Solar cell and preparation method thereof

Abstract

A preparation method of a solar cell comprises the steps that texturing treatment is carried out on a monocrystalline silicon substrate, and the monocrystalline silicon substrate comprises a front face and a back face which are opposite and side surfaces connected to the front face and the back face; boron diffusion; removing the boron-doped diffusion layer and the borosilicate glass layer on the back surface and the side surface; forming a tunneling oxide layer and a monocrystalline silicon film which are stacked in sequence on the back surface; performing phosphorus diffusion to form a phosphorus-doped monocrystalline silicon film; removing the winding plating; sequentially forming a front passivation film and an anti-reflection film on the front surface; forming a back passivation film on the back surface; and forming an electrode. The invention also provides a solar cell. By replacing a polycrystalline silicon film with a monocrystalline silicon film, parasitic absorption of incident light by the polycrystalline silicon film can be effectively reduced; for the mode of realizing the PN junction by using a passivation contact structure, the monocrystalline silicon film has fewer defects than the polycrystalline silicon film, so that the recombination in the film can be reduced, and the passivation performance is improved.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic material manufacturing and processing, and more specifically, to a solar cell and a method for preparing the same. Background Art

[0002] With the rapid advancement of solar cell technology, the solar cell industry has entered the era of N-type cells. N-type cells are available in a variety of technologies, with the Tunnel Oxide Passivated Contact (TOPCon) cell currently the mainstream in the market. TOPCon cells utilize back-side tunneling passivation technology to effectively passivate the back of the N-type silicon substrate, particularly improving the passivation level in the metal contact area. Combined with front-side aluminum oxide passivation, this has significantly improved the photovoltaic conversion efficiency of mass-produced crystalline silicon solar cells. However, further improvements and optimizations to TOPCon cells currently face a significant shortcoming: the polysilicon layer on the back of the cell exhibits strong parasitic absorption. Furthermore, the low crystallization rate of the polysilicon in the development of back-contact cells also leads to high parasitic absorption. This parasitic absorption results in poor long-wavelength response, hindering further improvements in cell conversion efficiency.

[0003] In order to improve the parasitic absorption problem of polysilicon, the current treatment methods include optimizing the existing structure, or looking for alternative materials or performing modification treatments. The optimization of the existing structure generally adopts the method of thinning the polysilicon film. In the specific implementation process, it is necessary to generate a doped polysilicon film of conventional thickness, and then adopt wet etching or laser thinning methods to achieve polysilicon film thinning. However, this method is complex and the yield is difficult to control. Alternative materials currently generally use metal oxide materials such as zinc oxide, tin oxide, tantalum oxide, etc., but the passivation effect of these materials is poor relative to the passivation contact of polysilicon, and the stability is not high. Carbon doping and nitrogen doping are generally used for the modification treatment of polysilicon film. Although the band gap width is increased, the passivation effect is not as good as that of conventional polysilicon film. Summary of the Invention

[0004] In view of this, the present application provides a method for preparing a solar cell, comprising: Performing a texturing process on a single crystal silicon substrate, wherein the single crystal silicon substrate comprises a front surface and a back surface opposite to each other, and a side surface connecting the front surface and the back surface; performing boron diffusion on the single crystal silicon substrate; removing the boron-doped diffusion layer and the borosilicate glass layer on the back surface and the side surface of the single crystal silicon substrate; forming a tunnel oxide layer and a single crystal silicon film stacked in sequence on the back side of the single crystal silicon substrate; performing phosphorus diffusion on the single crystal silicon substrate to form the phosphorus-doped single crystal silicon film; forming a front passivation film and an anti-reflection film in sequence on the side of the single crystal silicon substrate where the front surface is located; forming a back passivation film on the back side of the single crystal silicon substrate; and An electrode is formed on the single crystal silicon substrate.

[0005] The solar cell of the present application uses a single-crystal silicon film instead of a polycrystalline silicon film, which can effectively reduce the parasitic absorption of incident light by the polycrystalline silicon film; for the method of realizing a PN junction with a passivation contact structure, the single-crystal silicon film has fewer defects than the polycrystalline silicon film, which can reduce the recombination in the film and improve the passivation performance.

[0006] Furthermore, the step of forming the tunnel oxide layer and the single crystal silicon film stacked in sequence is implemented using a chemical vapor deposition device and includes: introducing oxygen to oxidize the surface layer of the back side of the single crystal silicon substrate to form a silicon oxide layer; Passing hydrogen gas to convert the surface layer of the silicon oxide layer into a base film of single crystal silicon, and the silicon oxide layer that does not react with the hydrogen gas forms the tunneling oxide layer; and Single crystal silicon is epitaxially grown on the single crystal silicon base film to form the single crystal silicon film.

[0007] Furthermore, in the step of introducing oxygen to oxidize the surface layer on the back side of the single crystal silicon substrate to form a silicon oxide layer, the ambient temperature is controlled to be 500-600° C., the flow rate of the introduced oxygen is 20,000-30,000 sccm, and the silicon oxide layer with a thickness of 5-10 nm is formed.

[0008] Furthermore, in the step of introducing hydrogen, the flow rate of the introduced hydrogen is 3000-30000 sccm, the ambient temperature is controlled to be 900-1000° C., and the thickness of the tunneling oxide layer is controlled to be 1-2 nm.

[0009] Furthermore, in the step of epitaxially growing single crystal silicon on the base film, a silicon source and hydrogen are introduced into the chemical vapor deposition equipment, the ambient temperature is controlled to be 900-1000° C., the flow rate of the silicon source is 3000-10000 sccm, and the flow rate of the hydrogen is 3000-30000 sccm; The silicon source includes at least one of SiH2Cl2, SiHCl3 and SiCl4.

[0010] Furthermore, after phosphorus is diffused into the single crystal silicon substrate and before the front passivation film and the anti-reflection film are sequentially formed on the front surface of the single crystal silicon substrate, the preparation method further includes: removing wrap-around plating.

[0011] Furthermore, in the step of epitaxially growing single crystal silicon on the base film, SiH 4 is introduced into the chemical vapor deposition equipment, the ambient temperature is controlled to be 900-1000° C., and the flow rate of SiH 4 is 3000-10000 sccm.

[0012] Furthermore, forming a tunneling oxide layer and a single crystal silicon film stacked in sequence on the back side of the single crystal silicon substrate includes: forming the tunneling oxide layer on the back surface of the single crystal silicon substrate; forming an amorphous silicon layer or a polysilicon layer on the surface of the tunnel oxide layer; and Metal-induced crystallization is used to low-temperature crystallize the amorphous silicon layer or the polycrystalline silicon layer at an ambient temperature of 300-400°C, and the single crystal silicon film is formed after cooling; or a laser beam is used to scan the surface of the amorphous silicon layer or the polycrystalline silicon layer to crystallize it, and the single crystal silicon film is formed after cooling.

[0013] Furthermore, the thickness of the single crystal silicon film is 50-120 nm.

[0014] The present application also provides a solar cell, which is manufactured using the above-mentioned manufacturing method. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Flowchart of the method for preparing a TOPCon solar cell according to an embodiment of the present application.

[0016] Figure 2 This is a sub-flow chart of the method for preparing a TOPCon solar cell according to an embodiment of the present application.

[0017] Figure 3 Schematic cross-sectional view of a TOPCon solar cell according to an embodiment of the present application.

[0018] Description of main component markings: Solar cell 100, single crystal silicon substrate 10, front surface 11, back surface 12, P-type emitter 20, front passivation film 30, Anti-reflection film 40, tunnel oxide layer 50, doped single crystal silicon film 60, back passivation film 70, front electrode 81, Back electrode 82. DETAILED DESCRIPTION

[0019] This application provides a novel passivated contact solar cell and its preparation method. In this cell structure, a single-crystal silicon film is grown epitaxially to replace the currently commonly used polycrystalline silicon film. The single-crystal silicon film itself has lower parasitic absorption than the polycrystalline silicon film in both short-wave and long-wave bands.

[0020] See also Figure 1, which is a flow chart of a method for preparing a solar cell according to a specific embodiment of the present invention. It should be noted that the method for preparing a solar cell according to the present invention is not limited to the order of the following steps. In other embodiments, the method for preparing a solar cell according to this embodiment may include only a portion of the following steps, or some of the steps may be omitted.

[0021] The following combination Figure 1 The steps of the process are described in detail for the preparation method of the solar cell provided by the specific embodiment of the present invention. The preparation method of the solar cell includes the following steps S1 to S9.

[0022] S1: Performing texturing treatment on the single crystal silicon substrate.

[0023] In the embodiments of the present application, the single crystal silicon substrate is an N-type single crystal silicon substrate internally doped with an N-type dopant element. The N-type dopant element may be at least one of Group V elements, such as phosphorus (P), bismuth (Bi), antimony (Sb), and arsenic (As). The single crystal silicon substrate includes a front surface, a back surface opposite the front surface, and a side surface connecting the front and back surfaces. In other embodiments, the single crystal silicon substrate may also be a P-type single crystal silicon substrate internally doped with a P-type dopant element.

[0024] The texturing treatment can be performed on only the front surface or on both the front and back surfaces of the single crystal silicon substrate. In the embodiment of the present application, the texturing treatment is performed on only the front surface. In step S1, the single crystal silicon substrate is placed in an alkaline solution for surface etching so that a pyramid-shaped textured surface is formed on the front surface. The silicon substrate is cleaned with alkali and hydrogen peroxide, and then rinsed clean with HF and HCl.

[0025] The purpose of texturing a monocrystalline silicon substrate is to remove the mechanical damage layer on the surface of the monocrystalline silicon substrate, remove surface oil, foreign particles, and metallic impurities, and form an undulating velvet surface structure. This increases the surface area of the monocrystalline silicon substrate and creates a light-trapping structure that increases sunlight absorption and reduces reflection. In some embodiments, the reflectivity of the front surface of the monocrystalline silicon substrate after texturing is less than 11%.

[0026] S2: Boron diffusion is performed on the single crystal silicon substrate.

[0027] The purpose of this step is to form a P-type emitter on the front side, thereby forming a PN junction in the single-crystal silicon substrate. The PN junction forms a space charge region and builds a built-in potential field.

[0028] In step S2, a boron source is used to diffuse boron into the single crystal silicon substrate, the temperature is controlled at 700-900°C, and then oxygen is introduced for oxidation advancement, and the oxidation advancement temperature is controlled at 950-1000°C.

[0029] The boron source can be selected from one or more precursors such as BCl3 and BBr3. During the boron diffusion process, a boron-doped diffusion layer is formed to a certain depth on the surface of the silicon substrate (including the front, back, and side surfaces). The boron-doped diffusion layer on the front side serves as the P-type emitter. Furthermore, a boron-silicate glass (BSG) layer is formed on the outermost surface of the silicon substrate, formed from the boron-doped silicon oxide layer.

[0030] S3: removing the boron-doped diffusion layer and the borosilicate glass (BSG) layer on the back and side surfaces of the single crystal silicon substrate.

[0031] The boron diffusion process in step S2 forms a boron-doped diffusion layer and a BSG layer on various surfaces of the silicon substrate. The boron-doped diffusion layer formed on the back and side surfaces of the silicon substrate is prone to short circuits and therefore needs to be removed. The purpose of step S3 is to remove the byproduct boron-doped diffusion layer and BSG layer formed on the back and side surfaces of the silicon substrate in step S2.

[0032] In some embodiments, step S3 includes: first, the silicon substrate is etched with the front side facing up through a chain-type BSG removal machine with a hydrofluoric acid solution to remove the BSG on the back and side surfaces, and then the silicon substrate is etched through a tank-type machine with an alkaline solution to remove the boron-doped diffusion layer on the back and side surfaces, forming a polished surface on the back. The silicon substrate is then post-cleaned with alkali and hydrogen peroxide, and then rinsed with HF and HCl. The polished surface formed in step S3 is conducive to better subsequent surface passivation, and the polished back surface can also increase more back light reflection absorption.

[0033] S4: forming a tunnel oxide layer and a single crystal silicon film stacked in sequence on the back side of the single crystal silicon substrate.

[0034] See also Figure 2 In the embodiment of the present application, step S4 is performed using chemical vapor deposition (CVD), i.e., step S4 is performed in a chemical vapor deposition device. A tunneling oxide layer and a single crystal silicon film are sequentially stacked on the back side of the single crystal silicon substrate. Step S4 further includes: S41: introducing oxygen to oxidize the surface layer on the back side of the single crystal silicon substrate to form a silicon oxide layer; S42: introducing hydrogen gas and controlling the reaction conditions so that the surface layer of the silicon oxide layer is converted into a base film of single crystal silicon, and the silicon oxide layer that does not react with the hydrogen gas forms a tunneling oxide layer; S43: epitaxially growing single crystal silicon on the single crystal silicon base film to form a single crystal silicon film.

[0035] In step S41, a silicon oxide layer is formed by oxidizing the surface of the silicon substrate by passing oxygen at high temperature. The ambient temperature is controlled at 500-600° C. and the flow rate of the oxygen is 20,000-30,000 sccm, ultimately forming a silicon oxide layer with a thickness of 5-10 nm.

[0036] In step S42, hydrogen (H2) is introduced, causing the surface portion of the silicon oxide layer to react with the hydrogen to reduce the silicon to single-crystalline silicon, forming a single-crystalline silicon base film of a certain thickness. The remaining silicon oxide layer that does not react with the hydrogen serves as a tunneling oxide layer. This single-crystalline silicon base film serves as the base film for CVD epitaxial growth of single-crystalline silicon. In step S42, the H2 flow rate is 3,000-30,000 seem, and the ambient temperature is controlled at 900-1,000°C.

[0037] Compared to polycrystalline silicon films, single-crystal silicon films require higher temperatures and a cleaner growth environment to facilitate their growth. During epitaxial growth of single-crystal silicon, a clean growth environment is essential. Atoms generated during gas reactions collide with the silicon wafer surface and migrate to appropriate positions, forming an orderly single crystal arrangement.

[0038] In some embodiments, in step S43, the CVD epitaxial growth of the single-crystalline silicon film can be performed in a chemical vapor deposition apparatus using a silicon source and hydrogen, wherein the silicon source includes at least one of SiH2Cl2, SiHCl3, and SiCl4. The single-crystalline silicon film is grown using the CVD epitaxial method, with the ambient temperature controlled at 900-1000°C. The silicon source and hydrogen are introduced simultaneously, with the silicon source having a flow rate of 3000-10000 sccm and the H2 having a flow rate of 3000-30000 sccm. In this manner, the single-crystalline silicon base film and the single-crystalline silicon subsequently epitaxially grown thereon together form the desired single-crystalline silicon film.

[0039] In some other embodiments, in step S43, SiH4 can be used for CVD epitaxial growth of single crystal silicon film without the need to introduce hydrogen simultaneously. The ambient temperature is controlled to be 900° C.-1000° C., and the flow rate of SiH4 is 3000-10000 sccm.

[0040] In some embodiments, the thickness of the tunnel oxide layer is 1-2 nm, and the thickness of the single crystal silicon film is 50-120 nm.

[0041] The method for forming a single-crystal silicon film in an embodiment of the present application involves partially reducing a silicon oxide layer that forms a tunneling oxide layer to form a single-crystal silicon base film. Single-crystal silicon is then grown on the single-crystal silicon base film using a CVD epitaxial method, thereby forming a single-crystal silicon film of a desired thickness. This method can effectively form a single-crystal silicon film of a desired thickness.

[0042] Single-crystal silicon film has a lower absorption coefficient than polycrystalline silicon film, which can reduce parasitic absorption, thereby improving long-wave response and quantum efficiency. In addition, the mobility of single-crystal silicon film is higher than that of polycrystalline silicon film, which improves conductivity, thereby bringing about an increase in the fill factor of the battery end.

[0043] It is understandable that the method of forming the tunnel oxide layer and the single crystal silicon film stacked in sequence on the back side of the single crystal silicon substrate is not limited to the above method, and other methods can also be used. For example, in other embodiments, step S4 further includes: S41: forming a tunneling oxide layer made of silicon oxide on the back side of the single crystal silicon substrate; S42: forming an amorphous silicon layer or a polysilicon layer on a surface of the tunnel oxide layer; S43: Using metal-induced crystallization, heating to an appropriate temperature causes the amorphous silicon layer or polycrystalline silicon layer to crystallize at low temperature, and cooling to form a single crystal silicon film. In some embodiments, an Al layer or a Ni layer is formed on the amorphous silicon layer or polycrystalline silicon layer by physical vapor deposition or spin coating, with the Al layer or Ni layer having a thickness of 1-29 nm. The amorphous silicon layer or polycrystalline silicon layer is then heated to a temperature of 300-400° C. to crystallize at low temperature.

[0044] Alternatively, step S43 uses a laser beam to scan the surface of the amorphous silicon layer or polycrystalline silicon layer, rapidly heating the amorphous silicon layer or polycrystalline silicon layer to crystallize it, and then cooling it to form a single crystal silicon film. In some embodiments, the laser power is 200-400W and the scanning speed is 700-1300mm / s.

[0045] In step S42, the polysilicon layer can be formed using LPCVD (low-pressure chemical vapor deposition) technology. Under low pressure, typical process conditions are 600°C and 0.1-1kPa, using the thermal decomposition reaction of silane gas to form a silicon thin film. This method can produce a highly uniform polysilicon layer.

[0046] In step S42, the amorphous silicon layer can be formed by PECVD (plasma enhanced chemical vapor deposition), which uses radio frequency glow discharge to excite the reaction gas (silicon source gas, such as monosilane or disilane) to deposit silicon atoms in an amorphous form on the surface of the tunnel oxide layer, and CVD growth can be achieved at a lower temperature.

[0047] S5: performing phosphorus diffusion on the single crystal silicon substrate to form a phosphorus-doped single crystal silicon film.

[0048] In step S5, a phosphorus diffusion process is performed on the back side of the single-crystal silicon substrate. The reaction sources are a phosphorus source (e.g., POCl3) and oxygen, and the diffusion temperature is 850-950°C. This results in a phosphorus-doped single-crystal silicon film on the back side. This step S5 forms an N+ doped passivation contact structure on the back side.

[0049] During the phosphorus diffusion process in step S5, the BSG layer on the front surface of the silicon substrate is transformed into a borophospho-silicate glass (BPSG) layer due to the diffusion of phosphorus by the gas phase, and a phospho-silicate glass (PSG) layer is formed on the outermost side of the back surface of the silicon substrate due to the high concentration of phosphorus. That is, a PSG layer is formed on the surface of the phosphorus-doped single crystal silicon film.

[0050] S6: Remove wrap-around plating.

[0051] Step S6 includes removing the BPSG layer formed on the front surface, the PSG layer on the front and side surfaces, the silicon oxide layer and the phosphorus-doped single crystal silicon film, and the PSG layer formed on the back surface of the silicon substrate in step S5.

[0052] In some embodiments, step S6 includes: etching the silicon substrate through a chain machine with a hydrofluoric acid solution at a temperature of 40-60°C to remove the PSG layer on the surface of the single-crystal silicon film deposited on the front side; etching the silicon substrate through a slot machine with an alkaline solution; removing the single-crystal silicon film deposited on the front side with an alkaline solution at a temperature of 60-80°C; and then removing the residual BPSG layer on the front side and the PSG layer on the back side with a hydrofluoric acid solution.

[0053] S7: depositing a front passivation film and an anti-reflection film in sequence on the side of the single crystal silicon substrate where the front surface is located.

[0054] In step S7, in some embodiments, a front-side passivation film is first deposited on the front side of the single-crystal silicon substrate using atomic layer deposition (ALD). This front-side passivation film is formed on the front-side boron-doped diffusion layer (P-type emitter). The front-side passivation film is made of aluminum oxide and has a thickness of 5-7 nm. A large amount of fixed negative charge is generated at the interface between the aluminum oxide and the P-type emitter, providing a strong field passivation effect.

[0055] In step S7, in some embodiments, the anti-reflection film is deposited by plasma enhanced chemical vapor deposition (PECVD) technology. The anti-reflection film is formed on the front passivation film. The material of the anti-reflection film may include SiN x 、SiON x and SiO xThe anti-reflection film provides anti-reflection and passivation effects, and also protects against photovoltaic induced degradation (PID) and UV radiation.

[0056] S8: depositing a back passivation film on the back side of the single crystal silicon substrate.

[0057] In step S8, in some embodiments, SiN is deposited on the back side of the single crystal silicon substrate using PECVD technology. x The back passivation film is made of a material with a thickness of 70-100 nm and a comprehensive refractive index of 1.9-2.1. The back passivation film is formed on the phosphorus-doped single-crystalline silicon film. This step S8 not only provides hydrogen passivation on the back surface, but also helps to increase the reflection of the back-transmitted light, which is beneficial for the reabsorption of the transmitted light.

[0058] In some embodiments, when the front anti-reflection film in step S7 and the back passivation film in step S8 are both SiN x The anti-reflection film on the front surface in step S7 and the passivation film on the back surface in step S8 can be completed in the same process.

[0059] S9: forming electrodes on the single crystal silicon substrate.

[0060] Step S9 includes forming electrodes on both the front side and the back side of the single crystal silicon. In some embodiments, step S9 includes printing a conductive metal paste on both the front anti-reflection film and the back passivation film, and solidifying the conductive metal paste by sintering to form metal electrodes, so that the metal atoms in the conductive metal paste are in contact with the silicon substrate.

[0061] It is understood that the conductive metal paste can be solidified by sintering to form a metal electrode bonded to the silicon substrate. The conductive metal paste is printed on the anti-reflection layer. During the sintering process, the metal atoms in the conductive metal paste pass through the passivation layer and the anti-reflection layer and contact the silicon substrate. The conductive metal paste can be silver paste, etc., but is not limited to this. In some embodiments, the conductive metal paste contains a mixture of multiple conductive metals. The conductive metal paste can be printed by screen printing or laser pattern transfer, etc., but is not limited to this.

[0062] Sintering can be performed in a sintering furnace. Generally, the front electrode requires a higher sintering temperature than the back electrode. In this step, the sintering furnace temperature is set to the required sintering temperature for the back electrode, so that the back electrode is completely sintered while the front electrode is not. Therefore, auxiliary sintering is required using the LECO technology in the subsequent step.

[0063] In some embodiments, screen printing technology is used to form an N+ electrode on the back side of a single-crystal silicon substrate using a conductive metal paste, and a P+ electrode is formed on the front side. Laser-enhanced contact optimization (LECO) is then used to sinter the front-side electrode of the silicon substrate. Using LECO, the silicon substrate is processed by scanning the electrode region on the surface of the silicon substrate with a laser while maintaining a reverse bias voltage on the single-crystal silicon substrate.

[0064] In some embodiments, the laser power is 30-50 W and the reverse bias voltage is 10-20 V. Step S9 enables the electrodes to form good ohmic contacts on the front and back surfaces. The addition of LECO technology not only further reduces the back surface contact resistance but also improves the passivation effect of the metal area.

[0065] LECO technology uses high-intensity laser irradiation on the cell to excite charge carriers, and at the same time applies a reverse bias voltage of more than 10V to the cell to generate a local current of several amperes, which then causes sintering at the laser-irradiated area on the cell to trigger mutual diffusion of metal conductive paste and silicon.

[0066] LECO technology assists in the sintering of conductive metal pastes, solidifying them to form metal electrodes. Through laser-assisted sintering of conductive metal pastes, LECO technology can directly form low-resistance ohmic contacts between metal and silicon without damaging the silicon substrate passivation layer, thereby reducing the contact resistance between the metal gate line and silicon without the need for additional doping steps.

[0067] The present application also provides a solar cell prepared by the above preparation method, which is a TOPCon cell. Figure 3 As shown, the solar cell 100 includes a single crystal silicon substrate 10 , which includes a front surface 11 and a back surface 12 opposite to each other, and the front surface 11 is a pyramid-shaped velvet surface.

[0068] like Figure 3 As shown, the solar cell 100 further includes a P-type emitter 20, a front passivation film 30, and an anti-reflection film 40 sequentially stacked on the front surface 11. The solar cell 100 further includes a tunneling oxide layer 50, a doped single crystal silicon film 60, and a back passivation film 70 sequentially stacked on the back surface 12.

[0069] like Figure 3 As shown, the solar cell 100 also includes a front electrode 81 and a back electrode 82. The front electrode 81 is located on the anti-reflection film 40 on the front surface 11 and passes through the front passivation film 30 and the anti-reflection film 40 to form an ohmic contact with the P-type emitter 20. The back electrode 82 is located on the back passivation film 70 on the back surface 12 and passes through the back passivation film 70 to form an ohmic contact with the doped single crystal silicon film 60.

[0070] The TOPCon cell of the present application uses a single-crystal silicon film instead of a polycrystalline silicon film, which can effectively reduce the parasitic absorption of incident light by the polycrystalline silicon film; for the method of realizing a PN junction with a passivation contact structure, the single-crystal silicon film has fewer defects than the polycrystalline silicon film, which can reduce the recombination in the film and improve the passivation performance.

[0071] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present application should not depart from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for preparing a solar cell, characterized in that: include: Performing a texturing process on a single crystal silicon substrate, wherein the single crystal silicon substrate comprises a front surface and a back surface opposite to each other, and a side surface connecting the front surface and the back surface; performing boron diffusion on the single crystal silicon substrate; removing the boron-doped diffusion layer and the borosilicate glass layer on the back surface and the side surface of the single crystal silicon substrate; forming a tunnel oxide layer and a single crystal silicon film stacked in sequence on the back side of the single crystal silicon substrate; performing phosphorus diffusion on the single crystal silicon substrate to form the phosphorus-doped single crystal silicon film; forming a front passivation film and an anti-reflection film in sequence on the side of the single crystal silicon substrate where the front surface is located; forming a back passivation film on the side of the single crystal silicon substrate where the back surface is located; as well as An electrode is formed on the single crystal silicon substrate.

2. The method for preparing a solar cell according to claim 1, wherein: The step of forming the sequentially stacked tunnel oxide layer and the single crystal silicon film is performed using a chemical vapor deposition device and includes: introducing oxygen to oxidize the surface layer of the back side of the single crystal silicon substrate to form a silicon oxide layer; Passing hydrogen gas to convert the surface layer of the silicon oxide layer into a base film of single crystal silicon, and the silicon oxide layer that does not react with the hydrogen gas forms the tunneling oxide layer; and Single crystal silicon is epitaxially grown on the single crystal silicon base film to form the single crystal silicon film.

3. The method for preparing a solar cell according to claim 2, wherein: In the step of introducing oxygen to oxidize the surface layer on the back side of the single crystal silicon substrate to form a silicon oxide layer, the ambient temperature is controlled to be 500-600° C., the flow rate of the introduced oxygen is 20,000-30,000 sccm, and the silicon oxide layer with a thickness of 5-10 nm is formed.

4. The method for preparing a solar cell according to claim 2, wherein: In the step of introducing hydrogen, the flow rate of the introduced hydrogen is 3000-30000 sccm, the ambient temperature is controlled to be 900-1000° C., and the thickness of the tunneling oxide layer is controlled to be 1-2 nm.

5. The method for preparing a solar cell according to claim 2, wherein: In the step of epitaxially growing single crystal silicon on the base film, a silicon source and hydrogen are introduced into the chemical vapor deposition equipment, the ambient temperature is controlled to be 900-1000° C., the flow rate of the silicon source is 3000-10000 sccm, and the flow rate of the hydrogen is 3000-30000 sccm; The silicon source includes at least one of SiH2Cl2, SiHCl3 and SiCl4.

6. The method for preparing a solar cell according to claim 5, wherein: After phosphorus is diffused into the single crystal silicon substrate and before the front passivation film and the anti-reflection film are sequentially formed on the front surface of the single crystal silicon substrate, the preparation method further comprises: removing wrap-around plating.

7. The method for preparing a solar cell according to claim 2, wherein: In the step of epitaxially growing single crystal silicon on the base film, SiH4 is introduced into the chemical vapor deposition equipment, the ambient temperature is controlled to be 900-1000°C, and the flow rate of SiH4 is 3000-10000sccm.

8. The method for preparing a solar cell according to claim 1, wherein: The step of forming a tunnel oxide layer and a single crystal silicon film stacked in sequence on the back side of the single crystal silicon substrate comprises: forming the tunneling oxide layer on the back surface of the single crystal silicon substrate; forming an amorphous silicon layer or a polysilicon layer on the surface of the tunnel oxide layer; and Metal-induced crystallization is used to low-temperature crystallize the amorphous silicon layer or the polycrystalline silicon layer at an ambient temperature of 300-400°C, and the single crystal silicon film is formed after cooling; or a laser beam is used to scan the surface of the amorphous silicon layer or the polycrystalline silicon layer to crystallize it, and the single crystal silicon film is formed after cooling.

9. The method for preparing a solar cell according to claim 1, wherein: The thickness of the single crystal silicon film is 50-120 nm.

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

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