Tin paste, preparation method thereof and solar cell

Abstract

The invention provides tin paste, a preparation method of the tin paste and a solar cell. The tin paste is prepared from, by mass, 80-95 parts of tin powder, 1-10 parts of organic carriers and 0.5-5 parts of glass powder. The organic carrier comprises a combination of an organic solvent and an additive, and the additive comprises any one of a thickening agent, a thixotropic agent and a surfactant or a combination of at least two of the thickening agent, the thixotropic agent and the surfactant. The tin paste is low in cost and excellent in conductivity, has excellent eutecticevaporability with a silver layer, and can form a compact and reliable conductive path on the surface of a battery. The tin paste is used for preparing a grid line electrode of a solar cell, the use amount of silver paste is effectively reduced, and therefore the production cost of the solar cell is reduced; meanwhile, a conductive path with excellent performance is formed in a tin layer made of the tin paste, and the tin layer is in good contact with a silver layer, so that the solar cell keeps excellent photoelectric conversion efficiency, and the tin paste has wide industrial application prospects.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic technology, specifically relating to a tin paste and its preparation method, and a solar cell. Background Technology

[0002] Solar energy, as a sustainable green energy source capable of replacing fossil fuels, has experienced rapid development in recent years. Due to the abundant reserves of silicon in the Earth's crust and its excellent electrical and mechanical properties, crystalline silicon solar cells are the mainstream product in the solar photovoltaic field. Improving the photoelectric performance of silicon solar cells and reducing their production costs are key research priorities in the future development of photovoltaic technology.

[0003] The fabrication process of crystalline silicon solar cells mainly includes texturing, diffusion to form PN junctions, etching, front-side coating, screen printing, and sintering. Among these processes, texturing forms a textured surface structure on the front side of the silicon wafer, increasing the absorption area of ​​sunlight and reducing the reflectivity of sunlight. Front-side coating forms a passivation layer with anti-reflection effect on the front side of the silicon wafer, and screen printing and sintering form the back electrode.

[0004] Currently, in the manufacturing process of crystalline silicon solar cells, apart from low-temperature structures such as HJT (Heterojunction with Intrinsic Thin-film) cells, most use silver paste screen printing to fabricate the electrode grid lines on the cell surface. For example, TOPCon (Tunnel Oxide Passivated Contact) cells and BC (back contact) cells require high-temperature (≥300℃) sintering. Silver paste accounts for approximately 33%-35% of the cost of non-silicon materials in solar cells, making it the largest non-silicon material in solar cells.

[0005] Silver paste's main components include silver powder, glass powder, and organic carriers, with silver powder accounting for up to 80 wt%. The large amount of expensive metallic silver contributes to the high cost of silver paste. Furthermore, the rapid development of N-type cells has increased the demand for silver paste, further raising the manufacturing cost of crystalline silicon solar cells. Silver paste production relies on specific silver ore resources, and the instability of these resources can lead to fluctuations in raw material supply, affecting the stability of the industrial chain and even creating a resource bottleneck for the further large-scale application of photovoltaic green energy. Therefore, how to reduce silver paste usage, lower cell costs, and achieve excellent photoelectric performance are urgent problems to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a tin paste, its preparation method, and a solar cell. Through the design and compounding of its components, the tin paste is not only inexpensive but also exhibits excellent eutectic properties with the silver layer, enabling the formation of a dense and reliable conductive path on the surface of the solar cell. Using this tin paste to prepare solar cells effectively reduces the amount of silver paste required, lowers costs, and imparts superior photoelectric performance to the solar cells.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a solder paste comprising, by weight, the following components:

[0009] 80-95 parts of tin powder

[0010] 1-10 parts of organic carrier

[0011] 0.5-5 parts glass powder;

[0012] The organic carrier comprises a combination of organic solvents and additives, wherein the additives include any one or a combination of at least two of thickeners, thixotropic agents, and surfactants.

[0013] This invention, through the design and specific dosage formulation of tin powder, organic carrier, and glass powder, achieves a low-cost tin paste with excellent conductivity and superior eutectic properties with the silver layer, enabling the formation of a dense and reliable conductive path on the cell surface. The tin paste is used to fabricate the grid electrodes of the solar cell, effectively reducing the amount of silver paste required and thus significantly lowering the production cost of the solar cell. Simultaneously, the tin layer formed by the tin paste creates a high-performance conductive path, resulting in excellent line resistance and contact resistance, thus maintaining the solar cell's excellent photoelectric conversion efficiency.

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0015] In the tin paste provided by the present invention, the mass fraction of the tin powder is 80-95 parts, for example, it can be 82 parts, 84 parts, 85 parts, 86 parts, 88 parts, 90 parts, 92 parts or 94 parts, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0016] The organic carrier is in the range of 1-10 parts by mass, for example, 2, 3, 4, 5, 6, 7, 8 or 9 parts, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific values ​​included in the range.

[0017] The glass powder is 0.5-5 parts by weight, for example, it can be 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts or 4.5 parts, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0018] Preferably, the tin powder comprises spherical tin powder.

[0019] It should be noted that the tin powder is made of pure tin or a tin alloy, preferably pure tin.

[0020] Preferably, the tin powder comprises a combination of micron-sized tin powder and nano-sized tin powder.

[0021] Preferably, the particle size of the micron-sized tin powder is 1-50 μm, for example, it can be 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 42 μm, 45 μm or 48 μm, as well as specific particle sizes between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific particle sizes included in the range, and 5-15 μm is further preferred.

[0022] Preferably, the particle size of the nano-tin powder is 10-1000nm, for example, it can be 50nm, 100nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm or 900nm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, and 200-800nm ​​is further preferred.

[0023] In this invention, both the micron-sized tin powder and the nano-sized tin powder can be purchased commercially.

[0024] Preferably, the mass percentage of nano-tin powder in the tin powder is 5-20%, for example, it can be 6%, 8%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 18% or 19%, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0025] As a preferred embodiment of the present invention, the tin powder includes nano-tin powder, the mass content of which is preferably 5-20%. The nano-tin powder can effectively fill the micropores and defects in the tin paste, and when combined with other components, it can improve the conductivity of the tin paste, enable the formation of better conductive paths in the tin layer, and increase the contact between the tin layer and the silver layer, thereby further optimizing the photoelectric performance of the solar cell.

[0026] Preferably, the organic carrier comprises the following components by weight percentage:

[0027]

[0028] Specifically, the organic solvent in the organic carrier has a mass percentage content of 40-95%, for example, it can be 45%, 50%, 55%, 60%, 65%, 68%, 70%, 72%, 75%, 80%, 85%, 90% or 92%, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0029] The mass percentage of the thickener in the organic carrier is 1-15%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12% or 14%, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0030] The thixotropic agent in the organic carrier has a mass percentage content of 0.1-30%, for example, it can be 0.5%, 1%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25% or 28%, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0031] The surfactant in the organic carrier has a mass percentage content of 0.1-15%, for example, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12% or 14%, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0032] Preferably, the organic solvent includes any one or a combination of at least two of terpineol, tributyl citrate, and butyl carbitol.

[0033] Preferably, the thickener comprises any one or a combination of at least two of polyisobutylene, ethyl cellulose, and nitrocellulose.

[0034] Preferably, the thixotropic agent comprises any one or a combination of at least two of the following: bentonite, sodium silicate, colloidal alumina, and polyamide wax.

[0035] Preferably, the surfactant includes any one or a combination of at least two of anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants.

[0036] Preferably, the surfactant includes any one or a combination of at least two of Span 85 (also known as "Span 85"), gelatin, and sodium lauryl sulfate.

[0037] Preferably, the glass powder comprises any one or a combination of at least two of silicon dioxide, titanium dioxide, and aluminum oxide.

[0038] Preferably, the solder paste further includes 0.01-3 parts by weight of an additive, wherein the parts by weight of the additive can be 0.05 parts, 0.1 parts, 0.2 parts, 0.5 parts, 0.8 parts, 1 part, 1.2 parts, 1.5 parts, 1.8 parts, 2 parts, 2.2 parts, 2.5 parts, or 2.8 parts, as well as specific values ​​between the above-mentioned values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0039] Preferably, the additives include methyl silicone oil and / or polyethylene wax.

[0040] In a preferred embodiment, the tin paste comprises the following components by weight:

[0041]

[0042] The tin powder comprises a combination of micron-sized tin powder and nano-sized tin powder, wherein the mass percentage of nano-sized tin powder in the tin powder is 5-20%.

[0043] Preferably, the tin powder in the tin paste has a mass percentage content of 80-95%, for example, it can be 82%, 85%, 88%, 90%, 92% or 94%, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range. More preferably, it is 85-94%, and more preferably, it is 89-94%.

[0044] Preferably, the organic carrier in the tin paste has a mass percentage content of 1-10%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, and it is further preferred to be 4.5-9.5%.

[0045] Preferably, the mass percentage of glass powder in the tin paste is 0.1-5%, for example, it can be 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or 4.5%, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, and 0.5-3% is further preferred.

[0046] Preferably, the fineness of the tin paste is ≤20μm, more preferably ≤15μm, and can be 7-14μm.

[0047] Preferably, the viscosity of the tin paste is ≤400 Pa·s, for example 50-400 Pa·s, more preferably ≤300 Pa·s, and can be 200-280 Pa·s; optionally, the viscosity test condition of the tin paste is 10R / 4min.

[0048] In a second aspect, the present invention provides a method for preparing tin paste as described in the first aspect, the method comprising: mixing and dispersing tin powder, an organic carrier, glass powder and optionally an additive to obtain the tin paste.

[0049] Preferably, the mixing apparatus includes a mortar and / or a mixer, more preferably a vacuum mixer.

[0050] Preferably, the organic carrier is prepared by the following method, which includes: mixing an organic solvent, a thickener, a thixotropic agent and a surfactant evenly to obtain the organic carrier.

[0051] Preferably, the dispersing device includes a planetary gravity mixer.

[0052] In a preferred embodiment, the method for preparing the tin paste includes the following steps:

[0053] Organic solvent, thickener, thixotropic agent and surfactant are mixed evenly to obtain organic carrier;

[0054] The organic carrier, tin powder, organic carrier, glass powder and additives are mixed in a vacuum mixer to obtain a premixed slurry;

[0055] The premixed slurry is dispersed using a planetary gravity mixer to obtain the tin paste, which has a fineness of ≤20μm and a viscosity of 50-400Pa·s.

[0056] Thirdly, the present invention provides a solar cell, the solar cell comprising a cell body and grid electrodes, the grid electrodes comprising a silver layer and a tin layer, the silver layer being located between the tin layer and the cell body; the tin layer being prepared by means of tin paste as described in the first aspect.

[0057] This invention does not impose any special limitations on the cell body; any conventional cell body that can be used in photovoltaic solar cells is applicable to this invention.

[0058] Preferably, the grid line electrode is located on the back side of the cell body.

[0059] Preferably, the thickness of the silver layer (thin silver gate) is 3-7 μm, for example, it can be 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.5 μm, 6 μm or 6.5 μm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0060] Preferably, the thickness of the tin layer is 2-8 μm, for example, it can be 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm or 7.5 μm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, and 3-6 μm is further preferred.

[0061] Fourthly, the present invention provides a method for preparing a solar cell, the method comprising: coating a silver paste on the back side of a cell body, sintering it to obtain a silver layer; coating a tin paste as described in the first aspect on the surface of the silver layer, and drying it to obtain the solar cell.

[0062] Preferably, the silver paste is applied by screen printing.

[0063] The solar cell fabrication method provided by this invention is implemented without changing existing solar cell production processes and equipment. A thin silver layer is formed by screen printing on the back of the cell body, and then a tin layer is superimposed on the thin silver layer using tin paste. This effectively reduces the amount of silver paste used and the thickness of the silver layer, thereby significantly reducing the production cost of the solar cell while maintaining the stability and continuity of the production line, and reducing the difficulty and cost of technology upgrades. The tin and silver layers have good eutectic properties, allowing the tin to melt and solidify on the cell surface to form a completely dense grid, creating a low-cost, high-reliability conductive path. Its line resistance and contact resistance are no worse than (better than) those of grids printed with conventional silver paste. This allows the solar cell prepared by this invention to maintain a photoelectric conversion efficiency comparable to conventional silver grid cells, making it suitable for TOPCon and other types of cells. While reducing costs, it does not sacrifice the performance of the solar cell, maintaining a photoelectric conversion efficiency comparable to conventional TOPCon cells, and has excellent prospects for industrial applications.

[0064] Preferably, the sintering temperature is 300-850℃, for example, it can be 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃ or 820℃, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range; the sintering enables the silver layer and the battery surface to form good conductive contact.

[0065] Preferably, the sintering time is 40-300s, for example, it can be 50s, 80s, 100s, 120s, 150s, 160s, 200s, 240s, 260s or 280s, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, and 60-180s is further preferred.

[0066] Preferably, the method for coating the tin paste includes screen printing.

[0067] Preferably, the drying temperature is 150-300℃, for example, it can be 160℃, 180℃, 200℃, 220℃, 240℃, 250℃, 260℃ or 280℃, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0068] Preferably, the drying time is 40-300s, for example, it can be 50s, 80s, 100s, 120s, 150s, 160s, 200s, 240s, 260s or 280s, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, and 60-180s is further preferred.

[0069] As a preferred embodiment of the present invention, the method for preparing the solar cell includes:

[0070] Silver paste is applied to the back of the battery cell body by screen printing and sintering at 300-850℃ for 60-180s to obtain a silver layer, which is a thin silver grid with a thickness of 3-7μm.

[0071] The surface of the silver layer is coated with tin paste as described in the first aspect by screen printing, and dried at 150-300°C for 60-180s to obtain a tin layer with a thickness of 2-8μm, thereby obtaining complete back-side main and secondary grid lines and the solar cell.

[0072] Compared with the prior art, the present invention has the following beneficial effects:

[0073] The tin paste provided by this invention, through the design and specific dosage of each component, achieves low cost and excellent conductivity. It exhibits excellent eutectic properties with the silver layer, enabling the formation of a dense and reliable conductive path on the cell surface. This tin paste is used to prepare the grid electrodes of solar cells, effectively reducing the amount of silver paste used and thus significantly lowering the production cost of solar cells. Simultaneously, the tin layer formed by the tin paste creates a high-performance conductive path with good contact with the silver layer, resulting in excellent line resistance and contact resistance, thus maintaining excellent photoelectric conversion efficiency of the solar cell. The tin paste and solar cell preparation method provided by this invention are applicable to TOPCon and other types of cells, reducing costs without sacrificing solar cell performance, and have broad industrial application prospects. Attached Figure Description

[0074] Figure 1 The grid line SEM image is of the solar cell provided in Example 1. Detailed Implementation

[0075] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0076] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not limited to those elements and may also include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0077] The specific information of the materials used in the following specific embodiments of the present invention is as follows, all of which are commercially available chemicals:

[0078] (1) Tin powder: Spherical micron-sized tin powder with an average particle size (D 50 The average particle size of the spherical nano-tin powder is 8 μm; 50 The wavelength is 500nm.

[0079] (2) Organic solvents: terpineol, tributyl citrate, butyl carbitol.

[0080] (3) Thickeners: polyisobutylene (PB1300); ethyl cellulose (analytical grade 99%).

[0081] (4) Thixotropic agents: sodium silicate, bentonite, polyamide wax (6900-20x).

[0082] (5) Surfactants: Span 85, gelatin, sodium dodecyl sulfate.

[0083] (6) Glass powder: silicon dioxide, titanium dioxide, aluminum oxide.

[0084] (7) Additives: Methyl silicone oil (201-50cs).

[0085] The following will describe in detail the specific components and preparation methods of the tin paste and solar cells described in this invention using several examples, but the components and preparation methods of the tin paste and solar cells described in this invention are not limited to these examples. In the following specific embodiments, the silver paste used is the same commercially available chemical.

[0086] Example 1

[0087] This embodiment provides a solder paste comprising the following components by weight:

[0088]

[0089] The tin powder comprises 85% micron-sized tin powder and 15% nano-sized tin powder.

[0090] The method for preparing the tin paste includes the following steps: mixing the components of the organic carrier according to the aforementioned formula, stirring for 30 minutes until colorless and transparent, to obtain the organic carrier; mixing the organic carrier, tin powder, glass powder, and additives using a vacuum mixer to obtain a premixed slurry; dispersing the premixed slurry using a planetary gravity mixer to obtain the tin paste.

[0091] This embodiment also provides a solar cell and its preparation method, including the following steps: silver paste is coated on the back of the cell body by screen printing, and sintered at 700°C for 120s to obtain a silver layer with a thickness of 3μm, i.e., a thin silver grid; then a layer of tin paste provided in this embodiment is superimposed on the thin silver grid by screen printing, and dried at 200°C for 120s to form a tin layer with a thickness of 5μm, thus completing the preparation of the back-side fine grid lines and obtaining the solar cell.

[0092] The grid line morphology (silver and tin stack) of the solar cell provided in this embodiment was tested using a scanning electron microscope (SEM, Hitachi-S4800), and the obtained SEM images are shown below. Figure 1 As shown, from Figure 1 As can be seen, the tin layer and the silver layer are printed in the same position, and the surface is smooth and dense, without obvious agglomeration or pores.

[0093] Example 2

[0094] This embodiment provides a solder paste comprising the following components by weight:

[0095]

[0096] The tin powder comprises 90% micron-sized tin powder and 10% nano-sized tin powder.

[0097] The method for preparing the tin paste includes the following steps: mixing the components of the organic carrier according to the aforementioned formula, stirring for 30 minutes until colorless and transparent, to obtain the organic carrier; mixing the organic carrier, tin powder, glass powder, and additives using a vacuum mixer to obtain a premixed slurry; dispersing the premixed slurry using a planetary gravity mixer to obtain the tin paste.

[0098] This embodiment also provides a solar cell and its preparation method, including the following steps: silver paste is coated on the back of the cell body by screen printing, and sintered at 600°C for 120s to obtain a silver layer with a thickness of 3μm, i.e., a thin silver grid; then a layer of tin paste provided in this embodiment is superimposed on the thin silver grid by screen printing, and dried at 180°C for 120s to form a tin layer with a thickness of 4μm, thus completing the preparation of the back-side fine grid lines and obtaining the solar cell.

[0099] Example 3

[0100] This embodiment provides a solder paste comprising the following components by weight:

[0101]

[0102] The tin powder comprises 95% micron-sized tin powder and 5% nano-sized tin powder.

[0103] The method for preparing the tin paste includes the following steps: mixing the components of the organic carrier according to the aforementioned formula, stirring for 30 minutes until colorless and transparent, to obtain the organic carrier; mixing the organic carrier, tin powder, glass powder, and additives using a vacuum mixer to obtain a premixed slurry; dispersing the premixed slurry using a planetary gravity mixer to obtain the tin paste.

[0104] This embodiment also provides a solar cell and its preparation method, including the following steps: silver paste is coated on the back of the cell body by screen printing, and sintered at 700°C for 120s to obtain a silver layer with a thickness of 3μm, i.e., a thin silver grid; then a layer of tin paste provided in this embodiment is superimposed on the thin silver grid by screen printing, and dried at 200°C for 120s to form a tin layer with a thickness of 5μm, thus completing the preparation of the back-side fine grid lines and obtaining the solar cell.

[0105] Example 4

[0106] This embodiment provides a tin paste, which differs from Embodiment 1 only in that it does not contain nano tin powder, i.e., the tin powder is 100% micron tin powder; the other components, dosages, and preparation methods of the tin paste are the same as in Embodiment 1.

[0107] This embodiment also provides a solar cell and its preparation method. The tin layer is prepared using the tin paste provided in this embodiment, and other materials, amounts and process parameters are the same as in Example 1.

[0108] Example 5

[0109] This embodiment provides a tin paste, which differs from Embodiment 1 only in that the D of the micron-sized tin powder... 50 The particle size is 18 μm; the other components, dosages, and preparation methods of the tin paste are the same as in Example 1.

[0110] This embodiment also provides a solar cell and its preparation method. The tin layer is prepared using the tin paste provided in this embodiment, and other materials, amounts and process parameters are the same as in Example 1.

[0111] Compare with Example 1

[0112] A solar cell and its preparation method include the following steps: coating silver paste on the back of the cell body by screen printing, sintering at 600°C for 120s to form a silver grid with a thickness of 5μm, thereby obtaining a solar cell.

[0113] The solder pastes provided in Examples 1-5, the solar cells provided in Examples 1-5 and Comparative Example 1 were tested using the following methods:

[0114] (1) Fineness: The fineness is tested by scraping the slurry from top to bottom with a fineness gauge to read the size of the particles.

[0115] (2) Viscosity: The viscosity was tested using a viscometer under the following conditions: rotor speed 10 R / 4 min.

[0116] (3) Grid line resistance and grid contact resistance: tested and calculated using a TLM contact resistance tester;

[0117] (4) The photoelectric properties of the battery, such as open-circuit voltage, short-circuit current, series resistance, parallel resistance, fill factor, and photoelectric conversion efficiency, are tested and calculated by the solar cell sorting machine.

[0118] The test data is shown in Table 1:

[0119] Table 1

[0120]

[0121] According to the test data in Table 1, the present invention uses a screen printing method to print grid electrodes on the back of the solar cell. First, a layer of silver paste is screen-printed on the back, and after sintering, a layer of tin paste provided by the present invention is superimposed on its surface, reducing the thickness of the silver layer and effectively reducing the amount of silver paste used. Because tin and silver have good eutectic properties, the grid lines formed by the tin paste on the cell surface are completely dense, forming a low-cost, high-reliability conductive path. This makes the grid line resistance of Examples 1-3 better than that of grid lines printed with conventional silver paste, while the contact resistance is basically the same as that of grid lines printed with conventional silver paste. The photoelectric conversion efficiency of the solar cell is consistent with, or even better than, that of conventional TOPCon, while the cost is significantly reduced. The tin paste in Example 4 does not contain nano-tin powder, and there are certain micropores in the tin layer, leading to increased resistance and a decrease in the photoelectric conversion efficiency of the solar cell. Furthermore, according to Examples 1 and 5, by designing the particle size of micron-sized tin powder, further optimization of the grid line and solar cell performance can be achieved.

[0122] The applicant declares that this invention illustrates the tin paste and its preparation method, as well as the solar cell, through the above embodiments. However, this invention is not limited to the above process steps, meaning that this invention does not necessarily rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of the raw materials used in this invention, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this invention.

Claims

1. A tin paste, characterized in that, The tin paste comprises the following components in parts by weight: 80-95 parts of tin powder 1-10 parts of organic carrier 0.5-5 parts glass powder; The organic carrier comprises a combination of organic solvents and additives, wherein the additives include any one or a combination of at least two of thickeners, thixotropic agents, and surfactants.

2. The tin paste according to claim 1, characterized in that, The tin powder includes a combination of micron-sized tin powder and nano-sized tin powder; Preferably, the particle size of the micron-sized tin powder is 1-50 μm, more preferably 5-15 μm; Preferably, the particle size of the nano-tin powder is 10-1000 nm, more preferably 200-800 nm; Preferably, the tin powder contains 5-20% nano-tin powder by mass.

3. The tin paste according to claim 1 or 2, characterized in that, The organic carrier comprises the following components by mass percentage:

4. The tin paste according to any one of claims 1-3, characterized in that, The organic solvent includes any one or a combination of at least two of terpineol, tributyl citrate, and butyl carbitol; Preferably, the thickener comprises any one or a combination of at least two of polyisobutylene, ethyl cellulose, and nitrocellulose; Preferably, the thixotropic agent comprises any one or a combination of at least two of bentonite, sodium silicate, colloidal alumina, and polyamide wax; Preferably, the surfactant comprises any one or a combination of at least two of Span 85, gelatin, and sodium dodecyl sulfate.

5. The tin paste according to any one of claims 1-4, characterized in that, The glass powder includes any one or a combination of at least two of silicon dioxide, titanium dioxide, and aluminum oxide. Preferably, the tin paste further comprises 0.01-3 parts by weight of additives; Preferably, the additives include methyl silicone oil and / or polyethylene wax.

6. A method for preparing tin paste as described in any one of claims 1-5, characterized in that, The preparation method includes: mixing and dispersing tin powder, organic carrier, glass powder and optional additives to obtain the tin paste.

7. The method for preparing tin paste according to claim 5, characterized in that, The mixing apparatus includes a vacuum mixer; Preferably, the dispersing device includes a planetary gravity mixer.

8. A solar cell, characterized in that, The solar cell includes a cell body and grid electrodes, the grid electrodes including a silver layer and a tin layer, the silver layer being located between the tin layer and the cell body; the tin layer is prepared by tin paste as described in any one of claims 1-5; Preferably, the thickness of the silver layer is 3-7 μm; Preferably, the thickness of the tin layer is 2-8 μm, and more preferably 3-6 μm.

9. A method for preparing a solar cell, characterized in that, The preparation method includes: coating the back of the cell body with silver paste, sintering to obtain a silver layer; coating the surface of the silver layer with tin paste as described in any one of claims 1-5, drying to obtain the solar cell.

10. The method for preparing a solar cell according to claim 9, characterized in that, The sintering temperature is 300-850℃; Preferably, the sintering time is 40-300s, more preferably 60-180s; Preferably, the drying temperature is 150-300℃; Preferably, the drying time is 40-300s, more preferably 60-180s.

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