A rework process for defective HJT battery cells

Abstract

This invention provides a rework process for defective HJT battery wafers. The rework process includes the following steps: P1. Collecting defective wafers and placing them in a specialized rework cleaning machine to remove the surface film; P2. Re-texturing the silicon wafers obtained in P1 in the cleaning machine. This rework process for defective HJT battery wafers is applicable to the rework of defective wafers produced after ITO, ATO, or Cu semiconductor or metal films have been deposited. First, a mixed solution of hydrochloric acid and hydrogen peroxide is used to remove the surface film and grid lines of the battery wafer; then, a mixed solution of nitric acid and hydrofluoric acid is used to treat the amorphous silicon film to remove the amorphous silicon layer; finally, the silicon wafer is re-textured to obtain a reworkable wafer ready for production. Therefore, this rework process effectively solves the rework problem of various defective wafers generated in HJT battery production; it enables mass production of defective HJT battery wafers, achieving a Grade A yield of 98% after rework, with cell efficiency comparable to that of cells produced in the normal process; it effectively improves production yield and saves more than 50% of silicon wafer raw material costs.

Description

Technical Field

[0001] This invention relates to the field of solar cells, and more particularly to a rework process for defective HJT solar cells. Background Technology

[0002] In the field of solar cell technology, heterojunction (HJT) cells possess significant advantages such as high efficiency, high on-state voltage, and good temperature characteristics due to the excellent passivation effect of their amorphous silicon layers. Furthermore, the HJT manufacturing process is simple, requiring only a few steps. Currently, the HJT industry has achieved considerable scale, and the costs of various materials required for production continue to decline. Silicon wafers, as the core raw material in the entire cell manufacturing process, account for as much as 50-60% of the cost. However, during cell production, defective cells inevitably occur, such as those with poor appearance or electrical performance. The presence of these defective cells reduces the production yield and increases the cost of silicon wafers. Therefore, reworking these defective cells into reusable silicon wafers is of great significance for further reducing the production cost of HJT cells. In existing technologies, the rework process for HJT defective solar cells after ITO, ATO, or Cu semiconductor or metal films is carried out using ozone-based processes to remove the thin film. While ozone processes are clean and do not produce secondary pollution, their equipment costs and operating expenses are high. Furthermore, in addition to ozone, various other chemicals are required for the rework process, increasing chemical consumption. Moreover, excessively high drying temperatures are detrimental to the long-term use of the fabric baskets, as their deformation capacity gradually decreases due to temperature variations. Therefore, existing rework processes for HJT defective solar cells after ITO, ATO, or Cu semiconductor or metal films have the following drawbacks: 1) The rework process mainly uses ozone chemical polishing, and ozone is easily volatilized and decomposed, posing potential risks to process control; 2) Existing rework processes consume a large amount of chemicals; 3) Excessively high drying temperatures affect the lifespan of the fabricated fabric baskets. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a rework process for defective HJT battery cells, characterized in that the rework process for defective HJT battery cells includes the following steps:

[0004] P1 collects defective wafers and sends them to a specialized rework cleaning machine to remove the surface film. The specific process includes:

[0005] P1.1 Water washing: Wash with pure water to remove impurities and dirt from the surface of defective films;

[0006] P1.2 Pickling: Defective wafers are pickled with a mixture of hydrochloric acid and hydrogen peroxide to remove surface metal grid lines, transparent conductive films, etc.

[0007] P1.3 Water washing: Wash with pure water to remove residual acid from the surface;

[0008] P1.4 Pre-cleaning solution wash: Clean the defective film with a mixture of ammonia and hydrogen peroxide to remove impurities and dirt remaining after film removal;

[0009] P1.5 Water Wash: Wash with pure water to remove the solution from the surface of the defective tablets;

[0010] P1.6 CP pickling: The defective wafers are pickled with a mixed solution of nitric acid and hydrofluoric acid to remove the amorphous silicon thin film layer;

[0011] P1.7 Water washing: Wash with pure water to remove the acid from the surface of the defective wafer and obtain the silicon wafer;

[0012] P1.8 SC2 solution wash: Wash the silicon wafer obtained from P1.7 with SC2 solution to further remove residues;

[0013] P1.9 Water washing: Wash with pure water to remove the surface solution;

[0014] P1.10 Pickling: The silicon wafer is pickled with hydrofluoric acid solution to achieve dehydration;

[0015] P1.11 Water washing: Wash with pure water to remove surface acid;

[0016] P1.12 Slow Lifting: Use pure water for slow lifting;

[0017] P1.13 Drying: The obtained silicon wafers are dried.

[0018] P2. The silicon wafer obtained in P1 is put into a cleaning machine for retexturing; the retexturing temperature is 70-80℃, which is 5-10℃ lower than the conventional texturing temperature; the retexturing etching amount is <0.5g;

[0019] Furthermore, in the P1.1 water washing step, the water washing time is 30-120 seconds;

[0020] Furthermore, in the P1.2 pickling step, the mass fraction of hydrochloric acid in the mixture of high-concentration hydrochloric acid and hydrogen peroxide is not less than 30%, the mass fraction of hydrogen peroxide is not less than 20%, the cleaning time is 400-2000s, and the cleaning temperature is 30-70℃.

[0021] Furthermore, in the P1.4 pre-cleaning solution washing step, the pre-cleaning solution is a mixed solution of ammonia and hydrogen peroxide, and the cleaning time is 3 min-6 min;

[0022] Furthermore, in the P1.6 CP pickling step, the mass fraction of nitric acid in the mixed solution of nitric acid and hydrofluoric acid is not less than 50%, the mass fraction of hydrofluoric acid is not less than 50%, and the cleaning time is 60-360s;

[0023] Furthermore, in the P1.8 SC2 liquid washing step, the SC2 liquid is a mixed solution of hydrochloric acid and hydrogen peroxide, wherein the mass fraction of hydrochloric acid is not less than 30% and the mass fraction of hydrogen peroxide is not less than 20%, the washing temperature is 40-85℃, and the washing time is 4min-6min.

[0024] Furthermore, in the P1.10 pickling step, the hydrofluoric acid solution contains a mass fraction of not less than 50% hydrofluoric acid.

[0025] Furthermore, in the P1.12 slow lifting step, the pure water temperature is 30-60℃, and the washing time is >30s;

[0026] Furthermore, in the drying step P1.13, the drying temperature is 30-90℃ and the drying time is 400-720s;

[0027] Furthermore, in the P1.3, P1.5, P1.7, P1.9 and P1.11 water washing steps, the water washing time is 90-240 seconds.

[0028] Furthermore, the rework process for defective HJT battery wafers is applicable to the rework of defective wafers that have already been coated with semiconductor or metal films such as ITO, ATO, or Cu.

[0029] The rework process for defective HJT battery wafers provided by this invention first uses a mixed solution of hydrochloric acid and hydrogen peroxide to remove the thin film and grid lines on the surface of the battery wafer. The hydrochloric acid removes various films on the surface of the battery wafer, while the hydrogen peroxide oxidizes the silicon wafer surface to further remove metal ions. After treatment, a texturing appearance similar to that after amorphous silicon plating is obtained. Then, a mixed solution of ammonia and hydrogen peroxide is used to pre-clean the silicon wafer to remove surface dirt and other impurities. Furthermore, in order to completely remove the surface amorphous silicon film, this invention uses a mixture of nitric acid and hydrofluoric acid to treat the amorphous silicon film. The oxidizing property of nitric acid is used to oxidize the Si surface to form SiO2. Then, hydrofluoric acid reacts with SiO2 to remove the SiO2 film. Using nitric acid and hydrofluoric acid, the amorphous silicon film can be completely removed within a treatment time of 60-360 seconds. After removal, a silicon wafer with no color difference and good surface cleanliness is obtained. The silicon wafer is then retextured. The texturing temperature and time of the retexturing process are reduced and shortened compared to the conventional texturing process, effectively reducing the etching thickness of the silicon wafer, ensuring the thickness of the reworked silicon wafer, and keeping the reflection within the required range. The rework etching amount is <0.5g, so it does not affect the textured surface of the retextured wafer.

[0030] Therefore, compared with the prior art, the rework process for defective HJT battery cells provided by the present invention has the following beneficial effects:

[0031] 1) Avoid using ozone treatment process, the process is stable and easy to control, effectively solving the rework problem of various defective cells generated in HJT battery production;

[0032] 2) The rework process can mass-produce defective HJT cells, and the A-grade yield after rework can reach 98%, and the cell efficiency is comparable to that of cells produced in the normal process.

[0033] 3) Effectively improved production yield and saved more than 50% of silicon wafer raw material costs. Attached Figure Description

[0034] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0035] Figure 1 A flowchart illustrating the rework process for defective HJT battery cells provided by this invention; Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0037] like Figure 1 As shown, this invention provides a rework process for defective HJT battery cells, comprising the following steps:

[0038] P1 collects defective wafers and sends them to a specialized rework cleaning machine to remove the surface film. The specific process includes:

[0039] P1.1 Water washing: Wash with pure water to remove impurities and dirt from the surface of the defective film; wherein the water washing time is 100s;

[0040] P1.2 Pickling: The defective wafers are pickled with a mixture of hydrochloric acid and hydrogen peroxide to remove surface metal grid lines, transparent conductive films, etc.; wherein, in the mixture of high-concentration hydrochloric acid and hydrogen peroxide, the mass fraction of hydrochloric acid is not less than 30% and the mass fraction of hydrogen peroxide is not less than 20%, the cleaning time is 1000s, and the cleaning temperature is 50℃.

[0041] P1.3 Water washing: Wash with pure water to remove residual acid from the surface; wherein the water washing time is 120s;

[0042] P1.4 Pre-cleaning solution wash: The defective sheet is cleaned with a mixture of ammonia and hydrogen peroxide to remove impurities and dirt remaining after the film is removed; wherein, the pre-cleaning solution is a mixture of ammonia and hydrogen peroxide, and the cleaning time is 5 minutes;

[0043] P1.5 Water washing: Wash with pure water to remove the solution from the surface of the defective tablets; wherein the water washing time is 120s;

[0044] P1.6 CP pickling: The defective wafer is pickled with a mixed solution of nitric acid and hydrofluoric acid to remove the amorphous silicon thin film layer; wherein, in the mixed solution of nitric acid and hydrofluoric acid, the mass fraction of nitric acid is not less than 50% and the mass fraction of hydrofluoric acid is not less than 50%, and the cleaning time is 240s;

[0045] P1.7 Water washing: Wash with pure water to remove the acid from the surface of the defective wafer, and obtain the silicon wafer; wherein, the water washing time is 180s;

[0046] P1.8 SC2 solution wash: Wash the silicon wafer obtained in P1.7 with SC2 solution to further remove residues; wherein, the SC2 solution is a mixed solution of hydrochloric acid and hydrogen peroxide, the mass fraction of hydrochloric acid is not less than 30%, the mass fraction of hydrogen peroxide is not less than 20%, the cleaning temperature is 60℃, and the cleaning time is 5min;

[0047] P1.9 Water washing: Wash with pure water to remove the surface solution; wherein the water washing time is 180s;

[0048] P1.10 Pickling: The silicon wafer is pickled with hydrofluoric acid solution to achieve dehydration; wherein the mass fraction of hydrofluoric acid in the hydrofluoric acid solution is not less than 50%;

[0049] P1.11 Water washing: Wash with pure water to remove surface acid; wherein the water washing time is 240s;

[0050] P1.12 Slow lifting: Slow lifting is performed using pure water; wherein the temperature of the pure water is 50℃ and the washing time is 60s;

[0051] P1.13 Drying: The obtained silicon wafer is dried; wherein the drying temperature is 70°C and the drying time is 600s;

[0052] P2. The silicon wafer obtained in P1 is put into a cleaning machine for retexturing. The retexturing temperature is 70-80℃, which is 5-10℃ lower than the conventional texturing temperature, and the retexturing etching amount is <0.5g.

[0053] The rework process for defective HJT battery wafers is applicable to the rework of defective wafers that have already been coated with semiconductor or metal films such as ITO, ATO, or Cu.

[0054] Test results show that after reprocessing defective solar cells using the HJT cell rework process provided by this invention, the average efficiency of the cells after being put back into production reaches 24.17%, and the A-grade rate reaches 98%, both comparable to those of cells produced through normal processes. This demonstrates that this invention successfully reprocesses defective solar cells into texturized silicon wafers. Specific test results are as follows:

[0055] Silicon wafer type Number of tests Isc Uoc FF Eta Grade A rate normal film 60978 9.8426 0.7455 83.145 24.21 99％ Defective film rework 20295 9.8402 0.7445 83.241 24.17 98％

[0056] The rework process for defective HJT cell wafers provided by this invention first uses a mixed solution of hydrochloric acid and hydrogen peroxide to remove the thin film and grid lines on the surface of the cell; then, a mixed solution of nitric acid and hydrofluoric acid is used to treat the amorphous silicon thin film to remove the amorphous silicon layer; finally, the silicon wafer is retextured to obtain a reworked wafer that can be put back into production. Therefore, the rework process for defective HJT cell wafers provided by this invention has the following advantages: 1) It avoids the use of ozone treatment, the process is stable and easy to control, and effectively solves the rework problem of various defective wafers generated in HJT cell production; 2) The rework process can mass-produce defective HJT cell wafers, and the A-grade yield after rework can reach 98%, and the cell efficiency is comparable to that of cells produced in the normal process; 3) It effectively improves the production yield and saves more than 50% of the silicon wafer raw material cost.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A rework process for defective HJT battery cells, characterized in that: The rework process for defective HJT battery cells includes the following steps: P1 collects defective wafers and sends them to a specialized rework cleaning machine to remove the surface film. The specific process includes: P1.1 Water washing: Wash with pure water to remove impurities and dirt from the surface of defective films; P1.2 Pickling: Pickling defective sheets with a mixture of hydrochloric acid and hydrogen peroxide to remove surface metal grid lines and transparent conductive film; P1.3 Water washing: Wash with pure water to remove residual acid from the surface; P1.4 Pre-cleaning solution wash: Clean the defective film with a mixture of ammonia and hydrogen peroxide to remove impurities and dirt remaining after film removal; P1.5 Water Wash: Wash with pure water to remove the solution from the surface of the defective tablets; P1.6 CP pickling: The defective wafers are pickled with a mixed solution of nitric acid and hydrofluoric acid to remove the amorphous silicon thin film layer; P1.7 Water washing: Wash with pure water to remove the acid from the surface of the defective wafer and obtain the silicon wafer; P1.8 SC2 solution wash: Wash the silicon wafer obtained from P1.7 with SC2 solution to further remove residues; P1.9 Water washing: Wash with pure water to remove the surface solution; P1.10 Pickling: The silicon wafer is pickled with hydrofluoric acid solution to achieve dehydration; P1.11 Water washing: Wash with pure water to remove surface acid; P1.12 Slow Lifting: Use pure water for slow lifting; P1.13 Drying: The obtained silicon wafers are dried. P2. The silicon wafer obtained in P1 is put into a cleaning machine for retexturing; the retexturing temperature is 70-80℃, which is 5-10℃ lower than the conventional texturing temperature; the retexturing etching amount is <0.5g.

2. The rework process for defective HJT battery cells according to claim 1, further characterized in that: In the P1.1 water washing step, the water washing time is 30-120 seconds.

3. The rework process for defective HJT battery cells according to claim 1, further characterized in that: In the P1.2 pickling step, the hydrochloric acid and hydrogen peroxide mixture has a mass fraction of not less than 30% and a mass fraction of not less than 20%. The pickling time is 400-2000s and the pickling temperature is 30-70℃.

4. The rework process for defective HJT battery cells according to claim 1, further characterized in that: In the P1.4 pre-cleaning solution washing step, the pre-cleaning solution is a mixed solution of ammonia and hydrogen peroxide, and the cleaning time is 3 min-6 min.

5. The rework process for defective HJT battery cells according to claim 1, further characterized in that: In the P1.6 CP pickling step, the mass fraction of nitric acid and hydrofluoric acid in the mixed solution is not less than 50%, the mass fraction of hydrofluoric acid is not less than 50%, and the CP pickling time is 60-360s.

6. The rework process for defective HJT battery cells according to claim 1, further characterized in that: In the P1.8 SC2 liquid washing step, the SC2 liquid is a mixed solution of hydrochloric acid and hydrogen peroxide, with the mass fraction of hydrochloric acid not less than 30% and the mass fraction of hydrogen peroxide not less than 20%. The SC2 liquid washing temperature is 40-85℃, and the SC2 liquid washing time is 4min-6min.

7. The rework process for defective HJT battery cells according to claim 1, further characterized in that: In the P1.10 pickling step, the mass fraction of hydrofluoric acid in the hydrofluoric acid solution is not less than 50%.

8. The rework process for defective HJT battery cells according to claim 1, further characterized in that: In the slow lifting step P1.12, the temperature of the pure water is 30-60℃, and the slow lifting cleaning time is >30s.

9. The rework process for defective HJT battery cells according to claim 1, further characterized in that: In the drying step P1.13, the drying temperature is 30-90℃ and the drying time is 400-720s.

10. The rework process for defective HJT battery cells according to claim 1, further characterized in that: In the P1.3, P1.5, P1.7, P1.9 and P1.11 water washing steps, the water washing time is 90-240 seconds.

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