Conductive paste and method of manufacture

Abstract

The conductive paste provided by this invention comprises a conductive metal, lead-free glass powder, and an organic binder. The conductive metal and the lead-free glass powder constitute the total solids content, wherein the content of the conductive metal in the total solids content is 75-99.8 wt%, and the content of the lead-free glass powder is 0.2-25 wt%. The lead-free glass powder is a Te-Bi oxide system, which includes tellurium oxide and bismuth oxide. Tellurium oxide, as a glass network former, mainly determines the softening point and fluidity of the glass, effectively reducing the melting point and imparting good fluidity. Bismuth oxide, as a network modifier, can regulate the chemical activity of the glass, allowing it to moderately corrode the passivation layer during sintering and promoting the formation of silver-silicon ohmic contacts. Adjusting the ratio of the two within this range allows for precise matching of the sintering temperature curves of different crystalline silicon solar cells, broadening the process window for lead-free glass. Furthermore, this invention also provides a method for preparing the conductive paste.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic materials technology, and in particular to a conductive paste and its preparation method. Background Technology

[0002] With the increasing global demand for renewable energy, the photovoltaic industry has developed rapidly. In the manufacturing process of crystalline silicon solar cells, conductive pastes (such as front silver paste, back silver paste, and aluminum paste) are one of the key materials determining the cell's efficiency and performance. Conductive pastes are typically composed of conductive metal powders, inorganic binders (glass powder), and organic carriers. Among them, glass powder plays an important role in etching the passivation layer, promoting silver-silicon contact, and forming conductive pathways during sintering, and has a crucial impact on the cell's electrical performance (such as open-circuit voltage, short-circuit current, and fill factor).

[0003] Currently, most mainstream photovoltaic conductive pastes on the market use lead-containing glass powders. Lead-containing glass powders have advantages such as low melting point, good chemical stability, excellent wettability, and strong adhesion to silicon substrates. The technology is mature and has a wide performance window, thus it is widely used in various conductive pastes. However, lead and its compounds are toxic and harmful substances. During the production, printing, sintering, and disposal of waste components, they can potentially harm human health and pose long-term pollution risks to soil, water, and other ecological environments. With increasingly stringent environmental regulations worldwide (such as the EU's RoHS Directive and China's "Regulations on the Management of Pollution Control of Electronic Information Products"), the lead-free transformation of electronic materials has become an inevitable trend in the industry.

[0004] To address environmental pressures, the industry has developed various lead-free glass systems, such as bismuth-based, tellurium-based, and zinc-based glass powders. Among them, Te-Bi glass has attracted widespread attention due to its good fluidity and its promoting effect on silver-silicon eutectic.

[0005] Compared to mature leaded glass systems, existing lead-free glass powders still face several technical bottlenecks. These mainly manifest in the following ways: their performance adjustment window is relatively narrow, they are more sensitive to temperature changes during sintering, and it is difficult to maintain excellent ohmic contact performance and weld adhesion simultaneously over a wide sintering temperature range; furthermore, when etching the silicon nitride passivation layer, lead-free glass powder is prone to over-reaction or under-reaction, leading to increased series resistance or decreased fill factor, thus affecting the photoelectric conversion efficiency of the solar cell. Summary of the Invention

[0006] In view of this, the present invention provides a conductive paste and a method for preparing the same, so as to provide a conductive paste that is environmentally friendly and has excellent electrical properties.

[0007] To solve the above problems, the present invention adopts the following technical solution:

[0008] One objective of this invention is to provide a conductive paste comprising a conductive metal, lead-free glass powder, and an organic binder. The conductive metal and the lead-free glass powder constitute the total solids content, wherein the content of the conductive metal in the total solids content is 75-99.8 wt%, and the content of the lead-free glass powder is 0.2-25 wt%. The lead-free glass powder is a Te-Bi oxide system, which includes tellurium oxide and bismuth oxide.

[0009] In some embodiments, based on the total weight of the conductive paste, the content of the conductive metal is 72-92 wt%, the content of the lead-free glass powder is 1.5-6 wt%, and the content of the organic binder is 6.5-15 wt%.

[0010] In some embodiments, the silver powder content in the conductive metal is 72-92 wt% of the total weight of the conductive metal.

[0011] In some embodiments, the silver powder is one or more of spherical silver powder and microcrystalline silver powder, with an average particle size of 0.5-3.0 μm.

[0012] In some embodiments, the conductive metal further includes one or more of aluminum, nickel, and tungsten.

[0013] In some embodiments, the Te-Bi oxide system comprises 40-80% by weight of Te oxide and 20-60% by weight of Bi oxide, wherein the weight percentage of oxides is based on the total weight of the Te-Bi oxide system.

[0014] In some embodiments, the lead-free glass powder contains, based on the total weight of the glass powder, 50-70% tellurium oxide, 20-30% bismuth oxide, 0.5-10% tungsten oxide, 0.5-5% silicon dioxide, 0.5-5% zinc oxide, 0.5-3% copper oxide, and 0.5-10% alkali metal oxides.

[0015] In some embodiments, the alkali metal oxide is one or more of lithium oxide, potassium oxide, and sodium oxide.

[0016] In some embodiments, the organic adhesive comprises a resin and a solvent, wherein the resin is selected from at least one of ethyl cellulose and acrylic resin; and the solvent is selected from at least one of terpineol and butyl carbitol.

[0017] A second objective of this invention is to provide a method for producing the aforementioned conductive paste, comprising the following steps:

[0018] The conductive slurry is obtained by mixing conductive metal, lead-free glass powder and organic binder in a certain proportion, followed by stirring, grinding and filtering.

[0019] The present invention adopts the above technical solution, and its beneficial effects are as follows:

[0020] The conductive paste provided by this invention comprises a conductive metal, lead-free glass powder, and an organic binder. The conductive metal and the lead-free glass powder constitute the total solids content, wherein the content of the conductive metal in the total solids content is 75-99.8 wt%, and the content of the lead-free glass powder is 0.2-25 wt%. The lead-free glass powder is a Te-Bi oxide system, which includes tellurium oxide and bismuth oxide. Tellurium oxide, as a glass network former, mainly determines the softening point and fluidity of the glass, effectively reducing the melting point and imparting good fluidity to the glass. Bismuth oxide, as a network modifier, can regulate the chemical activity of the glass, allowing it to corrode appropriately during sintering. The passivation layer promotes the formation of silver-silicon ohmic contacts. Adjusting the ratio of the two within this range allows for precise matching of the sintering temperature profiles of different crystalline silicon cells, broadens the process window for lead-free glass, and enables adaptation to unavoidable sintering temperature fluctuations in industrial production, ensuring the consistency of cell performance and yield. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to reference are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] In the description of this invention, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the indicated orientation or positional relationship, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. In this invention, all raw materials are commercially available, and all equipment used is conventional equipment in the art. Unless otherwise stated, all percentages mentioned in this invention are weight percentages.

[0025] This invention provides a novel photovoltaic conductive paste, comprising a conductive metal, lead-free glass powder, and an organic binder. The conductive metal and the lead-free glass powder constitute the total solids content. The conductive metal content in the total solids content is 75-99.8 wt%, and the lead-free glass powder content is 0.2-25 wt%. The lead-free glass powder is a Te-Bi oxide system, which includes tellurium oxide and bismuth oxide.

[0026] It is understandable that using the Te-Bi oxide system to replace traditional lead-containing glass powder eliminates the risk of lead toxicity to humans and environmental pollution to soil and water from the source, complying with RoHS and other environmental directives. The conductive metal content is adjustable between 75-99.8 wt%, making the slurry suitable for front electrodes requiring extremely high conductivity, and also adaptable to different applications such as back-side field or fine grid printing by adjusting the ratio. The inclusion of tellurium oxide and bismuth oxide in the Te-Bi oxide system ensures suitable thermal fluidity of the glass powder. Tellurium oxide effectively lowers the glass melting point, while bismuth oxide helps to moderately corrode the silicon nitride passivation layer during sintering, promoting the formation of silver-silicon contacts, thereby ensuring the basic electrical performance of the battery.

[0027] In this embodiment, based on the total weight of the conductive paste, the content of the conductive metal is 72-92 wt%, the content of the lead-free glass powder is 1.5-6 wt%, and the content of the organic binder is 6.5-15 wt%.

[0028] It is understood that this embodiment further limits the proportions of conductive metal, glass powder, and organic binder to a narrower preferred range, resulting in better printability of the paste. A moderate organic binder content (6.5-15wt%) ensures good transferability and shaping ability of the paste during screen printing, while also allowing for rapid evaporation during sintering, reducing residue. The glass powder content is controlled at 1.5-6wt%, avoiding excessively thick insulation layers or increased contact resistance due to excessive glass, and also avoiding insufficient silver-silicon bonding or decreased adhesion due to insufficient glass, thus achieving an optimal balance between conductivity, welding tensile strength, and contact performance.

[0029] In this embodiment, the silver powder content in the conductive metal is 72-92 wt% of the total weight of the conductive metal.

[0030] It is understood that the conductive metal serves as the conductive functional phase, and the conductive metal in this invention comprises at least silver powder. Silver powder possesses excellent conductivity and chemical stability. Based on the total weight of the conductive paste, the content of the conductive metal is preferably 72-92 wt%.

[0031] Furthermore, the silver powder is one or more of spherical silver powder and microcrystalline silver powder, with an average particle size of 0.5-3.0 μm.

[0032] It is understandable that spherical silver powder has good flowability, which is conducive to high-density packing; microcrystalline silver powder has high surface activity, which is beneficial for low-temperature sintering. The combination of the two can optimize the packing density and sintering activity of the silver powder. The average particle size of the silver powder is preferably between 0.5μm and 3.0μm. If the particle size is too fine (<0.5μm), the silver powder is prone to agglomeration, and the sintering activity is too high and difficult to control; if the particle size is too coarse (>3.0μm), it is easy to clog the screen, and the electrode formed after sintering is not dense, affecting conductivity.

[0033] In this embodiment, the conductive metal further includes one or more of aluminum, nickel, and tungsten.

[0034] It is understood that, to further optimize performance or reduce costs, the conductive metal may also include aluminum ( ),nickel( ), tungsten ( One or more of the following. For example, the introduction of aluminum helps to adjust the coefficient of thermal expansion of the electrode; the introduction of high-melting-point metals such as nickel and tungsten can suppress the migration of silver during sintering and improve the long-term reliability of the electrode.

[0035] It should be noted that, as an inorganic binder, this invention uses lead-free Te-Bi oxide system glass powder, avoiding the environmental and human health hazards of lead. Based on the total weight of the conductive paste, the preferred content of lead-free glass powder is 1.5-6 wt%. If the glass powder content is too low, poor silver-silicon contact and adhesion will occur; if the content is too high, an excessively thick glass layer will form after sintering, increasing contact resistance.

[0036] The Te-Bi oxide system contains tellurium oxide ( ) and bismuth oxide ( Te oxides are used as an essential component. Preferably, based on the total weight of the Te-Bi oxide system, the oxides of Te (in...) The content of Bi oxides is 40-80% (calculated as a percentage of total Bi content). The content (calculated) is 20-60%.

[0037] It is understandable that tellurium oxide (40-80%), as a glass network forging agent, primarily determines the softening point and fluidity of the glass, effectively lowering its melting point and imparting good fluidity. Bismuth oxide (20-60%), as a network modifier, can regulate the chemical activity of the glass, allowing it to corrode appropriately during sintering. The passivation layer promotes the formation of silver-silicon ohmic contacts. Adjusting the ratio of the two within this range allows for precise matching of the sintering temperature profiles of different crystalline silicon cells, broadening the process window for lead-free glass. Within this specific ratio range, the Te-O and Bi-O bond synergistically ensure that the glass powder has a suitable viscosity at peak temperatures to wet the silver powder and silicon wafer, while preventing lateral diffusion of the silver electrode (risk of gate breakage) due to excessive flow.

[0038] In a preferred embodiment of the present invention, the lead-free glass powder further comprises other functional oxide components to further optimize the overall performance of the glass powder. Based on the total weight of the glass powder, its composition is as follows: tellurium oxide (… The content is 50-70%, bismuth oxide ( The content is 20-30%, tungsten oxide ( The content is 0.5-10%, and the silica content is 0.5-10%. The content is 0.5-5%, zinc oxide ( The content is 0.5-5%, copper oxide ( The content of alkali metal oxides is 0.5-3%, and the content of alkali metal oxides is 0.5-10%.

[0039] It is understandable that tungsten oxide ( It can enhance the chemical stability of glass, prevent the slurry from deteriorating during storage, and adjust the coefficient of thermal expansion of glass to better match silicon wafers and reduce breakage rate.

[0040] It is understandable that silicon dioxide ( As a glass network forging body, it can improve the mechanical strength of glass, inhibit excessive crystallization of glass during sintering, and ensure stable fluidity of glass at high temperatures.

[0041] It is understandable that zinc oxide ( It can improve the wettability of glass to silver powder and silicon substrate, promote the tight bonding of the sintering interface, and help reduce contact resistance.

[0042] It is understandable that copper oxide ( It may participate in the alloy reaction during sintering, which helps to improve the adhesion of the electrode under humid heat aging conditions.

[0043] Furthermore, the alkali metal oxide is selected from lithium oxide ( ), potassium oxide ( Sodium oxide () One or more of the following.

[0044] It is understandable that lithium, potassium, and sodium ions have different ionic radii. The mobility and polarization capabilities of these compounds within the glass network also differ. One or more compound formulations can be selected based on the specific sintering process: lithium oxide has a small ion radius and migrates quickly, rapidly reducing the high-temperature viscosity of the glass, making it suitable for rapid sintering processes. Potassium oxide / sodium oxide has a significant impact on the glass expansion coefficient and can be used to adjust the thermal stress matching between the electrode and the silicon wafer. Furthermore, a variety of alkali metal oxides are available, increasing the flexibility of formulation design and facilitating targeted optimization based on different battery structures and production equipment.

[0045] Through the synergy of the above components, this glass powder system can achieve low melting point, moderate coefficient of expansion, good chemical stability and excellent adhesion without lead, with overall performance approaching or even surpassing that of traditional lead-containing systems.

[0046] Organic binders serve as carriers for the functional phases (conductive metals and glass powders), imparting suitable rheological properties to the paste to meet the requirements of screen printing processes. Based on the total weight of the conductive paste, the content of organic binders is preferably 6.5-15 wt%.

[0047] In this invention, the organic adhesive typically comprises resin, solvent, and necessary additives.

[0048] It is understandable that the resin mainly functions as a thickener and film-forming agent. It is preferably selected from at least one of ethyl cellulose and acrylic resin. Ethyl cellulose has good film-forming properties and excellent thixotropy; acrylic resin has better pyrolysis characteristics and leaves less residue.

[0049] It is understandable that the solvent is used to dissolve the resin and adjust the viscosity of the paste. Preferably, it is selected from at least one of terpineol and butylcarbitol. Terpineol has a moderate boiling point and a gentle volatilization curve; butylcarbitol has strong dissolving power and can effectively adjust the open time of the paste. The combined use of these two solvents ensures that the paste maintains stable rheological properties during printing, settling, and drying.

[0050] Furthermore, it may also include additives, such as dispersants (e.g., fatty acid esters), thixotropic agents (e.g., hydrogenated castor oil), leveling agents, etc., to further optimize the dispersibility, thixotropy, and leveling properties of the slurry.

[0051] The aforementioned organic carrier can completely volatilize and decompose during the sintering preheating stage, leaving no residual carbon or ash, thus avoiding contamination of the silver-silicon contact interface or obstruction of light.

[0052] The conductive paste provided by this invention comprises a conductive metal, lead-free glass powder, and an organic binder. The conductive metal and the lead-free glass powder constitute the total solids content, wherein the content of the conductive metal in the total solids content is 75-99.8 wt%, and the content of the lead-free glass powder is 0.2-25 wt%. The lead-free glass powder is a Te-Bi oxide system, which includes tellurium oxide and bismuth oxide. Tellurium oxide, as a glass network former, mainly determines the softening point and fluidity of the glass, effectively reducing the melting point and imparting good fluidity to the glass. Bismuth oxide, as a network modifier, can regulate the chemical activity of the glass, allowing it to corrode appropriately during sintering. The passivation layer promotes the formation of silver-silicon ohmic contacts. Adjusting the ratio of the two within this range allows for precise matching of the sintering temperature profiles of different crystalline silicon cells, broadens the process window for lead-free glass, and enables adaptation to unavoidable sintering temperature fluctuations in industrial production, ensuring the consistency of cell performance and yield.

[0053] Furthermore, this invention uses a Te-Bi oxide system to replace traditional lead-containing glass powder, eliminating the risk of lead toxicity to humans and environmental pollution to soil and water from the source, thus complying with RoHS and other environmental directives. The conductive metal content is adjustable between 75-99.8 wt%, making the slurry suitable for front electrodes with extremely high conductivity requirements, and also able to meet the needs of different applications such as back field or fine grid printing by adjusting the ratio. The Te-Bi oxide system is limited to include tellurium oxide and bismuth oxide, ensuring that the glass powder has suitable thermal fluidity. Tellurium oxide effectively lowers the glass melting point, while bismuth oxide helps to moderately corrode the silicon nitride passivation layer during sintering, promoting the formation of silver-silicon contacts, thereby ensuring basic electrical performance.

[0054] The present invention also provides a method for producing the conductive paste, comprising the following steps: mixing conductive metal, lead-free glass powder and organic binder in a certain proportion, and then stirring, grinding and filtering to obtain the conductive paste.

[0055] In this embodiment, the preparation method of lead-free glass powder is as follows:

[0056] According to the design proportions, accurately weigh using an electronic balance. , , , , , Raw materials such as alkali metal oxides.

[0057] Place the weighed raw materials into the mixer and mix thoroughly until homogeneous.

[0058] The mixture is placed in a high-temperature furnace and melted at 1000°C for 100 minutes to allow all components to fully melt and react, forming a uniform glass melt.

[0059] The molten glass is quickly poured into pure water for quenching and cooling, resulting in glass shards.

[0060] The glass slag was coarsely ground using a material crusher to obtain semi-finished glass powder with a D50 of approximately 50 μm.

[0061] The semi-finished glass powder is placed in an air jet mill for fine grinding, and its D50 is controlled at about 1.5μm to obtain high-performance finished lead-free glass powder.

[0062] In this embodiment, the conductive paste is prepared as follows:

[0063] According to the formula ratio, the conductive metal (such as silver powder, and other metal powders), the lead-free glass powder prepared in step (1) and the organic binder are added to the mixing tank of the double planetary mixer.

[0064] Start the dual planetary mixer to mix the materials evenly, so that the powder is initially wetted and mixed.

[0065] The pre-mixed slurry is transferred to a three-roll mill. By adjusting the roller gap and the number of grinding cycles, it is thoroughly ground and dispersed under high shear force to ensure that no agglomerates are present. The grinding time is usually 1-4 hours.

[0066] The well-ground and dispersed slurry is filtered (e.g., through a 300-mesh sieve) to remove possible impurities and large particles, thus obtaining the novel photovoltaic conductive slurry of the present invention.

[0067] The preparation method described in this invention produces high-performance lead-free glass powder through precise ingredient proportioning, high-temperature melting, quenching and cooling, and multi-stage pulverization. The glass powder is then combined with conductive metals and organic binders through stirring, grinding, and filtration to form a conductive paste. The entire process is rationally designed, precisely controlled, and highly adaptable, enabling the stable production of conductive pastes with excellent electrical and printing properties. This provides a reliable process implementation path for the product and has significant industrial practical value.

[0068] The beneficial effects of the present invention are further illustrated below through specific embodiments and comparative examples. In all embodiments and comparative examples, the preparation method of the slurry adopts the above-mentioned general preparation method, and the materials are added according to the formula in Table 1. For the photovoltaic novel conductive slurry of the present invention, the semi-finished glass powder will be tested for particle size distribution and softening point; the finished conductive slurry will be tested for viscosity and fineness; after the slurry is printed on the solar cell and sintered, the contact resistivity, PL corrosion, aspect ratio, electrical performance, and photoelectric conversion efficiency will be tested.

[0069] Example

[0070] (I) Preparation of glass powder

[0071] According to the formulations (weight percentage, wt%) shown in Table 1, Examples 1-3 were prepared using the methods described above.

[0072] Table 1 shows the composition comparison of the glass powder examples.

[0073]

[0074] (II) Preparation of conductive paste

[0075] According to the formulations shown in Table 2 (weight percentage, wt%, based on the total weight of the conductive paste), conductive paste samples S1-S3 were prepared using the glass powders from Examples 1-3 and following the general preparation method described above.

[0076] Table 2 shows the conductive paste formulation (wt%)

[0077]

[0078] (III) The contact resistivity and metal composite properties of conductive paste

[0079] Table 3. Performance comparison between the examples and commercial glass at different sintering temperatures

[0080]

[0081] The metal recombination value reflects the recombination current density at the metal-semiconductor interface. A lower value and a smaller change with temperature indicate better interface quality and better process stability. As shown in the table above:

[0082] Lower absolute values: At three temperature points (BL-50℃, BL, BL+30℃), the metal composite values ​​of Examples 1-3 were significantly lower than those of commercial glass, indicating that the glass powder of the present invention can maintain excellent interface passivation effect over a wider temperature range.

[0083] Lower temperature sensitivity: When the temperature rises from the reference temperature to BL+30℃, the metal composite value of the commercial glass surges from 166 to 287, an increase of 72.9%; while the increase in Examples 1-3 is only 32.0%~42.5%. This indicates that the glass powder in the examples will not excessively corrode the passivation layer due to temperature fluctuations during high-temperature sintering, ensuring stable interface quality.

[0084] Excellent low-temperature stability: At BL-50℃, the metal composite value of commercial glass reaches as high as 152, while the embodiment can still be controlled between 68-74. This indicates that the glass powder of the present invention can achieve good silver-silicon contact at relatively low temperatures without relying on a high-temperature sintering window.

[0085] Contact resistivity directly reflects the quality of the silver-silicon ohmic contact. A lower value and a more gradual change with temperature indicate a wider process window. As shown in the table above:

[0086] The advantages of low-temperature sintering are significant: under BL-50℃ (lower temperature sintering) conditions, the contact resistivity of commercial glass is as high as... Examples 1-3 are only The reduction is approximately 30-40%. This indicates that the glass powder of this invention can effectively etch at relatively low temperatures. The layers form good ohmic contacts, allowing for a wider lower limit of sintering temperature.

[0087] The high-temperature region also performs well: under BL+30℃ (higher temperature sintering) conditions, the contact resistivity of Examples 1-3 is ( ) and commercial glass ( The result is comparable to or even better than that of the previous one, indicating that the contact will not deteriorate due to excessive reaction at high temperatures.

[0088] Lower temperature sensitivity: In commercial glass, within an 80°C temperature range (BL-50°C to BL+30°C), the contact resistivity drops sharply from 2.45 to 0.54, with a fluctuation range as high as 1.91, indicating its extreme temperature sensitivity and narrow process window. The fluctuation range in Examples 1-3 is only 1.11-1.24, significantly smaller, indicating that its contact performance is not sensitive to temperature changes and has high process tolerance.

[0089] Based on the above data, the wider performance window of Examples 1-3 is mainly attributed to the formulation design of the glass powder in this invention:

[0090] Te-Bi ratio optimization: (50-70%) and The appropriate ratio of (20-30%) ensures that the glass powder maintains suitable viscosity and reactivity over a wide temperature range. It can effectively wet silver powder and silicon wafers at low temperatures, and will not degrade in performance due to excessive flow or corrosion at high temperatures.

[0091] Multi-component synergistic regulation: The addition of [a substance] enhances the chemical stability of the glass and prevents sudden changes in performance due to changes in the glass structure during high-temperature sintering. It inhibits excessive crystallization of glass during sintering, ensuring the temperature stability of glass fluidity; alkali metal oxides ( , , This effectively reduced the melting temperature of the glass and broadened the low-temperature sintering window; and Improved wettability of glass to silver powder and silicon substrate promotes interfacial bonding. Glass powder particle size control: D50 is controlled at around 1.5μm, ensuring uniform dispersion of glass powder in the slurry and consistent behavior during sintering, avoiding local performance differences caused by uneven particle size distribution. Advantages of the lead-free system: Compared to lead-containing systems, the Te-Bi oxide system of this invention has a flatter viscosity-temperature curve, meaning that viscosity changes gradually over a wider temperature range, thus being less sensitive to fluctuations in sintering temperature.

[0092] As shown in Table 3, the conductive pastes of Examples 1-3 of this invention maintain low and gradual changes in metal composite value and contact resistivity within a wide temperature range of BL-50℃ to BL+30℃, while the performance of mainstream commercial glass deteriorates sharply when the temperature deviates from the baseline. This indicates that the lead-free Te-Bi glass powder system of this invention, through optimized component design, successfully overcomes the technical challenge of the "narrow performance window" of traditional lead-free glass powders, achieving excellent ohmic contact with the silicon substrate and exhibiting excellent tolerance to sintering temperature fluctuations. It significantly broadens the process window, resulting in higher industrial production adaptability and yield assurance.

[0093] (iv) Comparison of photoelectric conversion efficiency of conductive pastes

[0094] Table 4. Comparison of conversion efficiency between the examples and commercial glass.

[0095]

[0096] The fill factor is a key parameter for measuring the output characteristics of a battery; the higher the value, the less internal loss the battery has. Series resistance is one of the core factors affecting the fill factor.

[0097] The series resistance of Examples 1-3 (2.30-2.33 mΩ) is significantly lower than that of mainstream commercial glass (2.47 mΩ), a reduction of approximately 5.7-6.9%. The series resistance mainly originates from the silver-silicon contact resistance, the silver electrode body resistance, and the silver-silicon interface resistance. The lower series resistance directly indicates that:

[0098] Superior silver-silicon ohmic contact: The glass powder of this invention can form a more ideal silver-silicon alloy layer during the sintering process, resulting in a lower contact barrier;

[0099] Better electrode conductivity: The ratio and dispersion uniformity of silver powder and glass powder are better, and the silver electrode formed after sintering is denser and the conductive channel is more continuous.

[0100] Furthermore, the lower series resistance directly translates into a higher fill factor (81.95-81.98% vs 81.75%), an improvement of approximately 0.20-0.23 percentage points. This increased fill factor indicates reduced internal power loss within the battery, allowing more photogenerated carriers to be effectively collected and output to the external circuitry.

[0101] In this invention (50-70%) and A reasonable ratio of (20-30%) ensures that the glass powder possesses suitable etching activity and fluidity during sintering, enabling it to effectively penetrate... The passivation layer forms an ohmic contact without excessive erosion that would lead to increased leakage current or increased contact resistance. , , The addition of additives further optimized the conductivity and interfacial bonding performance of the glass, and reduced the interfacial barrier. The good matching between the silver powder particle size (0.5-3.0μm) and the glass powder particle size (D50≈1.5μm) ensured the density and continuity of the silver electrode after sintering, and reduced the bulk resistance.

[0102] Furthermore, the short-circuit current (Isc) of Examples 1-3 is basically the same as that of mainstream commercial glass, all around 14.27A, indicating that the slurry of the present invention does not affect the collection ability of photogenerated carriers and the shading loss of the grid line is comparable.

[0103] The open-circuit voltage (Voc) of Examples 1-3 is slightly lower than that of mainstream commercial glass by about 1.0-1.1 mV, a negligible difference (about 0.15%), which falls within the normal batch fluctuation range in actual production. This slight difference in open-circuit voltage may be related to the type and content of alkali metal ions in the glass powder, but the overall impact is minimal. With Isc and Voc essentially equal, these examples achieve superior overall efficiency by reducing Rs and increasing FF, fully demonstrating the outstanding advantages of this invention in contact optimization.

[0104] IVRV2 reflects the leakage current level of the battery under reverse bias. The lower the value, the better the PN junction quality and the smaller the interface recombination loss.

[0105] The reverse leakage currents (0.018-0.022A) of Examples 1-3 are all lower than or equal to those of mainstream commercial glass (0.023A), especially Example 3, which shows a reduction of 21.7%. The reduction in reverse leakage current indicates that the etching of the silicon substrate by the glass powder is more uniform and controllable, and that excessive etching will not cause damage to the PN junction or the formation of local leakage channels; the reduction in interface recombination centers and the decrease in defect density at the metal-semiconductor interface help to improve the parallel resistance and dark-state characteristics of the battery.

[0106] This invention achieves precise control of the Te / Bi ratio and the addition of... , Network stabilizers ensure that the glass powder exhibits a smooth viscosity-temperature curve and stable chemical activity during sintering, preventing "over-attack" on the silicon surface. The uniform distribution of the glass powder particle size (1.5μm) ensures the uniformity of etching at the microscale, preventing excessively deep local etching.

[0107] As shown in Table 4, the conductive pastes of Examples 1-3 of the present invention significantly reduced the series resistance (Rs), increased the fill factor (FF), and improved the reverse leakage current characteristics (IVRV2) while maintaining the short-circuit current (Isc) and open-circuit voltage (Voc) at the same level as those of mainstream commercial glass, ultimately achieving a stable increase in photoelectric conversion efficiency (Eff).

[0108] This invention is achieved through (50-70%) and (20-30%) ratio adjustment, combined with , , , The synergistic effect of multiple components, including alkali metal oxides, gives the glass powder excellent fluidity, etching activity, and chemical stability during sintering, forming a low-resistance, uniform silver-silicon ohmic contact. The good particle size matching between silver powder (0.5-3.0μm) and glass powder (D50≈1.5μm) ensures the uniformity of slurry dispersion and the compactness of the electrode after sintering. The uniform and controllable etching effect reduces interfacial recombination centers, lowers reverse leakage current, and further optimizes the dark-state characteristics of the battery.

[0109] The above results fully demonstrate that the lead-free Te-Bi oxide glass powder system of the present invention has successfully solved the technical problem of "narrow performance window" of lead-free glass powder through refined component design and particle size control. Its comprehensive electrical properties have reached or even exceeded the level of mainstream lead-containing commercial slurries, and it has good prospects for industrial application.

[0110] The above are merely preferred embodiments of the present invention, and only specifically describe the technical principles of the present invention. These descriptions are only for explaining the principles of the present invention and should not be construed as limiting the scope of protection of the present invention in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention, as well as other specific embodiments of the present invention that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of the present invention.

Claims

1. A conductive paste, characterized in that, The product comprises a conductive metal, lead-free glass powder, and an organic binder. The conductive metal and the lead-free glass powder constitute the total solids content. The conductive metal content in the total solids content is 75-99.8 wt%, and the lead-free glass powder content is 0.2-25 wt%. The lead-free glass powder is a Te-Bi oxide system, which includes tellurium oxide and bismuth oxide.

2. The conductive paste as described in claim 1, characterized in that, Based on the total weight of the conductive paste, the content of the conductive metal is 72-92 wt%, the content of the lead-free glass powder is 1.5-6 wt%, and the content of the organic binder is 6.5-15 wt%.

3. The conductive paste as described in claim 1 or 2, characterized in that, The silver powder content in the conductive metal is 72-92 wt% of the total weight of the conductive metal.

4. The conductive paste as described in claim 3, characterized in that, The silver powder is one or more of spherical silver powder and microcrystalline silver powder, with an average particle size of 0.5-3.0 μm.

5. The conductive paste as described in claim 3, characterized in that, The conductive metal also includes one or more of aluminum, nickel, and tungsten.

6. The conductive paste as described in claim 1 or 2, characterized in that, The Te-Bi oxide system comprises 40-80% by weight of Te oxides and 20-60% by weight of Bi oxides, wherein the weight percentage of oxides is based on the total weight of the Te-Bi oxide system.

7. The conductive paste as described in claim 6, characterized in that, The lead-free glass powder contains, based on the total weight of the glass powder, 50-70% tellurium oxide, 20-30% bismuth oxide, 0.5-10% tungsten oxide, 0.5-5% silicon dioxide, 0.5-5% zinc oxide, 0.5-3% copper oxide, and 0.5-10% alkali metal oxides.

8. The conductive paste as described in claim 4, characterized in that, The alkali metal oxide is one or more of lithium oxide, potassium oxide, and sodium oxide.

9. The conductive paste according to claim 1, characterized in that, The organic adhesive comprises a resin and a solvent, wherein the resin is selected from at least one of ethyl cellulose and acrylic resin; and the solvent is selected from at least one of terpineol and butyl carbitol.

10. A method for preparing the conductive paste as described in claim 1, characterized in that, Includes the following steps: The conductive slurry is obtained by mixing conductive metal, lead-free glass powder and organic binder in a certain proportion, followed by stirring, grinding and filtering.

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