JP2006073897A - Solar cell manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell manufacturing method capable of mass manufacturing a solar cell having high conversion efficiency by using a hydrogen termination technique. <P>SOLUTION: The solar cell manufacturing method comprises the steps of forming a first electrode on one surface of a silicon substrate having a first polarity, irradiating the other surface of the silicon substrate with hydrogen plasmas after forming the first electrode, and forming a second electrode on the other surface of the silicon substrate after irradiation with hydrogen plasmas. In the method, the temperature of the silicon substrate during forming of the second electrode is preferably lower than the temperature of the silicon substrate during forming of the first electrode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a solar cell, and more particularly to a method for manufacturing a solar cell capable of mass-producing solar cells having high conversion efficiency using hydrogen termination technology.

In recent years, development of clean energy has been demanded due to the problem of depletion of energy resources and global environmental problems such as increase of CO _{2 in} the atmosphere. In particular, solar power generation using solar cells has been developed as a new energy source. It has been put to practical use and is on the path of development.

  As a manufacturing method of a solar cell using a polycrystalline silicon substrate for residential use, which is currently mass-produced, there is one disclosed in Patent Document 1, for example. The manufacturing process of this conventional solar cell is shown in the schematic sectional views of FIGS.

  First, as shown in FIG. 12A, a p-type silicon substrate 1 from which a slice damage layer has been removed by alkali etching or the like is prepared. Next, a solution containing an n-type impurity is dropped on the light receiving surface of the silicon substrate 1, the silicon substrate 1 is rotated at a high speed using a spin coater, and then the silicon substrate 1 is put into a diffusion furnace. As shown in FIG. 12B, an n-type impurity diffusion layer 4 is formed in the silicon substrate 1.

Next, as shown in FIG. 12C, a silicon nitride film 7 is formed as an antireflection film on the n-type impurity diffusion layer 4 by plasma CVD. 12D, the n-side electrode paste 11 is screen-printed on the silicon nitride film 7, and the p-side electrode paste 12 is screen-printed on the back surface of the silicon substrate 1. Then, as shown in FIG. Thereafter, by firing these electrode pastes, as shown in FIG. 12E, the n-side electrode paste 11 penetrates the silicon nitride film 7 by fire through and contacts the n-type impurity diffusion layer 4. Along with the electrode 9, the p-side electrode paste 12 forms the p-type impurity diffusion layer 3 in the silicon substrate 1 by baking, and becomes the p-side electrode 10 to complete the solar cell.
JP-A-2-33980 JP 59-136926 A JP 2003-347304 A Japanese Patent Publication No. 7-54854 M. Spiegel and 5 others, “Detailed Study on Microwave Induced Remote Hydrogen Plasma Passivation of Multicrystalline Silicon”, 13th EUROPEAN PHOTOVOLTAIC SOLAR ENERGY CONFERENCE, France, 23-27, OCTOBER 1995, p.421-424

  However, since the solar cell obtained as described above uses a polycrystalline silicon substrate, there is a problem that conversion efficiency is inferior to that of a solar cell using a single crystal silicon substrate. The main reason for this is that a polycrystalline silicon substrate has many crystal defects that become carrier recombination centers in the silicon substrate. There are many bonds, and the lifetime of the carrier is short.

  Therefore, in a solar cell using a polycrystalline silicon substrate, in order to approach the conversion efficiency of a solar cell using a single crystal silicon substrate, the polycrystalline silicon substrate is irradiated with hydrogen plasma to cause the conversion in the polycrystalline silicon substrate. Attempts have been made to terminate the dangling bonds of silicon in a crystal defect or the like with hydrogen (see, for example, Patent Document 2).

  For example, Patent Document 3 discloses a method of manufacturing a silicon substrate irradiated with hydrogen plasma using a vacuum process (see [0019] of Patent Document 3). However, in general, in the production of mass-produced consumer solar cells, a silicon substrate is heated to a high temperature of 600 ° C. or higher when forming a p-side electrode and an n-side electrode using an electrode paste (for example, Patent Documents). 1). As a result, there is a problem that a large amount of hydrogen forming Si—H bonds is detached from the silicon substrate in the silicon substrate terminated with hydrogen.

  In Patent Document 4, an antireflection film is formed on the light-receiving surface of a single crystal or polycrystalline silicon substrate by a plasma CVD method, and hydrogen is introduced into the silicon substrate at the same time. A method in which a mixed gas of silane and ammonia is introduced into a plasma CVD apparatus after being heated to form a blocking film on the back surface of the silicon substrate by plasma CVD, and then an electrode is formed at a firing temperature of 600 ° C. to 800 ° C. Is disclosed (see column 5 of Patent Document 4). However, in this method, after introducing hydrogen into the silicon substrate, the silicon substrate is heated to 400 ° C. or more and 600 ° C. or less before the formation of the blocking film, and further, 600 ° C. or more and 800 ° C. or less during the subsequent electrode formation. Therefore, even if a blocking film is formed, a hydrogen desorption reaction occurs in which hydrogen in the silicon substrate is desorbed from the silicon substrate, which is insufficient as a hydrogen termination for improving the conversion efficiency of the solar cell. It was.

  In view of the above circumstances, a solar cell manufacturing method using hydrogen termination technology that terminates dangling bonds of silicon in a silicon substrate with hydrogen by hydrogen plasma is not currently used for mass production of solar cells.

  The objective of this invention is providing the manufacturing method of the solar cell which can mass-produce the solar cell which has high conversion efficiency using a hydrogen termination | terminus technique.

  The present invention includes a step of forming a first electrode on one surface of a silicon substrate having a first polarity, a step of irradiating the other surface of the silicon substrate with hydrogen plasma after the formation of the first electrode, And a step of forming a second electrode on the other surface of the silicon substrate after irradiation with hydrogen plasma.

  Here, in the method for manufacturing a solar cell of the present invention, it is preferable that the temperature of the silicon substrate at the time of forming the second electrode is lower than the temperature of the silicon substrate at the time of forming the first electrode.

  Moreover, in the manufacturing method of the solar cell of this invention, it is preferable that the temperature of a silicon substrate at the time of formation of a 2nd electrode is 500 degrees C or less.

  Moreover, in the manufacturing method of the solar cell of this invention, it is preferable that a 2nd electrode is formed using a screen printing method or a vacuum evaporation method.

  In the method for manufacturing a solar cell of the present invention, it is preferable that the irradiation of hydrogen plasma is performed in a state where the temperature of the silicon substrate is 200 ° C. or higher and lower than the temperature at the time of forming the first electrode.

  In the method for manufacturing a solar cell of the present invention, an impurity diffusion layer having the second polarity can be formed on at least one surface of the silicon substrate.

  In the method for manufacturing a solar cell of the present invention, an impurity diffusion layer having the second polarity is formed on one surface of the silicon substrate, and the first surface having a higher impurity concentration than the silicon substrate is formed on the other surface of the silicon substrate. A polar impurity diffusion layer can be formed.

  In the method for manufacturing a solar cell of the present invention, an antireflection film is formed on at least one surface of the silicon substrate, and electrode paste is screen-printed on the antireflection film and then fired to form the first electrode. At least one of the second electrode and the second electrode may penetrate the antireflection film and be formed on the surface of the silicon substrate.

  In the method for manufacturing a solar cell of the present invention, the passivation film is formed on a part of at least one surface of the silicon substrate, and the exposed surface of the silicon substrate is exposed from the portion where the passivation film is not formed. In addition, at least one of the first electrode and the second electrode can be formed.

  In the method for manufacturing a solar cell according to the present invention, the first polarity impurity diffusion layer having an impurity concentration higher than that of the silicon substrate can be formed on the exposed surface of the silicon substrate.

  In the method for manufacturing a solar cell according to the present invention, when the first polarity is p-type, the second polarity is n-type, and when the first polarity is n-type, the second polarity is used. Can be p-type.

  In the method for manufacturing a solar cell of the present invention, when the first electrode is a p-side electrode, the second electrode is an n-side electrode, and when the first electrode is an n-side electrode, The two electrodes can be p-side electrodes.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the solar cell which can mass-produce the solar cell which has high conversion efficiency using a hydrogen termination | terminus technique can be provided.

  Embodiments of the present invention will be described below. In the drawings of the present application, the same reference numerals represent the same or corresponding parts.

(Silicon substrate)
The silicon substrate used in the present invention has the first polarity. Here, the first polarity is either p-type or n-type. Further, it is preferable that the concentration of the impurity doped in the silicon substrate for imparting the first polarity to the silicon substrate is 1 × 10 ¹³ / cm ³ or more and 1 × 10 ¹⁸ / cm ³ or less. Impurity concentration in the silicon substrate tends to have fill factor for resistance on the flow of diffusion current becomes high sheet resistance of the silicon substrate is increased to decrease if it is less than 1 × 10 ¹³ / cm ^3. In addition, when the impurity concentration in the silicon substrate is higher than 1 × 10 ¹⁸ / cm ³ , the sheet resistance of the silicon substrate decreases, but the defect (recombination center) concentration in the silicon substrate increases and the current value decreases. Tend to. Therefore, when the concentration of the impurity doped in the silicon substrate is 1 × 10 ¹³ / cm ³ or more and 1 × 10 ¹⁸ / cm ³ or less, the conversion efficiency of the solar cell tends to be further improved. . Further, the silicon substrate may be made of single crystal silicon or may be made of polycrystalline silicon. Among these, it is preferable to use a silicon substrate made of polycrystalline silicon having many silicon dangling bonds at crystal grain boundaries and crystal defects in the silicon substrate. However, even when the silicon substrate is made of single crystal silicon, for example, the single crystal silicon produced by the Czochralski method may have silicon dangling bonds due to crystal defects. It is also effective for silicon substrates made of silicon.

(electrode)
A first electrode is formed on one of the light receiving surface and the back surface of the silicon substrate, and a second electrode is formed on the surface on which the first electrode is not formed. The material constituting these electrodes is not particularly limited, and for example, materials such as aluminum, silver, titanium, palladium or gold conventionally used in the solar cell field are used, but silicon in contact with these electrodes is used. A material that can make ohmic contact with the surface of the substrate is preferably used. Further, the method for forming these electrodes is not particularly limited, and for example, a screen printing method or a vacuum deposition method can be used. From the viewpoint of improving mass productivity and reducing manufacturing costs, the electrode is formed by using the screen printing method. Is preferred. Formation of the electrode using the screen printing method is performed, for example, by printing a paste-like electrode paste containing a material constituting the electrode by the screen printing method and then firing the paste. In particular, when an electrode is formed on the light-receiving surface of a silicon substrate on which an antireflection film, which will be described later, is formed, the electrode paste is printed on the antireflection film by a screen printing method and then fired. The paste penetrates the antireflection film (fire through), and an electrode is formed on the light receiving surface of the silicon substrate. In addition, formation of the electrode using the vacuum deposition method is performed, for example, by evaporating a material constituting the electrode by heating and evaporating in a high vacuum and depositing the material on the light receiving surface and / or the back surface of the silicon substrate.

  Here, in the present invention, the temperature of the silicon substrate at the time of forming the second electrode formed after the hydrogen plasma irradiation is the same as that of the silicon substrate at the time of forming the first electrode formed before the hydrogen plasma irradiation. The temperature is preferably lower than the temperature. Specifically, the temperature of the silicon substrate at the time of forming the second electrode formed after the hydrogen plasma irradiation is preferably 500 ° C. or less, and more preferably 400 ° C. or less. In this case, hydrogen tends to be effectively prevented from leaving.

  FIG. 1 shows the relationship between the heating temperature of the silicon substrate after the hydrogen plasma irradiation and the carrier diffusion length. In FIG. 1, the horizontal axis indicates the heating temperature (° C.) of the silicon substrate after irradiation with hydrogen plasma, and the vertical axis indicates the carrier diffusion length (μm) after the silicon substrate is heated to the temperature on the horizontal axis. As shown in FIG. 1, when the heating temperature of the silicon substrate is higher than 500 ° C., the carrier diffusion length becomes shorter than when the silicon substrate is not heated (in the case of “No Heat” in FIG. 1). On the other hand, when the heating temperature of the silicon substrate is 400 ° C., the carrier diffusion length is long. Therefore, it can be seen from the results shown in FIG. 1 that the lower the temperature of the silicon substrate during the formation of the second electrode, the longer the carrier diffusion length, that is, the hydrogen is terminated without detachment. It is derived that the temperature of the silicon substrate at the time of forming is preferably 500 ° C. or less, and more preferably 400 ° C. or less, in which the carrier diffusion length is longer than when the silicon substrate is not heated. Note that the lower limit of the temperature of the silicon substrate at the time of forming the second electrode is the lowest temperature at which the second electrode can be formed. The lower limit of the temperature of the silicon substrate at the time of forming the second electrode is, for example, 200 ° C to 300 ° C. Here, the silicon substrate used for the measurement was manufactured by irradiating the silicon substrate from which the slice damage layer was removed by alkali etching or the like with hydrogen plasma, and then heat-treating each at a temperature of 400 ° C. to 800 ° C. for 5 minutes. A silicon substrate was used. The carrier diffusion length is determined by measuring the current value at each wavelength by spectral sensitivity measurement using monochromatic light of 800 to 1000 nm for each of the above silicon substrates from which the silicon oxide film on the surface has been removed by hydrofluoric acid. Then, it was measured by the SPV (Surface Photo Voltage) method for calculating the diffusion length.

  In the present invention, each of the first electrode and the second electrode is either a p-side electrode or an n-side electrode, and when the first electrode is a p-side electrode, the second electrode is n When the first electrode is an n-side electrode, the second electrode is a p-side electrode. Here, the p-side electrode is an electrode formed on the p-type side surface of the silicon substrate, and the n-side electrode is an electrode formed on the n-type side surface of the silicon substrate.

(Hydrogen plasma irradiation)
After the first electrode is formed on either the light receiving surface or the back surface of the silicon substrate, the other surface of the silicon substrate is irradiated with hydrogen plasma. Here, as a method of irradiating with hydrogen plasma, for example, there is a method using a catalytic CVD method or a plasma CVD method. The catalytic CVD method is a method in which, for example, a silicon substrate is irradiated with hydrogen plasma generated by bringing hydrogen molecules into contact with a tungsten filament heated to a high temperature. The plasma CVD method is a method in which a silicon substrate is irradiated with hydrogen plasma generated by collision of high energy electrons in the plasma with hydrogen molecules. Note that the method of irradiating the hydrogen plasma is not limited to the above-described catalytic CVD method and plasma CVD method, and an atmospheric pressure CVD method, a reduced pressure CVD method, a photo CVD method, or the like may be used.

  The hydrogen plasma irradiation is preferably performed in a state where the temperature of the silicon substrate is not lower than 200 ° C. and not higher than the temperature at the time of forming the first electrode. When irradiation with hydrogen plasma is performed in a state where the temperature of the silicon substrate is lower than 200 ° C., the hydrogen plasma tends not to be sufficiently diffused into the silicon substrate. Further, when irradiation with hydrogen plasma is performed in a state where the temperature of the silicon substrate is higher than the temperature at which the first electrode is formed, the Si—H bond is a weak bond, and thus the Si—H bond is in the bonded state. In this case, hydrogen tends to be released and silicon dangling bonds tend to increase, and the state of the first electrode formed on the silicon substrate tends to change.

(Impurity diffusion layer)
An impurity diffusion layer is formed on the light-receiving surface and / or back surface of the silicon substrate having the first polarity by diffusing impurities having the first polarity and / or the second polarity.

  Here, the method for forming the impurity diffusion layer is not particularly limited, and examples thereof include a coating diffusion method and a vapor phase diffusion method. In the coating diffusion method, for example, a dopant liquid containing an impurity of the first polarity or the second polarity is applied on the surface of the silicon substrate, and this is uniformly applied on the surface of the silicon substrate by a spin coater, and then a high-temperature diffusion furnace. In this method, the impurity diffusion layer is formed by doping the surface of the silicon substrate with impurities. In the vapor phase diffusion method, for example, a liquid containing a first polarity or second polarity impurity is gasified and sent to the surface of the silicon substrate, thereby doping the surface of the silicon substrate with impurities to form an impurity diffusion layer. It is a method of forming. Examples of the p-type impurity used for forming the impurity diffusion layer include boron, aluminum, and gallium. Examples of the n-type impurity include phosphorus and arsenic.

  In addition, as the timing of forming the impurity diffusion layer, the formation of the impurity diffusion layer may be performed before the formation of the electrode, or may be performed simultaneously with the formation of the electrode.

  Further, when the impurity diffusion layer having the second polarity is formed on the surface of the silicon substrate having the first polarity, a pn junction is formed in the silicon substrate. At this time, the impurity diffusion layer having the second polarity preferably has a thickness of 100 nm or more and 1000 nm or less from the surface of the silicon substrate toward the inside of the silicon substrate. In this case, a sufficient amount of current is generated by the incidence of sunlight, and current loss due to carrier recombination can be suppressed, so that the conversion efficiency of the solar cell tends to be further improved.

  Further, when a first polarity impurity diffusion layer having an impurity concentration higher than that of the silicon substrate is formed on the back surface of the silicon substrate having the first polarity, a back surface electric field layer is formed in the silicon substrate. Is done. The impurity diffusion layer having the first polarity at this time preferably has a thickness of 1000 nm or more and 10000 nm or less from the surface of the silicon substrate toward the inside of the silicon substrate. In this case, the back surface field effect by the back surface field layer is sufficient, and current loss due to carrier recombination can be suppressed, so that the conversion efficiency of the solar cell tends to be further improved.

  In the present invention, the first polarity and the second polarity are either p-type or n-type, respectively, and when the first polarity is p-type, the second polarity is n-type. When the first polarity is n-type, the second polarity is p-type.

(Antireflection film)
An antireflection film may be formed on the light receiving surface of the silicon substrate. Here, as the antireflection film, for example, a silicon nitride film, an aluminum oxide film, a silicon oxide film, a titanium oxide film, or the like is used. When a silicon nitride film or a silicon oxide film is used as the antireflection film, the antireflection film has a passivation effect on the light receiving surface of the silicon substrate. Furthermore, in the case of a solar cell using a polycrystalline silicon substrate, it is preferable to use a silicon nitride film containing hydrogen as an antireflection film from the viewpoint of improving conversion efficiency. The method for forming the antireflection film is not particularly limited. For example, CVD (Chemical Vapor Deposition) such as a plasma CVD method, a catalytic CVD method, an atmospheric pressure CVD method, a reduced pressure thermal CVD method, or a photo-CVD method. ), PVD (Physical Vapor Deposition) methods such as vacuum evaporation or sputtering, but when using a silicon nitride film as the antireflection film, the film thickness of the antireflection film is controlled. The plasma CVD method is preferably used from the viewpoint of easy.

(Passivation film)
A passivation film may be formed on at least one surface of the silicon substrate. Here, as the passivation film, for example, a film having a passivation effect such as a silicon oxide film or a silicon nitride film is used. Thereby, the passivation effect which suppresses the recombination of the carrier in the light-receiving surface (surface on the side where sunlight enters) and / or the back surface (the surface on the side where sunlight does not enter) of the silicon substrate can be obtained. The thickness of the passivation film is preferably 5 nm or more and 100 nm or less, and more preferably 5 nm or more and 30 nm or less. In this case, the passivation film can fully exhibit the passivation effect, and the solar cell absorption is thick enough not to contribute to current loss, thus improving the conversion efficiency of the solar cell. It tends to be able to be made. The method for forming the passivation film is not particularly limited. For example, a CVD method such as a plasma CVD method, a catalytic CVD method, an atmospheric pressure CVD method, a reduced pressure CVD method, or a photo CVD method is used.

(Embodiment 1)
The manufacturing process of the solar cell of this Embodiment is shown to typical sectional drawing of FIG. 2 (A)-(F). First, as shown in FIG. 2A, etching using an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide at 80 ° C. or higher and 100 ° C. or lower, or an acid solution such as a mixed solution of hydrofluoric acid and nitric acid at about room temperature. A p-type polycrystalline silicon substrate 1 from which the slice damage layer has been removed is prepared. Here, as the silicon substrate 1, for example, a substrate having a size of width 125 mm × length 125 mm or a size of width 155 mm × length 155 mm is used.

  Next, phosphorus, which is an n-type impurity, is diffused on the light receiving surface of the silicon substrate 1, thereby forming an n-type impurity diffusion layer 4 on the light receiving surface of the silicon substrate 1, as shown in FIG. Here, the sheet resistance of the n-type impurity diffusion layer 4 is preferably 10Ω / □ or more and 300Ω / □ or less. As described above, when the sheet resistance is larger than 300Ω / □, the resistance increases as the diffusion current flows, so the fill factor decreases. When the sheet resistance is less than 10Ω / □, defects (recombination) occur. Center) The concentration tends to increase and the current value tends to decrease. Therefore, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the n-type impurity diffusion layer 4 is preferably 10Ω / □ or more and 300Ω / □ or less.

As a method for forming the n-type impurity diffusion layer 4, a coating diffusion method, a vapor phase diffusion method, or the like is used. In the coating diffusion method, for example, a dopant liquid composed of phosphorus pentoxide and isopropyl alcohol is dropped onto the light receiving surface of the silicon substrate 1 and uniformly applied to the light receiving surface of the silicon substrate 1 using a spin coater. Then, the silicon substrate 1 is put into a diffusion furnace of 800 ° C. or higher and 950 ° C. or lower, and phosphorus is diffused on the light receiving surface of the silicon substrate 1. Here, the dripping amount of the dopant liquid is preferably 0.3 cm ³ or more and 5 cm ³ or less per 100 cm ² of the light receiving surface of the silicon substrate 1. Further, the spin coater is preferably rotated at a speed of 200 to 7000 rpm for 1 to 10 seconds. In the vapor phase diffusion method, for example, a silicon substrate is introduced by introducing nitrogen gas containing phosphorus oxychloride (POCl ₃ ) or phosphorus hydride (PH ₃ ), which is a liquid, into a high temperature furnace at 750 ° C. or higher and 950 ° C. or lower. Phosphorus is diffused on the light-receiving surface 1. Here, it is preferable that phosphorus is diffused while nitrogen or oxygen gas is introduced into the high temperature furnace to control the partial pressure of phosphorus as a dopant in the high temperature furnace.

Next, as shown in FIG. 2C, a silicon nitride film 7 having a thickness of 10 nm or more and 200 nm or less is formed as an antireflection film on the n-type impurity diffusion layer 4 by using, for example, a plasma CVD method. Here, examples of the source gas used in the plasma CVD method include silane (SiH ₄ ) and fluorinated silane (SiF ₄ ) containing silicon, ammonia (NH ₃ ) and nitrogen (N ₂ ) containing nitrogen. It is done. In a reaction vessel having a temperature of 200 ° C. or more and 500 ° C. or less and a pressure of 10 Pa or more and 200 Pa or less, silane is supplied at a flow rate of 10 sccm or more and 500 sccm or less, ammonia is supplied at a flow rate of 10 sccm or more and 1000 sccm or less, and nitrogen is supplied at 50 sccm or more and 1000 sccm or less. A plasma is generated by applying a high frequency or microwave. Here, in the generation of plasma, for example, a high frequency with a frequency of 13.56 MHz or 100 MHz, a microwave with a frequency of 2.45 GHz, or the like is used.

  Then, as shown in FIG. 2D, an n-side electrode 9 is formed on the light receiving surface of the silicon substrate 1. Here, as a method of forming the n-side electrode 9, for example, there is a method using a screen printing method or a vacuum deposition method. In the method using the screen printing method, for example, after the n-side electrode paste is screen-printed on the silicon nitride film 7, the silicon substrate 1 is baked at a temperature of 600 ° C. or higher and 800 ° C. or lower. As a result, the n-side electrode paste penetrates through the antireflection film 7 to form the n-side electrode 9 in contact with the n-type impurity diffusion layer 4 on the light receiving surface of the silicon substrate 1. Here, examples of the n-side electrode paste include a paste containing a metal capable of making ohmic contact with the n-type impurity diffusion layer 4 such as silver or titanium. In the method using the vacuum deposition method, for example, a photoresist is applied on the surface of the silicon nitride film 7 using a spin coater, and this is baked at 70 to 100 ° C. for 20 to 80 minutes. Then, the photoresist is patterned by removing a part of the photoresist by exposure using a glass mask or the like. Then, the silicon nitride film 7 is removed only from the portion where the photoresist has been removed with a hydrofluoric acid aqueous solution of about 1% to 50%, and the n-side electrode 9 is formed on the light receiving surface of the silicon substrate 1 by vacuum deposition. Thereafter, the photoresist is removed by ultrasonic cleaning using acetone or immersion in a solution obtained by adding hydrogen peroxide to concentrated sulfuric acid heated to a high temperature of a few hundred degrees. Here, the photoresist may be a positive type or a negative type. Alternatively, patterning may be performed while depositing the silicon nitride film 7 using a metal mask without using a photoresist.

  Subsequently, as shown in FIG. 2E, hydrogen plasma 13 is irradiated from the back side of the silicon substrate 1. For the irradiation of the hydrogen plasma 13, for example, a plasma CVD method, a catalytic CVD method, an atmospheric pressure CVD method, a reduced pressure thermal CVD method, a photo CVD method, or the like is used, and in particular, from the viewpoint of easily controlling the intensity of the plasma density. The CVD method is most suitable, and then the plasma CVD method used for the silicon nitride film is suitable. In the catalytic CVD method, for example, hydrogen plasma 13 is produced by bringing hydrogen at a flow rate of 10 sccm to 100 sccm into contact with tungsten wire heated to 1600 ° C. to 1800 ° C. in a reaction vessel having a pressure of 0.1 Pa to 10 Pa. The silicon substrate 1 that is generated and heated to 200 ° C. or more and below the temperature at which the n-side electrode 9 is formed is irradiated for 10 to 60 minutes.

  Finally, as shown in FIG. 2F, the solar cell is completed by forming the p-side electrode 10 on the back surface of the silicon substrate 1. Here, the p-side electrode 10 is preferably formed using, for example, a screen printing method or a vacuum evaporation method, and more preferably formed using a screen printing method. Good solar cell characteristics can be obtained by using either the screen printing method or the vacuum vapor deposition method. However, when the screen printing method is used, mass productivity can be improved and the manufacturing cost can be reduced. Because it is in. In the method using the screen printing method, for example, after printing the p-side electrode paste on almost the entire back surface of the silicon substrate 1, the temperature of the silicon substrate 1 is preferably 500 ° C. or lower, more preferably 400 ° C. or lower. Thus, the p-side electrode 9 is formed by firing. Here, as the p-side electrode paste, for example, a paste that can be in ohmic contact with the silicon substrate 1 such as a paste containing aluminum or a paste of a mixture of aluminum and a metal such as silver or titanium is used. In addition, the coating thickness of the p-side electrode paste at this time is preferably 1 μm or more and 200 μm or less, and more preferably 2 μm or more and 100 μm or less. In this case, the solar cell tends to be manufactured at a low manufacturing cost without reducing the mass productivity of the solar cell.

  Further, in the method using the vacuum deposition method, the metal constituting the p-side electrode 9 is vacuum-deposited on the back surface of the silicon substrate 1 and then fired, thereby sufficiently bringing the p-side electrode 9 and the silicon substrate 1 into contact with each other. It is preferable. Here, in the method using the vacuum vapor deposition method, for example, aluminum, titanium, palladium, silver, or the like is used as the metal constituting the p-side electrode 9, and in particular, considering the ohmic contact with the silicon substrate 1, Most preferred is aluminum. Further, from the viewpoint of characteristics such as a short circuit current, an open circuit voltage, and a fill factor of the solar cell, it is preferable to stack metal layers by vacuum deposition in the order of aluminum, titanium, palladium, and silver from the silicon substrate 1 side. Furthermore, also in the method using the vacuum evaporation method, the temperature of the silicon substrate 1 at the time of forming the p-side electrode 9 is preferably 500 ° C. or less, and more preferably 400 ° C. or less.

  Thus, in this embodiment, after the temperature of the silicon substrate is heated to 600 ° C. or more and 800 ° C. or less to form the n-side electrode, the hydrogen plasma is irradiated to the silicon substrate. When the p-side electrode is formed, the silicon substrate is preferably heated only to 500 ° C. or less, more preferably 400 ° C. or less, so that hydrogen in the silicon substrate is difficult to separate from the silicon substrate. As a result, the separation of hydrogen terminated in the silicon substrate can be suppressed, and the lifetime and diffusion length of carriers generated by the incidence of sunlight can be increased, thereby improving the conversion efficiency of the solar cell. be able to.

(Embodiment 2)
Unlike the first embodiment, this embodiment is characterized in that an n-type silicon substrate is used. The manufacturing process of the solar cell of this Embodiment is shown to typical sectional drawing of Fig.3 (A)-(F). First, as shown in FIG. 3A, an n-type polycrystalline silicon substrate 2 from which the slice damage layer has been removed by etching using an alkaline aqueous solution or an acid solution is prepared. Next, p-type impurity diffusion layers 3 are formed on the light-receiving surface of the silicon substrate 2 by diffusing boron, which is a p-type impurity, on the light-receiving surface of the silicon substrate 2 as shown in FIG. Here, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the p-type impurity diffusion layer 3 is preferably 10Ω / □ or more and 300Ω / □ or less. In the same manner as described above, this takes into consideration a decrease in fill factor due to an increase in sheet resistance and an increase in defect (recombination center) concentration due to a decrease in sheet resistance.

As a method for forming the p-type impurity diffusion layer 3, a coating diffusion method or a vapor phase diffusion method is used. In the coating diffusion method, for example, a dopant liquid composed of boron oxide and isopropyl alcohol is dropped on the light receiving surface of the silicon substrate 2 and uniformly applied to the light receiving surface of the silicon substrate 2 using a spin coater. Then, the silicon substrate 2 is put into a diffusion furnace having a temperature of 800 ° C. or higher and 950 ° C. or lower, and boron is diffused on the light receiving surface of the silicon substrate 2. Here, the dripping amount of the dopant liquid is preferably 0.3 cm ³ or more and 5 cm ³ or less per 100 cm ² of the light receiving surface of the silicon substrate 2. Further, the spin coater is preferably rotated at a speed of 200 to 7000 rpm for 1 to 10 seconds. In the vapor phase diffusion method, for example, nitrogen gas containing boron tribromide (BBr ₃ ) as a liquid or diborane (B ₂ H ₆ ) as a gas is introduced into a high-temperature furnace at 750 ° C. or higher and 1000 ° C. or lower. As a result, boron is diffused into the light receiving surface of the silicon substrate 2. Here, it is preferable that boron is diffused while nitrogen gas or oxygen gas is introduced into the high temperature furnace to control the partial pressure of boron as a dopant in the high temperature furnace.

  Next, as shown in FIG. 3C, a silicon nitride film 7 having a thickness of 30 nm or more and 200 nm or less is formed as an antireflection film on the p-type impurity diffusion layer 3 by using, for example, a plasma CVD method. Then, as shown in FIG. 3D, the p-side electrode 10 is formed on the light receiving surface of the silicon substrate 2. Here, the p-side electrode 10 is formed by, for example, a p-side electrode containing a material that can make ohmic contact with the p-type impurity diffusion layer 3 such as a paste containing aluminum or a paste containing aluminum and a metal such as silver. After the paste is screen-printed on the silicon nitride film 7, the silicon substrate 2 is baked at 600 ° C. or higher and 800 ° C. or lower.

  Subsequently, as shown in FIG. 3E, the hydrogen plasma 13 is irradiated from the back side of the silicon substrate 2. Finally, as shown in FIG. 3F, the n-side electrode 9 is formed on the back surface of the silicon substrate 2 to complete the solar cell. Here, the n-side electrode 9 is formed by screen-printing an n-side electrode paste made of, for example, a paste containing silver or titanium on almost the entire back surface of the silicon substrate 2, and the temperature of the silicon substrate 2 is preferably 500 ° C. or less. Preferably, it is formed in a state of 400 ° C. or lower. Further, the coating thickness of the n-side electrode paste at this time is preferably 1 μm or more and 200 μm or less, and more preferably 2 μm or more and 100 μm or less. In this case, the solar cell tends to be manufactured at a low manufacturing cost without reducing the mass productivity of the solar cell.

  Thus, in this embodiment, after the silicon substrate is heated to 600 ° C. or higher and 800 ° C. or lower to form the p-side electrode, the hydrogen plasma is irradiated to the silicon substrate. Since the silicon substrate is heated only to 500 ° C. or less, more preferably 400 ° C. or less when the n-side electrode is formed, hydrogen in the silicon substrate is unlikely to be detached from the silicon substrate. As a result, the separation of hydrogen terminated in the silicon substrate can be reduced compared to the conventional case, and the lifetime and diffusion length of carriers generated by the incidence of sunlight can be increased. Conversion efficiency can be improved.

(Embodiment 3)
Unlike the first embodiment, the present embodiment is characterized in that a back surface electric field layer is formed on the back surface of the silicon substrate. The manufacturing process of the solar cell of this Embodiment is shown to typical sectional drawing of FIG. 4 (A)-(G). First, as shown in FIG. 4A, a p-type polycrystalline silicon substrate 1 from which a slice damage layer has been removed by etching using an alkaline aqueous solution or an acid solution is prepared.

  Next, p-type impurity diffusion layers 3 are formed on the back surface of the silicon substrate 1 by diffusing boron, which is a p-type impurity, on the back surface of the silicon substrate 1 as shown in FIG. Here, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the p-type impurity diffusion layer 3 is preferably 5Ω / □ or more and 100Ω / □ or less. In the same manner as described above, this takes into consideration a decrease in fill factor due to an increase in sheet resistance and an increase in defect (recombination center) concentration due to a decrease in sheet resistance.

  Then, as shown in FIG. 4C, an n-type impurity diffusion layer 4 is formed on the light-receiving surface of the silicon substrate 1 by diffusing n-type impurities such as phosphorus on the light-receiving surface of the silicon substrate 1. Here, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the n-type impurity diffusion layer 4 is preferably 10Ω / □ or more and 300Ω / □ or less. Similarly to the above, this also takes into account the decrease in the fill factor due to the increase in sheet resistance and the increase in the defect (recombination center) concentration due to the decrease in sheet resistance.

  Next, as shown in FIG. 4D, a silicon nitride film 7 having a thickness of 30 nm or more and 200 nm or less is formed as an antireflection film on the n-type impurity diffusion layer 4 by using, for example, a plasma CVD method. And after apply | coating n side electrode paste on the silicon nitride film 7, the silicon substrate 1 is baked at 600 degreeC or more and 800 degrees C or less, and as shown in FIG.4 (E), it is n on the n-type impurity diffusion layer 4 as shown in FIG.4 (E). The side electrode 9 is formed. Subsequently, as shown in FIG. 4F, hydrogen plasma 13 is irradiated from the back side of the silicon substrate 1. Finally, as shown in FIG. 4G, the p-side electrode 10 on the p-type impurity diffusion layer 3 on the back surface of the silicon substrate 1 has a temperature of the silicon substrate 1 of preferably 500 ° C. or less, more preferably 400 ° C. or less. Thus, the solar cell is completed.

  As described above, in the present embodiment, in addition to suppressing the separation of hydrogen in the silicon substrate, the back surface electric field layer is formed on the back surface of the silicon substrate, and the recombination of carriers on the back surface of the silicon substrate can be more effectively suppressed. Thus, the conversion efficiency of the solar cell can be further improved.

(Embodiment 4)
Unlike the second embodiment, the present embodiment is characterized in that a back surface electric field layer is formed on the back surface of the silicon substrate. The manufacturing process of the solar cell of this Embodiment is shown to typical sectional drawing of Fig.5 (A)-(G). First, as shown in FIG. 5A, an n-type polycrystalline silicon substrate 2 from which the slice damage layer has been removed by etching using an alkaline aqueous solution or an acid solution is prepared. Next, p-type impurity diffusion layers 3 are formed on the light-receiving surface of the silicon substrate 2 by diffusing boron, which is a p-type impurity, on the light-receiving surface of the silicon substrate 2 as shown in FIG. Here, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the p-type impurity diffusion layer 3 is preferably 10Ω / □ or more and 300Ω / □ or less. In the same manner as described above, this takes into consideration a decrease in fill factor due to an increase in sheet resistance and an increase in defect (recombination center) concentration due to a decrease in sheet resistance.

  Then, as shown in FIG. 5C, an n-type impurity diffusion layer 4 is formed on the back surface of the silicon substrate 2 by diffusing n-type impurities such as phosphorus on the back surface of the silicon substrate 2. Here, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the n-type impurity diffusion layer 4 is preferably 5Ω / □ or more and 100Ω / □ or less. Similarly to the above, this also takes into account the decrease in the fill factor due to the increase in sheet resistance and the increase in the defect (recombination center) concentration due to the decrease in sheet resistance.

  Next, as shown in FIG. 5D, a silicon nitride film 7 having a thickness of 30 nm or more and 200 nm or less is formed on p-type impurity diffusion layer 3 by using, for example, a plasma CVD method. Then, after the p-side electrode paste is applied on the silicon nitride film 7, the silicon substrate 2 is baked at 600 ° C. or higher and 800 ° C. or lower, so that the p-side electrode 10 is formed on the silicon substrate 2 as shown in FIG. It is formed on the light receiving surface. Subsequently, as shown in FIG. 5F, the hydrogen plasma 13 is irradiated from the back side of the silicon substrate 2. Finally, as shown in FIG. 5 (G), the temperature of the silicon substrate 2 on the n-type impurity diffusion layer 4 on the back surface of the silicon substrate 2 is preferably 500 ° C. or less, more preferably 400 ° C. or less. A solar cell is completed by forming in this state.

  As described above, also in this embodiment, in addition to suppressing the desorption of hydrogen in the silicon substrate, the back surface electric field layer is formed on the back surface of the silicon substrate. Since it can suppress effectively, the conversion efficiency of a solar cell can be improved more.

(Embodiment 5)
Unlike the third embodiment, the present embodiment is characterized in that the n-type impurity diffusion layer on the light-receiving surface of the silicon substrate and the p-type impurity diffusion layer on the back surface are formed simultaneously. The manufacturing process of the solar cell of this Embodiment is shown to typical sectional drawing of FIG. 6 (A)-(F). First, as shown in FIG. 6A, a p-type polycrystalline silicon substrate 1 from which the slice damage layer has been removed by etching using an alkaline aqueous solution or an acid solution is prepared.

  Next, after applying a dopant liquid containing boron as a p-type impurity to the back surface of the silicon substrate 1, a dopant liquid containing phosphorus as an n-type impurity is applied to the light receiving surface of the silicon substrate 1. Then, the silicon substrate 1 with the dopant solution coated on the light receiving surface and the back surface is put into a diffusion furnace at 800 ° C. or higher and 1000 ° C. or lower, so that n is formed on the light receiving surface of the silicon substrate 1 as shown in FIG. At the same time when the type impurity diffusion layer 4 is formed, the p-type impurity diffusion layer 3 is formed on the back surface of the silicon substrate 1. Here, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the n-type impurity diffusion layer 4 is preferably 10Ω / □ or more and 300Ω / □ or less, and the sheet resistance of the p-type impurity diffusion layer 3 is It is preferably 5Ω / □ or more and 100Ω / □ or less. In the same manner as described above, this takes into consideration a decrease in fill factor due to an increase in sheet resistance and an increase in defect (recombination center) concentration due to a decrease in sheet resistance.

  Next, as shown in FIG. 6C, a silicon nitride film 7 having a thickness of 30 nm or more and 200 nm or less is formed as an antireflection film on the n-type impurity diffusion layer 4 by using, for example, a plasma CVD method. And after apply | coating n side electrode paste on the silicon nitride film 7, the silicon substrate 1 is baked at 600 degreeC or more and 800 degrees C or less, and as shown in FIG.6 (D), it is n on the n-type impurity diffusion layer 4 as shown in FIG.6 (D). The side electrode 9 is formed. Subsequently, as shown in FIG. 6E, hydrogen plasma 13 is irradiated from the back side of the silicon substrate 1. Finally, as shown in FIG. 6F, the p-side electrode 10 on the p-type impurity diffusion layer 3 on the back surface of the silicon substrate 1 has a temperature of the silicon substrate 1 of preferably 500 ° C. or less, more preferably 400 ° C. or less. A solar cell is completed by forming in this state.

  As described above, also in this embodiment, in addition to suppressing the desorption of hydrogen in the silicon substrate, the back surface electric field layer is formed on the back surface of the silicon substrate. Since it can suppress effectively, the conversion efficiency of a solar cell can be improved more.

(Embodiment 6)
Unlike the fourth embodiment, the present embodiment is characterized in that the p-type impurity diffusion layer on the light-receiving surface of the silicon substrate and the n-type impurity diffusion layer on the back surface are formed simultaneously. The manufacturing process of the solar cell of this Embodiment is shown to typical sectional drawing of Fig.7 (A)-(F). First, as shown in FIG. 7A, an n-type polycrystalline silicon substrate 2 from which the slice damage layer has been removed by etching using an alkaline aqueous solution or an acid solution is prepared.

  Next, after applying a dopant liquid containing boron as a p-type impurity to the light receiving surface of the silicon substrate 2, a dopant liquid containing phosphorus as an n-type impurity is applied to the back surface of the silicon substrate 2. Then, the silicon substrate 2 having the light receiving surface and the back surface coated with the dopant liquid is put into a diffusion furnace at 800 ° C. or higher and 1000 ° C. or lower, so that p is formed on the light receiving surface of the silicon substrate 2 as shown in FIG. The n-type impurity diffusion layer 4 is formed on the back surface of the silicon substrate 1 simultaneously with the formation of the type impurity diffusion layer 3. Here, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the p-type impurity diffusion layer 3 is preferably 10Ω / □ or more and 300Ω / □ or less, and the sheet resistance of the n-type impurity diffusion layer 4 is It is preferably 5Ω / □ or more and 100Ω / □ or less. In the same manner as described above, this takes into consideration a decrease in fill factor due to an increase in sheet resistance and an increase in defect (recombination center) concentration due to a decrease in sheet resistance.

  Next, as shown in FIG. 7C, a silicon nitride film 7 having a thickness of 30 nm or more and 200 nm or less is formed as an antireflection film on the p-type impurity diffusion layer 3 by using, for example, a plasma CVD method. Then, after applying the p-side electrode paste on the silicon nitride film 7, the silicon substrate 2 is baked at 600 ° C. or higher and 800 ° C. or lower, thereby forming p on the p-type impurity diffusion layer 3 as shown in FIG. The side electrode 10 is formed. Subsequently, as shown in FIG. 7E, hydrogen plasma 13 is irradiated from the back side of the silicon substrate 2. Finally, as shown in FIG. 7F, the temperature of the silicon substrate 2 on the n-type impurity diffusion layer 4 on the back surface of the silicon substrate 2 is preferably 500 ° C. or less, more preferably 400 ° C. or less. A solar cell is completed by forming in this state.

  As described above, also in this embodiment, in addition to suppressing the desorption of hydrogen in the silicon substrate, the back surface electric field layer is formed on the back surface of the silicon substrate. Since it can suppress effectively, the conversion efficiency of a solar cell can be improved more.

(Embodiment 7)
Unlike the third embodiment, the present embodiment is characterized in that a passivation film is formed on a part of the back surface of the silicon substrate. The manufacturing process of the solar cell of this Embodiment is shown to typical sectional drawing of FIG. 8 (A)-(H). First, as shown in FIG. 8A, a p-type polycrystalline silicon substrate 1 from which a slice damage layer has been removed by etching using an alkaline aqueous solution or an acid solution is prepared.

  Next, p-type impurity diffusion layers 3 are formed on the back surface of the silicon substrate 1 by diffusing boron, which is a p-type impurity, on the back surface of the silicon substrate 1 as shown in FIG. Here, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the p-type impurity diffusion layer 3 is preferably 5Ω / □ or more and 100Ω / □ or less. In the same manner as described above, this takes into consideration a decrease in fill factor due to an increase in sheet resistance and an increase in defect (recombination center) concentration due to a decrease in sheet resistance.

  Then, as shown in FIG. 8C, an n-type impurity diffusion layer 4 is formed on the light receiving surface of the silicon substrate 1 by diffusing n-type impurities such as phosphorus on the light receiving surface of the silicon substrate 1. Here, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the n-type impurity diffusion layer 4 is preferably 10Ω / □ or more and 300Ω / □ or less. Similarly to the above, this also takes into account the decrease in the fill factor due to the increase in sheet resistance and the increase in the defect (recombination center) concentration due to the decrease in sheet resistance.

  Next, as shown in FIG. 8D, a silicon nitride film 7 having a thickness of 30 nm or more and 200 nm or less is formed as an antireflection film on the n-type impurity diffusion layer 4 by using, for example, a plasma CVD method.

  Then, as shown in FIG. 8E, a passivation film 8 is formed on a part of the back surface of the silicon substrate. Here, a silicon oxide film is formed as the passivation film 8. The method for forming the passivation film 8 is not particularly limited. For example, in a reaction vessel having a temperature of 300 ° C. or more and 600 ° C. or less and a pressure of 10 Pa or more and 100,000 Pa or less, silane is supplied at a flow rate of 10 sccm or more and 500 sccm or less, and oxygen is supplied at 10 sccm or more and 500 sccm or less. There is a method of reacting on the back surface of the silicon substrate on which the metal mask is installed by flowing at a flow rate of 1 mm. Needless to say, a patterned photoresist may be used instead of the metal mask.

  Thereafter, the n-side electrode paste is applied on the silicon nitride film 7 and then the silicon substrate 1 is baked at 600 ° C. or higher and 800 ° C. or lower, thereby forming n on the n-type impurity diffusion layer 4 as shown in FIG. The side electrode 9 is formed. Subsequently, as shown in FIG. 8G, hydrogen plasma 13 is irradiated from the back side of the silicon substrate 1. Finally, as shown in FIG. 8H, the p-side electrode 10 on the p-type impurity diffusion layer 3 on the back surface of the silicon substrate 1 has a temperature of the silicon substrate 1 of preferably 500 ° C. or less, more preferably 400 ° C. or less. A solar cell is completed by forming in this state.

  As described above, in this embodiment, in addition to the suppression of hydrogen detachment in the silicon substrate and the formation of the back surface electric field layer, the passivation film can suppress carrier recombination on the back surface of the silicon substrate. Further improvement in conversion efficiency can be achieved.

(Embodiment 8)
Unlike the fourth embodiment, the present embodiment is characterized in that a passivation film is formed on a part of the back surface of the silicon substrate. The manufacturing process of the solar cell of this Embodiment is shown to typical sectional drawing of Fig.9 (A)-(H). First, as shown in FIG. 9A, an n-type polycrystalline silicon substrate 2 from which a slice damage layer has been removed by etching using an alkaline aqueous solution or an acid solution is prepared.

  Next, p-type impurity diffusion layers 3 are formed on the light-receiving surface of the silicon substrate 2 as shown in FIG. 9B by diffusing boron, which is a p-type impurity, on the light-receiving surface of the silicon substrate 2. Here, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the p-type impurity diffusion layer 3 is preferably 10Ω / □ or more and 300Ω / □ or less. In the same manner as described above, this takes into consideration a decrease in fill factor due to an increase in sheet resistance and an increase in defect (recombination center) concentration due to a decrease in sheet resistance.

  Then, as shown in FIG. 9C, an n-type impurity diffusion layer 4 is formed on the back surface of the silicon substrate 2 by diffusing n-type impurities such as phosphorus on the back surface of the silicon substrate 2. Here, from the viewpoint of improving the conversion efficiency of the solar cell, the sheet resistance of the n-type impurity diffusion layer 4 is preferably 5Ω / □ or more and 100Ω / □ or less. Similarly to the above, this also takes into account the decrease in the fill factor due to the increase in sheet resistance and the increase in the defect (recombination center) concentration due to the decrease in sheet resistance.

  Next, as shown in FIG. 9D, a silicon nitride film 7 having a thickness of 30 nm or more and 200 nm or less is formed as an antireflection film on the p-type impurity diffusion layer 3 by using, for example, a plasma CVD method. Then, as shown in FIG. 9E, a passivation film 8 is formed on a part of the back surface of the silicon substrate 2.

  After that, after applying the p-side electrode paste on the silicon nitride film 7, the silicon substrate 2 is baked at 600 ° C. or higher and 800 ° C. or lower, thereby forming the p on the p-type impurity diffusion layer 3 as shown in FIG. The side electrode 10 is formed. Subsequently, as shown in FIG. 9G, the hydrogen plasma 13 is irradiated from the back side of the silicon substrate 2. Finally, as shown in FIG. 9 (H), the temperature of the silicon substrate 2 on the n-type impurity diffusion layer 4 on the back surface of the silicon substrate 2 is preferably 500 ° C. or less, more preferably 400 ° C. or less. A solar cell is completed by forming in this state.

  As described above, in this embodiment, in addition to the suppression of hydrogen detachment in the silicon substrate and the formation of the back surface electric field layer, the passivation film can suppress carrier recombination on the back surface of the silicon substrate. Further improvement in conversion efficiency can be achieved.

(Embodiment 9)
Unlike the seventh embodiment, the present embodiment is characterized in that a p-type impurity diffusion layer is formed only on a part of the back surface of the silicon substrate. The manufacturing process of the solar cell of this Embodiment is shown to typical sectional drawing of FIG. 10 (A)-(G). First, as shown in FIG. 10A, a p-type polycrystalline silicon substrate 1 from which a slice damage layer has been removed by etching using an alkaline aqueous solution or an acid solution is prepared.

  Next, as shown in FIG. 10B, an n-type impurity diffusion layer 4 is formed on the light receiving surface of the silicon substrate 1, and a passivation film 8 is formed on a part of the back surface of the silicon substrate 1. Then, as shown in FIG. 10C, p-type impurities such as boron are diffused from the portion where the passivation film 8 is not formed on the back surface of the silicon substrate 1, and p-type is partially formed on the back surface of the silicon substrate 1. Impurity diffusion layer 3 is formed.

  Next, as shown in FIG. 10D, a silicon nitride film 7 having a thickness of 30 nm or more and 200 nm or less is formed as an antireflection film on the n-type impurity diffusion layer 4 by using, for example, a plasma CVD method. Then, after the n-side electrode paste is applied on the silicon nitride film 7, the silicon substrate 1 is baked at 600 ° C. or higher and 800 ° C. or lower, thereby forming n on the n-type impurity diffusion layer 4 as shown in FIG. The side electrode 9 is formed. Subsequently, as shown in FIG. 10F, hydrogen plasma 13 is irradiated from the back side of the silicon substrate 1. Finally, as shown in FIG. 10G, the p-side electrode 10 is formed on the back surface side of the silicon substrate 1 in a state where the temperature of the silicon substrate 1 is preferably 500 ° C. or lower, more preferably 400 ° C. or lower. This completes the solar cell.

  As described above, in the present embodiment, in addition to preventing the separation of hydrogen in the silicon substrate and forming a local back surface electric field layer formed on the back surface of the silicon substrate, carriers on the back surface of the silicon substrate are formed by the passivation film. Therefore, the conversion efficiency of the solar cell can be further improved.

(Embodiment 10)
Unlike the eighth embodiment, the present embodiment is characterized in that an n-type impurity diffusion layer is formed only on a part of the back surface of the silicon substrate. The manufacturing process of the solar cell of this Embodiment is shown to typical sectional drawing of FIG. 11 (A)-(G). First, as shown in FIG. 11A, an n-type polycrystalline silicon substrate 2 from which a slice damage layer has been removed by etching using an alkaline aqueous solution or an acid solution is prepared.

  Next, as shown in FIG. 11B, a p-type impurity diffusion layer 3 is formed on the light receiving surface of the silicon substrate 2. Then, as shown in FIG. 11C, after forming the passivation film 8 on a part of the back surface of the silicon substrate 2, an n-type such as phosphorus is formed on the back surface of the silicon substrate 2 where the passivation film 8 is not formed. Impurities are diffused to form an n-type impurity diffusion layer 4 on a part of the back surface of the silicon substrate 2.

  Next, as shown in FIG. 11D, a silicon nitride film 7 having a thickness of 30 nm or more and 200 nm or less is formed as an antireflection film on the p-type impurity diffusion layer 3 by using, for example, a plasma CVD method. Then, after applying the p-side electrode paste on the silicon nitride film 7, the silicon substrate 2 is baked at 600 ° C. or higher and 800 ° C. or lower, thereby forming p on the p-type impurity diffusion layer 3 as shown in FIG. The side electrode 10 is formed. Subsequently, as shown in FIG. 11F, hydrogen plasma 13 is irradiated from the back side of the silicon substrate 1. Finally, as shown in FIG. 11 (G), the temperature of the silicon substrate 2 on the n-type impurity diffusion layer 4 on the back surface of the silicon substrate 2 is preferably 500 ° C. or less, more preferably 400 ° C. or less. A solar cell is completed by forming in this state.

  As described above, in the present embodiment, in addition to preventing the separation of hydrogen in the silicon substrate and forming a local back surface electric field layer formed on the back surface of the silicon substrate, carriers on the back surface of the silicon substrate are formed by the passivation film. Therefore, the conversion efficiency of the solar cell can be further improved.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  According to the present invention, solar cells having high conversion efficiency can be mass-produced using the hydrogen termination technology, and therefore the present invention can be suitably used for the solar cell field, particularly for solar cells using a polycrystalline silicon substrate. it can.

It is the figure which showed the relationship between the heating temperature of the silicon substrate after irradiation of hydrogen plasma, and the diffusion length of a carrier. It is typical sectional drawing which showed the manufacturing process of the solar cell of Embodiment 1 in this invention. It is typical sectional drawing which showed the manufacturing process of the solar cell of Embodiment 2 in this invention. It is typical sectional drawing which showed the manufacturing process of the solar cell of Embodiment 3 in this invention. It is typical sectional drawing which showed the manufacturing process of the solar cell of Embodiment 4 in this invention. It is typical sectional drawing which showed the manufacturing process of the solar cell of Embodiment 5 in this invention. It is typical sectional drawing which showed the manufacturing process of the solar cell of Embodiment 6 in this invention. It is typical sectional drawing which showed the manufacturing process of the solar cell of Embodiment 7 in this invention. It is typical sectional drawing which showed the manufacturing process of the solar cell of Embodiment 8 in this invention. It is typical sectional drawing which showed the manufacturing process of the solar cell of Embodiment 9 in this invention. It is typical sectional drawing which showed the manufacturing process of the solar cell of Embodiment 10 in this invention. It is typical sectional drawing which showed an example of the manufacturing process of the conventional solar cell.

Explanation of symbols

  1, 2 silicon substrate, 3 p-type impurity diffusion layer, 4 n-type impurity diffusion layer, 7 silicon nitride film, 8 passivation film, 9 n-side electrode, 10 p-side electrode, 11 n-side electrode paste, 12 p-side electrode paste , 13 Hydrogen plasma.

Claims (12)

  Forming a first electrode on one surface of a silicon substrate having a first polarity; irradiating hydrogen plasma on the other surface of the silicon substrate after the formation of the first electrode; Forming a second electrode on the other surface of the silicon substrate after plasma irradiation.   2. The method of manufacturing a solar cell according to claim 1, wherein a temperature of the silicon substrate at the time of forming the second electrode is lower than a temperature of the silicon substrate at the time of forming the first electrode. .   The method for manufacturing a solar cell according to claim 1 or 2, wherein the temperature of the silicon substrate at the time of forming the second electrode is 500 ° C or lower.   4. The method for manufacturing a solar cell according to claim 1, wherein the second electrode is formed by using a screen printing method or a vacuum evaporation method. 5.   5. The solar cell according to claim 1, wherein the irradiation with the hydrogen plasma is performed in a state where the temperature of the silicon substrate is 200 ° C. or higher and lower than the temperature at the time of forming the first electrode. Manufacturing method.   6. The method of manufacturing a solar cell according to claim 1, wherein an impurity diffusion layer having a second polarity is formed on at least one surface of the silicon substrate.   An impurity diffusion layer having a second polarity is formed on one surface of the silicon substrate, and an impurity diffusion layer having a first polarity having an impurity concentration higher than that of the silicon substrate is formed on the other surface of the silicon substrate. A method for producing a solar cell according to claim 1, wherein:   An antireflection film is formed on at least one surface of the silicon substrate, and electrode paste is screen-printed on the antireflection film and then baked, so that at least one of the first electrode and the second electrode is The method for manufacturing a solar cell according to claim 1, wherein the solar cell is formed on the surface of the silicon substrate through the antireflection film.   A passivation film is formed on a part of at least one surface of the silicon substrate, and the first electrode and the second electrode are exposed on the exposed surface of the silicon substrate exposed from a portion where the passivation film is not formed. The method for manufacturing a solar cell according to claim 1, wherein at least one of the electrodes is formed.   10. The method of manufacturing a solar cell according to claim 9, wherein an impurity diffusion layer having a first polarity having an impurity concentration higher than that of the silicon substrate is formed on an exposed surface of the silicon substrate.   When the first polarity is p-type, the second polarity is n-type, and when the first polarity is n-type, the second polarity is p-type. A method for manufacturing a solar cell according to any one of claims 1 to 10.   When the first electrode is a p-side electrode, the second electrode is an n-side electrode, and when the first electrode is an n-side electrode, the second electrode is a p-side electrode. The method for producing a solar cell according to claim 1, wherein the method is provided.

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