Method for selective metallization of photovoltaic cells and inkjet printing device

Abstract

This invention discloses a selective metallization method and inkjet printing apparatus for photovoltaic cells, comprising the following steps: providing a substrate having a TOPCon structure on its back side, the TOPCon structure including a tunneling oxide layer, a doped polycrystalline silicon layer, and a silicon nitride film layer sequentially disposed from a silicon substrate to its surface; printing functional etching ink on a selected area of ​​the silicon nitride film layer; removing the silicon nitride film layer; and selectively retaining or removing the doped polycrystalline silicon layer and the tunneling oxide layer to form an opening area exposing the doped polycrystalline silicon layer or the silicon substrate; printing conductive ink containing base metal particles on the opening area and a preset conductive gate pattern; and sintering the printed substrate to form continuous conductive electrodes from the base metal particles and ohmic contacts with the exposed doped polycrystalline silicon layer or the silicon substrate. This invention uses inkjet printing to achieve metallized openings and base metal deposition, effectively avoiding thermal damage to the underlying material and significantly reducing metallization costs.

Description

Technical Field

[0001] This invention relates to the field of space photovoltaic cell technology, and in particular to a method for selective metallization of photovoltaic cells and an inkjet printing apparatus. Background Technology

[0002] With the development of aerospace technology, TOPCon batteries, leveraging their high efficiency, are gradually expanding into the field of space photovoltaics (spacecraft power sources). However, the high vacuum, ultra-low temperature alternation, and high-energy radiation characteristics of the space environment place far more stringent demands on the stability of the battery structure than on Earth. While the core tunneling oxide layer and doped polycrystalline silicon layer structure of TOPCon batteries exhibit excellent passivation performance, they are extremely sensitive to high-energy particles in space. Radiation easily leads to a surge in interface defects, causing a rapid degradation of passivation performance. Simultaneously, their high temperature coefficient also results in drastic fluctuations in power output under extreme temperature variations.

[0003] To achieve back-side contact, the mainstream process currently uses laser-guided aperture technology. However, this technology has fundamental drawbacks: First, it suffers from severe thermal damage, as the instantaneous high temperature generated by the high-energy laser destroys the lattice of the passivation layer around the aperture, significantly reducing minority carrier lifetime and fill factor; second, it has process limitations, as laser equipment is expensive, aperture precision is difficult to control, and it requires a high-cost screen-printed silver paste process, where the paste sintering process often further exacerbates the damage to the passivation layer.

[0004] Therefore, there is an urgent need to design a low-damage, high-precision selective metallization method to solve the compatibility problem of TOPCon cells in space photovoltaic applications. Summary of the Invention

[0005] To address the shortcomings of existing laser aperture technology, this invention proposes a selective metallization method for photovoltaic cells and an inkjet printing device. The method uses inkjet printing to achieve metallization apertures and base metal deposition, effectively avoiding thermal damage to the underlying material and significantly reducing metallization costs.

[0006] The technical solution adopted in this invention is to design a selective metallization method for photovoltaic cells, comprising the following steps:

[0007] A substrate is provided, the back side of which has a TOPCon structure, the TOPCon structure comprising a tunneling oxide layer, a doped polysilicon layer, and a silicon nitride film layer disposed sequentially from the silicon substrate to the surface.

[0008] Using inkjet printing, functional etching ink is printed on selected areas of the silicon nitride film to remove the silicon nitride film, and selectively retain or remove the doped polysilicon layer and tunnel oxide layer to form an opening area that exposes the doped polysilicon layer or silicon substrate.

[0009] Using inkjet printing, conductive ink containing base metal particles is printed on the opening area and the preset conductive grid pattern.

[0010] The printed substrate is sintered to form continuous conductive electrodes from base metal particles and to form ohmic contacts with the exposed doped polysilicon layer or silicon substrate.

[0011] This design replaces traditional laser-based aperture opening and screen printing processes with inkjet printing technology. Functional etching inks are used to chemically etch the multi-layered structure on the back of the TOPCon, achieving thermally damage-free aperture openings. By avoiding the thermal shock of high-energy lasers to the tunneling oxide layer and polycrystalline silicon passivation layer, the passivation integrity on the back of the battery is effectively protected, thus significantly improving the open-circuit voltage and fill factor. Simultaneously, integrating the aperture openings and metallization into the inkjet printing process greatly simplifies the process steps and improves the flexibility of graphic design.

[0012] Furthermore, the functional etching ink comprises, by weight percentage: 80% to 90% deionized water, 2% to 5% hydrofluoric acid, 8% to 9% ammonium fluoride, 2% to 2.5% glycerol, and 0.8% to 1% hydrogen peroxide.

[0013] This design achieves isotropic and controllable rate etching of silicon nitride and polycrystalline silicon layers by limiting the specific ratio of etching ink and utilizing the buffering synergy of hydrofluoric acid and ammonium fluoride. Glycerin, as a thickener, effectively controls the spreading radius of droplets on the silicon wafer surface, ensuring the accuracy of the aperture size. The addition of hydrogen peroxide helps to remove organic residues and oxidize the surface, improving the flatness of the aperture sidewalls and providing excellent interface conditions for the subsequent formation of ohmic contacts.

[0014] Furthermore, in the step of printing functional etching ink, the resolution of inkjet printing is controlled to be no less than 600 DPI; after printing, it is heated at 100°C to 150°C for 1 to 5 minutes to complete the chemical etching.

[0015] This design ensures the precision and uniformity of the micro-aperture array by controlling the printing resolution to no less than 600 DPI, avoiding the risk of leakage due to excessively large apertures or poor contact due to excessively small apertures. Simultaneously, limiting the heating conditions to a low temperature of 100℃ to 150℃ accelerates the chemical reaction kinetics while strictly controlling the thermal budget, preventing thermal degradation of the TOPCon structure due to high temperatures, perfectly meeting the stringent requirements of space photovoltaics for low-temperature processes.

[0016] Furthermore, the aperture of the opening region is 30 μm to 40 μm; the conductive gate pattern includes a fine gate and a main gate, the width of the fine gate is 10 μm to 60 μm, and the width of the main gate is 100 μm to 300 μm.

[0017] This design, by limiting the aperture opening to 30μm to 40μm, ensures sufficient contact area while maximizing the area of ​​the back passivation layer, thus balancing contact resistance and passivation performance. Simultaneously, the fine gate width design of 10μm to 60μm significantly reduces the electrode shading area or material consumption. Combined with the 100μm to 300μm main gate design, this effectively improves current collection efficiency and reduces series resistance.

[0018] Furthermore, the base metal particles in the conductive ink are nano-copper particles, nano-nickel particles, or nano-tin particles.

[0019] This design utilizes nanoscale base metal particles (copper / nickel / tin), leveraging their large specific surface area and low melting point to achieve sintering fusion and densification between particles at low temperatures of 120°C to 180°C, avoiding damage to the silicon wafer caused by high-temperature sintering. Compared to expensive silver paste, the use of nano-copper / nickel / tin base metal ink significantly reduces raw material costs (by more than 70%), while a solid content of 20% to 50% ensures the conductivity and aspect ratio of the printed lines.

[0020] Furthermore, the sintering process is low-temperature sintering, with a sintering temperature of 120°C to 180°C, and is carried out in a reducing mixed atmosphere of nitrogen and hydrogen, with a sintering time of 10 to 20 minutes.

[0021] This design employs a low-temperature sintering process, eliminating the risk of thermal stress damaging the ultra-thin silicon wafers and sensitive passivation layers of the space photovoltaic cells. In a reducing atmosphere of nitrogen and hydrogen, hydrogen effectively reduces the oxide layer on the surface of the nano-metal particles, promoting atomic diffusion and metallurgical bonding between particles, thereby forming a dense conductive network. This ensures good ohmic contact between the electrodes and the silicon substrate, reducing contact resistance.

[0022] Furthermore, after the sintering process, a transparent conductive oxide layer is printed on the surface of the conductive electrode using inkjet printing.

[0023] This design adds a transparent conductive oxide (TCO) layer to the surface of the base metal electrode. On the one hand, the high light transmittance and high conductivity of TCO further reduce the series resistance of the electrode. On the other hand, this layer, as a sealing packaging layer, effectively blocks the erosion and migration of atomic oxygen in the space environment to the underlying base metal (especially copper), significantly improving the long-term reliability and stability of the battery in the space environment.

[0024] Furthermore, the transparent conductive oxide layer is indium zinc oxide.

[0025] Indium zinc oxide (IZO) possesses excellent photoelectric properties and chemical stability. Using this material as a protective layer not only provides good conductivity but also allows for excellent energy level matching with the underlying copper electrode, further optimizing carrier transport and collection efficiency. Furthermore, its stable physicochemical properties enable it to better withstand the extreme conditions of space.

[0026] Furthermore, the aforementioned substrate is a silicon wafer used in space photovoltaic cells.

[0027] Because the entire process (hole opening and metallization) is carried out at low temperatures and laser-induced lattice damage is avoided, the radiation tolerance of the TOPCon structure is greatly protected when subjected to high-energy particle radiation. In addition, the low-temperature process reduces the thermal distortion of the silicon wafer, making it ideal for the extreme requirements of high stability, high reliability, and lightweight cells in space photovoltaics.

[0028] The present invention also proposes an inkjet printing apparatus for implementing the above-mentioned selective metallization method for photovoltaic cells. The inkjet printing apparatus is connected to a heat treatment furnace via a mechanical conveying mechanism. The inkjet printing apparatus includes:

[0029] The inkjet printing platform is equipped with a vacuum adsorption mechanism and a vision positioning system;

[0030] A printing mechanism comprising at least two inkjet printheads and a drive mechanism for driving the inkjet printheads, wherein one inkjet printhead is loaded with functional etching ink and the other inkjet printhead is loaded with conductive ink.

[0031] A heat treatment furnace, connected to an inkjet printing platform, is used to sinter the printed substrate.

[0032] The vision positioning system is configured to acquire and align the substrate before printing, and the inkjet printing platform is configured to switch between hole opening and electrode printing at the same station or consecutive stations.

[0033] This design integrates dual nozzles and a heat treatment furnace to achieve automated processing from chemical drilling to direct electrode writing. The processes of printing, etching, reprinting, and sintering can be completed efficiently on the same platform, significantly reducing the equipment footprint and process turnaround time, and improving production efficiency and yield.

[0034] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0035] 1. By using functional etching ink to perform controlled chemical etching on the silicon nitride layer, doped polycrystalline silicon layer, and tunneling oxide layer, the lattice thermal damage and defect introduction caused by the instantaneous high temperature generated during high-energy laser hole opening are avoided, thus maximizing the protection of the interface passivation quality of the TOPCon structure. At the same time, base metal-based conductive ink is used to replace the traditional expensive silver paste material, and the screen making and squeegee consumables in the screen printing process are eliminated, which greatly reduces the manufacturing cost and material cost of photovoltaic cells.

[0036] 2. By adding an indium zinc oxide (IZO) layer to the surface of the base metal electrode, not only is carrier transport optimized, but more importantly, a dense atomic oxygen barrier layer is formed. This structure effectively prevents the erosion and migration of atomic oxygen to the underlying copper electrode in the space environment, solves the problem of oxidation failure of base metals under vacuum irradiation, and significantly improves the long-term reliability of the device. Attached Figure Description

[0037] The present invention will now be described in detail with reference to the embodiments and accompanying drawings, wherein:

[0038] Figure 1 This is a flowchart illustrating the present invention;

[0039] Figure 2 It is an image of etched ink droplets printed on a substrate;

[0040] Figure 3 It is a pattern of fine grids and main grids printed on a substrate;

[0041] Figure 4 This is a schematic diagram of the opening pattern on the substrate;

[0042] Reference numerals: 1. Fine grid; 2. Main grid; 3. Opening area. Detailed Implementation

[0043] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0044] This invention provides a selective metallization method for photovoltaic cells, particularly suitable for space photovoltaic cells. This method achieves metallization openings and base metal deposition through inkjet printing, solving the problems of high thermal damage from traditional laser opening and high cost of screen-printed silver paste.

[0045] like Figure 1 As shown below, the technical solution of the present invention will be described in detail with reference to specific embodiments. The selective metallization method for photovoltaic cells includes the following steps:

[0046] A substrate is provided, which has a front emitter and a back TOPCon structure. The back TOPCon structure includes a tunneling oxide layer, a doped polysilicon layer, and a silicon nitride film layer disposed sequentially from the silicon substrate to the surface (from the inside to the outside). The silicon nitride film layer usually has both passivation and anti-reflection functions.

[0047] Using inkjet printing, functional etching ink is printed on selected areas of the silicon nitride film to chemically etch away the silicon nitride film, while selectively retaining or removing the doped polysilicon layer and tunneling oxide layer, forming an opening area that exposes the doped polysilicon layer or silicon substrate.

[0048] Using inkjet printing, conductive ink containing base metal particles is printed on the opening area and continuously deposited along a preset conductive grid pattern (including fine grid and main grid wiring), and the conductive grid pattern connects these openings.

[0049] The printed substrate undergoes a sintering process. Under a controlled thermal environment, the organic carrier in the conductive ink volatilizes and decomposes, while the base metal particles fuse due to the reduction in surface energy. This results in a dense metallurgical bond, or ohmic contact, between the base metal particles and the exposed silicon substrate or doped polycrystalline silicon layer in the open area. Simultaneously, the conductive ink distributed on the surface solidifies to form a continuous conductive grid network, thereby constructing conductive electrodes that penetrate from the internal structure of the substrate to the surface.

[0050] The "selective retention or removal of the doped polysilicon layer and tunnel oxide layer" mentioned above specifically refers to: functional etching ink removing only the silicon nitride film layer while completely retaining the doped polysilicon layer and tunnel oxide layer, achieving the effect of exposing the doped polysilicon layer in the opening area; or functional etching ink removing the silicon nitride film layer and part of the doped polysilicon layer while retaining the remaining doped polysilicon layer and tunnel oxide layer, achieving the effect of exposing the remaining doped polysilicon layer in the opening area; or functional etching ink removing the silicon nitride film layer, the doped polysilicon layer, and the tunnel oxide layer, achieving the effect of exposing the silicon substrate in the opening area.

[0051] This invention utilizes functional etching ink to perform controlled chemical etching of the silicon nitride layer, doped polycrystalline silicon layer, and tunneling oxide layer. This avoids lattice thermal damage and defect introduction caused by high-energy lasers to the passivation layer, maximizing the protection of the interface passivation quality of the TOPCon structure and thus significantly improving the open-circuit voltage stability of the battery. Thanks to the excellent interface passivation quality and non-destructive aperture process, this battery structure exhibits higher radiation tolerance and long-term reliability in harsh environments such as those with strong space radiation. Furthermore, the use of base metal conductive ink instead of expensive silver paste eliminates the need for screen printing and squeegee consumables, significantly reducing metallization costs.

[0052] like Figure 2As shown, based on the above method, in some embodiments of the present invention, the functional etching ink comprises, by mass percentage: 80% to 90% deionized water, 2% to 5% hydrofluoric acid, 8% to 9% ammonium fluoride, 2% to 2.5% glycerol, and 0.8% to 1% hydrogen peroxide.

[0053] Hydrofluoric acid (HF) serves as the primary etchant, reacting chemically with silicon nitride (SiNx) and silicon dioxide (SiO2, the tunneling oxide layer) to generate gaseous or soluble fluorosilicates, thereby removing the dielectric layer. However, hydrofluoric acid alone etches polycrystalline silicon (Poly-Si) too rapidly and is difficult to control. Therefore, this invention introduces ammonium fluoride (NH4F) as a buffer. Ammonium fluoride dissociates into F⁻ ions in water, forming a buffer system with HF, effectively suppressing drastic fluctuations in H⁺ concentration and transforming the etching process from "uncontrolled, strong corrosion" to "controlled, gentle dissolution." This synergistic effect is particularly suitable for the precise penetration of thin polycrystalline silicon layers in TOPCon structures, preventing over-etching damage to the silicon substrate.

[0054] Considering the stringent requirements of inkjet printing on droplet morphology, this invention incorporates glycerol as a thickener. Glycerol significantly modulates the surface tension and viscosity of the ink, preventing droplets from evaporating too quickly at the printhead nozzle and causing blockages. Simultaneously, it ensures that the droplets maintain a suitable spreading radius (30μm to 40μm) after impacting the silicon wafer surface, avoiding jagged edges or excessive flow, thereby guaranteeing the morphological accuracy of the micro-apertures.

[0055] In addition, the addition of hydrogen peroxide (H2O2) plays a dual role: on the one hand, its oxidizing properties help remove organic residues on the silicon wafer surface and clean the reaction interface; on the other hand, in the early stage of the corrosion reaction, H2O2 can form an extremely thin oxide layer on the silicon surface, regulate the attack rate of HF, and further improve the smoothness of the opening sidewalls.

[0056] Deionized water, as the main solvent, not only dissolves the above components to form a homogeneous solution, but also acts as a reaction medium to carry the reaction products away from the interface, ensuring the continuous progress of the corrosion reaction.

[0057] To improve the processing quality of micro-apertures, the preferred solution is to control the inkjet printing resolution to be no less than 600 DPI during the printing of functional etching inks. This ensures the fineness and uniformity of the micro-aperture array pattern, avoiding the risk of leakage due to excessively large apertures or poor contact due to excessively small apertures. After printing, heating at 100°C to 150°C for 1 to 5 minutes accelerates the chemical reaction kinetics and strictly limits the thermal budget, preventing thermal degradation of the TOPCon structure caused by high temperatures. This perfectly meets the stringent requirements of space photovoltaics for low-temperature processes.

[0058] like Figures 3 to 4As shown, in some feasible embodiments of the present invention, the aperture of the opening region 3 is 30 μm to 40 μm, which ensures sufficient contact area while maximizing the area of ​​the back passivation layer, thus balancing contact resistance and passivation performance. The conductive grid pattern includes a fine grid 1 and a main grid 2. The width of the fine grid 1 is 10 μm to 60 μm to reduce the electrode light-shielding area or material consumption, while the width of the main grid 2 is 100 μm to 300 μm, effectively improving current collection efficiency and reducing series resistance.

[0059] To reduce metallization costs, the preferred solution is to use nano-copper, nano-nickel, or nano-tin particles in the conductive ink, with particle sizes ranging from 10nm to 30nm. Compared to expensive silver paste, the use of nano-copper / nickel / tin base metal ink significantly reduces raw material costs (by more than 70%). Furthermore, nano-copper or nano-nickel particles possess a large specific surface area and low melting point, enabling sintering fusion and densification between particles at low temperatures (e.g., 120°C to 180°C), thus avoiding damage to the silicon wafer caused by high-temperature sintering.

[0060] As an example, in some embodiments, the conductive ink comprises copper nanoparticles, an organic binder, a dispersant, and a mixed solvent; the copper nanoparticles have a particle size of 20 nm; the organic binder is ethyl cellulose; the dispersant consists of 80% to 90% polyvinylpyrrolidone and 15% to 16% triethanolamine by mass; and the mixed solvent consists of 80% to 90% deionized water, 6% to 8% ethylene glycol, and 3% to 5% diethylene glycol by mass.

[0061] To minimize thermal damage to the silicon wafer during the sintering process, a low-temperature sintering method is preferred, with a sintering temperature of 120°C to 180°C, conducted in a reducing atmosphere of nitrogen and hydrogen, for 10 to 20 minutes. Hydrogen, as a strong reducing agent, effectively reduces the oxide layer on the surface of the nano-metal particles, breaking down interfacial barriers between particles, promoting atomic diffusion and metallurgical bonding, thereby forming a dense conductive network. This ensures good ohmic contact between the electrode and the silicon substrate, reducing contact resistance. Nitrogen, as an inert protective gas, isolates the intrusion of external oxygen and other impurities, preventing unintended oxidation of the nano-metal particles or silicon substrate at high temperatures and maintaining the purity of the sintering environment. It also dilutes the hydrogen concentration, balancing the reduction intensity and reducing the risk of flammability and explosion, providing a stable atmosphere for the hydrogen's reducing effect. Together, these two elements ensure the safety of the low-temperature sintering process and the quality of the electrodes.

[0062] After completing the low-temperature sintering process, to further optimize electrode performance, this invention also includes printing a transparent conductive oxide (TCO) layer on the surface of the conductive electrode using inkjet printing. This layer not only effectively reduces the series resistance of the electrode and improves carrier collection efficiency due to its high light transmittance and excellent conductivity, but more importantly, in space photovoltaic applications, the TCO layer acts as a dense atomic oxygen barrier and encapsulation layer. It effectively blocks the erosion and migration of high-energy particles and atomic oxygen to the underlying base metal (especially the copper electrode), preventing PN junction leakage or electrode failure caused by metal diffusion. This significantly improves the interface stability, chemical inertness, and reliability of the battery structure under long-term space irradiation.

[0063] Building upon this, the transparent conductive oxide layer is preferably indium zinc oxide (IZO), thus forming a generalized oxide-metal-oxide encapsulation structure (OMO structure) between the existing tunneling oxide layer (bottom inherent oxide), the metal electrode, and the IZO (top oxide). Because this material possesses both excellent photoelectric conversion performance and chemical inertness, it can not only achieve good energy level matching with the underlying copper electrode to optimize carrier transport and collection efficiency, but also act as a robust encapsulation barrier due to its dense physical structure, effectively resisting high-energy particle radiation and atomic oxygen erosion in the extreme environment of space, ensuring the structural integrity and electrical stability of the base metal electrode during long-term operation.

[0064] It should be noted that, because the method proposed in this invention is performed at low temperatures throughout the entire process (both aperture opening and metallization), and avoids laser-induced lattice damage, it greatly protects the radiation tolerance of the TOPCon structure when subjected to high-energy particle radiation. Furthermore, the low-temperature process reduces thermal distortion of the silicon wafer, making it ideally suited for the extreme requirements of high stability, high reliability, and lightweight cells in space photovoltaics.

[0065] The present invention also provides an inkjet printing apparatus for implementing the above-described selective metallization method for photovoltaic cells, the apparatus comprising an inkjet printing platform and a printing mechanism.

[0066] The inkjet printing platform is equipped with a vacuum adsorption mechanism and a vision positioning system. The vacuum adsorption mechanism includes an adsorption plate and a vacuum chamber connected to it. The surface of the adsorption plate is distributed with adsorption holes, and air is drawn in through an external pipeline to fix the substrate. The vision positioning system consists of a high-precision camera and a matching light source, used to acquire the position information of the substrate.

[0067] The printing mechanism includes at least two inkjet printheads and a drive unit for moving the inkjet printheads. In one embodiment, the printing mechanism is configured with two independent inkjet printheads: a first inkjet printhead loaded with functional etching ink and a second inkjet printhead loaded with conductive ink. The drive unit employs an XYZ linear motion module to move the inkjet printheads in both vertical and horizontal planes.

[0068] The heat treatment furnace is connected to the inkjet printing platform via a mechanical conveying mechanism (such as a conveyor belt or a robotic arm) to transport the printed substrate into the furnace for heat treatment. In addition, the heat treatment furnace is connected to a gas supply line for supplying process gases (such as nitrogen and hydrogen) into the furnace during the heat treatment process.

[0069] During operation, the substrate to be processed is placed on the inkjet printing platform. A vacuum adsorption mechanism firmly secures the substrate, while a vision positioning system acquires and precisely positions the substrate to ensure the printing accuracy of subsequent patterns. Then, the first inkjet printhead moves above the workstation and precisely jets etching ink onto the silicon nitride film layer according to a preset back-contact pattern, completing chemical opening—that is, forming the opening area. Next, the inkjet printing platform, through rapid switching between the same or consecutive workstations, drives the second inkjet printhead to move above the substrate with the completed openings, covering and printing conductive ink containing base metal particles onto the opening areas and printing the conductive grid lines connecting these openings. After printing, the substrate is transferred to a heat treatment furnace for low-temperature sintering.

[0070] This equipment integrates a dual-nozzle system with sintering functionality, automating the printing → etching → reprinting → sintering process. It consolidates the originally discrete multiple processes into a single device, significantly reducing the equipment footprint and process turnaround time, and substantially improving the production efficiency and yield of high-precision components such as space photovoltaic cells.

[0071] To facilitate understanding, the selective metallization method for photovoltaic cells will be described in detail below with some application examples of the present invention.

[0072] The TOPCon semi-finished silicon wafer (i.e., the substrate) is placed on a conveyor belt and transferred by a robotic arm to the suction plate of the inkjet printing platform. The suction holes on the surface of the suction plate are used to evacuate air and firmly fix the substrate. Subsequently, the inkjet platform, along with the substrate, moves under a high-precision camera for visual positioning. The precise coordinates of the substrate are obtained through image acquisition, providing an alignment reference for subsequent pattern printing.

[0073] After positioning, the inkjet printing platform moves to the printing station, and the first inkjet printhead, loaded with functional etching ink, moves to a position 0.8 mm to 1 mm directly above the substrate. The etching ink is configured by weight percentage as follows: 80% to 90% deionized water, 2% to 5% hydrofluoric acid, 8% to 9% ammonium fluoride buffer, 2% to 2.5% glycerol thickener, and 0.8% to 1% hydrogen peroxide. The first inkjet printhead is controlled to eject ink droplets of 2.4 pL to 10 pL onto the silicon nitride film at a speed of 3 m / min to 6 m / min, with a printing resolution of 600 DPI.

[0074] After printing is completed, the robotic arm transfers the substrate to a heat treatment furnace and heats it at 100°C for 2 minutes. The chemical etching action of the etching ink is used to remove the silicon nitride film, the doped polysilicon layer, and the tunneling oxide layer in sequence, exposing the silicon substrate and forming the opening area.

[0075] Subsequently, the robotic arm picks up the substrate with the holes opened and places it back onto the inkjet printing platform for secondary visual positioning. At this time, the second inkjet printhead loaded with nano-copper conductive ink moves to a position 0.7mm to 0.9mm above the substrate and operates at a printing speed of 3m / min and a resolution of 1200DPI. The ink droplet size is 6pL, ensuring that the ink completely covers the opening area and prints the conductive grid pattern connecting these openings.

[0076] Finally, the robotic arm sends the printed substrate into a heat treatment furnace, where it is sintered at 150°C for 15 minutes in a reducing atmosphere of nitrogen and hydrogen. This allows the nano-copper particles to form dense ohmic contacts with the silicon substrate at the openings, while simultaneously solidifying to form continuous conductive grid lines. The entire process is now complete.

[0077] It should be noted that the terminology used above is for describing specific embodiments only and is not intended to limit the exemplary embodiments of the present invention. When the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. The order of execution of actions, steps, etc., of the methods shown in the specification can be implemented in any order unless a specific express order is specified, and as long as the output of the preceding process is not used in the subsequent process. Similar sequential terms used for ease of description do not imply that such an order must be followed.

[0078] Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for selective metallization of photovoltaic cells, characterized in that, Includes the following steps: A substrate is provided, the back side of which has a TOPCon structure, the TOPCon structure comprising a tunneling oxide layer, a doped polysilicon layer, and a silicon nitride film layer disposed sequentially from the silicon substrate toward the surface; Using inkjet printing, functional etching ink is printed on selected areas of the silicon nitride film to remove the silicon nitride film, and the doped polysilicon layer and tunneling oxide layer are selectively retained or removed to form an opening area that exposes the doped polysilicon layer or the silicon substrate. Using inkjet printing, conductive ink containing base metal particles is printed into the opening area and the preset conductive grid pattern. The printed substrate is sintered to form continuous conductive electrodes from the base metal particles and to form ohmic contacts with the exposed doped polycrystalline silicon layer or the silicon substrate.

2. The selective metallization method for photovoltaic cells according to claim 1, characterized in that, The functional etching ink comprises, by weight percentage: 80% to 90% deionized water, 2% to 5% hydrofluoric acid, 8% to 9% ammonium fluoride, 2% to 2.5% glycerol, and 0.8% to 1% hydrogen peroxide.

3. The selective metallization method for photovoltaic cells according to claim 1, characterized in that, In the step of printing the functional etching ink, the resolution of the inkjet printing is controlled to be no less than 600 DPI; after printing, it is heated at 100°C to 150°C for 1 to 5 minutes to complete the chemical etching.

4. The selective metallization method for photovoltaic cells according to claim 1, characterized in that, The aperture of the opening region is 30μm to 40μm; the conductive grid pattern includes a fine grid and a main grid, the width of the fine grid is 10μm to 60μm, and the width of the main grid is 100μm to 300μm.

5. The selective metallization method for photovoltaic cells according to claim 1, characterized in that, The base metal particles in the conductive ink are nano-copper particles, nano-nickel particles, or nano-tin particles.

6. The selective metallization method for photovoltaic cells according to claim 1, characterized in that, The sintering process is low-temperature sintering, with a sintering temperature of 120°C to 180°C, and is carried out in a reducing mixed atmosphere of nitrogen and hydrogen, with a sintering time of 10 to 20 minutes.

7. The selective metallization method for photovoltaic cells according to claim 1, characterized in that, Following the sintering process, the process further includes: A transparent conductive oxide layer is printed on the surface of the conductive electrode using inkjet printing.

8. The selective metallization method for photovoltaic cells according to claim 7, characterized in that, The transparent conductive oxide layer is indium zinc oxide.

9. The selective metallization method for photovoltaic cells according to any one of claims 1 to 8, characterized in that, The substrate is a silicon wafer used in space photovoltaic cells.

10. An inkjet printing apparatus for implementing the selective metallization method for photovoltaic cells according to any one of claims 1 to 9, wherein the inkjet printing apparatus is connected to a heat treatment furnace via a mechanical conveying mechanism; characterized in that, The inkjet printing device includes: The inkjet printing platform is equipped with a vacuum adsorption mechanism and a vision positioning system; A printing mechanism includes at least two inkjet printheads and a drive device for driving the inkjet printheads to move, wherein one inkjet printhead is loaded with functional etching ink and the other inkjet printhead is loaded with conductive ink. The vision positioning system is configured to acquire and align the substrate before printing, and the inkjet printing platform is configured to switch between hole opening and electrode printing at the same station or consecutive stations.

Images