Solar cell and metallization method thereof, photovoltaic module and photovoltaic system

Abstract

The present application relates to the technical field of solar cells, and in particular to a solar cell and its metallization method, a photovoltaic module and a photovoltaic system. To solve the problem of reduced fill factor and open circuit voltage of solar cells in related technologies, resulting in efficiency loss of solar cells. A metallization method for solar cells, the solar cell includes a silicon substrate and a first passivation layer and a first grid line pattern arranged on the front of the silicon substrate; the metallization method includes: providing a silicon substrate, the front of the silicon substrate is formed with a first passivation layer; forming a first conductive paste with a first pattern on the first passivation layer; sintering and light injection of the silicon substrate formed with the first conductive paste to prepare a first grid line pattern; sintering the silicon substrate formed with the first conductive paste, including: a first heating stage, a first heat preservation stage and a first cooling stage performed in sequence, the heating rate of the first heating stage is greater than 50°C / s, and the peak temperature of the first heat preservation stage is less than 760°C.

Description

Technical Field

[0001] The present application relates to the technical field of solar cells, and in particular to a solar cell and a metallization method thereof, a photovoltaic module and a photovoltaic system. Background Art

[0002] Among solar cells, silicon solar cells are one of the mainstreams in the current photovoltaic power generation field. This is because silicon materials have extremely rich reserves in the earth's crust and have excellent electrical and mechanical properties. In the future development of photovoltaic technology, further improving the photoelectric conversion efficiency of silicon solar cells, reducing the production cost of solar cells, and enabling solar cells to be more widely used have become the research focus of silicon solar cells.

[0003] At present, Tunnel Oxide Passivation Contact (TOPCon) cells in silicon solar cells, especially N-type TOPCon cells, are favored due to their excellent passivation performance. The core of TOPCon cells lies in the ultra-thin tunneling oxide layer on the back and the heavily doped polysilicon layer, which can effectively improve the passivation of crystalline silicon cells, reduce the metal recombination on the back of crystalline silicon cells, and effectively reduce the back contact resistivity, thereby improving the conversion efficiency of crystalline silicon cells.

[0004] However, in the related art, when the N-type TOPCon battery is metallized by the sintering process, in order to ensure the ohmic contact effect between the silver paste on the front and the silicon, the silver paste on the back usually pierces the heavily doped polysilicon, and it is impossible to sinter the front and back sides at the appropriate sintering temperature at the same time, which leads to a decrease in the fill factor and open circuit voltage of the solar cell, resulting in efficiency loss of the solar cell. Summary of the invention

[0005] Based on this, it is necessary to provide a solar cell and a metallization method thereof, a photovoltaic module and a photovoltaic system to solve the problem in the related art that the fill factor and open circuit voltage of the solar cell are reduced, resulting in efficiency loss of the solar cell.

[0006] In a first aspect, a metallization method of a solar cell is provided, wherein the solar cell comprises a silicon substrate, and a first passivation layer and a first gate line pattern arranged on a front side of the silicon substrate, wherein the first gate line pattern passes through the first passivation layer and is connected to the silicon substrate; the metallization method comprises:

[0007] Providing a silicon substrate, wherein a first passivation layer is formed on the front surface of the silicon substrate;

[0008] forming a first conductive paste having a first pattern on the first passivation layer, wherein the first pattern has the same shape as the first gate line pattern;

[0009] Sintering and light-injecting the silicon substrate on which the first conductive paste is formed to prepare the first gate line pattern;

[0010] Among them, the silicon substrate formed with the first conductive paste is sintered, including: a first heating stage, a first insulation stage and a first cooling stage performed in sequence, the heating rate of the first heating stage is greater than 50°C / s, the peak temperature of the first insulation stage is less than 760°C, the cooling rate of the first cooling stage is greater than 70°C / s, and the insulation time of the first insulation stage is 0.2 s ~ 3s.

[0011] Optionally, the first heat preservation stage includes a second temperature rising stage before reaching the peak temperature and a second temperature falling stage after reaching the peak temperature;

[0012] The heating rate of the second heating stage is less than 50°C / s, and the cooling rate of the second cooling stage is less than 70°C / s.

[0013] Optionally, the starting temperature of the first insulation stage is 650°C~740°C.

[0014] Optionally, the solar cell further comprises a second passivation layer and a second gate line pattern disposed on the back side of the silicon substrate, and the second gate line pattern passes through the second passivation layer and is connected to the silicon substrate;

[0015] The metallization method further comprises:

[0016] forming a second conductive paste having a second pattern on the second passivation layer, wherein the second pattern has the same shape as the second gate line pattern;

[0017] sintering and light-injecting the silicon substrate formed with the second conductive paste;

[0018] The sintering and light injection of the silicon substrate formed with the second conductive paste are carried out in the same cavity as the sintering and light injection of the silicon substrate formed with the first conductive paste, and the difference between the starting temperature of the first insulation stage and the melting temperature of the second conductive paste is less than or equal to 200°C.

[0019] Optionally, the melting temperature of the first conductive paste is higher than the melting temperature of the second conductive paste.

[0020] Optionally, light injection into the silicon substrate formed with the first conductive paste occurs after sintering the silicon substrate formed with the first conductive paste, and the light injection into the silicon substrate formed with the first conductive paste is performed at a temperature lower than a peak temperature of the first insulation stage.

[0021] Optionally, the first temperature reduction stage is to reduce the temperature to a temperature lower than the melting temperature of the first conductive paste and the second conductive paste;

[0022] The light injection into the first conductive paste includes a third temperature rising stage, a second temperature keeping stage, a third temperature falling stage and a third temperature keeping stage performed in sequence.

[0023] Optionally, the heating rate in the third heating stage is greater than 10° C. / s.

[0024] Optionally, the difference between the temperature of the second insulation stage and the melting temperature of the second conductive paste is less than 100° C., and the duration of the second insulation stage is less than 5 s.

[0025] Optionally, the cooling rate of the third cooling stage is less than 20°C / s.

[0026] Optionally, the temperature of the third insulation stage is 200° C. to 400° C., and the insulation time of the third insulation stage is greater than 3 seconds.

[0027] Optionally, the light injection into the first conductive paste includes a second heat preservation stage, a third temperature reduction stage and a third heat preservation stage performed in sequence;

[0028] When the temperature in the first cooling stage drops to the temperature in the second heat preservation stage, the second heat preservation stage is entered.

[0029] Optionally, the difference between the temperature of the second insulation stage and the melting temperature of the second conductive paste is less than 100° C., and the duration of the second insulation stage is less than 5 s.

[0030] Optionally, the cooling rate of the third cooling stage is less than 20°C / s.

[0031] Optionally, the temperature of the third insulation stage is 200° C. to 400° C., and the insulation time of the third insulation stage is greater than 3 seconds.

[0032] Optionally, during the light injection process of the first conductive paste, the time from the beginning of cooling to the temperature being lower than 200° C. is greater than 10 seconds.

[0033] Optionally, the temperature of the second insulation stage varies within the range of 450°C to 650°C.

[0034] Optionally, the metallization method further comprises:

[0035] irradiating the first grid line pattern with laser, and applying an external electric field to the solar cell to perform electric field assisted laser sintering on the first grid line pattern;

[0036] The electric field direction of the external electric field is the same as the electric field direction of the built-in electric field of the solar cell.

[0037] Optionally, the voltage of the external electric field is 5 V to 30 V, and the application time is 0.3 s to 3 s;

[0038] The wavelength of the laser is greater than or equal to 530 nm, the power is greater than 20 W, the irradiation time is greater than 0.1 s, and the laser spot size is greater than 20 μm.

[0039] In a second aspect, a solar cell prepared by the metallization method as described in the first aspect is provided.

[0040] In a third aspect, a photovoltaic assembly is provided, comprising: a plurality of solar cells connected in series and / or in parallel;

[0041] At least one of the solar cells is a solar cell as described in the second aspect.

[0042] In a fourth aspect, a photovoltaic system is provided, comprising the photovoltaic assembly as described in the third aspect.

[0043] The above-mentioned solar cell and its metallization method, photovoltaic module and photovoltaic system have the following beneficial effects:

[0044] By controlling the heating rate of the first heating stage to be greater than 50°C / s, a greater heating intensity can be used to promote the contact and fusion of the silver particles and the emitter, reduce the ablation time of the glass material on the first passivation layer, and reduce the damage to the first passivation layer, so that the passivation effect of the first passivation layer can be maintained to a large extent and the open circuit voltage can be improved; at the same time, by controlling the temperature of the silver in the first insulation stage to be less than 760°C, the peak sintering temperature can be reduced as much as possible while ensuring that the first conductive paste forms an ohmic contact with the silicon substrate, thereby, it can be used to adapt to the lower sintering temperature of the back side, and the front and back sides can be sintered synchronously while adapting to the lower sintering temperature of the back side, which solves the problem in the related art that sintering is performed at a higher sintering temperature (such as the sintering peak temperature reaches 780°C or even above 800°C), thereby causing the silver paste on the back side to pierce the heavily doped polysilicon, etc., resulting in a reduction in the fill factor and open circuit voltage of the solar cell, resulting in a loss of efficiency of the solar cell.

[0045] In addition, during the above-mentioned sintering process, the hydrogen atoms in the solar cell will continue to overflow at high temperature, which is not conducive to the passivation of the solar cell by hydrogen atoms. Therefore, in the embodiment of the present application, by controlling the cooling rate of the first cooling stage to be greater than 70°C / s, and the insulation time of the first insulation stage to be 0.2 s ~ 3s, the overflow of hydrogen atoms can be reduced, thereby further improving the efficiency of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A schematic diagram of a cross-sectional structure of a solar cell provided in an embodiment of the present application;

[0047] Figure 2 A flow chart of a preparation method of a solar cell metallization method provided in an embodiment of the present application;

[0048] Figure 3 A temperature variation curve diagram of sintering and light injection of a solar cell provided in an embodiment of the present application;

[0049] Figure 4 Another temperature variation curve diagram of solar cell sintering and light injection provided in an embodiment of the present application. DETAILED DESCRIPTION

[0050] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0051] Unless the context requires otherwise, throughout the specification and claims, the term "including" is to be interpreted as an open, inclusive meaning, that is, "including, but not limited to". In the description of the specification, the terms "one embodiment", "some embodiments", "exemplary embodiments", "exemplarily" or "some examples" and the like are intended to indicate that specific features, structures, materials or characteristics associated with the embodiment or example are included in at least one embodiment or example of the present disclosure. The schematic representation of the above terms does not necessarily refer to the same embodiment or example. In addition, the specific features, structures, materials or characteristics may be included in any one or more embodiments or examples in any appropriate manner.

[0052] Exemplary embodiments are described herein with reference to cross-sectional views and / or plan views that are idealized exemplary drawings. In the drawings, the thickness of layers and regions are exaggerated for clarity. Therefore, variations in shape relative to the drawings due to, for example, manufacturing techniques and / or tolerances are conceivable. Therefore, the exemplary embodiments should not be interpreted as being limited to the shapes of the regions shown herein, but include shape deviations due to, for example, manufacturing. For example, an etched region shown as a rectangle will typically have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to illustrate the actual shape of regions of the device, and are not intended to limit the scope of the exemplary embodiments.

[0053] “A and / or B” includes the following three combinations: A only, B only, and a combination of A and B.

[0054] Herein, unless otherwise specified, "one or more" means one or more than or equal to two.

[0055] In this document, "for example", "such as", "example", "for example", etc. are used for descriptive purposes, indicating that the previous and subsequent different technical solutions are related in terms of the content covered, but should not be understood as limiting the previous technical solution, nor can they be understood as limiting the scope of protection of this document. In this document, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0056] In this article, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel options of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0057] In this document, the terms "first", "second", "third", "fourth", etc. in "first aspect", "second aspect", "third aspect", "fourth aspect", etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0058] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0059] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0060] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0061] In this document, "at least one" means more than one, such as one, two and more than two. "Multiple" or "several" means at least two, such as two, three, etc., and "multilayer" means at least two layers, such as two layers, three layers, etc., unless otherwise clearly and specifically defined. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0062] Herein, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​within the numerical interval is considered to be continuous and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when a numerical interval only refers to integers within the numerical interval, including the two endpoint integers of the numerical range, and each integer between the two endpoints, is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows broadly including numerical interval types such as percentage intervals, ratio intervals, and ratio intervals.

[0063] In this article, when it comes to percentage concentration, unless otherwise specified, it refers to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of the component.

[0064] Herein, %(w / w) and wt% both refer to weight percentage, %(v / v) refers to volume percentage, and %(w / v) refers to mass volume percentage.

[0065] In this article, when it comes to temperature parameters, unless otherwise specified, both constant temperature treatment and treatment within a certain temperature range are allowed. The constant temperature treatment allows the temperature to fluctuate within the accuracy range of instrument control.

[0066] Herein, the term "room temperature" or "normal temperature" generally refers to 4°C to 35°C, for example, 20°C ± 5°C. In some embodiments herein, "room temperature" or "normal temperature" refers to 10°C to 30°C. In some embodiments herein, "room temperature" or "normal temperature" refers to 20°C to 30°C.

[0067] As used in this article, fill factor (FF) refers to the ratio of the actual maximum achievable power (Pm or Vmp * Jmp) to the theoretical (not actually achievable) power (Jsc * Voc). Therefore, FF can be determined by the following formula:

[0068] FF = (Vmp * Jmp) / (Jsc * Voc)

[0069] Where Jmp and Vmp represent the current density and voltage at the maximum power point (Pm), which is obtained by changing the resistance in the circuit until J * V is the maximum value; Jsc and Voc represent the short-circuit current and open-circuit voltage, respectively. Fill factor is a key parameter for evaluating solar cells. Commercial solar cells usually have a fill factor of about 60% or more.

[0070] As used herein, open circuit voltage (Voc) is the potential difference between the anode and cathode of the device with no external load connected.

[0071] The power conversion efficiency (PCE) of a solar cell used in this article refers to the percentage of power converted from absorbed light to electrical energy. The power conversion efficiency (PCE) of a solar cell can be measured by the incident light irradiance (E: W / m 2 ) and the surface area of ​​the solar cell (Ac:m 2 ) divided by the maximum power point (Pm). STC usually refers to the temperature of 25℃ and the irradiance of 1000 W / m 2 , the spectrum of air quality 1.5 (AM1.5).

[0072] In this article, if there are multiple steps involved in the method flow, unless there is a clear different description in this article, there is no strict order restriction for the execution of these steps, and they can be executed in other orders than described. Moreover, any step can include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed in turn, alternating or simultaneously with other steps or parts of sub-steps or stages of other steps.

[0073] Taking the metallization treatment of N-type TOPCon battery as an example, the front side of the N-type TOPCon battery can be a boron-doped emitter, whose majority carriers are holes. When the sintering temperature is low and the time is long, during the sintering process, it is difficult for the silver ions in the slurry to obtain enough electrons on the surface of the emitter to undergo a reduction reaction to form silver particles, so that a higher sintering temperature and time are required to form a good ohmic contact; and the back side of the N-type TOPCon battery can be phosphorus-doped polycrystalline silicon, whose majority carriers are electrons, which can obtain enough electrons to undergo a reduction reaction to form silver particles at a lower sintering temperature, thereby achieving a good ohmic contact.

[0074] It can be seen that the different layer structures determine that the front and back sides of the N-type TOPCon battery need to be sintered at different sintering temperatures.

[0075] In the related art, the front and back sides of the N-type TOPCon cell are sintered and subsequently light injected in the same sintering furnace, making it difficult to separately control their respective sintering temperatures and durations as well as light injection temperatures and durations. In order to ensure the ohmic contact effect between the silver paste on the front side and silicon, the sintering is usually performed at a higher sintering temperature (such as a sintering peak temperature of 780°C or even above 800°C), which may result in defects such as the silver paste on the back side piercing the heavily doped polysilicon, resulting in reduced fill factor and open circuit voltage of the solar cell, and resulting in efficiency loss of the solar cell.

[0076] Based on the above technical problems, in the first aspect, some embodiments of the present application provide a metallization method for a solar cell, such as Figure 1 As shown, the solar cell includes a silicon substrate 1, a first passivation layer 2 and a first gate line pattern 3 arranged on the front side of the silicon substrate 1, and the first gate line pattern 3 passes through the first passivation layer 2 and is connected to the silicon substrate 1; Figure 1 and Figure 2 As shown, the metallization method includes the following steps S11) to S13):

[0077] S11), providing a silicon substrate 1, a first passivation layer 2 is formed on the front surface of the silicon substrate 1;

[0078] Taking the solar cell as an N-type TOPCon cell as an example, the silicon substrate 1 may be a NP + The silicon substrate of the junction, the first passivation layer 2 can exemplarily include a stacked structure of one or more layers of a silicon nitride layer and an aluminum oxide layer.

[0079] This has NP + The silicon substrate of the junction can be prepared by performing P-type ion doping (such as boron doping) on ​​a partial area of ​​an N-type silicon substrate, and the doped area forms a P-type emitter 10 .

[0080] S12), forming a first conductive paste having a first pattern on the first passivation layer 2, wherein the first pattern has the same shape as the first gate line pattern 3;

[0081] The first conductive paste may be silver paste, for example, and the first gate line pattern 3 is a front electrode pattern.

[0082] A first conductive paste having a first pattern may be formed on the first passivation layer 2 by using a screen printing process.

[0083] S13), sintering and light injection are performed on the silicon substrate 1 formed with the first conductive paste to prepare a first gate line pattern 3;

[0084] The silicon substrate formed with the first conductive paste is sintered. Figure 3As shown, it includes: a first heating stage D1, a first insulation stage E1 and a first cooling stage F1 performed in sequence, the heating rate of the first heating stage D1 is greater than 50°C / s, the peak temperature of the first insulation stage E1 is less than 760°C, the cooling rate of the first cooling stage F1 is greater than 70°C / s, and the insulation time of the first insulation stage E1 is 0.2 s~3s.

[0085] The above sintering process mainly includes the following stages: the first stage: the organic solvent in the first conductive paste evaporates; the second stage: the glass powder in the first conductive paste begins to melt and ablate the first passivation layer; the third stage: the sintering temperature reaches the peak temperature, the silver particles in the first conductive paste fuse with silicon (that is, the emitter mentioned above), and then the sintering is completed by cooling down.

[0086] During this process, in the first stage, at about 300°C~500°C, the organic solvent in the first conductive paste begins to volatilize and burn, and at more than 500°C, the glass powder begins to melt and begins to ablate the first passivation layer, entering the second stage, and when the sintering temperature reaches the peak temperature, it enters the third stage.

[0087] Based on this, the entire sintering process can be divided into a heating stage, a heat preservation stage and a cooling stage. Among them, the heating stage can correspond to the first heating stage D1 in the present application, the heat preservation stage can correspond to the first heat preservation stage E1 in the present application, and the cooling stage can correspond to the first cooling stage F1 in the present application, and the first heating stage D1 in the present application can be the stage when the organic solvent in the first conductive paste is completely volatilized and the glass powder begins to melt.

[0088] During the entire sintering process, in the first temperature rising stage D1, the first passivation layer is ablated by melting the glass material of the first conductive paste at high temperature. At the same time, the silver ions in the first conductive paste obtain the electrons in the emitter to undergo a reduction reaction to generate silver particles. The silver particles contact the surface of the emitter and fuse to form an alloy layer for connection. In this process, as the sintering temperature increases, the ablation area of ​​the glass material of the first conductive paste increases, thereby increasing the ohmic contact area and contact fusion degree of the silver particles and the emitter; otherwise, the ohmic contact area and fusion degree of the silver particles and the emitter will be reduced, thereby affecting the ohmic contact effect.

[0089] In the embodiment of the present application, by controlling the heating rate of the first heating stage D1 to be greater than 50°C / s, a greater heating intensity can be used to promote the contact and fusion of the silver particles and the emitter, reduce the ablation time of the glass material on the first passivation layer, and reduce the damage to the first passivation layer, so that the passivation effect of the first passivation layer can be maintained to a large extent, and the open circuit voltage can be improved; at the same time, by controlling the temperature of the first insulation stage to be less than 760°C, the peak temperature of sintering can be reduced as much as possible while ensuring that the first conductive paste forms an ohmic contact with the silicon substrate, thereby, it can be used to adapt to the lower sintering temperature of the back side, so that the front and back sides can be sintered synchronously while adapting to the lower sintering temperature of the back side, solving the problem in the related art that when sintering at a higher sintering temperature (such as the peak sintering temperature reaches 780°C or even above 800°C), the sintering temperature of the back side cannot be reduced to a large extent due to heat conduction, so that the silver paste on the back side pierces the heavily doped polysilicon, etc., resulting in a decrease in the fill factor and open circuit voltage of the solar cell, resulting in a loss of efficiency of the solar cell.

[0090] In addition, during the above-mentioned sintering process, the hydrogen atoms in the solar cell will continue to overflow at high temperature, which is not conducive to the passivation of the solar cell by hydrogen atoms. Therefore, in the embodiment of the present application, by controlling the cooling rate of the first cooling stage to be greater than 70°C / s and the insulation time of the first insulation stage to be shorter, the overflow of hydrogen atoms can be reduced, thereby further improving the efficiency of the solar cell.

[0091] The melting temperature of the first conductive paste is not specifically limited. In the embodiment of the present application, the melting temperature of the first conductive paste only needs to be sufficient to allow the first conductive paste to form an ohmic contact with the silicon substrate at the peak sintering temperature.

[0092] In some embodiments, the first temperature keeping stage includes a second temperature rising stage before reaching the peak temperature and a second temperature falling stage after reaching the peak temperature;

[0093] The heating rate of the second heating stage is less than 50°C / s, and the cooling rate of the second cooling stage is less than 70°C / s.

[0094] In these embodiments, by controlling the heating rate of the second heating stage to be less than 50°C / s and the cooling rate of the second cooling stage to be less than 70°C / s, insulation can be performed at relatively slow heating and cooling rates, so that the first conductive paste can ablate a certain area of ​​the first passivation layer as much as possible, thereby ensuring that good ohmic contact is formed between the first conductive paste and the silicon substrate.

[0095] In some embodiments, the starting temperature of the first insulation stage may be 650° C. to 740° C. At this starting temperature, the first conductive paste has a relatively high ablation temperature, thereby increasing the ablation area as much as possible and promoting the formation of a good ohmic contact between the first conductive paste and the silicon substrate.

[0096] In some embodiments, Figure 1 As shown, the solar cell further includes a second passivation layer 4 and a second grid line pattern 5 disposed on the back side of the silicon substrate 1, and the second grid line pattern 5 passes through the second passivation layer 4 and is connected to the silicon substrate 1; the metallization method further includes:

[0097] forming a second conductive paste having a second pattern on the second passivation layer, wherein the second pattern has the same shape as the second gate line pattern;

[0098] performing sintering and light injection treatment on the silicon substrate formed with the second conductive paste;

[0099] The sintering and light injection of the silicon substrate formed with the second conductive paste are carried out in the same cavity as the sintering and light injection of the silicon substrate formed with the first conductive paste, and the difference between the starting temperature of the first insulation stage and the melting temperature of the second conductive paste is less than or equal to 200°C.

[0100] Here, still taking the solar cell as an N-type TOPCon cell as an example, the silicon substrate 1 also includes a tunneling oxide layer 20 and a doped polysilicon layer 30 formed on the back of the silicon substrate, the second passivation layer 4 can be a silicon nitride layer, and the second gate line pattern 5 is a back electrode pattern. At this time, the second conductive paste can be a silver paste.

[0101] A second conductive paste having a second pattern may be formed on the second passivation layer by a screen printing process.

[0102] In these embodiments, by sintering and light injecting the silicon substrate formed with the second conductive paste and sintering and light injecting the silicon substrate formed with the first conductive paste in the same cavity, and controlling the difference between the starting temperature of the first insulation stage and the melting temperature of the second conductive paste to be less than or equal to 200° C., the influence of the temperature of the first insulation stage of the first conductive paste on the second conductive paste can be reduced, thereby improving the sintering effect of the back electrode pattern.

[0103] In some embodiments, the melting temperature of the first conductive paste is higher than the melting temperature of the second conductive paste.

[0104] In these embodiments, by selecting the melting temperature of the first conductive paste to be higher than the melting temperature of the second conductive paste, the corrosion of the first conductive paste on the first passivation layer can be reduced as much as possible while reducing the impact of the sintering peak temperature of the first conductive paste on the second conductive paste, thereby further improving the open circuit voltage.

[0105] In some embodiments, when the sintering and light injection of a silicon substrate formed with a second conductive paste are performed in the same cavity as the sintering and light injection of a silicon substrate formed with a first conductive paste, different heating sources can be used to heat the front and back sides of the silicon substrate to achieve simultaneous sintering of the first conductive paste and the second conductive paste at different sintering temperatures, thereby achieving precise control of the sintering temperature and improving the ohmic contact effect on the front and back sides.

[0106] In some embodiments, infrared lamps with different powers may be used to heat the front and back sides of the silicon substrate.

[0107] Light injection refers to a technology that uses photon energy to improve solar energy efficiency. The basic principle of solar cells is to use their photoelectric effect to convert photon energy into electron energy. In solar cells, light injection can increase the concentration of electrons and holes by stimulating the recombination of electrons and holes, thereby improving the conversion efficiency of solar cells. In addition, light injection can also improve the spectral response of solar cells, so that they can generate electricity under different wavelengths of light.

[0108] In some embodiments, Figure 3 and Figure 4 As shown, when the silicon substrate formed with the first conductive paste is sintered and light injected, the light injection into the silicon substrate formed with the first conductive paste occurs after the silicon substrate formed with the first conductive paste is sintered, and the temperature of the light injection into the silicon substrate formed with the first conductive paste is lower than the peak temperature of the first insulation stage E1.

[0109] In these embodiments, light injection into the silicon substrate formed with the first conductive paste occurs after sintering the silicon substrate formed with the first conductive paste. Sintering and light injection can be performed sequentially in a chain furnace, thereby reducing equipment investment and energy loss.

[0110] The specific implementation method of sintering and light injection into the silicon substrate of the first conductive paste is not limited, as long as light can be injected into the sintered solar cell to improve the passivation effect of the solar cell, thereby improving the photoelectric conversion efficiency of the solar cell.

[0111] In the embodiment of the present application, there are two possible implementation methods for sintering and light injection into the silicon substrate on which the first conductive paste is formed.

[0112] In the first possible implementation, Figure 3 As shown, in the first cooling stage F1, the temperature is lowered to a temperature lower than the melting temperature of the first conductive paste and the second conductive paste;

[0113] The light injection into the first conductive paste includes a third temperature rising stage D3, a second temperature keeping stage E2, a third temperature falling stage F3 and a third temperature keeping stage E3 performed sequentially;

[0114] Among them, the heating rate of the third heating stage D3 is greater than 10°C / s, the difference between the temperature of the second insulation stage E2 and the melting temperature of the second conductive paste is less than 100°C, the cooling rate of the third cooling stage F3 is less than 20°C / s, the time of the second insulation stage E2 is less than 5s, the temperature of the third insulation stage E3 is 200°C~400°C, and the insulation time of the third insulation stage E3 is greater than 3s.

[0115] In this possible implementation, sintering and light injection can be performed in different chambers, so that when the sintered solar cell is cooled to near room temperature, it is transferred to another chamber for light injection.

[0116] In this process, by controlling the heating rate of the third heating stage D3 to be greater than 10°C / s, it can be ensured that the heating rate is high and the residence time is short during the light injection process, thereby reducing the overflow of H atoms, and further using a larger heating intensity to promote the contact between the silver particles and the emitter, reducing the ablation time of the glass material in the first conductive paste on the first passivation layer, and at the same time, the secondary sintering of the silver particles and the emitter can be achieved in the second insulation stage E2, deepening the fusion of the silver particles and the emitter, thereby enhancing the ohmic contact effect. By controlling the cooling rate of the third cooling stage F3 to be less than 20°C / s and the time of the second insulation stage E2 to be less than 5s, the overflow of H atoms can also be reduced. At the same time, by controlling the insulation time of the third insulation stage E3 to be greater than 3s, a longer light injection time can be ensured to improve the passivation effect.

[0117] It should be noted that, in the above-mentioned entire light injection process, the third heating stage D3 and the second heat preservation stage E2 are both heated by infrared lamp irradiation. Therefore, it can also be regarded as having a certain light injection. When the temperature of the second heat preservation stage E2 begins to cool down, it enters the formal light injection stage. At this time, LED white light can be used for irradiation.

[0118] In the second possible implementation, Figure 4 As shown, the light injection into the first conductive paste includes a second heat preservation stage E2, a third temperature reduction stage F3 and a third heat preservation stage E3 performed sequentially;

[0119] When the first cooling stage F1 is cooled to the light injection temperature of the second heat preservation stage E2, the second heat preservation stage E2 is entered;

[0120] The difference between the temperature of the second insulation stage E2 and the melting temperature of the first conductive paste is less than 100°C, the cooling rate of the third cooling stage F3 is less than 20°C / s, the time of the second insulation stage E2 is less than 5s, the temperature of the third insulation stage E3 is 200°C~400°C, and the insulation time of the third insulation stage E3 is greater than 3s.

[0121] In this possible implementation, sintering and light injection can be performed in the same cavity, so that light injection can be performed on the sintered solar cell when the temperature is cooled to the temperature of the second insulation stage E2.

[0122] In this process, by controlling the difference between the temperature of the second insulation stage E2 and the melting temperature of the first conductive paste to be less than 100°C, the cooling rate of the third cooling stage F3 is less than 20°C / s, the time of the second insulation stage E2 is less than 5s, the temperature of the third insulation stage E3 is 200°C~300°C, and the insulation time of the third insulation stage E3 is greater than 3s, the sintered solar cells can be subjected to secondary sintering, and then formal light injection into the solar cells can be performed in a manner similar to the first possible implementation method mentioned above, which has the same technical effect as the first possible implementation method mentioned above, and can also save time and reduce equipment investment.

[0123] In some embodiments, in the two possible implementations described above, during the light injection process of the first conductive paste, the time from the beginning of cooling to the temperature being lower than 200° C. is greater than 10 seconds.

[0124] In these embodiments, the light injection effect can be ensured by limiting the time from starting to cool down to a temperature below 200° C. to be greater than 10 seconds.

[0125] In some embodiments, in the above two possible implementations, the temperature of the second insulation stage E2 varies within the range of 450°C to 650°C.

[0126] In these embodiments, the temperature of the second insulation stage E2 is controlled to vary within a range of 450° C. to 650° C., which can ensure that the hydrogen atoms in the first passivation layer move toward the surface and the interior of the silicon substrate, thereby better passivating the defects.

[0127] In some embodiments, the metallization method further comprises:

[0128] irradiating the first grid line pattern with a laser and applying an external electric field to the solar cell to perform electric field assisted laser sintering on the first grid line pattern;

[0129] The electric field direction of the external electric field is the same as the electric field direction of the built-in electric field of the solar cell.

[0130] Among them, laser is an electromagnetic wave, which is light generated and amplified during the stimulated radiation of matter.

[0131] In the embodiment of the present application, an external electric field is applied to the solar cell, and the electric field direction of the external electric field is the same as the electric field direction of the built-in electric field of the solar cell. Therefore, the electric field direction of the external electric field is from the N region of the PN junction to the P region, generating a current flow from the N region to the P region. At the same time, a laser is used to irradiate the surface of the solar cell, and a large number of non-equilibrium carriers are injected instantaneously by utilizing the ultra-high light intensity of the laser, and flow in a directional manner under the action of the external electric field, thereby generating a huge photocurrent in the laser irradiation area. The current can flow through the position where the silver particles in the first conductive paste do not form a good ohmic contact with silicon, and generate instantaneous high temperature due to the high resistance value, thereby promoting further mutual fusion and expansion of the silver particles and silicon, improving the ohmic contact effect between the silver particles and silicon in the first conductive paste, and greatly reducing the contact resistivity between silver and silicon.

[0132] There are no specific limitations on the intensity, wavelength and irradiation time of the laser, as well as the intensity of the electric field. As long as the silver ions can accelerate the acquisition of electrons and form a better ohmic contact with the emitter, they are within the protection scope of this application.

[0133] In some embodiments, the voltage of the external electric field is 5 V to 30 V, and the application time is 0.3 s to 3 s;

[0134] The wavelength of the laser is greater than or equal to 530 nm, the power is greater than 20 W, the irradiation time is greater than 0.1 s, and the laser spot size is greater than 20 μm.

[0135] In these embodiments, by controlling the voltage and time of the external electric field, and limiting the wavelength, power, irradiation time and laser spot size of the laser within the above ranges, it is possible to ensure that the first conductive paste and the silicon substrate are re-sintered at an instantaneous high temperature, thereby further ensuring the ohmic contact effect between the silver particles and the emitter, thereby improving the conversion efficiency of the battery.

[0136] In a second aspect, some embodiments of the present application provide a solar cell prepared according to the metallization method as described in the first aspect.

[0137] The solar cell is exemplarily an N-type TOPCon cell.

[0138] The beneficial effects of the solar cell provided in the second aspect of the present application are the same as the beneficial effects of the method for preparing the solar cell provided in the first aspect as described above, and will not be described in detail herein.

[0139] In a third aspect, some embodiments of the present application provide a photovoltaic assembly, the photovoltaic assembly comprising: a plurality of solar cells connected in series and / or in parallel;

[0140] At least one of the solar cells is a solar cell as described in the second aspect.

[0141] Since the photovoltaic module includes the solar cell provided by the above embodiment, it has the same beneficial effects as the solar cell described in the above second aspect, which will not be described in detail here.

[0142] In a fourth aspect, some embodiments of the present application provide a photovoltaic system, comprising the photovoltaic component as described in the third aspect.

[0143] Since the photovoltaic system includes the photovoltaic assembly provided by the above embodiment, it has the same beneficial effects as the solar cell described in the third aspect, which will not be described in detail here.

[0144] Photovoltaic systems can be used in photovoltaic power stations, such as ground power stations, rooftop power stations, water power stations, etc., and can also be used in equipment or devices that use solar energy to generate electricity, such as user solar power supplies, solar street lights, solar cars, solar buildings, etc. Of course, it is understandable that the application scenarios of photovoltaic systems are not limited to this, that is to say, photovoltaic systems can be used in all fields that require solar energy to generate electricity. Taking the photovoltaic power generation system network as an example, the photovoltaic system may include a photovoltaic array, a junction box and an inverter. The photovoltaic array can be an array combination of multiple solar cells. For example, multiple solar cells can form multiple photovoltaic arrays. The photovoltaic array is connected to the junction box. The junction box can converge the current generated by the photovoltaic array. The converged current flows through the inverter and is converted into the alternating current required by the mains power grid. After that, it is connected to the mains network to realize solar power supply.

[0145] In order to objectively evaluate the technical effects of the embodiments of the present application, the present application will be described in detail and exemplarily through the following embodiments and comparative examples.

[0146] In the following examples and comparative examples, all raw materials can be purchased commercially, and in order to maintain the reliability of the experiment, the raw materials used in the following examples and comparative examples have the same physical and chemical parameters or are prepared by the same processing method.

[0147] Example 1

[0148] The metallization method of the solar cell provided in Example 1 is as follows:

[0149] Step 1), forming a velvet surface on an N-type silicon substrate, forming a P-type emitter on the front side thereof by doping B ions, and forming a tunneling oxide layer and an N-type polysilicon layer on the back side of the N-type silicon substrate on which the P-type emitter is formed;

[0150] Step 2), forming a silicon nitride layer on the P-type emitter as a front passivation layer, and forming an aluminum oxide layer on the N-type polysilicon layer as a back passivation layer;

[0151] Step 3), forming a silver paste having a front electrode pattern and a silver paste having a back electrode pattern on the silicon nitride layer, and sintering and light injecting the silver paste having the front electrode pattern and the silver paste having the back electrode pattern;

[0152] When sintering the front side, the temperature is increased from 500°C to 700°C at a rate of 60°C / s, and then to 760°C at a rate of 40°C / s. When sintering the back side, the temperature is increased from 380°C to 750°C at a rate of 55°C / s.

[0153] During light injection, the solar cell that has been sintered and cooled to 100°C is moved to another sintering furnace. At the beginning, the heating rate of the front light injection is 20°C / s. When it reaches 550°C and the dwell time is about 1.5s, it starts to cool down and turns on the LED white light to cool down to below 400°C and keep the temperature above 200°C for 3s to complete the light injection.

[0154] Step 4), using laser to irradiate the front electrode pattern, and applying an external electric field to the solar cell to perform electric field assisted laser sintering on the front electrode pattern; wherein the laser wavelength is 1060nm, the power is 24W, the irradiation time is 0.7s, and the laser spot size is 80μm.

[0155] Example 2

[0156] The metallization method of the solar cell provided in Example 2 is substantially the same as the metallization method of the solar cell provided in Example 1, except that:

[0157] In step 3), a silver paste having a front electrode pattern and a silver paste having a back electrode pattern are formed on the silicon nitride layer, and the silver paste having the front electrode pattern and the silver paste having the back electrode pattern are sintered and light injected. When the silver paste is sintered on the front side, the temperature is increased from 500°C to 720°C at a rate of 60°C / s, and then increased to 740°C at a rate of 30°C / s for sintering. When the silver paste is sintered on the back side, the temperature is increased from 480°C to 730°C at a rate of 70°C / s for sintering. During light injection, the temperature is reduced to 550°C in the same sintering furnace as the above sintering. When the front light is injected, the temperature is lowered when the dwell time is about 2s, and the LED white light is turned on at the same time. The temperature is lowered to 350°C and kept at this temperature for 5s to complete the light injection.

[0158] Comparative Example 1

[0159] The metallization method of the solar cell in Comparative Example 1 is substantially the same as the metallization method of the solar cell in Example 1, except that:

[0160] When sintering the front side, the temperature is increased from 500°C to 800°C at a rate of 60°C / s, and when sintering the back side, the temperature is increased from 480°C to 790°C at a rate of 60°C / s.

[0161] During light injection, the solar cell that has been sintered and cooled to below 100°C is moved to another sintering furnace. Initially, the heating rate for front light injection is 20°C / s. When it reaches 550°C and the dwell time is about 1.5s, it starts to cool down, and the LED white light is turned on. The temperature is cooled down to 380°C and kept warm for 3s to complete the light injection.

[0162] Test Case

[0163] The open circuit voltage, short circuit current, fill factor and PCE of the solar cells provided in Examples 1-2 and Comparative Example 1 were tested and calculated to obtain the results shown in Table 1 below:

[0164] Table 1

[0165]

[0166] It can be seen from Table 1 that compared with Comparative Example 1 in which the sintering peak temperature of the front side is high and the sintering temperature of the back side cannot be reduced, the present application reasonably sets the relevant parameters such as the sintering and light injection of the silver paste with the front electrode pattern, and the short-circuit current, open-circuit voltage and fill factor of the solar cell are improved to a certain extent, thereby effectively improving the photoelectric conversion efficiency of the solar cell.

[0167] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0168] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A method for metallizing a solar cell, characterized in that: The solar cell comprises a silicon substrate, a first passivation layer and a first gate line pattern arranged on the front side of the silicon substrate, wherein the first gate line pattern passes through the first passivation layer and is connected to the silicon substrate; The metallization method comprises: Providing a silicon substrate, wherein a first passivation layer is formed on the front surface of the silicon substrate; forming a first conductive paste having a first pattern on the first passivation layer, wherein the first pattern has the same shape as the first gate line pattern; Sintering and light-injecting the silicon substrate on which the first conductive paste is formed to prepare the first gate line pattern; The sintering of the silicon substrate formed with the first conductive paste includes: a first heating stage, a first insulation stage and a first cooling stage performed in sequence, the heating rate of the first heating stage is greater than 50°C / s, the peak temperature of the first insulation stage is less than 760°C, the cooling rate of the first cooling stage is greater than 70°C / s, and the insulation time of the first insulation stage is 0.2s to 3s; The first heat preservation stage includes a second temperature rise stage before reaching the peak temperature and a second temperature drop stage after reaching the peak temperature; The heating rate of the second heating stage is less than 50°C / s, and the cooling rate of the second cooling stage is less than 70°C / s.

2. The metallization method according to claim 1, characterized in that: The starting temperature of the first insulation stage is 650°C to 740°C.

3. The metallization method according to claim 1, characterized in that: The solar cell further comprises a second passivation layer and a second gate line pattern disposed on the back side of the silicon substrate, wherein the second gate line pattern passes through the second passivation layer and is connected to the silicon substrate; The metallization method further comprises: forming a second conductive paste having a second pattern on the second passivation layer, wherein the second pattern has the same shape as the second gate line pattern; sintering and light-injecting the silicon substrate formed with the second conductive paste; The sintering and light injection of the silicon substrate formed with the second conductive paste are carried out in the same cavity as the sintering and light injection of the silicon substrate formed with the first conductive paste, and the difference between the starting temperature of the first insulation stage and the melting temperature of the second conductive paste is less than or equal to 200°C.

4. The metallization method according to claim 3, characterized in that: The melting temperature of the first conductive paste is higher than the melting temperature of the second conductive paste.

5. The metallization method according to claim 3, characterized in that: Light injection into the silicon substrate formed with the first conductive paste occurs after the silicon substrate formed with the first conductive paste is sintered, and the temperature of light injection into the silicon substrate formed with the first conductive paste is lower than the peak temperature of the first insulation stage.

6. The metallization method according to claim 5, characterized in that: The first temperature reduction stage reduces the temperature to a temperature lower than the melting temperature of the first conductive paste and the second conductive paste; The light injection into the first conductive paste includes a third temperature rising stage, a second temperature keeping stage, a third temperature falling stage and a third temperature keeping stage performed in sequence.

7. The metallization method according to claim 6, characterized in that: The heating rate of the third heating stage is greater than 10°C / s.

8. The metallization method according to claim 6, characterized in that: The difference between the temperature of the second heat preservation stage and the melting temperature of the second conductive paste is less than 100° C., and the duration of the second heat preservation stage is less than 5 seconds.

9. The metallization method according to claim 6, characterized in that: The cooling rate of the third cooling stage is less than 20°C / s.

10. The metallization method according to claim 6, characterized in that: The temperature of the third heat preservation stage is 200° C. to 400° C., and the heat preservation time of the third heat preservation stage is greater than 3 seconds.

11. The metallization method according to claim 5, characterized in that: The light injection into the first conductive paste includes a second heat preservation stage, a third temperature reduction stage and a third heat preservation stage performed in sequence; When the temperature in the first cooling stage drops to the temperature in the second heat preservation stage, the second heat preservation stage is entered.

12. The metallization method according to claim 11, characterized in that: The difference between the temperature of the second heat preservation stage and the melting temperature of the second conductive paste is less than 100° C., and the duration of the second heat preservation stage is less than 5 seconds.

13. The metallization method according to claim 11, characterized in that: The cooling rate of the third cooling stage is less than 20°C / s.

14. The metallization method according to claim 11, characterized in that: The temperature of the third heat preservation stage is 200° C. to 400° C., and the heat preservation time of the third heat preservation stage is greater than 3 seconds.

15. The metallization method according to claim 6 or 11, characterized in that: During the light injection process of the first conductive paste, the time from the start of cooling to the temperature being lower than 200° C. is greater than 10 seconds.

16. The metallization method according to claim 6 or 11, characterized in that: The temperature in the second heat-retaining stage varies within a range of 450°C to 650°C.

17. The metallization method according to any one of claims 1 to 14, characterized in that: The metallization method further comprises: irradiating the first grid line pattern with laser, and applying an external electric field to the solar cell to perform electric field assisted laser sintering on the first grid line pattern; The electric field direction of the external electric field is the same as the electric field direction of the built-in electric field of the solar cell.

18. The metallization method according to claim 17, characterized in that: The voltage of the external electric field is 5V to 30V, and the application time is 0.3s to 3s; The wavelength of the laser is greater than or equal to 530 nm, the power is greater than 20 W, the irradiation time is greater than 0.1 s, and the laser spot size is greater than 20 μm.

19. A solar cell prepared by the metallization method according to any one of claims 1 to 18.

20. A photovoltaic module, characterized in that: include: A plurality of solar cells connected in series and / or in parallel; At least one of the solar cells is the solar cell according to claim 19.

21. A photovoltaic system, characterized in that: Comprising the photovoltaic module as claimed in claim 20.

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