Method for preparing solar cell with local passivation contact and solar cell

Abstract

The present invention provides a method for preparing a solar cell with local passivation contact and a solar cell, and specifically relates to the technical field of solar cell preparation. The method for preparing a solar cell with local passivation contact comprises the following steps: immersing a silicon substrate with patterned grooves in a nickel electroplating solution, forming a nickel metal layer by segmented current electroplating, and finally forming a metal electrode to obtain a solar cell. The present invention controls the growth process of the nickel metal layer by segmented current electroplating, first generating dense and refined nickel grains, which are discontinuously and evenly distributed; then electroplating a silicon oxide layer in the area without nickel grains, thereby reducing the direct contact between the subsequently generated nickel metal layer and silicon, thereby reducing the reverse saturation current J0; finally, generating a complete nickel metal film layer, completing the preparation of the nickel metal layer, and realizing local passivation contact between the metal electrode and the silicon substrate.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cell preparation, in particular to a preparation method of a solar cell with local passivation contact and a solar cell. Background Art

[0002] During the preparation of crystalline silicon solar cells, the passivation layer between the metal electrode and the silicon substrate is completely removed by laser or chemical etching before the metal electrode is deposited, so that the metal electrode and the silicon substrate are in direct and full contact, thereby forming an ohmic contact. The van der Waals force between the metal atoms in the metal electrode and silicon ensures the bonding strength between the metal electrode and the silicon substrate.

[0003] Full contact between metal and silicon will cause the reverse saturation current J0 of the solar cell to be 2 to 3 orders of magnitude higher than that of traditional silver paste contact, resulting in a loss of nearly 10mV in the open-circuit voltage Uoc of the solar cell; growing a passivation layer between the metal and silicon can reduce the reverse saturation current J0, but it will cause the bonding strength of the metal electrodes to deteriorate, thereby affecting the reliability of the solar cell.

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

[0005] One of the objectives of the present invention is to provide a method for preparing a solar cell with local passivation contacts, aiming to solve at least one of the above-mentioned technical problems in the prior art.

[0006] A second object of the present invention is to provide a solar cell.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0008] A first aspect of the present invention provides a method for preparing a solar cell with locally passivated contacts, comprising the following steps:

[0009] The silicon substrate with the patterned grooves is immersed in a nickel electroplating solution, and a nickel metal layer is formed by segmented current electroplating, and finally a metal electrode is formed to obtain a solar cell.

[0010] Furthermore, the segmented current includes a forward pulse current, a reverse direct current and a forward direct current in sequence.

[0011] Furthermore, the frequency of the forward pulse current is 100 Hz to 1000 Hz.

[0012] Preferably, the duty cycle of the forward pulse current is 5% to 40%.

[0013] Preferably, the average current density of the forward pulse current is 0.75A / dm2 ~15A / dm 2 .

[0014] Preferably, the duration of the forward pulse current is 5s to 20s.

[0015] Furthermore, the average current density of the reverse direct current is 0.2A / dm 2 ~2A / dm 2 .

[0016] Preferably, the duration of the reverse direct current is 1s to 10s.

[0017] Furthermore, the average current density of the forward DC current is 2A / dm 2 ~15A / dm 2 .

[0018] Preferably, the duration of the forward direct current is 30s to 120s.

[0019] Furthermore, the nickel electroplating solution comprises 300 to 450 parts of nickel sulfamate, 10 to 40 parts of a buffer and 0 to 30 parts of an anode activator per unit volume.

[0020] Preferably, the buffer comprises at least one of boric acid, sodium borate, citric acid and sodium citrate.

[0021] Preferably, the anode activator includes at least one of nickel chloride, sodium chloride and nickel bromide.

[0022] Furthermore, the silicon substrate with the patterned grooves is obtained by opening the silicon substrate to form the patterned grooves.

[0023] Preferably, the method further includes a process of cleaning the silicon substrate with the patterned grooves, and then immersing the substrate in a nickel electroplating solution after cleaning.

[0024] Furthermore, the metal electrode is made of copper, silver or tin.

[0025] Preferably, the metal electrode is formed by electroplating or physical vapor deposition.

[0026] Furthermore, in the nickel electroplating process, the silicon substrate is used as the cathode and pure nickel is used as the anode; a segmented current is applied between the cathode and the anode to perform the electroplating.

[0027] A second aspect of the present invention provides a solar cell prepared by the method described in the first aspect.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] The preparation method provided by the present invention controls the growth process of the nickel metal layer through segmented current electroplating, and generates dense and refined nickel grains under forward pulse current control, and the nickel grains show a discontinuous and uniform distribution; then, under reverse direct current control, electrochemical oxidation is performed in the nickel grain-free area to generate a silicon oxide layer, and the silicon oxide has good passivation ability. The nickel metal layer subsequently generated on the silicon oxide layer forms a passivation contact with silicon, thereby reducing the reverse saturation current J0; finally, forward direct current electroplating is performed to generate a complete nickel metal film layer, completing the preparation of the nickel metal layer, and realizing local passivation contact between the metal electrode and the silicon substrate.

[0030] The solar cell provided by the present invention, in view of the advantages brought by the above-mentioned nickel metal layer, improves the bonding strength between the metal electrode and the silicon substrate in the solar cell, reduces the reverse saturation current J0 of the solar cell, and increases the open-circuit voltage Uoc of the solar cell, so that the prepared solar cell has better electrical performance and service life. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0032] Hereinafter, the terms "including", "having" and their cognates, which may be used in various embodiments of the present invention, are intended only to indicate specific features, numbers, steps, operations, elements, components or combinations of the foregoing items, and should not be understood as first excluding the existence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items or the possibility of adding one or more features, numbers, steps, operations, elements, components or combinations of the foregoing items.

[0033] A first aspect of the present invention provides a method for preparing a solar cell with locally passivated contacts, comprising the following steps:

[0034] The silicon substrate with the patterned grooves is immersed in a nickel electroplating solution, and a nickel metal layer is formed by segmented current electroplating, and finally a metal electrode is formed to obtain a solar cell.

[0035] The preparation method provided by the present invention controls the growth process of the nickel metal layer through segmented current electroplating, first generating dense and refined nickel grains with a discontinuous and uniform distribution of the nickel grains; then electrochemically oxidizing in the nickel grain-free area to generate a silicon oxide layer, the silicon oxide having good passivation ability, and subsequently forming a passivation contact between the nickel metal layer generated on the oxide layer and the silicon, thereby reducing the reverse saturation current J0; finally, generating a complete nickel metal film layer, completing the preparation of the nickel metal layer, and realizing local passivation contact between the metal electrode and the silicon substrate.

[0036] Furthermore, the segmented current includes a forward pulse current, a reverse direct current and a forward direct current in sequence.

[0037] In the specific implementation process of the present invention, a programmable high-speed dual-pulse DC power supply is used, and the current output program of the electroplated nickel metal layer is set to three stages, namely forward pulse current, reverse DC current and forward DC current.

[0038] Compared to DC electroplating, pulse plating has a higher grain nucleation rate than grain growth rate, which can form denser and finer grains. In the first stage of electroplating the nickel metal layer, the uniformity of nickel grain nucleation and growth rate is controlled by forward pulse current electroplating, so that the growing nickel grains are discontinuously and evenly distributed; uniformly dispersed and independent nickel grains grow on the surface of the silicon substrate to obtain a nickel grain layer. The uniform distribution of nickel grains in the nickel grain layer provides good and uniform contact resistance for the metal electrode. The nickel grains are in direct contact with the silicon and are the source of the bonding force of the upper metal electrode. Therefore, the uniformly distributed nickel grains provide good electrode bonding force.

[0039] The reverse DC current oxidizes the silicon in the area uncovered by the nickel grains into a silicon oxide layer through an electrochemical reaction. In this stage, the reverse DC current density and time are controlled to keep the thickness of the silicon oxide layer between 1nm and 2nm. The silicon oxide layer has good passivation ability and can effectively reduce the high reverse saturation current J0 generated by the contact between the nickel metal layer and the silicon in the subsequent third stage.

[0040] Furthermore, the thickness of the silicon oxide layer is 1 nm to 2 nm.

[0041] The thickness of the silicon oxide layer is controlled between 1nm and 2nm because a silicon oxide layer with a thickness below 2nm allows electrons to pass through by the tunneling effect and will not adversely affect the third-stage electroplated nickel metal layer; the third-stage deposition is completed to form a nickel metal layer with local passivation contact with the silicon substrate.

[0042] Furthermore, the frequency of the forward pulse current is 100 Hz to 1000 Hz.

[0043] The frequency of the forward pulse current is controlled at 100Hz to 1000Hz, which can ensure that the nucleation and grain size of the nickel grains are within a controllable range, which is beneficial to controlling the morphology of the nickel grains. When the duty cycle, average current density and duration of the forward pulse current are within the scope of the present invention, the frequency is lower than 100Hz. If the frequency is too low, the nucleation density of the nickel grains is low, the uniformity of the nucleus distribution is poor, and the grain growth size varies greatly, causing the contact resistance to be high after the metal electrode deposition is completed; when the frequency of the forward pulse current is higher than 1000Hz, the pulse cycle power-on time t onIt will be close to or even shorter than the double layer charging time t formed at the interface between the electrode and the solution c , which causes the pulse current to become a direct current and cannot achieve the effect of pulse plating.

[0044] Typically but not limitatively, the frequency of the forward pulse current may be, for example, 100 Hz, 200 Hz, 300 Hz, 400 Hz, 500 Hz, 600 Hz, 700 Hz, 800 Hz, 900 Hz or 1000 Hz, or any value within the range of 100 Hz to 1000 Hz.

[0045] Preferably, the duty cycle of the forward pulse current is 5% to 40%.

[0046] The duty cycle of the forward pulse current affects the size of the peak current density, thereby affecting the nucleation rate and grain growth rate of nickel grains. Controlling the duty cycle of the forward pulse current within 5% to 40% is conducive to balancing the relationship between the nucleation rate and the growth rate. When the frequency, average current density and duration of the forward pulse current are within the scope of the present invention, but the duty cycle of the forward pulse current is lower than 5%, the peak current density will be too high, so that the grain nucleation rate is greater than the grain growth rate. Under the required ampere-hour conditions, the grain size is too small and the specific surface area is greatly increased; in the subsequent reverse DC process, the nickel grain corrosion rate increases, resulting in severe nickel grain corrosion, increased metal electrode contact resistance, and decreased bonding strength; when the duty cycle of the forward pulse current is higher than 40%, the peak current density is too low, the nucleation rate decreases, and the grain growth rate accelerates, which will excessively consume the metal ions around the cathode, making it impossible for the metal ions to return to a concentration close to the initial concentration within the off time, resulting in concentration polarization, and reducing the quality and strength of the nickel grains.

[0047] Typically but not limitatively, the duty cycle of the forward pulse current may be, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40%, or any value within the range of 5% to 40%.

[0048] Preferably, the average current density of the forward pulse current is 0.75A / dm 2 ~15A / dm 2 .

[0049] The average current density of the forward pulse current affects the nucleation rate and grain growth rate of nickel grains, thereby affecting the contact resistance and bonding strength of the metal electrodes; the average current density is controlled at 0.75A / dm 2 ~15A / dm 2 , which is beneficial to balance the relationship between nucleation rate and growth rate. When the frequency, duty cycle and duration of the forward pulse current are within the scope of the present invention, but the average current density of the forward pulse current is lower than 0.75A / dm 2, which will lead to too low peak current density, reduced nucleation rate, accelerated grain growth rate, excessive consumption of metal ions around the cathode, making it impossible for the metal ions to return to a concentration close to the initial concentration within the off time, resulting in concentration polarization and reduced nickel grain quality and strength; when the average current density of the forward pulse current is higher than 15A / dm 2 , which will lead to the peak current density being too high, so that the grain nucleation rate is greater than the grain growth rate. Under the required ampere-hour conditions, the grain size is too small and the specific surface area increases significantly; in the subsequent reverse DC process, the nickel grain corrosion rate increases, resulting in severe nickel grain corrosion, increased metal electrode contact resistance, and decreased bonding strength.

[0050] Typically, but not limiting, the average current density of the forward pulse current may be, for example, 0.75 A / dm 2 , 1A / dm 2 、3A / dm 2 , 5A / dm 2 , 7A / dm 2 , 9A / dm 2 、11A / dm 2 、13A / dm 2 or 15A / dm 2 , or 0.75A / dm 2 ~15A / dm 2 Any value in the range.

[0051] Preferably, the duration of the forward pulse current is 5s to 20s.

[0052] The duration of the forward pulse current affects the growth size of the nickel grains. When the duration is controlled within the range of 5s to 20s, the nickel grains will not affect the performance of the metal electrode due to being too large or too small. When the frequency, duty cycle, and average current density of the forward pulse current are within the scope of the present invention, but the duration of the forward pulse current is less than 5s, the grain size is too small and the specific surface area increases significantly; in the subsequent reverse DC process, corrosion is severe, affecting the contact resistance and bonding strength of the metal electrode; when the duration of the forward pulse current is greater than 20s, the nickel grain size becomes larger, and the proportion of the overall film opening area increases, resulting in insufficient passivation area of the subsequent silicon oxide layer, increased metal recombination, and a decrease in the solar cell opening voltage.

[0053] Typically but not limitatively, the duration of the forward pulse current may be, for example, 5s, 7s, 9s, 11s, 13s, 15s, 17s, 19s or 20s, or any value within the range of 5s to 20s.

[0054] Furthermore, the average current density of the reverse direct current is 0.2A / dm 2 ~2A / dm 2 .

[0055] Preferably, the duration of the reverse direct current is 1s to 10s.

[0056] The average current density and duration of the reverse DC current control the growth thickness of the silicon oxide layer. When the average current density of the reverse DC current is lower than 0.2A / dm 2 And the duration is less than 1s, the silicon oxidation reaction is not sufficient, the thickness of the silicon oxide layer is insufficient and uneven, and a good passivation effect cannot be achieved; when the average current density of the reverse DC current is higher than 2A / dm 2 If the duration is longer than 10s, the resulting silicon oxide layer is too thick, and the tunneling probability of electrons between nickel and silicon through the silicon oxide layer is greatly reduced, resulting in increased contact resistance; at the same time, the oxidation reaction increases the corrosion of nickel grains, resulting in a decrease in the bonding strength of nickel and silicon.

[0057] Typically, but not limiting, the average current density of the reverse DC current may be, for example, 0.2 A / dm 2 , 0.5A / dm 2 , 0.7A / dm 2 , 1A / dm 2 , 1.5A / dm 2 or 2A / dm 2 , or 0.2A / dm 2 ~2A / dm 2 the duration of the reverse DC current can be, for example, 1s, 2s, 3s, 4s, 5s, 6s, 7s, 8s or 10s, or it can be any value within the range of 1s to 10s.

[0058] Furthermore, the average current density of the forward DC current is 2A / dm 2 ~15A / dm 2 .

[0059] Preferably, the duration of the forward direct current is 30s to 120s.

[0060] The average current density and duration of the forward DC current control the growth thickness of the nickel metal film layer. When the average current density of the forward DC current is lower than 2A / dm 2 If the duration is less than 30s, the obtained nickel metal film layer is too thin, the nickel coverage rate in the patterned area of the silicon substrate is insufficient, the contact resistance of the metal electrode increases, and the bonding force decreases; when the average current density of the forward DC current is higher than 15A / dm 2 If the duration is longer than 120 seconds, the obtained nickel metal film layer is too thick, the stress in the nickel metal film layer increases, and the nickel metal film layer is prone to breakage and falling off.

[0061] Typically, but not limiting, the average current density of the forward DC current may be, for example, 2 A / dm 2 , 4A / dm2 , 6A / dm 2 , 8A / dm 2 、10A / dm 2 or 15A / dm 2 , or 2A / dm 2 ~15A / dm 2 the duration of the forward DC current may be, for example, 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s or 120s, or may be any value within the range of 30s to 120s.

[0062] Furthermore, the nickel electroplating solution comprises 300 to 450 parts of nickel sulfamate, 10 to 40 parts of a buffer and 0 to 30 parts of an anode activator per unit volume.

[0063] Typically, but not limiting, the weight ratio of nickel sulfamate per unit volume may be, for example, 300 parts, 340 parts, 380 parts, 420 parts, or 450 parts, or any value within the range of 300 to 450 parts; the weight ratio of the buffer per unit volume may be, for example, 10 parts, 20 parts, 30 parts, or 40 parts, or any value within the range of 10 to 40 parts; the weight ratio of the anode activator per unit volume may be, for example, 0 parts, 5 parts, 10 parts, 20 parts, or 30 parts, or any value within the range of 0 to 30 parts.

[0064] Preferably, the buffer comprises at least one of boric acid, sodium borate, citric acid and sodium citrate.

[0065] Preferably, the anode activator includes at least one of nickel chloride, sodium chloride and nickel bromide.

[0066] Furthermore, the silicon substrate with the patterned grooves is obtained by opening the silicon substrate to form the patterned grooves.

[0067] Preferably, the process also includes cleaning the silicon substrate with the patterned grooves, followed by immersion in a nickel electroplating solution. The purpose of cleaning is to remove the oxide layer and passivation layer residue on the surface of the patterned area. The present invention does not specifically limit the cleaning solution used; any commonly used solution in the art that can remove oxide layers and passivation layers on silicon surfaces can be used.

[0068] Furthermore, the metal electrode is made of copper, silver or tin.

[0069] Preferably, the metal electrode is formed by electroplating or physical vapor deposition.

[0070] Furthermore, in the nickel electroplating process, the silicon substrate is used as the cathode and pure nickel is used as the anode; a segmented current is applied between the cathode and the anode to perform the electroplating.

[0071] A second aspect of the present invention provides a solar cell prepared by the method described in the first aspect.

[0072] The solar cell provided by the present invention, in view of the advantages brought by the above-mentioned nickel metal layer, improves the bonding strength between the metal electrode and the silicon substrate in the solar cell, reduces the reverse saturation current J0 of the solar cell, and increases the open-circuit voltage Uoc of the solar cell, so that the prepared solar cell has better electrical performance and service life.

[0073] The present invention is further illustrated below by specific examples and comparative examples. However, it should be understood that these examples are merely for the purpose of further explanation and should not be construed as limiting the present invention in any form. The raw materials used in the examples and comparative examples of the present invention, unless otherwise specified, were prepared under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0074] Example 1

[0075] This embodiment provides a method for preparing a solar cell, and the specific steps are as follows:

[0076] 1. Laser-opening a silicon substrate to form a patterned groove, wherein the width of the patterned groove is 20 μm, to obtain a silicon substrate after opening the film.

[0077] 2. Clean the silicon substrate after film opening, remove the anti-reflection layer and oxide layer on the surface of the patterned area, and obtain a silicon substrate with patterned grooves.

[0078] 3. Placing the silicon substrate with the patterned grooves in a nickel electroplating solution, using the silicon substrate as a cathode and pure nickel as an anode, and applying a segmented current between the cathode and the anode to perform nickel electroplating.

[0079] Among them, in the nickel electroplating solution, the concentration of nickel sulfamate is 375g / L, the concentration of nickel chloride is 15g / L, and the concentration of boric acid is 30g / L.

[0080] The frequency of the forward pulse current is 100Hz, the duty cycle is 5%, and the average current density is 0.75A / dm 2 , time is 20s.

[0081] The reverse DC current density is 0.2A / dm 2 , time is 10s.

[0082] Forward DC current density is 15A / dm2 , time is 30s.

[0083] 4. Electroplating and depositing copper electrodes on the nickel metal layer to obtain solar cells.

[0084] Example 2

[0085] This embodiment provides a method for preparing a solar cell. The difference from embodiment 1 is that in step 3, the frequency of the forward pulse current is 1000 Hz, the duty cycle is 40%, and the average current density is 14 A / dm 2 , time is 5s. Reverse DC current density is 2A / dm 2 The remaining steps are the same as those in Example 1 and will not be described in detail here.

[0086] Example 3

[0087] This embodiment provides a method for preparing a solar cell. The difference from embodiment 1 is that in step 3, the frequency of the forward pulse current is 500 Hz, the duty cycle is 15%, and the average current density is 10 A / dm 2 , time is 10s. Reverse DC current density is 1A / dm 2 The remaining steps are the same as those in Example 1 and will not be described in detail here.

[0088] Example 4

[0089] This embodiment provides a method for preparing a solar cell. The difference from Example 3 is that in step 3, the frequency of the forward pulse current is 50 Hz. The remaining steps are the same as those in Example 3 and are not described again here.

[0090] Example 5

[0091] This embodiment provides a method for preparing a solar cell. The difference from Example 3 is that in step 3, the frequency of the forward pulse current is 2000 Hz. The remaining steps are the same as those in Example 3 and are not described again here.

[0092] Example 6

[0093] This embodiment provides a method for preparing a solar cell. The difference from Example 3 is that in step 3, the duty cycle of the forward pulse current is 3%. The remaining steps are the same as those in Example 3 and are not described again here.

[0094] Example 7

[0095] This embodiment provides a method for preparing a solar cell. The difference from Example 3 is that in step 3, the duty cycle of the forward pulse current is 50%. The remaining steps are the same as those in Example 3 and are not described again here.

[0096] Example 8

[0097] This embodiment provides a method for preparing a solar cell. The difference from embodiment 3 is that in step 3, the average current density of the forward pulse current is 0.5A / dm 2 The remaining steps are the same as those in Example 3 and will not be repeated here.

[0098] Example 9

[0099] This embodiment provides a method for preparing a solar cell. The difference from embodiment 3 is that in step 3, the average current density of the forward pulse current is 20A / dm 2 The remaining steps are the same as those in Example 3 and will not be repeated here.

[0100] Example 10

[0101] This embodiment provides a method for preparing a solar cell. The difference from embodiment 3 is that in step 3, the average current density of the reverse DC current is 0.1A / dm 2 The remaining steps are the same as those in Example 3 and will not be repeated here.

[0102] Example 11

[0103] This embodiment provides a method for preparing a solar cell. The difference from embodiment 3 is that in step 3, the average current density of the reverse DC current is 5A / dm 2 The remaining steps are the same as those in Example 3 and will not be repeated here.

[0104] Example 12

[0105] This embodiment provides a method for preparing a solar cell. The difference from embodiment 3 is that in step 3, the average current density of the forward DC current is 1A / dm 2 The remaining steps are the same as those in Example 3 and will not be repeated here.

[0106] Example 13

[0107] This embodiment provides a method for preparing a solar cell. The difference from embodiment 3 is that in step 3, the average current density of the forward DC current is 20A / dm 2 The remaining steps are the same as those in Example 3 and will not be repeated here.

[0108] Example 14

[0109] This embodiment provides a method for preparing a solar cell. Unlike Example 3, in step 3, nickel electroplating is performed using only a reverse DC current and a forward DC current. The parameters of the reverse DC current and the forward DC current are the same as those in Example 1. The remaining steps are the same as those in Example 3 and are not further described here.

[0110] Example 15

[0111] This embodiment provides a method for preparing a solar cell. Unlike Example 3, in step 3, nickel electroplating is performed using only a forward pulse current and a forward direct current. The parameters of the forward pulse current and the forward direct current are the same as those in Example 1. The remaining steps are the same as those in Example 3 and are not further described here.

[0112] Comparative Example 1

[0113] This comparative example provides a method for preparing a solar cell, and the specific steps are as follows:

[0114] 1. Same as the step in Example 1.

[0115] 2. Same as the step in Example 1.

[0116] 3. Placing the silicon substrate with the patterned grooves in a nickel electroplating solution, using the silicon substrate as a cathode and pure nickel as an anode, and applying a forward direct current between the cathode and the anode to perform nickel electroplating.

[0117] Among them, in the nickel electroplating solution, the concentration of nickel sulfamate is 375g / L, the concentration of nickel chloride is 15g / L, and the concentration of boric acid is 30g / L.

[0118] The forward DC current density is 12A / dm 2 , time is 50s.

[0119] 4. Same as the step in Example 1.

[0120] Comparative Example 2

[0121] This comparative example provides a method for preparing a solar cell. Unlike Example 3, in step 3, only a forward pulse current is used for nickel electroplating, and the parameters of the forward pulse current are the same as those in Example 3. The remaining steps are the same as those in Example 3 and are not repeated here.

[0122] Comparative Example 3

[0123] This comparative example provides a method for preparing a solar cell. Unlike Example 3, in step 3, only reverse direct current is used for nickel electroplating, and the parameters of the reverse direct current are the same as those in Example 3. The remaining steps are the same as those in Example 3 and are not repeated here.

[0124] Test Case

[0125] The solar cells provided in the examples and comparative examples were subjected to electrical performance tests and welding tensile tests.

[0126] Electrical performance test

[0127] Specifically, the electrical performance of solar cells of the same scale was tested under the conditions of AM1.5, 1000W light intensity and 25℃ temperature. The J 0metal The results are shown in Table 1 below.

[0128] Welding tensile test

[0129] A welding tensile test was performed on the PAD points on the copper conductive layer of the solar cell under low temperature conditions (180-200°C). The average value of 12 points was tested. The specific test results are shown in Table 1 (where " / " indicates that welding could not be completed).

[0130] Table 1

[0131]

[0132] Among them, Uoc is the open circuit voltage, J0 metal It is the reverse saturation current caused by carrier recombination at the metal-semiconductor contact.

[0133] The average current density of the forward DC current of Example 13 is too large, and the nickel metal layer is too thick, so it breaks and falls off directly, making it impossible to proceed to the subsequent steps. The preparation method of Comparative Example 3 is only to oxidize the silicon substrate, and a silicon oxide layer is generated in the grid line area. The copper electrode cannot collect carriers, no current passes, and the open circuit point and reverse saturation current cannot be measured. As can be seen from Table 1, within the method and parameter range protected by the present invention, the metal electrode of the electroplated solar cell has good bonding force, and at the same time has obvious advantages over the traditional electroplated solar cell Uoc, J0 metal It is an order of magnitude lower than before.

[0134] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the above-described embodiments, those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the above-described embodiments within the technical scope disclosed by the present invention, or replace some of the technical features therein with equivalents. Such modifications, changes, or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a solar cell with local passivation contact, characterized in that: The following steps are involved: The silicon substrate with the patterned grooves is immersed in a nickel electroplating solution, and a nickel metal layer is formed by segmented current electroplating, and finally a metal electrode is formed to obtain a solar cell; Wherein, the segmented current includes a forward pulse current, a reverse direct current and a forward direct current in sequence; The growth process of the nickel metal layer is controlled by segmented current electroplating. Forward pulse current control generates dense and refined nickel grains, and the nickel grains show a discontinuous and uniform distribution. Then, reverse DC current control is used to electrochemically oxidize the nickel-free grain area to generate a silicon oxide layer. Silicon oxide has good passivation ability. The nickel metal layer subsequently generated on the silicon oxide layer forms a passivation contact with silicon. Finally, forward DC current electroplating generates a complete nickel metal film layer, completing the preparation of the nickel metal layer.

2. The preparation method according to claim 1, characterized in that The frequency of the forward pulse current is 100 Hz to 1000 Hz.

3. The preparation method according to claim 1, characterized in that The duty cycle of the forward pulse current is 5% to 40%.

4. The preparation method according to claim 1, characterized in that The average current density of the forward pulse current is 0.75A / dm 2 ~15 A / dm 2 .

5. The preparation method according to claim 1, characterized in that The duration of the forward pulse current is 5s to 20s.

6. The preparation method according to claim 1, characterized in that The average current density of the reverse direct current is 0.2A / dm 2 ~2A / dm 2 .

7. The preparation method according to claim 1, characterized in that The duration of the reverse direct current is 1s to 10s.

8. The preparation method according to claim 1, characterized in that The average current density of the forward DC current is 2A / dm 2 ~15A / dm 2 .

9. The preparation method according to claim 1, characterized in that The duration of the forward direct current is 30s to 120s.

10. The preparation method according to any one of claims 1 to 9, characterized in that The nickel electroplating solution comprises, per unit volume, 300 to 450 parts of nickel sulfamate, 10 to 40 parts of a buffer and 0 to 30 parts of an anode activator.

11. The preparation method according to claim 10, characterized in that: The buffering agent includes at least one of boric acid, sodium borate, citric acid and sodium citrate.

12. The preparation method according to claim 10, characterized in that The anode activator includes at least one of nickel chloride, sodium chloride and nickel bromide.

13. The preparation method according to any one of claims 1 to 9, characterized in that The silicon substrate with the patterned grooves is obtained by opening the silicon substrate to form the patterned grooves.

14. The preparation method according to any one of claims 1 to 9, characterized in that The method also includes a process of cleaning the silicon substrate with the patterned grooves, and then immersing the substrate in a nickel electroplating solution after cleaning.

15. The preparation method according to any one of claims 1 to 9, characterized in that The metal electrode is made of copper, silver or tin.

16. The preparation method according to any one of claims 1 to 9, characterized in that The metal electrodes are formed by electroplating or physical vapor deposition.

17. The method according to any one of claims 1 to 9, characterized in that During the nickel electroplating process, the silicon substrate is used as the cathode and pure nickel is used as the anode; a segmented current is applied between the cathode and the anode to perform the electroplating.

18. A solar cell, characterized in that: The method according to any one of claims 1 to 17 is used for preparation.

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