JP2014210226A - Material coating method, solar cell element electrode forming method, and solar cell element diffusion layer forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform printing capable of suppressing damage to a print target matter and achieving uniform and fine printing on a surface of the print target matter.SOLUTION: Paste supports (twisted yarns, etc.) 12 impregnated with paste are made to contact an upper surface of a print target matter 13 and then separate therefrom, thereby transferring the paste onto the print target matter 13 and coating the paste thereon. By arranging the paste supports 12 at predetermined intervals, it is possible to form a pattern at intended pitches on the print target matter 13. Since there is no need to apply a pressure to the print target matter 13 at a time of coating the paste, it is possible to easily form the pattern uniform on the surface without damaging the print target matter 13.

Description

  The present invention relates to a material coating method and a solar cell element manufacturing method.

  In general, a solar cell element has a structure shown in FIG. In FIG. 1, 1 is a plate shape having a size of 100 to 150 mm square and a thickness of 0.1 to 0.3 mm, and is made of polycrystal, single crystal silicon or the like, and doped with p-type impurities such as boron. It is a p-type semiconductor substrate. This substrate is doped with an n-type impurity such as phosphorus to form an n-type diffusion layer 2, an antireflection film 3 such as SiN (silicon nitride) is provided, and a conductive aluminum paste is formed on the back surface by screen printing. After printing, the back electrode 6 and the BSF (Back Surface Field) layer 4 are simultaneously formed by drying and firing, and after the conductive silver paste is printed on the surface, drying and firing are performed to form the surface electrode 5. It is manufactured by. The surface electrode 5 includes a bus bar electrode for taking out a photo-generated current generated in the solar cell element to the outside, and a finger electrode for collecting current connected to these bus bar electrodes. Hereinafter, the surface of the substrate that is the light receiving surface side of the solar cell is referred to as the front surface (front surface), and the surface of the substrate that is opposite to the light receiving surface side is referred to as the back surface (back surface).

  In a solar cell element manufactured by such a method, it is common to use a screen printing method for electrode formation as described above. The screen printing method is suitable for mass production of a thick film electrode with a high yield as compared with a photolithography method or the like that handles a photosensitive material, and has an advantage that the equipment cost is relatively low. Therefore, the screen printing method includes not only the formation of electrodes for solar cell elements but also the formation of patterns such as electrode layers, resistance layers, dielectric layers, or phosphor layers of large area displays such as plasma display panels and liquid crystal display panels. Widely used in the industry.

  A conventional screen printing method will be described with reference to the drawings. FIG. 2 is a schematic side view of a main part of a general screen printing machine. A series of printing operations will be described with reference to FIG. First, a paste is placed on the screen plate 7 in which a pattern to be formed is opened (the paste is not shown in FIG. 2). The paste is filled into the pattern of the opening of the screen plate 7 by moving the scraper 8 in a certain direction while applying pressure from above the paste. Next, the squeegee 9 is moved in the direction opposite to the scraper 8 while pressure is applied from above, so that the paste filled in the pattern of the opening of the screen plate 7 is placed on the printing stage 10. 11 is transferred. Subsequently, while the scraper 8 moves in the direction opposite to the squeegee 9, the remaining paste is filled again into the pattern of the opening of the screen plate 7. These series of operations are repeated.

  In such a screen printing method, the operation in which the squeegee 9 pushes the paste from the screen plate 7 occupies an important position. For example, a conductive paste containing silver powder, an organic vehicle, and glass frit is generally used to form finger electrodes and bus bar electrodes on the light receiving surface of a solar cell. In order to improve the performance, the conductive paste may be added with solids such as various inorganic oxides and conductive substances. In general, the conductive paste is applied to a semiconductor substrate by a screen printing method and baked to form an electrode of a solar cell element.

  In the screen printing method as described above, the opening of the screen plate is generally formed by a photolithography method. Specifically, a yarn having an appropriate wire diameter is knitted into a mesh pattern in a certain pattern, an emulsion is coated thereon, and a necessary opening is opened by a photolithography method. However, since this exposure technique has limitations such as irregular reflection, it is generally difficult to form a narrow opening of 50 μm or less. Not only that, it is inevitable that the mesh is distorted when the squeegee applies pressure to the screen plate, and it is difficult to repeat printing with high positional accuracy. In addition, when the squeegee applies pressure, the printed material is often damaged and cracked. In addition, since the mesh itself hinders the discharge of the paste, it is often a problem that the marks of the mesh remain in the printed pattern. In the method of applying a material to a solar cell element, it is necessary to minimize damage to the printed material at a low pressure and to perform uniform and fine printing in the surface of the printed material.

  In order to solve this problem, a method of forming notches at both ends of the squeegee has been disclosed (see, for example, Patent Document 1). However, this method cannot completely eliminate the pressure difference between the center and both ends of the squeegee, and the paste used for printing easily escapes sideways from the squeegee notch. There was a problem that had to be sent.

JP 2010-284853 A

  Accordingly, the present invention has been made to solve the above-described problems, and provides a method for repeatedly printing a fine pattern with high accuracy without damaging a printing portion as much as possible.

  Therefore, in the material application method according to the present invention, the linear material support with the material attached is applied to a predetermined position of the printed material, and then the material is applied to the predetermined position of the printed material by releasing the contact from the printed material. It is characterized by doing.

  Moreover, in said material application | coating method, it is good for a material support body to have an unevenness | corrugation on the surface.

  Moreover, in said material application | coating method, it is good for the material support body to be formed from the thread | yarn twisted in multiple numbers.

  In the material application method, a plurality of material supports may be formed at a predetermined interval.

  Further, in the method for forming an electrode of a solar cell element according to the present invention, the material is a conductive paste, and the conductive paste is applied to a printed material using the above-described material application method to form an electrode. To do.

  Moreover, in the diffusion layer forming method of the solar cell element according to the present invention, the material is a coating agent containing a dopant, the coating agent containing the dopant is applied to a silicon substrate using the material coating method, and the diffusion layer is formed. It is characterized by forming.

  Further, in the method for forming a diffusion layer of a solar cell element according to the present invention, the material is a coating agent containing an etchant, and the coating agent containing the etchant is applied to a printed material using the material coating method described above, and is selectively used. Etching is performed.

It is sectional drawing of a solar cell element. It is a side surface schematic diagram of the principal part of a general screen printer. It is a schematic diagram of the paste support body 12 and the to-be-printed material 13 by this invention. It is a side surface schematic diagram which shows the operation | movement which transfers the paste to the to-be-printed material 13 with the paste support body 12. FIG.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention can be implemented in a wide variety of other embodiments in addition to the following description, and the scope of the present invention is not limited to the following, but is described in the claims. is there. Further, the drawings are not shown to scale. In order to make the description and understanding of the present invention clearer, dimensions are enlarged depending on related members, and unimportant parts are not shown.

  As described above, FIG. 1 is a cross-sectional view showing a general structure of a solar cell element. In FIG. 1, 1 is a semiconductor substrate, 2 is a diffusion layer, 3 is an antireflection film / passivation film, 4 is a BSF layer, 5 is a front electrode, and 6 is a back electrode.

  Here, the manufacturing process of the solar cell element shown in FIG. 1 will be described. First, the semiconductor substrate 1 is prepared. The semiconductor substrate 1 is made of single crystal or polycrystalline silicon, and may be either p-type or n-type, but includes p-type semiconductor impurities such as boron, and has a specific resistance of 0.1 to 4.0 Ω · cm. A p-type silicon substrate is often used. Hereinafter, a solar cell element manufacturing method using a p-type silicon substrate will be described as an example. A plate-shaped member having a size of 100 to 150 mm square and a thickness of 0.05 to 0.30 mm is preferably used. Then, the surface of the p-type silicon substrate that becomes the light-receiving surface of the solar cell element is immersed in an acidic solution such as hydrofluoric acid or hydrofluoric nitric acid to remove surface damage caused by slicing, etc. A concavo-convex structure called a texture is formed by chemical etching with an alkali solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution, followed by washing and drying. The concavo-convex structure causes multiple reflection of light on the light receiving surface of the solar cell element. Therefore, by forming the concavo-convex structure, the reflectance is effectively reduced and the conversion efficiency is improved.

Thereafter, a sheet resistance is formed by a thermal diffusion method in which a p-type silicon substrate is placed in a high-temperature gas of 850 to 1000 ° C. containing, for example, POCl ₃ and diffuses an n-type impurity element such as phosphorus over the entire surface of the p-type silicon substrate. Is 30-300Ω / □
About n-type diffusion layer 2 is formed on the front side. When the n-type diffusion layer is formed by the thermal diffusion method, the n-type diffusion layer may be formed on both sides and the end face of the p-type silicon substrate. An unnecessary n-type diffusion layer can be removed by immersing a p-type silicon substrate in which the front side of the layer is coated with an acid-resistant resin in a hydrofluoric acid solution. Thereafter, the glass layer formed on the surface of the semiconductor substrate at the time of diffusion is removed by immersing in a chemical such as a diluted hydrofluoric acid solution, and washed with pure water.

Further, an antireflection film / passivation film 3 is formed on the front side of the p-type silicon substrate. The antireflection film / passivation film 3 is made of, for example, SiN, and is formed by, for example, a plasma CVD method in which a mixed gas of SiH ₄ and NH ₃ is diluted with N ₂ and is plasmatized by glow discharge decomposition and deposited. The This antireflection film / passivation film 3 is formed so as to have a refractive index of about 1.8 to 2.3 in consideration of a refractive index difference from the p-type silicon substrate, and has a thickness of about 500 to 1000 mm. Formed to prevent light from being reflected from the surface of the p-type silicon substrate and to effectively incorporate light into the p-type silicon substrate. In addition, this SiN also functions as a passivation film that has a passivation effect on the n-type diffusion layer when formed, and has the effect of improving the electrical characteristics of the solar cell element together with the antireflection function.

  Next, a conductive paste containing, for example, aluminum, glass frit, varnish and the like is screen-printed on the back surface and dried. Thereafter, a conductive paste containing, for example, silver, glass frit, varnish and the like is screen-printed on the front surface and dried. Thereafter, the BSF layer 4, the front electrode 5, and the back electrode 6 are formed by firing each electrode paste at a temperature of about 500 ° C. to 950 ° C.

  In a typical method for manufacturing a crystalline silicon solar cell element as described above, electrodes are formed by screen printing. In the conventional screen printing method, when a printing operation is performed in which the conductive paste is pushed out from the opening of the screen plate with a squeegee, if printing pressure is applied to the squeegee, an inclination may occur when the stage on which the substrate is placed and the squeegee come into contact. In addition, the squeegee bends because it receives a repulsive force to return to the original shape from the screen plate itself pressed by the printing pressure. For this reason, the force with which the squeegee presses the screen plate and the printing material does not become uniform, the tension applied to the plate becomes non-uniform, and it is difficult to make the printing pattern of the printing material uniform in the surface. Increasing the printing pressure can reduce the overall deflection of the squeegee, but it can damage the screen plate and make it easier to crack the substrate. For this reason, since it is necessary to clean the apparatus every time the screen plate or the substrate is cracked, there is a problem in that workability is lowered. The deflection can be reduced by adjusting the hardness of the squeegee, but if you use a squeegee with a low hardness, the amount of paste to be applied will be too large to print accurately, and if you use a squeegee with a high hardness, On the contrary, sufficient discharge of the paste is hindered. By using a sufficiently long squeegee, it is possible to make the pressure of the squeegee uniform only at the part of the screen plate pattern. There is a problem that it gets bigger. These problems are solved by the present invention. Specifically, in the method for producing a solar cell element according to the present invention, for example, at the time of electrode formation, the paste support immersed in the conductive paste is brought into contact with the substrate to be printed instead of screen printing. The conductive paste is transferred and applied. The paste support used here preferably has irregularities on the surface. Specifically, the paste support is preferably a yarn in which a plurality of strands are twisted together. The improvement of repeated printing accuracy according to the present invention is due to the following reason.

  A method for solving this problem will be described with reference to FIGS. The material application method in the embodiment of the present invention is characterized in that the paste support 12 is a linear or thread-like object to which the paste is attached. The paste is attached to the paste support 12, then brought into contact with the substrate 13 and then released to transfer the paste to the substrate 13. The paste support 12 is supported at both ends by two tensioners 14 and can be applied with tension, so that it can easily have linearity, and there is no need to apply excessive pressure to the substrate 13 during use. Therefore, it is difficult for distortion to occur, and the paste can be applied to the substrate 13 with good repeatability.

  Since the paste support 12 provided here has irregularities on the surface, the paste can be transferred more efficiently. Specifically, since the paste penetrates between the irregularities of the paste support 12, it becomes possible for the paste support 12 to hold more paste, and when the paste support 12 and the substrate 13 are in contact with each other. Therefore, it becomes possible to transfer more paste to the substrate 13. As for the unevenness of the surface of the paste support 12 provided here, the distance between the concave portions and the convex portions is desirably 0.1 μm or more and 50 μm or less, and more desirably 1 μm or more and 10 μm or less. . When this distance is shorter than this, it causes an increase in cost due to difficulty in forming irregularities. On the other hand, when this distance is longer than this, the amount of paste supported on the paste support 12 is reduced, and the effect of the present invention is weakened.

  Moreover, when the paste support body 12 provided here is formed from a plurality of twisted yarns, the transfer of the paste can be performed more efficiently. Specifically, since the paste penetrates between the twisted yarns, it becomes possible for the paste support 12 to hold a larger amount of paste, and the surface area when coming into contact with the substrate to be printed 13 becomes larger. More transfer to the printed material 13 becomes possible. Further, when the paste support 12 is a twisted yarn, the unevenness as described above can be formed naturally, so that the paste support 12 can be formed at a low manufacturing cost. The twisted yarn provided here preferably has a single yarn diameter of 10 μm to 100 μm, more preferably 18 μm to 60 μm. If the diameter of one yarn is thicker than this, it becomes difficult to form a desired fine line. On the other hand, if the diameter of one yarn is thinner than this, the cost of forming the yarn increases, and the strength of the yarn further decreases, detracting from the effect of the present invention.

  In addition, the material of the yarn provided here is not particularly limited, but, for example, a material that maintains a certain level of strength, such as polyester, nylon, and stainless steel, is desirable. Moreover, the method of twisting the yarn provided here is not particularly limited, and may be right-handed or left-handed. Further, the number of twists is not limited, and any of a twisted twist, a medium twist, a strong twist, or a very strong twist may be used. Further, the twisted form is not limited, and any of single twisted yarn, various twisted yarn, piece twisted yarn, wall twisted yarn and the like may be used.

  Further, since a plurality of paste supports 12 provided here are formed at a predetermined interval, a desired pattern can be formed on the substrate 13 by one transfer. For example, it is possible to form a collector electrode of a solar cell element accurately and inexpensively by a simple method. In forming the collector electrode, the interval between the paste supports 12 is not particularly limited as long as the conversion efficiency of the solar cell element can be maximized, but it is generally desirable that the interval be between 0.5 mm and 5 mm.

  In addition, the paste that is attached to the paste support 12 provided here and transferred to the substrate 13 is not particularly defined, but when the substrate 13 is a semiconductor substrate and the paste is a conductive paste, A collector electrode can be formed. When this paste is a coating agent containing a dopant, a selective emitter layer of a solar cell element can be formed. When this paste is a coating agent containing an etchant, a selective etching layer can be formed. Applications of the present invention are not limited to those described here, but can be utilized in a wide range of applications.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

  First, by performing outer diameter processing on a p-type silicon substrate made of p-type single crystal silicon having a specific resistance of about 1 Ω · cm, which is doped with boron and sliced to a thickness of 0.2 mm, a side of 15 cm is formed. The square plate shape. Then, this p-type silicon substrate is immersed in a hydrofluoric acid solution for 15 seconds for damage etching, and further chemically etched with a 70 ° C. solution containing 2% KOH and 2% IPA for 5 minutes, and then washed with pure water. The texture structure was formed on the p-type silicon substrate surface by drying.

An n layer was formed on the p-type silicon substrate by performing a thermal diffusion process on the p-type silicon substrate in a POCl ₃ gas atmosphere at a temperature of 850 ° C. for 30 minutes. The sheet resistance after heat treatment of the surface of the p-type silicon substrate prepared here was about 80Ω / □ on one side, and the diffusion depth of the n layer was 0.3 μm.

Thereafter, after forming an acid resistant resin on the n layer, the p-type silicon substrate was immersed in a hydrofluoric acid solution for 10 seconds to remove the portion of the n layer where the acid resistant resin was not formed. Thereafter, the acid-resistant resin was removed to form an n layer only on the surface of the p-type silicon substrate. Subsequently, SiN serving as an antireflection film and a passivation film is formed with a thickness of 1000 mm on the surface of the p-type silicon substrate on which the n layer is formed by plasma CVD using SiH ₄ , NH ₃ , and N _2. did. Next, a conductive aluminum paste was printed on the back surface of the p-type silicon substrate using a screen printing method, and dried at 150 ° C. Further, a conductive silver paste was printed on the front surface of the p-type silicon substrate using a screen printing method and dried at 150 ° C. to form a collecting electrode (Comparative Example). On the other hand, a conductive silver paste was transferred onto the front surface of the p-type silicon substrate using a paste support made of twisted yarn as shown in FIG. 3, and dried at 150 ° C. to form a collector electrode. In this case, the twisted yarn was twisted by three twists with medium twist, and one yarn having a diameter of 30 μm was set as Example 1, and 50 μm was set as Example 2. Thereafter, a conductive silver paste was printed on the bus bar electrode using a screen printing method so as to be orthogonal to the collector electrode for all the conditions of Comparative Example, Example 1 and Example 2, at 150 ° C. Dried. Finally, the solar cell element was produced by baking an electrically conductive paste from the processed substrate so far at a maximum temperature of 800 ° C. to form an electrode.

  In Table 1, by the method of each of the comparative example, Example 1, and Example 2, when the collector electrode of 1000 solar cell elements is formed, the substrate breakage rate, the average conversion efficiency of the solar cell elements, Average short circuit current, average open circuit voltage, average fill factor are shown.

  As shown in Table 1, by using the examples according to the present invention, it is possible to reduce the substrate breakage rate when forming the collector electrode of the solar cell element and to increase the average conversion efficiency of the solar cell element as compared with the comparative example. be able to. The reason why the substrate breakage rate can be reduced is that the collector electrode can be formed without damaging the substrate, so that the substrate is difficult to break, and the conversion efficiency is increased because the thin collector electrode pattern is uniform in the surface. This is because, in particular, the series resistance of the light-receiving surface electrode is reduced, and the fill factor and the short-circuit current are increased.

  According to the present invention, the paste support (twisted yarn or the like) dipped in the paste is brought into contact with the printed material and then released, whereby the paste can be transferred and applied onto the printed material. By disposing the paste support at predetermined intervals, a pattern with a target pitch can be formed on the substrate. Since it is not necessary to apply pressure to the printed material at the time of applying the paste, an in-plane uniform pattern can be easily formed without damaging the printed material. Thereby, the substrate breakage rate of the solar cell element can be reduced, and the average conversion efficiency of the solar cell element can be increased. In the future, it is expected that a selective emitter layer or the like may be formed on the silicon substrate according to the present invention to further increase the conversion efficiency.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Diffusion layer 3 Antireflection film / passivation film 4 BSF layer 5 Front surface electrode 6 Back surface electrode 7 Screen plate 8 Scraper 9 Squeegee 10 Printing stage 11 Substrate 12 Paste support 13 Substrate 14 Tensioner

Claims (7)

  A material characterized in that the material is applied to a predetermined position of the substrate by releasing a linear material support with the material adhered to the substrate at a predetermined position after contacting the substrate. Application method.   The material coating method according to claim 1, wherein the material support has irregularities on a surface.   The material application method according to claim 1 or 2, wherein the material support is formed of a plurality of twisted yarns.   The material application method according to any one of claims 1 to 3, wherein a plurality of the material supports are formed at a predetermined interval.   The method for forming an electrode of a solar cell element, wherein the material is a conductive paste, and the conductive paste is applied to a print using the material coating method according to any one of claims 1 to 4 to form an electrode. .   The said material is a coating agent containing a dopant, The solar cell which apply | coats the coating agent containing this dopant to to-be-printed material using the material coating method of any one of Claim 1 to 4, and forms a diffused layer A method for forming a diffusion layer of an element.   5. The sun in which the material is a coating agent containing an etchant, and the coating agent containing the etchant is applied to a substrate using the material coating method according to claim 1, and selective etching is performed. A method for forming a diffusion layer of a battery element.