JP2011165805A - Manufacturing method of solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a solar cell, with which the solar cell having an electrode with high contact strength and low electrode resistance even if a line is thinned is formed and having superior photoelectric conversion efficiency can be manufactured. <P>SOLUTION: The manufacturing method includes a process for forming an antireflection film formed of an insulating film on one face of a semiconductor substrate, a process for forming a light reception face-side glass layer on the antireflection film by arranging glass paste including glass particles in a shape almost similar to a light reception face-side electrode, a process for firing the light reception face-side glass layer at a temperature equal to or more than a glass transition point of the glass particles and penetrating the light reception face-side glass layer to the semiconductor substrate, a process for removing the light reception face-side glass layer and forming an opening reaching the semiconductor substrate in a region where the light reception face-side glass layer in the antireflection film is arranged, a process for arranging low temperature firing conductive paste including conductive nanoparticles and showing conductivity by low temperature firing in the opening and a process for firing the low temperature firing conductive paste at a low temperature and forming the light reception face-side electrode which is directly bonded to the semiconductor substrate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a solar cell.

  In a conventional solar cell, an n-type diffusion layer is formed on the entire surface of a polycrystalline silicon or single crystal silicon p-type silicon substrate, and a minute unevenness on the surface on the light-receiving surface side is provided. Further, an antireflection film is formed on the minute irregularities, and a light receiving surface side electrode is provided in a comb shape thereon. On the other hand, an electrode is provided on the entire back surface of the p-type silicon substrate.

  A method for manufacturing a solar cell will be described. For example, a wet etching process using a mixed solution of an alkali solution and alcohol, a mixed acid solution of hydrofluoric acid and nitric acid, or a dry etching process using a reactive ion etching (RIE) method is used. Micro unevenness is formed on the surface of the crystalline silicon substrate. The fine irregularities on the surface are formed to suppress the reflection of light from the outside, confine the light in the solar cell, and increase the efficiency of converting the light into electricity.

Next, for example, phosphorus is diffused on the surface of the p-type polycrystalline silicon substrate by a vapor phase diffusion method in phosphorus oxychloride (POCl ₃ ) gas to form an n-type diffusion layer. Next, the oxide film formed on the surface in the phosphorus diffusion step is removed by immersing the p-type polycrystalline silicon substrate in hydrogen fluoride. Thereafter, a silicon nitride film as an antireflection film is formed on the light-receiving surface side surface of the p-type polycrystalline silicon substrate (surface of the n-type diffusion layer) by plasma chemical vapor deposition (plasma CVD).

  Next, an electrode pattern of the light-receiving surface side electrode patterned in a comb shape is formed on the surface on the light-receiving surface side of the p-type polycrystalline silicon substrate by a printing method using a silver paste containing a glass component. Then, the patterned silver paste is dried at, for example, 200 ° C. and then fired at, for example, 700 ° C. to 800 ° C., whereby the antireflection film is removed by the glass component in the silver paste (fire-through), and the light-receiving surface side electrode Electrical conduction is obtained between the n-type diffusion layer and the n-type diffusion layer.

  Next, an electrode pattern of the back electrode is formed on almost the entire back surface of the p-type polycrystalline silicon substrate by a printing method using aluminum paste, and the back surface of the p-type polycrystalline silicon substrate is formed by a printing method using silver paste. An electrode pattern of an external extraction electrode is formed in a part. And after drying an electrode pattern at 200 degreeC, for example, it bakes at 700 degreeC-800 degreeC, for example, and forms a back surface side electrode. A solar cell is completed as described above.

  In the solar cell formed in this way, in order to increase the area of the light receiving surface and improve the conversion efficiency, the light receiving surface side electrode is thinned. However, when the electrode is thinned, the cross-sectional area of the electrode decreases and the electrode resistance value of the electrode increases. That is, when the electrode is thinned, the cross-sectional area of the formed electrode is small in one printing process, so that a sufficiently low electrode resistance value cannot be obtained, and the characteristics of the solar cell deteriorate.

  Therefore, the aspect ratio (electrode height / electrode width) in which the height of the electrode is increased with respect to the contact area between the electrode and the silicon substrate in order to secure the cross-sectional area of the electrode and reduce the electrode resistance. High electrode formation is required. High aspect ratio electrodes can be formed by multiple printing steps. However, in this case, there arises a problem of electrode peeling and a reduction in production efficiency. In particular, when the electrode width is 50 μm or less, a large number of laminated printings are required, and these problems become remarkable.

  Here, the light-receiving surface side electrode is formed using a paste containing silver as a main component and mixed with a low-melting glass, and the adhesion strength of the electrode can be improved by increasing the glass component contained in the paste. it can. However, since glass is an insulator, increasing the glass component increases the electrode resistance, which causes deterioration of the characteristics of the solar cell.

  As a method for solving this, for example, by forming and firing an electrode with a paste containing a low-melting glass, it is immersed in hydrofluoric acid, and the glass component in the electrode is dissolved to lower the resistance value of the electrode. An example of improving the characteristics of a solar cell is shown (for example, see Patent Document 1 and Patent Document 2).

JP-A-9-213979 Japanese Patent Laid-Open No. 10-233518

  However, melting the glass component in the electrode to lower the resistance value of the electrode as in the prior art described above has a problem in that the adhesion strength of the electrode is lowered and the reliability of the electrode is deteriorated.

  The present invention has been made in view of the above, and even when thinned, a solar cell that can produce a solar cell having high adhesion strength and low electrode resistance to form a solar cell with excellent photoelectric conversion efficiency. It aims at obtaining the manufacturing method of this.

  In order to solve the above-described problems and achieve the object, a method for manufacturing a solar cell according to the present invention is a method for manufacturing a solar cell having a light-receiving surface side electrode on one surface of a semiconductor substrate, A first step of forming an antireflection film made of an insulating film on one surface, and a glass paste containing glass particles in a region where the light receiving surface side electrode is formed on the antireflection film is substantially equivalent to the light receiving surface side electrode. A second step of forming a light-receiving surface side glass layer in a shape, and firing the light-receiving surface side glass layer at a temperature equal to or higher than a glass transition point of the glass particles to move the light-receiving surface side glass layer to the semiconductor substrate A third step of penetrating; a fourth step of removing the light-receiving surface side glass layer and forming an opening reaching the semiconductor substrate in a region of the antireflection film where the light-receiving surface side glass layer is disposed; The opening A fifth step of disposing a low-temperature fired conductive paste containing conductive nanoparticles and exhibiting conductivity by low-temperature firing; and the light-receiving surface side that is fired at a low temperature and directly bonded to the semiconductor substrate And a sixth step of forming an electrode.

  According to the present invention, it is possible to form a thin, low-resistance electrode without reducing the electrode strength, and to prevent a decrease in photoelectric conversion efficiency of the solar cell and electrode peeling due to the electric resistance value of the electrode. Thus, there is an effect that a solar cell having good solar cell characteristics can be produced.

1-1 is sectional drawing for demonstrating the structure of the solar cell concerning Embodiment 1 of this invention. FIGS. 1-2 is sectional drawing for demonstrating the structure of the solar cell concerning Embodiment 1 of this invention. FIGS. 1-3 is a figure for demonstrating the structure of the solar cell concerning Embodiment 1 of this invention, and is a top view of the solar cell seen from the light-receiving surface side. 1-4 is a figure for demonstrating the structure of the solar cell concerning Embodiment 1 of this invention, and is a bottom view of the solar cell seen from the light receiving surface and the other side. 1-5 is a figure for demonstrating the structure of the solar cell concerning Embodiment 1 of this invention, and is sectional drawing which expands and shows the light-receiving surface side of a solar cell. FIGS. 2-1 is sectional drawing for demonstrating an example of the manufacturing process of the solar cell concerning Embodiment 1 of this invention. FIGS. FIGS. 2-2 is sectional drawing for demonstrating an example of the manufacturing process of the solar cell concerning Embodiment 1 of this invention. FIGS. FIGS. 2-3 is sectional drawing for demonstrating an example of the manufacturing process of the solar cell concerning Embodiment 1 of this invention. FIGS. FIGS. 2-4 is sectional drawing for demonstrating an example of the manufacturing process of the solar cell concerning Embodiment 1 of this invention. FIGS. FIGS. 2-5 is sectional drawing for demonstrating an example of the manufacturing process of the solar cell concerning Embodiment 1 of this invention. FIGS. FIGS. 2-6 is sectional drawing for demonstrating an example of the manufacturing process of the solar cell concerning Embodiment 1 of this invention. FIGS. 2-7 is sectional drawing for demonstrating an example of the manufacturing process of the solar cell concerning Embodiment 1 of this invention. FIGS. 2-8 is sectional drawing for demonstrating an example of the manufacturing process of the solar cell concerning Embodiment 1 of this invention. FIGS. FIG. 3 is a flowchart for explaining an example of the manufacturing process of the solar cell according to the first embodiment of the present invention.

  Embodiments of a method for manufacturing a solar cell according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding. The same applies between the drawings.

Embodiment 1 FIG.
FIGS. 1-1 to 1-5 are diagrams for explaining the configuration of the solar cell 1 according to the first embodiment of the present invention. FIGS. 1-1 and 1-2 are cross-sectional views of the solar cell 1. FIGS. 1-3 is a top view of the solar cell 1 viewed from the light receiving surface side, and FIG. 1-4 is a bottom view of the solar cell 1 viewed from the side opposite to the light receiving surface. 1-1 is a cross-sectional view in the AA direction of FIGS. 1-3 and 1-4. 1-2 is a cross-sectional view in the BB direction of FIGS. 1-3 and 1-4. FIG. 1-5 is an enlarged cross-sectional view of the light receiving surface side of the solar cell 1.

  In the solar cell 1 according to the present embodiment, the second conductivity type n-type impurity diffusion layer 3 is formed by phosphorous diffusion on the light-receiving surface side of the p-type single crystal silicon substrate which is the first conductivity type semiconductor substrate 2. A semiconductor substrate 11 having a pn junction is formed with a thickness of about 0.2 μm, and an antireflection film 4 made of a silicon nitride film (SiN film) is formed on the n-type impurity diffusion layer 3. . Note that the first conductive semiconductor substrate is not limited to a p-type single crystal silicon substrate, and a p-type polycrystalline silicon substrate, an n-type polycrystalline silicon substrate, or an n-type single crystal silicon substrate is used. May be.

  In addition, on the surface on the light receiving surface side of the semiconductor substrate 11 (n-type impurity diffusion layer 3), minute unevenness 3a is formed with a depth of about 10 μm as a texture structure in order to improve the light utilization rate. The minute unevenness 3a has a structure that increases the area of the light receiving surface that absorbs light from the outside, suppresses the reflectance at the light receiving surface, and confines light.

The antireflection film 4 is made of an insulating film such as a silicon nitride film (SiN film), a silicon oxide film (SiO ₂ film), or a titanium oxide film (TiO ₂ ) film. Further, a plurality of long and narrow surface silver grid electrodes 5 are provided side by side on the light receiving surface side of the semiconductor substrate 11, and a thick surface silver bus electrode 6 electrically connected to the surface silver grid electrode 5 is connected to the surface silver grid electrode 5. They are provided so as to be substantially orthogonal to each other, and are electrically connected to the n-type impurity diffusion layer 3 at the bottom portions. The front silver grid electrode 5 and the front silver bus electrode 6 are made of a silver material. The front silver grid electrode 5 and the front silver bus electrode 6 are formed in the opening 4 a formed in the antireflection film 4.

  The front silver grid electrodes 5 are arranged substantially in parallel with a predetermined width and interval, and collect electricity generated inside the semiconductor substrate 11. The front silver bus electrodes 6 have a predetermined width and are arranged, for example, two to three per one solar cell, and take out the electricity collected by the front silver grid electrode 5 to the outside. The front silver grid electrode 5 and the front silver bus electrode 6 constitute a light receiving surface side electrode 12 as a first electrode. Since the light receiving surface side electrode 12 blocks sunlight incident on the semiconductor substrate 11, it is desirable to reduce the area as much as possible from the viewpoint of improving the power generation efficiency, and a comb-shaped surface as shown in FIG. In general, the silver grid electrode 5 and the bar-shaped front silver bus electrode 6 are arranged.

  On the other hand, a back aluminum electrode 7 made of an aluminum material is provided on the entire back surface (surface opposite to the light receiving surface) of the semiconductor substrate 11 and extends in substantially the same direction as the front silver bus electrode 6. A back silver electrode 8 made of is provided as an extraction electrode. The back aluminum electrode 7 and the back silver electrode 8 constitute a back electrode 13 as a second electrode.

  Further, an alloy layer of aluminum (Al) and silicon (Si) is formed by firing on the surface layer part on the back surface (surface opposite to the light receiving surface) side of the semiconductor substrate 11 and below the back aluminum electrode 7. Underneath, a p + layer (BSF (Back Surface Field)) (not shown) containing high concentration impurities by aluminum diffusion is formed. The p + layer (BSF) is provided to obtain the BSF effect, and the electron concentration in the p-type layer (semiconductor substrate 2) is increased by an electric field having a band structure so that electrons in the p-type layer (semiconductor substrate 2) do not disappear. To.

  In solar cell 1 configured in this way, sunlight is irradiated from the light-receiving surface side of solar cell 1 to the pn junction surface of semiconductor substrate 11 (the junction surface between semiconductor substrate 2 and n-type impurity diffusion layer 3). , Holes and electrons are generated. Due to the electric field at the pn junction, the generated electrons move toward the n-type impurity diffusion layer 3 and the holes move toward the p + layer. As a result, electrons are excessive in the n-type impurity diffusion layer 3 and holes are excessive in the p + layer, resulting in generation of photovoltaic power. This photovoltaic power is generated in the direction in which the pn junction is forward-biased, the light receiving surface side electrode 12 connected to the n-type impurity diffusion layer 3 becomes a negative pole, and the back aluminum electrode 7 connected to the p + layer becomes a positive pole. Thus, a current flows through an external circuit (not shown).

In the solar cell 1 according to the present embodiment configured as described above, for example, the electrical resistance value of the light-receiving surface side electrode 12 is set to a low resistance value of about 1.5 × 10 ⁻⁶ Ω · m or less, and further the semiconductor Adhesion strength with the substrate 11 (n-type impurity diffusion layer 3) is good. Thereby, in the solar cell 1 concerning this Embodiment, the fall of the photoelectric conversion efficiency of the solar cell resulting from the electrical resistance value of the light-receiving surface side electrode 12, and peeling of the light-receiving surface side electrode 12 are prevented, and a favorable solar cell A solar cell having characteristics has been realized. In such a solar cell 1 according to the present embodiment, even when the width of the front silver grid electrode 5 is reduced to, for example, 50 μm or less, a solar cell having good solar cell characteristics can be realized.

  Hereinafter, the manufacturing method of the solar cell 1 concerning this Embodiment is demonstrated along drawing. FIGS. 2-1 to 2-8 are cross-sectional views for explaining an example of the manufacturing process of the solar cell 1 according to the first embodiment of the present invention. FIG. 3 is a flowchart for explaining an example of the manufacturing process of the solar cell 1 according to the first embodiment of the present invention.

  First, as the semiconductor substrate 2, for example, a p-type single crystal silicon substrate having a thickness of several hundred μm is prepared, and substrate cleaning is performed. Since the p-type single crystal silicon substrate is manufactured by slicing an ingot formed by cooling and solidifying molten silicon with a wire saw, damage at the time of slicing remains on the surface. Therefore, the p-type single crystal silicon is generated when the silicon substrate is cut out by dipping the p-type single crystal silicon substrate in an acid such as hydrofluoric acid or a heated alkaline solution, for example, an aqueous sodium hydroxide solution and etching the surface. Remove damaged areas near the surface of the substrate. Then, it wash | cleans with a pure water (step S10, FIGS. 2-1).

  Subsequent to the damage removal, for example, the p-type single crystal silicon substrate is immersed in a mixed solution of sodium hydroxide and isopropyl alcohol (IPA) and anisotropic etching is performed on the p-type single crystal silicon substrate to obtain a p-type single crystal. A textured structure is formed by forming minute irregularities 3a with a depth of about 10 μm on the light receiving surface side of the silicon substrate (step S20, FIG. 2-2). By providing such a texture structure on the light-receiving surface side of the p-type single crystal silicon substrate, multiple reflection of light is generated on the surface side of the solar cell 1, and light incident on the solar cell 1 is efficiently transmitted to the semiconductor substrate 11. Can be absorbed, and the reflectance can be effectively reduced to improve the conversion efficiency. When the damaged layer is removed and the texture structure is formed with an alkaline solution, the concentration of the alkaline solution may be adjusted to a concentration according to each purpose, and continuous treatment may be performed. Further, the micro unevenness 3a having a depth of about 1 μm to 3 μm may be formed on the surface of the p-type single crystal silicon substrate by a dry etching process such as reactive ion etching (RIE).

Next, a diffusion process is performed to form a pn junction in the semiconductor substrate 2 (step S30). That is, a group V element such as phosphorus (P) is diffused into the semiconductor substrate 2 to form the n-type impurity diffusion layer 3 having a thickness of several hundred nm. Here, a pn junction is formed on a p-type single crystal silicon substrate having a texture structure on the surface by diffusing phosphorus by thermal diffusion at a high temperature by a vapor phase diffusion method in phosphorus oxychloride (POCl ₃ ) gas. . Thus, the semiconductor substrate 2 made of p-type single crystal silicon which is the first conductivity type layer, and the n-type impurity diffusion layer 3 which is the second conductivity type layer formed on the light receiving surface side of the semiconductor substrate 2, A semiconductor substrate 11 having a pn junction is obtained.

The concentration of phosphorus diffused at this time can be controlled by the concentration of phosphorus oxychloride (POCl ₃ ) gas, the temperature atmosphere, and the heating time. The sheet resistance of the n-type impurity diffusion layer 3 formed on the surface of the semiconductor substrate 2 is, for example, 40Ω / □ to 60Ω / □.

  Here, a glassy (phosphosilicate glass, PSG: Phospho-Silicate Glass) layer deposited on the surface during the diffusion treatment is formed on the surface immediately after the formation of the n-type impurity diffusion layer 3. Is removed using a hydrofluoric acid solution or the like.

  Although not shown in the figure, the n-type impurity diffusion layer 3 is formed on the entire surface of the semiconductor substrate 2. Therefore, in order to remove the influence of the n-type impurity diffusion layer 3 formed on the back surface or the like of the semiconductor substrate 2, the n-type impurity diffusion layer 3 is left only on the light-receiving surface side of the semiconductor substrate 2, and n in other regions is left. The type impurity diffusion layer 3 is removed.

Next, in order to improve the photoelectric conversion efficiency, the antireflection film 4 is formed with a uniform thickness on one surface of the light receiving surface of the semiconductor substrate 11, that is, on the n-type impurity diffusion layer 3 (step S40, FIG. 2-3). ). The film thickness and refractive index of the antireflection film 4 are set to values that most suppress light reflection. The antireflection film 4 is formed by using, for example, a plasma CVD method, using a mixed gas of silane (SiH ₄ ) gas and ammonia (NH ₃ ) gas as a raw material, for example, at 300 ° C. or higher and under reduced pressure. A silicon nitride film is formed as the film 4. The refractive index is, for example, about 2.0 to 2.2, and the film thickness is, for example, about 60 nm to 80 nm. Note that two or more films having different refractive indexes may be laminated as the antireflection film 4. In addition to the plasma CVD method, the antireflection film 4 may be formed by vapor deposition, thermal CVD, or the like. It should be noted that the antireflection film 4 formed in this way is an insulator, and simply forming the light receiving surface side electrode 12 thereon does not act as a solar cell.

  Subsequently, the back surface side electrode 13 (before baking) is formed by screen printing (step S50, FIGS. 2-4). First, a silver paste, which is an electrode material paste, is applied to the shape of the back silver electrode 8, which is an electrode that is electrically connected to the outside, by screen printing on the back surface side (opposite to the light receiving surface) of the semiconductor substrate 11 and dried. Let Next, an aluminum paste 7a, which is an electrode material paste, is applied to the shape of the back aluminum electrode 7 on the surface on the back surface side of the semiconductor substrate 11 excluding the back silver electrode 8, and dried. In the figure, only the aluminum paste 7a is shown, and the description of the silver paste is omitted. In the screen printing, a paste containing silver particles or aluminum particles is pushed into a printing mask with a squeegee, and the pattern is formed through the opening of the printing mask. In the printing mask, a resin film pattern extracted by photolithography is formed on a metal mesh.

  Next, a light receiving surface side electrode 12 composed of a plurality of surface silver grid electrodes 5 and several surface silver bus electrodes 6 is formed by screen printing using an electrode material paste containing silver (before firing). ). The light-receiving surface side electrode 12 has a function of collecting electrons generated on the surface of the solar cell 1, but is a portion that blocks sunlight and does not contribute to power generation. For this reason, it is desirable to reduce the area by reducing the width of the light receiving surface side electrode 12 as much as possible.

  However, in this case, the electrode cross-sectional area of the light-receiving surface side electrode 12 is reduced and the resistance is increased, which causes deterioration of solar cell characteristics. Therefore, it is preferable that the light receiving surface side electrode 12 is laminated to increase the height and the cross sectional area to be increased. However, electrode peeling easily occurs in the laminated portion, and the printing-drying process increases, so that the electrode needs to be aligned and the process becomes complicated.

  Therefore, by using a paste having higher conductivity than the conventional electrode material paste containing silver, for example, an electrode material paste containing silver nanoparticles and exhibiting conductivity by low-temperature firing, even a thin wire or a single layer or two layers can sufficiently conduct electricity. There is a possibility that a light receiving surface side electrode having a rate can be realized. Here, the low-temperature firing is firing at a temperature of about 100 ° C to 300 ° C. Actually, the electrode material paste containing silver nanoparticles exhibits conductivity in a drying process at a temperature of about 150 ° C. to 250 ° C.

  However, first, only the back silver electrode is formed using a silver paste by a high-temperature baking process, and then the electrode material paste containing silver nanoparticles and showing conductivity is applied and dried by low-temperature baking to form the light-receiving surface side electrode. Even so, since the antireflection film, which is an insulating film, is formed on one surface of the light receiving surface of the semiconductor substrate 11, that is, on the n-type impurity diffusion layer 3, the light receiving surface side electrode and the semiconductor substrate 11 (n-type impurity diffusion). Electrical connection with layer 3) is not possible.

  Also, a back silver electrode is formed using a silver paste (before firing), and an electrode material paste containing silver nanoparticles and showing conductivity by low temperature firing is applied and dried to form a light-receiving surface side electrode, and then back silver Even when the electrode and the light receiving surface electrode are simultaneously fired by a high temperature process, the light receiving surface side electrode and the semiconductor substrate 11 (n-type impurity diffusion layer 3) cannot be electrically connected.

  The silver paste used for forming the conventional light receiving surface electrode contains glass particles, and is fired through a high temperature process of at least 400 ° C. to melt the glass particles and fire through the antireflection film. The semiconductor substrate 11 (n-type impurity diffusion layer 3) is connected to be electrically connected. However, since the electrode material paste containing silver nanoparticles and exhibiting conductivity by low-temperature firing does not contain a glass component, the above-described method causes the light-receiving surface side electrode and the semiconductor substrate 11 (n-type impurity diffusion layer 3) to Electrical connection is not possible.

  Therefore, in the present embodiment, the light receiving surface side electrode is formed by the following method. That is, after the backside electrode 13 is formed, first, a glass paste is printed on the n-type impurity diffusion layer 3 in the same area as the light receiving surface side electrode 12 by a screen printing method in the formation region of the light receiving surface side electrode 12. Then, the light-receiving surface glass layer 21 is formed on the n-type impurity diffusion layer 3 (step S60, FIG. 2-5). The light-receiving surface glass layer 21 may be formed with a width that is slightly wider than the formation region of the light-receiving surface side electrode 12.

  The glass paste includes glass particles having an average particle diameter of 1 μm or less, a resin, and a solvent. The temperature (glass transition point) at which the glass particles melt depends on the average particle size of the glass particles. The smaller the average particle size of the glass particles, the lower the temperature (glass transition point) at which the glass particles melt, and the electrode particles are uniformly and finely dispersed on the antireflection film 4 and reflected by a nonuniform glass film. The top of the prevention film 4 can be covered. For this reason, it is preferable that the average particle diameter of the glass particle contained in a glass paste is 1 micrometer or less. Further, the lower limit of the average particle diameter of the glass particles contained in the glass paste is not particularly limited, but the lower limit of the average particle diameter of the glass particles is 0 in consideration of the average particle diameter of the glass particles that can actually be produced from a productive viewpoint. About 1 μm.

  The glass particle content in the glass paste is 2% by weight to 15% by weight. When the glass particle content in the glass paste is less than 2% by weight, the antireflection film 4 cannot be sufficiently fired through. Therefore, the light receiving surface side electrode and the semiconductor substrate 11 (n-type impurity diffusion layer 3) An electrical connection cannot be obtained. Further, when the glass particle content in the glass paste is greater than 15% by weight, the glass component is laminated thick, so that it is difficult to remove the light-receiving surface glass layer 21 in a later step, and the light-receiving surface. The antireflection film 4 is etched and thinned by an etching process for removing the glass layer 21, so that the function as the antireflection film 4 cannot be fully exhibited. In addition, if the etching process for removing the light-receiving surface glass layer 21 is insufficient, there is a problem that electrical connection between the light-receiving surface side electrode and the semiconductor substrate 11 (n-type impurity diffusion layer 3) cannot be obtained.

  In the present embodiment, a glass paste prepared by using 10% by weight of glass particles having an average particle size of 0.5 μm with respect to the weight of the glass paste, ethyl cellulose resin as a binder, and terpineol as a solvent is used. The light-receiving surface glass layer 21 was formed in a line shape corresponding to the light-receiving surface side electrode 12, that is, in a line shape corresponding to the front silver grid electrode 5 and the front silver bus electrode 6. As the light-receiving surface glass layer 21 corresponding to the surface silver grid electrode 5, the light-receiving surface glass layer 21 having a width of 100 μm and a thickness of 8 μm was formed.

  Next, a baking process is simultaneously performed with respect to the light-receiving surface glass layer 21 and the back surface side electrode 13 (before baking) (step S70, FIGS. 2-6). The baking process is performed at a temperature of, for example, 750 ° C. to 800 ° C. or more using, for example, an infrared heating furnace. The firing temperature is a temperature at least equal to or higher than the glass transition point of the glass particles contained in the light-receiving surface glass layer 21. The glass particles of the light-receiving surface glass layer 21 formed in the shape of the light-receiving surface-side electrode 12 are melted by this baking treatment, and erode the insulating film that is the antireflection film 4 formed on the n-type impurity diffusion layer 3 on the light-receiving surface. The semiconductor substrate 11 (n-type impurity diffusion layer 3) is reached.

  On the other hand, on the back surface (surface opposite to the light receiving surface) of the semiconductor substrate 11, the silver paste becomes the back silver electrode 8 by baking, and the aluminum paste 7a becomes the back aluminum electrode 7. In the drawing, only the back aluminum electrode 7 is shown, and the description of the back silver electrode 8 is omitted. Further, the aluminum (Al) of the back aluminum electrode 7 and the silicon (Si) of the semiconductor substrate 11 react with each other by firing to form an aluminum alloy layer below the back aluminum electrode 7, and an aluminum diffusion layer is formed below the aluminum alloy layer. A p + layer (BSF) (not shown) is formed.

  Next, the light receiving surface glass layer 21 formed on the light receiving surface is removed from the fired semiconductor substrate 11 (step S80, FIG. 2-7). The removal of the light-receiving surface glass layer 21 is performed, for example, by immersing and etching for 3 minutes in a liquid in which hydrofluoric acid and pure water are mixed at a volume ratio of 1:10. Thereby, the light-receiving surface glass layer 21 formed on the light-receiving surface is removed, and an opening 4 a reaching the semiconductor substrate 11 (n-type impurity diffusion layer 3) is formed in the antireflection film 4.

  After the light-receiving surface glass layer 21 is removed, the light-receiving surface-side electrode 12 is formed (before firing) using a low-temperature fired conductive paste that contains silver nanoparticles and exhibits conductivity by low-temperature firing (step S90). That is, the low-temperature fired conductive paste is applied by screen printing so as to fill the opening 4a in the formation region of the light-receiving surface side electrode 12 in the light-receiving surface of the semiconductor substrate 11 (n-type impurity diffusion layer 3), and dried. On the metal mesh of the printing mask used for printing the low-temperature fired conductive paste, a resin film pattern extracted by photolithography is formed at the same position as the mask on which the light-receiving surface glass layer 21 is formed. In the present embodiment, a low-temperature fired conductive paste was printed in a shape having a surface silver grid electrode width of 30 μm and a surface silver bus electrode width of 1.0 mm using this printing mask. The low-temperature fired conductive paste may be printed as a single layer or a multilayer layer. Further, conductive nanoparticles such as nano gold particles may be used instead of silver nanoparticles.

  Next, a low-temperature firing process is performed on the low-temperature fired conductive paste to form the light-receiving surface side electrode 12 (step S100, FIG. 2-8). The low-temperature baking treatment is performed for one hour at a temperature of, for example, 150 ° C. lower than the baking temperature of S700 using, for example, a drying oven. The light-receiving surface side electrode 12 is directly bonded to the semiconductor substrate 11 (n-type impurity diffusion layer 3), and is electrically connected.

By performing the steps as described above, the solar cell 1 according to the present embodiment shown in FIGS. 1-1 to 1-4 is completed. When the electrical resistance value of the light-receiving surface side electrode 12 of the solar cell 1 produced as described above was examined, it showed a low electrical resistance value of 1.5 × 10 ⁻⁶ Ω · cm. Further, the adhesion between the light receiving surface side electrode 12 and the semiconductor substrate 11 (n-type impurity diffusion layer 3) was good, and there was no problem in the adhesion.

  In the above description, the light-receiving surface glass layer 21 is formed in a line shape corresponding to the front silver grid electrode 5 and the front silver bus electrode 6, but the present invention may be applied only to the front silver grid electrode 5.

  As described above, in the method for manufacturing the solar cell according to the first embodiment, the light-receiving surface glass layer 21 is formed in the formation region of the light-receiving surface-side electrode 12 on the antireflection film 4 and fired, and then the light-receiving surface glass layer. By removing 21, an opening 4 a reaching the semiconductor substrate 11 (n-type impurity diffusion layer 3) is formed in the formation region of the light receiving surface side electrode 12 of the antireflection film 4. Then, the light-receiving surface side electrode 12 is formed by applying and drying the low-temperature fired conductive paste by screen printing so as to fill the opening 4a and firing at low temperature.

  In the method of manufacturing a solar cell according to the first embodiment, the light-receiving surface side electrode 12 that is directly bonded to and electrically connected to the semiconductor substrate 11 (n-type impurity diffusion layer 3) is easily manufactured. can do. Further, by using an electrode material paste containing silver nanoparticles and showing conductivity by low-temperature firing as the low-temperature fired conductive paste, the low-resistance light-receiving surface side electrode 12 having a sufficient conductivity in a single layer or two layers even with a thin wire. Can be realized. For this reason, it is not necessary to print the electrode paste many times to form a high aspect ratio electrode as in the prior art, and the production efficiency is excellent. Furthermore, the semiconductor substrate 11 (n-type impurity diffusion layer 3) and the light-receiving surface side electrode 12 can be bonded with high adhesion strength.

  Therefore, according to the manufacturing method of the solar cell according to the first embodiment, the decrease in the photoelectric conversion efficiency of the solar cell due to the electric resistance value of the light-receiving surface side electrode 12 and the peeling of the light-receiving surface side electrode 12 are prevented. A solar cell having excellent solar cell characteristics can be manufactured. By using the method for manufacturing a solar cell according to the first embodiment, even when the width of the surface silver grid electrode 5 is reduced to, for example, 50 μm or less, a solar cell having good solar cell characteristics is efficiently obtained. It can be manufactured well.

Embodiment 2. FIG.
In the second embodiment, an example in which a small amount of metal paste is mixed with the glass paste for forming the light-receiving surface glass layer 21 will be described. As described in the first embodiment, when the light-receiving surface glass layer 21 is removed from the baked semiconductor substrate 11 (step S80), if the light-receiving surface glass layer 21 is not completely removed, the glass component has a high resistance. Therefore, it is necessary to completely remove the light-receiving surface glass layer 21. However, since glass may partially remain due to etching unevenness or the like, if etching is performed so that the glass can be completely removed, the antireflection film 4 is simultaneously etched to become thin and functionally deteriorate. For this reason, the antireflection film 4 needs to be formed thick.

  Therefore, in this embodiment, a small amount of metal paste is mixed into the glass paste. As a result, even if the light receiving surface glass layer 21 is not completely removed and a glass component partially remains, a conductive layer is formed on the surface because metal particles or metal ions remain around the glass. As a result, the resistance is increased due to the electrical insulation, so that there is no significant deterioration in resistance.

  For example, 5% by weight to 10% by weight of metal particles are mixed with the glass paste made of glass particles, resin, and solvent having an average particle diameter of 1 μm or less shown in the first embodiment. The metal particles preferably have high conductivity, such as silver used in later electrode formation. By baking the light-receiving surface glass layer 21 formed by the screen printing method, the glass melts and erodes the antireflection film 4, and the metal particles diffuse to have conductivity. When the content of the metal particles in the glass paste is less than 5% by weight, the molten glass component increases, so that the electrical resistance between the light receiving surface side electrode formed in the next step and the semiconductor substrate increases. On the other hand, when the content of the metal particles in the glass paste is more than 10% by weight, the glass particles cannot sufficiently cover the surface of the antireflection film, fire through is insufficient, and a part of the antireflection film is an opening. Therefore, the electrical resistance between the light receiving surface side electrode formed in the next process and the semiconductor substrate is increased. Therefore, the content of the metal particles in the glass paste is preferably 5% by weight or more and 10% by weight or less.

  However, since it has a large resistance in this state, the light-receiving surface glass layer 21 is removed by, for example, hydrofluoric acid treatment as in the case of the first embodiment. Even if the glass component cannot be completely removed at this time, the metal particles around the glass have conductivity, so that the low-temperature fired conductive paste is applied on this and then fired at a low temperature in the case of the first embodiment. Similarly, the low-resistance light-receiving surface side electrode 12 can be realized.

  Therefore, according to the method for manufacturing a solar cell according to the second embodiment, the photoelectric conversion efficiency of the solar cell is reduced due to the electrical resistance value of the light-receiving surface side electrode 12 and the light-receiving surface side electrode 12 as in the first embodiment. Is prevented, and a solar cell having good solar cell characteristics can be manufactured.

  In addition, according to the method for manufacturing a solar cell according to the second embodiment, even when the light-receiving surface glass layer 21 cannot be completely removed and the glass component remains, the conductivity is ensured to suppress the deterioration of the characteristics. Since the low-resistance light-receiving surface side electrode 12 can be realized as in the case of 1, the work accuracy in the process of removing the light-receiving surface glass layer 21 can be relaxed.

  As described above, the method for manufacturing a solar cell according to the present invention is useful when the photoelectric conversion efficiency is improved by thinning the light receiving surface side electrode.

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Semiconductor substrate 3 N-type impurity diffusion layer 3a Minute unevenness 4 Antireflection film 4a Opening 5 Front silver grid electrode 6 Front silver bus electrode 7 Back aluminum electrode 7a Aluminum paste 8 Back silver electrode 8a Silver paste 11 Semiconductor substrate 12 Light reception Surface side electrode 13 Back side electrode 21 Light receiving surface glass layer

Claims (7)

A method of manufacturing a solar cell having a light-receiving surface side electrode on one surface of a semiconductor substrate,
A first step of forming an antireflection film made of an insulating film on one surface of the semiconductor substrate;
A second step of forming a light receiving surface side glass layer by arranging a glass paste containing glass particles in a shape substantially equivalent to the light receiving surface side electrode in a region where the light receiving surface side electrode is formed on the antireflection film;
A third step of firing the light-receiving surface side glass layer at a temperature equal to or higher than the glass transition point of the glass particles and penetrating the light-receiving surface side glass layer to the semiconductor substrate;
A fourth step of removing the light receiving surface side glass layer and forming an opening reaching the semiconductor substrate in a region where the light receiving surface side glass layer is disposed in the antireflection film;
A fifth step of disposing a low-temperature fired conductive paste containing conductive nanoparticles and exhibiting conductivity by low-temperature firing in the opening;
A sixth step of forming the light-receiving surface side electrode to be bonded directly to the semiconductor substrate by firing the low-temperature fired conductive paste at a low temperature;
The manufacturing method of the solar cell characterized by including. The average particle size of the glass particles is 1 μm or less,
The manufacturing method of the solar cell of Claim 1 characterized by these. The glass particle content in the glass paste is 2 wt% to 15 wt%,
The manufacturing method of the solar cell of Claim 1 characterized by these. The method for producing a solar cell according to claim 1, wherein the glass paste contains 5 wt% or more and 10 wt% or less of metal particles. Between the first step and the third step, there is a step of arranging a back side electrode material paste on the other side of the semiconductor substrate in the shape of a back side electrode formed on the other side of the semiconductor substrate. ,
In the third step, firing the light receiving surface side glass layer and the back surface side electrode material paste at the same time;
The manufacturing method of the solar cell of Claim 1 characterized by these. Forming micro unevenness on one surface of the semiconductor substrate before the first step;
The manufacturing method of the solar cell of Claim 1 characterized by these. In the sixth step, firing the low-temperature fired conductive paste at a temperature of 100 ° C. to 300 ° C.,
The manufacturing method of the solar cell of Claim 1 characterized by these.

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