Back contact solar cell, preparation method thereof and photovoltaic module

Abstract

The embodiment of the invention provides a back contact solar cell, a preparation method thereof and a photovoltaic module. The preparation method of the back contact solar cell comprises the following steps: providing a substrate, wherein the substrate comprises a silicon wafer, a first tunneling oxide layer and a first intrinsic amorphous silicon layer which are stacked in sequence; performing crystallization treatment on the first intrinsic amorphous silicon layer on the substrate so as to convert amorphous silicon in the first intrinsic amorphous silicon layer into polycrystalline silicon and obtain a first polycrystalline silicon layer; and carrying out boron diffusion on the first polycrystalline silicon layer to obtain a boron-doped layer. According to the method provided by the embodiment of the invention, after the first polycrystalline silicon layer is formed by performing crystallization treatment on the first intrinsic amorphous silicon layer, boron diffusion is performed on the first polycrystalline silicon layer, so that the boron-doped layer with a relatively good passivation effect can be obtained, and meanwhile, the process stability of preparing the back contact solar cell can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of solar cells, and in particular to a back-contact solar cell and a preparation method thereof, and a photovoltaic module. Background Art

[0002] Driven by the theme of cost reduction and efficiency improvement in the solar cell industry, solar cell technology has been updated and iterated. Among them, the back contact solar cell (TBC) is a tunnel oxide layer deposited between the substrate and the doping layer, and the positive and negative electrodes of the cell are distributed on the back in the form of interdigitated fingers.

[0003] At present, the preparation process of TBC battery is as follows: alkali polishing substrate, deposition of the first tunneling oxide layer and the first amorphous silicon layer on the back, boron diffusion doping to form a mask borosilicate glass (BSG layer), first grooving and cleaning, deposition of the second tunneling oxide layer and the second amorphous silicon layer on the back, phosphorus diffusion doping to form a mask phosphorus silicon glass layer (PSG layer), second grooving, cleaning and double-sided texturing, acid treatment, and deposition of Al0 x SiN is deposited on the back and front sides of the x Anti-reflection coating, screen printing, sintering and testing sorting.

[0004] Among them, the preparation process of the boron-doped silicon layer is more important, because the quality of the boron-doped silicon layer obtained is very important for the opening voltage of the battery and the contact of the metal electrode. However, the preparation of the boron-doped polysilicon layer still has many disadvantages. For example, it is difficult to improve the passivation effect of the boron-doped layer while taking into account the process stability, which leads to a low yield of the preparation of back-contact solar cells.

[0005] 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

[0006] The embodiments of the present application provide a back-contact solar cell and a method for preparing the same, and a photovoltaic module to solve or alleviate one or more of the technical problems raised above.

[0007] In a first aspect of an embodiment of the present application, a method for preparing a back-contact solar cell is provided. The method comprises: providing a substrate, the substrate comprising a silicon wafer, a first tunneling oxide layer, and a first intrinsic amorphous silicon layer stacked in sequence; performing a crystallization process on the first intrinsic amorphous silicon layer on the substrate to convert amorphous silicon in the first intrinsic amorphous silicon layer into polycrystalline silicon, and obtaining a first polycrystalline silicon layer; and performing boron diffusion on the first polycrystalline silicon layer to obtain a boron-doped layer.

[0008] The method of the embodiment of the present application performs a boron diffusion on the first polycrystalline silicon layer after crystallizing the first intrinsic amorphous silicon layer to form a first polycrystalline silicon layer, so as to improve the passivation contact effect of the obtained boron-doped layer, thereby improving the yield of the back-contact solar cell. In addition, the process of first converting amorphous silicon into polycrystalline silicon and then boron diffusion can also shorten the total formation time of the boron-doped layer and improve the stability of the process, which is particularly suitable for large-scale production of back-contact solar cells.

[0009] Specifically, the first intrinsic amorphous silicon is deposited on the first tunnel oxide layer, and the amorphous silicon is converted into polycrystalline silicon through crystallization treatment before boron diffusion. During the boron diffusion process, polycrystalline silicon has a better barrier effect on the diffusion of boron atoms than amorphous silicon. On the one hand, a thinner amorphous silicon layer can be used to complete the diffusion of boron atoms, thereby increasing the deposition rate of amorphous silicon and shortening the total time for forming a boron-doped layer, which is beneficial to obtaining the process stability of the boron-doped layer; on the other hand, polycrystalline silicon has a stronger barrier effect on boron atoms, which is beneficial to increasing the concentration of boron dopants when polycrystalline silicon is doped with boron, thereby improving field passivation, reducing the probability of carrier recombination on the surface of the silicon wafer, and thus better achieving the passivation effect of the boron-doped layer.

[0010] According to an embodiment of the present application, the method for preparing the substrate includes: forming a first tunneling oxide layer on the back side of the silicon wafer by laser thermal oxidation; and depositing a first intrinsic amorphous silicon layer on a side of the first tunneling oxide layer away from the silicon wafer.

[0011] According to an embodiment of the present application, the flow rate of oxygen in the laser thermal oxygenation process is 500~5000sccm.

[0012] According to an embodiment of the present application, the wavelength of the laser in the laser thermal oxidation process is 300~500nm.

[0013] According to an embodiment of the present application, the scanning speed of the laser during the laser thermal oxidation process is 300~500mm / s.

[0014] According to an embodiment of the present application, the deposition method includes: using low-pressure vapor phase chemistry for deposition.

[0015] According to an embodiment of the present application, the crystallization treatment method includes using a pulsed laser to irradiate the first intrinsic amorphous silicon layer to transform the amorphous silicon into polycrystalline silicon.

[0016] According to an embodiment of the present application, the wavelength of the laser in the pulse laser is 260~380nm.

[0017] According to an embodiment of the present application, the frequency of the laser in the pulsed laser is 1-100 Hz.

[0018] According to the embodiment of the present application, the energy density of the laser in the pulsed laser is 100-480 mJ / cm 2 .

[0019] According to an embodiment of the present application, the scanning speed of the laser in the pulse laser is 2~10mm / s.

[0020] According to an embodiment of the present application, the boron source in the boron diffusion process includes BH3 or BCl3.

[0021] According to an embodiment of the present application, the diffusion temperature during the boron diffusion process is 500-1200°C.

[0022] According to an embodiment of the present application, the diffusion time in the boron diffusion process is 30 to 200 minutes.

[0023] According to an embodiment of the present application, the ambient gas source in the boron diffusion process includes at least one of N2 and O2.

[0024] According to an embodiment of the present application, the thickness of the first tunneling oxide layer is 1~3nm; According to an embodiment of the present application, the thickness of the first intrinsic amorphous silicon layer is 50-150 nm.

[0025] The second aspect of the embodiment of the present application provides a back-contact solar cell. It includes: a substrate, the substrate includes a silicon wafer and a first tunneling oxide layer stacked in sequence; a boron-doped layer, the boron-doped layer is arranged on a side of the first tunneling oxide layer away from the silicon wafer, and the boron-doped layer is obtained by crystallizing and diffusing boron on a first intrinsic amorphous silicon layer located on a side of the first tunneling oxide layer away from the silicon wafer. The solar cell has a good photoelectric conversion efficiency. This is because a uniformly crystallized polycrystalline silicon layer can be obtained after the crystallization process, which can not only improve the passivation contact effect of the boron-doped layer, but also improve the photoelectric conversion efficiency, yield and process stability of the back-contact solar cell.

[0026] According to a third aspect of the embodiments of the present application, a photovoltaic module may be provided, wherein the photovoltaic module comprises a back-contact solar cell prepared by the method of the first aspect or the back-contact solar cell described in the second aspect.

[0027] In some embodiments, the photovoltaic module includes a plurality of solar cells connected in series and / or in parallel, wherein at least one solar cell is a back-contact solar cell as described above. A plurality of solar cells in series form a cell string, and adjacent back-contact solar cells can be connected together by string welding.

[0028] The embodiment of the present application can provide a photovoltaic system, including the photovoltaic module in any of the above embodiments. The photovoltaic system also has the advantages of the above photovoltaic modules, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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 according to the present application and should not be regarded as limiting the scope of the present application.

[0030] Figure 1 It is a schematic diagram of the structure of a back-contact solar cell according to some embodiments of the present application.

[0031] Description of reference numerals: 1: N-type silicon wafer; 2: first tunneling oxide layer; 3: boron-doped layer; 4: phosphorus-doped layer; 5: passivation layer; 6: anti-reflection layer; 7: electrode; 8: second tunneling oxide layer. DETAILED DESCRIPTION

[0032] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. In the accompanying drawings, for clarity, the sizes of layers and regions and their relative sizes may be exaggerated. The same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limitations on the present application. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0033] It should be understood that when a layer is referred to as being "on," "adjacent to," "connected to," or "coupled to" another layer, it may be directly on, adjacent to, connected to, or coupled to the other layer, or there may be intervening layers. It should be understood that although the terms first, second, third, etc. may be used to describe various regions, layers, and / or portions, these regions, layers, and / or portions should not be limited by these terms. These terms are merely used to distinguish one region, layer, or portion from another region, layer, or portion. Therefore, without departing from the teachings of the present application, the first region, layer, or portion discussed below may be represented as the second region, layer, or portion. When the second region, layer, or portion is discussed, it does not mean that the first region, layer, or portion necessarily exists in the present application.

[0034] 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.

[0035] In the present application, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to an integer in the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints, which is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed in the present application should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows for broadly including quantitative intervals such as percentage intervals, ratio intervals, and ratio intervals.

[0036] In the present application, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to an integer in the numerical interval, including the two endpoint integers of the numerical range, and each integer between the two endpoints, is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical range disclosed in the present application should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows for broadly including quantitative intervals such as percentage intervals, ratio intervals, and ratio intervals.

[0037] The boron-doped layer structure is realized by low-temperature chemical vapor deposition and thermal diffusion (tunneling layer + intrinsic amorphous silicon layer + boron diffusion). Since the solid solubility of boron atoms in silicon is low, boron atoms need more heat and higher temperature during the diffusion process. At the same time, the passivation effect of the boron-doped layer must be ensured, which is very demanding on the process quality of the tunneling layer and the intrinsic amorphous silicon layer, and is particularly unfavorable for large-scale production.

[0038] In a first aspect of an embodiment of the present application, a method for preparing a back-contact solar cell is provided, the method comprising: (1) providing a substrate, the substrate comprising a silicon wafer, a first tunneling oxide layer, and a first intrinsic amorphous silicon layer stacked in sequence; (2) performing a crystallization treatment on the first intrinsic amorphous silicon layer to convert the amorphous silicon in the first intrinsic amorphous silicon layer into polycrystalline silicon, and obtaining a first polycrystalline silicon layer; (3) performing boron diffusion on the first polycrystalline silicon layer to obtain a boron-doped layer.

[0039] The method of the embodiment of the present application performs a boron diffusion on the first polycrystalline silicon layer after crystallizing the first intrinsic amorphous silicon layer to form the first polycrystalline silicon layer, so as to improve the passivation contact effect of the obtained boron-doped layer, thereby improving the yield of the back-contact solar cell. In addition, the process of first converting amorphous silicon into polycrystalline silicon and then boron diffusion can also shorten the total formation time of the boron-doped layer and improve the stability of the process, which is particularly suitable for large-scale production of back-contact solar cells.

[0040] Specifically, the first intrinsic amorphous silicon is deposited on the first tunnel oxide layer, and the amorphous silicon is converted into polycrystalline silicon through crystallization treatment before boron diffusion. During the boron diffusion process, polycrystalline silicon has a better blocking effect on the diffusion of boron atoms than amorphous silicon. On the one hand, a thinner amorphous silicon layer can be used to complete the diffusion of boron atoms, thereby increasing the deposition rate of amorphous silicon and shortening the total time for forming a boron-doped layer, which is beneficial to obtaining the process stability of the boron-doped layer; on the other hand, polycrystalline silicon has a stronger blocking effect on boron atoms, which is beneficial to increasing the concentration of boron dopants when polycrystalline silicon is doped with boron, thereby improving field passivation, reducing the probability of minority carriers recombining on the surface of the silicon wafer, and thus better achieving the passivation effect of the boron-doped layer.

[0041] According to the method of the embodiment of the present application, in step (1), a substrate is provided.

[0042] In some embodiments, in step (1), the method for preparing the substrate includes: forming a first tunneling oxide layer on the back of the silicon wafer by laser thermal oxidation; and depositing a first intrinsic amorphous silicon layer on the surface of the first tunneling oxide layer away from the silicon wafer. The silicon oxide layer formed by laser induced thermal oxidation can effectively protect the silicon wafer material, and the formed first tunneling oxide layer is uniform and dense. The uniform and dense first tunneling layer is particularly suitable for the subsequent deposition of the first amorphous silicon layer, thereby promoting the acquisition of a boron-doped layer with a good passivation effect.

[0043] Optionally, the laser comprises an ultraviolet picosecond laser.

[0044] Optionally, the wavelength of the laser is 300-500 nm.

[0045] Optionally, the flow rate of oxygen during the laser thermal oxidation process is 500-5000 sccm. In this way, a first tunneling oxide layer with a suitable thickness can be obtained to enhance the tunneling effect of electrons.

[0046] Optionally, the laser thermal oxidation also requires an inert gas, and the volume ratio of the inert gas to oxygen is 1:(0.5-3).

[0047] In some embodiments, in step (1), the thickness of the first tunneling oxide layer is 1-3 nm, such as 1 nm, 2 nm, 3 nm, etc. This allows electrons to tunnel from the substrate to the doped silicon film layer (such as a boron-doped layer or a phosphorus-doped layer).

[0048] In some embodiments, in step (1), the first tunneling oxide layer comprises SiO X .

[0049] In some embodiments, in step (1), deposition is performed on a side of the first tunneling oxide layer away from the substrate to obtain a first intrinsic amorphous silicon layer.

[0050] In some embodiments, in step (1), the deposition method includes low-pressure chemical vapor deposition. The deposition temperature of low-pressure chemical vapor deposition is relatively low (e.g., 500° C. to 650° C.), so that the thickness uniformity of the formed first intrinsic amorphous silicon layer and the coverage of the first tunneling oxide layer are both good, and the cost is low.

[0051] Optionally, the conditions of low pressure chemical vapor deposition include a temperature of 500-650° C. and a time of 10-30 min.

[0052] In some embodiments, in step (1), the thickness of the first intrinsic amorphous silicon layer is 50-150 nm. The first intrinsic amorphous silicon layer in the aforementioned thickness range can improve the production capacity of the first intrinsic amorphous silicon layer while reducing the total time for subsequent formation of the boron doping layer and reducing the parasitic absorption of the boron doping layer, thereby improving the photoelectric conversion efficiency of the back contact solar cell formed by the method; in addition, it can also avoid as much as possible the problem of excessive boron atoms entering the silicon wafer due to the first intrinsic amorphous silicon layer being too thin, causing Auger recombination and affecting the passivation effect of the boron doping layer.

[0053] According to an embodiment of the present application, in step (2), the first intrinsic amorphous silicon layer is crystallized to convert the amorphous silicon in the first intrinsic amorphous silicon layer into polycrystalline silicon, and obtain a first polycrystalline silicon layer. In this step, hydrogenated amorphous silicon is a metastable structure, and the crystallization conversion requires energy. After the crystallization treatment, the amorphous silicon is converted into polycrystalline silicon. Polycrystalline silicon has a better barrier effect on the diffusion of boron atoms than amorphous or microcrystalline silicon, and thus boron atoms can be doped on the thinner first polycrystalline silicon layer.

[0054] In some embodiments, in step (2), the crystallization process is performed by pulsed laser crystallization.

[0055] In some embodiments, in step (2), the wavelength of the pulsed laser is 260-380 nm, such as 260 nm, 300 nm, 320 nm, 350 nm, 380 nm, etc. In this way, polycrystalline silicon with smaller grain size and more uniform distribution can be obtained.

[0056] In some embodiments, in step (2), the frequency of the pulsed laser is 1-100 Hz, such as 1 Hz, 20 Hz, 50 Hz, 80 Hz, 100 Hz, etc. This is beneficial to the formation and growth of polysilicon grains, thereby improving the crystallization rate.

[0057] In some embodiments, in step (2), the energy density of the pulsed laser is 100-480 mJ / cm 2 , for example 100mJ / cm 2 、200mJ / cm 2 、320mJ / cm 2 、400mJ / cm 2 、480mJ / cm 2 Etc. This is beneficial to the formation and growth of polysilicon grains, thereby improving the crystallization rate.

[0058] In some embodiments, in step (2), the scanning speed of the pulsed laser is 2-10 mm / s. For example, 2 mm / s, 5 mm / s, 8 mm / s, 10 mm / s, etc. By controlling the scanning speed within the aforementioned range, the "tailing" phenomenon at the scanning starting point can be reduced, thereby reducing defects such as abnormal crystal structure, grain enlargement or loose structure of polycrystalline silicon, thereby improving the passivation effect of the boron doped layer.

[0059] According to the method of the embodiment of the present application, in step (3), boron is diffused into the first polysilicon layer to obtain a boron-doped layer.

[0060] In some embodiments, in step (3), the boron diffusion also produces a borosilicate glass layer, which is located on a side of the boron-doped layer away from the substrate. The borosilicate glass layer can be used as a mask for the boron-doped layer to facilitate subsequent processes.

[0061] In some embodiments, in step (3), the boron source during the boron diffusion process is BH3 or BCl3.

[0062] In some embodiments, in step (3), the diffusion temperature during the boron diffusion process is 500-1200° C., such as 500° C., 800° C., 930° C., 1200° C., etc. This can improve the passivation effect of the boron doped layer and reduce the deterioration of the passivation performance of the boron doped layer caused by the entry of boron atoms into the silicon wafer.

[0063] In some embodiments, in step (3), the diffusion time during the boron diffusion process is 30 to 200 minutes, such as 30 minutes, 100 minutes, 200 minutes, etc. Thus, a boron-doped layer with a better passivation effect can be obtained.

[0064] In some embodiments, in step (3), the ambient gas source during the boron diffusion process includes at least one of N2 and O2.

[0065] In some embodiments, the method further includes step (4): performing a first groove opening process and a first cleaning process on the product after the boron diffusion is completed according to a first predetermined pattern to remove the borosilicate glass layer, the boron doped layer and the first tunneling oxide layer in areas other than the predetermined pattern.

[0066] Furthermore, the first grooving process is performed using laser, and the laser conditions include: using a square spot laser, the laser wavelength is 500~600nm; the overlap rate of the square spot is 80%; the laser frequency is 400~600kHz; the laser power is 10~50w.

[0067] Furthermore, the conditions of the first cleaning treatment include using a mixture of KOH solution and deionized water in a volume ratio of (1-2): (5-20) for cleaning. The concentration of KOH is 45-55wt%, the temperature of the first cleaning treatment is 50-80°C, and the time is 200-400s. In some embodiments, the method further includes step (5): preparing a second tunneling oxide layer on the back side of the product obtained after the first cleaning process.

[0068] Optionally, the second tunnel oxide layer is prepared by deposition using low-pressure vapor phase chemistry.

[0069] Optionally, the second tunnel oxide layer has a thickness of 1-3 nm, such as 1 nm, 2 nm, 3 nm, etc.

[0070] Optionally, the second tunnel oxide layer includes silicon dioxide.

[0071] In some embodiments, the method further includes step (6): forming a phosphorus-doped layer on a side of the second tunnel oxide layer away from the silicon wafer.

[0072] In some embodiments, in step (6), a second intrinsic amorphous silicon layer is formed by chemical vapor deposition on a side of the second tunneling oxide layer away from the substrate, and the second intrinsic amorphous silicon layer is phosphorus-doped and annealed to obtain a phosphorus-doped layer, and a phosphosilicate glass layer is formed on a side of the phosphorus-doped layer away from the substrate.

[0073] Optionally, the temperature of the annealing treatment is 600-800°C, for example, 600°C, 700°C, 800°C, etc.

[0074] Optionally, the thickness of the second intrinsic amorphous silicon layer is 50-150 nm, for example, 50 nm, 100 nm, 150 nm, etc.

[0075] In some embodiments, the step further includes: performing a second grooving process and a second cleaning process on the silicon wafer on which the phosphosilicate glass layer is formed according to a second predetermined pattern to remove the phosphosilicate glass layer, the phosphorus-doped layer and the second tunneling oxide layer in areas other than the second predetermined pattern.

[0076] Furthermore, the second grooving process is performed by laser, wherein the laser conditions include: a square spot is used, the wavelength of the laser is 500-600nm, the overlap rate of the laser is 70-80%, the frequency of the laser is 400-600kHz, and the power of the laser is 10-50w.

[0077] Further, the conditions of the second cleaning process include a first stage cleaning process and a second stage cleaning process.

[0078] Optionally, the first stage cleaning treatment includes: using a mixture of KOH solution and deionized water in a volume ratio of (2-8): (10-20) to clean the grooved area and simultaneously perform double-sided texturing, and the concentration of the KOH solution is 45-55wt%.

[0079] Optionally, the temperature of the first stage cleaning treatment is 50-80° C. and the time is 120-300 seconds. The second stage cleaning treatment uses a mixed solution of HF and deionized water with a volume ratio of (0.02-0.06) : (10-100) to remove the borosilicate glass layer and the phosphosilicate glass layer on the surface of the product obtained after the first stage cleaning treatment, and the time is 50-120 seconds.

[0080] In some embodiments, the method further includes step (8): depositing a passivation layer on the back side of the product obtained after the second stage cleaning.

[0081] Optionally, the passivation layer includes Al0 x .

[0082] Optionally, the thickness of the passivation layer is 4-10 nm.

[0083] In some embodiments, the method further includes step (9): depositing an anti-reflection layer on the front and back sides of the silicon wafer after the passivation layer is deposited, so as to obtain the solar cell.

[0084] Optionally, the anti-reflection layer comprises SiN x .

[0085] Optionally, the anti-reflection layer has a thickness of 70-100 nm.

[0086] In some embodiments, the method further includes step (10): forming a metal electrode by screen printing.

[0087] Optionally, the metal electrode comprises silver.

[0088] The second aspect of the embodiment of the present application provides a back-contact solar cell. The cell includes: a substrate, the substrate includes a silicon wafer and a first tunneling oxide layer stacked in sequence; a boron-doped layer, the boron-doped layer is arranged on a side of the first tunneling oxide layer away from the silicon wafer, and the boron-doped layer is obtained by crystallizing and diffusing boron on a first intrinsic amorphous silicon layer located on a side of the first tunneling oxide layer away from the silicon wafer. The back-contact solar cell has a good photoelectric conversion efficiency. This is because a uniformly crystallized polycrystalline silicon layer can be obtained after the crystallization process, which can not only improve the passivation contact effect of the boron-doped layer, but also improve the photoelectric conversion efficiency, yield and process stability of the back-contact solar cell.

[0089] In some embodiments, reference Figure 1The back contact solar cell comprises: an N-type silicon wafer 1; a first tunneling oxide layer 2; a boron doped layer 3; a phosphorus doped layer 4; a passivation layer 5; an anti-reflection layer 6; and an electrode 7. The boron doped layer 3 is away from one side of the first tunneling oxide layer 2, the phosphorus doped layer 4 is away from one side of the second tunneling oxide layer 3, and in the extension direction of the back contact solar cell, the anti-reflection layer 6 is arranged in the interval between the boron doped layer 3 and the phosphorus doped layer, and the first tunneling oxide layer 2 is arranged between the boron doped layer 3 and the N-type silicon wafer 1, and the second tunneling oxide layer 8 is also arranged between the phosphorus doped layer 4 and the N-type silicon wafer 1, and the electrode 7 is connected to the boron doped layer 3 and the phosphorus doped layer 4 respectively.

[0090] According to a third aspect of the embodiments of the present application, a photovoltaic module may be provided, wherein the photovoltaic module includes the back-contact solar cell according to the second aspect.

[0091] In some embodiments, the photovoltaic module includes a plurality of solar cells connected in series and / or in parallel, wherein at least one solar cell is a back-contact solar cell as described above. A plurality of solar cells in series form a cell string, and adjacent back-contact solar cells can be connected together by string welding.

[0092] The fourth aspect of the embodiments of the present application provides a photovoltaic system, including the photovoltaic module in any of the above embodiments. The photovoltaic system also has the advantages of the above photovoltaic modules, which will not be repeated here.

[0093] The above-mentioned photovoltaic system has a wide range of applications, not only limited to photovoltaic power stations, such as ground power stations, rooftop power stations and water power stations, but also includes various equipment and devices that use solar energy to generate electricity, such as user solar power supplies, solar street lights, solar cars and solar buildings. Of course, it is understandable that the application scenarios of photovoltaic systems are not limited to this, that is to say, photovoltaic systems can be used in all fields that require solar energy to generate electricity. Taking the photovoltaic power generation system network as an example, the photovoltaic system may include a photovoltaic array, a junction box and an inverter. The photovoltaic array may be an array combination of multiple photovoltaic components. For example, multiple photovoltaic components can form multiple photovoltaic arrays. The photovoltaic array is connected to the junction box. The junction box can converge the current generated by the photovoltaic array. The converged current flows through the inverter and is converted into the alternating current required by the mains power grid, and then connected to the mains network to realize solar power supply.

[0094] 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.

[0095] Example 1 S1: Polishing is performed on an N-type bare silicon wafer.

[0096] S2: In an oxygen atmosphere, the back of the silicon wafer is subjected to laser thermal oxidation treatment to form a first tunneling oxide layer (silicon dioxide), wherein the laser wavelength is 300nm, the laser scanning speed is 400mm / s, and the oxygen flow rate is 1000sccm. Then, the first intrinsic amorphous silicon layer is deposited using LPCVD, wherein: the first tunneling oxide layer has a thickness of 1.5nm, and the first intrinsic amorphous silicon has a thickness of 100nm.

[0097] S3: Use pulsed laser for crystallization to transform amorphous silicon into polycrystalline silicon, and control the wavelength of pulsed laser to 308nm, pulse width to 30ns, frequency to 60Hz, and energy density to 320mJ / cm 2 ,The laser scanning speed is 6mm / s. S4: Put the product obtained in step S3 into a boron diffusion furnace for boron diffusion. During the boron diffusion process, the boron source is BCl3, the diffusion temperature is 960°C, the boron source flow rate is 200-300 sccm, and the borosilicate glass formed is 50nm. At this time, a borosilicate glass layer is also formed on the first tunneling oxide layer and the boron doped layer.

[0098] S5: performing a first groove process and a first cleaning process on the silicon wafer after boron diffusion according to a first predetermined pattern to remove the borosilicate glass layer, the first polysilicon layer and the first tunneling oxide layer in areas other than the predetermined pattern.

[0099] S6: performing a second deposition on the back side of the silicon wafer after the first cleaning to obtain a second tunneling oxide layer (silicon dioxide) with a thickness of 1.5 nm.

[0100] S7: A 100nm second intrinsic amorphous silicon layer is formed by chemical vapor deposition on the side of the second tunneling oxide layer away from the substrate, and the second intrinsic amorphous silicon layer is phosphorus-doped and annealed to obtain a phosphorus-doped layer. The phosphorus doping process temperature is 880°C, the phosphorus source (PH3) flow rate is 300sccm, and a phosphorus-doped layer is formed on the back of the battery. At this time, a 50nm mask phosphorus silicon glass layer is formed on the second tunneling oxide layer (SiO2) and the phosphorus-doped silicon layer on the back.

[0101] S8: performing a second groove opening process and a second cleaning process on the silicon wafer having the phosphosilicate glass layer formed thereon according to a second predetermined pattern, so as to remove the phosphosilicate glass layer, the phosphorus-doped layer and the second tunnel oxide layer in areas other than the second predetermined pattern.

[0102] S9: Clean the grooved area of ​​the silicon wafer obtained in S8 and texturize both sides at the same time, wherein the concentration of KOH is 55wt%; the cleaning temperature is 80℃; the cleaning time is 180s; and then use HF with a concentration of 60wt% to remove the surface phosphosilicate glass layer for 120s.

[0103] S10: The cleaned silicon wafer is placed in the plate-type ALD equipment to deposit AlO with a film thickness of 8nm. x After completion, it is placed in a tubular PECVD device to deposit SiN on the back of the silicon wafer. x Anti-reflection film, the thickness of the anti-reflection film is 100nm. Then a layer of SiNx anti-reflection film is deposited on the front of the silicon wafer, the thickness of the anti-reflection film is 80nm.

[0104] S11: Screen printing, sintering, testing and sorting are performed on the silicon wafer obtained in step S10 to obtain a back-contact solar cell.

[0105] Examples 2 and 3 A back-contact solar cell was prepared according to the method of Example 1, except that in step S2: the scanning speeds of the laser were 300 mm / s and 500 mm / s respectively.

[0106] Examples 4 and 5 A back-contact solar cell was prepared according to the method of Example 1, except that in step S3: the energy density of the pulsed laser was 100 mJ / cm 2 and 480mJ / cm 2 .

[0107] Examples 6 and 7 Back-contact solar cells were prepared according to the method of Example 1, except that the thickness of the first tunneling oxide layer was 1 nm and 3 nm, respectively.

[0108] Examples 8 and 9 Back-contact solar cells were prepared according to the method of Example 1, except that the thickness of the first intrinsic amorphous silicon layer was 50 nm and 150 nm, respectively.

[0109] Example 10 A back contact solar cell was prepared according to the method of Example 1, except that the first tunnel oxide layer was obtained by thermal oxidation, wherein the conditions of the thermal oxidation method included: temperature 610° C., time 5 min, oxygen amount 30 slm.

[0110] Embodiment 11 A back-contact solar cell was prepared according to the method of Example 1, except that the first intrinsic amorphous silicon layer was crystallized by annealing at a temperature of 900°C.

[0111] Comparative Example 1 S1: Polishing is performed on an N-type bare silicon wafer.

[0112] S2: In an oxygen atmosphere, the back of the silicon wafer is subjected to laser thermal oxidation treatment to form a first tunneling oxide layer (silicon dioxide), wherein the laser wavelength is 300nm, the laser scanning speed is 400mm / s, and the oxygen flow rate is 1000sccm. Then, the first intrinsic amorphous silicon layer is deposited using LPCVD, wherein: the first tunneling oxide layer has a thickness of 1.5nm, and the first intrinsic amorphous silicon has a thickness of 100nm.

[0113] S3: Put the product obtained in step S2 into a boron diffusion furnace for boron diffusion. During the boron diffusion process, the boron source is BCl3, the diffusion temperature is 960°C, the boron source flow rate is 200-300 sccm, and the borosilicate glass formed is 50nm. At this time, a borosilicate glass layer is also formed on the first tunneling oxide layer and the boron doped layer.

[0114] S4: performing a first groove processing and a first cleaning processing on the silicon wafer after the boron diffusion is completed according to the first predetermined pattern to remove the borosilicate glass layer, the first polysilicon layer and the first tunneling oxide layer in the non-predetermined pattern area.

[0115] S5: performing a second deposition on the back side of the silicon wafer after the first cleaning to obtain a second tunneling oxide layer (silicon dioxide) with a thickness of 1.5 nm.

[0116] S6: A 100nm second intrinsic amorphous silicon layer is formed by chemical vapor deposition on the side of the second tunneling oxide layer away from the substrate, and the second intrinsic amorphous silicon layer is phosphorus doped and annealed to obtain a phosphorus doped layer. The phosphorus doping process temperature is 880°C, the phosphorus source (PH3) flow rate is 300sccm, and a phosphorus doped layer is formed on the back of the battery. At this time, a mask phosphorus silicon glass layer of about 50nm is formed on the second tunneling oxide layer (SiO2) and the phosphorus doped layer on the back.

[0117] S7: performing a second groove opening process and a second cleaning process on the silicon wafer having the phosphosilicate glass layer formed thereon according to a second predetermined pattern, so as to remove the phosphosilicate glass layer and the phosphorus-doped layer and the second tunnel oxide layer in areas other than the second predetermined pattern.

[0118] S8: The silicon wafer obtained in S8 is cleaned in the grooved area and textured on both sides at the same time, wherein the concentration of KOH is 55wt%; the temperature is 80°C; the time is 180s; and then HF with a concentration of 60wt% is used to remove the surface phosphosilicate glass layer for 120s.

[0119] S9: The cleaned silicon wafer is placed in the plate-type ALD equipment to deposit AlO with a film thickness of 8 nm. x After completion, it is placed in a tubular PECVD device to deposit a layer of SiN on the back of the silicon wafer. x Anti-reflection film, film thickness 100nm.

[0120] Then a layer of SiNx anti-reflection film with a thickness of 80nm is deposited on the front side of the silicon wafer.

[0121] S10: Screen printing, sintering, testing and sorting are performed on the silicon wafer obtained in step S9 to obtain a back-contact solar cell.

[0122] Test Example The above-mentioned battery was subjected to the following performance tests, and the results are shown in Table 1.

[0123] Photoelectric conversion efficiency, short-circuit current, open-circuit voltage, and fill factor testing: The specific testing method is to place the battery under a light source of 100 mW / cm 2 The results are obtained by connecting the source meter using the four-wire method under AM 1.5G simulated sunlight at 25°C.

[0124] Table 1

[0125] As can be seen from the above table, by comparing Examples 1-11 with Comparative Example 1, it can be seen that the first intrinsic amorphous silicon layer is first converted into polycrystalline silicon and then the boron is diffused, which can improve the passivation contact effect of the obtained boron doped layer, thereby improving the yield of the back contact solar cell. However, the first intrinsic amorphous silicon layer is directly diffused with boron, because the blocking effect of amorphous silicon on the diffusion of boron atoms is worse than that of polycrystalline silicon, which results in a decrease in the yield and photoelectric performance of the cell.

[0126] By comparing Example 1 with Example 10, it can be found that the photoelectric performance of the battery in Example 1 is better than that in Example 10. This is because the first tunneling oxide layer obtained by laser thermal oxidation has better density and uniformity than the first tunneling oxide layer obtained by low-temperature chemical deposition, which makes the boron-doped layer formed thereon have better passivation effect.

[0127] By comparing Example 1 with Example 11, it can be found that the photovoltaic performance and yield of the battery of Example 1 are better than those of Example 11. This is because the first intrinsic amorphous silicon layer is converted from amorphous silicon to polycrystalline silicon using a pulsed laser, which achieves better ion activation efficiency and activation depth than other methods (high temperature annealing) and does not damage the front side of the silicon wafer, which allows boron diffusion to proceed better.

[0128] It should also be noted that the "some embodiments", "other embodiments", "embodiments", etc. mentioned in this application 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. Furthermore, 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.

[0129] 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.

[0130] 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

1. A method for preparing a back contact solar cell, characterized in that: include: Providing a substrate, the substrate comprising a silicon wafer, a first tunneling oxide layer and a first intrinsic amorphous silicon layer stacked in sequence; Performing a crystallization process on the first intrinsic amorphous silicon layer on the substrate so as to convert amorphous silicon in the first intrinsic amorphous silicon layer into polycrystalline silicon, and obtaining a first polycrystalline silicon layer; Boron is diffused into the first polysilicon layer to obtain a boron-doped layer.

2. The preparation method according to claim 1, characterized in that: The method for preparing the substrate comprises: Forming the first tunneling oxide layer on the back side of the silicon wafer by laser thermal oxidation; The first intrinsic amorphous silicon layer is deposited on a side of the first tunnel oxide layer away from the silicon wafer.

3. The preparation method according to claim 2, characterized in that: The laser thermal oxidation satisfies at least one of the following conditions: The oxygen flow rate is 500~5000sccm; The wavelength of the laser is 300~500nm; The scanning speed of the laser is 300~500mm / s.

4. The preparation method according to claim 2, characterized in that: The deposition method includes: using low-pressure vapor phase chemical deposition.

5. The preparation method according to claim 1, characterized in that: The crystallization treatment method includes irradiating the first intrinsic amorphous silicon layer with a pulsed laser to transform the amorphous silicon in the first intrinsic amorphous silicon layer into polycrystalline silicon.

6. The preparation method according to claim 5, characterized in that: The pulse laser satisfies at least one of the following conditions: The wavelength is 260~380nm; Frequency: 1~100Hz; Energy density is 100~480mJ / cm 2 ; The scanning speed is 2~10mm / s.

7. The preparation method according to claim 1, characterized in that: The boron diffusion conditions include: Boron sources include BH3 or BCl3; Diffusion temperature is 500~1200℃; Diffusion time is 30~200min; The ambient gas source includes at least one of N2 and O2.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The thickness of the first tunneling oxide layer is 1~3nm; And / or, the thickness of the first intrinsic amorphous silicon layer is 50-150 nm.

9. A back contact solar cell, characterized in that: include: A substrate, the substrate comprising a silicon wafer and a first tunnel oxide layer stacked in sequence; A boron-doped layer is disposed on a side of the first tunnel oxide layer away from the silicon wafer, and is obtained by crystallizing and diffusing boron on a first intrinsic amorphous silicon layer located on a side of the first tunnel oxide layer away from the silicon wafer.

10. A photovoltaic module, characterized in that: The photovoltaic module comprises a back-contact solar cell prepared by the method of claims 1-8 or a back-contact solar cell as described in claim 9.

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