Back contact photovoltaic cell and preparation method thereof

Abstract

The invention relates to a back contact photovoltaic cell and a preparation method thereof, and relates to the field of photovoltaic technology. The preparation method comprises the steps that a silicon substrate is provided, the backlight surface of the silicon substrate is provided with a first to-be-diffused region and a second to-be-diffused region which are arranged at an interval, a mask layer is formed on the backlight surface and comprises a first to-be-removed part and a second to-be-removed part which are arranged at an interval, the first to-be-removed part is removed through laser, and the second to-be-removed part is removed; and removing the first to-be-removed part by using laser to form a first opening exposing the first to-be-diffused region, diffusing to the first to-be-diffused region to form a first diffusion layer, removing the second to-be-removed part by using laser to form a second opening exposing the second to-be-diffused region, and diffusing to the second to-be-diffused region to form a second diffusion layer spaced from the first diffusion layer. The service life of carriers generated by the back contact photovoltaic cell prepared by the preparation method is relatively long, so that the photoelectric conversion efficiency of the back contact photovoltaic cell is relatively high.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic cells, and particularly relates to a back-contact photovoltaic cell 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 disposed on the light-back side of the cell. The light-receiving surface (also known as the front surface or the front side) of the back-contact photovoltaic cell has a relatively large area. Therefore, the photoelectric conversion efficiency of the back-contact photovoltaic cell is relatively large. Since the photoelectric conversion efficiency of the back-contact photovoltaic cell is also positively correlated with the carrier lifetime, and in the related art, the carrier lifetime of the back-contact photovoltaic cell still needs to be improved. Summary of the Invention

[0003] In view of this, the present application provides a back-contact photovoltaic cell and a preparation method thereof. The carrier lifetime generated by the prepared back-contact photovoltaic cell is relatively long. Correspondingly, the photoelectric conversion efficiency of the back-contact photovoltaic cell is relatively large.

[0004] In a first aspect, the present application provides a preparation method of a back-contact photovoltaic cell. The preparation method includes the following contents.

[0005] Provide a silicon substrate. The silicon substrate includes a light-receiving surface and a light-back surface disposed back to back in a first direction. On the light-back surface, a first diffusion region to be diffused and a second diffusion region to be diffused are preset and spaced apart in a second direction. The first direction and the second direction are perpendicular. Form a mask layer on the light-back surface. The mask layer includes a first portion to be removed and a second portion to be removed spaced apart in the second direction. Use a laser to remove the first portion to be removed to form a first opening for exposing the first diffusion region to be diffused. Diffuse into the first diffusion region to be diffused to form a first diffusion layer. Use a laser to remove the second portion to be removed to form a second opening for exposing the second diffusion region to be diffused. Diffuse into the second diffusion region to be diffused to form a second diffusion layer spaced apart from the first diffusion layer in the second direction. Form a first metal electrode in ohmic contact with the first diffusion layer, and form a second metal electrode in ohmic contact with the second diffusion layer.

[0006] The back-contact photovoltaic cell prepared by the preparation method according to the present application may have the following advantages. The first diffusion layer and the second diffusion layer are in the same position in the first direction. That is to say, there is no height difference between the first diffusion layer and the second diffusion layer. Therefore, the average distance that the photo-generated holes generated in the silicon substrate diffuse to the first diffusion layer and the average distance that the photo-generated electrons generated in the silicon substrate diffuse to the second diffusion layer are the same or close. The probability that the photo-generated holes encounter the recombination centers and the probability that the photo-generated electrons encounter the recombination centers are both relatively small. The recombination rate of the photo-generated holes and the recombination rate of the photo-generated electrons are both relatively small. Therefore, the carrier lifetime of the prepared back-contact photovoltaic cell is relatively long. Correspondingly, the photoelectric conversion efficiency of the back-contact photovoltaic cell is relatively large.

[0007] Optionally, the preparation method of the present application further includes: after forming the first opening and before diffusing into the first diffusion region, etching the portion of the backlight surface located in the first diffusion region with an alkaline solution; after forming the second opening and before diffusing into the second diffusion region, etching the portion of the backlight surface located in the second diffusion region with an alkaline solution; controlling the etching depth in the first diffusion region to be the same as the etching depth in the second diffusion region.

[0008] Optionally, an alkaline solution including a polishing additive is used, or an alkaline solution including a texturing additive is used.

[0009] Optionally, the method for forming the mask layer on the backlight surface includes: diffusing oxygen into the backlight surface by a thermal diffusion process to form a silicon oxide mask layer; or depositing a silicon oxide mask layer on the backlight surface by a chemical vapor deposition process.

[0010] Optionally, there is a spacing distance D between the first opening and the second opening in the second direction, and the spacing distance D is controlled to be greater than or equal to 50 μm.

[0011] Optionally, the mask layer further includes a third portion to be removed, and the third portion to be removed is located between the first portion to be removed and the second portion to be removed. The first portion to be removed and the second portion to be removed are respectively spaced apart from the third portion to be removed in the second direction. The silicon substrate further includes an isolation portion located between the first diffusion region and the second diffusion region. After forming the second diffusion layer and before forming the first metal electrode and the second metal electrode, the preparation method of the present application further includes: removing the third portion to be removed by laser to form a third opening for exposing the isolation portion, etching the exposed portion of the isolation portion by an alkaline solution to form a groove recessed into the isolation portion, and making the groove spaced apart from the first diffusion layer in the second direction and also making the groove spaced apart from the second diffusion layer in the second direction.

[0012] Optionally, a set spacing distance L1 is provided between the bottom wall of the groove and the light-receiving surface, and a set spacing distance L2 is provided between either the first diffusion layer or the second diffusion layer and the light-receiving surface. The preparation method of the present application further includes: controlling the spacing distance L1 to be less than or equal to the spacing distance L2.

[0013] Optionally, a spacing distance D is provided between the first opening and the second opening in the second direction, satisfying 20 μm ≤ D ≤ 50 μm.

[0014] Optionally, after forming the groove and before forming the first metal electrode and the second metal electrode, the preparation method of the present application further includes: forming a passivation layer at least on the inner surface of the groove.

[0015] In a 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. Correspondingly, the lifetime of the carriers generated by the back-contact photovoltaic cell is relatively long, that is, the photoelectric conversion efficiency of the back-contact photovoltaic cell is relatively large.

[0016] It should be understood that the above general description and the following detailed description are only exemplary and do not limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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 in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 It is a schematic structural diagram of a silicon substrate in one embodiment; Figure 2 It is a schematic structural diagram of a silicon substrate and a mask layer in one embodiment; Figure 3 It is a schematic structural diagram of a silicon substrate and a mask layer in one embodiment, wherein the mask layer is provided with a first opening; Figure 4 It is a schematic structural diagram of a silicon substrate, a mask layer, a first diffusion layer and a first silicon glass layer in one embodiment; Figure 5 It is a schematic structural diagram of a silicon substrate, a mask layer, a first diffusion layer and a first silicon glass layer in one embodiment, wherein the mask layer is provided with a second opening; Figure 6 It is a schematic structural diagram of a silicon substrate, a mask layer, a first diffusion layer, a first silicon glass layer, a second diffusion layer and a second silicon glass layer in one embodiment; Figure 7Schematic diagram of the structure of a silicon substrate and a mask layer in another embodiment, wherein the backlight surface includes a first etched portion; Figure 8 Schematic diagram of the structure of a silicon substrate, a mask layer, a first diffusion layer, and a first silicon glass layer in another embodiment; Figure 9 Schematic diagram of the structure of a silicon substrate, a mask layer, a first diffusion layer, a first silicon glass layer in another embodiment, wherein the backlight surface includes a second etched portion; Figure 10 Schematic diagram of the structure of a silicon substrate, a mask layer, a first diffusion layer, a first silicon glass layer, a second diffusion layer, and a second silicon glass layer in another embodiment; Figure 11 Schematic diagram of the structure of a silicon substrate, a mask layer, a first diffusion layer, a first silicon glass layer, a second diffusion layer, and a second silicon glass layer in one embodiment, wherein the light-receiving surface of the silicon substrate includes a textured surface; Figure 12 Schematic diagram of the structure of a silicon substrate, a mask layer, a first diffusion layer, and a second diffusion layer in one embodiment; Figure 13 Schematic diagram of the structure of a silicon substrate, a mask layer, a first diffusion layer, a second diffusion layer, a back surface passivation layer, and a front surface passivation layer in one embodiment; Figure 14 Schematic diagram of the structure of the back-contact photovoltaic cell provided by the present application in one embodiment; Figure 15 Schematic diagram of the structure of a silicon substrate and a mask layer in yet another embodiment; Figure 16 Schematic diagram of the structure of a silicon substrate, a mask layer, a first diffusion layer, a first silicon glass layer, a second diffusion layer, and a second silicon glass layer in yet another embodiment; Figure 17 Schematic diagram of the structure of a silicon substrate, a mask layer, a first diffusion layer, a first silicon glass layer, a second diffusion layer, and a second silicon glass layer in yet another embodiment, wherein the isolation portion corresponds to a third opening; Figure 18 Schematic diagram of the structure of a silicon substrate, a mask layer, a first diffusion layer, a first silicon glass layer, a second diffusion layer, and a second silicon glass layer in yet another embodiment, wherein the isolation portion is provided with a groove; Figure 19 Schematic diagram of the structure of a silicon substrate, a mask layer, a first diffusion layer, a first silicon glass layer, a second diffusion layer, and a second silicon glass layer in yet another embodiment, wherein the light-receiving surface of the silicon substrate includes a textured surface and the groove includes a grooved textured surface; Figure 20 Schematic diagram of the structure of a silicon substrate, a mask layer, a first diffusion layer, and a second diffusion layer in yet another embodiment; Figure 21 It is a schematic structural diagram of a silicon substrate, a mask layer, a first diffusion layer, a second diffusion layer, a back passivation layer, and a front passivation layer in another embodiment; Figure 22 It is a schematic structural diagram of the back-contact photovoltaic cell provided by the present application in another embodiment.

[0019] Reference numerals: 1 - silicon substrate, 11 - light-receiving surface, 111 - textured surface, 12 - backlight surface, 121 - first diffusion region to be diffused, 121a - first etched portion, 1211 - first diffusion layer, 1212 - first silicon glass layer, 122 - second diffusion region to be diffused, 122a - second etched portion, 1221 - second diffusion layer, 1222 - second silicon glass layer, 123 - isolation portion, 1231 - groove, 1231a - grooved textured surface, 2 - mask layer, 21 - first portion to be removed, 21a - first opening, 22 - second portion to be removed, 22a - second opening, 23 - third portion to be removed, 23a - third opening, 24 - fourth portion to be removed, 3 - back passivation layer, 31 - passivation isolation portion, 4 - front passivation layer, 5 - positive metal electrode, 6 - negative metal electrode. Detailed implementation manners

[0020] In order to better understand the technical solution of the present application, the embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0021] It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts belong to the scope of protection of the present application.

[0022] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms of "a", "the", and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0023] It should be understood that the term " / and" used herein is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, a and / or b can represent: a exists alone, a and b exist simultaneously, and b exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0024] The direction X and the direction Y in the accompanying drawings of this article are perpendicular.

[0025] In a first aspect, the present application provides some embodiments of a method for manufacturing a back-contact photovoltaic cell, and the content of the manufacturing method is as follows.

[0026] Provide a substrate, which mainly refers to the structure before being prepared into a back-contact photovoltaic cell that can be put into use. The substrate may at least include, for example Figure 1 As shown, the silicon substrate 1, and another name for the silicon substrate 1 can be a silicon wafer. The surface of the silicon substrate 1 may include a light-receiving surface 11 and a light-back surface 12 that are arranged back to back in a first direction (a direction parallel to the direction X) of the silicon substrate 1. The light-receiving surface 11 refers to the surface that is directly irradiated by sunlight in the subsequent back-contact photovoltaic cell to be formed, and the light-back surface 12 refers to the surface that is not used to be directly irradiated by sunlight in the subsequent back-contact photovoltaic cell to be formed. The light-back surface 12 can be irradiated by the reflected light in the environment.

[0027] In some embodiments, please refer to Figure 1 As shown, the silicon substrate 1 can be an N-type silicon substrate, that is, at least one N-type element is doped in the silicon substrate 1, and the N-type element can be an element in the fifth main group of the periodic table of chemical elements such as phosphorus, arsenic, antimony, etc.

[0028] In some embodiments, please refer to Figure 1 As shown, a first diffusion zone to be formed 121 and a second diffusion zone to be formed 122 are preset on the light-back surface 12 at intervals in a second direction (a direction parallel to the direction Y). It can be understood that when observing the light-back surface 12 in the reverse direction of the direction X, a part of the area of the light-back surface 12 is the first diffusion zone to be formed 121, and a part of the area is also the second diffusion zone to be formed 122. In some embodiments, on the light-back surface 12 as Figure 1 shown, a mask layer 2 as Figure 2 shown is formed to cover the light-back surface 12 with the mask layer 2.

[0029] Among them, the method of forming the mask layer 2 may include using a chemical vapor deposition process, and the chemical vapor deposition process may include low-pressure chemical vapor deposition (LPCVD), plasma-enhanced chemical vapor deposition (PECVD), atmospheric pressure chemical vapor deposition (APCVD), catalytic chemical vapor deposition (CAT-CVD), or hot wire chemical vapor deposition (HWCVD).

[0030] In addition, the mask layer 2 deposited on the backlight surface 12 may include at least one of silicon oxide (SiO x ), silicon nitride (SiN x ), and silicon oxynitride (SiON).

[0031] In some other embodiments, the method of forming the mask layer may also include diffusing oxygen toward the backlight surface by using a thermal diffusion process to grow a silicon oxide-containing mask layer from the backlight surface into the silicon substrate.

[0032] Subsequent content in this article mainly describes by taking "depositing a mask layer on the backlight surface by chemical vapor deposition" as an example.

[0033] In some embodiments, please refer to Figure 2 As shown, the thickness dimension of the mask layer 2 in the first direction may be in the range of 30 nanometers (nm) to 120 nanometers (nm). Specifically, the thickness dimension of the mask layer 2 may be 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, or 120 nm.

[0034] In some embodiments, please refer to Figure 2 As shown, the mask layer 2 may include a first portion to be removed 21 and a second portion to be removed 22 that are spaced apart in the second direction. Among them, the projection range of the first portion to be removed 21 along the first direction on the silicon substrate 1 corresponds to Figure 1 the first diffusion region to be diffused 121 shown, and the projection range of the second portion to be removed 22 along the first direction on the silicon substrate 1 corresponds to Figure 1 the second diffusion region to be diffused 122 shown. In some embodiments, the first portion to be removed 21 is removed by using a laser to form a first opening 21a as shown in Figure 3 The first opening 21a may expose Figure 1 the first diffusion region to be diffused 121 shown. That is to say, the projection range of the first opening 21a along the first direction on the silicon substrate 1 corresponds to Figure 1 the first diffusion region to be diffused 121 shown.

[0035] In some embodiments, the power of the laser used to remove the first portion to be removed 21 may be in the range of 5 watts (W) to 30 watts (W). Among them, the power of the laser may specifically be 5 W, 6 W, 7 W, 8 W, 9 W, 10 W, 11 W, 12 W, 13 W, 14 W, 15 W, 16 W, 17 W, 18 W, 19 W, 20 W, 21 W, 22 W, 23 W, 24 W, 25 W, 26 W, 27 W, 28 W, 29 W, or 30 W.

[0036] In some embodiments, diffusion is performed toward the first diffusion region to be diffused 121 to form as shown in Figure 4The first diffusion layer 1211 shown. The method used may include diffusing a doping source gas containing at least one P-type element by a thermal diffusion process. The P-type element may be an element in the third main group of the periodic table of chemical elements such as boron, aluminum, gallium, etc. Therefore, at least one P-type element may be doped in the first diffusion layer 1211. A P-N junction may be formed between the silicon substrate 1 and the first diffusion layer 1211, and a built-in electric field may be formed in the P-N junction, which points from the silicon substrate 1 to the first diffusion layer 1211.

[0037] In some embodiments, the time required to diffuse the P-type element into the first diffusion region 121 may be in the range of 2 hours (h) to 5 hours (h), and the time may specifically be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, or 5 h.

[0038] In some embodiments, the ambient temperature required to diffuse the P-type element into the first diffusion region 121 may be in the range of 800 degrees Celsius (°C) to 1200 degrees Celsius (°C), and the ambient temperature may specifically be 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C, or 1200 °C.

[0039] In some embodiments, use a laser to remove Figure 4 the second portion to be removed 22 shown to form Figure 5 the second opening 22a shown. The second opening 22a may expose Figure 1 the second diffusion region 122 shown. That is to say, the projection range of the second opening 22a projected onto the silicon substrate 1 in the first direction corresponds to Figure 1 the second diffusion region 122 shown.

[0040] In some embodiments, the power of the laser used to remove the second portion to be removed 22 may be in the range of 5 W to 40 W. Among them, the power of the laser may specifically be 5 W, 6 W, 7 W, 8 W, 9 W, 10 W, 11 W, 12 W, 13 W, 14 W, 15 W, 16 W, 17 W, 18 W, 19 W, 20 W, 21 W, 22 W, 23 W, 24 W, 25 W, 26 W, 27 W, 28 W, 29 W, 30 W, 31 W, 32 W, 33 W, 34 W, 35 W, 36 W, 37 W, 38 W, 39 W, or 40 W.

[0041] In some embodiments, diffuse into the second diffusion region 122 to form as Figure 6The second diffusion layer 1221 shown. The method used may include diffusing a doping source gas containing at least one N-type element by a thermal diffusion process. Accordingly, at least one N-type element may be doped in the second diffusion layer 1221. Wherein, the concentration of the N-type element doped in the second diffusion layer 1221 needs to be greater than the concentration of the N-type element doped in the silicon substrate 1 to form a back electric field, and the direction of the back electric field is from the second diffusion layer 1221 to the silicon substrate 1.

[0042] In some embodiments, the time required to diffuse the N-type element into the second diffusion region 122 may be in the range of 1 hour (h) to 3 hours (h), and the time may specifically be 1 h, 1.5 h, 2 h, 2.5 h, or 3 h.

[0043] In some embodiments, the ambient temperature required to diffuse into the second diffusion region 122 may be in the range of 700 degrees Celsius (°C) to 1100 degrees Celsius (°C), and the ambient temperature may specifically be 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, or 1100 °C.

[0044] In some embodiments, a first metal electrode (not shown in the figure) may be formed and the first metal electrode may be in ohmic contact (also known as metallization contact) with the first diffusion layer 1211.

[0045] In some embodiments, a second metal electrode (not shown in the figure) may be formed and the second metal electrode may be in ohmic contact with the second diffusion layer 1221.

[0046] When the back-contact photovoltaic cell prepared by the preparation method described above is irradiated by sunlight, photo-generated electrons and photovoltaic holes may be generated in the silicon substrate 1. The photo-generated holes diffused to the P-N junction drift into the first diffusion layer 1211 under the action of the built-in electric field, so that relatively more photovoltaic holes accumulate in the first diffusion layer 1211. Accordingly, the first diffusion layer 1211 is positively charged, and correspondingly, the first metal electrode in ohmic contact with the first diffusion layer 1211 may be a positive metal electrode. The photo-generated electrons diffused to the back electric field will drift into the second diffusion layer 1221 under the action of the back electric field, so that relatively more photovoltaic electrons accumulate in the second diffusion layer 1221. Accordingly, the second diffusion layer 1221 is negatively charged, and correspondingly, the second metal electrode in ohmic contact with the second diffusion layer 1221 may be a negative metal electrode.

[0047] If a back-contact photovoltaic cell is prepared according to the preparation method of the back-contact photovoltaic cell in the related art, the height positions of the negatively charged doping layer and the positively charged doping layer in the back-contact photovoltaic cell in the related art are different. That is to say, the positions of the negatively charged doping layer and the positively charged doping layer in the thickness direction of the cell are different, and the difference between the average distance that the photo-generated holes generated in the silicon substrate move to the positively charged doping layer and the average distance that the photo-generated electrons generated in the silicon substrate move to the negatively charged doping layer is relatively large. If the average distance that the photo-generated holes generated in the silicon substrate move to the positively charged doping layer is relatively large, the probability that the photo-generated holes encounter a recombination center (a defect that promotes the recombination of electrons and holes by providing an intermediate energy level or a defect energy level) is relatively large, and the recombination rate of the photo-generated holes is relatively large. Similarly, if the average distance that the photo-generated electrons generated in the silicon substrate move to the negatively charged doping layer is relatively large, the probability that the photo-generated electrons encounter a recombination center is relatively large, and the recombination rate of the photo-generated electrons is relatively large. Therefore, the lifetimes of the carriers (photoelectric holes, photoelectrons) in the back-contact photovoltaic cell in the related art are relatively short. Correspondingly, the photoelectric conversion efficiency of the back-contact photovoltaic cell in the related art is relatively small.

[0048] Compared with the defects of the back-contact photovoltaic cell in the related art, the back-contact photovoltaic cell prepared according to some embodiments of the preparation method provided in the present application may have the following advantages. Please refer to Figure 6 As shown, the positions of the first diffusion layer 1211 and the second diffusion layer 1221 in the first direction are the same. That is to say, there is no height difference between the first diffusion layer 1211 and the second diffusion layer 1221. Therefore, the average distance that the photo-generated holes generated in the silicon substrate 1 diffuse to the first diffusion layer 1211 is the same as or close to the average distance that the photo-generated electrons generated in the silicon substrate 1 diffuse to the second diffusion layer 1221. The probabilities that the photo-generated holes and the photo-generated electrons encounter a recombination center are both relatively small, and the recombination rates of the photo-generated holes and the photo-generated electrons are both relatively small. Therefore, the lifetimes of the carriers in the prepared back-contact photovoltaic cell are relatively long. Correspondingly, the photoelectric conversion efficiency of the back-contact photovoltaic cell is relatively large.

[0049] In some embodiments, after forming the first opening 21a as shown in Figure 3 There may be some damage and impurities formed by laser removal in the part of the backlight surface 12 located in the first diffusion region 121. To reduce the damage and impurities, before diffusing into the first diffusion region 121, the part of the backlight surface 12 located in the first diffusion region 121 is etched with an alkaline solution to form as shown in Figure 7The first etched portion 121a shown. That is to say, the backlight surface 12 is changed from the original planar structure to a stepped structure, and the first etched portion 121a also belongs to a part of the new backlight surface 12, and the first etched portion 121a is also within the first diffusion region to be diffused 121. After forming the structure shown in Figure 7 diffusion is carried out into the first diffusion region to be diffused 121 to form the structure shown in Figure 8 After forming the structure shown in Figure 8 the second portion to be removed 22 is removed by using a laser. To reduce the damage and impurities formed by laser removal, the portion of the backlight surface 12 within the second diffusion region to be diffused 122 is also etched with an alkaline solution to form the second etched portion 122a shown in Figure 9 That is to say, the second etched portion 122a also belongs to a part of the new backlight surface 12, and the second etched portion 122a is also within the second diffusion region to be diffused 122. After forming the structure shown in Figure 9 diffusion is carried out into the second diffusion region to be diffused 122 to form the structure shown in Figure 10 the structure shown in

[0050] In some embodiments, the depth of etching the portion of the backlight surface 12 within the first diffusion region to be diffused 121 with an alkaline solution can be in the range of 1 micrometer (μm) to 5 micrometers (μm), and specifically can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm.

[0051] In some embodiments, the time for etching the portion of the backlight surface 12 within the first diffusion region to be diffused 121 with an alkaline solution can be in the range of 100 seconds (s) to 300 seconds (s), and specifically can be 100s, 150s, 200s, 250s or 300s.

[0052] In some embodiments, the depth of etching the portion of the backlight surface 12 within the second diffusion region to be diffused 122 with an alkaline solution can be in the range of 1μm to 5μm, and specifically can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm.

[0053] In some embodiments, the time for etching the portion of the backlight surface 12 within the second diffusion region to be diffused 122 with an alkaline solution can be in the range of 100 seconds (s) to 300 seconds (s), and specifically can be 100s, 150s, 200s, 250s or 300s.

[0054] In some embodiments, it is necessary to control the etching depth in the first diffusion region to be etched 121 to be the same as the etching depth in the second diffusion region to be etched 122. In other words, control the positions of the first etched portion 121a to be formed in the first direction and the second etched portion 122a to be formed in the first direction to be the same, so that the positions of the first diffusion layer 1211 to be formed subsequently in the first direction and the second diffusion layer 1221 to be formed in the first direction are the same, thereby making the photoelectric conversion efficiency of the back-contact photovoltaic cell to be prepared relatively large. The relevant specific effects have been described above and will not be elaborated here.

[0055] In some embodiments, an alkaline solution including a polishing additive can be used to make the surfaces of both the first etched portion 121a and the second etched portion 122a be polished surfaces.

[0056] In some embodiments, an alkaline solution including a texturing additive can be used to make the surfaces of both the first etched portion 121a and the second etched portion 122a be the textured surfaces (with multiple micron-sized grooves or pyramid structures) located on the backlight surface 12. The textured surface located on the backlight surface 12 can have a good antireflection effect and can improve the efficiency of light incident on the silicon substrate 1 through the backlight surface 12, so that the number of photogenerated electrons and photogenerated holes that the silicon substrate 1 can generate per unit time is relatively large, thereby making the photoelectric conversion efficiency of the back-contact photovoltaic cell to be prepared relatively large.

[0057] In some embodiments, please refer to Figure 4 As shown, during the process of diffusing to form the first diffusion layer 1211, the gas containing the doping source can further include oxygen to form a first silicon glass layer 1212 on the side of the first diffusion layer 1211 facing away from the silicon substrate 1. The first silicon glass layer 1212 can be a borosilicate glass layer (BSG). The first silicon glass layer 1212 has a protective effect on the first diffusion layer 1211 to reduce the possibility of the first diffusion layer 1211 being contaminated by subsequent diffusion processes and wet etching processes.

[0058] In some embodiments, the thickness dimension of the first silicon glass layer 1212 in the first direction can be in the range of 50 nm to 100 nm. The thickness dimension of the first silicon glass layer 1212 can specifically be 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, or 100 nm.

[0059] In some embodiments, please refer to Figure 6As shown, during the process of diffusing to form the second diffusion layer 1221, the gas containing the doping source may further include oxygen to form a second silicon glass layer 1222 on the side of the second diffusion layer 1221 facing away from the silicon substrate 1. The second silicon glass layer 1222 may be a phosphorosilicate glass layer (PSG), and the second silicon glass layer 1222 has a protective effect on the second diffusion layer 1221 to reduce the possibility of the second diffusion layer 1221 being damaged by subsequent wet etching processes.

[0060] In some embodiments, the thickness dimension of the second silicon glass layer 1222 in the first direction may be in the range of 20 nm to 100 nm. Specifically, the thickness dimension of the second silicon glass layer 1222 may be 20 nm, 25 nm, 30 nm, 35 nm, 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.

[0061] In some embodiments, please refer to Figure 6 or Figure 10 As shown, after forming the first diffusion layer 1211 and the second diffusion layer 1221 that are spaced apart in the second direction, correspondingly, an isolation portion 123 is formed in the silicon substrate 1 between the first diffusion layer 1211 and the second diffusion layer 1221. That is to say, the first diffusion layer 1211 and the second diffusion layer 1221 are isolated by the isolation portion 123. The isolation portion can reduce the possibility of photo-generated holes in the first diffusion layer 1211 moving to the second diffusion layer 1221, and the isolation portion can also reduce the possibility of photo-generated electrons in the second diffusion layer 1221 moving to the first diffusion layer 1211. That is, the isolation portion 123 can play an effect of reducing leakage current, thereby improving the photoelectric conversion efficiency of the prepared back-contact photovoltaic cell. The isolation effect of the isolation portion 123 is positively correlated with the size of the isolation portion 123 in the second direction. Therefore, as Figure 5 shown, it is necessary to make there be a spacing distance D between the first opening 21a and the second opening 22a in the second direction, and control the spacing distance D to be greater than or equal to 50 μm so that the size of the subsequent formed isolation portion 123 in the second direction is greater than or equal to 50 μm to ensure that the isolation portion 123 has a good isolation effect. Among them, the spacing distance D may specifically be 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, or 100 nm.

[0062] In some embodiments, when forming as Figure 6After the structure shown, the bypass diffusion layer (not shown in the figure) located on the light-receiving surface 11 of the silicon substrate 1 is etched using a front-side chain pickling process. The bypass diffusion layer is formed during the previous diffusion process.

[0063] In some embodiments, the acid solution used for pickling may include at least one of hydrofluoric acid (HF) and hydrochloric acid (HCl).

[0064] In some embodiments, after removing the bypass diffusion layer, the light-receiving surface 11 of the silicon substrate 1 is etched using an alkaline solution containing a texturing additive to form a Figure 11 textured surface 111 located on the light-receiving surface 11 as shown. The textured surface 111 can have a good antireflection effect, can increase the efficiency of sunlight incident on the silicon substrate 1 through the textured surface 111, so that the number of photo-generated electrons and photo-generated holes generated by the silicon substrate 1 per unit time is relatively large, thereby making the photoelectric conversion efficiency of the prepared back-contact photovoltaic cell relatively large.

[0065] In some embodiments, after forming the Figure 11 textured surface 111 located on the light-receiving surface 11 as shown, the first silicon glass layer 1212, the second silicon glass layer 1222, and the third portion to be removed 23 (the part of the mask layer 2 that remains and covers the isolation portion 123) are etched using a back-side chain pickling process to form a Figure 12 structure as shown.

[0066] In some embodiments, after forming the Figure 12 structure as shown, a back surface passivation layer 3 as shown is deposited on the backlight side of the silicon substrate 1 using a vapor deposition process. The vapor deposition process may include atomic layer deposition (ALD) and chemical vapor deposition. The back surface passivation layer 3 may include a stacked structure of an aluminum oxide passivation layer and a silicon nitride passivation layer, or the back surface passivation layer 3 may include a silicon nitride passivation layer. Figure 13 In some embodiments, after forming the

[0067] structure as shown, a front surface passivation layer 4 as shown is deposited on the light-receiving side of the silicon substrate 1 using a vapor deposition process. The front surface passivation layer 4 may include a stacked structure of an aluminum oxide passivation layer and a silicon nitride passivation layer, or the front surface passivation layer 4 may include a silicon nitride passivation layer. Figure 12 In some embodiments, after forming the Figure 13 structure as shown, a positive metal electrode 5 for forming an ohmic contact with the first diffusion layer 1211 is formed, and a

[0068] In some embodiments, after forming the Figure 13 back surface passivation layer 3 and the front surface passivation layer 4 as shown, a Figure 14 structure as shown is formed for the ohmic contact with the positive metal electrode 5 of the first diffusion layer 1211, and Figure 14The ohmic contact shown is the negative metal electrode 6 of the second diffusion layer 1221. Among them, the processes of forming the positive metal electrode 5 and the negative metal electrode 6 can both include screen printing and sintering. Further, laser-enhanced contact optimization (LECO) can also be used to form a better ohmic contact, thereby improving the photoelectric conversion efficiency of the back-contact photovoltaic cell.

[0069] In some other embodiments, the preparation method of the back-contact photovoltaic cell can include the following. Please refer to Figure 15 As shown, a mask layer 2 is formed on the backlight surface 12 of the silicon substrate 1. The mask layer 2 includes a first to-be-removed portion 21, a second to-be-removed portion 22, a third to-be-removed portion 23, and a fourth to-be-removed portion 24 arranged in the second direction. The first to-be-removed portion 21 and the second to-be-removed portion 22 are arranged at intervals along the second direction. The first to-be-removed portion 21 and the second to-be-removed portion 22 are respectively arranged at intervals from the third to-be-removed portion 23. The portion between the first to-be-removed portion 21 and the third to-be-removed portion 23 is the fourth to-be-removed portion 24, and the portion between the second to-be-removed portion 22 and the third to-be-removed portion 23 is also the fourth to-be-removed portion 24. After forming the mask layer 2, the first to-be-removed portion 21 is removed by laser to form a first opening 21a exposing the first to-be-diffused region, and then diffusion is performed in the first to-be-diffused region to form a first diffusion layer 1211 and a first silicon glass layer 1212. Then, the second to-be-removed portion 22 is removed by laser to form a second opening 22a exposing the second to-be-diffused region, and diffusion is performed in the second to-be-diffused region to form a second diffusion layer 1221 and a second silicon glass layer 1222, that is, the structure as shown in Figure 16 As shown, the structure between the first diffusion layer 1211 and the second diffusion layer 1221 is the isolation portion 123. It can also be said that the isolation portion 123 is between the first to-be-diffused region and the second to-be-diffused region preset before, and the isolation portion 123 is covered by the third to-be-removed portion 23 and the fourth to-be-removed portion 24. In the structure as shown in Figure 16 Based on the structure shown, the third to-be-removed portion 23 is removed by laser to form a third opening 23a as shown in Figure 17 As shown, a part of the isolation portion 123 is exposed by the third opening 23a. After forming the third opening 23a, the part of the isolation portion 123 exposed by the third opening 23a is etched with an alkaline solution to form a structure as shown in Figure 18The groove 1231 that is recessed into the isolation portion 123 is shown, and the groove 1231 is spaced from the first diffusion layer 1211 in the second direction. It can also be said that the structure of the isolation portion 123 located between the groove 1231 and the first diffusion layer 1211 is retained. The groove 1231 is also spaced from the second diffusion layer 1221 in the second direction. It can also be said that the structure of the isolation portion 123 located between the groove 1231 and the second diffusion layer 1221 is retained. In this setting, the path for electrons or holes to move between the first diffusion layer 1211 and the second diffusion layer 1221 needs to bypass the groove 1231. This path does not extend along the second direction, and the length of this path is relatively large. The difficulty for holes to move from the first diffusion layer 1211 to the second diffusion layer 1221 increases, and the difficulty for electrons to move from the second diffusion layer 1221 to the first diffusion layer 1211 increases. The leakage current that can be generated by the prepared back-contact photovoltaic cell is relatively small, and the photoelectric conversion efficiency of the back-contact photovoltaic cell is relatively large.

[0070] In some other embodiments, please refer to Figure 18 As shown, a set interval distance L1 may be provided between the bottom wall of the groove 1231 and the light-receiving surface 11, and a set interval distance L2 may be provided between either the first diffusion layer 1211 or the second diffusion layer 1221 and the light-receiving surface 11. During the preparation process, the interval distance L1 can be controlled to be less than the interval distance L2. It can also be said that the etching depth of the isolation portion 123 by the alkaline solution is controlled to be greater than the thickness dimension of either the first diffusion layer 1211 or the second diffusion layer 1221 in the first direction. In this setting, the length of the path for electrons or holes to move between the first diffusion layer 1211 and the second diffusion layer 1221 can be made greater than the distance between the first diffusion layer 1211 and the second diffusion layer 1221 along the second direction. The difficulty for holes to move from the first diffusion layer 1211 to the second diffusion layer 1221 increases, and the difficulty for electrons to move from the second diffusion layer 1221 to the first diffusion layer 1211 increases. The leakage current that can be generated by the prepared back-contact photovoltaic cell is relatively small, and the photoelectric conversion efficiency of the back-contact photovoltaic cell is relatively large.

[0071] In some other additional embodiments, the interval distance L1 can also be controlled to be equal to the interval distance L2.

[0072] In some other embodiments, please refer to Figure 16 As shown, a spacing distance D may be provided between the first opening 21a and the second opening 22a in the second direction, satisfying 20 μm ≤ D ≤ 50 μm, so that the size of the isolation portion 123 that can be formed in the second direction is within the range of 20 μm to 50 μm. Although the size of the isolation portion 123 in the second direction is relatively small, subsequent formations on the isolation portion 123, such as Figure 18The shown groove 1231 makes the path length for electron or hole movement relatively large. Therefore, the isolation effect of the isolation part 123 is still relatively good. Correspondingly, the lengths of the first diffusion layer 1211 and the second diffusion layer 1221 in the second direction that can be formed can both be relatively large. The efficiency of the first diffusion layer 1211 in collecting photo-generated holes and the efficiency of the second diffusion layer 1221 in collecting photo-generated electrons are both relatively high, and the photoelectric conversion efficiency of the prepared back-contact photovoltaic cell is relatively large. Among them, the spacing distance D can specifically be 20μm, 25μm, 30μm, 35μm, 40μm, 45μm or 50μm.

[0073] In some other embodiments, it is possible to Figure 17 on the basis of the shown structure, use an alkaline solution containing a texturing additive for texturing to form a textured surface 111 as shown in Figure 19 on the light-receiving surface 11, and at the same time form a groove 1231 as shown in Figure 19 on the isolation part 123, and make the inner surface of the groove 1231 include a groove textured surface 1231a. Both the textured surface 111 and the groove textured surface 1231a can have a good antireflection effect, and the photoelectric conversion efficiency of the prepared back-contact photovoltaic cell is relatively large. In addition, the synchronous texturing in this embodiment makes the preparation efficiency of the back-contact photovoltaic cell relatively high.

[0074] In some other additional embodiments, it is also possible to first form the textured surface 111 and then form the groove textured surface 1231a, or, it is also possible to first form the groove textured surface 1231a and then form the textured surface 111.

[0075] In some other additional embodiments, it is also possible to choose not to form the groove textured surface 1231a in the groove 1231, and the inner surface of the groove 1231 can be a polished surface.

[0076] The subsequent content of this article mainly describes the preparation method by taking "forming the groove textured surface 1231a in the groove 1231" as an example.

[0077] In some other embodiments, on the basis of forming the structure as shown in Figure 19 , use backside chain acid pickling to etch the first silicon glass layer 1212 and the second silicon glass layer 1222 to form the structure as shown in Figure 20 .

[0078] In some other embodiments, on the basis of the structure as shown in Figure 20 , form the structure as shown in Figure 21The back passivation layer 3 located on the backlight side of the silicon substrate 1 as shown covers the first diffusion layer 1211, the second diffusion layer 1221, the isolation portion 123, and the grooved texture 1231a of the groove 1231. The portion of the back passivation layer 3 located within the groove 1231 is the passivation isolation portion 31. The resistivity of the back passivation layer 3 is relatively larger than that of the silicon substrate 1. In other words, the resistivity of the passivation isolation portion 31 is relatively larger than that of the isolation portion 123. Photo-generated holes and photo-generated electrons are not easily moved in the second direction through the passivation isolation portion 31. That is to say, the passivation isolation portion 31 can also achieve the effect of reducing leakage current. In other words, even if the spacing distance in the second direction between the first diffusion layer 1211 and the second diffusion layer 1221 is relatively small (for example, less than 50 μm but greater than 20 μm), the composite barrier structure formed by the isolation portion 123 and the passivation isolation portion 31 stacked in the second direction can better reduce leakage current, so that the photoelectric conversion efficiency of the prepared back-contact photovoltaic cell is relatively large.

[0079] If the inner surface of the groove 1231 is not the grooved texture 1231a, that is, the inner surface of the groove 1231 is a polished surface, the passivation isolation portion 31 of the back passivation layer 3 located within the groove 1231 can also well reduce leakage current.

[0080] In some other embodiments, on the basis of the structure as shown in Figure 20 a front passivation layer 4 located on the light-receiving side of the silicon substrate 1 as shown in Figure 21 is formed.

[0081] Figure 21 The formation process, the included structure, and materials of the back passivation layer 3 and the front passivation layer 4 as shown can refer to the content described above and will not be elaborated here.

[0082] In some other embodiments, on the basis of the structure as shown in Figure 21 a positive metal electrode that forms an ohmic contact with the first diffusion layer 1211, and a negative metal electrode 6 that forms an ohmic contact with the second diffusion layer 1221 as shown in Figure 22 are formed.

[0083] In some other embodiments, a first diffusion layer containing N-type elements can be formed first, and then a second diffusion layer containing P-type elements can be formed. Correspondingly, the metal electrode in ohmic contact with the first diffusion layer can be a negative metal electrode, and the metal electrode in ohmic contact with the second diffusion layer can be a positive metal electrode.

[0084] Second aspect, the present application provides some embodiments of a back contact photovoltaic cell (Back Contact Solar Cell, BC Solar Cell), which is prepared by the preparation method described above. Correspondingly, the photoelectric conversion efficiency of the back contact photovoltaic cell is relatively large, and the relevant specific effects can be referred to the content described above, which will not be elaborated here.

[0085] In some embodiments, the structure of the back contact photovoltaic cell can be as Figure 14 shown.

[0086] In some embodiments, the structure of the back contact photovoltaic cell can also be as Figure 22 shown.

[0087] In some embodiments, the number of the first diffusion layers 1211 included in the back contact photovoltaic cell can be at least two, the number of the second diffusion layers 1221 included in the back contact photovoltaic cell can be at least two, and the first diffusion layers 1211 and the second diffusion layers 1221 can be alternately distributed and spaced along the second direction.

[0088] Third aspect, the present application provides some embodiments of a back contact photovoltaic module, which may include a laminate and a frame, and the frame is installed at the edge of the laminate. The laminate may include a photovoltaic glass, a first encapsulation film, a battery string, a second encapsulation film and a backsheet stacked. Alternatively, the laminate may include a first photovoltaic glass, a first encapsulation film, a battery string, a second encapsulation film and a second photovoltaic glass stacked. Among them, the battery string may be formed by electrically connecting a plurality of the back contact photovoltaic cells described above, and the number of the battery strings may be one, two or more.

[0089] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A preparation method of a back-contact photovoltaic cell, characterized in that The preparation method includes: Providing a silicon substrate, the silicon substrate includes a light-receiving surface and a backlight surface disposed away from each other in a first direction, and a first diffusion region to be diffused and a second diffusion region to be diffused are preset on the backlight surface at intervals in a second direction, and the first direction is perpendicular to the second direction; Forming a mask layer on the backlight surface, the mask layer includes a first portion to be removed and a second portion to be removed disposed at intervals in the second direction; Using a laser to remove the first portion to be removed to form a first opening for exposing the first diffusion region to be diffused; Diffusing into the first diffusion region to be diffused to form a first diffusion layer; Using a laser to remove the second portion to be removed to form a second opening for exposing the second diffusion region to be diffused; Diffusing into the second diffusion region to be diffused to form a second diffusion layer spaced from the first diffusion layer in the second direction; Forming a first metal electrode in ohmic contact with the first diffusion layer and forming a second metal electrode in ohmic contact with the second diffusion layer.

2. The preparation method of the back-contact photovoltaic cell according to claim 1, characterized in that, The preparation method further includes: After forming the first opening and before diffusing into the first diffusion region to be diffused, etching the portion of the backlight surface located in the first diffusion region to be diffused with an alkaline solution; After forming the second opening and before diffusing into the second diffusion region to be diffused, etching the portion of the backlight surface located in the second diffusion region to be diffused with an alkaline solution; Controlling the etching depth in the first diffusion region to be diffused to be the same as the etching depth in the second diffusion region to be diffused.

3. The preparation method of the back-contact photovoltaic cell according to claim 2, wherein, Using an alkaline solution including a polishing additive, or using an alkaline solution including a texturing additive.

4. The manufacturing method of the back contact photovoltaic cell according to claim 1, characterized in that, The method of forming a mask layer on the backlight surface includes: Diffusing oxygen onto the backlight surface using a thermal diffusion process to form a silicon oxide mask layer; Or depositing a silicon oxide mask layer on the backlight surface using a chemical vapor deposition process.

5. The preparation method of the back-contact photovoltaic cell according to any one of claims 1 to 4, characterized in that, Making the first opening and the second opening have a spacing distance D in the second direction, and controlling the spacing distance D to be greater than or equal to 50 μm.

6. The preparation method of the back-contact photovoltaic cell according to any one of claims 1 to 4, characterized in that, The mask layer further includes a third portion to be removed, the third portion to be removed is located between the first portion to be removed and the second portion to be removed, the first portion to be removed and the second portion to be removed are respectively spaced from the third portion to be removed in the second direction, and the silicon substrate further includes an isolation portion located between the first diffusion region to be diffused and the second diffusion region to be diffused; After forming the second diffusion layer and before forming the first metal electrode and the second metal electrode, the preparation method further includes: Using a laser to remove the third portion to be removed to form a third opening for exposing a part of the isolation portion, etching the part of the isolation portion exposed by the third opening with an alkaline solution to form a groove recessed into the isolation portion, making the groove spaced from the first diffusion layer in the second direction, and also making the groove spaced from the second diffusion layer in the second direction.

7. The manufacturing method of the back-contact photovoltaic cell according to claim 6, characterized in that, A preset spacing distance L1 is provided between the bottom wall of the groove and the light-receiving surface, and a preset spacing distance L2 is provided between either the first diffusion layer or the second diffusion layer and the light-receiving surface. The preparation method further includes: Controlling the spacing distance L1 to be less than or equal to the spacing distance L2.

8. The manufacturing method of the back contact photovoltaic cell according to claim 6, characterized in that, Enabling a spacing distance D to be provided between the first opening and the second opening in the second direction, where 20 μm ≤ D ≤ 50 μm.

9. The preparation method of the back-contact photovoltaic cell according to claim 6, characterized in that, After forming the groove and before forming the first metal electrode and the second metal electrode, the preparation method further includes: Forming a passivation layer at least on the inner surface of the groove.

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

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