A phosphorus diffusion process, N-POLY layer and solar cell based on a velvet surface solar cell

Abstract

The application provides a phosphorus diffusion process of a solar cell based on a texturing surface, an N-POLY layer and a solar cell. The process comprises the following steps: pre-oxidizing an intrinsic poly-silicon layer deposited on the surface of a silicon wafer after texturing in an oxygen-containing atmosphere, high-temperature heat treatment in a protective atmosphere, phosphorus diffusion deposition in a phosphorus-containing reaction atmosphere, and phosphorus diffusion promotion in a nitrogen or oxygen atmosphere. In the phosphorus diffusion process, the pre-oxidation and high-temperature heat treatment steps are added before the phosphorus diffusion deposition, which cooperatively improves the comprehensive performance of the solar cell. The pre-oxidation improves the uniformity of the phosphorus diffusion, the high-temperature heat treatment enhances the passivation effect and thus improves the open-circuit voltage, and the synergistic effect of the two optimizes the crystal structure and interface quality of the N-POLY layer, thereby improving the cell efficiency. Therefore, the solar cell has a high open-circuit voltage and high cell efficiency.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, and relates to a phosphorus diffusion process for textured solar cells, particularly to a phosphorus diffusion process for textured solar cells, an N-POLY layer, and a solar cell. Background Technology

[0002] A solar cell is a device that directly converts light energy into electrical energy based on the photovoltaic effect. In currently mass-produced crystalline silicon solar cells, tunnel oxide passivated contact (TOPCon) technology has become mainstream. This technology was first proposed by Fraunhofer in Germany in 2013. Its core structure involves fabricating an ultrathin layer of silicon oxide (approximately 1nm~2nm thick) and phosphorus-doped polycrystalline silicon on the silicon wafer surface. This structure effectively promotes minority carriers to pass through the oxide layer via quantum tunneling or local pinhole effects, while simultaneously blocking majority carrier recombination. This significantly reduces surface recombination losses in the metal-semiconductor contact area, improving the cell's open-circuit voltage and efficiency.

[0003] To further improve the performance of solar cell modules, one technical approach is to use N... + The emitter is based on a textured surface to form a tunneling passivation structure; however, it is difficult to achieve good passivation on the textured surface using existing technologies, resulting in unstable passivation effects and insufficient passivation level of the N-POLY layer on the textured surface, which limits the application of this technology in cells and restricts further improvement of solar cell performance.

[0004] For example, CN117438496A discloses a fabrication process and battery structure for a double-sided passivated contact battery. The process includes the following steps: selecting an N-type silicon wafer for double-sided polishing; depositing a tunneling silicon oxide layer and an intrinsic polycrystalline silicon layer on both sides of the silicon wafer, and doping to form a p-poly layer; performing single-sided etching; texturing the front side; depositing a silicon oxide layer and an intrinsic polycrystalline silicon layer on both sides, and doping to form an n-poly layer; performing single-sided etching on the back side; ablating the non-contact area using a laser; performing secondary texturing and cleaning the front PSG layer and the back BSG layer; forming a front oxide layer; depositing a front passivation layer; sequentially depositing a film layer with a negative surface charge and a back passivation layer on the back side; and printing to form a metal electrode.

[0005] For example, CN111584679A discloses a doping method for passivation of the back surface of N-type TOPCon cells. Compared with the prior art, it uses a two-step doping method, namely, firstly, a very shallow doping is performed on the substrate of the back surface, then a tunnel oxide layer and a polycrystalline silicon layer are deposited, and finally the polycrystalline silicon layer is doped; the doping of the back surface is completed by a combination of ion implantation and phosphorus diffusion.

[0006] For example, CN118173647A discloses a method and apparatus for matching Poly process and annealing process, which relates to the field of solar cell technology. It includes: texturing, front boron diffusion, back etching, LPCVD, phosphorus diffusion, front etching, front alumina passivation, back silicon nitride passivation, double-sided metallization, annealing preheating, main annealing, and cooling to realize the combination of processes. In the phosphorus diffusion process, the addition of a buffer layer between the high-thickness tunneling layer and the ultra-low doped layer is to optimize the performance of the solar cell. It can reduce the inward diffusion of phosphorus atoms from the Poly layer to the tunneling layer and improve the cell performance. By introducing the buffer layer, the opportunity for phosphorus atoms to directly contact the tunneling layer can be reduced. By optimizing the material and structure of the buffer layer, it can be matched with the high-temperature annealing process, thereby achieving a better crystallization effect and better realizing the cooling airflow circulation during the cell annealing process. The annealing apparatus can better match the annealing after the Poly process, and cooperate to make the cell crystallize better.

[0007] Existing phosphorus diffusion processes for textured solar cells have certain drawbacks, including difficulty in improving the passivation level of the N-POLY layer on the textured surface, thus limiting the improvement of the open-circuit voltage and cell efficiency of the solar cell. Therefore, it is crucial to develop and design a novel phosphorus diffusion process, N-POLY layer, and solar cell for textured solar cells. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a phosphorus diffusion process, an N-POLY layer, and a solar cell based on a textured surface. In the phosphorus diffusion process provided by the present invention, pre-oxidation and high-temperature heat treatment steps are added before phosphorus diffusion deposition, synergistically improving the overall performance of the cell. Specifically, pre-oxidation improves the uniformity of phosphorus diffusion, and high-temperature heat treatment enhances the passivation effect, thereby increasing the open-circuit voltage. The synergistic effect of these two steps optimizes the crystal structure and interface quality of the N-POLY layer, thus improving the cell efficiency. Therefore, the solar cell exhibits a higher open-circuit voltage and higher cell efficiency.

[0009] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a phosphorus diffusion process for a textured solar cell, the phosphorus diffusion process comprising: In an oxygen-containing atmosphere, the intrinsic poly silicon layer deposited on the surface of the texturized silicon wafer is pre-oxidized, then subjected to high-temperature heat treatment in a protective atmosphere, followed by phosphorus diffusion deposition in a phosphorus-containing reactive atmosphere, and then phosphorus diffusion propagation in a nitrogen or oxygen atmosphere.

[0010] In the phosphorus diffusion process provided by this invention, a pre-oxidation step is added before phosphorus diffusion deposition. On the one hand, pre-oxidation can achieve cleaning treatment of the silicon wafer surface. On the other hand, it can also pre-grow an oxide layer on the surface of the intrinsic poly silicon layer. The presence of the oxide layer is beneficial to improving the uniformity of phosphorus diffusion, thereby improving the open-circuit voltage and cell efficiency of the solar cell.

[0011] In the phosphorus diffusion process provided by this invention, a high-temperature heat treatment step is added between pre-oxidation and phosphorus diffusion deposition. The high-temperature heat treatment step improves the density of the tunnel oxide layer, thereby obtaining a better passivation effect and further improving the open-circuit voltage and cell efficiency of the solar cell.

[0012] In the phosphorus diffusion process provided by this invention, the synergistic effect of pre-oxidation and high-temperature heat treatment is beneficial to optimizing the crystal structure and interface characteristics of the N-POLY layer, forming a high-quality PN junction, thereby reducing surface defect recombination, improving carrier separation and collection efficiency, and achieving an increase in open-circuit voltage.

[0013] In the phosphorus diffusion process provided by this invention, phosphorus diffusion deposition is followed by phosphorus diffusion propagation, which is more conducive to improving solar cells. This is because the phosphorus source needs to undergo a certain propagation process after deposition to activate the doping elements.

[0014] In summary, the phosphorus diffusion process provided by this invention, by adding pre-oxidation and high-temperature heat treatment steps before the phosphorus diffusion heat treatment, synergistically improves the overall performance of the battery. Specifically, pre-oxidation improves the uniformity of phosphorus diffusion, and high-temperature heat treatment enhances the passivation effect, thereby increasing the open-circuit voltage. The synergistic effect of these two processes optimizes the crystal structure and interface quality of the N-POLY layer, thus improving battery efficiency. Therefore, the solar cell exhibits both high open-circuit voltage and high battery efficiency.

[0015] Preferably, the process further includes a deposition step prior to pre-oxidation, the deposition step comprising: sequentially depositing a tunneling oxide layer and an intrinsic poly silicon layer on at least one side surface of the texturized silicon wafer.

[0016] Preferably, the method for preparing a texturized silicon wafer includes: cleaning the silicon wafer and then texturing it to obtain a texturized silicon wafer.

[0017] Preferably, the pre-oxidation temperature is ≥750℃ and the time is 30s~300s.

[0018] In this invention, the pre-oxidation temperature is ≥750℃, for example, it can be 750℃, 760℃, 770℃, 780℃, 800℃, 820℃, 840℃, 860℃, 880℃, 900℃, 920℃, 940℃, 960℃, 980℃ or 1000℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0019] In this invention, the pre-oxidation time is 30s to 300s, for example, it can be 30s, 50s, 80s, 100s, 120s, 150s, 180s, 200s, 220s, 250s, 280s or 300s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the oxygen flow rate in the oxygen-containing atmosphere is 1000 sccm to 10000 sccm.

[0021] Preferably, the phosphorus diffusion process further includes a first heating before the pre-oxidation, wherein the heating rate of the first heating is 5°C / min to 20°C / min, the endpoint temperature is the pre-oxidation temperature, and the process is carried out in a protective atmosphere.

[0022] Preferably, the high-temperature heat treatment is performed at a temperature of 850℃ to 1000℃ for a duration of no more than 6000 seconds.

[0023] In this invention, the high-temperature heat treatment temperature is 850℃~1000℃, for example, it can be 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, 960℃, 970℃, 980℃, 990℃ or 1000℃, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0024] In this invention, the high-temperature heat treatment time is no more than 6000s, for example, it can be 1000s, 1500s, 2000s, 2500s, 3000s, 3500s, 4000s, 4500s, 5000s, 5500s or 6000s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0025] Preferably, the protective atmosphere includes nitrogen and / or an inert gas.

[0026] Preferably, the phosphorus diffusion process further includes a second heating between the pre-oxidation and the high-temperature heat treatment, wherein the heating rate of the second heating is 8°C / min to 18°C / min, the endpoint temperature is the temperature of the high-temperature heat treatment, and the process is carried out in a protective atmosphere.

[0027] Preferably, the protective atmosphere comprises an atmosphere of nitrogen and / or inert gas with a flow rate of 1000 sccm to 10000 sccm, for example, it can be 1000 sccm, 2000 sccm, 3000 sccm, 4000 sccm, 5000 sccm, 6000 sccm, 7000 sccm, 8000 sccm, 9000 sccm or 10000 sccm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] Preferably, the phosphorus diffusion process further includes a third heating or a first cooling between high-temperature heat treatment and phosphorus diffusion deposition.

[0029] Preferably, the third heating is carried out in a protective atmosphere for 360s to 600s, and the endpoint temperature is the temperature at which the phosphorus diffuses and deposits.

[0030] In this invention, the third heating time is 360s to 600s, for example, it can be 360s, 380s, 400s, 420s, 440s, 460s, 480s, 500s, 520s, 540s, 560s, 580s or 600s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, the first cooling is carried out in a protective atmosphere for 400s to 4000s, and the endpoint temperature is the temperature at which the phosphorus diffuses and deposits.

[0032] In this invention, the first cooling time is 400s to 4000s, for example, it can be 400s, 500s, 600s, 700s, 800s, 900s, 1000s, 1500s, 2000s, 2500s, 3000s, 3500s or 4000s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the phosphorus diffusion deposition temperature is 800℃~900℃ and the time is 5min~50min.

[0034] In this invention, the temperature of the phosphorus diffusion thermal deposition is 800℃~900℃, for example, it can be 800℃, 820℃, 840℃, 860℃, 880℃ or 900℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] In this invention, the time for phosphorus diffusion deposition is 5 min to 50 min, for example, it can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min or 50 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the phosphorus source in the phosphorus-containing reaction atmosphere includes phosphorus oxychloride.

[0037] Preferably, the phosphorus diffusion process further includes a fourth heating or a second cooling between phosphorus diffusion deposition and phosphorus diffusion propulsion.

[0038] Preferably, when the temperature for phosphorus diffusion propulsion is 750℃~950℃ and the time is 5min~50min, the fourth heating or the second cooling is carried out in a nitrogen atmosphere. The fourth heating time is 200s~1200s, and the endpoint temperature is the temperature for phosphorus diffusion propulsion. The second cooling time is 300s~3000s, and the endpoint temperature is the temperature for phosphorus diffusion propulsion.

[0039] In this invention, the temperature for phosphorus diffusion propulsion is 750℃~950℃, for example, it can be 750℃, 770℃, 790℃, 810℃, 830℃, 850℃, 870℃, 890℃, 910℃, 930℃ or 950℃, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0040] In this invention, the phosphorus diffusion propulsion time is 5 min to 50 min, for example, it can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min or 50 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] In this invention, the fourth heating time is 200s to 1200s, for example, it can be 200s, 300s, 400s, 500s, 600s, 700s, 800s, 900s, 1000s, 1100s or 1200s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] As a preferred embodiment of the phosphorus diffusion process of the present invention, the phosphorus diffusion process includes: (1) After cleaning the silicon wafer, texturing is performed to obtain a texturized silicon wafer. Then, a tunneling oxide layer and an intrinsic poly silicon layer are sequentially deposited on at least one side surface of the texturized silicon wafer. (2) In a nitrogen atmosphere with a nitrogen flow rate of 1000 sccm to 10000 sccm, the first heating is carried out at a heating rate of 5℃ / min to 20℃ / min until the temperature is ≥750℃. Then, in an oxygen atmosphere with an oxygen flow rate of 1000 sccm to 10000 sccm, the texturized silicon wafer with the tunnel oxide layer and intrinsic poly silicon layer deposited on the surface is pre-oxidized at ≥750℃ for 30s to 300s. (3) In nitrogen and / or inert gas, a second heating is carried out at a heating rate of 5℃ / min to 20℃ / min until the temperature reaches 850℃ to 1000℃, and then a high-temperature heat treatment of not more than 6000s is carried out in nitrogen and / or inert gas at 850℃ to 1000℃. (4) Then, in nitrogen and / or inert gas, perform a third heating for 300s to 600s or a first cooling for 400s to 4000s until the temperature is the temperature of phosphorus diffusion deposition. (5) In a phosphorus-containing reaction atmosphere, phosphorus diffusion deposition is carried out at a temperature of 800℃~900℃ for 5min~50min; (6) Then, in nitrogen and / or inert gas, perform a fourth heating process of 200s to 1200s or a second cooling process of 300s to 3000s until the temperature is the temperature for phosphorus diffusion propulsion, and then perform phosphorus diffusion propulsion. The phosphorus diffusion propulsion temperature is 750℃~950℃, and the time is 5min~50min.

[0043] In a second aspect, the present invention provides an N-POLY layer for a textured solar cell, wherein the N-POLY layer is prepared by the process described in the first aspect.

[0044] Thirdly, the present invention provides a textured solar cell, the solar cell comprising the N-POLY layer described in the third aspect.

[0045] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0046] Compared with the prior art, the present invention has the following beneficial effects: (1) In the phosphorus diffusion process provided by the present invention, a pre-oxidation step is added before phosphorus diffusion deposition. On the one hand, pre-oxidation can achieve cleaning treatment of the silicon wafer surface. On the other hand, it can also pre-grow an oxide layer on the surface of the intrinsic poly silicon layer. The presence of the oxide layer is beneficial to improving the uniformity of phosphorus diffusion, thereby improving the open circuit voltage and cell efficiency of the solar cell. (2) In the phosphorus diffusion process provided by the present invention, a high-temperature heat treatment step is added between the pre-oxidation and phosphorus diffusion deposition. The high-temperature heat treatment step improves the density of the tunnel oxide layer, thereby obtaining a better passivation effect and further improving the open circuit voltage and cell efficiency of the solar cell. (3) In the phosphorus diffusion process provided by the present invention, the synergistic effect of pre-oxidation and high-temperature heat treatment is beneficial to optimizing the crystal structure and interface characteristics of the N-POLY layer, forming a high-quality PN junction, thereby reducing surface defect recombination, improving the separation and collection efficiency of charge carriers, and realizing the improvement of open circuit voltage; (3) In the phosphorus diffusion process provided by the present invention, phosphorus diffusion is carried out after phosphorus diffusion deposition, which is more conducive to improving the solar cell. This is because the phosphorus source needs to undergo a certain propulsion process after deposition to activate the doping element. (4) In the phosphorus diffusion process provided by the present invention, the overall performance of the battery is synergistically improved by adding pre-oxidation and high-temperature heat treatment steps before phosphorus diffusion deposition. Among them, pre-oxidation improves the uniformity of phosphorus diffusion, and high-temperature heat treatment enhances the passivation effect, thereby improving the open-circuit voltage. The synergistic effect of the two optimizes the crystal structure and interface quality of the N-POLY layer, thereby improving the battery efficiency. Therefore, the solar cell exhibits a high open-circuit voltage and a high battery efficiency. Detailed Implementation

[0047] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0048] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0050] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0051] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0052] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0053] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0054] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0055] Example 1 This embodiment provides a phosphorus diffusion process for textured solar cells, the process including: (1) After cleaning the silicon wafer, texturing is performed to obtain a texturized silicon wafer. Then, a tunneling oxide layer and an intrinsic poly silicon layer are sequentially deposited on at least one side surface of the texturized silicon wafer. (2) In a nitrogen atmosphere with a nitrogen flow rate of 5000 sccm, the first heating is carried out at a heating rate of 12℃ / min until the temperature reaches 800℃. Then, in an oxygen atmosphere with an oxygen flow rate of 5000 sccm, the intrinsic poly silicon layer deposited on the surface of the texturized silicon wafer is pre-oxidized at 800℃ for 150s. (3) Then, in a nitrogen atmosphere, the temperature is increased at a rate of 12℃ / min until the temperature reaches 960℃. Then, in a nitrogen atmosphere, the temperature is increased for 2000s at 960℃. (4) Then, in a nitrogen atmosphere, perform a first cooling for 2500s until the temperature is the temperature at which phosphorus diffuses and deposits. (5) In a phosphorus-containing reaction atmosphere, phosphorus diffusion deposition is carried out at a temperature of 850°C for 25 minutes; (6) Then, in a nitrogen atmosphere, perform a second cooling process for 1000s until the temperature reaches the temperature for phosphorus diffusion propagation, and then perform phosphorus diffusion propagation. The phosphorus diffusion propulsion temperature is 800℃ and the time is 30 minutes.

[0056] Example 2 This embodiment provides a phosphorus diffusion process for textured solar cells, the process including: (1) After cleaning the silicon wafer, texturing is performed to obtain a texturized silicon wafer. Then, a tunneling oxide layer and an intrinsic poly silicon layer are sequentially deposited on at least one side surface of the texturized silicon wafer. (2) In a nitrogen atmosphere with a nitrogen flow rate of 1000 sccm, the first heating is carried out at a heating rate of 5℃ / min until the temperature reaches 750℃. Then, in an oxygen atmosphere with an oxygen flow rate of 1000 sccm, the intrinsic poly silicon layer deposited on the surface of the texturized silicon wafer is pre-oxidized at 750℃ for 30s. (3) Then, in an argon atmosphere, a second heating is carried out at a heating rate of 5℃ / min until the temperature reaches 850℃, and then a high-temperature heat treatment is carried out in an argon atmosphere at 850℃ for 6000s. (4) Then, in an argon atmosphere, perform a first cooling for 1000s until the temperature is the temperature at which phosphorus diffusion deposition occurs; (5) Then, in a phosphorus-containing reaction atmosphere, perform phosphorus diffusion deposition at a temperature of 800°C for 5 minutes; (6) Then, in an argon atmosphere, perform a second cooling process for 1000s until the temperature reaches the temperature for phosphorus diffusion propagation, and then perform phosphorus diffusion propagation. The phosphorus diffusion propulsion temperature is 750°C and the time is 50 minutes.

[0057] Example 3 This embodiment provides a phosphorus diffusion process for textured solar cells, the process including: (1) After cleaning the silicon wafer, texturing is performed to obtain a texturized silicon wafer. Then, a tunneling oxide layer and an intrinsic poly silicon layer are sequentially deposited on at least one side surface of the texturized silicon wafer. (2) In a nitrogen atmosphere with a nitrogen flow rate of 10000 sccm, the first heating is carried out at a heating rate of 20℃ / min until the temperature reaches 850℃. Then, in an oxygen atmosphere with an oxygen flow rate of 10000 sccm, the intrinsic poly silicon layer deposited on the surface of the texturized silicon wafer is pre-oxidized at 850℃ for 300s. (3) Then, in a nitrogen atmosphere, the temperature is increased at a rate of 20℃ / min until the temperature reaches 1000℃. Then, in a nitrogen atmosphere, the temperature is increased for 600s at 1000℃. (4) Then, in a nitrogen atmosphere, perform a first cooling for 2000s until the temperature is the temperature at which phosphorus diffuses and deposits. (5) Then, in a phosphorus-containing reaction atmosphere, phosphorus diffusion deposition is carried out at a temperature of 900℃ for 50 minutes; (6) Then, in a nitrogen atmosphere, perform a fourth heating for 600s until the temperature reaches the temperature for phosphorus diffusion propulsion, and then perform phosphorus diffusion propulsion. The phosphorus diffusion propulsion temperature is 950°C and the time is 5 minutes.

[0058] Example 4 This embodiment provides a phosphorus diffusion process for a textured solar cell. Except for step (2) of the phosphorus diffusion process, in which the pre-oxidation temperature is 600°C, the rest is the same as in embodiment 1.

[0059] Example 5 This embodiment provides a phosphorus diffusion process for a textured solar cell. Except for step (2) of the phosphorus diffusion process, in which pre-oxidation is carried out in an oxygen-containing atmosphere with an oxygen flow rate of 500 sccm, the rest is the same as in embodiment 1.

[0060] Example 6 This embodiment provides a phosphorus diffusion process for a textured solar cell. Except for step (2) of the phosphorus diffusion process, in which pre-oxidation is carried out in an oxygen-containing atmosphere with an oxygen flow rate of 15000 sccm, the rest is the same as in embodiment 1.

[0061] Example 7 This embodiment provides a phosphorus diffusion process for a textured solar cell. Except for step (3) of the phosphorus diffusion process, in which a high-temperature heat treatment is performed at 800°C in a nitrogen atmosphere, the rest is the same as in Embodiment 1.

[0062] Example 8 This embodiment provides a phosphorus diffusion process for a textured solar cell. Except for step (3) of the phosphorus diffusion process, where the high-temperature heat treatment temperature is 1100°C, the rest is the same as in embodiment 1.

[0063] Example 9 This embodiment provides a phosphorus diffusion process for a textured solar cell. Except for step (3) of the phosphorus diffusion process, where the high-temperature heat treatment time is 7000s, the rest is the same as in embodiment 1.

[0064] Comparative Example 1 This comparative example provides a phosphorus diffusion process for a textured solar cell, which is the same as in Example 1 except that step (2) of the phosphorus diffusion process is omitted.

[0065] Comparative Example 2 This comparative example provides a phosphorus diffusion process for a textured solar cell, which is the same as in Example 1 except that step (3) of the phosphorus diffusion process is omitted.

[0066] Comparative Example 3 This comparative example provides a phosphorus diffusion process for a textured solar cell. Except for omitting steps (2) and (3) of the phosphorus diffusion process, the rest is the same as in Example 1.

[0067] After preparing the N-POLY layer using the phosphorus diffusion process of the textured solar cell provided in the above embodiments and comparative examples, the layer is then immersed in an 8% dilute hydrofluoric acid solution. Next, a 100nm thick SiN layer is deposited on the light-receiving surface of the silicon wafer (i.e., the textured surface of the silicon wafer opposite the N-POLY layer) using plasma-enhanced chemical vapor deposition. x A passivation antireflection film was applied; finally, a silver electrode was fabricated on the front side of the cell and an aluminum electrode was fabricated on the N-POLY layer on the back side using screen printing technology, and the cells were sintered in a sintering furnace at 800°C to obtain a textured solar cell.

[0068] The cell efficiency, open-circuit voltage, and fill factor (FF) of the solar cells were then tested.

[0069] The battery efficiency test method is as follows: at a light source intensity of 1000W / m² 2 The test temperature was 25℃, and under the standard solar spectrum of AM 1.5G, a complete current-voltage characteristic curve scan of the battery was performed using a solar simulator and IV test system. From the open-circuit voltage point to the short-circuit current point, the maximum output power point (Pmax) was measured. The battery efficiency is the ratio of this maximum output power to the incident light power (1000W / m²). 2 The percentage value of the solar cell area (×) is used to obtain the cell efficiency of the solar cell, as shown in Table 1.

[0070] The test method for open-circuit voltage is as follows: at a light source intensity of 1000W / m 2 The test temperature was 25℃. Under the standard solar spectrum of AM 1.5G, the solar cell was irradiated using a solar simulator. The voltage value at both ends of the cell was directly measured using a high-precision digital source meter with the cell output terminal open (current zero). The open-circuit voltage of the solar cell is shown in Table 1.

[0071] The test method for fill factor is as follows: with a light source intensity of 1000 W / m². 2 The test temperature was 25℃, and under the standard solar spectrum of AM 1.5G, the complete current-voltage characteristic curve of the cell was scanned using a solar simulator and IV test system. The fill factor of the solar cell is shown in Table 1.

[0072] Table 1 From Table 1, we can obtain: (1) When preparing textured solar cells, the phosphorus diffusion process of textured solar cells provided in Examples 1 to 3 of this invention is used to prepare the N-POLY layer, and the resulting solar cells exhibit higher open-circuit voltage and higher cell efficiency. (2) By comparing Example 1 and Example 4, it can be seen that in the phosphorus diffusion process provided by the present invention, when the pre-oxidation temperature is ≥750℃, it is more conducive to improving the performance of solar cells. This is because if the oxidation process temperature is too low, the oxide layer grows slowly and the film layer is not dense enough, which cannot meet the corresponding process effect. (3) By comparing Example 1 with Examples 5 and 6, it can be seen that in the phosphorus diffusion process provided by the present invention, pre-oxidation in an oxygen-containing atmosphere with an oxygen flow rate of 1000 sccm to 10000 sccm is more conducive to improving the performance of solar cells. This is because when the oxygen flow rate is too high, the oxide layer grown by pre-oxidation is too thick, which blocks the phosphorus diffusion process and affects the cell opening voltage; when the oxygen flow rate is too low, the oxide layer grows slowly and the film density is poor, which cannot meet the corresponding process effect. (5) By comparing Example 1 and Example 7, it can be seen that in the phosphorus diffusion process provided by the present invention, when the temperature of the high-temperature heat treatment is ≥850℃, it is more conducive to improving the performance of solar cells. This is because at a lower temperature, the crystal structure of the tunneling oxide layer cannot be changed, so the compactness remains unchanged. (6) By comparing Example 1 and Example 8, it can be seen that in the phosphorus diffusion process provided by the present invention, when the high temperature heat treatment time is ≤1000℃, it is more conducive to improving the solar cell. This is because the excessively high temperature heat treatment temperature applies too much heat budget to the tunneling oxide layer, thereby destroying the passivation effect. (7) By comparing Example 1 and Example 9, it can be seen that in the phosphorus diffusion process provided by the present invention, when the high temperature heat treatment time is not higher than 6000s, it is more conducive to improving the solar cell. This is because excessively long high temperature heat treatment time can easily burn through the tunneling oxide layer and destroy the passivation effect. (8) By comparing Example 1 with Comparative Examples 1 to 3, it can be seen that in the phosphorus diffusion process provided by the present invention, a pre-oxidation step is added before phosphorus diffusion deposition. On the one hand, pre-oxidation can achieve cleaning treatment of the silicon wafer surface. On the other hand, an oxide layer can be pre-grown on the surface of the intrinsic poly silicon layer. The presence of the oxide layer is beneficial to improving the uniformity of phosphorus diffusion, thereby improving the open circuit voltage and cell efficiency of the solar cell. In the phosphorus diffusion process provided by this invention, a high-temperature heat treatment step is added between pre-oxidation and phosphorus diffusion deposition. The high-temperature heat treatment step improves the density of the tunnel oxide layer, thereby obtaining a better passivation effect and further improving the open-circuit voltage and cell efficiency of the solar cell. In the phosphorus diffusion process provided by this invention, the synergistic effect of pre-oxidation and high-temperature heat treatment is beneficial to optimizing the crystal structure and interface characteristics of the N-POLY layer, forming a high-quality PN junction, thereby reducing surface defect recombination, improving carrier separation and collection efficiency, and achieving an increase in open-circuit voltage. In summary, the phosphorus diffusion process provided by this invention, by adding pre-oxidation and high-temperature heat treatment steps before phosphorus diffusion deposition, synergistically improves the overall performance of the battery. Specifically, pre-oxidation improves the uniformity of phosphorus diffusion, and high-temperature heat treatment enhances the passivation effect, thereby increasing the open-circuit voltage. The synergistic effect of these two processes optimizes the crystal structure and interface quality of the N-POLY layer, thus improving battery efficiency. Therefore, the solar cell exhibits both high open-circuit voltage and high battery efficiency.

[0073] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A phosphorus diffusion process for textured solar cells, characterized in that, The process includes the following steps: In an oxygen-containing atmosphere, the intrinsic poly silicon layer deposited on the surface of the texturized silicon wafer is pre-oxidized, then subjected to high-temperature heat treatment in a protective atmosphere, followed by phosphorus diffusion deposition in a phosphorus-containing reactive atmosphere, and then phosphorus diffusion propagation in a nitrogen or oxygen atmosphere.

2. The phosphorus diffusion process according to claim 1, characterized in that, The process also includes a deposition step prior to pre-oxidation, the deposition step comprising: sequentially depositing a tunneling oxide layer and an intrinsic poly silicon layer on at least one side surface of the texturized silicon wafer; Preferably, the method for preparing a texturized silicon wafer includes: cleaning the silicon wafer and then texturing it to obtain a texturized silicon wafer.

3. The phosphorus diffusion process according to claim 1, characterized in that, The pre-oxidation temperature is ≥750℃, and the time is 30s~300s; Preferably, the oxygen flow rate in the oxygen-containing atmosphere is 1000 sccm to 10000 sccm; Preferably, the phosphorus diffusion process further includes a first heating before the pre-oxidation, wherein the heating rate of the first heating is 5°C / min to 20°C / min, the endpoint temperature is the pre-oxidation temperature, and the process is carried out in an oxygen-containing atmosphere.

4. The phosphorus diffusion process according to claim 1, characterized in that, The high-temperature heat treatment is performed at a temperature of 850℃~1000℃ for a duration not exceeding 6000s. Preferably, the protective atmosphere includes nitrogen and / or an inert gas; Preferably, the phosphorus diffusion process further includes a second heating between the pre-oxidation and the high-temperature heat treatment, wherein the heating rate of the second heating is 8°C / min to 18°C / min, the endpoint temperature is the temperature of the high-temperature heat treatment, and the process is carried out in a protective atmosphere.

5. The phosphorus diffusion process according to any one of claims 1 to 4, characterized in that, The phosphorus diffusion process also includes a third heating or a first cooling process between high-temperature heat treatment and phosphorus diffusion deposition. Preferably, the phosphorus diffusion process further includes a fourth heating or a second cooling between phosphorus diffusion deposition and phosphorus diffusion propulsion.

6. The phosphorus diffusion process according to claim 5, characterized in that, The third heating is carried out in a protective atmosphere for 300s to 600s, and the endpoint temperature is the temperature at which the phosphorus diffuses and deposits. The first cooling is carried out in a protective atmosphere for 400s to 4000s, and the endpoint temperature is the temperature at which the phosphorus diffuses and deposits.

7. The phosphorus diffusion process according to claim 5, characterized in that, The phosphorus diffusion deposition temperature is 800℃~900℃, and the time is 5min~50min; Preferably, the phosphorus source in the phosphorus-containing reaction atmosphere includes phosphorus oxychloride; Preferably, the fourth heating or the second cooling is carried out in a nitrogen atmosphere, the fourth heating time is 200s~1200s, and the endpoint temperature is the temperature at which phosphorus diffusion is promoted; the second cooling time is 300s~3000s, and the endpoint temperature is the temperature at which phosphorus diffusion is promoted; Preferably, the phosphorus diffusion propulsion temperature is 750℃~950℃ and the time is 5min~50min.

8. The phosphorus diffusion process according to claim 1, characterized in that, The phosphorus diffusion process includes: (1) After cleaning the silicon wafer, texturing is performed to obtain a texturized silicon wafer. Then, a tunneling oxide layer and an intrinsic poly silicon layer are sequentially deposited on at least one side surface of the texturized silicon wafer. (2) In a nitrogen atmosphere with a nitrogen flow rate of 1000 sccm to 10000 sccm, the first heating is carried out at a heating rate of 5℃ / min to 20℃ / min until the temperature is ≥750℃. Then, in an oxygen atmosphere with an oxygen flow rate of 1000 sccm to 10000 sccm, the texturized silicon wafer with the tunnel oxide layer and intrinsic poly silicon layer deposited on the surface is pre-oxidized at ≥750℃ for 30s to 300s. (3) In nitrogen and / or inert gas, a second heating is carried out at a heating rate of 5℃ / min to 20℃ / min until the temperature reaches 850℃ to 1000℃, and then a high-temperature heat treatment of not more than 6000s is carried out in nitrogen and / or inert gas at 850℃ to 1000℃. (4) Then, in nitrogen and / or inert gas, perform a third heating for 300s to 600s or a first cooling for 400s to 4000s until the temperature is the temperature of phosphorus diffusion deposition. (5) Then, in a phosphorus-containing reaction atmosphere, phosphorus diffusion deposition is carried out at a temperature of 800℃~900℃ for 5min~50min; (6) Then, in nitrogen and / or inert gas, perform a fourth heating process of 200s to 1200s or a second cooling process of 300s to 3000s until the temperature is the temperature for phosphorus diffusion propulsion, and then perform phosphorus diffusion propulsion. The phosphorus diffusion propulsion temperature is 750℃~950℃, and the time is 5min~50min.

9. An N-POLY layer for a textured solar cell, characterized in that, The N-POLY layer is prepared by the phosphorus diffusion process described in any one of claims 1 to 8.

10. A textured solar cell, characterized in that, The solar cell includes the N-POLY layer as described in claim 9.

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