Preparation method for selective emitter, n-type battery and preparation process therefor

Abstract

The present invention belongs to the technical field of solar cells. Provided are a preparation method for a selective emitter, an N-type battery and a preparation process therefor. The preparation method comprises: performing boron diffusion on a textured silicon wafer to form a heavily doped region; performing laser doping propulsion on a metal gate line region on the silicon wafer; oxidizing the silicon wafer subjected to laser doping, so as to form a first-stage lightly doped region in a non-metal gate line region; and depositing a mask layer in the metal gate line region on the silicon wafer, and using an etching solution to clean the silicon wafer, so as to change the first-stage lightly doped region into a second-stage lightly doped region, the boron-doped surface concentration of the second-stage lightly doped region being smaller than the boron-doped surface concentration of the first-stage lightly doped region. On the basis of a traditional boron diffusion SE process, the present invention adds micro-etching of lightly doped regions, thus further reducing the doping concentration of lightly doped regions, and effectively solving the problem of indistinct doping concentration difference between boron diffusion heavily doped regions and lightly doped regions.

Description

A method for preparing a selective emitter, an N-type battery and a preparation process thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to a Chinese patent application filed with the Patent Office of China on September 1, 2023, with application number 202311118439.X and application name “A method for preparing a selective emitter, an N-type battery and its preparation process”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention belongs to the technical field of solar cells, and in particular relates to a method for preparing a selective emitter, an N-type battery and a preparation process thereof. Background Art

[0004] Conventional N-type TOPCon cells use laser doping technology to create a selective emitter (SE) on the front to reduce cell recombination, improve the front short-wave response, and enhance the metal area contact.

[0005] For example, the prior art provides a preparation method, which specifically includes: first depositing a boron-doped amorphous silicon thin film layer, then using a laser to dope this thin film layer to form an emitter region, and then performing boron diffusion so that the emitter region forms a heavily diffused region and the remaining regions form lightly diffused regions.

[0006] However, the existing SE technology has the problem that the doping concentration difference between the boron diffusion heavy expansion area and the light expansion area is not obvious.

[0007] Therefore, how to reduce the damage to the suede surface and solve the problem of unclear difference in doping concentration between the heavily diffused and lightly diffused boron areas is a difficulty in current research.

[0008] Summary of the Invention

[0009] To address the shortcomings of the prior art, the present invention provides a method for fabricating a selective emitter, an N-type battery, and a process for fabricating the same. This invention, in addition to the traditional boron diffusion SE process, incorporates micro-etching of the lightly diffused region, further reducing the doping concentration in the lightly diffused region and effectively resolving the issue of unclear doping concentration differences between the heavily diffused and lightly diffused regions.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a method for preparing a selective emitter, the method comprising the following steps:

[0012] Boron diffusion is performed on the silicon wafer after texturing to form a re-expansion area;

[0013] Laser doping is performed on the metal gate line area on the silicon wafer;

[0014] Oxidizing the laser-doped silicon wafer to form a first-level light expansion area in the non-metallic gate line area;

[0015] Depositing a mask layer in the metal gate line area on the silicon wafer and cleaning the silicon wafer with an etching solution so that the first-level light expansion area becomes a second-level light expansion area;

[0016] The boron-doped surface concentration of the secondary lightly expanded region is less than the boron-doped surface concentration of the primary lightly expanded region.

[0017] Based on the traditional boron diffusion SE process, the present invention adds micro-etching of the light diffusion area, thereby further reducing the doping concentration of the light diffusion area and effectively solving the problem of unclear doping concentration difference between the boron diffusion heavy diffusion area and the light diffusion area.

[0018] The preparation method provided by the present invention can increase the blue light response in the short-wave region, reduce the emitter defect density and decrease the recombination rate.

[0019] It should be noted that the more obvious the difference in doping concentration between the boron diffusion heavy expansion area and the light expansion area, the more conducive it is to reducing the contact resistance between the silicon wafer and the electrode, reducing surface recombination, and improving battery life and conversion efficiency.

[0020] It should be noted that the re-expanded region refers to a P+ layer with a high boron surface concentration.

[0021] In the present invention, the purpose of performing laser doping on the metal gate line region on the silicon wafer is to reduce the ohmic contact between the metal gate line and the silicon wafer during metallization.

[0022] In the present invention, the purpose of depositing a mask layer in the metal gate line region on the silicon wafer is to prevent etching of the gate line re-expansion region when the silicon wafer is cleaned with an etching solution.

[0023] In the present invention, the mask layer can be removed in the following manner: the silicon wafer is cleaned with an etching solution and then placed in a mask tank for cleaning.

[0024] As a preferred technical solution of the present invention, the power range of the laser is 100 to 500W, for example, it can be 100W, 200W, 300W, 400W or 500W.

[0025] In the process of forming the re-expansion area, the present invention adopts a higher 20 cm -3 to 1.0×10 20 cm -3 ) boron doping concentration (1.1×10 20 to 1.5×10 20 cm -3), under these conditions, even with relatively low laser power, the SE region can be heavily doped. This not only allows boron atoms deposited on the silicon wafer surface or in borosilicate glass to be doped into the p+ layer, but also reduces damage to the wafer's textured surface.

[0026] Optionally, the speed of the laser is in the range of 10,000 to 50,000 mm / s, for example, 10,000 mm / s, 20,000 mm / s, 30,000 mm / s, 40,000 mm / s or 50,000 mm / s.

[0027] Optionally, the laser is a continuous laser or a laser with a frequency greater than 10 MHz.

[0028] Optionally, the wavelength of the laser is in the range of 500 to 1100 nm, for example, 500 nm, 700 nm, 900 nm or 1100 nm.

[0029] Optionally, after the laser doping is advanced, the boron doping concentration range of the metal gate line region is 1×10 19 to 3×10 19 cm -3 , for example, it can be 1×10 19 cm -3 , 1.5×10 19 cm -3 , 2×10 19 cm -3 , 2.5×10 19 cm -3 or 3×10 19 cm -3 wait.

[0030] In the present invention, in view of the fact that a relatively high boron doping surface concentration range (1.1×10 20 to 1.5×10 20 cm -3 ), so a smaller laser power can be used to make the boron doping concentration range of the metal gate line area be 1×10 19 to 3×10 19 cm -3 , a higher boron doping concentration is conducive to good ohmic contact with the silicon substrate during metallization, reducing contact resistance.

[0031] As a preferred technical solution of the present invention, the boron source for the boron diffusion includes any one of boron trichloride, boron tribromide, trimethylboron or diborane, or a combination of at least two thereof.

[0032] Optionally, the flow rate of the boron source ranges from 200 to 400 sccm, for example, it can be 200 sccm, 220 sccm, 240 sccm, 260 sccm, 280 sccm, 300 sccm, 320 sccm, 340 sccm, 360 sccm, 380 sccm or 400 sccm, etc.

[0033] Optionally, the boron diffusion temperature ranges from 900° C. to 950° C., for example, 900° C., 910° C., 920° C., 930° C., 940° C., or 950° C. Optionally, nitrogen is introduced during the boron diffusion process.

[0034] Optionally, the flow rate of the nitrogen gas is in a range of 2000 to 5000 sccm, for example, 2000 sccm, 2500 sccm, 3000 sccm, 3500 sccm, 4000 sccm, 4500 sccm or 5000 sccm.

[0035] Optionally, the boron diffusion time ranges from 80 to 140 min, for example, it may be 80 min, 90 min, 100 min, 110 min, 120 min, 130 min or 140 min.

[0036] In the present invention, the boron diffusion resistance can be effectively controlled by adjusting the boron diffusion temperature and the boron diffusion time.

[0037] As a preferred technical solution of the present invention, the square resistance range of the re-expanded area is 90 to 120 ohm / sq, for example, it can be 90 ohm / sq, 95 ohm / sq, 100 ohm / sq, 105 ohm / sq, 110 ohm / sq, 115 ohm / sq or 120 ohm / sq, etc.

[0038] In the present invention, if the sheet resistance of the heavy expansion region is too large, it will affect the ohmic contact during metallization. If the sheet resistance of the heavy expansion region is too small, it will affect the doping concentration of the primary light expansion region.

[0039] Optionally, the boron doping surface concentration of the re-expanded region is in the range of 1.1×10 20 to 1.5×10 20 cm -3 , for example, it can be 1.1×10 20 cm -3 , 1.2×10 20 cm -3 , 1.3×10 20 cm -3 , 1.4×10 20 cm -3 , 1.5×10 20cm -3 wait.

[0040] Optionally, the thickness of the re-expanded region is in the range of 200 to 350 nm, for example, 200 nm, 250 nm, 300 nm or 350 nm.

[0041] As a preferred technical solution of the present invention, during the oxidation process, the flow rate of oxygen is in the range of 15 to 30 slm, for example, 15 slm, 20 slm, 25 slm or 30 slm.

[0042] Optionally, the oxidation temperature ranges from 980 to 1050°C, for example, it may be 980°C, 1000°C, 1010°C, 1020°C, 1030°C, 1040°C or 1050°C.

[0043] In the present invention, when the oxidation temperature is too high, the sealing performance of the device is reduced, and the quartz carrier is easily deformed; when the oxidation temperature is too low, the proportion of activated B is reduced.

[0044] Optionally, the oxidation time ranges from 3600 to 7200 s, for example, it can be 3600 s, 4200 s, 4800 s, 5400 s, 6000 s, 6600 s or 7200 s.

[0045] Optionally, the boron doping surface concentration of the first-level light expansion region is in the range of 4×10 18 to 9×10 18 cm -3 , for example, it can be 4×10 18 cm -3 , 5×10 18 cm -3 , 6×10 18 cm -3 , 7×10 18 cm -3 , 8×10 18 cm -3 or 9×10 18 cm -3 wait.

[0046] As a preferred technical solution of the present invention, the thickness of the mask layer ranges from 30 to 50 μm, for example, it can be 30 μm, 35 μm, 40 μm, 45 μm or 50 μm.

[0047] Optionally, the mask layer is made of wax or graphite.

[0048] As a preferred technical solution of the present invention, the etching solution includes hydrofluoric acid and / or hydrochloric acid, preferably a mixed solution of hydrofluoric acid and hydrochloric acid.

[0049] Optionally, the concentration of the hydrofluoric acid is in the range of 5 to 10 wt.%, for example, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.% or 10 wt.%.

[0050] In the present invention, the concentration of hydrofluoric acid will affect the etching rate.

[0051] Optionally, the concentration of the hydrochloric acid ranges from 0.05 to 0.1 wt.%, for example, it can be 0.05 wt.%, 0.06 wt.%, 0.07 wt.%, 0.08 wt.%, 0.09 wt.% or 0.1 wt.%, etc.

[0052] Optionally, the etching solution also includes ozone O3.

[0053] In the present invention, the purpose of adding O3 into the etching solution is to enable the etching to proceed sufficiently.

[0054] Optionally, the concentration of O 3 ranges from 20 to 30 ppm, for example, it may be 20 ppm, 22 ppm, 24 ppm, 26 ppm, 28 ppm or 30 ppm.

[0055] In the present invention, the concentration of O3 affects the etching rate.

[0056] Optionally, the cleaning time ranges from 60 to 300 s, for example, it can be 60 s, 100 s, 150 s, 200 s, 250 s or 300 s.

[0057] In the present invention, the length of cleaning time will affect the depth of etching, and further affect the morphology of the suede surface.

[0058] Optionally, the surface resistance of the cleaned silicon wafer is in the range of 240 to 260 ohm / sq, for example, 240 ohm / sq, 245 ohm / sq, 250 ohm / sq, 255 ohm / sq or 260 ohm / sq.

[0059] Optionally, the boron doping surface concentration of the secondary light expansion region is in the range of 2×10 18 to 7×10 18 cm -3 , for example, it can be 2×10 18 cm -3 , 3×10 18 cm -3 , 4×10 18 cm -3 , 5×10 18 cm -3 , 6×10 18 cm -3, or 7×10 18 cm -3 wait.

[0060] In the present invention, the boron doping surface concentration range of the secondary light expansion region is 2×10 18 to 7×10 18 cm -3 , which is quite different from the concentration in the heavy-expansion zone, can effectively reduce the recombination probability of carriers when they flow laterally in the diffusion layer and improve the carrier collection efficiency; the higher the doping concentration in the heavy-expansion zone, the smaller the contact resistance during metallization.

[0061] Optionally, the boron-doped surface concentration of the secondary lightly expanded region is less than the boron-doped surface concentration of the primary lightly expanded region.

[0062] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0063] Boron diffusion is performed on the N-type silicon wafer after texturing to form a re-expansion area;

[0064] The boron source flow rate range of boron diffusion is 200 to 400 sccm, the nitrogen flow rate range is 2000 to 5000 sccm, the boron diffusion temperature range is 900 to 950 °C, the time range is 80 to 140 min, the control sheet resistance range is 90 to 120 ohm / sq, and the boron doping concentration range of the re-expansion area is 1.1×10 20 to 1.5×10 20 cm -3 , thickness ranges from 200 to 350 nm;

[0065] Laser doping is performed on the metal gate line area on the silicon wafer;

[0066] The laser power range is 100 to 500 W, the laser speed range is 10,000 to 50,000 mm / s, the laser is a continuous laser or a laser with a frequency greater than 10 MHz, the laser wavelength range is 500 to 1100 nm, and the boron doping surface concentration range of the metal grid line area after laser doping is 1×10 19 to 3×10 19 cm -3 ;

[0067] Oxidizing the laser-doped silicon wafer to form a first-level light expansion area in the non-metallic gate line area;

[0068] The oxygen flow rate range is 15 to 30 slm, the oxidation temperature range is 980 to 1050 °C, the oxidation time range is 3600 to 7200 s, and the boron doping surface concentration range of the first-level light expansion zone is 4×10 18 to 9×10 18 cm-3 ;

[0069] A mask layer with a thickness of 30 to 50 μm is deposited in the metal gate line area on the silicon wafer, and the silicon wafer is cleaned with an etching solution for a time range of 60 to 300 seconds, so that the first-level light expansion area becomes a boron-doped surface with a concentration range of 2×10 18 to 7×10 18 cm -3 Secondary light expansion zone;

[0070] The etching solution includes O3 with a concentration range of 20 to 30 ppm, hydrofluoric acid with a concentration range of 5 to 10 wt.%, and hydrochloric acid with a concentration range of 0.05 to 0.1 wt.%. The surface resistance of the silicon wafer after cleaning is in the range of 240 to 260 ohm / sq.

[0071] In a second aspect, the present invention provides a process for preparing an N-type battery based on the method for preparing a selective emitter according to the first aspect, the process comprising the following steps:

[0072] Boron is diffused on the silicon wafer after texturing to form a heavily boron-doped layer P+ layer;

[0073] Laser doping is performed on the metal gate line area on the silicon wafer;

[0074] Oxidizing the laser-doped silicon wafer to form a first-level light expansion area in the non-metallic gate line area;

[0075] Depositing a mask layer in the metal gate line area on the silicon wafer, and cleaning the silicon wafer with an etching solution, so that the non-metal gate line area forms a secondary light expansion area;

[0076] The boron doping surface concentration of the secondary light expansion region is less than the boron doping surface concentration of the primary light expansion region;

[0077] The borosilicate glass (BSG) layer and the expanded P+ layer on the back of the silicon wafer are removed, and a tunneling oxide layer and an amorphous silicon passivation layer are deposited on the back of the silicon wafer in sequence;

[0078] Removing the wrap-around and BSG layers on the front side of the silicon wafer and depositing an aluminum oxide passivation layer on the front side of the silicon wafer;

[0079] Depositing anti-reflection layers on the front and back sides of the silicon wafer;

[0080] Metal electrodes are prepared on both the front and back sides of the silicon wafer.

[0081] In a third aspect, the present invention provides an N-type battery, which is prepared using the preparation process described in the second aspect.

[0082] The N-type battery prepared by the present invention has excellent lifespan and conversion efficiency.

[0083] It should be noted that the present invention does not limit the specific type of N-type battery. For example, it can be a TOPCon battery.

[0084] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0085] Compared with the prior art, the present invention has the following beneficial effects:

[0086] (1) Based on the traditional boron diffusion SE process, the present invention adds micro-etching of the light diffusion area, thereby further reducing the doping concentration of the light diffusion area and effectively solving the problem of unclear doping concentration difference between the boron diffusion heavy diffusion area and the light diffusion area.

[0087] (2) The battery prepared based on the selective emitter preparation method provided by the present invention has excellent conversion efficiency and lifespan. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] FIG1 is a simplified process flow diagram of preparing a selective emitter in an embodiment provided by the present invention. DETAILED DESCRIPTION

[0089] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0090] Example 1

[0091] This embodiment provides a method for preparing a selective emitter, the process flow diagram of which is shown in FIG1 . The method comprises the following steps:

[0092] (1) Boron diffusion is performed on the N-type silicon wafer after texturing to form a re-expansion area;

[0093] The boron source for boron diffusion is boron trichloride with a flow rate of 300 sccm, the flow rate of nitrogen is 3500 ccm, the temperature of boron diffusion is 930 °C, the time is 110 min, the control square resistance is 110 ohm / sq, and the boron doping concentration in the re-expansion area is 1.24×10 20 cm -3 , thickness is 280nm;

[0094] (2) Laser doping of the metal gate line area on the silicon wafer;

[0095] The laser power is 300W, the laser speed is 30000mm / s, the laser is continuous laser, the laser wavelength is 800nm, and the boron doping surface concentration of the metal grid line area after laser doping is 2×10 19 cm -3 ;

[0096] (3) using an oxidation furnace to oxidize the laser-doped silicon wafer so that the non-metallic gate line area forms a first-level light expansion area;

[0097] The oxidation parameters are as follows: oxygen flow rate of 20 slm, oxidation temperature of 1020 °C, oxidation time of 5400 s, and boron doping surface concentration of the first-level light expansion area of ​​6×10 18 cm -3 ;

[0098] (4) A wax mask layer with a thickness of 40 μm was deposited in the metal gate line area on the silicon wafer, and the silicon wafer was cleaned with an etching solution for 180 s, so that the first-level light expansion area became a boron-doped surface with a concentration of 4.82×10 18 cm -3 Secondary light expansion zone;

[0099] The etching solution includes O3 with a concentration of 25 ppm, hydrofluoric acid with a concentration of 7 wt.%, and hydrochloric acid with a concentration of 0.07 wt.%. The surface resistance of the silicon wafer after cleaning is 250 ohm / sq.

[0100] This embodiment also provides a preparation process of a TOPCon battery, which comprises the following steps:

[0101] (a) After performing steps (1) to (4), the BSG layer and the expanded P+ layer on the back side of the silicon wafer are removed, and a tunneling oxide layer and an amorphous silicon passivation layer are sequentially deposited on the back side of the silicon wafer;

[0102] (b) removing the wrap-around and BSG layers on the front side of the silicon wafer, and depositing an aluminum oxide passivation layer on the front side of the silicon wafer;

[0103] (c) Silver paste electrodes are printed on the back of the silicon wafer and silver-aluminum paste electrodes are printed on the front, and then sintered to complete the battery preparation.

[0104] Example 2

[0105] This embodiment provides a method for preparing a selective emitter, the method comprising the following steps:

[0106] (1) Boron diffusion is performed on the N-type silicon wafer after texturing to form a re-expansion area;

[0107] The boron source for boron diffusion is boron trichloride with a flow rate of 200 sccm, the flow rate of nitrogen is 2000 sccm, the temperature of boron diffusion is 900℃, the time is 140 min, the control square resistance is 120 ohm / sq, and the boron doping concentration in the re-expansion area is 1.19×10 20 cm -3 , thickness is 200nm;

[0108] (2) Laser doping of the metal gate line area on the silicon wafer;

[0109] The laser power is 100W, the laser speed is 10000mm / s, the laser frequency is 15MHz, the laser wavelength is 500nm, and the boron doping surface concentration of the metal gate line area after laser doping is 1×10 19 cm -3 ;

[0110] (3) using an oxidation furnace to oxidize the laser-doped silicon wafer so that the non-metallic gate line area forms a first-level light expansion area;

[0111] The oxidation parameters are as follows: oxygen flow rate of 15 slm, oxidation temperature of 980 °C, oxidation time of 7200 s, and boron doping surface concentration of the first-level light expansion area of ​​6×10 18 cm -3 ;

[0112] (4) A wax mask layer with a thickness of 30 μm was deposited in the metal gate line area on the silicon wafer, and the silicon wafer was cleaned with an etching solution for 60 seconds, so that the first-level light expansion area became a boron-doped surface with a concentration of 4.57×10 18 cm -3 Secondary light expansion zone;

[0113] The etching solution includes O3 with a concentration of 20 ppm, hydrofluoric acid with a concentration of 5 wt.%, and hydrochloric acid with a concentration of 0.05 wt.%. The surface resistance of the silicon wafer after cleaning is 240 ohm / sq.

[0114] This embodiment also provides a preparation process of a TOPCon battery, which comprises the following steps:

[0115] (a) After performing steps (1) to (4), the BSG layer and the expanded P+ layer on the back side of the silicon wafer are removed, and a tunneling oxide layer and an amorphous silicon passivation layer are sequentially deposited on the back side of the silicon wafer;

[0116] (b) removing the wrap-around and BSG layers on the front side of the silicon wafer, and depositing an aluminum oxide passivation layer on the front side of the silicon wafer;

[0117] (c) Silver paste electrodes are printed on the back of the silicon wafer and silver-aluminum paste electrodes are printed on the front, and then sintered to complete the battery preparation.

[0118] Example 3

[0119] This embodiment provides a method for preparing a selective emitter, the method comprising the following steps:

[0120] (1) Boron diffusion is performed on the N-type silicon wafer after texturing to form a re-expansion area;

[0121] The boron source for boron diffusion is boron trichloride with a flow rate of 400 sccm, the flow rate of nitrogen is 5000 sccm, the temperature of boron diffusion is 950℃, the time is 80 min, the control square resistance is 90 ohm / sq, and the boron doping concentration in the re-expansion area is 1.35×10 20 cm -3 , thickness is 350nm;

[0122] (2) Laser doping of the metal gate line area on the silicon wafer;

[0123] The laser power is 500W, the laser speed is 50000mm / s, the laser frequency is 20Hz, the laser wavelength is 1100nm, and the boron doping surface concentration of the metal gate line area after laser doping is 3×10 19 cm -3 ;

[0124] (3) using an oxidation furnace to oxidize the laser-doped silicon wafer so that the non-metallic gate line area forms a first-level light expansion area;

[0125] The oxidation parameters are as follows: oxygen flow rate of 30 slm, oxidation temperature of 1050 °C, oxidation time of 3600 s, and boron doping surface concentration of the first-level light expansion area of ​​9×10 18 cm -3 ;

[0126] (4) A 50 μm thick graphite mask layer was deposited in the metal gate line area on the silicon wafer, and the silicon wafer was cleaned with an etching solution for 300 s, so that the first-level light expansion area became a boron-doped surface with a concentration of 5.19×10 18 cm -3 Secondary light expansion zone;

[0127] The etching solution includes O3 with a concentration of 30 ppm, hydrofluoric acid with a concentration of 10 wt.%, and hydrochloric acid with a concentration of 0.1 wt.%. The surface resistance of the silicon wafer after cleaning is 260 ohm / sq.

[0128] This embodiment also provides a preparation process of a TOPCon battery, which comprises the following steps:

[0129] (a) After performing steps (1) to (4), the BSG layer and the expanded P+ layer on the back side of the silicon wafer are removed, and a tunneling oxide layer and an amorphous silicon passivation layer are sequentially deposited on the back side of the silicon wafer;

[0130] (b) removing the wrap-around and BSG layers on the front side of the silicon wafer, and depositing an aluminum oxide passivation layer on the front side of the silicon wafer;

[0131] (c) Silver paste electrodes are printed on the back of the silicon wafer and silver-aluminum paste electrodes are printed on the front, and then sintered to complete the battery preparation.

[0132] Example 4

[0133] The difference between this embodiment and embodiment 1 is that the sheet resistance of the re-expansion region in step (1) is made 150 ohm / sq by adjusting the time of boron diffusion.

[0134] The rest of the preparation methods and parameters remained the same as in Example 1.

[0135] Example 5

[0136] The difference between this embodiment and embodiment 1 is that the power of the laser in step (2) is 600W.

[0137] The rest of the preparation methods and parameters remained the same as in Example 1.

[0138] Example 6

[0139] The difference between this embodiment and embodiment 1 is that the concentration of hydrofluoric acid in the etching solution in step (4) is 2 wt.%.

[0140] The rest of the preparation methods and parameters remained the same as in Example 1.

[0141] Example 7

[0142] The difference between this embodiment and embodiment 1 is that the concentration of hydrofluoric acid in the etching solution in step (4) is 15 wt.%.

[0143] The rest of the preparation methods and parameters remained the same as in Example 1.

[0144] Example 8

[0145] The difference between this embodiment and embodiment 1 is that the etching solution in step (4) does not contain O3.

[0146] The rest of the preparation methods and parameters remained the same as in Example 1.

[0147] Example 9

[0148] The difference between this embodiment and embodiment 1 is that the concentration of O3 in the etching solution in step (4) is 10 ppm.

[0149] The rest of the preparation methods and parameters remained the same as in Example 1.

[0150] Example 10

[0151] The difference between this embodiment and embodiment 1 is that the concentration of O3 in the etching solution in step (4) is 40 ppm.

[0152] The rest of the preparation methods and parameters remained the same as in Example 1.

[0153] Example 11

[0154] The difference between this embodiment and embodiment 1 is that the time for cleaning the silicon wafer in step (4) is 50 seconds.

[0155] The rest of the preparation methods and parameters remained the same as in Example 1.

[0156] Example 12

[0157] The difference between this embodiment and embodiment 1 is that the time for cleaning the silicon wafer in step (4) is 360 seconds.

[0158] The rest of the preparation methods and parameters remained the same as in Example 1.

[0159] Example 13

[0160] The difference between this embodiment and embodiment 1 is that the etching solution in step (4) does not include hydrochloric acid.

[0161] The rest of the preparation methods and parameters remained the same as in Example 1.

[0162] Comparative Example 1

[0163] The difference between this comparative example and Example 1 is that step (4) is not performed.

[0164] The rest of the preparation methods and parameters remained the same as in Example 1.

[0165] Comparative Example 2

[0166] The difference between this comparative example and Example 1 is that the mask layer is not deposited in the metal gate line area in step (4).

[0167] The rest of the preparation methods and parameters remained the same as in Example 1.

[0168] Performance Testing

[0169] The electrochemical performance of the TOPCon batteries prepared in Examples 1-13 and Comparative Examples 1-2 was tested.

[0170] The test method is: using the traditional Halm tester, under standard test conditions (25℃, 1000w / m 2 ) is carried out below.

[0171] The test results are shown in Table 1.

[0172] Table 1

[0173] analyze:

[0174] As can be seen from the table above, this invention, based on the traditional boron diffusion SE process, controls the boron diffusion square resistance and adds micro-etching in the light diffusion area. While achieving low-loss doping in the SE region (minimizing velvet loss to the silicon wafer), it also further reduces the doping concentration in the light diffusion area, effectively solving the problem of unclear doping concentration differences between the heavy and light diffusion areas. Furthermore, the battery produced using the selective emitter preparation method provided by this invention has excellent conversion efficiency and lifespan.

[0175] From the data results of Examples 1 and 4, it can be seen that if the sheet resistance of the re-expanded region is too large, the sheet resistance of the laser SE region will not decrease enough, resulting in poor ohmic contact in the metallized region and affecting battery efficiency.

[0176] It can be seen from the data results of Example 1 and Example 5 that if the laser power is too high, it will cause greater damage to the texture surface in the laser area, thereby causing the battery opening voltage and filling to be low, affecting the battery efficiency.

[0177] It can be seen from the data results of Example 1 and Examples 6-7 that if the concentration of hydrofluoric acid in the etching solution is too low, the micro-etching ability is insufficient, resulting in insufficient decrease in the concentration of the secondary light expansion zone; if the concentration of hydrofluoric acid in the etching solution is too high, the etching ability is enhanced, thereby affecting the suede morphology and affecting the battery current.

[0178] It can be seen from the data results of Example 1 and Example 8 that if the etching solution does not contain O 3 , the micro-etching ability is insufficient, resulting in insufficient concentration reduction in the secondary light expansion zone and low efficiency.

[0179] It can be seen from the data results of Examples 1 and 9-10 that if the concentration of O3 in the etching solution is too low, the micro-etching ability is insufficient, resulting in high surface recombination in the secondary light expansion area and reduced efficiency; if the concentration of O3 in the etching solution is too high, the etching ability is enhanced, but it will affect the suede morphology and affect the battery current.

[0180] It can be seen from the data results of Example 1 and Examples 11-12 that if the cleaning time of the silicon wafer is too short, the micro-etching ability is insufficient, resulting in high surface recombination in the secondary light expansion area and reduced efficiency; if the cleaning time of the silicon wafer is too long, the etching ability is enhanced, but it will affect the suede morphology and affect the battery current.

[0181] From the data results of Example 1 and Example 13, it can be seen that if the etching solution does not contain hydrochloric acid, the solubility of O3 in the etching solution will be affected, resulting in insufficient micro-etching ability, which will lead to high surface recombination in the secondary light expansion area and reduced efficiency.

[0182] It can be seen from the data results of Example 1 and Comparative Example 1 that if the silicon wafer is not etched, the surface concentration of the light absorption area will be too high, which will lead to high recombination on the battery surface and affect the battery opening voltage.

[0183] From the data results of Example 1 and Comparative Example 2, it can be seen that if the metal gate line region is not masked during the etching process, the SE region is exposed to the etching solution, resulting in an increase in the actual doping concentration of the SE region, affecting the ohmic contact during metallization.

[0184] The applicant declares that while the above-described embodiments illustrate the preparation method of the present invention, the present invention is not limited to these embodiments, and does not necessarily rely on these embodiments for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for raw materials in the product of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a selective emitter, characterized in that: The preparation method comprises: Boron diffusion is performed on the silicon wafer after texturing to form a re-expansion area; Laser doping is performed on the metal gate line area on the silicon wafer; Oxidizing the laser-doped silicon wafer so that the non-metallic gate line area forms a primary light expansion area; Depositing a mask layer in the metal gate line area on the silicon wafer, and cleaning the silicon wafer with an etching solution, so that the primary light expansion area becomes a secondary light expansion area; The boron-doped surface concentration of the secondary lightly expanded region is less than the boron-doped surface concentration of the primary lightly expanded region.

2. The preparation method according to claim 1, characterized in that: During the laser doping advancement process, the power of the laser is in the range of 100 to 500 W; The speed range of the laser is 10000 to 50000 mm / s; The laser is a continuous laser or a laser with a frequency greater than 10 MHz; The wavelength of the laser is in the range of 500 to 1100 nm; After the laser doping is advanced, the boron doping concentration range of the metal gate line area is 1×10 19 Up to 3×10 19 cm -3 .

3. The preparation method according to claim 1, characterized in that: The boron source for boron diffusion includes any one of boron trichloride, boron tribromide, trimethylboron or ethylenediborane, or a combination of at least two thereof; The flow rate of the boron source ranges from 200 to 400 sccm; The temperature range of the boron diffusion is 900 to 950°C; Nitrogen is also introduced during the boron diffusion process; The flow rate of the nitrogen gas is in the range of 2000 to 5000 sccm; The boron diffusion time ranges from 80 to 140 minutes.

4. The preparation method according to claim 1, characterized in that: The square resistance of the re-expanded area ranges from 90 to 120 ohm / sq; The boron doping surface concentration of the re-expanded region is in the range of 1.1×10 20 to 1.5×10 20 cm -3 ; The thickness of the re-expanded region is in the range of 200 to 350 nm.

5. The preparation method according to claim 1, characterized in that: During the oxidation process, the flow rate of oxygen is in the range of 15 to 30 slm; The oxidation temperature range is 980 to 1050°C; The oxidation time ranges from 3600 to 7200 s; The boron doping surface concentration range of the primary light expansion region is 4×10 18 Up to 9×10 18 cm -3 .

6. The preparation method according to claim 1, characterized in that: The thickness of the mask layer ranges from 30 to 50 μm; The material of the mask layer includes wax or graphite.

7. The preparation method according to claim 1, characterized in that: The etching solution includes hydrofluoric acid and / or hydrochloric acid; The concentration of the hydrofluoric acid is in the range of 5 to 10 wt.%; The concentration of the hydrochloric acid ranges from 0.05 to 0.1 wt.%; The etching solution also includes ozone O3; The concentration range of O3 is 20 to 30 ppm; The cleaning time ranges from 60 to 300 seconds; The surface resistance of the cleaned silicon wafer is in the range of 240 to 260 ohm / sq; The boron doping surface concentration range of the secondary light expansion region is 2×10 18 Up to 7×10 18 cm -3 .

8. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: Boron diffusion is performed on the N-type silicon wafer after texturing to form a re-expansion area; The boron source flow rate range of boron diffusion is 200 to 400 sccm, the nitrogen flow rate range is 2000 to 5000 sccm, the boron diffusion temperature range is 900 to 950 °C, the time range is 80 to 140 min, the control square resistance range is 90-120 ohm / sq, and the boron doping concentration range of the re-expansion area is 1.1×10 20 to 1.5×10 20 cm -3 , thickness ranges from 200 to 350 nm; Laser doping is performed on the metal gate line area on the silicon wafer; The power range of the laser is 100 to 500 W, the speed range of the laser is 10,000 to 50,000 mm / s, the laser is a continuous laser or a laser with a frequency greater than 10 MHz, the wavelength range of the laser is 500 to 1100 nm, and the boron doping surface concentration range of the metal grid line area after laser doping is 1×10 19 Up to 3×10 19 cm -3 ; Oxidizing the laser-doped silicon wafer so that the non-metallic gate line area forms a primary light expansion area; The oxygen flow rate range is 15 to 30 slm, the oxidation temperature range is 980 to 1050 °C, the time range is 3600 to 7200 s, and the boron doping surface concentration range of the primary light expansion zone is 4×10 18 Up to 9×10 18 cm -3 ; A mask layer with a thickness ranging from 30 to 50 μm is deposited in the metal gate line area on the silicon wafer, and the silicon wafer is cleaned with an etching solution for a time ranging from 60 to 300 seconds, so that the first-level light expansion area becomes a boron-doped surface with a concentration range of 2×10 18 Up to 7×10 18 cm -3 The secondary light expansion area; The etching solution includes O3 with a concentration range of 20 to 30 ppm, hydrofluoric acid with a concentration range of 5 to 10 wt.%, and hydrochloric acid with a concentration range of 0.05 to 0.1 wt.%. The surface resistance of the cleaned silicon wafer ranges from 240 to 260 ohm / sq.

9. A process for preparing an N-type battery based on the method for preparing a selective emitter according to any one of claims 1 to 8, characterized in that: The preparation process comprises the following steps: Boron is diffused on the silicon wafer after texturing to form a heavily boron-doped layer P+ layer; Laser doping is performed on the metal gate line area on the silicon wafer; Oxidizing the laser-doped silicon wafer so that the non-metallic gate line area forms a primary light expansion area; Depositing a mask layer in the metal gate line region on the silicon wafer, and cleaning the silicon wafer with an etching solution, so that the non-metal gate line region forms a secondary light expansion region; Wherein, the boron doping surface concentration of the secondary light expansion region is less than the boron doping surface concentration of the primary light expansion region; The borosilicate glass (BSG) layer and the expanded P+ layer on the back of the silicon wafer are removed, and a tunneling oxide layer and an amorphous silicon passivation layer are sequentially deposited on the back of the silicon wafer; Removing the wrap-around and BSG layers on the front side of the silicon wafer, and depositing an aluminum oxide passivation layer on the front side of the silicon wafer; Depositing anti-reflection layers on the front and back sides of the silicon wafer; Metal electrodes are prepared on both the front and back sides of the silicon wafer.

10. An N-type battery, characterized in that: The N-type battery is prepared by the preparation process as claimed in claim 9.

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