Back contact solar cell, preparation method thereof and photovoltaic module

Abstract

The invention discloses a back contact solar cell, a preparation method thereof and a photovoltaic module, and relates to the photovoltaic field. The method comprises the following steps: obtaining a semiconductor substrate; preparing an electrode on the surface of the semiconductor substrate by using the electrode slurry; the electrode slurry comprises 60%-80% of conductive metal particles, 15%-30% of an organic carrier and 5%-10% of an additive. The conductive metal particles comprise silver powder and aluminum powder, and the weight ratio of the silver powder to the aluminum powder is (2.5-7): 1; the additive comprises nano cerium oxide, a polyimide precursor and a sintering aid; the sintering aid is glass powder containing Bi2O3 and B2O3, and the weight ratio of the glass powder to the B2O3 is 1: (1.5-2.5). The resistivity of the electrode is reduced to 2.5 * 10 <-6 > omega.cm, and the series resistance of the electrode is reduced; the adhesive force between the electrode and the silicon substrate reaches 4B level, and the falling phenomenon is avoided; and a BC battery process is adapted, and the photoelectric conversion efficiency is improved by 0.5-0.8%.

Description

Technical Field

[0001] This application relates to the photovoltaic field, and in particular to a back-contact solar cell, its preparation method, and a photovoltaic module. Background Technology

[0002] With the growing global demand for clean energy, solar cells, as a crucial component of sustainable development, have become a focus of industry attention regarding their efficiency and cost. In recent years, back-contact cell technologies such as IBC, HBC, and HIT have demonstrated significant market potential due to their high efficiency. The core of these technologies lies in moving the front electrode to the back of the cell, thereby reducing electrode shading, increasing the light-receiving area, and improving the electrical properties of the cell surface. Among these technologies, the electrode paste is a key material for forming the solar cell electrodes, directly affecting the cell's electrical performance and reliability.

[0003] However, in back-contact (BC) solar cells, traditional electrode pastes often fail to meet the requirements due to the special electrode design and higher process requirements. Traditional BC cell electrode pastes are mainly silver-based, sometimes with a small amount of aluminum powder added to reduce costs. However, these pastes suffer from several drawbacks: insufficient conductivity (the metal particles have insufficient conductivity, especially after high-temperature sintering, increasing electrode series resistance, directly affecting the fill factor (FF) and reducing photoelectric conversion efficiency); poor adhesion (insufficient chemical bonding between the electrode and the silicon substrate, leading to poor adhesion during sintering and easy electrode detachment, especially during long-term cell operation, affecting cell stability and lifespan); unstable rheology (inconsistent flowability and stability of the paste during printing, easily causing grid breaks or edge diffusion, resulting in variations in electrode width and thickness, thus affecting electrode uniformity and electrical performance); and high silver resource consumption (due to the high cost of silver, using large amounts of silver-based paste increases the overall cost of the cell, limiting the commercialization of BC cells). Summary of the Invention

[0004] This application provides a back-contact solar cell, its preparation method, and a photovoltaic module, mainly addressing the problems of poor electrode conductivity and poor adhesion in back-contact solar cells.

[0005] According to one aspect of this application, a method for fabricating a back-contact solar cell is provided, comprising:

[0006] Obtaining a semiconductor substrate;

[0007] Electrodes are prepared on the surface of a semiconductor substrate using an electrode paste. The electrode paste comprises the following components by weight percentage: 60%–80% conductive metal particles, 15%–30% organic carrier, and 5%–10% additives. The conductive metal particles include silver powder and aluminum powder, with a weight ratio of silver powder to aluminum powder of (2.5–7):1. The additives include nano-cerium oxide, polyimide precursor, and sintering aid. The sintering aid is glass powder containing Bi2O3 and B2O3, with a weight ratio of Bi2O3 to B2O3 of 1:(1.5–2.5).

[0008] Furthermore, by weight percentage, the electrode paste comprises: 50-70% silver powder, 10-20% aluminum powder, 15-28% organic carrier, 0.5-2% nano-cerium oxide, 3-5% polyimide precursor, and 1-3% sintering aid.

[0009] Furthermore, the electrode paste comprises: 65-70% silver powder, 10-15% aluminum powder, 18-22% organic carrier, 1.2-1.8% nano-cerium oxide, 4.0-4.5% polyimide precursor, and 2-2.5% sintering aid.

[0010] Furthermore, the weight ratio of silver powder to aluminum powder is (4~7):1.

[0011] Furthermore, the weight ratio of nano-cerium oxide to the polyimide precursor is 1:(2~4).

[0012] Furthermore, the weight ratio of silver powder to aluminum powder is (4.5~6.5):1.

[0013] Furthermore, the weight ratio of nano-cerium oxide to polyimide precursor is 1:(2.5~3.5).

[0014] Furthermore, the polyimide precursor is a polyamic acid solution.

[0015] Furthermore, the weight ratio of the organic carrier to the polyimide precursor is (4~5):1.

[0016] Furthermore, the organic carrier includes ethyl cellulose, terpineol, and a dispersant; the weight ratio of ethyl cellulose, terpineol, and the dispersant is 1:(8~12):(0.1~0.3).

[0017] Furthermore, the weight ratio of Bi2O3 to B2O3 is 1:(1.8~2.3).

[0018] Furthermore, the weight ratio of conductive metal particles to sintering aid is 1:(0.03~0.05).

[0019] Furthermore, the particle size of the conductive metal particles is 50~150nm; among them, the D50 particle size of silver powder is 80~120nm, and the D50 particle size of aluminum powder is 100~150nm.

[0020] Furthermore, the particle size of the nano-cerium oxide is 10~50nm.

[0021] Furthermore, the preparation method of the above-mentioned electrode paste includes the following steps:

[0022] Step S1: Obtain raw materials according to the electrode slurry composition ratio; wherein, the electrode slurry includes 60%~80% conductive metal particles, 15%~30% organic carrier, and 5%~10% additives; wherein, the conductive metal particles include silver powder and aluminum powder, with a weight ratio of silver powder to aluminum powder of (2.5~7):1; the additives include nano-cerium oxide, polyimide precursor, and sintering aid; the sintering aid is glass powder containing Bi2O3 and B2O3, with a weight ratio of Bi2O3 to B2O3 of 1:(1.5~2.5);

[0023] Step S2: Mix the raw materials to obtain electrode slurry.

[0024] Further, step S2 includes the following steps:

[0025] Step S2-1: Mix the organic carrier, nano-cerium oxide and polyimide precursor to obtain the first mixture;

[0026] Step S2-2: Add silver powder and aluminum powder to the first mixture in multiple batches to obtain the second mixture;

[0027] Step S2-3: Add the sintering aid to the second mixture to obtain the third mixture;

[0028] Step S2-4: Vacuum degassing treatment is performed on the third mixture to obtain electrode slurry.

[0029] Further, in step S2-1, the organic carrier, nano-cerium oxide and polyimide precursor are subjected to ultrasonic treatment for 20-40 minutes.

[0030] Furthermore, after adding silver powder and aluminum powder to the first mixture, the mixture is ball-milled to obtain the second mixture; the ball-milling time is 4-6 hours.

[0031] According to a second aspect of this application, a back-contact solar cell is provided, which is obtained by the above-described method for preparing a back-contact solar cell.

[0032] According to a third aspect of this application, a photovoltaic module is provided, comprising at least one of the aforementioned back-contact solar cells;

[0033] Encapsulation layer, used to encapsulate back-contact solar cells;

[0034] The cover plate is placed on the encapsulation layer.

[0035] Furthermore, the photovoltaic module includes multiple back-contact solar cells, which are connected in series and / or in parallel.

[0036] According to a fifth aspect of this application, a power generation system is provided, including the aforementioned photovoltaic module.

[0037] The electrode paste for the back-contact solar cell provided in this application has at least the following advantages:

[0038] (1) By optimizing the composition and ratio of each component in the electrode slurry formulation, the electrode resistivity of the slurry after sintering can be reduced to 2.5 × 10⁻⁶. -6 Compared to traditional pastes, the resistivity is reduced by 30% (Ω·cm), effectively reducing electrode series resistance, thereby increasing the battery fill factor and enhancing the overall photoelectric performance of the battery.

[0039] (2) The adhesion between the electrode and the silicon substrate is significantly improved. The adhesion test result reaches level 4B, with no detachment, ensuring the stability and durability of the electrode on the solar cell.

[0040] (3) It is compatible with BC battery technology, which can effectively reduce the carrier recombination rate inside the battery, improve charge transport efficiency, and improve photoelectric conversion efficiency by 0.5~0.8%;

[0041] (4) The electrode paste has suitable rheological properties, which makes the paste more stable during the printing process, reduces grid breakage and edge diffusion, and increases the uniformity and consistency of the electrode.

[0042] (5) Reduce the demand for high-priced silver and significantly reduce the manufacturing cost while ensuring battery performance. Detailed Implementation

[0043] As can be seen from the background technology, the conductivity of metal particles in traditional BC battery electrode paste is not high enough. Especially after high-temperature sintering, the series resistance of the electrode increases, reducing the photoelectric conversion efficiency. During the sintering process, the poor adhesion between the metal particles and the silicon substrate can easily lead to electrode detachment. During the printing process, the paste is prone to grid breakage or edge diffusion, affecting the uniformity and electrical performance of the electrode. Silver resources are consumed in large quantities, resulting in high costs.

[0044] According to some embodiments of this application, one aspect of this application provides a method for preparing a back-contact solar cell, including obtaining a semiconductor substrate and preparing an electrode on the surface of the semiconductor substrate using an electrode paste; wherein, the electrode paste comprises, by weight percentage, 60%~80% conductive metal particles, 15%~30% organic carrier, and 5%~10% additives; wherein, the conductive metal particles include silver powder and aluminum powder, with a weight ratio of silver powder to aluminum powder of (2.5~7):1; the additives include nano-cerium oxide, polyimide precursor, and sintering aid; the sintering aid is glass powder containing Bi2O3 and B2O3, with a weight ratio of Bi2O3 to B2O3 of 1:(1.5~2.5).

[0045] The conductive metal particles in this application constitute any value or a range between 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, and 80% of the slurry; the organic carrier constitutes any value or a range between 15%, 18%, 20%, 22%, 25%, 28%, and 30% of the slurry; the additives constitute any value or a range between 5%, 6%, 7%, 8%, 9%, and 10% of the slurry; and silver powder and aluminum powder are also present. The weight ratio of Bi₂O₃ to B₂O₃ is any value from 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, 5.0:1, 5.5:1, 6.0:1, 6.5:1, 7.0:1, or any value between any two; the weight ratio of Bi₂O₃ to B₂O₃ is any value from 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, or any value between any two.

[0046] In the electrode paste formulation of the back contact solar cell of this application, the components have the following synergistic effect, which jointly optimizes the electrode performance.

[0047] Synergistic effect of conductive metal particles and sintering aids: During sintering, the sintering aids form a transitional liquid phase that effectively wets and bridges silver and aluminum particles, promoting their diffusion and rearrangement to form a more porous and denser conductive network. Simultaneously, the aid can react slightly with the silicon substrate surface to form stable chemical bonds (such as Si-OM bonds, where M is a metal element in the aid), thereby significantly improving adhesion while reducing electrode resistance.

[0048] Synergistic interaction between polyimide precursor and organic carrier: The polyimide precursor and ethyl cellulose in the organic carrier form an interpenetrating network through intermolecular forces. This structure provides excellent thixotropy and printability in the slurry, preventing particle sedimentation at high solids content. During sintering, ethyl cellulose decomposes, while the polyimide precursor undergoes cyclization and polycondensation simultaneously, generating a three-dimensional polyimide network in situ. This network not only acts as a toughening phase to encapsulate metal particles and buffer thermal stress, but also forms a composite with the residual carbon after the organic carrier decomposes, enhancing the mechanical strength and thermal stability of the electrode.

[0049] Nano-cerium oxide serves as a core bridge and is key to achieving multiple synergies in the electrode paste of this application.

[0050] Synergistic effect of cerium oxide nanoparticles and conductive metal particles: Cerium oxide nanoparticles can be adsorbed on the surface of silver and aluminum particles, inhibiting excessive grain growth during sintering and refining the electrode microstructure.

[0051] Synergistic effect of nano-cerium oxide and polyimide precursor: The active sites on its surface can combine with the functional groups of the polyimide precursor, so that the generated polyimide network is more uniformly anchored at the interface between the metal particles and the substrate.

[0052] Synergistic effect of nano-cerium oxide with sintering aids and substrates: Cerium oxide can act as an interface transition layer between sintering aids and silicon substrates, optimize the band structure of the contact area, and reduce the contact resistance and recombination loss of charge carrier transport.

[0053] The electrode slurry provided in this application systematically solves the contradiction between high conductivity, strong adhesion, high reliability and low cost of BC battery electrodes through four synergistic pathways: densification of the conductive network by sintering aids, toughening of polyimide-organic carrier composite, multi-interface bridging of nano-cerium oxide, and optimization of silver-aluminum ratio.

[0054] The electrode paste provided in this application, through optimized metal particle ratios, particularly the specific doping ratio of silver and aluminum powder, enables the electrode resistivity after sintering to be reduced to 2.5 × 10⁻⁶. -6Compared to traditional pastes, the resistivity is reduced by 30% in Ω·cm, effectively reducing electrode series resistance and thus improving the fill factor (FF) and overall photoelectric performance. By adding nano-cerium oxide as an interface modifier, combined with sintering aids, the bonding strength between the electrode and the silicon substrate is significantly improved, achieving an adhesion test result of 4B level with no detachment, ensuring the stability and durability of the electrode on the cell. This optimized electrode paste formulation is particularly suitable for BC battery processes, effectively reducing the carrier recombination rate inside the cell, improving charge transport efficiency, and increasing photoelectric conversion efficiency by 0.5~0.8%. The addition of a polyimide precursor improves the rheological properties of the electrode paste, making it more stable during printing and reducing grid breakage and edge diffusion. By increasing the proportion of aluminum powder in the paste, the dependence on high-priced silver is reduced, significantly reducing manufacturing costs while ensuring battery performance.

[0055] To further improve both electrode conductivity and adhesion, the electrode slurry formulation is further optimized. In some specific embodiments, the electrode slurry, by weight percentage, comprises: 50-70% silver powder, 10-20% aluminum powder, 15-28% organic carrier, 0.5-2% nano-cerium oxide, 3-5% polyimide precursor, and 1-3% sintering aid. Further, the electrode slurry comprises: 65-70% silver powder, 10-15% aluminum powder, 18-22% organic carrier, 1.2-1.8% nano-cerium oxide, 4.0-4.5% polyimide precursor, and 2-2.5% sintering aid. Preferably, the electrode paste comprises: 65-67% silver powder, 13-15% aluminum powder, 19-21% organic carrier, 1.4-1.6% nano-cerium oxide, 4.0-4.3% polyimide precursor, and 2.2-2.5% sintering aid. By employing the above-mentioned progressively optimized paste formulation, an optimal balance can be achieved between conductivity (high silver content) and cost control (limiting aluminum content to avoid excessive sacrifice of conductivity), and together with other components (such as the organic carrier content), the paste ensures excellent printing rheology and sintered film quality.

[0056] To better balance high electrode conductivity and cost control, the ratio of silver powder to aluminum powder is optimized. In some specific embodiments, the weight ratio of silver powder to aluminum powder is (4~7):1; for example, (4.5~6.5):1. By controlling the weight ratio of silver powder to aluminum powder within the above range, an optimized balance between performance and cost is achieved. At this ratio, aluminum can partially diffuse to the silver grain boundaries during sintering, which can effectively suppress silver ion migration, improve the electrode's resistance to potential-induced degradation (PID), and avoid a significant decrease in overall conductivity due to excessive aluminum content. By precisely limiting the ratio of silver powder to aluminum powder, the key ratio can be achieved to ensure that the electrode has high conductivity close to that of a pure silver electrode, while introducing the optimal ratio of aluminum to effectively suppress silver ion migration and improve the thermal expansion matching between the electrode and the silicon substrate, thereby improving the long-term reliability of the electrode and meeting the dual requirements of high conductivity and high reliability of BC batteries.

[0057] To fully leverage the synergistic effect between nano-cerium oxide and the polyimide precursor, the ratio of the two is optimized. In some specific embodiments, the weight ratio of nano-cerium oxide to the polyimide precursor is 1:(2~4); for example, any value or any range between 1:2, 1:2.5, 1:2.8, 1:3.0, 1:3.2, 1:3.5, and 1:4; or, for another example, 1:(2.5~3.5); the particle size of the nano-cerium oxide is 10~50 nm. The above-mentioned ratio allows for a better synergistic effect between nano-cerium oxide and the polyimide precursor. Nano-cerium oxide acts as an interface modifier, reducing contact resistance; the polyimide precursor, after sintering, forms a polymer network, providing mechanical adhesion and stress buffering. At this specific ratio, cerium oxide nanoparticles can be more uniformly dispersed and anchored in the polyimide network, forming an inorganic-organic composite interface layer, simultaneously and maximally achieving the effects of reducing resistance and enhancing adhesion. This structure can utilize cerium oxide to improve electrical contact and rely on the polyimide network to provide strong adhesion and stress buffering, which is superior to single components or other ratios.

[0058] To improve the density and reduce the resistance of the electrode after sintering, in some specific embodiments, the weight ratio of conductive metal particles to sintering aid is 1:(0.03~0.05); for example, 1:0.03, 1:0.04, 1:0.05. This ratio ensures that sufficient sintering aid forms a suitable liquid phase at low temperatures, fully wetting and bridging the metal particles, thus promoting densification; at the same time, it avoids excessive addition leading to an excessive insulating phase, which could impair the electrode's conductivity.

[0059] To balance the printing performance of the paste with the mechanical properties of the sintered film, in some specific embodiments, the mass ratio of organic carrier to polyimide precursor is (4~5):1; for example, 4:1, 4.5:1, 5:1. This ratio ensures that the paste has suitable viscosity and rheological properties for screen printing (mainly provided by the organic carrier), while ensuring sufficient precursor content to form a continuous and robust polyimide network after sintering, thereby obtaining an electrode film layer with strong adhesion and thermal shock resistance.

[0060] In some specific embodiments, the polyimide precursor is a polyamic acid solution; for example, a mixture of two monomers can be used: pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA), which are directly mixed and added to the slurry, and react to generate polyimide during sintering; another example is the use of a pre-reacted solution: a polyamic acid (PAA) solution; specifically, a viscous liquid in which pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) monomers are pre-reacted in N-methylpyrrolidone (NMP) solvent, which has more stable properties, is easier to mix in the slurry, and has a solid content of about 15%.

[0061] In some specific embodiments, the particle size of the conductive metal particles is 50-150 nm; wherein, the D50 particle size of the silver powder is 50-120 nm, preferably 80-100 nm; and the D50 particle size of the aluminum powder is 100-200 nm, preferably 100-150 nm. Using particles of the above particle sizes helps to form a dense, low-resistance sintered electrode film. The optimized particle size range of the metal particles balances conductivity, adhesion, and printability. Specifically, the silver powder particle size of 50-120 nm provides higher sintering activity and a larger specific surface area, which is beneficial for forming a dense, low-resistance conductive network at low temperatures and enhancing contact with the silicon substrate. The aluminum powder particle size of 100-200 nm, with its slightly larger particle size, helps to regulate the rheological properties of the paste, prevents excessive viscosity at high solid content, and ensures the clarity and uniformity of printed lines. Simultaneously, it can better complement and fill the silver powder particles during sintering, improving the density of the electrode film. The specific particle size combination of the aforementioned silver and aluminum powders, combined with the aforementioned preferred ratio, works synergistically to form a more stable metal-silicon contact interface after sintering, effectively reducing contact resistance and improving the battery fill factor. Furthermore, this particle size system also works in conjunction with the polyimide precursor and other functional components in the slurry to further enhance the mechanical adhesion and long-term reliability of the electrodes through interfacial reactions during the sintering process.

[0062] In some specific embodiments, the organic carrier includes ethyl cellulose, terpineol, and a dispersant; the weight ratio of ethyl cellulose, terpineol, and the dispersant is 1:(8~12):(0.1~0.3). This ratio makes the slurry viscosity, thixotropy, and drying speed more suitable for high-precision printing of the BC battery back electrode.

[0063] In some specific embodiments, the sintering aid is a glass powder containing Bi2O3 and B2O3; the weight ratio of Bi2O3 to B2O3 is 1:(1.8~2.3). Using this type of low-temperature glass powder as a sintering aid allows for good wetting at lower temperatures, promoting electrode co-firing without damaging the precise back passivation layer of the BC battery.

[0064] In some specific embodiments, the preparation method of the above-mentioned electrode paste includes the following steps:

[0065] Step S1: Obtain raw materials according to the electrode slurry composition ratio; wherein, the electrode slurry includes 60%~80% conductive metal particles, 15%~30% organic carrier, and 5%~10% additives; wherein, the conductive metal particles include silver powder and aluminum powder, with a weight ratio of silver powder to aluminum powder of (2.5~7):1; the additives include nano-cerium oxide, polyimide precursor, and sintering aid; the sintering aid is glass powder containing Bi2O3 and B2O3, with a weight ratio of Bi2O3 to B2O3 of 1:(1.5~2.5);

[0066] Step S2: Mix the raw materials to obtain electrode slurry.

[0067] In some specific implementations, step S2 includes the following steps:

[0068] Step S2-1: Mix the organic carrier, nano-cerium oxide and polyimide precursor to obtain the first mixture; preferably, the organic carrier, nano-cerium oxide and polyimide precursor are subjected to ultrasonic treatment for 20-40 min.

[0069] Step S2-2: Add silver powder and aluminum powder to the first mixture in multiple batches (e.g., 2-4 batches) to obtain the second mixture; preferably, after adding silver powder and aluminum powder to the first mixture, the mixture is ball-milled to obtain the second mixture; the ball-milling time is 4-6 hours.

[0070] Step S2-3: Add the sintering aid to the second mixture to obtain the third mixture;

[0071] Step S2-4: Vacuum degassing treatment is performed on the third mixture (gauge pressure of -0.08MPa~0.1MPa, absolute pressure of about 20~10kPA) to obtain electrode slurry.

[0072] More specifically, step S2 includes the following steps:

[0073] Step S2-1: Preparation of organic carrier: Ethyl cellulose, terpineol, and dispersant are mixed and dispersed evenly to obtain organic carrier;

[0074] Step S2-2 Preparation of functional premix: Add polyimide precursor and nano-cerium oxide to the organic carrier obtained in step S2-1, stir thoroughly or sonicate (e.g., for 20-40 minutes) to completely dissolve and uniformly disperse it to obtain the first mixture; this step ensures that the key additives achieve uniform molecular / nano-scale distribution in the liquid phase.

[0075] Step S2-3: Add conductive metal particles: Add silver powder and aluminum powder to the premix in multiple batches, and disperse them under high shear by ball milling (e.g., 4-6 hours) to obtain a second mixture; at this time, the surface of the metal particles can be effectively coated by the uniformly distributed functional additives.

[0076] Step S2-4: Add sintering aid and complete the slurry: Add the sintering aid to the second mixture and stir at medium-low speed until it is uniformly mixed to obtain the third mixture;

[0077] Step S2-5 Degassing treatment: Vacuum degassing treatment is performed on the third mixture to obtain electrode slurry.

[0078] The above mixing steps have the following advantages:

[0079] To address the uniformity issue, the polyimide precursor (usually a viscous PAA solution) and nano-cerium oxide are mixed with an organic carrier before being added to the solid powder. This leverages the uniformity advantage of liquid-liquid mixing, avoiding the process difficulty of uniform dispersion when subsequently added to a high-solids-content, high-viscosity metal powder paste.

[0080] The functional implementation logic is as follows: as an interface modifier, nano-cerium oxide needs to be fully dispersed in the carrier in order to effectively act on the subsequently added metal particles and the final silicon substrate interface; the polyimide precursor also needs to form a continuous network.

[0081] Optimize process flow: The role of sintering aids (mostly glass powder) mainly occurs in the sintering stage, and the requirements for dispersion uniformity are relatively low. Therefore, they are added in the last step, which can shorten the high-shear ball milling time and improve production efficiency.

[0082] Specifically, the electrode preparation method includes: applying the above electrode paste to the silicon substrate on the back of the battery using a screen printing process, and then sintering it in an inert atmosphere (such as nitrogen); the peak temperature of sintering is 750~850℃, the holding time is 1.5~3min, and finally the back electrode of the BC battery is formed.

[0083] According to a second aspect of this application, a back-contact solar cell is provided, which is obtained by the above-described preparation method.

[0084] Specifically, the aforementioned back-contact solar cell is a type of solar cell in which all electrodes (including the emitter and base contact electrodes) are fabricated on the back of the cell; its typical structure includes: the front of the cell has a textured surface and an anti-reflection layer to maximize light absorption; the back of the cell is formed by doping to form alternating P-type regions (P+) and N-type regions (N+); the back electrode is formed by screen printing and sintering the electrode paste of this application, and forms ohmic contacts with the P+ and N+ regions on the back, respectively, thereby collecting current.

[0085] According to a third aspect of this application, a photovoltaic module is provided, comprising at least one of the aforementioned back-contact solar cells;

[0086] Encapsulation layer, used to encapsulate back-contact solar cells;

[0087] The cover plate is placed on the encapsulation layer.

[0088] In some specific embodiments, the photovoltaic module includes multiple back-contact solar cells, which are connected in series and / or in parallel.

[0089] According to a fourth aspect of this application, a power generation system is provided, including the aforementioned photovoltaic module.

[0090] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0091] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0092] The embodiments of this application are described in detail below. However, those skilled in the art will understand that many technical details have been presented in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0093] Example 1

[0094] A method for fabricating a back-contact (BC) solar cell includes sintering an electrode paste onto the back side of the BC cell to obtain an electrode; wherein the electrode fabrication method includes:

[0095] (1) Preparation of electrode paste:

[0096] Step S1: Obtain the raw materials, by weight percentage: 60% silver powder (60nm particle size), 12.5% ​​aluminum powder (100nm particle size), 20% organic carrier (the weight ratio of ethyl cellulose, terpineol, and dispersant polyvinylpyrrolidone PVP is 1:10:0.2), 1.5% nano-cerium oxide (30nm particle size), 4% polyimide precursor (polyamic acid solution), and 2% Bi2O3-B2O3 composite material (Bi2O3:B2O3=1:2).

[0097] Step S2: Mix ethyl cellulose, terpineol, and dispersant, and sonicate for 30 min to obtain a homogeneous organic carrier; add polyimide precursor and nano-cerium oxide to the organic carrier sequentially, and sonicate for 30 min to obtain a first mixture; add silver powder and aluminum powder to the first mixture in three batches, and ball mill after each addition, for a total ball milling time of 5 h to obtain a uniformly dispersed second mixture; add Bi2O3-B2O3 composite material to the second mixture and stir at low speed until uniform; perform vacuum degassing treatment on the mixture (vacuum degree -0.09 MPa, time 20 min) to obtain the finished electrode slurry.

[0098] (2) Preparation of metal electrode: The above-mentioned finished electrode paste is screen printed on the back of the BC battery and sintered in a nitrogen atmosphere. The peak sintering temperature is 800℃ and the temperature is held for 2 minutes to obtain the back electrode of the BC battery.

[0099] The prepared BC back contact solar cell structure includes, from the light-incident side to the back-light side, the following layers in sequence: anti-reflection layer (SiNx layer), passivation layer (SiO2), silicon substrate, doped region (doped to form alternating P-type regions (P+) and N-type regions (N+)), passivation layer (SiNx layer), and metal electrode (positive electrode and negative electrode) prepared in step (2).

[0100] Example 2

[0101] The difference between Example 2 and Example 1 is that the electrode slurry formulation is replaced with:

[0102] The electrode paste, by weight percentage, comprises: 65% silver powder (60nm particle size), 10% aluminum powder (100nm particle size), 17% organic carrier (ethyl cellulose, terpineol, and dispersant polyvinylpyrrolidone PVP in a weight ratio of 1:10:0.2), 1.6% nano-cerium oxide (30nm particle size), 4.2% polyimide precursor (polyamic acid solution), and 2.2% Bi2O3 and B2O3 composite material (Bi2O3:B2O3=1:2); other steps are the same.

[0103] Example 3

[0104] The difference between Example 3 and Example 1 is that the electrode paste formulation is replaced with:

[0105] The electrode paste, by weight percentage, comprises: 50% silver powder (80nm particle size), 10% aluminum powder (150nm particle size), 30% organic carrier (ethyl cellulose, terpineol, and dispersant polyvinylpyrrolidone PVP in a weight ratio of 1:9:0.15), 2% nano-cerium oxide (20nm particle size), 5% polyimide precursor (polyamic acid solution), and 3% Bi2O3-B2O3 composite material (Bi2O3:B2O3=1:1.8); other steps are the same.

[0106] Example 4

[0107] The difference between Example 3 and Example 1 is that the electrode paste formulation is replaced with:

[0108] The electrode paste, by weight percentage, comprises: 69.6% silver powder (50 nm particle size), 10% aluminum powder (80 nm particle size), 15% organic carrier (ethyl cellulose, terpineol, and dispersant polyvinylpyrrolidone (PVP) in a weight ratio of 1:11:0.25), 0.9% nano-cerium oxide (15 nm particle size), 3.5% polyimide precursor (polyamic acid solution), and 1.0% Bi2O3-B2O3 composite material (Bi2O3:B2O3=1:1.5).

[0109] Replace step S2 with: mixing ethyl cellulose, terpineol, and a dispersant, and ultrasonically treating for 20 min to obtain a homogeneous organic carrier; sequentially adding a polyimide precursor and nano-cerium oxide to the organic carrier, and ultrasonically treating for 40 min to obtain a first mixture; adding silver powder and aluminum powder to the first mixture in four batches, ball milling after each addition, for a total ball milling time of 6 h to obtain a uniformly dispersed second mixture; adding the Bi2O3-B2O3 composite material to the second mixture and mixing at low speed until homogeneous; and performing vacuum degassing treatment on the mixture (vacuum degree -0.095 MPa, time 15 min) to obtain the finished electrode slurry.

[0110] (2) Electrode preparation: The above-mentioned finished electrode paste is screen printed on the back of the BC battery and sintered in a nitrogen atmosphere. The peak sintering temperature is 820℃ and the temperature is held for 1.8 min to obtain the back electrode of the BC battery.

[0111] Example 5

[0112] Example 5 differs from Example 1 in that the weight ratio of nano-cerium oxide to polyimide precursor in step S1 is replaced with 1:2; the other steps are the same.

[0113] Specific formula: 59.5% silver powder, 12.5% ​​aluminum powder, 20% organic carrier, 2% nano cerium oxide, 4% polyimide precursor, and 2% Bi2O3-B2O3 composite material.

[0114] Example 6

[0115] Example 6 differs from Example 1 in that the weight ratio of nano-cerium oxide to polyimide precursor in step S1 is replaced with 1:4; the other steps are the same.

[0116] Specific formula: 59.5% silver powder, 12.5% ​​aluminum powder, 20% organic carrier, 1.2% nano cerium oxide, 4.8% polyimide precursor, and 2% Bi2O3-B2O3 composite material.

[0117] Example 7

[0118] The difference between Example 7 and Example 1 is that the weight ratio of ethyl cellulose, terpineol, and dispersant polyvinylpyrrolidone (PVP) in step S1 is replaced with 1:8:0.3; the other steps are the same.

[0119] Comparative Example 1

[0120] The difference between Comparative Example 1 and Example 1 is that the electrode slurry in step S1 does not contain nano-cerium oxide; the other steps are the same.

[0121] Specifically, step S1: by weight percentage, the electrode paste includes: 62% silver powder (60nm particle size), 12.5% ​​aluminum powder (100nm particle size), 20% organic carrier (the weight ratio of ethyl cellulose, terpineol, and dispersant polyvinylpyrrolidone PVP is 1:10:0.2), 4% polyimide precursor (polyamic acid solution), and 1.5% Bi2O3-B2O3 composite material (Bi2O3:B2O3=1:2).

[0122] Comparative Example 2

[0123] The difference between Comparative Example 2 and Example 1 is that the weight ratio of silver powder to aluminum powder in step S1 is replaced with 2:1; the other steps are the same.

[0124] Specifically, the electrode paste includes: 40% silver powder (60nm particle size), 20% aluminum powder (100nm particle size), 32.5% organic carrier (the weight ratio of ethyl cellulose, terpineol, and dispersant polyvinylpyrrolidone (PVP) is 1:10:0.2), 1.5% nano-cerium oxide (30nm particle size), 4% polyimide precursor (polyamic acid solution), and 2% Bi2O3-B2O3 composite material (Bi2O3:B2O3=1:2).

[0125] Comparative Example 3

[0126] The difference between Comparative Example 3 and Example 1 is that the sintering aid ratio in step S1 is replaced with Bi2O3:B2O3 at a ratio of 1:0.5; the other steps are the same.

[0127] Comparative Example 4

[0128] The difference between Comparative Example 4 and Example 1 is that the electrode slurry in step S1 does not contain a polyamide precursor; the other steps are the same.

[0129] Specifically, the composition is as follows: 60.5% silver powder (60nm particle size), 12.5% ​​aluminum powder (100nm particle size), 23.5% organic carrier (the weight ratio of ethyl cellulose, terpineol, and dispersant polyvinylpyrrolidone PVP is 1:10:0.2), 1.5% nano-cerium oxide (30nm particle size), and 2% Bi2O3-B2O3 composite material (Bi2O3:B2O3=1:2).

[0130] Comparative Example 5

[0131] The difference between Comparative Example 5 and Example 1 is that the electrode slurry in step S1 is replaced with: 70% silver powder (particle size 1.5 μm), 5% aluminum powder (particle size 1.5 μm), 22% organic carrier (the weight ratio of ethyl cellulose, terpineol and castor oil derivative is 1:8:0.1), and 3% conventional glass powder (PbO-B2O3-SiO2 system); the organic carrier is mixed with metal powder and glass powder according to conventional process, ball milled and degassed.

[0132] Electrode preparation: The back electrode is formed by sintering at a peak temperature of 850°C for 3 minutes in an air atmosphere.

[0133] Performance testing:

[0134] The performance of each embodiment and each comparative example was tested using the following testing methods, and the results are shown in Table 1.

[0135] (1) Electrode conductivity: A four-probe resistance meter (such as a Keithley 2400 series source meter) was used to measure the sheet resistance (R□) of the sintered back electrode at 25℃, referring to the linear four-probe method principle of the national standard GB / T 1551-2021 "Method for Determination of Resistivity of Silicon Single Crystal". The unit is Ω / □. The lower the value, the better the electrode conductivity.

[0136] (2) Electrode adhesion: A universal testing machine (such as the Instron 3340 series) was used in conjunction with special adhesive tape to conduct quantitative testing according to the cross-cut test method of the national standard GB / T 9286-2021 "Paints and Varnishes - Cross-cut Test" (equivalent to the international standard ISO 2409). The results were reported as adhesion grades (0B-5B, with 5B being the best), and the percentage of electrode detachment area after tape peeling was recorded. The higher the grade and the smaller the detachment area, the stronger the adhesion.

[0137] (3) Photovoltaic performance of the cell: A solar cell IV test system (such as an AAA-level solar simulator, equipped with a Keithley 4200-SCS parameter analyzer) was used to measure the photoelectric conversion efficiency (η), open-circuit voltage (Voc), and fill factor (FF) of a complete BC cell under standard test conditions (STC: AM1.5G, 1000W / m², 25℃) in accordance with the national standard GB / T 6495.1-2022 "Photovoltaic Devices Part 1: Measurement of Photovoltaic Current-Voltage Characteristics". Conversion efficiency is the core indicator for comprehensively evaluating cell performance.

[0138] (4) Electrode microstructure: The cross-sectional morphology of the sintered electrode was observed using a scanning electron microscope (SEM, such as ZEISS Gemini series) to evaluate its density, porosity and bonding interface with the silicon substrate, providing morphological basis for the results of conductivity and adhesion.

[0139] Table 1

[0140]

[0141] As shown in Table 1, the electrode paste provided in this application, through optimization of the metal particle ratio, especially the specific doping ratio of silver and aluminum powder, can reduce the average electrode resistivity to 2.1 × 10⁻⁶ after sintering. -6Compared to traditional slurries, the resistivity is reduced by 30% in Ω·cm, effectively reducing electrode series resistance and thus improving the fill factor (FF) and overall photoelectric performance of the battery. The photoelectric conversion efficiency reaches over 25%. By adding nano-cerium oxide as an interface modifier and combining it with sintering aids, the bonding strength between the electrode and the silicon substrate is significantly improved. The adhesion test results average 4B level with no peeling, ensuring the stability and durability of the electrode on the battery cell.

[0142] In the electrode paste formulation for back-contact solar cells of this application, the selected conductive metal particles and sintering aids work synergistically to achieve low-temperature sintering, forming a dense metal network, reducing resistance, and enhancing electrode adhesion. The polyimide precursor, in synergy with ethyl cellulose and terpineol, improves the rheological properties of the paste, making it more suitable for screen printing processes and reducing grid breakage and edge diffusion. During sintering, the polyimide precursor is converted into polyimide, which enhances the thermal and chemical stability of the electrode. The synergistic effect of nano-cerium oxide, polyimide precursor, sintering aids, and conductive metal particles can reduce the sintering temperature, optimize the dispersion state of metal particles, improve the microstructure of the electrode, enhance the adhesion between the electrode and the silicon substrate, reduce electrode resistance, and enhance the long-term stability of the electrode, ultimately forming a highly efficient and stable battery electrode. The optimized electrode slurry formulation is particularly well-suited for BC battery technology, effectively reducing the carrier recombination rate inside the battery, improving charge transport efficiency, and increasing photoelectric conversion efficiency by 0.5~0.8%. By increasing the proportion of aluminum powder in the slurry, the dependence on high-priced silver is reduced, and the manufacturing cost is significantly reduced while ensuring battery performance.

[0143] Comparative Examples 1-5 show significantly worse overall performance than the embodiments of this application, with the highest resistivity reaching 8×10⁻⁶. -6 Ω·cm, with a photoelectric conversion efficiency of around 23%.

[0144] Comparative Example 1 (lacking nano-cerium oxide): Due to the lack of interface modification and bridging effect of nano-cerium oxide, an effective ohmic contact could not be formed between the metal particles and the silicon surface, the potential barrier increased, and the carrier transport was hindered; at the same time, the lack of anchoring effect of nanoparticles at the interface reduced the mechanical bonding force of the electrode.

[0145] Comparative Example 2 (Silver-Aluminum Ratio Imbalance): Excessive aluminum powder content severely diluted and blocked the continuous conductive network formed by the silver powder. Aluminum has a much lower conductivity than silver. The introduction of excessive aluminum creates a high-resistivity path after sintering and may generate a high-resistivity phase, leading to a sharp decline in the overall electrode conductivity.

[0146] Comparative Example 3 (Extreme Sintering Aid Ratio): Excessive Bi₂O₃ leads to an excessively low melting point and viscosity of the glass phase, causing excessive flow during sintering and eroding the silver-aluminum particles, thus disrupting the continuity of the conductive network. Simultaneously, excessive Bi may react excessively with the silicon substrate, damaging its surface passivation layer, increasing recombination, and resulting in a dual decline in electrical performance and reliability.

[0147] Comparative Example 4 (lacking polyimide precursor): The bonding phase that forms a polyimide polymer network during sintering is missing; the electrode relies only on the brittle glass phase and weak physical adhesion, which cannot withstand thermal expansion stress or mechanical stress, and is very easy to peel off from the silicon wafer surface, leading to battery failure.

[0148] Comparative Example 5 (Traditional Formulation): The densification ability of micron-sized metal particles is poor; the chemical bonding between traditional glass powder and silicon substrate is weak and the thermal matching is poor; there is a lack of any interface modification or organic toughening mechanism; its high sintering temperature is not suitable for the fine back structure of BC battery.

[0149] Comparative Example 1 (without nano-cerium oxide) and Comparative Example 4 (without polyimide precursor) removed the core functional materials used for interface modification and mechanical bonding, respectively. Test results showed that both resulted in a significant increase in electrode contact resistance, severe degradation of adhesion, and even complete failure. This demonstrates that nano-cerium oxide and the polyimide precursor are key and essential components for constructing a high-performance interface layer and achieving a synergistic effect of low resistance and high adhesion; their effects cannot be replaced or achieved by other conventional components.

[0150] Comparative Examples 2 (severe imbalance in silver-aluminum weight ratio) and 3 (excess Bi2O3 in the sintering aid) were used to verify the criticality of the specific ratio range described in the claims. The results show that deviation from any critical ratio directly leads to a sharp deterioration in the performance of the slurry or electrode, such as damage to the conductive network, loss of slurry rheology, or runaway sintering. This proves that the silver-aluminum ratio, organic carrier ratio, and sintering aid ratio described in this invention are precisely selected through optimization to achieve synergistic performance, rather than conventional ranges that can be easily adjusted by those skilled in the art.

[0151] Comparative Example 5 employed a conventional micron-level silver-aluminum paste formulation and traditional sintering process. Its performance data (resistivity, adhesion, conversion efficiency) were comprehensively and significantly inferior to all embodiments of the present invention. This comparison fundamentally demonstrates that the technological advancement of the present invention is not a simple improvement upon existing formulations, but rather a systemic breakthrough and unexpected technical effect achieved by introducing a novel functional component system (nano-cerium oxide, polyimide precursor, and specific composite sintering aids) and optimizing their synergistic ratio and process, from the material system to the final performance.

[0152] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A method for fabricating a back-contact solar cell, characterized in that, The preparation method includes: Obtaining a semiconductor substrate; Electrodes are prepared on the surface of the semiconductor substrate using an electrode paste; wherein the electrode paste comprises the following components: 60%~80% conductive metal particles, 15~30% organic carrier, and 5~10% additives by weight percentage; wherein the conductive metal particles include silver powder and aluminum powder, and the weight ratio of the silver powder to the aluminum powder is (2.5~7):1; the additives include nano-cerium oxide, polyimide precursor, and sintering aid; the sintering aid is glass powder containing Bi2O3 and B2O3, and the weight ratio of Bi2O3 to the B2O3 is 1:(1.5~2.5).

2. The method for preparing a back-contact solar cell according to claim 1, characterized in that, The electrode paste comprises, by weight percentage: 50-70% silver powder, 10-20% aluminum powder, 15-28% organic carrier, 0.5-2% nano-cerium oxide, 3-5% polyimide precursor, and 1-3% sintering aid.

3. The method for preparing a back-contact solar cell according to claim 1, characterized in that, The electrode paste comprises, by weight percentage: 65-70% silver powder, 10-15% aluminum powder, 18-22% organic carrier, 1.2-1.8% nano-cerium oxide, 4.0-4.5% polyimide precursor, and 2-2.5% sintering aid.

4. The method for preparing a back-contact solar cell according to any one of claims 1 to 3, characterized in that, The weight ratio of the silver powder to the aluminum powder is (4~7):1; And / or, the weight ratio of the nano-cerium oxide to the polyimide precursor is 1:(2~4).

5. The method for preparing a back-contact solar cell according to any one of claims 1 to 3, characterized in that, The weight ratio of the silver powder to the aluminum powder is (4.5~6.5):1; And / or, the weight ratio of the nano-cerium oxide to the polyimide precursor is 1:(2.5~3.5). And / or, the polyimide precursor is a polyamic acid solution.

6. The method for preparing a back-contact solar cell according to any one of claims 1 to 3, characterized in that, The weight ratio of the organic carrier to the polyimide precursor is (4~5):1; And / or, the organic carrier comprises ethyl cellulose, terpineol, and a dispersant; the weight ratio of the ethyl cellulose, the terpineol, and the dispersant is 1:(8~12):(0.1~0.3). And / or, the weight ratio of Bi2O3 to B2O3 is 1:(1.8~2.3).

7. The method for preparing a back-contact solar cell according to any one of claims 1 to 3, characterized in that, The weight ratio of the conductive metal particles to the sintering aid is 1:(0.03~0.05); And / or, the particle size of the conductive metal particles is 50~150nm; wherein, the D50 particle size of the silver powder is 50~120nm, and the D50 particle size of the aluminum powder is 100~200nm; And / or, the particle size of the nano-cerium oxide is 10~50nm.

8. The method for preparing a back-contact solar cell according to any one of claims 1 to 3, characterized in that, The preparation method of the electrode paste includes the following steps: Step S1: Obtain raw materials according to the electrode slurry composition ratio; wherein, the electrode slurry comprises 60%~80% conductive metal particles, 15%~30% organic carrier, and 5%~10% additives; wherein, the conductive metal particles comprise silver powder and aluminum powder, and the weight ratio of silver powder to aluminum powder is (2.5~7):1; the additives comprise nano-cerium oxide, polyimide precursor, and sintering aid; the sintering aid is glass powder containing Bi2O3 and B2O3, and the weight ratio of Bi2O3 to B2O3 is 1:(1.5~2.5); Step S2: Mix the raw materials to obtain the electrode slurry.

9. The method for preparing a back-contact solar cell according to claim 8, characterized in that, Step S2 includes the following steps: Step S2-1: Mix the organic carrier, the nano-cerium oxide and the polyimide precursor to obtain a first mixture; Step S2-2: The silver powder and the aluminum powder are added to the first mixture in multiple batches to obtain the second mixture; Step S2-3: Add the sintering aid to the second mixture to obtain the third mixture; Step S2-4: Perform vacuum degassing treatment on the third mixture to obtain the electrode slurry.

10. The method for preparing a back-contact solar cell according to claim 9, characterized in that, In step S2-1, the organic carrier, the nano-cerium oxide and the polyimide precursor are subjected to ultrasonic treatment for 20-40 minutes. And / or, after the silver powder and the aluminum powder are added to the first mixture, the mixture is ball-milled to obtain the second mixture; the ball-milling time is 4~6 hours.

11. A back-contact solar cell, characterized in that, The back-contact solar cell is the back-contact solar cell prepared by the method described in any one of claims 1 to 10.

12. A photovoltaic module, characterized in that, Includes at least one back-contact solar cell as described in claim 11.

Images