CN110690326A - Solar cell preparation method - Google Patents
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- CN110690326A CN110690326A CN201911031271.2A CN201911031271A CN110690326A CN 110690326 A CN110690326 A CN 110690326A CN 201911031271 A CN201911031271 A CN 201911031271A CN 110690326 A CN110690326 A CN 110690326A
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- 239000002253 acid Substances 0.000 claims description 12
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Abstract
The invention discloses a solar cell preparation method, which comprises the steps of etching a preset depth of the surface of one side, back to a substrate layer, of a selective emitter junction after the preset region of the surface of the emitter junction is irradiated by laser to form the selective emitter junction, so that the doping concentration of the exposed preset region is greater than that of a non-preset region in the surface of the selective emitter junction. The area of the surface of the selective emitter junction, which reduces the concentration of carriers due to laser irradiation, can be removed by etching the preset depth of the surface of one side of the selective emitter junction, which is back to the substrate layer, so that the independent adjustment of the surface concentration of the laser irradiation area and the non-laser irradiation area on the surface of the selective emitter junction can be realized, and the conversion efficiency of the solar cell is further improved.
Description
Technical Field
The invention relates to the technical field of photovoltaic cells, in particular to a solar cell preparation method.
Background
With the mass production application of the PERC technology in the field of monocrystalline silicon solar cells, the mass production efficiency of the PERC monocrystalline silicon solar cells is already above 21.5%, and is a significant leap over the conventional solar cells (the mass production efficiency is about 20.2%). To meet the requirement of further improving the cell conversion efficiency, the laser doping selective emitter junction technology is increasingly introduced into mass production by solar cell factories.
The laser doping selective emitter junction technology selectively and locally irradiates laser on a lightly doped emitter junction with high sheet resistance after phosphorus diffusion, and a heavily doped emitter junction with low sheet resistance is formed in a laser irradiated area. However, in the prior art, the improvement of the conversion efficiency of the solar cell by the laser doping selective emitter junction technology is limited, so how to improve the improvement of the conversion efficiency of the solar cell by the laser doping selective emitter junction technology is a problem that needs to be solved urgently by those skilled in the art.
Disclosure of Invention
The invention aims to provide a solar cell preparation method, which can effectively improve the conversion efficiency of a solar cell by a laser doping selective emitter junction technology.
In order to solve the above technical problems, the present invention provides a method for manufacturing a solar cell, comprising:
adding doped ions on the preset surface of the substrate layer to form an emitter junction;
irradiating a preset area on the surface of the emitter junction by laser to form a selective emitter junction;
etching the surface of one side, back to the substrate layer, of the selective emitter junction by a preset depth to enable the doping concentration of the exposed preset region to be larger than that of a non-preset region in the surface of the selective emitter junction;
and arranging a first electrode covering the preset area and a second electrode electrically connected with the substrate layer to manufacture the solar cell.
Optionally, the adding dopant ions to the preset surface of the substrate layer to form an emitter junction includes:
and performing phosphorus diffusion on the preset surface of the p-type substrate layer to form an emitter junction.
Optionally, the performing phosphorus diffusion on the predetermined surface of the p-type substrate layer to form the emitter junction includes:
performing phosphorus diffusion on the preset surface of the p-type substrate layer to form an emitter junction; the surface doping concentration of the emitter junction is not less than 3 x 1020/cm3。
Optionally, the irradiating a predetermined region of the surface of the emitter junction with laser light to form a selective emitter junction includes:
irradiating a preset area on the surface of the emitter junction by laser to form a selective emitter junction; the surface doping concentration of the preset region is not less than 2.8 multiplied by 1020/cm3。
Optionally, etching the selective emitter junction by a preset depth from the surface of one side of the substrate layer, so that the exposed doping concentration of the preset region is greater than the doping concentration of a non-preset region in the surface of the selective emitter junction, includes:
etching the surface of one side, back to the substrate layer, of the selective emitter junction by using an acid etching solution to a preset depth so that the doping concentration of the exposed preset area is greater than that of a non-preset area in the surface of the selective emitter junction.
Optionally, the acid etching solution includes hydrofluoric acid with a mass concentration of 0.1% -2% and nitric acid with a mass concentration of 30% -70%.
Optionally, the etching the selective emitter junction by a preset depth from the surface of one side of the substrate layer includes:
etching the surface of one side, back to the substrate layer, of the selective emitter junction by a preset depth; the preset depth ranges from 20nm to 150nm, inclusive.
Optionally, after the etching the selective emitter junction by the acid etching solution to a predetermined depth from the surface of the substrate layer side, the method further includes:
and removing the porous silicon formed on the surface of the selective emitter junction.
Optionally, the removing the porous silicon formed on the surface of the selective emitter junction includes:
removing the porous silicon formed on the surface of the selective emitter junction by using alkali solution; the solute of the alkali solution is sodium hydroxide or potassium hydroxide, and the concentration of the solute in the alkali solution is between 1 per thousand and 5 percent inclusive.
Optionally, after etching the selective emitter junction to a predetermined depth from the surface of the substrate layer, the method further includes:
and forming a protective layer on the surface of one side, back to the substrate layer, of the selective emitter junction.
According to the solar cell preparation method provided by the invention, after the preset area on the surface of the emitter junction is irradiated by laser to form the selective emitter junction, namely after the selective emitter junction technology is doped by the laser, the preset depth of the surface of one side, back to the substrate layer, of the selective emitter junction is etched, so that the doping concentration of the exposed preset area is greater than that of a non-preset area in the surface of the selective emitter junction. The laser irradiation can push carrier impurities in the selective emitter junction into the substrate layer, so that the surface concentration of a laser irradiated area in the surface of the selective emitter junction can not rise or fall. The area of the surface of the selective emitter junction, which reduces the concentration of current carriers due to laser irradiation, can be removed by etching the preset depth of the surface of one side of the selective emitter junction, so that the doping concentration of the exposed laser irradiation area is greater than that of the non-laser irradiation area in the surface of the selective emitter junction, the independent adjustment of the surface concentration of the laser irradiation area and the non-laser irradiation area on the surface of the selective emitter junction can be realized, the surface concentration of the heavily doped area in the selective emitter junction is not limited by the surface concentration of the lightly doped area, and the conversion efficiency of the solar cell can be further improved.
Drawings
In order to more clearly illustrate the embodiments or technical solutions of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
FIG. 1 is a diagram showing a distribution of impurity concentration in a non-laser-irradiated region and a laser-irradiated region in the prior art;
fig. 2 is a flowchart of a method for manufacturing a solar cell according to an embodiment of the invention;
fig. 3 is a flowchart illustrating a specific method for fabricating a solar cell according to an embodiment of the present invention;
FIG. 4 is a diagram showing the impurity concentration distribution in the non-laser-irradiated region and the laser-irradiated region in the embodiment of the present invention.
Detailed Description
The core of the invention is to provide a preparation method of a solar cell. Referring to fig. 1, fig. 1 is a graph showing impurity concentration distribution in a non-laser-irradiated region and a laser-irradiated region in the prior art. As can be seen from fig. 1, in the prior art, since the carrier impurities in the selective emitter junction are pushed into the substrate layer by the laser irradiation, the surface concentration of the laser irradiation region does not increase or decrease due to the selective emitter junction prepared by the laser doping selective emitter junction technology. This will make the emitting junction area irradiated by laser and the emitting junction obtained by original diffusion have strong correlation, and the surface concentration of the laser doped low sheet resistance emitting junction and the surface concentration of the laser doped high sheet resistance emitting junction can not be controlled independently. However, in order to further reduce the contact resistance between the metal electrode of the solar cell and the emitter junction, the fill factor of the solar cell is increased, and the doping concentration of the laser irradiation region in the selective emitter junction is required to be increased as much as possible. This limits the improvement of the conversion efficiency of the solar cell. In the prior art, the surface concentration of the emitting junction of the heavily doped region irradiated by laser is lower than that of the lightly doped region, and the sheet resistance of the emitting junction of the heavily doped region can be reduced by only 20-50ohm/sq compared with that of the emitting junction of the lightly doped region, namely, the sheet resistance is reduced from 100-150ohm/sq to 80-100 ohm/sq.
According to the solar cell preparation method provided by the invention, after the preset region on the surface of the emitter junction is irradiated by laser to form the selective emitter junction, namely after the selective emitter junction technology is doped by the laser, the preset depth of the surface of one side, back to the substrate layer, of the selective emitter junction is etched, so that the doping concentration of the exposed preset region is greater than that of a non-preset region in the surface of the selective emitter junction. The laser irradiation can push carrier impurities in the selective emitter junction into the substrate layer, so that the surface concentration of a laser irradiated area in the surface of the selective emitter junction can not rise or fall. The area of the surface of the selective emitter junction, which reduces the concentration of current carriers due to laser irradiation, can be removed by etching the preset depth of the surface of one side of the selective emitter junction, so that the doping concentration of the exposed laser irradiation area is greater than that of the non-laser irradiation area in the surface of the selective emitter junction, the independent adjustment of the surface concentration of the laser irradiation area and the non-laser irradiation area on the surface of the selective emitter junction can be realized, the surface concentration of the heavily doped area in the selective emitter junction is not limited by the surface concentration of the lightly doped area, and the conversion efficiency of the solar cell can be further improved.
In order that those skilled in the art will better understand the disclosure, the invention will be described in further detail with reference to the accompanying drawings and specific embodiments. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 2, fig. 2 is a flowchart illustrating a method for manufacturing a solar cell according to an embodiment of the invention.
Referring to fig. 2, in an embodiment of the present invention, a method for manufacturing a solar cell includes:
s101: and adding doping ions to the preset surface of the substrate layer to form an emitter junction.
In this step, emitter junctions are prepared at the surface of the substrate layer. The specific process for fabricating the emitter junction will be described in detail in the following examples of the invention. It should be noted that the surface concentration of each region of the emitter junction formed in this step is generally equal, that is, the emitter junction prepared in this step is generally prepared by a conventional diffusion process.
S102: a predetermined region of the surface of the emitter junction is irradiated with laser light to form a selective emitter junction.
In this step, a laser doping selective emitter junction technique is specifically used, and a predetermined region of the surface of the emitter junction formed in S101 is irradiated with laser light to form a selective emitter junction. In this step, the surface concentration of the laser-irradiated predetermined region may be lower than the surface concentration of the selective emitter junction surface non-predetermined region, i.e., the non-laser-irradiated region.
S103: and etching the surface of one side of the selective emitter junction, which is back to the substrate layer, by a preset depth so that the doping concentration of the exposed preset region is greater than that of a non-preset region in the surface of the selective emitter junction.
In this step, a predetermined depth of the surface of the selective emitter junction opposite to the substrate layer is etched away, so that the doping concentration of the exposed predetermined region irradiated by the laser is greater than the doping concentration of the non-predetermined region in the surface of the selective emitter junction, that is, the predetermined region not irradiated by the laser. The details of the specific etching process and the specific depth of etching will be described in detail in the following embodiments of the invention, and will not be described herein again.
It should be noted that, in this step, the surface of the whole selective emitter junction on the side opposite to the substrate layer is uniformly etched, so as to remove the structure in which the doping concentration of the laser irradiation region in the selective emitter junction on the side opposite to the substrate layer is less than the doping concentration of the non-laser irradiation region, so that the doping concentration of the exposed preset region is greater than the doping concentration of the non-preset region in the surface of the selective emitter junction.
S104: and arranging a first electrode covering the preset area and a second electrode electrically connected with the substrate layer to manufacture the solar cell.
In this step, a first electrode covering a predetermined region of the surface of the selective emitter, i.e., a laser irradiation region, is disposed on the surface of the selective emitter, and the first electrode collects current generated by the solar cell through a predetermined region having a low sheet resistance and a high doping concentration. In this step, a second electrode is also provided, electrically connected to the substrate layer, to collect the current generated by the solar cell. The second electrode is typically located on the back side of the solar cell, while the first electrode and the emitter junction are typically located on the front side of the solar cell. And collecting the current generated by the substrate layer and the selective emitter junction through the first electrode and the second electrode, thereby preparing the finished solar cell.
According to the solar cell preparation method provided by the embodiment of the invention, after the preset region on the surface of the emitter junction is irradiated by laser to form the selective emitter junction, namely after the selective emitter junction doping technology is applied, the preset depth of the surface of one side, back to the substrate layer, of the selective emitter junction is etched, so that the doping concentration of the exposed preset region is greater than that of a non-preset region in the surface of the selective emitter junction. The laser irradiation can push carrier impurities in the selective emitter junction into the substrate layer, so that the surface concentration of a laser irradiated area in the surface of the selective emitter junction can not rise or fall. The area of the surface of the selective emitter junction, which reduces the concentration of current carriers due to laser irradiation, can be removed by etching the preset depth of the surface of one side of the selective emitter junction, so that the doping concentration of the exposed laser irradiation area is greater than that of the non-laser irradiation area in the surface of the selective emitter junction, the independent adjustment of the surface concentration of the laser irradiation area and the non-laser irradiation area on the surface of the selective emitter junction can be realized, the surface concentration of the heavily doped area in the selective emitter junction is not limited by the surface concentration of the lightly doped area, and the conversion efficiency of the solar cell can be further improved.
The following embodiments of the present invention will be described in detail with reference to the following embodiments of the present invention.
Referring to fig. 3 and fig. 4, fig. 3 is a flowchart illustrating a method for manufacturing a solar cell according to an embodiment of the invention; FIG. 4 is a diagram showing the impurity concentration distribution in the non-laser-irradiated region and the laser-irradiated region in the embodiment of the present invention.
Referring to fig. 3, in an embodiment of the present invention, a method for manufacturing a solar cell includes:
s201: and performing phosphorus diffusion on the preset surface of the p-type substrate layer to form an emitter junction.
In this step, a p-type substrate layer is selected, and phosphorus diffusion is performed on a predetermined surface of the p-type substrate layer, typically the front surface of the p-type substrate layer, by a phosphorus diffusion process to form an emitter junction. The specific process of phosphorus diffusion can be referred to the prior art, and is not described herein.
In this step, the surface doping concentration of the emitter junction formed by phosphorus diffusion is usually not less than 3 × 1020/cm3. Of course, the surface doping concentration of the emitter junction in the embodiment of the present invention may have other values, and the specific value of the surface doping concentration of the emitter junction prepared in this step is not specifically limited in the embodiment of the present invention.
S202: a predetermined region of the surface of the emitter junction is irradiated with laser light to form a selective emitter junction.
This step is substantially similar to step S102 in the above-described embodiment of the invention, and the details have been described in the above-described embodiment of the invention, and are not described herein again. In this step, the surface doping concentration of the laser irradiation region, i.e., the predetermined region, is usually not less than 2.8 × 1020/cm3. Of course, in this documentThe surface doping concentration of the preset region in the embodiment of the present invention may have other values, and the specific value of the surface doping concentration of the preset region prepared in this step is not specifically limited in the embodiment of the present invention.
S203: and etching the surface of one side, back to the substrate layer, of the selective emitter junction by an acid etching solution to a preset depth so that the doping concentration of the exposed preset region is greater than that of a non-preset region in the surface of the selective emitter junction.
In this step, the surface of the selective emitter junction opposite to the substrate layer is etched to a predetermined depth by using an acid etching solution, which is usually hydrofluoric acid (HF) and nitric acid (HNO)3) The mixed acid solution of (1). Specifically, the acid etching solution generally includes hydrofluoric acid having a mass concentration of 0.1% to 2% and nitric acid having a mass concentration of 30% to 70%.
The surface of the selective emitter junction, which is back to the substrate layer side, can be effectively etched by the acid etching solution with the components. Specifically, in this step, it is generally required to etch a predetermined depth of the surface of the selective emitter junction on the side away from the substrate layer, where the predetermined depth is generally in a range from 20nm to 150nm, inclusive. That is, in this step, a portion of the structure with a thickness of 20nm to 150nm on the surface of the selective emitter junction is typically removed, so that the doping concentration of the exposed predetermined region is greater than the doping concentration of the non-predetermined region in the surface of the selective emitter junction. During etching, the temperature of the acid etching solution is generally required to be maintained between 10 ℃ and 30 ℃, inclusive; the etch time typically needs to be kept between 10s and 5min, inclusive.
At this time, the surface doping concentration of the exposed predetermined region of the surface of the selective emitter junction, i.e., the laser irradiated region, is usually maintained at 2.5 × 1020/cm3In the above, the surface doping concentration of the non-predetermined region of the selective emitter junction surface, i.e. the laser unirradiated region, is usually kept at 1.5 × 1020/cm3The following.
S204: and removing the porous silicon formed on the surface of the selective emitter junction.
When the selective emitter junction surface is etched in S203, unnecessary porous silicon may be formed on the selective emitter junction surface. In this step, the porous silicon formed on the surface of the selective emitter junction is removed to ensure the performance of the final solar cell.
Specifically, the step may specifically be removing the porous silicon formed on the surface of the selective emitter junction by an alkali solution; the solute of the alkali solution is sodium hydroxide or potassium hydroxide, and the concentration of the solute in the alkali solution is between 1 per thousand and 5 percent inclusive. That is, in this step, the porous silicon formed on the surface of the selective emitter junction is removed using an alkali solution. The solute of the alkaline solution is typically sodium hydroxide (NaOH) or potassium hydroxide (KOH), and the concentration of the solute in the alkaline solution is typically between 1% and 5%, inclusive. The alkaline solution containing the components can effectively remove the porous silicon formed on the surface of the selective emitter junction so as to avoid the influence of the porous silicon structure on the performance of the solar cell.
S205: and forming a protective layer on the surface of the selective emitter junction, which is opposite to the substrate layer.
In this step, before the electrode is disposed, a protective layer is formed on a surface of the selective emitter junction opposite to the substrate layer, and the protective layer covers the selective emitter junction to ensure that the selective emitter junction is not easily damaged in the subsequent steps.
Specifically, in the step, the surface of the selective emitter junction, which faces away from the substrate layer, is irradiated by ultraviolet ozone, or the surface of the selective emitter junction, which faces away from the substrate layer, is soaked in a hydrogen peroxide solution with a concentration of 5% -20%, so that an oxide layer, i.e., a protective layer, is formed on the surface of the selective emitter junction, so as to protect the selective emitter junction. Specifically, the thickness of the protective layer is usually about 2 nm.
After the step, processes such as film coating on the back surface of the substrate layer, film coating on the front surface of the substrate layer and the like can be performed in sequence, namely, a passivation film and an antireflection film are prepared, so that the conversion efficiency of the finally prepared solar cell is increased. For the above-mentioned coating process, reference may be made to the prior art, and further description is omitted here.
S206: and arranging a first electrode covering the preset area and a second electrode electrically connected with the substrate layer to manufacture the solar cell.
This step is substantially the same as S104 in the above-mentioned inventive embodiment, and in this step, it is generally necessary to perform laser grooving on the back surface of the substrate layer, and then perform screen printing on the back surface and the front surface of the substrate layer, respectively, to prepare a first electrode and a second electrode, where the first electrode needs to cover a preset region irradiated by laser in the selective emitter junction. The specific process in this step may refer to the prior art, and is not described herein again.
Referring to fig. 4, in the solar cell prepared in the embodiment of the present invention, the surface carrier impurity concentration of the region irradiated by the laser is separated from the surface carrier impurity concentration of the region not irradiated by the laser, so that the surface carrier impurity concentration of the region not irradiated by the laser is ensured to be at a higher level, and the surface carrier impurity concentration of the region not irradiated by the laser is further reduced, thereby continuously improving the open-circuit voltage and short-circuit current parameters of the solar cell, and simultaneously contributing to improving the fill factor of the solar cell, so as to finally improve the conversion efficiency of the solar cell.
The solar cell preparation method provided by the embodiment of the invention can realize the independent adjustment of the surface concentration of the laser irradiation area and the non-laser irradiation area of the selective emitter junction surface, and gets rid of the limitation that the surface concentration of the heavily doped area in the selective emitter junction is limited by the surface concentration of the lightly doped area, so that the conversion efficiency of the solar cell can be further improved.
The embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same or similar parts among the embodiments are referred to each other.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
Finally, it should also be noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The method for manufacturing the solar cell provided by the invention is described in detail above. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
Claims (10)
1. A method for manufacturing a solar cell, comprising:
adding doped ions on the preset surface of the substrate layer to form an emitter junction;
irradiating a preset area on the surface of the emitter junction by laser to form a selective emitter junction;
etching the surface of one side, back to the substrate layer, of the selective emitter junction by a preset depth to enable the doping concentration of the exposed preset region to be larger than that of a non-preset region in the surface of the selective emitter junction;
and arranging a first electrode covering the preset area and a second electrode electrically connected with the substrate layer to manufacture the solar cell.
2. The method of claim 1, wherein the adding dopant ions to the predetermined surface of the substrate layer to form the emitter junction comprises:
and performing phosphorus diffusion on the preset surface of the p-type substrate layer to form an emitter junction.
3. The method of claim 2, wherein the performing phosphorus diffusion on the predetermined surface of the p-type substrate layer to form the emitter junction comprises:
performing phosphorus diffusion on the preset surface of the p-type substrate layer to form an emitter junction; the surface doping concentration of the emitter junction is not less than 3 x 1020/cm3。
4. The method of claim 3, wherein the irradiating the predetermined region of the emitter junction surface with the laser to form the selective emitter junction comprises:
irradiating a preset area on the surface of the emitter junction by laser to form a selective emitter junction; the surface doping concentration of the preset region is not less than 2.8 multiplied by 1020/cm3。
5. The method of claim 2, wherein the etching the selective emitter junction to a predetermined depth from the surface of the substrate layer, so that the exposed predetermined region has a doping concentration greater than that of a non-predetermined region in the surface of the selective emitter junction comprises:
etching the surface of one side, back to the substrate layer, of the selective emitter junction by using an acid etching solution to a preset depth so that the doping concentration of the exposed preset area is greater than that of a non-preset area in the surface of the selective emitter junction.
6. The method of claim 5, wherein the acid etching solution comprises hydrofluoric acid at a mass concentration of 0.1-2% and nitric acid at a mass concentration of 30-70%.
7. The method of claim 6, wherein the etching the selective emitter junction to a predetermined depth from a side surface of the substrate layer comprises:
etching the surface of one side, back to the substrate layer, of the selective emitter junction by a preset depth; the preset depth ranges from 20nm to 150nm, inclusive.
8. The method of claim 5, wherein after the etching the selective emitter junction by the acid etching solution to a predetermined depth on a side surface facing away from the substrate layer, the method further comprises:
and removing the porous silicon formed on the surface of the selective emitter junction.
9. The method of claim 8, wherein the removing porous silicon formed on the surface of the selective emitter junction comprises:
removing the porous silicon formed on the surface of the selective emitter junction by using alkali solution; the solute of the alkali solution is sodium hydroxide or potassium hydroxide, and the concentration of the solute in the alkali solution is between 1 per thousand and 5 percent inclusive.
10. The method of claim 1, wherein after the etching the selective emitter junction to a predetermined depth away from the substrate layer side surface, the method further comprises:
and forming a protective layer on the surface of one side, back to the substrate layer, of the selective emitter junction.
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