Back contact solar cell, preparation method thereof and cell module

Abstract

The invention belongs to the technical field of back contact solar cells, and particularly relates to a back contact solar cell, a preparation method thereof and a cell assembly, the back contact solar cell comprises a P-type doped region, an N-type doped film layer and a co-doped region which are arranged at intervals on the surface of an intrinsic amorphous silicon layer, and phosphorus and boron are doped in the co-doped region; wherein the surface phosphorus doping concentration of the N-type doped film layer is less than or equal to 1e22cm <-3 >, and the surface phosphorus doping concentration of the N-type doped film layer is lower than or equal to the average phosphorus doping concentration of the N-type doped film layer; the surface boron-doped concentration of the P-type doped region is greater than or equal to 5e21cm <-3 >, and the surface boron-doped concentration of the P-type doped region is higher than or equal to the average boron-doped concentration of the P-type doped region. The contact resistance is effectively reduced, the cell filling factor is improved, the cell efficiency and reliability are improved, the cell yield is improved, multiple times of etching and cleaning in traditional structure preparation are not needed, the manufacturing process is simple, and the process difficulty and cost are reduced.

Description

Technical Field

[0001] This invention belongs to the field of back-contact solar cell technology, specifically relating to a back-contact solar cell, its preparation method, and a battery module. Background Technology

[0002] Back-contact solar cells, with all electrodes located on the back of the cell and no metal grid lines obstructing the front, increase the light-receiving area and are considered the most efficient solar cells, closest to the theoretical efficiency of crystalline silicon solar cells. However, because both the positive and negative electrodes of back-contact solar cells are located on the back, multiple laser etching or chemical etching steps are typically required to process the positive and negative areas separately, as well as multiple cleaning steps. Each step can increase the difficulty of the process and cause damage to the cell, affecting its efficiency. Especially during large-scale production, process control becomes more difficult, resulting in higher equipment investment and manufacturing costs, lower product yield, and hindering its large-scale industrial application.

[0003] Furthermore, in traditional back-contact solar cell fabrication processes, PECVD deposition is used to deposit n-type and p-type doped layers, inevitably forming an N / P semiconductor stack (i.e., N-type and P-type doped semiconductors are stacked in the thickness direction). This N / P semiconductor stack forms a junction with a built-in electric field. Even at zero bias, there may be trace carrier exchange in the space charge region of this junction, creating potential parasitic leakage paths that cause leakage losses, thereby reducing cell efficiency.

[0004] It should be noted that this part of the present invention only provides background technology related to the present invention, and does not necessarily constitute prior art or known technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing back-contact solar cell structures, such as leakage loss leading to low cell efficiency, low cell yield, and high manufacturing difficulty. This invention provides a back-contact solar cell, its fabrication method, and cell module. This invention effectively reduces contact resistance, increases cell fill factor, improves cell efficiency and reliability, and increases cell yield. Furthermore, it eliminates the need for multiple etching and cleaning processes required in traditional structure fabrication, simplifying the manufacturing process and reducing manufacturing difficulty and cost.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a back-contact solar cell, comprising a silicon wafer, an intrinsic amorphous silicon layer disposed on the back side of the silicon wafer, P-type doped regions spaced apart on the surface of the intrinsic amorphous silicon layer, an N-type doped film layer disposed outside the intrinsic amorphous silicon layer and located at the intervals between the P-type doped regions, and co-doped regions disposed on both ends of the N-type doped film layer connected to the P-type doped regions, wherein phosphorus and boron are doped in the co-doped regions; wherein the N-type doped film layer has a graded doping structure and the graded doping structure satisfies: the surface phosphorus concentration of the N-type doped film layer is ≤1e22cm³. -3 The surface phosphorus concentration of the N-type doped film is lower than or equal to the average phosphorus concentration of the N-type doped film; the P-type doped region has a graded doping structure and the graded doping structure satisfies: the surface boron concentration of the P-type doped region is ≥5e21cm. -3 The surface boron concentration of the P-type doped region is higher than or equal to the average boron concentration of the P-type doped region.

[0007] In some preferred embodiments of the present invention, the phosphorus doping concentration of the N-type doped film is 1e20cm⁻¹. -3 -1e22cm -3 And / or, the boron doping concentration of the P-type doped region is 1e20cm⁻¹. -3 -3e22cm -3 .

[0008] In some preferred embodiments of the present invention, the ratio of the surface phosphorus concentration of the N-type doped film to the average phosphorus concentration of the N-type doped film is (0.3-1):1, and / or the ratio of the surface boron concentration of the P-type doped region to the average boron concentration of the P-type doped region is (1-7):1.

[0009] In some preferred embodiments of the present invention, the sum of the thicknesses of the intrinsic amorphous silicon layer and the P-type doped region is less than the sum of the thicknesses of the intrinsic amorphous silicon layer and the N-type doped film.

[0010] In some preferred embodiments of the present invention, the thickness of the N-type doped film is 5-20 nm, and / or the thickness of the P-type doped region is 5-10 nm.

[0011] In some preferred embodiments of the present invention, the thickness of the intrinsic amorphous silicon layer is 8-20 nm, and / or the thickness of the co-doped region is 5-20 nm.

[0012] In some preferred embodiments of the present invention, the width of the co-doped region is 10-100µm, and / or the ratio of the width of the N-type doped film to the width of the P-type doped region and the co-doped region is 1:(1-2.4):(0.03-0.3).

[0013] In some preferred embodiments of the present invention, the phosphorus doping concentration of the co-doped region is 1e20cm⁻¹.-3 -1e22cm -3 Boron doping concentration of 1e20cm -3 -3e22cm -3 .

[0014] In some preferred embodiments of the present invention, the boron doping concentration of the P-type doped region gradually increases in the vertical direction outward from the back side of the silicon wafer; and / or, the boron doping concentration of the co-doped region gradually decreases in the direction away from the P-type doped region.

[0015] In some preferred embodiments of the present invention, the back-contact solar cell has at least one of the following structures:

[0016] Structure 1: The back contact solar cell also includes: a conductive film layer disposed on the overall outer surface of the N-type doped film layer, the P-type doped region, and the co-doped region; an isolation trench disposed in a portion of the conductive film layer between the N-type doped film layer and the P-type doped region; and metal electrodes disposed on the corresponding conductive film layers outside the N-type doped film layer and the P-type doped region.

[0017] Structure 2: Back-contact solar cells also include a passivation and anti-reflection layer disposed on the front side of the silicon wafer;

[0018] Structure 3: The N-type doped film is an N-type doped amorphous silicon, microcrystalline silicon, or nanocrystalline silicon layer, and the P-type doped region is a P-type doped amorphous silicon.

[0019] Secondly, the present invention provides a method for preparing a back-contact solar cell, comprising the following steps:

[0020] S1. Provide silicon wafers;

[0021] S2. Deposit an intrinsic amorphous silicon layer on the back side of the silicon wafer;

[0022] S3. Place a first mask in a preset first mask area outside the intrinsic amorphous silicon layer on the back side, and use PECVD deposition process to deposit an N-type doped film layer arranged at intervals outside the intrinsic amorphous silicon layer in the non-mask area.

[0023] S4. Then, place a second mask in the preset second mask area outside the N-type doped film layer on the back side. Using the PECVD ion implantation process, implant boron into the surface of the intrinsic amorphous silicon layer in the non-mask area to form a P-type doped region that is alternately arranged with the N-type doped film layer. At the same time, boron atoms enter the end of the N-type doped film layer to form a co-doped region. The co-doped region is located between the N-type doped film layer and the P-type doped region. Phosphorus and boron are doped in the co-doped region.

[0024] Among them, the N-type doped film layer is controlled to have a graded doping structure, and the graded doping structure satisfies: the surface phosphorus concentration of the N-type doped film layer is ≤1e22cm. -3The surface phosphorus concentration of the N-type doped film is lower than or equal to the average phosphorus concentration of the N-type doped film; the P-type doped region has a graded doping structure and the graded doping structure satisfies: the surface boron concentration of the P-type doped region is ≥5e21cm. -3 The surface boron concentration of the P-type doped region is higher than or equal to the average boron concentration of the P-type doped region.

[0025] In some preferred embodiments of the present invention, the conditions of the PECVD deposition process in S3 include: deposition temperature of 30-180°C, chamber pressure of 40-300Pa, and radio frequency power of 500-30000W.

[0026] In some preferred embodiments of the present invention, the PECVD deposition process in S3 is carried out under the condition of introducing a mixed gas of silane, phosphine and hydrogen, wherein the silane flow rate is 50-5000 sccm, the phosphine flow rate is 5-500 sccm, and the hydrogen flow rate is 1000-100000 sccm.

[0027] In some preferred embodiments of the present invention, the conditions of the PECVD ion implantation process in S4 include: a substrate temperature of 25-180°C and an accelerating voltage of 200-2000V.

[0028] In some preferred embodiments of the present invention, the PECVD ion implantation process in S4 is carried out under the condition of introducing a mixed gas of diborane, hydrogen and argon, wherein the flow rate of diborane is 20-2000 sccm, the flow rate of hydrogen is 1000-10000 sccm, and the flow rate of argon is 2000-100000 sccm.

[0029] In some preferred embodiments of the present invention, the preparation method further includes at least one of the following processes:

[0030] Process 1: The thickness of the intrinsic amorphous silicon layer is 8-20 nm;

[0031] Process 2: The N-type doped film is an N-type doped amorphous silicon, microcrystalline silicon, or nanocrystalline silicon layer;

[0032] Process 3: The sum of the thicknesses of the intrinsic amorphous silicon layer and the P-type doped region is less than the sum of the thicknesses of the intrinsic amorphous silicon layer and the N-type doped film.

[0033] Process 4: The phosphorus doping concentration of the N-type doped film is 1e20cm. -3 -1e22cm -3 The boron doping concentration in the P-type doped region is 1e20cm. -3 -3e22cm -3 ;

[0034] Process 5: The thickness of the N-type doped film is 5-20 nm, and the thickness of the P-type doped region is 5-10 nm;

[0035] Process 6: The width of the co-doped region is 10-100µm, and the thickness of the co-doped region is 5-20nm;

[0036] Process 7: The phosphorus doping concentration in the co-doped region is 1e20cm⁻¹ -3 -1e22cm -3 Boron doping concentration of 1e20cm -3 -3e22cm -3 ;

[0037] Process 8, the preparation method also includes: setting a passivation antireflection layer on the front side of the silicon wafer;

[0038] Process 9, the preparation method also includes the following steps:

[0039] S5. Deposit a conductive film outside the back co-doped region, the N-type doped film, and the P-type doped region;

[0040] S6. Etch on the corresponding conductive film layer located between the N-type doped film layer and the P-type doped region to form an isolation trench;

[0041] S7. Metal electrodes are respectively disposed on the outside of the conductive film layers corresponding to the N-type doped film layer and the P-type doped region.

[0042] Thirdly, the present invention provides a back-contact solar cell, which is prepared by the back-contact solar cell preparation method described in the second aspect.

[0043] Fourthly, the present invention provides a battery assembly comprising the back-contact solar cell described in the first aspect, or the back-contact solar cell described in the third aspect.

[0044] Beneficial effects:

[0045] This invention, through the aforementioned technical solution, particularly by setting a specific structure of P-type doped regions and N-type doped films on an intrinsic amorphous silicon layer, and by designating the ends of the N-type doped films as co-doped regions, and by controlling the surface phosphorus concentration range of the N-type doped film and ensuring it is lower than or equal to the average phosphorus concentration of the N-type doped film, and the surface boron concentration range of the P-type doped region and ensuring it is higher than or equal to the average boron concentration of the P-type doped region, achieves a structure in which the doping distribution of both the P-type and N-type doped regions exhibits a special gradient distribution. Combined with the connection of the phosphorus and boron co-doped regions, this ensures a smooth connection from the heavily doped contact region of the corresponding film layer to the intrinsic amorphous silicon layer (passivation region). This invention avoids resistance loss when charge carriers cross multiple abrupt interfaces, forming a good ohmic contact, effectively reducing contact resistance and improving the battery fill factor. Furthermore, the co-doped region provides effective physical isolation, and the entire isolation layer is formed from the same material as the N-type doped film, eliminating the mismatch in thermal expansion coefficients or intrinsic stress differences between the two layers formed under different deposition conditions. This avoids long-term reliability issues such as film delamination and cracking caused by stress, thus improving the long-term reliability of the battery. Moreover, this invention eliminates the need for N / P semiconductor stacks, effectively avoiding leakage losses. These combined effects synergistically improve battery efficiency and reliability, increasing battery yield.

[0046] Specifically, controlling the surface phosphorus concentration range of the N-type doped film and ensuring it is lower than or equal to the average phosphorus concentration of the N-type doped film is beneficial for improving the film's resistance to water vapor and alkaline corrosion. This reduces the impact of subsequent chemical treatments on the film's performance during the fabrication of back-contact solar cells, thus improving cell efficiency and reliability. Conversely, controlling the surface boron concentration range of the P-type doped region and ensuring it is higher than or equal to the average boron concentration of the P-type doped region creates a high-concentration, shallow-junction, and uniformly gradient boron doping. This helps reduce contact resistance, forms a good ohmic contact, increases the cell fill factor and open-circuit voltage, improves cell efficiency and reliability, and increases cell yield.

[0047] The preparation method of the present invention, through the above technical solution, especially after the intrinsic amorphous silicon layer on the back side, uses PECVD deposition process to deposit an N-type doped film layer based on the dry masking method, and uses PECVD ion implantation process to form a P-type doped region. It eliminates the need for multiple etching and cleaning in the traditional structure preparation, and the fabrication process is simple. At the same time, it can effectively reduce contact resistance and improve fill factor and open circuit voltage, thereby improving battery efficiency, reliability and battery yield.

[0048] Among these methods, the PECVD deposition process, which deposits an N-type doped film on the intrinsic amorphous silicon layer, yields a high-quality film with high hydrogen content and low defect state density, providing excellent surface passivation and ensuring a high open-circuit voltage for the battery. Combined with PECVD ion implantation to implant boron atoms onto the surface of the intrinsic amorphous silicon layer to form a P-type doped region, high doping concentration, shallow junction, and uniformly gradient boron doping can be achieved at low temperatures. This helps reduce contact resistance, forming a good ohmic contact. Furthermore, the boron doping gradient ensures a smooth connection from the heavily doped contact region to the intrinsic amorphous silicon layer (passivation region), avoiding resistance loss when carriers cross multiple abrupt interfaces. Simultaneously, the use of PECVD... The co-doped region formed by depositing an N-type doped film and then ion implanting boron atoms captures or compensates for the original free electrons, reducing the net carrier concentration of the co-doped region and creating a high-resistivity state. This provides excellent isolation and effectively blocks the adverse effects of subsequent processes on the surface film. Furthermore, the co-doped region provides effective physical isolation, and the entire isolation layer is made of the same material as the N-type doped film. There is no mismatch in the coefficient of thermal expansion or intrinsic stress difference between the two layers formed under different deposition conditions, avoiding long-term reliability issues such as film delamination and cracking caused by stress. This improves battery efficiency, reliability, and yield.

[0049] In this invention, different PECVD methods are used to control the surface phosphorus concentration of the N-type doped film and its level to be lower than or equal to the average phosphorus concentration of the N-type doped film, and to control the surface boron concentration of the P-type doped region and its level to be higher than or equal to the average boron concentration of the P-type doped region. This not only improves the reliability of the battery but also enhances its electrical performance, thereby increasing battery efficiency. This is because: the alkali resistance of the N-type doped film is inferior to that of the P-type doped region; the PECVD deposition method for the N-type doped film allows for better control of the surface doping concentration within a suitable and reliable range; the PECVD ion implantation method for the P-type doped region can achieve a higher surface doping concentration and is less affected by alkaline solutions, thereby reducing contact resistance and increasing the battery fill factor; thus improving battery efficiency, reliability, and yield. Attached Figure Description

[0050] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 This is a schematic diagram of the structure of a silicon wafer in one embodiment of the present invention.

[0052] Figure 2This is a schematic diagram of the structure of an intrinsic amorphous silicon layer deposited on a silicon wafer in one embodiment of the present invention.

[0053] Figure 3 This is a schematic diagram of a structure in which a first mask A is placed outside an intrinsic amorphous silicon layer in one embodiment of the present invention.

[0054] Figure 4 This is a schematic diagram of the structure of an intrinsic amorphous silicon layer deposited with an N-type doped film in one embodiment of the present invention.

[0055] Figure 5 This is a schematic diagram of a structure in which a first mask B is placed outside an N-type doped film layer in one embodiment of the present invention.

[0056] Figure 6 This is a schematic diagram of the structure of an intrinsic amorphous silicon layer formed by ion implantation to create a P-type doped region and a co-doped region, according to one embodiment of the present invention.

[0057] Figure 7 This is a partial structural schematic diagram of a back-contact solar cell in one specific embodiment of the present invention.

[0058] Explanation of reference numerals in the attached figures

[0059] 1. Silicon wafer, 2. Intrinsic amorphous silicon layer, 3. N-type doped film layer, 4. P-type doped region, 5. Co-doped region, 6. Transparent conductive film layer, 7. Isolation trench, 8. Metal electrode, A. First mask, B. Second mask. Detailed Implementation

[0060] In this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0061] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0062] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges. For numerical ranges, the endpoint values ​​of the ranges, the endpoint values ​​of the ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "optional" mean that they may or may not be included (or may or may not be present).

[0063] In this invention, the area closer to the silicon wafer is considered the inside, and the area farther from the silicon wafer is considered the outside.

[0064] In a first aspect, the present invention provides a back-contact solar cell, comprising a silicon wafer, an intrinsic amorphous silicon layer disposed on the back side of the silicon wafer, P-type doped regions spaced apart on the surface of the intrinsic amorphous silicon layer, an N-type doped film layer disposed outside the intrinsic amorphous silicon layer and located at the intervals between the P-type doped regions, and co-doped regions disposed on both ends of the N-type doped film layer connected to the P-type doped regions, wherein phosphorus and boron are doped in the co-doped regions.

[0065] Preferably, in this invention, the N-type doped film has a graded doping structure, and the graded doping structure satisfies the following: the surface phosphorus concentration of the N-type doped film is ≤1e22cm⁻¹. -3 The surface phosphorus concentration of the N-type doped film is lower than or equal to the average phosphorus concentration of the N-type doped film; the P-type doped region has a graded doping structure and the graded doping structure satisfies: the surface boron concentration of the P-type doped region is ≥5e21cm. -3 The surface boron concentration of the P-type doped region is higher than or equal to the average boron concentration of the P-type doped region. In this invention, a gradient doping structure refers to a structure where the doping concentration of the corresponding doping element exhibits a non-uniform doping concentration gradient. This can also be interpreted as the doping concentration at different locations being at least partially different, as long as the aforementioned surface doping concentration and average doping concentration requirements are met.

[0066] In this invention, the phosphorus concentration of the N-type doped film and the boron concentration of the P-type doped region are both adopted with a gradual doping distribution that satisfies the aforementioned doping concentrations. Combined with the connection of the co-doped regions of phosphorus and boron, a smooth connection is ensured from the heavily doped contact region of the corresponding film to the intrinsic amorphous silicon layer (passivation region). This avoids resistance loss when charge carriers cross multiple abrupt interfaces, forms a good ohmic contact, effectively reduces contact resistance, improves the battery fill factor, and thus improves battery efficiency and battery yield.

[0067] In this invention, the average phosphorus doping concentration of the N-type doped film was obtained by SIMS (secondary ion mass spectrometry). The average boron doping concentration of the P-type doped region was obtained similarly.

[0068] In some preferred embodiments of the present invention, the phosphorus doping concentration of the N-type doped film is 1e20cm⁻¹. -3 -1e22cm -3 And / or, the boron doping concentration of the P-type doped region is 1e20cm⁻¹. -3 -3e22cm -3 In this invention, the surface doping concentration and the internal doping concentration of the N-type doped film and the P-type doped region each need to satisfy the aforementioned corresponding ranges.

[0069] The surface phosphorus doping concentration of the N-type doped film is ≤1e22cm⁻¹ -3 For example, it can be 1e20cm -3 2e20cm -3 3e20cm -3 4e20cm -3 5e20cm -3 6e20cm -3 7e20cm -3 8e20cm -3 9e20cm -3 1e21cm -3 2e21cm -3 3e21cm -3 ,4e21cm -3 5e21cm -3 6e21cm -3 7e21cm -3 8e21cm -3 9e21cm -3 or 1e22cm -3 And the range between any two point values.

[0070] The surface boron doping concentration of the P-type doped region is ≥5e21cm. -3 For example, it could be 5e21cm -3 6e21cm -3 7e21cm -3 8e21cm -3 9e21cm -3 1e22cm -3 2e22cm -3 Or 3e22cm -3 And the range between any two point values.

[0071] In some preferred embodiments of the present invention, the ratio of the surface phosphorus concentration of the N-type doped film to the average phosphorus concentration of the N-type doped film is (0.3-1):1, for example, it can be 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1 or 1:1, etc., and any range between any two point values. In some specific embodiments, it is more preferred to be (0.3-0.9):1.

[0072] Preferably, the ratio of the surface boron concentration of the P-type doped region to the average boron concentration of the P-type doped region is (1-7):1. For example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.2:1, 2.5:1, 2.7:1, 3:1, 3.2:1, 3.5:1, 3.7:1, 4:1, 4.2:1, 4.5:1, 4.8:1, 5:1, 5.2:1, 5.5:1, 5.7:1, 5.8:1, 5.9:1, 6:1, or 7:1, as well as any range between two points. In some specific embodiments, (1.1-7):1 is more preferred.

[0073] By adopting the above-mentioned preferred embodiment of the present invention, the distribution of phosphorus doping concentration in the N-type doped film and boron doping concentration in the P-type doped region becomes more gradual, which is more conducive to forming good ohmic contact, effectively reducing contact resistance, improving battery fill factor, and thus improving battery efficiency and battery yield.

[0074] In some preferred embodiments of the present invention, the sum of the thicknesses of the intrinsic amorphous silicon layer and the P-type doped region is less than the sum of the thicknesses of the intrinsic amorphous silicon layer and the N-type doped film. This preferred embodiment of the present invention is more conducive to effectively reducing carrier recombination in the co-doped region.

[0075] In some preferred embodiments of the present invention, the thickness of the N-type doped film is 5-20 nm, for example, it can be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm or 20 nm, or any range between any two point values.

[0076] Preferably, the thickness of the P-type doped region is 5-10 nm, for example, it can be 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm or 10 nm, or any range between two points.

[0077] In some preferred embodiments of the present invention, the thickness of the intrinsic amorphous silicon layer is 8-20 nm, for example, it can be 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, or 20 nm, or any range between two points. The present invention uses an intrinsic amorphous silicon layer of suitable thickness as the passivation layer for the N-type doped film and the P-type doped region, which is more conducive to achieving good surface passivation for both the N-type doped film and the P-type doped region.

[0078] Preferably, the thickness of the co-doped region in this invention is 5-20 nm, for example, it can be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, or 20 nm, or any range between two values. The thickness of the co-doped region may be the same as or different from the thickness of the N-type doped film.

[0079] In some preferred embodiments of the present invention, the width of the co-doped region is 10-100µm, for example, it can be 10µm, 15µm, 20µm, 25µm, 30µm, 35µm, 40µm, 45µm, 50µm, 55µm, 60µm, 65µm, 70µm, 75µm, 80µm, 85µm, 90µm, 95µm, or 100µm, or any range between two points. The present invention uses a co-doped region of suitable width, which is more conducive to effectively isolating the N-type doped film and the P-type doped region.

[0080] Preferably, the width ratio of the N-type doped film to the P-type doped region and co-doped region is 1:(1-2.4):(0.03-0.3), for example, it can be 1:(1, 1.1, 1.2, 1.5, 1.7, 1.9, 2, 2.1, 2.2, 2.3 or 2.4 and any range between two points):(0.03, 0.05, 0.07, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.22, 0.25, 0.29 or 0.3 and any range between two points). Using an appropriate width ratio for the N-type doped film, P-type doped region, and co-doped region is more conducive to improving carrier collection efficiency and reducing leakage current.

[0081] In some preferred embodiments of the present invention, the phosphorus doping concentration of the co-doped region is 1e20cm⁻¹. -3 -1e22cm -3 Boron doping concentration of 1e20cm -3 -3e22cm -3This invention employs a co-doped region with an appropriate doping concentration, which is more conducive to improving the isolation and insulation effect, and further improving battery efficiency and yield.

[0082] In some preferred embodiments of the present invention, the boron doping concentration of the P-type doped region gradually increases in the vertical direction outward from the back side of the silicon wafer. This preferred scheme of a gradually increasing boron doping concentration in the P-type doped region is more conducive to reducing contact resistance, forming good ohmic contacts, improving the cell fill factor and open-circuit voltage, and enhancing cell efficiency, reliability, and yield.

[0083] Preferably, in this invention, the boron concentration in the co-doped region gradually decreases along the direction away from the P-type doped region. This preferred co-doped region design further enhances the isolation and insulation effect, thereby improving battery efficiency and yield.

[0084] In some preferred embodiments of the present invention, the back-contact solar cell further includes: a conductive film layer disposed on the overall outer surface of the N-type doped layer, the P-type doped region, and the co-doped region; an isolation trench disposed in a portion of the conductive film layer located between the N-type doped layer and the P-type doped region; and metal electrodes disposed on the outer surfaces of corresponding conductive film layers located outside the N-type doped layer and the P-type doped region. In the present invention, the conductive film layer is preferably a transparent conductive film layer. The type and thickness of the conductive film layer, the width of the isolation trench, and the structure and thickness of the metal electrodes can all refer to existing technologies and can all be used in the present invention, and will not be elaborated further here.

[0085] In some preferred embodiments of the present invention, the back-contact solar cell further includes a passivation and antireflection layer disposed on the front side of the silicon wafer. The passivation and antireflection layer can be, for example, a passivation layer and an antireflection layer, specifically a structure of an intrinsic passivation layer and a silicon nitride antireflection layer, or a front-side polycrystalline structure, or a structure of an aluminum oxide passivation layer and a silicon nitride antireflection layer. The type and thickness of the passivation layer and the antireflection layer can be referred to in the prior art, and all can be used in the present invention.

[0086] In some preferred embodiments of the present invention, the N-type doped film is an N-type doped amorphous silicon, microcrystalline silicon, or nanocrystalline silicon layer.

[0087] In this invention, the P-type doped region is formed by ion implantation of boron atoms into the intrinsic amorphous silicon layer, hence it is P-type doped amorphous silicon. The P-type doped region is more conducive to a smooth connection with the intrinsic amorphous silicon layer, thereby further reducing contact resistance.

[0088] Secondly, the present invention provides a method for preparing a back-contact solar cell, comprising the following steps:

[0089] S1. Provide silicon wafers;

[0090] S2. Deposit an intrinsic amorphous silicon layer on the back side of the silicon wafer;

[0091] S3. Place a first mask in a preset first mask area outside the intrinsic amorphous silicon layer on the back side, and use PECVD deposition process to deposit an N-type doped film layer arranged at intervals outside the intrinsic amorphous silicon layer in the non-mask area.

[0092] S4. Then, a second mask is placed in the pre-defined second mask area outside the N-type doped film layer on the back side. Using the PECVD ion implantation process, boron is implanted into the surface of the intrinsic amorphous silicon layer in the non-mask area to form a P-type doped region alternating with the N-type doped film layer. Simultaneously, boron atoms enter the end of the N-type doped film layer to form a co-doped region. The co-doped region is located between the N-type doped film layer and the P-type doped region. Phosphorus and boron are doped in the co-doped region. It can be understood that PECVD ion implantation process refers to plasma-assisted ion implantation technology.

[0093] Among them, the N-type doped film layer is controlled to have a graded doping structure, and the graded doping structure satisfies: the surface phosphorus concentration of the N-type doped film layer is ≤1e22cm. -3 The surface phosphorus concentration of the N-type doped film is lower than or equal to the average phosphorus concentration of the N-type doped film; the P-type doped region has a graded doping structure and the graded doping structure satisfies: the surface boron concentration of the P-type doped region is ≥5e21cm. -3 The surface boron concentration of the P-type doped region is higher than or equal to the average boron concentration of the P-type doped region. In the preparation method of the second aspect of the present invention, the structure and properties of the intrinsic amorphous silicon layer, the thickness of the P-type doped region, and the N-type doped film layer, as well as their corresponding doping concentrations, are the same as those of the corresponding film layers in the first aspect, and will not be repeated here.

[0094] In this invention, the width of the second mask in S4 can be less than or equal to the width of the N-type doped film, as long as it allows boron atoms to enter the end of the N-type doped film to form a co-doped region. Preferably, the width of the second mask is less than the width of the N-type doped film, so that the end of the N-type doped film is not covered by the second mask, which is more conducive to boron atoms entering the end of the N-type doped film to form a high-concentration doped co-doped region.

[0095] In some preferred embodiments of the present invention, the conditions for the PECVD deposition process in S3 include: deposition temperature of 30-180°C, chamber pressure of 40-300Pa, and RF power of 500-30000W. In the present invention, the surface phosphorus doping concentration and average phosphorus doping concentration of the N-type doped film, as well as the doping concentration of the co-doped region, can all be obtained by adjusting the various process parameters in this preferred embodiment.

[0096] In some preferred embodiments of the present invention, the PECVD deposition process in S3 is carried out under a mixed gas of silane, phosphine, and hydrogen, wherein the silane flow rate is 50-5000 sccm, the phosphine flow rate is 5-500 sccm, and the hydrogen flow rate is 1000-100000 sccm. In the present invention, the surface phosphorus doping concentration and average phosphorus doping concentration of the N-type doped film, as well as the doping concentration of the co-doped region, can all be obtained by adjusting the various process parameters in this preferred embodiment.

[0097] In some preferred embodiments of the present invention, the conditions for the PECVD ion implantation process in S4 include: a substrate temperature of 25-180°C and an accelerating voltage of 200-2000V. The surface phosphorus doping concentration and average phosphorus doping concentration of the P-type doped region, as well as the doping concentration of the co-doped region, can all be obtained by adjusting the process parameters in this preferred embodiment.

[0098] In some preferred embodiments of the present invention, the PECVD ion implantation process in S4 is carried out under a mixed gas of diborane, hydrogen, and argon, wherein the diborane flow rate is 20-2000 sccm, the hydrogen flow rate is 1000-10000 sccm, and the argon flow rate is 2000-100000 sccm. The surface phosphorus doping concentration and average phosphorus doping concentration of the P-type doped region, as well as the doping concentration of the co-doped region, can all be obtained by adjusting the process parameters in this preferred embodiment.

[0099] The deposition of the intrinsic amorphous silicon layer in S2 of this invention can be performed using the PECVD deposition method.

[0100] In some preferred embodiments of the present invention, the preparation method further includes: forming a passivation antireflection layer on the front side of the silicon wafer. The step of forming the passivation antireflection layer is preferably performed before S2.

[0101] In some preferred embodiments of the present invention, the preparation method further includes the following steps:

[0102] S5. Deposit a conductive film outside the back co-doped region, the N-type doped film, and the P-type doped region;

[0103] S6. Etch on the corresponding conductive film layer located between the N-type doped film layer and the P-type doped region to form an isolation trench;

[0104] S7. Metal electrodes are respectively disposed outside the conductive films corresponding to the N-type doped film layer and the P-type doped region. In this invention, the type and thickness of the conductive film layer, the width and etching method of the isolation trench, and the structure and thickness of the metal electrodes can all refer to the prior art and can all be used in this invention, and will not be described in detail here.

[0105] In this invention, it is understood that after depositing an N-type doped film layer in S3, the first mask is removed, followed by S4. After S4 is completed, the second mask is removed, and then S5 is performed. The first and second masks can be the same or different.

[0106] The preparation method of the present invention eliminates the need for multiple etching and cleaning processes in traditional structure preparation, simplifies the manufacturing process, and effectively reduces contact resistance while increasing fill factor and open-circuit voltage, thereby improving battery efficiency, reliability, and yield.

[0107] Thirdly, the present invention provides a back-contact solar cell, which is prepared by the method for preparing a back-contact solar cell described in the second aspect. The back-contact solar cell of the fourth aspect has the same structure and performance as the back-contact solar cell of the first aspect, and will not be described again here.

[0108] Fourthly, the present invention provides a battery assembly comprising the back-contact solar cell described in the first aspect, or comprising the back-contact solar cell described in the third aspect. The battery assembly of the present invention includes any device or base station that may utilize a back-contact solar cell.

[0109] The embodiments of the present invention described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0110] Example 1

[0111] A back-contact solar cell is obtained by the following preparation method:

[0112] S1, Provide a single-crystal silicon substrate, i.e., silicon wafer 1, such as Figure 1 ;

[0113] S2. After double-sided texturing and cleaning, a passivation layer (specifically an aluminum oxide layer) and an anti-reflection layer (specifically silicon nitride) are set on the front side of the silicon wafer.

[0114] S2. An intrinsic amorphous silicon layer 2 is deposited on the back side using PECVD deposition. The thickness of the intrinsic amorphous silicon layer 2 is 12 nm. Figure 2 ;

[0115] S3. A patterned N-type doped film layer 3 is formed using a dry method in the masking process. Specifically, a first mask A is placed in a preset first mask area on the back side of silicon wafer 1 in S2, such as... Figure 3The PECVD deposition process was employed (specific conditions were: silane, phosphine, and hydrogen gases were introduced; silane flow rate was 200 sccm; phosphine flow rate gradually increased from 10 sccm to 50 sccm; hydrogen flow rate was 4000 sccm; deposition temperature was 50℃; chamber pressure was 50 Pa; and RF power was 1500 W). An N-type doped film layer 3 (specifically, N-type doped amorphous silicon) was deposited outside the intrinsic amorphous silicon layer 2 (S2). Afterward, the first mask A was removed, as shown... Figure 4 As shown. The phosphorus doping concentration of the N-type doped film layer 3 is 8e20cm. -3 -7e21cm -3 The surface phosphorus doping concentration of the N-type doped film 3 is 3e21cm, with a thickness of 7nm and a range. -3 The surface phosphorus concentration of the N-type doped film 3 is lower than the average phosphorus concentration of the N-type doped film 3 (5e21cm). -3 .

[0116] S4. A patterned P-type doped region 4 is formed using a dry masking method. Specifically, a second mask B is placed in a pre-defined second mask area outside the N-type doped film layer 3 on the back side of S3, such as... Figure 5 As shown, PECVD ion implantation was used (specific conditions were: diborane, hydrogen, and argon were introduced; the diborane flow rate gradually increased from 40 sccm to 80 sccm; the hydrogen flow rate was 5000 sccm; the argon flow rate was 10000 smm; the substrate temperature was 50℃; and the accelerating voltage was 1000V). Boron was implanted into the surface of the intrinsic amorphous silicon layer 2 in the non-mask region. Boron atoms entered the intrinsic amorphous silicon layer 2 to form a P-type doped region 4. Boron atoms entered the interior of the part of the N-type doped film layer 3 adjacent to the P-type doped region 4, thus forming a co-doped region 5. The co-doped region 5 is located between the N-type doped film layer 3 and the P-type doped region 4, as shown in the figure. Figure 6 As shown. Then remove the first mask B.

[0117] Among them, the boron doping concentration of P-type doped region 4 is 3e20cm. -3 -8e21cm -3 The surface boron doping concentration of the P-type doped region 4 is 8e21cm, with a thickness of 6nm. -3 The surface boron concentration of P-type doped region 4 is higher than the average boron concentration of P-type doped region 4e21cm. -3 In the vertical direction outward from the back of silicon wafer 1, the boron doping concentration of the P-type doped region 4 gradually increases.

[0118] The thickness of the co-doped region 5 is the same as that of the N-type doped film layer 3. The width of the co-doped region 5 is 50 µm, and the phosphorus doping concentration is between 5e²⁰ and 8e²¹ cm⁻¹. -3 The range of boron doping concentration is 5e21-8e21cm. -3The width ratio of the N-type doped film 3 to the width of the P-type doped region 4 and the co-doped region 5 is 1:2.1:0.16.

[0119] S5. Deposit a transparent conductive film layer 6 on the back side obtained in S4;

[0120] S6. An opening is etched on the corresponding transparent conductive film 6 located between the N-type doped film 3 and the P-type doped region 4 to form an isolation trench 7.

[0121] S7. Metal electrodes 8 are formed on the outer surfaces of the corresponding transparent conductive films 6 in the regions where the N-type doped film layer 3 and the P-type doped region 4 are located. The resulting back-contact solar cell structure is as follows. Figure 7 As shown.

[0122] Example 2

[0123] The procedure was carried out in accordance with Example 1, except that in S3, the phosphorus doping concentration on the surface of the N-type doped film 3 was adjusted to 5e21cm. -3 The ratio of the surface phosphorus concentration to the average phosphorus concentration of the N-type doped film 3 is 0.8:1. To meet this condition, the PECVD deposition process parameters that need to be adjusted are: the phosphine flow rate is gradually increased from 10 sccm to 70 sccm.

[0124] Example 3

[0125] The procedure was carried out in accordance with Example 1, except that the surface boron doping concentration of the P-type doped region 4 was adjusted to 5e21cm. -3 The ratio of the surface boron concentration to the average boron concentration in the corresponding P-type doped region 4 is 1.2:1. To meet this condition, the PECVD ion implantation process parameters need to be adjusted as follows: the borane flow rate is gradually increased from 30 sccm to 60 sccm.

[0126] Example 4

[0127] The process was carried out in accordance with Example 1, except that the thickness of the N-type doped film 3 was adjusted to 5 nm. To meet this condition, the key parameter of the PECVD deposition process that needed to be adjusted was: a 20% reduction in deposition time.

[0128] Example 5

[0129] The procedure was carried out in accordance with Example 1, except that the thickness of the P-type doped region 4 was adjusted to 7 nm. The key parameter of the PECVD ion implantation process that needed to be adjusted to meet this condition was: a 20% increase in reaction time.

[0130] Example 6

[0131] The procedure was carried out in accordance with Example 1, except that the width of the co-doped region 5 was adjusted to 100µm. After calculation, the width ratio of the N-type doped film layer 3 to the width of the co-doped region 5 was 1:0.3. To meet this condition, the width of the mask needed to be adjusted.

[0132] Comparative Example 1

[0133] The procedure is carried out in accordance with Example 1, except that in S3, instead of using PECVD deposition to deposit an N-type doped film, PECVD ion implantation is used to implant phosphorus atoms onto the surface of the intrinsic amorphous silicon layer in the non-mask region to form an N-type doped region with a thickness of 5 nm. The difference from Example 1 is that the N-type doped region is a portion of the intrinsic amorphous silicon layer, not an independent film layer located on the outer surface of the intrinsic amorphous silicon layer. The PECVD ion implantation conditions required to meet this condition are: phosphine, hydrogen, and argon are introduced; the phosphine flow rate is 100 sccm, the hydrogen flow rate is 5000 sccm, the argon flow rate is 5000 smm, the substrate temperature is 50°C, and the accelerating voltage is 1000 V.

[0134] Comparative Example 2

[0135] The procedure was carried out in accordance with Example 1, except that in S4, instead of using PECVD ion implantation, a P-type doped film was deposited on the outer surface of the intrinsic amorphous silicon layer in the non-mask region using PECVD deposition. The difference from Example 1 is that the P-type doped film is an independent film located on the outer surface of the intrinsic amorphous silicon layer, and not part of a region of the intrinsic amorphous silicon layer. The thickness of the P-type doped film is 10 nm, and the doping concentration is the same as in Example 1. The PECVD deposition process conditions required to meet these conditions are as follows: Silane, diborane, and hydrogen gases are introduced; the gas flow rates are 200 sccm for silane, 20 sccm for diborane, and 2000 sccm for hydrogen; the deposition temperature is 50°C; the chamber pressure is 50 Pa; and the RF power is 1000 W.

[0136] Comparative Example 3

[0137] The procedure was carried out in accordance with Example 1, except that the phosphorus doping concentration of the N-type doped film was kept constant and without a gradual change in structure; the phosphorus doping concentration of the N-type doped film was 4e21cm. -3 The process parameters that need to be adjusted to meet this condition are: the phosphine flow rate must always be maintained at 30 sccm.

[0138] Comparative Example 4

[0139] The procedure was carried out in accordance with Example 1, except that the boron doping concentration of the P-type doped region was kept constant and without a gradual change in structure, and the surface boron doping concentration of the P-type doped region was 5e21cm. -3The process parameters that need to be adjusted to meet this condition are: the borane flow rate must always be maintained at 60 sccm.

[0140] Test case

[0141] The back-contact solar cells obtained in the above embodiments and comparative examples were subjected to performance tests, and the results are shown in Table 1. The cell yield test method was as follows: within a batch of production, cells with a yield of 27% were used as the dividing line, and the yield was calculated as: (Number of cells with a yield ≥ 27% / Total number of cells produced) × 100%. All performance indicators for each embodiment and comparative example were calculated using Embodiment 1 as the reference benchmark. The data for Embodiment 1 was normalized to a benchmark of 1.0000. Other examples were calculated based on Embodiment 1; for example, the cell yield of Comparative Example 1 / the cell yield of Embodiment 1 was 0.9441.

[0142] Table 1

[0143] Performance indicators Contact resistance Leakage current Open circuit voltage Fill factor Battery efficiency Battery yield Example 1 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 Example 2 1.1733 1.0882 0.9980 0.9925 0.9938 0.9753 Example 3 1.1139 1.2843 0.9991 0.9931 0.9949 0.9831 Example 4 1.0743 1.2549 0.9996 0.9957 0.9960 0.9857 Example 5 1.1040 1.3137 0.9976 0.9911 0.9917 0.9820 Example 6 1.0495 1.0294 0.9999 0.9947 0.9967 0.9854 Comparative Example 1 1.2426 1.1961 0.9951 0.9849 0.9855 0.9441 Comparative Example 2 1.2030 1.6471 0.9963 0.9879 0.9898 0.9717 Comparative Example 3 1.1881 1.3922 0.9967 0.9886 0.9888 0.9765 Comparative Example 4 1.1980 1.3431 0.9971 0.9896 0.9906 0.9786

[0144] The results above show that, compared with the comparative example, the embodiment of the present invention does not require multiple etching and cleaning processes in the traditional structure preparation, the manufacturing process is simple, and it can effectively reduce contact resistance and improve fill factor and open circuit voltage, thereby improving battery efficiency, reliability and battery yield.

[0145] Furthermore, as can be seen from Examples 1 and 2-6, the preferred scheme of the present invention is more conducive to improving battery efficiency and reliability, and battery yield.

[0146] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A back-contact solar cell, characterized in that, The product comprises a silicon wafer, an intrinsic amorphous silicon layer disposed on the back side of the silicon wafer, P-type doped regions spaced apart on the surface of the intrinsic amorphous silicon layer, an N-type doped film layer disposed outside the intrinsic amorphous silicon layer at the intervals between the P-type doped regions, and co-doped regions disposed on both ends of the N-type doped film layer connected to the P-type doped regions, wherein phosphorus and boron are doped in the co-doped regions; wherein the N-type doped film layer has a graded doping structure and the graded doping structure satisfies the following: the surface phosphorus concentration of the N-type doped film layer is ≤1e22cm³. -3 The surface phosphorus concentration of the N-type doped film is lower than or equal to the average phosphorus concentration of the N-type doped film; the P-type doped region has a graded doping structure and the graded doping structure satisfies: the surface boron concentration of the P-type doped region is ≥5e21cm. -3 The surface boron concentration of the P-type doped region is higher than or equal to the average boron concentration of the P-type doped region.

2. The back-contact solar cell according to claim 1, characterized in that, The phosphorus doping concentration of the N-type doped film is 1e20cm⁻¹. -3 -1e22cm -3 And / or, the boron doping concentration of the P-type doped region is 1e20cm⁻¹. -3 -3e22cm -3 .

3. The back-contact solar cell according to claim 1 or 2, characterized in that, The ratio of the surface phosphorus concentration to the average phosphorus concentration of the N-type doped film is (0.3-1):1, and / or the ratio of the surface boron concentration to the average boron concentration of the P-type doped region is (1-7):

1.

4. The back-contact solar cell according to claim 1, characterized in that, The sum of the thicknesses of the intrinsic amorphous silicon layer and the P-type doped region is less than the sum of the thicknesses of the intrinsic amorphous silicon layer and the N-type doped film.

5. The back-contact solar cell according to claim 1 or 4, characterized in that, The thickness of the N-type doped film is 5-20 nm, and / or the thickness of the P-type doped region is 5-10 nm.

6. The back-contact solar cell according to claim 1 or 4, characterized in that, The thickness of the intrinsic amorphous silicon layer is 8-20 nm, and / or the thickness of the co-doped region is 5-20 nm.

7. The back-contact solar cell according to claim 1, characterized in that, The width of the co-doped region is 10-100µm, and / or the ratio of the width of the N-type doped film to the width of the P-type doped region and the co-doped region is 1:(1-2.4):(0.03-0.3).

8. The back-contact solar cell according to claim 1 or 7, characterized in that, The phosphorus doping concentration in the co-doped region is 1e20cm. -3 -1e22cm -3 Boron doping concentration of 1e20cm -3 -3e22cm -3 .

9. The back-contact solar cell according to claim 1, characterized in that, In the vertical direction from the back of the silicon wafer outward, the boron doping concentration of the P-type doped region gradually increases; And / or, the boron doping concentration in the co-doped region gradually decreases along the direction away from the P-type doped region.

10. The back-contact solar cell according to claim 1, characterized in that, Back-contact solar cells have at least one of the following structures: Structure 1: The back contact solar cell also includes: a conductive film layer disposed on the overall outer surface of the N-type doped film layer, the P-type doped region, and the co-doped region; an isolation trench disposed in a portion of the conductive film layer between the N-type doped film layer and the P-type doped region; and metal electrodes disposed on the corresponding conductive film layers outside the N-type doped film layer and the P-type doped region. Structure 2: Back-contact solar cells also include a passivation and anti-reflection layer disposed on the front side of the silicon wafer; Structure 3: The N-type doped film is an N-type doped amorphous silicon, microcrystalline silicon, or nanocrystalline silicon layer, and the P-type doped region is a P-type doped amorphous silicon.

11. A method for fabricating a back-contact solar cell, characterized in that, Includes the following steps: S1. Provide silicon wafers; S2. Deposit an intrinsic amorphous silicon layer on the back side of the silicon wafer; S3. Place a first mask in a preset first mask area outside the intrinsic amorphous silicon layer on the back side, and use PECVD deposition process to deposit an N-type doped film layer arranged at intervals outside the intrinsic amorphous silicon layer in the non-mask area. S4. Then, place a second mask in the preset second mask area outside the N-type doped film layer on the back side. Using the PECVD ion implantation process, implant boron into the surface of the intrinsic amorphous silicon layer in the non-mask area to form a P-type doped region that is alternately arranged with the N-type doped film layer. At the same time, boron atoms enter the end of the N-type doped film layer to form a co-doped region. The co-doped region is located between the N-type doped film layer and the P-type doped region. Phosphorus and boron are doped in the co-doped region. Among them, the N-type doped film layer is controlled to have a graded doping structure, and the graded doping structure satisfies: the surface phosphorus concentration of the N-type doped film layer is ≤1e22cm. -3 The surface phosphorus concentration of the N-type doped film is lower than or equal to the average phosphorus concentration of the N-type doped film; the P-type doped region has a graded doping structure and the graded doping structure satisfies: the surface boron concentration of the P-type doped region is ≥5e21cm. -3 The surface boron concentration of the P-type doped region is higher than or equal to the average boron concentration of the P-type doped region.

12. The method for fabricating a back-contact solar cell according to claim 11, characterized in that, The conditions for the PECVD deposition process in S3 include: deposition temperature of 30-180℃, chamber pressure of 40-300Pa, and RF power of 500-30000W. And / or, In S3, the PECVD deposition process is carried out under a mixed gas of silane, phosphine, and hydrogen, with a silane flow rate of 50-5000 sccm, a phosphine flow rate of 5-500 sccm, and a hydrogen flow rate of 1000-100000 sccm.

13. The method for fabricating a back-contact solar cell according to claim 11 or 12, characterized in that, The conditions for the PECVD ion implantation process in S4 include: substrate temperature of 25-180℃ and accelerating voltage of 200-2000V; And / or, In S4, the PECVD ion implantation process is carried out under a mixed gas of diborane, hydrogen, and argon, with a diborane flow rate of 20-2000 sccm, a hydrogen flow rate of 1000-10000 sccm, and an argon flow rate of 2000-100000 sccm.

14. The method for fabricating a back-contact solar cell according to claim 11, characterized in that, The preparation method also includes at least one of the following processes: Process 1: The thickness of the intrinsic amorphous silicon layer is 8-20 nm; Process 2: The N-type doped film is an N-type doped amorphous silicon, microcrystalline silicon, or nanocrystalline silicon layer; Process 3: The sum of the thicknesses of the intrinsic amorphous silicon layer and the P-type doped region is less than the sum of the thicknesses of the intrinsic amorphous silicon layer and the N-type doped film. Process 4: The phosphorus doping concentration of the N-type doped film is 1e20cm. -3 -1e22cm -3 The boron doping concentration in the P-type doped region is 1e20cm. -3 -3e22cm -3 ; Process 5: The thickness of the N-type doped film is 5-20 nm, and the thickness of the P-type doped region is 5-10 nm; Process 6: The width of the co-doped region is 10-100µm, and the thickness of the co-doped region is 5-20nm; Process 7: The phosphorus doping concentration in the co-doped region is 1e20cm⁻¹ -3 -1e22cm -3 Boron doping concentration of 1e20cm -3 -3e22cm -3 ; Process 8, the preparation method also includes: setting a passivation antireflection layer on the front side of the silicon wafer; Process 9, the preparation method also includes the following steps: S5. Deposit a conductive film outside the back co-doped region, the N-type doped film, and the P-type doped region; S6. Etch on the corresponding conductive film layer located between the N-type doped film layer and the P-type doped region to form an isolation trench; S7. Metal electrodes are respectively disposed on the outside of the conductive film layers corresponding to the N-type doped film layer and the P-type doped region.

15. A back-contact solar cell, characterized in that, It is prepared by the method for preparing a back-contact solar cell as described in any one of claims 11-14.

16. A battery assembly, characterized in that, It includes a back-contact solar cell as described in any one of claims 1-10, or a back-contact solar cell as described in claim 15.

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