Silicon substrates, solar cells and photovoltaic modules

Abstract

A silicon substrate comprises a first surface and a second surface opposite to each other. The first surface is provided with a plurality of pits. The thickness of the silicon substrate is h1, and the depth of the pits is h2, wherein the difference △h between h1 and h2 satisfies h1>△h≥1 / A (λ=300nm) , where A (λ=300nm) is the light absorption coefficient of the silicon substrate at wavelength λ = 300nm, in cm ‑1 The present application also provides a solar cell and a photovoltaic module comprising the above silicon substrate. By setting pits and establishing a relationship between the depth of the pits and the thickness of the silicon substrate and the light absorption coefficient of the silicon substrate at the corresponding wavelength, the absorption of the pits to oblique incident light is improved, and the requirements for special wavelength response are met.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic technology, and more specifically, to a silicon substrate, a solar cell including the silicon substrate, and a photovoltaic module including the solar cell. Background Art

[0002] As a new type of clean photovoltaic energy, solar cells have developed rapidly in recent years, and the application scenarios of solar cells have also been continuously diversified. In addition to centralized power stations and distributed power stations, building curtain walls, vehicle-mounted photovoltaics, and aerospace have all become areas of exploration for photovoltaic applications. However, due to the limitation of the incident angle of light, in some special application scenarios, the current crystalline silicon photovoltaic modules face the problem of insufficient power generation, resulting in the absorption of crystalline silicon unable to meet the needs of photoelectric conversion, that is, the power generation cannot meet the needs of differentiated scenarios. The existing silicon substrate surface is usually provided with a velvet light-trapping structure, which can effectively improve the absorption of incident light at small angles, but cannot improve the absorption of incident light at large angles. Summary of the invention

[0003] In view of this, the present application provides a silicon substrate for a solar cell, which has a good absorption effect on incident light at a large angle, thereby improving the photoelectric conversion efficiency and achieving a larger power generation amount.

[0004] In a first aspect, the present application provides a silicon substrate, comprising:

[0005] The first surface and the second surface are opposite,

[0006] A plurality of pits are located on the first surface; the thickness of the silicon substrate is h1, the depth of the pit is h2, wherein the difference △h between h1 and h2 satisfies h1>△h≥1 / A (λ=300nm) , where A (λ=300nm) is the light absorption coefficient of the silicon substrate at wavelength λ = 300nm, in cm -1 .

[0007] In the present application, pits are arranged on the light-receiving surface of the silicon substrate of the solar cell, and a relationship is established between the difference △h between the thickness of the silicon substrate and the depth of the pits and the light absorption coefficient of the corresponding wavelength of the silicon substrate. By utilizing this relationship, the size of the pits can be designed according to different incident light conditions, ensuring that the pit structure is in the range of optimal response efficiency to the incident light, thereby improving the absorption of the pits to oblique incident light so that the pits can better play their light trapping function, improving the absorption of the pits to oblique incident light, and meeting the requirements for response to special wavelengths.

[0008] As a possible implementation method, when 0.5×h1<1 / A (λ=x) (λ=x) ​When <0.5×h1, △h satisfies 1 / A (λ=x) ≤△h≤0.5×h1, where A (λ=x) is the light absorption coefficient of the silicon substrate at wavelength x, where x≥900nm.

[0009] As a possible implementation manner, a projection size d of the pit on the first surface is 10-200 µm.

[0010] As a possible implementation manner, the pit includes a first pit, the first pit includes a first sidewall, and an angle between the first sidewall and a thickness direction of the silicon substrate is less than or equal to 15 degrees.

[0011] As a possible implementation manner, the pit includes a second pit, the second pit includes a second sidewall, and an angle between the second sidewall and a thickness direction of the silicon substrate is greater than 15 degrees and less than or equal to 60 degrees.

[0012] As a possible implementation manner, the pit further includes a second pit, the second pit includes a second sidewall, and an angle between the second sidewall and a thickness direction of the silicon substrate is greater than 15 degrees and less than or equal to 60 degrees;

[0013] The projections of the first pit and the second pit on the first surface do not overlap; and / or,

[0014] The first pit and the second pit are arranged along the thickness direction of the silicon substrate and are connected.

[0015] As a possible implementation, the thickness of the silicon substrate is in the range of 90-180 µm; or,

[0016] The thickness of the silicon substrate ranges from 110 to 180 μm.

[0017] As a possible implementation manner, a ratio of a sum of projection areas of the plurality of pits on the first surface to an area of ​​the first surface is 30%-80%.

[0018] As a possible implementation manner, the interval between adjacent pits is 2-200 μm; and / or,

[0019] The plurality of pits are distributed in an array.

[0020] As a possible implementation, the pit includes a bottom wall and a side wall connected to the bottom wall.

[0021] At least part of the side wall is provided with a suede structure, or,

[0022] At least a portion of the side wall and at least a portion of the bottom wall are also provided with a suede structure.

[0023] As a possible implementation, the projection size of the pit on the first surface is d,

[0024] when When the velvet structure is arranged at a position of the side wall close to the opening of the pit;

[0025] when When the velvet structure is disposed on the side wall near the opening of the pit or covers the entire side wall;

[0026] when When the velvet structure is arranged at a position of the side wall close to the bottom wall or covers the entire side wall;

[0027] when When the velvet structure is arranged at a position of the side wall close to the opening of the pit and covers the entire bottom wall, or the velvet structure covers the entire side wall and the bottom wall;

[0028] when When the velvet structure is arranged at a position of the side wall close to the bottom wall and covers the entire bottom wall, or the velvet structure covers the entire side wall and the bottom wall.

[0029] As a possible implementation manner, the velvet structure is a pyramid structure, the size of the pyramid base of the velvet structure is less than or equal to 7 µm, and / or the pyramid height of the velvet structure is less than or equal to 5 µm.

[0030] In a second aspect, the present application provides a solar cell, comprising the silicon substrate described in the first aspect.

[0031] By setting a pit structure on the light-receiving surface of the silicon substrate of the solar cell, and establishing a relationship between the difference △h between the thickness of the silicon substrate and the depth of the pit and the light absorption coefficient of the corresponding wavelength of the silicon substrate, the absorption of the pit to oblique incident light is improved, and the requirements for special wavelength response are met. The pit has a good absorption effect on large-angle incident light.

[0032] As a possible implementation manner, the solar cell includes a passivation layer, and the passivation layer is disposed on the first surface, the second surface, and the bottom wall and side walls of the pit, and does not completely fill the pit.

[0033] As a possible implementation, the solar cell includes an electrode;

[0034] The electrode comprises a plurality of collectors, and the collectors are arranged in the areas between the pits; or,

[0035] The electrode includes a plurality of bus electrodes and a plurality of collecting electrodes, wherein the collecting electrodes are arranged in the area between the pits, the bus electrodes are arranged in the area between the pits, or part of the bus electrodes are arranged in part of the pits and the other part is arranged in the area between the pits.

[0036] In a third aspect, the present application provides a photovoltaic assembly, comprising the solar cell described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 FIG. 1 is a schematic diagram of a silicon substrate according to an embodiment of the present application.

[0038] Figure 2 This is a graph showing the inverse of the absorption coefficient of crystalline silicon material corresponding to different wavelengths.

[0039] Figure 3 The graph is a graph showing the absorbance of two silicon substrates to light of different wavelengths.

[0040] Figure 4 Schematic diagram of a first pit and a second pit on a silicon substrate.

[0041] Figure 5 Schematic diagram of another type of pit in a silicon substrate.

[0042] Figure 6 Schematic diagram of a solar cell with double-sided electrodes.

[0043] Figure 7 Schematic diagram of a solar cell with a single-sided electrode.

[0044] Description of main component symbols:

[0045] Silicon substrate 10, first surface 11, second surface 12, first region 20, second region 30,

[0046] The pit 31, the first pit 31A, the second pit 31B, the first electrodes 13 and 24, the first functional layer 15,

[0047] The second functional layer 14, the second electrodes 16, 26, the first collector 131, the second collector 132,

[0048] The first passivation layer 21 , the functional layer 28 , the second passivation layer 22 , the bottom wall 32 , and the side walls 34 , 36 . DETAILED DESCRIPTION

[0049] In order to reduce the reflection of incident light on the surface of solar cells, increase the absorption effect of incident light, and improve the photoelectric conversion efficiency, solar cells are usually designed with a velvet structure with a pyramid structure and an inverted pyramid structure on the surface through a velvet making process. The velvet structure has a good anti-reflection effect for vertically incident light or incident light with a small incident angle, which can reduce the probability of the small-angle incident light being reflected out of the solar cell. However, it is not effective for incident light with a large incident angle, that is, the omnitropy of the solar cell is not good. Solar cells with poor omnitropy need to set the optimal light receiving angle or use a tracking bracket to achieve a higher photoelectric conversion efficiency. The optimal light receiving angle changes according to the geographical location, time and season, making it difficult to adjust the fixed bracket in real time to make the solar cell reach the optimal light receiving angle, and the tracking bracket is usually expensive, so improving the omnitropy of the solar cell is a relatively simple way to improve the photoelectric conversion efficiency.

[0050] The present application defines incident light with an incident angle greater than or equal to 45 degrees as high-angle incident light, and incident light with an incident angle less than 45 degrees as low-angle incident light. The incident angle is the angle formed by the incident light on the silicon substrate surface and the normal line in the thickness direction of the silicon substrate.

[0051] When large-angle incident light is irradiated on the area of ​​the velvet structure, it is reflected once by the pyramid and / or inverted pyramid structure in the velvet structure and then emitted in a direction away from the silicon substrate. Therefore, large-angle incident light has a very small optical path in the silicon substrate, resulting in poor absorption of large-angle incident light by the battery.

[0052] When small-angle incident light is irradiated on the area of ​​the velvet structure, it can be reflected multiple times in the velvet structure of the solar cell under the reflection effect of the pyramid and / or inverted pyramid structure in the velvet structure. Therefore, the small-angle incident light has a larger optical path in the silicon substrate, so that the battery has a better absorption effect on small-angle incident light.

[0053] It can be seen that a solar cell with only a velvet structure has a good absorption effect for light incident at a small angle, but a poor absorption effect for light incident at a large angle. Therefore, the omnidirectionality of the solar cell is not good. When a photovoltaic module including the solar cell is installed in an aircraft, a car or a building, the installation position is limited because the solar cell needs to have an optimal light receiving angle, or a tracking bracket is required to achieve a larger power generation, which is costly.

[0054] The present application provides a silicon substrate for a solar cell, which is beneficial to improving the absorption effect of large-angle incident light.

[0055] A silicon substrate (such as crystalline silicon) has different light absorption coefficients at different light wavelengths. In order to ensure front absorption when light is vertically irradiated on the silicon substrate while taking into account the absorption of oblique incident light, the present application proposes a silicon substrate structure that enhances the absorption of crystalline silicon.

[0056] like Figure 1 As shown, the present application provides a silicon substrate 10, including a first surface 11 and a second surface 12 that are opposite and parallel. In the embodiment of the present application, when the silicon substrate 10 is applied to a solar cell, at least one of the first surface 11 and the second surface 12 is a light-receiving surface, that is, a surface directly irradiated by incident light. Figure 1 The first surface 11 is taken as an example for description. The first surface 11 is provided with a plurality of pits 31 which are recessed relative to the first surface 11 .

[0057] The pit 31 is a large-angle light trapping structure. Thus, when light is obliquely irradiated onto the light receiving surface of the silicon substrate 10, the reflection and light trapping effects of the pit 31 structure can be used to increase the optical path, thereby enhancing the silicon substrate 10's absorption of oblique incident light.

[0058] Based on the fact that crystalline silicon materials respond to and absorb light within the spectrum, the present application sets pits on the surface of the silicon substrate 10 and correlates the depth of the pits 31 with the thickness of the silicon substrate 10 and the light absorption coefficient of the silicon substrate 10 to enhance the reflection of the silicon substrate 10 to inclined incident light and increase the optical path, thereby improving the absorption of inclined incident light and improving the response to the spectrum.

[0059] like Figure 1 As shown, the thickness of the silicon substrate 10 is h1, the depth of the pit 31 is h2, and the difference between the thickness h1 of the silicon substrate 10 and the depth h2 of the pit 31 is △h=h1-h2≥1 / A (λ=300nm) , where A is the light absorption coefficient of the silicon substrate at wavelength λ, in cm -1 , corresponding to light of different wavelengths, the silicon substrate 10 has different light absorption coefficients. (λ=300nm) is the light absorption coefficient of the silicon substrate at wavelength λ=300nm. In addition, the depth h2 of the pit 31 is less than the thickness h1 of the silicon substrate 10. It can be seen that the depth h2 of the pit 31 satisfies: h2≤h1-1 / A (λ=300nm) .

[0060] The thickness h1 of the silicon substrate 10 is the distance between the first surface 11 and the second surface 12 ; the depth h2 of the pit 31 is the distance between the highest point and the lowest point of the pit 31 along the thickness direction of the silicon substrate 10 .

[0061] The absorption coefficient of the silicon substrate 10 can be obtained by testing and fitting the silicon substrate 10 using an ellipsometer or a UV absorption meter. In the present application, a relationship is established between the difference between the thickness of the silicon substrate 10 and the depth of the pit 31 and the light absorption coefficient of the corresponding wavelength of the silicon substrate 10. The established relationship can be used to design the pit size according to different incident light conditions, ensuring that the pit 31 structure is in the range of the best response efficiency to the incident light, thereby increasing the utilization rate of light.

[0062] The absorption coefficients of crystalline silicon of different types and doping concentrations are also different. Usually, the wavelength response range of crystalline silicon cells that respond best is around 600nm-850nm. Figure 2 The inverse of the absorption coefficient A of the crystalline silicon substrate corresponding to different wavelengths is given in 1 / A. Further, in some embodiments, when 0.5×h1<1 / A (λ=x)

[0063] When 1 / A (λ=x) When Δh is less than 0.5×h1, the difference Δh between the thickness h1 of the silicon substrate 10 and the depth h2 of the pit 31 satisfies: 1 / A (λ=x) ≤△h≤0.5×h1. That is, the difference △h between h1 and h2 is greater than or equal to 1 / A (λ=x) , and is less than or equal to half of the thickness h1 of the silicon substrate 10. (λ=x) is the light absorption coefficient of the silicon substrate 10 at wavelength x, for example, the light absorption coefficient at x=900nm, x=1000nm, x=1100nm, x=1200nm or x=1300nm, and the wavelength x can be the above-mentioned values, but is not limited to the above values. Therefore, the depth h2 of the pit 31 satisfies: 0.5×h1≤h2≤h1-1 / A (λ=x) That is, the depth h2 of the pit 31 is greater than or equal to half of the thickness h1 of the silicon substrate 10 and less than or equal to the thickness h1 of the silicon substrate minus 1 / A. (λ=x) .

[0064] By reasonably setting the range of the difference Δh between h1 and h2, the pit 31 can better trap light, thereby improving the light absorption of the silicon substrate 10 and preventing the presence of the pit 31 from affecting the mechanical strength of the silicon substrate 10. Figure 2 It can be seen that for crystalline silicon material, for light with wavelength λ=900 nanometers, 1 / A=2×10 -3 ​cm=20µm. The difference between the thickness h1 of the silicon substrate 10 and the depth h2 of the pit 31 is △h≥20µm. For a silicon substrate with a specific thickness h1, the depth h2 of the pit 31 can be determined, h2≤h1-20µm.

[0065] Assume that two identical silicon substrates (thickness of 180 µm) are provided, and pits with simple circular hole structures are set. The other conditions of the two silicon substrates are the same. The difference is that when the depths of the pits of the two silicon substrates are set to 170 µm and 80 µm respectively, the absorption curves of the two silicon substrates are as follows: Figure 3 As shown in the figure, the depth h2 of the pit must satisfy h2≤h1-1 / A, where h1=180 µm, 1 / A=20 µm, i.e. h2≤160 µm for better absorption. Figure 3 The test results show that in the wavelength range of 600-900 nm, the absorption of the silicon substrate with a pit depth of 80 µm is indeed significantly higher than the absorption of the silicon substrate with a pit depth of 170 µm.

[0066] By setting a plurality of pits 31 on the light-receiving surface of the silicon substrate 10 of the solar cell, and establishing a relationship between the difference △h between the thickness of the silicon substrate 10 and the depth of the pit 31 and the light absorption coefficient of the corresponding wavelength of the silicon substrate 10, the size of the pit can be designed according to different incident light conditions to ensure that the pit 31 structure is in the range of the best response efficiency for the incident light, thereby improving the absorption of the oblique incident light by the pit 31. The micron-sized pit 31 has a certain absorption effect for small-angle incident light and a good absorption effect for large-angle incident light.

[0067] In some embodiments, the vertical projection size of the pit 31 on the light-receiving surface (the first surface 11 or the second surface 12) is 10-200 µm. In the present application, the vertical projection size refers to the maximum width of the cross section of the pit 31 parallel to the thickness direction of the silicon substrate. That is, the size of the pit 31 is in the micron level. By limiting the projection size of the pit 31, the pit 31 has an adapted opening size, which allows light to enter the pit 31 and does not affect the strength of the silicon substrate 10.

[0068] Compared with the light-trapping structure in which the vertical projection size of the pit on the light-receiving surface is nanometer-level, the structural size of the pit 31 is micrometer-level, which can avoid the passivation layer from being successfully prepared on the inner wall of the light-trapping structure, thereby ensuring that a uniform passivation layer can be generated on the surface of the solar cell. At the same time, the pit 31 can reduce the specific surface area of ​​the solar cell, thereby reducing the recombination rate of non-equilibrium carriers on the surface of the solar cell, and will not affect the lateral transmission and collection of carriers on the surface of the solar cell, ultimately improving the photoelectric conversion efficiency of the solar cell.

[0069] Figure 4 and Figure 5 Several shapes of the pits 31 are shown as schematic diagrams. Figure 4 As shown, the pit 31 includes a first pit 31A. The first pit 31A includes a bottom wall 32 and a first side wall 34 connected to the bottom wall 32, wherein the first side wall 34 is connected between the light-receiving surface and the bottom wall 32. The angle between the first side wall 34 and the thickness direction of the silicon substrate 10 is less than or equal to 15 degrees. For example, the angle between the side wall 34 and the thickness direction of the silicon substrate 10 can be any one of 0 degrees, 1 degree, 2 degrees, 3 degrees, 4 degrees, 5 degrees, 6 degrees, 7 degrees, 8 degrees, 9 degrees, 10 degrees, 11 degrees, 12 degrees, 13 degrees, 14 degrees, and 15 degrees. The embodiment of the present application does not limit the specific value of the angle. Figure 1 As shown in the figure, the angle between the first side wall 34 of the pit 31 and the thickness direction of the silicon substrate 10 is 0 degrees, that is, the first side wall 34 of the first pit 31A is perpendicular to the first surface 11 and the second surface 12. Although not shown in the figure, when the angle between the first side wall 34 of the pit 31 and the thickness direction of the silicon substrate 10 is greater than 0 degrees, the cross section of the pit 31 along the thickness direction of the silicon substrate 10 is trapezoidal. That is, the opening size of the pit 31 is increasing or decreasing along the thickness direction of the silicon substrate 10 and pointing to the light receiving surface. The first side wall 34 is conducive to absorbing incident light with a larger incident angle.

[0070] In some embodiments, such as Figure 4 As shown, the pit 31 may also include a second pit 31B. The second pit 31B includes a second sidewall 36, and the angle between the second sidewall 36 and the thickness direction of the silicon substrate 10 is greater than 15 degrees and less than or equal to 60 degrees. For example, the angle between the two second sidewalls 36 can be any one of 16 degrees, 18 degrees, 20 degrees, 22 degrees, 24 degrees, 27 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, and 60 degrees. The embodiment of the present application does not limit the specific value of the angle. The second sidewall 36 is conducive to absorbing incident light with a smaller incident angle. When the incident angle of the incident light is small, the incident light can be projected on the second sidewall 36 and reflected back and forth on the second sidewall 36, increasing the optical path of the incident light, improving the absorption degree of the incident light by the silicon substrate 10, and meeting the requirements of photoelectric conversion. The second pit 31B may also have a bottom wall.

[0071] In some embodiments, such as Figure 4 As shown, the projections of the first pit 31A and the second pit 31B on the first surface do not overlap. That is, there are two pits 31 with different structures distributed on the first surface 11 or the second surface 12.

[0072] In some embodiments, such as Figure 5 As shown, the first pit 31A and the second pit 31B are arranged along the thickness direction of the silicon substrate 10 and connected to form a pit 31 with a specific structure.

[0073] Figure 4 and Figure 5 Three different structures of the pit 31 are shown. It can be understood that the second region 20 can be provided with at least one of the three structures of the pit 31. In addition, the shape of the pit 31 is not limited to Figure 4 and Figure 5 As shown, other shapes are also possible as long as they can increase the absorption of light.

[0074] It is known from the prior art that silicon substrates of different thicknesses have different absorption in the visible spectrum. If the thickness of the silicon substrate is too thin, light will not be completely absorbed, causing waste. If the silicon substrate is too thick, it will increase the cost.

[0075] In some embodiments, the thickness of the silicon substrate 10 ranges from 90 to 180 μm. For example, the thickness of the silicon substrate may be 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, or 180 μm. Further, the thickness of the silicon substrate ranges from 110 to 180 μm.

[0076] For incident light with a large incident angle, the multiple pits 31 on the surface of the solar cell can reduce the probability of the large-angle incident light being reflected out of the solar cell. The large-angle incident light is reflected multiple times in the pits 31, and has a larger optical path in the solar cell, thereby improving the solar cell's absorption effect on the incident light. At the same time, compared with the nano-scale light trapping structure (velvet structure or pits with a small plane size), the structural size of the pits 31 is micron-scale, making it easier to generate a uniform passivation layer on the surface of the solar cell, while reducing the recombination rate of non-equilibrium carriers on the surface of the solar cell, thereby improving the photoelectric conversion efficiency of the solar cell.

[0077] In some embodiments, the interval between adjacent pits 31 may be 2-200 μm, so that other structures of the solar cell may be arranged in the area between adjacent pits 31 to achieve the function of the solar cell. In some embodiments, a plurality of pits 31 are distributed in an array on the surface of the silicon substrate.

[0078] The shape of the pit 31 is not limited. In some embodiments, the shape of the pit 31 can be any one or more of a cylindrical, conical, triangular pyramidal, quadrangular prism-shaped or irregular shape, so that when the incident light is irradiated on the bottom wall and side wall of the micron-sized pit 31, it can be reflected multiple times in the micron-sized pit 31.

[0079] In some embodiments, the ratio of the total projected area of ​​all the pits 31 on the light-receiving surface (e.g., the first surface 11) to the area of ​​the light-receiving surface may be 30%-80%. If the projected area of ​​the pits 31 is too large, it will affect the mechanical strength of the cell and make the cell easy to break. If the projected area of ​​the pits 31 is too small, it may not be able to effectively improve the absorption of oblique incident light by the silicon substrate 10.

[0080] In the embodiment of the present application, the proportion of the projected area of ​​the micron-sized pits 31 on the light-receiving surface can be determined according to the specific application scenario of the photovoltaic module including the solar cell. Specifically, for application scenarios where large-angle incident light accounts for a large proportion, the projection size of the pits 31 on the light-receiving surface can be increased, or the number of pits 31 can be increased, so that the ratio of the projection area of ​​the pits 31 on the light-receiving surface to the light-receiving surface is large, thereby increasing the absorption effect of the solar cell for large-angle incident light. For application scenarios where large-angle incident light accounts for a small proportion, the projection size of the pits 31 on the light-receiving surface can be reduced, or the number of pits 31 can be reduced, so that the ratio of the projection area of ​​the pits 31 on the light-receiving surface to the surface area of ​​the light-receiving surface is small, so that the solar cell has a better absorption effect for the incident light.

[0081] like Figure 1 As shown, the area between the pits 31 on the first surface 11 of the silicon substrate 10 is defined as the first area 20, and the area where the pits 31 are located is defined as the second area 30. That is, the first surface 11 is divided into the first area 20 and the second area 30. The first area 20 can be set to a suede structure or a plane. Figure 1 The first region 20 is shown as a plane. Figure 6 and Figure 7 All of them show that the first area 20 has a suede structure.

[0082] In addition to the area between the pits 31 (the first area 20) which can be selectively provided with a velvet structure, further, in some embodiments, at least a portion of the side wall 34 of the pit 31 is provided with a velvet structure, or at least a portion of the side wall 34 of the pit and at least a portion of the bottom wall 32 are also provided with a velvet structure.

[0083] In some embodiments, the projection size of the pit on the first surface is d, the depth of the pit is h2, and the setting position of the velvet structure has a certain relationship with the ratio of the depth h2 to the projection size d of the pit. Taking into account the mechanical strength of the silicon wafer and the depth of the pit that satisfies the light trapping effect, the ratio range of the depth h2 and the projection size d of the pit on the first surface is usually set to 0.1≤h2 / d≤2. If h2 / d is too small or too large, it will affect the probability of large-angle light incident into the pit and reduce the light trapping effect brought by the pit. h2 / d can be any one of 0.1, 0.3, 0.5, 0.7, 0.9, 1, 1.3, 1.5, 1.7, 1.9, and 2.

[0084] In the embodiment of the present application, the incident angle range of the large-angle incident light is 45°-70°. According to different ratios of h2 / d, the setting area of ​​the velvet structure includes the following situations.

[0085] (1) When When the pit depth and projection size satisfy the above relationship, and the velvet structure is arranged near the pit opening, the velvet structure can be placed near the pit opening, so that the incident light with a large angle can be irradiated on the velvet structure of the side wall, increasing the number of reflections of the incident light in the pit, increasing the possibility of the incident light being completely absorbed by the pit, and improving the utilization rate of light;

[0086] (2) When When the pit depth and projection size satisfy the above relationship, and the velvet structure is arranged near the pit opening or on the entire side wall, the incident light at a large angle can be irradiated on the velvet structure of the side wall, increasing the number of reflections of the incident light in the pit, increasing the possibility of the incident light being completely absorbed by the pit, and improving the utilization rate of light;

[0087] (3) When When the pit depth and projection size satisfy the above relationship, and the velvet structure is set on the side wall close to the bottom wall or covers the entire side wall. At this time, the large-angle incident light is more likely to irradiate the side wall of the pit close to the bottom wall. Therefore, when the pit depth and projection size meet the above relationship, and the velvet structure is set on the side wall of the pit close to the bottom wall or all the side walls, the large-angle incident light can be irradiated on the velvet structure of the side wall, increasing the number of reflections of the incident light in the pit, increasing the possibility of the incident light being completely absorbed by the pit, and improving the utilization rate of light;

[0088] (4) When When the velvet structure is arranged on the side wall near the opening of the pit and covers the entire bottom wall, or the velvet structure covers the entire side wall and the bottom wall. At this time, the large-angle incident light is more likely to irradiate the position of the pit side wall near the pit opening and the bottom wall of the pit. Therefore, when the pit depth and the projection size satisfy the above relationship, and the velvet structure is arranged on the side wall and the bottom wall of the pit near the opening or on all the side walls and the bottom wall, the large-angle incident light can irradiate the velvet structure of the side wall, increase the number of reflections of the incident light in the pit, increase the possibility of the incident light being completely absorbed by the pit, and improve the utilization rate of light;

[0089] (5) When When the velvet structure is arranged on the side wall near the bottom wall and covers the entire bottom wall, or the velvet structure covers the entire side wall and the bottom wall. At this time, the incident light at a large angle is more likely to irradiate the position of the side wall of the pit near the bottom wall and the bottom wall of the pit. Therefore, when the pit depth and the projection size satisfy the above relationship, and the velvet structure is arranged on the side wall of the pit near the bottom wall and on the bottom wall or on all the side walls and the bottom wall, the incident light at a large angle can be irradiated on the velvet structure of the side wall, increasing the number of reflections of the incident light in the pit, increasing the possibility of the incident light being completely absorbed by the pit, and improving the utilization rate of light.

[0090] When the velvet structure is disposed on the side wall near the opening of the pit, the area occupied by the velvet structure may be equal to half of the area of ​​the side wall, or less than half of the area of ​​the side wall, or greater than half of the area of ​​the side wall.

[0091] When the suede structure is disposed at a position of the side wall close to the bottom wall, the area occupied by the suede structure may be equal to half of the area of ​​the side wall, or less than half of the area of ​​the side wall, or greater than half of the area of ​​the side wall.

[0092] For a pit without a velvet structure on the bottom wall and the side wall, when the oblique incident light enters the pit, due to the smooth wall surface, part of the incident light may leave the crystalline silicon cell from the opening of the pit 31 after several reflections. When there is a velvet structure (micro-nano pyramid structure) on the wall surface, after the oblique incident light enters the pit, due to the synergistic effect of the pit and the velvet structure, the number of reflections of the incident light in the pit can be increased, and the possibility of the incident light being completely captured by the pit structure can be increased. Therefore, more light energy can be converted into electrical energy, thereby increasing the power generation / power of photovoltaic devices / modules.

[0093] In some embodiments, the velvet structure is a pyramid structure, the base size of the velvet structure is less than or equal to 7 µm, and / or the tower height of the velvet structure is less than or equal to 5 µm. The base size refers to the longest distance among the length, width or diagonal length of the base of the bottom surface of the pyramid structure, and the tower height refers to the vertical distance between the top of the pyramid and the bottom surface.

[0094] When the first region 20 is configured as a suede structure, the sizes of the suede structure of the first region 20 and the suede structure in the recess 31 may be the same or different.

[0095] When the first region 20 is set as a velvet structure, the crystal orientation of the pyramid velvet structure in the first region 20 is the same as the crystal orientation of the pyramid velvet structure on the bottom wall of the pit.

[0096] The crystal plane compositions of the velvet pyramids on the first surface, the velvet pyramids on the bottom wall of the pit and the velvet pyramids on the side wall are significantly different. The velvet pyramids on the first region 20 and the bottom wall 32 are composed of four crystal planes, namely [1,1,1], [-1,1,1], [1,-1,1], [-1,-1,1]. On the side wall 34 of the pit 31, the crystal plane compositions of the velvet pyramids are [1,1,1], [-1,1,1], [1,1,-1], [-1,1,-1] (or [1,1,1], [1,-1,1], [1,1,-1], [1,-1,-1], [1,-1,-1]).

[0097] The present application also provides a solar cell, comprising the above-mentioned silicon substrate 10.

[0098] The first region 20 can be set as a velvet structure, which is a small-angle light trapping structure. The velvet structure has a good anti-reflection effect for vertical incident light or incident light with a small incident angle, which can reduce the probability of the small-angle incident light being reflected out of the solar cell, thereby increasing the absorption effect of the small-angle incident light.

[0099] In this way, when light is obliquely irradiated onto the light receiving surface of the silicon substrate 10, the reflection and light trapping effects of the suede structure and the pit 31 structure can be used to increase the optical path, thereby effectively improving the silicon substrate's absorption of light.

[0100] The first region 20 with a velvet structure is composed of pyramids and / or inverted pyramid structures distributed on the light-receiving surface. The silicon substrate can be prepared from a single-crystal silicon wafer. Accordingly, the velvet structure is a regular or irregular pyramid and / or inverted pyramid structure prepared on the surface of a single-crystal silicon wafer by a velvet process. The silicon substrate 10 can also be prepared from a polycrystalline silicon wafer. Accordingly, the velvet structure is a regular or irregular pyramid and / or inverted pyramid structure prepared on the surface of a polycrystalline silicon wafer by a velvet process. The pit 31 can be formed by wet etching or dry etching.

[0101] By setting a plurality of pits 31 on the light-receiving surface of the silicon substrate 10 of the solar cell, and establishing a connection between the difference △h between the thickness of the silicon substrate 10 and the depth of the pits 31 and the light absorption coefficient of the corresponding wavelength of the silicon substrate 10, the absorption of the pits 31 to oblique incident light is improved, and the requirements for special wavelength response are met. The area between the pits 31 can be set as a velvet structure to enhance the absorption effect of small-angle incident light, and the micron-level pits 31 have a good absorption effect for large-angle incident light. Therefore, the solar cell has a high omnidirectionality. When the photovoltaic module containing the solar cell is installed in an aircraft, a car or a building, the solar cell can have a good incident light absorption effect without the need for adjusting the installation position and using a tracking bracket, thereby improving the photoelectric conversion efficiency of the photovoltaic module and achieving a larger power generation.

[0102] The solar cell also includes a passivation layer. The passivation layer is disposed on the bottom wall and side wall of the first region 20 and the pit 31. Compared with the nano-scale light trapping structure, the micron-scale pit 31 has a larger structural size. Therefore, a uniform passivation layer can be effectively generated on the surface of the solar cell to achieve surface passivation of the solar cell. In some embodiments, the passivation layer includes an aluminum oxide layer and an anti-reflection layer. The thickness of the aluminum oxide layer does not exceed 10 nm. The anti-reflection layer is made of Si y N x or Si z N x O y , with a thickness of usually no more than 100 nm.

[0103] The solar cell of the present application also includes an electrode. In some embodiments, the electrode includes a plurality of collecting electrodes, and the collecting electrodes are arranged in the area between the plurality of pits. In other embodiments, the electrode includes a plurality of collecting electrodes and a plurality of bus electrodes, and the collecting electrodes are arranged in the area between the plurality of pits; the bus electrode is arranged in the area between the plurality of pits, or part of the bus electrode is arranged in a part of the pit area, and the other part is arranged in the area between the plurality of pits. In short, the electrodes cannot be entirely arranged in the micron-sized pits 31, so as to reduce the filling of the micron-sized pits 31 by the electrodes, and avoid affecting the light trapping function of the micron-sized pits 31 for reflecting light at large angles.

[0104] Optionally, the solar cell in the embodiment of the present application may be a solar cell with double-sided electrodes, such as a tunneling oxide passivation contact cell (TOPCon). Figure 6 , shows a schematic structural diagram of a double-sided electrode solar cell provided in an embodiment of the present application, such as Figure 6As shown, the solar cell includes a silicon substrate 10, a first electrode 13 and a first passivation layer 15 arranged on a first surface 11 of the silicon substrate 10, and a second passivation layer 14 and a second electrode 16 arranged on a second surface 12 of the silicon substrate 10, wherein the first surface 11 is a light-receiving surface, and the first surface 11 is provided with a first region 20 and a second region 30.

[0105] Taking the TOPCon battery as an example, the first passivation layer 15 is arranged on the bottom wall and side wall of the pit 31 in the first area 20 and the second area 30, the first electrode 13 is located on the side of the first passivation layer 15 away from the silicon substrate 10, the second passivation layer 14 is arranged on the second surface 12 of the silicon substrate 10, and the second electrode 16 is located on the side of the second passivation layer 14 away from the silicon substrate 10.

[0106] Specifically, the silicon substrate 10 can be an n-type silicon substrate prepared from an n-type crystalline silicon wafer; the first passivation layer 15 can be a multi-layer structure, for example, the first passivation layer 15 can include silicon oxide and silicon nitride, which respectively play the role of surface passivation and anti-reflection on one side of the solar cell; the second passivation layer 14 can also be a multi-layer structure, for example, the second passivation layer 14 can include silicon oxide, doped polycrystalline silicon, aluminum oxide and silicon nitride, thereby realizing the surface passivation and anti-reflection function of the other side of the solar cell.

[0107] Furthermore, a first electrode 13 is provided on the first surface 11 of the silicon substrate 10, and a second electrode 16 is provided on the second surface 12 of the silicon substrate 10, thereby forming a solar cell with double-sided electrodes. Specifically, the electrodes can be prepared by screen printing, electroplating and other methods, and the electrode materials can include conductive materials such as Ag, Al, Ni, etc., which are not specifically limited here.

[0108] Optional, see Figure 6 The first electrode 13 may include a bus electrode and a collector, and the bus electrode is not shown in the figure. The collector includes a first collector 131 and a second collector 132, and the first collector 131 may be arranged in the pit 31 of the first region 20 and / or the second region 30, and the second collector 132 may be arranged in the first region 20.

[0109] It is understandable that in some embodiments, the busbar electrode may be omitted, that is, at least the first surface of the solar cell is designed without the busbar electrode.

[0110] Optionally, the solar cell in the embodiment of the present application may be a solar cell having a single-sided electrode, such as an interdigitated back contact cell (IBC).

[0111] See also Figure 7 , shows a schematic structural diagram of a passivated contact back contact solar cell provided by an embodiment of the present application, such as Figure 7 As shown, the solar cell includes a silicon substrate 10, a first passivation layer 21 disposed on a first surface 11 of the silicon substrate 10, and a functional layer 28, a second passivation layer 22, a first electrode 24, and a second electrode 26 disposed on a second surface 12 of the silicon substrate 10. The first surface 11 is a light-receiving surface, and the first surface 11 is provided with a first region 20 and a second region 30.

[0112] In some embodiments, the silicon substrate 10 may be an n-type silicon substrate prepared from an n-type crystalline silicon wafer.

[0113] The first passivation layer 21 is disposed in the region between the pits 31 and on the bottom wall and side wall of the pits 31. The first passivation layer 21 has the functions of passivation and anti-reflection on the first surface. Although not shown in the figure, the first passivation layer 21 is disposed in the region between the pits 31 of the first surface 11 and on the bottom wall and side wall of the pits 31, and the first passivation layer 21 does not fill the pits 31.

[0114] Although not shown, the functional layer 28 includes a stacked tunnel oxide layer and a doped polysilicon layer, wherein the doped polysilicon layer is located on the surface of the tunnel oxide layer away from the silicon substrate 10. The tunnel oxide layer is silicon oxide and has a thickness of several nanometers.

[0115] The second passivation layer 22 is disposed on the surface of the functional layer 28 away from the silicon substrate 10, and performs passivation and anti-reflection functions on the second surface 12. For example, the second passivation layer 22 includes a stacked aluminum oxide layer and an anti-reflection layer. The first electrode 24 and the second electrode 26 are disposed on the second passivation layer 22.

[0116] The first electrode 24 may include a first bus electrode (not shown) and a first collector electrode (not shown), and the second electrode 26 may include a second bus electrode (not shown) and a second collector electrode (not shown). It is understandable that the first bus electrode and / or the second bus electrode may also be omitted, that is, at least the first surface of the solar cell is designed without a bus electrode.

[0117] In the present application, a plurality of pits 31 are arranged on the light-receiving surface of the silicon substrate of the solar cell, and a relationship is established based on the difference △h between the thickness of the silicon substrate and the depth of the pit 31 and the light absorption coefficient of the corresponding wavelength of the silicon substrate. The established relationship can be used to design the pit size according to different incident light conditions to ensure that the pit 31 structure is in the range of the best response efficiency for the incident light, increase the utilization rate of light and improve the absorption of the pit 31 for oblique incident light. The micron-sized pits 31 have a good absorption effect for large-angle incident light. In addition, a velvet structure can be arranged in the area between the pits 31 to enhance the absorption effect for small-angle incident light. Therefore, the solar cell has a high omnidirectionality. When the photovoltaic module containing the solar cell is installed in an aircraft, a car and a building, the solar cell can have a good incident light absorption effect without the need to adjust the installation position and use a tracking bracket, thereby improving the photoelectric conversion efficiency of the photovoltaic module and achieving a large amount of power generation.

[0118] The above implementation modes are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the above preferred implementation modes, a person skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A silicon substrate, characterized in that: include: a first surface and a second surface that are opposite; A plurality of pits are located on the first surface; the thickness of the silicon substrate is h1, the depth of the pit is h2, wherein the difference △h between h1 and h2 satisfies h1>△h≥1 / A (λ=300nm) , where A (λ=300nm) is the light absorption coefficient of the silicon substrate at wavelength λ = 300nm, in cm -1 .

2. The silicon substrate according to claim 1, characterized in that When 0.5×h1<1 / A (λ=x) <h1, then △h≤0.5×h1; When 1 / A (λ=x) When <0.5×h1, △h satisfies 1 / A (λ=x) ≤△h≤0.5×h1, where A (λ=x) is the light absorption coefficient of the silicon substrate at wavelength x, where x≥900nm.

3. The silicon substrate according to claim 1, characterized in that A projection size d of the pit on the first surface is 10-200 μm.

4. The silicon substrate according to claim 1, characterized in that The pit includes a first pit, the first pit includes a first sidewall, and an angle between the first sidewall and a thickness direction of the silicon substrate is less than or equal to 15 degrees.

5. The silicon substrate according to claim 1 or 4, characterized in that: The pit includes a second pit, the second pit includes a second sidewall, and an angle between the second sidewall and a thickness direction of the silicon substrate is greater than 15 degrees and less than or equal to 60 degrees.

6. The silicon substrate according to claim 4, characterized in that The pit further includes a second pit, the second pit includes a second sidewall, and an angle between the second sidewall and the thickness direction of the silicon substrate is greater than 15 degrees and less than or equal to 60 degrees; The projections of the first pit and the second pit on the first surface do not overlap; and / or, The first pit and the second pit are arranged along the thickness direction of the silicon substrate and are connected.

7. The silicon substrate according to claim 1, characterized in that The thickness of the silicon substrate is in the range of 90-180 μm; or, The thickness of the silicon substrate ranges from 110 to 180 μm.

8. The silicon substrate according to claim 1, characterized in that The ratio of the sum of the projection areas of the plurality of pits on the first surface to the area of ​​the first surface is 30%-80%.

9. The silicon substrate according to claim 1, characterized in that The interval between adjacent pits is 2-200 μm; and / or, The plurality of pits are distributed in an array.

10. The silicon substrate according to claim 1, characterized in that The pit comprises a bottom wall and a side wall connected to the bottom wall, At least part of the side wall is provided with a suede structure, or, At least a portion of the side wall and at least a portion of the bottom wall are also provided with a suede structure.

11. The silicon substrate according to claim 10, characterized in that The projection size of the pit on the first surface is d, when When the velvet structure is arranged at a position of the side wall close to the opening of the pit; when When the velvet structure is disposed on the side wall near the opening of the pit or covers the entire side wall; when When the velvet structure is arranged at a position of the side wall close to the bottom wall or covers the entire side wall; when When the velvet structure is arranged at a position of the side wall close to the opening of the pit and covers the entire bottom wall, or the velvet structure covers the entire side wall and the bottom wall; when When the velvet structure is arranged at a position of the side wall close to the bottom wall and covers the entire bottom wall, or the velvet structure covers the entire side wall and the bottom wall.

12. The silicon substrate according to claim 10, characterized in that The velvet structure is a pyramid structure, the size of the pyramid base of the velvet structure is less than or equal to 7 µm, and / or the pyramid height of the velvet structure is less than or equal to 5 µm.

13. A solar cell, characterized in that: Comprising the silicon substrate according to any one of claims 1 to 12.

14. The solar cell according to claim 13, characterized in that: The solar cell includes a passivation layer, which is disposed on the first surface, the second surface, and a bottom wall and a side wall of the pit, and does not fill up the pit.

15. The solar cell according to claim 13, characterized in that: The solar cell comprises an electrode; The electrode comprises a plurality of collectors, and the collectors are arranged in the areas between the pits; Alternatively, the electrode includes a plurality of bus electrodes and a plurality of collecting electrodes, the collecting electrodes are arranged in the area between the pits, the bus electrodes are arranged in the area between the pits, or part of the bus electrode is arranged in a partial area of ​​the pits and the other part is arranged in the area between the pits.

16. A photovoltaic module, characterized in that: A solar cell comprising the solar cell according to any one of claims 13 to 15.

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