Solar cell and preparation method thereof

Abstract

The invention relates to the technical field of solar cells, in particular to a solar cell and a preparation method thereof, and the preparation method comprises the following steps: activating the surface of a cell substrate to activate an a-Si: H surface dangling bond; immersing the battery substrate into an organic molecule solution containing bifunctional groups; electroplating a grid line on the battery substrate; wherein the bifunctional group-containing organic molecule solution comprises at least one of a thiol molecule solution and a silane coupling agent. According to the preparation method, the binding force between the electroplated grid line and the cell substrate can be effectively improved, the problem that the grid line falls off is reduced, and the problem that the yield of the solar cell is reduced due to grid falling off is solved.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and more specifically, to solar cells and their fabrication methods. Background Technology

[0002] Solar cells provided by related technologies, such as heterojunction solar cells, are widely used due to their ultra-high open-circuit voltage (>740mV) and bifaciality (>95%).

[0003] Solar cell grid lines are typically fabricated using printing or electroplating. Printed silver grid lines are limited in linewidth, making it difficult to reduce the linewidth to create finer grid lines (less than 20 μm), resulting in significant light-shielding loss. Electroplated copper grid lines, on the other hand, can be made much finer, reducing light-shielding loss. Furthermore, electroplated copper grid lines achieve high conductivity, with a resistivity of approximately 2.0 μΩ·cm, only one-third that of silver paste.

[0004] However, the electroplating grid lines provided by the relevant technologies are difficult to improve the bonding force between copper and the battery substrate, which makes the grid lines prone to falling off, and reduces the production of solar cells due to "grid detachment". Summary of the Invention

[0005] The purpose of this invention is to provide a solar cell and a method for its fabrication. This method can effectively improve the bonding force between the electroplated grid lines and the cell substrate, reduce the problem of grid line detachment, and improve the problem of reduced solar cell yield caused by "grid detachment".

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a solar cell comprising: The battery substrate includes a transparent conductive layer; A conductive molecule self-assembled film layer, the conductive molecule self-assembled film layer being formed on a transparent conductive layer; and, Gate lines are formed in a self-assembled film layer of conductive molecules.

[0007] In an optional embodiment, the solar cell includes a plurality of grid lines spaced apart, with an insulating resin filling the space between adjacent grid lines.

[0008] Secondly, the present invention provides a method for preparing the aforementioned solar cell, comprising: The surface of the battery substrate is activated to activate the dangling bonds on the a-Si:H surface; The battery substrate is immersed in a solution of organic molecules containing bifunctional groups; Electroplating grid lines onto the battery substrate; among which... Solutions of organic molecules containing bifunctional groups include at least one of thiol molecular solutions and silane coupling agents.

[0009] In an optional embodiment, the solution of the organic molecule containing bifunctional groups is an alcoholic solution or an aqueous solution with a concentration of 0.1~1mM.

[0010] In an optional embodiment, the battery substrate is immersed in a solution of organic molecules containing bifunctional groups for 5 to 30 minutes.

[0011] In an optional implementation, the electroplated grid lines include pulse electroplating.

[0012] In an optional embodiment, the forward current density of the pulse electroplating is 3~5 mA / cm². 2 The ratio of forward current density to reverse current density is 1:(0.2~0.5), the pulse frequency is 10~100 Hz, and the duty cycle is 20~40%.

[0013] In an optional implementation, annealing is also included after pulse electroplating.

[0014] In an optional embodiment, the annealing temperature is 180-200°C.

[0015] In an optional embodiment, the method for preparing a solar cell further includes: after electroplating the grid lines, filling the gaps between the grid lines with insulating resin.

[0016] In an optional embodiment, the insulating resin includes a polyimide precursor.

[0017] The present invention has the following beneficial effects: The solar cell provided in this invention improves the bonding force of the grid lines by forming a self-assembled layer of conductive molecules in the transparent conductive layer, effectively reducing the problem of grid line detachment and improving the problem of reduced solar cell yield caused by "grid detachment".

[0018] In the solar cell fabrication method provided in this embodiment of the invention, before electroplating the grid lines, the cell substrate is treated with an organic molecular solution containing bifunctional groups. This process can form a molecular-level transition layer on the surface of the cell substrate that has both chemical bonding ability and conductivity. This helps to improve the bonding force between the electroplated grid lines and the cell substrate, effectively reducing the problem of grid line detachment and improving the problem of reduced solar cell yield caused by "grid detachment". Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of the solar cell disclosed herein; Figure 2 This is a process flow diagram for fabricating solar cells. Figure 1 ; Figure 3 This is a process flow diagram for fabricating solar cells. Figure 2 .

[0021] Icons: 010 - Solar cell; 100 - Cell substrate; 110 - Silicon substrate; 121 - First intrinsic amorphous silicon layer; 122 - First doped layer; 123 - First transparent conductive layer; 131 - Second intrinsic amorphous silicon layer; 132 - Second doped layer; 133 - Second transparent conductive layer; 141 - Conductive molecule self-assembled film layer; 142 - Gate line. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] The inventors found that the electroplating grid line methods provided by the related technologies still have some problems: (1) Roughening the TCO surface to increase mechanical interlocking mainly damages light transmittance and reduces short-circuit current (Jsc); (2) Adding a nickel / titanium transition layer (i.e., magnetron sputtering metal barrier layer) mainly has the problems of high cost, complex equipment, and the introduction of additional interface failure risk; (3) High-temperature annealing to promote copper-silicon interdiffusion, but does not meet the requirement that heterojunction batteries are sensitive to high temperatures (>250℃ destroys a-Si:H passivation); (4) Strong acid activation method, which uses hydrofluoric acid etching to remove oxides on the surface of the battery substrate to improve the bonding force between the copper grid line and the battery substrate, mainly has the problem that excessive etching will damage the TCO and reduce the on-state voltage (Voc).

[0024] To address the aforementioned issues, this disclosure provides a solar cell and its fabrication method that simultaneously achieves the following: 1) Molecular-level interfacial bonding: constructing strong chemical bonds between copper and a-Si:H, rather than relying on mechanical anchoring, thus improving light transmittance damage; 2) Suppressing electroplating side reactions: optimizing deposition kinetics and eliminating hydrogen evolution and lattice defects; 3) Enhancing environmental stability: blocking moisture / ion erosion pathways; 4) Mass production feasibility: compatible with existing heterojunction production lines, with controllable costs.

[0025] Please refer to Figure 1The solar cell 010 disclosed herein includes: a cell substrate 100, the cell substrate 100 including a transparent conductive layer; A conductive molecule self-assembled film layer 141 is formed on a transparent conductive layer; and... Gate line 142 is formed on conductive molecule self-assembled film layer 141.

[0026] By forming a self-assembled layer of conductive molecules in the transparent conductive layer, the bonding force of the grid line 142 is improved, effectively reducing the problem of grid line 142 detachment and improving the problem of reduced solar cell 010 yield caused by "grid detachment".

[0027] Please refer to Figure 1 and Figure 2 The method for fabricating the solar cell 010 disclosed herein includes: The surface of the battery substrate 100 is activated to activate the dangling bonds on the a-Si:H surface; The battery substrate 100 is immersed in a solution of organic molecules containing bifunctional groups; Electroplated grid lines 142 are applied to the battery substrate 100; wherein... Solutions of organic molecules containing bifunctional groups include at least one of thiol molecular solutions and silane coupling agents.

[0028] Before electroplating the grid lines 142, the preparation method uses an organic molecule solution containing bifunctional groups to treat the battery substrate 100, which can form a molecular-level transition layer (i.e., a conductive molecule self-assembled film layer 141) on the surface of the battery substrate 100, which has both chemical bonding ability and conductivity. This helps to improve the bonding force between the electroplated grid lines 142 and the battery substrate 100, effectively reduce the problem of grid line 142 falling off, and improve the problem of reduced solar cell 010 yield caused by "grid line detachment".

[0029] It should be noted that when using thiol molecules (such as HS-(CH2)... n When the battery substrate 100 is immersed in at least one of the following: a solution containing -COOH (n=8~12) and a silane coupling agent (e.g., NH2-(CH2)3-Si(OMe)3), one end of the organic molecule containing the bifunctional group (-SH or -Si(OMe)3) forms a covalent bond (S-Si or Si-O-Si) with the a-Si:H of the battery substrate 100, while the other end (-COOH or -NH2) is exposed to provide an active site.

[0030] In this way, the following mechanisms of action can be formed: (1) Chemical anchoring: The molecular chain is strongly bonded to a-Si:H, avoiding weak interfacial connections; (2) Stress buffering: The flexible molecular chain alleviates the difference in thermal expansion coefficients between copper and silicon (Cu: 17ppm / K; Si: 2.6ppm / K); (3) Nucleation sites: Exposed polar groups (-COOH or -NH2) adsorb Cu 2+ Ions promote the dense growth of the copper layer. Through the above mechanism, the bonding strength between the subsequently electroplated grid lines 142 and the battery substrate 100 can be effectively improved, effectively reducing the problem of grid line 142 detachment.

[0031] It should also be noted that the technology of self-assembled monolayers (SAMs) using organic molecular solutions containing bifunctional groups (a type of tightly packed thin film formed on the surface of a solid substrate by the spontaneous and orderly arrangement of molecules) can be directly integrated into the existing cleaning equipment for the production of solar cells, so as to better save costs and be compatible with production volume.

[0032] Optionally, the fabrication method of this disclosure can produce a heterojunction solar cell, wherein the cell substrate 100 includes a silicon substrate 110, a first intrinsic amorphous silicon layer 121, a first doped layer 122, and a first transparent conductive layer 123 sequentially formed on the front side of the silicon substrate 110, and a second intrinsic amorphous silicon layer 131, a second doped layer 132, and a second transparent conductive layer 133 sequentially formed on the back side of the silicon substrate 110. The electroplated grid lines 142 can refer to copper grid lines formed on either the first transparent conductive layer 123 or the second transparent conductive layer 133.

[0033] In other words, a conductive molecule self-assembled film layer 141 and grid lines 142 (e.g., copper grid lines) are sequentially formed on either the first transparent conductive layer 123 or the second transparent conductive layer 133 of the solar cell 010 disclosed herein.

[0034] Optionally, the method for activating the surface of the battery substrate 100 is similar to related technologies, including but not limited to treating the battery substrate 100 with ozone water (O3water) or oxygen plasma to thoroughly remove surface organic contaminants and activate the a-Si:H surface dangling bonds. Specific activation processes will not be elaborated further.

[0035] Optionally, the solution of the organic molecule containing the bifunctional group is an alcoholic solution or an aqueous solution with a concentration of 0.1~1mM (e.g., 0.1mM, 0.2mM, 0.3mM, 0.4mM, 0.5mM, 0.6mM, 0.7mM, 0.8mM, 0.9mM, 1.0mM, etc., which are not specifically limited here).

[0036] Optionally, the alcohol solvent used to prepare an alcohol solution containing a bifunctional organic molecule includes, but is not limited to, ethanol (99.9 vol%) and methanol (99.9 vol%).

[0037] Optionally, the battery substrate 100 is immersed in a solution of organic molecules containing bifunctional groups for 5 to 30 minutes, for example: 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, etc., without being specifically limited here.

[0038] Optionally, after soaking in a solution of organic molecules containing bifunctional groups, the battery substrate 100 can be rinsed with deionized water.

[0039] Alternatively, please refer to Figure 1 and Figure 3 The electroplated gate line 142 includes pulse electroplating. The synergistic pulse electroplating process can suppress interface defects to improve the bonding strength between the electroplated metal layer (e.g., copper) and the silicon substrate of the battery substrate 100, thereby reliably improving the gate delamination problem.

[0040] Optionally, the forward current density of pulse electroplating is 3~5 mA / cm². 2 (For example: 3mA / cm) 2 3.5 mA / cm 2 4mA / cm 2 4.5 mA / cm 2 5 mA / cm 2 The ratio of forward current density to reverse current density is 1:(0.2~0.5) (e.g., 1:0.2, 1:0.3, 1:0.4, 1:0.5, etc., not specifically limited here), the pulse frequency is 10~100 Hz (e.g., 10Hz, 20Hz, 30Hz, 40Hz, 50Hz, 60Hz, 70Hz, 80Hz, 90Hz, 100Hz, etc., not specifically limited here), and the duty cycle is 20~40% (e.g., 20%, 25%, 30%, 35%, 40%, etc., not specifically limited here).

[0041] The forward current density disclosed herein is lower than that of conventional DC electroplating, which can reduce the risk of hydrogen evolution and reduce interface bubbles; the optimized ratio of forward current density to reverse current density of 1:0.2~0.5 can dissolve dendrites and smooth the coating; the optimized pulse frequency (10~100 Hz) can enhance ion diffusion and improve coating uniformity; the optimized duty cycle (20~40%) can reduce concentration polarization.

[0042] In other words, the process optimization of pulse electroplating disclosed herein can be achieved through reverse pulse hydrogen removal, that is, removing H2 generated during the electrolysis of water in the reverse current phase. + It can neutralize residual H2 bubbles at the interface; at the same time, it forms a low-stress coating, releasing lattice stress during pulse intervals to prevent coating cohesion from damaging the interface.

[0043] Optionally, the linewidth of the electroplated grid line 142 can be 25±5μm (e.g., 20μm, 22μm, 25μm, 27μm, 30μm, etc., which are not specifically limited here), and the aspect ratio can be 0.4±0.1 (e.g., 0.3, 0.4, 0.5, etc., which are not specifically limited here).

[0044] Alternatively, please refer to Figure 3 The pulse electroplating process includes annealing. Following pulse electroplating, synergistic annealing further ensures the adhesion of the gate line 142 and protects the passivation effect of the heterojunction. Annealing promotes the recrystallization of the electroplated metal layer (e.g., copper layer) and the cross-linking of interfacial molecular chains, thereby further enhancing the adhesion of the gate line 142.

[0045] Optionally, the annealing temperature can be 180-200℃, such as 180℃, 185℃, 190℃, 195℃, 200℃, etc., without specific limitations. Controlling the annealing temperature to be less than or equal to 200℃ helps ensure that the temperature throughout the entire process of fabricating the 010 solar cell is less than or equal to 200℃, which is lower than the phase transition temperature of amorphous silicon, thus reliably protecting the heterojunction passivation effect.

[0046] Optionally, the annealing time is 10 to 15 minutes, such as 10 minutes, 12 minutes, 14 minutes, 15 minutes, etc., without specific limitation.

[0047] Alternatively, the annealing process can be carried out in an N2 atmosphere.

[0048] Alternatively, please refer to Figure 3 The fabrication method of solar cell 010 further includes: after electroplating the grid lines 142, filling the gaps between the grid lines 142 with insulating resin (not shown in the figure), that is, solar cell 010 includes multiple grid lines 142, which are spaced apart, and the gaps between two adjacent grid lines 142 are filled with insulating resin. Filling the gaps between the grid lines 142 with insulating resin forms end seals to block the migration of metal ions (e.g., copper ions) in the grid lines 142, prevent environmental moisture from eroding the interface (e.g., copper-silicon interface) between the grid lines 142 and the cell substrate 100, and improve the damp heat aging (85℃ / 85% RH) life of solar cell 010.

[0049] Optionally, the insulating resin includes a polyimide precursor.

[0050] The present invention will be further described in detail below with reference to the embodiments.

[0051] Example 1 Fabrication of solar cells: (1) Interface treatment: Clean the battery substrate with ozone water (5 min) to activate the surface; immerse in 0.5 mMHS-(CH2) 10 -COOH / ethanol solution (20 min).

[0052] (2) Pulse electroplating grid line, parameters: forward current: 4mA / cm 2 Reverse current: 1mA / cm 2 Frequency: 50Hz, Duty Cycle: 30%.

[0053] (3) Post-treatment: annealing at 200℃ with N2 for 10 min + end-capping with polyimide precursor (spin-coating the gaps between grid lines to seal with polyimide precursor).

[0054] Testing solar cells: (1) Peel force: 90° tape method (IPC-TM-650 2.4.1), >3 N / cm is acceptable; (2) Damp heat aging: 85℃ / 85% RH, 1000 hours, grid line detachment area <5% is acceptable; (3) Grid line resistivity is tested using the four-probe method. The results are shown in the table below.

[0055]

[0056] Example 2 Fabrication of solar cells: (1) Interface treatment: oxygen plasma cleaning (5 min) of battery substrate, activation of surface; immersion in 0.1 mM NH2-(CH2)3-Si(OMe)3 / water solution (30 min).

[0057] (2) Pulse electroplating grid line, parameters: forward current: 3 mA / cm 2 Reverse current: 1.5 mA / cm 2 Frequency: 10 Hz, duty cycle: 20%.

[0058] (3) Post-treatment: 180℃ N2 annealing for 15 min + polyimide precursor end capping (spray coating the gaps between the grid lines with polyimide precursor).

[0059] Example 3 Fabrication of solar cells: (1) Interface treatment: Clean the battery substrate with ozone water (5 min) to activate the surface; immerse in 1 mM HS-(CH2) 10-COOH / ethanol solution (5 min).

[0060] (2) Pulse electroplating grid line, parameters: forward current: 5 mA / cm 2 Reverse current: 1 mA / cm 2 Frequency: 100 Hz, duty cycle: 40%.

[0061] (3) Post-treatment: 190℃ N2 annealing for 12 min + polyimide precursor end capping (spray coating the gaps between the grid lines with polyimide precursor).

[0062] Comparative Example 1 Fabrication of solar cells: (1) Interface treatment: Rinse the battery substrate with HF acid to remove the TCO oxide layer of the battery substrate.

[0063] (2) Electroplated grid lines, parameters: DC 6 mA / cm 2 .

[0064] (3) Post-processing: No annealing / end sealing.

[0065] Testing solar cells: (1) Peel force: 90° tape method (IPC-TM-650 2.4.1), >3 N / cm is acceptable; (2) Damp heat aging: 85℃ / 85% RH, 1000 hours, grid line detachment area <5% is acceptable; (3) Grid line resistivity is tested using the four-probe method. The results are shown in the table below.

[0066]

[0067] Comparing the test results of Example 1 and Comparative Example 1, it can be seen that the preparation method of this disclosure can effectively improve the peeling force of the gate wire, that is, the preparation method of this disclosure can effectively improve the bonding force of the gate wire and reduce the phenomenon of gate detachment; at the same time, it can also reduce the resistivity of the gate wire and improve the ability of the gate wire to resist damp heat aging and detachment.

[0068] Comparative Example 2 Fabrication of solar cells: The difference between Comparative Example 2 and Example 1 is that the forward current density in step (2) is 6 mA / cm². 2 Other process parameters are the same as in Example 1.

[0069] Testing solar cells: (1) Peel force: 90° tape method (IPC-TM-650 2.4.1), >3 N / cm is acceptable; (2) Damp heat aging: 85℃ / 85% RH, 1000 hours, grid line detachment area <5% is acceptable; (3) Grid line resistivity is tested using the four-probe method. The results are shown in the table below.

[0070]

[0071] Comparative Example 3 Fabrication of solar cells: The difference between Comparative Example 3 and Example 1 is that the pulse electroplating frequency in step (2) is 5Hz. Other process parameters are the same as in Example 1.

[0072] Testing solar cells: (1) Peel force: 90° tape method (IPC-TM-650 2.4.1), >3 N / cm is acceptable; (2) Damp heat aging: 85℃ / 85% RH, 1000 hours, grid line detachment area <5% is acceptable; (3) Grid line resistivity is tested using the four-probe method. The results are shown in the table below.

[0073]

[0074] Comparative Example 4 Fabrication of solar cells: The difference between Comparative Example 4 and Example 1 is that the pulse electroplating frequency in step (2) is 110Hz. Other process parameters are the same as in Example 1.

[0075] Testing solar cells: (1) Peel force: 90° tape method (IPC-TM-650 2.4.1), >3 N / cm is acceptable; (2) Damp heat aging: 85℃ / 85% RH, 1000 hours, grid line detachment area <5% is acceptable; (3) Grid line resistivity is tested using the four-probe method. The results are shown in the table below.

[0076]

[0077] In summary, the method for preparing the 010 solar cell provided by this invention achieves a copper grid line bonding force of >5 N / cm at ≤200℃ through a molecular self-assembly interface reinforcement layer and pulse electroplating synergistic process, overcoming the grid detachment problem and removing key obstacles for the mass production of copper electroplating in heterojunction solar cells 010.

[0078] Specifically, by forming a molecular self-assembly interface reinforcement layer, the interface adhesion is increased by more than 50% by utilizing molecular bonding forces (measured peel force >5 N / cm); during the preparation process, the temperature is ≤200℃ throughout, forming a low-damage process and protecting the passivation effect of the heterojunction; the SAMs (conductive molecular self-assembly film technology) solution can be integrated into existing cleaning equipment, and the program parameters are optimized and adjusted by using pulse power electroplating, which is compatible with mass production; the end-capping layer blocks the migration of copper ions, improves the wet heat aging (85℃ / 85% RH) life, and ensures enhanced battery reliability.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A solar cell, characterized in that, include: A battery substrate, wherein the battery substrate includes a transparent conductive layer; A conductive molecule self-assembled film layer, wherein the conductive molecule self-assembled film layer is formed on the transparent conductive layer; as well as, A gate line formed on the self-assembled conductive molecule film layer.

2. The solar cell according to claim 1, characterized in that, The solar cell includes a plurality of grid lines, which are spaced apart, and an insulating resin is used to fill the space between two adjacent grid lines.

3. A method for fabricating a solar cell, characterized in that, The method for preparing the solar cell is used to prepare the solar cell according to claim 1 or 2; The method for preparing the solar cell includes: The surface of the battery substrate is activated to activate the dangling bonds on the a-Si:H surface; The battery substrate is immersed in a solution of organic molecules containing bifunctional groups; Electroplated grid lines are applied to the battery substrate; wherein... The organic molecular solution containing bifunctional groups includes at least one of thiol molecular solutions and silane coupling agents.

4. The method for preparing a solar cell according to claim 3, characterized in that, The organic molecule solution containing bifunctional groups is an alcoholic solution or an aqueous solution with a concentration of 0.1~1mM.

5. The method for preparing a solar cell according to claim 3, characterized in that, The battery substrate is immersed in the organic molecule solution containing bifunctional groups for 5 to 30 minutes.

6. The method for preparing a solar cell according to any one of claims 3-5, characterized in that, The electroplated grid lines include pulse electroplating; and / or, The method for preparing the solar cell further includes: after the electroplating of the grid lines, filling the gaps between the grid lines with insulating resin.

7. The method for preparing a solar cell according to claim 6, characterized in that, The forward current density of the pulse electroplating is 3~5 mA / cm². 2 The ratio of the forward current density to the reverse current density is 1:(0.2~0.5), the pulse frequency is 10~100 Hz, and the duty cycle is 20~40%.

8. The method for preparing a solar cell according to claim 6, characterized in that, The pulse electroplating process also includes annealing.

9. The method for preparing a solar cell according to claim 8, characterized in that, The annealing temperature is 180-200℃.

10. The method for preparing a solar cell according to claim 6, characterized in that, The insulating resin includes a polyimide precursor.

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