Metallization slurry, conductive thin film, preparation method of conductive thin film and metallization structure

Abstract

The invention discloses metallization slurry, a conductive film formed by the metallization slurry, a preparation method and a metallization structure. The slurry comprises the following components in percentage by weight: 0.05 wt%-30 wt% of a metal phase component, 1 wt%-10 wt% of glass powder and the balance of an organic carrier. The ultrathin metallized conductive film can be formed by coating and sintering the paste. According to the invention, two functions of forming an ohmic contact interface and constructing a high-conductivity electrode body are decoupled through a'conductive film 'design, a glass phase in the conductive film ensures attachment and contact modification with a silicon substrate, and a dispersed metal phase forms a conductive network. A grid line electrode layer containing base metal can be printed on the conductive thin film, and the grid line electrode layer and the conductive thin film form metallurgical bonding during sintering. According to the method, silver consumption is reduced by 70% or above, meanwhile, the efficiency of the battery is still kept or superior to that of a traditional high-silver scheme, and unification of high performance, low cost and high process stability is achieved.

Description

Technical Field

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

[0002] In the field of photovoltaic technology, the metallization process of crystalline silicon solar cells is one of the core factors determining their photoelectric conversion efficiency and manufacturing cost. This process aims to form an electrode structure on the silicon substrate surface of the cell that can efficiently collect and extract photogenerated carriers.

[0003] For a long time, the industry has generally used screen printing of conductive pastes with high silver content (typically >80 wt%), which are then sintered at high temperatures to directly form grid electrodes (e.g., CN102971268A, CN102958861A, which describe methods for achieving contact using lead-containing glass frit in conjunction with high-silver paste). Silver, with its excellent conductivity, solderability, and ability to easily form low-resistance ohmic contacts with silicon, has become the preferred electrode material. However, as a precious metal, silver's high and volatile price has become a major obstacle to the continued cost reduction of photovoltaics.

[0004] To reduce reliance on the precious metal silver, researchers are working to develop paste systems with lower silver content. One important technical approach is to use composite conductive pastes with a base metal (such as copper) as the main component and a small amount of silver as an interface modifier or coating layer, attempting to balance contact performance and bulk conductivity in a single material system. For example, Chinese patent application CN118969868A discloses a silver-copper composite electrode paste and its one-step molding process. This paste contains silver microcrystalline particles and silver-coated copper particles, and through laser sintering and other methods, aims to simultaneously form a silver-rich contact interface and a conductor primarily composed of silver-coated copper. While such integrated solutions can reduce total silver consumption, they still have significant limitations: First, to ensure effective precipitation and contact quality of silver microcrystals at the interface, a considerable proportion of silver content must still be maintained in the slurry, making further silver reduction a bottleneck; second, the formation of interface contacts is highly dependent on precisely controlled sintering kinetics (such as specific temperature profiles, laser parameters, or applied bias voltage), resulting in a narrow process window and high requirements for equipment and process stability; most importantly, this solution strongly couples the two key functions of "forming a high-quality silicon contact interface" and "constructing a high-conductivity electrode" into the same material system and process step, making it impossible to optimize the two independently, limiting the freedom of material design and process adjustment, and making contact reliability susceptible to the influence of phase slurry composition and sintering fluctuations.

[0005] When further attempts are made to directly fabricate electrodes using pure base metal pastes with extremely low or no silver content (such as pure copper paste), existing technologies face even more severe challenges. These pastes often struggle to form stable, low-resistance ohmic contacts with silicon substrates (especially high-efficiency cells with precise passivation contact structures such as tunneling oxide layers / polycrystalline silicon), leading to a surge in contact resistance, deterioration of adhesion, and severe damage to cell performance.

[0006] Therefore, how to ensure a stable and reliable low-resistance ohmic contact between the electrode and the silicon substrate while significantly reducing the noble metal content in the electrode bulk phase, or even using base metal materials entirely, is a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To overcome the technical challenge of achieving stable and reliable interfacial ohmic contacts and high bulk conductivity while significantly reducing the amount of precious metals used in existing technologies, this invention provides an innovative metallization paste, a conductive thin film formed from the paste, a method for preparing the paste, and a metallization structure comprising the thin film. Specifically, this invention provides the following technical solutions: In a first aspect, the present invention provides a slurry; comprising, by weight percentage of the total slurry: Metallic phase composition: content of 0.05 wt% ~ 30 wt%, based on the mass of elemental metal; Glass powder: content of 1 wt% ~ 10 wt%; The remaining organic carrier; The slurry is used to form a metallized conductive film, which is used to achieve low-resistance ohmic contact and electrical connection between the silicon substrate of the crystalline silicon solar cell and the grid electrode layer containing base metal.

[0008] The slurry provided by this invention solves the existing technical problems through the following design: First, by adopting a significantly reduced metal phase content (≤30 wt%) and combining it with an ultra-thin conductive film layer morphology, the amount of precious metals used is reduced to an extremely low level, while allowing the upper gate electrode to use base metal materials entirely or mainly, thereby significantly reducing manufacturing costs; Second, the conductive film formed by it separates the interface function of "forming a reliable ohmic contact with the silicon substrate", realizing complete decoupling from the "bulk conductivity" function of the upper electrode, allowing the two to be optimized separately, breaking through the material and process limitations caused by functional coupling in traditional integrated slurries; Third, the glass powder in the slurry can form a continuous matrix during sintering, which, together with the conductive network constructed by the metal phase, not only ensures the adhesion and contact performance with the silicon substrate, but also provides an active surface for the upper base metal electrode to be wetted and bonded, thereby effectively solving the fundamental problem of poor contact in pure base metal slurries.

[0009] In this invention, within the context of this invention: "Continuous glass phase matrix" refers to the amorphous solid phase formed by the melting and re-solidification of glass powder after heat treatment in the metallized conductive film, which is an integral part in three-dimensional space and constitutes the main structure that encapsulates and disperses the metal conductive units.

[0010] "Base metals" refer to metals or alloys that are significantly cheaper than precious metals such as silver and gold and that do not typically form ideal ohmic contact with silicon, such as copper, aluminum, nickel, tin and their alloys.

[0011] "Base metal conductive material" specifically refers to a material system that constitutes the main body of the gate electrode layer and uses the base metal as the main conductive phase, aiming to replace traditional high silver content thick films to significantly reduce the cost of the electrode bulk phase.

[0012] The metallic phase component is crucial for forming the conductive network in the final thin film. Its content, based on the mass of elemental metal, is 0.05 wt% to 25 wt% of the total slurry mass, preferably 3 wt% to 25 wt%, and more preferably 5 wt% to 20 wt%. The metallic phase component can be widely selected from at least one of metal powders, alloy powders, metal-coated particles, and metal compounds that can decompose or be reduced to elemental metals during subsequent heat treatment. Preferably, the metallic phase component contains silver, specifically selected from at least one of elemental silver powders, silver alloy powders, silver-coated particles, and silver compounds that can decompose or be reduced to elemental silver during heat treatment, specifically including but not limited to one or more combinations of the following categories: Metallic silver materials include silver powders of different morphologies and sizes, such as silver nanoclusters, silver nanowires, silver nanorods, silver nanoparticles (particle size 1-100nm), micron-sized silver powder (particle size 0.1-10μm), and flake-shaped silver powder, etc. Silver-coated materials: These are composite particles formed by coating a silver layer on the surface of non-metallic particles, such as silver-coated glass and silver-coated carbon, where the thickness of the silver layer can be 5-200 nm. Silver salt precursors include inorganic silver salts (such as silver nitrate, silver oxide, silver carbonate, silver phosphate, and silver halide) and organic silver salts (such as silver acetate, silver oxalate, silver formate, silver amine salts and their derivatives), which can be decomposed, reduced or converted into metallic silver during subsequent heat treatment. Silver-based alloys: alloy powders with silver as the main component, such as silver-nickel, silver-bismuth, silver-lead, and silver-tin alloys, with a silver content of not less than 50 wt%. Silver composite conductive phase: Intermediate phase, transition phase or composite conductive phase that can be formed by silver and other metals or metal oxides during heat treatment, which is eventually transformed into a conductive network dominated by silver.

[0013] Glass powder plays a crucial role in forming a continuous substrate, etching the underlying passivation layer, and achieving good adhesion. Its softening temperature is preferably 300°C to 600°C, more preferably 400°C to 550°C, to suit the sintering process window of crystalline silicon solar cells. The composition of the glass powder may include at least two oxides selected from lead oxide (PbO), tellurium oxide (TeO2), bismuth oxide (Bi2O3), silicon dioxide (SiO2), boron oxide (B2O3), lithium oxide (Li2O), sodium oxide (Na2O), potassium oxide (K2O), magnesium oxide (MgO), calcium oxide (CaO), barium oxide (BaO), zinc oxide (ZnO), tungsten oxide (WO3), copper oxide (CuO), germanium oxide (GeO2), molybdenum oxide (MoO3), vanadium oxide (V2O5), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), and zirconium oxide (ZrO2). By adjusting the composition, its etching activity, fluidity, and coefficient of thermal expansion can be balanced.

[0014] The specific preparation method of glass powder is as follows: weigh the above oxide raw materials according to the design ratio and mix them thoroughly; melt the mixture at 1250℃~1300℃ for about 1.5 hours, and then quench it to obtain glass fragments; pre-crush and sieve the glass fragments to obtain coarse powder; place the coarse powder in a ball mill, for example, using zirconia grinding balls with a diameter of 5-10mm, and ball mill at a speed of 250r / min for about 8 hours to obtain glass slurry; finally, sieve and dry the slurry to obtain functional glass powder with a particle size of about 0.5μm~5μm.

[0015] Organic carriers provide the slurry with the required rheological properties, dispersion stability, and film-forming properties, and typically constitute 65 wt% to 98.9 wt% of the total slurry weight. An organic carrier is a multi-component composite system containing: Organic resin: as a binder and film-forming agent, accounting for 5 wt% to 30 wt% of the total weight of the organic carrier. It can be selected from one or more of polyvinyl butyral (PVB) resin, rosin resin, acrylic resin, phenoxy resin, ethyl cellulose, polyurethane resin, epoxy resin, polyimide resin, acrylate-phenoxy copolymer, etc.

[0016] Thixotropic agents: used to adjust the thixotropic properties of the slurry and prevent sagging, with a content of 0.1 wt% to 5 wt% of the total weight of the organic carrier. Options include palmitic acid, stearic acid, silane coupling agents, dimethyl silicone oil, oleic acid, TDO dispersants, hydroxyphosphates, carboxylates, polyether-modified dispersants, surfactants, wetting agents, etc.

[0017] Solvent: Used to dissolve the resin and adjust its viscosity and drying rate, constituting the balance of the organic carrier. It can be selected from one or more of diethylene glycol butyl ether acetate, tripropylene glycol butyl ether, dibutyl phthalate, terpineol, tributyl citrate, butyl carbitol, triethylene glycol butyl ether, propylene glycol methyl ether, ethylene glycol monobutyl ether, cyclohexanone, isopropanol, and acetone.

[0018] Other additives: used to improve dispersibility, wettability, and slurry stability, with a content of 0.1 wt% to 3 wt% of the total weight of the organic carrier. These can be selected from silane coupling agents, dispersants (such as phosphate esters and carboxylates), surfactants, defoamers, etc.

[0019] The preparation method of the organic carrier is as follows: First, the organic resin is dissolved in a portion of the solvent and stirred until completely dissolved to form a homogeneous resin solution; then, a premixed additive solution is added and stirred evenly; next, a thixotropic agent is slowly added and ultrasonic or ball milling is performed to ensure full dispersion; finally, solvent is added to adjust the target solid content and viscosity, and a high-speed shear homogenizer or a three-roll mill is used for final homogenization treatment. After filtration, a homogeneous and stable organic carrier is obtained.

[0020] In a second aspect, the present invention provides a metallized conductive thin film formed from the slurry described in the first aspect by heat treatment. The thickness of the film is typically between 10 nm and 500 nm, preferably between 30 nm and 200 nm, and more preferably between 50 nm and 150 nm. The film has a unique microstructure: its main body is a continuous glass phase matrix, in which multiple nanometer to submicrometer-scale metal conductive units are dispersed, the average particle size of which is, for example, 1 nm to 500 nm, preferably 5 nm to 200 nm. These metal conductive units form a three-dimensional conductive network in the glass phase matrix, making both the upper surface (facing the subsequent electrode layer) and the lower surface (contacting the silicon substrate passivation layer) of the film electrically active. Some metal conductive units can penetrate the glass phase matrix, providing a direct vertical conductive path; simultaneously, the metal conductive units can be electrically connected through tunneling or mutual contact, jointly ensuring the conductivity of the film in the thickness direction.

[0021] Thirdly, the present invention provides a method for preparing the above-mentioned metallized conductive thin film, characterized by comprising the following steps: Provide the slurry as described in the first aspect; The paste is applied to the surface of a silicon substrate with a passivation layer by means of screen printing, inkjet printing, transfer printing or coating to form a wet film with a predetermined pattern. The wet film is sintered to form the metallized conductive thin film.

[0022] The sintering process is carried out in air or a controlled atmosphere, with a peak temperature of 400°C to 800°C, preferably 500°C to 750°C, and more preferably 580°C to 680°C; the residence time at the peak temperature (sintering time) is 10 seconds to 30 minutes, preferably 10 seconds to 5 minutes. During this process, the organic carrier is removed, the glass powder softens and flows to form a continuous matrix and modifies the underlying passivation layer, while the metallic phase components migrate, aggregate, sinter, or are reduced in situ, ultimately forming a conductive film with the conductive network.

[0023] Fourthly, the present invention provides a metallization structure for a crystalline silicon solar cell. The structure, from bottom to top, includes: Silicon substrate; Passivation layer located on the silicon substrate; A metallized conductive film, as described in the second aspect, located on the passivation layer; A gate electrode layer located on the metallized conductive film, the gate electrode layer comprising a base metal conductive material.

[0024] The gate electrode layer containing base metal conductive material is preferably formed by printing and sintering a conductive paste containing extremely low amounts of precious metals, such as silver-coated copper paste, pure copper paste, copper alloy paste, or other precious metals with extremely low content (e.g., ≤10 wt%). This gate electrode layer forms a strong metallurgical bond with the upper surface of the underlying conductive film during co-sintering, thereby constructing a complete, low-loss conductive path from the silicon substrate through the conductive film layer to the gate electrode.

[0025] The present invention has the following beneficial effects: 1. The content of metallic phase components in the conductive paste (based on the mass of elemental metal) is 0.05wt%-30wt%, which greatly reduces dependence on precious metals and costs; 2. By using an independent conductive thin film, the interfacial contact function and the bulk conductivity function are decoupled, allowing for step-by-step optimization; 3. It has good process compatibility, can adopt conventional printing and sintering processes, and is easy to integrate into industrial production. 4. The glass phase matrix provides good adhesion, and the metal conductive network ensures stable low-resistance current transmission; 5. Suitable for the metallization requirements of high-efficiency crystalline silicon solar cells such as TOPCon (Tunnel Oxide Passivated Contact) and BC (Back Contact), possessing good adaptability and scalability. Attached Figure Description

[0026] Figure 1 This is a top view of the metallized conductive thin film formed in Embodiment 1 of the present invention; Figure 2This is a cross-sectional view of the metallized conductive thin film formed in Embodiment 1 of the present invention; Figure 3 This is a cross-sectional view of the metallized conductive thin film formed in Embodiment 2 of the present invention; Figure 4 This is a cross-sectional view of the metallized conductive thin film formed in Embodiment 3 of the present invention. Figure 5 This is a cross-sectional view of the metallized conductive thin film formed in Embodiment 4 of the present invention. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solutions of this invention, the embodiments of this invention will be described in detail below with reference to the accompanying drawings and specific examples. It should be particularly noted that the embodiments and comparative examples listed below are merely specific examples of this invention, intended to more intuitively illustrate the technical solutions and beneficial effects of this invention, and are not intended to limit this invention to the specific materials, formulations, process parameters, or application scenarios described. Those skilled in the art can make various modifications, substitutions, and variations based on the teachings of this invention without departing from the spirit and scope of this invention.

[0028] The main testing and characterization methods involved in the embodiments of this invention are as follows: Thin film structure characterization: The cross-section and surface morphology of the metallized conductive thin film were observed using a scanning electron microscope (SEM, model: FEI NovaNano SEM450) to analyze the film thickness, glass phase continuity and distribution and size of metal particles.

[0029] Sheet resistance test of thin film: The sheet resistance of the sintered conductive thin film was measured at 25°C using a four-probe tester (model: Kyowariken K-705RS) combined with the transmission line model (TLM) method.

[0030] Battery current-voltage characteristic test: The IV curve of the complete solar cell was measured using an AAA-grade solar simulator (model: Newport Oriel Sol3A, equipped with Keithley 2400 source meter) under standard test conditions (AM1.5G, 1000W / m2, 25℃), and the photoelectric conversion efficiency (Eta), open circuit voltage (Uoc), short circuit current (Isc), fill factor (FF), and series resistance (Rs) were calculated based on the IEC60904-1 standard.

[0031] Component reliability testing: The following tests were performed on the packaged battery modules: Damp heat test: 1000 hours at 85℃ and 85% relative humidity; Thermal cycling test: 600 cycles between -40°C and 85°C; High-temperature storage test: Stored at 150℃ for 1000 hours. After the test, monitor the degradation of its electrical performance and changes in its appearance.

[0032] Example 1: Conductive paste Weigh the raw materials according to the following weight percentages: Metal phase component (silver nanoparticles, average particle size approximately 150 nm, from Sigma-Aldrich): 20 wt% Glass powder (softening temperature 480℃, particle size approximately 1.5μm): 5wt% Organic carrier: 75 wt% The glass powder was prepared in-house, and its composition, by weight percentage of oxides, was 60% PbO, 25% Bi2O3, 10% SiO2, and 5% B2O3. The preparation method was as follows: the aforementioned raw materials were mixed evenly, melted at 1250℃ for 1.5 hours, water quenched to obtain glass slag, and then ball-milled (zirconia balls, 250 rpm, 8 hours) and dried.

[0033] The organic carrier consists of: polyvinyl butyral (PVB) resin (Mowital B60H, purchased from Kuraray, accounting for 15 wt% of the carrier), ethyl cellulose (Ethocel STD 10, purchased from Dow, accounting for 15 wt% of the carrier), hydrogenated castor oil (accounting for 2 wt% of the carrier), silane coupling agent (KH-550, accounting for 1 wt% of the carrier), and the balance being diethylene glycol butyl ether acetate.

[0034] Preparation process: (1) Dissolve PVB resin and ethyl cellulose in a portion of diethylene glycol butyl ether acetate and heat and stir until completely dissolved; (2) Add silane coupling agent and stir until homogeneous; (3) Add hydrogenated castor oil and ultrasonically disperse for 30 minutes; (4) Add silver nanoparticles and glass powder, and vacuum stir in a double planetary mixer for 60 minutes; (5) The mixture is ground 4 times by a three-roll mill (roller speed ratio 1:3:9, roller spacing 10μm) to achieve a fineness of Hegman 7.5 (corresponding to a particle size ≤10μm), and then passed through a 300-mesh sieve to obtain a uniform slurry.

[0035] (ii) Conductive thin film Using a screen printing machine with a suitable screen, the above paste is printed onto the surface of a silicon wafer with a TOPCon cell structure to form a wet film with a linewidth of 30-40μm and a thickness of about 3μm.

[0036] The printed silicon wafers are placed in a chain sintering furnace for the first heat treatment: peak temperature 650℃, peak time 3 seconds, and total heating and cooling time approximately 40 seconds. After heat treatment, the wet film transforms into a continuous, dense metallized conductive film with a thickness of approximately 100-300 nm.

[0037] Reference Figure 1 and Figure 2 Scanning electron microscopy (SEM) revealed that the film had a uniform thickness of approximately 240 nm. The film consisted of a continuous glassy matrix with dispersed silver conductive units. Some silver particles penetrated the glassy phase, with their ends exposed on the upper and lower surfaces of the film, respectively. The upper surface exhibited discretely distributed silver particle protrusions, primarily with diameters of approximately 50-300 nm, uniformly dispersed with spacing of approximately 100-800 nm. Four-probe analysis (TLM method) showed a sheet resistivity of approximately 55 Ω / sq, indicating good conductivity.

[0038] Examples 2-4: Three slurries were prepared with metal phase contents of 5wt%, 15wt%, and 30wt% (content based on elemental silver, and all silver sources were silver nitrate), with glass powder content of 5wt% in each slurry and the remainder being an organic carrier (composition same as in Example 1).

[0039] After undergoing the same printing and first heat treatment process (peak temperature 620℃), three types of conductive films were obtained: Reference Figure 3 , Figure 4 and Figure 5 The sample film of Example 2 has a thickness of about 150 nm, with dense conductive units within the film and small, sparsely distributed silver particles. The sheet resistance of the film measured by TLM method is about 58 Ω / sq. The sample film of Example 3 has a thickness of about 150 nm, with dense conductive units within the film and larger, more densely distributed silver particles compared to the 5 wt% sample. The sheet resistance of the film measured by TLM method is about 59 Ω / sq. The sample of Example 4 has a thickness of about 150 nm, with dense conductive units within the film and very dense silver particles, some of which even form continuous conductive paths. The sheet resistance of the film measured by TLM method is about 58 Ω / sq.

[0040] The above results indicate that conductive films with excellent conductivity can be formed in the range of 5-30 wt% metal phase content. Within this range, the increase in metal phase content does not significantly change the electrical properties of the conductive film. As the metal phase content increases, more silver particles can be observed to precipitate and expose the film surface.

[0041] Comparative Example 1: Based on Example 1, the only difference was that the silver nanopowder content in the slurry was increased to 40 wt%, the glass powder content was 5 wt%, and the remainder was an organic carrier (composition same as Example 1). After the same printing and first heat treatment process (peak temperature 620°C), the thickness of the resulting film increased to approximately 300 nm, silver particle agglomeration increased, and uniformity decreased; the resistivity of the film was measured to be 56 Ω / sq, which was slightly higher than that of Example 1, and the cost of the conductive film increased significantly due to the use of more silver.

[0042] Example 5: This embodiment uses an N-type single-crystal silicon wafer (182mm × 182mm) with a SiNx antireflection layer on the front and a TOPCon passivation contact structure (tunneling oxide layer thickness of approximately 1.5nm and phosphorus-doped polycrystalline silicon layer thickness of approximately 150nm) on the back as an example to illustrate the metallization method of the present invention. The specific steps are as follows: Step S1: On the back of the silicon wafer, a paste with a predetermined pattern is printed using the paste and screen printing process of Example 1 to form a wet film. Subsequently, a first heat treatment is performed in a chain sintering furnace in an air atmosphere: peak temperature 650°C, peak time 3 seconds, and total heating and cooling time approximately 40 seconds, forming a metallized conductive film with a thickness of approximately 150 nm.

[0043] Step S2: Screen print silver-coated copper grid paste (copper content > 70 wt%) onto the conductive surface, followed by a second heat treatment: peak temperature 240℃, time 120 seconds (lower than the peak temperature of the first heat treatment).

[0044] Step S3: The cured solar cells undergo Laser Enhanced Contact Optimization (LECO) process and then enter the testing machine. The test results are shown in Table 1.

[0045] Comparative Example 2: Based on Example 5, the difference is that a commercial thick-film silver paste with a silver content of 88 wt% was used. The same image as in Example 5 was obtained using a screen printing machine, and the sintering and processing process of the commercial thick-film silver paste was followed to obtain the comparative solar cell. The test results are shown in Table 1.

[0046] Comparative Example 3: Based on Example 5, the difference is that a silver-nickel composite paste with a silver content of 78 wt% was used for one-time printing and laser sintering. The test results are shown in Table 1.

[0047] Comparative Example 4: Based on Example 5, the difference is that a commercially available 80% silver conductive seed layer paste was used. After screen printing and sintering under the same conditions to form contacts, the solar cell wafers were prepared using the same steps S2 and S3 as in Example 5 and then tested. The test results are shown in Table 1.

[0048] Comparative Example 5: Based on Example 5, the difference is that, on the same silicon wafer, no seed layer paste is printed; instead, silver-clad copper grid line paste is directly printed and sintered. This cell failed to form effective ohmic contacts, making it impossible to obtain reliable electrical performance data.

[0049] Table 1. Cell efficiency and IV test results

[0050] Note: Except for “Silver Consumption Calculated for Backside Paste”, the other data in Table 1 are relative differences calculated based on Comparative Example 2.

[0051] Using the solar cell printed with conventional high-silver thick-film paste in Comparative Example 2 as the first benchmark, the solar cell obtained in Example 5 has the same short-circuit current (Isc), same open-circuit voltage (Uoc), slightly higher fill factor (FF), lower series resistance (Rs), and an overall efficiency 0.01% higher. In terms of silver consumption, the back-side silver consumption in Example 5 is reduced from 35.2 mg to 9.8 mg compared to Comparative Example 2, a reduction of over 70%. Example 5 significantly reduces silver consumption while maintaining a slight improvement in solar cell photoelectric efficiency, demonstrating that the present invention can greatly reduce the dependence of photovoltaic cell metallization process on silver, which is beneficial for cost reduction and efficiency improvement in the photovoltaic industry.

[0052] Using the 80wt% silver conductive paste commonly found in Comparative Example 4 as a second benchmark, the short-circuit current (Isc) and open-circuit voltage (Uoc) of the solar cell obtained in Example 5 remained the same, while the fill factor (FF) was 0.24 higher, the series resistance (Rs) was lower, and the efficiency was 0.02% higher. In terms of silver consumption, the back-side silver consumption in Example 5 was reduced from 18.6mg to 9.8mg compared to Comparative Example 4, a reduction of nearly 50%, demonstrating a significant advantage in cost reduction and efficiency improvement.

[0053] The battery cell grid lines obtained in Example 5 passed the tensile test and met industrial standards. Electron microscopy observation showed that the highly active nano-silver powder particles in the grid line conductive layer slurry formed a good metallurgical bond with the silver protrusions on the surface of the conductive film, thus enabling the construction of an effective current-carrying network even with extremely low silver content, and ensuring that the grid line adhesion meets the requirements of industrial applications.

[0054] Example 6: This embodiment is based on Example 5, the difference being that the organic carrier formulation in the slurry is different.

[0055] Organic carrier composition: Ethyl cellulose: 8 wt% (as carrier) Polyamide wax: 1.5 wt% Diethylene glycol butyl ether acetate: 85.5 wt% Silane coupling agent: 0.5 wt% Surfactant: 0.5 wt% The remainder is terpineol.

[0056] The carrier has a viscosity of approximately 3000 cps and a suitable surface tension. When paired with a 3-20 μm printhead, it can be successfully used to print fine conductive patterns.

[0057] Examples 7-8: Based on Example 5, the difference lies in the composition of the glass powder: in Example 7, the glass powder adopts the PbO-TeO2-SiO2 system with a softening temperature of 300-450℃; in Example 8, the glass powder adopts the SiO2-B2O3-ZnO system (lead-free) with a softening temperature of 450-600℃.

[0058] The same formula is used to prepare the pulp and form a film.

[0059] The results showed that both could form good conductive films. The conductive film made from the glass powder in Example 7 had a film resistance of 60 Ω / sq. The glass powder in Example 8 was an environmentally friendly lead-free system, and the film resistance was 63 Ω / sq, demonstrating the environmental adaptability of the present invention.

[0060] Example 9: Based on Example 5, the difference is that this example uses a blend of two glass powders.

[0061] Glass powder A: PbO-Al2O3-Nb2O5-B2O3 system; Glass powder B: WO3-V2O5-MoO3-SiO2 system The conductive metal is silver. It is prepared by mixing 18wt% silver (silver content in the conductive metal) with a certain proportion of glass powder A and glass powder B, and selecting a suitable carrier.

[0062] Using this conductive paste, a thin film with excellent conductivity is formed through screen printing and high-temperature sintering. A paste containing more than 70 wt% copper can then be printed onto this conductive film to provide conductivity. By adjusting the combination of glass components, its application on the front side of photovoltaic cells is achieved, demonstrating the invention's greater adaptability.

[0063] The prepared solar cells were subjected to reliability testing: Damp heat test (85℃ / 85% RH, 1000 hours): Module efficiency degradation <3%; Thermal cycling test (-40℃↔85℃, 600 cycles): No grid wire detachment; High-temperature storage test (150℃, 1000 hours): Stable performance.

[0064] The results show that the metallized structure of the present invention has excellent long-term reliability.

[0065] Example 10: Slurry formulation: Metallic phase composition: 0.1 wt% micron-sized copper powder (average particle size approximately 1.0 μm, purchased from Alfa Aesar); Glass powder (softening temperature approximately 500°C, composition same as in Example 1): 5 wt% Organic carrier (composition same as in Example 1): 80 wt%.

[0066] Preparation and film formation: Prepare the slurry according to the method described in Example 1; The paste is printed onto the back of an N-type silicon wafer with a TOPCon structure using screen printing to form a wet film. The first heat treatment is carried out in a chain sintering furnace: peak temperature 650℃, peak time 3 seconds, total process time approximately 40 seconds; A metallized conductive film with a thickness of approximately 180 nm was obtained.

[0067] SEM observation showed that copper powder and silver nanoparticles together formed a conductive network in the film, and the silver particles were uniformly distributed on the surface of the copper powder and in the glass phase; the sheet resistance of the film was measured to be about 60 Ω / sq by four-probe testing (TLM method).

[0068] Subsequently, silver-coated copper grid line paste (copper content > 70 wt%) was printed, and after a second heat treatment (peak temperature 240 °C), the battery efficiency was comparable to that of Example 5 (η ≈ 24.86%), with a silver consumption of approximately 9.8 mg / piece.

[0069] Example 11: Slurry formulation: Metallic phase composition: Nickel-silver alloy powder (Ni:Ag=7:3, average particle size about 2.0μm, silver content 30wt%, purchased from Shanghai Buwei) 15wt% (based on the mass of elemental metal). Glass powder (softening temperature approximately 480°C, composition same as in Example 1): 5 wt% Organic carrier (composition same as in Example 1): 80 wt%.

[0070] Preparation and film formation: The slurry preparation process is the same as in Example 1; The printing and sintering processes are the same as in Example 10; A conductive thin film with a thickness of approximately 200 nm was obtained.

[0071] SEM showed that the alloy particles were uniformly dispersed in the glass phase, forming a continuous conductive channel; the sheet resistance of the thin film was about 65 Ω / sq; subsequent printing of grid lines using pure copper paste (copper content > 95 wt%) resulted in a cell efficiency of 24.82% and silver consumption was further reduced to about 7.5 mg / piece, proving that the nickel-silver alloy phase can also effectively achieve ohmic contact and conductivity.

[0072] Example 12: Slurry formulation: Metal phase composition: Silver-coated glass microspheres (glass core diameter about 1.5 μm, silver layer thickness about 50 nm, silver coverage > 90%, self-made) 12 wt% (based on the mass of elemental metal). Glass powder (softening temperature approximately 480°C, composition same as in Example 1): 5 wt% Organic carrier (composition same as in Example 1): 83 wt%.

[0073] Preparation and film formation: The slurry preparation process is the same as in Example 1; The printing and sintering processes are the same as in Example 10; A conductive thin film with a thickness of approximately 220 nm was obtained, and the sheet resistance of the film was measured to be approximately 58 Ω / sq. Subsequent printing of silver-coated copper grid lines resulted in a battery efficiency of 24.84% and a silver consumption of approximately 10.2 mg / piece, indicating that silver-coated composite particles are also suitable for the conductive film system of this invention.

[0074] The above embodiments and comparative examples fully demonstrate that the metallized conductive thin film, paste, and method provided by the present invention, by constructing a stepwise, functionally decoupled electrode structure with ultra-low silver content (≤30 wt%), successfully achieves a balance between high performance, low cost, high process stability, and good reliability. In particular, in direct comparison with existing technical solutions, the present invention significantly reduces dependence on precious metals while overcoming problems such as difficulty in process control and interface-bulk coupling in integrated solutions, providing a practical and innovative path for the metallization of high-efficiency crystalline silicon solar cells.

[0075] The specific raw materials, process parameters, and battery structures used in the above embodiments are examples selected to more clearly and completely demonstrate the technical solution of the present invention and verify its technical effects.

[0076] Those skilled in the art should understand that: The terms "metal phase component," "glass powder," and "organic carrier" used in the claims and specification of this invention cover all similar or equivalent substances capable of achieving the functions described herein.

[0077] The specific content range, temperature range, time range, etc., can all be determined through conventional experiments to achieve the purpose of this invention, including their endpoint values ​​and any values ​​within the range.

[0078] The paste, thin film, and method of the present invention are applicable to various types of crystalline silicon solar cell structures (such as TOPCon, BC, etc.), and are not limited to the types listed in the embodiments.

[0079] Any technical solution obtained by adopting equivalent substitution, equivalent change or reasonable extension based on the concept of this invention shall be deemed to fall within the protection scope of this invention.

Claims

1. A slurry, characterized in that: By percentage of total weight, it includes: The metallic phase composition is 0.05 wt% to 30 wt%, based on the mass of the elemental metal; Glass powder 1wt%~10wt%; The remaining organic carrier; The slurry is used to form a metallized conductive film, which is used to achieve low-resistance ohmic contact and electrical connection between the silicon substrate of the crystalline silicon solar cell and the grid electrode layer containing base metal.

2. The slurry according to claim 1, characterized in that: The metallic phase component is selected from at least one of metal powder, alloy powder, metal-coated particles, and metal compounds that can decompose or be reduced to generate elemental metals during heat treatment.

3. The slurry according to claim 2, characterized in that: The metallic phase component is selected from at least one of elemental silver powder, silver alloy powder, silver-coated particles, and silver compounds that can decompose or be reduced to elemental silver during heat treatment.

4. The slurry according to any one of claims 1-3, characterized in that: The metallic phase component accounts for 3wt%-25wt% of the total mass of the slurry, based on the mass of the elemental metal.

5. The slurry according to claim 4, characterized in that: The metallic phase component accounts for 5wt%-20wt% of the total mass of the slurry, based on the mass of the elemental metal.

6. The slurry according to any one of claims 1-3, characterized in that: The softening temperature of the glass powder is 300°C to 600°C.

7. A metallized conductive thin film, characterized in that: It is formed by heat treatment of the slurry as described in any one of claims 1-6.

8. A method for preparing a metallized conductive thin film, characterized in that, Includes the following steps: Provide the slurry as described in any one of claims 1-6; The slurry is coated onto the surface of a substrate to form a wet film; The wet film is sintered to form a metallized conductive film.

9. The preparation method according to claim 8, characterized in that: The peak temperature of the sintering process is 400°C to 800°C, and the sintering time is 10 seconds to 30 minutes.

10. A metallization structure for a crystalline silicon solar cell, characterized in that, From bottom to top, this includes: Silicon substrate; Passivation layer located on the silicon substrate; The metallized conductive film as described in claim 7 is located on the passivation layer; as well as A gate electrode layer containing base metal conductive material is located on the metallized conductive thin film.

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