Preparation process of single-crystal heterojunction battery

Abstract

The invention discloses a preparation process of a single crystal heterojunction cell, which comprises the following steps of: S10, coating a grid line pre-covering area of an n-type single crystal silicon wafer of which the two surfaces are textured with first film forming liquid, and curing the first film forming liquid to obtain a silicon wafer of which the back surface is covered with a first mask; s20, sequentially polishing and cleaning the back surface of the silicon wafer; s30, removing the first mask by using a water-based cleaning solution, and cleaning and drying the silicon wafer; s40, an amorphous silicon film and a TCO film are sequentially deposited on the two faces of the silicon wafer, and grid lines are printed on the surface of the silicon wafer in a silk-screen mode; the first film-forming liquid comprises the following components: UV curing resin and inorganic particles loaded with strong base. Inorganic particles loaded with strong base are introduced into the first film forming liquid, in the process that the first mask is removed through the low-concentration strong base solution, the strong base in the inorganic particles loaded with the strong base is separated out, and the part in the silicon wafer grid line pre-covering area reacts with the high-concentration strong base solution; and the binding force between the back grid line of the battery piece and the battery piece, the filling factor of the battery piece and the photoelectric conversion efficiency are improved.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic cells, and specifically to a fabrication process for a monocrystalline heterojunction cell. Background Technology

[0002] Silicon wafer back-side polishing technology is often used to improve the efficiency of the front side of photovoltaic crystalline silicon cells. Bifacial cells produced using silicon wafer back-side polishing technology are widely used in rooftop distributed photovoltaic power generation systems and floating photovoltaic power generation systems.

[0003] The essence of silicon wafer back polishing technology is to change the textured pyramid structure on the back of the bifacial cell into a planar structure. On the one hand, it can reduce the specific surface area on the back of the cell, thereby reducing the recombination of minority carriers and increasing the open-circuit voltage. On the other hand, it can enhance the mirror reflection of light on the back of the cell and increase the short-circuit current.

[0004] While silicon wafer back-side polishing technology can enhance the photoelectric performance of solar cells, the contact area between the back grid lines and the silicon substrate is sharply reduced after polishing, making the grid lines prone to detachment after long-term operation.

[0005] In response to the above situation, there is an urgent need to provide a fabrication process for monocrystalline heterojunction solar cells that uses silicon wafer back-side polishing technology to prevent the grid lines from detaching. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects in the prior art and provide a fabrication process for a single-crystal heterojunction solar cell with grid lines that are not easily detached.

[0007] To achieve the above-mentioned technical effects, the technical solution of the present invention is as follows: a fabrication process for a single-crystal heterojunction solar cell, comprising the following steps: S10: A first film-forming liquid is applied to the gate line pre-coverage area of ​​a double-sided textured n-type monocrystalline silicon wafer. After the first film-forming liquid is cured, a silicon wafer with a first mask on the back side is obtained. S20: Polish and clean the back side of the silicon wafer sequentially; S30: Use an aqueous cleaning solution to remove the first mask and clean and dry the silicon wafer; S40: Amorphous silicon film and TCO film are deposited sequentially on both sides of the silicon wafer, and gate lines are screen printed on the surface of the silicon wafer; The first film-forming liquid comprises a UV-curable resin and inorganic microparticles loaded with a strong alkali.

[0008] In a preferred embodiment, the inorganic microparticles are magnesium oxide microparticles, and the strong base supported on the inorganic microparticles is at least one of sodium hydroxide and potassium hydroxide.

[0009] A preferred embodiment is that the coating amount of the first film-forming solution is 0.3~0.4 mg / mm. 2The strong alkali is sodium hydroxide, and the inorganic particles in the first film-forming solution have a mass percentage of 2% to 6%, wherein the Na content of the inorganic particles is... + The load is 1% to 3%.

[0010] Furthermore, the coating amount of the first film-forming solution is 0.3, 0.33, 0.36, 0.39, or 0.4 mg / mm². 2 The point values ​​and the range of the two point values ​​mentioned above as the maximum and minimum values, the mass percentage of the inorganic particles in the first film-forming solution is 2%, 3%, 4%, 5%, 6%, point values ​​and the range of the two point values ​​mentioned above as the maximum and minimum values, the Na of the inorganic particles + The load values ​​are 1%, 1.5%, 2%, 2.5%, and 3%, and the two values ​​mentioned above are used as the range of maximum and minimum values.

[0011] A preferred embodiment includes S11 between S10 and S20: S11: A second film-forming liquid is coated on the back side of the silicon wafer, and after the second film-forming liquid is cured, a second mask covering the first mask is obtained; S30 further includes removing the second mask using an aqueous cleaning solution; the second film-forming solution is a UV-curable resin solution.

[0012] A preferred embodiment is that the n-type monocrystalline silicon wafer in S10 has a pyramid-shaped textured surface, the average height of which is 1.7~2.3μm, the average width of which is 1.9~2.5μm, and the density of which is 150,000~175,000 / mm². 2 The average particle size of the inorganic microparticles is 1~1.8μm.

[0013] Furthermore, the average height of the pyramid-shaped velvet surface is defined as point values ​​of 1.7, 1.9, 2.1, and 2.3 μm, plus a range of values ​​between these two points as the maximum and minimum. The average width of the pyramid structure is defined as point values ​​of 1.9, 2.1, 2.3, and 2.5 μm, plus a range of values ​​between these two points as the maximum and minimum. The density of the pyramid-shaped structure is defined as 150,000, 155,000, 160,000, 165,000, 170,000, and 175,000 pieces / mm. 2 The point values ​​and the interval values ​​of the two point values ​​mentioned above as the maximum and minimum values, wherein the average particle size of the inorganic particles is 1, 1.3, 1.5, 1.6, 1.8 μm.

[0014] A preferred embodiment is that the UV-curable resin comprises a difunctional polyester acrylate.

[0015] A preferred embodiment is that the aqueous cleaning solution comprises an inorganic alkali, wherein the inorganic alkali is at least one of sodium hydroxide and potassium hydroxide, the mass percentage of the inorganic alkali in the aqueous cleaning solution is 2% to 5%, and the cleaning temperature using the aqueous cleaning solution is 28 to 35°C.

[0016] Furthermore, the inorganic alkali in the aqueous cleaning solution is 2%, 3%, 4%, and 5% by mass, and the above two points are used as the range of maximum and minimum values. The cleaning temperature of the aqueous cleaning solution is 28, 29, 30, 33, and 35°C, and the above two points are used as the range of maximum and minimum values.

[0017] A preferred embodiment is that step S30 includes the following steps: S301: Immerse the silicon wafer in an aqueous cleaning solution for 50-60 seconds; S302: Remove the silicon wafer from the aqueous cleaning solution, heat it to 55~60℃, and hold it at that temperature for 15~60 seconds; S303: Immerse the silicon wafer in an aqueous cleaning solution for 70-80 seconds.

[0018] Furthermore, in S302, the silicon wafer is heated to 55, 57, 59, and 60°C, and the above two points are used as the range of maximum and minimum values. The holding time is 15, 20, 25, 30, 35, 40, 45, 50, 55, and 60 seconds, and the above two points are used as the range of maximum and minimum values.

[0019] A preferred embodiment is that step S301 includes ultrasonic treatment of the aqueous cleaning solution and the silicon wafer for 5-20 seconds, with an ultrasonic frequency of 80kHz or higher.

[0020] Furthermore, the ultrasonic treatment time for the aqueous cleaning solution and the silicon wafer is 5, 10, 15, and 20 seconds, and the above two points are used as the range of maximum and minimum values. The ultrasonic frequency is 80 k, 100 k, 120 k, and 140 kHz, and the above two points are used as the range of maximum and minimum values.

[0021] A preferred embodiment is that the polishing solution used for polishing the back side of the silicon wafer includes 19% to 25% hydrofluoric acid and 5% to 9% hydrochloric acid by mass percentage.

[0022] Furthermore, the mass percentage of hydrofluoric acid in the polishing solution is 19%, 21%, 23%, and 25%, with the above two points serving as the range of maximum and minimum values; the mass percentage of hydrochloric acid in the mixed solution is 5%, 6%, 7%, 8%, and 9%, with the above two points serving as the range of maximum and minimum values.

[0023] The advantages and beneficial effects of this invention are as follows: The fabrication process of the monocrystalline heterojunction solar cell of this invention is reasonable. By introducing inorganic microparticles loaded with strong alkali into the first film-forming solution, strong alkali is precipitated from the inorganic microparticles loaded with strong alkali during the removal of the first mask with a low-concentration strong alkali solution. Part of the pre-covered area of ​​the silicon wafer grid lines reacts with the high-concentration strong alkali solution, which is beneficial to improving the bonding force between the grid lines on the back of the solar cell and the solar cell, the fill factor of the solar cell, and the photoelectric conversion efficiency. Detailed Implementation

[0024] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0025] raw material: Magnesium oxide particles: average particle size 1 μm; Bifunctional polyester acrylate: T-7111N, Shenzhen Youyang Technology Co., Ltd.; 1. Examples and Comparative Examples The double-textured n-type monocrystalline silicon wafers of the examples and comparative examples (S10) all met the following criteria (selected using a focusing microscope): The height of the pyramid-shaped velvet surface is 1.9~2.1μm, the width of the pyramid structure is 2.2~2.4μm, and the density of the pyramid structure is 160,000~170,000 / mm. 2 .

[0026] Example 1

[0027] Preparation of inorganic microparticles loaded with strong bases: 50g of magnesium oxide microparticles were immersed in 1L of saturated sodium hydroxide solution at 24℃ for 5min, followed by solid-liquid separation. The solid was dried and calcined at 450℃ for 3h to obtain inorganic microparticles loaded with a strong base. The Na content of the inorganic microparticles was measured by electrode method. + The load is 2.1%.

[0028] The fabrication process of the single-crystal heterojunction solar cell in Example 1 is as follows: S10: The first film-forming liquid is printed on the gate line pre-coverage area of ​​the double-sided textured n-type monocrystalline silicon wafer using screen printing, with a printing area of ​​880 mm². 2 The printing volume of the first film-forming solution was 308 mg; The first film-forming solution consists of the following components by mass percentage: 3% inorganic microparticles loaded with a strong base, 70% difunctional polyester acrylate (T-7111N), and 27% propylene glycol methyl ether acetate. S11: Dry and UV-cur the first film-forming liquid to obtain a silicon wafer with the first mask on the back; S20: The back side of the silicon wafer is polished and cleaned sequentially, with acidic polishing solution used for polishing. The acidic polishing solution consists of the following components by mass percentage: 22% hydrofluoric acid, 7% hydrochloric acid, 0.1% sodium dodecylbenzenesulfonate, and 70.9% water. S30: Soak the silicon wafer in an aqueous cleaning solution to remove the first mask, and then clean and dry the silicon wafer; The aqueous cleaning solution is a 3% (mass percentage) sodium hydroxide solution. The cleaning temperature of the aqueous cleaning solution is 30℃, and the silicon wafer is treated with the cleaning solution for 130 seconds. S40: Amorphous silicon films and TCO films are deposited sequentially on both sides of the silicon wafer. Gate lines are then screen-printed on the silicon wafer surface, with a screen-printing area of ​​800 mm². 2 .

[0029] Example 2

[0030] The fabrication process of the single-crystal heterojunction solar cell in Example 2 is based on that in Example 1, except for steps S11 and S30: S11: Dry and UV-cur the first film-forming liquid to obtain a silicon wafer with the first mask on the back. Print the second film-forming liquid on the back of the silicon wafer (printing area is 900 mm²). 2 The second mask, formed after the second film-forming solution dries, covers the first mask; The second film-forming solution consists of the following components by mass percentage: 70% difunctional polyester acrylate (T-7111N) and 30% propylene glycol methyl ether acetate. S30: Soak the silicon wafer in an aqueous cleaning solution to remove the second and first masks, then clean and dry the silicon wafer; The aqueous cleaning solution is a 3% (by mass) sodium hydroxide solution. The cleaning temperature of the cleaning solution is 30°C, and the silicon wafer is treated with the cleaning solution for 160 seconds. Example 3

[0031] The fabrication process of the single-crystal heterojunction solar cell in Example 3 is based on Example 2, except that S30 includes the following steps: S301: Immerse the silicon wafer in a cleaning tank containing an aqueous cleaning solution for 55 seconds; S302: Remove the silicon wafer from the cleaning tank and place it in a constant temperature heating bath at 57°C. After the surface temperature of the silicon wafer reaches 57°C, keep it at that temperature for 8 seconds. S303: Immerse the silicon wafer in a cleaning tank containing an aqueous cleaning solution for 75 seconds (it was observed that the mask completely disappeared around the 60th second of immersion in the cleaning tank).

[0032] S304: The silicon wafer is introduced into a pure water cleaning tank and then dried.

[0033] Example 4

[0034] The fabrication process of the monocrystalline heterojunction solar cell in Example 4 is based on Example 3, except that in S301, the aqueous cleaning solution and the silicon wafer are ultrasonically treated for the first 10 seconds of immersion in the silicon wafer, and the ultrasonic frequency is 80kHz.

[0035] Example 5

[0036] The fabrication process of the monocrystalline heterojunction solar cell in Example 5 is based on Example 4, except that in S302: the silicon wafer is taken out from the cleaning tank and placed in a constant temperature heating bath at 57°C. After the surface temperature of the silicon wafer reaches 57°C, it is kept at that temperature for 70 seconds.

[0037] Example 6

[0038] The fabrication process of the monocrystalline heterojunction solar cell in Example 6 is based on Example 5, except that in S302: the silicon wafer is taken out of the cleaning tank and placed in a constant temperature heating bath at 57°C. After the surface temperature of the silicon wafer reaches 57°C, it is kept at that temperature for 20 seconds.

[0039] Comparative Example 1 The fabrication process of the comparative monocrystalline heterojunction solar cell is based on Example 1, except that the composition of the first film-forming solution is: 3% magnesium oxide particles, 70% bifunctional polyester acrylate (T-7111N), and 27% propylene glycol methyl ether acetate.

[0040] Comparative Example 2 The fabrication process of the single-crystal heterojunction solar cell in Comparative Example 2 is as follows: S1: The back side of the double-sided textured n-type monocrystalline silicon wafer is polished, cleaned, and dried sequentially; S2: Amorphous silicon film and TCO film are deposited sequentially on both sides of the silicon wafer, and gate lines are screen printed on the surface of the silicon wafer.

[0041] 2. The testing process for the performance of the monocrystalline heterojunction solar cells in the examples and comparative examples is as follows: 2.1. The photoelectric performance of the solar cells was tested using a PL / EL / IV tester to obtain data such as Eta, Voc, Isc, and FF. 2.2. Tensile testing was used to test the bonding strength between the cell grid lines and the silicon substrate. The peel force of each of the four grid lines was measured, and then the average value and standard deviation were calculated. Bond strength (N / mm) = Average peel force F (N) / Grid line width (mm).

[0042] The specific testing process is as follows: S1: First, cut the sample pieces, each containing 4 complete grid lines. Then, apply high-temperature resistant tape to the grid lines to be tested, ensuring full contact. S2: First, firmly attach the sample to the vacuum suction cup. After zeroing the machine, ensure that the tape is just taut and the tension display is zero. Set the machine parameters: peeling angle: 90° (absolute standard), peeling speed: 10-25 mm / min. S3: Start the tensile testing machine; the equipment will automatically record the force-displacement curve. S4: Observe and record the force-displacement curve. The average value of the curve is the peeling force.

[0043] 3. Performance test results of monocrystalline heterojunction solar cells in the examples and comparative examples

[0044] 4. Performance Analysis of Monocrystalline Heterojunction Cells in Examples and Comparative Cases Examples 1 and Comparative Examples 1 and 2 demonstrate that preserving the textured surface of the pre-printed grid line area on the back of the solar cell using a mask helps improve the cell's fill factor, short-circuit current, and open-circuit voltage, thereby increasing photoelectric conversion efficiency. It also helps improve the bonding strength between the grid lines and the silicon substrate. Furthermore, during the removal of the first mask using a low-concentration strong alkaline solution, strong alkali precipitates from the inorganic particles loaded with strong alkali. A portion of the pre-covered area of ​​the silicon wafer's grid lines reacts with the higher-concentration strong alkaline solution, which is beneficial for improving the bonding strength between the grid lines and the solar cell on the back, as well as the cell's fill factor and photoelectric conversion efficiency.

[0045] Examples 1 and 2 show that using a second mask helps to improve the bonding strength between the gate line and the silicon substrate.

[0046] Examples 2 and 3 show that heating the mask after it has been soaked in an aqueous cleaning solution helps to improve the bonding strength between the gate line and the silicon substrate.

[0047] Examples 3 and 4 show that when silicon wafers are soaked in an aqueous cleaning solution, ultrasonic treatment of the aqueous cleaning solution and silicon wafers helps to improve the bonding strength between the grid lines and the silicon substrate of the final prepared solar cell.

[0048] Examples 4, 5, and 6 show that when the heating time of the mask immersed in the aqueous cleaning solution is within a suitable range, the bonding strength between the gate line and the silicon substrate is higher.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fabrication process for a single-crystal heterojunction solar cell, characterized in that, Includes the following steps: S10: A first film-forming liquid is applied to the gate line pre-coverage area of ​​a double-sided textured n-type monocrystalline silicon wafer. After the first film-forming liquid is cured, a silicon wafer with a first mask on the back side is obtained. S20: Polish and clean the back side of the silicon wafer sequentially; S30: Use an aqueous cleaning solution to remove the first mask and clean and dry the silicon wafer; S40: Amorphous silicon film and TCO film are deposited sequentially on both sides of the silicon wafer, and gate lines are screen printed on the surface of the silicon wafer; The first film-forming liquid comprises a UV-curable resin and inorganic microparticles loaded with a strong alkali.

2. The fabrication process of the single-crystal heterojunction solar cell according to claim 1, characterized in that, The inorganic microparticles are magnesium oxide microparticles, and the strong base supported on the inorganic microparticles is at least one of sodium hydroxide and potassium hydroxide.

3. The fabrication process of the single-crystal heterojunction solar cell according to claim 2, characterized in that, The coating amount of the first film-forming solution is 0.3~0.4 mg / mm. 2 The strong alkali is sodium hydroxide, and the inorganic particles in the first film-forming solution have a mass percentage of 2% to 6%, wherein the Na content of the inorganic particles is... + The load is 1% to 3%.

4. The fabrication process of the single-crystal heterojunction solar cell according to claim 1, characterized in that, S11 is also included between S10 and S20: S11: A second film-forming liquid is coated on the back side of the silicon wafer, and after the second film-forming liquid is cured, a second mask covering the first mask is obtained; S30 further includes removing the second mask using an aqueous cleaning solution; the second film-forming solution is a UV-curable resin solution.

5. The fabrication process of the single-crystal heterojunction solar cell according to claim 1, characterized in that, The n-type single-crystal silicon wafer in S10 has a pyramid-shaped textured surface, the average height of which is 1.7~2.3μm, the average width of which is 1.9~2.5μm, and the density of which is 150,000~175,000 / mm². 2 The average particle size of the inorganic microparticles is 1~1.8μm.

6. The fabrication process of the single-crystal heterojunction solar cell according to claim 1, characterized in that, The UV-curable resin comprises a bifunctional polyester acrylate.

7. The fabrication process of the single-crystal heterojunction solar cell according to claim 1, characterized in that, The aqueous cleaning solution comprises an inorganic alkali, which is at least one of sodium hydroxide and potassium hydroxide. The inorganic alkali in the aqueous cleaning solution has a mass percentage of 2% to 5%, and the cleaning temperature using the aqueous cleaning solution is 28 to 35°C.

8. The fabrication process of the single-crystal heterojunction solar cell according to claim 7, characterized in that, S30 includes the following steps: S301: Immerse the silicon wafer in an aqueous cleaning solution for 50-60 seconds; S302: Remove the silicon wafer from the aqueous cleaning solution, heat it to 55~60℃, and hold it at that temperature for 15~60 seconds; S303: Immerse the silicon wafer in an aqueous cleaning solution for 70-80 seconds.

9. The fabrication process of the single-crystal heterojunction solar cell according to claim 8, characterized in that, S301 includes ultrasonic treatment of the aqueous cleaning solution and the silicon wafer for 5-20 seconds, with an ultrasonic frequency of 80kHz or higher.

10. The fabrication process of the single-crystal heterojunction solar cell according to claim 1, characterized in that, The polishing solution used for back-side polishing of silicon wafers includes 19% to 25% hydrofluoric acid and 5% to 9% hydrochloric acid by weight percentage.

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