A method for selective electrodeposition of grid lines in TOPCon solar cells

Abstract

This invention discloses a selective electrodeposition method for fabricating grid lines in TOPCon solar cells, belonging to the field of solar cell manufacturing technology. This method significantly shortens the process route and improves interfacial contact performance, thereby enhancing the photoelectric conversion efficiency of TOPCon solar cells. The invention first pre-treats the semi-finished TOPCon solar cell—blue film—then chemically deposits a Ni-B alloy on the front side or deposits Ag (containing P) on the back side. Then, using high-energy laser light, boron or phosphorus is diffused to form locally heavily doped regions, simultaneously forming nickel silicide and a silver transition layer on the back side, improving interfacial contact performance and thus enhancing the photoelectric conversion efficiency of the device.

Description

Technical Field

[0001] This invention belongs to the field of solar cell manufacturing technology, specifically relating to a method for selectively electrodepositing grid lines in TOPCon cells. Background Technology

[0002] TOPCon cells are one of the new mainstream monocrystalline silicon cells following PERC cells. However, the process route for high-efficiency TOPCon cells is relatively long and the cost remains high; among the reasons, due to factors such as the high price of silver, the cost of traditional screen-printed grid lines accounts for more than 20%, making electrodeposited grid lines the preferred choice for next-generation solar cells.

[0003] Current research on electrodeposition grid manufacturing technology mainly focuses on the following difficulties: (1) The process route for double-sided electrodeposition grids is too long, especially the use of masks during electroplating, which increases manufacturing costs. How to shorten the process route and achieve maskless electrodeposition of grids has become a key technology for reducing costs; (2) Improving the contact performance of the electrode area, reducing the contact resistance of the metal / silicon interface, and improving the grid bonding force. The bottleneck in the efficiency improvement process of TOPCon cells mainly comes from the contact recombination loss between the front-end metal electrode and the boron emitter. Improving the contact performance by increasing the carrier concentration in the local area through laser doping is a solution to this problem. Laser doping forms a heavily doped region at the contact between the metal electrode and the emitter, while other areas outside the electrode are lightly doped regions. Its advantages such as fast processing speed and high diffusion efficiency make it the dominant technology in the boron diffusion process of solar cell manufacturing.

[0004] In the current context of using electroplating technology instead of screen printing in crystalline silicon solar cells, the nickel layer acts as a diffusion barrier for the copper / silver layer. The nickel silicide formed after sintering and diffusion not only helps reduce the contact resistance at the interface but also improves the adhesion of the metal grid lines to the silicon surface. Therefore, using appropriate heat treatment methods to form high-quality nickel silicide is of great significance for improving the efficiency of crystalline silicon solar cell devices such as TOPCon.

[0005] Currently, there are two main routes for grid line electrodeposition technology in solar cells: (1) Mask method for grid line preparation: A mask is coated on a blue film, and after photolithography to create grooves, transition layers such as Ni are deposited on the front and back sides respectively, followed by the deposition of silver and copper grid lines, and finally the mask is removed. (2) Selective grid line electrodeposition technology: After laser grooving, nickel layers are plated on both sides, and silver and copper grid lines are electroplated on both sides. The former uses a mask and has a longer route, which increases the production cost; although the latter shortens the route, after double-sided nickel plating, the nickel on the back side cannot match the n-Si energy level, which reduces the open-circuit voltage and photoelectric conversion efficiency. Summary of the Invention

[0006] This invention provides a method for selectively electrodepositing grid lines in TOPCon solar cells. The method significantly shortens the process route and utilizes the high energy of a laser to diffuse B and P to form localized heavily doped regions, while simultaneously forming a transition layer, improving interfacial contact performance and thus enhancing the photoelectric conversion efficiency of TOPCon solar cells.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for selectively electrodepositing grid lines in a TOPCon solar cell includes the following steps:

[0009] S1: Pre-cleaning of battery cells: Clean in acetone and ethanol for 10-15 minutes respectively, then rinse with deionized water for at least 15 seconds; dry and set aside.

[0010] S2: Chemically deposited Ni-B alloy (front of battery) or P-containing Ag layer (back of battery):

[0011] S3: Place the obtained chemically deposited solar cell on a clean non-woven cloth, wipe off the chemically deposited layer on the other side, then rinse with deionized water for 30 seconds, and place at 60°C. o Dry in a drying oven at C for 15 minutes;

[0012] S4: Laser doping of the obtained solar cell: laser doping of the chemical deposition layer, laser grooving on the other side, controlling the laser parameters, and using the laser to dop the laser in a preset area on the surface of the silicon substrate, the preset area being the electrode deposition area;

[0013] S5: Remove excess coating from the laser-doped solar cell, then sonicate it in acetone and ethanol for 10-15 minutes respectively, and rinse it with deionized water for at least 15 seconds.

[0014] S6: Remove the surface oxide layer of the cleaned solar cells with HF; electrodeposit copper and silver layers on both sides of the resulting solar cells respectively, then 200-400 o After heat treatment at C for 20-40 minutes, a laser-doped Ni-B alloy TOPCon selective emitter is obtained.

[0015] In the steps described above, the chemical deposition process is as follows: first, soak in the sensitization solution for 1 minute, then rinse with deionized water for 15 seconds; then soak in the activation solution for 30 seconds, then rinse with deionized water for 15 seconds; and then perform chemical deposition.

[0016] The sensitizing solution is an acidic solution of stannous chloride (40 g / L stannous chloride + 40 mL / L hydrochloric acid), and should be prepared fresh for use in principle;

[0017] The activation solution is a 0.1 g / L palladium chloride solution;

[0018] The plating bath for chemical deposition of Ni-B alloys is as follows: sodium borohydride is used as the reducing agent, nickel chloride hexahydrate is used as the main salt, and ethylenediamine is used as the complexing agent. The concentrations are: sodium borohydride 1-5 g / L, nickel chloride hexahydrate 30-40 g / L, ethylenediamine 15-20 mL / L. The pH is adjusted to above 12 with sodium hydroxide, and the temperature is 50-70 °C. o C, chemical deposition time is 3-5 min;

[0019] The chemical deposition solution for phosphorus-containing Ag layers is prepared as follows: a silver ammonia solution consisting of 20-30 g / L silver nitrate and 100-150 mL / L dilute ammonia water; a reducing agent consisting of a mixture of 20 g / L glucose and 10 g / L sodium hypophosphite; the solution should be prepared fresh and used immediately; and the deposition temperature is 60-70 °C. o C, deposition time is 5-10 min;

[0020] S3 removes the chemically deposited layer on the other side by wiping away the Ni-B alloy with 10 vol% dilute hydrochloric acid, or by wiping away the P-containing Ag layer with a mixed solution of 15 vol% dilute nitric acid and 5 vol% hydrogen peroxide;

[0021] The laser parameters are as follows: the scanning speed is controlled at 150-250 mm / s, the laser power is 28-36 W, the laser etching depth is above 0.9 µm, the laser wavelength is 350-1050 nm, and the laser is a CW laser or a QCW laser.

[0022] Beneficial Effects: This invention provides a method for selectively electrodepositing grid lines in TOPCon solar cells. By pre-depositing Ni-B alloy or Ag (containing P), localized heavy doping of boron or phosphorus is achieved during laser doping. Simultaneously, the high energy of the laser during laser doping heats the Ni-B alloy and the P-containing Ag layer, improving the contact between the electrode and emitter, thus enhancing the device's photoelectric conversion efficiency. Furthermore, this invention shortens the process route and reduces industrial production costs compared to traditional electroplating and grooving processes, providing a promising approach for the future development of selective electrodeposition technology for TOPCon solar cell grid lines. Attached Figure Description

[0023] Figure 1 These are planar (a) and cross-sectional (b) SEM images of the chemically deposited Ni-B alloy in this embodiment of the invention;

[0024] Figure 2 This is a flowchart of the selective electrodeposition grid line fabrication method for TOPCon cells in this invention embodiment;

[0025] Figure 3These are the single-pulse energy curves corresponding to different powers when the laser wavelength is 532nm in this embodiment of the invention;

[0026] Figure 4 These are optical microscope images of the TOPCon blue film surface after laser treatment and removal of excess coating at a laser wavelength of 532nm, a scanning speed of 200mm / s, and a laser power of 28-36W in an embodiment of the present invention, wherein (a) is 28W, (b) is 30W, (c) is 32W, (d) is 34W, and (e) is 34W.

[0027] Figure 5 The XRD test results of TOPCon cells before and after laser doping of Ni-B alloy in this embodiment of the invention are shown below.

[0028] Figure 6 The figures show the Schott-Mottky test results of the Ni-B alloy before (a) and after (b) laser doping in this embodiment of the invention, and the carrier concentration statistics histogram calculated from the Schott-Mottky curve (c).

[0029] Figure 7 This is the EDS result of a chemically deposited P-containing Ag layer in an embodiment of the present invention. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments: Example 1

[0031] like Figure 2 As shown, a method for selectively electrodepositing grid lines in a TOPCon solar cell includes the following steps:

[0032] S1: Pre-cleaning of the battery cells: sonicate in acetone and ethanol for 10 minutes respectively, then rinse with deionized water for at least 15 seconds and dry with a hair dryer.

[0033] S2: The pre-cleaned battery cell is immersed in an acidic solution of stannous chloride (40 g / L stannous chloride + 40 mL / L hydrochloric acid) for 1 min, and then rinsed with deionized water for 15 s; then immersed in an activation solution of 0.1 g / L palladium chloride for 30 s, and rinsed with deionized water for 15 s, and then chemically deposited at 60℃ for 5 min. The plating solution is: sodium borohydride as the reducing agent, nickel chloride hexahydrate as the main salt, and ethylenediamine as the complexing agent, wherein sodium borohydride is 1 g / L, nickel chloride hexahydrate is 30 g / L, and ethylenediamine is 15 mL / L. The pH is adjusted to above 12 with sodium hydroxide. After deposition for 3 min, the cell is rinsed with deionized water and dried to obtain the battery cell after chemical deposition of Ni-B alloy.

[0034] S3: Place the obtained chemically deposited Ni-B alloy cell face down on a clean non-woven cloth, drop a small amount of dilute hydrochloric acid on the back, wipe off the Ni-B alloy on the back, then rinse with deionized water for 30 seconds, and place at 60°C. o Dry in a drying oven at C for 15 minutes;

[0035] S4: Laser doping of the chemically deposited solar cell: Control the laser parameters and use a laser to dope the surface of the silicon substrate. The laser parameters are: control the scanning speed to be 200 mm / s, the laser power to be 28-36 W, so that the laser etching depth is above 0.9 µm, the laser wavelength is 350-1050 nm, and the laser is a CW laser or a QCW laser. Figure 3 Table 1 and Table 2 respectively show the single-pulse energy curves of a 532nm laser at various powers and the specific energy values ​​corresponding to 28-36W in this embodiment.

[0036] Table 1. Single pulse energy of 532nm laser at various powers

[0037] Power / W 28 30 32 34 36 Pulse energy / µj 1.74 2.22 2.87 4.35 5.85

[0038] Figure 4 These are optical microscope images of the TOPCon blue film surface after removing excess coating when the laser power is 28-36W. Because a Ni-B alloy is pre-deposited on the battery surface, while laser doping allows B atoms to diffuse into the Si substrate, it is necessary to etch away the SiN in the predetermined area (electrode region). x A passivation layer is applied to expose the conductive portions, ensuring successful subsequent electrodeposition. For example... Figure 4 As shown in (a), at 28W, most of the laser energy is absorbed by the coating, and the underlying SiN... x The layer cannot be completely removed, and the laser spot trajectory shows several separate circles. As the laser power increases to 30W and 32W, the laser trajectory becomes continuous at 32W, and the linewidth is uniform, resulting in a better ablation effect. When the power continues to increase to 34W and 36W, the linewidth continues to increase, which will increase the shadowing of the electrode and adversely affect the performance. Therefore, the optimal laser doping power is 32W.

[0039] S5: Remove excess coating from the laser-doped solar cell in S4 using dilute nitric acid via ultrasonication, and rinse with deionized water for at least 15 seconds. Comparative Example 1

[0040] Pre-cleaning of the battery cells: sonicate in acetone and ethanol for 10 minutes respectively, then rinse with deionized water for at least 15 seconds, and dry the pre-cleaned battery cells with a hair dryer.

[0041] Laser grooving of the battery involves using a laser to laser-dope a predetermined area on the surface of the silicon substrate, which is the electrode deposition area. Since the battery surface has a silicon nitride and aluminum oxide passivation layer, specific laser parameters are controlled to perform laser grooving to remove the passivation layer, thus ensuring the smooth progress of subsequent electrodeposition. The laser parameters are: a scanning speed of 200 mm / s, a laser power of 32 W to achieve an etching depth greater than 0.9 µm, a laser wavelength of 350-1050 nm, and a CW or QCW laser.

[0042] Performance testing

[0043] The Ni-B alloy solar cell with frontal chemical deposition obtained in S2 of Example 1 was subjected to SEM testing. Figure 1 The images show the SEM planar (a) and cross-sectional (b) topographic images of the chemically deposited Ni-B alloy on the front side of the battery cell. The chemically deposited Ni-B alloy consists of spherical particles with a size of less than 500 nm. The particles are evenly distributed on the top and bottom of the pyramid texture on the front side of the battery. The cross-section shows that the Ni-B alloy is tightly covered and adhered to the pyramid, exhibiting good shape retention, which ensures the uniformity of energy distribution in subsequent laser processing.

[0044] The battery cells obtained in Example 1 and Comparative Example 1 were subjected to XRD tests, such as... Figure 5 As shown in the figure, the "doped sample" represents the XRD test results of the laser-doped battery in Example 1, corresponding to the standard PDF card for NiSi2. This indicates that after laser doping, the nickel annealing diffusion mainly forms NiSi2 between the nickel and the silicon substrate. The presence of NiSi2 can improve contact performance, thereby increasing photoelectric conversion efficiency. Furthermore, since the laser processing is not performed in a vacuum environment, silicon oxide is generated on the surface. Before subsequent electrodeposition, the oxide layer needs to be removed with HF to ensure successful electrodeposition.

[0045] The battery cells obtained in Example 1 and Comparative Example 1 were connected to copper wires using conductive silver paste, and a Schott-Mottky test was performed to calculate the carrier concentration of the battery after laser doping. Figure 6 As shown, due to the effective diffusion of boron atoms into the silicon substrate after laser doping, the carrier concentration of the battery increases from the original undoped 6.04*10⁻⁶. 20 cm -3 It has been improved to 9.71*10 20 cm -3 The increase in carrier concentration can not only enhance the conductivity of local areas, but also improve interfacial contact, reduce interfacial carrier recombination, and thus improve conversion efficiency.

[0046] Copper and silver layers were electrodeposited on the front and back sides of the solar cells obtained in Example 1 and Comparative Document 1, respectively, and then heat-treated at 200-400℃ for 20 min to obtain laser-doped and undoped Ni-B alloy TOPCon cells, respectively; in a standard solar cell (25 o C, AM 1.5G, 100mW·cm 2 The photoelectric performance of the obtained batteries was tested. Table 2 shows the open-circuit voltage V of the TOPCon batteries before and after laser doping. oc Short-circuit current J sc Fill factor FF, photoelectric conversion efficiency E ta The changes verified that the effective diffusion of boron atoms after laser doping increased the carrier concentration, improved the contact quality, reduced interfacial carrier recombination, and thus improved the battery conversion efficiency.

[0047] Table 2. Performance comparison of TOPCon batteries without laser doping and with laser doping.

[0048] Battery type / performance parameters <![CDATA[V oc (V)]]> <![CDATA[J sc (mA / cm 2 )]]> FF(%) <![CDATA[E ta (%)]]> Undoped by laser 0.5687 51.59 61.68 18.02 Laser doping 0.5774 54.62 59.49 18.72 Example 2

[0049] like Figure 2 As shown, a method for selectively electrodepositing grid lines in a TOPCon solar cell includes the following steps:

[0050] S1: Pre-cleaning of the battery cells: sonicate in acetone and ethanol for 10 minutes respectively, then rinse with deionized water for at least 15 seconds and dry with a hair dryer.

[0051] S2: Immerse the pre-cleaned battery cells in an acidic solution of stannous chloride (40 g / L stannous chloride + 40 mL / L hydrochloric acid) for 1 min, then rinse with deionized water for 15 s; next, immerse them in an activation solution of 0.1 g / L palladium chloride for 30 s, rinse with deionized water for 15 s, and then perform chemical deposition at 60°C for 5 min. The plating solution is a mixed solution of 20 g / L silver nitrate, 100 mL / L dilute ammonia, and 20 g / L glucose and 10 g / L sodium hypophosphite as a reducing agent, prepared fresh for immediate use. The deposition temperature is 60°C. o C, the deposition time is 10 min. After deposition, the cells are rinsed with deionized water and dried to obtain the battery cells with chemically deposited Ag layer containing P.

[0052] S3: Place the obtained chemically deposited Ag layer (containing P) on a clean non-woven fabric with the back side facing down. Drop a small amount of a mixed solution of dilute nitric acid and dilute hydrogen peroxide onto the front side, wipe off the Ag on the front side, then rinse with deionized water for 30 seconds, and place at 60°C. o Dry in a drying oven at C for 15 minutes;

[0053] S4: Laser doping of the solar cell obtained after chemical deposition: controlling the laser parameters, laser doping is performed on a preset area on the surface of the silicon substrate, the preset area being the electrode deposition area. The laser parameters are: the scanning speed is controlled at 200 mm / s, the laser power is 32 W, so that the laser etching depth is greater than 0.9 µm; the laser wavelength is 350-1050 nm, and the laser is a CW laser or a QCW laser.

[0054] S5: Remove excess coating from the laser-doped solar cell by ultrasonication with a mixed solution of dilute nitric acid and dilute hydrogen peroxide, and ultrasonicate in acetone and ethanol for 10 min respectively. Then rinse with deionized water for at least 15 s. Remove the surface oxide layer from the cleaned solar cell with HF.

[0055] S6: Electrodeposit copper and silver layers simultaneously on the front and back sides of the obtained solar cell, respectively, and then 200-400 o After heat treatment at C for 20 minutes, a TOPCon selective emitter with a P-doped Ag layer is obtained.

[0056] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, all of which fall within the protection scope of the present invention.

Claims

1. A method for selectively electrodepositing grid lines in a TOPCon solar cell, characterized in that, The following steps are involved: The battery cells are pre-cleaned and dried for later use. Ni-B alloy is deposited on the front side of the solar cell or a P-containing Ag layer is deposited on the back side of the solar cell. The deposition process is as follows: first, soak in the sensitization solution for 1 min, then rinse with deionized water for 15 s; then soak in the activation solution for 30 s, then rinse with deionized water for 15 s. Chemical deposition is then performed; the sensitizing solution is an acidic solution of stannous chloride, with 40 g / L stannous chloride dissolved in 40 mL / L hydrochloric acid, and is prepared fresh for each use; the activation solution is a 0.1 g / L palladium chloride solution; The plating bath for depositing the Ni-B alloy layer is as follows: sodium borohydride as the reducing agent, nickel chloride hexahydrate as the main salt, and ethylenediamine as the complexing agent. The concentrations are: sodium borohydride 1-5 g / L, nickel chloride hexahydrate 30-40 g / L, and ethylenediamine 15-20 mL / L. The pH is adjusted to above 12 with sodium hydroxide, and the deposition temperature is 50-70 °C. o C, deposition time is 3-5 min; the plating solution for depositing the P-containing Ag layer is: a silver ammonia solution prepared by mixing 20-30 g / L silver nitrate and 100-150 mL / L dilute ammonia water, and a reducing agent prepared by mixing 20 g / L glucose and 10 g / L sodium hypophosphite. The solution should be prepared fresh and used immediately. The deposition temperature is 60-70 °C. o C, deposition time is 5-10 min; Laser doping is performed on a predetermined area on one side of the solar cell after deposition. The high energy of the laser is used to diffuse B or P to form a local heavily doped region, while forming a transition layer. After removing the excess coating from the laser-doped solar cell, the oxide layer on the surface of the solar cell is removed after cleaning. Electrode layers are deposited on the obtained solar cell, and after heat treatment, laser-doped TOPCon selective emitters are obtained.

2. The method for selectively electrodepositing grid lines in a TOPCon battery according to claim 1, characterized in that, The laser doping parameters are: scanning speed 150-250 mm / s, laser power 28-36 W, and laser wavelength 350-1050 nm.

3. The method for selectively electrodepositing grid lines in a TOPCon battery according to claim 1 or 2, characterized in that, The etching depth in laser doping is above 0.9µm.

4. The method for selectively electrodepositing grid lines in a TOPCon cell according to claim 1, characterized in that, The preset area of ​​the battery cell is the electrode deposition area.

5. The method for selectively electrodepositing grid lines in a TOPCon cell according to claim 1 or 4, characterized in that, Copper and silver layers are electrodeposited on the front and back sides of the battery cell, respectively, in the electrodeposition electrode layer.

Images