A PERC crystalline silicon solar back silver paste and preparation method thereof

Abstract

The present invention relates to the technical field of H01B1 / 16, and specifically to a PERC crystalline silicon solar back side silver paste and a preparation method thereof. The silver paste comprises a silver powder paste combination, a mixed metal oxide paste and an inorganic auxiliary agent paste. The silver powder paste combination comprises a silver powder paste with a D50 of 50nm-1μm. By optimizing the back side silver paste formula, the silver content of the back side electrode silver paste for the PERC crystalline silicon solar cell is effectively reduced to 48-52% (weight percentage), thereby reducing the material cost of a cell sheet while ensuring the photoelectric conversion efficiency and welding performance of the cell sheet.

Description

Technical Field

[0001] The invention relates to the technical field of H01B1 / 16, and in particular to a PERC crystalline silicon solar back side silver paste and a preparation method thereof. Background Art

[0002] Photovoltaic solar cells continue to develop in the direction of high photoelectric conversion efficiency, low production cost and high production efficiency. With the increasing maturity of TOPCon technology and HJT technology, PERC crystalline silicon solar cell technology faces greater pressure on photoelectric conversion efficiency and cost. The non-silicon material part of PERC crystalline silicon solar cells, the front silver paste and the back silver paste have a greater impact on the photoelectric conversion efficiency and cost. Compared with the front silver paste, the back silver paste accounts for a small proportion of the material cost, but as a silver-containing back conductive electrode, it is not easy to reduce the silver content without affecting the photoelectric conversion efficiency of the cell.

[0003] Generally speaking, when the silver content of the back electrode silver paste is reduced, the resistance increases, resulting in a decrease in the photoelectric conversion efficiency of the cell; when the silver content is reduced, the adhesion of the back electrode after sintering is reduced, and the solderability and solder resistance deteriorate, resulting in poor soldering of the cell, causing the failure of the photovoltaic module. Therefore, the silver content of the mainstream PERC crystalline silicon solar cell back silver paste on the market at this stage is in the range of 55-67% (weight percentage). For example, a Chinese patent application (authorization announcement number CN 109949966B) discloses a high-reliability PERC crystalline silicon solar cell back silver conductive paste and its preparation process. Although the glass powder composition is optimized to meet the requirements of low firing temperature and high back electrode reliability of PERC cells, the silver powder content is as high as 55-65%. Therefore, how to reduce the silver content of the back electrode silver paste for PERC crystalline silicon solar cells to 48-52% (weight percentage), reduce the material cost of the cell, and ensure the photoelectric conversion efficiency and welding performance of the cell, has important practical significance. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a PERC crystalline silicon solar back side silver paste and a preparation method thereof, which effectively reduces the silver content of the back electrode silver paste for PERC crystalline silicon solar cells to 48-52% (weight percentage) by optimizing the back side silver paste formula, thereby reducing the material cost of the cell while ensuring the photoelectric conversion efficiency and welding performance of the cell.

[0005] On one hand, the present invention provides a PERC crystalline silicon solar back silver paste, which is composed of a silver powder paste combination, a mixed metal oxide paste and an inorganic auxiliary agent paste. The silver powder paste combination includes a silver powder paste with a D50 of 50nm-1μm.

[0006] As a preferred technical solution, the silver powder paste combination at least includes: silver powder A paste with a D50 of 0.5 to 1 micron, silver powder B paste with a D50 of 0.2 to 0.4 micron, and silver powder C paste with a D50 of 50 to 100 nanometers.

[0007] Preferably, the silver powder A in the silver powder A slurry is spherical or approximately spherical, with a D50 of 0.7 to 0.9 microns and a specific surface area of ​​0.8 to 1.5 m 2 / g.

[0008] Preferably, the silver powder B in the silver powder B slurry is spherical or approximately spherical, with a D50 of 0.2 to 0.4 microns and a specific surface area of ​​2.5 to 3.0 m 2 / g.

[0009] Preferably, the silver powder C in the silver powder C slurry is spherical or approximately spherical, with a D50 of 80-100 nm and a specific surface area of ​​>7.6 m 2 / g.

[0010] As a preferred technical solution, based on the total weight of the PERC crystalline silicon solar back silver paste, the weight percentage of the silver powder A is 43-47%, the weight percentage of the silver powder B is 3-5%, and the weight percentage of the silver powder C is 1-2%.

[0011] The back silver paste provided by the present invention is based on the actual problems existing in the back silver paste of the existing PERC crystalline silicon solar cell wafer, and an overall scheme design including scheme optimization and preparation process improvement is carried out to overcome the defect that the cost of silver paste and the performance of silver paste cannot be balanced. The inventors found in the process of optimizing the formula of the back silver paste that by using silver powder A paste, silver powder B paste, and silver powder C paste containing three silver powders with different particle sizes, especially controlling the weight percentage of the silver powder A to be 43-47%, the weight percentage of the silver powder B to be 3-5%, and the weight percentage of the silver powder C to be 1-2%, the production cost is effectively reduced, and the sintering density is optimized, and the solderability, solder resistance and adhesion of the back electrode after sintering are improved; the back electrode resistance is reduced, the welding and tension requirements of the component end are met, and the problem of reduced photoelectric conversion efficiency due to reduced silver powder content is effectively solved.

[0012] As a preferred technical solution, the mixed metal oxide in the mixed metal oxide slurry is a combination of at least four of silicon dioxide, lead oxide, copper oxide, titanium dioxide, bismuth trioxide, and tellurium dioxide. Preferably, by mass percentage, the mixed metal oxide includes 35-40% silicon dioxide, 25-35% lead oxide, 8-15% copper oxide, 8-15% titanium dioxide, 1-8% bismuth trioxide, and 1-8% tellurium dioxide. Further preferably, by mass percentage, the mixed metal oxide includes: 38% silicon dioxide, 32% lead oxide, 11% copper oxide, 11% titanium dioxide, 4.5% bismuth trioxide, and 3.5% tellurium dioxide.

[0013] As a preferred technical solution, the preparation method of the mixed metal oxide is as follows: according to the mass percentage, silicon dioxide, lead oxide, copper oxide, titanium dioxide, bismuth trioxide, and tellurium dioxide are placed in an alumina crucible, placed in a muffle furnace, heated to 1200-1400°C, and kept warm for 3-5 hours; then the heating is stopped and the temperature is naturally cooled, and the cooling rate is <2°C / minute; when the temperature in the muffle furnace is lower than 100°C, the crucible is taken out, and the metal mixed oxide in the crucible is first preliminarily crushed into particles, and then deionized water is used as a carrier and a zirconium ball with a diameter of 1.6-1.8cm is used as a grinding medium, and ball milling is performed for 1-3 hours; the zirconium ball with a diameter of 1.6-1.8cm is taken out, and the zirconium ball with a diameter of 0.8mm is used for ball milling for 5-7 hours. The zirconium ball is taken out, and the ball milling liquid is placed in a stainless steel plate, and the water is dried in an oven at 60-90°C to obtain a mixed metal oxide with a particle size distribution of D50≤0.8 microns.

[0014] As a preferred technical solution, based on the total weight of the PERC crystalline silicon solar back silver paste, the weight percentage of the mixed metal oxide is 1-3%.

[0015] The back silver paste provided by the present invention adds 1-3% by weight of a specific mixed metal oxide with a particle size distribution D50≤0.8 micron, which effectively solves the corrosion problem of the back film of the battery cell existing in the existing back silver paste containing glass powder, reduces the back recombination rate, and improves the opening voltage.

[0016] As a preferred technical solution, the silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry, and inorganic auxiliary agent slurry all include an organic carrier, and the organic carrier is composed of cellulose and a solvent. The cellulose is preferably ethyl cellulose, and the solvent is a combination of methyl nylonate, butyl carbitol, and alcohol ester dodeca.

[0017] Preferably, the organic carrier comprises, by mass percentage, at least 5-15% of ethyl cellulose (STD200), 35-45% of methyl nylonate, 20-40% of butyl carbitol, and 10-30% of alcohol ester dodecanedione.

[0018] As a preferred technical solution, the preparation method of the organic carrier is as follows: weigh the solvent according to the mass percentage and add it into the jacketed reactor; place the dispersion plate of the high-speed disperser in the middle of the weighed solvent in the jacketed reactor, turn on the high-speed disperser, and set the stirring speed to 100-300RPM, so as to mix the mixture in the reactor evenly; weigh cellulose and add it to the solvent in the stirring reactor; set the heating temperature of the water bath (or oil bath) of the jacketed reactor to 60-90°C, and set the stirring speed of the high-speed disperser to 600-800RPM; after the water bath (or oil bath) temperature of the jacketed reactor reaches the set heating temperature, maintain the set heating temperature and the stirring speed of the high-speed disperser, and dissolve the cellulose under this condition for 1-3 hours, and seal the dissolved organic carrier, and let it stand and cool.

[0019] The organic carrier provided in the present invention is prepared by controlling the process conditions so that ethyl cellulose (STD200) is completely dissolved in a mixed solvent consisting of methyl nylonate, butyl carbitol and alcohol ester dodecasol to obtain a uniform organic carrier.

[0020] As a preferred technical solution, based on the total weight of the PERC crystalline silicon solar back silver paste, the weight percentage of the organic carrier is 40-50%.

[0021] As a preferred technical solution, the silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry, and inorganic auxiliary agent slurry also include a dispersant, preferably a dispersant Dispersant TDO (Nouryon Duomeen TPO color paste dispersant).

[0022] As a preferred technical solution, the silver powder C slurry also includes a solvent diethylene glycol dibutyl ether.

[0023] As a preferred technical solution, the inorganic additive in the inorganic additive slurry is silicon dioxide, preferably silicon dioxide powder with a particle size of 1 to 2 microns and a purity requirement of 99.99%.

[0024] As a preferred technical solution, based on the total weight of the PERC crystalline silicon solar back silver paste, the weight percentage of the inorganic auxiliary agent is 0-0.5%.

[0025] The back silver paste provided by the present invention adds silicon dioxide powder with a particle size of 1 to 2 microns and a purity requirement of 99.99% as an inorganic auxiliary agent, which helps to adjust the shrinkage rate of the back electrode and improve the back electrode to match it with the aluminum electrode.

[0026] As a preferred technical solution, the raw materials for preparing the PERC crystalline silicon solar back silver paste include, by mass percentage, 79.70-82.20% silver powder A slurry, 9.03-11.29% silver powder B slurry, 4.03% silver powder C slurry, 3.83-4.68% mixed metal oxide slurry, and 0.30-0.91% inorganic auxiliary agent slurry.

[0027] The silver powder A slurry, by mass percentage, includes 56.93% of silver powder A, 42.82% of organic vehicle, and 0.25% of dispersant Dispersant TDO (Nouryon Duomeen TPO color paste dispersant).

[0028] The silver powder B slurry, by mass percentage, includes 44.30% of silver powder B, 55.37% of organic vehicle, and 0.33% of dispersant Dispersant TDO (Nouryon Duomeen TPO color paste dispersant).

[0029] The silver powder C slurry, by mass percentage, includes 24.81% of silver powder C, 49.63% of organic vehicle, 0.75% of dispersant Dispersant TDO (Nouryon Duomeen TPO color paste dispersant), and 24.81% of solvent diethylene glycol dibutyl ether.

[0030] The mixed metal oxide slurry, by mass percentage, includes 47.00% of mixed metal oxide, 52.22% of organic carrier, and 0.78% of dispersant Dispersant TDO (Nouryon Duomeen TPO color paste dispersant).

[0031] The inorganic auxiliary agent slurry includes, by mass percentage, 32.97% of inorganic auxiliary agent, 65.93% of organic carrier, and 1.10% of dispersant Dispersant TDO (Nouryon Duomeen TPO color paste dispersant).

[0032] As a preferred technical solution, the preparation process of the silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry, and inorganic auxiliary agent slurry is as follows: the raw materials in the silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry, and inorganic auxiliary agent slurry are respectively dispersed by high-speed stirring in an emulsifier, the speed is set to 1000-2000RPM, and the emulsification dispersion is performed for 20-40 minutes.

[0033] Each slurry in the back silver paste provided by the present invention adopts Dispersant TDO as a dispersant, optimizes the slurry ratio, and uses an emulsifier to wet and disperse three silver powders with different particle size distributions, mixed metal oxides, and inorganic additives under high-speed stirring conditions, so that silver powder A, silver powder B, silver powder C, mixed metal oxides, and inorganic additives are wetted and dispersed to form single particles in an organic carrier, which is helpful for the subsequent preparation of the back silver paste.

[0034] On the other hand, the present invention provides a method for preparing silver paste for the back side of PERC crystalline silicon solar cell, which comprises at least the following steps: stirring and dispersing the silver powder slurry combination, the mixed metal oxide slurry and the inorganic auxiliary agent slurry by a high-speed disperser, setting the rotation speed to 800-1200RPM, stirring and dispersing for 20-40 minutes, and obtaining a back side silver paste with a fineness of <10 microns.

[0035] Preferably, the method for preparing the PERC crystalline silicon solar back silver paste specifically comprises the following steps:

[0036] S1: preparing silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry, and inorganic additive slurry respectively;

[0037] S2: Use a high-speed disperser to stir and disperse silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry, and inorganic additive slurry. Set the speed to 800-1200RPM and stir and disperse for 20-40 minutes to obtain a back silver paste with a fineness of <10 microns.

[0038] The invention adopts a step-by-step wetting and dispersing process, wherein the wetted and dispersed silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry and inorganic auxiliary agent slurry are stirred and dispersed at 500-1200 RPM for 20-40 minutes, thereby ensuring the dispersion uniformity of various components of the back slurry, and reducing the problems of high production energy consumption and low production efficiency due to the use of a three-roll grinder for grinding and dispersing in the existing preparation process, and is easy to promote and use.

[0039] Beneficial Effects

[0040] 1. The present invention provides a PERC crystalline silicon solar back silver paste, which effectively reduces the silver content of the back electrode silver paste for PERC crystalline silicon solar cells to 48-52% (weight percentage) by optimizing the back silver paste formula, thereby reducing the material cost of the cell while ensuring the photoelectric conversion efficiency and welding performance of the cell.

[0041] 2. By using silver powder A slurry, silver powder B slurry, and silver powder C slurry containing three silver powders with different particle sizes, especially controlling the weight percentage of silver powder A to 43-47%, the weight percentage of silver powder B to 3-5%, and the weight percentage of silver powder C to 1-2%, the production cost can be effectively reduced while achieving optimal sintering density, improving the solderability, solder resistance and adhesion of the back electrode after sintering; reducing the back electrode resistance, meeting the welding and tension requirements of the component end, and effectively solving the problem of decreased photoelectric conversion efficiency due to reduced silver powder content.

[0042] 3. In the back silver paste provided by the present invention, a specific mixed metal oxide with a particle size distribution D50≤0.8 micron is added in a weight percentage of 1-3%, which effectively solves the corrosion problem of the back film of the battery cell existing in the existing back silver paste containing glass powder, reduces the back recombination rate, and improves the opening voltage.

[0043] 4. The back silver paste provided by the present invention adds silicon dioxide powder with a particle size of 1 to 2 microns and a purity requirement of 99.99% as an inorganic auxiliary agent, which helps to adjust the shrinkage rate of the back electrode and improve the back electrode to match it with the aluminum back field.

[0044] 5. Each slurry in the back silver paste provided by the present invention uses Dispersant TDO as a dispersant. By optimizing the slurry ratio, an emulsifier is used to wet and disperse three silver powders with different particle size distributions, mixed metal oxides, and inorganic additives under high-speed stirring conditions, so that silver powder A, silver powder B, silver powder C, mixed metal oxides, and inorganic additives are wetted and dispersed to form single particles in the organic carrier, which is helpful for the subsequent preparation of the back silver paste. DETAILED DESCRIPTION

[0045] Example 1

[0046] Embodiment 1 of the present invention provides a PERC crystalline silicon solar back silver paste, which comprises, by mass percentage, 82.20% silver powder A paste, 9.03% silver powder B paste, 4.03% silver powder C paste, 3.83% mixed metal oxide paste, and 0.91% inorganic auxiliary agent paste.

[0047] The silver powder A slurry, by mass percentage, includes 56.93% of silver powder A, 42.82% of organic vehicle, and 0.25% of dispersant Dispersant TDO (Nouryon Duomeen TPO color paste dispersant).

[0048] The silver powder B slurry, by mass percentage, includes 44.30% of silver powder B, 55.37% of organic vehicle, and 0.33% of dispersant Dispersant TDO (Nouryon Duomeen TPO color paste dispersant).

[0049] The silver powder C slurry, by mass percentage, includes 24.81% of silver powder C, 49.63% of organic vehicle, 0.75% of dispersant Dispersant TDO (Nouryon Duomeen TPO color paste dispersant), and 24.81% of solvent diethylene glycol dibutyl ether.

[0050] The silver powder A in the silver powder A slurry is approximately spherical, with a D50 of 0.78 microns and a specific surface area of ​​1.494 m 2 / g.

[0051] The silver powder B in the silver powder B slurry is approximately spherical, with a D50 of 0.4 microns and a specific surface area of ​​2.55 m 2 / g.

[0052] The silver powder C in the silver powder C slurry is approximately spherical, with a D50 of 100 nm and a specific surface area of ​​8.0±0.1 m 2 / g.

[0053] The mixed metal oxide slurry, by mass percentage, includes 47.00% of mixed metal oxide, 52.22% of organic carrier, and 0.78% of dispersant Dispersant TDO (Nouryon Duomeen TPO color paste dispersant).

[0054] Calculated by mass percentage, the mixed metal oxide includes: 38% silicon dioxide, 32% lead oxide, 11% copper oxide, 11% titanium dioxide, 4.5% bismuth trioxide, and 3.5% tellurium dioxide.

[0055] The preparation method of the mixed metal oxide is as follows: silicon dioxide, lead oxide, copper oxide, titanium dioxide, bismuth trioxide, and tellurium dioxide are placed in an alumina crucible according to mass percentage, placed in a muffle furnace, heated to 1300°C, and kept warm for 4 hours; then the heating is stopped and the temperature is naturally cooled down at a cooling rate of 2°C / minute; when the temperature in the muffle furnace is lower than 100°C, the crucible is taken out, and the metal mixed oxide in the crucible is first preliminarily crushed into particles, and then deionized water is used as a carrier and a zirconium ball with a diameter of 1.6 to 1.8 cm is used as a grinding medium, and ball milling is performed for 2 hours; the zirconium ball with a diameter of 1.6 to 1.8 cm is taken out, and ball milling is performed for 6 hours with a zirconium ball with a diameter of 1.0 mm. The zirconium ball is taken out, and the ball milling liquid is placed in a stainless steel plate, and the water is dried in an oven at 60-90°C to obtain a mixed metal oxide with a particle size distribution of D500.6 to 0.8 microns.

[0056] The inorganic auxiliary agent slurry includes, by mass percentage, 32.97% of inorganic auxiliary agent, 65.93% of organic carrier, and 1.10% of dispersant Dispersant TDO (Nouryon Duomeen TPO color paste dispersant).

[0057] The inorganic additive in the inorganic additive slurry is silicon dioxide, specifically silicon dioxide powder with a particle size of 1 to 2 microns and a purity requirement of 99.99%.

[0058] The organic carrier in the silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry and inorganic auxiliary agent slurry includes, by mass percentage, 10% ethyl cellulose (STD200), 40% nylon acid methyl ester, 30% butyl carbitol and 20% alcohol ester dodecyl alcohol.

[0059] The preparation method of the organic carrier comprises the following steps: weighing a solvent according to a mass percentage and adding the solvent into a jacketed reactor; placing a dispersing disk of a high-speed disperser in the middle of the weighed solvent in the jacketed reactor, turning on the high-speed disperser, and setting a stirring speed of 300RPM, so as to uniformly mix the mixture in the reactor; weighing cellulose and adding the solvent into the stirring solvent in the reactor; setting a water bath heating temperature of the jacketed reactor at 80°C, and setting a stirring speed of the high-speed disperser at 800RPM; after the water bath temperature of the jacketed reactor reaches the set heating temperature, maintaining the set heating temperature and stirring speed of the high-speed disperser, dissolving the cellulose for 2 hours under this condition, and sealing the dissolved organic carrier, and cooling it down to obtain the organic carrier.

[0060] The preparation process of the silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry and inorganic auxiliary agent slurry is as follows: each raw material in the silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry and inorganic auxiliary agent slurry is dispersed by high-speed stirring in an emulsifier, the speed is set to 1500RPM, and the emulsification dispersion is performed for 30 minutes.

[0061] Embodiment 1 of the present invention provides a method for preparing silver paste on the back side of PERC crystalline silicon solar cell, which specifically comprises the following steps:

[0062] S1: preparing silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry, and inorganic additive slurry respectively;

[0063] S2: Use a high-speed disperser to stir and disperse silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry, and inorganic additive slurry. Set the speed to 1000RPM and stir and disperse for 30 minutes to obtain a back silver paste with a fineness of <10 microns.

[0064] Example 2

[0065] Embodiment 2 of the present invention provides a PERC crystalline silicon solar back side silver paste and a preparation method thereof, and its specific implementation mode is the same as that of Embodiment 1, except that, by mass percentage, it includes 79.70% silver powder A paste, 11.29% silver powder B paste, 4.03% silver powder C paste, 4.68% mixed metal oxide paste, and 0.30% inorganic auxiliary agent paste.

[0066] Comparative Example 1

[0067] Comparative Example 1 of the present invention provides a PERC crystalline silicon solar back silver paste and a preparation method thereof. Its specific implementation manner is the same as that of Example 1, except that, by mass percentage, it includes 79.54% silver powder A slurry, 5.64% silver powder B slurry, 10.08% silver powder C slurry, 3.83% mixed metal oxide slurry, and 0.91% inorganic auxiliary agent slurry.

[0068] Comparative Example 2

[0069] Comparative Example 2 of the present invention provides a PERC crystalline silicon solar back silver paste and a preparation method thereof. Its specific implementation method is the same as that of Example 1, except that, by mass percentage, it includes 81.04% silver powder A slurry, 8.67% silver powder B slurry, 4.03% silver powder C slurry, 3.83% mixed metal oxide slurry, and 2.43% inorganic auxiliary agent slurry.

[0070] Comparative Example 3

[0071] Comparative Example 3 of the present invention provides a PERC crystalline silicon solar back silver paste, and the raw materials for preparing the paste are shown in Table 1.

[0072] Table 1

[0073]

[0074] The preparation process of the PERC crystalline silicon solar back silver paste is as follows: prepare the ingredients according to Table 1, use a high-speed disperser to stir and disperse, set the speed to 1000RPM, stir and disperse for 30 minutes, and then use a three-roll grinder to grind to a fineness of <10 microns.

[0075] Comparison Example

[0076] The control example of the present invention is the commercially available PERC crystalline silicon solar cell back side silver paste RB-P03T (Foshan Ruina New Materials Technology Co., Ltd.).

[0077] Performance Testing Methods

[0078] 1. The HALM IV tester was used to test the electrical performance of the PERC cells prepared in the embodiments, comparative examples and control examples in the industry standard test mode, wherein the blue film in the PERC cell: 182 size PERC monocrystalline bifacial cell, 11BB; back film: aluminum oxide + silicon nitride; cell production line: Maxwell; each embodiment, comparative example and control example used the same back aluminum slurry, main grid slurry, and front fine grid slurry; sintering peak temperature: 760°C, and the electrical performance test results are shown in Table 2.

[0079] Table 2

[0080]

[0081]

Claims

1. A PERC crystalline silicon solar back silver paste, characterized in that: The invention is composed of a silver powder slurry combination, a mixed metal oxide slurry and an inorganic auxiliary agent slurry, wherein the silver powder slurry combination includes a silver powder slurry with a D50 of 50nm-1μm; the silver powder slurry combination at least includes: a silver powder A slurry with a D50 of 0.5-1 micron, a silver powder B slurry with a D50 of 0.2-0.4 micron, and a silver powder C slurry with a D50 of 50-100 nanometers; based on the total weight of the PERC crystalline silicon solar back silver slurry, the weight percentage of the silver powder A is 43-47%, the weight percentage of the silver powder B is 3-5%, and the weight percentage of the silver powder C is 1-2%; the inorganic auxiliary agent slurry is silicon dioxide; by mass percentage, the mixed metal oxides in the mixed metal oxide slurry include 35-40% silicon dioxide, 25-3 5%, copper oxide 8-15%, titanium dioxide 8-15%, bismuth trioxide 1-8%, tellurium dioxide 1-8%; the preparation method of the mixed metal oxide is as follows: according to the mass percentage, silicon dioxide, lead oxide, copper oxide, titanium dioxide, bismuth trioxide, and tellurium dioxide are placed in an alumina crucible, placed in a muffle furnace, heated to 1200-1400°C, and kept warm for 3-5 hours; then the heating is stopped and the temperature is naturally cooled, and the cooling rate is <2°C / minute; when the temperature in the muffle furnace is lower than 100°C, the crucible is taken out, and the metal mixed oxide in the crucible is first preliminarily crushed into particles, and then deionized water is used as a carrier and a zirconium ball with a diameter of 1.6-1.8cm is used as a grinding medium, and ball milling is performed for 1-3 hours; the zirconium ball with a diameter of 1.6-1.8cm is taken out, and a 0.8 mm zirconium balls are ball-milled for 5-7 hours; the zirconium balls are taken out, the ball-milling liquid is placed in a stainless steel plate, and the water is dried in an oven at 60-90°C to obtain a mixed metal oxide with a particle size distribution of D50≤0.8 microns.

2. A PERC crystalline silicon solar back side silver paste according to claim 1, characterized in that: The silver powder A in the silver powder A slurry is spherical or approximately spherical, with a D50 of 0.7 to 0.9 microns and a specific surface area of ​​0.8 to 1.5 m 2 / g; the silver powder B in the silver powder B slurry is spherical or approximately spherical, with a D50 of 0.2~0.4 microns and a specific surface area of ​​2.5~3.0m 2 / g; the silver powder C in the silver powder C slurry is spherical or approximately spherical, D50 is 80~100nm, and the specific surface area is>7.6m 2 / g.

3. A PERC crystalline silicon solar back silver paste according to claim 2, characterized in that: Based on the total weight of the silver paste on the back side of the PERC crystalline silicon solar cell, the weight percentage of the mixed metal oxide is 1-3%.

4. A PERC crystalline silicon solar back side silver paste according to claim 3, characterized in that: The silver powder A slurry, the silver powder B slurry, the silver powder C slurry, the mixed metal oxide slurry and the inorganic auxiliary agent slurry all include an organic carrier, and the organic carrier is composed of cellulose and a solvent.

5. A PERC crystalline silicon solar back side silver paste according to claim 4, characterized in that: The preparation process of the silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry and inorganic auxiliary agent slurry is as follows: each raw material in the silver powder A slurry, silver powder B slurry, silver powder C slurry, mixed metal oxide slurry and inorganic auxiliary agent slurry is respectively dispersed by high-speed stirring in an emulsifier, the speed is set to 1000-2000RPM, and the emulsification dispersion is performed for 20-40 minutes.

6. A method for preparing a PERC crystalline silicon solar back silver paste according to any one of claims 1 to 5, characterized in that: At least the following steps are included: The silver powder slurry combination, the mixed metal oxide slurry and the inorganic additive slurry are stirred and dispersed by a high-speed disperser, the speed is set to 800-1200RPM, and the stirring and dispersion is performed for 20-40 minutes to obtain a back silver paste with a fineness of <10 microns.

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