A hot air sintering type silver paste for improving contact performance of TOPCon cell

Abstract

The application relates to the technical field of photovoltaic conductive paste, and discloses a hot-air sintering type silver paste for improving the contact performance of a TOPCon cell. 3+ is oxidized into Bi 5+ , which stably exists in the glass network, thereby inhibiting the precipitation and migration of the metal Bi, guaranteeing the uniform distribution of the internal components of the glass powder, so that the silver paste forms a continuous and uniform ohmic contact after hot-air sintering, the contact resistivity is reduced and the discreteness is reduced, the conversion efficiency of the cell is improved, and the continuous interface effectively resists acetic acid corrosion and damp heat aging, thereby prolonging the long-term reliability of the cell.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic conductive paste technology, and in particular to a hot-air sintered silver paste for improving the contact performance of TOPCon cells. Background Technology

[0002] In the metallization process of TOPCon (Tunnel Oxide Passivated Contact) batteries, the back silver paste is usually composed of silver powder, glass powder and organic carrier. Among them, glass powder plays a key role in etching the passivation layer and promoting the formation of ohmic contacts at the silver-silicon interface during sintering. In order to obtain ideal etching performance, the industry generally introduces Bi2O3 as the main network modifier into the glass powder, and balances the softening point, flowability and interfacial reactivity of the glass powder by controlling its content.

[0003] It is generally believed in the prior art that moderate etching and good contact between glass powder and silicon surface can be achieved by adjusting the Bi2O3 content. For example, Chinese Patent CN117843238A discloses a glass powder for the back silver paste of TOPCon battery main grid and its preparation method, with glass powder with TeO2, Bi2O3, B2O3, SiO2 and other main components as the main components, which is used in the back silver paste to reduce resistance. Chinese Patent CN118063099A discloses a glass powder for the back silver paste of TOPCon and its preparation and application, with a glass powder formula with PbO, TeO2 and Bi2O3 as the main components, which aims to balance contact resistivity and metal composite. However, in practical applications, the contact resistivity of silver paste using the above-mentioned Bi2O3-based glass powder is often high and has large dispersion under hot air sintering process, and the battery efficiency decreases significantly after damp heat aging.

[0004] In the hot air sintering process, the surface of the glass powder is preferentially heated by hot air convection, driving Bi2O3 to migrate to the surface. This results in a difference in the compositional distribution of Bi2O3 content between the surface and the interior of the glass powder. This compositional difference will cause a non-uniform distribution of Bi2O3 reduction reaction during subsequent sintering. That is, excessive reduction of Bi2O3 on the surface layer can easily form coarse or continuously distributed Bi-Ag-rich matrix phase, affecting the densification of silver grid lines and line resistance. On the other hand, insufficient reduction of Bi2O3 in the interior weakens the etching ability of the glass powder on the silicon surface oxide layer and the uniform nucleation and growth of silver grains. This non-uniform interface reaction leads to a reduction in the effective contact area of ​​the silver-silicon interface and a discontinuous distribution of contact points, which manifests as an increase in contact resistivity and increased dispersion. At the same time, this discontinuous interface is prone to become a preferential intrusion channel for corrosive media during humid heat aging, accelerating electrode failure and affecting the long-term reliability of the battery. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that in the existing hot air sintered silver paste, the Bi2O3 component contained in the glass powder is enriched by uncontrolled surface migration caused by hot air convection heating, resulting in discontinuous distribution of silver-silicon interface contact points, high contact resistivity and large dispersion. To this end, we propose a hot air sintered silver paste to improve the contact performance of TOPCon batteries.

[0006] To achieve the above objectives, this application adopts the following technical solution: a hot-air sintered silver paste for improving the contact performance of TOPCon batteries, comprising silver powder, glass powder, organic carrier, and additives. The glass powder consists of a glass powder matrix and an oxide active layer loaded on the surface of the glass powder matrix. The glass powder matrix contains Bi2O3, and the oxide active layer contains MnO2, Co3O4, and CeO2. Based on the mass of the glass powder matrix, the content of MnO2 in the oxide active layer is 0.5%-1.5%, the content of Co3O4 is 0.1%-0.4%, the content of CeO2 is 0.1%-0.3%, and the thickness of the oxide active layer is 5-20 nm.

[0007] Preferably, the silver powder is composed of a first spherical silver powder and a second spherical silver powder. The median particle size D50 of the first spherical silver powder is 0.6-0.9 μm, accounting for 60%-75% of the total mass of the silver powder. The median particle size D50 of the second spherical silver powder is 0.15-0.25 μm, accounting for 25%-40% of the total mass of the silver powder.

[0008] Preferably, by mass percentage, the silver powder content is 82%-88%, the glass powder content is 2.5%-4.5%, the organic carrier content is 8%-13%, the additive content is 0.3%-0.8%, and the sum of the mass percentages of all components is 100%.

[0009] Preferably, the glass powder matrix is ​​composed of the following components by mass percentage: 35%-50% Bi2O3, 15%-25% B2O3, 8%-15% ZnO, 5%-12% SiO2, with the balance being Al2O3 and / or BaO.

[0010] Preferably, the organic carrier is composed of the following components by mass percentage: 6%-10% resin, 1%-2% thixotropic agent, and the balance being a mixed solvent, wherein the resin is ethyl cellulose and the thixotropic agent is polyamide wax.

[0011] Preferably, the mixed solvent is composed of α-terpineol, butyl carbitol acetate and dibutyl phthalate in a mass ratio of 5:2:3.

[0012] Preferably, the additives include a dispersant and a thixotropic agent, wherein the dispersant is a phosphate ester dispersant, accounting for 0.2%-0.5% of the total mass of the silver paste, and the thixotropic agent is fumed silica, accounting for 0.1%-0.3% of the total mass of the silver paste.

[0013] A method for preparing hot air sintering type silver paste includes the following steps: S1: Silver powder, glass powder, organic carrier and additives are added to a planetary mixer and stirred at 600-900 r / min for 20-30 min to obtain a preliminary mixture; S2: The preliminary mixture is transferred to a three-roll mill and ground 3-5 times until the fineness measured by a scraper fineness gauge is less than or equal to 5 μm; S3: The ground paste is placed in a vacuum degassing machine and degassed at a vacuum degree of -0.09 MPa for 10-15 minutes, and the viscosity is adjusted to 250-350 Pa·s to obtain the finished silver paste.

[0014] The application of a hot-air sintering silver paste in the preparation of TOPCon batteries includes printing the hot-air sintering silver paste onto the back of the TOPCon battery by screen printing, sintering it in a hot-air sintering furnace, heating it from 200°C to 690-720°C at a rate of 30-50°C / second in an air atmosphere and holding it at that temperature for 2-5 seconds, for a total sintering time of 40-60 seconds.

[0015] The technical effects and advantages of this invention are as follows: In this invention, an oxidation active layer composed of MnO2, Co3O4, and CeO2 is loaded onto the surface of bismuth-containing base glass powder. This active layer, during the heating stage of hot air sintering, activates the Bi content in the glass powder matrix. 3+ Oxidation to Bi 5+ And make it stable in the glass network structure, thereby suppressing Bi 3+ Compared with existing hot-air sintering silver pastes using unmodified bismuth-containing glass powder, the silver-silicon interface formed by the silver paste of this invention has a continuous and uniform distribution of contact points, reduced contact resistivity, and reduced intra-cell dispersion. As a result, the fill factor and conversion efficiency of the TOPCon cells prepared are improved. At the same time, the continuous and dense interface effectively blocks the intrusion of corrosive media during humid heat aging, and the conversion efficiency decay rate and series resistance rise rate are reduced. This invention solves the technical problems of poor contact uniformity and insufficient long-term reliability by surface modification of glass powder without changing the existing hot-air sintering production line process. Attached Figure Description

[0016] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts: Figure 1The graph shows the contact resistivity test results of various silver paste samples of the present invention. Figure 2 This is a scanning electron microscope image of the silver-silicon interface in Embodiment 1 of the present invention; Figure 3 This is a scanning electron microscope image of the silver-silicon interface of Comparative Example 1 of the present invention; Figure 4 This is a scanning electron microscope image of the silver-silicon interface of Comparative Example 2 of the present invention; Figure 5 This is a comparison chart of the electrical performance of TOPCon batteries prepared from various silver paste samples according to the present invention. Detailed Implementation

[0017] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0018] The present invention provides a hot air sintering type conductive silver paste, which is composed of the following components by mass percentage: 82%-88% silver powder, 2.5%-4.5% glass powder, 8%-13% organic carrier, and 0.3%-0.8% additives, the sum of the mass percentages of each component being 100%.

[0019] The silver powder is composed of a mixture of first spherical silver powder and second spherical silver powder with different median particle sizes. The first spherical silver powder has a median particle size D50 of 0.6-0.9 μm and accounts for 60%-75% of the total mass of the silver powder. The second spherical silver powder has a median particle size D50 of 0.15-0.25 μm and accounts for 25%-40% of the total mass of the silver powder. Both the first and second spherical silver powders can be commercially available photovoltaic silver powders. After the two types of silver powders are mixed, the smaller-diameter silver powder fills the gaps between the larger-diameter silver powders to increase the packing density of the silver powders and reduce the line resistance of the grid lines after sintering.

[0020] The glass powder consists of a glass powder matrix and an oxidation active layer supported on the surface of the glass powder matrix.

[0021] The glass powder matrix, by mass percentage, consists of the following: 35%-50% Bi2O3, 15%-25% B2O3, 8%-15% ZnO, 5%-12% SiO2, with the balance being Al2O3 and / or BaO. The median particle size D50 of the glass powder matrix is ​​0.6-1.0 μm, its glass transition temperature (Tg) is 360-420℃, and its softening point (Ts) is 480-550℃.

[0022] The glass powder matrix is ​​prepared by the following method: Weigh each powdered raw material according to the above chemical composition, mix them evenly and place them in a crucible, heat and melt them at 1150-1250℃ for 60-90 minutes, stir 2-3 times during the melting process to homogenize the glass melt, pour the molten glass melt into deionized water for quenching, obtain glass fragments, coarsely crush the glass fragments and then grind them in an air jet mill until the median particle size D50 is 0.6-1.0μm to obtain the basic glass powder matrix.

[0023] Based on the mass of the glass powder matrix, the oxidation active layer is composed of the following nanoparticles: 0.5%-1.5% MnO2 nanoparticles, 0.1%-0.4% Co3O4 nanoparticles, and 0.1%-0.3% CeO2 nanoparticles. The thickness of the oxidation active layer is 5-20 nm, and the surface coverage is ≥70%.

[0024] MnO2 in the heating stage of hot blast sintering will reduce Bi in the glass powder 3+ Oxidation to Bi 5+ Co3O4 acts as a co-catalyst, lowering the activation energy of the oxidation reaction. CeO2 inhibits the aggregation of nanoparticles and maintains a localized oxidizing atmosphere during sintering, preventing Bi from forming. 5+ It was restored ahead of schedule.

[0025] The glass powder is prepared using the following method: C1: Prepare a mixed aqueous solution containing 0.5 mol / L Mn(NO3)2, 0.1 mol / L Co(NO3)2, and 0.05 mol / L Ce(NO3)3. Add 1 mol / L NaOH solution dropwise to the mixed solution while stirring to adjust the pH to 10.5, forming a coprecipitate. Filter the precipitate, wash it with deionized water, and dry it at 80℃ for 12 h. Calcine the dried precipitate at 400℃ for 2 h in air atmosphere to obtain a mixture of MnO2, Co3O4, and CeO2 nanoparticles. Disperse the obtained nanoparticle mixture ultrasonically in anhydrous ethanol to prepare a suspension with a mass fraction of 0.5%. C2: The glass powder matrix is ​​put into a planetary ball mill, and a suspension is added. The solid-liquid weight ratio of the glass powder matrix to the suspension is 1:2. The mixture is ball-milled at 200 r / min for 4 hours. After the ball milling is completed, it is vacuum-dried at 60℃ for 6 hours. C3: The dried powder is heat-treated at 300℃ for 2 hours under a nitrogen atmosphere to cause slight sintering and fixation of the nanoparticles with the surface of the glass powder. The powder is then passed through a 200-mesh sieve to obtain the surface-modified glass powder.

[0026] The organic carrier, by mass percentage, consists of the following components: 6%-10% resin, 1%-2% thixotropic agent, and the balance being a mixed solvent; The mixed solvent is composed of α-terpineol, butyl carbitol acetate (BCA) and dibutyl phthalate (DBP) in a mass ratio of 5:2:3; The resin is ethyl cellulose, and the thixotropic agent is polyamide wax.

[0027] The organic carrier is prepared by the following method: BCA, DBP and α-terpineol are mixed, heated to 80-100℃, ethyl cellulose is added and stirred until completely dissolved, cooled to below 40℃, polyamide wax is added, and stirring is continued for 30 minutes to obtain the carrier.

[0028] The additives include dispersants and thixotropic agents. Specifically, the dispersant is a phosphate ester dispersant, preferably BYK-110, which accounts for 0.2%-0.5% of the total silver paste by mass; the thixotropic agent is fumed silica, which accounts for 0.1%-0.3% of the total silver paste by mass.

[0029] This invention also provides a method for preparing the hot-air sintered conductive silver paste, specifically including the following steps: S1: Weigh out silver powder, glass powder, organic carrier and additives according to the above composition, put all materials into a planetary mixer, and stir at 600-900r / min for 20-30min to obtain the initial slurry. S2: Transfer the initial mixed slurry to a three-roll mill and grind it 3-5 times until the fineness is ≤5μm as measured by a scraper fineness gauge; S3: Place the ground slurry in a vacuum degassing machine and degas it for 10-15 minutes under a vacuum of -0.09MPa. The viscosity is measured to be 250-350Pa·s, which yields the finished silver paste.

[0030] The present invention also provides the application of the hot air sintering conductive silver paste in the metallization of TOPCon batteries, including: printing the above conductive silver paste onto the back of the TOPCon battery by screen printing, and after printing, sintering in a hot air sintering furnace, heating from 200°C to the peak temperature of 690-720°C at a heating rate of 30-50°C / s in an air atmosphere, and holding at the peak temperature for 2-5s, with a total sintering time of 40-60s.

[0031] During the heating stage of hot air sintering, the MnO2 in the oxide active layer will oxidize the Bi in the glass powder. 3+ Oxidation to Bi 5+ This temperature range is far below the softening point of the glass powder, so the oxidation reaction is completed before the glass powder flows, thus avoiding Bi... 3+ The migration and enrichment of Bi, followed by softening and flow of glass powder at higher temperatures, carrying silver powder to form a contact with the silicon substrate, where Bi has been converted into Bi. 5+The form is stable within the glass network, and no more metallic Bi is deposited, thus forming a continuous and uniform silver-silicon contact.

[0032] The present invention will be described in detail below with reference to specific embodiments. It should be noted that these embodiments are only used to explain the present invention and do not constitute any limitation on the scope of protection of the present invention. Those skilled in the art can make adaptive adjustments to the embodiments based on their understanding of the technical solutions of the present invention, and these adjustments still fall within the scope of protection of the present invention.

[0033] Example 1: This example provides a hot air sintering type conductive silver paste, which is composed of the following components by mass percentage: 85.0% silver powder, 3.5% glass powder, 11.0% organic carrier, and 0.5% additives; wherein the additives consist of 0.3% BYK-110 dispersant and 0.2% fumed silica.

[0034] The median particle size D50 of the first spherical silver powder is 0.8 μm, accounting for 70% of the total mass of the silver powder, and the median particle size D50 of the second spherical silver powder is 0.2 μm, accounting for 30% of the total mass of the silver powder.

[0035] The glass powder matrix comprises, by mass percentage: 42% Bi2O3, 20% B2O3, 12% ZnO, 8% SiO2, and 18% Al2O3.

[0036] Based on the mass of the glass powder matrix, the oxidation active layer is composed of 1.0% MnO2, 0.25% Co3O4, and 0.2% CeO2.

[0037] The organic carrier comprises, by mass percentage: 7% ethyl cellulose, 1% polyamide wax, and 92% mixed solvent, wherein the mixed solvent is composed of α-terpineol, butyl carbitol acetate, and dibutyl phthalate in a mass ratio of 5:2:3.

[0038] This embodiment also provides a method for preparing the above-mentioned hot air sintering type conductive silver paste, specifically including the following steps: S1: Weigh out silver powder, glass powder, organic carrier and additives according to the above composition, put all materials into a planetary mixer, and stir at 800 r / min for 25 min to obtain the initial slurry; S2: Transfer the initial mixed slurry to a three-roll mill and grind it 4 times until the fineness is ≤5μm as measured by a scraper fineness gauge; S3: Place the ground slurry in a vacuum degassing machine and degas for 12 minutes under a vacuum of -0.09MPa. The viscosity is measured to be 320Pa·s, which yields the finished silver paste.

[0039] Example 2: This example provides a hot air sintering type conductive silver paste and its preparation method. The difference from Example 1 is that the composition of the oxide active layer is different. Based on the mass of the base glass powder, the oxide active layer is composed of 0.5% MnO2, 0.1% Co3O4, and 0.1% CeO2.

[0040] Example 3: This example provides a hot air sintering type conductive silver paste and its preparation method. The difference from Example 1 is that the composition of the oxide active layer is different. Based on the mass of the base glass powder, the oxide active layer is composed of 1.5% MnO2, 0.4% Co3O4 and 0.3% CeO2.

[0041] Example 4: This example provides a hot air sintering type conductive silver paste and its preparation method. The difference from Example 1 is that the amount of glass powder added is reduced to 2.5%, the content of silver powder is increased by 86.0%, and the content of organic carrier and additives remains unchanged.

[0042] Example 5: This example provides a hot air sintering type conductive silver paste and its preparation method. The difference from Example 1 is that the amount of glass powder added is reduced to 4.5%, the content of silver powder is increased by 84.0%, and the content of organic carrier and additives remains unchanged.

[0043] Example 6: This example provides a hot air sintering type conductive silver paste and its preparation method. The difference from Example 1 is that the composition of the glass powder matrix is ​​adjusted. By mass percentage, it includes 35% Bi2O3, 25% B2O3, 12% ZnO, 8% SiO2, 10% Al2O3, and 10% BaO.

[0044] Example 7: This example provides a hot-air sintered conductive silver paste and its preparation method. The difference from Example 1 lies in adjusting the composition of the glass powder matrix. By mass percentage, it includes 50% Bi2O3, 15% B2O3, 12% ZnO, 8% SiO2, 10% Al2O3, and 5% BaO.

[0045] Comparative Example 1: This comparative example provides a hot air sintering type conductive silver paste and its preparation method. The difference from Example 1 is that it uses the same basic glass powder with the same composition and particle size as Example 1, but does not perform surface modification on the basic glass powder.

[0046] Comparative Example 2: This comparative example provides a hot air sintering type conductive silver paste and its preparation method. The difference from Example 1 is that the oxidative active layer is composed only of MnO2 and does not contain Co3O4 and CeO2.

[0047] Comparative Example 3: This comparative example provides a hot air sintering type conductive silver paste and its preparation method. The difference from Example 1 is that the oxidative active layer consists only of MnO2 and CeO2, and does not contain Co3O4.

[0048] Comparative Example 4: This comparative example provides a hot air sintering type conductive silver paste and its preparation method. The difference from Example 1 is that the oxidative active layer consists only of MnO2 and Co3O4, and does not contain CeO2.

[0049] Comparative Example 5: This comparative example provides a conductive silver paste, which differs from Example 1 in that it uses commercially available TOPCon backside silver paste instead of the silver paste of this invention.

[0050] Comparative Example 6: This comparative example provides a hot air sintering type conductive silver paste and its preparation method. The difference from Example 1 is that the composition of the base glass powder is different. By weight percentage, it includes 25% Bi2O3, 25% B2O3, 15% ZnO, 15% SiO2, 10% Al2O3, and 10% BaO. The base glass powder is not surface modified.

[0051] Comparative Example 7: This comparative example provides a hot air sintering type conductive silver paste and its preparation method. The difference from Example 1 is that the composition and amount of the oxide active layer are different. Based on the mass of the base glass powder, it includes 2.5% MnO2, 0.8% Co3O4, and 0.6% CeO2.

[0052] To verify the technical effect of the silver pastes prepared in the above embodiments and comparative examples of the present invention, performance tests were conducted on the silver pastes prepared in Examples 1-7 and Comparative Examples 1-7, respectively, to evaluate the actual effect of the technical solution of the present invention in solving the problem of uncontrolled surface migration and enrichment caused by hot air convection heating.

[0053] Experimental Example 1: This experimental example aims to measure the silver-silicon contact resistivity (ρc) and its on-chip coefficient of variation (CV%) of the silver paste in each embodiment and comparative example after hot air sintering using the transmission line method (TLM) to verify the effect of the oxide active layer of the present invention on reducing contact resistance and improving contact uniformity.

[0054] The hot-air sintered conductive silver pastes prepared in Examples 1-7 and Comparative Examples 1-7 were selected as experimental objects and denoted as E1-E7 and D1-D7, respectively. TOPCon battery semi-finished products from the same batch and with the same process were used as test substrates. The silver pastes from Examples 1-7 and Comparative Examples 1-7 were screen-printed onto the back of the substrates, with a line width of 100 μm and line spacing of 200 μm, 400 μm, 600 μm, 800 μm, and 1000 μm, with 5 lines in each group. Ten substrates were printed with each type of silver paste. After printing, the product is sintered in a hot air sintering furnace at a heating rate of 40℃ / s from 200℃ to 705℃, with a peak holding time of 3s and a total sintering time of 50s. The sintering atmosphere is air.

[0055] The test probes of the four-probe tester are respectively connected to two adjacent parallel lines. A constant current is applied, the voltage drop is measured, and the total resistance between the two lines is calculated. Based on the total resistance values ​​at different spacings, a linear regression is performed, and the intercept is twice the contact resistance (Rc). Then, the contact resistivity is calculated using the following formula: ; Where W is the linewidth and Lc is the transmission length, 10 test points were selected on each solar cell to measure the contact resistivity. The results are shown in Table 1 below. The average value, standard deviation, and coefficient of variation (CV) of each solar cell were calculated, and a dual Y-axis dot plot was plotted using OriginPro 2024. The results are shown in Table 1 below. Figure 1 As shown.

[0056] Table 1. Contact resistivity of each embodiment and comparative example

[0057] From Table 1 and Figure 2 According to the information, the contact resistivity of Example 1 is 1.1 mΩ·cm. 2 The coefficient of variation was 7.2%, which was better than the comparative example; The contact resistivity of Comparative Example 1 is 2.7 mΩ·cm. 2 The coefficient of variation was as high as 28.5%. Unmodified Bi₂O₃ glass powder, under hot air sintering, showed a high degree of variation. 3+ Migration and enrichment to the surface of glass powder leads to the formation of surface Bi. 3+ The reduction transition results in an excessively thick Ag-Bi phase, insufficient internal reduction, and discontinuous contact point distribution.

[0058] The contact resistivity of Comparative Example 2 is 2.0 mΩ·cm. 2 The coefficient of variation was 20.0%. Although MnO2 alone can partially reduce Bi... 3 + Oxidation to Bi 5+ However, due to the lack of Co3O4 to lower the activation energy of the oxidation reaction, the reaction is incomplete; the lack of CeO2 to maintain a local oxidation atmosphere also leads to some Bi... 5+ It was restored during subsequent heating, but local unevenness still exists on the interface.

[0059] The coefficients of variation for Comparative Examples 3 and 4 were 18.0% and 15.0%, respectively, both higher than those for Example 1. Co3O4 catalyzed the oxidation reaction to occur more fully at a lower temperature; CeO2 utilized its oxygen storage capacity to inhibit Bi... 5+The premature restoration of either component or the absence of either will lead to a decrease in interface uniformity.

[0060] The contact resistivity of Comparative Example 7 is 1.81 mΩ·cm. 2 The coefficient of variation was 15.0%, which was higher than that of Example 1. Excessive MnO2 may form an excessively thick oxide layer on the surface of the glass powder, which may hinder the softening and flow of the glass powder in the later stage of sintering, or introduce excessive lattice oxygen to affect the glass network structure, which is not conducive to uniform contact.

[0061] Example 2: This example aims to observe the microstructure of the silver-silicon interface in typical samples using scanning electron microscopy (SEM), analyze the continuity of silver grain distribution, interfacial porosity, and glass layer uniformity, and verify the role of the oxide active layer in inhibiting Bi from a microscopic level. 3+ It plays a role in migration and forming uniform contact.

[0062] Samples prepared in Example 1, Comparative Example 1, and Comparative Example 2 were selected as experimental objects. TOPCon solar cells were prepared for each silver paste according to the sintering method in Example 1. One solar cell was taken and a cross-section was cut along the direction perpendicular to the grid line.

[0063] The solar cells were cut into 5mm × 5mm pieces perpendicular to the grid lines and cold-mounted with epoxy resin. After the resin cured, the surface stress layer was removed by grinding and polishing. The silver-silicon interface was observed using a field emission scanning electron microscope in backscattered electron mode with an accelerating voltage of 15kV, a working distance of 8mm, and a magnification of 10,000x. Images were acquired from randomly selected cross-sections of each sample. The results are shown in […]. Figures 2-4 As shown.

[0064] Depend on Figures 2-4 The information shows that the interface porosity of Example 1 is lower than that of Comparative Example 1 and Comparative Example 2. The lower the porosity, the larger the effective contact area of ​​silver and silicon, which is consistent with the results of the low contact resistivity of Example 1 in Experimental Example 1.

[0065] Comparative Example 1 exhibits the worst Bi distribution uniformity and large fluctuations in glass layer thickness. This is due to the Bi distribution under hot air sintering conditions. 3+ Migration and enrichment to the surface of glass powder leads to the formation of surface Bi. 3+ Excessive reduction results in an excessively thick Ag-Bi phase, while insufficient internal reduction results in a thick glass layer and high interfacial porosity.

[0066] The uniformity of Bi distribution in Comparative Example 2 is better than that in Comparative Example 1 but worse than that in Example 1. Although MnO2 alone can oxidize some Bi... 3 + However, due to the lack of Co3O4 and CeO2, the oxidation reaction is incomplete and Bi 5+ Even after easy restoration, local Bi-rich areas still exist on the interface.

[0067] Example 1 exhibits the best Bi distribution uniformity and a uniform glass layer thickness. The synergistic effect of MnO2, Co3O4, and CeO2 enhances the Bi distribution. 3+ It is fully oxidized to Bi before the glass softens. 5+ It is stabilized within the glass network, avoiding migration and local reduction, and forming a continuous and uniform silver grain covering layer.

[0068] Experimental Example 3: This experimental example aims to quantitatively evaluate the electrical performance of the silver pastes in actual battery devices by testing the fill factor (FF) and photoelectric conversion efficiency (η) of the TOPCon battery.

[0069] Samples prepared in Examples 1-7 and Comparative Examples 1-7 were selected as experimental subjects. TOPCon cells were prepared for each silver paste according to the sintering method in Experiment 1, and 20 cells were prepared for each silver paste.

[0070] Using the same batch and the same process, TOPCon battery semi-finished products were screen-printed onto the back side of each silver paste and metallized using the same process as in Experiment 1. The front electrode was prepared using the same commercial silver paste.

[0071] Using a solar simulator at AM1.5G, 1000W / m 2 The battery performance of the cells was tested at 25°C. Twenty cells were tested for each silver paste, and the fill factor and conversion efficiency were recorded. The average value was taken. Using Comparative Example 5 as a baseline, the η difference between each example and the comparative example was calculated. The results are shown in Table 2 below. Figure 5 As shown.

[0072] Table 2 Battery electrical performance of each embodiment and comparative example

[0073] From Table 2 and Figure 5 The information shows that Example 1 has the highest fill factor and conversion efficiency; Comparative Example 1 has the lowest fill factor and conversion efficiency. Its high contact resistivity and high dispersion lead to increased series resistance. At the same time, the interface gap may increase minority carrier recombination, which degrades the overall electrical performance.

[0074] The fill factor and conversion efficiency of Comparative Examples 2-4 increased sequentially, consistent with the improvement trend of contact resistivity and dispersion in Experimental Example 1. Due to incomplete oxidation reaction, the contact resistance of Comparative Example 2 was still relatively high. After adding CeO2 or Co3O4, the contact uniformity improved and the fill factor increased accordingly.

[0075] The fill factor and conversion efficiency of Comparative Example 7 were lower than those of Example 1, consistent with the increase in contact resistivity in Experimental Example 1. Excess MnO2 hindered glass flow and instead increased contact resistance.

[0076] Experiment Example 4: This experiment aims to evaluate the stability of the silver-silicon interface formed by the silver paste of each typical sample under humid heat conditions through a damp heat aging test, and to verify whether the continuous interface can effectively inhibit the intrusion of corrosive media.

[0077] Five solar cells prepared in Examples 1-3 and Comparative Examples 1-7 were selected, with five cells of each type of silver paste; at the same time, modules were prepared using the same solar cells, with three modules of each type of silver paste.

[0078] The cells and modules to be tested were placed in a constant temperature and humidity chamber with a set temperature of 85℃±2℃ and a relative humidity of 85%±5% for 1000 hours of continuous aging. Samples were taken out before aging, after 500 hours of aging, and after 1000 hours of aging. After cooling to room temperature, the conversion efficiency and series resistance (Rs) were tested and recorded. After the test was completed, the samples were put back into the constant temperature and humidity chamber for aging until the next test node. The results are shown in Table 3 below.

[0079] Table 3 Performance changes of each example and comparative sample before and after aging

[0080] As shown in Table 3, Example 1 has the lowest conversion efficiency decay rate and series resistance increase rate; Comparative Example 1 has the highest conversion efficiency decay rate and series resistance increase rate. This difference is directly related to the initial interface porosity.

[0081] The conversion efficiency decay rate of Comparative Example 5 was higher than that of Example 1. Commercially available products do not use an oxidative active layer, and their interfaces have a certain degree of discontinuity, resulting in more obvious corrosion after aging.

[0082] The conversion efficiency decay rate of Comparative Examples 2-4 is between that of Comparative Example 5 and Example 1, and is positively correlated with its initial interface porosity. The lack of Co3O4 or CeO2 leads to insufficient interface uniformity, and corrosion intensifies after aging.

[0083] The conversion efficiency attenuation rate of Comparative Example 7 was higher than that of Example 1, which is related to its higher initial contact resistivity and possible oxide residues.

[0084] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A hot-air sintered silver paste, comprising silver powder, glass powder, an organic carrier, and additives, characterized in that, The glass powder consists of a glass powder matrix and an oxidation active layer supported on the surface of the glass powder matrix. The glass powder matrix contains Bi2O3, and the oxidation active layer contains MnO2, Co3O4, and CeO2. Based on the mass of the glass powder matrix, the content of MnO2 in the oxidation active layer is 0.5%-1.5%, the content of Co3O4 is 0.1%-0.4%, the content of CeO2 is 0.1%-0.3%, and the thickness of the oxidation active layer is 5-20 nm.

2. The hot-air sintering type silver paste according to claim 1, characterized in that: The silver powder is composed of a first spherical silver powder and a second spherical silver powder. The median particle size D50 of the first spherical silver powder is 0.6-0.9 μm, accounting for 60%-75% of the total mass of the silver powder. The median particle size D50 of the second spherical silver powder is 0.15-0.25 μm, accounting for 25%-40% of the total mass of the silver powder.

3. The hot-air sintering type silver paste according to claim 1, characterized in that: The silver powder content is 82%-88% by mass percentage, the glass powder content is 2.5%-4.5%, the organic carrier content is 8%-13%, the additive content is 0.3%-0.8%, and the sum of the mass percentages of all components is 100%.

4. The hot-air sintering type silver paste according to claim 1, characterized in that: The glass powder matrix is ​​composed of the following components by mass percentage: 35%-50% Bi2O3, 15%-25% B2O3, 8%-15% ZnO, 5%-12% SiO2, with the balance being Al2O3 and / or BaO.

5. The hot-air sintering type silver paste according to claim 1, characterized in that: The organic carrier is composed of the following components by mass percentage: 6%-10% resin, 1%-2% thixotropic agent, and the balance being a mixed solvent. The resin is ethyl cellulose, and the thixotropic agent is polyamide wax.

6. The hot-air sintering type silver paste according to claim 5, characterized in that: The mixed solvent is composed of α-terpineol, butyl carbitol acetate and dibutyl phthalate in a mass ratio of 5:2:

3.

7. The hot-air sintering type silver paste according to claim 1, characterized in that: The additives include dispersants and thixotropic agents. The dispersant is a phosphate ester dispersant, which accounts for 0.2%-0.5% of the total mass of the silver paste. The thixotropic agent is fumed silica, which accounts for 0.1%-0.3% of the total mass of the silver paste.

8. A method for preparing hot-air sintered silver paste as described in any one of claims 1-7, characterized in that, Includes the following steps: S1: Add silver powder, glass powder, organic carrier and additives into a planetary mixer and mix at 600-900 r / min for 20-30 min to obtain the initial slurry; S2: Transfer the initial mixed slurry to a three-roll mill and grind it 3-5 times until the fineness measured by a scraper fineness gauge is less than or equal to 5μm; S3: Place the ground slurry in a vacuum degassing machine and degas for 10-15 minutes under a vacuum of -0.09MPa. Adjust the viscosity to 250-350Pa·s to obtain the finished silver paste.

9. The application of the hot-air sintered silver paste as described in any one of claims 1-7 in the preparation of TOPCon batteries, characterized in that, The process includes printing the hot air sintering silver paste onto the back of the TOPCon battery using screen printing, sintering it in a hot air sintering furnace, heating it from 200°C to 690-720°C at a rate of 30-50°C / second in an air atmosphere and holding it at that temperature for 2-5 seconds, for a total sintering time of 40-60 seconds.

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