JP2003273382A - Solar cell element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a solar cell of high characteristics at a low cost. <P>SOLUTION: A front surface side of a silicon substrate 1 containing multiple fine projections 2 and one conductive type semiconductor impurities contains reverse conducting semiconductor impurities 3, with a passivation film 5 formed on the front surface. An etching rate of the passivation film 5 is 350 Å/min or below when solution of hydrofluoric acid, containing hydrogen fluoride by 46% at 32°C, hydrofluoric acid:water = 1:2 is used. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell element, and more particularly to a solar cell element having a large number of fine projections for preventing light reflection on its surface.

[0002]

2. Description of the Related Art As energy consumption has increased in recent years, securing an energy source has been emphasized. At present, most of the energy depends on thermal power generation and nuclear power generation. However, thermal power generation has a problem of global warming due to carbon dioxide. In nuclear power generation, problems such as the risk of radioactive contamination at the time of an accident and the method of treating radioactive wastes have been pointed out, and this poses a global environmental problem from a long-term perspective. Under such circumstances, solar cells that directly convert solar energy into electric energy have been highlighted in recent years from the viewpoint of pollution-free, and the importance of mass production technology and cost reduction and efficiency improvement technology has become important. It is rising.

Major solar cells are classified into crystalline type, amorphous type, compound type and the like depending on the kind of material used. Of these, most of the currently marketed products 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 an advantage that it is easy to achieve high efficiency because the quality of the substrate is good, but has a disadvantage that the manufacturing cost of the substrate is high. On the other hand, the polycrystalline silicon solar cell has a weak point that it is difficult to achieve high efficiency due to poor substrate quality, but has an advantage that it can be manufactured at low cost. However, recently, the conversion efficiency up to about 18% has been achieved at the research level due to the improvement of the quality of the polycrystalline silicon substrate and the progress of the cell technology.

On the other hand, mass-produced polycrystalline silicon solar cells have been distributed in the market because they are lower in cost than before, but the demand has been increasing in recent years due to environmental problems, and the cost is lower and High conversion efficiency has come to be required.

The manufacturing process of a conventional silicon solar cell will be described with reference to FIG. First, the silicon substrate 1 is prepared as shown in FIG. Then, as shown in FIG. 7B, the silicon substrate 1 is heat-treated in an n-type impurity atmosphere,
An n-type impurity is diffused to a constant depth all over the surface of the silicon substrate 1 to form an n-type diffusion layer 3. Next, as shown in FIG. 7C, C is formed on the surface of the silicon substrate 1.
The passivation film 5 is formed by a VD device or the like. After the diffusion layer 3 is separated, as shown in FIG. 7D, a silver paste is screen-printed on the front surface of the silicon substrate 1, and an aluminum paste and a silver paste are screen-printed on the back surface of the silicon substrate 1, and the front surface electrodes are baked. 6 and the back electrode 7 are formed at the same time. Finally, the silicon substrate 1 on which each electrode is formed is dipped in a solder bath to coat the light-receiving surface electrode and the silver electrode on the back surface with solder to form a solder layer.

Here, in the step of diffusing the n-type impurities for forming the diffusion layer 3, it is possible to obtain high light-generated power by lowering the impurity concentration. The diffused impurity concentration is measured as a sheet resistance by the 4-probe method, but it is known that a high generated current and voltage can be obtained by decreasing the impurity concentration and increasing the sheet resistance. However, in the so-called fire-through method in which an electrode is formed by screen-printing and firing a paste material directly on the passivation film,
It is difficult to stably melt the passivation film material formed on the surface of the silicon substrate provided with the shallow diffusion layer of about 0.3 to 0.5 μm. In this case, the semiconductor junction may be destroyed, which causes a problem of decreasing the fill factor of the solar cell characteristics.

As another method for improving the characteristics, there is a passivation technique. This is roughly classified into surface and bulk passivation. As described above, the polycrystalline silicon solar cell is inferior to the single crystal silicon solar cell in quality of the substrate, and thus there is a problem that it is difficult to achieve high efficiency. Therefore, bulk passivation is important in polycrystalline silicon solar cells. It has been conventionally performed that a bulk passivation effect is obtained by forming a passivation film containing hydrogen on the surface. This is to diffuse the hydrogen contained in the passivation film into the substrate. Here, as the concept of diffusion, the higher the impurity concentration in the film, the higher the diffusion effect, and the higher the diffusion temperature, the higher the diffusion effect. That is, increasing the hydrogen content during film formation of a passivation film used for a solar cell and raising the film formation temperature lead to higher characteristics of the solar cell. This can be realized by setting various deposition conditions such as raising the deposition temperature of the passivation film, changing gas conditions, and changing RF power. However, under these conditions, there is a problem that the etching rate of the passivation film becomes slow. When this method is combined with the above-mentioned fire-through method, the passivation film material becomes more difficult to melt than before when the electrode is formed due to the slow etching rate, so that the electrode forming temperature is raised, the forming time is extended, etc. , The electrodes are contacted with silicon by forming the electrodes under more severe conditions than before. In other words, without breaking the semiconductor junction,
It becomes even more difficult to melt the ionization film material and make good contact.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to inexpensively manufacture a solar cell having high characteristics.

[0009]

In order to achieve the above object, a solar cell element according to a first aspect of the present invention has a large number of fine protrusions and is provided on the surface side of a silicon substrate containing one conductivity type semiconductor impurity. A solar cell element containing a conductive semiconductor impurity and a passivation film formed on the surface thereof, wherein the passivation film contains hydrofluoric acid containing 32% of hydrogen fluoride of 46%: water = 1: 2. The etching rate when an aqueous solution is used is 350 Å / min or less.

In the above solar cell element, the hydrogen content of the passivation film is 1 × 10 ²² to 1 × 10 ²³ ato.
It is preferably ms / cm ³ .

Further, in the above solar cell element, the passivation film is preferably a silicon nitride film.

Further, in the above solar cell element, the silicon nitride film also serves as an antireflection film, and its refractive index is 1.8 to.
2.6, it is desirable that the thickness is 50 to 1200Å.

Further, in the above solar cell element, it is desirable that the width of the fine protrusion is 2 μm or less.

Further, in the above solar cell element, it is desirable that the height of the fine protrusions is 2 μm or less.

Further, in the above solar cell element, it is desirable that the aspect ratio of the fine protrusions is 0.1 to 2.

Further, in the above solar cell element, it is desirable that point defects exist in the skirt portion of the fine projections.

Further, in the above solar cell element, it is desirable that the sheet resistance of the surface of the silicon substrate is 60 to 300 Ω / □.

Further, in the above solar cell element, it is desirable that the silicon substrate is made of polycrystalline silicon.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a structure of a solar battery cell showing an embodiment according to the present invention. 1 in FIG.
Is a silicon substrate, 2 is a fine protrusion, 3 is a light receiving surface side impurity diffusion layer, 4 is a back surface side impurity diffusion layer (BSF), 5 is a front surface passivation film, 6 is a front surface electrode, and 7 is a back surface electrode.

The silicon substrate 1 is a monocrystalline or polycrystalline silicon substrate. This substrate 1 may be either p-type or n-type. In the case of single crystal silicon, it is formed by a pulling method, and in the case of polycrystalline silicon, it is formed by a casting method. Polycrystalline silicon can be mass-produced and is extremely advantageous over single crystal silicon in terms of manufacturing cost. The ingot formed by the pulling method or the casting method is sliced to a thickness of about 300 μm and cut into 10 cm ×
A silicon substrate is obtained by cutting into a size of about 10 cm or 15 cm × 15 cm.

On the surface side of the silicon substrate 1, fine projections 2 are formed in order to effectively take in the incident light without reflecting it.

When a solar cell element is formed using the silicon substrate 1, when the surface of the substrate 1 is etched with an alkaline aqueous solution such as sodium hydroxide, fine projections 2 (unevenness) are formed on the surface, and The reflection on the surface can be reduced to some extent.

When a single crystal silicon substrate having a plane orientation of (100) is used, a pyramid structure called a texture structure can be uniformly formed on the substrate surface by such a method, but a polycrystalline silicon substrate is used. When forming a solar cell element, there is a problem that the pyramid structure cannot be formed uniformly because the etching with the alkaline aqueous solution depends on the crystal plane orientation, and therefore the overall reflectance cannot be effectively reduced.

In order to solve such a problem, when the solar cell element is formed of a polycrystalline silicon substrate, the substrate 1
Reactive ion etching (Reac
It is desirable to form by the tiveion etching method. According to this method, the fine protrusions 2 can be uniformly formed without being influenced by the plane orientation of the irregular crystal in the polycrystalline silicon, and particularly in the solar cell element using the polycrystalline silicon, The rate can be reduced more effectively.

That is, a gas is introduced into a vacuumed chamber, the pressure is maintained at a constant pressure, and RF power is applied to an electrode provided in the chamber to generate plasma, which is the active species generated. The substrate surface is etched by the action of ions and radicals. This method, commonly referred to as the reactive ion etching (RIE) method, is shown in FIGS. In the apparatus shown in both figures, gas is introduced into the chamber evacuated by the vacuum pump 12 through the mass flow controller 8 and kept at a constant pressure by the pressure regulator 11, and the R in the chamber is kept constant.
By applying RF power to the F electrode 10, plasma is generated and etching is performed. Generally, a method of increasing the effect of ions on etching among the generated active species is called a reactive ion etching method. Although a similar method includes plasma etching and the like, the principle of plasma generation is basically the same, and the distribution of the types of active species acting on the substrate is changed by the chamber structure or the electrode structure. Therefore, the present invention is effective not only in the reactive ion etching method but also in a wide range of plasma etching methods in general for a solar cell element having irregularities with defects on the substrate surface. In the present invention, for example, oxygen (O
₂ ) at 10 sccm and SF ₆ at 80 sccm,
Reaction pressure 7 Pa, RF power 80 for generating plasma
Etching was performed at 0 W for 5 minutes. As a result, fine protrusions 2 (uneven structure) are formed on the surface of the silicon substrate 1.

The fine projections 2 have a conical shape or a shape in which they are continuous, and the size thereof can be changed by controlling the gas concentration or etching time by the RIE method. It is desirable that the width and height of each of the fine protrusions 2 be 2 μm or less. 2μ
This is because if the thickness is more than m, the entire convex portion cannot be made into the n-layer due to diffusion described later. In order to form the fine projections 2 uniformly and accurately with controllability over the entire necessary portion of the silicon substrate 1, 1 μm or less is preferable. The aspect ratio (height / width of the uneven portion) of the fine protrusions 2 is preferably 0.1 to 2. When the aspect ratio is 0.1 or less, for example, a wavelength of 500
The average reflectance of light of ˜1000 nm is about 25%,
The reflectance on the surface of the semiconductor substrate 1 increases. If the aspect ratio is 2 or more, fine projections 2
Is damaged, and when a solar cell element is formed, the leak current increases and good output characteristics cannot be obtained.

An impurity diffusion layer 3 is formed on the surface side of the silicon substrate 1. The impurity diffusion layer 3 is provided to form a semiconductor junction in the silicon substrate 1. For example, when diffusing n-type impurities, POC is used.
vapor diffusion method using l ₃ , coating diffusion method using P ₂ O ₅ ,
And P ⁺ ions are directly diffused by an ion implantation method or the like. The layer 3 containing the semiconductor impurities of the opposite conductivity type is formed to a depth of about 0.3 to 0.5 μm.

A passivation film 5 is formed on the surface side of the silicon substrate 1. On the other hand, in order to increase the efficiency of polycrystalline silicon solar cells, a technique of introducing hydrogen into polycrystalline silicon to passivate crystal defects and impurities is indispensable. In this, hydrogen interacts with crystal defects and impurities to move the level in the band gap near or in the conduction band or valence band. Regarding the passivation effect, it is known that point defects generated on the surface of the silicon substrate promote the diffusion of hydrogen (for example, Solar Energy Materials and Solar C
ells 41/42 (1996) 159-169 Hydrogen in silicon:
A discussion of diffusion and passivation mechanis
ms (hydrogen in silicon: consideration of diffusion and passivation mechanism)). The reactive ion etching method described above can effectively reduce the reflectance of the surface of the silicon substrate, and at the same time, positively and effectively generate this point defect.

By making the protrusions 2 (irregularities) on the surface as fine as 2.0 μm or less, the diffusion of phosphorus proceeds from both sides in the upper region of the protrusions 2. Since the depth to which phosphorus is diffused is about 0.4 μm, the entire upper part of the fine protrusion 2 is of n-type. Therefore, the impurity concentration increases and the resistance decreases in the upper portion of the protrusion 2.

FIG. 4 shows a cross-sectional TEM image of the interface between the surface electrode and the silicon formed by printing and baking the silver paste.
While the frit is accumulated in the lower portion (valley portion) 15 of the protrusion 2 (unevenness) and the space 16 exists, the electrode material (silver) is in contact with the upper portion 17 of the protrusion 2 (unevenness). Since phosphorus is diffused at a high concentration in the upper portion 17 of the protrusion 2 in contact with silver, even if the pass-through film 5 formed at a higher temperature than the conventional one and having a slower etching rate is subjected to the fire through method. It is unlikely that the junction will break, and the contact resistance between silver and silicon can be greatly reduced. That is, by forming a large number of fine protrusions 2 on the surface, it becomes possible to inexpensively manufacture a solar cell with high characteristics even if the sheet resistance is increased.

Then, in order to further improve the efficiency,
The surface of the substrate 1 is made by the reactive ion etching method and the like.
When using the dry etching method of
Damage (point defects) remains mainly in the recesses on the surface of plate 1.
After forming the protrusion 2 under etching conditions, plasma CVD
Method, the hydrogen concentration in the film is 1.0 × 10^{twenty two}~ 1.0 x 10 ^{twenty three}
atoms / cm³The silicon nitride film that is
It is also formed as an anti-reflection film.

When the silicon nitride film is formed by the plasma CVD method, the refractive index of the formed film is 1.8 to 2.
6. The film is formed under the condition that the film thickness is 50 to 1200Å. In addition, the passivation film 5 having an etching rate of 400 Å / min when an aqueous solution of hydrofluoric acid containing 46% hydrogen fluoride: water = 1: 2 was used at 32 ° C. at a 32 ° C. Hydrofluoric acid containing 46% hydrogen fluoride:
By controlling the etching rate to be 350 Å / min or less when an aqueous solution of water = 1: 2 is used, higher characteristics can be realized.
Such a film has a film-forming temperature of, for example, 50 to 300 conventionally.
It can be realized by raising the temperature by about ℃. Note that this method is an example, and the present invention is not limited to this. As mentioned above, changing the gas conditions, changing the RF power, combining each condition including temperature, etc.
It can be realized by setting various conditions for film formation to specific values. High characteristics can be realized by combining the conditions of the above refractive index, film thickness, and etching rate.

In the passivation film 5, diffusion of hydrogen in the film is promoted through the point defects generated mainly in the lower portion (recess) of the protrusion 2 (concavo-convex structure) previously formed, and impurities in the bulk are impaired. It is provided as an antireflection film for preventing the light from being reflected on the surface of the silicon substrate 1 and effectively taking in the light into the silicon substrate 1 at the same time as providing it for more effective passivation of crystal defects. The passivation film 5 is formed by, for example, a plasma CVD method,
A silicon nitride film that can simultaneously serve as a passivation film and an antireflection film is suitable, and the hydrogen concentration in the film is 1.0 × 10 ^{22 to} 1.0 × 10 ²³ a depending on the reaction gas ratio during film formation.
It is formed to have a thickness of toms / cm ³ . When the hydrogen concentration in the film is 1.0 × 10 ²² atoms / cm ³ or less, the passivation effect becomes insufficient and the characteristics are deteriorated. In addition, the hydrogen concentration in the film is 1.0 × 10 ²³ at
Even if it is oms / cm ³ or more, it does not lead to a larger passivation effect, resulting in a decrease in productivity such as an increase in the amount of reaction gas used during film formation and difficulty in controlling film formation conditions.

Further, generally, when the refractive index of the antireflection film (passivation film) is n and the film thickness is d, the refractive index of the peripheral material of the solar cell is n ₀ , the refractive index of the silicon substrate is n ₁ ,
If the wavelength of the incident light is λ, then n ₂ = n ₀ · n ₁ and 4
It is desirable to form an antireflection film such that nd = λ. The refractive index of the silicon substrate 1 is about 3.5, and when the periphery of the solar cell element is covered with air (n ₀ = 1), the refractive index of the antireflection film 5 is about 1.8 to 2.2. The film thickness is preferably about 600 to 900Å.

Considering the case where the solar cell element has a module structure, generally, glass and a resin filler such as ethylene vinyl acetate are pasted on the solar cell element, and incident light passes through these to the solar cell element. Will be absorbed. Since the glass and the filler have a refractive index of about 1.5, the antireflection film of the solar cell element has a refractive index of 2.
About 2 to 2.6 is preferable. Furthermore, a passivation film having an etching rate of 400 Å / min when an aqueous solution of hydrofluoric acid containing 46% hydrogen fluoride at a temperature of 32 ° C.:water=1:2 was used. mi
By controlling and forming so as to be n or less, higher characteristics can be realized.

The silicon substrate 1 according to the present invention
When the surface of is made rough, the antireflection effect can be obtained on the surface of the silicon substrate 1 itself, and thus a sufficient antireflection effect can be obtained even if the thickness of the antireflection film is reduced.
Even if the film thickness is reduced to 50Å, the characteristics will not be deteriorated. Similarly, when the film thickness is 900 Å or more,
Compared to the case where the surface is not roughened, the antireflection effect is less deteriorated and the characteristics are not significantly deteriorated up to about 1200 Å.

Therefore, considering the effect of the passivation film 5 as an antireflection film, the refractive index of 1.8-2.
6. It is necessary to form a passivation film having a film thickness of 50 to 1200Å. Furthermore, the etching rate is set to 35
In order to achieve 0 Å / min or less, the film formation temperature of the passivation film 5 needs to be 350 to 600 ° C. If the film forming temperature is 350 ° C. or lower, the silicon substrate 1
Since the diffusion rate of hydrogen into the inside is insufficient, the passivation effect is low and sufficient improvement in characteristics cannot be obtained. Further, when the film forming temperature is 600 ° C. or higher, the warp due to heat of the silicon substrate 1 during film forming is large, the film forming distribution becomes nonuniform, and the silicon substrate 1 is easily cracked due to the warp distortion. Cause

On the back surface side of the silicon substrate 1, it is desirable to form a layer 4 in which one conductivity type semiconductor impurity is diffused at a high concentration. The layer 4 in which the one conductivity type semiconductor impurity is diffused at a high concentration forms an internal electric field on the back surface side of the silicon substrate 1 in order to prevent a decrease in efficiency due to recombination of carriers near the back surface of the silicon substrate 1. is there. That is, as a result of the carriers generated near the back surface of the silicon substrate 1 being accelerated by this electric field, electric power is effectively taken out, the photosensitivity particularly at long wavelengths is increased, and the deterioration of solar cell characteristics at high temperatures is reduced. it can. The sheet resistance on the back surface side of the silicon substrate 1 on which the layer 4 in which the one-conductivity-type semiconductor impurity is diffused at a high concentration is formed is 15Ω /
□ It will be about.

A front surface electrode 6 and a back surface electrode 7 are formed on the front surface side and the back surface side of the silicon substrate 1. The front surface electrode 6 and the back surface electrode 7 are formed by screen-printing an Ag paste mainly composed of Ag powder, a binder, a frit, etc. and firing it to form a solder layer thereon. The surface electrodes 6 have a width of about 200 μm and a pitch of 3 mm, for example.
It is composed of a large number of finger electrodes formed to some extent and two bus bar electrodes that connect the large number of finger electrodes to each other. The back surface electrode 7 is composed of, for example, a large number of finger electrodes formed to have a width of about 300 μm and a pitch of about 5 mm, and two bus bar electrodes that connect the large number of finger electrodes to each other. Further, in order to improve the characteristics, an extraction electrode containing silver as a main component may be formed on the back surface, and a current collecting electrode containing aluminum as a main component may be formed on almost the entire surface except the extraction electrode. In that case, it is not necessary to form the layer 4 in which the one-conductivity-type semiconductor impurity is diffused at a high concentration before forming the electrodes.

[0040]

[Example] A thickness of 300 μm and a specific resistance of 1.5 Ω · c
A substrate made of polycrystalline silicon measuring 15 cm × 15 cm square of m was dipped in a solution of HNO ₃ : HF = 7: 1, and one side was
After etching 5 μm, oxygen (O ₂ ) is added at 10 scc
m, sulfur hexafluoride (SF ₆ ) was flowed at 80 sccm, and a fine uneven structure was formed on the substrate surface by the RIE method at a reaction pressure of 7 Pa and an RF power of 800 W. Next, phosphorus (P) was diffused so that the sheet resistance of the surface portion of the silicon substrate was 80Ω / □. Next, screen print aluminum (Al) paste on the back side of the silicon substrate, and
It was calcined at a temperature of 0 ° C. The sheet resistance on the back surface side of this silicon substrate was 15 Ω / □. Next, a silicon nitride film was formed on the surface side of the silicon substrate by the plasma CVD method.
This silicon nitride film was formed into five types by changing the content hydrogen concentration by changing the gas conditions and the like. At that time, the refractive index is 2.
The film was formed under the conditions of 0 to 2.4 and the film thickness of 800 to 900Å, and the film forming temperature was 500 ° C. Then, silver (Ag) was deposited on both front and back surfaces of the silicon substrate by a printing method to form an electrode, and a solder layer was formed on the electrode surface by a solder dipping method to form a solar cell element.

FIG. 5 shows the relationship between the etching rate and the characteristics when an aqueous solution of hydrofluoric acid: water = 1: 2 containing 46% hydrogen fluoride at 32 ° C. was used in the passivation film of each cell prepared. Show. Etching rate is 450Å /
The conversion efficiency, which was 14.21% at the time of min, was improved with the decrease of the etching rate, and the etching rate was 350.
When it is less than Å / min, it shows a characteristic exceeding 14.5%.
There is a clear correlation between etching rate and conversion efficiency. That is, when the etching rate of the passivation film when an aqueous solution of hydrofluoric acid containing 46% hydrogen fluoride at 32 ° C.:water=1:2 is used is 450 Å / min or less, the electrical characteristics are improved.

FIG. 6 shows the relationship between the hydrogen concentration in the silicon nitride film of each manufactured cell and the electrical characteristics. The hydrogen concentration in the silicon nitride film was measured by secondary ion mass spectrometry.
The film thickness and the refractive index were measured with an ellipsometer.

As can be seen from FIG. 6, when the hydrogen concentration in the silicon nitride film is 1.4 × 10 ²² atoms / cm ³ or more, the conversion efficiency is 14.45% or more, but 8.0 × 10.
^In the case of ²¹ atoms / cm ^3, a clear decrease in electrical characteristics is recognized, which is 14.09%. That is, when the hydrogen concentration in the film is 1.4 × 10 ²² atoms / cm ³ or more, the electric characteristics are improved.

[0044]

As described above, according to the present invention, the passivation film formed on the surface of the silicon substrate having a large number of fine protrusions has hydrofluoric acid containing 46% hydrogen fluoride at 32 ° C .: water. Since the etching rate when using an aqueous solution of = 1: 2 is 350 Å / min or less,
It becomes a silicon solar cell element with high conversion efficiency and can greatly contribute to the high performance of the silicon solar cell.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a solar cell according to the present invention.

FIG. 2 is a diagram showing an example of a reactive ion etching apparatus according to the present invention.

FIG. 3 is a diagram showing an example of a reactive ion etching apparatus according to the present invention.

FIG. 4 is a TEM image showing a cross section of a surface electrode and a silicon interface of the solar cell element according to the present invention.

FIG. 5 is a diagram showing the relationship between the etching rate and the electrical characteristics of the surface passivation film of the solar cell according to the present invention.

FIG. 6 is a diagram showing a relationship between a hydrogen concentration in a surface passivation film of a solar cell according to the present invention and electric characteristics.

FIG. 7 is a diagram showing a general structure of a conventional solar cell.

[Explanation of symbols]

1: silicon substrate, 2: surface uneven structure, 3: impurity diffusion layer, 4: back surface impurity diffusion layer, 5: passivation film,
6: front surface electrode, 7: back surface electrode, 8: mass flow controller, 9: silicon substrate, 10: RF electrode, 11: pressure regulator, 12: vacuum pump, 13: RF power supply, 14:
Gas, 15: lower part of unevenness, 16: space, 17: upper part of unevenness

Claims (10)

[Claims] 1. A solar cell element comprising a silicon substrate having a large number of fine protrusions and containing a semiconductor impurity of one conductivity type, wherein a semiconductor impurity of opposite conductivity type is contained on the surface side and a passivation film is formed on the surface. A solar cell, wherein the passivation film has an etching rate of 350 Å / min or less when an aqueous solution of hydrofluoric acid containing 46% hydrogen fluoride at 32 ° C.:water=1:2 is used. element. 2. The solar cell element according to claim 1, wherein the hydrogen content concentration of the passivation film is 1 × 10 ²² to 1 × 10 ²³ atoms / cm ³ . 3. The solar cell element according to claim 1, wherein the passivation film is a silicon nitride film. 4. The silicon nitride film also serves as an antireflection film, and has a refractive index of 1.8 to 2.6 and a thickness of 50 to 120.
It is 0Å, The solar cell element of Claim 3 characterized by the above-mentioned. 5. The solar cell element according to claim 1, wherein the fine projections have a width of 2 μm or less. 6. The solar cell element according to claim 1, wherein the height of the fine protrusions is 2 μm or less. 7. The aspect ratio of the fine protrusions is 0.1.
The solar cell element according to any one of claims 1 to 6, characterized in that 8. The solar cell element according to claim 1, wherein a point defect is present in a skirt portion of the fine protrusion. 9. The solar cell element according to claim 1, wherein the sheet resistance of the surface of the silicon substrate is 60 to 300 Ω / □. 10. The solar cell element according to claim 1, wherein the silicon substrate is made of polycrystalline silicon.