Solar cell, solar cell module, and encapsulating material

Abstract

The application provides a solar cell, a solar cell module and a packaging material. The solar cell comprises a substrate, a tunneling oxide layer, a gradient doped layer, a doped polysilicon layer and a back electrode. The tunneling oxide layer is arranged on the back of the substrate. The gradient doped layer is arranged on the side of the tunneling oxide layer away from the substrate. The doped polysilicon layer is arranged on the side of the gradient doped layer away from the tunneling oxide layer. The back electrode is arranged on the side of the doped polysilicon layer away from the gradient doped layer. The gradient doped layer comprises intrinsic amorphous silicon and boron elements. The boron elements are doped in the intrinsic amorphous silicon. The doping concentration of the boron elements gradually decreases along the thickness direction of the gradient doped layer and in the direction away from the tunneling oxide layer. The solar cell provided by the application can balance the 'passivation intensity' and the 'carrier transport efficiency', and the overall performance of the solar cell is improved.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, and in particular to a solar cell, a solar cell module, and an encapsulation material. Background Technology

[0002] In the development of high-efficiency solar cell technology, passivation contact structures with tunneling oxide layers at their core have become a key technological path to improve the photoelectric conversion efficiency of solar cells. However, conventional tunneling oxide layers used in existing solar cells generally suffer from the technical bottleneck of difficulty in precisely controlling the carrier transport barrier. While increasing the interface charge density and enhancing the interface passivation effect, it significantly increases the carrier tunneling barrier, hindering the efficient transport of majority carriers. Conversely, if the tunneling barrier is lowered to improve carrier transport capability, it leads to an increase in the interface defect state density and a significant decrease in passivation performance. Thus, there is an inherent contradiction between the interface passivation effect and the carrier transport efficiency, which restricts the overall performance of solar cells. Summary of the Invention

[0003] The purpose of this application is to provide a solar cell, a solar cell module, and an encapsulation material, which can achieve a balance between "passivation strength" and "carrier transport efficiency", thereby improving the overall performance of the solar cell.

[0004] This application provides a solar cell, which includes a substrate, a tunneling oxide layer, a gradient doped layer, a doped polysilicon layer, and a back electrode. The tunneling oxide layer is disposed on the back side of the substrate, the gradient doped layer is disposed on the side of the tunneling oxide layer away from the substrate, the doped polysilicon layer is disposed on the side of the gradient doped layer away from the tunneling oxide layer, and the back electrode is disposed on the side of the doped polysilicon layer away from the gradient doped layer. The gradient doped layer includes intrinsic amorphous silicon and boron. Boron is doped into the intrinsic amorphous silicon, and the doping concentration of boron gradually decreases along the thickness direction of the gradient doped layer and in the direction away from the tunneling oxide layer.

[0005] This application provides a solar cell that uses a gradient doped layer between a tunneling oxide layer and a doped polycrystalline silicon layer. By gradient doping boron in the gradient doped layer, carriers are prevented from accumulating at the interface between the tunneling oxide layer and the gradient doped layer, thus reducing the carrier transport barrier while maintaining passivation. This achieves a balance between "passivation strength" and "carrier transport efficiency," resolving the "passivation-transport contradiction" of traditional double-layer SiO2 and improving the overall performance of the solar cell.

[0006] In one possible implementation, the boron doping concentration in the gradient-doped layer on the side facing the tunneling oxide layer is 2.5 × 10⁻⁶. 19 cm- ³~3.5×10 19 cm - ³, the boron doping concentration in the gradient doped layer on the side facing away from the tunneling oxide layer is 0.5 × 10⁻⁶. 19 cm - ³~1.5×10 19 cm - ³.

[0007] In one possible implementation, the doped polysilicon layer has a slot, the opening of which is located on the surface of the doped polysilicon layer away from the gradient doped layer, and the back electrode is located within the slot.

[0008] In one possible implementation, along the thickness direction of the doped polysilicon layer, the distance between the bottom wall of the groove and the surface of the doped polysilicon layer facing the gradient doped layer is h, where h = 45 nm ~ 50 nm.

[0009] This application also provides a solar cell module, which includes a solar cell as described above and an encapsulation material layer, wherein the encapsulation material layer covers the solar cell.

[0010] In one possible implementation, the encapsulation material layer includes an EVA matrix and microcapsules added to the EVA matrix. Each microcapsule includes a core and a shell encapsulating the core. The core is a fluorosiloxane oligomer with the molecular formula (CH3)3Si-O-[Si(CH3)(CH2CH2CF3)-O]. n -Si(CH3)3, n=5~10.

[0011] In one possible implementation, the thermal decomposition temperature of the outer casing is ≥200°C.

[0012] In one possible implementation, the outer shell is made of urea-formaldehyde resin.

[0013] In one possible implementation, the encapsulation material layer comprises 90 wt% to 95 wt% of EVA matrix and 5 wt% to 10% of microcapsules, based on the mass of the encapsulation material layer.

[0014] In one possible implementation, there are multiple solar cells, and the solar cell module also includes electrical connectors that are electrically connected between the multiple solar cells. The electrical connectors include solder strips and silane coupling agents attached to the surface of the solder strips.

[0015] This application also provides an encapsulation material comprising an EVA matrix and microcapsules added to the EVA matrix. Each microcapsule includes a core and a shell encapsulating the core. The core is a fluorinated siloxane oligomer with the molecular formula (CH3)3Si-O-[Si(CH3)(CH2CH2CF3)-O]. n -Si(CH3)3, n=5~10. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is an exploded structural diagram of a solar cell module provided in an embodiment of this application; Figure 2 for Figure 1 The diagram shows the structure of the solar cell in the solar cell module.

[0018] Reference numerals: 1000, solar cell module; 1, solar cell; 100, substrate; 101, first surface; 103, second surface; 210, passivation layer; 230, front electrode; 310, tunneling oxide layer; 320, gradient doped layer; 330, doped polycrystalline silicon layer; 301, slot; 350, back electrode; 2, encapsulation material layer; 21, first encapsulation material layer; 22, second encapsulation material layer; 3, first protective layer; 4, second protective layer; 5, frame. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] Please see Figure 1 , Figure 1 This is an exploded structural diagram of the solar cell module 1000 provided in an embodiment of this application.

[0021] This application provides a solar cell module 1000, including a solar cell 1, an encapsulation material layer 2, a first protective layer 3, a second protective layer 4, and a frame 5.

[0022] The solar cell module 1000 includes multiple solar cells 1, and electrical connectors are electrically connected between the multiple solar cells 1 to connect them in series and then in parallel to form an array. In this embodiment, the electrical connectors include solder ribbons and a silane coupling agent attached to the surface of the solder ribbons. For example, the solder ribbons are tin-coated copper ribbons. Pre-treating the solder ribbons with a silane coupling agent can increase the hydroxyl (-OH) content on the surface of the solder ribbons. Hydroxyl groups are highly polar groups. On the one hand, hydroxyl groups can increase surface energy and reactivity. More hydroxyl groups can change the surface of the solder ribbons from a low-energy, inert state to a high-energy, highly active state, which can greatly improve the wettability of the encapsulation material layer 2 on the solder ribbons when encapsulating the solar cells 1, allowing the encapsulation material layer 2 to wrap the solder ribbons more tightly and reduce interfacial micro-voids. On the other hand, hydroxyl groups can provide more chemical bonding sites, providing more possibilities for forming stronger and more stable chemical bonds or hydrogen bonds with polar groups in the encapsulation material layer 2 (such as carbonyl groups in vinyl acetate units). The silane coupling agent on the solder ribbon can undergo the above-mentioned chemical bonding through hydroxyl groups, thereby forming a stable interface with the encapsulation material layer 2, improving the interface stability between the solder ribbon and the encapsulation material layer 2, thus effectively preventing moisture from penetrating along the interface between the solder ribbon and the encapsulation material layer 2, inhibiting electrochemical corrosion, and thus improving the performance of the solar cell module 1000 in a humid and hot aging environment.

[0023] The encapsulation material layer 2 covers the solar cell 1 to encapsulate the solar cell 1, thereby preventing moisture and other substances from penetrating into the solar cell 1 and causing damage. The encapsulation material layer 2 includes a first encapsulation material layer 21 and a second encapsulation material layer 22, which are located on opposite sides of the thickness direction of the solar cell 1.

[0024] The first protective layer 3 and the second protective layer 4 sandwich the encapsulation material layer 2 and the solar cell 1. The first protective layer 3 is the front protective layer of the solar cell 1, and the second protective layer 4 is the back protective layer of the solar cell 1. In this embodiment, the solar cell module 1000 is a double-glass module, meaning that both the first protective layer 3 and the second protective layer 4 are glass. In other embodiments, the solar cell module 1000 can also be a single-glass module, in which case the second protective layer 4 can be a polymer backsheet.

[0025] The frame 5 covers the edge of the first protective layer 3. In this embodiment, the frame 5 is an aluminum frame. It should be noted that in other embodiments, the solar cell module 1000 may not have the frame 5.

[0026] See Figure 2 , Figure 2 for Figure 1 A schematic diagram of the structure of solar cell 1 in the solar cell module 1000 shown.

[0027] In this embodiment, the solar cell 1 is a tunnel oxide passivated contact (TOPCon) cell. Solar cell 1 includes a substrate 100, a passivation layer 210, a front electrode 230, a tunnel oxide layer 310, a gradient doped layer 320, a doped polycrystalline silicon layer 330, and a back electrode 350. The substrate 100, passivation layer 210, and front electrode 230 constitute the front structure of solar cell 1, while the substrate 100, tunnel oxide layer 310, gradient doped layer 320, doped polycrystalline silicon layer 330, and back electrode 350 constitute the back structure of solar cell 1.

[0028] The substrate 100 includes a first surface 101 and a second surface 103, which are disposed opposite to each other along the thickness direction of the substrate 100. In this embodiment, the substrate 100 is an n-type silicon wafer, the first surface 101 is the front side of the n-type silicon wafer, and the second surface 103 is the back side of the n-type silicon wafer.

[0029] A passivation layer 210 is applied to the first surface 101 of the substrate 100 to achieve passivation layer 210 disposed on the substrate 100. The passivation layer 210 covers the front side of the substrate 100 to reduce surface recombination losses and improve the open-circuit voltage (Voc) of the solar cell 1. For example, the material of the passivation layer 210 can be alumina (Al2O3) or silicon nitride (SiNx), etc.

[0030] The front electrode 230 penetrates the passivation layer 210 and forms an ohmic contact with the substrate 100. The front electrode 230 is used to collect and transmit the current generated by the first surface 101. The front electrode 230 is a metal grid line, including fine grid lines and main grid lines. The fine grid lines and main grid lines can be formed on the passivation layer 210 using conductive paste through screen printing and then sintered to form the front electrode 230. For example, the conductive paste used in the front electrode 230 can be silver paste or copper paste.

[0031] A tunneling oxide layer 310 is disposed on the second surface 103, so that the tunneling oxide layer 310 is disposed on the side of the substrate 100 opposite to the passivation layer 210. The tunneling oxide layer 310 is disposed on the back side of the substrate 100, serving a tunneling function to allow charge carriers to pass through, and reducing recombination by isolating the back electrode 350 from the substrate 100. Exemplarily, the thickness of the tunneling oxide layer 310 is 0.5 nm to 1 nm. In this exemplary embodiment, the tunneling oxide layer 310 is made of amorphous silicon oxide (SiO2), prepared by ozone oxidation at an O3 concentration of 5 vol% to 10 vol% and a temperature of 300-350°C, and the surface defect density of the tunneling oxide layer 310 is <1 × 10⁻⁶. 10 cm- ², providing strong chemical passivation.

[0032] A gradient-doped layer 320 is disposed on the side of the tunneling oxide layer 310 facing away from the substrate 100. The gradient-doped layer 320 comprises intrinsic amorphous silicon (a-Si:H) and boron, with boron doped into the intrinsic amorphous silicon. The boron doping concentration gradually decreases along the thickness direction of the gradient-doped layer 320 and in the direction facing away from the tunneling oxide layer 310. By providing the gradient-doped layer 320, carrier accumulation at the interface between the tunneling oxide layer 310 and the gradient-doped layer 320 can be avoided, thus reducing the carrier transport barrier while maintaining passivation.

[0033] In this case, the boron doping concentration in the gradient doped layer 320 facing the tunneling oxide layer 310 is 2.5 × 10⁻⁶. 19 cm - ³~3.5×10 19 cm - ³, the boron doping concentration in the gradient doped layer 320 on the side opposite to the tunneling oxide layer 310 is 0.5 × 10³. 19 cm - ³~1.5×10 19 cm - ³. For example, the boron doping concentration of the gradient doped layer 320 near the tunneling oxide layer 310 is 3 × 10⁻⁶. 19 cm - ³, gradually decreasing to 1×10 towards the direction away from the tunneling oxide layer 310. 19 cm - ³.

[0034] For example, the thickness of the gradient doped layer 320 is 1 nm to 1.5 nm. In this embodiment, 1 nm to 1.5 nm of intrinsic amorphous silicon (a-Si:H) is first deposited on the surface of the tunneling oxide layer 310 using a plasma-enhanced chemical vapor deposition (PECVD) process, and then boron (B) is doped by ion implantation and rapid thermal annealing to form the gradient doped layer 320 (n + -a-Si:H:B layer).

[0035] A doped polysilicon layer 330 is disposed on the side of the gradient doped layer 320 opposite to the tunneling oxide layer 310. The doped polysilicon layer 330 is used to form a passivation contact structure, further reducing surface recombination and improving carrier collection efficiency. For example, the thickness of the doped polysilicon layer 330 is 150 nm to 200 nm. In this embodiment, the material of the doped polysilicon layer 330 is phosphorus-doped polysilicon, and the phosphorus doping concentration in the doped polysilicon layer 330 is 1 × 10⁻⁶. 20 cm- ³~1×10 21 cm - ³.

[0036] In this embodiment, the doped polycrystalline silicon layer 330 is provided with a groove 301, the opening of which is located on the surface of the doped polycrystalline silicon layer 330 facing away from the gradient doped layer 320. For example, along the thickness direction of the doped polycrystalline silicon layer 330, the distance between the bottom wall of the groove 301 and the surface of the doped polycrystalline silicon layer 330 facing the gradient doped layer 320 is h, where h = 45nm~50nm. In this embodiment, the doped polycrystalline silicon layer 330 is locally thinned to 45nm~50nm by laser grooving to form the groove 301, which helps to reduce the contact area between the back electrode 350 and the doped polycrystalline silicon layer 330, reducing the contact recombination current and thus improving the open-circuit voltage of the solar cell 1. For example, the wavelength of the laser grooving is 532nm and the power is 5W~10W.

[0037] The back electrode 350 is disposed on the side of the doped polysilicon layer 330 away from the gradient doped layer 320. In this embodiment, the back electrode 350 is disposed within the slot 301. The back electrode 350 serves as the main conductive path on the back side of the substrate 100, undertaking the function of current transmission. The back electrode 350 is a metallization layer, which can be formed on the doped polysilicon layer 330 using conductive paste through screen printing or electroplating, and then sintered to form the back electrode 350. In some embodiments, an ultrathin silver layer can be printed first as a "seed layer," followed by a copper paste layer to improve ohmic bonding and prevent copper diffusion.

[0038] In existing solar cells, the tunneling oxide layer typically employs a double-layer SiO2 structure to enhance passivation. However, both layers of SiO2 are undoped, making it impossible to control the carrier transport barrier, resulting in a trade-off between passivation and carrier transport efficiency. Furthermore, excessively thick double-layer SiO2 layers increase carrier transport resistance, thereby reducing the open-circuit voltage (Voc) of the solar cell.

[0039] To address the aforementioned issues, this application provides a solar cell 1. By setting a gradient doped layer 320 between the tunneling oxide layer 310 and the doped polycrystalline silicon layer 330, and by gradient doping boron elements in the gradient doped layer 320, the accumulation of charge carriers at the interface between the tunneling oxide layer 310 and the gradient doped layer 320 is avoided, thereby reducing the carrier transport barrier and maintaining the passivation effect. This achieves a balance between "passivation strength" and "carrier transport efficiency," resolving the "passivation-transport contradiction" of traditional double-layer SiO2, and thus improving the overall performance of the solar cell 1.

[0040] Furthermore, existing solar cell modules suffer from damp-heat aging when used in long-term humid and hot environments. In this case, the encapsulation material layer encapsulating the solar cell cracks, allowing moisture to enter and accumulate inside the solar cell module, leading to power degradation. To address these issues, this application embodiment also improves the encapsulation material layer, which is described in detail below.

[0041] Specifically, the encapsulation material layer 2 comprises an EVA (Ethylene-Vinyl Acetate) matrix and microcapsules added to the EVA matrix. In this embodiment, based on the mass of the encapsulation material layer, the encapsulation material layer comprises 90wt%~95wt% EVA matrix and 5%~10% microcapsules.

[0042] For example, the mass percentage of VA (vinyl acetate) units in the EVA matrix is ​​28% to 30%. By adjusting the content of VA units in the EVA matrix to increase, the flexibility of the EVA matrix can be improved.

[0043] The microcapsule comprises a core and a shell encapsulating the core. The core is a fluorosiloxane oligomer with the molecular formula (CH3)3Si-O-[Si(CH3)(CH2CH2CF3)-O]. n -Si(CH3)3, n=5~10. The fluorosiloxane oligomer can crosslink with the EVA matrix via siloxane bonds. For example, the boiling point of the fluorosiloxane oligomer is >300℃. The thermal decomposition temperature of the outer shell is ≥200℃. For example, the outer shell is urea-formaldehyde resin. For example, the wall thickness of the outer shell is 1μm~2μm.

[0044] In this embodiment, the microcapsules are prepared according to the following steps: Oil phase preparation: The fluorinated siloxane oligomer (CH3)3Si-O-[Si(CH3)(CH2CH2CF3)-O] is used as the core. n -Si(CH3)3 (n=5~10) is mixed with an appropriate amount of emulsifier (such as Span-80) to form a homogeneous oil phase.

[0045] Aqueous phase preparation: Add urea and formaldehyde (molar ratio usually about 1:1.5~2.0) as shells to deionized water, and adjust the pH value to weakly alkaline (e.g. 8-9), stir to dissolve and form urea-formaldehyde prepolymer aqueous solution.

[0046] Emulsification: Under high-speed shear (10000-15000 rpm), the oil phase is slowly added to the aqueous phase to emulsify and form a stable oil / water (O / W) emulsion, controlling the emulsion droplet size within the target range (50-200 μm).

[0047] Capsule wall polymerization and deposition: The emulsion system is transferred to a reactor and slowly heated to 50-65℃. Under the action of an acidic catalyst (ammonium chloride or citric acid, pH adjusted to 3-5), urea and formaldehyde undergo a condensation reaction on the surface of the oil droplets to form urea-formaldehyde resin prepolymer and deposit it on the surface of the oil droplets.

[0048] Curing and post-treatment: Gradually raise the temperature to 70-80℃ and hold for several hours to allow the capsule wall to fully cross-link and cure. After the reaction is complete, cool, filter, wash the obtained microcapsule solid with deionized water and ethanol, and finally vacuum dry at 40-50℃ to obtain the microcapsule product with a fluorinated siloxane oligomer as the core and a urea-formaldehyde resin as the shell.

[0049] The repair mechanism of the encapsulation material layer is as follows: When the fluorosiloxane oligomer encounters trace amounts of moisture in the environment (from damp heat aging), the terminal alkoxy group (-OR) undergoes hydrolysis to generate silanol groups (-SiOH). The reaction process is: -Si-OR + H2O → -Si-OH + R-OH. The two silanol groups generated by the hydrolysis of the fluorosiloxane oligomer can undergo dehydration condensation to form stable Si-O-Si bonds, allowing the fluorosiloxane oligomer to self-link into a network through condensation crosslinking. The specific reaction process is: -Si-OH + HO-Si- → -Si-O-Si- + H2O. When the solar cell module 1000 develops microcracks due to damp heat aging (e.g., the width of the microcracks > 1 μm), the microcapsules rupture and release the fluorosiloxane oligomer into the microcracks. Fluorinated siloxane oligomers can rapidly undergo the aforementioned hydrolysis and condensation crosslinking reactions within and at the interface of microcracks, ultimately forming a three-dimensional network structure with Si-O-Si bonds as the backbone and chemically linked to the EVA matrix. This network fills the voids in the microcracks, re-establishes adhesion, and, due to its fluorine-containing properties, blocks moisture, thus achieving self-healing.

[0050] This application provides an encapsulation material that can be used to encapsulate a solar cell 1 to form a solar cell module 1000. On the one hand, the EVA matrix in the encapsulation material has strong adhesion and good weather resistance, which can meet the requirements for long-term stable operation of the solar cell module. On the other hand, when the encapsulation material layer cracks due to damp heat aging, the microcapsules added to the encapsulation material can release fluorinated siloxane oligomers through rupture. The fluorinated siloxane oligomers can fill the cracks and crosslink with the EVA matrix, so that the encapsulation material restores its adhesive strength, thereby achieving the effect of self-repairing cracks. This effectively prevents water vapor penetration, avoids power decay of the solar cell module, and solves the problem of damp heat aging of the solar cell module.

[0051] The performance of the solar cell module provided in this application will be specifically explained below with reference to experiments.

[0052] Example 1: Example 1 provides a solar cell 1, based on an n-type monocrystalline silicon wafer (182mm × 182mm, resistivity 2 ± 0.2Ω·cm), with a process compatible with existing TOPCon production lines. Experimental data follows standards such as IEC 61215-2021 and IEC 60904-1, and is prepared according to the following steps: (1) Silicon wafers are cleaned and texturized: The silicon wafers are cleaned sequentially using RCA-1 alkaline cleaning solution and RCA-2 acidic cleaning solution on the RCA cleaning line, and then texturized in the KOH texturizing bath using texturizing solution. The pyramid size of the texturized silicon wafer is 2μm~3μm, and the reflectivity is 18%.

[0053] (2) A tunneling oxide layer 310 is prepared on a silicon wafer using an ozone oxidation process. The tunneling oxide layer 310 is made of SiO2, has a thickness of 0.8 nm, and a defect density of 8 × 10⁻⁶. 9 cm - ².

[0054] (3) Intrinsic amorphous silicon (a-Si:H) was prepared by plasma enhanced chemical vapor deposition (PECVD) with the following deposition parameters: silane (SiH4) flow rate of 100 sccm, hydrogen (H2) flow rate of 500 sccm, power of 200 W, chamber pressure of 200 mTorr, and deposition time of 10 min.

[0055] Then ion implantation B + Acceleration energy 30keV, injection dose 5×10¹ 5 cm - ². After implantation, rapid thermal annealing (RTA) was performed to obtain a gradient-doped layer 320 (n). + -a-Si:H:B layer), annealing temperature 700℃, annealing time 10s. The thickness of the obtained gradient doped layer 320 is 1.2nm.

[0056] (4) A doped polycrystalline silicon layer 330 was prepared on the gradient doped layer 320 using a low-pressure chemical vapor deposition (LPCVD) process. The deposition conditions were as follows: silane (SiH4) flow rate of 50 sccm, phosphine (PH3) flow rate of 5 sccm, and phosphorus concentration of 1.5 × 10². 0 cm - The deposition temperature was 550℃, the chamber pressure was 100 mTorr, and the deposition time was 30 min. The thickness of the doped polycrystalline silicon layer 330 was 180 nm, and the sheet resistance was 80 Ω / sq.

[0057] (5) Laser grooving is performed on the surface of the doped polysilicon layer 330 away from the gradient doped layer 320 to form a groove 301. The laser grooving power is 8W, the width of the groove 301 is 20μm, the depth of the groove 301 is 130nm, and the thickness of the doped polysilicon layer 330 at the groove 301 is reduced to 50nm.

[0058] (6) Print silver paste in the groove 301 of the doped polycrystalline silicon layer 330, and then sinter at 780°C for 10s to form the back electrode 350.

[0059] The detailed fabrication process parameters of the solar cell 1 in Example 1 are summarized in Table 1.

[0060] Table 1. Detailed fabrication process parameters of solar cell 1 in Example 1

[0061] As shown in Table 1, in the solar cell 1 prepared in Example 1, the gradient doped layer 320 was tested using X-ray photoelectron spectroscopy (XPS). The results showed that the B1s peak intensity was high at the interface (depth 0~0.5nm) near the tunneling oxide layer 310, corresponding to a boron concentration of 3×10⁻⁶. 19 cm - ³, the B1s peak intensity is low near the interface (depth 1.0 nm ~ 1.2 nm) of the doped polycrystalline silicon layer 330, corresponding to a boron concentration of 1 × 10⁻⁶. 19 cm - ³. This demonstrates that the boron concentration exhibits a gradient distribution along the thickness direction of the gradient-doped layer 320, consistent with the design.

[0062] The solar cell 1 from Example 1 was encapsulated to form a solar cell module 1000. The preparation process is as follows: 1) The solder strip is immersed in a silane coupling agent solution for 5 minutes, and then dried at 100°C for 10 minutes to obtain the electrical connector. The silane coupling agent solution is an ethanol solution of KH550 (γ-aminopropyltriethoxysilane) with a concentration of 1 wt%.

[0063] 2) 7 wt% of EVA matrix and 93 wt% of microcapsules were mixed, and the encapsulation material layer 2 was prepared using a film extruder. The EVA (ethylene-vinyl acetate copolymer) matrix contained 28% VA (vinyl acetate) units by mass. The microcapsules contained a core of fluorosiloxane oligomers with an average diameter of 100 μm, and a shell of urea-formaldehyde resin with a wall thickness of 1.5 μm.

[0064] 3) Use a laminator to laminate and encapsulate the solar cell 1 and the encapsulation material layer 2 to obtain the solar cell module 1000.

[0065] The detailed encapsulation process parameters of the solar cell module 1000 in Example 1 are shown in Table 2.

[0066] Table 2 Detailed encapsulation process parameters of the solar cell module 1000 in Example 1

[0067] As shown in Table 2, in the solar cell module 1000 prepared in Example 1, the crosslinking degree of the encapsulating material layer 2 was measured to be 82% using the xylene extraction method, and the peel strength between the encapsulating material layer 2 and the solar cell 1 was 12 N / mm. The xylene extraction method was performed as follows: Sample preparation: Precisely cut a small sample (e.g., 1cm × 1cm) from the film of the encapsulation material layer 2 to be tested. Weigh its initial mass using a precision balance and record it as W1 (accurate to 0.0001g). Wrap the sample in a metal mesh bag or filter paper to prevent dispersion in subsequent steps.

[0068] Extraction process: Place the packaged sample into a reflux extraction apparatus (such as a Soxhlet extractor) containing sufficient xylene solvent. Heat the xylene to its boiling point (approximately 140°C) and maintain reflux for 24 hours. During this process, all uncrosslinked EVA molecular chains, residual crosslinking agents, auxiliaries, and other soluble substances in the sample will dissolve into the xylene.

[0069] Drying and Weighing: After extraction, remove the sample and place it in a fume hood to allow the residual xylene to evaporate completely. Then, place the sample in a vacuum oven and dry at 80°C for 3 hours to thoroughly remove all solvent. Remove the sample, cool to room temperature, and immediately weigh its final mass using a precision balance, denoted as W2.

[0070] Calculating the degree of crosslinking: The formula for calculating the degree of crosslinking (Gel Content) is: Degree of crosslinking (%) = (W2 / W1) × 100%. Where W1 is the initial mass of the sample, and W2 is the mass of the insoluble matter after xylene extraction and drying. W2 represents the mass of the crosslinked EVA network.

[0071] Example 2: Example 2 provides a solar cell module 1000, which differs from the solar cell module 1000 of Example 1 in that, in the solar cell module 1000 of Example 2, in step (3) of the process of preparing solar cell 1, step B... + The injection dose was adjusted to 7×10¹ 5 cm -², the annealing temperature is 750℃, and the boron concentration at the interface of the prepared gradient doped layer 320 near the tunneling oxide layer 310 is 4×10⁻⁶. 19 cm - ³, the boron concentration at the interface near the doped polycrystalline silicon layer 330 is 1.5 × 10³. 19 cm - ³, in step (5), the power of laser grooving is reduced to 7W, the depth of grooving 301 is 135nm, and the thickness of the doped polycrystalline silicon layer 330 at grooving 301 is reduced to 45nm. In the process of preparing the solar cell module 1000, the mass ratio of VA (vinyl acetate) units in the EVA matrix of the encapsulation material layer 2 is 30%, the amount of microcapsules added is increased to 8wt%, the average diameter of the core in the microcapsules is increased to 150μm, and the wall thickness of the outer shell is 1.2μm.

[0072] Comparative Example 1: Comparative Example 1 provides a conventional tunneling oxide passivated contact (TOPCon) cell module. The difference between the TOPCon cell module and the solar cell module 1000 of Example 1 is that the solar cell of Comparative Example 1 does not contain a gradient doped layer 320, and the encapsulation material layer 2 is made of EVA and does not contain microcapsules.

[0073] Comparative Example 2: Comparative Example 2 provides a solar cell module that differs from the solar cell module 1000 of Example 1 in that the encapsulation material layer 2 in the solar cell module of Comparative Example 2 is made of EVA and does not contain microcapsules.

[0074] The solar cell module 1000 of Example 1 and the solar cell modules of Comparative Examples 1-2 were tested, and the performance of the solar cell modules is shown in Table 3. In Table 3, DH1000 (85℃ / 85%RH) represents the maximum power degradation rate after aging for 1000 hours in a humid heat environment of 85℃ and 85%RH. The test procedure for the water vapor transmission rate after humid heat aging in Table 3 is as follows: the solar cell module was aged in a humid heat environment of 85℃ and 85%RH for 1000 hours, and then the water vapor transmission rate of the aged solar cell module was tested using a MOCON water vapor transmission rate tester.

[0075] Table 3 Performance of solar cell modules 1000 in Examples 1-2 and solar cell modules in Comparative Examples 1-2

[0076] Comparing the solar cell modules 1000 of Examples 1-2 with the solar cell module of Comparative Example 1, compared to the solar cell module of Comparative Example 1, the solar cell module 1000 of Example 1 shows a 140% increase in minority carrier lifetime, a 1.56% increase in power, a 46% reduction in DH1000 degradation, a more than 5% increase in 10-year power retention rate, and a 75% reduction in water vapor transmission rate after damp heat aging. Compared to the solar cell module of Comparative Example 1, the solar cell module 1000 of Example 2 shows a 160% increase in minority carrier lifetime, a 1.75% increase in power, a 52% reduction in DH1000 degradation, and a more than 7% increase in 10-year power retention rate.

[0077] Furthermore, by comparing Comparative Example 2 with Comparative Example 1, the improvement in minority carrier lifetime in the solar cell module of Comparative Example 2 is mainly due to the adoption of solar cell 1 with a gradient doped layer 320, and the power increase mainly comes from the improvement in the efficiency of solar cell 1. The DH1000 degradation rates of the solar cell modules of Comparative Example 2 and Comparative Example 1 are similar, indicating that improving the structure of solar cell 1 alone cannot significantly improve the long-term damp heat resistance reliability of the solar cell module. The 10-year power retention rate and water vapor transmission rate after damp heat aging of the solar cell modules of Comparative Example 2 and Comparative Example 1 are similar, indicating that the long-term reliability and water vapor barrier performance of the solar cell are determined by the encapsulation material layer 2.

[0078] By comparing Example 1 and Comparative Example 2, the minority carrier lifetime of the solar cell module 1000 in Example 1 is essentially unchanged compared to that of the solar cell in Comparative Example 2, confirming that the minority carrier lifetime mainly depends on the passivation quality of the solar cell 1 in the solar cell module 1000, and has little to do with the encapsulation material of the encapsulation layer 2. The power of the solar cell module 1000 in Example 1 has a slight additional increase, which may be due to minor optimizations in the optical performance (transmittance) or stress management of the encapsulation material layer 2. The significant decrease in the DH1000 degradation rate of the solar cell module 1000 in Example 1 indicates that the improvement of the encapsulation material of the encapsulation layer 2 plays a decisive role in improving the long-term reliability of the solar cell module 1000. The water vapor transmittance after humid heat aging is significantly reduced by 75%, proving that the encapsulation material layer 2 has excellent effect in blocking water vapor.

[0079] Experimental results show that, compared with the traditional TOPCon module provided in Comparative Example 1, the solar cell module 1000 provided in this application significantly improves the efficiency of the solar cell module by adding a gradient doping layer 320 to the solar cell 1, thereby reducing the carrier transport barrier. This increases the minority carrier lifetime of the solar cell module 1000 from the traditional 50μs to 120μs~130μs, an improvement of up to 140%~160%. At the same time, the power of the solar cell module 1000 can reach 4.61W~4.62W (STC), which is 1.5%~1.76% (absolute value) higher than that of the traditional TOPCon module.

[0080] Furthermore, the solar cell module 1000 of Example 1 was subjected to 1000 hours of humid heat aging at 85°C and 85%RH. The encapsulation material layer 2 of the solar cell module 1000 before and after humid heat aging was observed using a scanning electron microscope (SEM). The results showed that the encapsulation material layer 2 of the solar cell module 1000 without humid heat aging was crack-free and had a smooth surface. However, the encapsulation material layer 2 of the solar cell module 1000 that underwent humid heat aging developed microcracks, with a width of approximately 2 μm. While observing the cracked areas using the SEM, a point-source elemental analysis was performed on the crack filling points, the interior of the filler, and the adjacent pure EVA matrix region using the equipped energy dispersive spectroscopy (EDS). The data showed that carbon (C) and oxygen (O) elemental signals were mainly detected in the pure EVA matrix region. In the crack-filled region, strong characteristic peaks of silicon (Si) and fluorine (F) were detected. The filler in the microcracks contained Si and F elements not found in EVA, consistent with the chemical composition of "fluorinated siloxanes," thus directly proving that the filler originated from the fluorinated siloxane oligomer in the core of the microcapsule. Experimental results showed that the microcracks were filled with fluorinated siloxane oligomers, and there was no obvious interface between them and the EVA matrix.

[0081] Furthermore, compared to the conventional TOPCon module provided in Comparative Example 1, the DH1000 degradation of the solar cell module 1000 provided in Example 1 was reduced from the conventional 5.2% to 2.5%~2.8%, a reduction of 46%~52%. At the same time, the 10-year power retention rate of the solar cell module 1000 exceeded 90%, which is significantly higher than that of the conventional TOPCon module. The water vapor transmission rate of the solar cell module 1000 was reduced from the conventional 1.2 g / (m²·day) to 0.3 g / (m²·day), a reduction of 75%, indicating that the encapsulation material layer 2 after microcapsule repair can effectively prevent water vapor penetration.

[0082] Experimental results show that after damp heat aging, the microcapsules in the encapsulation material layer 2 of the solar cell module 1000 provided in this application rupture, releasing fluorinated siloxane oligomers. These oligomers fill the cracks and crosslink with the EVA matrix, allowing the encapsulation material layer 2 to recover more than 90% of its initial bonding strength. The encapsulation material layer 2 can repair cracks through microcapsule rupture, effectively preventing moisture penetration and thus significantly enhancing the weather resistance of the solar cell module 1000. Furthermore, the manufacturing process of the solar cell module 1000 provided in this application is fully compatible with existing TOPCon production lines, requiring no major equipment modifications and possessing rapid mass production feasibility.

[0083] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A solar cell, characterized by, The solar cell includes a substrate, a tunneling oxide layer, a gradient doped layer, a doped polycrystalline silicon layer, and a back electrode. The tunneling oxide layer is disposed on the back side of the substrate, the gradient doped layer is disposed on the side of the tunneling oxide layer opposite to the substrate, the doped polycrystalline silicon layer is disposed on the side of the gradient doped layer opposite to the tunneling oxide layer, and the back electrode is disposed on the side of the doped polycrystalline silicon layer opposite to the gradient doped layer. The gradient doped layer comprises intrinsic amorphous silicon and boron. The boron is doped into the intrinsic amorphous silicon, and the doping concentration of the boron gradually decreases along the thickness direction of the gradient doped layer and in a direction away from the tunneling oxide layer.

2. The solar cell according to claim 1, characterized in that, The doping concentration of the boron element in the side of the gradient doping layer facing the tunneling oxide layer is 2.5 x 10 19 cm - ³~3.5 x 10 19 cm - ³, and the doping concentration of the boron element in the side of the gradient doping layer away from the tunneling oxide layer is 0.5 x 10 19 cm - ³~1.5 x 10 19 cm - ³.

3. The solar cell according to claim 1 or 2, characterized in that, The doped polysilicon layer has a slot, the opening of the slot is located on the surface of the doped polysilicon layer away from the gradient doped layer, and the back electrode is located in the slot.

4. The solar cell according to claim 3, characterized in that, Along the thickness direction of the doped polysilicon layer, the distance between the bottom wall of the groove and the surface of the doped polysilicon layer facing the gradient doped layer is h, where h = 45 nm ~ 50 nm.

5. A solar cell module characterized by comprising: The solar cell module includes a solar cell as described in any one of claims 1 to 4 and an encapsulation material layer, wherein the encapsulation material layer covers the solar cell.

6. The solar cell module according to claim 5, wherein The encapsulating material layer comprises an EVA base and microcapsules added in the EVA base, the microcapsules comprise a core and a shell covering the core, the core is a fluorosilicone oligomer, and the molecular formula of the fluorosilicone oligomer is (CH3)3Si-O-[Si(CH3)(CH2CH2CF3)-O] n -Si(CH3)3, n=5~10.

7. The solar cell module according to claim 6, wherein The thermal decomposition temperature of the outer shell is ≥200℃.

8. The solar cell module according to claim 6, wherein Based on the mass of the encapsulation material layer, the encapsulation material layer comprises 90wt% to 95wt% of the EVA matrix and 5% to 10% of the microcapsules.

9. The solar cell module according to any one of claims 5 to 8, characterized by, The solar cells are multiple, and the solar cell module further includes an electrical connector that is electrically connected between the multiple solar cells. The electrical connector includes a solder strip and a silane coupling agent attached to the surface of the solder strip.

10. An encapsulant material, characterized by, The encapsulating material comprises an EVA base and microcapsules added in the EVA base, the microcapsules comprise a core and a shell covering the core, the core is a fluorosilicone oligomer, the molecular formula of the fluorosilicone oligomer is (CH3)3Si-O-[Si(CH3)(CH2CH2CF3)-O] n -Si(CH3)3, n=5~10.

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