CN118248783A - Back contact solar cell and preparation method thereof - Google Patents

Abstract

The application provides a back contact solar cell and a preparation method thereof, wherein the preparation method of the back contact solar cell comprises the following steps: sequentially depositing an intrinsic polycrystalline silicon layer and a mask layer on the back surface of the substrate; forming an isolation structure by using the mask layer; respectively carrying out doped ion diffusion on two sides of the isolation structure to form a P region and an N region on the intrinsic polycrystalline silicon layer, wherein the intrinsic polycrystalline silicon layer comprises the P region, the N region and an isolation region which is positioned between the P region and the N region and is covered by the isolation structure; and removing the isolation structure. The application can improve the efficiency of the back contact solar cell.

Description

Back contact solar cell and method for preparing the same

Technical Field

The present application relates to the technical field of solar cells, and in particular to a back-contact solar cell and a method for preparing the same.

Background technique

Back-contact solar cells are a high-efficiency solar cell technology. This design is different from traditional solar cells. In traditional designs, electronic contacts are usually distributed on the front and back of solar cells. The design feature of back-contact solar cells is that the PN junction and metal contact are both on the back of the cell, aiming to reduce the shadow effect on the front of the cell and improve light capture and power conversion efficiency.

In a battery structure, the P region and N region of the back-contact solar cell are arranged alternately in a fork shape. In order to solve the contact leakage problem between the P region and the N region, the P region and the N region need to be isolated. If the PN junction is laser etched and grooved for isolation after the P and N polysilicon passivation layers are formed, the laser damage and cleaning etching caused by the laser will inevitably damage the polysilicon layer in the non-isolated area, resulting in a decrease in battery efficiency and poor stability of the preparation process.

Therefore, how to solve the problem that the laser groove isolation solution causes damage to the polysilicon layer in the non-isolation area, thereby causing a decrease in battery efficiency, has become a technical problem that urgently needs to be solved in this field.

It should be noted that the above content is not necessarily prior art, nor is it intended to limit the scope of patent protection of this application.

Summary of the invention

The embodiments of the present application provide a back-contact solar cell and a method for preparing the same to solve or alleviate one or more of the technical problems mentioned above.

As one aspect of an embodiment of the present application, an embodiment of the present application provides a method for preparing a back-contact solar cell, comprising: depositing an intrinsic polysilicon layer and a mask layer on the back side of a substrate in sequence; forming an isolation structure using the mask layer; performing doping ion diffusion on both sides of the isolation structure to form a P region and an N region in the intrinsic polysilicon layer, wherein the intrinsic polysilicon layer includes the P region, the N region, and an isolation region located between the P region and the N region and covered by the isolation structure; and removing the isolation structure.

Furthermore, the step of forming an isolation structure using the mask layer includes: printing the pattern of the isolation area on the mask layer; removing the unprinted area of the mask layer, wherein the retained portion of the mask layer forms the isolation structure; and removing the printed material on the surface of the mask layer.

Furthermore, the mask layer is a silicon oxide mask layer, and the printing material is wax that is resistant to acid but not resistant to alkali etching. The step of removing the unprinted area of the mask layer includes: using hydrofluoric acid to remove the area of the silicon oxide mask layer not covered by the wax; the step of removing the printing material on the surface of the mask layer includes: using alkali washing to remove the wax on the surface of the mask layer.

Furthermore, the steps of respectively performing doping ion diffusion on both sides of the isolation structure to form a P region and an N region in the intrinsic polysilicon layer include: depositing a borosilicate glass layer on the mask layer; printing the pattern of the P region on the borosilicate glass layer and covering the isolation structure; removing the unprinted area of the borosilicate glass layer and retaining the portion of the borosilicate glass layer located at the P region pattern and the isolation structure; removing the printed material on the surface of the borosilicate glass layer; and performing high-temperature diffusion in the intrinsic polysilicon layer to form the P region, and then performing high-temperature phosphorus diffusion to form the N region.

Furthermore, the printing material is a wax that is resistant to acid but not resistant to alkali etching, and the step of removing the unprinted area of the borosilicate glass layer includes: using hydrofluoric acid to remove the area of the borosilicate glass layer not covered by the printing material; the step of removing the printing material on the surface of the borosilicate glass layer includes: using alkali washing to remove the wax on the surface of the borosilicate glass layer.

Furthermore, the substrate is a silicon wafer, and the method also includes: before the step of depositing an intrinsic polysilicon layer on the back side of the substrate, performing texturing and cleaning on the silicon wafer to form a pyramid light-trapping structure on the front and back sides of the silicon wafer respectively; performing thermal oxygen treatment to generate a silicon oxide layer on the front and back sides of the silicon wafer respectively; removing the silicon oxide layer on the back side of the silicon wafer; using alkaline washing and polishing to polish the texturing surface on the back side of the silicon wafer into a flat polished surface; and depositing a tunneling silicon oxide layer on the flat polished surface, wherein the intrinsic polysilicon layer is deposited on the tunneling silicon oxide layer.

Furthermore, the method also includes: after the step of forming the P region and the N region on the intrinsic polysilicon layer and before the step of removing the isolation structure, forming a phosphosilicate glass layer on the borosilicate glass layer and the N region of the intrinsic polysilicon layer; removing the phosphosilicate glass layer and the borosilicate glass layer on the back side of the substrate; after the step of removing the isolation structure, forming an aluminum oxide layer on the back side of the substrate; preparing an anti-reflection film on the front side and a passivation film on the back side of the substrate; and printing the P region metal electrode and the N region metal electrode respectively and performing high temperature sintering.

Further, the P region, the isolation region and the N region are arranged in sequence in a first direction, and a width of the isolation structure in the first direction is 50 micrometers to 150 micrometers.

Furthermore, the second direction is a direction perpendicular to the substrate, and the thickness of the isolation structure in the second direction is 270 nm.

As another aspect of an embodiment of the present application, an embodiment of the present application provides a back-contact solar cell, which is prepared by any one of the above-mentioned methods for preparing a back-contact solar cell.

As another aspect of the embodiment of the present application, the embodiment of the present application provides a back-contact solar cell, which back-contact solar cell includes: a substrate, the front side of the substrate has a pyramid light-trapping structure, and the back side of the substrate is a flat polished surface; an anti-reflection film, located on one side of the pyramid light-trapping structure; a tunneling silicon oxide layer, located on one side of the flat polished surface; a polycrystalline silicon layer, located on a side of the tunneling silicon oxide layer away from the substrate, including a P region, an intrinsic polycrystalline silicon isolation region and an N region alternately arranged in sequence; an aluminum oxide passivation layer, located on a side of the polycrystalline silicon layer away from the tunneling silicon oxide layer; a silicon nitride passivation film, located on a side of the aluminum oxide passivation layer away from the polycrystalline silicon layer; a metal electrode, passing through the silicon nitride passivation film and the aluminum oxide passivation layer, including a P region electrode and an N region electrode, wherein the P region electrode is fixed to the P region, and the N region electrode is fixed to the N region.

In the preparation method of the back-contact solar cell provided in the present application, after depositing an intrinsic polysilicon layer on the back of the substrate to form a PN region, a mask layer is deposited to form an isolation structure for preventing dopants from mutually diffusing in the subsequent doping process, so that when doping ions are diffused on both sides of the isolation structure to form a P region and an N region, the isolation structure blocks the high-temperature diffusion of impurity ions, thereby achieving isolation between the P region and the N region. Through the present application, before high-temperature diffusion forms the P region and the N region, a mask layer is first prepared, and an isolation structure is formed at the junction of the P region and the N region to block the diffusion of impurity ions at the junction, and there is no need to use laser isolation, thereby avoiding the destruction of the polysilicon layer and laser damage, achieving effective isolation of the P and N regions, avoiding the risk of leakage, improving process stability, and improving battery efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the multiple drawings represent the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings only depict some embodiments disclosed in the present application and should not be regarded as limiting the scope of the present application.

1 to 13 are schematic diagrams of various steps in a method for preparing a back-contact solar cell according to an embodiment of the present application;

FIG. 14 is a schematic diagram of the structure of a back-contact solar cell provided in an embodiment of the present application.

Explanation of the reference numerals: 10-substrate; 11-front pyramid light-trapping structure; 12-back pyramid light-trapping structure; 13-flat polished surface; 31-front silicon oxide layer; 32-back silicon oxide layer; 40-tunneling silicon oxide layer; 50-intrinsic polysilicon layer; 51-P region; 52-N region; 53-isolation region; 60-mask layer; 61-isolation structure; 70-isolation region pattern; 80-borosilicate glass layer; 90-P region pattern; 100-phosphosilicate glass layer; 110-aluminum oxide layer; 121-front anti-reflection film; 122-back passivation film; 131-P region metal electrode; 132-N region metal electrode.

Detailed ways

In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

The inventors have conducted the following research on the preparation of back-contact solar cells in the related art:

In a method for preparing a back-contact solar cell, an intrinsic amorphous silicon passivation layer is first deposited on the backlight side of the substrate, and then N-type amorphous silicon and P-type amorphous silicon are respectively deposited on the intrinsic amorphous silicon passivation layer through a mask layer, and then an isolation groove is obtained by laser scribing at the junction of the N-type amorphous silicon and the P-type amorphous silicon. The grooved N-type amorphous silicon and P-type amorphous silicon are respectively formed into an N region and a P region to achieve isolation of the N region and the P region. With respect to this manufacturing method, the inventor has found that the isolation of the P region and the N region is achieved by laser ablation of part of the mask layer and the polysilicon layer, and then alkaline solution etching is used to remove the laser damage and the residual polysilicon layer, which damages the polysilicon layer of the emitter in the non-isolated area, and the laser damage is also difficult to repair.

In another method for preparing a back-contact solar cell, an intrinsic polysilicon layer is first deposited on the back of the substrate, and then a boron-containing doping slurry is used to coat it according to a predetermined pattern and diffuse it at high temperature to form a P region. During the thermal diffusion process, sufficient oxygen is introduced to form a thicker oxide layer. Then, a local film is opened on the oxide layer to reserve an area to be N-type doped. At the same time, a certain area width is left between the area to be N-type doped and the area that has been doped with boron, and the silicon oxide film is not removed. After the film opening area is etched and cleaned, thermal diffusion is performed to form a back N region, so that the silicon oxide film that has not been removed blocks the diffusion during the phosphorus diffusion process, and an isolation region between the P region and the N region is realized. With respect to this manufacturing method, the inventor has found that the silicon oxide film that has not been removed forms the isolation between the P region and the N region, but when the P region is formed by high-temperature diffusion, there will be excessive diffusion of boron impurity atoms, which ultimately leads to the simultaneous presence of boron and phosphorus impurity atoms at the PN junction. When boron and phosphorus exist in the same area at the same time, the doping effects may offset each other, resulting in charge neutralization, weakening the P-type or N-type conductivity of the semiconductor, affecting the overall performance of the PN junction, and may affect the chemical and physical stability of the semiconductor material.

Furthermore, in order to solve the problem of damage to the polysilicon layer in the non-isolated area caused by the laser groove isolation scheme, which in turn leads to a decrease in battery efficiency, while reducing the probability of the simultaneous existence of boron and phosphorus impurity atoms at the junction, the present application proposes a method for preparing a back-contact solar cell and a back-contact solar cell prepared by the preparation method. The preparation process does not use laser grooving to isolate the PN region, thereby avoiding laser damage and damage to the polysilicon layer. At the same time, the P region and N region are isolated before the polysilicon layer is formed to prevent the diffusion of impurity atoms at the junction.

The specific embodiments of the present application and the corresponding technical effects will be described in detail below.

Hereinafter, exemplary embodiments according to the present application will be described in more detail with reference to the accompanying drawings. It should be noted that these exemplary embodiments can be implemented in many different forms and should not be construed as being limited to the embodiments described herein.

As shown in Figures 1 to 14, a method for preparing a back-contact solar cell may include the following steps: depositing an intrinsic polysilicon layer 50 and a mask layer 60 on the back side of a substrate 10 in sequence; forming an isolation structure 61 using the mask layer 60; performing doping ion diffusion on both sides of the isolation structure 61 to form a P region 51 and an N region 52 in the intrinsic polysilicon layer 50, wherein the intrinsic polysilicon layer 50 includes a P region 51, an N region 52 and an isolation region 53 located between the P region 51 and the N region 52 and covered by the isolation structure 61; and removing the isolation structure 61.

Specifically, the back contact solar cell is designed so that all electronic contacts are located on the back of the cell, and such a design is intended to maximize the light capture area on the front side and reduce the shadow effect, thereby improving the efficiency of the cell. In this embodiment, the substrate 10 of the back contact solar cell can be made of single crystal silicon, polycrystalline silicon, N-type silicon, thin film silicon or heterogeneous materials (such as combining silicon with semiconductor material GaAs to take advantage of the advantages of different materials), etc.

The intrinsic (undoped) polysilicon layer 50 is deposited on the back side of the substrate 10 and initially acts as a non-doped passivation layer to increase the charge carrier lifetime on the silicon surface and reduce the recombination of charge carriers; at the same time, it provides a basis for subsequent doping of the P and N regions.

It should be noted that in the preparation method of the back-contact solar cell of the present application, one layer is formed on another layer, which only limits the relative position relationship of the two layers, and is not absolutely limited to the two layers being in contact with each other. In the actual preparation process, other layers may be provided between the two layers as needed. For example, the above-mentioned "intrinsic polysilicon layer 50 is deposited on the back of the substrate 10" does not limit the intrinsic polysilicon layer 50 to being in contact with the back of the substrate 10, but only limits the relative position relationship between the intrinsic polysilicon layer 50 and the substrate 10. Other material layers may be provided between the intrinsic polysilicon layer 50 and the substrate 10 as needed. In addition, the thickness dimensions of each layer in the figures of the present application do not indicate the actual thickness.

The mask layer 60 can be made of materials such as silicon oxide or silicon nitride, and is disposed on a side of the intrinsic polysilicon layer 50 away from the substrate 10, and defines the subsequent doping regions of the P region and the N region by protecting certain regions from the influence of dopants while allowing other regions to be doped. Specifically, the mask layer 60 is patterned to form a desired pattern on the mask layer, and an etching technique (such as dry etching or wet etching) can be used to remove the exposed portion of the mask layer 60, leaving the portion of the mask pattern, that is, the isolation structure 61, and the positions of the P region and the N region are defined by the isolation structure 61 to prevent the dopants of the P region and the N region from diffusing with each other during the subsequent doping process.

The mask layer 60 is used as a template to perform doping at its openings. Optionally, doping can be performed by thermal diffusion or ion implantation. A P-type dopant (such as boron) is introduced on one side of the isolation structure 61, and an N-type dopant (such as phosphorus) is introduced on the other side. Further heat treatment (annealing) can be performed to activate the dopant so that it diffuses deeper into the intrinsic polysilicon layer 50, forming a P region 51 and an N region 52 in the intrinsic polysilicon layer 50. The portion between the P region 51 and the N region 52 covered by the isolation structure 61 forms an undoped isolation region 53.

After the doping process is completed, the isolation structure 61 is removed using a chemical solution or dry etching technology, leaving only the P region 51 and the N region 52 formed in the intrinsic polysilicon layer and the undoped isolation region 53 therebetween. After removing the isolation structure 61, a cleaning step may be provided to remove any remaining impurities or etching products, ensure the cleanliness of the battery surface and the optimization of the battery performance, and perform subsequent preparation of related layers and electrodes, which will not be described in detail in this embodiment.

In the preparation method of the back-contact solar cell provided in this embodiment, after depositing an intrinsic polysilicon layer on the back of the substrate to form a PN region, a mask layer is deposited to form an isolation structure for preventing dopants from mutually diffusing in the subsequent doping process, so that when doping ions are diffused on both sides of the isolation structure to form a P region and an N region, the isolation structure blocks the high-temperature diffusion of impurity ions, thereby isolating the P region and the N region. Using the preparation method of the back-contact solar cell provided in this embodiment, before high-temperature diffusion to form the P region and the N region, a mask layer is first prepared, and an isolation structure is formed at the junction of the P region and the N region to block the diffusion of impurity ions at the junction, and there is no need to use laser isolation, thereby avoiding the destruction of the polysilicon layer and laser damage, achieving effective isolation of the P and N regions, avoiding the risk of leakage, improving process stability, and improving battery efficiency.

Optionally, in one embodiment, the step of forming the isolation structure 61 using the mask layer 60 includes: printing a pattern 70 of the isolation area 53 on the mask layer 60; removing an unprinted area of the mask layer 60, wherein the retained portion of the mask layer 60 forms the isolation structure 61; and removing the printed material on the surface of the mask layer 60.

Specifically, when the isolation structure 61 is formed using the mask layer 60, the pattern of the isolation area 53 is first printed on the mask layer 60. For example, a photosensitive material (photoresist) can be coated on the mask layer 60, and then ultraviolet light and a photomask are used to irradiate the photoresist. The photomask has a negative image of the isolation area pattern, allowing the ultraviolet light to irradiate specific areas of the photoresist to cause photochemical changes. After the photoresist is developed, the photoresist area that is not irradiated by ultraviolet light (or the irradiated area, depending on whether the type of photoresist used is positive or negative) will be removed to expose the mask layer 60 below. Then, etching technology (such as wet etching or dry etching) can be used to remove these exposed mask areas, leaving the mask portion corresponding to the pattern of the isolation area 61 to obtain the isolation structure 61. After the desired isolation structure 61 is formed, the removal of the surface printed material can be completed by solvent cleaning or oxygen plasma ashing.

The method for preparing a back-contact solar cell provided in this embodiment utilizes the pattern of the isolation area printed on the mask layer to ensure the position of the isolation structure, thereby optimizing the layout of the P region and the N region in the back-contact solar cell, reducing the recombination loss of carriers, and improving the efficiency and performance of the battery. The isolation structure formed on the mask layer can accurately define the future P region and the N region, preventing the diffusion of dopants in unnecessary areas, thereby maintaining the integrity and performance of the battery structure. Finally, the printed material on the surface of the mask layer, that is, the printed material on the surface of the isolation structure, is removed, which can prevent possible interference in subsequent process steps and ensure that the dopant can diffuse evenly.

Further optionally, in one embodiment, the mask layer 60 is a silicon oxide mask layer 60, and the printing material is wax that is resistant to acid but not resistant to alkali etching, and the step of removing the unprinted area of the mask layer 60 includes: using hydrofluoric acid to remove the area of the silicon oxide mask layer 60 that is not covered by the wax; the step of removing the printing material on the surface of the mask layer 60 includes: using alkali washing to remove the wax on the surface of the mask layer 60.

Specifically, in this embodiment, the mask layer 60 is defined as being made of silicon oxide, and the printing material is a wax that is acid-resistant but not alkali-resistant. On this basis, when removing the unprinted area of the mask layer 60, hydrofluoric acid is used to remove the area of the silicon oxide mask layer 60 that is not covered by the wax. Etching by hydrofluoric acid can selectively remove the silicon oxide material without damaging the intrinsic polysilicon layer 50 itself. Through this step, the area of the silicon oxide mask layer 60 that is not covered by the wax will be etched away by the HF solution, while the area covered by the wax protects the area of the silicon oxide mask layer 60 below from being etched, thereby forming an isolation structure 61.

When removing the printed material on the surface of the mask layer, based on the characteristics of the printed material being acid-resistant but not alkali-resistant, an alkaline solution (such as a hot alkaline solution) is used to remove the wax, thereby dissolving the wax without affecting the silicon oxide mask layer 60 and the intrinsic polysilicon layer 50 underneath.

By adopting the method for preparing a back-contact solar cell provided in this embodiment, by using silicon oxide as a mask layer combined with the selective etching characteristics of HF, the silicon oxide mask layer can be accurately removed to form a fine isolation structure to accurately define the P region and the N region in the back-contact solar cell. At the same time, since HF etching is a relatively mild process, the potential damage to the intrinsic polysilicon layer 50 is reduced; by using acid-resistant but alkali-resistant wax as a printing material combined with alkaline washing and removal technology, the wax of the silicon oxide mask layer can be removed without damaging the material of the isolation structure, providing a clean, impurity-free surface for the subsequent doping process, ensuring the consistency and reliability of the battery performance.

Optionally, in one embodiment, the steps of performing doping ion diffusion on both sides of the isolation structure 61 to form a P region 51 and an N region 52 in the intrinsic polysilicon layer 50 include: depositing a borosilicate glass layer 80 on the mask layer 60; printing a pattern 90 of the P region 51 on the borosilicate glass layer 80 and covering the isolation structure 61; removing the area of the borosilicate glass layer 80 not covered by the printed material, and retaining the portion of the borosilicate glass layer 80 located at the P region 51 pattern and the isolation structure 61; removing the printed material on the surface of the borosilicate glass layer 80; and performing high-temperature diffusion of the intrinsic polysilicon layer 50 to form the P region 51, and then performing high-temperature phosphorus diffusion to form the N region 52.

Specifically, atmospheric pressure chemical vapor deposition (APCVD) technology can be used to deposit a borosilicate glass layer 80 on the mask layer 60. Borosilicate glass (BSG) is a silicon-based glass containing boron, in which the boron element can be used as a source of P-type dopants in the subsequent high-temperature process. Then, a printing material is used to print the pattern of the P region on the BSG layer 80. This pattern not only defines the position of the P region, but also covers the isolation structure 61 below to protect it from the subsequent etching process. Then, an appropriate etchant is used to remove the area of the BSG layer 80 that is not covered by the printing material, and only the part of the BSG layer 80 above the P region pattern and the isolation structure 61 is retained. After the etching of the BSG layer 80 is completed, the printing material on the surface of the BSG layer 80 is removed to prepare for high-temperature diffusion doping of the P region. Then, high temperature diffusion is performed in the intrinsic polysilicon layer 50 to form a P region, and then high temperature phosphorus diffusion is performed to form an N region. Specifically, high temperature treatment can be performed first to promote the boron in the BSG layer 80 to diffuse downward into the intrinsic polysilicon layer 50 to form a P region, and then phosphorus diffusion is performed in the area not covered by the BSG layer 80 to form an N region.

In the preparation method of the back-contact solar cell provided in this embodiment, the use of the BSG layer provides a convenient doping method for the formation of the P region. Under high temperature, the boron in the BSG layer will diffuse into the intrinsic polysilicon layer below to form a P region. This method allows fine control of the doping depth and concentration, which is beneficial to improving the performance and efficiency of the battery; the P region pattern is printed on the BSG layer using printing materials to ensure the precise position and shape of the P region, while protecting the isolation structure to prevent it from being destroyed during subsequent doping and etching processes; by removing the excess BSG layer, the selectivity of the doping process is ensured, and only the predetermined area will be doped into P type, which can reduce unnecessary doping diffusion; the printing material of the remaining BSG layer is removed to ensure that in the subsequent high-temperature treatment process, the boron in the BSG layer can be evenly diffused into the intrinsic polysilicon layer below to form a P region. Finally, the two-step doping process forms a P region and an N region on both sides of the isolation region, respectively.

Optionally, in one embodiment, the printing material is a wax that is resistant to acid but not resistant to alkali etching, and the step of removing the area of the borosilicate glass layer 80 not covered by the printing material includes: using hydrofluoric acid to remove the area of the borosilicate glass layer 80 not covered by the printing material; the step of removing the printing material on the surface of the borosilicate glass layer 80 includes: using alkali washing to remove the wax on the surface of the borosilicate glass layer 80.

Specifically, in this embodiment, the printing material is defined as a wax that is acid-resistant but not alkali-resistant. On this basis, when removing the unprinted area of the borosilicate glass layer 80, hydrofluoric acid (HF) is used to remove the area of the borosilicate glass layer 80 that is not covered by the wax. Etching by hydrofluoric acid can selectively remove the borosilicate glass material without damaging the intrinsic polysilicon layer 50 itself. Through this step, the area of the borosilicate glass layer 80 that is not covered by the wax will be etched away by the HF solution, while the area covered by the wax protects the area of the borosilicate glass layer 80 below from being etched, providing conditions for forming the P region and protecting the isolation structure 61.

When removing the printed material on the surface of the borosilicate glass layer 80, based on the characteristics of the printed material being acid-resistant but not alkali-resistant, an alkaline solution (such as a hot alkaline solution) is used to remove the wax, thereby dissolving the wax without affecting the underlying borosilicate glass layer 80 and the intrinsic polysilicon layer 50.

By adopting the method for preparing a back-contact solar cell provided in this embodiment, the borosilicate glass layer can be accurately removed by utilizing the selective etching characteristics of HF, so as to prepare for the fine P region and N region. At the same time, since HF etching is a relatively mild process, the potential damage to the intrinsic polysilicon layer 50 is reduced; by using acid-resistant but alkali-resistant wax as a printing material combined with an alkali washing removal technology, the wax of the borosilicate glass layer can be removed without damaging the borosilicate material prepared for the P region.

Optionally, in one embodiment, the method further includes: the substrate is a silicon wafer, and before the intrinsic polysilicon layer 50 is deposited on the back side of the substrate 10, the silicon wafer is subjected to texturing and cleaning to form pyramid light trapping structures 11, 12 on the front and back sides of the silicon wafer respectively; thermal oxidation treatment is performed to generate silicon oxide layers 31, 32 on the front and back sides respectively; the silicon oxide layer 32 on the back side is removed; the texturing surface 12 on the back side is polished into a flat polished surface 13 by alkaline polishing; and a tunneling silicon oxide layer 40 is deposited on the flat polished surface 13, wherein the intrinsic polysilicon layer 50 is deposited on the tunneling silicon oxide layer 40.

Specifically, the substrate 10 is a silicon wafer. When preparing a back-contact solar cell, the front and back sides of the silicon wafer 10 are firstly subjected to texturing and cleaning to remove surface contaminants and possible damage layers, and then the front and back sides of the silicon wafer are wet-etched with an alkaline solution to form pyramid-shaped light-trapping structures 11 and 12. Then, thermal oxidation treatment is performed on the front and back sides of the silicon wafer 10 to generate a thin silicon oxide layer 31 and 32, respectively. Specifically, the silicon wafer 10 can be exposed to an oxygen-rich environment at high temperature to oxidize the silicon surface to form silicon dioxide to obtain a silicon oxide layer. Then, hydrofluoric acid (HF) or other appropriate etching solutions are used to remove the silicon oxide layer 12 on the back side of the silicon wafer 10 for subsequent back side processing. After removing the back side silicon oxide layer 12, the back side pyramid light-trapping structure 12 is polished into a flat polished surface 13 by alkaline washing and polishing. Finally, a thin tunneling silicon oxide layer 40 is deposited on the flat polished surface 13, and then an intrinsic polysilicon layer 50 is deposited thereon. The tunneling silicon oxide layer 40 and the intrinsic polysilicon layer 50 can both be formed by chemical vapor deposition (CVD) and other methods.

According to the preparation method of the back-contact solar cell provided in this embodiment, a pyramid-shaped light-trapping structure is set on the front side to effectively reduce the reflection of light and increase the path length of light inside the silicon, thereby improving the absorption of light and the photoelectric conversion efficiency of the battery. In addition, the texturing and cleaning also ensure the cleanliness and uniformity of the silicon wafer surface, providing a good foundation for the subsequent process steps. The front side will be removed in the subsequent steps, but at this stage, the pyramid-shaped light-trapping structure on the front side can be protected, and a silicon oxide layer is simultaneously formed on the back side and then removed, in order to realize the front silicon oxide layer using a simple process. After removing the silicon oxide layer on the back side, the smooth polished back side helps to reduce the surface recombination of electron-hole pairs and provides an ideal surface for the uniform deposition of the tunneling silicon oxide layer. At the same time, combined with the method of using an isolation structure to isolate the P region and the N region in the present application, the isolation region also retains the polished surface, thereby improving the back reflectivity. Finally, the tunneling silicon oxide layer can provide excellent surface passivation and allow charges to be effectively transferred through the quantum tunneling mechanism. The intrinsic polysilicon layer above it further improves the performance of the battery by providing excellent surface passivation and providing a basis for subsequent P-region and N-region doping.

Optionally, in one embodiment, the method further includes: after the step of forming the P region 51 and the N region 52 on the intrinsic polysilicon layer 50 and before the step of removing the isolation structure 61, forming a phosphosilicate glass layer 100 on the borosilicate glass layer 80 and the N region 52 of the intrinsic polysilicon layer 50; removing the silicon oxide layer 31 on the front side, the phosphosilicate glass layer 100 and the borosilicate glass layer 80 on the back side; after the step of removing the isolation structure 61, forming an aluminum oxide layer 110 on the back side; preparing a front anti-reflection film 121 and a back passivation film 122; and printing the P region metal electrode 131 and the N region metal electrode 132 respectively and performing high temperature sintering.

Specifically, after the intrinsic polysilicon layer 50 forms the P region and the N region, a phosphosilicate glass layer 100 (PSG) is formed thereon. Optionally, this can be achieved by introducing a phosphorus-containing gas into the chemical vapor deposition (CVD) process. The PSG layer 100 provides both passivation and N-type doping. Use a suitable etching solution (such as HF) to remove the silicon oxide layer 31 on the front side, as well as the PSG layer 100 and the BSG layer 80 on the back side, to expose the intrinsic polysilicon layer 50 underneath; after removing the isolation structure 61, a layer of aluminum oxide 110 is deposited on the intrinsic polysilicon layer 50 by atomic layer deposition (ALD) and other methods, and then a front anti-reflection film 121 is prepared to reduce light reflection, and a back passivation film 122 is prepared to further improve the back passivation effect. Finally, the metal electrodes 131 in the P region and the metal electrodes 132 in the N region are printed respectively, and then sintered at high temperature to form a good electrical contact.

In the preparation method of the back-contact solar cell provided by this embodiment, the PSG layer reduces surface defects by passivating the silicon surface and provides an additional doping source for the N region, which helps to improve the conductivity of the battery and reduce the recombination of electron-hole pairs, thereby improving the efficiency of the battery; removing the silicon oxide layer on the front, the phosphosilicate glass layer, the borosilicate glass layer and the isolation structure on the back can reduce the light loss on the front of the battery, and provide a clean surface for the subsequent anti-reflection film and passivation film formation, which helps to maximize the absorption of light and the collection efficiency of charges; the aluminum oxide layer provides an excellent surface passivation effect, which can effectively reduce the recombination of electron-hole pairs and further improve the efficiency of the battery; the anti-reflection film on the front maximizes the absorption of light, while the passivation film on the back improves the overall performance of the battery and reduces carrier recombination by reducing surface defects. The metal electrode is formed by high-temperature sintering, which ensures good contact between the electrode and the silicon wafer, minimizes the contact resistance, and further improves the performance of the battery.

Optionally, in one embodiment, the P region 51 , the isolation region 53 , and the N region 52 are arranged in sequence in the first direction a, and a width W of the isolation structure 61 in the first direction a is 50 micrometers to 150 micrometers.

By adopting the method for preparing the back-contact solar cell provided in this embodiment, the width of the isolation structure is limited to between 50 microns and 150 microns, which not only ensures that the isolation structure can effectively isolate the P region and the N region, but also avoids the isolation region being too wide to occupy the electrode region. At the same time, considering the preparation accuracy, it is possible to improve the stability and cost-effectiveness of production while ensuring the high efficiency of the battery.

Optionally, in one embodiment, the second direction b is a direction perpendicular to the substrate, and a thickness d of the isolation structure in the second direction b is 270 nm.

By adopting the method for preparing the back-contact solar cell provided in this embodiment, the thickness of the isolation structure is limited to 270 nanometers, which not only ensures that the isolation structure can effectively isolate the P region and the N region, but also facilitates the removal process and preparation accuracy.

As shown in FIGS. 1 to 14 , another method for preparing a back contact solar cell includes the following steps:

1) The silicon wafer 10 is textured and cleaned to form pyramid light trapping structures 11 and 12 on the front and back sides to reduce the reflectivity of the incident light on the front side and increase the absorption of the incident light, as shown in FIG1 .

2) Thermal oxidation generates front and back silicon oxide layers 31 and 32, as shown in FIG2 .

3) Chain HF washing is performed to remove the silicon oxide layer 32 on the back side, and alkali washing and polishing is performed to polish the velvet surface on the back side to a flat polished surface 13, as shown in FIG. 3 .

4) LPCVD sequentially deposits a tunneling silicon oxide layer 40 , an intrinsic i-poly layer 50 and a silicon oxide mask layer 60 on the back side of the silicon wafer 10 , as shown in FIG. 4 .

5) The isolation area is printed with wax on the back to form a pattern 70, as shown in FIG. 5 .

6) Chain HF is used to remove the silicon oxide mask layer 60 in the area not covered by the wax, and alkali washing is used to remove the wax in the isolation area, and the silicon oxide mask layer 60 in the isolation area is retained to form an isolation structure 61, as shown in FIG. 6 .

7) A BSG layer 80 is deposited on the back side of the battery by APCVD, as shown in FIG. 7 .

8) Use wax to print the P region pattern 90 and cover the isolation area as a mask layer, as shown in FIG. 8 .

9) HF is used to remove the BSG layer 80 outside the mask, and alkali washing is used to remove the surface mask wax, as shown in FIG. 9 .

10) High temperature diffusion forms the p-poly region 51, and then high temperature phosphorus diffusion is performed to form the n-poly region 52. The isolation 53 still has the isolation structure 61 as a mask to block the diffusion of impurity atoms. At the same time, a PSG layer 100 is formed on the back, as shown in FIG. 10.

11) HF removes all oxide layers 31, 80, 100 and isolation structure 61 on the front and back sides, and cleans the battery cell, as shown in FIG11.

12) An aluminum oxide passivation layer 110 is provided on the back side, as shown in FIG. 12 .

13) Prepare a front anti-reflection film 121 and a back passivation film 122, as shown in FIG. 13 .

14) Print the P-region metal electrode 131 and the N-region metal electrode 132 respectively, and perform high-temperature sintering.

Continuing to refer to Figure 14, a back-contact solar cell prepared by the above-mentioned back-contact solar cell preparation method includes: a substrate, the front side of the substrate has a pyramid light-trapping structure, and the back side of the substrate is a flat polished surface; an anti-reflection film, located on one side of the pyramid light-trapping structure; a tunneling silicon oxide layer, located on one side of the flat polished surface; a polycrystalline silicon layer, located on the side of the tunneling silicon oxide layer away from the substrate, including a P region, an intrinsic polycrystalline silicon isolation region and an N region arranged alternately in sequence; an aluminum oxide passivation layer, located on the side of the polycrystalline silicon layer away from the tunneling silicon oxide layer; a silicon nitride passivation film, located on the side of the aluminum oxide passivation layer away from the polycrystalline silicon layer; a metal electrode, passing through the silicon nitride passivation film and the aluminum oxide passivation layer, including a P region electrode and an N region electrode, wherein the P region electrode is fixed to the P region, and the N region electrode is fixed to the N region.

By using the back-contact solar cell and the preparation method thereof provided in this embodiment, laser grooving isolation is not used in the entire preparation process, thereby avoiding laser damage and destruction of the polysilicon layer; during the preparation process, the high-temperature diffusion of impurity atoms is blocked by the isolation structure, and the isolation of the P and N regions is achieved, thereby avoiding the risk of leakage and improving the process stability; at the same time, the back side of the substrate is polished during the preparation process, and combined with the setting of the isolation area, the final isolation area also retains the polished surface rather than the velvet groove, thereby improving the back reflectivity, and ultimately improving the photoelectric conversion efficiency of the battery, thereby improving the battery efficiency from various aspects.

It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and/or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and/or combinations thereof.

For the convenience of description, the orientation or position relationship indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, vertical, horizontal" and "top, bottom" is usually based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description. Unless otherwise stated, these directional words 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, and therefore cannot be understood as limiting the scope of protection of the present application; the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Therefore, the exemplary term "above..." can include both "above..." and "below..." orientations. The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used here are interpreted accordingly.

Unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

Unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is lower in level than the second feature.

Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values of the parts and steps set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

It should also be noted that "one embodiment", "another embodiment", "embodiment", etc. mentioned in this specification refer to the specific features, structures or characteristics described in conjunction with the embodiment included in at least one embodiment generally described in this application. The same expression appearing in multiple places in the specification does not necessarily refer to the same embodiment. Further, when a specific feature, structure or characteristic is described in conjunction with any embodiment, it is claimed that the realization of such feature, structure or characteristic in conjunction with other embodiments also falls within the scope of this application.

In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

It should also be noted that the above are only preferred embodiments of the present application, and the patent protection scope of the present application is not limited thereto. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present application.

Claims (11)

1. A method for preparing a back contact solar cell, comprising: Depositing an intrinsic polysilicon layer and a mask layer in sequence on the back side of the substrate; forming an isolation structure using the mask layer; Performing doping ion diffusion on both sides of the isolation structure to form a P region and an N region in the intrinsic polysilicon layer, wherein the intrinsic polysilicon layer includes the P region, the N region, and an isolation region located between the P region and the N region and covered by the isolation structure; and The isolation structure is removed. 2. The method for preparing a back contact solar cell according to claim 1, wherein the step of forming an isolation structure using the mask layer comprises: printing a pattern of the isolation area on the mask layer; removing the unprinted area of the mask layer, wherein the retained portion of the mask layer forms the isolation structure; and The printed material on the surface of the mask layer is removed. 3. The method for preparing a back-contact solar cell according to claim 2 is characterized in that the mask layer is a silicon oxide mask layer, the printing material is wax that is resistant to acid but not resistant to alkali etching, and the step of removing the unprinted area of the mask layer comprises: using hydrofluoric acid to remove the area of the silicon oxide mask layer not covered by the wax; the step of removing the printing material on the surface of the mask layer comprises: removing the wax on the surface of the mask layer by alkali washing. 4. The method for preparing a back-contact solar cell according to claim 1, wherein the step of respectively performing doping ion diffusion on both sides of the isolation structure to form a P region and an N region in the intrinsic polysilicon layer comprises: depositing a borosilicate glass layer on the mask layer; Printing the pattern of the P region on the borosilicate glass layer and covering the isolation structure; Removing the unprinted area of the borosilicate glass layer and retaining the portion of the borosilicate glass layer located at the P region pattern and the isolation structure; removing the printed material on the surface of the borosilicate glass layer; and The P region is formed by high temperature diffusion in the intrinsic polysilicon layer, and then high temperature phosphorus diffusion is performed to form the N region. 5. The method for preparing a back-contact solar cell according to claim 4 is characterized in that the printing material is a wax that is resistant to acid and not resistant to alkali etching, and the step of removing the unprinted area of the borosilicate glass layer comprises: using hydrofluoric acid to remove the area of the borosilicate glass layer not covered by the printing material; the step of removing the printing material on the surface of the borosilicate glass layer comprises: using alkali washing to remove the wax on the surface of the borosilicate glass layer. 6. The method for preparing a back-contact solar cell according to claim 1, wherein the substrate is a silicon wafer, and the method further comprises: Before the step of depositing an intrinsic polysilicon layer on the back side of the substrate, the silicon wafer is subjected to texturing and cleaning, and pyramid light trapping structures are formed on the front and back sides of the silicon wafer respectively; Thermal oxidation treatment generates silicon oxide layers on the front and back sides of the silicon wafer respectively; removing the silicon oxide layer on the back side of the silicon wafer; Using alkaline polishing to polish the velvet surface on the back of the silicon wafer into a flat polished surface; and A tunneling silicon oxide layer is deposited on the flat polished surface, wherein the intrinsic polysilicon layer is deposited on the tunneling silicon oxide layer. 7. The method for preparing a back contact solar cell according to claim 4, characterized in that the method further comprises: After the step of forming a P region and an N region on the intrinsic polysilicon layer and before the step of removing the isolation structure, forming a phosphosilicate glass layer on the borosilicate glass layer and the N region of the intrinsic polysilicon layer; removing the phosphosilicate glass layer and the borosilicate glass layer on the back side of the substrate; After the step of removing the isolation structure, forming an aluminum oxide layer on the back side of the substrate; Preparing a front anti-reflection film and a back passivation film on the substrate; and The P-region metal electrode and the N-region metal electrode are printed separately and sintered at high temperature. 8. The method for preparing a back-contact solar cell according to claim 1, characterized in that the P region, the isolation region and the N region are arranged sequentially in a first direction, and a width of the isolation structure in the first direction is 50 microns to 150 microns. 9 . The method for preparing a back-contact solar cell according to claim 1 , wherein the second direction is a direction perpendicular to the substrate, and the thickness of the isolation structure in the second direction is 270 nanometers. 10 . A back-contact solar cell, characterized in that the back-contact solar cell is prepared by the method for preparing a back-contact solar cell according to any one of claims 1 to 9. 11. A back contact solar cell, comprising: A substrate, wherein the front side of the substrate has a pyramid light trapping structure, and the back side of the substrate is a flat polished surface; An anti-reflection film, located on one side of the pyramid light trapping structure; A tunneling silicon oxide layer located on one side of the flat polished surface; A polysilicon layer, located on a side of the tunneling silicon oxide layer away from the substrate, comprising a P region, an intrinsic polysilicon isolation region and an N region which are alternately arranged in sequence; an aluminum oxide passivation layer, located on a side of the polysilicon layer away from the tunneling silicon oxide layer; A silicon nitride passivation film, located on a side of the aluminum oxide passivation layer away from the polysilicon layer; The metal electrode passes through the silicon nitride passivation film and the aluminum oxide passivation layer, and includes a P region electrode and an N region electrode, wherein the P region electrode is fixed to the P region, and the N region electrode is fixed to the N region.