TWI682012B - Method for manufacturing solar cell - Google Patents

Abstract

The present invention provides a method for manufacturing a solar cell. The method uses a specialized screen having knotless yarns and yarns with knots in screen printed process. The direction that electrode materials fall down is parallel to the direction of warps of the knotless yarns, so as to let electrode materials fall across the screen. The solar cell has more excellent photoelectric properties than one using traditional screen printing.

Description

Solar cell manufacturing method

The invention relates to a method for manufacturing a solar cell, and in particular to a method for manufacturing a solar cell by using a screen without a net junction.

The use of screen printing to print the electrodes of silicon crystal solar cells is one of the important manufacturing processes of silicon crystal solar cells. In order to improve the conversion efficiency of solar cells, the front electrode is usually made into a finger shape to reduce the shielding area of incident light.

Screen printing is to print the electrode pattern on the substrate through the electrode paste in a direct printing process, which is then formed by thermal curing. The screen used in the general screen printing process has a net yarn formed by interweaving warp yarns and weft yarns. The warp yarns and weft yarns overlap and cross at the interlace to form a net knot. As shown in FIG. 1 according to the prior art, the schematic diagram of the electrode paste 101 passing through the screen, the mesh knots 102 in the mesh will shield the electrode pattern, so that the electrode paste 101 cannot fall into the electrode pattern of the silicon substrate 100, resulting in The electrode paste 101 is not uniform, the resistance of the electrode will rise, and the conversion efficiency will deteriorate.

In addition, whether the screen is suitable for screen printing depends on the tension of the screen. The tension of various mesh fabrics is different, and the material, mesh, yarn diameter and angle of the screen need to be considered. Generally, the commercially available screens are of fixed specifications, and the yield of the manufactured solar cells may not meet the expectations of customers. Therefore, the plate-making technology of screen printing is also an important link in the manufacture of solar cells.

In order to solve the above-mentioned problems, the main object of the present invention is to provide a method for manufacturing a solar cell. Screen printing using a screen with no knots can improve the manufacturing yield of the solar cell.

The manufacturing method of the solar cell of the present invention includes the following steps: providing a silicon substrate; roughening the front surface of the silicon substrate with an etching solution; adding a doping source to the front surface of the silicon substrate to form a PN junction; Use an etchant to perform a wet edge process to remove the silicide on the back of the silicon substrate; form an anti-reflective layer on the front of the silicon substrate; use the electrode material and screen for the screen printing process; and perform a sintering process on the silicon substrate The front surface of the material forms a front electrode. The screen version has a netless mesh yarn and a netted mesh yarn. The netless mesh yarn is composed of warp yarns, and the netted mesh yarn is composed of warp yarns and weft yarns that intersect the warp yarn vertically. The distance between the warp yarns is smaller than the distance between the warp yarns with weft yarns and the weft yarns. On the netless yarns, the falling direction of the electrode material is parallel to the direction of the warp yarns, so that the electrode material passes through the screen.

Therefore, the manufacturing method of the solar cell of the present invention uses a mesh screen customized by calculating the aperture ratio, the mesh yarn at the corresponding front electrode does not have a knot, does not block the passage of the electrode paste, and the electrode pattern has uniformity, so that The printed front electrode has a flat surface, which can effectively improve the manufacturing yield of solar cells.

100、200‧‧‧Silicon substrate

101‧‧‧ electrode paste

102‧‧‧Knot

201‧‧‧Pyramid hole

202‧‧‧ Silicon dioxide layer

203‧‧‧doped layer

204‧‧‧Anti-reflection layer

205‧‧‧electrode material

206‧‧‧Back electric field

A‧‧‧net thickness

T‧‧‧thickness of electrode material

FIG. 1 is a schematic diagram of electrode paste passing through a screen according to the prior art.

2A to 2F are schematic diagrams of a method of manufacturing a solar cell according to an embodiment of the invention.

3A is a top view of a 3D optical microscope according to Example 1 of the present invention.

3B is a top view of a 3D optical microscope according to Comparative Example 1 of the present invention.

4A is a cross-sectional view of a 3D optical microscope according to Example 1 of the present invention.

4B is a cross-sectional view of a 3D optical microscope according to Comparative Example 1 of the present invention.

In order to make the above and other objects, features, and advantages of the present invention more obvious and understandable, the following will describe the manufacturing method of the solar cell, and provide related embodiments and examples thereof to specifically illustrate the present invention and its efficacy .

In one embodiment, the manufacturing method of the solar cell of the present invention is shown in FIGS. 2A to 2F. FIGS. 2A to 2F are schematic diagrams of the manufacturing method of the solar cell according to an embodiment of the present invention. First, a silicon substrate 200 is provided, which is divided into a P-type silicon substrate and an N-type silicon substrate. The material is, for example, a monocrystalline silicon wafer, a polycrystalline silicon wafer, and an amorphous silicon wafer. 2A, after cleaning the silicon substrate 200, the front surface of the silicon substrate 200 is roughened with an etching solution to form a pyramid-shaped hole 201 to reduce light reflection on a smooth surface. The etching solution is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, hydrofluoric acid, nitric acid, and acetic acid, but not limited thereto. In the case of monocrystalline silicon wafers, an alkaline etching solution is used for roughening, and in the case of polycrystalline silicon wafers, an acidic etching solution is used for roughening. Next, as shown in FIG. 2B, a diffusion process is performed, and a doping source such as phosphorus oxychloride or boron tribromide is added to the front surface of the silicon substrate 200 in a high-temperature furnace to form a P-N junction. Then, the thermal oxidation reaction (high temperature annealing) ends the diffusion reaction, and a silicon dioxide layer 202 is formed to cover the doped layer 203 to prevent the diffusion of the doping source. Next, as shown in FIG. 2C, a hydrofluoric acid etching solution is used to perform a wet edge process to remove the silicide (such as phosphosilicate glass) on the edge side of the silicon substrate 200, and the vertical direction of the silicon substrate 200 is removed by grinding Side. Next, as shown in FIG. 2D, anti-reflection of silicon nitride is formed on the front surface of the silicon substrate 200 by sputtering or chemical vapor deposition 层204。 Layer 204. Next, as shown in FIG. 2E, an electrode material 205 such as silver paste and a screen are used to perform a screen printing process. Finally, as shown in FIG. 2F, a sintering process is performed so that the electrode material 205 penetrates the anti-reflection layer 204 to contact the surface of the silicon substrate 200, and a front electrode can be formed on the front surface of the silicon substrate 200. And the aluminum paste of the back electrode will diffuse into the silicon substrate 200 by high-temperature sintering, and a silicon aluminum alloy is formed on the back to serve as the back field 206.

In one embodiment, the screen used in the screen printing process of the present invention has a netless mesh yarn and a netted mesh yarn. The netless mesh yarn is composed of warp yarns, and the direction of the warp yarns is the same as the direction of gravity; The net yarn is composed of warp yarns and weft yarns that perpendicularly intersect with the warp yarns, and the net knot is formed where the warp yarns and weft yarns intersect. The material of the warp yarn and the weft yarn is nylon, polyester, metal, or silk, preferably metal, but not limited to this. The distance between the warp yarns of the netless mesh yarn is smaller than the distance between the warp yarns of the netted mesh yarn and the weft yarn, and the distance between the warp yarns of the netted mesh yarn and the weft yarn is preferably 30 μm to 100 μm. The screen of the present invention is preferably a 90-degree screen (ie, the angle between the screen yarn and the frame), while the traditional screen plate is 22.5 degrees. In view of the tensile strength of the screen, the spacing between the warp yarns of the non-knotted screen yarn must be Dense, preferably 30 μm to 80 μm.

In an embodiment, the front electrode of the present invention has a number of bus bars less than 50 and finger electrodes of 60-300. The front electrode may not have a bus bar. The width of the bus bar is 0.15mm-2mm. The width of the finger electrode It is 5μm-40μm. When ordering the screen, the mesh size and mesh spacing are calculated based on the number and width of the bus bars and the number and width of the finger electrodes. Then, the mesh area and mesh area can also be calculated. The mesh area is divided by the mesh area to calculate the aperture ratio. As shown in Figure 1, the amount of glue (that is, coating is required) can be calculated by the mesh thickness (A), the aperture ratio, and the thickness of the electrode material (T) The amount of electrode material such as silver glue or aluminum glue).

At the meshless yarn, the electrode material falls in the same direction as the warp Yes, because there is no mesh shielding, the electrode material can pass through the screen and can be printed evenly on the anti-reflection layer. The busbars and finger electrodes of the front electrode are screen printed separately. The positions of the busbars and finger electrodes have been calculated before ordering the screen, so that the electrode material can fall on the front of the silicon substrate through the meshless mesh Where the finger electrode is to be formed, and can also fall on the front of the silicon substrate where the bus bar is to be formed.

The following provides details of different embodiments of the present invention to more clearly explain the present invention, however, the present invention is not limited to the following embodiments.

Examples

The substrate used is a P-type silicon wafer. The potassium hydroxide solution is used to clean the silicon wafer first, and then the silicon wafer is roughened with sodium hydroxide solution for 1 hour. Then, using phosphorus oxychloride, oxygen, and nitrogen, the silicon wafer was subjected to a diffusion process in a 1000°C high-temperature furnace for 30 minutes. Next, oxygen is introduced to perform thermal oxidation at 200°C. After taking out the silicon wafer and placing it to cool, it is immersed in a 10 wt% hydrofluoric acid solution for a wet edge process. Next, silicon nitride is formed on the front surface of the silicon wafer by sputtering. Apply silver glue (manufactured by DuPont) on the customized screen, and screen print the electrode structure on the front and back of the silicon wafer at a screen printing speed of 30mm/second from the screen with a pitch of 0.2mm. Bake at 150°C for 3 minutes, and finally place in a high-temperature oven at 700°C for 3 minutes. In Example 1, Example 2, and Example 3, the temperature of the diffusion process is set at 1000°C, 800°C, and 600°C, respectively.

Comparative example

In addition to using the traditional screen, the same process steps as in Example 1, Example 2, and Example 3 were used to make Comparative Example 1, Comparative Example 2, and Comparative Example 2 where the temperature of the diffusion process was set at 1000°C, 800°C, and 600°C. Comparative example 3.

Surface morphology testing

Using a 3D optical microscope at a magnification of 20 times, the thickness and surface condition of the solar cells of Example 1 and Comparative Example 1 were measured to obtain a bird's eye view of the 3D optical microscope according to Example 1 of the present invention of FIG. 3A and the basis of FIG. 3B A top view of the 3D optical microscope of Comparative Example 1 of the present invention, a cross-sectional view of the 3D optical microscope according to Example 1 of the present invention in FIG. 4A, and a cross-sectional view of the 3D optical microscope according to Comparative Example 1 of the present invention in FIG. 4B. It can be seen from FIGS. 3A and 3B that Example 1 has a better flatness than Comparative Example 1. It can be seen from FIGS. 4A and 4B that Example 1 has a smaller change in the height difference of the finger electrode compared to Comparative Example 1. Therefore, compared with the traditional screen, the height difference of the solar cell electrode printed by the non-mesh customized screen printing is smaller, and the surface smoothness is better.

Photoelectric characteristics test

Using the solar cell current-voltage measurement system, the short-circuit current (ISC), output power, and maximum power point of Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, and Comparative Example 3 can be measured ( PMPP). The ratio of the output power to the product of the incident light exposure and the surface area of the solar cell is defined as the photoelectric conversion efficiency (EFF), and the data is organized as shown in Table 1 below.

由表1可看出，實施例1、實施例2、實施例3的光電轉換效率、短路電流、最大功率點皆比比較例1、比較例2、比較例3的值高，代表光電特性較佳。因此，無網結的訂製網版所網印的太陽能電池的電極縮束與線高度均勻、表面較為平整，不會因摻雜源的擴散濃度不同而有所影響。

It can be seen from Table 1 that the photoelectric conversion efficiency, short-circuit current, and maximum power point of Example 1, Example 2, and Example 3 are all higher than those of Comparative Example 1, Comparative Example 2, and Comparative Example 3, indicating that the photoelectric characteristics are relatively good. Therefore, the electrode shrinkage and line height of the solar cell screen-printed on the customized screen without mesh connection are uniform, and the surface is relatively flat, and it will not be affected by the different diffusion concentration of the doping source.

The contents described in this specification are only examples, not limitations. Any equivalent modifications or changes made without departing from the spirit and scope of the present invention shall be included in the scope of the attached patent application.

Claims (8)

A method for manufacturing a solar cell, comprising: providing a silicon substrate; roughening the front surface of the silicon substrate with an etching solution; adding a doping source to the front surface of the silicon substrate to form a PN junction; and performing thermal oxidation Reaction to generate a silicon dioxide layer; use the etchant to perform a wet edge process to remove the silicide on the back of the silicon substrate; form an anti-reflective layer on the front of the silicon substrate; use electrode materials and screens to screen Printing process; and performing a sintering process to form a front electrode on the front surface of the silicon substrate; wherein, the screen has meshless mesh yarn and meshed mesh yarn, the meshless mesh yarn is composed of warp yarn, the The distance between the warp yarns of the netless mesh yarn is 30 μm to 80 μm. The netted mesh yarn is composed of a warp yarn and a weft yarn that intersects the warp yarn vertically. The warp yarn of the netted mesh yarn and the weft yarn The distance between them is 30 μm to 100 μm. In the meshless yarn, the falling direction of the electrode material is parallel to the direction of the warp yarn, so that the electrode material passes through the screen. The method for manufacturing a solar cell as described in item 1 of the patent application, wherein the material of the warp yarn and the weft yarn is nylon, polyester, metal, or silk. The method for manufacturing a solar cell as described in item 1 of the patent application scope, wherein the front electrode has bus bars with a number of less than 50 and finger electrodes with a number of 60-300, the width of the bus bar is 0.15mm-2mm, the fingers The width of the electrode is 5 μm-40 μm. The method for manufacturing a solar cell as described in item 3 of the patent application range, wherein in the screen printing process, the electrode material falls through the meshless screen yarn on the front of the silicon substrate where the finger electrode is to be formed. The method for manufacturing a solar cell as described in item 3 of the patent application range, wherein in the screen printing process, the electrode material falls through the meshless yarn onto the front surface of the silicon substrate where the bus bar is to be formed. The method for manufacturing a solar cell as described in item 1 of the patent application range, wherein the etching solution is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, hydrofluoric acid, nitric acid, and acetic acid. The method for manufacturing a solar cell as described in item 1 of the patent application scope, wherein the doping source is phosphorus oxychloride or boron tribromide. The method for manufacturing a solar cell as described in item 1 of the patent application, wherein the electrode material is silver glue and aluminum glue.

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