Self-repairing low-temperature silver paste for space photovoltaic and preparation method thereof

Abstract

The application provides a self-repairing low-temperature silver paste for space photovoltaics and a preparation method thereof. The self-repairing low-temperature silver paste for space photovoltaics comprises the following components in percentage by weight: modified silver powder 92-97 wt%, organic resin 3-8 wt%, organic solvent 1-6 wt% and auxiliary agent 0.1-1 wt%. The modified silver powder is a compound system of modified flaky silver powder, modified spherical silver powder and modified nano silver powder, the organic resin is a self-repairing resin containing a dynamic covalent bond in a main chain or a side chain, the modified silver powder forms a dynamic reversible bond with the organic resin, and the dynamic reversible bond reversibly breaks and recombines under thermal stimulation or high radiation. The three-level silver powder grading of flaky / submicron / nano is adopted to realize self-repairing of a conductive path. The silver powder is surface-functionalized through a dynamic covalent bond, and the resin forms a triple self-repairing of an interface-matrix-conductive phase to significantly improve the structural stability. The overall system is adapted to the environment of high vacuum, strong radiation and severe temperature change in space, and has high electrode crack repair efficiency and long service life.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic materials, and in particular to a self-healing low-temperature silver paste for space photovoltaics and its preparation method. Background Technology

[0002] In recent years, the low-Earth orbit (LEO) satellite and space photovoltaic (SPV) industries have developed rapidly, with P-type HJTs (Heterojunction with Intrinsic Thin Layer), perovskite, and tandem solar cells becoming the mainstream technologies for next-generation space photovoltaics. However, low-temperature silver paste, as a core electrode material, remains ill-suited to the extreme space environment, becoming a key bottleneck restricting battery performance and on-orbit lifespan. Therefore, the core bottleneck of existing space photovoltaic low-temperature silver pastes lies in the inherent contradiction between dispersibility and conductivity, making them prone to microcracks and interface failures under extreme environments. Furthermore, they lack a self-healing mechanism for active regulation, preventing them from meeting the long-life requirements of aerospace applications. Traditional low-temperature silver pastes suffer from inherent defects where dispersibility and conductivity contradict each other. They are prone to cracking and failure under extreme thermal cycling, high-energy irradiation, and high-vacuum environments in space, and lack self-healing capabilities for on-orbit space photovoltaics; damage leads to electrode failure. Current industry improvements largely focus on material formulation and process optimization, failing to address the core contradiction at the mechanistic level.

[0003] Among existing self-healing materials for space photovoltaics, polymer materials have limited repair cycles and are prone to failure in the vacuum environment of space; ceramic materials have stringent triggering conditions and are difficult to adapt to low-temperature sintering processes; while metallic materials can achieve atomic rearrangement and self-healing, they lack controllable response and active repair mechanisms. Related research shows that intrinsic self-healing materials for space photovoltaics can achieve multiple repairs through chemical bond breaking and recombination, and silver-based composite materials can achieve efficient self-healing for space photovoltaics and restore conductive pathways through atomic migration and rearrangement under radiation or thermal stimulation. However, there are currently no reports on combining intrinsic self-healing mechanisms for space photovoltaics with silver paste systems to solve the problem of microcracks in space photovoltaic electrodes. Based on this, a low-temperature silver paste for space photovoltaics is being developed that combines excellent dispersion conductivity, extreme environment stability, and on-orbit intrinsic self-healing capabilities. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a self-healing low-temperature silver paste for space photovoltaics and its preparation method, which can solve the problems that existing low-temperature silver pastes for space photovoltaics are prone to microcracks and interface failures in extreme environments and lack an active self-healing mechanism.

[0005] One embodiment of the present invention provides a self-healing low-temperature silver paste for space photovoltaics. By weight percentage, the silver paste comprises the following components: 92-97 wt% modified silver powder, 3-8 wt% organic resin, 1-6 wt% organic solvent, and 0.1-1 wt% additives. The modified silver powder is a composite system of modified flake silver powder, modified spherical silver powder, and modified nano-silver powder. The organic resin is a self-healing resin containing dynamic covalent bonds. The modified silver powder and the organic resin form dynamic reversible bonds, which undergo reversible breakage and recombination under thermal stimulation or high radiation.

[0006] Further, by weight percentage, the modified silver powder comprises the following components: 60-80 wt% modified flake silver powder, 15-25 wt% modified spherical silver powder, and 5-15 wt% modified nano silver powder.

[0007] Furthermore, the flake-shaped silver powder has a particle size D50 of 1.5-3 μm and a specific surface area of ​​0.3-0.8 m². 2 / g, tap density 3.0-4.5g / ml; the spherical silver powder has a particle size D50 of 0.3-0.8μm and a specific surface area of ​​1.2-2.5m². 2 / g, tap density 4.0-5.5g / ml; the nano silver powder has a particle size D50 of 20-50nm and a specific surface area of ​​5-12m². 2 / g, tap density 2.0-3.5g / ml.

[0008] Furthermore, the preparation method of the modified silver powder includes three-step surface modification: purification and impurity removal of multi-graded silver powder, activation with coupling agent, and functionalization of dynamic bonds.

[0009] Furthermore, the organic resin includes one or more of flexible thermoplastic acrylic resin, aliphatic polyurethane resin, ethyl cellulose, flexible alicyclic epoxy resin, and low-temperature decomposable silicone resin, and / or other self-healing resins containing dynamic covalent bonds in their molecular chains.

[0010] Furthermore, the dynamic covalent bond includes one or more of borate ester bonds, imine bonds, acylhydrazone bonds, and disulfide bonds. The dynamic covalent bond can be broken and rebonded at 120-180°C, and the residual carbon content is ≤1.0wt%. The dynamic bond functionalization treatment grafts the dynamic covalent bond surface of the organic resin onto silver powder to form one or more of the dynamic reversible bonds.

[0011] Furthermore, the organic solvent includes one or more of terpineol, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether, and propylene glycol methyl ether acetate; the organic solvent is completely volatile at 150-200°C.

[0012] Furthermore, the additives include one or more of curing agents, dispersants, and coupling agents; the dispersants include one or more of polyacrylate dispersants and phosphate dispersants; and the coupling agents include one or more of silane coupling agents and titanate coupling agents.

[0013] Furthermore, the curing agent is one or more of the following: modified aliphatic amine curing agent, low-temperature acid anhydride curing agent, low molecular weight polyamide curing agent, benzoyl peroxide, tert-butyl peroxide-2-ethylhexanoate, and blocked aliphatic isocyanate; the curing / unsealing temperature of the curing agent is 100-180℃, and the residual carbon content after curing is ≤0.8wt%.

[0014] Another embodiment of the present invention provides a method for preparing a self-healing low-temperature silver paste for space photovoltaics, comprising at least the following steps: S1: The modified silver powder, the organic resin, the organic solvent, and the additives are added to the reaction apparatus and mixed. S2: Stir to ensure that all materials are evenly wetted; S3: Perform three-roll mill grinding with a grinding gap of 10μm-120μm and a grinding speed of 50r / min-400r / min to finally obtain a slurry with a fineness of less than 10μm.

[0015] This invention provides a self-healing low-temperature silver paste for space photovoltaics and its preparation method. The self-healing low-temperature silver paste for space photovoltaics includes modified silver powder, organic resin, organic solvent, and additives. The modified silver powder is a composite system of modified flake silver powder, modified spherical silver powder, and modified nano-silver powder. The organic resin is a self-healing resin with dynamic covalent bonds in its main chain or side chains. The technical solution provided by this invention has the following beneficial effects: (1) A three-level silver powder gradation of sheet / submicron / nano is adopted to construct a dense conductive framework and repair channels. Under radiation and thermal stimulation, nano-silver can migrate, rearrange and conduct to cracks, realizing the self-repair of conductive pathways.

[0016] (2) Silver powder undergoes dynamic covalent surface functionalization, and reversible fracture and recombination occur under extreme conditions. It works in conjunction with the resin to form a triple self-repair mechanism of interface-matrix-conductive phase, which significantly improves structural stability.

[0017] (3) The low-temperature, low-carbon organic system is highly compatible with the powder. Sintering can be completed at ≤200℃. There is no residual carbon barrier, which ensures that the silver particles can migrate and contact fully, taking into account both high conductivity and efficient self-repair.

[0018] (4) The overall system is adapted to the high vacuum, strong radiation and drastic temperature change environment of space. It has high electrode crack repair efficiency and long life, solving the industry pain point that traditional silver paste cannot self-repair. Detailed Implementation

[0019] Specific embodiments of the present invention will now be described in detail. Obviously, the described embodiments are merely a part of the embodiments of the present invention, and not all of them. Based on the description of the present invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present invention.

[0020] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. It should be understood that in the various embodiments of this application, the sequence number of the above processes does not imply the order of execution. Some or all steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. The terminology used in the embodiments of this application is only for the purpose of describing specific embodiments and is not intended to limit this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. The weight of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as µg, mg, g, kg, etc. The terms “first” and “second” are used for descriptive purposes only to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. For example, without departing from the scope of the embodiments of this application, a first XX can also be referred to as a second XX, and similarly, a second XX can also be referred to as a first XX. Thus, a feature defined as “first” or “second” can explicitly or implicitly include one or more of that feature. The “scope” disclosed herein is in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this way are inclusive and composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values ​​are listed as 1 and 2, and if the maximum range values ​​are listed as 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0021] The first aspect of this application is to provide a self-healing low-temperature silver paste for space photovoltaics, which addresses the inherent contradiction between the dispersibility and conductivity of existing low-temperature silver pastes for space photovoltaics from a mechanistic perspective. These pastes are prone to microcracks and interface failures under extreme environments and lack an active self-healing mechanism, thus failing to meet the requirements for long lifespan in aerospace applications.

[0022] The self-healing low-temperature silver paste for space photovoltaics, calculated by weight percentage, comprises the following components: 92-97 wt% modified silver powder, 3-8 wt% organic resin, 1-6 wt% organic solvent, and 0.1-1 wt% additives. The modified silver powder is a composite system of modified flake silver powder, modified spherical silver powder, and modified nano-silver powder. The organic resin is a self-healing resin with dynamic covalent bonds in its main chain or side chains. The modified silver powder and the organic resin form dynamic reversible bonds, which undergo reversible breakage and recombination under thermal stimulation or high radiation. In this embodiment, high radiation can be defined as the strong radiation environment of space. In other embodiments, the low-temperature silver paste for space photovoltaics of the present invention can also be used in other thermally stimulated or high-radiation environments.

[0023] Specifically, based on the percentage of the total weight of the modified silver powder, the modified silver powder comprises the following components: 60-80 wt% modified flake silver powder, 15-25 wt% modified spherical silver powder, and 5-15 wt% modified nano silver powder; wherein the flake silver powder has a particle size D50 of 1.5-3 μm and a specific surface area of ​​0.3-0.8 m². 2 / g, tap density 3.0-4.5g / ml; the spherical silver powder has a particle size D50 of 0.3-0.8μm and a specific surface area of ​​1.2-2.5m². 2 / g, tap density 4.0-5.5g / ml; the nano silver powder has a particle size D50 of 20-50nm and a specific surface area of ​​5-12m². 2 / g, tap density 2.0-3.5g / ml.

[0024] Furthermore, the modified flake silver powder is preferably 70 wt%, the modified spherical silver powder is preferably 20 wt%, and the modified nano silver powder is preferably 10 wt%. At this preferred ratio, the flake silver powder can form a stable and continuous conductive framework, and the spherical silver powder can effectively fill the gaps between the flake silver powders, improving electrode density and structural stability. The nano silver powder, as a self-healing functional phase, has a moderate content, allowing it to migrate and rearrange to microcracks under thermal / radiative stimulation to achieve self-healing of the conductive pathway, without agglomeration due to excessive content, thus ensuring paste dispersibility and printing performance. The synergistic effect of these three components gives the electrode high conductivity, excellent environmental resistance, and efficient self-healing capability, making it ideally suited for the long-life, high-reliability service requirements of space photovoltaics.

[0025] The preparation method of the above-mentioned modified silver powder includes three steps of surface modification: purification and impurity removal of multi-graded silver powder, activation with coupling agent, and dynamic functionalization. The specific preparation steps are as follows: (1) The silver powder is purified and impurity removed; specifically, the purification and impurity removal process includes: ultrasonic washing with ethanol or isopropanol, followed by vacuum low-temperature drying. The purification and impurity removal process can remove adsorbed impurities and free organic matter from the surface of the silver powder, reduce the porosity under vacuum conditions, and improve the bonding strength and interface stability of subsequent surface modification.

[0026] (2) The silver powder after impurity removal is activated by a coupling agent; specifically, the coupling agent includes any one or two of silane coupling agents and mercaptoethyl borate. The activation treatment by the coupling agent can introduce active functional groups on the surface of the silver powder, improve the interfacial compatibility between the silver powder and the organic carrier, inhibit the agglomeration of silver powder, and improve the dispersion stability and printing uniformity of the paste.

[0027] (3) The activated silver powder is subjected to dynamic bond functionalization treatment to obtain modified silver powder with surface-loaded dynamic reversible bonds. Specifically, the dynamic bond functionalization treatment involves grafting any one or more of borate ester bonds, imine bonds, or acylhydrazone bonds onto the surface of the silver powder to form one or more dynamic reversible bonds, which can undergo reversible breakage and recombination under thermal stimulation or high radiation.

[0028] The dynamic bond functionalization treatment can construct a reversible dynamic interface layer on the surface of silver powder, maintain stable dispersion during low-temperature storage and dispersion, and achieve dynamic bond breaking under sintering or radiation stimulation. Dissociation eliminates interfacial barriers and promotes contact sintering of silver particles, fundamentally solving the conductivity reduction problem caused by traditional dispersants. Furthermore, the formed dynamic reversible bonds can break when microcracks appear in the electrode. Recombination drives the migration, rearrangement, and rebonding of nano-silver atoms, enabling intrinsic self-repair of the electrode, restoring the conductive pathway, and improving the structural stability and service life of space photovoltaic electrodes under extreme thermal cycling and high-energy irradiation environments.

[0029] In this invention, the organic resin can form dynamic reversible bonds with modified silver powder, thus the organic resin is a self-healing resin with dynamic covalent bonds in its main chain or side chains. Specifically, the organic resin includes one or more of flexible thermoplastic acrylic resin, aliphatic polyurethane resin, ethyl cellulose, flexible alicyclic epoxy resin, and low-temperature decomposable organosilicon resin, and / or other self-healing resins with dynamic covalent bonds in their molecular chains. The dynamic covalent bonds include one or more of borate ester bonds, imine bonds, acylhydrazone bonds, and disulfide bonds. These dynamic covalent bonds can break and recombine at 120-180℃, and the residual carbon content is ≤1.0 wt%. Dynamic bond functionalization can be understood as grafting the dynamic covalent bond surface of the organic resin onto the silver powder to form one or more dynamic reversible bonds, enabling the silver powder and resin to form a triple self-healing process involving the interface, matrix, and conductive phase, significantly improving structural stability.

[0030] In the high-energy radiation and extreme thermal cycling environment of space, when microcracks develop on the electrodes, the dynamic covalent bonds in the self-healing resin undergo reversible breakage. Under thermal or radiation stimulation, the broken chemical bonds can recombine, thus achieving self-healing of the resin matrix. Furthermore, the chain segment movement of the resin provides channels for the migration and rearrangement of silver nanoparticles, allowing silver nanoparticles to accumulate at the cracks and rebuild conductive pathways, forming a dual synergistic mechanism of resin structural self-healing and silver conductive pathway self-healing. Simultaneously, the low-temperature, low-carbon organic system is highly compatible with silver powder, achieving sintering at ≤200℃ without residual carbon obstruction, ensuring sufficient migration and contact of silver particles. This balances high conductivity and efficient self-healing, significantly improving the reliability and service life of space photovoltaic electrodes in extreme environments. The resulting system is adaptable to the high vacuum, strong radiation, and drastic temperature changes of space, exhibiting high electrode crack repair efficiency and long lifespan, thus addressing the industry pain points of traditional silver pastes being prone to failure and unable to self-heal.

[0031] In this invention, the organic solvent includes one or more of terpineol, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether, and propylene glycol methyl ether acetate. Furthermore, the organic solvent is completely volatile at 150–200°C, leaving no residue and low carbon residue, and does not hinder the migration and self-repair of silver nanoparticles.

[0032] The additives include one or more of curing agents, dispersants, and coupling agents. The dispersants include one or more of polyacrylate dispersants and phosphate dispersants; the coupling agents include one or more of silane coupling agents and titanate coupling agents; the curing agent is selected from one or more of modified aliphatic amine curing agents, low-temperature anhydride curing agents, low molecular weight polyamide curing agents, benzoyl peroxide, tert-butyl peroxide-2-ethylhexanoate, and blocked aliphatic isocyanates, and the curing / unsealing temperature of the curing agent is 100-180℃, with a residual carbon content ≤0.8 wt% after curing.

[0033] In summary, the second aspect of this application provides a method for preparing a self-healing low-temperature silver paste for space photovoltaics with the above-mentioned components, comprising at least the following steps: S1: Add modified silver powder, organic resin, organic solvent, and additives to the reaction apparatus and mix.

[0034] S2: Stir to ensure that all materials are evenly wetted; in some embodiments, the stirring time may be 45 minutes, but it is not limited to this.

[0035] S3: Perform three-roll mill grinding with a grinding gap of 10μm-120μm and a grinding speed of 50r / min-400r / min to finally obtain a slurry with a fineness of less than 10μm as measured by an FOG (Fineness of Grind) scraper fineness gauge.

[0036] First Embodiment In this embodiment, the self-healing low-temperature silver paste for space photovoltaics is made from the following raw materials by weight percentage: Modified flake silver powder (D50 1.5-3.5μm): 65.8%; Modified spherical silver powder (D50 0.3-0.8μm): 18.8%; Modified nano-silver powder (D50 20-50nm): 9.4%; Organic resins: Flexible aliphatic epoxy resin: 1.8%, borate ester bond self-healing resin: 1.2%; Organic solvents: terpineol: 1.5%, propylene glycol methyl ether acetate: 0.6%; Curing agent: Methyl ethyl ketone oxime blocked aliphatic isocyanate crosslinking agent (unsealing temperature 120℃): 0.3%; Additives: Modified polyacrylate dispersant (BASF Dispex® Ultra PA 4530): 0.3%, silane coupling agent KH550: 0.3%.

[0037] Following the above-mentioned method for preparing modified silver powder and the preparation steps S1, S2 and S3, the above-mentioned raw materials were added to a container to prepare a self-healing low-temperature silver paste for space photovoltaics.

[0038] Comparative Example The comparative example used commercially available HJT low-temperature silver paste.

[0039] To further verify the effectiveness of the technical solution provided by the present invention, the low-temperature silver paste of the first embodiment and the comparative example were used as samples. Each sample was printed on the same substrate and relevant property tests were conducted. The test process is as follows: 1. Viscosity test: Take a sample of 15-20g of slurry and use a Brookfield DV2 viscometer and a rotor SC-14 to measure the average viscosity of the slurry under the conditions of 25℃ / 10rpm / 60 seconds.

[0040] 2. Resistivity test: The resistance between the two ends of the electrode is tested using a four-probe ohmmeter.

[0041] 3. Printability Test: The conductive pastes from the above embodiments and comparative examples were printed onto the back of the silicon wafer using screen printing technology. The screen used for printability testing was a knotless, multi-aperture screen (550 mesh / 6μm wire diameter / film thickness 6-7μm / apertures of 14μm, 16μm, and 18μm respectively). The solar cells were dried in an infrared drying oven, and then the printability of the paste was observed with the naked eye and an optical microscope to determine whether there were any broken grids or incomplete prints.

[0042] 4. Aging Test: The silver paste electrode is fixed on a vacuum thermal cycling platform, and simulated extreme conditions in space are applied sequentially to induce controllable microcracks inside and on the surface of the electrode, including: (1) High-energy radiation bombardment: electron irradiation / proton irradiation (selected according to the research system), energy 200 keV, flux 1×10¹ 5 ions / cm², simulating space radiation damage.

[0043] (2) High and low temperature cycle aging: temperature range -180 ℃ ~ 150 ℃, heating and cooling rate 5 ℃ / min, holding temperature for 10 min per cycle, continuous cycle 100-1000 times.

[0044] The results are shown in the following tables. Table 1 summarizes the results of resistivity, viscosity, photoelectric conversion efficiency, and basic printability tests, while Table 2 summarizes the results of aging performance tests.

[0045]

[0046] Table 1 Comparison of Basic Performance

[0047] Table 2 Comparison of Aging Performance As can be seen from Tables 1 and 2, the initial photoelectric conversion efficiency of the low-temperature silver paste in the first embodiment is comparable to that of the conventional low-temperature silver paste in the comparative example. However, after 100, 500, and 1000 accelerated aging tests under simulated extreme space environment (-180 ℃ ~ 150 ℃ thermal cycling, 200 keV high-energy irradiation), the efficiency degradation rate of the first embodiment is consistently significantly lower than that of the comparative example. Traditional low-temperature silver paste (comparative example) exhibits a significant decrease in photoelectric conversion efficiency with increasing thermal cycling cycles, reaching a degradation rate of 33.38% after 1000 cycles. This is because under extreme thermal cycling and high-energy irradiation, microcracks generated within the silver paste continuously expand and penetrate, causing delamination and peeling at the silver-silicon interface. This leads to the breakage of the conductive network, a sharp increase in contact resistance, and ultimately severe degradation of electrode performance, making it difficult to meet the requirements for long-term on-orbit service.

[0048] The self-healing low-temperature silver paste of this invention (first embodiment) relies on the synergistic mechanism of multiple breakage and recombination of dynamic reversible bonds on the silver powder surface and the migration and rearrangement of nano-silver to continuously inhibit the propagation of microcracks: Under extreme thermal cycling and high-energy irradiation, the dynamic covalent bonds (boronate bonds) on the silver powder surface and in the resin matrix undergo reversible breakage, providing channels for the migration of nano-silver atoms; nano-silver accumulates, rearranges, and rebonds at the crack sites, rebuilding the conductive pathway; the dynamic bonds recombine again under thermal or radiation stimulation, repairing the resin matrix and silver-silicon interface, forming a triple self-healing mechanism of "interface-matrix-conductive phase". Therefore, even after 1000 cycles of enhanced aging, the efficiency decay rate of the first embodiment is only 13.54%, still maintaining a complete conductive network and high-efficiency output, exhibiting extremely strong resistance to extreme environmental fatigue and ultra-long service life, significantly superior to traditional silver pastes.

[0049] As can be seen, this invention constructs a dense conductive framework and repair channels by employing a three-tiered silver powder mix of sheet-like, submicron, and nano-sized particles. Under radiation and thermal stimulation, the nano-silver can migrate, rearrange, and conduct through cracks, achieving self-repair of the conductive pathways. Furthermore, the modified silver powder undergoes dynamic covalent bond surface functionalization, resulting in reversible fracture and recombination under extreme environments. This synergistic effect with the resin forms a triple self-repair mechanism involving the interface, matrix, and conductive phase, significantly improving structural stability. The low-temperature, low-residual-carbon organic system is highly compatible with the powder, allowing sintering to be completed at ≤200℃ without residual carbon obstruction, ensuring sufficient migration and contact of silver particles while balancing high conductivity and efficient self-repair. This makes the overall system suitable for the high vacuum, strong radiation, and drastic temperature changes of space environments, resulting in high electrode crack repair efficiency and long lifespan, effectively addressing the industry pain point of traditional silver paste's inability to self-repair.

[0050] In summary, the above embodiments of the present invention provide a self-healing low-temperature silver paste for space photovoltaics and its preparation method. The self-healing low-temperature silver paste comprises modified silver powder, organic resin, organic solvent, and additives. The modified silver powder is a composite system of modified flake silver powder, modified spherical silver powder, and modified nano silver powder. The combination of flake / submicron / nano-level silver powder constructs a dense conductive framework and repair channels, achieving self-repair of the conductive pathway. The organic resin is a self-healing resin with dynamic covalent bonds in its main chain or side chains. The modified silver powder undergoes a dynamic covalent bond surface functionalization reaction with the organic resin, synergistically forming a triple self-healing process involving the interface, matrix, and conductive phase. The two are highly compatible, balancing high conductivity and efficient self-healing.

[0051] This invention breaks the performance incompatibility between dispersion and conductivity at the mechanistic level by constructing radiation-responsive dynamic chemical bonds on the surface of silver powder and combining them with a multi-level silver powder gradation design. At the same time, it endows the silver paste with intrinsic self-healing ability under the high vacuum, high-energy radiation and extreme thermal cycling of space, realizing a technological leap from "passive tolerance" to "active adaptation", and providing core material support for the long-term reliable service of the next generation of space photovoltaic cells.

[0052] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A self-healing low-temperature silver paste for space photovoltaics, characterized in that, The silver paste comprises, by weight percentage, the following components: 92-97 wt% modified silver powder, 3-8 wt% organic resin, 1-6 wt% organic solvent, and 0.1-1 wt% additives; wherein the modified silver powder is a compound system of modified flake silver powder, modified spherical silver powder, and modified nano silver powder, the organic resin is a self-healing resin containing dynamic covalent bonds, the modified silver powder and the organic resin form dynamic reversible bonds, and the dynamic reversible bonds undergo reversible breakage and recombination under thermal stimulation or high radiation.

2. The self-healing low-temperature silver paste for space photovoltaics as described in claim 1, characterized in that, The modified silver powder comprises, by weight percentage, the following components: 60-80 wt% modified flake silver powder, 15-25 wt% modified spherical silver powder, and 5-15 wt% modified nano silver powder.

3. The self-healing low-temperature silver paste for space photovoltaics as described in claim 2, characterized in that, The flake-shaped silver powder has a particle size D50 of 1.5-3 μm and a specific surface area of ​​0.3-0.8 m². 2 / g, tap density 3.0-4.5g / ml; the spherical silver powder has a particle size D50 of 0.3-0.8μm and a specific surface area of ​​1.2-2.5m². 2 / g, tap density 4.0-5.5g / ml; the nano silver powder has a particle size D50 of 20-50nm and a specific surface area of ​​5-12m². 2 / g, tap density 2.0-3.5g / ml.

4. The self-healing low-temperature silver paste for space photovoltaics as described in any one of claims 1-3, characterized in that, The preparation method of the modified silver powder includes three-step surface modification: purification and impurity removal of multi-grade silver powder, activation with coupling agent, and functionalization of dynamic bonds.

5. The self-healing low-temperature silver paste for space photovoltaics as described in claim 4, characterized in that, The organic resin includes one or more of flexible thermoplastic acrylic resin, aliphatic polyurethane resin, ethyl cellulose, flexible alicyclic epoxy resin, and low-temperature decomposable silicone resin, and / or other self-healing resins whose molecular chains contain dynamic covalent bonds.

6. The self-healing low-temperature silver paste for space photovoltaics as described in claim 5, characterized in that, The dynamic covalent bond includes one or more of borate ester bonds, imine bonds, acylhydrazone bonds, and disulfide bonds. The dynamic covalent bond can be broken and rebonded at 120-180℃, and the residual carbon content is ≤1.0wt%. The dynamic bond functionalization treatment grafts the dynamic covalent bond surface of the organic resin onto silver powder to form one or more of the dynamic reversible bonds.

7. The self-healing low-temperature silver paste for space photovoltaics as described in claim 6, characterized in that, The organic solvent includes one or more of terpineol, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether, and propylene glycol methyl ether acetate; the organic solvent is completely volatile at 150-200°C.

8. The self-healing low-temperature silver paste for space photovoltaics as described in claim 1, characterized in that, The additives include one or more of curing agents, dispersants, and coupling agents; the dispersants include one or more of polyacrylate dispersants and phosphate dispersants; the coupling agents include one or more of silane coupling agents and titanate coupling agents.

9. The self-healing low-temperature silver paste for space photovoltaics as described in claim 8, characterized in that, The curing agent is one or more of the following: modified aliphatic amine curing agent, low-temperature acid anhydride curing agent, low molecular weight polyamide curing agent, benzoyl peroxide, tert-butyl peroxide-2-ethylhexanoate, and blocked aliphatic isocyanate; the curing / unsealing temperature of the curing agent is 100-180℃, and the residual carbon content after curing is ≤0.8wt%.

10. A method for preparing a self-healing low-temperature silver paste for space photovoltaics, characterized in that, At least the following steps are included: S1: The modified silver powder, the organic resin, the organic solvent, and the additives are added to the reaction apparatus and mixed. S2: Stir to ensure that all materials are evenly wetted; S3: Perform three-roll mill grinding with a grinding gap of 10μm-120μm and a grinding speed of 50r / min-400r / min to finally obtain a slurry with a fineness of less than 10μm.

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