Back-polished heterojunction solar cell and preparation method thereof

Abstract

The invention provides a back-polished heterojunction solar cell and a preparation method thereof, and the method comprises the following steps: sequentially depositing an intrinsic passivation layer, a first doping layer and a silicon nitride layer on the front surface of a double-sided texturing silicon substrate, and obtaining a first intermediate; carrying out annealing treatment on the first intermediate to obtain a second intermediate; carrying out back polishing cleaning treatment and acid pickling treatment on the second intermediate to obtain a third intermediate; sequentially depositing an intrinsic passivation layer and a second doping layer on the back surface of the third intermediate to obtain a fourth intermediate; and depositing transparent conductive films on the surfaces of the two sides of the fourth intermediate respectively and then preparing electrodes to obtain the back-polished heterojunction solar cell. The method provided by the invention has the technical effects of low production cost and capability of remarkably improving the performance of the solar cell.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic technology, and in particular to a back-mirrored heterojunction solar cell and a preparation method thereof. Background Art

[0002] As global energy demand increases and environmental problems become increasingly serious, solar energy, as a clean and renewable energy source, has received widespread attention. Heterojunction (HJT) solar cells have become a hot topic in the current photovoltaic industry due to their high efficiency and excellent electrical properties. In the process of producing heterojunction solar cells, back polishing technology is a key step, which has an important impact on the reflectivity and passivation effect of the back of the cell.

[0003] In the production process of heterojunction (HJT) solar cells, back polishing technology is generally used to increase the reflectivity of the back of the cell, improve the absorption of long-wave light inside the cell, and improve the passivation and grid line contact effect of the back. The reason is that the polished surface has a smaller specific surface area than the pyramid, and the surface has relatively fewer dangling bonds, which are easier to passivate. When the grid line silver paste contacts the back of the cell, if there is a velvet surface, due to the overhead effect of the pyramid, the contact area will be smaller and the contact resistance will increase; if it is a polished surface, the paste can fully contact with the back of the cell, thereby reducing the contact resistance.

[0004] At present, back polishing technology usually adopts double-sided texturing, double-sided thermal oxidation, chain single-sided pickling, alkali polishing and double-sided deposition processes. Among them, the double-sided thermal oxidation and chain single-sided pickling processes in the above processes require the use of special equipment, and the production cost is relatively high. Summary of the invention

[0005] The present invention provides a method for preparing a back-mirrored heterojunction solar cell, which achieves a technical effect of lower production cost.

[0006] The present invention also provides a solar cell, which achieves a technical effect of excellent electrical performance.

[0007] The present invention provides a method for preparing a back-mirrored heterojunction solar cell, which comprises the following steps:

[0008] Depositing an intrinsic passivation layer, a first doping layer and a silicon nitride layer in sequence on the front side of a double-sided textured silicon substrate to obtain a first intermediate;

[0009] Annealing the first intermediate, wherein the silicon nitride layer is suitable for releasing hydrogen and passivating dangling bonds on the front side of the silicon substrate, to obtain a second intermediate;

[0010] The second intermediate is subjected to back-polishing and acid washing to obtain a third intermediate;

[0011] Depositing an intrinsic passivation layer and a second doping layer in sequence on the back side of the third intermediate to obtain a fourth intermediate;

[0012] After depositing transparent conductive films on both sides of the fourth intermediate, electrodes are prepared to obtain the back-cast heterojunction solar cell;

[0013] The first doping layer is selected from one of a p-type doping layer and an n-type doping layer, and the second doping layer is selected from the other of the p-type doping layer and the n-type doping layer.

[0014] In the method for preparing a back-polished heterojunction solar cell as described above, the annealing treatment is performed at a temperature of 100 to 200° C. and for a time of 5 to 30 minutes.

[0015] In the method for preparing a back-polished heterojunction solar cell as described above, the refractive index of the silicon nitride layer is 1.5-2.0, and the thickness is 20-500 nm.

[0016] In the method for preparing a back-mirrored heterojunction solar cell as described above, the silicon nitride layer is deposited by a PECVD method, and the deposition temperature is less than or equal to 210°C.

[0017] The method for preparing a back-polished heterojunction solar cell as described above, wherein the back-polishing cleaning process includes a pre-cleaning process, a polishing process, and an RCA cleaning process performed in sequence;

[0018] Wherein, the pre-cleaning treatment uses a cleaning solution including an alkaline substance and hydrogen peroxide;

[0019] The polishing process uses a cleaning solution including an alkaline substance and a back-polishing additive;

[0020] The alkaline substance is selected from at least one of potassium hydroxide, sodium hydroxide and tetramethylammonium hydroxide.

[0021] The method for preparing a back-polished heterojunction solar cell as described above, wherein the mass fraction of the alkaline substance in the cleaning solution used for the pre-cleaning treatment is 0.1~10%, and the mass fraction of the hydrogen peroxide is 0.1~10%; preferably, the treatment temperature of the pre-cleaning treatment is 60~80°C, and the treatment time is 2~4min.

[0022] The method for preparing a back-polished heterojunction solar cell as described above, wherein the mass fraction of the alkaline substance in the cleaning solution used for the polishing treatment is 0.1~10%, and the mass fraction of the back-polishing additive is 0.1~10%. Preferably, the treatment temperature of the polishing treatment is 50~85°C, and the treatment time is 2~4min.

[0023] In the method for preparing a back-polished heterojunction solar cell as described above, the acid pickling treatment includes using hydrofluoric acid with a mass fraction of 0.5-10% to remove the silicon nitride layer on the front side of the back-polished cleaning product.

[0024] In the method for preparing a back-polished heterojunction solar cell as described above, the acid pickling treatment has a treatment temperature of 20-35° C. and a treatment time of 0.5-6 min.

[0025] The present invention also provides a back-polished heterojunction solar cell, which is prepared using any of the above-mentioned methods for preparing a back-polished heterojunction solar cell, wherein the back-polished heterojunction solar cell comprises a silicon substrate, wherein the back side of the silicon substrate is a smooth surface, and the front side is a velvet surface;

[0026] An intrinsic passivation layer and a first doping layer are sequentially stacked on the front side of the silicon substrate in a direction away from the silicon substrate; an intrinsic passivation layer and a second doping layer are sequentially stacked on the back side of the silicon substrate in a direction away from the silicon substrate;

[0027] A transparent conductive film and a metal electrode are provided on the side of the first doping layer and the second doping layer away from the silicon substrate.

[0028] The present invention proposes an improved back-polishing process, which adopts a method of preparing an intrinsic passivation layer and a first doping layer on the front side of a silicon substrate, and then using a silicon nitride layer as a protective layer for back-polishing to complete a single-side back-polishing cleaning process, and finally obtain a solar cell. This method can be completed without the use of special equipment, and has the advantages of low production cost and suitability for large-scale production. In addition, in the above process, the hydrogen released by the silicon nitride layer during the annealing process can effectively passivate the dangling bonds on the front side of the silicon substrate, thereby reducing the surface state density of the silicon substrate and improving the open circuit voltage and overall performance of the battery; in addition, the process of removing silicon nitride by pickling can reduce the thickness of the n-type doping layer to a certain extent, reduce light absorption, and increase the current density of the solar cell. Therefore, the use of the process provided by the present invention can also significantly improve the electrical performance of solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced one by one below. Obviously, the drawings in the following description are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0030] Figure 1 A flow chart of a method for preparing a back-mirrored heterojunction solar cell provided by the present invention;

[0031] Figure 2is a structural diagram of the first intermediate in an embodiment of the present invention;

[0032] Figure 3 is a structural diagram of the third intermediate in an embodiment of the present invention;

[0033] Figure 4 is a structural diagram of the fourth intermediate in an embodiment of the present invention;

[0034] Figure 5 A structural diagram of a back-mirrored heterojunction solar cell provided in an embodiment of the present invention.

[0035] Description of reference numerals:

[0036] 10-silicon substrate;

[0037] 20-intrinsic passivation layer;

[0038] 30-n-type doping layer;

[0039] 40-p-type doped layer;

[0040] 50-silicon nitride layer;

[0041] 60-transparent conductive film;

[0042] 70-metal electrode;

[0043] 80-Oxide layer. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] The first aspect of the present invention provides a method for preparing a back-mirrored heterojunction solar cell, referring to Figure 1 , the method comprises the following steps:

[0046] S10: depositing an intrinsic passivation layer, a first doping layer and a silicon nitride layer in sequence on the front side of the double-sided textured silicon substrate to obtain a first intermediate;

[0047] S20: performing annealing treatment on the first intermediate, wherein the silicon nitride layer is suitable for releasing hydrogen and then passivating the dangling bonds on the front side of the silicon substrate, to obtain a second intermediate;

[0048] S30: performing back-polishing and pickling treatments on the second intermediate to obtain a third intermediate;

[0049] S40: depositing an intrinsic passivation layer and a second doping layer in sequence on the back side of the third intermediate to obtain a fourth intermediate;

[0050] S50: depositing transparent conductive films on both sides of the fourth intermediate to prepare electrodes, thereby obtaining a back-mirrored heterojunction solar cell;

[0051] The first doped layer is selected from one of a p-type doped layer and an n-type doped layer, and the second doped layer is selected from the other of the p-type doped layer and the n-type doped layer, that is, when the first doped layer is an n-type doped layer, the second doped layer is a p-type doped layer. The following description is based on the case where the first doped layer is an n-type doped layer and the second doped layer is a p-type doped layer.

[0052] The following, combined Figures 2 to 5 The above solar energy preparation method is described in detail.

[0053] refer to Figure 2 The preparation method of the back-polished heterojunction solar cell provided by the present invention first starts with a double-sided textured silicon substrate 10. The texture process forms a microscopic texture structure on the silicon substrate 10 to reduce surface reflection and enhance light absorption efficiency. The double-sided textured silicon substrate 10 used in the present invention can be prepared using conventional methods. For example, an alkaline solution (such as potassium hydroxide or sodium hydroxide) is used to form a pyramid structure on the surface of the silicon substrate 10, and a surface roughness suitable for subsequent processes can be obtained by controlling the temperature and time. On this basis, an intrinsic passivation layer 20 and an n-type doping layer 30 (first doping layer) are sequentially deposited on the front side of the silicon substrate 10. The intrinsic passivation layer 20 is usually made of undoped amorphous silicon (a-Si), and is deposited using plasma enhanced chemical vapor deposition (PECVD), which can effectively reduce the recombination of surface carriers and increase the lifetime of photogenerated carriers. The n-type doping layer 30 is composed of a silicon layer doped with phosphorus, which is mainly used to improve electronic conductivity and contribute to more efficient carrier collection.

[0054] It is worth noting that, since the double-sided textured silicon substrate 10 has two surfaces, for the convenience of distinction, in the above steps, the surface on which the intrinsic passivation layer 20, the n-type doping layer 30 and the silicon nitride layer 50 are deposited is called the front surface, and the other surface is called the back surface. The front surface and back surface determined in the above steps are applicable in the remaining steps and do not change.

[0055] In order to further improve the passivation effect, the preparation method of the back-polished heterojunction solar cell provided by the present invention uses a plasma enhanced chemical vapor deposition (PECVD) process to deposit a layer of silicon nitride (SiNx) as a protective layer on the n-type doping layer 30. The silicon nitride layer 50 not only contributes to the passivation effect, but also can serve as a protective layer on the front side in the subsequent back-polishing and annealing treatment to prevent the introduction of impurities. After the deposition of the silicon nitride layer 50 is completed, a first intermediate is obtained, which includes a silicon substrate 10 that has been subjected to a double-sided texturing treatment, and an intrinsic passivation layer 20, an n-type doping layer 30 and a silicon nitride layer 50 are sequentially deposited on the front side of the silicon substrate 10. Subsequently, the first intermediate is subjected to an annealing treatment.

[0056] Annealing treatment refers to heating the first intermediate at a specific temperature for a specific time. The present invention does not limit the specific treatment conditions of the annealing treatment, and common treatment conditions in the field can be used. The second intermediate is obtained after the annealing treatment is completed.

[0057] refer to Figure 3 After the annealing treatment is completed, the second intermediate is subjected to back polishing and pickling treatment in sequence. The back polishing and pickling treatment can remove the pyramid morphology on the back of the second intermediate, and the pickling treatment can remove the silicon nitride layer 50 on the front of the second intermediate, so as to obtain Figure 2 The third intermediate is shown. Compared with the first intermediate, the pyramid structure on the back of the silicon substrate 10 in the third intermediate is absorbed and presents a smooth morphology; in addition, the silicon nitride layer 50 included in the first intermediate is also washed away.

[0058] The present invention does not limit the specific treatment method of the back-polishing cleaning treatment, and common treatment methods in the art can be used, for example, using an aqueous solution containing an alkaline substance (such as at least one of potassium hydroxide, sodium hydroxide, and tetramethylammonium hydroxide) to contact the second intermediate to meet the requirement of removing the pyramid morphology. The present invention also does not limit the specific treatment method of the pickling treatment, and an aqueous solution containing an acidic substance (such as hydrogen fluoride) can be used to contact the second intermediate to remove the silicon nitride layer 50 on the front side of the second intermediate to complete the back-polishing cleaning treatment.

[0059] refer to Figure 4 After the back cleaning and pickling treatment, an intrinsic passivation layer 20 and a p-type doping layer 40 are sequentially deposited on the back of the third intermediate to form a heterojunction structure on the back, and the following is obtained: Figure 3 Compared with the third intermediate, the fourth intermediate sequentially deposits an intrinsic passivation layer 20 and a p-type doping layer 40 on the back of the silicon substrate 10. The p-type doping layer 40 is usually realized by a boron-doped silicon layer, and together with the n-type doping layer 30 on the front of the silicon substrate 10, forms a pn junction.

[0060] refer to Figure 5In the fourth intermediate, a transparent conductive film 60 (such as indium tin oxide ITO or zinc aluminum oxide AZO) is deposited on the front and back sides respectively to ensure good light transmittance and conductivity of the battery. The metal electrodes 70 on the front and back are prepared by screen printing or electroplating technology, and finally a back-thrown heterojunction solar cell is obtained.

[0061] The inventors found that the solar cell prepared by the above method has good performance. The reason is that, firstly, since the silicon nitride layer 50 is rich in hydrogen, during the annealing process, the hydrogen atoms in the silicon nitride layer 50 diffuse through the n-type doping layer 30 and the intrinsic passivation layer 20 to the interface between the intrinsic passivation layer 20 and silicon, effectively passivating the dangling bonds located there, thereby significantly reducing the surface state density and improving the passivation effect of the interface; secondly, since the n-type doping layer 30 plays a passivation role, but the n-type doping layer 30 has a light absorption effect, which affects the current of the solar cell. In the process of removing silicon nitride by the etching method in the solar energy preparation method provided by the present invention, a weak etching effect is played on the n-type doping layer 30, which reduces the light absorption of the n-type doping layer 30, thereby improving the current of the solar cell. In the above process, since the enhanced passivation effect of hydrogen injection into silicon nitride is much greater than the passivation effect lost by etching the n-type doping layer 30, generally speaking, the solar cell prepared by the above method has good performance.

[0062] In addition, after the intrinsic passivation layer 20 and the n-type doping layer 30 are prepared on the front side of the silicon substrate 10, the silicon nitride layer 50 is used as a protective layer for back polishing to complete the single-side back polishing cleaning process, and finally a solar cell is obtained. This method can be completed without the use of special equipment, has the advantages of low production cost and is suitable for large-scale production.

[0063] In order to make the solar cell have better performance, in one embodiment, the annealing treatment temperature can be controlled to be 100-200°C, and the treatment time is 5-30min. Under the temperature and time conditions, the hydrogen atoms in the silicon nitride layer 50 obtain sufficient diffusion ability due to thermal energy and gradually migrate to the interface between the n-type doped layer 30 and the silicon substrate 10. Hydrogen atoms can passivate the dangling bonds on the silicon surface, reduce the interface state, and reduce the recombination probability of carriers, thereby achieving the passivation effect, and the solar cell obtained has better performance. At the same time, controlling the temperature below 200°C can avoid the generation of lattice defects or surface oxidation caused by excessive temperature, thereby maintaining the stability of the structure and performance of the battery. At the same time, controlling the temperature within the range of 100-200°C can avoid changes or contamination of the surface structure of the silicon substrate 10 caused by high temperature, thereby maintaining the stability and cleanliness of the device surface. This temperature range helps to achieve effective diffusion of hydrogen atoms without introducing new defects or damage.

[0064] In one embodiment, the refractive index of the silicon nitride layer 50 can be controlled to be 1.5-2.0, and the thickness can be 20-500nm. The refractive index of silicon nitride increases with the increase of its silicon content. When the refractive index of silicon nitride is 1.5-2.0, silicon nitride has a lower content of silicon, which can make it have excellent alkali resistance, so that it will not be corroded by alkaline substances in the subsequent back-polishing cleaning process, and play a role in protecting the structure covered by the silicon nitride layer 50. Further, the thickness of the silicon nitride layer 50 of 20-500nm provides sufficient structural integrity and chemical stability for subsequent processes, which can effectively passivate the surface and prevent the direct erosion of the silicon substrate 10 by the alkali washing and acid washing processes, so that the battery has higher reliability in subsequent processing and use.

[0065] In one embodiment, the silicon nitride layer 50 can be deposited conveniently and quickly using a PECVD method. To further improve the deposition temperature of the silicon nitride layer 50, the deposition temperature can be controlled to be less than or equal to 210°C. Depositing the silicon nitride layer 50 at a temperature below 210°C can make the hydrogen in the silicon nitride layer 50 more stably retained, reduce the escape of hydrogen atoms during the deposition process, and provide a sufficient source of hydrogen for subsequent annealing. Sufficient hydrogen atoms can diffuse into the silicon substrate 10 and passivate the dangling bonds in the subsequent annealing process, further improving the passivation effect.

[0066] In one embodiment, the back-polishing cleaning process includes a pre-cleaning process, a polishing process, and an RCA cleaning process performed sequentially;

[0067] The pre-cleaning treatment uses a cleaning solution including an alkaline substance and hydrogen peroxide;

[0068] Polishing uses a cleaning solution that includes an alkaline substance and a back-polishing additive;

[0069] The alkaline substance is selected from at least one of potassium hydroxide, sodium hydroxide and tetramethylammonium hydroxide.

[0070] Among them, the purpose of pre-cleaning is to remove organic pollutants and oxide layers on the back of the silicon substrate 10 to form a clean surface. This step is completed using a cleaning solution containing alkaline substances and hydrogen peroxide. Commonly used alkaline substances include at least one of potassium hydroxide (KOH), sodium hydroxide (NaOH) and tetramethylammonium hydroxide (TMAH). By controlling the concentration and temperature of the cleaning solution, effective removal of surface impurities can be achieved, thereby laying the foundation for subsequent polishing treatment. In specific implementation, the ratio of the alkaline component and hydrogen peroxide in the cleaning solution can be adjusted according to actual needs to ensure the best cleaning effect.

[0071] The purpose of the polishing treatment is to further improve the flatness and reflectivity of the back side of the silicon substrate 10 to optimize the optical properties of the back side. This step uses a cleaning solution containing an alkaline substance and a back-polishing additive to make the silicon surface smoother, thereby reducing light scattering and loss. The selection of the alkaline substance is consistent with the pre-cleaning treatment, and at least one of potassium hydroxide, sodium hydroxide or tetramethylammonium hydroxide can be selected, and the type and concentration of the back-polishing additive can be adjusted according to the actual process conditions. The polishing treatment controls the combination of alkaline substances and additives to achieve a good flattening effect on the back side, reduce surface roughness, and thus improve the photoelectric conversion efficiency.

[0072] The present invention does not limit the specific ingredients of the back-throwing additive, and the back-throwing additive commonly used in the art can be used. In one embodiment, the back-throwing additive includes sodium benzoate and a surfactant.

[0073] RCA cleaning is a key step to remove the metal ions and tiny particles remaining on the back of the silicon substrate 10 to further purify the back surface. RCA cleaning usually includes two steps of RCA1 and RCA2, using alkaline solution and acidic solution to treat the back, respectively, to remove residual organic matter and metal impurities. In the RCA1 step, the cleaning solution is composed of ammonia water or alkali (for example, at least one of potassium hydroxide, sodium hydroxide, and tetramethylammonium hydroxide) and hydrogen peroxide to remove organic matter and particles; in the RCA2 step, a mixed solution of hydrochloric acid and hydrogen peroxide is used to remove metal impurities. The conditions of RCA cleaning (such as solution concentration, temperature and time) can be optimized according to actual needs to ensure the purity of the surface of the silicon substrate 10 and provide an ideal interface for subsequent deposition processes.

[0074] Through the above-mentioned back polishing and cleaning treatment, the back side of the silicon substrate 10 reaches a high level of cleanliness and smoothness, laying a good foundation for subsequent production. This treatment method not only ensures high reflectivity and low surface recombination rate on the back side of the battery, but also effectively improves the photoelectric conversion efficiency and long-term stability of the battery.

[0075] In a specific embodiment, the back-polishing cleaning process includes the following steps: first, pre-cleaning is performed in a mixed solution of 0.1~10% alkaline substance and 0.1~10% hydrogen peroxide, the alkaline substance is preferably at least one of potassium hydroxide, sodium hydroxide, and tetramethylammonium hydroxide, the temperature is 60~80°C, and the cleaning time is 2~4min; then, the back side is polished in a mixed solution of 0.01~10% alkaline substance and 0.01~10% back-polishing additive, the alkaline substance is preferably at least one of potassium hydroxide, sodium hydroxide, and tetramethylammonium hydroxide, the temperature is 50~85°C, and the reaction time is 60~300s. Finally, RCA cleaning including RCA1 and RCA2 is performed. First, RCA1 cleaning is performed in a mixed solution of 0.1~10% alkaline substance and 0.1~10% hydrogen peroxide, at least one of potassium hydroxide, sodium hydroxide, and tetramethylammonium hydroxide, at a temperature of 60~80°C, and a cleaning time of 2~4 minutes. Then, RCA2 cleaning is performed using a mixed solution of 0.1~10% hydrochloric acid and 0.1~10% hydrogen peroxide, at a temperature of 60~80°C, and a cleaning time of 2~4 minutes.

[0076] In order to achieve better results in the pre-cleaning treatment, in one embodiment, the mass fraction of the alkaline substance in the cleaning solution used in the pre-cleaning treatment is 0.1-10%, and the mass fraction of hydrogen peroxide is 0.1-10%. Alkaline substances (such as potassium hydroxide, sodium hydroxide or tetramethylammonium hydroxide) have good dissolution and removal effects on organic pollutants in the concentration range of 0.1-10%, and can slightly etch the oxide layer 80, thereby cleaning the surface. However, due to the moderate concentration, the alkaline substance will not cause excessive corrosion to the silicon substrate 10, and can effectively control the surface roughness and integrity of the silicon substrate 10; hydrogen peroxide mainly plays the role of an oxidant in the cleaning solution, and achieves a cleaning effect by oxidizing and decomposing surface pollutants. Its appropriate use can promote the decomposition of organic matter, but controlling it within the concentration range of 0.1-10% avoids excessive oxidation of the silicon substrate 10 by hydrogen peroxide, making the surface cleaning more gentle.

[0077] Furthermore, the treatment temperature of the pre-cleaning treatment can be controlled to be 60~80℃, and the treatment time can be 2~4min. Appropriate treatment temperature and treatment time can achieve the technical effect of efficient cleaning and protection of the substrate surface. Within this temperature range, the reaction rate of the alkaline cleaning solution and hydrogen peroxide is moderate, which can accelerate the decomposition and removal of organic matter and the oxide layer 80, and significantly improve the cleaning efficiency. Thorough cleaning can be achieved in a short time, avoiding damage to the substrate surface caused by too long treatment. At the same time, this temperature control setting effectively reduces the deep etching of the silicon substrate 10, maintains the structural integrity of its surface, reduces the surface recombination rate, ensures that the cleaned silicon substrate 10 is smooth and pure, and provides a high-quality interface for subsequent polishing and passivation processes. The balance between temperature and time not only improves the cleaning effect, but also provides a good foundation for the photoelectric performance of the battery.

[0078] In order to achieve better results in the polishing process, in one embodiment, the mass fraction of the alkaline substance in the cleaning solution used for the polishing process can also be controlled to be 0.1~10%, and the mass fraction of the back-polishing additive can be 0.1~10%. The appropriate cleaning solution concentration can achieve a good surface flatness effect and optimized light reflection performance. Alkaline substances (such as potassium hydroxide, sodium hydroxide or tetramethylammonium hydroxide) can moderately etch the back of the silicon substrate 10 within this concentration range to remove tiny surface defects and impurities without causing excessive corrosion, thereby improving the surface flatness of the silicon substrate 10 in a relatively short time. After adding a back-polishing additive with a mass fraction of 0.1~10%, the corrosion rate can be further controlled, making the polishing process more uniform, ensuring that the treated substrate surface is smoother, helping to reduce surface light scattering, and improving the back reflection effect.

[0079] In the above process, the alkaline substance provides the chemical driving force for etching, and the back-polishing additive (such as isopropyl alcohol, EDTA) can change the viscosity of the solution or adjust the uniformity of etching, so that the surface of the silicon substrate 10 can be evenly polished in mild corrosion. The alkaline substance and additives in this concentration range work together to help effectively control the surface roughness and provide an interface with high reflectivity and low recombination rate on the back of the battery, thereby improving the photoelectric conversion efficiency and overall performance of the battery.

[0080] In one embodiment, the processing temperature of the polishing process can also be controlled to be 50~85°C, and the processing time is 2~4min. Appropriate processing conditions can achieve the technical effects of efficient flat polishing and surface protection of the silicon substrate 10. Within this temperature range, the chemical reaction rate of the alkaline substance and the back-polishing additive in the cleaning solution is moderate, which can effectively remove the tiny defects and irregular structures on the surface of the silicon substrate 10, making the surface smoother and reducing light scattering. Higher temperatures (close to 85°C) help to increase the etching rate, thereby completing polishing in a short time, while ensuring the gentle effect of the solution on the surface of the silicon substrate 10, avoiding excessive corrosion and damage to the surface structure.

[0081] Under this temperature and time condition, the polishing process can remove particles, slight oxide layer 80 and other impurities on the silicon surface with high efficiency, making the surface smooth. This temperature control range ensures the activity of the cleaning solution, but does not cause significant damage to the silicon substrate 10, maintaining the integrity and uniformity of the surface structure. In addition, the shorter treatment time (2-4 minutes) can avoid excessive corrosion caused by long-term treatment, ensure that the polishing process is limited to surface fine-tuning, and provide a high-quality flat interface for subsequent passivation processes. This optimized polishing effect ultimately improves the reflectivity and photoelectric conversion efficiency of solar cells, helping to improve overall performance.

[0082] The pickling treatment includes using hydrofluoric acid with a mass fraction of 0.5-10% to remove the silicon nitride layer 50 on the front and the oxide layer 80 on the back of the product obtained by the back-polishing cleaning treatment, so as to facilitate the remaining steps. Among them, the oxide layer 80 is generated in the RCA2 cleaning process. Specifically, the hydrogen peroxide used in the RCA2 cleaning process contacts the silicon substrate 10 to generate the oxide layer 80. In one embodiment, the treatment temperature of the pickling treatment can be controlled to be 20-35°C, and the treatment time is 0.5-6min. The above-mentioned treatment conditions can make the pickling treatment remove the silicon nitride layer 50 and the oxide layer 80 without damaging the silicon substrate 10 and other deposited layers, so that the obtained solar cell has better electrical performance.

[0083] The second aspect of the present invention provides a solar cell, which is prepared using any one of the methods for preparing solar cells provided in the first aspect of the present invention. The back-polished heterojunction solar cell comprises a silicon substrate 10, the back side of the silicon substrate 10 is a smooth surface, and the front side is a velvet surface. The front side of the silicon substrate 10 is stacked with an intrinsic passivation layer 20 and a first doping layer in sequence in a direction away from the silicon substrate 10; the back side of the silicon substrate 10 is stacked with an intrinsic passivation layer 20 and a second doping layer in sequence in a direction away from the silicon substrate 10;

[0084] A transparent conductive film 60 and a metal electrode 70 are disposed on the side of the first doped layer and the second doped layer facing away from the silicon substrate 10 .

[0085] The solar cell provided by the present invention has a technical effect with relatively excellent performance. Specifically, the solar cell provided by the present invention has the characteristics of relatively high Jsc (short-circuit current density), Uoc (open-circuit voltage), FF (fill factor), and Eta (photoelectric conversion efficiency).

[0086] Hereinafter, the method for preparing the solar cell provided by the present invention will be described in detail through specific embodiments.

[0087] Example 1

[0088] This embodiment uses the following method to prepare a back-cast heterojunction solar cell:

[0089] 1) An intrinsic passivation layer 20, an n-type doping layer 30 and a silicon nitride layer 50 are sequentially deposited on the front side of a double-sided textured silicon substrate 10 to obtain a first intermediate.

[0090] Wherein, the thickness of the intrinsic passivation layer 20 is 6 nm;

[0091] The thickness of the n-type doped layer 30 is 18 nm;

[0092] The refractive index of the silicon nitride layer 50 is 1.7;

[0093] The thickness of the silicon nitride layer 50 is 150 nm;

[0094] The deposition temperature of the silicon nitride layer 50 is 200° C.;

[0095] 2) annealing the first intermediate to obtain a second intermediate;

[0096] The annealing treatment time is 20 min and the treatment temperature is 150°C;

[0097] 3) performing back-throw cleaning treatment on the second intermediate to obtain a third intermediate;

[0098] The back-polishing cleaning process includes a pre-cleaning process, a polishing process, and an RCA cleaning process performed in sequence;

[0099] The alkaline substance in the cleaning solution used in the pre-cleaning treatment is potassium hydroxide with a mass fraction of 5%, and the mass fraction of hydrogen peroxide is 5%;

[0100] The treatment temperature of the pre-cleaning treatment is 70°C and the treatment time is 3min;

[0101] The alkaline substance in the cleaning liquid used for polishing is potassium hydroxide, with a mass fraction of 5%, and the back-polishing additive is 5, with a mass fraction of 3%;

[0102] The treatment temperature of the polishing treatment is 70°C and the treatment time is 2 min;

[0103] The RCA cleaning process includes RCA1 and RCA2 cleaning in sequence;

[0104] RCA1 cleaning treatment is performed using a cleaning solution including 5% alkaline substance and 5% hydrogen peroxide, the alkaline substance is potassium hydroxide, the temperature is 65°C, and the cleaning time is 4 minutes; then RCA2 cleaning is performed using a mixed solution of 5% hydrochloric acid and 5% hydrogen peroxide, the temperature is 65°C, and the cleaning time is 4 minutes; finally, 5% hydrofluoric acid is used to remove the silicon nitride layer 50 on the front and the oxide layer 80 on the back, the etching temperature is 25°C, and the etching time is 2 minutes.

[0105] 4) depositing an intrinsic passivation layer 20 and a p-type doping layer 40 in sequence on the back side of the third intermediate to obtain a fourth intermediate;

[0106] Wherein, the thickness of the intrinsic passivation layer 20 is 6 nm;

[0107] The thickness of the p-type doped layer 40 is 20 nm;

[0108] After transparent conductive films 60 are deposited on both side surfaces of the fourth intermediate, metal electrodes 70 are prepared to obtain a back-mirrored heterojunction solar cell A.

[0109] Comparative Example 1

[0110] 1) The double-sided textured silicon substrate 10 is oxidized on both sides by a diffusion furnace to obtain a silicon substrate 10 with a dense oxide layer 80 thick on the front and back sides;

[0111] 2) removing the oxide layer 80 on one side by a chain pickling machine, the acid being 5% HF, to obtain a first intermediate;

[0112] 3) performing back-throwing cleaning on the first intermediate to obtain a second intermediate;

[0113] The back-polishing cleaning process includes a pre-cleaning process, a polishing process, and an RCA cleaning process performed in sequence;

[0114] The alkaline substance in the cleaning solution used in the pre-cleaning treatment is potassium hydroxide with a mass fraction of 5%, and the mass fraction of hydrogen peroxide is 5%;

[0115] The treatment temperature of the pre-cleaning treatment is 70°C and the treatment time is 3min;

[0116] The alkaline substance in the cleaning liquid used for polishing is potassium hydroxide, with a mass fraction of 5%, and the back-polishing additive is 5, with a mass fraction of 3%;

[0117] The treatment temperature of the polishing treatment is 70°C and the treatment time is 2 min;

[0118] The RCA cleaning process includes RCA1 and RCA2 cleaning in sequence;

[0119] RCA1 cleaning treatment is performed using a cleaning solution including 5% alkaline substance and 5% hydrogen peroxide, the alkaline substance is potassium hydroxide, the temperature is 65°C, and the cleaning time is 4 minutes; then RCA2 cleaning is performed using a mixed solution of 5% hydrochloric acid and 5% hydrogen peroxide, the temperature is 65°C, and the cleaning time is 4 minutes; finally, 5% hydrofluoric acid is used to remove the oxide layer 80 on the front and back sides, the etching temperature is 25°C, and the etching time is 2 minutes.

[0120] 4) depositing an intrinsic passivation layer 20 on the front and back sides of the second intermediate, and then depositing an N layer on the front side and a p-type doping layer 40 on the back side to obtain a third intermediate;

[0121] The thickness of the intrinsic passivation layer 20 is 6 nm; the thickness of the n-type doping layer 30 is 18 nm.

[0122] The thickness of the p-type doped layer 40 is 20 nm;

[0123] After transparent conductive films 60 are deposited on both side surfaces of the fourth intermediate, metal electrodes 70 are prepared to obtain a back-mirrored heterojunction solar cell B.

[0124] Test example

[0125] The electrical performance of the back-thrown heterojunction solar cell A and the back-thrown heterojunction solar cell B were tested using a halm IV tester. The results are shown in Table 1.

[0126] Table 1 Electrical performance test data

[0127]

[0128] It can be seen from the data in Table 1 that compared with battery B, the short-circuit current density of battery A increased by 0.086 mA / cm², the open-circuit voltage increased by 0.0017 V, the fill factor increased by 0.27%, and the photoelectric conversion efficiency increased by 0.19%. This shows that the preparation method provided by the present invention can effectively improve the short-circuit current density, open-circuit voltage, fill factor and photoelectric conversion efficiency of the back-thrown heterojunction solar cell.

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a back-thrown heterojunction solar cell, characterized in that: The steps include: Depositing an intrinsic passivation layer, a first doping layer and a silicon nitride layer in sequence on the front side of a double-sided textured silicon substrate to obtain a first intermediate; Annealing the first intermediate, wherein the silicon nitride layer is suitable for releasing hydrogen and passivating dangling bonds on the front side of the silicon substrate, to obtain a second intermediate; The second intermediate is subjected to back-polishing and acid washing to obtain a third intermediate; Depositing an intrinsic passivation layer and a second doping layer in sequence on the back side of the third intermediate to obtain a fourth intermediate; After depositing transparent conductive films on both sides of the fourth intermediate, electrodes are prepared to obtain the back-cast heterojunction solar cell; The first doping layer is selected from one of a p-type doping layer and an n-type doping layer, and the second doping layer is selected from the other of the p-type doping layer and the n-type doping layer.

2. The preparation method according to claim 1, characterized in that: The annealing treatment has a treatment temperature of 100-200° C. and a treatment time of 5-30 min.

3. The preparation method according to claim 1, characterized in that: The refractive index of the silicon nitride layer is 1.5-2.0, and the thickness is 20-500 nm.

4. The preparation method according to claim 1, characterized in that: The silicon nitride layer is deposited by a PECVD method, and the deposition temperature is less than or equal to 210°C.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The back-polishing cleaning process includes a pre-cleaning process, a polishing process, and an RCA cleaning process performed in sequence; Wherein, the pre-cleaning treatment uses a cleaning solution including an alkaline substance and hydrogen peroxide; The polishing process uses a cleaning solution including an alkaline substance and a back-polishing additive; The alkaline substance is selected from at least one of potassium hydroxide, sodium hydroxide and tetramethylammonium hydroxide.

6. The preparation method according to claim 5, characterized in that: The mass fraction of alkaline substances in the cleaning solution used in the pre-cleaning treatment is 0.1-10%, and the mass fraction of hydrogen peroxide is 0.1-10%; The treatment temperature of the pre-cleaning treatment is 60-80° C., and the treatment time is 2-4 minutes.

7. The preparation method according to claim 5, characterized in that: The mass fraction of alkaline substances in the cleaning liquid used for the polishing process is 0.1-10%, and the mass fraction of the back-polishing additive is 0.1-10%; The polishing treatment is performed at a temperature of 50-85° C. and for a time of 2-4 minutes.

8. The preparation method according to claim 5, characterized in that: The pickling treatment includes using hydrofluoric acid with a mass fraction of 0.5-10% to remove the silicon nitride layer on the front side of the back-polishing cleaning product.

9. The preparation method according to claim 8, characterized in that: The pickling treatment has a treatment temperature of 20-35° C. and a treatment time of 0.5-6 min.

10. A rear-view heterojunction solar cell, characterized in that: The back-polished heterojunction solar cell is prepared by the method according to any one of claims 1 to 9, wherein the back-polished heterojunction solar cell comprises a silicon substrate, the back side of the silicon substrate is a smooth surface, and the front side is a velvet surface; An intrinsic passivation layer and a first doping layer are sequentially stacked on the front side of the silicon substrate in a direction away from the silicon substrate; an intrinsic passivation layer and a second doping layer are sequentially stacked on the back side of the silicon substrate in a direction away from the silicon substrate; A transparent conductive film and a metal electrode are provided on the side of the first doping layer and the second doping layer away from the silicon substrate.

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