A method for removing the plating on the front side of an N-type TOPCon battery

Abstract

The present invention relates to the technical field of solar cells, and in particular to a method for removing the front winding plating of an N-type TOPCon cell, comprising the following steps: step one, immersing the front of a silicon wafer after ultra-thin silicon oxide and polysilicon deposition and back phosphorus doping in a mixed acid solution of HF and HNO3 for pickling, the pickling time being 1 to 10 minutes; step two, immersing the entire silicon wafer after pickling in an alkaline solution with a concentration of 0.5% to 5% for alkali washing, the alkali washing time being 1 to 15 minutes; step three, immersing the alkali-washed silicon wafer in an HF solution with a concentration of 5% to 10% for cleaning, the cleaning time being 1 to 10 minutes. The present invention is simple to operate, can completely remove the phosphorus silicon glass layer in the front winding plating and the thin middle and thick edge Poly-Si layer, can also completely remove the borosilicate glass layer and the phosphorus-boron co-doped glass layer, and will not appear due to the surface being unqualified due to not being cleaned or excessively corroded, thereby greatly improving the qualified rate of the battery.

Description

Technical Field

[0001] The invention relates to the technical field of solar cells, and in particular to a method for removing wrap-around plating on the front side of an N-type TOPCon cell. Background Art

[0002] TOPCon (Tunnel Oxide Passivated Contact) cell is a solar cell with a new type of passivation contact technology. This cell has the characteristics of good stability and high conversion rate, and is the current development trend of high-efficiency N-type cells. This technology is based on an N-type silicon substrate, with a stacked film passivation process on the front surface and a tunnel oxide layer passivation contact structure based on ultra-thin silicon oxide and doped polysilicon (Poly-Si) on the back surface. This structure enables majority carriers to penetrate the oxide layer and block minority carriers, effectively realizing the selective permeability of carriers and greatly reducing the recombination rate of minority carriers. It can not only achieve a surface passivation effect equivalent to that of a heterostructure, but also be compatible with high-temperature processes and avoid the high recombination problem caused by the electrode contact.

[0003] However, a major problem faced by high-efficiency cells of this structure in the industrial production process is that the back surface will form a wrap-around plating on the front surface during the deposition of ultra-thin silicon oxide and doped polysilicon. If the front wrap-around plating is not removed or not removed cleanly, the passivation characteristics of the front side of the cell will be reduced, thereby affecting the conversion efficiency of the cell end. The front wrap-around plating of the N-type TOPCon cell includes a borosilicate glass layer, a Poly-Si layer, and a phosphorus silicon glass layer, wherein the Poly-Si layer is not evenly distributed on the entire front surface, i.e., it is thin in the middle and thick at the edge. At present, the Poly-Si layer in the front wrap-around plating is mainly removed by pickling in the industrial production process, but the wrap-around plating formed on the front side of some silicon wafers also contains a phosphorus-boron co-doped glass layer. Since the phosphorus-boron co-doped glass layer and the Poly-Si layer are corroded at different rates by chemical reagents, and the thickness of the phosphorus-boron co-doped glass layer and the Poly-Si layer are also different, the silicon wafer containing the phosphorus-boron co-doped glass layer in the front wrap-around plating is often not cleaned cleanly or excessively corroded, resulting in unqualified surface conditions, which leads to a lower qualified rate of TOPCon cells than PERC cells. Summary of the invention

[0004] Based on the above problems existing in the prior art, the present invention provides a method for removing the front-side winding plating of an N-type TOPCon battery. The method is simple to operate, and when removing the silicon wafer containing the phosphorus-boron co-doped glass layer in the front-side winding plating, the method can not only completely remove the phosphorus-silicate glass layer and the Poly-Si layer which is thin in the middle and thick at the edge in the front-side winding plating, but also completely remove the borosilicate glass layer and the phosphorus-boron co-doped glass layer, and will not cause the surface to be unqualified due to insufficient cleaning or excessive corrosion, thereby greatly improving the qualified rate of the battery and overcoming the defects of the prior art.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0006] In a first aspect, an embodiment of the present invention provides a method for removing the front-side wrap-around plating of an N-type TOPCon battery, comprising the following steps:

[0007] Step 1: immerse the front side of the silicon wafer after back-side ultra-thin silicon oxide and polysilicon deposition and back-side phosphorus doping in HF and HNO 3 The mixed acid solution is pickled for 1 to 10 minutes;

[0008] Step 2: immersing the entire acid-washed silicon wafer in an alkali solution with a concentration of 0.5wt% to 5wt% for alkali washing for 1 to 15 minutes;

[0009] Step 3: Immerse the alkali-washed silicon wafer in a 5% to 10% v / v HF solution for cleaning, and the cleaning time is 1 to 10 minutes.

[0010] The method for removing the front side plating of the N-type TOPCon battery of the present invention firstly uses HF and HNO 3 The front side of the silicon wafer after ultra-thin silicon oxide and polysilicon deposition and back side phosphorus doping was pickled with mixed acid, HF and HNO 3The reaction rate of the mixed acid with each part of the front winding plating is: Poly-Si layer>phosphorus silicon glass layer>phosphorus boron co-doped glass layer>borosilicate glass layer. The present invention controls the concentration of the mixed acid and the pickling time, while ensuring that the front of the silicon wafer is not damaged, so that the phosphorus silicon glass layer in the front winding plating is completely removed, and part of the Poly-Si layer, borosilicate glass layer and phosphorus boron co-doped glass layer are removed. Then, a low-concentration alkali solution is used to immerse the silicon wafer. Since the back of the silicon wafer is protected by the phosphorus silicon glass, the back of the silicon wafer will not react with the alkali solution, and the Poly-Si layer remaining in the front winding plating is completely removed by the alkali solution. Finally, the alkali-washed silicon wafer is immersed in an HF solution. By controlling the concentration of the HF solution and the cleaning time, the borosilicate glass layer, phosphorus boron co-doped glass layer and the phosphorus silicon glass layer on the back of the silicon wafer can be completely removed while ensuring that the front of the silicon wafer is not damaged. The present invention adopts the method of acid washing, alkali washing and acid washing again, which can not only completely remove the phosphosilicate glass layer and the thin middle and thick edge Poly-Si layer in the front side plating, but also completely remove the borosilicate glass layer and the phosphorus-boron co-doped glass layer, and will not cause surface unqualified due to insufficient cleaning or excessive corrosion, thereby greatly improving the qualified rate of the battery.

[0011] Preferably, HF, HNO 3 The volume ratio of the aqueous solution to deionized water is 2-10:125-135:65, and the cleaning time is 2-8 minutes.

[0012] Preferably, HF, HNO 3 The volume ratio of the deionized water is 4-10:128-130:65, and the cleaning time is 3-5 minutes.

[0013] The present invention controls HF, HNO 3 The volume ratio of deionized water and the pickling time are used to control the corrosion rate of the front side coating, while ensuring that the front side of the silicon wafer is not damaged, so that the phosphorus silicon glass layer in the front side coating is completely removed without being over-corroded.

[0014] Preferably, in step 2, the alkaline solution is a KOH aqueous solution or a NaOH aqueous solution.

[0015] Preferably, the concentration of the alkaline solution is 2 wt% to 4 wt%.

[0016] Preferably, the temperature of the alkaline solution is 50-80° C., and the alkaline washing time is 2-10 min.

[0017] By controlling the concentration, temperature and alkali washing time of the alkali solution, the Poly-Si layer remaining in the front-side plating can be quickly removed without corroding the borosilicate glass layer and the phosphorus-boron co-doped glass layer.

[0018] Preferably, in step three, the concentration of the HF solution is 5% to 8% v / v, and the cleaning time is 2 to 6 minutes.

[0019] By controlling the concentration of the HF solution and the cleaning time, the borosilicate glass layer and the phosphorus-boron co-doped glass layer remaining on the front side of the silicon wafer and the phosphorus-silicon glass layer on the back side of the silicon wafer can be completely removed without damaging the front side of the silicon wafer.

[0020] On the other hand, an embodiment of the present invention further provides an application of the above-mentioned method for removing the front-side plating of an N-type TOPCon battery in the preparation of an N-type TOPCon battery.

[0021] The normal process flow for preparing TOPCon cells is: 1. Alkaline texturing; 2. Front boron diffusion; 3. Back diffusion removal and cleaning; 4. Back ultra-thin oxide layer and polysilicon deposition; 5. Back phosphorus doping; 6. Front de-plating and glass removal and cleaning; 7. Front and back passivation; 8. Screen printing electrodes and sintering. The present invention is an improvement on step 6, and the other steps are carried out completely according to the normal process flow for preparing TOPCon cells.

[0022] The present invention removes the front side plating of the N-type TOPCon battery by first acid washing and then alkali washing. The corrosion rate of the front side plating is controlled by controlling the volume ratio of the mixed acid, the concentration, temperature and alkali washing time of the alkali solution, and the concentration and cleaning time of the HF solution. The phosphosilicate glass layer, the borosilicate glass layer and the thinner phosphorus-boron co-doped glass layer in the front side plating can be completely removed, and the Poly-Si layer that is thin in the middle and thick at the edge can be removed. There will be no surface unqualified situation due to incomplete cleaning or excessive corrosion, the occurrence of unqualified products and low-quality products is reduced, which is conducive to improving the qualified rate of the battery, and further improving the market competitiveness of the N-type TOPCon battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the front surface structure after ultra-thin silicon oxide and polysilicon deposition and back phosphorus doping in the process of preparing TOPCon cells;

[0024] Figure 2 This is the front appearance of the silicon wafer after ultra-thin silicon oxide and polysilicon deposition and back phosphorus doping;

[0025] Figure 3 This is a front view of a silicon wafer with an unqualified surface due to excessive corrosion at the edge of the plating.

[0026] Figure 4 This is a front appearance diagram of a silicon wafer after the wrap-around plating is removed and cleaned using the method for removing the wrap-around plating on the front side of an N-type TOPCon battery of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] The silicon wafers treated in the following embodiments and comparative examples after ultra-thin silicon oxide and polysilicon deposition and back phosphorus doping are all obtained according to the normal process flow for preparing TOPCon cells (1. alkali texturing; 2. front boron diffusion; 3. back diffusion removal and cleaning; 4. back ultra-thin oxide layer and polysilicon deposition; 5. back phosphorus doping), and the silicon wafer raw materials and process parameters of each step in the process flow are the same, and the process parameters of the front and back passivation steps, i.e., the subsequent steps, are also the same.

[0029] Example 1

[0030] This embodiment provides a method for removing the front-side wrap-around plating of an N-type TOPCon battery, comprising the following steps:

[0031] (1) Immerse the front side of the silicon wafer after back-side ultra-thin silicon oxide and polysilicon deposition and back-side phosphorus doping in HF and HNO 3 The mixed acid solution contains HF, HNO 3 The volume ratio of 2:130:65 and deionized water is 3min.

[0032] (2) The acid-washed silicon wafer is immersed in a KOH aqueous solution for alkaline washing. The concentration of the KOH aqueous solution is 0.5 wt %, the temperature of the KOH aqueous solution is 80° C., and the washing time is 2 min.

[0033] (3) The alkali-washed silicon wafer is immersed in a 10% v / v HF solution for cleaning for 1 min.

[0034] (4) The silicon wafer obtained in step (3) enters the normal TOPCon battery production process starting from the front and back passivation process.

[0035] Example 2

[0036] This embodiment provides a method for removing the front-side wrap-around plating of an N-type TOPCon battery, comprising the following steps:

[0037] (1) Immerse the front side of the silicon wafer after back-side ultra-thin silicon oxide and polysilicon deposition and back-side phosphorus doping in HF and HNO 3 The mixed acid solution contains HF, HNO 3 The volume ratio of iodine to deionized water is 10:125:65, and the cleaning time is 1 min.

[0038] (2) The acid-washed silicon wafer is immersed in a KOH aqueous solution for alkaline washing. The concentration of the KOH aqueous solution is 2.5 wt %, the temperature of the KOH aqueous solution is 50° C., and the washing time is 5 min.

[0039] (3) The alkali-washed silicon wafer was immersed in a 5% v / v HF solution for cleaning for 9 minutes.

[0040] (4) The silicon wafer obtained in step (3) enters the normal TOPCon battery production process starting from the front and back passivation process.

[0041] Example 3

[0042] This embodiment provides a method for removing the front-side wrap-around plating of an N-type TOPCon battery, comprising the following steps:

[0043] (1) Immerse the front side of the silicon wafer after back-side ultra-thin silicon oxide and polysilicon deposition and back-side phosphorus doping in HF and HNO 3 The mixed acid solution contains HF, HNO 3 The volume ratio of deionized water is 8:128:65, and the cleaning time is 5 minutes.

[0044] (2) The acid-washed silicon wafer is immersed in a KOH aqueous solution for alkaline washing. The concentration of the KOH aqueous solution is 2 wt %, the temperature of the KOH aqueous solution is 80° C., and the washing time is 1 min.

[0045] (3) The alkali-washed silicon wafer is immersed in an 8% v / v HF solution for cleaning for 2 minutes.

[0046] (4) The silicon wafer obtained in step (3) enters the normal TOPCon battery production process starting from the front and back passivation process.

[0047] Example 4

[0048] This embodiment provides a method for removing the front-side wrap-around plating of an N-type TOPCon battery, comprising the following steps:

[0049] (1) Immerse the front side of the silicon wafer after back-side ultra-thin silicon oxide and polysilicon deposition and back-side phosphorus doping in HF and HNO 3 The mixed acid solution contains HF, HNO 3 The volume ratio of 2-nitropropene and deionized water is 4:130:65, and the cleaning time is 6 min.

[0050] (2) The acid-washed silicon wafer is immersed in a NaOH aqueous solution for alkaline washing. The concentration of the NaOH aqueous solution is 4 wt %, the temperature of the NaOH aqueous solution is 50° C., and the washing time is 8 min.

[0051] (3) The alkali-washed silicon wafer is immersed in a 6% v / v HF solution for cleaning for 10 minutes.

[0052] (4) The silicon wafer obtained in step (3) enters the normal TOPCon battery production process starting from the front and back passivation process.

[0053] Example 5

[0054] This embodiment provides a method for removing the front-side wrap-around plating of an N-type TOPCon battery, comprising the following steps:

[0055] (1) Immerse the front side of the silicon wafer after back-side ultra-thin silicon oxide and polysilicon deposition and back-side phosphorus doping in HF and HNO 3 The mixed acid solution contains HF, HNO 3 The volume ratio of sodium bicarbonate and deionized water is 3:135:65, and the cleaning time is 10 min.

[0056] (2) The acid-washed silicon wafer is immersed in a NaOH aqueous solution for alkaline washing. The concentration of the NaOH aqueous solution is 3 wt %, the temperature of the NaOH aqueous solution is 80° C., and the washing time is 15 min.

[0057] (3) The alkali-washed silicon wafer is immersed in a 9% v / v HF solution for cleaning for 8 minutes.

[0058] (4) The silicon wafer obtained in step (3) enters the normal TOPCon battery production process starting from the front and back passivation process.

[0059] Example 6

[0060] This embodiment provides a method for removing the front-side wrap-around plating of an N-type TOPCon battery, comprising the following steps:

[0061] (1) Immerse the front side of the silicon wafer after back-side ultra-thin silicon oxide and polysilicon deposition and back-side phosphorus doping in HF and HNO 3 The mixed acid solution contains HF, HNO 3 The volume ratio of deionized water is 9:134:65, and the cleaning time is 8 minutes.

[0062] (2) The acid-washed silicon wafer is immersed in a NaOH aqueous solution for alkaline washing. The concentration of the NaOH aqueous solution is 5 wt %, the temperature of the NaOH aqueous solution is 65° C., and the washing time is 10 min.

[0063] (3) The alkali-washed silicon wafer is immersed in a 7% v / v HF solution for cleaning for 6 minutes.

[0064] (4) The silicon wafer obtained in step (3) enters the normal TOPCon battery production process starting from the front and back passivation process.

[0065] Comparative Example 1

[0066] This comparative example provides a method for removing the front-side wrap-around plating of an N-type TOPCon battery that has been tested during the research process, including the following steps:

[0067] (1) The front side of the silicon wafer after back side ultra-thin silicon oxide and polysilicon deposition and back side phosphorus doping is immersed in HF solution for pickling at a concentration of 8% v / v for 2 minutes.

[0068] (2) The acid-washed silicon wafer is immersed in a KOH aqueous solution for alkaline washing. The concentration of the KOH aqueous solution is 2 wt %, the temperature of the KOH aqueous solution is 80° C., and the washing time is 1 min.

[0069] (3) The silicon wafer obtained in step (2) enters the normal TOPCon battery production process starting from the front and back passivation process.

[0070] Comparative Example 2

[0071] This comparative example provides a method for removing the front-side wrap-around plating of an N-type TOPCon battery that has been tested during the research process, including the following steps:

[0072] (1) Immerse the front side of the silicon wafer after back-side ultra-thin silicon oxide and polysilicon deposition and back-side phosphorus doping in HF and HNO 3 The mixed acid solution contains HF, HNO 3 The volume ratio of deionized water is 8:128:65, and the cleaning time is 5 minutes.

[0073] (2) The silicon wafer obtained in step (1) enters the normal TOPCon cell production process starting from the front and back passivation process.

[0074] The battery efficiency of the batteries prepared in Examples 1-4 and Comparative Examples 1-2 was tested, and the specific test results are shown in Table 1.

[0075] Table 1

[0076]

[0077]

[0078] According to the results in Table 1, when removing the silicon wafer containing the phosphorus-boron co-doped glass layer during the front-side coating, Examples 1-6 can not only completely remove the phosphorus-silicate glass layer and the thin middle and thick edge Poly-Si layer during the front-side coating, but also completely remove the borosilicate glass layer and the phosphorus-boron co-doped glass layer, and there will be no surface unqualified situation due to insufficient cleaning or excessive corrosion. When the methods of Comparative Examples 1 and Comparative Examples 2 are used to remove the silicon wafer containing the phosphorus-boron co-doped glass layer during the front-side coating, the surface unqualified situation due to insufficient cleaning and excessive corrosion will occur. This shows that the method provided by the present invention can improve the qualified rate of the battery.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for removing the front-side plating of an N-type TOPCon battery, characterized in that: The steps include: Step 1, immersing the front side of the silicon wafer after back ultra-thin silicon oxide and polysilicon deposition and back phosphorus doping in a mixed acid solution of HF and HNO3 for pickling to remove all the phosphorus silicon glass layer and part of the Poly-Si layer, borosilicate glass layer and phosphorus-boron co-doped glass layer in the front side coating, the pickling time is 1 to 10 minutes; the volume ratio of HF, HNO3 and deionized water in the mixed acid solution is 2 to 10:125 to 135:65; Step 2: immerse the entire silicon wafer after acid washing in an alkaline solution with a concentration of 0.5wt% to 5wt% for alkaline washing to remove the Poly-Si layer remaining in the front side plating, and the alkaline washing time is 1 to 15 minutes; the alkaline solution is a KOH aqueous solution or a NaOH aqueous solution; Step three, immerse the alkali-washed silicon wafer in a 5% to 10% v / v HF solution to remove the borosilicate glass layer, phosphorus-boron co-doped glass layer and phosphorus-silicon glass layer on the front of the silicon wafer and the back of the silicon wafer. The cleaning time is 1 to 10 minutes.

2. The method for removing the front-side winding plating of an N-type TOPCon battery according to claim 1, characterized in that: In step 1, the pickling time is 2 to 8 minutes.

3. The method for removing the front-side winding plating of an N-type TOPCon battery as claimed in claim 2, characterized in that: The volume ratio of HF, HNO3 and deionized water in the mixed acid solution is 4-10:128-130:65, and the cleaning time is 3-5 minutes.

4. The method for removing the front-side winding plating of an N-type TOPCon battery according to claim 1, characterized in that: The concentration of the alkaline solution is 2 wt% to 4 wt%.

5. The method for removing the front-side wrap-around plating of an N-type TOPCon battery as claimed in claim 4, characterized in that: The temperature of the alkaline solution is 50-80° C., and the alkaline washing time is 2-10 minutes.

6. The method for removing the front-side wrap-around plating of an N-type TOPCon battery as claimed in claim 1, characterized in that: In step 3, the concentration of the HF solution is 5% to 8% v / v, and the cleaning time is 2 to 6 minutes.

7. Use of the method for removing the front-side winding plating of an N-type TOPCon battery according to any one of claims 1 to 6 in the preparation of an N-type TOPCon battery.

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