A solar cell and a method of manufacturing the same

Abstract

This invention provides a solar cell and its fabrication method. The passivation layer of the solar cell is a transparent conductive layer, which comprises a dense conductive layer and a mesoporous conductive layer stacked sequentially. The mesoporous conductive layer is in contact with the electrode. By replacing the passivation layer with a dense conductive layer and a mesoporous conductive layer stacked sequentially, and ensuring the mesoporous conductive layer is in contact with the electrode, this invention guarantees electron transport, optimizes defect recombination in the metal-nonmetal contact area, and increases the contact area of ​​the electrode in the structure. It features a simple structure, ease of industrial production, and structural stability.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a solar cell and its preparation method. Background Technology

[0002] TOPCon solar cells (Tunnel Oxide Passivated Contact) are solar cells that use an ultrathin oxide layer as the passivation layer structure. An ultrathin tunnel oxide layer and a highly doped polycrystalline silicon layer are fabricated on the back of the cell, together forming the passivation contact structure. This structure provides excellent surface passivation for the back of the silicon wafer. The ultrathin oxide layer allows majority carrier electrons to tunnel into the polycrystalline silicon layer while blocking minority carrier hole recombination. Electrons then undergo lateral transport within the polycrystalline silicon layer and are collected by the metal, thereby significantly reducing the metal contact recombination current and improving the cell's open-circuit voltage and short-circuit current.

[0003] In the TOPCon battery structure, the SiN on the back of the battery x The passivation layer cannot conduct electricity, so the paste needs to be burned through the SiN during electrode printing. x The passivation layer allows electrons to transfer between the electrode and the underlying polysilicon layer. However, this process can damage the polysilicon layer, leading to poor passivation in the metal-nonmetal contact area and increased defect recombination.

[0004] CN111106183A discloses a method for fabricating a fully passivated back-side contact solar cell using tubular PECVD and the solar cell itself. The method includes the following steps: pre-cleaning a silicon wafer, double-sided texturing, front-side boron diffusion, front-side laser selective doping, secondary cleaning, and back-side polishing; depositing a silicon dioxide thin film layer and a phosphorus-doped amorphous silicon carbide thin film layer on the back side using tubular PECVD equipment, followed by annealing to transform the amorphous silicon carbide into microcrystalline silicon carbide; depositing an Al2O3 passivation layer and an anti-reflection layer; screen printing and sintering to obtain the fully passivated back-side contact solar cell. This method has advantages such as simple process, convenient operation, low cost, good compatibility with existing production lines, good controllability, high efficiency, and good safety. It can fabricate high-efficiency fully passivated back-side contact solar cells and is suitable for large-scale fabrication, facilitating industrial applications and possessing high practical value and promising application prospects.

[0005] CN112670352A discloses a passivation structure for use in contact passivated batteries and its fabrication method, comprising an N-type substrate, two positive electrodes disposed on the front side of the N-type substrate, and two negative electrodes disposed on the back side of the N-type substrate. A SiO2 layer is disposed on the back side of the N-type substrate, and doped polycrystalline SiO2 is disposed on the SiO2 layer. x N yThis scheme replaces the polycrystalline silicon layer with a doped polycrystalline silicon oxynitride layer. By ensuring minimal change in contact resistance, and through appropriate doping and annealing, it reduces light absorption in the contact passivation layer and improves the efficiency of contact passivation type batteries.

[0006] Existing TOPCon battery structures suffer from problems such as complex fabrication methods, defects in metal-nonmetal contacts, and structural complexity. Therefore, how to ensure that the TOPCon battery structure is simple and easy to fabricate, while optimizing the recombination of defects in the metal-nonmetal contact area, increasing the contact area of ​​the electrode in the structure, and enhancing the robustness of the electrode has become an urgent problem to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a solar cell and its fabrication method. By replacing the passivation layer with a dense conductive layer and a mesoporous conductive layer stacked sequentially, and with the mesoporous conductive layer in contact with the electrode, electron transport is ensured. Furthermore, it optimizes defect recombination in the metal-nonmetal contact area and increases the contact area of ​​the electrode in the structure. The method features a simple structure, ease of industrial production, and structural stability.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a solar cell, wherein the passivation layer of the solar cell is a transparent conductive layer, the transparent conductive layer comprising a dense conductive layer and a mesoporous conductive layer stacked sequentially, the mesoporous conductive layer being in contact with an electrode.

[0010] This invention replaces the passivation layer in solar cells by using a stacked dense conductive layer and a mesoporous conductive layer. The dense conductive layer contacts one side of the polycrystalline silicon layer, while the mesoporous conductive layer contacts the electrode. This invention effectively prevents the paste from corroding the bottom polycrystalline silicon layer, while the dense conductive layer forms good contact with the polycrystalline silicon layer, facilitating electron transport. The mesoporous conductive layer allows the printed electrode paste to penetrate, resulting in a larger and stronger contact between the metal electrode and the mesoporous conductive layer. Furthermore, since the passivation effect of the polycrystalline silicon layer is achieved by high temperature-driven H... + It enters into the silicon, but at the same time some H... + It will escape outwards, and the dense conductive layer can effectively suppress most of the H. + It diffuses outwards, improving the passivation of the polycrystalline silicon layer.

[0011] Currently, although transparent conductive layers have been used to replace SiN... xThe structure is designed to isolate the paste from the polycrystalline silicon layer. However, this method of depositing a transparent conductive layer over the entire surface results in a reduced contact area between the electrodes and the transparent conductive layer compared to a normal structure, as the electrode paste can only contact the surface of the transparent conductive layer during printing. This will affect the tensile strength of the electrodes during subsequent component soldering.

[0012] It should be noted that the mesoporous conductive layer in this invention refers to a mesoporous conductive layer with a porous structure or a surface covered with through holes, that is, when printing electrode paste, the electrode paste can enter the pore structure, thereby improving the contact stability of the metal electrode; for dense conductive layers, there is no pore structure.

[0013] As a preferred embodiment of the present invention, the mesoporous conductive layer is in the form of a grid line structure or a completely covered structure.

[0014] It should be noted that the fully covered structure in this invention refers to a structure in which the mesoporous conductive layer completely covers the dense conductive layer.

[0015] Preferably, the mesoporous conductive layer has a gate line structure, and the gate line structure of the mesoporous conductive layer is the same as that of the adjacent electrode.

[0016] For example, a method for preparing a gate structure of a mesoporous conductive layer is provided. The preparation method involves covering the sample to be deposited with a mask plate that is in close contact with the sample, covering the non-deposition area, while the area to be deposited is exposed to the spraying environment, and then performing the above-mentioned spraying steps.

[0017] In this invention, the mesoporous conductive layer of the gate structure can reduce incident light loss and utilize the longitudinal transmission function of the transparent conductive layer to ensure the effective transmission of charge carriers. At the same time, it can also avoid defect recombination caused by direct contact between the metal electrode and polycrystalline silicon.

[0018] As a preferred embodiment of the present invention, the back passivation layer of the solar cell is a transparent conductive layer, which is composed of a dense conductive layer and a mesoporous conductive layer stacked sequentially.

[0019] Preferably, the back side of the solar cell substrate is provided with a tunneling layer, a polycrystalline silicon layer, a dense conductive layer, a mesoporous conductive layer and a back electrode stacked sequentially.

[0020] Preferably, the front side of the solar cell substrate is provided with an emitter layer, a front passivation layer and a front electrode stacked sequentially.

[0021] It should be noted that the present invention does not impose specific requirements or special limitations on the materials of the substrate, tunneling layer, polysilicon layer, back electrode, emitter layer, and front passivation layer. The selection of materials is not an innovation of the present invention. Those skilled in the art can reasonably select the materials of the substrate, tunneling layer, polysilicon layer, back electrode, emitter layer, and front passivation layer according to design requirements.

[0022] As a preferred embodiment of the present invention, the dense conductive layer includes one or a combination of at least two of the following: TiO2 layer, ZrO2 layer, Nb2O5 layer, boron-doped ZnO layer, aluminum-doped ZnO layer, IZO layer, IWO layer, ITO layer, FTO layer, SnO2 layer, Y2O3 layer, MgO layer, B2O3 layer, GeO2 layer, La2O3 layer, CeO2 layer, Nd2O3 layer, Gd2O3 layer, Dy2O3 layer, Er2O3 layer, Yb2O3 layer, SrTiO3 layer, BaTiO3 layer, PbTiO3 layer, PbZrO3 layer, or NdAlO3 layer.

[0023] Preferably, the thickness of the dense conductive layer is 10 to 100 nm, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm.

[0024] This invention ensures conductivity by controlling the thickness of the dense conductive layer to be 10-100 nm. If the thickness is less than 10 nm, the dense conductive layer will be too thin, making the preparation complex and resulting in uneven coverage and poor electrical transmission. If the thickness is greater than 100 nm, although the conductivity is improved, the thicker the layer, the more serious the light absorption problem will be.

[0025] As a preferred embodiment of the present invention, the mesoporous conductive layer includes one or a combination of at least two of the following: TiO2 layer, ZrO2 layer, Nb2O5 layer, boron-doped ZnO layer, aluminum-doped ZnO layer, IZO layer, IWO layer, ITO layer, FTO layer, SnO2 layer, Y2O3 layer, MgO layer, B2O3 layer, GeO2 layer, La2O3 layer, CeO2 layer, Nd2O3 layer, Gd2O3 layer, Dy2O3 layer, Er2O3 layer, Yb2O3 layer, SrTiO3 layer, BaTiO3 layer, PbTiO3 layer, PbZrO3 layer, or NdAlO3 layer.

[0026] Preferably, the thickness of the mesoporous conductive layer is 0.02 to 2 μm, for example, 0.02 μm, 0.06 μm, 0.08 μm, 0.10 μm, 0.20 μm, 0.40 μm, 0.60 μm, 0.80 μm, 1.00 μm, 1.20 μm, 1.40 μm, 1.60 μm, 1.80 μm or 2.00 μm.

[0027] This invention controls the thickness of the mesoporous conductive layer to be 0.02–2 μm, thereby avoiding excessive battery series resistance and ensuring the tensile strength of the electrode solder strip. If the thickness is less than 0.02 μm, the mesoporous conductive layer is too thin, which is not conducive to the penetration of electrode slurry and affects the tensile strength of the solder strip. If the thickness is greater than 2 μm, it will result in an excessively long electron transport path and an increase in battery series resistance.

[0028] As a preferred embodiment of the present invention, the diameter of the mesoporous conductive layer is larger than the diameter of the particles in the adjacent electrode.

[0029] This invention improves the bonding between the electrode and the mesoporous conductive layer by setting the diameter of the mesoporous conductive layer to be larger than the diameter of the electrode slurry particles, thereby allowing the particles in the electrode to enter the mesoporous layer and ensuring the stability of the electrode.

[0030] Preferably, the mesoporous conductive layer has a mesoporous diameter of 0.01 to 2 μm, for example, 0.01 μm, 0.06 μm, 0.08 μm, 0.10 μm, 0.20 μm, 0.40 μm, 0.60 μm, 0.80 μm, 1.00 μm, 1.20 μm, 1.40 μm, 1.60 μm, 1.80 μm or 2.00 μm.

[0031] It should be noted that the present invention does not impose specific requirements or special limitations on the thickness of the tunneling layer, the polysilicon layer, and the front passivation layer. Those skilled in the art can reasonably select the thickness of the tunneling layer, the polysilicon layer, and the front passivation layer according to the design requirements. For example, the thickness of the tunneling layer is 1 to 2 nm, the thickness of the polysilicon layer is 40 to 400 nm, and the thickness of the front passivation layer is 40 to 60 nm.

[0032] In a second aspect, the present invention provides a method for preparing a solar cell as described in the first aspect, the method comprising: sequentially preparing a dense conductive layer and a mesoporous conductive layer, and then printing an electrode paste on the surface of the mesoporous conductive layer to form an electrode.

[0033] As a preferred technical solution of the present invention, the dense conductive layer is prepared by one or a combination of at least two of the following methods: atomic force deposition, vapor deposition, spraying, coating, hydrothermal method, sol-gel method, spin coating or physical sputtering.

[0034] Preferably, the dense conductive layer is prepared by spraying, which specifically includes: dispersing the material of the dense conductive layer in a dispersant and spraying it at least twice in a cycle to form the dense conductive layer.

[0035] As a preferred technical solution of the present invention, the mesoporous conductive layer is prepared by one or a combination of at least two of the following methods: spraying, coating, hydrothermal method, sol-gel method or spin coating.

[0036] Preferably, the mesoporous conductive layer is prepared by spraying, which specifically includes: dispersing the mesoporous conductive layer material in a dispersant, spraying it in cycles at least twice, drying and sintering to form the mesoporous conductive layer.

[0037] Preferably, the sintering temperature is 450 to 550°C, for example, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C or 550°C.

[0038] Preferably, the sintering time is 25 to 35 minutes, for example, 25 minutes, 26 minutes, 27 minutes, 28 minutes, 29 minutes, 30 minutes, 31 minutes, 32 minutes, 33 minutes, 34 minutes or 35 minutes.

[0039] As a preferred embodiment of the present invention, the preparation method specifically includes the following steps:

[0040] An emitter layer, a front passivation layer, and a front electrode are formed on the front side of the substrate, and a tunneling layer, a polycrystalline silicon layer, a dense conductive layer, a mesoporous conductive layer, and a back electrode are formed on the back side of the substrate.

[0041] Exemplarily, a method for preparing the above-mentioned solar cell is provided, the method specifically including the following steps:

[0042] (1) The surface of the substrate is texturized and cleaned;

[0043] (2) After cleaning the substrate processed in step (1), place it in a diffusion furnace to perform boron diffusion on the textured surface, and form an emitter layer and borosilicate glass (BSG) on the front side.

[0044] (3) After step (2), the back side is cleaned and the back side coating is removed using a single-sided etching and cleaning machine. After the cleaning is completed, the front side has a BSG protective film. The back side is then polished.

[0045] (4) Using an LPCVD tube furnace, a tunneling layer is grown on the back side;

[0046] (5) After step (4), intrinsic amorphous silicon is deposited on the back side using low-pressure chemical vapor deposition. Then, phosphorus diffusion is performed on the intrinsic amorphous silicon and it is activated at high temperature to form a doped polycrystalline silicon layer.

[0047] (6) After step (5), perform HF cleaning to remove PSG from the front and back sides;

[0048] (7) After step (6), a passivation layer on the front side is prepared by plasma chemical vapor deposition.

[0049] (8) After step (7), a dense conductive layer is prepared by spraying. The silicon wafer is placed on the panel, and the dense conductive layer solution is sprayed onto the surface of the polycrystalline silicon layer using a spray gun. The spraying is repeated 6-7 times, and then dried in the furnace tube to form a dense conductive layer.

[0050] (9) After step (8), a mesoporous conductive layer is prepared by spraying. The silicon wafer is placed on the panel, the mesoporous conductive layer is dispersed in the dispersant, stirred evenly, and then sprayed onto the surface of the dense conductive layer with a spray gun. The spraying is repeated 7-8 times. After that, it is placed on the panel to dry, and then sintered at a high temperature of 450-550°C for 25-35 minutes to form a mesoporous conductive layer. For example, a method for preparing a mesoporous conductive layer with a gate structure is provided. A mask is used to cover the sample to be deposited, covering the non-deposited area, while the area to be deposited is exposed to the spraying environment. Then the above spraying steps are performed.

[0051] (10) After step (9), the front electrode and the back electrode are printed using electrode paste respectively.

[0052] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0054] This invention replaces the passivation layer in solar cells by using a stacked dense conductive layer and a mesoporous conductive layer. The dense conductive layer contacts one side of the polycrystalline silicon layer, while the mesoporous conductive layer contacts the electrode. This invention effectively prevents the paste from corroding the bottom polycrystalline silicon layer, while the dense conductive layer forms good contact with the polycrystalline silicon layer, facilitating electron transport. The mesoporous conductive layer allows the printed electrode paste to penetrate, resulting in a larger and stronger contact between the metal electrode and the mesoporous conductive layer. Furthermore, since the passivation effect of the polycrystalline silicon layer is achieved by high temperature-driven H... + It enters into the silicon, but at the same time some H... + It will escape outwards, and the dense conductive layer can effectively suppress most of the H. + It diffuses outwards, improving the passivation of the polycrystalline silicon layer. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the structure of a solar cell provided in a specific embodiment of the present invention;

[0056] Figure 2 This is a schematic diagram of the structure of the solar cell provided in Embodiment 9 of the present invention.

[0057] Wherein, 1-substrate; 2-tunneling layer; 3-polycrystalline silicon layer; 4-dense conductive layer; 5-mesoporous conductive layer; 6-back electrode; 7-emitter layer; 8-front passivation layer; 9-front electrode. Detailed Implementation

[0058] It should be understood that in the description of this invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0059] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0060] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0061] In one specific embodiment, the present invention provides a solar cell, such as... Figure 1 As shown, the passivation layer of the solar cell is a transparent conductive layer, which includes a dense conductive layer 4 and a mesoporous conductive layer 5 stacked sequentially, and the mesoporous conductive layer 5 is in contact with the electrode.

[0062] This invention replaces the passivation layer in a solar cell by using a dense conductive layer 4 and a mesoporous conductive layer 5 stacked together. The dense conductive layer 4 contacts one side of the polycrystalline silicon layer 3, and the mesoporous conductive layer 5 contacts the electrode. This invention effectively prevents the paste from corroding the bottom polycrystalline silicon layer 3, while the dense conductive layer 4 can form good contact with the polycrystalline silicon layer 3, facilitating electron transport. The mesoporous conductive layer 5 allows the printed electrode paste to penetrate, resulting in a larger and stronger contact between the metal electrode and the mesoporous conductive layer 5. Furthermore, since the passivation effect of the polycrystalline silicon layer 3 is achieved by high temperature-driven H... + It enters into the silicon, but at the same time some H... + It will escape outwards, and the dense conductive layer 4 can effectively suppress most of the H. + It diffuses outward, improving the passivation of polycrystalline silicon layer 3.

[0063] In this invention, the mesoporous conductive layer 5 represents a mesoporous conductive layer 5 with a porous structure or a surface covered with through holes, that is, when printing electrode paste, the electrode paste can enter the pore structure, thereby improving the contact stability of the metal electrode; as for the dense conductive layer 4, it does not have a pore structure.

[0064] Furthermore, the mesoporous conductive layer 5 has a grid line structure or a completely covered structure. Even further, the mesoporous conductive layer 5 has a grid line structure, and the grid line structure of the mesoporous conductive layer 5 is the same as the grid line structure of the adjacent electrode.

[0065] Furthermore, the back passivation layer of the solar cell is a transparent conductive layer, which is composed of a dense conductive layer 4 and a mesoporous conductive layer 5 stacked sequentially. Even further, the back side of the solar cell substrate 1 is sequentially stacked with a tunneling layer 2, a polycrystalline silicon layer 3, a dense conductive layer 4, a mesoporous conductive layer 5, and a back electrode 6; the front side of the solar cell substrate 1 is sequentially stacked with an emitter layer 7, a front passivation layer 8, and a front electrode 9.

[0066] Further, the dense conductive layer 4 includes one or a combination of at least two of the following: a TiO2 layer, a ZrO2 layer, a Nb2O5 layer, a boron-doped ZnO layer, an aluminum-doped ZnO layer, an IZO layer, an IWO layer, an ITO layer, an FTO layer, a SnO2 layer, a Y2O3 layer, a MgO layer, a B2O3 layer, a GeO2 layer, a La2O3 layer, a CeO2 layer, a Nd2O3 layer, a Gd2O3 layer, a Dy2O3 layer, an Er2O3 layer, a Yb2O3 layer, a SrTiO3 layer, a BaTiO3 layer, a PbTiO3 layer, a PbZrO3 layer, or a NdAlO3 layer. The thickness of the dense conductive layer 4 is 10–100 nm.

[0067] Further, the mesoporous conductive layer 5 includes one or a combination of at least two of the following: TiO2 layer, ZrO2 layer, Nb2O5 layer, boron-doped ZnO layer, aluminum-doped ZnO layer, IZO layer, IWO layer, ITO layer, FTO layer, SnO2 layer, Y2O3 layer, MgO layer, B2O3 layer, GeO2 layer, La2O3 layer, CeO2 layer, Nd2O3 layer, Gd2O3 layer, Dy2O3 layer, Er2O3 layer, Yb2O3 layer, SrTiO3 layer, BaTiO3 layer, PbTiO3 layer, PbZrO3 layer, or NdAlO3 layer. The thickness of the mesoporous conductive layer 5 is 0.02–2 μm.

[0068] Furthermore, the mesoporous conductive layer 5 has a mesopore diameter larger than the diameter of the electrode slurry particles. Even further, the mesopore diameter of the mesoporous conductive layer 5 is 0.01–2 μm.

[0069] Optionally, the thickness of the tunneling layer 2 is 1–2 nm. The thickness of the polysilicon layer 3 is 40–400 nm. The thickness of the front passivation layer 8 is 40–60 nm.

[0070] In another specific embodiment, the present invention provides a method for preparing the above-mentioned solar cell, the method specifically including the following steps:

[0071] (1) The surface of substrate 1 is texturized and cleaned;

[0072] (2) After cleaning the substrate 1 processed in step (1), it is placed in a diffusion furnace to perform boron diffusion on the textured surface, and an emitter layer 7 and borosilicate glass (BSG) are formed on the front side.

[0073] (3) After step (2), the back side is cleaned and the back side coating is removed using a single-sided etching and cleaning machine. After the cleaning is completed, the front side has a BSG protective film. The back side is then polished.

[0074] (4) Using an LPCVD tube furnace, a tunneling layer 2 is grown on the back side;

[0075] (5) After step (4), intrinsic amorphous silicon is deposited on the back side using low-pressure chemical vapor deposition. Then, phosphorus diffusion is performed on the intrinsic amorphous silicon and it is activated at high temperature to form a doped polycrystalline silicon layer 3.

[0076] (6) After step (5), perform HF cleaning to remove PSG from the front and back sides;

[0077] (7) After step (6), the front passivation layer 8 is prepared by plasma chemical vapor deposition.

[0078] (8) After step (7), a dense conductive layer 4 is prepared by spraying. The silicon wafer is placed on the panel, and the dense conductive layer 4 solution is sprayed onto the surface of the polycrystalline silicon layer 3 using a spray gun. The spraying is repeated 6-7 times, and then dried in the furnace tube to form a dense conductive layer 4.

[0079] (9) After step (8), a mesoporous conductive layer 5 is prepared by spraying. The silicon wafer is placed on the panel, and the mesoporous conductive layer 5 is dispersed in the dispersant. After stirring evenly, it is sprayed onto the surface of the dense conductive layer 4 with a spray gun. The spraying is repeated 7-8 times. After drying, it is placed on the panel and then sintered at a high temperature of 450-550℃ for 25-35 minutes to form the mesoporous conductive layer 5. When the mesoporous conductive layer has a grid structure, a mask is used to cover the sample to be deposited, which is close to the non-deposited area. The area to be deposited is exposed to the spraying environment. Then the above spraying steps are performed.

[0080] (10) After step (9), the front electrode 9 and the back electrode 6 are printed using electrode paste.

[0081] The dense conductive layer 4 can be prepared using one or a combination of at least two of the following methods: atomic force deposition, vapor deposition, spraying, coating, hydrothermal method, sol-gel method, spin coating, or physical sputtering. The mesoporous conductive layer 5 can be prepared using one or a combination of at least two of the following methods: spraying, coating, hydrothermal method, sol-gel method, or spin coating. Those skilled in the art can choose the appropriate method based on operational requirements.

[0082] Example 1

[0083] This embodiment provides a solar cell. Based on a specific implementation, the back passivation layer of the solar cell consists of a dense conductive layer 4 and a mesoporous conductive layer 5 sequentially stacked. Both the dense conductive layer 4 and the mesoporous conductive layer 5 are SnO2 layers. The thickness of the dense conductive layer 4 is 20 nm, the thickness of the mesoporous conductive layer 5 is 1 μm, and the mesoporous diameter of the mesoporous conductive layer 5 is 1 μm. The particle diameter in the electrode paste is 0.8 μm, and the thickness of the tunneling layer 2 is 1.5 nm. The thickness of the polycrystalline silicon layer 3 is 100 nm. The thickness of the front passivation layer 8 is 50 nm.

[0084] This embodiment also provides a method for preparing the above-mentioned solar cell, the method specifically including the following steps:

[0085] (1) The surface of the N-type substrate 1 is texturized and cleaned;

[0086] (2) After cleaning the substrate 1 processed in step (1), it is placed in a diffusion furnace to perform boron diffusion on the textured surface, and an emitter layer 7 and borosilicate glass (BSG) are formed on the front side.

[0087] (3) After step (2), the back side is cleaned and the back side coating is removed using a single-sided etching and cleaning machine. After the cleaning is completed, the front side has a BSG protective film. The back side is then polished.

[0088] (4) Using an LPCVD tube furnace, working at 800℃ for 7 min, a tunneling layer 2 with a thickness of 1.5 nm was grown on the back side;

[0089] (5) After step (4), intrinsic amorphous silicon is deposited on the back side using low-pressure chemical vapor deposition at a temperature of 600°C. Then, phosphorus diffusion is performed on the intrinsic amorphous silicon, and it is activated at a high temperature of 890°C to form a doped polycrystalline silicon layer 3 with a thickness of 100nm.

[0090] (6) After step (5), perform HF cleaning to remove PSG from the front and back sides;

[0091] (7) After step (6), a front passivation layer 8 with a thickness of 50 nm is prepared by plasma chemical vapor deposition.

[0092] (8) After step (7), a dense conductive layer 4 is prepared by spraying. The silicon wafer is placed on an 80°C panel, and SnO2 nano aqueous solution (concentration of 15% SnO2:H2O = 1:3) is sprayed onto the surface of the polycrystalline silicon layer 3 using a spray gun. The spraying is repeated 6-7 times. Then, the wafer is dried in a 150°C furnace tube for 10 minutes to form a dense conductive layer 4 with a thickness of 20nm.

[0093] (9) After step (8), a mesoporous conductive layer 5 is prepared by spraying. The silicon wafer is placed on an 80°C panel. SnO2 nanoparticles, ethyl cellulose, and terpineol (mass ratio of SnO2 nanoparticles: ethyl cellulose: terpineol = 1:0.5:3.5) are dispersed in an ethanol solution and stirred evenly. The mixture is then sprayed onto the surface of the dense conductive layer 4 using a spray gun. The spraying is repeated 7-8 times. After drying on the panel, the wafer is sintered at 500°C for 30 minutes to form a mesoporous conductive layer 5 with a thickness of 50 nm.

[0094] (10) After step (9), the front electrode 9 is printed using electrode silver aluminum paste, and the back electrode 6 is printed using silver paste.

[0095] Example 2

[0096] This embodiment provides a solar cell. Based on a specific implementation, the back passivation layer of the solar cell consists of a dense conductive layer 4 and a mesoporous conductive layer 5 sequentially stacked. Both the dense conductive layer 4 and the mesoporous conductive layer 5 are TiO2 layers. The thickness of the dense conductive layer 4 is 20 nm, the thickness of the mesoporous conductive layer 5 is 0.02 μm, and the mesoporous pore diameter of the mesoporous conductive layer 5 is 0.01 μm. The particle diameter in the electrode paste is 0.008 μm, and the thickness of the tunneling layer 2 is 1.5 nm. The thickness of the polycrystalline silicon layer 3 is 100 nm. The thickness of the front passivation layer 8 is 50 nm.

[0097] This embodiment also provides a method for preparing the above-mentioned solar cell, the method specifically including the following steps:

[0098] (1) The surface of the N-type substrate 1 is texturized and cleaned;

[0099] (2) After cleaning the substrate 1 processed in step (1), it is placed in a diffusion furnace to perform boron diffusion on the textured surface, and an emitter layer 7 and borosilicate glass (BSG) are formed on the front side.

[0100] (3) After step (2), the back side is cleaned and the back side coating is removed using a single-sided etching and cleaning machine. After the cleaning is completed, the front side has a BSG protective film. The back side is then polished.

[0101] (4) Using an LPCVD tube furnace, working at 800℃ for 7 min, a tunneling layer 2 with a thickness of 1.5 nm was grown on the back side;

[0102] (5) After step (4), intrinsic amorphous silicon is deposited on the back side using low-pressure chemical vapor deposition at a temperature of 600°C. Then, phosphorus diffusion is performed on the intrinsic amorphous silicon, and it is activated at a high temperature of 890°C to form a doped polycrystalline silicon layer 3 with a thickness of 100nm.

[0103] (6) After step (5), perform HF cleaning to remove PSG from the front and back sides;

[0104] (7) After step (6), a front passivation layer 8 with a thickness of 50 nm is prepared by plasma chemical vapor deposition.

[0105] (8) After step (7), a dense conductive layer 4 is prepared by spraying. The silicon wafer is placed on an 80°C panel, and TiO2 nanoparticle aqueous solution is sprayed onto the surface of the polycrystalline silicon layer 3 using a spray gun. The spraying is repeated 6-7 times. Then, it is dried in a 120°C furnace tube for 10 minutes to form a dense conductive layer 4 with a thickness of 20nm.

[0106] (9) After step (8), a mesoporous conductive layer 5 is prepared by spraying. The silicon wafer is placed on an 80°C panel, and an isopropanol solution containing TiO2 slurry (the mass ratio of TiO2 to isopropanol is 1:24) is sprayed onto the surface of the dense conductive layer 4. The spraying is repeated 7-8 times. Then, it is placed on a 120°C panel and dried for 12 minutes. After that, it is placed at a high temperature of 500°C for 30 minutes to form a mesoporous conductive layer 5 with a thickness of 60nm.

[0107] (10) After step (9), the front electrode 9 is printed using electrode silver aluminum paste, and the back electrode 6 is printed using silver paste.

[0108] Example 3

[0109] This embodiment provides a solar cell based on Embodiment 1, the difference being that the dense conductive layer 4 is a B2O3 layer, the mesoporous conductive layers 5 are all TiO2 layers, the thickness of the dense conductive layer 4 is 10 nm, the thickness of the mesoporous conductive layer 5 is 20 nm, the mesoporous conductive layer 5 has a mesopore diameter of 4 μm, the particle diameter in the electrode slurry is 3 μm, the thickness of the tunneling layer 2 is 1 nm, the thickness of the polycrystalline silicon layer 3 is 90 nm, and the thickness of the front passivation layer 8 is 40 nm. The remaining structure is completely identical to that of Embodiment 1.

[0110] Example 4

[0111] This embodiment provides a solar cell based on Embodiment 1, the difference being that the dense conductive layer 4 is an Er₂O₃ layer, the mesoporous conductive layer 5 is a BaTiO₃ layer, the thickness of the dense conductive layer 4 is 50 nm, the thickness of the mesoporous conductive layer 5 is 2 μm, the mesoporous diameter of the mesoporous conductive layer 5 is 2 μm, the particle diameter in the electrode slurry is 1 μm, the thickness of the tunneling layer 2 is 2 nm, the thickness of the polycrystalline silicon layer 3 is 110 nm, and the thickness of the front passivation layer 8 is 60 nm. The remaining structure is identical to that of Embodiment 1.

[0112] Example 5

[0113] This embodiment provides a solar cell. Compared with Embodiment 1, the difference is that the thickness of the dense conductive layer 4 is 5nm, while the rest of the structure and parameters are exactly the same as those in Embodiment 1.

[0114] Example 6

[0115] This embodiment provides a solar cell. Compared with Embodiment 1, the difference is that the thickness of the dense conductive layer 4 is 110 nm, while the rest of the structure and parameters are exactly the same as those in Embodiment 1.

[0116] Example 7

[0117] This embodiment provides a solar cell. Compared with Embodiment 1, the difference is that the thickness of the mesoporous conductive layer 5 is 0.008 μm, while the rest of the structure and parameters are exactly the same as those in Embodiment 1.

[0118] Example 8

[0119] This embodiment provides a solar cell. Compared with Embodiment 1, the difference is that the thickness of the mesoporous conductive layer 5 is 4μm, while the rest of the structure and parameters are exactly the same as those in Embodiment 1.

[0120] Example 9

[0121] This embodiment provides a solar cell, such as Figure 2 As shown, compared with Example 1, the difference is that the mesoporous conductive layer 5 has a gate line structure, while the rest of the structure and parameters are exactly the same as in Example 1.

[0122] Comparative Example 1

[0123] This comparative example provides a solar cell that differs from Example 1 in that the dense conductive layer 4 is replaced with a mesoporous conductive layer 5, while the rest of the structure and parameters are exactly the same as in Example 1.

[0124] Comparative Example 2

[0125] This comparative example provides a solar cell that differs from Example 1 in that the mesoporous conductive layer 5 is replaced with a dense conductive layer 4, while the rest of the structure and parameters are exactly the same as in Example 1.

[0126] The solar cells prepared in the above embodiments and comparative examples were subjected to electrical performance tests and electrode adhesion tests. The electrical performance tests included placing the solar cells under a simulated AM1.5 light source with an energy density of 100 mW / cm². 2 The light source was calibrated using a standard crystalline silicon cell, and the JV curve of the solar cell was tested using an FTC650. Direct sunlight shone on the solar cell surface, and the effective area of ​​the cell was 0.5 cm². 2 .

[0127] The test results are shown in Table 1.

[0128] Table 1

[0129] Photoelectric conversion efficiency / % Example 1 22.3 Example 2 22.6 Example 3 22.0 Example 4 22.4 Example 5 21.6 Example 6 22.7 Example 7 21.6 Example 8 21.2 Example 9 22.5 Comparative Example 1 19.2 Comparative Example 2 20.4

[0130] It can be seen from the above table:

[0131] (1) Compared with Examples 5 and 6, Example 1 has a better photoelectric conversion efficiency than Examples 5 and 6. It can be seen that the present invention ensures conductivity by controlling the thickness of the dense conductive layer 4 to be 10-100nm. If the thickness is less than 10nm, the dense conductive layer 4 will be thin and unevenly covered, resulting in poor electrical transmission performance. If the thickness is greater than 100nm, although the conductivity is improved, the thicker the thickness, the more serious the light absorption problem will be.

[0132] (2) Compared with Examples 7 and 8, Example 1 has a better photoelectric conversion efficiency than Examples 7 and 8. It can be seen that the present invention avoids excessive battery series resistance and ensures the tensile strength of electrode solder strip by controlling the thickness of the mesoporous conductive layer 5 to be 0.02-2μm. If the thickness is less than 0.02μm, the thickness of the mesoporous conductive layer 5 is too thin, which is not conducive to the penetration of electrode paste and affects the tensile strength of solder strip; if the thickness is greater than 2μm, it will lead to an excessively long electron transport path and an increase in battery series resistance.

[0133] (3) Compared with Example 9, Example 9 has a better photoelectric conversion efficiency than Example 1. It can be seen that the mesoporous conductive layer 5 of the gate structure in this invention can reduce the loss of incident light and utilize the longitudinal transmission function of the transparent conductive layer to ensure the effective transmission of carriers. At the same time, it can also avoid defect recombination caused by direct contact between the metal electrode and polycrystalline silicon.

[0134] (4) Compared with Comparative Examples 1 and 2, the photoelectric conversion efficiency of Example 1 is better than that of Comparative Examples 1 and 2. This shows that by using a dense conductive layer 4 and a mesoporous conductive layer 5 stacked together to replace the passivation layer in the solar cell, the present invention effectively prevents the paste from corroding the bottom polycrystalline silicon layer 3 while simultaneously allowing the dense conductive layer 4 to form good contact with the polycrystalline silicon layer 3, facilitating electron transport. The mesoporous conductive layer 5 allows the printed electrode paste to penetrate, resulting in a larger and stronger contact between the metal electrode and the mesoporous conductive layer 5. Furthermore, since the passivation effect of the polycrystalline silicon layer 3 is achieved by high temperature driving H... + It enters into the silicon, but at the same time some H... + It will escape outwards, and the dense conductive layer 4 can effectively suppress most of the H. + It diffuses outward, improving the passivation of polycrystalline silicon layer 3.

[0135] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A solar cell, characterized in that, The back passivation layer of the solar cell is a transparent conductive layer, which is composed of a dense conductive layer and a mesoporous conductive layer stacked sequentially, and the mesoporous conductive layer is in contact with the electrode. The mesoporous conductive layer has a porous structure or its surface is covered with through holes; the dense conductive layer does not have a channel structure. The back side of the solar cell substrate is provided with a tunneling layer, a polycrystalline silicon layer, a dense conductive layer, a mesoporous conductive layer and a back electrode stacked in sequence.

2. The solar cell according to claim 1, characterized in that, The mesoporous conductive layer has a grid structure or a completely covered structure.

3. The solar cell according to claim 1, characterized in that, The mesoporous conductive layer has a grid line structure, and the grid line structure of the mesoporous conductive layer is the same as that of the adjacent electrode, and the width of the grid line structure of the mesoporous conductive layer is greater than the width of the electrode grid line structure.

4. The solar cell according to claim 1, characterized in that, The solar cell has an emitter layer, a front passivation layer, and a front electrode stacked sequentially on the front side of its substrate.

5. The solar cell according to claim 1, characterized in that, The dense conductive layer includes one or a combination of at least two of the following: TiO2 layer, ZrO2 layer, Nb2O5 layer, boron-doped ZnO layer, aluminum-doped ZnO layer, IZO layer, IWO layer, ITO layer, FTO layer, SnO2 layer, Y2O3 layer, MgO layer, B2O3 layer, GeO2 layer, La2O3 layer, CeO2 layer, Nd2O3 layer, Gd2O3 layer, Dy2O3 layer, Er2O3 layer, Yb2O3 layer, SrTiO3 layer, BaTiO3 layer, PbTiO3 layer, PbZrO3 layer, or NdAlO3 layer.

6. The solar cell according to claim 1, characterized in that, The thickness of the dense conductive layer is 10–100 nm.

7. The solar cell according to claim 1, characterized in that, The mesoporous conductive layer includes one or a combination of at least two of the following: TiO2 layer, ZrO2 layer, Nb2O5 layer, boron-doped ZnO layer, aluminum-doped ZnO layer, IZO layer, IWO layer, ITO layer, FTO layer, SnO2 layer, Y2O3 layer, MgO layer, B2O3 layer, GeO2 layer, La2O3 layer, CeO2 layer, Nd2O3 layer, Gd2O3 layer, Dy2O3 layer, Er2O3 layer, Yb2O3 layer, SrTiO3 layer, BaTiO3 layer, PbTiO3 layer, PbZrO3 layer, or NdAlO3 layer.

8. The solar cell according to claim 1, characterized in that, The thickness of the mesoporous conductive layer is 0.02–2 μm.

9. The solar cell according to claim 1, characterized in that, The diameter of the mesoporous conductive layer is larger than the diameter of the particles in the adjacent electrode.

10. The solar cell according to claim 1, characterized in that, The mesoporous conductive layer has a mesoporous diameter of 0.01–2 μm.

11. A method for preparing a solar cell according to any one of claims 1-10, characterized in that, The preparation method includes: sequentially preparing a dense conductive layer and a mesoporous conductive layer, and then printing electrode paste on the surface of the mesoporous conductive layer to form an electrode.

12. The preparation method according to claim 11, characterized in that, The dense conductive layer is prepared by one or a combination of at least two of the following methods: atomic force deposition, vapor deposition, spraying, hydrothermal method, sol-gel method, spin coating, or physical sputtering.

13. The preparation method according to claim 12, characterized in that, The dense conductive layer is prepared by spraying, which specifically includes: dispersing the material of the dense conductive layer in a dispersant and spraying it at least twice in a cycle to form a dense conductive layer.

14. The preparation method according to claim 11, characterized in that, The mesoporous conductive layer is prepared by one or a combination of at least two of the following methods: spraying, hydrothermal, sol-gel, or spin coating.

15. The preparation method according to claim 14, characterized in that, The mesoporous conductive layer is prepared by spraying, which specifically includes: dispersing the mesoporous conductive layer material in a dispersant, spraying it at least twice in cycles, drying and sintering to form the mesoporous conductive layer.

16. The preparation method according to claim 15, characterized in that, The sintering temperature is 450–550°C.

17. The preparation method according to claim 15, characterized in that, The sintering time is 25 to 35 minutes.

18. The preparation method according to claim 11, characterized in that, The preparation method specifically includes the following steps: An emitter layer, a front passivation layer, and a front electrode are formed on the front side of the substrate, and a tunneling layer, a polycrystalline silicon layer, a dense conductive layer, a mesoporous conductive layer, and a back electrode are formed on the back side of the substrate.

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