Method for manufacturing photovoltaic cell, sintering device, photovoltaic cell and photovoltaic module

Abstract

This disclosure relates to the photovoltaic field, providing a method for preparing a photovoltaic cell, a sintering apparatus, a photovoltaic cell, and a photovoltaic module. The method for preparing the photovoltaic cell includes: providing a cell substrate; preparing a copper paste layer on the surface of the cell substrate; subjecting the cell substrate to a first microwave treatment, wherein the copper paste layer is heated to a first temperature; subjecting the cell substrate to a second microwave treatment, wherein the copper paste layer is heated to a second temperature; wherein the first temperature is lower than the second temperature; subjecting the copper paste layer to electromagnetic treatment, wherein the copper paste layer forms an electrode, thereby achieving both good ohmic contact and sintering cost.

Description

Technical Field

[0001] This disclosure relates to the photovoltaic field, and in particular to a method for preparing a photovoltaic cell, sintering equipment, a photovoltaic cell, and a photovoltaic module. Background Technology

[0002] In photovoltaic cells, sintering is a key process that uses atomic diffusion to create a metallurgical bond between powder particles. Currently, to further reduce the cost of sintering, copper paste is mostly used to prepare photovoltaic cells. Conventional copper paste sintering processes primarily utilize laser sintering to promote copper-silicon alloying.

[0003] However, current laser sintering processes cannot achieve both good welding quality and high sintering costs in photovoltaic cells. Summary of the Invention

[0004] This disclosure provides a method for preparing a photovoltaic cell, a sintering apparatus, a photovoltaic cell, and a photovoltaic module, thereby achieving a balance between good ohmic contact and sintering cost.

[0005] This disclosure provides a method for preparing a photovoltaic cell, comprising: providing a cell substrate; preparing a copper paste layer on the surface of the cell substrate; subjecting the cell substrate to a first microwave treatment, wherein the copper paste layer is heated to a first temperature; subjecting the cell substrate to a second microwave treatment, wherein the copper paste layer is heated to a second temperature; wherein the first temperature is lower than the second temperature; subjecting the copper paste layer to electromagnetic treatment, wherein the copper paste layer forms an electrode.

[0006] This disclosure also provides a sintering apparatus for performing the above-described method for preparing photovoltaic cells.

[0007] This disclosure also provides a photovoltaic cell, which is prepared by the photovoltaic cell preparation method described above.

[0008] This disclosure also provides a photovoltaic module, including the aforementioned photovoltaic cell.

[0009] In addition, the power of the first microwave processing is less than the power of the second microwave processing.

[0010] In addition, the first microwave processing satisfies at least one of the following conditions: the power of the first microwave processing is 3kW to 6kW; the duration of the first microwave processing is 5 seconds to 20 seconds; the first temperature is 150°C to 250°C; and / or, the second microwave processing satisfies at least one of the following conditions: the power of the second microwave processing is 6kW to 10kW; the duration of the second microwave processing is 10 seconds to 60 seconds; the second temperature is 300°C to 400°C.

[0011] In addition, the electromagnetic treatment satisfies at least one of the following conditions: the duration of the electromagnetic treatment is 3 to 10 seconds; the power of the electromagnetic treatment is 2 kW to 20 kW; and the temperature of the electromagnetic treatment is 600°C to 800°C.

[0012] In addition, the method further includes cooling the battery substrate during the electromagnetic processing.

[0013] In addition, the cooling process involves cooling the surface of the battery substrate away from the copper paste layer using a low-temperature medium.

[0014] In addition, the low-temperature medium can be any one of the following: an aqueous solution of methanol and ethanol, a calcium chloride solution, or a sodium chloride solution.

[0015] The technical solution provided in this disclosure has at least the following advantages: This disclosure involves performing a first microwave treatment on the battery substrate, utilizing the bulk heating characteristics of microwaves to preheat the copper paste layer to a first temperature, followed by a second microwave treatment on the battery substrate. This second microwave treatment rapidly raises the temperature of the copper paste layer to a second temperature, while the microwaves exert minimal heating effect on the battery substrate, thus preventing thermal damage. Subsequently, this disclosure further involves electromagnetic treatment of the copper paste layer, concentrating energy highly on the copper paste layer. The copper paste layer solidifies to form an electrode, creating a good ohmic contact between the copper paste layer and the battery substrate. This achieves both good welding quality and low sintering costs. Attached Figure Description

[0016] One or more embodiments are illustrated by way of example with corresponding pictures in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the pictures in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this disclosure or the conventional technology, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of a battery substrate in one embodiment of the present disclosure; Figure 2 This is a schematic diagram of the structure after a copper paste layer is prepared on a battery substrate in one embodiment of this disclosure; Figure 3 This is a schematic diagram of the structure after the first microwave processing and the second microwave processing in one embodiment of this disclosure; Figure 4 This is a schematic diagram of the structure after electromagnetic processing in one embodiment of this disclosure; Figure 5This is a schematic diagram of another structure of the battery substrate in one embodiment of the present disclosure; Figure 6 This is another structural schematic diagram after a copper paste layer is prepared on a battery substrate in one embodiment of the present disclosure; Figure 7 This is a schematic diagram of another structure after the first microwave processing and the second microwave processing in one embodiment of this disclosure; Figure 8 This is a schematic diagram of another structure after electromagnetic processing in one embodiment of this disclosure; Figure 9 This is a schematic diagram of the sintering equipment in one embodiment of the present disclosure; Figure 10 This is a schematic diagram of the structure of the TOPCON cell prepared by the photovoltaic cell preparation method described above. Figure 11 This is a schematic diagram of the structure of a BC cell prepared by the photovoltaic cell preparation method described above. Figure 12 This is a schematic diagram of the structure of a photovoltaic module according to an embodiment of this disclosure.

[0018] Explanation of reference numerals in the attached figures Battery substrate 1, substrate 11, doped layer 10, passivation layer 20, copper paste layer 30, electrode 31, aluminum oxide layer 21, microwave system 40, high-frequency electromagnetic induction system 50, cooling module 60, gas purification and circulation system 70, infrared thermometer 80, central control system 90, cover plate 41, back plate 42, photovoltaic cell 2. Detailed Implementation

[0019] As can be seen from the background technology, current laser sintering processes cannot simultaneously achieve good welding quality and sintering cost in photovoltaic cells.

[0020] Analysis reveals that the current laser sintering process for photovoltaic cells fails to achieve both good welding quality and low sintering cost due to several factors. Firstly, copper has very low absorption of near-infrared laser light at room temperature, resulting in significant energy loss and low laser energy utilization during the welding process. Secondly, copper particles have a high melting point (700°C to 800°C). While conventional laser sintering methods are less expensive, the copper paste needs to be heated to high temperatures by the laser, leading to deeper etching of the doped layer and thermal damage to the cell substrate at these temperatures, resulting in high ohmic contact. Furthermore, copper's excellent thermal conductivity contributes to its poor stability during laser welding. These factors necessitate the use of high-brightness lasers for infrared laser welding of copper to achieve relatively good welding quality. Therefore, the current laser sintering process for photovoltaic cells cannot simultaneously achieve good ohmic contact and low sintering cost.

[0021] This disclosure provides a method for preparing a photovoltaic cell, comprising: providing a cell substrate; preparing a copper paste layer on the surface of the cell substrate; subjecting the cell substrate to a first microwave treatment, thereby heating the copper paste layer to a first temperature; subjecting the cell substrate to a second microwave treatment, thereby heating the copper paste layer to a second temperature, wherein the first temperature is lower than the second temperature; and subjecting the copper paste layer to electromagnetic treatment, thereby forming an electrode.

[0022] This embodiment of the invention involves performing a first microwave treatment on the battery substrate, utilizing the bulk heating characteristics of microwaves to preheat the copper paste layer to a first temperature. Then, a second microwave treatment is performed on the battery substrate, again utilizing the bulk heating characteristics of microwaves to rapidly raise the temperature of the copper paste layer to a second temperature. Since microwaves have almost no heating effect on the battery substrate, thermal damage to the doped layer is avoided. Subsequently, this embodiment of the invention further performs an electromagnetic treatment on the copper paste layer, highly concentrating energy on it. The copper paste layer solidifies to form an electrode, creating a good ohmic contact between the copper paste layer and the battery substrate, thus achieving both good welding quality and low sintering costs.

[0023] In the description of the embodiments of this disclosure, 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 or secondary relationship of the indicated technical features. In the description of the embodiments of this disclosure, "multiple" means two or more, unless otherwise explicitly defined. Similarly, "multiple sets" refers to two or more sets (including two sets), and "multiple pieces" refers to two or more pieces (including two pieces).

[0024] 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 disclosure. 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.

[0025] In the description of the embodiments of this disclosure, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0026] In the description of the embodiments of this disclosure, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the embodiments of this disclosure and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the embodiments of this disclosure. For example, if the device or element in the illustration is inverted, then an element described as "below," "under," "down," or "bottom" of other elements or features will be oriented "above" or "top" of the other elements or features. Therefore, the term "below" may, depending on the context in which the term is used, encompass both above and below orientations, which will be apparent to those skilled in the art. Materials may be oriented in other ways (e.g., rotated 90 degrees, inverted, flipped), and the spatial relative descriptive terms used herein may be interpreted accordingly.

[0027] In the description of embodiments of this disclosure, the terms "about," "approximately," "roughly," or "about" for reference to a particular parameter include numerical values, and those skilled in the art will understand that deviations from the numerical values ​​are within acceptable tolerances for the particular parameter. For example, "about" or "about" for a numerical value may include additional numerical values ​​that are in the range of 90.0% to 110.0% of the numerical value, such as in the range of 95.0% to 105.0%, 97.5% to 102.5%, 99.0% to 101.0%, 99.5% to 100.5%, or 99.9% to 100.1%.

[0028] In the accompanying drawings corresponding to the embodiments of this disclosure, the thickness and / or area of ​​layers, films, panels, regions, etc., are enlarged for better understanding and ease of description. Throughout the specification, the same reference numerals denote the same elements. Furthermore, when describing a component as being "generally" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor on a portion of the edge of the entire surface.

[0029] In the description of embodiments of this disclosure, when a component "includes" another component, other components are not excluded unless otherwise stated, and may be further included. When a component (such as a layer, film, region, or substrate) is described as being on or on the surface of another component, the component may be "directly" located on the surface of the other component, or there may be an intermediate component between the two components. Conversely, when a component is described as being on the surface of another component, or a component is "directly" on another component, or another component is formed or disposed on the surface of a component, it indicates that there is no intermediate component between the two components. For simplicity and clarity, various components may be drawn at any scale. In the drawings, some components may be omitted for simplicity.

[0030] The “components” mentioned above can refer to layers, films, regions, parts, structures, etc.

[0031] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "component" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0032] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this disclosure to facilitate a better understanding of the disclosure. However, the technical solutions claimed in the embodiments of this disclosure can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0033] Figures 1 to 4 The diagram shows the structural schematics corresponding to each step of the photovoltaic cell fabrication method provided in this disclosure. The photovoltaic cell fabrication method of this disclosure includes the following steps.

[0034] refer to Figure 1 This is a schematic diagram of the battery substrate.

[0035] This disclosure first provides a battery substrate 1.

[0036] The photovoltaic cell fabrication method in this embodiment is at the stage after doping treatment in the photovoltaic cell fabrication process. To facilitate understanding of the implementation principle of this embodiment, the specific structure of the cell substrate 1 will be described in detail below.

[0037] The battery substrate 1 includes a substrate 11, a doped layer 10 disposed on the substrate, and a passivation layer 20 disposed on the surface of the doped layer away from the substrate 11.

[0038] refer to Figure 2 This is a schematic diagram of the structure after a copper paste layer is prepared on the battery substrate.

[0039] In this embodiment of the present disclosure, a copper paste layer 30 is prepared on the surface of a battery substrate 1, and the copper paste layer 30 is disposed on the surface of the passivation layer 20 in the battery substrate 1 away from the doped layer 10.

[0040] In this embodiment, the copper paste layer 30 is deposited on the passivation layer 20 using a screen printing process. The shape and size of the copper paste layer 30 are specifically set according to actual needs, and this embodiment does not impose specific limitations. During the sintering process, the glass frit in the copper paste layer 30 can penetrate the passivation layer 20, allowing the copper paste layer 30 to form an ohmic contact with the doped layer 10.

[0041] The doped layer 10 in this embodiment can be a P-type doped layer or an N-type doped layer. The P-type doped layer is a boron doped layer, and the doping source can be boron trichloride (BCl3), diborane (B2H6), or boron tribromide (BBr3). The resulting photovoltaic cell can be a passivated emitter and rear cell (PERC) cell. The N-type doped layer is a phosphorus doped layer, and the doping source can be phosphine (PH3) or phosphorus oxychloride (POCl3). The resulting photovoltaic cell can be a tunnel oxide passivated contact (TOPCon) cell, a heterojunction with intrinsic thin layer (HJT) cell, or an interdigitated back contact (IBC) cell.

[0042] refer to Figure 3 This is a schematic diagram of the structure after the first and second microwave processing.

[0043] In this embodiment, after preparing a copper paste layer 30 on the surface of the battery substrate 1, the battery substrate 1 undergoes a first microwave treatment. The first microwave treatment applies microwaves, such as 2.45 GHz microwaves, to the copper paste layer 30 using a microwave source, utilizing the bulk heating characteristics of microwaves to raise the temperature of the copper paste layer 30 to a relatively low first temperature. On one hand, by performing the first microwave treatment on the copper paste layer 30, the power of the subsequent second microwave treatment can be reduced, minimizing the rate of temperature rise of the copper paste layer 30 and ensuring that the glass frit in the copper paste layer 30 can melt sufficiently and slowly during the second microwave treatment. On the other hand, the first microwave treatment allows for the complete volatilization of organic matter in the copper paste layer 30 and initiates diffusion and initial necking between copper particles, achieving pre-densification of the paste layer. Simultaneously, the first microwave treatment has a low first temperature, below the thermal damage threshold of the doped layer 10, ensuring the performance of the doped layer 10. Furthermore, the first microwave treatment has almost no heating effect on the doped layer 10, ensuring that the temperature of the doped layer 10 remains within the thermal damage threshold range.

[0044] The first temperature is between 150°C and 250°C, for example, 150°C, 180°C, 200°C, 220°C, and 250°C. In this embodiment, by heating the copper paste layer 30 to a medium temperature, within this temperature range, the organic matter in the copper paste can more fully volatilize, thereby reducing the organic matter content in the copper paste layer 30 and thus reducing the ohmic contact of the final electrode 31. Simultaneously, within this medium temperature range, premature melting of the glass frit in the copper paste layer 30, which would corrode the passivation layer 20, can also be avoided. This ensures that the organic matter in the copper paste layer 30 is fully volatilized before the subsequent glass frit melting step, further reducing the ohmic contact of the photovoltaic cell.

[0045] In this embodiment of the present disclosure, after the first microwave treatment, the battery substrate 1 is subjected to a second microwave treatment, the copper paste layer 30 is heated to a second temperature, the copper paste layer 30 is etched to partially contact the passivation layer 20 and the doped layer 10, and a copper-silicon contact point is formed on the surface where the copper paste layer 30 and the doped layer 10 are in contact.

[0046] The second microwave treatment applies microwaves, such as 2.45 GHz microwaves, to the copper paste layer 30 using a microwave source. Utilizing the bulk heating characteristics of microwaves, the copper paste layer 30 can be rapidly heated to a second temperature, activating and diffusing the copper particles and providing sufficient conditions for subsequent electrode formation. Simultaneously, the second microwave treatment has almost no heating effect on the doped layer 10, ensuring that the temperature of the doped layer 10 remains within the thermal damage threshold range.

[0047] The formulation of copper paste layer 30 mainly consists of copper particles and glass frit. In the formulation of copper paste layer 30, the amount of copper particles is 85 to 95 parts, for example, 85 parts, 87 parts, 90 parts, 92 parts, or 95 parts, and the amount of glass frit is 0.8 to 5.5 parts, for example, 0.8 parts, 1 part, 2 parts, 3 parts, 4 parts, or 5 parts. The formulation of copper paste layer 30 may also include organic carriers such as resins and solvents to adjust the rheological properties of the paste. The organic carrier in the formulation of copper paste layer 30 may be 2 to 8 parts, for example, 2 parts, 4 parts, 6 parts, or 8 parts. The formulation of copper paste layer 30 may also include organic solvents to dissolve the resin and adjust the viscosity of the paste. The organic solvent in the formulation of copper paste layer 30 may be 2 to 5 parts, for example, 2 parts, 3 parts, 4 parts, or 5 parts.

[0048] The glass frit in the copper paste layer 30 melts at high temperature into a melt with specific chemical activity, which can corrode and penetrate the passivation layer 20, which is a silicon nitride film or a silicon oxide film. The melting point of the glass frit is relatively low compared to that of the copper particles, ranging from 300°C to 400°C. Therefore, the second temperature in this embodiment is 300°C to 400°C, for example, 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, etc. Since the thermal damage threshold of the doped layer 10 is less than 350°C, in order to further avoid thermal damage to the doped layer 10, the second temperature can be further limited to 300°C to 350°C, for example, 300°C, 310°C, 330°C, 340°C, 350°C. After the copper paste layer 30 is partially etched into the passivation layer 20, the copper particles in the copper paste layer 30 come into contact with the doped layer 10. The copper particles diffuse into the doped layer 10 and react with it to form local metal-semiconductor alloy contact points, i.e., copper-silicon contact points. After subsequent cooling, these copper-silicon contact points become low-resistance channels for current to flow from the semiconductor into the metal electrode.

[0049] In this embodiment, the copper paste layer 30 is heated to a second temperature by a second microwave treatment. On the one hand, this allows the glass frit to melt and etch through the passivation layer 20, and the copper particles in the copper paste layer 30 to form copper-silicon contact points with the doped layer 10 at the second temperature. On the other hand, the second temperature is lower than the melting point of the copper particles, which can prevent the doped layer 10 from suffering heat loss due to thermal conduction. At the same time, the glass frit melts slowly, which can reduce the etching depth of the glass frit on the doped layer 10, ensure the performance of the doped layer 10, and ensure that a good copper-silicon contact point is formed on the surface where the copper paste layer 30 and the doped layer 10 are in contact.

[0050] To ensure uniform heating of the glass frit in the copper paste layer 30, the power of the second microwave treatment in this embodiment is 6kW to 10kW, for example, 6kW, 7kW, 8kW, 9kW, or 10kW. Within this power range, the second microwave treatment allows for a relatively gradual heating rate of the copper paste layer 30, avoiding uneven heating caused by excessively rapid heating. Simultaneously, it ensures a uniform and controllable corrosion rate of the passivation layer 20 by the glass frit, preventing the area of ​​glass frit corrosion of the passivation layer 20 from becoming too large, thus ensuring the performance of the passivation layer 20 itself. Furthermore, a larger area of ​​glass frit corrosion of the passivation layer 20 leads to a larger width of the final electrode, resulting in a larger shading area of ​​the photovoltaic cell, reducing photogenerated carriers and lower light utilization. Therefore, by controlling the power of the second microwave treatment within the aforementioned range in this embodiment, it is possible to prevent the area of ​​glass frit corrosion of the passivation layer 20 from becoming too large, ensuring that the width of the final electrode is within a controllable range, resulting in better ohmic contact, thereby achieving good welding quality while guaranteeing the light utilization of the photovoltaic cell.

[0051] To ensure that the glass frit in the copper paste layer 30 can be fully melted, the duration of the second microwave treatment is between 10 and 60 seconds, for example, 10, 20, 30, 40, 50, or 60 seconds. Within this range, the duration of the second microwave treatment allows the copper paste layer 30 to be slowly heated to the second temperature, ensuring that the glass frit in the copper paste layer 30 can be fully melted. This allows the glass frit in the copper paste layer 30 to fully etch the passivation layer 20, thereby forming a good copper-silicon contact point with the doped layer 10, achieving good ohmic contact in the photovoltaic cell, and ensuring good welding quality of the photovoltaic cell.

[0052] refer to Figure 4 This is a schematic diagram of the structure after electromagnetic treatment.

[0053] In this embodiment, after the first microwave treatment and the second microwave treatment, the copper paste layer 30 is subjected to electromagnetic treatment, and the surface of the copper paste layer 30 away from the doped layer 10 is solidified, forming the electrode 31. At this time, the microwave heating of the bulk material of the copper paste layer 30 is stopped, allowing the interface region of the copper paste layer 30 to complete the final reconstruction under the action of high-frequency electromagnetic fields.

[0054] Electromagnetic processing applies a high-frequency induction field, such as 400kHz, to the copper paste layer 30 via a high-frequency induction coil. This high-frequency induction field, through the eddy current effect, preferentially heats the copper particles with good conductivity, particularly the surfaces of the copper particles far from the doped layer 10. In other words, this embodiment utilizes the "skin effect" and "proximity effect" of the high-frequency induction field to highly concentrate energy on the surfaces of the copper paste layer 30 far from the doped layer 10. This selective heating ensures that only the surfaces of the copper paste layer 30 far from the doped layer 10 continue to heat up, while the temperature of the interface region between the copper paste layer 30 and the doped layer 10 is below the thermal damage threshold of the doped layer 10 (the thermal damage threshold of the doped layer 10 is less than 350°C). This causes the surface of the copper paste layer 30 far from the doped layer 10 to instantly reach the micro-melting temperature of the copper particles, achieving "instantaneous liquid-phase sintering at the interface," i.e., the copper paste layer 30 solidifies and forms the electrode 31, ensuring a stable, low-resistance ohmic contact. This significantly improves adhesion with almost no increase in the overall thermal budget.

[0055] This embodiment of the invention involves performing a first microwave treatment on the battery substrate 1, utilizing the bulk heating characteristics of microwaves to preheat the copper paste layer 30 to a first temperature. Then, a second microwave treatment is performed on the battery substrate 1, using the bulk heating characteristics of microwaves to rapidly heat the copper paste layer 30 to a second temperature. The microwaves have almost no heating effect on the doped layer 10 of the battery substrate 1, thus avoiding thermal damage to the doped layer 10. Simultaneously, the copper paste layer 30 etches a portion of the passivation layer 20 into contact with the doped layer 10, forming copper-silicon contact points on the contact surface. Subsequently, this embodiment of the invention further performs electromagnetic treatment on the copper paste layer 30, solidifying it to form an electrode 31. With the formation of copper-silicon contact points on the contact surface between the copper paste layer 30 and the doped layer 10, a good ohmic contact is achieved between the copper paste layer 30 and the doped layer 10, thereby balancing good welding quality with low sintering costs.

[0056] The copper paste layer 30 in this embodiment further contains an interface activator. This interface activator promotes the formation of a eutectic alloy at the copper-silicon interface at low temperatures. The interface activator can be a trace element, such as Sn, In, or Ga. The copper paste layer 30 can achieve powder formulation optimization through glass frit and interface activator, resulting in a lower melting point. During electromagnetic processing, this reduces the temperature and time required to form excellent ohmic contacts. Simultaneously, the interface activator facilitates inter-fusion of copper particles during subsequent electromagnetic processing, thereby establishing connections between copper particles, forming excellent ohmic contacts, and ensuring the welding quality of the photovoltaic cell.

[0057] In this embodiment, the copper paste layer 30 is electromagnetically treated, causing it to continue heating to the sintering temperature away from the surface of the doped layer 10. If the sintering temperature is too low (e.g., less than 600°C), incomplete sintering will result in high contact resistance between the copper paste layer 30 and the doped layer 10; conversely, if the sintering temperature is too high (e.g., greater than 800°C), excessive diffusion of copper particles into the doped layer 10 may form recombination centers, reducing battery efficiency and potentially damaging the bulk lifetime and passivation layer of the doped layer 10 itself. Therefore, the sintering temperature in this embodiment is between 600°C and 800°C, such as 600°C, 650°C, 700°C, 750°C, and 800°C. The sintering temperature reaches the melting point of the copper particles, enhancing the adhesion between copper particles on the surface of the copper paste layer 30 away from the doped layer 10. The copper paste layer 30 is sintered and alloyed to form the electrode 31, which forms a good ohmic contact with the doped layer 10, ensuring the welding quality of the photovoltaic cell. Furthermore, since only the surface of the copper paste layer 30 away from the doped layer 10 is heated to the sintering temperature, thermal damage to the doped layer 10 is avoided. With a good copper-silicon contact point formed on the surface where the copper paste layer 30 contacts the doped layer 10, the contact resistance of the photovoltaic cell is low. To further improve the welding quality of the photovoltaic cell by forming a good ohmic contact between the copper particles and the silicon interface, the sintering temperature in this embodiment can be from 650°C to 750°C, such as 650°C, 680°C, 700°C, 720°C, 750°C, etc.

[0058] The electromagnetic processing power of this embodiment is from 2KW to 20KW, for example, 2KW, 5KW, 10KW, 15KW, and 20KW. Within this power range, the electromagnetic processing power of this embodiment can rapidly raise the temperature of the copper paste layer 30 surface to the sintering temperature. This allows the copper paste layer 30 to be solidified away from the surface of the doped layer 10 to form the electrode 31 while minimizing the duration of the electromagnetic processing and reducing the impact on the doped layer 10.

[0059] To further reduce the impact of high-frequency induction electromagnetic processing on the doped layer 10, the duration of the electromagnetic processing in this embodiment is 3 to 10 seconds, for example, 3 seconds, 4 seconds, 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, and 10 seconds. Within this range, a shorter high-frequency induction process can not only quickly solidify the copper paste layer 30 away from the surface of the doped layer 10 to form the electrode 31, but also reduce the impact on the doped layer 10 and prevent thermal damage to the doped layer 10.

[0060] The photovoltaic cell fabrication method of this disclosure further includes cooling the cell substrate 1 during the electromagnetic processing. Since the sintering temperature of the copper paste layer 30 is high, heat conduction can cause the surface temperature at the contact point between the copper paste layer 30 and the doped layer 10 to rise, leading to thermal damage to the doped layer 10. Therefore, to avoid the thermal conduction of the upper copper paste layer 30 affecting the thermal conduction at the contact point with the doped layer 10 and to prevent thermal damage to the doped layer 10, this disclosure embodiment cools the cell substrate 1 during the electromagnetic processing. Even with a high sintering temperature, this ensures a lower temperature for the doped layer 10, avoiding the risk of microcracks in the doped layer 10 due to thermal stress. This ensures good ohmic contact between the finally formed electrode 31 and the doped layer 10, improving the welding quality of the photovoltaic cell. Simultaneously, during the electromagnetic processing, the bulk temperature of the doped layer 10 gradually decreases through cooling, reducing the risk of copper particles from the copper paste layer 30 diffusing into the doped layer 10.

[0061] The cooling process involves cooling the surface of the battery substrate 1 away from the copper paste layer 30 using a low-temperature medium.

[0062] The low-temperature medium can be any of the following: an aqueous solution of methanol and ethanol, a calcium chloride solution, or a sodium chloride solution.

[0063] In the methanol and ethanol aqueous solution, the concentration of methanol is 30% to 35%, for example, 30%, 31%, 32%, 33%, 34%, 35%, and the concentration of ethanol is 10% to 15%, for example, 10%, 11%, 12%, 13%, 14%, 15%, with the total percentage of methanol and ethanol being approximately 45%. The temperature of the methanol and ethanol aqueous solution can be -97℃ to -117℃, for example: -97℃, -100℃, -105℃, -110℃, -115℃, -117℃. The concentration of calcium chloride solution can be 29.9%, and the temperature can not be lower than -55℃, for example: -50℃, -45℃, -40℃, -35℃, -30℃. The concentration of sodium chloride solution is 23.1%, and the temperature can not be lower than -21.2℃, for example: -20℃, -18℃, -16℃, -14℃, -12℃.

[0064] The cooling rate for the cooling process is from -10°C / s to -30°C / s, for example: -10°C / s, -15°C / s, -20°C / s, -25°C / s, -30°C / s. The cooling rate can be achieved by controlling the flow rate of the cryogenic medium or by controlling the temperature of the cryogenic medium. In this embodiment, by setting the cooling rate within this range, on the one hand, the problem of thermal damage to the doped layer 10 due to excessively low cooling rates is avoided, ensuring that the temperature of the doped layer 10 can be maintained within the thermal damage threshold range during electromagnetic processing; on the other hand, the problem of damage due to large temperature differences in the doped layer 10 caused by excessively high cooling rates is avoided. Therefore, while ensuring the performance of the doped layer 10, the cooling rate of the doped layer 10 is maximized, ensuring good ohmic contact between the finally formed electrode 31 and the doped layer 10, and improving the welding quality of the photovoltaic cell.

[0065] In this embodiment of the present disclosure, the aforementioned cooling process can also be performed during the second microwave processing. The cooling process removes heat from the doped layer 10, ensuring that even at a high second temperature, the heat is quickly dissipated, keeping the temperature of the doped layer 10 within the heat loss threshold range. Therefore, this embodiment of the present disclosure can appropriately increase the second temperature, slightly exceeding the heat loss threshold (350°C) of the doped layer 10. For example, the second temperature can be set within the range of 350°C to 400°C, specifically 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, etc., allowing the organic matter in the copper paste layer 30 to volatilize more fully, further reducing the organic matter content in the copper paste layer 30, reducing the ohmic contact of the final electrode 31, and reducing the fill factor (FF).

[0066] The power of the first microwave treatment in this embodiment is less than the power of the second microwave treatment. Both the first and second microwave treatments in this embodiment can use the same microwave source; only the microwave power needs to be changed, simplifying the sintering process. The first microwave treatment utilizes the bulk heating characteristics of microwaves to rapidly and uniformly heat the copper paste layer 30 to a medium-temperature first temperature, allowing for the full volatilization of organic matter and achieving pre-densification of the paste layer. Simultaneously, the first microwave treatment has almost no heating effect on the doped layer 10, ensuring that the temperature of the doped layer 10 remains within the thermal damage threshold range. Since the first temperature is a medium-temperature, below the thermal damage threshold of the doped layer 10, it ensures that the doped layer 10 does not suffer heat loss while allowing for the full volatilization of organic matter in the copper paste layer 30, achieving pre-densification of the paste layer.

[0067] The power of the first microwave processing in this embodiment is 3kW to 6kW, for example, 3kW, 4kW, 5kW, 6kW. The first microwave processing uses medium to low power. By setting the microwave processing within the above range, the temperature of the copper paste layer 30 can rise to the first temperature uniformly and slowly, while avoiding the problem of uneven heating caused by the copper paste layer 30 heating too quickly, avoiding splashing or voids caused by rapid vaporization, ensuring that the organic matter in the copper paste layer 30 can fully volatilize, and achieving pre-densification of the paste layer.

[0068] The duration of the first microwave treatment in this embodiment is 5 to 20 seconds, for example, 5 seconds, 10 seconds, 15 seconds, or 20 seconds. The duration of the first microwave treatment within this range ensures that the organic matter in the copper paste layer 30 can fully volatilize, minimizing the organic matter content in the copper paste layer 30, improving the density of the paste layer, ensuring good ohmic contact of the photovoltaic cell, and improving the welding quality of the photovoltaic cell.

[0069] In the first microwave processing of this embodiment, the temperature of the copper paste layer 30 rises steadily and uniformly, allowing the organic solvents and binders in the copper paste layer 30 to evaporate slowly and fully. While completing the full evaporation of organic matter, it avoids rapid vaporization that could lead to splashing or voids. Furthermore, this process achieves diffusion and preliminary necking between copper particles, thus realizing the pre-densification of the paste layer.

[0070] Because copper particles undergo severe oxidation at temperatures above 300°C, producing CuO or Cu2O, with melting points of 1232°C and 1326°C respectively—far exceeding the sintering temperature of copper particles—and because CuO or Cu2O forms an insulating barrier that hinders true metallurgical fusion, the photovoltaic cell fabrication method of this disclosure is carried out in an inert gas atmosphere. The inert gas is high-purity nitrogen or argon, with an oxygen content of less than 10 ppm, such as 5 ppm, 6 ppm, 7 ppm, 8 ppm, 9 ppm, or 10 ppm. This prevents copper particle oxidation, lowers the sintering temperature during the sintering process, ensures good ohmic contact in the photovoltaic cell, and improves the welding quality of the photovoltaic cell.

[0071] Compared to conventional silver sintering processes (Conventional Technology 1) and conventional copper paste sintering processes (Conventional Technology 2), the contact resistivity and FF fill factor of this embodiment are reduced. Table 1 shows a comparison of the contact resistivity and FF fill factor between the copper paste sintering process of this embodiment and Conventional Technology 1 and Conventional Technology 2. The photovoltaic cell obtained by the conventional silver sintering process (Conventional Technology 1) has a contact resistivity of 1.3 mΩ·cm. 2 The fill factor (FF) is a baseline value of 86%; the contact resistivity of the photovoltaic cells obtained by the conventional copper paste sintering process (conventional technology two) is 2.8 mΩ·cm.2 The fill factor of the FF is reduced by 0.3% compared to conventional technology, reaching 85.7%; the contact resistivity of the photovoltaic cell obtained by the copper paste sintering process of this embodiment is 2.3 mΩ·cm. 2 The FF fill factor is reduced by 0.15% compared to conventional technology one, reaching 85.85%. It can be seen that the contact resistivity of the photovoltaic cell obtained by the embodiment of this disclosure is significantly reduced compared to conventional technology two, and the FF fill factor is increased by 0.15% compared to conventional technology two, resulting in good ohmic contact of the photovoltaic cell obtained by the copper paste sintering process of the embodiment of this disclosure.

[0072] Table 1

[0073] The battery substrate 1 of this embodiment may further include other films, and an aluminum oxide layer may be disposed between the doped layer 10 and the passivation layer 20 to saturate surface dangling bonds and reduce the carrier recombination rate. Figure 5 The diagram shows another structural schematic of the battery substrate, where an aluminum oxide layer 21 can be disposed between the doped layer 10 and the passivation layer 20. Figure 6 The diagram shows another structural schematic after a copper paste layer has been prepared on the battery substrate. The copper paste layer 30 is disposed on the surface of the passivation layer 20 in the battery substrate 1, away from the aluminum oxide layer 21. Figure 7 The diagram shows another structural schematic after the first and second microwave treatments. During the first microwave treatment, the organic matter in the copper paste layer 30 is fully volatilized, and diffusion and initial necking between copper particles are initiated, achieving pre-densification of the paste layer. During the second microwave treatment, the glass frit in the copper paste layer 30 melts at high temperature into a melt with specific chemical activity, corroding and penetrating the passivation layer 20 and the alumina layer 21, and reacting with the doped layer 10 to form localized metal-semiconductor alloy contact points, i.e., copper-silicon contact points. Figure 8 As shown, another structural schematic diagram after electromagnetic treatment shows that the copper paste layer 30 is cured and forms the electrode 31.

[0074] Accordingly, another embodiment of this disclosure also provides a sintering apparatus, which can be used to implement the photovoltaic cell fabrication method provided in the above embodiments. The sintering apparatus provided in another embodiment of this disclosure will be described in detail below with reference to the accompanying drawings. For parts that are the same as or corresponding to the previous embodiment, please refer to the corresponding descriptions of the foregoing embodiments; detailed descriptions will not be repeated below.

[0075] like Figure 9 The diagram shown is a structural schematic of a sintering device provided in an embodiment of this disclosure. The sintering device includes a microwave system 40 and a high-frequency electromagnetic induction system 50.

[0076] refer to Figures 1 to 4 as well as Figure 9 The microwave system 40 is used to perform a first microwave treatment and a second microwave treatment on the battery substrate 1. The battery substrate 1 includes a substrate 11, a doped layer 10 disposed on the substrate 11, and a passivation layer 20 disposed on the surface of the doped layer 10 away from the substrate 11. A copper paste layer 30 is formed on the surface of the passivation layer 20 away from the doped layer 10. The first microwave treatment preheats the copper paste layer 30 to a first temperature, and the second microwave treatment heats the copper paste layer 30 to a second temperature. The copper paste layer 30 etches a portion of the passivation layer 20 into contact with the doped layer 10, and a copper-silicon contact point is formed on the surface of the copper paste layer 30 in contact with the doped layer 10. The microwave system 40 of this embodiment is a multi-source microwave system, including an upper microwave feed port and a lower microwave feed port. A microwave field is formed through multiple feed ports and a mode stirrer to ensure that the large-size battery substrate 1 can be uniformly heated in the microwave field, thereby improving the uniformity of heating of the copper paste layer 30.

[0077] refer to Figures 5 to 8 The battery substrate 1 may also have an aluminum oxide layer 21 between the doped layer 10 and the passivation layer 20. During the second microwave treatment, the glass material in the copper paste layer 30 melts at high temperature into a melt with specific chemical activity, which corrodes and penetrates the passivation layer 20 and the aluminum oxide layer 21, so that copper-silicon contact points are formed on the surface where the copper paste layer 30 and the doped layer 10 are in contact.

[0078] The high-frequency electromagnetic induction system 50 is used to electromagnetically process the copper paste layer 30, which then solidifies and forms the electrode 31. In this embodiment, the high-frequency electromagnetic induction system 50 is a planar high-frequency induction system. The coil in the high-frequency electromagnetic induction system 50 is shaped to match the battery substrate 1, achieving uniform induction heating of the entire area where the copper paste layer 30 is located.

[0079] The sintering apparatus of this embodiment further includes a cooling module 60; the cooling module 60 is used to cool the battery substrate 1 during the electromagnetic processing. To prevent the heat from the upper copper paste layer 30 from affecting the doped layer 10 below the copper paste layer 30 through heat conduction, the sintering apparatus is provided with a cooling module 60 below the battery substrate 1 to cool the battery substrate 1. For example, a low-temperature medium is used for cooling on the lower surface transport platform of the sintering apparatus. The low-temperature medium can be an aqueous solution of low-temperature methanol and ethanol, a calcium chloride solution, a sodium chloride solution, etc.

[0080] The sintering apparatus of this embodiment further includes a gas purification and circulation system 70; the gas purification and circulation system 70 is used to continuously introduce inert gas into the battery substrate 1, so that the battery substrate 1 in the sintering apparatus is always in an inert gas atmosphere, to avoid oxidation of the copper paste layer surface, to reduce the temperature during the sintering process as much as possible, to ensure the formation of good ohmic contact, and to reduce thermal damage to the doped layer.

[0081] The sintering equipment in this embodiment also includes an infrared thermometer 80. The infrared thermometer 80 can be a non-contact infrared thermometer, and the measurement point needs to avoid the copper paste layer 30. The infrared thermometer 80 monitors the temperature of the doped layer 10 in real time and dynamically adjusts the output power of the microwave system 40, the output power of the high-frequency electromagnetic induction system 50, or the flow rate of the cooling medium in the cooling module 60 to achieve precise control of the temperature of the doped layer 10, so that the sintering process can meet the temperature control curve requirements of Rapid Thermal Processing (RTP).

[0082] The sintering equipment in this embodiment also includes a central control system 90, which controls a microwave system 40, a high-frequency electromagnetic induction system 50, a cooling module 60, a gas purification and circulation system 70, and an infrared thermometer 80, enabling the sintering equipment to have real-time feedback and dynamic tuning capabilities. The sintering equipment forms a composite energy system, which enables the photovoltaic cells to have good ohmic contact and ensures the welding quality of the photovoltaic cells.

[0083] Accordingly, another embodiment of this disclosure also provides a photovoltaic cell, which is prepared by the photovoltaic cell preparation method described above.

[0084] The photovoltaic cells in this disclosure can be TOPCON cells and BC (Back Contact) cells, etc. Figure 10 The diagram shows the structure of a TOPCON cell fabricated using the aforementioned photovoltaic cell fabrication method. Electrodes are formed on both the front and back sides of the substrate 11 of the TOPCON cell using the same photovoltaic cell fabrication method. The substrate 11 is a silicon substrate. The passivation layer 20 on the front side is a front antireflection layer, which can be silicon nitride or silicon oxide. The doped layer 10 on the front side is a boron-doped layer. The copper paste layer on the front side is processed using the aforementioned process to form an ohmic contact with the doped layer 10, thereby forming the front electrode 31. The passivation layer 20 on the back side is a tunneling oxide layer, which can be silicon oxide. The doped layer 10 on the back side is a phosphorus-doped layer. The copper paste layer on the back side is processed using the aforementioned process to form an ohmic contact with the doped layer 10, thereby forming the back electrode 31.

[0085] like Figure 11The diagram shows a schematic of a BC cell fabricated using the photovoltaic cell fabrication method described above. All metal electrodes of the BC cell are located on the back side of the substrate 11. The back side of the BC cell is fabricated using the photovoltaic cell fabrication method described above to form electrodes. The back side of the BC cell is divided into N-regions and P-regions. The passivation layer 20 of the N-region can be silicon oxide or silicon oxide, and the doping layer 10 of the N-region is a phosphorus-doped layer. After the above process, the copper paste layer of the N-region forms an ohmic contact with the doping layer 10 to form the N-region electrode 31. The passivation layer 20 of the P-region can be silicon nitride or silicon oxide, and the doping layer 10 of the P-region is a boron-doped layer. The copper paste layer of the P-region forms an ohmic contact with the doping layer 10 through the above process to form the P-region electrode 31.

[0086] The photovoltaic cell of this embodiment is obtained through a first microwave treatment, a second microwave treatment, and an electromagnetic treatment. Under the premise of forming copper-silicon contact points on the surface where the copper paste layer and the doped layer meet, the copper paste layer and the doped layer can form a good ohmic contact. The photovoltaic cell achieves both good welding quality and low sintering cost, thereby improving the quality of the photovoltaic cell and reducing its cost.

[0087] Accordingly, another embodiment of this disclosure also provides a photovoltaic module, including the photovoltaic cell described above.

[0088] like Figure 12 The diagram shown is a structural schematic of a photovoltaic module according to an embodiment of this disclosure. The photovoltaic module of this embodiment includes a cover plate 41, a back plate 42, and a photovoltaic cell 2 located between the cover plate 41 and the back plate 42. The photovoltaic cell 2 is the photovoltaic cell described in the above embodiment. The cover plate 41 is the light-receiving surface of the photovoltaic module, and the back plate 42 is the backlight-receiving surface of the photovoltaic module.

[0089] The photovoltaic cell 2 in the photovoltaic module of this disclosure is obtained through a first microwave treatment, a second microwave treatment, and an electromagnetic treatment. Under the premise of forming copper-silicon contact points on the surface where the copper paste layer and the doped layer are in contact, the copper paste layer and the doped layer can form a good ohmic contact. The photovoltaic cell takes into account both good welding quality and low sintering cost, thereby improving the quality of the photovoltaic module and reducing the cost of the photovoltaic module.

[0090] Those skilled in the art will understand that the above embodiments are specific examples of implementing this disclosure, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of this disclosure. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this disclosure; therefore, the scope of protection of this disclosure should be determined by the scope defined in the claims.

Claims

1. A method for preparing a photovoltaic cell, characterized in that, include: Provide battery substrate; A copper paste layer is prepared on the surface of the battery substrate; The battery substrate is subjected to a first microwave treatment, and the copper paste layer is heated to a first temperature; The power of the first microwave processing is 3kW to 6kW; the first temperature is 150°C to 250°C; The battery substrate is subjected to a second microwave treatment, during which the copper paste layer is heated to a second temperature; the first temperature is lower than the second temperature; the power of the second microwave treatment is 6kW to 10kW; and the second temperature is 300°C to 400°C. The copper paste layer is subjected to electromagnetic treatment, and the copper paste layer forms an electrode; the electromagnetic treatment applies a high-frequency induction field to the copper paste layer through a high-frequency induction coil; the power of the electromagnetic treatment is 2KW to 20KW; the temperature of the electromagnetic treatment is 600°C to 800°C.

2. The method for preparing a photovoltaic cell according to claim 1, characterized in that, The power of the first microwave processing is less than the power of the second microwave processing.

3. The method for preparing a photovoltaic cell according to claim 1 or 2, characterized in that, The duration of the first microwave processing is 5 to 20 seconds; And / or, the duration of the second microwave treatment is 10 to 60 seconds.

4. The method for preparing a photovoltaic cell according to claim 1, characterized in that, The duration of the electromagnetic processing is 3 to 10 seconds.

5. The method for preparing a photovoltaic cell according to claim 1, characterized in that, The method further includes: During the electromagnetic processing, the battery substrate is cooled.

6. The method for preparing a photovoltaic cell according to claim 5, characterized in that, The cooling process involves cooling the surface of the battery substrate away from the copper paste layer using a low-temperature medium.

7. The method for preparing a photovoltaic cell according to claim 6, characterized in that, The cryogenic medium is any one of the following: Aqueous solutions of methanol and ethanol, calcium chloride solution, and sodium chloride solution.

8. A sintering apparatus, characterized in that, The sintering equipment is used to perform the method for preparing photovoltaic cells as described in any one of claims 1 to 7.

9. A photovoltaic cell, characterized in that, The photovoltaic cell is prepared by the photovoltaic cell preparation method according to any one of claims 1 to 7.

10. A photovoltaic module, characterized in that, include: The photovoltaic cell according to claim 9.

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