Silicon wafer structure and solar cell

Abstract

The invention provides a silicon wafer structure and a solar cell, and relates to the field of photovoltaic technology. At least one surface of the silicon wafer structure is provided with a plurality of reflection structures, each reflection structure comprises a first end and a second end, the first end is connected with the silicon wafer structure, and the cross sectional area of each reflection structure is gradually reduced along the direction from the first end to the second end; at least one side face of the reflection structure is recessed inwards to form a light trapping structure. Because the light trapping structure can reduce the reflection loss of single reflection of light and increase the probability that the light is absorbed, the silicon wafer structure provided by the invention is applied to the solar cell, and the light utilization rate of the solar cell can be improved.

Description

Technical Field

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

[0002] In the manufacture of photovoltaic cells, reducing the reflectivity of the silicon wafer surface is a key step in improving the light absorption efficiency. The reflectivity of the untreated single-crystal silicon surface in the visible light band (400-1100nm) is as high as over 30%, resulting in a large amount of incident light loss. Although traditional anti-reflection technologies (such as anti-reflection coatings) can partially improve the optical performance, their performance is highly dependent on the surface morphology of the substrate. Studies have shown that the reflection suppression effect of direct coating on the smooth single-crystal silicon surface is significantly inferior to that of the velvet structure substrate. The light trapping effect brought by the velvet structure substrate forms a synergistic effect with the refractive index gradient effect of the anti-reflection film, making the velvet process a necessary prerequisite for achieving low reflection in single-crystal silicon solar cells.

[0003] The wet-process pyramid structure forms a dense micron-scale pyramid array on the surface of the silicon wafer through chemical corrosion, and significantly reduces the reflectivity by using multiple reflections and light trapping effects. However, since the random pyramid structure still has a high reflectivity for incident light, the utilization rate of light by existing solar cells still needs to be improved. Summary of the Invention

[0004] The embodiments of the present invention provide a silicon wafer structure and a solar cell to solve the problem of low light utilization efficiency of existing solar cells.

[0005] In a first aspect, an embodiment of the present invention provides a silicon wafer structure, wherein at least one side of the silicon wafer structure has a plurality of reflective structures, wherein the reflective structures include a first end and a second end, wherein the first end is connected to the silicon wafer structure, and a cross-sectional area of ​​the reflective structures gradually decreases from the first end to the second end;

[0006] At least one side surface of the reflective structure is recessed inwardly to form a light trapping structure.

[0007] Optionally, the light trapping structure is formed to be recessed from the first end and the second end toward the interior of the reflective structure.

[0008] Optionally, the first ends of any two adjacent reflective structures are in contact with each other.

[0009] Optionally, the second end of the reflective structure is conical, and an angle corresponding to a projection of the second end on a longitudinal section of the reflective structure is an acute angle.

[0010] Optionally, the second end of the reflective structure is conical, and an angle corresponding to a projection of the second end on a longitudinal section of the reflective structure is an obtuse angle.

[0011] Optionally, the second end of the reflective structure is arc-shaped, and an outer surface of the second end protrudes toward the outside of the reflective structure.

[0012] Optionally, the second end of the reflective structure is flat-topped, and the perimeter of the edge of the end surface of the second end is 5 to 200 nm.

[0013] Optionally, a passivation film is provided on the surface of the reflective structure, and an anti-reflection film is provided on a side of the passivation film facing away from the reflective structure.

[0014] Optionally, the light trapping structure is a reflective arc surface formed by an inward concave side surface of the reflective structure, and the curvature radius of the reflective arc surface is 3 to 20 μm.

[0015] In a second aspect, an embodiment of the present invention further provides a solar cell, comprising an electrode and the silicon wafer structure described in the first aspect, wherein the electrode is provided on at least one surface of the silicon wafer structure.

[0016] In the technical solution provided by the present invention, at least one side of a silicon wafer structure has a plurality of reflective structures. The reflective structures include a first end and a second end, the first end being connected to the silicon wafer structure, and the cross-sectional area of ​​the reflective structures gradually decreases from the first end to the second end. At least one side of the reflective structure is inwardly recessed to form a light-trapping structure. The side of the reflective structure is an inclined surface, which causes incident light to be reflected multiple times in different directions. Because the side of the reflective structure is formed with the inwardly recessed light-trapping structure, compared to a reflective structure without light-trapping structures, the light-trapping structure can improve the silicon wafer structure's light utilization efficiency in at least two aspects. First, the inward recess of the light-trapping structure can change the local angle of incidence of light when it strikes the silicon interface, causing the light to enter at an angle closer to the normal of the silicon surface, thereby reducing reflection loss in a single reflection. Second, the light-trapping structure provides additional reflective interfaces for light, causing the light to undergo more reflections before escaping, increasing the probability of light absorption. In summary, since the light trapping structure can reduce the reflection loss of single light reflection and increase the probability of light absorption, the silicon wafer structure provided by the present invention can be applied to solar cells to improve the utilization rate of light by solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in describing the embodiments of the present invention. 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 any creative labor.

[0018] Figure 1 This is one of the structural diagrams of the reflective structure provided by an embodiment of the present invention;

[0019] Figure 2 This is the second structural diagram of the reflective structure provided by an embodiment of the present invention;

[0020] Figure 3 This is the third structural diagram of the reflective structure provided by an embodiment of the present invention;

[0021] Figure 4 This is the fourth structural diagram of the reflective structure provided by an embodiment of the present invention;

[0022] Figure 5 This is one of the surface SEM photos of the silicon wafer structure provided by an embodiment of the present invention;

[0023] Figure 6 This is the second surface SEM photo of the silicon wafer structure provided by an embodiment of the present invention;

[0024] Figure 7 This is the third surface SEM photograph of the silicon wafer structure provided by an embodiment of the present invention;

[0025] Figure 8 This is the fourth surface SEM photograph of the silicon wafer structure provided by an embodiment of the present invention;

[0026] Figure 9 This is a surface SEM photo of a traditional silicon wafer structure;

[0027] Figure 10 This is one of the structural schematic diagrams of a solar cell provided by an embodiment of the present invention;

[0028] Figure 11 This is the second structural schematic diagram of the solar cell provided by the embodiment of the present invention.

[0029] Reference numerals:

[0030] 100, reflective structure; 101, first end; 102, second end; 200, light trapping structure; 300, electrode; 400, passivation film; 500, anti-reflection film; 600, P-type silicon wafer; 700, N-type layer; 800, N-type silicon wafer; 900, P-type layer. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0032] An embodiment of the present invention provides a silicon wafer structure.

[0033] like Figures 1 to 8 As shown, at least one side of the silicon wafer structure has a plurality of reflective structures 100. The reflective structures 100 include a first end 101 and a second end 102. The first end 101 is connected to the silicon wafer structure, and the cross-sectional area of ​​the reflective structures 100 gradually decreases from the first end 101 to the second end 102. At least one side of the reflective structure 100 is recessed inward to form a light trapping structure 200.

[0034] In the present invention, the cross-sectional area of ​​the reflective structure 100 on the silicon wafer structure gradually decreases in the direction from the first end 101 to the second end 102, presenting a pyramid-like shape. The reflective structure 100 includes at least three side surfaces, the specific number of which is not limited and can be set according to needs. At least one side surface of the reflective structure 100 is recessed inward to form a light-trapping structure 200, that is, the number of sides of the reflective structure 100 on which the light-trapping structure 200 is formed is also not limited, and each side surface can form a light-trapping structure 200, which can be set according to needs. It should be noted that the more side surfaces of the reflective structure 100 and the more light-trapping structures 200 there are, the better the effect of the silicon wafer structure in reducing the reflectivity of light and improving the utilization rate of light.

[0035] like Figure 9 In the case where the side surfaces of the reflective structure 100 are inclined surfaces and do not form light-trapping structures 200, the inclined surfaces cause incident light to reflect multiple times in different directions. When light first strikes a certain inclined surface, some of it enters the silicon. Unabsorbed reflected light may encounter the inclined surfaces of adjacent pyramids, gaining a chance to enter the silicon again. This multiple reflection significantly increases the probability that light will be absorbed rather than directly reflected back into the air.

[0036] In the present invention, since the side of the reflective structure 100 is formed with an inwardly concave light-trapping structure 200, compared with the reflective structure 100 without the light-trapping structure 200, the light-trapping structure 200 can improve the utilization rate of light by the silicon wafer structure in at least the following two aspects: first, the light-trapping structure 200 is concave inward, which can change the local incident angle when the light hits the silicon interface, so that the light is incident at an angle closer to the normal of the silicon surface, thereby reducing the reflection loss of light in a single reflection; second, the light-trapping structure 200 can provide an additional reflection interface for the light, so that the light undergoes more reflections before escaping, increasing the probability of light being absorbed. In summary, since the light-trapping structure 200 can reduce the reflection loss of a single reflection of light and increase the probability of light being absorbed, the silicon wafer structure provided by the present invention can be applied to solar cells to improve the utilization rate of light by solar cells.

[0037] Optionally, the light trapping structure 200 is formed to be recessed from the first end 101 and the second end 102 toward the interior of the reflective structure 100 .

[0038] like Figures 1 to 4 As shown in the embodiment, the light-trapping structure 200 is recessed from both ends of the reflective structure 100 toward the center of the side surface of the reflective structure 100. In this case, the entire side surface of the reflective structure 100 is recessed inward to form the light-trapping structure 200. Compared with the method of recessing only a certain part of the side surface of the reflective structure 100 to form the light-trapping structure 200, the optimization of the incident angle of light by the local light-trapping structure 200 is limited to a local area. The overall recess in the embodiment is also understood as a continuous recess on the side surface of the reflective structure 100. This continuous recess forms a gradual interface similar to a gradient refractive index, which significantly reduces the refractive index mutation between air and silicon, and allows light to experience more reflections in adjacent structures (if it is a local recess, it is possible that when light enters a local recess of a reflective structure 100, the light is reflected to the non-recessed surface of another reflection result. In comparison, the overall recess has more reflections), significantly extending the optical path. Therefore, in this embodiment, the light-trapping structure 200 is an overall recessed structure formed by recessing from the first end 101 and the second end 102 toward the interior of the reflective structure 100. Compared with forming the light-trapping structure 200 only on a certain part of the side of the reflective structure 100, it has a higher utilization rate of light.

[0039] Optionally, the first ends 101 of any two adjacent reflective structures 100 are in contact with each other. Figures 1 to 4 As shown, the first ends 101, i.e., the bottoms, of adjacent reflective structures 100 are in contact with each other. Compared with a method in which a flat area exists between adjacent reflective structures 100, the method of this embodiment can make the angle between the side surfaces of adjacent reflective structures 100 smaller, thereby increasing the number of reflections of light between adjacent reflective structures 100. In addition, if a flat area exists between adjacent reflective structures 100, part of the light will be vertically incident and vertically reflected, resulting in a high reflection loss of the light. The method of this embodiment can avoid this situation, thereby reducing the reflection loss of the light. Therefore, the silicon wafer structure of this embodiment can improve the utilization rate of light.

[0040] Optionally, the second end 102 of the reflective structure 100 is conical, and the angle corresponding to the projection of the second end 102 on the longitudinal section of the reflective structure 100 is an acute angle. Figure 1 as well as Figures 5 to 8As shown, the conical top in the acute angle case can improve the capture efficiency of light with a large incident angle (for example, >60°), avoiding the situation where the traditional pyramid-shaped reflective structure 100 may allow such light to escape directly. The conical top can guide it into the silicon through secondary reflection. Therefore, the silicon chip structure of this embodiment can improve the utilization rate of light with a large incident angle.

[0041] Optionally, the second end 102 of the reflective structure 100 is conical, and the angle corresponding to the projection of the second end 102 on the longitudinal section of the reflective structure 100 is an obtuse angle. Figure 2 as well as Figures 5 to 8 As shown, the tapered tip at an obtuse angle can improve the capture efficiency of light with a small incident angle (e.g., an incident direction close to the horizontal direction), thereby enabling the silicon wafer structure of this embodiment to improve the utilization rate of light with a large incident angle. In addition, the above structure can also reduce damage to the tip of the reflective structure 100.

[0042] Optionally, the second end 102 of the reflective structure 100 is in an arc shape, and the outer surface of the second end 102 protrudes toward the outside of the reflective structure 100. Figure 3 and Figures 5 to 8 As shown, the second end 102 of the reflective structure 100 can be arc-shaped. The top of the arc acts like a microlens, focusing incident light onto the sidewalls of the adjacent reflective structure 100, increasing the light propagation path within the silicon. The arc surface also reduces random scattering from sharp edges, directing light more orderly toward the pyramid sidewalls and reducing the probability of light escaping. Therefore, the silicon wafer structure of this embodiment can improve light utilization. Furthermore, this structure can also reduce damage to the top of the reflective structure 100.

[0043] Optionally, the second end 102 of the reflective structure 100 is flat-topped. Figures 4 to 8 As shown, the second end 102 of the reflective structure 100 can be flat-topped, which can also reduce damage to the top of the reflective structure 100. Optionally, the perimeter of the edge of the end surface of the second end 102 is 5-200 nm. In a preferred embodiment, the perimeter of the edge of the end surface of the second end 102 is 10-150 nm. In this embodiment, the second end 102 is flat-topped. If the perimeter of the second end 102 increases, the area of ​​the flat top will also increase, thereby increasing the reflectivity. If the perimeter of the second end 102 decreases, the area of ​​the flat top will also decrease, which will make the top of the reflective structure 100 more susceptible to damage, thereby affecting the battery efficiency.

[0044] In an optional embodiment, the above-mentioned reflective structures 100 of various shapes may be included simultaneously on the same silicon wafer structure.

[0045] Optionally, a passivation film 400 is provided on the surface of the reflective structure 100, and an anti-reflection film 500 is provided on the side of the passivation film 400 facing away from the reflective structure 100. In this embodiment, the anti-reflection film 500 can be formed by uniformly depositing 60-100 nm of a material such as SiO2 or Si3N4 on the surface of the reflective structure 100. The anti-reflection film 500 can cause incident sunlight to undergo multiple reflections and interference between the film and the silicon wafer, thereby reducing reflection losses and improving light energy absorption efficiency. The passivation film 400 can be made of materials such as silicon dioxide and aluminum oxide. The passivation film 400 can reduce surface defects of the reflective structure 100, inhibit carrier recombination, and improve the electrical performance of the reflective structure 100. In another optional embodiment, the passivation film 400 and the anti-reflection film 500 can be a single-layer structure, that is, the passivation film 400 can also serve as the anti-reflection film 500. Compared with the embodiment with a double-layer structure, this reduces the difficulty of the manufacturing process.

[0046] Optionally, the light-trapping structure 200 is a reflective arc surface formed by the inward concavity of the side surface of the reflective structure 100, and the curvature radius of the reflective arc surface is 3 to 20 μm. When the curvature radius of the reflective arc surface is small, the edge of the light-trapping structure 200 is sharper, forming multiple micro-slopes, which easily cause light to escape after multiple reflections; although increasing the curvature radius of the reflective arc surface can extend the optical path, when the curvature radius of the reflective arc surface is large, the number of reflections of the light will be greatly reduced, and the optical path extension is limited, which may also lead to a decrease in light utilization. In this embodiment, the curvature radius of the reflective arc surface can preferably be 7 to 10 μm. In this case, while ensuring the optical path and number of reflections of the light, the excessive escape rate of the light can be avoided, thereby improving the utilization of light by the silicon wafer structure.

[0047] The reflective structure 100 of the present invention can be prepared as follows: a single crystal silicon wafer is immersed in a cleaning solution at 60-65°C in a cleaning tank for cleaning pretreatment, the cleaning pretreatment time being 2-5 minutes; the pretreated single crystal silicon wafer is immersed in an alkaline solution in an alkaline polishing tank for alkaline polishing, the alkaline polishing reaction temperature being 70-72°C and the reaction time being 1-3 minutes; the polished single crystal silicon wafer is textured in a specific texturing solution, the texturing solution temperature being 72-75°C and the reaction time being 300-410 seconds; the textured single crystal silicon wafer is then spray cleaned; the cleaned textured single crystal silicon wafer is placed in a drying chamber for drying; after drying, the reflective structure 100 having the light trapping structure 200 is obtained. Optionally, the above structure can also be formed by secondary modification after texturing.

[0048] An embodiment of the present invention further provides a solar cell, comprising an electrode 300 and the silicon wafer structure described in the first aspect, wherein the electrode 300 is provided on at least one surface of the silicon wafer structure.

[0049] like Figure 10 As shown, the solar cell includes a P-type silicon wafer 600 and an electrode 300. The P-type silicon wafer 600 is the silicon wafer structure. On one surface of the P-type silicon wafer 600, an N-type layer 700 is formed by diffusion technology or PECVD deposition technology to form a solar cell PN junction.

[0050] like Figure 11 As shown, the solar cell includes an N-type silicon wafer 800 and an electrode 300. The N-type silicon wafer 800 is the silicon wafer structure. On one side of the N-type silicon wafer 800, a P-type layer 900 is formed by diffusion technology or PECVD deposition technology, thereby forming a solar cell PN junction. The solar cells in this embodiment include but are not limited to simple PN junction cells, Passivated Emitter Rear Cell (PERC), Tunnel Oxide Passivated Contact (TOPCon), Heterojunction with Intrinsic Thin-film (HJT), and Interdigitated Back Contact (IBC).

[0051] Since the technical solution of this embodiment includes all the technical solutions of the above embodiments, it can at least achieve all the technical effects of the above embodiments, which will not be described one by one here.

[0052] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A silicon wafer structure, characterized in that: At least one side of the silicon wafer structure has a plurality of reflective structures, the reflective structures including a first end and a second end, the first end being connected to the silicon wafer structure, and the cross-sectional area of ​​the reflective structures gradually decreasing from the first end to the second end; At least one side surface of the reflective structure is recessed inwardly to form a light trapping structure.

2. The silicon wafer structure according to claim 1, wherein The light trapping structure is recessed from the first end and the second end toward the interior of the reflective structure.

3. The silicon wafer structure according to claim 1, wherein: The first ends of any two adjacent reflective structures are in contact with each other.

4. The silicon wafer structure according to claim 1, wherein: The second end of the reflective structure is tapered, and the angle corresponding to the projection of the second end on the longitudinal section of the reflective structure is an acute angle.

5. The silicon wafer structure according to claim 1, wherein: The second end of the reflective structure is tapered, and the angle corresponding to the projection of the second end on the longitudinal section of the reflective structure is an obtuse angle.

6. The silicon wafer structure according to claim 1, wherein: The second end of the reflective structure is in an arc shape, and an outer surface of the second end protrudes toward the outside of the reflective structure.

7. The silicon wafer structure according to claim 1, wherein: The second end of the reflective structure is in a flat top shape, and the perimeter of the edge of the end surface of the second end is 5 to 200 nm.

8. The silicon wafer structure according to any one of claims 1 to 7, characterized in that A passivation film is provided on the surface of the reflective structure, and an anti-reflection film is provided on a side of the passivation film facing away from the reflective structure.

9. The silicon wafer structure according to any one of claims 1 to 7, characterized in that The light trapping structure is a reflective arc surface formed by the inward concavity of the side surface of the reflective structure, and the curvature radius of the reflective arc surface is 3 to 20 μm.

10. A solar cell, characterized in that: The solar cell comprises an electrode and the silicon wafer structure according to any one of claims 1 to 9, wherein the electrode is provided on at least one surface of the silicon wafer structure.

Images