Sintering furnace and sintering method

Abstract

The invention provides a sintering furnace and a sintering method, relates to the technical field of photovoltaics, and aims to solve the technical problem that good ohmic contact between a back contact photovoltaic cell grid line and a cell piece is difficult to realize when the back contact photovoltaic cell grid line is sintered. The sintering furnace is used for forming grid lines on a back contact photovoltaic cell, the sintering furnace comprises a furnace body, at least one heating lamp and at least one grating, the heating lamp and the grating are arranged in the furnace body, and each grating is located on the side, facing the photovoltaic cell, of the corresponding heating lamp; the heating lamp is used for forming a plurality of high-temperature areas and low-temperature areas which are sequentially alternated on the photovoltaic cell through the optical grating, and the high-temperature areas and the low-temperature areas respectively correspond to the areas where the grid lines are located; wherein the grid lines in the high-temperature area and the grid lines in the low-temperature area are opposite in polarity. By means of the sintering furnace, it can be guaranteed that good ohmic contact is formed between the grid line and a photovoltaic cell in the sintering process.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, and more particularly to a sintering furnace and a sintering method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] In back-contact (BC) photovoltaic cells, the positive and negative grid lines are arranged alternately on the back of the cell. Typically, a paste is first printed onto the P / N regions of the photovoltaic cell using screen printing, followed by sintering to metallize and form the corresponding grid lines. Because the conductivity mechanisms of the metallized grid lines in the N / P regions differ, the pastes used also differ, and the sintering and curing temperatures also differ.

[0004] The sintering furnaces in related technologies are all N / P zone co-firing, which requires the preparation of slurries with matching sintering temperature windows. The slurry composition ratio is difficult to achieve, and it is difficult to achieve good ohmic contact between the grid lines and the solar cells during sintering. Summary of the Invention

[0005] The purpose of this invention is to provide a sintering furnace and sintering method to solve the technical problem that it is difficult to achieve good ohmic contact between the grid lines of back-contact photovoltaic cells and the cells during sintering.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a sintering furnace for forming grid lines on a back-contact photovoltaic cell, the sintering furnace comprising a furnace body and at least one heating lamp and at least one grating disposed within the furnace body, each of the gratings being located on the side of the corresponding heating lamp facing the photovoltaic cell;

[0008] The heating lamp is used to form multiple alternating high-temperature zones and low-temperature zones on the photovoltaic cell through the grating, and the high-temperature zone and the low-temperature zone respectively correspond to the area where the grating line is located; wherein the grating line located in the high-temperature zone has the opposite polarity to the grating line located in the low-temperature zone.

[0009] According to at least one embodiment of the present invention, the distance between the grating and the photovoltaic cell is adjustable; and / or,

[0010] The angle between the grating and the horizontal plane is adjustable.

[0011] According to at least one embodiment of the present invention, the distance between the grating and the photovoltaic cell ranges from 1 mm to 100 mm; and / or,

[0012] The angle between the grating and the horizontal plane is greater than or equal to 0° and less than 180°.

[0013] According to at least one embodiment of the present invention, the temperature difference between the high-temperature zone and the low-temperature zone ranges from 20°C to 100°C.

[0014] According to at least one embodiment of the present invention, the furnace body has a drying chamber and a sintering chamber, and the number of heating lamps is multiple;

[0015] The drying chamber is provided with at least one of the heating lamps; or, the drying chamber is provided with at least one of the heating lamps and at least one of the light gratings.

[0016] The sintering chamber is provided with at least one heating lamp and at least one grating.

[0017] According to at least one embodiment of the present invention, the number of heating lamps in the drying chamber is plurality of, at least one of the plurality of heating lamps is located on one side of the drying chamber, and at least another is located on the opposite side of the drying chamber; and / or,

[0018] The number of heating lamps in the sintering chamber is multiple, at least one of the multiple heating lamps is located on one side of the sintering chamber, and at least another is located on the opposite side of the sintering chamber.

[0019] According to at least one embodiment of the present invention, the furnace body further includes a cooling chamber located on the side of the sintering chamber opposite to the drying chamber.

[0020] According to at least one embodiment of the present invention, the temperature of the drying chamber ranges from 50°C to 600°C, and the drying time ranges from 10s to 120s; and / or,

[0021] The temperature of the sintering chamber ranges from 400℃ to 1000℃, and the sintering time ranges from 5s to 100s; and / or,

[0022] The cooling rate of the cooling chamber ranges from 2℃ / s to 30℃ / s.

[0023] According to at least one embodiment of the present invention, the sintering furnace further includes a conveying device for passing the photovoltaic cell through the furnace body, the conveying direction of the conveying device being parallel to the extension direction of the slit of the grating.

[0024] In a second aspect, the present invention also provides a sintering method, wherein sintering is performed using the sintering furnace described in the first aspect, the sintering method comprising:

[0025] The photovoltaic cells containing the slurry are placed inside the furnace.

[0026] The distance between the grating and the photovoltaic cell is adjusted to a preset spacing, and the diffraction angle of the grating is adjusted to a preset angle. Multiple alternating high-temperature and low-temperature zones are formed on the photovoltaic cell to sinter the slurry. The high-temperature zone and the low-temperature zone correspond to the areas where the grating lines are located. The polarity of the grating lines located in the high-temperature zone is opposite to that of the grating lines located in the low-temperature zone.

[0027] In one or more technical solutions provided in the exemplary embodiments of the present invention, at least one of the following beneficial effects can be achieved.

[0028] The sintering furnace of an exemplary embodiment of the present invention is used for sintering paste on a photovoltaic cell in back contact, forming alternating positive and negative grid lines on the back side of the photovoltaic cell. By placing a grating between the heating lamp and the photovoltaic cell within the furnace, the light, under the diffraction of the grating, forms bright stripes (high-temperature region) and dark stripes (low-temperature region) on the cell. This means that different temperatures are applied to the positive and negative grid line pastes respectively, thereby adapting to the different sintering temperatures required for the positive and negative grid line pastes. Based on this, both the positive and negative grid line pastes can be sintered at suitable temperatures, ensuring good ohmic contact between the positive and negative grid lines and the cell, thus guaranteeing the power generation efficiency of the photovoltaic cell.

[0029] Compared to existing technologies that employ laser-assisted sintering or localized shading using specific carriers to accommodate different sintering temperatures of the positive and negative electrode grid line pastes, the temperature changes of the solar cells caused by localized shading using specific masks cannot be directly monitored. Furthermore, with laser-assisted sintering, when sintering temperatures fluctuate significantly in different regions, it is difficult to determine whether the temperature anomaly is caused by the sintering light source itself or by the laser source, thus hindering precise temperature control. Therefore, the sintering furnace of the exemplary embodiment of this invention eliminates the need for additional laser light sources or high-precision masks, minimizing costs. Simultaneously, by utilizing the sintering furnace's own light source superimposed with a grating structure, the built-in temperature control element can monitor temperature changes in real time, thereby achieving precise temperature regulation. Attached Figure Description

[0030] The accompanying drawings illustrate exemplary embodiments of the invention and, together with the description thereof, serve to explain the principles of the invention. These drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification.

[0031] Figure 1 This is a cross-sectional structural schematic diagram of a sintering furnace according to an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the structure of a grating according to an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram of grating diffraction enhancement ripples according to an embodiment of the present invention;

[0034] Figure 4A This is a schematic diagram of the bright and dark stripes generated by the grating (L=18mm) according to an embodiment of the present invention;

[0035] Figure 4B This is a schematic diagram of the bright and dark stripes generated by the grating (L=36mm) according to an embodiment of the present invention;

[0036] Figure 5 This is a schematic diagram showing the corresponding positions of the bright and dark stripes generated by the grating according to an embodiment of the present invention and the grating lines.

[0037] Figure 6 This is a flowchart of a sintering method according to an embodiment of the present invention.

[0038] Figure label:

[0039] 10. Drying chamber;

[0040] 20. Sintering cavity;

[0041] 30. Cooling chamber; 31. Cooling device;

[0042] 40. Heating lamp;

[0043] 50. Grating; 51. High-temperature region; 52. Low-temperature region; 53. Slit;

[0044] 60. Conveying device;

[0045] 70. Exhaust device;

[0046] 81. Positive grid line; 82. Negative grid line. Detailed Implementation

[0047] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0048] BC cells typically use screen printing of silver paste to create metallized electrodes. After printing, the silver paste needs to be cured during high-temperature sintering. During this process, the organic carrier volatilizes, the glass powder softens and melts into a liquid, and corrodes and penetrates the anti-reflection insulating layer on the back of the photovoltaic cell, so that the silver powder and the crystalline silicon substrate of the photovoltaic cell can form a good ohmic contact, thereby forming grid lines (electrodes).

[0049] Figure 5 This is a schematic diagram showing the corresponding positions of the bright and dark fringes and grating lines generated by the grating according to an embodiment of the present invention. Figure 5 As shown, the back of the BC battery has alternating P-regions and N-regions, corresponding to the positive electrode grid line 81 and the negative electrode grid line 82, respectively. Due to the different conductivity mechanisms of the positive electrode grid line 81 and the negative electrode grid line 82, the slurry systems are different, and the sintering and curing temperatures are also different. The sintering furnaces in related technologies all employ a co-firing method for the positive electrode grid line 81 and the negative electrode grid line 82, requiring the selection of a precise sintering temperature window to match the different sintering temperatures of the positive electrode grid line 81 and the negative electrode grid line 82. This results in a high difficulty in slurry composition and a challenging sintering process.

[0050] To address the aforementioned issues, the sintering furnace provided in the exemplary embodiment of the present invention is equipped with a grating at its original heating lamp. The light and dark fringes formed by the diffraction of light create high-temperature and low-temperature zones in the areas where the grating lines of different polarities are located, in order to match the sintering temperature of different slurries. This allows for good ohmic contact between the grating lines and the silicon substrate of the solar cell, ensuring the photoelectric conversion efficiency of the photovoltaic cell.

[0051] Figure 1 This is a schematic cross-sectional view of a sintering furnace according to an embodiment of the present invention. See also... Figure 1 and Figure 5 The sintering furnace provided in the exemplary embodiment of the present invention is used for forming grid lines on a back-contact photovoltaic cell. The sintering furnace includes a furnace body and at least one heating lamp 40 and at least one grating 50 disposed in the furnace body. Each grating 50 is located on the side of the corresponding heating lamp 40 facing the photovoltaic cell. The heating lamp 40 is used to form a plurality of alternating high-temperature zones 51 and low-temperature zones 52 on the photovoltaic cell through the grating 50, and the high-temperature zones 51 and low-temperature zones 52 respectively correspond to the areas where the grid lines are located. The grid lines located in the high-temperature zone 51 have opposite polarities to the grid lines located in the low-temperature zone 52.

[0052] For example, the positive grid line 81 is used to form an ohmic contact with the P region of the battery cell, and the negative grid line 82 is used to form an ohmic contact with the N region of the battery cell. The sintering temperature of the silver paste forming the positive grid line 81 is greater than the sintering temperature of the silver paste forming the negative grid line 82.

[0053] In practical applications, a grating 50 is installed on the side of the heating lamp 40 facing the back of the solar cell inside the sintering furnace. When the heating lamp 40 is turned on, multiple alternating bright and dark stripes are formed through the grating 50, corresponding to the high-temperature zone 51 and the low-temperature zone 52, respectively. The silver paste forming the positive electrode grid lines 81 is located in the high-temperature zone 51, and correspondingly, the silver paste forming the negative electrode grid lines 82 is located in the low-temperature zone 52. Thus, by using the existing heating lamp 40 and simply superimposing the grating 50 inside the furnace, high-temperature zones 51 and low-temperature zones 52 of the paste with different sintering temperature requirements can be generated on the solar cell, so that the sintering temperature of the paste is adapted and a good ohmic contact is formed.

[0054] refer to Figure 5 High-temperature region 51 (bright stripes) is generated at the position of the cell forming the positive electrode grid line 81 through the grating 50, and low-temperature region 52 (dark stripes) is generated at the position of the cell forming the negative electrode grid line 82 through the grating 50.

[0055] In some embodiments, the distance between the grating 50 of the sintering furnace and the photovoltaic cell provided in the exemplary embodiment of the present invention is adjustable; the angle between the grating 50 and the horizontal plane is adjustable.

[0056] For example, the distance between the grating 50 and the photovoltaic cell ranges from 1mm to 100mm, and can be, for example, 5mm, 10mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, 55mm, 60mm, 65mm, 70mm, 75mm, 80mm, 85mm, 90mm, 95mm, etc.

[0057] For example, the angle between the grating 50 and the horizontal plane is greater than or equal to 0° and less than 180°, and can be, for example, 1°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 60°, 65°, 70°, 85°, 85°, 95°, 100°, 110°, 120°, 130°, 140°, 150°, 160°, 170°, etc.

[0058] Adjusting the distance between the grating 50 and the photovoltaic cell, as well as the angle between the grating 50 and the horizontal plane, allows for adaptation to sintering temperatures of different slurries. This increases the flexibility of the sintering furnace to accommodate photovoltaic cells with different grid patterns. The temperature regulation principle will be explained below.

[0059] Figure 2 This is a schematic diagram of the structure of the grating 50 according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the diffraction enhancement ripples of the grating 50 according to an embodiment of the present invention. (Combined with...) Figures 1-3As shown, the diffraction grating 50 can be considered to be composed of a set of infinitely long and infinitely narrow slits 53 arranged at equal intervals. When the incident light passes through the grating 50, the incident light will be dispersed into a series of bright and dark diffraction beams (bright fringes and dark fringes), thereby realizing the dispersion of light and the redistribution of light intensity.

[0060] For example, the width of the fully transparent part (slit 53) is a, the width of the partially transparent or opaque area is b, and the spacing between slits 53 is d = a + b, which is called the grating constant. It reflects the spatial periodicity of the grating 50, and its reciprocal 1 / d represents the number of slits 53 per unit distance, which is called the grating density.

[0061] The grating equation is dsinθ=kλ, where θ is the diffraction angle, k is the diffraction spectral order, and λ is the wavelength of the light wave.

[0062] When the optical path difference between the light rays emitted from two adjacent slits 53 reaching the interference point is an integer multiple of the wavelength of the light, i.e., dsinθ=±kλ (λ=0,1,2……), the two light rays are in phase, and interference enhancement occurs, resulting in bright fringes, i.e., the strong light region is the high-temperature region 51. Conversely, dark fringes are formed, i.e., the weak light region is the low-temperature region 52. Figure 5 As shown.

[0063] The spacing between adjacent stripes is Δx = λL / d, where L is the distance between the grating 50 and the photovoltaic cell, and d is the spacing of the slits 53.

[0064] According to the stripe spacing formula, by moving the grating 50 to change the height position L and / or the slit spacing d of slit 53, the spacing between adjacent stripes can be adjusted and correspond to the grating area.

[0065] Figure 4A This is a schematic diagram of the bright and dark stripes generated by the grating 50 (L = 18 mm) according to an embodiment of the present invention; Figure 4B This is a schematic diagram of the bright and dark stripes generated by the grating 50 (L = 36 mm) according to an embodiment of the present invention. Figure 4A and Figure 4B As shown, changing the distance L between the grating 50 and the solar cell results in a significant change in the spacing between the bright and dark stripes.

[0066] The intensity of the diffracted light after the light wave passes through grating 50 can be calculated by the following formula:

[0067] I = N 2 I0cos(πd / λ·sinθ);

[0068] Where I0 is the original light intensity and N is the number of slits 53, the light intensity after diffraction can be determined by the diffraction angle when other parameters remain unchanged. Therefore, the temperature of different regions can be adjusted by changing the angle between the grating 50 and the solar cell (or the horizontal plane).

[0069] As can be seen from the diffraction principle of the grating 50, by changing the relative position between the grating 50 and the battery cell or heating lamp 40, as well as the angle (diffraction angle θ) between the grating 50 and the battery cell, the corresponding bright fringes can be aligned with the high temperature region 51 required by the positive electrode grid line 81, and the dark fringes can be aligned with the low temperature region 52 required by the negative electrode grid line 82. The temperature range can be controlled by adjusting the diffraction angle θ.

[0070] It should be noted that the positions of the positive grid line 81 and the negative grid line 82 in the corresponding bright and dark stripes do not need to be absolutely centered. As long as they are within the corresponding stripe area, the temperature requirements can be met, which can reduce the precision of temperature control.

[0071] For example, one end of the grating 50 can be set on the output shaft of the motor, and the motor is set on the lifting mechanism, such as the extension end of a cylinder, electric cylinder, hydraulic cylinder, or linear motor.

[0072] In actual use, the height of the grating 50 is controlled by the extension and retraction of the cylinder, which adjusts the distance between the grating 50 and the heating lamp 40 and the battery cells. The tilt angle of the grating 50 can be adjusted by rotating the output shaft of the motor, thereby adjusting the light diffraction angle θ to obtain the desired high-temperature zone 51 and low-temperature zone 52. For example, the grating 50 can rotate within an angle range of 0° to 180°.

[0073] Optionally, the grating 50 can also be placed on a bracket or clamping device. The bracket or clamping device is a movable and rotatable spiral or sliding mechanism and is connected to a PLC. When the grating stripes returned by the PLC through the vision system are inconsistent with the direction of the grid lines of the battery cell, the position and angle of the bracket and clamping device can be adjusted by the PLC. That is, by adjusting the distance between the grating 50 and the heating lamp 40, the width of the bright and dark stripes can be adjusted. By adjusting the angle of the grating 50, the diffraction angle can be adjusted so that the bright and dark stripes are consistent with the direction of the grid lines. This allows the light emitted by the heating lamp 40 to be diffracted by the grating 50, and the diffraction stripes or light spots correspond to the positive grid line 81 and the negative grid line 82 of the battery cell, respectively.

[0074] According to Fraunhofer diffraction theory, the intensity of the diffraction pattern changes as the distance between the grating 50 and the light source changes. Specifically, the closer the grating 50 is to the light source, the weaker the intensity of the diffraction pattern; conversely, the farther the grating 50 is from the light source, the stronger the intensity of the diffraction pattern.

[0075] Considering the actual space size around the heating lamp 40 inside the sintering furnace, the temperature difference between the high-temperature zone 51 and the low-temperature zone 52 provided in the exemplary embodiment of the present invention is in the range of 20℃ to 100℃, for example, it can be 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, etc., depending on the sintering temperature required by the actual grid slurry.

[0076] Specifically, the relationship between light intensity and temperature can be calculated using the following formula:

[0077] The total energy radiated per unit surface area of ​​a blackbody per unit time (i.e., radiance j*) is proportional to the fourth power of its thermodynamic temperature T:

[0078] j*=εσT 4 ;

[0079] Where ε is the emissivity (0 < ε ≤ 1), representing how close an object is to a blackbody in terms of its ability to emit radiation, and σ is the Stefan-Boltzmann constant: σ ≈ 5.67 × 10⁻⁶. -8 W / (m 2 ·K 4 ).

[0080] Taking the heating lamp 40 inside the furnace with a set temperature of 750℃ as an example, after being adjusted by the grating 50, the P area has bright stripes (high temperature area 51), and the temperature controllable range is 750℃~830℃; the N area has dark stripes (low temperature area 52), and the temperature controllable range is 730℃~750℃.

[0081] The difference in sintering temperature between the positive grid line 81 and the negative grid line 82 of the BC battery mainly depends on the intrinsic differences in structure, doped ions, and electrical state between the N and P regions of the battery cell, as well as the matching ratio of the slurry system.

[0082] The general principle is that high-temperature sintering is required for polycrystalline silicon metallization in the P-region to solve the high contact resistance problem of the boron doped layer, while lower-temperature sintering is required in the N-region to promote silver ion migration and reduction, reducing the negative impact of high temperature on passivation. Therefore, through localized diffraction enhancement, the light intensity at the positive electrode grid line 81 on the P-region is increased to create a high-temperature region 51, and a low-temperature region 52 is created at the negative electrode grid line 82 on the N-region. This allows the two silver pastes with different compositions in the BC cell to be fully sintered, achieving a good sintering effect and improving photovoltaic cell performance.

[0083] For example, the slit 53 pattern of the grating 50 is pre-customized according to the layout of the cell grid lines, and the material of the grating 50 should be a high-temperature resistant material, such as silicon carbide, which can be used normally in the sintering furnace at 100°C to 1000°C.

[0084] Considering that the temperature is relatively high during sintering of the slurry in actual production, the slurry can be pre-dried before sintering in order to give it better electrical properties.

[0085] In some embodiments, the furnace body has a drying chamber 10 and a sintering chamber 20, and the number of heating lamps 40 is multiple; the drying chamber 10 is provided with at least one heating lamp 40; or, the drying chamber 10 is provided with at least one heating lamp 40 and at least one grating 50; the sintering chamber 20 is provided with at least one heating lamp 40 and at least one grating 50.

[0086] In practical applications, the battery cells printed with paste first enter the drying chamber 10 for pre-drying, and then enter the sintering chamber 20 for sintering. The temperature of the drying chamber 10 can be lower than the temperature of the sintering chamber 20.

[0087] For example, the heating lamp 40 of the drying chamber 10 is the same as the heating lamp 40 of the sintering chamber 20, such as a heating lamp tube, a heating bulb, or a heating wire. A grating 50 can also be provided between each heating lamp 40 of the drying chamber 10 and the battery cell to create a temperature difference in the battery cell areas where the positive grid line 81 and the negative grid line 82 are located. The temperature at the positive grid line 81 is higher than the temperature at the negative grid line 82, so as to achieve the corresponding drying effect in preparation for high-temperature sintering.

[0088] It is understandable that the drying chamber 10 may not use the grating 50, but only the heating lamp 40 to dry the slurry of the positive grid line 81 and the negative grid line 82 together.

[0089] It should be noted that, for both the drying chamber 10 and the sintering chamber 20, if there is a grating 50, the grating 50 is set on the side of the heating lamp 40 facing the back of the BC battery. That is, the heating lamp 40 needs to be set on the back side of the BC battery, while the heating lamp 40 can be set on the other side or not.

[0090] like Figure 1 As shown, the sintering furnace provided in the exemplary embodiment of the present invention further includes a conveying device 60 for passing photovoltaic cells through the furnace body, wherein the conveying direction of the conveying device 60 is parallel to the extension direction of the slit 53 of the grating 50.

[0091] For example, the conveying device 60 can be a conveyor belt or a conveying mechanism formed by multiple sets of rollers, and its conveying direction is as follows: Figure 1 As indicated by the arrow, the photovoltaic cells are placed on a conveyor belt, first dried in the drying chamber 10, and then sintered at high temperature in the sintering chamber 20. The conveyor belt is approximately located at the center line of the furnace body.

[0092] In some embodiments, the furnace body also includes a cooling chamber 30, which is located on the side of the sintering chamber 20 away from the drying chamber 10. That is, the furnace body has a drying chamber 10, a sintering chamber 20 and a cooling chamber 30 connected in sequence. The battery cells pass through the above three chambers in sequence by a conveyor belt and are dried, sintered and cooled to form metal grid lines.

[0093] For example, the extension direction of the grid line paste of the photovoltaic cell and the extension direction of the bright and dark stripes of the slit 53 are both parallel to the conveying direction of the conveyor belt, so that the high temperature zone 51 and low temperature zone 52 formed by the bright and dark stripes are always aligned with the corresponding grid line area during the entire sintering chamber 20 process of the photovoltaic cell.

[0094] Continue as Figure 1 As shown, there are multiple heating lamps 40 in the drying chamber 10, at least one of the multiple heating lamps 40 is located on one side of the drying chamber 10, and at least another is located on the opposite side of the drying chamber 10.

[0095] For example, the drying chamber 10 contains two heating lamps 40, located on opposite sides of the conveyor belt to create a uniform temperature field within the drying chamber 10. Optionally, the two heating lamps 40 are symmetrically arranged about the conveyor belt. The solar cells are placed on the conveyor belt with their backs facing upwards. A grating 50 can also be installed between the heating lamps 40 positioned above the conveyor belt and the solar cells to form a high-temperature zone 51 and a low-temperature zone 52, corresponding to the positions of the corresponding grid lines and slurry.

[0096] In another optional embodiment, the number of heating lamps 40 in the drying chamber 10 is two or more, with the heating lamps 40 located above the conveyor belt and the heating lamps 40 located below the conveyor belt arranged symmetrically about the conveyor belt. Along the conveying direction, the multiple heating lamps 40 are evenly spaced within the drying chamber 10. When the conveyor belt transports the battery cells at a constant speed within the drying chamber 10, this arrangement of heating lamps 40 can provide a relatively uniform temperature field distribution throughout the process, thereby facilitating better control of the drying effect of the grid line slurry.

[0097] It is understandable that a grating 50 corresponding to each heating lamp 40 can be set between the heating lamp 40 located above the conveyor belt in the drying chamber 10 and the conveyor belt. Alternatively, only one grating 50 can be set across each heating lamp 40. Bright stripes can be applied to the positive electrode grating line 81 that requires high temperature, and dark stripes can be applied to the negative electrode grating line 82 that requires low temperature.

[0098] Continue as Figure 1 As shown, there are multiple heating lamps 40 in the sintering chamber 20, at least one of the multiple heating lamps 40 is located on one side of the sintering chamber 20, and at least another is located on the opposite side of the sintering chamber 20.

[0099] For example, the sintering chamber 20 contains two heating lamps 40, which are located on opposite sides of the conveyor belt to create a uniform temperature field within the sintering chamber 20. Optionally, the two heating lamps 40 are symmetrically arranged about the conveyor belt. A grating 50 is also provided between the heating lamps 40 positioned above the conveyor belt and the solar cells to form a high-temperature zone 51 and a low-temperature zone 52, corresponding to the positions of the corresponding grating line slurry, in preparation for subsequent high-temperature sintering.

[0100] In another optional embodiment, the number of heating lamps 40 in the sintering chamber 20 is two or more, with the heating lamps 40 located above the conveyor belt and those located below the conveyor belt arranged symmetrically about the conveyor belt. Along the conveying direction, the multiple heating lamps 40 are evenly spaced within the sintering chamber 20. When the conveyor belt transports the battery cells at a constant speed within the sintering chamber 20, this arrangement of heating lamps 40 can provide a relatively uniform temperature field distribution throughout the process.

[0101] Furthermore, a grating 50 corresponding to each heating lamp 40 is provided between the heating lamp 40 located above the conveyor belt in the sintering chamber 20 and the conveyor belt. Alternatively, only one grating 50 can be provided across each heating lamp 40. Bright stripes can be applied to the positive electrode grid line 81 that needs to be cured at high temperature, and dark stripes can be applied to the negative electrode grid line 82 that needs to be cured at low temperature.

[0102] For example, the temperature of the drying chamber 10 ranges from 50°C to 600°C, optionally from 200°C to 500°C, and also optionally from 300°C to 400°C; the drying time ranges from 10s to 120s, optionally from 10s to 60s.

[0103] For example, the temperature of the sintering chamber 20 ranges from 400℃ to 1000℃, optionally from 500℃ to 900℃, and further optionally from 600℃ to 800℃; the sintering time ranges from 5s to 100s, optionally from 5s to 30s. It should be noted that when the sintering temperature exceeds 1000℃, the glass layer of the slurry thickens, the contact resistance increases, the fill factor decreases, and the power generation efficiency of the photovoltaic cell is reduced.

[0104] For example, the cooling rate of the cooling chamber 30 ranges from 2℃ / s to 30℃ / s, optionally from 5℃ / s to 20℃ / s, and also optionally from 10℃ / s to 15℃ / s.

[0105] The heating lamps 40 in both the drying chamber 10 and the sintering chamber 20 can be independently controlled, enabling temperature adjustment in each chamber and facilitating rapid drying or curing of the solar cell grid line slurry. For example, the temperature in each chamber can be monitored by multiple temperature sensors, thermocouples, etc., and the temperature in the drying chamber 10 or sintering chamber 20 can be controlled to be constant or gradually increased along the conveying direction, depending on actual needs.

[0106] Continue as Figure 1 As shown, multiple cooling devices 31, such as fans, can be symmetrically arranged about the conveyor belt in the cooling chamber 30 to cool the sintered battery cells. By independently controlling each fan, the cooling rate can be controlled according to actual needs.

[0107] In some embodiments, each chamber of the furnace body is provided with an exhaust device 70 that communicates with the corresponding chamber. Specifically, each exhaust device 70 can also be controlled independently. The exhaust device 70 includes an exhaust port, a blower, and a tail gas treatment device that communicate with the corresponding chamber. The exhaust device 70 can quickly discharge exhaust gas to prevent the exhaust gas from reacting with the solar cells and reducing the power generation efficiency of the photovoltaic cells.

[0108] In the drying chamber 10, the temperature distribution of the drying chamber 10 can be controlled to be uniform by the cooperation of the heating lamp 40 and the exhaust device 70.

[0109] In the sintering chamber 20, the organic waste gas generated during the sintering process can be controlled by the coordinated action of the heating lamp 40 and the exhaust device 70, preventing it from reacting with the battery cells and maintaining the uniformity and stability of the temperature field distribution in the sintering chamber 20.

[0110] In the cooling chamber 30, the heat after sintering is carried out of the furnace body through the cooperation of the exhaust device 70 and the cooling device 31, while the residual exhaust gas in the sintering zone is discharged, and the cooling rate of the cooling chamber 30 can be controlled.

[0111] Figure 6 This is a flowchart of a sintering method according to an embodiment of the present invention. See also... Figure 6 An exemplary embodiment of the present invention also provides a sintering method for sintering the grid line paste of a BC battery using the sintering furnace described in the above embodiments. The sintering method includes the following steps:

[0112] Step 601: Place the photovoltaic cells containing the slurry into the furnace.

[0113] Specifically, according to the different grid pattern of the solar cell, the distance L between the grating 50 of the drying chamber 10 and the solar cell and the diffraction angle θ are adjusted so that the high temperature zone 51 generated by the grating 50 is formed in the photovoltaic cell area where the positive grid line 81 is located, and the low temperature zone 52 is formed in the photovoltaic cell area where the negative grid line 82 is located.

[0114] The BC battery with grid line paste printed on it is placed on the conveyor belt with its back side facing up, and enters the drying chamber 10 of the furnace body under the transmission of the conveyor belt (at a constant speed). The paste is preheated in the drying chamber 10 to evaporate the organic components in it, in preparation for subsequent high-temperature sintering. The temperature of the drying chamber 10 is 350°C and the drying time is 40 seconds.

[0115] In practical applications, before entering the drying chamber 10, the position of the BC battery is adjusted to a suitable position by a straightening device, such as the center of the conveyor belt, with the deviation on both sides within ±2um, so as to ensure that the grid lines after entering the sintering chamber 20 are aligned with the high temperature zone 51 or low temperature zone 52 formed by the grating 50. The extension direction of the grid line slurry is parallel to the conveying direction of the conveyor belt.

[0116] Step 602: Adjust the distance between the grating 50 and the photovoltaic cell in the sintering chamber to the preset spacing, and adjust the diffraction angle of the grating 50 to form multiple alternating high-temperature zones 51 and low-temperature zones 52 on the photovoltaic cell to sinter the slurry, and the high-temperature zone 51 and low-temperature zone 52 correspond to the areas where the grating lines are located; wherein, the polarity of the grating lines located in the high-temperature zone 51 is opposite to that of the grating lines located in the low-temperature zone 52.

[0117] Specifically, by adjusting the distance L between the grating 50 and the solar cell and the diffraction angle θ in the sintering cavity 20, the high-temperature region 51 generated by the grating 50 is formed in the photovoltaic cell region where the positive grid line 81 is located, and the low-temperature region 52 is formed in the photovoltaic cell region where the negative grid line 82 is located.

[0118] In practical applications, the sintering temperature is 700℃ and the sintering time is 20s. During the sintering process, the organic components in the grid paste further volatilize and decompose. The silver paste glass phase on the regions corresponding to the positive grid line 81 and the negative grid line 82 etches the silicon nitride passivation antireflection film, so that the grid paste and the silicon wafer are eutectic at high temperature, thereby forming a good ohmic contact.

[0119] Furthermore, the sintering method also includes step 603: the sintered solar cells are conveyed into the cooling chamber 30 for cooling. The cooling rate is 6°C / s, the processing time is 30s, and the temperature drops to room temperature. The cooled solar cells are then transported from the sintering furnace by the conveyor belt.

[0120] As can be seen from the above, the sintering furnace provided by the exemplary embodiment of the present invention does not require the introduction of other light sources. It can use the heating lamp 40 of the original sintering furnace. The temperature can also be monitored by the temperature measuring element and program of the original sintering furnace, so as to achieve precise temperature control. While reducing costs, it will not cause disturbance to the overall temperature field distribution due to the introduction of an additional laser light source, thus preventing the inability to accurately control and measure the temperature.

[0121] Those skilled in the art should understand that the above embodiments are merely for illustrating the present invention and are not intended to limit the scope of the invention. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of the present invention.

Claims

1. A sintering furnace for forming grid lines on back-contact photovoltaic cells, characterized in that, The sintering furnace includes a furnace body and at least one heating lamp and at least one grating disposed in the furnace body, each of the gratings being located on the side of the corresponding heating lamp facing the photovoltaic cell; The heating lamp is used to form multiple alternating high-temperature zones and low-temperature zones on the photovoltaic cell through the grating, and the high-temperature zone and the low-temperature zone respectively correspond to the area where the grating line is located; wherein the grating line located in the high-temperature zone has the opposite polarity to the grating line located in the low-temperature zone.

2. The sintering furnace according to claim 1, characterized in that, The distance between the grating and the photovoltaic cell is adjustable; and / or, The angle between the grating and the horizontal plane is adjustable.

3. The sintering furnace according to claim 2, characterized in that, The distance between the grating and the photovoltaic cell ranges from 1mm to 100mm; and / or, The angle between the grating and the horizontal plane is greater than or equal to 0° and less than 180°.

4. The sintering furnace according to claim 1, characterized in that, The temperature difference between the high-temperature zone and the low-temperature zone ranges from 20℃ to 100℃.

5. The sintering furnace according to claim 1, characterized in that, The furnace body has a drying chamber and a sintering chamber, and the number of heating lamps is multiple; The drying chamber is provided with at least one of the heating lamps; or, the drying chamber is provided with at least one of the heating lamps and at least one of the light gratings. The sintering chamber is provided with at least one heating lamp and at least one grating.

6. The sintering furnace according to claim 5, characterized in that, The drying chamber contains a plurality of heating lamps, at least one of which is located on one side of the drying chamber, and at least another is located on the opposite side of the drying chamber; and / or, The number of heating lamps in the sintering chamber is multiple, at least one of the multiple heating lamps is located on one side of the sintering chamber, and at least another is located on the opposite side of the sintering chamber.

7. The sintering furnace according to claim 5, characterized in that, The furnace body also includes a cooling chamber, which is located on the side of the sintering chamber away from the drying chamber.

8. The sintering furnace according to claim 7, characterized in that, The temperature range of the drying chamber is 50℃ to 600℃, and the drying time ranges from 10s to 120s; and / or, The temperature of the sintering chamber ranges from 400℃ to 1000℃, and the sintering time ranges from 5s to 100s; and / or, The cooling rate of the cooling chamber ranges from 2℃ / s to 30℃ / s.

9. The sintering furnace according to any one of claims 1-8, characterized in that, The sintering furnace also includes a conveying device for passing the photovoltaic cells through the furnace body, the conveying direction of which is parallel to the extension direction of the slits of the grating.

10. A sintering method, characterized in that, Sintering is performed using the sintering furnace according to any one of claims 1-9, wherein the sintering method comprises: The photovoltaic cells containing the slurry are placed inside the furnace. The distance between the grating and the photovoltaic cell is adjusted to a preset spacing, and the diffraction angle of the grating is adjusted to a preset angle. Multiple alternating high-temperature and low-temperature zones are formed on the photovoltaic cell to sinter the slurry. The high-temperature zone and the low-temperature zone correspond to the areas where the grating lines are located. The polarity of the grating lines located in the high-temperature zone is opposite to that of the grating lines located in the low-temperature zone.

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