Omnidirectional light trapping structure and solar cell

Abstract

The invention discloses an omnidirectional light trapping structure and a solar cell, which are applied to the field of photovoltaic technology, and comprise a recess arranged on the surface of a substrate, and the recess extends from the surface of the substrate to the interior of the substrate along the thickness direction of the substrate; the wall surface extending from the opening of the recess in the recess is parallel to the thickness direction; the bottom of the recess has an inclined surface, so that the section of the bottom of the recess in the thickness direction forms a V-shaped structure; the projection of the slope in the slope normal direction does not exceed the opening. When the angle of the incident light is large, the incident light can irradiate the wall surface extending from the opening of the recess, so that the incident light can be refracted for multiple times in the recess; when the angle of the incident light is small, the incident light can be reflected towards the interior of the recess and cannot be reflected towards the opening, so that the incident light can be reflected for multiple times in the recess, and omnidirectional light trapping is realized.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic technology, and in particular to an omnidirectional light trapping structure and a solar cell. Background Art

[0002] Solar cells are one of the mainstream clean energy technologies in the world. Currently, the application of solar cell technology is mainly divided into centralized photovoltaic systems and distributed photovoltaic systems. Distributed photovoltaic construction is on the user side, and electricity is used immediately after it is generated, reducing the expenditure on power transmission and energy storage equipment. At the same time, distributed photovoltaic systems are mainly installed on the outer surface of buildings or on open spaces in parks, effectively saving land resources. Therefore, countries are vigorously carrying out application research on distributed photovoltaic technology. As the main application carrier of distributed photovoltaics, buildings consume about 40% of the world's energy, most of which is concentrated in heating and cooling. With the advancement of industrialization, the proportion of building energy consumption is expected to increase further. Building integrated photovoltaics (BIPV) offsets part of the building's energy consumption by installing solar cells on the surface of the building to generate electricity, which is one of the mainstream measures in the field of building energy conservation and distributed solar energy.

[0003] The current building photovoltaic integration (BIPV) solution is to install non-transparent solar cells on the facades and roofs of buildings, and the mainstream solution is to install photovoltaic modules on the roofs. Building facades, especially high-rise building facades, are rarely used. The main reason for this phenomenon is that the photovoltaic conversion efficiency of solar cells installed on the vertical surface is usually lower than that of horizontal surface installation. The main reason for the low efficiency of facade photovoltaic power generation is that the vertical installation causes a significant change in the range of the incident angle of the sun to the components. The horizontal solar cells mainly work within the range of 0°-40° incident angle, while the facade solar cells mainly work within the range of 50°-90°, which leads to a decrease in the light absorption capacity of the vertically installed solar cells, and then leads to a decrease in their photovoltaic conversion efficiency. Under actual working conditions, the cell efficiency of crystalline silicon solar cells is reduced by about 10%-60% due to light loss. Therefore, the current building photovoltaic integration is heavily dependent on the building roof area, and the high-rise buildings further reduce the proportion of the roof in the building's outer surface area, resulting in low power generation of the existing building photovoltaic integration system, which is difficult to promote and apply on a large scale in cities.

[0004] Therefore, solving the problem of large-angle light absorption of existing solar cells can promote the efficiency of solar cell modules installed on the facade, thereby developing and utilizing the entire building exterior surface, greatly increasing the total power generation of the building photovoltaic integrated system, and further promoting the large-scale application of this technology in cities. Therefore, how to provide an omnidirectional light trapping structure is an urgent problem that technicians in this field need to solve. Summary of the invention

[0005] An object of the present invention is to provide an omnidirectional light trapping structure that can achieve omnidirectional light trapping; another object of the present invention is to provide a solar cell that has a high light absorption efficiency for incident light at any angle.

[0006] In order to solve the above technical problems, the present invention provides an omnidirectional light trapping structure, comprising a depression arranged on the surface of a substrate, wherein the depression extends from the surface of the substrate to the inside of the substrate along the thickness direction of the substrate;

[0007] The wall surface extending from the opening of the depression is parallel to the thickness direction; the bottom of the depression has an inclined surface, so that the cross section of the bottom of the depression along the thickness direction forms a V-shaped structure; the projection of the inclined surface along the normal direction of the inclined surface does not exceed the opening.

[0008] Optionally, a height of a wall extending from the opening in the recess in parallel to the thickness direction is not less than a preset height, so that incident light within a target angle range directly irradiates the wall in parallel to the thickness direction after passing through the opening.

[0009] Optionally, the target angle range is in the range of 50° to 90°.

[0010] Optionally, the bottom of the depression is symmetrically distributed along the axis of the depression in the thickness direction.

[0011] Optionally, a transition section is provided between a wall surface of the recess extending from an opening of the recess and the inclined surface.

[0012] Optionally, the opening is circular or rectangular;

[0013] And / or, the bottom is in the shape of a quadrangular pyramid or a cone.

[0014] Optionally, the recesses are multiple and are distributed in an array.

[0015] Optionally, the depth-to-width ratio of the recess ranges from 1.2 to 4; and the included angle of the V-shaped structure ranges from 30° to 60°.

[0016] Optionally, the concave surface is provided with an anti-reflection layer.

[0017] The present invention also provides a solar cell, comprising the omnidirectional light trapping structure as described in any one of the above items.

[0018] The present invention provides an omnidirectional light trapping structure, comprising a depression arranged on a substrate surface, wherein the depression extends from the substrate surface to the inside of the substrate along the thickness direction of the substrate; a wall surface extending from an opening of the depression in the depression is parallel to the thickness direction; the bottom of the depression has an inclined surface, so that the cross section of the bottom of the depression along the thickness direction forms a V-shaped structure; and the projection of the inclined surface along the normal direction of the inclined surface does not exceed the opening.

[0019] When the incident light angle is large, it will illuminate the wall extending from the recess opening, so that the incident light will be refracted multiple times in the recess; when the incident light angle is small, although it will directly illuminate the inclined surface at the bottom of the recess, because the projection of the inclined surface along the normal direction of the inclined surface does not exceed the opening, the angle between the incident light and the direction of the inclined surface extending toward the opening is less than 90°, ensuring that the incident light will be reflected into the recess instead of toward the opening, so that the incident light will be reflected multiple times in the recess, thereby achieving omnidirectional light trapping. At the same time, because the omnidirectional light trapping structure does not increase the surface area of ​​the solar cell too much, it will not significantly increase the carrier surface recombination, ensuring that the solar cell has a high light absorption efficiency for incident light at any angle, while ensuring that the solar cell has a high conversion efficiency.

[0020] The present invention further provides a solar cell, which also has the above-mentioned beneficial effects, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 A schematic structural diagram of an omnidirectional light trapping structure provided by an embodiment of the present invention;

[0023] Figure 2 for Figure 1 A schematic diagram of the front view structure of

[0024] Figure 3 is a structural schematic diagram of a specific omnidirectional light trapping structure;

[0025] Figure 4 A schematic structural diagram of an omnidirectional light trapping structure array provided by an embodiment of the present invention;

[0026] Figure 5 A schematic structural diagram of another specific omnidirectional light trapping structure provided by an embodiment of the present invention;

[0027] Figure 6 This is a comparison of the average reflectivity of the omnidirectional light trapping structure and the inverted pyramid structure with an aspect ratio of 2;

[0028] Figure 7(a)-(e) are schematic diagrams of the monomer structures of omnidirectional light trapping structures with aspect ratios of 2.7, 2, 1.8, 1.7, and 1.6, respectively. (f) is a comparison of the relationship between the average reflectivity and the incident angle of the omnidirectional light trapping structures with different aspect ratios.

[0029] Figure 8 (a)-(d) are the comparison diagrams of the absorption rate of the omnidirectional light trapping structure and the inverted pyramid structure at incident angles of 0°, 30°, 60°, and 89° respectively;

[0030] Fig. 9 (a) is the relationship between the number of reflections and the incident angle of the omnidirectional light trapping structure and the inverted pyramid structure at the air-silicon interface;

[0031] Fig. 9 (b) is a comparison of the optical path propagation length inside the silicon absorption layer of the omnidirectional light trapping array structure and the inverted pyramid array structure;

[0032] Fig.10 (a) Schematic diagram of the principle of multiple capture of incident light by the omnidirectional light trapping structure;

[0033] Fig.10 (b) Schematic diagram of the light trapping effect on the top and bottom planes of the light trapping structure;

[0034] Fig.10 (c) is the tilt angle of the micron wire cone Schematic diagram of the impact on large-angle incident light;

[0035] Fig.11 This is a comparison chart of the average reflectivity and aspect ratio of the omnidirectional light trapping structure and the existing black silicon technology;

[0036] Fig.12 (a) is a diagram of an omnidirectional light trapping structure with a rectangular cross section;

[0037] Fig.12 (b) is a diagram of an omnidirectional light trapping structure with a circular cross section;

[0038] Fig.12 (c) is a diagram of an omnidirectional light trapping structure with a groove-shaped cross section;

[0039] Fig.12 (d) is a cross-sectional diagram of a hybrid omnidirectional light trapping structure.

[0040] In the figure: 1. base, 2. opening, 3. wall, 4. inclined surface, 5. transition section. DETAILED DESCRIPTION

[0041] The core of the present invention is to provide an omnidirectional light trapping structure. In the prior art, crystalline silicon solar cells are the most commercially successful solar cells with the largest market share at this stage, and are also the mainstream technology of non-transparent facade solar cell technology. The absorption layer of crystalline silicon solar cells is a crystalline silicon wafer. The front surface light trapping technology of the silicon absorption layer of commercial crystalline silicon solar cells can be divided into two categories: commercial texturing technology and black silicon technology.

[0042] The positive pyramid structure or inverted pyramid structure formed by commercial texturing technology has an average reflectivity of about 11.7% for the pyramid light-trapping structure with an anti-reflection layer on the front surface and about 6.44% for the inverted pyramid structure with an anti-reflection layer on the front surface when the light is incident vertically (the incident angle is 0°). However, its reflectivity increases with the increase of the incident angle. When the incident angle is greater than 70°, its reflectivity is usually higher than 20%. That is, for light with a large incident angle, the velvet surface formed by commercial texturing technology cannot effectively absorb it, and the velvet surface will directly reflect a large amount of light back to the outside world.

[0043] The above-mentioned black silicon technology usually refers to silicon-based light trapping technology with an average reflectivity of less than 5%, but the black silicon light trapping structure of the existing black silicon technology usually has a low reflectivity for light with a large incident angle, and the aspect ratio of the black silicon light trapping structure is usually greater than 5, which will make it difficult for the existing thin film deposition process to effectively passivate the black silicon surface, resulting in a large loss of electrical performance caused by surface recombination. As a result, the light absorption capacity is enhanced, but the actual photoelectric conversion efficiency of the solar cell is reduced.

[0044] The present invention provides an omnidirectional light trapping structure, including a depression arranged on the surface of a substrate, wherein the depression extends from the surface of the substrate to the inside of the substrate along the thickness direction of the substrate; a wall surface extending from the opening of the depression in the depression is parallel to the thickness direction; the bottom of the depression has an inclined surface, so that the cross-section of the bottom of the depression along the thickness direction forms a V-shaped structure; and the projection of the inclined surface along the normal direction of the inclined surface does not exceed the opening.

[0045] When the incident light angle is large, it will illuminate the wall extending from the recess opening, so that the incident light will be refracted multiple times in the recess; when the incident light angle is small, although it will directly illuminate the inclined surface at the bottom of the recess, the projection of the inclined surface along the normal direction of the inclined surface does not exceed the opening, so that the angle between the incident light and the extending direction of the inclined surface toward the opening side is less than 90°, ensuring that the incident light will be reflected into the recess instead of toward the opening, so that the incident light will still be reflected multiple times in the recess, thereby achieving omnidirectional light trapping. At the same time, because the omnidirectional light trapping structure does not increase the surface area of ​​the solar cell too much, it will not significantly increase the carrier surface recombination, ensuring that the solar cell has a high light absorption efficiency for incident light at any angle, while ensuring that the solar cell has a high conversion efficiency.

[0046] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0047] Embodiment 1

[0048] Please refer to Figures 1 to 4 , Figure 1 A schematic structural diagram of an omnidirectional light trapping structure provided by an embodiment of the present invention; Figure 2 for Figure 1 A schematic diagram of the front view structure of Figure 3 is a structural schematic diagram of a specific omnidirectional light trapping structure; Figure 4 A schematic diagram of the structure of an omnidirectional light trapping structure array provided by an embodiment of the present invention.

[0049] See also Figure 1 as well as Figure 2 In an embodiment of the present invention, the omnidirectional light trapping structure includes a depression arranged on the surface of the substrate 1, and the depression extends from the surface of the substrate 1 to the inside of the substrate 1 along the thickness direction of the substrate 1; the wall surface 3 extending from the opening 2 of the depression in the depression is parallel to the thickness direction; the bottom of the depression has a slope 4, so that the cross-section of the bottom of the depression along the thickness direction forms a V-shaped structure; the projection of the slope 4 along the normal direction of the slope 4 does not exceed the opening 2.

[0050] The above-mentioned substrate 1 is usually a cell, that is, the omnidirectional light trapping structure in this embodiment is mainly used in solar cells. The omnidirectional light trapping structure is suitable for crystalline silicon solar cells. It is usually arranged on the front surface of the solar cell, and the surface of the omnidirectional light trapping structure can be covered by a passivation layer or an anti-reflection layer. In this embodiment, the omnidirectional light trapping structure is generally a concave structure, that is, it is a concave arranged on the surface of the substrate 1, and the concave will extend from the surface of the substrate 1 to the inside of the substrate 1 along the thickness direction of the substrate 1. Of course, in this embodiment, in addition to being a cell, the above-mentioned substrate 1 can be glass, a flexible solar cell with the omnidirectional light trapping structure in this embodiment as a frame, etc. The substrate 1 can also be only a partial structure when preparing a cell, such as a silicon wafer, or a diffusion sheet that has undergone a diffusion process, etc. The specific material of the substrate 1 is not specifically limited here. The above-mentioned thickness direction is a direction perpendicular to the plane where the surface of the substrate 1 is located. In this embodiment, the omnidirectional light trapping structure will be arranged along the thickness direction of the substrate 1. The omnidirectional light trapping structure will form an opening 2 in the substrate 1 and extend from the position of the opening 2 to the inside of the substrate 1.

[0051] In this embodiment, the depression constituting the omnidirectional light trapping structure includes at least two parts along the thickness direction, one of which is the opening part and the other is the bottom part, and the opening part and the bottom part are arranged in sequence from the surface of the substrate 1 to the inside of the substrate 1 along the thickness direction. The opening part generally includes an opening 2 formed by the depression and a section of wall surface 3 extending from the opening 2 to the inside of the substrate 1. In this embodiment, the wall surface 3 extending from the opening 2 of the depression is parallel to the thickness direction, and the section of wall surface 3 extends from the opening 2 of the depression, that is, the end of the section of wall surface 3 surrounds the opening 2 of the depression. The extension direction of the section of wall surface 3 is parallel to the thickness direction of the substrate 1, that is, the section of wall surface 3 extends vertically downward. For a solar cell, the incident angle of its incident light is the angle between the incident light and the normal direction of the substrate 1, that is, the angle between the incident light and the thickness direction. When the incident angle of the incident light is large, for example, close to 90°, the incident light will directly irradiate the wall surface 3 extending from the opening 2, so that multiple reflections occur in the depression for absorption.

[0052] The above-mentioned bottom usually has an inclined surface 4, so that the cross section of the bottom of the depression along the thickness direction forms a V-shaped structure; in this embodiment, the cross section of the bottom of the depression along the thickness direction needs to be a V-shaped structure, so the bottom has at least one inclined surface 4, and the so-called inclined surface 4 is a surface where the surface of the inclined surface 4 is at a certain angle with the above-mentioned thickness direction and the surface of the base 1. For example, when the bottom of the depression is an inverted cone, the bottom of the depression has an arc-shaped inclined surface 4; when the bottom of the depression is an inverted pyramid, the bottom of the depression has multiple inclined surfaces 4. In this embodiment, the cross section of the bottom of the depression along the thickness direction forms a V-shaped structure, that is, the bottom of the depression will converge into a line or a point, and its structure depends on the specific situation and is not specifically limited here. Generally, in this embodiment, the bottom of the depression is symmetrically distributed along the axis of the depression along the thickness direction. That is, the bottom of the depression will converge on the axis of the depression along the thickness direction, that is, the inclination angles of the inclined surfaces 4 on both sides of the V-shaped structure are equal. Of course, the inclination angles of the inclined surfaces 4 on both sides of the V-shaped structure may be different, but the projection of the inclined surface 4 on any side along the normal direction of the inclined surface 4 must not exceed the opening 2 to ensure that multiple reflections can be achieved for light at any incident angle.

[0053] In actual situations, when the incident angle of the incident light is small, it can directly irradiate the inclined surface 4 at the bottom of the depression. In this embodiment, the projection of the inclined surface 4 along the normal direction of the inclined surface 4 does not exceed the opening 2 of the depression, that is, when the external light passes through the opening 2 and irradiates the above-mentioned inclined surface 4, it will not be reflected toward the side of the opening 2 due to the angle problem, but will be absorbed by multiple reflections in the depression. The projection of the inclined surface 4 along the normal direction of the inclined surface 4 does not exceed the opening 2 of the depression, which means that the normal of the inclined surface 4 toward the top of the opening 2 will not extend out of the opening 2, but will extend to the wall 3 extending from the opening 2 to the inside of the base 1. This means that due to the existence of the wall 3 whose extension direction is parallel to the thickness direction, the external light directly irradiates the position of the inclined surface 4 at the bottom of the depression, and the normal must be toward the side of the opening 2 at the irradiation position, so the reflected light must propagate toward the inside of the depression and will not propagate directly from the opening 2 of the depression to the outside world, thereby realizing multiple reflections of the light in the depression to ensure the light absorption efficiency of the base 1. Therefore, regardless of the size of the incident light angle, the light irradiated to the above-mentioned depression will be reflected multiple times in the depression, thereby achieving omnidirectional light trapping.

[0054] It should be noted that the wall surface 3 extending from the recessed opening 2 is parallel to the thickness direction, which means that the wall surface 3 is substantially parallel to the thickness direction, rather than absolutely parallel. If the angle between the wall surface 3 extending from the recessed opening 2 and the horizontal direction is , then the The value range of is usually 80° to 90°, and of course the value of the above α1 is preferably 90°.

[0055] The omnidirectional light trapping structure in this embodiment is particularly suitable for solar cells arranged on the facade of a building. Compared with solar cells arranged on the roof of a building, the incident angle of the light received by the solar cells arranged on the facade of the building is usually close to 90°, rather than the conventional range close to 0°. In this embodiment, the main incident angle value range of the light received by the solar cells arranged on the facade of the building is specifically determined as the target angle range, and the height of the wall surface 3 extending from the opening 2 in the recess parallel to the thickness direction is not less than the preset height, so that the incident light within the target angle range passes through the opening 2 and directly irradiates the wall surface 3 parallel to the thickness direction. That is, when the above-mentioned omnidirectional light trapping structure is applied to the facade of a building, most of its incident light will directly irradiate the wall surface 3 parallel to the thickness direction, so as to ensure that the light with an incident angle within the target angle range will be reflected as much as possible in the recess, so as to improve the light absorption efficiency of the solar cell. Generally, the value range of the target angle range in this embodiment is 50° to 90°. Of course, in this embodiment, the specific value of the target angle range is not specifically limited, depending on the specific situation.

[0056] See also Figure 3Specifically, in the present embodiment, a transition section 5 is provided between the wall surface 3 extending from the opening 2 of the recess and the inclined surface 4. In the present embodiment, the wall surface 3 extending from the opening 2 of the recess can be directly connected to the inclined surface 4 at the bottom of the recess, and the wall surface 3 and the inclined surface 4 can also be connected through the transition section 5. The cross section of the transition section 5 along the thickness direction can be formed by a curve or a multi-segment line with a similar slope, and the slope of the transition section 5 gradually transitions from the vertical or approximately vertical wall surface 3 on the upper side to the inclined surface 4 forming a V-shaped structure on the lower side. Of course, the transition section 5 may not be provided in the present embodiment, and no specific limitation is made here.

[0057] In this embodiment, the opening 2 is usually circular or rectangular; and / or the bottom is usually quadrangular pyramid or conical. Of course, in this embodiment, as long as the cross section of the above-mentioned depression along the thickness direction conforms to the above-mentioned structure, it has similar omnidirectional low reflectivity and omnidirectional light absorption ability, regardless of whether the top-view structure or the bottom-view structure of the above-mentioned depression is a polygon such as a triangle, rectangle, hexagon, a circle, an ellipse, a groove, or a mixed type, it can be any shape, and no specific limitation is made here.

[0058] See also Figure 4 Furthermore, in the present embodiment, the surface of the substrate 1 may include a plurality of the above-mentioned depressions, and the plurality of depressions are distributed in an array. At this time, when light is incident into the depression from the external direction, it will not only be reflected in one depression, but also further refracted between adjacent depressions, thereby further improving the efficiency of the solar cell in absorbing light. In the present embodiment, the depression opening 2 may be arranged to be rectangular, so that the array structure formed by the plurality of depressions can achieve a smaller array spacing, thereby greatly increasing its area share on the front surface of the silicon wafer. For example, under the condition of a side length of 5μm and a line width processing condition of 20nm, its area share can reach 99.2%, thereby making the front surface anti-reflection capability of the omnidirectional light trapping structure array close to that of a single omnidirectional light trapping structure (area share 100%).

[0059] Furthermore, in this embodiment, the concave surface is provided with an anti-reflection layer. Since the omnidirectional light trapping structure in this embodiment is relatively simple and the aspect ratio of the structure can be low, the aspect ratio of the structure can be less than 4, thereby ensuring that the surface of the omnidirectional light trapping structure can be completely covered with the anti-reflection layer, so as to further improve the light absorption efficiency of the substrate 1.

[0060] The present embodiment provides an omnidirectional light trapping structure. When the incident light angle is large, it will irradiate the wall surface 3 extending from the recess opening 2, so that the incident light will be refracted multiple times in the recess; when the incident light angle is small, although it will directly irradiate the inclined surface 4 at the bottom of the recess, because the projection of the inclined surface 4 along the normal direction of the inclined surface 4 does not exceed the opening 2, the angle between the incident light and the extending direction of the inclined surface 4 toward the opening 2 is less than 90°, ensuring that the incident light will be reflected into the recess instead of toward the opening 2, so that the incident light will be refracted multiple times in the recess, thereby achieving omnidirectional light trapping. At the same time, because the omnidirectional light trapping structure does not increase the surface area of ​​the solar cell too much, it will not significantly increase the carrier surface recombination, ensuring that the solar cell has a high light absorption efficiency for incident light at any angle, while ensuring that the solar cell has a high conversion efficiency.

[0061] The specific contents of the omnidirectional light trapping structure provided by the present invention will be described in detail in the following invention embodiments.

[0062] Embodiment 2

[0063] Please refer to Figures 5 to 12 , Figure 5 A schematic structural diagram of another specific omnidirectional light trapping structure provided by an embodiment of the present invention; Figure 6 This is a comparison of the average reflectivity of the omnidirectional light trapping structure and the inverted pyramid structure with an aspect ratio of 2; Figure 7 (a)-(e) are schematic diagrams of the monomer structures of omnidirectional light trapping structures with aspect ratios of 2.7, 2, 1.8, 1.7, and 1.6, respectively. (f) is a comparison of the relationship between the average reflectivity and the incident angle of the omnidirectional light trapping structures with different aspect ratios. Figure 8 (a)-(d) are the comparison diagrams of the absorption rate of the omnidirectional light trapping structure and the inverted pyramid structure at incident angles of 0°, 30°, 60°, and 89° respectively; Fig. 9 (a) is the relationship between the number of reflections and the incident angle of the omnidirectional light trapping structure and the inverted pyramid structure at the air-silicon interface; Fig. 9 (b) is a comparison of the optical path propagation length inside the silicon absorption layer of the omnidirectional light trapping array structure and the inverted pyramid array structure; Fig.10 (a) Schematic diagram of the principle of multiple capture of incident light by the omnidirectional light trapping structure; Fig.10 (b) Schematic diagram of the light trapping effect on the top and bottom planes of the light trapping structure; Fig.10 (c) is the tilt angle of the micron wire cone Schematic diagram of the impact on large-angle incident light; Fig.11 This is a comparison chart of the average reflectivity and aspect ratio of the omnidirectional light trapping structure and the existing black silicon technology; Fig.12 (a) is a diagram of an omnidirectional light trapping structure with a rectangular cross section; Fig.12 (b) is a diagram of an omnidirectional light trapping structure with a circular cross section; Fig.12 (c) is a diagram of an omnidirectional light trapping structure with a groove-shaped cross section; Fig.12 (d) is a cross-sectional diagram of a hybrid omnidirectional light trapping structure.

[0064] Different from the above-mentioned invention embodiment, the present invention embodiment further defines the omnidirectional light trapping structure on the basis of the above-mentioned invention embodiment. The rest of the contents have been described in detail in the above-mentioned invention embodiment and will not be repeated here.

[0065] See also Figure 5 In the embodiment of the present invention, the two-dimensional cross-sectional structure of the omnidirectional light trapping structure along the thickness direction includes a vertical or nearly vertical wall 3 on the upper side and a V-shaped structure as the bottom on the lower side. That is, the width of the opening 2 of the concave structure is L1, the height of the wall 3 extending from the opening 2 along the thickness direction is H1, and the angle between the wall 3 and the horizontal direction is The depth of the entire depression is H2, and the angle of the V-shaped structure at the bottom of the depression is , then the recommended size of the omnidirectional light trapping structure in this embodiment is , , , , , its aspect ratio . See Figure 3 In this embodiment, the concave three-dimensional structure can be specifically a mixed cone, the upper opening 2 can be a rectangular hole structure, and the lower bottom is a quadrangular pyramid structure, which can also achieve a smaller array spacing.

[0066] For an omnidirectional light trapping structure monomer with a depth-to-width ratio of 2 and a rectangular opening of 2, its average reflectivity (for light with a wavelength of 300nm-1100nm) is less than 3% within the incident angle range of 0°-90° (excluding the point of 90°), and a 75nm thick layer can be deposited on its front surface. After being used as an anti-reflection layer, its average reflectivity is further reduced to below 0.6%. At the same time, the specific surface area increase ratio of the structure is about 5.8.

[0067] See also Figure 6 In this embodiment, by changing the length of the upper side wall surface H1 of the omnidirectional light trapping structure, its aspect ratio, specific surface area increase ratio and corresponding average reflectivity can be changed. Figure 7 It can be seen that when the aspect ratio increases to 2.7, the The omnidirectional light-trapping structure of the anti-reflection layer has an average reflectivity of less than 0.2% within the incident angle range of 0°-90° (excluding 90°). When the aspect ratio is reduced to 1.6, its average reflectivity varies between 0%-2.2% within the incident angle range of 0°-90° (excluding 90°). Compared with the larger aspect ratio, its reflectivity has a certain increase. However, even an omnidirectional light-trapping structure with an aspect ratio of 1.6 can still achieve low reflectivity at all incident angles, that is, it still has the optical performance of omnidirectional anti-reflection. Taking into account the aspect ratio and the omnidirectional anti-reflection performance, this embodiment preferably has an omnidirectional light-trapping structure with an aspect ratio of 2.

[0068] See also Figure 8 The light absorption rate comparison results of the omnidirectional light trapping structure with an aspect ratio of 2 provided in this embodiment and the traditional inverted pyramid structure are as follows:

[0069] Both light trapping structures are based on The single crystal silicon wafer of the size is prepared, and the spacing between two adjacent light-trapping structures is set to 5.05μm, that is, the line width is 50 nm. The light absorption rate of the traditional inverted pyramid structure decreases with the increase of the incident angle, and the maximum absorption rate decreases by about 30%. The omnidirectional light-trapping structure provided in this embodiment can always maintain a high absorption rate over the entire wavelength range and at different incident angles, and is higher than the absorption rate of the inverted pyramid structure. Compared with the inverted pyramid, the omnidirectional light-trapping structure provided in this embodiment has an increasingly obvious light absorption advantage as the incident angle increases. In particular, at an incident angle of 89°, the omnidirectional light-trapping structure provided in this embodiment has an absorption rate of more than 94.7% for 300nm-1100nm light.

[0070] The omnidirectional light trapping structure proposed in this embodiment has low reflectivity and high absorptivity at all angles, mainly due to the following two factors:

[0071] First, multiple light captures inside a single omnidirectional light trapping structure.

[0072] See also Fig. 9 According to Fresnel's law, the reflectivity at the interface of two media is only related to the incident angle, refraction angle and the refractive index of the two media, and has nothing to do with the propagation distance of the light in the medium. Therefore, its total reflectivity Satisfies the following formula:

[0073]

[0074] In the above formula is the i-th reflectivity.

[0075] because Less than 1, total reflectivity It decreases exponentially with the increase of the number of reflections. Therefore, by increasing the number of reflections of the incident light in the light trapping structure, the reflectivity of the front surface can be effectively reduced. For planar silicon, there is always only one reflection, which is counted as 1, so that its average reflectivity is always higher than 37%. The average number of reflections of the inverted pyramid structure remains basically unchanged and greater than 2 within the range of incident angles of 0°-20°, and its average reflectivity is basically maintained at 10% within this range of incident angles. After that, its average number of reflections gradually decreases with the increase of the incident angle, and approaches 1 after the incident angle is 60°, and its average reflectivity also increases accordingly and approaches 37%.

[0076] The average reflectivity of the omnidirectional light-trapping structure proposed in this embodiment can basically be maintained at more than 4.5 times. In the range of incident angle of 40°-55°, the average reflection number is slightly reduced, and the minimum value is 4.36. The average reflectivity of the omnidirectional light-trapping structure also reaches a maximum of 2.7% here, and then the average reflection number is the maximum as the incident angle increases, and the average reflectivity decreases accordingly.

[0077] Compared with the omnidirectional light trapping structure proposed in this embodiment, the vertical hole structure has a deeper vertical wall surface and exhibits a higher reflection number at a large incident angle, making its average reflectivity close to 0% in the range of 60°-89°. However, the bottom plane is also prone to reflect light incident at a small angle back to the incident medium, making its average reflection number less, resulting in a higher average reflectivity in the range of 0°-40° incident angles, and as the angle decreases, the average reflectivity gradually increases and tends to be around 37%.

[0078] Second, multiple light captures between omnidirectional light trapping structure arrays.

[0079] In addition to the omnidirectional light-trapping structure capturing the incident light and its reflected light multiple times, the transmitted light escaping from the silicon will also be captured multiple times by the omnidirectional light-trapping structure array. Taking the large-angle incidence condition as an example, the incident light will pass through the nearly vertical wall 3 (silicon-air interface) of the light-trapping structure multiple times, so that the transmitted light will be captured multiple times by different omnidirectional light-trapping structures. It can be seen from Fresnel's law that the transmittance at the interface between two media is only related to the incident angle, refraction angle and the refractive index of the two media, and has nothing to do with the propagation distance of the light in the medium. Therefore, its total transmittance Satisfies the following formula:

[0080]

[0081] In the above formula is the i-th transmittance.

[0082] because Less than 1, the total transmittance of the above array It decreases exponentially with the increase of the number of transmissions. Therefore, the light trapping array with a vertical wall 3 structure can limit most of the energy of the large-angle incident light to a smaller size. However, for the light trapping structure without the vertical wall 3, such as the inverted pyramid structure, the light entering the silicon can only be transmitted on the upper and lower surfaces of the silicon substrate. At this time, the transmitted light will directly escape to the outside of the silicon body and be completely lost. Therefore, the light absorption of this type of structure is more dependent on the thickness of the absorption layer.

[0083] Fig. 9 (b) The optical path length within the light-trapping array, including the inverted pyramid structure and the proposed omnidirectional light-trapping structure, is plotted for a better understanding Figure 8 The potential mechanism of enhanced absorption is shown in Fig. 9 As shown in (b), the two structures show different changing trends. The optical path length of the inverted pyramid structure decreases monotonically with the increase of the incident angle, while the omnidirectional light trapping structure provided in this embodiment is the opposite, and its optical path length increases significantly with the increase of the incident angle. Although the optical path lengths of the two structures are still at the same order of magnitude at small incident angles, the difference in optical path lengths between the two structures gradually expands to 736 times as the incident angle increases.

[0084] By Beer-Lambert law It can be seen that by increasing the distance of light in the medium, the absorption rate of the medium to light can be effectively increased. It is precisely because the omnidirectional light trapping structure array of this embodiment can capture incident light, reflected light and transmitted light multiple times, and the captured light will produce multiple internal reflections inside the silicon, thereby increasing the total propagation distance of light inside the silicon, thereby improving the light absorption rate.

[0085] See also Fig.10 From the perspective of structural shape, the reason why the omnidirectional light trapping structure provided in this embodiment has the ability to capture multiple light at 0°-89° is mainly due to its relatively low top flat area and a bottom plane with an area ratio of 0. Compared with the omnidirectional light trapping structure, under the condition of a smaller incident angle, the vertical square hole and hollow cylindrical structure with poor light trapping effect have larger bottom plane and top plane respectively. For the top plane, the reflected light generated by the incident light at any angle will escape directly and cannot be reflected by the silicon surface for a second time, such as Fig.10 (b). In other words, the reflection escape angle range of the incident light on the top plane is 0°-90°, and its escape range is the entire upper half of the surface, and the probability of its first reflected light escaping is 100%. Therefore, reducing the top plane will help to further improve the light trapping effect. The micrometer wire structure in the prior art is precisely through the evolution of the cylinder into a cone structure, thereby reducing the top plane and achieving low reflection. However, the evolution of the micrometer wire structure from a cylinder to a cone to reduce the top surface will result in the inclination angle of the upper side wall. Less than 90°. When the reflected light is reflected away from the substrate 1, the reflected light will escape and no secondary reflection will occur. Fig.10 (c) and the maximum wall inclination angle Due to the limitation of aspect ratio, taking the currently most efficient micron-wire solar cell as an example, its aspect ratio is 5, and its wall inclination angle will be less than 78.7°. When the incident angle of light is greater than 78.7°, its reflected light will escape directly, and the anti-reflection effect will be reduced. Relatively speaking, the omnidirectional light trapping structure array provided in this embodiment only needs to reduce the hole spacing to reduce the top surface area, and the top surface area does not affect the anti-reflection effect of a single concave hole structure at a large angle.

[0086] For the bottom surface, the reflection escape angle of the incident light is also affected by the aspect ratio of the light trapping structure. For example, the reflection escape angle of the center point of the bottom plane between two pillars (or the center point of the bottom plane of the concave hole) is , where w is the width of the bottom surface of the hole or the distance between the cylinders, and h is the height of the cylinder or the depth of the hole. , its reflected light will be reflected twice with the wall of the light-trapping structure. As the aspect ratio of the column / hole increases, the reflection escape angle will decrease, and the probability of secondary reflection of the light incident on the bottom surface will increase. However, the aspect ratio is limited by the surface recombination and cannot be increased infinitely, which makes the reflection escape angle of the bottom plane always exist. As a result, under the condition of small angle incidence, some incident light cannot be reflected twice. Therefore, for the light-trapping structure with a bottom plane, the anti-reflection effect at small angle incidence is poor.

[0087] See also Fig.10 (a), the omnidirectional light-trapping structure provided in this embodiment adopts a concave structure, and the upper inner wall adopts the shape of a nearly vertical wall 3, which effectively avoids the restrictive relationship between the top plane area of ​​the micrometer-wire-type boss structure and the large-angle anti-reflection, so that low reflectivity at a large angle and a small top plane area can be achieved simultaneously. At the same time, the lower side of the omnidirectional light-trapping structure adopts an inverted pyramid-like V-shaped cone hole structure to avoid the existence of the bottom plane, and by adjusting the inclination angle of the lower inclined surface 4, the existence of the reflection escape angle at a small angle of incidence is avoided. The first reflected light will inevitably contact the inner wall of the light-trapping structure again, thereby achieving an average reflection number of more than 4.5 at an incident angle of 0°-89°. It is based on this that the omnidirectional light-trapping structure provided in this embodiment can achieve low reflectivity and high absorption rate at nearly full angles of 0°-89°.

[0088] Depend on Fig.11It can be seen that the omnidirectional light trapping structure with an aspect ratio of 2 provided in this embodiment realizes a silicon-based light trapping structure with an omnidirectional low reflectivity (<0.6%, reflected light wavelength range 300nm-1100nm) from 0-90° (excluding the 90° point), and its aspect ratio AR is only 2, which is more than 2.5 times lower than that of the traditional black silicon light trapping structure. At the same time, the thin film deposition process used for silicon surface passivation film deposition can cover the maximum aspect ratio of the recess, which is usually 3-5. Therefore, for the omnidirectional light trapping structure with an aspect ratio of 2, the existing thin film deposition process, such as magnetron sputtering or PECVD (plasma enhanced chemical vapor deposition), can easily make the silicon surface with the omnidirectional light trapping structure obtain a better passivation layer, thereby effectively reducing surface recombination. In addition, the surface area increase ratio of the omnidirectional light trapping structure is relatively small, about 5.8, while the surface area increase ratio of most traditional black silicon light trapping structures is about 10. Therefore, the omnidirectional light trapping structure with an aspect ratio less than or equal to 2 has good electrical performance potential.

[0089] Therefore, compared with the existing black silicon technology, the omnidirectional light trapping structure with an aspect ratio of 2 provided in this embodiment has an omnidirectional low reflectivity ( , reflected light wavelength range 300nm-1100nm), the better electrical performance potential brought by the smaller aspect ratio and surface area increase ratio makes it have better photoelectric conversion efficiency potential. It can solve the problem of weak light trapping ability of the silicon absorption layer of crystalline silicon solar cells, thus helping to increase the actual power generation of solar cells on the facade.

[0090] Specifically, the depth-to-width ratio of the concave in the omnidirectional light trapping structure provided in this embodiment is generally in the range of 1.2 to 4; the angle of the V-shaped structure is The value range is usually 30° to 60°. Recommended value , the cross section of the inclined surface 4 forming the V-shaped structure along the thickness direction can be a straight line or a curve with a similar slope, a multi-segment line, etc. Assume that the angle between the wall surface 3 extending from the concave opening 2 and the horizontal direction is , then the The value range is usually 80° to 90°, and the recommended The cross section of the wall surface 3 extending from the recessed opening 2 along the thickness direction can be a straight line or a curve or a multi-segment line with a similar slope. The corresponding aspect ratio of the omnidirectional light trapping structure ranges from 1.2 to 4. ,when , corresponding to , .

[0091] The wall surface 3 extending from the recessed opening 2 on the upper side adopts a shape of a nearly vertical wall surface 3, which effectively avoids the restrictive relationship between the top plane area of ​​the micrometer-line type boss structure and the large-angle anti-reflection, so that low reflectivity at a large angle and a small top plane area can be achieved at the same time. At the same time, the bottom of the omnidirectional light-trapping structure adopts a V-shaped structure to avoid the existence of the bottom plane, and by adjusting the inclination angle of the lower side inclined surface 4, the existence of the reflection escape angle when the incident angle is small is avoided. The first reflected light will inevitably contact the inner wall of the light-trapping structure again. Based on this, the omnidirectional light-trapping structure can achieve low reflectivity and high absorption rate at all angles of 0°-90°.

[0092] Since the omnidirectional light trapping structure provided in this embodiment is designed based on the principle of multiple light capture, The omnidirectional light trapping structure has basically the same full-angle light trapping capability, that is, scaling the size of the omnidirectional light trapping structure does not affect its full-angle light trapping effect.

[0093] See also Fig.12 For the three-dimensional structure of the omnidirectional light trapping structure, as long as the two-dimensional structural morphology of the cross-section along the thickness direction is the morphology described above, it has similar omnidirectional low reflectivity and omnidirectional light absorption ability. That is, no matter whether its cross section along the horizontal direction is a triangle, rectangle, hexagon or other polygon, circle, ellipse, groove, or mixed type, for example, the cross section along the horizontal direction of the mixed type can be generated by mixing more than two cross-sectional shapes to generate its three-dimensional structure, such as a rectangular cross section on the upper side and a circular cross section on the lower side.

[0094] Since the omnidirectional light-trapping structure of the present embodiment is based on the principle of multiple light capture, the above-mentioned omnidirectional light-trapping structure can achieve low reflectivity at all angles for materials with a reflectivity similar to that of silicon, or lower than that of silicon, such as materials with a reflectivity lower than 40% at vertical incidence. Therefore, the omnidirectional light-trapping structure can also be applied to omnidirectional anti-reflection on the front surface of glass. At the same time, it can be applied to flexible solar cells with an omnidirectional light-trapping structure as a frame, that is, the flexible solar cells are attached to the inner wall of the omnidirectional light-trapping structure, so that the flexible solar cells can also achieve an omnidirectional light-trapping effect. Therefore, the omnidirectional light-trapping structure in the present embodiment can be applied to omnidirectional anti-reflection of materials with a reflectivity lower than 40%. It can also be used as an omnidirectional anti-reflection frame for omnidirectional anti-reflection of flexible solar cells.

[0095] Embodiment 3

[0096] The embodiment of the present invention further provides a solar cell, which includes an omnidirectional light trapping structure as provided in any of the above embodiments of the invention. For other structures in the solar cell, reference may be made to the prior art and will not be repeated here.

[0097] Since the solar cell of this embodiment is provided with the omnidirectional light trapping structure provided by the above-mentioned invention embodiment, and since the omnidirectional light trapping structure can realize omnidirectional light trapping, incident light at any angle can be emitted multiple reflections in the omnidirectional light trapping structure. Therefore, the solar cell of this embodiment can have higher light absorption efficiency, and due to its low aspect ratio, the solar cell can have better electrical performance.

[0098] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0099] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0100] The above is a detailed introduction to an omnidirectional light trapping structure and solar cell provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. An omnidirectional light trapping structure, characterized in that: The method comprises a depression disposed on a surface of a substrate, wherein the depression extends from the surface of the substrate to the inside of the substrate along a thickness direction of the substrate; The wall surface extending from the opening of the depression is parallel to the thickness direction; the bottom of the depression has an inclined surface, so that the cross section of the bottom of the depression along the thickness direction forms a V-shaped structure; the projection of the inclined surface along the normal direction of the inclined surface does not exceed the opening.

2. The omnidirectional light trapping structure according to claim 1, characterized in that: The height of the wall extending from the opening in the recess in parallel with the thickness direction is not less than a preset height, so that incident light within a target angle range passes through the opening and directly irradiates the wall in parallel with the thickness direction.

3. The omnidirectional light trapping structure according to claim 2, characterized in that: The target angle range is in the range of 50° to 90°.

4. The omnidirectional light trapping structure according to claim 1, characterized in that: The bottom of the depression is symmetrically distributed along the axis of the depression in the thickness direction.

5. The omnidirectional light trapping structure according to claim 1, characterized in that: A transition section is provided between a wall surface of the recess extending from an opening of the recess and the inclined surface.

6. The omnidirectional light trapping structure according to claim 1, characterized in that: The opening is circular or rectangular; And / or, the bottom is in the shape of a quadrangular pyramid or a cone.

7. The omnidirectional light trapping structure according to claim 1, characterized in that: It comprises a plurality of the recesses, and the plurality of the recesses are distributed in an array.

8. The omnidirectional light trapping structure according to claim 1, characterized in that: The depth-to-width ratio of the depression ranges from 1.2 to 4; the included angle of the V-shaped structure ranges from 30° to 60°.

9. The omnidirectional light trapping structure according to claim 1, characterized in that: The concave surface is provided with an anti-reflection layer.

10. A solar cell, characterized in that: The invention comprises the omnidirectional light trapping structure as claimed in any one of claims 1 to 9.

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