Method of making tbc cells

Abstract

The present disclosure relates to a preparation method of a TBC battery. The method comprises: preparing P-type polysilicon on the back of a silicon substrate; removing P-type polysilicon in the interval region between the P region and the N region, and removing P-type polysilicon in the N region, to expose the silicon substrate in the interval region and the N region; preparing N-type polysilicon on the back of the silicon substrate; removing PSG in the P region and the interval region by using a first laser, wherein the irradiation direction of the first laser is at a first angle with the extension direction of the sidewall between the P region and the interval region, and the first angle is in the range of (0°, 90°]. Removing N-type polysilicon in the P region and the interval region; preparing a P region electrode in the P region and an N region electrode in the N region. Since the laser is deflected at a certain angle towards the sidewall, the PSG in the sidewall is removed more thoroughly, so that the N-poly protected by PSG on the sidewall of the P region is more easily removed, reducing the risk of TBC battery recombination and leakage.

Description

Technical Field

[0001] This disclosure relates to solar cell fabrication technology, specifically, to a method for fabricating a TBC cell. Background Technology

[0002] TBC cells are high-efficiency solar cells that combine tunnel oxide passivated contact (TOPCon) technology with back contact (BC) structure. Their full name is TOPCon BackContact or POLO-IBC cell.

[0003] The core of TBC batteries lies in combining the passivation contact characteristics of TOPCon technology with a back contact design. In TOPCon technology, excellent surface passivation is achieved through a tunneling oxide layer (e.g., SiO2) and a doped polycrystalline silicon layer (poly-Si), reducing carrier recombination and improving open-circuit voltage. In the back contact design, all metal electrodes are arranged in an interdigitated pattern on the back of the battery, eliminating front-side grid line obstruction, increasing the light absorption area, and thus improving conversion efficiency. Summary of the Invention

[0004] The purpose of this disclosure is to provide a method for preparing a TBC battery that can reduce recombination and leakage in the TBC battery.

[0005] To achieve the above objectives, this disclosure provides a method for preparing a TBC battery, the method comprising:

[0006] P-type polycrystalline silicon is fabricated on the back side of a silicon substrate;

[0007] Remove the P-type polysilicon in the spacer region between the P-region and the N-region, and remove the P-type polysilicon in the N-region, exposing the silicon substrate in the spacer region and the N-region;

[0008] N-type polycrystalline silicon is prepared on the back side of the silicon substrate;

[0009] The PSG in the P region and the spacer region is removed by a first laser, wherein the irradiation direction of the first laser on the sidewall between the P region and the spacer region forms a first angle with the direction of extension of the sidewall, and the value of the first angle is in the range of (0°, 90°).

[0010] Remove the N-type polysilicon from the P-region and the spacer region;

[0011] A P-region electrode is fabricated in the P-region, and an N-region electrode is fabricated in the N-region.

[0012] Optionally, in the P region and the interval region, the irradiation direction of the first laser is consistent with the direction of extension of the sidewall.

[0013] Optionally, the first angle can be in the range of [5°, 30°].

[0014] Optionally, the fabrication of P-type polycrystalline silicon on the back side of the silicon substrate includes:

[0015] First, a first tunneling oxide layer is deposited on the back side of the silicon substrate;

[0016] The P-type polycrystalline silicon is deposited on the first tunnel oxide layer.

[0017] Optionally, removing the P-type polysilicon from the spacer region between the P-region and the N-region, and removing the P-type polysilicon from the N-region, includes:

[0018] The BSG in the spacer region between the P region and the N region is removed using a second laser, and the BSG in the N region is also removed.

[0019] The P-type polycrystalline silicon in the spacer region and the N-region is removed by alkaline washing using a wet tank washing machine.

[0020] Optionally, before fabricating N-type polycrystalline silicon on the back side of the silicon substrate, the method further includes:

[0021] A second tunneling oxide layer is deposited on the back side of the silicon substrate.

[0022] Optionally, the deposition time of the second tunnel oxide layer is 500-1200s, the temperature is 590-630℃, and the thickness is 1.95±0.3nm.

[0023] Optionally, the removal of the N-type polysilicon from the P-region and the spacer region includes:

[0024] The N-type polysilicon in the P-region and the spacer region is removed by alkaline washing using a wet tank washing machine.

[0025] Optionally, the first laser power is 40-50W, the overlap rate is 50-60%, the frequency is 500-600kHz, and the pulse width is 0.8-1.2μs.

[0026] Optionally, the PSG has a thickness of 50±5 nm and a sheet resistance of 25±5.

[0027] Through the above technical solution, during the fabrication of TBC batteries, when using a laser to remove PSG from the P-region and gap (GAP) region on the back of the TBC battery, the PSG on the sidewall between the P-region and the GAP region is irradiated with a laser whose irradiation direction forms a first angle with the direction of the sidewall's extension. That is, when the laser moves to the position corresponding to the sidewall between the P-region and the gap region, the irradiation direction of the laser is deflected towards the sidewall at a certain angle. Compared to related technologies where the laser is always irradiated perpendicular to the bottom surface of the TBC battery, the PSG on the sidewall is removed more thoroughly because the laser is deflected towards the sidewall at a certain angle. This makes it easier to remove the N-poly protected by PSG on the P-region sidewall, reducing the risk of TBC battery recombination and leakage.

[0028] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0029] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0030] Figure 1 This is a flowchart of a method for preparing a TBC battery, provided in an exemplary embodiment.

[0031] Figure 2 This is a schematic diagram of a first laser irradiation angle provided in an exemplary embodiment.

[0032] Figure 3 This is a schematic diagram of a first laser irradiation angle provided in another exemplary embodiment.

[0033] Figure 4 This is a schematic diagram of deposited N-type polysilicon provided in an exemplary embodiment.

[0034] Figure 5 yes Figure 4 A schematic diagram of the first laser irradiation angle in the embodiment.

[0035] Figure 6 This is a schematic diagram of the process of removing PSG and cleaning N-type polysilicon using laser in related technologies.

[0036] Figure 7 This is a schematic diagram of an exemplary embodiment of a LP test prior to the removal of PSG by first laser irradiation.

[0037] Figure 8 This is a schematic diagram of LP testing after removing PSG and cleaning N-poly using laser without deflection in the existing technology.

[0038] Figure 9 This is a schematic diagram of the LP test after removing PSG and cleaning N-poly using a first laser irradiation according to an embodiment of this disclosure.

[0039] Explanation of reference numerals in the attached figures

[0040] 1N-type silicon substrate, 2 boron doped layer, 3P region corresponding tunneling layer

[0041] 4P-poly layer 5BSG layer 6P phosphorus doped layer

[0042] The tunneling layer corresponding to region 7N is the 8N-poly layer and the 9PSG layer.

[0043] 10 Irradiation area of ​​the first laser Detailed Implementation

[0044] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0045] In this disclosure, unless otherwise stated, directional terms such as "front" and "back" are used in accordance with the conventional descriptive methods for TBC batteries in the related art.

[0046] In related technologies, the area between the P-region and N-region on the back side of a TBC cell is called the gap region. During TBC cell fabrication, P-type polycrystalline silicon is fabricated on a silicon substrate, and N-type polycrystalline silicon is fabricated by creating grooves in the area outside the P-region, generating a phosphosilicate glass (PSG) layer. Subsequently, the P-region and gap region can be vertically irradiated with a laser to remove the PSG layer, followed by cleaning away the N-type polycrystalline silicon in both regions. Due to the height difference between the P-region and the gap region, vertical laser irradiation cannot completely remove the PSG on the P-region sidewalls, making it difficult to completely remove the PSG protected by the PSG from the P-region sidewalls using wet methods. Increasing the wet alkali concentration or extending the cleaning time to remove the N-poly may cause perforation of the N-region PSG, affecting the final efficiency. Therefore, this solution provides a TBC cell fabrication method that deflects the laser towards the P-region sidewalls at a certain angle, allowing for more thorough removal of the PSG from the P-region sidewalls.

[0047] Figure 1 This is a flowchart illustrating a method for preparing a TBC battery, as provided in an exemplary embodiment. Figure 1 As shown, the method includes the following steps.

[0048] Step S101: Prepare P-type polycrystalline silicon on the back side of the silicon substrate. The silicon substrate can be an N-type silicon substrate.

[0049] Step S102: Remove the P-type polysilicon from the GAP region between the P-region and the N-region, and remove the P-type polysilicon from the N-region, exposing the silicon substrate in the GAP region and the N-region.

[0050] Step S103: Prepare N-type polycrystalline silicon on the back side of the silicon substrate.

[0051] Step S104: Use a first laser to remove PSG from the P region and the GAP region, wherein the irradiation direction of the first laser on the sidewall between the P region and the GAP region forms a first angle with the direction of the sidewall extension, and the value of the first angle is (0°, 90°).

[0052] Step S105: Remove the N-type polysilicon from the P-region and GAP region.

[0053] Step S106: Prepare a P-region electrode in the P-region and an N-region electrode in the N-region.

[0054] In step S102, the P-type polysilicon in the GAP and N regions is removed, exposing the silicon substrate in the GAP and N regions. This is achieved by creating grooves in the GAP and N regions, thus creating sidewalls between the P and GAP regions. When subsequently fabricating N-type polysilicon, the sidewalls also contain N-type polysilicon and PSG (polysilicon-as-growth gas). In related technologies, the PSG in the P and GAP regions can be removed first using a laser, followed by cleaning away the N-type polysilicon in the P and GAP regions.

[0055] The sidewall extends from the back of the TBC cell towards the front, that is, perpendicular to the polycrystalline silicon surface in the P-region and N-region. In related technologies, when removing PSG from the P-region and GAP region using a laser, the laser irradiation direction is consistent with the sidewall extension direction. However, in existing technologies, perpendicular laser irradiation usually cannot completely remove PSG from the P-region sidewall. In this solution, on the sidewall between the P-region and GAP region, the irradiation direction of the first laser forms a first angle with the sidewall extension direction, the first angle ranging from (0° to 90°). Those skilled in the art will understand that the first laser should irradiate towards the sidewall. The power of the first laser can be 40-50W, the overlap rate can be 50-60%, the frequency can be 500-600kHz, and the pulse width can be 0.8-1.2μs.

[0056] Figure 2 This is a schematic diagram of a first laser illumination angle provided in an exemplary embodiment. As shown, for emphasis, Figure 2The diagram schematically shows only a portion of a P-region, an adjacent GAP region, and an adjacent N-region on the back side of a TBC cell. The protruding portion on the back side is the P-region, on which P-type polycrystalline silicon (not shown) is deposited. The recessed portion on the back side includes the N-region and the GAP region, with the GAP region located between the P-region and the N-region. After the N-type polycrystalline silicon is fabricated, PSG in the P-region and the GAP region is removed using a first laser. The first laser irradiates towards the sidewall of the P-region, and the PSG within the irradiated area 10 of the first laser can be removed. The irradiation direction of the first laser forms a first angle θ with the direction of the sidewall extension.

[0057] In actual operation, the laser emitter can emit a laser beam once every predetermined distance. When it moves to the position corresponding to the sidewall of region P, it can irradiate the sidewall of region P, making the irradiation direction form a first angle with the direction in which the sidewall extends. The value of the first angle can be determined in advance based on experiments or experience, preferably one that allows the first laser to completely cover the sidewall area.

[0058] Preferably, the first angle ranges from [5° to 30°]. Within this angle range, the laser can illuminate the sidewall of area P with a suitable tilt angle. This ensures that the laser is not too close to the sidewall due to an excessively small tilt angle, which would prevent the area near the light source from being irradiated, nor that too much laser light is irradiated outside the sidewall due to an excessively large tilt angle, which would result in energy waste and unnecessary interference to other areas. This ensures that the laser can fully cover the sidewall area, enabling effective detection, processing, or other expected operations in that area.

[0059] Meanwhile, an angle range of 5° to 30° is relatively moderate, making it easier to achieve and control in actual operation. Whether it's installing and adjusting the laser emitter or maintaining a stable illumination angle throughout the system's operation, it's relatively easy to achieve. Therefore, this angle range helps improve the stability and reliability of the entire operation process, reducing operational errors or poor results caused by angle deviations.

[0060] Through the above technical solution, during the fabrication of TBC batteries, when removing PSG from the P-region and GAP-region on the back of the TBC battery using a laser, the PSG on the sidewall between the P-region and GAP-region is irradiated with a laser whose irradiation direction forms a first angle with the direction of the sidewall's extension. That is, when the laser moves to the position corresponding to the sidewall between the P-region and GAP-region, the irradiation direction of the laser is deflected towards the sidewall at a certain angle. Compared to related technologies where the laser is always irradiated perpendicular to the bottom surface of the TBC battery, the deflection of the laser towards the sidewall at a certain angle allows for more thorough removal of PSG from the sidewall. This makes it easier to completely remove the N-poly protected by PSG on the P-region sidewall, reducing the risk of TBC battery recombination and leakage.

[0061] In another embodiment, in the P-region and GAP-region, the irradiation direction of the first laser is consistent with the direction of the sidewall extension. That is, in the P-region and GAP-region, the first laser irradiates in a direction perpendicular to the back of the TBC battery. Figure 3 This is a schematic diagram of a first laser irradiation angle provided in another exemplary embodiment. Figure 3 The illumination angles of the first laser on region P and the sidewall are shown. The first laser moves and illuminates at predetermined intervals. When it reaches region P, it illuminates vertically. When it reaches outside the sidewall, the illumination angle deflects to illuminate the sidewall at a first angle θ. It can then deflect back to continue illuminating region GAP (not shown) vertically.

[0062] In this embodiment, the P-zone, sidewall, and GAP-zone can all be irradiated to a large extent, resulting in good PSG removal effect and high laser utilization.

[0063] In another embodiment, P-type polycrystalline silicon is prepared on the back side of a silicon substrate, comprising: firstly depositing a first tunneling oxide layer on the back side of the silicon substrate; and secondly depositing a P-type polycrystalline silicon layer on the first tunneling oxide layer. The first tunneling oxide layer is a tunneling layer corresponding to the P-region.

[0064] For example, the deposition time of the first tunneling oxide layer is 1000-3000s, the deposition temperature is 590-630℃, and the thickness of the first tunneling oxide layer is 2±0.3nm; the deposition time of the P-type polycrystalline silicon layer is 11000-13000s, the deposition temperature is 550-570℃, and the thickness of the P-type polycrystalline silicon layer is 300±50nm.

[0065] The first tunneling layer can reduce surface recombination, form field passivation, and improve battery efficiency and stability.

[0066] When fabricating P-type polycrystalline silicon on the back side of a silicon substrate, a borosilicate glass (BSG) layer can be formed. For example, a low-pressure chemical vapor deposition (LPCVD) process can be used. The BSG layer can have a thickness of 60±5 nm and a sheet resistance of 120±20.

[0067] In another embodiment, removing the P-type polysilicon from the gap region between the P-region and the N-region, and removing the P-type polysilicon from the N-region, includes:

[0068] The second laser is used to remove the BSG in the gap between the P and N regions, and also to remove the BSG in the N region.

[0069] The P-type polysilicon in the GAP and N regions is removed by alkaline washing using a wet tank washing machine.

[0070] In the case of BSG formation, a second laser can be used to first remove the BSG layers in the GAP and N regions, and then the P-type polysilicon in the GAP and N regions can be cleaned away. For example, the power of the second laser can be 40-50W, the overlap ratio can be 50-60%, the frequency can be 500-600kHz, and the pulse width can be 0.8-1.2μs. A wet alkaline polishing tank machine can be used, with a tank temperature of 50-75℃ and a process time of 200-300s. The alkaline solution used for alkaline washing can be composed of H2O, NaOH, and polishing additives in a volume ratio of 450:25:7.

[0071] It is understood that the distinction between the first laser and the second laser is merely for the sake of convenience and is not intended to limit the order of implementation.

[0072] In yet another embodiment, prior to fabricating N-type polycrystalline silicon on the back side of the silicon substrate, the method further includes:

[0073] A second tunneling oxide layer is deposited on the back side of the silicon substrate. The second tunneling oxide layer is the tunneling layer corresponding to the N-region.

[0074] For example, the deposition time of the second tunneling oxide layer is 500-1200 s, the deposition temperature is 590-630℃, and the thickness of the formed second tunneling oxide layer is 1.95±0.3 nm; the deposition time of the N-type polycrystalline silicon layer is 3500-5000 s, the deposition temperature is 605-620℃, and the thickness of the formed N-type polycrystalline silicon layer is 280±30 nm. The thickness of the PSG layer can be 50±5 nm, and the sheet resistance is 25±5.

[0075] Depositing a second tunnel oxide layer can reduce surface recombination, form field passivation, and improve battery efficiency and stability.

[0076] In another embodiment, removing the N-type polysilicon from the P-region and GAP-region includes: performing alkaline washing by a wet tank washing machine to remove the N-type polysilicon from the P-region and GAP-region.

[0077] Using a wet cell mill, while removing N-type polysilicon from the P-region and GAP-region, a pyramidal textured surface can be formed on the Gap-region and the front side. The alkaline solution for texturing consists of H2O, NaOH, and texturing additives in a volume ratio of 470:6:11. The solution temperature is 70-80℃, and the process time is 450-650s.

[0078] Figure 4 This is a schematic diagram of deposited N-type polysilicon provided in an exemplary embodiment. (Combined with...) Figure 4 The steps of a method for preparing a TBC battery provided in an exemplary embodiment are as follows.

[0079] 1) The N-type silicon substrate 1 is polished on both sides in a wet alkaline polishing tank. The alkaline solution used is composed of H2O, NaOH and polishing additives in a volume ratio of 450:30:5. The process time is 250-400s, and the tank temperature of the wet alkaline polishing tank is 60-75℃.

[0080] 2) A tunneling layer 3 corresponding to the P region is deposited on the back side of the N-type silicon substrate 1. The deposition time of the tunneling layer 3 corresponding to the P region is 1000-3000s, the deposition temperature is 590-630℃, and the thickness of the tunneling layer 3 corresponding to the P region is 2±0.3nm.

[0081] 3) Intrinsic polycrystalline silicon is deposited on the tunneling layer 3 corresponding to the P region using LPCVD process, and boron diffusion is performed using high temperature boron diffusion process to generate P-poly layer 4 and BSG layer 5, and a boron internal doped layer (PN junction) 2 is formed between N-type silicon substrate 1 and tunneling layer 3 corresponding to the P region.

[0082] The deposition time of P-poly layer 4 is 11000-13000 s, the deposition temperature is 550-570℃, and the thickness of P-poly layer 4 is 300±50 nm. The pre-crystallization temperature of boron diffusion is 950-980℃, the crystallization time is 2500-3000 s; the diffusion temperature is 800-870℃, the diffusion time is 300-600 s; the advance temperature is 930-960℃, the advance time is 500-800 s; the oxidation temperature is 850-950℃, the oxidation time is 3000-3500 s; the post-annealing temperature is 950-980℃, the thickness of BSG layer 5 is 60±5 nm, and the sheet resistance is 120±20.

[0083] 4) Laser removal of the BSG layer between the N-region and the Gap region on the back side.5. Laser power is 40-50W, overlap rate is 50-60%, frequency is 500-600kHz, and pulse width is 0.8-1.2μs.

[0084] 5) Acid pickling is performed using a wet chain machine to remove BSG from the front and sides. The tank temperature of the wet acid pickling chain machine is 20-50℃, and the overall process time is 50-80s. The chain machine has two acid tanks. The acid solution in the first acid tank is composed of H2O and HF in a volume ratio of 2:5, and the acid solution in the second acid tank is composed of H2O and HF in a volume ratio of 3:4. Alkali washing is performed using a wet alkaline washing machine to remove the P-poly layer on the front and sides, as well as the P-poly layer in the Gap and N regions. The tank temperature of the wet alkaline polishing tank is 50-75℃, and the process time is 200-300s. The alkaline solution used for alkaline washing is composed of H2O, NaOH, and polishing additives in a volume ratio of 450:25:7.

[0085] 6) Deposit the tunneling layer 7 corresponding to the N region on the back side. The deposition time of the tunneling layer 7 corresponding to the N region is 500-1200s, the temperature is 590-630℃, and the thickness of the tunneling layer 7 corresponding to the N region is 1.95±0.3nm.

[0086] 7) Intrinsic polycrystalline silicon is deposited on the tunneling layer 7 corresponding to the N region using LPCVD process, and phosphorus diffusion is performed using high temperature phosphorus diffusion process to generate N-poly layer 8 and PSG layer 9, and phosphorus doped layer 6 is formed between BSG layer 5 and tunneling layer 7 corresponding to the N region.

[0087] The polycrystalline silicon deposition time was 3500-5000 s, the deposition temperature was 605-620℃, and the thickness was 280±30 nm. The phosphorus diffusion temperature was 800-820℃, the diffusion time was 1200-1500 s, the drive-through temperature was 870-890℃, the drive-through time was 800-1200 s, the oxidation temperature was 910-930℃, and the oxidation time was 600-900 s. The PSG layer 9 had a thickness of 50±5 nm and a sheet resistance of 25±5. The structure after PSG layer 9 formation is as follows... Figure 4 As shown.

[0088] 8) Laser removal of the PSG layer in the P-area and Gap-area on the back side: 9) Figure 5 yes Figure 4 A schematic diagram of the first laser irradiation angle in the embodiment. The laser wavelength can be 532nm, the pulse duration is 0.4-1.3μs, the pulse energy is 50-150μJ, the frequency is 300-1000kHz, and the pulse width is 0.8-1.2μs.

[0089] 9) Cleaning: Remove PSG from the front and sides using a wet chain machine. The chain machine tank temperature is 20-50℃, and the process time is 30-60s. The chain machine has two acid tanks. The acid solution in the first acid tank is composed of H2O and HF in a volume ratio of 2:5, and the acid solution in the second acid tank is composed of H2O and HF in a volume ratio of 3:4. The N-poly layer on the front and sides and the N-poly layer in the P area and Gap area on the back are removed by the tank machine.

[0090] Figure 6 This is a schematic diagram illustrating the laser removal of PSG and cleaning of N-type polysilicon in related technologies. In these technologies, the laser is always irradiated perpendicular to the bottom surface of the TBC cell. The PSG layer 9 in the sidewall is not completely removed, and the N-poly layer 8 protected by PSG on the P-region sidewall is not completely removed. Figure 6As shown. Compared with related technologies where the laser is always irradiated perpendicular to the bottom surface of the TBC battery, in this solution, the laser is deflected at a certain angle toward the sidewall, so that the laser energy can be distributed in the area near the bottom of the groove in the sidewall. The PSG in the sidewall is removed more thoroughly, making it easier to remove the N-poly protected by PSG on the P-area sidewall.

[0091] While removing the N-poly layer 8, a pyramidal velvet surface is formed in the gap area and on the front side. The alkaline solution for velvet formation consists of H2O, NaOH and velvet additives in a volume ratio of 470:6:11. The solution temperature is 70-80℃ and the process time is 450-650s.

[0092] 10) Using atomic layer deposition (ALD) technology, an aluminum oxide layer is deposited by back-to-back double insertion; the ALD process temperature is 300℃, the process time is 900s, and the thickness of the aluminum oxide layer is 4.3±1nm.

[0093] 11) Front-side coating process, temperature 540℃, consisting of 6 layers, deposited in the following order from the silicon substrate outwards: first silicon nitride layer, second silicon nitride layer, third silicon nitride layer, first silicon oxynitride layer, second silicon oxynitride layer, and silicon oxide layer. The difference between the silicon nitride and silicon oxynitride layers is their refractive index. The thickness of each layer is between 10-25 nm, with an overall film thickness of 75±5 nm and a refractive index of 2.10±0.05.

[0094] 12) Backside coating process, temperature 530℃, divided into 3 layers, deposited in the order of fourth silicon nitride layer, fifth silicon nitride layer and sixth silicon nitride layer from the substrate silicon. The difference between the silicon nitride layers is the refractive index. The thickness of each layer is 10-30nm, the overall thickness of the film is 84±6nm, and the refractive index is 2.12±0.05.

[0095] 13) Screen printing: Metal grid lines are formed on the back side through screen printing. The metal and semiconductor form ohmic contacts after high-temperature sintering to collect and conduct current. It can be done in three layers: the first layer prints the back main grid (9-24 grid lines); the second layer prints the back N-area fine grid (150-250 grid lines with a line width of 4-13µm); the third layer prints the back P-area fine grid (150-250 grid lines with a line width of 4-13µm). The peak sintering temperature is generally 680-750℃.

[0096] This disclosure also provides a characterization method for determining whether internal doping has occurred on the sidewall of the P-region, as follows:

[0097] The N-poly on the front side of the TBC battery is retained as the front passivation layer. After the laser removal in step 8) and the cleaning in step 9) on the back side, the P-region and N-region formed are passivated by P-poly and N-poly, respectively.

[0098] If the photoluminescence (PL) test after cleaning in step 9) is the same as before cleaning, and both show blackening, it indicates that severe recombination has occurred in this area, and the sidewall doping has not been completely removed. If the overall PL shows no blackening after cleaning, and there is a significant improvement compared to before cleaning in step 9), it indicates that the sidewall doping has been basically removed. This method can be used as a characterization tool to determine whether sidewall doping has occurred.

[0099] Figure 7 This is a schematic diagram of an exemplary embodiment of a LP test prior to the removal of PSG by first laser irradiation. Figure 8 This is a schematic diagram of LP testing after removing PSG and cleaning N-poly using laser without deflection in the existing technology. Figure 9 This is a schematic diagram of the LP test after removing PSG and cleaning N-poly using a first laser irradiation according to an embodiment of this disclosure.

[0100] Figures 7-9 In the diagram, the light intensity (unit: cd) gradually increases from black to yellow. Figure 7 In the first laser irradiation to remove PSG, the detected light intensity was very weak, indicating severe doping within the sidewalls. Figure 8 If some areas of the PL still turn black after cleaning, it indicates that severe recombination has occurred in these areas and the dopants in the sidewalls have not been completely removed. Figure 9 After cleaning, the PL test showed almost no blackened areas, indicating that no serious recombination occurred and the dopants inside the sidewalls were removed relatively cleanly.

[0101] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0102] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0103] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for preparing a TBC battery, characterized in that, The method includes: P-type polycrystalline silicon is fabricated on the back side of a silicon substrate; Remove the P-type polysilicon in the spacer region between the P-region and the N-region, and remove the P-type polysilicon in the N-region, exposing the silicon substrate in the spacer region and the N-region; N-type polycrystalline silicon is prepared on the back side of the silicon substrate; The PSG in the P region and the spacer region is removed by a first laser, wherein the irradiation direction of the first laser on the sidewall between the P region and the spacer region forms a first angle with the direction of extension of the sidewall, and the value of the first angle is in the range of (0°, 90°). Remove the N-type polysilicon from the P-region and the spacer region; A P-region electrode is fabricated in the P-region, and an N-region electrode is fabricated in the N-region.

2. The method according to claim 1, characterized in that, In the P region and the interval region, the irradiation direction of the first laser is consistent with the direction of extension of the sidewall.

3. The method according to claim 1, characterized in that, The first angle has a range of [5°, 30°].

4. The method according to claim 1, characterized in that, The fabrication of P-type polycrystalline silicon on the back side of a silicon substrate includes: First, a first tunneling oxide layer is deposited on the back side of the silicon substrate; The P-type polycrystalline silicon is deposited on the first tunnel oxide layer.

5. The method according to claim 1, characterized in that, The removal of the P-type polysilicon from the spacer region between the P-region and the N-region, and the removal of the P-type polysilicon from the N-region, includes: The BSG in the spacer region between the P region and the N region is removed using a second laser, and the BSG in the N region is also removed. The P-type polycrystalline silicon in the spacer region and the N-region is removed by alkaline washing using a wet tank washing machine.

6. The method according to claim 1, characterized in that, Before fabricating N-type polycrystalline silicon on the back side of the silicon substrate, the process further includes: A second tunneling oxide layer is deposited on the back side of the silicon substrate.

7. The method according to claim 6, characterized in that, The deposition time of the second tunnel oxide layer is 500-1200s, the temperature is 590-630℃, and the thickness is 1.95±0.3nm.

8. The method according to claim 1, characterized in that, The removal of the P-region and the spacer region from the N-type polysilicon includes: The N-type polysilicon in the P-region and the spacer region is removed by alkaline washing using a wet tank washing machine.

9. The method according to claim 1, characterized in that, The first laser has a power of 40-50W, an overlap rate of 50-60%, a frequency of 500-600kHz, and a pulse width of 0.8-1.2μs.

10. The method according to claim 1, characterized in that, The PSG has a thickness of 50±5nm and a sheet resistance of 25±5.

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