N-type topcon back surface fine grid paste organic carrier and application thereof

Abstract

The application discloses an organic carrier for N-type TOPCon back fine grid paste and application thereof, and belongs to the field of solar cell metallization printing. The organic carrier is composed of the following components in percentage by mass: 10-30% of resin, 65-85% of solvent, 1-7% of lubricant, 1-5% of thixotropic agent and 1-5% of dispersant; the resin is composed of the following components: poly-alpha-methylstyrene resin, ethyl cellulose resin, polyvinyl butyral resin and 3,5-dimethylpyrazole-closed HDI trimer resin. The composite organic carrier is excellent in printing adhesion and can greatly improve the power generation efficiency of a solar cell.

Description

Technical Field

[0001] This invention belongs to the field of metallization printing of solar cells, and relates to an organic carrier for N-type TOPCon back grid paste and its application. Background Technology

[0002] Among various photovoltaic cell technologies, N-type tunneling oxide passivation cells (TOPCON) have become the main development direction for high-efficiency photovoltaic cells due to their significant performance advantages.

[0003] The back grid of TOPCON cells is crucial in the cell metallization process, as it plays a key role in collecting and transmitting current. This places high demands on the grid printing process, requiring not only excellent contact and conductivity of the grid lines but also consideration of the impact of each process step. Typically, the back main grid is printed first, followed by the back grid, and then the front main grid and the front grid. This necessitates two drying cycles for the back grid. However, the drying strength of conventional organic resin slurries is insufficient, making them prone to scratching against the sintering furnace belt, leading to slurry detachment and grid breakage, severely impacting the cell's power generation efficiency.

[0004] Therefore, it is urgent to develop a high-performance organic carrier for fine grid printing on the back of TOPCON batteries. Summary of the Invention

[0005] [Technical Issues]

[0006] To address the shortcomings of existing technologies, this invention provides an organic carrier for N-TOPCon back-side fine grid paste and its application. This invention optimizes the printability of the paste, grid line height and width, adhesion, and grid line undulation leveling degree by controlling the type and ratio of the raw materials in the organic carrier.

[0007] [Technical Solution]

[0008] This invention provides an organic carrier for N-TOPCon back-side fine grid slurry, wherein the organic carrier comprises, by weight percentage: 10-30% resin, 65-85% solvent, 1-7% lubricant, 1-5% thixotropic agent, and 1-5% dispersant;

[0009] The resin is composed of the following components: poly(α-methylstyrene) resin, ethyl cellulose resin, polyvinyl butyral resin, and 3,5-dimethylpyrazole-blocked HDI trimer resin.

[0010] In one embodiment of the present invention, based on the mass fraction of the relative organic carrier, there are 10-25% poly(α-methylstyrene) resin, 0.5-3% polyvinyl butyral resin, 1-7% 3,5-dimethylpyrazole-blocked HDI trimer resin, and 0.5-3% ethyl cellulose resin.

[0011] In one embodiment of the present invention, the mass ratio of polyvinyl butyral resin to 3,5-dimethylpyrazole-blocked HDI trimer resin is 1:2 to 2:1. More preferably, it is 1:1.

[0012] In one embodiment of the present invention, based on the mass fraction of the relative organic carrier, there are 16-18% poly(α-methylstyrene) resin, 1-2% polyvinyl butyral resin, 1-2% 3,5-dimethylpyrazole-blocked HDI trimer resin, and 1-3% ethyl cellulose resin.

[0013] Further preferred formulation: by mass fraction of relative organic carrier, 16% poly(α-methylstyrene) resin, 1.5% polyvinyl butyral resin, 1.5% 3,5-dimethylpyrazole-blocked HDI trimer resin, and 2% ethyl cellulose resin.

[0014] In one embodiment of the present invention, the solvent is selected from any one or more combinations of the following: 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 solvent may specifically be selected as follows: based on the mass fraction relative to the organic carrier, 3-8% diethylene glycol monobutyl ether, 15-25% dodecyl alcohol ester, 10-30% diethylene glycol butyl ether acetate, 10-20% diisobutyl adipic acid, and 5-15% benzyl benzoate.

[0016] In one embodiment of the present invention, the lubricant is polydimethylsiloxane.

[0017] In one embodiment of the present invention, the thixotropic agent is polyamide wax.

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

[0019] In one embodiment of the present invention, the organic carrier, by mass fraction relative to the organic carrier, comprises the following: 16% poly(α-methylstyrene) resin, 1.5% polyvinyl butyral resin, 1.5% 3,5-dimethylpyrazole-blocked HDI trimer resin, 2% ethyl cellulose resin, 6% diethylene glycol monobutyl ether, 19% dodecyl alcohol ester, 16% diethylene glycol butyl ether acetate, 13% diisobutyl adipate, 10% benzyl benzoate, 6% polydimethylsiloxane, 8% polyamide wax, and 1% fatty alcohol polyoxyethylene ether.

[0020] In this invention, poly(α-methylstyrene) resin is selected as the filler resin, which not only provides viscosity but also good plasticity. Due to its small molecular weight and weak polarity, it experiences less entanglement during screen printing and wire shearing, allowing the ink to pass smoothly through a narrower screen opening, achieving high ink permeability and good flatness of the printed grid lines.

[0021] In this invention, polyvinyl butyral resin is used as a linear resin. Due to its good printing stability and wettability of silver powder, it is widely used in photovoltaic silver paste carriers. The main reason for choosing it as the linking resin is that polyvinyl butyral resin has abundant hydroxyl functional groups, which can undergo cross-linking reaction with the thermally decomposed 3,5-dimethylpyrazole-blocked HDI trimer resin to generate a structurally stable network resin. This product has advantages such as high temperature resistance and high friction hardness.

[0022] In this invention, the HDI trimer resin blocked by 3,5-dimethylpyrazole maintains good chemical stability at both room temperature and relatively high room temperature. It undergoes pyrolysis at around 120-160°C, and the 3,5-dimethylpyrazole end-capping group detaches from the 3,5-dimethylpyrazole-blocked HDI trimer. The exposed isocyanate groups on the HDI trimer structure then undergo a cross-linking reaction with the hydroxyl groups on the polyvinyl butyral resin, achieving high-temperature curing.

[0023] Ethyl cellulose resin was also chosen as the binder because it has good stringing properties in the paste, making it less prone to breakage during printing. This invention adjusts printability by varying the amount of poly(α-methylstyrene) resin, and adjusts the adhesion and drying strength of the paste by adjusting the ratio of polyvinyl butyral resin to 3,5-dimethylpyrazole-blocked HDI trimer resin.

[0024] This invention also uses polydimethylsiloxane and a thixotropic agent. Polydimethylsiloxane is insoluble in the slurry system and can adhere to the slurry surface to prevent the slurry from collapsing. If too much is used, the printed linear gourd knots will be more severe, and it is easy to cause false breaks after printing. If too little is used, the printed grid lines will collapse and widen, which will increase the light-blocking area and affect the luminous efficiency of the solar cell.

[0025] Polyamide wax resin can significantly improve the height and width of the printed paste. When the amount used is small, the grid lines after printing will be shorter; conversely, when the amount used is large, the grid lines will be taller, and the grid lines will be more prone to breakage. This invention adjusts the aspect ratio and leveling degree of the grid lines by adjusting the ratio of polydimethylsiloxane to the thixotropic agent amide wax.

[0026] This invention allows for the creation of organic carriers with varying drying strengths based on different drying temperatures during the two-stage printing process, according to customer requirements. These carriers not only offer excellent printability but also meet customers' requirements for line shapes with different aspect ratios in terms of printability. The carriers are stable not only at room temperature but also maintain their stability without cross-linking at low temperatures and temperatures below 70°C. After drying, the carriers cross-link with other components, becoming thermosetting resins. Therefore, they experience less stress shrinkage during the final high-temperature sintering process, reducing the likelihood of grid line warping and detachment.

[0027] The present invention also provides an N-TOPCon back-side fine grid paste, comprising the above-mentioned organic carrier, glass powder, and silver powder.

[0028] The present invention also provides a TOPCon battery containing the above-mentioned N-TOPCon back grid paste.

[0029] Compared with the prior art, the present invention has the following advantages and effects:

[0030] This invention improves the printability of the carrier by introducing poly(α-methylstyrene) resin, enabling it to perform well on screens with narrower linewidths and higher mesh counts. By adjusting the ratio of polyvinyl butyral resin to 3,5-dimethylpyrazole-blocked HDI trimer resin, a carrier with good wetting properties, excellent adhesion after drying, and superior abrasion resistance is obtained. Adjusting the ratio of polydimethylsiloxane to the thixotropic agent amide wax further yields a carrier with the desired linewidth and height, and excellent flatness of the printed grid lines. Combined with the stringing properties of ethyl cellulose resin, the composite carrier not only exhibits excellent printing adhesion but also significantly improves the power generation efficiency of solar cells. Detailed Implementation

[0031] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0032] Source of raw materials

[0033] Resins: including ethyl cellulose resin from Dow Chemical Company; Eastman TM Poly(α-methylstyrene) resin; Eastman TM Polyvinyl butyral resin; Wanhua Chemical's 3,5-dimethylpyrazole-blocked HDI trimer resin.

[0034] Dispersant: fatty alcohol polyoxyethylene ether from Haian Petrochemical.

[0035] Thixotropic agent: Nanben Disparon 6500 polyamide wax.

[0036] Lubricant: Polydimethylsiloxane with a viscosity of 200 cSt.

[0037] Example 1

[0038] An N-TOPCon back-side fine grid organic carrier, the formulation of which is shown in Table 1, and the specific preparation method includes:

[0039] (1) Weigh the solvent required for the preparation of the carrier according to the corresponding proportions in the formula and add it to a glass beaker of the appropriate capacity. (2) Pour the solvent into a reactor equipped with a high-speed dispersion plate. (3) Weigh the corresponding weights of poly(α-methylstyrene) resin, polyvinyl butyral resin, ethyl cellulose resin, and other components according to the formula in Table 1 and add them to the reactor. (4) Turn on the dispersion and stirring device to promote uniform dispersion of the resin in the solvent. (5) Turn on the heating device and gradually increase the temperature to 80 degrees Celsius within 20 minutes, and continue stirring at this temperature for 1 hour. (6) Turn off the heating device and continue stirring with the dispersion device until room temperature. (7) Collect the carrier for later use.

[0040] Preparation of an N-TOPCon back-side fine grid conductive paste: 8.5 wt% of the above-mentioned organic carrier is mixed with 89.5 wt% of silver powder (spherical silver powder with a particle size range of 1-2 μm) and 2.0 wt% of glass powder (particle size range of 1-2 μm, TG point of 350-400℃) to obtain a conductive paste.

[0041] Viscosity test: Take 30g of the above conductive paste and use a Brookfield DV2 viscometer and rotor SC-14 to measure the average viscosity of the paste under the conditions of 25℃ / 50rpm / 60 seconds.

[0042] Adhesion testing: The conductive paste described above was printed onto the back of the silicon wafer using screen printing technology. The adhesion testing screen used was a knotless 520-mesh screen with an 8μm wire diameter, a total thickness of 17μm, and an aperture of 10.5μm. The printed cells were dried in an infrared drying oven, and then the adhesion was tested using 3M tape. The adhesion was judged based on the proportion of silver wires that were removed from the tape. The best adhesion was 5B, and the worst was 0B.

[0043] Grid line printing morphology inspection: The morphology inspection of grid lines after screen printing is divided into grid line drying morphology inspection and grid line sintering morphology inspection. After printing, the undulation state of the grid lines can be observed through a high-magnification microscope, and the height and width of the grid lines can be measured to evaluate the printing performance of the organic carrier.

[0044] Method for determining photoelectric conversion efficiency: The above conductive paste is printed on the back of the TOPCon crystalline silicon solar cell by screen printing. The peak temperature of the cell sintering furnace is controlled between 650-780℃. After the cell is sintered and cooled to room temperature, the electrical performance of the cell is tested and characterized by HALM IV tester, and the conversion efficiency (Eta) is measured.

[0045] The specific test results are shown in Table 2.

[0046] Table 1. Formulations for S1 to S4 (in wt%)

[0047]

[0048] Table 2 Performance Test Results

[0049] Printing paste weight 34 33.4 33 32.3 Number of broken grid roots / piece 25 20 12 11 gate height / width 6.8 / 25.4 6.3 / 26.1 6.0 / 26.7 5.4 / 28 Conversion efficiency (Eta) 26.55 26.58 26.61 26.54

[0050] As shown in Table 1-2, the optimal grid line breakage and height / width parameters of the slurry are achieved when poly-α-methylstyrene resin accounts for 16% of the total carrier mass. When its proportion is low, there are more grid lines after printing, resulting in a higher wet weight, which does not meet the requirements. When its proportion is high, although grid line breakage is improved, the grid line height is low and the width is wide, which is not conducive to good contact after sintering, thus leading to a lower final conversion efficiency.

[0051] Example 2

[0052] An N-TOPCon back-side fine grid organic carrier, the formulation of which is shown in Table 3, S5-S10.

[0053] The corresponding conductive paste was prepared using the same method as in Example 1.

[0054] The performance results were tested according to the test method in Example 1. The results are shown in Table 4.

[0055] Table 3 shows the formulations for S5 to S10 (in wt%).

[0056]

[0057]

[0058] Table 4 Performance Test Results

[0059]

[0060] As shown in Table 3-4, compared to S3, adjusting the amount of polydimethylsiloxane and polyamide wax can regulate the height, width, undulation, and breakage of the grid lines. Comparing the data from S3, S5, and S6, as the amount of polydimethylsiloxane increases, the grid line width gradually narrows while the grid line height gradually increases. When the amount increases to 9%, the undulation of the grid lines increases, increasing the risk of grid breakage during printing. Therefore, the amount should be controlled at 6%. Similarly, comparing S6, S9, and S10, with a fixed amount of polydimethylsiloxane and an increased amount of polyamide wax, the degree of grid breakage gradually increases with the increase in polyamide wax usage, accompanied by an increase in grid line undulation, indicating an increased risk of grid breakage during printing. Compared with S5, S7, and S8, with a fixed amount of polydimethylsiloxane and an increased amount of polyamide wax, when the amount of polyamide wax is increased to 10%, the grid line undulation is high, the grid line width gradually narrows, and the grid line height increases, increasing the risk of grid breakage during printing. Therefore, it is advisable to control the amount at 6%-8%, which results in less grid line undulation and excellent grid breakage effect during printing, with better overall performance.

[0061] Example 3

[0062] An N-TOPCon back-side fine grid organic carrier, the formulation of which is shown in Table 5, S11-S15.

[0063] The corresponding conductive paste was prepared using the same method as in Example 1.

[0064] The performance results were tested according to the test method in Example 1. The results are shown in Table 6.

[0065] Table 5. Formulations for S11 to S15 (in wt%)

[0066] Poly-α-methylstyrene resin 16 16 16 16 16 16 Polyvinyl butyral resin 1 1.3 1.5 1.7 2 3 3,5-Dimethylpyrazole-blocked HDI trimer resin 2 1.7 1.5 1.3 1 0 Ethyl cellulose resin 2 2 2 2 2 2 Diethylene glycol monobutyl ether 6 6 6 6 6 6 Alcohol ester dodecyl 19 19 19 19 19 19 Diethylene glycol butyl ether acetate 16 16 16 16 16 16 Diisobutyl adipate 13 13 13 13 13 13 benzyl benzoate 10 10 10 10 10 10 polydimethylsiloxane 6 6 6 6 6 6 Polyamide wax 8 8 8 8 8 8 Fatty alcohol polyoxyethylene ether 1 1 1 1 1 1

[0067] Table 6 Adhesion Test Results

[0068]

[0069]

[0070] As can be seen from Tables 5-6, the adhesion of the grid lines after drying can be adjusted by changing the ratio of polyvinyl butyral resin to 3,5-dimethylpyrazole-blocked HDI trimer resin. The comparison of S7 and S11-S15 tests shows that the combination of 3,5-dimethylpyrazole-blocked HDI trimer resin and polyvinyl butyral resin can significantly improve the adhesion of the slurry; and when the ratio of the two is 1:1, the adhesion reaches 5B, which is the best adhesion.

[0071] Example 4

[0072] An N-TOPCon back-side fine grid organic carrier, the formulation of which is shown in S12.

[0073] The conductive paste was prepared using the same method as in Example 1, and its performance was tested. The results are shown in Table 7.

[0074] Table 7

[0075] Printing paste weight 35 mg Number of broken grid roots / piece 2 gate height / width 5.8 / 25.2 High / Medium / Low grid line undulation Low Adhesion 5B Conversion efficiency (Eta) 26.65

[0076] Viscosities of the conductive paste prepared by formula S12 and the backing paste A of the conventional epoxy curing system were tested. After sealing, the pastes were placed in an oven set at 70°C and kept at that temperature for 24 hours. The viscosity data of both pastes were then measured again. The two pastes were then printed on a screen printing plate, and the grid breakage of the two pastes was observed.

[0077] The experimental results are shown in Table 8. As can be seen from Table 8, the viscosity of S12 paste is not significantly different after being kept at 70℃ for 24 hours, and there is no difference in the printing grid break plan. The viscosity of paste A increases sharply under the same storage conditions as S12, making it almost unprintable. Therefore, S12 paste is superior to paste A in terms of high temperature resistance.

[0078] Table 8

[0079] S12 before drying 70.8 49.6 29.6 1 S12 after drying 71.4 48.9 30 2 A Before drying 80.3 55.4 31.7 2 After drying A 207 117.8 60.3 Silicon wafer with full-surface gate break

[0080] Comparative Example 1

[0081] Referring to formulation S12, the poly(α-methylstyrene) resin in the resin was replaced with an equal amount of other elastomer resins (as shown in Table 9), while other aspects remained unchanged, to obtain the corresponding organic carrier.

[0082] The conductive paste was prepared using the same method as in Example 1, and its performance was tested. The results are shown in Table 10.

[0083] Table 9 shows the formulations for S16 to S17 (in wt%).

[0084] Poly-α-methylstyrene resin 16 0 0 SEPS 0 16 0 SEBS 0 0 16 Polyvinyl butyral resin 1.5 1.5 1.5 3,5-Dimethylpyrazole-blocked HDI trimer resin 1.5 1.5 1.5 Ethyl cellulose resin 2 2 2 Diethylene glycol monobutyl ether 6 6 6 Alcohol ester dodecyl 19 19 19 Diethylene glycol butyl ether acetate 16 16 16 Diisobutyl adipate 13 13 13 benzyl benzoate 10 10 10 polydimethylsiloxane 6 6 6 Polyamide wax 8 8 8 Fatty alcohol polyoxyethylene ether 1 1 1

[0085] Table 10

[0086] Number of broken grid roots / piece 2 6 8 gate height / width 5.8 / 25.2 6.3 / 24.3 6.7 / 24.0 High / Medium / Low grid line undulation Low high high Adhesion 5B 5B 5B

[0087] Comparative Example 2

[0088] Referring to formulation S12, the 3,5-dimethylpyrazole-blocked HDI trimer resin in the resin was replaced with an equal amount of other resins (as shown in Table 11), while other aspects remained unchanged, to obtain the corresponding organic carrier.

[0089] The conductive paste was prepared using the same method as in Example 1, and its performance was tested. The results are shown in Table 12.

[0090] Table 11 Formulations for S18 to S21 (in wt%)

[0091]

[0092] Table 12

[0093] Number of broken grid roots / piece 2 12 9 6 5 gate height / width 5.8 / 25.2 6.3 / 22.3 4.2 / 29.7 5.7 / 25.6 6.2 / 24.4 High / Medium / Low grid line undulation Low high Low middle high Adhesion 5B 3B 3B 2B 4B

[0094] Comparative Example 3

[0095] Referring to formulation S12, the polyvinyl butyral resin in the resin was replaced with an equal amount of other resins (as shown in Table 13), while other aspects remained unchanged, to obtain the corresponding organic carrier.

[0096] The conductive paste was prepared using the same method as in Example 1, and its performance was tested. The results are shown in Table 14.

[0097] Table 13 Formulations for S22 to S24 (in wt%)

[0098]

[0099] Table 14

[0100] Number of broken grid roots / piece 2 3 3 2 gate height / width 5.8 / 25.2 5.0 / 26.7 5.6 / 25.8 5.7 / 25.3 High / Medium / Low grid line undulation Low Low Low Low Adhesion 5B 2B 2B 2B

[0101] The organic carrier selected in this invention is polyvinyl butyral resin containing abundant hydroxyl groups, which can undergo a cross-linking reaction with 3,5-dimethylpyrazole-blocked HDI trimer resin under high temperature conditions to generate a stable network structure macromolecule, which is beneficial for scratch resistance and adhesion.

[0102] 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 N-TOPCon back-side fine grid slurry, characterized in that, The organic carrier, by mass percentage, comprises the following: 10-30% resin, 65-85% solvent, 1-7% lubricant, 1-5% thixotropic agent, and 1-5% dispersant; The resin is composed of the following components: poly(α-methylstyrene) resin, ethyl cellulose resin, polyvinyl butyral resin, and 3,5-dimethylpyrazole-blocked HDI trimer resin. Based on the relative mass fraction of the organic carrier, poly(α-methylstyrene) resin 16-18%, polyvinyl butyral resin 1-2%, 3,5-dimethylpyrazole-blocked HDI trimer resin 1-2%, and ethyl cellulose resin 1-3%; The mass ratio of polyvinyl butyral resin to 3,5-dimethylpyrazole-blocked HDI trimer resin is 1:

1.

2. The organic carrier for N-TOPCon back-side fine grid slurry according to claim 1, characterized in that, Based on the relative mass fraction of the organic carrier, the composition is: 16% poly(α-methylstyrene) resin, 1.5% polyvinyl butyral resin, 1.5% 3,5-dimethylpyrazole-blocked HDI trimer resin, and 2% ethyl cellulose resin.

3. The organic carrier for N-TOPCon back-side fine grid slurry according to claim 1, characterized in that, The solvent is selected from any one or more combinations of the following: diethylene glycol monobutyl ether, dodecyl alcohol ester, diethylene glycol butyl ether acetate, diisobutyl adipate, and benzyl benzoate.

4. The organic carrier for N-TOPCon back-side fine grid slurry according to claim 1, characterized in that, The lubricant is polydimethylsiloxane, the thixotropic agent is polyamide wax, and the dispersant is fatty alcohol polyoxyethylene ether.

5. An N-TOPCon back-side fine grid slurry, characterized in that, It comprises the organic carrier, glass powder, and silver powder as described in any one of claims 1-4.

6. A TOPCon battery, characterized in that, It contains the N-TOPCon back-side fine grid slurry as described in claim 5.

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