A crystalline silicon photovoltaic cell and a method of making the same

Abstract

The application provides a crystalline silicon photovoltaic cell and a preparation method thereof, and belongs to the field of photovoltaic cells. The thickness of the substrate silicon wafer of the cell is δ1<105μm, and a light path control layer is arranged on the back surface. The light path control layer comprises a bottom reflecting surface, a light collecting window, a light collecting reflecting surface and a light active area window. The light path control layer covers the upper surface of the electrode grid line, and the ratio of the thickness δ2 of the light path control layer to the thickness δ1 of the substrate silicon wafer satisfies 0.5<(δ2 / δ1)≤14. The bottom reflecting surface reflects the transmitted light back to the light active area of the silicon wafer, and the light collecting reflecting surface collects the back surface scattered light and reflected light and makes them enter the light active area, thereby increasing the short circuit current. Meanwhile, with the aid of the grid-shaped light path control layer with large thickness, the stress of the substrate silicon wafer is dispersed, the expansion of microcracks is blocked, the mechanical strength of the cell wafer is improved, and the back surface heat dissipation area is increased. The light energy utilization rate, power generation capacity and structural reliability of the back electrode photovoltaic cell are effectively improved.

Description

Technical Field

[0001] This invention relates to photovoltaic cell manufacturing technology, and in particular to a crystalline silicon photovoltaic cell and its manufacturing method, wherein the crystalline silicon photovoltaic cell has a light path control layer. Background Technology

[0002] High-efficiency photovoltaic cells place great emphasis on the reception and utilization of reflected and scattered light from the back surface. Typically, reflected and scattered light from the back of the cell can account for 8% to 12% of the total solar irradiance. In extreme cases, such as on water surfaces or snow-covered ground, the proportion of backlight is even higher. Therefore, improving the reception of light from the back surface of photovoltaic cells, also known as the bifaciality of the cell, is receiving increasing attention.

[0003] However, the back electrode photovoltaic cell technology in high-efficiency batteries integrates all the positive and negative electrodes of the battery on the back side. Its core advantage lies in eliminating the shading of the front metal grid lines, reducing optical losses, obtaining the minimum carrier recombination on the front surface of the battery and the maximum front light-receiving area, which significantly improves the short-circuit current and conversion efficiency.

[0004] However, its disadvantages are also obvious. First, the rear grid lines reduce the bifaciality of the battery, affecting battery efficiency. Especially in space applications, in order to reduce battery weight, the battery is designed to be relatively thin, and in order to reduce series resistance, the electrode grid lines are designed to be denser and wider, further hindering the reception of light on the back of the battery. Second, the thin silicon wafer cannot fully absorb the received sunlight in time, and a large amount of long-wavelength light penetrates the silicon wafer, causing light loss, reducing the external quantum efficiency of the battery, and lowering the photoelectric conversion efficiency of the battery. Furthermore, when the aforementioned photovoltaic cells are applied in space, the following issues also arise: Third, thin battery cells have low mechanical strength and are fragile; Fourth, the battery operates at a high temperature when exposed to sunlight, and lacks air convection for heat dissipation, making radiative heat dissipation difficult. Summary of the Invention

[0005] To address the aforementioned technical problems, in a first aspect, the present invention provides a crystalline silicon photovoltaic cell, wherein the thickness δ1 of the substrate silicon wafer of the cell is less than 105 μm, a light path control layer is provided on the back side of the cell, and the light path control layer is provided with a bottom reflective surface, a light-collecting window, a light-collecting reflective surface, and a photoactive region window, the light path control layer covers the electrode grid lines, the bottom reflective surface faces the front side of the cell, the opening of the light-collecting window and the photoactive region window face the back side of the cell, and the ratio of the thickness δ2 of the light path control layer to the thickness δ1 of the substrate silicon wafer of the cell satisfies 0.5 < (δ2 / δ1) ≤ 14.

[0006] The optical path control layer has two reflective surfaces: a bottom reflective surface and a light-collecting reflective surface. The bottom reflective surface reflects transmitted light, allowing it to re-enter the photoactive region of the silicon wafer to generate current. The light-collecting reflective surface collects scattered and reflected light from the back of the battery, allowing it to enter the photoactive region of the silicon wafer through the photoactive region window to generate current.

[0007] By utilizing the optical path control layer with a thick mesh structure, especially the optical path control layer with a mesh structure that is preferably greater than or equal to the thickness of the substrate silicon wafer, the silicon wafer stress is dispersed, the propagation of microcracks is blocked, and the mechanical strength of the solar cell is improved.

[0008] By utilizing the grid structure of the optical path control layer, the heat dissipation area for heat convection and radiation on the back of the solar cell is increased. Simultaneously, the light-collecting and reflecting surface alters the direction of outward heat radiation, increasing its intensity and improving heat dissipation, thereby reducing the cell temperature. Ultimately, this increases the cell's short-circuit current output, enhancing the light energy utilization and power generation capacity of the back electrode photovoltaic cell.

[0009] Preferably, the ratio of the thickness δ2 of the optical path control layer to the thickness δ1 of the substrate silicon wafer of the battery satisfies 1 ≤ (δ2 / δ1) ≤ 14. Preferably, the thickness δ2 of the optical path control layer is greater than the thickness δ1 of the substrate silicon wafer of the battery.

[0010] Preferably, the thickness δ1 of the substrate silicon wafer of the battery is one of the following: a) 90μm≤δ1<105μm; b) 80μm≤δ1<90μm; c) 70μm≤δ1<80μm; d) 60μm≤δ1<70μm; e) 50μm≤δ1<60μm; f) 20μm≤δ1<50μm.

[0011] Furthermore, half of the cross-section of the light-collecting and reflecting surface at the xoz section is a quasi-parabolic shape, z = (1 / 2p)x. 2 One of them, and taken from 0.8p≤z<17p, where p / 2 is the focal length of the quasi-parabola.

[0012] The photoactive region window is located in the middle of the light-collecting window. The ratio of the upper horizontal diameter A of the light-collecting window to the horizontal diameter a of the photoactive region window satisfies 1.4≤(A / a)≤3. The ratio of the area S1 of the light-collecting window to the area S2 of the photoactive region window satisfies 1.4<(S1 / S2)≤9. The width-to-depth ratio of the light-collecting window satisfies 1≤(A / h)≤4, where h is the depth of the light-collecting window.

[0013] The term "horizontal diameter" in this application refers to "the distance between the two shortest straight lines passing through the centerline of the 'groove'; or the distance between the two shortest straight lines passing through the center of the inscribed circle of the 'pit'".

[0014] It is worth noting that the thickness δ2 of the optical path control layer of this invention can be up to 14 times the thickness δ1 of the silicon wafer substrate. When applied to terrestrial photovoltaics, the surface area for convective heat dissipation of the solar cell is far greater than the inherent surface area of ​​the solar cell, thus resulting in excellent heat dissipation. When applied to space photovoltaics, on the one hand, its thermal radiation surface area is far greater than the inherent surface area of ​​the photovoltaic cell; on the other hand, the far-infrared rays radiated from any point of the optical path control layer are reflected by the reflective surface of the light-collecting window, and most of the far-infrared rays are emitted in a direction away from the photovoltaic cell, thus also resulting in excellent heat dissipation. The optical path control layer, especially the honeycomb optical path control layer, also has a good structural strengthening effect on the crystalline silicon photovoltaic cell. When micro-cracks appear on the solar cell, the optical path control layer has the function of terminating the cracks. Furthermore, the optical path control layer also directly improves the various mechanical strength indicators of the thin silicon wafer.

[0015] The ratio of the area S1 of the light-collecting window to the area S2 of the photoactive region window reflects the light-gathering ratio (S1 / S2). For the same light-gathering ratio, a thicker optical path control layer δ2 is beneficial for collecting scattered and reflected light over a wider range of incident angles. Therefore, a larger light-gathering ratio and a thicker optical path control layer help reduce the loss of front-transmitted light and collect more back-scattered and reflected light. On the other hand, due to the non-linear relationship between the range of collected incident angles and thickness, an appropriately thick optical path control layer δ2 helps save on material, achieving the desired performance-to-price ratio.

[0016] Under the principle of minimum photoactive region window design, the ratio of the upper horizontal diameter A of the light-collecting window to the horizontal diameter a of the photoactive region window essentially limits the slope and variation of the quasi-parabola. The ratios of 1.4≤(A / a)≤3 and 1≤(A / h)≤4 in this invention are ranges with good overall effect, taking into account the back-light concentration multiple of the battery, the thickness of the optical path control layer, and the back-light receiving cone angle of the battery. Users can obtain a satisfactory design based on the required optical efficiency, mechanical and thermal properties, and process level through calculation or simulation. The calculation method is existing technology and will not be elaborated.

[0017] In a preferred embodiment, the main component of the optical path control layer is a metallic material, which also serves as the back electrode of the battery. In addition to the common advantages, metals offer the advantage of providing higher reflectivity and serving as a back electrode, which helps reduce transmission resistance. The metallic material can be any reasonably applicable material commonly used in crystalline silicon photovoltaic cells, and no specific limitation is made here.

[0018] In another preferred embodiment, the main component of the optical path control layer is an inorganic non-metallic material. The advantages of inorganic non-metallic materials are that they are lightweight and insulating, can provide high reflectivity, and can be used to prepare an optical path control layer with a thermal expansion coefficient very close to that of silicon. This is beneficial for reducing the mechanical stress of the battery and increasing the mechanical strength of the battery cell.

[0019] In a preferred embodiment, the main component of the optical path control layer is an inorganic non-metallic material, and it also includes a curing agent.

[0020] Furthermore, the main component of the optical path control layer is ceramic material; the ratio k of the thermal expansion coefficient of the optical path control layer to that of the substrate silicon wafer is adjusted to fall within one of the following ranges: 0.7 ≤ k < 1.1, 1.1 ≤ k < 1.4, 1.4 ≤ k < 1.8. The method for adjusting the thermal expansion coefficient of the optical path control layer is not specifically limited here; for example, it can be achieved by optimizing the blending of various ceramic materials in different proportions, or by purchasing commercially available ceramic materials that meet the thermal expansion coefficient requirements.

[0021] Preferably, the ceramic material comprises at least one of alumina, silicon oxide, silicon carbide, silicon nitride, zirconium oxide, boron nitride, cordierite, and aluminum titanate.

[0022] The relative linear expansion coefficients of the above ceramic materials are as follows:

[0023] For example, using cordierite alone to prepare an optical path control layer, or combining the above-mentioned ceramic materials, can yield ceramic materials with an expansion coefficient close to that of silicon.

[0024] Alternatively, the quasi-parabola z=(1 / 2p)x 2 A segment of a line with z≥(p / 2) in a given branch can be replaced by one or more straight line segments, which is convenient for design and manufacturing.

[0025] Preferably, the crystalline silicon photovoltaic cell is a back-contact crystalline silicon photovoltaic cell.

[0026] Preferably, the crystalline silicon photovoltaic cell is the bottom cell of a tandem cell.

[0027] Secondly, the present invention provides a method for preparing an optical path control layer on the back surface of the aforementioned crystalline silicon photovoltaic cell, wherein the method for transferring the optical path control layer, whose main component is a metallic material, to the back surface of the crystalline silicon photovoltaic cell comprises the following steps: S1. The bottom reflective surface of the optical path control layer prepared by the metal material is compositely embedded on the surface of the polymer film with the normal direction in the -z direction to obtain a transfer film; S2. Using the transfer film, the bottom reflective surface of the optical path control layer made of the metal material is attached to the back of the crystalline silicon photovoltaic cell; S3. The optical path control layer prepared by the metal material is bonded to the back surface of the crystalline silicon photovoltaic cell with the aid of external force.

[0028] The advantage of this method is that the metal wire has good light reflection properties and low resistivity, which can achieve the best reflection effect and the lowest transmission resistance.

[0029] Alternatively, the present invention provides a method for fabricating an optical path control layer on the back surface of the aforementioned crystalline silicon photovoltaic cell, comprising the following steps: T1. Deposit paste and curing agent at the predetermined location on the back surface of the crystalline silicon photovoltaic cell where the optical path control layer is to be prepared; T2. Using an imprinting mold, the shape of the optical path control layer is imprinted at the corresponding position of the pre-prepared optical path control layer, and the curing agent is triggered by a triggering factor to cure the slurry and form it. T3. Demolding and cleaning to form the optical path control layer.

[0030] The advantages of this method are that it is suitable for a variety of materials, the thermal expansion coefficient of the slurry can be adjusted, the mechanical stress of the battery cell is small, the process is simple, and the preparation cost is low.

[0031] In a preferred example, the slurry is a metallic conductive slurry or an inorganic non-metallic material.

[0032] In a preferred example, the curing agent is a heat-sensitive, pressure-sensitive, or ultraviolet-sensitive curing agent.

[0033] Furthermore, the optical path control layer can also be prepared using metal powder using this method; composite materials can combine the advantages of metal, non-metal, and polymer materials, overcome their shortcomings, and obtain better overall performance.

[0034] Beneficial effects: 1) The present invention provides an optical path control layer with a thickness of 0.5 to 14 times that of the substrate silicon wafer on the back side of a battery substrate silicon wafer with a thickness of less than 105 μm. On the one hand, it provides effective reflection for up to 90% or more of the back surface of the battery, so that long-wavelength light that penetrates the substrate silicon wafer from the front of the battery but has not been absorbed can be reflected and re-enter the substrate silicon wafer to fully absorb the transmitted light. On the other hand, with the help of the light-collecting and reflecting surface of the optical path control layer, more than 90% of the reflected and scattered light radiated to the back of the battery is focused on the window of the photoactive area, so that the reflected and scattered light can be fully utilized.

[0035] This invention makes full use of transmitted light, scattered light and reflected light, thereby improving the light energy utilization efficiency and current output of the battery.

[0036] 2) In this invention, the surface area of ​​the light-collecting and reflecting surface of the optical path control layer is generally 3 to 7 times the surface area of ​​the substrate silicon wafer. Moreover, after the thermal radiation of the light-collecting and reflecting surface is reflected by the light-collecting and reflecting surface, its radiation direction is away from the solar cell.

[0037] Therefore, the heat dissipation power of the battery of this invention is several times that of a planar substrate silicon wafer. This is particularly important for space batteries that can only rely on radiation for heat dissipation.

[0038] Similarly, in terrestrial applications, the heat dissipation effect of air convection is several times that of a planar silicon substrate.

[0039] 3) The present invention provides an optical path control layer with a thickness of 0.5 to 14 times that of the silicon substrate on the back side of the battery substrate silicon wafer. For example, by optimizing the ratio of ceramic materials, the same or similar coefficient of thermal expansion can be achieved as the silicon wafer, which is beneficial to improving the mechanical strength of the thin silicon wafer. The grid-like optical path control layer can terminate the microcracks of the silicon wafer, change the direction of stress transmission, eliminate stress concentration, and reduce the internal stress of the thin silicon wafer.

[0040] 4) In this invention, the optical path control layer made of metal material assists in electrical conduction, reduces the internal resistance of the battery, and improves the load-carrying capacity. Attached Figure Description

[0041] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings: Figure 1 This is a schematic diagram of the structure of a first back-contact crystalline silicon photovoltaic cell with an optical path control layer that can receive light from both sides, provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the transfer film structure used in Example 2 of the present invention when preparing the optical path control layer of Example 1 using the transfer film method; Figure 3 This is a schematic diagram of the structure of a second back-contact crystalline silicon photovoltaic cell with an optical path control layer that can receive light from both sides, as shown in Embodiment 3 of the present invention; Figure 4 This is a schematic diagram of the structure of a second back-contact crystalline silicon photovoltaic cell with an optical path control layer that can receive light from both sides, as shown in the AA view of Embodiment 3 of the present invention; Figure 5 This is a schematic diagram of the imprinting mold used in Example 4 of the present invention to prepare the optical path control layer of Example 3 using the imprinting method.

[0042] In the figure: 100 - First back contact crystalline silicon photovoltaic cell; 200 - Second back contact crystalline silicon photovoltaic cell; 101 - Transfer film; 201 - Imprinting mold; 1 - Substrate silicon wafer (photoactive region); 2 - Optical path control layer; 21 - Bottom reflective surface; 22 - Light collecting window; 23 - Light collecting and reflecting surface; 24 - Photoactive region window; 3 - Electrode grid line; 4 - Carrier film. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0044] Example 1: See appendix Figure 1 A first back-contact crystalline silicon photovoltaic cell 100 is disclosed. The substrate silicon wafer 1 of the first back-contact crystalline silicon photovoltaic cell 100 has a thickness δ1=90μm. A light path control layer 2 is provided on the back side of the first back-contact crystalline silicon photovoltaic cell 100. The light path control layer 2 has a bottom reflective surface 21, a light-collecting window 22, a light-collecting reflective surface 23, and a photoactive region window 24. The light path control layer 2 covers the top (z-direction) of the electrode grid lines 3. The normal of the bottom reflective surface 21 faces the front side of the first back-contact crystalline silicon photovoltaic cell 100. The opening of the strip-shaped light-collecting window 22 and the strip-shaped photoactive region window 24 face the back side of the first back-contact crystalline silicon photovoltaic cell 100. The thickness δ2=270μm of the light path control layer 2 is 3 times the thickness δ1 of the substrate silicon wafer of the cell.

[0045] In this embodiment, half of the intersection of the light-collecting and reflecting surface 23 and the xoz section is a quasi-parabola z=(1 / 2p)x 2 One of the branches, where z takes the value p≤z<8.5p, and the focal length of the quasi-parabola is p / 2. The photoactive region window 24 is located in the middle of the light-collecting window 22. The upper horizontal diameter of the light-collecting window 22 is A=300μm, and the horizontal diameter of the photoactive region window 24 is a=100μm. The ratio of the two (A / a)=3. The ratio of the area S1 of the light-collecting window 22 to the area S2 of the photoactive region window 24 (S1 / S2)=3. The width-to-depth ratio of the light-collecting window 22 (A / h)≈1.1, where h is the depth of the light-collecting window 22.

[0046] The main component of the optical path control layer 2 in this embodiment is silicon-aluminum alloy material. The optical path control layer 2 is connected in parallel with the electrode grid line 3 of the first back contact crystalline silicon photovoltaic cell 100.

[0047] The beneficial effects of this embodiment: 1) In this embodiment, a 270μm thick optical path control layer 2 is provided on the back side of the 90μm thick battery substrate silicon wafer 1. On the one hand, it provides effective reflection for 67% of the battery back surface, so that long-wavelength light that penetrates the substrate silicon wafer 1 from the front side of the first back contact crystalline silicon photovoltaic cell 100 but has not been absorbed can re-enter the substrate silicon wafer 1 after reflection, so that the transmitted light is fully absorbed. On the other hand, with the help of the light-collecting and reflecting surface 23 of the optical path control layer 2, more than 95% of the reflected and scattered light radiated to the back side of the first back contact crystalline silicon photovoltaic cell 100 is focused on the photoactive region window 24, so that the reflected and scattered light on the back side of the first back contact crystalline silicon photovoltaic cell 100 can be fully utilized.

[0048] This embodiment makes full use of transmitted light, scattered light and reflected light, thereby improving the light energy utilization efficiency and current output of the first back contact crystalline silicon photovoltaic cell 100.

[0049] Because the silicon substrate 1 is relatively thick, the amount of transmitted light available is limited. Therefore, a strip pattern is adopted, which simplifies the process and enhances compatibility, resulting in a high cost-performance ratio for the first back-contact crystalline silicon photovoltaic cell 100.

[0050] 2) In this embodiment, the surface area of ​​the light-collecting reflective surface 23 of the light path control layer 2 is about 2.5 times the surface area of ​​the substrate silicon wafer 1. Moreover, the thermal radiation rays emitted by the light-collecting reflective surface 23 are reflected by the opposite light-collecting reflective surface 23, and their radiation direction is away from the first back contact crystalline silicon photovoltaic cell 100.

[0051] Therefore, in this embodiment, the radiative heat dissipation power of the first back-contact crystalline silicon photovoltaic cell 100 is about 2.5 times that of the planar substrate silicon wafer 1, which is particularly important for space cells that can only rely on radiative heat dissipation.

[0052] Similarly, in terrestrial applications, the heat dissipation effect of air convection is several times that of a planar substrate silicon wafer1.

[0053] 3) In this embodiment, an aluminum-silicon alloy optical path control layer 2 with a thickness of 3 times that of the substrate silicon wafer 1 is provided on the back side of the substrate silicon wafer 1 of the first back contact crystalline silicon photovoltaic cell 100. This can achieve a matching with the thermal expansion coefficient of the substrate silicon wafer 1, which is beneficial to reduce the internal stress of the substrate silicon wafer 1 and improve the mechanical strength of the thin silicon wafer.

[0054] 4) In this embodiment, the optical path control layer 2 of silicon-aluminum alloy material assists the electrical conduction of the first back contact crystalline silicon photovoltaic cell 100, reduces the internal resistance of the cell, and improves the load-bearing capacity of the equipment.

[0055] Example 2: See appendix Figure 1 Appendix Figure 2A method for preparing an optical path control layer 2 of a first back-contact crystalline silicon photovoltaic cell 100, comprising the following steps: transferring the optical path control layer 2 of aluminum-silicon alloy material to the back surface of the first back-contact crystalline silicon photovoltaic cell 100. S1. The bottom reflective surface 21 of the optical path control layer 2 of aluminum-silicon alloy material is aligned with the -z direction and embedded in the surface of the polymer carrier film 4 to obtain the transfer film 101. S2. Using the transfer film 101, the bottom reflective surface 21 of the optical path control layer 2 of the aluminum-silicon alloy material is attached to the back side of the first back contact crystalline silicon photovoltaic cell 100, and the electrode grid line 3 is overlapped with the bottom reflective surface 21. S3. The optical path control layer 2 of the aluminum-silicon alloy material is bonded to the back surface of the first back contact crystalline silicon photovoltaic cell 100 by means of ultrasonic welding.

[0056] The beneficial effect of this embodiment is that the aluminum-silicon alloy material has good light reflection performance, low resistivity and a thermal expansion coefficient close to that of silicon, which can achieve the best reflection effect, the lowest transmission resistance and small thermal expansion deformation.

[0057] Example 3: See appendix Figure 3 Appendix Figure 4 A second back-contact crystalline silicon photovoltaic cell 200 has a substrate silicon wafer 1 with a thickness δ1 = 50 μm. A light path control layer 2 is provided on the back side of the second back-contact crystalline silicon photovoltaic cell 200. The light path control layer 2 has a bottom reflective surface 21, a light-collecting window 22, a light-collecting reflective surface 23, and a photoactive region window 24. The light path control layer 2 covers the top (z-direction) of the electrode grid lines 3. The normal of the bottom reflective surface 21 faces the front side of the second back-contact crystalline silicon photovoltaic cell 200. The opening of the rectangular light-collecting window 22 and the rectangular photoactive region window 24 face the back side of the second back-contact crystalline silicon photovoltaic cell 200. The thickness δ2 of the light path control layer 2 is 270 μm, and the ratio of the thickness δ1 of the substrate silicon wafer 1 to the thickness of the cell is 5.4.

[0058] In this embodiment, half of the intersection of the light-collecting and reflecting surface 23 and the xoz section is a quasi-parabola z=(1 / 2p)x 2 One of the branches, where z takes the value p≤z<8.5p, and the focal length of the quasi-parabola is p / 2. The photoactive region window 24 is located in the middle of the light-collecting window 22. The upper horizontal diameter of the light-collecting window 22 is A=300μm, and the horizontal diameter of the photoactive region window 24 is a=100μm. The ratio of the two (A / a)=3. The ratio of the area S1 of the light-collecting window 22 to the area S2 of the photoactive region window 24 (S1 / S2)=9. The width-to-depth ratio of the light-collecting window 22 (A / h)≈1.1, where h is the depth of the light-collecting window 22.

[0059] The main components of the optical path control layer 2 in this embodiment are aluminum oxide, silicon dioxide and organic photosensitive curing agent.

[0060] The beneficial effects of this embodiment: 1) In this embodiment, a 270μm thick optical path control layer 2 is provided on the back side of the 50μm thick battery substrate silicon wafer 1. On the one hand, it provides effective reflection for 90% of the battery back surface, so that long-wavelength light that penetrates the substrate silicon wafer 1 from the front of the second back contact crystalline silicon photovoltaic cell 200 but has not been absorbed can re-enter the substrate silicon wafer 1 after reflection, so that the transmitted light is fully absorbed. On the other hand, with the help of the light-collecting and reflecting surface 23 of the optical path control layer 2, more than 95% of the reflected and scattered light radiated to the back side of the second back contact crystalline silicon photovoltaic cell 200 is focused on the photoactive region window 24, so that the reflected and scattered light on the back side of the second back contact crystalline silicon photovoltaic cell 200 can be fully utilized.

[0061] This embodiment makes full use of transmitted light, scattered light and reflected light, thereby improving the light energy utilization efficiency and current output of the second back contact crystalline silicon photovoltaic cell 200.

[0062] This embodiment uses a planar rectangular shape, which allows more transmitted light to be reflected again to the photoactive area of ​​the second back-contact crystalline silicon photovoltaic cell 200, enhancing the reabsorption of transmitted light and increasing the current output of the second back-contact crystalline silicon photovoltaic cell 200. Under the same lighting conditions, the overall power generation of the second back-contact crystalline silicon photovoltaic cell 200 is increased by about 5%.

[0063] 2) In this embodiment, the surface area of ​​the light-collecting reflective surface 23 of the light path control layer 2 is about 4 times the surface area of ​​the substrate silicon wafer 1. Moreover, the thermal radiation rays emitted by the light-collecting reflective surface 23 are reflected by the opposite light-collecting reflective surface 23, and their radiation direction is away from the second back contact crystalline silicon photovoltaic cell 200.

[0064] Therefore, in this embodiment, the radiative heat dissipation power of the second back-contact crystalline silicon photovoltaic cell 200 is about 4 times that of the planar substrate silicon wafer 1, which is particularly important for space cells that can only rely on radiative heat dissipation.

[0065] Similarly, in terrestrial applications, the heat dissipation effect of air convection is several times that of a planar substrate silicon wafer1.

[0066] 3) In this embodiment, a ceramic optical path control layer 2 with a thickness 5.4 times that of the substrate silicon wafer 1 is provided on the back side of the substrate silicon wafer 1 of the second back contact crystalline silicon photovoltaic cell 200. By optimizing the material ratio, the thermal expansion coefficient can be the same as that of the substrate silicon wafer 1, which is beneficial to reduce the internal stress of the substrate silicon wafer 1 and improve the mechanical strength of the thin silicon wafer.

[0067] Example 4: See appendix Figure 5 In this embodiment, the optical path control layer 2 is prepared by imprinting a micro / nano imprinting mold 201 onto the back side of the second back contact crystalline silicon photovoltaic cell 200, and the following steps are involved: T1. Sufficient slurry and curing agent are deposited on the raised part of the optical path control layer 2 on the back side of the second back contact crystalline silicon photovoltaic cell 200. The slurry contains a mixed ceramic powder with high reflectivity and low expansion coefficient formed by complementary alumina and silicon oxide and an organic photosensitive adhesive. T2. Using a micro-nano imprinting quartz mold 201, the shape of the optical path control layer 2 is pressed onto the protruding part of the pre-prepared optical path control layer 2, and the curing agent is triggered by ultraviolet irradiation to cure the slurry and form it. T3. Demolding and cleaning to form the optical path control layer 2.

[0068] The beneficial effects of this embodiment: The ceramic powder and organic UV-curing binder have the characteristics of insulation, high reflectivity and low expansion coefficient, which makes the stress of the second back contact crystalline silicon photovoltaic cell 200 relatively low.

[0069] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A crystalline silicon photovoltaic cell, characterized by, The thickness of the substrate silicon wafer of the battery is δ1<105μm, the back surface of the battery is provided with a light path control layer, the light path control layer is provided with a bottom reflecting surface, a light collecting window, a light collecting reflecting surface, and a light active area window, the light path control layer covers the electrode grid lines, the bottom reflecting surface faces the front surface of the battery, the opening of the light collecting window and the light active area window face the back surface of the battery, and the ratio of the thickness δ2 of the light path control layer to the thickness δ1 of the substrate silicon wafer of the battery satisfies 0.5<(δ2 / δ1)≤14.

2. A crystalline silicon photovoltaic cell according to claim 1, characterised in that, The ratio of the thickness δ2 of the light path control layer to the thickness δ1 of the battery substrate silicon wafer satisfies 1≤(δ2 / δ1)≤14.

3. A crystalline silicon photovoltaic cell according to claim 1 or 2, characterised in that, The half of the cross section line of the light collecting reflection surface in the xoz cross section is a quasi-parabolic line z=(1 / 2p)x 2 In one of the branches, and taken from a section of 0.8p≤z<17p, wherein p / 2 is the focal length of the quasi-parabolic line; the photoactive region window is in the middle of the light collecting window, the ratio of the upper horizontal diameter A of the light collecting window to the horizontal diameter a of the photoactive region window satisfies 1.4≤(A / a)≤3, the ratio of the area S1 of the light collecting window to the area S2 of the photoactive region window satisfies 1.4<(S1 / S2)≤9, and the width-depth ratio of the light collecting window satisfies 1≤(A / h)≤4, wherein h is the depth of the light collecting window.

4. The crystalline silicon photovoltaic cell of claim 1, wherein, The thickness δ1 of the substrate silicon wafer of the battery is one of the following: a) 90μm≤δ1<105μm; b) 80μm≤δ1<90μm; c) 70μm≤δ1<80μm; d) 60μm≤δ1<70μm; e) 50μm≤δ1<60μm; f) 20μm≤δ1<50μm.

5. The crystalline silicon photovoltaic cell of claim 1, wherein, The main component of the light path control layer is a metal material, and part of the light path control layer also serves as the back electrode of the battery.

6. The crystalline silicon photovoltaic cell of claim 1, wherein, The main component of the light path control layer is an inorganic non-metallic material.

7. A crystalline silicon photovoltaic cell according to claim 6, characterised in that, The main component of the light path control layer is a ceramic material; the ratio k of the thermal expansion coefficient of the light path control layer to the thermal expansion coefficient of the substrate silicon wafer falls within one of the following ranges: 0.7≤k＜1.1； 1.1≤k＜1.4； 1.4≤k＜1.8。 8. A crystalline silicon photovoltaic cell according to claim 7, characterised in that, The ceramic material contains at least one of alumina, silica, silicon carbide, silicon nitride, zirconia, boron nitride, cordierite, and aluminum titanate.

9. A crystalline silicon photovoltaic cell according to claim 3, wherein, The quasi-parabolic z = (1 / 2p)x 2 A segment of the line z ≥ (p / 2) in one of the branches of the parabola z = (1 / 2p)x is replaced by more than one straight line segment.

10. The crystalline silicon photovoltaic cell of claim 1, wherein, The crystalline silicon photovoltaic cell is a back contact crystalline silicon photovoltaic cell.

11. A crystalline silicon photovoltaic cell according to claim 1, wherein, The crystalline silicon photovoltaic cell is a bottom cell of a stacked cell.

12. A method for preparing a light path control layer on the back surface of the crystalline silicon photovoltaic cell of claim 5, wherein the main component of the crystalline silicon photovoltaic cell is a light path control layer made of a metal material, and the method for transferring the light path control layer to the back surface of the crystalline silicon photovoltaic cell has the following steps: S1. The bottom reflecting surface of the light path control layer made of the metal material is composited and inlaid on the surface of a polymer polymer film in the normal direction towards -z direction to obtain a transfer film; S2. The bottom reflecting surface of the light path control layer made of the metal material is attached to the back surface of the crystalline silicon photovoltaic cell by means of the transfer film; S3. The light path control layer made of the metal material is bonded on the back surface of the crystalline silicon photovoltaic cell by means of external force.

13. A method for preparing a light path control layer on the back surface of the crystalline silicon photoelectric cell of claim 5 or 6, having the following steps: T1. Depositing a slurry and a curing agent at the position where the light path control layer is to be prepared on the back surface of the crystalline silicon photovoltaic cell; T2. The shape of the light path control layer is imprinted on the corresponding position where the light path control layer is to be prepared by means of an imprinting die, and the slurry is cured and formed by triggering the curing agent to cure; T3. Demolding and cleaning to form the light path control layer.

14. The method of claim 13, wherein the method is characterized by: The slurry is a metal conductive slurry or an inorganic non-metallic material.

15. The method of claim 13, wherein the method is characterized by: The curing agent is a heat-sensitive or pressure-sensitive or ultraviolet light-sensitive curing agent.

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