JPH11220146A - Manufacture of solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a rough surface shape to effectively confine light by etching an Si substrate having a rough surface formed by the mechanical slicing, using a water soln. contg. an alkali hydroxide in a specified concentration range. SOLUTION: An Si substrate having a rough surface formed by the mechanical slicing is etched, using a water soln. contg. an alkali hydroxide 0.25-3.0 mol/l. This method specifies an optimum alkali hydroxide concn., hence a surface layer part damaged by the slice step is removed and the rough shape formed by the slice step can be left. If it is either a single crystal Si or polycrystalline Si, a fine irregularity can be formed on the substrate surface. Accordingly the solar cell more absorbs the light to improve the performance. The etching for removing contaminants and that for forming the rough shape are made at once and the treating process can be lessened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a high-efficiency solar cell, and more particularly to a method effective for increasing the efficiency of a polycrystalline silicon solar cell.

[0002]

2. Description of the Related Art First, an example of a conventional solar cell manufacturing process will be described with reference to the drawings. (A) to (h) of FIG. 8 are views showing a general manufacturing process of a conventional solar cell (process flow). In the process flow of FIGS. 8A to 8H, 1 is a p-type Si substrate as a semiconductor substrate,
2 is an n-type diffusion layer, 3 is an aluminum paste electrode, 4 is p
^{The +} layer, 5 is a front surface silver paste electrode, 6 is a back surface silver paste electrode, 7 is damage to the substrate surface and contamination in the wafer slicing process, and 8 is an uneven shape formed on the surface.

FIG. 8A shows a substrate that has been sliced from an ingot. In the case of a solar cell, since a substrate that has been sliced from an ingot is often used, the substrate has substrate surface damage due to scratches such as an ID saw or a wire saw used for slicing and contamination 7 in a wafer slicing process.

Therefore, the step shown in FIG. 8B is a step for removing substrate surface damage due to scratches of a wire saw or the like used for these slices and contamination 7 in the wafer slice step. When this portion remains, the entire substrate does not function sufficiently as a semiconductor crystal. In order for the solar cell, which is a semiconductor device, to function effectively, the damaged portion needs to be removed. By this primary etching, about 10 to 20 μm
To the extent, the substrate surface is etched.

[0005] Open-circuit voltage (Voc) is a characteristic of a solar cell that can be used to determine the surface damage and the state of removal of contamination 7 in the wafer slicing process. This is the voltage when nothing is connected between the positive and negative electrodes of the solar cell. It is known that if the surface damage and the removal of the contamination 7 in the wafer slicing step are insufficient, the Voc decreases.

[0008] Subsequently, a step (c) of FIG. 8 is a step for forming the irregularities 8 on the surface (light receiving surface) of the solar cell. Due to this uneven shape 8, even light that escapes to the outside by one reflection if it is a normal flat light receiving surface,
The inclined surface can be reflected several times and introduced into the inside of the substrate. As a result, more light can be absorbed inside the solar cell, and the characteristics of the solar cell are improved.
The short-circuit photocurrent density (Js
There is a characteristic of the solar cell referred to as c). This connects the positive and negative electrodes of the solar cell with conducting wires while sunlight is incident,
This is the value obtained by dividing the current in the short-circuited state by the area of the solar cell. The larger the value of Jsc, the more light is absorbed inside the solar cell, and the above-mentioned uneven shape 8 is formed more efficiently.
Generally, by performing the step (c) in FIG. 8, for example, when a (100) single crystal silicon
Jsc can be improved by about 10%.

Next, in FIG. 8D, for example, phosphorus (P) is thermally diffused to form an n-type diffusion layer 2 whose conductivity type is inverted. Usually, phosphorus oxychloride (POCl ₃ ) is often used as a phosphorus diffusion source. Unless otherwise devised, the n-type diffusion layer is made of p-type Si.
It is formed on the entire surface of the substrate 1. The n-type diffusion layer 2 has a thickness of about several tens Ω / □, and the depth of the diffusion layer is about 0.3 to 0.5 μm.

Although not described in detail, the n-type diffusion layer 2 is protected by protecting one side with, for example, a resist, and then etched so as to leave the n-type diffusion layer 2 only on one main surface as shown in FIG. After removal, the resist is removed using an organic solvent or the like.

Thereafter, an aluminum paste electrode 3 is printed on the opposite surface of the n-type diffusion layer 2 in FIG. 8E by, for example, a screen printing method (or a roll coater method) as shown in FIG. 8F. As shown in FIG.
By baking in a furnace at 900 ° C. for several minutes to several tens minutes, aluminum is diffused as impurities from the aluminum paste into the p-type Si substrate, and the p ⁺ layer 4 containing high-concentration impurities is formed. This layer is generally made of BSF (Back Surfac)
e Field) layer, which contributes to the improvement of the energy conversion efficiency of the solar cell. Although not shown in FIG. 8 for simplicity, an antireflection film may be provided on the surface of the n-type diffusion layer thereafter.

Thereafter, as shown in FIG. 8 (h), silver paste electrodes 5 and 6 are printed on the front surface (light receiving surface) and the back surface, and firing is performed again to complete the solar cell. It is also possible to omit the firing step of FIG. 8 (g) for simplification of the process, and to complete the solar cell by one firing after FIG. 8 (h).

The step shown in FIG. 8C is related to the present invention and will be described in more detail here. In general, in silicon solar cells, it is indispensable to increase the efficiency of the solar cell by efficiently forming the unevenness on the surface and efficiently taking in the incident light from the surface, and various methods have been proposed so far. . The methods can be roughly classified into (1) mechanical methods and (2) chemical methods.
Hereinafter, these methods will be described in order.

(1) Mechanical method A first example is a method disclosed in Japanese Patent Publication No. Hei 7-105518, in which the surface of a polycrystalline silicon solar cell is mechanically V-shaped.
A groove is formed to form an uneven shape. FIG. 9 shows a cross-sectional structure formed by this example. The second example is 9th Int
national Photovoltaic Sc
issue and Engineering Con
RIE (Re)
A viramid-like structure is formed on the surface of the polycrystalline silicon solar cell by an etching method called active ion etching. FIG. 10 shows a micrograph of the concavo-convex shape formed by RIE.

The details of the above two examples will be described below. In the mechanical V-groove forming method of the first example, a plurality of rotary blades having a tip embedded with a material having a hardness higher than silicon such as diamond and silicon carbide are pressed against the substrate and run to form a V-shaped substrate surface. Shape the groove. The pitch of the V-groove is adjusted depending on the interval between the blades, but is generally about several hundreds of μm, and the depth of the V-groove is about several tens of μm. After the grooves are mechanically formed in this manner, the substrate is immersed in a solution capable of etching silicon, such as an aqueous alkaline solution, and a crystal defect layer generated at a contact portion with the blade is removed by machining. In the unevenness forming method by RIE of the second example, a process is performed by reacting silicon with chlorine ions and chlorine radicals generated by plasma under reduced pressure using chlorine gas as an etching gas and evaporating and removing silicon as chloride. The formation mechanism of the uneven shape is not disclosed because it is not disclosed, but since the etching is performed without an etching mask, a part of silicon chloride as a reaction product remains on the surface, and this residual It is presumed that a columnar projection is formed using the object as a micromask. After forming the uneven shape on the surface in this way, it is considered that the substrate is subjected to a series of treatments by removing products and the like remaining on the surface by wet cleaning.

(2) Chemical Method A third example is Progress in Photovolt
aics: Research and Applica
tions, Vol. 4,435-438 (1996)
In this method, an uneven shape (texture structure) is formed on the substrate surface by wet etching using a mixed aqueous solution of sodium hydroxide and isopropyl alcohol. Details will be described below. In the wet etching using an alkali aqueous solution such as sodium hydroxide or potassium hydroxide in the third example, a fine pyramid structure (quadrangular pyramid) called a texture structure is formed on the surface of the solar cell (light receiving surface).
Can be formed. This technique utilizes a difference in etching rate between crystal planes of a silicon crystal. That is, the etching rate by the alkaline aqueous solution is the fastest on the (100) plane of the silicon crystal and the slowest on the (111) plane. For this reason, when the above etching is performed on the (100) single crystal silicon substrate, (11)
1) When a surface is generated, the etching rate is low (111)
The surface will remain preferentially. At the final stage of the process, it is a plane equivalent to the (111) plane.

[0015]

(Equation 1)

A quadrangular pyramid-shaped projection composed of only these elements is formed, and finally these planes have an inclination of 54.7 degrees with respect to the (100) plane. As a specific treatment method disclosed, 10 vol% isopropyl alcohol is added to an aqueous solution of about 0.5 mol / l of sodium hydroxide added to 80 ° C., and 15% is applied to a mirror-finished (100) silicon substrate. Minute etching.

[0017]

SUMMARY OF THE INVENTION In the prior art,
In the method of mechanically forming the V-shaped groove shown in the first example, the processing must be performed for each wafer, and there is a problem in mass productivity. Moreover, since defects are formed in the surface layer of the crystal when the V-groove is formed, a step of removing the defective portion by wet etching after the formation of the V-groove is required. Furthermore, since the pitch of the V-groove is limited by the pitch of the rotating blade, grooves cannot be formed at minute intervals, and a deep groove must be formed in order to obtain an effective light confinement effect. Substrates are going to be thinner in order to reduce material costs,
Due to the deep grooves, problems occur such that cracks occur in the substrate and breakage occurs during the process. In the method by RIE shown in the second example, the problem of crystal defects can be avoided as in the case of V-groove formation. There is a problem that it is inferior. Finally, the method by wet etching using an alkaline aqueous solution and alcohols shown in the third example is a method of forming a quadrangular pyramid structure for a substrate having various crystal orientations in a plane such as polycrystalline silicon. Are formed perpendicularly to the (100) plane, and the planes appearing on the surface are oriented in random directions, so that a sufficient light confinement effect cannot be obtained as obtained by a single crystal. When isopropyl alcohol is added to the 0.5 mol / l potassium hydroxide aqueous solution heated to 80 ° C. shown in the above specific example, it takes about 15 minutes to stably form the texture structure on the single crystal silicon substrate. It shows that processing time is required. In addition, as a result of additional tests by the present inventors, a sufficient light confinement effect could not be obtained unless a longer treatment (30 to 60 minutes) was performed. As described above, this method has a problem that the processing time is long and the method is not necessarily high in productivity, and that isopropyl alcohol which is a dangerous substance must be used in a large amount (10 vol% or more).

The present invention solves the conventional problems as described above, and it is possible to form a concavo-convex shape for making light confinement effective by practical means, thereby realizing simplification of the process and reduction in cost. It is an object of the present invention to provide a method for manufacturing a solar cell that can be used.

[0019]

The invention according to claim 1 is
For the Si substrate having a rough surface formed by slicing by mechanical processing, in order to mainly remove the surface layer portion damaged in the slicing step and leave the concavo-convex shape formed in the slicing step , 0.25-3.
An object of the present invention is to provide a method for manufacturing a solar cell, wherein etching is performed using an aqueous solution containing 0 mol / l alkali hydroxide. The invention according to claim 2 is claim 1
The method according to claim 1, further comprising, after the first etching described in (1), mainly for forming an uneven structure that makes light confinement more effective and performing etching to further remove a surface layer portion damaged in a slicing step by machining. It is intended to provide a method for manufacturing a solar cell, wherein the second etching is performed at an alkali hydroxide concentration lower than the described alkali hydroxide concentration. The invention according to claim 3 is the solar cell according to claim 2, wherein the alkali hydroxide concentration of the aqueous solution containing alkali hydroxide in the second etching corresponds to 10 to 50% of the alkali hydroxide concentration in the first etching. A method for manufacturing a battery is provided. The invention according to claim 4 is a solar cell in which the concentration of alkali hydroxide in the aqueous solution containing alkali hydroxide used for the second etching according to claim 3 is particularly in the range of 0.16 to 0.80 mol / l. Is provided. The invention according to claim 5 is the method according to any one of claims 2 to 4, wherein isopropyl alcohol is added to the aqueous solution containing alkali hydroxide used for the second etching at a rate of 1 vol% or more and less than 10 vol%. It is intended to provide a method for manufacturing a solar cell. The invention according to claim 6 is characterized in that as the alkali hydroxide, at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and cesium hydroxide is used. It is intended to provide a method for producing the solar cell described in the section.

[0020]

According to the manufacturing method of the present invention, fine irregularities can be formed on the substrate surface of either single-crystal silicon or polycrystalline silicon, so that light is better absorbed by the solar cell, Performance can be improved. Further, according to this method, etching for removing substrate surface damage and contamination in the wafer slicing process due to scratches of a wire saw or the like used for slicing and etching for forming irregularities can be performed at the same time, thereby reducing the number of processing steps. be able to. As a result, a large number of substrates can be processed in a short time and at low cost.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 The substrate used is
It is called “As Slice polycrystalline silicon substrate”
After being cut out from the polycrystalline silicon ingot by machining such as a wire saw, a silicon polycrystalline substrate to which no treatment was applied was used. This is because, for example, a polycrystalline silicon ingot is multi-wire sawed with a wire diameter of 0.18 mmφ and a wire speed (one-way feed) of 50.
The wafer was cut to a thickness of about 350 μm using # 800 SiC abrasive grains of 0 to 700 m / min, and the average surface roughness Ra was about 6 to 8 μm.

Next, using an aqueous solution having three different sodium hydroxide concentrations (0.25, 0.50, 5.83 mol / l), the as-
The surface of the sliced polycrystalline silicon substrate was etched.
The processing temperature was 90 ° C. In addition, 5.83 mol / l
The relatively high concentration of sodium hydroxide near or above is well known as the concentration of alkaline etchants applied to remove surface damage and contamination in the wafer slicing process.

Thereafter, the steps of (d) to (h) of FIG. 8 described in the section of the prior art are performed to produce a solar cell, and the open-circuit voltage (Voc) and the short-circuit current density (Jsc) are evaluated. went. As described in the prior art section, Voc is a property related to whether or not surface damage and contamination in the wafer slicing process have been removed, and Jsc is a property related to how the surface irregularities are formed.

First, FIG. 1 shows the dependence of Voc on the concentration of sodium hydroxide and the dependence on the etching depth. From this, by performing etching of about 5 to 10 μm or more, Voc is saturated at about 0.6V. From this, surface damage and contamination in the wafer slicing process are about 5 to 1
It can be seen that it can be removed by etching of 0 μm or more.

Next, FIG. 2 shows the dependency of Jsc on the concentration of sodium hydroxide and the dependency on the etching depth. FIG. 2 shows, as a comparison, a sodium hydroxide concentration of 5.83 mol /
0.16mol heated to 90 ° C after treatment with 1 l aqueous solution
/ 15% by volume of isopropyl alcohol in an aqueous alkaline solution of about / l, and etching for 30 minutes,
The Jsc of the solar cell having an uneven shape (texture structure) on the surface is also plotted (shown by a black circle). 2, short-circuit current density (J) of a solar cell etched using an aqueous solution having a sodium hydroxide concentration of 0.25 mol / l (indicated by Δ) and 0.50 mol / l (indicated by □)
sc) is about 0.2 times lower than Jsc (shown by ○) treated with an aqueous solution having a sodium hydroxide concentration of 5.83 mol / l.
~ 1.0 mA / cm ² higher value is obtained. In addition, it can be seen that, when compared with the case where the uneven shape is formed after treatment with the aqueous solution having a sodium hydroxide concentration of 5.83 mol / l (indicated by black circles), the same level is obtained.

The above experimental results show that when etching is performed using an aqueous solution having a sodium hydroxide concentration of 0.25 and 0.50 mol / l, “damage removal of substrate surface + texture structure formation” can be performed simultaneously. ing.
In other words, using the process flow of FIG. 8 shown in the prior art, the process of FIG. 8B and FIG. 8C can be combined into one.

In order to investigate the cause of the increase in Jsc, evaluation was performed using an electron microscope. The surface of the as-sliced polycrystalline plate is shown in FIG. Next, FIG. 4A shows the case where the surface of the substrate after the etching treatment was etched around 10 μm using an aqueous solution having a sodium hydroxide concentration of 0.25 mol / l, and FIG. (B),
The case of 5.83 mol / l is shown in FIG. FIG.
From (a) to (c), even if the etching is the same at about 10 μm, the sodium hydroxide concentration is 5.83 mol / l.
It was found that the surface treated with 0.50 and 0.25 mol / l turned into a large number of fine terraces, whereas the flat surface portion was greatly expanded on the surface treated with. Although FIGS. 4A to 4C show a part of the substrate, it has been confirmed that this tendency is observed over almost all regions.

Sodium hydroxide concentration 0.50, 0.25
The reason why a large number of fine terraces were generated on the surface when the etching treatment was performed with an aqueous solution of mol / l is considered to be caused by the as-sliced polycrystalline substrate used. As shown in FIG. 3, the surface of the substrate after being cut out of the ingot by machining such as a wire saw is formed with fine irregularities and is rough.
It is considered that the aqueous solution having a sodium hydroxide concentration of 0.50 and 0.25 mol / l promotes the etching while maintaining the rough shape. Therefore, even in the case of a polycrystalline silicon substrate having various crystal orientations in the plane, if the surface is a rough as-sliced substrate, it is possible to form a good uneven shape over almost all regions in the plane. It turned out to be.

Further, the same experiment was conducted by expanding the range of the concentration of sodium hydroxide. The processing time was all four minutes. In this time, it is possible to remove surface damage and contamination in the wafer slicing process for all samples by about 5 to 10
An etching depth of at least μm was obtained. The processing temperature was 90 ° C. FIG. 5 shows the relationship between Jsc and the concentration of sodium hydroxide. The relationship showed such a tendency that Jsc had a maximum value in an aqueous solution having a sodium hydroxide concentration of about 3 mol / l. From the viewpoints of safety, material cost, waste liquid treatment cost, and the like, the concentration of the aqueous sodium hydroxide solution is preferably low. Therefore, it has been found that it is optimal to use an aqueous solution in which the Jsc is higher than before and the concentration of sodium hydroxide, which is a low concentration region, is 0.25 to 3 mol / l.

Embodiment 2 FIG. Embodiment 1 FIG. In addition to the processing shown in, a two-step etching was performed by further etching. First, Embodiment 1. As shown in, the aqueous solution having a sodium hydroxide concentration of 1.67 mol / l
"As slice polycrystalline silicon substrate" at 90 ° C, 4
Soaked for minutes. Then, the sodium hydroxide was 0.16mo
l / l, 3.85 isopropyl alcohol (IPA)
It was immersed in an aqueous solution containing 10% by volume for 9 minutes at 90 ° C. Then, after performing the above-described steps (d) to (h) in FIG. 8 to fabricate a solar cell, the short-circuit photocurrent density (Jsc) was evaluated. The Jsc (indicated by a black circle) of the two-step etching according to the present embodiment is described in the first embodiment. It is shown in FIG. 6 together with Jsc (shown by た) of single etching shown by. Note that the Jsc of the single etching in FIG. Are not the same as the values in FIG. As can be seen from FIG. 6, the two-stage etching according to the present embodiment enables the embodiment 1. In addition to the Jsc improvement effect obtained by
It was found that the Jsc of cm ² could be improved.

On the other hand, when the concentration of sodium hydroxide is 1.67 m
After immersing the “as-sliced polycrystalline silicon substrate” in an aqueous solution of 90.degree. When immersed at 9 ° C. for 9 minutes, Jsc decreased. Further experiments revealed that the concentration of alkali hydroxide in the first etching was 0.25 to 3.0 mol / l.
Within the range, when “concentration of sodium hydroxide in first etching”> “concentration of sodium hydroxide in second etching”, “Jsc of two-step etching”> “Jsc of first etching” is improved, When “concentration of sodium hydroxide in first etching” <“concentration of sodium hydroxide in second etching”, “Jsc of two-step etching” <Jsc of the first etching may be reduced. Do you get it.

In the second etching, IPA
Experiments with varying amounts were also performed. As a result, IPA is 10
When the content is more than vol%, the etching rate is extremely reduced, so that it is not suitable for mass production. Even if etching is performed without adding IPA, an improvement in Jsc can be expected. The effect is reduced, for example, the effect is reduced to about half as compared with the case where IPA is 3.85 vol%.)

Next, the same experiment was performed by changing the concentration of sodium hydroxide in the second etching. Using an aqueous solution containing 1.67 mol / l of sodium hydroxide, the first etching was performed at a processing temperature of 90 ° C. for 4 minutes, and then the second etching was performed. The processing time for the second etching was 9 minutes in all, and the processing temperature was 90 ° C. (containing 3.85 vol% of IPA). Jsc,
FIG. 7 shows the relationship between the concentrations of sodium hydroxide. The relationship is that the sodium hydroxide concentration is about 0.80 mol / l
Jsc tended to take the maximum value in the aqueous solution of (1).
From the viewpoints of safety, material cost, waste liquid treatment cost, and the like, the concentration of the aqueous sodium hydroxide solution is preferably low. Therefore, the effect of improving Jsc is obtained, and the concentration of sodium hydroxide, which is a low concentration region, is 0.16 to 0.80 mo.
It has been found optimal to use a 1 / l aqueous solution for the second etching.

Further, a similar experiment was conducted in the case where the concentration of sodium hydroxide in the first etching was in the range of 0.25 to 3.0 mol / l. The optimum concentration of sodium hydroxide in the second etching was as follows. It turned out to be relevant. [Optimal sodium hydroxide concentration in the second etching] = [Sodium hydroxide concentration in the first etching × 0.1] to [Sodium hydroxide concentration in the first etching × 0.5]

The first embodiment described above. And 2. Has mainly described an as-sliced polycrystalline silicon substrate. However, as-sliced single-crystal substrates, particularly (10)
0) Needless to say, the present invention can be applied to a substrate. In the above-described embodiment, sodium hydroxide is mainly described. However, even if potassium hydroxide or cesium hydroxide is used as another alkali metal, sodium hydroxide, potassium hydroxide, or cesium hydroxide may be used. It goes without saying that the invention can be applied even if one or more types are used.

[0036]

According to the first aspect of the present invention, Si having a rough surface formed by slicing by machining is provided.
In order to remove the surface layer portion mainly damaged in the slicing step and leave the concavo-convex shape formed in the slicing step on the substrate, 0.25 to 3.0 mol is used.
Since the etching is performed using an aqueous solution containing an alkali hydroxide of 1 / l, that is, the optimum alkali hydroxide concentration is specified, fine irregularities can be formed on the substrate surface, and the production of a solar cell having a high light confinement effect can be achieved. Obtained by a method with high mass productivity.

According to the second aspect of the present invention, following the first etching, formation of a concavo-convex structure mainly for making light confinement more effective, and a surface layer portion damaged by a slicing step by machining are further performed. Since the second etching is performed with an alkali hydroxide concentration lower than the alkali hydroxide concentration according to claim 1 in order to perform the etching for removing, the unevenness of the substrate surface becomes more dense and the light confinement effect is enhanced. . As a result, a solar cell with higher efficiency can be obtained.

According to the third aspect of the present invention, the alkali hydroxide concentration of the aqueous solution containing alkali hydroxide in the second etching is set to 10 to 50% of the alkali hydroxide concentration in the first etching. That is, since the alkali hydroxide concentration in the second etching is optimized, a solar cell with higher efficiency can be manufactured.

According to the fourth aspect of the present invention, since the second etching is performed with the sodium hydroxide concentration of 0.16 to 0.80 mol / l, a solar cell with lower cost and higher efficiency can be manufactured. Become.

According to the fifth aspect of the present invention, the aqueous solution containing an alkali hydroxide used for the second etching includes:
Since isopropyl alcohol is added at a ratio of 1 vol% or more and less than 10 vol%, a solar cell with higher efficiency can be manufactured.

According to the invention of claim 6, since the alkali hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide and cesium hydroxide, various compounds can be used if necessary, A wide production method can be obtained.

[Brief description of the drawings]

FIG. 1 is a first embodiment. FIG. 5 is a diagram showing the dependence of Voc on the concentration of sodium hydroxide and the dependence of Voc on the etching depth for explaining the following.

FIG. 2 is a first embodiment. FIG. 4 is a diagram showing the dependence of Jsc on the concentration of sodium hydroxide and the dependence on the etching depth for explaining the following.

FIG. 3 is a diagram showing a surface of an “as-sliced polycrystalline silicon substrate” used in the embodiment.

FIG. 4 (a) shows a sodium hydroxide concentration of 0.25mo.
It is a figure which shows the substrate surface at the time of etching using 1 / l aqueous solution, (b) shows the substrate surface at the time of etching using the aqueous solution of sodium hydroxide concentration 0.50mol / l. It is a figure, (c) is a figure showing the substrate surface at the time of etching using the aqueous solution of sodium hydroxide concentration 5.83mol / l.

FIG. 5 is a first embodiment. FIG. 4 is a diagram showing the relationship between Jsc and the concentration of sodium hydroxide for explaining the following.

FIG. 6 is a first embodiment. Jsc according to Embodiment 2. FIG. 7 is a diagram comparing Jsc with Jsc.

FIG. 7 shows a second embodiment. FIG. 4 is a diagram showing the relationship between Jsc and the concentration of sodium hydroxide.

FIGS. 8A to 8H are process flow charts of a solar cell generally performed.

FIG. 9 is a diagram showing a cross-sectional structure of a V-groove mechanically formed on the surface of a polycrystalline silicon solar cell.

FIG. 10 is a diagram showing an uneven shape formed by RIE.

[Explanation of symbols]

Reference Signs List 1 Si substrate, 2 n-type diffusion layer, 3 aluminum paste electrode, 4 P ⁺ layer, 5 surface silver paste electrode, 6 back surface silver paste electrode, 7 damage to substrate surface and contamination in wafer slicing process, 8 irregularities formed on surface shape.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Hamamoto 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Inside Mitsubishi Electric Corporation

Claims (6)

[Claims] An Si substrate having a rough surface formed by slicing by machining is mainly used to remove a surface layer portion damaged in the slicing step and to form irregularities formed in the slicing step. To leave the shape
A method for manufacturing a solar cell, wherein etching is performed using an aqueous solution containing 0.25 to 3.0 mol / l of an alkali hydroxide. 2. The method according to claim 1, further comprising: forming a concavo-convex structure mainly for making optical confinement more effective; and etching for further removing a surface layer portion damaged in a slicing step by machining. A method for manufacturing a solar cell, comprising: performing a second etching with an alkali hydroxide concentration lower than the alkali hydroxide concentration according to claim 1 to perform the etching. 3. The solar cell according to claim 2, wherein the alkali hydroxide concentration of the aqueous solution containing alkali hydroxide in the second etching corresponds to 10 to 50% of the alkali hydroxide concentration in the first etching. Method. 4. The method for producing a solar cell according to claim 3, wherein the alkali hydroxide concentration of the aqueous solution containing alkali hydroxide used for the second etching is in the range of 0.16 to 0.80 mol / l. . 5. An aqueous solution containing an alkali hydroxide used for the second etching, in an amount of 1 vol% to 10 vol%.
The method for producing a solar cell according to any one of claims 2 to 4, wherein isopropyl alcohol is added in a proportion of less than. 6. The method according to claim 1, wherein the alkali hydroxide is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and cesium hydroxide. Solar cell manufacturing method.