Laser processing device, method for preparing metal electrode and photovoltaic cell

Abstract

The invention relates to the technical field of photovoltaic cells, and provides a laser processing device, a method for preparing a metal electrode and a photovoltaic cell. When the laser processing system is used for preparing a metal electrode of a solar cell, accurate alignment of pulse laser and continuous laser processing positions can be achieved, and a copper circuit with complex patterns and high adhesive force can be rapidly and flexibly prepared. According to the method for preparing the metal electrode, the position of the copper electrode can be precisely machined, the problem of precision of current silk-screen printing is solved, damage to the amorphous silicon layer can be avoided, the prepared copper electrode has the large height-width ratio, and the light conversion efficiency can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of photovoltaic cells, and in particular to a laser processing device, a method for preparing a metal electrode and a photovoltaic cell. Background Art

[0002] Silicon heterojunction (HJT) cells are a type of high-efficiency solar cell. They have become one of the most promising solar cell technologies due to their advantages such as simple process, high conversion efficiency, low-temperature process, and double-sided power generation. The metal grid electrode is the most important structure and material in silicon heterojunction cells. Its main function is to collect carriers generated by the photovoltaic effect, thereby drawing out the current generated by the photovoltaic effect.

[0003] At present, the most commonly used method for preparing electrodes in the industry is screen printing silver paste, which has the advantages of simple and mature process and suitable for mass production. However, due to the precision of the printing plate, the electrode aspect ratio is small, the shading area is large, the screen printing process is becoming more and more difficult, and the yield rate caused by virtual printing and broken grids has dropped significantly, which limits the further improvement of the conversion efficiency of solar cells. On the other hand, due to the inherent characteristics of HJT cells, the processing technology needs to be controlled at around 200°C, and low-temperature silver paste needs to be used. However, low-temperature silver paste has poor conductivity, high contact resistance with ITO film (Transparent Conductive Oxide), poor printing performance, and a large weight gain of the paste of the heterojunction battery, accounting for about 30-40% of the cost of the entire heterojunction processing battery. In addition, the price of silver paste is expensive, which makes the manufacturing cost of solar cells high, which is not conducive to the development of batteries in the direction of high efficiency and low cost.

[0004] In order to reduce costs and increase efficiency, more and more solar cell manufacturers have turned to the development of copper electrodes with high conductivity and low cost. The most commonly used method at present is electroplating. The electroplating preparation of copper grid electrode is to first deposit a layer of seed copper on the surface of ITO, then pattern the mask, and then electroplate copper and tin. However, this method needs to consider the subsequent etching and removal of the mask and seed layer. The process is relatively cumbersome, and the bonding strength between the copper electrode and the substrate has always been a problem in the industry.

[0005] Therefore, it is of great significance to develop a method for preparing copper electrodes for silicon heterojunction solar cells with simple process and low cost. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art, and to provide a laser processing device, a method for preparing a metal electrode using the laser processing device, and a photovoltaic cell comprising a metal electrode obtained by the preparation method. When the laser processing system is used to prepare the metal electrode of a solar cell, it can achieve precise alignment of the pulsed laser and continuous laser processing positions, quickly and flexibly prepare a copper circuit with a complex pattern and high adhesion, solve the current problem of screen printing accuracy, and avoid damage to the amorphous silicon layer. The prepared copper electrode has a large aspect ratio, which can effectively improve the light conversion efficiency.

[0007] In order to achieve the above-mentioned object, the first aspect of the present invention provides a laser processing system, characterized in that it is used to prepare a metal electrode of a solar cell, and the laser processing system comprises: a mobile working platform, a first optical path system and a second optical path system;

[0008] The mobile working platform is used to carry the substrate of the metal electrode to be prepared;

[0009] The first optical path system includes a pulse laser and a first optical path adjustment system, wherein the pulse laser is used to emit a pulse laser, and the pulse laser acts on the substrate of the metal electrode to be prepared after passing through the first optical path adjustment system;

[0010] The second optical path system includes a continuous laser and a second optical path adjustment system. The continuous laser is used to emit continuous laser light. The continuous laser light acts on the substrate of the metal electrode to be prepared after passing through the second optical path adjustment system.

[0011] A second aspect of the present invention provides a method for preparing a metal electrode, which uses the laser processing system and copper electrode slurry described in the first aspect of the present invention to prepare the metal electrode.

[0012] A third aspect of the present invention provides a photovoltaic cell, comprising a metal electrode, wherein the metal electrode is prepared by the method described in the second aspect of the present invention.

[0013] The present invention adopts the above technical solution to achieve the following beneficial effects:

[0014] (1) The laser processing system provided by the present invention improves the laser system and can achieve precise alignment of pulsed laser and continuous laser processing positions when used to prepare metal electrodes of solar cells. Specific laser processing parameters can be used to draw processing patterns through CAD software, so that copper circuits with complex patterns and high adhesion can be quickly and flexibly prepared.

[0015] (2) The method for preparing a metal electrode provided by the present invention uses a copper electrode slurry using CuO and / or Cu2O nanoparticles as a precursor material, which has the advantages of good dispersibility and good reducibility, can effectively increase the bonding strength inside the copper circuit and with the substrate, and replaces the use of expensive silver paste, greatly reducing the production cost of solar cell electrodes, and can well meet the needs of high efficiency and low cost in industrial production.

[0016] (2) The method for preparing metal electrodes provided by the present invention can accurately process the position of the copper electrode due to the high controllability of laser processing, thus solving the current problem of screen printing accuracy. The prepared copper electrode has a larger aspect ratio.

[0017] (3) The method for preparing a metal electrode provided by the present invention adopts a multiple scanning method, which effectively solves the problem of poor adhesion between the copper electrode and the substrate by realizing the remelting and solidification of the copper electrode. At the same time, it avoids the step of high-temperature curing in a sintering furnace, reduces damage to the amorphous silicon layer, and improves the light conversion efficiency.

[0018] (4) Compared with the traditional seed layer plating method, the solar cell preparation method provided by the present invention does not require a mask, avoids the processes such as mask patterning and seed layer removal, simplifies the process and reduces the cost; and the processed pattern can be directly and flexibly changed through drawing software such as CAD, so that complex copper electrode circuit morphology can be processed more flexibly.

[0019] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Shown is a schematic structural diagram of a laser processing system in an example of the present invention.

[0021] Figure 2 The figure shows a process flow chart for preparing copper electrodes for solar cells in one embodiment of the present invention.

[0022] Figure 3 FIG. 1 is a schematic diagram of a laser processing operation in an embodiment of the present invention.

[0023] Figure 4 The figure shows a schematic diagram of the process for preparing a copper electrode for a heterojunction battery in one example of the present invention.

[0024] Figure 5Shown is a three-dimensional morphology of a copper electrode of a heterojunction battery in an example of the present invention.

[0025] Figure 6 Shown are metallographic phase diagrams of copper circuits of metal electrodes obtained in Examples 1-2 of the present invention and Comparative Example 1.

[0026] Figure 7 Shown is an electron microscope image of the metal electrode copper circuit obtained in Example 1 of the present invention.

[0027] Figure 8 Shown are metallographic images of metal electrode copper circuits obtained in Examples 3-4 of the present invention and Comparative Example 2.

[0028] Fig. 9 Shown are metallographic images of the copper circuits of the metal electrodes obtained in Examples 5-6 of the present invention and Comparative Example 3.

[0029] Fig.10 Shown is a metallographic diagram of the copper circuit of the metal electrode obtained in Example 7 of the present invention.

[0030] Figure markings: 1-pulse laser; 2-attenuation plate; 3-aperture; 4-wave plate; 5-first beam expander; 6-first reflector; 7-second reflector; 8-first galvanometer; 9-first positioning sensor; 10-first field mirror; 11-first monitoring device; 12-sample to be processed; 13-moving work platform; 14-continuous laser; 15-second beam expander; 16-third reflector; 17-fourth reflector; 18-second galvanometer; 19-second positioning sensor; 20-second field mirror; 21-second monitoring device; 22-first vertical guide; 23-second vertical guide; 24-first spatial light modulator, 25-first lens, 26-second lens, 27-second spatial light modulator, 28-third lens, 29-fourth lens; 30-heterojunction battery substrate; 31-metal electrode; 32-copper electrode slurry coating; 33-laser. DETAILED DESCRIPTION

[0031] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0032] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[0033] A first aspect of the present invention provides a laser processing system for preparing a metal electrode of a solar cell, the laser processing system comprising: a mobile working platform, a first optical path system and a second optical path system;

[0034] The mobile working platform is used to carry the substrate of the metal electrode to be prepared;

[0035] The first optical path system includes a pulse laser and a first optical path adjustment system, wherein the pulse laser is used to emit a pulse laser, and the pulse laser acts on the substrate of the metal electrode to be prepared after passing through the first optical path adjustment system;

[0036] The second optical path system includes a continuous laser and a second optical path adjustment system. The continuous laser is used to emit continuous laser light. The continuous laser light acts on the substrate of the metal electrode to be prepared after passing through the second optical path adjustment system.

[0037] In one example, the mobile working platform can be a two-dimensional mobile working platform or a three-dimensional mobile working platform. When the laser processing system is used to prepare metal electrodes of solar cells, the working platform is stationary and the galvanometer performs patterning according to a preset processing pattern.

[0038] In one example, the pulse laser emitted by the pulse laser is not limited in terms of laser pulse width and wavelength, and the pulse width may be femtosecond laser, picosecond laser or continuous laser.

[0039] In one example, the first optical path adjustment system includes a first optical element group, a first beam expander, a first reflector group, a first spatial light modulator, a first lens, a second lens, a first galvanometer and a first field mirror arranged in sequence, wherein the first optical element group is close to the pulse laser, the first field mirror is close to the mobile working platform, and the first optical element group is used to adjust at least one of the power of the pulse laser, the aperture angle of the light beam and the polarization of the polarized light.

[0040] In one example, if Figure 1 As shown, the first optical element group, the first beam expander 5, the first reflector group, and the first galvanometer 8 are all arranged in parallel. The first field mirror 10 is arranged below the first galvanometer 8 and is arranged perpendicular to the first optical element group. The mobile working platform 13 is located below the first field mirror 8. It should be noted that the reflector group is used to adjust the propagation direction of the light path, and the light path can propagate in any direction, not just parallel and vertical.

[0041] In one example, if Figure 1 As shown, the first reflector group, the first spatial light modulator 24, the first lens 25 and the second lens 26 are all arranged in parallel. The first spatial light modulator 24 is close to the first reflector group, and the second lens 26 is close to the first galvanometer 8.

[0042] In the first optical path adjustment system, the first beam expander can expand and collimate the laser beam output by the pulsed laser, reduce the spot size, and improve the accuracy of laser processing; the first reflector group can change the direction of the expanded and collimated laser beam; the first spatial light modulator shapes and diverges the light, the first lens can focus the diverged light, and the second lens can expand and collimate the light before performing the first galvanometer; the first galvanometer controls the laser beam to perform laser selective metal patterning to prepare metal electrodes according to the set processing path; the first field mirror can be an f-θ flat field scanning lens, which can focus the laser beam onto the surface of the sample to be processed.

[0043] In one example, if Figure 1 As shown, the first optical element group includes an attenuation plate 2, an aperture 3 and a wave plate 4 which are arranged in sequence, wherein the attenuation plate is close to the pulse laser, and the wave plate is close to the first beam expander.

[0044] In one embodiment, the attenuation plate, the aperture and the wave plate are all arranged in parallel.

[0045] In the first optical element group, the attenuation plate can attenuate the laser light emitted by the pulsed laser, which can effectively reduce the output power and control the output power within the range that the object can withstand, thereby preventing the amorphous silicon layer from being damaged by excessive laser energy; the aperture can adjust the aperture angle of the imaging light beam to improve the processing accuracy of the laser processing system; the wave plate can be a half-wave plate, which can change the polarization of polarized light to adjust the laser power, for example, it can change the polarization of the light beam by 180°.

[0046] In one example, if Figure 1 As shown, the first reflector group includes a first reflector 6 and a second reflector 7, the first reflector 6 is close to the first beam expander 5 and is arranged at a first preset angle to the first beam expander 5, the second reflector 7 is arranged parallel to the first reflector 6, and the second reflector 7 is close to the first galvanometer 8.

[0047] The first preset angle can be freely adjusted according to the required light path direction, for example, it can be freely set within the range of 0-180 degrees (excluding the endpoint value).

[0048] In one example, if Figure 1 As shown, the first preset angle may be 45 degrees or 135 degrees.

[0049] In one example, if Figure 1As shown, the second optical path adjustment system includes a second beam expander 15, a second reflector group, a second spatial light modulator 27, a third lens 28, a fourth lens 29, a second galvanometer 18 and a second field lens 20 which are arranged in sequence, wherein the second beam expander 15 is close to the continuous laser 14, and the second field lens 20 is close to the mobile working platform.

[0050] In one example, if Figure 1 As shown, the second beam expander 15, the second reflector group, and the second galvanometer 18 are all arranged in parallel. The second field mirror 20 is arranged below the second galvanometer 18. The mobile working platform 13 is located below the second field mirror 20.

[0051] In one example, if Figure 1 As shown, the second reflector group, the second spatial light modulator 27 , the third lens 28 and the fourth lens 29 are all arranged in parallel. The first spatial light modulator 27 is close to the second reflector group, and the fourth lens 29 is close to the second galvanometer 18 .

[0052] In the second optical path adjustment system, the second beam expander can expand and collimate the laser beam output by the continuous laser, reduce the spot size, and improve the accuracy of laser processing; the second reflector group can change the direction of the expanded and collimated laser beam; the second spatial light modulator shapes and diverges the light, the third lens can focus the diverged light, and the fourth lens can expand and collimate the light before the first galvanometer; the second galvanometer controls the laser beam to perform a second or multiple scans according to the processing path of the above-mentioned pulsed laser to achieve remelting and solidification of the electrode circuit, and further improve the bonding strength between the metal electrode and the transparent oxide conductive film; the second field mirror can be an f-θ flat field scanning lens, which can focus the laser beam of the continuous laser onto the surface of the sample to be processed.

[0053] In one example, if Figure 1 As shown, the second reflector group includes a third reflector 16 and a fourth reflector 17, wherein the third reflector 16 is close to the second beam expander 15 and is arranged at a second preset angle with the second beam expander 15, and the fourth reflector 17 is arranged parallel to the third reflector 16, and the fourth reflector 17 is close to the second galvanometer 20.

[0054] The second preset angle can be freely adjusted according to the required light path direction, for example, it can be freely set within the range of 0-180 degrees (excluding the endpoint value).

[0055] In one example, the second preset angle may be 45 degrees or 135 degrees.

[0056] In one example, if Figure 1As shown, the laser processing system further includes a first monitoring device 11, which is coaxially arranged with the first galvanometer 8 and is used for real-time monitoring of the processing process of the first optical path system.

[0057] In one example, the first monitoring device can monitor the processing process of the first optical path system in real time.

[0058] In one example, the laser processing system further includes a second monitoring device 21 , which is coaxially arranged with the second galvanometer 18 and is used to monitor the processing process of the second optical path system.

[0059] In one example, the second monitoring device can monitor the processing process of the second optical path system in real time.

[0060] The first monitoring device and the second monitoring device are independently selected from monitoring devices with an autofocus system. Exemplarily, the first monitoring device and the second monitoring device can be charge coupled device (CCD) cameras, which can also be called CCD image sensors, which can convert optical images into digital signals.

[0061] It should be noted that the "coaxial setting" does not refer to a physical connection, but only an optical connection. The coaxial setting can be understood as keeping the optical axis of the CCD camera and the rotation axis of the galvanometer as close to the same straight line as possible to ensure that the light can accurately pass through the galvanometer into the imaging area of ​​the CCD camera. By coaxially calibrating the CCD camera, the CCD camera and the galvanometer can be coaxially visually positioned to achieve real-time observation of the relative position of the laser beam and the workpiece to be processed, as well as real-time monitoring of the processing process.

[0062] In one example, if Figure 1 As shown, the laser processing system further includes a first positioning sensor 9, which is disposed on the first galvanometer 8 and is used to determine the position of the first galvanometer 8. The first positioning sensor 9 can be disposed below the first galvanometer 8 and close to the first field lens 10, so as to accurately process the metal electrode position and determine the laser processing position.

[0063] In one example, if Figure 1 As shown, the laser processing system further includes a second positioning sensor 19, which is disposed on the second galvanometer 18 and is used to determine the position of the second galvanometer 18. The second positioning sensor 19 can be disposed below the second galvanometer 18 and close to the second field lens 20, so that the continuous laser and the pulsed laser process the same position, ensuring the accuracy of the positions processed by the continuous laser beam and the pulsed laser beam.

[0064] In the laser processing system of the present invention, accurate alignment of pulse laser and continuous laser processing can be achieved through positioning sensors and monitoring equipment (CCD camera) with an automatic focusing system.

[0065] In one example, the first galvanometer and the first field mirror are both disposed on a first vertical guide rail, and the first vertical guide rail connects the first galvanometer and the first field mirror. The first vertical guide rail can move in the z-axis direction, thereby driving the first galvanometer and the first field mirror to move in the z-axis direction, and further adjusting the distance between the first field mirror and the processed object, so that the focus of the first optical path system is focused on the surface of the processed object.

[0066] In one example, the second galvanometer and the second field mirror are both disposed on a second vertical guide rail, and the second vertical guide rail connects the second galvanometer and the second field mirror. The second vertical guide rail can move in the z-axis direction, thereby driving the second galvanometer and the second field mirror to move in the z-axis direction, and further adjusting the distance between the second field mirror and the processed object so that the focus of the second optical path system is focused on the surface of the processed object.

[0067] It is understood that when the laser system includes the first vertical guide rail and the second vertical guide rail, the mobile working platform can be a two-dimensional mobile working platform. When the laser system does not include the first vertical guide rail and the second vertical guide rail, the mobile working platform can be a three-dimensional mobile working platform, and the three-dimensional mobile platform can move in the z-axis direction to replace the functions of the first vertical guide rail and the second vertical guide rail.

[0068] In one example, referring to Figure 1 Schematic diagram of the laser processing system, the laser processing system includes a pulse laser scanning system (i.e., the first optical path system) and a continuous laser scanning system (i.e., the second optical path system), wherein the pulse laser scanning system includes a pulse laser 1, and an attenuation plate 2, an aperture 3, a half-wave plate 4, a first beam expander 5, a first reflector 6, a second reflector 7, a first galvanometer 8, a first positioning sensor 9, a first field mirror 10, and a first CCD camera 11 are arranged on its output optical path, and the light beam output by the first field mirror is focused on the surface of the sample 12 to be processed on the mobile working platform 13. The continuous laser scanning system includes a continuous laser 14, and a second beam expander 15, a third reflector 16, a fourth reflector 17, a second galvanometer 18, a second positioning sensor 19, a second field mirror 20, and a first CCD camera 21 are arranged on its output optical path, and the light beam output by the second field mirror is focused on the surface of the sample 12 to be processed on the mobile working platform 13.

[0069] In one example, the process of preparing a metal electrode of a solar cell using the laser processing system may include the following steps:

[0070] (a) First, move the working platform, move the material to be processed to below the pulse laser scanning system (first optical path system), and adjust the first vertical guide rail so that the pulse laser focus output by the pulse laser scanning system is located on the surface of the material to be processed;

[0071] (b) then starting the pulse laser to output laser, using a first galvanometer (also called a first scanning galvanometer) to control the focused laser beam to perform metal patterning on the surface of the material to be processed according to a preset scanning area, thereby forming an initial circuit pattern (initial circuit diagram of the electrode);

[0072] (c) Turn off the pulse laser, start the mobile working platform, move the material to be processed to the bottom of the continuous laser scanning system (second optical path system), align the focused continuous laser beam with the initial circuit pattern through the second positioning sensor, and adjust the second vertical guide rail to make the focus point of the continuous laser beam output by the continuous laser scanning system shift to the initial circuit pattern;

[0073] (d) Starting the continuous laser to output continuous laser, using the second galvanometer (also called the second scanning galvanometer) to control the focused laser beam to perform secondary or multiple processing on the initially patterned circuit to achieve remelting and solidification of the electrode, and finally forming a copper electrode with low resistivity and high adhesion (i.e., the metal electrode of the solar cell).

[0074] A second aspect of the present invention provides a method for preparing a metal electrode, which uses the laser processing system and copper electrode slurry described in the first aspect of the present invention to prepare the metal electrode.

[0075] In one example, the copper electrode slurry includes a metal composition, a dispersing reducing agent and a composite curing agent; the metal composition includes at least copper powder, and optionally gold powder and / or silver powder; the composite curing agent includes a thermosetting resin and a latent curing agent.

[0076] It should be noted that, in addition to copper powder, the metal composition may also contain gold powder and / or silver powder, as well as other metal powders with good electrical conductivity. The metal composition may be a combination of one or more of various forms of the above-mentioned metal elements, such as simple substances, oxides, hydroxides or salts, which is not limited and can be selected according to actual needs. For example, the metal composition may be a combination of three metal simple substances of copper, gold and silver, or may be a combination of three metal oxides.

[0077] In one example, the metal composition is in powder form, and the particle size is nanometer scale.

[0078] In one example, the metal composition includes nano copper oxide and / or nano cuprous oxide.

[0079] In one example, the metal composition is nano copper oxide.

[0080] In one example, the metal composition is nano cuprous oxide.

[0081] In one example, the metal composition is a composition of nano-copper oxide and nano-cuprous oxide. The ratio of the two is not limited and can be adjusted according to the actual sequence. Exemplarily, the mass ratio of nano-copper oxide to nano-cuprous oxide can be (1-5):1.

[0082] The copper electrode slurry of the present invention has the advantages of good dispersibility and high reduction rate, and the composite curing agent prepared by using a thermosetting resin and a latent curing agent can make the bonding force of the electrode prepared by the copper electrode slurry higher.

[0083] In one example, the mass ratio of the metal composition to the composite curing agent is (7-30):1, for example, it can be 7:1, 10:1, 12:1, 15:1, 16.4:1, 18:1, 20:1, 22:1, 25:1, 28:1, 30:1.

[0084] In a preferred embodiment, the mass ratio of the metal composition to the composite curing agent is (15-20):1.

[0085] In order to further improve the performance of the copper electrode slurry and prepare a metal electrode with better physical properties, one or more of the characteristics may be optimized.

[0086] In one example, the thermosetting resin is selected from at least one of epoxy resin, polyurethane-modified epoxy resin, acrylic-modified epoxy resin, polyamide resin, polyurethane resin and acrylic resin.

[0087] In one example, the thermosetting resin is epoxy resin.

[0088] In one example, the latent curing agent includes a latent amine curing agent and / or an imidazole curing agent. The latent curing agent can be a latent amine curing agent alone, an imidazole curing agent, or a combination of a latent amine curing agent and an imidazole curing agent.

[0089] Exemplarily, the latent amine curing agent is a dicyandiamide curing agent, which exemplarily includes MY-24, MY-25 and MY-HK-1.

[0090] Exemplarily, the imidazole curing agent includes PN-23J, PN-50, PN-23, PN-31 and PN-40.

[0091] In one example, the latent curing agent is a latent amine curing agent and an imidazole curing agent. The mass ratio of the latent amine curing agent and the imidazole curing agent is not limited and can be freely adjusted according to actual needs.

[0092] Exemplarily, the mass ratio of the thermosetting resin to the latent curing agent may be (4-6):1, for example, 4:1, 5:1, or 6:1.

[0093] The combination of latent amine curing agent and imidazole curing agent, and thermosetting resin, especially epoxy resin therein, to form a composite curing agent can make the copper electrode slurry cure faster and improve the bonding strength between the copper electrode slurry and the contact surface.

[0094] In one embodiment, the reducing dispersant is selected from at least one of polyvinyl pyrrolidone and its derivatives. The specific type of the derivative is not limited, for example, it can be a copolymer of polyvinyl pyrrolidone, or a reactant of polyvinyl pyrrolidone and other compounds, as long as the derivative can play a similar or better dispersing and reducing role as polyvinyl pyrrolidone.

[0095] In one example, the mass ratio of the metal composition to the dispersing reducing agent is (2-9):1, for example, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 8.74:1, 9:1.

[0096] In a preferred embodiment, the mass ratio of the metal composition to the dispersing reducing agent is (2.5-6):1.

[0097] The present invention selects polyvinyl pyrrolidone and its derivatives which have both dispersing and reducing effects as dispersing reducing agents, and limits the mass ratio of the metal composition and polyvinyl pyrrolidone and its derivatives, so that the copper electrode slurry has the advantages of good dispersibility and high reduction rate, improves the process efficiency of subsequent copper electrode preparation, and makes it easier to obtain copper electrodes with uniform thickness.

[0098] The type of solvent is not specifically limited, as long as it can dissolve the metal composition, disperse the reducing agent, and the composite curing agent, and does not react with the solute components. In one example, the solvent can be selected from C1-C6 low-carbon alcohols, or other types of organic solvents can be selected in the art.

[0099] In one example, the low-carbon alcohol includes at least one of ethylene glycol, polyethylene glycol, pentanol, propanol, butanol and isobutanol.

[0100] In one example, the mass ratio of the metal composition to the solvent is (0.3-2):1, for example, 0.3:1, 0.34:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.86:1, or 2:1.

[0101] In a preferred embodiment, the mass ratio of the metal composition to the solvent is (1-1.6):1.

[0102] In one example, the mass ratio of the solvent to the dispersing reducing agent is (1.8-14):1, for example, it can be 1.8:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 13.6:1, 14:1.

[0103] In a preferred embodiment, the mass ratio of the solvent to the dispersing reducing agent is (2-5):1.

[0104] By limiting and optimizing the mass ratio of the metal composition and the solvent, as well as the mass ratio of the dispersing reducing agent and the solvent, the solid content of the copper electrode slurry can be controlled within an appropriate range, so that the copper electrode slurry contains more metal composition while having good dispersibility, which facilitates the coating of the copper electrode slurry and improves the thickness and uniformity of the prepared metal electrode.

[0105] In one example, the copper electrode slurry includes nano copper oxide, polyvinyl pyrrolidone, epoxy resin, latent amine curing agent, imidazole curing agent and ethylene glycol, wherein the proportion of each component is within the above-listed proportion range.

[0106] The present invention also provides a method for preparing a copper electrode slurry, which comprises the following steps:

[0107] (i) mixing the reducing dispersant and the solvent in the formulated amount in batches for multiple times to obtain a mixed solution under the combined action of heating, magnetic stirring and ultrasonic vibration;

[0108] (ii) adding the metal composition and the composite curing agent in the formulated amount to the mixed solution obtained in step (1) in batches for multiple times, and obtaining a copper electrode slurry under the combined action of heating, magnetic stirring and ultrasonic vibration.

[0109] The heating in steps (i) and (ii) can be performed in a water bath at 45-65° C. The number of batches is not limited and can be freely adjusted according to the different formulation contents.

[0110] The process conditions for heating, magnetic stirring and ultrasonic vibration in steps (i) and (ii) are not particularly limited and can be freely adjusted according to the amount and mixing state of the solution.

[0111] In one example, the metal electrode is a metal electrode in a solar cell, a secondary battery, a circuit board, a light emitting diode or a microelectronic device.

[0112] Preferably, the metal electrode is a metal electrode of a solar cell, for example, the metal electrode is a metal electrode (gate electrode) of a heterojunction cell.

[0113] The method for preparing a metal electrode of the present invention has a wider selection of substrates, and the substrate can be a semiconductor material and / or a conductor material. For example, the substrate can be at least one of single crystal silicon, polycrystalline silicon, ceramics, glass, flexible materials, metals and alloys. The method for preparing a metal electrode shown is particularly suitable for substrates that are not resistant to high temperatures, such as heterojunction battery substrates, and the processing temperature can be controlled below 200°C, reducing damage to the amorphous silicon layer.

[0114] The present invention also provides a method for preparing a solar cell grid line electrode, which uses the laser processing system described in the first aspect of the present invention and the copper electrode slurry described in the first aspect of the present invention to prepare a metal electrode, and particularly relates to a method for preparing a heterojunction solar cell grid line electrode.

[0115] In one example, referring to Figure 2 , Figure 3 and Figure 4 , the method for preparing a metal electrode for a solar cell comprises the following steps:

[0116] (1) placing a copper electrode slurry on the surface of a transparent conductive oxide film of a silicon substrate (e.g., a heterojunction battery substrate 30) to form a copper electrode slurry coating 32;

[0117] (2) starting the pulse laser and using the pulse laser 33 to perform a first laser scan on the copper electrode slurry coating 32 on the surface of the transparent conductive film in step (1);

[0118] (3) Start the continuous laser and use the continuous laser 33 to perform the 2nd to Nth (i.e., the 2nd to Nth) laser scans on the copper electrode slurry in step (2), N≧2; and finally obtain the metal electrode 31.

[0119] In one example, in step (1), the thickness of the copper electrode slurry coating can be controlled by selecting coater parameters. Exemplarily, the thickness of the copper electrode slurry can be set to 1 μm-40 μm.

[0120] In one example, in step (1), the copper electrode slurry is disposed on the surface of the transparent conductive film by coating, and then dried to obtain a dry copper electrode slurry coating. The drying method is not specifically limited, as long as the purpose of drying can be achieved. For example, a drying oven can be used for drying, the drying temperature can be 50°C-70°C, and the drying time can be 20-40 minutes.

[0121] In one example, in step (2), it is necessary to start the mobile work platform in advance to place the sample under the pulse laser scanning system, start the pulse laser, and the laser emitted by it passes through the attenuation plate, which can effectively reduce the output power, thereby controlling the power within the range that the object can bear; then pass through the aperture to adjust the aperture angle of the imaging beam; then pass through the half-wave plate to enter the first beam expander to expand and collimate the laser; the expanded and collimated laser beam passes through the first reflector and the second reflector to enter the first galvanometer; then pass through the first field mirror to focus on the surface of the sample to be processed, and use the first galvanometer to control the laser beam to perform laser selective metal patterning according to the set processing path to prepare copper electrodes. After the first laser scan is completed, turn off the pulse laser, start the mobile work platform, and move the sample to the bottom of the continuous laser scanning system.

[0122] In one example, the pulse laser has no limitation on the pulse width and wavelength, and the pulse width may be femtosecond laser, picosecond laser or continuous laser; and the wavelength may be 300nm-1100nm.

[0123] In one example, the processing parameters of the first laser scan are: laser pulse energy of 1nJ to 500nJ, laser scanning speed of 1mm / s to 500mm / s, defocus of +0mm to +2mm, laser pulse width of 100fs-20ps, frequency of 1KHz-70MHz, and laser wavelength of 300nm-1100nm.

[0124] In one example, in step (3), after the sample is moved to the bottom of the continuous laser scanning system, the continuous laser is turned on, and the emitted laser is expanded and collimated by the second beam expander, and then enters the second galvanometer through the third reflector and the fourth reflector. The second galvanometer is used to control the continuous laser, and the focused continuous laser beam is scanned for the 2nd to Nth time on the same path in step (2) through the second positioning sensor to achieve remelting and solidification of the copper circuit, thereby further improving the bonding strength between the copper electrode (i.e., the copper circuit) and the transparent conductive film.

[0125] The laser processing device used in the method for preparing a metal electrode provided by the present invention can achieve accurate alignment of two or more laser processing positions through a positioning sensor system and a CCD camera, thereby improving the accuracy of the metal electrode.

[0126] In one example, the processing parameters of the 2nd to Nth laser scans are: laser energy of 25nJ to 2000nJ, laser scanning speed of 1mm / s to 500mm / s, and defocus of +0mm to +2mm.

[0127] There is no limitation on the energy of the 2nd to Nth laser scans, and it can be less than, equal to, or greater than the energy of the first laser scan.

[0128] In the present invention, copper circuits with different porosities, different aspect ratios and complex structures can be obtained by changing the laser parameters and the thickness of the copper electrode slurry coating, and copper circuits with different patterns can be obtained by arbitrarily changing the laser processing path, which has flexible controllability.

[0129] In one example, when the energy of the 2-Nth laser scan is greater than the energy of the first laser scan, the copper electrode can be remelted and solidified by increasing the laser energy, so that the copper electrode and the transparent conductive film are connected with high quality, thereby improving the adhesion of the electrode to the surface of the transparent conductive film.

[0130] In one example, when the energy of the 2-Nth laser scan is less than or equal to the energy of the first laser scan, the laser energy can be accumulated by increasing the value of N and performing multiple scans. The copper electrode can also be remelted and solidified to achieve high-quality connection between the copper electrode and the transparent conductive film, thereby improving the adhesion of the electrode to the surface of the transparent conductive film.

[0131] In one example, the laser energy of the 2nd to Nth laser scan is higher than the laser energy of the first laser scan. Preferably, the energy of the 2nd to Nth laser scan is higher, and the preset metal electrode can be obtained by reducing the number of scans, saving processing procedures.

[0132] The inventors of the present invention have found that since laser selective metal patterning is a photochemical reaction, the required temperature is relatively low, and it is difficult to achieve effective connection between the copper electrode and the transparent conductive film, and the adhesion is poor. Usually, sintering is required to improve the bonding strength between the copper electrode and the silicon substrate. The present invention can achieve remelting and solidification of the copper electrode by increasing the laser energy for a small number of scans, or multiple scans with a low accumulated laser energy, to achieve high-quality connection between the copper electrode and the transparent oxide conductive film, so as to improve the adhesion. At the same time, due to the high controllability of the laser, only the copper electrode can be processed, and no sintering is required, thereby avoiding damage to the amorphous silicon layer by the sintering furnace.

[0133] In one embodiment, the method for preparing a solar cell further comprises step (4): rinsing with deionized water to remove the remaining copper electrode slurry coating in the laser unprocessed area to obtain a heterojunction solar cell copper electrode. The cleaning solution is not limited to the deionized water listed above, and other cleaning solutions may also be applicable to the present invention.

[0134] In one example, the method for preparing a metal electrode for a solar cell further includes a step of pre-cleaning a transparent conductive oxide film, wherein the transparent conductive oxide film is cleaned with a water-based cleaning agent before the copper electrode slurry is provided.

[0135] In one example, the water-based cleaning agent includes a nonionic surfactant, an anionic surfactant, a defoaming agent, and a phosphate detergent builder.

[0136] In one example, based on the total weight of the water-based cleaning agent, the content of the nonionic surfactant is 16-21% by weight, the content of the anionic surfactant is 1-3% by weight, the content of the defoaming agent is 1-3% by weight, and the content of the phosphate detergent builder is 1.5-6% by weight. The remaining components are water, and the sum of the components is the total weight of the water-based cleaning agent, which is calculated as 100%.

[0137] In one example, the nonionic surfactant as a main active agent may be selected from at least one of polyoxyethylene glycol lauryl alcohol ether (AEO-9), fatty alcohol polyoxyethylene ether (JFC-3) and alkylphenol polyoxyethylene ether (TX-10).

[0138] In one example, the compounded anionic surfactant can be selected from at least one of sodium dodecyl diphenyl ether disulfonate (2A1), isooctyl alcohol polyoxyethylene ether phosphate and fatty acid hydroxyethane sulfonate.

[0139] In one example, the defoamer can be alcohols, amides, phosphates, polyethers, etc. For example, the defoamer is ethylenediamine PO-EO block copolymer (ED 3060), and other defoamers include tributyl phosphate, distearyl ethylenediamine, polyoxyethylene polyoxypropylene block copolymer, etc.

[0140] In one example, the phosphate detergent builder may be at least one of sodium tripolyphosphate, anhydrous sodium metaphosphate and sodium pyrophosphate.

[0141] In one example, based on the total weight of the water-based cleaning agent, the content of 2A1 is 1-3 weight %, the content of AEO-9 is 15-18 weight %, the content of JFC-3 is 1-3 weight %, the content of ED 3060 is 1-3 weight %, the content of sodium tripolyphosphate is 1-5 weight %, the content of anhydrous sodium metaphosphate is 0.5-1 weight %, and the remaining components are water.

[0142] In the present invention, the main components of the above-mentioned water-based cleaning agent are surfactants, detergent aids and buffer solutions, etc. The above-mentioned water-based cleaning agent is used to degrease and clean the silicon substrate of the heterojunction battery. During the cleaning process, the organic matter adsorbed on the surface of the silicon substrate can be removed by relying on the emulsification and saponification effects of the surfactant, thereby achieving the purpose of increasing the surface wettability and improving the surface tension, making the surface of the heterojunction battery easy to accept the coating, and improving the adhesion of the copper electrode slurry.

[0143] The method for preparing solar cell grid line electrodes provided by the present invention uses laser to selectively metal pattern the copper electrode slurry coating, which can directly obtain a copper line with a large aspect ratio and low resistivity, and will not cause damage to the laser unprocessed area, thereby improving the conversion efficiency of the solar cell. The method does not require multiple operations to increase the electrode thickness, nor does it require mask patterning and subsequent corrosion processes, and the process is simple. The method of multiple laser scanning can effectively increase the adhesion of the copper electrode, and can achieve the purpose of high efficiency and low cost.

[0144] The method for preparing metal electrodes provided by the present invention can be applied to a variety of fields, such as: solar cells, secondary batteries, circuit boards, light-emitting diodes or microelectronic devices, and can also be batteries or instruments and equipment in other technical fields. As long as they contain metal electrodes prepared by the method of the present invention, they are within the protection scope of the present invention.

[0145] A third aspect of the present invention provides a photovoltaic cell, comprising a metal electrode, wherein the metal electrode is prepared by the method described in the second aspect of the present invention.

[0146] Exemplarily, the photovoltaic cell is a solar cell. The solar cell is a silicon solar cell, specifically a monocrystalline silicon solar cell, a polycrystalline silicon thin film solar cell, and an amorphous silicon thin film solar cell. Preferably, it is a heterojunction solar cell, and it can also be other types of solar cells. As long as the metal electrode of the solar cell is prepared by the copper electrode slurry provided by the present invention, or prepared by the method for preparing a metal electrode of the present invention, it is within the protection scope of the present invention.

[0147] In one example, the basic structure of a heterojunction battery mainly includes an n-type single crystal silicon wafer (c-Si), an intrinsic amorphous silicon thin film layer (ia-Si:H), a doped amorphous silicon film layer amorphous silicon thin film (pa-Si:H), a transparent conductive film (ITO) and a metal gate electrode.

[0148] In one embodiment, a method for preparing a heterojunction solar cell comprises the following steps:

[0149] (I) performing texturing and cleaning on an n-type single crystal silicon wafer, i.e. forming a texturing surface ("pyramid structure") on the surface of the silicon wafer;

[0150] (II) deposition of an amorphous silicon film, including deposition of an intrinsic amorphous silicon film and a doped amorphous silicon film, firstly depositing an intrinsic amorphous silicon film (ia-Si:H) and a p-type amorphous silicon film (pa-Si:H) on the front side of an n-type single crystal silicon wafer (c-Si), and then depositing an intrinsic amorphous silicon film (ia-Si:H) and an n-type amorphous silicon film (na-Si:H) on the back side of the silicon wafer to form a back surface field;

[0151] (III) Depositing transparent oxide conductive films on both sides of the cell.

[0152] In one example, in step (I), the texturing and cleaning can cause the incident light to be reflected and refracted multiple times on the surface of the single crystal silicon wafer, thereby extending the optical path, increasing the photogenerated carriers, and avoiding the recombination of carriers at the junction interface caused by defects and impurities introduced by uncleanliness.

[0153] In one example, in step (II), the amorphous silicon film is deposited by plasma enhanced chemical vapor deposition and hot wire chemical vapor deposition. Superior surface passivation ability is an important condition for obtaining higher cell efficiency. By utilizing the excellent passivation effect of amorphous silicon, the minority carrier lifetime of silicon wafers can be greatly improved.

[0154] In one example, in step (III), the deposition method of the transparent conductive film includes various physical vapor deposition (PVD), chemical vapor deposition (CVD), jet pyrolysis and sol-gel. Since amorphous silicon has poor conductivity, adding a transparent conductive film between the electrode and the amorphous silicon layer during the manufacturing process of heterojunction solar cells can effectively increase the collection of carriers, and can also play an anti-reflection role, and is a good window layer material.

[0155] In one example, the intrinsic amorphous silicon film (ia-Si:H) has a thickness of 0.1-10 nm.

[0156] In one example, the thickness of the p-type amorphous silicon film (pa-Si:H) is 0.1-10 nm.

[0157] In one example, the thickness of the n-type amorphous silicon film (na-Si:H) is 0.1-10 nm.

[0158] In one example, the thickness of the transparent conductive film (ITO) is 1-400 nm.

[0159] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0160] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0161] The present invention is described in detail below in conjunction with specific embodiments, which are used to understand but not to limit the present invention.

[0162] Preparation Example 1

[0163] A copper electrode slurry, the formula of which is as follows:

[0164] Metal composition: nano copper oxide (CuO NP) with a particle size of 30-50 nm, 10 parts by weight;

[0165] Dispersing reducing agent: polyvinyl pyrrolidone, 3.26 parts by weight;

[0166] Composite curing agent: bisphenol A epoxy resin epoxy equivalent 182-192g / eq, viscosity 11000-14000cps, 0.5 parts by weight; PN-23J, 0.1 parts by weight;

[0167] Solvent: ethylene glycol, 6.76 parts by weight;

[0168] The copper electrode slurry is prepared by the following method:

[0169] (1) mixing the polyvinyl pyrrolidone and ethylene glycol in the formulated amounts in batches for multiple times (e.g., 4-5 times) and obtaining a mixed solution under the combined action of heating in a water bath at 45-65° C., magnetic stirring and ultrasonic vibration;

[0170] (2) Adding the formulated amount of nano copper oxide particles, epoxy resin and PN-23J to the mixed solution obtained in step (1) in batches for multiple times (for example, 4-5 times), and obtaining a copper electrode slurry under the combined action of heating in a water bath at 45-65° C., magnetic stirring and ultrasonic vibration.

[0171] Preparation Example 2

[0172] The preparation was carried out in accordance with Preparation Example 1, except that the copper electrode slurry had the following formula:

[0173] Metal composition: nano cuprous oxide (Cu2O NP), 10 parts by weight;

[0174] Dispersing reducing agent: polyvinyl pyrrolidone, 4 parts by weight;

[0175] Composite curing agent: polyurethane modified epoxy resin, 0.54 parts by weight; MY-25, 0.13 parts by weight;

[0176] Solvent: ethylene glycol, 10 parts by weight.

[0177] Preparation Example 3

[0178] The preparation was carried out in accordance with Preparation Example 1, except that the copper electrode slurry had the following formula:

[0179] Metal composition: CuO NP, 5 parts by weight, Cu2O NP, 5 parts by weight;

[0180] Dispersing reducing agent: polyvinyl pyrrolidone, 1.67 parts by weight;

[0181] Composite curing agent: acrylic modified epoxy resin, 0.43 parts by weight; PN-23J, 0.07 parts by weight;

[0182] Solvent: ethylene glycol, 6.25 parts by weight.

[0183] Preparation Example 4

[0184] This group of preparation examples is used to illustrate the effect of adjusting the components and proportions in the composite curing agent on the performance of the copper electrode slurry.

[0185] Preparation Example 4-1 was prepared by referring to Preparation Example 1, except that the composite curing agent was: epoxy resin, 0.83 parts by weight; PN-23J, 0.17 parts by weight;

[0186] Preparation Example 4-2 was prepared by referring to Preparation Example 1, except that the composite curing agent was: epoxy resin, 0.3 parts by weight; PN-23J, 0.3 parts by weight;

[0187] Preparation Example 4-3 was carried out with reference to Preparation Example 1, except that the composite curing agent was: epoxy resin, 0.5 parts by weight; PN-23J, 0.05 parts by weight; and MY-25, 0.05 parts by weight.

[0188] Preparation Example D1

[0189] The preparation was carried out in accordance with Preparation Example 1, except that 0.6 parts by weight of epoxy resin was used as a curing agent.

[0190] Preparation Example D2

[0191] The preparation was carried out in accordance with Preparation Example 1, except that 0.6 parts by weight of PN-23J was used as a curing agent.

[0192] Example 1

[0193] A solar cell is obtained by the following preparation method:

[0194] (1) preparing a heterojunction battery substrate and depositing a transparent conductive film (ITO) on both sides of the substrate;

[0195] Specifically, the preparation of the heterojunction battery substrate includes the following steps: after texturing and cleaning the n-type monocrystalline silicon wafer, an intrinsic amorphous silicon film (ia-Si:H) and a p-type amorphous silicon film (pa-Si:H) are sequentially deposited on the front of the n-type monocrystalline silicon wafer (c-Si), and then an intrinsic amorphous silicon film (ia-Si:H) and an n-type amorphous silicon film (na-Si:H) are sequentially deposited on the back of the silicon wafer to form a back surface field; a transparent oxide conductive film is deposited on both sides of the battery. The texturing and cleaning, the deposition method of the intrinsic amorphous silicon film, and the deposition method of the transparent conductive film are as described above and will not be repeated here. The specific process parameters are carried out in accordance with the conventional operating methods in the field.

[0196] The thickness of the intrinsic amorphous silicon film (ia-Si:H) is 5 nm;

[0197] The thickness of the p-type amorphous silicon film (pa-Si:H) is 5 nm;

[0198] The thickness of the n-type amorphous silicon film (na-Si:H) is 5 nm;

[0199] The thickness of the transparent conductive film (ITO) is 100 nm.

[0200] (2) Using a water-based cleaning agent to clean the ITO surface of the heterojunction battery to remove impurities and grease on the ITO surface; wherein the total weight of the water-based cleaning agent is used as a reference, AEO-9 16 weight%, JFC-3 2 weight%, 2A1 content is 2 weight%, ED 3060 2 weight%, sodium tripolyphosphate 4 weight%, anhydrous sodium metaphosphate 0.8 weight%, and the remaining components are water.

[0201] (3) Using a four-sided coater, the copper electrode slurry provided in Preparation Example 1 is applied to the surface of the heterojunction battery ITO cleaned in step (2), and dried in a drying oven at 50° C.-70° C. for 20-40 min to obtain a dry copper electrode slurry coating with a coating thickness of 7 μm-15 μm.

[0202] (4) A laser processing system is used to perform laser selective metal patterning on the dried copper electrode slurry coating according to a designed path; the structural schematic diagram of the laser processing system is shown in FIG. Figure 1 As shown; the specific operation process of the laser processing system is as follows:

[0203] S1: Start the mobile work platform in advance, place the sample obtained in step (3) under the pulse laser scanning system, start the pulse laser, and the laser emitted by it passes through the attenuation plate, which can effectively reduce the output power; then passes through the aperture to adjust the aperture angle of the imaging beam; then passes through the half-wave plate to enter the first beam expander to expand and collimate the laser; the expanded and collimated laser beam passes through the first reflector and the second reflector to enter the first galvanometer; then passes through the first field mirror to focus on the surface of the sample to be processed, and uses the first galvanometer to control the laser beam to perform laser selective metal patterning to prepare copper electrodes according to the set processing path. After the first laser scan is completed, turn off the pulse laser and the first galvanometer, start the mobile work platform (such as a two-dimensional work platform), and move the sample to the bottom of the continuous laser scanning system.

[0204] The processing parameters of pulse laser scanning are: laser pulse energy of 79 nJ, laser scanning speed of 6 mm / s, defocus of +0.6 mm, number of laser scans of 1, laser pulse width of 9 ps, repetition frequency of 2 MHz, and laser wavelength of 532 nm.

[0205] S2: After the sample is moved to the bottom of the continuous laser scanning system, the continuous laser is turned on. The emitted laser is expanded and collimated by the second beam expander, and then enters the second galvanometer through the third reflector and the fourth reflector. The second galvanometer is used to control the continuous laser. Through the second positioning sensor, the focused continuous laser beam is scanned for the second time on the same path in step (3) to achieve remelting and solidification of the copper circuit, thereby further improving the bonding strength between the copper electrode (i.e., the copper circuit) and the transparent conductive film.

[0206] The processing parameters of continuous laser scanning are: laser energy is 500 nJ, laser scanning speed is 6 mm / s, defocus amount is +0.6 mm, and the number of laser scanning is 1.

[0207] (5) Rinse with deionized water to remove the remaining copper electrode slurry coating in the unprocessed area to obtain a heterojunction solar cell copper electrode.

[0208] The three-dimensional morphology of the Cu gate line obtained in this embodiment is shown in the schematic diagram of the structure. Figure 5 As shown, the metallographic diagram is as follows Figure 6 As shown in (b), a copper electrode with a uniform and fine surface and a line width of about 40 μm can be directly prepared by laser selective metal patterning. It should be noted that the copper electrode line width prepared by this laser processing system can be as small as 16 μm, but the improvement of resolution will lead to a decrease in resistivity, and the minimum width of the prepared copper electrode is related to the laser spot diameter. Changing the laser equipment can obtain a lower line width.

[0209] The surface of the copper electrode was observed using a field emission scanning electron microscope, and the elemental composition of the copper circuit was analyzed using EDS, such as Figure 7 As shown, it is found that the copper circuit structure obtained in this example is dense and can obtain a lower porosity; through X-ray energy spectrum analysis of element composition, the Cu:O of the copper electrode obtained in this example is increased from 1.8:1 before processing (copper electrode slurry) to 23.2:1, and the Cu / O content is greatly improved, reflecting that the Cu element is fully reduced at this time.

[0210] Example 2

[0211] The process was carried out in accordance with Example 1, except that the processing parameters of the pulsed laser scanning were: laser pulse energy of 100 nJ, laser scanning speed of 6 mm / s, defocus of +0.4 mm, laser scanning times of 1, laser pulse width of 9 ps, repetition frequency of 2 MHz, and laser wavelength of 532 nm. The obtained copper circuit metallographic image is shown in FIG. Figure 6 As shown in (c), the metallographic diagram of the prepared Cu circuit is tested by the same method as in Example 1, and it is found that a copper electrode with good surface morphology, low porosity and dense structure can be obtained.

[0212] Example 3

[0213] The process was carried out in accordance with Example 1, except that the processing parameters of the pulsed laser scanning were: laser pulse energy of 100 nJ, laser scanning speed of 5 mm / s, defocus of +0.6 mm, number of laser scans of 1, laser pulse width of 9 ps, repetition frequency of 2 MHz, and laser wavelength of 532 nm. The metallographic image of the copper circuit obtained is shown in FIG. Figure 8 As shown in (b), the prepared Cu circuit is tested by the same method as in Example 1. It is found that a copper electrode with good surface morphology, low porosity and dense structure can be obtained.

[0214] Example 4

[0215] The process was carried out in accordance with Example 1, except that the processing parameters of the pulsed laser scanning were: laser pulse energy of 100 nJ, laser scanning speed of 8 mm / s, defocus of +0.6 mm, laser scanning times of 1, laser pulse width of 9 ps, repetition frequency of 2 MHz, and laser wavelength of 532 nm. The obtained copper circuit metallographic image is shown in FIG. Figure 8 As shown in (c), the metallographic image of the prepared Cu circuit was tested by the same method as in Example 1. It was found that due to the increase in scanning speed and the reduction reaction time, the continuity of the copper electrode obtained in this example was poor, but the overall morphology was complete.

[0216] Example 5

[0217] The process was carried out in accordance with Example 1, except that the processing parameters of the pulsed laser scanning were: laser pulse energy of 79 nJ, laser scanning speed of 6 mm / s, defocus of +0.5 mm, laser scanning times of 1, laser pulse width of 9 ps, repetition frequency of 2 MHz, and laser wavelength of 532 nm. The obtained copper circuit metallographic image is shown in FIG. Fig. 9 As shown in (b), the prepared Cu circuit is tested by the same method as in Example 1. It is found that a copper electrode with good surface morphology, low porosity and dense structure can be obtained.

[0218] Example 6

[0219] The process was carried out in accordance with Example 1, except that the processing parameters of the pulsed laser scanning were: laser pulse energy of 79 nJ, laser scanning speed of 6 mm / s, defocus of +0.8 mm, laser scanning times of 1, laser pulse width of 9 ps, repetition frequency of 2 MHz, and laser wavelength of 532 nm. The obtained copper circuit metallographic image is shown in FIG. Fig. 9 As shown in (c), the metallographic image of the prepared Cu circuit was tested by the same method as in Example 1. It was found that due to the increase in defocus, the laser energy density decreased. Although there were a few defects in the morphology of the Cu circuit obtained in this example, the overall morphology was complete.

[0220] Example 7

[0221] The process was carried out in accordance with Example 1, except that the processing parameters of the continuous laser scanning were: laser energy of 500 nJ, laser scanning speed of 4 mm / s, defocusing amount of +0.8 mm, and laser scanning number of 1. The obtained copper circuit metallographic image is shown in FIG. Fig.10 As shown, the prepared Cu circuit is tested by the same method as in Example 1. It is found that the present embodiment can obtain a copper electrode with good surface morphology, low porosity and dense structure.

[0222] Examples 8-12

[0223] Examples 8-12 were carried out with reference to Example 1, except that in step (4) of Examples 8-12, the copper electrode slurries prepared by Preparation Example 2, Preparation Example 3, Preparation Example 4-1, Preparation Example 4-2 and Preparation Example 4-3 were used respectively.

[0224] Embodiment 13

[0225] The process is carried out in accordance with Example 1, except that after the laser scanning in step (5) is completed, 50 laser scans are further performed, and the processing parameters of the 2nd to 50th laser scans are: laser pulse energy of 35nJ, laser scanning speed of 6mm / s, defocus of +0.6mm, laser pulse width of 9ps, repetition frequency of 2MHz, and laser wavelength of 532nm.

[0226] Comparative Example 1

[0227] This comparative example is the same as Example 1, except that the laser parameters used in the pulse laser processing are: laser pulse energy of 35nJ, laser scanning speed of 6mm / s, defocus of +0.6mm, laser scanning number of 1, laser pulse width of 9ps, repetition frequency of 2MHz, and laser wavelength of 532nm. The metallographic image of the copper circuit obtained is as follows: Figure 6 As shown in (a), it can be found that the lower energy is not enough to completely reduce CuO to Cu, and the resulting copper circuit morphology is poor.

[0228] Comparative Example 2

[0229] This comparative example is the same as Example 1, except that the laser parameters used in the pulse laser processing are: laser pulse energy of 100nJ, laser scanning speed of 2mm / s, defocus of +0.6mm, laser scanning number of 1, laser pulse width of 9ps, repetition frequency of 2MHz, and laser wavelength of 532nm. The obtained copper circuit metallographic image is as follows: Figure 8 As shown in (a), the metallographic image of the prepared Cu circuit was tested by the same method as in Example 1. It was found that the copper circuit obtained in this example was severely oxidized due to the slow scanning speed.

[0230] Comparative Example 3

[0231] This comparative example is the same as Example 1, except that the laser parameters used in the pulse laser processing are: laser pulse energy of 79nJ, laser scanning speed of 6mm / s, defocus of +0.2mm, laser scanning number of 1, laser pulse width of 9ps, repetition frequency of 2MHz, and laser wavelength of 532nm. The obtained copper circuit metallographic image is as follows Fig. 9 As shown in (a), the prepared Cu circuit was tested by the same method as in Example 1. It was found that due to the small spot diameter and the excessive laser energy density, the CuO nano-coating was ablated and a good copper circuit could not be restored.

[0232] Comparative Example 4

[0233] This comparative example is the same as Example 1, except that the continuous laser scanning parameters are: laser energy of 800nJ, laser scanning speed of 6mm / s, defocusing amount of +0.6mm, and laser scanning number of 1. The metallographic image of the prepared Cu circuit was tested in the same way as in Example 1, and it was found that due to excessive energy, the copper electrode was ablated and gasified, and a good copper circuit could not be obtained.

[0234] Comparative Examples 5-6

[0235] The process was carried out with reference to Example 1, except that in step (3) of Comparative Examples 5 and 6, the copper electrode slurries prepared in Preparation Example D1 and Preparation Example D2 were used respectively.

[0236] Test Case

[0237] (1) For the solar cells obtained in the above Examples 1-13 and Comparative Examples 1-6, the resistivity of the metal electrodes was measured using a four-probe method. The results are recorded in Table 1.

[0238] (2) For the above-mentioned embodiments 1-13 and comparative examples 1-6, solar cells were obtained, and the binding strength of the metal electrodes was tested by the Hundred Grids method, wherein the test results were divided into six levels: 0B, 1B, 2B, 3B, 4B, and 5B, 0B-5B representing a greater binding strength, that is, 5B has the strongest binding strength. The results are recorded in Table 1.

[0239] Table 1

[0240]

[0241]

[0242] It can be seen from the experimental data in Table 1 that the method of preparing heterojunction solar cell copper electrodes by laser selective metal patterning, combined with the copper electrode slurry provided by the present invention, can obtain gate line electrodes with low resistivity and high bonding strength, and the laser multiple scanning method can effectively increase the bonding strength of the copper electrode.

[0243] In addition, it can be seen from the above experimental data that changing the total content of the composite curing agent will change the resistivity and adhesion. A high content of the composite curing agent will lead to an increase in the resistivity, and a low content of the composite curing agent will affect the adhesion. The internal ratio of the composite curing agent affects the curing effect, that is, the bonding force, and has little effect on the resistivity. The structure mainly affects the bonding force and has little effect on the resistivity. Combined with multiple laser processing, the resistivity can be reduced and the adhesion can be improved.

[0244] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A laser processing system, characterized in that: For preparing metal electrodes of solar cells, the laser processing system comprises: a mobile working platform, a first optical path system and a second optical path system; The mobile working platform is used to carry the substrate of the metal electrode to be prepared; The first optical path system includes a pulse laser and a first optical path adjustment system, wherein the pulse laser is used to emit a pulse laser, and the pulse laser acts on the substrate of the metal electrode to be prepared after passing through the first optical path adjustment system; The second optical path system includes a continuous laser and a second optical path adjustment system. The continuous laser is used to emit continuous laser light. The continuous laser light acts on the substrate of the metal electrode to be prepared after passing through the second optical path adjustment system.

2. The laser processing system according to claim 1, wherein: The first optical path adjustment system comprises a first optical element group, a first beam expander, a first reflector group, a first galvanometer and a first field mirror, which are arranged in sequence, wherein the first optical element group is close to the pulse laser, the first field mirror is close to the mobile working platform, and the first optical element group is used to adjust at least one of the power of the pulse laser, the aperture angle of the light beam and the polarization of the polarized light; Preferably, the first optical element group comprises an attenuation plate, an aperture and a wave plate which are arranged in sequence, wherein the attenuation plate is close to the pulse laser, and the wave plate is close to the first beam expander; Preferably, the first reflector group includes a first reflector and a second reflector, the first reflector is close to the first beam expander and is arranged at a first preset angle to the first beam expander, and the second reflector is arranged parallel to the first reflector and is close to the first galvanometer.

3. The laser processing system according to claim 2, wherein: The second optical path adjustment system comprises a second beam expander, a second reflector group, a second galvanometer and a second field mirror which are arranged in sequence, wherein the second beam expander is close to the continuous laser, and the second field mirror is close to the mobile working platform; Preferably, the second reflector group includes a third reflector and a fourth reflector, wherein the third reflector is close to the second beam expander and is arranged at a second preset angle with the second beam expander, and the fourth reflector is arranged parallel to the third reflector and is close to the second galvanometer.

4. The laser processing system according to claim 3, wherein: Also included is a first monitoring device, which is coaxially arranged with the first galvanometer and is used to monitor the processing process of the first optical path system; Preferably, the laser processing system further comprises a first positioning sensor, which is arranged on the first galvanometer and is used to determine the position of the first galvanometer; Preferably, the laser processing system further comprises a second monitoring device, which is coaxially arranged with the second galvanometer and is used to monitor the processing process of the second optical path system; Preferably, the laser processing system further comprises a second positioning sensor, which is arranged on the second galvanometer and is used to determine the position of the second galvanometer.

5. A method for preparing a metal electrode, characterized in that: The metal electrode is prepared by using the laser processing system and copper electrode slurry described in any one of claims 1 to 4.

6. The method according to claim 5, wherein: The copper electrode slurry comprises a metal composition, a dispersing reducing agent, a composite curing agent and optionally a solvent; the metal composition comprises at least copper powder, and optionally gold powder and / or silver powder; the composite curing agent comprises a thermosetting resin and a latent curing agent; And / or, the metal electrode is a metal electrode in a solar cell, a secondary battery, a circuit board, a light emitting diode or a microelectronic device; preferably, it is a metal electrode of a solar cell.

7. The method according to claim 5 or 6, wherein: The thermosetting resin is selected from at least one of epoxy resin, polyurethane-modified epoxy resin, acrylic-modified epoxy resin, polyamide resin, polyurethane resin and acrylic resin; And / or, the latent curing agent includes a latent amine curing agent and / or an imidazole curing agent; And / or, the reducing dispersant is selected from at least one of polyvinyl pyrrolidone and its derivatives; And / or, the solvent is selected from C1-C6 low-carbon alcohols; And / or, the metal composition includes nano copper oxide and / or nano cuprous oxide.

8. The method according to claim 5 or 6, wherein: The mass ratio of the metal composition to the composite curing agent is (7-30):1; And / or, the mass ratio of the thermosetting resin to the latent curing agent is (4-6):1; And / or, the mass ratio of the metal composition to the composite curing agent is (15-20): 1 And / or, the mass ratio of the metal composition to the dispersing reducing agent is (2-9):1, preferably (2.5-6):

1.

9. The method according to claim 6, wherein: The method for preparing a metal electrode for a solar cell comprises the following steps: (1) placing a copper electrode slurry on the surface of a transparent conductive oxide film on a silicon substrate; (2) starting a pulse laser to perform a first laser scan on the copper electrode slurry coating on the surface of the transparent conductive film in step (1); (3) starting the continuous laser to perform the Nth laser scan on the copper electrode slurry in step (2), where N≧2; Preferably, the laser energy of the Nth laser scan is higher than the laser energy of the first laser scan.

10. A photovoltaic cell comprising a metal electrode, characterized in that: The metal electrode is prepared by the method according to any one of claims 5 to 9.

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