Method for fabricating narrow line structures on the top surface of a target layer of a layer stack and its applications

Abstract

This application discloses a method for fabricating a narrow linear structure on the upper surface of a target layer of a layer stack, and its applications. The method for fabricating the linear structure includes the steps of: obtaining preset positions, designated as first and second lateral positions, on both sides of the linear structure on the upper surface of the target layer; generating a plurality of protrusions spaced apart along a lateral longitudinal direction at at least one of the first and second lateral positions on the upper surface of the target layer to form a protruding line at at least one lateral position; and applying and depositing a liquid linear structure material on one side of the protruding line to obtain a linear structure enclosed on one side of the protruding line.

Description

[Technical Field]

[0001] The present application relates to the field of thin film solar cell technology, and in particular to a method for fabricating narrow line structures on the top surface of a target layer of a layer stack and its applications. [Background technology]

[0002] Thin-film solar cells have a multi-layer structure. As is well known to those skilled in the art, the layer structure of a thin-film solar cell is composed of at least a substrate, a back electrode layer, an absorber layer, a buffer layer, and a front electrode layer, in order from bottom to top, in a substrate configuration, and is reversed in a superstrate configuration, but composed of the same layers. For large-area thin-film solar cells, to avoid high series resistance and subsequent high current loss, the module is usually designed as a series of monolithically interconnected cells. To achieve the division and series connection, P1, P2, and P3 lines are respectively arranged on the back electrode layer, absorber layer, buffer layer, and front electrode layer (as shown in Figure 1). Specifically, the fabrication method of a thin-film solar cell is as follows: providing a substrate; depositing a back electrode layer on one side of the substrate; subdividing the back electrode layer with P1 lines; depositing an absorber layer and a buffer layer, in that order, on the back electrode layer; simultaneously subdividing the absorber layer and the buffer layer along P2 lines; depositing a front electrode layer on the buffer layer; and subdividing the front electrode layer with P3 lines.

[0003] P1 and P3 insulate the back and front electrodes, and P2 serves as an electrical contact between the back and front electrodes, connecting two adjacent cells in series. Because the P1 / P2 / P3 structural area does not generate electricity, it is usually referred to as the "dead area" of the solar cell (as shown in Figures 1 and 3). The remaining area is referred to as the active area of ​​the solar cell.

[0004] In order to optimize the power conversion efficiency and application performance of a solar cell, it may be preferable to add a linear structure on the top surface of one layer. Considering that the width, thickness, and coverage area of ​​the linear structure on the surface of the layer affect the electrical and optical properties of the solar cell, it is necessary to limit the positions of both sides of the linear structure, the thickness of the linear structure, and other parameters. The purpose of this application is to provide a method for fabricating a linear structure, which can easily control and limit the positions of the sides of the linear structure, the thickness of the linear structure, and other parameters.

[0005] To optimize the power conversion efficiency of solar cells, it is common to increase the transmittance of the front electrode by, for example, reducing the thickness of the front electrode layer and thereby increasing the photocurrent generated. However, this increases the sheet resistance of the front electrode, thereby increasing conduction losses. To reduce this conduction loss in the front electrode layer, highly conductive narrow metal gridlines can be applied to the front electrode layer to improve the associated electrical conductivity, which is referred to as a metallization process for photovoltaic production. Thus, as shown in Figures 3, 4, and 5, metal gridlines G1 are applied at periodic intervals either laterally to the cell or perpendicularly to P1 / P2 / P3. These gridlines G1 are applied continuously across the solar cell. P3 interrupts the gridlines G1 to prevent short circuits between the front electrode of one cell and its adjacent cell.

[0006] As shown in Figure 6, for monolithically interconnected cells, the current collected by the metal grid lines G1 and flowing toward the edge of the cell is directly connected to the back electrode of the next cell via the P2 lines. The metal grid lines G1 reduce the conduction loss due to the thinned front electrode, thereby offsetting the increase in series resistance. However, they also cause an increase in dead area due to shadows cast by the opaque metal grid lines.

[0007] The shadow area of ​​the underlying absorber layer is determined by the width and length of the metal grid lines G1. Furthermore, while the length of the metal grid lines G1 should not be changed due to the beneficial effect of carrier collection in the metal grid lines and thinner front electrodes (increasing photocurrent without increasing series resistance), the width and thickness of the metal grid lines G1 can be optimized to reduce the shadow area to improve the photocurrent and efficiency of the solar cell. The relationship between the thickness and width of the metal grid lines G1 is called the aspect ratio. The series resistance of the metal grid lines G1 is determined by the specific series resistance and cross-sectional area of ​​the material. Therefore, to improve the efficiency of the solar cell, the width of the metal grid lines G1 must be reduced to reduce light shading and the thickness of the metal grid lines G1 must be increased to prevent conduction losses. Generally speaking, the purpose of using the metal grid lines G1 is to reduce the shadow cast by the metal grid lines G1 and keep the series resistance low by applying lines with a minimum width and sufficient thickness to increase the generated photocurrent and improve the efficiency of the solar cell.

[0008] As shown in Figure 6, for monolithically interconnected cells, current must be collected on the metal gridlines toward the end of a cell and evenly distributed at the beginning of the next cell. Otherwise, the front and back electrodes will cause additional conduction losses. Therefore, additional metal gridlines G2 can be used in the dead areas. As shown in Figures 14 and 15, the metal gridlines G2 are perpendicular to the metal gridlines G1 and deposited directly on or parallel to the P2 structure lines. The purpose of applying G2 is to evenly distribute the current and reduce electrical losses along the P2 interconnect between two adjacent cells caused by the high current collection of the G1 metal gridlines and their point connections to P2, as shown in Figures 16 and 17. Because G2 is located in the dead area, it does not cause additional optical loss due to shadowing. Furthermore, this can improve photocurrent generation by reflecting light from the gridlines G2 back to the cladding layer / front glass and further incident on the absorber layer.

[0009] Therefore, precise electrical and optical management of the dead zone requires accurate deposition of the G2 line. Furthermore, if G2 is deposited on the edges of the P1 and P3 lines, it can cause current shunting in the active cell area. Furthermore, mechanical scribing of the P3 pattern line can mechanically tear the G2 line, or masking the area designated for the laser P3 line can cause the P3 line to become discontinuous, which can lead to current shunting. Generally speaking, it is very important to ensure that the G2 line is contained within the boundaries of the P2 pattern line. A G2 that is significantly wider than P2 will increase the dead zone.

[0010] Furthermore, in the prior art, a method for fabricating metal grids, such as ALD (Aluminum Line Deposit) proposed by Solibro, combines thermal evaporation and a mask to deposit an aluminum wire structure. The resulting structure is shown in FIG. 7. This method has several drawbacks: 1) low throughput and yield due to the use of a mask; 2) high cost of this special mask for the production of large-area modules; 3) high material waste due to evaporation; 4) high workload of mask maintenance, which is crucial for the efficiency of solar cells; and 5) limited width (and aspect ratio) of the metal grid lines (mask openings that are too narrow, less than a few hundred micrometers, are prone to clogging during or after use).

[0011] For example, Nice Solar employs screen printing to deposit metal gridlines. For large-area printing, screen printing has significant technical limitations and is therefore unsuitable for use. Large printing patterns can result in poor deposition accuracy and poor line shape (wider lines), especially in the central region of large print areas (>1 m²). This is due to the low rigidity (bending) of large screens. Furthermore, printing narrow lines using screen printing requires high-quality screens, such as hardened and calendered stainless steel screens or knotless screens. For full-size thin-film solar cell modules (e.g., >1 m²), these high-quality, large screens are very difficult to manufacture (fewer than two suppliers worldwide can manufacture them) and are very expensive. Furthermore, the screens used in the screen printing process are prone to clogging and difficult to clean. In addition to the high cost of screen printing for large thin-film modules, changing the gridline printing pattern is also very inflexible when the line pitch needs to be adjusted during the production process.

[0012] Other process methods for producing metal grids, such as aerosol jet printing or dispensing, are new technologies for metallization processes, but still suffer from serious process stability issues. The nozzles used in aerosol jet printing or dispensing are prone to clogging by metal particles during long-term printing, which can cause frequent process downtime. Furthermore, these two methods can simultaneously print a maximum of 5–10 grid lines. Printing on large-area thin-film modules requires multiple printing runs. Currently, the throughput of aerosol jet printing is very low due to the significant difficulty of dispensing the paste / aerosol along the horizontal direction within the print head, making it extremely difficult to further increase the number of nozzles used for dispensing or aerosol jetting. Currently, 10 nozzles is essentially the bottleneck for these two technologies.

[0013] Other processes for fabricating metal grids, such as inkjet printing, involve printing a solvent-based ink or paste onto the surface of the front electrode layer to form metal grid lines. Inkjet printing is a digital printing technique (e.g., PCT / CN2022 / 074345), making it suitable for a variety of line shapes or morphologies. This makes it suitable for large-scale applications, particularly in thin-film photovoltaics. One of the main drawbacks of this technique is that the ink composition contains a small amount of metal particles and a large amount of solvent. This typically results in wide, thin lines on top of the solar cell's front electrode. Furthermore, due to the coffee ring effect, as shown in Figure 8, the edges of the jetted ink lines are thicker than the center of the lines.

[0014] In the prior art, solvent-based inks or pastes are commonly used to form metal gridlines on the surface of the front electrode of solar cells. The width of the metal gridlines is highly dependent on the surface tension and wettability of the ink or paste, which significantly limits the use of the material as a front electrode and / or the surface preparation and / or treatment for optimal aspect ratios. Furthermore, the metal gridlines require heating to remove the solvent and improve conductivity, which can lead to changes in the wiring shape after deposition. Solvent-based inks or pastes consist of a certain ratio of metal and solvent. While simply reducing the solvent-to-metal ratio (reforming) can reduce the line width, this method can lead to clogging of the print head or screen. Alternatively, the line width can be reduced by using less material (smaller droplets), but this method also leads to thinning of the metal gridlines, thereby increasing series resistance. To overcome this problem, a multi-coating solution is typically used to keep the line width small and increase the thickness of the metal lines. However, especially at the high speeds used for high throughput in mass production, this method presents a significant drawback, since the alignment of the generated lines is extremely important and variations in the generated lines occur. Summary of the Invention [Problem to be solved by the invention]

[0015] In view of the problems existing in the prior art, the present application provides a method for fabricating a narrow linear structure on the upper surface of a target layer of a layer stack, and its applications. A plurality of protrusions are formed on the side of the linear structure to form a protruding line. The protruding line can be used to restrict the lateral position of the linear structure so that the linear structure can be enclosed on one or both sides. Therefore, when the linear structure is enclosed on both sides, the width, thickness, and position of the linear structure can be restricted, thereby realizing control and optimization of the shape of the linear structure. Alternatively, when the linear structure is enclosed on one side, the position of the linear structure can be restricted, thereby preventing the linear structure from blocking some areas or target areas of the underlying film layer. The technical solutions of the present application are as follows: [Means for solving the problem]

[0016] In a first aspect, a method for fabricating narrow linear structures on a top surface of a target layer of a layer stack including at least two layers is provided, the method being applicable to a process for fabricating a thin film photovoltaic module. acquiring preset positions, which are first and second lateral positions, on both sides of the linear structure on the upper surface of the target layer; forming a protruding line at at least one lateral position by generating a plurality of protrusions spaced apart along a lateral longitudinal direction at at least one of the first lateral position and the second lateral position on the upper surface of the target layer; and applying and depositing a liquid linear structure material on one side of the protruding lines to obtain linear structures that are confined on one side by the protruding lines.

[0017] In some embodiments, the method for making a linear structure comprises: When a plurality of protrusions are formed at intervals along the lateral longitudinal direction at the first lateral position and the second lateral position on the upper surface of the target layer to form a first protruding line and a second protruding line, applying and depositing a liquid linear structure material between the first protruding line and the second protruding line to obtain a linear structure enclosed between the first protruding line and the second protruding line, i.e., a linear structure enclosed on both sides; or When a plurality of protrusions are formed at intervals along the lateral longitudinal direction to form a third protruding line at one of the first and second lateral positions on the upper surface of the target layer, a step of applying and depositing a liquid linear structure material on one side of the third protruding line to obtain a linear structure confined on the one side of the third protruding line is included.

[0018] In some embodiments, the spacing between two adjacent protrusions on the same protrusion line is small enough to prevent the linear structure material from spilling over from one side of the protrusion line to the other side of the protrusion line during deposition.

[0019] In some embodiments, the spacing between two adjacent protrusions on the same protrusion line is less than 10 micrometers.

[0020] In some embodiments, when the linear structure is enclosed on both sides, the protrusion of the first protruding line and the protrusion of the second protruding line are asymmetric along a center line between the first protruding line and the second protruding line.

[0021] In some embodiments, when the linear structure is enclosed on both sides, the protrusions of the first protruding line and the protrusions of the second protruding line are symmetrical along a center line between the first protruding line and the second protruding line.

[0022] In some embodiments, the spacing between two adjacent protrusions on the same protrusion line is uniform.

[0023] In some embodiments, the spacing between two adjacent protrusions on the same protrusion line is non-uniform.

[0024] In some embodiments, the height of the protrusions is large enough to prevent the material for forming the linear structures from spilling out of the protrusions during the formation of the linear structures.

[0025] In some embodiments, the height of the protrusions is determined based on characteristic parameters of the material used to form the linear structures.

[0026] In some embodiments, the characteristic parameters of the material for forming the linear structures must be properly selected, including at least the amount, viscosity, and surface tension of the material.

[0027] In some embodiments, the height of the protrusions is greater than 100 nanometers.

[0028] In some embodiments, the method for generating the protrusion includes irradiating a pulsed laser from above the target layer, irradiating the upper surface of the target layer with the pulsed laser to satisfy preset process parameters, so that the pulsed laser passes through the target layer and reaches an interface between two adjacent layers among a plurality of layers below the target layer, thereby melting and vaporizing a portion of the layer material at the interface between the two adjacent layers to form an upward protrusion.

[0029] In some embodiments, the preset process parameters of the pulsed laser satisfy a condition that the wavelength of the pulsed laser is greater than the optical bandgap of the target layer but less than the optical bandgap of at least one layer of the plurality of layers below the target layer.

[0030] In some embodiments, among the preset process parameters of the pulsed laser, a laser power of the pulsed laser is determined based on a thickness of the target layer and characteristic parameters of a material of the target layer.

[0031] In some embodiments, the characteristic parameters of the target layer material include at least the hardness, stiffness, tensile strength and adhesion of the front electrode layer material.

[0032] In some embodiments, the application method of the liquid linear structure material includes, but is not limited to, inkjet printing, aerosol jetting, screen printing, and dispensing.

[0033] In a second aspect, applications of the method for producing linear structures are provided, including applications in single-pass and / or multi-pass application of liquid-type linear structure materials.

[0034] In a third aspect, based on the method for fabricating linear structures, a method for fabricating metal grid lines based on the improved surface structure of a front electrode is provided, wherein the target layer is a front electrode layer, the plurality of layers below the target layer include a buffer layer, an absorber layer, a back electrode layer, and a substrate, and the linear structures are composed of metal grid lines located on an upper surface of the front electrode layer.

[0035] In some embodiments, the metal grid lines include metal grid lines G1 that are perpendicular to the P1, P2, and P3 lines, and metal grid lines G2 that are parallel to and above the P2 lines.

[0036] In some embodiments, the method for fabricating the metal gridlines G1 includes: a step G1(1) of obtaining preset positions on the surface of the front electrode on both sides of the metal grid lines G1, the preset positions being a first lateral preset position and a second lateral preset position; a step G1(2) of generating a plurality of protrusions spaced apart along a lateral longitudinal direction at the first lateral preset position and the second lateral preset position, respectively, to form a first protruding line and a second protruding line; and step G1(3) of applying and depositing a liquid metal grid line material between the first protruding lines and the second protruding lines, thereby obtaining the metal grid lines G1 enclosed between the first protruding lines and the second protruding lines; The method for producing the metal grid lines G2 includes: a step G2(1) of acquiring a position on the surface of the front electrode, the position being a third lateral position of the P2 line closer to the P3 line; a step G2(2) of generating a plurality of protrusions at intervals along the lateral longitudinal direction at the third lateral position to form a third protruding line; and step G2(3) of applying and depositing a liquid metal grid line material within the P2 lines to obtain the metal grid lines G2 whose sides closer to the P3 lines are enclosed by the third protruding lines.

[0037] In some embodiments, the material of the metal gridlines includes, but is not limited to, metallic inks and dielectric inks.

[0038] In a fourth aspect, based on the method for fabricating metal gridlines, there is provided a method for optimizing the aspect ratio of the metal gridlines based on the improved surface structure of the front electrode, the method comprising controlling the deposition width and thickness of the metal gridlines by controlling the distance between the first protruding lines and the second protruding lines, the height of the protrusions, and the amount of metal gridline material, thereby controlling and optimizing the aspect ratio of the metal gridlines.

[0039] In a fifth aspect, there is provided a method of fabricating a thin film solar cell based on a method of fabricating metal gridlines, said method comprising: forming a substrate, a back electrode layer, an absorber layer, a buffer layer and a front electrode layer of a thin film solar cell in sequence, or forming a substrate, a front electrode layer, a buffer layer, an absorber layer and a back electrode layer of a thin film solar cell in sequence; after forming the back electrode layer, disposing a P1 line on the back electrode layer, after forming the buffer layer, disposing a P2 line on the absorber layer and the buffer layer, after forming the front electrode layer, disposing a P3 line on the front electrode layer, and using the P1 line, the P2 line, and the P3 line to partition and series connect the large area thin-film solar cells; forming metal grid lines G1 and metal grid lines G2 on the surface of the front electrode layer farther from the buffer layer based on a method for fabricating metal grid lines, respectively. [Brief explanation of the drawings]

[0040] [Figure 1] FIG. 1 is a schematic cross-sectional view of a thin-film solar cell. [Figure 2] 1 is a schematic diagram of the cell width, active area, and dead area of ​​a thin-film solar cell. [Figure 3] FIG. 1 is a schematic cross-sectional view of a thin-film solar cell having metal gridlines G1. [Figure 4] FIG. 1 is a schematic diagram of the grid width and grid pitch of a thin-film solar cell having metal grid lines G1. [Figure 5] FIG. 1 is a plan view of three interconnected cells comprising a thin-film photovoltaic module with metal gridlines G1. [Figure 6] FIG. 1 is a schematic diagram of the direction of current flow in the metal grid lines G1. [Figure 7] FIG. 1 is a schematic diagram of a grid deposition process on a substrate using thermal evaporation and a mask. [Figure 8] FIG. 1 illustrates the "coffee ring" effect that occurs in inkjet printing technology. [Figure 9] FIG. 10 is a schematic diagram showing the formation of protrusions using a pulsed laser during the fabrication of the metal grid lines G1. [Figure 10]Figure 10A shows a 2D image and Figure 10B shows a 3D image taken with a confocal microscope when two protruding lines were formed on top of the front electrode during the fabrication of the metal gridlines G1. [Figure 11] 10 is a cross-sectional image of two protruding lines formed on top of the front electrode during fabrication of the metal gridlines G1. [Figure 12] FIG. 10 is a schematic diagram illustrating the containment effect of two protrusions on the first and second protruding lines with liquid metal gridline material inside. [Figure 13] 10 is a schematic diagram of possible position distributions of protrusions on a first protruding line and a second protruding line. FIG. [Figure 14] FIG. 1 is a cross-sectional view of the layer stack of a thin-film solar cell with two metal gridlines G1 and G2. [Figure 15] FIG. 1 is a plan view of a thin-film solar cell with two metal gridlines G1 and G2. [Figure 16] FIG. 1 is a plan view of three interconnected cells comprising a thin-film photovoltaic module with two metal gridlines G1 and G2. [Figure 17] FIG. 1 is a schematic diagram of the current direction in two metal grid lines G1 and G2. [Figure 18] FIG. 10 is a schematic diagram illustrating the generation of protrusions of the third protruding line using a pulsed laser. [Figure 19] 19A is a pseudo-3D grayscale image of the third protruding lines that can encapsulate the metal grid lines G2 on one side, and FIG. 19B is a pseudo-3D grayscale image of the grooves caused by ablation of the buffer layer and front electrode due to excessively high laser power applied while forming the protrusions. [Figure 20] 3 is a pseudo-2D grayscale image of the third protruding line. [Figure 21] 10 is a cross-sectional image of a protrusion of the third protruding line. [Figure 22]22A is a schematic diagram of depositing the metal grid line G2 material on the P2 line after forming the third protruding line, and FIG. 22B is a schematic diagram of the metal grid line G2 being sealed on one side near P3 after depositing the metal grid line G2 material. [Figure 23] FIG. 10 is a schematic diagram showing the positional distribution of protrusions on a third protrusion line. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present application is applied to a process for fabricating a thin-film photovoltaic module, which is composed of a layer stack. For example, the thin-film photovoltaic module includes, from bottom to top, a substrate, a back electrode layer, an absorber layer, a buffer layer, and a front electrode layer. In the process for fabricating a thin-film photovoltaic module, when it is necessary to fabricate a thin linear structure (e.g., a metal grid line) on the top surface of one layer, it is necessary to control and limit the width, thickness, and position of the thin linear structure. In consideration of this, the present application provides a method for fabricating a thin linear structure on the top surface of a target layer of a layer stack including at least two layers, which is applied to the process for fabricating a thin-film photovoltaic module. The method for fabricating the linear structure includes: acquiring preset positions, which are first and second lateral positions, on both sides of the linear structure on the upper surface of the target layer; forming a protruding line at at least one lateral position by generating a plurality of protrusions spaced apart along a lateral longitudinal direction at at least one of the first lateral position and the second lateral position on the upper surface of the target layer; and applying and depositing a liquid linear structure material on one side of the protruding lines to obtain linear structures enclosed by the one side of the protruding lines.

[0042] In an embodiment of the present application, multiple protrusions are formed on that side of the linear structure to form a protruding line, and the lateral positions of the linear structure are enclosed by the protruding line. When a first protruding line is formed at a first lateral position, when a liquid linear structure material is applied to the side of the first protruding line closer to the second lateral position, the first side of the linear structure obtained by deposition is enclosed in the region where the first protruding line is closer to the second lateral position, and the first side of the linear structure obtained by deposition does not reach the region where the first protruding line is far from the second side. In other words, the protruding line limits the lateral position of the deposited liquid linear structure material. Note that when the first protruding line and the second protruding line are formed at the first lateral position and the second lateral position, respectively, applying the liquid linear structure material between the first protruding line and the second protruding line can obtain a linear structure in which two lateral positions are enclosed, i.e., a linear structure enclosed between the first protruding line and the second protruding line. When a protruding line (referred to as a third protruding line) is formed at one of the first and second lateral positions, a liquid linear structure material is applied to one side of the third protruding line, and one side of the linear structure obtained by deposition is confined to that side of the third protruding line without reaching the other side of the third protruding line.

[0043] Furthermore, when a plurality of protrusions are formed at intervals along the lateral longitudinal direction at the first lateral position and the second lateral position on the upper surface of the target layer to form first protruding lines and second protruding lines, the liquid linear structure material is applied and deposited between the first protruding lines and the second protruding lines to obtain a linear structure enclosed between the first protruding lines and the second protruding lines, i.e., a linear structure enclosed on both sides; or When a plurality of protrusions are formed at intervals along the lateral longitudinal direction to form a third protruding line at one of the first and second lateral positions on the upper surface of the target layer, a liquid linear structure material is applied and deposited on one side of the third protruding line to obtain a linear structure that is confined on one side of the third protruding line, i.e., a linear structure that is confined on one side.

[0044] In embodiments of the present application, the linear structure may be enclosed on one or both sides by a protruding line formed by a plurality of closely adjacent protrusions.

[0045] In addition, according to a method for fabricating narrow linear structures on the upper surface of a target layer of a layer stack, taking into account the surface tension, wettability, and other properties of the linear structure material, as well as the difficulty in controlling the shape of the lines formed by the deposited linear structure material, when a liquid-type linear structure is used to fabricate the linear structures during mass production of thin-film solar cells, multiple upward protrusions are generated on the upper surface of the target layer of the thin-film solar cell. The multiple densely distributed protrusions surround the edges of the deposition area of ​​the linear structure material, thereby confining the deposition area and achieving control of the linear structure shape. Adjusting the position of the protrusions, i.e., changing the position of the protruding lines, can limit at least one lateral position of the linear structure, and limiting both lateral positions of the linear structure can change the line width. Of course, if the amount of linear structure material is fixed, as the line width of the linear structure decreases, the line thickness of the linear structure also increases. Alternatively, if the line width of the linear structure is not changed, the line thickness of the linear structure can also be increased by increasing the height of the protrusions, for example, by changing the amount of linear structure material applied.

[0046] Furthermore, after multiple upward protrusions are formed on the upper surface of the target layer of the thin-film solar cell, if the distance between two adjacent protrusions (protrusion A and protrusion B) is very small, the linear structure material cannot be accommodated between the two adjacent protrusions (protrusion A and protrusion B).Therefore, by connecting multiple protrusions A and B (the distance between multiple protrusions A and B is very small), a protruding line is formed, and the linear structure material is restricted so that it does not overflow from the position of the protruding line, thereby restricting the position of at least one side of the linear structure.

[0047] When the distance between two adjacent protrusions (protrusions C and D) is large and a "valley" is formed between protrusions C and D, the linear structure material can be accommodated between the two adjacent protrusions (protrusions C and D). Based on this, by ensuring that the heights of protrusions C and D are sufficiently high, the width of the linear structure material deposited between protrusions C and D can be freely controlled by adjusting the distance between protrusions C and D. Therefore, by changing the distance between the protrusions, the width of the linear structure line can be changed.

[0048] A plurality of protrusions A and B (the distance between protrusions A and B is very small) are connected to form a protruding line, which can be used to restrict the overflow of metal grid line material from the protruding line. When a plurality of protruding lines are used in combination, the area between adjacent or neighboring protruding lines can accommodate the linear structure material.

[0049] It should be noted that the linear structure may be linear or have other shapes, and linear structures of different shapes can be formed by deposition simply by adjusting the shape of the protruding lines. In the embodiments of the present application, for illustrative purposes, linear linear structures are taken as an example.

[0050] Specifically, in an embodiment of the present application, a method for encapsulating a linear structure on one or both sides includes the following steps.

[0051] (Step 1) Determine a preset position of a linear structure on the upper surface of the target layer, and determine preset positions on both sides of the linear structure on the upper surface of the target layer, which are a first lateral preset position and a second lateral preset position, in combination with a preset width of the linear structure, where this preset width is a preferred value that meets the width of the linear structure determined before the linear structure is created, and therefore the distance between the first lateral preset position and the second lateral preset position is the preferred width of the linear structure.

[0052] (Step 2) When two lateral positions of the linear structure need to be restricted, a plurality of protrusions are generated at intervals along the lateral longitudinal direction at the first lateral preset position and the second lateral preset position, respectively, to form a first protruding line and a second protruding line, and the linear structure is applied between the first protruding line and the second protruding line, and the region between the first protruding line and the second protruding line is the region where the linear structure is located.

[0053] (Step 3) If it is necessary to restrict one lateral position of the linear structure, a third protruding line is formed by forming a plurality of protrusions spaced apart along the lateral longitudinal direction at one of the first and second lateral preset positions, and a liquid linear structure material is applied and deposited on one side of the third protruding line to obtain a linear structure confined on the one side of the third protruding line.

[0054] Furthermore, for the first protruding line, the second protruding line, and the third protruding line in steps 1 to 3 above, the spacing between two adjacent protrusions on the same protruding line is sufficiently small to prevent the linear structure material from overflowing from one side of the protruding line to the other side of the protruding line during deposition.

[0055] In both the two-sided confinement achieved by the first and second protruding lines and the one-sided confinement achieved by the third protruding line, when the linear structure material is applied to one side of the protruding line, it is required that the linear structure material does not overflow to the other side of the protruding line after deposition. Specifically, when the linear structure is confined on both sides by the first and second protruding lines, the spacing between two adjacent protrusions on the first protruding line is sufficiently small, and the spacing between two adjacent protrusions on the second protruding line is sufficiently small, so that the linear structure material does not overflow from the region between the first and second protruding lines during deposition. When the linear structure is confined on one side by the third protruding line, the spacing between two adjacent protrusions on the third protruding line is sufficiently small so that the linear structure material does not overflow from one side of the third protruding line to the other side of the third protruding line during deposition.

[0056] In alternative embodiments, the spacing between two adjacent protrusions on the same protrusion line is less than 10 micrometers. That is, the spacing between two adjacent protrusions on a first protrusion line is less than 10 micrometers, and the spacing between two adjacent protrusions on a second protrusion line is less than 10 micrometers. In some embodiments, the spacing between two adjacent protrusions on the same protrusion line is several micrometers.

[0057] In one embodiment, when the linear structure is enclosed on both sides, the protrusion of the first protruding line and the protrusion of the second protruding line are asymmetric along the center line between the first protruding line and the second protruding line.

[0058] In another embodiment, when the linear structure is enclosed on both sides, the protrusions of the first protruding line and the protrusions of the second protruding line are symmetrical along the center line between the first protruding line and the second protruding line.

[0059] Specifically, referring to FIG. 13, when the linear structure is enclosed on both sides, in one embodiment, the distribution spacing between the protrusions of the first protruding line corresponds to the distribution spacing between the protrusions of the second protruding line, i.e., the distribution spacing between the protrusions of the first protruding line is related to the distribution spacing between the protrusions of the second protruding line. In another embodiment, the distribution spacing between the protrusions of the first protruding line does not need to correspond to the distribution spacing between the protrusions of the second protruding line, i.e., the distribution spacing between the protrusions of the first protruding line is not related to the distribution spacing between the protrusions of the second protruding line. A center line exists between the first protruding line and the second protruding line, and one protrusion on the first protruding line and one protrusion on the second protruding line may be symmetrical about the center line (as shown in FIG. 13A). Of course, one protrusion on the first protruding line and one protrusion on the second protruding line may be asymmetric about the center line (as shown in FIGS. 13B and 13C).

[0060] Furthermore, in one embodiment, the spacing between two adjacent protrusions on the same protrusion line is uniform. That is, when the linear structure is enclosed on both sides, the spacing between two adjacent protrusions on the first protrusion is uniform and / or the spacing between two adjacent protrusions on the second protrusion is uniform (as shown in FIGS. 13A and 13B). When the linear structure is enclosed on one side, the spacing between two adjacent protrusions on the third protrusion line is uniform, as shown in FIG.

[0061] In another embodiment, the spacing between two adjacent protrusions on the same protrusion line is non-uniform. That is, when the linear structure is enclosed on both sides, the spacing between two adjacent protrusions on a first protrusion is non-uniform and / or the spacing between two adjacent protrusions on a second protrusion is non-uniform (as shown in FIG. 13C). When the linear structure is enclosed on one side, the spacing between two adjacent protrusions on a third protrusion line is non-uniform, as shown in FIG. 23B.

[0062] In other words, as long as the spacing between two adjacent protrusions on the same protrusion line is small enough to prevent the linear structure material from spilling over from one side of the protrusion line to the other side of the protrusion line during deposition, the distribution spacing between protrusions on different protrusion lines does not affect each other.

[0063] There is also a requirement for the height of the protrusion to prevent the linear structure material from spilling from one side of the protrusion line to the other side during deposition, i.e., to prevent the linear structure material from spilling from one side of the protrusion to the other side during deposition. In one embodiment, the height of the protrusion is required to be large enough to prevent the material for forming the linear structure from spilling over the protrusion during formation of the linear structure. In another embodiment, the required height of the protrusion is determined based on the characteristic parameters of the linear structure material. For example, to prevent the linear structure material from spilling over the protrusion, the required height of the protrusion is determined based on the amount, viscosity, and surface tension of the linear structure material. In another embodiment, the height of the protrusion is required to be greater than 100 nanometers, and generally speaking, the height of the formed protrusion is usually in the range of several hundred nanometers to micrometers.

[0064] Next, a method for generating protrusions will be described.

[0065] A method for generating protrusions on a first protruding line, a second protruding line, and a third protruding line includes the steps of irradiating a target layer from above with a pulsed laser onto the upper surface of the target layer so as to satisfy preset process parameters, causing the pulsed laser to pass through the target layer and reach the interface between two adjacent layers among a plurality of layers below the target layer, thereby melting and vaporizing a portion of the layer material at the interface between the two adjacent layers to form an upward protrusion.

[0066] As shown in Figures 9 and 18, a pulsed laser is irradiated onto the top surface of the target layer and passes through the target layer to reach the interface between two of the multiple layers below the target layer, causing a portion of the layer material to melt and evaporate at the interface between the two adjacent layers, forming an upward protrusion, thereby realizing the formation of a protrusion on the top surface of the target layer.

[0067] The preset process parameters of the pulsed laser need to be set reasonably, including the wavelength, power, irradiation time, irradiation frequency, speed, and beam diameter of the pulsed laser. For illustrative purposes, the adjustment of the wavelength and power of the pulsed laser will be taken as an example below.

[0068] Because the wavelength of the pulsed laser is larger than the optical band gap of the target layer and smaller than the optical band gap of the material of at least one of the layers below the target layer, the pulsed laser can pass through the target layer and stop at any layer below the target layer, and the pulsed laser is not absorbed by the layer it passes through but is absorbed at the interface where it stops, causing a portion of the material at the interface to melt and vaporize, forming an upward protrusion.

[0069] The power of the pulsed laser must be adjusted to form an upward protrusion on the top surface of the target layer. If the power is too low, it will only cause localized heating and will not form a protrusion. If the power is too high, the layer through which the pulsed laser passes will be completely ablated, resulting in a hole rather than an upward protrusion.

[0070] Specifically, the laser power of the pulsed laser is adjusted according to the thickness of the target layer and the characteristic parameters of the material of the target layer, for example, the laser power of the pulsed laser is determined according to the hardness, stiffness, tension, adhesion and other characteristic parameters of the material of the front electrode layer.

[0071] In the present application, the application method of the liquid linear structure material includes, but is not limited to, inkjet printing, aerosol spraying, screen printing, and dispensing.

[0072] The present application provides a method for fabricating narrow line structures on the top surface of a target layer of a layer stack, which is applicable to the process of fabricating thin-film photovoltaic modules. The present application method is applicable to the fabrication of thin-film photovoltaic modules having a substrate structure and a superstrate structure, and to the fabrication of thin-film photovoltaic modules of the CIGS, CdTe, and perovskite types.

[0073] The method of the present application for producing narrow linear structures on the top surface of a target layer of a layer stack is also applicable to single-pass and / or multi-pass application of liquid-type linear structure materials.

[0074] For illustrative purposes, a linear structure composed of metal grid lines will be taken as an example. In this application, a metal grid line G1 needs to be fabricated. To optimize the aspect ratio of the metal grid line G1 by controlling and optimizing the shape (including width and thickness parameters) of the metal grid line G1 on the surface of the front electrode, two protruding lines are first formed on the surface of the front electrode at two lateral positions of the metal grid line G1, and the metal grid line material is deposited within the area between the two protruding lines to form the metal grid line G1. In this application, a metal grid line G2 needs to be formed. To control and confine the side of the metal grid line G2 closer to the P3 line so that it is not covered or divided by the P3 line, a third protruding line needs to be formed on the surface of the front electrode on the side of the P2 line closer to the P3 line, so that the deposited material of the metal grid line G2 closer to the P3 line does not overflow from the third protruding line. This limits the position of the metal grid line G2 closer to the P3 line so that it does not reach the P3 line.

[0075] Specifically, a method for fabricating metal grid lines based on an improved surface structure of a front electrode is provided, based on a method for fabricating narrow linear structures on the top surface of a target layer of a layer stack. The target layer is a front electrode layer, and multiple layers below the target layer include a buffer layer, an absorber layer, a back electrode layer, and a substrate. The linear structures are composed of metal grid lines located on the top surface of the front electrode layer. The metal grid lines include metal grid lines G1 that are perpendicular to the P1, P2, and P3 lines, and metal grid lines G2 that are parallel to and located above the P2 lines. In this embodiment, the width and thickness of the metal grid lines G1 must be controlled and optimized to optimize the aspect ratio of the metal grid lines G1, i.e., the positions of both sides of the metal grid lines G1 must be limited. In this embodiment, the position of one side of the metal grid lines G2 must be limited to prevent the side of the metal grid lines G2 closest to the P3 line from reaching the P3 line, i.e., preventing the P3 line from being uncovered or divided by the P3 line. Specifically, the method for producing the metal grid lines G1 is as follows: a step G1(1) of obtaining preset positions on the surface of the front electrode on both sides of the metal grid lines G1, the preset positions being a first lateral preset position and a second lateral preset position; a step G1(2) of generating a plurality of protrusions spaced apart along a lateral longitudinal direction at the first lateral preset position and the second lateral preset position, respectively, to form a first protruding line and a second protruding line; and step G1(3) of applying and depositing a liquid metal grid line material between the first protruding lines and the second protruding lines, thereby obtaining the metal grid lines G1 enclosed between the first protruding lines and the second protruding lines; The method for fabricating the metal grid lines G2 is as follows: a step G2(1) of acquiring a position on the surface of the front electrode, the position being a third lateral position of the P2 line closer to the P3 line; a step G2(2) of generating a plurality of protrusions at intervals along the lateral longitudinal direction at the third lateral position to form a third protruding line; and step G2(3) of applying and depositing a liquid metal grid line material within the P2 lines to obtain the metal grid lines G2 whose sides closer to the P3 lines are enclosed by the third protruding lines.

[0076] The width and thickness of the metal grid line G1 are controlled through steps G1(1), G1(2), and G1(3). Specifically, in step G1(1), a predetermined position of the metal grid line G1 on the surface of the front electrode is determined. The predetermined positions on both sides of the metal grid line G1 on the surface of the front electrode, which are recorded as first and second predetermined lateral positions, are determined in combination with the predetermined width of the metal grid line G1. The predetermined width is a preferred value of the width of the metal grid line that satisfies the aspect ratio condition of the metal grid line determined before fabrication of the metal grid line. Therefore, the distance between the first and second predetermined lateral positions is the preferred width of the metal grid line. In step G1(3), the method for applying the metal grid line material can be inkjet printing, aerosol spraying, screen printing, dispensing, etc., with inkjet printing being the preferred technique.

[0077] In the process of fabricating the metal grid lines G1 and G2, the protrusions are generated as follows: A pulsed laser is irradiated on the surface of the front electrode layer far from the buffer layer using preset process parameters, so that at least the front electrode layer protrudes upward at the laser irradiation position. Specifically, in this application, the pulsed laser is irradiated on the surface of the front electrode layer from above the thin-film solar cell, passing through the front electrode layer until one of the underlying layers, i.e., the buffer layer, absorber layer, back electrode layer, and substrate, absorbs the laser radiation. As the pulsed laser attempts to pass through the interface where it stops, part of the layer material melts and vaporizes, forming an upward protrusion at the pulsed laser irradiation position. The preset process parameters of the pulsed laser must be reasonably set, and include the wavelength, power, irradiation time, irradiation frequency, speed, and beam diameter of the pulsed laser. For example, in an embodiment of the present application, the wavelength of the pulsed laser irradiated onto the top surface of the front electrode layer must be greater than the optical bandgap of the front electrode layer, but smaller than the optical bandgap of at least one of the buffer layer, absorber layer, and back electrode layer, so that the pulsed laser can pass through the front electrode layer. For example, if the wavelength of the pulsed laser is greater than the optical bandgap of the front electrode layer and the buffer layer but smaller than the optical bandgap of the absorber layer, the laser will pass through the front electrode layer and the buffer layer and be absorbed when it reaches the interface between the buffer layer and the absorber layer, causing some of the material at the interface between the absorber layer and the buffer layer to melt and vaporize, creating an upward protrusion in the layer stack toward the front electrode.

[0078] The pulsed laser power must be determined to form upward protrusions on the surface of the front electrode layer. If the pulsed laser power is too low, it will only cause localized heating and fail to form protrusions. If the power is too high, as when laser P3 lines are scribed, the buffer layer and front electrode layer will be completely ablated, significantly reducing the interconnection area between the metal grid lines and the front electrode, resulting in wider lines and increased series resistance (up to the thickness of the front electrode layer). Specifically, the pulsed laser power is determined based on the thickness of the front electrode layer and the characteristic parameters of the material used for the front electrode layer. For example, the pulsed laser power is determined based on the hardness, stiffness, tension, adhesion, and other characteristic parameters of the material used for the front electrode layer.

[0079] For example, in the process of fabricating the metal grid lines G1 and G2, the process parameters of the pulsed laser used to form the protrusions may be as follows: for CIGS with an AZO (front electrode) thickness of 750 nm and a ZnOS (buffer) thickness of 65 nm, the laser power window is between 150 mW and 250 mW, the wavelength is 1064 nm, the laser pulse width is 15 ps, the repetition rate is 500 kHz, the process speed is 10800 mm / min, and the beam diameter is about 20 μm.

[0080] 10 shows a microscope image of the first and second protruding lines (the distance between the first and second protruding lines is 20 micrometers) during the process of fabricating the metal grid lines G1. FIG. 11 shows a cross-sectional image of the first and second protruding lines (the distance between the first and second protruding lines is 10 micrometers). Because the width of a single protrusion on the first and second protruding lines is within the range of approximately 10 micrometers, the distance between the first and second protruding lines needs to be greater than 10 micrometers, so that the material of the metal grid lines G1 can be accommodated between the first and second protruding lines to form the metal grid lines G1 between the first and second protruding lines.

[0081] Referring to FIG. 12, when the material of the metal grid line G1 is confined between two protrusions, the material of the metal grid line G1 fills the space between the two protrusions, and the coffee ring effect as shown in FIG. 8 is also avoided.

[0082] FIG. 18 shows a schematic diagram of the generation of protrusions of third-protruding lines using a pulsed laser in the process of fabricating metal grid lines G2. FIG. 19 shows a pseudo-3D grayscale image of the third-protruding lines in the process of fabricating metal grid lines G2. FIG. 19B shows a pseudo-3D grayscale image of the one-sided confinement of the metal grid lines G2 due to the formed third-protruding lines. FIG. 19B shows a pseudo-3D grayscale image of the case where the laser power is too high, resulting in the ablation of the buffer layer and front electrode, creating grooves. FIG. 20 shows a pseudo-2D grayscale image of the third-protruding lines to achieve one-sided confinement. FIG. 21 shows a cross-sectional image of the protrusions of the third-protruding lines, showing the maximum height, average height, and width of the protrusions of the third-protruding lines. FIG. 22 shows a schematic diagram of depositing the metal grid line G2 material on the P2 line after forming the third protruding line, FIG. 22A shows a schematic diagram of applying the metal grid line G2 material on the P2 line after forming the third protruding line, and FIG. 22B shows a schematic diagram of one side near P3 being sealed after depositing the metal grid line G2 material.

[0083] It should be noted that materials for the metal gridlines include, but are not limited to, metallic inks and dielectric inks.

[0084] Based on the above method for fabricating metal gridlines based on the improved surface structure of the front electrode, the present application further provides a method for optimizing the aspect ratio of the metal gridlines, the method comprising controlling the deposition width and thickness of the metal gridlines by controlling the distance between the first protruding lines and the second protruding lines, the height of the protrusions, and the amount of metal gridline material, thereby controlling and optimizing the aspect ratio of the metal gridlines.

[0085] Based on the method for fabricating metal gridlines based on the improved surface structure of the front electrode, a method for fabricating a thin film solar cell is provided, the method comprising the following steps:

[0086] The process for manufacturing a photovoltaic module involves sequentially forming a substrate, a back electrode layer, an absorber layer, a buffer layer, and a front electrode layer of a thin-film solar cell when a substrate approach is used to fabricate a photovoltaic module, and sequentially forming a substrate, a front electrode layer, a buffer layer, an absorber layer, and a back electrode layer of a thin-film solar cell when a top plate approach is used to fabricate a photovoltaic module. This process includes producing P1 lines, P2 lines, and P3 lines, in which after forming the back electrode layer, the P1 lines are placed on the back electrode layer; after forming the absorber layer and the buffer layer, the P2 lines are placed on the absorber layer and the buffer layer; after forming the front electrode layer, the P3 lines are placed on the front electrode layer, and the P1 lines, P2 lines, and P3 lines are used to segment and serially connect the large-area thin-film solar cells.

[0087] Fabrication process of metal grid lines G1 and G2: Based on the above method for fabricating metal grid lines, metal grid lines G1 and metal grid lines G2 are respectively formed on the surface of the front electrode layer farther from the buffer layer.

[0088] The present application is not limited to the specific embodiments described above, and various modifications made by those skilled in the art from the above ideas without any creative effort shall fall within the scope of protection of the present application. [Explanation of symbols]

[0089] 1 Front electrode layer 2. Buffer layer 3. Absorber layer 4 Back electrode layer 5. Substrate 6 Metal Grid Lines G1

Claims

1. 1. A method for fabricating a narrow linear structure on an upper surface of a target layer of a layer stack including at least two layers, the method being applicable to a process for fabricating a thin film photovoltaic module, the method for fabricating the linear structure comprising: acquiring preset positions, which are first and second lateral positions, on both sides of the linear structure on the upper surface of the target layer; generating a plurality of protrusions spaced apart along a lateral longitudinal direction at least one of the first lateral position and the second lateral position on the upper surface of the target layer, thereby forming a protruding line at at least one lateral position; and applying and depositing a liquid linear structure material on one side of the protruding lines to obtain a linear structure that is enclosed on one side by the protruding lines. A method for producing linear structures.

2. When a plurality of protrusions are formed at intervals along the lateral longitudinal direction at the first lateral position and the second lateral position on the upper surface of the target layer to form a first protruding line and a second protruding line, a liquid linear structure material is applied and deposited between the first protruding line and the second protruding line to obtain a linear structure enclosed between the first protruding line and the second protruding line, i.e., a linear structure enclosed on both sides; or When a plurality of protrusions are formed at intervals along the lateral longitudinal direction at one of the first and second lateral positions on the upper surface of the target layer to form a third protruding line, a liquid linear structure material is applied and deposited on one side of the third protruding line to obtain a linear structure that is confined on the one side by the third protruding line. The method for producing a linear structure according to claim 1 .

3. The spacing between two adjacent protrusions on the same protrusion line is small enough to prevent the linear structure material from spilling over from one side of the protrusion line to the other side of the protrusion line during deposition. The method for producing a linear structure according to claim 1 .

4. The distance between two adjacent protrusions on the same protrusion line is less than 10 micrometers The method for producing a linear structure according to claim 3 .

5. When the linear structure is enclosed on both sides, the protrusion of the first protruding line and the protrusion of the second protruding line are asymmetric along a center line between the first protruding line and the second protruding line. A method for producing a linear structure according to any one of claims 1 to 4.

6. When the linear structure is enclosed on both sides, the protrusion of the first protruding line and the protrusion of the second protruding line are symmetrical along a center line between the first protruding line and the second protruding line. A method for producing a linear structure according to any one of claims 1 to 4.

7. The spacing between two adjacent projections on the same projection line is uniform A method for producing a linear structure according to any one of claims 1 to 4.

8. The spacing between two adjacent projections on the same projection line is uneven A method for producing a linear structure according to any one of claims 1 to 4.

9. The height of the protrusion is large enough to prevent the material for forming the linear structure from spilling out of the protrusion during the formation of the linear structure. The method for producing a linear structure according to claim 1 .

10. The height of the protrusion is determined based on the characteristic parameters of the material used to form the linear structure. The method for producing a linear structure according to claim 9 .

11. The characteristic parameters of the material for forming the linear structure include at least the amount, viscosity, and surface tension of the material. The method for producing a linear structure according to claim 10.

12. The height of the protrusion is greater than 100 nanometers The method for producing a linear structure according to claim 10.

13. The method for generating the protrusion includes the steps of irradiating a pulsed laser from above the target layer with the pulsed laser at preset process parameters, so that pulses of the pulsed laser pass through the target layer and reach an interface between two adjacent layers among a plurality of layers below the target layer, thereby melting and vaporizing a portion of layer material at the interface between the two adjacent layers to form an upward protrusion. The method for producing a linear structure according to claim 1 .

14. The preset process parameters of the pulsed laser satisfy a condition that the wavelength of the pulsed laser is greater than the optical bandgap of the target layer but less than the optical bandgap of at least one layer of the plurality of layers below the target layer. The method for producing a linear structure according to claim 13.

15. Among the preset process parameters of the pulsed laser, the laser power of the pulsed laser is determined based on the thickness of the target layer and characteristic parameters of the material of the target layer. The method for producing a linear structure according to claim 13.

16. The characteristic parameters of the material of the target layer include at least the hardness, stiffness, tension and adhesion of the material of the front electrode layer. The method for producing a linear structure according to claim 15.

17. The application method of the liquid linear structure material includes, but is not limited to, inkjet printing, aerosol spraying, screen printing, and dispensing. The method for producing a linear structure according to claim 1 .

18. Including applications in single and / or multi-pass application of liquid linear structural materials 18. Application of the method for producing a linear structure according to any one of claims 1 to 17.

19. A method for fabricating metal grid lines based on the improved surface structure of a front electrode based on the method for fabricating linear structures according to any one of claims 1 to 17, wherein the target layer is a front electrode layer, the layers below the target layer include a buffer layer, an absorber layer, a back electrode layer, and a substrate, and the linear structures are composed of metal grid lines located on the top surface of the front electrode layer. A method for fabricating metal gridlines.

20. The metal grid lines include metal grid lines G1 that are perpendicular to the P1, P2, and P3 lines, and metal grid lines G2 that are parallel to the P2 lines and above the P2 lines.

20. The method of making a metal gridline of claim 19.

21. The method for producing the metal grid lines G1 includes the steps of: a step G1(1) of obtaining preset positions on the surface of the front electrode on either side of the metal grid lines G1, the preset positions being a first lateral preset position and a second lateral preset position; a step G1(2) of generating a plurality of protrusions spaced apart along a lateral longitudinal direction at the first lateral preset position and the second lateral preset position, respectively, to form a first protruding line and a second protruding line; and a step G1(3) of applying and depositing a liquid metal grid line material between the first protruding lines and the second protruding lines, thereby obtaining the metal grid lines G1 enclosed between the first protruding lines and the second protruding lines; The method for producing the metal grid lines G2 includes the steps of: A step G2(1) of acquiring a position on the surface of the front electrode, the position being closer to the P3 line than the P2 line, and being a third lateral position; Step G2(2) of generating a plurality of projections spaced apart along the lateral longitudinal direction at the third lateral position to form a third projecting line; and (G2(3)) applying and depositing a liquid metal grid line material within the P2 lines to obtain the metal grid lines G2 whose sides closer to the P3 lines are enclosed by the third protruding lines.

21. The method of making a metal gridline of claim 20.

22. Materials for the metal gridlines include, but are not limited to, metallic inks and dielectric inks.

20. The method of making a metal gridline of claim 19.

23. A method for optimizing the aspect ratio of metal grid lines based on the method for fabricating metal grid lines based on the improved surface structure of a front electrode according to any one of claims 19 to 22, comprising the steps of controlling the deposition width and thickness of the metal grid lines by controlling the distance between the first and second protruding lines, the height of the protrusions, and the amount of metal grid line material, thereby controlling and optimizing the aspect ratio of the metal grid lines. How to optimize the aspect ratio of metal gridlines.

24. 23. A method for fabricating a thin film solar cell based on the method for fabricating a metal gridline according to any one of claims 19 to 22, comprising: forming a substrate, a back electrode layer, an absorber layer, a buffer layer and a front electrode layer of a thin film solar cell in sequence, or forming a substrate, a front electrode layer, a buffer layer, an absorber layer and a back electrode layer of a thin film solar cell in sequence; after forming the back electrode layer, disposing a P1 line on the back electrode layer, after forming the buffer layer, disposing a P2 line on the absorber layer and the buffer layer, after forming the front electrode layer, disposing a P3 line on the front electrode layer, and using the P1 line, the P2 line, and the P3 line to segment and serially connect large area thin film solar cells; forming metal grid lines G1 and G2 on a surface of the front electrode layer remote from the buffer layer according to the method for fabricating metal grid lines of any one of claims 19 to 22; A method for making a thin film solar cell comprising:

25. Produced by the method of claim 24 Thin-film photovoltaic modules.

26. Use of a solar module according to claim 25 as part of a building envelope, in particular as a window, facade or roof element.

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