A method for preparing an electrode of a solar cell and a solar cell

Abstract

Provided are a method for preparing an electrode of a solar cell and the solar cell, the method comprising the following steps: grooving a surface of the solar cell to expose a contact layer, preparing a base metal electrode in the grooving area, the base metal electrode being in contact with the contact layer, annealing the solar cell, and light injection. The present application reduces the cost of preparing the electrode of the solar cell, guarantees a very low oxygen concentration on the electrode surface, is conducive to reducing the resistivity of the base metal electrode, activates H atoms in a passivation film, controls the valence state of the H atoms through light, and makes the H atoms combine with recombination centers in the emitter and the substrate to form non-recombination centers, thereby achieving good passivation.

Description

Technical Field

[0001] This invention belongs to the field of solar cell processing technology, and relates to a method for preparing electrodes for a solar cell and a solar cell. Background Technology

[0002] Currently, the industrialized method for metallizing solar cells is screen printing paste, although electroplating is also used. However, in actual production, the high cost of silver paste for screen printing paste increases costs; while electroplating solves the problem of high raw material costs, wastewater and waste liquid treatment remains unavoidable throughout the electroplating process. Summary of the Invention

[0003] This invention provides a method for preparing electrodes for a solar cell and a solar cell, aiming to solve the problems existing in the prior art.

[0004] On one hand, the present invention provides a method for preparing an electrode for a solar cell. The method includes the following steps: grooving the surface of the solar cell to expose a contact layer; preparing a base metal electrode in the grooved area, wherein the base metal electrode is in contact with the contact layer; and annealing and light injection of the solar cell.

[0005] In some embodiments, the surface of the solar cell includes a passivation layer disposed on the contact layer. The contact layer is exposed by grooving the surface of the solar cell by laser grooving the passivation layer according to a preset electrode pattern area. The contact layer is a doped layer.

[0006] In some implementations, the thickness of the passivation layer is 70–250 nm.

[0007] In some embodiments, the method for preparing the base metal electrode in the slotted area is physical vapor deposition, 3D printing, screen printing, or electroplating.

[0008] In some embodiments, the base metal electrode is made of any one or a combination of at least two of aluminum, copper, nickel, zinc, tin, or tungsten.

[0009] In some embodiments, the base metal electrode is a single layer with a thickness of 1–25 μm.

[0010] In some embodiments, the base metal electrode comprises two layers. The first base metal electrode layer near the contact layer is made of nickel or tungsten, and the second base metal electrode layer disposed on the first base metal electrode layer is made of aluminum, copper, or zinc. The thickness of the first base metal electrode layer is 5–1000 nm, and the thickness of the second base metal electrode layer is 1–25 μm.

[0011] In some embodiments, a third electrode layer is disposed on the second base metal electrode layer. The material of the third electrode layer is nickel, silver or tin, and the thickness of the third electrode layer is 10 to 500 nm.

[0012] In some embodiments, a mask with a cutout area is provided, the cutout area being identical to a preset electrode pattern, so that the surface of the solar cell contacts the mask, the grooved area on the surface of the solar cell corresponding to the cutout area of ​​the mask, and a base metal electrode in the grooved area is prepared by physical vapor deposition.

[0013] In some embodiments, annealing and light injection of the solar cell includes annealing in a non-oxidizing atmosphere at a temperature of 200–600°C, light injection in a non-oxidizing atmosphere at a temperature of 200–400°C, and a standard solar intensity of 10–100. After annealing and light injection, the oxygen content on the base metal electrode surface is <1 wt%, and the surface oxide layer thickness is <10 nm.

[0014] In some embodiments, after annealing and light injection of the solar cell, a laser-induced sintering step is also included.

[0015] In some embodiments, the cell is a TOPCon solar cell, the contact layer is a doped polycrystalline silicon layer, the thickness of the contact layer is 50-150 nm, and the doping amount is 5E18-3E21 cm⁻¹. -3 .

[0016] In some embodiments, the battery is a TOPCon solar cell, and the method further includes the following steps: laser grooving the passivation layer on the back of the solar cell according to a preset electrode pattern area to expose the doped polycrystalline silicon layer; printing metal paste on the front of the solar cell and pre-sintering it; preparing base metal electrodes in the grooved area; annealing and light injection of the solar cell; and laser-induced sintering.

[0017] In some embodiments, the battery is a TOPCon solar cell, and the method further includes the following steps: printing metal paste on the front side of the solar cell and pre-sintering it; laser-grooving the passivation layer on the back side of the solar cell according to a preset electrode pattern area to expose the doped polycrystalline silicon layer; preparing base metal electrodes in the grooved area; annealing and light injection of the solar cell; and laser-induced sintering.

[0018] In some embodiments, the battery is a TOPCon solar cell, and the method further includes the following steps: laser grooving the passivation layer on the back of the solar cell according to a preset electrode pattern area to expose the doped polycrystalline silicon layer; preparing base metal electrodes in the grooved area; printing metal paste on the front of the solar cell and pre-sintering it; annealing and light injection of the solar cell; and laser-induced sintering.

[0019] In some embodiments, the cell is a BC solar cell, and the contact layer is an N-type doped polycrystalline silicon layer and / or a P-type doped polycrystalline silicon layer; wherein the thickness of the N-type doped polycrystalline silicon layer is 100–170 nm, and the doping concentration is 3E18–5E21 cm⁻¹. -3 The thickness of the p-type doped polycrystalline silicon layer is 120–350 nm, and the doping concentration is 5E18–1E21 cm⁻¹. -3 .

[0020] In some embodiments, the cell is a BC solar cell, and the method further includes the following steps: laser grooving the passivation layer on the back of the solar cell according to a preset electrode pattern area to expose a phosphorus-doped polycrystalline silicon layer and / or a boron-doped polycrystalline silicon layer; fabricating a base metal electrode in the grooved area; and annealing and light-injecting the solar cell.

[0021] On the other hand, the present invention provides a solar cell including electrodes for current conduction, wherein the electrodes are fabricated using the aforementioned method.

[0022] The present invention reduces the electrode fabrication cost of solar cells through the above technical solution, ensures an extremely low oxygen concentration on the electrode surface, which is beneficial to reduce the resistivity of the base metal electrode, and activates H atoms in the passivation film. By controlling the valence state of H atoms through light irradiation, they combine with recombination centers in the emitter and substrate to form non-recombination centers, ultimately achieving good passivation. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 and Figure 2 This is a schematic diagram illustrating the process of fabricating the electrode of the solar cell with a doped polycrystalline silicon layer according to the present invention.

[0025] Figure 3 and Figure 4 This is a schematic diagram illustrating the process of preparing the electrode of a solar cell with a heavily doped layer according to the present invention.

[0026] Figure 5 and Figure 6 This is a schematic diagram illustrating the process of fabricating the electrode of the solar cell with an emitter according to the present invention.

[0027] In the figure, 1-passivation layer; 2-laser grooving area; 3-base metal electrode; 4-silicon substrate; 5-heavily doped layer; 6-doped polycrystalline silicon layer; 7-tunneling oxide layer. Detailed Implementation

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0030] This invention aims to provide a method for fabricating electrodes for solar cells, comprising the following steps: grooving the surface of the solar cell to expose a contact layer; fabricating a base metal electrode in the grouted area, wherein the base metal electrode is in contact with the contact layer; and annealing and light-injecting the solar cell. This method reduces the electrode fabrication cost of solar cells while ensuring an extremely low oxygen concentration on the electrode surface, which is beneficial for reducing the resistivity of the base metal electrode.

[0031] In the technical solution of this application, base metal refers to metals other than precious metals such as gold, silver, and platinum, such as lead, copper, nickel, zinc, tin, and tungsten. The base metal electrode of this application can be an electrode formed of base metal, or an electrode formed by first forming a base metal electrode and then superimposing a precious metal (such as silver).

[0032] In the solar cell manufacturing process, a passivation layer (such as a silicon nitride layer) is prepared on the surface of the substrate before the electrodes are fabricated. In this application, grooving the surface of the solar cell refers to grooving the surface of a solar cell (also called a semi-finished product or silicon wafer) after the passivation layer has been prepared but the electrodes have not yet been fabricated, exposing the contact layer, which is a doped layer. For ease of explanation, this application uses silicon wafers to describe the initial texturing or polishing steps, while subsequent processes are described using solar cells.

[0033] One possible implementation involves using a laser to create grooves on the surface of a solar cell where a passivation layer has been prepared but no electrodes have been fabricated. This removes the passivation layer corresponding to a predetermined electrode area, exposing the contact layer. Then, a base metal electrode is fabricated in the grooved area using physical vapor deposition or 3D printing, bringing the base metal into contact with the contact layer. The contact layer can be a silicon substrate, a heavily doped layer, or a doped polycrystalline silicon layer. The solar cell is then annealed and light-injected in a non-oxidizing atmosphere. This ensures an extremely low oxygen concentration on the electrode surface, which helps reduce the resistivity of the base metal electrode and activates H atoms in the passivation layer (such as silicon nitride). By controlling the valence state of these H atoms through light irradiation, they combine with recombination centers in the emitter and substrate to form non-recombination centers, ultimately achieving good passivation.

[0034] As one possible implementation, this method is applicable to solar cells with a doped polycrystalline silicon layer. Specifically, a laser is used to create a groove on one side of the solar cell containing the doped polycrystalline silicon layer, removing the passivation layer corresponding to a predetermined electrode region and exposing the doped polycrystalline silicon layer (contact layer). Then, a base metal electrode is fabricated in the laser-grouted area using methods such as physical vapor deposition or 3D printing, and the base metal is brought into contact with the doped polycrystalline silicon layer. The solar cell is then annealed and light-injected in a non-oxidizing atmosphere. This ensures an extremely low oxygen concentration on the electrode surface, which helps reduce the resistivity of the base metal electrode and activates H atoms in silicon nitride. By controlling the valence state of H atoms through light illumination, they combine with recombination centers in the emitter and substrate to form non-recombination centers, ultimately achieving good passivation. See also Figure 1 and Figure 2 This is a schematic diagram illustrating the process of fabricating a base metal electrode for a solar cell with a doped polycrystalline silicon layer according to the present invention. Figure 1 This is a schematic diagram of a structure where grooves are cut into the surface of a solar cell to expose the contact layer. Figure 2 This is a schematic diagram of the structure after fabricating a base metal electrode in a laser-grooved region. The doped polycrystalline silicon layer can be a phosphorus-doped polycrystalline silicon layer and / or a boron-doped polycrystalline silicon layer. The battery structure shown in the figure only displays the structure on one side with the doped polycrystalline silicon layer; the structure on the other side can be a prior art battery structure and is not shown in the figure.

[0035] As one possible implementation, this method is applicable to solar cells with heavily doped layers, where the heavily doped layer refers to a heavily doped functional layer that forms an ohmic electrode in direct contact with the metal electrode. Specifically, a laser is used to create a groove on one side of the solar cell containing the heavily doped layer, removing the passivation layer corresponding to a predetermined electrode region and exposing the heavily doped layer. Then, a base metal electrode is fabricated in the laser-grouted area using methods such as physical vapor deposition or 3D printing, and the base metal is brought into contact with the heavily doped layer. The solar cell is then annealed and photo-injected in a non-oxidizing atmosphere to activate H atoms in the silicon nitride. By controlling the valence state of the H atoms through illumination, they combine with recombination centers in the emitter and substrate to form non-recombination centers, ultimately achieving good passivation. See also... Figure 3 and Figure 4 This is a schematic diagram illustrating the process of preparing a base metal electrode for a solar cell with a heavily doped layer according to the present invention. Figure 3 This is a schematic diagram of a structure where grooves are cut into the surface of a solar cell to expose the contact layer. Figure 4 This is a schematic diagram of the structure after fabricating a base metal electrode in a laser-grooved region. The battery structure shown only illustrates the side with the heavily doped layer; the structure of the other side can be a conventional battery structure and is not shown in the figure.

[0036] As one possible implementation, this method is applicable to solar cells with an emitter layer. In this method, a laser is used to create a groove on one side of the solar cell containing the emitter layer, removing the passivation layer corresponding to a predetermined electrode area and exposing the silicon substrate. Then, a base metal electrode is fabricated in the laser-grooved area using methods such as physical vapor deposition, 3D printing, screen printing, or electroplating, and this base metal electrode is brought into contact with the silicon substrate. The solar cell is then annealed and light-injected to activate H atoms in the silicon nitride. By controlling the valence state of the H atoms through illumination, they combine with recombination centers in the emitter and substrate to form non-recombination centers, ultimately achieving good passivation. See also... Figure 5 and Figure 6 This is a schematic diagram illustrating the process of fabricating a base metal electrode for a solar cell with an emitter according to the present invention, wherein... Figure 5 A schematic diagram of a structure in which grooves are cut into the surface of a solar cell to expose the contact layer; Figure 6 This is a schematic diagram of the structure after fabricating a base metal electrode in the laser-grooved region. The battery structure shown only illustrates the side containing the base metal electrode; the other side can be a conventional battery structure and is not shown.

[0037] When preparing the base metal electrode in the trenched area, the physical vapor deposition method can be vacuum evaporation, sputtering, ion plating, etc. When preparing the base metal electrode in the trenched area using physical vapor deposition, a masking method can be used for directional preparation in the trenched area, or a method can be used to prepare the entire surface and then remove the base metal electrode from the non-trenched area.

[0038] More specifically, in the mask-based directional fabrication process, a mask is fabricated on the back of the battery, exposing the laser-grooved area (i.e., the pre-defined electrode area) and covering the remaining area. Base metal electrodes are then fabricated using physical vapor deposition. After fabrication, the base metal electrodes on the mask are removed simultaneously.

[0039] As a preferred technical solution, a mask plate can also be used for directional fabrication using a mask. The mask plate has cutout areas corresponding to a pre-set electrode pattern. The mask plate covers the back of the solar cell, and the grooved area on the solar cell surface corresponds to the cutout area on the mask plate. A base metal electrode is fabricated in the grooved area using physical vapor deposition (PVD). Then, the mask plate is removed from the back of the solar cell. More preferably, a positioning flange is provided on the edge of the mask plate. The solar cell is placed back-side down on the mask plate. The positioning flange serves to accommodate and position the solar cell, resulting in a better correspondence between the grooved area on the solar cell surface and the cutout area on the mask plate. Then, a base metal electrode is fabricated in the grooved area using PVD, and the cell is removed. Specifically, the mask plate is a glass mask with a thickness of 0.5–1 mm.

[0040] More specifically, the base metal electrode is prepared on the entire surface, and then the base metal electrode in the non-grooved area (i.e., the non-preset electrode area) is removed. The base metal electrode can be prepared by physical vapor deposition, and then the base metal electrode in the non-grooved area can be removed by laser etching or laser etching plus etchant etching.

[0041] Alternatively, a base metal electrode can be fabricated in the grooved area using 3D printing.

[0042] Alternatively, a base metal electrode can be fabricated in the grooved area using screen printing.

[0043] Alternatively, an electroplating method can be used to prepare base metal electrodes in the grooved area.

[0044] The base metal electrode prepared in the grooved region can be one or more layers. For example, the base metal electrode material is any one or a combination of at least two of aluminum, copper, nickel, zinc, tin, or tungsten. When the base metal electrode is a single layer, its thickness is 1–25 μm, or a point value or range thereof, for example, 1–2 μm, 2–3 μm, 3–4 μm, 4–5 μm, 5–6 μm, 6–7 μm, 7–10 μm, 10–15 μm, 15–20 μm, or 20–25 μm.

[0045] The base metal electrode may also comprise two layers. The first base metal electrode layer, located near the contact layer, is made of nickel or tungsten, and the second base metal electrode layer, disposed on the first base metal electrode layer, is made of aluminum, copper, or zinc. The thickness of the first base metal electrode layer is 5–1000 nm, or a specific value or range thereof, for example, 5–10 nm, 10–15 nm, 15–20 nm, 20–50 nm, 50–100 nm, 100–300 nm, 300–700 nm, or 700–1000 nm. The thickness of the second base metal electrode layer is 1–25 μm, or a specific value or range thereof, for example, 1–2 μm, 2–3 μm, 3–4 μm, 4–5 μm, 5–6 μm, 6–7 μm, 7–10 μm, 10–15 μm, 15–20 μm, or 20–25 μm.

[0046] A third electrode layer may also be included on the second base metal electrode. The third electrode layer is made of nickel, silver or tin, and the thickness of the third electrode layer is 10-500 nm, or a point value or range value thereof, for example, 10-20 nm, 20-30 nm, 30-50 nm, 50-70 nm, 70-100 nm, 100-150 nm, 150-200 nm, 200-300 nm, 300-400 nm, or 400-500 nm.

[0047] Base metal electrodes can be deposited using one or more methods, such as vacuum evaporation or vacuum sputtering. For example, when the base metal electrode is a single layer, it can be deposited using either vacuum evaporation or vacuum sputtering. When the base metal electrode is multilayered, both layers can be deposited using either vacuum evaporation or vacuum sputtering, or different methods can be used. For instance, the first layer can be deposited using vacuum evaporation, and the second layer can be deposited using vacuum sputtering.

[0048] After preparing the base metal electrode in the slotted area, the solar cell is further annealed and light injected in a non-oxidizing atmosphere. The annealing temperature is 200-600℃, or a point value or range thereof, such as 200-300℃, 300-400℃, 400-500℃, or 500-600℃. The annealing can be carried out in a chain multi-temperature zone manner or a fixed single-temperature zone manner. The treatment environment atmosphere is a non-oxidizing atmosphere such as N2 or N2 / H2 mixture. The light injection temperature is 200–400℃, or a specific value or range thereof, such as 200–300℃ or 300–400℃. This can be achieved using a chain-type multi-temperature zone method or a fixed single-temperature zone method. Under a standard solar intensity of 10–100, or a specific value or range thereof, such as 10–20, 20–30, 30–40, 40–50, 50–60, 60–70, or 70–100, the processing environment is a non-oxidizing atmosphere such as N2 or an N2 / H2 mixture. After annealing and light injection, the oxygen content on the base metal electrode surface is below 1 wt%, and the surface oxide layer thickness is <10 nm. The electrode surface maintains an extremely low oxygen concentration, which is beneficial for reducing the resistivity of the base metal electrode.

[0049] This step partially repairs the damage to the exposed surface of the laser-grooved area and prevents oxidation of the prepared base metal electrode surface from affecting conductivity and welding. Third, if the solar cell also has an electrode on the other side, the pre-sintering of the electrode on the other side can also be completed at the same time. This point will be further explained in subsequent embodiments.

[0050] In some more preferred embodiments, a laser-induced sintering step is also included.

[0051] Laser-induced sintering is used to apply a reverse bias voltage to the solar cell. The laser-induced sintering completes a secondary sintering process, which enables the electrode (non-base metal electrode) on the other side to form a better ohmic contact.

[0052] To enable those skilled in the art to better understand the embodiments of the present invention, the following examples are used for description. In the examples, the light-receiving surface of the solar cell is described as the front side, and the opposite side is described as the back side.

[0053] Example 1

[0054] This embodiment provides a method for a TOPCon (Tunnel Oxide Passivated Contact) battery, including a process for fabricating a base metal electrode, the steps of which include:

[0055] S1 cleans and texturizes the silicon wafer;

[0056] Specifically, the silicon wafer is textured on both sides to form a pyramidal textured surface.

[0057] S2 performs boron diffusion on the front side of the solar cell to form a boron extension layer;

[0058] Specifically, a boron-diffused emitter is prepared on the front side of the solar cell, and a BSG layer is formed.

[0059] S3 removes the BSG layer wrapped around the back of the solar cell and performs alkaline polishing on the back of the solar cell;

[0060] S4 prepares a tunneling oxide layer on the back of the solar cell and deposits an intrinsic amorphous silicon layer.

[0061] A tunneling oxide layer and an intrinsic amorphous silicon layer are grown on the back side of a solar cell using the LPCVD method. The thickness of the tunneling oxide layer is 1–5 nm, and the thickness of the intrinsic amorphous silicon layer is 50–150 nm.

[0062] S5 performs phosphorus diffusion on the back of the solar cell to form a phosphorus-doped polycrystalline silicon layer and PSG;

[0063] In this step, the thickness of the doped polycrystalline silicon layer is 50–150 nm, and the doping concentration is 5E18–3E21 cm⁻¹. -3 .

[0064] S6 removes the PSG (polysilicon coating) from the front and side surfaces of the solar cell, RCA cleaning removes the polysilicon winding layer, and removes the front BSG (polysilicon coating) and back PSG.

[0065] S7 prepares passivation layers on the front and back sides of the solar cell;

[0066] In this step, the front passivation layer can be a dielectric layer composed of one or more of aluminum oxide, silicon nitride, silicon oxynitride, and silicon oxide layers. For example, it can be a bilayer dielectric layer of aluminum oxide and silicon nitride.

[0067] The passivation layer on the back of a solar cell can be a silicon nitride layer.

[0068] S8 performs laser grooving on the back of the solar cell;

[0069] Laser grooving is performed according to the preset electrode pattern on the back side to remove the back passivation layer corresponding to the preset electrode area on the back side, exposing the phosphorus-doped polycrystalline silicon layer.

[0070] S9 is used to fabricate electrodes on the front side of a solar cell;

[0071] Specifically, a metal paste is printed on the front side of the solar cell using screen printing, followed by pre-sintering at a temperature of 550–720°C. This step, printing the metal paste on the front side of the solar cell using methods such as screen printing, can employ existing technologies. Typically, the metal paste used in this step is silver paste.

[0072] S10 pickling removes oxidation caused by laser grooving;

[0073] Specifically, HF acid cleaning is used on the back of the solar cell to remove oxidation caused by laser grooving. In some embodiments, laser grooving does not cause oxidation, or the oxidation it causes has little impact on subsequent processes, so this step can be omitted.

[0074] Base metal electrodes are fabricated in the grooved area on the back of S11;

[0075] Specifically, a base metal electrode is fabricated in the trenched area using physical vapor deposition or 3D printing. Specifically, a 10 nm thick nickel layer, a 5 μm thick aluminum layer, and a 100 nm thick tin layer are sequentially fabricated on the entire back side using vacuum evaporation. The process also includes a step of removing the electrode layer in the non-trenched areas using a laser, leaving only the base metal electrode in the trenched area.

[0076] S12 annealing treatment;

[0077] Chain-type multi-temperature zone annealing is adopted, and the treatment environment is a non-oxidizing atmosphere such as N2 or N2 / H2 mixture; wherein, the annealing treatment is carried out sequentially at 200-300℃ for 0.5 min, at 300-400℃ for 1 min, and at 400-450℃ for 0.5 min.

[0078] S13 optical injection processing;

[0079] Under standard solar intensity of 30–60, the treatment environment is a non-oxidizing atmosphere such as N2 or N2 / H2 mixture; a chain-type multi-temperature zone light injection is used, with sequential light injection treatment at 200–250℃ for 0.3 min, at 250–300℃ for 0.5 min, and at 300–350℃ for 0.5 min.

[0080] Alternatively, laser light injection: 80 standard solar intensity, temperature 250-300℃, time 15s.

[0081] After this step, the oxygen content on the surface of the base metal electrode is less than 1 wt%, and the thickness of the surface oxide layer is less than 10 nm, preventing the oxidation of the prepared base metal electrode surface from affecting conductivity and welding.

[0082] S14 laser-induced sintering.

[0083] Specifically, a reverse bias is applied to the solar cell, and laser-induced sintering is performed on the front electrode to complete a secondary sintering, resulting in a better ohmic contact on the front electrode.

[0084] Example 2

[0085] This embodiment is similar to Embodiment 1, with steps S1 to S7 being the same as in Embodiment 1. The difference lies in that the step of fabricating the electrode on the front side of the solar cell occurs before the laser grooving step on the back side of the solar cell. Specifically, the steps after S7 in this embodiment are as follows:

[0086] S8 is used to fabricate electrodes on the front side of a solar cell;

[0087] Specifically, a metal paste is printed on the front side of the solar cell using screen printing, followed by pre-sintering at a temperature of 550–720°C. This step, printing the metal paste on the front side of the solar cell using methods such as screen printing, can employ existing technologies. Typically, the metal paste used in this step is silver paste.

[0088] S9 performs laser grooving on the back of the solar cell;

[0089] Laser grooving is performed according to the preset electrode pattern on the back side to remove the back passivation layer corresponding to the preset electrode area on the back side, exposing the phosphorus-doped polycrystalline silicon layer.

[0090] S10 pickling removes oxidation caused by laser grooving;

[0091] Specifically, HF acid cleaning is used on the back of the solar cell to remove oxidation caused by laser grooving. In some embodiments, laser grooving does not cause oxidation, or the oxidation it causes has little impact on subsequent processes, so this step can be omitted.

[0092] S12 annealing treatment;

[0093] Chain-type multi-temperature zone annealing is adopted, and the treatment environment is a non-oxidizing atmosphere such as N2 or N2 / H2 mixture; wherein, the annealing treatment is carried out sequentially at 200-300℃ for 0.5 min, at 300-400℃ for 1 min, and at 400-450℃ for 0.5 min.

[0094] S13 optical injection processing;

[0095] Under standard solar intensity of 30–60, the treatment environment is a non-oxidizing atmosphere such as N2 or N2 / H2 mixture; a chain-type multi-temperature zone light injection is used, with sequential light injection treatment at 200–250℃ for 0.3 min, at 250–300℃ for 0.5 min, and at 300–350℃ for 0.5 min.

[0096] Alternatively, laser light injection: 80 standard solar intensity, temperature 250-300℃, time 15s.

[0097] After this step, the oxygen content on the surface of the base metal electrode is less than 1 wt%, and the thickness of the surface oxide layer is less than 10 nm, preventing the oxidation of the prepared base metal electrode surface from affecting conductivity and welding.

[0098] S14 laser-induced sintering.

[0099] Specifically, a reverse bias is applied to the solar cell, and laser-induced sintering is performed on the front electrode to complete a secondary sintering, resulting in a better ohmic contact on the front electrode.

[0100] Example 3

[0101] This embodiment is similar to Embodiment 1, with steps S1 to S7 being the same as in Embodiment 1. The difference is that the step of preparing the electrode on the front side of the solar cell is performed after the step of preparing the base metal electrode in the back groove area.

[0102] Specifically, the steps following S7 in this embodiment are as follows:

[0103] S8 performs laser grooving on the back of the solar cell;

[0104] Laser grooving is performed according to the preset electrode pattern on the back side to remove the back passivation layer corresponding to the preset electrode area on the back side, exposing the phosphorus-doped polycrystalline silicon layer.

[0105] S9 pickling removes oxidation caused by laser grooving;

[0106] Specifically, HF acid cleaning is used on the back of the solar cell to remove oxidation caused by laser grooving. In some embodiments, laser grooving does not cause oxidation, or the oxidation it causes has little impact on subsequent processes, so this step can be omitted.

[0107] Base metal electrodes are fabricated in the grooved area on the back of S10;

[0108] Specifically, a base metal electrode is fabricated in the trenched area using physical vapor deposition or 3D printing. Specifically, a 10 nm thick nickel layer, a 5 μm thick aluminum layer, and a 100 nm thick tin layer are sequentially fabricated on the entire back side using vacuum evaporation. The process also includes a step of removing the electrode layer in the non-trenched areas using a laser, leaving only the base metal electrode in the trenched area.

[0109] S11 is used to fabricate electrodes on the front side of a solar cell;

[0110] Specifically, a metal paste is printed on the front side of the solar cell using screen printing. The characteristics of this paste are different from those in Examples 1 and 2, and it requires a lower pre-sintering temperature of 250–550°C.

[0111] This step involves printing a metal paste onto the front side of the solar cell using methods such as screen printing, and existing technologies can be employed. Typically, the metal paste used in this step is silver paste.

[0112] S12 pre-sintering / annealing treatment;

[0113] A chain-type multi-temperature zone pre-sintering / annealing treatment is adopted, and the treatment environment is a non-oxidizing atmosphere such as N2 or N2 / H2 mixed gas; wherein, sintering is carried out sequentially at 100-200℃ for 0.3 min, at 200-500℃ for 0.2 min, and at 500-550℃ for 0.15 min.

[0114] S13 optical injection processing;

[0115] Under standard solar intensity of 30–60, the treatment environment is a non-oxidizing atmosphere such as N2 or N2 / H2 mixture; a chain-type multi-temperature zone light injection is used, with sequential light injection treatment at 200–250℃ for 0.3 min, at 250–300℃ for 0.5 min, and at 300–350℃ for 0.5 min.

[0116] Alternatively, laser light injection: 80 standard solar intensity, temperature 250-300℃, time 15s.

[0117] After this step, the oxygen content on the surface of the base metal electrode is less than 1 wt%, and the thickness of the surface oxide layer is less than 10 nm, preventing the oxidation of the prepared base metal electrode surface from affecting conductivity and welding.

[0118] S14 laser-induced sintering.

[0119] Specifically, a reverse bias is applied to the solar cell, and laser-induced sintering is performed on the front electrode to complete a secondary sintering, resulting in a better ohmic contact on the front electrode.

[0120] Compared to Example 1, Example 2 advances the preparation of the front electrode and sets a higher pre-sintering temperature for the front electrode (550-720℃). The earlier preparation and pre-sintering of the front electrode, along with the separate setting of a pre-sintering temperature suitable for the front electrode, facilitates the formation of the best sintering effect.

[0121] Compared to Example 1, Example 3 places the preparation of the front electrode after the preparation of the back electrode, changes the characteristics of the front electrode slurry to lower its pre-sintering temperature, and matches the annealing temperature (250-550°C) of the back base metal electrode, so that the annealing of the back base metal electrode and the pre-sintering of the front conventional silver electrode can be completed in one step.

[0122] As will be understood by those skilled in the art, although Examples 1 to 3 provide specific methods for preparing electrodes for TOPCon, this application is not limited thereto, and TOPCon batteries prepared by other methods are also applicable.

[0123] Example 4

[0124] This embodiment provides a method for preparing electrodes for a BC (Back Contact) solar cell, the steps of which include:

[0125] S1 silicon wafer polishing;

[0126] The silicon wafers are cleaned to remove damage and then polished.

[0127] S2 prepares a tunneling oxide layer and an intrinsic amorphous silicon layer on the back side of a silicon wafer, and performs boron diffusion to form a boron-doped polycrystalline silicon layer (P-type doped polycrystalline silicon layer).

[0128] The thickness of the boron-doped polycrystalline silicon layer is 120–350 nm, and the concentration is 5E18–1E21 cm⁻¹. -3 .

[0129] S3 laser is used to pattern the back of solar cells;

[0130] Specifically, laser scanning is used to modify the corresponding area of ​​region N.

[0131] S4 wet removal of laser-patterned areas;

[0132] Specifically, a wet process is used to remove the laser-patterned area. This area, after being modified by S3, is removed by wet etching, while the P-region is preserved.

[0133] S5 prepares a tunneling oxide layer and an intrinsic amorphous silicon layer on the back of the solar cell, and performs phosphorus diffusion to form a phosphorus-doped polycrystalline silicon layer (N-type doped polycrystalline silicon layer).

[0134] Specifically, in this step, the boron-doped polysilicon layer in the P-region serves as a mask, and the corresponding layer for this step is formed only in the N-region; wherein, the phosphorus-doped polysilicon layer has a thickness of 100-170 nm and a concentration of 3E18~5E21 cm⁻¹. -3 .

[0135] S6 laser performs secondary patterning on the back of the solar cell;

[0136] In this step, a laser is used to separate the PN region on the back side.

[0137] S7 texturing the front side of the solar cell;

[0138] S8 prepares passivation layers on the front and back sides of the solar cell;

[0139] In this step, the front passivation layer can be a dielectric layer composed of one or more of the following: an aluminum oxide layer, a silicon nitride layer, a silicon oxynitride layer, and a silicon oxide layer. For example, it can be a bilayer dielectric layer of aluminum oxide and silicon nitride.

[0140] The passivation layer on the back of a solar cell can be a silicon nitride layer.

[0141] S9 performs laser grooving on the back of the solar cell;

[0142] Laser grooving is performed according to the preset electrode pattern on the back side to remove the back passivation layer corresponding to the preset electrode area on the back side, exposing the phosphorus-doped polycrystalline silicon layer and the boron-doped polycrystalline silicon layer.

[0143] S9 pickling removes oxidation caused by laser grooving;

[0144] Specifically, HF acid cleaning is used on the back of the solar cell to remove oxidation caused by laser grooving. In some embodiments, laser grooving does not cause oxidation, or the oxidation it causes has little impact on subsequent processes, so this step can be omitted.

[0145] Base metal electrodes are fabricated in the grooved area on the back of S10;

[0146] Specifically, a base metal electrode is fabricated in the trenched area using physical vapor deposition or 3D printing. Specifically, a 10 nm thick nickel layer, a 5 μm thick aluminum layer, and a 100 nm thick tin layer are sequentially fabricated on the entire back side using vacuum evaporation. The process also includes a step of removing the electrode layer in the non-trenched areas using a laser, leaving only the base metal electrode in the trenched area.

[0147] S11 annealing treatment

[0148] Chain-type multi-temperature zone annealing is adopted, and the treatment environment is a non-oxidizing atmosphere such as N2 or N2 / H2 mixture; wherein, the annealing treatment is carried out sequentially at 200-300℃ for 0.5 min, at 300-400℃ for 1 min, and at 400-450℃ for 0.5 min.

[0149] S12 light injection processing

[0150] Under standard solar intensity of 30–60, the treatment environment is a non-oxidizing atmosphere such as N2 or N2 / H2 mixture; a chain-type multi-temperature zone light injection is used, with sequential light injection treatment at 200–250℃ for 0.3 min, at 250–300℃ for 0.5 min, and at 300–350℃ for 0.5 min.

[0151] Alternatively, laser light injection: 80 standard solar intensity, temperature 250-300℃, time 15s.

[0152] After this step, the oxygen content on the surface of the base metal electrode is less than 1 wt%, and the thickness of the surface oxide layer is less than 10 nm, preventing the oxidation of the prepared base metal electrode surface from affecting conductivity and welding.

[0153] Those skilled in the art will understand that, in the embodiments, a mask-based directional fabrication method is used when preparing the base metal electrode, and the method further includes a mask removal step in an appropriate manner. Alternatively, the entire surface can be prepared without a mask, and the base metal electrode in the non-electrode region can be removed in an appropriate step.

[0154] Examples 1 to 4 illustrate the electrode fabrication method of solar cells using a doped polycrystalline silicon contact layer as an example. Those skilled in the art can infer that for the electrode fabrication of solar cells with a heavily doped contact layer or an emitter layer, the laser grooving, preparation of base metal electrodes in the grooved area, annealing and light injection processes in Examples 1 to 4, as well as the optional laser-induced sintering step, can be referred to. The remaining steps can be carried out using existing technologies.

[0155] On the other hand, the present invention also provides a solar cell including electrodes for current conduction, the electrodes being fabricated using the aforementioned method.

[0156] The above description is merely a preferred embodiment of the present invention. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the scope of the technical solutions of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing electrodes for a solar cell, characterized in that: Includes the following steps, Grooves are cut into the surface of the solar cell to expose the contact layer; A base metal electrode is prepared in the slotted area, and the base metal electrode is in contact with the contact layer; Annealing and light injection are performed on the solar cells.

2. The method for preparing electrodes for a solar cell according to claim 1, characterized in that: The surface of the solar cell includes a passivation layer disposed on the contact layer. The step of grooving the surface of the solar cell to expose the contact layer is to perform laser grooving on the passivation layer according to a preset electrode pattern area to expose the contact layer. The contact layer is a doped layer.

3. The method for preparing electrodes for a solar cell according to claim 2, characterized in that: The thickness of the passivation layer is 70–250 nm.

4. The method for preparing electrodes for a solar cell according to claim 1, characterized in that: The method for preparing base metal electrodes in the slotted area is physical vapor deposition, 3D printing, screen printing, or electroplating.

5. The method for preparing electrodes for a solar cell according to claim 1, characterized in that: The base metal electrode is made of any one or a combination of at least two of the following: aluminum, copper, nickel, zinc, tin, or tungsten.

6. The method for preparing electrodes for a solar cell according to claim 5, characterized in that: The base metal electrode is a single layer with a thickness of 1–25 μm.

7. The method for preparing electrodes for a solar cell according to claim 5, characterized in that: The base metal electrode comprises two layers. The first base metal electrode layer near the contact layer is made of nickel or tungsten, and the second base metal electrode layer disposed on the first base metal electrode layer is made of aluminum, copper, or zinc. The thickness of the first base metal electrode layer is 5–1000 nm, and the thickness of the second base metal electrode layer is 1–25 μm.

8. The method for preparing electrodes for a solar cell according to claim 7, characterized in that: A third electrode layer is disposed on the second base metal electrode layer. The material of the third electrode layer is nickel, silver or tin, and the thickness of the third electrode layer is 10-500 nm.

9. The method for preparing electrodes for a solar cell according to claim 4, characterized in that: A mask with a hollowed-out area is provided, the hollowed-out area being identical to a preset electrode pattern, such that the surface of the solar cell contacts the mask, the grooved area corresponding to the hollowed-out area, and a base metal electrode in the grooved area is fabricated using physical vapor deposition.

10. The method for preparing electrodes for a solar cell according to any one of claims 1 to 9, characterized in that: The annealing and light injection of the solar cell includes annealing in a non-oxidizing atmosphere at a temperature of 200–600°C. Light injection is performed in a non-oxidizing atmosphere at a temperature of 200–400°C and a standard solar intensity of 10–100. After annealing and light injection, the oxygen content on the surface of the base metal electrode is <1 wt%, and the surface oxide layer thickness is <10 nm.

11. The method for preparing electrodes for a solar cell according to claim 10, characterized in that: After annealing and light injection of the solar cell, the process also includes a laser-induced sintering step.

12. The method for preparing electrodes for a solar cell according to claim 10, characterized in that: The battery is a TOPCon solar cell, the contact layer is a doped polysilicon layer, the thickness of the contact layer is 50-150 nm, and the doping amount is 5E18-3E21 cm -3 .

13. The method for preparing electrodes for a solar cell according to claim 10, characterized in that: The battery is a TOPCon solar cell, and the process also includes the following steps. Laser grooving is performed on the passivation layer on the back of the solar cell according to the preset electrode pattern area to expose the doped polycrystalline silicon layer. Metal paste is printed on the front side of the solar cell and then pre-sintered. Base metal electrodes are prepared in the slotted region; Annealing and light injection into solar cells; Laser-induced sintering.

14. The method for preparing electrodes for a solar cell according to claim 10, characterized in that: The battery is a TOPCon solar cell, and the process also includes the following steps. Metal paste is printed on the front side of the solar cell and then pre-sintered. Laser grooving is performed on the passivation layer on the back of the solar cell according to the preset electrode pattern area to expose the doped polycrystalline silicon layer. Base metal electrodes are prepared in the slotted region; Annealing and light injection into solar cells; Laser-induced sintering.

15. The method for preparing electrodes for a solar cell according to claim 10, characterized in that: The battery is a TOPCon solar cell, and the process also includes the following steps. Laser grooving is performed on the passivation layer on the back of the solar cell according to the preset electrode pattern area to expose the doped polycrystalline silicon layer. Base metal electrodes are prepared in the slotted region; Metal paste is printed on the front side of the solar cell and then pre-sintered. Annealing and light injection into solar cells; Laser-induced sintering.

16. The method for preparing electrodes for a solar cell according to claim 10, characterized in that: The battery is a BC solar cell, and the contact layer is an N-type doped polycrystalline silicon layer and / or a P-type doped polycrystalline silicon layer; wherein, the thickness of the N-type doped polycrystalline silicon layer is 100-170 nm, and the doping concentration is 3E18-5E21 cm⁻¹. -3 The thickness of the p-type doped polycrystalline silicon layer is 120–350 nm, and the doping concentration is 5E18–1E21 cm⁻¹. -3 .

17. The method for preparing electrodes for a solar cell according to claim 10, characterized in that: The battery is a BC solar cell, and the following steps are also included. Laser grooving is performed on the passivation layer on the back of the solar cell according to the preset electrode pattern area to expose the N-type doped polycrystalline silicon layer and / or the P-type doped polycrystalline silicon layer. Base metal electrodes are prepared in the slotted region; Annealing and light injection are performed on the solar cells.

18. A solar cell, characterized in that: The solar cell includes electrodes for current extraction, the electrodes being fabricated using the method described in any one of claims 1 to 17.

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