An auxiliary glass powder additive for silver paste and its preparation method

Abstract

The present invention relates to H01L. More specifically, the present invention relates to an auxiliary glass powder additive for silver paste and a preparation method thereof, including at least one of glass powder additive 1 and glass powder additive 2. The glass powder additive provided by the present invention can cooperate with the main glass powder during the sintering process. By utilizing the different softening points of different additives and the different redox reaction sequences, the problem that it is difficult for a single glass powder to achieve high battery conversion efficiency and high positive silver sintering effect can be improved. Moreover, the inventor has also found that when the two glass powder additives of the present invention and the main glass powder act together, it can promote the densification of silver powder during the sintering process, promote the complete corrosion of the front silicon nitride antireflection layer, promote the precipitation of silver crystals in the etched emitter, and precipitate a lot of silver colloids in the intermediate glass layer after sintering to achieve good ohmic contact, while providing good adhesion and obtaining high solar cell conversion efficiency.

Description

Technical Field

[0001] The present invention relates to H01L, and more specifically, the present invention relates to an auxiliary glass powder additive for silver paste and a preparation method thereof. Background Art

[0002] Currently, the mainstream solar cells on the market include PERC cells, Al-BSF cells, TOPCon cells, HJT cells, etc. Among them, PERC cells are dominant, accounting for about 90% of crystalline silicon solar cells. How to further improve the photoelectric conversion efficiency of PERC cells and reduce costs has always been the main goal of photovoltaic development.

[0003] Among them, in the process of preparing PERC cells, the last process is screen printing positive silver paste, and a positive electrode with good ohmic contact is formed through short-time high-temperature sintering. The positive silver paste mainly includes silver powder for ohmic contact, organic additives such as organic carriers for achieving good printing performance, and glass powder which is a key preparation raw material for achieving ohmic contact. Although the proportion of glass powder in the positive silver paste is very small, it has an important impact on the corrosion of the front silicon nitride film, the precipitation of silver grains, and the silver-silicon ohmic contact, thus significantly affecting the conversion efficiency of the battery.

[0004] Therefore, it is necessary to develop glass powder that is more beneficial to the interaction between the silver paste and the positive electrode. Currently, there are many types of glass powder, such as Te-Si-Pb-Bi series crystalline glass powder, Pb-Bi-B-Si series glass powder, Bi-Si-B series glass powder, Bi-B-Ba series lead-free glass powder, etc. However, the current research on glass powder mainly focuses on the main glass powder, such as CN106892567A, etc. However, it is difficult for a single glass powder to achieve a good sintering effect and thus improve the conversion efficiency. Summary of the Invention

[0005] In order to solve the above problems, in the first aspect of the present invention, an auxiliary glass powder additive for silver paste is provided. The preparation raw materials of the glass powder additive include at least one of glass powder additive one and glass powder additive two:

[0006] Glass powder additive one includes SiO2, Bi2O3, ZnO, WO3, PbO, CuO, TeO2;

[0007] Glass powder additive two includes SiO2, Bi2O3, ZnO, WO3, PbO, TeO2.

[0008] As a preferred technical solution of the present invention, the raw materials for preparing the first glass powder additive, by weight percentage, include: SiO2 25-45%, Bi2O3 15-35%, ZnO 5-15%, WO3 5-20%, PbO 5-15%, CuO 1-10%, TeO2 1-10%.

[0009] As a preferred technical solution of the present invention, the raw materials for preparing the first glass powder additive, by weight percentage, include: SiO2 30-40%, Bi2O3 15-30%, ZnO 5-10%, WO3 5-25%, PbO 5-10%, CuO 1-5%, TeO2 1-5%.

[0010] As a preferred technical solution of the present invention, the raw materials for preparing the first glass powder additive, by weight percentage, include: SiO2 33-38%, Bi2O3 25-30%, ZnO 5-10%, WO3 8-15%, PbO 8-10%, CuO 1-5%, TeO2 1-5%.

[0011] The inventors found that by increasing the content of large polarizability ions such as Bi 3+ and Pb 2+ etc., the melting temperature of the first glass powder additive can be reduced, so as to obtain a glass powder additive with a medium softening point, thereby promoting the bonding of silver powder after subsequent silver paste printing and sintering with the main glass powder, forming a denser structure, and significantly promoting the increase of Rsh. However, the inventors also found that if the softening point is too low and it melts earlier, the precipitation of Pb etc. will also occur, which will also affect the deposition of Ag grains and ohmic contact, resulting in problems such as an increase in Rser and a decrease in FF, affecting the final Eta.

[0012] As a preferred technical solution of the present invention, the raw materials for preparing the second glass powder additive, by weight percentage, include: SiO2 65-85%, TeO2 5-15%, PbO 5-15%, WO3 1-15%, Bi2O3 1-15%, ZnO 1-10%.

[0013] As a preferred technical solution of the present invention, the raw materials for preparing the second glass powder additive, by weight percentage, include: SiO2 70-80%, TeO2 5-10%, PbO 5-15%, WO3 1-10%, Bi2O3 1-10%, ZnO 1-10%.

[0014] As a preferred technical solution of the present invention, the raw materials for preparing the glass powder additive II include, by weight percentage: 70-75% of SiO2, 5-10% of TeO2, 5-12% of PbO, 3-8% of WO3, 2-8% of Bi2O3, and 1-4% of ZnO.

[0015] The inventor also found that by adding the glass powder additive II and controlling a high Si 4+ content to form a main structure of silicon-oxygen tetrahedrons and a structure with PbO as an external network body, a glass powder with a high softening point is obtained. Thus, during the process of acting together with the main glass powder and silver powder, it promotes the deposition of silver grains at the Ag / Si interface and forms an ohmic contact, reducing the penetration of the positive electrode. However, it will also cause a decrease in density and an increase in Rser. Therefore, by adding WO3, TeO2, ZnO, etc., the inventor found that a glass powder with a higher FF and Rsh can be obtained, reducing the increase in Rser and obtaining a silver paste with a higher Eta.

[0016] As a preferred technical solution of the present invention, the weight ratio of the glass powder additive I to the glass powder additive II is (1-2):(1-2).

[0017] The inventor found that when the glass powder additive I and the glass powder additive II act together with the main glass powder, during the printing and sintering process, on the one hand, a small amount of molten state is formed by the glass powder additive to connect the main glass powder, the glass powder additive II, and the silver powder, promoting the dissolution of a small amount of silver powder. Along with the melting of the main glass powder, it promotes the separation of Ag and Pb. While silver grains adhere to the main glass powder and the unmolten glass powder additive II, through a series of complex redox reactions, the post-molten glass powder additive is also beneficial to reducing the influence of the precipitation of Pb, etc. on the sintering stability, thereby promoting the formation of a dense and high-ohmic contact structure, promoting the increase of Uoc, Isc, FF, and Rsh, and the decrease of Rser, thus obtaining a battery with a high Eta.

[0018] As a preferred technical solution of the present invention, the D50 of the glass powder additive is 1.5-2 um.

[0019] In order to improve properties such as wetting and optimize glass powder doping, a small amount of other oxides can also be added. As a preferred technical solution of the present invention, the glass powder additive I further includes at least one of MgO, Ni2O, BaO, and SnO. The at least one of MgO, Ni2O, BaO, and SnO accounts for 0-5% by mass of the glass powder additive I, preferably 0-3%, and more preferably 0-1.5%.

[0020] As a preferred technical solution of the present invention, the glass powder additive II further includes at least one of Na2O, K2O, and Li2O, and the mass percentage of at least one of Na2O, K2O, and Li2O in the glass powder additive I is 0-10%, preferably 0-5%, and more preferably 1-2%.

[0021] The second aspect of the present invention provides a preparation method of the auxiliary glass powder additive for silver paste, including:

[0022] Preparation of glass powder additive I: Heating, sintering, cooling, and grinding the preparation raw materials of glass powder additive I to obtain the glass powder additive I;

[0023] Preparation of glass powder additive II: Heating, sintering, cooling, and grinding the preparation raw materials of glass powder additive II to obtain the glass powder additive II.

[0024] As a preferred technical solution of the present invention, the preparation method of the auxiliary glass powder additive for silver paste includes:

[0025] Preparation of glass powder additive I: Heating the preparation raw materials of glass powder additive I to 1100-1300 °C for sintering for 0.5-1 h, cooling, drying at 100-120 °C for 2-3 h, ball milling for 0.5-1 h, and air milling to D50 of 1.5-2 μm to obtain the glass powder additive I;

[0026] Preparation of glass powder additive II: Heating the preparation raw materials of glass powder additive II to 1100-1300 °C for sintering for 0.5-1 h, cooling, drying at 100-120 °C for 2-3 h, ball milling for 0.5-1 h, and air milling to D50 of 1.5-2 μm to obtain the glass powder additive II.

[0027] The second aspect of the present invention provides a silver paste, which, by weight percentage, includes 0.05-0.3% of the auxiliary glass powder additive for silver paste, 1-3% of Te-Si-Pb-Bi series crystalline glass powder, 80-90% of silver powder, and 5-12% of organic carrier.

[0028] The present invention has the following beneficial effects compared with the prior art:

[0029] The present invention provides a glass powder additive that can be matched with the main glass powder during the sintering process, and utilizes the softening points of different additives and the different redox reaction sequences to improve the problem that a single glass powder is difficult to achieve high battery conversion efficiency and high front silver sintering effect. The inventors also found that when the two glass powder additives of the present invention and the main glass powder act together, the densification of the silver powder during the sintering process can be promoted, while promoting the complete corrosion of the front silicon nitride anti-reflection layer, promoting the precipitation of silver crystals from the etching emitter, and the precipitation of a lot of silver colloids from the intermediate glass layer after sintering to achieve good ohmic contact, while providing good adhesion to obtain high solar cell conversion efficiency. The glass powder additive provided by the present invention can be well added to the original silver paste, and is particularly suitable for the front silver paste of p-type PERC crystalline silicon solar cells, without changing the printing and sintering processes of the original paste, and the preparation method is simple, low cost, and high yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the energy spectrum of commercially available Te-Si-Pb-Bi crystalline glass powder. DETAILED DESCRIPTION

[0031] Example

[0032] Comparative Example

[0033] The comparative example provides a commercially available Te-Si-Pb-Bi system crystalline glass powder, the energy spectrum of which is as follows: Figure 1 As shown, a front silver paste including commercially available glass powder is prepared, wherein the front silver paste includes, by weight, 2.3 parts of commercially available Te-Si-Pb-Bi crystalline glass powder, 89 parts of silver powder, and 8.7 parts of commercially available organic carrier (7.1 parts of hydroxyethyl cellulose resin, 0.3 parts of diethylene glycol butyl ether acetate solvent, 0.8 parts of dibutyl phthalate plasticizer, and 0.5 parts of sorbitan monooleate dispersant), which are mixed uniformly by a V-type mixer and then ground on a three-roll pulping mill to obtain a front silver paste for solar cells.

[0034] Example 1

[0035] This example provides an auxiliary glass powder additive 1, which includes, by weight, 36.3 parts of SiO2, 27.2 parts of Bi2O3, 8.4 parts of ZnO, 10.9 parts of WO3, 9.8 parts of PbO, 2.7 parts of CuO, 3.9 parts of TeO2 and 0.8 parts of MgO.

[0036] This example also provides a method for preparing the auxiliary glass powder additive 1 as described above, comprising:

[0037] The raw materials for preparing the auxiliary glass powder additive 1 are uniformly mixed to obtain a mixed powder, which is loaded into a crucible. Then, the crucible is placed in a box-type resistance furnace, and the resistance furnace is heated to 1200 °C and kept at a constant temperature for melting for 0.8 h to obtain a uniform glass melt. The glass melt is poured into a stainless-steel container filled with deionized water with stirring for quenching, and the obtained glass particles are placed in a constant-temperature drying oven at 110 °C, dried, finely ground, and air-milled to obtain the auxiliary glass powder additive 1 with a D50 of 1.5 - 2 μm.

[0038] This example also provides a silver paste, which, by weight, includes 2.2 parts of commercially available Te-Si-Pb-Bi system crystalline glass powder, 0.1 part of the auxiliary glass powder additive 1, 89 parts of silver powder, and 8.7 parts of a conventional organic carrier. After being uniformly mixed using a V-type mixer and then ground on a three-roll milling machine, the positive silver paste for solar cells is obtained.

[0039] Example 2

[0040] This example provides an auxiliary glass powder additive 2, which, by weight, includes 72.8 parts of SiO2, 8.0 parts of TeO2, 8.0 parts of PbO, 4.6 parts of WO3, 4.0 parts of Bi2O3, 1.1 parts of ZnO, and 1.5 parts of Na2O.

[0041] This example also provides a preparation method for the auxiliary glass powder additive 2 as described above, including:

[0042] The raw materials for preparing the auxiliary glass powder additive 1 are uniformly mixed to obtain a mixed powder, which is loaded into a crucible. Then, the crucible is placed in a box-type resistance furnace, and the resistance furnace is heated to 1300 °C and kept at a constant temperature for melting for 1 h to obtain a uniform glass melt. The glass melt is poured into a stainless-steel container filled with deionized water with stirring for quenching, and the obtained glass particles are placed in a constant-temperature drying oven at 100 - 120 °C, dried, finely ground, and air-milled to obtain the auxiliary glass powder additive 1 with a D50 of 1.5 - 2 μm.

[0043] This example also provides a silver paste, which, by weight, includes 2.2 parts of commercially available Te-Si-Pb-Bi system crystalline glass powder, 0.1 part of the auxiliary glass powder additive 2, 89 parts of silver powder, and 8.7 parts of a conventional organic carrier. After being uniformly mixed using a V-type mixer and then ground on a three-roll milling machine, the positive silver paste for solar cells is obtained.

[0044] Example 3

[0045] This example provides an auxiliary glass powder additive, which includes the glass powder additive 1 provided in Example 1 and the glass powder additive 2 provided in Example 2.

[0046] This example also provides a silver paste which, by weight, comprises 2.1 parts of commercially available Te-Si-Pb-Bi-based crystalline glass powder, 0.1 part of auxiliary glass powder additive I, 0.1 part of auxiliary glass powder additive II, 89 parts of silver powder, and 8.7 parts of a conventional organic carrier. After mixing evenly using a V-type blender, it is placed on a three-roll mill for grinding to obtain the positive silver paste for solar cells.

[0047] Performance evaluation

[0048] The positive silver pastes in the examples and comparative examples were printed on p-type PERC crystalline silicon solar cells. After drying, a film with a thickness of 20 microns was obtained. After high-temperature sintering at 780 °C, solar cells were obtained. The open-circuit voltage (Uoc), Isc (short-circuit current), fill factor (FF), conversion efficiency (Eta), series resistance (Rser), and Rsh (shunt resistance) were tested using a solar simulator. The results are shown in Table 1.

[0049] Table 1

[0050] Electrical Performance Uoc (mV) Isc (A) FF (%) Eta (%) Rser (mΩ) Rsh (mΩ) Comparative Example 0.6550 10.8002 79.93 20.645 0.001082 44.5 Example 1 0.6582 10.6685 79.26 20.323 0.001143 186.4 Example 2 0.6646 10.7701 79.57 20.800 0.002126 69.9 Example 3 0.6673 10.819 80.37 21.194 0.001086 54.7

[0051] It can be seen from the test results that by adding the glass powder additive provided by the present invention to the silver paste, the functions of the glass powder and silver powder in the original silver paste can be improved, the corrosion of the front silicon nitride layer can be promoted, and the conversion efficiency of the battery can be effectively increased.

Claims

1. An auxiliary glass powder additive for silver paste, characterized in that, The preparation raw materials of the glass powder additive include glass powder additive one and glass powder additive two: The preparation raw materials of the glass powder additive one, by weight percentage, include: SiO2 30-40%, Bi2O3 15-30%, ZnO 5-10%, WO3 5-25%, PbO 5-10%, CuO 1-5%, TeO2 1-5%; The preparation raw materials of the glass powder additive two, by weight percentage, include: SiO2 70-80%, TeO2 5-10%, PbO5-15%, WO3 1-10%, Bi2O3 1-10%, ZnO 1-10%; The weight ratio of the glass powder additive one to the glass powder additive two is (1~2):(1~2); The silver paste includes a glass powder additive, Te-Si-Pb-Bi series crystalline glass powder, silver powder and an organic carrier.

2. The auxiliary glass powder additive for silver paste according to claim 1, characterized in that The glass powder additive one further includes at least one of MgO, Ni2O, BaO, and SnO.

3. The auxiliary glass powder additive for silver paste according to claim 2, characterized in that, The glass powder additive two further includes at least one of Na2O, K2O, and Li2O.

4. A preparation method of the auxiliary glass powder additive for silver paste according to any one of claims 1 to 3, characterized in that, Including: Preparation of glass powder additive one: Heat, sinter, cool and grind the preparation raw materials of the glass powder additive one to obtain the glass powder additive one; Preparation of glass powder additive two: Heat, sinter, cool and grind the preparation raw materials of the glass powder additive two to obtain the glass powder additive two.

5. A silver paste, characterized in that, By weight percentage, it includes 0.05-0.3% of the auxiliary glass powder additive for silver paste according to any one of claims 1 to 3, 1~3% of Te-Si-Pb-Bi series crystalline glass powder, 80~90% of silver powder and 5~12% of organic carrier.

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