Front-side structure of solar cell, solar cell and preparation method therefor, and photovoltaic module

Abstract

Provided in the present disclosure are a front-side structure of a solar cell, a solar cell and a preparation method therefor, and a photovoltaic module. The front-side structure of a solar cell comprises: a boron emitter layer; a passivation film layer; and front-side current collection grid lines, wherein the front-side current collection grid lines and the boron emitter layer form direct physical contact in some areas, and form indirect physical contact in some areas by means of the passivation film layer; and the total doping concentration of the boron emitter layer ranges from 2.8×1018atoms / cm3 to 4.0×1018atoms / cm3. Therefore, the performance of the solar cell can be improved.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present disclosure claims priority to Chinese patent application No. 202411189196.3, filed with the China National Intellectual Property Administration on August 28, 2024, and entitled “FRONT-SIDE STRUCTURE OF SOLAR CELL, SOLAR CELL AND PREPARATION METHOD THEREFOR, AND PHOTOVOLTAIC MODULE”, the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present disclosure relates to the field of solar cells, and in particular to a front-side structure of a solar cell, a solar cell and a preparation method thereof, and a photovoltaic module. BACKGROUND

[0003] In the front-side structure of existing solar cells, a relatively large number of defects may be introduced into the boron emitter layer due to the high-temperature boron source diffusion process. In particular, with respect to the portion of the boron emitter layer corresponding to the metallized region and the portion of the boron emitter layer corresponding to the light-absorbing region, there is a need to balance the influence of the metal-semiconductor contact resistivity in the metallized region and the spectral response and defect-induced carrier recombination loss in the light-absorbing region on the photoelectric conversion efficiency of the solar cell. This has become a technical issue in the industry that urgently needs to be addressed for the development of high-efficiency solar cell technology. SUMMARY

[0004] To address the above technical issue, the present disclosure provides a solar cell, a preparation method thereof, and a photovoltaic module, so as to reduce, in the front-side structure, recombination losses in a contact region between the boron emitter layer and the front-side current-collecting grid lines, thereby improving the performance of the solar cell.

[0005] In a first aspect, the present disclosure provides a front-side structure of a solar cell, including:

[0006] a boron emitter layer,

[0007] a passivation film layer, and

[0008] front-side current-collecting grid lines, the front-side current-collecting grid lines being in direct physical contact with the boron emitter layer at a part of a region therebetween, and the front-side current-collecting grid lines being in indirect physical contact with the boron emitter layer via the passivation film layer at another part of the region therebetween;

[0009] a total doping concentration of the boron emitter layer is in a range from 2.8^1018 atoms / cm3 to 4.0*1018 atoms / cm3.

[0010] In some embodiments of the present disclosure, the total doping concentration of the boron emitter layer is in a range from 2.8*1018 atoms / cm3 to 3.2*1018 atoms / cm3.

[0011] In some embodiments of the present disclosure, a junction depth of the boron emitter layer is in a range from 0.5 gm to 2.0 gm; and / or

[0012] a sheet resistance of the boron emitter layer is in a range from 300 Q / sq to 1500 Q / sq.

[0013] In some embodiments of the present disclosure, the sheet resistance of the boron emitter layer is in a range from 500 Q / sq to 1000 Q / sq.

[0014] In some embodiments of the present disclosure, the junction depth of the boron emitter layer is in a range from 0.5 gm to 0.8 gm.

[0015] In some embodiments of the present disclosure, the junction depth of the boron emitter layer is in a range from 0.8 gm to 1.5 gm.

[0016] In some embodiments of the present disclosure, a region corresponding to the direct physical contact includes a silver-silicon eutectic substrate and a silver-silicon eutectic overflow body, and the region corresponding to the direct physical contact further includes a silver crystalline body electrically connected to the silver-silicon eutectic substrate and the silver-silicon eutectic overflow body.

[0017] In some embodiments of the present disclosure, the silver crystalline body includes a crystalline main chain and a crystalline side chain extending from the crystalline main chain in a growth direction different from that of the crystalline main chain.

[0018] In some embodiments of the present disclosure, a region corresponding to the indirect physical contact has an electrically conducting aggregate, and the passivation film layer is located between the electrically conducting aggregate and the boron emitter layer; wherein the electrically conducting aggregate includes a glass phase material and conductive metal particles, and the conductive metal particles and the silver crystalline body have a same type of metal element.

[0019] In a second aspect, the present disclosure provides a solar cell including the front-side structure of the solar cell as described in the second aspect.

[0020] In a third aspect, the present disclosure provides a method for preparing the solar cell as described in the second aspect, including the following steps:

[0021] providing a textured silicon wafer as a silicon substrate, placing the silicon substrate in a boron diffusion furnace, and forming a boron emitter layer on a front side of the silicon substrate by a boron diffusion process;

[0022] sequentially forming a tunneling passivation layer and a phosphorus-doped polysilicon layer on a rear side of the silicon substrate;

[0023] sequentially forming a passivation film layer on the boron emitter layer, and forming a rear-side passivation layer on the phosphorus-doped polysilicon layer;

[0024] printing an electrode paste on the passivation film layer and the rear-side passivation layer;

[0025] performing high-temperature pre-sintering to form a front-side current-collecting grid line precursor from the electrode paste printed on the passivation film layer, and to form a rear electrode from the electrode paste printed on the rear-side passivation layer; and

[0026] subjecting the front-side current-collecting grid line precursor to a laser-induced contact treatment to form front-side current-collecting grid lines.

[0027] In some embodiments of the present disclosure, forming the boron emitter layer on the front side of the silicon substrate by the boron diffusion process includes:

[0028] a pre-oxidation process, in which a temperature of the boron diffusion furnace is T1, a furnace tube pressure is P1, and oxygen gas and nitrogen gas are introduced into the boron diffusion furnace, wherein 750 °C < Ti < 850 °C, 230 mPa < Pi < 270 mPa, an oxygen gas flow rate is in a range from 800 sccm to 2000 sccm, and a nitrogen gas flow rate is in a range from 200 sccm to i000 sccm;

[0029] a multi-stage deposition process, in which a temperature of the boron diffusion furnace is T2, a furnace tube pressure is P2, and oxygen gas, nitrogen gas and a boron source gas are introduced in the boron diffusion furnace in multiple stages, with a furnace temperature in each stage being increased stage by stage, wherein 750 °C < T2 < 850 °C, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, 230 mPa < P2 < 270 mPa, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to i50 sccm;

[0030] a multi-stage PN junction drive-in process, in which a temperature of the boron diffusion furnace is T3, a furnace tube pressure is P3, and nitrogen gas is introduced into the boron diffusion furnace, wherein 850 °C < T3 < 950 °C, 580 mPa < P3 < 620 mPa, and a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm; and

[0031] a post-oxidation process, in which a temperature of the boron diffusion furnace is T4, a furnace tube pressure is P4, and oxygen gas is introduced into the boron diffusion furnace to form a silicon oxide mask layer having a thickness of 50 nm to i20 nm, wherein 950 °C < T4 < i050 °C, 780 mPa < P4 < 820 mPa, and an oxygen gas flow rate is in a range from 10000 sccm to 30000 sccm.

[0032] In some embodiments of the present disclosure, P4 > P3; and / or P4 > P2; and / or P4 > P1; and / or P3 > P2; and / or P3 > P1.

[0033] In some embodiments of the present disclosure, T2 > T1; and / or T3 > T2; and / or T4 > T3.

[0034] In some embodiments of the present disclosure, in the multi-stage deposition process, the number of deposition stages is in a range from 2 to 5.

[0035] In some embodiments of the present disclosure, the multi-stage deposition process includes:

[0036] a first deposition stage, in which a temperature of the boron diffusion furnace is T21, a furnace tube pressure is P21, and oxygen gas, nitrogen gas and a boron source gas are introduced into the boron diffusion furnace, wherein 750 °C < T21 < 850 °C, 230 mPa < P21 < 270 mPa, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to 150 sccm;

[0037] a second deposition stage, in which a temperature of the boron diffusion furnace is T22, a furnace tube pressure is P22, and oxygen gas, nitrogen gas and a boron source gas are introduced into the boron diffusion furnace, wherein 750 °C < T22 < 850 °C, T22 > T21, 230 mPa < P22 < 270 mPa, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to 150 sccm; and

[0038] a third deposition stage, in which a temperature of the boron diffusion furnace is T23, a furnace tube pressure is P23, and oxygen gas, nitrogen gas and a boron source gas are introduced into the boron diffusion furnace, wherein 750 °C < T23 < 850 °C, T23 > T22, 230 mPa < P23 < 270 mPa, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to 150 sccm.

[0039] In some embodiments of the present disclosure, subjecting the front-side current-collecting grid line precursor to the laser-induced contact treatment includes:

[0040] subjecting the front-side current-collecting grid line precursor to the laser-induced contact treatment on the front side of the silicon substrate.

[0041] In a fourth aspect, the present disclosure provides a photovoltaic module. The photovoltaic module includes the solar cell as described in the second aspect, or the photovoltaic module includes a solar cell prepared by the method as described in the third aspect.

[0042] Compared with the prior art, the present disclosure has at least the following beneficial effects:

[0043] The present disclosure provides a front-side structure of a solar cell, a solar cell and a preparation method thereof, and a photovoltaic module. By controlling the total doping concentration of the boron emitter layer to be in a range from 2.8*1018 atoms / cm3 to 4.0*1018 atoms / cm3, recombination losses in the boron emitter layer of the front-side structure can be reduced, and the total doping concentration of the boron emitter layer will not be excessively low, thus not reducing a thin-layer carrier transport capability of the boron emitter layer, thereby improving the photoelectric conversion performance of the solar cell. In addition, by adopting the laser-induced sintering technology to form a metal-semiconductor contact structure having a relatively low resistivity in the metallized region, a resistance loss at the metal-semiconductor contact structure is reduced, and a corrosion area of the surface passivation film layer corroded by a glass phase in the silver paste in the metallized region is reduced to a certain extent, thereby increasing the open-circuit voltage of the solar cell and further enhancing the photoelectric conversion efficiency of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] To illustrate the technical solutions in the embodiments of the present disclosure more clearly, the drawings used in the embodiments will be described briefly. Apparently, the following described drawings are merely for the embodiments of the present disclosure, and other drawings can be derived by those of ordinary skill in the art without any creative effort.

[0045] FIG. 1 is a schematic structural view of a front-side structure of a solar cell according to an embodiment of the present disclosure.

[0046] FIG. 2 is a schematic view of a contact region between a front-side current-collecting grid line and a boron emitter layer according to an embodiment of the present disclosure.

[0047] FIG. 3 is a schematic diagram showing an electrochemical capacitance-voltage (ECV) curve according to an embodiment of the present disclosure.

[0048] FIG. 4 is a schematic morphology diagram of a silver crystalline body according to an embodiment of the present disclosure.

[0049] FIG. 5 is a schematic structural diagram of a solar cell according to an embodiment of the present disclosure.

[0050] Reference signs: silicon substrate-1, boron emitter layer-2, passivation film layer-3, front-side current-collecting grid line-4, tunneling passivation layer-5, phosphorus-doped polysilicon layer-6, rear-side passivation layer-7, rear electrode-8, first metal-semiconductor contact region-41, second metal-semiconductor contact region-42, silver-silicon eutectic substrate-411, silver-silicon eutectic overflow body-412, silver crystalline body-413, electrically conducting aggregate-421, crystalline main chain-4131, crystalline side chain-4132. DETAILED DESCRIPTION

[0051] The technical solutions according to the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings used in the embodiments of the present disclosure. Obviously, the described embodiments are merely some of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the scope of protection of the present disclosure.

[0052] In the present disclosure, the terms “upper”, “lower”, “left”, “right”, “front”, “rear”, “top”, “bottom”, “inner”, “outer”, “vertical”, “horizontal”, “transverse”, “longitudinal”, and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. These terms are mainly used to better describe the present disclosure and the embodiments thereof, and are not intended to limit the indicated apparatuses, elements, or components to having a particular orientation or being constructed or operated in a particular orientation.

[0053] Moreover, some of the foregoing terms, in addition to indicating orientations or positional relationships, may also indicate other meanings. For example, in some cases, the term “upper” may also indicate a certain attachment relationship or connection relationship. The specific meanings of these terms in the present disclosure can be understood by those skilled in the art according to the particular circumstances.

[0054] In addition, the terms “mounted”, “disposed”, “provided with”, “connected”, and “coupled” should be construed in a broad sense. For example, they may refer to a fixed connection, a detachable connection, or an integral structure, may refer to a mechanical connection or an electrical connection, may refer to a direct connection, an indirect connection through an intermediate medium, or an internal communication between two apparatuses, elements, or components. The specific meanings of the foregoing terms in the present disclosure can be understood by those skilled in the art according to the particular circumstances.

[0055] In addition, the terms “first”, “second”, and the like are mainly used to distinguish different apparatuses, elements, or components that may have the same or different specific types and configurations, and are not intended to indicate or imply the relative importance or quantity of the indicated apparatuses, elements, or components. Unless otherwise specified, the term “a plurality of” means two or more.

[0056] The technical solutions of the present disclosure will be further described below with reference to the embodiments and the accompanying drawings.

[0057] In a first aspect, the present disclosure provides a front-side structure of a solar cell. As shown in FIG. 1, the front-side structure of the solar cell includes a boron emitter layer 2, a passivation film layer 3, and front-side current-collecting grid lines 4, wherein the boron emitter layer 2 is located on a front side of a silicon substrate 1, and the passivation film layer 3 is located on a front side of the boron emitter layer 2. A metal-semiconductor contact region is disposed between the front-side current-collecting grid line 4 and the boron emitter layer 2. As shown in FIG. 2, the front-side current-collecting grid line 4 is in direct physical contact with the boron emitter layer 2 at a part of the region therebetween, and this region corresponding the direct physical contact includes a first metal-semiconductor contact region 41 as shown in FIG. 2. The front-side current-collecting grid line 4 is in indirect physical contact with the boron emitter layer 2 via the passivation film layer 3 at another part of the region therebetween, and this region corresponding to the indirect physical contact includes a second metal-semiconductor contact region 42 as shown in FIG. 2. The first metal-semiconductor contact region 41 and the second metal-semiconductor contact region 42 constitute the metal-semiconductor contact region.

[0058] A total doping concentration of the boron emitter layer 2 is in a range from 2.8x1018 atoms / cm3 to 4.0x1018 atoms / cm3. For example, the total doping concentration of the boron emitter layer is 2.8x1018 atoms / cm3, 3.0x1018 atoms / cm3, 3.2x1018 atoms / cm3, 3.5x1018 atoms / cm3, 4.0x1018 atoms / cm3, or any value between any two of the above numerical values.

[0059] In the present disclosure, the total doping concentration Ctotal of the boron emitter layer refers to an integrated area under an ECV curve of the boron emitter layer. For example, referring to FIG. 3, from the first target test point to the x-th target test point, the integrated area is an area enclosed by the ECV curve, an abscissa value (L1) of the first target test point, an abscissa value (Lx) of the x-th target test point, and the horizontal axis. The target test point refers to a specific boron atom doping concentration corresponding to a specific junction depth when a single-point value of the ECV curve is obtained. Since a resistivity of an N-type silicon substrate currently used is in a range from 0.6 Q^cm to 16 tfcm, in order to appropriately define an upper limit of selecting test points of the ECV curve, an upper-limit doping concentration of selecting the test points of the ECV curve is defined as greater than 1.0x1017 atoms / cm3, that is, test points with a doping concentration less than 1.0x1017 atoms / cm3 do not fall within a selection range of the test points of the ECV curve.

[0060] The total doping concentration Ctotal of the boron emitter layer can be calculated according to the following formula:

[0061] Ctotal=D1XL1+D2X(L2-L1)+D3X(L3-L2)+......+DX X (Lx-Lx-1)     (1)

[0062] In formula (1), D1 represents a doping concentration corresponding to the first target test point, L1 represents a junction depth corresponding to the first target test point, Dx represents a doping concentration corresponding to the x-th target test point, and Lx represents a junction depth corresponding to the x-th target test point.

[0063] It should be noted that the total doping concentration Ctotal of the boron emitter layer in the present disclosure is used to characterize an overall doping level of the boron emitter layer. When sunlight irradiates the front side of a solar cell, short-wavelength photons having relatively high energy are preferentially absorbed at the front side of the solar cell, and the boron emitter layer corresponds to a short-wavelength spectral band in the solar spectrum. In order to sufficiently absorb photons in the short-wavelength spectral band, adopting a boron emitter layer having a relatively low doping concentration is beneficial to improving a short-wavelength spectral response of the boron emitter layer, and a lower doping concentration is more beneficial to improving the short-wavelength spectral response of the boron emitter layer. However, the doping concentration of the boron emitter layer also needs to have a carrier transport capability for transporting photogenerated carriers from a generation site to the front-side current-collecting grid lines, that is, a sheet resistance of the boron emitter layer in a light-receiving region affects a current loss of the photogenerated carriers before being transported to the front-side current-collecting grid lines. In order to achieve an optimal balance between the short-wavelength spectral response of the boron emitter layer and a transmission loss caused by the sheet resistance, the total doping concentration Ctotal of the boron emitter layer needs to be controlled within an appropriate range.

[0064] In the front-side structure of a solar cell provided by the present disclosure, by controlling the total doping concentration of the boron emitter layer to be in a range from 2.8x1018 atoms / cm3 to 4.0x1018 atoms / cm3, the total doping concentration of the boron emitter layer is maintained in a suitable range, which is beneficial to reducing recombination losses in a contact region between the boron emitter layer and the front-side current-collecting grid lines in the front-side structure, and the total doping concentration of the boron emitter layer will not be excessively low, thus not reducing a thin-layer carrier transport capability of the boron emitter layer, thereby improving the performance of the solar cell. In addition, by adopting the laser-induced sintering technology to form a metal-semiconductor contact structure having a relatively low resistivity in a metallized region, a resistance loss at the metal-semiconductor contact structure is reduced, and a corrosion area of the surface passivation film layer corroded by the glass phase in the silver paste in the metallized region is reduced to a certain extent, thereby increasing the open-circuit voltage of the solar cell and further enhancing the photoelectric conversion efficiency of the solar cell.

[0065] In some embodiments of the present disclosure, the total doping concentration of the boron emitter layer is in a range from 2.8*1018 atoms / cm3 to 3.2x1018 atoms / cm3. For example, the total doping concentration of the boron emitter layer is 2.8x1018 atoms / cm3, 2.9x1018 atoms / cm3, 3.0x1018 atoms / cm3, 3.1x1018 atoms / cm3, 3.2x1018 atoms / cm3, or any value between any two of the above numerical values. By adjusting the total doping concentration of the boron emitter layer within the above range, an optimal balance can be achieved between the short-wavelength spectral response of the boron emitter layer and the transmission loss caused by the sheet resistance. Especially after the laser-induced sintering treatment is performed on the front-side metallized region or after a denser arrangement of current-collecting grid lines is provided on the front side, a boron emitter layer with a more moderate doping concentration range can be adopted, at the expense of the carrier transmission losses, to further improve the short-wavelength spectral response of the boron emitter layer.

[0066] In some embodiments of the present disclosure, a junction depth of the boron emitter layer is in a range from 0.5 pm to 2.0 pm; and / or a sheet resistance of the boron emitter layer is in a range from 300 Q sq to 1500 Q / sq. For example, the junction depth of the boron emitter layer is 0.5 pm, 0.6 pm, 0.8 pm, 1.0 pm, 1.2 pm, 1.5 pm, or 2.0 pm. The sheet resistance of the boron emitter layer is 300 Q / sq, 500 Q / sq, 800 Q / sq, 1000 Q / sq, 1200 Q / sq, or 1500 Q / sq. Adjusting the junction depth and / or the sheet resistance of the boron emitter layer within the above ranges can reduce the thin-layer transport resistance loss during transport of photogenerated carriers to the front-side current-collecting grid lines.

[0067] In some embodiments of the present disclosure, the sheet resistance of the boron emitter layer is in a range from 500 Q / sq to 1000 Q / sq. For example, the sheet resistance of the boron emitter layer is 500 Q / sq, 600 Q / sq, 700 Q / sq, 800 Q / sq, 900 Q / sq, or 1000 Q / sq. Adjusting the sheet resistance of the boron emitter layer within the above range can reduce the thin-layer transport resistance loss during transport of photogenerated carriers to the front-side current-collecting grid lines while taking into account the short-wavelength spectral response of the boron emitter layer, thereby achieving a relatively good balance between the two.

[0068] In some embodiments of the present disclosure, the junction depth of the boron emitter layer is in a range from 0.5 gm to 0.8 gm. For example, the junction depth of the boron emitter layer is 0.5 gm, 0.6 gm, 0.7 gm, or 0.8 gm. Adjusting the junction depth of the boron emitter layer within the above range can reduce the thin-layer transport resistance loss during transport of photogenerated carriers to the front-side current-collecting grid lines while taking into account the short-wavelength spectral response of the boron emitter layer, thereby achieving a relatively good balance between the two.

[0069] In some embodiments of the present disclosure, the junction depth of the boron emitter layer is in a range from 0.8 gm to 1.5 gm. For example, the junction depth of the boron emitter layer is 0.8 gm, 1.0 gm, 1.3 gm, or 1.5 gm. Adjusting the junction depth of the boron emitter layer within the above range, can maximumly reduce the thin-layer transport resistance loss during transport of photogenerated carriers to the front-side current-collecting grid lines.

[0070] In some embodiments of the present disclosure, referring to FIG. 4, the region corresponding to the direct physical contact, that is, the first metal-semiconductor contact region 41, includes a silver-silicon eutectic substrate 411 and a silver-silicon eutectic overflow body 412, and the region corresponding to the direct physical contact further includes a silver crystalline body 413 electrically connected to the silver-silicon eutectic substrate 411 and the silver-silicon eutectic overflow body 412. The front-side structure of a solar cell of the present disclosure includes the silver crystalline body 413 having a relatively high electrical conductivity, and the silver-silicon eutectic substrate 411 and the silver-silicon eutectic overflow body 412 for improving the electrical conductivity of the boron emitter layer, so that an electrical conductivity of the metal-semiconductor contact conductive structure for outputting photogenerated carriers is significantly improved, thereby effectively improving contact performance between the front-side current-collecting grid lines and the boron emitter layer by optimizing the conductive structure. Therefore, by modifying and optimizing the front-side structure of the solar cell, contact performance between the boron emitter layer and the front-side current-collecting grid lines can be improved, contact resistance can be reduced, and a carrier transport capability can be enhanced, thereby effectively increasing both the open-circuit voltage and the photoelectric conversion efficiency of the solar cell.

[0071] In some embodiments of the present disclosure, referring to FIG. 4, the silver crystalline body 413 includes a crystalline main chain 4131 and crystalline side chains 4132 extending from the crystalline main chain 4131 in growth directions different from that of the crystalline main chain 4131, so that the silver crystalline body 413 as a whole has a dendritic structure. Such a silver crystalline body formed after crystallization of silver element has a relatively high purity and a relatively high electrical conductivity, thereby reducing the series resistance of the solar cell and enhancing the photoelectric conversion efficiency.

[0072] In some embodiments of the present disclosure, referring to FIG. 2, the region corresponding to the indirect physical contact, that is, the second metal-semiconductor contact region 42, has an electrically conducting aggregate 421; and the passivation film layer 3 having a relatively high dielectric constant is further interposed between the electrically conducting aggregate 421 and the boron emitter layer 2, wherein the electrically conducting aggregate includes a glass phase material and conductive metal particles, and the conductive metal particles and the silver crystalline body have the same type of metal element, such as silver element.

[0073] In a second aspect, the present disclosure provides a solar cell including the front-side structure of a solar cell according to any one of the above embodiments.

[0074] In some embodiments of the present disclosure, the solar cell is a tunnel oxide passivated contact (TOPCon) cell. As shown in FIG. 5, the solar cell includes: a silicon substrate 1. A boron emitter layer 2, a passivation film layer 3, and front-side current-collecting grid lines 4 are sequentially disposed on a front side of the silicon substrate 1 in a direction away from the front side. A tunneling passivation layer 5, a phosphorus-doped polysilicon layer 6, a rear-side passivation layer 7, and a rear electrode 8 are sequentially disposed on a rear side of the silicon substrate 1 in a direction away from the rear side.

[0075] The material of the tunneling passivation layer can include various dielectric materials, for example, at least one of silicon oxide, amorphous silicon, polysilicon, and silicon carbide. Specifically, the tunneling passivation layer can be a silicon oxide layer containing silicon oxide. This is because the silicon oxide layer has excellent passivation performance, can minimize carrier recombination loss at a surface of a semiconductor substrate, and is a thin film having excellent durability against subsequent high-temperature processes. The tunneling passivation layer can further have a pinhole channel structure, allowing carriers in the solar cell to move freely, and heavily doped polysilicon selectively allows majority carriers to pass therethrough, which is beneficial to reducing recombination loss of minority carriers. The phosphorus-doped polysilicon layer is a polysilicon layer doped with phosphorus. The rear-side passivation layer is a passivation layer whose material can be any one selected from silicon oxide, aluminum oxide, silicon carbide, silicon nitride, or silicon oxynitride, or can be any combination of these materials.

[0076] The structural film layers on the front side of the solar cell are described above. It can be understood that, according to structural characteristics of different types of solar cells, film layers with other structural characteristics, such as an anti-reflection layer, may further be disposed on the front side and the rear side of the solar cell. In addition, conventional approaches in the prior art may also be adopted for forming the structural film layers. For example, a silicon substrate having a textured surface structure is obtained by texturing, and a passivation film layer, an anti-reflection layer, and the like are obtained by an atomic layer deposition (ALD) process or a plasma-enhanced chemical vapor deposition (PECVD) process. In addition, the present disclosure may also adopt conventional treatments such as polishing and cleaning according to whether a wrap-around deposition layer, a borosilicate glass layer, or a phosphosilicate glass layer is formed during the formation of the structural film layers, and the present disclosure is not limited thereto.

[0077] In a third aspect, the present disclosure provides a method for preparing a solar cell, including the following steps:

[0078] Step A: providing a textured silicon wafer as a silicon substrate, placing the silicon substrate in a boron diffusion furnace, and forming a boron emitter layer on a front side of the silicon substrate by a boron diffusion process;

[0079] Step B: sequentially forming a tunneling passivation layer and a phosphorus-doped polysilicon layer on a rear side of the silicon substrate;

[0080] Step C: sequentially forming a passivation film layer on the boron emitter layer, and forming a rear-side passivation layer on the phosphorus-doped polysilicon layer;

[0081] Step D: printing an electrode paste on the passivation film layer and the rear-side passivation layer;

[0082] Step E: performing high-temperature pre-sintering to form a front-side current-collecting grid line precursor from the electrode paste printed on the passivation film layer, and to form a rear electrode from the electrode paste printed on the rear-side passivation layer; and

[0083] Step F: subjecting the front-side current-collecting grid line precursor to a laser-induced contact treatment to form front-side current-collecting grid lines.

[0084] In Step A, the front side of the silicon substrate can be textured in advance to form a pyramid-shaped textured surface structure, which is beneficial to reducing the reflectivity of the surface of the silicon substrate and increasing refraction and scattering of light within the silicon substrate. The boron diffusion process of the present disclosure can be performed based on a dry-oxygen process or a wet-oxygen process. When the wet-oxygen process is adopted, the growth rate of a silicon oxide mask layer in wet-oxygen gas conditions is relatively great, and the temperature for forming the silicon oxide mask layer (i.e., the post-oxidation process) can be controlled at about 1000 °C, which is lower than the temperature of the post-oxidation process in the dry-oxygen process. The lower temperature can significantly prolong a service life of a quartz tube in the diffusion furnace. In addition, the pre-oxidation process, the multi-stage deposition process, the multi-stage PN junction drive-in process, and the post-oxidation process can all be completed in one diffusion furnace, thereby reducing the number of devices used and lowering production costs. Moreover, although the growth rate of the silicon oxide mask is relatively great in the wet-oxygen process, when the process is applied to a TOPCon cell, the silicon oxide mask formed in the boron diffusion stage of the TOPCon cell is only used as a mask, and therefore is not required to have high denseness. Accordingly, the wet-oxygen process of the present disclosure is more suitable for the boron diffusion process of a TOPCon cell.

[0085] In addition, in Step A, a silicon oxide mask layer is further formed on a surface of the boron emitter layer. The silicon substrate can be an N-type silicon substrate, and a thickness of the silicon substrate is in a range from 100 gm to 200 gm, which is not particularly limited in the present disclosure.

[0086] In Step B, the tunneling passivation layer and the phosphorus-doped polysilicon layer can be formed by using a tubular PECVD device, which is not particularly limited in the present disclosure.

[0087] In Step C, an aluminum oxide layer can be deposited on the boron emitter layer using an ALD device to serve as the front-side passivation film layer; and a silicon oxynitride layer can be deposited on the phosphorus-doped polysilicon layer using a PECVD device to serve as the rear-side passivation layer.

[0088] In Step D, an electrode paste can be printed on the passivation film layer located on the front side and the rear-side passivation layer located on the rear side respectively by a screen printing method to form electrode grid lines. The electrode grid lines of the present disclosure can include busbars and fingers. The electrode paste of the present disclosure includes but is not limited to a pure silver electrode paste and a silver-aluminum electrode paste.

[0089] In Step E, the temperature of the high-temperature pre-sintering can be in a range from 650 °C to 780 °C, which is not particularly limited in the present disclosure, as long as the front-side current-collecting grid line precursor and the rear electrode can be formed.

[0090] In Step F, subjecting the front-side current-collecting grid line precursor to the laser-induced contact treatment is beneficial to forming a silver-silicon eutectic substrate and a silver crystalline body conductively connected to the silver-silicon eutectic substrate in the region where the front-side current-collecting grid lines are in direct physical contact with the boron emitter layer, so that the electrical conductivity of the conductive structure of the solar cell for outputting holes or electrons is significantly improved. As such, by optimizing the conductive structure, contact performance between the front-side current-collecting grid lines and the boron emitter layer can be effectively improved.

[0091] In the method for preparing a solar cell provided by the present disclosure, the boron emitter layer of the present disclosure is formed on the front side of the silicon substrate based on the boron diffusion process, and the front-side current-collecting grid lines are formed by performing the laser-induced contact treatment on the front-side current-collecting grid line precursor, thereby forming the boron emitter layer of the present disclosure, which are beneficial to forming a silver-silicon eutectic substrate and a silver crystalline body electrically connected to the silver-silicon eutectic substrate in the region where the front-side current-collecting grid lines are in direct physical contact with the boron emitter layer, improving contact performance between the front-side current-collecting grid lines and the boron emitter layer, thereby enhancing the performance of the solar cell.

[0092] In some embodiments of the present disclosure, forming the boron emitter layer on the front side of the silicon substrate by the boron diffusion process includes:

[0093] a pre-oxidation process, in which a temperature of the boron diffusion furnace is T1, a furnace tube pressure is P1, and oxygen gas and nitrogen gas are introduced into the boron diffusion furnace, wherein 750 °C < Ti < 850 °C, 230 mPa < Pi < 270 mPa, an oxygen gas flow rate is in a range from 800 sccm to 2000 sccm, and a nitrogen gas flow rate is in a range from 200 sccm to i000 sccm;

[0094] a multi-stage deposition process, in which a temperature of the boron diffusion furnace is T2, a furnace tube pressure is P2, and oxygen gas, nitrogen gas and a boron source gas are introduced in the boron diffusion furnace in multiple stages, with a furnace temperature in each stage being increased stage by stage, wherein 750 °C < T2 < 850 °C, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, 230 mPa < P2 < 270 mPa, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to 150 sccm;

[0095] a multi-stage PN junction drive-in process, in which a temperature of the boron diffusion furnace is T3, a furnace tube pressure is P3, and nitrogen gas is introduced into the boron diffusion furnace, wherein 850 °C < T3 < 950 °C, 580 mPa < P3 < 620 mPa, and a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm; and

[0096] a post-oxidation process, in which a temperature of the boron diffusion furnace is T4, a furnace tube pressure is P4, and oxygen gas is introduced into the boron diffusion furnace to form a silicon oxide mask layer having a thickness of 50 nm to 120 nm, wherein 950 °C < T4 < 1050 °C, 780 mPa < P4 < 820 mPa, and an oxygen gas flow rate is in a range from 10000 sccm to 30000 sccm.

[0097] In the pre-oxidation process, T1 can be 750 °C, 770 °C, 800 °C, 820 °C, or 850 °C; P1 can be 230 mPa, 240 mPa, 250 mPa, 260 mPa, or 270 mPa; the oxygen gas flow rate can be 800 sccm, 1000 sccm, 1300 sccm, 1500 sccm, or 2000 sccm; and the nitrogen gas flow rate can be 200 sccm, 400 sccm, 600 sccm, 700 sccm, or 1000 sccm. A duration of the pre-oxidation process can be in a range from 220 seconds (s) to 260 s. By adjusting the temperature T1 of the boron diffusion furnace, the furnace tube pressure P1, the oxygen gas flow rate, the nitrogen gas flow rate, and the duration of the pre-oxidation process within the above ranges, a thin oxide layer having a thickness of about 1 nm to about 3 nm is formed on a surface of the silicon substrate as a barrier layer, which can reduce a diffusion rate of boron atoms in the next step and enables a more uniform diffusion of boron atoms.

[0098] The inventors have found through research that introducing a large amount of boron source at one time would cause the boron source to be incompletely used and thus wasted, and would also cause the temperature at the gas inlet of the diffusion furnace to be too low, resulting in an excessively large temperature difference in the boron diffusion furnace and affecting the deposition effect. Based on this, the present disclosure adopts the multi-stage deposition process, that is, the deposition process is divided into a plurality of stages. The temperature of the boron diffusion furnace, the furnace tube pressure, and the respective flow rates of oxygen gas, nitrogen gas and the boron source gas are adjusted for each deposition stage, and the furnace temperature is increased stage by stage, which can improve the utilization rate of the boron source and prevent an excessively large temperature difference in the boron diffusion furnace, and is beneficial to obtaining the boron emitter layer of the present disclosure.

[0099] In some embodiments of the present disclosure, P4 > P3; and / or P4 > P2; and / or P4 > P1; and / or P3 > P2; and / or P3 > P1. By adjusting the furnace tube pressures P1, P2, P3, and P4 of the above pre-oxidation process, multi-stage deposition process, multi-stage PN junction drive-in process, and post-oxidation process to satisfy the above relationships, on one hand, as the furnace tube pressure increases, the pressure difference between inside and outside of the quartz furnace tube gradually decreases, thereby reducing stress on the furnace tube and lowering the risk of latent cracking of the furnace tube; on the other hand, for the wet-oxygen process, a larger furnace tube pressure in the post-oxidation process can increase the concentration of wet-oxygen gas, thereby increasing the oxidation rate and shortening the oxidation time.

[0100] In the multi-stage PN junction drive-in process, T3 can be 850 °C, 870 °C, 900 °C, 920 °C, or 950 °C; P3 can be 580 mPa, 590 mPa, 600 mPa, 610 mPa, or 620 mPa; the nitrogen gas flow rate can be 3000 sccm, 3500 sccm, 4000 sccm, 4500 sccm, or 5000 sccm; and oxygen gas and the boron source gas are not introduced in this process.

[0101] The multi-stage PN junction drive-in process of the present disclosure can include at least two drive-in stages, wherein a duration of a first drive-in stage can be in a range from 350 s to 400 s, and a duration of a second drive-in stage can be in a range from 300 s to 340 s.

[0102] In the post-oxidation process, T4 can be 950 °C, 980 °C, 1000 °C, 1040 °C, or 1050 °C; P4 can be 780 mPa, 790 mPa, 800 mPa, 810 mPa, or 820 mPa; the oxygen gas flow rate can be 10000 sccm, 15000 sccm, 20000 sccm, 25000 sccm, or 30000 sccm; and a duration of the post-oxidation process is 4000 s to 8000 s.

[0103] In some embodiments of the present disclosure, T2 > T1; and / or T3 > T2; and / or T4 > T3. By adjusting the temperatures T1, T2, T3, and T4 of the boron diffusion furnace in the above pre-oxidation process, multi-stage deposition process, multi-stage PN junction drive-in process, and post-oxidation process to satisfy the above relationships, it is beneficial to achieving more uniform and effective doping of boron atoms on the front side of the silicon substrate, and activating boron atoms to reduce the formation probability of a dead boron-doped layer.

[0104] In some embodiments of the present disclosure, in the multi-stage deposition process of the present disclosure, the number of deposition stages is in a range from 2 to 5. For example, the deposition stages can include 2 stages, 3 stages, 4 stages, or 5 stages.

[0105] In some embodiments of the present disclosure, the multi-stage deposition process includes:

[0106] a first deposition stage, in which a temperature of the boron diffusion furnace is T21, a furnace tube pressure is P21, and oxygen gas, nitrogen gas and a boron source gas are introduced into the boron diffusion furnace, wherein 750 °C < T21 < 850 °C, 230 mPa < P21 < 270 mPa, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to 150 sccm; the duration of the first deposition stage is in a range from 100 s to 140 s.

[0107] a second deposition stage, in which a temperature of the boron diffusion furnace is T22, a furnace tube pressure is P22, and oxygen gas, nitrogen gas and a boron source gas are introduced into the boron diffusion furnace, wherein 750 °C < T22 < 850 °C, T22 > T21, 230 mPa < P22 < 270 mPa, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to 150 sccm; the duration of the second deposition stage is in a range from 200 s to 250 s; and

[0108] a third deposition stage, in which a temperature of the boron diffusion furnace is T23, a furnace tube pressure is P23, and oxygen gas, nitrogen gas and a boron source gas are introduced into the boron diffusion furnace, wherein 750 °C < T23 < 850 °C, T23 > T22, 230 mPa < P23 < 270 mPa, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to 150 sccm; the duration of the third deposition stage is in a range from 200 s to 250 s.

[0109] In some embodiments of the present disclosure, subjecting the front-side current-collecting grid line precursor to a laser-induced contact treatment includes:

[0110] subjecting the front-side current-collecting grid line precursor to the laser-induced contact treatment on the front side of the silicon substrate, wherein a reverse bias voltage of 10 V to 25 V is applied in this process. In one aspect, the reverse bias voltage can further enhance the built-in electric field of the solar cell at the contact interface between the boron emitter layer and the front-side current-collecting grid line precursor; in another aspect, a large number of photogenerated carriers are generated by the laser-induced contact treatment. Through a combined action of these two aspects, electron carriers and hole carriers are separated by the electric field, and the carriers of one charge polarity are rapidly transported to the boron emitter layer under an accelerating action of the electric field. These carriers generate a large amount of heat when passing through a glass phase material having a relatively large resistivity, which is beneficial to forming a silver-silicon eutectic substrate and a silver-silicon eutectic overflow body, as well as a silver crystalline body electrically connected to the silver-silicon eutectic substrate and the silver-silicon eutectic overflow body, in the region where the front-side current-collecting grid lines are in direct physical contact with the boron emitter layer.

[0111] In some embodiments of the present disclosure, after the passivation film layer is formed, a silicon oxynitride layer can further be deposited on the passivation film layer using a PECVD device to serve as a front-side anti-reflection layer.

[0112] In a third aspect, the present disclosure provides a photovoltaic module. The photovoltaic module includes a solar cell prepared by the method according to the first aspect, or the photovoltaic module includes the solar cell according to the second aspect.

[0113] The present disclosure further provides a photovoltaic module. The photovoltaic module is configured for converting received light energy into electrical energy and transmitting the electrical energy to an external load. The photovoltaic module includes at least one cell string, wherein the cell string is formed by connecting a plurality of the above solar cells; an encapsulating adhesive film covering a surface of the cell string; and a cover plate covering a surface of the encapsulating adhesive film facing away from the cell string.

[0114] The present disclosure will be further described below in conjunction with more specific examples. The electrode paste and other materials used in the following examples are commercially available. For example, the paste for forming the front-side current-collecting grid line is a commercially available silver electrode paste of model T129 from Zhejiang Gonad Electronic Technology Co., Ltd., wherein in the electrode paste, an Al content is in a range from 0.05 wt% to 0.10 wt%, and an oxygen gas content is in a range from 1.0 wt% to 5.0 wt%. The element content in the silver electrode paste can be measured using an energy dispersive spectrometer (EDS).

[0115] Example 1

[0116] This example provides a solar cell having a front-side structure, wherein a post-oxidation process thereof is performed based on a wet-oxygen process. The preparation method is as follows:

[0117] <Pre-oxidation process>

[0118] A textured silicon wafer having a thickness of 125 gm was provided as a silicon substrate. The silicon substrate was placed in a boron diffusion furnace. The temperature T1 of the boron diffusion furnace was 820 °C, the furnace tube pressure P1 was 250 mPa, the oxygen gas flow rate was 1000 sccm, and the nitrogen gas flow rate was 500 sccm, so as to form an oxide layer having a thickness of 1 nm to 3 nm on a surface of the silicon substrate.

[0119] <Multi-stage deposition process>

[0120] <First deposition stage>

[0121] The temperature T21 of the boron diffusion furnace was 825 °C, the furnace tube pressure P21 was 250 mPa. Oxygen gas, nitrogen gas and a boron source gas were introduced into the boron diffusion furnace at an oxygen gas flow rate of 300 sccm, a nitrogen gas flow rate of 4000 sccm, and a boron source gas flow rate of 100 sccm for 120 s, followed by purging.

[0122] <Second deposition stage>

[0123] The temperature T22 of the boron diffusion furnace was 835 °C, the furnace tube pressure P22 was 250 mPa. Oxygen gas, nitrogen gas and a boron source gas were introduced into the boron diffusion furnace, at an oxygen gas flow rate of 300 sccm, a nitrogen gas flow rate of 4000 sccm, and a boron source gas flow rate of 100 sccm for 210 s, followed by purging.

[0124] <Third deposition stage>

[0125] The temperature T23 of the boron diffusion furnace was 845 °C, the furnace tube pressure P23 was 250 mPa. Oxygen gas, nitrogen gas and a boron source gas were introduced into the boron diffusion furnace at an oxygen gas flow rate of 300 sccm, a nitrogen gas flow rate of 4000 sccm, and a boron source gas flow rate of 100 sccm for 210 s, followed by purging.

[0126] <Multi-stage PN junction drive-in>

[0127] <First drive-in stage>

[0128] The temperature T31 of the boron diffusion furnace was 885 °C, the furnace tube pressure P31 was 600 mPa, and nitrogen gas was introduced into the boron diffusion furnace at a nitrogen gas flow rate of 4000 sccm for 360 s.

[0129] <Second drive-in stage>

[0130] The temperature T32 of the boron diffusion furnace was 885 °C, the furnace tube pressure P32 was 600 mPa, and nitrogen gas was introduced into the boron diffusion furnace at a nitrogen gas flow rate of 4000 sccm for 330 s, thereby forming a boron emitter layer.

[0131] <Post-oxidation process>

[0132] The temperature T4 of the boron diffusion furnace was 1020 °C, the furnace tube pressure P4 was 800 mPa. Nitrogen gas was bubbled through a water-vapor bottle so that the nitrogen gas carried water molecules, and at the same time oxygen gas was introduced into the boron diffusion furnace at an oxygen gas flow rate of 18000 sccm for 5900 s, thereby forming a silicon oxide mask layer having a thickness of 100 nm to 150 nm on the boron emitter layer.

[0133] <Alkaline polishing>

[0134] The borosilicate glass formed on the rear side of the silicon substrate due to boron diffusion wrap-around was removed using a chain-type HF device, and then P-N junctions on the rear side and edges of the silicon substrate were removed using a tank-type alkaline polishing machine.

[0135] <Preparation of tunneling passivation layer>

[0136] A silicon oxide tunneling passivation layer was deposited on the rear side of the silicon substrate using a tubular PECVD device.

[0137] <Preparation of phosphorus-doped polysilicon layer>

[0138] A phosphorus-doped polysilicon layer was deposited on the tunneling passivation layer using a tubular PECVD device.

[0139] <Annealing>

[0140] Annealing was performed by using a tubular annealing furnace.

[0141] <RCA cleaning>

[0142] The phosphorus-doped polysilicon layer wrapped around the front side and the silicon oxide mask layer were removed using hydrofluoric acid having a mass concentration of 5% in a chain-type device, and then the substrate was transferred to a tank-type alkaline polishing machine to remove the layer wrapped around the front side.

[0143] <Deposition of passivation layers>

[0144] An aluminum oxide layer was deposited on the boron emitter layer using an ALD device to serve as a front-side passivation film layer. A silicon oxynitride layer was deposited on the phosphorus-doped polysilicon layer using a PECVD device to serve as a rear-side passivation layer. Both the front-side passivation film layer and the rear-side passivation layer can be understood as passivation layers disposed on the boron emitter layer.

[0145] <Printing of electrode paste>

[0146] An electrode paste was screen-printed on the front-side passivation film layer and the second passivation layer respectively.

[0147] <High-temperature pre-sintering>

[0148] High-temperature pre-sintering was performed at 740 °C to form a front-side current-collecting grid line precursor from the electrode paste printed on the passivation film layer, and to form a rear electrode from the electrode paste printed on the rear-side passivation layer.

[0149] <Laser-induced contact treatment>

[0150] Laser-induced  contact treatment was performed on the  front-side current-collecting grid line precursor to form front-side current-collecting grid lines.

[0151] Example 2

[0152] Except that the post-oxidation process was performed based on a dry-oxygen process, the rest was the same as in Example 1.

[0153] <Post-oxidation process>

[0154] The temperature T4 of the boron diffusion furnace was 1030 °C, the furnace tube 5 pressure P4 was 800 mPa. oxygen gas was introduced into the boron diffusion furnace at an oxygen gas flow rate of 18000 sccm for 5900 s, thereby forming a silicon oxide mask layer having a thickness of 100 nm to 150 nm on the boron emitter layer.

[0155] The front-side structure of a solar cell, a solar cell and a preparation method thereof, and a photovoltaic module disclosed in the present disclosure were described in 10 detail. Specific examples are applied herein to illustrate the principles and implementations of the present disclosure. The descriptions of the above examples are only used to help understand the technical solutions and core inventive points of the embodiments of the present disclosure. Moreover, for those of ordinary skill in the art, changes may be made to the specific implementations and application scopes according to the idea of the present 15 disclosure. In summary, the content of this specification should not be construed as a limitation on the present disclosure.

Claims

1. A front-side structure of a solar cell, comprising:a boron emitter layer,a passivation film layer, andfront-side current-collecting grid lines, the front-side current-collecting grid lines being in direct physical contact with the boron emitter layer at a part of a region therebetween, and the front-side current-collecting grid lines being in indirect physical contact with the boron emitter layer via the passivation film layer at another part of the region therebetween;wherein a total doping concentration of the boron emitter layer is in a range from 2.8X1018 atoms / cm3 to 4.0*1018 atoms / cm3.

2. The front-side structure of the solar cell according to claim 1, wherein the total doping concentration of the boron emitter layer is in a range from 2.8x1018 atoms / cm3 to 3.2x1018 atoms / cm3.

3. The front-side structure of the solar cell according to claim 1, wherein a junction depth of the boron emitter layer is in a range from 0.5 pm to 2.0 pm; and / ora sheet resistance of the boron emitter layer is in a range from 300 Q / sq to 1500 Q / sq.

4. The front-side structure of the solar cell according to claim 2, wherein the sheet resistance of the boron emitter layer is in a range from 500 Q / sq to 1000 Q / sq.

5. The front-side structure of the solar cell according to claim 2, wherein the junction depth of the boron emitter layer is in a range from 0.5 pm to 0.8 pm.

6. The front-side structure of the solar cell according to claim 2, wherein the junction depth of the boron emitter layer is in a range from 0.8 pm to 1.5 pm.

7. The front-side structure of the solar cell according to claim 1, wherein a region corresponding to the direct physical contact comprises a silver-silicon eutectic substrate and a silver-silicon eutectic overflow body, and a region corresponding to the direct physical contact further comprises a silver crystalline body electrically connected to the silver-silicon eutectic substrate and the silver-silicon eutectic overflow body.

8. The front-side structure of the solar cell according to claim 7, wherein the silver crystalline body comprises a crystalline main chain and a crystalline side chain extending from the crystalline main chain in a growth direction different from that of the crystalline main chain.

9. The front-side structure of the solar cell according to claim 7, wherein a region corresponding to the indirect physical contact has an electrically conducting aggregate, and the passivation film layer is located between the electrically conducting aggregate and theboron emitter layer; wherein the electrically conducting aggregate comprises a glass phase material and conductive metal particles, and the conductive metal particles and the silver crystalline body have a same type of metal element.

10. A solar cell, wherein the solar cell comprises the front-side structure of the solar cell according to any one of claims 1 to 9.

11. A method for preparing the solar cell according to claim 10, comprising following steps: providing a textured silicon wafer as a silicon substrate, placing the silicon substrate ina boron diffusion furnace, and forming a boron emitter layer on a front side of the silicon substrate by a boron diffusion process;sequentially forming a tunneling passivation layer and a phosphorus-doped polysilicon layer on a rear side of the silicon substrate;sequentially forming a passivation film layer on the boron emitter layer, and forming a rear-side passivation layer on the phosphorus-doped polysilicon layer;printing an electrode paste on the passivation film layer and the rear-side passivation layer;performing high-temperature pre-sintering to form a front-side current-collecting grid line precursor from the electrode paste printed on the passivation film layer, and to form a rear electrode from the electrode paste printed on the rear-side passivation layer; andsubjecting the front-side current-collecting grid line precursor to a laser-inducedcontact treatment to form front-side current-collecting grid lines.

12. The method according to claim 11, wherein forming the boron emitter layer on the front side of the silicon substrate by the boron diffusion process comprises:a pre-oxidation process, in which a temperature of the boron diffusion furnace is T1, a furnace tube pressure is P1, and oxygen gas and nitrogen gas are introduced into the boron diffusion furnace, wherein 750 °C < Ti < 850 °C, 230 mPa < Pi < 270 mPa, an oxygen gas flow rate is in a range from 800 sccm to 2000 sccm, and a nitrogen gas flow rate is in a range from 200 sccm to i000 sccm;a multi-stage deposition process, in which a temperature of the boron diffusion furnace is T2, a furnace tube pressure is P2, and oxygen gas, nitrogen gas and a boron source gas are introduced in the boron diffusion furnace in multiple stages, with a furnace temperature in each stage being increased stage by stage, wherein 750 °C < T2 < 850 °C, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, 230 mPa < P2 < 270 mPa, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to i50 sccm;a multi-stage PN junction drive-in process, in which a temperature of the boron diffusion furnace is T3, a furnace tube pressure is P3, and nitrogen gas is introduced into the boron diffusion furnace, wherein 850 °C < T3 < 950 °C, 580 mPa < P3 < 620 mPa, and a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm; anda post-oxidation process, in which a temperature of the boron diffusion furnace is T4, afurnace tube pressure is P4, and oxygen gas is introduced into the boron diffusion furnace to form a silicon oxide mask layer having a thickness of 50 nm to 120 nm, wherein 950 °C < T4 < 1050 °C, 780 mPa < P4 < 820 mPa, and an oxygen gas flow rate is in a range from 10000 sccm to 30000 sccm.

13. The method according to claim 12, wherein P4 > P3; and / or P4 > P2; and / or P4 > P1; and / or P3 > P2; and / or P3 > P1.

14. The method according to claim 12, wherein T2 > T1; and / or T3 > T2; and / or T4 > T3.

15. The method according to claim 12, wherein in the multi-stage deposition process, a number of deposition stages is in a range from 2 to 5.

16. The method according to claim 12, wherein the multi-stage deposition process comprises:a first deposition stage, in which a temperature of the boron diffusion furnace is T21, a furnace tube pressure is P21, and oxygen gas, nitrogen gas and a boron source gas are introduced into the boron diffusion furnace, wherein 750 °C < T21 < 850 °C, 230 mPa < P21 < 270 mPa, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to 150 sccm;a second deposition stage, in which a temperature of the boron diffusion furnace is T22, a furnace tube pressure is P22, and oxygen gas, nitrogen gas and a boron source gas are introduced into the boron diffusion furnace, wherein 750 °C < T22 < 850 °C, T22 > T21, 230 mPa < P22 < 270 mPa, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to 150 sccm; anda third deposition stage, in which a temperature of the boron diffusion furnace is T23, a furnace tube pressure is P23, and oxygen gas, nitrogen gas and a boron source gas are introduced into the boron diffusion furnace, wherein 750 °C < T23 < 850 °C, T23 > T22, 230 mPa < P23 < 270 mPa, an oxygen gas flow rate is in a range from 200 sccm to 600 sccm, a nitrogen gas flow rate is in a range from 3000 sccm to 5000 sccm, and a boron source gas flow rate is in a range from 80 sccm to 150 sccm.

17. The method according to claim 11, wherein subjecting the front-side current-collecting grid line precursor to the laser-induced contact treatment comprises:subjecting the front-side current-collecting grid line precursor to the laser-induced contact treatment on the front side of the silicon substrate.

18. A photovoltaic module, comprising the solar cell according to claim 10, or a solar cell prepared by the method according to any one of claims 11 to 17

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