An organic carrier for a topcon backside fine grid conductive paste for doped nickel powder and application thereof

Abstract

This invention discloses an organic carrier for conductive paste with a fine grid on the back side of TOPCon doped with nickel powder and its application. The organic carrier, by mass percentage, comprises: 10-30% resin, 65-85% solvent, 2-7% thixotropic agent, 0.5-1.5% dispersant, and 1-7% polydimethylsiloxane. The resin is a mixture of one or more of the following: a latent curing agent, epoxy resin, ethyl cellulose, cellulose acetate butyrate, polyvinyl butyral, styrene-ethylene-propylene-styrene block copolymer, and acrylic resin. This organic carrier can significantly or even completely prevent the oxidation of base metals during sintering, greatly improving the conductivity of the grid lines after sintering the base metal-doped silver paste, effectively reducing the bulk resistance of the grid lines, providing strong support for subsequent carrier collection, and thus improving the photoelectric conversion efficiency of the base metal silver paste.

Description

Technical Field

[0001] This invention relates to the field of conductive materials technology, and in particular to an organic carrier for TOPCon back-side fine grid conductive paste doped with nickel powder and its application. Background Technology

[0002] Currently, silver powder is the primary conductive phase in the back-side grid paste of TOPCon batteries. Silver possesses excellent conductivity and chemical stability, meeting the high conductivity requirements of solar cells. However, silver is a precious metal, with a high and volatile price, resulting in silver paste costs accounting for a significant proportion of the total cost of TOPCon batteries. This severely restricts further cost reduction, efficiency improvement, and large-scale adoption in the photovoltaic industry. With the rapid expansion of the global photovoltaic market, the demand for silver has increased dramatically, and the supply pressure of silver resources has become increasingly prominent. If we continue to rely on silver powder as the main conductive material for slurry, we may face a shortage of silver resources in the future, which will undoubtedly pose a threat to the sustainable development of the photovoltaic industry. Faced with the dual challenges of high cost and limited resources in silver paste, developing technologies to replace silver powder with base metals has become a research hotspot and an inevitable trend in the photovoltaic industry. Existing technologies are actively exploring solutions for replacing silver powder with base metals, and some companies are already selling products doped with base metals. However, the photoelectric conversion efficiency of these products has not yet fully reached the performance of conductive silver paste made from pure silver powder. The main reasons include the generally lower conductivity of base metals compared to silver; and the severe oxidation of base metals after high-temperature sintering, which leads to increased grid resistivity and consequently decreased photoelectric conversion efficiency in solar cells. Therefore, solving the problem of severe oxidation of base metals during sintering has become a pressing issue in this field, making base metal-doped silver paste a viable alternative to pure silver paste. Summary of the Invention

[0003] To address the aforementioned problems in existing technologies, this invention proposes an organic carrier for conductive paste on the back side of TOPCon doped with nickel powder and its application. This organic carrier can significantly or even completely prevent the oxidation of base metals during sintering, greatly improving the conductivity of the gate lines after sintering the base metal-doped silver paste, effectively reducing the bulk resistance of the gate lines, providing strong support for subsequent carrier collection, and thus improving the photoelectric conversion efficiency of the base metal silver paste.

[0004] The technical solution of the present invention is as follows: The first objective of this invention is to provide an organic carrier for a TOPCon back-side fine grid conductive paste doped with nickel powder. The organic carrier, by mass percentage, comprises: 10-30% resin, 65-85% solvent, 2-7% thixotropic agent, 0.5-1.5% dispersant, and 1-7% polydimethylsiloxane. The resin is a latent curing agent, epoxy resin, and a mixture of one or more of the following: ethyl cellulose, cellulose acetate butyrate, polyvinyl butyral, styrene-ethylene-propylene-styrene block copolymer, and acrylic resin.

[0005] In one embodiment of the present invention, the latent curing agent is an aliphatic solvent-based closed-type curing agent.

[0006] In one embodiment of the present invention, the latent curing agent is an HDI-blocked curing agent that cures with epoxy resin at 100-200°C.

[0007] In one embodiment of the present invention, the amount of latent curing agent is 20-45% of the mass of epoxy resin.

[0008] In one embodiment of the present invention, ethyl cellulose is any one of STD4-STD20 from Dow Chemical Company, USA.

[0009] In one embodiment of the invention, cellulose acetate butyrate is any one of Eastman™ CAB381-2 to CAB381-20.

[0010] In one embodiment of the present invention, the polyvinyl butyral resin is any one of Eastman™ PVB-16H-VB-60H.

[0011] In one embodiment of the present invention, the styrene-ethylene-propylene-styrene block copolymer is Kraton 1701E.

[0012] In one embodiment of the present invention, the acrylic resin is BR113 from Mitsubishi Corporation of Japan.

[0013] In one embodiment of the present invention, the epoxy resin is EP CYD-014U; the thermal decomposition end temperature of the epoxy resin is between 500-700°C.

[0014] In one embodiment of the present invention, the solvent is one or more of diethylene glycol monobutyl ether, dodecyl alcohol ester, diethylene glycol butyl ether acetate, diisobutyl adipate, and benzyl benzoate.

[0015] In one embodiment of the present invention, the organic carrier is 100%, and the solvent includes 3-6% diethylene glycol monobutyl ether, 19% dodecyl alcohol ester, 25% diethylene glycol butyl ether acetate, 13% diisobutyl adipate, and 10% benzyl benzoate.

[0016] In one embodiment of the present invention, the thixotropic agent is polyamide wax; the dispersant in the organic carrier is fatty alcohol polyoxyethylene ether.

[0017] In one embodiment of the present invention, the polyamide wax is Nambendi Spallon 6500.

[0018] In one embodiment of the present invention, the fatty alcohol polyoxyethylene ether is the fatty alcohol polyoxyethylene ether from Haian Petrochemical.

[0019] In one embodiment of the present invention, the viscosity of polydimethylsiloxane is 100 cSt.

[0020] A second objective of this invention is to provide a TOPCon back-side fine grid conductive paste containing the aforementioned organic carrier and doped nickel powder, further comprising silver powder, nickel powder, and glass powder.

[0021] In one embodiment of the present invention, the silver powder has a particle size of 1-2 μm and is spherical.

[0022] In one embodiment of the present invention, the nickel powder has a particle size of 3-8 μm and is spherical.

[0023] In one embodiment of the present invention, the particle size of the glass powder is 1-4 μm.

[0024] In one embodiment of the present invention, the raw material composition of the conductive paste, by mass percentage, is: 65-75% silver powder, 15-20% nickel powder, 3-5% glass powder, and 5-10% organic carrier.

[0025] A third objective of this invention is to provide a method for preparing the above-mentioned nickel-doped TOPCon back-side fine-gate conductive paste, comprising the following steps: (1) Mix the organic carrier and nickel powder for 10-30 min; (2) Continue to add silver powder and glass powder, stir for 5-20 minutes, grind evenly, filter after fineness reaches below 5μm, and obtain the TOPCon back grid conductive paste doped with nickel powder.

[0026] A third objective of this invention is to provide a TOPCon battery containing the aforementioned nickel-doped TOPCon back-side fine grid conductive paste.

[0027] Beneficial effects: This invention, through the specific combination of resin components, ensures that the surface of the nickel powder in the slurry is coated with resin before the silver powder and glass powder fully coat the nickel powder, preventing it from contacting the air and thus achieving the purpose of preventing nickel powder oxidation. At the same time, by adjusting the proportion of different resins, the glass flow rate can be affected, thereby improving the photoelectric conversion efficiency of the slurry. Detailed Implementation

[0028] The present invention will be described in detail below through specific embodiments.

[0029] Raw materials used in the examples: Ethyl cellulose: STD-7; Cellulose acetate (CBE): CAB381-2; Polyvinyl butyral resin: PVB-20H; Styrene-ethylene-propylene-styrene block copolymer: 1701E; Acrylic resin: BR113; Bisphenol A type epoxy resin: EP CYD-014U; Polyamide wax: Kusumoto Disparon 6500; Latent curing agent SD150: HDI-blocked trimer; Silver powder: Particle size 1-2μm, spherical; Nickel powder: 3-8μm particle size, spherical; Glass powder: Particle size 1-4μm.

[0030] Detection method: 1) Detection of the thermal decomposition temperature of organic carriers: The thermal decomposition temperature of the organic carrier is determined by testing its TGA curve, which in turn determines the amount of organic carrier remaining in each temperature range.

[0031] 2) Adhesion test: Conductive paste is printed onto the back of a silicon wafer using screen printing technology. The printed cells are then dried in an infrared drying oven, and their adhesion is tested using 3M tape.

[0032] 3) Inspection of grid line printing morphology: After printing and sintering, the height and width of the grid lines, as well as the degree of grid line undulation, are measured to evaluate the printing performance of the organic carrier.

[0033] 4) Methods for measuring photoelectric conversion efficiency: Battery efficiency was tested using a HALM IV tester.

[0034] Examples 1-23 The method for preparing the organic support includes the following steps: Resin, solvent, thixotropic agent, dispersant and lubricant polydimethylsiloxane were mixed and dispersed in a dispersing pan at room temperature and a rotation speed of 1000 r / min for 30 min to obtain organic carriers, numbered S1-S23.

[0035] The composition of each raw material in Example 23 is shown in Tables 1-1, 1-2, and 1-3 below.

[0036] Table 1-1

[0037] Table 1-2

[0038] Table 1-3

[0039] Application Example 1-23 The preparation method of conductive silver paste includes the following steps: After adding the organic carrier with silver powder, nickel powder and glass powder in a certain proportion, the mixture is stirred thoroughly for 1 hour at 200 r / min using a mixer, and then rolled on a three-roll mill to obtain conductive silver paste, numbered N1-N23.

[0040] The composition of each raw material in Application Example 1-23 is shown in Tables 2-1, 2-2, and 2-3 below.

[0041] Table 2-1

[0042] Table 2-2

[0043] Table 2-3

[0044] Test example: 1. The organic carriers prepared in Examples 1-23 were subjected to thermal decomposition temperature detection. The initial decomposition temperature and the temperature at the end of decomposition were obtained by using the TGA curve (thermogravimetric analysis curve) of the organic carrier. The results are shown in Tables 3-1, 3-2 and 3-3 below.

[0045] Table 3-1

[0046] Table 3-2

[0047] Table 3-3

[0048] 2. Adhesion Testing: The conductive paste prepared in Application Examples 1-23 was printed onto the back of a silicon wafer using screen printing technology. The screen specifications used for adhesion testing were a knotless 520-mesh screen with 8μm wire diameter, 17μm total thickness, and 10.5μm opening. The printed cells were dried in an infrared drying oven, and then adhesion was tested using 3M tape. 3M tape was applied to the printed grid lines, and the tape was manually pressed to ensure complete adhesion between the tape and the grid lines. The tape was then peeled off the silicon wafer, and the adhesion of the paste was judged based on the number of grid lines peeled off per unit area. The best adhesion was 5B, and the worst was 0B.

[0049] The results are shown in Table 4 below.

[0050] Table 4

[0051] 3. The conductive paste prepared in Example 1-23 was screen-printed onto photovoltaic cells. The printing parameters for the back fine grid were: 640-5-13-2.5-12.5 (640 mesh, 5μm wire diameter, 13μm yarn thickness, 2.5μm film thickness, 12.5μm screen opening). The sintering conditions were: actual peak sintering temperature 760℃, sintering furnace belt speed 17m / min, and length 14 meters. After sintering in a conventional sintering furnace, their line resistance was measured, and their volume resistivity was calculated by measuring the height and width of the printed lines. The results are shown in Tables 5-1, 5-2, and 5-3.

[0052] Table 5-1

[0053] Table 5-2

[0054] Table 5-3

[0055] Table 3 shows the decomposition temperature of each organic carrier, and Table 5 shows the volume resistivity of the corresponding paste for each organic carrier. From the thermal decomposition temperature of the carrier and the volume resistivity of the corresponding carrier paste after printing, it can be seen that the higher the decomposition temperature of the organic carrier, the lower the volume resistivity of the paste. This may be because organic carriers with lower decomposition temperatures decompose too quickly, causing the organic carrier coating the nickel powder surface to decompose prematurely. This exposes the nickel powder prematurely to oxidation reactions with oxygen in the air at high temperatures. Since nickel oxide has much lower conductivity than nickel powder, the corresponding paste has a much lower volume resistivity. Overall, the higher the resin decomposition temperature, the lower its volume resistivity, indicating that the presence of resin effectively protects the nickel powder from oxidation at high temperatures.

[0056] 4. The efficiency of the solar cells was tested using a HALM IV tester. The test results are shown in Tables 6-1, 6-2, and 6-3 below.

[0057] Table 6-1

[0058] Table 6-2

[0059] Table 6-3

[0060] Organic carriers N5 and N6 use purely adhesive resins. The Rser data for N5 slurry reflects a higher series resistance, primarily due to the lower decomposition temperature of the acrylic resin. This causes the resin on the nickel powder surface to decompose completely before the sintering process is finished, resulting in severe oxidation of the nickel powder during subsequent sintering. In contrast, the epoxy resin used in N6 slurry has a higher decomposition temperature. During the majority of the slurry sintering process, the resin surface is protected from oxygen oxidation of the nickel powder, resulting in a lower Rser data. Consequently, the bulk resistance of the grid lines is significantly lower, leading to a greater increase in the photoelectric conversion efficiency of the solar cell.

[0061] Comparing the data from N8 to N15 reveals that the electrical properties and Rser data for N8-N11 slurry are in the same tier, as are those for N12-N15 slurry. The main difference between the two slurry formulations is that N8-N11 slurry uses a combination of ordinary long-chain resin and acrylic resin, while N12-N15 slurry uses a combination of ordinary long-chain resin and epoxy resin. Overall, the electrical properties and Rser data for N8-N11 slurry are slightly worse than those for N12-N15, primarily because the decomposition temperature of acrylic resin is significantly lower than that of epoxy resin.

[0062] N16-N19 slurry is based on N8-N11 slurry with the addition of a curing agent. The curing agent will undergo a cross-linking reaction with the acrylic resin during the high-temperature drying process, resulting in a three-dimensional resin with a higher decomposition temperature. TGA data shows that the thermal decomposition temperature of the organic carrier of N16-N19 slurry is about 100°C higher than that of N8-N11 slurry. Its corresponding electrical properties and Rser data are also superior to those of N8-N11 slurry.

[0063] N20-N21 slurry is based on N12-N15 slurry with the addition of a curing agent. The curing agent will undergo a cross-linking reaction with the epoxy resin during the high-temperature drying process, resulting in a three-dimensional resin with a higher decomposition temperature. TGA data shows that the thermal decomposition temperature of the organic carrier of N20-N23 slurry is about 30℃-70℃ higher than that of N12-N15 slurry. Its corresponding electrical properties and Rser data are also superior to those of N12-N15 slurry.

[0064] A longitudinal comparison of N6 and N12-N15 slurries shows little difference in their electrical properties and Rser data. However, it is observed that N6 slurries have more broken grids in their EL printing. This is because the adhesive resins acrylic and epoxy have shorter molecular chains and smaller molecular weights, resulting in poorer printing continuity and a greater likelihood of grid breakage. In contrast, slurries containing high molecular weight long-chain resins, such as N12-N15 slurries, have superior printability.

[0065] A longitudinal comparison of N12-N15 and N20-N23 pastes reveals that N20-N23 incorporates a curing agent on top of N12-N15 paste. The addition of the curing agent to the epoxy resin results in a higher decomposition temperature and better electrical properties, while the continuous resin is retained, thus ensuring the printability of the paste. Therefore, the N20-N23 paste system is the most perfectly matched.

[0066] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. An organic carrier for a TOPCon back-side fine grid conductive paste doped with nickel powder, characterized in that, The raw material composition of the organic carrier, by mass percentage, is: 10-30% resin, 65-85% solvent, 2-7% thixotropic agent, 0.5-1.5% dispersant, and 1-7% polydimethylsiloxane; The resin is a latent curing agent, epoxy resin, and a mixture of one or more of the following: ethyl cellulose, cellulose acetate butyrate, polyvinyl butyral, styrene-ethylene-propylene-styrene block copolymer, and acrylic resin.

2. The organic carrier according to claim 1, characterized in that, The latent curing agent is an aliphatic solvent-based, closed-type curing agent.

3. The organic carrier according to claim 1, characterized in that, The latent curing agent is an HDI-blocked curing agent, and its dosage is 20-45% of the epoxy resin mass.

4. The organic carrier according to claim 1, characterized in that, The solvent is one or more of diethylene glycol monobutyl ether, dodecyl alcohol ester, diethylene glycol butyl ether acetate, diisobutyl adipate, and benzyl benzoate.

5. The organic carrier according to claim 1, characterized in that, The thixotropic agent is polyamide wax; the dispersant is fatty alcohol polyoxyethylene ether.

6. A TOPCon back-side fine grid conductive paste containing nickel powder doped with the organic carrier of claim 1, characterized in that, It also includes silver powder, nickel powder, and glass powder.

7. The TOPCon back-side fine grid conductive paste doped with nickel powder according to claim 6, characterized in that, Silver powder has a particle size of 1-2 μm and is spherical; nickel powder has a particle size of 3-8 μm and is spherical; glass powder has a particle size of 1-4 μm.

8. The TOPCon back-side fine grid conductive paste doped with nickel powder according to claim 6, characterized in that, The raw material composition, by mass percentage, is: 65-75% silver powder, 15-20% nickel powder, 3-5% glass powder, and 5-10% organic carrier.

9. A method for preparing a TOPCon back-side fine grid conductive paste doped with nickel powder as described in any one of claims 6-8, characterized in that, The preparation method includes the following steps: (1) Mix the organic carrier and nickel powder for 10-30 min; (2) Continue to add silver powder and glass powder, stir for 5-20 minutes, grind evenly, filter after fineness reaches below 5μm, and obtain the TOPCon back grid conductive paste doped with nickel powder.

10. A TOPCon battery, characterized in that, TOPCon back-side fine grid conductive paste containing the nickel-doped powder as described in any one of claims 6-8.

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