation passivation contact structure for a solar cell

[0059] A method for preparing a tunneling oxidation passivation contact structure for a solar cell, the specific preparation method is as follows:

[0060] Step 1: Prepare silicon wafers. Select N-type single crystal silicon wafers with a thickness of 180 μm and a resistivity of 1 Ω·cm to 10 Ω·cm. Cut the silicon wafers into appropriate sizes, clean them, and texture them for later use.

[0061] Texturing conditions: Use a mixed solution of 2% by volume NaOH solution and 6% by volume IPA (IPA) solution (the volume ratio of NaOH solution to IPA solution is 4:1), the process temperature is 75°C, and the general corrosion depth is 3μm.

[0062] Step 2: Preparation of the front emitter. Put the textured silicon wafer into a high-temperature tube furnace for boron diffusion to form p + The emitter is then locally heavily doped on its front surface using a nanosecond pulse laser, causing boron ions to quickly advance from the borosilicate glass layer (BSG) to the p+ emitter region, forming a p ++ Selective emitter.

[0063] Boron diffusion source: BCl3; diffusion temperature: 980℃; diffusion resistance: 300Ω / SP; borosilicate glass layer surface concentration 4×10 18 cm -3 ; Nanosecond pulse laser conditions: nanosecond pulse laser with a wavelength of 532nm and a pulse energy of 80μJ~300μJ.

[0064] Step 3: Back alkaline polishing: Use a diluted 5% hydrofluoric acid solution to remove the remaining BSG layer, and use a mixed solution of hydrofluoric acid and nitric acid (50% hydrofluoric acid by volume: 63% nitric acid by volume = 1:3) to etch the edge of the silicon wafer and polish the back side.

[0065] Back polishing conditions: polishing time 320s, polishing temperature 70℃.

[0066] Step 4: Dipping the silicon wafer. Use the first conveyor belt 2 to transport the cleaned silicon wafer to Figure 1 In the device shown, the silicon wafer is slowly advanced by roller 5, and its back side is immersed in HNO3 solution with a concentration of 9 mol / L during the advancement process. The temperature of HNO3 solution is controlled at 25°C, and the conveying speed of roller 5 is set to 0.5 m / min, so that the immersion time of the silicon wafer in HNO3 solution with a concentration of 9 mol / L is 5 minutes. An ultra-thin nano-layer SiOx is generated on the back side of the silicon wafer by nitric acid oxidation method, i.e., tunneling oxidation passivation contact structure, and then the thickness of the ultra-thin nano-layer SiOx is measured and recorded.

[0067] Step 5: Phosphorus diffusion. Poly-Si(n) is formed on the back. + ). Phosphorus ion implantation is performed on the back of the silicon wafer with the ultra-thin nano-layer SiOx to form n + Back surface field.

[0068] Phosphorus diffusion conditions: POCl3 was used as the diffusion source at 800°C to form a junction depth of 0.2 μm, a sheet resistance of 37 Ω / SP, and a surface concentration of 7×10 20 cm -3 n + Back surface field.

[0069] Step 6: Prepare the passivation film and anti-reflection film. On the back of the annealed silicon wafer, a 4nm thick Al2O3 layer is prepared by atomic layer deposition (ALD) to form a passivation film on the back of the silicon wafer. A SiNx:H anti-reflection film with a fixed thickness of 75nm is deposited on both sides of the silicon wafer using PECVD equipment.

[0070] Step 7: Metallization: Prepare the front Ag / Al and back Ag electrode grid lines by screen printing metallization method, and co-sinter in an infrared belt sintering furnace to form a good ohmic contact between the metal semiconductor.

[0071] The thickness of the ultra-thin nano-layer SiOx prepared in step 4 of the above method was measured to be 1.5 nm, and the ultra-thin nano-layer SiOx prepared had good uniformity and compactness.

[0072] Example 3: A method for preparing a tunneling oxidation passivation contact structure for a solar cell

[0073] A method for preparing a solar cell tunneling oxidation passivation contact structure (process flow chart as shown in Figure 3 The specific preparation method is as follows:

[0074] Step 1: Prepare silicon wafers. Select N-type single crystal silicon wafers with a thickness of 180 μm and a resistivity of 1 Ω·cm to 10 Ω·cm. Cut the silicon wafers into appropriate sizes, clean them, and texture them for later use.

[0075] Texturing conditions: Use a mixed solution of 2% by volume NaOH solution and 6% by volume IPA solution, the process temperature is 75°C, and the general corrosion depth is 3μm.

[0076] Step 2: Preparation of the front emitter. Put the textured silicon wafer into a high-temperature tube furnace for boron diffusion to form p + The emitter is then locally heavily doped on its front surface using a nanosecond pulse laser, which rapidly pushes boron ions from the borosilicate glass layer (BSG) to the p + The emission region forms p ++ Selective emitter.

[0077] Boron diffusion source: BCl3; diffusion temperature: 980℃; diffusion resistance: 300Ω / SP; borosilicate glass layer surface concentration 4×10 18 cm-3 ; Nanosecond pulse laser conditions: nanosecond pulse laser with a wavelength of 532nm and a pulse energy of 80 to 300μJ.

[0078] Step 3: Back alkaline polishing: Use a diluted 5% hydrofluoric acid solution to remove the remaining BSG layer, and use a mixed solution of hydrofluoric acid and nitric acid (50% hydrofluoric acid by volume: 63% nitric acid by volume = 1:3) to etch the edge of the silicon wafer and polish the back side.

[0079] Back polishing conditions: polishing time 320s, polishing temperature 70℃.

[0080] Step 4: Dipping the silicon wafer. Use the first conveyor belt 2 to transport the cleaned silicon wafer to Figure 1 In the device shown, the silicon wafer is slowly advanced by roller 5, and its back side is immersed in HNO3 solution with a concentration of 9 mol / L during the advancement process. The temperature of HNO3 solution is controlled at 25°C, and the conveying speed of roller 5 is set to 0.36 m / min, so that the immersion time of the silicon wafer in HNO3 solution with a concentration of 9 mol / L is 7 minutes. An ultra-thin nano-layer SiOx is generated on the back side of the silicon wafer by nitric acid oxidation method, and then the thickness of the ultra-thin nano-layer SiOx is measured and recorded.

[0081] Step 5: Phosphorus diffusion. Poly-Si(n) is formed on the back. + ). Phosphorus ion implantation is performed on the back of the silicon wafer with the ultra-thin nano-layer SiOx to form n + Back surface field.

[0082] Phosphorus diffusion conditions: POCl3 was used as the diffusion source at 800°C to form a junction depth of 0.2 μm, a sheet resistance of 37 Ω / SP, and a surface concentration of 7×10 20 cm -3 n + Back surface field.

[0083] Step 6: Prepare the passivation film and anti-reflection film. On the back of the annealed silicon wafer, a 4nm thick Al2O3 layer is prepared by atomic layer deposition (ALD) to form a passivation film on the back of the silicon wafer. A SiNx:H anti-reflection film with a fixed thickness of 75nm is deposited on both sides of the silicon wafer using PECVD equipment.

[0084] Step 7: Metallization. Prepare the front Ag / Al and back Ag electrode grid lines by screen printing metallization method, and co-sinter in an infrared belt sintering furnace to form a good ohmic contact between the metal semiconductor. The battery structure prepared in the present invention is as follows Figure 4 shown.

[0085] The thickness of the ultra-thin nano-layer SiOx prepared in step 4 of the method provided in this embodiment is measured to be about 1.53 nm, and the ultra-thin nano-layer SiOx prepared has good uniformity and density.

[0086] Example 4: A method for preparing a tunneling oxidation passivation contact structure for a solar cell

[0087] A method for preparing a tunneling oxidation passivation contact structure for a solar cell, the specific preparation method is as follows:

[0088] Step 1: Prepare silicon wafers. Select N-type single crystal silicon wafers with a thickness of 180 μm and a resistivity of 1 Ω·cm to 10 Ω·cm. Cut the silicon wafers into appropriate sizes, clean them, and texture them for later use.

[0089] Texturing conditions: Use a mixed solution of 2% by volume NaOH solution and 6% by volume IPA solution, the process temperature is 75°C, and the general corrosion depth is 4μm.

[0090] Step 2: Preparation of the front emitter. Put the textured silicon wafer into a high-temperature tube furnace for boron diffusion to form p + The emitter is then locally heavily doped on its front surface using a nanosecond pulse laser, which rapidly pushes boron ions from the borosilicate glass layer (BSG) to the p + The emission region forms p ++ Selective emitter.

[0091] Boron diffusion source: BCl3; diffusion temperature: 980℃; diffusion resistance: 300Ω / SP; borosilicate glass layer surface concentration 4×10 18 cm -3 ; Nanosecond pulse laser conditions: nanosecond pulse laser with a wavelength of 532nm and a pulse energy of 80μJ~300μJ.

[0092] Step 3: Back alkaline polishing: Use a diluted 5% hydrofluoric acid solution to remove the remaining BSG layer, and use a mixed solution of hydrofluoric acid and nitric acid (50% hydrofluoric acid by volume: 63% nitric acid by volume = 1:3) to etch the edge of the silicon wafer and polish the back side.

[0093] Back polishing conditions: polishing time 320s, polishing temperature 70℃.

[0094] Step 4: Dipping the silicon wafer. Use the first conveyor belt 2 to transport the cleaned silicon wafer to Figure 1In the device shown, the silicon wafer is slowly advanced by roller 5, and its back side is immersed in HNO3 solution with a concentration of 8 mol / L during the advancement process. The temperature of HNO3 solution is controlled at 22°C, and the conveying speed of roller 5 is set to 0.25 m / min, so that the immersion time of the silicon wafer in HNO3 solution with a concentration of 8 mol / L is 10 minutes. An ultra-thin nano-layer SiOx is generated on the back side of the silicon wafer by nitric acid oxidation method, i.e., tunneling oxidation passivation contact structure, and then the thickness of the ultra-thin nano-layer SiOx is measured and recorded.

[0095] Step 5: Phosphorus diffusion. Poly-Si(n) is formed on the back. + ). Phosphorus ion implantation is performed on the back of the silicon wafer with the ultra-thin nano-layer SiOx to form n + Back surface field.

[0096] Phosphorus diffusion conditions: POCl3 was used as the diffusion source at 800°C to form a junction depth of 0.2 μm, a sheet resistance of 37 Ω / SP, and a surface concentration of 7×10 20 cm -3 n + Back surface field.

[0097] Step 6: Prepare the passivation film and anti-reflection film. On the back of the annealed silicon wafer, a 4nm thick Al2O3 layer is prepared by atomic layer deposition (ALD) to form a passivation film on the back of the silicon wafer. A SiNx:H anti-reflection film with a fixed thickness of 75nm is deposited on both sides of the silicon wafer using PECVD equipment.

[0098] Step 7: Metallization: Prepare the front Ag / Al and back Ag electrode grid lines by screen printing metallization method, and co-sinter in an infrared belt sintering furnace to form a good ohmic contact between the metal semiconductor.

[0099] The thickness of the ultra-thin nano-layer SiOx prepared in step 4 of the above method was measured to be about 1.48 nm, and the ultra-thin nano-layer SiOx prepared had good uniformity and density.

[0100] Example 5: A method for preparing a tunneling oxidation passivation contact structure for a solar cell

[0101] A method for preparing a tunneling oxidation passivation contact structure for a solar cell, the specific preparation method is as follows:

[0102] Step 1: Prepare silicon wafers. Select N-type single crystal silicon wafers with a thickness of 180 μm and a resistivity of 1 Ω·cm to 10 Ω·cm. Cut the silicon wafers into appropriate sizes, clean them, and texture them for later use.

[0103] Texturing conditions: using a mixed solution of 2% by volume NaOH solution and 6% by volume IPA solution, the process temperature is 75°C, and the corrosion depth is 6μm.

[0104] Step 2: Preparation of the front emitter. Put the textured silicon wafer into a high-temperature tube furnace for boron diffusion to form p + The emitter is then locally heavily doped on its front surface using a nanosecond pulse laser, which rapidly pushes boron ions from the borosilicate glass layer (BSG) to the p + The emission region forms p ++ Selective emitter.

[0105] Boron diffusion source: BCl3; diffusion temperature: 980℃; diffusion resistance: 300Ω / SP; borosilicate glass layer surface concentration 4×10 18 cm -3 ; Nanosecond pulse laser conditions: nanosecond pulse laser with a wavelength of 532nm and a pulse energy of 80 to 300μJ.

[0106] Step 3: Back alkaline polishing: Use a diluted 5% hydrofluoric acid solution to remove the remaining BSG layer, and use a mixed solution of hydrofluoric acid and nitric acid (50% hydrofluoric acid by volume: 63% nitric acid by volume = 1:3) to etch the edge of the silicon wafer and polish the back side.

[0107] Back polishing conditions: polishing time 320s, polishing temperature 70℃.

[0108] Step 4: Dipping the silicon wafer. Use the first conveyor belt 2 to transport the cleaned silicon wafer to Figure 1 In the device shown, the silicon wafer is slowly advanced by roller 5, and its back side is immersed in HNO3 solution with a concentration of 9 mol / L during the advancement process. The temperature of HNO3 solution is controlled at 20°C, and the conveying speed of roller 5 is set to 0.5 m / min, so that the immersion time of the silicon wafer in HNO3 solution with a concentration of 9 mol / L is 5 minutes. An ultra-thin nano-layer SiOx is generated on the back side of the silicon wafer by nitric acid oxidation method, i.e., tunneling oxidation passivation contact structure, and then the thickness of the ultra-thin nano-layer SiOx is measured and recorded.

[0109] Step 5: Phosphorus diffusion. Poly-Si(n) is formed on the back. + ). Phosphorus ion implantation is performed on the back of the silicon wafer with the ultra-thin nano-layer SiOx to form n + Back surface field.

[0110] Phosphorus diffusion conditions: POCl3 was used as the diffusion source at 800°C to form a junction depth of 0.2 μm, a sheet resistance of 37 Ω / SP, and a surface concentration of 7×10 20 cm -3 n+ Back surface field.

[0111] Step 6: Prepare the passivation film and anti-reflection film. On the back of the annealed silicon wafer, a 4nm thick Al2O3 layer is prepared by atomic layer deposition (ALD) to form a passivation film on the back of the silicon wafer. A SiNx:H anti-reflection film with a fixed thickness of 75nm is deposited on both sides of the silicon wafer using PECVD equipment.

[0112] Step 7: Metallization: Prepare the front Ag / Al and back Ag electrode grid lines by screen printing metallization method, and co-sinter in an infrared belt sintering furnace to form a good ohmic contact between the metal semiconductor.

[0113] The thickness of the ultra-thin nano-layer SiOx prepared in step 4 of the above method was measured to be about 1.55 nm, and the ultra-thin nano-layer SiOx prepared had good uniformity and density.

[0114] Comparative Example 1

[0115] Compared with Example 2, the difference in the preparation method of Comparative Example 1 is that in step 4, the concentration of the HNO3 solution is 6 mol / L, and the other conditions are the same as those in Example 2.

[0116] Comparative Example 2

[0117] Compared with Comparative Example 1, the difference in the preparation method of Comparative Example 2 is that in step 4, the time for immersing the silicon wafer in the HNO3 solution is 10 minutes, and the other conditions are the same as those of Comparative Example 1.

[0118] Comparative Example 3

[0119] Compared with Example 2, the difference in the preparation method of Comparative Example 3 is that in step 4, the time for immersing the silicon wafer in the HNO3 solution is 10 minutes, and the other conditions are the same as those of Comparative Example 1.

[0120] Comparative Example 4

[0121] Compared with Example 2, the difference in the preparation method of Comparative Example 4 is that in step 4, the time for immersing the silicon wafer in the HNO3 solution is 20 minutes, and the other conditions are the same as those of Comparative Example 1.

[0122] The performance of the battery cells prepared by the methods provided in Examples 2 to 5 and the battery cells prepared by the methods provided in Comparative Examples 1 to 4 was tested. The test data are shown in Table 1.

[0123] Table 1 Performance test data of cells prepared by different preparation methods

[0124] Preparation method Eta Uoc Isc FF RsDf RshuntDf Example 2 26.06 731.0 14.045 84.95 1.256 7120 Example 3 26.04 734.3 16.002 84.61 0.899 6343 Example 4 26.11 735.3 16.014 84.66 0.897 5997 Example 5 25.93 733.1 15.937 84.73 0.903 6541 Comparative Example 1 25.86 730.2 14.000 84.66 1.311 6340 Comparative Example 2 25.86 729.2 14.030 84.50 1.319 6224 Comparative Example 3 25.89 730.2 14.028 84.60 1.302 6301 Comparative Example 4 25.88 730.1 13.991 84.81 1.301 6376

[0125] Note: In the table, Eta (efficiency) indicates the ratio of solar energy converted into electrical energy by the cell; Uoc indicates open circuit voltage; Isc indicates short circuit current; FF indicates fill factor; RserDf indicates series resistance; and RshuntDf indicates parallel resistance.

[0126] As can be seen from Table 1, the cell tunneling oxidation passivation contact structure using the methods provided in Examples 2 to 5 can efficiently produce a high-quality SiOx layer, thereby improving the interface passivation performance and improving the performance of the solar cell. Compared with the prior art using thermal oxidation to prepare ultra-thin nano-layer SiOx, it can avoid reacting at high temperatures and the problem of poor controllability of high-temperature furnace tube reactions, and the cells produced using Examples 2 to 5 also have excellent performance.

[0127] As shown in Table 1, when the silicon wafer is impregnated with a 6 mol / L nitric acid solution, after 5 minutes of reaction, the Eta, Uoc, Isc, FF, and RshuntDf of the battery cell obtained are all lower than those in Example 2. It can be seen that the silicon oxide (SiOx, x = 1...2) prepared by the wet chemical method contains a variety of components: monohydrogenated silicon, dihydrogenated silicon, trihydrogenated silicon (Si(-H)y, y = 1...3) and Si-OH hydroxyl. The passivation performance of the SiOx film is related to the stoichiometry of the interface SiOx. When the oxygen stoichiometry is higher, the passivation performance of the film is better. At the same reaction time, it is speculated that when the nitric acid concentration is dilute, the stoichiometric coefficient of the SiOx produced is lower, resulting in differences in battery performance.

[0128] When low concentration nitric acid is used for the reaction, the reaction time is prolonged, and similarly, the values ​​of the determination results of Eta, Uoc, Isc, FF, and RshuntDf are also lower than those in Example 2. It can be seen that the main product of the reaction of concentrated nitric acid and Si is NO2, which plays a catalytic oxidation role and is an oxygen atom donor of the reducing agent, while the main product at low concentration is NO, and it is speculated that the product with the standard stoichiometric coefficient SiO2 is less, and more SiO, Si2O and other products are mixed, which affects the passivation performance.

[0129] In the present invention, the reaction time of preparing SiOx layer under concentrated nitric acid is also explored, and the results are shown in Table 1. The Eta, Uoc, Isc, FF, and RshuntDf test results of the battery cell obtained by extending the reaction time are the same as those in Example 2. It can be seen that when the reaction time is too long, SiO2 is generated to prevent HNO3 from continuing to react with Si; when the reaction time is short, the thickness of SiOx generated is not enough to meet the requirements, and the passivation performance is poor. The thickness increases with the increase of the reaction time, and does not increase with time after reaching a certain thickness.

[0130] In summary, when nitric acid is used to oxidize and impregnate silicon wafers, concentrated nitric acid can be used to react at low temperatures to obtain a faster reaction rate, and a tunneling oxidation passivation contact structure can be more efficiently prepared under low temperature conditions.

[0131] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0132] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A preparation device for a solar cell tunneling oxidation passivation contact structure, characterized in that: include: A base (1), on which a first conveyor belt (2), a silicon wafer dipping assembly and a second conveyor belt (3) are arranged from left to right; The first conveyor belt (2) is used to transport the silicon wafers to the silicon wafer dipping device; The second conveyor belt (3) is used to transport the silicon wafers after impregnation; The silicon wafer dipping assembly comprises: a nitric acid pool (4), the nitric acid pool (4) is in the shape of a rectangular parallelepiped with an open top surface, and a plurality of rollers (5) are rotatably connected to the nitric acid pool (4); each of the rollers (5) rotates at the same speed, and when each of the rollers (5) rotates, the silicon wafer moves in a horizontal direction; A driving assembly is used to drive the plurality of rollers (5) to move.

2. The preparation device of the solar cell tunneling oxidation passivation contact structure according to claim 1, characterized in that: The roller (5) passes through the inner wall of the nitric acid pool (4) and is rotatably connected to the nitric acid pool (4); a cylindrical gear (6) is fixedly connected to one end of the roller (5) passing through the nitric acid pool (4), and a first bevel gear (7) is also fixedly connected to the outside of the cylindrical gear (6); The driving assembly comprises: a rotating shaft (8) rotatably connected to the side wall of the nitric acid tank (4); a second bevel gear (9) and a first sprocket are fixedly connected to the rotating shaft (8), and the second bevel gear (9) is meshed with the first bevel gear (7); The rotary motor (10) comprises a fixed end and an output end; the fixed end is connected to the base (1), a second sprocket is fixedly connected to the output end, and the first sprocket and the second sprocket are connected in transmission via a chain (11).

3. The preparation device of the solar cell tunneling oxidation passivation contact structure according to claim 1, characterized in that: The distance between the first conveyor belt (2) and the second conveyor belt (3) and the nitric acid pool (4) is less than 1 / 3 of the length of the battery cell.

4. A method for preparing a solar cell tunneling oxidation passivation contact structure, characterized in that: include: Placing a silicon wafer on the equipment for preparing a tunneling oxidation passivation contact structure for a solar cell according to any one of claims 1 to 3, wherein the back side of the silicon wafer contacts the equipment for preparing a tunneling oxidation passivation contact structure for a solar cell, and immersing the silicon wafer in the nitric acid solution. After the immersion is completed, a tunneling oxidation passivation contact structure is formed on the back side of the silicon wafer; The concentration of the nitric acid solution is 8 moL / L to 9 moL / L; the immersion temperature is 20° C. to 25° C.; and the immersion time is 5 min to 10 min.

5. The preparation method according to claim 4, characterized in that: After pretreatment, the silicon wafer is placed on the equipment for preparing the tunneling oxidation passivation contact structure of the solar cell; The pre-processing comprises: S1, cleaning and texturing the silicon wafer; S2, after the texturing is completed, a front emitter is prepared on the front side of the silicon wafer; S3, after the emitter is prepared, alkaline polishing is performed on the back side of the silicon wafer.

6. The preparation method according to claim 5, characterized in that: In S1, the texturing conditions are: using a mixed solution of 1% to 3% NaOH and 5% to 7% isopropanol by volume, at 75°C, with a corrosion depth of 3μm to 6μm; the volume ratio of the NaOH solution to the isopropanol solution is 3 to 4:

1.

7. The preparation method according to claim 5, characterized in that: In S2, after the texturing is completed, the silicon wafer is placed in the tube furnace for boron diffusion to form p + Emitter.

8. The preparation method according to claim 5, characterized in that: In S3, a hydrofluoric acid solution with a volume fraction of 4% to 5% is used to remove the residual BSG layer, and a mixed solution of hydrofluoric acid with a volume fraction of 45% to 55% and nitric acid with a volume fraction of 60% to 65% is used to etch the edge of the silicon wafer, and then a mixed solution of hydrofluoric acid and nitric acid is used to polish the back of the silicon wafer; the volume ratio of hydrofluoric acid with a volume fraction of 45% to 55% and nitric acid with a volume fraction of 60% to 65% in the mixed solution is 1:2 to 3; The back side polishing conditions are: polishing time 300s-400s, polishing temperature 65°C-75°C.

9. A solar cell, characterized in that: The invention comprises a tunneling oxide passivation contact structure prepared by the method described in any one of claims 4 to 8.

10. The solar cell according to claim 9, characterized in that The thickness of the tunneling oxide passivation contact structure is 1.45 nm to 1.55 nm.

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