JP2015130367A - Solar cell and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method of manufacturing a solar cell in which the bleeding paste is prevented from spreading.SOLUTION: A method of manufacturing a solar cell includes the steps of:forming grooves 4 on both sides of a light-receiving surface electrode forming area of a first conductivity type semiconductor substrate 1 on the light-receiving surface side in the extension direction; forming a second conductivity type layer 3 different from the first conductivity type by diffusing impurities in the surface of the semiconductor substrate on the light-receiving surface side following to formation of the grooves; forming an antireflection film 5 on the second conductivity type layer; and forming a light-receiving surface electrode 6 on the light-receiving surface electrode forming area by screen printing.

Description

  The present invention relates to a solar cell and a manufacturing method thereof.

  One of the technologies for improving the efficiency of solar cells is to make the grid electrode thin. It is important to reduce the occupied area of the grid electrode formed on the light receiving surface of the solar cell so as not to block light and increase the light contributing to photoelectric conversion. Further, in order to output the generated photocurrent to the outside without loss, it is necessary to form a grid electrode having a lower resistance. As the most suitable shape of the grid electrode for solar cells, a thin wire and a thick film having a high aspect ratio are required. The grid electrode of a solar cell is generally formed using screen printing.

  Since screen printing is very simple and inexpensive, it is easy to introduce into mass production processes. However, since the properties of the paste, which is an electrode material, greatly affect electrode performance and printability, there are many problems other than printing technology. The silver paste for solar cell electrodes is mainly made of a mixture of silver filler, organic solvent, resin, and glass powder. An attempt has been made to increase the aspect ratio by improving the paste material (see, for example, Patent Document 1 and Patent Document 2). In order to obtain a thin-wire / high-aspect solar cell grid electrode, printing technology and paste performance must be compatible.

JP 2007-95663 A JP 2010-199034 A JP 2006-32698 A

  However, according to the conventional technique, when the grid electrode for solar cell is formed by screen printing, after the paste is transferred to the substrate, the paste cannot maintain its shape, and sagging and bleeding occur. Therefore, the line width increases and the incident light on the light receiving surface decreases, resulting in a decrease in solar cell output.

  In order to prevent this bleeding, Patent Document 3 proposes a method of forming a high aspect ratio electrode by forming a groove on the light receiving surface of a solar cell and embedding an electrode in the groove. However, in order to reduce the cost, if a wafer having a substrate thickness of about 100 to 200 μm is used and a groove having a width of 40 to 80 μm and a depth of 30 to 60 μm is formed, the substrate is easily broken and the yield during mass production is reduced. There is. Further, in the screen printing on the groove, the bottom of the groove and the paste are difficult to come into contact with each other. In order to increase the filling force, there is a method of adjusting the composition and viscosity of the paste. However, the state of the paste needs to be managed, which is expensive. In addition, in order to increase the filling force and prevent disconnection, it is necessary to reduce the processing speed, and there is a problem that the tact time increases.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a solar cell and a method for manufacturing the same, in which the spread of paste spread is prevented and the characteristics are improved.

  In order to solve the above-described problems and achieve the object, the present invention includes a step of forming grooves on both sides along the extending direction of the light-receiving surface electrode formation scheduled region on the light-receiving surface side of the first conductivity type semiconductor substrate. And forming a second conductivity type layer different from the first conductivity type by diffusing impurities on the light receiving surface side surface of the semiconductor substrate after forming the groove; and The method includes a step of forming an antireflection film thereon, and a step of forming a light receiving surface electrode on the light receiving surface electrode formation scheduled region using screen printing.

  According to the present invention, since the grooves are formed around the electrodes, the spread of paste bleeding can be prevented and the electrode width can be reduced. This produces the effect of increasing the amount of power generation and improving the solar cell characteristics. Further, during printing, the substrate and the paste are easily in contact with each other, and printing can be stably performed without adjusting the composition and viscosity of the paste. For this reason, paste management becomes easy, and there is an effect that yield can be improved and tact time can be shortened.

FIG. 1 is a cross-sectional view for explaining a method of manufacturing a solar cell according to an embodiment of the present invention. FIG. 2 is a cross-sectional view for explaining a method for manufacturing a solar cell according to an embodiment of the present invention. FIG. 3 is a cross-sectional view for explaining a method for manufacturing a solar cell according to an embodiment of the present invention. FIG. 4 is a cross-sectional view for explaining a method for manufacturing a solar cell according to an embodiment of the present invention. FIG. 5 is a cross-sectional view for explaining a method for manufacturing a solar cell according to an embodiment of the present invention.

  Embodiments of a solar cell and a method for manufacturing the solar cell according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited to the following description.

Embodiment.
1 to 5 show cross-sectional views at each step for explaining a method for manufacturing a solar cell according to an embodiment of the present invention. The solar cell shown in FIG. 5 manufactured in this way has a second conductivity type layer 3 formed on a first conductivity type semiconductor substrate 1 having minute irregularities (textures) 2 formed on the surface (light receiving surface). The antireflection film 5 and the front silver electrode 6 (light-receiving surface grid electrode) are formed on the semiconductor substrate 1, and the back surface aluminum electrode 7 (back surface electrode) is attached to the back side of the semiconductor substrate 1. The front silver electrode 6 extends in the direction perpendicular to the paper surface.

  As the semiconductor substrate 1 shown in FIG. 1, a p-type single crystal or polycrystalline silicon substrate is used. The wafer surface sliced from the silicon ingot and the vicinity of the surface have physical damage such as cracks during slicing. Therefore, in order to remove this damaged layer, it is immersed in a heated alkaline solution and etched. The semiconductor substrate 1 is not limited to the p-type but may be an n-type substrate.

  Next, as shown in FIG. 2, fine irregularities 2 are formed on the semiconductor substrate 1 by a technique such as alkali etching. On the surface of the solar cell, minute pyramids 2 are formed in order to capture as much light as possible. As a result, the area of the light receiving surface can be increased, the reflected light is reduced, and as much light as possible can be captured. In addition to the pyramid shape, there is an inverted pyramid structure in which a V-shaped groove is formed as the shape of the minute irregularities 2. The fine irregularities 2 can be formed by mixing an additive such as IPA (isopropyl alcohol) in an alkaline solution such as sodium hydroxide and immersing the wafer. The shape of the micro unevenness 2 can be adjusted by the solution concentration, the amount of additive, temperature, and time. As another forming method, the fine irregularities 2 can be formed on the light receiving surface by RIE (Reactive Ion Etching) which is dry etching. RIE is effective in the case of a polycrystalline substrate.

  Next, as shown in FIG. 3, grooves 4 are formed on both sides of the light receiving surface electrode formation scheduled region 10. Since the light receiving surface electrode formation scheduled region 10 extends in the direction perpendicular to the paper surface, the grooves 4 on both sides also extend in the direction perpendicular to the paper surface. As a method of forming the groove 4, for example, there is a method of forming by scribing using a laser. The spacing between the grooves 4 on both sides of the light receiving surface electrode formation scheduled region 10 is, for example, 50 to 90 μm, the groove width is 5 to 10 μm, and the groove depth is 15 to 30 μm. Such a condition is desirable in order to narrow the width of the light receiving surface grid electrode so as not to exceed the groove even if paste bleeding occurs in screen printing described later. The width, depth, and shape of the groove 4 can be adjusted by changing the laser output and wavelength. Examples of the shape include a V shape, a U shape, and a rectangle. The depth of the groove 4 is generally deeper than the depth of the unevenness of the minute unevenness 2.

  Contrary to the above-described procedure, there is also a method of forming the groove 4 by performing scribing using a laser on both sides of the electrode forming portion before forming the minute unevenness 2. After removing the damaged layer in FIG. 1, laser scribing is performed on both sides of the electrode formation scheduled region 10. Thereafter, by performing alkali etching as shown in FIG. 2, it is possible to remove the laser damage and simultaneously form a V-shaped groove.

  Further, after removing the damaged layer, an oxide film is formed, laser irradiation is performed on both sides of the light-receiving surface electrode formation planned region 10, and after opening the oxide film, the groove portion is formed into a V shape by performing hydrofluoric acid and alkali treatment. be able to. After that, it is possible to shift to the formation of the minute unevenness 2 in FIG. 2, but it is also possible to make an inverted pyramid structure by regularly forming minute openings with a diameter of 5 to 20 μm by laser on this oxide film mask. . In the oxide film, a straight opening is formed on the side of the electrode, and a small opening is formed on the other side, and a hydrofluoric acid and alkali treatment are performed, so that a V-shaped groove (groove 4) and an inverted pyramid (micro unevenness 2) beside the electrode. Can be formed simultaneously.

  In addition, there are a method of patterning an etching paste on the groove forming portion by screen printing and a method of mechanically forming the groove 4 using a dicing saw. As described above, the groove 4 can be formed by any method such as laser processing, dry / wet etching, or dicing. Note that the formation of the micro unevenness 2 is not indispensable, and the groove 4 may be formed on both sides of the light receiving surface electrode formation scheduled region 10, so that the light receiving surface electrode formation planned portion may be flat.

  In addition, it is desirable that the formation direction of the groove on the side of the electrode is parallel to the (110) direction, for example.

Subsequently, as shown in FIG. 4, a second conductivity type layer 3 (n-type impurity layer) having a conductivity type different from that of the semiconductor substrate 1 is formed on the semiconductor substrate 1 to form a pn junction. Since there is a pn junction, charges generated by light irradiation are separated and taken out to an external circuit. The second conductivity type layer 3 in which impurities different from those of the semiconductor substrate 1 are diffused is vapor-phase diffusion in a furnace temperature of 700 to 1000 ° C. in the atmosphere of POCl _{3 for} phosphorus diffusion and BBr _{3 for} boron diffusion. And formed on the surface of the semiconductor substrate 1. The thickness of the second conductivity type layer 3 is about 100 to 300 nm. This layer can be adjusted by furnace temperature, processing time, gas flow rate, and the like.

  Next, as shown in FIG. 5, the antireflection film 5 is formed on the second conductivity type layer 3 (n-type impurity layer). As the antireflection film 5, for example, an insulating film such as a silicon nitride film or a silicon oxide film is used. The formation method includes a plasma CVD method and an atmospheric pressure CVD method.

  Further, as shown in FIG. 5, the back surface aluminum electrode 7 is formed on the back surface of the semiconductor substrate 1, and the front silver electrode 6 is formed on the light receiving surface. The back surface aluminum electrode 7 and the front silver electrode 6 on the light receiving surface are formed by screen printing. Screen printing is formed by using a printing mask in which electrode shapes are patterned and a conductive paste such as silver or aluminum. The printing speed is, for example, 100 to 300 mm / s. First, the back surface aluminum electrode 7 is solid-printed and temporarily dried. Thereafter, the surface silver electrode 6 is formed between the grooves 4 formed on the light receiving surface side. At this time, even when the printing paste bleeds or sags, the groove 4 is formed, so that the bleed or sag beyond the groove 4 can be reduced. In addition, the space between the two grooves 4 where the surface silver electrode 6 is printed is the same height as the light receiving area occupying most of the outside of the groove 4, and the screen and the light receiving surface electrode are scheduled to be formed during printing. Since the gap between the region 10 is small and the extruded paste and the substrate are in contact with each other, stable printing can be performed without the electrode grid being scraped or broken without adjusting the composition and viscosity of the paste. Accordingly, paste management is facilitated, yield can be improved, and tact time can be shortened. In addition, since the micro unevenness | corrugation 2 is formed in the light-receiving surface electrode formation plan area 10, since the adhesiveness of a paste and a board | substrate increases, more stable printing can be performed. This makes it possible to print without reducing the printing speed.

  After printing and drying, if the surface silver electrode 6 on the light receiving surface is fired at a high temperature of 700 to 800 ° C., the antireflection film 5 (nitride film) breaks through the fire-through and reaches the second conductivity type layer 3 (diffusion layer). The back surface aluminum electrode 7 forms a BSF (Back Surface Field).

  As described above, according to the method for manufacturing a solar cell according to the embodiment, the groove 4 is formed on both sides of the light receiving surface electrode formation scheduled region 10 to suppress the spread of printing paste bleeding in screen printing. It becomes possible. That is, the electrode width of the light receiving surface grid electrode can be reduced. Thereby, it becomes possible to reduce the shadow loss of the light-receiving surface, increase the amount of power generation, and improve the solar cell characteristics.

  Furthermore, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention in the implementation stage. Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent requirements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the above embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and is described in the column of the effect of the invention. In the case where a certain effect can be obtained, a configuration from which this configuration requirement is deleted can be extracted as an invention. Furthermore, the constituent elements over different embodiments may be appropriately combined.

  As described above, the solar cell and the method for manufacturing the solar cell according to the present invention are useful for the solar cell for forming the light-receiving surface grid electrode using screen printing and the method for manufacturing the solar cell. It is suitable for a solar cell having a ratio light receiving surface grid electrode and a method for manufacturing the solar cell.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Micro unevenness 3 2nd conductivity type layer 4 Groove 5 Antireflection film 6 Surface silver electrode (light-receiving surface electrode)
7 Back surface aluminum electrode 10 Light receiving surface electrode formation planned area

Claims (9)

Forming grooves on both sides along the extending direction of the light receiving surface electrode formation scheduled region on the light receiving surface side of the semiconductor substrate of the first conductivity type;
Forming a second conductivity type layer different from the first conductivity type by diffusing impurities on the light receiving surface side surface of the semiconductor substrate after the formation of the groove;
Forming an antireflection film on the second conductivity type layer;
Forming a light-receiving surface electrode on the light-receiving surface electrode formation planned area using screen printing;
The manufacturing method of the solar cell characterized by including. 2. The method according to claim 1, further comprising a step of forming, on the light receiving surface side of the semiconductor substrate, minute irregularities having irregularities smaller than the depth of the groove before the step of forming the second conductivity type layer. The manufacturing method of the solar cell of description. The method for manufacturing a solar cell according to claim 1, wherein the groove is formed so that the width is 5 to 10 μm and the depth is 15 to 30 μm. The said groove | channel is formed so that the space | interval of the groove | channels of the both sides may be 50-90 micrometers. The manufacturing method of the solar cell of Claim 1, 2, or 3 characterized by the above-mentioned. The solar cell according to any one of claims 1 to 4, wherein the groove is formed so that a shape in a cross section perpendicular to the extending direction of the groove is V-shaped, U-shaped, or rectangular. Manufacturing method. The said extending | stretching direction is parallel to a (110) direction. The manufacturing method of the solar cell of any one of Claims 1-5 characterized by the above-mentioned. 7. The method according to claim 1, further comprising: contacting the light receiving surface electrode with the second conductivity type layer by heating to a temperature of 700 to 800 ° C. after forming the light receiving surface electrode. The manufacturing method of the solar cell of Claim 1. The method for manufacturing a solar cell according to any one of claims 1 to 7, wherein the first conductivity type is p-type, and the second conductivity type is n-type. It manufactured with the manufacturing method of the solar cell of any one of Claims 1-8. The solar cell characterized by the above-mentioned.

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