Back junction double-sided passivation solar cell

Abstract

The utility model discloses a back-junction double-sided passivated solar cell, which relates to the technical field of solar cell manufacturing and comprises a silicon substrate, a back-junction double-sided passivated solar cell and a back-junction double-sided passivated solar cell, metal areas with micro-textured structures and non-metal areas with textured structures are alternately arranged on one side of the silicon substrate in the thickness direction; the suede structure and the micro suede structure are different in tower footing size; a first tunneling oxide layer and a first doping layer doped with a first doping element are stacked on the metal region from inside to outside; according to the embodiment, the metal areas with the micro-textured structures and the non-metal areas with the textured structures are alternately arranged on one side of the thickness direction of the silicon substrate, so that the non-metal areas can be ensured to be the textured structures without front fields, the passivation effect is reserved and optimized to the greatest extent, and the transverse transmission of charges is not influenced. And meanwhile, the first tunneling oxide layer and the first doping layer are arranged on the micro suede structure of the metal region, so that enough tensile stress can be provided on the basis of not influencing passivation and contact performance.

Description

Technical Field

[0001] The utility model relates to the technical field of solar cell manufacturing, in particular to a back-junction double-sided passivated solar cell. Background Art

[0002] At present, most of the N-type passivated solar cells on the market have only the tunnel passivation structure on the back side, and the front side is still P + Diffused emitter structure. During the front metallization process, the metal paste will burn through the passivation layer on the front and form an ohmic contact with the silicon substrate, which will cause a large amount of metal composite loss, affecting the passivation performance and battery efficiency. In the prior art, in order to reduce the impact of the front metal composite loss, the front is also made into a full-velvet tunneling oxide structure, that is, a double-sided passivated solar cell. However, the doped polysilicon in the tunneling oxide structure will produce serious parasitic absorption problems. Therefore, there is an urgent need to provide a double-sided passivated contact solar cell that can take into account both passivation performance and charge transfer. Utility Model Content

[0003] In light of this, embodiments of the present invention provide a back-junction, double-sided passivated solar cell. By alternating metal regions with micro-texture structures and non-metal regions with velvet structures along one side of the silicon substrate in the thickness direction, the non-metal region can be guaranteed to have a velvet structure without a front field, thereby maximizing and optimizing the passivation effect without affecting the lateral transfer of charge. Simultaneously, a first tunneling oxide layer and a first doped layer are disposed on the micro-texture structure of the metal region, providing sufficient tensile stress without affecting passivation or contact performance.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] In the first aspect, the utility model provides a back-junction double-sided passivated solar cell, comprising: a silicon substrate; a metal region of a micro-velvet structure and a non-metallic region of a velvet structure alternately arranged on one side of the silicon substrate in the thickness direction; the velvet structure and the tower base of the micro-velvet structure have different side lengths; a first tunneling oxide layer stacked from the inside to the outside on the metal region and a first doping layer doped with a first doping element.

[0006] Optionally, the velvet structure is in a pyramidal morphology, and the side length of the pyramid base is 1-2 μm.

[0007] Optionally, the micro-suede structure is a stacked multi-layer tower structure; wherein the side length of the lower tower base in the multi-layer tower structure is 5-8 μm, and the side length of the upper tower base is 0.5-2 μm.

[0008] Optionally, the width of the metal region is 20-300 μm; and / or the projected area of ​​the metal region accounts for 1%-10% of the projected area of ​​the main surface of the silicon substrate.

[0009] Optionally, a second tunneling oxide layer and a second doping layer doped with a second doping element are stacked from inside to outside on the other side of the silicon substrate in the thickness direction.

[0010] Optionally, the thickness of the first tunnel oxide layer is 0.2-2 nm; and / or the thickness of the second tunnel oxide layer is 0.2-2 nm.

[0011] Optionally, the thickness of the first doping layer is 20-500 nm; and / or the thickness of the second doping layer is 20-200 nm.

[0012] Optionally, a passivation anti-reflection layer is provided on the exposed textured structure in the non-metallic region and the first doped layer; and / or a passivation layer is provided on the second doped layer.

[0013] Optionally, it also includes: a first fine gate electrically connected to the first doped layer set in the metal area, and a second fine gate electrically connected to the second doped layer set on the other side of the silicon substrate; wherein the width of the first fine gate and / or the second fine gate is 10-50μm.

[0014] Optionally, the silicon substrate is an N-type silicon substrate; the first element is phosphorus, and the active doping concentration of phosphorus atoms in the first doping layer is 2E 20 -1E 21 atoms / cm 3 The second element is boron, and the active doping concentration of boron atoms in the second doping layer is 5E 19 -5E 20 atoms / cm 3 .

[0015] In a second aspect, the present invention provides a method for preparing a back-junction double-sided passivated solar cell, comprising:

[0016] Step 1: Texturing the main surface on one side of the silicon substrate in the thickness direction to form a micro-texture structure;

[0017] Step 2: preparing a first tunneling oxide layer and a first doping layer doped with a first doping element on the surface of the micro-texture structure from the inside to the outside in sequence;

[0018] Step 3, removing the first doped layer and the first tunneling oxide layer in a partial area on the main surface to form a non-metallic area;

[0019] Step 4, re-texturing the non-metallic area to form a velvet structure; wherein the velvet structure and the micro-velvet structure have different lengths of the tower base;

[0020] Step 5: using an acid solution to remove the first silicon glass layer remaining on one side of the silicon substrate in the thickness direction.

[0021] The technical solution of the first aspect of the above utility model has the following advantages or beneficial effects:

[0022] By alternately setting a metal area of ​​a micro-velvet structure and a non-metal area of ​​a velvet structure on one side of the silicon substrate in the thickness direction, it is possible to ensure that the non-metal area is a velvet structure without a front field, thereby retaining and optimizing the passivation effect to the greatest extent. Among them, the combination of the micro-velvet structure and the velvet structure will not affect the contact performance of the battery due to its large contact surface area; at the same time, the small square resistance difference between the velvet structure non-metal area and the micro-velvet structure metal area will not affect the lateral transmission of the charge. Specifically, the first tunneling oxide layer is set on the micro-velvet structure of the metal area. Since the micro-velvet structure has a regular surface than the velvet structure, it is conducive to improving the growth uniformity of the first tunneling oxide layer. In this way, the tensile stress of the silicon substrate on the first tunneling oxide layer can be increased without affecting the passivation and contact performance, thereby increasing the strength and stability of the solar cell. In addition, since the tunneling oxide structure (i.e., the first tunneling oxide layer and the first doped layer) is only set on the metal area on one side in the thickness direction, compared with the prior art in which the entire tunneling oxide structure is set on one side in the thickness direction, the parasitic absorption problem of the non-metallic area is reduced from the source. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are provided to facilitate a better understanding of the present invention and do not constitute an undue limitation of the present invention.

[0024] Figure 1 This is a schematic structural diagram of a back-junction double-sided passivated solar cell according to an embodiment of the present utility model;

[0025] Figure 2 This is a front view of the microstructure of the upper tower base in a multi-layer tower structure according to an embodiment of the present utility model;

[0026] Figure 3 This is a top view of the microstructure of the lower tower base in the multi-layer tower structure according to an embodiment of the present utility model;

[0027] Figure 4 This is a top view of the overall microstructure of the multi-tower structure according to an embodiment of the present utility model;

[0028] Figure 5 is a front view of a multi-layer tower structure according to an embodiment of the present utility model;

[0029] Figure 6 This is a schematic flow chart of a method for preparing a back-junction double-sided passivated solar cell according to an embodiment of the present utility model;

[0030] Figure 7 1 is a schematic diagram of the cross-sectional structure of the silicon substrate before step S601 according to an embodiment of the present utility model;

[0031] Figure 8 is a schematic diagram of the cross-sectional structure of the silicon substrate obtained after step S602 according to an embodiment of the present utility model;

[0032] Figure 9 1 is a schematic diagram of the cross-sectional structure of the silicon substrate before step S603 according to an embodiment of the present utility model;

[0033] Figure 10 is a schematic diagram of the cross-sectional structure of the silicon substrate after step S603 provided according to an embodiment of the present utility model;

[0034] Figure 11 is a schematic diagram of the cross-sectional structure of the silicon substrate after step S605 provided according to an embodiment of the present utility model;

[0035] Figure 12 It is a flow chart of the preparation method after step S605 according to an embodiment of the present invention.

[0036] The reference numerals are as follows:

[0037] 1-silicon substrate; 2-first tunneling oxide layer; 3-first doping layer; 4-second tunneling oxide layer; 5-second doping layer; 6-passivation anti-reflection layer; 7-passivation layer; 8-first fine gate; 9-second fine gate; 10-first silicon glass layer; 11-second silicon glass layer; 12-third doping layer; 13-third silicon glass layer; 100-upper tower base; 200-lower tower base. DETAILED DESCRIPTION

[0038] A solar cell is a photoelectric semiconductor wafer that uses sunlight to generate electricity directly. It is also called a "solar chip" or "photocell". As long as it is illuminated by light that meets certain illumination conditions, it can instantly output voltage and generate current in the presence of a circuit. In physics, it is called solar photovoltaic (PV), or photovoltaic for short. In order to conveniently and clearly describe the preparation method of the solar cell and the solar cell of the present invention, the following exemplary embodiments of the present invention are described in conjunction with the accompanying drawings, which include various details of the embodiments of the present invention to aid understanding, and they should be considered as merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for the sake of clarity and conciseness, the description of well-known functions and structures is omitted in the following description.

[0039] Double-sided passivated contact solar cells are divided into two structures: positive junction double-sided passivated contact solar cells (PN junction is established on the front) and back junction double-sided passivated contact solar cells (PN junction is established on the back). Among them, for positive junction double-sided passivated contact solar cells, since it is necessary to prepare the emitter and tunnel passivation structure separately on the front, the existing technology usually adopts the "laser oxidation mask method", which uses laser oxidation technology to form an oxidation mask layer in some areas, and prepare the emitter and tunneling structure separately to avoid the influence of each other's structure when preparing the emitter and tunneling passivation structure separately, and remove the oxidation mask layer after preparation to form the final battery structure. Although this method can prepare different structures in different areas separately, it requires a complex mask / demask process, and at the same time has high requirements for the cleaning process and additive selectivity, and the preparation process is cumbersome. Therefore, the preparation method of the positive junction double-sided passivated contact solar cell cannot be directly applied to the back junction double-sided passivated contact solar cell.

[0040] In order to solve the above problems existing in the prior art, the embodiments of the present invention provide a back-junction double-sided passivated solar cell with a novel structure and a preparation method thereof.

[0041] In one embodiment of the present invention, Figure 1 As shown, the back-junction bifacial passivated solar cell provided in this embodiment may include: a silicon substrate 1; a metal region with a micro-suede structure and a non-metallic region with a suede structure alternately arranged on one side of the silicon substrate 1 in the thickness direction; the tower bases of the suede structure and the micro-suede structure have different side lengths; a first tunneling oxide layer 2 and a first doping layer 3 doped with a first doping element stacked from the inside to the outside on the metal region. The one side in the thickness direction may be the light-receiving side, i.e., the front side of the back-junction bifacial passivated solar cell. The specific structure of the other side in the thickness direction, i.e., the back side of the back-junction bifacial passivated solar cell, will be described later.

[0042] It is understandable that, compared to the micro-suede structure, the velvet structure can cause light to undergo multiple reflections and scattering inside the battery, increasing the battery's absorption rate of light and improving contact performance. However, correspondingly, for the tunneling passivation structure, the surface irregularity of the velvet is significantly higher than that of the micro-suede, so the uniformity of the growth of the tunneling oxide layer is poor, resulting in the passivation performance of the tunneling passivation structure on the velvet structure being worse than that of the tunneling passivation structure on the micro-suede structure. Therefore, the embodiment of the utility model can retain the passivation performance while improving the contact performance by preparing the metal area and the non-metal area into different structures.

[0043] Specifically, the difference between the velvet structure and the micro-velvet structure lies mainly in the size of the tower base. In an optional embodiment, the velvet structure is a pyramid morphology, and the side length of the tower base is 1-2 μm, such as 1 μm, 1.2 μm, 1.5 μm, 1.8 μm or 2 μm, etc. For the pyramid morphology, the tower base refers to the basic part located at the bottom of the tower structure, that is, the lower foundation of the tower structure, which is usually square in cross-section. Therefore, the side length of the tower base defined in this application can be understood as the side length of the square cross-section at the bottom of the pyramid structure. The embodiment of the utility model can retain the passivation effect of the area to the greatest extent by setting the non-metallic area as a velvet structure with only a single-layer tower structure. In a further optional embodiment of the utility model, the micro-velvet structure is a multi-layer tower structure arranged in layers, preferably a two-layer tower structure. Among them, in an optional embodiment, the multi-layer tower structure such as Figures 2 to 5 shown. Specifically, Figure 2 This is a front view of the microstructure of the upper tower base in a multi-layer tower structure. Figure 3 This is a top view of the microstructure of the lower tower base in a multi-layer tower structure. Figure 4 This is a top view of the overall microstructure of the multi-tower structure. Figure 5 This is a front view of a multi-story tower structure. Figures 2 to 5 It can be seen that the lower tower base 200 can actually be understood as a plurality of cubes of different thicknesses, and the front view is the front surface of the cube, while the upper tower base 100 can be understood as a pyramid (quadrangular pyramid) formed on cubes of different thicknesses, and the front view is one of the side surfaces of the quadrangular pyramid. In a further optional embodiment, the micro-suede structure in the embodiment of the utility model is not a quadrangular pyramid grown on all cubes, but is grown on a part of the cubes, and the base area and height of the quadrangular pyramid are different, forming Figure 4 and Figure 5 The quadrangular pyramid structures shown are of different sizes when viewed from above.

[0044] Regarding the size of the upper tower base 100 and the lower tower base 200 in the multi-layer tower structure, in an optional embodiment, the side length of the lower tower base in the multi-layer tower structure is 5-8 μm, that is, the side length of the bottom surface of the cube is 5-8 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, etc., and the side length of the upper tower base is 0.5-2 μm, that is, the side length of the bottom surface of the quadrangular pyramid is 0.5-2 μm, such as 0.5 μm, 1 μm, 1.5 μm, 2 μm, etc. In the embodiment of the present invention, it was found that setting the size of the upper tower base to 0.5-2 μm can better balance passivation and contact performance. If the upper tower base is too small, the passivation performance is poor, and if the upper tower base is too large, the contact performance will be affected. Therefore, the embodiment of the present invention provides sufficient tensile stress while taking into account passivation and contact performance by setting the silicon substrate surface 1 of the metal area to a micro-suede structure with a two-layer tower structure.

[0045] In an optional embodiment, the projected area of ​​the metal region accounts for 1-10% of the projected area of ​​the main surface of the silicon substrate 1. If the area of ​​the metal region is set too large, it will lead to increased parasitic absorption, affecting the overall current of the solar cell. In a further optional embodiment, for conventional cell widths, the width of the metal region can be set to 20-300μm, for example, 20μm, 50μm, 100μm, 150μm, 250μm, 300μm, etc.

[0046] In an optional embodiment, the back-junction double-sided passivated solar cell provided by the present invention further includes: a second tunneling oxide layer 4 and a second doping layer 5 doped with a second doping element are stacked from the inside to the outside on the other side of the silicon substrate 1 in the thickness direction. For the back-junction double-sided passivated solar cell, the first tunneling oxide layer 2 and the second tunneling oxide layer 4 can both be SiO2, but the first doping element and the second doping element are usually different. For example, when the silicon substrate 1 is an N-type silicon substrate, the first doping element is phosphorus and the second doping element is boron. In an optional embodiment, the other side of the N-type silicon substrate in the thickness direction can be a planar structure with a tower base size of 10-30μm, such as 10μm, 12μm, 15μm, 18μm, 20μm, 30μm, etc.

[0047] In addition, the active doping concentration of the atoms in the first doping layer 3 and the second doping layer 5 can also be further limited to ensure that the first element and the second element can meet the activity requirements of the solar cell. Specifically, in an optional embodiment, the active doping concentration of the phosphorus atoms in the first doping layer 3 is 2E 20 -1E 21 atoms / cm 3 The active doping concentration of boron atoms in the second doping layer 4 is 5E 19 -5E 20atoms / cm 3 .

[0048] In an optional embodiment, the thickness of the first tunneling oxide layer 2 and / or the second tunneling oxide layer 4 is 0.2-2 nm, for example, 0.2 nm, 0.5 nm, 1.0 nm, 1.2 nm, 1.5 nm, 2.0 nm, etc. Correspondingly, the thickness of the first doping layer 3 is 20-500 nm, for example, 20 nm, 50 nm, 100 nm, 200 nm, 350 nm, 500 nm, etc.; the thickness of the second doping layer 5 is 20-200 nm, for example, 20 nm, 50 nm, 70 nm, 150 nm, 180 nm, 200 nm, etc. For the doping layer, if the thickness is too large, parasitic absorption will increase, thereby affecting the magnitude of the generated current, while if the thickness is too small, it will be detrimental to the sintering of the slurry.

[0049] In an optional embodiment of the present invention, the provided back-junction bifacial passivated solar cell further comprises: a passivation anti-reflection layer 6 disposed on the exposed velvet structure in the non-metallic region and the first doped layer 3; and / or a passivation layer 7 disposed on the second doped layer 5. The passivation anti-reflection layer 6 can reduce light reflection, and disposing it on the front side of the back-junction bifacial passivated solar cell can effectively improve the absorption of sunlight and enhance the photovoltaic conversion efficiency of the cell.

[0050] In an optional embodiment of the present invention, a first fine gate 8 electrically connected to the first doped layer 3 is provided in the metal region, and a second fine gate 9 electrically connected to the second doped layer 5 is provided on the other side of the silicon substrate 1. The width of the first fine gate 8 and / or the second fine gate 9 is 10-50 μm. Specifically, the first fine gate 8 and the second fine gate 9 can be formed by printing silver paste. The first fine gate 8 can be understood as the positive electrode fine gate, and the second fine gate 9 can be understood as the back electrode fine gate.

[0051] In summary, the back-junction double-sided passivated solar cell provided by the embodiment of the present invention can ensure that the non-metallic area is a velvet structure without a front field by alternately arranging a metal area with a micro-velvet structure and a non-metallic area with a velvet structure on one side of the silicon substrate in the thickness direction, thereby retaining and optimizing the passivation effect to the greatest extent. Among them, the combination of the micro-velvet structure and the velvet structure will not affect the contact performance of the battery due to its large contact surface area; at the same time, the small square resistance difference between the non-metallic area with the velvet structure and the metal area with the micro-velvet structure will not affect the lateral transmission of charges. Specifically, the first tunneling oxide layer is arranged on the micro-velvet structure of the metal area. Since the surface of the micro-velvet structure is more regular than that of the velvet structure, it is beneficial to improve the growth uniformity of the first tunneling oxide layer. In this way, the tensile stress of the silicon substrate on the first tunneling oxide layer can be increased without affecting the passivation and contact performance, thereby increasing the strength and stability of the solar cell. In addition, since the tunneling oxide structure (i.e., the first tunneling oxide layer and the first doping layer) is only provided on the metal area on one side in the thickness direction, compared with the prior art in which the entire tunneling oxide structure is provided on one side in the thickness direction, the parasitic absorption problem of the non-metallic area is reduced from the source.

[0052] Figure 6 The main process of the method for preparing a back-junction double-sided passivated solar cell provided by the embodiment of the present invention is shown as follows: Figure 6 As shown, the preparation method of the back-junction double-sided passivated solar cell provided by the present invention includes:

[0053] Step S601, texturing the main surface on one side in the thickness direction of the silicon substrate 1 to form a micro-texture structure;

[0054] Step S602 , forming a first tunneling oxide layer 2 and a first doping layer 3 doped with a first doping element on the surface of the micro-texture structure from the inside out.

[0055] Step S603 , removing the first doped layer 3 and the first tunneling oxide layer 2 in a partial area on the main surface to form a non-metallic area;

[0056] Step S604: re-texturing the non-metallic area to form a velvet structure; wherein the velvet structure and the micro-velvet structure have different lengths of the tower base;

[0057] Step S605 , using an acid solution to remove the first silicon glass layer 10 remaining on one side of the silicon substrate 1 in the thickness direction.

[0058] One side of the silicon substrate 1 in the thickness direction can be understood as the front side of the back-junction double-sided passivated solar cell, and the other side in the thickness direction can be understood as the back side of the back-junction double-sided passivated solar cell.

[0059] In an optional embodiment, while forming the first doped layer 3, a first silica glass layer 10 doped with the first doping element is simultaneously formed outside the first doped layer 3. Therefore, after step S602 and before step S603, the process further includes: removing the first silica glass layer 10 from a portion of the main surface using laser etching; and step S603 further includes: removing the first doped layer 3 and the first tunneling oxide layer 2 not covered by the first silica glass layer 10 using a first alkaline solution. Through the above process, the first silica glass layer 10, the first doped layer 3, and the first tunneling oxide layer 2 from a portion of the main surface can be sequentially removed to obtain a non-metallic region.

[0060] In a further optional embodiment, the other side of the silicon substrate 1 in the thickness direction may be prepared before step 1, specifically comprising: forming a second tunneling oxide layer 4, a second doping layer 5 doped with a second doping element, and a second silicon glass layer 11 on the main surface of the other side in the thickness direction of the silicon substrate 1 in sequence from the inside out. It is understood that the diffusion process of different doping elements requires different process temperatures, and diffusion in a high-temperature process may affect the diffusion process in a low-temperature process. Therefore, in an embodiment of the present invention, when the silicon substrate is an N-type silicon substrate, the first doping element is phosphorus (i.e., phosphorus is on the front of the silicon substrate), and the second doping element is boron (i.e., boron is on the back of the silicon substrate), a boron diffusion process with a higher diffusion process temperature is selected to be prepared first, that is, the process of preparing the second tunneling oxide layer 4, the second doping layer 5 and the second silicon glass layer 11 must be performed before step 1, and the phosphorus diffusion process with a lower diffusion process temperature cannot be selected first, that is, the first tunneling oxide layer 2, the first doping layer 3 and the first silicon glass layer 10 on the back cannot be removed by an etching process after step 2, and then the second tunneling oxide layer 4, the second doping layer 5 and the second silicon glass layer 11 can not be prepared. For example, the N-type silicon substrate 1 can be polished on both sides first, and then a tunneling oxide layer, a doping layer and a silicon glass layer are sequentially prepared on both sides of the silicon substrate 1 in the thickness direction. Subsequently, a single-sided etching process is used to remove the silicon glass layer on one side (front) in the thickness direction of the silicon substrate 1, and an alkaline solution is used to remove the tunneling oxide layer and the doping layer, that is, the tunneling oxide layer, the doping layer and the silicon glass layer on one side (front) in the thickness direction of the silicon substrate 1 are all removed, leaving only the second tunneling oxide layer 4, the second doping layer 5 and the second silicon glass layer 11 on the other side (back) in the thickness direction of the silicon substrate 1. Through the above steps, the following can be obtained: Figure 7 The structural diagram shown is a schematic diagram of the silicon substrate structure before executing step S601. Figure 7 It can be seen that the back side of the silicon substrate 1 is sequentially covered with the second tunneling oxide layer 4 , the second doping layer 5 , and the second silicon glass layer 11 , while the front side of the silicon substrate 1 is a bare silicon substrate.

[0061] In an optional embodiment, while forming the first doping layer 3 and the first silica glass layer 10 in step S602, a third doping layer 12 doped with the first doping element and a third silica glass layer 13 doped with the first doping element are also formed on the surface of the second silica glass layer 11 from the inside to the outside. Figure 8 As shown, the third doped layer 12 is essentially the same as the first doped layer 3, and the third silicon glass layer 13 is essentially the same as the first silicon glass layer 10. The different names and numbers used in the present embodiment are to illustrate the differences in the positions and thicknesses of the two layers. In fact, they are the same material produced in the same step.

[0062] In an optional embodiment, before step S603, the method further includes: removing the third silicon glass layer 13 formed on the second silicon glass layer 11 by using an acid solution, and removing the third doping layer 12 formed on the second silicon glass layer 11 by using a first alkaline solution, to obtain Figure 9 The silicon substrate structure shown. Since different regions on the front of the silicon substrate 1 need to be prepared into different morphological structures, in order to save process flow, laser etching is selected to remove the first silicon glass layer 10 on the front. The back of the silicon substrate 1 does not involve the process of preparing different regions. Therefore, the embodiment of the utility model chooses to use an acid solution to remove the third silicon glass layer 13 on the back. The complete covering third silicon glass layer 13 can be completely removed at one time, which is simple and efficient.

[0063] In order to ensure that the first alkaline solution does not damage the first silicon glass layer 10 on the front side during the process of removing the third doping layer 12 on the back side, in an optional embodiment of the present invention, a highly selective silicon / silicon oxide additive is added to the first alkaline solution, that is, the highly selective silicon / silicon oxide additive is used to ensure that the first alkaline solution does not react with the first silicon glass layer 10.

[0064] Figure 10 The schematic diagram of the structure of the silicon substrate obtained after step S603 of the embodiment of the present invention is shown. It is understandable that laser etching usually causes damage to the etched area due to its high energy. The embodiment of the present invention uses the first doped layer 3 and the first tunneling oxide layer 2 covered by the first silicon glass layer 10 to eliminate the effect of the laser on the silicon substrate 1. Even if damage is caused to the covered structure, it only damages the first doped layer 3 that will be removed later, and will not cause damage to the structure retained in the solar cell. At the same time, since a highly selective silicon / silicon oxide additive is added to the first alkaline solution, the second silicon glass layer 11 on the back will not be affected during the process of removing part of the first doped layer 3 and the first tunneling oxide layer 2 on the front side.

[0065] Regarding the specific parameters of laser etching, in an optional embodiment, the power density of laser etching is 0.01-10kW / cm 2; and / or, the laser wavelength for laser etching is any one of 355nm, 532nm, and 1064nm pulse light; and / or, the laser emission frequency is 10-250kHz, the scanning speed is 5-50m / s, and the overlap between lasers is 0-100%. By setting the above parameters, it is possible to ensure that the depth of laser etching does not damage the silicon substrate 1, while completely removing the first silicon glass layer 10. In the embodiment of the present invention, the thickness of the first silicon glass layer 10 is 20-100μm.

[0066] Figure 11 The schematic diagram of the structure of the silicon substrate obtained after step S604 and step S605 is shown in the embodiment of the present invention. Figure 9 As can be seen, prior to step S605, both sides of the silicon substrate 1 in the thickness direction comprised a silicon glass layer. Specifically, the outermost layer of the metal region on the front side was a first silicon glass layer 10, while the back side was covered with a second silicon glass layer 11. Therefore, step S605, while simultaneously removing the first silicon glass layer 10, also includes simultaneously removing the second silicon glass layer 11 using an acid solution. Using the acid solution, the silicon glass layers on both the front and back sides of the silicon substrate 1 can be removed simultaneously, simplifying the process and improving production efficiency.

[0067] In an optional embodiment, after step S605, the following steps may be performed: Figure 12 Shown, including:

[0068] Step S1201 , forming a passivation anti-reflection layer 6 on the first doped layer 3 and the textured structure of the non-metallic region, and forming a passivation layer 7 outside the second doped layer 5 ;

[0069] In step S1202 , a first fine gate 8 and a second fine gate 9 are formed on the passivation anti-reflection layer 6 and the passivation layer 7 , respectively. The first fine gate 8 is electrically connected to the first doped layer 3 , and the second fine gate 9 is electrically connected to the second doped layer 5 by sintering.

[0070] Through the above steps S1201 and S1202, we can get Figure 1 In the back-junction double-sided passivated solar cell provided by the embodiment of the present invention shown, the number and position of the first fine grids 8 and the second fine grids 9 can be set correspondingly or adjusted according to actual conditions, and the present invention does not impose any limitation on this.

[0071] It should be noted that the texturing process involved in the present invention can all be done using commonly used alkali texturing, but the mass concentration of the alkali solution is different, and the resulting velvet structure will also be different. Therefore, in an optional embodiment, in step S601, the non-metallic area is re-textured using a second alkali solution; in step S604, the non-metallic area is re-textured using a third alkali solution; wherein the mass concentration of the third alkali solution is higher than the mass concentration of the second alkali solution. In a further optional embodiment, the mass concentration of the first alkali solution and / or the third alkali solution can be 0.00005%-5%, for example, 0.00005%, 0.1%, 1%, 2%, 4%, 5%, etc.; and / or, the mass concentration of the second alkali solution is 0.00005%-1%, for example, 0.00005%, 0.001%, 0.01%, 0.1%, 0.5%, etc. In the texturing process of the embodiment of the present invention, too high an additive concentration will reduce the reaction rate, while too low an additive concentration is not conducive to the formation of pyramid structures and micro-velvet surfaces.

[0072] In addition, to ensure that the texturing process does not affect the first silica glass layer 10 on the metal area on the front side of the silicon substrate 1 and the second silica glass layer 11 on the back side of the silicon substrate 1, a highly selective silicon / silicon oxide additive may also be added to the second alkaline solution and / or the third alkaline solution. Specifically, in an optional embodiment, the highly selective silicon / silicon oxide additive is tetramethylammonium hydroxide.

[0073] In summary, the preparation method of the back-junction double-sided passivated solar cell provided by the embodiment of the present invention can obtain a metal area with a micro-velvet structure and a non-metallic area with a velvet structure alternately arranged on one side of the thickness direction of the silicon substrate, ensuring that the non-metallic area is a velvet structure without a front field, and retaining and optimizing the passivation effect to the greatest extent. Among them, the combination of the micro-velvet structure and the velvet structure will not affect the contact performance of the battery due to its large contact surface area; at the same time, the small square resistance difference between the non-metallic area with the velvet structure and the metal area with the micro-velvet structure will not affect the lateral transmission of charges. Specifically, the first tunneling oxide layer is arranged on the micro-velvet structure of the metal area. Since the surface of the micro-velvet structure is more regular than that of the velvet structure, it is beneficial to improve the growth uniformity of the first tunneling oxide layer. In this way, the tensile stress of the silicon substrate on the first tunneling oxide layer can be increased without affecting the passivation and contact performance, thereby increasing the strength and stability of the solar cell. In addition, since the tunneling oxide structure (i.e., the first tunneling oxide layer and the first doping layer) is only provided on the metal area on one side in the thickness direction, compared with the prior art in which the entire tunneling oxide structure is provided on one side in the thickness direction, the parasitic absorption problem of the non-metallic area is reduced from the source.

[0074] Example 1

[0075] Step 1: Double-sided polishing of an N-type silicon substrate with a resistivity of 0.8 Ωcm and a thickness of 150 μm is performed, and alkaline texturing is performed using a 5% potassium hydroxide solution for an etching time of 200 seconds to form a 10-15 μm tower base on the surface of the silicon substrate;

[0076] Step 2: Place the dried silicon wafer in an LPCVD quartz boat and introduce 2000 sccm of oxygen. Under low pressure, gradually raise the temperature to 600°C to deposit a 1.5nm thick SiO2 layer (oxide layer) on the front and back of the silicon substrate.

[0077] Step 3: After the SiO2 layer is grown, silane is introduced and an intrinsic polysilicon layer with a thickness of 180 nm is prepared on the SiO2 layer on both sides of the silicon substrate in the thickness direction;

[0078] Step 4: Raise the temperature to 950°C and introduce a boron source and oxygen to diffuse the boron element into the intrinsic polysilicon layer, forming a doped layer and a silicon glass layer on both sides of the silicon substrate in the thickness direction;

[0079] Step 5: Etching the front side of the silicon substrate with an HF solution to remove the silicon glass layer, and removing the doped layer and the oxide layer on the front side with an alkaline solution to form a silicon substrate having only the second tunneling oxide layer, the second doped layer, and the second silicon glass layer on the back side of the silicon substrate;

[0080] Step 6: Place the silicon base substrate in an alkaline solution containing 0.001% TMAH, and texturize the front surface to form a micro-texture structure.

[0081] Step 7: Place the dried silicon substrate with a micro-texture structure in an LPCVD quartz boat and use a thermal oxidation process to prepare a 1.5nm thick SiO2 layer (first tunneling oxide layer) on the front surface. Then, introduce silane to prepare a 150nm thick intrinsic polysilicon layer.

[0082] Step 8: Raise the temperature and introduce phosphorus oxychloride (650 sccm) and oxygen (1500 sccm) at 890°C to diffuse phosphorus into the intrinsic polysilicon layer to form a first doped layer and a first silicon glass layer; wherein the doping concentration of phosphorus is 6E 20 atoms / cm 3 , the thickness of the first silicon glass layer is 50 nm;

[0083] In the process of step 7 and step 8, a third doping layer and a third silicon glass layer are formed outside the second silicon glass layer on the back side of the silicon substrate.

[0084] Step 9, etching the back of the silicon substrate with an acid solution to remove the third silicon glass layer, and then removing the third doped layer in an alkaline solution added with 0.02% TMAH by mass concentration;

[0085] Step 10: Etching the first silicon glass layer in the front non-metallic contact area by laser etching to a depth of about 50 nm;

[0086] Step 11, etching the first doped layer and the first tunnel oxide layer in the non-metallic region using an alkaline solution added with 0.02% TMAH by mass;

[0087] Step 12: using an alkaline solution to which TMAH is added at a mass concentration of 0.05% to texture the non-metallic contact area on the front side, to form a pyramid texture surface with a tower base size of 2 μm;

[0088] Step 13, using an HF solution to clean the first silicon glass layer on the front side of the silicon substrate and the second silicon glass layer on the back side of the silicon substrate;

[0089] Step 14: In a plate-type atomic layer deposition device, an Al2O3 film (passivation anti-reflection layer) is deposited on the front and back sides of the silicon wafer. The thickness of the Al2O3 layer is 5nm, and then a 2nm oxide layer is grown on the passivation anti-reflection layer to enhance the field passivation effect. At the same time, in a plasma-enhanced chemical vapor deposition device, silane and ammonia are introduced to complete the anti-reflection layer SiN x Deposition of thin films (75 nm);

[0090] Step 15: Print silver paste on the front and back sides of the silicon substrate respectively by screen printing, and sinter at high temperature to prepare the first fine grid and the second fine grid.

[0091] The present invention also provides the following technical solutions:

[0092] Technical solution 1. A back-junction double-sided passivated solar cell, characterized in that it includes: a silicon substrate 1; a metal area of ​​a micro-velvet structure and a non-metallic area of ​​a velvet structure alternately arranged on one side of the silicon substrate 1 in the thickness direction; the velvet structure and the tower base of the micro-velvet structure have different side lengths; a first tunneling oxide layer 2 and a first doping layer 3 doped with a first doping element stacked from the inside to the outside on the metal area.

[0093] Technical Solution 2. The back-junction double-sided passivated solar cell according to Technical Solution 1 is characterized in that the velvet structure is a pyramid morphology, and the side length of the pyramid base is 1-2 μm.

[0094] Technical Solution 3. The back-junction double-sided passivated solar cell according to Technical Solution 1 or 2 is characterized in that the micro-suede structure is a stacked multi-layer tower structure; wherein the side length of the lower tower base in the multi-layer tower structure is 5-8 μm, and the side length of the upper tower base is 0.5-2 μm.

[0095] Technical Solution 4. The back-junction double-sided passivated solar cell according to Technical Solution 1 is characterized in that the width of the metal area is 20-300 μm; and / or the projected area of ​​the metal area accounts for 1-10% of the projected area of ​​the main surface of the silicon substrate 1.

[0096] Technical Solution 5. The back-junction double-sided passivated solar cell according to Technical Solution 1 is characterized in that it also includes: a second tunneling oxide layer 4 and a second doping layer 5 doped with a second doping element stacked from the inside to the outside on the other side of the silicon substrate 1 in the thickness direction.

[0097] Technical Solution 6. The back-junction double-sided passivated solar cell according to Technical Solution 5 is characterized in that the thickness of the first tunneling oxide layer 2 is 0.2-2 nm; and / or the thickness of the second tunneling oxide layer 4 is 0.2-2 nm.

[0098] Technical Solution 7. The back-junction double-sided passivated solar cell according to Technical Solution 5 is characterized in that the thickness of the first doping layer 3 is 20-500nm; and / or the thickness of the second doping layer 5 is 20-200nm.

[0099] Technical Solution 8. The back-junction double-sided passivated solar cell according to Technical Solution 5 is characterized in that a passivation anti-reflection layer 6 is provided on the exposed velvet structure in the non-metallic area and the first doped layer 3; and / or a passivation layer 7 is provided on the second doped layer 5.

[0100] Technical Solution 9. The back-junction double-sided passivated solar cell according to Technical Solution 1 is characterized in that it also includes: a first fine gate 8 electrically connected to the first doped layer 3 arranged in the metal area, and a second fine gate 9 electrically connected to the second doped layer 5 arranged on the other side of the silicon substrate 1; wherein the width of the first fine gate 8 and / or the second fine gate 9 is 10-50 μm.

[0101] Technical Solution 10. The back-junction double-sided passivated solar cell according to Technical Solution 5 is characterized in that the silicon substrate is an N-type silicon substrate; the first doping element is phosphorus, and the active doping concentration of phosphorus atoms in the first doping layer 3 is 2E 20 -1E 21 atoms / cm 3 ;

[0102] The second doping element is boron, and the active doping concentration of boron atoms in the second doping layer 4 is 5E 19 -5E 20 atoms / cm 3 .

[0103] Technical Solution 11. A method for preparing a back-junction double-sided passivated solar cell, characterized in that it includes: step 1, texturing the main surface on one side of the silicon substrate 1 in the thickness direction to form a micro-texture structure; step 2, preparing a first tunneling oxide layer 2 and a first doping layer 3 doped with a first doping element on the surface of the micro-texture structure from the inside to the outside; step 3, removing the first doping layer 3 and the first tunneling oxide layer 2 in a partial area of ​​the main surface to form a non-metallic area; step 4, re-texturing the non-metallic area to form a velvet structure; wherein the velvet structure and the tower base side length of the micro-velvet structure are different; step 5, using an acid solution to remove the first silicon glass layer 10 remaining on one side of the silicon substrate 1 in the thickness direction.

[0104] Technical Solution 12. The method according to Technical Solution 11 is characterized in that, while forming the first doping layer 3, a first silicon glass layer 10 doped with a first doping element is synchronously formed on the outside of the first doping layer 3; after step 2 and before step 3, it also includes: using laser etching to remove the first silicon glass layer 10 in a partial area on the main surface; step 3 includes: using a first alkaline solution to remove the first doping layer 3 and the first tunneling oxide layer 2 not covered by the first silicon glass layer 10.

[0105] Technical Solution 13. The method according to Technical Solution 11 is characterized in that, before step 1, it includes: preparing a second tunneling oxide layer 4, a second doping layer 5 doped with a second doping element, and a second silicon glass layer 11 in sequence from the inside to the outside on the main surface on the other side of the thickness direction of the silicon substrate 1.

[0106] Technical Solution 14. The method according to Technical Solution 12 is characterized in that, while forming the first doping layer 3 and the first silicon glass layer 10 in step 2, it also includes: forming a third doping layer 12 doped with the first doping element and a third silicon glass layer 13 doped with the first doping element on the surface of the second silicon glass layer 11 from the inside to the outside; before step 3, it also includes: using an acid solution to remove the third silicon glass layer 13 formed on the second silicon glass layer 11, and using the first alkaline solution to remove the third doping layer 12 formed on the second silicon glass layer 11.

[0107] Technical Solution 15. The method according to Technical Solution 13 or 14 is characterized in that, while removing the first silicon glass layer 10 in step 5, it also includes: using the acid solution to simultaneously remove the second silicon glass layer 11.

[0108] Technical Solution 16. The method according to Technical Solution 15 is characterized in that, after step 5, it also includes: step 6, preparing a passivation anti-reflection layer 6 on the velvet structure of the first doping layer 3 and the non-metallic area, and preparing a passivation layer 7 on the outside of the second doping layer 5; step 7, preparing a first fine gate 8 and a second fine gate 9 on the passivation anti-reflection layer 6 and the passivation layer 7, respectively, and electrically connecting the first fine gate 8 to the first doping layer 3 and the second fine gate 9 to the second doping layer 5 through sintering.

[0109] Technical Solution 17. The method according to Technical Solution 11 is characterized in that, in step 1, the non-metallic area is textured using a second alkaline solution; in step 4, the non-metallic area is re-textured using a third alkaline solution; wherein the mass concentration of the third alkaline solution is higher than the mass concentration of the second alkaline solution.

[0110] Technical Solution 18. The method according to Technical Solution 17 is characterized in that the mass concentration of the first alkaline solution is 0.00005%-5%; and / or the mass concentration of the second alkaline solution is 0.00005%-1%; and / or the mass concentration of the third alkaline solution is 0.00005%-5%.

[0111] Technical Solution 19. The method according to Technical Solution 17 is characterized in that a highly selective silicon / silicon oxide additive is added to the first alkaline solution; and / or a highly selective silicon / silicon oxide additive is added to the second alkaline solution; and / or a highly selective silicon / silicon oxide additive is added to the third alkaline solution; wherein the highly selective silicon / silicon oxide additive is tetramethylammonium hydroxide.

[0112] Technical Solution 20. The method according to Technical Solution 11 is characterized in that the power density of the laser etching is 0.01-10kW / cm 2 ; and / or, the laser wavelength of the laser etching is any one of 355nm, 532nm, and 1064nm pulse light; and / or, the laser emission frequency is 10-250kHz, the scanning speed is 5-50m / s, and the overlap rate between lasers is 0-100%; and / or, the thickness of the first silicon glass layer 10 is 20-100μm.

[0113] The above steps are merely intended to help you understand the structure, method, and core concept of the present invention. A person skilled in the art would be able to make improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications would also fall within the scope of protection of the claims of the present invention.

Claims

1. A back-junction double-sided passivated solar cell, characterized in that: include: Silicon substrate (1); Metal regions of a micro-texture structure and non-metal regions of a texture structure are alternately arranged on one side of the silicon substrate (1) in the thickness direction; The side lengths of the tower bases of the velvet structure and the micro-velvet structure are different; the micro-velvet structure is a multi-layer tower structure arranged in layers; wherein the side length of the lower tower base in the multi-layer tower structure is 5-8 μm, and the side length of the upper tower base is 0.5-2 μm; A first tunneling oxide layer (2) and a first doping layer (3) doped with a first doping element are stacked from the inside to the outside on the metal region.

2. The back-junction double-sided passivated solar cell according to claim 1, characterized in that: The velvet structure is in a pyramidal morphology, and the side length of the pyramid base is 1-2 μm.

3. The back-junction double-sided passivated solar cell according to claim 1, characterized in that: The width of the metal region is 20-300 μm; and / or, The projected area of ​​the metal region accounts for 1%-10% of the projected area of ​​the main surface of the silicon substrate (1).

4. The back-junction double-sided passivated solar cell according to claim 1, characterized in that: Also includes: A second tunneling oxide layer (4) and a second doping layer (5) doped with a second doping element are stacked from the inside to the outside on the other side of the silicon substrate (1) in the thickness direction.

5. The back-junction double-sided passivated solar cell according to claim 4, characterized in that: The thickness of the first tunneling oxide layer (2) is 0.2-2 nm; and / or, The thickness of the second tunneling oxide layer (4) is 0.2-2 nm.

6. The back-junction double-sided passivated solar cell according to claim 4, characterized in that: The thickness of the first doping layer (3) is 20-500 nm; and / or, The thickness of the second doping layer (5) is 20-200 nm.

7. The back-junction double-sided passivated solar cell according to claim 4, characterized in that: A passivation anti-reflection layer (6) is provided on the exposed velvet structure in the non-metallic area and the first doped layer (3); and / or, A passivation layer (7) is provided on the second doped layer (5).

8. The back-junction double-sided passivated solar cell according to claim 4, characterized in that: Also includes: a first fine gate (8) provided in the metal region and electrically connected to the first doped layer (3), and a second fine gate (9) provided on the other side of the silicon substrate (1) and electrically connected to the second doped layer (5); Wherein, the width of the first fine grid (8) and / or the second fine grid (9) is 10-50 μm.

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