High-efficiency back contact solar cell and preparation method thereof

Abstract

The invention provides a high-efficiency back contact solar cell and a preparation method thereof. The back surface of the cell sequentially comprises a substrate, a composite back passivation layer, P-type electrodes and N-type electrodes, wherein the P-type electrodes and the N-type electrodes are arranged on the back surface of the cell in a staggered manner; the composite back passivation layer is a SiO2 / Al2O3 double-layer passivation layer; the composite back passivation layer is etched to form a contact window, and a P-type doped region and an N-type doped region are formed in the contact window region. According to the high-efficiency back contact solar cell and the preparation method thereof, the photoelectric conversion efficiency is effectively improved, the manufacturing cost is reduced, the comprehensive performance of the solar cell is improved, and the preparation method can simplify the process steps and reduce the process difficulty and the dependence on high-precision equipment, so that the manufacturing cost is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and more specifically, to a high-efficiency back-contact solar cell and its fabrication method. Background Technology

[0002] Traditional solar cells, such as PERC (passivated emitter and partial back contact cell) and TOPCon (tunneling oxide passivated contact cell), have front electrodes that block incident light, inevitably causing optical losses and limiting further improvements in the cell's photoelectric conversion efficiency.

[0003] Back-contact (BC) cells move all electrodes to the back side, effectively increasing the light-receiving area and theoretically possessing higher potential photoelectric conversion efficiency. However, BC cells currently face several technical challenges in practical applications: First, there is a risk of leakage between the back-side electrodes, which reduces the cell's output power and stability; second, its manufacturing process relies on complex masking and alignment techniques, leading to low production efficiency and significantly increased costs; third, the long transport path of charge carriers within the cell makes recombination losses prone to occur, affecting the cell's photoelectric conversion performance. Existing BC cell technology suffers from technical defects such as back-side electrode leakage, complex manufacturing processes, and significant carrier recombination losses.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-efficiency back-contact solar cell and its fabrication method. This invention overcomes the technical problems of leakage current in the back-side electrode of traditional BC cells, complex processes, and large carrier recombination losses. It effectively improves photoelectric conversion efficiency, reduces manufacturing costs, and enhances the overall performance of solar cells. The fabrication method simplifies process steps, reduces process difficulty and dependence on high-precision equipment, thereby reducing manufacturing costs and improving production efficiency.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A high-efficiency back-contact solar cell includes a substrate, a composite back passivation layer, and P-type and N-type electrodes arranged alternately on the back of the cell. The composite back passivation layer is a SiO2 / Al2O3 double passivation layer. A contact window is etched on the composite back passivation layer, and P-type doped regions and N-type doped regions are formed in the contact window region.

[0007] Furthermore, the substrate is an N-type single-crystal silicon wafer, and a pyramid structure with a height of 2~5μm is formed on both sides of the substrate.

[0008] Furthermore, a composite back passivation layer is deposited on the surface of the N-type single-crystal silicon wafer, and the total thickness of the composite back passivation layer is 90~130nm.

[0009] Furthermore, the ratio of the electrode spacing to the width of the P-type electrode and the N-type electrode is 1.2 to 1.8.

[0010] A method for fabricating the above-mentioned high-efficiency back-contact solar cell includes the following steps: Step S1, Substrate processing: Take an N-type monocrystalline silicon wafer and perform double-sided texturing. Step S2, Composite Back Passivation Layer: A SiO2 / Al2O3 double-layer passivation layer is formed using PECVD process; Step S3, Laser Grooving: Use an ultraviolet laser to etch a contact window on the double passivation layer; Step S4, Laser Doping: P-type and N-type doped regions are formed in the contact window area by laser doping; Step S5, Electrode Printing: P-type and N-type electrodes with an alternating finger-like arrangement are formed on the back surface of the battery by printing. Step S6, Sintering: The battery is sintered to form the back electrode; Step S7: Prepare the front electrode to obtain the BC solar cell.

[0011] Furthermore, during the deposition process in step S2, an ellipsometry is used to monitor and precisely calibrate the passivation layer thickness in real time, ensuring that a 30-50 nm SiO2 layer and a 60-80 nm Al2O3 layer are sequentially deposited on the surface of the texturized N-type single crystal silicon wafer, with a total SiO2 / Al2O3 double passivation layer thickness of 90-130 nm.

[0012] Furthermore, in step S3, the ultraviolet laser wavelength is 355~370nm and the contact window width is 20~30μm.

[0013] Furthermore, in step S4, the laser energy density of the laser doping is controlled within the range of 0.8~1.2 J / cm². 2 The doping concentration is 1x10 19 ~5x10 19 cm -3 The doping depth is 0.5~1.5μm.

[0014] Furthermore, in step S5, the ratio of the distance between the P-type electrodes and the width of the interleaved finger-shaped P-type electrodes and N-type electrodes is 1.2 to 1.8.

[0015] Furthermore, the sintering temperature in step S6 is 750~800℃.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The high-efficiency back-contact solar cell of this invention can effectively improve the photoelectric conversion efficiency, achieving a conversion efficiency of 26.15%, which is significantly improved compared to the conversion efficiency of 25.20% for traditional BC cells and 23.50% for traditional PERC cells. It can more effectively convert light energy into electrical energy and improve the power generation capacity of solar cells.

[0017] 2. The high-efficiency back-contact solar cell of this invention possesses excellent electrical performance, as shown in Table 1: ① Improved open-circuit voltage: The open-circuit voltage (Voc) of the cell of this invention is 720mV, higher than the 705mV of the traditional BC cell. A higher open-circuit voltage means that the cell can output a higher voltage under no-load conditions, laying the foundation for improving overall power generation performance; ② Increased short-circuit current density: The short-circuit current density (Jsc) reaches 42.5mA / cm². 2 The traditional BC battery has an A / cm² value of 41.8 mA / cm². 2 The increased short-circuit current density indicates that the battery can output a larger current under short-circuit conditions, reflecting the battery's stronger ability to collect and transport photogenerated carriers; ③ Optimized fill factor: The fill factor (FF) of this invention is 85.3%, which is better than the 84.1% of the traditional BC battery. The improved fill factor indicates that the battery of this invention can more effectively utilize its open-circuit voltage and short-circuit current in actual operation, and output electrical energy closer to the theoretical maximum power.

[0018] 3. The high-efficiency back-contact solar cell fabrication method of the present invention can reduce costs and improve process feasibility: ① The optimized electrode layout and fabrication process reduce the use of complex masking and alignment processes, reduce the process difficulty in the production process and the dependence on high-precision equipment, thereby reducing manufacturing costs and improving production efficiency; ② The reasonable passivation layer design and laser doping parameter optimization simplify some process steps while ensuring the high performance of the cell, further reducing production costs and making the technology of the present invention more promising for industrial application. Attached Figure Description

[0019] 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.

[0020] Figure 1 This is a schematic diagram of the high-efficiency back-contact solar cell structure of the present invention; Figure 2 A bar chart comparing the photoelectric conversion efficiency of the BC battery prepared in Example 1 of the present invention with that of Comparative Examples 1 and 2. Figure 3 This is a band structure diagram of the SiO2 passivation layer and Al2O3 passivation layer deposited in Example 1 of the present invention. Detailed Implementation

[0021] 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.

[0022] A high-efficiency back-contact solar cell, wherein the back side of the cell includes a substrate, a composite back passivation layer, and P-type and N-type electrodes arranged alternately on the back side of the cell; the composite back passivation layer is a SiO2 / Al2O3 double passivation layer; a contact window is etched on the composite back passivation layer, and a P-type doped region and an N-type doped region are formed in the contact window region; Preferably, the front side of the battery comprises, in sequence, a substrate, a SiO2 passivation layer, an Al2O3 passivation layer, and a front anti-reflection layer; Preferably, the substrate is an N-type single-crystal silicon wafer with a resistivity of 1~3 Ω·cm; Preferably, a pyramid structure with a height of 2~5μm is formed on both sides of the substrate. The pyramid structure can effectively increase the number of light reflections on the surface of the battery, increase the light absorption area, and improve the light absorption efficiency. Preferably, a composite back passivation layer is deposited on the surface of the N-type single crystal silicon wafer, and the total thickness of the composite back passivation layer is 90~130nm; Preferably, the ratio of the electrode spacing to the width of the P-type electrode and the N-type electrode is 1.2 to 1.8. Through the electrode layout design, while ensuring good electrical contact, the risk of leakage between the back electrodes is effectively reduced, the carrier collection path is optimized, and the recombination loss during carrier transport is reduced.

[0023] A method for fabricating a high-efficiency back-contact solar cell includes the following steps: Step S1, Substrate processing: Take an N-type single crystal silicon wafer and perform double-sided texturing to form a uniformly distributed pyramid structure with a height of 2~5μm on the surface of the silicon wafer; Step S2, Composite Back Passivation Layer: Using plasma-enhanced chemical vapor deposition (PECVD) technology, a 30-50nm SiO2 layer and a 60-80nm Al2O3 layer are sequentially deposited on the surface of the texturized N-type single crystal silicon wafer to form a SiO2 / Al2O3 double passivation layer. The SiO2 / Al2O3 double passivation layer can effectively reduce carrier recombination on the silicon wafer surface and improve the open-circuit voltage and fill factor of the battery. Step S3, Laser Grooving: Use an ultraviolet laser to etch a contact window with a width of 20~30μm on the double passivation layer. This contact window is used for good electrical contact between the subsequent electrode and the silicon wafer. The precisely controlled window width helps to optimize the transport and collection of charge carriers. Step S4, Laser Doping: P-type and N-type doped regions are formed in the contact window area by laser doping; Step S5, Electrode Printing: P-type and N-type electrodes with an alternating finger-like arrangement are formed on the back surface of the battery by screen printing. Step S6, Sintering: The battery is sintered to form the back electrode; Step S7: Prepare the front electrode to obtain the BC solar cell; Preferably, during the deposition process in step S2, an ellipsometry is used to monitor and precisely calibrate the passivation layer thickness in real time to ensure that the total thickness of the SiO2 / Al2O3 double passivation layer reaches 90~130nm, thereby achieving a good surface passivation effect. Preferably, the ultraviolet laser wavelength in step S3 is 355~370nm; Preferably, in step S4, the laser energy density of the laser doped laser is controlled between 0.8 and 1.2 J / cm². 2 ; Preferably, the doping concentration in step S4 is 1x10⁻⁶. 19 ~5x10 19 cm -3 The doping depth is 0.5~1.5μm, and the doping concentration and depth are precisely controlled to optimize the electrical performance of the battery; Preferably, in step S5, silver paste with a solid content of 85% to 90% is used for screen printing; Preferably, in step S5, the ratio of the electrode spacing to the width of the staggered finger-arranged P-type and N-type electrodes is 1.2 to 1.8. Preferably, the sintering temperature in step S6 is 750~800℃, so that the silver paste and silicon wafer form good ohmic contact.

[0024] Example 1 A method for fabricating a high-efficiency back-contact solar cell includes the following steps: 1. Take an N-type monocrystalline silicon wafer and perform double-sided texturing to form a uniformly distributed pyramid structure with a height of 2~5μm on the surface of the silicon wafer; 2. Using plasma-enhanced chemical vapor deposition (PECVD) process, a 40nm SiO2 layer and a 60nm Al2O3 layer are sequentially deposited on the surface of the textured single-crystal silicon wafer to form a SiO2 / Al2O3 double passivation layer with a total thickness of 100nm. Step S3, Laser Grooving: Use a 355nm ultraviolet laser to etch a contact window with a width of 20μm on the double passivation layer; Step S4, Laser Doping: The desired P-type and N-type doped regions are formed in the contact window area by laser doping. The laser energy density for laser doping is 0.8 J / cm². 2 The doping concentration is 5x10 19 cm -3 The doping depth is 1.5 μm; Step S5, Electrode Printing: Silver paste with a solid content of 85% is screen printed on the back surface of the battery to form P-type and N-type electrodes arranged in an alternating finger pattern. The ratio of the electrode spacing to the width of the P-type and N-type electrodes is 1.2. Step S6, Sintering: The battery is sintered at 750°C to form the back electrode; Step S7: Prepare the front electrode to obtain the BC solar cell.

[0025] Example 2 A method for fabricating a high-efficiency back-contact solar cell includes the following steps: 1. Take an N-type monocrystalline silicon wafer and perform double-sided texturing to form a uniformly distributed pyramid structure with a height of 2~5μm on the surface of the silicon wafer; 2. Using plasma-enhanced chemical vapor deposition (PECVD) process, a 30nm SiO2 layer and a 60nm Al2O3 layer are sequentially deposited on the surface of the textured single-crystal silicon wafer to form a SiO2 / Al2O3 double passivation layer with a total thickness of 90nm. Step S3, Laser Grooving: Use a 360nm ultraviolet laser to etch a contact window with a width of 25μm on the double passivation layer; Step S4, Laser Doping: The desired P-type and N-type doped regions are formed in the contact window area by laser doping. The laser energy density for laser doping is 1 J / cm². 2 The doping concentration is 1.9 x 10⁻⁶. 19 cm -3 The doping depth is 0.5 μm; Step S5, Electrode Printing: Silver paste with a solid content of 87% is screen printed on the back surface of the battery to form P-type and N-type electrodes arranged in an alternating finger pattern. The ratio of the electrode spacing to the width of the P-type and N-type electrodes is 1.5. Step S6, Sintering: The battery is sintered at 780°C to form the back electrode; Step S7: Prepare the front electrode to obtain the BC solar cell.

[0026] Example 3 A method for fabricating a high-efficiency back-contact solar cell includes the following steps: 1. Take an N-type monocrystalline silicon wafer and perform double-sided texturing to form a uniformly distributed pyramid structure with a height of 2~5μm on the surface of the silicon wafer; 2. Using plasma-enhanced chemical vapor deposition (PECVD) process, a 50nm SiO2 layer and an 80nm Al2O3 layer are sequentially deposited on the surface of the textured single-crystal silicon wafer to form a SiO2 / Al2O3 double passivation layer with a total thickness of 130nm. Step S3, Laser Grooving: Use a 370nm ultraviolet laser to etch a contact window with a width of 30μm on the double passivation layer; Step S4, Laser Doping: The desired P-type and N-type doped regions are formed in the contact window area by laser doping. The laser energy density for laser doping is 1.2 J / cm². 2 The doping concentration is 2x10 19 cm -3 The doping depth is 1.0 μm; Step S5, Electrode Printing: Silver paste with a solid content of 90% is screen printed on the back surface of the battery to form P-type and N-type electrodes arranged in an alternating finger pattern. The ratio of the electrode spacing to the width of the P-type and N-type electrodes is 1.8. Step S6, Sintering: The battery is sintered at 800°C to form the back electrode; Step S7: Prepare the front electrode to obtain the BC solar cell.

[0027] Comparative Example 1 Traditional BC battery.

[0028] Comparative Example 2 Traditional PERC batteries.

[0029] Experimental example: I. Photoelectric conversion efficiency of BC cells prepared in Example 1 and conventional BC cells in Comparative Example 1 and conventional PERC cells in Comparative Example 2 are as follows: Figure 2 As shown.

[0030] II. The energy band diagrams of the SiO2 passivation layer and the Al2O3 passivation layer in the composite back passivation layer deposited in Example 1 are as follows: Figure 3 As shown.

[0031] like Figure 3 As shown, the band structure (distance-energy relationship) of the SiO2 passivation layer and the Al2O3 passivation layer differs significantly: ① SiO2 passivation layer (black curve): The distance fluctuates little in the low energy range (e.g., 0 - 1 eV), indicating that the SiO2 passivation layer has stable carrier binding / transport characteristics in this energy range; the distance increases in the high energy range (1 - 2 eV), which may be related to electronic transitions and interface state changes at high energy levels, reflecting the response of its passivation effect with energy.

[0032] ② Al2O3 passivation layer (gray curve): Energy changes have a more significant impact on distance, especially after 1 eV the distance increases rapidly, reflecting the difference in interface characteristics of Al2O3 passivation layer at different energies. The complementary energy bands of the bilayer structure can synergistically optimize carrier recombination and transport, and improve battery performance (such as adapting to different photogenerated carrier energies and reducing surface recombination).

[0033] III. The performance parameters of the BC battery prepared in Example 1 and the conventional BC battery in Comparative Example 1 are compared in Table 1.

[0034] Table 1. Comparison of performance parameters between the BC battery prepared in Example 1 and the conventional BC battery in Comparative Example 1.

[0035] As shown in Table 1, the BC battery of the present invention achieves higher conversion efficiency, open-circuit voltage, short-circuit current density and fill factor than the conventional BC battery.

Claims

1. A high-efficiency back-contact solar cell, characterized in that, The back of the battery includes, in sequence, a substrate, a composite back passivation layer, and P-type and N-type electrodes arranged alternately on the back of the battery; the composite back passivation layer is a SiO2 / Al2O3 double passivation layer; a contact window is etched on the composite back passivation layer, and a P-type doped region and an N-type doped region are formed in the contact window region.

2. The high-efficiency back-contact solar cell according to claim 1, characterized in that, The substrate is an N-type single-crystal silicon wafer, and a pyramid structure with a height of 2~5μm is formed on both sides of the substrate.

3. The high-efficiency back-contact solar cell according to claim 2, characterized in that, A composite back passivation layer is deposited on the surface of the N-type single crystal silicon wafer, and the total thickness of the composite back passivation layer is 90~130nm.

4. The high-efficiency back-contact solar cell according to claim 1, characterized in that, The ratio of the electrode spacing to the width of the P-type electrode and the N-type electrode is 1.2 to 1.

8.

5. A method for preparing a high-efficiency back-contact solar cell as described in any one of claims 1 to 4, characterized in that: Includes the following steps: Step S1, Substrate processing: Take an N-type monocrystalline silicon wafer and perform double-sided texturing. Step S2, Composite Back Passivation Layer: A SiO2 / Al2O3 double-layer passivation layer is formed using PECVD process; Step S3, Laser Grooving: Use an ultraviolet laser to etch a contact window on the double passivation layer; Step S4, Laser Doping: P-type and N-type doped regions are formed in the contact window area by laser doping; Step S5, Electrode Printing: P-type and N-type electrodes with an alternating finger-like arrangement are formed on the back surface of the battery by printing. Step S6, Sintering: The battery is sintered to form the back electrode; Step S7: Prepare the front electrode to obtain the BC solar cell.

6. The method for fabricating a high-efficiency back-contact solar cell according to claim 5, characterized in that, In step S2, during the deposition process, an ellipsometry is used to monitor and precisely calibrate the passivation layer thickness in real time, ensuring that a 30-50 nm SiO2 layer and a 60-80 nm Al2O3 layer are sequentially deposited on the surface of the texturized N-type single crystal silicon wafer, and the total thickness of the SiO2 / Al2O3 double passivation layer reaches 90-130 nm.

7. The method for fabricating a high-efficiency back-contact solar cell according to claim 5, characterized in that, In step S3, the ultraviolet laser wavelength is 355~370nm and the contact window width is 20~30μm.

8. The method for fabricating a high-efficiency back-contact solar cell according to claim 5, characterized in that, In step S4, the laser energy density of the laser doped laser is controlled between 0.8 and 1.2 J / cm². 2 The doping concentration is 1x10 19 ~5x10 19 cm -3 The doping depth is 0.5~1.5μm.

9. The method for fabricating a high-efficiency back-contact solar cell according to claim 5, characterized in that, In step S5, the ratio of the distance between the P-type electrodes and the width of the N-type electrodes arranged in an alternating finger pattern is 1.2 to 1.

8.

10. The method for fabricating a high-efficiency back-contact solar cell according to claim 5, characterized in that, The sintering temperature in step S6 is 750~800℃.

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