JPH0823109A - Solar battery - Google Patents

Abstract

PURPOSE:To provide a solar battery with less re-coupling of carries and high photoelectric conversion efficiency. CONSTITUTION:An n-type layer is formed on a p-type crystal silicon substrate 5. A p-type diamond thin film 6 is provided on a side opposite to the junction. The diamond thin film 6 has an energy forbidden band width greater than that of the p-type crystal silicon substrate 5. In addition, the diamond thin film 6 has an impurity density higher than that of the p-type crystal silicon substrate 5. Therefore, on the interface between the diamond thin film 6 and the p-type silicon substrate 5, a high potential barrier can be produced. The diamond thin film 6 deteriorate little in film quality even with high density of impurity contained therein. Therefore, the diamond thin film 6 can extract majority of carriers from the p-type silicon substrate 5 with higher efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell, and more particularly to a solar cell having improved photoelectric exchange efficiency.

[0002]

2. Description of the Related Art A silicon semiconductor solar cell is an energy converter utilizing a pn junction.

In order to improve the energy conversion efficiency, there is a conventional structure in which the recombination of minority carriers on the substrate surface is reduced by the following structure.

A so-called passivation film such as an oxide film or a nitride film is formed on the surface of the substrate to stabilize the surface of the substrate to reduce recombination centers.

By forming a high impurity concentration layer having the same conductivity type as the substrate body on the surface of the semiconductor substrate, an electric field is created between the semiconductor substrate and the substrate, and the electric field keeps the minority carriers away from the substrate surface. thing.

In the above structure, when the electric field is formed on the light incident side, it is called a front surface field or FSF (Front Surface Field), and the electric field is formed on the opposite side to the light incident side. If formed, the back surface field or BSF (Ba
ck Surface Field).

The above-mentioned electric field implants impurity ions into the silicon substrate, gas diffuses the impurities into the silicon substrate, prints and fires the impurities into the silicon substrate, and vapor-deposits the impurities into the silicon substrate. It can be created by doing.

Further, the electric field causes a silicon microcrystalline thin film, a silicon carbide microcrystalline thin film, or an amorphous thin film in which an impurity of the same conductivity type having a wider energy forbidden band width than crystalline silicon is added at a high concentration on the silicon substrate. It can also be produced by depositing (Japanese Patent Publication No. 5-63103 or Japanese Patent Publication No. 5-75189).

In order to form a thin film having an energy forbidden band width wider than that of the single crystal silicon substrate on the single crystal silicon substrate to move minority carriers on the surface of the single crystal silicon substrate away from the substrate surface by an electric field, On a single crystal silicon substrate having an energy band gap of about 1.1 eV, a silicon microcrystalline thin film having an energy band gap of about 1.9 to 2.0 eV or an energy band gap of about 1.8 to 2 is formed. It is necessary to form a silicon carbide microcrystalline thin film or an amorphous thin film of 0.3 eV.

[0010]

However, in a film obtained by adding a high concentration of impurities to the above-mentioned microcrystalline thin film and amorphous thin film, the film quality is poor and the recombination of carriers in the film increases.
Therefore, there is a problem that a high electric field effect cannot be obtained even if the above-mentioned microcrystalline thin film and amorphous thin film doped with impurities at a high concentration are deposited on a silicon substrate.

[0011] Therefore, an object of the present invention is to provide a solar cell with a small recombination of carriers and a high photoelectric conversion efficiency.

[0012]

In order to achieve the above object, the invention of claim 1 is a crystalline silicon in which a first conductivity type crystalline silicon semiconductor layer and a second conductivity type crystalline silicon semiconductor layer are joined. In the solar cell, having a diamond film of the first conductivity type formed on the opposite surface of the crystalline silicon semiconductor layer of the first conductivity type on the opposite side of the bonding surface of the crystalline silicon semiconductor layer of the first conductivity type, The diamond thin film is characterized by having an energy bandgap wider than the energy bandgap of the first-conductivity-type crystalline silicon semiconductor layer.

Further, the invention of claim 2 is a crystalline silicon solar cell in which a crystalline silicon semiconductor layer of the first conductivity type and a crystalline silicon semiconductor layer of the second conductivity type are joined together,
A first conductivity type diamond thin film formed on the opposite surface of the first conductivity type crystalline silicon semiconductor layer on the opposite side of the bonding surface of the first conductivity type crystalline silicon semiconductor layer;
The diamond thin film is characterized by containing impurities at a concentration higher than that of the first conductivity type crystalline silicon semiconductor layer.

Further, the invention of claim 3 is a crystalline silicon solar cell in which a crystalline silicon semiconductor layer of the first conductivity type and a crystalline silicon semiconductor layer of the second conductivity type are joined together,
A first conductivity type diamond thin film formed on the opposite surface of the first conductivity type crystalline silicon semiconductor layer on the opposite side of the bonding surface of the first conductivity type crystalline silicon semiconductor layer;
The diamond thin film has an energy forbidden band width wider than that of the first conductivity type crystalline silicon semiconductor layer, and the first conductivity type crystalline silicon semiconductor layer includes the energy forbidden band width. It is characterized in that it contains a higher concentration of impurities than the concentration of impurities.

The invention of claim 4 relates to claims 1 to 3.
In the solar cell described in any one of the above 1, the diamond thin film has a film thickness of 20 nm or more.

The invention of claim 5 relates to claims 1 to 4.
In the solar cell according to any one of items 1 to 3, the diamond thin film contains hydrogen.

[0017]

In the solar cell of the first aspect of the present invention, the first conductivity type diamond thin film is formed on the surface opposite to the first conductivity type crystalline silicon semiconductor layer. The diamond thin film has a sufficiently large energy band gap as compared with the crystalline silicon semiconductor layer. Since the diamond thin film has an energy band gap of about 5.5 eV, it has a larger energy band gap than conventional microcrystalline thin films and amorphous thin films. Therefore, at the interface between the diamond thin film and the first-conductivity-type silicon semiconductor layer, a potential barrier higher than the conventional one is generated. Therefore, more minority carriers than in the past are pushed back from the vicinity of the interface to a deeper inside of the first conductivity type silicon semiconductor layer. Therefore, the recombination of the minority carriers at the interface is further suppressed, and the carriers can be collected more efficiently than in the conventional case. In addition, the first conductivity type diamond thin film has a larger energy band gap (about 5.5 eV, a wavelength of about 0.23 μm for light energy) than that of a conventional crystalline silicon semiconductor layer or a conventional microcrystalline thin film or a non-quality thin film. (Equivalent), the diamond thin film has a wavelength of 5.5 eV or less and a wavelength of about 0.23μ.
Light above m is difficult to be absorbed (there is absorption related to the level in the forbidden band). In the case of a crystalline silicon solar cell, the wavelength of light available for photoelectric conversion is about 0.3 to 1.2 μm.
Therefore, according to the present invention, the amount of light absorption can be reduced,
The photoelectric conversion efficiency is improved. For example, when this diamond thin film is used on the back side, the light passing through the silicon substrate and
(Actually, the wavelength is about 1.0 μm or more) is reflected by the back surface metal electrode, returned to the silicon semiconductor layer and used for photoelectric conversion. Even when used on the light-receiving surface side, light having a wavelength of about 0.3 to 1.2 μm is not absorbed by the diamond thin film and reaches the silicon semiconductor layer for photoelectric conversion.

In the solar cell according to the second aspect of the present invention, the first conductivity type diamond thin film is formed on the surface opposite to the first conductivity type crystalline silicon semiconductor layer. The diamond thin film contains a higher concentration of impurities than the first conductivity type silicon semiconductor layer. Moreover, unlike the conventional microcrystalline thin film or amorphous thin film, the diamond thin film contains a high concentration of impurities. Even if it contains it, the film quality does not deteriorate. Therefore, according to the second aspect of the invention, the majority carriers can be efficiently extracted from the first conductivity type silicon semiconductor layer, and the photoelectric conversion efficiency can be improved, as compared with the conventional case.

In the solar cell according to the third aspect of the present invention, the first conductivity type diamond thin film is formed on the surface opposite to the first conductivity type crystalline silicon semiconductor layer. The diamond thin film has an energy band gap that is sufficiently larger than that of the crystalline silicon semiconductor layer. Moreover, the diamond thin film contains impurities at a higher concentration than the first conductivity type silicon semiconductor layer.

Therefore, according to the invention of claim 3, the diamond thin film having a large energy band gap compared to the conventional microcrystalline thin film or amorphous thin film,
At the interface between the diamond thin film and the first-conductivity-type silicon semiconductor layer, a potential barrier higher than that in the conventional case is generated, and recombination of minority carriers at the interface is more significantly suppressed.
In addition, the first conductivity type diamond thin film has a larger energy band gap than the conventional microcrystalline thin film and the non-quality thin film as well as the crystalline silicon semiconductor layer. Can be made smaller.

Moreover, unlike a conventional microcrystalline thin film or an amorphous thin film, the diamond thin film does not deteriorate in quality even if it contains a high concentration of impurities. Therefore, the diamond thin film containing the above high concentration of impurities exists. As a result, the majority carriers can be efficiently extracted from the first conductivity type silicon semiconductor layer as compared with the conventional case.

As described above, according to the third aspect of the invention, the recombination of the minority carriers can be suppressed and the majority carriers can be efficiently extracted, so that the photoelectric conversion efficiency is significantly improved as compared with the conventional case. Can be made.

Further, in the solar cell according to the invention of claim 4, since the diamond thin film has a film thickness of 20 nm or more, the photoelectric conversion efficiency becomes the highest level as shown in FIG. Further, in the invention of claim 5, since the diamond thin film contains hydrogen, compared to the case where the diamond thin film does not contain hydrogen, the crystalline silicon semiconductor layer of the first conductivity type and the first conductivity type are The passivation effect at the interface with the diamond thin film is high. Therefore, claim 5
According to the invention of 1, the recombination of carriers at the interface can be particularly suppressed.

[0024]

EXAMPLES Examples of the present invention will be described below.

FIG. 1A shows a schematic cross section of a first embodiment of the solar cell of the present invention. This embodiment has a P-type single crystal silicon substrate 5 and is manufactured by the process shown in FIG. That is, in the silicon substrate 5, after cleaning, the surface 5a on the light incident side is made uneven by alkali etching called texture etching, and light reflection on the surface 5a is reduced. .

Further, the first embodiment, the surface 5a of the incident side of the light, phosphorus from phosphorus oxychloride (POCl ₃₎
The n-type layer 4 is formed by thermally diffusing (P). That is, the substrate 5 includes the p-type layer 5b and the n-type layer 4,
The interface between the p-type layer 5b and the n-type layer 4 is the pn junction surface Z1. The n-type layer 4 is covered with the silicon oxide film 3 formed by dry thermal oxidation. Further, RF (radio wave) is formed on the surface of the silicon oxide film 3.
A silicon nitride film 2 as an antireflection film formed by the discharge plasma CVD method is formed.

Then, in the groove formed by removing a part of the silicon oxide film 3 and the silicon nitride film 2, a multi-layer electrode 1 as an electrode on the light receiving surface side in contact with the n-type layer 4 is formed. This multi-layer electrode 1 consists of Ti (titanium), Pd (lead) and Ag.
(Silver) is a multilayer electrode and is formed by the electron beam vacuum deposition method and the lift-off method.

On the back surface 5c of the p-type substrate 5 opposite to the light-incident side, the same p-type impurity as the p-type substrate 5 contains.
A diamond thin film 6 is formed in which the type impurities are added at a higher concentration than the p-type substrate 5. The rear surface metal electrode 7 is formed on the surface 6a of the diamond thin film 6 by vapor deposition of Al.

The diamond thin film 6 is formed on the back surface 5c of the p-type substrate 5 by the vapor phase growth method. here,
A microwave plasma CVD method was used as the vapor phase growth method. Then, as the reaction conditions, CH ₄ / H ₂ gas having a concentration of 1 vol% (volume percent) is used at a flow rate of 250 sccm.
And diborane gas diluted to 1% with hydrogen at a flow rate of 3 sccm, a gas pressure of 20 Torr, a substrate temperature of 500 ° C., a microwave power of 300 W, a reaction time of 20 minutes (min), and a film thickness of 200 nm. A diamond thin film was deposited on the back surface 5c of the p-type substrate 5.

In this embodiment, the microwave plasma CVD method is used as the vapor phase growth method for forming the diamond thin film 6, but the hot filament CVD method, the direct current (DC) discharge plasma CVD method, and the radio frequency (RF) method are used. Discharge plasma CV
D method and electron cyclotron resonance (ECR) plasma CV
Method D or the like may be used. Even if a diamond thin film is deposited by any of these methods, the same electric field effect as in this embodiment can be obtained.

FIG. 1B shows an enlarged energy band structure in the n-type layer 4, the p-type layer 5b and the diamond thin film 6 of the solar cell of this example. In FIG. 1B, the horizontal dashed line F represents the Fermi level. The curve C above the Fermi level F represents the lower limit energy level of the conduction band, and the lower curve V represents the upper limit energy level of the valence band.

As shown in FIG. 1B, the diamond thin film 6 has a larger energy forbidden band than the p-type layer 5b, and also has a larger energy forbidden band than the conventional microcrystalline thin film or amorphous thin film. It has a band width. Therefore,
The diamond thin film 6 can form a higher potential barrier C _B in the conductive band C near the interface between the substrate 5 and the diamond thin film 6 with a strong electric field than in the conventional case.

Therefore, according to this embodiment, the effect of pushing back the electrons, which are minority carriers, into the inside of the substrate 5 becomes greater than the conventional one by the potential barrier C _B which is higher than the conventional one in the electric field and higher. Therefore, recombination of electrons, which are minority carriers, can be significantly suppressed as compared with the conventional case.

Further, the diamond thin film 6 contains a p-type impurity at a higher concentration than the substrate 5, and the film quality is deteriorated due to the impurity being added at a high concentration. And less than amorphous thin films. Therefore, according to this embodiment, the holes, which are the majority carriers, can be efficiently extracted to the electrode 7. Therefore, according to this embodiment, the photoelectric conversion efficiency can be improved as compared with the conventional case.

Further, since the diamond thin film 6 has a larger energy band gap than the conventional microcrystalline thin film or amorphous thin film as well as the single crystal silicon substrate 5, the light transmitted through the substrate 5 is diamond. It is hardly absorbed in the thin film 6, is reflected by the back surface metal electrode 7, and is returned to the inside of the substrate 5.

Since the diamond thin film 6 has little light absorption loss and less deterioration in film quality due to addition of high-concentration impurities, when the diamond thin film 6 is used as a film for forming a back surface electric field, carrier recovery in the film is reduced. It is possible to form a stronger internal electric field with a smaller bond and to enhance the light exchange efficiency of the solar cell.

FIG. 2 shows the concentration of boron which is a p-type impurity contained in the diamond thin film 6 of the solar cell of the above embodiment,
The relationship of the photoelectric exchange efficiency which shows the solar cell characteristic is shown. The p-type layer 5b of the silicon substrate 5 contains 5 × 10 ¹⁶ boron /
Contains cm ³ . Referring to FIG. 2, it can be seen that if the boron concentration in the diamond thin film 6 is equal to or higher than the boron concentration in the p-type layer 5b of the silicon substrate 5, the photoelectric conversion characteristics of the solar cell are significantly improved.

FIG. 3 shows the relationship between the film thickness of the diamond thin film 6 of the solar cell of the above embodiment and the photoelectric exchange efficiency.
As can be seen from FIG. 3, the photoelectric conversion efficiency of the solar cell is improved as the film thickness of the diamond thin film 6 is increased, and the efficiency is stabilized when the film thickness is 20 nm or more.

Next, FIG. 4 shows a schematic cross section of a second embodiment of the solar cell of the present invention. The pn junction surface Z of the second embodiment
The structure between 2 and the light receiving surface is the same as that of the first embodiment. Therefore, in the second embodiment, the structure between the surface opposite to the light receiving surface and the pn junction surface Z2 will be mainly described.

In the second embodiment described above, the silicon oxide film 28 is formed on the back surface 25c of the silicon substrate 25, and the silicon oxide film 28 has a plurality of openings K, K ... It is provided. Then, the above-mentioned openings K, K
, And the diamond thin film 26 is deposited on the surface 28a of the silicon oxide film 28. The diamond thin film 26 penetrates the opening K of the silicon oxide film 28 and is in contact with the silicon substrate 25.

In the solar cell having the above structure, the diamond thin film 26 faces the opening K of the silicon oxide film 28 on the back surface 25c of the silicon substrate 25, and only the portion which needs to be connected to the electrode 27 is formed. The diamond thin film 26 is brought into contact with.

Therefore, this diamond thin film 26
Is the same as the diamond thin film 6 of the first embodiment,
The recombination of electrons, which are minority carriers, can be significantly suppressed as compared with the conventional one, and the holes, which are the majority carriers, can be efficiently extracted to the electrode 27 by the potential barrier C _B that is higher than the conventional one and has a higher potential barrier. In addition, since it has a larger energy band gap than conventional ones, it hardly absorbs light.

Moreover, in the second embodiment, most of the back surface 25c of the silicon substrate 25 is passivated by the silicon oxide film 28, so that the back surface 25c of the substrate 25 is stabilized and the recombination center is formed. Be reduced. Therefore, the energy conversion efficiency is improved by the amount that the recombination of minority carriers on the back surface 25c of the substrate 25 is reduced.

That is, the second embodiment has the recombination center reducing effect by the silicon oxide film 28 in addition to the recombination suppressing effect by the diamond thin film 26, the majority carrier extraction effect and the light absorption suppressing effect. Therefore, according to the second embodiment, the energy conversion efficiency can be further improved as compared with the first embodiment.

Next, FIG. 5 shows a schematic cross section of a third embodiment of the solar cell of the present invention. The third embodiment differs from the first embodiment only in that a high-concentration p-type layer 39 is formed in a portion of the p-type silicon substrate 35 which is in contact with the p-type diamond thin film 36.

The impurity concentration of the high-concentration p-type layer 39 is
The impurity concentration is lower than the impurity concentration contained in the diamond thin film 36, but higher than the impurity concentration contained in the p-type layer 35b of the silicon substrate 35.

In the third embodiment, the high-concentration p-type layer 3 is used.
Since 9 is covered with the diamond thin film 36, a two-step back surface electric field layer is formed by the presence of the high-concentration p-type layer 39 and the diamond thin film 36. Therefore, recombination of electrons can be significantly suppressed as compared with the conventional example. Therefore, according to the third embodiment, the photoelectric conversion efficiency can be significantly improved as compared with the conventional example.

Next, FIG. 6 shows a schematic cross section of a fourth embodiment of the solar cell of the present invention. The fourth embodiment has both the features of the second embodiment and the features of the third embodiment. That is, the fourth embodiment is different from FIG. 4 only in that the high-concentration p-type layer 49 is formed in the portion in contact with the p-type diamond thin film 46 in the p-type silicon substrate 45.
Different from the second embodiment shown in FIG.

The diamond thin film 46 of the fourth embodiment.
Is a plurality of openings K formed in the silicon oxide film 48,
It is in contact with the high-concentration p-type layer 49 via K ...

In the fourth embodiment, the diamond thin film 46 is used.
In addition to the effect of suppressing recombination and the effect of extracting majority carriers by the silicon oxide film 48, the effect of reducing the recombination center is obtained by the silicon oxide film 48. Furthermore, the existence of the high-concentration p-type layer 49 and the existence of the diamond thin film 46 are synergistic. Due to the effect, recombination of electrons can be greatly suppressed. Therefore, according to the fourth embodiment, the photoelectric conversion efficiency can be greatly improved as compared with the conventional example.

Next, FIG. 7 shows a schematic cross section of a fifth embodiment of the solar cell of the present invention. In the fifth embodiment, the high-concentration p-type layer 59 is formed only in the vicinity of the plurality of openings K, K ... Of the silicon oxide film 58, and in a region not facing the opening K. It is different from the fourth embodiment only in that it is not formed. That is, this fifth embodiment is similar to the p-type silicon substrate 5
5 is different from the fourth embodiment only in that the high-concentration p-type layers 59, 59, 59, ... Are formed only in the portion in 5 which is in contact with the p-type diamond thin film 56.

Therefore, in the fifth embodiment, all of the high-concentration p-type layers 59, 59, 59, ... Are in contact with and covered with the diamond thin film 56. Therefore, according to the fifth embodiment, the effect of suppressing recombination of electrons equivalent to that in the fourth embodiment can be realized even if the formation region of the high-concentration p-type layer is smaller than that in the fourth embodiment.

Next, FIG. 8A shows a schematic cross section of a sixth embodiment of the solar cell of the present invention. The sixth embodiment differs from the first embodiment shown in FIG. 1 only in the following three points.

That is, in the sixth embodiment, the n-type layer 6 is replaced with the silicon oxide film 3 shown in FIG. 1 and the multilayer electrode 1 existing in the opening formed in the silicon oxide film 3.
4, a diamond thin film 60 having an n-type impurity added at a higher concentration than that of 4, and the diamond thin film 6 is provided between the p-type single crystal silicon substrate 5 and the back surface metal electrode 7 shown in FIG. Points not included and p-type silicon substrate 6
5 has a high concentration in a portion in contact with the back surface metal electrode 67.
It differs from the first embodiment only in that a p-type layer 69 is formed.

FIG. 8B shows an enlarged energy band structure in the diamond thin film 60, the n-type layer 64 and the p-type substrate 65 of the sixth embodiment. In FIG. 8B, F indicates the Fermi level, and the Fermi level F
The upper curve C shows the lower energy level of the conduction band, and the lower curve V shows the upper energy level of the valence band.

The diamond thin film 60 has an energy band gap larger than that of the n-type layer 64. Therefore, the diamond thin film 60 forms a high potential barrier V _B in the valence band V near the interface between the n-type layer 64 and the diamond thin film 60 under a strong electric field.

Due to the high potential barrier V _B at this strong electric field,
The force that pushes the holes, which are minority carriers, back into the n-type layer 64 is increased. Therefore, recombination of holes, which are minority carriers, can be significantly suppressed.

Since the diamond thin film 60 of the sixth embodiment is doped with n-type impurities in a higher concentration than the n-type layer 64, electrons which are majority carriers can be efficiently extracted to the electrode 61. You can Furthermore, since the diamond thin film 60 has an energy band gap larger than that of the n-type layer 64, the light incident on the diamond thin film 60 is hardly absorbed in the diamond thin film 60 and the n-type layer 64 is not absorbed. Can be incident on 64.

Next, FIG. 9 shows a seventh embodiment of the solar cell of the present invention.
The schematic cross section of an Example is shown. The seventh embodiment differs from the first embodiment shown in FIG. 1 only in the following points. That is, in the seventh embodiment, in place of the silicon oxide film 3 and the multilayer electrode 1 existing in the opening formed in the silicon oxide film 3 shown in FIG. It differs from the first embodiment only in that a diamond thin film 70 added in a high concentration is formed.

That is, this seventh embodiment is based on the silicon substrate 7
5, a diamond thin film 70 is provided on the light receiving surface side, and a diamond thin film 76 is provided on the back surface side of the silicon substrate 75. Therefore, according to the seventh embodiment, the diamond thin film 70 provided on the light-receiving surface side allows the incident light to be incident on the silicon substrate 75 without loss.
Can be reached inside. Further, due to the diamond thin film 76 provided on the back surface side, the light transmitted through the silicon substrate 75 passes through the back surface without loss, is reflected by the metal electrode 77 on the back surface side, and again the silicon substrate 7
Go back to 5. That is, according to the seventh embodiment, the two diamond thin films 70 and 76 can minimize the loss of light and greatly improve the photoelectric conversion efficiency.

In the first to seventh embodiments described above, the solar cell provided with the p-type single crystal silicon substrate has been described, but the present invention is also applicable to the solar cell provided with the n-type single crystal silicon substrate. You can In that case, a p-type impurity layer on the light incident side of the n-type single crystal silicon substrate is used, and a diamond thin film for forming a back surface electric field is formed by adding a high concentration of n-type impurities. As the diamond thin film for forming the light-receiving surface electric field, a p-type impurity added at a high concentration is used.

Although the diamond thin film is made of diamond in the above embodiment, it may be replaced with diamond-like carbon.

[0063]

As is apparent from the above, the solar cell of the first aspect of the present invention has the first conductivity type diamond thin film formed on the surface opposite to the bonding surface of the first conductivity type crystalline silicon semiconductor layer. There is. The diamond thin film has a sufficiently large energy band gap as compared with the crystalline silicon semiconductor layer. And the diamond thin film,
Since the energy band gap is about 5.5 eV, it has a larger energy band gap than the conventional microcrystalline thin film or amorphous thin film.

Therefore, at the interface between the diamond thin film and the first-conductivity-type silicon semiconductor layer, a potential barrier higher than before is generated. Therefore, more minority carriers than in the past are pushed back from the vicinity of the interface to a deeper inside of the first conductivity type silicon semiconductor layer. Therefore, the recombination of the minority carriers at the interface is further suppressed, and the carriers can be collected more efficiently than in the conventional case. Further, the first conductivity type diamond thin film has a larger energy bandgap than that of the conventional crystalline silicon semiconductor layer or the conventional microcrystalline thin film or non-quality thin film, so that the amount of light absorption can be reduced and The conversion efficiency can be improved.

The solar cell of the invention of claim 2 is the first
A first conductivity type diamond thin film is formed on the surface of the conductivity type crystalline silicon semiconductor layer opposite to the bonding surface. The diamond thin film contains impurities at a concentration higher than that of the first conductivity type silicon semiconductor layer, and
Unlike conventional microcrystalline thin films and amorphous thin films, the diamond thin film does not deteriorate in film quality even if it contains a high concentration of impurities. Therefore, according to the second aspect of the invention, the majority carriers can be efficiently extracted from the first conductivity type silicon semiconductor layer, and the photoelectric conversion efficiency can be improved, as compared with the conventional case.

The solar cell of the invention of claim 3 is the first
A first conductivity type diamond thin film is formed on the surface of the conductivity type crystalline silicon semiconductor layer opposite to the bonding surface. The diamond thin film has an energy band gap that is sufficiently larger than that of the crystalline silicon semiconductor layer. Moreover, the diamond thin film contains impurities at a higher concentration than the first conductivity type silicon semiconductor layer.

Therefore, according to the invention of claim 3, the diamond thin film having an energy band gap of about 5.5 eV is superior to conventional microcrystalline thin films and amorphous thin films.
Has a large energy band gap. Therefore,
At the interface between the diamond thin film and the first-conductivity-type silicon semiconductor layer, a potential barrier higher than that in the conventional case is generated, and recombination of minority carriers at the interface is more significantly suppressed.
In addition, the first conductivity type diamond thin film has a larger energy bandgap than that of the conventional microcrystalline thin film or the non-quality thin film as well as the crystalline silicon semiconductor layer. Can be made smaller.

Moreover, unlike a conventional microcrystalline thin film or an amorphous thin film, the diamond thin film does not deteriorate in quality even if it contains a high concentration of impurities. Therefore, the diamond thin film containing the above high concentration of impurities exists. As a result, the majority carriers can be efficiently extracted from the first conductivity type silicon semiconductor layer as compared with the conventional case.

As described above, according to the third aspect of the present invention, the recombination of the minority carriers can be suppressed and the majority carriers can be efficiently taken out, so that the photoelectric conversion efficiency is significantly improved as compared with the conventional case. Can be made.

Further, in the solar cell according to the invention of claim 4, since the diamond thin film has a film thickness of 20 nm or more, the photoelectric conversion efficiency becomes the highest level as shown in FIG. Further, in the invention of claim 5, since the diamond thin film contains hydrogen, compared with the case where the diamond thin film does not contain hydrogen, the crystalline silicon semiconductor layer of the first conductivity type and the first conductivity type crystalline silicon semiconductor layer The passivation effect at the interface with the diamond thin film is high. Therefore, claim 5
According to the invention of 1, the recombination of carriers at the interface can be particularly suppressed.

[Brief description of drawings]

1 (A) is a schematic sectional view of a first embodiment of a solar cell of the present invention, FIG. 1 (B) is an energy band structure diagram of the first embodiment, and FIG. [FIG. 3] is an explanatory diagram of a manufacturing process of the first embodiment.

FIG. 2 is a characteristic diagram showing the relationship between the concentration of impurities contained in the diamond thin film of the solar cell of the first example and the photoelectric conversion efficiency of the solar cell.

FIG. 3 is a characteristic diagram showing the relationship between the film thickness of the diamond thin film of the solar cell of the first example and the photoelectric conversion efficiency of the solar cell.

FIG. 4 is a schematic cross-sectional view of a second embodiment of the solar cell of the present invention.

FIG. 5 is a schematic cross-sectional view of a third embodiment of the solar cell of the present invention.

FIG. 6 is a schematic sectional view of a fourth embodiment of the solar cell of the present invention.

FIG. 7 is a schematic sectional view of a fifth embodiment of the solar cell of the present invention.

FIG. 8 (A) is a schematic sectional view of a sixth embodiment of the solar cell of the present invention, and FIG. 8 (B) is an enlarged view of the energy band structure of the sixth embodiment.

FIG. 9 is a schematic sectional view of a seventh embodiment of the solar cell of the present invention.

[Explanation of symbols]

1, 21, 31, 41, 51, 61, 71 ... Grid electrodes,
2, 22, 32, 42, 52, 62, 72 ... Antireflection film, 3,
23, 33, 43, 53 ... Silicon oxide film, 4, 24, 34,
44, 54, 64, 74 ... n-type silicon layer, 5, 25, 35,
45, 55, 65, 75 ... p-type silicon substrate, 5b, 25b,
35b, 45b, 55b ... p-type layer, 6, 26, 36, 46, 5
6,76 ... p-type diamond thin film, 7,27,37,47,
57, 67, 77 ... Back side metal electrode, 8, 28, 48, 58 ...
Silicon oxide film, 39, 49, 59, 69 ... High-concentration p-type silicon layer, 70 ... N-type diamond thin film, Z1 to Z7
... pn junction surface, K ... open hole.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ichiro Yamazaki 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within SHARP Co., Ltd. Within the corporation

Claims (5)

[Claims] 1. A crystalline silicon solar cell in which a first-conductivity-type crystalline silicon semiconductor layer and a second-conductivity-type crystalline silicon semiconductor layer are bonded together, wherein a bonding surface of the first-conductivity-type crystalline silicon semiconductor layer is A first conductivity type diamond thin film formed on an opposite surface of the first conductivity type crystalline silicon semiconductor layer on the opposite side, wherein the diamond thin film is included in the first conductivity type crystalline silicon semiconductor layer; A solar cell having an energy forbidden band wider than the existing energy forbidden band. 2. A crystalline silicon solar cell in which a first-conductivity-type crystalline silicon semiconductor layer and a second-conductivity-type crystalline silicon semiconductor layer are bonded together, wherein the bonding surface of the first-conductivity-type crystalline silicon semiconductor layer is A first conductivity type diamond thin film formed on the opposite surface of the first conductivity type crystalline silicon semiconductor layer on the opposite side, wherein the diamond thin film includes the first conductivity type crystalline silicon semiconductor layer; A solar cell characterized by containing a higher concentration of impurities than the concentration of existing impurities. 3. A crystalline silicon solar cell in which a first-conductivity-type crystalline silicon semiconductor layer and a second-conductivity-type crystalline silicon semiconductor layer are bonded together, wherein the bonding surface of the first-conductivity-type crystalline silicon semiconductor layer is A first conductivity type diamond thin film formed on an opposite surface of the first conductivity type crystalline silicon semiconductor layer on the opposite side, wherein the diamond thin film is included in the first conductivity type crystalline silicon semiconductor layer; The energy forbidden band width is wider than the present energy forbidden band width, and contains a higher concentration of impurities than the concentration of impurities contained in the first conductivity type crystalline silicon semiconductor layer. Solar cells to do. 4. The solar cell according to claim 1, wherein the diamond thin film has a film thickness of 20 nm or more. 5. The solar cell according to any one of claims 1 to 4, wherein the diamond thin film contains hydrogen.