A method for improving laser scribing damage of silicon nitride in a solar cell

Abstract

This invention relates to a method for improving silicon nitride laser grooving damage in solar cells. The method includes the following steps: retaining a PSG layer in the laser grooving area, and performing laser grooving after sequential oxidation and coating. By retaining the PSG layer in the laser grooving area, this invention removes the remaining PSG grid lines and silicon nitride simultaneously using a laser during laser grooving, reducing PN junction damage and thus reducing Uoc and Eta losses. Furthermore, the method of this invention can further eliminate SE doping, reducing production steps and lowering production costs. Simultaneously, it avoids damage to the silicon wafer caused by excessive SE doping, thereby further ensuring the performance of the solar cell.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, and relates to a method for producing solar cells, and more particularly to a method for improving the damage caused by laser grooving of silicon nitride in solar cells. Background Technology

[0002] In the process of reducing the cost of solar cells, electroplating electrodes have received increasing attention. The main steps of electroplating are generally as follows: silicon wafer, texturing, diffusion, SE (solidification), pre-oxidation, etching, post-oxidation, back-side coating, front-side coating, back-side laser grooving, back-side printing and sintering, front-side laser grooving, electroplating, annealing, and testing. Among these, there are two main methods for front-side laser grooving. The first is laser grooving, where a laser is used to irradiate the silicon wafer with deposited silicon nitride according to the grid pattern. After the laser energy is absorbed by the silicon, the molten silicon is sputtered, thereby removing the silicon nitride covering it. The second is removing silicon nitride by masking and HF acid etching. This method mainly uses a mask material to protect the silicon nitride in the non-grid area, and then uses an HF acid solution to react with the silicon nitride in the area corresponding to the grid line to remove the silicon nitride under the grid line.

[0003] However, relatively speaking, laser grooving has high precision, large output, and is simpler and more environmentally friendly to operate. However, when a normal nanosecond or picosecond laser heats a silicon wafer, the molten silicon sputtering will carry away the doped atoms, causing lattice damage and PN junction destruction, which will lead to Uoc loss and Eta loss.

[0004] CN 110676346A discloses a method for fabricating PERC cells using laser grooving. The method includes: texturing, diffusion, etching, front oxidation annealing, back passivation, front coating, laser grooving, back oxidation annealing, and printing sintering. A laser grooving device is used to groove the back of a silicon wafer according to a specific pattern. The laser grooving area design is not limited to line segments, straight lines, or dots. Through the passivation effect of the silicon dioxide film, the damaged layer of the silicon wafer at the laser grooving location is passivated, eliminating carrier recombination caused by silicon wafer damage at the laser grooving location, thereby improving the photoelectric conversion efficiency of the final cell.

[0005] However, this method cannot avoid the defects caused by molten silicon sputtering carrying away doped atoms, and cannot avoid lattice damage and PN junction destruction.

[0006] CN 105470347A discloses a method for fabricating a PERC cell, comprising: cleaning and texturing a silicon wafer; forming a pn junction through diffusion; fabricating a passivation film on the front side of the silicon wafer; covering the back side of the silicon wafer with a photomask and depositing an Al2O3 thin film using the photomask, followed by annealing and then depositing a Si3N4 thin film; removing the photomask to form a grooved passivation film pattern; and fabricating a front electrode and a back electrode. By forming a grooved passivation film pattern, this method achieves localized back contact in the crystalline silicon cell while avoiding damage caused by laser grooving, thereby reducing recombination, lowering contact resistance, and improving cell conversion efficiency. However, this fabrication method is complex.

[0007] CN 110176522A discloses an alkaline etching process for SE solar cells, comprising the following steps: 1) diffusion; 2) laser doping; 3) fabrication of an alkaline-resistant etching mask: fabricating an alkaline-resistant etching mask on the front side of the silicon wafer; 4) removal of the backside PSG of the silicon wafer; 5) alkaline etching; 6) removal of the alkaline-resistant etching mask and the frontside PSG of the silicon wafer; 7) cleaning and drying. This method involves fabricating an alkaline-resistant etching mask on the front side of the silicon wafer after laser doping and before removing the backside PSG. This mask protects the laser-grooved area during alkaline etching, preventing corrosion of the laser-grooved area by the alkaline etching solution. However, this method fabricates the mask on the front side without distinguishing the protected area, and does not optimize the area of ​​the SE-doped region, which is detrimental to reducing the manufacturing cost of PERC cells.

[0008] To address this, a method is needed to improve the damage caused by laser grooving of silicon nitride in solar cells. This method should be able to reduce lattice damage and PN junction damage in the corresponding region during laser grooving. Furthermore, it should enable SE doping and laser grooving to be completed simultaneously, further reducing the damage of SE doping to the silicon wafer and further improving the performance of the solar cell. Summary of the Invention

[0009] The purpose of this invention is to provide a method for improving the damage caused by laser grooving of silicon nitride in solar cells. The method can reduce the damage to the laser-grooved area caused by laser grooving and reduce the damage to the silicon wafer caused by SE doping, thereby ensuring the performance of the solar cell.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] This invention provides a method for improving silicon nitride laser grooving damage in solar cells, the method comprising the following steps:

[0012] The PSG layer is retained in the laser-grooved area, and after oxidation and coating, laser grooving is performed.

[0013] The PSG layer described in this invention is a phosphosilicate glass layer. By retaining the PSG layer in the laser-grooved region, a process similar to SE doping is generated during laser grooving, reducing damage to the lattice and PN junction in the laser-grooved region during silicon nitride removal. Furthermore, in conventional SE doping, the PSG is removed, and some phosphorus atoms in the SE region are lost irreplaceably during laser grooving. The method provided by this invention propels phosphorus atoms from the PSG into the silicon wafer during laser grooving, eliminating the need for the SE process, further reducing damage to the original silicon wafer caused by SE doping, and further improving the performance of the solar cell.

[0014] Preferably, the method includes sequentially performing texturing, diffusion, mask printing, etching, oxidation, coating, laser grooving, and electroplating;

[0015] The printed mask and etching retain the PSG layer in the laser-grooved area.

[0016] Preferably, the method for printing the mask includes screen printing and / or transfer printing.

[0017] The method provided by the present invention involves screen printing a corrosion-resistant layer with the same groove pattern onto the diffusion surface PSG; in order to ensure the protection of the grooved area by the corrosion-resistant layer, the width of the corrosion-resistant layer is slightly wider than the groove width of the grooved area.

[0018] Preferably, the etching removes the PSG layer outside the laser-grooved area while retaining the PSG layer in the laser-grooved area.

[0019] Preferably, the etching method includes acid etching or mixed etching.

[0020] For example, the acid used for acid etching according to the present invention includes a mixed acid of HF and HNO3.

[0021] The mixed acid used in this invention is obtained by mixing HF, HNO3 and deionized water. The volume ratio of HF, HNO3 and H2O is (45-55):(330-370):(100-130), for example, it can be 45:330:100, 55:370:130, 45:370:100, 55:330:130 or 45:370:130, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] The mass concentration of HF in the mixed acid used in this invention is 48-49%, for example, it can be 48%, 48.1%, 48.2%, 48.3%, 48.4%, 48.5%, 48.6%, 48.7%, 48.8%, 48.9% or 49%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] The mass concentration of HNO3 in the mixed acid used in this invention is 69-71%, for example, it can be 69%, 69.5%, 70%, 70.5% or 71%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] For example, the hybrid etching described in this invention includes first performing HF to PSG etching, and then performing NaOH alkaline polishing etching.

[0025] Preferably, the temperature for the flocking process is 80-90℃ and the time is 300-900s.

[0026] The temperature for forming the flocking process described in this invention is 80-90℃, for example, it can be 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃ or 90℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] The fabrication time described in this invention is 300-900s, for example, it can be 300s, 400s, 500s, 600s, 700s, 800s or 900s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] The texturing solution used in the texturing process described in this invention is a conventional texturing solution in the field, and this invention does not impose any further limitations on it.

[0029] Preferably, the oxidation temperature is 650-750℃, for example, it can be 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃ or 750℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0030] Preferably, the oxidation time is 15-35 min, for example, it can be 15 min, 20 min, 25 min, 30 min or 35 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the oxidation is carried out in a mixed atmosphere of nitrogen and oxygen.

[0032] Preferably, the flow rate of the nitrogen gas is 2-10 slm, for example, it can be 2 slm, 3 slm, 4 slm, 5 slm, 6 slm, 7 slm, 8 slm, 9 slm or 10 slm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the oxygen flow rate is 4-20 slm, for example, it can be 4 slm, 5 slm, 6 slm, 8 slm, 10 slm, 12 slm, 15 slm, 16 slm, 18 slm or 20 slm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] Preferably, the coating temperature is 380-520℃, for example, it can be 380℃, 400℃, 420℃, 450℃, 480℃, 500℃ or 520℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0035] Preferably, the thickness of the coating is 71-81 nm, for example, it can be 71 nm, 72 nm, 75 nm, 76 nm, 78 nm, 80 nm or 81 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the thickness of the back film of the coating is 104-116 nm, for example, it can be 104 nm, 105 nm, 106 nm, 108 nm, 110 nm, 112 nm, 115 nm or 116 nm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0037] The coating methods described in this invention include, but are not limited to, plasma-enhanced chemical vapor deposition (PECVD).

[0038] Preferably, the laser grooving involves removing the PSG layer retained in the laser-grooved area using a laser, while simultaneously removing silicon nitride.

[0039] Preferably, the process between printing the mask and etching includes mask heat treatment.

[0040] Preferably, the temperature of the mask heat treatment is 170-190℃ and the time is 5-300s.

[0041] The temperature for the mask heat treatment described in this invention is 170-190℃, for example, it can be 170℃, 175℃, 180℃, 185℃ or 190℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] The heat treatment time for the mask described in this invention is 5-300s, for example, it can be 5s, 10s, 30s, 50s, 80s, 100s, 150s, 200s, 250s or 300s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] This invention uses mask heat treatment to solidify the corrosion-resistant layer, thereby improving its stability.

[0044] As a preliminary technical solution for the method described in this invention, the method includes...

[0045] The processes are texturing, diffusion, printing mask, etching, oxidation, coating, laser grooving and electroplating, performed sequentially.

[0046] The printing mask and etching retain the PSG layer in the laser grooving area; the etching removes the PSG layer outside the laser grooving area while retaining the PSG layer in the laser grooving area; the laser grooving removes the PSG layer retained in the laser grooving area while removing silicon nitride.

[0047] The etching method includes acid etching or mixed etching;

[0048] The oxidation is carried out at a temperature of 650-750℃ for a time of 15-35 min; the oxidation is carried out in a mixed atmosphere of nitrogen and oxygen, with a nitrogen flow rate of 2-10 slm and an oxygen flow rate of 4-20 slm.

[0049] The coating temperature is 380-520℃, the thickness of the front film is 71-81nm, and the thickness of the back film is 104-116nm.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] This invention retains the PSG layer in the laser-grooved area, generating a process similar to SE doping during laser grooving. This reduces damage to the lattice and PN junction in the laser-grooved area during silicon nitride removal. Furthermore, the method can further eliminate SE doping, reducing production steps and lowering production costs. At the same time, it avoids damage to the silicon wafer caused by excessive SE doping, thereby further ensuring the performance of the solar cell. Attached Figure Description

[0052] Figure 1 A process flow diagram of the method provided in Embodiment 1 of the present invention is provided.

[0053] Figure 2 A process flow diagram of the method is provided for Comparative Example 1 of the present invention. Detailed Implementation

[0054] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0055] Example 1

[0056] This embodiment provides a method for improving silicon nitride laser grooving damage in solar cells, and the process flow diagram of the method is shown below. Figure 1 As shown, the process includes texturing, diffusion, printing mask, etching, oxidation, coating, laser grooving and electroplating performed sequentially.

[0057] The texturing temperature is 85℃, and the time is 600s;

[0058] The printing mask and etching retain the PSG layer in the laser grooving area; the etching removes the PSG layer outside the laser grooving area while retaining the PSG layer in the laser grooving area; the laser grooving removes the PSG layer retained in the laser grooving area while removing silicon nitride.

[0059] The etching method is acid etching; the acid used for acid etching is a mixture of HF and HNO3; the mixture consists of HF, HNO3 and H2O in a volume ratio of 50:350:115, the mass concentration of HF is 49wt% and the mass concentration of HNO3 is 70%.

[0060] The oxidation was carried out at a temperature of 700°C for 25 minutes; the oxidation was carried out in a mixed atmosphere of nitrogen and oxygen, with a nitrogen flow rate of 5 slm and an oxygen flow rate of 10 slm.

[0061] The coating was performed using the PECVD method at a temperature of 450°C. The thickness of the front film was 76 nm, and the thickness of the back film was 110 nm.

[0062] Example 2

[0063] This embodiment provides a method for improving the damage caused by laser grooving of silicon nitride in solar cells. The method includes sequentially performing texturing, diffusion, mask printing, etching, oxidation, coating, laser grooving, and electroplating.

[0064] The texturing temperature is 80℃ and the time is 900s;

[0065] The printing mask and etching retain the PSG layer in the laser grooving area; the etching removes the PSG layer outside the laser grooving area while retaining the PSG layer in the laser grooving area; the laser grooving removes the PSG layer retained in the laser grooving area while removing silicon nitride.

[0066] The etching method is acid etching; the acid used for acid etching is a mixture of HF and HNO3; the mixture consists of HF, HNO3 and H2O in a volume ratio of 45:330:130, the mass concentration of HF is 49wt% and the mass concentration of HNO3 is 70%.

[0067] The oxidation was carried out at a temperature of 650°C for 35 minutes; the oxidation was carried out in a mixed atmosphere of nitrogen and oxygen, with a nitrogen flow rate of 2 slm and an oxygen flow rate of 4 slm.

[0068] The coating was performed using the PECVD method at a temperature of 350°C. The thickness of the front film was 71 nm, and the thickness of the back film was 104 nm.

[0069] Example 3

[0070] This embodiment provides a method for improving the damage caused by laser grooving of silicon nitride in solar cells. The method includes sequentially performing texturing, diffusion, mask printing, etching, oxidation, coating, laser grooving, and electroplating.

[0071] The texturing temperature is 90℃, and the time is 300s;

[0072] The printing mask and etching retain the PSG layer in the laser grooving area; the etching removes the PSG layer outside the laser grooving area while retaining the PSG layer in the laser grooving area; the laser grooving removes the PSG layer retained in the laser grooving area while removing silicon nitride.

[0073] The etching method is acid etching; the acid used for acid etching is a mixture of HF and HNO3; the mixture consists of HF, HNO3 and H2O in a volume ratio of 55:370:100, the mass concentration of HF is 49wt% and the mass concentration of HNO3 is 70%.

[0074] The oxidation was carried out at a temperature of 750°C for 15 minutes; the oxidation was carried out in a mixed atmosphere of nitrogen and oxygen, with a nitrogen flow rate of 10 slm and an oxygen flow rate of 20 slm.

[0075] The coating was performed using the PECVD method at a temperature of 520°C. The thickness of the front film was 81 nm, and the thickness of the back film was 116 nm.

[0076] Comparative Example 1

[0077] This comparative example provides a method for laser grooving of silicon nitride in solar cells, and the process flow diagram of the method is shown below. Figure 2 As shown, the process includes texturing, diffusion, SE, etching, oxidation, coating, laser grooving and electroplating performed sequentially.

[0078] The SE is a conventional SE in the art. Specifically, it uses a nanosecond laser with a laser power of 20-30W, controls the laser spot size to be 100nm, the laser frequency to be 200kHz, the real-to-virtual line ratio to be 100%, and the engraving speed to be 22550mm / s. The laser is used to irradiate the silicon wafer made of PSG to heat the silicon wafer, so that the P atoms in the PSG can further diffuse into the silicon wafer.

[0079] Performance Characterization

[0080] The silicon wafers obtained after laser grooving in the examples and the silicon wafers obtained in the comparative examples were successively subjected to electroplating and annealing to obtain solar cells. The electrochemical performance of the obtained solar cells was characterized based on the electrical performance parameters measured by a Halmmeter. The characterization included open-circuit voltage (Uoc), short-circuit current (Isc), series resistance (Rser), parallel resistance (Rshunt), fill factor (FF), and photoelectric conversion efficiency (Eta). The results are shown in Table 1.

[0081] Table 1

[0082]

[0083]

[0084] In summary, this invention retains the PSG layer in the laser-grooved region, generating a process similar to SE doping during laser grooving. This reduces damage to the lattice and PN junction in the laser-grooved region during silicon nitride removal. Furthermore, since the SE process can be omitted, the damage to the original silicon wafer caused by SE doping can be further eliminated, thereby further improving the performance of the solar cell.

[0085] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for improving silicon nitride laser grooving damage in solar cells, characterized in that, The method includes sequentially performing texturing, diffusion, printing mask, etching, oxidation, coating, laser grooving and electroplating; The printing mask and etching retain the PSG layer in the laser grooving area; the etching removes the PSG layer outside the laser grooving area while retaining the PSG layer in the laser grooving area; the laser grooving removes the PSG layer retained in the laser grooving area by laser, while simultaneously removing silicon nitride.

2. The method according to claim 1, characterized in that, The method of printing the mask includes screen printing and / or transfer printing.

3. The method according to claim 1, characterized in that, The etching methods include acid etching or mixed etching.

4. The method according to claim 1, characterized in that, The temperature for the flocking process is 80-90℃, and the time is 300-900s.

5. The method according to claim 1, characterized in that, The oxidation temperature is 650-750℃.

6. The method according to claim 1, characterized in that, The oxidation time is 15-35 minutes.

7. The method according to claim 1, characterized in that, The oxidation is carried out in a mixed atmosphere of nitrogen and oxygen.

8. The method according to claim 7, characterized in that, The flow rate of the nitrogen gas is 2-10 slm.

9. The method according to claim 7, characterized in that, The oxygen flow rate is 4-20 slm.

10. The method according to claim 1, characterized in that, The coating temperature is 380-520℃.

11. The method according to claim 1, characterized in that, The thickness of the coating is 71-81 nm.

12. The method according to claim 1, characterized in that, The thickness of the back film of the coating is 104-116 nm.

13. The method according to claim 1, characterized in that, Between the printing mask and the etching, a mask heat treatment is also included.

14. The method according to claim 13, characterized in that, The mask heat treatment temperature is 170-190℃, and the time is 5-300s.

15. The method according to claim 1, characterized in that, The method includes sequentially performing texturing, diffusion, printing mask, etching, oxidation, coating, laser grooving and electroplating; The texturing temperature is 80-90℃, and the time is 300-900s; The printing mask and etching retain the PSG layer in the laser grooving area; the etching removes the PSG layer outside the laser grooving area while retaining the PSG layer in the laser grooving area; the laser grooving removes the PSG layer retained in the laser grooving area while removing silicon nitride. The etching method includes acid etching or mixed etching; The oxidation is carried out at a temperature of 650-750℃ for a time of 15-35 min; the oxidation is carried out in a mixed atmosphere of nitrogen and oxygen, with a nitrogen flow rate of 2-10 slm and an oxygen flow rate of 4-20 slm. The coating temperature is 380-520℃, the thickness of the front film is 71-81nm, and the thickness of the back film is 104-116nm.

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