A method for preparing a SE structure and a solar cell

Abstract

This application discloses a method for preparing an SE structure and a solar cell, belonging to the field of solar cells. The method comprises: printing a polymer film on the front surface of N-type crystalline silicon; printing a boron paste in the metal contact area on the polymer film; allowing the boron paste to contact the N-type crystalline silicon through the polymer film; irradiating the boron paste with a laser to dope boron ions in the boron paste into the N-type crystalline silicon, forming a heavily doped region in the metal contact area; cleaning the front surface of the N-type crystalline silicon and removing the polymer film; and performing boron diffusion on the cleaned front surface of the N-type crystalline silicon to form a lightly doped region in the non-metallic contact area, thereby forming an SE structure. The present application utilizes a polymer film barrier to prevent ion sputtering during laser irradiation, narrowing and controllable the width of the heavily doped region; and effectively reducing damage and recombination centers caused by direct laser doping, thereby effectively improving the battery's opening voltage and contact resistance.

Description

Technical Field

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

[0002] Selective Emitter (SE) technology involves heavily doping the battery's electrode region and lightly doping the emitter region. This technology not only reduces the minority carrier recombination rate in the diffusion layer, improving the battery's short-wave response and open-circuit voltage, but also reduces the battery's series resistance, improves the battery's short-circuit current and fill factor, and thus increases conversion efficiency.

[0003] Currently, the most commonly used SE technique is the laser method: laser energy is used to propagate dopant sources in phosphorosilicate glass (PSG) or borosilicate glass (BSG), creating heavily doped regions and shallowly doped regions in unlased areas. Laser SE for P-type cells is achieved by using laser pulses to melt the surface of the silicon wafer. Phosphorus atoms in the PSG covering the emitter electrode penetrate the silicon surface layer. After solidification, the doped phosphorus atoms replace silicon atoms, forming a doped layer with high concentration and high impurity activation rate in the laser-melted layer. However, laser SE for N-type cells relies on boron doping. Boron atoms are more likely to reside in the BSG oxide layer, making it difficult to dope them in. Furthermore, many of the incorporated boron atoms, due to their lattice mismatch with the silicon, form a dead layer between two silicon atoms, preventing them from replacing silicon atoms. Due to the low doping concentration, SE formation is difficult, and it is difficult to reduce contact resistance and metal recombination in the heavily doped regions, which is not conducive to improving the open-circuit voltage. At the same time, using laser energy for doping can, on the one hand, cause ion sputtering during the doping process, leading to epitaxial growth of heavily doped areas; on the other hand, direct laser doping can damage the silicon wafer and create recombination centers, thus affecting the battery's opening voltage and contact resistance. Therefore, how to improve the battery's opening voltage and contact resistance is a technical problem currently in need of solution by those skilled in the art. Summary of the Invention

[0004] The purpose of this application is to provide a method for preparing a SE structure and a solar cell, thereby improving the battery opening voltage and contact resistance.

[0005] To achieve the above objectives, the present application provides a method for preparing a SE structure, comprising:

[0006] Printing a polymer film on the front side of N-type crystalline silicon;

[0007] Printing boron paste on the metal contact area on the polymer film; the boron paste penetrates the polymer film and contacts the N-type crystalline silicon;

[0008] irradiating the boron slurry with a laser to dope the boron ions in the boron slurry into the N-type crystalline silicon, thereby forming a heavily doped region in the metal contact region;

[0009] Cleaning the front surface of the N-type crystalline silicon to remove the polymer film;

[0010] The boron slurry is used to diffuse boron on the front surface of the cleaned N-type crystalline silicon to form a lightly doped region in the non-metallic contact region to form an SE structure.

[0011] Optionally, after the boron slurry is used to diffuse boron on the front surface of the cleaned N-type crystalline silicon to form a lightly doped region in the non-metallic contact region to form the SE structure, the method further includes:

[0012] The boron in the area outside the front surface of the N-type crystalline silicon is removed; the boron in the area outside the front surface of the N-type crystalline silicon is the boron diffused into the area outside the front surface of the N-type crystalline silicon after the boron slurry is used to diffuse boron on the front surface of the N-type crystalline silicon.

[0013] Optionally, the width of the printed boron paste ranges from 40 μm to 120 μm, including both ends.

[0014] Optionally, the doping depth ranges from 0.8 μm to 2 μm, including both end values.

[0015] Optionally, the power range of the laser is 100W to 1000W, including both ends.

[0016] Optionally, before printing the polymer film on the front surface of the N-type crystalline silicon, the method further includes:

[0017] Texturing N-type crystalline silicon to form a velvet surface;

[0018] Accordingly, the printing of a polymer film on the front surface of the N-type crystalline silicon comprises:

[0019] A polymer film is printed on the velvet surface on the front side of the N-type crystalline silicon.

[0020] Optionally, the sheet resistance of the heavily doped region ranges from 10Ω / □ to 90Ω / □, including both ends.

[0021] Optionally, the sheet resistance of the lightly doped region ranges from 60Ω / □ to 200Ω / □, including both ends.

[0022] Optionally, the polymer film includes: resin, silicon oxide and pore-forming agent.

[0023] To achieve the above objectives, the present application further provides a solar cell, comprising: a SE structure prepared by the SE structure preparation method as described above.

[0024] The present application provides a method for preparing an SE structure, comprising: printing a polymer film on the front surface of N-type crystalline silicon; printing a boron paste in a metal contact area on the polymer film; allowing the boron paste to penetrate the polymer film and contact the N-type crystalline silicon; irradiating the boron paste with a laser to dope boron ions in the boron paste into the N-type crystalline silicon, forming a heavily doped region in the metal contact area; cleaning the front surface of the N-type crystalline silicon to remove the polymer film; and diffusing boron on the cleaned front surface of the N-type crystalline silicon using the boron paste to form a lightly doped region in the non-metallic contact area to form an SE structure.

[0025] Apparently, this application involves brushing a polymer film before boron diffusion, then printing a boron paste on the surface at the grid lines. Laser irradiation of the boron paste allows boron ions to be incorporated into the silicon substrate in the patterned area. The polymer film then blocks the boron ions, preventing ion sputtering during laser doping, narrowing and controlling the width of the heavily doped region. Furthermore, it effectively reduces damage and recombination centers caused by direct laser doping, thereby effectively improving the cell's opening voltage and contact resistance. This application also provides a solar cell with the aforementioned beneficial effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without any creative work.

[0027] Figure 1 A flowchart of a method provided in an embodiment of the present application;

[0028] Figure 2 A schematic diagram of a process for preparing a SE structure provided in an embodiment of the present application;

[0029] Figure 3 A diagram of the solar cell structure provided in an embodiment of the present application. DETAILED DESCRIPTION

[0030] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0031] Currently, the most commonly used SE technique is the laser method: laser energy is used to propagate the dopant source in the PSG or BSG layer, creating heavily doped regions and shallowly doped regions in unlased areas. Laser SE for P-type cells is achieved by using laser pulses to melt the silicon wafer surface. Phosphorus atoms in the PSG layer covering the emitter electrode penetrate the silicon wafer surface layer. After solidification, the doped phosphorus atoms replace silicon atoms, forming a doped layer with high concentration and high impurity activation rate in the laser-melted layer. However, laser SE for N-type cells uses boron doping. Boron atoms tend to reside in the BSG oxide layer, making it difficult to dope in. Furthermore, many incorporated boron atoms, due to lattice mismatch with the silicon, form dead zones between two silicon atoms, preventing them from replacing silicon atoms. The low doping concentration makes SE formation difficult, making it difficult to reduce contact resistance and metal recombination in the heavily doped regions, hindering the improvement of open-circuit voltage. Furthermore, using laser energy for doping can generate ion sputtering during the doping process, leading to epitaxial growth in the heavily doped regions. Furthermore, direct laser doping can damage the silicon wafer and create recombination centers, which can affect the cell's open-circuit voltage and contact resistance. Therefore, the present application provides a method for preparing an SE structure, in which a polymer film is first brushed before boron diffusion, and a boron paste is printed at the grid line position on its surface. The boron paste is irradiated with a laser, and the boron ions are laser-doped into the silicon matrix in the pattern area and blocked by the polymer film, thereby improving the battery opening voltage and contact resistance.

[0032] Please refer to Figure 1 , Figure 1 A flow chart of a method for preparing an SE structure provided in an embodiment of the present application, the method may include:

[0033] S101: Printing a polymer film on the front side of the N-type crystalline silicon.

[0034] This embodiment does not limit the specific composition of the polymer film, and the specific composition of the polymer film can be determined according to actual needs. For example, the polymer film can include: resin, silicon oxide, and a pore-forming agent.

[0035] In order to improve the light trapping effect of the silicon wafer and increase light absorption, before printing the polymer film on the front side of the N-type crystalline silicon, this embodiment may further include: texturing the N-type crystalline silicon to form a velvet surface; accordingly, printing the polymer film on the front side of the N-type crystalline silicon includes: printing the polymer film on the velvet surface on the front side of the N-type crystalline silicon. This embodiment does not limit the specific method of texturing. For example, it may be alkali texturing of the N-type crystalline silicon; or it may be acid texturing of the N-type crystalline silicon. This embodiment does not limit the specific type of velvet. The specific type of velvet is determined according to different texturing methods. For example, it may be alkali texturing of the N-type crystalline silicon to form a pyramid velvet; or it may be acid texturing of the N-type crystalline silicon to form a wormhole-shaped velvet.

[0036] S102: Printing boron paste on the metal contact area on the polymer film; the boron paste penetrates the polymer film and contacts the N-type crystalline silicon.

[0037] It should be noted that the metal contact area is the area where the metal electrode is printed, located on the front surface of the N-type crystalline silicon. The metal electrode is a grid-shaped metal electrode, i.e., a gate line, and the metal contact area is the pattern area corresponding to the gate line. This embodiment does not limit the specific width of the printed boron paste. For example, the width of the printed boron paste can range from 40 μm to 120 μm, inclusive.

[0038] S103: The boron slurry is irradiated with a laser to dope the boron ions in the boron slurry into the N-type crystalline silicon, thereby forming a heavily doped region in the metal contact region.

[0039] This embodiment does not limit the specific depth of doping. For example, the doping depth range can be 0.8μm to 2μm, and the values ​​at both ends are inclusive. This embodiment does not limit the specific power of the laser. For example, the power range of the laser can be 100W to 1000W, and the values ​​at both ends are inclusive. This embodiment does not limit the specific value of the square resistance of the heavily doped region. The specific value of the square resistance of the heavily doped region can be determined according to actual conditions. For example, the square resistance of the heavily doped region can range from 10Ω / □ to 90Ω / □, and the values ​​at both ends are inclusive.

[0040] S104: Cleaning the front surface of the N-type crystalline silicon to remove the polymer film;

[0041] This embodiment does not limit the specific cleaning method, as long as it can ensure that the polymer film can be removed.

[0042] S105: Boron slurry is used to diffuse boron on the front surface of the cleaned N-type crystalline silicon to form a lightly doped region in the non-metallic contact region to form an SE structure.

[0043] This embodiment does not limit the specific value of the square resistance of the lightly doped region. The specific value of the square resistance of the heavily doped region can be determined according to actual conditions. For example, the square resistance of the lightly doped region can range from 60Ω / □ to 200Ω / □, inclusive.

[0044] In this embodiment, the sequence for implementing the boron SE structure is to first print a polymer film, then print a boron paste on the metal contact area, perform laser-assisted boron source doping, and finally perform boron diffusion. Alternatively, boron diffusion may be performed first and then laser-assisted boron source doping. This embodiment does not limit the specific order of S103 and S105; for example, S103 may be performed first and then S105, or S105 may be performed first and then S103.

[0045] Furthermore, in order to remove excess boron from the surface of the N-type crystalline silicon, boron slurry is diffused on the front surface of the cleaned N-type crystalline silicon to form a lightly doped region in the non-metallic contact region to form an SE structure. In this embodiment, boron in the area outside the front surface of the N-type crystalline silicon is the boron that diffuses into the area outside the front surface of the N-type crystalline silicon after the boron slurry is diffused on the front surface of the N-type crystalline silicon.

[0046] It should be noted that the embodiment can also print phosphorus paste on the metal contact area on the polymer film; the phosphorus paste contacts the N-type crystalline silicon through the polymer film; the phosphorus ions in the phosphorus paste are doped into the N-type crystalline silicon by laser irradiation, forming a heavily doped area in the metal contact area; the front side of the N-type crystalline silicon is cleaned to remove the polymer film; the phosphorus paste is diffused on the front side of the N-type crystalline silicon after cleaning, forming a lightly doped area in the non-metallic contact area to form a phosphorus SE structure.

[0047] Based on the above embodiments, the present application first applies a polymer film before boron diffusion, and prints a boron paste at the grid line position on its surface. By laser irradiating the boron paste, boron ions are laser-doped into the silicon matrix in the pattern area and blocked by the polymer film. On the one hand, it can prevent ion sputtering during laser doping, making the width of the heavily doped area narrow and controllable; on the other hand, it can effectively reduce the damage and recombination centers caused by direct laser doping, thereby effectively improving the battery opening voltage and contact resistance.

[0048] An embodiment of the present application further provides a solar cell, comprising: a SE structure prepared by the SE structure preparation method described in the above embodiment.

[0049] Based on the above embodiments, the present application first applies a polymer film before boron diffusion, and prints a boron paste at the grid line position on its surface. By laser irradiating the boron paste, boron ions are laser-doped into the silicon matrix in the pattern area and blocked by the polymer film. On the one hand, it can prevent ion sputtering during laser doping, making the width of the heavily doped area narrow and controllable; on the other hand, it can effectively reduce the damage and recombination centers caused by direct laser doping, thereby effectively improving the battery opening voltage and contact resistance.

[0050] The following is a specific example to illustrate the preparation process of the above SE structure. Please refer to Figure 2 and Figure 3 , Figure 2 A schematic diagram of a process for preparing a SE structure provided in an embodiment of the present application is shown. Figure 3 A solar cell structure diagram is provided in an embodiment of the present application. The process is as follows:

[0051] 1. Perform alkali texturing on N-type crystalline silicon to form a pyramid texture surface;

[0052] 2. Printing polymer film, the polymer film is composed of resin, silicon oxide and pore-forming agent, etc. The polymer film material can be purchased;

[0053] 3. Print boron paste in the metal contact area with a printing width of 40-120μm;

[0054] 4. Through laser thermal energy and radiation energy, the surface boron ions are doped into the silicon substrate in the pattern area to form a heavily doped area in the pattern area. The heavily doped area has a square resistance of 10-90Ω / □ and a doping depth of 0.8-2μm. The laser power is set to 100-1000W.

[0055] 5. Clean and remove residual dirt on silicon wafers, such as polymer films;

[0056] 6. Boron diffusion is performed on the front side of the N-type silicon wafer to obtain a heavily doped region with a square resistance of 10-90Ω / □ in the patterned area and a lightly doped region with a square resistance of 60-200Ω / □ in the non-patterned area, ultimately forming a boron selective emitter structure;

[0057] 7. Use etching equipment to remove borosilicate glass and polish the back surface;

[0058] 8. Grow a SiO2 (silicon dioxide) thin film on the back of the N-type crystalline silicon as a tunneling layer with a thickness of 0.5-2 nm; the SiO2 growth method is high-temperature thermal oxidation, nitric acid oxidation, ozone oxidation or CVD (Chemical Vapor Deposition) deposition;

[0059] 9. Use LPCVD (Low Pressure Chemical Vapor Deposition) equipment to deposit a polysilicon film on the surface of the tunneling layer. The film thickness is 100-300nm. The thicker the polysilicon film, the more severe the light absorption. However, if the thickness is too thin, the phosphorus implant will contact the N-type silicon substrate, resulting in more defects and increased recombination.

[0060] 10. Use diffusion equipment to dope the polysilicon layer with phosphorus to form an N+ emitter. Ion implantation can also be used for diffusion to obtain a phosphorus diffusion layer with a square resistance of 20-90Ω / □.

[0061] 11. Use alkaline solution to remove the coated polysilicon layer and remove the phosphorus silicon glass, with the cleaning temperature being 50-90°C;

[0062] 12. Use ALD (Atomic Layer Deposition) equipment to plate AlOx (aluminum oxide) on the front of the cell, with a film thickness of 2-10nm;

[0063] 13. Using plasma chemical vapor deposition equipment, pass silane, ammonia, nitrogen and other gases to deposit a layer of SiNx:H (silicon nitride) film with a thickness of 60-90nm and a refractive index of 2.0-2.3;

[0064] 14. Deposit a SiNx:H (silicon nitride) film with a thickness of 100-150nm on the back;

[0065] 15. Screen printing and drying;

[0066] 16. Sintering. The final structure of the solar cell is shown in Figure 3 .

[0067] This article uses specific examples to illustrate the principles and implementation methods of this application, and the various embodiments are in a progressive relationship. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other. For the solar cells disclosed in the embodiments, please refer to the corresponding method section description. The description of the above embodiments is only used to help understand the method of this application and its core ideas. For ordinary technicians in this technical field, without departing from the principles of this application, several improvements and modifications can be made to this application, and these improvements and modifications also fall within the scope of protection of the claims of this application.

[0068] It should also be noted that, in this specification, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

Claims

1. A method for preparing a SE structure, characterized in that: include: Printing a polymer film on the front side of N-type crystalline silicon; printing a boron paste on the metal contact area of ​​the polymer film; The boron slurry penetrates the polymer film and contacts the N-type crystalline silicon; irradiating the boron slurry with a laser to dope the boron ions in the boron slurry into the N-type crystalline silicon, thereby forming a heavily doped region in the metal contact region; Cleaning the front surface of the N-type crystalline silicon to remove the polymer film; The boron slurry is used to diffuse boron on the front surface of the cleaned N-type crystalline silicon to form a lightly doped region in the non-metallic contact region to form an SE structure.

2. The method for preparing a SE structure according to claim 1, wherein: After the boron slurry is used to diffuse boron on the front surface of the cleaned N-type crystalline silicon to form a lightly doped region in the non-metallic contact region to form an SE structure, the method further includes: The boron in the area outside the front surface of the N-type crystalline silicon is removed; the boron in the area outside the front surface of the N-type crystalline silicon is the boron diffused into the area outside the front surface of the N-type crystalline silicon after the boron slurry is used to diffuse boron on the front surface of the N-type crystalline silicon.

3. The method for preparing a SE structure according to claim 1, wherein: The width of the printed boron paste ranges from 40 μm to 120 μm, inclusive.

4. The method for preparing a SE structure according to claim 1, wherein: The doping depth ranges from 0.8 μm to 2 μm, inclusive.

5. The method for preparing a SE structure according to claim 1, wherein: The power of the laser is in the range of 100 W to 1000 W, inclusive.

6. The method for preparing a SE structure according to claim 1, wherein: Before printing the polymer film on the front surface of the N-type crystalline silicon, the method further comprises: Texturing N-type crystalline silicon to form a velvet surface; Accordingly, the printing of a polymer film on the front surface of the N-type crystalline silicon comprises: A polymer film is printed on the velvet surface on the front side of the N-type crystalline silicon.

7. The method for preparing a SE structure according to claim 1, wherein: The sheet resistance of the heavily doped region ranges from 10Ω / □ to 90Ω / □, inclusive.

8. The method for preparing a SE structure according to claim 1, wherein: The sheet resistance of the lightly doped region ranges from 60Ω / □ to 200Ω / □, inclusive.

9. The method for preparing a SE structure according to any one of claims 1 to 8, characterized in that: The polymer film comprises resin, silicon oxide and pore-forming agent.

10. A solar cell, characterized in that: include: The SE structure prepared by the SE structure preparation method according to any one of claims 1 to 9.

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