Boron-doped emitter, TOPcon battery and preparation method

Abstract

The invention relates to the technical field of solar cells, particularly provides a boron-doped emitter, a TOPcon cell and a preparation method, and aims to solve the problem that in the prior art, a boron-doped p + emitter formed through one-time deposition cannot give consideration to the surface recombination rate and the contact performance at the same time. In order to achieve the purpose, at least two borosilicate glass layers are deposited on the front face of a silicon substrate, a silicon dioxide layer is deposited between every two adjacent borosilicate glass layers, and the molar ratio of boron to oxygen in each borosilicate glass layer is gradually increased layer by layer in the direction gradually away from the silicon substrate. According to the invention, the silicon dioxide layer is arranged, and the B / O ratio of the outer borosilicate glass layer is greater than that of the inner borosilicate glass layer, so that the surface recombination rate and the contact performance can be considered, a high surface shallow junction is formed, and the open-circuit voltage and the fill factor are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, specifically providing a boron-doped emitter, a TOPcon cell, and a method for its fabrication. Background Technology

[0002] As a type of photovoltaic crystalline silicon cell, TOPcon cells are increasingly widely used due to their significant advantages such as high conversion efficiency, low degradation performance, and high cost-effectiveness in mass production. TOPcon cells can be either P-type or N-type silicon cells. Compared with P-type silicon cells, N-type silicon cells have higher conversion efficiency, better resistance to degradation, higher bifaciality, and longer minority carrier lifetime, and have a better development prospect.

[0003] Currently, boron-doped p is typically formed using large-pressure diffusion (LP) in a furnace tube. + Emitter. However, although this method is widely used, it still has the following drawbacks: 1. High energy consumption and long process cycle; 2. Poor control over wafer edges; 3. Deep diffusion and poor activation control, resulting in a high surface recombination rate (J0, pass); 4. Unsatisfactory contact performance, affecting the device open-circuit voltage (Voc) and fill factor (FF).

[0004] To address the aforementioned issues, current research reports the formation of boron-doped p-type boron through chemical deposition. + Emitter, but usually boron-doped p is formed in a single deposition. + The emitter cannot simultaneously achieve both surface recombination rate and contact performance.

[0005] Accordingly, a new technical solution is needed in this field to solve the above problems. Summary of the Invention

[0006] The present invention aims to solve the above-mentioned technical problems, namely, to solve the problem of boron-doped p-type boron formed by a single deposition in the prior art. + The emitter cannot simultaneously address the issues of surface recombination rate and contact performance.

[0007] In a first aspect, the present invention also provides a method for preparing a boron-doped emitter, comprising the following steps:

[0008] At least two borosilicate glass layers are deposited on the front side of a silicon substrate, and a silicon dioxide layer is deposited between two adjacent borosilicate glass layers, wherein the molar ratio of boron to oxygen in each borosilicate glass layer increases layer by layer along the direction gradually away from the silicon substrate.

[0009] The boron-doped emitter is formed by performing a first annealing process.

[0010] Under the premise of adopting the above technical solution, the molar ratio of boron to oxygen (hereinafter referred to as B / O ratio) in each borosilicate glass layer increases layer by layer along the direction away from the silicon substrate. That is, relative to the silicon substrate, the B / O ratio of the outermost borosilicate glass layer is always greater than that of the innermost borosilicate glass layer. The innermost borosilicate glass layer has a lower B / O ratio and a higher oxygen content. The excess oxygen atoms can diffuse to the interface, which helps to repair defects such as dangling bonds and oxygen vacancies in the silicon substrate, effectively improving the passivation effect. At the same time, there is less boron near the silicon substrate, which can prevent boron from damaging the band structure of the n-type substrate surface and reduce the surface recombination rate. The outermost borosilicate glass layer has a higher B / O ratio and a higher boron content, which can provide an effective boron diffusion source, form a shallow junction, reduce surface recombination, improve blue light response, and its high surface concentration can greatly reduce the series resistance and contact resistance of the emitter. Simultaneously, the silica layer prevents boron diffusion between adjacent borosilicate glass layers, thus preventing boron from diffusing from the outer layer to the inner layer and ensuring that the B / O ratio of the outermost borosilicate glass layer is always greater than that of the innermost layer. This design balances surface recombination rate and contact performance, forming a high-surface-shallow junction and significantly improving open-circuit voltage and fill factor.

[0011] In the preferred embodiment of the above preparation method, the borosilicate glass layer and the silicon dioxide layer are deposited using plasma-enhanced chemical vapor deposition.

[0012] In the preferred embodiment of the above preparation method, the deposition conditions of the borosilicate glass layer closer to the silicon substrate satisfy at least one of the following conditions:

[0013] The deposition time is 90s~120s;

[0014] The flow volume of SiH4 is 2000 sccm~5000 sccm;

[0015] The flow volume of B2H4 is 200 sccm~500 sccm;

[0016] The flow rate of N2O is 12000 sccm~15000 sccm.

[0017] In the preferred embodiment of the above preparation method, the deposition conditions of the borosilicate glass layer farther from the silicon substrate satisfy at least one of the following conditions:

[0018] The deposition time is 200s~400s;

[0019] The flow volume of SiH4 is 2000 sccm~5000 sccm;

[0020] The flow volume of B2H4 is 800 sccm~1000 sccm;

[0021] The flow rate of N2O is 8000 sccm~10000 sccm.

[0022] In the preferred embodiment of the above preparation method, the deposition conditions of the silicon dioxide layer satisfy at least one of the following conditions:

[0023] The flow rate of N2O is 9000 sccm~20000 sccm;

[0024] The duty cycle NO:OFF is 20:1800~20:2200;

[0025] The deposition time is 80s~120s.

[0026] In the preferred embodiment of the above preparation method, the first annealing treatment is performed under an inert atmosphere; and / or

[0027] The first annealing process conditions satisfy at least one of the following conditions:

[0028] The annealing temperature is 960℃~1000℃;

[0029] Annealing time is 1.5h~2h.

[0030] In a preferred embodiment of the above preparation method, the preparation method further includes:

[0031] A first borosilicate glass layer, a silicon dioxide layer, and a second borosilicate glass layer are sequentially deposited on the front side of the silicon substrate, wherein the molar ratio of boron to oxygen in the second borosilicate glass layer is greater than the molar ratio of boron to oxygen in the first borosilicate glass layer.

[0032] In the preferred embodiment of the above preparation method, the thickness of the first borosilicate glass layer is 10 nm to 12 nm; and / or

[0033] The thickness of the second borosilicate glass layer is 23 nm to 33 nm; and / or

[0034] The thickness of the silicon dioxide layer is 1 nm to 2 nm.

[0035] Secondly, the present invention also provides a boron-doped emitter, which is prepared by the preparation method described in any of the foregoing schemes.

[0036] In the preferred embodiment of the above-mentioned boron-doped emitter, the junction depth of the boron-doped emitter is 0.45 μm to 0.7 μm; and / or

[0037] The doping concentration of the boron-doped emitter is 5.4E+19cm. -3 ~6.1E+19cm -3 .

[0038] It should be noted that this boron-doped emitter possesses all the technical effects of the aforementioned preparation method, which will not be elaborated upon here.

[0039] Thirdly, the present invention also provides a method for preparing a TOPcon battery, comprising the following steps:

[0040] A silicon substrate is provided, and the silicon substrate is pretreated;

[0041] A boron-doped emitter is deposited on the front side of the silicon substrate using the fabrication method described in any of the preceding schemes;

[0042] Etching residual source layer;

[0043] Polish the back side after removing the borosilicate glass layer;

[0044] Deposition of tunneling oxide layer and amorphous silicon layer;

[0045] Perform a second annealing process;

[0046] Deposit silicon nitride antireflection layer;

[0047] Silver paste is printed on the silicon nitride antireflection layer, dried and sintered, and then photoinjection is performed.

[0048] The TOPcon battery was prepared by laser-assisted sintering.

[0049] It should be noted that this preparation method possesses all the technical effects of the aforementioned boron-doped emitter preparation method, which will not be elaborated here.

[0050] Fourthly, the present invention also provides a TOPcon battery, which is prepared by the aforementioned method for preparing a TOPcon battery.

[0051] It should be noted that this TOPcon battery possesses all the technical effects of the aforementioned boron-doped emitter preparation method, which will not be elaborated here. Attached Figure Description

[0052] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0053] Figure 1 This is a schematic diagram of the structure of a TOPcon battery according to an embodiment of the present invention.

[0054] Figure label:

[0055] 1. Front metal grid lines; 2. Front anti-reflective coating; 3. Passivation film; 4. p + 5. Emitter; 6. n-type silicon substrate; 7. Ultrathin tunneling oxide layer; 8. Phosphorus-doped polycrystalline silicon layer; 9. Back antireflection coating; 10. Back metal gate line. Detailed Implementation

[0056] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0057] In one possible implementation, the present invention provides a method for preparing a boron-doped emitter, specifically comprising the following steps:

[0058] Step 1: Deposit at least two borosilicate glass layers on the front side of the silicon substrate, and deposit a silicon dioxide layer between two adjacent borosilicate glass layers, wherein the molar ratio of boron to oxygen (hereinafter referred to as B / O ratio) in each borosilicate glass layer increases layer by layer along the direction gradually away from the silicon substrate.

[0059] Specifically, the pretreated silicon substrate is placed in a plasma-enhanced chemical vapor deposition (PECVD) apparatus, and silicon, boron, nitrogen, and oxygen sources are fed into the apparatus. First, a borosilicate glass layer is deposited on the front side of the silicon substrate. Then, a silicon dioxide layer (e.g., a silicon dioxide layer) is deposited on the surface of the borosilicate glass layer. Then, silicon, boron, nitrogen, and oxygen sources are fed in again, and another borosilicate glass layer is deposited on the surface of the silicon dioxide layer. Then, silicon and oxygen sources are fed in again, and another silicon dioxide layer is deposited on the surface of the borosilicate glass layer. This process of alternating deposition of borosilicate glass layers and silicon dioxide layers is repeated to form at least two borosilicate glass layers on the front side of the silicon substrate and a silicon dioxide layer is deposited between adjacent borosilicate glass layers.

[0060] During the deposition process, by controlling the parameters, the B / O ratio in each borosilicate glass layer increases progressively away from the silicon substrate. In other words, relative to the silicon substrate, the B / O ratio of the outermost borosilicate glass layer is greater than that of the innermost layer. The innermost borosilicate glass layer has a lower B / O ratio and a higher oxygen content. Excess oxygen atoms can diffuse to the interface, helping to repair defects such as dangling bonds and oxygen vacancies in the silicon substrate, effectively improving passivation. Simultaneously, the lower boron content near the silicon substrate prevents boron from disrupting the band structure of the n-type substrate surface, reducing surface recombination and metal-to-metal recombination, and significantly increasing the open-circuit voltage by more than 1 mV. The outermost borosilicate glass layer has a higher B / O ratio and higher boron content, providing an effective boron diffusion source, forming a shallow junction, and creating a boron-doped emitter on the silicon substrate surface. This reduces surface recombination, improves blue light response, and the high surface concentration significantly reduces the series resistance and contact resistance of the emitter, greatly increasing the fill factor by more than 0.05%. Meanwhile, the silicon dioxide barrier height for holes (approximately 4.5 eV~4.8 eV) in the silicon dioxide layer is greater than its barrier height for electrons (approximately 3.1 eV). This high barrier at the silicon dioxide slows down the diffusion rate of minority carrier holes (boron), preventing the diffusion of boron from the outer layer to the inner layer. This ensures that the B / O ratio in the outer borosilicate glass layer is always greater than that in the inner borosilicate glass layer, ensuring a sufficient source of boron diffusion while creating a high-low concentration gradient, preventing the boron concentration in adjacent borosilicate glass layers from becoming uniform. This configuration balances surface recombination rate and contact performance, forming a high-surface-shallow junction, thereby improving the open-circuit voltage and fill factor.

[0061] It should be noted that borosilicate glass layers and silicon dioxide layers can also be deposited using atmospheric pressure chemical vapor deposition (APCVD) or other chemical vapor deposition methods.

[0062] In one possible implementation, during plasma-enhanced chemical vapor deposition, the equipment temperature is 400°C to 450°C, and the equipment power is 10,000W to 15,000W. For example, the furnace tube temperature can be 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, etc., and the furnace tube power can be 10,000W, 11,000W, 12,000W, 13,000W, 14,000W, 15,000W, etc. Preferably, the equipment temperature is 430°C, and the equipment power is 12,000W.

[0063] In one possible implementation, the deposition conditions of the borosilicate glass layer include deposition time, and the flow rates and volumes of the silicon, boron, nitrogen, and oxygen sources. In this embodiment, the silicon source is SiH4, the boron source is B2H4, and the nitrogen source is N2O. By controlling SiH4, B2H4, N2O, and the deposition time, the thickness of each borosilicate glass layer and the B / O ratio of each borosilicate glass layer are adjusted to ensure that the B / O ratio of the borosilicate glass layer farther from the silicon substrate is greater than that of the borosilicate glass layer closer to the silicon substrate.

[0064] Of course, the boron source can also be trimethylboron ((CH3)3B), diborane (B2H6), etc., and the nitrogen and oxygen sources can also be a mixture of N2O and NH3, or a mixture of O2 and N2 or O2 and NH3. Without departing from the basic principles of this application, those skilled in the art can flexibly select the boron source, silicon source, nitrogen source, and oxygen source to deposit and form a borosilicate glass layer according to the actual application scenario, as long as a borosilicate glass layer can be deposited.

[0065] In one possible implementation, the deposition conditions of the borosilicate glass layer close to the silicon substrate include: a deposition time of 90s to 120s, a SiH4 flow rate of 2000sccm to 5000sccm, a B2H4 flow rate of 200sccm to 500sccm, and an N2O flow rate of 12000sccm to 15000sccm. For example, the deposition time can be 90s, 95s, 100s, 105s, 110s, 115s, 120s, etc.; the flow volume of SiH4 can be 2000sccm, 2500sccm, 3000sccm, 3500sccm, 4000sccm, 4500sccm, 5000sccm, etc.; the flow volume of B2H4 can be 200sccm, 250sccm, 300sccm, 350sccm, 400sccm, 450sccm, 500sccm, etc.; and the flow volume of N2O can be 12000sccm, 12500sccm, 13000sccm, 13500sccm, 14000sccm, 14500sccm, 15000sccm, etc. Preferably, the deposition time is 90 s, the flow rate volume of SiH4 is 2000 sccm, the flow rate volume of B2H4 is 200 sccm, and the flow rate volume of N2O is 12000 sccm.

[0066] In one possible implementation, the deposition conditions of the borosilicate glass layer located far from the silicon substrate include: a deposition time of 200s to 400s, a SiH4 flow rate of 2000sccm to 5000sccm, a B2H4 flow rate of 800sccm to 1000sccm, and an N2O flow rate of 8000sccm to 10000sccm. For example, the deposition time can be 200s, 250s, 300s, 350s, 400s, etc.; the SiH4 flow rate volume can be 2000sccm, 2500sccm, 3000sccm, 3500sccm, 4000sccm, 4500sccm, 5000sccm, etc.; the B2H4 flow rate volume can be 800sccm, 850sccm, 900sccm, 950sccm, 1000sccm, etc.; and the N2O flow rate volume can be 8000sccm, 8300sccm, 8500sccm, 9000sccm, 9300sccm, 9600sccm, 10000sccm, etc. Preferably, the deposition time is 300s, the SiH4 flow rate volume is 3300sccm, the B2H4 flow rate volume is 900sccm, and the N2O flow rate volume is 9000sccm.

[0067] In one possible embodiment, the preparation method of the present invention includes: sequentially depositing a first borosilicate glass layer, a silicon dioxide layer, and a second borosilicate glass layer on the front side of a silicon substrate, wherein the molar ratio of boron to oxygen in the second borosilicate glass layer is greater than that in the first borosilicate glass layer. That is, two borosilicate glass layers and one silicon dioxide layer are deposited on the front side of the silicon substrate, forming a roughly sandwich-like structure. The first borosilicate glass layer, with its low B / O ratio, ensures better passivation and increases the open-circuit voltage. The second borosilicate glass layer, with its high B / O ratio, ensures high surface concentration, forms a shallow surface, and increases the fill factor. The silicon dioxide layer ensures that the B / O ratio of the second borosilicate glass layer is always greater than that of the first borosilicate glass layer, thereby better balancing surface recombination rate and contact performance, and improving both the open-circuit voltage and the fill factor.

[0068] It should be noted that three, four, five, or even more borosilicate glass layers can be deposited on the front side of the silicon substrate. Correspondingly, the number of silicon dioxide layers can also be two, three, four, or even more. Without departing from the basic principles of this application, those skilled in the art can flexibly select the specific number of borosilicate glass layers and silicon dioxide layers according to the specific application scenario, as long as the surface recombination rate and contact performance, as well as the open-circuit voltage and fill factor, can be balanced.

[0069] In one possible implementation, the deposition conditions of the silica layer include deposition time, flow rate and volume of the silicon and oxygen sources, and duty cycle. In this embodiment, the silicon source is SiH4, and the oxygen source is N2O. The thickness of the silica layer is adjusted by controlling the SiH4, N2O, and deposition time. Of course, the oxygen source can also be O2.

[0070] In one possible implementation, the deposition conditions for the silica layer include: a flow rate and volume of N2O of 9000 sccm to 20000 sccm, a duty cycle of NO:OFF of 20:1800 to 20:2200, and a deposition time of 80 s to 120 s. For example, the flow rate and volume of N2O can be 9000 sccm, 10000 sccm, 11000 sccm, 12000 sccm, 13000 sccm, 14000 sccm, 15000 sccm, 16000 sccm, 17000 sccm, 18000 sccm, 19000 sccm, 20000 sccm, etc., and the deposition time can be 80s, 90s, 100s, 110s, 120s, etc., and the duty cycle can be 20:1800, 20:1900, 20:2000, 20:2100, 20:2200, etc. Preferably, the flow rate and volume of N2O are 15000 sccm, the duty cycle NO:OFF = 20:2000, and the deposition time is 110s.

[0071] In one possible implementation, the thickness of the first borosilicate glass layer is 10 nm to 12 nm, for example, its thickness can be 10 nm, 10.5 nm, 11 nm, 11.5 nm, 12 nm, etc. Preferably, the thickness of the first borosilicate glass layer is 11 nm.

[0072] In one possible implementation, the thickness of the second borosilicate glass layer is 23 nm to 33 nm, for example, its thickness can be 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, etc. Preferably, the thickness of the second borosilicate glass layer is 28 nm.

[0073] In one possible implementation, the thickness of the silicon dioxide layer is 1 nm to 2 nm, for example, its thickness can be 1 nm, 1.2 nm, 1.4 nm, 1.5 nm, 1.8 nm, 2 nm, etc. Preferably, the thickness of the silicon dioxide layer is 1 nm.

[0074] Step 2: Perform the first annealing treatment to form a boron-doped emitter.

[0075] In one possible implementation, the first annealing process is carried out in an inert atmosphere, which can be formed by inert gases such as N2, argon, or helium.

[0076] In one possible implementation, the conditions for the first annealing treatment include annealing temperature and annealing time, wherein the annealing temperature is 960℃~1000℃, and the annealing time is 1.5h~2h. For example, the annealing temperature can be 960℃, 965℃, 970℃, 975℃, 980℃, 985℃, 990℃, 995℃, 1000℃, etc., and the annealing time can be 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h, etc. Preferably, the annealing temperature is 980℃, and the annealing time is 1.5h. If the annealing temperature is higher and the annealing time is longer, the diffusion depth will be increased, the band structure of the silicon substrate will be damaged, and the recombination rate will be increased.

[0077] In one possible implementation, the present invention also provides a boron-doped emitter prepared by the aforementioned preparation method.

[0078] The boron-doped emitter prepared in the above manner balances surface recombination rate and contact performance, forming a high-shallow junction with a high open-circuit voltage and fill factor.

[0079] In one possible implementation, the junction depth of the boron-doped emitter is 0.45 μm to 0.7 μm, and the doping concentration is 5.4E+19 cm⁻¹. -3 ~6.1E+19cm -3 For example, the junction depth of a boron-doped emitter can be 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, etc., and the doping concentration can be 5.4E+19 cm⁻¹. -3 5.6E+19cm -3 5.8E+19cm -3 6E+19cm -3 6.1E+19cm -3 Boron-doped emitters with junction depths and doping concentrations within this range can balance surface recombination rates and contact performance, forming a high-shallow junction and improving open-circuit voltage and fill factor. If the doping concentration is too high, severe Auger recombination will occur, significantly reducing the open-circuit voltage and fill factor. Preferably, the boron-doped emitter has a junction depth of 0.5 μm and a doping concentration of 6E+19 cm⁻¹. -3 .

[0080] In one possible implementation, the present invention also provides a method for preparing a TOPcon battery, comprising the following steps:

[0081] (1) Provide a silicon substrate and pretreat the silicon substrate.

[0082] (2) At least two borosilicate glass layers are deposited on the front side of the silicon substrate, and a silicon dioxide layer is deposited between two adjacent borosilicate glass layers, wherein the molar ratio of boron to oxygen in the borosilicate glass layer farther from the silicon substrate is greater than the molar ratio of boron to oxygen in the borosilicate glass layer closer to the silicon substrate.

[0083] (3) Perform the first annealing treatment.

[0084] (4) Etching the residual source layer.

[0085] (5) Polish the back side after removing the borosilicate glass layer.

[0086] (6) Deposit tunneling oxide layer and amorphous silicon layer.

[0087] (7) Perform a second annealing process.

[0088] (8) Deposit silicon nitride antireflection layer.

[0089] (9) Print silver paste on the silicon nitride antireflection layer, dry and sinter it, and then perform photoinjection treatment.

[0090] (10) TOPcon batteries were prepared by laser-assisted sintering.

[0091] It should be noted that the specific processes and parameters of steps (4) to (10) above are all implemented using conventional technical means in the industry, and will not be repeated here.

[0092] In one possible implementation, the present invention also provides a TOPcon battery, which is prepared by the aforementioned method.

[0093] A schematic diagram of the TOPcon battery in one possible implementation. Figure 1 As shown. Figure 1 The TOPcon battery includes a front metal grid line 1 and a front anti-reflective film (SiN) arranged sequentially. x 2. Passivation film (Al2O3) 3. p + 4. Emitter; 5. n-type silicon substrate; 6. Ultrathin tunneling oxide layer (SiO2); 7. Phosphorus-doped polycrystalline silicon layer (poly-Si(n) + 7. Front anti-reflective coating (SiN) x 8. Metal grid lines on the back. 9.

[0094] The following describes possible implementations of the boron-doped emitter of the present invention in conjunction with specific embodiments and comparative examples.

[0095] All raw materials used in the embodiments and comparative examples are commercially available products.

[0096] Example 1

[0097] (1) Texturing of silicon wafers: Texturing of silicon wafers is carried out using a hot alkaline solution, which is a KOH solution with isopropanol added.

[0098] (2) Deposition of the first borosilicate glass layer (hereinafter referred to as BSG-1): Using a plasma enhanced chemical vapor deposition (PECVD) device, at 430°C and 12000W, SiH4, B2H4 and N2O are introduced into the device for deposition. The flow rate of SiH4 is 2000 sccm, the flow rate of B2H4 is 200 sccm, and the flow rate of N2O is 12000 sccm. After 90s of deposition, a BSG-1 layer with a thickness of 10nm is deposited on the front side of the silicon wafer.

[0099] (3) Deposition of silicon dioxide layer: SiH4 and N2O were introduced into the equipment at 430℃ and 12000W for deposition. The flow rate and volume of SiH4 were 2000sccm and the flow rate and volume of N2O were 12000sccm. The duty cycle NO:OFF=20:2000 and the deposition was carried out for 80s to form a silicon dioxide layer with a thickness of 1nm on the surface of BSG-1.

[0100] (4) Deposition of the second borosilicate glass layer (hereinafter referred to as BSG-2): SiH4, B2H4 and N2O are introduced into the equipment at 430℃ and 12000W for deposition. The flow rate of SiH4 is 2000 sccm, the flow rate of B2H4 is 800 sccm and the flow rate of N2O is 8000 sccm. After 20s of deposition, a BSG-2 layer with a thickness of 23nm is deposited on the surface of the silica layer.

[0101] (5) First annealing treatment: The equipment was purged with N2 and kept in an N2 atmosphere. The temperature inside the equipment was controlled at 960℃ for 1.5h. The junction depth of the boron-doped emitter was 0.53μm and the doping concentration was 6E+19cm. -3 .

[0102] Example 2

[0103] The difference from Example 1 is that the deposition time in step (2) is 120 s, the SiH4 flow rate volume is 5000 sccm, the B2H4 flow rate volume is 350 sccm, the N2O flow rate volume is 15000 sccm, and the BSG-1 thickness is 12 nm. The junction depth of the formed boron-doped emitter is 0.45 μm, and the doping concentration is 5.8E+19 cm⁻¹. -3 .

[0104] Example 3

[0105] The difference from Example 1 is that the deposition time in step (2) is 120 s, the SiH4 flow rate volume is 5000 sccm, the B2H4 flow rate volume is 500 sccm, the N2O flow rate volume is 15000 sccm, and the BSG-1 thickness is 11 nm. The junction depth of the formed boron-doped emitter is 0.46 μm, and the doping concentration is 5.68E+19 cm⁻¹. -3 .

[0106] Example 4

[0107] The difference from Example 1 is that the deposition time in step (4) is 400 s, the SiH4 flow rate volume is 5000 sccm, the B2H4 flow rate volume is 1000 sccm, the N2O flow rate volume is 10000 sccm, and the BSG-2 thickness is 33 nm. The junction depth of the formed boron-doped emitter is 0.69 μm, and the doping concentration is 6.1E+19 cm⁻¹. -3 .

[0108] Example 5

[0109] The difference from Example 1 is that the deposition time in step (4) is 300 s, the SiH4 flow rate volume is 2500 sccm, the B2H4 flow rate volume is 900 sccm, the N2O flow rate volume is 9000 sccm, and the BSG-2 thickness is 28 nm. The junction depth of the formed boron-doped emitter is 0.65 μm, and the doping concentration is 6.05E+19 cm⁻¹. -3 .

[0110] Example 6

[0111] The difference from Example 1 is that the deposition time in step (3) is 120 s, the SiH4 flow rate volume is 5000 sccm, the N2O flow rate volume is 20000 sccm, the duty cycle NO:OFF = 20:2000, and the thickness of the silicon dioxide layer is 2 nm. The junction depth of the formed boron-doped emitter is 0.51 μm, and the doping concentration is 6.08E+19 cm⁻¹. -3 .

[0112] Example 7

[0113] The difference from Example 1 is that the deposition time in step (3) is 400 s, the SiH4 flow rate volume is 5000 sccm, the N2O flow rate volume is 15000 sccm, the duty cycle NO:OFF = 20:2000, and the silicon dioxide layer thickness is 1.5 nm. The junction depth of the formed boron-doped emitter is 0.55 μm, and the doping concentration is 6.05E+19 cm⁻¹. -3 .

[0114] Example 8

[0115] The difference from Example 1 is that the annealing temperature in step (5) is 1000℃ and the annealing time is 2h. The resulting boron-doped emitter has a junction depth of 0.68μm and a doping concentration of 6.1E+19cm. -3 .

[0116] Comparative Example 1

[0117] The difference from Example 1 is that step (3) was not performed. The junction depth of the formed boron-doped emitter is 0.81 μm and the doping concentration is 4.8E+19 cm⁻¹. -3 .

[0118] Comparative Example 2

[0119] The difference from Example 1 is that steps (3) and (4) were not performed. The junction depth of the formed boron-doped emitter is 0.41 μm and the doping concentration is 3.6E+19 cm⁻¹. -3 .

[0120] Comparative Example 3

[0121] The difference from Example 1 is that steps (2) and (3) were not performed. The junction depth of the formed boron-doped emitter is 0.8 μm and the doping concentration is 4.5E+19 cm⁻¹. -3 .

[0122] The thicknesses of BSG-1, silicon dioxide layer, and BSG-2 obtained in the above embodiments and comparative examples are shown in Table 1 below.

[0123] Table 1 plan BSG-1 thickness / nm Thickness of silicon dioxide layer / nm BSG-2 thickness / nm Junction depth / μm <![CDATA[Doping concentration / cm -3 > Example 1 10 1 23 0.53 6E+19 Example 2 12 1 23 0.45 5.8E+19 Example 3 11 1 23 0.46 5.68E+19 Example 4 10 1 33 0.69 6.1E+19 Example 5 10 1 28 0.65 6.05E+19 Example 6 10 2 23 0.51 6.08E+19 Example 7 10 1.5 23 0.55 6.05E+19 Example 8 10 1 23 0.68 6.1E+19 Comparative Example 1 10 none 23 0.81 4.8E+19 Comparative Example 2 10 none none 0.41 3.6E+19 Comparative Example 3 none none 23 0.8 4.5E+19

[0124] Boron-doped emitters were formed on the surface of a silicon substrate using the methods described in the above embodiments and comparative examples, and TOPcon cells were fabricated based on these emitters.

[0125] Fabrication of TOPcon batteries:

[0126] Based on step (5) in the above embodiments, the following steps are continued:

[0127] (6) Etching residual source layer: Etching is performed using diluted hydrofluoric acid etching solution to remove the borosilicate glass layer and silicon dioxide layer. The ratio of the etching solution is HF:H2O=1:100. After etching is completed, the surface is immediately rinsed with ultrapure water and dried to terminate the etching reaction and remove all chemical residues.

[0128] (7) Polishing treatment: The etched surface is polished by using alkaline colloidal silica polishing liquid through chemical-mechanical synergy.

[0129] (8) Deposition of tunneling oxide layer and amorphous silicon layer: SiH4 and N2O are introduced into the equipment at 430℃ and 12000W for deposition. The flow rate of SiH4 is 2000sccm and the flow rate of N2O is 8000sccm. After 20s of deposition, a tunneling oxide layer with a thickness of 2nm is deposited on the surface of the silicon dioxide layer.

[0130] Then, after evacuating the vacuum and purging the equipment with nitrogen, SiH4, PH3 and H2 were introduced into the equipment at 200℃ and 12000W. The flow rate of SiH4 was 2000 sccm, the flow rate of H2 was 8000 sccm and the flow rate of PH3 was 500 sccm. After 560s of deposition, an 80nm thick amorphous silicon layer was deposited on the surface of the tunneling oxide layer.

[0131] (9) Perform a second annealing treatment: Perform a second annealing treatment at 900℃ for 30 minutes.

[0132] (10) Deposition of silicon nitride antireflection layer: SiH4 and NH3 are introduced into the equipment at 430°C and 12000W for deposition. The flow rate of SiH4 is 2000 sccm and the flow rate of NH3 is 3000 sccm. After 520s, a silicon nitride antireflection layer with a thickness of 75nm is deposited on the surface.

[0133] (11) Printing silver paste, drying, sintering, and photoinjection treatment: Silver paste is printed on the silicon nitride antireflection layer and dried in a drying oven to form electrodes; it is then passed through a chain sintering furnace in an inert atmosphere at a sintering temperature of 700℃ to form ohmic contacts; and then at a temperature of 550℃ and a light intensity of 30kW / m 2 Light injection processing is performed under the specified conditions.

[0134] (12) Laser-assisted sintering process: The solar cell is irradiated with a high-intensity laser and a 12V deflection voltage is applied at the same time to reduce the contact resistance between the metal and the semiconductor.

[0135] Based on the TOPcon battery prepared above, performance tests were conducted:

[0136] The photoelectric conversion efficiency, short-circuit current, open-circuit voltage, and fill factor of the above embodiments and comparative examples were tested, and the test results are shown in Table 2.

[0137] The test methods for photoelectric conversion efficiency (Eta), short-circuit current (Isc), open-circuit voltage (Voc), and fill factor (FF) are as follows:

[0138] Place the battery in a light source with a power of 100 mW / cm². 2Under simulated sunlight at AM 1.5G and 25°C, voltage scanning was performed using a four-wire connection to the source meter, with corresponding current values ​​recorded simultaneously to obtain current-voltage (IV) curves. From these current-voltage (IV) curves, the photoelectric conversion efficiency, short-circuit current, open-circuit voltage, and fill factor can be directly obtained.

[0139] Table 2 Performance Number Eta / % Voc / mV Isc / A FF / % Example 1 25.91 740.6 18.488 83.45 Example 2 25.90 741.1 18.483 83.39 Example 3 25.89 740.9 18.485 83.40 Example 4 25.87 738.1 18.473 83.52 Example 5 25.88 738.6 18.478 83.48 Example 6 25.90 740.1 18.479 83.43 Example 7 25.91 740.3 18.483 83.48 Example 8 25.89 738.1 18.471 83.41 Comparative Example 1 25.78 736.1 18.488 83.32 Comparative Example 2 25.80 737 18.490 83.19 Comparative Example 3 25.76 736.2 18.469 83.16

[0140] As shown in Table 2 above, compared with Comparative Examples 1 to 3, the cell efficiency of Examples 1 to 8 is better when the BSG-1 thickness is 10nm~12nm, the SiO2 thickness is 1nm~2nm, and the BSG-2 thickness is 23nm~33nm, with significant improvements in open-circuit voltage (Voc) and fill factor (FF). Increasing the thickness of BSG-1 is beneficial to improving the open-circuit voltage (Voc), and increasing the thickness of BSG-2 is beneficial to improving the fill factor (FF). The silicon dioxide layer in the 1nm~2nm thickness range has no significant effect on efficiency. Therefore, this application can balance surface recombination rate and contact performance by depositing at least two borosilicate glass layers on the front side of the silicon substrate, depositing a silicon dioxide layer between two adjacent borosilicate glass layers, and making the B / O ratio of the outer borosilicate glass layer greater than that of the inner layer, thereby forming a high-surface-shallow junction and improving the open-circuit voltage and fill factor.

[0141] Although the steps in the above embodiments are described in the aforementioned sequence, those skilled in the art will understand that, to achieve the effects of this embodiment, different steps do not necessarily need to be executed in this order; they can be executed simultaneously (in parallel) or in a reversed order. These simple variations are all within the scope of protection of this application. The technical solution of the present invention has now been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, those skilled in the art will readily understand that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions resulting from these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a boron-doped emitter, characterized in that, Includes the following steps: At least two borosilicate glass layers are deposited on the front side of a silicon substrate, and a silicon dioxide layer is deposited between two adjacent borosilicate glass layers, wherein the molar ratio of boron to oxygen in each borosilicate glass layer increases layer by layer along the direction gradually away from the silicon substrate. The boron-doped emitter is formed by performing a first annealing process.

2. The preparation method according to claim 1, characterized in that, The borosilicate glass layer and the silicon dioxide layer are deposited using plasma-enhanced chemical vapor deposition.

3. The preparation method according to claim 2, characterized in that, The deposition conditions of the borosilicate glass layer closer to the silicon substrate satisfy at least one of the following conditions: The deposition time is 90s~120s; The flow volume of SiH4 is 2000 sccm~5000 sccm; The flow volume of B2H4 is 200 sccm~500 sccm; The flow rate of N2O is 12000 sccm~15000 sccm.

4. The preparation method according to claim 2, characterized in that, The deposition conditions of the borosilicate glass layer located far from the silicon substrate satisfy at least one of the following conditions: The deposition time is 200s~400s; The flow volume of SiH4 is 2000 sccm~5000 sccm; The flow volume of B2H4 is 800 sccm~1000 sccm; The flow rate of N2O is 8000 sccm~10000 sccm.

5. The preparation method according to claim 1, characterized in that, The deposition conditions of the silicon dioxide layer satisfy at least one of the following conditions: The flow rate of N2O is 9000 sccm~20000 sccm; The duty cycle NO:OFF is 20:1800~20:2200; The deposition time is 80s~120s.

6. The preparation method according to claim 1, characterized in that, The first annealing process is performed under an inert atmosphere; and / or The first annealing process conditions satisfy at least one of the following conditions: The annealing temperature is 960℃~1000℃; Annealing time is 1.5h~2h.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The preparation method includes: A first borosilicate glass layer, a silicon dioxide layer, and a second borosilicate glass layer are sequentially deposited on the front side of the silicon substrate, wherein the molar ratio of boron to oxygen in the second borosilicate glass layer is greater than the molar ratio of boron to oxygen in the first borosilicate glass layer.

8. The preparation method according to claim 7, characterized in that, The thickness of the first borosilicate glass layer is 10 nm to 12 nm; and / or The thickness of the second borosilicate glass layer is 23 nm to 33 nm; and / or The thickness of the silicon dioxide layer is 1 nm to 2 nm.

9. A boron-doped emitter, characterized in that, The boron-doped emitter is prepared by the preparation method of any one of claims 1 to 8.

10. The boron-doped emitter according to claim 9, characterized in that, The junction depth of the boron-doped emitter is 0.45 μm to 0.7 μm; and / or The doping concentration of the boron-doped emitter is 5.4E+19cm. -3 ~6.1E+19cm -3 .

11. A method for preparing a TOPcon battery, characterized in that, Includes the following steps: A silicon substrate is provided, and the silicon substrate is pretreated; A boron-doped emitter is formed on the front side of the silicon substrate using the fabrication method as described in any one of claims 1 to 8. Etching residual source layer; Polish the back side after removing the borosilicate glass layer; Deposition of tunneling oxide layer and amorphous silicon layer; Perform a second annealing process; Deposit silicon nitride antireflection layer; Silver paste is printed on the silicon nitride antireflection layer, dried and sintered, and then photoinjection is performed. The TOPcon battery was prepared by laser-assisted sintering.

12. A TOPcon battery, characterized in that, The TOPcon battery is prepared by the preparation method described in claim 11.

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