Back contact solar cell and preparation process thereof, laminated cell, photovoltaic module

Abstract

The application provides a back contact solar cell, a preparation process thereof, a laminated cell and a photovoltaic module. The preparation process comprises the following steps: obtaining a cell substrate, printing a conductive material on the cell substrate, and then drying, sintering and annealing to form an electrode, thereby obtaining the back contact solar cell; the conductive material comprises first aluminum powder, silver-coated aluminum powder, glass powder and a laser-sensitive additive; the silver-coated aluminum powder comprises an aluminum core and a silver layer coated on the outer surface of the aluminum core; the surface of the cell substrate is divided into first zones and second zones arranged alternately, and the first laser sintering and the second laser sintering are performed respectively; the power of the first laser sintering is less than that of the second laser sintering, and the scanning speed of the first laser sintering is greater than that of the second laser sintering. The above preparation process is combined with the partition laser sintering process of the conductive material, thereby reducing the amount of silver, and significantly improving the metallization quality and photoelectric conversion efficiency of the BC cell.

Description

Technical Field

[0001] This application relates to the photovoltaic field, and in particular to a back-contact solar cell and its fabrication process, tandem cells, and photovoltaic modules. Background Technology

[0002] Back-contact (BC) solar cells, with both front and back electrodes located on the back and no metal grid lines obstructing the light absorption layer on the front, significantly improve the optical utilization of the cell, resulting in higher short-circuit current and conversion efficiency. The core technological challenge of BC cells lies in the complex patterning and metallization process of the interdigitated electrodes on the back, particularly the precise differentiation between P-type and N-type electrodes and the construction of high-quality ohmic contacts.

[0003] Currently, screen printing technology is mainly used for metallization of solar cells, with traditional silver paste dominating due to its excellent conductivity and mature process system. However, with silver prices remaining high, silver consumption has become a key factor restricting cost reduction in photovoltaics. To reduce silver usage, alternatives such as aluminum-silver composite pastes or pure aluminum pastes have attracted much attention. Aluminum resources are abundant and inexpensive, and can effectively reduce metallization costs. However, the metallization process for BC cells still requires targeted optimization. Summary of the Invention

[0004] The main objective of this invention is to provide a back-contact solar cell and its fabrication process, a tandem cell, and a photovoltaic module, in order to solve the problem of aluminum spikes in aluminum-silver composite electrodes leading to cell efficiency and lifespan degradation in the prior art.

[0005] According to some embodiments of this application, one aspect of this application provides a fabrication process for a back-contact solar cell. The fabrication process includes: obtaining a cell substrate; printing conductive material on the cell substrate; performing a first drying, sintering, and annealing treatment to form electrodes, thereby obtaining a back-contact solar cell; wherein the conductive material includes first aluminum powder, silver-coated aluminum powder, glass powder, and a laser-sensitive additive; the silver-coated aluminum powder includes an aluminum core and a silver layer coating the outer surface of the aluminum core; the laser-sensitive additive includes a composite metal oxide, wherein the metal element in the composite metal oxide is selected from at least two of indium, tin, zinc, titanium, and strontium; the surface of the cell substrate is divided into alternating first and second regions; the first region is subjected to first laser sintering; the second region is subjected to second laser sintering; the power of the first laser sintering is less than the power of the second laser sintering, and the scanning speed of the first laser sintering is greater than the scanning speed of the second laser sintering.

[0006] In some embodiments, the first aluminum powder is aluminum powder with a first surface passivation. The preparation method of the first surface passivated aluminum powder includes: heat-treating the aluminum powder raw material to form a first passivation layer on the outer surface of the aluminum powder raw material; the heat treatment atmosphere is an oxygen-containing atmosphere, the heat treatment temperature is 150~250℃, and the heat treatment time is 30~90min; the first passivation layer includes aluminum oxide, and the thickness of the first passivation layer is 5~15nm.

[0007] In some embodiments, the first aluminum powder is a second surface passivated aluminum powder. The preparation method of the second surface passivated aluminum powder includes: immersing the aluminum powder raw material in a passivation reagent and stirring, then filtering and drying it to form a second passivation layer on the outer surface of the aluminum powder raw material; the passivation reagent is a solution containing a silane coupling agent and / or a phosphate ester, and the mass concentration of the passivation reagent is 0.1~0.5%; the stirring temperature is 20~30℃, the stirring time is 20~60min; and the thickness of the second passivation layer is 5~15nm.

[0008] In some embodiments, the first aluminum powder is spherical aluminum powder, and the D50 particle size of the first aluminum powder is 1.5~3.5μm.

[0009] In some embodiments, the silver-coated aluminum powder is obtained by immersing a second aluminum powder in an immersion plating solution to undergo a displacement reaction, thereby depositing a silver layer on the surface of the second aluminum powder; wherein the immersion plating solution is a silver nitrate and / or silver ammonia solution, and the pH value of the immersion plating solution is 9~11; the temperature of the displacement reaction is 45~55°C, and the time of the displacement reaction is 45~75 min.

[0010] In some embodiments, the D50 particle size of the silver-coated aluminum powder is 2.5~4.5μm; the thickness of the silver layer in the silver-coated aluminum powder is 50~150nm.

[0011] In some embodiments, the laser-sensitive additive is selected from any one or more of nano-indium tin oxide, nano-indium zinc oxide, and nano-strontium titanate, and the D50 particle size of the laser-sensitive additive is 20~100nm.

[0012] In some embodiments, the glass powder is bismuth-based glass powder and / or tellurium-based glass powder; wherein, by weight, the bismuth-based glass powder includes 40-60 parts of Bi2O3, 15-30 parts of B2O3, 10-20 parts of ZnO, 5-15 parts of BaO and 1-5 parts of Al2O3; and by weight, the tellurium-based glass powder includes 45-65 parts of TeO2, 15-30 parts of Bi2O3, 10-20 parts of ZnO, 2-8 parts of Li2O and 1-5 parts of Na2O.

[0013] In some embodiments, the mass ratio of the first aluminum powder to the silver-coated aluminum powder is 1:(0.3~1); the mass ratio of the total mass of the first aluminum powder and the silver-coated aluminum powder, the mass of the glass powder, and the mass of the laser-sensitive additive is (65~85):(3~8):(0.5~5).

[0014] In some embodiments, sintering is laser sintering, the laser wavelength of laser sintering is 800~1100nm, the laser spot diameter of laser sintering is 30~100μm, the laser power of laser sintering is 20~80W, and the laser scanning speed of laser sintering is 500~3000mm / s.

[0015] In some embodiments, the power of the first laser sintering is 40~60W, and the scanning speed of the first laser sintering is 1000~2000mm / s; the power of the second laser sintering is 50~80W, and the scanning speed of the second laser sintering is 800~1500mm / s.

[0016] In some embodiments, the annealing temperature is 350~450°C and the annealing time is 5~20 min; and / or, the first drying temperature is 100~150°C and the first drying time is 5~15 min.

[0017] According to some embodiments of this application, another aspect of this application provides a back-contact solar cell, which is prepared by the back-contact solar cell preparation method described above.

[0018] According to some embodiments of this application, another aspect of this application provides a stacked battery, which includes a top battery and a bottom battery, wherein the bottom battery is the aforementioned back-contact solar cell.

[0019] According to some embodiments of this application, another aspect of this application provides a photovoltaic module, which includes: a battery string, an encapsulating film, and a cover plate; the battery string is formed by connecting multiple back-contact solar cells as described above, or stacked cells as described above; the encapsulating film is used to cover the surface of the battery string; and the cover plate is used to cover the surface of the encapsulating film away from the battery string.

[0020] The technical solution provided in this application has at least the following advantages: The back-contact solar cell fabrication process provided in this application, through the combination of the aforementioned conductive materials and the partitioned laser sintering process, can significantly improve the metallization quality and photoelectric conversion efficiency of BC cells. Specifically, this application uses aluminum-based materials instead of traditional silver-based materials, which can significantly reduce costs. By introducing silver-coated aluminum powder into the conductive material, and using the silver layer as a conductive bridge and sintering promoter, the contact resistance can be reduced while simultaneously lowering costs. Adding laser-sensitive additives can enhance the absorption of near-infrared lasers by the conductive material, thereby achieving localized and precise heating. During the sintering process, the glass powder melts first, and the resulting liquid glass erodes the passivation layer on the surface of the silicon substrate, opening a channel for metal contact; the silver layer of the silver-coated aluminum powder then melts and wets the exposed silicon surface through the molten glass; finally, the aluminum core melts and diffuses into the silicon substrate through the molten silver layer to form a silver-aluminum-silicon eutectic alloy contact. Laser sintering can flexibly adjust the depth of aluminum diffusion, avoiding the problem of "aluminum spikes," thereby further improving the conductivity of the electrode while ensuring low silver consumption. By performing zoned sintering on the battery substrate surface, with different laser sintering powers and scanning speeds for different regions, the electrode performance of the first and second regions can be controlled through differentiated laser parameters, resulting in a greater aluminum diffusion depth in the first region than in the second region. The first laser sintering process in the first region employs relatively low power and a relatively high scanning speed, utilizing the liquid interface formed by the melting of the silver shell to promote moderate aluminum diffusion and create an ohmic contact with low contact resistance. The second laser sintering process in the second region employs relatively high power and a relatively low scanning speed, using rapid heat input to instantly densify the silver shell, forming a physical barrier and restricting aluminum diffusion into the silicon, effectively preventing aluminum penetration. This sintering process allows the first region to maintain good conductivity while better protecting the surface passivation quality of the second region, thereby further improving the open-circuit voltage and fill factor of the battery. In summary, the back-contact solar cell fabrication process of this application can reduce the amount of silver used, and through the above sintering process optimization, achieve high-performance metallization, enabling large-scale production of BC batteries. Attached Figure Description

[0021] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the drawings in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1A schematic diagram of the back-contact solar cell in Embodiment 1 of this application is shown;

[0023] Figure 2 A schematic diagram of the structure of the stacked battery of this application is shown;

[0024] Figure 3 A schematic diagram of the structure of the photovoltaic module of this application is shown.

[0025] The above figures include the following reference numerals:

[0026] 1. Silicon substrate; 2. First passivation stack; 3. First electrode; 4. Second passivation stack; 5. Second electrode; 6. Top cell; 7. Bottom cell; 8. Cell string; 9. Encapsulation film; 10. Cover plate. Detailed Implementation

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] According to background technology analysis, although aluminum can replace some silver, there is a risk of "aluminum spikes" during the sintering process. This means that aluminum atoms penetrate into the silicon matrix and create recombination centers, which leads to a reduction in minority carrier lifetime and battery efficiency degradation, and may even cause microcracks and reliability issues in the battery cells.

[0029] As analyzed above, the existing technology has the problem of aluminum spikes in the aluminum strip silver composite electrode, which leads to the degradation of battery efficiency and lifespan. In order to solve the above problems, this application provides a back contact solar cell and its preparation process, a tandem cell, and a photovoltaic module.

[0030] In a typical embodiment of this application, a fabrication process for a back-contact solar cell is provided. The process involves obtaining a cell substrate, printing conductive material onto the substrate, and then performing a first drying, sintering, and annealing treatment to form electrodes, thereby obtaining a back-contact solar cell. The conductive material includes first aluminum powder, silver-coated aluminum powder, glass powder, and a laser-sensitive additive. The silver-coated aluminum powder includes an aluminum core and a silver layer coating the outer surface of the aluminum core. The laser-sensitive additive includes a composite metal oxide, wherein the metal element in the composite metal oxide is selected from at least two of indium, tin, zinc, titanium, and strontium. The surface of the cell substrate is divided into alternating first and second regions. The first region is subjected to a first laser sintering, and the second region is subjected to a second laser sintering. The power of the first laser sintering is less than the power of the second laser sintering, and the scanning speed of the first laser sintering is greater than the scanning speed of the second laser sintering.

[0031] The back-contact solar cell fabrication process provided in this application, through the combination of the aforementioned conductive materials and a zoned laser sintering process, can significantly improve the metallization quality and photoelectric conversion efficiency of BC cells. Specifically, this application uses aluminum-based materials instead of traditional silver-based materials, which can significantly reduce costs. By introducing silver-coated aluminum powder into the conductive material, and utilizing the silver layer as a conductive bridge and sintering promoter, the contact resistance can be reduced while simultaneously lowering costs. Adding laser-sensitive additives can enhance the absorption of near-infrared lasers by the conductive material, thereby achieving localized and precise heating. During the sintering process, the glass powder melts first, and the resulting liquid glass erodes the passivation layer on the silicon substrate surface, opening channels for metal contact. The silver layer of the silver-coated aluminum powder then melts and wets the exposed silicon surface through the molten glass. Finally, the aluminum core melts and diffuses into the silicon substrate through the molten silver layer to form a silver-aluminum-silicon eutectic alloy contact. Laser sintering allows for flexible adjustment of the aluminum diffusion depth, avoiding the problem of "aluminum spikes," thereby further improving the conductivity of the electrodes while ensuring low silver consumption. By performing zoned sintering on the battery substrate surface, with different laser sintering powers and scanning speeds for different regions, the electrode performance of the first and second regions can be controlled through differentiated laser parameters, resulting in a greater aluminum diffusion depth in the first region than in the second region. The first laser sintering process in the first region employs relatively low power and a relatively high scanning speed, utilizing the liquid interface formed by the melting of the silver shell to promote moderate aluminum diffusion and create an ohmic contact with low contact resistance. The second laser sintering process in the second region employs relatively high power and a relatively low scanning speed, using rapid heat input to instantly densify the silver shell, forming a physical barrier and restricting aluminum diffusion into the silicon, effectively preventing aluminum penetration. This sintering process allows the first region to maintain good conductivity while better protecting the surface passivation quality of the second region, thereby further improving the open-circuit voltage and fill factor of the battery. In summary, the back-contact solar cell fabrication process of this application can reduce the amount of silver used, and through the above sintering process optimization, achieve high-performance metallization, enabling large-scale production of BC batteries.

[0032] Optionally, the first region is a P-region, and the second region is an N-region. The P-region is typically doped with boron, and it corresponds to the P-type electrode of the battery (usually connected to the positive electrode). In the back contact structure, the P-region is responsible for collecting hole current. Because the P-region needs to form a good ohmic contact and has a certain tolerance for minority carrier (electron) recombination, its aluminum diffusion depth can be deeper than that of the N-region to form a good back surface field (BSF) and reduce back surface recombination. The N-region is typically doped with phosphorus, and it corresponds to the N-type electrode of the battery (usually connected to the negative electrode). In the back contact structure, the N-region is responsible for collecting electron current. The N-region is more sensitive to recombination caused by metal contacts.

[0033] The conductive material of this application needs to be printed after being prepared as a conductive paste. The composite paste includes the aforementioned conductive material, an organic carrier, and additives. Controlling the mass ratio of the first aluminum powder and silver-coated aluminum powder, the organic carrier, and the additives to (65~85):(12~25):(0.5~2) helps to fully disperse each component in the organic carrier, thereby improving the uniformity of the conductive paste. The organic carrier includes resin and solvent. The resin includes ethyl cellulose and acrylic resin. Controlling the mass ratio of ethyl cellulose and acrylic resin to 2~4:1 helps to improve the flexibility and adhesion of the conductive material. The solvent includes terpineol and diethylene glycol butyl ether acetate. Controlling the mass ratio of terpineol and diethylene glycol butyl ether acetate to 3~5:1 helps to improve leveling performance. The additives are selected from any one or more of dispersants, leveling agents, and thixotropic agents; wherein, the dispersant includes, but is not limited to, high-molecular-weight polyester dispersants, which help to promote full dispersion of raw materials. The leveling agent includes, but is not limited to, polyacrylate leveling agents, which help to reduce surface tension and eliminate pinholes. Thixotropic agents, including but not limited to fumed silica, help improve the thixotropy and anti-settling ability of conductive pastes.

[0034] The preparation method of the conductive paste includes the following steps: Step S1, dispersing the resin in a solvent, mixing at 70~85℃ for 2~3h, cooling and filtering to obtain an organic carrier; Step S2, mixing the first aluminum powder, silver-coated aluminum powder, glass powder, laser-sensitive additives, auxiliaries and organic carrier, and grinding them to a fineness ≤8μm using a three-roll mill to obtain a ground paste; Step S3, filtering the ground paste through a 200~300 mesh sieve and vacuum degassing for 30~60min to obtain a conductive paste. Before performing the first laser sintering and the second laser sintering, the above conductive paste needs to be printed on the surface of a silicon substrate to form an interdigitated electrode pattern, and then subjected to drying, sintering and annealing treatments in sequence to form electrodes, thus obtaining a back contact solar cell.

[0035] In one embodiment of this application, the first aluminum powder is aluminum powder with a first surface passivation. The preparation method of the first surface passivated aluminum powder includes: heat-treating the aluminum powder raw material to form a first passivation layer on the outer surface of the aluminum powder raw material; the heat treatment atmosphere is an oxygen-containing atmosphere, which may be oxygen and / or air, the heat treatment temperature is 150~250℃, and the heat treatment time is 30~90min; the first passivation layer includes aluminum oxide, and the thickness of the first passivation layer is 5~15nm.

[0036] The first aluminum powder prepared by the above method is a surface-passivated aluminum powder. Controlling the atmosphere, temperature, and time of the heat treatment within the above range helps to form a first passivation layer on the outer surface of the first aluminum powder (pure aluminum powder), thereby helping to reduce the oxidation of the first aluminum powder. This passivation layer helps to control the diffusion of aluminum atoms into the silicon substrate during subsequent laser sintering, thereby reducing aluminum spikes. Controlling the surface coating of the first aluminum powder with alumina and controlling the thickness of the first passivation layer within the above range helps to reduce the severe oxidation reaction of the first aluminum powder during subsequent laser sintering, while also enabling the aluminum core to directly alloy with the silicon substrate, forming a low-resistance ohmic contact.

[0037] In one embodiment of this application, the first aluminum powder is a second surface passivated aluminum powder. The preparation method of the second surface passivated aluminum powder includes: immersing the aluminum powder raw material in a passivation reagent and stirring, then filtering and drying it to form a second passivation layer on the outer surface of the aluminum powder raw material; the passivation reagent is a solution containing a silane coupling agent and / or a phosphate ester, and the mass concentration of the passivation reagent is 0.1~0.5%; the stirring temperature is 20~30℃, and the stirring time is 20~60min; the thickness of the second passivation layer is 5~15nm.

[0038] Using the aforementioned passivating agents to passivate the surface of aluminum powder raw materials facilitates coordination or chemical reaction with the aluminum powder, forming a second passivation layer on the surface of the aluminum powder, thereby reducing the oxidation of the first aluminum powder. The silane coupling agents include, but are not limited to, KH-550 and KH-560, and the phosphate esters include, but are not limited to, hydroxyethyl methacrylate phosphate and hydroxypropyl acrylate phosphate. The solvents for the passivating agents include, but are not limited to, ethanol and isopropanol.

[0039] In one embodiment of this application, the first aluminum powder is spherical aluminum powder, and the D50 particle size of the first aluminum powder is 1.5~3.5μm.

[0040] The first aluminum powder is spherical, which helps to improve the printability of the conductive paste by utilizing the good flowability and packing density of spherical aluminum powder, thereby forming electrodes with uniform linewidth and vertical sidewalls. Controlling the D50 particle size of the first aluminum powder within the above-mentioned range helps to optimize the particle packing density and reduce porosity. Combined with the alumina coating on the outer surface of the first aluminum powder, it helps the aluminum nuclei to fully diffuse during sintering to form low-resistance contacts, and also reduces poor contact caused by excessively large particle size, thereby reducing contact resistance and improving the fill factor of the battery.

[0041] D50 particle size (median diameter) is the particle size value that corresponds to 50% of the cumulative volume (or weight) in the particle size distribution curve of a particle sample.

[0042] In one embodiment of this application, silver-coated aluminum powder is obtained by immersing a second aluminum powder in an immersion plating solution to undergo a displacement reaction, thereby depositing a silver layer on the surface of the second aluminum powder; wherein, the immersion plating solution is silver nitrate and / or silver ammonia solution, and the pH value of the immersion plating solution is 9~11; the temperature of the displacement reaction is 45~55℃, and the time of the displacement reaction is 45~75min.

[0043] The above-mentioned method for preparing silver-coated aluminum powder utilizes the principle of displacement reaction to form a silver layer with good conductivity and chemical stability on the outer surface of the second aluminum powder (pure aluminum powder). This not only helps reduce the cost of conductive materials, but the silver layer also serves as an excellent conductive channel, further reducing the contact resistance between the electrode and the silicon substrate. Controlling the type of immersion plating solution within the above-mentioned range helps to form a dense and strongly bonded silver coating layer on the surface of the aluminum powder through the displacement reaction. Controlling the pH value of the immersion plating solution within the above-mentioned range helps to provide an alkaline reaction environment, which is beneficial for controlling the reduction rate of silver ions and promoting the formation of a fine-grained, uniform, continuous, and strongly adhered silver coating layer. Controlling the temperature and time of the displacement reaction within the above-mentioned range helps to fully reduce silver ions and form a dense, continuous, and strongly adhered silver coating layer on the surface of the aluminum core.

[0044] In one embodiment of this application, the D50 particle size of the silver-coated aluminum powder is 2.5~4.5μm; the thickness of the silver layer in the silver-coated aluminum powder is 50~150nm.

[0045] Controlling the D50 particle size of silver-coated aluminum powder within the aforementioned range helps optimize particle size distribution and structural stability. If the silver layer in the silver-coated aluminum powder is too thin, it cannot effectively isolate aluminum oxidation or provide sufficient wettability; if the silver layer is too thick, it hinders aluminum nucleus diffusion and increases cost. Therefore, controlling the thickness of the silver layer in the silver-coated aluminum powder within the aforementioned range helps maintain a continuous liquid interface during sintering, fully wetting the silicon substrate, while allowing the aluminum nucleus to diffuse controllably to form alloyed contacts, thereby reducing aluminum spikes, lowering contact resistance, and improving electrode stability.

[0046] In one embodiment of this application, the laser-sensitive additive is selected from any one or more of nano-indium tin oxide, nano-indium zinc oxide, and nano-strontium titanate, and the D50 particle size of the laser-sensitive additive is 20~100nm.

[0047] Controlling the types of laser-sensitive additives within the aforementioned range helps enhance the absorption of near-infrared lasers by the conductive paste, enabling precise localized heating. This accelerates the melting and fusion of the first aluminum powder and silver-coated aluminum powder particles, speeds up the softening and flow of the glass powder, and further promotes the formation of a good ohmic contact surface between the conductive material and the substrate during sintering, reducing the contact resistance between the electrode and the substrate. Controlling the D50 particle size of the photosensitive additives within the aforementioned range helps provide sufficient specific surface area, thereby further improving the conversion efficiency of laser and thermal energy.

[0048] In one embodiment of this application, the glass powder is bismuth-based glass powder and / or tellurium-based glass powder; wherein, by weight, the bismuth-based glass powder includes 40-60 parts of Bi2O3, 15-30 parts of B2O3, 10-20 parts of ZnO, 5-15 parts of BaO and 1-5 parts of Al2O3; and by weight, the tellurium-based glass powder includes 45-65 parts of TeO2, 15-30 parts of Bi2O3, 10-20 parts of ZnO, 2-8 parts of Li2O and 1-5 parts of Na2O.

[0049] Bismuth-based or tellurium-based glass powders are selected, utilizing their low melting point to rapidly melt and form a liquid phase during the low-temperature stage of laser sintering, promoting contact and alloying between aluminum and the substrate. Simultaneously, the glass powder fills electrode pores, enhancing the adhesion between the conductive material and the substrate. Controlling the composition of the bismuth-based glass powder within the aforementioned range helps it melt rapidly during laser sintering, thus providing good fluidity. Bismuth-based glass powders have good reducing power, which helps to quickly dissolve the oxide layer on the surface of the aluminum powder in the early stages of sintering, promoting direct contact between aluminum and the substrate. Controlling the composition of the tellurium-based glass powder within the aforementioned range helps to provide high wettability, thereby facilitating the formation of a smoother and denser electrode interface, further reducing contact resistance. Optionally, the softening points of the bismuth-based and tellurium-based glass powders are each independently 380~450℃, and the average particle size is each independently 0.5~2μm.

[0050] In one embodiment of this application, the mass ratio of the first aluminum powder to the silver-coated aluminum powder is 1:(0.3~1); the ratio of the total mass of the first aluminum powder and the silver-coated aluminum powder, the mass of the glass powder, and the mass of the laser-sensitive additive is (65~85):(3~8):(0.5~5).

[0051] Controlling the mass ratio of the first aluminum powder to the silver-coated aluminum powder within the aforementioned range not only helps to further reduce raw material costs but also helps to optimize the conductive network and control the depth of aluminum diffusion. Controlling the total mass ratio of the first aluminum powder and the silver-coated aluminum powder, the mass ratio of the glass powder, and the mass ratio of the laser-sensitive additive within the aforementioned range helps to achieve low sheet resistance and high conductivity in the electrode, and allows the glass powder to better soften and fill voids and provide adhesion during sintering. Simultaneously, it helps the laser-sensitive additive to better regulate local heating to promote interfacial reactions, thereby further reducing contact resistance while maintaining the mechanical strength of the electrode, and ultimately improving the photoelectric conversion efficiency of the back-contact solar cell.

[0052] In one embodiment of this application, the sintering is laser sintering, the laser wavelength of the laser sintering is 800~1100nm, the laser spot diameter of the laser sintering is 30~100μm, the laser sintering power is 20~80W, and the laser sintering scanning speed is 500~3000mm / s.

[0053] Controlling the laser wavelength during laser sintering within the aforementioned range helps match its absorption peak with that of the laser-sensitive additive, thereby improving photothermal conversion efficiency. Controlling the laser spot diameter within the aforementioned range helps improve the uniformity of the sintered area. Controlling the laser sintering power and scanning speed within the aforementioned range helps regulate the heat input density, reducing thermal damage to the silicon substrate, deep aluminum diffusion, or silver migration caused by excessive energy, thus forming electrodes with low contact resistance and high adhesion. Laser sintering is performed in a nitrogen or argon atmosphere with an oxygen content <100 ppm.

[0054] In one embodiment of this application, the power of the first laser sintering is 40~60W, and the scanning speed of the first laser sintering is 1000~2000mm / s; the power of the second laser sintering is 50~80W, and the scanning speed of the second laser sintering is 800~1500mm / s.

[0055] This application achieves precise control of electrode performance in different regions of the battery substrate through differentiated parameter adjustment, thereby ensuring that the diffusion depth of aluminum in the first region is greater than that in the second region. Controlling the power and scanning speed of the first laser sintering within the aforementioned range helps to ensure uniform aluminum diffusion, forming a stable back field and ohmic contact, while reducing excessive thermal damage. Controlling the power and scanning speed of the second laser sintering within the aforementioned range helps to fully melt the glass powder through higher energy density and promotes tight wetting of the silver-coated aluminum powder with the substrate, forming a dense and low-resistance interface layer, while simultaneously controlling the depth of aluminum diffusion through rapid melting and solidification.

[0056] After the aforementioned partitioned sintering, a first electrode is formed in the first region, and a second electrode is formed in the second region; both the first and second electrodes are independently interdigitated electrodes. The aluminum diffusion depth in the first electrode is 1~3μm, and its deeper diffusion creates a strong aluminum back field effect, which helps reflect minority carriers and reduce contact resistance. The aluminum diffusion depth in the second electrode is 0.1~0.5μm, which helps maintain good ohmic contact, improves minority carrier lifetime, and thus improves the photoelectric conversion efficiency of the back contact solar cell.

[0057] In one embodiment of this application, the annealing temperature is 350~450℃ and the annealing time is 5~20min; and / or, the second drying temperature is 100~150℃ and the second drying time is 5~15min.

[0058] Controlling the annealing temperature and time within the above range helps reduce thermal stress and promotes a denser sintering interface between the metal particles and glass powder, while controlling the diffusion of aluminum on the silicon surface to form good ohmic contact. Controlling the second drying temperature and time within the above range helps remove solvent from the conductive paste, reducing electrode cracking or leaks caused by rapid solvent evaporation, thereby improving film integrity.

[0059] In another typical embodiment of this application, a back-contact solar cell is provided, which is prepared by the back-contact solar cell preparation method described above.

[0060] The electrodes in the back-contact solar cells prepared by the above method have high conductivity and good mechanical adhesion, which can effectively reduce series resistance and thus improve the photoelectric conversion efficiency of the back-contact solar cells.

[0061] In another typical embodiment of this application, a stacked battery is provided, which includes a top battery and a bottom battery, wherein the bottom battery is the aforementioned back-contact solar cell.

[0062] The tandem solar cell, including the aforementioned back-contact solar cell (as the bottom cell), can more fully absorb long-wavelength light and reduce carrier loss, thereby effectively matching the spectral effect of the top cell and thus improving the overall photoelectric conversion efficiency of the tandem solar cell.

[0063] In another typical embodiment of this application, a photovoltaic module is provided, including a battery string, an encapsulating film, and a cover plate; the battery string is formed by connecting multiple back-contact solar cells or stacked cells as described above; the encapsulating film is used to cover the surface of the battery string; and the cover plate is used to cover the surface of the encapsulating film away from the battery string.

[0064] Photovoltaic modules, including those with back-contact solar cells or tandem cells, can improve photoelectric conversion efficiency while reducing manufacturing costs. Furthermore, the protection provided by the encapsulating film and cover plate gives the cells high mechanical strength and good environmental adaptability in long-term outdoor environments, thus enabling the photovoltaic modules to maintain high photoelectric conversion efficiency while having a longer service life.

[0065] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0066] Example 1

[0067] Preparation of silver-coated aluminum powder: Second aluminum powder (pure aluminum powder) was subjected to a displacement reaction at 50°C for 60 min in a plating solution (silver nitrate solution) with a pH of 10. The mixture was then filtered and dried to obtain silver-coated aluminum powder. The silver-coated aluminum powder consists of an aluminum core and a silver layer coating the outer surface of the aluminum core. The D50 particle size of the silver-coated aluminum powder is 3.5 μm, and the thickness of the silver layer is 100 nm.

[0068] Preparation of glass powder: By weight, the bismuth-based glass powder consists of 50 parts Bi2O3, 25 parts B2O3, 15 parts ZnO, 10 parts BaO and 2 parts Al2O3. After melting, water quenching and grinding, glass powder with an average particle size of 1 μm and a softening point of 420℃ is obtained.

[0069] Preparation of the first aluminum powder: Pure spherical aluminum powder raw material is heat-treated at 200°C for 60 minutes in an oxygen atmosphere to generate aluminum oxide on the outer surface of the pure aluminum powder, forming a first passivation layer with a thickness of 10 nm, and obtaining aluminum powder with a first surface passivation and a D50 particle size of 2 μm.

[0070] The conductive paste, by weight, comprises: 50 parts of first aluminum powder (aluminum powder after first surface passivation), 25 parts of silver-coated aluminum powder, 6 parts of bismuth-based glass powder, 3 parts of laser-sensitive additive (nano-zinc indium oxide with a D50 particle size of 50 nm), 20 parts of organic carrier, and 1 part of additives (dispersant BYK-110, leveling agent BYK-358N, and thixotropic agent fumed silica in a mass ratio of 0.5:0.2:0.3). Preparation of the conductive paste: The resin (ethyl cellulose and acrylic resin in a mass ratio of 3:1) is dissolved in a solvent (terpineol and diethylene glycol butyl ether acetate in a mass ratio of 4:1), mixed at 80°C for 3 hours, cooled, and filtered to obtain the organic carrier. The first aluminum powder, silver-coated aluminum powder, glass powder, laser-sensitive additives, auxiliaries and organic carrier are mixed and ground to a fineness of 6μm by a three-roll mill to obtain a ground slurry. The ground slurry is then sieved through a 300-mesh screen and vacuum degassed for 50 minutes to obtain a conductive slurry.

[0071] Conductive paste was printed onto the surface of a silicon substrate for a BC battery to form an interdigitated electrode pattern, which was then dried at 130°C for 10 minutes. The surface of the battery substrate was divided into alternating first (P-region) and second (N-region) areas. The first region of the battery substrate was subjected to a first laser sintering to form the first electrode. The first laser sintering used a power of 50W, a scanning speed of 1500mm / s, a spot diameter of 50μm, and a laser wavelength of 900nm. The second region of the battery substrate was then subjected to a second laser sintering to form the second electrode. The second laser sintering used a power of 65W, a scanning speed of 1200mm / s, a spot diameter of 50μm, and a laser wavelength of 900nm. The laser sintering atmosphere was argon. After laser sintering, the aluminum diffusion depth of the first electrode in the first region was 2μm, and the aluminum diffusion depth of the second electrode in the second region was 0.2μm, resulting in the sintered battery.

[0072] The sintered cells were placed in a tube furnace and annealed at 400°C for 15 minutes under a nitrogen atmosphere. They were then cooled to room temperature in the furnace to obtain a back-contact solar cell, the structure of which is shown below. Figure 1 As shown, the back-contact solar cell includes a silicon substrate 1, on which a first region and a second region are alternately divided. The first region includes a first passivation stack 2 and a first electrode 3, and the second region includes a second passivation stack 4 and a second electrode 5.

[0073] Example 2

[0074] Preparation of silver-coated aluminum powder: Second aluminum powder (pure aluminum powder) was subjected to a displacement reaction at 55°C for 45 min in a plating solution (silver ammonia solution) with a pH of 9. The mixture was then filtered and dried to obtain silver-coated aluminum powder. The silver-coated aluminum powder consists of an aluminum core and a silver layer coating the outer surface of the aluminum core. The D50 particle size of the silver-coated aluminum powder is 2.5 μm, and the thickness of the silver layer is 50 nm.

[0075] Preparation of glass powder: By weight, the bismuth-based glass powder consists of 40 parts Bi2O3, 15 parts B2O3, 10 parts ZnO, 5 parts BaO and 1 part Al2O3. After melting, water quenching and grinding, glass powder with an average particle size of 0.5 μm and a softening point of 380℃ is obtained.

[0076] Preparation of the first aluminum powder: Pure spherical aluminum powder raw material is heat-treated at 150°C for 30 minutes in an oxygen atmosphere to generate aluminum oxide on the outer surface of the pure aluminum powder, forming a first passivation layer with a thickness of 5nm, and obtaining aluminum powder with a first surface passivation and a D50 particle size of 1.5μm.

[0077] The conductive paste, by weight, comprises: 65 parts of first aluminum powder (aluminum powder after first surface passivation) and silver-coated aluminum powder (mass ratio of 1:1), 3 parts of bismuth-based glass powder, 0.5 parts of laser-sensitive additive (nano-indium tin oxide with a D50 particle size of 20 nm), 12 parts of organic carrier, and 0.5 parts of additives (dispersant BYK-110, leveling agent BYK-358N, and thixotropic agent fumed silica, mass ratio of 0.2:0.2:0.1). Preparation of the conductive paste: The resin (ethyl cellulose and acrylic resin, mass ratio of 2:1) is dissolved in a solvent (terpineol and diethylene glycol butyl ether acetate, mass ratio of 3:1), mixed at 70°C for 3 hours, cooled, and filtered to obtain the organic carrier. The first aluminum powder, silver-coated aluminum powder, glass powder, laser-sensitive additives, auxiliaries and organic carrier are mixed and ground to a fineness of 8μm by a three-roll mill to obtain a ground slurry. The ground slurry is then sieved through a 250-mesh screen and vacuum degassed for 30 minutes to obtain a conductive slurry.

[0078] Conductive paste was printed onto the surface of a silicon substrate for a BC battery to form an interdigitated electrode pattern, which was then dried at 100°C for 15 minutes. The surface of the battery substrate was divided into alternating first (P-region) and second (N-region) areas. The first region of the battery substrate was subjected to a first laser sintering to form the first electrode. The first laser sintering used a power of 40W, a scanning speed of 1000mm / s, a spot diameter of 30μm, and a laser wavelength of 800nm. The second region of the battery substrate was then subjected to a second laser sintering to form the second electrode. The second laser sintering used a power of 50W, a scanning speed of 800mm / s, a spot diameter of 50μm, and a laser wavelength of 800nm. The laser sintering atmosphere was argon. After laser sintering, the aluminum diffusion depth of the first electrode in the first region was 1μm, and the aluminum diffusion depth of the second electrode in the second region was 0.1μm, resulting in the sintered battery.

[0079] After sintering, the cells are placed in a tube furnace and annealed at 350°C for 20 minutes under a nitrogen atmosphere. The cells are then cooled to room temperature in the furnace to obtain a back-contact solar cell.

[0080] Example 3

[0081] Preparation of silver-coated aluminum powder: Second aluminum powder (pure aluminum powder) was subjected to a displacement reaction at 45°C for 75 min in a plating solution (silver ammonia solution) with a pH of 11. The mixture was then filtered and dried to obtain silver-coated aluminum powder. The silver-coated aluminum powder consists of an aluminum core and a silver layer coating the outer surface of the aluminum core. The D50 particle size of the silver-coated aluminum powder is 4.5 μm, and the thickness of the silver layer is 150 nm.

[0082] Preparation of glass powder: By weight, the components of tellurium-based glass powder include 50 parts of TeO2, 20 parts of Bi2O3, 15 parts of ZnO, 4 parts of Li2O and 3 parts of Na2O. After melting, water quenching and grinding, glass powder with an average particle size of 0.5 μm and a softening point of 400℃ is obtained.

[0083] Preparation of the first aluminum powder: Pure aluminum powder raw material was immersed in a 0.3% (w / w) silane coupling agent (KH-550) ethanol solution, stirred at 25°C for 60 min, and then filtered and dried to form a second passivation layer with a thickness of 15 nm on the outer surface of the pure aluminum powder, resulting in aluminum powder with a second surface passivation and a D50 particle size of 3.5 μm.

[0084] The conductive paste, by weight, comprises: 85 parts of first aluminum powder (second surface passivated aluminum powder) and silver-coated aluminum powder (mass ratio 1:0.8), 8 parts of bismuth-based glass powder, 5 parts of laser-sensitive additive (nano-strontium titanate with a D50 particle size of 100 nm), 12 parts of organic carrier, and 2 parts of additives (dispersant BYK-110, leveling agent BYK-358N, and thixotropic agent fumed silica, mass ratio 1:0.5:0.5). Preparation of the conductive paste: The resin (ethyl cellulose and acrylic resin, mass ratio 4:1) is dissolved in a solvent (terpineol and diethylene glycol butyl ether acetate, mass ratio 5:1), mixed at 85°C for 2 hours, cooled, and filtered to obtain the organic carrier. The first aluminum powder, silver-coated aluminum powder, glass powder, laser-sensitive additives, auxiliaries and organic carrier are mixed and ground to a fineness of 7μm by a three-roll mill to obtain a ground slurry. The ground slurry is then sieved through a 300-mesh screen and vacuum degassed for 60 minutes to obtain a conductive slurry.

[0085] Conductive paste was printed onto the surface of a silicon substrate for a BC battery to form an interdigitated electrode pattern, which was then dried at 150°C for 5 minutes. The surface of the battery substrate was divided into alternating first (P-region) and second (N-region) areas. The first region of the battery substrate was subjected to a first laser sintering process to form the first electrode. The first laser sintering parameters were 60W power, 2000mm / s scanning speed, 100μm spot diameter, and 1064nm laser wavelength. The second region of the battery substrate was then subjected to a second laser sintering process to form the second electrode. The second laser sintering parameters were 80W power, 1500mm / s scanning speed, 80μm spot diameter, and 1064nm laser wavelength. The laser sintering atmosphere was argon. After laser sintering, the aluminum diffusion depth of the first electrode in the first region was 3μm, and the aluminum diffusion depth of the second electrode in the second region was 0.5μm, resulting in the sintered battery.

[0086] After sintering, the cells are placed in a tube furnace and annealed at 350°C for 20 minutes under a nitrogen atmosphere. The cells are then cooled to room temperature in the furnace to obtain a back-contact solar cell.

[0087] Example 4

[0088] The difference from Example 1 is in the preparation of the first aluminum powder: pure spherical aluminum powder raw material is heat-treated at 250°C for 90 minutes in an oxygen atmosphere to generate aluminum oxide on the outer surface of the pure aluminum powder, forming a first passivation layer with a thickness of 15nm, thus obtaining aluminum powder with the first surface passivation, and finally obtaining a back contact solar cell.

[0089] Example 5

[0090] The difference from Example 1 is in the preparation of the first aluminum powder: pure spherical aluminum powder raw material is heat-treated at 120°C for 120 minutes in an oxygen atmosphere to generate aluminum oxide on the outer surface of the pure aluminum powder, forming a first passivation layer with a thickness of 20nm, thus obtaining aluminum powder with the first surface passivation, and finally obtaining a back contact solar cell.

[0091] Example 6

[0092] The difference from Example 1 is that the first aluminum powder is pure spherical aluminum powder, without surface passivation treatment, and finally a back contact solar cell is obtained.

[0093] Example 7

[0094] The difference from Example 1 lies in the preparation of the silver-coated aluminum powder: Second aluminum powder (pure aluminum powder) was subjected to a displacement reaction at 45°C for 65 minutes in an immersion solution (silver nitrate solution) with a pH of 11, followed by filtration and drying to obtain the silver-coated aluminum powder. The silver-coated aluminum powder consists of an aluminum core and a silver layer coating the outer surface of the aluminum core. The D50 particle size of the silver-coated aluminum powder is 3.5 μm, and the thickness of the silver layer is 50 nm, ultimately resulting in a back-contact solar cell.

[0095] Example 8

[0096] The difference from Example 1 lies in the preparation of the silver-coated aluminum powder: Second aluminum powder (pure aluminum powder) was subjected to a displacement reaction at 65°C for 30 minutes in an immersion solution (silver nitrate solution) with a pH of 8, followed by filtration and drying to obtain the silver-coated aluminum powder. The silver-coated aluminum powder consists of an aluminum core and a silver layer coating the outer surface of the aluminum core. The D50 particle size of the silver-coated aluminum powder is 3.5 μm, and the thickness of the silver layer is 30 nm, ultimately resulting in a back-contact solar cell.

[0097] Example 9

[0098] The difference from Example 1 is that the mass ratio of the first aluminum powder to the silver-coated aluminum powder is 1:0.3, and the mass ratio of the total mass of the first aluminum powder and the silver-coated aluminum powder, the mass of the glass powder, and the mass of the laser-sensitive additive is 65:3:0.5, ultimately resulting in a back-contact solar cell.

[0099] Example 10

[0100] The difference from Example 1 is that the mass ratio of the first aluminum powder to the silver-coated aluminum powder is 1:0.1, and the mass ratio of the total mass of the first aluminum powder and the silver-coated aluminum powder, the mass of the glass powder, and the mass of the laser-sensitive additive is 65:3.4:0.1, ultimately resulting in a back-contact solar cell.

[0101] Example 11

[0102] The difference from Example 1 is that the conditions for the first laser sintering are: power of 40W, scanning speed of 1000mm / s, and aluminum diffusion depth of the first electrode in the first region of 1μm; the conditions for the second laser sintering are: power of 80W, scanning speed of 1500mm / s, and aluminum diffusion depth of the second electrode in the second region of 0.5μm, ultimately resulting in a back contact solar cell.

[0103] Example 12

[0104] The difference from Example 1 is that the conditions for the first laser sintering are: power of 30W, scanning speed of 2000mm / s, and aluminum diffusion depth of the first electrode in the first region of 0.5μm; the conditions for the second laser sintering are: power of 40W, scanning speed of 600mm / s, and aluminum diffusion depth of the second electrode in the second region of 0.05μm, ultimately resulting in a back contact solar cell.

[0105] Example 13

[0106] The difference from Example 1 is that the conditions for the first laser sintering are: power of 70W, scanning speed of 2500mm / s, and aluminum diffusion depth of the first electrode in the first region of 4μm; the conditions for the second laser sintering are: power of 95W, scanning speed of 2000mm / s, and aluminum diffusion depth of the second electrode in the second region of 1.5μm, ultimately resulting in a back contact solar cell.

[0107] Comparative Example 1

[0108] The difference from Example 1 is that the conductive material is silver paste, and the back contact solar cell is prepared by screen printing.

[0109] Comparative Example 2

[0110] The difference from Example 1 is that the conductive material is pure aluminum paste (without silver-coated aluminum powder), and laser sintering is replaced by belt furnace sintering (peak temperature of 780°C and sintering time of 60s), which finally produces a back contact solar cell.

[0111] Comparative Example 3

[0112] The difference from Example 1 is that the conditions for the first laser sintering are: 65W, scanning speed of 1200mm / s, and aluminum diffusion depth of the first electrode in the first region of 0.5μm; the conditions for the second laser sintering are: power of 50W, scanning speed of 1500mm / s, and aluminum diffusion depth of the second electrode in the second region of 1μm, ultimately resulting in a back contact solar cell.

[0113] Test method:

[0114] Contact resistance: Tested according to T / CPIA 0051-2023 "Test method for contact resistivity of metal electrodes of crystalline silicon photovoltaic cells - transmission line model method (TLM)".

[0115] Electrode adhesion: Tested according to GB / T 29195-2012 "General Specification for Crystalline Silicon Solar Cells for Ground Use".

[0116] Battery conversion efficiency: Tested in accordance with GB / T 34160-2017 "Test Method for Photovoltaic Conversion Efficiency of Ground-mounted Photovoltaic Modules" and IEC 60904 series standards.

[0117] Aluminum diffusion depth test of the electrode: Secondary ion mass spectrometry (SIMS) was used to perform elemental depth analysis on the interface between the electrode and the silicon substrate. The depth at which the aluminum element signal intensity drops to half of the peak value was recorded as the aluminum diffusion depth.

[0118] The electrodes and back-contact solar cells of the above embodiments and comparative examples were tested for performance. Twenty cells were used for each example, and the average value was calculated. The test results are shown in Table 1.

[0119] Table 1

[0120]

[0121] in, Figure 2 This is a schematic diagram of the structure of a tandem battery. Figure 2 As can be seen from the diagram, the tandem solar cell includes a top cell 6 and a bottom cell 7, with the bottom cell 7 being the aforementioned back-contact solar cell.

[0122] Figure 3 This is a schematic diagram of the structure of a photovoltaic module. Figure 3As can be seen from the diagram, the photovoltaic module includes a battery string 8, an encapsulating film 9, and a cover plate 10; the battery string 8 is formed by connecting multiple back-contact solar cells or stacked cells as described above; the encapsulating film 9 is used to cover the surface of the battery string 8, and the cover plate 10 is used to cover the surface of the encapsulating film 9 that is away from the battery string 8.

[0123] As shown above, Comparative Example 1 uses silver paste, resulting in higher silver consumption and therefore higher costs. Comparative Example 2 uses pure aluminum paste combined with traditional furnace firing, leading to uncontrolled aluminum diffusion and the presence of aluminum spikes (aluminum peaks) penetrating the PN junction. This causes increased leakage current, a decrease in fill factor, and the high resistivity and contact resistance of the aluminum electrode further contribute to the presence of aluminum spikes. In Comparative Example 3, the power of the first laser sintering is greater than that of the second laser sintering, while the scanning speed of the first laser sintering is lower than that of the second laser sintering. This results in insufficient aluminum diffusion depth in the first region, failing to form an effective aluminum back field. In the second region, excessive aluminum diffusion damages the minority carrier lifetime, ultimately manifesting as high contact resistance and decreased conversion efficiency. This demonstrates that laser power and scanning speed must be matched to the functional requirements of the corresponding region.

[0124] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0125] The back-contact solar cell fabrication process provided in this application, through the combination of the aforementioned conductive materials and a zoned laser sintering process, can significantly improve the metallization quality and photoelectric conversion efficiency of BC cells. Specifically, this application uses aluminum-based materials instead of traditional silver-based materials, which can significantly reduce costs. By introducing silver-coated aluminum powder into the conductive material, and utilizing the silver layer as a conductive bridge and sintering promoter, the contact resistance can be reduced while simultaneously lowering costs. Adding laser-sensitive additives can enhance the absorption of near-infrared lasers by the conductive material, thereby achieving localized and precise heating. During the sintering process, the glass powder melts first, and the resulting liquid glass erodes the passivation layer on the silicon substrate surface, opening channels for metal contact. The silver layer of the silver-coated aluminum powder then melts and wets the exposed silicon surface through the molten glass. Finally, the aluminum core melts and diffuses into the silicon substrate through the molten silver layer to form a silver-aluminum-silicon eutectic alloy contact. Laser sintering allows for flexible adjustment of the aluminum diffusion depth, avoiding the problem of "aluminum spikes," thereby further improving the conductivity of the electrodes while ensuring low silver consumption. By performing zoned sintering on the battery substrate surface, with different laser sintering powers and scanning speeds for different regions, the electrode performance of the first and second regions can be controlled through differentiated laser parameters, resulting in a greater aluminum diffusion depth in the first region than in the second region. The first laser sintering process in the first region employs relatively low power and a relatively high scanning speed, utilizing the liquid interface formed by the melting of the silver shell to promote moderate aluminum diffusion and create an ohmic contact with low contact resistance. The second laser sintering process in the second region employs relatively high power and a relatively low scanning speed, using rapid heat input to instantly densify the silver shell, forming a physical barrier and restricting aluminum diffusion into the silicon, effectively preventing aluminum penetration. This sintering process allows the first region to maintain good conductivity while better protecting the surface passivation quality of the second region, thereby further improving the open-circuit voltage and fill factor of the battery. In summary, the back-contact solar cell fabrication process of this application can reduce the amount of silver used, and through the above sintering process optimization, achieve high-performance metallization, enabling large-scale production of BC batteries.

[0126] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fabrication process for a back-contact solar cell, characterized in that, A battery substrate is obtained, and conductive material is printed on the battery substrate. Then, a first drying, sintering and annealing process is performed to form an electrode, thereby obtaining the back contact solar cell. The conductive material includes first aluminum powder, silver-coated aluminum powder, glass powder, and laser-sensitive additives. The silver-coated aluminum powder includes an aluminum core and a silver layer covering the outer surface of the aluminum core; The laser-sensitive additive comprises a composite metal oxide, wherein the metal element in the composite metal oxide is selected from at least two of indium, tin, zinc, titanium, and strontium. The surface of the battery substrate is divided into alternating first and second regions. The first region is subjected to a first laser sintering, and the second region is subjected to a second laser sintering. The power of the first laser sintering is less than that of the second laser sintering, and the scanning speed of the first laser sintering is greater than that of the second laser sintering.

2. The fabrication process of the back-contact solar cell according to claim 1, characterized in that, The first aluminum powder is aluminum powder with a first surface passivation. The preparation method of the first surface passivated aluminum powder includes: heat-treating the aluminum powder raw material to form a first passivation layer on the outer surface of the aluminum powder raw material; the heat treatment atmosphere is an oxygen-containing atmosphere, the heat treatment temperature is 150~250℃, and the heat treatment time is 30~90min; the first passivation layer includes aluminum oxide, and the thickness of the first passivation layer is 5~15nm.

3. The fabrication process of the back-contact solar cell according to claim 1, characterized in that, The first aluminum powder is aluminum powder with a second surface passivation. The preparation method of the second surface passivated aluminum powder includes: immersing the aluminum powder raw material in a passivation reagent and stirring, then filtering and drying it to form a second passivation layer on the outer surface of the aluminum powder raw material; the passivation reagent is a solution containing a silane coupling agent and / or a phosphate ester, and the mass concentration of the passivation reagent is 0.1~0.5%; the stirring temperature is 20~30℃, and the stirring time is 20~60min; the thickness of the second passivation layer is 5~15nm.

4. The fabrication process of the back-contact solar cell according to claim 1, characterized in that, The first aluminum powder is spherical aluminum powder, and the D50 particle size of the first aluminum powder is 1.5~3.5μm.

5. The fabrication process of a back-contact solar cell according to any one of claims 1 to 4, characterized in that, The silver-coated aluminum powder is obtained by immersing a second aluminum powder in an immersion plating solution to undergo a displacement reaction, and depositing the silver layer on the surface of the second aluminum powder; The immersion plating solution is silver nitrate and / or silver ammonia solution, and the pH value of the immersion plating solution is 9-11; the temperature of the displacement reaction is 45-55℃, and the time of the displacement reaction is 45-75 min.

6. The fabrication process of a back-contact solar cell according to any one of claims 1 to 4, characterized in that, The D50 particle size of the silver-coated aluminum powder is 2.5~4.5μm; the thickness of the silver layer in the silver-coated aluminum powder is 50~150nm.

7. The fabrication process of a back-contact solar cell according to any one of claims 1 to 4, characterized in that, The laser-sensitive additive is selected from any one or more of nano-indium tin oxide, nano-indium zinc oxide, and nano-strontium titanate, and the D50 particle size of the laser-sensitive additive is 20~100nm.

8. The fabrication process of a back-contact solar cell according to any one of claims 1 to 4, characterized in that, The glass powder is bismuth-based glass powder and / or tellurium-based glass powder; wherein, by weight, the bismuth-based glass powder comprises 40-60 parts of Bi₂O₃, 15-30 parts of B₂O₃, 10-20 parts of ZnO, 5-15 parts of BaO, and 1-5 parts of Al₂O₃; and by weight, the tellurium-based glass powder comprises 45-65 parts of TeO₂, 15-30 parts of Bi₂O₃, 10-20 parts of ZnO, 2-8 parts of Li₂O, and 1-5 parts of Na₂O.

9. The fabrication process of a back-contact solar cell according to any one of claims 1 to 4, characterized in that, The mass ratio of the first aluminum powder to the silver-coated aluminum powder is 1:(0.3~1); the mass ratio of the total mass of the first aluminum powder and the silver-coated aluminum powder, the mass of the glass powder and the mass of the laser-sensitive additive is (65~85):(3~8):(0.5~5).

10. The fabrication process of a back-contact solar cell according to any one of claims 1 to 4, characterized in that, The sintering is laser sintering, the laser wavelength of the laser sintering is 800~1100nm, the laser spot diameter of the laser sintering is 30~100μm, the laser sintering power is 20~80W, and the laser sintering scanning speed is 500~3000mm / s.

11. The fabrication process of the back-contact solar cell according to claim 10, characterized in that, The power of the first laser sintering is 40~60W, and the scanning speed of the first laser sintering is 1000~2000mm / s; the power of the second laser sintering is 50~80W, and the scanning speed of the second laser sintering is 800~1500mm / s.

12. The fabrication process of a back-contact solar cell according to any one of claims 1 to 4, characterized in that, The annealing temperature is 350~450℃, and the annealing time is 5~20min; and / or, the first drying temperature is 100~150℃, and the first drying time is 5~15min.

13. A back-contact solar cell, characterized in that, The back-contact solar cell is prepared by the back-contact solar cell preparation process according to any one of claims 1 to 12.

14. A stacked battery, the stacked battery comprising a top battery and a bottom battery, characterized in that, The bottom cell is the back-contact solar cell as described in claim 13.

15. A photovoltaic module, characterized in that, include: A battery string is formed by connecting multiple back-contact solar cells as described in claim 13, or stacked cells as described in claim 14. An encapsulating film is used to cover the surface of the battery string; as well as A cover plate is used to cover the surface of the encapsulating film that faces away from the battery string.

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