TWI656655B - Solar cell manufacturing method and solar cell obtained by the manufacturing method - Google Patents

Abstract

The invention relates to a method for manufacturing a solar cell, comprising the steps of: preparing a second diffusion type doped second diffusion agent and a first conductivity type doped first diffusion agent, and first diffusion a step of applying the agent to the second main surface of the first conductive type semiconductor substrate, and a step of partially applying the second diffusing agent to the first main surface, and coating the first diffusing agent and the second diffusing agent by heat treatment The semiconductor substrate has a step of forming a high concentration second diffusion layer, a low concentration second diffusion layer, and a first diffusion layer, and a step of forming a thermal oxide film on the semiconductor substrate on which the diffusion layer is formed.

Thereby, the manufacturing process is simplified, the problem of automatic doping is released, and the manufacturing method of the solar cell excellent in electrical characteristics can be provided.

Description

Solar cell manufacturing method and solar cell obtained by the manufacturing method

The present invention relates to a method of manufacturing a solar cell and a solar cell obtained by the method of the invention.

When manufacturing solar cells for consumers, it is an important issue to increase the efficiency and reduce the manufacturing cost, and extensively research on double-sided light-receiving solar cells has been conducted. The details are as follows, for example.

First, a p-type germanium substrate obtained by slicing a single crystal germanium ingot produced by a diesel crystal pulling (CZ) method or a polycrystalline germanium ingot produced by a casting method is prepared by a multi-line method. Then, after the damage caused by the slicing on the surface of the substrate is removed by the alkali solution, fine irregularities (textures) having a maximum height of about 10 μm are formed on both surfaces of the light-receiving surface and the back surface. Next, the doping heat of different conductivity types is diffused on both surfaces of the substrate by an organic photoresist or the like by using a photomask method, and an n-type phosphorus-doped gas phase which is opposite to the substrate is diffused by using a POCl ₃ gas. An n-type diffusion layer is formed on the first main surface of the light-receiving surface, and p-type boron which is of the same conductivity type as the substrate is doped with BBr ₃ gas and diffused by a vapor phase diffusion method on the second main surface which becomes the opposite surface, and becomes an electrode. Take ohmic contact. Next, TiO ₂ or SiNx is deposited on the light-receiving surface and the reverse surface, for example, at a film thickness of about 80 nm to form an anti-reflection film. Next, a paste for a counter electrode having silver as a main component was comb-printed on the reverse side and dried. On the other hand, the light-receiving surface electrode is, for example, a slurry for a light-receiving surface electrode containing silver as a main component in a comb shape of about 100 μm in width, and dried. Finally, the two-sided light-receiving solar cell is completed by firing the light-receiving surface electrode and the counter-surface electrode to form an electrode in ohmic contact.

The double-sided light-receiving solar cell thus produced can suppress the surface re-bonding of the aluminum electrode field on the reverse side of the substrate, and the BSF (back surface field) effect of the boron diffusion layer is compared with the crystal enthalpy having a general reverse-side aluminum electrode. High photoelectric conversion characteristics. Moreover, the two-sided light-receiving solar cell has a smaller warpage of the substrate and less cracking during the modularization than the crystal enthalpy having a general reverse-side aluminum electrode.

However, in the case of the different conductivity type diffusion layers described above, and the same conductivity type and diffusion layers having different concentrations are formed by a photomask method using photoresist or the like, the steps of mask formation or mask removal are increased, and diffusion heat treatment is also increased. The number of times becomes high in manufacturing costs.

Then, as a method of diffusing impurities of the same conductivity type at a different concentration by heat treatment at one time, the diffusion agent is partially coated by screen printing and heat-treated, and the region directly under the diffusing agent is used as a high-concentration diffusion layer. A technique in which other fields are used as a low-concentration diffusion layer (for example, Patent Document 1).

In this method, the high-concentration diffusion layer directly under the electrode suppresses the low contact resistance, and the light-receiving surface is made into a low-concentration diffusion layer, so that the amount of power generation can be increased, and a solar cell having high conversion efficiency can be produced.

[Advanced technical literature] [Patent Literature]

[Patent Document 1] JP-A-2007-235174

Further, the impurities of different conductivity types are diffused while being heat-dissipated by one heat treatment, and the impurities having different conductivity types are thermally diffused in the same heat treatment furnace, so that the cost is reduced by the step shortening, and it becomes possible to produce a highly competitive one. Solar battery.

However, a phosphorus diffusing agent of an n-type impurity source is partially applied to the first main surface, and a boron diffusing agent of a p-type impurity source is entirely applied to the second main surface, and then diffused simultaneously, in the first main surface. A low-concentration phosphorus diffusion layer (n ⁺ layer) which becomes a surface other than the electrode directly under the surface is doped by boron doping of the boron diffusion agent of the second main surface, and is doped to cause contamination and reduce electrical characteristics of the solar cell. problem.

The present invention has been made in view of the above problems, and it is possible to simplify the manufacturing steps and solve the problem of automatic doping, and to provide a method for manufacturing a solar cell capable of producing a solar cell excellent in electrical characteristics as an object of the invention.

In order to achieve the above object, the first main surface of the first conductivity type semiconductor substrate provided in the present invention is formed opposite to the first conductivity type described above. a high concentration second diffusion layer diffused by the second conductivity type doping and a low concentration second diffusion layer diffused by the lower concentration doping of the high concentration second diffusion layer on the second main surface of the semiconductor substrate A method of manufacturing a solar cell in which the first conductivity type doped diffusion first diffusion layer is formed, characterized in that: (a) preparing a doped second diffusion agent including the second conductivity type and including a step of coating the first conductivity type doped first diffusion agent, and (b) applying the first diffusion agent to the second main surface, and (c) partially coating the first main surface a step of the second diffusing agent, and (d) forming a high-concentration second diffusion layer, the low-concentration second diffusion layer, by heat-treating a semiconductor substrate coated with the first diffusing agent and the second diffusing agent, And the step of forming the thermal diffusion film on the semiconductor substrate on which the diffusion layer is formed, and the step of (e) forming the thermal diffusion film.

According to this method of manufacturing a solar cell, it is possible to simplify the manufacturing process and reduce the manufacturing cost by diffusing the impurities of different conductivity types by one heat treatment. Further, by the heat treatment in the step (d), the doping of the first conductivity type which is automatically doped in the low concentration second diffusion layer is formed by the formation of the thermal oxide film of the step (e). As a result, a solar cell unit having excellent electrical characteristics can be produced.

Further, the semiconductor substrate is a p-type germanium substrate, and the second diffusing agent is used to obtain a vitrified phosphorus diffusing agent by the heat treatment, and the first diffusing agent is used to obtain a vitrified boron diffusing agent by the heat treatment. It is better.

By using a vitrifying diffusing agent by heat treatment, a high concentration second diffusion layer can be easily formed. Moreover, if such a diffusing agent is used, it can be easily removed.

Further, it is preferred to carry out the above steps (d) and (e) in the same heat treatment batch.

If the solar cell manufacturing method is thus used, the manufacturing steps can be further reduced.

Further, after the step (d) and before the step (e), it is preferred to have (f) removing the first diffusion agent and the second diffusion agent which have been subjected to the heat treatment.

According to this method of manufacturing a solar cell, a solar cell unit having more excellent electrical characteristics can be manufactured.

Further, it is preferable that the film thickness of the thermal oxide film formed in the step (e) is 10 to 20 nm.

When the film thickness is as large, it is easy to lower the concentration of the first conductivity type doping which is automatically doped to the low concentration second diffusion layer.

Further, it is preferable that the peak concentration of the first conductivity type doping of the low concentration second diffusion layer is 5.0 × 10 ¹⁷ atoms/cm ³ or less.

Under such conditions, the sheet resistance of the resulting solar cell can be lowered.

Further, it is preferable that the peak concentration of the second conductivity type doping of the low concentration second diffusion layer is 1.0 × 10 ¹⁸ atoms/cm ³ or more.

If this is the case, it is not easy to lower the resulting solar cell. Short circuit current.

Further, it is preferable that the peak concentration ratio of the second conductivity type doping of the low concentration second diffusion layer to the first conductivity type doping is 10.0 or more.

Under such conditions, the conversion efficiency of the obtained solar cell can be further improved.

Further, it is preferable to have the following steps: after the step (e), (g) forming a passivation film on the first main surface and the second main surface, and (h) forming the passivation film The step of applying the electrode material to the one main surface and the second main surface, and (i) firing the step of coating the electrode material.

If the solar cell is manufactured in such a manner, a solar cell with higher conversion efficiency can be obtained.

Further, the present invention provides a solar battery characterized by the manufacture of the solar cell manufacturing method of the present invention described above.

If such a solar cell is used, it is possible to obtain an excellent conversion efficiency even at a low cost.

According to the method of manufacturing a solar cell of the present invention, the first conductive type first diffusion layer is formed on the second main surface, and the opposite conductive type high concentration second diffusion layer is formed on the first main surface. Low concentration of the second diffusion layer, low concentration and automatic doping to low concentration The first conductivity type impurity of the second diffusion layer. As a result, a solar cell excellent in electrical characteristics can be produced in a high yield. Further, by diffusing the different conductivity type impurities by the heat treatment once, the manufacturing steps can be simplified and the manufacturing cost can be reduced.

Fig. 1 is a flow chart showing a method of producing a solar cell of Example 1 (a case where a diffusion layer is formed and a thermal oxide film is formed in the same heat treatment batch).

Fig. 2 is a flow chart showing a method for producing a solar cell of Example 3 (a case where a vitrified diffusing agent is removed from the surface of the substrate after heat treatment, and then a thermal oxide film is formed and removed).

Fig. 3 is a flow chart showing a method for producing a solar cell of Example 2 (a case where a vitrified diffusing agent is removed from the surface of the substrate after heat treatment, and then a thermal oxide film is formed).

Fig. 4 is a schematic view showing an example of a solar cell obtained by the method for producing a solar cell of the present invention.

Fig. 5 is a schematic view showing another example of a solar cell obtained by the method for producing a solar cell of the present invention.

Fig. 6 is a view showing a coating mode of a first diffusing agent and a second diffusing agent before simultaneous diffusion.

FIG. 7 is a conceptual diagram of a high concentration second diffusion layer, a low concentration second diffusion layer, and a first diffusion layer which are formed after doping simultaneously.

[Fig. 8] is a low concentration second diffusion layer formed after doping simultaneously diffusion Conceptual diagram of the field of automatic doping.

9 is a flow chart showing a method of fabricating a solar cell of Comparative Example 1.

[Formation of the Invention]

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

As described above, it is required to simplify the manufacturing steps, solve the problem of automatic doping, and manufacture a solar cell solar cell having excellent electrical characteristics.

As a result of careful examination of the above-mentioned objects, the inventors of the present invention have found that the method for producing a solar cell having the following steps can solve the above problems and complete the present invention. That is, the first main surface of the first conductivity type semiconductor substrate is formed with a second conductivity type opposite to the first conductivity type, and the high concentration second diffusion layer is diffused and lower than the high concentration second diffusion layer. a method for manufacturing a solar cell having a low concentration second diffusion layer diffused by concentration and forming a first diffusion layer of the first conductivity type doped diffusion on the second main surface of the semiconductor substrate, characterized in that a step of preparing a doped second diffusing agent comprising the second conductivity type and a doped first diffusing agent comprising the first conductivity type, and (b) coating the second main surface a step of coating the first diffusing agent, and (c) partially coating the second diffusing agent on the first main surface, and (d) coating the first diffusing agent and the second by heat treatment Expand a step of forming a high-concentration second diffusion layer, the low-concentration second diffusion layer, and the first diffusion layer on the semiconductor substrate of the powder, and (e) forming a thermal oxide film on the semiconductor substrate on which the diffusion layer is formed .

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

[solar battery]

First, a solar cell obtained by the method for producing a solar cell of the present invention will be described with reference to Figs. 4 and 5 .

4 and 5 are schematic views showing an example of a solar cell obtained by the method for producing a solar cell of the present invention. As shown in FIG. 4 and FIG. 5, the solar cell obtained by the method for manufacturing a solar cell of the present invention is formed on the first main surface of the first conductivity type semiconductor substrate to form a second conductivity type doping opposite to the first conductivity type. a high concentration second diffusion layer 2 diffused by the impurity and a low concentration second diffusion layer 3 diffused at a lower concentration than the high concentration second diffusion layer, forming a first conductivity type doping region on the second main surface The diffused first diffusion layer 4 forms an electrode (reverse 栉-shaped electrode) 7 and an electrode (light-receiving surface 电极-shaped electrode) 8 on the first main surface and the second main surface. A passivation film 6 is usually formed on the first main surface and on the second main surface.

Specific examples of the first conductive type semiconductor substrate include a p-type substrate such as a boron-doped p-type single crystal germanium substrate. In the case where the substrate is p-type, as the first conductivity type doping, p-type doping such as B (boron) or Ga (gallium) can be used. As the second conductivity type doping, P (phosphorus) can be used, N-type doping of Sb (锑), As (arsenic), and the like.

At this time, the high concentration second diffusion layer becomes the n ⁺⁺ layer, the low concentration second diffusion layer becomes the n ⁺ layer, and the first diffusion layer becomes the p ⁺ layer.

As the passivation film, for example, a tantalum nitride film or the like can be given. As shown in FIG. 5, a passivation film may be laminated on the thermal oxide film 5 such as a ruthenium oxide film.

[Method of Manufacturing Solar Cell]

Hereinafter, an example of a method of manufacturing a solar cell of the present invention will be described as an example of a p-type substrate, but the present invention is not limited thereto. Further, in the following semiconductor substrate-based p-type germanium substrate, the case where the first conductive type doping is doped with boron and the second conductive type doped with phosphorus is described as an example. Therefore, the high concentration second diffusion layer, the low concentration second diffusion layer, and the first diffusion layer are also referred to as an n ⁺⁺ layer, an n ⁺ layer, and a p ⁺ layer. Further, the first main surface and the second main surface are also referred to as a light receiving surface and a reverse surface, and may be received from the second main surface (reverse surface).

First, a semiconductor substrate such as a boron-doped p-type single crystal germanium substrate is prepared. A single crystal substrate obtained by slicing an ingot produced by a method such as a Czochralski (CZ) method or a floating zone (FZ) method. When a high-performance solar cell is produced, the specific resistance of the substrate is preferably 0.1 to 20 Ω ‧ cm, and particularly preferably 0.5 to 2.0 Ω ‧ cm.

Next, the prepared substrate was immersed in an aqueous sodium hydroxide solution, and the damaged layer was removed by etching. It is not necessary to remove the damage of the substrate by using a strong alkali aqueous solution such as potassium hydroxide. Further, even an aqueous acid solution such as fluoronitric acid may achieve the same purpose.

The substrate subjected to the damage etching forms a random texture.

It is preferable that the solar cell system generally has a concave-convex shape on the surface. The reason for this is that in order to reduce the reflectance in the visible light region, it is necessary to perform reflection twice or more on the light receiving surface as much as possible. The size of the surface irregularities of the ones may be about 1 to 20 μm. Examples of the surface uneven structure include V grooves and U grooves. This may be formed using a grinder. Further, when a random uneven structure is produced, it is immersed in an aqueous solution of sodium hydroxide to which isopropyl alcohol has been added, and then wet-etched, or acid etching or reactive ‧ ion etching may be used.

Next, a second diffusing agent containing a second conductivity type doping and a first diffusing agent containing a first conductivity type doping are prepared. It is preferred that the first diffusing agent and the second diffusing agent are vitrified by heat treatment. In particular, when a p-type germanium substrate is used, a phosphorus diffusing agent which is vitrified by heat-treating a second diffusing agent is obtained, and a boron diffusing agent which is vitrified by heat-treating the first diffusing agent is preferably obtained.

A phosphorus diffusing agent which is vitrified by heat treatment is obtained by mixing P ₂ O ₅ , pure water, PVA (polyvinyl alcohol), TEOS (tetraethyl orthosilicate). A boron diffusing agent which is vitrified by heat treatment can be obtained by mixing B ₂ O ₃ , pure water, or PVA (polyvinyl alcohol).

Next, a first diffusing agent is applied to the second main surface, and the second diffusing agent is partially applied to the first main surface. The order in which the first diffusing agent and the second diffusing agent are applied to the substrate is not particularly limited. Fig. 6 is a view showing a coating mode of the first diffusing agent and the second diffusing agent before simultaneous diffusion. As shown in FIG. 6, a second diffusing agent (for example, a phosphorus diffusing agent) 9 is partially applied to the first main surface of the substrate 1, and a first diffusing agent (for example, a boron diffusing agent) 10 is applied to the second main surface.

As a specific example of the above coating step, first on the reverse side After the boron diffusion agent of the p-type impurity is applied, it is dried. As the coating method, a spin coating method, an inkjet method, a screen printing method, or the like is suitably used. Next, a phosphorus diffusing agent of an n-type impurity is partially applied to the light-receiving surface, followed by drying. The coating method of the diffusing agent is preferably a screen printing method, an inkjet method, a spray coating method, or the like.

When the second diffusing agent is partially applied to the first main surface, it is preferably applied to the field where the electrode is formed (the area immediately below the electrode).

Next, a high-concentration second diffusion layer, a low-concentration second diffusion layer, and a first diffusion layer are simultaneously formed by heat-treating the semiconductor substrate coated with the first diffusion agent and the second diffusion agent. Specifically, the surface of the first diffusing agent coated with the boron diffusing agent or the like is placed in a state of being opposed to each other, and then heat-treated at 900 to 1000 ° C for 10 to 60 minutes. Although it is used as a treatment atmosphere in an inert gas such as nitrogen or argon, it may contain oxygen at a concentration of 5% or less. By this heat treatment, a high concentration second diffusion layer and a low concentration second diffusion layer are formed on the light receiving surface side, and a uniform first diffusion layer is formed on the reverse side.

FIG. 7 is a conceptual diagram of a high concentration second diffusion layer, a low concentration second diffusion layer, and a first diffusion layer formed after doping simultaneously. As shown in FIG. 7, a high concentration second diffusion layer 2 is formed in the field of the second diffusion agent on the first main surface of the coated substrate 1, and a low concentration second diffusion layer is formed in the field where the second diffusion agent is not applied. 3. A first diffusion layer 4 is formed on the second main surface. Further, a heat-treated second diffusing agent 11 is formed in the field of the diffusing agent coated with the first main surface, and a heat-treated first diffusing agent 12 is formed on the second main surface.

At this time, it is preferred that the first diffusing agent and the second diffusing agent are vitrified by heat treatment. At this time, the first diffusing agent and the second diffusing agent are Vitrification is carried out by the above heat treatment.

Here, the conductivity type of the substrate 1 is p-type, the second diffusion agent is a phosphorus diffusion agent which is vitrified by heat treatment, and the first diffusion agent is a boron diffusion agent which is vitrified by heat treatment, and the second diffusion The layer becomes an n-type diffusion layer. At this time, the field of the coated phosphorus diffusing agent becomes a high-concentration phosphorus diffusion layer (n ⁺⁺ layer), and the uncoated region becomes a low-concentration phosphorus diffusion layer (n ⁺ layer). On the other hand, the first diffusion layer (p-type diffusion layer) serves as a boron diffusion layer (p ⁺ layer).

At this time, the phosphorus diffusing agent and the boron diffusing agent are vitrified by heat treatment. As a result, the phosphorus glass 11 is formed in the field of the diffusing agent coated with the first main surface, and the borosilicate glass 12 is formed on the second main surface.

FIG. 8 is a conceptual diagram of an automatic doping field of a low concentration second diffusion layer formed after doping simultaneously. As shown in FIG. 8, a high concentration second diffusion layer 2 is formed in the field in which the heat-treated second diffusion agent 11 is formed, and a low concentration second diffusion layer 15 is formed in the field in which the heat-treated second diffusion agent 11 is not formed. Here, the low concentration second diffusion layer 15 is composed of an autodoped layer 14 having a high first conductivity type doping concentration and an autodoped layer 13 having a high second conductivity type doping concentration.

The first conductivity type doping is automatically doped to the low concentration second diffusion layer by the above heat treatment, and thus the peak concentration ratio of the second conductivity type doping and the first conductivity type doping of the second diffusion layer at a low concentration point at this time ( The peak concentration of the second conductivity type doping/peak concentration of the first conductivity type doping is small. Thereafter, by performing the step of forming a thermal oxide film, the peak concentration ratio is increased, and the peak concentration of the first conductivity type doping of the low concentration second diffusion layer can be lowered.

Next, pn junction separation was performed using a plasma etcher. In this step, the plasma or radical does not intrude into the light-receiving surface or the reverse surface, and the sample is laminated, and the end surface is cut by several micrometers in this state. This may be carried out before the removal of the pn separation borosilicate glass and the phosphor glass by plasma etching, or may be performed after removal. As an alternative to pn separation, it is also possible to form a trench by laser.

Next, a thermal oxide film is formed on the semiconductor substrate on which the high concentration second diffusion layer, the low concentration second diffusion layer, and the first diffusion layer are formed. By the above heat treatment, this step is a step of lowering the concentration of the first conductivity type doping which is automatically doped to the low concentration second diffusion layer.

After the heat treatment step, and before the step of forming the thermal oxide film, the step of removing the heat-treated first diffusing agent and the second diffusing agent may be performed. At this time, the heat-treated diffusing agent (phosphorus glass and borosilicate adhered to the substrate) can be removed by a high concentration of a hydrofluoric acid solution or the like. Subsequently, the substrate is washed.

Next, the substrate from which the heat-treated diffusing agent (glass or the like) is removed is heat-treated by, for example, a 100% oxygen atmosphere, 850 to 950 ° C, and a treatment time of 10 to 60 minutes to form an oxide film. According to this method of manufacturing a solar cell, a solar cell unit having more excellent electrical characteristics can be manufactured.

Here, although the thermal oxidation film is formed after being removed by the heat treatment diffusion agent (phosphorus glass and borosilicate glass), the heat treatment step and the step of forming the thermal oxide film may be performed in the same heat treatment batch. At this time, the substrate is placed in a heat treatment furnace, for example, after heat treatment at 900 to 1000 ° C in an inert atmosphere to form a high concentration second diffusion layer, a low concentration second diffusion layer, and a first diffusion layer, and then switch to 100% oxygen. Under the conditions of the atmosphere The heat treatment film is formed by heat treatment at 850 to 950 ° C for 10 to 60 minutes. If the solar cell manufacturing method is thus used, the manufacturing steps can be reduced.

In the step of forming the thermal oxide film, the film thickness of the formed thermal oxide film is preferably 10 to 20 nm. By adjusting the film thickness of the oxide film, the peak concentration of the first conductivity type doping (p type impurity) of the low concentration second diffusion layer (n ⁺ layer) can be adjusted. When the film thickness is 10 nm or more, it is easy to lower the concentration of the first conductivity type doping which is automatically doped to the low concentration second diffusion layer. When it is 20 nm or less, re-diffusion of the second conductivity type doping can be suppressed.

Further, the peak concentration of the first conductivity type doping (p type impurity) of the low concentration second diffusion layer (n ⁺ layer) is set to 5.0 × 10 ¹⁷ atoms/cm ³ or less, and the second conductivity type is doped (n The peak concentration of the type impurity is preferably 1.0 × 10 ¹⁸ atoms/cm ³ or more. When the peak concentration of the first conductivity type doping is 5.0 × 10 ¹⁷ atoms/cm ³ or less, the sheet resistance can be lowered. When the peak concentration of the second conductivity type doping is 1.0 × 10 ¹⁸ atoms/cm ³ or more, it is not easy to reduce the short-circuit current. In addition, although the peak concentration upper limit of the second conductivity type doping of the low concentration second diffusion layer is not particularly limited, it may be, for example, 1.0 × 10 ¹⁹ atoms/cm ³ . The peak concentration lower limit value of the second conductivity type doping of the high concentration second diffusion layer is not particularly limited, but may be, for example, 1.0 × 10 ²⁰ atoms/cm ³ .

Further, it is preferable that the peak concentration ratio of the second conductivity type doping of the low concentration second diffusion layer to the first conductivity type doping is 10.0 or more. When the peak concentration ratio is 10.0 or more, the conversion efficiency of the obtained solar cell can be more surely improved.

The above peak can be determined by SIMS (Secondary Ion Mass Spectrometry) concentration.

Next, a tantalum nitride film of a passivation film was deposited on the light-receiving surface and the reverse surface by using a direct plasma CVD apparatus. At this time, as shown in FIG. 5, the passivation film 6 may be deposited on the thermal oxide film 5. Since the film thickness-passivation film of the passivation film also has an anti-reflection film, the film thickness of the oxide-containing film is adjusted so that the respective surfaces have a film thickness in the range of 80 nm to 100 nm. Other antireflection films include a ruthenium dioxide film, a titanium dioxide film, a zinc oxide film, a tin oxide film, an aluminum oxide film, and the like, and may be used as a substitute, or a laminated structure may be used. Further, in addition to the film formation method, there are a remote control plasma CVD method, a coating method, a vacuum deposition method, an ALD (atomic layer deposition) method, and the like, and can be suitably used.

When the heat treatment step and the step of forming the thermal oxide film are carried out in the same heat treatment batch, it is preferred to form a passivation film after removing the heat treatment diffusion agent (phosphorus glass and borosilicate glass).

Next, using a screen printing apparatus, a slurry made of, for example, silver is applied to the light-receiving surface side and the reverse surface side in the shape of a crucible electrode, and then dried. Finally, it is fired in a baking furnace to obtain a desired solar cell.

The solar cell is produced by the above method, and the increase in electric resistance caused by the automatic doping of the p-type impurity of the n ⁺ diffusion layer and the formation of the high-concentration p-type diffusion layer occur in the simultaneous diffusion treatment, and the electrical characteristics can be excellent. Solar battery.

In the above, the case of the p-type substrate has been described as an example. Even in the case of the n-type substrate, the above-mentioned dopant material may be used instead, without any problem.

[Examples]

Hereinafter, the present invention will be more specifically described by way of examples and comparative examples, but these are not intended to limit the invention.

(Manufacture of solar cells) (Example 1)

The solar cell of Fig. 4 was fabricated by heat treatment in which phosphorus and boron were simultaneously diffused. At this time, the solar cell was fabricated in accordance with the flow chart shown in FIG. Fig. 1 is a flow chart showing a method of manufacturing a solar cell of Example 1 (a case where a diffusion layer is formed and a thermal oxide film is formed in the same heat treatment batch).

At this time, the prepared substrate was a boron-doped p-type single crystal crucible having a crystal plane orientation (100), a 15.6 cm square 200 μm thickness, and an untreated slice specific resistance of 2 Ω ‧ cm (doping concentration 7.2×10 ¹⁵ cm ⁻³ ). Substrate. After the damage etching and the texture etching were performed with an aqueous NaOH solution, the surface of the substrate was subjected to RCA cleaning to form a textured structure on the surface of the substrate. The thickness of the substrate became 180 μm (Fig. 1 (1) (2)).

Next, P ₂ O ₅ , pure water, PVA (polyvinyl alcohol), and TEOS (tetraethyl orthosilicate) were mixed to prepare a phosphorus diffusing agent, and screen printing was performed in a field directly under the electrode on the side of the light receiving surface. The pattern was applied and dried at 100 ° C for 20 minutes (Fig. 1 (3)).

Further, a boron diffusing agent was prepared by mixing B ₂ O ₃ , pure water, and PVA (polyvinyl alcohol), and spin coating was performed on the reverse side, and dried at 80 ° C for 1 minute to uniformly form a film of a boron diffusing agent (Fig. 1 (4) )).

Next, the boron faces were placed in a state opposite to each other and placed in a quartz boat, and heat-treated at 950 ° C for 30 minutes. Further, after this stage, the stage of forming a thermal oxide film at 900 ° C for 40 minutes was switched to a 100% oxygen atmosphere, and then the substrate was taken out from the heat treatment furnace by cooling (Fig. 1 (5)).

Next, pn junction separation is performed using a plasma etching apparatus. The etching gas system uses CF ₄ gas, and the plasma or radical does not intrude into the light receiving surface or the reverse surface, and the sample is laminated, and in this state, the end surface is cut by several micrometers (Fig. 1 (6)).

The phosphor glass and the borosilicate glass which are simultaneously diffused on the surface of the substrate are removed by a hydrofluoric acid aqueous solution, and washed (Fig. 1 (7)).

Next, a passivation film of a passivation film was formed on the light-receiving surface and the back surface by a plasma CVD apparatus at a thickness of 85 nm (Fig. 1 (8)).

Silver paste was formed on the light-receiving surface side and the reverse surface side by screen printing, dried, and baked at 800 ° C for 20 minutes (Fig. 1 (9) (10) (11)).

(Example 2)

The thermal oxide film of Example 1 which was obtained by removing the phosphorus glass and the borosilicate glass of the solar cell shown in Fig. 5 was produced. At this time, the solar cell was fabricated in accordance with the flow chart shown in FIG. Fig. 3 is a flow chart showing a method of manufacturing a solar cell of Example 2 (a case where a vitrified diffusing agent is removed from the surface of the substrate after heat treatment, and then a thermal oxide film is formed).

Specifically, in addition to the simultaneous diffusion of the phosphorus and boron of Example 1, the thermal oxide film formation is not performed in the same batch, and the substrate is taken out for pn. Separation (Fig. 3 (5) (6)), after the phosphoric acid aqueous solution was immersed in the phosphor glass and the borosilicate glass on the surface of the substrate and removed (Fig. 3 (7)), and again subjected to a heat treatment furnace of 100% oxygen atmosphere at 900 ° C, 40 After a minute of treatment, a 15 nm thermal oxide film is formed (Fig. 3 (8)). Further, in the subsequent step, the CVD film is deposited with a light-receiving surface and a reverse surface by 70 nm, respectively, and the total thickness of the oxide film and the vaporized film on the light-receiving surface and the reverse surface. A solar cell was produced in the same manner as in Example 1 except that it was adjusted to 85 nm (Fig. 3 (9)).

(Example 3)

After the thermal oxide film of Example 2 of the solar cell shown in Fig. 4 was formed, the thermal oxide film was removed. At this time, the solar cell was fabricated in accordance with the flow chart shown in FIG. Fig. 2 is a flow chart showing a method for producing a solar cell of Example 3 (a case where a thermally oxidized film is formed and removed after removing a vitrified diffusing agent from a surface of the substrate after heat treatment).

Specifically, in addition to the formation of the thermal oxide film of Example 2, the substrate is immersed in a hydrofluoric acid aqueous solution to remove the thermal oxide film formed on the surface of the substrate (Fig. 2 (9)), and further, the CVD film system of the subsequent step is used. A solar cell was produced in the same manner as in Example 2 except that 85 nm was deposited on the light-receiving surface and the reverse surface (Fig. 2 (10)).

(Example 4)

A solar cell in which a thermal oxide film of 5 nm was formed was fabricated in Example 1.

Specifically, the thermal oxide film formation stage at the time of simultaneous diffusion heat treatment of the phosphorus-boron of Example 1 was adjusted to 850 ° C for 40 minutes. An oxide film of 5 nm was formed. The substrate which was taken out was laminated and separated by pn bonding by plasma etching, and the borosilicate glass and the phosphor glass were removed by using fluoric acid, and then the CVD film on the light-receiving surface and the reverse surface was deposited to a thickness of 85 nm, and the solar cell was produced in the same manner as in the first embodiment. battery.

(Example 5)

A solar cell in which a thermal oxide film of 25 nm was formed in Example 1 was produced.

Specifically, the thermal oxide film formation stage at the time of simultaneous diffusion heat treatment of the phosphorus-boron of Example 1 was adjusted to 950 ° C for 40 minutes to form an oxide film of 25 nm. The substrate which was taken out was laminated and separated by pn bonding by plasma etching, and the borosilicate glass and the phosphor glass were removed by using fluoric acid, and then the CVD film on the light-receiving surface and the reverse surface was deposited to a thickness of 85 nm, and the solar cell was produced in the same manner as in the first embodiment. battery.

(Example 6)

In Example 2, a solar cell in which a thermal oxide film of 5 nm was formed was produced.

Specifically, a thermal oxide film of 5 nm was formed by adjusting the formation of the thermal oxide film of Example 2 to 850 ° C for 40 minutes. A solar cell was produced in the same manner as in Example 2 except that the CVD films on the light-receiving surface and the back surface were deposited by 80 nm.

(Example 7)

A solar cell in which a thermal oxide film of 25 nm was formed in Example 2 was produced.

Specifically, in addition to forming the thermal oxide film of Example 2 The solar cell was produced in the same manner as in Example 2 except that a thermal oxide film of 25 nm was formed at 950 ° C for 40 minutes, and a CVD film of the light-receiving surface and the reverse surface was deposited by 60 nm.

(Example 8)

In Example 3, a solar cell in which a thermal oxide film of 5 nm was formed was produced.

Specifically, a thermal oxide film of 5 nm was formed by adjusting the formation of the thermal oxide film of Example 3 to 850 ° C for 40 minutes. After the hot oxide film was removed by immersion in a hydrofluoric acid aqueous solution, a solar cell was produced in the same manner as in Example 3 except that the CVD film on the light-receiving surface and the reverse surface was deposited at 85 nm.

(Example 9)

In Example 3, a solar cell in which a thermal oxide film of 25 nm was formed was produced.

Specifically, the thermal oxide film of Example 3 was adjusted to 950 ° C for 40 minutes to form an oxide film of 25 nm, and after immersing in a hydrofluoric acid aqueous solution to remove the thermal oxide film, the CVD film on the light-receiving surface and the reverse surface was deposited at 85 nm. A solar cell was produced in the same manner as in Example 3 except for the above.

(Comparative Example 1)

For comparison, a solar cell in which the thermal oxide film was not formed in Example 1 was produced. At this time, the solar cell was fabricated in accordance with the flow chart shown in FIG. 9 is a flow chart showing a method of fabricating a solar cell of Comparative Example 1.

Specifically, it is not provided except for the simultaneous diffusion heat treatment of phosphorus and boron. At the stage of forming the thermal oxide film (Fig. 9 (5)), the taken-out substrate is laminated, and pn bonding is performed by plasma etching (Fig. 9 (6)), and after removing the borosilicate glass and the phosphorus glass by using hydrofluoric acid ( (7)) A solar cell was produced in the same manner as in Example 1 except that the CVD film on the light-receiving surface and the back surface was deposited at 85 nm (Fig. 9 (8)).

The conditions of the examples and comparative examples are shown in Table 1.

[peak concentration ratio]

The peak concentration ratio of the boron doping and phosphorus doping of the n ⁺ layer was measured by SIMS on the substrate before film formation of the respective conditions of the CVD film by SIMS. The results are shown in Table 2.

[Measurement of sheet resistance]

Further, sheet resistance measurement of the n ⁺ layer was carried out using a sheet resistance measuring machine of a four-probe method. The results are shown in Table 2.

[current and voltage characteristics]

In the atmosphere of 25 ° C, the solar cell produced under various conditions was measured for current and voltage characteristics in a solar simulator (light intensity: 1 kW/m ² , spectrum: AM 1.5 balls), and the results were as shown in Table 2. Further, the conversion efficiency in the table is the average value of 50 units of the examples and comparative examples.

As shown in Table 2, in Examples 1 to 3 in which high conversion efficiency was obtained, the peak concentration of boron doping of the n ⁺ layer was 5.0 × 10 ¹⁷ atoms/cm ³ or less and the peak concentration of phosphorus doping was 1.0×10 ¹⁸ atoms/cm ³ or more, the peak concentration ratio (phosphorus/boron) of phosphorus and boron doping in the n ⁺ layer is 10.0 or more. These conditions are good conditions for obtaining high conversion efficiency.

This is formed by a thermal oxide film, and the boron doping which is automatically doped to the n ⁺ diffusion layer is lowered to lower the sheet resistance of the n ⁺ layer, and is reduced by the effect of reducing the lateral flow resistance.

Further, in Examples 4 to 3, in Examples 4, 6, and 8 in which the thickness of the thermal oxide film was small, the low concentration of boron doping was sufficient, and the sheet resistance of the n ⁺ layer was lowered, so that the conversion efficiency was higher.

Further, in Examples 5, 7, and 9, which thicken the thermal oxide film, the thermal oxide film is not excessively formed in the n ⁺ layer, thereby preventing the boron doping from being low in concentration and preventing the phosphorus-doped redispersion. . Thereby, the peak concentration of the phosphorus doping of the n ⁺ layer is not lowered, the diffusion depth is not deepened, and the rebonding speed in the vicinity of the light receiving surface is lowered.

Further, in Examples 4, 6, and 8, the thickness of the thermal oxide film was thinner than in Example 1, but in this case, Comparative Example 1 was a solar cell which can obtain high conversion efficiency.

On the other hand, in Examples 5, 7, and 9 in which the thermal oxide film was thickened, the short-circuit current was slightly lower than that in Examples 1 to 3. In this case, Comparative Example 1 was a solar cell in which high conversion efficiency was obtained.

On the other hand, in Comparative Example 1, since the formation of the thermal oxide film doped with boron at a low concentration was not performed, the peak concentration ratio (phosphorus/boron) of the doping of phosphorus and boron in the n ⁺ layer was small, and the conversion efficiency was low.

According to the method for producing a solar cell of the present invention, it is known that the boron diffusion layer (first diffusion layer) and the phosphorus diffusion layer (high concentration second diffusion layer, low concentration second diffusion layer) having different concentrations are once. When the heat treatment is simultaneously formed, boron doping (first conductivity type doping) and phosphorus doping (second conductivity) which are automatically doped to the n ⁺ diffusion layer (low concentration second diffusion layer) can be controlled by forming a thermal oxide film. The peak concentration of the type doping) can produce a solar cell with high conversion efficiency.

Furthermore, the present invention is not limited to the above embodiments. For example, in the present embodiment, a solar cell having a p-type substrate is used. However, even when phosphorus and boron using an n-type substrate are simultaneously diffused, the above effects may be achieved, and a solar cell having high conversion efficiency may be produced. The above-described embodiments are exemplified and have substantially the same configuration as the technical idea described in the patent application scope of the present invention, and any of the functions and effects are included in the technical scope of the present invention.

Claims (9)

A method for manufacturing a solar cell, wherein a first high-concentration second diffusion layer of a second conductivity type opposite to the first conductivity type is formed on a first main surface of a first conductivity type semiconductor substrate; a high concentration second diffusion layer is doped at a lower concentration and diffused by the low concentration second diffusion layer, and the solar cell of the first conductivity type doped diffusion first diffusion layer is formed on the second main surface of the semiconductor substrate The method is characterized in that: (a) preparing a second diffusing agent comprising the second conductivity type and a step of doping the first diffusing agent comprising the first conductivity type, and (b) a step of coating the first diffusion agent on the second main surface, and (c) partially coating the second diffusion agent on the first main surface, and (d) coating the foregoing by heat treatment a semiconductor substrate of a diffusing agent and the second diffusing agent, a step of forming the high-concentration second diffusion layer, the low-concentration second diffusion layer, and the first diffusion layer, and (e) forming the diffusion layer Step of forming a thermal oxide film on a semiconductor substrate . The method for producing a solar cell according to the first aspect of the invention, wherein the semiconductor substrate is a p-type germanium substrate, and the second diffusing agent is heat-treated to form a vitrified phosphorus diffusing agent, and the heat treatment is performed by the heat treatment. The first diffusing agent is used to form a vitrified boron diffusing agent. The method for producing a solar cell according to claim 1 or 2, wherein the steps (d) and (e) are carried out in the same batch which has been subjected to heat treatment. The method for manufacturing a solar cell according to claim 1 or 2, wherein after the step (d), and before the step (e), further comprising (f) removing the first diffusion agent and the second diffusion by the heat treatment. The steps of the agent. The method for producing a solar cell according to claim 1 or 2, wherein the film thickness of the thermal oxide film formed in the step (e) is 10 to 20 nm. The method for producing a solar cell according to the first or second aspect of the invention, wherein the peak concentration of the first conductivity type doping of the low concentration second diffusion layer is 5.0 × 10 ¹⁷ atoms/cm ³ or less. The method for producing a solar cell according to the first or second aspect of the invention, wherein the peak concentration of the second conductivity type doping of the low concentration second diffusion layer is 1.0 × 10 ¹⁸ atoms/cm ³ or more. The method of manufacturing a solar cell according to claim 1 or 2, wherein the peak concentration ratio of the second conductivity type doping of the low concentration second diffusion layer to the first conductivity type doping is adjusted to 10.0 or more . The method for manufacturing a solar cell according to claim 1 or 2, further comprising the steps of: (e) forming a passivation film on the first main surface and the second main surface after the step (e); And (h) the step of coating the electrode material on the first main surface and the second main surface on which the passivation film is formed, and (i) the step of firing the coated electrode material.