Solar cell, preparation method thereof and photovoltaic module

Abstract

The invention provides a solar cell, a preparation method thereof and a photovoltaic module. The method for preparing the solar cell comprises the steps that a silicon substrate is provided, a first borosilicate glass layer and a second borosilicate glass layer are sequentially deposited on the front face, and the percentage of oxygen atoms in the first borosilicate glass layer is larger than the percentage of oxygen atoms in the second borosilicate glass layer; the percentage of boron atoms in the first borosilicate glass layer is smaller than that in the second borosilicate glass layer; and annealing the first borosilicate glass layer and the second borosilicate glass layer, and forming a boron emission electrode layer on the surface of the silicon substrate. Therefore, the preparation method can effectively improve the interface passivation effect, reduce the interface defects, facilitate the formation of a battery structure with a high-concentration boron emission electrode layer and a shallow PN junction, improve the carrier transport and improve the battery efficiency.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to solar cells, their fabrication methods, and photovoltaic modules. Background Technology

[0002] In the development of high-efficiency silicon solar cells, boron diffusion forms p + The emitter is a key component of the N-type battery structure. BSG (borosilicate glass) is deposited using PECVD (plasma-enhanced chemical vapor deposition) as the p-type electrode. + The emitter diffusion source features low-temperature deposition (energy saving), strong source layer controllability, and high process compatibility. However, the BSG deposition structure still struggles to balance low surface recombination rate and excellent contact performance, resulting in limited improvement in solar cell efficiency. Summary of the Invention

[0003] This invention aims to at least partially address one of the technical problems in related technologies. Therefore, one object of this invention is to provide a method for fabricating solar cells that optimizes surface passivation, diffusion depth, contact performance, etc., within the cell.

[0004] In one aspect of the present invention, a method for fabricating a solar cell is provided. According to an embodiment of the present invention, the method for fabricating a solar cell includes: providing a silicon substrate having a front side and a back side disposed opposite to each other; sequentially depositing a first borosilicate glass layer and a second borosilicate glass layer on the front side, wherein the oxygen atom percentage in the first borosilicate glass layer is greater than the oxygen atom percentage in the second borosilicate glass layer, and the boron atom percentage in the first borosilicate glass layer is less than the boron atom percentage in the second borosilicate glass layer; annealing the first borosilicate glass layer and the second borosilicate glass layer; and forming a boron emission electrode layer on the surface of the silicon substrate. Therefore, by setting two borosilicate glass layers with different percentages of boron and oxygen atoms in the two layers, during the annealing process, in the first borosilicate glass layer, oxygen atoms entering the interstitial sites will form Si-O-Si structures or BO bonds, which severely hinder the migration and rearrangement of silicon atoms. This allows the higher concentration of oxygen in the first borosilicate glass layer to precipitate SiO2 clusters (i.e., silicon and oxygen combine to form an ultrathin silicon oxide layer) or boron-oxygen complexes, which can passivate the interface and reduce interface defects. Furthermore, silicon oxide itself carries a negative charge (especially under oxygen-rich conditions), which generates a fixed electric field. This electric field causes the n-type silicon substrate to produce... The generation of negative charges repels electrons (minority carriers), further reducing interfacial recombination. The low boron content also prevents excessive boron diffusion, thus facilitating the formation of a shallow PN junction and improving carrier transport. During annealing, the high boron content in the second borosilicate glass layer acts as a boron diffusion source, providing sufficient boron atoms to the silicon substrate to form a boron emitter electrode layer. However, as boron atoms diffuse downwards, the diffusion depth is suppressed by the silicon oxide layer formed at the bottom layer, resulting in a high-concentration boron emitter electrode layer but a shallower PN junction. This improves the battery's contact performance, thermal stability, and bandgap control, thereby enhancing battery efficiency.

[0005] According to an embodiment of the present invention, the percentage of boron atoms in the first borosilicate glass layer is 1% to 5%, the percentage of oxygen atoms in the first borosilicate glass layer is 45% to 60%, and / or, the percentage of boron atoms in the second borosilicate glass layer is 20% to 35%, and the percentage of oxygen atoms in the second borosilicate glass layer is 5% to 20%.

[0006] According to an embodiment of the present invention, the conditions for depositing the first borosilicate glass layer include: a flow rate of B2H6 of 500-1000 sccm, a flow rate of SiH4 of 5000-12000 sccm, a flow rate of N2O of 5000-12000 sccm, a temperature of 400-600°C, and a time of 20-120 s; the conditions for depositing the second borosilicate glass layer include: a flow rate of B2H6 of 1000-5000 sccm, a flow rate of SiH4 of 2000-10000 sccm, a flow rate of N2O of 2000-10000 sccm, a temperature of 400-600°C, and a time of 60-250 s.

[0007] According to an embodiment of the present invention, the thickness of the first borosilicate glass layer is 10~15nm, and the thickness of the second borosilicate glass layer is 20~25nm.

[0008] According to an embodiment of the present invention, the method for preparing a solar cell further includes depositing a third borosilicate glass layer between the first borosilicate glass layer and the second borosilicate glass layer, wherein the percentage of boron atoms in the third borosilicate glass layer is greater than the percentage of boron atoms in the first borosilicate glass layer and less than the percentage of boron atoms in the second borosilicate glass layer, and the percentage of oxygen atoms in the third borosilicate glass layer is less than the percentage of oxygen atoms in the first borosilicate glass layer and greater than the percentage of oxygen atoms in the second borosilicate glass layer.

[0009] According to an embodiment of the present invention, the percentage of boron atoms in the third borosilicate glass layer is 5% to 20%, and the percentage of oxygen atoms in the third borosilicate glass layer is 20% to 45%. Optionally, the conditions for depositing the third borosilicate glass layer include: a flow rate of B2H6 of 800 to 2000 sccm, a flow rate of SiH4 of 3500 to 10000 sccm, a flow rate of N2O of 3500 to 10000 sccm, a temperature of 400 to 600°C, and a time of 40 to 200 s.

[0010] According to an embodiment of the present invention, the annealing process includes performing a first annealing and a second annealing in sequence, wherein the temperature of the first annealing is lower than the temperature of the second annealing. Optionally, the temperature of the first annealing is 920~980℃ and the time is 200~800s; the temperature of the second annealing is 960~1050℃ and the time is 500~1500s.

[0011] According to an embodiment of the present invention, the method for fabricating a solar cell further includes: sequentially depositing a tunneling oxide layer and an n-type doped polycrystalline silicon layer on the back surface; removing the first borosilicate glass layer and the second borosilicate glass layer on the front surface; sequentially forming a passivation layer and a front antireflection layer on the side of the boron emitter electrode layer away from the silicon substrate; forming a back antireflection layer on the side of the n-type doped polycrystalline silicon layer away from the silicon substrate; and forming a first gate line and a second gate line on the front surface and the back surface, respectively.

[0012] In another aspect of the invention, a solar cell is provided. According to an embodiment of the invention, the solar cell is prepared by the method described above. Therefore, the solar cell has high efficiency. Those skilled in the art will understand that this solar cell possesses all the features and advantages of the solar cell preparation described above, and will not be elaborated further here.

[0013] In another aspect, the present invention provides a photovoltaic module. According to an embodiment of the invention, the photovoltaic module includes the aforementioned solar cell. Therefore, the photovoltaic module has a high photoelectric conversion efficiency.

[0014] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0015] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart illustrating the fabrication of a solar cell in one embodiment of the present invention; Figure 2 This is a flowchart illustrating the fabrication of a solar cell in another embodiment of the present invention; Figure 3 and Figure 4 This is a structural flowchart of the preparation of a solar cell in another embodiment of the present invention. Detailed Implementation

[0016] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0017] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0018] In one aspect, the present invention provides a method for fabricating a solar cell. According to an embodiment of the present invention, referring to... Figure 1 Methods for preparing solar cells include: S100: Provides a silicon substrate having a front side and a back side arranged opposite to each other.

[0019] According to some embodiments of the present invention, the silicon substrate may be an N-type silicon substrate or a P-type silicon substrate.

[0020] According to some embodiments of the present invention, the solar cell prepared by this method can be a TOPCon cell, and the mechanism is the same as that of a TOPCon cell. Thus, the front side of the silicon substrate has a textured surface.

[0021] S200: A first borosilicate glass layer 21 and a second borosilicate glass layer 22 are sequentially deposited on the front side. The percentage of oxygen atoms in the first borosilicate glass layer 21 is greater than that in the second borosilicate glass layer 22, while the percentage of boron atoms in the first borosilicate glass layer 21 is less than that in the second borosilicate glass layer 22. Thus, the boron-oxygen ratio in the first borosilicate glass layer is less than that in the second borosilicate glass layer. This double-layered borosilicate glass effectively balances multiple requirements, including passivation, contact performance, and efficient boron source supply.

[0022] According to some embodiments of the present invention, the percentage of boron atoms in the first borosilicate glass layer is 1% to 5% (e.g., 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.), and the percentage of oxygen atoms in the first borosilicate glass layer is 45% to 60% (e.g., 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, etc.). Therefore, the aforementioned percentage of boron atoms effectively prevents the transitional diffusion of boron atoms from the first borosilicate glass layer to the silicon substrate, facilitating the formation of a shallow PN junction and improving carrier transport. The high concentration of oxygen atoms can form an ultrathin silicon oxide layer during annealing, which can passivate the interface and reduce interface defects and interfacial recombination.

[0023] According to some embodiments of the present invention, a first borosilicate glass layer can be deposited by PECVD (plasma-enhanced chemical vapor deposition). The deposition conditions include: a B₂H₆ flow rate of 500-1000 sccm, a SiH₄ flow rate of 5000-12000 sccm, an N₂O flow rate of 5000-12000 sccm, a temperature of 400-600°C, and a deposition time of 20-120 s. Thus, the above deposition conditions can effectively obtain the first borosilicate glass layer with the aforementioned boron-oxygen atomic percentage.

[0024] According to an embodiment of the present invention, the thickness of the first borosilicate glass layer is 10~15nm, such as 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, etc.

[0025] According to some embodiments of the present invention, the percentage of boron atoms in the second borosilicate glass layer is 20% to 35% (e.g., 20%, 21%, 22%, 23%, 24%, 25%, 26%, 277%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, etc.), and the percentage of oxygen atoms in the second borosilicate glass layer is 5% to 20% (e.g., 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.). Thus, the high boron content in the second borosilicate glass layer allows it to act as a boron diffusion source, providing sufficient boron atoms to the silicon substrate to form a boron emitter electrode layer. However, as boron atoms diffuse downwards, the diffusion depth is suppressed due to the silicon oxide layer formed at the bottom layer. This facilitates the formation of a high-concentration boron emitter electrode layer but a shallower PN junction, improving contact performance, thermal stability, and bandgap control, thereby enhancing battery efficiency.

[0026] According to some embodiments of the present invention, a second borosilicate glass layer can be deposited by PECVD (plasma-enhanced chemical vapor deposition). The deposition conditions for the second borosilicate glass layer include: a B₂H₆ flow rate of 1000-5000 sccm, a SiH₄ flow rate of 2000-10000 sccm, an N₂O flow rate of 2000-10000 sccm, a temperature of 400-600°C, and a deposition time of 60-250 s. Therefore, the above deposition conditions can effectively obtain the second borosilicate glass layer with the aforementioned boron-oxygen atomic percentage.

[0027] According to some embodiments of the present invention, the thickness of the second borosilicate glass layer is 20~25 nm.

[0028] According to some embodiments of the present invention, with reference to Figure 3The method for fabricating solar cells further includes depositing a third borosilicate glass layer 23 between a first borosilicate glass layer 21 and a second borosilicate glass layer 22. Specifically, the first borosilicate glass layer 21, the third borosilicate glass layer 23, and the second borosilicate glass layer 22 are sequentially deposited on the front side of the silicon substrate. The percentage of boron atoms in the third borosilicate glass layer 23 is greater than that in the first borosilicate glass layer 21 and less than that in the second borosilicate glass layer 22 (i.e., the percentage of boron atoms in the third borosilicate glass layer is between that in the first and second borosilicate glass layers). The percentage of oxygen atoms in the third borosilicate glass layer is less than that in the first borosilicate glass layer and greater than that in the second borosilicate glass layer (i.e., the percentage of oxygen atoms in the third borosilicate glass layer is between that in the first and second borosilicate glass layers). This creates a favorable gradient in both the percentage of boron atoms and the percentage of oxygen atoms, thereby improving the passivation effect of the cell, reducing interface defects and surface recombination, and facilitating the formation of a cell structure with a high-doped boron emitter electrode layer but a shallow PN junction.

[0029] According to some embodiments of the present invention, the percentage of boron atoms in the third borosilicate glass layer is 5% to 20% (e.g., 5%, 7%, 9%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, etc.), and the percentage of oxygen atoms in the third borosilicate glass layer is 20% to 45% (e.g., 20%, 22%, 24%, 25%, 26%, 28%, 30%, 32%, 34%, 35%, 38%, 40%, 42%, 44%, 45%, etc.). This allows for the formation of favorable gradients in both the percentage of boron atoms and the percentage of oxygen atoms, thereby improving the passivation effect of the battery, reducing interface defects and surface recombination, and facilitating the formation of a battery structure with a high-doped boron emitter electrode layer but a shallower PN junction.

[0030] According to some embodiments of the present invention, the conditions for depositing the third borosilicate glass layer include: a B₂H₆ flow rate of 800-2000 sccm, a SiH₄ flow rate of 3500-10000 sccm, an N₂O flow rate of 3500-10000 sccm, a temperature of 400-600°C, and a time of 40-200 s. Therefore, the above deposition conditions can effectively obtain the third borosilicate glass layer with the aforementioned boron-oxygen atomic percentage.

[0031] S300: Annealing is performed on the first borosilicate glass layer 21 and the second borosilicate glass layer 22 to form a boron emission electrode layer 30 on the surface of the silicon substrate 10. The annealing process can be performed in an inert atmosphere, such as a nitrogen atmosphere.

[0032] According to some embodiments of the present invention, the annealing process includes sequentially performing a first annealing and a second annealing, wherein the temperature of the first annealing is lower than the temperature of the second annealing. Thus, the lower temperature of the first annealing and the higher temperature of the second annealing promote the formation of silicon-oxygen bonds, helping to improve the interface passivation effect, while the shorter, higher temperature second annealing effectively drives the diffusion of boron atoms in the second borosilicate glass layer, forming a shallow PN junction structure.

[0033] In some embodiments, the first annealing temperature is 920~980℃ for 200~800s; the second annealing temperature is 960~1050℃ for 500~1500s. Thus, under the above temperature conditions, the first annealing temperature is relatively low, and the second annealing temperature is relatively high. The low-temperature first annealing can promote the formation of silicon-oxygen bonds, helping to improve the interface passivation effect, while the high-temperature, short-duration second annealing can effectively drive the diffusion of boron atoms in the second borosilicate glass layer, forming a shallow PN junction structure.

[0034] According to an embodiment of the present invention, in the above preparation method, two borosilicate glass layers are formed by deposition, and the percentages of boron and oxygen atoms in the two borosilicate glass layers are different. During the annealing process, in the first borosilicate glass layer, oxygen atoms enter the interstitial sites of the lattice and form Si-O-Si structures or BO bonds, which severely hinder the migration and rearrangement of silicon atoms. This allows the higher concentration of oxygen in the first borosilicate glass layer to precipitate SiO2 clusters (i.e., silicon and oxygen combine to form an ultrathin silicon oxide layer) or boron-oxygen complexes, which play a role in interface passivation, thereby reducing interface defects. Furthermore, silicon oxide itself carries a negative charge (especially under oxygen-rich conditions), which generates a fixed electric field. This process generates a negative charge on the n-type silicon substrate, which repels electrons (minority carriers), further reducing interfacial recombination. The low boron content also prevents excessive boron diffusion, thus facilitating the formation of a shallow PN junction and improving carrier transport. During annealing, the high boron content in the second borosilicate glass layer acts as a boron diffusion source, providing sufficient boron atoms to the silicon substrate to form a boron emitter electrode layer. However, as boron atoms diffuse downwards, the diffusion depth is suppressed by the silicon oxide layer formed at the bottom layer, resulting in a high-concentration boron emitter electrode layer but a shallower PN junction. This improves the battery's contact performance, thermal stability, and bandgap control, thereby enhancing battery efficiency.

[0035] In some embodiments, the thickness of the obtained boron emission electrode layer can be 0.4~1.0 micrometers, and the doping concentration is 4×10⁻⁶. 18 ~6×10 19 Therefore, it can be seen that the method of the present invention can effectively form a battery structure with a high concentration of boron emitter electrode layer but a shallow PN junction.

[0036] According to some embodiments of the present invention, with reference to Figure 3 and Figure 4 Other methods for preparing solar cells include: S400: A tunneling oxide layer 40 and an n-type doped polysilicon layer 50 are sequentially deposited on the back surface.

[0037] In some embodiments, a specific method for forming a tunneling oxide layer and an n-type doped polysilicon layer may include: sequentially depositing a tunneling oxide layer and a polysilicon layer on the back surface using LPCVD; and then performing n-type impurity doping (such as phosphorus doping) on ​​the polysilicon layer to obtain an n-type doped polysilicon layer.

[0038] In some specific embodiments, the conditions for depositing the tunneling oxide layer include: an oxygen flow rate of 27,000-36,000 sccm, a temperature of 590-615°C, a process time of 500-1800 s, and a tube blanching period of 300-1000 s, forming a tunneling silicon dioxide layer with a thickness of 1.8-2.3 nm.

[0039] In some specific embodiments, the conditions for depositing the polycrystalline silicon layer include: a deposition temperature of 590-615℃, a process time of 2000±300s, and silane flow rates of 190±20, 440±20, and 620±20 sccm for the three-stage gas inlet method, respectively, resulting in a final poly thickness of 145±5nm.

[0040] In some embodiments, the polycrystalline silicon layer is subjected to phosphorus diffusion doping. The phosphorus source flow rate is 900-1400 sccm, the temperature is 780-830°C, and the process time is 960-1500 s; the advance step temperature is 860-900°C, and the process time is 900-1300 s; the oxidation temperature is 870°C, the oxygen flow rate is 1500-3000 sccm, and the oxidation time is 540 s. The final structure formed is an N-poly (n-type doped polycrystalline silicon layer 50) + PSG (phosphosilicate glass) layer 51, wherein the N-poly thickness is 110-120 nm, the PSG layer thickness is 45-55 nm, and the sheet resistance is 45 ± 5.

[0041] S500: Remove the first borosilicate glass layer 21 and the second borosilicate glass layer 22 on the front side.

[0042] In some embodiments, the first borosilicate glass layer 21 and the second borosilicate glass layer 22 can be removed by hydrofluoric acid solution.

[0043] In some specific embodiments, the phosphosilicate glass formed on the front and sides is first removed by a wet chain machine, then the n-type doped polysilicon layer deposited on the front and sides is removed by a wet alkaline bath, and finally the BSG (including all stacked borosilicate glass) on the front and the PSG layer 51 on the back are removed by an acid bath.

[0044] In some specific embodiments, the temperature of the chain machine tank is 40±5℃, the process time is 30±5s, and the acid solution is composed of H2O and HF in a volume ratio of 5:1; the temperature of the alkali polishing tank is 50~75℃, the process time is 300±20s, and the alkali solution includes sodium hydroxide, wherein the NaOH concentration is about 3%; the temperature of the acid tank (hydrofluoric acid solution) is 40±5℃, and the process time is 120±20s.

[0045] S600: A passivation layer 60 and a front antireflection layer 70 are sequentially formed on the side of the boron emission electrode layer 30 away from the silicon substrate 10.

[0046] In some embodiments, the passivation layer can be deposited by methods such as atomic layer deposition, physical vapor deposition, or chemical vapor deposition. The material of the passivation layer includes aluminum oxide, and the thickness can be 3-6 nm.

[0047] In some embodiments, the front antireflective layer can be formed by a coating process. The front antireflective layer may include multiple layers of sub-antireflective layers stacked together. The materials of the sub-antireflective layers include at least one of silicon nitride, silicon oxynitride, and silicon oxide, and the refractive indices of sub-antireflective layers made of different materials are different. Further, in some embodiments, the thickness of the sub-antireflective layers can be 10~25 nm, resulting in a final overall front antireflective layer thickness of 75±5 nm and a refractive index of 2.10±0.05.

[0048] S700: A back antireflection layer 80 is formed on the side of the n-type doped polysilicon layer 50 away from the silicon substrate 10.

[0049] In some embodiments, the back antireflective layer can be formed by a coating process. The back antireflective layer may include multiple layers of sub-antireflective layers stacked together. The materials of the sub-antireflective layers include at least one of silicon nitride, silicon oxynitride, and silicon oxide, and the refractive indices of sub-antireflective layers made of different materials are different. Further, in some embodiments, the thickness of the sub-antireflective layers can be 10~30 nm, resulting in a final overall front antireflective layer thickness of 84±6 nm and a refractive index of 2.12±0.05.

[0050] S800: A first grid line 91 and a second grid line 92 are formed on the front and back sides, respectively.

[0051] In some embodiments, the first and second gate lines can be prepared by screen printing, and then obtained by sintering and laser-assisted sintering. The materials of the first and second gate lines can be silver, silver-clad copper, etc., respectively.

[0052] In another aspect of the invention, a solar cell is provided. According to an embodiment of the invention, the solar cell is prepared by the method described above. Therefore, the solar cell has high efficiency. Those skilled in the art will understand that this solar cell possesses all the features and advantages of the solar cell preparation described above, and will not be elaborated further here.

[0053] In another aspect, the present invention provides a photovoltaic module. According to an embodiment of the invention, the photovoltaic module includes the aforementioned solar cell. Therefore, the photovoltaic module has a high photoelectric conversion efficiency.

[0054] Example 1 Methods for preparing TOPCon batteries include: Step 1: Texturing the n-type silicon substrate using a sodium hydroxide alkaline solution with a NaOH concentration of 1%, a solution temperature of 70°C, and a process time of 450 seconds to form a double-sided textured structure.

[0055] Step 2: A first borosilicate glass layer and a second borosilicate glass layer are sequentially deposited on the front surface of a silicon substrate using PECVD. The deposition conditions for the first borosilicate glass layer are: a flow rate of 700 sccm for B2H6, a flow rate of 8000 sccm for SiH4, a flow rate of 8000 sccm for N2O, a temperature of 500℃, and a time of 70 s. The thickness of the first borosilicate glass layer is 12 nm, with a boron atom percentage of 3.1% and an oxygen atom percentage of 51%. The deposition conditions for the second borosilicate glass layer are: a flow rate of 3000 sccm for B2H6, a flow rate of 6500 sccm for SiH4, a flow rate of 6500 sccm for N2O, a temperature of 500℃, and a time of 160 s. The thickness of the second borosilicate glass layer is 23 nm, with a boron atom percentage of 27.5% and an oxygen atom percentage of 12.4%.

[0056] Step 3: The first and second borosilicate glass layers are subjected to a first annealing and a second annealing, respectively. The first annealing temperature is 940℃ for 400s; the second annealing temperature is 980℃ for 1000s. After annealing, a 0.5 μm thick boron emitter electrode layer is obtained, with a boron doping concentration of 4 × 10⁻⁶. 19 .

[0057] Step 4: Remove the back side BSG using a wet acid tank chain machine and polish it. Remove the back side and sides using an alkaline polishing tank to form an expanded PN junction. The acid tank chain machine temperature is 40℃, the process time is 40s, and the solution is composed of H2O and HF in a volume ratio of 5:1. The alkaline polishing tank temperature is 60℃, the process time is 300s, and the NaOH concentration in the alkaline solution is approximately 3%.

[0058] Step 5: A tunneling oxide layer and a polysilicon layer are sequentially deposited on the back surface using LPCVD. The polysilicon layer is then phosphorus-doped to obtain a phosphorus-doped polysilicon layer. The conditions for depositing the tunneling oxide layer include: oxygen flow rate of 31000 sccm, temperature of 600℃, process time of 1200 s, and tube shut-in for 700 s, forming a 2 nm thick tunneling oxide layer. For phosphorus diffusion doping: phosphorus source flow rate of 1200 sccm, temperature of 800℃, process time of 1200 s; advance step temperature of 880℃, process time of 1100 s; oxidation temperature of 870℃, oxygen flow rate of 2100 sccm, and oxidation time of 540 s, ultimately forming a structure of a phosphorus-doped polysilicon layer + PSG layer. The thickness of the phosphorus-doped polysilicon layer is 115 nm, the thickness of the PSG layer is 50 nm, and the sheet resistance is 45 ohms.

[0059] Step 6: First, the PSG layer formed on the front and sides is removed using a wet chain mill. Then, the phosphorus-doped polysilicon layer deposited on the front and sides is removed using a wet alkaline bath. Finally, the first and second borosilicate glass layers on the front and the PSG layer on the back are removed using an acid bath. The chain mill tank temperature is 40℃, the process time is 30s, and the acid solution is composed of H2O and HF in a 5:1 volume ratio. The alkaline bath temperature is 60℃, the process time is 300s, and the NaOH concentration in the alkaline solution is approximately 3%. The hydrofluoric acid solution temperature in the acid bath is 40℃, and the process time is 120s.

[0060] Step 7: Deposit an aluminum oxide layer with a thickness of 4.5 nm on the side of the boron emitter electrode layer away from the silicon substrate by atomic layer deposition.

[0061] Step 8: Deposit a front antireflective layer on the surface of the aluminum oxide layer at a temperature of 540℃. The layer consists of 6 layers, deposited in the following order from the silicon substrate outwards: silicon nitride 1, silicon nitride 2, silicon nitride 3, silicon oxynitride 1, silicon oxynitride 2, and silicon oxide. The thickness of each layer is between 10-25nm, and the final overall film thickness is 75nm with a refractive index of 2.10.

[0062] Step 9: Deposit a back antireflection layer on the side of the phosphorus-doped polycrystalline silicon layer away from the silicon substrate. The deposition temperature is 530℃. The layer consists of 3 films, deposited in the following order from the silicon substrate outwards: silicon nitride 1, silicon nitride 2, and silicon nitride 3. The thickness of each film is between 10-30nm, and the final overall film thickness is 84nm with a refractive index of 2.12.

[0063] Step 10: Form the first metal grid line and the second metal grid line on the front and back sides respectively by screen printing. Sinter the metal at 730℃ to form an ohmic contact with the silicon substrate to collect and conduct current.

[0064] Example 2 The method for preparing TOPCon batteries is basically the same as in Example 1, except for steps 2 and 3: A first borosilicate glass layer and a second borosilicate glass layer were sequentially deposited on the front surface of a silicon substrate using PECVD. The deposition conditions for the first borosilicate glass layer were: a flow rate of 550 sccm for B₂H₆, a flow rate of 6000 sccm for SiH₄, a flow rate of 6000 sccm for N₂O, a temperature of 500℃, and a deposition time of 70 s. The thickness of the first borosilicate glass layer was 12 nm, with a boron atom percentage of 1.1% and an oxygen atom percentage of 47%. The deposition conditions for the second borosilicate glass layer were: a flow rate of 2000 sccm for B₂H₆, a flow rate of 3500 sccm for SiH₄, a flow rate of 3500 sccm for N₂O, a temperature of 500℃, and a deposition time of 160 s. The thickness of the second borosilicate glass layer was 23 nm, with a boron atom percentage of 20% and an oxygen atom percentage of 5.1%.

[0065] Step 3: The borosilicate glass layer is subjected to a first annealing treatment and a second annealing treatment sequentially. The first annealing temperature is 940℃ for 400s; the second annealing temperature is 980℃ for 1000s. After annealing, a 0.5 μm thick boron emitter electrode layer is obtained, with a boron doping concentration of 8 × 10⁻⁶. 18 .

[0066] Example 3 The method for preparing TOPCon batteries is basically the same as in Example 1, except for steps 2 and 3: A first borosilicate glass layer and a second borosilicate glass layer were sequentially deposited on the front surface of a silicon substrate using PECVD. The deposition conditions for the first borosilicate glass layer were: a flow rate of 900 sccm for B₂H₆, a flow rate of 10000 sccm for SiH₄, a flow rate of 10000 sccm for N₂O, a temperature of 500℃, and a deposition time of 70 s. The thickness of the first borosilicate glass layer was 12 nm, with a boron atomic percentage of 4.89% and an oxygen atomic percentage of 59.3%. The deposition conditions for the second borosilicate glass layer were: a flow rate of 4000 sccm for B₂H₆, a flow rate of 8500 sccm for SiH₄, a flow rate of 8500 sccm for N₂O, a temperature of 500℃, and a deposition time of 160 s. The thickness of the second borosilicate glass layer was 23 nm, with a boron atomic percentage of 33.9% and an oxygen atomic percentage of 19.4%.

[0067] Step 3: The borosilicate glass layer is subjected to a first annealing treatment and a second annealing treatment sequentially. The first annealing temperature is 940℃ for 400s; the second annealing temperature is 980℃ for 1000s. After annealing, a 0.8 μm thick boron emitter electrode layer is obtained, with a boron doping concentration of 4.5 × 10⁻⁶. 19 .

[0068] Example 4 The method for preparing TOPCon batteries is basically the same as in Example 1, except for step 3: Step 3: Perform a one-time annealing treatment on the borosilicate glass layer at a temperature of 960℃ for 1200s. After annealing, a 0.8 μm thick boron emitter electrode layer is obtained, with a boron doping concentration of 2 × 10⁻⁶. 19 .

[0069] Comparative Example 1 The method for preparing TOPCon batteries is basically the same as in Example 1, except for the processes in steps 2 and 3: Step 2: A borosilicate glass layer is sequentially deposited on the front surface of the silicon substrate using PECVD. The deposition conditions for the borosilicate glass layer are as follows: B2H6 flow rate of 2000 sccm, SiH4 flow rate of 5500 sccm, N2O flow rate of 5500 sccm, temperature of 500℃, and time of 210 s. The thickness of the borosilicate glass layer is 35 nm, with boron atoms accounting for 18.5% and oxygen atoms accounting for 10.2%.

[0070] Step 3: The borosilicate glass layer is subjected to a first annealing treatment and a second annealing treatment sequentially. The first annealing temperature is 940℃ for 400s; the second annealing temperature is 980℃ for 1000s. After annealing, a 0.5 μm thick boron emitter electrode layer is obtained, with a boron doping concentration of 6 × 10⁻⁶. 18 .

[0071] The TOPCon batteries obtained in Example 1 and Comparative Example 1 were subjected to performance tests. The specific test method was as follows: using a solar simulator and IV tester, the batteries obtained in the above examples and comparative examples were tested for electrical performance under a standard solar intensity by steady-state power output test. The test results are shown in Table 1.

[0072] Table 1

[0073] As can be seen from the data in Table 1, compared with the solar cell of Comparative Example 1, the passivation and contact performance of the cell can be effectively optimized by setting a double borosilicate glass layer and controlling the percentage of boron and oxygen atoms in the first and second borosilicate glass layers, while ensuring an effective boron source supply. Moreover, a cell structure with a high doping concentration of boron emitter electrode layer but a shallow PN junction can be formed, thereby improving the photoelectric conversion efficiency of the cell.

[0074] The terms "first" and "second" used in this document are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature marked "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 explicitly specified.

[0075] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0076] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a solar cell, characterized in that, include: A silicon substrate is provided, the silicon substrate having a front side and a back side disposed opposite to each other; A first borosilicate glass layer and a second borosilicate glass layer are sequentially deposited on the front side, wherein the percentage of oxygen atoms in the first borosilicate glass layer is greater than the percentage of oxygen atoms in the second borosilicate glass layer, and the percentage of boron atoms in the first borosilicate glass layer is less than the percentage of boron atoms in the second borosilicate glass layer. Annealing is performed on the first borosilicate glass layer and the second borosilicate glass layer to form a boron emission electrode layer on the surface of the silicon substrate.

2. The method according to claim 1, characterized in that, The first borosilicate glass layer contains 1% to 5% boron atoms and 45% to 60% oxygen atoms. And / or, the percentage of boron atoms in the second borosilicate glass layer is 20% to 35%, and the percentage of oxygen atoms in the second borosilicate glass layer is 5% to 20%.

3. The method according to claim 2, characterized in that, The conditions for depositing the first borosilicate glass layer include: a flow rate of B2H6 of 500-1000 sccm, a flow rate of SiH4 of 5000-12000 sccm, a flow rate of N2O of 5000-12000 sccm, a temperature of 400-600℃, and a time of 20-120s. The conditions for depositing the second borosilicate glass layer include: a flow rate of B2H6 of 1000-5000 sccm, a flow rate of SiH4 of 2000-10000 sccm, a flow rate of N2O of 2000-10000 sccm, a temperature of 400-600℃, and a time of 60-250 s.

4. The method according to any one of claims 1 to 3, characterized in that, The thickness of the first borosilicate glass layer is 10~15nm, and the thickness of the second borosilicate glass layer is 20~25nm.

5. The method according to any one of claims 1 to 3, characterized in that, It also includes depositing a third borosilicate glass layer between the first borosilicate glass layer and the second borosilicate glass layer, wherein the percentage of boron atoms in the third borosilicate glass layer is greater than the percentage of boron atoms in the first borosilicate glass layer and less than the percentage of boron atoms in the second borosilicate glass layer, and the percentage of oxygen atoms in the third borosilicate glass layer is less than the percentage of oxygen atoms in the first borosilicate glass layer and greater than the percentage of oxygen atoms in the second borosilicate glass layer.

6. The method according to claim 5, characterized in that, The third borosilicate glass layer contains 5% to 20% boron atoms and 20% to 45% oxygen atoms. Optionally, the conditions for depositing the third borosilicate glass layer include: a flow rate of B2H6 of 800~2000 sccm, a flow rate of SiH4 of 3500~10000 sccm, a flow rate of N2O of 3500~10000 sccm, a temperature of 400~600℃, and a time of 40~200s.

7. The method according to any one of claims 1 to 3, characterized in that, The annealing process includes performing a first annealing and a second annealing sequentially, wherein the temperature of the first annealing is lower than the temperature of the second annealing. Optionally, the temperature of the first annealing is 920~980℃ and the time is 200~800s; the temperature of the second annealing is 960~1050℃ and the time is 500~1500s.

8. The method according to any one of claims 1 to 3, characterized in that, Also includes: A tunneling oxide layer and an n-type doped polysilicon layer are sequentially deposited on the back surface; Remove the first borosilicate glass layer and the second borosilicate glass layer on the front side; A passivation layer and a front antireflection layer are sequentially formed on the side of the boron emission electrode layer away from the silicon substrate; A back antireflection layer is formed on the side of the n-type doped polysilicon layer away from the silicon substrate; A first grid line and a second grid line are formed on the front side and the back side, respectively.

9. A solar cell, characterized in that, It is prepared by the method according to any one of claims 1 to 8.

10. A photovoltaic module, characterized in that, Includes the solar cell as described in claim 9.

Images