Back-contact photovoltaic cell piece, back-contact photovoltaic cell assembly and preparation methods of back-contact photovoltaic cell piece and back-contact photovoltaic cell assembly

Abstract

The invention relates to a back contact photovoltaic cell piece, a back contact photovoltaic cell assembly and a preparation method, and relates to the technical field of photovoltaic cell pieces. According to the preparation method, at least part of the structure of the surface of the silicon substrate is subjected to at least two times of texturing treatment to form a textured surface, in the two adjacent times of texturing treatment, the concentration of a texturing solution used in the later texturing treatment is smaller than that of a texturing solution used in the previous texturing treatment, the substrate is dried by ozone, and the textured surface is formed. And at least forming a silicon oxide passivation layer on the textured surface. Through at least two times of texturing treatment, the average size of the pyramid structure of the formed textured surface is relatively small, the density of the pyramid structure of the textured surface is relatively large, and the distribution uniformity degree of the pyramid structure of the textured surface is relatively large. The back contact photovoltaic cell prepared according to the preparation method has the advantages of relatively low light reflectivity and relatively low recombination rate, so that the prepared back contact photovoltaic cell can have relatively high photoelectric conversion efficiency.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic cells, and in particular to a back-contact photovoltaic cell, a back-contact photovoltaic cell assembly and a preparation method thereof. Background Art

[0002] A back-contact photovoltaic cell is a cell in which both the positive electrode and the negative electrode are arranged on the backlight side of the cell. The light-receiving area of ​​the light-receiving side of the back-contact photovoltaic cell is relatively large, so the photoelectric conversion efficiency of the back-contact photovoltaic cell is relatively large. The photoelectric conversion efficiency is also negatively correlated with the light reflectivity of the back-contact photovoltaic cell. However, the light reflectivity of the back-contact photovoltaic cell in the related art needs to be reduced. Summary of the invention

[0003] In view of this, the present application provides a back-contact photovoltaic cell, a back-contact photovoltaic cell assembly and a preparation method to reduce the light reflectivity of the back-contact photovoltaic cell, thereby improving the photoelectric conversion efficiency of the back-contact photovoltaic cell.

[0004] In a first aspect, the present application provides a method for preparing a back-contact photovoltaic cell sheet, and the preparation method includes the following contents.

[0005] A substrate is provided, which includes a silicon base, and at least a part of the structure on the surface of the silicon base is subjected to at least two texturing treatments to form a texturing surface, wherein in two adjacent texturing treatments, the concentration of the texturing liquid used in the latter texturing treatment is less than the concentration of the texturing liquid used in the former texturing treatment, and the substrate is dried using ozone to form a silicon oxide passivation layer at least on the texturing surface.

[0006] In the present application, through at least two velvet making processes, the average size of the pyramid structures included in the velvet surface formed is relatively small, the density of the pyramid structures included in the velvet surface formed is relatively large, and the distribution uniformity of the pyramid structures included in the velvet surface formed is relatively large.

[0007] When light is first irradiated to the pyramid structure of the velvet surface, part of the light can directly enter the silicon substrate, and part of the light is reflected. The reflected light can also easily irradiate other nearby pyramid structures. Part of the reflected light can directly enter the silicon substrate, and another part of the reflected light continues to be reflected. Another part of the reflected light is still easy to irradiate other nearby pyramid structures. Therefore, the amount of light that can enter the silicon substrate can be increased through multiple reflections, that is, the prepared velvet surface can have a lower light reflectivity. The light reflectivity of the silicon substrate of the back-contact photovoltaic cell formed by the preparation method of the present application is low, and the silicon substrate can absorb more light to generate more photogenerated carriers.

[0008] After the velvet surface is formed and before ozone drying, the velvet surface is not smooth and the density of the pyramid structure is relatively high, so the number of dangling bonds on the velvet surface is relatively large. Dangling bonds refer to unpaired electronic states formed when the valence bond of an atom is not fully combined with other atoms on the surface, interface or defect of the crystal. More dangling bonds mean more recombination centers, which are defects that can promote the recombination of electrons and holes by providing intermediate energy levels (defective energy levels), that is, more recombination centers will increase the rate of recombination of photogenerated holes and photogenerated electrons. It can also be said that in order to reduce the light reflectivity, the recombination rate will increase instead.

[0009] After the velvet surface is formed, the substrate can be dried with ozone. On the one hand, the liquid on the surface of the substrate treated by the wet method can be evaporated, thereby drying the surface of the substrate. On the other hand, a silicon oxide passivation layer can be formed on the basis of the velvet surface. In detail, during the ozone drying process, the oxygen atoms in the ozone will combine with the nearby silicon atoms in the velvet surface to form silicon oxide (SiO x ), the formed silicon oxide passivation layer mainly grows from the suede surface to the inside of the silicon substrate. Importantly, the oxygen atoms in the ozone will combine with the dangling bonds of the silicon atoms to reduce the number of dangling bonds and the number of recombination centers, that is, the formed silicon oxide passivation layer can play a good chemical passivation role on the suede surface.

[0010] Since the average size of the pyramid structure included in the prepared velvet is relatively small, the density is relatively large, and the distribution is relatively uniform, the number of stress concentration sources of the velvet is relatively small, and the stress concentration peak of the velvet is relatively small. The number of stress concentration sources of the silicon oxide passivation layer formed on the velvet is also relatively small, and the stress concentration peak of the silicon oxide passivation layer is relatively small. Therefore, the structural stability of the formed silicon oxide passivation layer is relatively large. In the subsequent preparation process and in the actual use of the prepared back contact photovoltaic cell sheet, the silicon oxide passivation layer is not easy to be damaged, the silicon-oxygen chemical bond is not easy to break, and it is not easy to form relatively more new dangling bonds on the velvet, that is, the reliability of the chemical passivation effect of the silicon oxide passivation layer is relatively large.

[0011] According to the above content, it can be known that the back-contact photovoltaic cell prepared according to the preparation method of the back-contact photovoltaic cell of the present application can take into account the advantages of lower light reflectivity and lower recombination rate. In detail, the lower light reflectivity allows the silicon substrate to generate more photogenerated electrons and photogenerated holes when absorbing light energy, and the lower recombination rate makes the lifetimes of the photogenerated electrons and photogenerated holes longer, so that the prepared back-contact photovoltaic cell has a larger short-circuit current and fill factor, that is, the prepared back-contact photovoltaic cell has a larger photoelectric conversion efficiency.

[0012] Optionally, the method of drying the substrate using ozone satisfies at least one of settings a, b and c. Setting a: The drying temperature is within the range of 85° C. to 120° C. Setting b: Ozone with a flow rate within the range of 100 sccm to 1000 sccm is used. Setting c: The drying time is within the range of 5 min to 20 min.

[0013] Optionally, after drying the substrate with ozone, the preparation method of the present application further includes: first depositing an aluminum oxide passivation layer on the silicon oxide passivation layer by atomic layer deposition, and then depositing a silicon nitride passivation layer on the aluminum oxide passivation layer by plasma enhanced chemical vapor deposition.

[0014] Optionally, before the texturing treatment, the preparation method of the present application further includes: forming a first tunneling oxide passivation contact structure and a second tunneling oxide passivation contact structure that are alternately and spaced apart on the backlight side of the silicon substrate.

[0015] Optionally, before the texturing treatment, the preparation method of the present application further includes: forming a mask layer at least on the first tunneling oxide passivation contact structure and the second tunneling oxide passivation contact structure.

[0016] Optionally, the method of drying the substrate using ozone further includes: forming a silicon oxide passivation layer on the first tunneling oxide passivation contact structure, and forming a silicon oxide passivation layer on the second tunneling oxide passivation contact structure.

[0017] Optionally, before the texturing process, a window is formed between the first tunneling oxide passivation contact structure and the second tunneling oxide passivation contact structure, wherein a portion of the backlight surface of the silicon substrate is exposed by the window.

[0018] Optionally, the method of at least two texturing treatments includes: a first texturing treatment on the surface of the silicon substrate, the first texturing liquid used in the first texturing treatment includes an alkaline substance with a concentration in the range of 1.5Wt%~3Wt%, and / or the first texturing liquid used in the first texturing treatment includes a texturing additive with a concentration in the range of 1Wt%~1.5Wt%.

[0019] Optionally, the method of at least two texturing treatments includes: a second texturing treatment on the surface of the silicon substrate, the second texturing liquid used in the second texturing treatment includes an alkaline substance with a concentration in the range of 0.9Wt%~1.3Wt%, and / or the second texturing liquid used in the second texturing treatment includes a texturing additive with a concentration in the range of 0.7Wt%~0.9Wt%.

[0020] Optionally, the method of at least two texturing treatments includes: a third texturing treatment on the surface of the silicon substrate, the third texturing liquid used in the third texturing treatment includes an alkaline substance with a concentration in the range of 0.5Wt%~0.7Wt%, and / or the third texturing liquid used in the third texturing treatment includes a texturing additive with a concentration in the range of 0.2Wt%~0.5Wt%.

[0021] In the second aspect, the present application provides a back-contact photovoltaic cell, which is prepared by the preparation method of the back-contact photovoltaic cell described above. According to the above content, the back-contact photovoltaic cell of the present application can take into account the advantages of lower light reflectivity and lower recombination rate, so that the back-contact photovoltaic cell of the present application has a larger short-circuit current and fill factor, and the back-contact photovoltaic cell of the present application can have a larger photoelectric conversion efficiency.

[0022] Optionally, the pyramid structure of the velvet surface of the back contact photovoltaic cell has a set height H, satisfying 0.5µm≤H≤1.5µm.

[0023] Optionally, the base of the pyramid structure of the velvet surface of the back contact photovoltaic cell has a set width W, satisfying 0.5µm≤W≤2.5µm.

[0024] Optionally, the back-contact photovoltaic cell comprises a silicon substrate and a stacked structure, the silicon substrate has a velvet surface, the stacked structure comprises a silicon oxide passivation layer, an aluminum oxide passivation layer and a silicon nitride passivation layer, the silicon oxide passivation layer is arranged on the velvet surface, and the aluminum oxide passivation layer is located between the silicon oxide passivation layer and the silicon nitride passivation layer.

[0025] Optionally, the back-contact photovoltaic cell further includes a tunneling oxide passivation contact structure, the tunneling oxide passivation contact structure is located on the backlight side of the silicon substrate, and the silicon oxide passivation layer is also disposed on the tunneling oxide passivation contact structure.

[0026] In a third aspect, the present application provides a back-contact photovoltaic cell assembly, which includes at least one cell string, and the cell string is formed by electrically connecting the back-contact photovoltaic cell sheets described above. Accordingly, the back-contact photovoltaic cell assembly of the present application can have a greater photoelectric conversion efficiency.

[0027] 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

[0028] 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.

[0029] Figure 1 is a schematic diagram of a local structure of a silicon substrate in a specific embodiment; Figure 2 is a schematic diagram of a local structure of a silicon substrate after the first texturing treatment in a specific embodiment; Figure 3 is a schematic diagram of a partial structure of a silicon substrate after a second texturing treatment in a specific embodiment; Figure 4 is a schematic diagram of a local structure of a silicon substrate after the third texturing treatment in a specific embodiment; Figure 5 is a schematic diagram for comparing the sizes of the first pyramid structure, the second pyramid structure and the third pyramid structure; Figure 6 is a schematic diagram of the local structure of a silicon substrate and a silicon oxide passivation layer in a specific embodiment; Figure 7 is a schematic diagram of the local structure of a silicon substrate, a silicon oxide passivation layer and an aluminum oxide passivation layer in a specific embodiment; Figure 8 is a schematic diagram of the partial structure of a silicon substrate, a silicon oxide passivation layer, an aluminum oxide passivation layer and a silicon nitride passivation layer in a specific embodiment; Fig. 9 It is a schematic diagram of the local structure of a silicon substrate, a first tunneling oxide passivation contact structure, a second tunneling oxide passivation contact structure and a window in a specific embodiment; Fig.10 A schematic diagram of a local structure of a silicon substrate, a first tunneling oxide passivation contact structure, a second tunneling oxide passivation contact structure, a first mask layer, a second mask layer and a window in a specific embodiment; Fig.11 is a schematic structural diagram of a silicon substrate in a specific embodiment; Fig.12 It is a schematic structural diagram of a silicon substrate, a first tunneling oxide passivation contact structure and a wrap-around coating in a specific embodiment; Fig.13 It is a schematic structural diagram of a silicon substrate, a first tunneling oxide passivation contact structure, a first mask layer and a wrap-around coating layer in a specific embodiment; Fig.14A schematic diagram of the structure of a silicon substrate, a first tunneling oxide passivation contact structure, a first mask layer, a bypass coating and an opening in a specific embodiment; Fig.15 A schematic diagram of the structure of a silicon substrate, a first tunneling oxide passivation contact structure, a first mask layer, a second tunneling oxide passivation contact structure and a wrap-around coating in a specific embodiment; Fig.16 A schematic diagram of the structure of a silicon substrate, a first tunneling oxide passivation contact structure, a first mask layer, a second tunneling oxide passivation contact structure, a second mask layer and a wrap-around coating in a specific embodiment; Fig.17 A schematic diagram of the structure of a silicon substrate, a first tunneling oxide passivation contact structure, a first mask layer, a second tunneling oxide passivation contact structure, a second mask layer, a coating layer and a window in a specific embodiment; Fig.18 A schematic diagram of the structure of a silicon substrate, a first tunneling oxide passivation contact structure, a first mask layer, a second tunneling oxide passivation contact structure, a second mask layer and a window in a specific embodiment; Fig.19 The structure diagram of a silicon substrate, a first tunneling oxide passivation contact structure, a first mask layer, a second tunneling oxide passivation contact structure and a second mask layer in a specific embodiment, wherein the silicon substrate has a velvet surface; Fig. 20 A schematic structural diagram of a silicon substrate, a first tunneling oxide passivation contact structure, a second tunneling oxide passivation contact structure and a silicon oxide passivation layer in a specific embodiment; Fig.21 A schematic diagram of the structure of a silicon substrate, a first tunneling oxide passivation contact structure, a second tunneling oxide passivation contact structure, a silicon oxide passivation layer and an aluminum oxide passivation layer in a specific embodiment; Fig. 22 A schematic diagram of the structure of a silicon substrate, a first tunneling oxide passivation contact structure, a second tunneling oxide passivation contact structure, a silicon oxide passivation layer, an aluminum oxide passivation layer, and a silicon nitride passivation layer in a specific embodiment; Fig.23 A schematic diagram of the structure of a back-contact photovoltaic cell provided in the present application in a specific embodiment.

[0030] Reference numerals: 10-substrate, 1-silicon base, 1a-light-receiving side, 1b-backlight side, 101-first velvet surface, 1011-first pyramid structure, 102-second velvet surface, 1021-second pyramid structure, 103-third velvet surface, 1031-third pyramid structure, 11-light-receiving surface, 111-front velvet surface, 12-backlight surface, 121-back velvet surface, 2a-silicon oxide passivation layer, 2b-aluminum oxide passivation layer, 2c-silicon nitride passivation layer, 3-first tunneling oxide passivation contact structure, 3a-opening, 31-first tunneling oxide layer, 32-first doping layer, 4-second tunneling oxide passivation contact structure, 41-second tunneling oxide layer, 42-second doping layer, A34-window, 5a-first mask layer, 5b-second mask layer, 6a-positive metal electrode, 6b-negative metal electrode, 20-wrap coating. DETAILED DESCRIPTION

[0031] 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 are within 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 attached 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 kinds of 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 associated objects before and after are in an "or" relationship. Direction X and direction Y are perpendicular in the drawings of this article.

[0032] In a first aspect, the present application provides some embodiments of a method for preparing a back-contact photovoltaic cell, and the preparation method mainly includes the following contents.

[0033] A substrate is provided, the substrate includes a silicon substrate (also known as a silicon substrate), and the surface of the silicon substrate may include a light-receiving surface and a backlight surface that are arranged opposite to each other in the thickness direction of the substrate. The light-receiving surface refers to the surface used to be directly irradiated by sunlight in the back-contact photovoltaic cell to be formed later, and the backlight surface refers to the surface not used to be directly irradiated by sunlight in the back-contact photovoltaic cell to be formed later, and the backlight surface is mainly irradiated by reflected light in the environment. Before forming the back-contact photovoltaic cell, at least part of the structure of the light-receiving surface of the silicon substrate needs to be processed to reduce the light reflectivity. After forming the back-contact photovoltaic cell, in the process of light passing through the light-receiving surface with relatively low light reflectivity and incident into the silicon substrate, less light is reflected, that is, the silicon substrate can absorb more light, and the silicon substrate can generate more photogenerated carriers (photogenerated holes and photogenerated electrons). Similarly, at least part of the structure of the backlight surface of the silicon substrate also needs to be processed to reduce the light reflectivity, so that the silicon substrate can absorb more light, thereby causing the silicon substrate to generate more photogenerated carriers.

[0034] In some embodiments of the preparation method of the present application, the light-receiving surface can be processed to reduce the light reflectivity of the light-receiving surface.

[0035] In some embodiments of the preparation method of the present application, the backlight surface may be processed to reduce the light reflectivity of the backlight surface.

[0036] In some embodiments of the preparation method of the present application, both the light-receiving surface and the backlight surface can be processed so that the light reflectivity of the light-receiving surface and the light reflectivity of the backlight surface are reduced.

[0037] by Figure 1 Taking the silicon substrate 1 included in the substrate 10 as an example, the surface of the silicon substrate 1 can be the whole or part of the light-receiving surface, and the surface of the silicon substrate 1 can also be the whole or part of the backlight surface.

[0038] make Figure 1 The surface of the silicon substrate 1 shown is subjected to texturing treatment at least twice.

[0039] In some embodiments, three texturing processes may be performed. Figure 1 After the first texturing treatment, the silicon substrate 1 shown in FIG. Figure 2 The first velvet surface 101 shown in the figure includes a plurality of first pyramid structures 1011. Figure 2 After the second texturing treatment, the silicon substrate 1 shown in FIG. Figure 3 The second velvet surface 102 shown in the figure includes a plurality of second pyramid structures 1021. Figure 3 After the third texturing treatment, the silicon substrate 1 shown in FIG. Figure 4The third suede surface 103 shown includes a plurality of third pyramid structures 1031 .

[0040] In some embodiments, during two adjacent texturing processes, the post-texturing process will continue etching on the basis of the velvet surface formed by the previous texturing process. Since the concentration of the texturing liquid used in the post-texturing process is less than that of the previous texturing process, the etching amount of the post-texturing process will be less than that of the previous texturing process, and the etching accuracy of the post-texturing process is higher than that of the previous texturing process. Therefore, the average size of the pyramid structure included in the velvet surface formed by the post-texturing process is smaller than the average size of the pyramid structure included in the velvet surface formed by the previous texturing process, the density of the pyramid structure included in the velvet surface formed by the post-texturing process is greater than the density of the pyramid structure included in the velvet surface formed by the previous texturing process, and the distribution uniformity of the pyramid structure included in the velvet surface formed by the post-texturing process is greater than the distribution uniformity of the pyramid structure included in the velvet surface formed by the previous texturing process.

[0041] In such Figure 1-Figure 4 In the three texturing processes shown, the concentration of the texturing liquid used in the second texturing process is less than that of the texturing liquid used in the first texturing process, the average size of the second pyramid structure 1021 included in the second velvet surface 102 is smaller than the average size of the first pyramid structure 1011 included in the first velvet surface 101, the density of the second pyramid structure 1021 included in the second velvet surface 102 is greater than the density of the first pyramid structure 1011 included in the first velvet surface 101, and the distribution uniformity of the second pyramid structure 1021 included in the second velvet surface 102 is greater than the distribution uniformity of the first pyramid structure 1011 included in the first velvet surface 101. The concentration of the texturing liquid used in the third texturing treatment is lower than the concentration of the texturing liquid used in the second texturing treatment, the average size of the third pyramid structure 1031 included in the third velvet surface 103 is smaller than the average size of the second pyramid structure 1021 included in the second velvet surface 102, the density of the third pyramid structure 1031 included in the third velvet surface 103 is greater than the density of the second pyramid structure 1021 included in the second velvet surface 102, and the distribution uniformity of the third pyramid structure 1031 included in the third velvet surface 103 is greater than the distribution uniformity of the second pyramid structure 1021 included in the second velvet surface 102.

[0042] In some embodiments, please refer to Figure 5As shown, the average size of the first pyramid structure 1011 involves an average height H1 and an average width W1 at the bottom of the pyramid, the average size of the second pyramid structure 1021 involves an average height H2 and an average width W2 at the bottom of the pyramid, and the average size of the third pyramid structure 1031 involves an average height H3 and an average width W3 at the bottom of the pyramid. H1>H2>H3 is satisfied, and W1>W2>W3 is satisfied.

[0043] The average height H1 may be in the range of 1.5µm (micrometer) to 2.5µm (micrometer), and may specifically be 1.5µm, 1.6µm, 1.7µm, 1.8µm, 1.9µm, 2µm, 2.1µm, 2.2µm, 2.3µm, 2.4µm or 2.5µm. The average height H2 may be in the range of 1µm to 2µm, and may specifically be 1µm, 1.1µm, 1.2µm, 1.3µm, 1.4µm, 1.5µm, 1.6µm, 1.7µm, 1.8µm, 1.9µm or 2µm. The average height H3 may be in the range of 0.5µm to 1.5µm, and the average height H3 may specifically be 0.5µm, 0.6µm, 0.7µm, 0.8µm, 0.9µm, 1µm, 1.1µm, 1.2µm, 1.3µm, 1.4µm or 1.5µm.

[0044] In addition, the average width W1 can be in the range of 1.5µm (micrometer) to 3.5µm (micrometer), and the average width W1 can specifically be 1.5µm, 1.6µm, 1.7µm, 1.8µm, 1.9µm, 2µm, 2.1µm, 2.2µm, 2.3µm, 2.4µm, 2.5µm, 2.6µm, 2.7µm, 2.8µm, 2.9µm, 3µm, 3.1µm, 3.2µm, 3.3µm, 3.4µm or 3.5µm. The average width W2 can be in the range of 1µm to 3µm, and the average width W2 can specifically be 1µm, 1.1µm, 1.2µm, 1.3µm, 1.4µm, 1.5µm, 1.6µm, 1.7µm, 1.8µm, 1.9µm, 2µm, 2.1µm, 2.2µm, 2.3µm, 2.4µm, 2.5µm, 2.6µm, 2.7µm, 2.8µm, 2.9µm or 3µm. The average width W3 may be in the range of 0.5µm to 2.5µm, and the average width W3 may specifically be 0.5µm, 0.6µm, 0.7µm, 0.8µm, 0.9µm, 1µm, 1.1µm, 1.2µm, 1.3µm, 1.4µm, 1.5µm, 1.6µm, 1.7µm, 1.8µm, 1.9µm, 2µm, 2.1µm, 2.2µm, 2.3µm, 2.4µm or 2.5µm.

[0045] In some embodiments, if the distribution uniformity is low, the density difference of the pyramid structures included in different parts of the suede surface is large, and if the distribution uniformity is high, the density difference of the pyramid structures included in different parts of the suede surface is small.

[0046] Since the density of the pyramid structure included in the third velvet surface is relatively large and the distribution is relatively uniform, when light is first irradiated to the pyramid structure of the third velvet surface, part of the light can directly enter the silicon substrate, and part of the light is reflected. The reflected light is also relatively easy to irradiate other nearby pyramid structures. Part of the reflected light can directly enter the silicon substrate, and another part of the reflected light continues to be reflected, and another part of the reflected light is still easy to irradiate other nearby pyramid structures. Therefore, multiple reflections can be used to increase the amount of light that can enter the silicon substrate, that is, the third velvet surface can have a lower light reflectivity. The light reflectivity of the silicon substrate of the back-contact photovoltaic cell formed by the preparation method of some embodiments of the present application is low, and the silicon substrate can absorb more light to generate more photogenerated carriers.

[0047] In other embodiments, the surface of the silicon substrate may be subjected to two texturing treatments, four texturing treatments, or other texturing treatments, all of which may have the effect of reducing light reflectivity. The following content of this article mainly describes the third textured surface formed by three texturing treatments as an example.

[0048] After forming the third velvet surface, the substrate can be dried using ozone. On the one hand, the liquid on the surface of the substrate treated by the wet method can be evaporated, thereby drying the surface of the substrate. On the other hand, please refer to Figure 6 As shown, a silicon oxide passivation layer 2a can be formed on the basis of the third velvet surface 103. In detail, during the ozone drying process, the oxygen atoms in the ozone will combine with the silicon atoms nearby within the third velvet surface to form silicon oxide (SiO x ), the formed silicon oxide passivation layer 2a mainly grows from the third velvet surface toward the inside of the silicon substrate 1.

[0049] Since the third velvet surface is not smooth and the density of the pyramid structure included is relatively large, the number of dangling bonds existing in the third velvet surface is relatively large. Dangling bonds refer to unpaired electronic states formed by the valence bonds of a certain atom not fully combined with other atoms on the surface, interface or defect of the crystal. More dangling bonds mean more recombination centers, and the recombination centers are defects that can promote the recombination of electrons and holes by providing intermediate energy levels (defective energy levels), that is, more recombination centers will increase the rate at which photogenerated holes and photogenerated electrons recombine. It can also be said that in order to reduce the light reflectivity, the recombination rate will increase instead. To reduce the recombination rate, in some embodiments of the preparation method of the present application, the substrate after the velvet treatment is dried with ozone. During the ozone drying process, the oxygen atoms in the ozone will combine with the dangling bonds of the silicon atoms to reduce the number of dangling bonds and the number of recombination centers, that is, the silicon oxide passivation layer 2a formed can play a good chemical passivation role on the third velvet surface.

[0050] Since the average size of the pyramid structure included in the third velvet surface is relatively small, the density is relatively large, and the distribution uniformity is relatively large, the number of stress concentration sources of the third velvet surface is relatively small, and the stress concentration peak value of the third velvet surface is relatively small. The number of stress concentration sources of the silicon oxide passivation layer 2a formed on the third velvet surface is also relatively small, and the stress concentration peak value of the silicon oxide passivation layer 2a is relatively small. Therefore, the structural stability of the formed silicon oxide passivation layer 2a is relatively large. In the subsequent preparation process and in the process of actually using the prepared back contact photovoltaic cell sheet, the silicon oxide passivation layer 2a is not easy to be damaged, the silicon-oxygen chemical bond is not easy to break, and it is not easy to form relatively more new hanging bonds on the third velvet surface, that is, the reliability of the chemical passivation effect of the silicon oxide passivation layer 2a is relatively large.

[0051] According to the above content, it can be known that the back-contact photovoltaic cell prepared according to some embodiments of the method for preparing a back-contact photovoltaic cell of the present application can take into account the advantages of lower light reflectivity and lower recombination rate. In detail, the lower light reflectivity allows the silicon substrate to generate more photogenerated electrons and photogenerated holes when absorbing light energy, and the lower recombination rate allows the lifetimes of the photogenerated electrons and photogenerated holes to be longer, so that the prepared back-contact photovoltaic cell has a larger short-circuit current and fill factor, that is, the prepared back-contact photovoltaic cell has a larger photoelectric conversion efficiency.

[0052] Optionally, during the first texturing process, the first texturing liquid used in the first texturing process includes an alkaline substance having a concentration in the range of 1.5Wt% to 3Wt%. The concentration of the alkaline substance may specifically be 1.5Wt%, 1.6Wt%, 1.7Wt%, 1.8Wt%, 1.9Wt%, 2Wt%, 2.1Wt%, 2.2Wt%, 2.3Wt%, 2.4Wt%, 2.5Wt%, 2.6Wt%, 2.7Wt%, 2.8Wt%, 2.9Wt% or 3Wt%.

[0053] Optionally, during the first texturing process, the first texturing liquid used in the first texturing process includes a texturing additive having a concentration in the range of 1Wt% to 1.5Wt%. The concentration of the texturing additive may specifically be 1Wt%, 1.1Wt%, 1.2Wt%, 1.3Wt%, 1.4Wt% or 1.5Wt%.

[0054] Optionally, during the first texturing treatment, the time for immersing the substrate in the first texturing liquid can be in the range of 100 seconds (s) to 250 seconds (s), and the time for immersing the substrate in the first texturing liquid can specifically be 100s, 110s, 120s, 130s, 140s, 150s, 160s, 170s, 180s, 190s, 200s, 210s, 220s, 240s or 250s.

[0055] Optionally, during the first texturing treatment, the temperature of the first texturing liquid is in the range of 75 degrees Celsius (℃) to 90 degrees Celsius (℃), and the temperature of the first texturing liquid can specifically be 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃ or 90℃.

[0056] Optionally, during the second texturing process, the second texturing liquid used in the second texturing process includes an alkaline substance with a concentration in the range of 0.9Wt% to 1.3Wt%. The concentration of the alkaline substance may specifically be 0.9Wt%, 1Wt%, 1.1Wt%, 1.2Wt% or 1.3Wt%.

[0057] Optionally, during the second texturing process, the second texturing liquid used in the second texturing process includes a texturing additive having a concentration in the range of 0.7Wt% to 0.9Wt%. The concentration of the texturing additive may specifically be 0.7Wt%, 0.75Wt%, 0.8Wt%, 0.85Wt% or 0.9Wt%.

[0058] Optionally, during the second texturing treatment, the time for immersing the substrate in the second texturing liquid can be in the range of 200s to 300s, and the time for immersing the substrate in the second texturing liquid can specifically be 200s, 210s, 220s, 230s, 240s, 250s, 260s, 270s, 280s, 290s or 300s.

[0059] Optionally, during the second texturing treatment, the temperature range of the second texturing liquid can refer to the temperature range of the first texturing liquid, and the specific temperature value of the second texturing liquid can refer to the specific temperature value of the first texturing liquid, which will not be repeated here.

[0060] Optionally, during the third texturing treatment, the third texturing liquid used in the third texturing treatment includes an alkaline substance with a concentration in the range of 0.5Wt% to 0.7Wt%. The concentration of the alkaline substance may specifically be 0.5Wt%, 0.55Wt%, 0.6Wt%, 0.65Wt% or 0.7Wt%.

[0061] Optionally, during the third texturing treatment, the third texturing liquid used in the third texturing treatment includes a texturing additive having a concentration in the range of 0.2Wt% to 0.5Wt%. The concentration of the texturing additive may specifically be 0.2Wt%, 0.25Wt%, 0.3Wt%, 0.35Wt%, 0.4Wt%, 0.45Wt% or 0.5Wt%.

[0062] Optionally, during the third texturing treatment, the time for immersing the substrate in the third texturing liquid can be in the range of 80s to 150s, and the time for immersing the substrate in the third texturing liquid can specifically be 80s, 90s, 100s, 110s, 120s, 130s, 140s or 150s.

[0063] Optionally, during the third texturing treatment, the temperature range of the third texturing liquid can refer to the temperature range of the first texturing liquid, and the specific temperature value of the third texturing liquid can refer to the specific temperature value of the first texturing liquid, which will not be repeated here.

[0064] In some embodiments, "wt%" represents weight percentage, the alkaline substance may include potassium hydroxide (KOH) and / or sodium hydroxide (NaOH), and the texturing additive may include at least one of polyvinyl alcohol, isopropyl alcohol, ethanolamine, ethylenediamine, sodium lauryl sulfate, and polyethylene glycol.

[0065] In some embodiments, before the first texturing treatment, the substrate may be pre-cleaned to remove impurities, oxides or organic matter on the surface of the substrate. The pre-cleaning uses a hydrofluoric acid solution with a volume concentration in the range of 8% to 20%, and the concentration may be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%. The pre-cleaning temperature is in the range of 10°C to 30°C, and the temperature may be 10°C, 15°C, 20°C, 25°C or 30°C. The pre-cleaning time is in the range of 15s to 90s, and the time may be 15s, 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s, 60s, 65s, 70s, 75s, 80s, 85s or 90s.

[0066] In some embodiments, after the third texturing treatment and before drying with ozone, the substrate may be post-cleaned using a mixed solution of potassium hydroxide and hydrogen peroxide (H2O2) to remove impurities and organic matter on the surface of the substrate.

[0067] In some embodiments, after post-cleaning and before ozone drying, the substrate can be subjected to hydrophobic cleaning using a mixed solution including hydrochloric acid and hydrofluoric acid. Hydrochloric acid is used to remove metal ions, and hydrofluoric acid is used to make the substrate surface hydrophobic, thereby making the adsorbents on the substrate surface more easily detached from the substrate surface. Hydrochloric acid and hydrofluoric acid can also be used to neutralize the alkaline substance used previously.

[0068] In some embodiments, after the hydrophobic cleaning and before the ozone drying, the substrate can be slowly pulled to dehydrate the substrate. The main technical principle of slow pulling dehydration is to control the rate at which the substrate is slowly pulled from the liquid, and to achieve uniform drying by the surface tension of the liquid and the gravity to avoid water stains or contaminants. The pulling speed of slow pulling dehydration can be in the range of 0.1 mm / s to 2 mm / s, and the pulling speed can be specifically 0.1 mm / s, 0.5 mm / s, 1 mm / s, 1.5 mm / s or 2 mm / s.

[0069] Optionally, the method of drying the substrate using ozone may satisfy at least one of setting a, setting b and setting c.

[0070] In setting a, the drying temperature can be within the range of 85°C to 120°C, and the drying temperature can be specifically 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C. As can be seen from the above, in the process of drying the substrate with ozone, a silicon oxide passivation layer will also be formed on the third velvet surface. If the drying temperature is within the range of 85°C to 120°C, the temperature for forming the silicon oxide passivation layer is relatively low, the thermal stress generated in the formed silicon oxide passivation layer is relatively small, the structural stability of the silicon oxide passivation layer is relatively high, and it is not easy to generate many new dangling bonds later, that is, the reliability of the chemical passivation effect of the silicon oxide passivation layer is relatively high.

[0071] In setting b, ozone with a flow rate in the range of 100 sccm to 1000 sccm can be used, where sccm means standard cubic centimeters per minute. The flow rate of ozone can be specifically 100 sccm, 200 sccm, 300 sccm, 400 sccm, 500 sccm, 600 sccm, 700 sccm, 800 sccm, 900 sccm or 1000 sccm. Ozone with a flow rate in the range of 100 sccm to 1000 sccm can not only meet the drying requirements, but also form the required silicon oxide passivation layer with good chemical passivation.

[0072] In setting c, the drying time can be within the range of 5 minutes (min) to 20 minutes (min), and the drying time can be specifically 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min, 15min, 16min, 17min, 18min, 19min or 20min. The drying time within the range of 5min to 20min can not only meet the drying needs, but also form the required silicon oxide passivation layer with good chemical passivation effect.

[0073] After drying the substrate with ozone, atomic layer deposition (ALD) is used to deposit Figure 7 An aluminum oxide passivation layer 2b is deposited on the silicon oxide passivation layer 2a, wherein the chemical formula of aluminum oxide can be Al x O y. The aluminum oxide passivation layer 2b formed by atomic layer deposition is relatively dense, that is, the aluminum oxide passivation layer 2b has the advantage of strong structural stability. In the process of depositing the aluminum oxide passivation layer 2b on the silicon oxide passivation layer 2a, an aluminum-oxygen-silicon chemical bond (Al-O-Si) can be formed between aluminum oxide and silicon oxide. The bonding force of this chemical bond is relatively strong, that is, the bonding force between the silicon oxide passivation layer 2a and the aluminum oxide passivation layer 2b is strong, that is, the aluminum oxide passivation layer 2b can provide good physical support for the silicon oxide passivation layer 2a, so that the structural stability of the silicon oxide passivation layer 2a is higher. In the subsequent annealing process, the structural stability of the aluminum oxide passivation layer 2b is not easy to decrease, so that in the subsequent annealing process, the high structural stability of the silicon oxide passivation layer 2a can be maintained.

[0074] After forming the aluminum oxide passivation layer, plasma enhanced chemical vapor deposition (PECVD) can also be used to deposit the aluminum oxide passivation layer. Figure 8 A silicon nitride passivation layer 2c is deposited on the aluminum oxide passivation layer 2b, wherein the chemical formula of silicon nitride can be SiN x . The silicon nitride passivation layer 2c has a good anti-reflection effect or anti-reflection effect, that is, the silicon nitride passivation layer 2c has a lower light reflectivity, so that the silicon substrate can absorb more light, so that the silicon substrate can generate more photogenerated carriers. In the subsequent annealing process, the silicon nitride passivation layer 2c will also release hydrogen ions, and the hydrogen ions can also combine with the dangling bonds of the suede to form a good chemical passivation effect. If the number of hydrogen ions is too large, it is easy to form hydrogen pores near the suede and near the silicon oxide passivation layer 2a, which is easy to cause hydrogen explosion problems, that is, it is easy to damage the suede and the silicon oxide passivation layer 2a, which is easy to cause the suede to deteriorate and the chemical passivation effect of the silicon oxide passivation layer 2a to deteriorate. It can be seen from the above that before the silicon nitride passivation layer 2c is formed, the oxygen atoms in the ozone have been combined with the dangling bonds of the suede, that is, the chemical passivation effect is achieved in advance, and it is not too dependent on the chemical passivation effect of the hydrogen ions in the silicon nitride passivation layer 2c to be formed later. In addition, the aluminum oxide passivation layer 2b acts as a buffer layer, and the aluminum oxide passivation layer 2b can absorb a portion of hydrogen ions. Moreover, the aluminum oxide passivation layer 2b itself is relatively dense, and has a certain hindering effect on the diffusion of hydrogen ions, that is, the aluminum oxide passivation layer 2b can reduce the number of hydrogen ions that can diffuse to the velvet and silicon oxide passivation layers, so as to reduce the possibility of hydrogen explosion problems, thereby making the velvet and silicon oxide passivation layers 2a less likely to be damaged. Therefore, the back-contact photovoltaic cell prepared by the preparation method of some embodiments of the present application can well and durably maintain the advantages of lower light reflectivity and lower recombination rate, that is, the prepared back-contact photovoltaic cell can well and durably maintain the advantages of greater photoelectric conversion efficiency.

[0075] Before implementing the first texturing process described above, please refer to Fig. 9 As shown, first tunneling oxide passivation contact structures 3 and second tunneling oxide passivation contact structures 4 that are alternately and spaced apart may also be formed on the backlight side 1 b of the silicon substrate 1 .

[0076] Please refer to Fig. 9 As shown, the first tunneling oxide passivation contact structure 3 may include a first tunneling oxide layer 31 and a first doping layer 32. The first tunneling oxide layer 31 is deposited on the backlight surface 12 of the silicon substrate 1 and is located between the backlight surface 12 of the silicon substrate 1 and the first doping layer 32.

[0077] Please refer to Fig. 9 As shown, the first tunnel oxide layer 31 may include silicon oxide (SiO X )、Silicon Nitride(SiN X ) and at least one of silicon oxynitride (SiON). The thickness dimension (dimension along direction Y) of the first tunneling oxide layer 31 can be in the range of 0.5nm~3nm, and the thickness dimension can specifically be 0.5nm, 1nm, 1.5nm, 2nm, 2.5nm or 3nm. In some cases, the first tunneling oxide layer 31 can also be referred to as the first tunneling layer. After being prepared into the desired back contact photovoltaic cell, the photogenerated carriers (such as photogenerated holes) generated by the silicon substrate 1 can tunnel through the first tunneling oxide layer 31 by utilizing the tunneling effect and migrate to the first doping layer 32, so that the first doping layer 32 collects the photogenerated holes.

[0078] Please refer to Fig. 9 As shown, the first doping layer 32 may be doped with at least one P-type element (a third main group element in the periodic table of chemical elements), such as boron, aluminum, gallium, and other P-type elements. The first doping layer 32 may include at least one of polycrystalline silicon, amorphous silicon, and microcrystalline silicon. The first doping layer 32 is in ohmic contact with the positive metal electrode during a subsequent metallization process.

[0079] Also, please refer to Fig. 9 As shown, the second tunneling oxide passivation contact structure 4 may include a second tunneling oxide layer 41 and a second doping layer 42. The second tunneling oxide layer 41 is deposited on the backlight surface 12 of the silicon substrate 1 and is located between the backlight surface 12 of the silicon substrate 1 and the second doping layer 42.

[0080] Please refer to Fig. 9 As shown, the second tunnel oxide layer 41 may include silicon oxide (SiO X )、Silicon Nitride(SiN X) and at least one of silicon oxynitride (SiON). The thickness of the second tunneling oxide layer 41 can be in the range of 0.5nm to 3nm, and the thickness can specifically be 0.5nm, 1nm, 1.5nm, 2nm, 2.5nm or 3nm. In some cases, the second tunneling oxide layer 41 can also be referred to as a second tunneling layer. After being prepared into the desired back contact photovoltaic cell, the photogenerated carriers (such as photogenerated electrons) generated by the silicon substrate 1 can tunnel through the second tunneling oxide layer 41 by utilizing the tunneling effect and migrate to the second doping layer 42, so that the second doping layer 42 collects the photogenerated electrons.

[0081] Please refer to Fig. 9 As shown, the second doping layer 42 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. The second doping layer 42 may include at least one of polycrystalline silicon, amorphous silicon and microcrystalline silicon. The second doping layer 42 is in ohmic contact with the negative metal electrode in the subsequent metallization process.

[0082] In some embodiments, please refer to Fig. 9 As shown, the silicon substrate 1 can 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. If the silicon substrate 1 is doped with N-type elements, the back-contact photovoltaic cell to be prepared is an N-type back-contact photovoltaic cell. Accordingly, the concentration of the N-type element doped in the second doping layer 42 is greater than the concentration of the N-type element doped in the silicon substrate 1. Under this setting, a high-low junction (N + / N), the high-low junction promotes the migration of photogenerated electrons from the silicon substrate 1 to the second doping layer 42.

[0083] In other embodiments, please refer to Fig. 9 As shown, the silicon substrate 1 can be doped with at least one P-type element (the third main group element in the periodic table of chemical elements) such as boron, aluminum, gallium and other P-type elements. If the silicon substrate 1 is doped with N-type elements, the back-contact photovoltaic cell to be prepared is a P-type back-contact photovoltaic cell. Accordingly, the concentration of the P-type element doped in the first doping layer 32 is greater than the concentration of the P-type element doped in the silicon substrate 1. Under this setting, a high-low junction (P + / P), the high-low junction promotes the migration of photogenerated holes from the silicon substrate 1 to the first doped layer 32.

[0084] After forming the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4, and before performing the first texturing process described above, please refer to Fig.10As shown, a mask layer is formed on at least the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4, for example, a first mask layer 5a is arranged on the first tunneling oxide passivation contact structure 3, and a second mask layer 5b is arranged on the second tunneling oxide passivation contact structure 4. The mask layer (including the first mask layer 5a and the second mask layer 5b) can protect the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4 from being corroded and damaged by the alkaline substances or alkaline liquids used in the subsequent texturing treatment and post-cleaning.

[0085] The mask layer forming method may include depositing silicon oxide (SiO 2 ) on the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4 by PECVD. X ) or silicon nitride (SiN X Alternatively, silicon oxide (SiO X ) or silicon nitride (SiN X ). Alternatively, a thermal diffusion process is used for oxidation treatment to form a silicon glass layer on the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4. Alternatively, a mask is formed using a photoresist. The above masking methods can protect the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4 from being corroded and damaged during the subsequent wet processing.

[0086] Please refer to Fig. 9 and Fig.10 As shown, after forming the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4, and before the texturing treatment, it is also necessary to form a window A34 between the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4, and the window A34 is used to isolate the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4 to reduce the recombination rate. Among them, the backlight surface 12 of the silicon substrate 1 is partially exposed by the window A34. After the texturing treatment is implemented, the portion of the backlight surface 12 of the silicon substrate 1 exposed by the window A34 can form a velvet surface (not shown in the figure, it can also be called a back velvet surface), and the shape of the velvet surface exposed by the window A34 can refer to Figure 4 The third velvet surface 103 shown, the velvet surface exposed by the window A34 can increase the light located on the backlight side 1b that can be absorbed by the silicon substrate 1. Accordingly, a silicon oxide passivation layer will be formed on the velvet surface exposed by the window A34 later.

[0087] In other embodiments (not shown in the figures), no window may be provided between the first tunneling oxide passivation contact structure and the second tunneling oxide passivation contact structure. For example, intrinsic amorphous silicon may be provided between the first tunneling oxide passivation contact structure and the second tunneling oxide passivation contact structure, and the intrinsic amorphous silicon may also serve to isolate the first tunneling oxide passivation contact structure and the second tunneling oxide passivation contact structure.

[0088] Before ozone drying, the mask layer needs to be removed by acid washing or laser removal because there may be defects, impurities or corrosive liquids on the surface of the mask layer.

[0089] In the related art, if an aluminum oxide passivation layer is formed directly on the first doping layer and the second doping layer, since the aluminum oxide passivation layer carries a negative charge, the aluminum oxide passivation layer can provide a good field passivation effect for the second doping layer for collecting electrons, but a built-in electric field that is not conducive to increasing the hole lifetime will be formed between the aluminum oxide passivation layer and the first doping layer for collecting holes. In the related art, if a silicon nitride passivation layer is formed directly on the first doping layer and the second doping layer, although the silicon nitride passivation layer has a good chemical passivation effect, it is easy to produce a hydrogen explosion problem. Therefore, after forming the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4, and after implementing the above-mentioned texturing treatment, the substrate is dried using ozone. In this process, a silicon oxide passivation layer is also formed on the first tunneling oxide passivation contact structure 3, and a silicon oxide passivation layer is formed on the second tunneling oxide passivation contact structure 4. The silicon oxide passivation layer is mainly formed by inward growth on the surface of the first doping layer 32, and the silicon oxide passivation layer is mainly formed by inward growth on the surface of the second doping layer 42. Since the surfaces of the first doping layer 32 and the second doping layer 42 are not velvet, the formed silicon oxide passivation layer does not have a velvet surface. However, the silicon oxide passivation layer without a velvet surface can also provide good chemical passivation for the first doping layer 32 and the second doping layer 42 without considering the incompatibility of field passivation and hydrogen explosion problems.

[0090] In other embodiments, the above-described texturing process can be used on a silicon substrate to form a desired velvet surface, an ozone drying method can be used to form a silicon oxide passivation layer on the velvet surface, an aluminum oxide passivation layer can be deposited on the silicon oxide passivation layer by ALD, and a silicon nitride passivation layer can be deposited on the aluminum oxide passivation layer by PECVD. After that, a laser can be used to remove a local structure of the stacked structure including the silicon oxide passivation layer, the aluminum oxide passivation layer, and the silicon nitride passivation layer, so that the stacked structure including the silicon oxide passivation layer, the aluminum oxide passivation layer, and the silicon nitride passivation layer is patterned, and a plurality of windows that can expose a local part of the surface of the silicon substrate are formed accordingly, and the part of the surface of the silicon substrate exposed by the window can be alkali polished. A first tunneling oxide passivation contact structure can be formed in some windows, and a second tunneling oxide passivation contact structure can be formed in some other windows.

[0091] The following content of this article mainly introduces a relatively specific embodiment of the preparation method of the back-contact photovoltaic cell, and the preparation method may include the following content.

[0092] Please refer to Fig.11 As shown, a substrate 10 is provided, and the substrate mainly refers to the structure before being prepared into a photovoltaic cell sheet that can be put into use. Fig.11 The substrate 10 shown currently includes a silicon substrate 1 (e.g., an N-type silicon substrate). The direction Y may represent the direction from the backlight side 1b of the silicon substrate 1 to the light receiving side 1a, or the direction Y may represent the direction from the backlight surface 12 of the silicon substrate 1 to the light receiving surface 11. In addition, both the light receiving surface 11 and the backlight surface 12 of the silicon substrate 1 need to be alkali polished.

[0093] Using LPCVD Fig.11 The backlight side 1b of the silicon substrate 1 shown in FIG. 1 is sequentially deposited with a first tunnel oxide layer and a first intrinsic layer, and then a P-type element is diffused into the first intrinsic layer by a diffusion process to form a first doped layer, thereby forming a Fig.12 The first tunneling oxide passivation contact structure 3 is shown.

[0094] Please refer to Fig.13 As shown, a first mask layer 5 a is formed on the first tunneling oxide passivation contact structure 3 .

[0095] Please refer to Fig.14 As shown, the laser removes the local structure of the first tunneling oxide passivation contact structure 3 and the local structure of the first mask layer 5a, so that the first tunneling oxide passivation contact structure 3 and the first mask layer 5a are both patterned, thereby forming an opening 3a.

[0096] Using LPCVD Fig.14 A second tunnel oxide layer and a second intrinsic layer are sequentially deposited on the backlight side of the silicon substrate 1 shown in FIG. 1 , and then an N-type element is diffused into the second intrinsic layer by a diffusion process to form a second doped layer, thereby forming a Fig.15 The second tunneling oxide passivation contact structure 4 is shown.

[0097] Please refer to Fig.16 As shown, a second mask layer 5 b is formed on the second tunneling oxide passivation contact structure 4 .

[0098] Please refer to Fig.17 As shown, laser removes the local structure of the first tunneling oxide passivation contact structure 3, the local structure of the first mask layer 5a, the local structure of the second tunneling oxide passivation contact structure 4, and the local structure of the second mask layer 5b, so as to pattern the first tunneling oxide passivation contact structure 3, the first mask layer 5a, the second tunneling oxide passivation contact structure 4 and the second mask layer 5b, thereby forming window A34.

[0099] The silicon substrate 1 is pickled on one side by a chain machine to remove the coating layer 20 on the light-receiving side of the silicon substrate 1 (an incidental structure on the light-receiving side formed in the process of forming the tunneling oxide layer and the intrinsic layer by LPCVD). After pickling, the following can be formed: Fig.18 The structure shown is for Fig.18 The structure shown implements the pre-cleaning described above.

[0100] Please refer to Fig.19 As shown, the three-time texturing process described above is performed to form a front velvet surface 111 on the light-receiving surface of the silicon substrate 1 and a back velvet surface 121 on a part of the backlight surface of the silicon substrate 1. The front velvet surface 111 and the back velvet surface 121 may include Figure 4 The third pile surface 103 and the corresponding plurality of third pyramid structures 1031 are shown.

[0101] against Fig.19 The structure shown is subjected to the above-described post-cleaning, hydrophobic cleaning and slow pull-up dehydration treatments. The acid solution used in the hydrophobic cleaning can remove the first mask layer 5a and the second mask layer 5b, or the first mask layer 5a and the second mask layer 5b can be removed using an acid solution prepared with other acidic substances (e.g., nitric acid, sulfuric acid), or the first mask layer 5a and the second mask layer 5b can be removed using a laser.

[0102] Ozone drying to form Fig. 20 A silicon oxide passivation layer 2a is shown.

[0103] exist Fig. 20 Based on the structure shown, double-sided deposition using ALD is performed as Fig.21 Aluminum oxide passivation layer 2b is shown.

[0104] exist Fig.21 Based on the structure shown, double-sided deposition using PECVD is performed as Fig. 22 A silicon nitride passivation layer 2c is shown.

[0105] exist Fig. 22 Based on the structure shown, the Fig.23 The ohmic contact shown is made to the positive metal electrode 6a of the first tunneling oxide passivation contact structure 3, and the Fig.23 The ohmic contact is shown to the negative metal electrode 6 b of the second tunneling oxide passivation contact structure 4 .

[0106] Among them, the method for forming the metal electrode 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. 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 can be used, and if used to form a positive metal electrode, a silver-aluminum slurry can be used. The slurry may also include other additives such as glass frit, solvent, modifier, non-volatile polymer or resin.

[0107] In other embodiments, the method for forming the metal electrode may also include laser transfer, electroplating, inkjet or sputtering.

[0108] In the second aspect, the present application provides some embodiments of a back contact photovoltaic cell (BC Solar Cell), which is prepared by the preparation method of the back contact photovoltaic cell described above, so the back contact photovoltaic cell can take into account the advantages of lower light reflectivity and lower recombination rate, and the back contact photovoltaic cell can have a higher photoelectric conversion efficiency. The relevant specific technical effects have been described above and will not be repeated here.

[0109] Please refer to Fig.23 As shown, both sides of the back-contact photovoltaic cell sheet along the direction Y are provided with a velvet surface. The pyramid structure of the velvet surface of the back-contact photovoltaic cell sheet can have a set height H, and the range of the height H can refer to the range of the average height H3 of the third velvet surface described above (for example, 0.5µm~1.5µm), and the specific value of the height H can refer to the specific value of the average height H3 of the third velvet surface described above (for example, 0.5µm, 0.6µm, 0.7µm, 0.8µm, 0.9µm, 1µm, 1.1µm, 1.2µm, 1.3µm, 1.4µm or 1.5µm). The bottom of the pyramid structure of the velvet surface of the back contact photovoltaic cell may have a set width W, the range of the width W may refer to the range of the average width W3 of the bottom of the third velvet surface described above (for example, 0.5µm~2.5µm), and the specific value of the width W may refer to the specific value of the average width W3 of the third velvet surface described above (for example, 0.5µm, 0.6µm, 0.7µm, 0.8µm, 0.9µm, 1µm, 1.1µm, 1.2µm, 1.3µm, 1.4µm, 1.5µm, 1.6µm, 1.7µm, 1.8µm, 1.9µm, 2µm, 2.1µm, 2.2µm, 2.3µm, 2.4µm or 2.5µm).

[0110] In addition, the light reflectivity of the back-contact photovoltaic cell can be in the range of 6% to 9%, and the light reflectivity of the back-contact photovoltaic cell can specifically be 6%, 6.5%, 7%, 7.5%, 8%, 8.5% or 9%. The light reflectivity of the back-contact photovoltaic cell is relatively low, and the silicon substrate can absorb more light to generate more photogenerated carriers.

[0111] Optionally, the back contact photovoltaic cell comprises Fig.23 The silicon substrate 1 and the laminated structure shown, the silicon substrate 1 has a velvet surface, the laminated structure includes a silicon oxide passivation layer 2a, an aluminum oxide passivation layer 2b and a silicon nitride passivation layer 2c, the silicon oxide passivation layer 2a is arranged on the velvet surface, and the aluminum oxide passivation layer 2b is located between the silicon oxide passivation layer 2a and the silicon nitride passivation layer 2c. According to the above description, the silicon oxide passivation layer 2a can provide a good chemical passivation effect for the velvet surface, the aluminum oxide passivation layer 2b can enhance the structural stability of the silicon oxide passivation layer 2a, and the silicon nitride passivation layer 2c can reduce the light reflectivity, which will not be repeated here.

[0112] It can be seen from the above content that during the ozone drying process, the silicon oxide passivation layer 2 a is mainly formed by the velvet surface of the silicon substrate 1 growing toward the inside of the silicon substrate 1 .

[0113] In addition, the portion of the silicon oxide passivation layer 2a formed on the velvet surface of the silicon substrate 1 also has a velvet surface. Correspondingly, the aluminum oxide passivation layer 2b and the silicon nitride passivation layer 2c also have a velvet surface, that is, the stacked structure includes multiple stacked velvet surfaces, which can better reduce the light reflectivity.

[0114] Optionally, the back contact photovoltaic cell further includes a tunnel oxide passivating contact structure (Tunnel Oxide Passivating Contacts, TOPCon), for example Fig.23 The first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4 are shown, and the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4 are both located on the backlight side of the silicon substrate 1, and the silicon oxide passivation layer 2a is also arranged on the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4. It can be seen from the above content that the silicon oxide passivation layer 2a can provide good chemical passivation for the first tunneling oxide passivation contact structure 3 and the second tunneling oxide passivation contact structure 4.

[0115] Fig.23 The back contact photovoltaic cell shown can also be called a TBC photovoltaic cell, the full name of which is a photovoltaic cell formed by combining a tunneling oxide passivation contact structure (TOPCon) with a back contact structure (BC), also known as a POLO-BC photovoltaic cell.

[0116] Optionally, the thickness of the silicon oxide passivation layer 2a may be in the range of 1 nm to 10 nm, specifically 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 9 nm or 10 nm.

[0117] Optionally, the thickness of the aluminum oxide passivation layer 2b may be in the range of 1 nm to 10 nm, specifically 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 9 nm or 10 nm.

[0118] Optionally, the thickness of the silicon nitride passivation layer 2c may be in the range of 40 nm to 100 nm, specifically 40 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.

[0119] Fig.23 The back-contact photovoltaic cell shown also includes a positive metal electrode 6a and a negative metal electrode 6b located on the backlight side, the positive metal electrode 6a is in ohmic contact with the first doped layer (not shown in the figure) of the first tunneling oxide passivation contact structure 3, and the first doped layer can be called a P-type doped polysilicon layer, and the negative metal electrode 6b is in ohmic contact with the second doped layer (not shown in the figure) of the second tunneling oxide passivation contact structure 4, and the second doped layer can be called an N-type doped polysilicon layer.

[0120] In this article, "doped with N-type elements" mainly means that the chemical elements of the doped impurities include N-type elements. Similarly, in this article, "doped with P-type elements" mainly means that the chemical elements of the doped impurities include P-type elements.

[0121] In a third aspect, the present application provides some embodiments of a back-contact photovoltaic cell assembly, which may include a laminate and a frame, wherein the frame is installed at the edge of the laminate. The laminate may include a stacked photovoltaic glass, a first encapsulation film, a battery string, a second encapsulation film, and a backplane. Alternatively, the laminate may include 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 may be formed by electrically connecting a plurality of the back-contact photovoltaic cells described above, and the number of battery strings may be one, two, or more.

[0122] 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 back contact photovoltaic cell, characterized in that: The preparation method comprises: Providing a substrate, the substrate comprising a silicon substrate; Subjecting at least a portion of the surface structure of the silicon substrate to at least two texturing treatments to form a velvet surface, wherein in two adjacent texturing treatments, the concentration of the texturing liquid used in the latter texturing treatment is less than the concentration of the texturing liquid used in the former texturing treatment; The substrate is dried by ozone to form a silicon oxide passivation layer at least on the suede surface.

2. The method for preparing a back-contact photovoltaic cell according to claim 1, characterized in that: The method of drying the substrate using ozone satisfies at least one of the following settings: Setting a: Keep the drying temperature within the range of 85℃~120℃; Setting b: using ozone with a flow rate in the range of 100 sccm to 1000 sccm; Setting c: Make the drying time within the range of 5min~20min.

3. The method for preparing a back contact photovoltaic cell according to claim 1, characterized in that: After drying the substrate with ozone, the preparation method further comprises: An aluminum oxide passivation layer is first deposited on the silicon oxide passivation layer by atomic layer deposition, and then a silicon nitride passivation layer is deposited on the aluminum oxide passivation layer by plasma enhanced chemical vapor deposition.

4. The method for preparing a back-contact photovoltaic cell according to any one of claims 1 to 3, characterized in that: Before the texturing process, the preparation method further comprises: A first tunneling oxide passivation contact structure and a second tunneling oxide passivation contact structure are formed alternately and spaced apart on the backlight side of the silicon substrate.

5. The method for preparing a back contact photovoltaic cell according to claim 4, characterized in that: Before the texturing process, the preparation method further comprises: A mask layer is formed at least on the first tunneling oxide passivation contact structure and the second tunneling oxide passivation contact structure.

6. The method for preparing a back contact photovoltaic cell according to claim 4, characterized in that: The method of drying the substrate using ozone further includes: forming a silicon oxide passivation layer on the first tunneling oxide passivation contact structure, and forming a silicon oxide passivation layer on the second tunneling oxide passivation contact structure.

7. The method for preparing a back contact photovoltaic cell according to claim 4, characterized in that: Before the texturing process, a window is formed between the first tunneling oxide passivation contact structure and the second tunneling oxide passivation contact structure, wherein a portion of the backlight surface of the silicon substrate is exposed by the window.

8. The method for preparing a back-contact photovoltaic cell according to any one of claims 1 to 3, characterized in that: The method of at least two texturing processes comprises: The surface of the silicon substrate is subjected to a first texturing treatment, wherein a first texturing liquid used in the first texturing treatment comprises an alkaline substance having a concentration in the range of 1.5Wt% to 3Wt%, and / or the first texturing liquid used in the first texturing treatment comprises a texturing additive having a concentration in the range of 1Wt% to 1.5Wt%.

9. The method for preparing a back-contact photovoltaic cell according to any one of claims 1 to 3, characterized in that: The method of at least two texturing processes comprises: The surface of the silicon substrate is subjected to a second texturing treatment, and a second texturing liquid used in the second texturing treatment includes an alkaline substance with a concentration in the range of 0.9Wt%~1.3Wt%, and / or the second texturing liquid used in the second texturing treatment includes a texturing additive with a concentration in the range of 0.7Wt%~0.9Wt%.

10. The method for preparing a back-contact photovoltaic cell according to any one of claims 1 to 3, characterized in that: The method of at least two texturing processes comprises: The surface of the silicon substrate is subjected to a third texturing treatment, and the third texturing liquid used in the third texturing treatment includes an alkaline substance with a concentration in the range of 0.5Wt%~0.7Wt%, and / or the third texturing liquid used in the third texturing treatment includes a texturing additive with a concentration in the range of 0.2Wt%~0.5Wt%.

11. A back contact photovoltaic cell, characterized in that: The back-contact photovoltaic cell sheet is prepared by the method for preparing a back-contact photovoltaic cell sheet according to any one of claims 1 to 10.

12. The back contact photovoltaic cell according to claim 11, characterized in that: The pyramid structure of the velvet surface of the back contact photovoltaic cell has a set height H, which satisfies 0.5µm≤H≤1.5µm; And / or, the base of the pyramid structure of the velvet surface of the back contact photovoltaic cell has a set width W, which satisfies 0.5µm≤W≤2.5µm.

13. The back contact photovoltaic cell according to claim 11, characterized in that: The back contact photovoltaic cell comprises a silicon substrate and a stacked structure, wherein the silicon substrate has a velvet surface, and the stacked structure comprises a silicon oxide passivation layer, an aluminum oxide passivation layer and a silicon nitride passivation layer, wherein the silicon oxide passivation layer is arranged on the velvet surface, and the aluminum oxide passivation layer is located between the silicon oxide passivation layer and the silicon nitride passivation layer.

14. The back contact photovoltaic cell according to claim 13, characterized in that: The back-contact photovoltaic cell further comprises a tunneling oxide passivation contact structure, which is located on the backlight side of the silicon substrate, and the silicon oxide passivation layer is also disposed on the tunneling oxide passivation contact structure.

15. A back contact photovoltaic cell assembly, characterized in that: The back-contact photovoltaic cell assembly comprises at least one cell string, and the cell string is formed by electrically connecting the back-contact photovoltaic cell sheets according to any one of claims 11 to 14.

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