Preparation method of photovoltaic cell, photovoltaic cell and photovoltaic module

Abstract

The invention relates to a preparation method of a photovoltaic cell, the photovoltaic cell and a photovoltaic module, and relates to the technical field of photovoltaic cells. In the application, the preparation method can comprise the steps of removing a local structure of a silica glass layer by using laser to form a window, performing wet etching on a local structure of a doped layer through the window to form a sunken part, enabling the depth size of the sunken part to be smaller than the thickness size of the doped layer, removing the silica glass layer by using a wet method, and forming a metal electrode in ohmic contact with the sunken part. According to the preparation method provided by the invention, the contact resistance of the metal electrode can be reduced, so that the photoelectric conversion efficiency of the prepared photovoltaic cell is relatively high.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic cells, and in particular to a method for preparing 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 to a certain extent by the ohmic contact resistance of the metal electrode. In the related art, the ohmic contact resistance around the metal electrode of the photovoltaic cell is relatively large, which makes the photoelectric conversion efficiency of the photovoltaic cell relatively low. Summary of the invention

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

[0004] In a first aspect, the present application provides a method for preparing a photovoltaic cell, the method comprising: providing a silicon substrate, a doping layer and a silicon glass layer, wherein the doping 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 the local structure of the doping layer through the window to form a recessed portion, wherein the depth of the recessed portion is smaller than the thickness of the doping layer; wet-removing the silicon glass layer; and forming a metal electrode that is in ohmic contact with the recessed portion.

[0005] In the preparation method of the present application, since a recessed portion is provided on the side of the doping layer facing away from the silicon substrate, the surface area of ​​the recessed portion is relatively larger than the area of ​​the plane or the polished surface, so that the area of ​​ohmic contact between the recessed portion and the metal electrode is relatively large, the contact resistance between the recessed portion and the metal electrode is relatively small, and the conductivity between the recessed portion 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 of the doping layer close to the silicon substrate, nor do they act on the interface of the silicon substrate close to the doping layer, that is, these interfaces are not easily damaged. The number of recombination centers that can exist in the photovoltaic cell to be prepared subsequently is relatively small, and the rate of recombination of electrons and holes is relatively low, so that the photoelectric conversion efficiency of the prepared photovoltaic cell is relatively high.

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

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

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

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

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

[0011] Optionally, the method of wet etching the local structure of the doping layer through the window to form the recessed portion includes: wet etching the local structure of the doping layer using an alkali solution containing an alkali polishing additive, or wet etching the local structure of the doping layer using an alkali solution containing a texturing additive.

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

[0013] Optionally, the method of wet etching a local structure of the doping layer through a window to form a recessed portion satisfies: setting a: the length of wet etching time is in the range of 10s to 150s, and / or setting b: the temperature of wet etching is in the range of 50°C to 90°C.

[0014] Optionally, the method of making the depth dimension of the recessed portion smaller than the thickness dimension of the doping layer satisfies: making the ratio of the depth dimension of the recessed portion to the thickness dimension of the doping layer within a range of 0.5 to 0.8.

[0015] Optionally, an alkali solution is first used to wet-etch a local structure of the doping layer through the window to form a recessed portion, and then an acid solution is used to wet-etch the silicon glass layer.

[0016] Optionally, the method of forming a metal electrode in ohmic contact with a recessed portion includes: forming a metal electrode in ohmic contact with at least two recessed portions disposed at intervals.

[0017] In a second aspect, the present application provides a photovoltaic cell, which is prepared by the method for preparing the photovoltaic cell described above. Accordingly, 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 recessed portion etched by a wet method, the metal electrode includes an ohmic contact portion, the ohmic contact portion includes a main body portion, the main body portion is located in the recessed portion and is in ohmic contact with the recessed portion, and 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 tunneling oxide passivation contact photovoltaic cell, a back contact photovoltaic cell or a heterojunction photovoltaic cell.

[0018] In a third aspect, the present application provides a photovoltaic module, the photovoltaic module comprising at least one battery string, the battery string being formed by electrically connecting the photovoltaic cells described above.

[0019] It should be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0021] Figure 1 is a schematic diagram of a partial cross-sectional structure of a substrate in an embodiment; Figure 2 is a schematic diagram of a partial cross-sectional structure of a substrate in a first embodiment, wherein a window is provided on the silicon glass layer; Figure 3 is a schematic diagram of a partial cross-sectional structure of a substrate in a first embodiment, wherein a recessed portion is provided in the doping layer; Figure 4 is a schematic diagram of a partial cross-sectional structure of a substrate in a first embodiment, wherein the doped layer is not covered by the silicon glass layer; Figure 5 is a schematic diagram of laser energy distribution in the first embodiment; Figure 6 is a schematic diagram of laser energy distribution in a second embodiment; Figure 7 is a schematic diagram of a partial cross-sectional structure of a substrate in a second embodiment, wherein a window is provided on the silicon glass layer; Figure 8 is a schematic diagram of a partial cross-sectional structure of a substrate in a second embodiment, wherein a recessed portion is provided in the doping layer; Fig. 9 is a schematic diagram of a partial cross-sectional structure of a substrate in a second embodiment, wherein the doped layer is not covered by the silicon glass layer; Fig.10 is a schematic diagram of laser energy distribution in a third embodiment; Fig.11 is a schematic diagram of a partial cross-sectional structure of a substrate in a third embodiment, wherein the silicon glass layer is provided with a window; Fig.12 is a schematic diagram of a partial cross-sectional structure of a substrate in a third embodiment, wherein a recessed portion is provided in the doping layer; Fig.13 is a schematic diagram of a partial cross-sectional structure of a substrate in a third embodiment, wherein the doped layer is not covered by the silicon glass layer; Fig.14 is a schematic diagram of laser energy distribution in a fourth embodiment; Fig.15 is a schematic diagram of a partial cross-sectional structure of a substrate in a fourth embodiment, wherein the silicon glass layer is provided with a window; Fig.16 is a schematic diagram of a partial cross-sectional structure of a substrate in a fourth embodiment, wherein a recessed portion is provided in the doping layer; Fig.17 is a schematic diagram of a partial cross-sectional structure of a substrate in a fourth embodiment, wherein the doped layer is not covered by the silicon glass layer; Fig.18 is a schematic diagram of a partial cross-sectional structure of a doping layer in a fourth embodiment; Fig.19 is a partial cross-sectional structural diagram of a doping layer and a silicon glass layer in a first embodiment; Fig. 20 is a partial cross-sectional structural diagram of a doping layer and a silicon glass layer in a first embodiment; Fig.21 is a partial cross-sectional structural diagram of a doping layer and a silicon glass layer in a second embodiment; Fig. 22 is a partial cross-sectional structural diagram of a doping layer and a silicon glass layer in a second embodiment; Fig.23 is a partial cross-sectional structural diagram of a doping layer and a silicon glass layer in a third embodiment; Fig.24 is a partial cross-sectional structural diagram of a doping layer and a silicon glass layer in a third embodiment; Fig.25 is a partial cross-sectional structural diagram of a doping layer and a silicon glass layer in a fourth embodiment; Fig.26 is a partial cross-sectional structural diagram of a doping layer and a silicon glass layer in a fourth embodiment; Fig. 27This is a scanning electron microscope image of the brim structure; Fig.28 is a schematic diagram of a partial cross-sectional structure of a substrate in a first embodiment, wherein the doped layer is covered by a passivation layer; Fig.29 is a schematic diagram of a partial cross-sectional structure of a substrate in a first embodiment, wherein a recessed portion of the doping layer is in ohmic contact with a metal electrode; Fig.30 is a schematic diagram of a partial cross-sectional structure of a substrate in a second embodiment, wherein the doped layer is covered by a passivation layer; Fig.31 is a schematic diagram of a partial cross-sectional structure of a substrate in a second embodiment, wherein the recessed portion of the doping layer is in ohmic contact with the metal electrode; Fig.32 is a schematic diagram of a partial cross-sectional structure of a substrate in a third embodiment, wherein the doped layer is covered by a passivation layer; Fig.33 is a schematic diagram of a partial cross-sectional structure of a substrate in a third embodiment, wherein the recessed portion of the doping layer is in ohmic contact with the metal electrode; Fig.34 is a schematic diagram of a partial cross-sectional structure of a substrate in a fourth embodiment, wherein the doped layer is covered by a passivation layer; Fig.35 is a schematic diagram of a partial cross-sectional structure of a substrate in a fourth embodiment, wherein the recessed portion of the doping layer is in ohmic contact with the metal electrode; Fig.36 A schematic diagram of the distribution of the area to be metallized and the non-metallized area in the substrate; Fig.37 It is a schematic diagram of the structure of a photovoltaic cell in one embodiment; Fig.38 It is a partial cross-sectional structural diagram of the negative metal electrode, back passivation layer and doped conductive layer.

[0022] Reference numerals: 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-recessed portion, 32-spacer portion, 33-convex portion, 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, 612-extension portion, 62-electrical connection portion, 6b-positive metal electrode, 201-energy distribution, 202-focal plane, 203-optical axis, 7-emitter layer. DETAILED DESCRIPTION

[0023] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail in conjunction with the accompanying drawings. It should be clear that the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work 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", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should be understood that the term "and / or" used in this article is only a kind of association relationship describing the associated objects, indicating that there can be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the front and back associated objects are an "or" relationship. In the drawings of this article, the direction X and the direction Y are perpendicular, wherein the direction Y can represent the thickness direction of the photovoltaic cell, or the 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).

[0024] In a first aspect, the present application provides some embodiments of a method for preparing a photovoltaic cell. The method may include: during the preparation process, providing or forming Figure 1 The substrate shown 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 .

[0025] In some embodiments, the silicon substrate 1 may be also known as a silicon substrate, and the silicon substrate 1 may include an N-type substrate. The silicon substrate 1 may be doped with at least one N-type element (element of the fifth main group in the periodic table of chemical elements), such as phosphorus, arsenic, antimony and other N-type elements.

[0026] In some embodiments, the tunneling layer 2 may include at least one of silicon oxide, silicon nitride and silicon oxynitride. The thickness of the tunneling layer 2 in the direction Y may be in the range of 0.5 nm to 3 nm, and the thickness may specifically 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 the desired photovoltaic cell is prepared, the electrons in the conduction band may use the tunneling effect to pass through the tunneling layer 2 to reach the doping layer 3.

[0027] In some embodiments, the doping layer 3 may include at least one of polycrystalline silicon, amorphous silicon and microcrystalline silicon. The doping layer 3 may also be doped with at least one N-type element (element of the fifth main group in the periodic table of chemical elements), such as phosphorus, arsenic, antimony and other N-type elements. Accordingly, 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.

[0028] In some embodiments, the tunneling layer 2 and the doping layer 3 can be used as a tunneling oxide passivated contact structure (TOPCon) in the photovoltaic cell to be prepared subsequently. The tunneling oxide passivated contact structure is used to provide field passivation, chemical passivation and selective carrier passing. In some cases, the tunneling oxide passivated contact structure can also be referred to as a tunneling passivation contact structure.

[0029] 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 forming the doping layer 3 using a diffusion process. If the doping layer 3 is doped with phosphorus, the silicon glass layer 4 may include phosphorosilicate glass (PSG).

[0030] In providing or forming Figure 1 After the substrate is formed, a laser can be used to remove the local structure of the silicon glass layer 4 to form a substrate as shown in FIG. Figure 2 The window 41 is shown. In this configuration, part of the structure of the doped layer 3 can be exposed by the window 41.

[0031] The laser may be an infrared laser (with a wavelength in the range of 700nm to 1100nm), a green laser (with a wavelength in the range of 510nm to 550nm) or a violet laser (with a wavelength in the range of 400nm to 450nm).

[0032] In the formation of Figure 2 After the window 41 is formed, the local structure of the doped layer 3 is wet-etched through the window 41 to form a Figure 3 The recessed portion 31 shown. The depth dimension (dimension along direction Y) of the recessed portion 31 needs to be smaller than the thickness dimension (dimension along direction Y) of the doping layer 3. In other words, the recessed portion 31 to be formed does not penetrate the doping layer 3.

[0033] In the wet etching process, for example, Figure 2 The structure shown is transformed to Figure 3In the process of the structure shown, the silicon glass layer 4 can play a protective role or a masking role for the doping layer 3, so that the local structure near the window 41 in the doping layer 3 is wet-etched, thereby forming a recessed portion 31 near the window 41 in the direction X.

[0034] In the formation of Figure 3 After the recess 31 is shown, the silicon glass layer 4 is removed by wet method to form a Figure 4 In the structure shown, it can also be said that the side of the doped layer 3 facing away from the silicon substrate 1 is not covered or masked by the silicon glass layer.

[0035] After removing the silicon glass layer, a metal electrode is formed in ohmic contact with the recessed portion. Among them, another name for ohmic contact may be metallized contact. After the desired photovoltaic cell is prepared, the metal electrode and the doped layer can be used to transmit current, and the metal electrode can also be used to electrically connect to an external circuit. If the doped layer is doped with N-type elements, the metal electrode in ohmic contact with the recessed portion of the doped layer can be used as a negative metal electrode, and electrons can be transmitted from the doped layer to the external circuit via the negative metal electrode.

[0036] In some embodiments of the preparation method of the present application, since a recessed portion is provided on one side of the doping layer away from the silicon substrate, the surface area of ​​the recessed portion is relatively large compared to the surface area of ​​the plane or the polished surface, so that the area of ​​the ohmic contact between the recessed portion and the metal electrode is relatively large, the contact resistance between the recessed portion and the metal electrode is relatively small, and the conductivity between the recessed portion 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 do they act on the interface between the silicon substrate 1 and the tunneling layer 2, the interface between the silicon substrate 1 and the tunneling layer 2 and the interface between the tunneling layer 2 and the doping layer 3 are not damaged. The tunneling oxidation passivation contact structure in the photovoltaic cell to be prepared and formed later can provide good field passivation, chemical passivation and selective carrier passing. Therefore, the photovoltaic cell prepared according to some embodiments of the preparation method of the present application has a relatively high photoelectric conversion efficiency (a measure of the ability of the cell to convert light energy into electrical energy) and a fill factor (a characterization of the degree to which the cell output characteristics are close to the ideal value).

[0037] Optionally, the method of using a laser to remove a local structure of a silicon glass layer to form a window includes: modulating a focal depth range of the laser within a thickness range of the silicon glass layer.

[0038] 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. Figure 5As 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 of effective action of the laser energy 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 the effective energy density value is 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 (for example, removed or modified).

[0039] Please refer to Figure 5 As shown, before forming the window, 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 the thickness direction (the direction parallel to the direction Y) according to the position and thickness of the silicon glass layer 4 through the laser modulator. In detail, 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 middle surface of the silicon glass layer 4 in the thickness direction. Accordingly, the focal depth size of the laser can be modulated to the thickness size of the silicon glass layer 4. Under 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 doping layer is not easily affected by the large energy of the laser, that is, the temperature inside the doping layer is not easily increased significantly. Accordingly, it is not easy to generate large thermal stress inside the doping layer, and the mechanical strength of the doping layer is not easily reduced. Therefore, the photovoltaic cells prepared according to some embodiments of the preparation method of the present application are not prone to structural problems such as cracking and breakage, so that the prepared photovoltaic cells are not prone to produce a large number of recombination centers, that is, it is not easy to increase the recombination rate of electrons and holes, thereby making the photoelectric conversion efficiency and fill factor of the prepared photovoltaic cells relatively high.

[0040] Please refer to Figure 5As shown, the silicon glass layer 4 has a certain range (i.e., thickness range) in the thickness direction (the direction parallel to the direction Y), and the thickness of the silicon glass layer 4 can be in the range of 30nm~200nm. The thickness 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 of the laser can be modulated within the range of 30nm~200nm according to the thickness of the above-mentioned silicon glass layer 4, and the focal depth 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.

[0041] 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 the middle surface away from the silicon substrate. Correspondingly, the focal depth of the laser can also be modulated to be smaller than the thickness of the silicon glass layer 4. Although the removal effect of the laser on the silicon glass layer 4 within the effective range of the laser energy in this embodiment cannot achieve the effect of forming a window at one time, the required window can be gradually formed by removing in batches, that is, under the condition that the focal depth size remains unchanged, the focal plane 202 of the latter laser removal is closer to the silicon substrate than the focal plane 202 of the previous laser removal. In this embodiment, due to the stepwise removal structure, the heat generated by each laser removal is relatively small, and there can be an interval time between two adjacent laser removals, and heat can be dissipated 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. Accordingly, it is not easy to generate large thermal stress 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.

[0042] In some embodiments, when the laser removes the local structure of the silicon glass layer, the portion of the doped layer close to the silicon glass layer may have slight surface damage, but the surface damage will not significantly increase the stress inside the doped layer. In addition, the surface damage will also be etched away in the subsequent wet etching process.

[0043] Please refer to Figure 5 As shown, the energy distribution 201 of the laser can be modulated into a rectangular distribution, and the portion of the silicon glass layer 4 located within the rectangular energy distribution 201 can be effectively removed by the laser, after which a structure as shown in FIG. Figure 2The window 41 shown in the figure may have a rectangular cross-sectional shape. Accordingly, the window 41 may be formed by wet etching. Figure 3 The cross-sectional shape of the recessed portion 31 shown may also include a rectangle.

[0044] In some embodiments, Figure 5 The shape of the energy distribution 201 of the laser in the embodiment may not be an absolute rectangle but a shape close to a rectangle. The rectangular distribution may also be called a flat-top distribution. Figure 3 and Figure 4 In the embodiment, the rectangular shape included in the cross-sectional shape of the recessed portion 31 may not be an absolute rectangle but may be a shape close to a rectangle.

[0045] In addition to modulating the energy distribution of the laser into a rectangular distribution, lasers with other types of energy distributions may be used to remove the local structure of the silicon glass layer multiple times to fit and process to form a window having a cross-sectional shape including a rectangle.

[0046] In other embodiments, the energy distribution 201 of the laser can be modulated as follows: Figure 6 In this setting, the following Gaussian distribution (also known as normal distribution) can be processed on the silicon glass layer 4: Figure 7 The cross-sectional shape shown includes a triangular window 41. Accordingly, the subsequent wet etching process forms a Figure 8 The cross-sectional shape of the recessed portion 31 shown may also include a triangle.

[0047] In some embodiments, Figure 7 and Figure 8 The triangle in may not be an absolute triangle but a shape close to a triangle.

[0048] In addition to modulating the energy distribution of the laser into a Gaussian distribution, lasers with other types of energy distributions may be used to remove the local structure of the silicon glass layer multiple times to fit and process to form a window with a cross-sectional shape including a triangle.

[0049] In the formation of Figure 8 After the structure shown in FIG. 1 , the silicon glass layer 4 can be removed by wet method to form a Fig. 9 The structure shown.

[0050] In other embodiments, the energy distribution 201 of the laser can be modulated as follows: Fig.10 Under this setting, the following trapezoidal distribution can be processed on the silicon glass layer 4: Fig.11 The cross-sectional shape shown includes a trapezoidal window 41. Accordingly, the subsequent wet etching process forms a Fig.12 The cross-sectional shape of the recessed portion 31 shown may also include a trapezoidal shape.

[0051] In some embodiments, Fig.11 and Fig.12 The trapezoid in may not be an absolute trapezoid but a shape close to a trapezoid.

[0052] In addition to modulating the energy distribution of the laser into a trapezoidal distribution, lasers with other types of energy distributions may be used to remove the local structure of the silicon glass layer multiple times to fit and process to form a window having a cross-sectional shape including a trapezoid.

[0053] In the formation of Fig.12 After the structure shown in FIG. 1 , the silicon glass layer 4 can be removed by wet method to form a Fig.13 The structure shown.

[0054] In other embodiments, the energy distribution 201 of the laser can be modulated as follows: Fig.14 Under this setting, the following concave distribution can be processed on the silicon glass layer 4: Fig.15 The cross-sectional shape shown in the figure includes a concave window 41. Accordingly, the subsequent wet etching process forms a Fig.16 The cross-sectional shape of the recessed portion 31 shown may also include a concave shape. Fig.15 and Fig.16 The concave shape in the figure 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 rectangle or tooth shape with a notch, or the concave shape may also be regarded as a composite shape formed by a combination of multiple rectangles and triangles.

[0055] In addition to modulating the energy distribution of the laser into a concave-shaped 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 process to form a window with a concave cross-sectional shape.

[0056] In the formation of Fig.16 After the structure shown in FIG. 1 , the silicon glass layer 4 can be removed by wet method to form a Fig.17 The structure shown.

[0057] In other embodiments, windows having cross-sectional shapes including at least two of triangle, trapezoid, rectangle and concave shape may be processed, and recessed portions having cross-sectional shapes including at least two of triangle, trapezoid, rectangle and concave shape may be processed.

[0058] Optionally, a plurality of spaced local structures of the silicon glass layer are removed by laser to form a Figure 2 , Figure 7 , Fig.11 or Fig.15As shown in FIG. 1 , a plurality of windows 41 are arranged at intervals along the direction X. Accordingly, after wet etching, the following can be formed: Figure 3 , Figure 8 , Fig.12 or Fig.16 The multiple recessed portions 31 spaced apart along the direction X shown in the figure can subsequently be in ohmic contact with the same metal electrode (not shown in the figure). Under 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 doping layer 3 can be dispersed through multiple and spaced locations to reduce the possibility of structural damage to the doping layer 3.

[0059] Wherein, after wet etching, a plurality of recessed portions arranged at intervals are formed, please refer to Fig.18 As shown, the doping layer 3 may also be provided with a protruding spacer 32 between two spaced recesses 31. In the subsequent process of forming the metal electrode, the uncured material (such as slurry, ink and other fluids) used to form the metal electrode will flow into the recesses 31 on both sides of the spacer 32 respectively. In particular, 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, and the spacer 32 is easier to disperse. It can also be said that 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, a relatively large number of silver crystal grains can be formed in the spacer 32, and the relatively large number of silver crystal grains can further reduce the contact resistance between the doping 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 doping layer 3 are of the same type (e.g., N-type element or P-type element), a heavily doped region can be formed in the spacer 32. Accordingly, some parts of the doping 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 (e.g., N + / N, or, P + / P). In the photovoltaic cell to be formed subsequently, the high-low junction can have a good field passivation effect, which helps to increase the migration length of carriers (electrons or holes) and reduce the rate of carrier recombination, thereby improving the photoelectric conversion efficiency.

[0060] In addition, the spacing distance L between two adjacent recessed portions 31 (which may also be the width dimension of the spacing portion 32) may be in the range of 1nm to 100nm, and the spacing distance L may specifically be 1nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm or 100nm. If the spacing distance L is in the range of 10nm to 50nm, the spacing portion 32 is more easily dispersed during the sintering and curing process, and the spacing portion 32 is more mixed with the material used to form the metal electrode, so that more and evenly distributed silver grains can be formed to better reduce the contact resistance, and 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.

[0061] Furthermore, the specific number of the plurality of recessed portions arranged at intervals along the direction X may be two, three, four, five or more.

[0062] In addition, the cross-sectional shape of any one of the two recessed portions disposed at intervals may be different from the cross-sectional shape of the other one. The types of relevant cross-sectional shapes can refer to the contents described above and will not be repeated here.

[0063] Optionally, after wet etching, refer to Fig.18As shown, if the cross-sectional shape of the recessed portion 31 includes a concave shape, correspondingly, the doping layer 3 may also include a convex portion 33 protruding into the space half-enclosed by the recessed portion 31, the height dimension (dimension along direction Y) of the convex portion 33 is smaller than the depth dimension (dimension along direction Y) of the recessed portion 31, and the width dimension (dimension along direction X) of the convex portion 33 is smaller than the width dimension (dimension along direction X) of the recessed portion 31. In the subsequent process of forming the metal electrode, the uncured material (such as slurry, ink and other fluids) used to form the metal electrode will flow into the space on both sides of the convex portion 33 respectively, especially in the process of sintering and curing, the materials used to form the metal electrode on both sides of the convex portion 33 can enter the interior of the convex portion 33, and the convex portion 33 is easier to disperse. It can also be said that the mixing degree of the convex 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 in the convex portion 33, and relatively more silver crystal grains can further reduce the contact resistance between the doping 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 doping layer 3 are of the same type (e.g., N-type element or P-type element), a heavily doped region can be formed in the protrusion 33. Accordingly, some parts of the doping layer 3 other than the protrusion 33 can be regarded as lightly doped regions (relative to the protrusion 33), that is, a high-low junction (e.g., N + / N, or, P + / P). In the photovoltaic cell to be formed subsequently, the high-low junction can have a good field passivation effect, which helps to increase the migration length of carriers (electrons or holes) and reduce the rate of carrier recombination, thereby improving the photoelectric conversion efficiency. The cross-sectional shape of the protrusion 33 may include a rectangle, a trapezoid, a triangle, a fan or a semicircle.

[0064] Optionally, the laser parameters may be modulated to satisfy at least one of the following settings: Setting 1: The scanning rate of the modulated laser is in the range of 5000 mm / s to 40000 mm / s. The scanning rate can be specifically 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.

[0065] If the scanning rate is less than 5000mm / s, the efficiency of forming the window is low, and too much laser heat per unit time is likely to accumulate in the adjacent range, and large thermal stress is likely to be generated inside the doping layer, and the mechanical strength of the doping layer is likely to be reduced. If the scanning rate is greater than 40000mm / s, there may be residues in the structure to be removed in the silicon glass layer, and the residues may block the window to be formed, resulting in relatively low dimensional accuracy of the recessed portion to be formed subsequently, thereby easily increasing the contact resistance between the recessed portion in ohmic contact and the metal electrode. Therefore, the laser scanning rate is preferably within the range of 5000mm / s~40000mm / s.

[0066] Setting 2: The diameter of the modulated laser spot is in the range of 20nm to 200nm, and the diameter can be specifically 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm or 200nm. In some embodiments, the spot refers to the projection range of the laser irradiation on the surface of the irradiated object along the optical axis. If the diameter of the laser spot is less than 20nm, and the structure is removed by one scan, the size of the window along the direction X that can be formed is too small, the amount of liquid for wet etching that can pass through the window is too small, and the wet etching rate is too low. If the diameter of the laser spot is less than 20nm, 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 larger than 200nm, the area of ​​the laser energy distribution range is too large, and the volume of the structure that can be removed per unit time is too large. At the same time, too much heat is generated per unit time, and it is easy to generate large thermal stress inside the doping layer, and the mechanical strength of the doping layer is easy to reduce. Therefore, the diameter of the laser spot is preferably in the range of 20nm~200nm.

[0067] Optionally, the shape of the light spot of the modulated laser light includes a rectangle or a circle.

[0068] Optionally, the wet etching described above may be alkaline etching, and the local structure of the doping layer may be removed through the window using the configured alkaline solution to form a desired recessed portion.

[0069] In some embodiments, if it is necessary to form Figure 3 The cross-sectional shape shown includes a rectangular recessed portion 31, and the local structure of the doped layer can be wet-etched using an alkali solution containing an alkali polishing additive. The alkali polishing additive has a polishing effect, and the surface of the recessed portion 31 formed by the alkali solution containing the alkali polishing additive is relatively smooth, so that the cross-sectional shape of the recessed portion 31 can be closer to a rectangle.

[0070] In some embodiments, if it is necessary to form Figure 8 The cross-sectional shape shown includes a triangular concave portion 31, and the local structure of the doped layer can be wet-etched using an alkali solution containing a texturing additive. The texturing additive has a texturing effect, and the bottom of the concave portion 31 formed by the alkali solution containing the texturing additive is relatively sharp, so that the cross-sectional shape of the concave portion 31 can be closer to a triangle.

[0071] In some embodiments, if it is necessary to form Fig.12 The cross-sectional shape shown includes a trapezoidal recessed portion 31, and the local structure of the doped layer can be wet-etched using an alkali solution containing an alkali polishing additive. The alkali polishing additive has a polishing effect, and the surface of the recessed portion 31 formed by the alkali solution containing the alkali polishing additive is relatively smooth, so that the cross-sectional shape of the recessed portion 31 can be closer to a trapezoid.

[0072] In some embodiments, if it is necessary to form Fig.16 The cross-sectional shape shown includes a concave-shaped depression 31, and the local structure of the doping layer can be wet-etched using an alkali solution containing an alkali polishing additive. The alkali polishing additive has a polishing effect, and the surface of the depression 31 formed by the alkali solution containing the alkali polishing additive is relatively smooth, so that the cross-sectional shape of the depression 31 can be closer to a concave shape.

[0073] in, Figure 8 , Fig.12 and Fig.16 The width dimension (dimension along the direction X) of the recessed portion 31 shown in FIG. 3 is smaller as it is closer to the silicon substrate 1 , that is, Figure 8 , Fig.12 and Fig.16 The portion of the recessed portion 31 shown in the figure that is closer to the silicon substrate 1 has a certain hindering effect or slowing effect on the flow or penetration of the uncured material used to form the metal electrode. The possibility of the uncured material used to form the metal electrode penetrating the doping layer 3 or even the tunneling layer 2 is relatively low, and the possibility of the tunneling oxidation passivation contact structure being destroyed is relatively low. Accordingly, the uncured material used to form the metal electrode in the recessed portion 31 can enter the doping layer 3 from the recessed portion 31 in a direction close to parallel to the direction X or in a lateral direction. Under the condition that the type of doping elements included in the material used to form the metal electrode is the same as the type of doping elements included in the doping layer 3, it can also be beneficial to form a heavily doped region in the portion of the doping layer 3 away from the silicon substrate 1, thereby facilitating the formation of a high-low junction. In the photovoltaic cell to be formed subsequently, the high-low junction can have a good field passivation effect, which helps to increase the migration length of carriers (electrons or holes) and reduce the rate of carrier recombination, thereby improving the photoelectric conversion efficiency.

[0074] In some embodiments, the volume percentage of the alkali polishing additive included in the alkali solution can be in the range of 3% to 5%, specifically 3%, 3.5%, 4%, 4.5% or 5%.

[0075] In some embodiments, the volume percentage of the texturing additive included in the alkali solution may be in the range of 3% to 5%, specifically 3%, 3.5%, 4%, 4.5% or 5%.

[0076] In some embodiments, the alkali solution also includes alkaline substances, such as potassium hydroxide and / or sodium hydroxide. The volume percentage of the alkaline substances included in the alkali solution can be in the range of 2% to 6%, specifically 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5% or 6%.

[0077] Please refer to Fig.19 As shown, after wet etching, the recessed portion 31 (whose cross-sectional shape includes a rectangle) may have a set depth dimension H, and the depth dimension H may be in the range of 50nm to 150nm. Specifically, the depth dimension H may be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm or 150nm.

[0078] Please refer to Fig.19 As shown, after wet etching, the recessed portion 31 (whose cross-sectional shape includes a rectangle) has a set width dimension W, and the width dimension W may be in the range of 20nm to 200nm. Specifically, the width dimension W may be 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm or 200nm.

[0079] Please refer to Fig.19 As shown, in the process of forming the recessed portion 31 by wet etching with alkali solution, the direction in which the doping layer 3 is wet-etched with alkali solution can be Fig.19 The direction indicated by the hollow triangle arrow F shown in FIG. Although the edge 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 the 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 rate at which the silicon glass layer 4 is wet-etched by the alkali solution is relatively small, and the rate at which the doping layer 3 is wet-etched by the alkali solution is relatively large, so the alkali solution can be regarded as being mainly used for wet-etching the doping layer 3.

[0080] In other embodiments, since the rate at which the silicon glass layer is wet-etched by the alkali solution is lower than the rate at which the doped layer is wet-etched by the alkali solution, after the wet etching, the following may be formed: Fig. 20 In the structure shown, the width dimension of the window 41 along the direction X is smaller than the width dimension of the recessed portion 31 along the direction X. Accordingly, a brim structure A34 can be formed at the connection between the window 41 and the recessed portion 31. The brim structure can also be called a step structure.

[0081] Similarly, please refer to Fig.21 As shown, after wet etching, the recessed portion 31 (whose cross-sectional shape includes a triangle) may have a set depth dimension H. The range and specific value of the depth dimension H may refer to the content about the depth dimension H described above, which will not be repeated here. After wet etching, the opening of the recessed portion 31 (whose cross-sectional shape includes a triangle) may have a set width dimension W. The range and specific value of the width dimension W may refer to the content about the width dimension W described above, which will not be repeated here.

[0082] In other embodiments, since the rate at which the silicon glass layer is wet-etched by the alkali solution is lower than the rate at which the doped layer is wet-etched by the alkali solution, after the wet etching, the following may be formed: Fig. 22 In the structure shown, the width dimension of the window 41 along the direction X is smaller than the width dimension of the opening of the recessed portion 31 along the direction X. Accordingly, a brim structure A34 can be formed at the connection between the window 41 and the recessed portion 31 .

[0083] Similarly, please refer to Fig.23 As shown, after wet etching, the recessed portion 31 (whose cross-sectional shape includes a trapezoid) may have a set depth dimension H. The range and specific value of the depth dimension H may refer to the contents of the depth dimension H described above, which will not be repeated here. After wet etching, the opening of the recessed portion 31 (whose cross-sectional shape includes a trapezoid) may have a set width dimension W. 1 , the width dimension W 1 The range and specific value of the width dimension W can refer to the content about the width dimension W described above. The bottom wall of the recessed portion 31 (whose cross-sectional shape includes a trapezoid) can have a set width dimension W. 2 , the width dimension W 2 The range and specific value of can refer to the content about the width dimension W described above, but it is necessary to satisfy the width dimension W 2 Smaller than width dimension W 1 settings.

[0084] In other embodiments, since the rate at which the silicon glass layer is wet-etched by the alkali solution is lower than the rate at which the doped layer is wet-etched by the alkali solution, after the wet etching, the following may be formed: Fig.24In the structure shown, the width dimension of the window 41 along the direction X is smaller than the width dimension of the recessed portion 31 along the direction X. Accordingly, a brim structure A34 can be formed at the connection between the window 41 and the recessed portion 31 .

[0085] Similarly, please refer to Fig.25 As shown, after wet etching, the recessed portion 31 (whose cross-sectional shape includes a concave shape) may have a set depth dimension H. The range and specific value of the depth dimension H may refer to the content about the depth dimension H described above, and will not be repeated here. After wet etching, the opening of the recessed portion 31 (whose cross-sectional shape includes a concave shape) may have a set width dimension W. The range and specific value of the width dimension W may refer to the content about the width dimension W described above, and will not be repeated here.

[0086] In other embodiments, since the rate at which the silicon glass layer is wet-etched by the alkali solution is lower than the rate at which the doped layer is wet-etched by the alkali solution, after the wet etching, the following may be formed: Fig.26 In the structure shown, the width dimension of the window 41 along the direction X is smaller than the width dimension of the recessed portion 31 along the direction X. Accordingly, a brim structure A34 can be formed at the connection between the window 41 and the recessed portion 31 .

[0087] Scanning electron microscope observation shows that the microstructure of the brim structure A34 is as follows Fig. 27 shown.

[0088] As can be seen from 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 nanometer level (no more than one micrometer in size), and accordingly, the size level of the window that can be formed can also be nanometer level. During the laser removal process, the heat that can be generated per unit time is relatively small, and the heat that can be conducted to the doping layer per unit time is relatively small, and it is not easy to generate large thermal stress in the doping layer. Although the size level of the window is nanometer level, a relatively large recessed portion can still be formed by wet etching, for example, the size of the recessed portion in the direction X can be greater than or equal to the size of the window in the direction X, and / or, for example, the size of the recessed portion in the direction Y can be greater than or equal to the size of the window in the direction Y, so as to meet the need for a relatively large ohmic contact area between the recessed portion and the metal electrode.

[0089] Optionally, it is necessary to make the ratio of the depth dimension H of the recessed portion 31 to the thickness dimension of the doped layer 3 within the range of 0.5 to 0.8, and 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 recessed portion 31 is too large, and in the process of forming the metal electrode, the material used to form the metal electrode is easy to burn through the doped layer 3, thereby easily destroying 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 recessed portion 31 is too small, the ohmic contact area between the recessed portion 31 and the metal electrode is relatively small, and the contact resistance between the recessed portion 31 and the metal electrode is relatively large. Therefore, it is better to make the ratio of the depth dimension H of the recessed portion 31 to the thickness dimension of the doped layer 3 within the range of 0.5 to 0.8.

[0090] Optionally, during wet etching, at least one of the following settings may be met to meet the requirement of forming the size of the above-mentioned recessed portion: Setting a: The time length of the wet etching is in the range of 10s to 150s, wherein the time length can specifically be 10s, 20s, 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, 130s, 140s or 150s.

[0091] Setting b: The temperature of the wet etching is in the range of 50° C. to 90° C., wherein the temperature may specifically be 50° C., 60° C., 70° C., 80° C. or 90° C.

[0092] Alternatively, if the doping layer is wet-etched by an alkali solution to form a recessed portion, the silicon glass layer can be subsequently removed by an acid solution wet method. The acid solution used later can achieve an acid-base neutralization effect with the previously residual alkali solution, so as to reduce the possibility that any of the corrosive liquids, the alkali solution and the acid solution, damages the surface morphology of the doping layer away from the silicon substrate, thereby reducing the possibility that there are more recombination centers on the surface of the doping layer away from the silicon substrate. In addition, the effect of reducing the pollution degree of the generated waste liquid can also be achieved.

[0093] In some embodiments, the acid may include relatively corrosive hydrofluoric acid. During the process of pickling to remove the silicon glass layer, the rate at which the acid corrodes the silicon glass layer is relatively large compared to the rate at which the acid corrodes the doped layer, that is, the acid can be considered to be mainly used to remove the silicon glass layer.

[0094] In some embodiments, after the acid wash to remove the silica glass layer, water wash may be performed.

[0095] In other embodiments, a strong oxidizing acid solution containing at least one of nitric acid, aqua regia and sulfuric acid may be used to remove the local structure of the polysilicon to form a recessed portion, and then an alkaline solution (containing sodium hydroxide and / or potassium hydroxide) may be used to remove the silicon glass layer. When removing the silicon glass layer, an inhibitor may be used simultaneously to suppress the rate at which the alkaline solution corrodes the doping layer. The inhibitor may include isopropyl alcohol, benzotriazole, hydrogen peroxide, etc. Before removing the silicon glass layer with the alkaline solution, the silicon glass layer may be treated with a laser to modify the silicon glass layer, or in other words, to make the silicon glass layer loose, so as to increase the rate at which the silicon glass layer is subsequently removed with the alkaline solution.

[0096] Optionally, in forming Figure 4 After the structure shown in FIG. 1 , a doped layer 3 may be deposited on the side away from the silicon substrate 1 to form a Fig.28 After forming the passivation layer 5, the passivation layer 5 is further formed. Fig.29 The metal electrode 6 is shown.

[0097] Similarly, in the formation of Fig. 9 After the structure shown in FIG. 1 , a doped layer 3 may be deposited on the side away from the silicon substrate 1 to form a Fig.30 After forming the passivation layer 5, the passivation layer 5 is further formed. Fig.31 The metal electrode 6 is shown.

[0098] Similarly, in the formation of Fig.13 After the structure shown in FIG. 1 , a doped layer 3 may be deposited on the side away from the silicon substrate 1 to form a Fig.32 After forming the passivation layer 5, the passivation layer 5 is further formed. Fig.33 The metal electrode 6 is shown.

[0099] Similarly, in the formation of Fig.17 After the structure shown in FIG. 1 , a doped layer 3 may be deposited on the side away from the silicon substrate 1 to form a Fig.34 After forming the passivation layer 5, the passivation layer 5 is further formed. Fig.35 The metal electrode 6 is shown.

[0100] If the doping layer 3 is doped with an N-type element, the passivation layer may include silicon nitride, such as amorphous silicon nitride (SiN x ), the passivation layer can play a good anti-reflection effect, surface passivation and body passivation effect, so that the photoelectric conversion efficiency and fill factor of the photovoltaic cell to be prepared can be higher.

[0101] In addition, any of the passivation layers 5 described above may be provided with a pit 51 located close to the depressed portion in the direction X. The pit 51 may guide and gather the uncured material (e.g., slurry, ink, or other fluid) used to form the metal electrode, so that the uncured material used to form the metal electrode may flow toward the depressed portion of the doping layer, thereby achieving good ohmic contact between the depressed portion and the metal electrode.

[0102] In other embodiments, after removing the silicon glass layer and before forming the metal electrode capable of making ohmic contact with the recessed portion, the passivation layer may not be deposited on the side of the doped layer facing away from the silicon substrate.

[0103] For details, please refer to Fig.36 As shown, the substrate 10 described above may be provided with areas to be metallized 10a and non-metallized areas 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 area to be metallized 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 area to be metallized 10a. The non-metallized area 10b refers to a range that does not overlap with the range of the projection of the metal electrode to be formed subsequently in the direction Y. In the substrate 10, the doped layer and the silicon glass layer that may be formed are located in the area to be metallized 10a but not in the non-metallized area 10b. Accordingly, the passivation layer to be formed subsequently may be located in the non-metallized area 10b but not in the area to be metallized 10a. It is also possible that the passivation layer is formed earlier than the doped layer and the silicon glass layer. For example, when the substrate 10 includes a silicon base but does not include a tunneling layer, a doping layer and a silicon glass layer, a passivation layer is deposited on one side of the silicon base, and a portion of the passivation layer located in the area to be metallized 10a is selectively removed by laser, or a mask process and a wet etching process are used to selectively remove the portion of the passivation layer located in the area to be metallized 10a. Accordingly, a penetration hole penetrating the passivation layer is formed, and the penetration hole is located in the area to be metallized 10a. Then, a tunneling layer, a doping layer and a silicon glass layer can be formed in sequence in the penetration hole, and then the method described above for forming a window, a recess and a metal electrode can be implemented.

[0104] Optionally, the method for forming a metal electrode in 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 are to print a metal-containing slurry on a 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 in ohmic contact with the doped layer. The slurry may include a silver-containing slurry or a silver-aluminum slurry. If used to form a negative metal electrode, a silver-containing slurry may be used, and if used to form a positive metal electrode, a silver-aluminum slurry may be used. The slurry may also include other additives such as glass frit, solvent, modifier, non-volatile polymer or resin.

[0105] In other embodiments, the method for forming the metal electrode in ohmic contact with the doping layer may also include laser transfer, electroplating, inkjet or sputtering.

[0106] In other embodiments, Figure 1 In the substrate shown, the silicon substrate 1 may be doped with at least one P-type element (element of the third main group in the chemical periodic table), such as boron, aluminum, gallium, and other P-type elements. The doping layer 3 may also be doped with at least one P-type element, and accordingly, the concentration of the P-type element doped in the doping layer 3 is greater than the concentration of the P-type element doped in the silicon substrate 1.

[0107] In other embodiments, Figure 1 In the substrate shown, the silicon substrate 1 can be doped with at least one N-type element, and the doping layer 3 can be doped with at least one P-type element, or the silicon substrate 1 can be doped with at least one P-type element, and the doping layer 3 can be doped with at least one N-type element. Under this setting, a PN junction can be formed between the silicon substrate 1 and the doping layer 3.

[0108] In other embodiments (not shown), Figure 1 The substrate shown may also not include a tunneling layer, that is, the substrate may include a stacked silicon substrate, a doped layer, and a silicon glass. Among them, the doped layer may be an emitter layer or a diffusion layer formed directly on the silicon substrate using 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. Under this setting, a PN junction may be formed between the silicon substrate and the doped layer, and the PN junction is used to form a built-in electric field for separating electrons and holes.

[0109] According to the preparation method described above, the photovoltaic cells that can be prepared may include tunnel oxide passivated contact photovoltaic cells (Tunnel Oxide Passivated Contact Solar Cell, TOPCon Solar Cell), back contact photovoltaic cells (Back Contact Solar Cell, BC Solar Cell) or heterojunction photovoltaic cells (Heterojunction Technology Solar Cell, HJT Solar Cell).

[0110] The present application provides a relatively specific embodiment of a preparation method, which can be used to prepare a tunneling oxide passivation contact photovoltaic cell. It is assumed that the silicon substrate needs to be doped with N-type elements, the doping layer needs to be doped with N-type elements, and the emitter layer needs to be doped with P-type elements. The preparation method may include: using an alkali solution containing a texturing agent to texturize the front surface (also known as the light-receiving surface or top surface) of the silicon substrate to form a velvet surface (with multiple micron-sized grooves and protrusions) located on the front surface of the silicon substrate. Diffusion of impurities on the velvet surface using a diffusion process to form an emitter layer. Polishing the back surface (also known as the backlight surface or bottom surface) of the silicon substrate using an alkali solution containing a polishing agent to form a back polished surface. Depositing a tunneling layer and an undoped amorphous silicon layer (the amorphous silicon layer may also include polycrystalline silicon) on the back polished surface in sequence. Diffusion of impurities into the amorphous silicon layer using a diffusion process to form a doping layer. Diffusion of oxygen using a diffusion process in the process of forming the doping layer, or diffusion of oxygen using a diffusion process after the doping layer is formed, to form a silicon glass layer (e.g., phosphorus-containing silicon glass). A local structure of the silicon glass layer is removed by laser to form a window. The local structure of the doped layer is wet-etched through the window to form a recessed portion, wherein the depth dimension of the recessed portion is smaller than the thickness dimension of the doped layer. The silicon glass layer is wet-removed. The plating layer and the expansion layer previously formed in the process of forming the tunneling layer, the amorphous silicon layer and the doped layer are removed. An aluminum oxide passivation layer is deposited on the side of the emitter layer away from the silicon substrate. A silicon nitride passivation layer is deposited on the side of the aluminum oxide passivation layer away from the emitter layer, and a silicon nitride passivation layer is deposited on the side of the doped layer away from the tunneling layer. Metal electrodes are formed on both sides, wherein the metal electrode located on the side of the doped layer away from the silicon substrate is in ohmic contact with the recessed portion of the doped layer. Annealing treatment.

[0111] According to the above preparation method, the structure of the tunneling oxide passivation contact photovoltaic cell sheet can be as follows: Fig.37 As 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 a metal electrode 6. Among them, after the doped layer mentioned above is annealed, the crystallization rate inside the doped layer is improved, the volume proportion of polycrystalline silicon inside the doped layer is larger than the volume proportion of amorphous silicon, and the conductivity of the doped layer is increased. Therefore, the doped layer after annealing can be regarded as a doped conductive layer, and of course the doped conductive layer can also be called 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 electrode 6 may include a negative metal electrode 6a and a positive metal electrode 6b. The photovoltaic cell 101 is provided with a metallized area 10c and a non-metallized area 10b. The recessed portion formed in the doped conductive layer 3a is at least in the metallized area 10c, so that the negative metal electrode 6a is in ohmic contact with the recessed portion. The relevant specific effects have been described above and will not be repeated here. The positive metal electrode 6 b is in ohmic contact with the emitter layer 7 .

[0112] In some embodiments, the above-mentioned deposition can be chemical vapor deposition or physical vapor deposition. Chemical vapor deposition can be low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD) or atmospheric pressure chemical vapor deposition (APCVD).

[0113] In some embodiments, the structure of the photovoltaic cell that can be prepared by the preparation method of some embodiments of the present application is not limited to Fig.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 area 10b, and the tunneling oxide passivation contact structure (including the doped conductive layer and the tunneling layer) may be mainly located in the metallized area 10c. Alternatively, for example, the thickness of the portion of the tunneling oxide passivation contact structure (including the doped conductive layer and the tunneling layer) located in the non-metallized area 10b is smaller than the thickness of the portion of the tunneling oxide passivation contact structure (including the doped conductive layer and the tunneling layer) located in the metallized area 10c. Alternatively, 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 illuminated by sunlight), and accordingly, the emitter layer may be located on the backlight side of the silicon substrate (the side not directly illuminated by sunlight). Alternatively, 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. Alternatively, 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 a doped conductive layer and a tunneling layer), and the type of element doped in the tunneling oxide passivation contact structure on the light-receiving side is different from the type of element doped in the tunneling oxide passivation contact structure on the backlight side.

[0114] In the second aspect, the present application provides some embodiments of photovoltaic cells, which can be prepared by the preparation method described above, so the photovoltaic cell has a high photoelectric conversion efficiency and a filling factor, which will not be described in detail here. Fig.37 As shown, of course, the structure of the photovoltaic cell is not limited to Fig.37 The structure shown, the structural types of other types of photovoltaic cells have been described above. Specifically, they can be selectively heavily doped photovoltaic cells, double tunneling oxidation passivation contact photovoltaic cells, back contact photovoltaic cells, heterojunction photovoltaic cells and other types of photovoltaic cells.

[0115] Optionally, see Fig.37 As shown, in the photovoltaic cell 101, taking the silicon substrate 1 doped with N-type elements, the doped conductive layer 3a doped with N-type elements and the emitter layer 7 doped with P-type elements as an example, the doped conductive layer 3a can be provided with a recessed portion formed by wet etching in the preparation method described above, and the negative metal electrode 6a can be in ohmic contact with the recessed portion. Fig.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 in the recessed portion and is in ohmic contact with the recessed portion, and the cross-sectional shape of the main body portion 611 may include a triangle.

[0116] As can be seen from the above, the cross-sectional shape of the main body 611 includes a triangle because the cross-sectional shape of the recessed portion formed in the wet etching process includes a triangle. If the cross-sectional shape of the recessed portion formed by wet etching includes a trapezoid, a rectangle, or a concave shape, the cross-sectional shape of the main body 611 may also include a trapezoid, a rectangle, or a concave shape, and even the cross-sectional shape of the main body 611 may also include at least two of the triangle, trapezoid, rectangle, and concave shape.

[0117] Optionally, see Fig.38 As shown, the doped conductive layer 3a may be provided with a plurality of recessed portions spaced apart along the direction X, and the negative metal electrode 6a may include a plurality of ohmic contact portions 61 spaced apart along the direction X, each ohmic contact portion 61 having a main body portion 611, and each main body portion 611 is in ohmic contact with the corresponding recessed portion. In some embodiments, the ohmic contact portion 61 also includes an extension portion 612, and the extension portion 612 extends into the doped conductive layer 3a, especially the number of extension portions 612 existing in the portion of the doped conductive layer 3a located between two adjacent main bodies 611 is relatively large. The extension portion 612 may include silver grains, and accordingly, according to the above, the number of silver grains existing in the portion of the doped conductive layer 3a located between two adjacent main bodies 611 is also relatively large, which can well reduce the contact resistance. The extension portion 612 may also include more doping elements (from the material used to form the metal electrode). According to the above, the portion of the doped conductive layer 3a located between the two adjacent main portions 611 may include a heavily doped region, that is, a high-low junction may be formed in the doped conductive layer 3a. The high-low junction can provide a good field passivation effect, thereby greatly improving the photoelectric conversion efficiency and fill factor of the photovoltaic cell.

[0118] The spacing distance (dimension in direction X) between two adjacent main bodies 611 may be in the range of 10nm to 50nm, specifically 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 55nm or 50nm. As can be seen from the above, under the setting of this size range, more and evenly distributed silver grains can be formed between two adjacent main bodies 611 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.

[0119] In addition, the negative metal electrode 6a may further include an electrical connection portion 62, which is integrally formed with the ohmic contact portion 61, and penetrates the back passivation layer 5a, and is used to electrically connect to an external circuit (such as a welding strip).

[0120] In other embodiments (not shown in the figures), the silicon substrate may be doped with P-type elements, the doped conductive layer may be doped with P-type elements, and the emitter layer may be doped with N-type elements. The metal electrode in ohmic contact with the emitter layer may be a negative metal electrode, and the metal electrode in ohmic contact with the doped conductive layer may be a positive metal electrode.

[0121] In some embodiments, "doped with N-type elements" in this article mainly means that the chemical elements of the doped impurities include N-type elements. Similarly, "doped with P-type elements" in this article mainly means that the chemical elements of the doped impurities include P-type elements.

[0122] In a third aspect, the present application provides some embodiments of a photovoltaic module, which includes a laminate and a frame, and the frame is installed at the edge of the laminate. The laminate includes a stacked photovoltaic glass, a first encapsulation film, a battery string, a second encapsulation film and a backplane. Alternatively, the laminate includes a stacked first photovoltaic glass, a first encapsulation film, a battery string, a second encapsulation film and a second photovoltaic glass. Among them, the battery string can be formed by electrically connecting a plurality of photovoltaic cells described above.

[0123] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a photovoltaic cell, characterized in that: The preparation method comprises: Providing a silicon substrate, a doping layer and a silicon glass layer, wherein the doping layer is located between the silicon substrate and the silicon glass layer; Using laser to remove the 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 recessed portion, wherein the depth of the recessed portion is smaller than the thickness of the doping layer; Wet-removing the silicon glass layer; A metal electrode is formed in ohmic contact with the recessed portion.

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

3. The method for preparing a photovoltaic cell according to claim 1, characterized in that: The method of using laser to remove the local structure of the silicon glass layer to form a window includes: The energy distribution of the modulated laser includes at least one of Gaussian distribution, rectangular distribution, trapezoidal distribution and annular distribution.

4. The method for preparing a photovoltaic cell according to claim 1, characterized in that: The method of using laser to remove the local structure of the silicon glass layer to form a window includes: The laser is used to process a window in the silicon glass layer, the window having a cross-sectional shape including at least one of a triangle, a trapezoid, a rectangle and a concave shape.

5. The method for preparing a photovoltaic cell according to claim 1, characterized in that: The method of using laser to remove the local structure of the silicon glass layer to form a window includes: The laser is used to remove a plurality of spaced local structures of the silicon glass layer to form a plurality of spaced windows.

6. The method for preparing a photovoltaic cell according to claim 1, characterized in that: The method of using 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: modulate the scanning rate of the laser to be within the range of 5000 mm / s to 40000 mm / s; Setting 2: The diameter of the laser spot is modulated to be in the range of 20 nm to 200 nm.

7. The method for preparing a photovoltaic cell according to any one of claims 1 to 6, characterized in that: The method of wet etching a local structure of the doping layer through the window to form a recessed portion comprises: The local structure of the doped layer is wet-etched using an alkali solution containing an alkali polishing additive, or the local structure of the doped layer is wet-etched using an alkali solution containing a texturing additive.

8. The method for preparing a photovoltaic cell according to any one of claims 1 to 6, characterized in that: The method of wet etching a local structure of the doping layer through the window to form a recessed portion comprises: A concave portion having a cross-sectional shape of at least one of a triangle, a trapezoid, a rectangle and a concave shape is formed in the doping layer by wet etching.

9. The method for preparing a photovoltaic cell according to any one of claims 1 to 6, characterized in that: The method of wet etching the local structure of the doping layer through the window to form a recessed portion satisfies at least one of the following settings: Setting a: The wet etching time is in the range of 10s~150s; Setting b: The temperature of wet etching is in the range of 50°C to 90°C.

10. The method for preparing a photovoltaic cell according to any one of claims 1 to 6, characterized in that: The method of making the depth dimension of the recessed portion smaller than the thickness dimension of the doping layer satisfies: The ratio of the depth dimension of the recessed portion to the thickness dimension of the doping layer is within the range of 0.5 to 0.

8.

11. The method for preparing a photovoltaic cell according to any one of claims 1 to 6, characterized in that: Firstly, an alkali solution is used to wet-etch the local structure of the doping layer through the window to form the recessed portion, and then an acid solution is used to wet-etch the silicon glass layer.

12. The method for preparing a photovoltaic cell according to any one of claims 1 to 6, characterized in that: The method of forming a metal electrode in ohmic contact with the recessed portion comprises: A metal electrode is formed in ohmic contact with at least two recessed portions disposed at intervals.

13. A photovoltaic cell, characterized in that: The photovoltaic cell is prepared by the method for preparing a photovoltaic cell according to any one of claims 1 to 12.

14. The photovoltaic cell according to claim 13, characterized in that: The photovoltaic cell comprises a doped conductive layer and a metal electrode, the doped conductive layer comprises a recessed portion formed by wet etching, and the metal electrode comprises an ohmic contact portion; The ohmic contact portion includes a main body portion, the main body portion is located in the recessed portion and is in ohmic contact with the recessed portion; The cross-sectional shape of the main body portion includes at least one of a triangle, a trapezoid, a rectangle and a concave shape.

15. The battery cell according to claim 13, characterized in that: The photovoltaic cell comprises a tunneling oxidation passivation contact photovoltaic cell, a back contact photovoltaic cell or a heterojunction photovoltaic cell.

16. A photovoltaic module, characterized in that: The photovoltaic module comprises at least one battery string, and the battery string is formed by electrically connecting the photovoltaic battery sheets according to any one of claims 13 to 15.

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