JP2008034583A - Method of manufacturing solar battery element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for obtaining a stably high output solar battery element. <P>SOLUTION: The method of manufacturing a solar battery element comprises the steps of immersing a semiconductor substrate showing one conductive type in a solution containing ozone, and forming a reverse conductive type region showing a conductive type reverse to one conductive type on at least a part of the semiconductor substrate raised from the solution. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a solar cell element, and in particular, a reverse conductivity type semiconductor formed by diffusing a doping impurity element in a main surface side of a semiconductor substrate as a semiconductor forming step for forming a PN junction using a diffusion furnace. The present invention relates to a method for manufacturing a solar cell element having a region.

  A solar cell converts incident light energy into electrical energy. Major solar cells are classified into crystalline, amorphous, and compound types depending on the type of materials used. Of these, most of those currently on the market are crystalline silicon solar cells.

  This crystalline silicon solar cell is further classified into a single crystal type and a polycrystalline type. The single crystal silicon solar cell has the advantage that it is easy to increase the efficiency because the quality of the single crystal silicon substrate forming the solar cell is good, but has the disadvantage that the production of the substrate is expensive. On the other hand, a polycrystalline silicon solar cell has an advantage that it can be manufactured at a low cost although it has a disadvantage that it is difficult to increase efficiency because the quality of the polycrystalline silicon substrate forming the solar cell is inferior. In recent years, conversion efficiency of about 18% has been achieved at the research level due to the improvement of the quality of the polycrystalline silicon substrate and the advancement of cell technology.

  On the other hand, mass-produced polycrystalline silicon solar cells have been distributed in the market because of their low cost. However, in recent years, demand has increased further as environmental issues have been addressed, resulting in higher conversion efficiency at lower costs. Is now required.

  Various attempts have been made for solar cells in order to improve the conversion efficiency into electric energy. One of the technologies is to reduce the reflection of light incident on the surface of the solar cell element. For example, by reducing the reflection of light on the surface of the solar cell element by providing fine irregularities on the light receiving surface side of the semiconductor substrate. The conversion efficiency to electrical energy can be increased.

  Further, as a reverse conductivity type semiconductor forming step for forming a PN junction, reverse conductivity is provided on one main surface side (light receiving surface side) of a semiconductor substrate having one conductivity type, that is, on the same surface side as the above-described fine unevenness is provided. There is a method of forming a type semiconductor region.

This reverse conductivity type semiconductor region is generally formed as an impurity diffusion source by flowing POCl ₃ (phosphorus oxychloride) using a carrier gas while heating in a container provided with a semiconductor substrate as a vapor phase diffusion method. Phosphorous glass is formed on the surface of the semiconductor substrate, and at the same time, thermal diffusion is performed on the surface of the semiconductor substrate.

When a thermal diffusion method using POCl ₃ as a diffusion source is used, for example, a reverse conductivity type semiconductor region can be formed by diffusing a doping impurity element on the surface of a semiconductor substrate at a temperature of about 700 to 1000 ° C. . At this time, the thickness of the reverse conductivity type semiconductor region is about 0.2 to 1 μm, and this can be set to a desired thickness by adjusting the diffusion temperature and the diffusion time.
JP 2004-356361 A

At this time, it is considered that the thickness of the reverse conductivity type semiconductor region is affected by a natural oxide film grown on the surface of the semiconductor substrate. In the diffusion of doping impurities, generally, as a vapor phase diffusion method, POCl ₃ (phosphorus oxychloride) is flowed using a carrier gas while heating in a container in which a semiconductor substrate is placed, thereby forming a phosphorus impurity serving as a diffusion source of doping impurities. Glass is formed on the surface of the semiconductor substrate, and at the same time, thermal diffusion to the surface of the semiconductor substrate is performed. If a natural oxide film is formed on the semiconductor substrate at that time, the thermal diffusion is hindered and the natural oxide film is formed. Therefore, the film thickness varies, which affects the contact between the semiconductor substrate surface and the doping impurity gas, thermal diffusion, and the thickness of the reverse conductivity type semiconductor region cannot be adjusted to the desired thickness, and the reverse conductivity type inside the substrate surface. It is difficult to form the semiconductor region uniformly.

  When the reverse conductivity type semiconductor region formed inside the semiconductor substrate is non-uniform, the junction depth inside the semiconductor substrate becomes non-uniform, and an increase in short-circuit current (Isc) due to the arrival of light is not expected in part. . As a result, the power generation efficiency from the entire surface of the substrate is lowered.

As described above, in the conventional manufacturing method, the semiconductor substrate is left in the atmosphere before the diffusion of the doping impurities, so that a non-uniform natural oxide film is grown on the substrate surface. It is thought that the generation efficiency was lost due to the uneven depth. In order to solve the above problem, a thermal oxidation treatment is performed to form an oxide film having a thickness of 5 to 50 nm on the surface of the semiconductor substrate, and then a homogeneous reverse conductivity type semiconductor region is formed on the semiconductor substrate by vapor phase diffusion. Is disclosed. (For example, see Patent Document 1)
However, in the solar cell element produced using the above method, sufficient improvement in element characteristics was not observed.

  This invention is made | formed in view of the problem of such a prior art, and it aims at providing the manufacturing method for obtaining a solar cell element stably high output.

  In order to achieve the above object, a method for manufacturing a solar cell element according to the present invention includes a step of immersing a semiconductor substrate exhibiting one conductivity type in a solution containing ozone, and a step of the semiconductor substrate lifted from the solution. Forming a reverse conductivity type region having a conductivity type opposite to the one conductivity type at least partially.

  Moreover, the manufacturing method of the other solar cell element of this invention further has the process of forming many unevenness | corrugations in one main surface of the said semiconductor substrate, It is characterized by the above-mentioned.

  Moreover, the manufacturing method of the other solar cell element of this invention is a process of etching the said unevenness | corrugation formation process and the said semiconductor substrate in which the unevenness | corrugation was formed by this process in a hydrofluoric acid solution prior to the said immersion process. It is characterized by performing.

  Moreover, the manufacturing method of the other solar cell element of this invention is characterized by the said solution using water as a solvent.

  In another method for manufacturing a solar cell element of the present invention, the reverse conductivity type region is formed by a diffusion method using a predetermined doping element.

  Furthermore, in another method for manufacturing a solar cell element of the present invention, the reverse conductivity type region is formed at a peak temperature of 700 ° C. or more and 1000 ° C. or less.

  According to the method for manufacturing a solar cell element of the present invention, a step of immersing a semiconductor substrate showing one conductivity type in a solution containing ozone, and at least a part of the semiconductor substrate lifted from the solution, Forming a reverse conductivity type region showing a conductivity type opposite to the one conductivity type, and forming a dense and uniform oxide film on the surface of the semiconductor substrate by an immersion process in an ozone solution. By forming the reverse conductivity type region, it is possible to make the depth of the reverse conductivity type region uniform and thereby to increase the short-circuit current of the solar cell element.

  According to another method of manufacturing a solar cell element of the present invention, the method further includes the step of forming a number of irregularities on one main surface of the semiconductor substrate. On the other hand, in particular, it is possible to effectively control the uniform depth of the reverse conductivity type region.

  Further, according to another method for manufacturing a solar cell element of the present invention, the concavo-convex forming step and the step of etching the semiconductor substrate on which the concavo-convex has been formed in the hydrofluoric acid solution are included in the dipping step. By performing the process in advance, it is possible to improve the uniformity of the ozone oxide film by removing impurities on the surface of the semiconductor substrate in the hydrofluoric acid solution, and to effectively make the semiconductor substrate hydrophobized in the hydrofluoric acid solution. By making it hydrophilic, drainage can be improved and formation of a watermark can be suppressed.

  Moreover, according to the manufacturing method of the other solar cell element of this invention, the said solution can aim at reduction of solution cost by using water as a solvent.

  In addition, according to another method of manufacturing a solar cell element of the present invention, the reverse conductivity type region is formed by a vapor phase diffusion method using a predetermined doping element, so that a large amount of semiconductors are formed at a time. The substrate can be processed, the in-plane variation of the semiconductor substrate is suppressed, and the depth uniformity of the reverse conductivity type region can be easily controlled.

  Furthermore, according to another method for manufacturing a solar cell element of the present invention, the reverse conductivity type region is formed at a peak temperature of 700 ° C. or more and 1000 ° C. or less, so that the depth of the reverse conductivity type region is increased. Can be optimized, and the uniformity can be controlled more easily.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a structural diagram of a solar cell element formed by the method for manufacturing a solar cell element according to the present invention. In FIG. 1, 1 is a semiconductor substrate, 2 is a reverse conductivity type semiconductor region, 3 is an uneven structure, 4 is an antireflection film, 5 is a P ⁺ region (BSF: Back Surface Field) on the back side, 6 is a surface electrode, 7 Denotes a back electrode, 7a denotes an output extraction electrode, and 7b denotes a current collecting electrode.

  In the present invention, a polycrystalline silicon substrate has been described as an example, but any type of bulk solar cell using a crystalline substrate may be used.

  The semiconductor substrate 1 may be either p-type or n-type, but here, for convenience, a p-type semiconductor silicon substrate containing B (boron) as a doping impurity element will be described.

  An example of a method for forming a solar cell element according to the present invention is shown in the flowchart of FIG.

  First, the semiconductor substrate 1 is formed in a semiconductor substrate forming process for forming a semiconductor substrate. As the ingot for cutting out the substrate, a single crystal silicon ingot made by a method such as the CZ method, the FZ method, or the EFG method, or a polycrystalline silicon ingot cast by a cast method can be used. Polycrystalline silicon can be mass-produced and is extremely advantageous over single-crystal silicon in terms of manufacturing cost.

  The formed ingot is cut into a size of about 10 cm × 10 cm or 25 cm × 25 cm by the above-described method, and sliced with a wire saw or the like to a thickness of 300 μm or less, more preferably 200 μm or less, to obtain a semiconductor substrate 1. be able to. Further, in order to clean the mechanical damage layer and the contamination layer on the cut or sliced surface, it is desirable that the surface is etched by a very small amount with NaOH, KOH, hydrofluoric acid, or hydrofluoric acid.

  The semiconductor substrate 1 may be doped by adding an appropriate amount of a doping impurity element at the time of manufacturing the ingot, or adding an appropriate amount of an additional semiconductor material whose doping concentration is already known in the same material as the semiconductor substrate 1. These may be melted to form a semiconductor ingot having a predetermined dope concentration.

  Next, in order not to reflect sunlight, a roughening process for forming a concavo-convex structure on the surface of the semiconductor substrate, the concavo-convex for effectively capturing incident light on the surface side of the semiconductor substrate 1 without reflecting it. Structure 3 is formed. As a forming method, a dry etching method such as RIE or a wet etching method such as NaOH is used.

  Next, the oxide film is removed from the semiconductor substrate 1 by a first oxide film removal step for removing the natural oxide film formed on the surface of the semiconductor substrate. In particular, since the fine uneven structure 3 has a large surface area, a natural oxide film is easily formed on the surface. By removing this, a semiconductor junction layer can be formed on a clean surface in the reverse-conductivity-type semiconductor region forming step, which is a subsequent step, and the characteristics of the solar cell element are improved.

  Further, this oxide film removing step is a solution containing hydrofluoric acid, for example, an aqueous solution of 0.1 to 50% by weight hydrofluoric acid, or a mixed acid (hydrofluoric acid and nitric acid are mixed at a ratio of 1:10, for example. It is desirable that the wet etching process be performed by a method. Thus, in the oxide film removal step, if a solution containing hydrofluoric acid is used, the silicon oxide film can be efficiently removed particularly in a silicon-based solar cell.

  In the present invention, after the first oxide film removing step, in the step of immersing in the ozone solution to form a forced oxide film by immersing the semiconductor substrate in a solution such as water or organic solvent in which ozone is dissolved. A forced oxide film is formed. The ozone dissolved in the dipping solution is preferably 1 ppm or more and 30 ppm or less, and a desired oxide film can be formed by dipping for a short time of several seconds and 1 minute or less. If the dissolved ozone concentration is higher than the above range, the influence of the self-decomposition of ozone is great, and it is difficult to make the dissolved ozone concentration constant in the solution. Absent. By immersing in an aqueous solution in which ozone is dissolved, the oxide film can be formed in a thickness of 15 to 40 mm in a short time.

  Thereafter, as a reverse conductivity type semiconductor forming step for forming a PN junction, reverse conductivity is provided on one main surface side of the semiconductor substrate 1 having one conductivity type, that is, on the same surface side as the above-described fine uneven structure 3 is provided. A type semiconductor region 2 is formed.

  A dense and uniform oxide film is formed on the surface of the semiconductor substrate by an immersion process in an ozone solution, and then the reverse conductivity type region is formed to make the depth of the reverse conductivity type region uniform. An increase in the short-circuit current can be achieved.

  In addition, it is possible to effectively control the uniformization of the depth of the reverse conductivity type region, particularly for the semiconductor substrate on which the unevenness is formed in the roughening step.

  Further, the step of forming the unevenness and the step of etching the semiconductor substrate on which the unevenness has been formed by the step in a hydrofluoric acid solution are performed prior to the dipping step. By removing impurities on the substrate surface, the uniformity of the ozone oxide film can be improved, and the drainage can be improved by effectively hydrophilizing the semiconductor substrate hydrophobized in the hydrofluoric acid solution.

This reverse conductivity type semiconductor region 2 is generally formed as a method of vapor phase diffusion by doping POCl ₃ (phosphorus oxychloride) with a carrier gas while heating it in a container in which the semiconductor substrate 1 is installed. Phosphorous glass serving as a diffusion source is formed on the surface of the semiconductor substrate 1 and, at the same time, thermal diffusion to the surface of the semiconductor substrate 1 is also performed.

  Since the reverse conductivity type region is formed by a vapor phase diffusion method using a predetermined doping element, it becomes easy to control the uniformity of the depth of the reverse conductivity type region.

When a thermal diffusion method using POCl ₃ as a diffusion source is used, for example, the reverse conductivity type semiconductor region 2 is formed by diffusing a doping impurity element on the surface of the semiconductor substrate 1 at a temperature of about 700 to 1000 ° C. Can do. At this time, the thickness of the reverse conductivity type semiconductor region is about 0.2 to 1 μm, and this can be set to a desired thickness by adjusting the diffusion temperature and the diffusion time.

  The reverse conductivity type region is formed at a peak temperature of 700 ° C. or more and 1000 ° C. or less in the vapor phase diffusion method, thereby making it easier to control the uniformity of the depth of the reverse conductivity type region.

  In order to make the oxide film formation according to the present invention more effective, the diffusion condition may be controlled so that the power generation efficiency is optimized for the thickness of the reverse conductivity type semiconductor region.

In a normal diffusion method, a diffusion region is also formed on the surface opposite to the target surface and the edge portion of the substrate, but this portion may be etched later or removed by a laser or the like. Alternatively, as will be described later, when the P ⁺ region 5 on the back surface side is formed of an Al paste, Al having a high diffusion coefficient, which is a p-type doping impurity element, can be diffused to a sufficient concentration and a sufficient depth. Therefore, the influence of the already diffused shallow n-type reverse conductivity semiconductor region can be ignored.

  The sheet resistance on the surface side of the reverse conductivity type semiconductor region 2 is preferably about 60 to 300Ω / □. This value can be measured by the four probe method. That is, four metal needles arranged in a straight line are brought into contact with the surface of the semiconductor substrate 1 while being pressed, and a voltage generated between the two inner needles when a current is passed through the two outer needles. Measure the resistance value from this voltage and the flowing current according to Ohm's law.

  By setting the value of the sheet resistance to 60 to 300Ω / □, the short-circuit current when the solar cell is formed can be greatly increased. The reason is estimated as follows. First, when the fine concavo-convex structure 3 as described above is formed on the surface of the semiconductor substrate 1, the doping impurity element is diffused to the surface side of the semiconductor substrate 1 as compared with the case where such a concavo-convex structure 3 is not formed. The doping impurity element is deep and diffused in large quantities. Therefore, the semiconductor junction is formed in a deep place away from the surface of the semiconductor substrate 1, and light does not easily reach the semiconductor junction and the short-circuit current is not improved. As described above, when a large number of fine concavo-convex structures 3 are formed on the surface of the semiconductor substrate 1, if the sheet resistance value of the surface portion of the semiconductor substrate 1 is set to be higher than that of the conventional product, the semiconductor junction becomes a semiconductor. Since the substrate 1 is formed in a relatively shallow place, the short-circuit current value can be improved.

  However, when the sheet resistance value on the surface of the substrate is less than 60Ω / □, the short circuit current decreases, and when it exceeds 300Ω / □, it is difficult to uniformly diffuse the reverse conductivity type semiconductor impurities over the entire surface side of the semiconductor substrate 1. As a result, the power generation efficiency decreases.

  In the present invention, in a method of manufacturing a solar cell element in which a reverse conductivity type semiconductor region is formed on a one conductivity type semiconductor substrate, the semiconductor substrate is immersed in an aqueous solution in which ozone is dissolved, and then a doping impurity element is diffused into the semiconductor substrate. By doing so, a uniform reverse conductivity type semiconductor region can be formed, the short circuit current (Isc) is increased, and the power generation efficiency is increased.

  FIG. 3 shows the difference in oxide film thickness between when the semiconductor substrate is left in the normal atmosphere and when it is immersed in an aqueous solution in which 20 ppm of ozone is dissolved.

  This is because a silicon substrate was left in the atmosphere as a semiconductor substrate and a silicon substrate immersed in an aqueous solution in which 20 ppm of ozone was dissolved. The density transition region up to the SiN film is observed by the GI-XR method (total reflection X-ray diffraction analysis).

The X-ray irradiation range by the GI-XR method is 2 mmφ on the surface of the semiconductor substrate, and it is shown that a portion showing the density of SiO ₂ exists between the ranges where the densities of Si and SiN are different.

In the case of a sample left in the air, this SiO ₂ region is about 10 mm, which is presumed to be the presence of a natural oxide film. Moreover, the ozone aqueous solution immersion sample has a SiO ₂ region of about 15 to 20%, which is presumed to be caused by forced oxidation due to the ozone aqueous solution immersion.

In the natural standing sample, the density of SiO ₂ is slightly unclear and the transition region of SiO ₂ —SiN is also unclear, whereas in the sample immersed in an ozone solution, the density of SiO ₂ is clear. And the transition region of SiO ₂ —SiN is also reduced.

In a natural standing sample in which the SiO ₂ region is unclear, the boundary is not clear because there are a portion where SiO ₂ exists and a portion where SiO ₂ does not exist in the X-ray irradiation range ₂ mmφ by the GI-XR method. Moreover, the aspect in which the density gradually changes from SiO ₂ to SiN is the same reason.

In contrast, the sample immersed in the ozone solution clearly shows the SiO ₂ density, and the SiO ₂ —SiN transition layer is also small. This indicates that the oxide film by ozone exists more uniformly than the natural oxide film that exists unevenly.

  The presence of such a more uniform oxide film than the natural oxide film is more effective for the area of the semiconductor substrate.

  Further, in the oxide film formed by the thermal oxidation treatment, the short circuit current (Isc) was not increased and the power generation efficiency was not increased. This is not only the effect of removing organic substances on the substrate surface by immersing in an aqueous solution in which ozone is dissolved, but also the oxide film formed by the present invention and the oxide film formed by thermal oxidation treatment, It is believed that the film uniformity and film quality are different.

  Accordingly, a semiconductor substrate having an oxide film formed according to the present invention and a semiconductor substrate having an oxide film formed by thermal oxidation treatment are immersed in a tank filled with pure water so that the substrate surface is vertical. The wettability of water when pulled up was confirmed.

  In a semiconductor substrate having an oxide film formed according to the present invention, immediately after pulling, a water film is uniformly formed with the substrate surface completely wet, and then the water scrapes the surface water with gravity. Move to the bottom to take and dry from the top.

  In a semiconductor substrate having an oxide film formed by thermal oxidation treatment, partial drying occurs immediately after the pulling, and then there is a tendency to dry from the top, but it is sparsely dried.

  In addition, in order to evaluate wettability in a semiconductor substrate having an oxide film formed by the present invention and a semiconductor substrate having an oxide film formed by thermal oxidation treatment, contact angle instrument DM500R manufactured by Kyowa Interface Chemical Co., Ltd. When the contact angle when pure water (25 ° C.) is dropped is measured by the semiconductor substrate, the semiconductor substrate having the oxide film formed according to the present invention shows a considerable hydrophilicity of 15 degrees or less, more preferably 10 degrees or less. In the case of a semiconductor substrate having an oxide film formed by oxidation treatment, the temperature was 25 to 40 degrees.

  In this way, it can be inferred that the oxide film formed by immersing in an aqueous solution in which ozone is dissolved has a different film quality compared to the oxide film formed by thermal oxidation treatment, and a uniform and dense ultrathin film is formed. As a result, a more uniform reverse conductivity type semiconductor region can be formed, and the short circuit current (Isc) increases as element characteristics.

  Next, in the second oxide film removing step, the uniform oxide film formed before diffusion according to the present invention and the oxide film containing the impurity element obtained from the semiconductor substrate 1 by thermal diffusion or the like are removed. By removing the oxide film, it is possible to perform a necessary process on a clean surface in a subsequent process, for example, an antireflection film forming process or an electrode forming process. improves.

  Furthermore, in the method for manufacturing a solar cell element, the second oxide film removing step is similar to the first oxide film removing step in a solution containing hydrofluoric acid, for example, 0.1 to 50% by weight hydrofluoric acid. It is desirable that the wet etching process be performed using an aqueous solution of the above or a mixed acid (a mixture of hydrofluoric acid and nitric acid in a ratio of, for example, 1:10). In this way, in the oxide film removal step, if a solution containing hydrofluoric acid is used, the oxide film according to the present invention can be removed particularly efficiently.

  Then, the antireflection film 4 is formed on the surface side of the semiconductor substrate 1 in the antireflection film forming step of forming the antireflection film. The antireflection film 4 can be formed by plasma CVD, vapor deposition, sputtering, or the like. Usually, it is formed using a plasma CVD method.

As the material of the antireflection film 4, Si ₃ N ₄ film, TiO ₂ film, SiO ₂ film, MgO film, ITO film, SnO ₂ film, ZnO film, or the like can be used. In general, the Si ₃ N ₄ film is preferably used because it has passivation properties. As a raw material gas, a mixed gas of silane and ammonia is converted into plasma by RF or microwave to generate Si ₃ N ₄ for reflection. The prevention film 5 is formed.

Further, it is desirable to form the P ⁺ layer 5 on the back surface side of the semiconductor substrate 1 in a P ⁺ layer forming process for forming the P ⁺ layer 5 in which one conductivity type semiconductor impurity is diffused at a high concentration. B (boron) or Al (aluminum) can be used as the impurity element, and an ohmic contact can be obtained with the back electrode 7 described later by setting the impurity element concentration to a high concentration and p + type.

As a production method, a thermal diffusion method using BBr ₃ (boron tribromide) as a diffusion source is used and formed at a temperature of about 800 to 1100 ° C. Especially in the case of Al, an Al powder, an organic solvent, a binder, etc. A method in which the paste is applied by a printing method and then heat-treated (fired) at a temperature of about 700 to 850 ° C. to diffuse Al can be used. When the P ⁺ layer 5 is formed by the thermal diffusion method, it is desirable to previously form a diffusion barrier such as an oxide film in the reverse conductivity type semiconductor region 2 that has already been formed. If a method of printing and baking Al paste is used, a desired diffusion layer can be formed not only on the printed surface, but also on the back side simultaneously with the formation of the reverse conductivity type semiconductor region 2 as described above. It is not necessary to remove the n-type reverse conductivity type diffusion layer. Further, the fired Al can be used as it is as the collecting electrode 7b of the back electrode without removing it. The P ⁺ layer 5 forms an internal electric field on the back surface side of the semiconductor substrate 1 in order to prevent a decrease in efficiency due to carrier recombination near the back surface of the semiconductor substrate 1.

  On the front surface side and the back surface side of the semiconductor substrate 1, the front surface electrode 6 and the back surface electrode 7 are formed in an electrode forming process for forming the front surface electrode and the back surface electrode. These electrodes can be produced by using a thick film forming process such as a printing method using a paste containing a metal powder such as Ag, glass frit, an organic solvent or a binder, or a vacuum such as sputtering or vapor deposition. A film forming process using the process can be used.

The material of the surface electrode 6 is not particularly limited, but it is desirable to use a material containing at least one low-resistance metal such as Ag, Cu, or Al. Further, the material of the back electrode 7 is not particularly limited. However, when the silicon-based semiconductor substrate 1 is used, it is desirable to use a metal whose main component is Ag having a high reflectance with respect to silicon. These electrode materials are not limited to one type, and a plurality of materials can be laminated or mixed according to the purpose. Further, a metal containing Ag as a main component may be used for the output extraction electrode 7a, and a metal containing Al as a main component may be used for the collector electrode 7b.

  In addition, the electrode material pattern may be a pattern generally used for collecting current from the solar cell element, for example, a general comb pattern in the case of the surface electrode 6. Furthermore, the material and shape of the mask for making the electrode into a predetermined shape are not particularly limited, and any mask can be used as long as it does not significantly affect the internal atmosphere. From the viewpoint of the workability of the mask in accordance with the electrode pattern, it is easy to make it from metal.

  Thus, the solar cell element of the present invention is formed.

  It should be noted that the solar cell element produced as described above is usually a weather-resistant material in a state where a plurality of series and parallel electrical connections are made so that the required output voltage and output current can be obtained. It is covered with a solar cell module. For example, a light transmissive plate such as a glass plate or a synthetic resin plate is disposed on the light receiving surface of the solar cell element, and a film made of Teflon (registered trademark) (DuPont) or PVF (polyfluoride) is provided on the non-light receiving surface as the back surface. Weather resistant films such as vinyl chloride and PET (polyethylene terephthalate) are applied. A transparent synthetic resin made of, for example, EVA (ethylene-vinyl acetate copolymer resin) is interposed as a filler between the light transmission plate and the weather resistant film. Then, the light transmitting plate, the solar cell element, and the weatherproof film are stacked on the main body so as to sandwich the frame made of aluminum, SUS, or the like around each side, thereby increasing the strength of the entire solar cell module. It is increasing.

  Further, a plurality of such solar cell modules are arranged to form a solar cell array, and the electric power generated by the solar cell array is transmitted to an inverter for grid interconnection and supplied to a general AC load, or It is now possible to sell electricity to power companies through grid connection.

It should be noted that the embodiment of the present invention is not limited to the above-described example, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

  For example, in the above description, the structure in which the electrodes are formed on both main surface sides has been described, but a back contact structure in which the output extraction electrode is provided only on the non-light receiving surface side may be used.

(Example)
The damaged layer on the surface of the p-type semiconductor substrate 1 of polycrystalline silicon having a thickness of 250 μm and an outer shape of 15 cm × 15 cm was etched and washed with NaOH. Next, a fine concavo-convex structure 3 was formed on the substrate surface by a dry etching method using RIE. Then, before the diffusion of the doping impurities, as an example, it was immersed in an aqueous solution in which 20 ppm of ozone was dissolved for 30 seconds. Further, as Comparative Example 1, the next diffusion was performed without any treatment, and as Comparative Example 2, the semiconductor substrate was heated at 900 ° C. for 60 minutes in an oxygen atmosphere. Each semiconductor substrate 1 is placed in a diffusion furnace and heated in phosphorus oxychloride (POCl ₃ ) to diffuse phosphorus atoms on the surface of the semiconductor substrate 1, and the sheet resistance is 60 Ω / □. An n-type reverse conductivity type semiconductor region 2 was formed. A silicon nitride film to be the antireflection film 4 was formed thereon by plasma CVD.

Then, an aluminum paste was applied to the entire back side and heated to form a P ⁺ layer and a collecting electrode 7b for the back electrode 7.

  Silver paste was applied to the front side and the back side of the semiconductor substrate 1 and heated to form output extraction electrodes for the front electrode 6 and the back electrode 7. The surface electrode 6 was formed to have a comb pattern.

Element characteristics were measured for each of the 50 solar cell elements obtained by the above method, and the results of the average values for each condition are shown in Table 1.

  As shown in Table 1, the effect of the present invention is clear, and Comparative Example 2 shows a slightly higher value than the short-circuit current of Comparative Example 1. It was confirmed that the increase of

It is a figure which shows the solar cell element sectional structure concerning this invention. The flowchart of an example of the formation method of the solar cell element concerning this invention is shown. Si on a semiconductor substrate according to GI-XR analysis according to the present invention, showing the density transition of SiO 2, _SiN.

Explanation of symbols

1: Semiconductor substrate 2: Reverse conductivity type semiconductor region 3: Uneven structure 4: Antireflection film 5: P ⁺ region 6: Front electrode 7: Back electrode 7a: Output extraction electrode 7b: Current collecting electrode

Claims (6)

Immersing a semiconductor substrate having one conductivity type in a solution containing ozone to oxidize the surface of the semiconductor substrate;
Forming a reverse conductivity type region having a conductivity type opposite to the one conductivity type on at least a part of the semiconductor substrate drawn from the solution.   The method for manufacturing a solar cell element according to claim 1, further comprising a step of forming a large number of irregularities on one main surface of the semiconductor substrate.   3. The solar cell element according to claim 2, wherein the unevenness forming step and the step of etching the semiconductor substrate on which the unevenness is formed by the step in a hydrofluoric acid solution are performed prior to the dipping step. Manufacturing method.   4. The method for manufacturing a solar cell element according to claim 1, wherein the solution uses water as a solvent.   The method for manufacturing a solar cell element according to claim 1, wherein the reverse conductivity type region is formed by a vapor phase diffusion method using a predetermined doping element.   The method for manufacturing a solar cell element according to claim 5, wherein the reverse conductivity type region is formed at a peak temperature of 700 ° C. or more and 1,000 ° C. or less.

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