Nano-silver paste for solar cell and preparation process of nano-silver paste

Abstract

The invention discloses nano-silver paste for a solar cell and a preparation process of the nano-silver paste, and relates to the technical field of conductive silver paste. When the nano-silver paste for the solar cell is prepared, silver nitrate is used as a precursor, ethylene glycol is used as a reducing agent, polyvinylpyrrolidone is used as an adsorbent, ferric trichloride is used as a guiding agent, and a hydrothermal reaction is carried out to prepare nano-silver wires; silver nitrate is used as a precursor, glucose is used as a reducing agent, and nano-silver particles are prepared through a liquid phase reduction method; preparing lead-free silver doped glass powder by adopting a sol-gel method; and uniformly mixing the nano silver wire, the nano silver particles, the lead-free silver doped glass powder and the organic carrier to prepare the nano silver paste for the solar cell. The prepared nano silver paste for the solar cell can improve the photoelectric conversion efficiency of the solar cell.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive silver paste, in particular to a nano silver paste for solar cells and a preparation process thereof. Background Art

[0002] Faced with the impending depletion of fossil energy and environmental pollution, people are turning their attention to clean, renewable energy sources such as wind, geothermal, and solar energy. One way to utilize solar energy is through crystalline silicon solar cells. For crystalline silicon solar cells, front-side silver paste is a crucial component. This paste primarily consists of a conductive phase—silver powder—which primarily determines the printing of the front electrode silver grid lines and the cell's electrical performance. During high-temperature sintering, it determines the density of the silver grid lines. An inorganic binder phase—glass powder—is used to etch away the arc (ARC) deposited on the silicon wafer surface, allowing for a good metallized contact (i.e., a good ohmic contact) between the silver grid lines and the silicon substrate. It also acts as a binder, effectively bonding the silver powder to the silicon substrate, improving the soldering strength and extending the cell's lifespan. An organic carrier—the carrier medium—acts as a solvent between the silver powder particles and the glass powder, ensuring a smooth mixing process and preventing ash from volatilizing during high-temperature sintering. Ultimately, this ensures that the resulting front-side silver paste has excellent viscosity and thixotropy. To enable widespread application of crystalline silicon solar cells, researchers urgently need to improve the photovoltaic efficiency of solar cells. Summary of the Invention

[0003] The purpose of the present invention is to provide a nano silver paste for solar cells and a preparation process thereof, so as to solve the problems existing in the prior art.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions: A nano silver paste for solar cells, which is prepared by uniformly mixing nano silver wires, nano silver particles, lead-free silver-doped glass powder, and an organic carrier; The silver nanowires are prepared by hydrothermal reaction using silver nitrate as a precursor, ethylene glycol as a reducing agent, polyvinyl pyrrolidone as an adsorbent, and ferric chloride as a guiding agent. The nano silver particles are prepared by liquid phase reduction method using silver nitrate as precursor and glucose as reducing agent; The organic carrier is prepared by uniformly mixing alpha-terpineol, 2-ethoxyethyl acetate and ethyl cellulose.

[0005] A process for preparing nano silver paste for solar cells, the method comprising the following steps: (1) At room temperature, under stirring conditions of 180-200 r / min, 0.4-0.5 times the mass of solution B was uniformly added dropwise to solution A within 10 min, placed in a reactor, and hydrothermally reacted at 159-161 ° C for 3-4 h, cooled to room temperature, centrifuged, and washed with anhydrous ethanol and deionized water for 3-5 times each, and dried under vacuum conditions at 50-60 ° C for 7-8 h to obtain nanosilver wires; (2) The silver nitrate solution and the glucose solution were mixed uniformly at a molar ratio of silver nitrate to glucose of 2:1, stirred at 60-62°C and 200-300 rpm for 40-50 min, centrifuged, washed 3-5 times with anhydrous ethanol and deionized water, dried at 50-60°C under vacuum for 10-12 h, placed in a ball mill, and ball-milled at 500-600 rpm for 20-24 h to obtain nanosilver particles; (3) Mix the reaction solution X, aluminum nitrate and zinc nitrate in a mass ratio of 1:(0.03~0.04):(0.06~0.08) to prepare the reaction solution Y; mix glycerol, bismuth nitrate, boric acid and silver nitrate in a mass ratio of 1:(0.7~0.8):(0.1~0.12):(0.02~0.03) to prepare the reaction solution Z; mix the reaction solution Y and the reaction solution Z in a mass ratio of 1:(0.7~0 8) mixing uniformly, stirring at room temperature at 200-300 rpm for 2-3 hours, and standing at 60-62° C. for 6-8 hours to obtain a mixed gel; drying the mixed gel at 200-210° C. for 9-10 hours to obtain a dry coagulation; calcining the dry coagulation in a muffle furnace at 500-520° C. for 30-40 minutes, and ball milling in a ball mill at 500-600 rpm for 20-24 hours to obtain a lead-free silver-doped glass powder; (4) α-terpineol, 2-ethoxyethyl acetate and ethyl cellulose were mixed uniformly in a mass ratio of 1: (0.41-0.43): (0.24-0.26), stirred at 58-60 ° C and 100-200 r / min for 20-30 min, and cooled to room temperature to prepare an organic carrier; 12-14 parts of nanosilver wires, 70-72 parts of nanosilver particles, 4-6 parts of lead-free silver-doped glass powder and 10-11 parts of organic carrier were weighed by mass; the nanosilver wires, nanosilver particles, lead-free silver-doped glass powder and organic carrier were mixed uniformly to prepare nanosilver paste for solar cells.

[0006] As an optimization, the preparation method of the solution A in step (1) is as follows: anhydrous ferric chloride and ethylene glycol are uniformly mixed in a mass ratio of 1:(24~25), stirred at 200~300 r / min for 8~10 min at room temperature, and polyvinyl pyrrolidone (0.7~0.8 times the mass of anhydrous ferric chloride) is added, and stirring is continued for 20~22 min to obtain solution A.

[0007] As an optimization, the model of the polyvinyl pyrrolidone is PVP K60.

[0008] As an optimization, the preparation method of the solution B in step (1) is: silver nitrate and ethylene glycol are uniformly mixed in a mass ratio of 1:(57~59) to obtain solution B.

[0009] As an optimization, the preparation method of the silver nitrate solution in step (2) is: silver nitrate and deionized water are uniformly mixed in a mass ratio of 1:(234~236) to prepare a silver nitrate solution.

[0010] As an optimization, the preparation method of the glucose solution in step (2) is: glucose and deionized water are uniformly mixed in a mass ratio of 1:(295~297) to prepare a glucose solution.

[0011] As an optimization, the preparation method of the reaction solution X in step (3) is as follows: ethyl orthosilicate, anhydrous ethanol, and deionized water are uniformly mixed in a mass ratio of 1:(78-80):(6-7), stirred at 200-300 r / min for 2-3 h at room temperature, and then ammonia water 4-5 times the mass of ethyl orthosilicate and anhydrous ethanol 78-80 times the mass of ethyl orthosilicate are added and mixed uniformly to obtain reaction solution X.

[0012] As an optimization, the molecular weight of the ethyl cellulose in step (4) is 40,000 to 50,000.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The invention prepares nano silver paste for solar cells by using silver nitrate as a precursor, ethylene glycol as a reducing agent, polyvinyl pyrrolidone as an adsorbent, and ferric chloride as a guiding agent to produce nano silver wires through hydrothermal reaction; using silver nitrate as a precursor and glucose as a reducing agent to produce nano silver particles through liquid phase reduction; using a sol-gel method to prepare lead-free silver-doped glass powder; and uniformly mixing the nano silver wires, nano silver particles, lead-free silver-doped glass powder, and an organic carrier to produce the nano silver paste for solar cells.

[0014] First, silver nanowires were prepared through a hydrothermal reaction using silver nitrate as a precursor, ethylene glycol as a reducing agent, polyvinyl pyrrolidone as an adsorbent, and ferric chloride as a directing agent. Compared with silver nanoparticles, silver nanowires have a higher aspect ratio, which is conducive to overlapping the conductive network, reducing tunnel resistance, and improving the conductivity of the silver nanopaste used in solar cells, thereby improving the photoelectric conversion efficiency of solar cells.

[0015] Secondly, a sol-gel method is used to prepare lead-free silver-doped glass powder. Traditionally, glass powder is prepared by melt quenching, but this method is energy-intensive, the chemical composition is difficult to control, and the resulting glass blocks after quenching are hard and difficult to crush and refine. Compared with the melt quenching method, glass powder prepared by the sol-gel method has more obvious advantages, such as uniform composition, high purity, easy doping, easy powder refinement, and the glass powder tends to have a smaller average particle size. By doping the glass powder with silver, the concentration of silver crystals in the glass layer is increased after sintering, thereby reducing the series resistance of the battery and increasing the short-circuit current, ultimately improving the photovoltaic conversion efficiency of the solar cell. DETAILED DESCRIPTION

[0016] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only 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 making creative efforts are within the scope of protection of the present invention.

[0017] Example 1: A process for preparing nano silver paste for solar cells, the method comprising the following steps: (1) Anhydrous ferric chloride and ethylene glycol were mixed in a mass ratio of 1:24, stirred at 200 r / min for 10 min at room temperature, and polyvinyl pyrrolidone (0.7 times the mass of anhydrous ferric chloride) was added, and the stirring was continued for 22 min to obtain solution A; silver nitrate and ethylene glycol were mixed in a mass ratio of 1:57 to obtain solution B; at room temperature, under stirring conditions of 180 r / min, solution B (0.4 times the mass of solution A) was uniformly added dropwise to solution A within 10 min, placed in a reactor, hydrothermally reacted at 159 ° C for 4 h, cooled to room temperature, centrifuged, washed with anhydrous ethanol and deionized water for 3 times each, and dried at 50 ° C for 8 h under vacuum conditions to obtain nanosilver wires; (2) Silver nitrate and deionized water were mixed at a mass ratio of 1:234 to prepare a silver nitrate solution; glucose and deionized water were mixed at a mass ratio of 1:295 to prepare a glucose solution; the silver nitrate solution and the glucose solution were mixed at a molar ratio of silver nitrate to glucose of 2:1, stirred at 60°C and 200 rpm for 50 minutes, centrifuged, washed with anhydrous ethanol and deionized water three times each, dried at 50°C under vacuum for 12 hours, placed in a ball mill, and ball milled at 500 rpm for 24 hours to obtain nanosilver particles; (3) Ethyl orthosilicate, anhydrous ethanol and deionized water were mixed evenly in a mass ratio of 1:78:6, stirred at 200 r / min for 3 h at room temperature, and then ammonia water 4 times the mass of ethyl orthosilicate and anhydrous ethanol 78 times the mass of ethyl orthosilicate were added and mixed evenly to prepare reaction solution X; reaction solution X, aluminum nitrate and zinc nitrate were mixed evenly in a mass ratio of 1:0.03:0.06 to prepare reaction solution Y; glycerol, bismuth nitrate, boric acid and silver nitrate were mixed evenly in a mass ratio of 1:0.03:0.06 to prepare reaction solution Y; :0.7:0.1:0.02 were mixed to prepare reaction solution Z; reaction solution Y and reaction solution Z were mixed at a mass ratio of 1:0.7, stirred at room temperature at 200 r / min for 3 hours, and allowed to stand at 60°C for 8 hours to prepare a mixed gel; the mixed gel was dried at 200°C for 10 hours to prepare a dry condensate; the dry condensate was placed in a muffle furnace, calcined at 500°C for 40 minutes, placed in a ball mill, and ball milled at 500 rpm for 24 hours to prepare a lead-free silver-doped glass powder; (4) α-terpineol, 2-ethoxyethyl acetate and ethyl cellulose were mixed in a mass ratio of 1:0.41:0.24, stirred at 58°C and 100 r / min for 30 min, and cooled to room temperature to prepare an organic carrier; 12 parts of nanosilver wires, 70 parts of nanosilver particles, 4 parts of lead-free silver-doped glass powder and 10 parts of organic carrier were weighed by mass; the nanosilver wires, nanosilver particles, lead-free silver-doped glass powder and organic carrier were mixed evenly to prepare nanosilver paste for solar cells.

[0018] Example 2: A process for preparing nano silver paste for solar cells, the method comprising the following steps: (1) Anhydrous ferric chloride and ethylene glycol were mixed in a mass ratio of 1:24.5, stirred at 250 r / min for 9 minutes at room temperature, and polyvinyl pyrrolidone (0.75 times the mass of anhydrous ferric chloride) was added, and the stirring was continued for 21 minutes to obtain solution A; silver nitrate and ethylene glycol were mixed in a mass ratio of 1:58 to obtain solution B; at room temperature, under stirring conditions of 190 r / min, solution B (0.45 times the mass of solution A) was uniformly added dropwise to solution A within 10 minutes, placed in a reactor, hydrothermally reacted at 160°C for 3.5 hours, cooled to room temperature, centrifuged, washed with anhydrous ethanol and deionized water for 4 times each, and dried at 55°C under vacuum conditions for 7.5 hours to obtain nanosilver wires; (2) Silver nitrate and deionized water were mixed at a mass ratio of 1:235 to prepare a silver nitrate solution; glucose and deionized water were mixed at a mass ratio of 1:296 to prepare a glucose solution; the silver nitrate solution and the glucose solution were mixed at a molar ratio of silver nitrate to glucose of 2:1, stirred at 61°C and 250 rpm for 45 minutes, centrifuged, washed with anhydrous ethanol and deionized water for 4 times, dried at 55°C for 11 hours under vacuum conditions, placed in a ball mill, and ball milled at 550 rpm for 22 hours to obtain nanosilver particles; (3) Ethyl orthosilicate, anhydrous ethanol and deionized water were mixed evenly in a mass ratio of 1:79:6.5, stirred at room temperature and 250 r / min for 2.5 h, and then ammonia water 4.5 times the mass of ethyl orthosilicate and anhydrous ethanol 79 times the mass of ethyl orthosilicate were added and mixed evenly to prepare reaction solution X; reaction solution X, aluminum nitrate and zinc nitrate were mixed evenly in a mass ratio of 1:0.035:0.07 to prepare reaction solution Y; glycerol, bismuth nitrate, boric acid and silver nitrate were mixed evenly in a mass ratio of 1:0.035:0.07 to prepare reaction solution Y; :0.75:0.11:0.025 were mixed to prepare reaction solution Z; reaction solution Y and reaction solution Z were mixed at a mass ratio of 1:0.75, stirred at room temperature at 250 r / min for 2.5 hours, and allowed to stand at 61°C for 7 hours to prepare a mixed gel; the mixed gel was dried at 205°C for 9.5 hours to prepare a dry condensate; the dry condensate was placed in a muffle furnace, calcined at 510°C for 35 minutes, placed in a ball mill, and ball milled at 550 rpm for 22 hours to prepare a lead-free silver-doped glass powder; (4) α-terpineol, 2-ethoxyethyl acetate and ethyl cellulose were mixed uniformly in a mass ratio of 1:0.42:0.25, stirred at 59°C and 150 r / min for 25 min, and cooled to room temperature to prepare an organic carrier; 13 parts of nanosilver wires, 71 parts of nanosilver particles, 5 parts of lead-free silver-doped glass powder and 10.5 parts of organic carrier were weighed by mass; the nanosilver wires, nanosilver particles, lead-free silver-doped glass powder and organic carrier were mixed uniformly to prepare nanosilver paste for solar cells.

[0019] Example 3: A process for preparing nano silver paste for solar cells, the method comprising the following steps: (1) Anhydrous ferric chloride and ethylene glycol were mixed in a mass ratio of 1:25, stirred at 300 r / min for 8 min at room temperature, and polyvinyl pyrrolidone (0.8 times the mass of anhydrous ferric chloride) was added, and the stirring was continued for 20 min to obtain solution A; silver nitrate and ethylene glycol were mixed in a mass ratio of 1:59 to obtain solution B; at room temperature, under stirring conditions of 200 r / min, solution B (0.5 times the mass of solution A) was uniformly added dropwise to solution A within 10 min, placed in a reactor, hydrothermally reacted at 161 ° C for 3 h, cooled to room temperature, centrifuged, washed with anhydrous ethanol and deionized water for 5 times each, and dried at 60 ° C for 7 h under vacuum conditions to obtain nanosilver wires; (2) Silver nitrate and deionized water were mixed at a mass ratio of 1:236 to prepare a silver nitrate solution; glucose and deionized water were mixed at a mass ratio of 1:297 to prepare a glucose solution; the silver nitrate solution and the glucose solution were mixed at a molar ratio of silver nitrate to glucose of 2:1, stirred at 62°C and 300 rpm for 40 minutes, centrifuged, washed with anhydrous ethanol and deionized water for 5 times each, dried at 60°C for 10 hours under vacuum conditions, placed in a ball mill, and ball milled at 600 rpm for 20 hours to obtain nanosilver particles; (3) Ethyl orthosilicate, anhydrous ethanol and deionized water were mixed in a mass ratio of 1:80:7, stirred at room temperature and 300 r / min for 2 h, and then ammonia water 5 times the mass of ethyl orthosilicate and anhydrous ethanol 80 times the mass of ethyl orthosilicate were added and mixed to obtain reaction solution X; reaction solution X, aluminum nitrate and zinc nitrate were mixed in a mass ratio of 1:0.04:0.08 to obtain reaction solution Y; glycerol, bismuth nitrate, boric acid and silver nitrate were mixed in a mass ratio of 1:0.04:0.08 to obtain reaction solution Y; :0.8:0.12:0.03 were mixed to prepare reaction solution Z; reaction solution Y and reaction solution Z were mixed at a mass ratio of 1:0.8, stirred at room temperature at 300 r / min for 2 hours, and allowed to stand at 62°C for 6 hours to prepare a mixed gel; the mixed gel was dried at 210°C for 9 hours to prepare a dry condensate; the dry condensate was placed in a muffle furnace, calcined at 520°C for 30 minutes, placed in a ball mill, and ball-milled at 600 rpm for 20 hours to prepare a lead-free silver-doped glass powder; (4) α-terpineol, 2-ethoxyethyl acetate and ethyl cellulose were mixed uniformly in a mass ratio of 1:0.43:0.26, stirred at 60°C and 200 r / min for 20 min, and cooled to room temperature to prepare an organic carrier; 14 parts of nanosilver wires, 72 parts of nanosilver particles, 6 parts of lead-free silver-doped glass powder and 11 parts of organic carrier were weighed by mass; the nanosilver wires, nanosilver particles, lead-free silver-doped glass powder and organic carrier were mixed uniformly to prepare nanosilver paste for solar cells.

[0020] Comparative Example 1: The method for preparing a nanosilver paste for solar cells in Comparative Example 1 differs from that in Example 2 in that step (1) is omitted and step (4) is modified as follows: α-terpineol, ethyl 2-ethoxylate, and ethyl cellulose are uniformly mixed in a mass ratio of 1:0.42:0.25, stirred at 59°C and 150 rpm for 25 minutes, and cooled to room temperature to prepare an organic vehicle; 84 parts of nanosilver particles, 5 parts of lead-free silver-doped glass powder, and 10.5 parts of the organic vehicle are weighed by mass; the nanosilver particles, lead-free silver-doped glass powder, and the organic vehicle are uniformly mixed to prepare a nanosilver paste for solar cells. The remaining steps are the same as in Example 2.

[0021] Comparative Example 2: The preparation method of nano silver paste for solar cells in Comparative Example 2 is different from that in Example 2 in that steps (3) and (4) are different. Step (3) is modified as follows: ethyl orthosilicate, anhydrous ethanol and deionized water are mixed evenly in a mass ratio of 1:79:6.5, stirred at room temperature at 250r / min for 2.5h, and then ammonia water 4.5 times the mass of ethyl orthosilicate and anhydrous ethanol 79 times the mass of ethyl orthosilicate are added and mixed evenly to prepare reaction solution X; reaction solution X, aluminum nitrate and zinc nitrate are mixed evenly in a mass ratio of 1:0.035:0.07 to prepare reaction solution Y; propylene glycol, bismuth nitrate and boric acid are mixed evenly in a mass ratio of 1:0.75:0.11 to prepare reaction solution Z; reaction solution Y and reaction solution Z are mixed evenly in a mass ratio of 1:0.75, stirred at room temperature at 250r / min for 2.5h. / min stirring for 2.5h, and standing at 61℃ for 7h to obtain a mixed gel; the mixed gel was dried at 205℃ for 9.5h to obtain a dry condensate; the dry condensate was placed in a muffle furnace, calcined at 510℃ for 35min, placed in a ball mill, and ball milled at 550rpm for 22h to obtain a lead-free glass powder; step (4) was modified as follows: α-terpineol, 2-ethoxyethyl acetate, and ethyl cellulose were mixed uniformly in a mass ratio of 1:0.42:0.25, stirred at 59℃ and 150r / min for 25min, and cooled to room temperature to obtain an organic carrier; 13 parts of nano silver wires, 71 parts of nano silver particles, 5 parts of lead-free glass powder, and 10.5 parts of organic carrier were weighed by mass; the nano silver wires, nano silver particles, lead-free glass powder, and organic carrier were mixed uniformly to obtain a nano silver paste for solar cells. The remaining steps were the same as in Example 2.

[0022] Test Example 1 Testing of the photoelectric conversion efficiency performance of solar cells Testing Method: The examples and comparative examples were screen-printed onto polycrystalline silicon wafers with a thickness of 200 μm, an area of ​​156 mm × 156 mm, and a sheet resistance of 80 Ω / sq. A 360-mesh screen with a line diameter of 16 μm and a line width of 37 μm was used for screen printing. The wafers were then dried in a 120°C oven for 20 minutes and sintered in an 800°C tube furnace at a belt speed of 236 inches / min and 5967 mm / min. The photovoltaic efficiency of the solar cells was measured using a cell performance tester. The results are shown in Table 1.

[0023] Table 1

[0024] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 2 in Table 1, it can be found that the nano silver paste for solar cells prepared by the present invention can improve the photoelectric conversion efficiency of solar cells.

[0025] By comparison, the photoelectric conversion efficiency of Examples 1 to 3 is greater than that of Comparative Example 1, indicating that nanosilver wires are prepared by hydrothermal reaction using silver nitrate as a precursor, ethylene glycol as a reducing agent, polyvinyl pyrrolidone as an adsorbent, and ferric chloride as a guiding agent; compared with nanosilver particles, nanosilver wires have a higher aspect ratio, which is conducive to overlapping the conductive network, reducing tunnel resistance, and improving the conductivity of nanosilver paste for solar cells, thereby improving the photoelectric conversion efficiency of solar cells.

[0026] By comparison, the photoelectric conversion efficiency of Examples 1-3 is greater than that of Comparative Example 2, demonstrating the effectiveness of the sol-gel method in preparing lead-free, silver-doped glass powder. Traditionally, glass powder is prepared using a melt-quenching method, but this method is energy-intensive, difficult to control chemical composition, and the resulting glass blocks after quenching are relatively hard and difficult to crush and refine. Compared to the melt-quenching method, glass powder prepared using the sol-gel method offers significant advantages, such as uniform composition, high purity, ease of doping, easy powder refinement, and a tendency for the glass powder to have a smaller average particle size. Silver-doping the glass powder increases the silver crystal concentration in the glass layer after sintering, thereby reducing the series resistance of the cell and increasing the short-circuit current, ultimately improving the photoelectric conversion efficiency of the solar cell.

[0027] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A nano silver paste for solar cells, characterized in that: The nano silver paste for solar cells is prepared by uniformly mixing nano silver wires, nano silver particles, lead-free silver-doped glass powder and an organic carrier; The silver nanowires are prepared by hydrothermal reaction using silver nitrate as a precursor, ethylene glycol as a reducing agent, polyvinyl pyrrolidone as an adsorbent, and ferric chloride as a guiding agent. The nano silver particles are prepared by liquid phase reduction method using silver nitrate as precursor and glucose as reducing agent; The organic carrier is prepared by uniformly mixing alpha-terpineol, 2-ethoxyethyl acetate and ethyl cellulose.

2. A process for preparing nano silver paste for solar cells, characterized in that: The preparation method of the nano silver paste for solar cells comprises the following preparation steps: (1) At room temperature, under stirring conditions of 180-200 r / min, 0.4-0.5 times the mass of solution B was uniformly added dropwise to solution A within 10 min, placed in a reactor, and hydrothermally reacted at 159-161 ° C for 3-4 h, cooled to room temperature, centrifuged, and washed with anhydrous ethanol and deionized water for 3-5 times each, and dried under vacuum conditions at 50-60 ° C for 7-8 h to obtain nanosilver wires; (2) The silver nitrate solution and the glucose solution were mixed uniformly at a molar ratio of silver nitrate to glucose of 2:1, stirred at 60-62°C and 200-300 rpm for 40-50 min, centrifuged, washed 3-5 times with anhydrous ethanol and deionized water, dried at 50-60°C under vacuum for 10-12 h, placed in a ball mill, and ball-milled at 500-600 rpm for 20-24 h to obtain nanosilver particles; (3) The reaction solution X, aluminum nitrate and zinc nitrate were mixed evenly in a mass ratio of 1:(0.03~0.04):(0.06~0.08) to prepare reaction solution Y; propylene glycol, bismuth nitrate, boric acid and silver nitrate were mixed evenly in a mass ratio of 1:(0.7~0.8):(0.1~0.12):(0.02~0.03) to prepare reaction solution Z; reaction solution Y and reaction solution Z were mixed evenly in a mass ratio of 1:(0.7~0.8), stirred at 200~300 r / min for 2~3 h at room temperature, and allowed to stand at 60~62°C for 6~8 h to prepare a mixed gel; the mixed gel was dried at 200~210°C for 9~10 h to prepare a dry coagulation; The dry condensed product was placed in a muffle furnace, calcined at 500-520°C for 30-40 minutes, and then placed in a ball mill, and ball milled at 500-600 rpm for 20-24 hours to obtain lead-free silver-doped glass powder. (4) α-terpineol, 2-ethoxyethyl acetate and ethyl cellulose were mixed uniformly in a mass ratio of 1: (0.41-0.43): (0.24-0.26), stirred at 58-60 ° C and 100-200 r / min for 20-30 min, and cooled to room temperature to prepare an organic carrier; 12-14 parts of nanosilver wires, 70-72 parts of nanosilver particles, 4-6 parts of lead-free silver-doped glass powder and 10-11 parts of organic carrier were weighed by mass; the nanosilver wires, nanosilver particles, lead-free silver-doped glass powder and organic carrier were mixed uniformly to prepare nanosilver paste for solar cells.

3. The process for preparing nano silver paste for solar cells according to claim 2, wherein: The preparation method of the solution A in step (1) is as follows: anhydrous ferric chloride and ethylene glycol are uniformly mixed in a mass ratio of 1:(24~25), stirred at 200~300 r / min for 8~10 minutes at room temperature, 0.7~0.8 times the mass of anhydrous ferric chloride is added with polyvinyl pyrrolidone, and stirring is continued for 20~22 minutes to obtain solution A.

4. The process for preparing nano silver paste for solar cells according to claim 3, wherein: The model of the polyvinyl pyrrolidone is PVP K60.

5. The process for preparing nano silver paste for solar cells according to claim 2, wherein: The preparation method of the solution B in step (1) is as follows: silver nitrate and ethylene glycol are uniformly mixed in a mass ratio of 1:(57~59) to obtain solution B.

6. The process for preparing nano silver paste for solar cells according to claim 2, wherein: The preparation method of the silver nitrate solution in step (2) is as follows: silver nitrate and deionized water are uniformly mixed in a mass ratio of 1:(234~236) to prepare a silver nitrate solution.

7. The process for preparing nano silver paste for solar cells according to claim 2, wherein: The preparation method of the glucose solution in step (2) is as follows: glucose and deionized water are uniformly mixed in a mass ratio of 1:(295~297) to prepare a glucose solution.

8. The process for preparing nano silver paste for solar cells according to claim 2, wherein: The preparation method of the reaction solution X in step (3) is as follows: ethyl orthosilicate, anhydrous ethanol, and deionized water are uniformly mixed in a mass ratio of 1:(78-80):(6-7), stirred at 200-300 r / min for 2-3 hours at room temperature, and then ammonia water 4-5 times the mass of ethyl orthosilicate and anhydrous ethanol 78-80 times the mass of ethyl orthosilicate are added and mixed uniformly to obtain the reaction solution X.

9. The process for preparing nano silver paste for solar cells according to claim 2, characterized in that: The molecular weight of the ethyl cellulose in step (4) is 40,000 to 50,000.

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