Preparation method of photovoltaic cell, photovoltaic cell and photovoltaic module

Abstract

This application relates to a preparation method of a photovoltaic cell, a photovoltaic cell and a photovoltaic module, and belongs to the technical field of photovoltaic cells. In this application, the preparation method may include: using a laser to remove a local structure of a silicon glass layer to form a window, and wet-etching a local structure of a doping layer through the window to form a recess, wherein the depth dimension of the recess is smaller than the thickness dimension of the doping layer, and wet-etching the silicon glass layer to form a metal electrode in ohmic contact with the recess. The preparation method of this application can reduce the contact resistance of the metal electrode, so that the prepared photovoltaic cell has a relatively high photoelectric conversion efficiency.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic cells, and particularly to a preparation method of a photovoltaic cell, a photovoltaic cell and a photovoltaic module. Background Art

[0002] Photovoltaic cells are used to convert light energy into electrical energy. The photoelectric conversion efficiency of photovoltaic cells is affected by the ohmic contact resistance of metal electrodes to a certain extent. In the related art, the ohmic contact resistance around the metal electrodes of photovoltaic cells is relatively large, resulting in a relatively low photoelectric conversion efficiency of photovoltaic cells. Summary of the Invention

[0003] In view of this, the present application provides a preparation method of a photovoltaic cell, a photovoltaic cell and a photovoltaic module to improve the problem of relatively low photoelectric conversion efficiency of photovoltaic cells.

[0004] In a first aspect, the present application provides a preparation method of a photovoltaic cell, the preparation method including: providing a silicon substrate, a doped layer and a silicon glass layer, wherein the doped layer is located between the silicon substrate and the silicon glass layer; using a laser to remove a local structure of the silicon glass layer to form a window; wet etching a local structure of the doped layer through the window to form a recess, wherein the depth dimension of the recess is less than the thickness dimension of the doped layer; wet removing the silicon glass layer; and forming a metal electrode in ohmic contact with the recess.

[0005] In the preparation method of the present application, since a recess is provided on a side surface of the doped layer facing away from the silicon substrate, and the surface area of the recess is relatively larger than the area of a flat surface or a polished surface, the area of the ohmic contact between the recess and the metal electrode is relatively large, the contact resistance between the recess and the metal electrode is relatively small, and the conductivity between the recess and the metal electrode is relatively good. At the same time, since the mentioned laser removal, wet etching and wet removal do not act on the interface of the doped layer close to the silicon substrate, nor on the interface of the silicon substrate close to the doped layer, that is, these interfaces are not easily damaged. The number of recombination centers that can exist in the subsequently prepared photovoltaic cell is relatively small, and the recombination rate of electrons and holes is relatively low, resulting in a relatively high photoelectric conversion efficiency of the prepared photovoltaic cell.

[0006] Optionally, the method of using a laser to remove a local structure of the silicon glass layer to form a window includes: modulating the focal depth range of the laser within the thickness range of the silicon glass layer.

[0007] Optionally, the method of using a laser to remove a local structure of the silicon glass layer to form a window includes: modulating the energy distribution of the laser to include at least one of a Gaussian distribution, a rectangular distribution, a trapezoidal distribution and an annular distribution.

[0008] Optionally, the method of using a laser to remove a local structure of a silicon glass layer to form a window includes: using a laser to process a window in the silicon glass layer, the cross-sectional shape of which includes at least one of a triangle, a trapezoid, a rectangle, and a concave shape.

[0009] Optionally, the method of using a laser to remove a local structure of a silicon glass layer to form a window includes: using a laser to remove multiple spaced local structures of the silicon glass layer to form multiple spaced windows.

[0010] Optionally, the method of using a laser to remove a local structure of a silicon glass layer to form a window satisfies: Setting 1: modulating the scanning rate of the laser within the range of 5000 mm / s to 40000 mm / s, and / or, Setting 2: modulating the diameter of the laser spot within the range of 20 nm to 200 nm.

[0011] Optionally, the method of wet-etching a local structure of a doped layer through a window to form a recess includes: wet-etching a local structure of the doped layer with an alkali solution containing an alkali polishing additive, or wet-etching a local structure of the doped layer with an alkali solution containing a texturing additive.

[0012] Optionally, the method of wet-etching a local structure of a doped layer through a window to form a recess includes: wet-etching a recess in the doped layer, the cross-sectional shape of which includes at least one of a triangle, a trapezoid, a rectangle, and a concave shape.

[0013] Optionally, the method of wet-etching a local structure of a doped layer through a window to form a recess satisfies: Setting a: the time length of the wet-etching is within the range of 10 s to 150 s, and / or, Setting b: the temperature of the wet-etching is within the range of 50 °C to 90 °C.

[0014] Optionally, the method of making the depth dimension of the recess less than the thickness dimension of the doped layer satisfies: making the ratio of the depth dimension of the recess to the thickness dimension of the doped layer within the range of 0.5 to 0.8.

[0015] Optionally, first use an alkali solution to wet-etch a local structure of the doped layer through a window to form a recess, and then use an acid solution to wet-remove the silicon glass layer.

[0016] Optionally, the method of forming a metal electrode in ohmic contact with the recess includes: forming a metal electrode in ohmic contact with at least two spaced recesses.

[0017] Second aspect, the present application provides a photovoltaic cell, which is prepared by the preparation method of the photovoltaic cell described above. Correspondingly, the photovoltaic cell has a relatively large photoelectric conversion efficiency. Optionally, the photovoltaic cell includes a doped conductive layer and a metal electrode. The doped conductive layer includes a recess etched by wet etching. The metal electrode includes an ohmic contact portion. The ohmic contact portion includes a main body portion. The main body portion is located within the recess and is in ohmic contact with the recess. The cross-sectional shape of the main body portion includes at least one of a triangle, a trapezoid, a rectangle, and a concave shape. Optionally, the photovoltaic cell includes a tunnel oxide passivated contact photovoltaic cell, a back contact photovoltaic cell, or a heterojunction photovoltaic cell.

[0018] Third aspect, the present application provides a photovoltaic module, which includes at least one battery string formed by electrically connecting the photovoltaic cells described above.

[0019] It should be understood that the above general description and the following detailed description are only exemplary and do not limit the present application. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 Partial cross-sectional structural schematic diagram of the substrate in the embodiment;

[0022] Figure 2 Partial cross-sectional structural schematic diagram of the substrate in the first embodiment, wherein the silicon glass layer is provided with a window;

[0023] Figure 3 Partial cross-sectional structural schematic diagram of the substrate in the first embodiment, wherein the doped layer is provided with a recess;

[0024] Figure 4 Partial cross-sectional structural schematic diagram of the substrate in the first embodiment, wherein the doped layer is not covered by the silicon glass layer;

[0025] Figure 5 Schematic diagram of the energy distribution of the laser in the first embodiment;

[0026] Figure 6 Schematic diagram of the energy distribution of the laser in the second embodiment;

[0027] Figure 7 Partial cross-sectional structural schematic diagram of the substrate in the second embodiment, wherein the silicon glass layer is provided with a window;

[0028] Figure 8 Schematic diagram of the partial cross-sectional structure of the substrate in the second embodiment, wherein the doped layer is provided with a recess;

[0029] Figure 9 Schematic diagram of the partial cross-sectional structure of the substrate in the second embodiment, wherein the doped layer is not covered by the silicon glass layer;

[0030] Figure 10 Schematic diagram of the energy distribution of the laser in the third embodiment;

[0031] Figure 11 Schematic diagram of the partial cross-sectional structure of the substrate in the third embodiment, wherein the silicon glass layer is provided with a window;

[0032] Figure 12 Schematic diagram of the partial cross-sectional structure of the substrate in the third embodiment, wherein the doped layer is provided with a recess;

[0033] Figure 13 Schematic diagram of the partial cross-sectional structure of the substrate in the third embodiment, wherein the doped layer is not covered by the silicon glass layer;

[0034] Figure 14 Schematic diagram of the energy distribution of the laser in the fourth embodiment;

[0035] Figure 15 Schematic diagram of the partial cross-sectional structure of the substrate in the fourth embodiment, wherein the silicon glass layer is provided with a window;

[0036] Figure 16 Schematic diagram of the partial cross-sectional structure of the substrate in the fourth embodiment, wherein the doped layer is provided with a recess;

[0037] Figure 17 Schematic diagram of the partial cross-sectional structure of the substrate in the fourth embodiment, wherein the doped layer is not covered by the silicon glass layer;

[0038] Figure 18 Schematic diagram of the partial cross-sectional structure of the doped layer in the fourth embodiment;

[0039] Figure 19 Schematic diagram of the partial cross-sectional structure of the doped layer and the silicon glass layer in the first embodiment;

[0040] Figure 20 Schematic diagram of the partial cross-sectional structure of the doped layer and the silicon glass layer in the first embodiment;

[0041] Figure 21 Schematic diagram of the partial cross-sectional structure of the doped layer and the silicon glass layer in the second embodiment;

[0042] Figure 22 Partial cross-sectional structure diagram of the doped layer and the silicon glass layer in the second embodiment;

[0043] Figure 23 Partial cross-sectional structure diagram of the doped layer and the silicon glass layer in the third embodiment;

[0044] Figure 24 Partial cross-sectional structure diagram of the doped layer and the silicon glass layer in the third embodiment;

[0045] Figure 25 Partial cross-sectional structure diagram of the doped layer and the silicon glass layer in the fourth embodiment;

[0046] Figure 26 Partial cross-sectional structure diagram of the doped layer and the silicon glass layer in the fourth embodiment;

[0047] Figure 27 Scanning electron microscope image of the brim structure;

[0048] Figure 28 Partial cross-sectional structure diagram of the substrate in the first embodiment, where the doped layer is covered by a passivation layer;

[0049] Figure 29 Partial cross-sectional structure diagram of the substrate in the first embodiment, where the recess of the doped layer is in ohmic contact with the metal electrode;

[0050] Figure 30 Partial cross-sectional structure diagram of the substrate in the second embodiment, where the doped layer is covered by a passivation layer;

[0051] Figure 31 Partial cross-sectional structure diagram of the substrate in the second embodiment, where the recess of the doped layer is in ohmic contact with the metal electrode;

[0052] Figure 32 Partial cross-sectional structure diagram of the substrate in the third embodiment, where the doped layer is covered by a passivation layer;

[0053] Figure 33 Partial cross-sectional structure diagram of the substrate in the third embodiment, where the recess of the doped layer is in ohmic contact with the metal electrode;

[0054] Figure 34 Partial cross-sectional structure diagram of the substrate in the fourth embodiment, where the doped layer is covered by a passivation layer;

[0055] Figure 35 Partial cross-sectional structure diagram of the substrate in the fourth embodiment, where the recess of the doped layer is in ohmic contact with the metal electrode;

[0056] Figure 36 It is a schematic diagram of the distribution of the area to be metallized and the non-metallized area in the substrate;

[0057] Figure 37 It is a schematic structural diagram of a photovoltaic cell in an embodiment;

[0058] Figure 38 It is a partial cross-sectional structural diagram of a negative metal electrode, a back passivation layer, and a doped conductive layer.

[0059] Reference numerals:

[0060] 10 - Substrate, 101 - Photovoltaic cell, 10a - Area to be metallized, 10b - Non-metallized area, 10c - Metallized area, 1 - Silicon substrate, 2 - Tunneling layer, 3 - Doped layer, 3a - Doped conductive layer, 31 - Depression, 32 - Spacing portion, 33 - Protrusion, 4 - Silicon glass layer, 41 - Window, A34 - Brim structure, 5 - Passivation layer, 5a - Back passivation layer, 5b - Front passivation layer, 51 - Pit, 6 - Metal electrode, 6a - Negative metal electrode, 61 - Ohmic contact portion, 611 - Main body portion, 612 - Extension portion, 62 - Electrical connection portion, 6b - Positive metal electrode, 201 - Energy distribution, 202 - Focal plane, 203 - Optical axis, 7 - Emitter layer. Specific embodiments

[0061] To better understand the technical solutions of the present application, the embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present application. The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms of "a", "the", and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should be understood that the term " / " used herein is generally used to indicate that the associated objects before and after are in an "or" relationship. In the accompanying drawings of the present application, direction X and direction Y are perpendicular, where direction Y can represent the thickness direction of the photovoltaic cell, or direction Y can represent the thickness direction of the substrate (the structure before being prepared into a photovoltaic cell that can be put into use).

[0062] In a first aspect, the present application provides some embodiments of a method for manufacturing a photovoltaic cell. The manufacturing method may include: During the manufacturing process, it is possible to provide or form asFigure 1 The substrate shown, which may include a silicon substrate 1, a tunneling layer 2, a doping layer 3, and a silicon glass layer 4. The tunneling layer 2 may be located between the silicon substrate 1 and the doping layer 3, and the doping layer 3 may be located between the tunneling layer 2 and the silicon glass layer 4.

[0063] In some embodiments, the silicon substrate 1 may also be referred to as a silicon wafer. The silicon substrate 1 may include an N-type substrate, and at least one N-type element (the elements in the fifth main group of the periodic table of chemical elements), such as phosphorus, arsenic, antimony, etc., may be doped into the silicon substrate 1.

[0064] In some embodiments, the tunneling layer 2 may include at least one of silicon oxide, silicon nitride, and silicon oxynitride. The thickness dimension of the tunneling layer 2 in the Y direction may be in the range of 0.5 nm to 3 nm, and the specific thickness dimension may be 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, or 3 nm. In some cases, the tunneling layer may also be referred to as a tunneling oxide layer. After being fabricated into the desired photovoltaic cell, the electrons in the conduction band can utilize the tunneling effect to pass through the tunneling layer 2 and reach the doping layer 3.

[0065] In some embodiments, the doping layer 3 may include at least one of polycrystalline silicon, amorphous silicon, and microcrystalline silicon. At least one N-type element (the elements in the fifth main group of the periodic table of chemical elements), such as phosphorus, arsenic, antimony, etc., may also be doped into the doping layer 3. Correspondingly, the concentration of the N-type element doped in the doping layer 3 is greater than the concentration of the N-type element doped in the silicon substrate 1.

[0066] In some embodiments, the tunneling layer 2 and the doping layer 3 in the subsequently fabricated photovoltaic cell may serve as a tunnel oxide passivated contact (TOPCon) structure, which is used to provide field passivation, chemical passivation, and selective carrier passing effects. In some cases, the tunnel oxide passivated contact structure may also be abbreviated as a tunnel passivated contact structure.

[0067] In some embodiments, the silicon glass layer 4 may be a structure formed by introducing oxygen during the process of forming the doping layer 3 using a diffusion process, and / or the silicon glass layer 4 may be a structure formed by introducing oxygen after the doping layer 3 is formed using a diffusion process. If phosphorus is doped into the doping layer 3, the silicon glass layer 4 may include phosphorosilicate glass (PSG).

[0068] After providing or forming the substrate as shown in Figure 1 it is possible to use a laser to remove a local structure of the silicon glass layer 4 to form as shown in Figure 2The window 41 shown. In this setting, a partial structure of the doped layer 3 can be exposed by the window 41.

[0069] Among them, the laser can be an infrared laser (wavelength in the range of 700nm - 1100nm), a green laser (wavelength in the range of 510nm - 550nm), or a violet laser (wavelength in the range of 400nm - 450nm).

[0070] After forming the window 41 as Figure 2 shown, wet-etch the local structure of the doped layer 3 through the window 41 to form a recess 31 as Figure 3 shown. Among them, it is necessary to make the depth dimension (dimension along the direction Y) of the recess 31 smaller than the thickness dimension (dimension along the direction Y) of the doped layer 3. In other words, the recess 31 to be formed does not penetrate the doped layer 3.

[0071] Among them, during the wet-etching process, for example, during the process of transforming from the structure as Figure 2 shown to the structure as Figure 3 shown, the silicon glass layer 4 can play a protective role or a masking role for the doped layer 3, so that the local structure of the doped layer 3 near the window 41 is wet-etched, thereby forming a recess 31 near the window 41 in the direction X.

[0072] After forming the recess 31 as Figure 3 shown, wet-remove the silicon glass layer 4 to form a structure as Figure 4 shown. In other words, the side surface of the doped layer 3 facing away from the silicon substrate 1 is not covered or masked by the silicon glass layer.

[0073] After removing the silicon glass layer, form a metal electrode for ohmic contact with the recess. Among them, the alias of the ohmic contact can be a metallized contact. After preparing the required photovoltaic cell, the metal electrode and the doped layer can be used to transmit current, and the metal electrode can also be used for electrical connection with an external circuit. If the doped layer is doped with an N-type element, the metal electrode for ohmic contact with the recess of the doped layer can be used as a negative metal electrode, and electrons can be transmitted from the doped layer through the negative metal electrode to the external circuit.

[0074] In some embodiments of the preparation method of the present application, since a recess is provided on the side of the doping layer facing away from the silicon substrate, the surface area of the recess is relatively larger than that of a flat surface or a polished surface. As a result, the area of the ohmic contact between the recess and the metal electrode is relatively large, the contact resistance between the recess and the metal electrode is relatively small, and the conductivity between the recess and the metal electrode is relatively good. At the same time, since the laser removal, wet etching, and wet removal mentioned above do not act on the interface between the tunneling layer 2 and the doping layer 3, nor on the interface between the silicon substrate 1 and the tunneling layer 2, the interfaces between the silicon substrate 1 and the tunneling layer 2 and between the tunneling layer 2 and the doping layer 3 are not damaged. The tunneling oxide passivation contact structure in the photovoltaic cell to be prepared subsequently can well provide field passivation, chemical passivation, and selective carrier passing effects. Therefore, the photoelectric conversion efficiency (measuring the ability of the cell to convert light energy into electrical energy) and fill factor (characterizing the degree to which the cell output characteristics approach the ideal value) of the photovoltaic cell prepared according to some embodiments of the present application are relatively high.

[0075] Optionally, the method of using a laser to remove a local structure of the silicon glass layer to form a window includes: modulating the focal depth range of the laser within the thickness range of the silicon glass layer.

[0076] In some embodiments, the focal depth range of the laser is mainly related to the focal plane of the laser and the focal depth size of the laser. Please refer to Figure 5 As shown, the focal plane 202 of the laser is the plane where the focus of the laser is located. The focal plane 202 is perpendicular to the optical axis 203 of the laser, and the energy density value of the laser is the largest at the focal plane 202. The focal depth size (also known as the Rayleigh length) is used to measure the size of the range where the laser energy acts effectively on both sides of the focal plane 202. Within the focal depth range or within the focal depth size, the effective energy density value is greater than or equal to half of the energy density value at the focal plane and less than or equal to the energy density value at the focal plane. The sum of the absolute value of the +H distance on one side of the focal plane 202 and the absolute value of the -H distance on the other side of the focal plane 202 is the focal depth size. When the object to be acted on by the laser is within the focal depth range, the object to be acted on by the laser can be effectively acted on by the laser (such as removed or modified).

[0077] Please refer to Figure 5As shown, before forming the window, according to the position and thickness dimension of the silicon glass layer 4, the focal depth range of the laser generated by the laser generator can be modulated within the range of the silicon glass layer 4 in its own thickness direction (the direction parallel to the Y direction) by a laser modulator. Specifically, the position of the focal plane 202 of the laser can be modulated within the silicon glass layer 4. For example, the position of the focal plane 202 can be the middle part or the middle plane of the silicon glass layer 4 in the thickness direction. Correspondingly, the focal depth dimension of the laser can be modulated to the thickness dimension of the silicon glass layer 4. In this setting, the required window can be formed in the silicon glass layer 4. At the same time, since the effective action range of the laser energy is within the silicon glass layer 4, the doped layer is not easily affected by the large energy of the laser, that is, the temperature inside the doped layer is not easily increased significantly. Correspondingly, large thermal stress is not easily generated inside the doped layer, and the mechanical strength of the doped layer is not easily reduced. Therefore, the photovoltaic cell prepared according to some embodiments of the preparation method of the present application is not easily cracked, broken or other structural problems, so that the prepared photovoltaic cell is not easily generated with more recombination centers, that is, the recombination rate of electrons and holes is not easily increased, thereby making the photoelectric conversion efficiency and fill factor of the prepared photovoltaic cell relatively high.

[0078] Please refer to Figure 5 As shown, the silicon glass layer 4 has a certain range (i.e., thickness range) in the thickness direction (the direction parallel to the Y direction). The thickness dimension of the silicon glass layer 4 can be in the range of 30nm to 200nm. The thickness dimension of the silicon glass layer 4 can specifically be 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm or 200nm. Correspondingly, the focal depth dimension of the laser can be modulated within the range of 30nm to 200nm according to the above thickness dimension of the silicon glass layer 4. The focal depth dimension of the laser can specifically be 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm or 200nm.

[0079] In other embodiments, the position of the focal plane 202 of the laser can also be modulated at the middle part of the silicon glass layer 4 or on the side of the middle surface away from the silicon substrate. Correspondingly, the focal depth size of the laser can also be modulated to be smaller than the thickness size of the silicon glass layer 4. Although the removal effect of the laser on the silicon glass layer 4 within the effective action range of the laser energy cannot achieve the effect of forming a window at one time, the required window can be gradually formed by means of removing in multiple times, that is, under the condition that the focal depth size remains unchanged, the focal plane 202 removed by the laser in the subsequent time is closer to the silicon substrate than the focal plane 202 removed by the laser in the previous time. In this embodiment, due to the structure of removing in multiple times, the heat generated by each laser removal is relatively small, and there can be an interval time between two adjacent laser removals. Heat dissipation can be carried out during the interval time, the doping layer is not easily affected by the large energy of the laser, and the temperature inside the doping layer is not easily increased by a large margin. Correspondingly, large thermal stress is not easily generated inside the doping layer. Therefore, the photoelectric conversion efficiency and fill factor of the photovoltaic cell prepared according to some embodiments of the preparation method of the present application are relatively high.

[0080] In some embodiments, when locally removing the silicon glass layer by laser, there may be slight surface damage to the part of the doping layer close to the silicon glass layer, but this surface damage will not significantly increase the stress inside the doping layer. In addition, this surface damage will also be etched away during the subsequent wet etching process.

[0081] Please refer to Figure 5 as shown, the energy distribution 201 of the laser can be modulated into a rectangular distribution, and the part of the silicon glass layer 4 located within the rectangular energy distribution 201 can be effectively removed by the laser. After that, a window 41 as shown in Figure 2 can be formed. The cross-sectional shape of the window 41 can include a rectangle. Correspondingly, the cross-sectional shape of the recess 31 formed by subsequent wet etching as shown in Figure 3 can also include a rectangle.

[0082] In some embodiments, Figure 5 the shape of the energy distribution 201 of the laser in Figure 3 and Figure 4 may not be an absolute rectangle but a shape close to a rectangle. The rectangular distribution can also be referred to as a flat-top distribution. Correspondingly, in

[0083] the rectangle included in the cross-sectional shape of the recess 31 may not be an absolute rectangle but a shape close to a rectangle.

[0084] In other embodiments, the energy distribution 201 of the laser can also be modulated to a Gaussian distribution (also known as a normal distribution) as shown in Figure 6 . In this setting, a window 41 with a cross-sectional shape including a triangle as shown in Figure 7 can be machined on the silicon glass layer 4. Correspondingly, the cross-sectional shape of the recess 31 formed by subsequent wet etching as shown in Figure 8 can also include a triangle.

[0085] In some embodiments, Figure 7 and Figure 8 the triangles in may not be absolute triangles but shapes close to triangles.

[0086] In addition to modulating the energy distribution of the laser to a Gaussian distribution, lasers with other types of energy distributions can also be used to remove the local structure of the silicon glass layer multiple times to fit and machine a window with a cross-sectional shape including a triangle.

[0087] After forming the structure as shown in Figure 8 , the silicon glass layer 4 can be removed by wet etching to form the structure as shown in Figure 9 .

[0088] In other embodiments, the energy distribution 201 of the laser can also be modulated to a trapezoidal distribution as shown in Figure 10 . In this setting, a window 41 with a cross-sectional shape including a trapezoid as shown in Figure 11 can be machined on the silicon glass layer 4. Correspondingly, the cross-sectional shape of the recess 31 formed by subsequent wet etching as shown in Figure 12 can also include a trapezoid.

[0089] In some embodiments, Figure 11 and Figure 12 the trapezoids in may not be absolute trapezoids but shapes close to trapezoids.

[0090] In addition to modulating the energy distribution of the laser to a trapezoidal distribution, lasers with other types of energy distributions can also be used to remove the local structure of the silicon glass layer multiple times to fit and machine a window with a cross-sectional shape including a trapezoid.

[0091] After forming the structure as shown in Figure 12 , the silicon glass layer 4 can be removed by wet etching to form the structure as shown in Figure 13 .

[0092] In other embodiments, the energy distribution 201 of the laser can also be modulated to a concave-shaped distribution as shown in Figure 14 . In this setting, a window can be machined on the silicon glass layer 4 as shown in Figure 15The cross-sectional shape of the structure shown includes a concave-shaped window 41. Correspondingly, the cross-sectional shape of the recessed portion 31 formed by subsequent wet etching, as shown in Figure 16 can also include a concave shape. In some embodiments, Figure 15 and Figure 16 the concave shape may not be an absolute concave shape but a shape close to a concave shape. In some embodiments, the concave shape may also be referred to as a rectangular shape with a notch or a tooth shape. Alternatively, the concave shape may also be regarded as a composite shape formed by combining multiple rectangles and triangles.

[0093] In addition to modulating the energy distribution of the laser into a concave shape distribution, lasers with other types of energy distributions can also be used to remove local structures of the silicon glass layer multiple times to fit and process a window with a cross-sectional shape including a concave shape.

[0094] After forming the structure as shown in Figure 16 , the silicon glass layer 4 can be removed by wet etching to form the structure as shown in Figure 17 .

[0095] In other embodiments, a window with a cross-sectional shape including at least two of a triangle, a trapezoid, a rectangle, and a concave shape can also be processed, and a recessed portion with a cross-sectional shape including at least two of a triangle, a trapezoid, a rectangle, and a concave shape can also be processed.

[0096] Optionally, local structures at multiple intervals of the silicon glass layer are removed by laser to form multiple windows 41 arranged at intervals along the direction X, as shown in Figure 2 , Figure 7 , Figure 11 or Figure 15 . Correspondingly, after wet etching, multiple recessed portions 31 arranged at intervals along the direction X can be formed, as shown in Figure 3 , Figure 8 , Figure 12 or Figure 16 . The multiple recessed portions 31 arranged at intervals along the direction X can subsequently be in ohmic contact with the same metal electrode (not shown in the figure). In this method, the contact resistance can be further reduced by further increasing the ohmic contact area, and the internal stress generated when the metal electrode is metallized and combined with the doped layer 3 can also be dispersed by multiple and spaced parts to reduce the possibility of structural damage to the doped layer 3.

[0097] Among them, when multiple spaced recessed portions are formed after wet etching, please refer to Figure 18As shown, a protruding spacer 32 can also be provided between two recesses 31 arranged at intervals in the doped layer 3. During the subsequent process of forming the metal electrode, the uncured material (such as slurry, ink, etc., a fluid) used to form the metal electrode will flow into the recesses 31 on both sides of the spacer 32 respectively. Especially during the sintering and curing process, the materials used to form the metal electrode on both sides of the spacer 32 can enter the interior of the spacer 32. The spacer 32 is relatively easy to disperse. That is to say, the mixing degree of the spacer 32 and the material used to form the metal electrode is relatively high. If the material used to form the metal electrode includes silver, relatively more silver crystal grains can be formed in the spacer 32, and the relatively more silver crystal grains can further reduce the contact resistance between the doped layer 3 and the metal electrode. If the material used to form the metal electrode includes a doping element, and the doping element included in the material used to form the metal electrode and the doping element included in the doped layer 3 are of the same type of element (such as an N-type element or a P-type element), a heavily doped region can be formed in the spacer 32. Correspondingly, some parts of the doped layer 3 other than the spacer 32 can be regarded as lightly doped regions (relative to the spacer 32), that is, a high-low junction can be formed (such as N + / N, or, P + / P). In the photovoltaic cell to be formed subsequently, this high-low junction can have a good field passivation effect, which helps to increase the migration length of carriers (electrons or holes), reduce the recombination rate of carriers, and thus improve the photoelectric conversion efficiency.

[0098] In addition, the interval distance L between two adjacent recesses 31 (which can also be the width dimension of the spacer 32) can be in the range of 1 nm to 100 nm. The interval distance L can specifically be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm or 100 nm. If the interval distance L is in the range of 10 nm to 50 nm, during the sintering and curing process, the spacer 32 is more likely to disperse, and the mixing degree of the spacer 32 and the material used to form the metal electrode is higher, and more and evenly distributed silver grains can be formed to better reduce the contact resistance. A uniform heavily doped region can also be formed, that is, a good high-low junction can be formed to produce a better field passivation effect.

[0099] Furthermore, the specific number of the plurality of recesses arranged at intervals along the direction X can be two, three, four, five or more.

[0100] In addition, the cross-sectional shape of any one of the two spaced-apart recessed portions may be different from that of the other. The types of relevant cross-sectional shapes may refer to the content described above and will not be elaborated here.

[0101] Optionally, after wet etching, please refer to Figure 18 As shown, if the cross-sectional shape of the recessed portion 31 includes a concave shape, correspondingly, the doped layer 3 may further include a protruding portion 33 that protrudes into the space semi-surrounded within the recessed portion 31. The height dimension (dimension along the direction Y) of the protruding portion 33 is smaller than the depth dimension (dimension along the direction Y) of the recessed portion 31, and the width dimension (dimension along the direction X) of the protruding portion 33 is smaller than the width dimension (dimension along the direction X) of the recessed portion 31. During the subsequent process of forming the metal electrode, the uncured material (such as fluid like slurry, ink, etc.) used to form the metal electrode will flow into the spaces on both sides of the protruding portion 33 respectively. Especially during the sintering and curing process, the materials used to form the metal electrode located on both sides of the protruding portion 33 can enter the interior of the protruding portion 33. The protruding portion 33 is relatively easy to disperse. That is to say, the degree of mixing of the protruding portion 33 and the material used to form the metal electrode is relatively high. If the material used to form the metal electrode includes silver, relatively more silver crystal grains can be formed within the protruding portion 33. The relatively more silver crystal grains can further reduce the contact resistance between the doped layer 3 and the metal electrode. If the material used to form the metal electrode includes a doped element, and the doped element included in the material used to form the metal electrode and the doped element included in the doped layer 3 are of the same type of element (such as an N-type element or a P-type element), then a heavily doped region can be formed within the protruding portion 33. Correspondingly, some parts of the doped layer 3 other than the protruding portion 33 can be regarded as lightly doped regions (relative to the protruding portion 33), that is, a high-low junction can be formed (such as N + / N, or, P + / P). In the photovoltaic cell to be formed subsequently, this high-low junction can have a good field passivation effect, which helps to increase the migration length of carriers (electrons or holes), reduce the recombination rate of carriers, and thus can improve the photoelectric conversion efficiency. Among them, the cross-sectional shape of the protruding portion 33 may include a rectangle, a trapezoid, a triangle, a sector, or a semi-circle.

[0102] Optionally, the laser parameters can be modulated to meet at least one of the following settings:

[0103] Setting 1: Modulate the scanning rate of the laser within the range of 5000 mm / s to 40000 mm / s. The scanning rate can specifically be 5000 mm / s, 10000 mm / s, 15000 mm / s, 20000 mm / s, 25000 mm / s, 30000 mm / s, 35000 mm / s, or 40000 mm / s.

[0104] If the scanning rate is less than 5000 mm / s, the efficiency of forming the window is relatively low, and excessive laser heat is likely to accumulate in the adjacent range per unit time. Also, relatively large thermal stress is likely to be generated inside the doped layer, and the mechanical strength of the doped layer is likely to decrease. If the scanning rate is greater than 40000 mm / s, residues may exist in the structure to be removed in the silicon glass layer. The residues may block the window to be formed, resulting in relatively low dimensional accuracy of the recess to be formed subsequently, thereby easily increasing the contact resistance between the recess for ohmic contact and the metal electrode. Therefore, it is preferable that the scanning rate of the laser is in the range of 5000 mm / s to 40000 mm / s.

[0105] Setting 2: The diameter of the laser spot is in the range of 20 nm to 200 nm, and specifically, the diameter can be 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm or 200 nm. In some embodiments, the spot refers to the projection range of the laser along the optical axis on the surface of the irradiated object. If the diameter of the laser spot is less than 20 nm and the structure is removed by one scan, the size of the window formed in the X direction is too small, and the amount of liquid for wet etching passing through the window is too small, resulting in too low a wet etching rate. If the diameter of the laser spot is less than 20 nm and the structure is removed by multiple scans to form a window, the removal efficiency is relatively low. If the diameter of the laser spot is greater than 200 nm, the area of the laser energy distribution range is too large, the volume of the structure that can be removed per unit time is too much, and at the same time, too much heat is generated per unit time. Also, relatively large thermal stress is likely to be generated inside the doped layer, and the mechanical strength of the doped layer is likely to decrease. Therefore, it is preferable that the diameter of the laser spot is in the range of 20 nm to 200 nm.

[0106] Optionally, the shape of the laser spot that can be modulated includes a rectangle or a circle.

[0107] Optionally, the wet etching described above can be alkali etching. The local structure of the doped layer can be removed through the window by using the configured alkali solution to form the required recess.

[0108] In some embodiments, if it is necessary to form a recess 31 with a cross-sectional shape including a rectangle as shown in Figure 3 it is possible to wet-etch the local structure of the doped layer by using an alkali solution containing an alkali polishing additive. The alkali polishing additive has a polishing effect, and the surface of the recess 31 formed by using the alkali solution containing the alkali polishing additive is relatively smooth, which can make the cross-sectional shape of the recess 31 relatively close to a rectangle.

[0109] In some embodiments, if it is necessary to form aFigure 8 The cross-sectional shape of the shown recess 31 includes a triangular shape, and the local structure of the doped layer can be wet-etched using an alkaline solution containing a texturing additive. The texturing additive has a texturing effect, and the bottom end of the recess 31 formed by the alkaline solution containing the texturing additive is relatively sharp, which can make the cross-sectional shape of the recess 31 relatively close to a triangle.

[0110] In some embodiments, if it is necessary to form a recess 31 whose cross-sectional shape is as shown in Figure 12 and includes a trapezoidal shape, the local structure of the doped layer can be wet-etched using an alkaline solution containing an alkaline polishing additive. The alkaline polishing additive has a polishing effect, and the surface of the recess 31 formed by the alkaline solution containing the alkaline polishing additive is relatively smooth, which can make the cross-sectional shape of the recess 31 relatively close to a trapezoid.

[0111] In some embodiments, if it is necessary to form a recess 31 whose cross-sectional shape is as shown in Figure 16 and includes a concave shape, the local structure of the doped layer can be wet-etched using an alkaline solution containing an alkaline polishing additive. The alkaline polishing additive has a polishing effect, and the surface of the recess 31 formed by the alkaline solution containing the alkaline polishing additive is relatively smooth, which can make the cross-sectional shape of the recess 31 relatively close to a concave shape.

[0112] Among them, Figure 8 , Figure 12 and Figure 16 in the recess 31 shown, the width dimension (the dimension along the direction X) of the part closer to the silicon substrate 1 is smaller, that is, Figure 8 , Figure 12 and Figure 16 in the recess 31 shown, the part closer to the silicon substrate 1 has a certain hindering or slowing effect on the flow or penetration of the uncured material used to form the metal electrode. The possibility that the uncured material used to form the metal electrode penetrates the doped layer 3 or even penetrates the tunneling layer 2 is relatively low, and the possibility of the tunneling oxidation passivation contact structure being damaged is relatively low. Correspondingly, the uncured material used to form the metal electrode located in the recess 31 can enter the interior of the doped layer 3 along a direction close to parallel to the direction X or along the transverse direction from within the recess 31. Under the condition that the doping element type included in the material used to form the metal electrode is the same as the doping element type included in the doped layer 3, it is also beneficial to form a heavily doped region in the part of the doped layer 3 far from the silicon substrate 1, thereby facilitating the formation of a high-low junction. In the photovoltaic cell to be formed subsequently, this high-low junction can have a good field passivation effect, which helps to increase the migration length of carriers (electrons or holes), reduce the recombination rate of carriers, and thus can improve the photoelectric conversion efficiency.

[0113] In some embodiments, the volume percentage of the alkali polishing additive included in the alkali solution may be in the range of 3% to 5%, and specifically may be 3%, 3.5%, 4%, 4.5% or 5%.

[0114] In some embodiments, the volume percentage of the texturing additive included in the alkali solution may be in the range of 3% to 5%, and specifically may be 3%, 3.5%, 4%, 4.5% or 5%.

[0115] In some embodiments, the alkali solution further includes an alkaline substance, such as potassium hydroxide and / or sodium hydroxide. The volume percentage of the alkaline substance included in the alkali solution may be in the range of 2% to 6%, and specifically may be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5% or 6%.

[0116] Please refer to Figure 19 As shown, after wet etching, the recess 31 (whose cross-sectional shape includes a rectangle) may have a set depth dimension H. The depth dimension H may be in the range of 50 nm to 150 nm, and the depth dimension H may specifically be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm or 150 nm.

[0117] Please refer to Figure 19 As shown, after wet etching, the recess 31 (whose cross-sectional shape includes a rectangle) has a set width dimension W. The width dimension W may be in the range of 20 nm to 200 nm, and the width dimension W may specifically be 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm or 200 nm.

[0118] Please refer to Figure 19 As shown, during the process of forming the recess 31 by wet etching with the alkali solution, the direction in which the doped layer 3 is wet-etched by the alkali solution may be Figure 19 the direction indicated by the triangular hollow arrow F shown in. Although the edge portion of the silicon glass layer 4 near the window 41 may also be wet-etched by the alkali solution. For example, before being wet-etched, the range of the window is between two dotted lines, and after being wet-etched, the range of the window 41 is larger than the range between the two dotted lines. However, the wet-etching rate of the silicon glass layer 4 by the alkali solution is relatively small, and the wet-etching rate of the doped layer 3 by the alkali solution is relatively large. Therefore, the alkali solution can be regarded as mainly used for wet-etching the doped layer 3.

[0119] In other embodiments, since the etching rate of the silicon glass layer by the alkaline solution in wet etching is less than that of the doped layer by the alkaline solution in wet etching, after wet etching, a structure as shown in Figure 20 can also be formed. The width dimension of the window 41 in the X direction is less than the width dimension of the recess 31 in the X direction. Correspondingly, a brim structure A34 can be formed at the connection between the window 41 and the recess 31. The brim structure can also be referred to as a stepped structure.

[0120] Similarly, please refer to Figure 21 as shown. After wet etching, the recess 31 (the cross-sectional shape of which includes a triangle) can have a set depth dimension H. The range and specific value of the depth dimension H can refer to the content about the depth dimension H described above and will not be elaborated here. After wet etching, the opening of the recess 31 (the cross-sectional shape of which includes a triangle) can have a set width dimension W. The range and specific value of the width dimension W can refer to the content about the width dimension W described above and will not be elaborated here.

[0121] In other embodiments, since the etching rate of the silicon glass layer by the alkaline solution in wet etching is less than that of the doped layer by the alkaline solution in wet etching, after wet etching, a structure as shown in Figure 22 can also be formed. The width dimension of the window 41 in the X direction is less than the width dimension of the opening of the recess 31 in the X direction. Correspondingly, a brim structure A34 can be formed at the connection between the window 41 and the recess 31.

[0122] Similarly, please refer to Figure 23 as shown. After wet etching, the recess 31 (the cross-sectional shape of which includes a trapezoid) can have a set depth dimension H. The range and specific value of the depth dimension H can refer to the content about the depth dimension H described above and will not be elaborated here. After wet etching, the opening of the recess 31 (the cross-sectional shape of which includes a trapezoid) can have a set width dimension W1. The range and specific value of the width dimension W1 can refer to the content about the width dimension W described above. The bottom wall of the recess 31 (the cross-sectional shape of which includes a trapezoid) can have a set width dimension W2. The range and specific value of the width dimension W2 can refer to the content about the width dimension W described above, but it is required to satisfy the setting that the width dimension W2 is less than the width dimension W1.

[0123] In other embodiments, since the etching rate of the silicon glass layer by the alkaline solution in wet etching is less than that of the doped layer by the alkaline solution in wet etching, after wet etching, a structure as shown in Figure 24 can also be formed. The width dimension of the window 41 in the X direction is less than the width dimension of the recess 31 in the X direction. Correspondingly, a brim structure A34 can be formed at the connection between the window 41 and the recess 31.

[0124] Similarly, please refer to Figure 25 As shown, after wet etching, the recess 31 (whose cross-sectional shape includes a concave shape) can have a set depth dimension H. The range and specific value of this depth dimension H can refer to the content described above regarding the depth dimension H, and will not be elaborated here. After wet etching, the opening of the recess 31 (whose cross-sectional shape includes a concave shape) can have a set width dimension W. The range and specific value of this width dimension W can refer to the content described above regarding the width dimension W, and will not be elaborated here.

[0125] In other embodiments, since the etching rate of the silicon glass layer by the alkaline solution is less than the etching rate of the doped layer by the alkaline solution, after wet etching, a structure as Figure 26 shown can also be formed. The width dimension of the window 41 in the X direction is less than the width dimension of the recess 31 in the X direction. Correspondingly, a capping structure A34 can be formed at the connection between the window 41 and the recess 31.

[0126] Observed by a scanning electron microscope, the microstructure of the capping structure A34 is as Figure 27 shown.

[0127] According to the above, in some embodiments of the preparation method of the present application, the laser can be modulated so that the size level of the local structure removed by the laser in the silicon glass layer is at the nanometer level (a size not exceeding one micrometer). Correspondingly, the size level of the window that can be formed can also be at the nanometer level. During the laser removal process, the heat generated per unit time is relatively small, and the heat conducted to the doped layer per unit time is relatively small, and it is not easy to generate large thermal stress in the doped layer. Although the size level of the window is at the nanometer level, a recess with a relatively large size can still be formed by wet etching. For example, the size of the recess in the X direction can be greater than or equal to the size of the window in the X direction, and / or, for example, the size of the recess in the Y direction can be greater than or equal to the size of the window in the Y direction, to meet the need for a relatively large ohmic contact area between the recess and the metal electrode.

[0128] Optionally, it is necessary to make the ratio of the depth dimension H of the recess 31 to the thickness dimension of the doped layer 3 within the range of 0.5 to 0.8. The ratio can specifically be 0.5, 0.6, 0.7, or 0.8. If the ratio is less than 0.5, the depth dimension H of the recess 31 is too large. During the formation of the metal electrode, the material used to form the metal electrode is likely to burn through the doped layer 3, thus easily damaging the interface between the tunneling layer 2 and the doped layer 3 and the interface between the tunneling layer 2 and the silicon substrate 1. If the ratio is greater than 0.8, the depth dimension H of the recess 31 is too small, and the ohmic contact area between the recess 31 and the metal electrode is relatively small, and the contact resistance between the recess 31 and the metal electrode is relatively large. Therefore, it is better to make the ratio of the depth dimension H of the recess 31 to the thickness dimension of the doped layer 3 within the range of 0.5 to 0.8.

[0129] Optionally, in the wet etching, at least one of the following settings can be satisfied to meet the need for the size required to form the above-mentioned recess:

[0130] Setting a: The time length of the wet etching is within the range of 10 s to 150 s. Specifically, the time length can be 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, 120 s, 130 s, 140 s, or 150 s.

[0131] Setting b: The temperature of the wet etching is within the range of 50 °C to 90 °C. Specifically, the temperature can be 50 °C, 60 °C, 70 °C, 80 °C, or 90 °C.

[0132] Optionally, if the doped layer is wet-etched with an alkaline solution to form a recess, the silicon glass layer can be removed by wet etching with an acid solution subsequently. The acid solution used later can achieve an acid-base neutralization effect with the remaining alkaline solution before, so as to reduce the possibility of any corrosive liquid in the alkaline solution and the acid solution damaging the surface morphology of the doped layer away from the silicon substrate, thereby reducing the possibility of a relatively large number of recombination centers existing on the surface of the doped layer away from the silicon substrate. In addition, it can also achieve the effect of reducing the pollution degree of the generated waste liquid.

[0133] In some embodiments, the acid solution can include hydrofluoric acid with relatively strong corrosiveness. During the process of pickling and removing the silicon glass layer, the etching rate of the acid solution on the silicon glass layer is relatively larger than the etching rate of the acid solution on the doped layer, that is, the acid solution can be regarded as mainly used to remove the silicon glass layer.

[0134] In some embodiments, after pickling and removing the silicon glass layer, water washing can also be performed.

[0135] In other embodiments, an acid solution containing at least one of nitric acid, aqua regia, and sulfuric acid, which has strong oxidizing properties, can be used to remove the local structure of polysilicon to form a recess, and then an alkali solution (containing sodium hydroxide and / or potassium hydroxide) is used to remove the silicon glass layer. When removing the silicon glass layer, an inhibitor also needs to be used simultaneously to inhibit the etching rate of the alkali solution on the doped layer. The inhibitor can include isopropyl alcohol, benzotriazole, hydrogen peroxide, etc. Before using the alkali solution to remove the silicon glass layer, the silicon glass layer can also be treated with a laser to modify the silicon glass layer, that is to say, make the silicon glass layer loose, so as to increase the rate of subsequent removal of the silicon glass layer by the alkali solution.

[0136] Optionally, after forming the structure as Figure 4 shown, a passivation layer 5 as Figure 28 shown can be deposited on the side of the doped layer 3 facing away from the silicon substrate 1. After forming the passivation layer 5, a metal electrode 6 as Figure 29 shown is formed.

[0137] Similarly, after forming the structure as Figure 9 shown, a passivation layer 5 as Figure 30 shown can be deposited on the side of the doped layer 3 facing away from the silicon substrate 1. After forming the passivation layer 5, a metal electrode 6 as Figure 31 shown is formed.

[0138] Similarly, after forming the structure as Figure 13 shown, a passivation layer 5 as Figure 32 shown can be deposited on the side of the doped layer 3 facing away from the silicon substrate 1. After forming the passivation layer 5, a metal electrode 6 as Figure 33 shown is formed.

[0139] Similarly, after forming the structure as Figure 17 shown, a passivation layer 5 as Figure 34 shown can be deposited on the side of the doped layer 3 facing away from the silicon substrate 1. After forming the passivation layer 5, a metal electrode 6 as Figure 35 shown is formed.

[0140] Among them, if the doped layer 3 is doped with an N-type element, the passivation layer can include silicon nitride, such as amorphous silicon nitride (SiN x ), then the passivation layer can achieve good antireflection effect, surface passivation and bulk passivation effects, so that the photoelectric conversion efficiency and fill factor of the photovoltaic cell to be prepared are relatively high.

[0141] In addition, any of the passivation layers 5 described above may be provided with a pit 51 that is positioned close to the recess in the direction X. The pit 51 can guide and gather the uncured material (such as fluid like slurry, ink, etc.) used to form the metal electrode, so that the uncured material used to form the metal electrode can flow toward the recess of the doped layer, thereby enabling good ohmic contact between the recess and the metal electrode.

[0142] In other embodiments, after removing the silicon glass layer and before forming the metal electrode capable of making ohmic contact with the recess, a passivation layer may not be deposited on the side of the doped layer facing away from the silicon substrate.

[0143] Specifically, please refer to Figure 36 As shown, the substrate 10 described above may be provided with metallization regions 10a and non - metallization regions 10b that are alternately distributed along the direction X. The range of the projection of the metal electrode to be formed subsequently in the direction Y is within the metallization region 10a. Generally, the range of the projection of the metal electrode in the direction Y is less than or equal to the range of the metallization region 10a. The non - metallization region 10b refers to the range that does not overlap with the projection range of the metal electrode to be formed subsequently in the direction Y. Within this substrate 10, the doped layer and the silicon glass layer that may be formed are located within the metallization region 10a rather than within the non - metallization region 10b. Correspondingly, the passivation layer to be formed subsequently may be located within the non - metallization region 10b rather than within the metallization region 10a, and it is also possible that the time to form the passivation layer is earlier than the time to form the doped layer and the silicon glass layer. For example, when the substrate 10 includes a silicon substrate but does not include a tunneling layer, a doped layer, and a silicon glass layer, a passivation layer is deposited on one side of the silicon substrate, and the part of the passivation layer located within the metallization region 10a is selectively removed by using a laser or, alternatively, by using a mask process and a wet etching process. Correspondingly, a through - hole penetrating the passivation layer is formed, and the through - hole is located within the metallization region 10a. Then, a tunneling layer, a doped layer, and a silicon glass layer can be sequentially formed within the through - hole, and then the methods described above for forming the window, the recess, and the metal electrode can be implemented.

[0144] Optionally, the method for forming a metal electrode that makes ohmic contact with the doped layer may include slurry printing and sintering. Slurry printing may include screen printing or steel plate printing, both of which print the metal - containing slurry on the substrate and make the slurry printed on the substrate in a line shape. After printing, the slurry is dried and then sintered to form a metal electrode that makes ohmic contact with the doped layer. Among them, the slurry may include silver - containing slurry or silver - aluminum - containing slurry. If it is used to form a negative metal electrode, silver - containing slurry can be used. If it is used to form a positive metal electrode, silver - aluminum - containing slurry can be used. The slurry may also include other additives such as glass frit, solvent, modifier, non - volatile polymer, or resin.

[0145] In other embodiments, the method for forming a metal electrode for making an ohmic contact with a doped layer may also include laser transfer, electroplating, inkjet printing, or sputtering.

[0146] In other embodiments, in a substrate as Figure 1 shown, the silicon substrate 1 may be doped with at least one P-type element (elements in the third main group of the periodic table), such as P-type elements like boron, aluminum, gallium, etc. The doped layer 3 may also be doped with at least one P-type element. Correspondingly, the concentration of the P-type element doped in the doped layer 3 is greater than the concentration of the P-type element doped in the silicon substrate 1.

[0147] In other embodiments, in a substrate as Figure 1 shown, the silicon substrate 1 may be doped with at least one N-type element, and the doped layer 3 may be doped with at least one P-type element, or the silicon substrate 1 may be doped with at least one P-type element, and the doped layer 3 may be doped with at least one N-type element. In this setting, a PN junction can be formed between the silicon substrate 1 and the doped layer 3.

[0148] In other embodiments (not shown in the figure), Figure 1 the substrate shown may also not include a tunneling layer, that is, the substrate may include a silicon substrate, a doped layer, and silicon glass arranged in layers. The doped layer may be an emitter layer or a diffusion layer directly formed on the silicon substrate by a diffusion process. The silicon substrate may be doped with at least one N-type element, and the doped layer may be doped with at least one P-type element, or the silicon substrate may be doped with at least one P-type element, and the doped layer may be doped with at least one N-type element. In this setting, a P-N junction can be formed between the silicon substrate and the doped layer, and the P-N junction is used to form a built-in electric field for separating electrons and holes.

[0149] According to the preparation method described above, the photovoltaic cell slices that can be prepared may include Tunnel Oxide Passivated Contact Solar Cell (TOPCon Solar Cell), Back Contact Solar Cell (BC Solar Cell), or Heterojunction Technology Solar Cell (HJT Solar Cell).

[0150] The present application provides a relatively specific embodiment of a preparation method, which can be used to prepare a tunnel oxide passivated contact photovoltaic cell. Here, it is first assumed that the silicon substrate needs to be doped with an N-type element, the doping layer needs to be doped with an N-type element, and the emitter layer needs to be doped with a P-type element. Then, the preparation method may include: texturing the front surface (also known as the light-receiving surface or the top surface) of the silicon substrate with an alkaline solution containing a texturing agent to form a textured surface (with multiple micron-sized grooves and protrusions) on the front surface of the silicon substrate. Diffusing impurities on the textured surface using a diffusion process to form an emitter layer. Polishing the back surface (also known as the backlight surface or the bottom surface) of the silicon substrate with an alkaline solution containing a polishing agent to form a back-polished surface. Sequentially depositing a tunneling layer and an undoped amorphous silicon layer (the amorphous silicon layer may also include polycrystalline silicon) on the back-polished surface. Diffusing impurities into the amorphous silicon layer using a diffusion process to form a doping layer. During the formation of the doping layer, oxygen is diffused using a diffusion process, or after the formation of the doping layer, oxygen is diffused using a diffusion process to form a silicon glass layer (such as phosphosilicate glass). Using a laser to remove a local structure of the silicon glass layer to form a window. Wet-etching a local structure of the doping layer through the window to form a recess, where the depth dimension of the recess is less than the thickness dimension of the doping layer. Wet-removing the silicon glass layer. Removing the bypass plating layer and the bypass diffusion layer formed during the formation of the tunneling layer, the amorphous silicon layer, and the doping layer. Depositing an aluminum oxide passivation layer on the side of the emitter layer facing away from the silicon substrate. Depositing a silicon nitride passivation layer on the side of the aluminum oxide passivation layer facing away from the emitter layer, and depositing a silicon nitride passivation layer on the side of the doping layer facing away from the tunneling layer. Forming metal electrodes on both sides, where the metal electrode located on the side of the doping layer facing away from the silicon substrate is in ohmic contact with the recess of the doping layer. Annealing treatment.

[0151] According to the above preparation method, the structure of the tunnel oxide passivated contact photovoltaic cell that can be formed can be as Figure 37 shown. The photovoltaic cell 101 may include a silicon substrate 1, a tunneling layer 2, a doped conductive layer 3a, a back passivation layer 5a, an emitter layer 7, a front passivation layer 5b, and metal electrodes 6. Among them, after the doping layer mentioned above undergoes annealing, the crystallization rate inside the doping layer increases, the volume ratio of polycrystalline silicon inside the doping layer is relatively large compared to the volume of amorphous silicon, and the conductivity of the doping layer increases. Therefore, the doped layer after annealing can be regarded as a doped conductive layer. Of course, the doped conductive layer can also be referred to as a doped polycrystalline silicon layer. The back passivation layer 5a may include a silicon nitride passivation layer, and the front passivation layer 5b may include an aluminum oxide passivation layer and a silicon nitride passivation layer. The metal electrodes 6 may include a negative metal electrode 6a and a positive metal electrode 6b. The photovoltaic cell 101 is provided with a metallization region 10c and a non-metallization region 10b. The recess formed in the doped conductive layer 3a is at least within the metallization region 10c so that the negative metal electrode 6a is in ohmic contact with the recess. The relevant specific effects have been described above and will not be elaborated here. The positive metal electrode 6b is in ohmic contact with the emitter layer 7.

[0152] In some embodiments, the above deposition may be chemical vapor deposition or physical vapor deposition. The chemical vapor deposition may be low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), or atmospheric pressure chemical vapor deposition (APCVD).

[0153] In some embodiments, the structure of the photovoltaic cell wafer prepared by the preparation method according to some embodiments of the present application is not limited to Figure 37 the structure shown. For example, the tunneling oxide passivation contact structure (including the doped conductive layer and the tunneling layer) may not be located in the non-metallized region 10b, and the tunneling oxide passivation contact structure (including the doped conductive layer and the tunneling layer) is mainly located in the metallized region 10c. Or, for example, the thickness of the part of the tunneling oxide passivation contact structure (including the doped conductive layer and the tunneling layer) located in the non-metallized region 10b is smaller than the thickness of the part of the tunneling oxide passivation contact structure (including the doped conductive layer and the tunneling layer) located in the metallized region 10c. Still or, for example, the tunneling oxide passivation contact structure (including the doped conductive layer and the tunneling layer) may be located on the light-receiving side of the silicon substrate (the side directly irradiated by sunlight), and correspondingly, the emitter layer may be located on the backlight side of the silicon substrate (the side not directly irradiated by sunlight). Or again, for example, both the tunneling oxide passivation contact structure (including the doped conductive layer and the tunneling layer) and the emitter layer may be located on the backlight side of the silicon substrate. Even more or, for example, both the light-receiving side and the backlight side of the silicon substrate may be provided with a tunneling oxide passivation contact structure (including the doped conductive layer and the tunneling layer), and the type of element doped in the tunneling oxide passivation contact structure located on the light-receiving side is different from the type of element doped in the tunneling oxide passivation contact structure located on the backlight side.

[0154] In a second aspect, the present application provides some embodiments of a photovoltaic cell wafer. The photovoltaic cell wafer can be prepared by the preparation method described above. Therefore, the photovoltaic cell wafer has relatively high photoelectric conversion efficiency and fill factor, which will not be elaborated here. Among them, the structure of the photovoltaic cell wafer can be as Figure 37 shown. Of course, the structure of the photovoltaic cell wafer is not limited to Figure 37 the structure shown. The structural types of other types of photovoltaic cell wafers have been described above. Specifically, it may be other types of photovoltaic cell wafers such as a selectively heavily doped photovoltaic cell wafer, a double tunneling oxide passivation contact photovoltaic cell wafer, a back contact photovoltaic cell wafer, and a heterojunction photovoltaic cell wafer.

[0155] Optionally, please refer to Figure 37 As shown, within the photovoltaic cell 101, taking the case where the silicon substrate 1 is doped with an N-type element, the doped conductive layer 3a is doped with an N-type element, and the emitter layer 7 is doped with a P-type element as an example, the doped conductive layer 3a may be provided with a recess formed by wet etching in the preparation method described above, and the negative metal electrode 6a may be in ohmic contact with the recess. Please refer to Figure 38 As shown, the negative metal electrode 6a may include an ohmic contact portion 61. The ohmic contact portion 61 includes a main body portion 611. The main body portion 611 is located within the recess and is in ohmic contact with the recess. The cross-sectional shape of the main body portion 611 may include a triangle.

[0156] According to the above, the cross-sectional shape of the main body portion 611 includes a triangle because the cross-sectional shape of the recess formed during the wet etching process includes a triangle. If the cross-sectional shape of the recess etched by wet etching includes a trapezoid, a rectangle, or a concave shape, the cross-sectional shape of the main body portion 611 may also include a trapezoid, a rectangle, or a concave shape. Even the cross-sectional shape of the main body portion 611 may include at least two of a triangle, a trapezoid, a rectangle, and a concave shape.

[0157] Optionally, please refer to Figure 38 As shown, the doped conductive layer 3a may be provided with a plurality of recesses spaced along the direction X. The negative metal electrode 6a may include a plurality of ohmic contact portions 61 spaced along the direction X. Each ohmic contact portion 61 has a main body portion 611, and each main body portion 611 is in ohmic contact with the corresponding recess. In some embodiments, the ohmic contact portion 61 further includes an extension portion 612. The extension portion 612 extends into the doped conductive layer 3a. In particular, the number of extension portions 612 present in the portion of the doped conductive layer 3a located between two adjacent main body portions 611 is relatively large. The extension portion 612 may include silver grains. Correspondingly, according to the above, the number of silver grains present in the portion of the doped conductive layer 3a located between two adjacent main body portions 611 is also relatively large, which can better reduce the contact resistance. The extension portion 612 may also include a relatively large amount of doped elements (from the material used to form the metal electrode). According to the above, the portion of the doped conductive layer 3a located between two adjacent main body portions 611 may include a heavily doped region, that is, a high-low junction can be formed in the doped conductive layer 3a. The high-low junction can provide a good field passivation effect, thereby can well improve the photoelectric conversion efficiency and fill factor of the photovoltaic cell.

[0158] Among them, the spacing distance (dimension in the X direction) between two adjacent main body parts 611 can be in the range of 10 nm to 50 nm, specifically it can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm. According to the above, with the setting within this dimension range, more and evenly distributed silver grains can be formed between two adjacent main body parts 611, so as to better reduce the contact resistance, and a relatively uniform heavily doped region can also be formed, that is, a good high-low junction can be formed to produce a better field passivation effect.

[0159] In addition, the negative metal electrode 6a may further include an electrical connection part 62. The electrical connection part 62 is integrally formed with the ohmic contact part 61. The electrical connection part 62 penetrates through the back passivation layer 5a, and the electrical connection part 62 is used for electrical connection with an external circuit (such as a solder strip).

[0160] In other embodiments (not shown in the figure), it may also be that the silicon substrate is doped with a P-type element, the doped conductive layer is doped with a P-type element, and the emitter layer is doped with an N-type element. Then, the metal electrode in ohmic contact with the emitter layer can be a negative metal electrode, and the metal electrode in ohmic contact with the doped conductive layer can be a positive metal electrode.

[0161] In some embodiments, "doped with an N-type element" herein mainly means that the chemical element of the doped impurity includes an N-type element. Similarly, "doped with a P-type element" herein mainly means that the chemical element of the doped impurity includes a P-type element.

[0162] In a third aspect, the present application provides some embodiments of a photovoltaic module. The photovoltaic module includes a laminate and a frame, and the frame is installed at the edge of the laminate. The laminate includes a photovoltaic glass, a first encapsulation film, a battery string, a second encapsulation film and a backsheet stacked. Alternatively, the laminate includes a first photovoltaic glass, a first encapsulation film, a battery string, a second encapsulation film and a second photovoltaic glass stacked. Among them, the battery string can be formed by electrically connecting a plurality of photovoltaic cells described above.

[0163] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A preparation method of a photovoltaic cell, characterized in that, The preparation method includes: Providing a silicon substrate, a doped layer, and a silicon glass layer, wherein the doped layer is located between the silicon substrate and the silicon glass layer; Using a laser with a concave-shaped energy distribution to remove the local structure of the silicon glass layer to form at least two windows with a concave-shaped cross-section arranged at intervals, and a first protrusion is reserved on one side of each window close to the doped layer, wherein the thickness dimension of the first protrusion is made smaller than the thickness dimension of the silicon glass layer; Wet-etching the local structure of the doped layer through the window to form at least two recesses with a concave-shaped cross-section arranged at intervals, and a second protrusion is reserved on the bottom side of each recess, wherein the thickness dimension of the second protrusion is made smaller than the depth dimension of the recess, and the depth dimension of the recess is made smaller than the thickness dimension of the doped layer; Wet-removing the silicon glass layer; Forming metal electrodes in ohmic contact with at least two of the recesses.

2. The preparation method of the photovoltaic cell according to claim 1, characterized in that, The method of using a laser to remove the local structure of the silicon glass layer to form a window includes: Modulating the focal depth range of the laser within the thickness range of the silicon glass layer.

3. The manufacturing method of the photovoltaic cell according to claim 1, wherein The method of using a laser to remove the local structure of the silicon glass layer to form a window includes: Using the laser to remove multiple spaced local structures of the silicon glass layer to form multiple spaced windows.

4. The manufacturing method of the photovoltaic cell according to claim 1, characterized in that, The method of using a laser to remove the local structure of the silicon glass layer to form a window satisfies at least one of the following settings: Setting 1: Modulating the scanning rate of the laser within the range of 5000 mm / s to 40000 mm / s; Setting 2: Modulating the diameter of the laser spot within the range of 20 nm to 200 nm.

5. The preparation method of the photovoltaic cell according to any one of claims 1 to 4, characterized in that, The method of wet-etching the local structure of the doped layer through the window to form a recess includes: Wet-etching the local structure of the doped layer with an alkaline solution containing an alkali polishing additive, or wet-etching the local structure of the doped layer with an alkaline solution containing a texturing additive.

6. The preparation method of the photovoltaic cell according to any one of claims 1 to 4, characterized in that The method of wet-etching the local structure of the doped layer through the window to form a recess satisfies at least one of the following settings: Setting a: The time length of the wet-etching is within the range of 10 s to 150 s; Setting b: The temperature of the wet-etching is within the range of 50 °C to 90 °C.

7. The manufacturing method of a photovoltaic cell according to any one of claims 1 to 4, characterized in that The method of making the depth dimension of the recess smaller than the thickness dimension of the doped layer satisfies: Making the ratio of the depth dimension of the recess to the thickness dimension of the doped layer within the range of 0.5 to 0.

8.

8. The manufacturing method of a photovoltaic cell according to any one of claims 1 to 4, characterized in that, First, wet-etch the local structure of the doped layer through the window with an alkaline solution to form the recess, and then wet-remove the silicon glass layer with an acidic solution.

9. A photovoltaic cell, characterized in that, The photovoltaic cell is prepared by the preparation method of the photovoltaic cell according to any one of claims 1 to 8.

10. The photovoltaic cell according to claim 9, characterized in that, The photovoltaic cell includes a doped conductive layer and a metal electrode, the doped conductive layer includes recesses formed by wet-etching, and the metal electrode includes an ohmic contact portion; The ohmic contact portion includes a main body portion, the main body portion is located within the recess and is in ohmic contact with the recess; The cross-sectional shape of the main body portion includes a concave shape.

11. The photovoltaic cell according to claim 9, characterized in that, The photovoltaic cell includes a tunnel oxide passivated contact photovoltaic cell, a back contact photovoltaic cell or a heterojunction photovoltaic cell.

12. A photovoltaic module, characterized in that, The photovoltaic module includes at least one cell string, and the cell string is formed by electrically connecting the photovoltaic cells described in any one of claims 9 to 11.

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