JP2002299661A - THIN-FILM CRYSTALLINE Si SOLAR CELL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To overcome the problem that the increase in a leakage current cannot be inhibited, and at the same time there are substantial restrictions in the characteristic length and an angle of inclination of uneven structure. SOLUTION: In the thin-film crystalline Si solar cell, a back transparent conductive layer that becomes a back electrode, a semiconductor layer having semiconductor junction where an photoactive layer section is formed by crystalline Si, a front transparent conductive layer that becomes a front electrode, and a front collector electrode are successively laminated on one main surface side of a translucent substrate. The uneven structure is provided in the thin-film crystalline Si solar cell. In the uneven structure, other main surface sides in the translucent substrate are made of a plurality of polygonal pyramids being at least a trigonal pyramid. The average distance between the vertexes of adjacent polygonal pyramids in the uneven structure is 100 nm or longer, and, additionally, a light reflection layer made of metal should be formed on the uneven structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photoelectric conversion element represented by a thin-film crystalline Si solar cell and the like.

[0002]

2. Description of the Related Art Thin-film crystalline Si solar cells typified by thin-film polycrystalline Si solar cells have attracted attention as next-generation solar cells. Since it is not a sufficiently large value, it is particularly important to improve the light use efficiency by introducing a light confinement structure to obtain a sufficient photocurrent value.

As a light confinement technique, it has been known to form an anti-reflection film on the light incident surface side or to form a concavo-convex structure, and has long been applied to solar cells and put to practical use.

However, in a thin-film crystalline Si solar cell, since the light absorption coefficient of crystalline Si is small on the long wavelength side, light absorption is sufficiently generated at a film thickness of about several μm or less to more efficiently perform photoelectric conversion. To do so, the incident light must be crystalline S
It is particularly important to form a structure in which light can be more effectively confined by reflecting and reciprocating a number of times in the i-film. For this reason, in the thin-film crystalline Si solar cell, in addition to forming the concavo-convex structure on the light incident surface side surface of the conventional semiconductor layer, the concavo-convex structure is also formed on the opposite side of the semiconductor layer from the light incident surface. Studies are underway to more effectively confine light.

[0005] These conventional examples are disclosed in, for example, Japanese Patent No. 2713.
No. 847, Japanese Patent No. 2771414, Japanese Patent No. 27848
No. 41, Japanese Patent No. 3027669, Japanese Patent No. 302916
9, JP-A-5-218469, JP-A-6-1967
No. 38, JP-A-10-117006, JP-A-11-2
No. 33800 and the like, and in each case, the result that the photocurrent is increased and the conversion efficiency is improved is obtained.

Here, typical element structures are shown in FIG. 3, FIG. 4, and FIG. 3, 4, and 5, 31, 41, and 51 are substrates, 32, 42, and 52 are back electrode layers, 33, 43, and 53 are back transparent conductive layers, 34, 44, and 54 are semiconductor layers, and 35, and 4
5, 55 are front transparent conductive layers, and 36, 46, 56 are front collecting electrodes.

However, in the conventional double-sided uneven structure in which both surfaces of the semiconductor layer shown in FIGS. 3, 4 and 5 are uneven, the semiconductor layers 34, 44 and 54 are formed by depositing the surface on which the uneven structure has already been formed on the deposition surface. Will grow as. This is originally undesirable for growing an electrically good semiconductor film. This is because, when a thin film is grown on a flat surface, the number of unnecessary nucleation sites due to the uneven structure is small, so that it is easy to increase the crystal grain size, and all crystals are oriented in a direction perpendicular to the flat surface. This has the advantage that the crystal grains grown do not collide with each other to form crystal grain boundaries, and that the crystal orientation is easily aligned in one direction and that the desired crystal orientation characteristics can be easily controlled. On the other hand, these advantages are lost when the thin film is grown on the uneven structure surface.

In particular, in a solar cell, an increase in crystal grain boundaries due to a small crystal grain size and generation of crystal grain boundaries due to collision between growing crystal grains are caused by the crystal grain boundary portions serving as a path for generating a leak current. The electrical characteristics of the semiconductor layers 34, 44, and 54 are deteriorated, which is a fatal negative factor that causes a decrease in open-circuit voltage characteristics and a decrease in fill factor characteristics.

[0009] In fact, regarding the relationship between the concavo-convex shape and the open-circuit voltage, the 61st Autumn Meeting of the Japan Society of Applied Physics 6a-C-6
p.829 (2000), 6a-C-7, p.830
(2000), which increases the unevenness (increases in the average size (characteristic length) of the unevenness units forming the uneven structure and the inclination angle of the surface on which the uneven structure is formed with respect to the horizontal direction of the substrate). It is stated that the current increases but the open-circuit voltage decreases.

As described above, in the conventional double-sided uneven structure in which both surfaces of the semiconductor layer are uneven, even if an optically desirable uneven structure can be formed to increase the photocurrent, the increase in leak current can be suppressed. However, there is a problem that the characteristic level cannot be originally expected.

In the crystalline Si layer which is a photoactive layer portion, the crystal orientation characteristic is set to be (110) orientation in order to spontaneously form an uneven shape suitable for light confinement on the growth surface. Is important, but the semiconductor layers 34, 4
If the concavo-convex shape is already formed before forming 4, 54, the controllability of this orientation is disturbed, and there is a problem that it is difficult to obtain an ideal strong (110) orientation.

On the other hand, the present inventors have already filed Japanese Patent Application No.
No. 001-20623 discloses a double-sided concavo-convex structure element capable of reducing the amount of leak current as compared with the conventional example, which is shown in FIGS. 6 and 7. FIG. 6 and 7, 61 and 71 are substrates, 62 and 72 are back electrode layers, 63 and 73 are back transparent conductive layers, 64 and 74 semiconductor layers, 65 and 75 are front transparent conductive layers,
66 and 76 are surface collecting electrodes. In these element structures,
Since the semiconductor layers 64 and 74 can be grown on the flattened surface with respect to the element structure shown in FIGS.
4 can be obtained.

However, even in this case, the back electrode layer 62,
When the characteristic length and the inclination angle of the concave-convex structure on the surface of the surface 72 become a certain value or more, in order to completely cover and embed the back transparent conductive layers 63 and 73, the back transparent conductive layers 63 and 73 are formed to be considerably thick. It is necessary to form a film, and this film formation process takes a long time, and the thicker the film is, the more the unevenness of the surface reflecting the crystal structure of the transparent conductive layer is increased, so that a certain leveling process is required. Was. For this reason, even if it is known that it is optically desirable to increase the unevenness of the surface of the back electrode layers 62 and 72, the characteristic length and the inclination angle of the unevenness are still substantially restricted. Was.

The present invention solves the problem of the conventional double-sided uneven structure that the increase in leakage current cannot be suppressed,
Further, the present invention solves another conventional problem that the characteristic length and the inclination angle of the uneven structure are still substantially restricted.

[0015]

According to a first aspect of the present invention, there is provided a thin-film crystalline Si solar cell according to the first aspect, wherein a back transparent conductive layer serving as a back electrode is provided on one principal surface side of the translucent substrate. In a thin-film crystalline Si solar cell in which a semiconductor layer having a semiconductor junction in which a photoactive layer portion is formed of crystalline Si, a front transparent conductive layer serving as a front electrode, and a front electrode are sequentially stacked, The main surface side has an uneven structure composed of a large number of polygonal pyramids of three or more pyramids, the average distance between vertices of adjacent polygonal pyramids of the irregularity structure is 100 nm or more, and light reflection made of metal on the uneven structure A layer is formed.

Further, in the thin-film crystalline Si solar cell according to claim 2, the concave portion of the concave-convex structure has a curved surface,
The average distance between the lowest points of adjacent concave portions of the concave-convex structure is 1
It is characterized in that it is not less than 00 nm.

Further, in the thin film crystalline Si solar cell according to the third aspect, a back transparent conductive layer serving as a back electrode and a semiconductor junction having a photoactive layer formed of crystalline Si are provided on one principal surface side of the substrate. In a thin-film crystalline Si solar cell in which a semiconductor layer, a front transparent conductive layer serving as a front electrode, and a front electrode are sequentially laminated, one main surface side of the substrate has a concavo-convex structure or a concave portion formed of a number of polygonal pyramids of three or more pyramids. Has an uneven structure consisting of curved surfaces,
The average distance between the vertices of adjacent polygonal pyramids of the concavo-convex structure or the average distance between the lowest points of adjacent concave portions of the concavo-convex structure is 100 nm or more. A translucent thin film layer having a substantially flat surface is formed between the two.

In the thin-film crystalline Si solar cell, when the substrate is a light-transmitting substrate, a light-reflecting layer made of metal is provided between the light-transmitting substrate and the light-transmitting thin film layer. It is characterized by having.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to FIG. In the figure, 11 is a translucent substrate, 12 is a light reflecting layer, 13 is a back transparent conductive layer, 14 is a semiconductor layer having a semiconductor junction in which a photoactive layer portion is formed of crystalline Si, 15 is a front transparent conductive layer, Reference numeral 16 denotes a surface collecting electrode. FIG. 1 is for describing claim 1. However, in describing claim 2, it should be understood that the uneven structure is interpreted as having the shape described in claim 2. To

On one main surface side of the light-transmitting substrate 11, a back transparent conductive layer 13 serving as a back electrode, a semiconductor layer 14 having a semiconductor junction in which a photoactive layer portion is formed of crystalline Si, and a front transparent electrode serving as a front electrode. The conductive layer 15 and the surface electrode 16 are sequentially laminated. The other main surface side of the light-transmitting substrate has an uneven structure composed of a large number of polygonal pyramids of three or more pyramids, and the average distance between vertices of adjacent polygonal pyramids of the uneven structure is 100 nm or more. The light reflection layer 12 made of metal is formed on the uneven structure.

According to this element structure, of the two-sided uneven structure, the back-side uneven structure located on the side opposite to the light incident surface is formed on the back surface of the light-transmitting substrate 11 on the opposite side to the semiconductor forming surface side. Therefore, the semiconductor layer 14 is formed on a substantially flat surface, so that it is possible to avoid an increase in leakage current caused by the semiconductor layer 14 being formed on the uneven surface, and to make the transparent conductive film The step of planarizing the surface of the layer 13 can also be omitted. In addition, substantial restrictions on the characteristic length of the concavo-convex structure and the upper limit of the inclination angle can be completely eliminated. Therefore, the electrical characteristics (leakage characteristics) of the device
There is no need to consider the trade-off at all, and it is possible to realize an element structure that can be optically optimized independently.

The part of the light incident from the element surface which reaches the interface between the semiconductor layer 14 and the back transparent conductive layer 13 is partially reflected toward the semiconductor layer 14, and the rest is reflected on the back transparent conductive layer 13. To the interface between the light-transmitting substrate 11 and a part of the latter, which is reflected toward the semiconductor layer 14, and the rest of the light-transmitting substrate 1.
1 and reaches the light reflection layer 12. The light that reaches the light reflecting layer 12 is obliquely reflected toward the semiconductor layer 14 according to the inclination angle of the back-side uneven structure. Of the reflected light, the light reaching the element surface is obliquely reflected toward the semiconductor layer 14 in accordance with the inclination angle on the uneven surface reflecting the spontaneous uneven structure of crystalline Si formed on the element surface. You. As described above, in the concavo-convex structure introducing device, photoelectric conversion is performed by reflecting the incident light many times in the device at a certain inclination angle, but the light traveling obliquely in the semiconductor layer is not reflected on the front transparent conductive layer 15. Since the interface between the semiconductor layer 14 and the semiconductor layer 14 and the interface between the semiconductor layer 14 and the back transparent conductive layer 13 are more likely to satisfy the condition of total reflection, a very high light confinement effect can be obtained.

In this element structure, there is no upper limit to the inclination angle of the back-side uneven structure, so that it is possible to form a very steep inclined surface exceeding, for example, 45 °. The emitted light can travel in a more horizontal direction. Light traveling in a more horizontal direction can travel a longer distance before being next reflected in the semiconductor layer 14, so that the number of times of reflection of light in the semiconductor layer 14 with respect to the traveling distance can be reduced, and the light can be slightly reflected. It is possible to realize more efficient photoelectric conversion in which the resulting cumulative loss of light absorption is kept lower.

The average distance between the vertices of adjacent arbitrary pyramids in the concavo-convex structure on the back surface of the substrate 11 (hereinafter referred to as the average size of the concavo-convex structure unit or the characteristic length) is set to 100 nm or more. The reason for this is that below this, it is regarded as optically flat, and the expected light scattering effect cannot be obtained.

That is, in general, an uneven structure having a characteristic length of about 1/4 of the light wavelength is regarded as optically flat. Therefore, in order to obtain an uneven structure having an expected light scattering effect, the characteristic length must be at least. 1/1 of the wavelength of the light in question
It is necessary to be 4 or more, preferably １ ／ or more.

In the case of the present invention, since the semiconductor film as the photoactive layer is composed of crystalline Si, the longest light wavelength that can be used is about 1200 nm. In other words, the wavelength of light to be considered in the present case is up to 1200 nm. At this time, if glass is taken as an example of a typical material of the translucent substrate 11 or the translucent thin film layer 22 (described later), its refractive The rate is about 1.5
Therefore, the light wavelength in this material medium can be regarded as 800 nm. In other words, the characteristic length of the concavo-convex structure is at least 800 n so that light having a wavelength of 1200 nm is obliquely reflected by the light reflection layer on the back surface side of the element and is effectively confined inside the element.
m, 200 nm or more, preferably 1/2, 40
It is necessary to be 0 nm or more. Actually, even if only the light confinement effect is obtained for light up to a wavelength of about 800 nm, there is a substantial substantial characteristic improvement effect.
In this case, the minimum characteristic length may be at least about 133 nm or more, desirably about 267 nm or more, which is the reason that the characteristic length is set to 100 nm or more.

Even if plastic or resin is used other than glass for the light-transmitting substrate 12 and the light-transmitting thin film layer 22 described later, the refractive index is still about 1.5, so the above-mentioned numerical values are still effective. .

The concave portion of the concave-convex structure on the back surface of the light-transmitting substrate 11 may have a curved surface.

Next, a method for manufacturing the above-mentioned thin-film crystalline Si solar cell will be described. First, a plate material or a film material made of glass, plastic, resin, or the like is prepared as the translucent substrate 11, and the back surface of the substrate 11 is processed into an uneven shape.

Here, when it is desired to form a concave-convex structure composed of a large number of triangular pyramids or more as described in claim 1, as the concave-convex structure on the back surface of the substrate 11, gold having a negative structure in advance is used. Prepare a negative replica such as a mold,
Accordingly, if the surface of the substrate 11 is pressed under an appropriate temperature condition, it can be easily realized at a relatively low cost. Here, the average distance between the vertices of adjacent arbitrary polygonal pyramids in the concavo-convex structure is 100 nm or more, more preferably 200 nm or more.
nm or more. In addition, as an original concavo-convex structure for producing a negative replica, for example, a concavo-convex structure that reflects a plane orientation of a Si crystal formed by etching a crystalline Si substrate under predetermined wet etching conditions or dry etching conditions is used. Can be
A spontaneous surface unevenness structure obtained by forming a transparent conductive film such as O ₂ under predetermined conditions can be used, and various materials can be used according to the unevenness structure to be obtained.

As the uneven structure on the back surface of the substrate 11,
In the case where the concave portion described in claim 2 forms a concave-convex structure having a curved surface, it can be realized at relatively low cost by processing using a dry etching method or a wet etching method. In particular, RIE, a type of dry etching method
It is described in Japanese Patent Application No. 2000-301419, for example, that a desired concavo-convex shape can be obtained depending on etching conditions such as a gas type, a gas pressure, and a plasma power. The average distance between the lowest points of the curved surfaces of the concave portions in the concave-convex structure is 100 nm or more, more preferably 200 nm or more. It is to be noted that the above-described press working method using a negative replica can be used for forming the uneven structure.

Next, a metal film to be the light reflection layer 12 is formed on the back surface side of the light transmitting substrate 11 on which the above-mentioned uneven structure is formed. Al and Ag which are excellent in light reflection characteristics as metal materials
It is desirable to use such as. Known techniques such as a vapor deposition method, a sputtering method, and an ion plating method can be used as a film forming method. At this time, the film thickness is 0.01 μm.
m or more. The light reflecting layer 12 and the light transmitting substrate 1
When the bonding strength with the substrate 1 is low, a thin metal film, such as Ti, which is easily oxidized may be inserted between the light reflecting layer 12 and the light transmitting substrate 11 with a thickness of about 1 to 10 nm.

Next, the back transparent conductive layer 13 is
Formed on the surface side of As the transparent conductive film material, SnO
₂ , known materials such as ITO and ZnO can be used. However, when a Si film to be subsequently deposited is used, the film is exposed to a hydrogen gas atmosphere due to the use of SiH ₄ and H _2. It is desirable to form a ZnO film having excellent reducibility at least as a final surface. As a film forming method, a known technique such as a CVD method, an evaporation method, an ion plating method, and a sputtering method can be used. At this time, the film thickness is set to 10 nm or more, more preferably 20 nm or more, in consideration of the fact that the back transparent conductive layer 13 also serves as the back electrode, in order to sufficiently reduce the sheet resistance value. In addition, since the transparent conductive layer tends to have an uneven shape due to its crystal structure as the film thickness increases, an expected substantially flat surface shape may not be obtained depending on conditions. In this case, a substantially flat surface shape can be obtained by first forming the transparent conductive layer 13 in an amorphous state and then crystallizing it by a thermal annealing treatment or the like.

Next, a semiconductor layer 14 having a semiconductor junction in which the photoactive layer is formed of crystalline Si is formed. The process is roughly divided into formation of a base layer, formation of a photoactive layer, and formation of a junction (each not shown). In the formation of these semiconductor layers, unnecessary nucleation is suppressed because the semiconductor deposition surface is already substantially flat as described above, so that the semiconductor crystal grains can be easily increased in size. Since both crystal grains grow in a columnar shape in parallel with the direction perpendicular to the substrate, generation of crystal grain boundaries due to collision between crystal grains can be suppressed, and deterioration of the quality of the semiconductor film due to crystal grain boundaries is suppressed as much as possible. Semiconductor layer formation can be performed. In addition, since strong (110) orientation characteristics can be obtained relatively easily,
An ideal spontaneous uneven structure suitable for confining light can be formed on the surface of the semiconductor layer 14.

First, a non-single-crystal Si film is formed as a base layer by a method such as a catalytic CVD method or a plasma CVD method. The film thickness is about 10 to 500 nm. The concentration of the doping element is about 1 × 1E18 to 1E21 / cm ³ , and the p ⁺ type (or n ⁺ type) is used.

Next, a crystalline Si film is formed as a photoactive layer by a method such as catalytic CVD or plasma CVD. The thickness is about 0.5 to 10 μm. The conductivity type is
It is of the same conductivity type with a lower doping concentration than that of the underlayer, or is substantially i-type.

Next, in order to form a semiconductor junction, a non-single-crystal Si film is formed by a method such as a catalytic CVD method or a plasma CVD method. The thickness is about 5 to 500 nm. The doping element concentration is set to about 1 × 1E18 to 1E21 / cm ^3, and is set to n ⁺ (or p ⁺ type) having a conductivity type opposite to that of the above-described underlayer. In order to further improve the bonding characteristics, substantially non-single-crystal silicon of i-type is provided between the photoactive layer and the bonding layer.
Layers may be inserted. At this time, the thickness of the insertion layer is crystalline S
The thickness is about 10 to 500 nm in the case of an i layer, and about 1 to 20 nm in the case of amorphous Si.

Next, the front transparent conductive layer 15 is formed. Known materials such as SnO ₂ , ITO, and ZnO can be used as the transparent conductive film material. As the film forming method, C
Known techniques such as a VD method, an evaporation method, an ion plating method, and a sputtering method can be used. At this time, the film thickness is 60 to 300 nm in consideration of the optical interference effect.
About.

Finally, a metal film to be the front electrode 16 is formed. Al and Ag which have excellent conductivity as metal film materials
It is desirable to use such as. As the film forming method, known techniques such as a vapor deposition method, a sputtering method, an ion plating method, and a screen printing method can be used. The electrode pattern can be formed into a desired pattern by using a masking method, a lift-off method, or the like. In order to enhance the adhesive strength with the front transparent conductive layer 15, it is effective to insert a metal material having excellent adhesive strength with an oxide material such as Ti between the front transparent conductive layer 15 and the surface electrode 16. It is a target.

As described above, a highly efficient thin-film crystalline Si solar cell having a double-sided concavo-convex optical confinement structure that does not increase the leakage current can be obtained.

Next, claim 3 and claim 4 will be described with reference to FIG.
An embodiment according to the present invention will be described. In the figure, 20 is a substrate, 21 is a light reflection layer made of metal, 22 is a light-transmitting thin film layer, 23 is a back transparent conductive layer serving as a back electrode, and 24 is a semiconductor junction in which a photoactive layer is formed of crystalline Si. , 25 is a front transparent conductive layer serving as a front electrode, and 26 is a front collecting electrode.

First, a plate or film made of glass, plastic, metal such as stainless steel or the like is prepared as the substrate 20, and one main surface of the substrate is processed into an uneven shape. At this time, one principal surface of the substrate 20 has an uneven structure composed of a large number of triangular pyramids or more by using the method described in the first embodiment. May be an uneven structure such that the average distance is 100 nm or more, more preferably 200 nm or more, or the recess has an uneven structure having a curved surface, and the average between the lowest points of adjacent recesses of the uneven structure. Distance is 100n
m or more, more preferably 200 nm or more. Next, the light reflection layer 21 made of metal is formed. As this metal material, it is desirable to use Al, Ag, or the like which has excellent light reflection characteristics. Known techniques such as a vapor deposition method, a sputtering method, and an ion plating method can be used as a film forming method. At this time, the film thickness is about 0.01 to 1 μm. The light reflecting layer 21
When the adhesive strength between the substrate and the substrate 20 is weak, a thin metal film, such as Ti, which is easily oxidized and has a thickness of about 1 to 10 nm
1 and the substrate 20. In addition, the substrate 2
When 0 is made of a light-reflective metal such as stainless steel, the light-reflective layer 21 can be omitted because the substrate 20 itself can also function as a light-reflective layer. Next, a glass layer, a plastic layer, a resin layer, or the like is deposited as the light-transmitting thin film layer 22. At this time, if these materials are made to be in a fluid state under appropriate conditions and are deposited in an appropriate amount on the light reflection layer 21, the surface of the light-transmitting thin film layer 22 is naturally formed by the fluidity effect. And a substantially flat surface with reduced irregularities can be obtained. The flattening treatment by fluidization may be performed after the material is deposited. Further, if necessary, a flattening process may be added. When the adhesive strength between the light-transmitting thin film layer 22 and the light reflecting layer 21 is weak, a thin metal film, such as Ti, which is easily oxidized and has a thickness of about 1 to 10 nm is formed on the light-transmitting thin film layer 22 and the light reflecting layer 21. It is good to be inserted between. Less than,
A back transparent conductive layer 23, a semiconductor layer 24 having a semiconductor junction in which the photoactive layer portion is formed of crystalline Si, a front transparent conductive layer 25,
The surface collecting electrodes 26 are sequentially formed, but the details thereof are omitted since they are the same as those described in the first embodiment.

According to this device structure, the semiconductor layer 24 can be formed on a substantially flat surface, as described in the first embodiment, so that the electrical characteristics (leakage characteristics) of the device can be improved. There is no need to consider the trade-off of
It is possible to realize an element structure that can achieve optically optimal structuring completely independently. Further, in the element structure of the second embodiment, since the light-transmitting substrate in the first embodiment is a light-transmitting thin film layer, the light traveling distance in the light-transmitting material can be shortened. It is possible to reduce a slight loss of light absorption occurring in this translucent material. Furthermore, if a metal material is used as the substrate, the formation of the light reflection layer can be omitted, and the cost can be reduced.

[0044]

As described above, according to the first and second aspects of the present invention, in a thin film crystalline Si solar cell,
Since a two-sided concavo-convex optical confinement structure without increasing the leak current can be realized, it is possible to manufacture a thin-film crystalline Si solar cell with higher efficiency than before.

According to the third and fourth aspects of the present invention, since a light-transmitting thin film layer is used, light absorption loss in this material can be reduced, and a metal material can be used as a substrate. By using, the formation of the light reflection layer can be omitted, so that the cost can be further reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a thin-film crystalline Si solar cell according to claims 1 and 2 of the present invention.

FIG. 2 is a cross-sectional view showing one embodiment of a thin-film crystalline Si solar cell according to claims 3 and 4 of the present invention.

FIG. 3 is a cross-sectional view showing an example of a conventional thin-film crystalline Si solar cell having a double-sided uneven structure.

FIG. 4 is a cross-sectional view showing another example of a conventional thin-film crystalline Si solar cell having a double-sided uneven structure.

FIG. 5 is a cross-sectional view showing another example of a conventional thin-film crystalline Si solar cell having a double-sided uneven structure.

FIG. 6 is a cross-sectional view showing an example of the prior art made to solve the problem of the conventional double-sided uneven structure thin film crystalline Si solar cell.

FIG. 7 is a cross-sectional view showing another example of the prior art made to solve the problem of the conventional double-sided uneven structure thin film crystalline Si solar cell.

[Explanation of symbols]

11; translucent substrate; 12; light reflecting layer; 13; back transparent conductive layer; 14; semiconductor layer having a semiconductor junction in which the photoactive layer is formed of crystalline Si; 15; front transparent conductive layer; Collector electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F051 AA03 CA15 CB15 CB21 CB24 DA04 FA03 FA04 FA14 GA02 GA03 GA06 GA14 GA20

Claims (4)

[Claims] 1. A back transparent conductive layer serving as a back electrode, a semiconductor layer having a semiconductor junction in which a photoactive layer portion is formed of crystalline Si, and a front transparent conductive serving as a front electrode are provided on one main surface side of a light transmitting substrate. In the thin-film crystalline Si solar cell in which the layers and the collecting electrodes are sequentially stacked, the other main surface side of the light-transmitting substrate has a concavo-convex structure composed of a large number of pyramids of three or more pyramids, and is adjacent to the concavo-convex structure. An average distance between vertices of a polygonal pyramid is 100 nm or more, and a light reflecting layer made of metal is formed on the uneven structure. 2. The thin film crystal according to claim 1, wherein the concave portion of the concave-convex structure has a curved surface, and the average distance between the lowest points of adjacent concave portions of the concave-convex structure is 100 nm or more. Quality Si solar cell. 3. A back transparent conductive layer serving as a back electrode, a semiconductor layer having a semiconductor junction in which a photoactive layer portion is formed of crystalline Si, a front transparent conductive layer serving as a front electrode, and a surface on one principal surface side of the substrate. In a thin-film crystalline Si solar cell in which collector electrodes are sequentially stacked, one main surface side of the substrate has a concavo-convex structure composed of a large number of polygonal pyramids of three or more pyramids, or a concave-convex structure in which a concave portion has a curved surface. The average distance between the vertices of adjacent polygonal pyramids or the average distance between the lowest points of adjacent concave portions of the concavo-convex structure is 100 nm or more, and the surface between the concavo-convex structure and the back transparent conductive layer has a surface. A thin-film crystalline Si solar cell, wherein a substantially flat translucent thin-film layer is formed. 4. The light-transmitting substrate according to claim 3, wherein a light-reflecting layer made of metal is provided between the light-transmitting substrate and the light-transmitting thin film layer. A thin-film crystalline Si solar cell as described.