Flaky silver powder for heterojunction low-temperature silver paste fine line printing and preparation method thereof

Abstract

The application provides sheet silver powder for heterojunction low-temperature silver paste fine line printing and a preparation method thereof, and belongs to the technical field of heterojunction photovoltaic cells.The method comprises the following steps: in a stirring state, adding acetic acid into a 100-200 g / L silver nitrate solution, and reacting for 5-15 min at a temperature of 25-30 DEG C; continuously adding acetic acid until the pH value is 1-6, then adding a 20-26 g / L nucleating agent solution and performing ultrasonic treatment; uniformly adding a 100-500 g / L reducing agent solution into the ultrasonic-treated solution, and reacting for 25-35 min; then, separating, ethanol washing, modifying and drying to obtain thick sheet silver powder; mixing zirconium oxide beads and the thick sheet silver powder, adding ethanol, ball milling for 20-40 min, passing through a 38-42 mesh screen, and then using ethanol to wash, so as to obtain sheet silver powder.The sheet silver powder has good printing suitability and high conductivity.

Description

Technical Field

[0001] This invention belongs to the field of heterojunction photovoltaic cell technology, and particularly relates to a sheet-like silver powder for heterojunction low-temperature silver paste fine line printing and its preparation method. Background Technology

[0002] Heterojunction photovoltaic (HJT) technology has gained significant market favor due to its fewer production steps, higher yield, and weaker degradation. Silver powder, used in photovoltaic silver paste, is a key material for semiconductor silicon metallization and directly impacts the photoelectric conversion efficiency of solar cells. The new generation of N-type solar cells requires silver powder with advantages such as high tap density, controllable particle size distribution, good dispersibility, and low-temperature sintering activity, leading to increasing demand. However, domestic technology for preparing thick-sheet silver powder for HJT silver paste is still immature and relies heavily on imports. With the promotion of SMBB (16-busbar and above) process solutions, the main busbars are becoming increasingly finer. Thick-sheet silver powder for HJT silver paste must possess higher filling density and sintering activity to meet performance requirements such as paste resistivity, printability, and solderability. While domestic companies have some relatively stable products for thick-sheet silver powder in HJT silver paste, these products suffer from low volume resistivity and low main busbar tension, failing to meet the needs of fine-line printing. There is still a significant gap between domestic and foreign manufacturers' technologies, and the domestic market for HJT silver paste remains monopolized by foreign companies. Therefore, it is necessary to focus on the structural and performance kinetics control of silver powder to prepare thick sheet-like silver powder with high conductivity that can be printed with fine lines.

[0003] Currently, the preparation of flake-shaped silver powder with the required particle size and morphology generally uses polymeric or macromolecular reagents as dispersants. However, the low-temperature slurry used in HJT technology has difficulty burning off these macromolecular compounds, and the residues that cannot be broken down affect the conductivity of the slurry. At the same time, achieving the required performance of flake-shaped silver powder through secondary ball milling of near-spherical silver powder requires a long milling time and consumes a lot of energy. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing flake silver powder for low-temperature silver paste fine-line printing in heterojunctions. This method can prepare flake silver powder with good printability and high conductivity during low-temperature curing, thus meeting the requirements for low-temperature silver paste fine-line printing in heterojunction solar cells.

[0005] The second objective of this invention is to provide a sheet-like silver powder for fine-line printing of heterojunction low-temperature silver paste.

[0006] To achieve one of the above objectives, the present invention employs the following technical solution:

[0007] A method for preparing flake silver powder for low-temperature silver paste fine-line printing in heterojunctions, the method comprising the following steps:

[0008] Step S1: Under stirring, add acetic acid to a silver nitrate solution of 100-200 g / L, react at 25-30°C for 5-15 min, continue to add acetic acid until the pH value is 1-6, then add a nucleating agent solution of 20-26 g / L and sonicate.

[0009] The mass ratio of silver nitrate in the acetic acid and silver nitrate solution is 1:5-20;

[0010] The mass ratio of the nucleating agent in the nucleating agent solution to the silver nitrate in the silver nitrate solution is 1–5:100;

[0011] Step S2: After uniformly adding 100-500 g / L of reducing agent solution to the ultrasonicated solution, react for 25-35 minutes, then separate, wash with ethanol, modify and dry to obtain thick sheet silver powder with a diameter-to-thickness ratio of 3-6:1.

[0012] The molar ratio of the reducing agent in the reducing agent solution to the silver nitrate in the silver nitrate solution is 1:0.4 to 1;

[0013] Step S3: After mixing zirconium oxide beads with a diameter of 1.3 to 1.7 mm and thick sheet silver powder, add ethanol, ball mill for 20 to 40 minutes, pass through a 38 to 42 mesh sieve, and then wash with ethanol to obtain sheet silver powder.

[0014] The mass ratio of the zirconium oxide beads, thick sheet silver powder, and ethanol is 4–5:1:0.6–0.8.

[0015] This invention utilizes silver nitrate solution and acetic acid to obtain silver acetate, a silver precursor with weak reducing power, thereby reducing the reaction rate. A nucleating agent composed of various small-molecule organic acids is used to induce anisotropic growth of crystal nuclei, while the adsorption of numerous small molecules on the crystal surface prevents particle aggregation. Ultrasonic oscillation ensures uniform distribution of the small-molecule organic acids around the silver acetate, keeping each silver acetate molecule relatively separated. This allows for slow particle growth during subsequent silver acetate dissolution, as the molecules can deposit nearby on silver crystal nuclei with higher surface energy. A shorter ball milling time enhances the sintering activity of the flake silver powder, resulting in better printability and higher conductivity during low-temperature curing.

[0016] Furthermore, in step S1, the mass ratio of acetic acid to silver nitrate is 1:8 to 17;

[0017] The mass ratio of the nucleating agent to silver nitrate is 3-4:100.

[0018] Furthermore, in step S1, the nucleating agent is a mixture of two or more of succinic acid, tartaric acid, citric acid, or ethylenediaminetetraacetic acid.

[0019] Furthermore, in step S1, the stirring speed is 50-70 r / min;

[0020] The frequency of the ultrasound is 20–40 kHz, and the duration is 4–20 min.

[0021] Furthermore, in step S2, the molar ratio of the reducing agent to silver nitrate is 1:0.6 to 0.8.

[0022] Furthermore, in step S2, the reducing agent solution is added over a period of 3 to 5 minutes.

[0023] Furthermore, in step S2, the reducing agent is one or a mixture of two of ascorbic acid, ferrous sulfate, hydroxylamine sulfate, sodium hypophosphite, and hydrazine hydrate.

[0024] Furthermore, in step S2, succinic acid is used for modification;

[0025] The mass ratio of succinic acid to silver nitrate is 0.2–0.7:100.

[0026] To achieve the second objective mentioned above, the present invention employs the following technical solution:

[0027] A sheet-like silver powder for low-temperature silver paste fine-line printing in heterojunctions, wherein the sheet-like silver powder is prepared by the preparation method described above.

[0028] Furthermore, the D10, D50, and D100 of the flake silver powder are 1.1–1.3 μm, 2.5–3.1 μm, and 4.4–5.0 μm, respectively, and the tap density and specific surface area are 4.0–5.5 g / cm³, respectively. 3 and 0.26~0.32m 2 / g, volume resistivity is 6.7*10 -7 ~2.2*10 -5 Ω·cm.

[0029] In summary, the technical solution of the present invention has the following beneficial effects:

[0030] This invention uses silver acetate, which has a weak reducing ability, as a silver precursor. A nucleating agent composed of various small-molecule organic acids is used, and ultrasonic vibration ensures that each small organic molecule is uniformly dispersed around the silver acetate precipitate. Then, a reducing agent is added at a uniform rate using a reverse feeding method, avoiding simultaneous nucleation and growth during silver powder synthesis, thus producing flake-shaped silver powder with a small aspect ratio. Short-time mechanical ball milling ensures that the flake-shaped silver powder exhibits good printability and high conductivity during low-temperature curing, meeting the requirements for low-temperature silver paste fine-line printing in heterojunction solar cells. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1:

[0033] S1. Under stirring at 60 r / min, add industrial acetic acid to a 100 g / L silver nitrate solution. After it is completely converted into silver acetate precipitate, add acetic acid until the pH value is 6. Then add 20 g / L succinic acid solution and 2 g / L ethylenediaminetetraacetic acid solution, and sonicate at 30 kHz for 10 min.

[0034] The mass ratio of acetic acid to silver nitrate is 1:17. The mass ratio of nucleating agent (i.e., succinic acid and ethylenediaminetetraacetic acid) to silver nitrate is 4:100.

[0035] S2. Add 200 g / L ascorbic acid solution to the solution prepared in S1 at a uniform rate. The addition time is controlled at 5 minutes. After the addition is completed, continue the reaction for half an hour. Then separate, wash, modify with succinic acid, and dry to obtain thick sheet silver powder with a diameter-to-thickness ratio of 4:1.

[0036] The molar ratio of ascorbic acid to silver nitrate is 1:0.8. The mass ratio of succinic acid to silver nitrate is 0.7:100.

[0037] S3. Mix the flake silver powder with 1.3mm diameter zirconium oxide beads, add ethanol, and then put the mixture into a vibrating ball mill jar for ball milling for 20 minutes. After passing through a 40-mesh sieve, wash with ethanol to obtain flake silver powder suitable for low-temperature silver paste fine line printing in heterojunction solar cells.

[0038] The mass ratio of zirconium oxide beads, thick sheet silver powder and ethanol is 4:1:0.7.

[0039] The printing conditions for the flake silver powder in this embodiment are 20 μm, continuous printing. The conductivity and printability test results are as follows:

[0040] The D10, D50, and D100 values ​​are 1.2 μm, 2.5 μm, and 4.4 μm, respectively, and the tap density and specific surface area are 4.0 g / cm³. 3 and 0.26m 2 / g, volume resistivity is 2.2*10 -5The curing temperature and curing time were 160℃ and 30min, respectively, and the printed lines test results showed no broken lines.

[0041] Example 2:

[0042] S1. Under stirring at 70 r / min, add industrial acetic acid to a 200 g / L silver nitrate solution. After it is completely converted into silver acetate precipitate, add acetic acid until the pH value is 3. Then add 20 g / L succinic acid solution and 6 g / L tartaric acid solution, and sonicate at 40 kHz for 20 min.

[0043] The mass ratio of acetic acid to silver nitrate is 1:20. The mass ratio of nucleating agent (i.e., succinic acid and tartaric acid) to silver nitrate is 5:100.

[0044] S2. Add 500 g / L of ferrous sulfate solution to the solution prepared in S1 at a uniform rate. The addition time is controlled at 3 minutes. After the addition is completed, continue for 25 minutes. Then separate, wash, modify with succinic acid, and dry to obtain thick sheet silver powder with a diameter-to-thickness ratio of 3:1.

[0045] The molar ratio of ferrous sulfate to silver nitrate is 1:0.4. The mass ratio of succinic acid to silver nitrate is 0.2:100.

[0046] S3. Mix the flake silver powder with 1.5mm diameter zirconium oxide beads, then add ethanol and put it into a vibrating ball mill jar for ball milling for 40 minutes. After passing through a 42-mesh sieve, wash with ethanol to obtain flake silver powder suitable for low-temperature silver paste fine line printing of heterojunction solar cells.

[0047] The mass ratio of zirconium oxide beads, thick sheet silver powder and ethanol is 5:1:0.8.

[0048] The printing conditions for the flake silver powder in this embodiment are 20μm, continuous printing, and the results of the conductivity and printability tests are as follows:

[0049] The D10, D50, and D100 values ​​are 1.3 μm, 3.1 μm, and 5.0 μm, respectively, and the tap density and specific surface area are 5.5 g / cm³. 3 and 0.32m 2 / g, volume resistivity is 6.7*10 -7 The curing temperature and curing time were 160℃ and 30min, respectively, and the printed lines test results showed no broken lines.

[0050] Example 3:

[0051] S1. Under stirring at 70 r / min, add industrial acetic acid to a 150 g / L silver nitrate solution. After it is completely converted into silver acetate precipitate, add acetic acid until the pH value is 1. Then add 10 g / L succinic acid solution, 6 g / L citric acid solution and 4 g / L ethylenediaminetetraacetic acid solution. Sonicate at 20 kHz for 4 min.

[0052] The mass ratio of acetic acid to silver nitrate is 1:5. The mass ratio of nucleating agent (i.e., succinic acid, citric acid, and ethylenediaminetetraacetic acid) to silver nitrate is 1:100.

[0053] S2. Add 100 g / L sodium hypophosphite solution to the solution prepared in S1 at a uniform rate. The addition time is controlled at 4 minutes. After the addition is completed, continue the reaction for 35 minutes. Then separate, wash, modify with succinic acid, and dry to obtain thick sheet silver powder with a diameter-to-thickness ratio of 6:1.

[0054] The molar ratio of sodium hypophosphite to silver nitrate is 1:1. The mass ratio of succinic acid to silver nitrate is 0.3:100.

[0055] S3. Mix flake silver powder with 1.7mm diameter zirconium oxide beads, then add ethanol and place in a vibrating ball mill jar for ball milling for 30 minutes. After passing through a 38-mesh sieve, wash with ethanol to obtain flake silver powder suitable for low-temperature silver paste fine-line printing in heterojunction solar cells.

[0056] The mass ratio of zirconium oxide beads, thick sheet silver powder, and ethanol is 4:1:0.6.

[0057] The printing conditions for the flake silver powder in this embodiment are 20μm, continuous printing, and the results of the conductivity and printability tests are as follows:

[0058] The D10, D50, and D100 values ​​are 1.1 μm, 2.9 μm, and 4.6 μm, respectively, and the tap density and specific surface area are 4.7 g / cm³. 3 and 0.30m 2 / g, volume resistivity is 4.2*10 -6 The curing temperature and curing time were 160℃ and 30min, respectively, and the printed lines test results showed no broken lines.

[0059] Example 4:

[0060] S1. Under stirring at 65 r / min, add industrial acetic acid to a 180 g / L silver nitrate solution. After it is completely converted into silver acetate precipitate, add acetic acid until the pH value is 2. Then add 18 g / L succinic acid solution and 2 g / L ethylenediaminetetraacetic acid solution, and sonicate at 35 kHz for 15 min.

[0061] The mass ratio of acetic acid to silver nitrate is 8:17, and the mass ratio of nucleating agent (i.e., succinic acid and ethylenediaminetetraacetic acid) to silver nitrate is 3:100.

[0062] S2. Add 300 g / L hydroxylamine sulfate solution to the solution prepared in S1 at a uniform rate. The addition time is controlled at 4 minutes. After the addition is completed, continue the reaction for 28 minutes. Then separate, wash, modify with succinic acid, and dry to obtain thick sheet silver powder with a diameter-to-thickness ratio of 5:1.

[0063] The molar ratio of hydroxylamine sulfate to silver nitrate is 1:0.6. The mass ratio of succinic acid to silver nitrate is 0.5:100.

[0064] S3. Mix the flake silver powder with 1.6mm diameter zirconium oxide beads, then add ethanol and put it into a vibrating ball mill jar for ball milling for 28 minutes. After passing through a 36-mesh sieve, wash with ethanol to obtain flake silver powder suitable for low-temperature silver paste fine line printing in heterojunction solar cells.

[0065] The mass ratio of zirconium oxide beads, thick sheet silver powder, and ethanol is 5:1:0.6.

[0066] The printing conditions for the flake silver powder in this embodiment are 20μm, continuous printing, and the results of the conductivity and printability tests are as follows:

[0067] The D10, D50, and D100 values ​​are 1.2 μm, 2.8 μm, and 4.5 μm, respectively, and the tap density and specific surface area are 4.8 g / cm³. 3 and 0.28m 2 / g, volume resistivity is 4.8*10 -6 The curing temperature and curing time were 160℃ and 30min, respectively, and the printed lines test results showed no broken lines.

[0068] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing flake silver powder for fine-line printing of heterojunction low-temperature silver paste, characterized in that, The preparation method includes the following steps: Step S1: Under stirring, add acetic acid to a 100-200 g / L silver nitrate solution and react at 25-30°C for 5-15 minutes. Continue to add acetic acid until the pH value is 1-6. Then add 20-26 g / L nucleating agent solution and sonicate. The mass ratio of silver nitrate in the acetic acid and silver nitrate solution is 1:5~20; The mass ratio of the nucleating agent in the nucleating agent solution to the silver nitrate in the silver nitrate solution is 1~5:100; In step S1, the nucleating agent is two or more of succinic acid, tartaric acid, citric acid, or ethylenediaminetetraacetic acid. Step S2: After uniformly adding 100~500g / L of reducing agent solution to the ultrasonic solution, react for 25~35 minutes, then separate, wash with ethanol, modify and dry to obtain thick sheet silver powder with a diameter-to-thickness ratio of 3~6:

1. The molar ratio of the reducing agent in the reducing agent solution to the silver nitrate in the silver nitrate solution is 1:0.4~1; Step S3: After mixing zirconium oxide beads with a diameter of 1.3~1.7mm and thick sheet silver powder, add ethanol, ball mill for 20~40 minutes, pass through a 38~42 mesh sieve, and then wash with ethanol to obtain sheet silver powder. The mass ratio of the zirconium oxide beads, thick sheet silver powder, and ethanol is 4-5:1:0.6-0.

8.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of acetic acid to silver nitrate is 1:8~17; The mass ratio of the nucleating agent to silver nitrate is 3~4:

100.

3. The preparation method according to claim 2, characterized in that, In step S1, the stirring speed is 50~70 r / min; The frequency of the ultrasound is 20~40kHz, and the duration is 4~20min.

4. The preparation method according to claim 3, characterized in that, In step S2, the molar ratio of the reducing agent to silver nitrate is 1:0.6~0.

8.

5. The preparation method according to claim 4, characterized in that, In step S2, the reducing agent solution is added over a period of 3 to 5 minutes.

6. The preparation method according to claim 5, characterized in that, In step S2, the reducing agent is one or a mixture of two of ascorbic acid, ferrous sulfate, hydroxylamine sulfate, sodium hypophosphite, and hydrazine hydrate.

7. The preparation method according to claim 6, characterized in that, In step S2, succinic acid is used for modification; The mass ratio of succinic acid to silver nitrate is 0.2~0.7:

100.

8. A sheet-like silver powder for fine-line printing of heterojunction low-temperature silver paste, characterized in that, The flake silver powder is prepared using the preparation method described in any one of claims 1 to 7.

9. The flake-shaped silver powder according to claim 8, characterized in that, The flake-shaped silver powder has D10, D50, and D100 values ​​of 1.1–1.3 μm, 2.5–3.1 μm, and 4.4–5.0 μm, respectively, and a tap density and specific surface area of ​​4.0–5.5 g / cm³. 3 and 0.26~0.32m 2 / g, volume resistivity 6.7×10 -7 ~2.2×10 -5 Ω•cm.