A rework method for manufacturing crystalline silicon solar cells

Abstract

This invention belongs to the field of solar cell manufacturing technology, specifically relating to a manufacturing rework method for crystalline silicon solar cells. The manufacturing rework method for crystalline silicon solar cells of this invention includes the following steps: (1) classifying defective wafers: defective wafers are classified into five types: Class I defective wafers, Class II defective wafers, Class III defective wafers, Class IV defective wafers, and Class V defective wafers; (2) different rework methods are used for different types of defective wafers. The crystalline silicon solar cells obtained by classifying and reworking defective wafers according to this invention have a cell conversion efficiency of over 24.1%, a quality rate of 93%-95%, and a fragmentation rate of less than 0.9%. The difference between these and crystalline silicon solar cells obtained through normal production is minimal. Compared to conventional rework methods that do not classify defective wafers and uniformly retexturize them, the crystalline silicon solar cells obtained through this invention show a significant improvement in both cell conversion efficiency and quality rate, while the fragmentation rate is significantly reduced.

Description

Technical Field

[0001] This invention belongs to the field of solar cell manufacturing technology, specifically relating to a method for reworking the manufacture of crystalline silicon solar cells. Background Technology

[0002] With the development of crystalline silicon solar cell technology, the mass production conversion efficiency of n-type passivated contact solar cells (Tunnel Oxide Passivated Contact, also known as TOPCon cells) currently exceeds 24%, making them a highly competitive next-generation cell after PERC cells. Structurally, n-type TOPCon cells use an n-type silicon wafer as the substrate. A p+ doped layer is obtained on the front side through boron diffusion, while a tunneling oxide layer and polycrystalline silicon are deposited on the back side. An n+ doped layer is obtained on the back side through in-situ phosphorus doping or intrinsic phosphorus diffusion. AlO2 is deposited on the front side. X Layer, SiN deposited on both sides X Layers; the corresponding metal electrodes are typically obtained using screen printing, with silver-aluminum paste used on the front and silver paste on the back. A typical manufacturing process flow diagram can be found here. Figure 1 As shown.

[0003] Defective wafers may be generated at any stage of the manufacturing process. These defective wafers can be remanufactured into battery cells through a rework process. Traditional rework processes involve removing the coating, re-etching and texturing, and then... Figure 1 The conventional process shown is used to produce TOPCon cells, which allows for further thinning of silicon wafers, contrary to the current trend of thinner silicon wafers. This results in a high breakage rate of reworked wafers and a long manufacturing process for reworked wafers, leading to increased manufacturing costs for TOPCon cells. This rework method is not targeted and the overall quality rate of cells is not high. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a manufacturing rework method for crystalline silicon solar cells. The manufacturing rework method of this invention can shorten the rework process, reduce the silicon wafer breakage rate, and lower the manufacturing cost of TOPCon cells.

[0005] To achieve the above technical objectives, the technical solution adopted in the embodiments of the present invention is as follows:

[0006] A method for reworking the manufacture of a crystalline silicon solar cell includes the following steps:

[0007] (1) Classification of defective films: Defective films are classified into five types: Category I defective films, Category II defective films, Category III defective films, Category IV defective films, and Category V defective films.

[0008] (2) Different types of defective films are reworked using different methods.

[0009] Furthermore, the first type of defective wafer is a wafer that has normal sheet resistance after the "boron diffusion" process, but has an oxide layer thickness of less than 80nm and an abnormal appearance color; wherein the normal range of sheet resistance is 100-140Ω / □.

[0010] The second type of defective sheet is a sheet with an abnormal appearance on the back after the "back cleaning process";

[0011] The third type of defective wafers are batches of defective wafers produced due to malfunctions in the deposition equipment after the "deposition of tunneling oxide layer & polysilicon" process.

[0012] The fourth type of defective sheet is a sheet with abnormal back resistance or appearance after the "annealing" process.

[0013] The fifth type of defective sheet is "front-deposited AlO". X SiN deposited on both the front and back sides X Defective sheets with abnormal appearance after the "layer" process.

[0014] Furthermore, the rework method for the first type of defective wafers includes: pickling → diffusion oxygenation → etching & backside cleaning → subsequent normal production process; wherein, after pickling and diffusion oxygenation, the thickness of the oxide layer is 80-100nm.

[0015] Furthermore, pickling is performed using hydrofluoric acid with a mass fraction of 1% to 10% for 200 to 500 seconds;

[0016] When using diffusion oxygen, the oxygen flow rate is 5000–50000 sccm, and the oxidation time is 1800–10800 s.

[0017] Furthermore, the rework method for the second type of defective wafers includes: back side alkaline cleaning → deposition of tunneling oxide layer & polysilicon → back side phosphorus doping → subsequent normal production process; wherein, during back side alkaline cleaning, the temperature is 60-85℃ and the time is 100-600s.

[0018] Furthermore, the rework method for the third type of defective sheet includes: pickling → backside cleaning treatment → subsequent normal production process, wherein the pickling is performed for 10 to 50 seconds using hydrofluoric acid with a mass fraction of 0.5%-5%.

[0019] Furthermore, the rework method for the fourth type of defective sheet includes: first pickling → alkaline etching → second pickling → backside cleaning treatment → subsequent normal production process; wherein, alkaline etching is performed for 200 to 400 seconds using a sodium hydroxide or potassium hydroxide solution with a mass fraction of 0.5% to 3% at 60 to 85°C.

[0020] Furthermore, during the first acid cleaning, hydrofluoric acid with a mass fraction of 0.5%-5% is used for acid cleaning for 50-200 seconds;

[0021] During the second acid cleaning, use hydrofluoric acid with a mass fraction of 10%-30% for 20-100 seconds.

[0022] Furthermore, the rework method for the fifth type of defective wafer includes: mixed pickling → front-side AlO2 deposition. X Layer → SiN deposition on both sides X Layer → Screen printing & sintering → Subsequent normal production process; The mixed acid is a mixture of hydrofluoric acid and hydrochloric acid, wherein the mass fraction of hydrofluoric acid is 10%-25% and the mass fraction of hydrochloric acid is 2%-8%, and the mixed acid washing is performed for 500-2000 seconds.

[0023] The beneficial effects of the technical solution provided by the embodiments of the present invention are as follows:

[0024] 1. The rework method of the present invention classifies defective wafers and adopts different rework methods for different types of defective wafers. It is targeted, which can shorten the manufacturing time of rework wafers, avoid the need for all defective wafers to be retextured in the same way, which would cause the silicon wafers to be further thinned, thereby reducing the breakage rate, improving the quality rate of rework wafers, and helping to reduce the production cost of TOPCon cells.

[0025] 2. The crystalline silicon solar cells obtained by classifying and reworking defective wafers according to this invention have a cell conversion efficiency of over 24.1%, a quality rate of 93%-95%, and a fragmentation rate of less than 0.9%. The difference between these cells and those obtained through normal production is minimal. Compared with the conventional rework method that does not classify and uniformly retexturize defective wafers, the crystalline silicon solar cells obtained by this invention have significantly improved both the cell conversion efficiency and quality rate, while significantly reducing the fragmentation rate. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the manufacturing process of an n-type TOPCon battery in an embodiment of the present invention.

[0027] Figure 2 This is a flowchart of the rework process for the first type of defective wafer in this embodiment of the invention.

[0028] Figure 3 This is a rework process flow diagram for the second type of defective wafer in this embodiment of the invention.

[0029] Figure 4 This is a flowchart of the rework process for the third type of defective wafer in this embodiment of the invention.

[0030] Figure 5 This is a rework process flow diagram for the fourth type of defective sheet in this embodiment of the invention.

[0031] Figure 6 This is a rework process flow diagram for the fifth type of defective sheet in this embodiment of the invention. Detailed Implementation

[0032] 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.

[0033] Example 1

[0034] A method for reworking the manufacture of a crystalline silicon solar cell includes the following steps:

[0035] (1) Classification of defective films: Defective films are classified into five types: Category I defective films, Category II defective films, Category III defective films, Category IV defective films, and Category V defective films.

[0036] (2) Different types of defective films are reworked using different methods.

[0037] The crystalline silicon solar cell in this embodiment is an n-type TOPCon cell, employing, as shown in... Figure 1 The manufacturing process shown is used for manufacturing.

[0038] Specifically, the first type of defective wafers are those with normal sheet resistance after the "boron diffusion" process, but with an oxide layer thickness of less than 80nm and abnormal appearance; the normal range for sheet resistance is 100-140Ω / □.

[0039] The second type of defective film is the defective film with abnormal appearance on the back after the "back cleaning treatment" process.

[0040] The third type of defective wafers are batches of defective wafers produced after the "deposition of tunneling oxide layer & polysilicon" process due to abnormalities in the deposition equipment;

[0041] The fourth type of defective sheet is a sheet with abnormal back resistance or appearance after the "annealing" process.

[0042] The fifth type of defective film is "front-side deposited AlO". X SiN deposited on both the front and back sides X Defective sheets with abnormal appearance after the "layer" process.

[0043] like Figure 2 As shown, the rework method for the first type of defective wafers includes: pickling → diffusion oxygenation → etching & backside cleaning → subsequent normal production process; wherein, after pickling and diffusion oxygenation, the thickness of the oxide layer is 80-100nm.

[0044] Pickling is performed using hydrofluoric acid with a mass fraction of 1% to 10% for 200 to 500 seconds; during diffusion oxygenation, the oxygen flow rate is 5000 to 50000 sccm, and the oxidation time is 1800 to 10800 seconds.

[0045] Abnormal oxide layers are removed by hydrofluoric acid pickling, and then an oxide layer of acceptable thickness (80-120nm) is rapidly grown by diffusion oxygenation.

[0046] like Figure 3 As shown, the rework method for the second type of defective wafers includes: back side alkaline cleaning → deposition of tunneling oxide layer & polysilicon → back side phosphorus doping → subsequent normal production process; wherein, during back side alkaline cleaning, the temperature is 60~85℃ and the time is 100~600s.

[0047] When performing alkaline cleaning on the back side, use a sodium hydroxide or potassium hydroxide solution with a mass fraction of 0.5%-3%. To facilitate the adjustment of the reaction rate and uniformity, an appropriate amount of surfactant can be added.

[0048] like Figure 4 As shown, the rework method for the third type of defective wafers includes: pickling → backside cleaning → subsequent normal production process. The pickling process uses 0.5%-5% hydrofluoric acid for 10-50 seconds. The purpose of HF cleaning is to remove the oxide layer on the backside; when the backside is dehydrated, it indicates that the oxide layer has been completely removed.

[0049] like Figure 5 As shown, the rework method for the fourth type of defective wafers includes: first pickling → alkaline etching → second pickling → backside cleaning → subsequent normal production process; wherein, alkaline etching is performed at 60-85℃ using a 0.5%-3% sodium hydroxide or potassium hydroxide solution for 200-400 seconds. The purpose of alkaline etching is to remove the polycrystalline silicon on the backside. To facilitate adjustment of the reaction rate and uniformity, an appropriate amount of surfactant can be added.

[0050] During the first acid cleaning, use hydrofluoric acid with a mass fraction of 0.5%-5% for 50-200 seconds; the purpose of the first acid cleaning is to remove the oxide layer on the back side.

[0051] During the second acid cleaning, hydrofluoric acid with a mass fraction of 10%-30% is used for pickling for 20-100 seconds. The purpose of the second acid cleaning is to remove the tunneling oxide layer on the back side.

[0052] like Figure 6 As shown, the rework method for the fifth type of defective wafers includes: mixed pickling → front-side AlO2 deposition. X Layer → SiN deposition on both sides XLayer → Screen printing & sintering → Subsequent normal production process; the mixed acid is a mixture of hydrofluoric acid and hydrochloric acid, wherein the mass fraction of hydrofluoric acid is 10%-25% and the mass fraction of hydrochloric acid is 2%-8%, and the mixed acid washing is performed for 500-2000 seconds. The purpose of the mixed acid washing is to remove AlO2 from the front side. X and front and back SiN X Film layer. After mixed acid washing, the silicon's natural color is exposed, and the surface is in a dehydrated state, indicating successful cleaning.

[0053] Comparative Example 1

[0054] The crystalline silicon solar cell in this example is an n-type TOPCon cell, employing methods such as... Figure 1 The manufacturing process shown is used for normal production without rework.

[0055] Comparative Example 2

[0056] The crystalline silicon solar cell in this example is an n-type TOPCon cell, employing methods such as... Figure 1 The manufacturing process shown is used to manufacture the pieces. Defective pieces are not classified and are all reworked from the flocking process.

[0057] The crystalline silicon solar cells prepared in Example 1 and Comparative Examples 1-2 were compared, and the comparison results are shown in Table 1.

[0058] Table 1. Comparison results of crystalline silicon solar cells prepared in Example 1 and Comparative Examples 1-2

[0059]

[0060] As can be seen from Table 1, the crystalline silicon solar cells obtained by classifying and reworking defective wafers in Example 1 of this invention have a cell conversion efficiency of over 24.1%, a quality rate of 93%-95%, and a fragmentation rate of less than 0.9%. The difference between these cells and those obtained by normal production in Comparative Example 1 is small. Compared with Comparative Example 2, which does not classify defective wafers and uniformly reworks them through texturing, the crystalline silicon solar cells obtained by reworking them are significantly improved.

[0061] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for reworking the manufacture of a crystalline silicon solar cell, characterized in that, Includes the following steps: (1) Classification of defective wafers: Defective wafers are classified into five types: first type, second type, third type, fourth type and fifth type. The first type of defective wafer is a wafer with normal sheet resistance but an oxide layer thickness of less than 80nm and abnormal appearance color after the "boron diffusion" process. The second type of defective sheet is a sheet with an abnormal appearance on the back after the "back cleaning process"; The third type of defective wafers are batches of defective wafers produced due to malfunctions in the deposition equipment after the "deposition of tunneling oxide layer & polysilicon" process. The fourth type of defective sheet is a sheet with abnormal back sheet resistance or appearance after the "annealing" process. The fifth type of defective sheet is "front-side deposited AlO". X SiN deposited on both the front and back sides X Defective sheets with abnormal appearance after the "layer" process; (2) Different types of defective films are reworked using different methods; The rework method for the first type of defective wafers includes: pickling → diffusion oxygenation → etching & backside cleaning → subsequent normal production process; wherein, after pickling and diffusion oxygenation, the thickness of the oxide layer is 80~100nm; The rework method for the second type of defective wafers includes: back side alkaline cleaning → deposition of tunneling oxide layer & polysilicon → back side phosphorus doping → subsequent normal production process; wherein, when performing back side alkaline cleaning, the temperature is 60~85℃ and the time is 100~600s; The rework method for the third type of defective film includes: pickling → back cleaning treatment → subsequent normal production process, in which hydrofluoric acid with a mass fraction of 0.5%~5% is used for pickling for 10~50 seconds; The rework method for the fourth type of defective sheet includes: first pickling → alkaline etching → second pickling → back cleaning treatment → subsequent normal production process; wherein, at 60~85℃, alkaline etching is performed for 200~400s using a sodium hydroxide or potassium hydroxide solution with a mass fraction of 0.5%-3%; The rework method for the fifth type of defective wafers includes: mixed pickling → front-side AlO2 deposition. X Layer → SiN deposition on both sides X Layer → Screen printing & sintering → Subsequent normal production process; The mixed acid is a mixture of hydrofluoric acid and hydrochloric acid, wherein the mass fraction of hydrofluoric acid is 10%-25% and the mass fraction of hydrochloric acid is 2%-8%, and the mixed acid washing is performed for 500~2000s.

2. The rework method for manufacturing crystalline silicon solar cells according to claim 1, characterized in that, Pickling is performed using hydrofluoric acid with a mass fraction of 1%~10% for 200~500s; When using diffusion oxygen, the oxygen flow rate is 5000~50000 sccm, and the oxidation time is 1800~10800 s.

3. The method for reworking the manufacture of a crystalline silicon solar cell according to claim 1, characterized in that, For the first acid cleaning, use hydrofluoric acid with a mass fraction of 0.5%-5% for 50-200 seconds. During the second acid cleaning, use hydrofluoric acid with a mass fraction of 10%-30% for 20-100 seconds.

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