Lead-free and bismuth-free glass powder for non-contact silver paste of crystalline silicon solar cell and preparation method of lead-free and bismuth-free glass powder

Abstract

The invention discloses lead-free and bismuth-free glass powder for non-contact silver paste of a crystalline silicon solar cell, the lead-free and bismuth-free glass powder comprises the following raw material components in percentage by mass: 10-30% of SiO2, 12-20% of B2O3, 0-10% of MoO3, 0-2% of Li2CO3, 0-4% of TeO2, 0-3% of Al2O3, 30-50% of RO and 10-30% of RO2, RO is one or more of CuO, CaO, BaO, ZnO and MgO, and RO2 is one or more of TiO2 and MnO2. The prepared silver paste glass powder does not contain lead, bismuth and vanadium elements, and the defects that lead-free and bismuth-free glass powder is high in softening point, not prone to glass forming and the like are overcome through the reasonable matching of other oxides with good reactivity on silver powder and the saline water quenching preparation method. The lead-free and bismuth-free glass powder has a softening point suitable for a non-contact silver paste sintering process of a solar cell and good wettability to silver powder and a silicon wafer, high welding tension of a silver thick film is ensured, meanwhile, due to the fact that lead and bismuth elements are not used, the lead-free and bismuth-free glass powder basically does not react with a SiNx film on the surface of the silicon wafer, only physical wetting exists, and the welding performance of the silicon wafer is improved. The completeness of the passivation structure is greatly ensured, and the photoelectric conversion efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cells, and more specifically, relates to a lead-free and bismuth-free glass powder for a non-contact silver paste for a crystalline silicon solar cell and a preparation method thereof. Background Art

[0002] In the preparation process of crystalline silicon solar cells, silver paste as an electrode material directly affects the photovoltaic conversion efficiency and long-term reliability of the battery. Glass powder, as the core functional component of silver paste, plays a role throughout the key steps of the sintering process, such as silver particle fusion, silicon substrate etching, and ohmic contact formation. The traditional glass powder system is based on PbO-Bi2O3-SiO2, in which the lead (Pb) element can significantly reduce the softening temperature of the glass phase and promote the densification of silver particles; the bismuth (Bi) element can enhance the selective etching ability of the silicon substrate and optimize the contact resistance by regulating the glass network structure. However, with the tightening of environmental protection regulations and the demand for sustainable development in the photovoltaic industry, lead and bismuth system glass powders are facing severe replacement pressure.

[0003] Current lead-free technology routes are mainly divided into two categories: 1. Bismuth-containing lead-free system: Bi2O3 is the main component, supplemented by oxides such as ZnO and B2O3. Although it can partially inherit the sintering characteristics of the traditional system, the high Bi content easily triggers glass phase crystallization, limiting its application conditions. 2. Bismuth replacement system: heavy metal oxides such as Te, V, and Mo or phosphate glass are used. Although this type of system achieves "double-free" (lead-free and bismuth-free), the reactivity of this glass powder with solder is strong, and when used in non-contact silver paste, it cannot provide sufficient welding tension.

[0004] For example, the patent CN11215911B mentions the use of V2O5, B2O3, and SiO2 to construct a lead-free bismuth glass structure, which can be applied to PERC solar cell aluminum paste. However, when such a solution is applied to non-contact silver paste, due to the strong silver solubility of this type of glass powder, it is easy to cause excessive corrosion to the passivation layer and increase the composite loss.

[0005] As mentioned in the patent CN105590663B, SnO and P2O5 are used to construct a lead-free bismuth glass structure, which can be applied to contact silver paste. However, for non-contact silver paste, its main function is to serve as a soldering pad. If the glass powder contains more SnO, it will react too quickly with the tin solder and cannot provide welding tension.

[0006] Therefore, the existing solutions are difficult to meet the demand of non-contact silver paste for lead-free bismuth glass powder, and cannot be used in industrial applications due to problems such as low photoelectric conversion efficiency and inability to provide welding tension. Summary of the Invention

[0007] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0008] In order to achieve these objects and other advantages of the present invention, a lead-free and bismuth-free glass powder for non-contact silver paste of crystalline silicon solar cells is provided. The raw material components of the lead-free and bismuth-free glass powder include, by mass ratio, 10% to 30% SiO2, 12% to 20% B2O3, 0% to 10% MoO3, 0% to 2% Li2CO3, 0% to 4% TeO2, 0% to 3% Al2O3, 30% to 50% RO, and 10 to 30% RO2, wherein RO is one or more of CuO, CaO, BaO, ZnO, and MgO, and RO2 is one or more of TiO2 and MnO2.

[0009] The present invention also provides a method for preparing lead-free and bismuth-free glass powder for non-contact silver paste of crystalline silicon solar cells, comprising:

[0010] Step 1: Weigh the raw materials in proportion and mix them evenly in a three-dimensional powder mixer;

[0011] Step 2: Place the mixed raw materials into an alumina crucible, keep warm and melt until the raw materials react completely and no obvious bubbles are generated at high temperature, thereby obtaining a glass melt;

[0012] Step 3: quickly pouring the uniform glass melt into salt water for water quenching to obtain glass slag;

[0013] Step 4: After filtering the glass slag from the salt water, the glass slag is washed with deionized water to remove excess salt on the surface of the glass slag, and then ball milled. After ball milling, the glass slag is dried and sieved to obtain lead-free and bismuth-free glass powder.

[0014] Preferably, in the step 2, the holding melting temperature is 1300-1550° C., and the holding melting time is 40-60 minutes.

[0015] Preferably, in step 3, the solute of the brine is one or more of NaCl, KCl2, and CaCl2, and the solvent is deionized water.

[0016] Preferably, in step 3, the concentration of the brine should be 5% to 30%.

[0017] Preferably, in step three, the ball milling beads used in ball milling are composed of 0.5 μm and 0.3 μm zirconium beads in a ratio of 1:3, the ball milling medium is deionized water, and the mass ratio of glass slag, ball milling beads and deionized water is 12:9:4.

[0018] Preferably, in step 4, when using deionized water to wash the glass slag, deionized water should be added to the glass slag at a solid-liquid ratio of 1:5 to 1:10, and ultrasonic treatment should be performed for 15 to 30 minutes.

[0019] Preferably, in step 4, the particle size D50 of the lead-free and bismuth-free glass powder obtained is controlled to be 0.5-2 μm, and the softening temperature is 500-620° C.

[0020] The present invention includes at least the following beneficial effects: the non-contact silver paste glass powder for crystalline silicon solar cells provided by the present invention does not contain lead, bismuth and vanadium elements. By selecting a reasonable combination of other oxides with good reactivity to silver powder, and innovatively using salt water as a quenching medium, compared with deionized water, salt water has higher thermal conductivity, makes the glass more uniform, can increase the proportion of amorphous phase, and changes the shortcomings of lead-free and bismuth-free glass powder such as a high softening point and difficulty in glass formation. The prepared lead-free and bismuth-free glass powder has a softening point suitable for the non-contact silver paste sintering process of solar cells and good wettability to silver powder and silicon wafers, ensuring high welding tensile strength of the silver thick film. At the same time, since it does not use lead and bismuth elements, it basically does not react with the SiNx film on the surface of the silicon wafer, and only physical wetting occurs, which greatly ensures the integrity of the passivation structure and improves the photoelectric conversion efficiency.

[0021] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the embodiments so that those skilled in the art can implement the invention with reference to the description.

[0023] It should be understood that terms such as “having”, “including” and “comprising” used herein do not preclude the existence or addition of one or more other elements or combinations thereof.

[0024] Example 1

[0025] A method for preparing lead-free and bismuth-free glass powder for contactless silver paste of crystalline silicon solar cells, comprising:

[0026] Step 1: Weigh 1.4kg SiO2, 1.8kg B2O3, 0.8kg MoO3, 0.2kg Li2CO3, 0.2kg TeO2, 0.2kg Al2O3, 1.0kg CuO, 1.0kg ZnO, 1.0kg CaO, 1.2kg TiO2, and 1.2kg MnO2 in a three-dimensional powder mixer and mix them evenly;

[0027] Step 2: Place the mixed raw materials into an alumina crucible and melt them at 1300° C. for 40 minutes to obtain a glass melt;

[0028] Step 3: Weigh 46 kg of deionized water, add 4 kg of potassium chloride, and stir until completely dissolved as quenching brine;

[0029] Step 4: quickly pouring the uniform molten glass into the above-mentioned salt water for quenching to obtain glass slag;

[0030] Step 5: After filtering the glass slag from the brine, add deionized water at a solid-liquid ratio of 1:5, and then use ultrasonic cleaning for 15 minutes;

[0031] Step 6. Filter out the washed glass slag and dry it. Ball-mill the dried glass slag for 4 hours. Add 7.5 kg of ball milling beads and 3.33 kg of deionized water according to the mass ratio of glass slag, ball milling beads and deionized water of 12:9:4, wherein the ball milling beads are composed of 0.5 μm and 0.3 μm zirconium beads in a ratio of 1:3. After ball milling, dry and sieve to obtain lead-free and bismuth-free glass powder with a particle size D50 of 0.5 μm and a softening temperature of 524°C.

[0032] Example 2

[0033] A method for preparing lead-free and bismuth-free glass powder for contactless silver paste of crystalline silicon solar cells, comprising:

[0034] Step 1: Weigh 2.2kg SiO2, 2.0kg B2O3, 0.2kg Li2CO3, 0.2kg Al2O3, 1.0kg CuO, 1.0kg ZnO, 1.0kg MgO, 1.2kg TiO2, and 1.2kg MnO2 in a three-dimensional powder mixer and mix them evenly;

[0035] Step 2: Place the mixed raw materials into an alumina crucible and melt them at 1400° C. for 60 minutes to obtain a glass melt;

[0036] Step 3: Weigh 33.8 kg of deionized water, add 6.48 kg of calcium chloride and 9.72 kg of potassium chloride, and stir until completely dissolved as quenching brine;

[0037] Step 4: quickly pouring the uniform molten glass into the above-mentioned salt water for quenching to obtain glass slag;

[0038] Step 5: After filtering the glass slag from the brine, add deionized water at a solid-liquid ratio of 1:5, and then use ultrasonic cleaning for 15 minutes;

[0039] Step 6. Filter out the washed glass slag and dry it. Ball-mill the dried glass slag for 6 hours. Add 7.5 kg of ball milling beads and 3.33 kg of deionized water according to the mass ratio of glass slag, ball milling beads and deionized water of 12:9:4, wherein the ball milling beads are composed of 0.5 μm and 0.3 μm zirconium beads in a ratio of 1:3. After ball milling, dry and sieve to obtain lead-free and bismuth-free glass powder with a particle size D50 of 0.8 μm and a softening temperature of 592°C.

[0040] Example 3

[0041] A method for preparing lead-free and bismuth-free glass powder for non-contact silver paste of crystalline silicon solar cells, comprising:

[0042] Step 1: Weigh 1.8kg SiO2, 1.4kg B2O3, 0.8kg MoO3, 0.2kg Li2CO3, 0.2kg TeO2, 0.2kg Al2O3, 2.0kg BaO, 1.4kg MgO, 0.8kg TiO2, and 1.2kg MnO2 in a three-dimensional powder mixer and mix them evenly;

[0043] Step 2: Place the mixed raw materials into an alumina crucible and melt them at 1300°C for 40 minutes to obtain a glass melt;

[0044] Step 3: Weigh 22.0 kg of deionized water, add 5.6 kg of calcium chloride, 5.6 kg of potassium chloride, and 16.8 kg of sodium chloride, and stir until completely dissolved as quenching brine;

[0045] Step 4: quickly pouring the uniform molten glass into the above-mentioned salt water for quenching to obtain glass slag;

[0046] Step 5: After filtering the glass slag from the brine, deionized water was added according to a solid-liquid ratio of 1:10, and then ultrasonically washed for 30 minutes;

[0047] Step 6. Filter out the washed glass slag and dry it. Ball-mill the dried glass slag for 4 hours. Add 7.5 kg of ball milling beads and 3.33 kg of deionized water according to the mass ratio of glass slag, ball milling beads and deionized water of 12:9:4, wherein the ball milling beads are composed of 0.5 μm and 0.3 μm zirconium beads in a ratio of 1:3. After ball milling, dry and sieve to obtain lead-free and bismuth-free glass powder with a particle size D50 of 0.6 μm and a softening temperature of 543°C.

[0048] Comparative Example 1

[0049] This comparative example differs from Example 1 in that conventional deionized water was used for quenching, rather than salt water. The remaining steps were identical to those in Example 1. The resulting lead-free and bismuth-free glass powder had a particle size D50 of 0.9 μm and a softening temperature of 603°C. It can be seen that the glass powder quenched with conventional deionized water had a higher softening point and larger particle size.

[0050] Comparative Example 2

[0051] As comparative example 2, lead-based glass powder commonly used in commercially available main grid silver paste was used.

[0052] Comparative Example 3

[0053] According to the method in the patent publication CN105590663B, 0.43 kg of SnO and 1.07 kg of P2O5 were weighed and mixed evenly in a three-dimensional powder mixer, then placed in a crucible, heated at 900°C for 30 minutes, quenched with deionized water, ball milled, dried, and sieved to obtain lead-free and bismuth-free glass powder as comparative example 3.

[0054] To further illustrate the advantages of the present invention, 3 g of each of the lead-free and bismuth-free glass powders in Examples 1-3 and Comparative Examples 1-3 were used, along with 78 g of the same main grid silver powder and 20 g of the same organic carrier. After stirring and grinding, main grid silver pastes containing different lead-free and bismuth-free materials were prepared. The same fine grid paste was used and silicon solar cells were made under the same printing and sintering conditions. Examples 1-3 were recorded as S1-3, and Comparative Examples 1-3 were recorded as D1-3.

[0055] The main grid silver paste prepared based on Example 1-4 was screen printed under the same conditions, and after drying and sintering, welding tension and IV tests were performed.

[0056] The welding tensile test method is as follows: prepare the comparative example and embodiment silver paste on the crystalline silicon cell according to the industrial application standard to form the main grid electrode, use the same welding ribbon to weld the front and back of the cell respectively at 360°C, and then use a horizontal tensile tester to perform the tensile test.

[0057] The IV test method is: prepare the comparative example and embodiment silver paste on the crystalline silicon solar cell according to the industrial application standard, match it with the same auxiliary gate paste to form the main gate electrode, and then perform IV test.

[0058] The test results are shown in Table 1 below.

[0059] Table 1 Performance test of Examples 1-3 and Comparative Examples 1-3

[0060] Grouping Eta (%) Voc(V) Isc(A) FF(%) Tensile force (N) S1 26.45 0.74 13.89 85.53 3.08 S2 26.43 0.74 13.89 85.54 3.32 S3 26.41 0.74 13.88 85.63 3.02 D1 26.25 0.74 13.91 85.06 2.74 D2 26.31 0.60 13.88 85.26 3.11 D3 13.47 0.55 1.05 56.42 0.53

[0061] The test results in Table 1 show that the busbar silver paste prepared using the lead-free, bismuth-free glass frit of the present invention exhibits superior photoelectric conversion efficiency (Eta) and comparable soldering strength to the commercially available lead-based glass frit D2. However, the lead-free, bismuth-free glass frits S1-3 exhibit superior Voc, due to their reduced corrosion of the passivation layer. This indicates that the glass frit of the present invention does not substantially damage the hydrogenated silicon nitride (SiNx:H) film of crystalline silicon solar cells, contributing to improved photoelectric conversion efficiency. Compared to the lead-free, bismuth-free glass frit D1 quenched with conventional deionized water, the lead-free, bismuth-free glass frit S1 quenched with salt water exhibits a higher fill factor (FF) and, consequently, a higher Eta. This is because salt water has a higher thermal conductivity than deionized water, increasing the proportion of the amorphous phase in the glass frit, thereby achieving a more uniform and dense silver electrode during sintering. However, when constructing the lead-free, bismuth-free glass frit D3 using SnO and P2O5 as substitutes, its Eta and soldering strength are extremely low, failing to meet the requirements of industrial applications.

[0062] The present invention provides a lead-free and bismuth-free glass powder for non-contact silver paste for silicon solar cells and a preparation method thereof. By rationally matching different oxides and optimizing the preparation method, the powder can be well applied to silver paste for crystalline silicon solar cells. By selecting oxides with good high-temperature reactivity with silver powder, the shortcomings of poor wettability of lead-free and bismuth-free glass powder with silver powder and inability to provide welding tension are improved. Innovative salt aqueous solution is used as a quenching medium. Compared with deionized water, salt water has a higher thermal conductivity, making the glass more uniform and increasing the proportion of amorphous phase, thus changing the shortcomings of lead-free and bismuth-free glass powder such as a high softening point and difficulty in glass formation. The non-contact silver paste prepared using the glass powder of the present invention can greatly improve the photoelectric conversion efficiency of crystalline silicon solar cells, especially the improvement of open-circuit voltage, while providing reliable welding tension.

[0063] Although specific embodiments of the present invention have been described in detail above, this does not mean that the present invention is limited to the scope of application listed in the specification and embodiment. The present invention is fully applicable to other fields consistent with its basic principles. It is very easy for those skilled in the art to implement other modifications and variations. Therefore, without departing from the core concepts defined by the claims of the present invention and their equivalents, the present invention is not limited to the specific details or examples.

Claims

1. A lead-free and bismuth-free glass powder for contactless silver paste of crystalline silicon solar cells, characterized in that: The raw material components of the lead-free and bismuth-free glass powder include, by mass ratio, 10% to 30% SiO2, 12% to 20% B2O3, 0% to 10% MoO3, 0% to 2% Li2CO3, 0% to 4% TeO2, 0% to 3% Al2O3, 30% to 50% RO, and 10 to 30% RO2, wherein RO is one or more of CuO, CaO, BaO, ZnO, and MgO, and RO2 is one or more of TiO2 and MnO2.

2. A method for preparing the lead-free and bismuth-free glass powder for the non-contact silver paste for crystalline silicon solar cells according to claim 1, characterized in that: include: Step 1: Weigh the raw materials in proportion and mix them evenly in a three-dimensional powder mixer; Step 2: Place the mixed raw materials into an alumina crucible, keep warm and melt until the raw materials react completely and no obvious bubbles are generated at high temperature, thereby obtaining a glass melt; Step 3: quickly pouring the uniform glass melt into salt water for water quenching to obtain glass slag; Step 4: After filtering the glass slag from the salt water, the glass slag is washed with deionized water to remove excess salt on the surface of the glass slag, and then ball milled. After ball milling, the glass slag is dried and sieved to obtain lead-free and bismuth-free glass powder.

3. The method for preparing the lead-free and bismuth-free glass powder for the non-contact silver paste for crystalline silicon solar cells according to claim 2, characterized in that: In the step 2, the heat preservation and melting temperature is 1300-1550° C., and the heat preservation and melting is carried out for 40-60 minutes.

4. The method for preparing the lead-free and bismuth-free glass powder for the non-contact silver paste for crystalline silicon solar cells according to claim 2, characterized in that: In step 3, the solute of the brine is one or more of NaCl, KCl2, and CaCl2, and the solvent is deionized water.

5. The method for preparing the lead-free and bismuth-free glass powder for the non-contact silver paste for crystalline silicon solar cells according to claim 2, characterized in that: In step 3, the concentration of the brine should be 5% to 30%.

6. The method for preparing the lead-free and bismuth-free glass powder for the non-contact silver paste for crystalline silicon solar cells according to claim 2, characterized in that: In the step 3, the ball milling beads used in the ball milling are composed of 0.5 μm and 0.3 μm zirconium beads in a ratio of 1:3, the ball milling medium is deionized water, and the mass ratio of glass slag, ball milling beads and deionized water is 12:9:

4.

7. The method for preparing the lead-free and bismuth-free glass powder for the non-contact silver paste for crystalline silicon solar cells according to claim 2, characterized in that: In the fourth step, when using deionized water to wash the glass slag, deionized water should be added to the glass slag at a solid-liquid ratio of 1:5 to 1:10, and ultrasonic treatment should be performed for 15 to 30 minutes.

8. The method for preparing the lead-free and bismuth-free glass powder for the non-contact silver paste for crystalline silicon solar cells according to claim 2, characterized in that: In the step 4, the particle size D50 of the obtained lead-free and bismuth-free glass powder is controlled to be 0.5-2 μm, and the softening temperature is 500-620° C.