A bc battery, a preparation method thereof and a photovoltaic module

Abstract

The application provides a BC battery, a preparation method thereof and a photovoltaic module, and relates to the photovoltaic field. The BC battery comprises a silicon substrate; a first aluminum oxide layer and a first silicon nitride layer are sequentially arranged on a light-receiving surface of the silicon substrate; a P region and an N region are arranged on a back surface of the silicon substrate; the P region comprises a boron-doped layer; the N region comprises a first phosphorus diffusion layer and a second phosphorus diffusion layer; a second aluminum oxide layer and a second silicon nitride layer are sequentially arranged on surfaces of the P region and the N region; and the content of phosphorus in the second phosphorus diffusion layer decreases along a side of the second aluminum oxide layer to a side of the first phosphorus diffusion layer. Through the synergistic effect of the second phosphorus diffusion layer with gradient phosphorus doping and the aluminum oxide layer and the silicon nitride layer, the BC battery improves the carrier lifetime, and solves the problems of high leakage current and poor doping uniformity in the prior art.

Description

Technical Field

[0001] This application relates to the photovoltaic field, and more particularly to a BC cell, its preparation method, and a photovoltaic module. Background Technology

[0002] Current BC (back contact) batteries commonly employ POCl3 thermal diffusion combined with masking technology in phosphorus diffusion processes, but this technology still has the following problems: 1. Insufficient doping uniformity: Traditional masking processes can easily lead to blurred boundaries between P / N regions, increasing the risk of leakage. 2. Severe thermal damage: The high-temperature diffusion process causes lattice damage to the silicon wafer surface, affecting carrier lifetime.

[0003] Therefore, there is an urgent need to provide a BC battery that solves the above problems. Summary of the Invention

[0004] The purpose of this application is to provide a BC cell, a method for its preparation, and a photovoltaic module to solve the above-mentioned problems.

[0005] To achieve the above objectives, the first aspect of this application provides a BC battery, including a silicon substrate; The light-facing surface of the silicon substrate is sequentially provided with a first aluminum oxide layer and a first silicon nitride layer; The back surface of the silicon substrate is provided with a P-region and an N-region; the P-region includes a boron doped layer; the N-region includes a first phosphorus diffusion layer and a second phosphorus diffusion layer; a second aluminum oxide layer and a second silicon nitride layer are sequentially disposed on the surfaces of the P-region and the N-region. The phosphorus content in the second phosphorus diffusion layer decreases gradually from one side of the second alumina layer to one side of the first phosphorus diffusion layer.

[0006] Optionally, the BC battery satisfies at least one of the following conditions: A. The phosphorus concentration of the first phosphorus diffusion layer is 3.5 × 10⁻⁶. 20 cm -3 -4.5×10 20 cm -3 ; B. The surface phosphorus content of the second phosphorus diffusion layer near the second alumina layer is 1.5 × 10⁻⁶. 21 cm -3 -4.5×10 21 cm -3 The surface phosphorus content of the second phosphorus diffusion layer, which is closer to the first phosphorus diffusion layer, is 1.5 × 10⁻⁶. 20 cm -3 -3×10 20 cm -3 .

[0007] Optionally, the BC battery satisfies at least one of the following conditions: A. The thickness of the first phosphorus diffusion layer is 20nm-30nm; B. The thickness of the second phosphorus diffusion layer is 8nm-12nm.

[0008] Optionally, the BC battery satisfies at least one of the following conditions: A. The thicknesses of the first alumina layer and the second alumina layer are each 3-5 nm independently; B. The thicknesses of the first silicon nitride layer and the second silicon nitride layer are each independently 70-90 nm; C. The refractive indices of the first silicon nitride layer and the second silicon nitride layer are each independently 1.76-2.05.

[0009] A second aspect of this application provides a method for preparing the BC battery described above, comprising: Silicon wafers are supplied; The silicon wafer is pretreated, boron diffused, laser patterned, and alkaline cleaned to obtain an alkaline cleaned silicon wafer. POCl3 is introduced to clean the silicon wafer with alkali, and then high-temperature phosphorus diffusion is performed to obtain a high-temperature phosphorus diffusion layer. Silicon phosphide nanoparticles were treated with a picosecond laser on the surface of a high-temperature phosphorus diffusion layer to obtain a silicon wafer with gradient phosphorus diffusion. A first aluminum oxide layer and a first silicon nitride layer are sequentially disposed on the light-facing side of the gradient phosphorus-diffused silicon wafer, and a second aluminum oxide layer and a second silicon nitride layer are sequentially disposed on the back-facing side to obtain a BC battery.

[0010] Optionally, the method for preparing the BC battery satisfies at least one of the following conditions: A. The particle size of the silicon phosphide nanoparticles is 5-10 nm; B. The purity of the silicon phosphide nanoparticles is ≥99.99%.

[0011] Optionally, the scanning speed of the picosecond laser processing is 80-120 mm / s, and the energy density is 0.8-1.2 J / cm². 2 The pulse duration is 5-15 ps, and the wavelength is 1030-1080 nm.

[0012] Optionally, the doping depth of the picosecond laser treatment is <50nm.

[0013] Optionally, the method for preparing the BC battery satisfies at least one of the following conditions: A. The temperature for the high-temperature phosphorus diffusion is 800-820℃; B. The junction depth of the high-temperature phosphorus diffusion is >50 nm; C. The sheet resistance of the high-temperature phosphorus diffusion is 50Ω-80Ω; D. The set temperature of the first alumina layer and the second alumina layer is 180-220℃.

[0014] A third aspect of this application provides a photovoltaic module, including the aforementioned BC cell.

[0015] Compared with the prior art, the beneficial effects of this application include: The BC battery provided in this application improves carrier lifetime through the synergistic effect of the gradient phosphorus-doped second phosphorus diffusion layer, the alumina layer, and the silicon nitride layer, and solves the problems of high leakage current and poor doping uniformity in the prior art.

[0016] The method for preparing BC batteries provided in this application employs ultrashort picosecond laser treatment to perform secondary doping modification on phosphorus diffusion. The doping depth is precisely controlled by the laser energy density, avoiding the thermal damage of traditional thermal diffusion. Furthermore, the laser wavelength of the picosecond laser treatment matches the bandgap characteristics of silicon (1064nm), and gradient doping activation is achieved by utilizing the photothermal effect, reducing non-radiative recombination. Additionally, the silicon phosphide nanoparticles undergo lattice reconstruction under laser irradiation, forming a high-concentration doped region to reduce contact resistance.

[0017] The photovoltaic modules provided in this application have low leakage current. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0019] Figure 1 A schematic diagram of the BC battery structure provided in Example 1; Figure 2 A schematic diagram of the BC battery structure provided for Comparative Example 3.

[0020] Explanation of key component symbols: 100 - Silicon substrate; 200 - Boron doped layer; 310 - First phosphorus diffusion layer; 320 - Second phosphorus diffusion layer; 410 - First alumina layer; 420 - Second alumina layer; 510 - First silicon nitride layer; 520 - Second silicon nitride layer; 610 - Ag back contact electrode; 620 - Ag-Al back contact electrode. Detailed Implementation

[0021] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0022] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0023] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0024] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0025] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0026] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0027] The first aspect of this application provides a BC battery, including a silicon substrate; The light-facing surface of the silicon substrate is sequentially provided with a first aluminum oxide layer and a first silicon nitride layer; It should be noted that the grid-free design on the light-facing side effectively reduces light reflectivity and significantly improves photocurrent density; in some embodiments, the grid-free design on the front side reduces light reflectivity from 11% to 1.5% and increases photocurrent density (Jsc) by 7%. The back surface of the silicon substrate is provided with a P-region and an N-region; the P-region includes a boron doped layer; the N-region includes a first phosphorus diffusion layer and a second phosphorus diffusion layer; a second aluminum oxide layer and a second silicon nitride layer are sequentially disposed on the surfaces of the P-region and the N-region. It is important to note that the second alumina layer and the second silicon nitride layer form a gradient passivation structure, which can suppress back surface recombination; the increased refractive index forms an equivalent ohmic contact, and in some embodiments, the refractive index increases from 1.6 to 2.05, and the contact resistivity increases from 1.2 mΩ·cm. 2 Reduced to 0.4 mΩ·cm 2 ; The phosphorus content in the second phosphorus diffusion layer decreases gradually from one side of the second alumina layer to one side of the first phosphorus diffusion layer.

[0028] It is important to note that the gradient phosphorus doping in the second phosphorus diffusion layer enhances minority carrier mobility, and the phosphorus concentration gradient distribution creates a built-in electric field gradient (in some embodiments, E = 100-500 V / cm). At the boundary between the P-region and the NN++ region, the high phosphorus concentration generates a strong electric field (in some embodiments, E = 5 × 10⁻⁶ V / cm). 4 The V / m value accelerates holes (minority carriers), increasing their migration speed (in some embodiments, this can be increased to 1.2 × 10⁻⁶). 3 cm 2 / (V·s). For example, gradient electric fields reduce the residence time of holes at recombination centers, experimentally increasing the minority carrier lifetime from 20 μs to 80 μs. Gradient doping extends the space charge region from 0.5 μm to 1.2 μm, improving carrier collection efficiency by 40%. Gradient doping brings the Fermi level closer to the conduction band in the N++ region (Ec-Ef=0.1 eV) and closer to the valence band in the P region (Ev-Ef=0.3 eV), forming a stepped band structure and reducing carrier recombination across regions.

[0029] The passivation layer suppresses recombination centers. Al₂O₃ passivates dangling bonds on the silicon surface through Si-O-Al bonds (bond energy 460 kJ / mol), reducing the surface state density from 10⁻⁶. 10 cm -2 Reduced to 10 8 cm -2 This improves dangling bond passivation. The oxygen vacancy defect concentration in Al2O3 decreases, and the interface density of states (Dit) increases from 10. 11 cm -2·eV -1 Reduced to 10 10 cm -2 ·eV -1 This reduces the interface state density. (SiN) x The layer (refractive index 1.76-2.05) forms a potential barrier (Φ=0.7eV) at the interface, suppressing metal-induced recombination. SiN x The equivalent refractive index gradient (1.76→2.05) matches the refractive index of silicon (3.4), reducing carrier reflection losses.

[0030] The gradient electric field accelerates carrier transport, while the passivation layer suppresses recombination, thus improving carrier collection efficiency. The reduced recombination rate increases minority carrier lifetime from 20 μs to 80 μs, resulting in a significant improvement in the lifetime of the BC cell.

[0031] In some embodiments, the BC battery satisfies at least one of the following conditions: A. The phosphorus concentration of the first phosphorus diffusion layer is 3.5 × 10⁻⁶. 20 cm -3 -4.5×10 20 cm -3 ; Optionally, the phosphorus concentration of the first phosphorus diffusion layer can be 3.5 × 10⁻⁶. 20 cm -3 4×10 20 cm -3 4.5×10 20 cm -3 Or 3.5×10 20 cm -3 -4.5×10 20 cm -3 Any value between; B. The surface phosphorus content of the second phosphorus diffusion layer near the second alumina layer is 1.5 × 10⁻⁶. 21 cm -3 -4.5×10 21 cm -3 The surface phosphorus content of the second phosphorus diffusion layer, which is closer to the first phosphorus diffusion layer, is 1.5 × 10⁻⁶. 20 cm -3 -3×10 20 cm -3 .

[0032] Optionally, the surface phosphorus content of the second phosphorus diffusion layer near the second alumina layer can be 1.5 × 10⁻⁶. 21 cm -3 2×10 21 cm -3 2.5×10 21cm -3 3×10 21 cm -3 3.5×10 21 cm -3 4×10 21 cm -3 4.5×10 21 cm -3 Or 1.5 × 10 21 cm -3 -4.5×10 21 cm -3 For any value between these ranges, the surface phosphorus content of the second phosphorus diffusion layer, closer to the first phosphorus diffusion layer, can be 1.5 × 10⁻⁶. 20 cm -3 2×10 20 cm -3 2.5×10 20 cm -3 3×10 20 cm -3 Or 1.5 × 10 20 cm -3 -3×10 20 cm -3 Any value between.

[0033] In some embodiments, the BC battery satisfies at least one of the following conditions: A. The thickness of the first phosphorus diffusion layer is 20nm-30nm; Optionally, the thickness of the first phosphorus diffusion layer can be any value between 20 nm, 25 nm, 30 nm, or 20 nm and 30 nm. B. The thickness of the second phosphorus diffusion layer is 8nm-12nm.

[0034] Optionally, the thickness of the second phosphorus diffusion layer can be any value between 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, or 8 nm - 12 nm.

[0035] In some embodiments, the BC battery satisfies at least one of the following conditions: A. The thicknesses of the first alumina layer and the second alumina layer are each 3-5 nm independently; Optionally, the thickness of the first alumina layer and the second alumina layer can each be independently 3nm, 4nm, 5nm or any value between 3-5nm; B. The thicknesses of the first silicon nitride layer and the second silicon nitride layer are each independently 70-90 nm; Optionally, the thickness of the first silicon nitride layer and the second silicon nitride layer can each be independently 70nm, 80nm, 90nm or any value between 70-90nm; It is important to note that the chemical passivation effect of alumina is closely related to its thickness. When the thickness is <3 nm, the passivation of surface dangling bonds is incomplete (interface state density >10). 11 cm -2 ·eV -1 This leads to an increased recombination rate; when the thickness is >5 nm, excess Al... 3+ It will form positive charge centers, weakening the field passivation effect; a 3-5 nm Al2O3 layer can form a stable negative charge density (1×10⁻⁶). 12 cm -2 A strong electric field (>5×10) is formed on the silicon surface. 4 (V / cm) suppresses minority carrier recombination while avoiding carrier tunneling loss caused by excessive thickness.

[0036] The thickness of the first and second silicon nitride layers is 70-90 nm. A gradual change in refractive index (n=1.76→2.05) achieves a full-band reflectivity of <2.5%, thus extending the light absorption path. This thickness range allows for the formation of dense Si-N bonds, suppressing metal-induced recombination, and stabilizing the contact resistivity at 0.4 mΩ·cm. 2 Below. 70-90nm SiN x The layer can reduce sodium ion mobility to 1×10 -15 cm 2 / (V·s), SiN x The difference in thermal expansion coefficients between (ΔL / L=0.04%@1000℃) and silicon (ΔL / L=0.025%@1000℃) is small, which avoids interlayer stress cracking in high-temperature processes and has strong resistance to PID and thermal stability.

[0037] C. The refractive indices of the first silicon nitride layer and the second silicon nitride layer are each independently 1.76-2.05.

[0038] Optionally, the refractive indices of the first silicon nitride layer and the second silicon nitride layer can each be independently 1.76, 1.8, 1.9, 2, 2.05 or any value between 1.76 and 2.05.

[0039] A second aspect of this application provides a method for preparing the BC battery described above, comprising: Silicon wafers are supplied; The silicon wafer is pretreated, boron diffused, laser patterned, and alkaline cleaned to obtain an alkaline cleaned silicon wafer. POCl3 is introduced to clean the silicon wafer with alkali, and then high-temperature phosphorus diffusion is performed to obtain a high-temperature phosphorus diffusion layer. Silicon phosphide nanoparticles were treated with a picosecond laser on the surface of a high-temperature phosphorus diffusion layer to obtain a silicon wafer with gradient phosphorus diffusion. It is important to note that picosecond laser treatment forms a uniform doped layer, enhancing edge passivation. Under laser irradiation, silicon phosphide nanoparticles undergo lattice reconstruction, forming a nanocrystalline structure. The high surface activity of this structure, combined with the chemical passivation effect of the alumina passivation layer, significantly reduces the surface recombination rate. The nanocrystalline particles have an atomic ratio of 30%-50% on their surface, resulting in a significant increase in surface energy and promoting chemical reactivity. The dangling bond density on the nanocrystalline surface reaches 102. 12 cm -2 The high-density reaction sites provided by the nanocrystals, along with the high-density dislocations and grain boundaries on the nanocrystal surface, act as carrier traps, reducing minority carrier recombination time and increasing minority carrier lifetime. The nanocrystal grain boundaries hinder the lateral diffusion of sodium ions in the Al₂O₃ layer, forming a passivation layer penetration inhibition, reducing recombination centers, and stabilizing the contact resistivity at 0.4 mΩ·cm. 2 The following describes how gradient phosphorus doping creates a built-in electric field (E=100-500V / cm), accelerating hole migration to the P-region, reducing recombination loss, and further decreasing the surface recombination rate.

[0040] A first aluminum oxide layer and a first silicon nitride layer are sequentially disposed on the light-facing side of the gradient phosphorus-diffused silicon wafer, and a second aluminum oxide layer and a second silicon nitride layer are sequentially disposed on the back-facing side to obtain a BC battery.

[0041] It is important to note that the gradient passivation layer improves edge leakage current: a chemical passivation interface is formed by depositing a 3-5 nm alumina layer via ALD, combined with the field passivation effect of silicon nitride via PECVD, to construct the gradient passivation layer. The atomic-level deposition precision (±0.1 nm) of ALD ensures the uniformity of the passivation layer thickness and suppresses the P / N region boundary blurring problem caused by traditional masking processes. IV testing shows that this structure reduces the edge leakage current to <0.1 μA / cm. 2 (Traditional process is 0.5-1μA / cm) 2 Thermal damage suppression: Picosecond laser is used for non-contact secondary doping, with a laser pulse width of <12ps and energy density controlled between 0.8-1.2J / cm². 2 Through the synergistic effect of "photothermal-lattice reconstruction", a nanoscale crystal structure is formed on the silicon surface, avoiding the lattice dislocation density >1×10⁻⁶ caused by traditional high-temperature diffusion at 700-900℃. 6 cm -2 The problem is that optimizing the bandgap material reduces recombination. A gradient passivation layer composed of ALD alumina (electron affinity 4.06 eV) and PECVD silicon nitride (conduction band offset 0.5 eV) forms a continuous bandgap structure. This design reduces the minority carrier recombination rate to <102. 3cm / s. The lattice constant of silicon phosphide nanoparticles (5.43 Å) achieves lattice matching with silicon (5.43 Å), reducing the surface recombination rate and avoiding non-radiative recombination centers generated by the high-temperature diffusion of traditional POCl3.

[0042] In some embodiments, an alumina layer is prepared by ALD deposition; and a silicon nitride layer is prepared by PECVD.

[0043] In other embodiments, the passivation layer openings are achieved using laser-induced grooving technology, with a hole diameter accuracy of ±2μm, avoiding contamination caused by traditional photoresist stripping. For example, the laser-induced pulse width is 50ps and the energy density is 1.5J / cm². 2 At this time, the slotting precisely penetrates the passivation layer, exposing the silicon substrate to form interdigitated electrode contact windows. The self-aligned design ensures that the metal gate line (40 μm wide) precisely overlaps with the N+ / P+ region, reducing the light-shielding area to less than 1%. In addition, in some embodiments, the resulting interdigitated electrode layout reduces the lateral resistance, with the series resistance (Rs) decreasing from 0.5 Ω·cm. 2 Reduced to 0.2 Ω·cm 2 The fill factor (FF) was increased to 84%.

[0044] In some embodiments, the method for preparing the BC battery satisfies at least one of the following conditions: A. The particle size of the silicon phosphide nanoparticles is 5-10 nm; Optionally, the particle size of silicon phosphide nanoparticles can be any value between 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, or 5-10nm. B. The purity of the silicon phosphide nanoparticles is ≥99.99%.

[0045] Optionally, the purity of the silicon phosphide nanoparticles can be any value of 99.99%, 99.999%, 99.9999%, or ≥99.99%.

[0046] In some embodiments, the scanning speed of the picosecond laser processing is 80-120 mm / s, and the energy density is 0.8-1.2 J / cm². 2 The pulse duration is 5-15 ps, and the wavelength is 1030-1080 nm.

[0047] Optionally, the scanning speed of the picosecond laser processing can be any value between 80 mm / s, 90 mm / s, 100 mm / s, 110 mm / s, 120 mm / s, or 80-120 mm / s, and the energy density can be 0.8 J / cm². 2 0.9J / cm 2 1 J / cm 2 1.1 J / cm2 1.2 J / cm 2 Or 0.8-1.2 J / cm 2 The pulse can be any value between 5ps, 10ps, 15ps or any value between 5 and 15ps, and the wavelength can be any value between 1030nm, 1050nm, 1080nm or 1030-1080nm.

[0048] It is worth noting that selective doping and patterning are achieved through ultrashort pulse lasers (picosecond laser processing), solving the heat accumulation problem of traditional photolithography processes. Picosecond lasers offer high energy density (0.8-1.2 J / cm²). 2 It can instantly vaporize the surface of silicon phosphide nanoparticles to form a localized high-concentration doped region, while avoiding thermal damage to the silicon substrate (heat-affected zone <0.1μm); the scanning speed of picosecond laser processing (80-120mm / s) works synergistically with the leveling properties of the silicon phosphide nanoparticle suspension to make the phosphorus doping concentration gradient (junction depth <50nm) steeper, reducing leakage current in the P / N region; and, by using picosecond laser processing for direct writing, replacing traditional mask lithography, 30% of the process steps can be reduced.

[0049] In some embodiments, the doping depth of the picosecond laser treatment is <50nm.

[0050] Optionally, the doping depth of the picosecond laser treatment can be any value of 1nm, 5nm, 10nm, 20nm, 30nm, 40nm, 49nm or <50nm.

[0051] In some embodiments, the method for preparing the BC battery satisfies at least one of the following conditions: A. The temperature for the high-temperature phosphorus diffusion is 800-820℃; Optionally, the temperature for high-temperature phosphorus diffusion can be 800℃, 810℃, 820℃ or any value between 800℃ and 820℃; B. The junction depth of the high-temperature phosphorus diffusion is >50 nm; Optionally, the junction depth of high-temperature phosphorus diffusion can be any value of 55nm, 60nm, 70nm, 80nm, 90nm, 100nm or >50nm; C. The sheet resistance of the high-temperature phosphorus diffusion is 50Ω-80Ω; Optionally, the sheet resistance of high-temperature phosphorus diffusion can be any value between 50Ω, 60Ω, 70Ω, 80Ω, or 50Ω-80Ω; D. The set temperature of the first alumina layer and the second alumina layer is 180-220℃.

[0052] Optionally, the temperature of the first alumina layer and the first alumina layer can be set independently to 180℃, 200℃, 220℃ or any value between 180℃ and 220℃.

[0053] A third aspect of this application provides a photovoltaic module, including the aforementioned BC cell.

[0054] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0055] Example 1 The first aspect of this embodiment provides a BC battery, the specific structure of which is as follows: Figure 1 As shown, the device includes a silicon substrate 100. The back surface of the silicon substrate is provided with a P-region and an N-region. The P-region includes a boron doped layer 200, and the N-region includes a first phosphorus diffusion layer 310 and a second phosphorus diffusion layer 320. A second alumina layer 420 and a second silicon nitride layer 520 are sequentially disposed on the surfaces of the P-region and the N-region. An Ag back contact electrode 610 is also disposed in the N-region, and an Ag-Al back contact electrode 620 is disposed in the P-region. The light-facing surface of the silicon substrate 100 is sequentially provided with a first alumina layer 410 and a first silicon nitride layer 510.

[0056] The first phosphorus diffusion layer 310 has a thickness of 25 nm and a phosphorus concentration of 4 × 10⁻⁶. 20 cm -3 ; The phosphorus content in the second phosphorus diffusion layer 320 decreases gradually from one side of the second alumina layer 420 to the side of the first phosphorus diffusion layer 310. The surface phosphorus content of the second phosphorus diffusion layer 320 near the second alumina layer 420 is 3 × 10⁻⁶. 21 cm -3 The surface phosphorus content of the second phosphorus diffusion layer 320, located near the first phosphorus diffusion layer 310, is 2.3 × 10⁻⁶. 20 cm -3 The thickness of the second phosphorus diffusion layer 320 is 10 nm. The thicknesses of the first alumina layer 410 and the first silicon nitride layer 510 are 4 nm and 80 nm, respectively, and the thicknesses of the second alumina layer 420 and the second silicon nitride layer 520 are 4 nm and 80 nm, respectively; the refractive indexes of the first silicon nitride layer 510 and the second silicon nitride layer 520 are 2.05.

[0057] The second aspect of this embodiment provides a method for preparing a BC battery, the specific steps of which are as follows: S1: Silicon wafer pretreatment: Using 182mm×182mm N-type monocrystalline silicon wafers (resistivity 0.5Ω·cm), surface impurities are removed by chemical cleaning, and the reflectivity after texturing is 40%; S2: Boron diffusion forms a P+ emitter. BBr3 tube diffusion is used, and BBr3 gas is introduced at 830℃-850℃ to form a boron doped layer (sheet resistance is 125Ω). S3: Laser patterning to remove boron doping: Using a green laser (pulse width 10ps, wavelength 1064nm), power 67W, and marking speed 36000mm / S, the BSG layer is penetrated and modified. S4: Alkaline cleaning: Use 5% NaOH solution to clean for 110 seconds to remove modified BSG, exposing the silicon substrate to facilitate the next step of N+ emitter preparation; S5: High-temperature phosphorus diffusion is used to prepare the N+ back field. POCl3 gas is introduced at 810℃, and the N+ region is formed by conventional masking process (junction depth > 50nm, sheet resistance 50-80Ω). S6: Selective laser doping was used to prepare the N++ back field. Silicon phosphide nanoparticles (8nm diameter, ≥99.99% purity) were activated by the laser thermal effect, forming a heavily doped N++ region with a doping concentration gradient on the N+ surface, thus suppressing leakage current. Laser type: picosecond laser (10ps pulse width, 1064nm wavelength), energy density 0.8J / cm². 2 The scanning speed is 100 mm / s, which accurately penetrates the phosphorus-expanded PSG layer; S7: ALD alumina layer, deposited at 200℃, forming a dense alumina passivation layer; PECVD silicon nitride layer: A silicon nitride layer is formed on the surface of an alumina layer; S8: Laser grooving and metallization: Laser parameters: pulse width 50ps, energy density 1.5J / cm² 2 The groove depth extends to the bottom of the polysilicon layer; Then, screen printing is performed using silver-aluminum paste (sintering temperature 780℃), with a contact resistivity of <0.5mΩ·cm. 2 , thus obtaining BC battery.

[0058] Example 2 The difference from Example 1 is that in step S6, the energy density is 1.2 J / cm³. 2 .

[0059] Example 3 The difference from Example 1 is that the surface phosphorus content of the second phosphorus diffusion layer near the second alumina layer is 1.5 × 10⁻⁶. 21 cm -3 The surface phosphorus content of the second phosphorus diffusion layer, located near the first phosphorus diffusion layer, is 1.5 × 10⁻⁶. 20cm -3 The thickness of the second phosphorus diffusion layer 320 is 8 nm.

[0060] Comparative Example 1 The difference from Example 1 is that in step S6, the energy density is 0.5 J / cm³. 2 .

[0061] Comparative Example 2 The difference from Example 1 is that in step S6, the energy density is 1.5 J / cm³. 2 .

[0062] Comparative Example 3 The difference from Example 1 is that the BC battery is prepared using conventional processes, wherein the thickness of the second silicon nitride layer 520 is 100 nm, and the thickness of the first silicon nitride layer 510 is 100 nm; the specific structure is as follows. Figure 2 As shown, the relevant preparation methods are as follows: S9: PECVD silicon nitride layer: Silane 200 sccm, ammonia 150 sccm, silicon oxynitride 50 sccm, nitrogen 2000 sccm, pressure 30 pA, auxiliary heating temperature 420℃, deposition for 25 min to prepare silicon nitride layer.

[0063] Comparative Example 4 The difference from Example 1 is that in step S6, an N++ back field is prepared using a 15wt% POCl3 liquid source. The specific preparation method is as follows: A low nitrogen flow rate of 1200 sccm (nitrogen source), a temperature of 800℃ for 2.5 min deposition, and a temperature increase to 880℃ for 2 min propagation were used to prepare the N++ back field.

[0064] Comparative Example 5 The difference from Example 1 is that no aluminum oxide layer is provided in step S7.

[0065] The BC batteries prepared in Examples 1 and 2 and Comparative Examples 1, 2 and 3 were subjected to performance tests, and the specific results are shown in Table 1.

[0066] Table 1 Performance Tests

[0067] The doping uniformity of the BC batteries prepared in the above examples and comparative examples was tested, and the specific results are shown in Table 2.

[0068] Table 2 Doping Uniformity Test

[0069] analyze: As can be seen from the above results, the embodiment effectively improved the CV value by forming gradient doping through laser phosphorus doping, and combined with the passivation layer, it reduced the recombination rate and improved the passivation effect, resulting in a significant advantage in minority carrier lifetime.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0071] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A BC battery, characterized in that, Including silicon substrate; The light-facing surface of the silicon substrate is sequentially provided with a first aluminum oxide layer and a first silicon nitride layer; The back surface of the silicon substrate is provided with a P-region and an N-region; the P-region includes a boron doped layer; the N-region includes a first phosphorus diffusion layer and a second phosphorus diffusion layer; a second aluminum oxide layer and a second silicon nitride layer are sequentially disposed on the surfaces of the P-region and the N-region. The phosphorus content in the second phosphorus diffusion layer decreases gradually from one side of the second alumina layer to one side of the first phosphorus diffusion layer.

2. The BC battery according to claim 1, characterized in that, At least one of the following conditions must be met: A. The phosphorus concentration of the first phosphorus diffusion layer is 3.5 × 10⁻⁶. 20 cm -3 -4.5×10 20 cm -3 ; B. The surface phosphorus content of the second phosphorus diffusion layer near the second alumina layer is 1.5 × 10⁻⁶. 21 cm -3 -4.5×10 21 cm -3 The surface phosphorus content of the second phosphorus diffusion layer, which is closer to the first phosphorus diffusion layer, is 1.5 × 10⁻⁶. 20 cm -3 -3×10 20 cm -3 .

3. The BC battery according to claim 1, characterized in that, At least one of the following conditions must be met: A. The thickness of the first phosphorus diffusion layer is 20nm-30nm; B. The thickness of the second phosphorus diffusion layer is 8nm-12nm.

4. The BC battery according to claim 1, characterized in that, At least one of the following conditions must be met: A. The thicknesses of the first alumina layer and the second alumina layer are each 3-5 nm independently; B. The thicknesses of the first silicon nitride layer and the second silicon nitride layer are each independently 70-90 nm; C. The refractive indices of the first silicon nitride layer and the second silicon nitride layer are each independently 1.76-2.

05.

5. A method for preparing a BC battery as described in any one of claims 1-4, characterized in that, include: Silicon wafers are supplied; The silicon wafer is pretreated, boron diffused, laser patterned, and alkaline cleaned to obtain an alkaline cleaned silicon wafer. POCl3 is introduced to clean the silicon wafer with alkali, and then high-temperature phosphorus diffusion is performed to obtain a high-temperature phosphorus diffusion layer. Silicon phosphide nanoparticles were treated with a picosecond laser on the surface of a high-temperature phosphorus diffusion layer to obtain a silicon wafer with gradient phosphorus diffusion. A first aluminum oxide layer and a first silicon nitride layer are sequentially disposed on the light-facing side of the gradient phosphorus-diffused silicon wafer, and a second aluminum oxide layer and a second silicon nitride layer are sequentially disposed on the back-facing side to obtain a BC battery.

6. The method for preparing a BC battery according to claim 5, characterized in that, At least one of the following conditions must be met: A. The particle size of the silicon phosphide nanoparticles is 5-10 nm; B. The purity of the silicon phosphide nanoparticles is ≥99.99%.

7. The method for preparing a BC battery according to claim 5, characterized in that, The picosecond laser processing has a scanning speed of 80-120 mm / s and an energy density of 0.8-1.2 J / cm². 2 The pulse duration is 5-15 ps, and the wavelength is 1030-1080 nm.

8. The method for preparing a BC battery according to claim 5, characterized in that, The doping depth of the picosecond laser treatment is <50nm.

9. The method for preparing a BC battery according to claim 5, characterized in that, At least one of the following conditions must be met: A. The temperature for the high-temperature phosphorus diffusion is 800-820℃; B. The junction depth of the high-temperature phosphorus diffusion is >50 nm; C. The sheet resistance of the high-temperature phosphorus diffusion is 50Ω-80Ω; D. The setting temperatures of the first alumina layer and the second alumina layer are each independently 180-220℃.

10. A photovoltaic module, characterized in that, Includes the BC battery as described in any one of claims 1-4.

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