JP2016046400A - Method of manufacturing solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a solar cell which allows for stabilized manufacturing of a solar cell excellent in the conversion efficiency, by using a gallium-doped substrate.SOLUTION: In a method of manufacturing a solar cell having a step for forming an n-type diffusion layer on the first principal surface of a p-type semiconductor substrate by thermal diffusion of an n-type dopant, a step for forming a p-type diffusion layer on the second principal surface of the semiconductor substrate by thermal diffusion of a p-type dopant, and a step for forming an electrode connected electrically with the n-type diffusion layer and p-type diffusion layer, the semiconductor substrate is a gallium-doped silicon substrate, the peak temperatures when performing thermal diffusion of the n-type dopant and p-type dopant are 800°C-900°C, respectively, and the peak temperature holding time is 1-90 minutes.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a solar battery cell and a manufacturing method thereof.

  Conventionally, a p-type conductivity type of a semiconductor substrate used as a solar cell has been the mainstream, and boron is usually added as a dopant to the p-type semiconductor substrate. And the single crystal rod used as the material of this semiconductor substrate can be manufactured using methods, such as CZ method (Czochralski method) and FZ method (floating zone method or floating zone melting method). However, in the FZ method, the manufacturing cost of the single crystal rod is higher than that in the CZ method, and in addition, the CZ method is easier to manufacture a silicon single crystal having a large diameter. Therefore, the semiconductor substrate for solar cells is usually manufactured by a CZ method capable of producing a single crystal having a large diameter at a relatively low cost.

  However, the boron-doped single crystal produced by the CZ method, which is the mainstream of current single crystal rod manufacturing methods, reduces the lifetime of the solar cell substrate when it is irradiated with strong light when it is processed into a solar cell. Therefore, sufficient conversion efficiency cannot be obtained because light degradation occurs. Therefore, improvement is also required in terms of the performance of solar cells. Here, the “conversion efficiency” is a value indicating the “ratio of energy that can be extracted by converting into electric energy by the solar battery with respect to the energy of light incident on the solar battery cell”. ).

  When a solar cell is manufactured using this CZ method silicon single crystal, the cause of light degradation when the strong light is applied to the solar cell is due to the influence of boron and oxygen present in the single crystal substrate. It is known that there is.

  In order to solve such a problem of photodegradation, Patent Document 1 proposes to use gallium instead of boron as a p-type dopant. By using gallium as a dopant in this way, it has become possible to prevent a decrease in lifetime due to the influence of boron and oxygen.

International Publication No. WO2000 / 073542 Pamphlet

  In order to manufacture a solar cell, an emitter layer or a BSF (back surface field) layer is formed on a semiconductor substrate by thermally treating the semiconductor substrate and thermally diffusing dopants such as boron and phosphorus on the surface of the semiconductor substrate. There is a way to do it. When manufacturing a solar cell using a silicon substrate doped with gallium (hereinafter also referred to as a gallium-doped substrate), the conversion efficiency of the manufactured solar cell is low when such a dopant diffusion heat treatment is performed. There was a problem.

  This invention is made | formed in view of the said problem, Comprising: The manufacturing method of the photovoltaic cell which can manufacture stably the photovoltaic cell excellent in conversion efficiency using a gallium dope board | substrate is provided. For the purpose.

In order to achieve the above object, in the present invention, a second conductivity type dopant, which is a conductivity type opposite to the first conductivity type, is thermally diffused on a first main surface of a first conductivity type semiconductor substrate. A step of forming a second conductivity type diffusion layer, a step of thermally diffusing the first conductivity type dopant on the second main surface of the semiconductor substrate to form a first conductivity type diffusion layer, and the second conductivity type. A step of forming a diffusion layer and an electrode electrically connected to the first conductivity type diffusion layer,
The semiconductor substrate is a silicon substrate doped with gallium,
The peak temperatures when the thermal diffusion of the second conductivity type dopant and the thermal diffusion of the first conductivity type dopant are performed are 800 ° C. or more and 900 ° C. or less, respectively, and the holding time of the peak temperature is 1 minute or more and 90 ° C. The manufacturing method of the photovoltaic cell characterized by setting it as less than a minute is provided.

  If it is a manufacturing method of such a photovoltaic cell, it can manufacture stably the solar cell by which photodegradation was suppressed by having used the gallium dope board | substrate as what has the further excellent conversion efficiency. it can.

In addition, thermal diffusion of the second conductivity type dopant is performed by applying a material containing the second conductivity type dopant on the first main surface of the semiconductor substrate, and performing heat treatment.
It is preferable that the thermal diffusion of the first conductivity type dopant is performed by applying a material containing the first conductivity type dopant on the second main surface of the semiconductor substrate and performing a heat treatment.

By using such a so-called coating diffusion method, mask formation and mask removal steps are performed as compared with the case of using a vapor phase diffusion method in which POCl ₃ , BBr _3, or the like is introduced into a heat treatment furnace together with a carrier gas and diffused. Therefore, the manufacturing cost of the solar battery cell can be suppressed.

  In this case, it is preferable to perform thermal diffusion of the second conductivity type dopant and thermal diffusion of the first conductivity type dopant in one heat treatment.

  Thus, by performing simultaneous diffusion in which dopants of different conductivity types are diffused by a single heat treatment, the number of manufacturing steps can be further reduced, and the manufacturing cost can be further suppressed.

  In the step of forming the electrode, a passivation film is laminated on the second conductive type diffusion layer and the first conductive type diffusion layer, and conductive particles and glass frit are formed at predetermined positions on the passivation film. Applying the conductive paste contained, firing the semiconductor substrate coated with the conductive paste, penetrating the passivation film, and electrically connected to the second conductive type diffusion layer and the first conductive type diffusion layer It is preferable to carry out by forming the prepared electrode.

  Thus, by laminating the passivation film on each diffusion layer, the recombination rate of minority carriers generated in the vicinity of the silicon surface can be reduced.

  In the step of forming the second conductivity type diffusion layer and the step of forming the first conductivity type diffusion layer, thermal diffusion of the second conductivity type dopant and thermal diffusion of the first conductivity type dopant are performed. The atmosphere at the time of holding the peak temperature is preferably a mixed gas of an inert gas and an active gas, and the ratio of the inert gas / active gas in the mixed gas is preferably 50 to 300.

  In the present invention, the atmosphere at the time of holding the peak temperature is preferably set in this way. The reason is that oxygen, which is preferably used as an active gas, is introduced together with an inert gas to control the growth of the dopant-containing glass formed on the substrate surface during diffusion, and has a good thickness distribution. This is because the contained glass can be formed and the sheet resistance distribution after the heat treatment can be eliminated.

  Furthermore, in this invention, it manufactures using the manufacturing method of the photovoltaic cell of the said invention, The solar cell characterized by the above-mentioned is provided.

  If it is such a photovoltaic cell, it is excellent in conversion efficiency. In addition, since this solar battery cell uses a gallium-doped substrate, the lifetime is not easily lowered even when strong light is applied, and the light deterioration is suppressed.

  If it is the manufacturing method of the photovoltaic cell of this invention, it can manufacture stably the solar cell by which photodegradation was suppressed by using a gallium dope board | substrate as what has the further excellent conversion efficiency. it can. The solar battery cell of the present invention is excellent in conversion efficiency. In addition, since this solar battery cell uses a gallium-doped substrate, the lifetime is not easily lowered even when strong light is applied, and the light deterioration is suppressed.

It is the graph which showed the relationship of the peak temperature (degreeC) and cell conversion efficiency (%) in Examples 1-6 and Comparative Examples 1-18. It is the graph which showed the relationship between the peak temperature (degreeC) and the board | substrate lifetime (microsecond) after thermal diffusion in Examples 1-6 and Comparative Examples 1-6. It is the graph which showed the relationship of holding time (minute) of peak temperature and cell conversion efficiency (%) in Examples 7-10 and Comparative Examples 19-26. It is a flowchart which shows an example of the manufacturing method of the photovoltaic cell of this invention. It is a cross-sectional schematic diagram which shows an example of the photovoltaic cell of this invention.

  Hereinafter, the present invention will be described in more detail.

  As described above, a solar cell manufacturing method that can stably manufacture a solar cell excellent in conversion efficiency by using a gallium-doped substrate is demanded.

  The present inventors have intensively studied to achieve the above object. As a result, it has been found that a method for manufacturing a solar cell in which the peak temperature and the retention time of the peak temperature during the thermal diffusion of the dopant are within a specific range can solve the above-mentioned problems, and the present invention has been completed. .

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings, but the present invention is not limited thereto.

  First, the solar cell obtained by the method for manufacturing a solar cell of the present invention will be described with reference to FIG. FIG. 5 is a schematic cross-sectional view showing an example of the solar battery cell of the present invention. As shown in FIG. 5, a solar battery cell 10 obtained by the method for manufacturing a solar battery cell of the present invention includes a first conductivity type semiconductor substrate 11. A second conductivity type diffusion layer (n-type) in which a second conductivity type dopant, which is a conductivity type opposite to the first conductivity type, is diffused on a first main surface (hereinafter also referred to as a light receiving surface) of the semiconductor substrate 11. A diffusion layer) 12 is formed, and a first conductivity type diffusion layer (p-type diffusion layer) 13 in which a first conductivity type dopant is diffused on a second main surface (hereinafter also referred to as a back surface) of the semiconductor substrate 11. Is formed. A light receiving surface electrode 16 electrically connected to the second conductivity type diffusion layer 12 is formed on the light receiving surface, and a back electrode 17 electrically connected to the first conductivity type diffusion layer 13 is formed on the back surface. Yes. Usually, a light-receiving surface passivation film 14 is formed on the second conductivity type diffusion layer 12, and a back surface passivation film 15 is formed on the first conductivity type diffusion layer 13. Here, the second conductivity type diffusion layer 12 can function as an emitter layer, and the first conductivity type diffusion layer 13 can function as a BSF layer.

  In the present invention, the first conductivity type semiconductor substrate 11 is a silicon substrate doped with gallium which is a p-type dopant. Therefore, hereinafter, the first conductivity type is also referred to as p-type and the second conductivity type is also referred to as n-type.

  The solar battery cell 10 of the present invention can be a double-sided light-receiving solar battery in addition to a normal single-sided light-receiving solar battery by changing the pattern of the back electrode 17.

  Here, examples of the n-type dopant diffused on the light receiving surface include P (phosphorus), Sb (antimony), As (arsenic), and Bi (bismuth). Examples of the p-type dopant diffused on the back surface include B (boron), Ga (gallium), Al (aluminum), and In (indium).

  Next, the manufacturing method of the photovoltaic cell of this invention is demonstrated with reference to FIG. FIG. 4 is a flowchart showing an example of a method for producing a solar battery cell of the present invention. The method described below is a typical example, and the present invention is not limited to this. First, as shown in FIG. 4A, a gallium doped substrate is prepared. The silicon single crystal from which the gallium-doped substrate is cut out can be manufactured using, for example, the CZ method. In this case, gallium and a polycrystalline raw material may be put together in a crucible to form a raw material melt. In particular, since it is necessary to finely adjust the concentration for mass production, a high concentration gallium-doped silicon single crystal is prepared, and then finely crushed to prepare a dopant, which is melted to a desired concentration after polycrystalline silicon is melted. It is desirable to adjust and input so that A gallium-doped substrate can be obtained by slicing the gallium-doped silicon single crystal thus obtained.

  Here, the specific resistance of the substrate is not particularly limited, but may be, for example, in the range of 0.1 to 5 Ω · cm. The thickness of the substrate is not particularly limited, and can be, for example, 100 to 200 μm. The shape and area of the main surface of the substrate are not particularly limited.

  Next, as shown in FIG. 4B, slicing damage on the substrate surface is caused by a high concentration alkali such as sodium hydroxide or potassium hydroxide having a concentration of 5 to 60%, or a mixed acid of hydrofluoric acid and nitric acid. Can be used for etching.

  Subsequently, minute unevenness called texture can be formed on the substrate surface. Texture is an effective method for reducing the reflectance of solar cells. The texture is immersed for about 10 to 30 minutes in an alkali solution (concentration 1 to 10%, temperature 60 to 100 ° C.) such as heated sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium hydrogen carbonate, etc. Produced. A predetermined amount of 2-propanol (IPA: isopropyl alcohol) is often dissolved in the solution to promote the reaction.

  After the damage etching and texture formation, it is preferable to clean the substrate as shown in FIG. Washing can be performed, for example, using hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, or the like, or an acidic aqueous solution of a mixed solution thereof, or using pure water.

  Next, as shown in FIG. 4D, a second conductivity type dopant, which is the conductivity type opposite to the first conductivity type, is thermally diffused on the first main surface of the first conductivity type semiconductor substrate. A two-conductive type diffusion layer is formed. Further, as shown in FIG. 4E, the first conductivity type diffusion layer is formed by thermally diffusing the first conductivity type dopant on the second main surface of the first conductivity type semiconductor substrate. The order in which the step (d) and the step (e) are performed is not particularly limited, and the step (d) and the step (e) may be performed simultaneously as shown below.

  In the present invention, the peak temperatures at the time of thermal diffusion of the second conductivity type dopant and thermal diffusion of the first conductivity type dopant are set to 800 ° C. or more and 900 ° C. or less, respectively. In addition, the peak temperature holding time is 1 minute or more and 90 minutes or less. Here, the peak temperature is preferably 800 ° C. or higher and 850 ° C. or lower. It was found that by setting such peak temperature, the lifetime of the gallium-doped substrate can be prevented from decreasing, and the conversion efficiency of the solar battery cell can be increased. The reason for this is not necessarily clear, but it is considered that if heat treatment at over 900 ° C. is performed on the gallium-doped substrate, defects due to oxygen precipitates are likely to occur in the gallium-doped substrate, and swirl appears. Such a phenomenon that the conversion efficiency is deteriorated by heat treatment exceeding 900 ° C. is particularly remarkable in a gallium-doped substrate, and is not a problem in a conventional solar cell using a silicon substrate (boron-doped substrate) doped with boron. It was. The holding time of the peak temperature is preferably 20 minutes or more and 40 minutes or less. When the peak temperature is less than 800 ° C., it is difficult for the dopant to thermally diffuse, and it is not suitable for forming a diffusion layer of the solar battery cell. When the peak temperature exceeds 900 ° C., the lifetime is lowered. In the present invention, the peak temperature is the maximum temperature in a diffusion heat treatment furnace in which a gallium-doped substrate is introduced and heat treated when the second conductivity type dopant and the first conductivity type dopant are thermally diffused. . When the holding time of the peak temperature is less than 1 minute, the thermal diffusion of the dopant becomes insufficient. When the holding time of the peak temperature exceeds 90 minutes, productivity deteriorates.

In the step (d) and the step (e), the method for thermally diffusing the dopant is not particularly limited. For example, a vapor phase diffusion method in which POCl ₃ or BBr ₃ or the like is introduced into a heat treatment furnace together with a carrier gas and diffused, or a coating diffusion method in which a material containing phosphorus or boron is coated on a substrate and then heat treated is used. Can do. Examples of the coating method in the coating diffusion method include a spin coating method, a spray coating method, an ink jet method, and a screen printing method.

  In the present invention, it is preferable to use a coating diffusion method that can reduce the steps of mask formation and mask removal and suppress the manufacturing cost as compared with the vapor phase diffusion method. Specifically, the thermal diffusion of the second conductivity type dopant is performed by applying a material containing the second conductivity type dopant on the first main surface of the semiconductor substrate and heat-treating the first conductivity type dopant. It is preferable that the thermal diffusion of the dopant is performed by applying a material containing the dopant of the first conductivity type on the second main surface of the semiconductor substrate and performing a heat treatment.

  At this time, it is more preferable to perform thermal diffusion of the second conductivity type dopant and thermal diffusion of the first conductivity type dopant by a single heat treatment. Thereby, the number of manufacturing steps can be further reduced, and the manufacturing cost can be further suppressed. In this case, for example, first, a material containing an n-type dopant is applied to the light receiving surface, the substrate is placed in a drying furnace, and the material is dried to form an n-type dopant-containing film. Then, a p-type dopant-containing film is formed on the back surface. Thereafter, heat treatment is performed, and the n-type diffusion layer and the p-type diffusion layer can be simultaneously formed by one heat treatment. Note that one of the n-type diffusion layer and the p-type diffusion layer can be formed using a coating diffusion method, and the other can be formed using a vapor phase diffusion method.

Here, as the material containing the second conductivity type dopant, a phosphorus diffusing agent that vitrifies by heat treatment can be used. As the phosphorus diffusing agent, a known one can be used, and for example, it can be obtained by mixing P ₂ O ₅ , pure water, PVA (polyvinyl alcohol), and TEOS (tetraethylorthosilicate).

As the material containing the first conductivity type dopant, a boron diffusing agent that vitrifies by heat treatment can be used. As the boron diffusing agent, a known one can be used, and for example, it can be obtained by mixing B ₂ O ₃ , pure water, and PVA.

In the present invention, in the step (d) and the step (e), the atmosphere at the time of holding the peak temperature when performing the thermal diffusion of the second conductivity type dopant and the thermal diffusion of the first conductivity type dopant is the inert gas and the active gas. It is preferable to use a mixed gas of At this time, the ratio of inert gas / active gas in the mixed gas is preferably 50 to 300. Here, as the inert gas, N ₂ gas can be used, and as the active gas, O ₂ gas can be used. The inert gas / active gas ratio is a volume flow rate ratio. By flowing a small amount of O ₂ gas together with N ₂ gas during thermal diffusion, the growth of the dopant-containing glass formed on the substrate surface during diffusion can be controlled, and a dopant-containing glass without a good film thickness distribution can be formed. This is because the sheet resistance distribution after the heat treatment can be eliminated.

  When the thermal diffusion is performed, a glass layer is formed on the surface of the semiconductor substrate. Therefore, as shown in FIG. 4F, the glass on the surface is removed with hydrofluoric acid or the like.

  Next, as shown in FIG. 4G, a pn junction is separated using a plasma etcher. In this process, the sample is stacked so that plasma and radicals do not enter the light-receiving surface and back surface, and in this state, the end surface is cut by several microns. This pn separation by plasma etching may be performed before or after the removal of boron glass and phosphorus glass. As an alternative method of pn separation, groove formation by a laser may be performed.

Next, an electrode electrically connected to the second conductivity type diffusion layer and the first conductivity type diffusion layer is formed. For example, the electrodes can be formed by the method shown in FIGS. 4 (h) to 4 (j). First, as shown in FIG. 4H, a light-receiving surface passivation film is formed on the second conductivity type diffusion layer, and a back surface passivation film is formed on the first conductivity type diffusion layer. Here, the light-receiving surface passivation film also functions as an antireflection film. As the passivation film, a SiNx film or a SiO ₂ film that can be formed using a plasma CVD apparatus can be used, and a thermal oxide film can also be used. A film thickness of 85 to 105 nm is preferable because the effect of reducing the reflectance is maximized.

  Next, as shown in FIG. 4I, a conductive paste containing conductive particles and glass frit is applied to predetermined positions on each passivation film. As the conductive particles, for example, silver can be used. In this case, a conductive silver paste containing silver and glass frit can be printed on each of the light receiving surface and the back surface of the substrate in a comb pattern. Note that the conductive paste can be formed on the substrate by a vapor deposition method, a sputtering method, or the like in addition to a printing method such as a screen printing method.

  Next, as shown in FIG. 4 (j), the semiconductor substrate coated with the conductive paste is baked to penetrate through the passivation film (fire through), and the second conductivity type diffusion layer and the first conductivity type diffusion layer An electrically connected electrode is formed. The back electrode and the light-receiving surface electrode can be baked at the same time.

  In this way, the solar battery cell of FIG. 5 can be manufactured. The solar cell manufacturing method of the present invention is characterized mainly by the use of a gallium-doped substrate and the peak temperature when forming the diffusion layer in steps (d) and (e). It can be applied to a manufacturing method.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to this Example.

(Examples 1-6, Comparative Examples 1-6)
First, by performing external processing on a p-type silicon substrate made of p-type single crystal silicon doped with gallium and sliced to a thickness of 0.2 mm and having a specific resistance of about 1 Ω · cm, A square plate was formed (FIG. 4A). The p-type silicon substrate is dipped in a hydrofluoric acid solution for 15 seconds for damage etching, and further chemically etched with a 70 ° C. solution containing 2% KOH and 2% IPA for 5 minutes, followed by washing with pure water. Then, by drying, a texture structure was formed on the surface of the p-type silicon substrate (FIGS. 4B and 4C).

  After applying the phosphorus-containing dopant paste P101 of Soltech NV, Belgium on the entire surface of the p-type silicon substrate, which will be the light receiving surface (hereinafter referred to as the front surface), using a screen printing method, a drying furnace And dried and fixed at 200 ° C. for 10 minutes to form a phosphorus-containing film.

  Thereafter, a boron-containing ink of Honeywell International Co. of the United States is applied to the entire surface of the p-type silicon substrate opposite to the light-receiving surface (hereinafter referred to as the back surface) using a screen printing method, and then dried. A boron-containing film was formed by placing in a furnace, drying and fixing at 200 ° C. for 10 minutes.

Thereafter, the p-type silicon substrate was put into a diffusion heat treatment furnace, and diffusion heat treatment was performed under the following conditions. The inside of the diffusion furnace is in a mixed atmosphere of N ₂ gas / O ₂ gas ratio = 200, and peak temperatures (peak thermal diffusion temperatures) are 750 ° C., 800 ° C., 850 ° C., 900 ° C., 950 ° C., and 1000 ° C. By performing diffusion heat treatment for 20 minutes or 40 minutes at the peak heat diffusion temperature, an n-type diffusion layer was formed on the front surface of the substrate, and a p-type diffusion layer was formed on the back surface (FIG. 4D). ), FIG. 4 (e)).

Thereafter, the diffusion glass remaining on the surface of the substrate was removed by immersing in a 25% aqueous hydrofluoric acid solution for 5 minutes and then rinsing with pure water for 5 minutes (FIG. 4 (f)). Furthermore, the outer periphery of the substrate is pressed by a jig that covers the entire front and back surfaces of the substrate, put into the chamber with only the outer periphery of the substrate exposed, and subjected to plasma etching of CF ₄ gas for 30 minutes. The n-type diffusion layer and the p-type diffusion layer were separated by etching (FIG. 4G). Subsequently, SiN serving as an antireflection film and a passivation film was formed to a thickness of 1000 mm on both the front and back surfaces of the substrate by plasma CVD using SiH ₄ , NH ₃ , and N ₂ (FIG. 4 ( h)).

  Next, a conductive silver paste was printed in a comb pattern using a screen printing method on the back surface of the substrate that had been treated so far, and dried at 150 ° C. Further, a conductive silver paste was printed in a comb pattern on the front side of the substrate using a screen printing method and dried at 150 ° C. (FIG. 4 (i)). The substrate coated with the conductive silver paste was put into a baking furnace, and the conductive silver paste was baked at a maximum temperature of 800 ° C. for 5 seconds to produce a solar battery cell (FIG. 4 (j)).

(Comparative Examples 7-18)
A p-type silicon substrate made of p-type single crystal silicon doped with boron and sliced to a thickness of 0.2 mm and having a specific resistance of about 1 Ω · cm is processed into a 15 cm side. A solar battery cell was produced by performing the same treatment as in Examples 1 to 6 and Comparative Examples 1 to 6, except that the square plate was used.

  Tables 1 and 2 and FIG. 1 show the results of Examples 1 to 6 and Comparative Examples 1 to 18. Table 1 shows the substrate lifetime (μ seconds) and cell conversion efficiency (%) after thermal diffusion of Examples 1 to 6 and Comparative Examples 1 to 6. Table 2 shows the cell conversion efficiency (%) of Comparative Examples 7 to 18.

  FIG. 1 is a graph showing the relationship between peak temperature (° C.) and cell conversion efficiency (%) in Examples 1 to 6 and Comparative Examples 1 to 18. In FIG. 1, using a boron-doped substrate (boron-doped p-type silicon substrate) and a gallium-doped substrate (gallium-doped p-type silicon substrate) by the above method, the peak temperatures are 750 ° C., 800 ° C., 850 ° C., 900 ° C. , 950 ° C., 1000 ° C., and the peak temperature holding time is 20 minutes or 40 minutes. When the diffusion heat treatment is performed, 10 solar cells are manufactured for each condition. Average conversion efficiency is shown. Note that “holding time” in FIGS. 1 and 2 indicates the holding time of the peak temperature.

  As shown in Table 1, Table 2, and FIG. 1, when the peak temperature is 800 ° C. or higher and 900 ° C. or lower and a gallium doped substrate is used (Examples 1 to 6), the peak temperature is 800 ° C. or higher and 900 ° C. or lower. The average conversion efficiency of the solar cells can be increased more than when the boron-doped substrate is used (Comparative Examples 8 to 10 and Comparative Examples 14 to 16). If the gallium-doped substrate is thermally diffused at a temperature higher than this (Comparative Examples 2, 3, 5, 6), the lifetime will be lowered. This is thought to be due to the fact that oxygen defects are likely to precipitate and swirl is developed. Further, at lower temperatures (Comparative Examples 1 and 4), the dopant is difficult to thermally diffuse and is not suitable for forming a diffusion layer of a solar battery cell.

  FIG. 2 is a graph showing the relationship between the peak temperature (° C.) and the substrate lifetime (μ seconds) after thermal diffusion in Examples 1 to 6 and Comparative Examples 1 to 6. As shown in Table 1 and FIG. 2, the lifetime of the gallium-doped substrate is determined when the peak temperature condition is 800 ° C. or higher and 900 ° C. or lower (Examples 1 to 6), particularly 800 ° C. or higher and 850 ° C. or lower. It turns out that it becomes high.

(Examples 7 to 10, Comparative Examples 19 to 20)
The solar cell was processed in the same manner as in Example 2 (Example in which the peak temperature was 850 ° C.) except that the holding time of the peak temperature was 30 seconds, 1 minute, 30 minutes, 50 minutes, 90 minutes, and 100 minutes. A battery cell was produced.

(Comparative Examples 21-26)
The solar cell was processed in the same manner as in Comparative Example 9 (Comparative Example in which the peak temperature was 850 ° C.) except that the holding time of the peak temperature was 30 seconds, 1 minute, 30 minutes, 50 minutes, 90 minutes, and 100 minutes. A battery cell was produced.

  In Table 3 and FIG. 3, the result of Examples 7-10 and Comparative Examples 19-26 is shown. Table 3 shows the cell conversion efficiencies (%) of Examples 7 to 10 and Comparative Examples 19 to 26.

  FIG. 3 is a graph showing the relationship between peak temperature retention time (minutes) and cell conversion efficiency (%) in Examples 7 to 10 and Comparative Examples 19 to 26. In FIG. 3, the results of Examples 2 and 5 and Comparative Examples 9 and 15 are also plotted. As shown in FIG. 3, the peak temperature holding time is 1 minute or more and 90 minutes or less, and when a gallium doped substrate is used (Examples 7 to 10), the peak temperature holding time is 1 minute or more and 90 minutes or less. The average conversion efficiency of the solar battery cells can be increased more than when the boron-doped substrate is used (Comparative Examples 22 to 25). When the holding time of the peak temperature was less than 1 minute, it was too short, and the conversion efficiency was insufficient. A retention time of 90 minutes or less is sufficient for the peak temperature. Exceeding this does not improve the conversion efficiency. From the viewpoint of productivity, the peak temperature holding time is 90 minutes or less.

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

10 ... solar cell, 11 ... first conductivity type semiconductor substrate,
12 ... Second conductivity type diffusion layer (n-type diffusion layer), 13 ... First conductivity type diffusion layer (p-type diffusion layer),
14 ... Light-receiving surface passivation film, 15 ... Back surface passivation film,
16 ... Light-receiving surface electrode, 17 ... Back electrode.

Claims (6)

Forming a second conductivity type diffusion layer by thermally diffusing a second conductivity type dopant which is the conductivity type opposite to the first conductivity type on the first main surface of the first conductivity type semiconductor substrate; A step of thermally diffusing the first conductive type dopant on the second main surface of the semiconductor substrate to form a first conductive type diffusion layer; and the second conductive type diffusion layer, the first conductive type diffusion layer, and the electric A step of forming an electrically connected electrode, comprising the steps of:
The semiconductor substrate is a silicon substrate doped with gallium,
The peak temperatures when the thermal diffusion of the second conductivity type dopant and the thermal diffusion of the first conductivity type dopant are performed are 800 ° C. or more and 900 ° C. or less, respectively, and the holding time of the peak temperature is 1 minute or more and 90 ° C. The manufacturing method of the photovoltaic cell characterized by being less than or equal to minutes. Thermal diffusion of the second conductivity type dopant is performed by applying a material containing the second conductivity type dopant on the first main surface of the semiconductor substrate, and performing a heat treatment.
The thermal diffusion of the first conductivity type dopant is performed by applying a material containing the first conductivity type dopant on the second main surface of the semiconductor substrate and performing a heat treatment. The manufacturing method of the photovoltaic cell of description.   The method of manufacturing a solar battery cell according to claim 2, wherein thermal diffusion of the second conductive type dopant and thermal diffusion of the first conductive type dopant are performed by a single heat treatment.   The step of forming the electrode includes laminating a passivation film on the second conductive type diffusion layer and the first conductive type diffusion layer, and containing conductive particles and glass frit at predetermined positions on the passivation film. An electrode electrically conductively connected to the second conductive diffusion layer and the first conductive diffusion layer by applying a conductive paste, firing a semiconductor substrate coated with the conductive paste, penetrating the passivation film It forms by forming, The manufacturing method of the photovoltaic cell of any one of Claims 1-3 characterized by the above-mentioned.   In the step of forming the second conductivity type diffusion layer and the step of forming the first conductivity type diffusion layer, thermal diffusion of the second conductivity type dopant and thermal diffusion of the first conductivity type dopant are performed. The atmosphere at the time of holding the peak temperature is a mixed gas of an inert gas and an active gas, and the ratio of the inert gas / active gas in the mixed gas is set to 50 to 300. The manufacturing method of the photovoltaic cell of Claim 1.   A solar battery cell manufactured using the method for manufacturing a solar battery cell according to any one of claims 1 to 5.

Images