Solar cell and preparation method thereof

Abstract

The embodiment of the invention relates to the field of photovoltaic technology, provides a solar cell and a preparation method thereof, and can effectively reduce the resistance of a copper electrode so as to improve the photoelectric conversion efficiency of the solar cell. The preparation method comprises the steps that copper paste is printed on the first surface of the substrate to obtain a substrate to be sintered, and the first surface of the substrate is the front face of the substrate and / or the back face of the substrate; the multiple to-be-sintered substrates are sequentially arranged in a wafer box in a laminated mode, so that a to-be-sintered wafer box is obtained; preset pressure is applied to the to-be-sintered wafer box in the direction intersecting with the first surface of the to-be-sintered substrate; and when the to-be-sintered wafer box bears the preset pressure, the copper paste of the to-be-sintered substrate is sintered.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic, in particular to a solar cell and a preparation method thereof. BACKGROUND

[0002] At present, electrodes on solar cells are generally prepared by silver paste printing technology. With the continuous rise of silver price, the production cost of solar cells is also increasing. In order to reduce the production cost of solar cells, copper paste with low price can be used to replace silver paste to make electrodes. However, when copper electrodes are prepared by sintering process, the problem of large resistance increase is prone to occur, thereby leading to the reduction of photoelectric conversion efficiency of solar cells. SUMMARY

[0003] The embodiments of the present application provide a solar cell and a preparation method thereof, which can effectively reduce the resistance of copper electrodes, and further improve the photoelectric conversion efficiency of solar cells.

[0004] According to some embodiments of the present application, the embodiments of the present application provide a preparation method of a solar cell, the solar cell comprising a substrate; the substrate comprising a front surface and a back surface arranged oppositely; the preparation method comprising:

[0005] printing copper paste on a first surface of the substrate to obtain a sintering substrate, wherein the first surface of the substrate is the front surface of the substrate and / or the back surface of the substrate;

[0006] sequentially stacking a plurality of the sintering substrates in a sheet box to obtain a sintering sheet box;

[0007] applying a preset pressure to the sintering sheet box along a direction intersecting the first surface of the sintering substrate;

[0008] sintering the copper paste of the sintering substrate when the sintering sheet box bears the preset pressure.

[0009] According to some embodiments of the present application, the sintering sheet box comprises a cover plate and a bottom plate arranged oppositely, a side plate connected with the bottom plate, and a plurality of the sintering substrates arranged between the cover plate and the bottom plate, and the first surface of the sintering substrate is arranged opposite to the cover plate;

[0010] applying a preset pressure to the sintering sheet box along a direction intersecting the first surface of the sintering substrate, comprising:

[0011] applying a preset pressure to the cover plate and / or the bottom plate along a direction intersecting the first surface of the sintering substrate.

[0012] According to some embodiments of the present application, the range of the preset pressure is [0.2MPa, 1MPa].

[0013] According to some embodiments of the present application, after stacking the plurality of substrates to be sintered in sequence in the sheet box and before applying the preset pressure to the sheet box in a direction intersecting the first surface of the substrate to be sintered, the preparation method further includes:

[0014] Placing the sheet box to be sintered in a vacuum sintering furnace, wherein a controllable pressing piece is provided in the vacuum sintering furnace;

[0015] Applying the preset pressure to the sheet box to be sintered along a direction intersecting the first surface of the substrate to be sintered comprises:

[0016] The controllable pressing member is used to apply the preset pressure to the sheet box to be sintered along a direction intersecting with the first surface of the substrate to be sintered.

[0017] According to some embodiments of the present application, a control device is further provided in the vacuum sintering furnace, and the control device is electrically connected to the controllable pressure element;

[0018] The controllable pressure piece is used to apply the preset pressure to the sheet box to be sintered along a direction intersecting the first surface of the substrate to be sintered, comprising:

[0019] The control device controls the moving distance of the controllable pressing member so that the controllable pressing member presses the sheet box to be sintered along a direction intersecting with the first surface of the substrate to be sintered.

[0020] According to some embodiments of the present application, when the sheet box to be sintered is subjected to the preset pressure, the copper paste of the substrate to be sintered is sintered, including:

[0021] When the sheet box to be sintered is subjected to the preset pressure, the vacuum sintering furnace is used to heat the substrate to be sintered at a preset heating speed under a preset vacuum degree until the preset temperature is reached and maintained for a preset time to obtain a sintered substrate.

[0022] According to some embodiments of the present application, the preset vacuum degree range is [10E-5Pa, 10E-3Pa], the heating rate range is [5℃ / min, 50℃ / min], the preset temperature range is [250℃, 350℃], and the preset time range is [0.5min, 10min].

[0023] According to some embodiments of the present application, stacking a plurality of substrates to be sintered in sequence in the cassette includes:

[0024] The substrate to be sintered and the separator paper are alternately stacked in sequence and arranged in the sheet box.

[0025] According to some embodiments of the present application, after printing the copper paste on the first surface of the substrate, and before sequentially stacking a plurality of the substrates to be sintered in the cassette, the preparation method further comprises:

[0026] drying the substrate printed with the copper paste at a preset drying temperature, wherein the preset drying temperature is less than the sintering temperature of the copper paste.

[0027] Another aspect of the embodiments of the present application provides a solar cell, comprising a substrate, wherein the substrate comprises a front surface and a back surface arranged oppositely; and a copper electrode arranged on a first surface of the substrate, wherein the copper electrode is obtained by using the above preparation method, and the first surface of the substrate is the front surface of the substrate and / or the back surface of the substrate.

[0028] The embodiments of the present application provide a solar cell and a preparation method thereof. The solar cell comprises a substrate; the substrate comprises a front surface and a back surface arranged oppositely; the preparation method of the solar cell comprises the following steps: printing a copper paste on a first surface of the substrate to obtain a substrate to be sintered, wherein the first surface of the substrate is the front surface of the substrate and / or the back surface of the substrate; sequentially stacking a plurality of the substrates to be sintered in a cassette to obtain a cassette to be sintered; applying a preset pressure to the cassette to be sintered along a direction intersecting the first surface of the substrate to be sintered; and sintering the copper paste of the substrate to be sintered when the cassette to be sintered bears the preset pressure. The preparation method of the solar cell provided by the embodiments of the present application can effectively reduce the resistance and improve the conductivity of the copper electrode, and further improve the photoelectric conversion efficiency of the solar cell, by applying the preset pressure to the cassette to be sintered, so that the plurality of the substrates to be sintered are tightly pressed, and the gap between the copper powder particles is greatly reduced when the copper paste of the substrate to be sintered is sintered, thereby forming a tight connection structure. BRIEF DESCRIPTION OF DRAWINGS

[0029] One or more embodiments are illustrated by way of example in the figures that are part of this disclosure and which are illustrative, but not limiting of the embodiments, unless otherwise specifically indicated, the drawings shown in the figures do not necessarily show all customary features, reference signs in the figures do not limit the scope of the claims, the figures in the drawings are not necessarily to scale, and in some instances, features may have been omitted or simplified for the sake of clarity. Obviously, the embodiments described herein can be modified and varied as appropriate and can be used in combination with other apparatuses, methods and materials, other than those described herein. Accordingly, other embodiments are within the scope of the following claims.

[0030] Figure 1 A structural schematic diagram of a solar cell provided by the embodiments of the present application is shown in the figure;

[0031] Figure 2A flowchart of a preparation method of a solar cell provided in an embodiment of the present application is shown in FIG. 1.

[0032] Figure 3 A structural diagram of a sheet box provided in an embodiment of the present application is shown in FIG. 2.

[0033] Figure 4 A structural diagram of a sheet box to be sintered provided in an embodiment of the present application is shown in FIG. 3.

[0034] Figure 5 A structural diagram of a sheet box to be sintered provided in an embodiment of the present application is shown in FIG. 3.

[0035] Figure 6 A flowchart of another preparation method of a solar cell provided in an embodiment of the present application is shown in FIG. 4. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described below in conjunction with the embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0037] In the description of the embodiments of the present application, the meaning of "multiple" is two or more than two, the meaning of "multiple layers" is two layers or more than two layers, and the meaning of "multiple sheets" is two sheets or more than two sheets, unless otherwise explicitly and specifically limited.

[0038] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0039] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of existence of A, existence of A and B, and existence of B. In addition, the character " / " in this paper generally represents a "or" relationship between the front and rear associated objects.

[0040] In this paper, the phrase "embodiment" means that the specific features, structures or characteristics described in conjunction with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described in this paper can be combined with other embodiments.

[0041] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the present application. For example, if the devices or elements in the drawings are inverted, the elements described as "below" or "under" or "lower" or "bottom" of other elements or features will be oriented "above" or "top" of the other elements or features. Therefore, the term "below" can encompass both upward and downward orientations depending on the context in which the term is used, which will be apparent to those of ordinary skill in the art. The materials can be oriented in other ways (e.g., rotated 90 degrees, inverted, flipped), and the spatially relative descriptors used herein can be interpreted accordingly.

[0042] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connecting", "connecting", "fixing", and the like should be understood broadly, for example, can be fixedly connected, or can be detachably connected, or can be integrated; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0043] In the description of the embodiments of the present application, when a certain component "includes" another component, unless otherwise specified, other components are not excluded, and other components can also be further included. The second component is formed or arranged above or on the first component, or is formed or arranged on the surface of the first component, or is formed or arranged on one side of the first component, which can include embodiments in which the first component and the second component are in direct contact, and can also include embodiments in which additional components can be between the first component and the second component, so that the first component and the second component can not be in direct contact. For simplicity and clarity, various components can be arbitrarily drawn in different proportions. In the drawings, some layers / components can be omitted for simplicity. Unless otherwise specified, the formation or arrangement of the second component on the surface of the first component means that the first component is in direct contact with the second component. Among them, the above "component" can refer to: layer, film, region, part, structure, etc.

[0044] As can be known from the foregoing background, although the copper paste exhibits great potential in reducing the cost of solar cells, its industrial application still faces many technical challenges. The resistance of the copper electrode formed by using the sintering process is greatly increased, thereby reducing the photoelectric conversion efficiency of the solar cell.

[0045] Therefore, an embodiment of the present application provides a preparation method of a solar cell. The solar cell includes a substrate. The substrate includes a front surface and a back surface arranged oppositely. The preparation method includes the following steps. A copper paste is printed on a first surface of the substrate to obtain a substrate to be sintered, wherein the first surface of the substrate is the front surface of the substrate and / or the back surface of the substrate. A plurality of substrates to be sintered are arranged in a sheet box in sequence to obtain a sheet box to be sintered. A preset pressure is applied to the sheet box to be sintered along a direction intersecting the first surface of the substrate to be sintered. The copper paste of the substrate to be sintered is subjected to a sintering process when the sheet box to be sintered bears the preset pressure. The preparation method of the solar cell provided by the embodiment of the present application can effectively reduce the resistance and improve the conductivity of the copper electrode, thereby improving the photoelectric conversion efficiency of the solar cell, by applying the preset pressure to the sheet box to be sintered, so that the plurality of substrates to be sintered arranged in layers are tightly compressed, and the gap between the copper powder particles is greatly reduced when the copper paste of the substrate to be sintered is subjected to the sintering process, thereby forming a tight connection structure.

[0046] The above and other embodiments of the present application will be more apparent from the following description of specific embodiments, taken in conjunction with the accompanying drawings, in which: Figure 1 As shown in FIG. 1, the solar cell includes a substrate 1. The substrate 1 includes a front surface 101 and a back surface 102 arranged oppositely.

[0047] In the embodiment of the present application, the substrate is used to receive incident light and generate photo-generated carriers. The front surface of the substrate is usually the side that receives sunlight, and the back surface is the side opposite to the front surface. The type of the substrate is not limited, and for example, the substrate can be an N-type semiconductor substrate or a P-type semiconductor substrate. The N-type semiconductor substrate is doped with an N-type doping element, which can be any one of a group V element such as a phosphorus (P) element, a bismuth (Bi) element, an antimony (Sb) element or an arsenic (As) element. The P-type semiconductor substrate is doped with a P-type element, which can be any one of a third main group element such as a boron (B) element, an aluminum (Al) element, a gallium (Ga) element or an indium (In) element.

[0048] In the embodiments of the present application, the material of the substrate is not limited, and for example, the material of the substrate can be an elemental semiconductor material. The elemental semiconductor material can be composed of a single element, for example, silicon or germanium. The elemental semiconductor material can be in a single crystal state, a polycrystalline state, an amorphous state, or a microcrystalline state (a state that has both a single crystal state and an amorphous state, referred to as a microcrystalline state), for example, silicon can be at least one of single crystal silicon, polycrystalline silicon, amorphous silicon, or microcrystalline silicon. Alternatively, the material of the substrate can also be a compound semiconductor material, for example, silicon germanium, silicon carbide, gallium arsenide, indium gallium, perovskite, cadmium telluride, or copper indium selenium, etc.

[0049] In the embodiments of the present application, the specific type of the solar cell is not limited, and for example, the solar cell includes but is not limited to one or any combination of a PERC cell (Passivated Emitter Rear Cell), a BC cell (Back Contact), a TOPCon cell (Tunnel Oxide Passivated Contact), a HIT / HJT cell (Heterojunction Technology), a solar thin film cell, or a stacked cell. The solar thin film cell includes but is not limited to a perovskite solar thin film cell, a copper indium selenium solar thin film cell, a gallium arsenide solar thin film cell, or a cadmium sulfide solar thin film cell. The stacked cell includes but is not limited to a perovskite cell stacked with a crystalline silicon cell, a perovskite cell stacked with a perovskite cell, or a perovskite cell stacked with a thin film cell. In some embodiments, the solar cell can be a single crystal silicon solar cell, a polycrystalline silicon solar cell, an amorphous silicon solar cell, or a multi-element compound solar cell, and the multi-element compound solar cell can be a cadmium sulfide solar cell, a gallium arsenide solar cell, a copper indium selenium solar cell, or a perovskite solar cell. The size of the solar cell is also not limited, and for example, the solar cell can be a complete cell piece, a half cell piece, or a quarter cell piece.

[0050] Reference Figure 2 As shown, the method for manufacturing a solar cell provided in the embodiments of the present application includes:

[0051] S1, printing copper paste on a first surface of a substrate to obtain a sintering substrate, wherein the first surface of the substrate is the front surface of the substrate and / or the back surface of the substrate.

[0052] In the embodiments of the present application, the copper paste forms a copper electrode after sintering, and the copper electrode can be used as a gate line, which can be a main gate and / or a sub gate. According to actual needs, the copper paste can be printed on the front surface and / or the back surface of the substrate.

[0053] It should be noted that before step S1, the preparation method of the solar cell can further include a step of forming other film layers (for example, a passivation layer, an anti-reflection layer, or a reflection electrode, etc.) on one side of the substrate, and the embodiments of the present application only emphasize the content related to the invention point, and other structural content can be obtained by referring to the related technology.

[0054] In the embodiments of the present application, the electrode of the solar cell can be entirely made of copper paste to form an electrode with a single metal layer structure; or the electrode of the solar cell can be first made of silver paste to form a silver metal layer, and then made of copper paste to form a copper metal layer on the silver metal layer, so as to form an electrode with a silver grid line 2 and a copper grid line 3 stacked as shown in the figure. Figure 1

[0055] S2, a plurality of substrates to be sintered are sequentially stacked in a sheet box to obtain a sintering sheet box. The specific shape of the sheet box can be determined according to the shape of the solar cell. For example, the shape of the sheet box can be a cuboid, a ladder, or a cylinder, etc. In the embodiments of the present application, the sheet box provided with a plurality of substrates to be sintered is referred to as a sintering sheet box.

[0056] S3, a predetermined pressure is applied to the sintering sheet box in a direction intersecting the first surface of the substrate to be sintered.

[0057] The direction of the applied pressure intersects the first surface of the substrate to be sintered, so as to ensure that the pressure can be conducted to the copper paste on the substrate to be sintered through the sheet box. The angle between the direction of the applied pressure and the first surface of the substrate to be sintered can be 30 degrees, 45 degrees, 60 degrees, 75 degrees, or 90 degrees. In order to ensure that sufficient pressure is generated on the copper paste, thereby helping the copper paste to form a dense conductive layer during the sintering process, the direction of the applied pressure can be perpendicular to the first surface of the substrate to be sintered.

[0058] It should be noted that if the first surface of the substrate is the front surface of the substrate, the direction intersecting the first surface of the substrate to be sintered refers to the direction intersecting the front surface of the substrate to be sintered; if the first surface of the substrate is the back surface of the substrate, the direction intersecting the first surface of the substrate to be sintered refers to the direction intersecting the back surface of the substrate to be sintered; if the first surface of the substrate is the front surface and the back surface of the substrate, the direction intersecting the first surface of the substrate to be sintered refers to the direction intersecting the front surface of the substrate to be sintered, or the direction intersecting the back surface of the substrate to be sintered.

[0059] S4, the copper paste of the substrate to be sintered is subjected to a sintering process while the sintering sheet box bears the predetermined pressure.

[0060] ​The sintering process can be performed in a specific sintering device (for example, a vacuum sintering furnace). During the sintering process, the organic components in the copper paste volatilize, and the copper powder is sintered to form a continuous conductive layer; since the copper paste of the to-be-sintered substrate continuously bears pressure, the gaps between the copper powder particles are greatly reduced, thereby forming a very dense electrode.

[0061] The method for preparing a solar cell provided in the embodiments of the present application can effectively reduce the resistance and improve the conductivity of the copper electrode, thereby improving the photoelectric conversion efficiency of the solar cell. The solar cell prepared by the method has a copper electrode with good conductivity and adhesion, can effectively collect and conduct the current generated by the solar cell, and improves the conversion efficiency of the solar cell.

[0062] In some embodiments, referring to Figure 4 As shown in the figure, the to-be-sintered sheet box 4 includes oppositely arranged cover plates 41 and bottom plates 42, side plates 43 connected to the bottom plates 42, and a plurality of to-be-sintered substrates 10 arranged between the cover plates 41 and the bottom plates 42, and the first surface of the to-be-sintered substrate 10 is arranged opposite to the cover plate 41.

[0063] S3, a preset pressure is applied to the to-be-sintered sheet box 4 in a direction intersecting the first surface of the to-be-sintered substrate 10, including:

[0064] S3', a preset pressure is applied to the cover plate 41 and / or the bottom plate 42 in a direction intersecting the first surface of the to-be-sintered substrate 10.

[0065] In the embodiments of the present application, the sheet box includes oppositely arranged cover plates and bottom plates, side plates connected to the bottom plates, and the cover plates, side plates and bottom plates can form a containing space. Among them, the cover plate and the side plate can be fixedly connected, or the cover plate and the side plate are not fixedly connected. In order to facilitate the to-be-sintered substrate into the sheet box, referring to Figure 3 As shown in the figure, the side plates 43 can be arranged on the front side, the back side and the left side, and the right side is not provided with a side plate. In order to better compact the plurality of to-be-sintered substrates arranged in layers, the cover plate can be covered after the stacking is completed. In order to avoid the cover plate from shaking or falling off, referring to Figure 3 and Figure 4As shown, a limiting plate 44 can be arranged above the cover plate 41, and the limiting plate 44 is fixedly connected with the side plate 43. The specific size of the sheet box can be determined according to the size of the solar cell. For example, the internal size of the sheet box (i.e., the size of the internal space formed by the side plate and the bottom plate of the sheet box) can be 230±10mm in length, 195±5mm in width, and 250±10mm in height. The specific number of the plurality of sintering substrates arranged in the stack can be determined according to the size of the sheet box. For example, the number of the sintering substrates in the stack can be 100-800.

[0066] In the embodiments of the present application, it is referred to Figure 4 As shown, the plurality of sintering substrates 10 are placed between the cover plate 41 and the bottom plate 42, and the first surface (i.e., the surface printed with copper paste) of the sintering substrate 10 is arranged opposite to the cover plate 41. In this way, when a predetermined pressure is applied to the cover plate 41 and / or the bottom plate 42 in a direction intersecting the first surface of the sintering substrate 10, the pressure can uniformly act on the copper paste, thereby improving the uniformity of the conductivity of the copper electrode.

[0067] In some embodiments, the predetermined pressure is in the range of [0.2MPa, 1MPa]. For example, the predetermined pressure can be 0.2MPa, 0.4MPa, 0.6MPa, 0.8MPa or 1MPa. If the predetermined pressure is less than 0.2MPa, it is difficult to significantly reduce the gap between the copper powder particles during the sintering process of the copper paste, and a dense conductive layer cannot be formed, thereby cannot effectively reduce the resistance, and ultimately affect the performance of the solar cell. If the predetermined pressure is greater than 1MPa, it can cause mechanical damage to the sintering substrate, and even cause the sintering substrate to break. By optimizing the predetermined pressure, the predetermined pressure is controlled in the range of [0.2MPa, 1MPa], which can ensure that the copper paste forms a dense conductive layer during the sintering process, and at the same time, the sintering substrate is not mechanically damaged.

[0068] In actual production process, appropriate pressure value can be selected in the range of 0.2MPa to 1MPa according to specific copper paste formula and substrate material characteristics. For example, for a thinner silicon substrate, a lower pressure value can be selected, for example, 0.3MPa; for a thicker silicon substrate, a higher pressure value can be selected, for example, 0.8MPa.

[0069] In some embodiments, after the plurality of sintering substrates are sequentially arranged in the sheet box in step S2, and before the predetermined pressure is applied to the sintering sheet box in a direction intersecting the first surface of the sintering substrate in step S3, it is referred to Figure 6 As shown, the preparation method further comprises: S100, placing the sintering sheet box in a vacuum sintering furnace, wherein the vacuum sintering furnace is provided with a controllable pressure device.

[0070] Step S3, applying a preset pressure to the sintering sheet box along a direction intersecting the first surface of the sintering substrate, comprising:

[0071] S3", applying a preset pressure to the sintering sheet box along a direction intersecting the first surface of the sintering substrate by using a controllable pressure piece.

[0072] In the embodiments of the present application, after the plurality of sintering substrates are sequentially stacked in the sheet box to form the sintering sheet box, the sintering sheet box needs to be placed in the vacuum sintering furnace for sintering treatment. Referring to Figure 5 As shown in the figure, the vacuum sintering furnace 6 is provided with a controllable pressure piece 60, which can apply a controllable pressure to the sintering sheet box during the sintering process. The controllable pressure piece can be a mechanical pressure device, such as an elastic metal pressure head, an air cylinder or an electric push rod, which can apply a stable pressure to the sintering sheet box during the sintering process. The pressure acting direction of the controllable pressure piece intersects the first surface of the sintering substrate, so as to ensure that the pressure can be transmitted to the copper paste on the sintering substrate through the sheet box. The angle between the pressure acting direction of the controllable pressure piece and the first surface of the sintering substrate can be 30 degrees, 45 degrees, 60 degrees, 75 degrees or 90 degrees. In order to ensure that sufficient pressure is generated on the copper paste, thereby helping the copper paste to form a dense conductive layer during the sintering process, the pressure acting direction of the controllable pressure piece can be selected to be perpendicular to the first surface of the sintering substrate.

[0073] Referring to Figure 6 As shown in the figure, the vacuum sintering furnace 6 includes a feeding area A, a heating area B and a cooling area C, and the controllable pressure piece 60 is arranged in the heating area B; the sintering sheet box 4 is first placed in the feeding area A, then in the heating area B for sintering, and finally in the cooling area C for cooling.

[0074] By using the controllable pressure piece to apply pressure in the vacuum sintering furnace, stable and controllable pressure can be applied to the sintering sheet box during the sintering process, thereby improving the sintering quality and the photoelectric conversion efficiency of the solar cell.

[0075] In some embodiments, referring to Figure 5 As shown in the figure, the vacuum sintering furnace 6 is further provided with a control device 61, which is electrically connected with the controllable pressure piece 60.

[0076] S3", applying a preset pressure to the sintering sheet box along a direction intersecting the first surface of the sintering substrate by using a controllable pressure piece.

[0077] S3"', the control device controls the moving distance of the controllable pressure piece, so that the controllable pressure piece extrudes the sintering sheet box along a direction intersecting the first surface of the sintering substrate.

[0078] In the embodiments of the present application, the control device can be an electronic controller, a programmable logic controller (PLC), a computer control system, or the like, for controlling the action of the controllable pressure member. The control device is electrically connected to the controllable pressure member and can send a control signal to the controllable pressure member to control the action of the controllable pressure member. The control device can be integrated into the original control system of the vacuum sintering furnace, or the control device can be separately provided.

[0079] The control device can adjust the movement distance of the controllable pressure member according to a pre-set program or real-time monitored parameters, thereby controlling the pressure applied to the sintering sheet box. For example, the control device can dynamically adjust the movement distance of the controllable pressure member according to the temperature change in the sintering process to maintain a stable pressure.

[0080] By using the control device to control the movement distance of the controllable pressure member, the pressure applied to the sintering sheet box during the sintering process can be accurately controlled, thereby ensuring that the voids between the copper powder particles are greatly reduced, and a dense conductive layer is formed, effectively reducing the resistance, and ultimately improving the photoelectric conversion efficiency of the solar cell.

[0081] In some embodiments, if the sheet box adopts the structure as shown in Figure 3 The step S3" specifically includes: using the controllable pressure member to apply a preset pressure to the cover plate and / or the bottom plate in a direction intersecting the first surface of the sintering substrate; and the step S3"' specifically includes: the control device controls the movement distance of the controllable pressure member, so that the controllable pressure member extrudes the cover plate and / or the bottom plate in a direction intersecting the first surface of the sintering substrate.

[0082] When the sintering sheet box as shown in Figure 4 is placed in the vacuum sintering furnace 6 as shown in Figure 5 , the vertical placement mode (i.e., the cover plate, the bottom plate, and the sintering substrate are placed in the vertical direction) or the horizontal placement mode (i.e., the cover plate, the bottom plate, and the sintering substrate are placed in the horizontal direction) as shown in Figure 5 may be used. When the horizontal placement mode is used, the controllable pressure member can be used to apply a preset pressure to the cover plate and / or the bottom plate in a direction perpendicular to the first surface of the sintering substrate; to further simplify the operation, the preset pressure can be applied only to the cover plate. When the vertical placement mode is used, the controllable pressure member can be used to apply a preset pressure to the cover plate and / or the bottom plate in a direction perpendicular to the first surface of the sintering substrate.

[0083] Since copper is easily oxidized in high temperature environment, thereby reducing the conductivity; therefore, the embodiment of the application adopts low temperature sintering process to prepare copper electrode. The copper paste used in the embodiment of the application can contain copper powder, organic carrier and additives, etc. By adjusting the composition of the copper paste, the sintering temperature can be changed, thereby being suitable for low temperature sintering process to reduce oxidation as much as possible and improve the conductivity. In the embodiment of the application, the sintering temperature of the copper paste ranges from 250°C to 350°C. For example, the sintering temperature of the copper paste is 250°C, 280°C, 300°C, 320°C, 330°C or 350°C.

[0084] In some embodiments, S4, when the to-be-sintered sheet box bears the preset pressure, performs sintering treatment on the copper paste of the to-be-sintered substrate, including:

[0085] S4', when the to-be-sintered sheet box bears the preset pressure, uses a vacuum sintering furnace to heat the to-be-sintered substrate at a preset heating rate under a preset vacuum degree until a preset temperature is reached and maintained for a preset time length, to obtain the sintered substrate.

[0086] Sintering the copper paste of the to-be-sintered substrate in the vacuum sintering furnace can reduce the oxidation reaction and improve the sintering quality. In the heating process, the organic components in the copper paste will gradually volatilize, and the copper powder begins to sinter. When the temperature reaches the preset temperature, it needs to be maintained at this temperature for a preset time length, thereby ensuring that the copper paste is fully sintered.

[0087] During the entire sintering process, the to-be-sintered sheet box bears the preset pressure all the time, which helps the copper paste to form a dense conductive layer. After sintering is completed, the sintered substrate is obtained, that is, the copper electrode is formed on the substrate of the solar cell.

[0088] By sintering the copper paste in a vacuum environment at a controlled heating rate and temperature, while applying appropriate pressure, a solar cell copper electrode with excellent performance can be obtained.

[0089] In some embodiments, the preset vacuum degree ranges from 10E-5 Pa to 10E-3 Pa, the heating rate ranges from 5°C / min to 50°C / min, the preset temperature ranges from 250°C to 350°C, and the preset time length ranges from 0.5 min to 10 min.

[0090] In order to effectively reduce the oxidation reaction, reduce copper oxidation and improve the sintering quality, the following can be used, for example: Figure 5The vacuum pump 63 shown sets the preset vacuum degree of the furnace chamber of the vacuum sintering furnace to 10E-5 Pa to 10E-3 Pa, creating a low-oxygen or oxygen-free sintering environment. For example, the preset vacuum degree can be 10E-5 Pa, 10E-4.5 Pa, 10E-4 Pa, 10E-3.5 Pa, or 10E-3 Pa. If the vacuum degree is lower than 10E-5 Pa, the equipment requirements and costs will increase; if the vacuum degree is higher than 10E-3 Pa, the copper paste will be oxidized during the sintering process, affecting the conductivity.

[0091] To ensure that the organic components in the copper paste are fully volatilized, while avoiding bubbles or cracks caused by rapid heating, the preset heating speed can range from 5°C / min to 50°C / min, and can be, for example, Figure 5 The resistance 62 shown is heated by resistance heating or induction heating, while ensuring that the temperature deviation is within ±5°C. If the heating speed is lower than 5°C / min, the sintering time may be prolonged, reducing production efficiency; if the heating speed is higher than 50°C / min, the organic components in the copper paste may volatilize too quickly, forming bubbles or cracks.

[0092] The low-temperature sintering process adopted by the embodiments of the present application reduces copper oxidation, and the preset temperature range is set to 250°C to 350°C. For example, the preset temperature can be 250°C, 280°C, 300°C, 320°C, or 350°C. The preset temperature range can be consistent with the sintering temperature range of the copper paste, thereby ensuring that the copper paste is fully sintered to form a good conductive layer. If the temperature is lower than 250°C, the copper paste may not be fully sintered; if the temperature is higher than 350°C, the cost will increase.

[0093] To ensure that the copper paste is fully sintered, while avoiding increased energy consumption or thermal damage to the substrate caused by excessive sintering time, the preset time range can be 0.5 min to 10 min. For example, the preset time can be 0.5 min, 1 min, 3 min, 5 min, 7 min, 9 min, or 10 min. If the time is shorter than 0.5 min, the copper paste may not be fully sintered; if the time is longer than 10 min, the energy consumption will increase or the substrate will be thermally damaged.

[0094] In actual production processes, appropriate parameter values can be selected within the above ranges according to the specific copper paste formula and substrate material properties. For example, for a copper paste with more organic components, a lower heating speed and a longer holding time can be selected; for a copper paste with fewer organic components, a higher heating speed and a shorter holding time can be selected.

[0095] By controlling the appropriate preset vacuum degree, preset heating speed, preset temperature and preset time length, the copper paste can form a uniform and dense conductive layer in the sintering process, thereby improving the performance and reliability of the solar cell.

[0096] In some embodiments, S2, sequentially stacking a plurality of sintering substrates in the sheet box, comprises: S2', alternately stacking the sintering substrates and the separator paper in the sheet box.

[0097] In some embodiments, as shown in FIG. 2, the reference Figure 4 The separator paper 5 is used to isolate the adjacent sintering substrates 10, prevent the printed copper paste from falling off due to friction, and prevent the copper paste on the adjacent sintering substrates from contacting or adhering to each other, thereby avoiding short circuit or substrate adhesion in the sintering process. In addition, the separator paper can also absorb the volatile organic components in the copper paste, reducing the pollution to the sintering environment. The thickness of the separator paper ranges from [0.05mm, 5mm], thereby ensuring the isolation effect while minimizing the thickness and reducing the cost as much as possible. The material of the separator paper can be any one of anti-static PP (polypropylene) synthetic paper, polyvinyl alcohol isolation film, ethylene-vinyl acetate copolymer isolation film, polyolefin elastomer isolation film, sulfur-free paper, ceramic fiber paper, glass fiber paper, aramid paper, boron nitride paper, and silicon carbide paper.

[0098] In actual production process, a piece of separator paper can be placed on the bottom plate of the sheet box first, then a piece of sintering substrate is placed, and then a piece of separator paper is placed, and so on, forming an alternating stacking structure of "separator paper 5-sintering substrate 10-separator paper 5-sintering substrate 10-…", as shown in FIG. 3. Figure 4 The last layer is usually a separator paper, and then a cover plate is covered.

[0099] In order to ensure the precise alignment of the separator paper and the sintering substrate, a visual recognition positioning correction device can be used to automatically adjust the position of the separator paper by capturing the edge features of the sintering substrate and the separator paper through a high-definition camera.

[0100] In some embodiments, as shown in FIG. 1, the reference Figure 6 After printing the copper paste on the first surface of the substrate in S1, and before sequentially stacking a plurality of sintering substrates in S2, the preparation method further comprises:

[0101] S200, drying the substrate printed with the copper paste at a preset drying temperature, wherein the preset drying temperature is less than the sintering temperature of the copper paste.

[0102] After printing the copper paste, the substrate printed with the copper paste needs to be dried to remove part of the solvent in the copper paste, so that the copper paste has a certain strength, which is convenient for subsequent operation and processing.

[0103] The drying treatment can be performed in an oven or an infrared drying device. The drying temperature needs to be controlled at a preset drying temperature, and the preset drying temperature is less than the sintering temperature of the copper paste. In this way, it can be ensured that the solvent in the copper paste can be volatilized during the drying process, but the copper powder will not be sintered. For example, if the sintering temperature range of the copper paste is [250℃, 350℃], the preset drying temperature range can be [100℃, 200℃], and specifically, the preset drying temperature can be 100℃, 130℃, 150℃, 170℃ or 200℃. The drying temperature is set in the preset drying temperature range, which on the one hand ensures that the solvent in the copper paste can be fully volatilized to ensure the strength of the copper paste, and on the other hand avoids the copper powder from starting to sinter, which affects the subsequent sintering quality. The drying time can be determined according to the characteristics of the copper paste and the drying temperature. For example, the drying time range can be [5s, 15s], and the drying time can be 5s, 7s, 9s, 11s, 13s or 15s. After drying, the copper paste will form a film with a certain strength, but it has not been completely sintered.

[0104] In some embodiments, with reference to Figure 6 As shown in S4, after the sintering treatment of the to-be-sintered substrate in the to-be-sintered cassette under the preset pressure, the preparation method further comprises:

[0105] S300, cooling the substrate after the sintering treatment.

[0106] In some embodiments, step S300 can adopt vacuum natural cooling, for example: reducing the furnace temperature to below 80℃ within 30 minutes; or, step S300 can also adopt nitrogen gas purging rapid cooling, for example: completing the temperature reduction within 10 minutes with a high-purity nitrogen gas flow of 10L per minute, so as to effectively control the thermal stress in the cooling process.

[0107] The following will take the overprinting of copper grid lines on the silver grid lines on the front and back surfaces of a solar cell as an example to specifically explain the preparation method thereof. The preparation method of the solar cell comprises:

[0108] S11, printing copper paste on the silver grid lines on the front and back surfaces of a solar cell.

[0109] S12, placing the solar cell with printed copper paste into a drying furnace, the drying temperature is 150℃, and the drying time is 10s.

[0110] S13, placing the dried solar cell into a cassette one by one, and the internal dimensions of the cassette are 230mm in length, 195mm in width and 250mm in height. After placing one solar cell, a piece of ceramic fiber separation paper is immediately placed above the solar cell.

[0111] S14, adopt visual recognition positioning correction device, through high-definition camera captures the edge features of the battery and the paper, automatically adjusts the position, ensures the solar cell and the paper accurate alignment.

[0112] S15, continuously stack solar cells, when the number of stacked pieces reaches 800, place a cover plate on the top of the piece box, and fix it with a buckle to ensure the stability of the stacked structure.

[0113] S16, place the piece box containing solar cells horizontally into the vacuum sintering furnace, start the control device of the vacuum sintering furnace, make the elastic metal pressure head uniformly press on the cover plate of the piece box, apply a pressure of 0.5 MPa, and ensure that the piece box remains stable during sintering.

[0114] S17, close the furnace door of the vacuum sintering furnace, start the vacuum pump system, and after 10 minutes of pumping, the vacuum degree in the furnace reaches 5*10E-4 Pa.

[0115] S18, use resistance heating method to heat the furnace, set the heating speed to 20℃ / min, monitor the temperature in real time, and ensure that the temperature deviation is controlled within ±3℃. When the temperature rises to 300℃, start the heat preservation, and the heat preservation time is set to 5 minutes.

[0116] S19, after the heat preservation is over, stop heating, and start the nitrogen blowing rapid cooling system. High-purity nitrogen is introduced into the furnace at a flow rate of 10L per minute, and the temperature in the furnace is reduced to below 80℃ within 30 minutes.

[0117] By executing steps S11-S19, the electrode structure of the silver grid line 2 and the copper grid line 3 superimposed as shown in Figure 1 can be obtained. On the one hand, the copper paste replaces part of the silver paste, which can greatly reduce the cost; on the other hand, by applying pressure to the piece box, the gap between copper powder particles is greatly reduced during sintering of the copper paste, thereby forming a tight connection structure, effectively reducing the resistance and improving the conductivity of the copper electrode, thereby improving the photoelectric conversion efficiency of the solar cell.

[0118] The embodiment of the present application also provides a solar cell, comprising: a substrate, the substrate comprising a front surface and a back surface arranged oppositely; the solar cell further comprises a copper electrode arranged on a first surface of the substrate, wherein the copper electrode is obtained by using any one of the preparation methods of the solar cell provided by the embodiment of the present application, and the first surface of the substrate is the front surface of the substrate and / or the back surface of the substrate.

[0119] In the embodiment of the present application, the substrate can be a silicon wafer, such as a single crystal silicon wafer or a polycrystalline silicon wafer. The substrate comprises a front surface and a back surface arranged oppositely, the front surface is usually the side that receives sunlight, and the back surface is the side opposite to the front surface.

[0120] The copper electrode is arranged on the first surface of the substrate. The first surface of the substrate can be the front surface of the substrate, or the back surface of the substrate, or the front surface and the back surface of the substrate. For example, when the first surface of the substrate is the front surface of the substrate, the copper electrode can form a grid line structure for collecting the current generated by the front surface of the solar cell. When the first surface of the substrate is the back surface of the substrate, the copper electrode can form a back electric field structure for collecting the current generated by the back surface of the solar cell. When the first surface of the substrate is the front surface and the back surface of the substrate, the copper electrode simultaneously forms the front surface grid line structure and the back surface electric field structure.

[0121] The related description of the preparation method of the solar cell involved in the embodiments of the present application can refer to the foregoing embodiments, which will not be described here. The copper electrode obtained by using the preparation method described in the foregoing embodiments has good conductivity and adhesion, and can effectively collect and conduct the current generated by the solar cell, thereby improving the photoelectric conversion efficiency of the solar cell. The solar cell has low cost and high photoelectric conversion efficiency.

[0122] Those skilled in the art can understand that the above-mentioned embodiments are specific embodiments for implementing the present application, and in actual application, various changes can be made in form and details without departing from the spirit and scope of the present application. Any person skilled in the art can make various modifications and changes without departing from the spirit and scope of the present application, therefore the protection scope of the present application should be limited by the scope defined in the claims.

Claims

1. A method for preparing a solar cell, characterized in that: The solar cell includes a substrate; the substrate includes a front surface and a back surface arranged opposite to each other, and the preparation method includes: Printing copper paste on the first surface of the substrate to obtain a substrate to be sintered, wherein the first surface of the substrate is the front side of the substrate and / or the back side of the substrate; stacking a plurality of substrates to be sintered in sequence in a sheet box to obtain a sheet box to be sintered; Applying a preset pressure to the sheet box to be sintered along a direction intersecting the first surface of the substrate to be sintered; When the sheet box to be sintered is subjected to the preset pressure, the copper paste of the substrate to be sintered is sintered.

2. The preparation method according to claim 1, characterized in that The sheet box to be sintered comprises a cover plate and a bottom plate arranged opposite to each other, a side plate connected to the bottom plate, and a plurality of substrates to be sintered arranged between the cover plate and the bottom plate, wherein the first surface of the substrate to be sintered is arranged opposite to the cover plate; Applying a preset pressure to the sheet box to be sintered along a direction intersecting the first surface of the substrate to be sintered, comprising: A preset pressure is applied to the cover plate and / or the bottom plate along a direction intersecting the first surface of the substrate to be sintered.

3. The preparation method according to claim 1, characterized in that The preset pressure range is [0.2MPa, 1MPa].

4. The preparation method according to claim 1, characterized in that After stacking the plurality of substrates to be sintered in sequence in the sheet box and before applying the preset pressure to the sheet box in a direction intersecting the first surface of the substrate to be sintered, the preparation method further includes: Placing the sheet box to be sintered in a vacuum sintering furnace, wherein a controllable pressing piece is provided in the vacuum sintering furnace; Applying the preset pressure to the sheet box to be sintered along a direction intersecting the first surface of the substrate to be sintered comprises: The controllable pressing member is used to apply the preset pressure to the sheet box to be sintered along a direction intersecting with the first surface of the substrate to be sintered.

5. The preparation method according to claim 4, characterized in that The vacuum sintering furnace is further provided with a control device, which is electrically connected to the controllable pressure piece; The controllable pressure piece is used to apply the preset pressure to the sheet box to be sintered along a direction intersecting the first surface of the substrate to be sintered, comprising: The control device controls the moving distance of the controllable pressing member so that the controllable pressing member presses the sheet box to be sintered along a direction intersecting with the first surface of the substrate to be sintered.

6. The preparation method according to claim 4, characterized in that When the sheet box to be sintered is subjected to the preset pressure, the copper paste of the substrate to be sintered is sintered, comprising: When the sheet box to be sintered is subjected to the preset pressure, the vacuum sintering furnace is used to heat the substrate to be sintered at a preset heating speed under a preset vacuum degree until the preset temperature is reached and maintained for a preset time to obtain a sintered substrate.

7. The preparation method according to claim 6, characterized in that The preset vacuum degree range is [10E-5Pa, 10E-3Pa], the heating rate range is [5℃ / min, 50℃ / min], the preset temperature range is [250℃, 350℃], and the preset time range is [0.5min, 10min].

8. The preparation method according to claim 1, characterized in that The method comprises stacking a plurality of substrates to be sintered in sequence in the sheet box, comprising: The substrate to be sintered and the separator paper are alternately stacked in sequence and arranged in the sheet box.

9. The preparation method according to claim 1, characterized in that After printing the copper paste on the first surface of the substrate and before stacking the plurality of substrates to be sintered in sequence in the cassette, the preparation method further comprises: The substrate printed with the copper paste is dried at a preset drying temperature, wherein the preset drying temperature is lower than the sintering temperature of the copper paste.

10. A solar cell, characterized in that: include: A substrate, the substrate comprising a front side and a back side arranged opposite to each other; the solar cell further comprising a copper electrode arranged on the first surface of the substrate, wherein the copper electrode is obtained by the preparation method according to any one of claims 1 to 9, and the first surface of the substrate is the front side of the substrate and / or the back side of the substrate.

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