JP2011018748A - Method of manufacturing solar battery cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a solar battery cell that can manufacture a solar battery having superior photoelectric conversion efficiency, by removing a dead layer of a surface layer of an impurity diffusion layer in a simple and sure way.SOLUTION: A method of manufacturing a solar battery cell having a light-receiving surface side electrode on one side of a semiconductor substrate, includes: a first step of forming an impurity diffusion layer in which a second conductivity-type impurity element is diffused on one side of the semiconductor substrate of a first conductivity-type; a second step of removing a natural oxide film formed on a surface layer of the impurity diffusion layer using the solution containing hydrofluoric acid by etching; a third step of carrying out a water cleaning process and a drying process to the surface layer of the impurity diffusion layer, to oxygenize the surface layer of the impurity diffusion layer and form a first oxidation layer; a fourth step of removing the first oxidation layer using the solution containing hydrofluoric acid by etching; a fifth step of forming an antireflection film on the impurity diffusion layer; and a sixth step of forming the light-receiving surface side electrode that penetrates the antireflection film and which is electrically connected to the impurity diffusion layer, on the antireflection film.

Description

  The present invention relates to a method for manufacturing a solar battery cell for realizing high photoelectric conversion efficiency of a solar battery.

  Conventionally, bulk solar cells are generally manufactured by the following method. First, for example, a p-type silicon substrate is prepared as a first conductivity type substrate, and a damage layer on the silicon surface generated when slicing from a cast ingot is removed by a thickness of 10 to 20 μm with, for example, several to 20 wt% caustic soda or carbonated caustic soda. Then, anisotropic etching is performed with a solution obtained by adding IPA (isopropyl alcohol) to a similar alkali low-concentration solution to form a texture so that the silicon (111) surface appears.

Subsequently, for example, treatment is performed at a mixed gas atmosphere of, for example, phosphorus oxychloride (POCl ₃ ), nitrogen, and oxygen, for example, at 800 to 900 ° C./several tens of minutes, and the n-type layer is uniformly formed as a second conductivity type impurity layer on the front surface. Form. By setting the sheet resistance of the n-type layer uniformly formed on the silicon surface to about 30 to 80 Ω / □, good electric characteristics of the solar cell can be obtained. Thereafter, the substrate is immersed in a hydrofluoric acid aqueous solution, and the glassy material (PSG) deposited on the surface during the diffusion treatment is removed by etching.

  Next, the n-type layer formed in an unnecessary region such as the back surface of the substrate is removed. The removal of the n-type layer is performed, for example, by applying a polymer resist paste to the light-receiving surface side of the substrate by screen printing in order to protect the n-type layer formed on the light-receiving surface side of the substrate. This is performed by immersing the substrate in a potassium oxide solution for several minutes. Thereafter, the resist is removed with an organic solvent. As another method of removing the n-type layer such as the back surface of the substrate, there is a method of performing end face separation by laser or dry etching at the end of the process.

Next, an insulating film such as a silicon oxide film, a silicon nitride film, or a titanium oxide film is formed with a uniform thickness on the surface of the n-type layer as an insulating film (antireflection film) for the purpose of preventing reflection. In the case of forming a silicon nitride film as the antireflection film, it is formed by, for example, plasma CVD using SiH ₄ gas and NH ₃ gas as raw materials under conditions of 300 ° C. or higher and reduced pressure. The refractive index of the antireflection film is about 2.0 to 2.2, and the optimum film thickness is about 70 nm to 90 nm. It should be noted that the antireflection film formed in this way is an insulator, and merely forming the surface-side electrode thereon does not act as a solar cell.

  Next, using a grid electrode forming mask and a bus electrode forming mask, a silver paste to be a surface side electrode is applied to the shape of the grid electrode and the bus electrode on the antireflection film by a screen printing method and dried.

  Next, apply the back aluminum electrode paste to be the back aluminum electrode and the back silver paste to be the back silver bus electrode to the back surface of the substrate by the screen printing method on the back aluminum electrode shape and back silver bus electrode shape, respectively, and dry Let

  Next, the electrode paste applied to the front and back surfaces of the silicon substrate is simultaneously fired at about 600 ° C. to 900 ° C. for several minutes. Thereby, a grid electrode and a bus electrode are formed on the antireflection film as the front surface side electrode, and a back aluminum electrode and a back silver bus electrode are formed on the back surface of the silicon substrate as the back surface side electrode. Here, on the surface side of the silicon substrate, the silver material comes into contact with silicon and re-solidifies while the antireflection film is melted with the glass material contained in the silver paste. Thereby, electrical connection between the surface side electrode and the silicon substrate (n-type layer) is ensured. Such a process is called a fire-through method. Also, the back aluminum electrode paste reacts with the back surface of the silicon substrate, and a p + layer is formed immediately below the back aluminum electrode.

As one method for further improving the efficiency of the solar cell formed as described above, for example, a technique for etching the surface of the n-type layer to the order of submicron has been reported (for example, see Non-Patent Document 1). This is intended to remove the outermost surface layer of the n-type layer called a dead layer. The dead layer is a layer in which the impurity density in the vicinity of the surface of the n-type layer is about 1021 cm ⁻³ , and decreases the lifetime of holes that are minority carriers, which causes a decrease in photoelectric conversion efficiency of the solar cell.

  As a method for etching the dead layer, for example, a method in which an oxide film is formed on the surface of the n-type layer by steam oxidation after the formation of the n-type layer and the oxide layer is removed by wet etching (for example, non-etching) is reported. Patent Document 2). As another method, etching using a mixed solution of hydrofluoric acid and nitric acid is widely known as a silicon etching method.

J. Lindmayer & J. Allison “AN IMPROVED SILICON SOLAR CELL-THE VIOLET CELL” IEEE Photovoltaic Specialists Conference 9th p.83 The Institute of Electrical Engineers of Japan "Solar Cell Handbook" The Institute of Electrical Engineers of Japan 1985

  However, in the case of the above-described method using steam oxidation, it is necessary to newly introduce equipment, and the process becomes complicated. In addition, when a desired oxide film thickness cannot be formed by one process, a steam oxidation process is required again, which is troublesome and fine adjustment of the film thickness is difficult.

  On the other hand, in the case of etching with a mixture of hydrofluoric acid and nitric acid, it is necessary to use nitric acid, which is regulated by the Poisonous and Deleterious Substances Control Law and the Occupational Safety and Health Law. is required. Further, in this etching method, it is necessary to pay close attention to the liquid concentration management such as the mixing ratio and the liquid life and the in-plane distribution by etching.

  The present invention has been made in view of the above, and a solar cell manufacturing method capable of manufacturing a solar cell excellent in photoelectric conversion efficiency by removing a dead layer on the surface of an impurity diffusion layer easily and reliably. The purpose is to obtain.

  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 side of a semiconductor substrate. A first step of forming an impurity diffusion layer in which an impurity element of the second conductivity type is diffused on one surface side of the semiconductor substrate of the conductivity type, and a natural oxide film formed on a surface layer of the impurity diffusion layer are made of hydrofluoric acid And a second step of etching and removing using a solution containing, a third step of oxidizing the surface layer of the impurity diffusion layer by subjecting the surface layer of the impurity diffusion layer to a water washing process and a drying process to form a first oxide layer A fourth step of etching and removing the first oxide layer using a solution containing hydrofluoric acid, a fifth step of forming an antireflection film on the impurity diffusion layer, and penetrating the antireflection film. Electrically into the impurity diffusion layer A sixth step of forming the light-receiving surface side electrode connected onto the anti-reflecting layer, characterized in that it comprises a.

  According to the present invention, the surface dead layer of the impurity diffusion layer is simply and surely removed using only hydrofluoric acid, which is a general chemical solution used in the manufacturing process of ordinary solar cells, and photoelectric conversion is performed. There is an effect that a solar cell excellent in efficiency can be manufactured.

FIG. 1-1 is a top view of a solar battery cell according to an embodiment of the present invention as viewed from the light receiving surface side. FIG. 1-2 is a bottom view of the solar battery cell according to the embodiment of the present invention as viewed from the side opposite to the light receiving surface. 1-3 is principal part sectional drawing in the AA direction of FIGS. 1-2 of the photovoltaic cell concerning embodiment of this invention. 1-4 is principal part sectional drawing in the BB direction of FIGS. 1-2 of the photovoltaic cell concerning embodiment of this invention. FIG. 2 is a flowchart for explaining an example of the manufacturing process of the solar battery cell according to the embodiment of the present invention. FIGS. 3-1 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning embodiment of this invention. FIGS. 3-2 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning embodiment of this invention. FIGS. 3-3 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning embodiment of this invention. FIGS. 3-4 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning embodiment of this invention. 3-5 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning embodiment of this invention. 3-6 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning embodiment of this invention. 3-7 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning embodiment of this invention. FIGS. 3-8 is sectional drawing for demonstrating an example of the manufacturing process of the photovoltaic cell concerning embodiment of this invention. FIGS.

  Embodiments of a method for manufacturing a solar battery 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 FIGS. 1-1 to 1-4 are diagrams for explaining the configuration of a solar battery cell 1 according to an embodiment of the present invention, and FIG. 1-1 shows the sun as seen from the light-receiving surface side. Fig. 1-2 is a top view of the battery cell 1, Fig. 1-2 is a bottom view of the solar cell 1 viewed from the side opposite to the light receiving surface, and Fig. 1-3 is a schematic diagram of the solar cell 1 in the AA direction of Fig. 1-2. FIG. 1-4 is a partial cross-sectional view of the solar cell 1 in the BB direction of FIG. 1-2.

  In the solar cell 1 according to the present embodiment, an n-type impurity diffusion layer 3 is formed by phosphorous diffusion on the light receiving surface side of a semiconductor substrate 2 made of p-type single crystal silicon, and a semiconductor substrate 11 having a pn junction is formed. In addition, an antireflection film 4 made of a silicon nitride film (SiN film) is formed on the n-type impurity diffusion layer 3. The semiconductor substrate 2 is not limited to a p-type single crystal silicon substrate, and may be a p-type polycrystalline silicon substrate, an n-type polycrystalline silicon substrate, or an n-type single crystal silicon substrate.

  In addition, fine irregularities are formed as a texture structure on the surface of the semiconductor substrate 11 (n-type impurity diffusion layer 3) on the light receiving surface side. The micro unevenness increases the area for absorbing light from the outside on the light receiving surface, suppresses the reflectance on the light receiving surface, and has a structure for confining 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. In addition, a plurality of long and narrow surface silver grid electrodes 5 are arranged side by side on the light receiving surface side of the semiconductor substrate 11, and a surface silver bus electrode 6 electrically connected to the surface silver grid electrode 5 is substantially the same as the surface silver grid electrode 5. They are provided so as to be orthogonal to each other, and are respectively electrically connected to the n-type impurity diffusion layer 3 at the bottom portion. 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 has a width of, for example, about 100 μm to 200 μm and is arranged substantially in parallel at an interval of about 2 mm, and collects electricity generated inside the semiconductor substrate 11. Moreover, the surface silver bus electrode 6 has a width of about 1 mm to 3 mm, for example, and is disposed in a number of 2 to 3 per solar cell, and takes out the electricity collected by the surface 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. A comb-shaped table as shown in FIG. In general, the silver grid electrode 5 and the bar-shaped front silver bus electrode 6 are arranged.

  As the electrode material of the light receiving surface side electrode of the silicon solar battery cell, a silver paste is usually used, for example, lead boron glass is added. This glass has a frit shape and is composed of, for example, a composition of 5-30 wt% lead (Pb), 5-10 wt% boron (B), 5-15 wt% silicon (Si), and 30-60 wt% oxygen (O). Furthermore, zinc (Zn), cadmium (Cd), etc. may be mixed by several wt%. Such lead boron glass has a property of melting by heating at several hundred degrees C. (for example, 800.degree. C.) and eroding silicon at that time. In general, in a method for manufacturing a crystalline silicon solar battery cell, a method of obtaining electrical contact between a silicon substrate and a silver paste by using the characteristics of the glass frit is used.

  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. The back silver electrode 8 which consists of is provided. The back aluminum electrode 7 and the back silver electrode 8 constitute a back electrode 13 as a second electrode. The back aluminum electrode 7 is also expected to have a BSR (Back Surface Reflection) effect in which long-wavelength light passing through the semiconductor substrate 11 is reflected and reused for power generation.

  Low cost and performance can be achieved by using silver as the material for the light receiving surface side electrode 12 as described above, aluminum as the material for the back surface side electrode, and, if necessary, a material mainly composed of silver in a partial region. It is common in terms of improvement.

  Further, a p + layer (BSF (Back Surface Field)) 9 containing a high-concentration impurity is formed on the surface layer portion on the back surface (surface opposite to the light receiving surface) of the semiconductor substrate 11. The p + layer (BSF) 9 is provided to obtain the BSF effect, and the electron concentration of 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. Like that.

  In the solar cell 1 configured as described above, sunlight is applied to the pn junction surface (the junction surface between the semiconductor substrate 2 and the n-type impurity diffusion layer 3) of the semiconductor substrate 11 from the light receiving surface side of the solar cell 1. Then, 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 9. As a result, electrons are excessive in the n-type impurity diffusion layer 3 and holes are excessive in the p + layer 9. As a result, a photovoltaic force is generated. This photovoltaic force is generated in the direction of biasing the pn junction in the forward direction, 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 9 becomes a positive pole. Thus, a current flows through an external circuit (not shown).

In the solar battery cell 1 according to the present embodiment configured as described above, the outermost surface layer of the n-type impurity diffusion layer 3 called a dead layer is surely removed and directly on the n-type impurity diffusion layer 3. An antireflection film 4 and a light receiving surface side electrode 12 are provided. The dead layer is a layer in which the impurity density in the vicinity of the surface of the n-type impurity diffusion layer 3 is about 1021 cm ⁻³ and reduces the lifetime of holes that are minority carriers. Causes a drop. In this solar cell 1, since such an n-type impurity diffusion layer 3 does not exist on the outermost surface of the n-type impurity diffusion layer 3, it is possible to prevent a decrease in photoelectric conversion efficiency of the solar cell due to the dead layer, which is favorable. Solar cells having cell characteristics have been realized.

  Hereinafter, the manufacturing method of the photovoltaic cell 1 concerning this Embodiment is demonstrated along drawing. FIG. 2 is a flowchart for explaining an example of the manufacturing process of the solar battery cell 1 according to the embodiment of the present invention. FIGS. 3-1 to 3-8 are cross-sectional views for explaining an example of the manufacturing process of the solar battery cell 1 according to the 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 (FIG. 3-1). 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 substrate is etched near the surface of the p-type single crystal silicon substrate by etching the surface by immersing the surface in an acid or heated alkaline solution, for example, an aqueous sodium hydroxide solution. Remove the damage area that exists in the. For example, the surface is removed by a thickness of 10 μm to 20 μm with several to 20 wt% caustic soda or carbonated caustic soda. The p-type silicon substrate used for the semiconductor substrate 2 may be either a single crystal or a polycrystal, but here, the specific resistance is 0.1 Ω · cm to 5 Ω · cm, and the p-type single substrate has a (100) plane orientation. A crystalline silicon substrate will be described as an example.

  Following the removal of damage, anisotropic etching of the p-type single crystal silicon substrate is performed with a solution obtained by adding IPA (isopropyl alcohol) to the same low-concentration alkali solution, and the p-type single crystal is formed so that the silicon (111) surface appears. The texture structure 2a is formed by forming minute irregularities on the light receiving surface side of the silicon substrate (step S10, FIG. 3-2). 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 battery cell 1, and the light incident on the solar battery cell 1 is efficiently semiconductor The light can be absorbed in the substrate 11, and the conversion efficiency can be improved by effectively reducing the reflectance. 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.

Next, a pn junction is formed in the semiconductor substrate 2 (step S20, FIG. 3-3). 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 by diffusing phosphorus oxychloride (POCl ₃ ) by thermal diffusion with respect to a p-type single crystal silicon substrate having a texture structure on the surface. 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.

In this diffusion step, the p-type single crystal silicon substrate is placed in a mixed gas atmosphere of, for example, phosphorus oxychloride (POCl ₃ ) gas nitrogen gas and oxygen gas at a high temperature of, for example, 800 ° C. to 900 ° C. for several tens of minutes. Then, the n-type impurity diffusion layer 3 in which phosphorus (P) is diffused is uniformly formed in the surface layer of the p-type single crystal silicon substrate by thermal diffusion. Good electrical characteristics of the solar cell can be obtained when the sheet resistance range of the n-type impurity diffusion layer 3 formed on the surface of the semiconductor substrate 2 is about 30Ω / □ to 80Ω / □.

  Here, since 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, the phosphorus glass layer 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.

  For example, in order to protect the n-type impurity diffusion layer 3 on the light receiving surface side of the semiconductor substrate 2, a polymer resist paste is applied to the light receiving surface side of the semiconductor substrate 2 by a screen printing method and dried. Then, the semiconductor substrate 2 is immersed in a 20 wt% potassium hydroxide solution for several minutes, for example, and the n-type impurity diffusion layer 3 formed on the surface other than the light receiving surface side of the semiconductor substrate 2 is removed. Thereafter, the polymer resist is removed with an organic solvent. Thereby, the n-type impurity diffusion layer 3 can be left only on the light receiving surface side of the semiconductor substrate 2. As another method for removing the influence of the n-type impurity diffusion layer 3 such as the back surface of the semiconductor substrate 2, end face separation may be performed by laser or dry etching at the end of the process. Alternatively, n-type impurity diffusion layer 3 may be formed only on the light-receiving surface side of semiconductor substrate 2 in advance.

  Next, the semiconductor substrate 2 is immersed in a hydrofluoric acid aqueous solution, and a natural oxide film (not shown) formed on the surface of the semiconductor substrate 2 is removed by etching (step S30). Subsequently, the semiconductor substrate 2 is washed with water and dried at room temperature to form a new oxide film 3a on the surface of the semiconductor substrate 2 (step S40, FIG. 3-4). Here, on the surface of the n-type impurity diffusion layer 3, the dead layer formed in the outermost surface layer is oxidized to form a new oxide film 3a. Next, the semiconductor substrate 2 is again immersed in a hydrofluoric acid aqueous solution, and the new oxide film 3a formed on the surface of the semiconductor substrate 2 is removed by etching (step S50, FIG. 3-5).

  Then, said step S40 and step S50 are made into 1 cycle, and this cycle is repeated until the etching amount of the surface of the semiconductor substrate 2 reaches a desired etching amount. That is, steps S40 and S50 are repeated until the dead layer formed on the outermost surface layer of the n-type impurity diffusion layer 3 is reliably removed. Thus, after removing the natural oxide film formed on the surface of the semiconductor substrate 2 by immersing it in a hydrofluoric acid aqueous solution, a process of forming a new oxide film 3a on the surface of the semiconductor substrate 2 by washing with water and drying. And by repeating the process of removing the new oxide film 3a by immersing the semiconductor substrate 2 in the hydrofluoric acid aqueous solution again, the dead layer is etched and removed little by little, and finally all dead layers are surely Can be removed.

  By implementing the above method, only the usual hydrofluoric acid used in the manufacturing process of ordinary solar cells is used as the chemical solution, and the processing equipment can be reliably dead by changing the sequence of the existing processing equipment. The layer can be removed. That is, for example, the above processing can be performed only by reciprocating the robot arm that holds and moves the semiconductor substrate 2 between the processing regions.

  Further, since the formation of the new oxide film 3a proceeds at room temperature, the new oxide film 3a is formed with a substantially uniform film thickness within the surface of the semiconductor substrate 11. Thereby, after removal of the dead layer, the film thickness of the n-type impurity diffusion layer 3 is also made substantially uniform, and the solar cell fabricated using this semiconductor substrate can obtain uniform characteristics.

  In the above description, the case where the washing process and the drying process are performed as a method for forming a new oxide film 3a on the surface of the semiconductor substrate 2 has been described. However, the formation of the new oxide film 3a is not limited to this method. For example, a new oxide film 3a can be formed on the surface of the semiconductor substrate 2 by steam oxidation treatment or thermal oxidation treatment. Moreover, when using steam oxidation treatment or thermal oxidation treatment, it is difficult to adjust the thickness of the oxide film. Therefore, as a method for finely adjusting the thickness of the oxide film, a steam oxidation treatment or a thermal oxidation treatment is combined with the above method. That is, first, a new oxide film 3a having an approximate target film thickness is formed by a steam oxidation process or a thermal oxidation process, and the new oxide film 3a is removed by a hydrofluoric acid aqueous solution. Next, the above-described water washing treatment, drying treatment, and removal of the new oxide film 3a with a hydrofluoric acid aqueous solution are performed, and the remaining dead layer is removed. Even with such a method, all the dead layers can be finally removed reliably.

  In the above description, the dead layer is removed after removing the vitreous (PSG) layer. However, the dead layer may be removed directly after the n-type impurity diffusion layer 3 is formed.

Next, in order to improve the photoelectric conversion efficiency, the antireflection film 4 is formed with a uniform thickness on one surface of the p-type single crystal silicon substrate on the light receiving surface side (step S60, FIGS. 3-6). 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, and at 300 ° C. or higher and under reduced pressure. 4, a silicon nitride film is formed. The refractive index is, for example, about 2.0 to 2.2, and the optimum antireflection film thickness is, for example, 70 nm to 90 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 manner is an insulator, and simply forming the light receiving surface side electrode 12 on the surface does not act as a solar battery cell.

  Next, electrodes are formed by screen printing. First, the light-receiving surface side electrode 12 is produced (before firing). That is, a silver paste 12a, which is an electrode material paste containing glass frit, is formed on a screen of an antireflection film 4 which is a light receiving surface of a p-type single crystal silicon substrate in the shape of a surface silver grid electrode 5 and a surface silver bus electrode 6. After applying by printing, the silver paste is dried (step S70, FIG. 3-7).

  Next, an aluminum paste 7a, which is an electrode material paste, is applied to the shape of the back aluminum electrode 7 by screen printing on the back side of the p-type single crystal silicon substrate, and further, a silver, which is an electrode material paste, is applied to the shape of the back silver electrode 8. The paste 8a is applied and dried (step S80, FIGS. 3-7). In the figure, only the aluminum paste 7a is shown, and the description of the silver paste 8a is omitted.

  Thereafter, the electrode paste on the front surface and the back surface of the semiconductor substrate 11 is simultaneously fired at, for example, 600 ° C. to 900 ° C., so that the antireflection film 4 is melted with the glass material contained in the silver paste 12a on the front side of the semiconductor substrate 11. During this time, the silver material comes into contact with the silicon and resolidifies. As a result, the front silver grid electrode 5 and the front silver bus electrode 6 as the light receiving surface side electrode 12 are obtained, and conduction between the light receiving surface side electrode 12 and the silicon of the semiconductor substrate 11 is ensured (step S90, FIG. 3). -8). Such a process is called a fire-through method.

  Also, the aluminum paste 7 a reacts with the silicon of the semiconductor substrate 11 to obtain the back aluminum electrode 7, and the p + layer 9 is formed immediately below the back aluminum electrode 7. Further, the silver material of the silver paste 8a comes into contact with silicon and re-solidifies to obtain the back silver electrode 8 (FIGS. 3-8). In the figure, only the front silver grid electrode 5 and the back aluminum electrode 7 are shown, and the description of the front silver bus electrode 6 and the silver paste 8a is omitted.

  By performing the steps as described above, the solar battery cell 1 according to the present embodiment shown in FIGS. 1-1 to 1-4 can be manufactured. In addition, the order of arrangement of the paste, which is an electrode material, on the semiconductor substrate 11 may be switched between the light receiving surface side and the back surface side.

  Next, the solar cell of Sample 1 to Sample 9 was manufactured by changing the processing conditions of Steps S30 to S50 described above by the solar cell manufacturing method according to the present embodiment described above. The manufacturing conditions of each photovoltaic cell were as follows.

Sample 1: The sheet resistance (Ω / □) of the surface of the n-type impurity diffusion layer before processing in steps S30 to S50 (hereinafter referred to as sheet resistance before processing) is 35Ω / □, and the processing in steps S30 to S50. The number of times (hereinafter referred to as the number of processes) is 0 (none).
Sample 2: Sheet resistance before processing is 35Ω / □, and the number of processing is 5 times.
Sample 3: Sheet resistance before processing is 35Ω / □, and the number of processing is 10 times.

Sample 4: Sheet resistance before processing is 45Ω / □, and the number of processing is 0 (none).
Sample 5: The sheet resistance before processing is 45Ω / □, and the number of processing is 5 times.
Sample 6: The sheet resistance before processing is 45Ω / □, and the number of processing is 10 times.

Sample 7: The sheet resistance before processing is 55Ω / □, and the processing count is 0 (none).
Sample 8: The sheet resistance before processing is 55Ω / □, and the number of processing is 5 times.
Sample 9: The sheet resistance before processing is 55Ω / □, and the number of processing is 10 times.

  As manufacturing conditions for the solar cells of Samples 1 to 9, sheet resistance before processing (Ω / □), number of processing (times), sheet resistance of the surface of the n-type impurity diffusion layer after processing in Steps S30 to S50 Table 1 summarizes (Ω / □) (hereinafter referred to as the sheet resistance after treatment).

  In step S40, the semiconductor substrate was washed with water for 3 minutes and then dried. In step S50, the semiconductor substrate was immersed in an aqueous solution obtained by diluting a hydrofluoric acid solution having a concentration of about 50 wt% with about 10 times pure water. This cycle was performed 5 times and 10 times with different conditions.

Moreover, the produced solar cell was actually operated, and the power generation characteristics were measured and evaluated. As a result, the open circuit voltage (V) and the short circuit current density (mA / cm ₂ ) are also shown in Table 1.

  From Table 1, the sheet resistance after the processing of Step S30 to Step S50 is about 40Ω / □ to 70Ω / □ in any case where the value of the sheet resistance before processing is 35Ω / □, 45Ω / □, or 55Ω / □. It can be seen that both the open circuit voltage and the short circuit current are improved within the range of. In addition, it can be seen that good results can be obtained when the difference in sheet resistance between before and after the processing of step S30 to step S50 is 6Ω / □ to 16Ω / □.

  On the other hand, the fill factor decreases when this process is performed. However, the curve factor also depends on the pattern of the light receiving surface side electrodes (the number and width of the grid electrodes and the number and width of the bus electrodes). Therefore, by adjusting the pattern of the light receiving surface side electrode, it is possible to suppress the decrease in the fill factor, and to cover the decrease in the fill factor due to this processing.

  That is, in order to fabricate a solar cell having high photoelectric conversion efficiency, first, the sheet resistance after the processing of step S30 to step S50 is set to a range of 40Ω / □ to 70Ω / □ (at this time, the sheet before and after this processing). The resistance difference is preferably 6Ω / □ to 16Ω / □), and the open circuit voltage and the short circuit current density are improved. Next, the electrode mask pattern used in the electrode paste printing process is finely adjusted, that is, the number and width of the grid electrodes and the number and width of the bus electrodes are optimized to suppress and prevent the reduction of the fill factor. Thereby, the photovoltaic cell which has the high photoelectric conversion efficiency excellent in the open circuit voltage and the short circuit current density can be produced.

  As described above, according to the method for manufacturing a solar battery cell according to the present embodiment, the outermost surface layer of the n-type impurity diffusion layer 3 called a dead layer is used as a chemical solution in a normal solar battery manufacturing process. It can be removed easily and reliably with high accuracy using only general hydrofluoric acid. Thereby, the fall of the photovoltaic cell characteristic resulting from a dead layer can be prevented.

  In addition, according to the method for manufacturing a solar battery cell according to the present embodiment, the formation of the new oxide film 3a proceeds at room temperature, so that the new oxide film 3a is a substantially uniform film in the plane of the semiconductor substrate 11. Formed with thickness. Thereby, after removal of the dead layer, the film thickness of the n-type impurity diffusion layer 3 is also made substantially uniform, and the solar cell fabricated using this semiconductor substrate can obtain uniform characteristics.

  Therefore, according to the method for manufacturing a solar cell according to the present embodiment, the dead layer on the surface layer of the n-type impurity diffusion layer 3 is simply and reliably removed, and a solar cell excellent in photoelectric conversion efficiency is manufactured. be able to.

  As described above, the method for manufacturing a solar battery cell according to the present invention is useful for preventing the deterioration of the solar battery cell characteristics due to the dead layer formed on the surface layer of the impurity diffusion layer.

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Semiconductor substrate 2a Texture structure 3 N-type impurity diffusion layer 3a New oxide film 4 Antireflection film 5 Front silver grid electrode 6 Front silver bus electrode 7 Back aluminum electrode 7a Aluminum paste 8 Back silver electrode 8a Silver paste 9 p + layer (BSF)
DESCRIPTION OF SYMBOLS 11 Semiconductor substrate 12 Light-receiving surface side electrode 12a Silver paste 13 Back surface side electrode

Claims (6)

A method of manufacturing a solar cell having a light receiving surface side electrode on one surface side of a semiconductor substrate,
Forming an impurity diffusion layer in which an impurity element of a second conductivity type is diffused on one surface side of the semiconductor substrate of the first conductivity type;
A second step of removing the natural oxide film formed on the surface of the impurity diffusion layer by etching using a solution containing hydrofluoric acid;
A third step of oxidizing the surface layer of the impurity diffusion layer by subjecting the surface layer of the impurity diffusion layer to a water washing treatment and a drying treatment to form a first oxide layer;
A fourth step of removing the first oxide layer by etching using a solution containing hydrofluoric acid;
A fifth step of forming an antireflection film on the impurity diffusion layer;
A sixth step of forming, on the antireflection film, the light receiving surface side electrode that penetrates the antireflection film and is electrically connected to the impurity diffusion layer;
The manufacturing method of the photovoltaic cell characterized by including. Between the second step and the third step,
Forming a second oxide layer by oxidizing the surface layer of the impurity diffusion layer by subjecting the surface layer of the impurity diffusion layer to steam oxidation treatment or thermal oxidation treatment;
Etching and removing the second oxide layer using a solution containing hydrofluoric acid;
The method for producing a solar battery cell according to claim 1, comprising: Performing the third step and the fourth step as one cycle, repeating the cycle a plurality of times;
The manufacturing method of the photovoltaic cell of Claim 1 or 2 characterized by these. Repeatedly performing the cycle until the value of the sheet resistance of the surface layer of the impurity diffusion layer is 40Ω / □ to 70Ω / □,
The manufacturing method of the photovoltaic cell of Claim 3 characterized by these. Repeating the cycle until the difference from the sheet resistance value of the surface layer of the impurity diffusion layer after completion of the first step is 6Ω / □ to 16Ω / □,
The manufacturing method of the photovoltaic cell of Claim 3 characterized by these. Between the first step and the second step,
Having a step of removing the vitreous layer formed on the surface layer of the impurity diffusion layer;
The manufacturing method of the photovoltaic cell of Claim 1 characterized by these.

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