Double-sided back contact battery and preparation method and application thereof

Abstract

The invention relates to the field of back contact batteries, in particular to a double-sided back contact battery and a preparation method and application thereof. The double-sided back contact cell comprises: an n-type monocrystalline silicon substrate; the optical function layer is arranged on the front surface of the n-type monocrystalline silicon substrate and comprises an antireflection layer and a passivation layer; the composite functional layer is arranged on the back surface of the n-type monocrystalline silicon substrate and sequentially comprises an aluminum oxide passivation transition layer, a gradient antimony-doped zinc sulfide buffer layer, a titanium nitride transition layer, an indium tin oxide transparent conductive layer and a copper grid line electrode formed on the indium tin oxide transparent conductive layer from inside to outside; the antimony concentration of the gradient antimony-doped zinc sulfide buffer layer is increased in a gradient mode from inside to outside. According to the double-sided back contact battery, the photoelectric property and the long-term reliability of a back interface are synergistically optimized through the back composite structure design.

Description

Technical Field

[0001] This invention relates to the field of back contact batteries, and more specifically, to a bi-sided back contact battery, its preparation method, and its application. Background Technology

[0002] Bifacial BC crystalline silicon solar cells, due to their structural advantages of "unobstructed front and reflected light reception on the back," generate 15% to 20% more power than single-sided BC cells in practical applications, making them one of the mainstream development directions for high-efficiency photovoltaic cells. However, the multi-performance synergy requirements of the back interface (silicon substrate-transparent electrode-metal grid lines) have not yet been effectively met by existing technologies. The core technical challenges are as follows: 1. Coupling failure of ion diffusion and electrochemical corrosion: Cu on the back copper grid 2+ It can easily diffuse into the silicon substrate through grain boundary defects of the transparent electrode (ITO), and the photogenerated carriers generated by light on the back side will accelerate the electrochemical corrosion of the interface, resulting in a ≥12% decrease in the back short-circuit current density (Jsc_back) after 1000h of damp heat aging, which seriously affects the long-term reliability of the battery. 2. Difficulty in balancing passivation and conductivity: Existing back buffer layers (such as pure ZnS and Al2O3) are either insulating materials (requiring additional deposition of conductive layers, increasing process costs and interface defects) or conductive but with poor passivation performance (interface state density Dit ≥ 7 × 10¹¹ eV). - ¹cm - ²), resulting in a back-side carrier collection efficiency of ≤72%; 3. Insufficient interfacial adhesion of the membrane layer: The sulfide buffer layer has poor chemical compatibility with ITO, and the interfacial adhesion is ≤5N / mm. After thermal cycling at -40℃~85℃, the membrane layer is prone to peeling off, which cannot meet the requirements for long-term outdoor use. 4. Poor process compatibility: Some existing solutions use vacuum evaporation to prepare the buffer layer, which has high equipment costs and low mass production efficiency, making it difficult to adapt to the large-scale production needs of the photovoltaic industry.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The technical problem to be solved by this invention is as follows: 1. Inhibit Cu 2+ Diffusion and electrochemical corrosion resulted in a Jsc_back attenuation of ≤4.5% after 1000h of damp heat aging (85℃ / 85%RH). 2. Balance passivation and conductivity to achieve a backside Dit ≤ 2.8 × 10⁻⁶ 11 eV -1 cm -2 The resistivity of the buffer layer is ≤1×10 -3 Ω cm, back-side carrier collection efficiency ≥88%; 3. The interfacial bonding force between the buffer layer and ITO is increased to ≥8N / mm, and no film layer peeling occurs after 500 thermal cycles (-40℃~85℃); 4. Optimize process compatibility by adopting low-cost, scalable preparation methods to avoid reliance on high-cost vacuum equipment.

[0005] To solve the above-mentioned technical problems, the following technical solution is adopted: One aspect of the present invention relates to a bi-sided back contact battery, comprising: n-type single-crystal silicon substrate; An optical functional layer disposed on the front side of the n-type single crystal silicon substrate, the optical functional layer comprising, from the outside to the inside: an anti-reflection layer and a passivation layer; And, a composite functional layer disposed on the back side of the n-type single-crystal silicon substrate, the composite functional layer comprising, from the inside to the outside: An alumina passivation transition layer, a gradient antimony-doped zinc sulfide buffer layer, a titanium nitride transition layer, an indium tin oxide transparent conductive layer, and a copper grid electrode formed on the indium tin oxide transparent conductive layer; In this layer, the antimony concentration increases gradually from the inside to the outside.

[0006] The aforementioned bifacial back-contact solar cell, through a rear-side composite structure design, synergistically optimizes the photoelectric performance and long-term reliability of the back-side interface. The gradient antimony-doped zinc sulfide layer, with its increasing antimony concentration from the inside out, achieves excellent passivation near the silicon side and provides good conductivity near the conductive side, thereby increasing the back-side carrier collection efficiency to over 88% and significantly increasing the back-side short-circuit current density. The titanium nitride transition layer effectively suppresses the diffusion of copper ions into the silicon substrate and enhances the interlayer bonding force. This overall structure is compatible with existing mass production processes, ultimately enabling the bifacial back-contact solar cell to achieve a conversion efficiency of up to 25.5%, while also possessing high reliability and mass production feasibility.

[0007] Another aspect of the present invention relates to a method for preparing the aforementioned bifacial back contact battery, comprising the following steps: (a) A passivation layer and an antireflection layer are sequentially deposited on the front side of an n-type single-crystal silicon substrate; (b) An alumina passivation transition layer, a gradient antimony-doped zinc sulfide buffer layer, a titanium nitride transition layer, and an indium tin oxide transparent conductive layer are sequentially deposited on the back side of an n-type single-crystal silicon substrate. (c) A copper grid electrode is formed on the indium tin oxide transparent conductive layer.

[0008] The method for preparing the bifacial back contact battery is seamlessly integrated with traditional photovoltaic mass production steps (such as ALD, vapor deposition, and electroplating). This ensures the precise preparation of the "passivation-conductivity-barrier-bonding" composite functional structure on the back side while achieving high efficiency, stability, and low cost throughout the entire production process. Ultimately, this ensures that the high performance and high reliability of the bifacial back contact battery can be stably achieved in large-scale manufacturing.

[0009] Another aspect of the present invention relates to a photovoltaic module comprising the aforementioned bifacial back contact cell or a bifacial back contact cell prepared by the method thereof.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The bifacial back-contact battery provided by this invention achieves a synergistic breakthrough in passivation, conductivity, corrosion resistance, and interfacial bonding by introducing a composite buffer layer structure consisting of an alumina passivation transition layer, a gradient antimony-doped zinc sulfide buffer layer, and a titanium nitride transition layer. This structure reduces the back-side interface state density to 2.5 × 10⁻⁶. 11 eV -1 cm -2 Below, the resistivity is as low as 8.5 × 10⁻⁶. -4 The back-side carrier collection efficiency was improved to 90% (Ω·cm). Simultaneously, the combined effect of the gradient antimony doping design and the TiN transition layer reduced the copper ion diffusion rate by two orders of magnitude, resulting in a back-side current decay rate of only 4.2% after wet heat aging, an improved interfacial adhesion of 8.2 N / mm, and no film delamination after thermal cycling. Ultimately, the overall battery conversion efficiency reached 25.5%, and the back-side short-circuit current density increased to 12.8 mA / cm². 2 This significantly improves bifacial power generation capability and long-term reliability.

[0011] (2) The method for preparing bifacial back contact solar cells provided by this invention employs chemical bath deposition (CBD) combined with a staged antimony source addition process, achieving low-cost and controllable preparation of gradient antimony-doped zinc sulfide buffer layers, and is fully compatible with existing photovoltaic mass production equipment. This method increases the deposition rate to three times that of traditional vacuum processes, and reduces the cost per cell by approximately 8%. Simultaneously, by integrating low-temperature annealing with standardized cleaning, sputtering, and electroplating processes, the method avoids damage to the front passivation structure caused by high temperatures while ensuring a film crystallinity of ≥82%, significantly improving process stability and mass production adaptability, and providing a reliable path for the large-scale production of high-efficiency bifacial back contact solar cells. Attached Figure Description

[0012] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of the structure of a double-sided back contact battery provided in an embodiment of the present invention. Detailed Implementation

[0014] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and 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.

[0015] One aspect of the present invention relates to a double-sided back contact battery, such as Figure 1 As shown, it includes: n-type single-crystal silicon substrate; An optical functional layer disposed on the front side of the n-type single crystal silicon substrate, the optical functional layer comprising, from the outside to the inside: an anti-reflection layer and a passivation layer; And, a composite functional layer disposed on the back side of the n-type single-crystal silicon substrate, the composite functional layer comprising, from the inside to the outside: An alumina passivation transition layer, a gradient antimony-doped zinc sulfide buffer layer, a titanium nitride transition layer, an indium tin oxide transparent conductive layer, and a copper grid electrode formed on the indium tin oxide transparent conductive layer; In this layer, the antimony concentration increases gradually from the inside to the outside.

[0016] The aforementioned bifacial back-contact solar cell utilizes a composite structure design on the back side consisting of an "alumina passivation transition layer / gradient antimony-doped zinc sulfide buffer layer / titanium nitride transition layer" to synergistically optimize the photoelectric performance and long-term reliability of the back-side interface. The gradient antimony-doped zinc sulfide layer, through its increasing antimony concentration from the inside out, achieves excellent passivation near the silicon side and provides good conductivity near the conductive side, thereby increasing the back-side carrier collection efficiency to over 88% and significantly increasing the back-side short-circuit current density. The titanium nitride transition layer effectively suppresses the diffusion of copper ions into the silicon substrate and enhances the interlayer bonding force. This overall structure is compatible with existing mass production processes, ultimately enabling the bifacial back-contact solar cell to achieve a conversion efficiency of up to 25.5%, while also possessing high reliability and mass production feasibility.

[0017] The aforementioned double-sided back contact battery has the following advantages: 1. Corrosion protection and ion diffusion inhibition: The lattice densification of the graded antimony-doped zinc sulfide buffer layer (porosity ≤ 0.8% + the physical barrier effect of the titanium nitride transition layer) prevents Cu from being affected. 2+ The diffusion rate decreased to 1.5 × 10⁻⁶. -10 cm 2 / s (traditional scheme is 1.5×10 - 8 cm 2 / s), after 1000h of damp heat aging, Jsc_back decays by only 4.2% (compared to 12.5% ​​for the traditional solution), meeting the outdoor 25-year service life requirement; 2. Passivation-Conductivity Synergistic Optimization: Achieving Dit=2.5×10 on the low-concentration Sb side of the gradient antimony-doped zinc sulfide buffer layer. 11 eV -1 cm -2 The high Sb concentration on the side resulted in a buffer layer resistivity of 8.5 × 10⁻⁶. -4 Ω cm, with a back-side carrier collection efficiency of 90% and Jsc_back increased to 12.8 mA / cm. 2 (Traditional solution 9.8mA / cm) 2 The total battery conversion efficiency reaches 25.5% (compared to approximately 23.1% for traditional bifacial BC batteries). 3. Improved interfacial adhesion: The titanium nitride transition layer improves the interfacial compatibility between Sb-ZnS and ITO through chemical bonding, increasing the interfacial adhesion from 5.2 N / mm in the traditional solution to 8.2 N / mm. After 500 thermal cycles (-40℃~85℃), the film peeling rate is 0 (compared to 15% in the traditional solution). 4. Process compatibility and cost advantages: No new special equipment is required. CBD, ALD, magnetron sputtering, and electroplating are all mature equipment in mass production in the photovoltaic industry and can be directly compatible with existing BC battery production lines. Cost reduction: The gradient antimony-doped zinc sulfide buffer layer has both passivation and conductivity functions, reducing one process of evaporating conductive layer, and reducing the cost per watt by about 8%. Mass production efficiency is increased by 15% (CBD deposition rate is 3 times that of vacuum evaporation).

[0018] The alumina passivation transition layer provides an excellent interfacial chemical passivation basis for the back-side composite functional structure. Its dense and negatively charged properties effectively suppress carrier recombination on the silicon surface. At the same time, it provides a stable and compatible ideal growth substrate for the uniform deposition of the subsequent gradient antimony-doped zinc sulfide buffer layer, and achieves equipment sharing and cost synergy with the front-side passivation process.

[0019] Furthermore, the antireflection layer comprises, from the inside out: a first SiN x Layers and SiO x layer.

[0020] Furthermore, the thickness of the antireflection layer is 70~80nm, including but not limited to a point value of any one of 70nm, 73nm, 75nm, 78nm or 80nm or a range between any two.

[0021] Furthermore, the first SiN x The thickness of the layer is 40~45nm, including but not limited to a point value of 40nm, 43nm or 45nm or a range between any two.

[0022] Furthermore, the SiO x The thickness of the layer is 30~35nm, including but not limited to a point value of 30nm, 33nm or 35nm or a range between any two.

[0023] Furthermore, for incident light in the wavelength range of 400~1100nm, the antireflection layer allows at least 91% of the light energy to pass through. The antireflection layer can be mass-produced using PECVD equipment.

[0024] Furthermore, the passivation layer comprises, from the inside out: an Al2O3 layer and a second SiN layer. x layer.

[0025] Furthermore, the thickness of the Al2O3 layer is 10~15nm (for example, it can be a point value of any one of 10nm, 13nm or 15nm or a range of any two), and it is prepared using ALD.

[0026] Furthermore, the second SiN xThe layer thickness is 50~60nm (for example, it can be a point value or a range between any two of 50nm, 53nm, 55nm, 58nm or 60nm). It is prepared by PECVD.

[0027] Furthermore, the interface state density (Dit) of the passivation layer is ≤3×10⁻⁶. 11 eV -1 cm -2 .

[0028] Furthermore, the resistivity of the n-type single-crystal silicon substrate layer is 2~4Ω. cm, with a thickness of 150~170μm (for example, it can be a point value or a range of any one of 150μm, 155μm, 160μm, 165μm or 170μm, for example, a value between any two), minority carrier lifetime ≥300μs, and commercially mass-produced silicon wafers can be purchased directly.

[0029] Furthermore, the thickness of the alumina passivation transition layer is 5-8 nm, including but not limited to a single value of 5 nm, 6 nm, 7 nm, or 8 nm, or a range between any two. The alumina passivation transition layer can be prepared by ALD, is compatible with the front passivation process, requires no additional equipment, and improves the interfacial adhesion with the silicon substrate. This thickness range ensures that the alumina passivation transition layer can form a dense and complete film, fully utilizing its negatively charged field-effect passivation effect to significantly reduce the silicon interface state density. Simultaneously, this thickness is sufficient to block impurity diffusion and chemical etching during the process, without introducing significant resistance or stress due to excessive thickness, providing a stable and reliable interfacial foundation for subsequent multilayer structures.

[0030] Furthermore, the thickness of the gradient antimony-doped zinc sulfide buffer layer is 18~22nm, including but not limited to a value of any one of 18nm, 19nm, 20nm, 21nm, or 22nm, or a range between any two. This thickness optimization allows the gradient doping effect to be fully manifested, ensuring sufficient carrier transport capacity and lateral conductivity while maintaining good optical transmittance and reducing absorption of back-incident light. At the same time, this thickness is well matched with the upper and lower layers in terms of deposition stress and coefficient of thermal expansion, ensuring the mechanical stability of the multilayer structure.

[0031] Furthermore, in the gradient antimony-doped zinc sulfide buffer layer, the antimony concentration near the alumina passivation transition layer is 2 at% to 3 at% (for example, it can be any one of 2 at%, 2.5 at%, or 3 at%, or a range between any two), and the antimony concentration near the titanium nitride transition layer is 3 at% to 5 at% (for example, it can be any one of 3 at%, 4 at%, or 5 at%, or a range between any two). The region near the alumina passivation transition layer uses a low concentration of antimony doping to ensure the passivation effect, while the region near the titanium nitride transition layer uses a high concentration of antimony doping to improve conductivity.

[0032] The graded antimony-doped zinc sulfide buffer layer is prepared by chemical bath deposition of CBD, which does not require vacuum equipment and has low mass production cost.

[0033] Furthermore, the crystallinity of the gradient antimony-doped zinc sulfide buffer layer is ≥82%. This ensures that the material has a high degree of structural order (crystallinity ≥82%), effectively reducing the density of grain boundary defects, thereby significantly improving the carrier mobility and lateral conductivity of the film, and enhancing its compactness as a barrier layer. This fundamentally guarantees the passivation-conductivity synergy and long-term stability expected by the gradient antimony-doped design.

[0034] Furthermore, the resistivity of the gradient antimony-doped zinc sulfide buffer layer is 8 × 10⁻⁶. -4 ~1×10 -3 Ω cm.

[0035] Furthermore, the thickness of the titanium nitride transition layer is 3-6 nm, including but not limited to a value of any one of 3 nm, 4 nm, 5 nm, or 6 nm, or a range between any two. The titanium nitride transition layer is prepared by magnetron sputtering, compatible with conventional photovoltaic electrode sputtering equipment. The titanium nitride transition layer can enhance the interfacial adhesion with ITO and suppress oxidation. This ultra-thin thickness design allows the titanium nitride transition layer to effectively utilize its high chemical stability, forming a dense physical barrier layer between Sb-ZnS and ITO, significantly suppressing copper ion diffusion and interfacial oxidation; at the same time, its moderate thickness ensures excellent interfacial adhesion and improves adhesion while avoiding additional light absorption and resistance introduced by excessive thickness, maintaining the overall optical transmittance and electrical performance of the back-side light-receiving area.

[0036] Furthermore, the thickness of the indium tin oxide transparent conductive layer is 85~95nm, including but not limited to a point value of any one of 85nm, 88nm, 90nm, 93nm or 95nm or a range between any two.

[0037] Furthermore, the sheet resistance of the indium tin oxide transparent conductive layer is ≤15Ω / sq.

[0038] Furthermore, for incident light in the wavelength range of 400~1100nm, the proportion of light energy allowed to pass through the indium tin oxide transparent conductive layer is not less than 88%. Existing vapor deposition equipment can achieve mass production.

[0039] Furthermore, the copper grid electrode has a width of 45-55 μm and a thickness of 2-3 μm. It can be prepared by electroplating, a mature process in the photovoltaic industry.

[0040] Another aspect of the present invention relates to a method for preparing the aforementioned bifacial back contact battery, comprising the following steps: (a) A passivation layer and an antireflection layer are sequentially deposited on the front side of an n-type single-crystal silicon substrate; (b) An alumina passivation transition layer, a gradient antimony-doped zinc sulfide buffer layer, a titanium nitride transition layer, and an indium tin oxide transparent conductive layer are sequentially deposited on the back side of an n-type single-crystal silicon substrate. (c) A copper grid electrode is formed on the indium tin oxide transparent conductive layer.

[0041] The method for preparing the bifacial back contact battery seamlessly integrates innovative processes such as chemical bath deposition of a gradient antimony-doped zinc sulfide buffer layer and magnetron sputtering of a titanium nitride transition layer with traditional photovoltaic mass production steps (such as ALD, evaporation, and electroplating). This ensures the precise fabrication of the "passivation-conductivity-barrier-bonding" composite functional structure on the back side while achieving high efficiency, stability, and low cost throughout the entire production process. Ultimately, this ensures that the high performance and high reliability of the bifacial back contact battery can be stably achieved in large-scale manufacturing.

[0042] Furthermore, the n-type single-crystal silicon substrate undergoes pretreatment before use, the pretreatment including: 1. Front-side texturing: The front side is treated with a 1wt%~2wt% NaOH solution and kept at 80~84℃ for 22~28min to form a pyramidal texturing surface with a height of 2.0~2.5μm, creating a light-trapping structure on the front side to reduce incident light reflection; 2. Backside polishing: The backside is polished using chemical mechanical polishing (CMP). The polishing slurry is silica sol with an average particle size of 75nm. The polishing pressure is 0.1~0.2MPa, the rotation speed is 345~355rpm, and the roughness is Ra=0.2~0.3nm, ensuring the uniformity of the backside buffer layer deposition. 3. RCA standard cleaning removes organic impurities and metal ions: SC-1: The silicon wafer is cleaned using a cleaning solution with the following composition: NH4OH:H2O2:H2O = 1:1:5 (volume ratio). The cleaning solution is applied at 65°C for 12 minutes. SC-2: The silicon wafer is cleaned using a cleaning solution with the following composition: HCl:H2O2:H2O = 1:1:5 (volume ratio). The cleaning solution is applied at 65°C for 12 minutes.

[0043] Furthermore, the antireflection layer is prepared by PECVD deposition, and the preparation parameters include: The flow rate of silane is 22~28 sccm, the flow rate of ammonia is 10~14 sccm, the flow rate of oxygen is 6~10 sccm, the temperature is 320~330℃, and the pressure is 395~405 Pa.

[0044] Furthermore, an Al2O3 layer was prepared using ALD deposition, with the following preparation parameters: The flow rate of trimethylaluminum is 6~10 sccm, the flow rate of water vapor is 10~14 sccm, and the temperature is 220~230℃.

[0045] Furthermore, PECVD was used to prepare deposited second SiN x Layer, preparation parameters include: The flow rate of silane is 22~28 sccm, the flow rate of ammonia is 10~14 sccm, the flow rate of oxygen is 6~10 sccm, the temperature is 320~330℃, and the pressure is 395~405 Pa.

[0046] Furthermore, an alumina passivation transition layer was prepared using ALD, with the following preparation parameters: The flow rate of trimethylaluminum is 6~10 sccm, the steam flow rate is 10~14 sccm, and the temperature is 220~230℃. It shares equipment with the front-side process, reducing costs.

[0047] Furthermore, a gradient antimony-doped zinc sulfide buffer layer is prepared using CBD, including the following steps: The first deposition reaction was carried out after adding an antimony source to the reaction solution; The reaction solution includes: a zinc source, a sulfur source, and a complexing agent; After the first deposition reaction is completed, the antimony source is added to the reaction system, followed by a second deposition reaction and post-treatment. This step, through timing control, achieves a step change in the concentration of antimony ions in the reaction system. It is the core process operation for forming a vertical antimony concentration gradient within the thin film, ensuring that the buffer layer preferentially obtains excellent passivation characteristics near the silicon side and gradually enhances conductivity near the electrode side, forming a functional gradient structure.

[0048] Furthermore, the reaction solution comprises: 0.08–0.12 mol / L zinc source, 0.18–0.22 mol / L sulfur source, and 0.03–0.07 mol / L complexing agent. This concentration ratio optimizes the kinetics of chemical bath deposition, ensuring an appropriate deposition rate and film density while stabilizing metal ions and improving co-deposition uniformity through the complexing agent. This provides a stable reaction basis for obtaining a gradient buffer layer with high crystallinity (≥82%) and controllable composition.

[0049] Furthermore, in the reaction system of the first deposition reaction, Sb 3+ The concentration ranges from 0.002 to 0.003 mol / L. This low concentration range ensures that an appropriate amount of antimony is incorporated during the initial film growth stage of deposition, which not only maintains the excellent passivation properties of zinc sulfide but also provides a smooth transition for subsequent concentration increases. This is the key to achieving the "high passivation, low recombination" interface characteristics.

[0050] In some specific embodiments, 20-30 μL of 0.1 mol / L SbCl3 solution is added dropwise to the reaction solution to control the Sb concentration in the reaction system of the first deposition reaction. 3+ The concentration is 0.002~0.003 mol / L.

[0051] Furthermore, in the reaction system of the second deposition reaction, Sb 3+ The concentration ranges from 0.003 to 0.005 mol / L. This increased concentration range actively increases the antimony doping in the later stages of deposition, significantly enhancing the carrier concentration and conductivity of the film. This results in a low-resistance channel near the electrode side, effectively improving the collection and transport efficiency of carriers on the back side.

[0052] In some specific embodiments, 10-20 μL of 0.1 mol / L SbCl3 solution is added to the reaction system after the first deposition reaction to control the Sb concentration in the reaction system for the second deposition reaction. 3+ The concentration is 0.003~0.005 mol / L.

[0053] Furthermore, the first deposition reaction takes 13-15 minutes. This duration control ensures that a sufficiently thick and structurally complete "low-antimony region" film can be deposited under low antimony concentration conditions, allowing its passivation function to be fully utilized, while also laying a clear starting layer for the establishment of the concentration gradient.

[0054] Furthermore, the second deposition reaction takes 13-15 minutes. This matching duration ensures that a sufficiently thick "high-antimony region" film can be formed in a high-antimony concentration environment, resulting in a significant increase in conductivity and a smooth functional transition with the previous stage, together forming a complete gradient buffer layer with a total thickness of 18-22 nm and a natural performance transition.

[0055] Furthermore, the first deposition reaction process parameters include: pH 8.7~8.9, temperature 75~78℃, magnetic stirring throughout the process, and rotation speed of 280~320rpm to ensure uniform concentration.

[0056] Furthermore, the second deposition reaction process parameters include: pH 8.7~8.9, temperature 75~78℃, magnetic stirring throughout the process, and a rotation speed of 280~320rpm to ensure uniform concentration.

[0057] The pH of the first and second deposition reactions can be adjusted with ammonia, making mass production easier to control.

[0058] Furthermore, the zinc source includes: ZnSO4 7H2O.

[0059] Furthermore, the sulfur source includes thiourea.

[0060] Furthermore, the complexing agent includes sodium citrate. The complexing agent improves the uniformity of co-deposition.

[0061] In some specific embodiments, the reaction solution is prepared (by volume 1L): ZnSO4 7H2O2 8.7g (0.1mol / L) + thiourea 12.0g (0.2mol / L) + sodium citrate 14.7g (0.05mol / L) + deionized water to a final volume of 1L.

[0062] Furthermore, the post-processing includes: washing, nitrogen purging and drying, and nitrogen atmosphere annealing.

[0063] Furthermore, the washing is performed 3 to 5 times, each time for 4 to 6 minutes.

[0064] Furthermore, the pressure of the nitrogen purging and drying is 0.2~0.4 MPa.

[0065] Furthermore, the nitrogen atmosphere annealing temperature is 195~205℃, and the time is 28~32min. Low-temperature annealing does not damage the existing layer structure. Nitrogen atmosphere annealing effectively isolates oxygen and water vapor and prevents harmful oxidation, while significantly promoting atomic rearrangement and lattice repair of the film, thereby improving its crystallinity (≥82%) and structural density.

[0066] Furthermore, a TiN transition layer was prepared using magnetron sputtering, with the following preparation parameters: The target material is Ti (99.9% purity), the argon to nitrogen flow ratio is 3~5:1, the power is 95~105W, the deposition temperature is 145~155℃, and the vacuum degree is 5×10⁻⁶. -5 ~5×10 -4Pa. This can be achieved with conventional sputtering equipment.

[0067] Furthermore, an indium tin oxide transparent conductive layer was prepared using a vapor deposition process, with the following preparation parameters: ITO target material was used (In2O3 and SnO2 mass ratio of 9:1), the evaporation temperature was 175~185℃, and the vacuum degree was 3×10⁻⁶. -5 ~3×10 -4 Pa.

[0068] Furthermore, the copper grid line electrode is prepared using an electroplating process, the preparation process including: Photoresist is applied and exposed to reveal the electrode area; electroplating is then performed using an acidic copper sulfate plating solution with a current density of 1.0~1.4 A / dm³. 2 The electroplating time is 6~10 minutes.

[0069] Furthermore, the acidic copper sulfate electroplating solution comprises: 220 g / L copper sulfate, 55 g / L sulfuric acid, and 50 ppm chloride ions.

[0070] Furthermore, the method for preparing the bifacial back contact battery further includes: Plasma etching: The gas is CF4 / O2=3:1 (flow rate 30sccm, 10sccm), the power is 250W, and a 1.2mm wide conductive layer is removed from the edge of the silicon wafer to avoid short circuits; Performance testing: Electrical performance and reliability tests are conducted in accordance with IEC 60904-1 and IEC 61215 standards.

[0071] Another aspect of the present invention relates to a photovoltaic module comprising the aforementioned bifacial back contact cell or a bifacial back contact cell prepared by the method thereof.

[0072] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0073] Example 1: Target Battery Fabrication (Complete Replication of Mass Production Process) 1. Silicon substrate: Commercially available n-type monocrystalline silicon wafers with a resistivity of 3Ω are used. cm, with a thickness of 160μm and a minority carrier lifetime of 320μs, after texturing, polishing, and RCA cleaning; 2. Front optical functional layer: 32nm thick SiO2 deposited by PECVD xLayer and 43nm thick SiN x The layer serves as an antireflective layer → ALD deposition of a 12nm thick Al2O3 layer and a 55nm thick SiN layer. x The layer serves as a passivation layer; 3. Backside composite functional layer: 3.1. A 6nm thick alumina passivation transition layer was deposited using ALD. 3.2 Preparation of graded antimony-doped zinc sulfide buffer layers using CBD: Preparation of reaction solution (per 1L volume): ZnSO4 7H2O2 8.7g (0.1mol / L) + thiourea 12.0g (0.2mol / L) + sodium citrate 14.7g (0.05mol / L) + deionized water to a final volume of 1L; Gradient antimony doping is achieved by adding 0.1 mol / L SbCl3 solution in two stages: Early stage (0-13 min, low antimony deposition zone): Add 25 μL of SbCl3 solution dropwise, increasing the Sb³ content in the reaction solution. + Concentration 0.0025 mol / L; Later stage (13-26 min, high antimony deposition zone): Add 15 μL of SbCl3 solution to increase the Sb³ content in the reaction solution. + Concentration 0.004 mol / L; Process parameters: pH=8.8, temperature 76℃, heat preservation for 26 min, magnetic stirring throughout, speed 300 rpm; Post-treatment: Washed with deionized water 3 times, 5 min each time, purged with nitrogen at a pressure of 0.3 MPa, and then annealed at 200℃ in a nitrogen atmosphere for 30 min, with a total thickness of 20 nm; 3.3 Magnetron sputtering of a 4nm thick TiN transition layer; 3.4. Evaporate a 90nm thick transparent conductive layer of indium tin oxide; 3.5 Electroplated copper grid line electrodes, with a width of 50μm and a thickness of 2.5μm; 4. Edge isolation: Plasma etching is used to create a 1.2mm conductive layer at the edge to complete the battery fabrication.

[0074] Example 2 1-2, Same as Example 1; 3. Backside composite functional layer: 3.1. A 5nm thick alumina passivation transition layer was deposited using ALD. 3.2 Preparation of graded antimony-doped zinc sulfide buffer layers using CBD: Reaction solution preparation: Same as in Example 1; Gradient antimony doping is achieved by adding 0.1 mol / L SbCl3 solution in two stages: Early stage (0-14 min, low antimony deposition zone): SbCl3 solution is added dropwise, and the Sb³ in the reaction solution... + Concentration 0.003 mol / L; Later stage (14-28 min, high antimony deposition zone): Add SbCl3 solution to increase the Sb³ content in the reaction solution. + Concentration 0.003 mol / L; Process parameters: pH=8.9, temperature 78℃, heat preservation for 25 min, magnetic stirring throughout, speed 300 rpm; Post-treatment: Washed with deionized water 4 times, 5 min each time, purged with nitrogen at a pressure of 0.4 MPa, and then annealed at 205℃ in a nitrogen atmosphere for 28 min, with a total thickness of 18 nm. 3.3 Magnetron sputtering of a 3nm thick TiN transition layer; 3.4 Same as Example 1; 3.5. Same as Example 1; 4. Same as Example 1.

[0075] Example 3 1-2, Same as Example 1; 3. Backside composite functional layer: 3.1. An 8 nm thick alumina passivation transition layer is deposited using ALD. 3.2 Preparation of graded antimony-doped zinc sulfide buffer layers using CBD: Reaction solution preparation: Same as in Example 1; Gradient antimony doping is achieved by adding 0.1 mol / L SbCl3 solution in two stages: Early stage (0-15 min, low antimony deposition zone): SbCl3 solution is added dropwise, and the Sb³ in the reaction solution... + Concentration 0.002 mol / L; Later stage (15-30 min, high antimony deposition zone): Add SbCl3 solution to increase the Sb³ content in the reaction solution. + Concentration 0.005 mol / L; Process parameters: pH=8.7, temperature 75℃, heat preservation for 28 min, magnetic stirring throughout, speed 300 rpm; Post-treatment: Washed with deionized water 5 times, 5 min each time, purged with nitrogen at a pressure of 0.2 MPa, and then annealed at 195℃ in a nitrogen atmosphere for 32 min, with a total thickness of 22 nm. 3.3 Magnetron sputtering of a 6nm thick TiN transition layer; 3.4 Same as Example 1; 3.5. Same as Example 1; 4. Same as Example 1.

[0076] Comparative Example 1 There is no buffer layer on the back; ITO and copper grid lines are directly vapor-deposited (existing mass-produced bifacial BC cell structure).

[0077] Comparative Example 2 The back side is a pure ZnS buffer layer (without antimony doping, without TiN transition layer, prepared by CBD, with a thickness of 20nm).

[0078] Comparative Example 3 The back side is a uniform antimony-doped ZnS buffer layer (Sb concentration of 3 at%, no gradient, no TiN transition layer, prepared by CBD, thickness of 20 nm).

[0079] Experimental Example Performance test results were obtained according to IEC standards, using the average value of three parallel samples. The data is repeatable, and the results are shown in Table 1.

[0080] Table 1

[0081] This invention has the following advantages: (I) Breakthrough in core performance: Synergistic effect of four functions: passivation, conductivity, corrosion prevention and bonding strength Optimal balance between passivation and conductivity: Gradient antimony doping design (2~3 at% in low antimony region + 3~5 at% in high antimony region) reduces the back-side interface state density (Dit) to 2.5 × 10⁻⁶. 11 eV -1 cm -2 The resistivity of the buffer layer is as low as 8.5 × 10⁻⁶. -4 Ω cm, with a back-side carrier collection efficiency of 90%, which is 18 percentage points higher than the traditional scheme; Significant corrosion resistance and ion diffusion inhibition: The dual barrier of the TiN transition layer and the dense gradient Sb-ZnS reduces the copper ion diffusion rate to 1.5 × 10⁻⁶. -10 cm 2 / s, after 1000h of damp heat aging, the Jsc on the back side decreases by only 4.2% (compared to 12.5% ​​for traditional solutions), meeting the requirement of a 25-year service life outdoors; Doubled interfacial adhesion: The TiN transition layer improves the chemical compatibility of Sb-ZnS and ITO, increasing the interfacial adhesion from 5.2 N / mm to 8.2 N / mm. No film peeling occurs after 500 thermal cycles (-40℃~85℃) (the peeling rate of the traditional solution is 15%).

[0082] (ii) Significant improvement in conversion efficiency and power generation The overall conversion efficiency of the battery reaches 25.5%, which is 2.4 percentage points higher than the existing mass-produced bifacial BC battery (23.1%). The back-side short-circuit current density (Jsc_back) has been increased to 12.8 mA / cm². 2 The power generation contributed by the back side receiving sunlight is 10% to 12% higher than that of traditional solutions, which meets the core requirements of bifacial photovoltaics.

[0083] (iii) It has strong process compatibility and requires no additional special equipment. The core processes (CBD deposition of gradient Sb-ZnS, ALD deposition of Al2O3, magnetron sputtering of TiN, and electroplating of copper grid lines) are all mature mass-production processes in the photovoltaic industry, which can be directly compatible with existing BC cell production lines without additional equipment costs. The low-temperature process design (maximum annealing temperature 200℃) will not damage the front passivation layer and silicon substrate structure, resulting in high process stability.

[0084] (iv) It has a significant cost advantage and is suitable for large-scale mass production. Gradient Sb-ZnS combines passivation and conductivity, eliminating the need for a single process step in traditional solutions that requires an "insulating buffer layer + additional conductive layer," thus reducing the cost per watt by approximately 8%. The CBD deposition rate is 3 times that of vacuum evaporation, increasing mass production efficiency by 15% and further reducing unit manufacturing costs. The core raw materials (ZnSO4, SbCl3, and Ti target) are all low-cost chemical raw materials, and there is no reliance on scarce materials.

[0085] 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.

Claims

1. A double-sided back contact battery, characterized in that, include: n-type single-crystal silicon substrate; An optical functional layer disposed on the front side of the n-type single crystal silicon substrate, the optical functional layer comprising, from the outside to the inside: an anti-reflection layer and a passivation layer; And, a composite functional layer disposed on the back side of the n-type single-crystal silicon substrate, the composite functional layer comprising, from the inside to the outside: An alumina passivation transition layer, a gradient antimony-doped zinc sulfide buffer layer, a titanium nitride transition layer, an indium tin oxide transparent conductive layer, and a copper grid electrode formed on the indium tin oxide transparent conductive layer; In this layer, the antimony concentration increases gradually from the inside to the outside.

2. The double-sided back contact battery according to claim 1, characterized in that, In the gradient antimony-doped zinc sulfide buffer layer, the antimony concentration in the region near the alumina passivation transition layer is 2 at% to 3 at, and the antimony concentration in the region near the titanium nitride transition layer is 3 at% to 5 at.

3. The double-sided back contact battery according to claim 1, characterized in that, The thickness of the alumina passivation transition layer is 5~8 nm.

4. The double-sided back contact battery according to claim 1, characterized in that, The thickness of the gradient antimony-doped zinc sulfide buffer layer is 18~22nm.

5. The double-sided back contact battery according to claim 1, characterized in that, The thickness of the titanium nitride transition layer is 3~6 nm.

6. The method for preparing a bifacial back-contact battery according to any one of claims 1 to 5, characterized in that, Includes the following steps: (a) A passivation layer and an antireflection layer are sequentially deposited on the front side of an n-type single-crystal silicon substrate; (b) An alumina passivation transition layer, a gradient antimony-doped zinc sulfide buffer layer, a titanium nitride transition layer, and an indium tin oxide transparent conductive layer are sequentially deposited on the back side of the n-type single crystal silicon substrate; (c) A copper grid electrode is formed on the indium tin oxide transparent conductive layer.

7. The method for preparing a double-sided back contact battery according to claim 6, characterized in that, The preparation of the gradient antimony-doped zinc sulfide buffer layer includes the following steps: The first deposition reaction was carried out after adding an antimony source to the reaction solution; The reaction solution includes: a zinc source, a sulfur source, and a complexing agent; After the first deposition reaction is completed, the antimony source is added to the reaction system, followed by a second deposition reaction and post-treatment.

8. The method for preparing a double-sided back contact battery according to claim 7, characterized in that, Sb in the reaction system of the first deposition reaction 3+ The concentration is 0.002~0.003 mol / L; And / or, Sb in the reaction system of the second deposition reaction 3+ The concentration is 0.003~0.005 mol / L.

9. The method for preparing a double-sided back contact battery according to claim 7, characterized in that, The first deposition reaction takes 13-15 minutes; And / or, the second deposition reaction takes 13 to 15 minutes.

10. A photovoltaic module, characterized in that, The bi-sided back contact battery includes the bi-sided back contact battery prepared by the preparation method of the bi-sided back contact battery according to any one of claims 1 to 5 or any one of claims 6 to 9.

Images