Method for the production of a surface reinforced silicon wafer substrate for photovoltaic cells

Abstract

The application relates to the technical field of photovoltaic cells, in particular to a preparation method of a surface-strengthened silicon wafer substrate of a photovoltaic cell. After texturing of a silicon wafer substrate, twice surface-strengthening treatment is carried out to obtain a surface-strengthened silicon wafer substrate. The twice surface-strengthening treatment specifically comprises: in the first surface-strengthening treatment, etching solution A is used to round and smooth the surface morphology defects of the silicon wafer substrate; and in the second surface-strengthening treatment, etching solution B is used to smooth the surface lattice defects of the silicon wafer substrate. The acidic etching solution B comprises hydrofluoric acid, an oxidizing agent and deionized water, and the oxidizing agent is a combination of one or several of nitro compounds and nitroso compounds. The beneficial effect is that the twice surface-strengthening treatment improves the bending fracture strength of the silicon wafer substrate and finally improves the bending fracture strength of the crystalline silicon photovoltaic cell; the method can be completed without using special equipment, has the advantages of low production cost and suitability for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic cell technology, and in particular to a method for preparing a surface-strengthened silicon wafer substrate for photovoltaic cells. Background Technology

[0002] Currently, most photovoltaic modules are encapsulated using high-efficiency crystalline silicon photovoltaic cells. Common high-efficiency crystalline silicon photovoltaic cells include PERC cells, TOPCon cells, and HJT cells. HJT cells are typically made using a double-sided pyramid-textured silicon wafer substrate; PERC and TOPCon cells typically have a pyramid-textured front and a polished pyramid-textured back. The pyramid-textured surface has pyramid apex, pyramid edges, and pyramid-base junctions; the polished pyramid-textured surface also has pyramid edges and pyramid-base junctions. These areas are prone to stress concentration when the silicon wafer substrate is subjected to bending stress, leading to wafer substrate breakage.

[0003] When photovoltaic modules are subjected to impact, vibration, or bending during use, the crystalline silicon photovoltaic cells in the modules are prone to microcracks and fragmentation due to bending stress, which leads to a decrease in module performance and reliability.

[0004] Therefore, measures need to be taken to reduce the likelihood of photovoltaic modules developing microcracks and fragments when subjected to bending, vibration, and impact.

[0005] The bending fracture strength of photovoltaic cells is determined by the silicon wafer substrate. In existing technologies, to address this issue, techniques are employed to smooth, passivate, or polish the edges of the texturized silicon wafer substrate, thereby improving its bending fracture strength. However, this requires additional processing steps and is difficult to implement. Summary of the Invention

[0006] The technical problem to be solved by this invention is that the surface strength of existing crystalline silicon photovoltaic cells is relatively low, and they are prone to microcracks and fragmentation when subjected to bending, impact, and vibration.

[0007] The technical solution adopted by the present invention to solve its technical problem is: a method for preparing a surface-strengthened silicon wafer substrate for photovoltaic cells, wherein the silicon wafer substrate is texturized and then subjected to two surface strengthening treatments to obtain a surface-strengthened silicon wafer substrate. The two surface strengthening treatments are: in the first surface strengthening treatment, etching solution A is used to smooth the surface morphology defects of the silicon wafer substrate, and in the second surface strengthening treatment, etching solution B is used to smooth the surface lattice defects of the silicon wafer substrate.

[0008] Etching solution B is an acidic etching solution. The acidic etching solution B contains hydrofluoric acid, an oxidant, and deionized water. The oxidant is one or a combination of nitro compounds and nitroso compounds.

[0009] In some embodiments, the etching solution A may be an alkaline etching solution or an acidic etching solution.

[0010] In some embodiments, the etching solution A is optionally an alkaline etching solution, wherein the alkaline etching solution A contains 0.5 to 10 wt% inorganic alkali and the balance is deionized water;

[0011] The etching temperature for the first surface strengthening treatment is 20–40℃, and the time is 1–10 min.

[0012] The inorganic base is one or a combination of two of NaOH and KOH.

[0013] In some embodiments, optionally, the alkaline etching solution A further comprises 0.1 to 1 vol% additive A1, wherein additive A1 comprises 0.1 to 1 wt% chelating agent and 0.1 to 5 wt% surfactant, with the balance being deionized water.

[0014] In some embodiments, the etching solution A is optionally an acidic etching solution, which comprises 0.2 to 20 wt% hydrofluoric acid, 2 to 30 wt% hydrochloric acid and 0.5 to 10 wt% oxidant, with the balance being deionized water.

[0015] The etching temperature for the first surface strengthening treatment is 5–30℃, and the time is 0.5–10 min.

[0016] The oxidizing agent is one or a combination of several of the following: persulfate, hypochlorite, chlorite, perchlorate, bromate, iodate, and peracetate.

[0017] In some embodiments, optionally, the acidic etching solution B comprises 0.5 to 10 wt% hydrofluoric acid and 1 to 10 wt% oxidant, with the balance being deionized water;

[0018] The etching temperature during the second surface strengthening treatment is 5–30℃, and the time is 0.5–10 min.

[0019] In some embodiments, the acidic etching solution B may optionally contain 0.1 to 5 wt% surfactant.

[0020] In some embodiments, the etching solution A may be an acidic etching solution, wherein the acidic etching solution A is a mixed solution of hydrofluoric acid and nitric acid, or the acidic etching solution A is a mixed solution of hydrofluoric acid and ozone.

[0021] In some embodiments, optionally, the photovoltaic cell is a TOPCon cell, including the following steps:

[0022] Step S1: Texturing the silicon wafer substrate to form a pyramidal textured surface on the silicon wafer substrate;

[0023] Step S2: Boron diffusion is performed on the texturized silicon wafer substrate to form a boron-doped emitter layer on the surface of the silicon wafer substrate;

[0024] Step S3: Perform single-sided BSG film removal and alkaline polishing on the boron-diffused silicon wafer substrate to form a boron-doped textured surface on the front side of the silicon wafer substrate and an undoped polishing tower-based textured surface on the back side.

[0025] Step S4: Perform two surface strengthening treatments on the silicon wafer substrate after back-side polishing.

[0026] The beneficial effects of this invention are: by performing two surface strengthening treatments, the bending fracture strength of the silicon wafer substrate is improved, and ultimately the bending fracture strength of the crystalline silicon photovoltaic cell is increased. Specifically, in the first surface strengthening treatment, the surface morphology defects of the silicon wafer substrate are smoothed to reduce the stress concentration points on the surface of the textured silicon wafer substrate, thereby improving the bending fracture strength of the silicon wafer substrate. In the second surface strengthening treatment, the surface lattice defects of the silicon wafer substrate are smoothed to reduce the potential microcrack points on the surface of the textured silicon wafer substrate, thereby further improving the bending fracture strength of the silicon wafer substrate.

[0027] Compared to existing technologies that round, passivate, or polish the edges of texturized silicon wafer substrates, this solution only requires simple adjustments to existing wet cleaning equipment and processes. It does not require the addition of coating, PECVD mask, or plasma edge etching equipment. The method is simple, easy to implement, and has the advantages of lower production costs and suitability for large-scale production.

[0028] Textured surfaces of silicon wafer substrates with different morphological characteristics, especially textured surfaces of monocrystalline silicon wafer substrates, including positive pyramid textured surfaces, inverted pyramid textured surfaces, polished pyramid textured surfaces, and black silicon textured surfaces, can significantly improve their bending fracture strength.

[0029] Suitable for improving the bending strength of different types of crystalline silicon photovoltaic cells, including HJT, PERC, TOPCon, and BC cells. Attached Figure Description

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments;

[0031] Figure 1 This is a flowchart illustrating the preparation method of the surface-strengthened silicon wafer substrate for photovoltaic cells according to the present invention. Detailed Implementation

[0032] like Figure 1As shown, a method for preparing a surface-strengthened silicon wafer substrate for photovoltaic cells involves texturing the silicon wafer substrate and then performing two surface strengthening treatments to obtain a surface-strengthened silicon wafer substrate. The two surface strengthening treatments are as follows: in the first surface strengthening treatment, etching solution A is used to smooth the surface morphology defects of the silicon wafer substrate, and in the second surface strengthening treatment, etching solution B is used to smooth the surface lattice defects of the silicon wafer substrate.

[0033] Etching solution A selectively etches surface morphology defects such as textured surfaces on the silicon wafer substrate, achieving a smooth surface finish for these defects. Etching solution B, using a low etching rate (approximately 1 / 5 to 1 / 100 of etching solution A), selectively etches surface lattice defects on the silicon wafer substrate, achieving a smooth surface finish for these defects.

[0034] Etching solution B is an acidic etching solution containing hydrofluoric acid, an oxidant, and deionized water. The oxidant reacts with the silicon substrate to form silicon oxide on its surface. The hydrofluoric acid then reacts with the silicon oxide to etch it away. A weak oxidant is used, resulting in a slow etching rate for etching solution B. This allows for selective etching of surface lattice defects on the silicon substrate, achieving a smoothing effect on these defects.

[0035] Etching solution A is either an alkaline etching solution or an acidic etching solution.

[0036] The first approach to performing two surface strengthening treatments on a silicon wafer substrate after texturing is as follows.

[0037] A method for preparing a surface-strengthened silicon wafer substrate for photovoltaic cells involves texturing the silicon wafer substrate and then performing two surface strengthening treatments to obtain a surface-strengthened silicon wafer substrate. The two surface strengthening treatments are as follows: in the first surface strengthening treatment, etching solution A is used to smooth the surface morphology defects of the silicon wafer substrate, and in the second surface strengthening treatment, etching solution B is used to smooth the surface lattice defects of the silicon wafer substrate.

[0038] The etching solution A used in the first surface strengthening treatment is an alkaline etching solution. The alkaline etching solution A contains 0.5-10 wt% inorganic alkali and 0.1-1 vol% additive A1, with the remainder being deionized water.

[0039] The etching temperature for the first surface strengthening treatment is 20–40℃, and the time is 1–10 min.

[0040] The inorganic base is one or a combination of two of NaOH and KOH;

[0041] Additive A1 contains 0.1–1 wt% chelating agent and 0.1–5 wt% surfactant, with the balance being deionized water.

[0042] The chelating agent is one or a combination of several of the following: polyphosphates, aminocarboxylic acids, hydroxycarboxylic acids, hydroxyaminocarboxylic acids, organic polyphosphonic acids, and polycarboxylic acid compounds. The chelating agent can complex trace metal elements in the etching tank, preventing metal ions from being reduced and deposited on the silicon substrate surface or from combining with sodium silicate to form insoluble silicate precipitates.

[0043] The surfactant in additive A1 is one or a combination of several of the following: sodium dodecyl sulfate, fatty alcohol ether sulfate, fatty alcohol ether carboxylate, fatty acid methyl ester sulfonate, fatty alcohol phosphate, and fatty alcohol ether phosphate.

[0044] The etching solution B used in the second surface strengthening treatment is an acidic etching solution. The acidic etching solution B contains 0.5-10 wt% hydrofluoric acid, 1-10 wt% oxidant and 0.1-5 wt% surfactant, with the balance being deionized water.

[0045] The etching temperature for the second surface strengthening treatment is 5–30℃, and the time is 0.5–10 min.

[0046] The oxidizing agent is one or a combination of several nitro compounds and nitroso compounds.

[0047] The role of the oxidant is to react with the silicon substrate to form silicon oxide on the surface of the silicon substrate, and then react with hydrofluoric acid to etch away the silicon oxide. In this scheme, the oxidant in the acidic etching solution has weak oxidizing power, which can selectively etch the surface lattice defects of the silicon substrate, and achieve smoothing treatment of the surface lattice defects of the silicon substrate, such as nanoscale steps, protrusions or depressions on the surface of the silicon substrate. These areas are potential microcrack initiation points. After smoothing treatment, the bending fracture strength of the textured silicon substrate can be further improved.

[0048] More specifically, the surfactant in the acidic etching solution B is one or a combination of several of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, lauryl ether phosphate, monolauryl phosphate, and hexadecyltrimethylammonium bromide.

[0049] The etching solution A used in the first surface strengthening treatment can smooth out submicron-level protrusions, depressions and other surface morphology defects on the textured surface of the silicon wafer substrate.

[0050] When both the front and back surfaces of the silicon wafer substrate are pyramidal textured surfaces, or when the front and back surfaces of the silicon wafer substrate are pyramidal textured surfaces and polished pyramidal textured surfaces, respectively, the submicron-level protrusions, depressions, and other surface morphology defects of the textured surfaces of the silicon wafer substrate include the pyramidal textured surface on the front surface of the silicon wafer substrate, the pyramidal textured surface on the back surface, the pyramidal textured surface on the back surface, or the pyramidal textured surface on the back surface, or the pyramidal textured surface on the back surface, or the pyramidal textured surface on the back surface.

[0051] The etching solution B used in the second surface strengthening process further smooths the nanoscale lattice defects such as steps, protrusions or depressions on the surface of the silicon wafer substrate after the rounding treatment.

[0052] The above-mentioned secondary surface strengthening treatment can reduce stress concentration points and potential microcrack points on the surface of the texturized silicon wafer substrate, thereby improving the bending fracture strength of the final photovoltaic cell.

[0053] The second approach to performing two surface strengthening treatments on the silicon wafer substrate after texturing is as follows.

[0054] A method for preparing a surface-strengthened silicon wafer substrate for photovoltaic cells involves texturing the silicon wafer substrate and then performing two surface strengthening treatments to obtain a surface-strengthened silicon wafer substrate. The two surface strengthening treatments are as follows: in the first surface strengthening treatment, etching solution A is used to smooth the surface morphology defects of the silicon wafer substrate, and in the second surface strengthening treatment, etching solution B is used to smooth the surface lattice defects of the silicon wafer substrate.

[0055] The etching solution A used in the first surface strengthening treatment is an acidic etching solution. The acidic etching solution A contains 0.2-20 wt% hydrofluoric acid, 2-30 wt% hydrochloric acid, 0.5-10 wt% oxidant and 0.1-2 wt% surfactant, with the balance being deionized water.

[0056] The etching temperature for the first surface strengthening treatment is 5–30℃, and the time is 0.5–10 min.

[0057] The oxidizing agent is one or a combination of several of the following: persulfate, hypochlorite, chlorite, perchlorate, bromate, iodate, and peracetate.

[0058] More specifically, the surfactant in the acidic etching solution A is one or a combination of several of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, lauryl ether phosphate, monolauryl phosphate, and hexadecyltrimethylammonium bromide.

[0059] The oxidant in the acidic etching solution used in the first surface strengthening treatment reacts with the silicon substrate to form silicon oxide on the substrate surface. This silicon oxide then reacts with hydrofluoric acid to etch it away. Due to the strong oxidizing power of the oxidant, coupled with the catalytic effect of hydrochloric acid, the reaction is sufficient to overcome the potential barriers at submicron-level protrusions and depressions on the textured surface, such as the barriers at the apex, corners, and base of a pyramid textured surface. This smooths out submicron-level protrusions and depressions, reducing stress concentration points on the textured silicon substrate surface.

[0060] The second surface strengthening treatment in this scheme is the same as the second surface strengthening treatment in the first scheme.

[0061] The above-mentioned secondary surface strengthening treatment can reduce stress concentration points and potential microcrack points on the surface of the texturized silicon wafer substrate, thereby improving the bending fracture strength of the final photovoltaic cell.

[0062] In both of the above-mentioned methods for preparing surface-strengthened silicon wafer substrates for photovoltaic cells, surfactants are used to increase the contact between the strengthening solution and the silicon wafer substrate, enabling the etching reaction to proceed effectively, while reducing the residence time of bubbles on the silicon wafer substrate surface and solving the problem of uneven etching.

[0063] The two methods for preparing surface-strengthened silicon wafer substrates for photovoltaic cells described above can significantly improve the bending fracture strength of silicon wafer substrates with different morphological characteristics, especially the textured surface of monocrystalline silicon wafer substrates, including positive pyramid textured surface, inverted pyramid textured surface, polished pyramid textured surface, black silicon textured surface, etc.

[0064] The acidic etching solution A can also be a mixture of hydrofluoric acid and nitric acid or a mixture of hydrofluoric acid and ozone.

[0065] The two solutions described above are further illustrated below with several embodiments.

[0066] Example 1: A method for preparing a surface-strengthened silicon wafer substrate for HJT batteries, comprising the following steps:

[0067] Step S1: Texturing the silicon wafer substrate to form a pyramidal textured surface on the silicon wafer substrate;

[0068] Step S2: Perform two surface strengthening treatments on the textured silicon wafer substrate. First, use etching solution A to smooth the surface morphology defects such as the pyramid tip, pyramid edge, and pyramid base junction of the textured silicon wafer substrate. Then, use etching solution B to smooth the surface lattice defects such as nanoscale steps, protrusions, or depressions on the surface of the smoothed silicon wafer substrate.

[0069] The etching solution A used in the first surface strengthening treatment is an alkaline etching solution. The alkaline etching solution A contains 2wt% NaOH and 0.5vol% additive A1, with the remainder being deionized water.

[0070] The etching temperature for the first surface strengthening treatment is 20–40℃, and the time is 4–8 min.

[0071] Additive A1 contains 0.1–1 wt% chelating agent and 0.1–5 wt% surfactant, with the balance being deionized water;

[0072] The chelating agent is one or a combination of several of the following: polyphosphates, aminocarboxylic acids, hydroxycarboxylic acids, hydroxyaminocarboxylic acids, organic polyphosphonic acids, and polycarboxylic acid compounds;

[0073] The surfactant is one or a combination of several of the following: sodium dodecyl sulfate, fatty alcohol ether sulfate, fatty alcohol ether carboxylate, fatty acid methyl ester sulfonate, fatty alcohol phosphate, and fatty alcohol ether phosphate.

[0074] The etching solution B used in the second surface strengthening treatment is an acidic etching solution. The acidic etching solution B contains 5 wt% hydrofluoric acid, 2 wt% oxidant and 0.3 wt% surfactant, with the balance being deionized water.

[0075] The etching temperature for the second surface strengthening treatment is 20–30℃, and the time is 3–8 min.

[0076] The oxidizing agent is one or a combination of several nitro compounds and nitroso compounds;

[0077] The surfactant is one or a combination of several of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, lauryl ether phosphate, monolauryl phosphate, and hexadecyltrimethylammonium bromide;

[0078] Step S3: Clean and dry the silicon wafer substrate after two surface strengthening treatments in sequence.

[0079] The silicon wafer substrate after the above two surface strengthening treatments is then processed through subsequent processes, including PECVD deposition of front and back amorphous silicon intrinsic layers and doped layers, PVD deposition of front and back transparent conductive layers, screen printing of low-temperature metal electrodes, curing and light injection, and finally fabrication of HJT cells.

[0080] The bending fracture strength of HJT batteries was measured using the three-point bending strength test method and compared with that of an untreated reference group. The results are as follows:

[0081]

[0082] It is evident that the bending fracture strength of the HJT battery was improved through two surface strengthening treatments.

[0083] Example 2, a method for preparing a surface-strengthened silicon wafer substrate for a back-polished HJT cell, comprising the following steps:

[0084] Step S1: The silicon wafer substrate is texturized and polished on one side, forming a pyramid textured surface on the front side and a polished pyramid textured surface on the back side.

[0085] Step S2: Perform two surface strengthening treatments on the textured silicon wafer substrate after single-sided polishing. First, use etching solution A to smooth the surface morphology defects such as the apex, corner, and base of the pyramid textured surface on the front side of the textured silicon wafer substrate, as well as the pedestal corner and base of the polished pyramid textured surface on the back side. Then, use etching solution B to smooth the nanoscale steps, protrusions, or depressions on the surface of the smoothed silicon wafer substrate.

[0086] The etching solution A used in the first surface strengthening treatment is an acidic etching solution. The acidic etching solution A contains 5 wt% hydrofluoric acid, 5 wt% hydrochloric acid, 3 wt% oxidant and 0.5 wt% surfactant, with the remainder being deionized water.

[0087] The etching temperature for the first surface strengthening treatment is 5–30℃, and the time is 3–6 min.

[0088] The oxidizing agent is one or a combination of several of the following: persulfate, hypochlorite, chlorite, perchlorate, bromate, iodate, and peracetate.

[0089] The surfactant is one or a combination of several of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, lauryl ether phosphate, monolauryl phosphate, and hexadecyltrimethylammonium bromide;

[0090] The etching solution B used in the second surface strengthening treatment is an acidic etching solution. The acidic etching solution B contains 1 wt% hydrofluoric acid, 3 wt% oxidant and 0.5 wt% surfactant, with the balance being deionized water.

[0091] The etching temperature for the second surface strengthening treatment is 5–30℃, and the time is 0.5–10 min.

[0092] The oxidizing agent is one or a combination of several nitro compounds and nitroso compounds;

[0093] The surfactant is one or a combination of several of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, lauryl ether phosphate, monolauryl phosphate, and hexadecyltrimethylammonium bromide;

[0094] Step S3: Clean and dry the silicon wafer substrate after two surface strengthening treatments in sequence.

[0095] The silicon wafer substrate, after being textured and polished on one side using the above two surface strengthening treatments, is then processed through subsequent processes, including PECVD deposition of front and back amorphous silicon intrinsic layers and doped layers, PVD deposition of front and back transparent conductive layers, screen printing of low-temperature metal electrodes, curing and light injection, and finally fabrication into a back-polished HJT cell.

[0096] The bending fracture strength of back-polished HJT cells was measured using the three-point bending strength test method and compared with a reference group without surface treatment. The results are as follows:

[0097]

[0098] It is evident that, through two surface strengthening treatments, the bending fracture strength of both the front and back sides of the back-polished HJT battery is significantly improved, and the difference in bending strength between the front textured surface and the back polished tower base textured surface is significantly reduced.

[0099] Example 3: A method for preparing a surface-strengthened silicon wafer substrate for a TOPCon battery, comprising the following steps:

[0100] Step S1: Texturing the silicon wafer substrate to form a pyramidal textured surface on the silicon wafer substrate;

[0101] Step S2: Boron diffusion is performed on the texturized silicon wafer substrate to form a boron-doped emitter layer on the surface of the silicon wafer substrate;

[0102] Step S3: Perform single-sided BSG film removal and alkaline polishing on the boron-diffused silicon wafer substrate to form a boron-doped textured surface on the front side of the silicon wafer substrate and an undoped polishing tower-based textured surface on the back side.

[0103] Step S4: Perform two surface strengthening treatments on the silicon wafer substrate after back-side polishing. First, use etching solution A to smooth the surface morphology defects such as the pyramid tip, pyramid edge, pyramid base junction on the front side of the textured silicon wafer substrate, as well as the pyramid edge and pyramid base junction on the back-side polished pyramid base textured surface. Then, use etching solution B to smooth the surface lattice defects such as nanoscale steps, protrusions, or depressions on the surface of the smoothed silicon wafer substrate.

[0104] The etching solution A used in the first surface strengthening treatment is an acidic etching solution. The acidic etching solution A contains 4 wt% hydrofluoric acid, 6 wt% hydrochloric acid, 5 wt% oxidant and 0.3 wt% surfactant, with the remainder being deionized water.

[0105] The etching temperature for the first surface strengthening treatment is 5–30℃, and the time is 3–6 min.

[0106] The oxidizing agent is one or a combination of several of the following: persulfate, hypochlorite, chlorite, perchlorate, bromate, iodate, and peracetate;

[0107] The surfactant is one or a combination of several of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, lauryl ether phosphate, monolauryl phosphate, and hexadecyltrimethylammonium bromide;

[0108] The etching solution B used in the second surface strengthening treatment is an acidic etching solution. The acidic etching solution B contains 2 wt% hydrofluoric acid, 4 wt% oxidant and 0.2 wt% surfactant, with the balance being deionized water.

[0109] The etching temperature for the second surface strengthening treatment is 5–30℃, and the time is 0.5–10 min.

[0110] The oxidizing agent is one or a combination of several nitro compounds and nitroso compounds.

[0111] The surfactant is one or a combination of several of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, lauryl ether phosphate, monolauryl phosphate, and hexadecyltrimethylammonium bromide;

[0112] Step S5: Clean and dry the silicon wafer substrate after two surface strengthening treatments in sequence.

[0113] The silicon wafer substrate with boron diffusion on the back side after the above two surface strengthening treatments is then processed by subsequent processes, including LPCVD deposition of tunneling oxide layer and intrinsic amorphous silicon, phosphorus diffusion to form doped polycrystalline silicon, poly-plating removal and cleaning, front ALD deposition of AlOx, PECVD deposition of front and back SiNx antireflection layers, screen printing of metal paste electrodes, sintering and light injection, and finally fabrication of TOPCon cell.

[0114] The bending fracture strength of TOPCon batteries was measured using the three-point bending strength test method and compared with a reference group without surface treatment. The results are as follows:

[0115]

[0116] It is evident that through two surface strengthening treatments, the bending fracture strength of the front and back sides of the TOPCon battery is significantly improved, and the difference in bending strength between the textured front surface and the polished back surface is significantly reduced.

Claims

1. A method for preparing a surface-strengthened silicon wafer substrate for photovoltaic cells, characterized in that: After texturing the silicon wafer substrate, two surface strengthening treatments are performed to obtain a surface-strengthened silicon wafer substrate. The two surface strengthening treatments are as follows: in the first surface strengthening treatment, etching solution A is used to smooth the surface morphology defects of the silicon wafer substrate, and in the second surface strengthening treatment, etching solution B is used to smooth the surface lattice defects of the silicon wafer substrate. The etching solution B is an acidic etching solution. The acidic etching solution B contains hydrofluoric acid, an oxidant, and deionized water. The oxidant is one or a combination of nitro compounds and nitroso compounds.

2. The method for preparing the surface-strengthened silicon wafer substrate for photovoltaic cells according to claim 1, characterized in that: The etching solution A is an alkaline etching solution or an acidic etching solution.

3. The method for preparing the surface-strengthened silicon wafer substrate for photovoltaic cells according to claim 1, characterized in that: The etching solution A is an alkaline etching solution, which contains 0.5 to 10 wt% inorganic alkali and the remainder is deionized water. The etching temperature for the first surface strengthening treatment is 20–40℃, and the time is 1–10 min. The inorganic base is one or a combination of two of NaOH and KOH.

4. The method for preparing the surface-strengthened silicon wafer substrate for photovoltaic cells according to claim 3, characterized in that: The alkaline etching solution A also contains 0.1 to 1 vol% additive A1, which contains 0.1 to 1 wt% chelating agent and 0.1 to 5 wt% surfactant, with the balance being deionized water.

5. The method for preparing a surface-strengthened silicon wafer substrate for photovoltaic cells according to claim 1, characterized in that: The etching solution A is an acidic etching solution, which contains 0.2-20 wt% hydrofluoric acid, 2-30 wt% hydrochloric acid and 0.5-10 wt% oxidant, with the balance being deionized water. The etching temperature for the first surface strengthening treatment is 5–30℃, and the time is 0.5–10 min. The oxidizing agent is one or a combination of several of the following: persulfate, hypochlorite, chlorite, perchlorate, bromate, iodate, and peracetate.

6. The method for preparing the surface-strengthened silicon wafer substrate for photovoltaic cells according to claim 1, characterized in that: The acidic etching solution B contains 0.5–10 wt% hydrofluoric acid and 1–10 wt% oxidant, with the balance being deionized water; The etching temperature during the second surface strengthening treatment is 5–30℃, and the time is 0.5–10 min.

7. The method for preparing the surface-strengthened silicon wafer substrate for photovoltaic cells according to claim 6, characterized in that: The acidic etching solution B also contains 0.1 to 5 wt% surfactant.

8. The method for preparing the surface-strengthened silicon wafer substrate for photovoltaic cells according to claim 1, characterized in that: The etching solution A is an acidic etching solution. The acidic etching solution A is a mixed solution of hydrofluoric acid and nitric acid, or a mixed solution of hydrofluoric acid and ozone.

9. The method for preparing the surface-strengthened silicon wafer substrate for photovoltaic cells according to claim 1, characterized in that: The photovoltaic cell is a TOPCon cell, and the process includes the following steps: Step S1: Texturing the silicon wafer substrate to form a pyramidal textured surface on the silicon wafer substrate; Step S2: Boron diffusion is performed on the texturized silicon wafer substrate to form a boron-doped emitter layer on the surface of the silicon wafer substrate; Step S3: Perform single-sided BSG film removal and alkaline polishing on the boron-diffused silicon wafer substrate to form a boron-doped textured surface on the front side of the silicon wafer substrate and an undoped polishing tower-based textured surface on the back side. Step S4: Perform two surface strengthening treatments on the silicon wafer substrate after back-side polishing.

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