JP2016184709A - Method of manufacturing solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar battery manufacturing method that does not need to prepare a complicated step and a special material, and can form a diffusion layer having a portion of a high dopant concentration and a portion of a low dopant concentration by a simple method, and achieve a solar battery having high performance with a high yield at low cost.SOLUTION: A solar battery manufacturing method which comprises a step of applying coating agent containing boron onto the surface of a semiconductor substrate, a step of performing a diffusion heat treatment for diffusing boron on a surface layer portion of the surface coated with the coating agent of the semiconductor substrate, a step of coating the surface coated with the coating agent with a paste containing oxide-based ceramic fine particles in a pattern-form before the diffusion heat treatment step, and a step of increasing the temperature to a temperature lower than the temperature of the diffusion heat treatment, and performing a low-temperature heat treatment containing a heat cycle for decreasing the temperature after the temperature increase on the semiconductor substrate at least once after the coating of the paste. The diffusion heat treatment is performed on the semiconductor substrate which has been subjected to the low temperature heat treatment at least once.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a solar cell including a step of forming a diffusion layer.

  FIG. 2 is a schematic diagram showing an example of a general high-efficiency solar cell when a single crystal n-type silicon substrate is used, and FIG. 3 is a schematic diagram showing an example of a cross-sectional structure. As shown in FIGS. 2 and 3, the solar cell 200 generally has a light receiving surface electrode 203 including finger electrodes 201 and bus bar electrodes 202 on the light receiving surface. The finger electrodes 201 are current collecting electrodes on the light receiving surface, and generally have a width of several tens to hundreds of micrometers, and a large number are arranged on the light receiving surface. The interval between the finger electrodes 201 is generally about 1 mm to 3 mm. The bus bar electrodes 202 are current collecting electrodes for connecting cells constituting the solar battery 200, and generally two to four are disposed on the light receiving surface. Examples of the method for forming these light receiving surface electrodes 203 include vapor deposition and sputtering. From the viewpoint of cost, a metal paste in which metal fine particles such as Ag are mixed with an organic binder is printed using a screen plate or the like. A method of performing heat treatment at several hundred degrees and bonding to a substrate is widely used.

Further, as shown in FIG. 3, the portion other than the light receiving surface electrode 203 of the light receiving surface of the solar cell 200 is covered with an antireflection film 204 made of SiN _x or the like. A p-type diffusion layer 206 opposite to the conductivity type of the substrate is formed on the surface layer portion of the surface of the single crystal n-type silicon substrate 205. An n-type diffusion layer 208, a back surface passivation film 209, and a back surface electrode 210 are formed on the surface opposite to the light receiving surface (hereinafter also referred to as a back surface). In particular, a p-type diffusion layer 207 having a higher concentration than the p-type diffusion layer 206 is formed immediately below the light-receiving surface electrode 203 in order to reduce the contact resistance between the p-type diffusion layer 206 and the light-receiving surface electrode 203. Several methods for forming the high-concentration and low-concentration p-type diffusion layers (p-type selective emitters) 206 and 207 are disclosed.

  Patent Document 1 discloses a technique for forming a dopant concentration in a diffusion layer using two types of printing pastes having different dopant concentrations. In the technique disclosed in Patent Document 1, it is necessary to prepare two types of materials in order to create printing pastes having different concentrations, and two printing steps are necessary. Therefore, it takes time to implement the method of Patent Document 1. Patent Documents 2 and 3 disclose techniques for forming a dopant concentration in the diffusion layer by utilizing the property that boron in a silicon substrate moves into a thermal oxide film. In the techniques disclosed in Patent Document 2 and Patent Document 3, once the dopant is diffused, it takes time and effort to mask and heat the oxide.

  Patent Document 4 discloses a technique in which a material in which a dopant is mixed with fine silicon particles is printed and doped with a laser. In this case, it is necessary to prepare a special material. In addition, damage to the substrate by the laser is unavoidable, and the product may become defective and the yield may be deteriorated. Patent Document 5 discloses a technique using a property that a damaged layer on a substrate surface diffuses a dopant in a high concentration. However, it is difficult to selectively form a damaged layer, and photogenerated carriers are recombined in the damaged layer.

JP 2014-197578 A JP 2013-218900 A JP 2010-186900 A JP 2012-178546 A JP 2012-49424 A

  As described above, in the manufacture of solar cells, when trying to form a diffusion layer having a portion with a high dopant concentration and a portion with a low dopant concentration, such as a selective emitter, on the surface layer portion of the surface of the semiconductor substrate, Any of the conventional manufacturing methods has a problem that a certain amount of labor and materials are required, the performance of the manufactured solar cell is inferior, and the yield is deteriorated.

  The present invention has been made in view of the above-mentioned problems, and it is not necessary to prepare complicated processes and special materials, and diffusion having a high concentration portion and a low concentration portion by a simple method. An object of the present invention is to provide a method of manufacturing a solar cell that can form a layer and can obtain a high-performance solar cell at a low cost and a high yield.

  To achieve the above object, the present invention includes a step of applying a boron-containing coating agent on a surface of a semiconductor substrate, and a diffusion for diffusing the boron in a surface layer portion of the surface of the semiconductor substrate on which the coating agent is applied. A step of applying a heat treatment, and a step of applying, in a pattern, a paste containing oxide ceramic fine particles on the surface on which the coating agent has been applied, prior to the diffusion heat treatment step, and The low-temperature heat treatment includes a step of performing low-temperature heat treatment including a thermal cycle in which the temperature is lowered to a temperature lower than the temperature of the diffusion heat treatment and lowering the temperature after the temperature rise on the semiconductor substrate after the paste is applied. A method for manufacturing a solar cell is provided, wherein the diffusion heat treatment is performed on the semiconductor substrate after the step is performed at least once.

  After applying the boron source, a paste containing oxide ceramic fine particles (hereinafter also referred to simply as “oxide paste”) is applied in a pattern, and then the boron source moves to the oxide paste side by applying low-temperature heat treatment. . Thereafter, by performing diffusion heat treatment, a boron diffusion layer having a low concentration can be formed in the portion where the oxide paste is applied to the surface of the semiconductor substrate, and a high concentration boron diffusion layer can be formed in the non-application portion. According to the method of the present invention, it is not necessary to prepare complicated steps or special materials, and a diffusion layer having a high boron concentration portion and a low boron concentration portion can be formed by a simple method. Can be obtained at a cost.

  At this time, the oxide ceramic fine particles may be silica fine particles or aluminum oxide fine particles.

  Among oxide ceramic fine particles, such fine particles are preferred because they are general-purpose and easy to handle.

  At this time, it is preferable that the maximum temperature of the thermal cycle in the low-temperature heat treatment step is 300 ° C. or more and 600 ° C. or less, and the minimum temperature is 15 ° C. or more and less than 300 ° C.

  By applying a low-temperature heat treatment in such a temperature range, a diffusion layer having a portion having a high boron concentration and a portion having a low concentration can be more reliably formed in the subsequent diffusion heat treatment.

  In the method for manufacturing a solar cell of the present invention, the semiconductor substrate is an n-type semiconductor substrate, the surface of the semiconductor substrate on which the boron is diffused is a light receiving surface, and a light receiving surface electrode is formed on the light receiving surface. And a step of forming a back electrode on the surface of the semiconductor substrate opposite to the surface on which the boron is diffused.

  When an n-type semiconductor substrate is used as a semiconductor substrate in the production of a solar cell, a high-efficiency solar cell having a p-type selective emitter in which boron is diffused on the light receiving surface is used if the method for producing a solar cell of the present invention is used. The battery can be manufactured by a simple method.

  Further, in the method for manufacturing a solar cell of the present invention, the semiconductor substrate is a p-type semiconductor substrate, the surface opposite to the surface on which the boron is diffused of the semiconductor substrate is a light receiving surface, and the surface layer portion of the light receiving surface is further provided. Forming a n-type diffusion layer on the semiconductor substrate, forming a light-receiving surface electrode on the n-type diffusion layer, and forming a back electrode on the boron diffused surface of the semiconductor substrate. Can do.

  In the production of solar cells, when a p-type semiconductor substrate is used as the semiconductor substrate, if the method for producing a solar cell of the present invention is used, a boron concentration is high on the back surface opposite to the light-receiving surface of the p-type semiconductor substrate. A diffusion layer having a portion and a low portion can be easily formed. Thereby, for example, a solar cell in which an electrode is localized in a portion having a high boron concentration and a non-electrode part is a BSF (Back Surface Field) layer can be easily manufactured.

  If it is the manufacturing method of the solar cell of this invention, it is not necessary to prepare a complicated process and a special material, and it can form the diffused layer which has a high concentration part and a low concentration part by a simple method. Thus, a high-performance solar cell can be obtained at a low cost and with a high yield.

In the manufacturing method of the solar cell of this invention, it is a general-view figure of the n-type semiconductor substrate after carrying out printing application | coating of the silica paste (oxide paste) in the pattern form. It is the schematic which showed an example of the structure of a general solar cell. It is the schematic diagram which showed an example of the cross-section of a general solar cell.

  Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.

  In the specific example of the solar cell manufacturing method of the present invention described below, a case where a solar cell is manufactured using an n-type semiconductor substrate will be mainly described. However, the method for manufacturing a solar cell of the present invention is not limited to the specific examples described below, and a solar cell may be manufactured using a p-type semiconductor substrate.

(Preparation process of semiconductor substrate)
As an n-type semiconductor substrate that can be used in the manufacture of solar cells, high purity silicon is doped with a group V (group 15) element such as phosphorus, arsenic, or antimony, and an as-cut single-layer having a specific resistance of 0.1 to 5 Ω · cm. A crystal {100} n-type silicon substrate (hereinafter sometimes simply referred to as an n-type silicon single crystal substrate) can be prepared. The n-type silicon single crystal substrate may be produced by a method such as a CZ (Czochralski) method or an FZ (Floating Zone) method. Further, the substrate is not necessarily made of single crystal silicon, but may be polycrystalline silicon.

(Damage removal process)
Next, the mechanical damage of the surface formed on the silicon single crystal substrate when slicing and grinding from the ingot is applied to a high concentration alkali such as sodium hydroxide or potassium hydroxide having a concentration of 5 to 60%. Alternatively, etching can be performed using a mixed acid of hydrofluoric acid and nitric acid. The damage removing step is not necessarily required depending on the texture forming conditions in the next step, and can be omitted.

(Texture formation process)
Subsequently, fine irregularities called textures are formed on the surface of the n-type silicon single crystal substrate. Texture is an effective way to reduce solar cell reflectivity. The texture is obtained by heating an n-type silicon single crystal substrate in a heated alkaline solution such as sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, or sodium bicarbonate (for example, concentration 1 to 10%, temperature 60 to 90 ° C.). Can be produced by immersing for 10 to 30 minutes. In many cases, a predetermined amount of 2-propanol is dissolved in the solution to promote the reaction.

(Washing process)
After a texture is formed on the surface of the n-type silicon single crystal substrate, it is washed in an acidic aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, or a mixture thereof.

(Application process of boron-containing coating agent)
Next, a boron-containing coating agent is applied to the surface of the n-type silicon single crystal substrate. In this description, since the semiconductor substrate is an n-type semiconductor substrate, the surface of the semiconductor substrate on which boron is diffused can be the light receiving surface. The coating agent can be composed of at least a boron source and a solvent. As the boron source, borate salts such as sodium metaborate and sodium tetraborate can be used, but the boron source is not particularly limited, and boric acid or the like may be used. As the solvent, water, ethanol, or alcohol such as methanol can be used. Furthermore, you may thicken by adding polyvinyl alcohol etc. to a solvent. Any coating method may be used as long as the coating agent can be applied to the surface of the n-type silicon single crystal substrate. Moreover, you may dry suitably after apply | coating a coating agent.

(Application process of paste containing oxide ceramic fine particles)
Next, a paste containing oxide ceramic fine particles is applied in a pattern on the surface of the n-type silicon single crystal substrate on which the coating agent is applied, that is, on the surface that becomes the light receiving surface when a solar cell is formed. The oxide paste can be composed of oxide ceramic fine particles, an organic binder, and an organic solvent.

  Examples of the oxide ceramic fine particles include fine particles made of silica, alumina, zircon, zirconia, barium titanate, lead zirconate titanate, ferrite, forsterite, mullite, steatite, cordierite, etc. May be used. Of these, silica fine particles and alumina (aluminum oxide) fine particles are particularly preferred because they are versatile and easy to handle. Hereinafter, a case where silica fine particles are used as the oxide ceramic fine particles will be described.

  Specific examples of organic binders include polyvinyl acetate, acrylic resins (polyacrylic acids and their salts, homopolymers and copolymers of hydroxyethyl acrylate, homopolymers and copolymers of hydroxypropyl acrylate, homopolymers and copolymers of hydroxybutyl acrylate) , Polyvinyl acetal resin (polyvinyl acetate or hydrolyzed polyvinyl acetate, polyvinyl formal, polyvinyl butyral, polyvinyl alcohol having a hydrolysis degree of 60% by mass or more, preferably 80% by mass or more), polyurethane resin, polyurea resin, polyimide resin, polyamide Resin, epoxy resin, methacrylic resin (polymethacrylic acids and their salts, homopolymers and copolymers of hydroxymethacrylate, hydride Methacrylate homopolymers and copolymers), polystyrene resin, novolak phenolic resins, polyester resins, synthetic rubber, natural rubber (gum arabic), and the like.

  It also functions as a thixotropic agent by combining fine particle silica that is a solid content and one or more organic binders selected from the above substances. Thereby, the ratio of the paste viscosity when high shear stress is generated and when low shear stress is generated can be increased.

  In the present invention, the organic solvent is preferably a high-boiling solvent having a boiling point of 100 ° C. or higher. This is because the volatilization of the solvent is suppressed, the composition change of the paste is reduced, and stable printing can be performed.

  In particular, specific examples of suitable organic solvents include TPM (isobutyric acid 3-hydroxy-2,2,4-trimethylpentyl ester) as a high-boiling point solvent, such as TPM (isobutyric acid 3-hydroxy-2,2,4-trimethylpentyl ester). Can be used. However, the compound that can be used as the high boiling point solvent is not limited thereto.

  Examples of the high boiling point solvent include aliphatic hydrocarbon solvents, carbitol solvents, cellosolve solvents, higher fatty acid ester solvents, higher alcohol solvents, higher fatty acid solvents, aromatic hydrocarbon solvents and the like. . Examples of the carbitol solvent include methyl carbitol, ethyl carbitol, butyl carbitol and the like, and examples of the cellosolve solvent include ethyl cellosolve, isoamyl cellosolve, hexyl cellosolve and the like. Examples of higher fatty acid ester solvents include dioctyl phthalate, dibutyl succinic acid isobutyl ester, adipic acid isobutyl ester, dibutyl sebacate, di-2-ethylhexyl sebacate, and higher alcohol solvents include methyl hexanol, oleyl. Examples include alcohol, trimethylhexanol, trimethylbutanol, tetramethylnonanol, 2-pentylnonanol, 2-nonylnonanol, 2-hexyldecanol and the like. Examples of higher fatty acid solvents include caprylic acid, 2-ethylhexanoic acid, and oleic acid, and examples of aromatic hydrocarbon solvents include butylbenzene, diethylbenzene, dipentylbenzene, and diisopropylnaphthalene.

  These organic solvents can be used alone, but in order to adjust the viscosity, etc., the dispersibility of the fine particle silica, which is a solid content, into the organic binder, the wettability with the textured silicon crystal substrate, A plurality of types can be used in combination as appropriate.

  As the paste application method, the screen printing method is the simplest and preferable, but an ink jet method or the like can also be used. The method for applying the paste is not particularly limited, and such a method can be used as long as a pattern is drawn.

  As shown in FIG. 1, the paste pattern on the light receiving surface of the n-type silicon single crystal substrate 10 has a line shape in which the width of the non-printing portion 12 where the paste is not printed is 0.1 mm to 0.5 mm. This is preferable because high cell characteristics can be obtained. That is, it is preferable that the paste pattern has a line shape in which the period c of the printing unit 11 of the paste shown in FIG. 1 is 1 mm to 3 mm and the width d of the printing unit 11 is 0.5 mm to 2.9 mm.

(Low temperature heat treatment process)
Subsequently, the n-type silicon single crystal substrate 10 on which the paste is applied in a pattern is subjected to low-temperature heat treatment. The low temperature heat treatment in the present invention is a heat treatment including a heat cycle in which the temperature is raised to a temperature lower than the temperature of the diffusion heat treatment, which is a subsequent process, and the temperature is lowered after the temperature rise. In addition, the temperature may be lowered after the temperature is maintained at a constant temperature.

  In the present invention, it is preferable that the maximum temperature of the thermal cycle in the low-temperature heat treatment step is 300 ° C. or more and 600 ° C. or less, and the minimum temperature is 15 ° C. or more and less than 300 ° C. The maximum temperature here is the temperature before the start of temperature decrease after the end of temperature increase, and the minimum temperature is the temperature at the end of temperature decrease. For example, the low-temperature heat treatment involves a thermal cycle in which the maximum temperature is raised to 300 ° C. to 600 ° C., the n-type silicon single crystal substrate 10 is heated for several minutes to several tens of minutes, and the lowest temperature is lowered to around room temperature. Heat treatment. The atmosphere during the low-temperature heat treatment is desirably an oxygen atmosphere or air. The low temperature heat treatment may be repeated a plurality of times.

(Diffusion heat treatment process)
After the low-temperature heat treatment, diffusion heat treatment at a temperature higher than that of the low-temperature heat treatment, for example, 900 ° C. to 1000 ° C. is performed. Thereby, a boron diffusion layer having a relatively low concentration is formed on the surface layer portion of the silica paste printing portion, that is, the light receiving surface of the n-type silicon single crystal substrate 10 in the vicinity of the printing portion 11 in FIG. On the other hand, a relatively high concentration boron diffusion layer is formed in the non-printing portion of the silica paste, that is, the surface layer portion of the surface that becomes the light receiving surface of the n-type silicon single crystal substrate 10 in the vicinity of the non-printing portion 12 in FIG.

  The difference in boron concentration in the diffusion layer is considered to occur as follows. Boron changes to boron oxide by low-temperature heat treatment. Since boron oxide has a low melting point, it exists as a liquid at a temperature of about 300 ° C. to 600 ° C. When silica (silicon dioxide) is in contact with liquid boron oxide, dissolution of silicon dioxide at the contact portion proceeds. Then, a silica-boron oxide intermediate phase is formed during cooling and cooling, and the pure boron oxide concentration in the silica printing part is reduced. In this state, when a diffusion heat treatment at 900 ° C. to 1000 ° C. is performed, the concentration of boron diffused in the substrate can be reduced in the silica printed portion compared to the silica non-printed portion. Furthermore, this reaction further proceeds by repeating a heat cycle of temperature increase to temperature decrease, that is, repeated low temperature heat treatment. That is, if the low-temperature heat treatment is repeatedly performed, the density difference between the silica printed portion and the non-printed portion can be further increased. The same phenomenon appears even when silica is replaced with other oxide ceramics.

Further, the diffusion heat treatment may be performed in the following manner. First, a general silicon solar cell needs to form a pn junction only on the light receiving surface. In order to form a pn junction only on the light receiving surface, the diffusion heat treatment is performed in a state where the light receiving surfaces of the two substrates are overlapped at the time of the diffusion heat treatment, or the back surface (the surface serving as the light receiving surface is defined before the diffusion heat treatment). On the other hand, an SiO ₂ film, SiN _x film or the like may be formed as a diffusion mask on the reverse surface, so that a PN junction cannot be formed on the back surface. In particular, diffusion heat treatment can be performed by superimposing the light receiving surfaces of the n-type silicon single crystal substrate to form a set of two sheets, and, for example, phosphorus oxychloride gas can be introduced into the furnace. With such a method, an n-type diffusion layer can be formed on the back surface of the n-type silicon single crystal substrate simultaneously with boron diffusion.

(Glass removal process)
Next, the glass on the surface of the substrate generated by the heat treatment is removed with hydrofluoric acid or the like.

(Antireflection film forming process)
Next, an antireflection film is formed on the light receiving surface. A silicon nitride film or a silicon oxide film can be used as the antireflection film. In the case of forming a silicon nitride film, it is preferable to form the silicon nitride film with a film thickness of about 100 nm using a plasma CVD (Plasma-enhanced Chemical Vapor Deposition) apparatus. Monosilane (SiH ₄ ) and ammonia (NH ₃ ) are often used as a reaction gas as a raw material for the silicon nitride film, but nitrogen can be used instead of NH ₃ . In addition, hydrogen may be mixed with the reaction gas in order to adjust the process pressure and dilute the reaction gas. When a silicon oxide film is formed, a CVD method may be used, but a silicon oxide film obtained by a thermal oxidation method can provide higher cell characteristics.

(Back electrode forming process)
Next, as the back electrode, for example, a paste containing Ag is formed by a screen printing method. The electrode formation region may be the entire back surface, or a localized electrode method in which the entire back surface is covered with a silicon nitride film or a silicon oxide film and a part thereof is opened with a laser or the like to form an electrode only at the opening. Further, the back electrode forming method is not limited to screen printing, and may be formed using vapor deposition or sputtering.

(Light-receiving surface electrode formation process)
It is preferable to use a screen printing method for forming the light-receiving surface electrode, and it is preferable to print an Ag paste in which Ag powder and glass frit are mixed with an organic binder. At this time, the Ag paste is printed at the same location as the silica paste non-printing portion printed first. Specifically, a screen plate having an opening of 40 μm to 100 μm and an opening having the same period as the period of the silica paste printing part (see FIG. 1) is prepared, and the silica paste non-printing part and the light receiving surface electrode overlap. The substrate position may be adjusted so that printing is performed. The method of forming the light-receiving surface electrode is not limited to the screen printing method, and may be an ink jet method, or a sputtering method or a vapor deposition method using a mask as long as the electrode can be formed at the same place as the silica paste non-printing part. .

As described above, after the Ag paste is printed, the electrode is formed by firing. Even when the Ag paste is formed on the SiN _x film, passed through the Ag powder in the SiN _x film by the heat treatment (fire-through), it is possible to conduct the electrode and the silicon. The back electrode and the light-receiving surface electrode can be fired at the same time. Baking can be performed by processing for 5 to 30 minutes normally at the temperature of 700-800 degreeC. The formation of the light receiving surface electrode and the back surface electrode may be reversed. Thus, a solar cell can be manufactured using an n-type semiconductor substrate.

  In the above, the example which manufactures a solar cell using an n-type silicon single crystal substrate was demonstrated. On the other hand, when a p-type substrate is used, the procedure for diffusing boron on the surface of the substrate can be the same as that when an n-type silicon single crystal substrate is used. When a p-type substrate is used, the surface on which boron is diffused can be the back surface, and the opposite surface can be the light receiving surface.

  In this case, in addition to the above-described semiconductor substrate preparation step to diffusion heat treatment step, a step of forming an n-type diffusion layer on the surface layer portion of the surface to be a light-receiving surface, a step of forming a light-receiving surface electrode on the n-type diffusion layer A step of forming a back electrode on the back surface of the semiconductor substrate can be added. When the production method of the present invention is applied to the production of a solar cell using an n-type silicon single crystal substrate, a diffusion layer having a high boron concentration portion and a low boron portion can be formed on the back surface of the substrate. It is possible to manufacture a solar cell having a structure in which an electrode is localized and a non-electrode portion is a BSF (back surface field) layer.

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

  In order to confirm the effectiveness of the present invention, the characteristics of the solar cells manufactured in Examples 1 and 2 and Comparative Example 3 as described below were compared. First, 18 phosphorous-doped {100} n-type as-cut silicon substrates having a thickness of 200 μm and a specific resistance of 1 Ω · cm were prepared. Subsequently, a 2% boric acid aqueous solution was spin-coated on the surface to be the light-receiving surface of all the substrates.

Example 1
Six substrates after the boric acid application prepared as described above were taken out, and a silica paste was pattern printed on the taken out substrates. As a silica paste, a mixture of 23% polyvinyl alcohol, 23% silica, 47% ethanol, and 7% water was used. A screen printer was used for printing. The width of the printed part of the silica paste was 1.6 mm, and the cycle was 2.0 mm.

  These were put into a belt furnace, subjected to heat treatment at a maximum temperature of 400 ° C. for about 5 minutes and cooled to room temperature (low temperature heat treatment).

  Next, the substrate after the low-temperature heat treatment was subjected to diffusion heat treatment in a horizontal furnace. As diffusion heat treatment conditions, the temperature was raised to 950 ° C. and maintained for 30 minutes. At this time, the boric acid application surfaces (surfaces to be light-receiving surfaces) were overlapped to form a set of two sheets, and phosphorus oxychloride was introduced into the horizontal furnace to form a phosphorus diffusion layer on the back surface side. After the diffusion heat treatment, the surface glass was removed by immersing in hydrofluoric acid having a concentration of 12%.

After the above processing, a SiN _x film was formed as an antireflection film on the surface serving as the light receiving surface using a plasma CVD apparatus. Next, a SiN _x film was also formed on the back surface under the same conditions. Next, Ag paste as a back electrode was screen-printed in a comb-like shape on the entire back surface and dried. Next, the Ag paste was printed and dried so as to overlap the silica paste non-printing portion on the surface to be the light receiving surface, and fired in an air atmosphere at 780 ° C. to complete the solar cell.

The current-voltage characteristics of the solar cell thus manufactured under simulated sunlight were measured. Characteristic evaluation is conducted in an atmosphere of 25 ° C. under a solar simulator (irradiation intensity: 1 kW / m ² , spectrum: AM1.5 global), electrical measurement (short-circuit current density, open-circuit voltage, curve factor (form factor), conversion Efficiency).

(Example 2)
Six substrates different from Example 1 were taken out and used from the substrates after the above boric acid application, and a solar cell was basically manufactured by the same procedure as Example 1. However, in Example 2, the low temperature heat treatment was performed twice by performing the heat treatment using the belt furnace performed in Example 1 twice. The current-voltage characteristics of the solar cell thus manufactured under simulated sunlight were measured in the same manner as in Example 1.

(Comparative Example 1)
Among the substrates after the boric acid application, the remaining six substrates were used to manufacture a solar cell basically in the same procedure as in Example 1. However, in Comparative Example 1, the silica paste was not printed on the surface of the substrate, and the low temperature heat treatment using a belt furnace was not performed.

  Table 1 summarizes the results of implementation in Examples 1 and 2 and Comparative Example 1. The numerical values shown in Table 1 are all average values.

  In Examples 1 and 2, since the selective emitter was formed by the method for manufacturing a solar cell of the present application, the short-circuit current and the open-circuit voltage were greatly improved, and the conversion efficiency was also improved. Thus, it was confirmed that a selective emitter can be formed by a simple method, and a solar cell with good performance can be easily obtained.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

  DESCRIPTION OF SYMBOLS 10 ... n-type semiconductor substrate, 11 ... Printing part, 12 ... Non-printing part.

Claims (5)

The manufacturing method of a solar cell which has the process of apply | coating the coating agent containing boron to the surface of a semiconductor substrate, and the process of performing the diffusion heat treatment which diffuses the said boron in the surface layer part of the surface where the said coating agent of the said semiconductor substrate was apply | coated. Because
Before the diffusion heat treatment step,
Applying a paste containing oxide-based ceramic fine particles in a pattern on the surface coated with the coating agent;
A step of raising the temperature to a temperature lower than the temperature of the diffusion heat treatment, and performing a low-temperature heat treatment including a thermal cycle of lowering the temperature after the temperature rise on the semiconductor substrate after applying the paste one or more times,
A method for manufacturing a solar cell, comprising performing the diffusion heat treatment on a semiconductor substrate after being subjected to the low-temperature heat treatment at least once.   The method for producing a solar cell according to claim 1, wherein the oxide ceramic fine particles are silica fine particles or aluminum oxide fine particles.   3. The method of manufacturing a solar cell according to claim 1, wherein the maximum temperature of the thermal cycle in the low-temperature heat treatment step is 300 ° C. or more and 600 ° C. or less, and the minimum temperature is 15 ° C. or more and less than 300 ° C. 3. .   The semiconductor substrate is an n-type semiconductor substrate, the surface of the semiconductor substrate on which the boron is diffused is used as a light receiving surface, and a light receiving surface electrode is formed on the light receiving surface, and the boron on the semiconductor substrate is diffused. The method of manufacturing a solar cell according to claim 1, further comprising a step of forming a back electrode on a surface opposite to the surface that has been formed.   Forming a semiconductor substrate as a p-type semiconductor substrate, a surface opposite to the surface of the semiconductor substrate on which the boron has been diffused as a light-receiving surface, and further forming an n-type diffusion layer in a surface layer portion of the light-receiving surface; 4. The method according to claim 1, further comprising: forming a light-receiving surface electrode on the n-type diffusion layer; and forming a back electrode on the surface of the semiconductor substrate where the boron is diffused. The manufacturing method of the solar cell of any one of Claims 1.

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