Low-temperature passivation method and application of BC battery

Abstract

The invention provides a low-temperature passivation method and application of a BC battery, and relates to the technical field of solar batteries. Specifically, the method comprises the following steps: sequentially depositing on the surface of a silicon substrate to obtain a La-doped Al2O3 layer, a SiO2 layer and an F-doped SiNx layer, and further obtaining a silicon material loaded with a three-layer passivation structure; all deposition temperatures in the low-temperature passivation method are less than or equal to 180 DEG C. The ultralow-temperature passivation process is provided for the back contact solar cell, the plasma-assisted ALD deposition process and the material doping modification method are innovatively combined, the temperature of the passivation process is reduced to 180 DEG C or below, and meanwhile the efficient passivation effect that iVoc is larger than or equal to 738 mV is achieved; and the problems of electrode warping, interface composite defects or unstable hydrogen passivation and the like caused by a high-temperature process are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and more specifically, to a low-temperature passivation method for BC cells and its application. Background Technology

[0002] Back-contact (BC) solar cells achieve unobstructed light absorption on the front by placing both the positive and negative electrodes on the back of the cell, thereby improving photoelectric conversion efficiency. The core structure of a BC solar cell can be summarized as a front light-absorbing layer and a back composite functional layer; specifically, the front structure includes an anti-reflection layer and a silicon substrate, while the back structure includes a passivation layer, a doped layer, electrodes, and an insulating layer. During the fabrication of BC solar cells, a passivation layer needs to be deposited on one side of the silicon substrate. Common passivation components include Al₂O₃ and SiN. x Passivation is a key process for improving the efficiency of BC cells. Its core objective is to reduce the surface recombination rate, thereby reducing carrier loss. It is a critical step in the fabrication of BC solar cells.

[0003] In current conventional passivation processes, for example, a two-layer passivation film structure is used: the bottom layer is Al2O3 deposited at 220℃, which utilizes its high negative fixed charge density to achieve field-effect passivation and suppress surface recombination; the top layer is SiN deposited at 200℃. x Hydrogenation further passivates defects in the silicon substrate and simultaneously acts as an antireflective layer to enhance light absorption; SiON is used as the bottom and top transition layer. In this case, during the subsequent metallization process of silver paste sintering, the mismatch in the thermal expansion coefficients between the film layer and the silicon substrate leads to interfacial stress concentration; at the same time, nitrogen plasma treatment may introduce nitrogen doping, changing the stoichiometry of the SiON transition layer and reducing its elastic modulus. Ultimately, this results in local warping of the silver paste region, with height differences reaching 5~10 μm, causing electrode breakage or increased contact resistance.

[0004] In another case, a ZnO / Al2O3 mixed passivation layer was first generated by alternately introducing Zn(CH3)2 and Al(CH3)3 precursors at 250°C using atomic layer deposition; then, SiN was deposited at 200°C. x In this case, ultraviolet light-assisted SiN photoluminescence is required. x Curing, ultraviolet photon energy can excite SiN x The Si-H bonds in the film break, generating active Si radicals, which promotes increased crosslinking density and reduces defect state density. Further laser-induced localized annealing is needed to repair damage to the electrode region caused by UV light treatment, and to reduce recombination centers through localized lattice reconstruction. Therefore, while laser-induced localized annealing is necessary, it significantly increases operational complexity and production costs.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a low-temperature passivation method for BC batteries, which addresses the defects caused by high-temperature processes, such as electrode warping, high composite interface density, and unstable hydrogen passivation.

[0007] A second objective of the present invention is to provide a passivation layer for a BC battery.

[0008] A third objective of this invention is to provide an application of the aforementioned low-temperature passivation method.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A low-temperature passivation method for BC batteries includes the following steps: (1) A La-doped Al2O3 layer was obtained on the surface of a silicon substrate by plasma-enhanced atomic layer deposition. (2) A SiO2 layer is obtained on the surface of the Al2O3 layer by plasma-enhanced atomic layer deposition or plasma-enhanced chemical vapor deposition, and the thickness of the SiO2 layer is 1.5 nm to 3 nm. (3) F-doped SiN was obtained on the surface of the SiO2 layer by plasma-enhanced chemical vapor deposition. x The layers are then used to obtain a silicon material with a three-layer passivation structure. The deposition temperature in the low-temperature passivation method is ≤180℃.

[0010] Preferably, the low-temperature passivation method further includes: pre-treating the silicon substrate before step (1); The pretreatment includes treating the silicon substrate at 45℃~55℃ for 3min~15min using dual-frequency plasma technology; the dual-frequency plasma includes high-frequency plasma and low-frequency plasma, wherein the frequency of the high-frequency plasma is 12MHz~15MHz and the frequency of the low-frequency plasma is 250kHz~300kHz. More preferably, the working gas of the dual-frequency plasma technology includes hydrogen and argon, with a volume ratio of 5%~30%:70%~95%.

[0011] Preferably, for the La-doped Al2O3 layer, the mass ratio of La to Al2O3 is 0.5%~5%: 95%~99.5%.

[0012] Preferably, for the F-doped SiN x Layer, F and SiN x The mass ratio is 1%~8%: 92%~99%.

[0013] Preferably, the thickness of the La-doped Al2O3 layer is 4.5 nm to 6 nm.

[0014] Preferably, the F-doped SiN x The thickness of the layer is 65nm~75nm.

[0015] Preferably, the total thickness of the passivation layer is 72nm~86nm.

[0016] Preferably, the deposition temperature of the plasma-enhanced atomic layer deposition method in step (1) is 80℃~180℃; The raw materials include an aluminum source, a lanthanum source, and an oxygen source, wherein the aluminum source includes trimethylaluminum, the lanthanum source includes at least one of tris(cyclopentadienyl)lanthanum or β-diketone lanthanum complexes, and the oxygen source includes at least one of oxygen or water vapor.

[0017] Preferably, the deposition temperature of the plasma-enhanced atomic layer deposition method in step (2) is 100℃~180℃; The raw materials include a silicon source and an oxygen source, wherein the silicon source includes at least one of bis(tert-butylamino)silane or tris(dimethylamino)silane, and the oxygen source includes at least one of oxygen or ozone.

[0018] Preferably, the deposition temperature of the plasma-enhanced chemical vapor deposition method in step (2) is 80℃~180℃; The raw materials include a working gas, a reactant gas, and an auxiliary gas; wherein the working gas includes argon with a flow rate of 50 sccm to 150 sccm; the reactant gas includes at least one of nitrous oxide or oxygen with a flow rate of 5 sccm to 30 sccm; and the auxiliary gas includes nitrogen with a flow rate of 200 sccm to 500 sccm.

[0019] Preferably, the deposition temperature of the plasma-enhanced chemical vapor deposition method in step (3) is 150°C to 180°C; The raw materials include a silicon source, a nitrogen source, and a fluorine source, wherein the silicon source includes silane, the nitrogen source includes at least one of ammonia or nitrogen, and the fluorine source includes at least one of silicon tetrafluoride or nitrogen trifluoride.

[0020] And the passivation layer prepared by the low-temperature passivation method described above.

[0021] And the application of the low-temperature passivation method as described in BC solar cells.

[0022] This invention proposes an ultra-low temperature passivation process for back-contact solar cells. By innovatively combining plasma-assisted ALD deposition and material doping modification methods, the passivation process temperature is reduced to below 180℃. Compared to the minimum passivation temperature of 220℃~250℃ in existing technologies, this invention uses a La-doped Al2O3 layer as the base passivation layer, introduces a low-nanoscale SiO2 layer as a transition layer, and combines it with an F-doped SiN... x The "layer" serves as a capping layer, integrally constructing a passivation structure. While achieving highly efficient passivation with iVoc≥738mV, it also addresses electrode warpage (warpage amplitude <0.05mm) and interface recombination (interface state density <7×10⁻⁶) caused by high-temperature processes. 10 cm -2 It also has technical defects such as unstable hydrogen passivation (hydrogen escape temperature increases to 450℃).

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Breakthrough in ultra-low temperature process: This invention adopts innovative plasma-assisted ALD technology and dual-frequency PECVD process to reduce the passivation process temperature from above 220℃ to below 180℃. This not only completely avoids the thermal damage of electrode silver paste caused by high temperature, reduces electrode warping and avoids electrode damage, but also reduces process energy consumption by 40%.

[0024] (2) Significantly improved interface performance: Through the original La-doped Al2O3 and the design of a low-nanoscale SiO2 layer with precise atomic layer control, this invention improves the interface state density from the traditional 3×10 11 cm -2 Reduced to 7×10 10 cm -2 (77% reduction), improving minority carrier lifetime by 54% to 2.8ms, while achieving efficient passivation effect with iVoc≥738mV, effectively improving battery conversion efficiency.

[0025] (3) Significantly improved stability and uniformity: This invention uses F-doped SiN x By combining dual-frequency plasma control technology, the hydrogen escape temperature is increased from 350℃ to 450℃, the decay rate is reduced to 0.7% (better than the traditional 1.5%), and the film thickness uniformity reaches ±0.8% (the traditional is only ±12%), achieving high stability and high uniformity far exceeding the industry average. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0027] The first aspect of the present invention is to provide a low-temperature passivation method for BC batteries, which mainly includes the following steps (1) to (3): (1) A La-doped Al2O3 layer was obtained on the surface of a silicon substrate by plasma-enhanced atomic layer deposition. (2) A SiO2 layer is obtained on the surface of the Al2O3 layer by plasma-enhanced atomic layer deposition, and the thickness of the SiO2 layer is 1.5 nm to 3 nm. (3) F-doped SiN was obtained on the surface of the SiO2 layer by plasma-enhanced chemical vapor deposition. x The layers are then used to obtain a silicon material with a three-layer passivation structure.

[0028] It is worth noting that in the low-temperature passivation method of the present invention, the deposition temperature for the above three-layer structure is ≤180℃; it can also be understood that any heat treatment temperature involved in the low-temperature passivation method is ≤180℃.

[0029] As a preferred embodiment, the low-temperature passivation method further includes: performing a pretreatment of the silicon substrate before step (1); and the pretreatment includes: treating the silicon substrate at 45°C to 55°C for 3 min to 15 min using dual-frequency plasma technology.

[0030] It is worth noting that in the pretreatment, the silicon substrate needs to be directly contacted with dual-frequency plasma, but this does not mean touching the silicon wafer surface with a solid electrode. Instead, the silicon substrate is directly exposed to an atmosphere filled with highly reactive reactants generated by dual-frequency plasma.

[0031] In a more preferred embodiment, the dual-frequency plasma includes high-frequency plasma and low-frequency plasma; wherein the frequency of the high-frequency plasma is 12MHz~15MHz, and the frequency of the low-frequency plasma is 250kHz~300kHz.

[0032] In a more preferred embodiment, the working gas of the dual-frequency plasma technology includes hydrogen and argon, with a volume ratio of 5%~30%:70%~95%. In some atypical embodiments, the volume ratio of hydrogen to argon is 25%:75%, at which point a relatively high proportion of hydrogen is already present. The working gas focuses on chemical reduction and in-situ hydrogen passivation, while physical bombardment is weaker, resulting in less damage to the surface lattice and the generation of more Si-H bonds.

[0033] In a more preferred embodiment, the power of the working gas is 250W~350W and 120W~180W. It is understood that the gas power determines the ion energy bombarding the silicon wafer surface; the higher the energy, the stronger the physical sputtering or bombardment effect. On the one hand, in the low-temperature process of this invention, the ion energy must be strictly controlled to avoid lattice damage; on the other hand, sufficient energy needs to be provided to clean the surface (typically >20eV for sputtering oxides), but far below the threshold for causing bulk damage (above ~50eV).

[0034] It is worth noting that in some atypical embodiments, the working gas includes oxygen. However, if not properly controlled, the resulting oxide layer may be too thick or of poor quality, which could hinder the deposition of the subsequent Al2O3 layer and affect the interface quality. Therefore, it is not a primary preferred feature. Argon, on the other hand, is the main source of plasma generation. Argon ions can effectively remove the outermost natural oxide layer and trace organic contaminants through physical bombardment or sputtering, exposing a fresh silicon surface. Simultaneously, it increases surface roughness at the nanoscale, improving the adhesion of subsequent films. Furthermore, hydrogen can achieve chemical reduction. Hydrogen ions and hydrogen radicals can reduce the thin layer of natural silicon oxide already present on the silicon surface, converting it into volatile water molecules or silicon tetrahydride, which are then removed, further cleaning the surface. In addition, hydrogen radicals can combine with the dangling bonds on the cleaned silicon surface to form Si-H bonds, achieving preliminary passivation of the surface states. This is highly beneficial for obtaining excellent final passivation results.

[0035] In a preferred embodiment, the mass ratio of La to Al2O3 in the La-doped Al2O3 layer is 0.5%~5%:95%~99.5%. In this invention, the lower limit of the La content in this layer is higher than 0.5 wt.%, ensuring sufficient La atoms to effectively modify the film structure and interface properties of Al2O3. Simultaneously, the upper limit of the La content in this layer is lower than 5 wt.%, to avoid excessive doping leading to a decrease in film quality, the formation of defects, and a reduction in passivation effect. In some more preferred embodiments, the mass ratio of La to Al2O3 is 2%:98%, a ratio that balances performance improvement with matrix structure stability.

[0036] As a preferred embodiment, for the F-doped SiN x Layer, F and SiN x The mass ratio is 1%~8%: 92%~99%; in this invention, the lower limit of the F content in this layer is higher than 1 wt.% to ensure sufficient F atoms to have a measurable positive effect on the film. If it is lower than this value, the doping effect may be negligible; at the same time, the upper limit of the F content in this layer is lower than 8 wt.% to prevent excessive F content from causing problems in SiN. x The dense network structure becomes loose and porous, thereby reducing its passivation quality and environmental stability, such as a decrease in its ability to block water vapor and sodium ions. In some preferred embodiments, F in the F-doped SiN x The mass content of the layer is 2% to 5%. Within this range, F can effectively play its positive role while avoiding obvious negative effects.

[0037] In a preferred embodiment, the thickness of the La-doped Al2O3 layer is 4.5 nm to 6 nm, more preferably 5 nm. This thickness range represents the "sweet spot" for Al2O3 to achieve optimal field-effect passivation. On one hand, the lower thickness limit (~4.5 nm) ensures that the film is sufficiently continuous and dense to form an effective negative charge layer for field-effect passivation. If it is too thin (e.g., <3 nm), it may lead to charge inhomogeneity or film discontinuity. On the other hand, the upper thickness limit (~6 nm) is as thin as possible while ensuring performance, because the ALD deposition rate of Al2O3 is relatively slow, and a thinner layer means a shorter production time. Simultaneously, for the entire stacked structure, a thicker SiN layer allows for... x A thicker layer allows for better anti-reflective properties.

[0038] As a preferred embodiment, the F-doped SiN x The layer thickness is 65nm~75nm. This is understandable for crystalline silicon solar cells, where SiN... x As an antireflective layer, its optimal thickness is determined by the formula d=λ / (4n); where λ is the target wavelength (typically 600nm, i.e., the green light region most sensitive to human eyes and solar cells), and n is the SiN... x The refractive index of F-doped SiN deposited at low temperature in this invention is... x The refractive index is calculated to be approximately 2.0, and the optimal thickness for this layer is obtained through calculation.

[0039] Calculation: Optimal thickness d = 600nm / (4 × 2.0) = 75nm.

[0040] In a preferred embodiment, the total thickness of the passivation layer is 72nm~86nm.

[0041] In the silicon material system with a three-layer passivation structure prepared in this invention, each layer has a different function and sensitivity to thickness: the La-doped Al2O3 layer is the "functional core," and its thickness only needs to meet the field-effect passivation threshold; further thickness is not beneficial but increases cost and time, and it is more preferable to account for 6.5% of the total thickness. The F-doped SiN... x The first layer, the "volume matrix and optical control layer," determines the anti-reflective effect and mechanical protection performance of the entire stack, and preferably accounts for 91% of the total thickness. The SiO2 layer is the "interface layer," with a fixed, atomically thin thickness, mainly used for interface adjustment and not involved in the proportional distribution. Therefore, a more reasonable concept of "proportion" is: while ensuring the core function of Al2O3, allow SiN... x The layer achieves its optically optimal thickness, but there is no universal "passivation layer / silicon substrate thickness ratio". The silicon wafer thickness (for mechanical strength and light absorption) and the passivation layer thickness (for passivation and anti-reflection) should be optimized separately.

[0042] In a preferred embodiment, the temperature of the plasma-enhanced atomic layer deposition (ALD) in step (1) is 80°C to 180°C, and the raw materials include an aluminum source, a lanthanum source, and an oxygen source. The aluminum source includes trimethylaluminum (TMA, Al(CH3)3), the lanthanum source includes at least one of tri(cyclopentadienyl)lanthanum (La(Cp)3) or β-diketone lanthanum complexes (such as La(thd)3), and the oxygen source includes at least one of oxygen or water vapor.

[0043] As a preferred embodiment, the plasma-enhanced atomic layer deposition (ALD) method in step (1) includes the following specific steps: S1. Cavity preparation: The cleaned silicon substrate is sent into the ALD reaction chamber, evacuated and heated to the set temperature. S2. Introduce aluminum and oxygen sources into the ALD reaction chamber and pulse 20-30 times. Then, switch to pulsed introduction of lanthanum and oxygen sources and pulse 1-3 times. Repeat step S3 and step S2 20 to 50 times until the desired thickness of the La-doped Al2O3 layer is obtained.

[0044] In a preferred embodiment, the temperature of the plasma-enhanced atomic layer deposition (ALD) in step (2) is 100°C to 180°C, i.e., thermal ALD; the raw materials include a silicon source and an oxygen source, wherein the silicon source includes aminosilanes, including at least one of bis(tert-butylamino)silane (BTBAS, SiH2(NHC(CH3)3)2) or tris(dimethylamino)silane (3DMAS), and the oxygen source includes at least one of oxygen or ozone.

[0045] As a preferred embodiment, the plasma-enhanced atomic layer deposition (ALD) method in step (2) includes specific steps adapted to the method in step (1) above.

[0046] In a preferred embodiment, the plasma-enhanced chemical vapor deposition (PECVD) in step (2) employs dual-frequency PECVD. Silicon atoms are generated by sputtering a silicon target using LF power, while oxygen free radicals are generated by exciting the reactive gas using HF power. These two processes react on the surface of the previously prepared substrate to form a SiO2 layer. Furthermore, a high-purity silicon target is used as the upper electrode (cathode), and the substrate is placed on the lower electrode (anode).

[0047] As a preferred embodiment, the plasma-enhanced chemical vapor deposition (PECVD) in step (2) includes one or more of the following features: (A) The working gas includes argon, and the flow rate of the working gas is 50 sccm to 150 sccm.

[0048] (B) The reaction gas includes at least one of nitrous oxide (N2O) or oxygen (O2), and the flow rate of the reaction gas is 5 sccm to 30 sccm; in this invention, the reaction gas provides an oxygen source, wherein nitrous oxide decomposes in plasma into nitrogen gas and reactive oxygen free radicals, which react with sputtered silicon atoms to generate SiO2; nitrous oxide is milder than oxygen, easier to control the oxidation rate, and more suitable for ultrathin layers.

[0049] (C) The auxiliary gas includes nitrogen, and the flow rate of the auxiliary gas is 200 sccm to 500 sccm. In this invention, the auxiliary gas can dilute the gas concentration, stabilize the plasma, and help control the deposition rate to achieve precise control of the ultrathin layer. Furthermore, it is necessary to control the flow rate of the auxiliary gas, thereby indirectly controlling the ratio between the reactive gas and the working gas to prevent excessively rapid deposition and excessive oxidation of the silicon target surface.

[0050] (D) The pressure in the deposition chamber is 3~20 mTorr, or the pressure in the deposition chamber is 0.4 Pa~2.7 Pa; lower pressure is conducive to the formation of directional, high-energy ion flow, thereby obtaining a denser film with fewer defects, which is the key to obtaining a high-quality ultrathin SiO2 layer.

[0051] (E) The high-frequency (HF) plasma of the dual-frequency plasma has a frequency of 12MHz~28MHz and a power of 250W~350W; the low-frequency (LF) plasma has a frequency of 100kHz~400kHz and a power of 120W~180W. In this invention, the main function of the high-frequency plasma is to generate high-density plasma and efficiently decompose the reactive gases to produce a large number of oxygen free radicals; while the main function of the low-frequency plasma is to control the sputtering rate of argon ions on the silicon target. The higher the power, the more silicon atoms are sputtered and the faster the deposition rate. For ultrathin layers, a lower LF power must be used to reduce the deposition rate for easier control; at the same time, high LF power should be avoided to prevent damage to the underlying substrate.

[0052] (F) The deposition temperature is 80℃~180℃, which fully meets the requirement of ≤180℃; the deposition chamber is a high vacuum environment, and the background vacuum level is recommended to be better than 1.0×10⁻⁶. -5 Torr is designed to minimize pollution.

[0053] (G) The deposition time is 5s~30s; at the same time, the film thickness is monitored in real time with an in-situ ellipsometry, and deposition is stopped immediately when the thickness reaches the target midpoint.

[0054] In a preferred embodiment, the temperature of the plasma-enhanced chemical vapor deposition (PECVD) in step (3) is 150°C to 180°C; the reaction gas includes a silicon source, a nitrogen source and a fluorine source, wherein the silicon source includes silane (SiH4), the nitrogen source includes at least one of ammonia (NH3) or nitrogen (N2), and the fluorine source includes at least one of silicon tetrafluoride (SiF4) or nitrogen trifluoride (NF3).

[0055] As a preferred embodiment, the plasma-enhanced chemical vapor deposition (PECVD) in step (3) includes the following specific steps: S1. The precursor obtained in step (2) is sent into the PECVD reaction chamber, evacuated and heated to the set temperature. S2. Reactant gas and carrier gas are introduced into the reaction chamber, and then plasma is excited and a deposition reaction is carried out to obtain the F-doped SiN. x layer.

[0056] In some embodiments, by activating the radio frequency power supply, a glow discharge is generated in the reaction chamber to form plasma, which dissociates the reaction gas into highly active free radicals and ions. These active groups undergo chemical reactions and are deposited on the silicon wafer surface. After deposition is completed, the power supply and reaction gas are turned off, and the wafer is cooled in a carrier gas atmosphere to obtain the final product.

[0057] As a more preferred embodiment, the plasma-enhanced chemical vapor deposition (PECVD) in step (3) includes one or more of the following features: (A) In the reaction gas, the flow rate of the silicon source is 10 sccm to 50 sccm, the flow rate of the nitrogen source is 100 sccm to 500 sccm, and the flow rate of the fluorine source is 5 sccm to 20 sccm; the carrier gas is an inert gas, including but not limited to helium, neon, argon, etc.

[0058] (B) The process pressure is 80~300 mTorr, or the process pressure is 10 Pa~40 Pa; when the pressure is higher, the plasma is "softer" and the film uniformity is good, but it may be more porous; when the pressure is lower, the ion bombardment energy is enhanced and the film is more dense; for the low temperature process of the present invention, the above-mentioned medium and low pressure range is preferred, and 150~250 mTorr is even more preferred, so as to balance the film quality and uniformity.

[0059] (C) Dual-frequency PECVD is used. The dual-frequency plasma parameters include: high frequency (HF) frequency of 13MHz~28MHz and power of 250W~350W. High-density plasma is generated through high-frequency plasma, which decomposes the reactive gases to generate active free radicals (such as SiH3). + The primary energy source for ions (N, H) determines the deposition rate. Additionally, the low-frequency (LF) plasma, with a frequency of 250kHz–300kHz and a power of 120W–180W, controls the bombardment energy of ions on the grown film surface. Appropriate low-frequency power can: 1) increase film density through the "hammering" effect of ion bombardment, making the film more compact; 2) regulate stress, shifting the internal stress of the film from tensile stress to compressive stress, which is beneficial for passivation performance; and 3) promote F incorporation, as appropriate bombardment helps F atoms bond more effectively to SiN. x In the network. Meanwhile, under the low-temperature conditions of this invention, the LF power should not be too high to avoid ion damage to the underlying ultrathin layers.

[0060] (D) The deposition temperature is 150℃~180℃, which fully meets the requirement of ≤180℃; the deposition chamber is a high vacuum environment, and the background vacuum level is recommended to be better than 5.0×10⁻⁶. -6 Torr is designed to minimize pollution.

[0061] (E) The deposition rate is 2nm / s to 5nm / s, and the deposition time is calculated based on the preset thickness and deposition rate of this layer. At the same time, the thickness and refractive index are monitored in real time using an in-situ laser reflectometer or ellipsometry to ensure that the thickness and optical constants meet the requirements.

[0062] (F) The F-doped SiN xThe refractive index of the layer (n@632.8nm) is 1.95~2.10. In this invention, the incorporation of F usually slightly reduces the refractive index. The film stress is ideal under slight compressive stress (-100 to -400MPa).

[0063] A second aspect of the present invention is to provide a passivation layer prepared by the low-temperature passivation method described in the first aspect.

[0064] A third aspect of the invention is to provide the use of the low-temperature passivation method as described in the first aspect in BC solar cells.

[0065] Example 1 (1) Deposit a La-doped Al2O3 layer on the silicon substrate: This step is the core of the passivation layer and is responsible for providing excellent field-effect passivation.

[0066] Deposition is performed using plasma-enhanced atomic layer deposition (ALD), with the following specific cycle steps: (1.1) Chamber preparation: The cleaned silicon substrate is sent into the ALD reaction chamber, evacuated and heated to the set temperature (e.g., 150°C).

[0067] (1.2) Al2O3 sub-loop (executed 24 times in total): Pulsed TMA 0.1s: TMA vapor is pulsed into the cavity, and TMA molecules will be chemically adsorbed on the silicon wafer surface; 8s purging: Purge with an inert gas (such as high-purity nitrogen) to remove excess precursors and byproducts.

[0068] Pulsed oxygen plasma 4s: Oxygen is introduced and radio frequency (RF) plasma is activated to generate active oxygen free radicals, which react with adsorbed TMA to generate Al2O3; Purge for 8 seconds: Purge again to remove reaction byproducts.

[0069] (1.3) La2O3 sub-loop (executes 1 loop): Pulsed La precursor 3s: Heated La precursor La(Cp)3 vapor (170℃) is pulsed into the cavity, causing it to adsorb onto the surface; Purge for 12 seconds: Purge to remove excess La precursors; Pulsed oxygen plasma 4s: O2 plasma is also used to oxidize it to form La2O3; Purge for 8 seconds: Purge to remove byproducts.

[0070] (1.4) By precisely controlling “24 Al2O3 cycles + 1 La2O3 cycle” as a “supercycle” and repeating it multiple times, uniform La doping can be achieved at the atomic scale, and La-doped Al2O3 films can be obtained. Perform the supercycle k times (e.g., k=40, to obtain the final required layer thickness of 5nm).

[0071] (2) Deposit an ultrathin SiO2 layer on the surface of the Al2O3 layer. This step requires the deposition of an extremely uniform and dense ultrathin layer.

[0072] Deposition is performed using plasma-enhanced atomic layer deposition (ALD), and the specific operational steps are as follows: (2.1) Cavity preparation: After completing the previous step, this step can be performed directly in the same ALD device while maintaining the previous temperature and vacuum environment.

[0073] (2.2) ALD loop: Pulsed Si precursor 4s: The selected silicon source precursor is pulsed into the cavity, causing it to be chemically adsorbed on the surface of the La-doped Al2O3 layer. Purge for 10 seconds: Thoroughly purge with argon gas; Pulse reactant 4s: Introduce oxygen source O3; Blow for 10 seconds: Blow again.

[0074] (2.3) Thickness control: The thickness of SiO2 is precisely controlled by the number of ALD cycles; each cycle grows approximately 0.1~0.12 nm of SiO2. In this embodiment, a thickness of 2 nm requires 20 cycles; in this way, the uniformity of the film and precise thickness control can be ensured.

[0075] (3) Deposit F-doped SiN on the surface of the SiO2 layer x This layer acts as a protective cap layer, providing anti-reflection, surface protection, and additional hydrogen passivation.

[0076] Deposition was performed using plasma-enhanced chemical vapor deposition (PECVD), and the specific operational steps are as follows: (3.1) Chamber preparation: The sample is sent into the PECVD reaction chamber, vacuumed and heated to the set temperature.

[0077] (3.2) Introducing reaction gas: Introducing reaction gas into the cavity at a precisely controlled flow rate.

[0078] (3.3) Excite plasma: Start the radio frequency (RF) power supply to generate glow discharge in the reaction chamber and form plasma; the plasma dissociates the reaction gas into highly active free radicals and ions.

[0079] (3.4) Deposition reaction: These active groups undergo a chemical reaction on the silicon wafer surface, depositing to form F-doped SiN. x film.

[0080] (3.5) Deposition complete: After the preset deposition time is reached, the RF power supply and reaction gas are turned off, and the layer with a thickness of 75nm is obtained by cooling in an inert atmosphere.

[0081] The specific parameters for this step are shown in Table 1 below.

[0082] Table 1

[0083] Example 2 The process is basically the same as in Example 1, except that: in step (2), plasma-enhanced chemical vapor deposition (dual-frequency PECVD) is used for deposition. The specific operation steps are the same as in step (3) of Example 1, and the specific raw materials and parameters are shown in Table 2 below.

[0084] Table 2

[0085] Comparative Example 1: Step (1) of Example 1 was performed only to obtain a La-doped Al2O3 layer (5 nm) loaded on a silicon substrate.

[0086] Comparative Example 2: Only step (3) of Example 1 was performed, and no silicon source gas was introduced in step (3) to obtain SiN loaded on a silicon substrate. x Layer (75nm).

[0087] Comparative Example 3: Basically the same as Example 1, except that: La doping is not performed in step (1) (step 1.3 is not operated), and silicon source gas is not introduced in step (3), resulting in Al2O3-SiO2-SiN loaded on a silicon substrate. x Layer (70nm).

[0088] Test case All examples and comparative examples are based on the standard process flow of BC cells for n-type silicon wafers. The corresponding BC cells were prepared and tested, and the results are shown in Table 3 below.

[0089] Table 3

[0090] As can be seen from Table 3: Comparative Example 1 has the following characteristics: a) Low Jsc and high reflectivity: lack of SiN xThe anti-reflective cap layer results in significant long-wavelength light loss and extremely low short-circuit current density. b) Insufficient Voc: Although La-Al2O3 itself provides adequate passivation, the lack of a protective layer makes it susceptible to damage during subsequent electrode sintering and other processes, exhibiting the worst stability. This confirms that a single layer of Al2O3 cannot meet the optical and stability requirements of BC batteries.

[0091] Comparative Example 2 exhibits the following characteristics: lowest Voc and efficiency: The high-temperature process of 400℃ severely damaged the delicate doped junctions on the back of the BC cell (especially heterojunctions or sensitive doped regions), leading to a surge in interfacial recombination and a significant drop in open-circuit voltage. This demonstrates that a low-temperature process (≤180℃) is essential for BC cells, and traditional high-temperature SiN… x The process is not applicable.

[0092] Comparative Example 3 exhibits the following characteristics: good performance: Al2O3 / SiO2 / SiN x The composite structure itself combines excellent passivation and anti-reflection capabilities, and its performance is significantly superior to that of a single-layer structure. Although not as good as the embodiments of the present invention, it still verifies the rationality and fundamental advantages of the composite layered structure.

[0093] Example 1 has the following features: a) Comprehensive performance advantages: Highest Voc (750mV): La doping optimizes the negative charge density and stability of Al2O3, and F doping enhances SiN x The chemical passivation capability, through synergistic effect, achieves a top-tier passivation level. (b) Highest Jsc (42.2 mA / cm²) 2 ): F-SiN x It provides optimal anti-reflection performance and better internal reflection. c) Highest efficiency (25.6%) and best stability: Comprehensive performance improvements and a dense thin-film structure result in higher conversion efficiency and excellent long-term reliability.

[0094] Therefore, this invention exhibits significant advantages in passivation quality, optical performance, and long-term stability, making it an ideal passivation solution for achieving high-efficiency and high-reliability BC batteries.

[0095] Furthermore, the passivation process of this invention achieves a decrease in overall process temperature without affecting the effect: existing passivation requires at least 220°C, and the high temperature can easily deform the metal electrode on the back side. This invention uses special gas and plasma technology, and the passivation only requires 180°C. The temperature is lower, but the effect is better, and it will not damage the electrode. Furthermore, the present invention features a more refined intermediate layer: existing passivation patent transition layer materials result in significant internal losses within the battery; the present invention, through an ultra-thin buffer layer, significantly reduces internal losses within the battery.

[0096] Furthermore, this invention achieves comprehensive performance improvement: low temperature, high efficiency, long lifespan, and low cost, resulting in a significant overall performance enhancement.

[0097] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A low-temperature passivation method for BC batteries, characterized in that, Includes the following steps: (1) A La-doped Al2O3 layer was obtained on the surface of a silicon substrate by plasma-enhanced atomic layer deposition. (2) A SiO2 layer is obtained on the surface of the Al2O3 layer by plasma-enhanced atomic layer deposition or plasma-enhanced chemical vapor deposition, and the thickness of the SiO2 layer is 1.5 nm to 3 nm. (3) F-doped SiN was obtained on the surface of the SiO2 layer by plasma-enhanced chemical vapor deposition. x The layers are then used to obtain a silicon material with a three-layer passivation structure. The deposition temperature in the low-temperature passivation method is ≤180℃.

2. The low-temperature passivation method according to claim 1, characterized in that, The low-temperature passivation method further includes: performing a pretreatment of the silicon substrate before step (1); The pretreatment includes treating the silicon substrate at 45℃~55℃ for 3min~15min using dual-frequency plasma technology; the dual-frequency plasma includes high-frequency plasma and low-frequency plasma, wherein the frequency of the high-frequency plasma is 12MHz~15MHz and the frequency of the low-frequency plasma is 250kHz~300kHz. Preferably, the working gas of the dual-frequency plasma technology includes hydrogen and argon, with a volume ratio of 5%~30%:70%~95%.

3. The low-temperature passivation method according to claim 1, characterized in that, For the La-doped Al2O3 layer, the mass ratio of La to Al2O3 is 0.5%~5%: 95%~99.5%; And / or, for the F-doped SiN x Layer, F and SiN x The mass ratio is 1%~8%: 92%~99%.

4. The low-temperature passivation method according to claim 1, characterized in that, The thickness of the La-doped Al2O3 layer is 4.5 nm to 6 nm; And / or, the F-doped SiN x The thickness of the layer is 65nm~75nm; And / or, the total thickness of the passivation layer is 72nm~86nm.

5. The low-temperature passivation method according to claim 1, characterized in that, The deposition temperature of the plasma-enhanced atomic layer deposition method in step (1) is 80℃~180℃; The raw materials include an aluminum source, a lanthanum source, and an oxygen source, wherein the aluminum source includes trimethylaluminum, the lanthanum source includes at least one of tris(cyclopentadienyl)lanthanum or β-diketone lanthanum complexes, and the oxygen source includes at least one of oxygen or water vapor.

6. The low-temperature passivation method according to claim 1, characterized in that, The deposition temperature of the plasma-enhanced atomic layer deposition method in step (2) is 100℃~180℃; The raw materials include a silicon source and an oxygen source, wherein the silicon source includes at least one of bis(tert-butylamino)silane or tris(dimethylamino)silane, and the oxygen source includes at least one of oxygen or ozone.

7. The low-temperature passivation method according to claim 1, characterized in that, The deposition temperature of the plasma-enhanced chemical vapor deposition method in step (2) is 80℃~180℃; The raw materials include a working gas, a reactant gas, and an auxiliary gas; wherein the working gas includes argon with a flow rate of 50 sccm to 150 sccm; the reactant gas includes at least one of nitrous oxide or oxygen with a flow rate of 5 sccm to 30 sccm; and the auxiliary gas includes nitrogen with a flow rate of 200 sccm to 500 sccm.

8. The low-temperature passivation method according to claim 1, characterized in that, The deposition temperature of the plasma-enhanced chemical vapor deposition method in step (3) is 150℃~180℃; The raw materials include a silicon source, a nitrogen source, and a fluorine source, wherein the silicon source includes silane, the nitrogen source includes at least one of ammonia or nitrogen, and the fluorine source includes at least one of silicon tetrafluoride or nitrogen trifluoride.

9. The passivation layer prepared by the low-temperature passivation method according to any one of claims 1 to 8.

10. Use of the low-temperature passivation method as described in any one of claims 1 to 8 in BC solar cells.

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