TOPCon photovoltaic cell and preparation method thereof
By controlling the deposition process in multiple steps, the problem of white edge defects in the LPCVD deposition process was solved, and the uniformity of the amorphous silicon layer thickness and the performance of the solar cell were improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-31
- Publication Date
- 2026-03-13
AI Technical Summary
In the manufacturing process of TOPCon photovoltaic cells, the white edge defect commonly encountered during LPCVD deposition leads to a decrease in the electrical performance and appearance yield of the cells.
A multi-step deposition process is adopted to control the deposition temperature, pressure and reactive gas flow rate in the furnace mouth zone, furnace middle zone and furnace tail zone. By using low flow rate and low pressure in the early stage of deposition and gradually increasing the pressure and flow rate, the uniformity of the amorphous silicon layer thickness is ensured and the white edge defect is eliminated.
It effectively improved the difference in film thickness between the edge and center areas of the silicon wafer, eliminated white edge defects, and improved the electrical performance and appearance yield of the solar cells.
Smart Images
Figure CN121665724A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of photovoltaic cell technology, and in particular to a TOPCon photovoltaic cell and its preparation method. Background Technology
[0002] In the manufacturing process of TOPCon (tunneling oxide passivated contact) photovoltaic cells, an amorphous silicon layer is prepared on the back of the silicon wafer using low-pressure chemical vapor deposition (LPCVD) technology. Then, through subsequent processing (annealing, doping), a polycrystalline silicon layer is formed as a passivation contact layer. The polycrystalline silicon layer and the tunneling oxide layer together form a highly efficient passivation contact structure, which is crucial for improving the cell conversion efficiency.
[0003] White edge is a common defect in LPCVD deposition. The color difference between the edge and the middle of this white edge defect is obvious, which will seriously affect the electrical performance and appearance yield of the solar cell. Summary of the Invention
[0004] The first aspect of this application provides a method for preparing TOPCon photovoltaic cells. The LPCVD furnace is a tubular diffusion furnace, and the LPCVD furnace is provided with a furnace mouth zone, a furnace middle zone, and a furnace tail zone; the furnace mouth zone, the furnace middle zone, and the furnace tail zone are respectively provided with reaction gas outlets; the method includes: In the deposition chamber of the LPCVD furnace, an amorphous silicon layer is prepared using an n-step deposition process, where n ≥ 2, and: In each step, the deposition temperature in the furnace mouth area is not lower than the deposition temperature in the furnace middle area and the furnace tail area; The deposition temperature of the furnace mouth area in the i-th step is not lower than the deposition temperature of the furnace mouth area in the (i+1)-th step, where i is an integer from 1 to n-1; The deposition pressure in step i is lower than the deposition pressure in step i+1. The flow rate of the reactant gas in the furnace mouth area of step i is lower than that in the furnace mouth area of step i+1.
[0005] In one alternative, the temperature range of the furnace mouth zone in the deposition step is 590°C-620°C; and / or, the pressure range of the deposition step is 8Pa-30Pa; and / or, the reaction gas is silane, and the gas flow rate range of the furnace mouth zone is 50sccm-500sccm.
[0006] In one alternative approach, the temperature difference between the furnace mouth zones of adjacent deposition steps is 0°C-20°C; and / or, the pressure difference between adjacent deposition steps is 5Pa-10Pa; and / or, the difference in reaction gas flow rates between the furnace mouth zones of adjacent deposition steps is 50sccm-200sccm.
[0007] In one alternative approach, the multi-step deposition process is a three-step deposition process: The deposition temperature in the first step furnace mouth zone is 600℃-620℃, the pressure is 8Pa-20Pa, and the reaction gas flow rate in the furnace mouth zone is 50sccm-150sccm. The deposition temperature in the second step furnace mouth zone is 600℃-620℃, the pressure is 15Pa-25Pa, and the reaction gas flow rate in the furnace mouth zone is 100sccm-200sccm. The deposition temperature in the third step furnace mouth area is 590℃-620℃, the pressure is 20Pa-30Pa, and the reaction gas flow rate in the furnace mouth area is 250sccm-500sccm.
[0008] In one alternative approach, the reactant gas flow rate in the tail zone is greater than or equal to the reactant gas flow rate in the middle zone and greater than the reactant gas flow rate in the mouth zone. Preferably, Step 1: The flow rate of the reacting gas in the furnace mouth zone is 50-100 sccm; the flow rate of the reacting gas in the furnace middle zone is 100-150 sccm; the flow rate of the reacting gas in the furnace tail zone is 100-150 sccm. Step 2: The flow rate of the reacting gas in the furnace mouth zone is 100-150 sccm; the flow rate of the reacting gas in the furnace middle zone is 150-200 sccm; and the flow rate of the reacting gas in the furnace tail zone is 150-200 sccm. Step 3: The flow rate of the reacting gas in the furnace mouth zone is 250-300 sccm; the flow rate of the reacting gas in the furnace middle zone is 300-500 sccm; and the flow rate of the reacting gas in the furnace tail zone is 300-500 sccm.
[0009] In one alternative approach, the duration of each deposition step is 10 seconds to 3000 seconds; Preferably, the duration of deposition in the i-th step is less than the duration of deposition in the (i+1)-th step; More preferably, the duration of the first deposition step is 50-100 seconds, and the duration of the nth deposition step is 2000-3000 seconds; More preferably, in the three-step deposition process: The deposition time for steps 1 and 2 is 50-100 seconds, and the deposition time for step 3 is 2000-3000 seconds.
[0010] In one alternative approach, in each step, the deposition temperature difference between the furnace mouth zone and the furnace middle zone and / or furnace tail zone is 0°C to 15°C.
[0011] In one alternative, the LPCVD furnace is continuously purged with an inert protective gas, which is either nitrogen or argon, during the deposition process. Preferably, the ratio of the flow rate of the inert protective gas to the flow rate of the reactant gas is in the range of 1:1 to 10:1.
[0012] In one alternative embodiment, the reaction gas outlet of the LPCVD furnace at the furnace opening includes an annular inlet pipe located at the end of the furnace opening and an outlet facing the furnace cavity; and / or, The LPCVD furnace includes a reaction gas outlet extending from the furnace tail to the furnace mouth, with the outlet located in a first gas inlet pipe within the furnace; and / or... The reaction gas outlet of the LPCVD furnace at the furnace tail includes a second gas inlet pipe extending from the furnace tail to the furnace opening and having an outlet at the furnace tail.
[0013] The second aspect of this application provides a TOPCon photovoltaic cell prepared by the method for preparing TOPCon photovoltaic cells provided in the first aspect of this application.
[0014] This application effectively suppresses gas accumulation at the furnace opening by depositing an amorphous silicon layer in multiple steps and by controlling the deposition temperature, flow rate and pressure. This effectively improves the uniformity of the silicon wafer thickness at the furnace opening and eliminates the white edge defect in the appearance of the solar cell. Attached Figure Description
[0015] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A schematic diagram of one embodiment of the LPCVD furnace of this application is shown; Figure 2 A schematic diagram of one embodiment of the furnace opening of the LPCVD furnace of this application is shown; Figure 3 A physical image of a silicon wafer with white edge defects is shown; Figure 4 A physical image of a normal silicon wafer is shown.
[0016] Figure label: 100 - Furnace opening; 200 - Furnace tail; 301 - Reaction gas outlet at the furnace opening; 3011 - Annular inlet pipe; 3012 - Outlet hole; 302 - Reaction gas outlet in the furnace; 3021 - First inlet pipe; 303 - Reaction gas outlet at the furnace tail; 3031 - Second inlet pipe; 401 - Furnace opening area; 402 - Furnace middle area; 403 - Furnace tail area; 500 - Boat; 501 - First boat near the furnace opening. Detailed Implementation
[0017] Embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.
[0018] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise expressly specified. "Several" means one or more, unless otherwise expressly specified.
[0019] Currently, the industry mostly uses a furnace inlet gas intake mode when performing LPCVD amorphous silicon deposition, or supplements it with a furnace in-furnace gas supply hardware structure. The accompanying deposition process is generally a single-layer film process, which maintains a fixed set of process parameters (such as temperature, pressure, and reactive gas flow rate) throughout the deposition process. This gas intake mode and single-layer film process will produce obvious "white edge" defects on the appearance of the silicon wafer. Figure 3 This is a photograph of a silicon wafer with white edge defects. Figure 4 This is a photograph of a normal silicon wafer; such as... Figure 3-4 As shown, silicon wafers with white edge defects have obvious white edges. This white edge is a defect that will seriously affect the electrical performance and appearance yield of subsequent solar cells.
[0020] The inventors discovered that silicon wafers with white edge defects mainly occur within the boat-shaped vessel in the furnace opening area, and silicon wafers with higher film thickness and poor intra-wafer uniformity in the edge region are more likely to have white edge defects. Therefore, the first aspect of this application provides a method for fabricating TOPCon photovoltaic cells, which reduces white edge defects by improving the film thickness in the edge region of the silicon wafer.
[0021] like Figure 1As shown, the LPCVD furnace provided in this application is a tube diffusion furnace, which is provided with a furnace mouth area 401, a furnace middle area 402 and a furnace tail area 403 from the furnace mouth 100 to the furnace tail 200; a boat 500 loaded with silicon wafers is provided in the furnace, and the boat near the furnace mouth is the first boat 501; this application provides a reaction gas outlet 301 in the furnace mouth area 401, a reaction gas outlet 302 in the furnace middle area 402 and a reaction gas outlet 303 in the furnace tail area 403.
[0022] It is worth noting that the LPCVD furnace has multiple temperature control zones inside, each equipped with an independent heating module and temperature sensor, which allows for precise control of the temperature gradient along the length of the furnace tube. The furnace mouth zone is the control position of one-third of the temperature control zones located from the furnace mouth area; the furnace middle zone is the control position of one-third of the temperature control zones located in the middle; the furnace tail zone is the control position of one-third of the temperature control zones located from the furnace tail area; the deposition temperature of the furnace mouth zone is the temperature value of the first temperature control zone closest to the furnace mouth; the deposition temperature of the furnace middle zone is the temperature value of the first temperature control zone in the furnace middle zone; the deposition temperature of the furnace tail zone is the temperature value of the first temperature control zone in the furnace tail zone. For example, an LPCVD furnace has six temperature control zones; the control positions of the two temperature control zones closest to the furnace mouth are the furnace mouth zone; the control positions of the two temperature control zones in the middle are the furnace middle zone; and the control positions of the two temperature control zones closest to the furnace tail are the furnace tail zone. Assuming that the six temperature control zones from the furnace mouth to the furnace tail are, in order, the first, second, third, fourth, fifth, and sixth temperature control zones, then the deposition temperature of the furnace mouth zone is the set temperature of the first temperature control zone; the deposition temperature of the furnace middle zone is the set temperature of the third temperature control zone; and the deposition temperature of the furnace tail zone is the set temperature of the fifth temperature control zone.
[0023] The method provided in this application includes: preparing an amorphous silicon layer in the deposition chamber of an LPCVD furnace using an n-step deposition process, where n ≥ 2, wherein: In each step, the deposition temperature in the furnace mouth area shall not be lower than the deposition temperature in the furnace middle area and the furnace tail area; The deposition temperature of the furnace mouth area in the i-th step is not lower than the deposition temperature of the furnace mouth area in the (i+1)-th step, where i is an integer from 1 to n-1; The deposition pressure in step i is lower than the deposition pressure in step i+1. The flow rate of the reactant gas in the furnace mouth area of step i is lower than that in the furnace mouth area of step i+1.
[0024] It is worth noting that since the furnace mouth area, furnace middle area and furnace tail area are connected, there is only one pressure in the furnace cavity. The deposition pressure in step i is lower than the deposition pressure in step i+1, which means that the deposition pressure in the entire furnace cavity in step i is lower than the deposition pressure in the entire furnace cavity in step i+1.
[0025] It is worth noting that, as mentioned above, since there are three reaction gas outlets in LPCVD, and the three reaction gas outlets are controlled by independent airflow, the reaction gas flow rate in the furnace mouth area of this application is controlled by the reaction gas outlet in the furnace mouth area; while the reaction gas flow rate in the furnace middle area mentioned later is controlled by the reaction gas outlet in the furnace middle area; and the reaction gas flow rate in the furnace tail area is controlled by the reaction gas outlet in the furnace tail area.
[0026] This application controls the outlet location of the reactive gases and the deposition temperatures in the furnace mouth, furnace middle, and furnace tail zones. Combined with the preparation of multilayer amorphous silicon films, a low flow rate and low pressure are used at the furnace mouth during the initial deposition stage to effectively reduce the initial concentration and residence time of the reactive gases in the furnace mouth region, avoiding premature and rapid gas decomposition that could lead to furnace mouth accumulation. Subsequently, the pressure and flow rate are gradually increased. This ensures the film formation rate and efficiency during the main deposition stage, and because a uniform film formation foundation has already been established in the early stages, the overall film thickness uniformity is significantly improved, particularly eliminating the film thickness difference between the edge and center regions of the silicon wafer within the furnace mouth boat.
[0027] In the deposition chamber of the LPCVD furnace, an amorphous silicon layer is prepared using a multi-step deposition process, which includes at least two deposition steps. Specifically, the substrate for TOPCon cells is typically an n-type silicon wafer, such as an n-type monocrystalline silicon wafer or an n-type polycrystalline silicon wafer. The silicon wafer is first texturized, boron-doped, and alkaline polished. Then, the processed substrate is placed in a boat along the length of the furnace tube and pushed into the LPCVD furnace. The furnace door is then closed, the furnace tube is evacuated, and an automatic leak detection program is performed to ensure good airtightness of the equipment.
[0028] Specifically, LPCVD refers to the process of preparing a tunneling oxide layer on a silicon wafer surface through thermal oxidation by heating and stimulating the decomposition of precursors such as silane under low pressure. Then, an amorphous silicon layer is deposited in the LPCVD equipment described in this application, followed by secondary phosphorus doping to form a polycrystalline silicon layer. It is worth noting that the preparation method in this application occurs during the LPCVD deposition process and does not involve phosphorus doping; therefore, it belongs to the preparation of an amorphous silicon layer rather than a polycrystalline silicon layer.
[0029] In a specific embodiment, such as Figure 1-2As shown, the reaction gas outlet 301 of the LPCVD furnace at the furnace mouth includes an annular inlet pipe 3011 located at the end of the furnace mouth and outlet holes 3012 facing the furnace cavity. Specifically, the annular inlet pipe 3011 is located inside the end of the furnace mouth, and multiple outlet holes 3012 are evenly distributed on the inner side of the annular inlet pipe 3011 facing the furnace cavity; the inner diameter of the annular inlet pipe 3011 is 3-6 mm; the number of outlet holes 3012 is 4-20, and the diameter of the outlet holes 3012 is 1-3 mm.
[0030] In a specific embodiment, such as Figure 1 As shown, the reaction gas outlet 302 of the LPCVD furnace includes a first gas inlet pipe 3021 extending from the tail of the furnace to the opening of the furnace and having its outlet in the furnace. The first gas inlet pipe 3021 extends from the tail of the furnace to the middle zone 402 of the furnace. The gas source enters from the tail of the furnace, extends along the direction of the pipe body from the tail of the furnace to the middle zone 402 of the furnace, and is discharged in the gas outlet of the middle zone 402 of the furnace.
[0031] In a specific embodiment, such as Figure 1 As shown, the reaction gas outlet 303 of the LPCVD furnace at the furnace tail includes a second gas inlet pipe 3031 extending from the furnace tail to the furnace opening and with its outlet located at the furnace tail; the second gas inlet pipe 3031 extends from the furnace tail to the furnace tail area 403, the gas source enters from the furnace tail, extends along the pipe body direction from the furnace tail to the furnace tail area 403, and is discharged in the gas outlet of the furnace tail area 403.
[0032] In one alternative, the first air inlet pipe 3021 and / or the second air inlet pipe 3031 are made of silicon carbide. Silicon carbide air inlet pipes are resistant to high temperatures and are less prone to deformation and damage compared to traditional metal air inlet pipes, thus avoiding contamination of the furnace tubes and blockage of the air inlet pipes.
[0033] In one alternative configuration, the first intake pipe 3021 and / or the second intake pipe 3031 are straight-through pipes; a straight-through pipe means that the side of the pipe is not perforated, and the gas flows from the tail of the intake pipe to the inlet of the intake pipe without any other outlets in between. This avoids the problems of easy clogging, easy deformation, and short service life associated with multi-hole outlets.
[0034] In one alternative configuration, the outlet ends of the first air inlet pipe 3021 and / or the second air inlet pipe 3031 are flush; the pipe openings are not slotted, thus preventing dust inside the furnace tube from falling back and accumulating at the slotted position.
[0035] In one alternative configuration, the first air inlet pipe 3021 and / or the second air inlet pipe 3031 are disposed at the bottom of the furnace body, so that the gas flows upward toward the corresponding boat 500, further reducing the thickness difference of the amorphous silicon film.
[0036] In one alternative embodiment, the inner diameter of the first intake pipe 3021 and / or the second intake pipe 3031 is 8 to 16 mm.
[0037] In one alternative approach, the length of the LPCVD furnace body is 3-6 meters; the inner diameter of the LPCVD furnace body is 300mm-600mm.
[0038] In one alternative approach, the LPCVD furnace is also equipped with a vacuum system, which enables precise control of the furnace pressure.
[0039] In one alternative approach, an n-step deposition process is used to prepare the amorphous silicon layer, where 2 ≤ n ≤ 4, for example, n can be 2, 3, or 4.
[0040] In one alternative approach, the temperature range of the furnace mouth zone in the deposition step is 590°C to 620°C; for example, it can be 590°C, 592°C, 595°C, 598°C, 600°C, 602°C, 605°C, 608°C, 610°C, 612°C, 615°C, 618°C, or 620°C.
[0041] In one alternative approach, the pressure range for the deposition step is 8 Pa to 30 Pa; for example, it can be 8 Pa, 8.5 Pa, 9 Pa, 10 Pa, 12 Pa, 15 Pa, 18 Pa, 20 Pa, 22 Pa, 25 Pa, 27 Pa, 29 Pa, or 30 Pa.
[0042] In one alternative configuration, the reactant gas is silane, and the gas flow rate in the furnace opening zone ranges from 50 sccm to 500 sccm; for example, it can be 60 sccm, 80 sccm, 100 sccm, 120 sccm, 150 sccm, 180 sccm, 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm, or 500 sccm.
[0043] In one alternative approach, the temperature difference in the furnace mouth zone between adjacent deposition steps is 0°C to 20°C; for example, it can be 0°C, 1°C, 2°C, 3°C, 5°C, 7°C, 8°C, 10°C, 12°C, 13°C, 15°C, 17°C, 18°C, or 20°C.
[0044] In one alternative approach, the pressure difference between adjacent deposition steps is 5 Pa to 10 Pa; for example, it can be 5 Pa, 5.2 Pa, 5.5 Pa, 6 Pa, 6.5 Pa, 7 Pa, 7.5 Pa, 8 Pa, 8.5 Pa, 9 Pa, 9.5 Pa, or 10 Pa.
[0045] In one alternative approach, the difference in reactant gas flow rate in the furnace mouth zone between adjacent deposition steps is 50 sccm to 200 sccm; for example, it can be 50 sccm, 55 sccm, 60 sccm, 70 sccm, 80 sccm, 90 sccm, 100 sccm, 110 sccm, 120 sccm, 130 sccm, 140 sccm, 150 sccm, 160 sccm, 170 sccm, 180 sccm, 190 sccm, or 200 sccm.
[0046] In one alternative approach, the multi-step deposition process is a three-step deposition process, wherein the deposition temperature in the first step at the furnace mouth is 600℃-620℃, for example, 600℃, 602℃, 605℃, 608℃, 610℃, 612℃, 615℃, 618℃, or 620℃. The pressure is 8Pa-20Pa, for example, 8Pa, 8.5Pa, 9Pa, 10Pa, 12Pa, 15Pa, 18Pa, 20Pa, 22Pa, 25Pa, 27Pa, 29Pa, or 30Pa. The reaction gas flow rate in the furnace mouth is 50sccm-150sccm; 50sccm, 55sccm, 60sccm, 70sccm, 80sccm, 90sccm, 100sccm, 110sccm, 120sccm, 130sccm, 140sccm, or 150sccm. The deposition temperature in the second step, the furnace mouth zone, is 600℃-620℃, for example, 600℃, 602℃, 605℃, 608℃, 610℃, 612℃, 615℃, 618℃, or 620℃. The pressure is 15Pa-25Pa, for example, 5Pa, 18Pa, 20Pa, 22Pa, or 25Pa. The reaction gas flow rate in the furnace mouth zone is 100sccm-200sccm; for example, 100sccm, 120sccm, 150sccm, 180sccm, or 200sccm. The deposition temperature in the third step, the furnace mouth zone, is 590℃-620℃, for example, 592℃, 595℃, 598℃, 600℃, 602℃, 605℃, 608℃, 610℃, 612℃, 615℃, 618℃, or 620℃. The pressure is 20Pa-30Pa, for example, it could be 20Pa, 22Pa, 25Pa, 27Pa, 29Pa, or 30Pa. The flow rate of the reaction gas in the furnace mouth zone is 250sccm-500sccm. For example, it could be 250sccm, 300sccm, 350sccm, 400sccm, 450sccm, or 500sccm.
[0047] In one alternative approach, the reactant gas flow rate in the tail zone is greater than or equal to the reactant gas flow rate in the middle zone, which in turn is greater than the reactant gas flow rate in the mouth zone. The slightly higher flow rate at the tail zone creates a thrust from the tail zone to the mouth zone, preventing buildup caused by the high flow rate at the mouth zone and further reducing film thickness differences.
[0048] Preferably, the multi-step deposition process is a three-step deposition process: Step 1: The reaction gas flow rate in the furnace inlet zone is 50 sccm-100 sccm; for example, it can be 52 sccm, 55 sccm, 60 sccm, 65 sccm, 70 sccm, 75 sccm, 80 sccm, 85 sccm, 90 sccm, 95 sccm, or 100 sccm; the reaction gas flow rate in the furnace middle zone is 100 sccm-150 sccm; for example, it can be 102 sccm, 105 sccm, 110 sccm, or 115 sccm. The flow rates of the reactant gas in the tail zone are 100-150 sccm; for example, they can be 102 sccm, 105 sccm, 110 sccm, 115 sccm, 120 sccm, 125 sccm, 130 sccm, 135 sccm, 140 sccm, 145 sccm, or 150 sccm.
[0049] Step 2: The reaction gas flow rate in the furnace inlet zone is 100-150 sccm; for example, it could be 102 sccm, 105 sccm, 110 sccm, 115 sccm, 120 sccm, 125 sccm, 130 sccm, 135 sccm, 140 sccm, 145 sccm, or 150 sccm; the reaction gas flow rate in the furnace middle zone is 150-200 sccm; for example, it could be 152 sccm, 155 sccm, 160 sccm, or 160 sccm. 5 sccm, 170 sccm, 175 sccm, 180 sccm, 185 sccm, 190 sccm, 195 sccm or 200 sccm; the reaction gas flow rate in the tail zone is 150 sccm-200 sccm; for example, it can be 152 sccm, 155 sccm, 160 sccm, 165 sccm, 170 sccm, 175 sccm, 180 sccm, 185 sccm, 190 sccm, 195 sccm or 200 sccm.
[0050] Step 3: The reaction gas flow rate in the furnace inlet zone is 250 sccm-300 sccm; for example, it can be 255 sccm, 260 sccm, 265 sccm, 270 sccm, 275 sccm, 280 sccm, 285 sccm, 290 sccm, 295 sccm, or 300 sccm; the reaction gas flow rate in the furnace middle zone is 300 sccm-500 sccm; for example, it can be 310 sccm, 325 sccm, 340 sccm, 350 sccm, 365 sccm, 380 sccm, or 390 sccm. m, 400sccm, 415sccm, 430sccm, 450sccm, 470sccm, 485sccm or 500sccm; the reaction gas flow rate in the tail zone is 300sccm-500sccm; for example, it can be 310sccm, 325sccm, 340sccm, 350sccm, 365sccm, 380sccm, 390sccm, 400sccm, 415sccm, 430sccm, 450sccm, 470sccm, 485sccm or 500sccm.
[0051] In one alternative approach, the duration of each deposition step is 10 seconds to 3000 seconds; for example, it can be 15 seconds, 20 seconds, 30 seconds, 50 seconds, 100 seconds, 200 seconds, 500 seconds, 800 seconds, 1000 seconds, 1500 seconds, 2000 seconds, 2500 seconds, 2800 seconds, or 3000 seconds.
[0052] In one alternative approach, the duration of deposition in step i is less than the duration of deposition in step i+1. In one alternative approach, the duration of the first deposition step is 50 to 100 seconds, for example, 52, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 seconds; the duration of the nth deposition step is 2000 to 3000 seconds, for example, 2050, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, or 3000 seconds. In one alternative approach, in a three-step deposition process: the duration of the first and second deposition steps is 50 to 100 seconds, for example, 52, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 seconds; the duration of the third step is 2000 to 3000 seconds, for example, 2050, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, or 3000 seconds.
[0053] In one alternative approach, in each step, the deposition temperature difference between the furnace mouth zone and the furnace middle zone and / or furnace tail zone is 0°C to 15°C; for example, it can be 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 5.5°C, 6°C, 6.5°C, 7°C, 7.5°C, 8°C, 8.5°C, 9°C, 9.5°C, 10°C, 10.5°C, 11°C, 11.5°C, 12°C, 12.5°C, 13°C, 13.5°C, 14°C, 14.5°C, or 15°C.
[0054] In one alternative approach, an inert protective gas, either nitrogen or argon, is continuously introduced into the LPCVD furnace during the deposition process. Preferably, the ratio of the flow rate of the inert protective gas to the flow rate of the reactant gas is in the range of 1:1 to 10:1; for example, it can be 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1 or 10:1.
[0055] In one alternative approach, a tunneling oxide layer is prepared prior to the deposition step, wherein the preparation process is as follows: Oxygen is introduced to create an oxygen-filled atmosphere, with the oxygen-filled temperature ranging from 580℃ to 620℃. For example, it can be 585℃, 590℃, 592℃, 595℃, 598℃, 600℃, 602℃, 605℃, 608℃, 610℃, 612℃, 615℃, 618℃, or 620℃.
[0056] The oxygen flow rate is 30,000 sccm-50,000 sccm, for example, it can be 31,000 sccm, 32,500 sccm, 34,000 sccm, 35,000 sccm, 36,500 sccm, 38,000 sccm, 39,000 sccm, 40,000 sccm, 41,500 sccm, 43,000 sccm, 45,000 sccm, 47,000 sccm, 48,500 sccm or 50,000 sccm.
[0057] The oxygen-holding time is 300s to 400s, for example, it can be 305s, 310s, 320s, 330s, 340s, 350s, 355s, 360s, 365s, 370s, 380s, 390s, 395s or 400s.
[0058] After the tunneling oxide layer is prepared, the oxygen in the furnace tube is evacuated to prepare for amorphous silicon deposition. Then, the first deposition step is performed; followed by the second deposition step. Each deposition step uses different deposition temperature, deposition pressure, and reaction gas flow rate.
[0059] The second aspect of this application provides a TOPCon photovoltaic cell prepared by the method for preparing TOPCon photovoltaic cells provided in the first aspect of this application.
[0060] The following describes in detail, with several specific embodiments, the method for preparing the TOPCon photovoltaic cell disclosed in the first aspect and the TOPCon photovoltaic cell disclosed in the second aspect of this application. It is to be understood that the following description is merely illustrative and not intended to limit the invention.
[0061] The data for each example and comparative example below were collected from a complete batch of silicon wafers in an LPCVD furnace. After the deposition process was completed, the silicon wafers in the first boat located at the furnace opening were inspected. The inspection items included film thickness uniformity and the proportion of white edge defects. The specific inspection and statistical methods are as follows: (1) Film thickness measurement: The film thickness of each silicon wafer was measured at the center point and four corner positions (2 cm from the two edges) using an ellipsometry, and the standard deviation of the five measurements for each silicon wafer was calculated to evaluate the film thickness uniformity. The average of the standard deviation of the film thickness of all silicon wafers in the batch was calculated; the standard deviation of the film thickness was calculated by taking the square root of the difference between the average of the five values at the center point and four corner positions and these five values, using the same method as the calculation method of STDEV.S in the Excel spreadsheet.
[0062] (2) White edge statistics: The appearance of silicon wafers is inspected manually to identify and count the silicon wafers with white edge defects. The white edge ratio is calculated by dividing the number of silicon wafers with white edge defects in the batch by the total number of silicon wafers inspected.
[0063] Example 1
[0064] This embodiment provides a specific method for preparing an amorphous silicon layer on the back of a TOPCon cell using a three-step deposition process. The LPCVD equipment is a tubular diffusion furnace, which has three independent silane gas outlets on its furnace tube: furnace inlet, furnace middle, and furnace tail. The flow rate of each gas inlet can be independently controlled.
[0065] The furnace body has six independent temperature control zones, which can realize longitudinal temperature gradient control.
[0066] The N-type silicon wafers that have undergone boron diffusion and alkaline polishing are loaded into boats, and then the boats are pushed into the LPCVD furnace. There are a total of 12 boats in the entire tube. Close the furnace door, evacuate the furnace tubes, and perform an automatic leak detection program to ensure good airtightness of the equipment; High-purity oxygen is introduced into the furnace tube, with the oxygen flow rate controlled at 40,000 sccm, the furnace temperature maintained at 600℃, and the oxygen suffocation time lasting 360 seconds.
[0067] After the oxygen-filled furnace is sealed, the oxygen inside the furnace tubes is removed to prepare for amorphous silicon deposition.
[0068] The deposition process consists of three steps: First deposition step: The temperature of the first zone at the furnace opening is set to 615℃, and the temperatures of the remaining zones in the furnace and at the furnace tail are set to 605℃. The pressure inside the furnace tube is controlled at 15 Pa. Silane gas is introduced, and the flow rate is independently controlled through three inlets: 100 sccm at the furnace opening, 150 sccm in the furnace, and 150 sccm at the furnace tail; simultaneously, nitrogen is introduced as both carrier gas and protective gas; deposition lasts for 60 seconds.
[0069] Second deposition step: Maintain the same temperature in each zone as in the first step (615℃ in the first zone, 605℃ in the others). Increase the pressure inside the furnace tube to 20 Pa. Gradually increase the silane gas flow rate: adjust the flow rate at the furnace inlet to 150 sccm, the flow rate in the furnace to 200 sccm, and the flow rate at the furnace outlet to 200 sccm. Deposition lasts for 60 seconds.
[0070] Third step deposition: Maintain the temperature of the first zone at the furnace opening at 615°C, and finely adjust the temperatures of the middle and tail zones at 605°C. Further increase the pressure inside the furnace tubes to 25 Pa. Increase the silane gas flow rate to the levels required for the main deposition: 300 sccm at the furnace opening, 400 sccm in the middle of the furnace, and 400 sccm at the tail of the furnace. Deposition lasts for 2100 seconds.
[0071] After deposition is complete, stop the silane supply, evacuate the furnace tube, and then fill it with high-purity nitrogen to atmospheric pressure.
[0072] The boat is removed from the furnace tube to complete the LPCVD amorphous silicon deposition process.
[0073] Example 2
[0074] Unlike Example 1, the deposition process in Example 2 consists of two steps: First deposition step: The temperature of the first zone at the furnace opening is set to 615℃, and the temperatures of the remaining zones in the furnace and at the furnace tail are set to 605℃. The pressure inside the furnace tube is controlled at 20 Pa. Silane gas is introduced, with the flow rate independently controlled through three inlets: 100 sccm at the furnace opening, 200 sccm in the furnace, and 200 sccm at the furnace tail. Simultaneously, nitrogen is introduced as both carrier gas and protective gas. Deposition lasts for 60 seconds.
[0075] Second deposition step: Maintain the same temperature in each zone as in the first step (615℃ in the first zone, 605℃ in the others). Increase the pressure inside the furnace tube to 25 Pa. Increase the silane gas flow rate to: 300 sccm at the furnace inlet, 400 sccm in the furnace, and 400 sccm at the furnace outlet. Deposition lasts for 2100 seconds.
[0076] Example 3
[0077] Unlike Example 1, the deposition process in Example 3 consists of four steps: First deposition step: Temperature set at 615℃ (first temperature zone) / 605℃ (other temperature zones), pressure controlled at 10 Pa. Silane flow rate controlled as follows: 50 sccm at the furnace inlet, 200 sccm in the furnace middle, and 200 sccm at the furnace outlet. Deposition lasts 60 seconds.
[0078] Second deposition step: Temperature remains constant. Pressure is increased to 15 Pa. Silane flow rate is adjusted as follows: 100 sccm at the furnace inlet, 200 sccm in the furnace middle, and 200 sccm at the furnace outlet. Deposition lasts 60 seconds.
[0079] Third step deposition: Temperature remains constant. Pressure is further increased to 20 Pa. Silane flow rate is adjusted to: 150 sccm at the furnace inlet, 200 sccm in the furnace middle, and 200 sccm at the furnace outlet. Deposition lasts 60 seconds.
[0080] Fourth step deposition: Temperature remains constant. Pressure is stabilized at 25 Pa. Silane flow rate is increased to: 300 sccm at the furnace opening, 400 sccm in the furnace, and 400 sccm at the furnace tail. Deposition lasts 2040 seconds.
[0081] Example 4
[0082] Unlike Example 1, the deposition temperature in Example 4 is different from that in Example 1: Throughout all deposition steps, the controlled temperature for all temperature zones was 605°C.
[0083] Comparative Example 1
[0084] Unlike Example 1, the deposition step in the comparative example is a single step, specifically: The temperature of the first zone at the furnace inlet was set to 605℃, and the temperatures of the remaining zones in the furnace middle and tail were also set to 605℃. The pressure inside the furnace tubes was controlled at 25 Pa. Silane gas was introduced, with its flow rate independently controlled through three outlets: 300 sccm at the furnace inlet, 400 sccm in the furnace middle, and 400 sccm at the furnace tail. Simultaneously, nitrogen was introduced as both carrier gas and protective gas. Deposition lasted for 2220 seconds.
[0085] Comparative Example 2
[0086] The silane flow rate of Comparative Example 2 differs from that of Example 1 in that: The silane flow rate gradually decreases from the first step to the third step, specifically as follows: Step 1: 300 sccm at the furnace opening, 400 sccm in the furnace middle, and 400 sccm at the furnace tail; Step 2: 150 sccm at the furnace opening, 200 sccm in the furnace middle, and 200 sccm at the furnace tail; Step 3: 100 sccm at the furnace opening, 200 sccm in the furnace middle, and 200 sccm at the furnace tail; Comparative Example 3
[0087] The silane flow rate of Comparative Example 3 differs from that of Example 1 in that: The silane flow rate is the same for each deposition step: the flow rate at the furnace opening is constant at 300 sccm, the flow rate in the furnace is constant at 400 sccm, and the flow rate at the furnace tail is constant at 400 sccm.
[0088] Comparative Example 4
[0089] The pressure in Comparative Example 4 differs from that in Example 1, in that: The reaction pressure gradually decreases from the first step to the third step, specifically as follows: Step 1: Pressure is 25 Pa; Step 2: Pressure is 20 Pa; Step 3: The pressure is 15 Pa.
[0090] Comparative Example 5
[0091] The pressure of the comparative example differs from that of Example 1, in that: The pressure for each deposition step was kept constant at 25 Pa.
[0092] Comparative Example 6
[0093] The deposition temperature of Comparative Example 6 differs from that of Example 1, in that: In all deposition steps, the temperature of the first temperature zone at the furnace mouth was set to 600℃, and the temperature of the remaining temperature zones was set to 605℃.
[0094] Table 1 below shows the test data for Examples 1-4 and Comparative Examples 1-6. As can be seen from the table, (1) compared with Comparative Example 1, the average value of the standard deviation of film thickness and the proportion of white edge defects in Example 1 are improved. (2) compared with Example 1, Example 2 uses a two-step deposition to prepare the amorphous silicon layer. Compared with Example 1, the average value of the standard deviation of film thickness is larger, that is, the uniformity is worse; this also leads to a higher proportion of white edge defects than in Example 1. (3) compared with Example 1, Example 3 uses a four-step deposition to prepare the amorphous silicon layer. Compared with Example 1, the average value of the standard deviation of film thickness is larger, and the proportion of white edge defects is higher. (4) compared with Example 1, Example 4 uses the same temperature. Compared with Example 1, the average value of the standard deviation of film thickness is larger, and the proportion of white edge defects is higher. (5) Compared with Example 1, in Comparative Example 2, the silane flow rate gradually decreases from the first step to the third step; the silane flow rate in Comparative Example 3 is equal; the average standard deviation of film thickness in Comparative Example 2 and Comparative Example 3 is large and the proportion of white edge defects is very high. The reason may be that the flow rate in the early stage of film formation in Comparative Example 2 is too high, which causes the gas flow to accumulate at the furnace mouth, resulting in uneven film thickness; while in Comparative Example 3, a constant silane flow rate is used, and the gas in the furnace mouth area is prone to accumulate due to the high flow rate in the early stage, and the gas supply in the furnace tail area is insufficient in the later stage; resulting in a relatively poor average standard deviation of film thickness and proportion of white edge defects. (6) Compared with Example 1, in Comparative Example 4, the deposition pressure gradually decreases from the first step to the third step; the deposition pressure in Comparative Example 5 is equal in each step; the average standard deviation of film thickness in Comparative Example 4 and Comparative Example 5 is large and the proportion of white edge defects is very high; the reason may be that the gas pressure at the film formation outlet is too high, which causes the gas flow to accumulate, resulting in uneven film thickness. (7) Compared with Example 1, the deposition temperature in the furnace mouth area of Comparative Example 6 is lower than that in the furnace middle area and the furnace tail area. Due to the low temperature of the furnace mouth, the silane decomposition rate in the furnace mouth area is lower than that in the furnace middle and furnace tail areas, resulting in a thinner amorphous silicon layer deposition thickness on the silicon wafer surface and an increased regional difference; which leads to a large average standard deviation of film thickness and a high proportion of white edge defects.
[0095] Table 1 Test data of Examples 1-4 and Comparative Examples 1-6
[0096] Although this application has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the accompanying drawings, disclosure, and appended claims, will understand and implement other variations of the disclosed embodiments in carrying out the claimed application. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple instances. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.
[0097] Although this application has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made thereto without departing from the spirit and scope of this application. Accordingly, this specification and drawings are merely exemplary illustrations of this application as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from the spirit and scope of this application. Thus, if such modifications and modifications of this application fall within the scope of the claims of this application and their equivalents, this application is also intended to include such modifications and modifications.
Claims
1. A method for preparing TOPCon photovoltaic cells, characterized in that, The LPCVD furnace is a tubular diffusion furnace, and the LPCVD furnace is provided with a furnace mouth zone, a furnace middle zone, and a furnace tail zone; the furnace mouth zone, the furnace middle zone, and the furnace tail zone are respectively provided with reaction gas outlets; the method includes: In the deposition chamber of the LPCVD furnace, an amorphous silicon layer is prepared using an n-step deposition process, where n ≥ 2, and: In each step, the deposition temperature in the furnace mouth area is not lower than the deposition temperature in the furnace middle area and the furnace tail area; The deposition temperature of the furnace mouth area in the i-th step is not lower than the deposition temperature of the furnace mouth area in the (i+1)-th step, where i is an integer from 1 to n-1; The deposition pressure in step i is lower than the deposition pressure in step i+1. The flow rate of the reactant gas in the furnace mouth area of step i is lower than that in the furnace mouth area of step i+1.
2. The method as described in claim 1, characterized in that, The temperature range of the furnace mouth zone in the deposition step is 590℃-620℃; and / or, the pressure range of the deposition step is 8Pa-30Pa; and / or, the reaction gas is silane, and the gas flow rate range of the furnace mouth zone is 50sccm-500sccm.
3. The method as described in claim 2, characterized in that, The temperature difference in the furnace mouth zone between adjacent deposition steps is 0℃-20℃; and / or, the pressure difference between adjacent deposition steps is 5Pa-10Pa; and / or, the difference in reactant gas flow rate in the furnace mouth zone between adjacent deposition steps is 50sccm-200sccm.
4. The method as described in claim 2 or 3, characterized in that, The multi-step deposition process is a three-step deposition process: The deposition temperature in the first step furnace mouth zone is 600℃-620℃, the pressure is 8Pa-20Pa, and the reaction gas flow rate in the furnace mouth zone is 50sccm-150sccm. The deposition temperature in the second step furnace mouth zone is 600℃-620℃, the pressure is 15Pa-25Pa, and the reaction gas flow rate in the furnace mouth zone is 100sccm-200sccm. The deposition temperature in the third step furnace mouth area is 590℃-620℃, the pressure is 20Pa-30Pa, and the reaction gas flow rate in the furnace mouth area is 250sccm-500sccm.
5. The method as described in claim 4, characterized in that, in, The flow rate of reactant gas at the tail zone reaction outlet is greater than or equal to the flow rate of reactant gas at the middle zone reaction outlet, which is greater than the flow rate of reactant gas at the mouth zone reaction outlet. Preferably, Step 1: The flow rate of the reacting gas in the furnace mouth zone is 50-100 sccm; the flow rate of the reacting gas in the furnace middle zone is 100-150 sccm; the flow rate of the reacting gas in the furnace tail zone is 100-150 sccm. Step 2: The flow rate of the reacting gas in the furnace mouth zone is 100-150 sccm; the flow rate of the reacting gas in the furnace middle zone is 150-200 sccm; and the flow rate of the reacting gas in the furnace tail zone is 150-200 sccm. Step 3: The flow rate of the reacting gas in the furnace mouth zone is 250-300 sccm; the flow rate of the reacting gas in the furnace middle zone is 300-500 sccm; and the flow rate of the reacting gas in the furnace tail zone is 300-500 sccm.
6. The method of claim 2, wherein the duration of each deposition step is 10 seconds to 3000 seconds; Preferably, the duration of deposition in the i-th step is less than the duration of deposition in the (i+1)-th step; More preferably, the duration of the first deposition step is 50-100 seconds, and the duration of the nth deposition step is 2000-3000 seconds; More preferably, in the three-step deposition process: The deposition time for steps 1 and 2 is 50-100 seconds, and the deposition time for step 3 is 2000-3000 seconds.
7. The method as described in claim 1, characterized in that, In each step, the deposition temperature difference between the furnace mouth area and the furnace middle area and / or furnace tail area is 0°C to 15°C.
8. The method as described in claim 1, characterized in that, During the deposition process, the LPCVD furnace continuously introduces an inert protective gas, which is either nitrogen or argon. Preferably, the ratio of the flow rate of the inert protective gas to the flow rate of the reactant gas is in the range of 1:1 to 10:
1.
9. The method as described in claim 1, characterized in that, The LPCVD furnace's reaction gas outlet at the furnace mouth includes an annular inlet pipe located at the end of the furnace mouth and an outlet facing the furnace cavity; and / or, The LPCVD furnace includes a reaction gas outlet extending from the furnace tail to the furnace mouth, with the outlet located in a first gas inlet pipe within the furnace; and / or... The reaction gas outlet of the LPCVD furnace at the furnace tail includes a second gas inlet pipe extending from the furnace tail to the furnace opening and having an outlet at the furnace tail.
10. A TOPCon photovoltaic cell, characterized in that, It is prepared by any one of the preparation methods described in claims 1-9.