JP2012182161A - Thin film solar cell and method for manufacturing thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film solar cell capable of improving light utilization efficiency, and a method for manufacturing a thin film solar cell.SOLUTION: A thin film solar cell 10 includes: a transparent substrate 11; a light transmission layer 12 formed on the transparent substrate 11; and a transparent electrode 13 formed on the light transmission layer 12. A transmittance of a material forming the light transmission layer 12 is higher than that of a material forming the transparent electrode 13, and a texture 12a comprising projecting parts is formed on a surface on a transparent electrode 13 side of the light transmission layer 12. A texture 13a comprising projecting parts having a forming period shorter than that of the texture 12a in the light transmission layer 12 is formed on a surface of the transparent electrode 13, the surface being on the opposite side to the light transmission layer 12.

Description

  The present invention relates to a thin film solar cell, and more particularly to a thin film solar cell having a texture structure that increases the amount of sunlight incident on a power generation layer by scattering sunlight, and a method of manufacturing the thin film solar cell.

  Conventionally, as described in Patent Document 1, for example, a thin film solar cell having a silicon thin film formed by an evaporation method such as a plasma CVD method as a power generation layer is known. A cross-sectional structure of such a thin film solar cell is shown in FIG.

  As shown in FIG. 8, on the transparent substrate 101 of the thin film solar cell, the transparent electrode 102, the first power generation layer 103, the intermediate layer 104, the second power generation layer 105, the buffer layer 106, and the back electrode 107 are made of light. They are stacked in order from the incident side. Among these, a so-called texture 102a composed of a plurality of convex portions is formed on the surface of the transparent electrode 102 on the back electrode 107 side. The texture 102a lengthens the optical path length in the power generation layers 103 and 105 by multiply scattering the light incident on the thin film solar cell. For this reason, the amount of light absorbed by the power generation layers 103 and 105 increases, so the power generation amount per unit volume of the power generation layers 103 and 105 increases. Since it is known that the texture 102a easily scatters light having a wavelength corresponding to the period of the convex portion, the shape of the texture 102a depends on the wavelength absorbed by the power generation layers 103 and 105. It is assumed.

  By the way, the first power generation layer 103 and the second power generation layer 105 are formed of materials having different absorption sensitivity characteristics. Specifically, the first power generation layer 103 is formed of amorphous silicon that absorbs light on a relatively short wavelength side, while the second power generation layer 105 is microcrystalline silicon that absorbs light on a longer wavelength side. Is formed by. Thereby, the range of the wavelength of the light which contributes to electric power generation in a single thin film solar cell can be expanded, and the utilization efficiency of the light in a thin film solar cell can be improved.

  However, the wavelength of light that is easily scattered by the texture 102a is determined by the period of the convex portion. Therefore, in the shape of the texture 102a as shown in FIG. 8, it is difficult to multiplex-scatter both light having wavelengths that are easily absorbed by the first power generation layer 103 and the second power generation layer 105. Therefore, as shown in FIG. 9, after forming the first texture 112a having the first period 112c having a relatively long period of the top part t1 of the convex part with respect to the transparent electrode 112 on the transparent substrate 111, A second texture 112b having a second period 112d in which the period of the top part t2 of the convex part is relatively short is formed on the surface. As a result, both light having wavelengths that are easily absorbed by the first power generation layer 103 and the second power generation layer 105 can be subjected to multiple scattering.

International Publication No. 2010/032490

  On the other hand, the transparent electrode 112 having the two textures 112a and 112b is formed of various conductive oxide films such as indium tin oxide (ITO). Although the conductive oxide film is translucent, the transmissivity is lower than that of other transparent members constituting the thin film solar cell, such as a transparent substrate. Then, if a texture having a relatively long period of convex portions like the first texture 112a is formed of a conductive oxide, the conductive oxide film must be naturally thickened accordingly. The amount of light that passes through the transparent electrode 112 to the power generation layer side is reduced. As a result, even if the range of wavelengths that can be subjected to multiple scattering is expanded, the amount of light transmitted to the power generation layer side is reduced, so that it is difficult to increase the light use efficiency in the thin-film solar cell.

  Such a problem is not limited to a thin film solar cell having two power generation layers having different absorption wavelengths, and the transparent electrode as described above is adopted even in a thin film solar cell having a single power generation layer. In this case, it occurs in common.

  This invention is made | formed in view of the said situation, The objective is to provide the manufacturing method of the thin film solar cell which can improve the utilization efficiency of light, and a thin film solar cell.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
The invention according to claim 1 is formed on the transparent substrate, the first light transmission layer formed on the transparent substrate, the transparent electrode formed on the first light transmission layer, and the transparent electrode. The first light transmission layer is made of a material having a higher transmittance than the material for forming the transparent electrode, and a plurality of the first light transmission layer is provided on the surface on the transparent electrode side. The first convex portion is formed, and a thin film solar cell in which a plurality of second convex portions are formed in the transparent electrode at a smaller interval than the first convex portion is taken as a gist.

  According to the above configuration, the first light transmission layer formed of a material having a higher transmittance than the material for forming the transparent electrode is formed with the first convex portions having relatively large intervals, and the transparent electrode Only the 2nd convex part with a comparatively small space | interval is formed. As a result, light having a wavelength corresponding to the interval between the first convex portions is scattered at the boundary between the first light transmission layer and the transparent electrode, and the interval between the second convex portions at the boundary between the transparent electrode and the photoelectric conversion layer. Accordingly, light having a wavelength corresponding to is scattered. With such a structure, since the thickness of the layer necessary for forming the first convex portion is compensated by the first light transmission layer different from the transparent electrode, two types of convex portions having different intervals are photoelectrically converted. Although it is formed between the layer and the transparent substrate, it is possible to suppress an increase in the thickness of the transparent electrode due to the formation of such convex portions. Therefore, by reducing the transmittance by reducing the thickness of the transparent electrode while multiply diffusing light of a wider range of wavelengths than when having a convex portion with one cycle, the convex portion having two different periods can reduce the transmittance. As a result, the utilization efficiency of light incident on the transparent substrate can be increased.

  According to a second aspect of the present invention, in the thin-film solar cell according to the first aspect, the second light transmissive layer includes a second light transmissive layer formed between the first light transmissive layer and the transparent electrode. The gist is that the layer is made of a material having a higher transmittance than the material for forming the transparent electrode, and the second light transmission layer fills a space between the first convex portions adjacent to each other.

  According to the above configuration, since the second light transmission layer made of a material having a higher transmittance than the material for forming the transparent electrode is provided between the first light transmission layer and the transparent electrode, the transmittance decreases. The film structure on the transparent substrate side with respect to the transparent electrode, that is, the base structure of the transparent electrode is easily flattened. Thereby, the transparent electrode formed on the second light transmission layer is easily formed uniformly in the plane of the transparent substrate at the time of formation.

The gist of the invention of claim 3 is that, in the thin film solar cell of claim 2, the refractive index of the second light transmission layer and the refractive index of the transparent electrode are equal to each other.
According to the above configuration, since the refractive index of the second light transmission layer and the refractive index of the transparent electrode are equal to each other, no light is reflected at the interface between the second light transmission layer and the transparent electrode. Therefore, the light use efficiency in the power generation layer can be further increased.

  The invention according to claim 4 is a step of forming a first light transmission layer on a transparent substrate, a step of forming a transparent electrode on the first light transmission layer, and a photoelectric conversion layer on the transparent electrode. In the step of forming the first light transmission layer, the first light transmission layer is formed of a material having a higher transmittance than the material for forming the transparent electrode, and the first light transmission layer is formed on the first light transmission layer. In the step of forming a plurality of first protrusions on the surface on the transparent electrode side and forming the transparent electrode, a plurality of second protrusions are formed in the transparent electrode at a smaller interval than the first protrusions. The manufacturing method of a thin film solar cell is summarized.

  According to the above method, the first light transmission layer is formed of a material having a higher transmittance than the material for forming the transparent electrode, and the first protrusions having a relatively large interval with respect to the first light transmission layer are formed. Like to do. In this method, the second convex portions having a relatively small interval with respect to the transparent electrode are formed. Therefore, in the formed thin film solar cell, the transparent electrode is formed by multiply diffusing light having a wider range of wavelengths than the case of having a convex portion having one cycle by a convex portion having two different periods. By reducing the film thickness, it is possible to suppress a decrease in transmittance, and to increase the utilization efficiency of light incident on the transparent electrode.

  Invention of Claim 5 is a manufacturing method of the thin film solar cell of Claim 4, Comprising: The process of forming a 2nd light transmissive layer between the said 1st light transmissive layer and the said transparent electrode, The said, The gist of the step of forming the second light transmission layer is to fill a space between the first convex portions adjacent to each other by the second light transmission layer made of a material having a higher transmittance than the material for forming the transparent electrode. .

  According to the above method, the second light transmission layer made of a material having a higher transmittance than the material for forming the transparent electrode is formed between the first light transmission layer and the transparent electrode. In addition, a space between the first convex portions adjacent to each other is filled with the second light transmission layer. As a result, the film structure on the transparent substrate side with respect to the transparent electrode, that is, the base structure of the transparent electrode is flattened while suppressing a decrease in transmittance, so that the transparent electrode can be uniformly formed in the plane of the transparent substrate. become.

  The invention according to claim 6 is the invention according to claim 4 or 5, wherein in the step of forming the first light transmission layer, the first convex portion of the first light transmission layer is formed by a nanoimprint method. This is the gist.

  According to the above method, since the first convex portion is formed by the nanoimprint method, the first convex portion can be formed only by transferring the mold. Therefore, it can be performed easily and inexpensively compared with a method of forming the convex portion through a lithography process, an etching process, or the like.

The figure which shows the perspective structure of 1st Embodiment in the thin film solar cell of this invention. (A) (b) (c) The figure which shows the manufacturing process of 1st Embodiment in the manufacturing method of the thin film solar cell of this invention in order. (A) (b) (c) (d) (e) The figure which shows the manufacturing process of the embodiment in order. The figure which shows the perspective structure of 2nd Embodiment in the thin film solar cell of this invention. (A) (b) The figure which shows the manufacturing process of 2nd Embodiment in the manufacturing method of the thin film solar cell of this invention in order. (A) (b) The figure which shows the manufacturing process in the same embodiment in order. The figure which shows the cross-section of the transparent substrate and transparent electrode in a modification. The figure which shows the cross-section of the conventional thin film solar cell. The figure which shows the cross-section of the conventional transparent electrode.

[First Embodiment]
Hereinafter, a first embodiment that embodies a thin film solar cell and a method for manufacturing the thin film solar cell of the present invention will be described with reference to FIGS.
[Structure of thin film solar cell]
First, the structure of the thin film solar cell in this embodiment is demonstrated with reference to FIG. As shown in FIG. 1, the thin film solar cell 10 includes a transparent substrate 11, a light transmission layer 12, a transparent electrode 13, a first power generation layer 14, an intermediate layer 15, a second power generation layer 16, a buffer layer 17, and a back electrode. 18 is laminated in order from the light incident side.

  Among these, the transparent substrate 11 is formed of an insulating material such as various types of glass and transparent resin. The light transmission layer 12 is formed of a transparent material having a higher transmittance than the lower transparent electrode, and the surface of the light transmission layer 12 on the back electrode 18 side has a concavo-convex structure, so-called texture 12a. The transparent electrode 13, the intermediate layer 15, and the buffer layer 17 are all formed from a transparent conductive oxide thin film. Examples of the conductive oxide include translucent conductive oxide films (TCO) such as aluminum-containing zinc oxide (AZO), gallium-containing zinc oxide (GZO), indium tin oxide (ITO), and fluorine-containing tin oxide (FTO). Can be used. The surface on the back electrode 18 side of the transparent electrode 13 has textures 13 a at intervals smaller than the texture 12 a of the light transmission layer 12.

  The first power generation layer 14 is formed of an amorphous silicon thin film, and in order from the light incident side, a first p-type semiconductor layer 14p to which p-type impurities are added, a first i-type semiconductor layer 14i to which no impurities are added, And a first n-type semiconductor layer 14n doped with an n-type impurity. The second power generation layer 16 is formed of a microcrystalline silicon thin film, and similarly to the first power generation layer 14, a second p-type semiconductor layer 16p to which p-type impurities are added in order from the light incident side, and to which impurities are added. This is a structure in which the second i-type semiconductor layer 16i that has not been added and the second n-type semiconductor layer 16n to which an n-type impurity is added are stacked. The back electrode 18 is formed of a light reflecting film having conductivity such as silver or aluminum.

In such a thin film solar cell 10, the first power generation layer 14 and the second power generation layer 16 convert incident light into electric power. In addition, the first power generation layer 14 and the second power generation layer 16 are different from each other in the wavelength range of light to be photoelectrically converted, so that the first power generation layer 14 and the second power generation layer 16 are compared with the thin film solar cell having only the first power generation layer 14 or the second power generation layer 16. , The efficiency of converting light into electric power increases.
[Method for Manufacturing Thin Film Solar Cell]
Next, the manufacturing method of the thin film solar cell in this embodiment, especially the manufacturing method of the light transmission layer 12 and the transparent electrode 13, is demonstrated with reference to FIG.2 and FIG.3. 2 and 3 are diagrams showing the cross-sectional structure in each manufacturing process along the line AA in FIG. 1, and the cross-sectional structure is in order of the manufacturing process of the thin-film solar cell 10. It is shown. 2 and 3, the light incident side surface of the transparent substrate is shown as the lower surface of the transparent substrate.

  As shown in FIG. 2A, a sol-gel liquid transparent material 22 is applied to one surface of the transparent substrate 21 by a bar coater, a spray or the like. The transparent substrate 21 can be formed of various glass substrates such as soda lime silicate glass, aluminosilicate glass, borate glass, lithium aluminosilicate glass, and quartz glass. The transparent substrate 21 can also be formed of various resins such as polyethylene terephthalate, polyimide, polycarbonate, and acrylic.

When the transparent material 22 forms a silicon oxide film on the transparent substrate 21, for example, organoalkoxysilane such as methoxytriethylsilane, phenyltriethoxysilane, triethoxysilane, ethanol, water, hydrochloric acid, and the like. Or silsesquioxane. When the transparent material 22 is the above mixture, the molar ratio of ethanol, water, and hydrochloric acid to the organosiloxane is, for example, “1: 4: 2 × 10 ⁻³ ”. The transmittance of the transparent material 22 of such a mixture is higher than the transmittance of the material for forming the transparent electrode 13. Further, for example, when a film of a resin material is formed on the transparent substrate 21, the transparent material 22 is a thermoplastic resin such as an epoxy resin, a phenol resin, and an acrylic resin. The transmittance of these resins is higher than the transmittance of the material for forming the transparent electrode 13.

  When the transparent material 22 is applied on the transparent substrate 21 in this way, after the drying process for drying the transparent material 22 for a predetermined time is performed, as shown in FIG. A mold 31 formed of a polymethylpentene film or the like is pressed.

  The mold 31 is pressed against the transparent material 22 with a pressure of, for example, 1 MPa or less, preferably about 0.1 MPa or more and 0.4 MPa or less. The degree of drying of the transparent material 22 in the previous step is such that the transparent material 22 pressed against the mold 31 is deformed so as to follow the shape of the mold 31 in such a pressure range and the shape is maintained. Adjusted to

  Next, as shown in FIG. 2C, the transparent material 22 is heated in a state where the mold 31 is pressed, whereby the transparent material 22 is dried. For example, when the mold 31 is formed of the polymethylpentene film, it is preferable to heat at a temperature of about 40 ° C. or more and 50 ° C. or less. By drying the transparent material 22 at such a temperature, deformation of the mold 31 due to heat can be suppressed, so that the shape of the mold 31 can be accurately transferred to the transparent material 22.

  Subsequently, after the transparent material 22 is dried, the mold 31 is removed from the transparent material 22 as shown in FIG. Thereafter, as shown in FIG. 3B, the transparent material 22 is baked at 400 ° C. for 60 minutes, thereby forming a light transmission layer 23 made of, for example, silicon oxide. The light transmission layer 23 has a texture composed of a plurality of convex portions 23 a that are convex in a direction away from the transparent substrate 21. The plurality of convex portions 23a (first convex portions) are formed so that the period which is the interval between the adjacent top portions 23t is a relatively long first period 23p, for example, 0.7 μm or more and 2.6 μm or less. .

  In the present embodiment, the process described with reference to FIGS. 2 (a) to 2 (c) and FIGS. 3 (a) to 3 (b) is a texture using a so-called nanoimprint method. It is a forming process.

  Then, as shown in FIG. 3C, by sputtering a conductive oxide target with a plasma 32 generated from an inert gas such as argon, as shown in FIG. A transparent electrode 24 is formed on the transmission layer 23. The target forming material is, for example, zinc oxide to which aluminum or gallium is added in a proportion of 0.1 to 10% by weight. The transparent electrode 24 is formed by a first process that is a sputtering process under a relatively low pressure condition and a second process that is a sputtering process under a relatively high pressure condition. The pressure in the first step is set to 2 mTorr or more and less than 10 mTorr. On the other hand, the pressure during the second step is set to 10 mTorr or more, preferably 30 mTorr or more and less than 50 mTorr. In the first step and the second step, the temperature of the transparent substrate 21 is set to 100 ° C. or more and 600 ° C. or less. For example, AZO is selected as a material for forming the transparent electrode 24.

When the transparent electrode 24 is formed, the surface of the transparent electrode 24 is wet-etched using an etching solution 33 as shown in FIG. In the wet etching, the transparent electrode 24 is immersed in 0.01% hydrochloric acid as the etching solution 33 for 90 seconds. As a result, as shown in FIG. 3E, a texture composed of a plurality of convex portions 24 a is formed on the surface of the transparent electrode 24 opposite to the light transmission layer 23. The plurality of convex portions 24a (second convex portions) have a second period 24p that is a relatively short period, for example, a period that is an interval between adjacent top parts 24t, for example, 0.2 μm or more and 0.6 μm or less. Is formed. That is, the second period 24 p in the transparent electrode 24 is set to a length different from the first period 23 p in the light transmission layer 23.
[Power generation layer]
The various electrodes and power generation layers shown in FIG. 1 are formed by the following method, for example. First, the first power generation layer 14 formed of amorphous silicon is formed on the transparent electrode 13. The first power generation layer 14 is formed by, for example, a plasma CVD method. In forming the first power generation layer 14, first, the first p-type semiconductor layer 14p, which is an amorphous silicon layer to which boron as a p-type impurity is added, is formed by, for example, monosilane (SiH ₄ ) gas, hydrogen (H ₂ ) gas, And diborane (B ₂ H ₆ ) gas. Next, a first i-type semiconductor layer 14i, which is an amorphous silicon layer to which no impurity is added, is formed on the first p-type semiconductor layer 14p by, for example, monosilane gas. Then, the first n-type semiconductor layer 14n, which is an amorphous silicon layer to which phosphorus as an n-type impurity is added, is formed by, for example, monosilane gas, hydrogen gas, and phosphine (PH ₃ ) gas.

  Next, after the intermediate layer 15 is formed by the same method as the transparent electrode 13, the second power generation layer 16 formed of microcrystalline silicon is formed. The second p-type semiconductor layer 16p, the second i-type semiconductor layer 16i, and the second n-type semiconductor layer 16n constituting the second power generation layer 16 are, for example, a layer having the same conductivity type that constitutes the first power generation layer 14. While using the same gas, it is formed by plasma CVD under a relatively higher pressure than when amorphous silicon is formed. Then, after the buffer layer 17 is formed by the same method as the transparent electrode 13, the back electrode 18 is formed by various vapor deposition methods such as sputtering a silver or aluminum target.

As described above, according to the first embodiment, the effects listed below can be obtained.
(1) The light transmission layer 12 formed of a material having a higher transmittance than the material for forming the transparent electrode 13 is formed with a texture 12a having a relatively large interval, and the transparent electrode 13 is relatively Only the texture 13a having a small interval is formed. Thereby, at the boundary between the light transmission layer 12 and the transparent electrode 13, light having a wavelength corresponding to the interval of the texture 12a is scattered, and at the boundary between the first power generation layer 14 and the transparent electrode 13 constituting the photoelectric conversion layer. The light having a wavelength corresponding to the interval between the textures 13a is scattered. With such a structure, the thickness of the layer necessary for the formation of the texture 12a is supplemented by the light transmitting layer 12 different from the transparent electrode 13, so that two types of convex portions having different intervals are formed with the photoelectric conversion layer. Although formed between the transparent substrate 11 and the projections, the increase in the thickness of the transparent electrode 13 can be suppressed. Thereby, the transmission amount of the light to the photoelectric converting layer side can be increased.

  Therefore, by forming a layer having the same film thickness only by the transparent electrode while multiply diffusing light of a wider range of wavelengths than the case of having a convex portion having one cycle by a convex portion having two different periods. However, the transmittance is improved, and as a result, the utilization efficiency of light incident on the transparent electrode can be increased.

(2) In the step of forming the light transmission layer 12, the texture 12a in the light transmission layer 12 is formed by the nanoimprint method. According to such a method, the texture 12 a can be formed only by transferring the mold 31. Therefore, compared with the method of forming the texture 12a through the lithography process, the etching process, etc., the light transmission layer 12 itself can be formed together with the texture 12a, so that the manufacture of the antireflection body is simpler and less expensive. Can be done.
[Second Embodiment]
Hereinafter, a thin film solar cell according to a second embodiment of the present invention and a method for manufacturing the thin film solar cell will be described with reference to FIGS. In addition, the thin film solar cell of this embodiment differs from the thin film solar cell of the said 1st Embodiment only in the structure of a light transmissive layer and a transparent electrode. Therefore, in this embodiment, it demonstrates focusing on the structure and manufacturing method of these light transmission layers and transparent electrodes.
[Structure of thin film solar cell]
First, the structure of the thin film solar cell in this embodiment is demonstrated with reference to FIG. As shown in FIG. 4, the thin film solar cell 40 includes a transparent substrate 41, a first light transmission layer 42, a second light transmission layer 43, a transparent electrode 44, a first power generation layer 45, an intermediate layer 46, and a second power generation layer. 47, a buffer layer 48, and a back electrode 49 are laminated in order from the light incident side.

Among these, on the transparent substrate 41, the first light transmission layer 42 having the texture 42a on the surface on the back electrode 49 side is formed. In the first light transmission layer 42, a second light transmission layer 43 is formed so as to embed a concave portion constituting the texture 42a. Therefore, the surface on the back electrode 49 side of the second light transmission layer 43 is a flat surface. On the flat surface of the second light transmission layer 43, a transparent electrode 44 made of a conductive oxide as exemplified in the first embodiment is formed. On the surface of the transparent electrode 44 on the back electrode 49 side, a texture 44 a having convex portions formed at a cycle shorter than the texture 42 a of the first light transmission layer 42 is formed.
[Method for Manufacturing Thin Film Solar Cell]
Next, the manufacturing method of the thin film solar cell in this embodiment, especially the manufacturing method of the said 1st light transmission layer 42, the 2nd light transmission layer 43, and the transparent electrode 44 is demonstrated with reference to FIG.5 and FIG.6. 5 and 6 are diagrams showing a cross-sectional structure in each manufacturing process along the line BB in FIG. 4, and the cross-sectional structure is in order of the manufacturing process of the thin-film solar cell 40. It is shown. 5 and 6, the light incident side surface of the transparent substrate is shown as the lower surface of the transparent substrate.

  As shown in FIG. 5A, the second light transmission layer 53 is formed so as to cover the entire convex portion 52 a in the first light transmission layer 52 on the transparent substrate 51. As the transparent substrate 51, a substrate made of the same material as that of the transparent substrate 21 in the first embodiment can be used. The first light transmission layer 52 is formed using the same material and method as the light transmission layer 23 of the first embodiment. The surface of the first light transmission layer 52 opposite to the transparent substrate 51 has a texture constituted by a plurality of convex portions 52a. In addition, the some convex part 52a is formed so that the period which is the space | interval of the adjacent top part 52t may become the relatively long 1st period 52p.

  The second light transmission layer 53 is formed by applying a sol-gel liquid transparent material to the surface of the first light transmission layer 52. As a material for forming the second light transmission layer 53, a material having a refractive index substantially equal to that of the transparent electrode 44 formed on the second light transmission layer 53 is preferably used.

  For example, when the transparent electrode 44 is made of AZO, the refractive index is about 1.9. At this time, if a sol-gel solution containing titanium alkoxide is used as the transparent material, the refractive index of the second light transmission layer 53 can be set to about 1.9. The transparent material forming the second light transmission layer 53 is applied with a thickness that allows the top 52t of the convex portion 52a of the first light transmission layer 52 to be embedded in the transparent material. Therefore, the surface opposite to the transparent substrate 51 in the second light transmission layer 53 is flat.

  After the second light transmission layer 53 is dried, as shown in FIG. 5B, the plasma 61 generated from an inert gas such as argon is used as the conductive oxide target as in the first embodiment. As shown in FIG. 6A, the transparent electrode 54 is formed on the second light transmission layer 53 by sputtering. The target forming material, the sputtering pressure, the substrate temperature, and the like are the same as those in the first embodiment. In the present embodiment, the entire surface of the convex portion 52a of the first light transmission layer 52 is covered with the second light transmission layer 53, so that the surface of the second light transmission layer 53 on which the transparent electrode 54 is formed is flattened. Therefore, the transparent electrode 54 can be uniformly formed on the entire surface of the second light transmission layer 53.

  Next, as shown in FIG. 6A, the transparent substrate 51 on which the transparent electrode 54 is formed is immersed in the etching solution 62. Thereby, the surface of the transparent electrode 54 is wet-etched. The composition of the etching solution 62 and the processing time for wet etching are the same as those in the first embodiment.

  In this way, as shown in FIG. 6B, a texture composed of a plurality of convex portions 54a is formed on the surface of the transparent electrode 54 opposite to the transparent substrate 51. In addition, the some convex part 54a is formed so that the period which is the space | interval of the adjacent top part 54t may become the relatively short 2nd period 54p.

As described above, according to the second embodiment, the effects listed below can be obtained in addition to the effects obtained by the first embodiment.
(3) Since the second light transmission layer 53 is provided between the first light transmission layer 52 and the transparent electrode 54, the film structure on the transparent substrate 41 side with respect to the transparent electrode 54, that is, the underlying structure of the transparent electrode 54 Becomes easy to be flattened. Therefore, the transparent electrode 54 formed on the second light transmission layer 53 is easily formed uniformly within the surface of the transparent substrate at the time of formation.

(4) Since the refractive index of the second light transmission layer 53 and the refractive index of the transparent electrode 54 are substantially equal, light reflection hardly occurs at the interface between the second light transmission layer 53 and the transparent electrode 54. Therefore, the light use efficiency in each of the power generation layers 45 and 47 can be further increased.
[Modification]
In addition, the said embodiment can also be suitably changed and implemented as follows.

  -In 1st Embodiment and 2nd Embodiment, the thin film solar cell in this invention is embodied as a thin film solar cell which has the 1st electric power generation layers 14 and 45 and the 2nd electric power generation layers 16 and 47 which were formed with a mutually different material. It has become. However, the present invention is not limited to this, and the thin film solar cell in the present invention may be embodied as a thin film solar cell having only one power generation layer or a thin film solar cell including a plurality of power generation layers made of the same material.

  In the first and second embodiments, the first period, which is a relatively long period, is set to 0.7 μm or more and 2.6 μm or less, and the second period, which is a relatively short period, is set to 0.2 μm or more. It was made to be 0.6 μm or less. Not only this but the length of the 1st period and the 2nd period will be light absorbed in the power generation layer with which thin film solar cells 10 and 40 are provided, if the conditions that the 1st period is longer than the 2nd period are satisfied. It can be appropriately changed according to the wavelength and the like.

  The mold 31 may be formed of a material other than the polymethylpentene film, such as a metal. In short, any material that can transfer the shape of the convex portion to the transparent material 22 may be used.

  The light transmitting layer 23 (12) in the first embodiment and the first light transmitting layer 52 (42) in the second embodiment are formed of a material containing organosiloxane as a material capable of forming silicon oxide. . However, the present invention is not limited to this, and other materials may be used as long as silicon oxide can be formed and the shape can be transferred by the mold 31.

  The light transmissive layer 23 (12) in the first embodiment and the first light transmissive layer 52 (42) in the second embodiment are materials having the above-described transmittance and refractive index and form the above texture. If possible, the material may be formed of a material other than a material capable of forming silicon oxide and a resin material.

  In the second embodiment, the material for forming the second light transmission layer 53 (43) is a material having substantially the same refractive index as that of the transparent electrode 54 (44), and the transparent electrode 54 (44) A material other than the titanium alkoxide may be used as long as the material has higher transmittance than the forming material.

The material for forming the second light transmission layer 53 (43) may be any material having a higher transmittance than the material for forming the transparent electrode 54 (44), and the refractive indexes of these materials may be different from each other. .
The firing temperature when forming each of the light transmissive layers 23, 42, 43 and the transparent electrodes 13, 44 can be changed as appropriate as long as these can be formed.

The composition of the etching solutions 33 and 62 and the wet etching treatment time can be changed as appropriate within a range in which the texture can be formed on the transparent electrodes 13 and 44.
In the first embodiment and the second embodiment, the texture is formed on the transparent electrodes 24 and 44 by wet etching. However, the present invention is not limited to this, and the texture may be formed by dry etching.

  The textured transparent electrodes 24 and 44 are formed by sputtering and wet etching. However, the present invention is not limited to this, and a transparent electrode having a texture on the back electrodes 18 and 49 may be formed by MOCVD (Metal Organic Chemical Vapor Deposition).

  The texture is formed on the light transmission layer 23 and the first light transmission layer 52 by using a nanoimprint method. However, the present invention is not limited to this, and it may be formed by other methods such as etching using a mask or etching without using a mask.

  In the second embodiment, the entire first light transmission layer 52 (42) is embedded by the second light transmission layer 53 (43). Not limited to this, as shown in FIG. 7, the second light transmission layer 73 may be formed up to the middle of the convex portion 72 a in the first light transmission layer 72 formed on the transparent substrate 71. And you may make it form the transparent electrode 74 so that the top part 72t of the convex part 72a in the 1st light transmission layer 72 may be covered.

  In the second embodiment, the transparent electrode 54 (44) is formed on the second light transmission layer 53 (43), and a texture is formed on the surface opposite to the second light transmission layer 53 by the transparent electrode 54. I tried to do it. Without being limited thereto, before forming the transparent electrode 54 (44), a texture is formed on the surface of the second light transmission layer 53 (43), which is the base of the transparent electrode 54, and the texture is provided on the surface. A transparent electrode 54 (44) is formed on the two light transmission layer 53 (43). Then, a texture is formed on the surface of the second light transmission layer 53 (44) side by the transparent electrode 54 (44) by the texture formed on the surface of the second light transmission layer 53 (43) as the base. You may do it.

  According to such a configuration and method, while the texture is formed on the transparent electrode 54, the surface on the power generation layer side can be made flat by the transparent electrode 54. Therefore, it is possible to prevent the structure of the power generation layer from becoming complicated.

  DESCRIPTION OF SYMBOLS 10,40 ... Thin-film solar cell, 11, 21, 41, 51, 71, 101, 111 ... Transparent substrate, 12, 23 ... Light transmission layer, 12a, 13a, 42a, 44a, 102a ... Texture, 13, 24, 44 , 54, 74, 102, 112 ... transparent electrode, 14, 45, 103 ... first power generation layer, 14p, 45p ... first p-type semiconductor layer, 14i, 45i ... first i-type semiconductor layer, 14n, 45n ... first n-type Semiconductor layer 15, 46, 104 ... intermediate layer, 16, 47, 105 ... second power generation layer, 16p, 47p ... second p-type semiconductor layer, 16i, 47i ... second i-type semiconductor layer, 16n, 47n ... second n-type Semiconductor layer 17, 48, 106 ... buffer layer, 18, 49, 107 ... back electrode, 22 ... transparent material, 23a, 24a, 52a, 54a, 72a, 74a ... convex, 23p, 52p, 72p, 12c ... 1st period, 23t, 24t, 52t, 54t, 72t, 74t, t1, t2 ... Top part, 24p, 54p, 74p, 112d ... 2nd period, 31 ... Mold, 32, 61 ... Plasma, 33, 62 ... Etching solution, 42, 52, 72 ... 1st light transmission layer, 43, 53, 73 ... 2nd light transmission layer, 112a ... 1st texture, 112b ... 2nd texture.

Claims (6)

A transparent substrate;
A first light transmission layer formed on the transparent substrate;
A transparent electrode formed on the first light transmission layer;
A photoelectric conversion layer formed on the transparent electrode,
The first light transmission layer is made of a material having a higher transmittance than the material for forming the transparent electrode, and a plurality of first protrusions are formed on the surface of the first light transmission layer on the transparent electrode side. ,
A plurality of second convex portions are formed on the transparent electrode at intervals smaller than the first convex portions. A second light transmission layer formed between the first light transmission layer and the transparent electrode;
The second light transmission layer is made of a material having a higher transmittance than the material for forming the transparent electrode,
The thin film solar cell according to claim 1, wherein the second light transmission layer fills a space between the first convex portions adjacent to each other. The thin film solar cell according to claim 2, wherein a refractive index of the second light transmission layer and a refractive index of the transparent electrode are equal to each other. Forming a first light transmission layer on a transparent substrate;
Forming a transparent electrode on the first light transmission layer;
Forming a photoelectric conversion layer on the transparent electrode,
In the step of forming the first light transmission layer,
Forming the first light transmission layer with a material having a higher transmittance than the material for forming the transparent electrode, and forming a plurality of first protrusions on the surface on the transparent electrode side in the first light transmission layer;
In the step of forming the transparent electrode,
A method of manufacturing a thin-film solar cell, wherein a plurality of second protrusions are formed on the transparent electrode at intervals smaller than the first protrusions. Forming a second light transmission layer between the first light transmission layer and the transparent electrode;
In the step of forming the second light transmission layer,
The method for manufacturing a thin-film solar cell according to claim 4, wherein a space between the first convex portions adjacent to each other is filled with the second light transmission layer made of a material having a higher transmittance than the material for forming the transparent electrode. In the step of forming the first light transmission layer,
The method for manufacturing a thin-film solar cell according to claim 4 or 5, wherein the first convex portion of the first light transmission layer is formed by a nanoimprint method.

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