Reprocessing method for defect pieces after heterojunction cell CVD

Abstract

The application provides a rework process method for a defect wafer after a heterojunction cell CVD, which comprises the following steps: placing the defect wafer in an HF acid washing solution containing an oxidant to perform acid washing to remove at least part of an amorphous silicon layer, wherein the oxidant is ozone and / or hydrogen peroxide and / or hypochlorous acid and / or concentrated sulfuric acid; placing the defect wafer after acid washing in an alkali solution to perform alkali washing to remove the remaining amorphous silicon layer and obtain a silicon wafer with a flat surface, wherein the alkali in the alkali solution is potassium hydroxide or sodium hydroxide or tetramethylammonium hydroxide; the amorphous silicon layer, in particular a P-type amorphous silicon layer, can be completely removed, and a silicon wafer with a flat surface can be obtained, which is beneficial to forming a uniform texturing on the surface of the silicon wafer after subsequent texturing, and is beneficial to improving the uniformity of subsequent film plating, and further improving the cell efficiency.

Description

Technical Field

[0001] This invention relates to solar cells, and more particularly to a rework process for defective wafers after CVD of heterojunction solar cells. Background Technology

[0002] Currently, the core of large-scale development and utilization of solar photovoltaic power generation lies in improving the photoelectric conversion efficiency of solar cells and reducing their production costs. Silicon-based heterojunction solar cells with intrinsic layers can reduce silicon wafer thickness to as low as 100μm while maintaining high conversion efficiency, effectively reducing silicon material consumption. Furthermore, in the fabrication process of silicon-based heterojunction solar cells, low-temperature amorphous silicon deposition technology below 200℃ can replace the high-temperature processes in traditional crystalline silicon cell production. Therefore, it is expected to become a low-cost alternative to monocrystalline silicon cells, and has significant application prospects in realizing low-cost, high-efficiency solar cells.

[0003] Compared to PERC solar cells, the need for high-quality silicon substrates in silicon-based heterojunction solar cells is a significant factor contributing to their higher cost. Currently, silicon wafers account for nearly 40% of the cost of silicon-based heterojunction solar cells, making wafer cost control one of the effective ways to reduce overall costs. Regarding silicon wafers, silicon-based heterojunction solar cells utilize thinner wafers to reduce costs, and reworking defective wafers during the production process can further reduce cost losses associated with silicon wafers.

[0004] In the fabrication of silicon-based heterojunction solar cells, especially in the CVD process, high requirements are placed on the cleanliness and passivation effect of the silicon wafer surface. Defective wafers are easily generated due to equipment or human factors. Currently, the commonly used rework process for defective wafers after CVD is to directly remove the amorphous silicon film from the wafer surface through secondary texturing. However, secondary texturing is difficult to completely remove the amorphous silicon layer and cannot obtain a clean and uniform silicon wafer. During the re-coating process, it will contaminate the coating chamber, leading to cross-contamination within the chamber during subsequent CVD coating processes, which can easily generate more defective wafers.

[0005] In view of this, it is necessary to provide a new rework process for defective wafers after CVD of heterojunction solar cells to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a rework process for defective wafers after CVD of heterojunction solar cells, which can completely remove the amorphous silicon layer in the defective wafer and obtain a silicon wafer with a smooth surface, which is beneficial for forming a uniform textured surface on the silicon wafer after subsequent texturing.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a rework process for defective wafers after CVD of heterojunction solar cells; comprising the following steps:

[0008] The defective wafer is placed in an HF pickling solution containing an oxidant to remove at least part of the amorphous silicon layer. The oxidant is ozone and / or hydrogen peroxide and / or hypochlorous acid and / or concentrated sulfuric acid.

[0009] The acid-washed defective wafer is placed in an alkaline solution for alkaline washing to remove the remaining amorphous silicon layer and obtain a silicon wafer with a smooth surface. The alkaline solution is potassium hydroxide, sodium hydroxide, or tetramethylammonium hydroxide.

[0010] As a further improvement of the present invention, the concentration of the oxidant in the HF pickling solution containing the oxidant is 30-50 ppm.

[0011] As a further improvement of the present invention, the HF content in the HF pickling solution containing oxidant is 2% to 5% by volume.

[0012] As a further improvement of the present invention, the pickling time for "pickling the defective piece in an HF pickling solution containing an oxidant" is 180s to 240s.

[0013] As a further improvement of the present invention, the alkali content in the alkaline solution is 15% by volume.

[0014] As a further improved technical solution of the present invention, the alkaline washing temperature of "placing the acid-washed defective piece in an alkaline solution for alkaline washing" is 75℃~85℃ and the alkaline washing time is 140s~260s.

[0015] As a further improvement of the present invention, after obtaining a silicon wafer with a smooth surface, the rework process further includes the following steps: cleaning the silicon wafer in a mixture of alkali and hydrogen peroxide; wherein the alkali is potassium hydroxide, sodium hydroxide, or ammonium hydroxide.

[0016] As a further improvement to the present invention, after "cleaning the silicon wafer in a mixture of alkali and hydrogen peroxide", the rework process further includes the following steps:

[0017] The cleaned silicon wafers are then texturized to obtain silicon wafers with a textured surface.

[0018] As a further improvement to the present invention, after obtaining a textured silicon wafer, the rework process further includes the following steps:

[0019] The textured silicon wafer is placed in a mixture of alkali and hydrogen peroxide for cleaning; the alkali is potassium hydroxide, sodium hydroxide, or ammonium hydroxide.

[0020] The silicon wafers, after being cleaned by a mixture of alkali and hydrogen peroxide, are placed in a mixture of hydrochloric acid and hydrogen peroxide for acid washing.

[0021] The pickled silicon wafers are placed in HF pickling solution for pickling again.

[0022] drying.

[0023] As a further improvement of the present invention, the alkali content in the mixture of alkali and hydrogen peroxide is 1.5% and the hydrogen peroxide content is 8% by volume.

[0024] As a further improvement of the present invention, the cleaning temperature in "the silicon wafer is placed in a mixture of alkali and hydrogen peroxide for cleaning" is 60℃~70℃ and the cleaning time is 240s~360s.

[0025] The beneficial effects of this invention are as follows: In the rework process of defective wafers after CVD of heterojunction solar cells in this invention, the defective wafers are first placed in an HF pickling solution containing an oxidant for pickling before rework, which can effectively promote the removal of amorphous silicon in the P-type amorphous silicon layer. After pickling, they are placed in an alkaline solution for alkaline washing (rough polishing), which can completely remove the remaining amorphous silicon layer and obtain a silicon wafer with a smooth surface. This is beneficial for forming a uniform textured surface on the silicon wafer after texturing, which is beneficial for improving the uniformity of subsequent coating and thus improving the cell efficiency. Attached Figure Description

[0026] Figure 1 The diagram shows a flowchart of the rework process in this invention. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. Please refer to the accompanying drawings for further details. Figure 1 The figures shown represent preferred embodiments of the present invention. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent modifications or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0028] Please refer to Figure 1 As shown, the present invention provides a rework process method for defective wafers after CVD of heterojunction solar cells, comprising the following steps:

[0029] The defective wafer is placed in an HF pickling solution containing an oxidant to remove at least part of the amorphous silicon layer. The oxidant is ozone and / or hydrogen peroxide and / or hypochlorous acid and / or concentrated sulfuric acid.

[0030] The acid-washed defective wafer is placed in an alkaline solution for alkaline washing to remove the remaining amorphous silicon layer and obtain a silicon wafer with a smooth surface. The alkaline solution is potassium hydroxide, sodium hydroxide, or tetramethylammonium hydroxide.

[0031] The following description uses an example of a defective wafer after CVD of a heterojunction solar cell where the amorphous silicon layer includes an intrinsic amorphous silicon layer, a P-type amorphous silicon layer, and an N-type amorphous silicon layer. It is understood that the rework process in this invention is also applicable to the rework of defective wafers where the amorphous silicon layer consists only of an intrinsic amorphous silicon layer, or where the amorphous silicon layer includes both an intrinsic amorphous silicon layer and a P-type amorphous silicon layer, or where the amorphous silicon layer includes both an intrinsic amorphous silicon layer and an N-type amorphous silicon layer.

[0032] In this invention, the defective wafer is first pickled in an HF pickling solution containing an oxidant before rework, which effectively promotes the removal of amorphous silicon from the P-type amorphous silicon layer. After pickling, it is then placed in an alkaline solution for alkaline washing (rough polishing), which can completely remove the remaining amorphous silicon layer and obtain a silicon wafer with a smooth surface. This is beneficial for forming a uniform textured surface on the silicon wafer after texturing, which helps improve the uniformity of subsequent coatings and thus improves battery efficiency.

[0033] Specifically, during the pickling process of the defective wafer in an HF pickling solution containing an oxidizing agent, the oxidizing agent first oxidizes the silicon on the surface of the amorphous silicon layer into silicon oxide, and the silicon oxide then reacts with HF to generate S. i F4 gas and water can effectively promote the removal of amorphous silicon in the P-type amorphous silicon layer, thereby preventing boron from remaining in the P-type amorphous silicon layer in the reworked silicon wafer and contaminating the coating cavity.

[0034] Meanwhile, the oxidant used is ozone and / or hydrogen peroxide and / or hypochlorous acid and / or concentrated sulfuric acid, and the concentration of the oxidant in the HF pickling solution containing the oxidant is 30-50 ppm. That is, the oxidant content is relatively small, making the oxidation reaction relatively mild and allowing control of the reaction process, thus preventing the removal of excessive silicon wafers. Experiments have shown that the silicon wafers obtained after this rework process can have a thinning of less than 7 μm per side compared to the untreated wafers, which can adapt to the trend of wafer thinning.

[0035] Specifically, the thinning amount on each side of the silicon wafer mentioned above refers to the thinning amount on the front side and the thinning amount on the back side of the silicon wafer.

[0036] It is understandable that the above-mentioned control of the reaction process can be achieved by controlling the pickling time.

[0037] Furthermore, the pickling time is 180s to 240s. Experiments have shown that after pickling for 180s to 240s, the P-type amorphous silicon layer can be completely removed, thereby preventing boron from the P-type amorphous silicon layer from remaining in the reworked silicon wafer and contaminating the coating cavity.

[0038] In one specific embodiment, the oxidant is ozone and / or hydrogen peroxide, which is low in cost and pollution-free.

[0039] Furthermore, by volume, the HF content in the HF pickling solution containing the oxidant is 2% to 5%.

[0040] Furthermore, the alkali content in the alkaline solution is 15% by volume.

[0041] Furthermore, the alkaline washing temperature for "placing the acid-washed defective wafer in an alkaline solution for alkaline washing" is 75℃~85℃, and the alkaline washing time is 140s~260s. This can completely remove the remaining amorphous silicon layer and obtain a silicon wafer with a smooth surface, which is beneficial for forming a uniform textured surface on the silicon wafer after texturing, improving the uniformity of subsequent coatings, and thus improving battery efficiency.

[0042] Furthermore, after obtaining a smooth silicon wafer through rough polishing, the rework process further includes the following steps: cleaning the silicon wafer in a mixture of alkali and hydrogen peroxide; wherein the alkali is potassium hydroxide, sodium hydroxide, or ammonium hydroxide.

[0043] By cleaning the silicon wafer in a mixture of alkali and hydrogen peroxide, residues on the surface of the silicon wafer can be removed, resulting in a clean silicon wafer and preventing residual contamination of the coating cavity.

[0044] Specifically, by volume, the mixture of alkali and hydrogen peroxide contains 1.5% alkali and 8% hydrogen peroxide.

[0045] Specifically, the cleaning temperature in the step of "cleaning the silicon wafer in a mixture of alkali and hydrogen peroxide" is 60℃~70℃, and the cleaning time is 240s~360s. This is to remove residues from the surface of the silicon wafer and obtain a clean silicon wafer.

[0046] Furthermore, after "cleaning the silicon wafer in a mixture of alkali and hydrogen peroxide", the rework process further includes the following steps:

[0047] The cleaned silicon wafers are then texturized to obtain silicon wafers with a textured surface.

[0048] Specifically, "texturing the cleaned silicon wafers" involves placing the cleaned silicon wafers in a texturing solution and treating them at a temperature of 75℃~85℃ for 350s~480s to form a pyramidal textured surface on the silicon wafers, trapping light and reducing surface reflection.

[0049] Specifically, the texturing solution contains 3% potassium hydroxide or sodium hydroxide.

[0050] Furthermore, after "obtaining a silicon wafer with a textured surface", the rework process further includes the following steps:

[0051] The textured silicon wafer is placed in a mixture of alkali and hydrogen peroxide for cleaning; the alkali is potassium hydroxide, sodium hydroxide, or ammonium hydroxide.

[0052] The silicon wafers, after being cleaned by a mixture of alkali and hydrogen peroxide, are placed in a mixture of hydrochloric acid and hydrogen peroxide for acid washing.

[0053] The pickled silicon wafers are placed in HF pickling solution for pickling again.

[0054] drying.

[0055] Specifically, by cleaning the textured silicon wafer in a mixture of alkali and hydrogen peroxide, organic residues and particulate contamination on the surface of the silicon wafer can be removed.

[0056] Specifically, by volume, the mixture of alkali and hydrogen peroxide contains 1.5% alkali and 8% hydrogen peroxide.

[0057] Specifically, the cleaning temperature in the step of "cleaning the textured silicon wafer in a mixture of alkali and hydrogen peroxide" is 60°C to 70°C, and the cleaning time is 240s to 360s.

[0058] Furthermore, placing the silicon wafers, after being cleaned with a mixture of alkali and hydrogen peroxide, into a mixture of hydrochloric acid and hydrogen peroxide for pickling can remove residual metal ions from the silicon wafer surface and prevent residual metal ions from contaminating the coating cavity.

[0059] Specifically, by volume, the mixture containing hydrochloric acid and hydrogen peroxide contains 1.5% hydrochloric acid and 8% hydrogen peroxide.

[0060] Furthermore, the pickling temperature in the phrase "the silicon wafers cleaned with a mixture of alkali and hydrogen peroxide are placed in a mixture of hydrochloric acid and hydrogen peroxide for pickling" is 60℃~70℃, and the pickling time is 240s~360s.

[0061] The pickled silicon wafers are placed in HF pickling solution for a second pickling to remove the oxide layer on the silicon wafer surface, making the silicon wafer surface hydrophobic and obtaining a clean textured surface.

[0062] Specifically, by volume, the HF pickling solution contains 2% to 5% HF, and the pickled silicon wafer is placed in the HF pickling solution and pickled again at room temperature for 120 to 240 seconds.

[0063] Further, the drying step specifically involves drying the silicon wafer after the second acid washing at a temperature of 70°C to 90°C for at least 700 seconds.

[0064] The dried silicon wafer can be directly used for the fabrication of heterojunction solar cells.

[0065] Specifically, the fabrication of heterojunction solar cells includes the following steps:

[0066] Using the PECVD process, intrinsic amorphous silicon layers are deposited on the front and back sides of the dried silicon wafer, and then P-type amorphous silicon layers and N-type amorphous silicon layers are deposited on the surfaces of the two intrinsic amorphous silicon layers, respectively.

[0067] TCO conductive films were deposited on the surfaces of P-type and N-type amorphous silicon layers using PVD / RPD processes.

[0068] Metal electrodes are formed on the surface of the TCO conductive film using a screen printing process.

[0069] In summary, in the rework process of defective wafers after CVD of heterojunction solar cells in this invention, the defective wafers are first pickled in an HF pickling solution containing an oxidant before rework, which can effectively promote the removal of amorphous silicon in the P-type amorphous silicon layer. After pickling, they are then placed in an alkaline solution for alkaline washing (rough polishing), which can completely remove the remaining amorphous silicon layer and obtain a silicon wafer with a smooth surface. This is beneficial for forming a uniform textured surface on the silicon wafer after texturing, which helps to improve the uniformity of subsequent coating and thus improve the cell efficiency.

[0070] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0071] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A rework process for defective wafers after CVD of heterojunction solar cells; characterized in that: The rework process includes the following steps: The defective wafer is placed in an HF pickling solution containing an oxidant to remove at least part of the amorphous silicon layer. The oxidant is ozone and / or hydrogen peroxide and / or hypochlorous acid and / or concentrated sulfuric acid. The acid-washed defective wafer is placed in an alkaline solution for alkaline washing to remove the remaining amorphous silicon layer and obtain a silicon wafer with a smooth surface. The alkali in the alkaline solution is potassium hydroxide, sodium hydroxide, or tetramethylammonium hydroxide. The alkali content in the alkaline solution is 15% by volume. The alkaline washing temperature is 75℃~85℃ and the alkaline washing time is 140s~260s.

2. The rework process for defective wafers after CVD of heterojunction solar cells as described in claim 1, characterized in that: The concentration of the oxidant in the HF pickling solution containing the oxidant is 30~50 ppm.

3. The rework process method for defective wafers after CVD of heterojunction solar cells as described in claim 1, characterized in that: The HF content in the HF pickling solution containing oxidant is 2% to 5% by volume.

4. The rework process for defective wafers after CVD of heterojunction solar cells as described in claim 1, characterized in that: The pickling time for "pickling the defective piece in an HF pickling solution containing an oxidant" is 180 s to 240 s.

5. The rework process method for defective wafers after CVD of heterojunction solar cells as described in claim 1, characterized in that: After obtaining a silicon wafer with a smooth surface, the rework process further includes the following steps: cleaning the silicon wafer in a mixture of alkali and hydrogen peroxide; the alkali is potassium hydroxide, sodium hydroxide, or ammonium hydroxide.

6. The rework process method for defective wafers after CVD of heterojunction solar cells as described in claim 5, characterized in that: After "cleaning the silicon wafer in a mixture of alkali and hydrogen peroxide", the rework process further includes the following steps: The cleaned silicon wafers are then texturized to obtain silicon wafers with a textured surface.

7. The rework process method for defective wafers after CVD of heterojunction solar cells as described in claim 6, characterized in that: After obtaining a textured silicon wafer, the rework process further includes the following steps: The textured silicon wafer is placed in a mixture of alkali and hydrogen peroxide for cleaning; the alkali is potassium hydroxide, sodium hydroxide, or ammonium hydroxide. The silicon wafers, after being cleaned by a mixture of alkali and hydrogen peroxide, are placed in a mixture of hydrochloric acid and hydrogen peroxide for acid washing. The pickled silicon wafers are placed in HF pickling solution for pickling again. drying.

8. The rework process method for defective wafers after CVD of heterojunction solar cells as described in claim 5 or 7, characterized in that: By volume, the mixture of alkali and hydrogen peroxide contains 1.5% alkali and 8% hydrogen peroxide.

9. The rework process for defective wafers after CVD of heterojunction solar cells as described in claim 5 or 7, characterized in that: The cleaning temperature in the phrase "the silicon wafer is placed in a mixture of alkali and hydrogen peroxide for cleaning" is 60℃~70℃, and the cleaning time is 240s~360s.

Images