High-mechanical-strength crystalline silicon cell and preparation method thereof

Abstract

The application discloses a kind of high mechanical strength crystalline silicon cell and preparation method thereof, belong to crystalline silicon cell technical field, the application is gradually discharged by hot isostatic pressing process, inter-particle attractive force is dominant in high-pressure and high-temperature environment, the microstructure of monocrystalline silicon wafer is changed by physical method, the defects of monocrystalline silicon wafer are solved, not only improve mechanical strength, fatigue life and electron mobility, improve the surface area of monocrystalline silicon wafer after texturing.

Description

Technical Field

[0001] This invention belongs to the field of crystalline silicon battery technology, specifically relating to a high mechanical strength crystalline silicon battery cell and its preparation method. Background Technology

[0002] Currently, the silicon wafers used in the crystalline silicon solar cells produced in the industry are all monocrystalline silicon wafers, which are composed of single crystals of silicon. They have a complete lattice structure, strong conductivity, high photoelectric conversion efficiency, and extremely high purity requirements. They are mainly used to manufacture semiconductor devices and high-efficiency solar cells.

[0003] However, single-crystal silicon wafers still have some defects: vacancies left by atoms leaving their equilibrium positions affect the periodicity of the crystal lattice; atoms running into the interstitial spaces of the crystal lattice disrupt the crystal structure; foreign atoms entering the crystal, such as oxygen and carbon, combine with silicon to form bonds; complexes formed by the combination of impurity atoms and vacancies affect the carrier concentration; linear defects in the crystal structure, including edge dislocations and screw dislocations; and poor toughness and low mechanical strength, making silicon wafers very fragile.

[0004] Metal impurities and crystal defects inside the battery can become recombination centers for minority carriers, affecting battery performance. Under illumination, the formation of certain recombinations can lead to early light-induced degradation of monocrystalline cells. Summary of the Invention

[0005] This invention provides a high mechanical strength crystalline silicon solar cell and its preparation method. By physically altering the microstructure of the monocrystalline silicon wafer, the inherent defects of the monocrystalline silicon wafer are solved, which not only improves the mechanical strength and fatigue life, but also increases the surface area and electron mobility of the monocrystalline silicon wafer.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a high mechanical strength crystalline silicon solar cell includes the following steps: S1: Perform a hot isostatic pressing on the selected monocrystalline silicon wafer. The hot isostatic pressing pressure is 10 MPa to 300 MPa, the temperature is heated to 350°C to 700°C, and the duration is 30 minutes to 100 minutes. The gas introduced is an inert gas with a small molecular diameter that does not chemically react with monocrystalline silicon. S2: After hot isostatic pressing, the pressure is released and high-purity oxygen is introduced at a pressure of 10 MPa to 300 MPa. The temperature is then raised to 80°C to 200°C for 30 to 200 minutes. Under high temperature and high pressure conditions, oxygen and single-crystal silicon come into direct contact. The oxygen reacts with silicon atoms on the silicon wafer surface to generate silicon oxide, which serves as the seed layer (tunneling oxide layer) for the next step and helps PECVD deposition of silicon oxide thin film growth. S3: PECVD double-sided deposition of silicon oxide layer; S4: Perform a second hot isostatic pressing, wherein the pressure of the hot isostatic pressing is 10 MPa to 300 MPa, the temperature is heated to 350°C to 700°C, and the duration is 30 minutes to 200 minutes; wherein the gas introduced is an inert gas with a small molecular diameter; S5: By using femtosecond laser etching, the silicon oxide layer on the front side of the silicon wafer is divided into multiple small battery areas according to the specified pattern, and the N-region and P-region are distinguished. S6: Selective N+ and P+ implantation is performed on the front small battery area. N+ is implanted with phosphorus ions for heavy doping, and P+ is implanted with boron ions for heavy doping. Both form a PN junction with the N-type silicon wafer. N- is implanted with phosphorus ions for light doping on the back side of the silicon wafer, forming a PN junction with the N-type silicon wafer. S7: PECVD deposited SiN x A thin film is used to protect both sides of the battery cell.

[0007] In the steps described above, the selected monocrystalline silicon wafer is an N-type monocrystalline silicon wafer with a thickness of 80um~120um; the gas introduced by hot isostatic pressing is high-purity helium (He); and the thickness of the silicon oxide film deposited on both sides by PECVD is 5um~20um.

[0008] Beneficial effects: This invention provides a high mechanical strength crystalline silicon solar cell and its preparation method, which has the following advantages compared with the prior art: Improved density: Through hot isostatic pressing, single-crystal silicon wafers can become denser in a high-temperature and high-pressure helium environment, reducing internal defects and improving the overall quality of the material; Improved surface smoothness: Helium, as a pressure transfer medium, helps to make the silicon wafer surface smoother during hot isostatic pressing, reducing surface roughness and improving the appearance quality of the silicon wafer. Enhanced mechanical strength: Hot isostatic pressing can enhance the mechanical strength of monocrystalline silicon wafers, making them more resistant to external pressure and impact, and improving the durability of the silicon wafers; Improved electron mobility: As the silicon wafer becomes denser and smoother, the mobility of electrons in the silicon wafer is improved, which helps to improve the electrical performance of the silicon wafer; This invention alters the microstructure of monocrystalline silicon wafers through hot isostatic pressing (HIP). Under high pressure and high temperature, the gas inside the monocrystalline silicon wafer is gradually expelled, and the interparticle attraction becomes dominant, increasing density and improving microstructure. By physically altering the microstructure of the monocrystalline silicon wafer, the inherent defects of the monocrystalline silicon wafer are solved, which not only improves mechanical strength, fatigue life, and electron mobility, but also increases the surface area of ​​the monocrystalline silicon wafer after texturing. Attached Figure Description

[0009] Figure 1 This is a top view of the etched silicon wafer prepared in an embodiment of the present invention; Figure 2This is a cross-sectional view of the etched silicon wafer prepared in an embodiment of the present invention. Detailed Implementation

[0010] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments: The preparation method of high mechanical strength crystalline silicon solar cells specifically includes the following steps: 1. N-type monocrystalline silicon wafers are selected, with a thickness range of 80um~120um; 2. First Hot Isostatic Pressing (HIP): The monocrystalline silicon wafer is placed in a sealed container and filled with high-purity helium (He). The diameter of helium molecules is 0.26 nm. The smaller the molecular diameter of the gas, the denser the force exerted on the monocrystalline silicon wafer. The gas selected is an inert gas with a small molecular diameter that cannot chemically react with the monocrystalline silicon. The container pressure range is 10 MPa to 300 MPa. The container is heated to 350°C to 700°C for 30 to 100 minutes. The above parameters are defined according to the actual process.

[0011] Based on Pascal's Law, which states that pressure in a medium (liquid or gas) within a closed container can be transmitted equally in all directions, this principle is utilized. High-pressure gas is used as the pressure medium, acting uniformly on the product to achieve densification under the combined effects of high temperature and high pressure. Helium gas, under the simultaneous action of pressure and heat, applies equal pressure to the silicon wafer in all directions, causing it to densify under high temperature and high pressure, resulting in changes to its microstructure. This achieves the following improvements: 1) Increased density: Through hot isostatic pressing (HIP), monocrystalline silicon wafers become denser in a high-temperature and high-pressure helium environment, reducing internal defects and improving the overall quality of the material; 2) Improved surface smoothness: Helium, as a pressure-transmitting medium, helps to smooth the surface of the silicon wafer during HIP, reducing surface roughness and improving the appearance quality of the silicon wafer; 3) Enhanced mechanical strength: HIP can enhance the mechanical strength of monocrystalline silicon wafers, making them more resistant to external pressure and impact, and improving the durability of the silicon wafers; 4) Increased electron mobility: As the silicon wafers become denser and smoother, the electron mobility within the wafers is also improved, which helps to improve the electrical properties of the silicon wafers.

[0012] Crystal orientation refers to the directionality of the atomic arrangement in a crystal. For single-crystal silicon, its crystal orientation is determined during the growth process, and due to the anisotropy of silicon, properties may differ in different growth directions. However, hot isostatic pressing (HIP) primarily affects the material's density, microstructure, and mechanical properties, without altering the crystal orientation. This is because crystal orientation is determined by the thermodynamic and kinetic conditions during crystal growth and, once formed, is relatively stable.

[0013] Electron transport speed: For grain refinement and intergranular distance, hot isostatic pressing (HIP) can refine the grains of single-crystal silicon and reduce the intergranular distance. This usually has a positive impact on the electrical properties of the material because finer grains and smaller intergranular distances reduce obstacles to electron transport.

[0014] Crystal structure and impurity concentration: Commonly used silicon wafer crystal structures are as follows: <100> <110> <111> This is a common low-resistivity orientation in single-crystal silicon, which is beneficial for electron transport. Simultaneously, the requirement that the impurity concentration in the single-crystal silicon wafer be ≤50ppm minimizes its adverse effects on electron transport. The grain refinement and reduced intergranular distance resulting from hot isostatic pressing, along with the lower impurity concentration (≤50ppm), all work together to increase the electron transport speed in single-crystal silicon.

[0015] The mechanical strength of monocrystalline silicon after hot isostatic pressing is significantly improved, reaching the theoretical strength value of monocrystalline silicon (CRSS~4 GPa), showing a great optimization of material properties.

[0016] Increased elastic limit: The elastic limit of the treated monocrystalline silicon is significantly increased, which means that the material can better maintain its shape and stability when subjected to stress.

[0017] In addition to increasing strength, hot isostatic pressing can also improve the wear resistance, corrosion resistance and mechanical properties of materials, and increase fatigue life by 10 to 100 times.

[0018] Hot isostatic pressing (HIP) involves applying uniform pressure to single-crystal silicon in a high-temperature and high-pressure environment, resulting in a significant improvement in material properties.

[0019] Internal defect elimination: Hot isostatic pressing (HIP) technology treats monocrystalline silicon under high temperature and high pressure, effectively eliminating internal defects such as porosity and shrinkage, reducing corrosion initiation points, and fundamentally improving corrosion resistance. Microstructure optimization: The microstructure of monocrystalline silicon undergoes rearrangement and refinement. Grain refinement increases the surface area of ​​the material, making it more difficult to react with corrosive media and further improving corrosion resistance.

[0020] Enhanced surface properties: Dense material surfaces are less susceptible to penetration by corrosive media, and may form dense oxide films or passivation layers to prevent corrosion.

[0021] 3. After the first step is completed, the sealed container is depressurized and then filled with high-purity oxygen (O2). The pressure range is 10 MPa to 300 MPa. The container is heated to 80°C to 200°C for 30 to 200 minutes. Under high temperature and pressure conditions, oxygen and monocrystalline silicon come into direct contact and a chemical reaction occurs. Oxygen reacts with silicon atoms on the silicon wafer surface to form silicon oxide. The chemical equation for this reaction can be expressed as: Si + O2 (high temperature) = SiO2. The oxidation of monocrystalline silicon usually requires a certain amount of time, and high temperature is a key factor in accelerating this reaction. The high-pressure environment may further promote the contact and reaction between oxygen and monocrystalline silicon. This forms a silicon oxide film on both sides of the silicon wafer, which serves as a seed layer (tunneling oxide layer) for the next process step, facilitating the growth of the PECVD deposited silicon oxide film. The SiO2 film thickness is 1 nm to 5 nm.

[0022] 4. PECVD double-sided deposition of silicon oxide layers, with a film thickness range of 5µm to 20µm. Using methods commonly used in the field, deposition is first performed on one side (e.g., the front side), then the substrate is removed, flipped, and placed back into the reaction chamber for deposition on the other side (e.g., the back side). The specific deposition process is as follows: Preliminary preparation and chamber cleaning: Use oxygen plasma or CF4 / O2 mixed gas to clean the reaction chamber and remove residues left from the previous process; Substrate loading and temperature stabilization: The cleaned silicon wafer is transferred into the reaction chamber and heated to the set temperature. Several minutes are required for the substrate temperature to stabilize and become uniform. Passivation / calibration deposition: Before the formal deposition, a co-deposition is performed on a substrate using a predetermined recipe for a few minutes. By measuring the film thickness and refractive index on the co-deposition substrate, the current deposition rate can be calibrated to ensure the accuracy of the formal process. Formal deposition: The silicon wafer is transferred into the cavity, and the pre-set process formula is executed. During the deposition process, the gas flow rate, cavity pressure, RF power, and deposition time are precisely controlled, as shown in Table 1. Table 1 Parameter settings for the deposition process

[0023] Sample removal and post-processing: After deposition, the sample is removed, and the cavity is usually cleaned with plasma again to prepare for the next process.

[0024] 5. Secondary Hot Isostatic Pressing (HIP): High-purity helium (He) is introduced. Helium molecules have a diameter of 0.26 nm; the smaller the molecular diameter, the denser the forces acting together. Pressure range: 10 MPa~300 MPa. The container is heated to 350℃~700℃ for 30~200 minutes. Benefits include: 1) Improved density and uniformity of silicon oxide films: 1) HIP enhances the density and uniformity of silicon oxide films, reduces internal defects, and improves the overall quality of the film. 2) Optimized optical and electrical properties: HIP improves the optical and electrical properties of silicon oxide films, such as transmittance, reflectivity, and insulation properties, thereby enhancing the performance of semiconductor devices. 3) Increased film hardness: HIP helps increase the hardness of silicon oxide films, making them more resistant to external wear and scratches and extending their service life. 4) Improved mechanical properties: HIP also improves the mechanical properties of silicon oxide films, such as flexural strength and compressive strength, making them more resistant to external pressure and impact.

[0025] 6. Femtosecond laser etching: such as Figures 1-2 As shown, the silicon oxide layer on the front side of the silicon wafer is divided into multiple small battery regions according to the specified pattern, and the N-region and P-region are distinguished; femtosecond laser can perform non-destructive etching, with an etching depth up to the seed layer and an etching width of 1µm~20µm. 7. Selective ion implantation: N+ and P+ selectively implant N+ and P+ into the small battery area on the front side. N+ is implanted with phosphorus ions for heavy doping, and P+ is implanted with boron ions for heavy doping. Both form a PN junction with the N-type silicon wafer. On the back side, N- is implanted with phosphorus ions for light doping, forming a PN junction with the N-type silicon wafer. 8. Double-sided protection of solar cells: PECVD deposition of SiN x Thin films of 70-80nm improve the efficiency and stability of solar cells.

[0026] This process combines multiple advanced technologies to fabricate solar cells with high mechanical strength and high stability. Hot isostatic pressing (HIP) improves the density and mechanical strength of the silicon wafer; PECVD deposition of silicon oxide and silicon nitride films achieves passivation and protection of the cell; and femtosecond laser selective etching and selective ion implantation form a PN junction, thereby fabricating a crystalline silicon solar cell with photovoltaic effect.

[0027] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-mechanical-strength crystalline silicon solar cell, characterized in that, Includes the following steps: S1: Perform a hot isostatic pressing on the selected monocrystalline silicon wafer, wherein the gas introduced is an inert gas with a small molecular diameter that does not chemically react with monocrystalline silicon. S2: After the first hot isostatic pressing is completed, the pressure is released and high-purity oxygen is introduced. Under high temperature and high pressure conditions, oxygen and single crystal silicon come into direct contact. The oxygen reacts with silicon atoms on the surface of the silicon wafer to generate silicon oxide, which serves as the seed layer for the next step. S3: PECVD double-sided deposition of silicon oxide layer; S4: Perform secondary hot isostatic pressing, in which the gas introduced is an inert gas with a small molecular diameter; S5: By using femtosecond laser etching, the silicon oxide layer on the front side of the silicon wafer is divided into multiple small battery areas according to the specified pattern, and the N-region and P-region are distinguished. S6: Selective N+ and P+ implantation is performed on the front small battery area to form a PN junction, and N- implantation is performed on the back of the silicon wafer to form a PN junction with the N-type silicon wafer. S7: PECVD deposited SiN x A thin film is used to protect both sides of the battery cell.

2. The method for preparing high mechanical strength crystalline silicon solar cells according to claim 1, characterized in that, The selected monocrystalline silicon wafer is an N-type monocrystalline silicon wafer.

3. The method for preparing high mechanical strength crystalline silicon solar cells according to claim 1 or 2, characterized in that, The thickness of a single-crystal silicon wafer is 80um~120um.

4. The method for preparing high mechanical strength crystalline silicon solar cells according to claim 1, characterized in that, The pressure of the first hot isostatic pressing is 10 MPa to 300 MPa, and the temperature is heated to 350°C to 700°C for 30 to 100 minutes.

5. The method for preparing a high mechanical strength crystalline silicon solar cell according to claim 1 or 4, characterized in that, After the first hot isostatic pressing is completed, the pressure is released and high-purity oxygen is added. The pressure is 10 MPa to 300 MPa. The temperature is then raised to 80°C to 200°C for 30 to 200 minutes.

6. The method for preparing a high mechanical strength crystalline silicon solar cell according to claim 1, characterized in that, The secondary hot isostatic pressing is performed at a pressure of 10 MPa to 300 MPa, heated to 350°C to 700°C, for a duration of 30 to 200 minutes.

7. The method for preparing a high mechanical strength crystalline silicon solar cell according to claim 4 or 6, characterized in that, The gas introduced during hot isostatic pressing is high-purity helium.

8. The method for preparing high mechanical strength crystalline silicon solar cells according to claim 1, characterized in that, The thickness of the silicon oxide film deposited on both sides by PECVD is 5um~20um.

9. The method for preparing a high mechanical strength crystalline silicon solar cell according to claim 1, characterized in that, On the front side of the silicon wafer, the small battery area is heavily doped with N+ phosphorus ions and heavily doped with P+ boron ions, forming a PN junction with the N-type silicon wafer; on the back side of the silicon wafer, the N- phosphorus ions are lightly doped, forming a PN junction with the N-type silicon wafer.

10. A high mechanical strength crystalline silicon solar cell, characterized in that, The battery cell is prepared by the method described in any one of claims 1-9.

Images