Method for improving passivation contact of back surface of TOPCon battery
By adopting laser oxidation and annealing crystallization technology in TOPCon batteries, combining alkali polishing and cleaning treatment, the doping distribution and interface passivation layer of the polycrystalline silicon layer are optimized, and the parasitic absorption problems caused by infiltration of doped polycrystalline silicon are solved, and the battery is improved The conversion efficiency and cleaning difficulty achieve more efficient passivation effect.
Patent Information
- Application Number
- CN202411367380.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-29
- Publication Date
- 2024-12-27
AI Technical Summary
The infiltration of doped polysilicon in TOPCon batteries leads to severe parasitic absorption of light in the long-band, affecting the battery conversion efficiency. The existing methods are difficult to clean after laser oxidation, and it is difficult to effectively reduce the recombination of the gold-semi-contact region.
The tunneling oxide layer and doped amorphous silicon layer are prepared by alkali velvet making treatment, boron diffusion, alkali polishing, PECVD, laser oxidation turns polycrystalline silicon into SiO/SiO2, annealing and crystallization, HF acid removes phosphorus silicon glass, cleaning treatment, ALD prepared an alumina film layer, screen-printed metal electrode, light injection and laser-treated gate lines to optimize the doping distribution and interface passivation layer of the polysilicon layer.
The coverage area and thickness of the polysilicon layer are reduced, parasitic light absorption is reduced, the short-circuit current Isc and back-side efficiency of the battery are improved, the difficulty of cleaning after laser oxidation is reduced, and the overall efficiency and double-sided rate of the battery are improved.
Smart Images
Figure CN119208451A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of solar cells, and in particular to a method for improving the back passivation contact of a TOPCon cell. Background Art
[0002] At present, the mainstream route in the crystalline silicon battery industry is TOPCon. According to industry forecasts, it will remain the main technical route in the industry in the next few years. The core of the TOPCon battery is the passivation contact on its back, and its structure consists of an ultra-thin tunneling oxide layer and a doped polysilicon (Poly-Si) layer. The silicon oxide between the interface of Poly-Si and the substrate Si can significantly reduce the interface state density between the substrate Si and Poly-Si through chemical passivation, reduce the recombination of the gold-semiconductor contact area, and effectively improve the photoelectric conversion efficiency of the battery.
[0003] However, the internal penetration of doping elements in doped polysilicon will lead to more serious parasitic absorption of light in the long wavelength band. This phenomenon is more obvious in high doping concentrations and thicker polysilicon layers, which in turn affects the conversion efficiency of the battery.
[0004] Patent 202410685454.0 discloses a method of adding laser oxidation after annealing to oxidize the poly-Si in the gate line area as a mask to thin the poly-Si in the non-oxidized area. The method adds laser after annealing, and the thickness of the laser oxidation layer and the subsequent cleaning and protection are difficult.
[0005] Therefore, it is necessary to provide a method for improving the back passivation contact of TOPCon cells to solve the above technical problems. Summary of the invention
[0006] The invention provides a method for improving the back passivation contact of a TOPCon battery, which solves the problems in the background technology.
[0007] In order to solve the above technical problems, the method for improving the back passivation contact of TOPCon cells provided by the present invention comprises the following steps:
[0008] S1. Performing alkali texturing treatment on N-type silicon wafer;
[0009] S2, diffusing boron into the silicon wafer to form a boron-doped emitter on the front side;
[0010] S3, removing the borosilicate glass on the back and sides of the silicon wafer, and performing alkali polishing on the back of the silicon wafer;
[0011] S4, using PECVD technology to prepare a tunneling oxide layer and a doped amorphous silicon layer on the back side of the silicon wafer;
[0012] S5, using laser to oxidize the metal electrode area and gate line area on the back of the silicon wafer, so that the polysilicon is converted into SiO / SiO2, which serves as a subsequent mask;
[0013] S6, high temperature annealing and crystallization, activating the doping elements of the doping layer to convert it into doped polysilicon;
[0014] S7, using a chain machine to use HF acid to remove the phosphorus silicon glass on the front and sides; then using a tank machine to use alkaline solution and organic additives to clean the poly layer, and then using hydrogen peroxide and alkali to remove the influence of organic additives, and finally using HF solution to clean the oxide on the front and back of the silicon wafer;
[0015] S8, preparing an aluminum oxide film layer on both sides by using tubular ALD;
[0016] S9, using PECVD method to prepare front and back silicon nitride anti-reflection film layers;
[0017] S10, printing metal paste on the front and back sides of the silicon wafer by screen printing, and preparing metal electrodes after sintering;
[0018] S11, light injection to passivate the hanging bonds on the surface of the battery;
[0019] S12. Use laser to process the grid lines on the front of the battery to make the silver-silicon contact better, thereby reducing the contact resistance.
[0020] Preferably, in S4, the structure of the back side of the silicon wafer is tunneling oxide layer 1 + phosphorus-doped amorphous silicon 1 + tunneling oxide layer 2 + phosphorus-doped amorphous silicon 2.
[0021] Preferably, in S5, the laser light source is green light, the laser power is 60%, the marking speed is 30000 mm / min, the laser frequency is 1000 Hz, and the width of the laser oxidation area is greater than the grid line printing width.
[0022] Preferably, in S7, a chain machine is used to remove silicon oxide on the front and side surfaces of the silicon wafer using HF equipment, wherein the volume ratio of HF to deionized water is 1:3.
[0023] Preferably, to ensure that a portion of the poly layer in the non-laser area can be cleaned off, the reaction time of hydrogen peroxide and weak alkaline solution is 350s, the volume ratio of organic additives to alkali in the initial solution is 1:4.5, and the volume ratio of organic additives to alkali added during the process is 1:1.5.
[0024] Preferably, the cleaning tank temperature of the tank machine in S7 is 75°C.
[0025] Preferably, in order to further remove the laser oxidized area and the oxide layers on the front and back sides, the HF pickling time is 140 seconds, and the volume ratio of HF acid to water in the initial solution is 1:3.9.
[0026] Preferably, the concentration of alkali in the alkali polishing step in S3 is 1wt% to 2wt%, the concentration of alkali polishing additive is 0.5wt% to 1.5wt%, the temperature in the alkali polishing step is 60°C to 70°C, and the polishing time is 130s to 270s.
[0027] Preferably, the annealing in S6 is performed in an oven or a tube furnace, the annealing temperature is between 300-500° C., and the annealing time is 10-30 min.
[0028] Compared with the related art, the method for improving the back passivation contact of TOPCon cells provided by the present invention has the following beneficial effects:
[0029] The present invention provides a method for improving the back passivation contact of a TOPCon cell. The present invention uses laser oxidation to oxidize the poly-Si in the grid line area after poly, then anneals and crystallizes it, and then uses a wet etching method to corrode and remove part of the poly in the non-laser area. Under the premise of satisfying poly passivation, the poly coverage area and thickness are reduced, parasitic light absorption is reduced, and the short-circuit current Isc of the cell is increased, so as to improve the cell efficiency, back efficiency, and bifaciality. At the same time, the cleaning difficulty after laser oxidation can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 A schematic flow chart of a preferred embodiment of the method for improving the back side passivation contact of a TOPCon cell provided by the present invention. DETAILED DESCRIPTION
[0031] The present invention will be further described below in conjunction with the accompanying drawings and implementation modes.
[0032] Please refer to Figure 1 ,in, Figure 1 A flow chart of a preferred embodiment of the method for improving the back passivation contact of a TOPCon cell provided by the present invention. The method for improving the back passivation contact of a TOPCon cell comprises the following steps:
[0033] S1. Performing alkali texturing treatment on N-type silicon wafer;
[0034] S2, diffusing boron into the silicon wafer to form a boron-doped emitter on the front side;
[0035] S3, removing the borosilicate glass on the back and sides of the silicon wafer, and performing alkali polishing on the back of the silicon wafer;
[0036] S4, using PECVD technology to prepare a tunneling oxide layer and a doped amorphous silicon layer on the back side of the silicon wafer;
[0037] S5, using laser to oxidize the metal electrode area and gate line area on the back of the silicon wafer, so that the polysilicon is converted into SiO / SiO2, which serves as a subsequent mask;
[0038] S6, high temperature annealing and crystallization, activating the doping elements of the doping layer to convert it into doped polysilicon;
[0039] S7, using a chain machine to use HF acid to remove the phosphorus silicon glass on the front and sides; then using a tank machine to use alkaline solution and organic additives to clean the poly layer, and then using hydrogen peroxide and alkali to remove the influence of organic additives, and finally using HF solution to clean the oxide on the front and back of the silicon wafer;
[0040] S8, preparing an aluminum oxide film layer on both sides by using tubular ALD;
[0041] S9, using PECVD method to prepare front and back silicon nitride anti-reflection film layers;
[0042] S10, printing metal paste on the front and back sides of the silicon wafer by screen printing, and preparing metal electrodes after sintering;
[0043] S11, light injection to passivate the hanging bonds on the surface of the battery;
[0044] S12. Use laser to process the grid lines on the front of the battery to make the silver-silicon contact better, thereby reducing the contact resistance.
[0045] In the above S4, the back side structure of the silicon wafer is tunneling oxide layer 1+phosphorus-doped amorphous silicon 1+tunneling oxide layer 2+phosphorus-doped amorphous silicon 2.
[0046] Preferably, considering that the tunneling layer 1 and the tunneling layer 2 are deposited on different substrates, the substrate of the tunneling layer 1 is a silicon substrate with a certain texture, and the substrate of the tunneling layer 2 is a phosphorus-doped polysilicon of a certain thickness. The laughing gas flow rate, pressure and power used for the deposition of the two oxide layers are consistent, and the time and radio frequency pulse are different, but the oxide layer thickness is 1.5-2nm;
[0047] Preferably, the phosphorus-doped amorphous silicon 2 is completed in two steps, the doping concentration close to the tunneling layer 2 is relatively low, and the doping concentration of the layer far away is the highest, forming a concentration gradient, which improves the passivation effect while reducing light loss caused by other factors;
[0048] Preferably, the two layers of phosphorus-doped amorphous silicon 1 and phosphorus-doped amorphous silicon 2 are mainly different in doping concentration and thickness, and the main parameter difference is deposition time and phosphine flow rate, and other parameters such as silane flow rate, pressure, power and radio frequency pulse are the same.
[0049] Adopt gradient doping or selective doping techniques to optimize the doping distribution of the polysilicon layer and improve the carrier collection efficiency and battery performance. High concentration doping is performed on the surface of the polysilicon layer to improve the conductivity of the metal contact, while low concentration doping is performed inside to reduce recombination losses.
[0050] In the above S5, the laser light source is green light, the laser power is 60%, the marking speed is 30000 mm / min, the laser frequency is 1000 Hz, and the width of the laser oxidation area is greater than the grid line printing width.
[0051] In S7, a chain machine is used to remove silicon oxide on the front and side surfaces of the silicon wafer using HF equipment, wherein the volume ratio of HF to deionized water is 1:3.
[0052] To ensure that part of the poly layer in the non-laser area can be cleaned off, the reaction time of hydrogen peroxide and weak alkaline solution is 350s, the volume ratio of organic additives to alkali in the initial solution is 1:4.5, and the volume ratio of organic additives to alkali added during the process is 1:1.5.
[0053] The cleaning tank temperature of the tank machine in S7 is 75°C.
[0054] In order to further remove the laser oxidation area and the oxide layer on the front and back sides, the HF pickling time is 140 seconds, and the volume ratio of HF acid to water in the initial solution is 1:3.9.
[0055] In the alkali polishing step in S3, the concentration of alkali is 1wt% to 2wt%, the concentration of alkali polishing additive is 0.5wt% to 1.5wt%, the temperature in the alkali polishing step is 60°C to 70°C, and the polishing time is 130s to 270s.
[0056] The annealing in S6 is carried out in an oven or a tubular furnace, the annealing temperature is between 300-500° C., and the annealing time is 10-30 minutes.
[0057] The thickness and uniformity of the interface passivation layer are precisely controlled to ensure the stability and consistency of its passivation effect, and the annealing process of the interface passivation layer is optimized to improve its passivation effect and stability. The use of appropriate annealing temperature and time can promote hydrogen diffusion and passivation in the interface passivation layer and improve battery performance.
[0058] Through experiments or simulations, determine the best annealing temperature and time. If the annealing temperature is too high or the time is too long, the structure and performance of the passivation layer may change, and even damage the substrate; if the annealing temperature is too low or the time is too short, the passivation layer may not be fully crystallized and solidified, affecting the passivation effect. During the annealing process, keep the annealing atmosphere pure and stable to avoid the introduction of impurities and oxidation.
[0059] Post-processing is also included: the passivation layer after annealing is post-processed, such as cleaning, drying, etc., to remove residual substances and impurities on the surface. The passivation layer can be cleaned with deionized water or an organic solvent, and then blown dry with high-purity nitrogen.
[0060] The working principle of the method for improving the back passivation contact of TOPCon cells provided by the present invention is as follows:
[0061] The N-type silicon wafer is subjected to alkali texturing treatment; then the silicon wafer is subjected to boron diffusion to form a boron-doped emitter on the front side; the borosilicate glass on the back and sides of the silicon wafer is removed, and the back side of the silicon wafer is subjected to alkali polishing; the tunneling oxide layer and the doped amorphous silicon layer are prepared on the back side of the silicon wafer using PECVD technology; the metal electrode area and the gate line area on the back side of the silicon wafer are oxidized using a laser to convert the polysilicon into SiO / SiO2 as a subsequent mask; high-temperature annealing and crystallization are then performed to activate the doping elements of the doped layer to convert it into doped polysilicon; the phosphorus on the front and sides is removed using HF acid using a chain machine Silicon glass; then use a slot machine to use alkaline solution and organic additives to clean the poly layer, then use hydrogen peroxide and alkali to remove the influence of organic additives, and finally use HF solution to clean the oxide on the front and back of the silicon wafer; use tubular ALD to prepare aluminum oxide film on both sides; use PECVD to prepare front and back silicon nitride anti-reflection film layers; use screen printing technology to print metal paste on the front and back of the silicon wafer, and prepare metal electrodes after sintering; then inject light to passivate the hanging bonds on the surface of the battery; use laser to process the grid line on the front of the battery to make the silver-silicon contact better, thereby reducing the contact resistance.
[0062] Compared with the related art, the method for improving the back passivation contact of TOPCon cells provided by the present invention has the following beneficial effects:
[0063] The present invention uses laser oxidation to oxidize the poly-Si in the gate line area after poly, then anneals and crystallizes it, and then uses a wet etching method to corrode and remove part of the poly in the non-laser area. Under the premise of satisfying poly passivation, the poly coverage area and thickness are reduced, parasitic light absorption is reduced, and the battery short-circuit current Isc is increased to improve battery efficiency, back efficiency, and bifaciality. At the same time, it can reduce the difficulty of cleaning after laser oxidation.
[0064] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.
Claims
1. A method for improving the back passivation contact of a TOPCon cell, characterized in that: The following steps are involved: S1. Performing alkali texturing treatment on N-type silicon wafer; S2, diffusing boron into the silicon wafer to form a boron-doped emitter on the front side; S3, removing the borosilicate glass on the back and sides of the silicon wafer, and performing alkali polishing on the back of the silicon wafer; S4, using PECVD technology to prepare a tunneling oxide layer and a doped amorphous silicon layer on the back side of the silicon wafer; S5, using laser to oxidize the metal electrode area and gate line area on the back of the silicon wafer, so that the polysilicon is converted into SiO / SiO2, which serves as a subsequent mask; S6, high temperature annealing and crystallization, activating the doping elements of the doping layer to convert it into doped polysilicon; S7, using a chain machine to remove the phosphosilicate glass on the front and sides using HF acid; Then use a tank machine to clean the poly layer with alkaline solution and organic additives, then use hydrogen peroxide and alkali to remove the influence of organic additives, and finally use HF solution to clean the oxide on the front and back of the silicon wafer; S8, preparing an aluminum oxide film layer on both sides by using tubular ALD; S9, using PECVD method to prepare front and back silicon nitride anti-reflection film layers; S10, printing metal paste on the front and back sides of the silicon wafer by screen printing, and preparing metal electrodes after sintering; S11, light injection to passivate the hanging bonds on the surface of the battery; S12. Use laser to process the grid lines on the front of the battery to make the silver-silicon contact better, thereby reducing the contact resistance.
2. The method for improving the back passivation contact of a TOPCon cell according to claim 1, characterized in that: In the above S4, the back side structure of the silicon wafer is tunneling oxide layer 1+phosphorus-doped amorphous silicon 1+tunneling oxide layer 2+phosphorus-doped amorphous silicon 2.
3. The method for improving the back passivation contact of a TOPCon cell according to claim 2, characterized in that: In the above S5, the laser light source is green light, the laser power is 60%, the marking speed is 30000 mm / min, the laser frequency is 1000 Hz, and the width of the laser oxidation area is greater than the grid line printing width.
4. The method for improving the back passivation contact of a TOPCon cell according to claim 1, characterized in that: In S7, a chain machine is used to remove silicon oxide on the front and side surfaces of the silicon wafer using HF equipment, wherein the volume ratio of HF to deionized water is 1:
3.
5. The method for improving the back passivation contact of a TOPCon cell according to claim 4, characterized in that: To ensure that part of the poly layer in the non-laser area can be cleaned off, the reaction time of hydrogen peroxide and weak alkaline solution is 350s, the volume ratio of organic additives to alkali in the initial solution is 1:4.5, and the volume ratio of organic additives to alkali added during the process is 1:1.
5.
6. The method for improving the back passivation contact of a TOPCon cell according to claim 4, characterized in that: The cleaning tank temperature of the tank machine in S7 is 75°C.
7. The method for improving the back passivation contact of a TOPCon cell according to claim 4, characterized in that: In order to further remove the laser oxidation area and the oxide layer on the front and back sides, the HF pickling time is 140 seconds, and the volume ratio of HF acid to water in the initial solution is 1:3.
9.
8. The method for improving the back passivation contact of a TOPCon cell according to claim 1, characterized in that: In the alkali polishing step in S3, the concentration of alkali is 1wt% to 2wt%, the concentration of alkali polishing additive is 0.5wt% to 1.5wt%, the temperature in the alkali polishing step is 60°C to 70°C, and the polishing time is 130s to 270s.
9. The method for improving the back passivation contact of a TOPCon cell according to claim 1, characterized in that: The annealing in S6 is carried out in an oven or a tubular furnace, the annealing temperature is between 300-500° C., and the annealing time is 10-30 minutes.